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Title: Synthesis, structure, spectroelectrochemical and theoretical investigations of Formation of a cobalt complexed stannacycle via a mixed alkyne-stannylene cycloaddition reaction
Authors: Schneider, J. J.
Hagen, J.
Heinemann, O.
Krüger, C.
Fabrizi De Biani, Fabrizia 
Zanello, Piero
Issue Date: 1998
Project: None 
Reacting 2-butyne with the cobalt stannylene complexes [Cp-R(C2H4)Co-Sn{CH{Si(CH3)(3)}(3)}(2)] (R=H (5), Me-5 (6)) affords different cyclotrimerization products depending on the Cp ligand used. For the CpR (R=H) derivative 5, reaction with 2-butyne is exclusively intermolecular, resulting in the formation of a 5:4:1 mixture of a 20e sandwich complex [(eta(5)-Cp)Co( eta(6)-C6Me6)], free hexamethylbenzene (hmb), and free stannylene [Sn{CH(SiMe3)(2)}(2)]. Replacing Cp against Me5Cp affords only trace amounts of the 20e sandwich complex [(eta(5)-Me5Cp)Co(eta(6)-C6Me6)], no free hmb and stannylene. The main product of the reaction is the cobalt-stannacyclopentadiene complex 8 [ (eta(5)-Me5Cp)Co(eta(4)-MeC=CMe-CMe=CMe)Sn{CH(SiMe3)(2)}(2)] which is formed via cycloaddition of two alkyne molecules and an SnR2 (R = CH(SiMe3)(2)) fragment. Crystalline 8 is characterized by single-crystal structure analysis which reveals a cobalt bonded stannacyclopentadiene ring Ligand with a distorted tetrahedrally coordinated Sn atom and an eta(4) coordinated cobalt atom. Electrochemistry coupled with electron paramagnetic resonance spectroscopy and extended Huckel calculations shows that the Co(I) complex 8 undergoes reversibly one-electron oxidation to the corresponding Co(II) monocation [8](+), whereas further oxidation to the Co(III) congener [8](2+) is followed by chemical complications
ISSN: 0020-1693
DOI: 10.1016/S0020-1693(98)00141-8
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