Synthesis, Structures, Bonding, and Redox Chemistry of Ditungsten Butadiyne Complexes with W≡C-C≡W Backbones

Complexes of the form XL4W≡C—C≡WL4X (L = 1/2 dmpe, 1/2 depe, P(OMe)3; X = Cl, OTf) have been synthesized from (ButO)3WCCW(OBut)3 in two steps via Cl3(dme)WCCW(dme)Cl3, which undergoes facile four-electron reduction in the presence of L. The compounds possess formal d2−d2 electron configurations. The molecular structures of Cl(dmpe)2WCCW(dmpe)2Cl and Cl{P(OMe)3}4WCCW{P(OMe)3}4Cl were determined by X-ray crystallography; bond distances within the backbone are consistent with a W≡C—C≡W canonical structure. Density-functional-theory calculations on Cl(dmpe)2WCCW(dmpe)2Cl and the model compound Cl(PH3)4WCCW(PH3)4Cl, and on their monometallic analogs W(CH)(dmpe)2Cl and W(CH)(PH3)4Cl, indicate that the WCCW backbone is strongly π-conjugated; this is supported by the observation of low-energy π → π* transitions for the compounds. The calculations predict that δ symmetry dxy-derived orbitals should be (or lie near) the highest occupied molecular orbital. Consistent with this prediction, the electronic spectra of t...