摘要:

Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Weak long-range spin–spin exchange interactions in a copper(II) complex Gennadii M. Larin,*a Viktor F. Shul’ginb and Elena A. Sarnitb aN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow, Russian Federation. Fax: +7 095 954 1279; e-mail: lagema@ionchran.rinet.ru bDepartment of Natural Sciences, Simferopol State University, 333036 Simferopol, Ukraine.Fax: +7 0652 23 2310; e-mail: vshul@ccssu.crimea.ua The molecular structure of the binuclear copper complex [Cu2L·2py·2MeOH]·2H2O of glutaric acid bis(salicylidene)hydrazone (H4L) was found by single-crystal X-ray diffraction analysis, and the EPR spectrum of this complex in solution was interpreted. The synthesis and EPR spectra of binuclear copper complexes of dicarbonic acid bis(salicylidene)hydrazones in which two copper atoms are connected by a polymethylene chain have been described recently.1 It was suggested that an exchange interaction between the paramagnetic ions through a chain of s-bonds in these complexes takes place.Here we report the results of single-crystal X-ray diffraction analysis of the copper complex of glutaric acid bis(salicylidene)hydrazone (H4L): The compound was prepared according to the procedure described earlier.1 Single crystals were prepared by recrystallization from a mixture of methanol with pyridine (20–30 vol%).The composition of the complex corresponds to the formula [Cu2L·2py·2MeOH]·2H2O (1). The crystal structure and EPR spectra of compound 1 were examined.† We found that molecular crystals of 1 are formed of discrete binuclear complexes [Cu2L·2py·2MeOH] (Figure 1) without short † The X-ray diffraction analysis of a single crystal of complex 1 with the linear dimensions 0.25×0.26×0.50 mm was carried out at ambient temperature on an Enraf-Nonius CAD-4 four-circle diffractometer (MoKa radiation, l = 0.71069 Å, the ratio of scanning speeds w/2q was 1.2, qmax 27°, segment of sphere –27 £ h £ 24, 0 £ k £ 21, 0 £ l £ 13).For the determination of the parameters of an elementary cell and the orientation matrix, 22 reflections with 12.4 < q < 12.9° were used. 4122 reflections were collected (3787 unique reflections). Crystals of 1 are monoclinic, a = 21.383(16) Å, b = 16.866(8) Å, c = 10.712(11) Å, b = 114.75(7)°, V = 3508.4 Å3, M = 749.76, Z = 4, dcalc = 1.42 g cm–3, m = 12.68 cm–1.Space group C2/c. The structure was solved by a direct method and refined by a full-matrix least-squares technique using the CRYSTALS structure solution package.2 In the specification, 2672 reflections with I > 4s(I) (207 refined parameters, the number of reflections per parameter 8.7) were used.All hydrogen atoms (except for H atoms of the disordered methyl group) were revealed objectively from the difference synthesis of electron densities and were included in the specification with fixed thermal and item parameters. The consideration of the absorption in a crystal was performed by the method of azimuth scanning.3 In the refinement, the Tchebycheff weight function4 with the parameters 1.20, –0.86, 0.45 and –0.84 was used.The final values were R = 0.059 and Rw = 0.065. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 1999. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/52.The EPR spectra were recorded on a PS 100X spectrometer5 [concentration ~5×10–3 M, solution in CHCl3 + pyridine (20 vol%)]. The simulation of the EPR spectrum was carried out using the program package described elsewhere.6 intermolecular contacts. Two outer-sphere water molecules are located in the cavities of the crystal structure.The coordination polyhedra of the copper atoms are equivalent and connected by the second-order axis; the Cu–Cu distance is 9.182 Å. The coordination polyhedra of the copper atoms exhibit the geometry of a distorted tetragonal pyramid the base of which is formed by a nitrogen atom and two oxygen atoms of the twice-deprotonated imidol form of salicylidenehydrazone and the nitrogen atom of pyridine.The apex of the pyramid is occupied by a weekly bonded methanol molecule. The angles at the copper atom are deflected from the ideal values 90.0 and 180.0° by 9.5°. The distances Cu–O(2) (1.969 Å) and Cu–N(1) (1.926 Å) are typical of copper complexes with the deprotonated imidol form of salicylidenehydrazone (1.96–1.98 and 1.92–1.94 Å, respectively).7,8 At the same time, the copper–phenoxyl oxygen distance (1.901 Å) is shorter that that in dimeric complexes (1.92–2.04 Å) with bridging oxygen.7,8 This can result from the disappearance of steric hindrances upon terminal coordination of the phenoxyl unit of the ligand.The distance between the copper atom and the oxygen atom of a methanol molecule suggests the formation of a weak coordination bond, which is typical of square-pyramidal copper complexes of salicylidenehydrazone.However, the Cu–O distance (2.422 Å) is longer than an analogous bond length of a coordinated ethanol molecule (2.22–2.31 Å) in dimeric complexes.7,8 The carbon atom of a methyl group is disordered and occupies two approximately equivalent positions. The bonds C(1)–O(1) (1.309 Å), C(8)–O(2) (1.274 Å) and N(1)–N(2) (1.392 Å) are noticeably shorter that ordinary bonds; moreover, the bonds C(8)–N(2) (1.312 Å) and C(7)–N(1) (1.285 Å) are longer than double bonds.9 This fact OH N H N H O N O N H H HO C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(8a) C(9) C(9a) C(10) C(11) C(12) C(13) C(14) C(15) O(1) O(2) O(3) N(1) N(2) N(3) Cu(1) Figure 1 Molecular structure of complex 1 (the symbol ‘a’ was utilised for the atoms connected with initial by the axis 2).Selected bond lengths (Å): Cu(1)–O(1) 1.901(3), Cu(1)–O(2) 1.969(3), Cu(1)–O(3) 2.422(12), Cu(1)–N(1) 1.926(4), Cu(1)–N(3) 2.008(4), O(1)–C(1) 1.309(5), O(2)– C(8) 1.274(5), N(1)–N(2) 1.392(4), N(1)–C(7) 1.285(5), N(2)–C(8) 1.312(5), N(3)–C(11) 1.343(6), N(3)–C(15) 1.335(6), C(6)–C(7) 1.435(5), C(8)– C(9) 1.511(5), C(9)–C(10) 1.525(4); selected bond angles (°): O(1)–Cu(1)– O(2) 170.49(13), O(1)–Cu(1)–O(3) 94.7(3), O(2)–Cu(1)–O(3) 92.9(3), O(1)–Cu(1)–N(1) 92.99(16), O(2)–Cu(1)–N(1) 80.78(15), O(3)–Cu(1)– N(1) 94.0(3), O(1)–Cu(1)–N(3) 90.88(16), O(2)–Cu(1)–N(3) 94.57(16), O(3)–Cu(1)–N(3) 91.8(3), N(1)–Cu(1)–N(3) 172.69(14), Cu(1)–O(1)–C(1) 126.6(3), Cu(1)–O(2)–C(8) 109.8(2), Cu(1)–N(1)–N(2) 114.7(2), Cu(1)– N(1)–C(7) 127.2(3), N(2)–N(1)–C(7) 118.0(3), N(1)–N(2)–C(8) 109.5(3), Cu(1)–N(3)–C(11) 120.5(3), Cu(1)–N(3)–C(15) 121.2(3), C(11)–N(3)– C(15) 118.3(4).Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) may be indicative of delocalization of the double bonds in the chelates and formation of a pseudo-aromatic system.The bond lengths and valence angles of hydrazone hydrocarbon radicals and pyridine take standard values. The group Cu(1)–O(1)–O(2)–N(1–3)–C(1–8,11–15) is approximately planar; the deviations of atoms from a plane are no higher than 0.38 Å. The atoms C(9) and C(10) are deflected from the plane by 0.51 and 0.52 Å, respectively. The Cu(1)– O(1)–N(1)–C(1)–C(6)–C(7) heterocycle is planar to within 0.078 Å, but the Cu(1)–O(2)–N(1)–N(2)–C(8), C(1–6) and N(3)–C(11–15) rings form dihedral angles of 7.2, 6.8 and 17.0°, respectively.The symmetrically connected groups Cu(1)–O(1)– O(2)–N(1)–N(2)–C(1–8) and Cu(1a)–O(1a)–O(2a)–N(1a)–N(2a)– C(1a–8a) are virtually perpendicular to one another; the corresponding dihedral angle is 81.88°. Thus, the X-ray diffraction analysis demonstrated that binuclear complex 1 is monomeric and contains two copper cations connected by a chain of eight s-bonds at a distance of 9.182 Å.Because of this, an independent behaviour of the paramagnetic centres would be expected. However, the EPR spectrum of a solution of complex 1 in MeCl–pyridine exhibits a seven-line isotropic signal of hyperfine structure with the intensity ratio 1:2:3:4:3:2:1 and the parameters g = 2.106; aCu = 39.9×10–4 cm–1 (Figure 2) was observed.This spectrum was interpreted as a result of single-electron interactions with two equivalent nuclei of copper atoms. The solution of the spin-Hamiltonian for this system10 shows that the hyperfine structure constant is equal to a half of the constant for the monomeric complexes, i.e., about 40×10–4 cm–1.A theoretical simulation of the EPR spectrum confirms this conclusion (Figure 2). Seven lines with the above intensity ratio and hyperfine structure constants were usually observed in EPR spectra at forbidden transitions of dimeric copper complexes10,11 which exhibit strong antiferromagnetic interactions (of several tens or hundreds of cm–1).At allowed transitions, the isotropic EPR spectra of the binuclear copper complexes exhibit seven lines of the hyperfine structure at a lower energy (0.1–1 cm–1).6,12,13 It is believed that the bond lengths and valence angles in molecules of 1 in solution and in the solid state are similar, because the Cu–Cu distance in solutions and single crystals are similar. Consequently, the weak spin–spin exchange interaction in compound 1 can be realised by delocalization of single electrons via a s-bond chain of the polymethylene bridge.References 1 V. F. Shul’gin, E. A. Sarnit and G. M. Larin, Koord. Khim., 1998, 24, 22 (Russ. J. Coord. Chem., 1998, 24, 20). 2 D. J. Watkin, C. K. Prout, J. R. Carruthers and P.W. Betteridge, Crystals, Issue 10, Chemical Crystallography Laboratory, Univ.of Oxford, 1996. 3 A. C. T. North, D. C. Phillips, F. Scott and F. S. Mathews, Acta Cryst. (A), 1968, 24, 351. 4 J. R. Carruthers and D. J. Watkin, Acta Cryst. (A), 1979, 35, 698. 5 G. M. Larin, S. V. Skokov, V. V. Minin and O. L. Kaliya, Koord. Khim., 1993, 19, 305 (Russ. J. Coord. Chem., 1993, 19, 346). 6 Yu. V. Rakitin, G. M. Larin and V. V. Minin, Interpretatsiya spektrov EPR koordinatsionnykh soedinenii (Interpretation of EPR spectra of coordination compounds), Nauka, Moscow, 1993 (in Russian). 7 V. F. Shul’gin, O. V. Konnik, K. V. Rabotyagov, I. L. Eremenko, S. E. Nefedov, O. G. Ellert, V. M. Sherbakov, Yu. T. Strutchkov and V. M. Novotortsev, Zh. Neorg. Khim., 1994, 39, 450 (Russ. J. Inorg. Chem., 1994, 39, 428). 8 V. F. Shul’gin, O. V. Konnik, K. V. Rabotyagov, I. L. Eremenko, O. G. Ellert, V. M. Sherbakov, Yu. T. Strutchkov and V. M. Novotortsev, Koord. Khim., 1994, 20, 703 (Russ. J. Coord. Chem., 1994, 20, 661). 9 G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G. Watson and R. Taylor, J. Chem. Soc., Dalton Trans., 1989, 1. 10 T. D. Smith and J. R. Pilbrow, Coord. Chem. Rev., 1974, 13, 173. 11 Yu. V. Rakitin, Koord. Khim., 1981, 7, 1311 (Sov. J. Coord. Chem., 1981, 7, 656). 12 G. M. Larin, B. B. Umarov, V. V. Minin, Yu. V. Rakitin, V. G. Yusupov, N. A. Parpiev and Yu. A. Buslaev, Dokl. Akad. Nauk SSSR, 1988, 303, 139 (in Russian). 13 G. M. Larin, Yu. V. Rakitin and V. V. Minin, Neorg. Mater., 1994, 30, 1424 [Inorg. Mater. (Engl. Transl.), 1994, 30, 1327]. 1 2 2800 3200 3600 H/G Figure 2 (1) Experimental and (2) theoretical EPR spectra of complex 1. Received: 24th March 1999; Com. 99/1466

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Cryochemical synthesis and properties of silver nanoparticle dispersions stabilised by poly(2-dimethylaminoethyl methacrylate) Boris M. Sergeev,*a Viktor A. Kasaikin,a Ekaterina A. Litmanovich,a Gleb B. Sergeeva and Andrei N. Prusovb a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation.E-mail: bms@cryo.chem.msu.su b A. N. Belozersky Institute of Physico-chemical Biology, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 3181 A cryochemical synthesis of silver nanoparticles stabilised by poly(2-dimethylaminoethyl methacrylate) (poly-DMAEMA) has been performed; it has been found using optical spectroscopy, dynamic light scattering and electron microscopy that silver sols prepared with these nanoparticles in water, acetone and toluene are sterically stabilised by macromolecular poly-DMAEMA layers formed at the surface of nanoparticles, and the thickness of these layers depends on the nature of the solvent.The cryochemical synthesis of nanoparticles includes simultaneous evaporation of a metal and a volatile component, for example, an organic monomer, followed by co-condensation of the vapours onto a cold surface of the vacuum reactor.1 Previously, stable silver organosols in the presence of methyl acrylate and poly(methyl acrylate) films containing metal particles of sizes not exceeding 15 nm were prepared.2 In this study, we decided on poly(2-dimethylaminoethyl methacrylate) (poly-DMAEMA) as a polymer stabiliser for silver nanoparticles.In contrast to poly(methyl acrylate), poly- DMAEMA is soluble in solvents different in polarity. This fact made it possible to disperse the nanoparticles, stabilised by this polymer in the course of the cryochemical synthesis of the Ag–DMAEMA system, in water, acetone and toluene and to examine the sols by optical absorption spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering. The procedures used for the cryochemical synthesis of Ag– DMAEMA organic dispersions and for the evaluation of the DMAEMA conversion into poly-DMAEMA were analogous to those described earlier.2 We found that the conversion was 1.7–1.9% and remained unchanged as the Ag:DMAEMA molar ratio increased from 1:4000 to 1:1000.The mechanism of DMAEMA polymerization in the test system is of particular interest and does not enter into the scope of this work. The stability of an Ag–DMAEMA organic dispersion obtained at the molar ratio Ag:DMAEMA ª 1:4000 in the co-condensate was examined by optical absorption spectroscopy (Figure 1). It can be seen that the surface plasmon band of small isolated spherical silver particles3,4 in the spectrum of the freshly prepared Ag–DMAEMA organosol (Figure 1, curve 1) was broadened and insignificantly shifted towards the short-wave region three days after, and a long-wave shoulder appeared (curve 2).These spectral changes are indicative of the formation of an amount of silver nanoparticle aggregates in the test organosol.4–6 The fact that the spectrum remained almost unchanged over a month (Figure 1, curve 3) indicates that the sol is highly stable at room temperature.A solid silver-containing poly-DMAEMA film was formed after the removal of DMAEMA from the initial organic dispersion under vacuum. Silver sols in solvents of different polarity can be prepared by dispersing this film in water, acetone and toluene.Because the spectra of these sols (Figure 2) are similar to those shown in Figure 1 (curves 2 and 3), we can conclude that drying of the organic dispersion was also accompanied by partial aggregation. The