Naphthyl-derived orthometalated Ru^II-NHC complexes have been developed for catalytic applications considering the stereoelectronic profiles of the NHC ligands, which can be modified easily via alteration of the NHC donors (ImNHC/1,2,4-tzNHC) as well as their substitution pattern at the naphthyl ring. The azolium salts [(2a–c)-H]Br, precursors for the NHC ligands, react with [Ru(p-cymene)Cl₂]₂ in the presence of a base to deliver the ortho-metalated Ru^II-NHC complexes 3a–c with the general formula [(NHC)Ru(p-cymene)Br]. Orthometalation in these complexes can be exploited for further functionalization of the NHC ligands. This is depicted by the generation of the diphenylethylene-inserted isolable intermediate complex 4, from the reaction of 3a with diphenylacetylene in a 1:1 ratio, which eventually provides an annulated salt 5a-Br via reductive elimination. Gratifyingly, this process can also be made catalytic, which directly provides several mono-/bis-annulated cationic N-heterocyclic compounds starting from the imidazolium salts [(2a,b)-H]Br using [Ru(p-cymene)Cl₂]₂ as a precatalyst. Furthermore, subtle variations in the electronic profiles of the complexes 3a–c in combination with steric alterations are observed to influence their activity in the transfer hydrogenation of acetophenone, a model for the hydride transfer process. Among all the complexes studied here, complex 3b with an ImNHC donor at the second position of the naphthyl ring was identified as a superior catalyst in comparison to 3a,c featuring either a different NHC donor or substitution pattern with a low loading of 0.1 mol%.

中文翻译：

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萘衍生的正金属Ru ^II -NHC配合物：NHC供体和/或取代方式对其合成和催化活性的影响

考虑到NHC配体的立体电子特征，已开发出萘基正金属化Ru ^II -NHC配合物，可通过改变NHC供体（ImNHC / 1,2,4-tzNHC）及其它们萘环上的取代模式。NHC配体的前体偶氮盐[（2a – c）-H] Br与[Ru（p- Cymene）Cl ₂ ] ₂在碱存在下反应，以提供邻位金属化的Ru ^II -NHC配合物图3a - ç与通式[（NHC）钌（p-cymene）Br]。这些复合物中的正金属化可用于NHC配体的进一步功能化。这是由3a与二苯基乙炔以1：1的比例反应生成的，插入二苯乙烯的可分离中间体配合物4生成的，该化合物最终通过还原消除反应提供了环化盐5a-Br。令人欣慰的是，该方法也可以催化使用，直接使用[Ru（p- Cymene）Cl ₂ ]从咪唑鎓盐[（2a，b）-H] Br开始提供几种单/双环阳离子N-杂环化合物] ₂作为前催化剂。此外，观察到配合物3a - c电子构型的细微变化与空间变化共同影响其在苯乙酮（氢化物转移过程的模型）的转移氢化中的活性。在本文研究的所有配合物中，与3a，c相比，在萘环第二位具有ImNHC供体的配合物3b被认为是一种优异的催化剂，其特征在于不同的NHC供体或具有0.1 mol％低载量的取代模式。