Department of Chemistry and Biochemistry , The University of Alabama , Box 870336, Tuscaloosa , Alabama 35487-0336 , United States.
Inorg Chem. 2019 Oct 7;58(19):13299-13313. doi: 10.1021/acs.inorgchem.9b02164. Epub 2019 Sep 25.
A series of [(PNp)Pd(Ar)Br] complexes (PNp = trineopentylphosphine, Ar = 4-tolyl, 4--butylphenyl, 2-tolyl, 4-methoxy-2-methylphenyl, 2-isopropylphenyl, and 2,6-dimethylphenyl) were synthesized and structurally characterized by X-ray crystallography and density functional theory optimized structures. The trineopentylphosphine ligand is able to accommodate coordination of other sterically demanding ligands through changes in its conformation. These conformational changes can be seen in changes in percent buried volume of the PNp ligand. The binding equilibria of the [(PNp)Pd(Ar)Br] complexes with pyridine derivatives were determined experimentally and analyzed computationally. The binding equilibria are sensitive to the steric demand of the pyridine ligand and less sensitive to the steric demand of the aryl ligand on palladium. In contrast to previous studies, the binding equilibria do not correlate with pyridine basicity. The binding equilibria results are relevant to fundamental ligand coordination steps in cross-coupling reactions, such as Buchwald-Hartwig aminations.
一系列 [(PNp)Pd(Ar)Br] 配合物（PNp = 三新戊基膦，Ar = 4-甲苯基、4--丁基苯基、2-甲苯基、4-甲氧基-2-甲基苯基、2-异丙基苯基和 2,6-二甲基苯基）通过 X 射线晶体学和密度泛函理论优化结构进行了合成和结构表征。三新戊基膦配体能够通过改变其构象来容纳其他空间要求高的配体的配位。这种构象变化可以从 PNp 配体的百分比埋体积变化中看出。通过实验确定并通过计算分析了 [(PNp)Pd(Ar)Br] 配合物与吡啶衍生物的结合平衡。结合平衡对吡啶配体的空间需求敏感，对钯上芳基配体的空间需求不太敏感。与以前的研究不同，结合平衡与吡啶碱性无关。结合平衡结果与交叉偶联反应中的基本配体配位步骤有关，例如 Buchwald-Hartwig 胺化反应。
