Insertion and cleavage reactions of [closo-3,1,2-Ta(NMe2)3(C2B9H11)] with nitriles, phenols and thiols; structural characterisation of N,N-dimethylamidinate ligands

Abstract

The tantalum complex [closo-3,1,2-Ta(NMe₂)₃(C₂B₉H₁₁)] underwent insertion into the NC bond of acetonitrile and p-fluorobenzonitrile to give the N,N-dimethylacetamidinate complex [closo-3,1,2-Ta{NC(Me)NMe₂}₃(C₂B₉H₁₁)], and p-fluoro-N,N-dimethylbenzamidinate, [closo-3,1,2-Ta{NC(C₆H₄F)NMe₂}₃(C₂B₉H₁₁)], respectively. Attempted re-crystallisation of the latter from chlorinated solvents led to [closo-3,1,2-Ta{NC(C₆H₄F)NMe₂}₂Cl(C₂B₉H₁₁)], in which one amidinate ligand has been replaced by a chloride. [closo-3,1,2-Ta(NMe₂)₃(C₂B₉H₁₁)] reacts with cyclohexylisocyanide to give [Ta(NMe₂)₂{η²-N(Cy)CNMe₂}(C₂B₉H₁₁)]. The structures of the novel N,N-dialkylamidinate complexes have been determined by single crystal X-ray diffraction, and reveal the extensive delocalisation and strong π-donor character of the amidinate ligands. The M–N bonds of [closo-3,1,2-Ta(NMe₂)₃(C₂B₉H₁₁)] are cleaved by protic reagents, and it reacts with 2,6-dimethylphenol to give [closo-3,1,2-Ta(OC₆H₃Me₂-2,6)₃(C₂B₉H₁₁)] and with benzenethiol to give the charge-compensated complex [closo-3-Ta(SC₆H₅)₄(9-NHMe₂-1,2-C₂B₉H₁₀)] where the β-boron of the C₂B₃ face bears a NHMe₂⁺ substituent. The structures of the last two compounds have also been determined.