Enantioselective synthesis of tungsten trimetallic cluster chalcogenides

Abstract

Excision of {W3Q7Br4}n (Q = S, Se) of polymeric phases using chiral diphosphines is a general procedure to synthesize optically pure trinuclear clusters. Chiral transfer from the enantiomerically pure diphosphines (+)-1,2-bis[2,5-(dimethylphospholan-1-yl)]ethane, (R,R)-Me-BPE, (−)-1,2-bis[2,5-(dimethylphospholan-1-yl)]ethane, (S,S)-Me-BPE, and (−)-1,2-bis[2,5-(dimethylphospholan-1-yl)]benzene, (R,R)-DUPHOS, to the inorganic phase affords enantiopure P-[W3S4Br3((R,R)-Me-BPE)3]+, M-[W3S4Br3((S,S)-Me-BPE)3]+ (M-1+), P-[W3Se4Br3((R,R)-Me-BPE)3]+ (P-2+) and P-[W3S4Br3((R,R)-DUPHOS)3]+ (P-3+) clusters. The central W3(μ3-Q)(μ-Q) unit defines an incomplete cuboidal core with the capping chalcogen lying on a threefold axis and an effective C3 symmetry. Symbols P- and M- are used to indicate the rotation of the bromine atoms around the C3 axis, with the chalcogen atom pointing towards the viewer. Invariably, P-W3Q4 complexes are obtained starting from (R,R)-diphosphines, while its M-W3Q4 enantiomer is isolated in the presence of (S,S)-diphosphines. All complexes have been structurally characterized by single crystal X-ray diffraction and their enantiomeric character confirmed by CD spectroscopy.