Synthesis and isocyanate insertion reactions of tungsten(IV) imido complexes formed from W(CO)(acac)(N3)(PMe3)3 with azide as the oxidant

Addition of excess trimethylphosphine and a halide source to a solution of W(CO)(acac)2(η2-L) (L = NCPh and OCMe2) leads to displacement of L and one acetylacetonate chelate to produce electron-rich, seven-coordinate complexes of the formula W(CO)(acac)(X)(PMe3)3 (X = Cl, Br, and I). Use of NaN3 instead of a halide source leads primarily to loss of carbon monoxide and dinitrogen, and protonation from adventitious water yields the cationic imido complex [W(NH)(acac)(PMe3)3]+. Heating [W(NH)(acac)(PMe3)3]+ in aromatic isocyanates at high temperature results in isocyanate insertion into the NH imido bond to form new C–N bonds. An alternate route to related imido complexes involves heating [W(O)(acac)(PMe3)3]+ with phenyl isocyanate at high temperatures to yield the substituted imido complex [W(NPh)(acac)(PMe3)3]+.