state of poly-DMAEMA layers that stabilise the nanoparticles in water, acetone and toluene was examined by dynamic light scattering. The measurements were performed on an ALV-5 scattered laser light goniometer (Germany) at an angle of 90°.A He–Ne laser (25 mW, l = 633 nm) was used as the light source. The mean radii Rm of light-scattering particles in sols (Table 1) were calculated by the method of cumulants.7 Afterwards, the particle size distribution of sols as determined by analysing the autocorrelation functions G(t) of scatteredlight intensity fluctuations using the Tikhonov regularisation procedure8 with an accuracy of 25% or better.The size-distribution functions of all examined sols showed two distinct modes differing in translation diffusion coefficients. As an example, Figure 3 (points) shows the experimental function G(t) obtained by examining an aqueous sol at an aquisition time 2.5 2.0 1.5 1.0 0.5 0.0 300 400 500 600 700 800 3 2 1 Absorption l/nm 1 2,3 Figure 1 Absorption spectra of an Ag–DMAEMA organic dispersion, measured (1) after completion of the cryochemical synthesis and (2) 3 or (3) 30 days later. Optical path length, 2 mm.lmax1 = 433 nm lmax2 = 429 nm lmax3 = 428 nm 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 300 400 500 600 700 800 l/nm 1 2 3 Absorption 2 1 3 lmax1 = 428 nm lmax2 = 425 nm lmax3 = 438 nm Figure 2 Absorption spectra of sols prepared by dispersing 3 mg portions of dry silver-containing poly-DMAEMA in 6 ml portions of (1) water, (2) acetone and (3) toluene.Optical path length, 2 mm. Table 1 Characteristics of silver sols stabilised by poly-DMAEMA in water, acetone and toluene according to dynamic light scattering data. Dispersion medium Rm/nm R1/nm R2/nm water 179.2±33.7 53.3 323.5 acetone 80.8±3.7 18.5 111.9 toluene 125.6±27.7 19.8 183.9Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) of 25 min (the signal-to-noise ratio was higher than 15). This function is adequately approximated by the sum of two exponentials (Figure 3, curve). This means that the size distribution of the light-scattering particles is bimodal.In our opinion, this bimodality indicates that both individual silver nanoparticles and their aggregates are present in the sols. Table 1 summarises the radii R1 and R2 of equivalent hydrodynamic spheres corresponding to each diffusional mode, namely, individual particles and their aggregates, respectively. These values were calculated by the Stokes–Einstein equation.It can be seen in Table 1 that the R1 and R2 values exceed the size of even the largest silver particles (~25–30 nm), which was found by TEM (Figure 4). The reason is that the radius of an equivalent hydrodynamic sphere that corresponds to a lightscattering particle is the sum of the radius of the metal core and the thickness of the polymer adsorption layer, which depends on the nature of the solvent.It can be seen in Table 1 that, in an aqueous solution, the radius R1 of individual particles is more than two times greater than the particle size in acetone and toluene. In our opinion, the difference is due to the fact that, in aqueous media, poly-DMAEMA chains (which contain hydrated and partially protonated amino groups) bonded to the surface of silver nanoparticles form a more bulky layer than that in acetone and toluene, and this bulky layer sterically stabilises silver nanoparticles.Thus, the cryochemical synthesis of nanoparticles in the Ag– DMAEMA system allowed us to prepare silver dispersions (sols) stabilised by poly-DMAEMA in different media. A set of data obtained by optical spectroscopy, TEM and light scattering suggests that both individual silver nanoparticles sterically stabilised by macromolecules and their aggregates are present in the sols.The optical and aggregative properties of the sols indicate that the thickness of the layer that stabilises the nanoparticles depends on the nature of the solvent (dispersion medium). This work was supported by the Russian Foundation for Basic Research (grant no. 96-03-33970). References 1 K. J. Klabunde, Free Atoms, Clusters and Nanoscale Particles, Academic Press, New York, 1994. 2 B. M. Sergeev, G. B. Sergeev, Y. J. Lee, A. N. Prusov and V. A. Polyakov, Mendeleev Commun., 1997, 151. 3 P. Mulvaney, Langmuir, 1996, 12, 788. 4 U. Kreibig and M. Vollmer, Optical Properties of Metal Clusters, Springer, Berlin, 1995. 5 U. Kreibig, Z. Phys. D: At., Mol. Clusters, 1986, 3, 239. 6 M. Sastry, N. Lala, V. Patil, S. P. Chavan and A. G. Chittiboyina, Langmuir, 1998, 14, 4138. 7 D. E. Koppel, J. Chem. Phys., 1972, 57, 4814. 8 A. N. Tikhonov and A. A. Arsenin, Metody resheniya nekorrektno postavlennykh zadach (Procedures for solving ill-posed problems), Nauka, Moscow, 1979, p. 279 (in Russian). 1.0 0.8 0.6 0.4 0.2 0.0 1.2 1.4 t/ms G(t) 0.2 0.4 0.6 0.8 1.0 Figure 3 A typical plot of the autocorrelation function of intensity fluctuations of light scattered by silver nanoparticles stabilised by poly- DMAEMA in water. 100 nm Figure 4 Photomicrograph of silver particles in an Ag–DMAEMA organic dispersion freshly prepared by the cryochemical synthesis. Received: 30th November 1998; Com. 98/1407 (8/09473J)

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) EPR detection of the radical–molecule complex NH2–HF stabilised in solid argon Ilya U. Goldschleger, Alexander V. Akimov and Eugenii Ya. Misochko* Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. E-mail: misochko@icp.ac.ru The radical–molecule complex NH2–HF is stabilised in a solid argon matrix as an intermediate species in the chemical reaction of F atoms with NH3 molecules.The initial interest to study the atom–molecule chemical reaction in a gas phase: was motivated by attempts to use it as a source for chemical lasers.1 However, these attempts to obtain an inverse HF excitation in reaction (1) were unsuccessful, despite the high exothermicity. 2,3 It was assumed that the reason was the formation of long-lived FNH3 intermediate species during the reaction. The existence of this intermediate complex can cause randomisation of the excess energy among its internal modes. The ab initio calculations performed by Goddard et al.4 predicted the formation of the NH2–HF complex in the exit channel of reaction (1) with the binding energy ~12 kcal mol–1.We have observed stabilised NH2–HF complexes formed in reaction (1) and measured their hyperfine (hf) constants for the first time. A comparison of experimental hf constants with the calculated data shows that the structure of the complex is close to that predicted by Goddard et al.4 Recently we have proposed5 an experimental technique to study reaction (1) in a solid argon matrix at cryogenic temperatures.This approach is based on the widely used matrix isolation technique and high mobility of fluorine atoms in solid argon.6 It was shown that translationally excited fluorine atoms generated by UV photolysis of F2 molecules migrate through several lattice periods, whereas thermal F atoms diffuse in Ar at T > 20 K.Upon heating above 20 K, diffusing F atoms react with impurity molecules. The crystalline environment, which prevents reaction products from flying apart and promotes fast relaxation of excess energy, results in stabilization of reaction intermediates. EPR spectroscopy allowed us to detect and to identify the radical products of atom–molecule reaction (1).7–9 Two facts drastically diminish inhomogeneous broadening of EPR spectra: zero nuclear spin of Ar and homogeneous distribution of radicals, [R] £ 1016 cm–3, in the sample.Hyperfine interaction of an unpaired electron with magnetic nuclei in the radical–molecule complex, which is an intermediate of reaction (1), is very sensitive to the distance between the radical R and the molecule HF and to their mutual orientation.Therefore, the geometry of the complex can be determined from a comparison of the measured hf constants with the results of quantumchemical calculations. The experimental technique has been described elsewhere.8 Solid argon films with the reactant molecules F2 and NH3 were formed by vapour deposition of the gases through two separate gas inlets onto a cold substrate at 14 K.Typically, we used the dilution ratio Ar:F2:NH3 = 1000:1:1. Fluorine atoms were generated by UV photolysis of F2 molecules at l = 337 nm (N2 pulsed laser, average power of 20 mW). The EPR spectra of freshly prepared samples exhibit no lines due to paramagnetic species. Photolysis of the samples with Ar:F2:NH3 = 1000:1:1 at 7.7 K leads to the appearance of a complex anisotropic spectrum.Temperature changes in the spectra of photolysed samples are reversible in the region 7.7–18 K and make it possible to distinguish two paramagnetic species generated during photolysis. The EPR spectrum of one of these species consists of nine narrow lines: two triplet groups with hf splitting of 1.05 and 2.40 mT, and g = 2.0058. Both the hf constants and the g-factor are in good agreement with published data10 for the radical NH2 in solid Ar.It allows us to conclude that one of the photolysis products is the free radical NH2, which is formed in reaction (1) between a translationally excited F atom with an NH3 molecule. The EPR lines of the other species are anisotropic and exhibit strong reversible temperaturedependent broadening.They become practically invisible at 7.7 K. To initiate reactions of thermal F atoms, we annealed the photolysed samples at T > 20 K. A comparison of the spectra before and after annealing shows that the concentration of NH2 radicals remained unchanged, whereas the intensity of lines of the other radical increased by a factor of four becuase of the reaction of diffusing F atoms.Upon heating above 30 K, the lines of this radical become narrow and isotropic [Figure 1(a)]. The EPR spectrum consists of 14 lines with a width of 0.10 mT and corresponds to three hf splittings: the triplet 1:1:1 with aN = 1.20 mT, the triplet 1:2:1 with aH = 2.40mT, and the doublet with aF = 0.70 mT. Because aN ª 2×aH, four lines of the spectrum are compound lines. Thus, only 14 lines are resolved in the spectrum, instead of 18 lines corresponding to this assignment.To ascribe the hf coupling constants to magnetic nuclei, a series of similar experiments with isotopically substituted NH3 was carried out. The EPR spectra obtained after annealing of the photolysed Ar/F2 /15NH3 and Ar/F2/14ND3 samples are shown in Figures 1(b) and 1(c). The isotopic substitution for nitrogen atom, 14N (S = 1) 15N (S = 1/2), F + NH3 HF + NH2; DH0 0 ª –31 kcal mol–1 (1) (a) (b) (c) aF a14N aH aF a15N aH aF aD a14N 311 314 317 320 H/mT Figure 1 EPR spectra of the samples after photolysis at 15 K and subsequent annealing at 25 K: (a) Ar/14NH3/F2; (b) Ar/15NH3/F2; (c) Ar/14ND3/F2. All spectra were recorded at 35 K.(The 14ND3 used in experiments contained ~10% 14NH3.Therefore, weak outer lines in the spectra correspond to the complex 14NH2–HF).Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) leads to the replacement of the triplet aN (14N) = 1.20 mT with the doublet aN (15N) = 1.55 mT. In Ar/F2/14ND3 samples, only the triplet aH = 2.40 mT is replaced by the quintet aD = 0.37 mT. These findings allows us to assign unambigously the hf constants aN and aH to the NH2 group.At the same time, the doublet splitting 0.70 mT (which remained unchanged by the above isotopic substitution) should be attributed to the 19F atom, because it is the only atom having the magnetic nucleus S = 1/2 in the system. Since NH2F is a closed-shell molecule, we can attribute the considered EPR spectrum to the radical–molecule complex NH2–HF, assuming that the hf constant at the H atom of the HF molecule aH is less than 0.05 mT.We carried out quantum-chemical computations in order to clarify the structure of the NH2–HF complex. All of the calculations were performed using the GAUSSIAN-94 program11 at the N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences (grant no. 98-07-90290 from the Russian Foundation for Basic Research). The density functional method B3LYP with the EPR-3 basis set12 was used. The calculated steady-state configuration of the complex NH2–HF corresponds to the collinear C2v geometry, which is similar to that calculated earlier by Goddard et al.4 The binding energy of the complex is equal to 12.3 kcal mol–1.The geometry and hf constants of the complex are given below: The calculated hf constants aN, aH and aF are in good agreement with the experimental data. The hf constant aH' at the proton of the HF molecule is less than 0.05 mT, and this splitting cannot be resolved under given experimental conditions. Therefore, the radical–molecule complex NH2–HF is the main product in the reactions of thermal F atoms with NH3 molecules in a solid argon matrix: We optimised the arrangement of the complex in an argon lattice starting from the calculated structure.Each isolated NH3 molecule occupies a singly substitutional argon lattice site; therefore, we anticipated that the NH2 group of the complex is also located at the same type of sites. The minimisation of the total energy of a doped argon cluster containing 365 atoms was done using molecular dynamics simulation as described in ref. 8. The resulting configuration of the complex is shown in Figure 2. The position of the nitrogen atom of the NH2 group is close to the substituted site (0, 0, 0). The fluorine atom of the HF molecule occupies the nearest octahedral interstitial site Oh (–a/2, 0, 0), where a = 0.54 nm is the fcc lattice parameter. This is possible only due to the fact that the distance between F and N atoms in the complex is close to the one-half lattice period a/2.This commensurability leads to a minor deformation of the complex in the crystal lattice: the distance between the NH2 radical and the H atom of HF is 0.005 nm shorter than that in the gas-phase complex, and the out-of-plane deformation of the complex does not exceed 4°.These distortions do not result in changes of the hf constants with respect to those obtained for an equilibrium geometry of the complex. In summary, the radical–molecule complex NH2–HF was observed for the first time as an intermediate product in reactions of mobile F atoms with NH3 molecules in solid argon.The EPR spectrum of the complex is characterised by three hyperfine constants (aN = 1.20 mT, aH = 2.40 mT, and aF = = 0.70 mT). The hf constant for the H atom of the HF molecule is less than 0.05 mT. The quantum-chemical calculation revealed that the NH2–HF complex has a planar C2v structure and a binding energy of 12.3 kcal mol–1. The calculated hf parameters of the complex and the experimental data are in good agreement.The complex in somewhat distorted in an argon lattice with respect to its equilibrium geometry in the gas phase. This work was supported by the Russian Foundation for Basic Research (grant no. 98-03-33175). References 1 W. H. Duewar and D. W. Setser, J. Chem. Phys., 1973, 58, 2310. 2 D. J. Donaldson, J. J. Sloan and J. D. Goddard, J. Chem.Phys., 1985, 82, 4524. 3 S. Wategaonkar and D. W. Setser, J. Chem. Phys., 1987, 86, 4477. 4 D. Goddard, D. J. Donaldson and J. J. Sloan, Chem. Phys., 1987, 114, 321. 5 V. A. Benderskii, A. U. Goldschleger, A. V. Akimov, E. Ya. Misochko and C. A. Wight, Mendeleev Commun., 1995, 245. 6 J. Feld, H. Kunti and V. A. Apkarian, J. Chem. Phys., 1990, 93, 1009. 7 E. Ya. Misochko, V. A. Benderskii, A.U. Goldschleger and A. V. Akimov, J. Am. Chem. Soc., 1995, 117, 11997. 8 E. Ya. Misochko, V. A. Benderskii, A. U. Goldschleger, A. V. Akimov, A. V. Benderskii and C. A. Wight, J. Chem. Phys., 1997, 106, 3146. 9 A. U. Goldschleger, E. Ya. Misochko, A. V. Akimov, I. U. Goldschleger and V. A. Benderskii, Chem. Phys. Lett., 1997, 267, 288. 10 S. N. Foner, E. L. Cochran, V.A. Bowers and C. K. Jen, Phys. Rev. Lett., 1958, 1, 91. 11 M. J. Frisch, G.W. Trucks, H. B. Schlegel, P. M.W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian-94, Revision D.1, Gaussian, Inc., Pittsburgh PA, 1995. 12 V. Barone, in Recent Advances in Density Functional Methods, ed. D. P. Chong, World Scientific, Singapore, 1995, part 1, p. 287. x y z Ar F H N H H Figure 2 Arrangement of the complex NH2–HF in an argon lattice. Twelve nearest neighbouring Ar atoms are shown. H F H' N H 0.937 Å 1.783 Å 1.022 Å 105.14° a(calc)/mT –0.70 0.02 1.15 –2.30 a(exp)/mT –0.70 < 0.05 1.20 –2.40 (2) F + NH3 NH2–HF (3) Received: 16th March 1999; Com. 99/1463

