摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 1969–1972 1969 Structure and magnetic and electrochemical properties of (Ï-aryloxo)- bis(Ï-carboxylato)diruthenium(III) complexes Yuji Mikata,*,a Nao Takeshita,a Tomoko Miyazu,a Yuki Miyata,a Tomoaki Tanase,*,a Isamu Kinoshita,b Akio Ichimura,b Wasuke Mori,c Satoshi Takamizawa d and Shigenobu Yano *,a a Department of Chemistry, Faculty of Science, Nara Women’s University, Nara 630, Japan b Department of Chemistry, Faculty of Science, Osaka City University, Sumiyoshi-ku, Osaka 558, Japan c Department of Chemistry, Faculty of Science, Kanagawa University, Hiratsuka, Kanagawa 259-12, Japan d Department of Chemistry, Faculty of Science, Osaka University, Toyonaka-shi, Osaka 550, Japan The dinuclear diruthenium complexes ligated by the (m-aryloxo)bis(m-carboxylato) system M[Ru2L(m-O2CR)2] (M = Na, R = Me 1; M = Na, R = Ph 2; M = K, R = Me 3; M = K, R = Ph 4; H5L = 2-hydroxy-5-methyl-mphenylenedimethylenedinitrilotetraacetic acid) were prepared by the reaction of [RuCl2(Me2SO)4] with L52 and carboxylic acid.The structure of the benzoate-bridged complex 4?0.5MeOH?0.5EtOH?4H2O was elucidated by X-ray crystallography. The Ru ? ? ?Ru distance was 3.416 Å (average for two crystallographically independent molecules), comparable to those of (m-alkoxo)bis(m-carboxylato)diruthenium complexes. The magnetic properties were analysed by a general isotropic exchange Hamiltonian H = 22JS1?S2 (S1 = S2 = ��� ), yielding meaningfully large antiferromagnetic spin coupling constants (2J = 728 and 649 cm21 for 1 and 2, respectively).The cyclic voltammogram of 4 in dmf demonstrated two reduction and one oxidation wave corresponding to the four redox states RuII 2, RuIIRuIII, RuIII 2, RuIIIRuIV. The intervalence coupling constant KC estimated from the potential gap between RuII 2/RuIIRuIII and RuIIRuIII/RuIII 2 indicated that the introduction of the m-aryloxo bridge stabilizes the RuIIRuIII mixed-valence species.Oxo-, hydroxo- and alkoxo-bridged diiron complexes are of considerable interest as models for hemerythrin, ribonucleotide reductase, and methane monooxygenase.1–3 The parallel chemistry by utilizing ruthenium centres is also a prospective subject since it allows a wide variety of oxidation states,4–7 which is useful to establish new physical and chemical properties. Recently, we have reported the (m-alkoxo)bis- (m-carboxylato)diruthenium(III) complexes, [Ru2(dhpta)(m- O2CR)2]2 (H5dhpta = 2-hydroxytrimethylenedinitrilotetraacetic acid), which involve a related system to non-heme diiron active centres and indicate that their physical properties could be tuned by varying the monoatom-bridging group.8,9 We report herein the synthesis and characterization of (m-aryloxo)bis- (m-carboxylato)diruthenium(III) complexes, [Ru2L(m-O2CR)2]2 (H5L = 2-hydroxy-5-methyl-m-phenylenedimethylenedinitrilotetraacetic acid), in which the aryloxo-bridge significantly influences their electrochemical and magnetic properties.Experimental Instrumental Proton NMR spectra were recorded on a Varian GEMINI 2000 and a JEOL GX-400 spectrometer at 300 and 400 MHz, respectively, in D2O, electronic absorption spectra on a JASCO V-570 spectrophotometer. Cyclic voltammograms were obtained using a BASCV-50W voltammetric analyser using a three-electrode system, i.e. glassy carbon (working electrode), platinum wire (counter electrode) and Ag–AgPF6 reference electrode. Magnetic susceptibility data were recorded by the Faraday method over a temperature range 78–300 K with a Cahn 1000 RH electrobalance; values at room temperature were also measured by the Gouy method.The diamagnetism of the complexes was corrected from Pascal’s constants. The temperature dependence of the molar susceptibility was analysed by a similar method to that reported 9 based on a general isotropic exchange Hamiltonian H = 22JS1?S2 (S1 = S2 = ��� ), using the van Vleck equation (1), where N = Avogadro’s number, b = Bohr magneton and k = Boltzmann’s constant.cm = SNg 2b2 3kT D 1 1 1 (1/3)exp(22J/kT) 1 Na (1) General method for preparation of M[Ru2L(Ï-O2CR)2] (M 5 Na, R 5 Me 1; M 5 Na, R 5 Ph 2; M 5 K, R 5 Me 3; M 5 K, R 5 Ph 4) To an aqueous solution (pH 5) of MnH52nL (M = Na or K, n = 1 or 2)10 (0.17 g, 0.50 mmol), [RuCl2(Me2SO)4] (0.49 g, 1.0 mmol) was added and the mixture heated to 90–95 8C.Keeping the pH at 5 by addition of aqueous NaOH or KOH, the reaction mixture was stirred for 20–60 min. Then, an aqueous solution (pH 5) of the carboxylate (1.0 mmol) was added and stirred for 20 h with heating at 90–95 8C. The progress of the reaction was monitored by UV/VIS spectra around 500 nm. The resulting dark red solution was concentrated in vacuo and purified by gel permeation chromatography (Sephadex G-15, eluted by water). Recrystallisation of the crude product from water–ethanol gave dark violet crystals in 3–15% yield.Na[Ru2L(Ï-O2CMe)2]?6H2O (1?6H2O). Yield: 13 mg (0.015 mmol, 3%). 1H NMR in D2O (300 MHz): d 27.93 (d, br, 2 H), 26.50 (d, br, 2 H), 23.68 (d, br, 2 H), 23.36 (d, br, 2 H), 22.90 (d, br, 2 H), 0.50 (d, br, 2 H), 3.27 (s, 6 H), 5.91 (s, 3 H) and 8.87 (s, 2 H) (Found: C, 29.47; H, 3.87; N, 3.23. Calc. for 1?6H2O: C, 29.79; H, 4.41; N, 3.31%). lmax/nm (dmf) (e/M21 cm21) 479 (1.42 × 103) and 386 (1.66 × 103).Na[Ru2L(Ï-O2Ph)2]?3.5H2O (2?3.5H2O). Yield: 24 mg (0.026 mmol, 5%). 1H NMR in D2O (300 MHz): d 27.81 (d, br, 2 H), 26.48 (d, br, 2 H), 23.58 (s, br, 4 H), 23.47 (s, br, 2 H), 0.43 (d,1970 J. Chem. Soc., Dalton Trans., 1998, Pages 1969–1972 br, 2 H), 5.68 (s, 3 H), 7.24 (s, 10 H) and 8.82 (s, 2 H) (Found: C, 40.41; H, 3.68; N, 3.14. Calc. for 2?3.5H2O: C, 40.87; H, 4.16; N, 2.89%). lmax/nm (dmf) (e/M21 cm21) 480 (1.54 × 103) and 382 (2.30 × 103). K[Ru2L(Ï-O2CMe)2]?7H2O (3?7H2O).Yield: 31 mg (0.035 mmol, 7%). 1H NMR in D2O (300 MHz): d 27.96 (d, br, 2 H), 26.55 (d, br, 2 H), 23.72 (d, br, 2 H), 23.40 (d, br, 2 H), 22.95 (d, br, 2 H), 0.46 (d, br, 2 H), 3.23 (s, 6 H), 5.88 (s, 3 H) and 8.85 (s, 2 H) (Found: C, 28.71; H, 3.81; N, 3.22. Calc. for 3?7H2O: C, 28.70; H, 4.24; N, 3.19%). lmax/nm (dmf) (e/M21 cm21) 483 (1.51 × 103) and 386 (1.79 × 103). K[Ru2L(Ï-O2CPh)2]?5H2O (4?5H2O). Yield: 73 mg (0.076 mmol, 15%). 1H NMR in D2O (300 MHz): d 27.84 (s, br, 2 H), 26.48 (d, br, 2 H), 23.60 (s, br, 4 H), 23.44 (s, br, 2 H), 0.42 (d, br, 2 H), 5.68 (s, 3 H), 7.23 (s, 10 H) and 8.83 (s, 2 H) (Found: C, 38.61; H, 3.86; N, 2.83.Calc. for 4?5H2O: C, 38.51; H, 3.86; N, 2.90%). lmax/nm (dmf) (e/M21 cm21) 484 (1.94 × 103) and 382 (2.92 × 103). X-Ray crystallography A violet crystal of complex 4?0.5MeOH?0.5EtOH?4H2O grown from a methanol–ethanol–water mixed solvent was mounted on the end of a glass fibre with Paraton N oil at 2137 8C.Crystal data and experimental conditions are given in Table 1. Data were collected on a Rigaku AFC7R diVractometer with graphite-monochromated Mo-Ka radiation using the w–2q scanning technique. The data were corrected for Lorentzpolarization eVects and for absorption eVects by the y-scan method. The intensities of three representative reflections were measured every 150 and showed no systematic decrease in intensity. The structure was solved by direct methods (SIR 92),11 and refined with full-matrix least-squares techniques.Hydrogen atoms were calculated at positions with C]H 0.95 Å and not refined. The final refinement was carried out with anisotropic thermal parameters for all non-hydrogen atoms, minimizing Sw(|Fo| 2 |Fc|) 2 using standard neutral atom dispersion factors and anomalous dispersion corrections.12,13 All calculations were performed using the TEXSAN crystallographic package.14 Perspective drawings were drawn by using ORTEP.15 CCDC reference number 186/982. Results and Discussion Compounds M[Ru2L(m-O2CR)2] (M = Na, R = Me 1; M = Na, R = Ph 2; M = K, R = Me 3; M = K, R = Ph 4) were synthesized in 3–15% yield from [RuCl2(Me2SO)4] by a procedure similar to that for (m-alkoxo)bis(m-carboxylaum complexes 8,9 using H5L10 in place of H5dhpta.Their IR and electronic absorption spectra were similar to those of (m-alkoxo)- diruthenium complexes. In the IR spectra, stretching vibrations around 1645–1500 and 1470–1325 cm21, assigned to nasym(CO2) and nsym(CO2), respectively, were detected, and in the visible spectra lmax around 400 and 500 nm were observed.These spectroscopic properties are similar to those of corresponding (m-alkoxo)bis(m-carboxylato)diruthenium derivatives. The rather sharp 1H NMR spectra of these complexes in D2O indicated a strong antiferromagnetic interaction between two ruthenium centres at room temperature. Fig. 1 shows the 400 MHz 1H NMR spectra of 1 and 2 together with the proton assignment derived from a two-dimensional experiment.The paramagnetic upfield shifts for the methylene protons of the carboxylate arms of L (d 27.8 to 27.9 and 26.5) were larger than those observed in the corresponding (m-alkoxo)- bis(m-carboxylato)diruthenium complex, K[Ru2(dhpta)(m-O2- CMe)2] 5 (d 25.7 and 24.0). The spectra indicated the presence of one kind of carboxylate ligand, whereas that of 5 exhibited two non-equivalent ones.This indicates a diVerent symmetrical structure of 3 from that of the alkoxo-bridged complex 5 having Cs symmetry. A suitable single crystal of complex 4?0.5MeOH?0.5EtOH? 4H2O obtained from a methanol–ethanol–water mixed solvent was subjected to X-ray crystallography. The experimental details are shown in Table 1. The asymmetric unit contains two crystallographically independent complex anions, their structures being almost identical and possessing a pseudo-C2 axis along the aryloxo C]O bond.The complex anions were revealed to comprise a (m-aryloxo)bis(m-carboxylato)- diruthenium(III) centre ligated by L and two benzoate ligands (Fig. 2, only one complex anion is illustrated). Selected bond distances and angles are listed in Table 2. The average Ru]Ru interatomic distance is 3.416 Å, which is comparable to those of (m-alkoxo)bis(m-carboxylato)diruthenium complexes (3.420– 3.433 Å).8,9 The most conspicuous feature is in the planar structure of the m-phenolate oxygen atoms, the sum of the three bond angles being 359.98 (average), in contrast with that of the m-alkoxo oxygen atoms in 5 which deviate considerably from planarity (average 3518). The phenyl ring delocalizes the lonepair electron density of the aryloxo oxygen and increases the p character of its valence orbitals, as evidenced by the longer Ru]O distances (average 1.985 Å) and the smaller Ru]O]Ru angles (average 118.88) than those observed in the m-alkoxo complex 5 (average Ru]O 1.947 Å, average Ru]O]Ru 122.98).These slight but meaningful structural changes should be responsible for the magnetic and electrochemical properties although the Ru ? ? ?Ru distance is unchanged in comparison with 5 (see below). Complexes 1 and 2 are paramagnetic at room temperature as is shown by the isotropically shifted 1H NMR spectra. The temperature-dependent magnetic susceptibilities of 1 and 2 were measured and analysed by a general isotropic exchange Hamiltonian, H = 22JS1?S2 (S1 = S2 = ��� ), to generate an antiferromagnetic intramolecular spin coupling constant 2J, Lande’s g factor and temperature-independent paramagnetism (Na).The results are presented in Fig. 3 and Table 3. The anti- Fig. 1 400 MHz 1H NMR spectra in D2O and peak assignments of diruthenium complexes 1 (a) and 2 (b). Asterisks denote peaks due to solvents and impuritiesJ. Chem. Soc., Dalton Trans., 1998, Pages 1969–1972 1971 ferromagnetic spin coupling constants for 1 and 2 are meaningfully larger than those for the dhpta complexes 9 in spite of similar interruthenium distances (3.416–3.433 Å).The stronger metal–metal antiferromagnetic interaction might be ascribable to an increasing overlap between d orbitals of Ru atoms and the p orbital of the phenolate oxygen atom on the basis of the crystal structure of 4. The electrochemical properties of complexes 1–4 were investigated by cyclic voltammetry in dmf solution with 0.1 M tetrabutylammonium hexafluorophosphate as supporting electrolyte. The potentials were referenced to a Ag–AgPF6 electrode in MeCN.The cyclic voltammogram of 4 demonstrated two reduction and one oxidation waves at E2� 1 = 21.78, 21.18 and 0.76 V, presumably corresponding to the respective one-electron redox processes of RuIIRuII–RuIIRuIII (E1 2� 1 ), RuIIRuIII–RuIIIRuIII (E2 2� 1 ) and RuIIIRuIII–RuIIIRuIV (E3 2� 1 ) (Fig. 4, Table 4). The RuIII 2 complexes of L undergo one-electron oxidation and reduction at more positive potentials than those of the dhpta complexes, 8,9 which is consistent with the poor electron donating ability of aryloxo compared with alkoxo groups.The reduction Fig. 2 An ORTEP drawing for one of the two independent complex anions of K[Ru2L(m-O2CPh)2] 4 Table 1 Crystallographic and experimental data for complex 4?0.5MeOH?0.5EtOH?4H2O Formula M Crystal size/mm Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 Transmission factors 2q Range/8 No.unique data No. observed data No. variables Ra R9 b Goodness of fit C32.5H40KN2O18Ru2 987.91 0.45 × 0.30 × 0.20 Monoclinic P21/n 17.751(7) 14.575(5) 29.949(9) 100.25(3) 7624(4) 8 1.72 0.82–0.99 3–50 14 009 9588 [I > 3s(I)] 999 0.050 0.057 1.90 a S||Fo| 2 |Fc||/S |Fo|. b [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� , w = 1/s2(Fo). process RuIIRuII–RuIIRuIII in L complexes, however, occurred at almost the same potential with dhpta complexes. The comproportionation constants (KC) for equation (2), estimated from Fig. 3 Temperature dependence of the magnetic susceptibility data for diruthenium complexes 1 and 2. The solid lines are best fits with equation (1) Table 2 Selected bond distances (Å) and angles (8) for complex 4?0.5MeOH?0.5EtOH?4H2O Ru(11) ? ? ?Ru(12) Ru(11)]O(1) Ru(11)]O(2) Ru(11)]O(4) Ru(11)]O(11) Ru(11)]O(13) Ru(11)]N(11) Ru(12)]O(1) Ru(12)]O(3) Ru(12)]O(5) Ru(12)]O(21) Ru(12)]O(23) Ru(12)]N(12) O(1)]Ru(11)]O(2) O(1)]Ru(11)]O(4) O(1)]Ru(11)]O(11) O(1)]Ru(11)]O(13) O(1)]Ru(11)]N(11) O(2)]Ru(11)]O(4) O(2)]Ru(11)]O(11) O(2)]Ru(11)]O(13) O(2)]Ru(11)]N(11) O(4)]Ru(11)]O(11) O(4)]Ru(11)]O(13) O(4)]Ru(11)]N(11) O(11)]Ru(11)]O(13) O(11)]Ru(11)]N(11) O(13)]Ru(11)]N(11) O(1)]Ru(12)]O(3) O(1)]Ru(12)]O(5) O(1)]Ru(12)]O(21) O(1)]Ru(12)]O(23) O(1)]Ru(12)]N(12) O(3)]Ru(12)]O(5) O(3)]Ru(12)]O(21) O(3)]Ru(12)]O(23) O(3)]Ru(12)]N(12) O(5)]Ru(12)]O(21) O(5)]Ru(12)]O(23) O(5)]Ru(12)]N(12) O(21)]Ru(12)]O(23) O(21)]Ru(12)]N(12) O(23)]Ru(12)]N(12) Ru(11)]O(1)]Ru(12) Ru(11)]O(1)]C(111) Ru(12)]O(1)]C(111) 3.439(1) 1.983(5) 2.056(5) 2.085(5) 1.987(5) 2.012(5) 2.033(6) 1.983(5) 2.075(5) 2.039(5) 2.003(5) 2.008(5) 2.031(6) 88.8(2) 93.2(2) 90.7(2) 173.5(2) 94.4(2) 91.9(2) 175.7(2) 86.2(2) 91.4(2) 92.4(2) 91.3(2) 171.8(2) 93.8(2) 84.4(2) 81.5(2) 94.4(2) 89.7(2) 89.4(2) 173.2(2) 94.7(2) 91.0(2) 89.8(2) 90.3(2) 169.0(2) 178.8(2) 85.3(2) 95.1(2) 95.6(2) 84.3(2) 81.2(2) 120.3(2) 121.2(4) 118.3(4) Ru(21) ? ? ?Ru(22) Ru(21)]O(6) Ru(21)]O(7) Ru(21)]O(9) Ru(21)]O(31) Ru(21)]O(33) Ru(21)]N(21) Ru(22)]O(6) Ru(22)]O(8) Ru(22)]O(10) Ru(22)]O(41) Ru(22)]O(43) Ru(22)]N(22) O(6)]Ru(21)]O(7) O(6)]Ru(21)]O(9) O(6)]Ru(21)]O(31) O(6)]Ru(21)]O(33) O(6)]Ru(21)]N(21) O(7)]Ru(21)]O(9) O(7)]Ru(21)]O(31) O(7)]Ru(21)]O(33) O(7)]Ru(21)]N(21) O(9)]Ru(21)]O(31) O(9)]Ru(21)]O(33) O(9)]Ru(21)]N(21) O(31)]Ru(21)]O(33) O(31)]Ru(21)]N(21) O(33)]Ru(21)]N(21) O(6)]Ru(22)]O(8) O(6)]Ru(22)]O(10) O(6)]Ru(22)]O(41) O(6)]Ru(22)]O(43) O(6)]Ru(22)]N(22) O(8)]Ru(22)]O(10) O(8)]Ru(22)]O(41) O(8)]Ru(22)]O(43) O(8)]Ru(22)]N(22) O(10)]Ru(22)]O(41) O(10)]Ru(22)]O(43) O(10)]Ru(22)]N(22) O(41)]Ru(22)]O(43) O(41)]Ru(22)]N(22) O(43)]Ru(22)]N(22) Ru(21)]O(6)]Ru(22) Ru(21)]O(6)]C(211) Ru(22)]O(6)]C(211) 3.3921(9) 1.985(5) 2.077(5) 2.042(5) 1.999(5) 2.017(5) 2.034(6) 1.987(5) 2.046(5) 2.083(6) 1.989(6) 2.009(5) 2.031(7) 94.5(2) 87.9(2) 89.3(2) 172.9(2) 95.1(2) 93.6(2) 90.2(2) 89.7(2) 169.0(2) 175.4(2) (2) 84.7(2) 81.2(2) 87.7(2) 95.1(2) 90.4(2) 175.1(2) 94.8(2) 93.3(2) 176.4(2) 88.3(2) 92.8(2) 90.0(2) 88.0(2) 168.6(2) 93.4(2) 84.2(2) 82.6(2) 117.3(2) 120.8(4) 121.8(4) Estimated deviations are given in parentheses.1972 J.Chem. Soc., Dalton Trans., 1998, Pages 1969–1972 [RuIIRuIIL(O2CR)2]32 1 [RuIIIRuIIIL(O2CR)2]2 KC 2[RuIIRuIIIL(O2CR)2]22 (2) the redox potential gap between the two reduction processes (DE1,2 = |E1 2� 1 2 E2 2� 1 |) for L complexes as depicted in equation (3), KC = expSDE1,2n1n2F RT D (3) where n1 and n2 are the number of electrons being transferred in the redox processes E1 and E2, are also listed in Table 4.The values are remarkably larger than those for the corresponding dhpta complex, indicating that the RuIIRuIII mixed-valence state could be fairly stabilized by the aryloxo-bridged structure. The electron withdrawing nature of the phenolate oxygen promotes the one-electron reduction of RuIII 2 species generating mixed-valence complexes, whereas intervalence stabilization between two metal centres resists further one-electron reduction resulting in rather negative second reduction potentials (E1 2� 1 ).Fig. 4 Cyclic voltammogram for K[Ru2L(m-O2CPh)2] 4 in 1 mM dmf solution with 0.1 M [NBun 4][PF6] as supporting electrolyte. Potentials were referenced to Ag–AgPF6 Table 3 Magnetic parameters derived from curve fitting of the temperature dependence of molar susceptibility data for diruthenium derivatives Compound 126 Na[Ru2(dhpta)(m-O2CMe)2] * 7 Na[Ru2(dhpta)(m-O2CPh)2] * g 2.3 2.3 2.4 2.0 2J/cm21 728 649 470 310 106 Na/ cm3 mol21 196 184 263 180 * From ref. 9. Table 4 Electrochemical data for diruthenium derivatives in dmf a E2� 1 /V Compound 12346 Na[Ru2(dhpta)- (m-O2CMe)2] b 7 Na[Ru2(dhpta)- (m-O2CPh)2] b 1 21.80 21.74 21.74 21.78 21.81 21.64 2 21.23 21.13 21.15 21.18 21.28 21.24 3 0.73 0.81 0.79 0.76 0.57 0.59 DE1,2/V 0.57 0.61 0.59 0.60 0.53 0.40 Kc 4.4 × 109 2.1 × 1010 9.6 × 109 1.4 × 1010 9.1 × 108 5.8 × 106 a vs.Ag–AgPF6. b From ref. 9. Conclusion To explore novel functions of diruthenium cores, the present work has been carried out by utilizing ligand L and modifying the monoatom bridge from a m-alkoxo to a m-aryloxo group. The (m-aryloxo)bis(m-carboxylato)diruthenium(III) complexes M[Ru2L(m-O2CR)2] 1–4 (M = Na or K, R = Me or Ph) were successfully prepared and characterized, revealing that their magnetic and electrochemical properties can be altered by varying the monoatom bridging group.Meaningfully large antiferromagnetic spin coupling constants (2J = 728 and 649 cm21 for 1 and 2, respectively) and intervalence coupling constants for the RuII–RuIII couple (KC = 4.4 × 109–2.1 × 1010) were obtained. The m-aryloxo group increases the metal–metal electronic interaction through its p orbitals without any dramatic structural changes: single-crystal X-ray crystallography of 4 revealed that the Ru ? ? ?Ru distance is preserved at around 3.4 Å.Acknowledgements This work was partially supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture 10131247 and 10894022, and grants from Nippon Itagarasu and Rigaku-Denki and the San-Ei Gen Foundation. The authors thank Professor Kotaro Osakada of the Tokyo Institute of Technology, Professor Yuzo Nishida of Yamagata University, Professor Masaaki Haga of Mie University and Yoichi Sasaki of Hokkaido University for their helpful suggestions.References 1 S. J. Lippard, Angew. Chem., Int. Ed. Engl., 1988, 27, 344. 2 D. M. Kurtz, jun., Chem. Rev., 1990, 90, 585. 3 A. Feig and S. J. Lippard, Chem. Rev., 1994, 94, 759. 4 P. Neubold, K. Wieghardt, B. Nuber and J. Weiss, Inorg. Chem., 1989, 28, 459. 5 P. Neubold, B. S. P. C. Della Vedva, K. Wieghardt, B. Nuber and J. Weiss, Inorg. Chem., 1990, 29, 3355. 6 B. K. Das and A. R. Chakravarty, Inorg. Chem., 1991, 30, 4978. 7 C. Sudha, S. K. Mandal and A. R. Chakravarty, Inorg. Chem., 1993, 32, 3801. 8 T. Tanase, M. Kato, Y. Yamada, K. Tanaka, K. Lee, Y. Sugihara, A. Ichimura, I. Kinoshita, M. Haga, Y. Sasaki, Y. Yamamoto, T. Nagano and S. Yano, Chem. Lett., 1994, 1853. 9 T. Tanase, Y. Yamada, K. Tanaka, T. Miyazu, M. Kato, K. Lee, Y. Sugihara, W. Mori, A. Ichimura, I. Kinoshita, Y. Yamamoto, M. Haga, Y. Sasaki and S. Yano, Inorg. Chem., 1996, 35, 6230. 10 B. P. Murch, F. C. Bradley, P. D. Boyle, V. Papaefthmiou and L. Que, jun., J. Am. Chem. Soc., 1987, 109, 7993. 11 G. M. Sheldrick, in Crystallography Computing, eds. G. M. Sheldrick, C. Kruger and R. Goddard, Oxford University Press, Oxford, 1985, p. 175. 12 D. T. Cromer and J. T. Weber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4. 13 D. C. Creagh and W. J. McAuley, International Tables for Crystallography, Kluwer, Boston, 1992, vol. C. 14 TEXSAN, Molecular Structure Corporation, The Woodlands, TX, 1985 and 1992. 15 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Received 2nd February 1998; Paper

ISSN:1477-9226    

DOI:10.1039/a800857d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 1973–1977 1973 DiVerential binding of a facultative tridentate ligand 4-(benzimidazol-2-yl)-3-thiabutanoic acid to CuII and NiII Craig J. Matthews,a Sarah L. Heath,a Mark R. J. Elsegood,a William Clegg,a Troy A. Leese b and Joyce C. Lockhart *,a a Department of Chemistry, University of Newcastle Upon Tyne, UK NE1 7RU b Zeneca Specialties, PO Box 42, Hexagon House, Blackley, Manchester, UK M9 8ZS The crystal structure of a new tridentate ligand 4-(benzimidazol-2-yl)-3-thiabutanoic acid (HL), which provides a benzimidazole, a thioether and a carboxyl donor group that can be regarded as mimics of His, Met and Asp/Glu side chains in proteins, has been determined, together with those of its octahedral [CuL2] (brilliant blue) and [NiL2] (bright turquoise) complexes and the ligand field spectra of the chelates, for which the ligands provide an S2N2O2 donor set, in each case, but diVerent positional isomers for the copper (t,c,c) and the nickel (c,c,c) chelates.The customary geometry of CuII in biological systems with His donors is distorted tetrahedral.1,2 Where a Met donor is present the Cu ? ? ? S distance is apparently quite variable 3 and may be the key to the rate at which electron transfer occurs in Type I blue copper proteins. For the known nickel sites in biological systems, four-co-ordinate square planar and six-co-ordinate octahedral geometries are known4–7 and the availability of hard and soft donors is highly relevant.Geometrical information concerning biomimetic and related nickel complexes has been reviewed.8 Tridentate 4-(benzimidazol-2-yl)-3-thiabutanoic acid (HL) (Scheme 1), produced as a synthon for asymmetric bis- (benzimidazoles),9 features as an interesting biomimetic ligand in its own right. It contains benzimidazole, thioether and carboxyl donors (N, S and O donors) which can be regarded as mimics of the amino acid side chains of His, Met and Glu or Asp, which are involved, for example, in the co-ordination of Cu in electron transport proteins 1 and of nickel in various enzymes.8 Thus the co-ordination of the new ligand to metal ions of biological interest may assist the search for new structural models of metalloenzymes. 4-(5-Methylimidazol-4-yl)-3- thiabutanoic acid (abbreviated Hitba), reported by Bouwman and Reedijk,10 also has donor N, S and O in a superficially rather similar relation to those of our new ligand; however the side chain is anchored to the 4 position of imidazole, not the 2 position as in the benzimidazole.The respective nitrogen donors are of diVerent basicity (relevant pK of benzimidazole 5.5 and histidine 6.0) and have diVerent steric requirements in the two ligands, since the side chain is on the polar side of the imidazole ring of the new ligand on the hydrophobic side for Hitba. The preparation and structure of the bis-chelates formed by HL with NiII and CuII are described in this paper.The data of Darensbourg and co-workers 11,12 provide a useful comparison for the nickel(II) structure; their recent attempts to obtain five-co-ordinate NiII produced instead six-co-ordinate NiII with S2N2OX and S2N2O2 donor sets 11,12 or square planar NiII with an S2N2 donor set. Bouwman and Reedijk 10 found octahedral co-ordination of CoII and CuII with the S2N2O2 donor set. Allowing for Jahn–Teller distortion of the copper(II) complex, they inferred a similar structure for the nickel(II) chelate.The positional isomers are diVerent from those reported here. A suitable descriptor of the geometry is shown in Scheme 2 for the chelates prepared in this work and the [Cu(itba)2] chelate; this follows ref. 8, in describing the cis/trans relation of the two sulfur, the two nitrogen and the two oxygen (or oxygen/ halogen) atoms, in that sequence, thus the [Cu(itba)2] chelate is t,t,t. The formation of complexes in solution was studied by UV/VIS spectra, and these are compared with literature data where possible.Experimental Reagents and solvents used were of commercially available reagent grade quality. Elemental analysis was performed on a Carlo Erba 1106 elemental analyser; fast atom bombardment and electron impact mass spectra were obtained on a KRATOS MS80 RF, UV/VIS solution spectra in methanol solution with a Perkin-Elmer 550S instrument from 300 to 800 nm and fingerprint IR spectra (from KBr discs) on a Nicolet 20 PC-IR spectrometer.Preparations 4-(Benzimidazol-2-yl)-3-thiabutanoic acid (HL). This compound was prepared as previously described.9 Crystals suitable Scheme 1 N N H S CO2H (a) N N H S CO2 – (b) + H Scheme 2 Positional isomers for S2N2O2 donor sets from the new ligand and from Hitba. Clockwise from top left, t,c,c for copper chelate I, t,t,t for the [Cu(itba)2] chelate,10 c,c,c for the first molecule of the nickel chelate E, c,c,c for the second molecule F.The descriptor refers to mutual relation (cis or trans) of the two sulfur, the two nitrogen and the two oxygen atoms in sequence for these N,S,O tridentate donors, and follows the nomenclature from ref. 8 S O N M S N N S M O O S N M O S t,c,c t,t,t c,c,c c,c,c O N M S NO NS NO SO1974 J. Chem. Soc., Dalton Trans., 1998, Pages 1973–1977 Table 1 Crystallographic data Formula M Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z m/mm21 Reflections measured Unique reflections Rint R [F2 > 2s(F2)] wR (F2, all data) HL?H2O C10H12N2O3S 240.3 Monoclinic I2/a (non-standard C2/c) 14.716(2) 8.9259(13) 16.860(3) 102.929(4) 2158.5(6) 8 0.29 4483 1789 0.0384 0.0371 0.0944 [CuL2]?2H2O C20H22CuN4O6S2 542.1 Monoclinic P21/n 13.6273(9) 9.0560(6) 18.5755(12) 105.149(2) 2212.7(3) 4 1.22 13 398 5150 0.0209 0.0272 0.0653 [NiL2]?3CH3OH C23H30N4NiO7S2 597.3 Monoclinic P21/n 19.2174(8) 13.7698(6) 21.2575(9) 106.469(2) 5394.4(4) 8 0.92 32 938 12 423 0.0396 0.0642 0.1328 for X-ray diVraction were obtained by slow evaporation of an aqueous solution.[CuL2]. The compound CuBr2 (0.12 g, 0.54 mmol) in distilled deionised water (10 cm3) was added to a hot stirred solution of HL (0.23 g, 1.04 mmol) in distilled deionised water (25 cm3). The resulting pale blue solution was refluxed for 2 h, after which time the complex precipitated as a pale blue solid, and was collected by miniature filtration apparatus, washed with cold water, and recrystallised from a saturated aqueous solution to give brilliant blue single crystals suitable for X-ray diVraction. Yield 0.18 g, 36 mmol, 67%.Analytical data were obtained for a dried, powdered sample (Found: C, 43.9; H, 4.1; N, 10.2. C20H18CuN4O4S2?2.5H2O requires C, 43.6; H, 4.2; N, 10.2%). [NiL2]. In a similar procedure to that described above for [CuL2], a turquoise precipitate was isolated from the addition of HL (0.20 g, 0.90 mmol) and NiBr2 (0.10 g, 0.46 mmol).Turquoise single crystals suitable for X-ray diVraction were grown from a saturated methanolic solution; they lost solvent slowly on exposure to air. Yield 0.14 g, 0.28 mmol, 61%. Data for a sample powdered and dried in vacuo [Found: C, 45.0; H, 4.4; N, 9.8%; FAB m/z 501 (M 1 H1). C20H18N4NiO4S2? CH3OH?1.5H2O requires C, 45.0; H, 4.5; N, 10.0%]. Crystals of a corresponding zinc complex could not be obtained pure. X-Ray crystallography Crystal data are in Table 1, together with other information on the structure determinations.For all three structures: T = 160 K, l(Mo-Ka) = 0.710 73 Å. Hydrogen atoms were located in diVerence syntheses and included in the refinement with idealised positions and riding model constraints. Programs were as in refs. 13 and 14. Selected geometry for the three structures is given in Tables 2–4. CCDC reference number 186/981. See http://www.rsc.org/suppdata/dt/1998/1973/ for crystallographic files in .cif format.Results and Discussion Crystal structure of the acid HL?H2O The compound (Fig. 1) is present in the crystal in zwitterionic form with essentially symmetric ionised carboxylate groups and with both nitrogens of the benzimidazole bearing protons, as shown in Scheme 1(b). The intermolecular interactions provided by hydrogen bonding involve both oxygens of the carboxylate, both N]H groups of the benzimidazole, and both hydrogens of the molecule of water of crystallisation. Each carboxylate O atom receives one hydrogen bond from an N]H group and one from a water molecule.The water molecules function as hydrogen bond donors but not acceptors. The hydrogen bonding, for which geometrical information is given in Table 5, generates a two-dimensional network of molecules. Metal complexes From the complexation of HL with CuII and NiII in methanol, neutral, solvated ML2 complexes, the latter of unusual colour, precipitated. Crystal structure determination reveals approximately octahedral co-ordination through an S2N2O2 donor set in each case, but diVerent isomeric polyhedra (Scheme 2).Crystal structure of [CuL2]?2H2O. The two oxygen and two nitrogen donors form a square planar co-ordination around the central copper, with a slight tetrahedral distortion, the O(1)]Cu]N(3) and O(3)]Cu]N(1) bond angles being reduced to 169.22(6) and 167.84(6)8 respectively. Each oxygen is trans to nitrogen and cis to the other oxygen. The two sulfurs are approximately axial [S(2)]Cu]S(1) 161.98(2)8] and at distances of 2.7439(5) and 2.7460(5) Å from the central copper (Fig. 2). Fig. 1 Structure of HL, including hydrogen atoms and atom labelling Table 2 Selected bond lengths (Å) and angles (8) for HL?H2O O(1)]C(1) C(1)]C(2) S]C(3) C(4)]N(1) N(1)]C(5) C(5)]C(6) O(2)]C(1)]O(1) O(1)]C(1)]C(2) C(2)]S]C(3) N(1)]C(4)]N(2) N(2)]C(4)]C(3) C(4)]N(2)]C(6) 1.259(3) 1.522(3) 1.808(2) 1.329(3) 1.393(3) 1.397(3) 123.73(19) 116.88(17) 99.90(10) 110.10(17) 123.92(18) 108.62(16) O(2)]C(1) C(2)]S C(3)]C(4) C(4)]N(2) N(2)]C(6) O(2)]C(1)]C(2) C(1)]C(2)]S C(4)]C(3)]S N(1)]C(4)]C(3) C(4)]N(1)]C(5) 1.252(2) 1.800(2) 1.478(3) 1.331(3) 1.389(3) 119.35(19) 117.08(14) 114.02(14) 125.91(18) 108.52(16)J.Chem. Soc., Dalton Trans., 1998, Pages 1973–1977 1975 The donor set can be described as t,c,c and is shown in Scheme 2. A search of the Cambridge Structural Database 15 yielded 103 observations of Cu]S (thioether) distances in octahedral environments; statistical analysis of this set of structures gives a mean of 2.488 (sample s 0.186 Å, minimum 2.294 and maximum 3.014 Å).Only 13% of the structures have distances >2.74 Å. The Cu]S is slightly longer than for the recently examined 16 cucumber basic protein (ca. 2.63 Å) but much shorter than the interaction in a typical azurin,17 where it is 3.13 Å. The Cu]S distances in our complex can thus be regarded as long in the context of small molecules, but within the known range for small electron transfer proteins, and an example of axial distortion due to the Jahn–Teller eVect.The [Cu(itba)2] complex10 (J in Table 6) has bond lengths very close to those found here. However, Bouwman and Reedijk 10 found that donor atoms were in mutually trans positions (see t,t,t in Scheme 2). This itba chelate is unsolvated, and has hydrogen bonding between carboxyl and imidazole nitrogen. Thus the detailed coordination geometries are in fact quite diVerent, possibly because of the diVerent steric requirements round the nitrogens in the two diVerent ligands, the diVerent hydrophobicities, and the slightly lower basicity of the benzimidazole nitrogen; the crystal packing is also diVerent, partly because of the diVerence in solvation.The structure is a dihydrate, the water molecules providing a link between metal complexes by a three-dimensional hydrogen bonding network involving the water molecules (as donors and, in one case, as acceptor), the co-ordinated and unco-ordinated oxygen of each carboxyl (as acceptors), and the benzimidazole N]H groups (as donors).Geometrical details of the hydrogen bonds are given in Table 5. Crystal structure of [NiL2]?3CH3OH. The crystal structure of the brilliant turquoise nickel complex contains two crys- Fig. 2 Structure of the [CuL2] complex Table 3 Selected bond lengths (Å) and angles (8) for [CuL2]?2H2O Cu]N(1) Cu]O(1) Cu]S(1) C(10)]O(1) C(20)]O(3) O(1)]Cu]N(3) S(2)]Cu]S(1) N(3)]Cu]N(1) N(3)]Cu]O(3) N(3)]Cu]S(2) O(3)]Cu]S(2) N(3)]Cu]S(1) O(3)]Cu]S(1) 1.9899(14) 1.9539(12) 2.7460(5) 1.274(2) 1.284(2) 169.22(6) 161.978(16) 92.29(6) 89.04(6) 80.21(4) 77.55(4) 110.85(4) 88.18(4) Cu]N(3) Cu]O(3) Cu]S(2) C(10)]O(2) C(20)]O(4) N(1)]Cu]O(3) O(1)]Cu]N(1) O(1)]Cu]O(3) O(1)]Cu]S(2) N(1)]Cu]S(2) O(1)]Cu]S(1) N(1)]Cu]S(1) 1.9693(14) 2.0028(12) 2.7439(5) 1.238(2) 1.234(2) 167.84(6) 90.85(6) 90.06(5) 89.11(4) 114.59(4) 79.86(4) 80.05(4) tallographically independent molecules of the nickel chelate.Molecule 1 (Fig. 3) has the two sulfurs cis [at 101.48(4)8], the nitrogens cis [102.15(13)8] and the oxygens cis [89.04(11)8]. One sulfur is trans to oxygen, and the other to nitrogen. The second molecule is the same positional isomer, with slightly diVerent angles, having cis sulfurs [at 100.17(4)8], cis nitrogens [100.07(12)8], cis oxygens [90.57(11)8], and essentially the same bond lengths. The molecules are linked by a complex two-dimensional hydrogen bonding network involving the six crystallographically independent molecules of methanol of crystallisation, the unco-ordinated and half the co-ordinated carboxylate oxygen atoms, and the benzimidazole N]H groups.Geometrical details are given in Table 5. Table 6 makes a comparison of the geometries for the nickel complexes (E and F) found in this work with those for several Table 4 Selected bond lengths (Å) and angles (8) for [NiL2]?3CH3OH Ni(1)]N(1) Ni(1)]O(1) Ni(1)]S(1) C(10)]O(1) C(20)]O(3) Ni(2)]N(5) Ni(2)]O(5) Ni(2)]S(3) C(30)]O(5) C(40)]O(7) N(3)]Ni(1)]O(1) N(1)]Ni(1)]S(2) O(3)]Ni(1)]N(3) O(3)]Ni(1)]O(1) N(1)]Ni(1)]S(1) O(1)]Ni(1)]S(1) N(3)]Ni(1)]S(2) S(1)]Ni(1)]S(2) O(7)]Ni(2)]S(4) O(7)]Ni(2)]N(5) N(5)]Ni(2)]N(7) N(5)]Ni(2)]O(5) N(7)]Ni(2)]S(4) O(7)]Ni(2)]S(3) O(5)]Ni(2)]S(3) 2.045(3) 2.076(3) 2.4750(10) 1.272(5) 1.253(4) 2.036(3) 2.081(3) 2.4659(11) 1.272(4) 1.258(4) 167.29(12) 173.50(10) 94.29(12) 89.04(11) 82.20(9) 80.93(8) 82.86(9) 101.48(4) 169.98(8) 92.78(11) 100.07(12) 90.61(12) 95.90(9) 83.76(8) 86.35(8) Ni(1)]N(3) Ni(1)]O(3) Ni(1)]S(2) C(10)]O(2) C(20)]O(4) Ni(2)]N(7) Ni(2)]O(7) Ni(2)]S(4) C(30)]O(6) C(40)]O(8) O(3)]Ni(1)]S(1) O(3)]Ni(1)]N(1) N(1)]Ni(1)]N(3) N(1)]Ni(1)]O(1) N(3)]Ni(1)]S(1) O(3)]Ni(1)]S(2) O(1)]Ni(1)]S(2) N(7)]Ni(2)]O(5) N(5)]Ni(2)]S(3) O(7)]Ni(2)]N(7) O(7)]Ni(2)]O(5) N(5)]Ni(2)]S(4) O(5)]Ni(2)]S(4) N(7)]Ni(2)]S(3) S(4)]Ni(2)]S(3) 2.047(3) 2.027(3) 2.4807(11) 1.233(5) 1.254(5) 2.044(3) 2.023(3) 2.4569(10) 1.238(5) 1.246(4) 168.52(9) 92.28(11) 102.15(13) 89.96(12) 96.71(9) 83.13(8) 85.37(8) 168.27(12) 175.36(9) 93.70(11) 90.57(11) 82.75(9) 80.54(7) 83.28(9) 100.17(4) Table 5 Hydrogen bonding in the crystal structures Donor atom D Acceptor atom A D? ? ? A/Å D]H? ? ? A/8 HL?H2O N(1) N(2) O(3) (solvent) O(1) O(2) O(1) O(2) 2.680 2.689 2.938 2.865 163 165 162 156 [CuL2]?2H2O N(2) N(4) O(10) (solvent) O(11) (solvent) O(10) (solvent) O(3) (co-ordinated) O(1) (co-ordinated) O(2) (unco-ordinated) O(4) (unco-ordinated) 2.815 2.723 2.907 2.753 2.903 3.055 169 168 160 173 163 160 [NiL2]?3CH3OH N(2) N(4) N(6) N(8) O(50) (solvent) O(51) (solvent) O(52) (solvent) O(53) (solvent) O(54) (solvent) O(55) (solvent) O(8) (unco-ordinated) O(1) (co-ordinated) O(4) (unco-ordinated) O(5) (co-ordinated) O(8) (unco-ordinated) O(4) (unco-ordinated) O(54) (solvent) O(2) (unco-ordinated) O(6) (unco-ordinated) O(53) (solvent) 2.777 2.749 2.740 2.759 2.770 2.679 2.684 2.775 2.714 2.815 145 174 151 172 172 140 163 172 166 1671976 J.Chem. Soc., Dalton Trans., 1998, Pages 1973–1977 Table 6 Comparison of metal co-ordination distances for complexes of Ni and Cu M Compound X M]N M]N M]S M]S M]O M]X Descriptor S2N2 Nia A — 1.974 1.970 2.207 2.213 S2N2 Nia B — 1.98 1.97 2.174 2.143 S2N2OX Nia C Cl 2.101 2.110 2.400 2.444 2.293 2.465 c,c,t S2N2OX Nia D Br 2.088 2.060 2.390 2.380 2.270 2.510 c,c,t S2N2OX Ni E O 2.045 2.047 2.475 2.481 2.027 2.076 c,c,c S2N2OX Ni F O 2.044 2.036 2.466 2.457 2.023 2.081 c,c,c S2N2OX Nib GO 2.108 2.100 2.402 2.438 2.062 2.096 c,c,t S2N2OX Nic HO 2.094 2.435 2.067 c,c,t S2N2OX Cu I O 1.969 1.990 2.746 2.744 1.954 2.003 t,c,c S2N2OX Cud J O 1.986 2.715 1.988 t,t,t a Ref. 11: A = [N,N9-bis(5-hydroxy-3-thiapentyl)-1,5-diazacyclooctane-N,N9,S,S9]nickel(II) iodide, B = [(5-hydroxy-2,2,8,8-tetramethyl-3,7- dithianonanediyl)-1,5-diazacyclooctane-N,N9,S,S9]nickel(II) bromide, C = [N,N9-bis(5-hydroxy-3-thiapentyl)-1,5-diazacyclooctane-O,N,N9,S,S9]- chloronickel(II) iodide, D = [(5-hydroxy-3,7-dithianonanediyl)-1,5-diazacyclooctane-O,N,N9,S,S9]bromonickel(II) bromide.This work: E, F and I. b Ref. 12: G = [N-(3-thiabutyl)-N9-(3-thiapentanoate)-1,5-diazacyclooctane]nickel(II) iodide (polymer). c Ref. 18: H = D-[1,5-diazacyclooctane-1,5- diylbis(3-thiapentanoato)]nickel(II). d Ref. 10: J = [Cu(itba)2]. relevant complexes found in the literature (C, D, G, H).The Ni]S length appears elongated by 0.17–0.3 Å in the octahedral (S2N2OX) relative to the square planar (S2N2) environment as shown in Table 6 (A, B). The Ni]N distances are slightly longer in the octahedral form. In the molecules reported here the distances from nickel to oxygen and to nitrogen are marginally shorter, while the nickel–sulfur distances are longer than with the diazaoctane ligand.11,12 Nickel to sulfur distances in thiomacrocycle complexes 19 range from 2.3694 to 2.442 Å.A search of the Cambridge Structure Database 15 for bonds from Ni to S (thioether) indicated a bimodal distribution with the shorter distance median ca. 2.2 Å presumably corresponding to four-co-ordination and a longer one, median about 2.4 Å, corresponding to six-co-ordination. Restricting the search to six-coordinate Ni, there were 197 observations; statistical analysis of this set of data gave a mean Ni]S of 2.426 Å (sample s 0.06, minimum 2.313, maximum 2.943 Å).The structures of the chelates C, D, G and H in Table 6, determined by Darensbourg and co-workers,11,12,18 involve a diazacyclooctane ligand, having the two nitrogens forced to lie cis and pendant donor chains completing the donor sequence OSNNSO. These all have the descriptor c,c,t with oxygen trans. A tridentate ligand with the ONS sequence used by Choudhury et al.20 gave bis-chelates of nickel(II) with axial nitrogens, descriptor c,t,c.Bouwman and Reedijk 10 prepared a nickel(II) complex of Hitba (NSO sequence) which seemed isostructural with its copper(II) and cobalt(II) analogues but X-ray data were only quoted for a powder sample. This would require mutually trans ligands Fig. 3 One of the crystallographically independent molecules of the [NiL2] complex (descriptor t,t,t), which again is quite diVerent to what is observed here. Comparing the copper(II) and nickel(II) structures, it can be seen that the positional isomer found for the former is diVerent from those found for the latter (Scheme 2).The Cu]S bond length considerably exceeds the Ni]S one (Table 6) while the Cu]N and Cu]O distances are shorter than the nickel ones. The axial elongation found in I accords with the expectation of Jahn–Teller distortion. Neither complex is perfectly octahedral nor are the L]M]L angles perfectly rectangular so the description of fac or mer does not strictly apply. However fac is more accurate for Ni (where trans angles are almost linear).For CuII the preference for tight square planar co-ordination is satisfied by the two nitrogen and two oxygen donors which define a plane, while weaker axial interaction with the thioether sulfurs completes the Jahn–Teller axially distorted octahedron. The positional isomer found for the copper(II) complex I is diVerent to that found for the [Cu(itba)2] (Scheme 2 and J in Table 6) with a very similar donor set, and very similar bond lengths (Table 6).UV/VIS spectra. Octahedral nickel(II) complexes have three spin-allowed ligand field transitions. In the spectra of the turquoise nickel complex in methanolic solution two of these arise at 605 and 383 nm with e values of 20.9 and 30.9 dm3 mol21 cm21 respectively; the UV region is complicated by the absorptions of the ligand and charge transfer bands. These wavelengths are similar to those for a green macrocycle complex of NiII,19 [Ni2([12]aneS4)2Cl2][BF4]2 absorbing at 608 (e 31) and 384 nm (e 93 dm3 mol21 cm21).All the chelates with c,c,t geometries in Table 6 had similar UV absorptions in solution. The Darensbourg data for absorbance of the S2N2OCl complex (C in Table 6) which is blue-green are 598 (e 87) and 382 nm (e 119 dm3 mol21 cm21) in CH3CN.11,12 For comparison, the polymer G absorbed at 592 (e 100) and 376 nm, while H (described as aquamarine blue) absorbed at 600 (e 49) and 364 (e 31 dm3 mol21 cm21).The [Ni(itba)2] complex was reported to be lilac, and thus unlikely to be the same isomer. The relevant ligand field absorptions 10 were at 694, 546 and 350 nm. The brilliant blue copper(II) complex obtained in this work absorbs at 645 nm with an e value of 50.3 dm3 mol21 cm21. The [Cu(itba)2] complex has a sharp absorption band at 617 and a broad one at 787 nm in this region. These visible spectral data are consistent with the diVerent positional isomers discovered in the crystal structure analyses. Acknowledgements We wish to thank EPSRC (equipment grant to W.C. and CASE award to C. J. M.) and Zeneca Specialties (CASE award) for financial support.J. Chem. Soc., Dalton Trans., 1998, Pages 1973–1977 1977 References 1 K. D. Karlin and Z. Teklar (Editors), Bioinorganic Chemistry of Copper, Chapman and Hall, New York, 1993. 2 E. T. Adman, Adv. Protein Chem., 1991, 42, 145. 3 C. Dennison, E. Vijgenboom, W. R. Hagen and G. W. Canters, J.Am. Chem. Soc., 1996, 118, 7406. 4 J. R. Lancaster (Editor), the Bioinorganic Chemistry of Nickel, VCH, New York, 1988. 5 R. Cammack, Adv. Inorg. Chem., 1988, 32, 297. 6 M. K. Eidsness, R. S. Sullivan, J. R. Schwartz, P. L. Hartzell, R. D. Wolfe, A.-M. Flank, S. P. Cramer and R. A. Scott, J. Am. Chem. Soc., 1986, 108, 3120. 7 J. Van Elp, G. Peng, B. G. Searle, S. Mitra-Kirtley, Y.-H. Huang, M. K. Johnson, Z. H. Zhou, M. W. W. Adams, M. J. Maroney and S. P. Cramer, J. Am. Chem. Soc., 1994, 116, 1918. 8 M. A. Halcrow and G. Christou, Chem. Rev., 1994, 94, 2421. 9 C. J. Matthews, T. A. Leese, W. Clegg, M. R. J. Elsegood, L. Horsburgh and J. C. Lockhart, Inorg. Chem., 1996, 35, 7563. 10 E. Bouwman and J. Reedijk, Inorg. Chim. Acta, 1994, 215, 151. 11 D. C. Goodman, R. M. Buonomo, P. J. Farmer, J. H. Reibenspeis and M. Y. Darensbourg, Inorg. Chem., 1996, 35, 4029. 12 D. C. Goodman, P. J. Farmer, M. Y. Darensbourg and J. H. Reibenspeis, Inorg. Chem., 1996, 35, 4989. 13 SMART (diVractometer control) and SAINT (integration) software for area detectors, Bruker AXS, Madison, WI, 1994. 14 G. M. Sheldrick, SHELXTL User Manual, Version 5, Bruker AXS, Madison, WI, 1994. 15 F. H. Allen and O. Kennard, Chem. Des. Automat. News, 1993, 8, 31. 16 B. A. Fields, J. M. Gess and H. C. Freeman, J. Mol. Biol., 1991, 222, 1053. 17 G. E. Norris, B. F. Anderson and E. N. Baker, J. Am. Chem. Soc., 1986, 108, 2784. 18 D. C. Goodman, T. Tuntulani, P. J. Farmer, M. Y. Darensbourg and J. H. Reibenspeis, Angew. Chem., Int. Ed. Engl., 1993, 32, 116. 19 A. J. Blake, M. A. Halcrow and M. Schroder, J. Chem. Soc., Dalton Trans., 1994, 1463. 20 S. B. Choudhury, D. Ray and A. Chakravorty, Angew. Chem., Int. Ed. Engl., 1991, 30, 193. Received 20th January 1998; Paper 8/00543E

