Reactions of Group 4 metallocene complexes with mono- and diphenylacetonitrile: formation of unusual four- and six-membered metallacycles.

Reactions of Group 4 metallocene alkyne complexes [Cp'2M(η(2)-Me3SiC2SiMe3)] (1: M = Zr, Cp' = Cp* = η(5)-pentamethylcyclopentadienyl; 2 a: M = Ti, Cp' = Cp*, and 2 b: M = Ti, Cp'2 = rac-(ebthi) = rac-1,2-ethylene-1,1'-bis(η(5)-tetrahydroindenyl)) with diphenylacetonitrile (Ph2CHCN) and of the seven-membered zirconacyclocumulene 3 with phenylacetonitrile (PhCH2CN) were investigated. Different compounds were obtained depending on the metal, the cyclopentadienyl ligand and the reaction temperature. In the first step, Ph2CHCN coordinated to 1 to form [Cp2Zr(η(2)-Me3SiC2SiMe3)(NCCHPh2)] (4). Higher temperatures led to elimination of the alkyne, coordination of a second Ph2CHCN and transformation of the nitriles to a keteniminate and an imine ligand in [Cp2Zr(NC2Ph2)(NCHCHPh2)] (5). The conversion of 4 to 5 was monitored by using (1)H NMR spectroscopy. The analogue titanocene complex 2 a eliminated the alkyne first, which led directly to [Cp*2Ti(NC2Ph2)2] (6) with two keteniminate ligands. In contrast, the reaction of 2 b with diphenylacetonitrile involved a formal coupling of the nitriles to obtain the unusual four-membered titanacycle 7. An unexpected six-membered fused zirconaheterocycle (8) resulted from the reaction of 3 with PhCH2CN. The molecular structures of complexes 4, 5, 6, 7 and 8 were determined by X-ray crystallography.