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Diazaporphyrins: synthesis, characterization and X-ray crystal structure of (3,7,13,17-tetramethyl-2,8,12,18-tetrabutyl-5,15-diazaporphinato)chloroindium(III) Pavel A. Stuzhin,*a Melanie Goeldner,b Heiner Homborg,b Aleksandr S. Semeikin,a Irina S. Migalovac and Stanislaw Wolowiecd a Department of Organic Chemistry, Ivanovo State University of Chemical Technology, 153460 Ivanovo, Russian Federation. Fax: +7 0932 37 7743; e-mail: stuzhin@icti.ivanovo.su b Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany c Institute of Solution Chemistry, Russian Academy of Sciences, 153045 Ivanovo, Russian Federation d Department of Chemistry, University of Wroclaw, PL-50-383 Wroclaw, Poland The reaction of 3,7,13,17-tetramethyl-2,8,12,18-tetrabutyl-5,15-diazaporphine [H2DAPMB] 1 with indium(III) acetate in acetic acid leads to the formation of acetatoindium(III) complex [In(OAc)DAPMB] 2, which is easily converted to chloroindium(III) complex [In(Cl)DAPMB] 3.The size of the central coordination cavity in the porphyrin-type macrocycles, along with the operating specific electronic factors, has a large influence on the coordination properties of these ligands and on the structure of their metal complexes. Thus, the sterical correspondence between the radii of the coordination cavity (Ct–Npyr distance) and the metal ion (rM) often determines the location of the metal in respect to the plane of the macrocycle, conditions and strength of their s- and p-bonding, and the stability of the complex to dissociation.1 The numerous structural data which are available for complexes of common porphyrins, phthalocyanines (tetrabenzotetraazaporphyrins) and since recently for alkyl-substituted tetraazaporphyrins have shown that the replacement of four methine bridges in the porphyrin core with four meso-nitrogen atoms leads to a significant decrease in the central coordination cavity.2 Complexes of azaporphyrins containing less than four meso-nitrogen atoms are very poorly investigated, and the structural data are available only for monoazaporphyrins.3,4 In order to reveal the effect of diaza substitution of meso-methine bridges in the porphyrin macrocycle on the structure and coordination properties, we have started a systematic investigation of trans-diazaporphyrins. 5,6 Here we report the synthesis of (3,7,13,17-tetramethyl- 2, 8,12,18-tetrabutyl -5,15-diazaporphinato)chloroindium(III) [In(Cl)DAPMB] 3, which is the first example of a diazaporphyrin characterised by X-ray crystallography. Refluxing 3,7,13,17-tetramethyl-2,8,12,18-tetrabutyl-5,15- diazaporphine [H2DAPMB]6 1 (0.17 mmol) with indium(III) acetate (1.7 mmol) in glacial acetic acid (50 ml) yielded intermediate acetatoindium(III) complex [In(OAc)DAPMB] 2, which was extracted with CH2Cl2 and washed thoroughly with water.A solution of 2 was then treated with aqueous HCl and, after washing with water and drying over MgSO4, chromatographed on alumina (III grade, eluent: CH2Cl2–MeOH, 100:1). Pinkviolet complex 3 was precipitated after the addition of n-hexane to the partly evaporated eluate (60% yield).† Slow diffusion of methanol into the chloroform solution of 3 gave violet crystals of the chloroform solvate 3·CHCl3.One of these crystals with dimensions of 0.2×0.3×0.7 mm was suitable for an X-ray diffraction study.‡ Perspective and side views of 3 are displayed in Figure 1.The indium atom is located outside the mean plane of the four-coordinating pyrrole-type nitrogen atoms Npyr, and the diazaporphyrin skeleton has a slight ‘doming’ in the opposite direction (the average displacement of its atoms increased from the centre to the periphery: ca. 0.09, 0.06, 0.15 and 0.22 Å for Ca, Cmeso, Nmeso and Cb atoms, respectively). It is noteworthy that in 3 the displacement of the In atom from the (Npyr)4 mean plane (0.68 Å) is larger and the average In–Npyr bond length [2.135(6) Å] is slightly shorter than that in meso-tetraphenylporphinatochloroindium( III) [In(Cl)TPP], having a similar † Analysis for 3. 1H NMR (300 MHz, CDCl3, 297 K) d: 10.21 (s, 2H, meso-CH), 4.05 (m, 8H, a-CH2), 3.66 (s, 12H, a-Me), 2.28 (q, 8H, b-CH2), 1.80 (s, 8H, g-CH2), 1.15 (t, 12H, d-Me).UV–Vis [benzene, lmax/nm (lg e)]: 379 (4.94), 399sh, 536sh, 550 (4.14), 558 (4.15), 571sh, 583 (4.49), 595 (4.96). IR (KBr, n/cm–1): 524w, 672w, 718m, 748s, 769m, 860m, 927m, 940vw, 986s, 1104m, 1159vs, 1194w, 1300w, 1381s, 1460s, 2860s, 2935s, 2960m. Found (%): C, 61.46; H, 6.86; N, 11.25. Calc. for C38H50ClInN6 (%): C, 61.58; H, 6.80; N, 11.34. Cl In N(1) N(2) N(3) N(4) N(5) N(6) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) Figure 1 Molecular structure of [In(Cl)DAPMB]·CHCl3; with 50% probability, thermal ellipsoids show all non-hydrogen atoms: (top) a perspective view and (bottom) a side view along the axis through the meso-nitrogen atoms.Selected average bond lengths (Å): In–Cl 2.376(2), In–Npyr 2.135, Npyr–Ca(Cmeso) 1.377, Npyr–Ca(Nmeso) 1.367, Ca–Cmeso 1.396, Ca–Nmeso 1.337, Cb–Ca(Cmeso) 1.459, Cb–Ca(Nmeso) 1.448, Cb–Cb 1.361; selected average bond angles (°): Ca–Npyr–Ca 107.7, Npyr–Ca–Cmeso 124.1, Npyr– Ca–Nmeso 127.7, Ca–Cmeso–Ca 127.6, Ca–Nmeso–Ca 124.4, Npyr–In–Npyr 85.0 (Cmeso), 83.3 (Nmeso) and 142.9 (opposite).Npyr: N(1), N(2), N(4), N(5); Nmeso: N(3), N(6); Ca: C(1), C(3), C(6), C(7), C(10), C(12), C(15), C(16); Cb: C(4), C(5), C(8), C(9), C(13), C(14), C(17), C(18); Cmeso: C(2), C(11).Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) ‘doming’ of the macrocyclic skeleton (0.61 and 2.156 Å, respectively).7 These changes in the coordination geometry of the In atom are a consequence of the trans-diaza substitution, decreasing the diameter of the core of the macrocyclic ligand from 4.134 Å in [In(Cl)TPP] to 4.049 Å in 3.Whereas the four pyrrole N atoms in [In(Cl)TPP] form a square with sides of 2.923 Å, the distance between the pyrrole-type N atoms adjacent to the meso-N bridge (2.839 Å) in 3 is shorter than that between N atoms adjacent to the meso-CH bridge (2.887 Å).The contraction of the coordination cavity and its square distortion result mainly from the changes in the bond lengths and bond angles of the meso-atom bridges. Indeed, the Nmeso–Ca bond (1.337 Å) in 3 is shorter than the Cmeso–Ca bond {1.396 Å; 1.402 Å in [In(Cl)TPP]7} and �(Ca–Nmeso–Ca) of 124.4° is smaller than �(Ca–Cmeso–Ca) {127.6°; 126.2° in [In(Cl)TPP]7}. Shortening of the Npyr–Ca bonds (1.37 Å) and elongation of the Ca–Cb bonds (1.45 Å), which were observed for 3 in comparison with [In(Cl)TPP] (1.38 and 1.43 Å, respectively), may indicate an increase of the conjugation in the internal 16-membered ring due to diaza substitution.A further interesting aspect is the conformation of the n-butyl groups in respect to the mean plane of the macrocycle: two of them neighbouring to one meso-CH bridge are stretched below, and the two other, above the mean plane of the macrocycle.As can be seen from the side view in Figure 1, the n-butyl groups positioned at the same side as the In–Cl moiety cause a deviation of the In–Cl bond from a normal to the mean plane by ca. 4.5°. The In–Cl bond in 3 [2.376(2) Å] is longer than in [In(Cl)TPP]7 (2.369 Å).The 1H NMR spectra of 3 in CDCl3, displayed in Figure 2, reveal two diastereotopic a-CH2 protons of the butyl groups. Their inequivalence, arising from a slow rotation of the butyl ‡ Crystal data for 3·CHCl3: C39H51Cl4InN6, M = 860.48, triclinic, space group P1, a = 12.582(2) Å, b = 13.217(2) Å, c = 13.268(3) Å, a = = 112.47(1)°, b = 90.19(2)°, g = 103.64(1)°, V = 1970.7(6) &Ari, Z = 2, Dc = 1.450 g cm–3, m = 0.907mm–1, F(000) = 888.Data were measured using a CAD4 Enraf Nonius diffractometer {T = 170 K, graphite-monochromated MoKa radiation, l = 0.71069 Å, q = 2.07–29.96°, q/2q scan mode, 7522 reflections were collected of which 7179 were unique [R(int) = 0.0617]}. The structure was solved by direct methods using the SHELXS-86 and SHELXL-93 programs.Refinement on F2 in an anisotropic approximation for all non-hydrogen atoms (hydrogen atoms isotropic) by a full-matrix least-squares method converged to R1 = = 0.0675 [I > 2s(I)], wR2 = 0.1972 (all data) and S = 1.020 based on 451 parameters and 7179 unique reflections. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 1999. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/49. groups, already seen at 297 K, is clearly discernible at 213 K by splitting of the a-CH2 signal. The UV–Vis spectrum of 3 in CH2Cl2 (Figure 3) is typical of metal complexes of azaporphyrins.As a result of diaza substitution, the symmetry of the macrocyclic chromophore is lowered from D4h in porphyrins and tetraazaporphyrins to D2h (or even C2v, if the out-of-plane position of the In atom is taken into account). There is no splitting of the p ® p* transition band in the long-wave region. This correlates with the theoretical work,8 which predicted a very large difference in the intensities of the Q1 (fr = 0.100) and Q2 (fr = 0.0006) transitions and a small energy gap between both of the transitions (310 cm–1) for complexes of diazaporphyrins. Addition of CF3COOH to a solution of 3 in CH2Cl2 results in a bathochromic shift of the Q-band (860 cm–1), which is consistent with the complete acid– base interaction with one of two meso-nitrogen atoms.9 Complex 3 is stable in CF3COOH, but dissolving it in conc.H2SO4 is followed by rapid demetallation. Under comparable conditions (ca. 17.6 M H2SO4), 3 is 100 times less stable to dissociation than [In(Cl)TPP]10 (kobs 298 = 4.394×10–4 and 0.065×10–4 s–1, respectively). It was found previously5 that the corresponding Cu complex of 1 [CuDAPMB] exibits a much higher stability in conc.H2SO4 than the Cu complexes of common porphyrins. Evidently, the opposite effect of the diaza substitution on the stability of CuII and InIII complexes is connected with differences in the steric correspondence of these ions to the coordination cavities of porphyrins and diazaporphyrins. The smaller size of the diazaporphyrin core determines its stronger s- and p-bonding with the CuII cation (rM = 0.72 Å), located in the plane of the macrocyclic ring, and weaker bonding with the larger InIII cation (rM = 0.81 Å), which is located outside the plane of the macrocyclic ring.This work was supported by the Russian Foundation for Basic Research (grant no. 98-03-04080) and Deutsche Forschungsgemeinschaft [grant no. 436 RUS 113/436/0 (HO 726/4-1)].References 1 B. D. Berezin and N. S. Enikolopyan, Metalloporfiriny (Metalloporphyrins), Nauka, Moscow, 1988 (in Russian). 2 P. A. Stuzhin and O. G. Khelevina, Coord. Chem. Rev., 1996, 147, 41. 3 A. J. Abeysekera, R. Grigg, J. F. Malone, T. J. Kingand and J. O. Morley, J. Chem. Soc., Perkin Trans. 2, 1985, 395. 4 A. L. Balch, M. M. Olmstead and N. Safari, Inorg. Chem., 1993, 32, 291. 5 O. G. Khelevina, N. V. Chizhova, P. A. Stuzhin, A. S. Semeikin and B. D. Berezin, Koord. Khim., 1996, 22, 866 (Russ. J. Coord. Chem., 1996, 22, 811). 6 O. G. Khelevina, N. V. Chizhova, P. A. Stuzhin, A. S. Semeikin and B. D. Berezin, Zh. Fiz. Khim., 1997, 71, 81 (Russ. J. Phys. Chem., 1997, 71, 74). 7 R. G. Ball, K. M. Lee, A. G. Marshall and J. Trotter, Inorg. Chem., 1980, 19, 1463. 297 K 213 K 10 5 0 d/ppm a-Me a-CH2 b-CH2 g-CH2 d-Me * meso-CH Figure 2 1H NMR spectra of [In(Cl)DAPMB] in CDCl3 at 297 and 213 K. A 1 0 400 500 600 l/nm 1 2 Figure 3 UV–Vis spectra of [In(Cl)DAPMB] in (1) CH2Cl2 and (2) CF3COOH.Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) 8 S. S. Dvornikov, V. N. Knyukshto, V. A. Kuzmitski, A. M. Shulga and K. N. Solovyov, J. Luminescence, 1981, 23, 373. 9 P. A. Stuzhin, O. G. Khelevina and B. D. Berezin, in Phthalocyanines: Properties and Applications, eds. C. C. Leznoff and A. B. P. Lever, VCH Publishers, New York, 1996, vol. 4, p. 19. 10 T. N. Lomova, L. P. Shormanova and M. E. Klyueva, in Uspekhi Khimii Porfirinov (Advances in Porphyrin Chemistry), ed. O. A. Golubchikov, NII Khimii SPbGU, St. Petersburg, 1997, vol. 1, p. 129 (in Russian). Received: 15th January 1999; Com. 99/1428

