STUDIES OF THE OXIDATIVELY PROMOTED CARBONYLATION OF ETA-CP(CO)(L)FEME IN METHYLENE-CHLORIDE - APPLICATIONS OF THE QUANTITATIVE-ANALYSIS OF LIGAND EFFECTS

The carbonylation of eta-Cp(CO)(L)FeMe+ (L = PPhMe2, PEt3, PPh2Me, PEt2Ph, PPh2Et, P(p-MeOPh)3, P(p-MePh)3, PPh3, P(p-FPh)3, P(p-ClPh)3, P(p-CF3Ph)3, PPh2Cy, PPhCy2, PCy3) in methylene chloride has been studied by a combination of kinetic, sterochemical, isotopic labeling ligand effect, and electrochemical experiments. Redox-catalyzed (ferrocenium tetrafluoroborate) carbonylation of (+)-eta-Cp-(CO)(PPh3)FeMe gives racemic eta-Cp(CO)(PPh3)FeCOMe. The results of control experiments suggest that the racemization is attributable to the configurational instability of eta-Cp(CO)(PPh3)FeMe+. The redox-catalyzed carbonylation of eta-Cp(CO)(PPh3)FeMe under 1 atm of (CO)-C-13 affords eta-Cp(CO)-C-13(PPh3)FeCOMe. The rate of the electrochemically promoted carbonylation of eta-Cp(CO)(L)FeMe is independent of the concentration of the starting complex, carbon monoxide, and the supporting electrolyte, tetrabutylammonium hexafluorophosphate (TBAH). Kinetic data for the carbonylation of eta-Cp(CO)(L)FeMe+, which is first order in complex and zero order in carbon monoxide, were obtained by computer simulation analysis of cyclic and square-wave voltammetry data. Analysis of the data for L = P(p-ClPh)3 and P(p-CF3Ph)3 reveals enthalpies of activation (DELTA-H Double-ended-dagger = 7.8 +/- 2.0, 6.7 +/- 0.8 kcal/mol) and entropies of activation (DELTA-S double ended-dagger = -23 +/- 7, -25 +/- 3 eu), respectively. Quantitative analysis of the ligand effect (QALE) data shows that the carbonylation of eta-Cp(CO)(L)FeMe+ is accelerated by poorer electron-donor ligands; the steric profile shows a region of steric inhibition for small ligands with a steric threshold at 150-degrees-C after which the rate of reaction rises rapidly. Analysis of the E-degrees values for the eta-Cp(CO)(L)FeMe/eta-Cp(CO)(L)FeMe+ couple also reveals a steric threshold at 150-degrees.