ISSN:1477-9226    

DOI:10.1039/a800543e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1975–1980 1975 Synthesis and some octahedral complexes of a chiral triaza macrocycle Simon W. Golding,a Trevor W. Hambley,b GeoVrey A. Lawrance,*a Stephan M. Luther,a Marcel Maeder a and Peter Turner b a Department of Chemistry, The University of Newcastle, Callaghan 2308, Australia b School of Chemistry, The University of Sydney, New South Wales 2006, Australia Received 23rd November 1998, Accepted 7th April 1999 The chiral and bulky tacn (1,4,7-triazacyclononane, L1) analogue chtacn (2,5,8-triazabicyclo[7.4.01,9]tridecane, L2), which has a cyclohexane ring fused to the tacn framework, has been synthesized commencing with (±), (1)- or (2)-trans-cyclohexane-1,2-diamine. Syntheses and properties of cobalt(III), nickel(II), chromium(III) and iron(III) complexes are described.In the complex bis(RR-2,5,8-triazabicyclo[7.4.01,9]tridecane)cobalt(III) chloride hexafluorophosphate the cyclohexane rings and pairs of adjacent secondary amines occupy an approximate plane around the cobalt ion, with the remaining secondary amines in each tridentate ligand in trans dispositions.A large positive Cotton eVect occurs under the low energy absorption band in the circular dichroism spectrum of this cobalt(III) complex of the R,R-(2)-chtacn ligand. In the dinuclear complex aqua-di-m-chloro-chlorobis(SS-2,5,8-triazabicyclo[ 7.4.01,9]tridecane)dinickel(II) perchlorate each nickel atom is bound to a tridentate macrocyclic ligand in diVerent dispositions, with the distorted octahedron of each nickel completed by two bridging chloride ions and either a chloride ion or aqua molecule. For [M(Ln)2]n1 complexes, electronic maxima are shifted slightly to lower energy and reduction potentials slightly to more negative potential in the case of L2 compared with L1.Introduction The triazamacrocycle tacn (1,4,7-triazacyclononane, L1) represents the simplest and most studied example of a cyclic polyamine capable of co-ordinating facially to an octahedral complex.First reported by Koyama and Yoshino,1 the coordination chemistry of this molecule has been comprehensively investigated, particularly by Chaudhuri, Weighardt and co-workers.2 It forms metal complexes which in all cases exceed in thermodynamic stability those of the closely related acyclic triamine 3-azapentane-1,5-diamine, an eVect associated with the favourable entropy eVects arising from the endodentate conformation of the tacn ligand where all ligating atoms are directed towards the macrocycle centre, diminishing rearrangement on co-ordination. Co-ordination of tacn to octahedral complexes occurs dominantly facially involving all three secondary amines; with two ligands bound, the metal ion is eVectively ‘sandwiched’ between them.For co-ordination to square-planar metal ions, chelation by two donors only occurs, leaving one unbound but available for protonation or other interactions.The range of complexes prepared involving tacn is both extensive and diverse.2 A number of other triazamacrocycles have been prepared and aspects of their co-ordination chemistry examined. These include examples containing larger rings,1,3 pendants on the ring,2 or incorporating aromatic units as part of the ring.4 Further, examples with mixed donor sets such as N2O,5,6 N2S7 and NS2,8 as well as O3- and S3-tacn analogues,9,10 have been reported.We have been examining tetraaza macrocycles incorporating cyclohexane rings fused to the macrocycle, which introduce chirality, bulk and rigidity to the ligand system.11 As an extension of this study, we are now investigating triazamacrocycles with cyclohexane rings fused to the macrocycle framework. Details of the syntheses of the analogue chtacn (2,5,8-triazabicyclo[7.4.01,9]tridecane, L2) and aspects of its co-ordination chemistry to cobalt(III), chromium(III), iron(III) and nickel(II), including crystal structure determinations of a cobalt(III) and nickel(II) complex, are reported herein.Experimental Syntheses The polyamine macrocycle (L2) was prepared by a variation of the well studied Richman–Atkins procedure,3,12–15 as described for the successive steps below. N,N9-Bis( p-tolylsulfonyl)-trans-cyclohexane-1,2-diamine. A combination of 7.58 g (66.4 mmol) of (1)-, (2)- or (±)-trans- 1,2-diaminocyclohexane and 5.70 g (138.2 mmol) of NaOH was dissolved in 70 cm3 water and 26.38 g (138.4 mmol) of purified p-toluenesulfonyl chloride dissolved in 150 cm3 of diethyl ether were added dropwise over 4 h under vigorous stirring.After addition was completed, the mixture was stirred for 45 min before 10 cm3 methanol were added. The mixture was filtered and the solid washed with water, then methanol, and recrystallised from hot methanol, giving big colourless crystals (17.7 g, 63%). NMR spectra (CDCl3): 1H, d 7.75 (d, 4 H), 7.3 (d, 4 H), 4.97 (br, 2 H), 2.78 (br, 2 H), 2.4 (s, 6 H), 1.81 (br, 2 H), 1.55 (br, 2 H) and 1.11 (br, 4 H); 13C (1H decoupled), d 143.5, 137.2, 129.8, 127.3, 56.6, 33.3, 24.2 and 21.6.N,N-bis[2-( p-tolylsulfonyloxy)ethyl]toluene-p-sulfonamide.14 A mixture of 14 g (132 mmol) of diethanolamine and 130 cm3 of dry pyridine was cooled to <0 8C in an ice-salt bath. Next, 76.3 g (400.2 mmol) of purified p-toluenesulfonyl chloride were added in small portions so that the temperature stayed below 0 8C, and the solution was stirred for 2 h at 0 8C after completion NH NH NH NH NH NH NH NH NH L1 L2 L3 CH31976 J.Chem. Soc., Dalton Trans., 1999, 1975–1980 of the addition. Then 250 cm3 of 5 mol dm23 HCl were slowly added so that the temperature always stayed <10 8C. A sticky red oil has formed and the mixture was allowed to stir overnight. The solid formed was filtered oV, washed with ice–water and recrystallised from methanol (53.8 g, 72%). NMR spectra (CDCl3): 1H, d 7.75 (d, 4 H), 7.6 (d, 2 H), 7.33 (d, 4 H), 7.27 (d, 2 H), 4.11 (t, 4 H), 3.37 (t, 4 H), 2.45 (s, 6 H) and 2.41 (s, 3 H); 13C (1H decoupled), d 145.2, 144.2, 135.4, 132.5, 130.1, 130.0, 128.0, 127.3, 68.3, 48.5, 21.7 and 21.5. 2,5,8-Tris( p-tolylsulfonyl)-2,5,8-triazabicyclo[7.4.01,9]tridecane. N,N9-Bis(p-tolylsulfonyl)-trans-cyclohexane-1,2-diamine (6 g, 14.2 mmol) was dissolved in 190 cm3 of dry DMF, 4.61 g (33.4 mmol) of dry K2CO3 were added and the mixture was heated to 50 8C for an hour.Then 9.9 g (17.4 mmol) of N,Nbis[ 2-( p-tolylsulfonyloxy)ethyl]toluene-p-sulfonamide dissolved in 100 cm3 of dry DMF were added dropwise within 26 h. The reaction mixture was kept at 50 8C for 7 d. The solution was evaporated to 50 cm3 and was poured into 2 dm3 of ice– water acidified with 10 cm3 of 10 mol dm23 HCl. The precipitate was vacuum filtered, washed with ice–water and refluxed in EtOH for an hour. The solid was filtered oV and dried (2.56 g, 28%). 2,5,8-Triazabicyclo[7.4.01,9]tridecane L2. 2,5,8-Tris(p-tolylsulfonyl)- 2,5,8-triazabicyclo[7.4.01,9]tridecane (2.32 g, 3.6 mmol) and dry Na2HPO4 (2.58 g, 18.2 mmol) were suspended in 60 cm3 of dry methanol. After addition of 3% w/w sodium amalgam (33.54 g, 43.76 mmol) the mixture was refluxed overnight. The addition of equivalent amounts of Na2HPO4 and sodium amalgam was repeated two times with further refluxing overnight after each addition. Water (300 cm3) was added, Hg decanted, and the solid collected and washed with water.The solution was evaporated to 100 cm3 and extracted with CH2Cl2 (5 × 100 cm3). The organic phase was dried over Na2SO4, filtered and evaporated to yield a colourless oil (0.64 g, 97%). NMR spectra (CDCl3): 1H, d 2.9–2.6 (m, 8 H), 2.35 (br, 3 H), 2.25 (br, 2 H), 1.81 (br, 2 H), 1.68 (br, 2 H) and 1.19 (br, 4 H); 13C (1H decoupled), d 60.0, 46.9, 44.5, 33.9 and 26.1. The trihydrochloride salt was prepared by dissolving the above oily product in 25 cm3 of ethanol and adding 5 cm3 of 10 mol dm23 HCl.The solution was evaporated to dryness. Dry diethyl ether was added and the product collected by vacuum filtration (Found: C, 38.5; H, 8.3; N, 13.1. Calc. for C10H24Cl3N3? H2O: C, 38.6; H, 8.4; N, 13.5%). Metal complexes. All syntheses below were performed successfully with either racemic, RR- or SS-L2, with products diVering in chiroptical properties only. Bis(2,5,8-triazabicyclo[7.4.01,9]tridecane)cobalt(III) perchlorate, [Co(L2)2][ClO4]3.A solution of L2?3HCl (185 mg, 0.63 mmol) and CoCl2?6H2O (75 mg, 0.32 mmol) in water (50 cm3) and 1 mol dm23 HCl (10 cm3) was aerated for 24 h, then activated charcoal was added and the solution refluxed for 6 h. The charcoal was filtered oV and the solution diluted to 200 cm3 and loaded onto a Dowex 50W-X2 cation-exchange column (2 × 20 cm). Elution with 3 mol dm23 HCl gave only two bands, a major orange and a minor red band, which were collected and evaporated to dryness.The major product was dissolved in 10 cm3 of water, the pH adjusted to 7, and 4 cm3 of 1 mol dm23 NaClO4 were added. The solution was allowed to stand for crystallisation. The orange crystals of the major band were collected, washed with cold ethanol and diethyl ether and dried (193 mg, 84%) (Found: C, 32.6; H, 5.7; N, 10.9. Calc. for C20H42Cl3CoN6O12?H2O: C, 32.4; H, 6.0; N, 11.3%). Electronic spectrum (water): lmax 336 (96) and 469 nm (e 97 dm3 mol21 cm21).NMR spectra (D2O): 1H, d 3.49 (br, 2 H), 3.38–2.76 (br, 18 H), 2.38 (br, 2 H), 2.08 (br, 2 H), 1.79 (br, 8 H) and 1.26 (br, 4 H); 13C (1H decoupled), d 69.2, 64.1, 56.2, 53.9, 50.9, 44.5, 32.0, 31.5, 26.9 and 26.0. The perchlorate salt did not produce crystals suitable for X-ray crystallography, but good quality crystals were obtained for the RR isomer by rotary evaporation of the yellow band obtained from column chromatography to dryness and recrystallisation of this chloride salt from water in the presence of an excess of sodium hexafluorophosphate, which yielded crystals of formula [Co(RR-L2)2][PF6]2Cl? 2.5H2O.The minor product did not crystallise, but was assigned as trichloro(2,5,8-triazabicyclo[7.4.01,9]tridecane)cobalt(III) by spectroscopy. Electronic spectrum (water): lmax 393 and 568 nm. NMR spectra (D2O–water): 13C (1H decoupled), d 60.1, 45.7, 42.7, 32.1 and 26.5. Aquachloro-di-m-chloro-bis(2,5,8-triazabicyclo[7.4.01,9]tridecane) dinickel(II) perchlorate, [Ni2(L2)2Cl3(OH2)][ClO4].A mixture of L2 (486 mg, 2.65 mmol) and NiCl2?6H2O (630 mg, 2.65 mmol) was dissolved in ethanol (50 cm3), 1 mol dm23 NaClO4 (5 cm3) was added and the solution was allowed to stand for crystallisation. Blue crystals formed and were collected, washed with cold ethanol and recrystallised from water (0.96 g, 52%) (Found: C, 33.75; H, 6.3; N, 11.6. Calc. for C20H44Cl4N6Ni2O5: C, 33.9; H, 6.3; N, 11.85%).Electronic spectrum (water): lmax 352 (18), 433 (sh), 575 (10) and 780 nm (e 6 dm3 mol21 cm21). Crystals employed for X-ray crystallography contained SS-L2. Bis(2,5,8-triazabicyclo[7.4.01,9]tridecane)nickel(II) nitrate, [Ni(L2)2][NO3]2. Compound L2 (425 mg, 2.32 mmol) and Ni(NO3)2?6H2O (337 mg, 1.16 mmol) were dissolved in water (75 cm3). The pH was adjusted to 8 with NaOH, and the solution set aside to crystallise. The pink crystalline product formed was collected, washed with cold ethanol and recrystallised from water (0.26 g, 45%) (Found: C, 43.65; H, 7.8; N, 20.8.Calc. for C20H42N8NiO6: C, 43.7; H, 7.7; N, 20.4%). Electronic spectrum (water): lmax 290 (23), 508 (7) and 812 (e 9 dm3 mol21 cm21) and 880 (sh) nm. Bis(2,5,8-triazabicyclo[7.4.01,9]tridecane)chromium(III) chloride perchlorate pentahydrate, [Cr(L2)2]Cl2[ClO4]?5H2O. The compound CrCl3?6H2O (727 mg, 2.73 mmol) was dissolved in DMSO (40 cm3) at 190 8C and the solution evaporated to 25 cm3.The solution was cooled to 70 8C and 1 g (5.45 mmol) of L2 in 10 cm3 ethanol was added. The temperature was raised to 170 8C and the DMSO completely evaporated. The product was dissolved in water, diluted to 500 cm3 and loaded onto a Dowex 50W-X2 cation-exchange column (3 × 25 cm). After washing with 1 mol dm23 HCl to remove unco-ordinated CrIII, first a red and then a major orange second band were eluted with 4 mol dm23 HCl. The volume was reduced to 15 cm3, solid NaClO4 was added and the solution set aside to crystallise (226 mg, 15%; further crops on extended standing) (Found: C, 35.6; H, 7.8; N, 12.1.Calc. for C20H52Cl3CrN6O9: C, 35.4; H, 7.7; N, 12.35%). Electronic spectrum (water): lmax 345 (55) and 446 nm (e 83 dm3 mol21 cm21). Bis(2,5,8-triazabicyclo[7.4.01,9]tridecane)iron(III) chloride hexahydrate, [Fe(L2)2]Cl3?6H2O. The compound FeCl3?6H2O (740 mg, 2.73 mmol) was dissolved in DMSO (30 cm3) at 140 8C, the resultant solution cooled to 25 8C, L2 (1 g, 5.45 mmol) in ethanol (10 cm3) added with stirring and the temperature raised to 150 8C.The solution was evaporated to 10 cm3 and the yellow-brown precipitate collected. The product was washed with cold ethanol and recrystallised from water. Orange crystals were collected, washed with ethanol and diethyl ether and air dried (413 mg, 29%) (Found: C, 37.2; H, 8.3; N, 12.7. Calc. for C20H42Cl3FeN6?6H2O: C, 37.7; H, 8.5; N, 13.2%). Electronic spectrum (water): lmax 347 (281), 435 (e 73 dm3 mol21 cm21) and 512 (sh) nm.Spectroscopic methods Absorption spectra were recorded using a Hitachi 150-20 spectrophotometer and circular dichroism spectra using a JASCO J-710 spectropolarimeter operating with J-700 Windows software, employing aqueous solutions. InfraredJ. Chem. Soc., Dalton Trans., 1999, 1975–1980 1977 spectra were recorded on a Bio-Rad FTS-7 FT-IR spectrometer for compounds dispersed in KBr discs, and NMR spectra on a Bruker Avance DPX300 spectrometer in either CDCl3 solution (for ligands) or D2O (for complexes). Voltammetry in aqueous solution (with 0.1 mol dm23 sodium perchlorate as electrolyte) employed a conventional three-electrode system and nitrogen purge gas, using a BAS Model CV-27 electrochemical controller.A glassy carbon working electrode polished with alumina before measurement of each voltammogram, a Ag–AgCl reference electrode and a platinum wire auxiliary electrode were used. The potentials reported were converted into those referred to the normal hydrogen electrode (NHE).The scan rate for cyclic voltammetry results reported was usually 100 mV s21. Microanalyses were performed by the Research School of Chemistry Microanalytical Service at the Australian National University. X-Ray crystallography Cell constants were determined by least-squares fits to the setting parameters of 25 independent reflections, measured and refined on a Rigaku AFC7R diVractometer, [Ni2(SS-L2)2- Cl3(OH2)][ClO4] A, or an Enraf-Nonius CAD4-F diVractometer [Co(RR-L2)2][PF6]2Cl?2.5H2O B, employing graphite monochromated Cu-Ka radiation (1.5418 Å) for A and Mo-Ka (0.71069 Å) for B.Data reduction and application of Lorentzpolarisation and y scan and analytical absorption corrections (A and B respectively) were carried out using TEXSAN.16 The structures were solved by direct methods using SHELXS 8617 and refined using full-matrix least-squares methods with TEXSAN.16 Hydrogen atoms were included at calculated sites with thermal parameters derived from the parent atoms.The hydrogen atoms of one of the co-ordinated water molecules of A were located in the diVerence map and included at these sites without further refinement. Non-hydrogen atoms were refined anisotropically. Scattering factors and anomalous dispersion terms for Ni and Co (neutral atoms) were taken from ref. 18. Anomalous dispersion eVects were included in Fc; 19 the values for Df 9 and Df 0 were those of Creagh and McAuley.20 The values for the mass attenuation coeYcients are those of Creagh and Hubbell.21 All other calculations were performed using TEXSAN.16 Selected bond lengths and angles are listed in Tables 2 and 3.The atomic nomenclature is defined in Figs. 2 and 3.22 Crystal data. [Ni2(SS-L2)2Cl3(OH2)][ClO4], C20H44Cl4N6- Ni2O5, M = 707.80, monoclinic, space group P21, a = 14.406(3), b = 7.845(1), c = 26.639(41) Å, b = 102.60(1)8, U = 2938(1) Å3, Dc (Z=4) = 1.600 Mg m23, m(Cu-Ka) = 3.069 mm21, F(000) = 1480, T = 294 K.Specimen: purple needles; N = 4953, No = 3996 [|Fo| > 2.5s(|Fo|), 38 < q < 618], hkl 0 to 16, 0 to 8, 229 to 29. Final R = 0.0426, R9 = 0.0475, parameters = 665, goodness of fit = 2.420. Residual extrema 10.49, 20.56 e Å23. [Co(RR-L2)2][PF6]2Cl?2.5H2O, C20H47ClCoF12N6O2.5P2, M = 795.94, monoclinic, space group C2, a = 20.443(2), b = 9.994(2), c = 8.8967(7) Å, b = 112.78(1)8, U = 1682.1(4) Å3, Dc (Z= 2) = 1.577 Mg m23, m(Mo-Ka) = 0.782 mm21, F(000) = 882, T = 294 K.Specimen: orange needles; N = 1585, No = 1485 [|Fo| > 2.5s(|Fo|), 2 < q < 258], hkl 224 to 22, 0 to 11, 0 to 10. Final R = 0.0526, R9 = 0.0534, parameters = 202, goodness of fit = 4.442. Residual extrema 10.62, 20.40 e Å23. CCDC reference number 186/1416. See http://www.rsc.org/suppdata/dt/1999/1975/ for crystallographic files in .cif format. Results and discussion The molecule L2, as a triazamacrocycle with a nine-membered saturated ring, is a close analogue of the well known L1,2 but with one of the CH2CH2 links between two secondary amine groups replaced by a cyclohexane unit.This is achieved by commencing with tosylated trans-cyclohexane-1,2-diamine and reacting with tosylated diethanolamine in a Richman– Atkins procedure, a process which yields the target small ring macrocycle with a reasonable yield of approximately 30%. An alternative procedure of treating dibromocyclohexane with a tritosylated triamine was not successful.Failure of this particular route can be interpreted in terms of steric hindrance of the initial substitution step, similar to arguments proposed earlier for a bulky nucleophile attacking a sterically hindered site.15 Steric hindrance is reduced in the successful method developed here, but the yield remains lower than achieved for the less bulky tacn. The free amine is obtained from the tosylated intermediate by employing sodium amalgam as the detosylating agent, a highly eYcient reaction where the triamine is recovered in essentially stoichiometric yield provided a large amount of freshly prepared amalgam is employed.Spectroscopy is consistent with the formulation of the product as L2; for example, five resonances are detected in the methylene region of the proton-decoupled 13C NMR spectrum, as required. Confirmation of the structure comes in the structural studies reported later.The potentially tridentate ligand L2 possesses two chiral carbon centres, and resolution of the precursor diamine prior to macrocycle synthesis yields an optically active macrocycle, since the chiral centres are not involved in any of the chemistry. In addition, the cyclohexane ring fused to the ring framework provides both a bulkier and more rigid macrocycle. As expected, the co-ordination chemistry (apart from chiroptical properties) of the racemic, RR- or SS-L2 forms is identical, and hence in discussion below reference to a particular optical isomer is made only when discussing circular dichroism spectroscopy.Octahedral complexes of cobalt(III), chromium(III), iron(III) and nickel(II) with two L2 molecules co-ordinated as tridentate ligands to two opposite octahedral faces have been prepared. The octahedral cobalt(III) complex has been characterised by a crystal structure analysis, and may represent the common isomer met in the series, although this awaits further structural studies.No great diYculty in preparing the bis(triamine) complexes was encountered, although it is known that some triazamacrocycles form only 1 : 1 complexes.2 In addition to the 1 : 2 nickel(II) complex, a dinuclear nickel(II) complex where a single L2 is co-ordinated to each of two nickel(II) ions was isolated and characterised by a crystal structure analysis. Again, tridentate co-ordination of the macrocycle is observed. There is no evidence to suggest that the 1 : 1 complex is preferred, the dinuclear mono and mononuclear bis complexes arising from slightly diVerent syntheses. The bis(L2) metal complexes can in principle exist in two geometric isomers (1 and 2 below).We did not detect in the chromatographic isolation of complexes more than one band assignable to bis(L2) species, with any minor additional band characteristic of a mono(L2) complex. This may mean that only one isomer is formed following equilibration, or else that separation is not readily achieved.However, at least for the diamagnetic cobalt(III) complex, NMR spectroscopy of the crude evaporated band oV the column does not show multiple sets of resonances, indicative of dominantly one isomer (1). Co NH NH NH NH NH NH Co NH NH NH NH NH NH 1 21978 J. Chem. Soc., Dalton Trans., 1999, 1975–1980 Previously, the only substituted chiral analogue of tacn reported was the R-2-methyl-1,4,7-triazacyclononane (L3).23 Examination of this system arose following the observation that crystals of the unsubstituted [Co(L1)2]Cl3 spontaneously resolve on crystallising, the individual chelate rings in a bound ligand having a preferred common configuration lll (or ddd).Optical activity cannot arise as a result of disposition of the ligands in this system, but solely from the dissymmetric chelate ring conformations, producing a relatively large Cotton eVect. With R-L3, the largest ring-conformation optical activity reported was observed.Unfortunately, X-ray crystallography showed orientational disorder of the methyl group,24 and nine geometrical and configurational isomers are possible, partly separated by chromatography on SP-Sephadex.25 Orientational disorder is removed and the number of possible isomers is reduced in the present study with L2. The CD of the cobalt(III) complex of the R,R-(2) isomer of L2 is dominated by a very strong Cotton eVect under the lowest energy transition at 486 nm of De 151.4 dm2 mol21 (Fig. 1). The maximum lies to lower energy than the absorption maximum (469 nm), and is most likely associated with the low-energy 1A1 æÆ 1E component under the 1A1g æÆ 1T1g octahedral transition envelope, similar to the behaviour for [Co(nn)3]31 complexes (nn = ethane-1,2-diamine, R-propane-1,2-diamine or R,R-cyclohexane-1,2-diamine).26 For these and related complexes a positive Cotton eVect is associated with the D absolute configuration of the complex.Whereas the distribution of chelate rings is an important component in these tris(bidentate ligand) systems, in the L2 complex the large Cotton eVect arises chiefly from the dissymmetric chelate ring conformations. The ddd conformations in the L2 complex produce the same sign of Cotton eVect under the low energy d–d transition as the ddd conformations in L3, with the size of the transition larger (by ca. 20%) for the L2 complex. A much less intense set of bands occurs under the higher energy 1A1g æÆ 1T2g octahedral transition envelope, with additional strong Cotton eVects between 180 and 300 nm presumably associated with charge transfer transitions and n æÆ p* transitions of the ligand.A comparison of the electronic spectra and metal-centred redox properties of bis(triamine)metal complexes of L1 and L2 appears in Table 1. It is immediately noticeable that, in all cases, Fig. 1 Circular dichroism spectrum of [Co(RR-L2)2][ClO4]3.Table 1 Comparison of the electronic spectra and redox potentials of [M(L1)2]n1 and [M(L2)2]n1 complexes Mn1 CoIII CrIII FeIII NiII Ligand L1 L2 L1 L2 L1 L2 L1 L2 lmax/nm (emax/dm3 mol21 cm21) 333 (89), 458 (100) 336 (96), 469 (97) 340 (64), 439 (88) 345 (55), 446 (83) 336 (288), 430 (82), 500 (sh) 347 (281), 435 (73), 512 (sh) 308 (12), 505 (5), 800 (7), 870 (sh) 290 (23), 508 (7), 812 (9), 880 (sh) E1/2/V vs. NHE 20.41 20.46 21.14 21.21 10.13 10.03 10.95 10.86 maxima for the L2 complexes are shifted to slightly lower energy than those for the L1 complex, indicative of a slightly weaker ligand field for the new ligand L2 compared with L1.Calculation of 10Dq for L2 from spectroscopy of the nickel(II) compounds yields ca. 12 300 cm21 compared with a value of ca. 12 500 cm21 reported for L1.27 The origins of this small diVerence are presumably steric, related to the bulk of the cyclohexane ring fused to the macrocycle ring adjacent to two of the nitrogen donors.Although there is no required relationship between redox potentials and electronic maxima, it is also notable that a reasonably consistent shift in redox potentials from L1 to L2 also occurs (Table 1). All four [M(L2)2]n1 complexes display reversible or quasireversible couples in the cyclic voltammetry (50 mV s21 scan rate, glassy carbon working electrode, aqueous 0.1 mol dm23 NaClO4) varying in potential from 10.86 V (DE 90 mV) for the NiIII/II couple, 10.03 V (DE 74 mV) for FeIII/II, 20.46 V (DE 76 mV) for CoIII/II, and to 21.21 V (DE 90 mV) for CrIII/II, cited versus the NHE.These range from 50 to 100 mV more negative than the values reported for the corresponding compound in the [M(L1)2]n1 series. The [Co(RR-L2)2][PF6]2Cl?2.5H2O complex crystallised in the C2 space group. The structure (Fig. 2) consists of a complex cation located on a crystallographic twofold rotation axis, a chloride anion also on a twofold rotation axis, a hexafluorophosphate anion and two water molecules, one at a general site and the other on a twofold rotation axis.The complex cation displays a distorted octahedral geometry and has the cyclohexane groups located trans to one another. There are no obvious steric reasons for this arrangement being preferred. As with the nickel complex discussed below, bond lengths and angles are not abnormal, although the Co–N(3) bond [1.948(5) Å] is significantly shorter than the two Co–N bond adjacent to the cyclohexane ring [Co–N(1) 1.976(7), Co–N(2) 1.976(8) Å] and is at the short end of the range for hexaaminecobalt(III) systems.With the two longer bonds associated with the two secondary nitrogen atoms adjacent to the cyclohexane ring, it is tempting to assign the elongation to steric eVects. However, the longer and not the shorter distances are very similar to the average distance reported for [Co(L3)2]31 of 1.974 Å,24 which suggests that steric influences of the cyclohexane ring are not marked.Fig. 2 A view of the [Co(RR-L2)2]31 cation, including atom numbering. Table 2 Selected bond distances (Å) and angles (8) for [Co(RR-L2)2]31 Co(1)–N(1) Co(1)–N(2) Co(1)–N(3) N(1)–Co(1)–N(1*) N(1)–Co(1)–N(2*) N(1)–Co(1)–N(3*) N(1*)–Co(1)–N(2*) N(1*)–Co(1)–N(3*) N(2)–Co(1)–N(3) N(2*)–Co(1)–N(3) N(3)–Co(1)–N(3*) 1.976(7) 1.976(8) 1.948(5) 92.4(4) 176.0(4) 97.4(3) 84.8(2) 85.3(3) 85.2(4) 92.3(3) 176.1(7) Co(1)–N(1*) Co(1)–N(2*) Co(1)–N(3*) N(1)–Co(1)–N(2) N(1)–Co(1)–N(3) N(1*)–Co(1)–N(2) N(1*)–Co(1)–N(3) N(2)–Co(1)–N(2*) N(2)–Co(1)–N(3*) N(2*)–Co(1)–N(3*) 1.977(7) 1.975(8) 1.948(5) 84.8(2) 85.3(3) 176.0(4) 97.4(3) 98.1(4) 92.3(3) 85.1(4)J.Chem. Soc., Dalton Trans., 1999, 1975–1980 1979 The contraction of the additional bond resembles the contraction observed with C-pendant macrocycles, such as in (trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13- diamine)cobalt(III), where the bond distance (to the pendant amine) is significantly reduced compared to the other two, a result of steric demands of the ligand in that case.28 However, there are in the present case no unique deformations around N(3) and adjacent atoms which distinguish it from N(1) and N(2), and the close approach may simply reflect the absence of constraining cyclohexane rings on the carbon chains joined to N(3).Fig. 3 A view of the [Ni2(SS-L2)2Cl3(OH2)]1 cation, including atom numbering.Table 3 Selected bond distances (Å) and angles (8) for [Ni2(SS-L2)2- Cl3(OH2)]1 Ni(1)–Cl(1) Ni(1)–Cl(3) Ni(1)–N(2) Ni(2)–Cl(1) Ni(2)–O(1) Ni(2)–N(5) Ni(3)–Cl(4) Ni(3)–Cl(6) Ni(3)–N(8) Ni(4)–Cl(4) Ni(4)–O(2) Ni(4)–N(11) Cl(1)–Ni(1)–Cl(2) Cl(1)–Ni(1)–N(1) Cl(1)–Ni(1)–N(3) Cl(2)–Ni(1)–N(1) Cl(2)–Ni(1)–N(3) Cl(3)–Ni(1)–N(2) N(1)–Ni(1)–N(2) N(2)–Ni(1)–N(3) Cl(1)–Ni(2)–O(1) Cl(1)–Ni(2)–N(5) Cl(2)–Ni(2)–O(1) Cl(2)–Ni(2)–N(5) O(1)–Ni(2)–N(4) O(1)–Ni(2)–N(6) N(4)–Ni(2)–N(6) Cl(4)–Ni(3)–Cl(5) Cl(4)–Ni(3)–N(7) Cl(4)–Ni(3)–N(9) Cl(5)–Ni(3)–N(7) Cl(5)–Ni(3)–N(9) Cl(6)–Ni(3)–N(8) N(7)–Ni(3)–N(8) N(8)–Ni(3)–N(9) Cl(4)–Ni(4)–O(2) Cl(4)–Ni(4)–N(11) Cl(5)–Ni(4)–O(2) Cl(5)–Ni(4)–N(11) O(2)–Ni(4)–N(10) O(2)–Ni(4)–N(12) N(10)–Ni(4)–N(12) Ni(1)–Cl(1)–Ni(2) Ni(3)–Cl(4)–Ni(4) 2.471(3) 2.480(2) 2.060(9) 2.460(2) 2.169(5) 2.056(7) 2.381(2) 2.454(2) 2.081(7) 2.442(3) 2.151(6) 2.087(7) 85.62(9) 98.0(3) 91.8(3) 176.4(3) 97.1(2) 94.6(2) 82.3(3) 83.0(3) 87.3(2) 174.6(3) 88.0(2) 99.4(3) 172.2(3) 96.7(4) 83.6(4) 85.84(9) 96.3(2) 94.4(2) 177.0(2) 95.6(3) 92.0(2) 83.0(3) 81.9(3) 89.1(2) 93.7(3) 88.4(2) 179.2(2) 173.6(3) 90.4(3) 83.9(4) 92.7(1) 95.2(1) Ni(1)–Cl(2) Ni(1)–N(1) Ni(1)–N(3) Ni(2)–Cl(2) Ni(2)–N(4) Ni(2)–N(6) Ni(3)–Cl(5) Ni(3)–N(7) Ni(3)–N(9) Ni(4)–Cl(5) Ni(4)–N(10) Ni(4)–N(12) Cl(1)–Ni(1)–Cl(3) Cl(1)–Ni(1)–N(2) Cl(2)–Ni(1)–Cl(3) Cl(2)–Ni(1)–N(2) Cl(3)–Ni(1)–N(1) Cl(3)–Ni(1)–N(3) N(1)–Ni(1)–N(3) Cl(1)–Ni(2)–Cl(2) Cl(1)–Ni(2)–N(4) Cl(1)–Ni(2)–N(6) Cl(2)–Ni(2)–N(4) Cl(2)–Ni(2)–N(6) O(1)–Ni(2)–N(5) N(4)–Ni(2)–N(5) N(5)–Ni(2)–N(6) Cl(4)–Ni(3)–Cl(6) Cl(4)–Ni(3)–N(8) Cl(5)–Ni(3)–Cl(6) Cl(5)–Ni(3)–N(8) Cl(6)–Ni(3)–N(7) Cl(6)–Ni(3)–N(9) N(7)–Ni(3)–N(9) Cl(4)–Ni(4)–Cl(5) Cl(4)–Ni(4)–N(10) Cl(4)–Ni(4)–N(12) Cl(5)–Ni(4)–N(10) Cl(5)–Ni(4)–N(12) O(2)–Ni(4)–N(11) N(10)–Ni(4)–N(11) N(11)–Ni(4)–N(12) Ni(1)–Cl(2)–Ni(2) Ni(3)–Cl(5)–Ni(4) 2.404(2) 2.081(7) 2.075(8) 2.421(3) 2.080(7) 2.07(1) 2.518(3) 2.103(9) 2.074(7) 2.444(2) 2.054(7) 2.06(1) 90.72(9) 174.7(2) 90.03(8) 94.1(2) 90.0(2) 172.6(2) 82.8(3) 85.50(9) 100.4(2) 92.6(3) 92.0(3) 174.8(3) 90.5(2) 81.9(3) 82.7(3) 91.56(9) 176.4(2) 89.1(1) 94.8(2) 93.0(2) 172.6(2) 82.1(3) 86.16(9) 96.4(3) 175.4(3) 95.4(2) 98.4(2) 92.4(2) 83.9(3) 81.8(3) 95.3(1) 91.7(1) The structure (Fig. 3) of the dinickel(II) complex of SS-L2 consists of two independent dimeric complex cations and two perchlorate anions. Tridentate co-ordination of the ligand L2 is confirmed. The dimers consist of two Ni(L2) units bridged by two m-chloro ligands.The co-ordination sphere of one of the Ni atoms is completed by a chloro ligand and the other by an aqua ligand with an intramolecular hydrogen bond [O(1) ? ? ? Cl(3) 3.316(7), O(2) ? ? ? Cl(6) 3.347 Å] between these two ligands producing a bend in the Ni2Cl2 plane. Additional assymetry in the dimers arises from the orientation of the L2 ligand. In both of the independent molecules one ligand has the cyclohexane ring lying in the Ni2Cl2 plane and the other ligand has it lying perpendicular to this plane.It is not clear whether this is a consequence of the diVerence in the nature of the axial ligands but there are no obvious steric reasons for the diVerence. It is possible that a number of isomers form in solution and this is the one that crystallises preferentially; the solution is very likely a complex mixture, as the bis(triamine)nickel(II) ions also crystallise from a similar reaction solution. The two independent molecular cations have the same arrangement of the tridentate ligands but are diastereomers.It is also not clear why the complex forms with one axial chloro ligand and one axial aqua ligand. However, if both axial ligands were chlorides the repulsion between them would lead to a folding in the opposite direction and a consequent repulsion between the amine ligands. Bond lengths and angles about the Ni are normal for amine complexes of this type and do not indicate that co-ordination of the tridentate ligand is accompanied by the induction of significant stress.The presence of a cyclohexane ring fused onto the basic tacn framework clearly influences the co-ordination chemistry involving this ligand somewhat. Nevertheless, the ability of a relatively rigid chiral tacn ligand to form 1 : 2 complexes with octahedral metal ions has been established, and aspects of the co-ordination chemistry of these described. We are extending our studies to examine the eVect of increasing the number of fused rings around the tacn core.Acknowledgements Support of the Australian Research Council for this project is gratefully acknowledged. References 1 H. Koyama and T. Yoshino, Bull. Chem. Soc. Jpn., 1972, 45, 481. 2 P. Chaudhuri and K. Wieghardt, Prog. Inorg. Chem., 1987, 35, 329 and refs. therein. 3 J. E. Richman and T. J. Atkins, J. Am. Chem. Soc., 1974, 96, 2268. 4 L. T. Taylor and D. H. Busch, J. Am. Chem. Soc., 1967, 89, 5372. 5 W. Rasshofer, W. Wehner and F. Vögtle, Liebigs Ann. Chem., 1976, 916. 6 R. D. Hancock and V. J. Thöm, J. Am. Chem. Soc., 1982, 104, 291. 7 A. McAuley and S. Subramanian, Inorg. Chem., 1990, 29, 2830. 8 L. R. Gahan, G. A. Lawrance and A. M. Sargeson, Aust. J. Chem., 1982, 35, 1119. 9 D. Parker, Macrocycle Synthesis: A Practical Approach, Oxford University Press, 1996. 10 L. A. Ochrymowycz, D. Gerber, P. Chongsawangvirod and A. K. Leung, J. Org. Chem., 1977, 42, 2644. 11 P. V. Bernhardt, B. Elliott, G. A. Lawrance, M. Maeder, M. A. O’Leary, G. Wei and E. N. Wilkes, Aust. J. Chem., 1994, 47, 1771. 12 T. J. Atkins, J. E. Richman and W. F. Oettle, Org. Synth., 1979, 58, 86. 13 F. Chavez and A. D. Sherry, J. Org. Chem., 1989, 54, 2290. 14 G. H. Searle and R. J. Geue, Aust. J. Chem., 1984, 37, 959. 15 P. G. Graham and D. C. Weatherburn, Aust. J. Chem., 1983, 36, 2349. 16 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, The Woodlands, TX, 1985 and 1992. 17 G. M. Sheldrick, SHELXS 86, in Crystallographic Computing 3, eds. G. M. Sheldrick, C. Krüger and R. Goddard, Oxford University Press, pp. 175–189. 18 D. T. Cromer and J. T. Waber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV.1980 J. Chem. Soc., Dalton Trans., 1999, 1975–1980 19 J. A. Ibers and W. C. Hamilton, Acta Crystallogr., 1964, 17, 781. 20 D. C. Creagh and W. J. McAuley, International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer, Boston, 1992, vol. C, Table 4.2.6.8, pp. 219–222. 21 D. C. Creagh and J. H. Hubbell, International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer, Boston, 1992, vol. C, Table 4.2.4.3, pp. 200–206. 22 C. K. Johnson, ORTEP, A Thermal Ellipsoid Plotting Program, Oak Ridge National Laboratory, Oak Ridge, TN, 1965. 23 S. F. Mason and R. D. Peacock, Inorg. Chim. Acta, 1976, 19, 75. 24 M. Mikami, R. Kuroda, M. Konno and Y. Saito, Acta Crystallogr., Sect. B, 1977, 33, 1485. 25 M. Nonoyama, Inorg. Chim. Acta, 1978, 9, 211. 26 C. F. Hawkins, Absolute Configuration of Metal Complexes, Wiley- Interscience, New York, 1971, ch. 5. 27 S. M. Hart, J. C. A. Boeyens and R. D. Hancock, Inorg. Chem., 1983, 22, 982. 28 P. V. Bernhardt, G. A. Lawrance and T. W. Hambley, J. Chem. Soc., Dalton Trans., 1989, 1059. Paper 8/09125K

