Substituent effects on Ni-61 NMR chemical shifts

Abstract

Ni-61 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 delta(Ni-61) 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 Ni-61 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 Ni-61 NMR line for the all-cis-cdt complex, rationalizing the apparent failure to record the NMR spectrum experimentally.