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 (<b>1</b>) was treated with CoI₂ under reducing conditions, permitting isolation of the Ti/Co complex [(μ-Cl)Ti(XylNPⁱPr₂)₂CoI]₂ (<b>2</b>). One electron reduction of complex <b>2</b> affords ClTi(XylNPⁱPr₂)₂CoPMe₃ (<b>3</b>), 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 (<b>4</b>). A cooperative mechanism involving bimetallic C[double bond, length as m-dash]O bond activation and a cobalt carbene intermediate is proposed.