Phosphino-(α-sulfinylalkyl)phosphonium ylide complexes (Rh,Pd) with a configurationally stable asymmetric ylidic carbon |
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Authors: | Remigiusz Zurawinski Christine Lepetit Yves Canac Laure Vendier Marian Mikolajczyk Remi Chauvin |
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Institution: | 1. CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse, France;2. Université de Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France;3. Centre of Molecular and Macromolecular Studies, Department of Heteroorganic Chemistry, Polish Academy of Sciences, 90-363 Lodz, Sienkiewicza 112, Poland |
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Abstract: | The synthesis and structure of Rh(I) and Pd(II) complexes of chiral P,C-chelating phosphino-(α-sulfinylalkyl)phosphonium ylide ligands with a trisubstituted asymmetric ylidic center P+–C1R(S1(O)p-Tol)–M (R = alkyl group) have been investigated, and compared to those of the analogous disubstituted ylide complexes (R = H). Reaction of the ethyl onium ylide of o-bis(diphenylphosphino)benzene with (?)-menthyl-(S)-p-tolylsulfinate afforded the corresponding racemic erythro phosphino-(α-sulfinylethyl)phosphonium in 90% de (R = Me). The racemization process is interpreted by a Berry-like pseudorotation mechanism driven by the steric repulsion between the α-methyl substituent and the bulky menthyloxy S-substituent or sulfur lone pair in the intermediate ylide-sulfinyl adduct. The ylide of phosphino-(α-sulfinylethyl)phosphonium reacts with Rh(cod)2]PF6] and PdCl2(MeCN)2 to afford the corresponding P,C1-chelated threo-Rh(I) and erythro-Pd(II) mononuclear complexes in 70% yield and total diastereoselectivity. These respective complexes act as efficient catalytic precursors for the hydrogenation of (Z)-α-acetamidocinnamic acid and allylic substitution of 3-acetoxy-1,3-diphenyl-1-propene with sodium dimethyl malonate. The bonding features of the erythro-Pd(II) complex exhibiting a sulfinyl O?Pd interaction are studied theoretically at the DFT level using ELF and MESP analyses. The η2-P,C haptomeric form of the ylide ligand is estimated to compete at 19% with the η1-C haptomeric form dominating at 81%. |
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