Tantalum η2‑Vinyl Complexes Bearing an [η5:σ-Me2C(C5H4)(C2B10H10)]2– Ligand: Syntheses and Structural Characterizations

Transition-metal η2-vinyl complexes, also known as 1-metallacyclopropenes, constitute an important subset of metal alkenyl complexes, which are limited to groups 6–8 metals only. We report in this paper a strategy for the synthesis of Ta η2-vinyl complexes. Hydrogenolysis of tantalum alkyl complex LTaMe3 (1, L = [η5:σ-Me2C(C5H4)(C2B10H10)]) in the presence of dmpe ([Me2PCH2]2) followed by addition of p-tolylacetylene gave an η2-vinyl complex, LTa(η2-H2CCC6H4CH3)(dmpe) (2). Replacement of p-tolylacetylene with t-butyl acetylene resulted in the formation of an alkynyl η2-vinyl complex LTa(η2-HCCtBu)(Me2PCH2CH2PMe2)(CCtBu) (3). Using trimethylsilyl acetylene as the substrate gave both LTa(η2-H2CCSiMe3)(dmpe) (4) and LTa(η2-HCCSiMe3)(Me2PCH2CH2PMe2)(CCSiMe3) (5). A mechanistic study revealed that the Ta η2-vinyl complexes 2–5 were formed through a tantalum trihydride intermediate, which was trapped by CO to give LTaH(CO)(dmpe) (6).