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Kinetic isotope effects in the activation of H–H bonds by palladium clusters Victor M. Mamaev,*a Igor P. Gloriozov,a Andrew V. Prisyajnukb and Yuri V. Babinb a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: + 7 095 932 8846; e-mail: vmam@nmr.chem.msu.su b Far-East Academy of Economics and Management, 690091 Vladivostok, Russian Federation. Fax: +7 4232 40 6634; e-mail: yub@mail.primorye.ru The mechanism of oxidative dihydrogen addition to palladium clusters has been analysed in terms of the reaction-path Hamiltonian approximation, and the abnormal H/D kinetic isotope effect has been explained.The oxidative addition of alkanes and dihydrogen molecules to atoms, clusters and complexes of transition metals are the key steps of catalytic cycles of alkane functionalization under mild conditions.1 Theoretical studies of H–H and C–H bond activation, as a rule, are restricted to structures corresponding to the stationary points of potential-energy surfaces (PESs) [i.e., to precursor complexes (PC), transition states (TS), intermediates and products (PR) of reactions] for model reactions with the use of various ab initio methods.2 Experimental studies of H–H and C–H bond activation by transition metal clusters in a gas phase3–5 demonstrated that neutral palladium clusters were more active than palladium atoms.A clearly defined relationship between the reactivity of the clusters and the number of metal atoms was found.For Pdn clusters (n = 1–5), the maximum reactivity was observed for Pd2.3 Fayet et al.3 have detected an inverse H/D kinetic isotope effect (KIE) (i.e., kH/kD < 1) for the reaction Pd2 + H2. They have suggested that this effect is due to a higher rate of the reverse reaction of reductive H2 elimination from the product of addition in comparison with the deuterated analogues.Some model trajectories of the oxidative dihydrogen addition to Pd2 cluster were studied by MC SCF6,7 and MCPF8 techniques using relativistic effective core potentials for the Pd atom. Because different atomic basis sets and different ab initio techniques were used, and a constrained geometry optimization was performed, the energies and geometry parameters of the structures of the stationary points of PESs are in only qualitative agreement.Mamaev et al.9 analysed the PES of the oxidative H2 addition to the Pd2 cluster within the reaction-path Hamiltonian (RPH) approximation10 on the basis of the semiempirical CNDO/S2 method.11 The H2 addition to the Pd2 cluster is known to occur without a potential-energy barrier.6–9 It was found9,12 that the results of CNDO/S2 calculations of the structures of the stationary points of the PESs of the H–H bond activation by both the Pd atom and the Pd2 cluster are in a good agreement with the data of ab initio calculations that took into account correlation and relativistic effects.According to our CNDO/S2 calculations for the 1Sg + state of a Pd2 cluster, the equilibrium Pd–Pd distance is equal to 2.93 Å; wQ(Pd–Pd) = 103 cm–1; the dissociation energy D0 = 16.7 kJ mol–1.These results agree with the MC SCF data14 (where Re = 2.87Å; wQ(Pd–Pd) = 121 cm–1; D0 = 29.3 kJ mol–1). However, the calculations of the stationary points of the PES of the Pd2 + H2 oxidative addition by ab initio methods6–8 cannot explain the abnormal KIE in this reaction. For this purpose, the reaction probabilities and rate constants for molecular systems (MSs) in the ground electronic state and without vibrational excitation should be computed at least at a semiclassical approximation. The use of rigorous ab initio schemes to compute the PES of this reaction is impossible because these calculations (complex calculations of Coulomb correlations of d-electrons and relativistic effects for motion of the inner electrons in transition metal atoms) are very labour intensive.Therefore, we employed the semiempirical SCF CNDO/S2 method specially developed to study MSs containing palladium and nickel atoms and clusters.11 According to the RPH formalism, the PES of the reaction is computed on normal coordinates. To calculate the semiclassical rate constants, we used the transition state theory (TST) with tunnel corrections.15 In terms of the TST, the cumulative thermal rate constant kCUM of a bimolecular reaction of MS transfer from the left unbound state to the right bound state is computed as follows: where Q is the translational partial function of the reactants, EA is the activation barrier and P(E) is the reaction probability.The quasiclassical function P(E) is calculated15 by solving the timedependent Schrödinger equation. In the case of a parabolic barrier (i.e., near the saddle point): where q(E) is the quasiclassical tunnel integral where VG(s) is the vibrationally adiabatic potential function, m is the reduced mass of the molecular system, s is the intrinsic reaction coordinate, and s< and s> are the points of the turns.The transmission factor c(T) is introduced to evaluate the quantity of the tunnel effect in the reaction. c(T) is equal to the ratio of the cumulative rate constant to the over-the-barrier constant kACT found from the Arrhenius equation: The fn(T) functions represent the contributions from the separate vibrational states of the reactants to the rate constants; kACT(n,T) may be computed by equation (1) if P(n,E) is replaced with the Heaviside step function.15 Mamaev et al.12 proposed the use of quasiclassical reaction probability (2) instead of the 24 16 8 0 –8 –16 –24 4000 3000 2000 1000 0 –1000 –1.5 –1.0 –0.5 0.0 0.5 E/kJ mol–1 w/cm–1 s/Å×mH 1/2 w1,2 w3 w4 w5 w6 Figure 1 The V0(s) potential function for reaction (I) along the minimumenergy path (dashed line): w1–w6 are the frequencies of the normal vibrations; s is the intrinsic reaction coordinate; w < 0 reflect an imaginary frequency.kCUM(T) = P(E)exp – dE, 1 Qò 0 • EA kBT ( ) (1) 1 1 + exp[2q(E)] P(E) = , (2) q(E) = [2m{VG(s) – E}]ds, 1 h ò s< s> (3) c(T) = . fn(T)kCUM(n,T) kACT(T) SnMendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) classical one for calculations of kACT, because it allows us to take into account the effect of the over-the-barrier reflection of the MS. If the over-the-barrier reflection is neglected, then the values of c may be less than 1; this is inconsistent with the definition of c.12 Thus, the values c � 2 show that the reaction occurs mainly by a tunnel mechanism at the given temperature.Here, we have studied the mechanism of the H–H and D–D bond activation by the Pd2 cluster in terms of the RPH approximation: We have obtained three stationary points in the PES, namely, PC, TS and a product corresponding to a bifurcation point (BP) [its Hessian has two negative eigenvalues of w1 2 and w2 2 (Figure 1)]. Along the entire reaction path (RP), the MS conserves the C2v symmetry.There are six vibrational modes of the following symmetry types: G = 3A1 + B1 + 2B2. An analysis of the eigenvector of the Hessian directed tangentially to the RP (the RP vector) showed that for s > –0.5 Å×mH 1/2 (mH is the proton mass, equal to 1834 amu) displacements of the atoms, corresponding to this vector, are mainly defined by a variation in one internal coordinate, namely, the a(H–Pd–H) angle.The modes whose frequencies w1, w2, w5 are zero in the dissociation limit turn to the b(PdPdH), rPd–Pd and q–(Pd–H) modes of B2, B2 and B1 symmetry, respectively. As the MS moves along the RP, the q(H–H) vibration of the dihydrogen molecule transforms to the stretching q+(Pd–H) mode (w6, A1 symmetry). The frequency w3 of the totally symmetric Q(Pd–Pd) vibration changes slightly along the entire RP.In the BP, the values of w1 and w2 are equal to 213i and 167i cm–1, respectively, i.e., the eigenvectors of the Hessian ofhe b(PdPdH) and rPd–Pd shapes point at directions of descent into two different minima on the PES (processes IIIA and IIIB, respectively). We have constructed the RPHs for both of these processes and found the two descents to lead to the structures corresponding to the true PR: A rhombic structure of the D2d symmetry with bridging protons7,8 corresponds to the global PR minimum.Its six normal vibrations belong to the following symmetry subspaces: G = = A2u + 2A1g + A2g + 2B2u. The cPdH PdH vibration of the A2u symmetry has the frequency w1 = 179 cm–1; the Q(Pd–Pd) vibration of the A1g symmetry has the frequency w2 = 225 cm–1.The shapes of w3–w6 modes are synchronous and asynchronous motions of the protons along the Pd–Pd and H–H axes, respectively. In going from BP to PR, the rearrangement of the protons occurs by path IIIA asynchronously, and the RP vector represented in the basis of displacements of the internals changes significantly along the entire RP (Figure 2).Since the potential functions of processes IIIA and IIIB are even, we trace the variation in the shape of the RP vector on the positive s semi-axis. In the region from s = 0 to sª4 the bridging Pd–H–Pd bond is formed, whereas the other proton is fixed at the Pd–Pd axis [in Figure 2, this is seen as the behaviour of w5(s) and w6(s) functions].Near s ª 4, the first bridging bond is completely formed, and w5(s) is quickly dropped by 600 cm–1, while the frequency of the vibration of the other proton, w6(s), bonded by an ordinary bond to a palladium atom, does not change. In the region of a small plateau at s ª 4, the shape of the RP vector changes abruptly: the first proton stands between the palladium atoms, and the other proton moves back to form the second bridging bond.Unlike to path IIIA, the motion of protons via path IIIB is synchronous, because the MS conserves the sV-plane of symmetry, which is perpendicular to the plane of the molecule in BP, and the RP vector is of the A' symmetry along the entire RP. The RP vector is of the rPd–Pd shape at the BP (s = 0). In the region from s << 1.5 to s >> 4, variations in the a(H–Pd–H) angles contribute significantly to the RP vector (up to 50%).In the vicinity of both minima, the RP vector corresponds 30 –10 –50 –90 –130 –170 –8 –6 –4 –2 0 2 4 6 8 2400 2000 1600 1200 800 400 0 –400 E/kJ mol–1 w/cm–1 s/Å×mH 1/2 w2 w3 w4 w5 w6 w1 PR BP PR Figure 2 The V0(s) potential function (solid line) and the w(s) functions (dashed lines) for reaction (IIIA).The vibrations are enumerated at the PR point. Pd2 + H2 Pd H Pd Pd2 + D2 Pd Pd Pd Pd H H H H H (I) (II) Pd D Pd Pd Pd Pd Pd D D D D D PC TS BP 3.0 2.5 2.0 1.5 1.0 0.5 0 1 2 3 4 5 6 7 8 9 10 11 kH/kD Th = 1 1000T–1/K–1 Figure 3 The semiclassical hclass (dashed line) and cumulative hcum (solid line) KIEs for reaction (I) as functions of inverse temperature. BP PR rPd–Pd b(PdPdH) Pd Pd H H (III) Pd H Pd H PR PR PRMendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) to the cPdH PdH vibration. Vibrations with the frequencies w3–w6 become a(H–Pd–H), b(PdPdH), q–(Pd–H) and q+(Pd–H) vibrations in the BP. According to refs. 6 and 7, the H2 addition to Pd2 clusters by trajectories without the formation of the BP structure occurs with no barrier.Thus, the formation of the BP structure from the separated reactants with an activation barrier of 22.2 kJ mol–1 is the rate-limiting step of reaction (I), and consequently, the abnormal H/D KIE of reaction (I)3 can be assessed by construction of the RPH for reaction (II). In the framework of our dynamic model, the KIE appears by three reasons.First, at the stage of composing the vibrationally adiabatic potential functions, the barrier heights for R–H and R–D bond activation become different because of differences in the values of corresponding wi(s) functions for MSs containing protons and deuterons (i.e., a so-called semiclassical KIE appears). Second, because of employing mass-weighted Cartesians in the computation of the RP H/D substitution causes V0(s) functions to expand in the ratio of the effective masses of the reactive MSs.Third, as the protons are replaced with deuterons, the RP curvature diminishes, leading to a decrease in the tunnel contribution to the cumulative rate constant. At the stage of the formation of the vibrationally adiabatic function V(s) of the H–H bond activation, an abnormal difference in the energies of the stationary points of the PESs of reactions (I) and (II) appears. The unique peculiarity of the H–H bond activation in comparison with C–H and C–C bond activation is that the addition of the zero point vibrational energy to the V0(s) causes the energies of BP and TS to raise by 3.3 kJ mol–1 for reaction (I).This fact was first detected in the course of construction of the dynamic model of the reaction Pd + H2.12 Finally, the heights of the barriers of H–H and D–D bond activation differ by 0.6 kJ mol–1.Note that, for Pd + CH4, the H/D substitution leads to an increase in the energies of TS and PR.16 For reaction (I), the shape of the kCUM(1/T) function is typical of tunnel chemical processes. If the RP curvature is taken into account in the computation of the reaction probability, kCUM grows by a factor of 1.5 at T = 150 K or by 10% at 300 K.The temperature dependence of the transmission factor shows that the tunnel mechanism dominates in reaction (I) at T < 400K. For instance, at 200 K, the tunnel contribution to the rate constant exceeds the activation barrier by a factor of 8; at 280 K, the former is three times greater than the latter.For reaction (II), the tunnel contribution to kCUM exceeds the activation barrier at T < 280 K. The H/D substitution lowers the height of the potential barrier by 0.6 kJ mol–1, i.e., the kACT component in the rate constant grows. This leads to the appearance of the inverse semiclassical KIE (hclass) of reaction (I), which was observed in practice3 (Figure 3).However, the ratio between the cumulative rate constants of reactions (I) and (II) (hcum) exhibits a KIE of the normal sign at T < 400 K, i.e., where c > 2 for reaction (I). An inverse KIE is observed only in the temperature region where the activation mechanism of the oxidative addition prevails. Thus, the reactions of H–H bond activation can exist, for which the H/D substitution increases the thermal rate constant because of the influence of the frequencies of vibrations transverse to the RP by the height of the potential barrier.References 1 A. E. Shilov, The Activation of Saturated Hydrocarbons by Transition Metal Complexes, Riedel, Dordrecht, 1984. 2 A. Weillard, Chem. Rev., 1991, 91, 743. 3 P.Fayet, A. Kaldor and D. M. Cox, J. Chem. Phys., 1990, 92, 254. 4 D. C. Parent and S. L. Anderson, Chem. Rev., 1992, 92, 1541. 5 A. Kaldor, D. M. Cox and M. R. Zakin, Adv. Chem. Phys., 1988, 70, 211. 6 H. Nakatsuji, M. Hada and T. Yonezawa, J. Am. Chem. Soc., 1987, 109, 1902. 7 S. Castillo, A. Cruz, V. Bertin, E. Poulain, J. S. Arellano and G. del Angel, Int J. Quant. Chem., 1997, 62, 29. 8 M. R. A. Blomberg, P. E. M. Siegbahn and M. Svensson, J. Phys. Chem., 1992, 96, 5783. 9 V. M. Mamaev, I. P. Gloriozov, V. V. Simonyan, E. V. Zernova, A. V. Prisyajnyuk and Yu. A. Ustynyuk, Mendeleev Commun., 1997, 246. 10 W. H. Miller, N. C. Handy and J. E. Adams, J. Chem. Phys., 1980, 72, 99. 11 M. J. Filatov, O. A. Gritsenko and G. M. Zhidomirov, J. Mol. Catal., 1989, 54, 462. 12 V. M. Mamaev, I. P. Gloriozov, V. A. Khmara, V. V. Orlov and Yu. A. Ustynyuk, Dokl. Ross. Akad. Nauk, 1991, 338, 65 [Dokl. Chem. (Engl. Transl.), 1991, 338, 171]. 13 J. J. Low and W. A. Goddard III, J. Am. Chem. Soc., 1984, 106, 6928. 14 K. Balasubramaniam, J. Chem. Phys., 1988, 89, 6310. 15 D. Truhlar, W. Hase and R. Hynes, J. Phys. Chem., 1983, 87, 2664. 16 V. M. Mamaev, I. P. Gloriozov, S. Ya. Ischenko, V. V. Simonyan, E. M. Myshakin, A. V. Prisyajnyuk and Yu. A. Ustynyuk, J. Chem. Soc., Faraday Trans., 1995, 91, 3779. Received: 11th January 1999; Com. 99/1422

