Efficient Hydroboration of Esters and Nitriles Using a Quinazolinone-Supported Titanium(IV) Multitasking Catalyst

We report catalytic hydroboration of esters as well as nitriles under solvent-free and mild conditions using single titanium(IV) metal complex, [{& kappa;(2)-C6H4C(O)N(Pr-i)C(N-Pr-i)=N}{& kappa;(3)-(Pr-i)N=C(O)-C6H4-NC(NMe2)N(Pr-i)}TiNMe2] 1 as a sustainable, economical, and efficient pre-catalyst. The molecular structure of the Ti-IV complex in the solid state reveals the unique coordination of Ti-IV metal with N, N, and O atoms of one quinazolinone unit via in-situ rearrangement, while another quinazolinone moiety coordinates in bidentate fashion via both N atoms only. The Ti-IV complex demonstrates excellent activity as a pre-catalyst towards the hydroboration of a wide array of esters and nitriles with pinacolborane (HBpin) to afford alkoxyboranes and diboryl amines in high yield (up to 99 %) with greater tolerance to a variety of electron-withdrawing and electron-donating functional groups. A most plausible mechanism of hydroboration of esters is also proposed based on kinetics and NMR studies, which suggests the formation of titanium-hydride species as an active catalyst.