A Theoretical Investigation of One-Bond Phosphorus−Phosphorus Indirect Nuclear Spin−Spin Coupling Tensors, 1J(31P,31P), Using Density Functional Theory

In the present study, one-bond 31 P, 31 P indirect nuclear spin−spin coupling tensors, 1 J ( 31 P, 31 P), are calculated using nonrelativistic and relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) methods for the following model molecules and ions: P 2, cis- MeP PMe, trans- RP PR (R = H, Me, Ph), ( cis- η 1 -PhP PPh)Cr(CO) 5, ( cis - and trans- η 1 -MeP PMe)Cr(CO) 5, H 2 P−PH 2, H 2 P−PF 2, cis - and trans- diphosphetes, a phosphole tetramer, [O 3 P−PO 3 ] 4-, [HO 3 P−PO 3 H] 2-, [FO 2 P−PO 2 F] 2-, Me 2 (S)P−P(S)Me 2, [MeN⋮P−PMe 3 ] +, and Me 3 P−PF 5 . These compounds have been chosen because the values of 1 J ( 31 P, 31 P) iso in these systems vary from approximately −480 to +770 Hz, thereby spanning the known range of experimentally measured one-bond 31 P, 31 P indirect nuclear spin−spin coupling constants. However, in many cases, the sign of 1 J ( 31 P, 31 P) iso has not been determined by experiment. Our DFT results for 1 J ( 31 P, 31 P) iso and the anisotropy of J are in qualitative agreement with experimental values; furthermore, our calculations provide the absolute sign of 1 J ( 31 P, 31 P) iso in cases where it is unknown experimentally. A number of empirical trends between 1 J ( 31 P, 31 P) iso and various structural parameters have been reproduced by our calculations. Inspection of the mechanisms which contribute to 1 J ( 31 P, 31 P) iso indicates that the Fermi contact (FC) mechanism dominates in all cases where formal single P,P bonds exist and that the paramagnetic spin−orbit mechanism is of equal or greater importance in comparison with the FC mechanism in cases where formal multiple P,P bonds exist. Results from relativistic ZORA DFT calculations differ from the nonrelativistic calculations by less than 10%, indicating that inclusion of relativistic effects is not crucial, as anticipated, given that the systems investigated herein contain relatively light atoms ( Z ≤ 24).