Abstract: We describe the development of [(NHC)Pd(cinnamyl)Cl] complexes of ImPy (ImPy = imidazo[1,5-a]pyridin-3-ylidene) as a versatile class of precatalysts for cross-coupling reactions. These precatalysts feature fast activation to monoligated Pd(0) with 1:1 Pd to ligand ratio in a rigid imidazo[1,5-a]pyridin-3-ylidene template. Steric matching of the C5-substituent and N2-wingtip in the catalytic pocket of the catalyst framework led to the discovery of ImPyMesDipp as a highly reactive imidazo[1,5-a]pyridin-3-ylidene ligand for Pd-catalyzed cross-coupling of nitroarenes by challenging C–NO2 activation. Kinetic studies demonstrate fast activation and high reactivity of this class of well-defined ImPy–Pd catalysts. Structural studies provide full characteristics of this new class of imidazo[1,5-a]pyridin-3-ylidene ligands. Computational studies establish electronic properties of sterically-restricted imidazo[1,5-a]pyridin-3-ylidene ligands. Finally, a scalable synthesis of C5-substituted imidazo[1,5-a]pyridin-3-ylidene ligands through Ni-catalyzed Kumada cross-coupling is disclosed. The method obviates chromatographic purification at any of the steps, resulting in a facile and modular access to ImPy ligands. We anticipate that well-defined [Pd–ImPy] complexes will find broad utility in organic synthesis and catalysis for activation of unreactive bonds.
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With dicyclohexyl-(2',6'-dimethoxybiphenyl-2-yl)-phosphane; potassium phosphate; palladium diacetate; In tetrahydrofuran; water; at 100℃; for 24h;Inert atmosphere; Schlenk technique;
Under an argon atmosphere in a Schlenk flask,Followed by loading 3mmol of <strong>[10485-09-3]2-bromoindene</strong> (Shanghai Bi Pharmaceutical Technology Co., Ltd.)1.5 mmol of 2,4,6-triisopropylbenzeneboronic acid (Shanghai Biomedical Technology Co., Ltd.),3 mmol% of palladium acetate, 6 mmol% of S-Phos and 3 mmol of potassium phosphate,A mixture of 20 mL of tetrahydrofuran and 10 mL of water was added to dissolve the reactants and reacted at 100 C for 24 hours.After cooling, the reaction mixture was extracted with ethyl acetate, the organic phase was dried over anhydrous sodium sulfate, the organic phase solvent was removed,Column chromatography was carried out using petroleum ether as a developing solvent (Rf = 0.8)2- (2,4,6-Triisopropylphenyl) indene was obtained in a yield of 85%
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