Stereoisomerism of bis(σ-Zincane) Complexes: Evidence for an Intramolecular Pathway
Olga Ekkert1, Andrew J P White1, Mark R Crimmin1
1Department of Chemistry, Imperial College London, South Kensington, London, SW7 2AZ, UK.
Abstract:
The first bis(σ-zincane) complexes, heterotri- metallic species [M(CO)4 (η2 -HZnBDI)2 ], have been prepared (BDI=κ2 -{2,6-(iPr)2 C6 H3 NCMe}2 CH). For M=Cr, a single stereoisomer is observed in solution and the solid-state. For M=Mo and W, cis and trans isomers were found to reversibly interconvert at 297 K. Despite the huge steric demands of the ligand on zinc, the cis isomer was found to be the most thermodynamically stable in all cases. The activation parameters for the isomerisation when M=Mo are ΔH≠ =20.8 kcal mol-1 and ΔS≠ =-12.8 cal K-1 mol-1 . In combination with DFT calculations, the negative activation entropy suggests an intramolecular rotation mechanism for isomerisation.
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