Substituent Effects on <SUP>103</SUP>Rh NMR Chemical Shifts and Reactivities. A Density Functional Study

¹⁰³Rh chemical shifts, computed using the SOS-DFPT approach (sum-over-states density functional perturbation theory), large basis sets, and optimized geometries, correlate well with the corresponding experimental data for [Rh(C<INF>5</INF>H<INF>5</INF>)<INF>2</INF>]⁺, [Rh(CO)<INF>2</INF>(C<INF>5</INF>H<INF>4</INF>X)] (X = H, NMe<INF>2</INF>, Cl, NO<INF>2</INF>), [Rh(CO)<INF>4</INF>]^-, [RhCl<INF>2</INF>(CO)<INF>2</INF>]^-, and [Rh(acac)L<INF>2</INF>] (acac = acetylacetonato, L<INF>2</INF> = (C<INF>2</INF>H<INF>4</INF>)<INF>2</INF>, 1,5-cyclooctadiene, cyclooctatetraene). The slope of the regression line, however, is only ca. 0.8 instead of unity. Scaled appropriately, the theoretical δ(¹⁰³Rh) values differ from experiment by less than 100 ppm (mean absolute deviation), over a range of 3600 ppm. In the [Rh(CO)<INF>2</INF>(C<INF>5</INF>H<INF>4</INF>X)] series, the computed activation barriers of PH<INF>3</INF> addition correlate well with the experimental rate constants for CO/PPh<INF>3</INF> displacement, thereby reproducing theoretically the relation between reactivities and ¹⁰³Rh chemical shifts that has been reported experimentally.