Reactions of group 4 metallocene complexes with mono- and diphenylacetonitrile: Formation of unusual four- and six-membered metallacycles

Abstract

Reactions of Group 4 metallocene alkyne complexes [Cp'2M(η 2-Me3SiC2SiMe3)] (1: M=Zr, Cp'=Cp*=η5-pentamethylcyclopentadienyl; 2 a: M=Ti, Cp'=Cp*, and 2 b: M=Ti, Cp'2=rac-(ebthi)=rac-1,2-ethylene-1,1'- bis(η5-tetrahydroindenyl)) with diphenylacetonitrile (Ph 2CHCN) 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 [Cp*2Zr(η2-Me3SiC 2SiMe3)(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 [Cp*2Zr(NC2Ph2)(NCHCHPh2)] (5). The conversion of 4 to 5 was monitored by using 1H NMR spectroscopy. The analogue titanocene complex 2 a eliminated the alkyne first, which led directly to [Cp*2Ti(NC2Ph 2)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. Metal made modes: [Cp'M2] complexes with different metals and Cp' ligands react differently with Ph 2CHCN (see scheme). M=Zr gives keteniminate and imine ligands as [Cp*2Zr(NC2Ph2)(NCHCHPh2)], M=Ti forms two keteniminates as [Cp*2Ti(NC2Ph 2)2]. If Cp'2=rac-(ebthi)=rac-1,2-ethylene-1, 1'-bis(η5-tetrahydroindenyl) and M=Ti, an unusual four-membered titanacycle is formed. [Cp2Zr(η2-Me 3SiC4SiMe3)] reacts with PhCH2CN to give an unexpected six-membered fused zirconaheterocycle. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.