Reactivity of trans-[M(CO)(DMF)(Ph2PCH2CH2PPh2)2] (M = Mo, W) toward Terminal Alkynes: Synthesis of Alkynylhydrido and Vinylidene Complexes

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Abstract
Treatment of trans-[Mo(CO)(DMF)(dppe)2] (1a; dppe = Ph2PCH2CH2PPh2) with HC≡CCOOMe in benzene at room temperature or at reflux afforded an alkynylhydrido complex [Mo(C≡CCOOMe)H(CO)(dppe)2] (4a), whereas the reactions of 1a with arylacetylenes HC≡CR in benzene at reflux resulted in the formation of vinylidene complexes cis-[Mo(=C=CHR)(CO)(dppe)2] (R = Ph (6a) or 4-MeC6H4). The W analogue trans-[W(CO)(DMF)(dppe)2] (1b) gave only alkynylhydrido complexes [W(C≡CR)H(CO)(dppe)2] (R = COOMe (4b) or Ph) by treatment with either HC≡CCOOMe or HC≡CPh. From the Mo vinylidene complex 6a was obtained an alkylidyne complex cis-[Mo(≡CCH2Ph)(CO)(dppe)2][BF4] (9a) upon treatment with aqueous HBF4, whereas the reactions of Mo and W alkynylhydrido complexes 4 with HBF4·Et2O also resulted in the formation of the alkylidyne complexes cis-[M(≡CCH2COOMe)(CO)(dppe)2][BF4] (10). The vinylidene complexes cis-[M(=C=CHCOOMe)(CO)(dppe)2] (11) were readily derived from 10 by the reactions with NaOMe; these were not accessible from direct treatment of 1 with HC≡CCOOMe. The detailed structures of 4a, 4b, 9a, and 11b (M = W) have been established by single-crystal X-ray analyses.

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