DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, 3727–3730 3727 Resolution of a cyclopalladated ferrocenylketimine Yang Jie Wu,* Xiu Ling Cui, Chen Xia Du, Wen Ling Wang, Rui Yun Guo and Rong Feng Chen Department of Chemistry, Zhengzhou University, Zhengzhou 450052, P.R. China. E-mail: wyj@mail.zzu.edu.cn Received 19th May 1998, Accepted 23rd September 1998 The cyclopalladated ferrocenylketimine, [{Pd[(h5-C5H5)Fe{h5-C5H3C(CH3)]] N(C6H4CH3-4)}](m-Cl)}2] 1 was resolved into optically active diastereomers by using (S)-leucine as chiral auxiliary. The new optically active (S)-leucinato complexes of PdII containing ferrocenylketimine could be converted into optically active dimers with the same absolute configurations in the ferrocene moiety.The structure of the chiral dimer (Rp,Rp)-1 was determined by X-ray diVraction, on the basis of which the absolute configurations of all the optically active compounds studied were ascertained. Introduction Cyclometallated compounds are important intermediates for synthesizing ortho-disubstituted aromatic compounds as well as heterocycles.1 Chiral cyclopalladated compounds are valuable reagents for asymmetric reaction, resolution, the determination of enantiomeric excess and absolute configuration of chiral substrates.2 On the other hand, optically active ferrocene derivatives are of increasing importance in the synthesis of chiral ligands used in asymmetric catalysis and asymmetric synthesis.3 Therefore much eVort has gone into developing practical methodologies for asymmetric synthesis and resolution of cyclopalladated ferrocene derivatives, such as: (a) enantiopure ferrocenes were mainly obtained by resolution methods with a chiral amino acid;4 (b) Sokolov et al.5 have developed useful methods to aVord the planar chiral cyclopalladated ferrocene derivatives in the presence of the salts of optically active amino acids as nucleophilic catalysts.However most of the documented researches involving optically active cyclopalladated ferrocene derivatives have focused on 1-ferrocenyl- N,N-dimethylethylamine and its analogues; there have been few reports on other ligands.6 Although the cyclopalladation reaction of ferrocenylimines has been extensively studied,7 the cyclopalladated ferrocenylimines have not been resolved.In this paper will be reported the resolution and structure of a cyclopalladated ferrocenylketimine. Results and discussion A useful candidate for this study was the complex 1 prepared by the published method.7a Reaction of complex 1 with Na2CO3 and (S)-leucine gave the (S)-leucinato complex of PdII containing ferrocenylketimine as a solid in 84% yield (Scheme 1).The diastereomers 2 shown in Scheme 1 were assumed to be the trans-N, N form, similar to ortho-palladated complexes.4,8 It was found that diastereomers 2 could be resolved both by chromatography and fractional crystallization techniques and the former was a most eYcient method.Their isolation was easily achieved by chromatography of the reaction mixture on a silica gel plate developed with CH2Cl2–CH3COCH3 (1 : 1), since the diastereomer (1)-2 exhibited a higher Rf value than that of the diastereomer (2)-2. Both of the compounds were characterized by elemental analysis, IR and 1H NMR spectra. The