H-1 AND C-13 NMR EVIDENCE FOR THE INTERMEDIATE SPECIES [(CPZRCL)(MU-ETA-1-ETA-5-C5H4)]2 - CYCLOPENTADIENYL C-H BOND ACTIVATION BY THERMOLYSIS OF [CP2ZR(H)CL]N, CP2ZR(R)CL, AND [CP2ZRCL]2

Thermal decomposition at 80°C of [Cp2Zr(H)Cl]n (1) (Cp = η5-C5H5), Cp2Zr(R)Cl (2b) (R = cyclohexyl) and (Cp2ZrCl)2 gives the fulvalenide dizirconium complex [(CpZrCl)2(μ-η5 : η5-C5H4-C5H4)] (4) via the intermediate [(CpZrCl)(μ-η1 : η5-C5H4)]2 (5). Complex (5) can also be prepared by treating Cp2ZrCl2 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 Cp2Zr(η3-C8H11)Cl. This is the first example in zirconium(IV) chemistry of cyclopentadienyl CH bond activation resulting in hydrogenation of unsaturated substrates. © 1990.