DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 317–320 317 Synthesis and characterization of Group 11 and 12 complexes containing a new thioether-functionalized and pyridine-based bis(phosphine) ligand, 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl] pyridine Shan-Ming Kuang,a Zheng-Zhi Zhang *,b and Thomas C. W. Mak*,a a The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong b Elemento-Organic Chemistry Laboratory, Nankai University, Tianjin, China The new ligand 2,6-bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2C5H3N (L1), has been synthesized.Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar equivalent of L1 gave [CuL1][CF3SO3] 1 or [AgL1][NO3] 2, in good yield. Reaction of equimolar quantities of L1 and AuI, followed by precipitation with AgO3SCF3, gave [AuL1][CF3SO3] 3. In the crystal structure of 2?H2O, L1 co-ordinates to Ag via a P2S2 donor set in a distorted tetrahedral geometry.Reaction of M(O3SCF3)2 (M = Zn or Cd) with 1 molar equivalent of L1 gave [ML1(O3SCF3)2] (M = Zn 4 or Cd 5). Crystal structure analysis of 5 showed that the molecule has symmetry 2, with all five donor atoms of L1 and a pair of monodentate CF3SO3 2 ligands arranged in an unusual distorted pentagonal bipyramidal co-ordination geometry about the cadmium centre. Acyclic phosphine ligands are well known to form stable complexes with many metal ions, whereas acyclic thioether complexes tend to be less stable and often hydrolyse readily.1 As the NS2 donor set in 2,6-bis(R-sulfanylmethyl)pyridine has been found to be good for the stabilization of transition-metal ions,2 we reasoned that the incorporation of heteroatom donors, such as nitrogen or sulfur, on sites within a diphosphine bridge might result in transition-metal complexes co-ordinated by sulfur (or nitrogen) and the phosphorus centres.We anticipated that, as phosphines are better s donors compared to thioethers, stabilization of a mixed phosphine–thioether co-ordination complex could be achieved by inhibiting decomplexation of the more weakly bound thioether in solution. In this context, recent reports by Darensbourg and co-workers 3 and Reid and coworkers 4 have demonstrated the development and coordination chemistry of dithiobis(phosphine) chelates.We report here the synthesis and characterization of Group 11 and 12 complexes with a new thioether-functionalized and pyridine-based bis(phosphine) ligand, 2,6-bis[2-(diphenylphosphino) ethylsulfanylmethyl]pyridine, 2,6-(Ph2PCH2CH2SCH2)2- C5H3N (L1), which displays an unusual co-ordination mode toward Cd21.Experimental General procedure, measurement and materials All reactions were routinely carried out under a nitrogen atmosphere using Schlenk techniques. The solvents were puri- fied by standard methods. The 1H and 13C-{1H} NMR spectra were recorded on a Bruker-300 spectrometer using SiMe4 as the external standard and CDCl3 as solvent, 31P-{1H} NMR spectra on a Bruker-500 spectrometer at 202.45 MHz using (PhO)3P as the external standard and CDCl3 as solvent and mass spectra on a Hewlett-Packard 5989B spectrometer. The compounds [Cu(MeCN)4][CF3SO3] 5 and M(O3SCF3)2 (M = Zn or Cd)6 were prepared by the literature procedures.Preparations 2,6-Bis[2-(diphenylphosphino)ethylsulfanylmethyl]pyridine, L1. A solution of LiBun in hexane (1.60 M, 17.0 cm3) was added dropwise to a solution of Ph2PH (4.65 g, 25 mmol) in tetrahydrofuran (thf, 50 cm3) at 278 8C.To this mixture, a solution of ethylene sulfide (thiirane) (1.50 cm3, 25 mmol) in thf (20 cm3) was added. The resulting solution was continuously stirred until 0 8C was reached, and a solution of 2,6-bis(chloromethyl)- pyridine (2.20 g, 12.5 mmol) in thf (80 cm3) was then added over a period of 3 h with the temperature maintained at 0 8C. After the addition the mixture was stirred at room temperature for 48 h.The thf was removed in vacuum and water (100 cm3) added. The water phase was next extracted with diethyl ether (3 × 50 cm3) and the organic phase dried with anhydrous Na2SO4 overnight. Most of the diethyl ether was removed in vacuum and hexane (100 cm3) was added. Cooling to 230 8C for 8 h yielded a colourless solid. Recrystallization from CH2Cl2–hexane afforded L1 as an analytically pure product, 5.30 g (71%) (Found: C, 70.24; H, 5.88; N, 2.27. C35H35NP2S requires C, 70.56; H, 5.92; N, 2.35%), m.p. 52–53 8C. 1H NMR (CDCl3): d 7.52 (t, J = 3.5, 1 H), 7.36–7.25 (m, 20 H), 7.05 (d, J = 2.2 Hz, 2 H), 3.73 (s, 4 H), 2.50 (m, 4 H) and 2.26 (m, 4 H). 13C-{1H} NMR (CDCl3): d 28.73 (d, J = 20.3), 28.96 (d, J = 14.9 Hz), 38.56 (s) and 121.65–138.57 (m). 31P-{1H} NMR: d 24.54. FAB mass spectrum: m/z = 596; Calc. 595 for (Ph2PCH2CH2- SCH2)2C5H3N. [CuL1][CF3SO3] 1. To a solution containing compound L1 (0.30 g, 0.5 mmol) in CH2Cl2 (20 cm3) was added solid [Cu- (MeCN)4][CF3SO3] (0.19 g, 0.5 mmol).The resulting solution was stirred at room temperature for 2 h. Subsequent diffusion of diethyl ether into the concentrated solution gave complex 1 as air-stable colourless crystals (yield 0.34 g, 84%) (Found: C, 53.21; H, 4.71; N, 1.78. C36H35CuF3NO3P2S3 requires C, 53.49; H, 4.36; N, 1.73%). 31P-{1H} NMR: d 34.72. [AgL1][NO3] 2. The procedure used was similar to that above, except that AgNO3 (0.09 g, 0.5 mmol) was employed instead of [Cu(MeCN)4][CF3SO3].Recrystallization of the product from CH2Cl2–diethyl ether afforded complex 2?H2O as colourless crystals. Yield: 0.29 g (76%) (Found: C, 54.99; H, 4.61; N, 3.55. C35H35AgN2O3P2S2?H2O requires C, 54.86; H, 4.72; N, 3.57%). 31P-{1H} NMR: d 43.14. [AuL1][CF3SO3] 3. The complex K[AuCl4]?2H2O (0.10 g, 0.25 mmol) was reduced to AuI by 2,29-thiodiethanol (0.06 g, 0.5318 J. Chem. Soc., Dalton Trans., 1998, Pages 317–320 mmol) in methanol (20 cm3) for 30 min.Compound L1 (0.15 g, 0.25 mmol) in CH2Cl2 (10 cm3) was added and stirred for 10 min, and then AgO3SCF3 (0.26 g, 1.0 mmol) in methanol (20 cm3) was added to the mixture and stirred for 30 min. Filtration followed by solvent removal and subsequent recrystallization from CH2Cl2–hexane afforded complex 3 as colourless crystals. Yield: 0.15 g (81%) (Found: C, 45.78; H, 3.77; N, 1.41. C36H35AuF3NO3P2S3 requires C, 45.91; H, 3.75; N, 1.49%). 31P- {1H} NMR: d 42.91.[ZnL1][CF3SO3]2 4. To a solution containing compound L1 (0.30 g, 0.5 mmol) in CH2Cl2 (20 cm3) was added solid Zn(O3- SCF3)2 (0.18 g, 0.5 mmol). The resulting solution was stirred at room temperature for 2 h. Subsequent diffusion of diethyl ether into the concentrated solution gave complex 4 as air-stable colourless crystals (yield 0.40 g, 77%) (Found: C, 43.95; H, 3.67; N, 1.33. C37H35F6NO3P2S4Zn?CH2Cl2 requires C, 43.71; H, 3.57; N, 1.34%). 31P-{1H} NMR: d 56.53. [CdL1(O3SCF3)2] 5.The procedure used was similar to that above, except that Cd(O3SCF3)2 (0.21 g, 0.5 mmol) was used instead of Zn(O3SCF3)2. Recrystallization of the product from CH2Cl2–hexane afforded complex 5 as colourless crystals. Yield: 0.32 g (64%) (Found: C, 43.37; H, 3.49; N, 1.34. C37H35- CdF6NO6P2S4 requires C, 44.16; H, 3.51; N, 1.39%). 