infrared spectra of the imine showed a band at 1561 cm21. Other IR bands were found at ca. 1000 and 1100 cm21, which indicated an unsubstituted cyclopentadienyl ring.7a The IR features of the pair of diastereomers 2 were very similar.The 1H NMR spectrum of (1)-2 showed signals of H-3 at d 4.66 (d), H-4 at d 4.37 (t) and that of H-5 at d 4.60 (d), while the other (2)-2, showed peaks at d 4.72 (d), 4.38 (t) and 4.61 (d), respectively. The signal of H-3 was used as an indication of complete separation of the diastereomers. The complex (1)-[Pd{C5H5FeC5H3C(CH3)]] N(C6H4CH3- 4)}(S-LeuO)] (1)-2 was mixed with LiCl in acetic acid and stirred at room temperature for 10 min, giving (1)-1 (Scheme 2) with the same absolute configuration of the ferrocene moiety, which was confirmed by CD spectra. The CD spectra of the pair of diastereomers 2 are shown in Fig. 1 together with the CD spectrum of (1)-1. The CD spectra of the diastereomers 2 were nearly enantiomeric to each other and the CD spectrum of (1)-1 was similar to that of (1)-2, which indicated that compound (1)-1 had the same absolute configuration in the ferrocene moiety as that of (1)-2.The chiral dimer (1)-1 was air stable, soluble in dicholoromethane, acetone, and other common organic solvents. Moreover, it underwent a bridgesplitting reaction with PPh3 to produce quantitatively the Scheme 13728 J. Chem. Soc., Dalton Trans., 1998, 3727–3730 Scheme 2 Scheme 3 monomeric triphenylphosphine derivative (1)-3, a typical reaction of chloride-bridged binuclear complexes of palladium 9 (Scheme 3). The CD spectrum of (1)-3 is compared with that of (1)-1 in Fig. 2. The results also showed that the absolute configuration of the ferrocene moiety in (1)-3 was same as that in (1)-1, consistent with the addition of triphenylphosphine leading only to cleavage of the di-m-chloro bridges without breaking of Pd–C and Pd–N bonds. As has been previously described, the (S)-leucinato complexes of cyclopalladated ferrocenylimines can be successfully Fig. 1 The CD spectra of methanol solutions of (a) complexes (Rp,Rp)- 1, (b) (Rp,Sc)-2 and (c) (Sp,Sc)-2. Fig. 2 The CD spectra of methanol solutions of complexes (a) (Rp,Rp)-1 and (b) (Rp)-3. converted into dimers with the same configuration in the ferrocene moiety, but their single crystals are diYcult to obtain. Therefore, the optically active dimer (1)-1 was chosen to determine the absolute configuration by X-ray diVraction. The structure is shown in Fig. 3. Selected bond lengths and angles are listed in Tables 1 and 2, respectively.The structure shows clearly that (1)-1 is a binuclear complex of palladium, and that both the palladium atoms are linked to ortho positions of the substituted ferrocenyl rings resulting in two five membered metallocycles. The two metallocycles, which are nearly planar, form a dihedral angle of 62.708 with each other. The plane Table 1 Selected bond distances (Å) for complex (Rp,Rp)-1 Pd(1)–Cl(1) Pd(1)–N(1) Pd(2)–Cl(1) Pd(2)–N(2) Fe(1)–C(1) Fe(1)–C(3) Fe(1)–C(5) Fe(1)–C(7) Fe(1)–C(9) Fe(2)–C(20) Fe(2)–C(22) Fe(2)–C(24) Fe(2)–C(26) Fe(2)–C(28) N(1)–C(11) N(2)–C(30) C(1)–C(2) C(2)–C(3) C(3)–C(4) C(6)–C(7) C(7)–C(8) C(9)–C(10) C(20)–C(24) C(21)–C(30) C(23)–C(24) C(25)–C(29) C(27)–C(28) 2.328(3) 2.071(8) 2.490(3) 