Palladium Complexes of Methylene-Bridged P-Stereogenic, Unsymmetrical Diphosphines

Abstract

Optically pure P-stereogenic methylphosphine− boranes P(BH 3 )PhArMe (Ar = 1-naphthyl (1-Np), 9-phenanthryl (1-Phen), 2-biphenylyl (1-Biph)) have been used to prepare six diphosphines of the type PPhAr−CH 2 −PR 2 (R = Ph or i-Pr; 3-ArR) with a methylene bridge between the phosphorus atoms and a single P-stereogenic moiety. The ligands have been reacted with [PdCl 2 (COD)] to furnish the corresponding [PdCl 2 (P−P′)] complexes. The reaction with [PdCl(η 3 -2-methylallyl)] 2 and NH 4 PF 6 has produced the expected [Pd(η 3 -2-methylallyl)(P− P′)]PF 6 complexes as stable species in solution only for the ligands containing the diisopropylphosphino group. The other ligands produced a mixture of species in solution, from which the dimeric complex [Pd 2 (η 3 -2-methylallyl) 2 (PNpPh-CH 2 -PPh 2 ) 2 ](PF 6 ) 2 , and the coordination compound [Pd(PBiphPh-CH 2 -PPh 2 ) 2 ](PF 6 ) 2 could be crystallographically characterized.

Rhodium and ruthenium complexes of methylene-bridged, P-stereogenic, unsymmetrical diphosphanes

“…The methylene-bridged diphosphanes ArPhP 1 CH 2 P 2 R 2 ( ArR ; Ar = 2-biphenylyl (Biph) and 1-naphthyl (Np); R = iPr, t Bu or Ph) contain an enantiopure P -stereogenic moiety (denoted as P 1 ) and a non- P -stereogenic moiety (denoted as P 2 ). The ligands were prepared from optically pure methylphosphane–boranes ( ArMe ) by deprotonation of the methyl group and phosphination of the resulting carbanion with the corresponding chlorophosphane 29 (Fig. 2).…”

“…The formation of Biph t Bu·BH 3 (with both phosphorus boronated) could only be observed by 31 P{ 1 H} NMR spectroscopy in solution in the presence of an excess of BH 3 ·THF as two broad signals at δ P +50.3 and +26.3 ppm, corresponding to P 2 and P 1 , respectively. After following the aqueous work-up as in the previously reported procedure, 29 the species Biph t Bu·2-BH 3 was obtained, meaning that P 1 had suffered a spontaneous deboronation reaction. This result can be explained first by the reduced basicity of the diarylphosphane P 1 compared to the trialkylphosphane P 2 and, second, by the steric hindrance exerted by the bis( tert -butyl)phosphane moiety of P 2 , weakening the B–P 1 bond.…”

“…The 31 P{ 1 H} NMR spectra of ligands Biph t Bu ( δ P 1 = −24.1 ppm, δ P 2 = +15.3 ppm; J P 1 –P 2 = 127.7 Hz) and Np t Bu ( δ P 1 = −28.1 ppm, δ P 2 = +13.8 ppm; J P 1 –P 2 = 143.8 Hz) consist of two doublets while the hydrogen atoms of the tert -butyl groups appear in the 1 H NMR spectra as two sharp doublets ( J H–P 2 = 10.8 Hz) at around 0.8 ppm, in accordance with other methylene-bridged diphosphanes. 29,38,39…”

“…After the study of the coordination chemistry of the ligands in the square-planar environments of d 8 palladium( ii ) 29 and rhodium( i ) we decided to study their behaviour with the well-known ruthenium( ii )- p -cymene unit, to form octahedral, d 6 Ru( ii ) complexes. Two ligands with a 2-biphenylyl moiety ( BiphiPr and BiphPh ) were chosen because it seems to lead to more stable and crystalline complexes.…”

Betti base derived P-stereogenic phosphine-diamidophosphite ligands with a single atom spacer and their application in asymmetric catalysis

“…1a). Grabulosa and co-workers developed unsymmetrical methylene bridged diphosphines 20 akin to the C 1 -symmetric unsymmetrical MiniPHOS originally developed by Imamoto.…”