Substituent Effects on 103 Rh NMR Chemical Shifts and Reactivities. A Density Functional Study

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