RUTHENIUM(II) TRIS(PYRAZOLYL)BORATE COMPLEXES - REVERSIBLE VINYLIDENECOMPLEX-FORMATION

A convenient high-yield route to [Ru{HB(pz)3}Cl(PPh3)(=C-CHR)] (pt = p yrazolyl; R = Ph,SiMe3, Bu-u, Bu-t, CO2Et or C6H9) has been found thro ugh the intermediary [Ru{HB(pz)(3)}(PPh3)(dmf)] (dmf = dimethyl- forma mide) which has been crystallographically characterized. This complex is readily obtained on treatment of [Ru{HB(pz)(3)}Cl(cod)] (cod = cycl oocta-1,5-diene) with 1 equivalent of PPh3 in boiling dmf. The vinylid ene moiety in complexes of the type [Ru{HB(pz)(3)}Cl(PPh3)(=C-CHR)] is remarkably labile being easily replaced by nucleophiles L = PMe3, PPh 3, MeCN, pyridine or CO to give [Ru{HB(pz)(3)}Cl(PPh3)L]. With the exc eptions of L = PMe3 or CO, these reactions are reversible. The complex [Ru{HB(pz)(3)}Cl(PPh3)(CO)] has been characterized by X-ray crystallo graphy. On treatment of [Ru{HB(pz)(3)}Cl(PPh3)(=C-CHPh)] with an exces s of HC=CR' (R' = SiMe3, Bu-n, Bu-t, CO2Et or C6H9) the neutral vinyli dene complex [Ru{HB(pz)(3)}Cl(PPh3)(=C=CHR')] was reversibly formed. C omparative studies and extended-Huckel molecular orbital calculations have been performed to elucidate the nature of the bonding in the vari ous vinylidene complexes. The bonding between the metal center and the vinylidene ligand is dominated by the d(yz) (metal)-p (vinylidene) in teraction If this contribution is small, reconversion of the vinyliden e complex into an eta(2)-alkyne complex can be accomplished.