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Synthesis and Reactions with Carbon Dioxide of Mono(σ-alkynyl) Titanocene(III) Complexes Cp*2Ti(C⋮CR) (R = Me, t-Bu) and the Corresponding “Ate” Complexes [Cp*2Ti(C⋮CR)2Li(THF)n] (R = SiMe3, t-Bu, Ph)

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journal contribution
posted on 14.11.2001, 00:00 by Frank G. Kirchbauer, Paul-Michael Pellny, Hongsui Sun, Vladimir V. Burlakov, Perdita Arndt, Wolfgang Baumann, Anke Spannenberg, Uwe Rosenthal
The reactions of the titanium(III) complex Cp*2TiCl with lithium acetylides RC⋮CLi depend strongly on the solvents used. In THF only the lithium tweezer compounds [Cp*2Ti(C⋮CR)2Li(THF)n] (Cp* = η5-C5Me5; R = SiMe3, n = 1 (1); R = t-Bu, n = 1 (2); R = Ph, n = 2 (3)), not the expected mono(σ-alkynyl) titanocene(III) complexes, were obtained, whereas in n-hexane these complexes Cp*2Ti(C⋮CR) were isolated for R = Me (4), t-Bu (5). The reaction of the complex [Cp*2Ti(C⋮CSiMe3)2Li(THF)] (1) with carbon dioxide results in the titanafuranone 6, which presumably is formed by insertion of carbon dioxide into the η2-butadiyne complex Cp*2Ti(η2-Me3SiC⋮CC⋮CSiMe3). The complex [Cp*2Ti(C⋮C-t-Bu)2Li(THF)] (2) reacts with carbon dioxide to yield the permethyltitanocene carboxylate Cp*2Ti(O2CC⋮C-t-Bu) (7) via insertion into the σ-acetylide bond of the in situ formed titanium(III) intermediate [Cp*2Ti−C⋮C-t-Bu]. Compound 7 was also obtained in the reaction of the isolated titanium(III) complex Cp*2Ti−C⋮C-t-Bu (5) with carbon dioxide. The interaction of [Cp*2Ti(C⋮CPh)2Li(THF)2] (3) with carbon dioxide gives the stable bis(σ-acetylide) permethyltitanocene Cp*2Ti(C⋮CPh)2 (8) without coupling of the σ-acetylide groups (as found for 1) and without insertion into the σ-acetylide bond (as found for 2). The syntheses and reactions of these compounds are compared to those of similar complexes of unsubstituted titanocene compounds. Complexes 1, 5, and 7 were investigated by X-ray crystal structure analysis.