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.

中文翻译：

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定义明确、空气和水分稳定的钯-咪唑并[1,5-a]吡啶-3-亚基配合物：L形NHC配体交叉偶联反应的多功能催化剂平台

我们描述了 ImPy 的 [(NHC)Pd(肉桂基)Cl] 配合物 (ImPy = imidazo[1,5 - a ]pyridin-3-ylidene) 作为交叉偶联反应的通用类预催化剂的发展。这些预催化剂的特点是在刚性咪唑并[1,5- a ]吡啶-3-亚基模板中以 1:1 的 Pd 与配体比率快速激活单配位 Pd(0) 。催化剂骨架催化袋中 C5 取代基和 N2 翼尖的空间匹配导致发现 ImPyMesDipp 作为Pd 催化交叉偶联的高反应性咪唑并[1,5- a ]吡啶-3-亚基配体硝基芳烃通过挑战 C-NO ₂激活。动力学研究证明了这类定义明确的 ImPy-Pd 催化剂的快速活化和高反应性。结构研究提供了这类新的咪唑并[1,5 - a ]吡啶-3-亚基配体的全部特征。计算研究确定了空间受限的咪唑并[1,5 - a ]吡啶-3-亚基配体的电子特性。最后，C5-取代的咪唑[1,5- a]pyridin-3-ylidene 配体通过 Ni 催化的 Kumada 交叉偶联被公开。该方法避免了任何步骤的色谱纯化，从而可以轻松和模块化地访问 ImPy 配体。我们预计，定义明确的 [Pd-ImPy] 配合物将在有机合成和催化活化非反应性键方面具有广泛用途。