Zirconium Complex as an Efficient Catalyst in the Hydroboration of Nitriles, Alkynes, and Carboxylic Esters: A Combined Experimental and Computational Study

We report the synthesis of a zirconium complex {κ2-[Ph2P­(S)­NCH2CH2N­(CH2CH2)­O]­Zr­(C5H5)2Cl} (2) supported by a flexible amidophosphinosulfide ligand [Ph2P­(S)­N­(CH2)2N­(CH2CH2)2O]− (1). The solid-state structure of zirconium complex 2 was established through single-crystal X-ray diffraction analysis. Complex 2 proved to be a competent catalyst in the hydroboration of organic nitriles, alkynes, and carboxylic esters with pinacolborane (HBpin) in neat reaction conditions. The reactions were accomplished with efficient catalytic reactivity demonstrated by complex 2 under mild temperatures and solvent-free conditions, affording a high yield of the corresponding N-borylamines, vinyl boranes, and benzyl boronate esters. The protocol for the catalytic reaction presented in this paper is simple and efficient, with diverse substrate scope for nitriles, alkynes, and carboxylic esters, showing excellent functional group tolerance. The kinetic study reveals that the nitrile reduction proceeded with first-order dependence on the concentrations of nitrile, HBpin, and catalyst 2. DFT calculations have been performed to gain mechanistic insights into the catalytic hydroboration of nitriles.