A general benzylic C-H activation and C-C coupling reaction of zirconocenes mediated by C-N bond cleavage in tert-butylisocyanide - unusual formation of iminoacyl complexes

Dalton Trans. 2019 Nov 12;48(44):16525-16533. doi: 10.1039/c9dt03120k.

Abstract

Reactions of the zirconocene alkyne complex [rac-(ebthi)Zr(η2-Me3SiC2SiMe3)] (rac-(ebthi) = rac-1,2-ethylene-1,1'-bis(η5-tetrahydroindenyl)) with tert-butylisocyanide and methylbenzenes were investigated. Depending on the stoichiometry, the solvent and the reaction temperature different products were obtained. Starting with the end-on coordination of the isocyanide to the zirconium centre (2), elevated reaction temperatures and an excess of tert-butylisocyanide resulted after the elimination of the alkyne in the formation of zirconocene η2-iminoacyl cyanide complexes 3a-d. These complexes are formed by coupling with a benzyl fragment through C-H bond activation of a methyl group of methylbenzene. The dimeric cyanide bridged zirconocene complex 4 is formed as a side-product of this process. The unexpected dimer and the heterometallacycles were fully characterised, including X-ray crystallography.