197658-80-3Relevant academic research and scientific papers
Diastereoselectivity in the reaction of RCH2C[CH2P(Ar)(Li)]3 with electrophiles: Enhancement of diastereoselective control by η3-coordination in RCH2C[CH2P(Ar)(Li)]3Mo(CO)3
Buechner, Michael,Huttner, Gottfried,Winterhalter, Ute,Frick, Axel
, p. 1379 - 1392 (1997)
Following a procedure developed for RCH2C[CH2P(Ar)(Li)]3 (la) as the starting compound, various tripod ligands RCH2C-[CH2P(Ar)2]3 (1) have been transformed into the trilithiotriphosphides RCH2C[CH2P(Ar)(Li)]3 by reductive cleavage of their P-Ar bonds by metallic lithium. The triphosphides are readily protonated to produce RCH2C[CH2P(Ar)(H)]3 (2). Reaction of RCH2C[CH2P(Ar)(Li)]3 with various electrophiles R'-Hal leads to the two diastereomers of RCH2C[CH2P-(Ar)(R′)]3 (6) with an (RRR/SSS : RRS/SSR) ratio close to the statistical value of 1:3, except when Ar = Ph and R′ = Bzl, where the RRS/SSR diastereomer is obtained almost exclusively. In contrast, the reaction of RCH2C[CH2P(Ar)(Li)]3)-Mo(CO)3 (4) with electrophiles R′-Hal tends to favour the formation of the homochiral RRR/SSS diastereomers. The triphosphide coordination compounds 4 are available by two different routes: either the complexes {RCH2C[CH2P-(Ar)(H)]3]Mo(CO)3, obtained from 2 and (CH3CN)3Mo(CO)3, are deprotonated by MeLi, or the trilithiotriphosphides RCH2C[CH2P(Ar)(Li)]3 are reacted with (CH3CN)3Mo(CO)3 to produce 4 in high yields. The ratio in which the two diastereomeric forms of 5 are obtained depends on the nature of the electrophile: the greatest diastereomeric discrimination is obtained for Ar = Ph, R = Ph,′ = Bzl, where the homochiral RRR/SSS enantiomeric pair is produced in a fourfold excess relative to the RRS/SSR pair. Two-dimensional NMR spectra and simulations of one-dimensional spectra are used to ascertain the diastereomeric excess in each case. X-ray analyses of three compounds of type 5 (5d, Ar = Ph, R = H,′ = Bzl; 5k, Ar = 3,5-Me2C6H3, R = H,′ = Bzl; 51, Ar = Ph, R = Ph,′ = Bzl) indicate the remarkable conformational stability of the tripod metal scaffolding, with the conformations observed for these three compounds in three different solid-state environments being closely similar, even with respect to the torsional arrangement of the phosphorus-bound benzyl groups. WILEY-VCH Verlag GmbH,.
