ACYL, CARBENE, VINYL, AND AZAVINYLIDENE LIGANDS IN TUNGSTEN(II) HYDRIDOTRIS(3,5-DIMETHYLPYRAZOLYL)BORATE ALKYNE COMPLEXES

Reaction of [Tp'(CO)2W (PhC2Me)][BF4] with LiCuR2 (R = Ph, Me) generates neutral eta1-acyl complexes Tp'(CO)(PhC2Me)W(eta1-C(O)R) in which the alkyne ligand remains as a four-electron donor. Deprotonation of the alkyne methyl in Tp'(CO)(PhC2Me)W(eta1-C(O)Me) produces a nucleophilic propargyl synthon which reacts with Mel to yield an ethyl alkyne complex. Protonation or methylation of the neutral eta1-acyl complexes at the acyl oxygen results in the formation of Fischer-type hydroxy- or methoxycarbene cations, [Tp'(CO)(PhC2Me)W=C-(OE)R]+ (E = H, Me; R = Me, Ph, n-C4H9). Crystals of the methoxybutylcarbene complex belong to the orthorhombic space group P2(1)2(1)2(1), Z = 4, with unit cell dimensions of a = 15.090-(6), b = 16.562(4), and c = 14.624(4) angstrom. Refinement of 273 variables over 2187 reflections led to an R value of 6.4% with R(w) = 6.7%. The alkyne ligand aligns itself parallel to the cis metal-carbonyl axis and perpendicular to the plane of the carbene ligand. Reaction of [Tp'-(CO)(PhC2Me)W=C(OMe)Me][CF3SO3] with NaOH in MeOH generates a neutral sigma-vinyl complex, Tp'(CO)(PhC2Me)W(eta1-C(OMe)=CH2), via deprotonation of the carbene methyl group. Reaction of [Tp'(CO)(PhC2Me)W=C(OMe)Ph][CF3SO3] with 2 equiv of KCN in MeOH yields a neutral azavinylidene complex, Tp'(CO)(PhC2Me)WN=C(CN)CH(OMe)Ph, in which the lone pair of electrons on the nitrogen of the azavinylidene ligand competes with the alkyne pi(perpendicular-to) donor orbital for donation to the lone vacant metal dpi orbital.