Highly Chemoselective Hydroboration of Alkynes and Nitriles Catalyzed by Group 4 Metal Amidophosphine-Borane Complexes.

We report a series of titanium and zirconium complexes supported by dianionic amidophosphine-borane ligands, synthesized by amine elimination and salt metathesis reactions. The Ti complex [{PhP(BH)N}CHTi(NMe)] () was obtained by the reaction between tetrakis-(dimethylamido)titanium(IV) and the protic aminophosphine-borane ligand [{PhP(BH)NH}CH] () at ambient temperature. Both the heteroleptic zirconium complexes-[η-(CH)Zr{PhP(BH)N}CH] () and [[{PhP(BH)N}CH]ZrCl] ()-and the homoleptic zirconium complex [[{PhP(BH)N}CH]Zr] () were obtained in good yield by the salt metathesis reaction of either zirconocene dichloride [η-(CH)ZrCl] or zirconium tetrachloride with the dilithium salt of the ligand [{PhP(BH)NLi}CH] (), which was prepared in situ. The molecular structures of the complexes , , and in their solid states were confirmed by single-crystal X-ray diffraction analysis. Of these complexes, only titanium complex acts as an effective catalyst for the facile hydroboration of terminal alkynes, yielding exclusive -isomers. The hydroboration of organic nitriles yielded diborylamines with a broad substrate scope, including broad functional group compatibility. The mechanism of hydroboration occurs through the formation of titanium hydride as an active species.