Co-ordinatively unsaturated alkyne complexes of molybdenum and tungsten: Reactions and dynamic nuclear magnetic resonance studies of [m(SC6F5)(CO)(CF3C≡CCF 3)(η5-C5H5)] (M = Mo or W) complexes

Jack L. Davidson

Research output: Contribution to journalArticle

Abstract

Variable-temperature 19F n.m.r. studies of the hexafluorobut-2-yne complex [W(SC6F5)(CO)(CF3C=CCF 3)(?5-C5H5)] reveal three distinct phases of fluxional behaviour between -90 and +80°C, attributed to restricted rotation about (a) the S-C6F5 bond, (b) the W-SC6F5 bond, and (c) the CF3CCCF3-W bond ('propeller rotation'), in increasing order of energy. The oxo complex [W(SC6F5)(O)(CF3C=CCF 3)(?5-C5H5)], obtained by air oxidation of the parent carbonyl in diethyl ether, in contrast shows only restricted rotation about the W-SC6F5 bond over the same temperature range. Reactions of the carbonyls [M(SC6F5)(CO)(CF3C=CCF 3)(?5-C5H5)] (M = Mo or W) with tertiary phosphines and phosphites (L) give carbonyl-substitution products [M(SC6F5)(L)(CF3C=CCF 3)(?5-C5H5)] [M = Mo or W, L = P(OMe)3, PMe2Ph, or PEt3; M = Mo, L = PPh3 or PMePh2] under unusually mild conditions which undergo alkyne propeller rotation according to 19F n.m.r. studies. In the case of alkylphosphines, carbonyl substitution was observed to proceed via thermally unstable intermediates, [M(SC6F5)(CO){?2-C(CF3)C(CF 3)L}(?5-C5H5)], isolated and characterised for the case M = W, L = PEt3. N.m.r. data indicate the presence of two isomeric forms containing an ?2-vinyl ligand C(CF3)C(CF3)L resulting from attack of the phosphine at an alkyne carbon atom.

Original languageEnglish
Pages (from-to)2423-2431
Number of pages9
JournalJournal of the Chemical Society, Dalton Transactions
Issue number11
DOIs
Publication statusPublished - 1986

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