Mononuclear bis-aminocarbyne complexes of tungsten with Tp′ ligands; theory of metal-centred carbyne-carbyne coupling

Alexander C. Filippou, Peter Hofmann, Paul Kiprof, Helmut R. Schmid, Carola Wagner

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28 Scopus citations

Abstract

An efficient procedure for the synthesis of mononuclear bis-aminocarbyne complexes of tungsten is reported starting from Tp′(CO)2WCN (R)Et (1a: R Me; 1b: R Et) (Tp′= hydrido(3,5-dimethylpyrazol-1-yl)borate). In the first step oxidative decarbonylation of 1a and 1b with Br2 occurs to afford the six-coordinate aminocarbyne complexes Tp′(Br)2WCN(R)Et (2a, 2b) in high yield. Similarly, complexes 1a and 1b are converted by I2 into the diiodo derivatives Tp′(I)2WCN(R)Et (3a, 3b). Reductive dehalogenation of 3a and 3b by Na/Hg in the presence of EtNC gives the electron-rich mono-aminocarbyne complexes Tp′(EtNC)2WCN(R)Et (4a, 4b), which are finally alkylated with [Et3O]BF4 at one isocyanide-nitrogen to yield the bis- aminocarbyne complexes {Tp′(EtNC)W[{A figure is presented}CN(R)Et][{A figure is presented}CNEt2]}BF4 (5a, 5b). Extended-Hückel calculations on the hypothetical 18e bis-carbyne complex [CpW(CO)(CH)2]+ predict a spontaneous rearrangement to the energetically favoured 16e acetylene complex [CPW(CO)(HCCH)]+ and show, in full agreement with the experimental work, that introduction of amino-substituents on both carbyne-carbons stabilizes the bis-carbyne form relative to the alkyne isomer. The solid-state structure of 2b was determined by a single- crystal X-ray diffraction study revealing a distorted octahedral complex with a short WCcarbyne bond. The short Ccarbyne N bond and the planar amino-nitrogen indicate a high degree of π-bonding between the carbyne-carbon and the amino-nitrogen.

Original languageEnglish (US)
Pages (from-to)233-247
Number of pages15
JournalJournal of Organometallic Chemistry
Volume459
Issue number1-2
DOIs
StatePublished - Oct 19 1993
Externally publishedYes

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