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.