136736-88-4Relevant academic research and scientific papers
Ligand effects on the rates of the migratory insertion in rhodium(III) methyl carbonyl complexes
Monti, Donate,Bassetti, Mauro,Sunley, Glenn J.,Ellis, Paul,Maitlis, Peter
, p. 4015 - 4020 (1991)
The complexes (η5-C5Me5)Rh(CO)(X)(Me) (X = I, Br, Cl, MeCO2, CF3CO2) react readily with triphenylphosphine in toluene at 25 °C to yield quantitatively the corresponding acyl species (η5-C5Me5)-Rh(COMe)(X)(PPh3). The reactions of the halide complexes are first order in both the substrate and the phosphine. The rate increases in the order I ? = 56 ± 2 (I), 46 ± 3 (Br), 36 ± 2 (Cl) kJ mol-1; ΔS? = -79 ± 4 (I), -93 ± 5 (Br), -122 ± 3 (Cl) J K-1 mol-1) indicate that the order of reactivity is dominated by changes in ΔH?. The carboxylate complexes exhibit saturation kinetics, typical of the formation of an intermediate and unprecedented for migratory insertion in a nonpolar solvent. It is proposed that the intermediate is (η5-C5Me5)Rh(η2-O 2CR)(COMe) (R = Me, CF3), where the carboxylate moiety acts as a bidentate ligand to stabilize the otherwise unsaturated species. The rate constant for the formation of the intermediate, determined from the reactions with different nucleophiles, is somewhat larger for X = CF3CO2 (k1 = 0.16 s-1) than for X = MeCO2 (k1 = 0.105 s-1).
