Portal de Periódicos da CAPES

Interplay of ketenyl and nitrile ligands on d6-transition metal centres. Acetonitrile as an end-on (two-electron) and a side-on (four-electron) ligand

1999; Elsevier BV; Volume: 587; Issue: 2 Linguagem: Inglês

10.1016/s0022-328x(99)00328-9

1872-8561

Hubert Wadepohl, Ulrich Arnold, Hans Pritzkow, Maria José Calhorda, Luı́s F. Veiros,

Coordination Chemistry and Organometallics

Carbyne carbonyl coupling takes place in acetonitrile solutions of the Fischer-type carbyne complexes [tpb′(CO)2MoCC6H4Me-4] (4b) (tpb′=tris(3,5-dimethylpyrazolyl)hydroborate) and [(C5Me5) (CO)2WCSiPh3] (5). The product [tpb′(CO)(NCMe)Mo{C(C6H4Me-4)CO}] (7b) has conventional η1-nitrile and η2-ketenyl ligands. In contrast, the product [(C5Me5)(CO)(NCMe)W{C(SiPh3)CO}] (8) displays a highly unusual 'four-electron-donor' η2-nitrile and a η1-ketenyl ligand. The structures of 4b, [tpb′(CO)2WCC6H4Me-4] 6, 7b and 8 were determined by X-ray crystallography. Extended Hückel and density functional theory (DFT) calculations on model compounds show that the observed coordination geometry around W is the electronically preferred for 8. The side-on nitrile in this and other related complexes binds to the metal donating from the two highest occupied orbitals (corresponding to the nitrogen lone pair and the π⊥), in contrast to two-electron donors where only the HOMO is involved in bonding. Back-donation takes place for all the side-on bound nitriles.