HIGH-PRESSURE NMR KINETICS .54. N,N-DIMETHYLFORMAMIDE EXCHANGE ON HEXAKIS(N,N-DIMETHYLFORMAMIDE)TITANIUM(III) - A VARIABLE-TEMPERATURE AND VARIABLE-PRESSURE H-1 AND O-17 NMR-STUDY

Dimethylformamide (DMF) exchange on [Ti(DMF)6]3+ has been studied as a function of temperature (192-355 K) and pressure (up to 200 MPa, at two temperatures) by proton and oxygen-17 NMR spectroscopy at 4.7 and 9.4 T. The following kinetic parameters were obtained: k(ex)298 = (6.6 +/- 0.1) x 10(4) s-1, DELTA-H double-ended-dagger = 23.6 +/- 0.3 kJ mol-1, DELTA-S double-ended-dagger = -73.6 +/- 1.1 J K-1 mol-1, DELTA-V double-ended-dagger = -5.7 +/- 0.6 cm3 mol-1, and DELTA-beta double-ended-dagger = -(1.3 +/- 0.6) x 10(-2) cm3 mol-1 MPa-1. The negative volume of activation suggests an associative interchange, I(a), mechanism for the DMF exchange on titanium(III), and confirms the mechanistic changeover (from I(a) to I(d)) along the hexasolvated trivalent first-row transition-metal ions previously observed in water, dimethyl sulfoxide, and trimethyl phosphate.