RH-103 NMR SHIELDING CORRELATION WITH RATE DATA FOR ARYL MIGRATION IN RHCP-ASTERISK-I(CO)(P-XC(6)H(4)) - MECHANISTIC IMPLICATIONS

The rhodium-103 NMR chemical shifts of the complexes RhCp*I[CO(p-XC(6)H(4))]PPh(3) (Cp* = C(5)Me(5); X = H, Me, CI, CHO, CN, NO2) exhibit a linear correlation (R(2) = 0.991) with In(k(rel)), where k(rel) is the relative rate constant for the PPh(3)-assisted migration of a coordinated aryl group to a coordinated CO in the complexes RhCp*I(CO)(p-XC(6)H(4)) reported by Bassetti et al. This is the first example of a correlation of the transition-metal chemical shifts of the product with reaction rates and leads to the postulate that such reactions are characterized by a product-like (late) transition state.