2.091(9) 2.04(1) 2.06(1) 2.06(1) 2.04(1) 2.08(1) 2.02(1) 2.05(1) 2.04(1) 2.09(1) 2.08(1) 1.30(1) 1.30(1) 1.40(2) 1.42(2) 1.44(2) 1.34(2) 1.36(2) 1.48(3) 1.42(2) 1.44(2) 1.38(2) 1.43(3) 1.42(3) Pd(1)–Cl(2) Pd(1)–C(1) Pd(2)–Cl(2) Pd(2)–C(20) Fe(1)–C(2) Fe(1)–C(4) Fe(1)–C(6) Fe(1)–C(8) Fe(1)–C(10) Fe(2)–C(21) Fe(2)–C(23) Fe(2)–C(25) Fe(2)–C(27) Fe(2)–C(29) N(1)–C(13) N(2)–C(32) C(1)–C(5) C(2)–C(11) C(4)–C(5) C(6)–C(10) C(8)–C(9) C(20)–C(21) C(21)–C(22) C(22)–C(23) C(25)–C(26) C(26)–C(27) C(28)–C(29) 2.470(3) 1.969(9) 2.321(3) 1.96(1) 2.02(1) 2.04(1) 2.04(1) 2.04(1) 2.03(2) 2.06(1) 2.03(1) 2.06(2) 2.04(2) 2.05(2) 1.43(1) 1.42(1) 1.43(1) 1.48(2) 1.42(1) 1.41(3) 1.38(3) 1.40(2) 1.44(2) 1.44(2) 1.38(3) 1.43(2) 1.41(3)J.Chem. Soc., Dalton Trans., 1998, 3727–3730 3729 Fig. 3 Molecular structure of complex (Rp,Rp)-1. Pd(1)Cl(2)Pd(2) forms a dihedral angle of 129.678 with plane Pd(2)Cl(1)Pd(1). Owing to the co-ordination between the palladium atoms and the nitrogen atoms, the angles Pd(1)– C(1)–C(2), C(1)–C(2)–C(11), Pd(2)–C(20)–C(21) and C(20)– C(21)–C(30) are decreased to 113.5, 116.8, 114.1 and 116.78, respectively, compared with the normal value of 1268.7a The Pd(1)–N(1) and Pd(2)–N(2) distances are 2.071(8) and 2.091(9) Å, respectively, suggesting the formation of Pd–N bonds.The two halves of the molecule are in a cis arrangement and exhibit Table 2 Selected bond angles (8) for complex (Rp,Rp)-1 Cl(1)–Pd(1)–Cl(2) Cl(1)–Pd(1)–C(1) Cl(2)–Pd(1)–C(1) Cl(1)–Pd(2)–Cl(2) Cl(1)–Pd(2)–C(20) Cl(2)–Pd(2)–C(20) Pd(1)–Cl(1)–Pd(2) Pd(1)–N(1)–C(11) C(11)–N(1)–C(13) Pd(2)–N(2)–C(32) Pd(1)–C(1)–Fe(1) Pd(1)–C(1)–C(5) C(1)–C(2)–C(11) N(1)–C(11)–C(2) C(2)–C(11)–C(12) N(1)–C(13)–C(15) Pd(2)–C(20)–C(21) C(22)–C(21)–C(30) N(2)–C(30)–C(31) N(2)–C(32)–C(33) 87.0(1) 92.5(3) 177.2(3) 86.6(1) 179.2(4) 93.4(4) 81.96(9) 116.4(7) 120.9(9) 121.4(7) 119.9(5) 138.7(9) 116.8(10) 112.3(9) 118.9(10) 121.9(10) 114.1(9) 133(1) 125(1) 120(1) Cl(1)–Pd(1)–N(1) Cl(2)–Pd(1)–N(1) N(1)–Pd(1)–C(1) Cl(1)–Pd(2)–N(2) Cl(2)–Pd(2)–N(2) N(2)–Pd(2)–C(20) Pd(1)–Cl(2)–Pd(2) Pd(1)–N(1)–C(13) Pd(2)–N(2)–C(30) C(30)–N(2)–C(32) Pd(1)–C(1)–C(2) C(3)–C(2)–C(11) N(1)–C(11)–C(12) N(1)–C(13)–C(14) Pd(2)–C(20)–Fe(2) Pd(2)–C(20)–C(24) C(20)–C(21)–C(30) N(2)–C(30)–C(21) C(21)–C(30)–C(31) N(2)–C(32)–C(34) 168.7(3) 100.6(2) 80.4(4) 100.5(3) 169.7(2) 79.5(5) 82.55(9) 122.2(7) 115.6(8) 122(1) 113.5(7) 133(1) 128(1) 119.2(10) 124.1(6) 138(1) 116.7(10) 113(1) 120(1) 121(1) identical planar chirality (R configuration).10 So the compound (1)-2 had the same absolute R configuration in the ferrocene moiety, and (2)-2 had the S configuration, and (1)-2, (2)-2, (1)-1 and (1)-3 were assigned as (Rp,Sc)-2, (Sp,Sc)-2, (Rp,Rp)-1 and Rp-3, respectively.Experimental General Melting points were measured on a WC-1 apparatus and are uncorrected. Elemental analyses were determined with a Carlo Erba 1160 elemental analyzer. Proton NMR spectra were recorded on a Bruker DPX 400 spectrometer using Me2SO as the solvent and SiMe4 as an internal standard, IR spectra on a Perkin-Elmer FTIR 1750 spectrophotometer. Preparative TLC was performed on dry silica gel plates developed with dichloromethane–acetone (1 : 1).Optical rotations at 5890 Å were determined by a Perkin-Elmer 341 polarimeter at 20 8C. The CD spectra