Metallacarborane diene ?-complexes. I. Synthesis of rhodacarboranes with η2,η3-2-methylenenorbornadienyl ligand at the rhodium vertex

Article abstract of DOI:10.1016/0022-328X(88)87096-7

Novel 18-electron rhodacarboranes with a 2-methylenenorbornadienyl ligand η²,η³-coordinated to a rhodium atom of closo-3,3-(η²,η³-C7H7CH2)-1,2-R¹R²-3,1,2-RhC2B9H9 (IIIa-IIId, R¹ = R² = H (a), R¹ = R² = Me (b), R¹ = Me or Ph, R² = H (c,d) and closo-2,2-(η²η³-C7H7CH2)-2,1,7-RhC2B9H11 (VIII) have been prepared.The structures IIIa-IIId, and VIII were deduced from their IR, 1HNMR and 13C NMR spectra.Two alternative synthetic routes to the above complexes have been suggested: (a) reactions of 16-electron complexes of (η⁴-C7H7-2-CH2OH-Rh(acac) or <(η⁴-C7H7-2-CH2OH)RhCl>2 with appropriate dicarbollide anions with a subsequent acidification by HPF6 and (b) reactions of unsubstituted and C-monosubstituted 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, R¹ = R² = Me, confirmsthat there is allylolefin type metal-ligand bonding.