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

[Image: see text] 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(IV) complex [{Ph(2)P(BH(3))N}(2)C(6)H(4)Ti(NMe(2))(2)] (1) was obtained by the reaction between tetrakis-(dimethylamido)titanium(IV) and the protic aminophosphine–borane ligand [{Ph(2)P(BH(3))NH}(2)C(6)H(4)] (LH2) at ambient temperature. Both the heteroleptic zirconium complexes—[η(5)-(C(5)H(5))(2)Zr{Ph(2)P(BH(3))N}(2)C(6)H(4)] (2) and [[{Ph(2)P(BH(3))N}(2)C(6)H(4)]ZrCl(2)] (3)—and the homoleptic zirconium complex [[{Ph(2)P(BH(3))N}(2)C(6)H(4)](2)Zr] (4) were obtained in good yield by the salt metathesis reaction of either zirconocene dichloride [η(5)-(C(5)H(5))(2)ZrCl(2)] or zirconium tetrachloride with the dilithium salt of the ligand [{Ph(2)P(BH(3))NLi}(2)C(6)H(4)] (LLi2), which was prepared in situ. The molecular structures of the complexes 1, 2, and 4 in their solid states were confirmed by single-crystal X-ray diffraction analysis. Of these complexes, only titanium complex 1 acts as an effective catalyst for the facile hydroboration of terminal alkynes, yielding exclusive E-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.