Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) Iminophosphites as new chiral P,N-bidentate ligands Konstantin N. Gavrilov,*a Alexei I. Polosukhin,b Oleg G. Bondarev,b Andrei V. Korostylev,b Sergey E. Lyubimov,a Alexei A. Shiryaev,a Zoya A. Starikovab and Vadim A. Davankovb a Department of Chemistry, S. A. Esenin Ryazan State Pedagogical University, 390000 Ryazan, Russian Federation.Fax: +7 095 135 6471; e-mail: chem@ttc.ryazan.ru b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation 10.1070/MC2001v011n01ABEH001356 The coordination of new chiral P,N-hybrid ligands possessing a phosphite-type phosphorus donor centre and azomethine nitrogen to [Rh(CO)2Cl]2 and PdCl2(cod) was examined. In the mid-1980¡�s, H.Brunner introduced chiral phosphoruscontaining ligands bearing a distant imino group . iminophosphines. 1 In the last years, such P,N-bidentate compounds were widely used in asymmetric metal complex catalysis and coordination chemistry.2.5 Although they vary in molecular structure, all iminophosphines possess identical diphenylphosphine phosphorus centres.On the other hand, increasing the P-centre ¥�-acidity of the P,N-bidentate ligand is well known to favour high chemical and optical yields in a number of catalytic reactions. The most effective way to increase the ¥�-acidity and catalytic efficiency is to replace carbon atoms in the first coordination sphere of phosphorus by oxygen and/or nitrogen atoms. Some impressive results have been already achieved this way.6.9 Hence, the inclusion of a distant imino group into a phosphorous acid ester molecule results in P,N-bidentate ligands of a new type, iminophosphites, which are promising for enantioselective catalysis.In this study, we prepared the first optically active compounds of this class based on our previous experience in developing chiral aminophosphites.9 New chiral iminophosphites 1a.c bearing a distant azomethine group have been obtained by one-step phosphorylation¢Ó of corresponding iminoalcohols¢Ô (Scheme 1).Compounds 1a.c¡× are readily soluble in organic solvents and stable on keeping dry for several months. Their complexation¢Ò leads to metal chelates with cis-oriented phosphorus and nitrogen atoms (Scheme 2).In the case of 2a.c, it is proved by n(CO), n(Rh.Cl) and 1J(P,Rh) values (Table 1), which are characteristic of chlorocarbonyl RhI complexes with chelate-forming nitrogen-containing phosphites.14 It should be added that 1J(C,Rh) values are in the range 68.75 Hz typical of cis-[Rh(CO)Cl(PN)] chelates.14 The presence of a Pd.P bond in the complexes 3a,b is proved by dP and .dP values (Table 2) typical of six-membered palladium chelates with acyclic nitrogen-containing phosphites.15 Two equally intense n(Pd.Cl) bands in the far IR region of 3a,b result from the cis-configuration of chlorine ligands and different trans-influences of phosphorus and nitrogen centres (Table 2).A comparison between the spectral data for free and coordinated iminophosphites demonstrates significant downfield coordination shifts of the resonances of carbon atoms adjacent to phosphorus (.dC 2.8 ppm) and nitrogen atoms.The azomethine carbon exhibits a large value of .dC (9.11 ppm), which is indicative of binding an imine nitrogen atom to a metal atom. Compounds 2a and 2b were isolated as single crystals and their structures were determined by X-ray diffraction studies.¢Ó¢Ó The angular distortions of the Rh coordination geometries in both 2a and 2b molecules are almost equal, a Rh atom is situated at 0.073(2) A (2a) and 0.101(2) A (2b) from the P(1)Cl(1)N(1)C(1) basal plane.The chelate metal rings exhibit asymmetrically distorted Rh(1),C(3)-boat and N(1),O(2)-boat conformations in 2a and 2b, respectively. ¢Ó General procedure. An equimolar mixture of (RO)2PNEt2 [R = (1S)- endo-(.)