Detailed understanding of the mechanistic processes that underpin transition metal-catalysed reactions allows for the rational and de novo development of complexes with enhanced activity, efficacy and wider substrate scope. Directly observing bond-cleaving and -forming events underpinning a catalytic reaction is non-trivial as the species that facilitate these steps are frequently short-lived and present at low concentrations. Here, we describe how the photochemical activation of a manganese precatalyst, [Mn(ppy)(CO)₄] (ppy = 2-phenylpyridine), results in selective loss of a carbonyl ligand simulating entry into the catalytic cycle for manganese-promoted C–H bond functionalization. Time-resolved infrared spectroscopy (on the ps–ms timescale) allows direct observation of the species responsible for the essential C–C bond formation step and an evaluation of the factors affecting its rate. This mechanistic information prompted the discovery of a new photochemically initiated manganese-promoted coupling of phenylacetylene with 2-phenylpyridine. This study provides unique insight into the mechanistic pathways underpinning catalysis by an Earth-abundant metal, manganese.

对支撑过渡金属催化反应的机理的详细了解有助于合理，从头开发具有增强的活性，功效和更广泛的底物范围的配合物。直接观察支撑催化反应的键断裂和形成事件是不平凡的，因为促进这些步骤的物质通常寿命短且以低浓度存在。在这里，我们描述了锰预催化剂[Mn（ppy）（CO）₄]（ppy = 2-苯基吡啶），会导致羰基配体的选择性损失，从而模拟进入锰促进的C–H键功能化的催化循环。时间分辨红外光谱（以ps-ms为单位）可以直接观察负责基本C-C键形成步骤的物种，并可以评估影响其速率的因素。这种机理信息促使人们发现了一种新的光化学引发的锰促进的苯乙炔与2-苯基吡啶的偶联反应。这项研究提供了独特的见解，证明了富含地球的金属锰对催化作用的机理的支持。