31P-{1H} NMR: d 55.09. X-Ray crystallography Intensity data for complexes 2?H2O and 5 were collected at 294 K in the variable w-scan mode on a four-circle diffractometer (Siemens R3m/V) using Mo-Ka radiation (l = 0.710 73 Å, 50 kV, 25 mA; 2qmin = 3, 2qmax = 558).Empirical absorption corrections were applied by fitting a pseudo-ellipsoid to the y-scan data of 25 selected strong reflections over a range of 2q angles.7a Structure solution by the direct method yielded the positions of all non-hydrogen atoms, which were refined using anisotropic thermal parameters. Hydrogen atoms were all generated geometrically (C]H bond lengths fixed at 0.96 Å), assigned appropriate isotropic thermal parameters, and allowed to ride on their parent carbon atoms.All the H atoms were held stationary and included in the structure-factor calculation in the final stage of full-matrix least-squares refinement. All computations were performed on an IBM-compatible 486 personal computer with the SHELTX PC, version 5.03, program package.7b Information concerning X-ray data collection and structure refinement of all compounds is summarized in Table 1.CCDC reference number 186/780. Results and Discussion The synthesis of a new thioether-functionalized and pyridinebased bis(phosphine) ligand, namely 2,6-bis[2-(diphenylphosphino) ethylsulfanylmethyl]pyridine (L1), was accomplished in two steps in good yield, as outlined in Scheme 1. Reaction of Ph2PLi (prepared ‘in situ’ from Ph2PH and LiBun) with ethylene sulfide at low temperature gave the lithium 2-diphenylphosphinoethanethiolate salt, which then reacted with 2,6-bis- (chloromethyl)pyridine to give the designed phosphine ligand.The structure of 2,6-(Ph2PCH2CH2SCH2)2C5H3N, L1, was confirmed by elemental analysis and 1H, 13C-{1H}, 31P-{1H} NMR spectroscopy and FAB mass spectrometry. In the 1H NMR spectrum the SCH2C5H3N methylene protons appeared as a singlet at d 3.73 and two groups of signals attributed to the SCH2CP and SCCH2P methylene protons coupled with the phosphorus atoms were observed at d 2.50 and 2.26.In the 13C- {1H} NMR spectrum the SCC5H3N carbon atom appeared as a singlet at d 38.56, whereas the SCCP carbon atoms appeared as a pair of doublets centred at d 28.73 (J = 20.3) and 28.96 (J = 14.9 Hz). On the basis of literature data for P]C coupling constants 8 and the observed chemical shifts for related phosphine-containing ligands, we assigned the first and second doublets to the carbon atoms located in the a and b positions, respectively, with respect to the phosphorus atom.The FAB mass spectrum showed the molecular ion at m/z = 596, and the 31P-{1H} NMR spectrum exhibited a singlet at d 24.54. Reaction of [Cu(MeCN)4][CF3SO3] or AgNO3 with 1 molar equivalent of L1 in degassed dichloromethane, followed by precipitation with diethyl ether, gave [CuL1][CF3SO3] 1 or [AgL1][NO3] 2, as white solids in good yield. Reaction of equimolar amounts of L1 and AuI, generated in situ by the reduction of K[AuCl4] with 2,29-thiodiethanol in methanol, gave a colourless solution at room temperature.Addition of AgO3SCF3 to the solution precipitated [AuL1][CF3SO3] 3, as a white solid. The 31P-{1H} NMR spectra of complexes 1 and 2 at 298 K showed a singlet at d 34.72 and 43.14, respectively, and no Ag]P coupling was observed for 2. For complex 3 the 31P-{1H} NMR spectrum displayed a high-frequency shift of 47.4 ppm relative to the free phosphine. This shift is similar to those of the complexes [Au{(Ph2PCH2CH2SCH2)2}][PF6] (49.2 ppm) and [Au{(Ph2PCH2CH2SCH2)2CH2}][PF6] (46.1 ppm),4b both of which involve averaged P2 co-ordination in solution.In view of the similarity of these species, we expect that in the solid state 3 also adopts a similar primary P2 co-ordination about AuI and a distorted linear geometry. Crystals of [AgL1][NO3]?H2O suitable for single-crystal Xray study were obtained by layering a solution of the complex