Synthesis and chemistry of [Os3(CO)9(.mu.3-CCO)]2-. Metal ensemble effects on the reactions of the CCO ligand

Abstract

The acylation of (Os/sub 3/(CO)/sub 11/)/sup 2 -/ followed by reductive CO cleavage produces (Os/sub 3/(CO)/sub 9/(CCO))/sup 2 -/ (1) which undergoes a variety of reactions on the metal centers or the CCO ligand. Protonation yields (HOs/sub 3/(CO)/sub 9/(CCO))/sup -/ and the previously reported H/sub 2/Os/sub 3/(CO)/sub 9/(CCO). The CCO ligand-centered reactions of 1 are dependent on the presence or absence of CO in the reaction. Hence under a CO atmosphere 1 is attacked by 2 equiv of CH/sub 3/OSO/sub 2/CF/sub 3/ to give the acetylene cluster Os/sub 3/(C-O)/sub 10/(CH/sub 3/C identical with COCH/sub 3/) (4) while in the absence of CO the alkylidyne cluster Os/sub 3/(CO)/sub 9/(..mu../sub 3/-COCH/sub 3/) (3) along with a small amount of 4, is produced. The origins of the reactivity differences between the (M/sub 3/(CO)/sub 9/(CCO))/sup 2 -/ clusters (M = Fe, Ru, Os) were explored from the standpoint of electronic structure and steric accessibility. A single-crystal X-ray structure determination of 1 reveals that the CCO ligand is tilted 26/sup 0/ away from the normal to the Os/sub 3/ plane toward one of the Os atoms. Thus it is structurally similar to (Fe/sub 3/(CO)/sub 9/(CCO))/sup 2 -/ but quite different from (Ru/sub 3/(CO)/sub 9/(CCO))/sup 2more » -/. (PPh/sub 4/)/sub 2/(Os/sub 3/(CO)/sub 9/(CCO)) crystallizes in the triclinic space group, P anti 1, with a = 12.762 (2) A, b = 20.447 (5) A, c = 10.779 (2) A, ..cap alpha.. = 97.68 (2)/sup 0/, ..beta.. = 110.33 (2)/sup 0/, and ..gamma.. = 89.27 (2)/sup 0/.« less