1H and 13C NMR evidence for the intermediate species [(CpZrCl)(μ-η 1:η 5-C 5H 4)] 2. Cyclopentadienyl CH bond activation by thermolysis of [Cp 2Zr(H)Cl] n, Cp 2Zr(R)Cl, and [Cp 2ZrCl] 2

Abstract

Thermal decomposition at 80°C of [Cp 2Zr(H)Cl] n ( 1) (Cp = η 5-C 5H 5), Cp 2Zr(R)Cl ( 2b) (R = cyclohexyl) and (Cp 2ZrCl) 2 gives the fulvalenide dizirconium complex [(CpZrCl) 2(μ-η 5 : η 5-C 5H 4-C 5H 4)] ( 4) via the intermediate [(CpZrCl)(μ-η 1 : η 5-C 5H 4)] 2 ( 5). Complex ( 5) can also be prepared by treating Cp 2ZrCl 2 with sodium amalgam (1.5 eq) in refluxing toluene. In the presence of cyclic polyenes, such as 1,5-cyclooctadiene (1,5-COD) thermolysis of 1 takes place at room temperature probably to give initially a labile π allyl species, which can be formulated in the case of the reaction with 1,5-COD as Cp 2Zr(η 3-C 8H 11)Cl. This is the first example in zirconium(IV) chemistry of cyclopentadienyl CH bond activation resulting in hydrogenation of unsaturated substrates.