REACTIONS OF LOW-VALENT GROUP-V DICARBONYL PHOSPHINE COMPLEXES WITH CARBON-BASED ELECTROPHILES TO PRODUCE METAL ALKYL, ACYL, CARBYNE, AND ACETYLENE COMPLEXES

The [V(CO)(2)(dmpe)(2)](-) anion reacts with Et(3)OBF(4) and EtOTf to afford the unexpected product of formal C-alkylation, [V(eta(2)-C(O)Et )(CO)(dmpe)(2)], which has been structurally characterized by X-ray cr ystallography (space group Pna2(1), a = 12.917(2) Angstrom, b = 12.335 (2) Angstrom c = 14.331(2) Angstrom, V = 2283.4(5) Angstrom(3)). The f ormation of species derived by O-acylation of the CO ligands in the [T a(CO)(2)(dmpe)(2)](-) and [Ta(CO)(2)(depe)(2)](-) anions was indirectl y established by isolation and characterization of products in which t wo CO ligands had coupled to form acetylene complexes. Addition of 2 e quiv of acetyl chloride to Na[Ta(CO)(2)(dmpe)(2)] or Na[Ta(CO)(2)(depe )(2)] yielded the acetylene complexes [Ta(AcOC=COAc)(dmpe or depe)(2)C l]. The structure of the dmpe derivative was confirmed in a single-cry stal X-ray determination (space group C2, a = 14.964(2) Angstrom, b = 11.960(2) Angstrom, c = 31.710(5) Angstrom, beta = 102.77(1)degrees, V = 5535(1) Angstrom(3)). Additional proof of direct alkylation at term inal CO ligands was provided by isolation of mixed siloxy/alkoxyacetyl ene coupled products [M(R(3)(')SiOC=COR)(dmpe)(2)X] (R = Et, Ac, CO(2) Me; R'Si-3 = (t)BuPh(2)Si, (Pr3Si)-Pr-i) and [M(R'3SiOC=COR)(depe)(2)X ] (R = Et, Ac; R'Si-3 = (t)BuPh(2)Si, (Pr3Si)-Pr-i, Me(3)Si) from reac tions of the siloxycarbyne precursors [M(COSiR'(3))-(CO)(dmpe)(2)] and [M(COSiR'(3))(CO)(depe)(2)] (M = Nb, Ta) with carbon-based electrophi les. The proper choice of carbon-based electrophile and reaction condi tions is crucial in order to avoid oxidation of these low-valent metal complexes to [M(CO)(2)(dmpe)(2)X], which can occur competitively or e xclusively.