Mechanisms of alkyne trimerisation at molybdenum and tungsten centres leading to novel metallacycles: Crystal and molecular structures of two isomeric forms of [Mo{C(CF3)C(CF3)C(CF3)C(CF 3)C(CO2Me)C(CO2Me)-(SPr i)}(η5-C5H5)]

Naz M. Agh-Atabay, Laurence Carlton, Jack L. Davidson, Graeme Douglas, Kenneth W. Muir

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The ?2-C,C vinyl complexes [M{?3-C(CF3)C(CF3)SR}(CF 3C=CCF3)(?5-C5H 5)] 1 (M = Mo, R = Pri; M = W, R = Me, Et or Pri) reacted with dimethyl acetylenedicarboxylate R'C=CR' (R' = CO2Me) to give products of alkyne trimerisation containing two different oligomerisation sequences depending on whether R'C=CR' occupies a terminal or central position in the alkyne trimer chain, i.e. C(CF3)C(CF3)C(CF3)C(CF 3)C(R')C(R') and C(CF3)C(CF3)C(R')C(R')C(CF 3)C(CF3). With M = Mo, kinetic 19F NMR studies established a reaction sequence proceeding above ca. -30°C via two different butadienyl complexes [M{?2-C(CF3)C(CF 3)C(R')-C(R')SPri}(CF 3C=CCF3)(?5-C5H 5)] 2 and 3 to give isomeric trienyl derivatives [Mo{?6-C(CF3)C(CF3)C(CF 3)C(CF3)C(R')C(R')SPri}(? 5-C5H5)] 4 and [Mo{?5-C(CF3)C(CF3)C(CF 3)C(CF3)C(R')SPriC(R')}(? 5-C5H5)] 5 which were isolated at room temperature. X-Ray diffraction studies established that in each case the trienyl ligand is bound to the metal via an ?2-C,C alkenyl linkage, and two s carbon-metal bonds. In 4 this is accompanied by co-ordination of a CO unit of a carbomethoxy carbonyl whereas in 5 the thiolate sulfur is bonded to the metal. Above room temperature 5 isomerises to give species 6 and ultimately 7 which appears to result from thiolate transfer to the metal to give a seven-membered metallacycle. With M = W, the reactions also proceed via a butadienyl complex 2 but this isomerises via two other intermediates to give trienyl products [W{?6-C(CF3)C(CF 3)C(R')C(R')C(CF3)C(CF3)SR}(? 5-C5H5)] and [WF{?5-C(=CF2)C(CF 3)C(R')C(R')C(CF3)C(CF 3)SR}(?5-C5H5)]. X-Ray diffraction studies established that the trienyl ligand in the former is co-ordinated via one s, two p alkene linkages and a thiolate sulfur. Two isomeric forms were structurally characterised which differ only in the orientation of the thiolate isopropyl substituent which can adopt syn or anti positions. In the fluoride a CF3 fluorine has been transferred to the metal and this has generated a hexatrienyl attachment via a quasi p-allylic interaction and through W-C and W-S s bonds.

Original languageEnglish
Pages (from-to)999-1011
Number of pages13
JournalJournal of the Chemical Society, Dalton Transactions
Issue number6
Publication statusPublished - 21 Mar 1996

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