Stoichiometric reactions and catalytic hydrogenation with a reactive intramolecular Zr(+)/amine frustrated Lewis pair.

Abstract

Methyl anion abstraction from Cp*2Zr(CH3)OCH2CH2N(i)Pr2 (13) with trityl cation generates [Cp*2Zr(OCH2CH2N(i)Pr2)](+) (14). Complex 14 behaves as a reactive Zr(+)/amine frustrated Lewis pair (FLP). It reacts with dichloromethane to give the [Zr]Cl[OCH2CH2N(CH2Cl)(i)Pr2](+) cation (15), it slowly loses H2 upon standing at 60 °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[OCH2CH2NH(i)Pr2](+) 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 H2) using between 1 and 4 mol % FLP catalyst 14.