Zinc Catalyzed Hydroelementation (HE; E = B, C, N, and O) of Carbodiimides: Intermediates Isolation and Mechanistic Insights
Rajata Kumar Sahoo, A. Ganesh Patro, Nabin Sarkar, Sharanappa Nembenna
Abstract
The conjugated bis-guanidinate (CBG) supported zinc hydride, [{LZnH} 2; L = {(ArHN)(ArN)-C═N–C═(NAr)(NHAr); Ar = 2,6-Et 2 -C 6 H 3 }] ( 1 ) (pre)-catalyzed addition of E–H (E = B, C, N, and O) to carbodiimides is presented. Compound 1 catalyzed the reduction of carbodiimides with pinacolborane (HBpin), terminal alkynes, primary amines, and alcohols, gave a series of N -boryl formamidines, propiolamidines, guanidines, and isoureas with high conversions. All these reactions display good tolerance of functional groups. These reactions proceeded through the active catalysts and intermediate of zinc amidinate ( Zn-1, Zn-1′, and Zn-3 ), zinc alkynyl ( Zn-2, and Zn-2′ ), zinc anilide ( Zn-4 ), and zinc alkoxide ( Zn-5 ) complexes, which have been characterized by multinuclear NMR and HRMS analyses. Moreover, compounds Zn-1′, Zn-2′, Zn-4, and Zn-5 were confirmed by single-crystal X-ray diffraction studies. Complete catalytic cycles have been proposed based on well-defined intermediates and stoichiometric experiments.