Abstract
Anionic tungsten complexes have been prepared in which the ligand environment is dominated by alkyne ligands. Reduction of [W(PhC=CPh)3CO] with lithium naphthalenide leads to formation of an anionic complex suggested to be [W(PhC=CPh)3]2TM, the first homoleptic anionic alkyne complex of a transition metal. The dianion has been characterized chemically by derivatization with Ph3SnCl to form [W(PhC=CPh)3SnPh3]“, isolated as [W(PhC=CPh)3SnPh3]NEt4 (2) and structurally characterized by a single-crystal X-ray diffraction study. The acetylenic carbons form a tapered triagonal-prismatic coordination sphere for the W, with the Ph3Sn ligand capping a trigonal face. Dynamic 13C NMR studies have shown that 2 undergoes a rapid fluxional process, with a free energy of activation of 13.0 kcal molTM1 at room temperature, which is suggested to involve rotation of the alkyne ligands.