Equilibrium between ylidene and isocyanide complexes: Synthesis and crystal structure of cis-(N-methyl-1,2-dihydrobenzoxazol-2-ylidene)-(triphenylphosphine) tetracarbonyltungsten

Article abstract of DOI:10.1021/om00005a069

Reaction of 2-(trimethylsiloxy)phenyl isocyanide (1) with [W(THF)(CO)₅] gives the complex [W(1)(CO)₅] (2a). Hydrolysis of the Si-O bond leads to the formation of an equilibrium between complexes with a 2-hydroxyphenyl isocyanide (3a) or a 1,2-dihydrobenzoxazol-2-ylidene ligand (4a), which lies mostly on the side of the ylidene complex 4a. Substitution of one cis-CO ligand in 2a for P(C₆H₅)₃ enhances metal-to-ligand (d → p)π-back-bonding and shifts the equilibrium toward the isocyanide complex 3e. The equilibrium can again be shifted toward the ylidene complex by deprotonation and alkylation of the ylidene nitrogen to give (N-methyl-1,2-dihydrobenzoxazol-2-ylidene)(triphenylphosphine) tetracarbonyltungsten (4f) which was characterized by single-crystal X-ray structure analysis.