were recorded on GJASCO J-20C automatic recording spectropolarimeter at 20 8C. Syntheses [Pd{C5H5FeC5H3C(CH3)]] N(C6H4CH3-4)}(S-LeuO)] 2. To a methanol suspension (10 ml) of complex 1 (1.0 g, 1.1 mmol) was added a slight excess of (S)-leucine (0.16 g, 1.2 mmol) and Na2CO3 (0.13 g, 1.2 mmol) and stirred for 6 h at room temperature until the solution became clear.After evaporation of the solvent in vacuo the crude residue was treated with CH2Cl2 in order to remove the unchanged amino acid. Further evapor-3730 J. Chem. Soc., Dalton Trans., 1998, 3727–3730 ation of the CH2Cl2 and treatment of the residue with CH2Cl2– light petroleum (bp 60–90 8C) (1 : 3) aVorded a 1 : 1 mixture of diastereomers 2 in 84% yield. Their separation was easily achieved by TLC of the mixture on a silica gel plate developed with dichloromethane–acetone (1: 1); the first band was (Rp,Sc)-2, the second (Sp,Sc)-2.(Rp,Sc)-(1)-[Pd{C5H5FeC5H3C(CH3)]] N(C6H4CH3-4)}(SLeuO)] (Rp,Sc)-2: red crystals, mp >250 8C (decomp.), [a]D 20 12209.3 deg cm3 g21 dm21 (c 0.0086 g per 100 ml in CH3OH), Rf 0.68 (Found: C, 54.32; H, 5.48; N, 5.15. Calc. for C25H30- FeN2O2Pd: C, 54.32; H, 5.47; N, 5.07%). IR(KBr): 3287, 3091, 2955, 2867, 1619, 1561, 1508, 1474, 1106, 1001, 817, 722 and 669 cm21. 1H NMR: d 4.66 (d, 1 H, J = 2.0, H-3), 4.60 (d, 1 H, J = 2.4, H-5), 4.37 (t, 1 H, J = 2.2, H-4), 4.32 (s, 5 H, H-19), 7.17 (d, 2 H, J = 8.0, NC6H4), 7.00 (d, 2 H, J = 8.0, NC6H4), 2.05 (s, 3 H, CH3); 2.31 (s, 3 H, CH3), 1.53 [m, 1 H, CH(CH3)2], 1.66 (m), 1.85 (m, 2 H, CH2), 3.20 (m, 1 H, NH2CH), 0.88, 0.86 [d, 6 H, J = 6.6 Hz, (CH3)2CH]. (Sp,Sc)-(2)-[Pd{C5H5FeC5H3C(CH3)]] N(C6H4CH3-4)}(SLeuO)] (Sp,Sc)-2: red crystals, mp >250 8C (decomp.), [a]D 20 22344.8 deg cm3 g21 dm21 (c 0.0116 g per 100 ml in CH3OH), Rf 0.58 (Found: C, 54.32; H, 5.42; N, 5.12.Calc. for C25H30- FeN2O2Pd: C, 54.32; H, 5.47; N, 5.07%). IR(KBr): 3290, 3092, 2954, 2868, 1618, 1561, 1508, 1471, 1106, 1001, 815, 720 and 669 cm21. 1H NMR: d 4.72 (d, 1 H, J = 2.0, H-3), 4.61 (d, 1 H, J = 2.4, H-5), 4.38 (t, 1 H, J = 2.2, H-4), 4.32 (s, 5 H, H-19), 7.18 (d, 2 H, J = 8.0, NC6H4), 6.98 (d, 2 H, J = 8.0, NC6H4), 2.06 (s, 3 H, CH3), 2.32 (s, 3 H, CH3), 1.68 [m, 1 H, CH(CH3)2], 1.92, 1.78 (m, 2 H, CH2), 3.17 (m, 1 H, NH2CH), 0.95, 0.99 [2d, 6 H, J = 6.4 Hz, (CH3)2CH].Rp,Rp-(1)-[{PdCl[C5H5FeC5H3C(CH3)]] N(C6H4CH3-4)]}2] (Rp,Rp)-1. A methanol solution (1 ml) of 0.1 g of complex (Rp,Sc)- 2 and 2 mol of LiCl was mixed with acetic acid (6 ml). The mixture was stirred at room temperature for about 10 min, then filtered, and washed with light petroleum three times. The solid obtained was recrystallized from CH2Cl2–light petroleum (bp 60–90 8C) to produce compound (Rp,Rp)-1.Red crystals, yield 92.4%, mp >210 8C (decomp.), [a]D 20 13212.5 deg cm3 g21 dm21 (c 0.0080 g per 100 ml in CHCl3) (Found: C, 49.92; H, 3.91; N, 2.93. Calc. for C19H18ClFeNPd: C, 49.82; H, 3.96; N, 3.06%). IR(KBr): 3090, 2920, 1551, 1508, 1474, 1105, 999, 817, 721 and 693 cm21. 1H NMR: d 5.14 (2 H, H-3), 4.73 (2 H, H-5), 4.48 (2 H, H-4), 4.38 (s, 10 H, H-19), 2.01 (s, 6 H, CH3), 2.31 (s, 6 H, CH3), 7.14 (d, 4 H, J = 8.0, NC6H4) and 6.94 (d, 4 H, J = 6.8 Hz, NC6H4).Compound (Rp)-3. This was prepared by the published method.7a Red crystals, yield 79.2%. mp >220 8C (decomp.). [a]D 20 11704.5 deg cm3 g21 dm21 (c 0.0088 g per 100 ml in CHCl3) (Found: C, 61.48; H, 4.67; N, 1.93. Calc. for C37H33ClFeNPPd: C, 61.72; H, 4.62; N, 1.94%). IR(KBr): 3067, 3049, 2921, 1569, 1507, 1480, 1094, 998, 817, 758 and 700 cm21. 