ISSN:1477-9226    

DOI:10.1039/a809125k

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 1979–1984 1979 Spectral, magnetic and electrochemical properties of metal oxa- and oxathia-porphyrins † Bashyam Sridevi,a Seenichamy Jeyaprakash Narayanan,a Alagar Srinivasan,a Tavarekere K. Chandrashekar *,a and Japyesan Subramanianb a Department of Chemistry, Indian Institute of Technology, Kanpur-208016, U.P., India b Department of Chemistry, Pondicherry University, Pondicherry-605014, India Metal derivatives (CuII, NiII) of monooxa-, dioxa- and oxathia-tetraphenylporphyrins and their one-electron oxidised and reduced species have been studied.Electronic spectra of the monooxa and oxathia derivatives exhibit split Soret bands and a complicated pattern of Q-bands revealing their lower symmetry. The spectra of one-electron reduced species show only marginal shifts while the one-electron oxidised product of copper monooxaporphyrins show broad, red-shifted bands. Cyclic voltammetric studies indicated one-electron metalcentered reduction at fairly low potentials forming copper(I) and nickel(I) porphyrins.The ring-oxidised product exhibits weak antiferromagnetic interaction between the unpaired electrons of copper and the porphyrin ring. The ESR spectra of the copper dioxa- and oxathia-porphyrins exhibit rhombic symmetry with unusually small metal hyperfine couplings. A comparison of ACu values and the E2� 1 values for metal reduction suggests that distortion towards tetrahedral symmetry and the presence of a soft donor atom like sulfur in porphyrins are required to generate spectral and electrochemical properties like those observed for the type I copper center in proteins.Replacement of pyrrole N atoms in the porphyrin core by other heteroatoms such as S, Se, Te and O alters the core sizes and electronic structure.1,2 Recent studies on these systems have resulted in the synthesis of diverse porphyrins such as tetrathiaporphyrin dication,3 tetraoxaporphyrin dication,4 tetraoxa[22]porphyrin 5 and tetraoxa[26]porphyrin dications ([22] and [26] refer to the number of p electrons),6 dithia-, diselena-, monothia-, monoselena- and monotelluraporphyrins. 1,2 The tetrathia and tetraoxa derivatives cannot bind metal ions because of their dicationic nature while metal complexes of dithia and diselena derivatives have not been reported. However, monothiaporphyrin forms complexes with metal ions such as FeII, CuII, NiII and RhII, etc.; 7,8 only the nickel(II) complex of monoselenaporphyrin has been reported.9 The crystal structure of nickel(II) thiaporphyrin revealed a distorted square pyramid around the metal with an axial chloride ligand, leading to five-co-ordination.7,8 The unique feature of the structure is the co-ordinated thiophene ring which is bent out of the plane of the remainder of the ligand core and bound to the metal in a h1 fashion.Further, it has been shown that the derivatives of CuII and NiII undergo one-electron metalcentered reduction 10 to form the corresponding complexes of CuI and NiI and the nickel(I) ion has a nearly planar geometry and surprisingly short Ni]N and Ni]S bonds.11 However, relatively few reports 2 exist on the synthesis of oxaporphyrins and mixed oxathiaporphyrins in which one or more pyrrole rings have been replaced by furan rings and/or thiophene rings.To the best of our knowledge there are only two recent reports on the metal (NiII) binding properties of oxaporphyrins by Latos-Grazynski and co-workers 12 and Gross et al.13 Both monooxa- and dioxa-porphyrins form nickel(II) complexes, which can easily be reduced to the corresponding nickel(I) derivative and the crystal structures reveal a nearly in-plane co-ordination of the furan moiety as opposed to the side-on co-ordination observed for the thiophene and selenophene porphyrins.7 We have been interested in the core modification of tetraarylporphyrins and our earlier studies on thiaporphyrins have revealed many interesting similarities and diVerences in optical, electrochemical and photochemical properties.14 Further, our recent study 15 on free base oxa- † Non-SI units employed: G = 1024 T, mB ª 9.27 × 10224 J T21. and oxathia-porphyrins revealed that the oxaporphyrins behave more like the parent tetraphenylporphyrin in their spectroscopic properties while their electrochemical properties resemble those of thiaporphyrins.In this paper we report the metal binding (CuII and NiII) properties of monooxa-, dioxa- and oxathia-porphyrins and their one-electron reduced and oxidised species.Specifically, electronic absorption spectra have been used to study groundstate properties while the redox chemistry has been monitored by cyclic voltammetry. The changes occurring in the electron delocalisation pathway and the metal–ligand bond strength upon binding of CuII have been studied by ESR spectroscopy.It has been shown that the first reduction is metal centered, corresponding to the formation of complexes of CuI and NiI, while the first oxidation of copper monoxaporphyrins is ring based with a weak antiferromagnetic coupling between the metal and the ring unpaired electrons. Results The metallation of oxaporphyrins can readily be done using literature methods.12 The copper(II) and nickel(II) derivatives of monooxa and monothia derivatives are stable both in the solid and solution states, the dioxa derivative on a chromatographic column undergoing gradual demetallation while the oxathia derivative on standing for few hours in the solid decomposes to give the corresponding free base porphyrin.The electronic absorption spectra of various neutral, one-electron-reduced and -oxidised copper oxaporphyrins are shown in Fig. 1 and the data are in Table 1. In general, the optical bands are red shifted both in the Soret and Q-band region relative to the parent [M(tpp)] (M = Cu or Ni) and the magnitude of the shifts are smaller for oxaporphyrins compared to their thiaporphyrin counterpart.14 The e values are significantly reduced for the core-modified porphyrins relative to the parent [M(tpp)].16 The EPR spectra of the copper porphyrins described here were recorded in toluene–CH2Cl2 (1 : 1) at room and liquid nitrogen temperature. Fig. 2 compares room temperature spectra of [CuLS(Cl)] and [CuLO(Cl)]. Only the former exhibited superhyperfine couplings from the co-ordinated nitrogens at room temperature.However, at low temperature, these couplings are observed for monooxaporphyrins while the1980 J. Chem. Soc., Dalton Trans., 1998, Pages 1979–1984 Table 1 Electronic spectral data of various copper and nickel porphyrins in CH2Cl2 lmax/nm (1024 e/M21 cm21) Porphyrin [CuLS(Cl)] [CuLO(Cl)] [CuLO,Me(Cl)] [CuLO,OMe(Cl)] [CuLO,Br(Cl)] [CuL2OCl2] Soret band 463 (8.5) 430 (7.0) 434 (11.5) 436 (5.5) 434 (10.6) 417 (7.6) 429 (9.2) 416 (7.9) 421 (10.1) — 418 (7.0) — Q-bands 705 (5.4) 625 (1.4) 634 (2.1) 639 (1.9) 636 (3.0) 670 (3.0) 557 (12.2) 572 (6.3) 575 (7.1) 580 (4.5) 579 (8.2) 600 (2.6) — 534 (8.0) 538 (9.3) 542 (5.9) 538 (10.9) 507 (8.1) [CuLOSCl2] 454 (12.4) 437 (12.5) 688 (12.6), 644 (13.2), 578 (11.9), 538 (14.4) [NiLS(Cl)] 466 (8.0) 428 (17.6) 710 (6.9), 675 (7.0), 612 (8.8), 547 (11.6), 511 (22.7) [NiLO(Cl)] 428 (8.6) 416 (8.4) 738 (1.6), 707 (1.7), 633 (2.8), 579 (8.6), 551 (7.6) [NiL2OCl2] 417 (13.5) — 688 (4.6), 665 (4.5), 604 (4.1), 504 (14.0) dioxa- and oxathia-porphyrins did not show any superhyperfine couplings in frozen solution or in the solid diluted in a diamagnetic matrix (free base dioxaporphyrin) even at low temperature (Fig. 3). The spin Hamiltonian parameters 17 evaluated from the observed spectra are listed in Table 2. In general, the EPR spectra reveal the presence of a distorted tetragonal copper site 17,18 in the monooxa derivative while the dioxa and oxathia derivatives show rhombic spectra.Replacement of a N-donor atom of a pyrrole ring by O or S results in a decrease in the ACu values with a concomitant increase in g values.19 The nitrogen superhyperfine splittings observed for some derivatives show only a minor variation on going from [Cu(tpp)] to its oxa and thia derivatives, suggesting a predominantly isotropic interaction.178 Cyclic voltammetric studies in CH2Cl2 containing NBu4ClO4 N N N O M Cl Monooxaporphyrin R1 H Me OMe Br R2 H H H H R3 H H H H M = Cu2+ [CuLO(Cl)] [CuLO,Me(Cl)] [CuLO,OMe(Cl)] [CuLO,Br(Cl)] M = Ni2+ [NiLO(Cl)] O N N O Ph Ph Ph Ph M Cl Cl N S O N Ph Ph Ph Ph M Cl Cl Dioxaporphyrin Oxathiaporphyrin M = Cu2+ [CuL2OCl2] M = Ni2+ [NiL2OCl2] M = Cu2+ [CuLOSCl2] R1 R3 R2 R3 R2 R1 as the supporting electrolyte show one-electron quasi-reversible (DEp 90–140 mV) reduction at fairly low potentials except for [NiLO(Cl)] and [CuLOSCl2] which show irreversible reduction.Fig. 4 compares cyclic voltammograms of [NiLS(Cl)], [CuLS(Cl)] and [CuLO(Cl)]. In all the cases the separation between the anodic and cathodic peaks was dependent on the Fig. 1 Electronic absorption spectra of (A) copper monooxa derivatives and their one-electron-oxidised and -reduced species in CH2Cl2. The concentrations used were: Soret band, 2.6 × 1026; and Q-bands, 2.6 × 1025 M. (B) Copper dioxa and oxathia derivatives and oneelectron- reduced copper dioxaporphyrin in CH2Cl2; concentrations as in (A) Table 2 Spin Hamiltonian parameters evaluated from ESR spectra for various copper porphyrins Porphyrin [Cu(tpp)] [CuLS(Cl)] [CuLO(Cl)] [CuLO,Me(Cl)] [CuLO,OMe(Cl)] [LO,Br(Cl)] A|| Cu 209 159 118 115 114 110 A^ Cu 32.8 28.4 25.7 25.5 27.2 n.r.A^ N 16.4 14.2 12.9 12.7 13.6 n.r. g|| 2.1870 2.2120 2.2493 2.2506 2.2561 2.2569 g^ 2.032 2.056 2.036 2.042 2.040 2.036 a2 0.8277 0.7218 0.6540 0.6528 0.6535 0.6390 [CuL2OCl2] [CuLOSCl2] Axx 75 78 Ayy 30 29 Azz 102 99 gxx 2.01 2.01 gyy 2.08 2.085 gzz 2.29 2.31 The A values are in 1024 cm21.n.r. = Not resolved.J. Chem. Soc., Dalton Trans., 1998, Pages 1979–1984 1981 scan rate and an illustration of this eVect for [CuLOSCl2] along with cyclic voltammograms of the dioxa derivatives of CuII and NiII are shown in Fig. 5. The half wave potentials (Table 3) evaluated for this reduction in all the cases are outside the range accessible to porphyrin ring reduction in the same solvent. For example, the first ring reductions of the free oxa, dioxa and oxathia base derivatives fall in the range 20.90 to 21.20 V.15 Based on earlier work on thiaporphyrins from this laboratory 14 and others 7 and the electronic spectra of the ring-reduced products,20 this reduction is assigned to the metal-centered reduction corresponding to the formation of porphyrins of CuI and NiI. It is pertinent that Latos-Grazynski and co-workers 12 have recently isolated the nickel(I) complexes of oxa- and dioxaporphyrins.The chemical oxidation of copper(II) monooxa derivatives with a one-electron oxidant leads to the formation of ringoxidised products and the absorption spectra exhibit the changes which would be expected upon ring oxidation 20 [Fig. 1(A)]. The oxidised species are EPR silent both in the solid and solution state at room temperature suggesting their diamagnetic Fig. 2 Room temperature EPR spectra of copper monooxa (LO) and monothia (LS) complexes in toluene–CH2Cl2 (1 : 1).The concentrations used were ª1023 M; dpph = diphenylpicrylhydrazyl Fig. 3 (a) The EPR spectrum of copper dioxaporphyrin frozen in toluene–CH2Cl2 (1 : 1). The concentration used was ª1023 M. (b) Simulated spectrum; spin Hamiltonian parameters in Table 2 nature. Repeated magnetic susceptibility measurements at room temperature show a small magnetic moment in the range 0.8– 1.1 mB suggesting a weak antiferromagnetic interaction. This value may be contrasted with 2.40 mB measured for [Cu(tpp)] radical cation in CD2Cl2.21 A recent study from this laboratory on a distorted copper(II) porphyrin cation radical also showed an antiferromagnetic interaction between the two unpaired electrons of the metal and ring both in the solid and solution state.22 Chemical oxidation of [CuL2OCl2] and [CuLOSCl2] resulted in demetallation leading to free base dications as revealed by the absorption spectra.Discussion Electronic absorption spectra The absorption spectra of the metal oxa and thia derivatives show characteristic Soret and Q-bands in the region 400–800 nm.16 The monooxa, monothia and oxathia derivatives exhibit split Soret bands and a complicated pattern of Q-bands, unlike [M(tpp)] (M = Cu or Ni), revealing their lower symmetry.On the other hand, the spectra of metal dioxaporphyrins are not too much diVerent from those of the corresponding free base derivatives.15 The one-electron-reduced species show small blue shifts of absorption bands while the one-electron-oxidised [CuLO(Cl)] exhibits significant changes.This is not surprising considering the fact that the first ring reduction involves the metal center and on going from MII to MI the porphyrin ring does not undergo any major change in its p-electron conjugation. On the other hand, the oxidation of the porphyrin ring aVects the porphyrin p-electron conjugation because of the removal of an electron from the p system 10,20 and is expected to show broad red-shifted Q-bands and the Soret band as observed.The e values of the metal derivatives are about 50% smaller than those of the corresponding free base derivatives, suggesting a decreased p-electron conjugation upon metal Fig. 4 Cyclic voltammograms of copper monooxa-, monothia- and nickel monothia-porphryins in CH2Cl2 recorded at 100 mV s21 scan speed; 0.1 M NBu4ClO4 was used as the supporting electrolyte in CH2Cl2 Table 3 Reduction potential for the MII–MI coupling for various copper and nickel porphyrins Porphyrin [CuLS(Cl)] [CuLO(Cl)] [CuLO,Me(Cl)] [CuLO,OMe(Cl)] [CuLO,Br(Cl)] [CuL2OCl2] [CuLOSCl2] [NiLS(Cl)] [NiLO(Cl)] [NiL2OCl2] E2� 1 (MII–MI)/V 20.05 20.22 20.24 20.25 20.24 20.37 20.11 20.06 20.42 20.36 DEp/mV 130 131 145 118 114 105 294 106 350 971982 J.Chem. Soc., Dalton Trans., 1998, Pages 1979–1984 interaction. This probably is due to the distorted geometry of the porphyrin ring around the metal (see below).ESR spectra The spread of g values, g|| in particular, for CuX4 systems with X = S, O and N is well documented.19,23 Generally, the g|| values decrease and increase respectively for X = S and O donors relative to X = N. This has been interpreted in terms of the relative hard and soft nature of the donor atoms.24 Thus, on going from CuN4 to CuN3S for a monothiaporphyrin the value is expected to decrease slightly if the core structure around the metal remains square planar in CuN3S.However, the g|| value increases slightly (Dg|| = 0.025) for CuN3S suggesting a distortion from the regular planar geometry. The dioxa and the oxathia derivatives result in further distortion around the metal centre and the lower symmetry is reflected in the rhombic spectra observed for these complexes. The decrease in the A values has been attributed to the direct mixing of 4s metal orbitals with the ground state of CuII caused by the symmetry lowering.7 This is substantiated by recent work of Solomon and co-workers 25 on the reduced and oxidised site of blue copper proteins.They have ascribed the small EPR hyperfine splittings observed for the oxidised form of blue copper proteins to the extremely high covalency of the copper 3dx2 2 y2 HOMO which is highly anisotropic with 42% Cu and 36% S (cysteine) and <2% on each histidine nitrogen. It has been shown that only the mixing of the unoccupied 4s/4p orbitals and the half occupied copper 3dx2 2 y2 orbital with the filled ligand levels contributes to the strength of the individual Cu]L bonds.In the present study the changes occurring upon distortion can at least be evaluated for the Cu]N in-plane s bond through the covalency factor a2 which represents the bonding coeYcient of the b1 molecular orbital.18 The stronger the in-plane s bond between the CuII and N, the higher is the Fig. 5 Cyclic voltammograms of (A) the copper oxathiaporphyrin in CH2Cl2 at various scan speeds.(B) Comparison of cyclic voltammograms of copper and nickel dioxaporphyrins in CH2Cl2 at scan speed 200 mV s21 energy of the b1 molecular orbital because of its antibonding character. The gradual decrease in the value of a2 observed on distortion (Tle 2) suggests a lowering of the energy of the b1 molecular orbital relative to that of [Cu(tpp)] and a weaker Cu]N s bond in the distorted porphyrins. Strong support for such a conclusion comes from (a) the observed small decrease in A^ N values for copper(II) monooxaporphyrins relative to [Cu(tpp)] and (b) comparison of measured bond distances for Cu]N in [Cu(tpp)] 26 [1.981(7) Å] and [CuLS(HCO3)] 7 (1.993, 2.042 and 2.067 Å).The energy-optimised structures calculated for the monooxa, dioxa and oxathia copper(II) derivatives shown in Fig. 6 further confirm the existence of distortion. However, it should be pointed out that the geometry-optimised structures give only a rough idea about the geometry around the metal centre and this should be taken as a qualitative explanation.A comparison of structures revealed maximum distortion for the oxathia derivative which is not surprising because of the diVerent coordination modes of thiophene sulfur and furan oxygen. It is known from the crystal structures reported for nickel(II) complexes of thia- and oxa-porphyrins that the furan oxygen coordinates in a h1 fashion without serious distortion while the thiophene sulfur is bent out of the plane of the porphyrin ring upon co-ordination.11 However, the observed distortion for [CuL2OCl2] is surprising in view of the reported structure of [NiL2OCl2] which shows a pseudo-octahedral geometry in which the pyrrole and furan rings are coplanar.It is possible that Cu21 being a Jahn–Teller ion can still be distorted and this is not expected for the corresponding nickel(II) derivative. The observation that the Soret band of [CuL2OCl2] is broad compared to that of [NiL2OCl2] probably suggests a lower symmetry in the copper(II) complexes. Only crystal structures can confirm this point.Electrochemical studies The electrochemical data of the complexes establish the presence of one-electron metal-centered reduction in each case and Fig. 6 Calculated optimised structures of [CuLO(Cl)], [CuL2OCl2] and [CuLOSCl2]. The meso phenyl rings are omitted for clarityJ. Chem. Soc., Dalton Trans., 1998, Pages 1979–1984 1983 the reduction potentials are raised to more positive values by partial replacement of N-donors by S and/or O.However, the individual E2� 1 values vary depending on the metal and the number and nature of the donor atoms. For the copper porphyrins, E2� 1 varies as [CuLS(Cl)] > [CuLO(Cl)] > [CuL2OCl2] while for the nickel porphyrins [NiLS(Cl)] > [NiL2O(Cl)] > [NiLO(Cl)]. In both cases the thiaporphyrins show more positive values compared to those of the oxaporphyrins. This establishes that the presence of a soft donor atom like S may be one of the factors responsible for the more positive values by stabilisation through its p-acceptor capability.23,27 Comparison of Ni]S bond distances measured from the crystal structures of thiaporphyrins of NiII and NiI establishes this possibility (NiII]S 2.296 and NiI]S 2.143).If, on the other hand, the magnitude of distortion towards tetrahedral geometry is the only deciding factor for the more positive E2� 1 value, then [CuL2OCl2] and [CuLOSCl2] would be expected to show more positive E2� 1 values relative to the others.Since the measured E2� 1 values do not show this trend, clearly both the geometrical changes upon reduction and the nature of the donor atom in the porphyrin core are important in deciding the magnitude of E2� 1 for the MII– MI couple. This is further substantiated by the conclusions of Solomon and co-workers 25 in their electronic structure studies on the reduced and oxidised site of blue copper proteins.It has been pointed out that the two factors which are important for high reduction potentials are: (a) the weakening of the copper–thioether axial bond in the oxidised state and (b) the formation of a strong copper–thiolate equatorial p bond through the overlap of p orbitals on S with the 3dx2 2 y2 orbital on Cu. However, it should be mentioned that recent work on bis(pyrazole) complexes of CuII with only N and O donors also revealed high reduction potentials for the CuII–CuI couple and this has been explained on the basis of the availability of an appropriate ligand geometry for stabilisation of CuI.28 In general, the reversibility of the MII–MI couple depends on the structural change accompanying the reduction process.29 If no hindrance is expected to the adoption of a tetrahedral stereochemistry upon reduction, then the redox couple exhibits Nernstian behaviour, while any structural change such as ligand loss or ligand substitution under the reaction conditions results in a quasi-reversible or irreversible couple.For example, the irreversible nature of [Cu(Me4cyclam)]21 (Me4cyclam = 1,4,8,11- tetramethyl-1,4,8,11-tetraazacyclotetradecane) reduction is associated with ligand substitution in the reduced form, while the reversible nature of the [Cu(dth)2]21–[Cu(dth)2]1 (dth = 2,5-dithiahexane) couple is assigned to the adoption of tetrahedral symmetry without hindrance.19,23 The deviation from the electrochemical reversibility of porphyrin complexes of Cu and Ni observed in the present study suggests that the MII–MI reduction is accompanied by a relatively slow structural rearrangement because of the macrocyclic constraints.That the peak separation depends on the scan rate further justifies such a conclusion. Magnetic studies Earlier magnetic studies 21,30 on the [Cu(tpp)]~1 radical indicate that the radical cation is completely diamagnetic in the solid state and paramagnetic (S = 1) in solution.The diamagnetism in the solid was explained on the basis of the dimeric nature of the radical cation and the crystal 21 structure reveals the presence of a ruZed core which removes the orthogonality between the metal dx2 2 y2 orbital and the porphyrin a1 (p) orbital, facilitating d–p coupling. However, in solution, it was assumed that [Cu(tpp)]~1 is monomeric with a planar core where a strict orthogonality of magnetic orbitals prevents d–p coupling.The observed weak antiferromagnetic coupling for the copper monooxa radicals here again supports the presence of distorted cores at the metal both in solution and in the solid as revealed by EPR spectra. Conclusion It has been demonstrated that the core-modified oxa- and oxathia-porphyrins bind metal ions and their spectral and electrochemical properties parallel those observed for the thiaporphyrins. The metallation of oxathiaporphyrin establishes the co-ordination of pyrrole nitrogen, thiophene sulfur and furan oxygen in a single porphyrin unit.The unusually small ACu values observed for [CuL2OCl2] and [CuLOSCl2] represent the lowest values observed to date for any copper(II) porphyrin. Furthermore, this study has demonstrated that the maximum distortion towards tetrahedral symmetry does not necessarily shift the reduction potential for the MII–MI couple to more positive values at least for porphyrin systems, and the presence of a soft donor atom is necessary to generate the low ACu values and the more positive reduction potentials observed for blue copper proteins.Probably the copper(II) complex of a dithiaporphyrin could highlight this observation. Unfortunately, the dithiaporphyrin reported in which the two thiophene rings are opposite to each other does not form a copper(II) complex. Currently, we are exploring the synthesis of core-modified expanded porphyrins in which a CuN2S2 co-ordination geometry can be achieved.Experimental Syntheses of complexes Free base oxa- and dioxa-porphyrins were prepared and characterised following the reported procedure 2c,12 and the oxathiaporphyrin was prepared and characterised as described in our earlier work.15 All the chemicals used for the syntheses were reagent grade unless otherwise specified. Solvents for spectroscopic measurements were purified and dried according to the standard methods.[CuLO(Cl)]. A solution of CuCl2?2H2O (0.040 g, 1.173 mmol) in ethanol (5 cm3) was added to a solution of 5,10,15,20- tetraphenyl-21-oxaporphyrin (0.030 g, 0.048 mmol) in dichloromethane (50 cm3) and the mixture refluxed for 3 h w. It was cooled and then the solvent was removed under reduced pressure. The solid was dissolved in dichloromethane and washed several times with water. The organic fraction was dried over anhydrous sodium sulfate and chromatographed on a basic alumina column using dichloromethane–methanol (95 : 5).The first fraction was identified as free base and the metallated porphyrin was eluted next with dichloromethane– methanol (90 : 1). The solid obtained after evaporation of solvent under reduced pressure was dried in vacuum which gave pure [CuLO(Cl)] (0.027 g, 79%). FAB mass spectrum: m/z 678 (M 2 Cl) (calc. 678.27) (Found: C, 74.4; H, 3.8; N, 5.5. C44H28ClCuN3O requires C, 74.04; H, 3.95; N, 5.88%).A similar procedure was followed for other copper(II) monooxaporphyrins. [CuL2OCl2]. A solution of CuCl2?2H2O (0.030 g, 0.879 mmol) in ethanol (5 cm3) was added to a solution of 5,10,15,20- tetraphenyl-21,23-dioxaporphyrin (0.040 g, 0.065 mmol) in dichloromethane (50 cm3) with stirring. The mixture was heated under reflux for 8 h. It was cooled and the solvent removed under reduced pressure. The solid was washed with water till the filtrate was colourless, then extracted with dichloromethane and the solution concentrated.An equal volume of hexane was added and kept for crystallisation. Attempted purification by column chromatography using alumina resulted in demetallation. The solid residue was separated by filtration which gave the pure product [CuL2OCl2] (0.022 g, 46.1%). FAB mass spectrum: m/z 680 (M 2 2Cl) (calc. 680.26) (Found: C, 70.1; H, 3.5; N, 3.6. C44H28Cl2CuN2O2 requires C, 70.35; H, 3.72; N, 3.75%). [CuLOSCl2]. This complex was prepared using the same pro-1984 J.Chem. Soc., Dalton Trans., 1998, Pages 1979–1984 cedure as above. When kept for a long time even in the solid state slow demetallation of copper to form the free base occurred. Attempts to record the FAB mass spectrum resulted in demetallation giving the free base. Combustion analysis also indicated demetallation. Only UV/VIS and ESR spectra were used to infer the formation of [CuLOSCl2]. [CuLO(Cl)]~1[SbCl6]2. The complex [CuLO(Cl)] (0.010 g, 0.014 mmol) in dichloromethane (10 cm3) was stirred for 10 min under argon and 1.1 equivalent of tris(p-bromophenyl)- ammonium hexachloroantimonate (0.012 g, 0.015 mmol) solution in dichloromethane (5 cm3) was added and stirred for about 3 h.The progress of the reaction was monitored by checking the absorption spectra at diVerent time intervals. After completion of the reaction the solution was filtered, solvent evaporated under reduced pressure and the product obtained recrystallised from dichloromethane–hexane (yield 0.010 g, 80%) (Found: C, 50.34; H, 2.51; N, 4.35.C44H28Cl7- CuN3OSb requires C, 50.42; H, 2.69; N, 4.01%). The nickel(II) derivatives of the monooxa- and dioxaporphyrins were prepared following the reported procedure.12 Measurements The electronic spectra were recorded on a Shimadzu UV-160 spectrophotometer, proton NMR spectra on a Bruker 200 MHz spectrometer. Analyses (C, H, N) were done on a Heraeus Carlo Erba 1108 elemental analyser.The FAB mass spectra were recorded using a JEOL SX-120/DA6000 spectrometer with Ar as the FAB gas, ESR spectra on a Varian E-109 X-band spectrometer at room and liquid nitrogen temperature. Cyclic voltammetric and controlled potential coulometric studies were done on a EG/G Par model 273A polarographic analyser interfaced to a computer. A three-electrode system consisting of a platinum working electrode, a platinum-mesh counter electrode and a commercially available saturated calomel electrode (SCE) as the reference electrode were used.This reference electrode was separated from the bulk of solution by a fritted glass bridge filled with the solvent–supporting electrolyte mixture. Half-wave potentials were measured as the average of the cathodic and anodic peak potentials. Solid-state magnetic susceptibility measurements were done by the Faraday technique using a locally built magnetometer. The set-up consisted of an electromagnet with constant-gradient pole gaps (Polytronic Corporation, Bombay, India) and a Sartorius M25-D/S balance (Germany).The system was calibrated using Hg[Co(SCN)4]. Susceptibilities were corrected for diamagnetic contribution. The energy-optimised structures were calculated using HYPERCHEM version 5.0 software 31 on a Pentium 120 MHZ personal computer. A MM1 force field was employed with the use of the Polare-Ribere conjugated gradient with convergence limit at 0.001. Acknowledgements T.K. C. thanks the Department of Science and Technology and Council of Scientific and Industrial Research for the financial support. We thank Professor R. N. Mukherjee for the help in measurement of magnetic susceptibility and Professor Dogra for help in calculations. References 1 A. Ulman and J. Manassen, J. Am. Chem. Soc., 1975, 97, 6540; A. Ulman, J. Manassen, F. Frolow and D. Rabinovich, J. Am. Chem. Soc., 1979, 101, 7055; A. Ulman and J. Manassen, J. Chem. Soc., Perkin Trans. 1, 1979, 1069; Tetrahedron Lett., 1978, 167; L. Hill, M. Gouterman and A. Ulman, Inorg. Chem., 1982, 21, 1450. 2 (a) A. Ulman, J. Manassen, F. Frolow and D. Rabinovich, Inorg. Chem., 1981, 20, 1987; (b) P. Stein, A. Ulman and T. G. Spiro, J. Phys. Chem., 1984, 88, 369; (c) M. J. Broadhurst, R. Grigg and A. W. Johnson, J. Chem. Soc. C, 1971, 3681; (d ) L. Latos-Grazynski, E. Pacholska, P. J. Chmielewski, M. M. Olmstead and A. L. Balch, Angew. Chem., Int. Ed. Engl., 1995, 34, 2252. 3 E. Vogel, P. Rohrig, M. Sicken, B. Knipp, A. Herrmann, M. Pohl, H. Schmickler and J. Lex, Angew. Chem., Int. Ed. Engl., 1989, 28, 1651. 4 M. Pohl, M. Schmickler, J. Lex and E. Vogel, Angew. Chem., Int. Ed. Engl., 1991, 30, 1693. 5 G. Markl, H. Sauer, P. Kreitmeier, T. Burgermeister, F. Kastner, G. Adolin, H. Noth and K. Polborn, Angew Chem., Int. Ed. Engl., 1994, 33, 1151. 6 E. Vogel, Pure Appl. Chem., 1993, 63, 143. 7 L. Latos-Grazynski, J. Lisowski, M. M. Olmstead and A. L. Balch, J.Am. Chem. Soc., 1987, 109, 4428; Inorg. Chem., 1989, 28, 1183; J. Lisowski, M. Grzeszczuk and L. Latos-Grazynski, Inorg. Chim. Acta, 1989, 161, 153; L. Latos-Grazynski, J. Lisowski, M. M. Olmstead and A. L. Balch, Inorg. Chem., 1989, 28, 3328. 8 R. P. Pandian and T. K. Chandrashekar, J. Chem. Soc., Dalton Trans., 1993, 119. 9 L. Latos-Grazynski, E. Pacholska, P. J. Chmielewski, M. M. Olmstead and A. L. Balch, Inorg. Chem., 1996, 35, 566. 10 P. Chmielewski, M. Grzeszczuk, L.Latos-Grazynski and J. Lisowski, Inorg. Chem., 1989, 28, 3546. 11 L. Latos-Grazynski, M. M. Olmstead and A. L. Balch, Inorg. Chem., 1989, 28, 4065. 12 P. Chmielewski, L. Latos-Grazynski, M. M. Olmstead and A. L. Balch, Chem. Eur. J., 1997, 3, 268. 13 Z. Gross, I. Saltsman, R. P. Pandian and C. M. Barzilay, Tetrahedron Lett., 1997, 38, 2383. 14 R. P. Pandian, D. Reddy, N. Chidambaram and T. K. Chandrashekar, Proc. Indian Acad. Sci. (Chem. Sci.), 1990, 102, 307; R. P. Pandian, T.K. Chandrashekar and H. V. Willigen, Chem. Phys. Lett., 1992, 198, 163; R. P. Pandian, T. K. Chandrashekar, G. S. S. Saini and A. L. Verma, J. Chem. Soc., Faraday Trans., 1993, 677; R. P. Pandian, T. K. Chandrashekar and H. V. Willigen, Chem. Phys. Lett., 1993, 202, 127; M. Ravikanth and T. K. Chandrashekar, Struct. Bonding (Berlin), 1995, 82, 105; R. P. Pandian and T. K. Chandrashekar, Inorg. Chem., 1994, 33, 3317. 15 B. Sridevi, S. J. Narayanan, A. Srinivasan, M.V. Reddy and T. K. Chandrashekar, J. Porphyrins Phthalocyanines, 1998, 2, 69. 16 M. Gouterman, The Porphyrins, ed. D. Dolphin, Academic Press, New York, 1979, vol. 3, ch.1. 17 J. M. Assour, J. Chem. Phys., 1965, 43, 2477. 18 W. C. Lin, The Porphyrins, ed. D. Dolphin, Academic Press, New York, 1979, vol. 4, p. 355; A. H. Maki and B. R. McGarvey, J. Chem. Phys., 1958, 29, 31. 19 J. Bednarek and S. Schlick, J. Am. Chem. Soc., 1990, 112, 5019; U. Sakaguchi and A. W. Addison, J. Chem. Soc., Dalton Trans., 1979, 600 and refs. therein. 20 J. H. Fuhrhop, The Porphyrins, ed. D. Dolphin, Academic Press, New York, 1979, vol. 2, ch. 5. 21 B. S. Erler, W. F. Scholz, Y. J. Lee, W. R. Scheidt and C. A. Reed, J. Am. Chem. Soc., 1987, 109, 2644; W. F. Scholz and C. A. Reed, J. Am. Chem. Soc., 1982, 104, 6791. 22 M. Ravikanth, A. Misra, T. K. Chandrashekar, S. Sathiah and H. D. Bist, Inorg. Chem., 1994, 33, 392. 23 H. Yokoi and A. W. Addison, Inorg. Chem., 1977, 16, 1341; J. Pesiach and W. E. Blumberg, Arch. Biochem. Biophys., 1974, 165, 691; T. Vanngard, Biological Applications of Electron Spin Resonance, eds. H. M. Swartz, J. R. Bolton and D. C. Borg, Wiley- Interscience, New York 1972, p. 411; J. R. Wasson, H. W. Richardson and W. E. Hatfield, Z. Naturforsch., Teil B, 1977, 32, 551. 24 B. R. McGarvey, J. Phys. Chem., 1967, 71, 51; J. I. Zink and R. S. Drago, J. Am. Chem. Soc., 1972, 94, 4550. 25 J. A. Guckert, M. D. Lowery and E. I. Solomon, J. Am. Chem. Soc., 1995, 117, 2817; K. W. Penfield, A. A. Gewirth and E. I. Solomon, J. Am. Chem. Soc., 1985, 107, 4519. 26 B. Fleischer, C. K. Miller and L. E. Webb, J. Am. Chem. Soc., 1974, 86, 2342. 27 E. R. Dockal, T. E. Jones, W. F. Sokol, R. J. Engerer, D. B. Rorabacher and L. A. Ochrymowyez, J. Am. Chem. Soc., 1976, 98, 4322; D. P. Freyber, G. M. Mockler and E. Sinn, Inorg. Chem., 1977, 16, 1660. 28 C. F. Martens, A. P. H. J. Schenning, M. H. Feiters, H. W. Berens, J. G. M. Van der Linden, G. Admiraal, P. T. Beurskens, H. Kooijman, A. L. Spek and R. J. M. Nolte, Inorg. Chem., 1995, 34, 4735. 29 A. W. Addison and J. H. Stenhouse, Inorg. Chem., 1978, 17, 2161. 30 G. M. Godziela and H. M. GoV, J. Am. Chem. Soc., 1986, 108, 2237. 31 HYPERCHEM release, HyperCube Inc., Waterloo, Ontario, 1996. Received 10th March 1998; Paper 8/01934G