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年代:1999

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Intercalation compounds of fluorinated graphite with camphor Vera M. Paasonen* and Albert S. Nazarov Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 34 4489; e-mail: albert@che.nsk.su The title compounds of the composition C2.22FHaly·zC10H16O (y = 0.1 and 0.02 for Hal = Cl and Br, respectively) have been prepared and found to be the compounds of stage at z = 0.14.The synthesis methods for intercalation compounds of fluorinated graphite (ICFG) with different organic compounds exhibiting mutual solubility are well known.1,2 These methods are based on the following exchange reactions: where x ª 2. ICFG with ClF3 or BrF3, which were obtained according to procedures described in refs. 3 and 4 were used as the initial CnHalFm. However, there is no publications on the methods providing intercalation of solids from solutions into fluorinated graphite using reactions (1) and (2). Methods based on the intercalation of solids from their solutions are widely used to synthesise intercalated graphite compounds.5,6 Because of this, the development of the intercalation of solids from their solutions into fluorinated graphite is topical.We studied the intercalation of camphor from acetone, ethanol and acetic acid solutions into fluorinated graphite. The solvents are able to form ICFG,1,2 i.e., to penetrate into the interstitial space of fluorinated graphite according to reactions (1) and (2).For this reason, the solutions of camphor as a model substance to be intercalated were examined in this study. The synthesis of ICFG is described below. A weighed portion of CnHalFm (1–2 g) was placed in a Teflon vessel, acetone (20 ml) was added, and the mixture was kept at room temperature for 3 days. The solid phase was filtered off through a glass filter, washed two or three times with 5% camphor solutions in appropriate solvents, and kept in these solutions for 5 days.Next, the solid product was placed onto a filter and washed with the corresponding solvent to remove solid camphor impurities. Finally, the product was dried in a nitrogen flow to a constant mass. The absence of solid camphor in the resulting ICFG was checked by X-ray diffraction analysis. 1H NMR spectra were recorded on a pulse Bruker SXP-4-100 spectrometer at a frequency of 90.01 MHz. IR spectra were recorded on a Specord 75-IR spectrometer. The samples of mass 3–3.5 mg were prepared as pellets with KBr. The composition of the ICFG was studied by elemental analysis for C, F, H and Cl (or Br). X-ray diffraction patterns were recorded on a DRON-3 diffractometer using filtered CuKa radiation (Ni filter).The patterns of samples under a layer of the liquid phase were recorded using a special Teflon cell covered with a Teflon film 5 mm in thickness. The patterns of dried samples were recorded using a quartz cell with applied vacuum grease. 1H NMR spectra of dried ICFG with camphor at 298 K contained a single (within the range 0–25 kHz) rather narrow signal (DH1/2 ª 2.151 kHz), which is characteristic of the intercalated substances.This is the evidence of high mobility of camphor in the interstitial space of fluorinated graphite, which is typical of monomolecular layers of intercalated substances in layered compounds.7,8 X-ray diffraction patterns of dry samples exhibit (i) the retention of stage 1 in the ICFG with camphor, (ii) the transition of stage 1 into stage 2 for the ICFG with acetone, ethanol and acetic acid.The latter case is a common feature of the ICFG formed according to reactions (1) and (2) with volatile intercalants. 1,2 Interlayer distances in fluorinated graphite containing no intercalants (in the initial ICFG with BF3) are 6 Å.9 This allows us to estimate the ‘thickness’ of intercalated monolayers of intercalants in the stage 1 ICFG as di a = Jc – 6 Å and the identity period for stage 2 ICFG as Jc b = Jc + 6 Å.X-ray data (Table 1) suggest that Jc for the stage 1 ICFG synthesised using 5% camphor solutions is ~11.6 Å and does not depend on the nature of solvent, i.e., it is determined by the size and orientation of intercalated camphor molecules.Figure 1 shows the IR spectra of the initial camphor, ICFG with acetone and ICFG obtained using a 5% camphor solution in acetone. The IR spectra of ICFG exhibit bands in the C–F bond absorption region (1100–1200 cm–1), which are characteristic of the initial CnHalFm compounds and ICFG with liquid intercalants obtained from these compounds. The absorption bands characteristic of individual camphor (1020, 1050, 1385, 1410, 1450, 1740, 2840 and 2950 cm–1) are observed in the IR spectrum of ICFG with camphor, similarly to the spectrum of the initial camphor, but the absorption bands corresponding to acetone (530, 1220, 1360, 1420, 1715, 2920 and 3000 cm–1) are absent in this case (while they are observed in ICFG with acetone).The IR spectra of dry ICFG obtained from the solutions CnHalFm + Me2CO ® CxFHaly·z1Me2CO + R1 ® CxFHaly·z2R1 + z1Me2CO, CxFHaly·z2R1 + R2®CxFHaly·z3R2 + z2R1, (1) (2) a di a denotes the calculated data of the ‘thickness’ of intercalated monomolecular layers; Jc b denotes the calculated data of the identity period for the stage 2 ICFG.Initial compound is ICFS with BrF3. Table 1 X-Ray diffraction data for ICFG.a Intercalated compound Under liquid solvent After drying in air Jc = d001/Å di a = Jc – 6/Å Jc/Å (experiment) Jc b = d001 + 6/Å (calculation) Acetone 9.6 3.6 15.4 15.6 Ethanol — — 15.6 — Acetic acid 9.3 3.3 15.6 15.3 5% camphor solution in: Acetone 11.5 5.5 11.5 17.5 Ethanol 11.6 5.6 11.6 17.6 Acetic acid 11.6 5.6 11.6 17.6 a ICFG were prepared using a 5% camphor solution in ethanol (experiment nos. 1 and 2) or a 5% camphor solution in acetone (experiment nos. 3 and 4). Table 2 Composition of ICFG with camphor after drying in air.a Experiment Elemental analysis, found (calculated) (%) Calculated (%) Empirical formula C F Br Cm Cc R 1 64.56 (62.85) 27.89 (28.27) 2.00 (2.64) 39.12 25.44 32.27 C2.22FBr002·0.144R 2 64.22 (63.21) 28.13 (27.63) 2.30 (2.58) 39.42 24.80 31.46 C2.22FBr002·0.140R 3 61.49 (63.25) 26.82 (27.56) 2.40 (2.56) 37.62 23.87 30.29 C2.22FBr002·0.141R 4 61.47 (63.33) 26.62 (28.43) 2.10 (2.57) 37.32 24.15 30.64 C2.22FBr002·0.143RMendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) of camphor in ethanol and acetic acid are similar to the above spectra. These data allow us to assume that the solvents are absent from dry ICFG with camphor.Based on this assumption and on the elemental analysis data (Table 2), the empirical formulae of dry ICFG with camphor (R) were calculated. In the absence of solvents in these ICFG, the total carbon (C) content of the ICFG described as CxFHaly·zC10H16O is evidently determined by the carbon of the matrix (Cm) and the carbon of camphor (Cc), or C = Cm + Cc. Cm was calculated using the atomic ratio of carbon to fluorine (Cm/F) in ICFG formed in reactions (1) and (2).It is known10 that this ratio is close to 2.22 when CnBrFm is used. Cc was calculated as the difference C – Cm. This allowed us to calculate the empirical formulae of the obtained ICFG with camphor. The data in Table 2 are the evidence of good reproducibility of the syntheses and show that the calculated camphor content of the dry ICFG is practically independent of the nature of solvent.This confirms the assumption that the solvents are absent from dry ICFG, which was based on the IR-spectral data. Table 2 shows that the empirical formula of dry ICFG obtained according to reactions (1) and (2) using CnBrFm and 5% camphor solutions in acetone, ethanol and acetic acid is close to C2.22FBr0.02·zC10H16O, where z ~ 0.14.Similar experiments and calculations showed that the composition of dry ICFG with camphor obtained using CnClFm is close to C2.23FCl0.1·zC10H16O, where z ~ 0.14. Thus, reactions (1) and (2) can be used to synthesise ICFG with solids. The decomposition of stage 1 ICFG in air, which was described in ref. 10 is not a common feature of ICFG.The stage 1 ICFG stable in air can be prepared when solids are intercalated from their solutions by reactions (1) and (2). Of course, the kinetic stability of these compounds is implied. References 1 N. F. Yudanov, A. S. Nazarov and I. I. Yakovlev, Tezisy dokladov VI Vsesoyuznogo simpoziuma po khimii neorganicheskikh ftoridov (Proceedings of VI All-Union Symposium on Chemistry of Inorganic Fluorides), Novosibirsk, 1981, p. 94 (in Russian). 2 V. G. Makotchenko, A. S. Nazarov, G. C. Yur’ev and I. I. Yakovlev, Zh. Neorg. Khim., 1991, 36, 1950 (Russ. J. Inorg. Chem., 1991, 36, 1110). 3 A. S. Nazarov, V. G. Makotchenko and I. I. Yakovlev, Zh. Neorg. Khim., 1978, 23, 1680 (Russ. J. Inorg. Chem., 1978, 23, 925). 4 Y. I. Nikonorov and L.L. Gornostaev, Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk, 1978, 9, 55 (in Russian). 5 E. Stumpp, Mater. Sci. Eng., 1977, 31, 53. 6 R. Vangelisti and A. Herold, Mater. Sci. Eng., 1977, 31, 67. 7 A. M. Panich, A. M. Danilenko, S. P. Gabuda and I. I. Yakovlev, Zh. Strukt. Khim., 1988, 29 (2), 55 [J. Struct. Chem. (Engl. Transl.), 1988, 29, 211]. 8 A. M. Panich and N. F. Yudanov, Zh. Strukt. Khim., 1991, 32 (2), 79 [J. Struct. Chem. (Engl. Transl.), 1991, 32, 220]. 9 N. F. Yudanov and L. T. Chernyavski, Zh. Strukt. Khim., 1988, 29 (3), 78 [J. Struct. Chem. (Engl. Transl.), 1988, 29, 412]. 10 N. F. Yudanov and L. T. Chernyavski, Zh. Strukt. Khim., 1987, 28 (4), 86 [J. Struct. Chem. (Engl. Transl.), 1987, 28, 534]. 400 1000 2000 3000 n/cm–1 Absorption Figure 1 IR spectra of (1) camphor and (2)–(4) ICFG: (2) CnBrFm, (3) ICFG with a 5% camphor solution in acetone and (4) ICFG with acetone. 1 2 3 4 Received: 2nd April 1998; Com. 98/1285 (8/02790K)

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Collapse of polyhedral two-dimensional foams Petr M. Kruglyakov* and Tat’yana N. Khaskova Penza State Academy of Architecture and Construction, 440028 Penza, Russian Federation. Fax: + 7 8412 43 7277; e-mail: kpyotr10@alpha.stup.ac.ru The comparative experiments with monolayer and bulk foams of the same composition gave the reliable evidence of collective effects at the collapse of bulk foams. It is well known that the lifetime of a foam depends on the pressure drop across the liquid phase of the foam.1 Moreover, a critical pressure drop at which a foam was completely broken in 0.5–2.5 min was found for many foams.1–3 In foams stabilised with non-ionic surfactants like oxyethyl derivatives of alcohols, acids and alkylphenols, this critical pressure strongly depends on temperature. The properties of films in a three-dimensional foam are different from the properties of individual (model) foam films.This difference results form the fact that the size and shape of films in a foam are different, and the kinetics of attaining hydrostatic equilibrium in the films is more complicated in comparison with free films.In addition, co-operative effects occur in foams. These effects are a consequence of the transfer of local perturbations, caused by ruptures of particular films and by the disturbance of a local balance, to neighbouring films and bubbles.1 The aim of this work was to examine the effect of pressure drop in the liquid phase of a foam at constant temperature (T = const) and the effect of temperature at DP = const on the lifetime of a two-dimensional (monolayer) foam and to compare the obtained data to the analogous properties of threedimensional foams for revealing the role of co-operative effects in the collapse (break) of a foam column.The foam was produced by bubbling a gas through a porous membrane (the filter pore diameter was 40 mm) into a surfactant solution.The average diameter of the generated bubbles was about 0.9 mm. The foam was arranged on a glass filter between two glass plates placed in a plane 1 cm apart and covered with a cover glass at the top. Thus, the foam was in contact with the porous membrane on one side and with glass plates on other three sides. In different experiments, the glass thickness (and, correspondingly, the foam layer thickness) was 1, 2 or 4 mm.The entire system was placed in a thermostatted jacket to maintain a required constant temperature. This method for studying a foam monolayer differs from known methods,1,4 in particular, from the method of studying a dynamic (renewable) bubble monolayer on the surface of a surfactant solution.5 The method used allowed us to produce a fully polyhedral foam throughout the height of the monolayer with a controlled positive (capillary) pressure of the liquid phase; the pressure could be varied in particular experiments.The kinetics of attaining steady-state pressure in the borders of a monolayer foam is beyond the scope of this work since it is well known that the equilibrium capillary pressure was attained rather rapidly (in 1–1.5 min) in a porous membrane even at high pressure drops (up to 10 kPa)1 and in a monolayer foam.6 We studied monolayer foams of solutions for which threedimensional foams exhibited different break patterns when a reduced pressure was produced in the liquid phase of the foams.Three-dimensional foams were examined in a thermostatted cell; a Por 40 filter served as the bottom of the cell.In the gravitational field (without a pressure drop applied), monolayer foams of non-ionic surfactants on a porous membrane at 20 °C and a foam of a lysozyme solution exhibited the lifetimes of longer than a hour and about 0.5 h, respectively. The previously developed method1 was used for producing a pressure drop in the foam and the corresponding equilibrium capillary (and disjoining) pressure.According to this method, the foam was brought into contact with a porous membrane the pressure beneath which was reduced. The difference in the pressures above the foam and below the porous membrane was no higher than the capillary pressure in the filter pores in order for only the liquid and not the gas can pass through the pores.Figure 1 demonstrates the functions tp = f(DP), where tp is the foam lifetime at the pressure drop, for monolayer, bilayer and three-dimensional foams produced from a mixture of OP-7 and OP-4 (commercial oxyethylated octylphenols) solutions in the ratio 1:2 (ctotal = 0.3 wt%) with the addition of NaCl (0.2 mol dm–3) at 20 °C. The break of the three-dimensional foam of this solution was avalanche-like at pressure drops higher than 3.5 kPa.A further increase in the pressure did almost not shorten the foam lifetime. As can be seen in Figure 1, the lifetime of monolayer foams of the non-ionic surfactants progressively decreased as the pressure was increased from 2 to 20 kPa. In this case, only a 20 15 10 5 4 8 12 16 20 DP/kPa tp/min Figure 1 The lifetime of foams as a function of the pressure drop for foams prepared of a mixture (2:1) of OP-7 and OP-4 solutions (ctotal = = 0.3 wt% + 0.2 mol dm–3 NaCl): (1) two-dimensional foam, (1a) bilayer foam and (2) three-dimensional foam (h = 2 cm). 