NCN pincer ligand precursor 1·HX (X = Cl, PF₆), having a six-membered N-heterocyclic carbene central moiety and pyridyl pendant arms, was prepared via N–C cross-coupling of 2-bromo-6-tert-butylpyridine with propane-1,3-diamine, followed by ring closure with triethylorthoformate. The free ligand 1 was not accessible via deprotonation, yet its copper(I) complex 2 was prepared by reacting 1·HCl with CuI and potassium hexamethyldisilazide. It was used further as a transmetalation agent to prepare nickel(II) and ruthenium(II) dihalide NCN-pincer complexes 3a, 4a, and 4b, featuring a distorted square-pyramidal geometry at the metal, with the carbene ligand in the axial position. The rhodium(III) NCN-pincer complex 6b was obtained from 2 and [Rh(cod)Cl]₂ via transmetalation followed by oxidation with Cu(I) in THF. The rhodium(III) NCC-pincer complex 9b was prepared under similar conditions in acetonitrile, where a spontaneous rollover cyclometalation occurred. Complex 9b has a distorted octahedral geometry, with the acetonitrile ligand trans to the carbene. Very short Ru–C_NHC and Rh–C_NHC bonds were measured in complexes 4a, 4b, and 9b. Halogen exchange was observed by ¹H and ¹³C NMR spectroscopy in both ruthenium and rhodium systems during the transmetalation stage, and the purification was accomplished by pushing the respective equilibrium with excess halide.

中文翻译：

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镍，钌和铑NCN-Pincer配合物，具有六元N-杂环卡宾中心部分和吡啶基悬挂臂

NCN钳形配体前体1 ·HX（X =氯，PF ₆），具有6元N-杂环卡宾中央部分和吡啶基侧挂臂，经由N-C制备的交叉偶联2-溴-6-叔-丁基吡啶与1,3-丙烷丙烷的混合物，然后用原甲酸三乙酯闭环。游离的配体1不能通过去质子化而获得，但是其铜（I）络合物2是通过使1 ·HCl与CuI和六甲基二硅叠氮化钾反应制备的。进一步用作过渡金属化试剂以制备二卤化镍（II）和钌（II）NCN-钳子配合物3a，4a和4b，在金属上具有扭曲的方金字塔形几何形状，卡宾配体在轴向位置。铑（III）NCN-钳子配合物6b是通过2和[Rh（cod）Cl] ₂经重金属化，然后在THF中用Cu（I）氧化而获得的。在类似条件下，在乙腈中制备铑（III）NCC-钳子配合物9b，在该条件下发生自发侧翻环化金属。配合物9b具有扭曲的八面体几何形状，其中乙腈配体反过来转移至卡宾。在复合物4a，4b和9b中测量到非常短的Ru–C _NHC和Rh–C _NHC键。在过渡金属化阶段，通过钌和铑体系的¹ H和¹³ C NMR光谱观察到卤素交换，并且通过用过量的卤化物推动各自的平衡来完成纯化。