Moto Jean Ongagna, Adjieufack Abel Idrice, Ndika Ngomb Simon Claude, D'ambassa Gaël Mouzong, Djendo Mazia Suzane Leonie, Bikele Désiré Mama
Computational and Theoretical Chemistry Unit, Department of Chemistry, Faculty of Science, University of Douala P.O. Box 24157 Douala Cameroon
Physical and Theoretical Chemistry Laboratory, University of Yaoundé I P.O. Box 812 Yaoundé Cameroon
RSC Adv. 2024 Jul 3;14(29):21075-21088. doi: 10.1039/d4ra03893b. eCollection 2024 Jun 27.
Bis-N-heterocyclic carbene ligands (bis(NHC)) have introduced a new approach to designing homogeneous and heterogeneous catalysts, demonstrating the versatility of ligand concepts in catalysis. This study presents a computational analysis of palladium (+ii and +iv) complexes containing either a normally (bis(nNHC)) or an abnormally (bis(aNHC)) bound CH-bridged bis-N-heterocyclic carbene ligand; in addition, ancillary ligands are permuted from chlorides (X = Cl) to bromides (X = Br). Density functional theory at the B3PW91/6-31G(d)/Lanl2DZ level in the gas phase was used to investigate the electronic structure and bonding properties of bis(NHC)PdX and bis(NHC)PdX for bis(NHC) palladium(ii) dihalide and palladium(iv) tetrachloride complexes, respectively. Results indicate that all of the palladium complex structures prefer a flexible boat-type conformation with an average symmetry, according to bond property (C-Pd and Pd-Cl[Br]) analysis. The strength of these bonds depends on coordinating halide ions (Cl and Br), the type of ligand (bis(nNHC) and bis(aNHC)), and the palladium oxidation state (+ii and +iv). Analysis of thermodynamic parameters (Δ , Δ , and Δ ) shows an increase in values from an abnormal to normal chelating mode in tetrahalides, whereas the opposite is observed for dihalide complexes. The lower π-backbonding ability of the metal, which is influenced by the quantity and size of halide ions involved, could be one possible explanation for this deficiency.
双氮杂环卡宾配体（双（NHC））为均相和多相催化剂的设计引入了一种新方法，展示了配体概念在催化中的多功能性。本研究对含有正常（双（nNHC））或异常（双（aNHC））键合的CH桥连双氮杂环卡宾配体的钯（+ii和+iv）配合物进行了计算分析；此外，辅助配体从氯化物（X = Cl）置换为溴化物（X = Br）。在气相中使用B3PW91/6-31G（d）/Lanl2DZ水平的密度泛函理论分别研究了双（NHC）钯（ii）二卤化物和钯（iv）四氯化物配合物的双（NHC）PdX和双（NHC）PdX的电子结构和键合性质。结果表明，根据键性质（C-Pd和Pd-Cl[Br]）分析，所有钯配合物结构均偏好具有平均对称性的柔性船型构象。这些键的强度取决于配位卤离子（Cl和Br）、配体类型（双（nNHC）和双（aNHC））以及钯的氧化态（+ii和+iv）。热力学参数（Δ 、Δ 和Δ ）分析表明，四卤化物中从异常螯合模式到正常螯合模式的值增加，而二卤化物配合物则观察到相反的情况。金属较低的π-反馈键合能力受所涉及卤离子的数量和大小影响，这可能是这种不足的一种可能解释。
