ISSN:
0009-2940
Keywords:
Chiral tripod ligands
;
Tripod Mo(CO)3 compounds
;
Diastereoselective synthesis
;
Separation of diastereomers
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Following a procedure developed for H3CC[CH2P(Ph)2]3 (1a) as the starting compound, various tripod ligands RCH2C[CH2P(Ar)2]3 (1) have been transformed into the trilithiotriphosphides 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)]3Mo(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 ration 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, R′=Bzl, where the homochiral 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, R′=Ph, R′=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.
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19971301006
