A heterobimetallic complex featuring a Ti-Co multiple bond and its application to the reductive coupling of ketones to alkenes

Abstract

To explore metal-metal multiple bonds between first row transition metals, Ti/Co complexes supported by two phosphinoamide ligands have been synthesized and characterized. The Ti metalloligand Cl2Ti(XylNPiPr2)2 (1) was treated with CoI2 under reducing conditions, permitting isolation of the Ti/Co complex [(μ-Cl)Ti(XylNPiPr2)2CoI]2 (2). One electron reduction of complex 2 affords ClTi(XylNPiPr2)2CoPMe3 (3), which features a metal-metal triple bond and an unprecedentedly short Ti-Co distance of 2.0236(9) Å. This complex is shown to promote the McMurry coupling reaction of aryl ketones into alkenes, with concomitant formation of the tetranuclear complex [Ti(μ3-O)(NXylPiPr2)2CoI]2 (4). A cooperative mechanism involving bimetallic C=O bond activation and a cobalt carbene intermediate is proposed.