ELECTROPHILIC ADDITION TO CYANIDE LIGANDS IN TUNGSTEN(II) 4-ELECTRON-DONOR ALKYNE COMPLEXES

Extended reflux of Tp'(CO)(I)W(RC=CR') (Tp' = hydridotris(3,5-dimethyl pyrazolyl)borate) complexes in ethyl acetate in the presence of silver cyanide produces Tp'(CO)(CN)W(RC=CR') complexes in moderate to high y ields. A single-crystal X-ray structure of Tp'(CO)-(CN)W(PhC=CMe) show s that the alkyne is aligned parallel to the M-CO axis. Electrophilic attack at the nitrogen of the cyanide ligand with methyl triflate or t riflic acid yields cationic isocyanide complexes, whereas attack with HBF4 results in neutral BF3 adduct complexes. Coordination of the Tp'( CO)(PhC=CMe)W+ fragment to the cyanide nitrogen of Tp'(CO)-(CN)W(HC=CB un) to form a CN-bridged dinuclear complex has been achieved. Variable -temperature H-1 NMR measurements reflect acetylene rotation barriers in the Tp'(CO)(L)W-(HC=CH)(n+) series (L = CO, CNH, CNMe {n = 1}; CN-, CNBF3- {n = 0}) and, thus, quantify it-effects for the cyanide and is ocyanide ligands with respect to steric considerations. Extended Hucke l molecular orbital calculations were carried out on a series of model complexes, [H-3(Co)(L)W(HC=CH)(n-) (L the experimental data. CO, CNH {n = 1}; CN-, H- {n = 2}) to augment the experimental data.