A ligand influence on the stability of heterobimetallic complexes containing the Ti(mu-O)A1 skeleton.Transformation of heterometallic systems to the homometallic Ti(IV) and Al(III) complexes

摘要

The influence of the ligands on the formation and stability of mu-oxo-bridged Ti(IV) complexes has been studied.Reaction of LTiCl3,(1) and LAlMe(OLi) (L=HC(CMeN(2,6-iPr2C6H3))2,"NacNac") afforded intermediate LTiCl2(mu-O)AlMeL (5) in solution,which was converted to LTiCl(mu-O)2TiClL (6) and LAlMeCl within 2 days.The decomposition of 5 was estimated to be thermodynamically favorable.The interaction of LTiMe3 (3) and LAlMe(OH) yielded the intermediate LTiMe2(mu-O)AlMeL (7).Complex 7 decomposes in solution giving the titanium oxo complex LTiMe(O) (8) and LAlMe2.The calculated DELTA G~(298) for this reaction is -128 kJ mol~(-1).The degradation of LTiMe2(mu-O)AlMeL is slow and follows first order kinetics with k2=4.09(7) x 10~(-7) s~(-1).The dimeric complex LTiMe(mu-O)2TiMeL-toluene (9a) was isolated from the reaction of 3 with LAlMe(OH) in toluene and LTiMe(mu-O)2TiMeL-hexane (9b) from hexane.The dimerization of 8 yielding LTiMe(mu-O)2TiMeL (9) is marginally endothermic,with a calculated DELTA G~(298) of+27 kJ mol~(-1).The formation of the solid 9 is due to the lattice stabilization.The solid mu-oxo-bridged complex 9 and Mes3Ga were obtained from the reaction of LTiMe3 with [Mes2Ga(OH)]2-THF in toluene,and 9 was also isolated from the reaction of LTiMe3 with 1 equiv.of H2O in toluene.Compounds LTiCl3 (1),LTiCl(mu-O)2TiClL (6),9a and 9b have been characterized by X-ray single crystal structure,NMR,IR,EI-MS and elemental analysis.Complexes 5,7 and 8 have been characterized by NMR.Compounds 3,6 and 9 possess moderate catalytic activity in the polymerization of ethylene.