Interaction of oxygen functionalized alkenes with a methylaluminoxane–zirconocene catalyst studied by NMR

Abstract

Reactions of hydroxyl, ether and carbonyl functionalized alkenes with methylaluminoxane prepared in toluene- d 8 (MAO) and zirconocenedichloride (Cp 2ZrCl 2) were investigated by 1H- and 13C-NMR spectroscopy at 27°C. The 11 alkenes studied bear a terminal CC bond separated by 7–9 (–CH 2–) units from the heteroatom moiety. Intramolecular connectivities in mono (alkene), bi (alkene and MAO) and tri (alkene, MAO and Cp 2ZrCl 2) component mixtures were determined by 2D HSQC, HMBC, ROESY and NOESY NMR techniques. The five studied alkenols formed aluminium alkoxides with MAO even in the case of a substantial steric hindrance around the OH group. Zirconocene enhanced the formation of aluminium alkoxides. Decomposition to free alkenol was observed only for the straight chain alkenol (10-undecen-1-ol). The OTMS derivatives formed dimers of the type CH 2CR 1R 2 along with methyl derivatives, CH 2C(Me)(R) and (Me)CHCH(R), in the presence of MAO and Cp 2ZrCl 2. 10-Undecenyl methyl ether and methyl decenoate remained mainly as a free comonomer in the presence of MAO or MAO/Cp 2ZrCl 2, though a transient coordination of the former to MAO was deduced. Unsaturated species Me 2CCH–Al–X and CH 2CH(CH 2) 5CH 2CHC( t-Bu)O–Al–X (X=MAO oligomer) were formed in the reaction of t-butyl undecenoate or 2,2-dimethyl-11-dodecen-3-one with MAO or MAO/Cp 2ZrCl 2. Interaction of the CH 2CH part of the functionalized alkenes with zirconocene was not observed. A possible coordination of the CC bond to MAO was observed only for the sec alkenols.