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

Synthesis, structure, and catalytic use of a novel quinazolinone Ti^IV complex are reported. This Ti^IV complex was found to be an effective catalyst for the reduction of esters as well as nitriles with pinacolborane (HBpin) to afford the corresponding boryl ethers and diboryl amines at ambient temperature under solvent-free conditions in high yields and with wide functional group tolerance.

Abstract

We report catalytic hydroboration of esters as well as nitriles under solvent-free and mild conditions using single titanium(IV) metal complex, [{κ ²-C₆H₄C(O)N( ⁱ Pr)C(N- ⁱ Pr)=N}{κ ³-( ⁱ Pr)N=C(O)−C₆H₄−NC(NMe₂)N( ⁱ Pr)}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.

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