Exploring Dinuclear Titanium Complexes in Titanium(III) Catalysis

The synthesis of one achiral and two chiral propylene-bridged dititanocenes and their evaluation as catalysts in titanium(III) catalyzed ketone-nitrile coupling reactions are reported. A reaction progress kinetics analysis of the cross-coupling between acetophenone and benzyl cyanide reveals that, using a dinuclear titanocene catalyst, the order in catalyst is reduced from two to one in comparison to a mononuclear catalyst. Although the obtained coupling yields and enantioselectivities did not reach the results obtained with the latter, these examples constitute a proof of concept for the templated C & horbar;C coupling through coordination of ketone and nitrile to the two tethered titanium centers of a dinuclear catalyst. In this proof of principle study, the synthesis of one achiral and two chiral dinuclear titanocenes and their evaluation in the catalytic-reductive ketone-nitrile coupling are reported. A reduction in catalyst order compared to mononuclear titanocenes supports the catalyst-templated dual activation in the coupling transition state. image