Data from: A synthetic, catalytic and theoretical investigation of an unsymmetrical SCN pincer palladacycle

The SCN ligand 2-{3-[(methylsulfanyl)methyl]phenyl}pyridine, 1, has been synthesized starting from an initial Suzuki–Miyaura (SM) coupling between 3-((hydroxymethyl)phenyl)boronic acid and 2-bromopyridine. The C–H activation of 1 with in situ formed Pd(MeCN)4(BF4)2 has been studied and leads to a mixture of palladacycles, which were characterized by X-ray crystallography. The monomeric palladacycle LPdCl 6, where L-H = 1, has been synthesized, and tested in SM couplings of aryl bromides, where it showed moderate activity. Density functional theory and the atoms in molecules (AIM) method have been used to investigate the formation and bonding of 6, revealing a difference in the nature of the Pd–S and Pd–N bonds. It was found that S-coordination to the metal in the rate determining C–H bond activation step leads to better stabilization of the Pd(II) centre (by 13–28 kJ mol−1) than with N-coordination. This is attributed to the electron donating ability of the donor atoms determined by Bader charges. The AIM analysis also revealed that the Pd–N bonds are stronger than the Pd–S bonds influencing the stability of key intermediates in the palladacycle formation reaction pathway.

本研究以3-(羟甲基)苯硼酸与2-溴吡啶的初始铃木-宫浦（Suzuki–Miyaura, SM）偶联反应为起始步骤，成功合成了SCN配体2-{3-[(甲硫基)甲基]苯基}吡啶（化合物1）。针对化合物1与原位生成的四(乙腈)合钯(II)四氟硼酸盐[Pd(MeCN)₄(BF₄)₂]的C-H活化反应，本研究展开了系统探究，反应产物为多种环钯化合物的混合物，后续通过X射线晶体衍射（X-ray crystallography）对其完成了结构表征。我们成功合成了单核环钯配合物LPdCl 6（其中L-H即化合物1），并将其应用于芳基溴化物的铃木-宫浦偶联反应催化测试，结果显示该配合物具备中等催化活性。本研究借助密度泛函理论（Density functional theory）与分子中的原子（atoms in molecules, AIM）方法，对配合物6的形成过程与成键特征展开了理论计算分析，揭示了Pd-S键与Pd-N键成键本质的差异。研究发现，在决速步C-H活化阶段，硫原子对金属中心的配位相较于氮原子配位，可使Pd(II)中心获得更优的稳定化效果（稳定化能差值为13~28 kJ·mol⁻¹）。该现象可归因于供体原子的给电子能力差异，该差异由巴德电荷（Bader charges）的计算结果得以明确。AIM分析同时表明，Pd-N键的键强高于Pd-S键，这一差异会对环钯化合物形成反应路径中关键中间体的稳定性产生显著影响。