1 1a 2 ln tp T–1/10–3 K–1 1 2 3 4 8 6 4 2 3.0 3.1 3.2 3.3 3.4 Figure 2 The function tp = f(1/T) for monolayer foams prepared of a mixture (2:1) of OP-7 and OP-4 solutions; DP = (1) 2, (2) 3, (3) 5 and (4) 7 kPa.Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) decrease in the average degree of dispersity of the foam was observed over a long time as a consequence of the diffusive gas transfer from small to larger bubbles, which were further combined by lateral coalescence to form two-dimensional cavities.The lifetime of foam monolayers shortened from 25 to 5 min as the pressure was increased from 2 to 10 kPa. The lifetime of a foam microvolume (of an approximately bilayer foam) was closer to the lifetime of a three-dimensional foam. In going to microvolumes (a foam height of 2 mm) at T = 20 °C and DP = 2–10 kPa, a decrease in the foam lifetime to 10 or 3–4 min was observed at DP = 2 or 10 kPa, respectively, for the mixture of OP-7 and OP-4 solutions.As the pressure was increased, the formation of cavities, which occupied 1/4 to 1/3 of the total foam volume, was occasionally observed on the periphery of a microvolume; these cavities were formed very rapidly (like an avalanche). The monolayer foams of lysozyme solutions exhibited a different behaviour.Thus, at DP = 1 kPa, initially, the bubbles rapidly enlarged by diffusion within the first minute; next, intense coalescence primarily on the periphery of the monolayer was observed in 3–4 min. The foam was completely broken by five minutes. Lysozyme foam microvolumes were broken at and separated from the filter. The lifetime of these foams was no longer than 2 min.Figure 2 demonstrates a semilogarithmic plot of the lifetime of monolayer foams as a function of the reciprocal of temperature (1/T) at different pressure drops. The foams were obtained from a mixture of OP-7 and OP-4 solutions in the ratio 2:1 (ctotal = 0.3 wt%) with NaCl added (0.2 mol dm–3). The experiments were performed at temperatures below the cloud point, which is 58 °C for the above mixture. It can be seen in Figure 2 that the lifetime of the twodimensional foam shortened with increasing pressure drop in the liquid phase and with increasing temperature.However, a critical temperature at which the break becomes avalanche-like was not observed. Similar tp(1/T) functions were obtained for a foam of a Triton X-100 solution (5×10–3 mol dm–3 + 0.4 mol dm–3 KCl).The lifetimes of two-dimensional foams prepared from this solution shortened with increasing pressure drop at T = const. For example, at 40 °C, tp = 720, 620 and 210 s at DP = 3, 5 and 10 kPa, respectively. As was mentioned above, the critical pressure for a foam of a mixture of OP-7 and OP-4 at T = 20 °C was equal to DP = 3.5 kPa. Because of this, the temperature dependence of the lifetime of these foams at a height of 2 cm was studied at DP < DPc; this dependence is shown in Figure 3.As can be seen, the pressure drop DP = 0.5 kPa was not critical at any temperature up to the cloud point. At a pressure drop of 1 or 2 kPa, the break of the foam became avalanche-like at T = 50 or 44.5 °C, respectively. Curves 2 and 3 in Figure 3 exhibit inflection points, which were shifted towards lower temperatures with decreasing capillary pressure.The temperature function tp(1/T) for non-ionic surfactants is the exponential, which is typical of activation processes with overcoming energy barriers,1,7,8 where Ep is the effective (apparent) activation energy of the break of foams; R is the gas constant; and T is the absolute temperature.This function corresponds to the linear portions of the curves to the right of the inflection points. The Ep values for foams of a mixture of OP-7 and OP-4 were graphically found from the slopes of the linear portions of curves 2 and 3 to be equal to 70.63 and 62.33 kJ mol–1 (at DP = = 1 and 2 kPa, respectively). To elucidate the mechanism of the break of foams of Triton X-100 solutions, in addition to a monolayer foam, foam microvolumes 2 and 4 mm in height (which correspond to ~2 and 4 bubble layers) were also examined.The tp(1/T) curves also exhibited inflection points typical of three-dimensional foams prepared from the same solution.7,8 The lifetimes of foams shortened with increasing thickness of the layer at constant temperature. We found that an increase in the positive (capillary) pressure in the liquid phase resulted in a decrease in the lifetime of all foams.However, the lifetime of a monolayer foam was significantly longer at all pressure drops, and the mechanism of breaking was different from that in three-dimensional foams. In a monolayer foam, the lifetime shortened as the pressure was increased because of accelerating outflow of the liquid and attaining successively higher disjoining pressures.This resulted in a decrease in the film thickness and the activation barrier of rupture. For this reason, the diffusive gas transfer (diffusion enlargement of the average size) and the lateral coalescence were accelerated. However, a critical pressure with the instantaneous break of the entire foam was not attained in solutions of the non-ionic surfactants examined. It is evident that this behaviour of monolayer foams is due to restricted possibilities for the transfer of local perturbations from one bubble to another in the course of the film rupture because of fixation of the Plateau–Gibbs borders of the foam by a solid support on all sides.On the other hand, the lifetime and the character of breaking were almost identical in monolayer and three-dimensional foams with structured adsorption layers having high surface viscosity. Thus, comparative experiments with monolayer and threedimensional foams provided a convincing demonstration of the occurrence of co-operative effects which come into play in a foam even in thin layers, beginning with a foam bilayer. References 1 D.Exerowa and P. M. Kruglyakov, Foam and Foam Films: Theory, Experiment, Application, Elsevier, Amsterdam, 1998. 2 Kh. I. Khristov, D. R. Ekserova and P. M. Kruglyakov, Kolloidn. Zh., 1981, 43, 101, 195 [Colloid J. USSR (Engl. Transl.), 1981, 80, 166]. 3 Kh. Khristov, P. M. Kruglyakov and D. Exerowa, Colloid Polym. Sci., 1979, 257, 506. 4 F.Schutz, Trans. Faraday Soc., 1942, 38, 85. 5 V. V. Krotov, A. G. Nekrasov and A. I. Rusanov, Mendeleev Commun., 1996, 178. 6 P. M. Kruglyakov and A. A. Tyurin, Materialy XXVIII nauchno-tekhnicheskoi konferentsii (Proceedings of the XXVIII Scientific and Technical Conference), Penza, 1995, part II, p. 183 (in Russian). 7 N. G. Fokina and P. M. Kruglyakov, Trudy vsesoyuznogo seminara po kolloidnoi khimii i fiziko-khimicheskoi mekhanike pishchevykh i bioaktivnykh dispersnykh sistem (Proceedings of the All-Union Conference on the Colloid Chemistry and Physico-chemical Mechanics of Food and Biologically Active Disperse Systems), Nauka, Moscow, 1991, p. 71 (in Russian). 8 P. M. Kruglyakov, N. G. Fokina and S. N. Alenkina, Kolloidn. Zh., 1990, 52, 365 [Colloid J. USSR (Engl. Transl.), 1990, 315]. 8 7 6 5 4 3 2 1 3.0 3.1 3.2 3.3 3.4 3.5 ln tp T–1/10–3 K–1 Figure 3 The function tp = f(1/T) for three-dimensional foams prepared of a mixture (2:1) of OP-7 and OP-4 solutions at different capillary pressures; DP = (1) 0.5, (2) 1 and (3) 2 kPa. 1 2 3 tp = tp 0exp(Ep/RT), Received: 16th December 1998; Com. 98/1411

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年代:1999

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Experimental measurements and a group additivity approach for estimating the standard molar enthalpies of formation of dioxins Victor P. Kolesov,*a Olga V. Dorofeeva,b Vladimir S. Iorish,b Tatiana S. Papina,a Vera A. Lukyanovaa and Svetlana V. Melkhanovaa a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation.Fax: +7 095 932 8846; e-mail: kolesov@thermo.chem.msu.su b V. P. Glushko Thermal Centre, High Energy Density Research Centre, Joint Institute for High Temperatures, Russian Academy of Sciences, 127412 Moscow, Russian Federation The enthalpies of formation of dibenzo-p-dioxin and its polychlorinated derivatives have been measured, and a complete set of the enthalpies of formation has been constructed.Understanding the reasons of the unusual stability of polychlorinated dibenzo-p-dioxins (PCDDs) is of primary importance. These reasons can be of kinetic or thermodynamic origin. In any case, reliable thermodynamic data are needed for the thermodynamic modelling of their formation. Meanwhile, the most important thermodynamic data, the standard molar enthalpies of formation (DfH0m ), have never been measured experimentally; there are only some estimates of these values.In particular, the DfH0m values of all 75 PCDDs were estimated by Shaub.1 Recent re-estimations2,3 of these values differ considerably from the Shaub’s result. There is no doubt that all estimates will be more accurate, if reliable experimental values of DfH0m for several model compounds will be available.The aim of this work is to obtain experimentally the reliable values of DfH0m for some PCDDs and based on these data to construct a complete set of enthalpies of formation of PCDDs. Unsubstituted dibenzo-p-dioxin 1, 1-chlorodibenzo-p-dioxin 2, 2-chlorodibenzo-p-dioxin 3 and 2,3-dichlorodibenzo-p-dioxin 4 have been prepared by a standard procedure.4 The substances were purified by recrystallization from ethanol or o-xylene and subsequently by vacuum distillation.The purity of the samples was determined using a Mettler differential scanning calorimeter (DSC-30). The melting temperatures, Tfus, and molar enthalpies of fusion, DfusH0 m, were also measured (Table 1). A rotating-bomb calorimeter,5 was used in the combustion experiments.The platinum-lined bomb of volume 0.120 dm3 was fitted with a tantalum lid. The temperature rise was measured with a copper resistance thermometer and a bridge circuit. The sensitivity of the temperature measurements was ª 5×10–5 K. The products of combustion were analysed after each run according to a procedure described in ref. 6. The enthalpies of sublimation were measured on a Calvet microcalorimeter using a standard procedure.6 The results and the derived thermochemical quantities (at T = 298.15 K) are presented in Table 2. The derived values of DfH0m (g) differ considerably from those estimated by Shaub1 but they are close to recent estimates.2 The DfH0 m (g) values given in Table 2 indicate that the displacement of two hydrogen atoms in the 2- and 3-positions by chlorine atoms causes a difference in DfH0 m (g) values equal to –52.7 kJ mol–1.The analogous difference between the DfH0 m (g) values of o-dichlorobenzene and benzene is equal to –52.4 kJ mol–1. Almost the same heat effects of chlorination can be deduced from the enthalpies of formation of 2,3- and 3,4-dichlorophenols (–55.2 kJ mol–1 and –53.9 kJ mol–1 respectively7). For 2, the effect of chlorination on the enthalpy of formation is equal to –29.0 kJ mol–1.This value is also very close to that in monochlorobenzene (–30.6 kJ mol–1). Obviously, the energetic effect of oxygen–chlorine interactions in PCDDs is not large, contrary to Shaub’s estimation.1 The DfH0 m (g) value of 3 represents the only exception to the general rule.To all appearances, a redeterminaton of this value is needed. This attempt was made recently with a sample of 3 (0.8 g, 0.9985 purity). Unfortunately, because the amount of the substance was small, we failed to determine accurately the combustion energy. However, the –DcU0m (cr) value for 3 obtained in the preliminary experiments was about 12–15 kJ mol–1 lower than the value given in Table 2 in brackets, and thus the –DfH0m (g) value was about 12–15 kJ mol–1 higher.In this situation, only the DfH0m (g) values for 1, 2 and 4 can be considered as a basis for estimating the DfH0m (g) values of PCDDs. To estimate the enthalpies of formation of all PCDDs, we used the difference method,8,9 which is completely consistent with group additivity.Because the available experimental data on PCDDs are insufficient to develop an additive scheme for the prediction of enthalpies of formation of PCDDs, chlorinated benzenes were considered in this work as model compounds. This is in agreement with the above experimental results on the effect of chlorination. The enthalpies of formation were estimated on the assumption that the difference between these values for anyone of PCDDs and dibenzo-p-dioxin (DD) is equal to the difference between appropriate chlorinated benzene(s) and benzene.The chlorination of each ring in PCDDs is considered to have no influence on the other benzene ring. The enthalpies of formation for model compounds were obtained in this work for DD and taken from refs. 10 and 11 for benzene and chlorinated benzenes.An example is shown in Figure 1. The same result can be obtained using group contribution values from Table 3. According to designation by Benson,12 groups A and B can be written as CB–(H) and CB–(Cl), Table 1 Temperature and enthalpy of fusion and purity of the compounds. Compound Tfus/K DfusH0m / kJ mol–1 Purity, mole fraction 1 392.45±0.10 21.9±0.6 0.9990 2 373.95±0.14 20.0±1.1 0.9976 3 360.75±0.10 22.1±0.4 0.9975 4 431.60±0.20 27.1±0.6 0.9996 aPreliminary results.A new determination of this value is needed. Table 2 Experimental results and calculated values (kJ mol–1). Compound –DcU0m (cr) –DcH0m (cr) –DfH0m (cr) DsubH0m –DfH0m (g) this work Ref. 1 Ref. 2 1 5714.2±4.1 5716.7±4.1 148.7±4.4 89.55±0.72 59.2±4.4 62.8 55.0 2 5561.5±4.4 5562.7±4.4 183.4±4.7 95.20±1.10 88.2±4.8 95.0 84.5 3 (5573.6±2.8)a (5574.8±2.8)a (171.3±3.2)a 97.24±0.55 (74.1±3.3)a 137.7 84.5 4 5406.4±6.6 5406.4±6.6 220.5±6.8 108.60±1.00 111.9±6.9 204.0 106.5Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) respectively. The group D consists of two O–(CB)2 and four CB–(CB)2(O) groups and describes the dioxin frame as a whole.Six D corrections are used for 1,2-, 1,3-, 1,4-, 1,2,3-, 1,2,4- and 1,2,3,4-interactions of chlorine atoms. For example, We estimate the error in the enthalpies of formation, calculated from the group increments, to be 10–40 kJ mol–1 depending on the chlorine content. To estimate the gas-phase enthalpies of formation of PCDDs, Thompson2 has developed a group contribution method based on the experimental data for chlorinated benzenes, quinones, hydroquinones and phenols.Pointing to the experimental errors in enthalpies of formation of chlorinated organic compounds, which are often considerable, Thompson2 has excluded the experimental data by Platonov and Simulin11 from consideration. At the same time, Thompson2 has included the DfH0 (298.15 K) value for hexachlorobenzene, which was recommended by Pedley10 although this value seems to be overestimated.Here, we prefered to base on the work,11 which was made using carefully purified materials and properly tested methods. Different attitudes to the experimental data11 are the main reason for discrepancies (up to 40 kJ mol–1) in the enthalpies of formation estimated for PCDDs with high degrees of chlorination in this work and by Thompson.2 We believe that, to remove the contradictions between these two models, reliable experimental data should be obtained for chlorinated benzenes and chlorinated dibenzo-p-dioxins with three or more chlorine atoms.This work was supported by the Russian Foundation for Basic Research (grant no. 96-02-016223).References 1 W. M. Shaub, Thermochim. Acta, 1982, 55, 59. 