in CH2Cl2 at ca. 220 8C with toluene. The structure of the molecular cation with the atom numbering scheme is depicted in Fig. 1. The co-ordination geometry around silver(I) may be described as a very distorted tetrahedron with a P]Ag]P angle of 144.4(1)8 (Table 2), far higher than the idealized value of 109.58. This is certainly caused by the repulsion between two phenyl rings [C(26) ? ? ? C(36) 3.690 Å] which has the further consequence of narrowing the S]Ag]P bond angles to 80.2(1) and 81.3(1)8. A similar effect has been reported in [Ag(Ph2PScheme 1 S N Cl Cl Ph2PH Ph2PLi Ph2P SLi N S PPh2 S PPh2 LiBun Fig. 1 Perspective view of the cation in [Ag{(Ph2PCH2CH2SCH2)2- C5H3N}][NO3]?H2O, 2?H2O. The atoms are shown as 35% thermal ellipsoidsJ. Chem. Soc., Dalton Trans., 1998, Pages 317–320 319 CH2CH2SEt)2][ClO4] with a P]Ag]P angle of 148.9(1)8.9 The Ag(1) ? ? ? N(1) distance of 2.689 Å, much longer than the corresponding distance of 2.368(6) Å in [AgL2][PF6] [L2 = 6,9,12- trioxa-3,15-dithia-21-azabicyclo[15.3.1]henicosa-1(21),17,19- triene],10 indicates that the Ag ? ? ? N interaction is very feeble, which is consistent with the fact that the nitrogen lone pair does not point directly toward the silver atom (Fig. 1). The Ag]P distances of 2.455(3) and 2.448(3) Å are within the expected range for silver tertiary phosphine complexes. The Ag]S distances of 2.869(3) and 2.846(3) Å, which are longer than 2.694(2) Å in [Ag(Ph2PCH2CH2SEt)2][ClO4] 9 and 2.589(2) Å (average) in [Agn(PhSCH2CH2CH2SPh)2n][BF4]n?0.5nH2O,11 suggest that the silver ion is weakly bound to the sulfur atoms.Reactions of M(O3SCF3)2 (M = Zn or Cd) with 1 molar equivalent of L1 in dichloromethane at room temperature gave a colourless solution which on addition of diethyl ether gave [ML1(O3SCF3)2] (M = Zn 4 or Cd 5). The 31P-{1H} NMR spectra of 4 and 5 at 298 K showed a singlet at d 56.53 and 55.09, respectively, and no Cd]P coupling was observed for 5. Diffraction-quality crystals of [CdL1(O3SCF3)2] 5 were obtained by vapour diffusion of diethyl ether into a solution of the complex in CH2Cl2 at room temperature. A perspective view of the molecular structure of 5, which possesses a crystallographically imposed two-fold axis passing through Cd, N and C(6), is illustrated in Fig. 2. The co-ordination geometry about the cadmium centre is a distorted pentagonal bipyramid, with Table 1 Crystal and structural data for complexes 2?H2O and 5 Formula M Crystal system Space group a/Å b/Å c/Å U/Å3 ZF (000) Dc/g cm23 m/cm21 Goodness of fit No.unique reflections (Rint) No. observed reflections [|F | > 4s(F)] No. variables, p RF a R9F 2 b C35H35AgN2O3P2S2? H2O 2?H2O 783.6 Orthorhombic P212121 9.875(1) 12.585(5) 28.362(3) 3524.7(12) 4 1608 1.477 0.821 1.22 4909 (0.027) 3183 410 0.053 0.087 C37H35CdF6NO6P2S4 5 1006.2 Trigonal P3221 18.072(3) 18.072(3) 12.099(2) 3425(2) 3 1524 1.464 0.797 1.10 4876 (0.030) 4561 263 0.049 0.052 a S(|Fo| 2 |Fc|)/S|Fo|. b {w[S(|Fo| 2 |Fc|)2]/S|Fo|2}� �� .Table 2 Selected bond lengths (Å) and angles (8) of complexes 2?H2O and 5 2?H2O Ag]P(1) Ag]S(1) P(1)]Ag]P(2) P(1)]Ag]S(2) S(1)]Ag]S(2) 2.455(3) 2.869(3) 144.4(1) 110.5(1) 142.7(1) Ag]P(2) Ag]S(2) P(1)]Ag]S(1) P(2)]Ag]S(1) P(2)]Ag]S(2) 2.448(3) 2.846(3) 80.2(1) 111.2(1) 81.3(1) 5 Cd]P(1) Cd]O(1) P(1)]Cd]S(1) S(1)]Cd]O(1) S(1)]Cd]N P(1)]Cd]P(1a) O(1)]Cd]O(1a) P(1)]Cd]O(1a) 2.590(1) 2.455(2) 79.9(1) 75.8(1) 70.1(1) 166.8(1) 69.5(2) 93.8(1) Cd]S(1) Cd]N(1) P(1)]Cd]O(1) P(1)]Cd]N O(1)]Cd]N S(1)]Cd]S(1a) P(1)]Cd]S(1a) S(1)]Cd]O(1a) 2.821(1) 2.695(3) 97.1(1) 83.4(1) 145.2(1) 140.1(1) 95.6(1) 143.7(1) coplanar O(1), S(1), N, S(1a) and O(1a) atoms at the equatorial