The pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5a) and [CrIIIBr2.3Cl0.7(CNC)] (5b), where CNC = 3,3'‐(pyridine‐2,6‐diyl)bis(1‐mesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4 ≅ 0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet‐triplet energy difference on the size of the N‐substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5‐membered imidazolin‐2‐ylidene pincer analogues. The octahedral CrIII metal center in 5a and 5b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH) = 3,3'‐(pyridine‐2,6‐diylbis(methylene))bis(1‐mesityl‐3,4,5,6‐tetrahydropyrimidin‐1‐ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.

中文翻译：

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具有扩环 NHC 的新型吡啶二碳烯配体及其镍铬配合物

钳配合物 [NiIIBr(CNC)]Br (4)、[CrIIIBr3(CNC)] (5a) 和 [CrIIIBr2.3Cl0.7(CNC)] (5b)，其中 CNC = 3,3'-(吡啶-2) ,6-二基)双(1-异三叉基-3,4,5,6-四氢嘧啶-2-亚基)，由新型配体CNC获得，由前体(CHNCH)Br2和[NiIIBr2(PPh3)原位生成2]或分别通过氨解得到[CrII{N(SiMe3)2}2(THF)2]和(CHNCH)Br2。四面体扭曲的方形平面 (τ4 ≅ 0.30) 几何形状和 4 中 Ni 的单线态基态归因于 CNC 主干的空间约束。计算方法强调了配位几何形状和单重态-三重态能量差对四氢嘧啶翼尖N-取代基大小的依赖性，并将其与5元咪唑啉-2-亚基钳类似物的情况进行了对比。 5a 和 5b 中的八面体 CrIII 金属中心可能是在 CH2Cl2 的一个电子氧化后形成的。 4/MAO和5a/MAO分别是乙烯低聚和聚合的中等活性催化剂。类似的 (CH^N^CH)Br2 前体，其中 (CH^N^CH) = 3,3'-(吡啶-2,6-二基双(亚甲基))bis(1-mesityl-3,4,5,还制备了 6-四氢嘧啶-1-ium)，但由于所得游离 C^N^C 配体固有的不稳定性，未对其配位化学进行研究。