Alkyne, cyclobutadiene and cyclopentadienone complexes of molybdenum and tungsten

Jack L. Davidson

Research output: Contribution to journalArticle

Abstract

Reactions of [MoX(CO)3(?5-C5H5)] (X = Br, I) with CF3CCCF3 in a sealed tube give the tetrakis(trifluoromethyl)cyclopentadienone derivatives [MoX(CO){?4-C4(CF3)4CO}(?5-C5H5)] (3b, c) whereas if the liberated carbon monoxide is removed at intervals the bis-alkyne complexes [MoX(CF3-CCCF3)2(?5-C5H5] (2b, c) are obtained preferentially. With X = 1 the former reaction also gives [MoI(CO){?4-C4(CF3)4}(?5-C5H5)] (4a) containing an ?4-tetrakis(trifluoromethyl)cyclobutadine ring. Under similar conditions the tungsten complexes [WX(CO)3(?5-C5H5)] and CF3CCCF3 give only the bis-alkyne derivative [WX(CF3CCCF3)2(?5-C5H5)] (X = Br, I) with no evidence for alkyne cyclisation products. [MoCl(CF3CCCF3)2(?5-C5H5)] reacts with carbon monoxide to give [MoCl(CO){?4-C4(CF3)4CO}(?5C5H5)] (3a), showing that the bis alkyne complexes are intermediates in the formation of the tetrakis(trifluoromethyl)cyclopentadienone derivatives. Complexes [MoX(CO){?4-C4(CF3)4CO}(?5-C5H5] and [MoI(CO){?4-C4(CF3)4}(?5-C5H5)] react with t-butyl isocyanide to give carbonyl substitution products [MoX(CNtBu){?4-C4(CF3)4CO}(?5-C5H5] (X = Br, I) (3d, e) and [MoI(CNtBu){?4-C4(CF3)4}(?5C5H5)] (4b), respectively. Isomerism in complexes 3 has been studied by 19F NMR spectroscopy and ascribed to the existence of ?2- and ?4-bonded C4(CF3)4CO ring systems, each of which can adopt two preferred orientations prone and supine. Dynamic 19F NMR studies of 4a, b revealed a high barrier to cyclobutadiene rotation about the metal-ring axis. © 1991.

Original languageEnglish
Pages (from-to)137-149
Number of pages13
JournalJournal of Organometallic Chemistry
Volume419
Issue number1-2
Publication statusPublished - 12 Nov 1991

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