CHIRAL QUADRUPLE-BONDED DIMOLYBDENUM COMPLEXES CONTAINING CHELATING DIPHOSPHINE LIGANDS STRUCTURAL AND CHIROPTICAL PROPERTIES OF ALPHA-MO2CL4[(R,R)-ME-DUPHOS](2) AND ALPHA-MO2CL4[(S,S)-ME-DUPHOS](2), WHERE ME-DUPHOS IS 1,2-BIS(2,5-DIMETHYLPHOSPHOLANO)BENZENE

The complexes alpha-Mo2Cl4[(R,R)-Me-DuPHOS](2), 1, and alpha-Mo2Cl4[(S ,S)-Me-DuPHOS](2), 2, were prepared by reactions of (NH4)(5)Mo2Cl9 wit h (R,R)-Me-DuPHOS and (S,S)-Me-DuPHOS, respectively, in methanol. Thei r UV-vis and circular dichroism spectra have been recorded and the X-r ay crystal structure of 1 has been determined. The chiral diphosphine ligands are chelated to the metal centers with an average twist angle of 5.2 degrees about the metal-metal bond in the clockwise direction. The absorption spectra are typical for compounds with a Mo-Mo quadrupl e bond. The lowest energy bands at 690 nm for both 1 and 2 can be assi gned to delta(xy)-->delta(xy) transitions. The CD spectra of both cco mplexes 1 and 2 show two prominent bands at 695 and 520 nm and form mi rror images of each other. Copyright (C) 1996 Elsevier Science Ltd