Semeniuchenko Volodymyr, Sharif Sepideh, Rana Neha, Chandrasoma Nalin, Braje Wilfried M, Baker R Tom, Manthorpe Jeffrey M, Pietro William J, Organ Michael G
Centre for Catalysis Research and Innovation (CCRI), Department of Chemistry and Biomolecular Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
NMR Core Facility, Faculty of Science, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
J Am Chem Soc. 2024 Oct 23;146(42):29224-29236. doi: 10.1021/jacs.4c12203. Epub 2024 Oct 10.
Use of the branched N-heterocyclic carbene (NHC) ligand 1,3-bis(2,6-bis(3-methyl-1-(2-methylpropyl)butyl)phenyl)-4,5-dichloro-1,3-dihydro-2-imidazole-2-ylidene (DiMeIHept) facilitated the stabilization of several relevant intermediates for Pd(NHC)-catalyzed C-N cross-coupling reactions. Complexes Pd(DiMeIHept), Pd(DiMeIHept), and Pd(DiMeIHept)(pyridine), representing zerovalent Pd(NHC) bearing labile ligands, were isolated and structurally characterized, along with divalent PdCl(Ph)(DiMeIHept) and PdCl(Ph)(DiMeIHept)(-propylamine). The former is a 14-electron Pd complex, which is stable under air and chromatography on silica gel or neutral alumina. One possible reason for this exceptional stability is the numerous dispersion interactions between the NHC alkyl chains and the Pd-Ph group. Detailed investigations of catalyst activation and oxidative addition confirmed that "Pd(NHC)" is formed from many known Pd(II)(NHC) precatalysts and provided activation rates for these different precatalysts.
使用支链 N-杂环卡宾（NHC）配体 1,3-双（2,6-双（3-甲基-1-（2-甲基丙基）丁基）苯基）-4,5-二氯-1,3-二氢-2-咪唑亚基（DiMeIHept）有助于稳定钯（NHC）催化的 C-N 交叉偶联反应中的几种相关中间体。分离并对代表带有不稳定配体的零价钯（NHC）的配合物Pd(DiMeIHept)、Pd(DiMeIHept)和 Pd(DiMeIHept)(吡啶)以及二价 PdCl(Ph)(DiMeIHept)和 PdCl(Ph)(DiMeIHept)(-丙胺)进行了结构表征。前者是一种 14电子钯配合物，在空气中以及在硅胶或中性氧化铝上进行色谱分离时都很稳定。这种特殊稳定性的一个可能原因是 NHC 烷基链与钯-苯基基团之间存在大量色散相互作用。对催化剂活化和氧化加成的详细研究证实，“钯（NHC）”由许多已知的钯（II）（NHC）预催化剂形成，并提供了这些不同预催化剂的活化速率。