ISSN:1477-9226    

DOI:10.1039/a801934g

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1981–1986 1981 Synthesis and characterisation of 1-(diphenylphosphino)-19- (methylsulfanyl)ferrocene and a series of metal (CuI, AgI)– ferrocenylene complexes Nicholas J. Long,*a JeV Martin,a Giuliana Opromolla,b Andrew J. P. White,a David J. Williams a and Piero Zanello b a Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London, UK SW7 2AY b Dipartimento di Chimica dell’ Universita di Siena, Pian dei Mantellini, I-53100 Siena, Italy Received 3rd December 1998, Accepted 5th May 1999 A novel phosphorus/sulfur-substituted ferrocenylene ligand, 1-(diphenylphosphino)-19-(methylsulfanyl)ferrocene has been synthesized by two routes and fully characterised.The co-ordination chemistry of this species and analogous phosphorus/phosphorus- and sulfur/sulfur-substituted ferrocenylene ligands, 1,19-bis(diphenylphosphino)ferrocene, 1,19-bis(methylsulfanyl)ferrocene and 1,19-bis(isopropylthio)ferrocene has been demonstrated by reaction with copper and silver tetrakis(acetonitrile) salts to form a series of metal–ferrocenylene complexes where the metal atom acts as a bridging group of two ring systems.Crystal structure determinations have been carried out on [Ag{(C5H4P- (C6H5)2)2Fe}2]BF4 and [Cu{(C5H4SCH3)2Fe}2]PF6 and illustrate that the former shows a distorted tetrahedral geometry around silver and a significant asymmetry in the geometries of the two pseudo six-membered chelate rings and that the latter possesses S4 symmetry with a pronounced exo orientation of the four methyl groups.Introduction Ferrocene-containing complexes are currently undergoing something of a renaissance due to their increasing role in the rapidly growing area of materials science.1 The substitution of ferrocenes by various donor heteroatoms has led to a series of chelating ligands that have found wide application, e.g. incorporation of phosphines for homogeneous catalysis in organic synthesis, chiral phosphines for enantiomeric synthesis and amino alcohols for asymmetric catalysis.1,2 EVorts have been made to control the 1,19-hetero- or homo-substitution of ferrocene, normally via lithio intermediates,3–10 to allow the formation of a number of useful substituted-ferrocenyl synthetic precursors, i.e.halides,11,12 aldehydes,13 phosphines,14–17 amines,18 and stannyl species.19 By linking the heteroatoms, or by the incorporation of a preformed linkage, metallocenophanes (or ansa-metallocenes) (species that feature linking of the cyclopentadienyl rings by the introduction of a heteroannular bridge or bridges) can be formed.Bridged Group 4 metallocenes have come to the fore as catalysts in stereoselective olefin polymerisation 20 and strained, ring-tilted iron group metallocenophanes have been found to undergo thermal ringopening polymerisation (ROP), leading to rare examples of well defined, high molecular mass, soluble polymers with transition metals in the main polymer chain.21 Ferrocenyl dichalcogenide ligands and the Group 4 elements Si, Ge and Sn are known to form ‘spiro’ 22 compounds in which two [3]ferrocenophane rings share the bridge atom in position 2,23–26 e.g.[Z(E2Fc)2] (where Z = Si, Ge or Sn; E = S, Se or Te; Fc = {(C5H4)2Fe}). Whilst metal complexes with two 1,19- bis(diphenylphosphino)ferrocene ligands are well known,1,27,28 to date the only transition metal complex with two chelating ferrocenyl dichalcogenide ligands is the anion of the diamagnetic brown rhenate(V) salt, e.g.[P(C6H5)4][ReO(S2Fc)2].29 To explore the formation of novel ferrocenophanes further, we have synthesized the first mixed phosphorus/sulfur-substituted ferrocenylene ligand, 1-(diphenylphosphino)-19-(methylsulfanyl) ferrocene (PSF) L1, along with the more well known phosphorus/phosphorus- and sulfur/sulfur-substituted species, 1,19-bis(diphenylphosphino)ferrocene (BPPF) L2, 1,19-bis- (methylsulfanyl)ferrocene (BMSF) L3 and 1,19-bis(isopropylsulfanyl) ferrocene (BIPSF) L4 respectively and treated them with labile tetrakis(acetonitrile)-copper(I) or -silver(I) centres to form a series of novel metal–ferrocenylene complexes 1–9.Experimental General All preparations were carried out using standard Schlenk techniques. 30 All solvents were distilled over standard drying agents under nitrogen directly before use and all reactions were carried out under an atmosphere of nitrogen.Alumina gel (type UG-1) was used for chromatographic separations. All NMR spectra were recorded on a JEOL 270 MHz instrument. Chemical shifts are reported in d using CDCl3 (1H, d 7.26) as the reference for 1H spectra, whilst the 31P-{1H} spectra were referenced to 85% H3PO4. Mass spectra were recorded using positive FAB methods, on a Micromass Autospec Q spectrometer. Microanalyses were carried out at the Department of Chemistry, Imperial College of Science, Technology and Medicine.Starting materials The ligands L2,31 L3 10 and L4 10 were synthesized by following literature procedures, as were [Cu(CH3CN)4]PF6,32 1,19-dilithioferrocene 8 and 1,19-phenylphosphinoferrocenophane7 and were characterised by 1H NMR and mass spectrometry; [Ag(CH3CN)4]BF4 was purchased from Aldrich Chemical Co. Ligands 1-(Diphenylphosphino)-19-(methylsulfanyl)ferrocene L1. Method 1. 1-Diphenylphosphino-19-lithioferrocene was prepared using the method of Seyferth and Withers 16 from 1,19- phenylphosphinoferrocenophane (6.28 g, 21.50 mmol) and a 10–15 fold excess of C6H5Li (1 M solution in diethyl ether).The resultant orange-brown precipitate was treated with (CH3)2S21982 J. Chem. Soc., Dalton Trans., 1999, 1981–1986 (1.93 cm3, 21.50 mmol) in diethyl ether (20 cm3) and the mixture stirred overnight. Water (100 cm3) was added and stirred for 2 h, then the organic layer decanted and the aqueous layer washed with diethyl ether (2 × 20 cm3).The extracts were combined and dried over MgSO4, filtered and subjected to column chromatography using an 80% hexane–20% diethyl ether solution and isolated as an orange solid after evaporation of the solvents. Overall yield from 1,19-phenylphosphinoferrocenophane, 1.64 g (18%). Method 2. A suspension of 1,19-dilithioferrocene (6.75 g, 21.50 mmol) in hexane (100 cm3) was treated with a premixed solution of (CH3)2S2 (1.93 cm3, 21.50 mmol) and P(C6H5)2Cl (3.85 g, 21.50 mmol) in hexane (10 cm3) and the mixture stirred overnight.Water (20 cm3) was added and stirred for 1 h, then the organic layer decanted and the aqueous layer washed with hexane (2 × 10 cm3). The extracts were combined and dried over MgSO4, filtered, then purified by column chromatography using first hexane (to remove the starting materials), then an 80% hexane–20% diethyl ether solution, to give the product, after evaporation of the solvents, as a light orange microcrystalline powder.Further purification was achieved by recrystallisation from hexane–diethyl ether (1 : 1) as orange crystals, 3.44 g (38%) (Calc. for C23H21FePS: C, 66.35; H, 5.05. Found: C, 66.57; H, 4.87%). 1H NMR (CDCl3): d 2.23 (s, 3 H, SCH3), 4.06 (t, 2 H, C5H4), 4.11 (q, 2 H, C5H4), 4.20 (t, 2 H, C5H4), 4.38 (t, 2 H, C5H4) and 7.31 (m, 10 H, C6H5). 31P-{1H} NMR (CDCl3): d 216.78. Complexes Formation of the complexes followed the same general procedure as for the formation of 5 using either [Cu(CH3CN)4]PF6 or [Ag(CH3CN)4]BF4 and the appropriate bidentate ligand.[Cu(L1)2]PF6 1. The salt [Cu(CH3CN)4]PF6 (0.09 g, 2.33 mmol) was added to a solution of ligand L1 (0.19 g, 4.66 mmol) in CH2Cl2 (20 cm3) and stirred for 1 h. The resulting dark brown solution was reduced under vacuum, washed with diethyl ether (10 cm3) and dried (MgSO4) to yield a brown microcrystalline solid, 0.16 g (66%) (Calc.for C46H42CuF6Fe2P3S2: C, 53.03; H, 4.04. Found: C, 53.02, H, 4.31%). 1H NMR (CDCl3): d 2.61 (br, 3 H, SCH3), 4.29 (br, 4 H, C5H4), 4.50 (br, 2 H, C5H4), 4.65 (br, 2 H, C5H4), 7.41 (br, 5 H, C6H5) and 7.58 (br, 5 H, C6H5). m/z 896 [(L1)2Cu], 480 [(L1)Cu], 416 (L1). [Ag(L1)2]BF4 2. From the salt [Ag(CH3CN)4]BF4 (0.14 g, 3.80 mmol) and ligand L1 (0.32 g, 7.64 mmol). Orange microcrystalline solid, 0.30 g (77%) (Calc. for C46H42AgBF4Fe2P2S2: C, 53.75; H, 4.09. Found: C, 54.09; H, 4.07%). 1H NMR (CDCl3): d 2.22 (s, 3 H, SCH3), 4.14 (t, 2 H, C5H4), 4.19 (t, 2 H, C5H4), 4.29 (t, 2 H, C5H4), 4.61 (t, 2 H, C5H4) and 7.45 (m, 10 H, C6H5).m/z 941 [(L1)2Ag], 523 [(L1)Ag], 416 (L1) and 401 [(C5H4PPh2)Fe(C5H4S)]. [Cu(L2)2]PF6 3. From the salt [Cu(CH3CN)4]PF6 (0.07 g, 1.81 mmol) and ligand L2 (0.20 g, 3.61 mmol). The complex was allowed to recrystallise from the CH2Cl2 solution, producing light orange crystals, 0.17 g (71%) (Calc. for C68H56CuF6Fe2P5: C, 61.96: H, 4.25.Found: C, 61.64; H, 4.60%). 1H NMR (CDCl3): d 4.10 (br, 4 H, C5H4), 4.31 (br, 4 H, C5H4), 7.25 (m, 10 H, C6H5) and 7.40 (m, 10 H, C6H5). m/z 1172 [(L2)2Cu], 617 [(L2)Cu] and 554 (L2). [Ag(L2)2]BF4 4. From ligand L2 (0.10 g, 0.18 mmol) and [Ag(CH3CN)4]BF4 (0.03 g, 0.09 mmol). Light orange solid, 0.076 g (65%) (Calc. for C68H56AgBF4Fe2P4: C, 62.62; H, 4.30. Found: C, 62.66; H, 3.95%). 1H NMR (CDCl3): d 4.10 (br, 4 H, C5H4), 4.40 (br, 4 H, C5H4), 7.10 (m, 10 H, C6H5) and 7.30 (m, 10 H, C6H5).m/z 1216 [(L2)2Ag], 1139 [(L2)Ag(C5H4PPh2)- Fe(C5H4PPh)], 661 [(L2)Ag] and 554 (L2). [Cu(L3)2]PF6 5. From [Cu(CH3CN)4]PF6 (0.19 g, 0.52 mmol) and ligand L3 (0.29 g, 1.04 mmol) in CH2Cl2 (20 cm3). The resulting dark brown solution was reduced under vacuum, washed with hexane (10 cm3) and dried to yield a brown crystalline solid, 0.38 g (96%) (Calc. for C24H28CuF6Fe2PS4: C, 37.65; H, 3.66. Found: C, 37.48; H, 3.14%). 1H NMR (CDCl3): d 2.68 (br s, 3 H, SCH3) and 4.43 (br s, 4 H, C5H4).m/z 620 [(L3)2Cu], 341 [(L3)Cu], 326 [(C5H4SMe)Fe(C5H4S)Cu] and 278 (L3). Suitable crystals for X-ray analysis were grown as transparent brown pyramids by cooling a saturated CH2Cl2 solution. [Ag(L3)2]BF4 6. From [Ag(CH3CN)4]BF4 (0.30 g, 0.85 mmol) and ligand L3 (0.47 g, 1.69 mmol). Dark brown solution reduced under vacuum to a brown solid, 0.42 g (67%) (Calc. for C24H28AgBF4Fe2S4: C, 38.35; H, 3.73. Found: C, 38.10; H, 3.74%). 1H NMR (CDCl3): d 2–3 (br s, 3 H, SCH3) and 4–5 (m, 4 H, C5H4).m/z 664 [(L3)2Ag], 385 [(L3)Ag] and 278 (L3). [Cu(L4)2]PF6 7. From ligand L4 (0.52 g, 1.56 mmol) and [Cu(CH3CN)4]PF6 (0.29 g, 0.78 mmol). Dark brown oily solid formed on evaporation of solvent, brown solid formed on cooling, 0.53 g (78%) (Calc. for C32H44CuF6Fe2PS4: C, 43.79; H, 5.02. Found: C, 43.82; H, 5.06%). 1H NMR (CDCl3): d 1.39 [d, 6 H, SCH(CH3)2], 3.30 [septet, 1 H, SCH(CH3)2], 4.40 (br, 2 H, C5H4) and 4.51 (br, 2 H, C5H4).m/z 732 [(L4)2Cu], 471 [(L4)CuC5H4SCH(CH3)2Fe(C5H4)], 397 [(L4)Cu] and 334 (L4). [Ag(L4)2]BF4 8. From ligand L4 (0.41 g, 1.2 mmol) and [Ag(CH3CN)4]BF4 (0.22 g, 0.61 mmol). Light orange solid, 0.38 g (72%) (Calc. for C32H44AgBF4Fe2S4: C, 44.50; H, 5.10. Found: C, 44.41; H, 4.84%). 1H NMR (CDCl3): d 1.38 [d, 6 H, SCH(CH3)2], 3.22 [septet, 1 H, SCH(CH3)2], 4.34 (t, 2 H, C5H4) and 4.52 (t, 2 H, C5H4). m/z 776 [(L4)2Ag], 472 [(L4)AgS], 442 [(L4)Ag], 398 [AgC5H4SCH(CH3)2)Fe(C5H4)S] and 334 (L4).[Cu(L3){P(C6H5)3}2]PF6 9. A solution of [Cu(L3)2]PF6 (0.35 g, 4.58 mmol) was treated with P(C6H5)3 (0.24 g, 9.15 mmol) and stirred for 1 h. The solution was reduced under vacuum and washed with diethyl ether (2 × 10 cm3) to leave an orange solid, 0.31 g (67%) (Calc. for C48H44CuF6FeP3S2: C, 56.97; H, 4.35. Found: C, 57.71; H, 4.36%). 1H NMR (CDCl3): d 2.29 (s, 6 H, SCH3), 4.31 (t, 4 H, C5H4), 4.95 (t, 4 H, C5H4), 7.11 (m, 15 H, C6H5) and 7.41 (m, 15H, C6H5). m/z 603 [(L3)Cu(PPh3)], 587 [Cu(PPh3)2], 341 [(L3)Cu] and 278 (L3).X-Ray crystallography Table 2 provides a summary of the crystal data, data collection and refinement parameters for complexes 4 and 5. The structures were solved by direct methods and the heavy atom method for 5 and 4 respectively, and refined by full matrix least squares based on F 2. In 5 the complex and the PF6 anion were found to be disordered over independent crystallographic S4 positions. In the case of the complex two discrete half-occupancy orientations were identified, with only their copper and iron centres in common, and refined anisotropically, with the cyclopentadienyl rings treated as optimised rigid bodies.The disorder in the anion was modelled by the assignment of suYcient electron density around the central phosphorus atom to match a single quarter-occupancy (due to site symmetry) molecule, all atoms being refined anisotropically. In 4 the complex was ordered and refined anisotropically with the phenyl rings treated as optimised rigid bodies (the cyclopentadienyl rings were not optimised). The BF4 anion was found to be distributed over three partial occupancy sites (two of which were located proximal to crystallographic special positions); only the major occupancy atoms were refined anisotropically.In both structures the hydrogen atoms were placed in calculated positions, assigned isotropic thermal parameters, U(H) = 1.2Ueq(C), and allowed toJ.Chem. Soc., Dalton Trans., 1999, 1981–1986 1983 ride on their parent atoms. The polarity of 5 was determined by R-factor tests [R1 1 = 0.031, R1 2 = 0.039] and by use of the Flack parameter [x1 = 20.03(4), x2 = 11.03(4)]. Computations were carried out using the SHELXTL PC program system.33 CCDC reference number 186/1452. See http://www.rsc.org/suppdata/dt/1999/1981/ for crystallographic files in .cif format. Results and discussion Synthesis The new hetero-donor ligand, PSF (L1), may be prepared by two methods (Scheme 1) which involve the initial formation of the well known intermediate 1,19-dilithioferrocene.Addition of dichlorophenylphosphine produces 1,19-phenylphosphinoferrocenophane (Method 1),7 which was isolated and characterised spectroscopically. This [1]ferrocenophane was then treated with a 10–15 fold excess of phenyllithium (1 M solution in diethyl ether) to cleave one of the P–C bonds and yield the air- and moisture-sensitive 1-diphenylphosphino-19-lithioferrocene.16 The orange-brown precipitate was treated in situ with dimethyl disulfide to give a crude dark orange oil (L1).Purification was eVected by column chromatography on neutral grade II alumina (hexane–diethyl ether (80 : 20)) to give an orange solid in an overall yield from ferrocene of 11%, or 18% from 1,19- phenylphosphinoferrocenophane. Method 2 was more direct and involved treating a hexane suspension of the 1,19-dilithioferrocene intermediate with a mixture (1 : 1) of dimethyl disulfide and dichlorophenylphosphine, also in hexane.Perhaps surprisingly, a reasonable yield of the desired product was obtained (along with mainly BMSF and monosubstituted ferrocenes as by-products) which was again purified by column chromatography using first hexane as eluent (to remove the starting materials) and then hexane– diethyl ether (80 : 20) to give the orange solid (yield 38% from ferrocene). As mentioned in the Introduction, hetero-donor substituted ferrocenes are known but to date most have featured pnictinide substituents.The diVerent co-ordinating abilities of the phosphorus and sulfur substituents in L1, along with the possibility for further donor atom substitution around the same ferrocene unit,34 opens up diverse co-ordination chemistry of these systems which is the subject of ongoing studies. As a starting point for the co-ordination chemistry and as a comparison to the more well known analogues 1,19-bis(diphenylphosphino)ferrocene (BPPF) (L2), 1,19-bis(methylsulfanyl)ferrocene (BMSF) (L3) and 1,19-bis(isopropylsulfanyl)ferrocene (BPSF) (L4), each ligand was treated with simple copper and silver tetrakis- (acetonitrile) complexes.Using a 2 : 1 ratio of ligand to metal, the acetonitrile moieties could be displaced within a few minutes by stirring at room temperature, to yield a tetrasubstituted Scheme 1 Two methods for the synthesis of ligand L1.Fe Li Li Fe TMEDA TMEDA Fe PC6H5 PCl2C6H5 Method 1 Fe P(C6H5)2 Li Fe P(C6H5)2 SCH3 (CH3)2S2 C6H5Li PCl(C6H5)2, (CH3)2S2 Method 2 n-BuLi metal complex with two ferrocenylene ligands (Scheme 2). Each complex 1–8 appears to possess the same structure where the metal atom acts as a bridging group of two ring systems. The air- and moisture-stable orange solids were formed in excellent yields and could be recrystallised from saturated chlorocarbon solutions. Spectroscopy Each complex 1–8 displays broadened signals in the cyclopentadienyl ring region of its room temperature 1H NMR spectrum which was initially thought to be due to fluxional processes, such as pyramidal sulfur inversion or bridge reversal,35 being observed in solution. However, dynamic NMR experiments and, in particular, cooling solutions to low temperatures (ca. 280 8C) failed to elucidate any fine structure on the cyclopentadienyl proton signals. This could be due to a lack of slowing of the fluxional processes but is thought more likely to be a dissociative process in solution (breaking of the metal– heteroatom bonds) giving rise to an averaged set of peaks.To elucidate this phenomenon, a solution of 5 was treated with two equivalents of P(C6H5)3 and substitution of a labile ligand indeed occurred to form a [3]ferrocenophane 9 (Scheme 3). (NB 9 was also formed by the addition of [Cu(CH3CN)2{(P- (C6H5)3)}2]PF6 to a stirred solution of the ligand L3). The lack of sulfur inversion is perhaps surprising but there is clearly something of a ‘potential well’ in the thermodynamics of the structure especially when considering the crystal structure determination (see later).The methyl groups are ‘locked’ into a very stable exo orientation and this seems to preclude any movement and therefore fluxional behaviour of these units. Electrochemistry A preliminary investigation on dichloromethane solutions of the reported complexes using platinum electrodes illustrated the occurrence of interfering adsorption phenomena, whereas the use of glassy-carbon electrodes overcame these problems. Figs. 1 and 2, which compare the cyclic voltammetric responses of the ligands L1 and L2 with those of their copper(I) and silver(I) complexes, show the subtle electronic eVects that govern the redox behaviour of these species. With respect to the ligand L1, the bis(ferrocenediyl) copper(I) and silver(I) complexes 1 and 2 undergo anodic oxidations at potentials shifted toward more positive potential values by about 0.25 V (Fig. 1). In particular, the copper complex 1 Scheme 2 The syntheses of complexes 1–8.1984 J. Chem. Soc., Dalton Trans., 1999, 1981–1986 exhibits two substantially overlapping one-electron oxidations, which could not be resolved with additional use of diVerential pulse voltammetry, and simply aVorded a rounded peak. On the other hand, the silver complex 2 displays a single two-electron oxidation.In spite of the apparent chemical reversibility of these anodic processes on the cyclic voltammetric timescale, cyclic voltammetric tests on solutions from exhaustive twoelectron oxidation of both complexes showed partial decomposition of the corresponding trications. Interestingly, L2, which is known to undergo a one-electron oxidation coupled to chemical complications,36 when part of the metal complexes 3 and 4 gives rise to oxidation processes with features of chemical reversibility (also in these cases it is limited to the cyclic voltammetric timescale), Fig. 2. In addition, a slight wave splitting occurs for the silver complex 4. As Table 1 summarises, analogous behaviour is seen for the remaining complexes. The oxidations of the metal complexes occur at potentials which range from 0.25 to 0.42 V higher than those of the corresponding ligands. It has to be taken into account that these shifts must be attributed either to the electrostatic eVect of removing electrons from monocations, or to the metals themselves. The minor wave splittings observed for some Fig. 1 Cyclic voltammetric responses recorded at a glassy-carbon electrode on CH2Cl2 solutions containing [NBu4][PF6] (0.2 mol dm23) and (a) L1 (1.0 × 1023 mol dm23), (b) complex 1 (0.4 × 1023 mol dm23), (c) complex 2 (0.8 × 1023 mol dm23). Scan rate 0.05 V s21. Scheme 3 The synthesis of complex 9. Fe S S Cu CH3 CH3 2 PF6 + 2 P(C6H5)3 Fe S S Cu CH3 CH3 PF6 (P(C6H5)3)2 + Fe S S CH3 CH3 complexes suggest slight communication between the two ferrocene units, but it can be deduced that the communication is probably attributable to the nature of the ferrocene ligands rather than to that of the metals.X-Ray crystallography The X-ray analysis of complex 5 reveals a structure that has 50/ 50 reflection disorder about a non-crystallographic mirror plane perpendicular to the a direction, the two orientations having essentially identical geometries. The complex has crystallographic S4 symmetry, the copper lying at the S4 position and the two iron atoms on the C2 axis (Fig. 3). The geometry at copper is slightly distorted tetrahedral, the bite angles of the two chelating ligands being 112.3(1)8. The Cu–S distance of 2.33(1) Å is unexceptional. There is a marked departure from tetrahedral geometry at sulfur with the C5–S–Me angles contracted to 101(1)8, the other two angles being 109(1) [Cu–S–C5] and 110(1)8 [Cu–S–Me]. The ferrocenyl C5H4 rings are staggered (488), the two S–C5 vectors being skewed by ca. 248, with an essentially parallel orientation of the two rings. The Cu ? ? ?Fe distance of 4.02 Å is too long for any significant metal–metal interaction. When viewed down the metal–metal–metal axis the exo orientation of the four methyl groups is particularly pronounced (Fig. 4), a geometry that is dominant in solution as Fig. 2 Cyclic voltammetric responses recorded at a glassy-carbon electrode on CH2Cl2 solutions containing [NBu4][PF6] (0.2 mol dm23) and (a) L2 (0.8 × 1023 mol dm23), (b) complex 3 (1.0 × 1023 mol dm23), (c) complex 4 (0.9 × 1023 mol dm23).Scan rates: (a, c) 0.05; (b) 0.1 V s21. Fig. 3 The molecular structure of one of the two 50% orientations of the S4-symmetric cation present in the structure of complex 5. The Cu–S and S–C5 bond lengths are 2.331(2) [2.327(2)] and 1.746(5) [1.755(6) Å] respectively. The associated bite and interligand S–Cu–S angles are 112.28(10) [112.33(10)] and 108.08(5) [108.06(5)8] respectively; the Cu–S–C5 angles are 109.2(3) [109.6(3)8], the number in [ ] referring to the alternative orientation present in the crystal.J.Chem. Soc., Dalton Trans., 1999, 1981–1986 1985 Table 1 Formal electrode potentials (in V, vs. SCE) and peak-to-peak separations (in mV) for the anodic oxidation of the ferrocenediyl ligands L1–L4 and their metal derivatives 1–8 in CH2Cl2 solutions Compound E8 (0/1) DEp a E8 (1/21) E8 (21/31) E8 (1/31) DEp a L1 L2 L3 L4 1234578 10.48 10.56 b 10.37 c 10.43 85 69 94 180 10.68 d 10.89 d 10.74 d 10.78 d 10.84 d 10.64 d 10.75 10.84 10.85 e 10.85 f 115 140 90 a Measured at 0.1 V s21.b Coupled to chemical complications. c See ref. 37. d Measured according to ref. 38. e Irreversible two electron step. f Coupled to slight adsorption of the reagent. shown by the NMR experiments. There are no intermolecular interactions of note, the packing being normal van der Waals.In the solid state structure of complex 4 (Fig. 5) the geometry at silver is distorted tetrahedral with angles ranging between 97.8(1) and 118.9(1)8. There is a pronounced asymmetry in the geometries of the two pseudo six-membered chelate rings (Fig. 6), an asymmetry that includes both the bond lengths and angles (Table 2) and their conformations. The Ag/Fe(1) ring has a skewed “l” conformation, the C2Fe plane being “rotated” by 238 out of the P2Ag plane about the Fe ? ? ? Ag axis.In contrast the Ag/Fe(2) ring has a slightly twisted envelope conformation, the Ag atom being 1.38 Å out of the plane of the other five atoms which are coplanar to within 0.09 Å, corresponding to a fold about the P(3) ? ? ? P(4) vector of ca. 548. The angle at silver within the skewed ring is 105.5(1)8 whereas that in the ring with the envelope conformation is 97.8(1)8. Possibly most surprising is the disparity in the Ag–P distances within each pseudo chelate ring, though the asymmetry is remarkably consistent there Fig. 4 The view down the Fe ? ? ? Cu ? ? ?Fe direction in the structure of complex 5 showing the radial orientation of the SMe groups. Table 2 Selected bond lengths (Å) and angles (8) for complex 4 Ag–P(1) Ag–P(3) P(1)–C(17) P(3)–C(51) P(1)–Ag–P(2) P(1)–Ag–P(4) P(2)–Ag–P(4) Ag–P(1)–C(17) Ag–P(3)–C(51) 2.662(3) 2.622(3) 1.790(12) 1.811(14) 105.51(10) 109.34(11) 118.92(11) 106.4(4) 106.4(4) Ag–P(2) Ag–P(4) P(2)–C(22) P(4)–C(56) P(1)–Ag–P(3) P(3)–Ag–P(3) P(3)–Ag–P(4) Ag–P(2)–C(22) Ag–P(4)–C(56) 2.558(3) 2.553(3) 1.775(12) 1.832(13) 114.65(11) 110.98(11) 97.76(10) 113.5(4) 110.0(4) being one “short” and one “long” bond in each ring, 2.662(3) [P(1)] and 2.558(3) Å [P(2)] in the skewed ring and 2.622(3) [P(3)] and 2.553(3) Å [P(4)] in the envelope ring.The transannular Ag ? ? ?Fe(1) and Ag ? ? ?Fe(2) distances are 4.25 and 4.15 Å respectively. The analogous complex [Ag(L2)2]ClO4? 2CHCl3 27 has also been studied and shows a more regular tetrahedral geometry around Ag with the bite angles of the diphosphine P(1)–Ag–P(2) and P(3)–Ag–P(4) being 105.71(4) and 98.39(4)8 respectively.However, no mention is made of any asymmetry in the pseudo six-membered chelate rings. Both ferrocenyl ring systems have slightly staggered geometries [ca. 158 for Fe(1) and ca. 118 for Fe(2)], though whereas the C5 rings are essentially parallel in the Fe(1) ferrocenyl unit [28] they are significantly inclined in the Fe(2) unit [88].Accompanying the aforementioned staggering of the rings are very diVerent relative orientations of the P–C5 bonds which are skewed by 538 for the Fe(1) chelate but by only 108 in the Fe(2) chelate which has the “envelope” conformation. There are no noteworthy intermolecular interactions. Conclusion A new 1,19-heterodisubstituted ferrocenediyl ligand featuring P and S substituents has been synthesized by two routes. Its coordination chemistry with labile copper(I) and silver(I) centres gives metal-bridged bis(ferrocenylene) species in analogy to other more well known P/P- and S/S-substituted ligands, Fig. 5 The molecular structure of the cation in complex 4.1986 J. Chem. Soc., Dalton Trans., 1999, 1981–1986 though structural determinations illustrate some significant distortion and asymmetry within the structures. Electrochemical investigations show some subtle electronic eVects and there are significant shifts to more positive potentials of the cyclic voltammetric responses of the complexes with respect to those of the ligands.Acknowledgements We wish to thank the EPSRC for a studentship (to J. M.) and Fig. 6 The two “pseudo six-membered chelate” rings in complex 4, showing their skewed [Fe(1)] and envelope [Fe(2)] conformations respectively. Table 3 Crystal data, data collection and refinement parameters for complexes 4 and 5a 5 4 Formula M Colour, habit Crystal size/mm Lattice type Space group symbol, number a/Å b/Å c/Å b/8 V/Å3 Z Dc/g cm23 F (000) Radiation used m/mm21 q Range/8 No.unique reflections measured No. observed reflections, |Fo| > 4s(|Fo|) Absorption correction Maximum, minimum transmission No. variables R1 wR2 Largest diVerence peak, hole/e Å23 C24H28CuF6Fe2PS4 764.9 Orange tetrahedra 0.33 × 0.33 × 0.27 Tetragonal I4� , 82 10.493(1) — 13.340(1) — 1468.8(2) 2 b 1.730 772 Mo-Ka 2.08 2.5–30.0 1209 1060 Semi-empirical 0.50, 0.38 164 0.031 0.078 0.21, 20.41 C68H56AgBF4Fe2P4 1303.4 Orange-yellow prisms 0.18 × 0.16 × 0.09 Monoclinic I2/a, 15 22.627(5) 23.575(6) 22.970(6) 100.92(1) 12031(5) 8 1.439 5312 Cu-Ka 7.84 2.7–60.0 7891 4658 Semi-empirical 0.99, 0.45 651 0.085 0.197 1.08, 21.81 a Details in common: graphite monochromated radiation, w scans, Siemens P4 diVractometer, 293 K.b The molecule has crystallographic S4 symmetry. Dr Keith Orrell (University of Exeter) for helpful NMR discussions. References 1 For a detailed review see Ferrocenes: homogeneous catalysis, organic synthesis, materials science, eds.A. Togni and T. Hayashi, VCH, Weinheim, 1995. 2 For an overview see N. J. Long, in Metallocenes - An Introduction to Sandwich Complexes, Blackwell Science, Oxford, 1998. 3 E. Moret, O. Desponds and M. Schlosser, J. Organomet. Chem., 1991, 409, 32. 4 H. Schottenberger, M. Buchmeiser, J. Polin and K. E. Schwarzhans, Z. Naturforsch., Teil B, 1993, 48, 1524. 5 U. T. Mueller-WesterhoV, Z. Zang and G.Ingram, J. Organomet. Chem., 1993, 463, 163. 6 D. Guilloneuse and H. Kagan, J. Org. Chem., 1995, 60, 2502. 7 A. G. Osborne, R. H. Whiteley and R. E. Meads, J. Organomet. Chem., 1980, 193, 345. 8 J. J. Bishop, A. Davison, M. L. Katcher, D. W. Lichtenberg, R. E. Merrill and J. C. Smart, J. Organomet. Chem., 1971, 27, 241. 9 B. McCulloch and C. H. Brubaker, Jr., Organometallics, 1984, 3, 1707. 10 B. McCulloch, D. L. Ward, J. D. Woollins and C. H. Brubaker, Jr., Organometallics, 1985, 4, 1425. 11 L.-L. Lai and T.-Y. Dong, J. Chem. Soc., Chem. Commun., 1994, 1078. 12 T.-Y. Dong, C.-K. Chang, S.-H. Lee, L.-L. Lai, Y.-N. Chiang and K.-J. Lin, Organometallics, 1997, 16, 5816. 13 G. Iftime, C. Moreau-Bossuet, E. Manoury and G. G. A. Balavoine, Chem. Commun., 1996, 527. 14 I. R. Butler and W. R. Cullen, Organometallics, 1983, 3, 1846. 15 I. R. Butler and R. A. Davies, Synthesis, 1995, 1350. 16 D. Seyferth and H. P. Withers, Jr., Organometallics, 1982, 1, 1275. 17 H. P. Withers, Jr., D. Seyferth, J. D. Fellmann, P. E. Garrou and S. Martin, Organometallics, 1982, 1, 1283. 18 I. R. Butler, J. Organomet. Chem., 1997, 552, 53. 19 M. E. Wright, Organometallics, 1990, 9, 853. 20 H. H. Brintzinger, D. Fischer, R. Mülhaupt, B. Rieger and R. M. Waymouth, Angew. Chem., 1995, 107, 1255; Angew. Chem., Int. Ed. Engl., 1995, 34, 1143. 21 I. Manners, Angew. Chem., 1996, 108, 1712; Angew. Chem., Int. Ed. Engl., 1996, 35, 1602. 22 Dictionary of Chemical Terminology, Elsevier, Oxford, 1980. 23 M. Herberhold, C. Dornhofer, A. Scholz and G.-X. Jin, Phosphorus Sulfur Silicon Relat. Elem., 1992, 64, 161. 24 M. Herberhold, M. Hubner and B. Wrackmeyer, Z. Naturforsch., Teil B, 1993, 48, 940. 25 A. G. Osborne, R. E. Hollands and A. G. Nagy, J. Organomet. Chem., 1989, 373, 229. 26 A. G. Osborne, A. J. Blake, R. E. Hollands, R. F. Bryan and S. Lockhart, J. Organomet. Chem., 1985, 287, 39. 27 M. C. Gimeno, P. G. Jones, A. Laguna and C. Sarraca, J. Chem. Soc., Dalton Trans., 1995, 1473. 28 U. Casellato, B. Corain, R. Graziani, B. Longato and G. Pilloni, Inorg. Chem., 1990, 29, 1193; V. Di Noto, G. Valle, B. Zarli, B. Longato, G. Pilloni and B. Corain, Inorg. Chim. Acta, 1995, 233, 165. 29 J. R. Dilworth and S. K. Ibrahim, Transition Met. Chem., 1991, 16, 239. 30 D. F. Shriver, in Manipulation of Air-Sensitive Compounds, McGraw-Hill, New York, 1969. 31 G. P. Sollot, J. L. Snead, S. Portnoy, W. R. Peterson, Jr. and H. E. Mertwoy, US Dep. Commer., OV. Tech. Serv., AD 611869, 1965, 2, 441. 32 G. J. Kubas, Inorg. Synth., 1990, 28, 68. 33 SHELXTL PC, version 5.03, Siemens Analytical X-Ray Instruments, Inc., Madison, WI, 1994. 34 N. J. Long, J. Martin, D. J. Williams and A. J. P. White, J. Chem. Soc., Dalton Trans., 1997, 3083. 35 E. W. Abel, S. K. Bhargava and K. G. Orrell, Prog. Inorg. Chem., 1984, 32, 1. 36 T. M. Miller, K. J. Ahmed and M. S. Wrighton, Inorg. Chem., 1989, 28, 2347. 37 H. Ushijima, T. Akiyama, M. Kajitani, K. Shimizu, M. Aoyama, S. Masuda, Y. Harada and A. Sugimori, Bull. Chem. Soc. Jpn., 1990, 63, 1015. 38 D. E. Richardson and H. Taube, Inorg. Chem., 1981, 20, 1278. Paper 9/0353

ISSN:1477-9226    

DOI:10.1039/a903539g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 1985 Formation, crystal structure and co-ordination chemistry of the [MnIII(oespz)(SH)] [oespz22 5 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)- 5,10,15,20-tetraazaporphyrinate dianion] complex Giampaolo Ricciardi,a Alessandro Bencini,b Sandra Belviso,a Alfonso Bavoso a and Francesco Lelj *,a a Dipartimento di Chimica, Università della Basilicata, Via N. Sauro 85, 85100 Potenza, Italy b Dipartimento di Chimica, Università di Firenze, Via Maragliano 77, 50144 Firenze, Italy Reaction of [Mn(oespz)] [oespz22 = 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-tetraazaporphyrinate dianion (porphyrazinate)] with CS2 and, subsequently, with THF, aVorded the hydrogensulfido(12)manganese(III) ethylsulfanylporphyrazinate [Mn(oespz)(SH)], in high yield.The S]H stretching absorptions are not observed in the IR spectrum of the complex, whereas a peak at d 10.3 (vs. SiMe4) ascribed to the hydrogensulfido proton resonance, is observed in the 1H NMR spectrum.The complex was shown to be isostructural with [M(oespz)Cl] (M = Fe or Mn) by X-ray crystallography. The crystal packing of the complex consists of slipped stacks of dimeric units with the monomers positioned in a trans fashion with respect to the Mn]Sapical bond. Magnetic data are consistent with weakly antiferromagnetically coupled high spin (S = 2) manganese(III) centers. A possible pathway to the oxidative addition of CS2 to the manganese(II) center has been proposed.In CHCl3 [Mn(oespz)(SH)] reacts reversibly through the axial hydrosulfido ligand with the sterically hindered base 2,4,6-trimethylpyridine, whereas the complex co-ordinates 1-methylimidazole reversibly on the vacant site of manganese. Treatment of the complex with 1-methylimidazole in benzene leads to a MnIII–MnII redox process, as deduced from the UV/VIS spectra. The recently synthesized complex [Mn(oespz)] [oespz = 2,3,7,8,12,13,17,18-octakis(ethylsulfanyl)-5,10,15,20-tetraazaporphyrinate (porphyrazinate)] possesses, compared to the congener MnII–tetrapyrroles, an unusually nucleophilic metallic center.1,2 The easy abstraction of halogen atoms from halogenated hydrocarbons by [Mn(oespz)], via oxidative addition of the halogen to manganese, represents a clear example of how this feature may work.2,3 While exploring the reactivity of [Mn(oespz)] towards weak electrophiles we have found that it reacts with carbon disulfide to aVord the hydrogensulfido derivative [Mn(oespz)(SH)]. This reaction seemed intriguing to us.Although, for instance, CS2 has a widely studied organometallic chemistry 4 and, upon electrochemical or chemical reduction (normally by alkaline-earth metals in DMF) becomes the basic building block of 1,3-dithiol-2-thione-4,5- dithiolate (dmit),5 or ethylenetetrathiolate (ett),6 ligands, direct reaction of a MnII–tetrapyrrole complex with carbon disulfide is unprecedented.In addition, the chemistry of SH2 containing complexes could be relevant to metal sulfide hydrosulfurization catalysts 7 and transition-metal tetrapyrroles with a hydrosulfido axial ligand are well suited to mimic the spectral properties of cytochrome P-450 and chloroperoxidase.8 Moreover mono- and poly-nuclear MnIII is of central importance in biological systems such as superoxide dismutase 9 and catalase,10 while MnIII porphyrins 11 and phthalocyanines (pc) 12 have been used as building blocks in the construction of molecule-based magnets.Thus we decided to investigate the reaction of [Mn(oespz)] with CS2 and the physicochemical properties of the resulting complex, [Mn(oespz)(SH)]. This paper reports the synthesis, structural characterization and magnetic properties of [Mn(oespz)(SH)]. The co-ordinating capability of the complex towards strong s-donors such as 1-methylimidazole (1-mim) as well as toward sterically hindered organic bases such as 2,4,6- trimethylpyridine is also explored with the aim of elucidating the structure of the complex in solution and the possible eVects of the sixth ligand on the electronic structure of the complex.Experimental Materials All chemicals and solvents (Aldrich Chemicals Ltd.) were of reagent grade and used in the syntheses as supplied. Solvents used in physical measurements were of spectroscopic or HPLC grade. The compound [Mn(O2CMe)2] was obtained from Strem.Anhydrous ethanol, tetrahydrofuran (THF) and dimethylformamide (DMF) were obtained according to the procedures described in the literature.13 Silica gel used for chromatography was Merck Kiselgel 60 (270–400 mesh). Dichloromethane for voltammetric studies was refluxed under nitrogen with CaH2 for at least 48 h and stored over 4 Å molecular sieves. The salt [NBun 4][BF4] was recrystallized from ethanol and dried under partial vacuum. Air- and moisturesensitive chemicals were handled under an inert nitrogen atmosphere using standard Schlenk techniques or in a glove box.Carbon disulfide was purged of H2S and H2O contaminants by reaction with lead acetate [typically CS2 (100.0 cm3) was shaken with lead acetate (0.1 g) under N2 for 24 h] and subsequent distillation from CaH2. Physical measurements Microanalyses were performed by the Analytische Laboratorien of Professor H. Malissa and G. Reuter Gmbh, Gummersbach, Germany and by the Butterworth Laboratories Ltd, Teddington, UK.Infrared spectra were run as KBr disks on a 5PC Nicolet FT-IR spectrometer over the range 400–4000 cm21. Fast-atom bombardment mass spectra (FAB MS) were recorded on a VG ZAB 2SE double focusing mass spectrometer equipped with a caesium gun operating at 25 kV (2 mA) using a 3-nitrobenzyl alcohol (NBA) matrix. Solution electronic spectra in 1 or 10 cm path length quartz cells or on thin film in the region 200–2500 nm were performed on a UV-VIS-NIR 05E Cary spectrophotometer.Thin films for electronic spectroscopy studies were built by spreading, under a N2 stream, 1.0 cm3 of a 1.0 × 1025 M degassed sample solution in CHCl3, on a quartz1986 J. Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 slide (Corning, 1.0 × 3.0 × 0.1 cm). Cuvettes for spectroscopic titrations were filled in a glove box under N2 and the titrant was added with the help of a microsyringe. Proton NMR spectra were performed on a Bruker AM 300 MHz spectrometer.Polycrystalline powder EPR spectra were measured in the temperature range 4.2–300 K using a Varian E-9 spectrometer. Liquid-helium temperature was reached with an ESR90 cryostat (Oxford Instruments). In a typical experiment instrument settings were: modulation frequency, 100 kHz; modulation amplitude, 0.5 Gauss; receiver gain, 6.2 × 102; microwave power, 10 mW. Variable-temperature magnetic measurements were performed in the temperature range 2.5–270 K using a Metronique Ingegnierie SQUID apparatus.Electrochemical measurements were performed with an EG&G Princeton Applied Research (PAR) potentiostat/ galvanostat, Model 273, or with an AMEL 5000 System, in conjunction with a Linseis X-Y recorder; for all readings a three-electrode system in CH2Cl2 containing 0.1 M of supporting electrolyte was employed. Cyclic voltammetric measurements were obtained with a double platinum electrode and a Ag–AgCl reference electrode equipped with a Luggin capillary under an atmosphere of purified N2.Synthesis H2oespz. The free-base porphyrazine [H2oespz)] was synthesized according to the procedure reported earlier.1,2 The product was carefully purified by flash chromatography on silica gel (first band) using a 1 : 1 CH2Cl2–hexane mixture as eluent (Found: C, 48.25; H, 5.27; N, 14.01; S, 32.15. C32H42N8 S8 requires C, 48.33; H, 5.32; N, 14.09; S, 32.26%). 1H NMR: dH(300 MHz, CDCl3) 20.95 (2 H), 1.52 (24 H, t), 4.25 (24 H, q); UV/VIS (CH2Cl2): l/nm (log e) 360 (4.67) (Soret); 490 (4.17); 520 (4.18); 632 (4.58), 670 (sh) (4.56), 655 (4.60), 715 (4.81) (Q bands).FAB-MS (NBA matrix, positive ion mode): m/z 794, cluster, M1 (calc. 794). [Mn(oespz)]. The complex was prepared as previously reported.1,2 In an inert atmosphere glove box reaction of H2oespz (0.100 g, 0.13 mmol) with [Mn(O2CMe)2] (0.035 g, 0.20 mmol) in refluxing dry EtOH (10.0 cm3) led, in 24 h, to a dark Table 1 Data collection and refinement parameters for [Mn(oespz)- (SH)] Formula M Crystal system Space group l(Cu-Ka)/Å a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 m/cm21 T/K F(000) Crystal size/mm 2q Range/8 h, k, l Ranges Unique reflections Observed reflections [I > 3s(I)] Goodness of fit No.parameters Maximum D/s Maximum, minimum Dr/e Å23 Ra R9 b C32H41MnN8S9 881.29 Monoclinic P21/c 1.541 84 15.876(4) 17.932(4) 15.642(3) 117.61(2) 3946.0(1) 4 1.48 74.3 298 1828 0.18 × 0.39 × 0.51 1–69 219 to 19, 0–21, 0–21 7474 3631 2.64 451 0.2 0.481, 20.09 0.051 0.053 a R = S(||Fo| 2 |Fc||)/S|Fo|. b R9 = [Sw(||Fo| 2 |Fc||)2/Sw|Fo|2]� �� .blue solution that, after freezing at 270 8C overnight, filtration and washing with hexane, aVorded metallic needle-like crystals of [Mn(oespz)] (yield ª 70%) (Found: C, 45.49; H, 4.37; N, 13.55; S, 30.17. C32H40N8MnS8 requires C, 45.31; H, 4.75; N, 13.21; S, 30.24%). UV/VIS (EtOH): l/nm (log e) 280 (4.28); 345 (4.37) (Soret); 420 (3.96), 450 (3.92); 590 (4.40), 640 (4.18), 720 (4.09) (Q bands).[Mn(oespz)(SH)]. All reactions and manipulations were performed under an inert atmosphere. The complex [Mn(oespz)] (0.10 g, 0.12 mmol) was dissolved at 20 8C in freshly purified CS2 (20.0 cm3) under vigorous stirring. The solution immediately turned red. After 1 h, anhydrous THF (5.0 cm3) was added dropwise to the solution and some small crystals started to form. The mixture was allowed to stand at 4.0 8C for 48 h. The precipitate was collected by filtration, washed with hexane and recrystallised from CS2–hexane (yield > 90%) (Found: C, 44.00; H, 4.43; N, 12.76.C32H41N8MnS9 requires C, 43.61; H, 4.69; N, 12.71%). UV/VIS (C6H6): l/nm (log e) 337 (4.35); 418 (4.23) (Soret); 522 (4.27), 571 (4.22); 718 (4.33) (Q bands). Crystallography Crystal data, details of data collection and refinement parameters for [Mn(oespz)(SH)] are given in Table 1 and selected bond lengths and angles are given in Table 2.All data were collected at room temperature on an Enraf-Nonius CAD-4 diVractometer using graphite-monochromatized Cu-Ka radiation. The unit cell was determined from 25 well-centered reflections. The intensity data were collected in an w–2q scan mode. A total of 7474 reflections were measured to qmax = 698; 3631 reflections with I > 3s(I) were used. Data reduction Table 2 Selected bond lengths (Å) and angles (8) with estimated standard deviations in parentheses for [Mn(oespz)(SH)] Mn]Sapical Mn]N(1) Mn]N(2) Mn]N(3) Mn]N(4) S(1)]C(2) S(2)]C(3) S(3)]C(6) S(4)]C(7) S(5)]C(10) S(6)]C(11) S(7)]C(14) S(8)]C(15) N(1)]C(1) N(1)]C(4) N(2)]C(5) N(2)]C(8) N(3)]C(9) N(3)]C(12) N(4)]C(13) N(4)]C(16) Sapical]Mn]N(1) Sapical]Mn]N(2) Sapical]Mn]N(3) Sapical]Mn]N(4) N(1)]Mn]N(2) N(1)]Mn]N(4) N(2)]Mn]N(3) N(3)]Mn]N(4) C(1)]N(1)]C(4) C(5)]N(2)]C(8) C(9)]N(3)]C(12) C(13)]N(4)]C(16) C(4)]N(5)]C(5) C(8)]N(6)]C(9) C(12)]N(7)]C(13) C(1)]N(8)]C(16) 2.374(3) 1.949(5) 1.938(4) 1.955(5) 1.945(4) 1.751(7) 1.717(6) 1.727(6) 1.723(6) 1.725(6) 1.738(6) 1.727(6) 1.724(7) 1.373(7) 1.361(7) 1.371(7) 1.392(8) 1.370(7) 1.362(7) 1.380(7) 1.377(8) 100.6(2) 100.1(2) 96.6(2) 96.9(2) 88.8(2) 88.4(2) 88.9(2) 88.7(2) 107.1(5) 105.6(4) 107.6(5) 106.6(4) 121.9(5) 123.2(5) 122.2(5) 122.9(5) N(5)]C(4) N(5)]C(5) N(6)]C(8) N(6)]C(9) N(7)]C(12) N(7)]C(13) N(8)]C(1) N(8)]C(16) C(1)]C(2) C(2)]C(3) C(3)]C(4) C(5)]C(6) C(6)]C(7) C(7)]C(8) C(9)]C(10) C(10)]C(11) C(11)]C(12) C(13)]C(14) C(14)]C(15) C(15)]C(16) C(17)]C(18) N(1)]C(1)]C(2) N(2)]C(5)]C(6) N(3)]C(9)]C(10) N(4)]C(13)]C(14) C(1)]C(2)]C(3) C(5)]C(6)]C(7) C(9)]C(10)]C(11) C(13)]C(14)]C(15) S(1)]C(2)]C(3) S(2)]C(3)]C(2) S(3)]C(6)]C(7) S(4)]C(7)]C(6) S(5)]C(10)]C(11) S(6)]C(11)]C(10) S(7)]C(14)]C(15) S(8)]C(15)]C(14) 1.328(7) 1.340(8) 1.319(8) 1.305(7) 1.323(7) 1.326(9) 1.320(7) 1.328(8) 1.436(9) 1.368(7) 1.471(9) 1.438(8) 1.377(9) 1.435(7) 1.464(8) 1.370(7) 1.459(9) 1.447(8) 1.365(9) 1.440(7) 1.51(1) 109.3(4) 111.4(5) 109.1(4) 110.2(6) 108.5(5) 105.6(5) 107.0(5) 105.7(5) 127.7(5) 137.4(5) 124.1(5) 122.0(4) 137.1(5) 130.2(5) 126.7(5) 122.8(4)J.Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 1987 included correction for background and Lorentz-polarizations eVects. An absorption correction was applied according to ref. 14. The intensities of two reflections were measured every hour during data collection as a check of the stability of the diVractometer and the crystal; no appreciable decay of the intensities was observed.The crystal orientation was checked every 200 intensity measurements using two control reflections. Structure analysis and refinement. The structure of [Mn- (oespz)(SH)] was solved by means of direct methods using MULTAN.15 The analysis of the E-map derived from the set of phases with the best combined figure of merit revealed the position of most of the non-hydrogen atoms. In both cases the remaining atoms were located from successive Fourier syntheses. The structures were anisotropically refined by full-matrix least-squares procedures to an R value of 0.051 (R9 = 0.053).The minimized function was Sw(|Fo| 2 |Fc|)2, with w = 1 for all the observed I > 3s(I) reflections. Hydrogen atoms, included in the structural model in stereochemically calculated positions, were refined but restrained to ride on the atoms to which they are bonded. The relatively large value of D/s maxima are due to the presence of the C(22) carbon atom which shows unresolved disorder.Atomic scattering factors and anomalous dispersion corrections were taken from ref. 16. All the computations were performed by the MOLEN package 17 running on a DEC VAX 6510 computer. CCDC reference number 186/993. Results and Discussion Preparation and properties of [Mn(oespz)(SH)] The formation of [Mn(oespz)(SH)] occurs in two steps: (i) reaction of [MnII(oespz)] with CS2 to give an unstable adduct, (ii) reaction of this adduct with THF.The reaction of [MnII- (oespz)], a complex with a highly nucleophilic metallic center, and CS2, is fast. On mixing, the solution of the manganese complex and carbon disulfide immediately turns from blue to red. The reaction consists of an oxidative addition of CS2 to the manganese(II) center, leading, through equilibrium (1), to the [MnII(oespz)] 1 CS2 [MnIII(oespz)1(CS2)~2] (1) adduct [MnIII(oespz)1(CS2)~2]. Oxidative addition of the Cl? radical to the manganese(II) center was invoked to explain the easy C]Cl bond cleavage upon reaction of [Mn(oespz)] with chlorinated hydrocarbons.2,3 The formation of the adduct [MnIII(oespz)1(CS2)~2] in CS2 can be justified on the basis of experimental evidence, whereas its structure can be tentatively predicted on the basis of theoretical arguments.Indeed, we have found that removal of excess CS2 from the reaction mixture by a N2 stream leads to the recovery of the manganese(II) complex.It can be concluded, therefore, that the reaction simply involves the abstraction of a sulfur atom from CS2. The UV/VIS spectrum of the proposed adduct [MnIII(oespz)1(CS2)~2] shows typical absorptions of a manganese(III) porphyrazine,2 and significantly diVers from that of [MnIII(oespz)(SH)] in CS2. The Soret and the Q band of [MnIII(oespz)(SH)] lie, in CS2, at 340 and 705 nm, respectively, whereas these bands occur at 350 and 726 nm in the case of the adduct.As for the structure of [MnIII(oespz)1(CS2)~2] a h1-C arrangement (a) (see below) seems rather unlikely, on the basis of steric arguments. Although, in fact, the a2u(p*) LUMO orbital of a linear (Dh) CS2 molecule (this orbital becomes a1 for a slightly bent CS2 molecule with C2v symmetry) 18,19 which becomes semi-occupied upon reaction with [Mn(oespz)] is largely localized on the carbon atom, a h1-C structure would lead to severe CS2–macrocycle repulsive interactions. Similar arguments might hold, in part, for a h2-C,S arrangement (b), leaving a h1-S structure (c) of the adduct as the most likely.Unlike the h2-C,S, co-ordination mode, however, the h1-S coordi mode of CS2 has not been characterized and has been only proposed for a few organometallic compounds.4 This co-ordination mode is predicted, in fact, based on electronic structure considerations, to lead to highly unstable systems. A structure in between b and c seems more appropriate in interpreting the last step of the reaction, and would involve either H or H? radical abstraction from THF by the highly reactive [MnIII(oespz)1(CS2)~2] leading to C]S bond cleavage and to the formation of CS1 or CS and [Mn(oespz)(SH)].Carbon– sulfur bond cleavage in h2- bound CS2 and related ligands is a facile process and is observed,20 for instance, in the insertion of the chalcogen atom of COS into a metal–hydride bond. On the other hand, formation of hydrogensulfide ligands from metal sulfides and hydrogen has been also reported.21 Interestingly, the compound [Mn(oespz)(SH)] can be also obtained by the reaction of [Mn(oespz)] with a saturated ethanolic solution of H2S.Besides the [Mn(oespz)(SH)] complex, the reaction leads to production of H2. As inferred from the gas-chromatographic quantitative analysis 22 of the evolved H2, the stoichiometry of this reaction agrees with equation (2). 2[MnII(oespz)] 1 2H2S = 2[MnIII(oespz)(SH)] 1 H2 (2) A detailed description of the mechanistic aspects of this reaction will be presented elsewhere.23 Unlike [Fe(TAP)(SH)] [TAP = 5,10,15,20-tetrakis(p-methoxyphenyl) porphyrinato dianion], [Mn(oespz)(SH)] is not very oxygen sensitive in solution and we did not find evidence for the formation of the m-oxo dimer, as in the case of the iron complex, upon exposure to dry oxygen.8a The MnIII æÆ MnII process occurs reversibly (ipa/ipc = 1, DEp = 60 mV, where ipa and ipc are, respectively, the anodic peak current and the cathodic peak current) at E2� 1 = 0.178(5) V (vs.Ag–AgCl). This value is, similar to that found in [Mn(oespz)Cl], considerably anodically shifted relative to manganese porphyrins and might be an origin of the unusual stability of this complex.2 That this value is only slightly more anodic than in [Mn(oespz)Cl] confirms the observed tendency of porphyrazines to stabilize the low oxidation states of first-row transition metals.1,2 This also indicates that axial ligands of diVerent s-donor capability, but with scarce p-acceptor capability,24 only marginally influence the MnIII–MnII redox process in manganese tetraazaporphyrins.In the IR spectrum of [Mn(oespz)(SH)], taken as a CCl4 solution or as KBr pellets, no bands due to S]H vibration are seen, as hydrogensulfide stretches in metal complexes are generally weak and often not observed.7a,25 The near-IR spectrum of a thin film of the complex is shown in Fig. 1. It is, in the higher energy region, qualitatively similar to that observed for chloromanganese( III) porphyrazine in solution. Moreover the spectrum reveals rather intense bands in the ranges 1300–1800 and 2300–2800 nm, that are not present in the solution spectrum. In order to check if these signals are caused by S]H vibrations or to electronic transitions, we recorded a near-IR spectrum of a hydrosulfido compound (2-naphthalenethiol). Since the thin film near-IR spectrum of 2-naphthalenethiol did not show significant absorptions in the ranges 1300–1800 and 2300–2800 nm, it appears plausible that the lowest lying bands in the near-1988 J.Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 IR spectra of the complex are due to lattice intermolecular interactions rather than to S]H vibrations. The room-temperature 1H NMR spectrum of [Mn(oespz)- (SH)] taken in CD3OD, instead, reveals a broad peak at d 10.3 ascribed, on integration, to the hydrogensulfide proton resonance.The 1H NMR resonance of this proton occurs at d 21.21 in CDCl3 for [Rh(SH)(CO)(PPh3)2] 7a and at d 218.4 for [RhCl(H)(m-SH)(PPh3)2]2?2CH2Cl2,7b indicative of the large sensitivity of the hydrogensulfide proton resonance to the nature of the metal and the other ligands. Nevertheless the 1H NMR resonance of the sulfur-bound proton in [Mn(oespz)- (SH)] compares well with that of [Fe(TAP)(SH)] occurring at d 6.75.8a It can be concluded that the 1H NMR signal at d 10.3 in [Mn(oespz)(SH)] is due to a proton bound to a pyrrolic nitrogen. Infrared spectra in CCl4 did not show any evidence of N]H bond stretching in the region 3000–3400 cm21.Based on these data, the possible interchange of the hydrogensulfide proton between the apical sulfur and a pyrrolic nitrogen also appears to be quite unlikely (see below). Description of the crystal structure The complex [Mn(oespz)(SH)] is isostructural with [Mn- (oespz)Cl] and [Fe(oespz)Cl] 2 and, for this reason, its structure will be briefly described.Fig. 2 is a computer-drawn model of the [Mn(oespz)(SH)] molecules as it exists in the crystal. The co-ordination geometry around the manganese atom is that of a slightly distorted square pyramid. The displacement of the metal atom out of the planar (Np)4 (Np = pyrrolic nitrogen atoms) donor set is 0.294(1) Å. Thus the MN4 group is only slightly more pyramidal than in [Mn(oespz)Cl]2 and in [Mn- (tpp)Cl] (H2tpp = meso-5,10,15,20-tetraphenylporphyrin).27 We notice that the Fe out-of-plane distance is 0.33 Å in the parent, low-spin (S = ��� ) [Fe(TAP)(SH)] complex.8a The average Mn]Np distance is 1.946(5) Å, a value comparable to that in [Mn- (oespz)Cl] [1.951(6) Å] and in the MnIII–phthalocyaninato m-oxo dimer, [Mn2(pc)2(py)2O] [1.960(3) Å], but shorter than in [Mn(tpp)(Cl)] [2.082(2) Å].2,19,20 That the Mn]Np distance is shorter than in [Mn(tpp)(Cl)] Fig. 1 Near-IR absorption spectrum of a thin film of [Mn(oespz)- (SH)] deposited on a quartz slide and the extent of MnN4 pyramidalization are consistent with the remarkable contraction of the co-ordinating cavity in the porphyrazines and with the presence of an unoccupied antibonding dx2 2 y2 orbital.It should be considered, however, that a contribution to the pyramidalization arises from the necessity to minimize non-bonded contacts between the hydrosulfido axial ligand and the (Np)4 core atoms. The Mn]Sapical distance of 2.374(3) Å is in the range expected for this bond in transition-metal hydrosulfido complexes. Actually, M]S distances of 2.298(3), 2.418(3) and 2.340(2) Å respectively have been found in [Fe(TAP)(SH)], trans-[Rh(SH)(CO)(PPh3)2] and cis-[Pt(SH)2(PPh3)2].7a,8a,28 On the other hand, M]S distances ranging from 2.395(3) to 2.591(5) Å are found in manganese(II) complexes containing thiolate ligands.29 For the tetraazaporphyrinato core, the dimensional variations in bond length and angles of chemically analogous bond types diVer immaterially from four-fold geometry. However, as previously noted in other structurally characterized porphyrazines, the Cb]Cb bonds are significantly contracted with respect to [M(pc)] complexes [average bond lengths of 1.365(5) vs. 1.395(5) Å].1 The crystal packing of [Mn(oespz)(SH)] consists of slipped stacks of dimeric units. The monomers are slipped within each dimer, positioned in a trans fashion with respect to the Mn]Sapical bond and weakly associated via long contacts between the Mn and S(1) atoms of the adjacent molecule [Mn? ? ? S(1) 3.250(3) Å].Intradimer interactions at the van der Waals limit also occur between the N(3) and N(4) atoms and the S(1) atom of the adjacent molecule: N(3) ? ? ? S(1) 3.262(7), N(4) ? ? ? S(1) 3.285(7) Å. Owing to the peculiar structure of the dimer, the repulsion between the N(3) and N(4) out-of-plane lone pairs and the S(1) lone pair, prevents a closer Mn ? ? ? S(1) approach.Along the stack weak interdimer interactions [3.612(2) Å] arise from S(5) ? ? ?Sapical contacts [S(5) at 2x, ��� 1 y, ��� 2 z]. EPR and magnetic susceptibility data The nature and the strength of the intradimer interactions account for the solid-state magnetic behaviour of [Mn(oespz)- (SH)]. The temperature dependence of the magnetic susceptibility, c versus T, measured in the temperature range 3.5–240 K is shown in Fig. 3. The high temperature eVective magnetic moment, meff = 8kT = 6.8 mB with the spin-only value expected for two S = 2 non-interacting spins (meff = 6.9 mB).The c versus T curve shows a clear maximum around 5 K indicating that an antiferromagnetic interaction is operative between the two spin centers. The compound was found to be EPR silent down to 4.3 K, as expected for a Fig. 2 An ORTEP26 plot of [Mn(oespz)(SH)] with the atom numbering scheme used; ellipsoids are scaled to enclose 50% of the electron density and hydrogen atoms are omittedJ.Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 1989 non-Kramers spin system.30 Using the isotropic exchange hamiltonian in the form H = JS1 · S2 to describe the magnetic interaction, the equation describing the temperature dependence of the magnetization takes the form (3). c = Ng2m2 B kT 2e2J/kT 1 10e23J/kT 1 28e2J/kT 1 60e210J/kT 1 1 3e2J/kT 1 5e23J/kT 1 7e26J/kT 1 9e210J/kT (3) The magnetic data have been fitted by minimizing function (4) where coj and coj , are the observed and the computed values at F = oj (cj o 2 cj c)2 (4) temperature Tj, using a Simplex minimization routine.31 The best fit curve, obtained with g = 1.99(2) and J = 1.90(6) cm21, is shown in Fig. 3 as a solid line. Co-ordination chemistry of [Mn(oespz)(SH)] In order to elucidate the structure of the complex in solution and the possible eVects of the sixth ligand on the electronic structure of the complex, we studied the co-ordinating capability of the complex towards strong s-donors such as 1-mim as well as towards sterically hindered organic bases such as 2,4,6- Fig. 3 Temperature dependence of the magnetic susceptibility of [Mn(oespz)(SH)]. The solid line is the best fit curve Fig. 4 Spectroscopic titration of [Mn(oespz)(SH)] (– – –) with 2,4,6- trimethylpyridine in chloroform at 20 ± 0.1 8C. [Mn]tot = 1.02 × 1025 M, [2,4,6-trimethylpyridine] = 0–0.05 M trimethylpyridine. Treatment, at 20.0 ± 0.1 8C, of a chloroform solution of [Mn(oespz)(SH)] (1.0 × 1025 M) with aliquots of a solution of 2,4,6-trimethylpyridine (tmpy) in chloroform, leads to an isosbestic change in the visible spectrum, as shown in Fig. 4. At relatively high concentrations of 2,4,6- trimethylpyridine (0.05 M) a limiting spectrum, indicative of saturation is obtained. The spectra were analyzed by plotting ln[(A0 2 A)/(A 2 Af)] versus ln[2,4,6-methylpyridine] at 320 and 725 nm.31,32 The two plots were linear with an average slope of 1.0 ± 0.1 indicating the formation of the [Mn(oespz)S2][H1tmpy] adduct.The changes in the electronic spectra of a chloroform solution of [Mn(oespz)(SH)] upon progressive addition of a 1- methylimidazole–chloroform solution at the same temperature are displayed in Fig. 5(a). Addition of a strong s-donor, sterically unhindered base, is accompanied by a marked increase of the absorbance at 417 nm, a decrease at 450 and at 718 nm leading to isosbestic points at 370 and 435 nm.At relatively high concentration of 1-mim a limiting spectrum is obtained. In the plots of ln[(A0 2 A)/(A 2 Af)] versus ln[1-mim] at 725 nm the data lie on a single straight line of average slope 1.0 ± 0.1 indicating the formation of the 1 : 1 six-co-ordinated [Mn(oespz)- Fig. 5 (a) Spectroscopic titration of [Mn(oespz)(SH)] (– – –) with 1-mim in chloroform at 20 ± 0.1 8C. [Mn]tot = 1.02 × 1025 M, [1-mim] = 0–0.17 M. (b) Plot of ln[(A0 2 A)/(A 2 Af)] as a function of ln[1-mim] as monitored by the decrease of the absorbance maximum at 718 nm1990 J.Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 (SH)(1-mim)] complex [see Fig. 5(b)]. It is remarkable that the spectroscopic changes noted upon addition of 1-mim are qualitatively similar to those observed when [Mn(oespz)X] (X = halogen) are titrated with the same base in chloroform.3 These results support the conclusion that, contrary to 2,4,6- trimethylpyridine, the 1-mim attack occurs on the manganese atom rather than on the hydrosulfido axial ligand and confirm, de facto, the presence of an apical S]H group (see Scheme 1) in the complex.Notably, on dilution, the main spectral features of pure [Mn(oespz)(SH)] are restored. Thus the processes earlier described are reversible and the eVect of dilution can be understood in light of the fact that it acts, most likely, on the saturation conditions. Upon treatment of a diluted benzene solution of [Mn(oespz)- (SH)] with aliquots of solutions of 1-mim in the same solvent, the spectral changes indicate that the co-ordination of the organic base to manganese is accompanied by a redox process, and a saturation concentration of 1-mim is not reached (Fig. 6). Actually the spectra become progressively similar to that of [Mn(oespz)] indicating that a MnIII æÆ MnII process is occurring. 1 As a matter of fact, the intensity of the Q band at 590 nm progressively increases whereas, concomitantly, that of the band at 720 nm decreases. It was recently demonstrated that Scheme 1 Fig. 6 Spectroscopic titration of [Mn(oespz)(SH)] (– – –) with 1-mim in benzene at 20 ± 0.1 8C. [Mn]tot = 0.76 × 1025 M, [1-mim] = 0–0.17 M the occurrence of an intense band at 590 nm is diagnostic of the MnII systems in the manganese porphyrazines.2 These results clearly indicate that the dimerization of the complex is a solid-state process and that in solution the Mn? ? ? S intermolecular interactions no longer exist or, at least, can be easily replaced by interactions of the metal with a ligand having stronger s-donor capability than that of the sulfanyl function.Co-ordination of the sixth ligand induces important changes in the spectrum of the complex, especially in the region 350–500 nm where ligand-to-metal charge transfer (LMCT) transitions are normally found in redox-active transition-metal porphyrazines.1,2 Depending on the solvent, additional redox processes involving the metal may occur as well.Thus the electrochemical stability and the rich co-ordination chemistry of this complex may stimulate further studies on related complexes to understand the spectroelectrochemical behavior of tetrapyrrole systems of biological interest. In the presence of 2,4,6-trimethylpyridine the axial SH transforms into an out-of-plane thiolate co-ordinating site. Polynuclear complexes of gold(I) or mercury(II) which easily co-ordinate the thiolate ligand, can be built up exploiting this important feature of the complex.33 These possibilities are currently being explored in our laboratory.Conclusion Oxidative addition of CS2 to [Mn(oespz)] aVords the [Mn- (oespz)(SH)] complex that has been characterized by conventional spectroscopies and by cyclic voltammetry. The crystal structure of the complex, that represents the second case of a porphyrin-like complex with a hydrosulfido axial ligand that has been structurally characterized, does not diVer significantly from that of similar manganese(III) porphyrazines.The high spin (S = 2) ground state is consistent with the geometry of the MnN4 core and the weak antiferromagnetic coupling [J = 1.90(6) cm21] between magnetic centers within [Mn(oespz)- (SH)]2 dimers. In CHCl3 [Mn(oespz)(SH)] reacts reversibly with the sterically hindered base 2,4,6-trimethylpyridine through the axial hydrosulfido ligand, whereas the complex co-ordinates reversibly 1-mim on the vacant site of manganese.Treatment of the complex with 1-mim in benzene leads to a MnIIIæÆMnII redox process, as deduced from the UV/VIS spectra. Acknowledgements Thanks are expressed to Dr. A. Caneschi, University of Firenze, for performing magnetic measurements. Thanks are due to the Servizio di Spettrometria di Massa, University of Napoli, for performing FAB mass spectra and to Professor P. Pucci for helping in their interpretation, to Mr. S. Laurita for collecting X-ray data and to Mr.C. Barlabà for technical support. Financial support from Ministero della Università e della Ricerca Scientifica e Tecnologica (MURST) and from Consiglio Nazionale delle Ricerche (CNR) is also gratefully acknowledged. References 1 G. Ricciardi, A. Bencini, A. Bavoso, A. Rosa and F. Lelj, J. Chem. Soc., Dalton Trans., 1996, 3243. 2 G. Ricciardi, A. Bavoso, A. Bencini, A. Rosa, F. Lelj and F. Bonosi, J. Chem. Soc., Dalton Trans., 1996, 2799. 3 G. Ricciardi, S. Belviso, K.Pilat and F. Lelj, unpublished work. 4 C. Bianchini, C. Mealli, A. Meli and M. Sabat, Stereochemistry of Organometallic and Inorganic Compounds, ed. I. Bernal, Elsevier, Amsterdam, 1986, vol 1, p. 146. 5 G. Steimecke, R. Kirmse and E. Hoyer, Z. Chem., 1975, 15, 28. 6 E. Hoyer, Comments Inorg. Chem., 1983, 2, 261. 7 (a) T. R. GaVney and J. A. Ibers, Inorg. Chem., 1982, 21, 2857; (b) A. M. Mueting, P. Boyle and L. H. Pignolet, Inorg. Chem., 1984, 23, 44; (c) T. B. Rauchfuss and C.RuZing, Organometallics, 1982, 1, 400. 8 (a) D. R. English, D. N. Hendrickson, K. S. Suslick, C. W.J. Chem. Soc., Dalton Trans., 1998, Pages 1985–1991 1991 Eigenbrot, jun. and W. R. Scheidt, J. Am. Chem. Soc., 1984, 106, 7258; (b) J. H. Dawson, J. R. Trudell, G. Barth, R. E. Linder, E. Bunnenberg, C. Djerassi, R. Chiang and L. P. Hager, J. Am. Chem. Soc., 1976, 98, 3709; (c) S. W. McCann, F. V. Wells, H. H. Wickmann, T. N. Sorrell and J. P. Collman, Inorg.Chem., 1980, 19, 621. 9 I. Fridovich, Annu. Rev. Biochem., 1995, 64, 97. 10 G. C. Dismukes, Chem. Rev., 1996, 96, 2909. 11 J. S. Miller, J. C. Calabrese, R. S. McLean and A. J. Epstein, Adv. Mater., 1992, 4, 498. 12 J. S. Miller, C. Vasquez, J. C. Calabrese, R. S. McLean and A. J. Epstein, Adv. Mater., 1994, 6, 217. 13 D. D. Perrin and W. L. F. Armarego, Purification of laboratory chemicals, Pergamon Press, Oxford, 3rd edn., 1988. 14 N. Walker and D. Stuart, Acta Crystallogr., Sect.A, 1983, 39, 159. 15 MULTAN 82, Structure determination package, B. A. Frentz and Associates, College Station, TX, 1982. 16 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV, p. 99. 17 C. K. Fair, MOLEN, Structure Determination System, Delft, The Netherlands, 1990. 18 R. S. Alvarez, R. Vicente and R. HoVmann, J. Am. Chem. Soc., 1985, 107, 6253. 19 C. Mealli, R. HoVmann and A. Stockis, Inorg. Chem., 1984, 23, 56. 20 H. L. M. van Gaal and J. P. J. Verlaan, J. Organomet. Chem., 1977, 133, 93; H. Werner and O. Kolb, Angew. Chem., Int. Ed. Engl., 1979, 18, 865; T. R. GaVney and J. A. Ibers, Inorg. Chem., 1982, 21, 2851. 21 M. Rakowski DuBois, M. C. Van Derveer, D. L. DuBois, R. C. Haltiwanger and W. K. Miller, J. Am. Chem. Soc., 1980, 102, 7456. 22 R. Henning, W. Schlamann and K. Kisch, Angew. Chem., Int. Ed. Engl., 1980, 19, 645. 23 G. Ricciardi, S. Belviso and F. Lelj, unpublished work. 24 G. M. Brown, F. R. Hopf, T. J. Meyer and D. G. Whitten, J. Am. Chem. Soc., 1975, 97, 5385; F. A. Walker, D. Beroiz and K. M. Kadish, J. Am. Chem. Soc., 1976, 98, 3484. 25 J. P. Collman, R. K. Rothrock and R. A. Stark, Inorg. Chem., 1977, 16, 437. 26 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 27 L. H. Vogt, A. Zalkin and D. H. Templeton, Inorg. Chem., 1967, 6, 1725. 28 C. E. Briant, G. R. Hughes, P. C. Minshall and D. M. P. Mingos, J. Organomet. Chem., 1980, 202, C18. 29 H. O. Stephan and G. Henkel, Polyhedron, 1996, 15, 501; J. A. Castro, J. Romero, J. A. Garcia-Vazquez, A. Castineiras, A. Sousa and J. Zubieta, Polyhedron, 1995, 14, 2841; B. Krebs and G. Henkel, Angew. Chem., Int. Ed. Engl., 1991, 30, 769; A. Silver, S. A. Koch and M. Millar, Inorg. Chim. Acta, 1993, 205, 9. 30 A. Abragam and B. Bleaney, Electron paramagnetic resonance of transition ions, Oxford Press, Oxford, 1970. 31 C. J. O’Connor, Prog. Inorg. Chem., 1982, 29, 203. 32 H. JaVé and M. Orchin, Theory and Applications of Ultraviolet Spectroscopy, Wiley, New York, 1992, p. 578. 33 J. Fitzgerald, B. S. Haggerty, A. N. Rheingold and L. May, Inorg. Chem., 1992, 31, 2006. 34 J. M. Foward, D. Bohmann, J. P. Falcker, jun. and R. J. Staples, Inorg. Chem., 1995, 6330. Received 7th November 1997; Paper 7/08033F

ISSN:1477-9226    

DOI:10.1039/a708033f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1987–1991 1987 Synthesis and characterisation of some dimeric Á2-diyne compounds of cobalt Xue-Nian Chen,a Jie Zhang,a Shu-Lin Wu,a Yuan-Qi Yin,*a Wen-Ling Wang b and Jie Sun c a State Key Laboratory for Oxo Synthesis and Selected Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China. E-mail: hcom@ns.lzb.ac.cn b Department of Chemistry, Zhengzhou University, Zhengzhou 450052, China c Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China Received 26th January 1999, Accepted 15th April 1999 The organometallic dimers [{Co2(CO)6}2(diyne)] [diyne = C6H4(CO2CH2C2H)2-1,2 1, HC2CH2OC6H4OCH2C2H 2 or HC2(CH2)5C2H 3] have been synthesized from reactions between [Co2(CO)8] and the appropriate diyne ligands.However, the reaction of [Co2(CO)8] with diprop-2-ynyl ether HC2CH2OCH2C2H under similar conditions gave the expected product [{Co2(CO)6}2(m-HC2CH2OCH2C2H)] 4 and the unexpected product [Co4(CO)10(m-CO){m4-h:h3- CC(CH2OCH2)CCH2}] 5.The products have been characterised by infrared, 1H NMR spectroscopy and C/H analyses, and 2, 4 and 5 also by single-crystal X-ray crystallography. In 2 and 4 both “yne” fragments of the diyne ligand are bonded to a Co2(CO)6 fragment with the C]] ] C vector essentially perpendicular to the Co–Co vector. However, in 5 hydrogen migration and new C–C bond formation has led to novel structural features, such as m3-CCo3 and h3-C3Co units and a “C4O” ring.Octacarbonyldicobalt has been shown to react with alkynes at room temperature to give the m-alkyne complexes [Co2- (CO)6(RC]] ] CR9)].1,2 In other reactions between alkynes and [Co2(CO)8], cyclic products,3–5 benzene or their derivatives, bilactones and cyclopentenone are formed by way of dinuclear cobalt intermediates. Recently, diyne clusters have been receiving considerable attention because of their potential application as polymeric materials, moreover also their unusual structures and reactions.6 A dimer containing two linked Co2(CO)6C2 units has been reported previously.7,8 Seyferth 9 and Rubin 10 and co-workers also synthesized similar polymers containing the Co2(CO)6C2 unit.As an extension, we have continued to study the reactions between [Co2(CO)8] and diyne ligands and found unexpected results. Results and discussion Treatment of diyne ligands with two molar equivalents of [Co2(CO)8] in appropriate solvents at room temperature gives tetranuclear clusters [{Co2(CO)6}2(diyne)] [diyne = C6H4(CO2- CH2C2H)2-1,2 1, HC2CH2OC6H4OCH2C2H 2 or HC2(CH2)5- C2H 3].Under the same conditions, reaction of diprop-2-ynyl ether with [Co2(CO)8] not only produces the expected product [{Co2(CO)6}2(m-HC2CH2OCH2C2H)] 4, but also the unexpected product [Co4(CO)10(m-CO){m4-h1 :h3-CC(CH2OCH2)CCH2}] 5 (Scheme 1). High yields are obtained in all reactions at room temperature.In all cases the reactions were monitored by TLC, showing the disappearance of the starting complexes. The products were purified by column chromatography, followed by crystallisation from benzene– or hexane–CH2Cl2 at 220 8C to give red or brown crystals. They are stable in air as solids and soluble in common organic solvents. At the present stage the mechanism concerning the formation of compound 5 remains unclear, but it is certain that the migration of hydrogen and cyclisation are included.This is similar to the reaction of alkynes with triosmium clusters, in which the presence of a terminal hydrogen or CH2OH group in the molecule of the parent alkyne makes possible a profound rearrangement of the ligand, including hydride transfer to the ligand, subsequent dehydration and cyclisation with the formation of an oxygen-containing “C4O” ring.6,11,12 However, no products similar to compound 5 are observed in the other reactions, the possible reason being that a stable pentaatomic ring could not be formed in these cases.The products were characterised by IR spectroscopy, microanalysis and 1H NMR spectroscopy. In the case of the complexes 2, 4 and 5 the characterisations have been confirmed and the molecular geometry established by single-crystal X-ray crystallography. Scheme 1 Formation of complexes 1–5. 2Co2(CO)8 HC C R C CH HC C R C CH Co Co Co Co (CO)3 (CO)3 (CO)3 (CO)3 CH2 O CH2 CH2 C CH C CH Co2(CO)8 O CH2 CH2 C CH C CH Co Co (CO)3 (CO)3 Co Co (CO)3 (CO)3 C O CH2 CH2 C C Co Co Co Co O (CO)2 (CO)2 (CO)3 (CO)3 C 1 R = C6H4(CO2CH2)2–1,2 2 R = CH2OC6H4OCH2 3 R = (CH2)5 4 51988 J.Chem. Soc., Dalton Trans., 1999, 1987–1991 Infrared spectroscopy The IR spectra of complexes 1–4 all show the characteristic carbonyl pattern observed for previously reported cobalt– alkyne compounds13 with six bands in the terminal carbonyl stretching region. Since these spectra and those of known cobalt–alkyne derivatives are very similar it is reasonable to conclude that a similar co-ordination mode for the alkyne is adopted but in this case that both alkyne linkages are coordinated to cobalt atoms.No C]] ] C stretches were observed in the region of 2100 cm21, and more importantly no C–H stretch (expected at 3290 cm21) was present. This we take to indicate the absence of a C]] ] C triple bond consistent with the view that both alkyne linkages are co-ordinated to Co2 units.For the IR spectrum of complex 5, in addition to the absorption bands of terminal carbonyl, those of bridging carbonyl appear at 1838 cm21 and this is consistent with its crystal structure. Proton NMR spectroscopy The 1H NMR spectroscopic data for the complexes 1–5 are consistent with the overall geometry established in the solid state for 2, 4 and 5, and with the IR spectroscopy studies. For complexes 1–4 which contain a terminal alkyne hydrogen a single resonance is observed in the region d 6.14–6.02.As expected,14,15 because of the reduction in the C]] ] C triple-bond character, there is a downfield shift in the position of these terminal protons with respect to the “free” ligand (at around d 2.50–1.90). Similarly, they possess methylene protons which exhibit a singlet in the region d 5.52–2.89 in their 1H NMR spectra, which also undergo a distinct downfield shift when the C]] ] C group is co-ordinated to Co–Co. Complexes 1 and 2 have aromatic rings and consequently their 1H NMR spectra contain peaks in the region d 7.81–6.90.For 2 the appearance of a singlet at d 6.90 (integral 4 H) indicates that the four aromatic protons are equivalent and that the aromatic ring must be rotating about the C(10)–O(7) bond (Fig. 1). The 1H NMR spectrum for 1 reveals non-equivalent aromatic protons and appears as a multiplet in the region d 7.81–7.57. In the 1H NMR spectrum of complex 5 no signals due to protons of a terminal alkyne are observed.The multiplet at d 5.03 is assignable to two protons of the C(12)H2 group.16 Since 5 is asymmetric the four protons of the two CH2 groups in the “C4O” ring are in diVerent environments. This results in the CH2 protons giving rise to two sets of peaks.17 Crystal and molecular structures of [{Co2(CO)6}2(Ï-HC2CH2- OC6H4OCH2C2H)] 2 and [{Co2(CO)6}2(Ï-HC2CH2OCH2C2H)] 4 The crystal structures of complexes 2 and 4 consist of discrete molecules of [{Co2(CO)6}2(m-HC2CH2OC6H4OCH2C2H)] and [{Co2(CO)6}2(m-HC2CH2OCH2C2H)] in which the two Co2(CO)6(alkyne) fragments are linked by the CH2OC6H4- OCH2 and CH2OCH2 groups, respectively.The molecular structures are shown in Figs. 1 and 2; selected bond lengths and angles are listed in Tables 1 and 2, respectively. As seen in Fig. 1, Fig. 1 Molecular structure of complex 2. the molecule sits on a crystallographic centre of symmetry which lies at the centre of the aryl ring. The Co2C2 core adopts a pseudo-tetrahedral geometry with the C(7)–C(8) alkyne bond lying essentially perpendicular to the Co(1)–Co(2) vector.Each of the cobalt atoms is co-ordinated to three terminal carbonyl ligands which display linear geometries. The Co(1)–Co(2) bond length found in 2 lies within the range 2.460–2.477 Å observed for other dicobalt systems that are bridged by perpendicular alkyne ligands,7,18–20 but is shorter than the value of 2.52 Å found in the parent carbonyl [Co2(CO)8]. The C(1)–C(8) length is slightly shorter than the range 1.33–1.36 Å of values for the alkynic C–C bond in the same set of related dicobalt complexes.7,18–20 This C–C distance shows a lengthening of ca. 0.13 Å from the value of 1.18 Å found in the free alkyne, an observation that is consistent with the delocalisation of electron density into the Co2 unit. As seen in Fig. 2, the Co2C2 core also adopts a pseudo-tetrahedral geometry and the overall conformations of the two Co2C2 moieties in 4 resemble each other and are similar to that found in 2.The two Co–Co and C–C bond lengths are slightly longer than the value found in 2 but still lie within the normal range. The Co–C bond distances in the Co2C2 cores are in the range 1.938(6)–1.961(4) Å, comparable with those of related dicobalt complexes.7,18–20 No Fig. 2 Molecular structure of complex 4. Table 1 Selected bond lengths (Å) and angles (8) for complex 2 with estimated standard deviations (e.s.d.s) in parentheses Co(1)–Co(2) Co(1)–C(8) Co(2)–C(8) Co(2)–Co(1)–C(7) C(7)–Co(1)–C(8) Co(1)–Co(2)–C(8) Co(1)–C(7)–Co(2) Co(2)–C(7)–C(8) Co(1)–C(8)–C(7) C(7)–C(8)–C(9) 2.4746(8) 1.953(3) 1.943(3) 50.7(1) 39.3(1) 50.75(10) 78.9(1) 69.9(2) 70.0(2) 107.1(3) Co(1)–C(7) Co(2)–C(7) C(7)–C(8) Co(2)–Co(1)–C(8) Co(1)–Co(2)–C(7) C(7)–Co(2)–C(8) Co(1)–C(7)–C(8) Co(1)–C(8)–Co(2) Co(2)–C(8)–C(7) 1.944(4) 1.953(3) 1.309(4) 50.38(9) 50.4(1) 39.3(1) 70.7(2) 78.9(1) 70.8(2) Table 2 Selected bond lengths (Å) and angles (8) for complex 4 with e.s.d.s in parentheses Co(1)–Co(2) C(13)–C(14) Co(1)–C(13) Co(1)–C(14) Co(2)–C(13) Co(2)–C(14) Co(2)–Co(1)–C(13) Co(2)–Co(1)–C(14) C(13)–Co(1)–C(14) Co(1)–Co(2)–C(13) Co(1)–Co(2)–C(14) C(13)–Co(2)–C(14) Co(1)–C(13)–C(14) Co(2)–C(14)–C(13) 2.4686(9) 1.308(6) 1.948(5) 1.939(4) 1.939(5) 1.958(5) 50.4(1) 51.0(1) 39.3(2) 50.7(1) 50.3(1) 39.2(2) 69.9(3) 69.6(3) Co(3)–Co(4) C(17)–C(18) Co(3)–C(17) Co(3)–C(18) Co(4)–C(17) Co(4)–C(18) Co(4)–Co(3)–C(17) Co(4)–Co(3)–C(18) C(17)–Co(3)–C(18) Co(3)–Co(4)–C(17) Co(3)–Co(4)–C(18) C(17)–Co(4)–C(18) Co(3)–C(17)–C(18) Co(4)–C(18)–C(17) 2.4866(9) 1.316(6) 1.959(4) 1.938(5) 1.952(4) 1.961(4) 50.4(1) 50.8(1) 39.5(2) 50.6(1) 50.0(1) 39.3(2) 69.4(3) 70.0(3)J. Chem.Soc., Dalton Trans., 1999, 1987–1991 1989 symmetry centre occurs in compound 4 and this is inconsistent with 2. Crystal and molecular structure of [Co4(CO)10(Ï-CO){Ï4-Á:Á3- CC(CH2OCH2)CCH2}] 5 In order to establish the structure of complex 5 a suitable crystal of it was subjected to X-ray diVraction analysis.The molecular structure is shown in Fig. 3, while selected lengths and angles are collected in Table 3. It is confirmed that the complex contains a “C4O” ring and m3-CCo3 and h3-C3Co units. The formation of the “C4O” ring and asymmetric molecule are consistent with the 1H NMR spectrum of 5 showing Fig. 3 Molecular structure of complex 5. Table 3 Selected bond lengths (Å) and angles (8) for complex 5 with e.s.d.s in parentheses Co(1)–Co(2) Co(2)–Co(3) Co(1)–C(17) Co(3)–C(17) Co(4)–C(13) Co(3)–C(9) C(12)–C(13) C(13)–C(16) C(16)–C(17) Co(2)–Co(1)–Co(3) Co(3)–Co(1)–C(17) Co(1)–Co(2)–C(17) Co(1)–Co(3)–Co(2) Co(2)–Co(3)–C(17) Co(2)–Co(3)–Co(4) Co(3)–Co(4)–C(16) C(13)–Co(4)–C(16) O(12)–C(14)–C(13) Co(4)–C(13)–C(12) Co(4)–C(13)–C(16) C(12)–C(13)–C(14) Co(4)–C(16)–C(13) Co(4)–C(16)–C(17) C(15)–C(16)–C(17) C(16)–C(17)–Co(1) C(16)–C(17)–Co(3) Co(1)–C(17)–Co(3) Co(4)–C(12)–C(13) 2.502(2) 2.519(2) 1.93(1) 1.97(1) 2.11(1) 1.90(1) 1.37(2) 1.45(1) 1.42(1) 60.76(5) 51.4(3) 49.7(3) 60.07(5) 49.1(3) 105.46(6) 79.6(3) 39.8(4) 105.8(9) 73.9(7) 71.9(6) 129(1) 68.4(8) 86.1(6) 127.5(9) 127.8(8) 130.9(8) 78.7(4) 68.7(6) Co(1)–Co(3) Co(3)–Co(4) Co(2)–C(17) Co(4)–C(12) Co(4)–C(16) Co(4)–C(9) C(13)–C(14) C(15)–C(16) Co(2)–Co(1)–C(17) Co(1)–Co(2)–Co(3) Co(3)–Co(2)–C(17) Co(1)–Co(3)–C(17) Co(4)–Co(3)–C(17) Co(1)–Co(3)–Co(4) C(12)–Co(4)–C(13) C(12)–Co(4)–C(16) O(12)–C(15)–C(16) Co(4)–C(13)–C(14) C(12)–C(13)–C(16) C(14)–C(13)–C(16) Co(4)–C(16)–C(15) C(13)–C(16)–C(15) C(13)–C(16)–C(17) C(16)–C(17)–Co(2) Co(1)–C(17)–Co(2) Co(2)–C(17)–Co(3) 2.478(2) 2.649(2) 1.93(1) 2.17(1) 2.15(1) 1.98(1) 1.51(2) 1.49(2) 49.7(3) 59.16(5) 50.6(3) 49.9(3) 63.4(3) 99.75(6) 37.4(4) 70.3(4) 106.4(9) 121.5(8) 123(1) 106.4(10) 123.3(8) 107.4(8) 124.5(10) 137.2(8) 80.6(4) 80.3(4) several peaks from d 5.03 to 2.59.All of the Co–Co and C–C bond lengths are in the normal region.The C(12)–C(13) distance is 1.37(2) Å in the range of C–C double-bond distances, but the C(16)–C(17) distance of 1.42(1) Å is shorter than C–C single-bond distances of 1.53 Å and is longer than C–C double-bond distances of 1.337 Å. The C–Co bond lengths in the m3-CCo3 unit are also in the normal region but are longer than that in the h3-C3Co. It is possible that a s-coordinated form occurs in the m3-CCo3 unit and a p-coordinated form in the h3-C3Co unit.The C(9)O(9) carbonyl is bridging and the others are terminal; this coexistence of both terminal and bridging carbonyls is consistent with the IR spectrum of complex 5 showing several strong absorption bands from 2092 to 1838 cm21. Experimental All reactions were carried out under pure nitrogen using standard Schlenk techniques. Hexane, benzene and light petroleum (60–90 8C) were dried by sodium while dichloromethane was distilled from CaH2. Chromatographic separations were performed on silica columns (160–200 mesh) of varying length.Thin-layer chromatography (TLC) was carried out on commercial Merck plates coated with a 0.20 mm layer of silica. Infrared spectra were recorded in NaCl cells on a Nicolet FT-IR 10 DX spectrometer. Spectra of compounds in the solid state were recorded as pressed KBr discs. Proton NMR spectra were recorded on a Bruker Am 300 (300 MHz) in CDCl3 deuteriated solvent. Chemical shifts are given on the d scale relative to SiMe4 (0.0 ppm).Elemental analyses were carried out on a Carlo Erba 1106 type analyzer. Nona-1,8-diyne was purchased from Aldrich Chem. Co. Dicobalt octacarbonyl 21 and diynes C6H4(CO2CH2C2H)2-1,2,22 HC2CH2OC6H4OCH2C2H,22 HC2CH2OCH2C2H23 were prepared by literature methods or slight modifications thereof. Preparations [{Co2(CO)6}2{Ï-C6H4(CO2CH2C2H)2-1,2}] 1. In a typical reaction [Co2(CO)8] (684 mg, 2 mmol) and C6H4(CO2CH2- C2H)2-1,2 (242 mg, 1 mmol) were dissolved in benzene (40 cm3).The solution was stirred at room temperature for 2 h. A change from brown to red was observed and TLC monitoring showed the disappearance of the starting material [Co2(CO)8]. After addition of a small amount of silica the solvent was removed and the residue chromatographed. Elution with benzene produced red bands and the volume of the resulting solution was reduced to ca. 10 cm3. Crystallisation at 220 8C yielded a reddish purple crystalline material (648 mg, 79.6%) (Found: C, 38.38; H, 1.20.Calc. for C13H5Co2O8: C, 38.36; H, 1.24%) mp 82–84 8C. IR: n(CO) 2098s, 2055vs, 2031vs, 2022vs, 2016vs, 2002vs and n(C]] O) 1737m and 1715 cm21. 1H NMR: d 7.81– 7.57 (m, 4 H, C6H4), 6.14 (s, 2 H, 2CH) and 5.52 (s, 4 H, 2CH2). [{Co2(CO)6}2(Ï-HC2CH2OC6H4OCH2C2H)] 2. Dicobalt octacarbonyl (684 mg, 2 mmol) and HC2CH2OC6H4OCH2C2H (186 mg, 1 mmol) were dissolved in dichloromethane (30 cm3). The solution was stirred at room temperature for 3 h then separated on a silica gel column using CH2Cl2–light petroleum (1 : 5) as eluent.Only one red band was collected. Crystallisation at 220 8C yielded a reddish purple crystalline material (445 mg, 58.7%) which was separated by filtration at room temperature. Recrystallisation from hexane–CH2Cl2 at 220 8C gave red crystals suitable for single-crystal X-ray analysis (Found: C, 38.08; H, 1.30. Calc. for C12H5Co2O7: C, 38.02; H, 1.33%), mp 102–104 8C. IR: n(CO) 2096s, 2058vs, 2024vs, 2002vs(sh), 2000vs(sh) and 1976m cm21. 1H NMR: d 6.90 (s, 4 H, C6H4), 6.04 (s, 2 H, 2CH) and 5.15 (s, 4 H, 2CH2). [{Co2(CO)6}2{Ï-HC2(CH2)5C2H}] 3. In a similar reaction, a solution of [Co2(CO)8] (684 mg, 2 mmol) and nona-1,8-diyne1990 J. Chem. Soc., Dalton Trans., 1999, 1987–1991 Table 4 Summary of the crystallographic data for compounds 2, 4 and 5 Molecular formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 V/Å3 Z Dc/g cm23 Crystal size/mm Crystal habit T/K F(000) m/cm21 No.measured reflections No. observed reflections No. variables RR 9 Goodness of fit Largest peak in final diVerence map/e Å23 2 C24H10Co4O14 758.07 Triclinic P1� (no. 2) 8.567(2) 11.476(1) 8.088(2) 102.44(1) 104.15(2) 102.55(1) 721.7(2) 1 1.744 0.20 × 0.20 × 0.30 Red 293 374 23.25 2726 1846 [I > 2.50s(I)] 191 0.030 0.035 1.15 0.29 4 C18H6Co4O13 665.97 Monoclinic P21/c (no. 14) 18.149(2) 7.0111(7) 20.897(2) 115.318(7) 2403.7(5) 4 1.840 0.20 × 0.20 × 0.30 Red 293 1304 27.76 3977 2372 [I > 2.00s(I)] 316 0.030 0.031 1.20 0.25 5 C17H6Co4O12 637.96 Monoclinic Cc (no. 9) 14.808(2) 10.346(3) 14.401(5) 105.591 2125.0801 4 1.994 0.60 × 0.60 × 0.40 Brown 288 1248 31.31 2256 1943 [I > 3.00s(I)] 299 0.046 0.066 1.21 0.85 (120 mg, 1 mmol) in hexane (30 cm3) was stirred for 3 h. The solution was separated on a silica gel column using light petroleum as eluent. Crystallisation at 220 8C yielded a red oil (489 mg, 69.7%) (Found: C, 36.39; H, 1.80.Calc. for C21H12Co4O12: C, 36.44; H, 1.75%). IR: n(CO) 2093s, 2049vs, 2017vs, 1976(sh), 1940m and 1873w cm21. 1H NMR: d 6.02 (s, 2 H, 2CH), 2.89 (s, 4 H, 2CH2) and 1.68 (m, 6 H, CH2CH2CH2). [{Co2(CO)6}2(Ï-HC2CH2OCH2C2H)] 4 and [Co4(CO)10(Ï- CO){Ï4-Á:Á3-CC(CH2OCH2)CCH2}] 5. Stirring a solution of [Co2(CO)8] (684 mg, 2 mmol) and HC2CH2OCH2C2H (94 mg, 1 mmol) in hexane (40 cm3) for 2 h and TLC monitoring showed the disappearance of the starting material [Co2(CO)8]. Chromatography as above produced a major red and minor brown band, respectively.The solution of the major red band was reduced in volume to ca. 10 cm3. Crystallisation at 220 8C yielded a red-purple crystalline material 4 (406 mg, 61.0%). Recrystallisation by slow layer diVusion of hexane into a hexane–CH2Cl2 mixture at 220 8C gave red prismatic crystals of 4 suitable for single-crystal X-ray analysis (Found: C, 32.42; H, 0.98. Calc. for C18H6Co4O13: C, 32.46; H, 0.91%), mp 52– 54 8C.IR: n(CO) 2095s, 2060vs, 2039vs, 2022vs, 2010vs and 1995s cm21. 1H NMR: d 6.07 (s, 2 H, 2CH) and 4.85 (s, 4 H, 2CH2). The solution of the minor brown band was reduced in volume to ca. 5 cm3. Crystallisation at 220 8C yielded a brown crystalline material 5 (140 mg, 22.0%). Recrystallisation from hexane at 220 8C gave crystals of 5 suitable for single-crystal X-ray analysis (Found: C, 31.96; H, 1.02. Calc. for C17H6Co4- O12: C, 32.00; H, 0.95%), mp 158 8C (decomp.). IR: n(CO) 2092s, 2057vs, 2036vs, 2024vs, 2009vs, 1989s and 1838s cm21. 1H NMR: d 5.03 (m, 2 H, CH2), 4.52 (br s, 1 H, CHH), 4.30 (br s, 1 H, CHH ), 3.59 (s, 1 H, CHH) and 2.59 (s, 1 H, CHH). Crystal structure determination and refinements Suitable crystals of the compounds 2, 4 and 5 were mounted on glass fibers with epoxy resin. Details of crystal data, data collection and refinement parameters are given in Table 4. Data were collected by the w–2q scan method on a Rigaku AFC7R diffractometer (2, 4) or AXIS-IV imaging plate area detector (5) with Mo-Ka radiation.The cobalt atoms in each of the three structures were located by centrosymmetric direct methods, and the remaining nonhydrogen atoms from subsequent Fourier-diVerence syntheses. The structures were refined to convergence by full-matrix least squares with all non-hydrogen atoms assigned anisotropic displacement parameters. Weighting schemes were applied. All atoms were assigned neutral-atom scattering factors taken from ref. 24. Calculations were performed using TEXSAN.25 CCDC reference number 186/1426. See http://www.rsc.org/suppdata/dt/1999/1987/ for crystallographic files in .cif format. Acknowledgements This work was supported by the National Natural Science Foundation of China, and the foundation of the Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. References 1 B. Happ, T. Bartik, C. Zucchi, M. C. Rossi, F. Ghelfi, G.Palyi, G. Varadi, G. Szalontai, I. T. Horrath, A. Chiesi-Villa and C. Guastini, Organometallics, 1995, 14, 809. 2 A. T. Chalk and J. F. Harrod, J. Am. Chem. Soc., 1965, 87, 1133. 3 H. Jabic, C. C. Santini and C. Coulombean, Inorg. Chem., 1991, 30, 3088. 4 R. F. Heck, J. Am. Chem. Soc., 1964, 86, 2819. 5 J. C. Sauer, R. D. Cramer, V. A. Engelhardt, T. A. Ford, H. E. Holmquist and B. W. Howk, J. Am. Chem. Soc., 1959, 81, 3677. 6 M. G. Karpov, S. P. Tunik, V. R. Denisov, G. L.Starova, A. B. Nikolskii, F. M. Dolgushin, A. I. Yanovshy and Yu. T. Struchkov, J. Organomet. Chem., 1995, 485, 219. 7 C. E. Housecroft, B. F. G. Johnson, M. S. Khan, J. Lewis, P. R. Raithby, M. E. Robson and D. A. Wilkinson, J. Chem. Soc., Dalton Trans., 1992, 3171. 8 P. Magnus and D. P. Becker, J. Chem. Soc., Chem. Commun., 1985, 640. 9 D. Seyferth and H. P. Withers, Inorg. Chem., 1983, 22, 2931. 10 Y. Rubin, C. B. Knobler and F. Diederich, J. Am. Chem. Soc., 1990, 112, 4966. 11 S. Aime, A. Tiripicchio, M. Tiripicchio-Camellini and A. J. Deeming, Inorg. Chem., 1981, 20, 2027. 12 S. Aime and A. J. Deeming, J. Chem. Soc., Dalton Trans., 1983, 1807. 13 G. Cetini, O. Gambino, R. Rosetti and E. Sappa, J. Organomet. Chem., 1967, 8, 149.J. Chem. Soc., Dalton Trans., 1999, 1987–1991 1991 14 A. Aimi, L. Milone, R. Rosetti and P. L. Stanghellini, Inorg. Chim. Acta, 1977, 22, 135. 15 R. K. Karris, Nuclear Magnetic Resonance Spectroscopy: a Physicochemical View, Pitman, London, 1983. 16 P. Brum, G. M. Dawkins, M. Green, R. M Mills, J.-Y. Salaun, F. G. A. Stone and P. Woodward, J. Chem. Soc., Dalton Trans., 1983, 1357. 17 J. E. Davies, M. J. Mays, P. R. Raithly, V. Sarreswaran and G. P. S Shields, J. Chem. Soc., Dalton Trans., 1998, 775. 18 W. Sly, J. Am. Chem. Soc., 1959, 81, 18. 19 D. A. Brown, J. Chem. Phys., 1960, 33, 1037. 20 F. A. Cotton, J. D. Jamerson and B. J. Stults, J. Am. Chem. Soc., 1976, 98, 1774. 21 R. B. King, Organometallic Syntheses, Vol. 1, Transition-Metal Compounds, Academic Press, New York, 1965, p. 98. 22 X.-N. Chen, J. Zhang and Y.-Q. Yin, Chem. Res. (Chinese), 1998, 4, 25. 23 L. Brandsma, Preparative Acetylenic Chemistry, Elsevier, Amsterdam, 1988, p. 261. 24 D. T. Cromer and J. T. Waber, International Tables for Crystallography, Kynoch Press, Birmingham, 1974, vol. IV, Table 2.2 A. 25 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1985 and 1992. Paper 9/0070

ISSN:1477-9226    

DOI:10.1039/a900706g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON PERSPECTIVE J. Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 1991 C2 Building blocks in the co-ordination sphere of electron-poor transition metals. Aspects of the chemistry of early-transition-metal carbenoide complexes † Rüdiger Beckhaus * Department of Inorganic Chemistry, Technical University Aachen, D-52056 Aachen, Germany Our understanding of the chemistry of the transition-metal–carbon s bond is improved by investigations of the chemistry of alken-1-yl complexes of electron-poor transition metals.There is no other system known in which we can easily switch between the possible reaction pathways, depending on the nature of the metal, the ligands L and the alken-1-yl group. Only reductive elimination, a- and b-H elimination reactions give high selectivity. a-Hydrogen elimination from Cp*2Ti(CH]] CH2)R (Cp* = h-C5Me5) derivatives leads to the versatile titana–allene intermediate [Cp*2Ti]] C]] CH2] 8. A wide range of cycloaddition products of high thermal stability can be prepared using 8.In reactions of 8 with copper and gold complexes, heterodinuclear m-vinylidene compounds, Cp*2Ti(m-C]] CH2)(m-X)M9L, are formed. Additionally the first examples of intermolecular carbene–carbene coupling reaction of a Fischer- and a Schrock-carbene ligand are reported by using the strong nucleophilic vinylidene fragment 8. The possibility of stabilising highly reactive intermediates as well as short-lived molecules is one of the great advantages of organometallic chemistry, located on the borderline between organic and inorganic chemistry.1,2 Well known examples are illustrated in Scheme 1.The formal co-ordination of carbenes to metal fragments, was first achieved in Fischer- and Schrocktype complexes,3 but more recently, stable carbenes in the form of imidazol-2-ylidene ligands,4,5 have been co-ordinated to transition metals to give well characterised complexes.6 Cyclobutadiene, vinylidene and aryne molecules can be well stabilised in the co-ordination sphere of transition metals, leading to compounds which can be handled under acceptable conditions.This knowledge of structure and bonding relationships has developed our understanding of organometallic chemistry and led to useful applications of organometallic reagents in organic synthesis and catalysis. In many cases the actual reactive species, which participates in further reactions, must be generated in the first reaction step from the corresponding organometallic sources.In connection with this, I want to draw the attention of the reader to such complexes of titaniumgroup metals, which are characterised by the primary formation of an intermediate exhibiting a titanium–carbon double bond.7 Especially starting from alken-1-yl transition-metal complexes the general reactivity of a transition-metal–carbon s bond can be well understood.8 The generation of an M]C double bond in a primary reaction step can occur from quite different types of starting molecules. Some schematic drawings are given in Fig. 1. Complexes which act as primary sources of carbene complexes or intermediates, will henceforth be referred to as ‘carbenoide transition metal’ complexes. Different types of titanium-group metal complexes characterised by primary carbene complex formation are known.9 Sometimes, such carbene complexes exist in the form of isolable molecules 10–13 or occasionally in the form of intermediates.7,14–16 Reactants which are characterised by primary titanium carbene complex formation are the Tebbe reagent 1,9 the Takai reagent 2,17,18 metallacyclobutanes 3 19–21 or complexes exhibiting Schrock-type reactivity (4).22 For the * E-Mail: r.beckhaus@ac.rwth-aachen.de † Dedicated to Professor Wolfgang Beck on the occasion of his 65th birthday. generation of Ti]] C intermediates, Me2AlCl must be removed by bases (pyridine) if 1 is used as the starting material,19 additional reducing agents must react with 2,17 olefins must be thermally liberated when 3 is used,19,23 and with 4, a-H elimination of hydrocarbons must occur.24–26 These reactions can be formally defined as 1,2-eliminations.Other sources of Ti]] C species exist, including diazo compounds,27 small cyclic olefins 28 and 1,1-dilithio compounds.29 On the other hand, carbenoide complexes of main-group metals, as investigated by Boche and co-workers (5 and 6), are characterised by the possibility of 1,1-elimination reactions and carbene intermediate formation thereof.30–33 Depending on the nature of the metal, the leaving group (LG), and the reaction conditions, electrophilic as well as nucleohilic properties of the carbon centre are observed.30,31 For several years we have been interested in the chemistry of early-transition-metal complexes, exhibiting M]C double bonds in a cumulative unit.During the experimental work on my habilitation thesis we observed the easy transformation of vinyl complexes 7 via (Cp* = h-C5Me5) vinylidene intermediates 8 and 9 to a metallacyclobutane 10.34,35 This reaction is characterised by the selective transfer of a proton from one vinyl group to the other. In contrast to the well developed chemistry of metalla–allenes of late transition metals,36 the observation of the transformation 7Æ10 was the first discovery in the new research field of vinylidene chemistry of early transition metals.37,38 Petasis and Bzowej 22 reported the successful use of simple Cp2TiMe2 (Cp = h-C5H5) in carbonyl olefination reactions 11Æ12.It was the first instance of use of Ti]] C intermediates in organic synthesis.7 The greatest advantage of this method lies in the application of substituted and functionalised alkylidenes.39–41 A detailed study of the thermolysis of Cp*2- TiMe2 via a [Cp*2Ti]] CH2] intermediate has been published,42 but at that time, attempts to trap the carbene intermediate were unsuccessful.Alken-1-yl Ligands in the Co-ordination Sphere of Early Transition Metals By comparison of the thermal stability of the vinyl, phenyl and alkyl complexes of titanium-group metals, it becomes obvious that the vinyl derivative is the most reactive one.8 As well as a-1992 J. Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 Scheme 1 elimination processes, b- and reductive-elimination reactions are also observed. In each case, only one reaction pathway results in high selectivity.Generally, reductive elimination reactions are the most preferred reactions of organometallic complexes from the thermodynamic point of view.43 However, for alkyl derivatives, H-transformation reactions are kinetically preferred. In the Fig. 1 Organometallic sources of Ti]] C intermediates (carbenoide complexes 1–4) (1 Tebbe reagent; 2 Takai reagent; 3 metallacyclobutanes; 4 complexes of Schrock-type reactivity), and main-group metal carbenoides 5 and 6 bearing leaving groups and metal atoms on the same carbon atom case of alken-1-yl compounds of the titanium-group metals we find that there is a correlation between the rotational barriers of the alken-1-yl ligand around the M]C s bond and the observed reaction pathways (Fig. 3). If free rotation is possible, reductive elimination products become dominant. Owing to the orientation of the acceptor orbitals of the bent metallocene fragment Fig. 2 Schematic drawing of possible subsequent products obtained from vinyl complexes of titanium-group metals Fig. 3 Proposed transition states of reductive elimination A, a-H elimination B and b-H elimination C from Cp2M alkenyl derivatives (M = Ti, Zr or Hf )J. Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 1993 in the equatorial plane between the Cp ligands, electron transfer from the C]C double bond to the transition-metal centre in this 16 electron complex becomes possible if the vinyl group is orientated perpendicular to it (Fig. 3, A). This rotameric orientation leads to a suitable transition state for the reductive elimination, owing to the differences in partial charge of the a-carbon atoms, as calculated by ab initio methods. Generally, for d0 systems, concerted reductive elimination reactions are forbidden by symmetry, although reductive elimination might actually be possible, especially if charge-transfer processes are involved.44,45 On the other hand, if this rotation is hindered by using bulky ligands (Cp* instead of Cp,46 or substituted alken- 1-yl groups instead of the simple CH]] CH2 ligand 47) C]H bond activation reactions become dominant (Fig. 3, B and C). Whereas the a-CH bond is activated in titanium complexes, b-CH activation occurs in zirconium complexes.34 The preferred formation of dienes as the product of reductive elimination is exemplified by reaction of the tetrahalides of titanium, zirconium and hafnium with vinyllithium in a molar ratio of 1 : 4.In all cases, the formation of diene complexes 14 can be proved by using chelating phosphine ligands or by ligand substitution reactions, as in the case of titanium to give [Ti(bipy)3] 13 (bipy = 2,29-bipyridyl).48 Hydrogen elimination from carbon sp2 centres can only occur in a mononuclear manner if the a-CH bond is directed towards the leaving group (C]H inside conformation 16). This name results from the central, as opposed to the lateral (C]H outside) orientation of the acceptor orbitals at the metallocene fragment.However, compounds of type Cp*2Ti(CH]] CH2)X show the C]H outside conformation 15 in solid-state structures and in solution [X = F,49 OC(C6H11)CH2,50 CCPh51 or CH3 52 ]. This means that the C]H inside conformation 16 must be realised in the first step. The energy necessary for the rotation process in Cp*2Ti- (CH]] CH2)2, is found from MMX-force field calculations to be about 52.1 kJ mol21, compared to Cp2Ti(CH]] CH2)2 for which a value of 18.3 kJ mol21 is calculated.43 Therefore we can conclude that the rotation barrier is the main contribution to the activation energy of C]H elimination as determined by kinetic measurements for the process 17Æ8Æ18 [87.9(5) kJ mol21].53 Selective liberation of methane occurs from complex 17 in the temperature range 5–20 8C, forming (via 8) the dark green fulvene complex 18.53 In solution, only the C]H outside rotamer of 17 can be observed by NOE measurements.52 The alternative elimination of ethylene and formation of a [Cp*2Ti]] CH2] intermediate is not observed.The Titana–Allene Building Block [Cp*2Ti]] C]] CH2] The existence of the titana–allene 8 as a real intermediate, generated from 17 by methane elimination (5–20 8C)53 or from 10 by ethylene liberation (70–100 8C),37,38 can be proved by several trapping experiments (see later). Substrates such as ketones, alcohols, cumulenes and heterocumulenes do not react directly with 17 or 10.Generally the formation of 8 is the ratedetermining step in reactions of 10 and 17. Substitution products 21 or ring-opened derivatives 20 could not be detected in reactions of 10 and 17 with acidic substrates. However, strong acidic substrates, e.g. thiophenol lead to formation of products of type 20.49 Several attempts were made to stabilise the vinylidene intermediate 8 itself by using electron-donating ligands like phosphines, pyridines or by using the Jutzi ligand C5(CH3)4CH2CH2NMe2 instead of one Cp*.54 In all of these experiments C]H bond activation, forming the fulvene complex 18, is dominant.Owing to its electronic structure, the vinylidene intermediate 8 is very useful in cycloaddition reactions.37,43 By using isocyanides an azabutatriene complex 22 is formed in the first reaction step in a [2 1 1] cycloaddition.55,56 Owing to the high reactivity of the intermediate 22 subsequent reactions occur, forming the five-membered metallacycle 23, which exhibits a heteroradialene substructure.56 The metallacyclic four-membered ring compounds 24 are synthesised in high yields by [2 1 2] cycloaddition reactions.All1994 J. Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 these complexes were isolated as crystalline solids of high thermal stability, which allowed an extensive investigation of the reactivity of these molecules.57–63 Oxatitanacyclobutanes 64 and azatitanacyclobutenes 65–67 are discussed as intermediates in reactions of carbenoide titanium complexes with carbonyl compounds or nitriles, but could not be isolated because of the generally high electrophilicity of the metal centre.Spontaneous ring-opening reactions afford carbonyl olefination,19 or products of vinylimido intermediates.66,68 Metallaoxetanes, such as Cp2TiCH2CR2O, have been proposed as intermediates in various transition-metal catalysed oxygen-transfer reactions.64,69,70 Only a few metallaoxetanes, formed in the reaction of transition-metal carbenes with carbonyl compounds‡,71 or by the reaction of a terminal metal oxide fragment (Cp*2Ti]] O) Fig. 4 Comparison of the energies of products derived from Cl2Ti]] CH2 or Cl2Ti]] C]] CH2 and O]] CH2, results of ab initio calculations ‡ Known structurally characterised metallaoxetanes comprise Ta,71 Mo,72 Ti 63,57 and Cr.73 with an allene,74 have been characterised by X-ray diffraction methods. The striking characteristic of the metallacycles 24 is their high thermal stability compared to products derived from a titanium methylene intermediate.From ab initio calculations on Cl2Ti]] C]] CH2 model complexes and derivatives thereof it can be shown that the formation of the carbonyl olefination products from Cl2Ti]] C]] CH2 and H2C]] O is 101 kJ mol21 less exothermic than the model system Cl2Ti]] CH2 1 O]] CH2 (Fig. 4).43 Our attempts to obtain titanaoxetanes from 8 and ketones have so far failed.In all cases, the formation of enolates 25 is observed. Due to the preferred six-membered transition state 26 compared to the side-on geometry 27, the reaction leads in a stereo- and regio-selective manner to D1 and E-configured products.50 The crystal structure (R1 = H, R2 = C6H11) and reactivity of the enolates 25 show typical alkoxide character instead of nucleophilic properties on the b-C atom.50 A similar behaviour is observed for enolates derived from a Cp*2Ti]] CH2 intermediate.75 However, under less sterically crowded conditions, the formation of oxetanes 29 by reaction of 28 with ketones is proposed from the formation of the carbonyl olefination products 30.76 This reaction is very useful for the formation of substituted allenes.The higher electrophilicity of the Cp2Ti fragment compared to the permethylated Cp*2Ti in 8 prohibited the isolation or even the spectroscopic characterisation of 29. Remarkably, depending on the nature of the heteroatom, different subsequent reactions of the titanacycles 24 are observed.In the case of the titanacyclobutane 10, cycloreversion reactions are dominant, forming the vinylidene intermediate 8. In the case of the oxetanes 24a, metathesis reactions are observed in the mass spectrometer, whereas the bimetallic oxetanes 24c fragment to give the starting materials. These characteristics lead into the classification of classical and non-classical reaction behaviour of titanaoxetanes.Classical behaviour means that the formation of Ti]] O metathesis products dominates, whereasJ. Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 1995 the inverse cycloreversion from the oxetane to Ti]] C is observed in complexes exhibiting non-classical behaviour, see Scheme 2. Fast ring-opening reactions occur in the case of the azatitanacyclobutenes, leading to products of insertion into the Ti]C bond, which exhibit the exo-methylene group.60 This behaviour is explained by the orientation of the lone pair on the heteroatom in 10 towards the acceptor orbitals in the equatorial plane of the metallocene Cp*2Ti fragment.77 The best orbital overlap can be expected in the case of the azatitanacyclobutenes 24d, because the lone pair at the nitrogen atom and the lateral acceptor orbital of the titanium centre are orientated in the same plane, leading to fast ring opening. The imido intermediate 31 is formed and when a further nitrile molecule is added, the formation of 32 is observed.60 On the other hand, if the hybridisation of the nitrogen atom is changed, as in the azatitanacyclobutanes 24g, no electrocyclic ring-opening reaction is observed.In the molecule 24g the nitrogen lone pair is orientated perpendicular to the acceptor orbital on titanium.78 A similar orientation of donor and acceptor orbitals is expected also in the case of titanacyclobutenes, leading to substituent controlled reactions. For titanacyclobutenes of type 24f exhibiting large substituents (a-R = SiMe3, b-R = Ph), a long internal C]C single bond of 1.502(7) Å is found by Scheme 2 X-ray structural analysis, and the reactivity is characterised by cycloreversion processes at higher temperatures.On the other hand, with smaller substituents (R = R = Me) the internal C]C single bond is found to be shorter [1.434(4) Å] indicating a transition in the reactivity of the titanacyclobutene. Indeed, electrocyclic ring opening reactions are only observed for the non-substituted titanacyclobutene Cp*2TiCH]] CHC]] CH2 24f9 leading via 33 and 34 to the formation of trans-polyacetylene 35.51,79 The observed reactivity of the titanacycles 24 is in accordance with the general observation, that the reactivity of bent metallocene complexes is determined by the electron deficient character of the metal centre in combination with the orientation of the acceptor orbitals in the equatorial plane of the metallocene fragment.This can be additionally illustrated by the orientation of the substituents on nitrogen atoms in Cp*2- TiNR9R0 complexes. If there is no steric hindrance, the substituents on the nitrogen atom (R9 = R0 = H;80 R9 = H, R0 = Me81) are rotated out of the equatorial plane of the metallocene to maximise overlap between the nitrogen lone pair (located in the pz orbital) and the metal lowest unoccupied molecular orbital (LUMO). This effect is also found in the case of Cp*2Hf(H)(NHMe).82 If larger substituents are present, as in Cp*2TiN(CH3)(Ph) the methyl and the phenyl group are now located in the equatorial plane, and consequently a dp–pp interaction is no longer possible.83 If the heteroatoms are incorporated in a planar metallacyclic ring as in 24, such dp–pp interactions are the cause of the different reaction behaviour.In a similar manner, these reactivity patterns can also be observed in the insertion behaviour of the titanacycles 24 (Scheme 3). In the case of titanacyclobutane 1084 and cyclobutenes 51 24f, insertion of small molecules such as isocyanides is observed only into the Ti]C bond opposite the exo-methylene group.For1996 J. Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 Scheme 3 the titanacyclobutene 24d, a spontaneous ring enlargement by insertion of a further nitrile molecule is observed 24dÆ32, due to the activation of the Ti]C sp2 bond by the lone pair on the nitrogen centre.In a similar manner the oxetanes 24a and 24c show insertion reactions into this Ti]C bond forming mono- (38) or double-insertion products (39).85 On the other hand, azatitanacyclobutanes 24g are inert to ring enlargement reactions with isocyanides even at higher temperatures. In some cases, cycloaddition reactions involving a titana– allene intermediate are useful in organic synthesis. The preparation of allenylketenimines 40 becomes possible in high yields via complexes of type 37 (Cp instead of Cp*) by extrusion of ‘Cp2Ti’.86 Additionally, the intramolecular cycloaddition of the titanocene vinylidene complex, formed by dechloroalumination of 41,87 with an alkene (or alkyne) affords bicyclic titanacyclobutanes and 42 (or butenes).88 This cyclisation has proven to be possible in all such complexes.The remaining carbon–metal bond in the metallacycles 42 offers great potential for further elaboration to give organic products. This is illustrated for complex 42 in reactions with N-bromosuccinimide (NBS), which gave the dibromide 45.The insertion reaction of isocyanide affords the imino complex 43 which gave the aldehyde 44 on acidic work-up; alternatively, reaction with carbon monoxide followed by acidic work-up gave the ketone 47, presumably via the ene–diolate complex 46.88 Regioisomers We have demonstrated that the formation of the titanacyclobutanes and butenes 24 occur in a regioselective manner. Big differences in the partial charge of the X, Y atoms, determined e.g.by 13C NMR measurements in the case of alkynes,51 lead to stereochemically pure compounds with the more negative carbon bonded to titanium. a- and b-Regioisomers are obtained by using substrates with small partial charge differences. This is the case for alkynes 51 or phosphaalkynes.60 As well as the electronically controlled reactions, leading mostly to kinetic products, sterically controlled reactions are also observed.Thus from a mixture of both cycloaddition products of 8 with the phosphaalkyne ButC]] ] P 24e and 48, only the product exhibiting the bulky tert-butyl group in the b position (24e) crystallised from the solution. In the case of mixtures of regioisomers obtained from unsymmetrical acetylenes, the more bulky group rearranged to the b position upon heating.51 The effect of electronic and steric control can be observed in the reaction of the titanocenevinylidene intermediate [Cp*2Ti]] C]] CH2] 8 with 1,3-diynes (see Fig. 5), yielding titanacyclobutene complexes (50).61 Only one regioisomer is formed, containing the acetylide group in the a position of the metallacyclic ring. The regioselectivity is in accordance with the polarities of the diynes and stereochemical conditions in the cyclobutene ring. This behaviour is in agreement with ab initio calculations and the results of molecular modelling. Using unsymmetric diynes, metallacyclobutenes exhibiting the larger substituent in the b position are formed, as shown for 50e.61 The only primary regioisomer formed by cycloaddition of 8 with isothiocyanates is 24b, which contains the sulfur atom in the a position of the metallacyclic ring.When heated in the presence of pyridine, 24b can be isomerised into the other possible regioisomer 51;58 C]] N cycloaddition products are not observed. The quantitative isomerisation 24bÆ51 shows that the lower polarity of the C]] S unit in the RNCS molecule allows the formation of a second isomer.In this respect, the behaviour of titanathietanes is quite different from the behaviour of titanaoxetanes, which normally react to give Ti]] O fragments (classical behaviour). In cycloaddition reactions of 8 with CS2, only the regioisomer with the sulfur atom in the bring position is observed.89 The inverse regiochemistry results from the difference in reactivity of a carbonyl and a thiocarbonyl group with strong carbanionic molecules and shows the thiophilic character of the nucleophilic carbene complex 8.90–92 Structure Isomerisation, Vinylidene–Acetylene Rearrangement The stabilisation of the vinylidene group H2C]] C:, tautomeric to acetylene, has enabled the investigation of vinylidene complexes of late transition metals.The 1,2-proton shift is a characteristic feature in the synthesis of vinylidene complexes formed from acetylenes.93–95 Depending on the relative stability of theJ. Chem.Soc., Dalton Trans., 1997, Pages 1991–2001 1997 vinylidene complex compared to the acetylene derivative, the formation of vinylidene complexes is often preferred by late transition metals (Scheme 4). On the other hand, a reverse proton shift, from a vinylidene to an acetylene intermediate, is observed on heating solutions of the bimetallic oxetanes 24c, generating the oxatitanacyclopentene complexes 52.38,57,59 This transformation corresponds to the behaviour of a ‘free’ vinylidene C]] CH2 molecule, in the gas phase.The five-membered dinuclear complexes 52 are crystalline materials of high thermal stability (up to 220 8C). In contrast to the vinylidene–acetylene rearrangement observed for the bimetallic ‘non-classical’ oxetanes 24c, the ‘classical’ oxetanes 24a are not able to rearrange to fivemembered rings. That means that there must be a destabilising effect by the second transition metal, which can be explained by a cycloreversion process in the first step and formation of an h2- C]C bonded bridged vinylidene complex, which initiates the vinylidene–acetylene rearrangement.In this regard, the structure of heterodinuclear vinylidene bridged complexes is of general interest. Remarkably an unusual vinylidene–acetylene rearrangement is also observed for vinylidene bridged homodinuclear molybdenum complexes.96 Using intermediate 8, the formation of different vinylidene bridged complexes should be possible. These are the symmetrically bridged 1,1-dimetallaethylene and the unsymmetrically bridged structures, characterised by different types of dp–pp interaction with the Ti]] C or the C]] C double bond of 8 (Fig. 6).97 These structure types are in accordance with CO- and CS-bridged binuclear complexes. The s,s-bridging mode is generally dominant.36,98–102 Examples of side-on bridged vinylidene complexes are rare.96,97,103–109 The semi-bridging type complexes are known for CO,110,111 CS112 but for vinylidene to our knowledge only one example of a Mo]Ru complex is published.105 Indeed in reactions of 17 with copper and gold complexes, dinuclear vinylidene bridged complexes can be isolated as crystalline materials [m.p.(decomp.) 93 8C 53a, 180 8C 53b].113 In the case of 53a–53d, the 13C NMR data are indicative of the semi-bridging structural type, due to the low field shift of the bridging a-vinylidene carbon atom in the range d 330 (53a)–300 (53d). Intermolecular Carbene–Carbene Coupling By reacting the nucleophilic Schrock-type carbene intermediate 8 with other carbene complexes 54, the formation of the dinuclear 1,3- as well as 1,2-dimetallacyclobutanes 55 and 56 should be possible.Remarkably, in reactions of thermally generated 8 from 17 with the Fischer carbene complex (OC)5Cr]] C(OMe)Me, a new type of C]C coupling reaction is found. The products 59 and 60 could be separated by chromatography. The structure of 59 was Fig. 5 Schematic drawing of electronically determined regiochemsitry (left) and sterically controlled reactions (right)1998 J. Chem.Soc., Dalton Trans., 1997, Pages 1991–2001 determined by X-ray diffraction.114 In 59 the octahedral geometry at the chromium centre is realised by co-ordination of the methoxy ligand, whereas in 60 an additional carbon monoxide molecule is co-ordinated. Overall, C]C bond formation occurs between carbon atoms of a vinylidene, carbene and carbonyl ligand. The most remarkable feature of the structures of 59 and 60 is the fact that both metal atoms are bonded to different Scheme 4 Fig. 6 Different structure types of vinylidene bridged heterodinuclear complexes atoms than in the starting materials. The formation of 59 and 60 is in accordance with a carbene–carbene coupling via intermediate generation of the allene complex 58. This reaction step becomes clear considering the primary interaction of the nucleophilic and electrophilic carbene carbon atoms, supported by CO co-ordination to the oxophilic titanium as shown in 57.Titanium-centred cycloaddition of the allene molecule with the remaining Cr(CO)x fragment leads directly to 59 and, after fast CO addition, to 60. The described reaction represents to our knowledge the first example of an intermolecular coupling of inversely polarised carbene ligands 63Æ64, although intramolecular carbene–carbene coupling reactions 61Æ62 have been reported.115 This new method of achieving metal-centred coupling ofJ.Chem. Soc., Dalton Trans., 1997, Pages 1991–2001 1999 several carbon atoms of different substrates can potentially be used in syntheses. With other carbon electrophiles further types of C]C coupling reactions are observed. The reaction of 17 with the aminocarbene complex 65 leads to the dinuclear titanium complex 66 after chromatographic work-up. The dimeric structure is confirmed by the mass spectrum and the crystal-structure analysis.116 The surprising feature of 66 is its dark blue colour.In contrast, the monomeric units of the type 24f and 50 are dark red compounds. As observed in the crystal structure of 66 there is a twist angle between the cyclobutene planes of nearly 508. Other carbon electrophiles are also able to undergo C]C coupling reactions at the nucleophilic carbon centre of 8. By treating allylpalladium chloride 67 with 8 in the presence of PMe3 the formation of the coupling product 68 can be observed.117 Closing Remarks and Outlook The high reactive selectivity of alken-1-yl ligands in the coordination sphere of electron-deficient metals has proved to be a powerful tool in the classification of organometallic reactivity.From this, we can learn what is easy and what is difficult for a transition-metal–carbon s-bond to do. The transformation of titanium vinyl complexes to titanium vinylidene intermediates under mild thermal conditions in particular has significantly improved the access to short-lived carbene complexes of early transition metals.This has widened the spectrum of preparative and catalytic applications of [Ti]] C] generating derivatives considerably. Different types of stable cycloaddition products of 8 are isolable, allowing investigation of structures and reactivity relationships. However, many questions still remain open. First, what have we learned from the easy proton elimination from vinyl groups (which does not occur in comparable alkyl ligands), and are useful Heliminations from other substrates in the co-ordination sphere of metallocene complexes also possible under similar conditions? As well as the discussed Ti]] C systems, Ti]] Si,118 M]] N119 (M = Ti 120,121 or Zr 120,122), Zr]] P,123,124 Zr]] O,125,126 Zr]] S,125,126 and even intermediates exhibiting Ti]] ] C bonds,127,128 are available.Secondly, what about axial chirality in the titana–allene building block? From the preferred Cs symmetric ground state and the calculated Ti]C rotation energy (134 kJ mol21) 37 for the titana–allene compound, axial chiral complexes must be available. Thirdly, which types of further cycloaddition products are available? What about the possibility of syntheses of new types of molecules, like radialenes derived from reactions of 8 and butatrienes or from molecules of type 23.What further types of molecules can be prepared by new C]C coupling reactions? Finally, are acetylene–vinylidene rearrangements possible in the case of electron-deficient transition-metal complexes? The fact that the polymerisation of acetylene seems to proceed via a vinylidene intermediate suggests that this could be the case, but up to now, there is no definitive proof of such a rearrangement.79,129 Many reactions discussed before seem to be sterically controlled. This means that other ligand systems must also be able to realise the role of the Cp* ligand.130,131 Let’s go and find them! Acknowledgements I wish to express my particular thanks to my active co-workers, Dr.Jürgen Oster, Dr. Javier Sang, Dipl.-Chem. Jürgen Heinrichs, Dipl.-Chem. Martin Wagner and Dipl.-Chem. Isabelle Strauß, who are working on the titana–allene project. I am indebted to all my colleagues for constructive discussions and suggestions, in particular Dr. Uwe Böhme (University Bergakademie Freiberg) for ab initio calculations. I wish to express my gratitude to Mr.Edward Pritchard (York), for checking the English version of the manuscript. I especially wish to thank the Institute of Inorganic Chemistry at Aachen Technical University, where I was a guest and have done research for the last five years, the research group for crystal-structure determination, and in particular to Dr. Trixie Wagner for solving the numerous crystal-structure determinations. I gratefully acknowledge that my research was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.The BAYER AG Leverkusen and the DEGUSSA AG are also acknowledged for generous financial support. References 1 C. Elschenbroich and A. Salzer, Organometallchemie, B. G. 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Santamaria, Organometallics, 1994, 13, 2159. 129 H. G. Alt, H. E. Engelhardt, M. D. Rausch and L. B. Kool, J. Organomet. Chem., 1987, 329, 61. 130 See for example, R. R. Schrock, C. C. Cummins, T. Wilhelm, S. Lin, S. M. Reid, M. Kol and W. M. Davis, Organometallics, 1996, 15, 1470 and refs. therein. 131 J. S. Freundlich, R. R. Schrock and W. M. Davis, Organometallics, 1996, 15, 2777. Received 10th February 1997; Paper 7/00920H

ISSN:1477-9226    

DOI:10.1039/a700920h

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1993–1997 1993 Syntheses and crystal structures of the dimer [{Zn(SPh)2(bpy)}2(Ï-bpy)] and two forms of the zigzag coordination polymer [{Zn(SPh)2(Ï-bpy)}n], (bpy 5 4,49-bipyridyl) Jeyagowry T. Sampanthar and Jagadese J. Vittal* Department of Chemistry, National University of Singapore, Kent Ridge, 119 260, Singapore. E-mail: chmjjv@nus.edu.sg Received 22nd February 1999, Accepted 23rd April 1999 The reaction between Zn(SPh)2 and bpy proceeded through the polymer intermediate [{Zn(SPh)2(m-bpy)}n] to form the dimer [{Zn(SPh)2(bpy)}2(m-bpy)].The isolation of the products depended on the crystallisation chemistry, i.e. the nature of the solvents, reaction time and method of preparation (diVusion or evaporation techniques). The dimer was isolated from DMF–THF or DMF–THF–DMSO by the evaporation method when the ratio of Zn(SPh)2:bpy was 1 : (1.5–4.0). A one dimensional zigzag co-ordination polymer was isolated from the same reactants by the diVusion method, from a three layer system containing Zn(SPh)2 in DMF and/or DMSO, bpy in CH2Cl2, CHCl3, MeCN, MeOH, THF or acetone and Et2O as the top layer.In the diVusion method two forms of co-ordination polymers, namely solvated and unsolvated [{Zn(SPh)2(m-bpy)}n], were obtained depending on the concentration of CH2Cl2 in the reaction mixture. The crystalline products were structurally characterised by X-ray crystallography. Introduction Factors influencing the formation of co-ordination polymers are not well understood.For a simple bifunctional ligand 4,49- bipyridyl (bpy) the metal to ligand ratio is important in the construction of novel architectures 1 such as linear, zigzag chains, square grids, diamondoid, honeycomb, T-shaped, ladder, brick wall, etc. Various other factors like the nature of the metal ions (co-ordination number and geometry) 2 and the counter anions (shape, size and charge) 3 may also influence the formation of one structure over the other.Experimental conditions such as the choice of the solvent,4 concentration, temperature, 5 pH of the solution,6 etc. can add to the complexity of the problem and variation of these may lead to polymorphism.7 Very recently, two papers have reported the important role that solvents may play in the formation of molecular architectures. 8,9 In the present work we report the influence of crystallisation chemistry on the nature of products formed between Zn(SPh)2 and bpy.Factors studied include the nature of the solvents used, concentration, reaction time and method used for synthesis (diVusion, evaporation techniques, etc.). We also present the crystal structures of the dimer [{Zn(SPh)2- (bpy)}2(m-bpy)] 1, and two forms (‘pseudo polymorphs’) of co-ordination polymers [{Zn(SPh)2(m-bpy)}n] 2 and [{Zn- (SPh)2(m-bpy)}n]?0.25CH2Cl2?H2O 3. Results and discussion The dimer 1 was prepared by the slow addition of bpy (in DMSO, THF, MeOH, acetone, MeCN, CH2Cl2 or CHCl3) to Zn(SPh)2 in DMF, in the ratio of (1.5–4.0) : 1 to get a clear solution which was left for slow evaporation to dryness.Yellow crystals in the shape of distorted hexagonal blocks were obtained in high yield and characterised by elemental analysis, NMR spectroscopy, and by single crystal X-ray diVraction techniques. A slow diVusion method, using the same ratio of the above reactants, in the presence of CH2Cl2, yielded unsolvated, 2, or solvated, 3, co-ordination polymers depending on the ratio of the CH2Cl2 solvent in the reaction mixture.For instance, 2 was obtained when the ratio CH2Cl2 :DMF was 2 : 1 v/v while 3 formed when this ratio was 6 : 1 v/v. When the ratio was in between these two values both 2 and 3 were formed. The yellow crystals of 3 lose solvent and change slowly into opaque orange crystals on standing in air. The crystals of 2 are unchanged on standing. Initially it was thought that the products obtained were influenced by the presence or absence of CH2Cl2 solvent.In order to determine the exact role of the solvents, a series of experiments was conducted that include change of solvent, concentration of the reactants, ratios of the solvents, reaction time and method of synthesis (diVusion and evaporation method). The results are summarised below. The products in each experiment were characterised by one or more of elemental analysis, visual observation and/or determination of cell parameters of the single crystals, X-ray powder pattern, or integration of peaks in 1H NMR spectra.The compound Zn(SPh)2 is soluble in DMF or DMSO only. When a DMF and/or DMSO solution of it was mixed slowly with bpy in CH2Cl2, CHCl3, MeCN, Et2O, MeOH, THF or acetone, in the ratio of 1 : (1.5–4.0) by the diVusion method, yellow elongated block-like crystals started depositing in 5 min to 1 h. These crystals analysed as the 1 : 1 polymer, 2.When the reaction mixture was left alone the crystals redissolved and distorted hexagonal shaped crystals started appearing in 2–3 d. These were found to be the dimer, 1. The formation and/or the disappearance of 2 depend on the concentration of solutes and solvents, the ratios and the nature of the solvents used. When the solution was diluted with liquids such as CH2Cl2, CHCl3, MeCN, Et2O, MeOH, THF or acetone, 2 crystallised from the solution quantitatively. If the same reaction mixture was left aside it was found that 2 redissolved slowly.When the solution was concentrated by evaporation over two days at room temperature, the dimer 1 started crystallising from the solution. In the absence of the CH2Cl2, CHCl3, MeCN, Et2O, MeOH, THF or acetone only 1 was isolated as the final product. It appears that the first product to form in the reaction between Zn(SPh)2 and bpy is the 1 : 1 compound, 2, as given in Scheme 1. However, this product was isolable only when the solution was diluted with CH2Cl2, CHCl3, MeCN, MeOH, acetone, Et2O or THF in which it is poorly soluble.During the course of the reaction at room temperature 2 redissolved due to1994 J. Chem. Soc., Dalton Trans., 1999, 1993–1997 Zn(SPh)2 1 (1.5–4.0) bpy æÆ [{Zn(SPh)2(m-bpy)}n] æÆ [{Zn(SPh)2(bpy)}2(m-bpy)] co-ordination polymer dimer Scheme 1 the evaporation of these volatile components over 2 d, and the crystallisation of 1 occurred upon the evaporation of DMF and/or DMSO over several days.Bridging behaviour by thiolates has been well established.10 Thiolates are, therefore, expected to compete as well as, if not better than, bpy for bridging sites between zinc(II) centres. In order to test the bridging ability of the PhS2 in the presence of bpy a synthesis of the [(bpy)2Zn(m-SPh)2Zn(bpy)2]21 cation was attempted. However, the product obtained analysed as dimer 1. Many attempts to prepare the monomer [Zn(SPh)2(bpy)2] also resulted in the formation of 1.Benzenethiolate, therefore, appears to be a poor bridging ligand for ZnII in the presence of bpy. We were unable to isolate any other compounds under the experimental conditions used. Crystal and molecular structures A perspective view of compound 1 is shown in Fig. 1 and selected bond distances and the bond angles are given in Table 1. The compound is a discrete neutral dimer in which two zinc atoms are bridged by a bpy, and tetrahedral co-ordination of zinc atoms is completed by two terminal benzenethiolates and a monodentate, non-bridging bpy.Each terminal bpy ligand has an unco-ordinated N atom. There is a crystallographically imposed centre of symmetry in the molecule. The Zn–S distances, 2.2672(7) and 2.2882(7) Å, are not equal. The C–S– Zn angles, 102.56(8) and 109.84(8)8, are also diVerent. The Zn(1)–N(1) distance is slightly longer than Zn(1)–N(3). It is Fig. 1 A perspective view of the dimer 1.The non-hydrogen atoms are drawn as 50% probability thermal ellipsoids. Table 1 Selected bond lengths (Å) and angles (8) in compound 1 Zn(1)–N(1) Zn(1)–N(3) Zn(1)–S(1) Zn(1)–S(2) S(1)–C(1A) S(2)–C(1B) N(3)–Zn(1)–N(1) N(3)–Zn(1)–S(1) N(1)–Zn(1)–S(1) N(3)–Zn(1)–S(2) N(1)–Zn(1)–S(2) S(1)–Zn(1)–S(2) C(1A)–S(1)–Zn(1) C(1B)–S(2)–Zn(1) 2.113(2) 2.094(2) 2.2672(7) 2.2882(7) 1.776(2) 1.766(2) 98.17(7) 114.88(6) 103.06(5) 99.73(6) 109.04(6) 128.17(3) 102.56(8) 109.84(8) N(1)–C(1) N(1)–C(5) N(2)–C(6) N(2)–C(6) N(3)–C(15) N(3)–C(11) C(1)–N(1)–C(5) C(1)–N(1)–Zn(1) C(5)–N(1)–Zn(1) C(10)–N(2)–C(6) C(15)–N(3)–C(11) C(15)–N(3)–Zn(1) C(11)–N(3)–Zn(1) 1.316(3) 1.329(3) 1.319(4) 1.375(4) 1.326(3) 1.330(3) 116.2(2) 117.9(2) 125.8(2) 114.9(3) 115.9(2) 119.1(2) 124.7(2) interesting that the two rings of the bpy ligand are almost on the same plane.The dihedral angle between the two pyridine rings of the bridging bpy is 0.0(2)8 and the same for the terminal bpy is 2.9(2)8.X-Ray crystallography confirmed the structures of compounds 2 and 3. Selected bond lengths and bond angles are given in Table 2 for 2 and Table 3 for 3. A segment of the zigzag co-ordination polymer, 2, is shown in Fig. 2. There are two independent [Zn(SPh)2(bpy)] units (“dimers”) in 2 and four such units in 3. Each zinc metal is bound to two nitrogen atoms, one from each of two bpy ligands, and two S atoms of the terminal benzenethiolate ligands, to give a tetrahedral coordination geometry.The dihedral planes between the pyridine rings of the bpy have increased [24.0(6) and 34.6(5)8 in 2 and 21.0(3) to 43.5(3)8 in 3] as compared to those in 1. Although the structures of the co-ordination polymers in 2 and 3 are quite similar, the way these strands are arranged in three-dimensional space is diVerent. The polymer strand runs along the c axis in 2 as shown in Fig. 3, In contrast, these one dimensional ‘zigzag’ co-ordination polymers in 3 are packed in the bc plane as depicted in Fig. 4. The solvent molecules occupy the space between the phenyl rings. An inspection of Table 4 indicates that the volume per [Zn(SPh)2(bpy)] unit is smaller (increase in density) for the solvated lattice in compound 3 as compared to that in 2. In other words the packing eYciency of the solvated crystal 3 is better than that of 2. The empty voids available are better used for the guest solvents in 3. The presence of disordered CH2Cl2 and water in the crystal structure of 3 indicates that the space available can accommodate bigger guest solvents.This may also be attributed to the shape misfit of the small molecules in the lattice. Unfortunately, disorder present in the solvent region Fig. 2 A segment of the zigzag co-ordination polymer 2. The hydrogen atoms and minor disordered phenyl rings are omitted for clarity. Fig. 3 Packing diagram of compound 2 viewed down the b axis. The hydrogen atoms and the minor disordered phenyl rings are omitted for clarity.J.Chem. Soc., Dalton Trans., 1999, 1993–1997 1995 precludes any further analysis. The presence of phenyl ring disorder and high thermal motions (see Experimental section) appears to indicate, again, that there is more free space available in the crystal lattices of 2 and 3. There appears to be no phenyl ring stacking. Investigations are underway to study the influence of the bulky solvents on the packing of these polymers. Thermogravimetric analysis The TG traces of compounds 1 and 2 are given in Fig. 5. The dimer 1 started decomposing around 190 8C under N2. The weight of the residue corresponds to the formation of ZnS (observed, 19.7%; expected, 18.8%). The TG curve of polymer 2 is also very similar to that of 1. The final product of decomposition appears to be ZnS based on the residual weight (observed, 22.0%; calculated, 22.1%). It appears that both compounds 1 and 2 are potential ‘single-source’ precursors for Fig. 4 Packing diagram of compound 3 viewed down the a axis. The hydrogen atoms and the minor disordered phenyl rings are omitted for clarity. Only one layer of the polymer network is shown. Table 2 Selected bond lengths (Å) and angles (8) in compound 2 Zn(1)–N(1) Zn(1)–N(3) Zn(1)–S(1) Zn(1)–S(2) Zn(2)–N(4) Zn(2)–N(21) Zn(2)–S(3) Zn(2)–S(4) S(1)–C(1A) S(1)–C(1A9) S(2)–C(1B) N(3)–Zn(1)–N(1) N(3)–Zn(1)–S(1) N(1)–Zn(1)–S(1) N(3)–Zn(1)–S(2) N(1)–Zn(1)–S(2) S(1)–Zn(1)–S(2) N(4)–Zn(2)–N(21) N(4)–Zn(2)–S(3) N(21)–Zn(2)–S(3) N(4)–Zn(2)–S(4) N(21)–Zn(2)–S(4) S(3)–Zn(2)–S(4) C(1A)–S(1)–C(1A9) C(1A)–S(1)–Zn(1) C(1A9)–S(1)–Zn(1) C(1B)–S(2)–Zn(1) 2.123(10) 2.121(11) 2.277(4) 2.285(4) 2.105(11) 2.112(10) 2.264(3) 2.288(4) 1.766(11) 1.782(16) 1.723(9) 99.1(4) 107.7(3) 105.9(3) 101.1(3) 111.3(3) 127.84(16) 97.5(4) 105.7(3) 106.8(3) 107.5(3) 108.1(3) 127.33(15) 76.4(19) 98.8(6) 108.8(19) 110.3(6) S(3)–C(1C) S(3)–C(1C9) S(4)–C(1D) N(1)–C(1) N(1)–C(5) N(2)–C(6) N(2)–C(10) N(3)–C(11) N(3)–C(15) N(4)–C(16) N(4)–C(20) C(1C)–S(3)–C(1C9) C(1C)–S(3)–Zn(2) C(1C9)–S(3)–Zn(2) C(1D)–S(4)–Zn(2) C(1)–N(1)–C(5) C(1)–N(1)–Zn(1) C(5)–N(1)–Zn(1) C(6)–N(2)–C(10) C(6)–N(2)–Zn(2 2) C(10)–N(2)–Zn(2 2) C(11)–N(3)–C(15) C(11)–N(3)–Zn(1) C(15)–N(3)–Zn(1) C(20)–N(4)–C(16) C(20)–N(4)–Zn(2) C(16)–N(4)–Zn(2) 1.719(11) 1.721(11) 1.760(10) 1.288(14) 1.301(15) 1.325(14) 1.361(14) 1.334(15) 1.357(15) 1.364(17) 1.320(15) 93.9(9) 111.6(6) 114.4(6) 100.9(5) 116.8(11) 122.4(8) 120.8(8) 116.6(10) 120.7(8) 122.6(7) 116.6(12) 121.9(9) 121.6(10) 116.1(12) 122.4(10) 121.4(10) Symmetry transformations used to generate equivalent atoms: 1 x, y, z 1 1; 2 x, y, z 2 1.the ZnS materials. Further investigations are in progress in this direction. Conclusion We consider the following features of this study to be particularly salient. The reaction between Zn(SPh)2 and bpy proceeds to the formation of dimer [{Zn(SPh)2(bpy)}2(m-bpy)] 1 through the intermediate, 1 : 1 polymer [{Zn(SPh)2(bpy)}n], 2.Crystallisation chemistry plays an important role in the nature of the products isolated. With slow mixing of reactants (the diVusion method) when the ratio of bpy to Zn is low the insoluble polymer crystallises, but when the proportion of bpy increases (on mixing through diVusion) the dimer crystallises. Dilution with various solvents facilitates the isolation of the polymer in quantitative yield. By changing the concentration of CH2- Cl2, either the solvated or unsolvated crystalline form of [{Zn(SPh)2(bpy)}n] has been isolated.Our present investigation indicates that benzenethiolate is a poor bridging ligand between Zn atoms in the presence of bpy. The formation of Table 3 Selected bond lengths (Å) and angles (8) in compound 3 Zn(1)–N(1) Zn(1)–N(3) Zn(1)–S(1) Zn(1)–S(2) Zn(2)–N(5) Zn(2)–N(4) Zn(2)–S(4) Zn(2)–S(3) Zn(3)–N(6) Zn(3)–N(7) Zn(3)–S(5) Zn(3)–S(6) Zn(4)–N(21) Zn(4)–N(8) Zn(4)–S(7) Zn(4)–S(8) S(1)–C(1A) S(1)–C(1A9) S(2)–C(1B) S(3)–C(1C) S(4)–C(1D) N(1)–Zn(1)–N(3) N(1)–Zn(1)–S(1) N(3)–Zn(1)–S(1) N(1)–Zn(1)–S(2) N(3)–Zn(1)–S(2) S(1)–Zn(1)–S(2) N(5)–Zn(2)–N(4) N(5)–Zn(2)–S(4) N(4)–Zn(2)–S(4) N(5)–Zn(2)–S(3) N(4)–Zn(2)–S(3) S(4)–Zn(2)–S(3) C(1A)–S(1)–C(1A9) C(1A)–S(1)–Zn(1) C(1A9)–S(1)–Zn(1) C(1B)–S(2)–Zn(1) C(1C)–S(3)–Zn(2) C(1D)–S(4)–Zn(2) C(1E)–S(5)–Zn(3) C(1F)–S(6)–Zn(3) C(1G)–S(7)–Zn(4) C(1H)–S(8)–Zn(4) C(5)–N(1)–C(1) C(5)–N(1)–Zn(1) C(1)–N(1)–Zn(1) C(10)–N(2)–C(6) C(10)–N(2)–Zn(4 2) C(6)–N(2)–Zn(4 2) C(11)–N(3)–C(15) 2.099(7) 2.113(8) 2.265(3) 2.271(3) 2.095(7) 2.119(7) 2.261(3) 2.270(3) 2.082(7) 2.093(6) 2.270(2) 2.275(2) 2.101(7) 2.104(7) 2.265(3) 2.268(3) 1.751(12) 1.824(16) 1.771(8) 1.782(7) 1.775(6) 97.1(3) 105.7(2) 109.5(2) 110.0(2) 100.6(2) 129.28(12) 97.5(3) 103.8(2) 110.2(2) 108.9(2) 106.6(2) 126.15(11) 8.0(9) 104.1(6) 106.9(7) 107.2(4) 100.6(3) 106.5(2) 98.1(2) 107.9(2) 108.3(2) 102.9(4) 116.4(8) 120.7(6) 122.9(6) 117.5(8) 121.3(6) 121.0(5) 116.8(8) S(5)–C(1E) S(6)–C(1F) S(7)–C(1G) S(8)–C(1H) N(1)–C(5) N(1)–C(1) N(2)–C(10) N(2)–C(6) N(3)–C(11) N(3)–C(15) N(4)–C(20) N(4)–C(16) N(5)–C(25) N(5)–C(21) N(6)–C(30) N(6)–C(26) N(7)–C(35) N(7)–C(31) N(8)–C(36) N(8)–C(40) N(6)–Zn(3)–N(7) N(6)–Zn(3)–S(5) N(7)–Zn(3)–S(5) N(6)–Zn(3)–S(6) N(7)–Zn(3)–S(6) S(5)–Zn(3)–S(6) N(21)–Zn(4)–N(8) N(21)–Zn(4)–S(7) N(8)–Zn(4)–S(7) N(21)–Zn(4)–S(8) N(8)–Zn(4)–S(8) S(7)–Zn(4)–S(8) C(11)–N(3)–Zn(1) C(15)–N(3)–Zn(1) C(20)–N(4)–C(16) C(20)–N(4)–Zn(2) C(16)–N(4)–Zn(2) C(25)–N(5)–C(21) C(25)–N(5)–Zn(2) C(21)–N(5)–Zn(2) C(30)–N(6)–C(26) C(30)–N(6)–Zn(3) C(26)–N(6)–Zn(3) C(35)–N(7)–C(31) C(35)–N(7)–Zn(3) C(31)–N(7)–Zn(3) C(36)–N(8)–C(40) C(36)–N(8)–Zn(4) C(40)–N(8)–Zn(4) 1.801(6) 1.780(6) 1.782(6) 1.770(9) 1.328(12) 1.341(11) 1.318(11) 1.344(11) 1.342(12) 1.343(12) 1.338(11) 1.341(11) 1.337(11) 1.341(11) 1.323(10) 1.344(10) 1.331(10) 1.335(10) 1.336(10) 1.347(11) 98.6(3) 106.4(2) 107.9(2) 111.7(2) 101.4(2) 127.0(1) 96.9(3) 111.5(2) 99.9(2) 105.9(2) 108.3(2) 129.3(1) 120.7(6) 122.5(6) 116.6(8) 122.3(6) 121.1(6) 117.4(7) 121.0(6) 121.6(6) 116.0(7) 121.7(6) 122.1(6) 117.4(7) 120.3(5) 122.3(5) 117.1(7) 123.1(6) 119.8(6) Symmetry transformations used to generate equivalent atoms: 1 x, y 2 1, z 2 1; 2 x, y 1 1, z 1 1.1996 J.Chem. Soc., Dalton Trans., 1999, 1993–1997 Table 4 Crystal data and structure refinement for compounds 1, 2 and 3 1 2 3 Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/Mg m23 m/mm21 F(000) Tmax, Tmin Data [I > 2s(I)]/parameters Goodness of fit on F2 Final R1 and wR2 [I > 2s(I)] (all data) Extinction coeYcient C54H44N6S4Zn2 1035.93 Monoclinic P21/c 14.4276(3) 17.5358(1) 9.9439(2) 104.85(1) 2431.78(7) 4 1.415 1.202 1068 0.7353, 0.5562 4312/299 1.039 0.0426, 0.0754 0.0697, 0.0839 0.0006(3) C44H36N4S4Zn2 879.75 Triclinic P1� 10.8329(4) 13.7844(5) 17.0215(4) 69.593(1) 88.253(2) 87.946(1) 2380.25(14) 2 1.227 1.215 904 0.8016, 0.6050 3440/324 1.058 0.1183, 0.3297 0.1871, 0.3663 0.009(2) C44.25H38.5Cl0.5N4OS4Zn2 919.0 Triclinic P1� 13.6823(3) 19.7171(3) 20.2532(4) 65.093(1) 71.897(1) 73.909(1) 4642.0(2) 4 1.315 1.278 1890 0.7872, 0.6005 11427/686 1.132 0.1023, 0.2337 0.1345, 0.2549 0.00042(17) the co-ordination polymer 2 or 3 does not depend on the metal : ligand ratio only.We were not able to isolate any other network by varying this ratio under the experimental conditions employed.Compounds 1 and 2 appear to be potential candidates as ‘single-source’ precursors for ZnS materials as they thermally decompose to ZnS in the temperature range 190–500 8C. Experimental The chemicals and solvents were obtained commercially and used as received. The solvents were dried over 3 Å molecular sieves. The Microanalytical laboratory at National University of Singapore performed the elemental analyses. The 1H and 13C-{1H} NMR spectra were recorded on a Bruker ACF spectrometer at 300 MHz using TMS as an internal reference at 25 8C in d6-DMSO solvent.X-Ray powder patterns were obtained using a D5005 Siemens diVractrometer. Thermogravimetric analyses were carried out using a SDT 2980 TGA thermal analyser with a heating rate of 10 8C min21 in a nitrogen atmosphere using a sample size of about 5–10 mg per run. Syntheses All the three compounds once isolated in the solid state were found to be insoluble in most of the solvents tried (MeCN, acetone, CH2Cl2, CHCl3, alcohols and water), but sparingly Fig. 5 Thermogravimetry of compounds 1 (as full line) and 2 (dashed line). soluble in DMF and DMSO. The solubilities of 1 and 2 in DMF at 25 8C are 8.5 and 13.6 mg ml21 respectively. [{Zn(SPh)2(bpy)}2(Ï-bpy)] 1. A solution of bpy (0.165 g, 1.06 mmol) in 10 ml of THF was added dropwise with stirring to a solution of Zn(SPh)2 (0.200 g, 0.70 mmol) in 2 ml of DMF to obtain a clear yellow solution. On leaving the solution for slow evaporation, hexagonal shaped crystals were obtained.These were separated by decantation, washed with MeOH and Et2O and dried in air (78% yield). Compound 1 was also obtained when the synthesis was done in DMF– and DMSO–THF mixtures (Calc. for C27H22N3S2Zn: C, 62.60; H, 4.28; N, 8.11; S, 12.38%. Found: C, 62.45; H, 4.39; N, 8.16; S, 12.25%), mp 211– 213 8C. 1H NMR: d 8.72 (d, J = 6, 12 H, Ha(bpy)); 7.85 (d, J = 6, 12 H, Hb(bpy)); 7.34 (d, J = 9, 8 H, H2 (SPh)); 6.98 (t, J = 7, 8 H, H3 (SPh) and 6.85 (t, J = 7 Hz, 4 H, H4 (SPh)). 13C NMR: d 150.23 (Ca(bpy)); 144.59 (Cg(bpy)); 142.67 (C1 (SPh)); 132.30 (C2 (SPh)); 127.67 (C3 (SPh)); 121.95 (C4 (SPh)) and 121.56 (Cb(bpy)). [{Zn(SPh)2(Ï-bpy)}n] 2. A solution of bpy (55 mg, 0.35 mmol) in 6.0 ml of CH2Cl2 was added to a solution of Zn(SPh)2 (100 mg, 0.35 mmol) in 3 ml DMF. The clear yellow solution formed was layered with Et2O to obtain yellow crystals within a few minutes. The crystals were washed with MeOH and diethyl ether.Yield: 83% (Calc. for C22H18N2S2Zn: C, 60.07; H, 4.12; N, 6.37; S, 14.58; Zn, 14.86. Found: C, 59.49; H, 3.97; N, 6.66; S, 14.59, Zn, 14.88%), mp 222–225 8C. 1H NMR: d 8.72 (d, J = 6, 12 H, Ha(bpy)); 7.85 (d, J = 6, 12 H, Hb(bpy)); 7.32 (d, J = 9, 8 H, H2 (SPh)); 6.98 (t, J = 7, 8 H, H3 (SPh)) and 6.85 (t, J = 7 Hz, 4 H, H4 (SPh)). 13C NMR: d 150.28 (Ca(bpy)); 144.52 (Cg(bpy)); 142.72 (C1 (SPh)); 132.30 (C2 (SPh)); 127.67 (C3 (SPh)); 121.93 (C4 (SPh)) and 121.47 (Cb(bpy)).[{Zn(SPh)2(Ï-bpy)}n]?0.25CH2Cl2?H2O 3. A solution of bpy (56 mg, 0.36 mmol) in 6 ml of CH2Cl2 was added to a solution of Zn(SPh)2 (100 mg, 0.35 mmol) in 1 ml DMF. A clear yellow solution formed immediately, which was left to form yellow crystals. These were washed with MeOH and diethyl ether. Yield: 74% (Calc. for C44.25H36.5Cl0.5N4S4Zn2: C, 58.98; H, 4.08; N, 6.22; S, 14.22. Found: C, 58.46; H, 3.93; N, 6.65; S, 14.95%). Attempted synthesis of [(bpy)2Zn(Ï-SPh)2Zn(bpy)2][ClO4]2. The compounds Zn(SPh)2 (100 mg, 0.35 mmol) and Zn(ClO4)2 (137 mg, 0.37 mmol) were dissolved in 2 ml DMF then diluted by 3 ml of THF.A solution containing bpy (220 mg, 1.41 mmol) in 6 ml of THF was added slowly dropwise. Yellow crystalsJ. Chem. Soc., Dalton Trans., 1999, 1993–1997 1997 were obtained when the clear yellow solution was left for slow evaporation. They analysed as 1. Attempted synthesis of [Zn(SPh)2(bpy)2]. The compounds Zn(ClO4)2 (500 mg, 1.34 mmol) and bpy (524 mg, 3.35 mmol) were dissolved in 20 ml of MeOH to obtain a clear solution.A methanolic solution of NaSPh [prepared from PhSH (0.3 ml, 2.69 mmol) and Na (65 mg, 2.69 mmol) in 8 ml of MeOH] was added as a layer on top of this and the whole was left for slow evaporation to obtain yellow crystals which were analysed as dimer 1. In another experiment Zn(SPh)2 (103 mg, 0.36 mmol) in 2 ml DMF and bpy (116 mg, 0.73 mmol) in 10 ml of CH2Cl2 or THF gave a yellow solution.Yellow block-like crystals of compound 2 were obtained in 10 min and when the mixture was left aside and the solvents evaporated completely hexagonal-shaped crystals of 1 were obtained. X-Ray crystallography The diVraction experiments were carried out on a Bruker AXS SMART CCD 3-circle diVractometer with a Mo-Ka sealed tube at 23 8C. The softwares used were: SMART11 for collecting frames of data, indexing reflections and determinatof lattice parameters; SAINT11 for integration of intensity of reflections and scaling; SADABS12 for empirical absorption correction; and SHELXTL13 for space group determination, structure solution and least-squares refinements on F2.The crystals of compounds 2 and 3 were sealed in glass capillary tubes. Full details are given in Table 4. Compound 1. Total of 15177 reflections collected in the 2q range 1.87–29.288 (218 £ h £ 19, 224 £ k £ 116, 213 £ l £ 13) of which 5936 (Rint = 0.0270) were independent.Anisotropic thermal parameters were refined for all the non-hydrogen atoms. An extinction coeYcient was refined to 0.0006(3). The electron densities fluctuated between 0.268 and 20.213 e Å23 in the Fourier diVerence map. Compound 2. The number of reflections collected in the 2q range 2.25–25.08 (212 £ h £ 12, 27 £ k £ 16, 220 £ l £ 20) was 9260, of which 7208 (Rint = 0.0452) were independent. A few of the phenyl rings show large thermal motions indicating the possibility of disorder.However, the disordered phenyl rings were resolved only for those attached to S1 and S3. Common isotropic thermal parameters were refined (with occupancies of 0.75 and 0.25 for the S1 phenyl ring and 0.55 and 0.45 for the S3 phenyl ring). Common isotropic thermal parameters were refined for the phenyl rings attached to S2 and S4. Isotropic thermal parameters were refined for the rest of the thiolate phenyl rings. Compound 3. In total 29776 reflections were collected in the 2q range 1.66–25.008 (216 £ h £ 16, 223 £ k £ 23, 223 £ l £ 24) of which 15334 (Rint = 0.0605) were independent.Anisotropic thermal parameters were refined for all Zn, S, N and bpy carbon atoms. The isotropic thermal parameters of the carbon atoms of the thiolate phenyl rings were relatively high indicating the possibility of disorder. However, disorder models were successfully resolved only for the phenyl ring attached to S1. The Fourier-diVerence routine showed severely disordered solvent regions.These were assigned to 0.25CH2Cl2 (the Cl atoms were disordered) and one H2O disordered in 10 diVerence places in the crystal lattice. The assignment of oxygen atoms of water was quite arbitrary and may have come from the solvents used for synthesis. To improve the quality of the structures 2 and 3, data were collected using crystals from diVerent batches at room temperature. The problem of disorder and higher thermal activity of the phenyl rings persisted.In spite of high agreement factors, the connectivity in the polymeric network is well established beyond any doubt. CCDC reference number 186/1437. See http://www.rsc.org/suppdata/dt/1999/1993/ for crystallographic files in .cif format. Acknowledgements Grant RP970618 to J. J. V. from the National University of Singapore supported this research. The authors would like to oVer sincere thanks to the referees for their suggestions which led to reinvestigations of results.References 1 M. J. Zaworotko, in Crystal Engineering: The Design and Application of Functional Solids, eds. R. Seddon and M. J. Zaworotko, NATO, ASI series, 1998. 2 L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, J. Chem. Soc., Chem. Commun., 1994, 2755; O. M. Yaghi and H. Li, J. Am. Chem. Soc., 1996, 118, 295; L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, J. Am. Chem. Soc., 1995, 117, 4562; Inorg. Chem., 1995, 34, 5698; O. M. Yagi and G. Li, Angew.Chem., Int. Ed. Engl., 1995, 34, 207. 3 L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, Angew. Chem., Int. Ed. Engl., 1995, 34, 1895; T. Soma, H. Yuge and T. Iwamoto, Angew. Chem., Int. Ed. Engl., 1994, 33, 1665. 4 S. Subramanian and M. J. Zaworotko, Angew. Chem., Int. Ed. Engl., 1995, 34, 2127; R. W. Gable, B. F. Hoskins and R. Robson, J. Chem. Soc., Chem. Commun., 1990, 1677; J. Lu, T. Paliwala, S. C. Lim, C. Yu, T. Niu and A. J. Jacobson, Inorg. Chem., 1997, 36, 923; F. Robinson and M. J. Zaworotko, J. Chem. Soc., Chem. Commun., 1995, 2413; T. L. Hennigar, D. C. MacQuarrie, P. Losier, R. D. Rogers and M. J. Zaworotko, Angew. Chem., Int. Ed. Engl., 1997, 36, 972. 5 P. S. Halasyamani, M. J. Drewitt and D. O’Hare, Chem. Commun., 1997, 867; O. M. Yaghi and H. Li, J. Am. Chem. Soc., 1995, 117, 10401. 6 M. Tong, B. Ye, J. Cai, X. Chen and S. Ng, Inorg. Chem., 1998, 37, 2645. 7 G. R. Desiraju, Science, 1997, 278, 404 J. Dunitz and J. Bernstein, Acc. Chem. Res., 1995, 28, 193; A. Anthony, G. R. Desiraju, R. K. R. Jetti, S. S. Kuduva, N. N. L. Madhavi, A. Nangia, R. Thaimattam and V. R. Thalladi, Crystal Eng., 1998, 1, 1. 8 O.-S. Jung, S. H. Park, K. M. Kim and H. G. Jang, Inorg. Chem., 1998, 37, 5781. 9 G. Baum, E. C. Constable, D. Fenske, C. E. Housecroft and T. Kulke, Chem. Commun., 1998, 2659. 10 P. J. Blower and J. R. Dilworth, Coord. Chem. Rev., 1987, 76, 121; I. G. Dance, Polyhedron, 1986, 5, 1037. 11 SMART & SAINT Software Reference Manuals, Version 4.0, Siemens Energy & Automation, Inc., Analytical Instrumentation, Madison, WI, 1996. 12 G. M. Sheldrick, SADABS, a software for empirical absorption correction, University of Göttingen, 1996. 13 SHELXTL Reference Manual, Version 5.03, Siemens Energy & Automation, Inc., Analytical Instrumentation, Madison, WI, 1996. Paper 9/01416K

