DFT Analysis of the 31P NMR Chemical Shift in CP Motifs

The 31P NMR chemical shifts of the diamagnetic CP derivatives span approximately 750 ppm. To understand the origins of this large variance and provide an intuitive understanding, selected CP derivatives, the anionic [CP]−, [OCP]−, [SCP]−, [SeCP]−, [iPrNCP]−, and [(F3C)3BCP]− and the neutral molecules [(DippPDI)CoCP], [(DippPDI)RhCP], [(IDipp)AuCP], [(DippBDI)MgCP], Me3SiCP, MesCP, tBuCP, HCP, and iPr3SiOCP (Dipp = 2,6-diisopropyl-phenyl, PDI = pyridine-diimine, IDipp = 1,3-Dipp-2-ylidene, and BDI = β-diketiminate), were computationally investigated. The chemical shielding tensors are strongly anisotropic. Natural Chemical Shielding (NCS) analysis reveals that the chemical shielding is primarily driven by its paramagnetic component perpendicular to the C–P axis, specifically the contribution of σ(CP) and 3s(P) orbitals. Additionally, the planar complexes [(DippPDI)RhCP], [(DippPDI)CoCP] and MesCP show significant deshielding in the component parallel to the C–P axis as a result of the planar coordination environment of the α atom. NBO and QTAIM analyses were conducted to examine the nature of the CP bond, allowing one to establish correlations between chemical shift and bond properties such as the delocalization index in different groups.