The chemistry of cycloheptatrienyl complexes of molybdenum and tungsten: The synthesis and reactions of some vinylidene and alkynyl derivatives

Reaction of the terminal alkyne HC≡CPh with [Mo(sol)(dppe)(η- C7H7)] [PF6] [(2a), sol = NCMe; (2b), sol = acetone; dppe = Ph2PCH2CH2PPh2] in refluxing acetone yields the phenylvinylidene complex [Mo(C=CHPh)(dppe)(η- C7H7)] [PF6] (3) which is readily deprotonated to give the alkynyl complex [Mo(C≡CPh) (dppe) (η-C7H 7)] (4). A similar reaction sequence-starting from HC≡CBu t and (2b) yields [Mo(C≡CBut)(dppe)(η-C 7H7)] (6). Protonation of (4) with H[BF 4]·Et2O reforms [Mo(C=CHPh)(dppe)(η-C 7H7)]+. Electrochemical studies show that (4) and (6) undergo a reversible one-electron oxidation at a glassy carbon electrode in CH2Cl2 and chemical oxidation with [Fe(η-C 5H5)2][BF4] yields the radical cations [Mo(C≡CR)(dppe)(η-C7H7)][BF4] [(5), R = Ph; (7), R = But] which have been studied by e.s.r. spectroscopy. Reaction of LiC≡CPh with [MX(CO)2(η-C 7H7)] (M = Mo or W; X = I or Cl) affords the parent dicarbonylalkynyl complexes [M(C≡CPh)(CO)2(η-C 7H7)] [(8), M = Mo; (9), M = W].