2 D. Thompson, Thermochim. Acta, 1995, 261, 7. 3 O. V. Dorofeeva and L. V. Gurvich, Zh. Fiz. Khim., 1996, 70, 7 (Russ. J. Phys. Chem., 1996, 70, 1). 4 A. D. Kuntsevich, V. F. Golovkov, S. A. Chernov, V. R. Rembovsky, N. M. Troshkin and S. I. Baulin, Dokl. Ross. Akad. Nauk, 1993, 332, 461 [Dokl. Chem. (Engl. Transl.), 1993, 332, 225]. 5 V. P. Kolesov, G. M. Slavutskaya, S. M. Alekhin and S. M. Skuratov, Zh. Fiz. Khim., 1969, 43, 1046 (Russ. J. Phys. Chem., 1969, 43, 585). 6 T. S. Papina, V. P. Kolesov, V. P. Vorobieva and V. F. Golovkov, J. Chem. Thermodyn., 1996, 28, 307. 7 M. A. V. Ribeiro da Silva, M. L. C. C. H. Ferrao and F. Jiye, J. Chem. Thermodyn., 1994, 26, 839. 8 D. R. Stull, E. F. Westrum, Jr.and G. C. Sinke, The Chemical Thermodynamics of Organic Compounds, Wiley, New York, 1969. 9 N. Cohen and S. W. Benson, Chem. Rev., 1993, 93, 2419. 10 J. B. Pedley, Thermochemical Data and Structures of Organic Compounds, Thermodynamics Research Center, College Station, Texas, Vol. 1, 1994. 11 (a) V. A. Platonov and Y. N. Simulin, Zh. Fiz. Khim., 1983, 57, 1387 (Russ. J. Phys.Chem., 1983, 57, 840); (b) V. A. Platonov and Y. N. Simulin, Zh. Fiz. Khim., 1984, 58, 2682 (Russ. J. Phys. Chem., 1984, 58, 1630); (c) V. A. Platonov and Y. N. Simulin, Zh. Fiz. Khim., 1985, 59, 300 (Russ. J. Phys. Chem., 1985, 59, 179); (d) V. A. Platonov and Y. N. Simulin, Zh. Fiz. Khim., 1985, 59, 1378 (Russ. J. Phys. Chem., 1985, 59, 814). 12 S. W. Benson, Thermochemical Kinetics, Wiley, New York, 1976. Table 3 Group additivity values for estimating the enthalpies of formation of PCDDs. Group Value/kJ mol–1 A 13.765 B –16.835 D –169.32 D12 8.8 D13 4.3 D14 1.1 D123 13.0 D124 1.1 D1234 14.4 DfH0m (2,3,7,8-TCDD) = D + 4A + 4B + 2D12 = –164.0 kJ mol–1 O O Cl Cl Cl Cl O O Cl Cl = 2 DfH0 –164.0 –59.2 + 2 [ 30.2 – 82.6 ] Figure 1 The derivation of the enthalpy of formation (kJ mol–1) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Received: 19th November 1998; Com. 98/1401 (8/09456J)

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Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Role of electronic factors in the formation of a standard quasi-stable mixture of toxic polychlorinated dibenzo-para-dioxins and polychlorinated dibenzofurans Sergei S. Yufit N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation. Fax: +7 095 135 5328; e-mail: yufit@ioc.ac.ru Only electronic factors are responsible for the kinetics and mechanism of consecutive chlorination of 2,3,7,8-tetrachlorodibenzopara- dioxin and 2,3,7,8-tetrachlorodibenzofuran; this results in the formation of a standard quasi-stable mixture of chlorination products (congeners), polychlorinated dibenzo-p-dioxins and dibenzofurans, whose composition was independent of the sample type and the place of sampling.Polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) containing chlorine atoms in the 2,3,7,8-positions are extremely toxic substances (the entire group of these compounds is usually referred to as dioxins). The major quantity of these substances is formed as a result of incineration of municipal and hospital wastes and other hightemperature processes in which chlorine-containing substances are produced, destroyed or treated.1 Because dioxins are a serious hazard to the environment and human health, the mechanism of their formation is studied intensively (see the recent data in ref. 2). Unfortunately, the data acquired hitherto are inadequate to develop the commonly accepted mechanism of the formation and reactions of dioxins because of great experimental difficulties and very expensive analysis for dioxins.Here a new approach to the elucidation of some details in the mechanism of dioxin formation is suggested. It is based on the analysis of mixtures formed in different sources of contamination. It is believed that, in all cases, the chlorination of 2,3,7,8- tetrachlorodibenzo-para-dioxin (TCDD) or 2,3,7,8-tetrachlorodibenzofuran (TCDF) proceeds consecutively with the participation of the same chlorinating agent at all stages of the production of completely chlorinated products.The chlorination path depends on the ortho-para-directing effects of oxygen and chlorine in the molecule. The quasi-steady-state concentrations of products (congeners) in the mixture formed depend on only the activity of a particular site in the reacting dioxin molecule and the rate of ‘discharge’ (consumption) of the congener formed.In the course of a thorough examination of the contamination of human milk with PCDDs and PCDFs in Russia, which was performed within the framework of the WHO programme ‘Second Round of Exposure Studies on Levels of PCBs, PCDDs and PCDFs in Human Milk’, we found that the composition of PCDD/PCDF contaminants in human milk sampled in different Russian cities was very similar.3–5 A comparison with the data obtained by other researchers in different countries6 supported this observation.In this case, the toxicity of milk expressed in the toxic equivalents I-TEQ (i.e., referred to the toxicity of TCDD, which was taken to be unity on the international scale of the equivalent toxicity factors I-TEF) could differ widely (Figure 1).As an example, Table 1 summarises the data for milk from two cities in Russia and for bottom sediment samples from the river of Severnaya Dvina (these data were obtained in different analytical laboratories). To explain the similar distribution of congeners (not the different TEQ level), we used a mechanism of the consecutive chlorination of aromatic rings in TCDD and TCDF, the precursors of toxic PCDD and PCDF groups, and compared these qualitative data to the experimental data published in terms of ‘more–less’. We considered the slopes between two neighbouring points in graphs of the kind shown in Figure 1.The expression of analytical data in terms of molar concentrations did not affect the results obtained.The qualitative composition of the produced mixture can be determined on the basis of simple chemical notions using the model of the formation of a mixture of 17 toxic PCDDs and PCDFs. This approach seems to be very useful taking into account that the analytical data are extremely difficult to obtain.In this mechanism, TCDD 1 and TCDF 8 (see Table 1 for the compound numbers) are the starting substances. In the consideration of the sequence (probability) of replacement by chlorine in aromatic rings, only a single assumption will be used: the reaction proceeds as usual electrophilic substitution in the aromatic series; therefore, ortho-substitution with respect to aThe data for Salavat (Russia) were obtained in the laboratory of A.K. D. Liem (RIVM, the Netherlands) and for Volgograd (Russia), in the laboratory of W. A. Traag (RIKILT-DLO, the Netherlands). bThe data (averaged over eight samples) were obtained in the laboratory of N. A. Klyuev (Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Russia). cn. d.= not detected (the limit of detection was ~0.1 pg per gramm of fat). Table 1 Dioxin concentrations in human milka (pg per gramm of fat) and bottom sediments from the river Severnaya Dvinab (pg kg–1) (data in terms of 10– 4 pmol g–1 for milk and pmol kg–1 for bottom sediments are given in parentheses). Compound Code Congener Mr Salavat Volgograd Severnaya Dvina 1 D4 2,3,7,8-tetraCDD 322 5.3 (164.6) 2.73 22 (0.068) 2 D5 1,2,3,7,8-pentaCDD 365.5 3.9 (106.7) 1.47 20 (0.056) 3 D6(1) 1,2,3,4,7,8-hexaCDD 391 1.0 (25.58) 1.14 39 (0.1) 4 D6(2) 1,2,3,6,7,8-hexaCDD 391 2.7 (69.05) 3.26 48 (0.123) 5 D6(3) 1,2,3,7,8,9-hexaCDD 391 0.7 (17.9) n.d.c 40 (0.102) 6 D7 1,2,3,4,6,7,8-heptaCDD 425.5 3.4 (79.9) 3.98 4420 (0.987) 7 D8 octaCDD 460 16.4 (356.5) 18.32 3900 (8.48) 8 F4 2,3,7,8-tetraCDF 306 0.8 (26.14) 1.44 54 (0.18) 9 F5(1) 1,2,3,7,8-pentaCDF 340.5 0.4 (11.7) 0.62 20 (0.06) 10 F5(2) 2,3,4,7,8-pentaCDF 340.5 6.9 (202.6) 8.37 17 (0.05) 11 F6(1) 1,2,3,4,7,8-hexaCDF 375 3.7 (98.7) 4.64 48 (0.13) 12 F6(2) 1,2,3,6,7,8-hexaCDF 375 2.0 (53.4) 2.32 28 (0.08) 13 F6(3) 1,2,3,7,8,9-hexaCDF 375 0.7 (18.7) n.d. 7 (0.02) 14 F6(4) 2,3,4,6,7,8-hexaCDF 375 0.1 (2.7) 0.82 68 (0.18) 15 F7(1) 1,2,3,4,6,7,8-heptaCDF 409.5 1.5 (36.6) 1.34 370 (0.9) 16 F7(2) 1,2,3,4,7,8,9-heptaCDF 409.5 0.1 (2.4) n.d. 41 (0.1) 17 F8 octaCDF 444 0.3 (6.76) n. d. 1100 (2.48)Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) the oxygen atom is predominant. Correspondingly, isomers that are formed by ortho-substitution will exhibit higher concentrations in the mixture.The consumption of a formed isomer at the following step of chlorination will be considered as a correction factor. The resulting mixture of congeners is considered to be standard (independent of the sources of contamination) and quasi-stable. As an example, we consider the chlorination of TCDF 8 (Scheme 1). At the first step of the reaction, two pentachloro isomers 9 and 10 can be formed because, in contrast with dioxin 1, not all positions accessible to chlorination in initial furan 8 are equivalent.Using the accepted model, it is easy to predict that the amount of isomer 10 formed at the first step will be significantly greater than that of isomer 9. The ratio between these isomers can serve as a measure of the reactivity of the ortho-position with respect to oxygen in this system (the 4- and 6-positions) and of the ortho-position with respect to chlorine atoms (1- and 9-positions).To determine the excess of isomer 10 over isomer 9, the rates of consumption (‘discharge’) of these isomers at the following step of chlorination should be considered. Furan 9 has two ortho-positions accessible to chlorination, whereas furan 10 has only one position of this kind.Hence it follows that 9 will be consumed at the second step of the reaction more rapidly than 10. Thus, furan 9 will be formed more slowly and consumed more rapidly than furan 10. As a consequence, the concentration of furan 9 in the formed mixture of congeners will be lower than that of furan 10. This conclusion ([10] > [9]) is supported by data obtained by different authors.At the third step of chlorination, four hexachloro derivatives of furan (11, 12, 13 and 14) are formed. Among these compounds, furan 13 can be mentioned. To form 13, the substitution in the ortho-position with respect to chlorine in 9 is required. At the same time, the consumption of 13 is maximally facilitated by two active sites in the 4- and 6-positions.Consequently, among the hexachloro isomers, the rates of formation and consumption of isomer 13 are lowest and highest, respectively, and isomer 13 will exhibit the lowest concentration among all hexachloro isomers. This fact is in complete agreement with analytical data. The formation of isomer 11 also requires unfavourable replacement in the 1-position of isomer 10.However, isomer 11 will be formed at a higher rate than 13 because, in this case, 11 can also be formed from isomer 9. It is evident from a comparison between the rates of formation of isomers 14 and 12 that the formation of 12 is more probable than the formation of 14: there are two active sites (the 4- and 6-positions) for the formation of 12 from 9 and only a single active site (the 6-position) for the formation of 14 from 10.Thus, at the stage of production, isomer 13 will be formed in the smallest amount. However, the distribution of the other three isomers is not so obvious, and it is more reasonable to compare the rates of ‘discharge’ (consumption). Isomer 13 is the most readily consumed, and its concentration in the mixture will be low (see above).This is a good reference compound for testing the model. Isomer 14 is poorly consumed (the two unfavourable 1- and 9-positions); this fact would result in its accumulation. However, this isomer cannot be formed from 9; consequently, it has only a single channel of formation in contrast with 11 and 12. Isomers 11 and 12 are not dissimilar in the ortho-positions; however, 11 is produced from both of pentachloro isomers 9 and 10, and 12 cannot be produced from 10.It is believed that the concentrations of 11 and 12 will be O Cl Cl Cl Cl O Cl Cl Cl Cl O Cl Cl Cl Cl Cl Cl O Cl Cl Cl Cl O Cl Cl Cl Cl O Cl Cl Cl Cl O Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl O Cl Cl Cl Cl O Cl Cl Cl Cl O Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl 8 9 10 11 12 13 14 15 16 17 [10] > [9] [11] � [12] � [14] > [13] [15] > [16] 1 2 3 4 6 7 8 9 2 3 7 8 2 3 7 8 2 3 7 8 2 3 7 8 2 3 7 8 2 3 7 8 2 3 7 8 2 3 7 8 2 3 7 8 4 6 9 1 6 9 1 9 4 6 4 9 6 9 9 6 Scheme 1 Chlorination of furans (see Table 1 for the numeration of compounds).Honolulu, USA South Vietnam West Germany Suzdal, Russia Salavat, Russia Congeners Concentration (pg per gramm of fat) 102 101 100 10–1 10–2 10–3 10–4 10–5 D4 D5 D6 D6 D6 D7 D8 F4 F5 F5 F6 F6 F6 F6 F7 F7 F8 Figure 1 Comparison between the contamination of human milk in different countries, expressed as the toxic equivalents TEQ of the scale I-TEF.The data for Honolulu, Suzdal (Russia) and Salavat (Russia) were taken from refs. 4 and 5, for West Germany and South Vietnam, from refs. 6 and 7. The points at a level of 10–4 are below the limit of detection. The codes of congeners correspond to those in Table 1.Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) not strongly different; however, 11 will be somewhat predominant. Thus, the concentration distribution in the mixture of hexachloro isomers will be as follows: [11] � [12] > [14] > [13].At the fourth step of the reaction, isomer 15 can be produced from three hexachloro isomers 11, 12 and 14, and isomer 16, from isomers 11, 12 and 13 (the amount of 13 in the mixture is always small). The comparison between the rates of ‘discharge’ of these isomers shows that isomer 16 will be consumed more rapidly than 15, which has no free ortho 6-position favourable for chlorination.Hence it follows that isomer 15 will be formed more rapidly and consumed more slowly than 16. Therefore, the concentration of isomer 15 will be higher than that of 16, which is the case. As for the concentration of 17, it will not be used for evaluating the reliability of the mechanism suggested, as is the case with octachloro dioxin 7. The reason is that concentrations of these compounds, as well as concentrations of tetrachloro isomers 1 and 8, can vary significantly for unknown reasons.The same mechanism can also be applied to the chlorination of TCDD. Thus, the following concentration ratio in the standard quasistable mixture of toxic PCDD and PCDF congeners was found: For statistical checking, published data on the PCDD/PCDF contamination of various matrices of both biological (blood, milk and foods) and anthropogenic origin (sludge, slimes, bottom sediments, soils, wastewater etc.)8,9 were considered.The total number of analyses was 70; the total number of experimental points was 1190; 910 points were used for comparison with the predicted composition of the mixture. The slopes for the first and last members of the series were not compared because of the absence of data on the initial concentrations.Deviations from the predicted slops were observed for 40 points (4.3%). References 1 The Inventory of Sources of Dioxin in the United States, US EPA, External review draft, April 1998. Report #EPA/600/P-98/002Aa. 2 Organohalogen Compounds. Annual Reports of the International Symposium on Chlorinated Dioxins and Related Compounds. 3 S. S.Yufit, Organohalogen Compounds, 1997, 33, 165. 4 W. A. Traag and S. S. Yufit, Organohalogen Compounds, 1997, 33, 524. 5 A. K. D. Liem and R. M. C. Theelen, Dioxins: Chemical Analysis, Exposure and Risk Assessment, Tauw Milieu, The Netherlands, 1997, p. 186. 6 A. Schecter, J. R. Startin, V. Rose, C. Wright, I. Parker, D. Woods and H. Hansen, Chemosphere, 1990, 20, 919. 7 A. Schecter, P. Fürst, C. Fürst and O. Päpke, Chemosphere, 1991, 23, 1903. 8 Z. Amirova and E. Kruglov, Dioksiny v okruzhayushchei srede, nagruzka na cheloveka i immunologicheskie aspekty vliyaniya iskhodnogo urovnya zagryazneniya dioksinami v kogortnykh gruppakh (Dioxins environment, load on human being and immunological aspects of dioxin influence on background level in cohort groups), Reactiv, Ufa, 1998, p. 115 (in Russian). 9 S. S. Yufit, N. A. Klyuev and E. S. Brodsky, in Dioksiny — supertoksikanty XXI veka (Dioxins as the supertoxicatns of XXI century), ed. Yu. A. Arsky, VINITI RAS, Moscow, 1998 (in Russian). Dioxins [1]/[2] not found [4] > [3], [5] [6]/[7] not found Furans [8]/([9] + [10]) not found [10] > [9] [13] < [11], [12], [14] [11] � [12] � [14] > [13] [15] > [16] ([15] + [16])/[17] not found Received: 4th December 1998; Co

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) New 2,5-diazabicyclo[2.2.1]heptanes and their application in the asymmetric addition of diethylzinc to benzaldehyde Ulrich Jordis,*a Martin Kesselgruber,a Sven Nerdingera and Kurt Mereiterb a Institut für Organische Chemie der TU Wien, A-1060 Wien, Austria. Fax: +43 1 58801 15499; e-mail: ulrich.jordis@tuwien.ac.at b Institut für Mineralogie, Kristallographie und Strukturchemie der TU Wien, A-1060 Wien, Austria New (1S,4S)-2,5-diazabicyclo[2.2.1]heptane derivatives synthesised by directed ortho metalation result in enantioselectivities of up to 78% e.e.when used as catalysts in the addition of diethylzinc to benzaldehyde. The addition of diethylzinc to prochiral aldehydes is a convenient model for testing chiral ligands as enantioselective catalysts for this fundamental carbon–carbon bond-forming reaction.Enantiopure b-amino alcohols1 often are used as catalysts for these reactions. Compounds structurally related to proline were found to be particularly efficient for the preparation of highly effective chiral ligands.2–4 Recently, Guijarro et al.5 introduced a related class of catalysts using the 2-azabicyclo[2.2.1]heptane moiety which was prepared via a hetero Diels–Alder reaction.Here we report 2,5-diazabicyclo[ 2.2.1]heptane derivatives as a new class of chelating ligands for organozinc compounds. N-Boc-substituted pyrrolidines are readily deprotonated by sec-butyllithium to yield a-lithio amino synthetic equivalents.6–8 The inclusion of (–)-sparteine as the chiral auxiliary9 provides excellent stereochemical control.However, when an enantiopure compound, such as (1S,4S)-2-methyl-2,5-diazabicyclo[2.2.1]- heptane 1, prepared by the ‘chiral-pool’ synthesis from trans- 4-hydroxy-L-proline10 is used as the starting material, the need for an additional chiral base is eliminated. We investigated the deprotonation of 2, which contains three possible sites for metalation (Figure 1) and relies on the highly directing and activating power of carbamate groups.11 Compound 2 was prepared in five steps starting from (S,trans)- 4-hydroxyproline.10 However, the N-tosyl-O,O'-dimesyl-protected (S,trans)-4-hydroxy-2-pyrrolidinemethanol replaced the previously reported tritosyl-protected substance.10 The deprotonations were performed using 1.7 equiv.of sec-butyllithium/TMEDA and the subsequent addition of a selected electrophile.† The reactivity depends on the choice of solvent, e.g., the use of dry diethyl ether instead of THF enhances the regioselectivity but decreases the conversion and yield. For most electrophiles, substitution at the 4-position appears to be favoured over the 6-position; however, in the presence of benzophenone, 3,3'-bis- (trifluoromethyl)benzophenone or diphenyl disulfide, the 6- substituted products can be isolated by chromatography.On the basis of the structure determination of 4b by X-ray diffraction (Figure 2),‡ it was possible to assign the configuration of all other products: as shown in Figure 2, the orientation of the substituent at the 6-position was found to be equatorial. The sterically more hindered electrophiles (c, e) resulted in the substitution predominantly on the bridgehead (Table 1).† Preparation and analysis of 3a and 5a. A solution of 882 mg (8.00 mmol) of TMEDA in 15 ml of dry THF was cooled to –78 °C and 6.2 ml of 1.3 M BusLi in hexane (8.00 mmol; 1.7 equiv.) was added dropwise. After stirring for 30 min at this temperature, a solution of 1 g (4.70 mmol) of 2 in 10 ml of dry THF was added dropwise at –78 °C or below. The mixture was additionally stirred for 3 h at this temperature. 2.92 g (16.00 mmol) of benzophenone in 10 ml of dry THF was added. Then the mixture was warmed slowly to room temperature and quenched with 30 ml of saturated aqueous ammonium chloride. The layers were separated, and the aqueous phase was extracted with diethyl ether (3×30 ml).The organic layers were collected, dried over sodium sulfate and evaporated. The residue was purified by column chromatography (silica gel, light petroleum–ethyl acetate, 2:1). The two fractions (3a and 5a) were recrystallised from diisopropyl ether yielding 500 mg of 3a (27%) and 300 mg of 5a (16%) as colourless crystals.For 3a: mp 125–126 °C. 1H NMR (200 MHz, CDCl3) d: 1.21 (s, 9H, Boc–Me), 1.32 (d, 1H, H-7, J 11 Hz), 2.33 (s, 3H, NMe), 2.36 (d, 1H, H-7, J 11 Hz), 3.10 (d, 1H, H-3, J 10 Hz), 3.14 (d, 1H, H-3, J 10 Hz), 3.18–3.22 (m, 1H, H-1), 3.53 (d, 1H, H-6, J 12 Hz), 3.84 (d, 1H, H-6, J 12 Hz), 7.07–7.65 (m, 10H, aromatic H). 13C NMR (50 MHz, CDCl3) d: 28.10, 41.32, 42.23, 54.60, 60.72, 61.73, 76.82, 77.91, 80.40, 126.37, 126.68, 127.21, 127.33, 127.70, 144.97, 146.88, 155.56.Found (%): C, 72.79; H, 7.78; N, 7.09. Calc. for C24H30N2O3 (%): C, 73.07; H, 7.66; N, 7.10. For 5a: mp 135–136 °C. 1H NMR (200 MHz, CDCl3) d: 1.18 (s, 9H, Boc–Me), 1.39 (d, 1H, H-7, J 10 Hz), 1.67 (d, 1H, H-7, J 10 Hz), 2.15 (s, 3H, NMe), 2.35 (d, 1H, H-3, J 10 Hz), 3.30–3.34 (m, 1H, H-1), 3.67 (d, 1H, H-3, J 10 Hz), 4.38 (d, H-6, J 3 Hz), 4.68–4.72 (m, 1H, H-1), 7.10–7.80 (m, 10H, aromatic H). 13C NMR (50 MHz, CDCl3) d: 27.73, 33.68, 42.95, 59.92, 63.26, 66.95, 68.27, 78.81, 79.78, 126.08, 126.51, 126.85, 127.15, 127.19, 127.88, 145.62, 146.96, 157.46. Found (%): C, 72.70; H, 7.68; N, 7.07. Calc. for C24H30N2O3 (%): C, 73.07; H, 7.66; N, 7.10. ‡ Crystal data for 4b: C26H28F6N2O3, orthorhombic, space group P212121, a = 9.070(3) Å, b = 12.011(4) Å, c = 24.835(6) Å, V = 2705.5 Å3, Z = 4, T = 297 K. Details of the crystal structure determination may be obtained from the Director of the Cambridge Crystallographic Data Centre, Lensfield Road, Cambridge CB21EW (UK) quoting the reference number CCD-103148.N N R Me H H H <6e> <6a> <4> 1 R = H 2 R = Boc Figure 1 Deprotonation sites in 2.aIsolated yield after flash chromatography. Table 1 Products obtained by lithiation of 2 and quenching with various electrophiles. Substituent R Yield of 3 (%)a Yield of 4 (%)a Yield of 5 (%)a a Diphenylhydroxymethyl 27 — 16 b [3,3'-Bis(trifluoromethyl)- diphenyl]hydroxymethyl 12 12 4 c 9-Hydroxy-9H-fluoren-9-yl 26 — 14 d Phenylmercapto 31 — 32 e 9-hydroxy-9H-xanth-9-yl 24 — — f N-Phenylaminocarbonyl — — 13 N N Boc Me N N Boc Me R N N Boc Me R 3 4 5 RMendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Cleavage of the Boc group was achieved in moderate to excellent yields either by using TFA or (in the case of 3a, 5a and 4b) by refluxing with aqueous sodium hydroxide.8 The resulting compounds were tested for their ability to direct chiral selectivity in the addition of diethylzinc to benzaldehyde.§ As summarised in Table 2, the highest enantiomeric excess was observed for ligand 6a.Generally, the compounds with flexible phenyl substituents (6a, 6b and 8a) resulted in higher e.e. values than more rigid derivatives (6c and 6e). The yields of the catalysed reactions were moderate giving up to 50% of benzyl alcohol as a by-product. When the reaction was conducted using catalyst 6a in dry light petroleum instead of toluene, a decrease in the enantioselectivity from 78% to 38% e.e.was observed. In summary, we have introduced a new class of chiral catalysts capable of inducing moderate-to-high e.e. values in the addition of diethylzinc to benzaldehyde with moderate yields.These catalysts are synthesised by directed lithiation of 2, which can be produced in technical-scale amounts. Further studies investigating the effects of different catalyst ligand substituents on the stereoselectivity of this addition reaction are in progress. § A solution of 15 mg (0.05 mmol) of 3a in 2 ml of dry toluene was cooled to 0 °C and treated with 2.2 ml (2.2 mmol) of 1.0 M diethylzinc in hexane.After stirring for 30 min at this temperature, 0.1 ml of benzaldehyde (1.0 mmol) was added dropwise. The mixture was stirred at 0 °C for 24 h, quenched with 10 ml of saturated aqueous ammonium chloride and extracted with diethyl ether (3×10 ml). The organic layers were collected, dried over sodium sulfate and evaporated.The oily residue was filtered through silica gel (light petroleum–ethyl acetate, 9:1). We are grateful to the Sanochemia group for the donation of chemicals. We thank Professor Andreas Rizzi for supplying the chiral HPLC column. S. N. thanks the Fonds zur Förderung der wissenschaftlichen Forschung (FWF) for his postdoctoral scholarship (Lise-Meitner grant no.M0435-CHE). References 1 (a) R. Noyori and M. Kitamura, Angew. Chem., 1991, 103, 35; (b) K. Soai and S. Niwa, Chem. Rev., 1992, 92, 833. 2 A. Ookawa and K. Soai, J. Chem. Soc., Perkin Trans. 1, 1987, 1465. 3 E. J. Corey, P. Yuen, F. J. Hannon and D. A. Wierda, J. Org. Chem., 1990, 55, 784. 4 M. Shi, Y. Satoh and Y. Masaki, J. Chem. Soc., Perkin Trans. 1, 1998, 2547. 5 D. Guijarro, P.Pinho and P. G. Andersson, J. Org. Chem., 1998, 63, 2530. 6 P. Beak, W. J. Zajdel and D. B. Reitz, Chem. Rev., 1984, 84, 471. 7 P. Beak and W. K. Lee, J. Org. Chem., 1993, 58, 1109. 8 D. J. Gallagher, S. Wu, N. A. Nikolic and P. Beak, J. Org. Chem., 1995, 60, 8148. 9 D. Hoppe, F. Hintze, P. Tebben, M. Paetow, H. Aherns, J. Schwerdtfeger, P. Sommerfeld, J. Haller, W. Guarnieri, S.Kolczewski, T. Hense and I. Hoppe, Pure Appl. Chem., 1994, 50, 1479. 10 T. F. Braish and D. E. Fox, J. Org. Chem., 1990, 55, 1684. 11 (a) V. Snieckus, Chem. Rev., 1990, 90, 879; (b) P. Beak, A. Basu, D. J. Gallagher, Y. S. Park and S. Thayumanavan, Acc. Chem. Res., 1996, 29, 552. C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(23) C(24) C(25) C(26) F(1) F(2) F(3) F(4) F(5) F(6) O(1) O(2) O(3) N(1) N(2) Figure 2 Structure of 4b in the solid state.Selected bond lengths (Å): C(1)–C(2) 1.549, C(1)–C(12) 1.574, C(1)–N(1) 1.475, C(4)–N(1) 1.483, N(1)–C(7) 1.361, C(12)–O(3) 1.426; selected bond angles (°): N(1)–C(1)– C(12) 116.5, C(2)–C(1)–C(12) 114.4, N(1)–C(1)–C(2) 100.0; torsional angle C(12)–C(1)–C(2)–N(2) 164.4°. aSubstituents R: see Table 1. bEnantiomeric excesses were determined by HPLC analysis using a chiral column (Daicel Chiralcel OD-H, 5% PriOH– n-hexane, 0.5 ml min–1, detection at 254 nm). cBoc-protected ligand. dReaction conducted in dry light petroleum. Table 2 Results of the asymmetric addition of diethylzinc to benzaldehyde.a e.e.b Configuration 6a 78 R 6ac 38 R 6b 37 R 6c 2 R 6d 10 S 6e 4 S 7b 11 S 8a 38 R 8fd 16 R NH N Me NH N Me R NH N Me R 6 7 8 R Received: 18th December 1998; Com. 98/1416

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC