Tri-coordinated zinc alkyl complexes with N^S/Se coordination of imino-phosphanamidinate chalcogenide ligands as precursors for efficient hydroboration of nitriles and esters

Abstract

A series of tri-coordinated zinc alkyl complexes with the general molecular formula [κ²_NE-{NHI^RP(Ph)(E)N-Dipp}ZnEt] [R = Dipp (2,6-diisopropylphenyl), E = S (3a), Se (3b) and R = ^tBu (tert-butyl), E = S (4a), Se (4b)] bearing imino-phosphanamidinate chalcogenide ligands were prepared in good yields from the reaction between the protic imino-phosphanamidinate chalcogenide ligand [NHI^RP(Ph)(E)NH-Dipp] [R = Dipp, E = S (1a), Se (1b) and R = ^tBu, E = S (2a), Se (2b)] and diethylzinc at room temperature. The molecular structures of all the zinc complexes were established by single-crystal X-ray diffraction analysis. In the solid state, all complexes exhibited a distorted trigonal planar geometry around the zinc ion. Metal-chalcogenide (Zn–S/Se) interactions were observed in the coordination sphere. These zinc alkyl complexes were employed as pre-catalysts in the hydroboration reaction of nitriles and esters to obtain the corresponding N,N-diborylamines and boronate esters, respectively, under ambient conditions. A wide substrate scope of nitriles and esters is presented.