-bornyl,10 Pri 11] (0.01 mol) and a corresponding iminoalcohol in toluene (20 ml) was stirred under reflux for 4 h.Then, the solvent was evaporated and the residue was distilled at 0.8 mmHg (65.80% yield). [a]D 20 = .4.63 (c 2.42, CHCl3, 1a), [a]D 15 = +17.35 (c 1, CHCl3, 1b), [a]D 20 = .7.71 (c 1.2, CHCl3, 1c). ¢Ô Syntheses of the iminoalcohols {(2R)-2-[N-(benzylideneamino)]-3- methylpropan-1-ol12 and (2R)-2-[N-(p-dimethylaminobenzylideneamino)]- 3-methylbutan-1-ol, [a]D 19 = +9.82 (c 10, CH2Cl2)} are analogous to the described procedures.13 ¡× All compounds gave spectroscopic and analytical data consistent with the proposed structure. (RO)2PNEt2 HO N R1 Ar N R1 Ar O P RO RO 1a.c a R = Pri, R1 = Et, Ar = Ph Me Me b R = , R1 = Et, Ar = Ph c R = R1 = Pri, Ar = 4-Me2NC6H4 Scheme 1 Me .HNEt2 ¢Ò General procedure. A solution of 1a.c, 4 (3.6¡¿10.4 mol) in CH2Cl2 (5 ml) was added dropwise to a solution of [Rh(CO)2Cl]2 (1.8¡¿10.4 mol) or PdCl2(cod) (3.6¡¿10.4 mol) in the same solvent (15 ml) at 20 ¡ÆC with stirring. The reaction mixture was stirred at 20 ¡ÆC for 0.5 h. The excess of the solvent was then removed in a vacuum (40 mmHg), and 10 ml of hexane (in the case of 2a.c, 5) or diethyl ether (in the case of 3b,c) was added to the residue.The precipitate obtained was separated by centrifugation, washed with hexane (10 ml) or diethyl ether and dried in a vacuum (1.5 mmHg) to give a product in 80.95% yield. Table 1 Selected spectroscopic data for compounds 2a.c and 5.IR/cm.1 31P NMR 13C (CO) NMR n(CO), CHCl3 (KBr) n(Rh.Cl) CHCl3 (Nujol) dP/ppm 1J(P,Rh)/ Hz dC(CO)/ ppm 1J(C,Rh)/ Hz 2J(C,P)/ Hz 2a 2019 (1999) 289 (285) 128.20 250.9 188.42 73.76 18.16 2b 2016 (2012) 290 (294) 130.22 254.3 187.46 72.95 18.77 2c 2014 (1996) 291 (288) 129.65 255.4 187.61 72.13 18.61 5 2022 (2011) 296 (296) 128.00 264.8 185.34 71.53 20.85 Table 2 Selected spectroscopic data for compounds 3a,b.IR, n(Pd.Cl)/cm.1, CHCl3 (Nujol) 31P NMR (CDCl3) dP /ppm .dP a / ppm a.dP = dP(complex) . dP(ligand). 3a 339, 328, 298 (335, 326, 295) 76.10 .63.1 3b 344, 294 (342, 284) 76.62 .64.2Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) When designing chiral P,N-bidentate ligands, not only the ¥�-acceptor ability of a phosphorus centre but also the ¥ä-donor ability of nitrogen should be taken into account.Thus, in a series of ferrocene-based phosphinopyrazoles, optical yields in Rh-catalysed hydroboration.oxidation of alkenes16,17 and in Pd-catalysed hydrosilylation.oxidation of alkenes18 increased with the electron- donor ability of a pyrazole unit. In this connection, a concept of electronically non-symmetric ligands was suggested (the higher the ¥�-acceptor ability of the P-centre and the ¥ä-donor ability of the N-centre, the more electronically asymmetric the compound).This parameter can be estimated using the value of n(CO) in the IR spectrum of the chlorocarbonyl complex [Rh(CO)Cl(PN)].17 In particular, for structurally similar complexes with identical phosphorus centres and different nitrogen centres, a compound with a lower value of n(CO) possesses a more active ¥ò-donor nitrogen-containing centre and hence is more electronically asymmetric.¢Ô¢Ô On this basis, we synthesised a Rh(I) chlorocarbonyl complex with the same P-centre as in 2b but bearing a tertiary amino group¡×¡× (Scheme 3).Selected spectral data for 5 are shown in Tables 1 and 2. Note that n(CO) (in CHCl3) for 2b is 6 cm.1 lower than that for 5 (Table 1).It indicates a higher electron-donating ability of an imino group in comparison to an amino group and, therefore, a more pronounced electronic asymmetry of iminophosphite 1b. An increase in the electron-donor ability of a nitrogen-containing unit causes a decrease of 1J(P,Rh) (Table 1). A similar behaviour was observed when the spectral parameters of 2a and its recently obtained11 analogue 5 [R = Pri, n(CO) 2022 cm.1 (CHCl3), 1J(P,Rh) 261.7 Hz (CDCl3)] were compared.