Intramolecular carbyne-isocyanide coupling to an alkyne ligand at a d(4) tungsten center

Oxidative decarbonylation of Cp*(CO)(2)W = CNEt2 (1) with PhICl2 affords th e aminocarbyne complex cis-Cp* (Cl)(2)(CO)W = CNEt2 (2), which reacts with tBuNC to give Me CO substitution product cis-Cp*(Cl)(2)(tBuNC)W = CNEt2 (3) (Cp* = C5Me5). Complex 3 undergoes a carbyne-isocyanide coupling reaction with HCl to yield the alkyne complex Cp*(Cl)(2)W[eta(2)-tBu(H)NC = CNEt2] ( 4). In comparison, the reaction of cis-Cp*(Cl)(2)[P(OMe)(3)]W = CNEt2 (5) w ith HCl affords the 16e carbene complex Cp*(Cl)(3)W = C(H)NEt2 (6) after el imination of P(OMe)(3). Complex 5 was obtained from the CO ligand-exchange reaction of 2 with P(OMe)(3). Treatment of 6 with tBuNC yields the cationic 18e carbene complex [Cp*(Cl)(2)(tBuNC)(2)W = C(H)NEt2]Cl (7). The mechanis m of the C-C coupling reaction of 3 to give 4 is discussed and the crystal structures of 4 and 6 are described.