Titanium-Catalyzed Hydroamination and Multicomponent Coupling with a Simple Silica-Supported Catalyst

Abstract

Hydroamination and multicomponent coupling reactions catalyzed by homogeneous Ti(IV) complexes can produce valuable imines, amines, and other nitrogen-containing organic building blocks. Typically catalysts for this transformation are very sensitive to ancillary ligand design and often suffer from catalyst deactivation, necessitating use in a single reaction. Here, we have attempted to address these issues by moving toward a solid-supported Ti catalyst active for these reaction types. We present initial results to synthesize and probe the catalytic reactivity of silica-supported titanium amide precatalysts. With minimal treatment of commercially available fumed silica, Ti(NMe2)2/SiO2200 can be isolated upon addition of Ti(NMe2)4. This species gives high yields and high regioselectivity for hydroamination of a variety of alkynes with anilines. The solid-supported species is also an active catalyst for the formation of tautomers of unsymmetrical 1,3-diimines via three-component coupling of bulky anilines, alkynes, and isonitriles. Reusability and possible catalyst deactivation pathways are also discussed.