Stoichiometric Reactions and Catalytic Hydrogenation with a Reactive Intramolecular Zr+/Amine Frustrated Lewis Pair

Methyl anion abstraction from Cp*Zr-2(CH3)(OCH2CH2NPr2)-Pr-i (13) with trityl cation generates [Cp*Zr-2((OCH2CH2NPr2)-Pr-i)](+) (14). Complex 14 behaves as a reactive Zr+/amine frustrated Lewis pair (FLP). It reacts with dichloromethane to give the [Zr]Cl[OCH2CH2N(CH2Cl)Pr-i(2)](+) cation (15), it slowly loses H-2 upon standing at 60 degrees C to give a metallacyclic iminium cation product 18, and it reacts with terminal alkynes to give the [Zr]-alkynyl/ammonium systems 19. The organometallic FLP 14 cleaves dihydrogen heterolytically at near to ambient conditions to give the [Zr]H[(OCH2CH2NHPr2)-Pr-i](+) complex 20, which reduces benzaldehyde to the respective [Zr]OCH2Ph product 21 and is able to transfer the H+/H- pair to styrene to give ethylbenzene. Consequently, the Zr+/amine FLP 14 was used as an active hydrogenation catalyst for a series of alkenes and internal alkynes. The catalytic hydrogenation reactions were carried out under mild conditions (r.t., 1.5 bar of H-2) using between 1 and 4 mol % FLP catalyst 14.