abstracts - Институт катализа им. Г.К. Борескова

KS-II-6NOCl NO C 2 H 4 NOCH 13 MAO* S 2 CH 2 CH CHTiNTiTin 2 CH 2 3OCl N13 CH 3 NOO13MeMAO* - 4 MeMAO* -MAO* = 13 C-MAOTo be effective, MAO must be used in large excess with respect to the transition metalcomponent. For practical applications, it would be desirable to decrease the amount of MAOactivator due to the large cost of MAO. It was found that additions of triisobutyl aluminum(TIBA) increase the co-catalytic of MAO. The nature of this positive effect of TIBA has beenelucidated in our studies.Solutions containing mixtures of methylalumoxane (MAO) and i Bu 3 Al give rise to1 H NMR signals indicative of the presence of the mixed alkyl aluminum dimers i Bu 2 Al(μ-Me) 2 Al i Bu 2 and of mixed clusters of the type (AlMe i (1+2x-y) Bu y O (1-x) ) n . These mixed clustersappear to have stronger Lewis acidic sites and greater hydrodynamic radii than comparableclusters present in solutions of MAO alone, as judged from EPR signals observed in thesesolutions upon addition of TEMPO. When (SBI)ZrCl 2 (SBI = rac-Me 2 Si(ind) 2 ) is reacted withone of these mixed activator reagents, the mixed heterobinuclear cation [(SBI)Zr(μ-Me) 2 AlMe i Bu] + appears to be formed, together with its methyl counterpart [(SBI)Zr(μ-Me) 2 AlMe 2 ] + , normally predominant in the system (SBI)ZrCl 2 /MAO at [Al] MAO /[Zr] ratiosabove 100. In the presence of i Bu 3 Al the formation of heterobinuclear cations is suppressed infavor of ion pairs containing the cation [(SBI)ZrMe] + in contact with a (MAO+TIBA)-derived counter-anion. The greater reactivity of these contact-ion pairs, as compared to thenormally prevalent AlMe 3 adducts, as well as an increased Lewis acidity of modified MAOand the ensuing decreased coordination ability of [Me-(MAO+TIBA)] − counter ion ascompared to [Me-MAO] − are likely to contribute to the positive effects of TIBA additions onthe co-catalytic activity of MAO.The work was supported by RFBR grant 03-03-33034, INTAS grant 00-841 and RoyalSociety, grant no. 2004/R1-FSU.50