1H NMR: d 3.15 (1 H, H-3), 4.65 (1 H, H-5), 4.17 (1 H, H-4), 3.30 (s, 5 H, H-19), 2.05 (s, 3 H, CH3); 2.31 (s, 3 H, CH3), 7.15 (d, 2 H, J = 7.6, NC6H4), 6.89 (d, 2 H, J = 7.6 Hz, NC6H4), 7.48 m, 7.70 m (15 H, PPh3).Crystal structure determination of complex (Rp,Rp)-1 Crystal data. C38H36Cl2N2Fe2Pd2, M = 916.12, red prismatic, crystal size 2.70 × 0.10 × 1.00 mm, monoclinic, space group P21 (no. 4), a = 11.64(1), b = 12.083(2), c = 13.004(2) Å, b = 94.445(3)8, Z = 2, V = 1824.1 Å3, Dc = 1.668 g cm23, F(000) = 912, m(Mo-Ka) = 19.25 cm21. Data collection. All measurements were made on a Rigaku RAXIS-IV imaging plate area detector with graphite monochromated Mo-Ka radiation (l = 0.71070 Å).The data were collected at 15 ± 1 8C to a maximum 2q value of 55.08. A total of 45 images of 4.008 oscillation were collected, each being exposed for 16.0 min. The crystal-to-detector distance was 110.00 mm with the detector at the zero swing position. The data were corrected for Lorentz-polarization eVects. The structure was solved by direct methods 11 and expanded using Fourier techniques.The non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. The final cycle of full-matrix least-squares refinement was based on 3374 observed reflections [I > 3.00s(I)] and 416 variable parameters. The function minimized was Sw(|Fo| 2 |Fc|)2. The maximum and minimum peaks on the final Fourierdi Verence map corresponded to 1.89 and 21.45 e Å23, respectively. The absolute configuration of complex (Rp,Rp)-1 was confirmed by the significance of the diVerence between the two sigma weighted R factors, as judged by the Hamilton test.12 The final R factors were 0.042 (R9 = 0.062) and 0.043 (0.063) for the R and S configuration in the ferrocene moiety, respectively.All calculations were performed using the TEXSAN crystallographic software package.13 CCDC reference number 186/1177. See http://www.rsc.org/suppdata/dt/1998/3727/ for crystallographic files in .cif format. Acknowledgements We are grateful to the National Science Foundation of China (Project 29592066) and the Natural Science Foundation of Henan Province for financial support.We thank Professors V. I. Sokolov, Weiwei Huang and Hongwen Hu for valuable dicussion. References 1 M. I. Bruce, Angew. Chem., Int. Ed. Engl., 1977, 16, 73; C. H. Chao, D. W. Hast, R. Bau and R. F. Heck, J. Organomet. Chem., 1979, 179, 301; N. Beydoun and M. PfeVer, Synthesis, 1990, 729; M. PfeVer, J. P. Sutter, A. Decian and J. Fischer, Organometallics, 1993, 12, 1167. 2 S. Y. M. Chooi, P. H. Leung, C. C. Lim, K. F. Mok, G. H. Quek, K. Y. Sim and M. K. Tam, Tetrahedron: Asymmetry, 1992, 3, 529; S. Y. M. Chooi, S. Y. Siah, P. H. Leung and K. F. Mok, Inorg. Chem., 1993, 32, 4812; J. L. Bookham and W. Mcfarlane, J. Chem. Soc., Chem. Commun., 1993, 1352; D. G. Allen, G. M. Mclaughlin, G. B. Robertson, W. L. SteVen, G. Salem and S. B. Wild, Inorg. Chem., 1982, 21, 1007; R. T Aplin, H. Doucet, M. W. Hooper and J. M. 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