sites, and P(1) and P(1a) occupying the axial positions.The seven-co-ordinate geometry observed in this complex is largely a result of the constraints imposed by the pentadentate ligand. Since there is no ligand-field stabilization effect in Cd21, the stereochemistry of its complexes is in general determined by ionic size, electrostatics, and covalent bonding energies.13 Owing to its size, Cd21 commonly has a co-ordination number of six as in CdCl2, [CdCl2(NH3)2], [CdCl(OH)], K4[CdCl4], CdI2 and Cd(OH)2.14 However, a seven-co-ordinate, distorted pentagonal bipyramidal complex of Cd21 containing a thioether ligand is known, namely [Cd([15]aneS5)][ClO4]2?H2O ([15]- aneS5 = 1,4,7,10,13-pentathiacyclopentadecane).15 The P(1)]Cd]S(1) and P(1)]Cd]N angles are somewhat acute [79.9(1) and 83.4(1)8, respectively], while P(1)]Cd]S(1a) and P(1)]Cd]O(1) are somewhat obtuse [95.6(1) and 97.1(1)8].This distortion is attributable to the geometrical constraints imposed by the ligand, as the ethylene bridges between S and P atoms do not allow P(1) and P(1a) to pull away far enough from each other. The P(1)]Cd]P(1a) angle of 166.8(1)8 is accordingly less than the ideal value of 1808. The P]Cd bond length of 2.590(1) Å is close to the sum of covalent radii for cadmium and phosphorus (1.48 1 1.10 = 2.58 Å) 16 and also comparable to 2.602(2) Å found in [Cd{P(C6H11)3}2][NO3]2?CH2Cl2.17 The Cd]S bond length of 2.821(1) Å is comparable to those of [Cd([15]aneS5)][ClO4]2?Cd]Sav 2.76 Å) 15 and significantly longer than 2.703(1) Å in the six-co-ordinate complex [{CdL2Cl2?H2O}2] [L2 = 2,6- bis(ethylsulfanylmethyl)pyridine] 18 and four-co-ordinate complex [Cd([16]aneS4)][ClO4]2 (Cd]Sav 2.65 Å) ([16]aneS4 = 1,5,9,13-tetrathiacyclohexadecane).19 It has been observed that in mercury(II) thioether complexes 20 the metal–sulfur bond lengths are a function of the number of donor atoms.As the co-ordination number of the metal centre goes up, its bonds to sulfur are lengthened. Hence it is not surprising that the seven-co-ordinate complex 5 has such long Cd]S bonds compared to those of an analogous six- or four-co-ordinate complex. The Cd]N bond distance of 2.695(3) Å is also longer than 2.380(3) Å in the six-co-ordinate, dimeric complex [{CdL2Cl2?H2O}2].18 Acknowledgements This work is supported by Hong Kong Research Grants Council Earmarked Grant Ref.No. CUHK 311/94P and the National Natural Science Foundation of China. Fig. 2 An ORTEP12 view of the [Cd{(Ph2PCH2CH2SCH2)2C5H3N}- (O3SCF3)2] molecule, 5. The atoms are shown as 35% thermal ellipsoids. Note that a two-fold symmetry axis passes through the Cd, N and C(6) atoms320 J. Chem. Soc., Dalton Trans., 1998, Pages 317–320 References 1 S.G. Murray and F. R. Hartley, Chem. Rev., 1981, 81, 365. 2 See, for example, F. Teixidor, L. Escriche, J. Casabó, E. Molins and C. Miravitlles, Inorg. Chem., 1986, 25, 4060; J. Casabó, L. Escriche, S. Alegret, C. Jaime, C. Perez-Jimenez, L. Mestres, J. Rius, E. Molins, C. Miravitlles and F. Teixidor, Inorg. Chem., 1991, 30, 1893; F. Teixidor, G. Sánchez-Castelló, N. Lucena, L. Escriche, R. Kivekäs, M. Sundberg and J. 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Chem., 1986, 39, 7. 18 F. Teixidor, L. Escriche, I. Rodriguez, J. Casabó, J. Rius, E. Molins, B. Martínez and C. Miravitlles, J. Chem. Soc., Dalton Trans., 1989, 1381. 19 W. N. Setzer, Y. Tang, G. J. Grant and D. G. VanDerveer, Inorg. Chem., 1991, 30, 3652. 20 W. N. Setzer, Q. Guo, G. J. Grant, J. L. Hubbard, R. S. Glass and D. G. VanDerveer, Heteroatom Chem., 1990, 1, 317. Received 8th September 1997; Paper 7/06543D © Copyright 1998 by the Royal Society of Chemistry