Chiral Phosphino(sulfinylmethyl)triarylphosphonium Ylide Ligands:  Rhodium Complexes and Catalytic Properties

Abstract

A novel phosphine-phosphonium ylide ligand bearing a chiral sulfinyl moiety was prepared by reaction of (o-diphenylphosphinophenyl)diphenylphosphonium methylide with (S)-menthyl p-tolylsulfinate. Reaction of this ylide with [Rh(cod) 2 ][PF 6 ] gave stable cationic disymmetrically P,C-chelated rhodium complexes with an asymmetric ylidic carbon atom anchored to the metal center. The configuration of this carbon is controlled by the S-configuration of the adjacent sulfinyl group. The stereoselectivity of the complexation is reversed from 9:1 at 20 °C to 1:9 at -45 °C. An X-ray diffraction analysis of the thermodynamic complex shows that the stereoselectivity is not directed by chelation of the SO group which lies at a nonbonding distance from the rhodium center. In the presence of triethylamine, epimerization occurs via a putative neutral P,C-chelated complex bearing an yldiide ligand. In the presence of HPF 6 and PPh 3 , cleavage of the ylidic carbon-rhodium bond takes place simultaneously with displacement of the phosphino-phosphonium ligand by PPh 3 . The phosphine end of the ligand is intended to preserve at least one phosphine-rhodium bond, which is a common feature of all the rhodium catalysts derived from the Wilkinson complex. Indeed, we found that the phosphino-phosphonium ylide complexes are activesthough poorly enantioselectives as catalysts for hydrogenation of (Z)-R-acetamidocinnamic acid and hydrosilylation of acetophenone.

An Atropo‐Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex Thereof

“…The analogy is not only geometric, but also electronic (Scheme 2): although the σ-donating character is particularly strong for the former "P + C" ligands (of X-type), it should be particularly weak for the latter "C + P" ligands (of L-type). Whereas aryl-bridged phosphane-phosphonium ylide Ph 2 P-[Ph 2 P + C] ligands afforded stable and catalytically active complexes, [14] their reverted phosphane-amidiniophosphane Ph 2 P-[N 2 C + PPh 2 ] version is hereafter studied with bimionap (D) as an example.…”

Palladium complexes of a chiral P,C-chelating phosphino-(sulfinylmethyl)phosphonium ylide ligand

“…Known chiral P,C-and C,C-chelated phosphonium ylide complexes in the enantiomerically pure rhodium(I) series and in the racemic palladium(II) series. effect of temperature on the stereoselectivity of the complexation is therefore less pronounced than in the rhodium series, where opposite kinetic and thermodynamic complexation stereoselectivities were observed [13].…”

“…Reaction of 5 with optically pure menthyl-ðSÞ-ptoluenesulfinate followed by quenching with NH 4 PF 6 affords the (sulfinylmethyl)phosphonium salt [ðS S Þ-6H][PF 6 ] [13,16]. Deprotonation of (S S )-6H þ in THF regenerates the ylide (S S )-6, which in situ reacted with PdCl 2 (MeCN) 2 .…”

“…As we were writing this report, efficient asymmetric allylic substitution was shown to be promoted by a catalyst in situ generated from Pd(dba) 2 and yliphos [11b]. Simultaneously, a second generation of phosphine-phosphonium ylide ligands bearing an appending chiral sulfinyl center was designed [13], and both epimers of the rhodium complex 2 (Scheme 1) were shown to catalyze the hydrogenation of acetamidocinnamic acid and the hydrosilylation of acetophenone [13]. The coordination chemistry of the latter type of ligands is here extended in the palladium series.…”

Olefin Metathesis with Ru-Based Catalysts Exchanging the Typical N-Heterocyclic Carbenes by a Phosphine–Phosphonium Ylide

“…The coordinating ylide-bearing local analogy with the anionic Cl ligands, it could thus substitute one of them while making the Ru center electron-deficient with a 14-electron count. In order to concomitantly restore the 16-electron count, a pending 2-electron neutral donor is envisaged in the bidentate phosphine-phosphonium ylide Ph 2 P-C 6 H 4 -Ph 2 P=CH 2 , previously illustrated to behave as a P,C-chelating ligand in Rh(I) complexes [35,36]. Beyond their widest application in the Wittig reaction, phosphonium ylides-and in particular phosphine-phosphonium ylides-were punctually used as ligands in homogeneous catalysis, in particular, asymmetric catalysis [37][38][39].…”