Substituent effects on 61Ni NMR chemical shifts

Abstract

⁶¹Ni chemical shifts of Ni(all-trans-cdt)L (cdt = cyclododecatriene, L = none, CO, PMe₃), Ni(CO)₄, Ni(C₂H₄)₂(PMe₃), Ni(cod)₂ (cod = cyclooctadiene) and Ni(PX₃)₄ (X = Me, F, Cl) are computed at the GIAO (gauge-including atomic orbitals), BPW91, B3LYP and BHandHLYP levels, using BP86-optimised geometries and an indirect referencing scheme. For this set of compounds, substituent effects on δ(⁶¹Ni) are better described with hybrid functionals than with the pure BPW91 functional. On going from Ni(all-trans-cdt) to Ni(all-cis-cdt) the computations predict substantial shielding of the ⁶¹Ni nucleus by nearly 700 ppm, as well as a sharp increase of the electric field gradient at this position. The latter result is predicted to afford an undetectably broad ⁶¹Ni NMR line for the all-cis-cdt complex, rationalizing the apparent failure to record the NMR spectrum experimentally.