Department of Chemistry and Biochemistry, The University of Alabama, Box 870336, Tuscaloosa, Alabama 35487-0336, United States.
Inorg Chem. 2020 Apr 20;59(8):5579-5592. doi: 10.1021/acs.inorgchem.0c00266. Epub 2020 Apr 9.
Steric properties of crystallographically and computationally determined structures of linear palladium(0) and square planar palladium(II) complexes of di(-butyl)neopentylphosphine (P(-Bu)Np), -butyldineopentylphosphine (P(Bu)Np), and trineopentylphosphine (PNp) have been determined. Structures of linear palladium(0) complexes show that steric demand increases as -butyl groups are replaced with neopentyl groups (P(-Bu)Np < P(Bu)Np < PNp). In square planar palladium(II) complexes, PNp gives the smallest steric parameters, whereas P(Bu)Np has the largest steric demand. The change in the steric demand of PNp compared to P(-Bu)Np and P(Bu)Np results from a significant conformational change in PNp depending on the coordination number of the metal. The steric properties of these ligands were also probed by measuring the equilibrium constant for coordination of free phosphine to dimeric [(RP)Pd(μ-Cl)Cl] complexes. Binding equilibria follow the same trend as the steric parameters for square planar complexes with PNp having the highest binding constant. In contrast to the normal trend, the neopentylphosphines show increased pyramidalization at phosphorus with increasing steric demand. We hypothesize that this unusual dependence reflects the low back side strain of the neopentyl group, which allows the ligand to be more pyramidalized while still exerting a significant front side steric demand.
线性钯(0)和平面正方形钯(II)配合物的晶体学和计算确定结构的立体性质已经被确定。线性钯(0)配合物的结构表明，随着 - 丁基被新戊基取代，立体需求增加（P(-Bu)Np < P(Bu)Np < PNp）。在平面正方形钯(II)配合物中，PNp 给出最小的立体参数，而 P(Bu)Np 具有最大的立体需求。与 P(-Bu)Np 和 P(Bu)Np 相比，PNp 的立体需求变化是由于 PNp 的构象发生显著变化，这取决于金属的配位数。还通过测量游离膦与二聚 [(RP)Pd(μ-Cl)Cl] 配合物配位的平衡常数来探测这些配体的立体性质。结合平衡遵循与平面正方形配合物相同的趋势，其中 PNp 具有最高的结合常数。与正常趋势相反，随着立体需求的增加，新戊基膦在磷上表现出增加的三角化。我们假设这种不寻常的依赖性反映了新戊基的低背面应变，这允许配体在仍然施加显著正面立体需求的情况下更具三角化。
