METAL-ION COMPLEXATION IN ORGANOMETALLIC CROWN-ETHERS - STRUCTURAL AND RATE EFFECTS ON THE MIGRATORY INSERTION OF CARBON-MONOXIDE IN INDENYL AND CYCLOPENTADIENYL IRON(II) COMPLEXES

The iron complexes [Fe(eta(5)-ligand)(CO)(2)R][ligand = C5H5 (Cp), R = Me (1); ligand = C5H5, R = CHMe2 (2); ligand = C9H7 (Ind) R=Me (3)] r eact with the crown ether functionalized phosphine [Ph2P-CH2-(aza-15-c rown-5)] (L) to give the products of alkyl migratory insertion [Fe(eta (5)-ligand)(COR)(CO)(L)] 4, 5 and 6, respectively. The cyclopentadieny l methyl complex [Fe(eta(5)-C5H5)(Co)(2)Me] reacts with L only in refl uxing hexane. The reactions of 2 and 3, in acetonitrile or chloroform, have been followed by FT-IR spectroscopy, or by UV-Vis. The presence of sodium or calcium salts, NaI, NaPF6, or CaI2, does not affect the r eactivity of the cyclopentadienyl complex 2, whereas it increases two to three times the rate of reaction of the indenyl complex 3. The acet yl complexes [Fe(eta(5)-ligand)(CoMe)(CO)(L)], (ligand = Cp, 4; ligand = Ind, 6) exhibit a shift of the stretching band v(COMe) to lower fre quencies, in the presence of metal salts, up to 40 cm(-1) in the case of 6 . NaPF6 in chloroform, and up to 46 cm(-1) in the case 6 . KPF6 i n dichloromethane, as a result of coordination of the carbonyl oxygen to the crown ether held cation. This shift is absent or small in the m ore polar solvents tetrahydrofuran, acetonitrile, or dioxane, and it i s not observed for the isopropyl complex 5, suggesting that steric hin drance of the alkyl group prevents acyl coordination to the metal ion. The terminal carbonyl group of complexes 4, 5 and 6 displays a shift of the v(CO) band to higher frequencies in most solvents, up to 27 cm( -1) for 6 . NaPF6 in acetonitrile and to 26 cm(-1) for 6 . LiClO4 in d ichloromethane, arising from electronic polarization by the metal ion and indicating electronic communication between the two metal centres. (C) 1998 Elsevier Science S.A.