CARBONYLATION REACTION OF ALKYL COMPLEXES OF IRON AND MOLECULAR-STRUCTURE OF CIS,TRANS-[FE(CO)(2)(PME3)(2)(CH3)I] AND TRANS,TRANS-[FE(CO)(2)(PME3)(2)(CH3)I]

The carbonylation reaction of cis,trans-[Fe(CO)(2)(PMe3)(2)(CH3)I] (Mc ) to cis,trans-[Fe(CO)(2)(PMe3)(2)(COCH3)I] (Ac) and the isomerization of Ac to trans,trans-[Fe(CO)(2)(PMe3)(2)(COCH3)I] (At) were studied i n polar and apolar solvents. The results suggest that the first step o f the carbonylation is the formation of the ionic intermediate [Fe(CO) (3)(PMe3)(2)(CH3)]I (In); complexes Ac and At are both formed from the intermediate In at different rates due to the differential cooperativ e effect of the anion. Further information was obtained by a structura l study of complexes Mc and trans.trans-[Fe(CO)(2)(PMe3)(2)(CH3)I] (Mt ), using single crystal X-ray diffraction. The structure models were r efined to R = 0.034 for 2270 independent reflections for Me and R = 0. 056 for 2381 independent reflections for Mt. Crystal data: monoclinic, space group P2(1)/c for both molecules: a = 13.656(2), b = 9.032(3), c = 13.880(6)Angstrom, beta = 106.78(3)degrees for Mc; a = 13.818(3), b = 8.957(2), c = 13.826(3)Angstrom, beta = 105.21(3)degrees for Mt. B oth complexes present octahedral coordination of the ligands around th e metal centre.