Quantum Chemical Calculations of ³¹P NMR Chemical Shifts in Nickel Complexes: Scope and Limitations

Abstract

The scope and limitations of a simple approach for the 31 P NMR chemical shift calculations of phosphorus atoms directly involved in the formation of coordination bonds with Ni have been analyzed. A comparative analysis of calculated versus experimental 31 P NMR shifts for the wide range of model nickel complexes based on small/-medium-sized organophosphorus ligands was carried out. Several functional−basis set combinations were tested. In general, for neutral singlet Ni complexes based on σand π-type ligands the 31 P NMR shifts can be calculated quite well in the framework of the Kohn−Sham level of theory with hybrid functionals (PBE0, B3LYP, B97-2). In the case of charged complexes, the predictions are less accurate due to the inherent fluxionality of the systems. For complexes with triplet contamination this approach cannot be used. The most accurate results were reached with the PBE0/6-311G(2d,2p)//PBE0/6-31+G(d) combination (RMSE < 7 ppm), while the GGA type functionals showed the most unreliable results, particularly for the π-donating phosphorus. There are only two examples where calculated values disagreed with experiment. In the first case of a three-coordinate nickel phosphinidene complex, although calculations reproduce the exceptional low-field shift, the qualitative agreement is worse; this may be due to the effects of high spin states and medium effects. In the second case, a dramatic disagreement between calculations and experiment is due to the incorrect establishment of the structure. On the basis of these calculations, the structure should be revised. Thus, we concluded that in Ni complexes the Kohn−Sham level calculations can be safely used to predict 31 P NMR shifts of directly coordinated phosphorus. Moreover, the approach allows for the assignment of challenging structures with several coordination types.

DFT Approach for Predicting 13C NMR Shifts of Atoms Directly Coordinated to Nickel

“…Such effects were previously detected when evaluating δ 31 P for nickel complexes with π-donating ligands. 40 The calculations for this group showed that, indeed, in the Ni−diimine alkyne complexes, the triplet levels are much lower (0.1−19.2 kcal/mol, Table S4) than in other complexes, including other complexes with η 2 -C≡C ligands (>29 kcal/mol). Thus, it seems that in such systems, the contribution of high-spin states is possible, which may result in residual paramagnetism and, when this is not explicitly accounted for, leads to a worse agreement between calculation and experiment.…”

“…At the same time, calculations using the B3PW91, B3LYP, and B97-2 functionals give good correlation coefficients (from 0.995 to 0.996, Figure 4a and Table S3, entries 12−14), comparable to the values for PBE0. Thus, as in the case of phosphorus NMR shift calculations, 40 GGA functionals have a clear "shortcoming" in the calculations of CSs for a few types of carbons (details are discussed later).…”

“…Interestingly, the same was also found in the case of δ 31 P calculations for the π-donating phosphorus. 40 Therefore, a serious question arises as to the applicability of such functionals for CS calculations. It should be noted that GGA functionals are more cost-effective than hybrid ones.…”

Nickel Complexes in C‒P Bond Formation

“…Later, Ganushevich et al characterized, for the first time, the product of an oxidative addition of primary phosphane to a nickel(0) complex. The terminal phosphanido hydride nickel complex, [NiH{P(Dmp)(H)}(dtbpe)], where Dmp-2,6-dimesitylphenyl and dtbpe-1,2-bis(di-tert-butylphosphino)ethane, has been formed in this process [51][52][53]. Chiral metal complexes have been used to promote and control the asymmetric P-H addition reaction.…”

Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes

“…Haptotropic rearrangement processes in sandwich-type complexes have also been investigated by DFT approaches [ 13 , 14 , 15 ]. Similarly, DFT has been used to gain insight into the fluxionality of various ligands, such as phosphines, in transition metal complexes by way of simulated NMR spectroscopy [ 16 , 17 ].…”