31P NMR Chemical Shift Tensors: Windows into Ruthenium Phosphinidene Complex Electronic Structures

A series of octamethylcalix[4]pyrrole/ruthenium phosphinidene complexes (Na-2[1=PR]) can be accessed by phosphinidene transfer from the corresponding RPA (A = C14H10, anthracene) compounds (R = Bu-t, Pr-i, OEt, NH2, NMe2, NEt2, (NPr2)-Pr-i, NA, dimethylpiperidino). Isolation of the tert-butyl and dimethylamino derivatives allowed comparative studies of their P-31 nuclear shielding tensors by magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Density functional theory and natural chemical shielding analyses reveal the relationship between the P-31 chemical shift tensor and the local ruthenium/phosphorus electronic structure. The general trend observed in the P-31 isotropic chemical shifts for the ruthenium phosphinidene complexes was controlled by the degree of deshielding in the delta(11) principal tensor component, which can be linked to the sigma(RuP)/pi(RuP)* energy gap. A delta(22)-delta(33) crossover effect for R = Bu-t was also observed, which was caused by different degrees of deshielding associated with polarizations of the sigma(PR) and sigma(PR)* natural bond orbitals.

Automated summary

A series of octamethylcalix[4]pyrrole/ruthenium phosphinidene complexes were synthesized, and their P-31 chemical shifts were studied using solid-state nuclear magnetic resonance spectroscopy and density functional theory. The results revealed that the degree of deshielding controls the isotropic chemical shifts of P-31 in the complexes, which is related to the local ruthenium/phosphorus electronic structure.