¢Ó¢ÓCrystallographic data for 2a: at .80 ¡ÆC crystals of C18H are monoclinic, space group P21, a = 9.042(4), b = 8.727(4), c = = 13.904(7) A, b = 92.32(4)¡Æ, V = 1096.3(9) A3, Z = 2, M = 491.74, m(MoK¥á) = 0.995 mm.1, 2778 reflections were measured, 2567 (Rint = = 0.0443) independent reflections were used in all calculations.The final wR(F2) was 0.0883 (all data), R1(F) = 0.0327 [F, 2298 reflections with I > 2s(I)]. All hydrogen atoms (except from six atoms) were located from the difference Fourier syntheses and refined in an isotropical approximation, the hydrogen atoms in two Me groups [C(14)H3 and C(15)H3] were placed in geometrically calculated positions and included in the refinement using the rigid model approximation with the temperature factors Uiso = 1.5Ueq(C), where Ueq(C) is the equivalent isotropical temperature factor for carbon atom bonding to the corresponding hydrogen atom.Crystallographic data for 2b¡�0.25CH2Cl2: at .163 ¡ÆC crystals of C32.25H48Cl1.50NO4PRh are tetragonal, space group I4, a = 30.230(2), b = 30.230(2), c = 7.5935(5) A, V = 6939.5(7) A3, M = 700.77, Z = 8, m(MoK¥á) = 0.688 mm.1, 37077 reflections were measured, 9499 (Rint = = 0.0610) independent reflections were used in all calculations.The final wR(F2) was 0.1431 (all data), R1(F) = 0.0606 [F, 5092 reflections with I > 2s(I)]. All hydrogen atoms were placed in geometrically calculated positions and included in the refinement using the rigid model approximation with the temperature factors Uiso = 1.2Ueq(Ci) or 1.5(Cii), where Ci and Cii are sp2- and sp3-carbon atoms to which the corresponding hydrogen atom is attached.The solvate CH2Cl2 molecules are disordered over several positions in channels along a four-fold axis. Yellow crystals of 2a and 2b¡�CH2Cl2 were obtained from dichloromethane solutions by slow evaporation.A Bruker SMART (2a) or Syntex P21 diffractometer (2b¡�CH2Cl2) was used. The structures were solved using direct methods and refined by full-matrix least-squares on F2. All calculations were performed using the SHELXTL PLUS 5.0 program. Atomic coordinates, bonds 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, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/75.C(5) C(4) C(3) Cl(1) N(1) 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(1) C(2) O(1) O(2) O(3) Rh(1) P(1) O(4) Figure 1 General view of a molecule of 2a.Selected bond lengths (A): Rh(1).C(1) 1.813(6), Rh(1).N(1) 2.123(4), Rh(1).P(1) 2.186(2), Rh(1). Cl(1) 2.400(2), O(2).C(2) 1.436(7); principal bond angle (¡Æ): N(1).Rh(1). P(1) 88.02(13). L P O N Rh OC Cl Ar R1 RO RO P O N Pd Cl Cl Ph Et RO RO 1/2[Rh(CO)2Cl]2 L = 1a.c [PdCl2(cod)] L = 1a,b 2a.c 3a, b Scheme 2 .CO . cod ¢Ô¢Ô In the alkylation of dimethyl malonate with 1,3-diphenylprop-2-enyl acetate catalysed by [Pd(All)Cl]2, ligands 1a and 1c gave ee 13 (S) and 57% (S), respectively (the chemical yield is quantitative). We are grateful to R. Hilgraf (University of Basel, Switzerland) for catalytic experiments. ¡×¡× Synthesis of ligand 4 was described previously.10 P O N Rh OC Cl RO RO 1/2[Rh(CO)2Cl]2 5 Scheme 3 N O P RO RO Me Me Me Me Me Me 4 R = Me .CO C(5) C(4) C(3) Cl(1) N(1) 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(1) C(2) O(1) O(2) O(3) Rh(1) P(1) O(4) Figure 2 General view of a molecule of 2b. Selected bond lengths (A): Rh(1).C(1) 1.833(7), Rh(1).N(1) 2.114(5), Rh(1).P(1) 2.164(2), Rh(1). Cl(1) 2.405(2), O(2).C(2) 1.441(7); principal bond angle (¡Æ): N(1).Rh(1).P(1) 86.1(2). C(19) C(20) C(21) C(22) C(23) C(24) C(25) C(26) C(27) C(28) C(29) C(30) C(31) C(32)Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) References 1 H. Brunnel and H. Weber, Chem. Ber., 1985, 118, 3380. 2 T. Hayashi, C. Hayashi and Y. Uozumi, Tetrahedron: Asymmetry, 1995, 6, 2503. 3 H. Brunnel, I.Deml, W. Dirnberger, K.-P. Ittner, W. Rei¥âer and M. Zimmermann, Eur. J. Inorg. 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