Template Catalysis by Metal–Ligand Cooperation. C–C Bond Formation via Conjugate Addition of Non-activated Nitriles under Mild, Base-free Conditions Catalyzed by a Manganese Pincer Complex

The first example
of a catalytic Michael addition reaction of non-activated
aliphatic nitriles to α,β-unsaturated carbonyl compounds
under mild, neutral conditions is reported. A new de-aromatized pyridine-based
PNP pincer complex of the Earth-abundant, first-row transition metal
manganese serves as the catalyst. The reaction tolerates a variety
of nitriles and Michael acceptors with different steric features and
acceptor strengths. Mechanistic investigations including temperature-dependent
NMR spectroscopy and DFT calculations reveal that the cooperative
activation of alkyl nitriles, which leads to the generation of metalated
nitrile nucleophile species (α-cyano carbanion analogues), is
a key step of the mechanism. The metal center is not directly involved
in the catalytic bond formation but rather serves, cooperatively with
the ligand, as a template for the substrate activation. This approach
of “template catalysis” expands the scope of potential
donors for conjugate addition reactions.

首次报道了在温和、中性条件下，非活化脂肪族腈对α,β-不饱和羰基化合物的催化迈克尔加成反应的实例。一种新的去芳香化吡啶基PNP抓取型配位复合物，由地球上丰富的第一行过渡金属锰所催化。该反应能够容忍多种具有不同立体特征和受体强度的腈和迈克尔受体。机理研究包括温度依赖性NMR光谱学和DFT计算揭示，烷基腈的协同活化，导致金属化腈亲核物种（α-氰基碳负离子类似物）的生成，是机理中的关键步骤。金属中心并未直接参与催化键的形成，而是与配体协同作用，作为底物活化的模板。这种‘模板催化’方法扩展了共轭加成反应潜在供体的范围。