Zinc Hydride-Catalyzed Dihydroboration of Isonitriles and Nitriles: Mechanistic Studies with the Structurally Characterized Zinc Intermediates
Rajata Kumar Sahoo, Sagrika Rajput, Sneha Dutta, Kasturi Sahu, Sharanappa Nembenna
Abstract
The conjugated bis-guanidinate (CBG)-stabilized zinc hydride, [{LZnH} 2; (L = {(ArNH)(ArN)–C═N–C═(NAr)(NHAr)}; Ar = 2,6-Et 2 -C 6 H 3 )] ( Zn-1 ), is shown to be a highly active catalyst for the double reduction of isonitriles and nitriles with pinacolborane (HBpin) in this study. A wide array of isonitriles and nitriles, including aryl and alkyl groups, underwent hydroboration to afford exclusively 1,2- and 1,1-diborylated amine products, respectively. A series of stoichiometric reactions were performed to understand the reaction mechanisms. Hydroboration of isonitrile proceeds through the formation of zinc formimidoyl complex, [LZnC( H )N( t Bu)] 2 ( Zn-2 ), while nitrile hydroboration through zinc vinylidenamido complex, [LZnNC(H)(C 6 H 5 )] 2 ( Zn-3 ). Moreover, compounds Zn-2 and Zn-3 are isolated and thoroughly characterized. Such molecular zinc complexes are rare in the literature.