Carbon–Carbon Bond Forming Reactions with Tantalum Diamidophosphine Complexes That Incorporate Alkyne Ligands

The incorporation of o-phenylene-linked diamidophosphine ligands onto the readily available alkyne complexes Ta(alkyne)Cl3(DME) (where alkyne = hex-3-yne or 1,2-bis(trimethylsilylacetylene); DME = 1,2-dimethoxyethane) results in the formation of a versatile set of starting materials of the general formula [PhNPN*]Ta(alkyne)Cl (where [PhNPN*] = PhP(2-(N-mesityl)-5-Me-C6H3)2). Upon reaction with KBEt3H, the synthesis of the corresponding hydride complexes [PhNPN*]Ta(alkyne)H can be achieved; these complexes feature extremely downfield (δ ∼21 ppm) doublet resonances (2JHP = ∼35 Hz) in the respective 1H NMR spectra that are assigned to the newly formed Ta–H moieties. Subsequent reaction of these Ta hydrides with 2,6-dimethylphenylisocyanide and phenylacetylene results in the insertion of these species into the Ta–H bond and the formation of the corresponding iminoformyl and phenylvinyl complexes, respectively. While the former intermediate cannot be detected, the latter was characterized by NMR spectroscopy. ...