Metallacarborane diene π-complexes. I. Synthesis of rhodacarboranes with a η 2,η 3-2-methylenenorbornadienyl ligand at the rhodium vertex

Abstract

Novel 18-electron rhodacarboranes with a 2-methylenenorbornadienyl ligand, η 2,η 3-coordinated to a rhodium atom of closo-3,3-(η 2,η 3-C 7H 7CH 2)-1,2-R 1R 2-3,1,2-RhC 2B 9H 9 (IIIa–IIId, R 1  R 2  H (a), R 1  R 2  Me (b), R 1  Me or Ph, R 2  H (c,d) and closo-2,2-(η 2,η 3-C 7H 7CH 2)-2,1,7-RhC 2B 9H 11 (VIII) have been prepared. The structures of IIIa–IIId, and VIII were deduced from their IR, 1H NMR and 13C NMR spectra. Two alternative synthetic routes to the above complexes have been suggested: (a) reactionis of 16-electron complexes of (η 4-C 7H 7-2-CH 2OH)- Rh(acac) or [(η 4-C 7H 7-2-CH 2OH)RhCl] 2 with appropriate dicarbollide anions with a subsequent acidificatiion by HPF 6 and (b) reactions of unsubstituted and C-mono-substituted closo-bis(triphenylphosphine)hydridorhodacarboranes with 2-(hydroxymethyl)norbornadiene on heating in benzene. The possible mechanisms of these reactions are discussed. An X-ray study of complex IIIb, R 1  R 2  Me, confirms that there is allylolefin type metal-ligand bonding.