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Diastereoselectivity in the Reaction of RCH 2 C[CH 2 P (Ar)(Lr)] 3 with Electrophiles: Enhancement of Diastereoselective Control by η 3 ‐Coordination in {RCH 2 C[CH 2 P(Ar)(Li) 3 }Mo(Co) 3
Author(s) -
Büchner Michael,
Huttner Gottfried,
Winterhalter Ute,
Frick Axel
Publication year - 1997
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19971301006
Subject(s) - diastereomer , chemistry , electrophile , deprotonation , stereochemistry , nmr spectra database , medicinal chemistry , spectral line , organic chemistry , catalysis , ion , physics , astronomy
Following a procedure developed for H 3 CC[CH 2 P(Ph) 2 ] 3 ( 1a ) as the starting compound, various tripod ligands RCH 2 C[CH 2 P(Ar) 2 ] 3 ( 1 ) have been transformed into the trilithiotriphosphides RCH 2 C[CH 2 P(Ar)(Li)] 3 with various electrophiles R′ — Hal leads to the two diastereomers of RCH 2 C[CH 2 P‐(Ar)(R)] 3 ( 6 ) with an ( RRR/SSS : RRS/SSR ) ratio close to the statistical value of 1:3, except when ArPh and R′Bzl, where the RRS/SSR diastereomer is obtained almost exclusively. In contrast, the reaction of [RCH 2 C[CH 2 P(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 (RCH 2 C[CH 2 P‐(Ar)(H)] 3 Mo(CO) 3 , obtained from 2 and (CH 3 CN) 3 Mo(CO) 3 , are deprotonated by MeLi, or the trilithiotriphosphides RCH 2 C[CH 2 P(Ar)(Li)] 3 are reacted with (CH 3 CN) 3 Mo(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 ArPh, RPh, 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 , ArPh, RH, 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.