Reactions of low-valent group V dicarbonyl phosphine complexes with carbon-based electrophiles to produce metal alkyl, acyl, carbyne, and acetylene complexes

Article abstract of DOI:10.1021/om00005a018

The [V(CO)₂(dmpe)₂]^- anion reacts with Et₃OBF₄ and EtOTf to afford the unexpected product of formal C-alkylation, [V(η²-C(O)Et)(CO)(dmpe)₂], which has been structurally characterized by X-ray crystallography (space group Pna2₁, a = 12.917(2) A?, b = 12.335(2) A?, c = 14.331(2) A?, V = 2283.4(5) A?³). The formation of species derived by O-acylation of the CO ligands in the [Ta(CO)₂(dmpe)₂]^- and [Ta(CO)₂(depe)₂]^- anions was indirectly established by isolation and characterization of products in which two CO ligands had coupled to form acetylene complexes. Addition of 2 equiv 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)₂Cl]. The structure of the dmpe derivative was confirmed in a single-crystal X-ray determination (space group C2, a = 14.964(2) A?, b = 11.960(2) A?, c = 31.710(5) A?, β = 102.77(1)°, V = 5535(1) A?³). Additional proof of direct alkylation at terminal CO ligands was provided by isolation of mixed siloxy/alkoxyacetylene coupled products [M(R′₃SiOC≡COR)(dmpe)₂X] (R = Et, Ac, CO₂Me; R′₃Si = ^tBuPh₂Si, ⁱPr₃Si) and [M(R′₃SiOC≡COR)(depe)₂X] (R = Et, Ac; R′₃Si = ^tBuPh₂Si, ⁱPr₃Si, Me₃Si) from reactions of the siloxycarbyne precursors [M(COSiR′₃)-(CO)(dmpe)₂] and [M(COSiR′₃)(CO)(depe)₂] (M = Nb, Ta) with carbon-based electrophiles. The proper choice of carbon-based electrophile and reaction conditions is crucial in order to avoid oxidation of these low-valent metal complexes to [M(CO)₂(dmpe)₂X], which can occur competitively or exclusively.