Zinc Catalyzed Hydroelementation (HE; E = B, C, N, and O) of Carbodiimides: Intermediates Isolation and Mechanistic Insights

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 singlecrystal X-ray diffraction studies. Complete catalytic cycles have been proposed based on well-defined intermediates and stoichiometric experiments.

Zinc-Catalyzed Chemoselective Reduction of Nitriles to N-Silylimines through Hydrosilylation: Insights into the Reaction Mechanism

“…Previously, we investigated the CBG supported zinc hydride [{L 1 ZnH} 2 ; (L 1 = {(ArNH)­(ArN)–CN–C(NAr)­(NHAr)}; Ar = 2,6-Et 2 -C 6 H 3 )] ( Zn-1 ) (Figure ), catalyzed hydrofunctionalization of unsaturated organic substrates . As mentioned, only a few examples of metal-catalyzed chemoselective reduction of nitriles have been reported.…”

Zinc Hydride-Catalyzed Dihydroboration of Isonitriles and Nitriles: Mechanistic Studies with the Structurally Characterized Zinc Intermediates

“…As previously established by our group, the active zinc catalyst [LZnH] 2 (L = {(ArNH)­(ArN)–CN–C(NAr)­(NHAr)}; Ar = 2,6-Et 2 -C 6 H 3 ) ( Zn-1 ) can be obtained easily by the reaction between [LZnI] 2 and KNH­( i Pr )­BH 3 (Figure ). Moreover, we used complex Zn-1 as an effective catalyst for the hydroboration of various unsaturated organic substrates. ,, Very recently, we also established mechanistic studies of DiethylCBG zinc hydride ( Zn-1 ) catalyzed hydrofunctionalization of N-heteroarenes …”

Insights into the Regioselectivity of Metal-Catalyzed Aryne Reactions

“…We screened a variety of symmetrical ligand systems to establish a consistent baseline selectivity of the o-methyl aryne towards its phenanthridinone regioisomers (Figure 6). 60 Figure 6 Establishing baseline regioselectivity. Yield determined as the sum of both regioisomers through 1 H NMR spectroscopy with mesitylene as an internal standard.…”