ISSN:1477-9226    

DOI:10.1039/a901416k

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1999–2004 1999 Synthesis, crystal structures and properties of copper(II) complexes of SchiV base derivatives containing imidazole and ‚-alanine groups La-Sheng Long, Shi-Ping Yang, Ye-Xiang Tong, Zong-Wan Mao, Xiao-Ming Chen * and Liang-Nian Ji School of Chemistry and Chemical Engineering, Zhongshan University, Guangzhou 510275, China. E-mail: cescxm@zsu.edu.cn Received 22nd December 1998, Accepted 23rd April 1999 Four copper(II) complexes with SchiV base ligands N-[(5-methylimidazol-4-yl)methylene]-b-alanine (HL1) and N-[(1-methylimidazol-2-yl)methylene]-b-alanine (HL2) and their reduced forms N-[(5-methylimidazol-4-yl)methyl]- b-alanine (HL3) and N,N-bis[(5-methylimidazol-4-yl)methyl]-b-alanine (HL4) have been synthesized. The crystal structures of [CuL1(H2O)(ClO4)] 1, [CuL2(H2O)(ClO4)] 2, [CuL3(Py)(ClO4)] 3 and [Cu2(L4)2][ClO4]2?2H2O 4 have been determined.Complexes 1 and 2 are structurally very similar, the copper(II) atom being tridentately chelated by the SchiV base using one carboxy oxygen atom and two nitrogen atoms at the equatorial positions, with the fourth equatorial position being occupied by another carboxy oxygen atom from an adjacent SchiV base; one aqua ligand and one perchlorate oxygen atom ligate at the axial positions, resulting in an elongated octahedral geometry.Each carboxy group in 1 and 2 acts in the syn-anti mode and bridges two adjacent copper(II) atoms via two equatorial positions, resulting in one-dimensional helical (Cu–O–C–O–Cu)n chains.In 3 the copper(II) atom is ligated by two nitrogen atoms, one carboxy oxygen atom from an L3 ligand and another nitrogen atom from pyridine at the equatorial position; the axial positions are occupied by one perchlorato oxygen atom and one carboxy oxygen atom from another L3 ligand, tridentately chelating an adjacent copper(II) atom, resulting in an elongated octahedral geometry.Complex 4 contains a dimeric cation with two very similar square-pyramidally co-ordinated copper(II) atoms. Each L4 ligand chelates a copper(II) atom in a tetradentate mode with the three nitrogen atoms occupying the equatorial positions and the carboxy oxygen atom the apical position. The fourth equatorial position is taken by a carboxy oxygen atom from another L4 ligand chelating another copper(II) atom, resulting in a bis(carboxylato-O)- bridged dimeric structure. The electronic and EPR spectra and redox properties of 1–4 are also discussed.Considerable attention has previously been given to SchiV base adducts formed between pyridoxal or its analogues and amino acids.1,2 Particularly, pyridoxal phosphate (PLP) acts as a cofactor in many enzymes catalysing transformations of amino acids.3–5 Investigations have been conducted on ternary copper(II) complexes of N-salicylideneglycine and its derivatives with imidazole, pyrazole or pyridine by EPR and their redox properties.6–9 Of particular importance are the chelates containing histidine residues; not only do the polydentate SchiV base ligands provide a useful framework to establish relationships between spectral properties of the complexes and the binding mode of the histidine residue,10 but also the histidinelike binding modes of amino acid residues may model structural features in biological systems.The investigation of the structures and spectral properties of metal complexes containing histidine 11 or histidyl residues 10,12 is thus very important for elucidating structure/function relations in histidine-containing biological systems.However, the only reported crystal structure containing a histidine SchiV base appears to be a cobalt complex [Co(SalHis)(Ala)]?2H2O [SalHis = a-N-(o-hydroxybenzyl)- L-histidinate, Ala = L-alaninate].13 We have recently reported the synthesis, structures and properties of a series of metal complexes with imidazole-containing ligands relevant to structure/function relations of some metalloenzymes. 14 As a sequel, in this paper we report the synthesis of the SchiV base ligands N-[(5-methylimidazol-4-yl)methylene]- b-alanine (HL1), N-[(1-methylimidazol-2-yl)methylene]- b-alanine (HL2) and their reduced forms N-[(5-methylimidazol- 4-yl)methyl]-b-alanine (HL3) and N,N-bis[(5-methylimidazol- 4-yl)methyl]-b-alanine (HL4), and crystal structures, electronic and EPR spectra and redox properties of their copper( II) complexes, [CuL1(H2O)(ClO4)] 1, [CuL2(H2O)(ClO4)] 2, [CuL3(Py)(ClO4)] 3 and [Cu2(L4)2][ClO4]2?2H2O 4.Experimental All reagents were commercially available and used as received. Solvents were dried by conventional procedures prior to use. All samples were thoroughly dried prior to elemental analyses. Physical measurements The C, H and N elemental analyses were performed on a Perkin-Elmer 204 elemental analyser. The IR spectra were recorded on a Nicolet 5DX FT-IR spectrophotometer with KBr discs in the 4000–400 cm21 region, electronic spectra on a Shimadzu MPS-200 spectrometer in DMF solutions and X-band EPR spectra from crystalline samples on a Bruker ER- 420 spectrometer operating at 77 K in DMF solution.Cyclic voltammetry was performed on an electrochemical analyser in DMF. A platinum wire working electrode, a platinum plate auxiliary electrode and a saturated calomel reference electrode (SCE) were employed. CAUTION: perchlorate salts of metal complexes are potentially explosive and should be handled in small quantities with care.Synthesis of ligands HL3. To a solution of b-alanine (0.89 g, 10 mmol) in methanol (10 cm3) containing KOH (0.56 g, 10 mmol) was added2000 J. Chem. Soc., Dalton Trans., 1999, 1999–2004 5-methylimidazole-4-carbaldehyde (1.10 g, 10 mmol) in methanol (10 cm3). The solution was refluxed with stirring for 2 h. The yellowish solution was cooled in an ice-bath, then reduced with an excess of NaBH4 (0.46 g, 12 mmol) in methanol containing a few drops of sodium hydroxide solution.The yellowish colour slowly discharged, and after 10 min the solution was evaporated and extracted with dry methanol, then acidified with HCl gas. The resulting solid was filtered oV, washed with dry methanol and diethyl ether, and dried, which yielded 45.6% (Calc. for C8H13N3O2?2HCl: C, 37.50; H, 5.86; N, 16.41. Found: C, 37.53; H, 6.03; N, 16.34%). IR (KBr, cm21): 3163m, 3100s, 3071s, 2980s, 2790m, 2600m, 1735s, 1602w, 1539w, 1468m, 1398w, 1370m, 1264m, 1208s, 1159m, 1068m, 1004w, 962w, 871w, 800w, 772m, 695w, 603w, 470w and 435w.HL4. To a solution of HL3?2HCl (2.56 g, 10 mmol) in methanol (10 cm3) containing KOH (1.68 g, 30 mmol) was added 5-methylimidazole-4-carbaldehyde (1.10 g, 10 mmol) in methanol (10 cm3). The solution was refluxed with stirring for 2 h. The yellowish solution was cooled in an ice-bath, then reduced with an excess of NaBH4 (0.46 g, 12 mmol) in methanol containing a few drops of sodium hydroxide solution.The yellowish colour slowly discharged, and after 10 min the solution was evaporated and extracted with dry methanol, then acidified with HCl gas. The resulting solid was filtered oV, washed with dry methanol and diethyl ether, and then dried, which yielded 0.98 g of a solid containing HL4?4HCl (82%) and HL3?2HCl (18%). The percentages of each were calculated according to elemental analysis (Found: C, 36.95; H, 5.76; N, 16.43%).Preparation of metal complexes (a) [CuL1(H2O)(ClO4)] 1. To a solution of b-alanine (0.089 g, 1.0 mmol) in methanol (10 cm3) containing KOH (0.056 g, 1.0 mmol) was added 5-methylimidazole-4-carbaldehyde (0.11 g, 1.0 mmol) in methanol (10 cm3). The solution was refluxed with stirring for 2 h. To the yellowish solution was added a solution of copper(II) nitrate hydrate (0.20 g, 1.0 mmol) and a solution of sodium perchlorate (0.14 g, 1.0 mmol) in aqueous methanol (10 cm3, 1 : 5 v/v).The reaction mixture turned deep blue immediately. After allowing it to stand in air at room temperature for two days, the deposited deep blue crystals of complex 1 were collected and washed with ethanol, yield 67%. A single crystal suitable for X-ray work was obtained by recrystallization in MeCN (Calc. for C8H12ClCuN3O7: C, 26.59; H, 3.32; N, 11.63. Found: C, 26.39; H, 3.35; N, 11.54%). IR (cm21): 3430s, 3128s, 3015s, 2910m, 2853m, 1637s, 1560s, 1518s, 1440m, 1426m, 1398m, 1349w, 1293w, 1236w, 1215w, 1124s, 1089s, 1075s, 976w, 878w, 765w, 695w and 632s.(b) [CuL2(H2O)(ClO4)] 2. Complex 2 was prepared as for 1. Deep blue needle crystals were obtained, yield 65% (Calc. for C8H12ClCuN3O7: C, 26.59; H, 3.32; N, 11.63. Found: C, 26.35; H, 3.28; N, 11.61%). IR (cm21): 3655s, 3325s, 3142s, 3029s, 2910m, 2853m, 1637s, 1567s, 1518s, 1454m, 1426s, 1356w, 1293w, 1250w, 1215w, 1145s, 1110s, 1075s, 962w, 828w, 765w, 674w and 632s.(c) [CuL3(Py)(ClO4)] 3. To an ethanol (10 cm3) solution of L3?2HCl (0.256 g, 1.0 mmol) containing KOH (0.17 g, 3.0 mmol) and pyridine (0.079 g, 1.0 mmol), an aqueous ethanol (10 cm3, 50% v/v) solution of copper(II) nitrate hydrate (0.20 g, 1.0 mmol) and NaClO4?H2O (0.14 g, 1.0 mmol) was added dropwise while stirring. After filtration, the deep blue solution was allowed to stand at room temperature in air, yielding transparent deep blue polyhedral crystals of complex 3, yield 57% (Calc.for C13H17ClCuN4O6: C, 36.80; H, 4.01; N, 13.20. Found: C, 36.39; H, 3.95; N, 13.54%). IR (cm21): 3571s, 3458s, 3148s, 3043s, 2903m, 2714m, 1630s, 1581s, 1525s, 1447m, 1426m, 1384m, 1328w, 1278w, 1243w, 1138s, 1117s, 1082s, 990w, 878w, 821w, 667w and 632s. (d) [Cu2(L4)2][ClO4]2?2H2O 4. To an ethanol (10 cm3) solution of L4?4HCl (0.423 g, 1.0 mmol) containing NaOH (0.20 g, 5.0 mmol), an aqueous ethanol (10 cm3, 50% v/v) solution of copper(II) nitrate hydrate (0.20 g, 1.0 mmol) and NaClO4?H2O (0.14 g, 1.0 mmol) was added dropwise while stirring.After filtration, the blue solution was allowed to stand at room temperature in air, yielding transparent deep blue polyhedral crystals of complex 4, yield 35% (Calc. for C13H20ClCuN5O7: C, 34.14; H, 4.38; N, 15.32. Found: C, 34.39; H, 4.35; N, 15.54%). IR (cm21): 3655s, 3325s, 3142s, 3029s, 2910m, 2853m, 1560s, 1518s, 1454m, 1426s, 1356w, 1293w, 1250w, 1215w, 1145s, 1110s, 1075s, 962w, 828w, 765w, 674w and 632s.X-Ray crystallography DiVraction intensities for the four complexes were collected at 293 K on a Siemens R3m diVractometer. Lorentz-polarization and absorption corrections were applied. The structure solution and full-matrix least-squares refinement based on F2 were performed with the SHELXS 97 and SHELXL 97 program packages, respectively.15,16 Complex 2 crystallizes in a noncentrosymmetric space group; the absolute structure has been determined with a Flack parameter of 0.10(6).17 All the nonhydrogen atoms were refined anisotropically. Hydrogen atoms of the organic ligands were generated geometrically (C–H 0.96 Å) and those of the aqua ligands located from the diVerence maps; all the hydrogen atoms were assigned the same isotropic thermal parameters and included in the structure-factor calculations.Analytical expressions of neutral-atom scattering factors were employed, and anomalous dispersion corrections incorporated.18 The crystallographic data for 1–4 are summarized in Table 1.Selected bond distances and angles are given in Table 2. CCDC reference number 186/1439. See http://www.rsc.org/suppdata/dt/1999/1999/for crystallographic files in .cif format. Results and discussion Crystal structures (a) [CuL1(H2O)(ClO4)] 1. An ORTEP19 view of the coordination environment of complex 1 is shown in Fig. 1. The surrounding of each copper(II) atom is (412). The L1 ligand acts in a tridentate chelate mode for the copper(II) atom, utilizing the two nitrogen atoms and one carboxy oxygen atom to bind the metal atom at the equatorial positions; the fourth equatorial position is occupied by an oxygen atom O(2a) Fig. 1 An ORTEP view of the co-ordination geometry and hydrogen bonding scheme in complex 1.J. Chem. Soc., Dalton Trans., 1999, 1999–2004 2001 Table 1 Crystal data and structure refinement for complexes 1–4 1 2 3 4 Empirical formula Formula weight Crystal system Space group a/Å b/Å c/Å b/8 ZV /Å3 m(Mo-Ka)/cm21 R1 (I > 2s) R2 (all data) C8H12ClCuN3O7 361.20 Monoclinic C2/c 14.916(7) 7.458(4) 23.687(12) 97.89 4 2610(2) 1.914 0.0728 0.2041 C8H12ClCuN3O7 361.20 Orthorhombic Pna21 12.793(10) 13.167(8) 7.731(3) 4 1302.3(8) 1.918 0.0618 0.1858 C13H17ClCuN4O6 424.29 Monoclinic P21/n 10.314(12) 8.167(4) 19.468(16) 102.09 4 1604(2) 1.569 0.0566 0.1508 C26H40Cl2Cu2N10O14 914.66 Monoclinic P21/c 8.240(3) 18.185(5) 23.445(6) 90.96(3) 4 3512.6(18) 1.445 0.0559 0.1367 belonging to the carboxy group of an adjacent and symmetryrelated fragment.The bond lengths Cu(1)–N(1) and Cu(1)– N(3) are 1.937(6) and 1.967(5) Å, respectively; the Cu–O Table 2 Selected bond lengths (Å) and angles (8) for complexes 1–4 1 Cu(1)–O(1) Cu(1)–O(2a) N(3)–C(6) N(3)–C(5) Cu(1) ? ? ? O(1w) N(2) ? ? ? O(5b) C(5)–N(3)–C(6) C(6)–N(3)–Cu(1) 1.913(5) 1.953(5) 1.443(13) 1.263(8) 2.624(8) 2.976(1) 122.3(6) 123.5(4) Cu(1)–N(1) Cu(1)–N(3) C(4)–C(5) Cu(1) ? ? ? O(5) C(5)–N(3)–Cu(1) 1.937(6) 1.967(5) 1.424(8) 2.701(8) 114.2(5) 2 Cu(1)–O(2a) Cu(1)–O(1) Cu(1) ? ? ? O(1w) N(3)–C(5) O(2)–Cu(1b) C(5)–N(3)–C(6) C(6)–N(3)–Cu(1) 1.933(4) 1.941(5) 2.489(6) 1.278(9) 1.933(4) 123.7(5) 125.2(4) Cu(1)–N(1) Cu(1)–N(3) Cu(1) ? ? ? O(3) N(3)–C(6) C(4)–C(5) C(5)–N(3)–Cu(1) 1.937(6) 2.025(5) 2.749(10) 1.408(10) 1.385(10) 111.2(5) 3 Cu(1)–O(1) Cu(1)–N(3) N(3)–C(5) N(3)–C(6) Cu(1)–O(2a) N(2)–O(2b) C(5)–N(3)–C(6) C(5)–N(3)–Cu(1) 1.916(4) 1.991(5) 1.455(6) 1.453(6) 2.722(4) 2.758(6) 113.8(4) 111.2(3) Cu(1)–N(1) Cu(1)–N(4) C(4)–C(5) Cu(1)–O(5) C(6)–N(3)–Cu(1) 1.952(4) 2.001(5) 1.492(7) 2.795(6) 117.5(3) 4 Cu(1)–N(4) Cu(1)–O(3) Cu(1)–O(1) Cu(2)–N(6) Cu(2)–O(1) Cu(2)–O(3) N(2)–O(11) N(3)–C(5) N(5)–O(2w) N(8)–C(26) N(7)–O(1w) N(10)–O(8) O(2w)–O(4b) C(5)–N(3)–C(6) C(5)–N(3)–Cu(1) 1.935(4) 1.949(4) 2.263(4) 1.931(4) 1.955(3) 2.259(4) 3.054(8) 1.495(7) 2.763(7) 1.492(7) 2.729(6) 2.862(7) 2.786(6) 109.5(5) 106.6(3) Cu(1)–N(1) Cu(1)–N(3) Cu(1)–Cu(2) Cu(2)–N(9) Cu(2)–N(8) N(3)–C(6) N(3)–C(11) C(4)–C(5) N(8)–C(31) N(8)–C(25) O(1w)–O(2a) N(2)–O(12) C(6)–N(3)–Cu(1) C(5)–N(3)–C(11) 1.937(4) 2.081(4) 3.2557(15) 1.940(4) 2.077(4) 1.489(7) 1.497(7) 1.488(8) 1.479(7) 1.493(7) 2.734(6) 2.979(7) 111.2(5) 107.6(4) Symmetry codes: for 1, a, 2x 1 3/2, y 2 1/2, 2z 1 1/2; b, x, y 2 1, z; c, 2x 1 3/2, y 1 1/2, 2z 1 1/2; for 2, a, 2x, 2y 1 1, z 2 1/2; b, 2x, 2y 1 1, z 1 1/2; for 3, a, 2x 1 3/2, y 1 1/2, 2z 1 3/2; b, x 2 1/2, 2y 1 1/2, z 2 1/2; for 4, a, 2x 1 1, y 1 1/2, 2z 1 1/2; b, 2x, 2y, 2z.(carboxy) distances are 1.913(5) and 1.953(5) Å. An aqua ligand and a perchlorate oxygen atom ligate the copper(II) atom at the axial positions with much longer bond distances [Cu(1)–O(1w) 2.624(8), Cu(1)–O(5) 2.701(8) Å], resulting in an elongated octahedral geometry. It is interesting that each carboxylate group acts in the bidentate syn-anti mode and bridges each pair of adjacent copper(II) atoms (C ? ? ? Cu 4.757 Å ) via the two equatorial positions, giving rise to one-dimensional (Cu–O–C–O–Cu)n skeletons running parallel to the crystallographic a axis (Fig. 2), which may best be visualized as helix-like chains, being similar to an example previously documented.20 (b) [CuL2(H2O)(ClO4)] 2. An ORTEP19 view of the coordination environment of complex 2 is shown in Fig. 3. The crystal structure of 2 is very similar to that of 1. The bond lengths Cu(1)–N(1) and Cu(1)–N(3) are 1.937(6) and 2.025(5) Å, and Cu(1)–O(1) and Cu(1)–O(2a) are 1.941(4) and 1.933(4) Å, respectively. The diVerences of the corresponding values of the co-ordination bonds between 1 and 2 may be attributed to the diVerence in the imidazole groups in L1 and L2, where the Fig. 2 An ORTEP view of the helical chain of complex 1 running along the a axis.2002 J. Chem. Soc., Dalton Trans., 1999, 1999–2004 imidazole group in L1 is hydrogen bonded to a perchlorate group and that in L2 is methylated; this may result in diVerent co-ordination abilities for the two organic ligands.21,22 Also similar to that of complex 1, each carboxylate group acts in a bidentate syn-anti mode and bridges each pair of adjacent copper atoms (Cu ? ? ? Cu 4.867 Å) via the two equatorial positions, giving rise to one-dimensional (Cu–O–C– O–Cu)n helix-like chains in the solid.(c) [CuL3(Py)(ClO4)] 3. An ORTEP19 view of the molecular structure of complex 3 is shown in Fig. 4.The crystal structure consists primarily of discrete molecules of 3 with the copper(II) atom in a distorted square-planar geometry. The metal atom is tridentately chelated by an L3 ligand and the co-ordination sphere is completed by a pyridine ligand. One perchlorate oxygen atom and a carboxy oxygen atom from an adjacent molecule have weak interaction with the metal through the axial positions [Cu(1) ? ? ? O(5) 2.795(6), Cu(1) ? ? ? O(2a) 2.722(4) Å]. The significantly weaker axial interaction of the copper(II) atom may be attributed to the stronger donor ability of pyridine in 3, in comparison to that of a carboxy group in 1 and 2.The copper(II)–imidazole Cu(1)–N(1) bond [1.952(4) Å] is slightly shorter than that of the copper(II)–pyridine Cu(1)–N(4) bond [2.001(5) Å] and that of the copper(II)–amine Cu(1)–N(3) Fig. 3 An ORTEP view of the co-ordination geometry and hydrogen bonding scheme in complex 2. Fig. 4 An ORTEP view of the co-ordination geometry and hydrogen bonding scheme in complex 3.bond [1.991(5) Å]. The successful in situ reduction of the imine group is evident from the N(3)–C(5) distance [1.455(6) Å] compared with those [1.263(8) and 1.278(9) Å] for the related ligand (L1 and L2) in 1 and 2. Furthermore, the bond length C(4)–C(5) [1.492(7) Å] is typical of a single bond, which is significantly longer than the corresponding bonds in 1 and 2 [1.424(8) and 1.385(10) Å], and indicates the loss of conjugation. 23 The bond angles centred about the N(3) atom are 113.8(4), 117.5(3) and 111.2(3)8 for C(5)–N(3)–C(6), C(6)– N(3)–Cu(1) and C(5)–N(3)–Cu(1), respectively, being consistent with a sp3 tetrahedral configuration, and similar to those for [Co(SalHis)(Ala)].13 (d) [Cu2(L4)2][ClO4]2?2H2O 4. The crystal structure of complex 4 consists of discrete carboxylate-bridged dimeric cations, perchlorate anions and lattice water molecules. An ORTEP19 view of the dimeric cation is shown in Fig. 5, in which the two crystallographically independent copper(II) atoms are in very similar co-ordination environments. The anionic L4 ligand chelates a square-pyramidally co-ordinated copper(II) atom in a tetradentate fashion with the three nitrogen atoms occupying the equatorial positions and the carboxy oxygen atom occupying the apical position. The fourth equatorial position is taken by a carboxy oxygen atom from another L4 ligand chelating another copper(II) atom in the dimeric cation.The bond lengths Cu(1)–N(1), Cu(1)–N(3) and Cu(1)–N(4) are 1.937(4), 2.081(4) and 1.935(4) Å, respectively, while Cu(2)–N(6), Cu(2)–N(8) and Cu(2)–N(9) are 1.931(4), 2.077(4) and 1.940(4) Å, respectively. The two C–O distances of each carboxylate group are markedly diVerent [1.264(6) and 1.216(7); 1.270(6) and 1.213(7) Å], due to the monodentate m-carboxylate-O bridging mode, and similar to those documented for some bis(carboxylato)- dicopper(II) complexes.24 The intradimeric Cu(1) ? ? ? Cu(2) distance [3.256(2) Å], mainly dominated by the nature and coordination mode of the bridging groups,24,25 is shorter than those found in related dinuclear copper(II) complexes (average Cu ? ? ? Cu 3.4 Å).25 The bond lengths Cu(1)–O(1) [2.263(4) Å] and Cu(2)–O(3) [2.259(4) Å] are significantly longer than Cu(2)–O(1) [1.955(3) Å] and Cu(1)–O(3) [1.949(4) Å], respectively, which is due to the Jahn–Teller-distorted copper(II).26 Similar to complex 3, the reduction of the imine group in 4 is also evident from the bond lengths of N(3)–C and N(8)–C [1.479(7) to 1.497(7) Å].The bond angles centred about the N(3) atom are 109.5(5), 111.2(5), 106.6(3) and 107.6(4)8 for C(6)–N(3)–C(5), C(6)–N(3)–Cu(1), C(5)–N(3)–Cu(1) and C(5)–N(3)–C(11), respectively, which are consistent with a sp3 tetrahedral configuration and show smaller deviations from the idealized geometry. Electronic and EPR spectra The electronic spectral data of the four complexes are listed in Table 3.The UV spectra exhibit an intense absorption band Fig. 5 An ORTEP view of the co-ordination geometry and hydrogen bonding scheme in complex 4.J. Chem. Soc., Dalton Trans., 1999, 1999–2004 2003 at 270–300 nm in DMF solution, which can be attributed to a p* �æ p transition of the conjugated imine chromophore. The complexes exhibit additional weaker and approximately symmetrical absorption bands in visible region at 660–690 nm, which are assigned to d–d transitions.27 It is important to note that the violet shift of the p* �æ p transition for 3 and 4 in comparison to those for 1 and 2 indicates that the imine groups have been reduced, and reinforces this assignment; these observations are consistent with those found for copper(II) complexes with unreduced and reduced SchiV bases condensed with salicylaldehyde and glycine.23 In contrast to the copper(II) complex of the SchiV base derived from Fig. 6 Cyclic voltammograms for complexes (a) 1, (b) 2 and (c) 4 in DMF at room temperature with 0.1 mol L21 Bun 4NPF6 as electrolyte at platinum electrode and SCE reference electrode.Conditions: 1.0 × 1024 mol L21, v = 100 mV s21. Table 3 Electronic and EPR data of complexes 1–4 Electronic spectra (nm) EPR data Complex d–d p* �æ p g|| g^ A||/G 123 4 670.1 688.5 666.5 668.3 299.7 332.9 279.1 272.7 2.307 2.331 2.291 2.301 2.031 2.034 2.042 2.031 180.5 183.5 177.5 g 4.2 2-formylpyridine and histidine, we did not observe decomposition of 1 and 2.6 The EPR spectra recorded on microcrystalline samples at 77 K in DMF solution show axial spectra for complexes 1–3 (Table 3), indicating that 1, 2 and 3 were deaggragated in solution and the copper(II) atom adopts elongated octahedral or squareplanar co-ordination geometry in DMF solution.28 For 4 the EPR spectrum shows an axial spectrum with g|| = 2.301 and g^ = 2.024 and a very weak half-field resonance with g = 4.2 under the same conditions, indicating that 4 remains dimeric in solution. Electrochemistry Complexes 1, 2 and 4 underwent an overall cyclic voltammetric process in DMF containing 0.1 mol L21 of Bun 4NPF6 in the range 2.0 to 22.0 V at room temperature starting with oxidation as shown in Fig. 6. Cyclic voltammetry of 1 displays one reversible wave, one irreversible wave and one quasi-reversible wave. The quasi-reversible redox couple occurs with the oxidation peak at 10.68 V and the corresponding reduction peak at 10.31 V, which may be assigned to the imidazole group of a ligand-based redox couple.The irreversible redox couple occurs with the reduction peak at 20.28 V is assigned to the reaction [CuIIL1]1 1 e æÆ [CuIL1]1 by comparison with the reduction potential value (20.27 V vs. SCE) of CuII–CuI.29 The reversible redox couple (reduction peak at 21.05 V) may be assigned to the imine group of the L1 ligand. Complex 2 exhibits one reversible wave and one irreversible wave [Fig. 6(b)], which supports the assignment of the quasi-reversible redox couple in 1 for the redox of the imidazole group in L1 since 2 does not show a similar quasi-reversible wave in the redox process. Similar to 1, the irreversible and reversible redox couples in 2 were assigned to the reactioIL2]1 1 e æÆ [CuIL2]1 and the imine group of L2, respectively. Cyclic voltammetry of 4 displays two reversible waves, one irreversible and one quasi-reversible. The quasi-reversible redox couple occurs with the oxidation peak at 10.66 V and the corresponding reduction peak at 10.30 V, which is assigned to a ligand-based redox couple.The irreversible redox couple occurs with the reduction peak at 20.28 V and is assigned to the reaction [CuII 2(L4)2]21 1 e æÆ [CuICuII( L4)2]21. The reversible redox couple occurs with the reduction peak at 20.85 V and the corresponding oxidation peak at 20.75 V is a single-electron process, which may be assigned to the reaction [CuICuII(L4)2]21 1 e [CuI 2(L4)2]21.The reversible redox couple occurs at 21.02/20.90 V and may be assigned to a redox process of L4. These observations suggest that ligands L1, L2 and L4 can stabilize the copper(I) ions in the complexes due to the imidazole groups forming p back bonding with the copper(I) atoms. Conclusion The SchiV base ligands containing an imidazole group and balanine and imine-reduced ligands bonding copper(II) have yielded complexes with tri- or tetra-dentate co-ordination modes.The EPR spectra indicate that 1, 2 and 3 were deaggragated in DMF solution, while 4 remains dimeric. The cyclic voltammograms of 1, 2 and 4 indicate that ligands L1, L2 and L4 can stabilize the copper(I) ions in the complexes due to the imidazole groups forming p back bonding with the copper(I) atoms. 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Chem. Soc., 1995, 117, 1965. Paper 9/03154E

ISSN:1477-9226    

DOI:10.1039/a903154e

出版商:RSC    

年代:1999

数据来源: RSC