Computation of Phosphorus-31 NMR chemical shifts of nickel complexes using density functional theory

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Steinert, Ryan M.
Mitchell-Koch, Katie R.
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The largest density functional theory benchmark study, to date, of calculated chemical shifts of phosphorus-containing ligands in nickel(0), nickel(II), and nickel(I) complexes is presented. Calculated shifts are directly compared to experiment. Many of these complexes are synthetically useful and on the cutting edge of rational catalyst design. Excellent results are obtained for the set of 56 nickel(0) complexes, with a root mean square error (RMSE) of 6 ppm. This result is obtained by computing the isotropic shielding at the PBE0/cc-pVTZ//PBE0/6- 31+G(d) level; the continuous set of gauge transformations (CSGT) is utilized to address the gauge problem and triphenylphosphine is used as the reference. Integration grid size does not affect the accuracy of shielding calculations, and the SG1 grid (50 radial shells, 194 angular points per shell) in the Gaussian program may be utilized to save time. This new method for nickel(0) complexes offers the following advantages over two methods recently published in Organometallics: a larger data set (n = 100 vs. n = 72 and n = 18), use of a single reference compound, no linear scaling factors are needed, and purely electrostatic solvation models and mixed basis sets are avoided. For the set of 33 nickel(II) complexes, reasonable results are obtained (RMSE = 16 ppm, n = 40) using the following scheme: PBE0/6-311++G(d,p)//PBE0/6-31+G(d) with CSGT and phosphoric acid as the reference. For the set of 13 nickel(I) complexes, the computation scheme used for nickel(0) complexes yields an RMSE of 16 ppm if one outlier (complex D7) is excluded (n = 12). It is unclear why better results for nickel(II) and nickel(I) complexes are not obtained. Single point energy calculations show the singlet state to be lower in energy for all nickel(II) complexes under investigation. The singlet state nickel(II) complexes were screened for multireference character by examining Etriplet – Esinglet (ΔE) and the HOMO-LUMO energy gap as recommended in the literature; no evidence of multireference character was found.

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Thesis (Ph.D.)-- Wichita State University, College of Liberal Arts and Sciences, Department of Chemistry and Biochemistry
Wichita State University
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