THERMODYNAMIC AND KINETIC-STUDIES OF MIGRATORY CO INSERTION IN ALKYL COMPLEXES OF IRON(II)

The reaction of cis,trans-Fe(CO)2(PMe3)2MeX with carbon monoxide to gi ve the corresponding cis,trans- and trans,trans-acetyls has been studi ed in toluene for X = Cl, Br, or I at various temperatures. The format ion rates and the equilibrium constants of cis,trans-acetyl with respe ct to cis,trans-methyl follow the order NCS congruent-to CN > Cl > Br > I and are determined by the withdrawing power of X, while the equili brium constants of trans,trans-acetyl as compared to cis,trans-acetyl follow the order I > Br > Cl >> CN, Me and are influenced by the steri c hindrance of the ligands. trans,trans-Fe(CO)2(PMe3)2MeI has been pre pared and characterized. Its reaction rate with CO is much slower than that of the corresponding cis,trans complex and is not influenced by the carbon monoxide concentration. Other trans,trans-methyl complexes with L = PPhMe2, P(OMe)3, P(n-Bu)3, and PPh2Me have been prepared and characterized by H-1 NMR spectroscopy.