Reactions at the rhodium vertex of isomeric closo-bis(triphenylphosphine)hydridorhodacarboranes, alkenyl acetate cleavage and subsequent reactions

Abstract

The isomeric hydridophosphinorhodacarboranerhodium(III) clusters, [ closo-3,3-(PPh 3) 2-3-H-3,1,2-RhC 2B 9H 11] ( 1a); [ closo-2,2-(PPh 3) 2-2-H-2,1,7-RhC 2B 9H 11] ( 1b); and [ closo-2,2-(PPh 3) 2-2-H-2,1,12-RhC 2B 9H 11] ( 1c) react with isopropenyl acetate and vinyl acetate under mild conditions to give ester CO bond scission, expulsion of alkene, and formation of bidentate or monodentate acetate complexes of the form (PPh 3)(η 2-CH 3COO)RhC 2B 9H 11 or (PPh 3) 2(η 1-CH 3COO)RhC 2B 9H 11. These acetate complexes react readily with hydrogen to regenerate the parent compounds. A very stable alkyl complex chelated through the carbonyl oxygen could be isolated from the reaction of 1b with vinyl acetate at lower temperatures, whereas the reaction of 1a with either isopropenyl acetate or vinyl acetate at higher temperatures led to the formation of an ortho-metallated complex whose crystal structure is reported. When allyl acetate was employed as substrate, complexes of the form (PPh 3)(η 3-C 3H 5)RhC 2B 9H 11 resulted with concomitant elimination of acetic acid. The relevance of the novel compounds reported here to the catalytic hydrogenolysis of alkenyl acetates using 1a–1c as catalyst precursors is discussed.