IR FREQUENCIES AND INTENSITIES OF THE VIBRATIONAL-MODES OF CXHY FRAGMENTS BONDED TO METAL-COMPLEXES - RELATIONSHIP WITH STRUCTURE, BONDING AND REACTIVITY

The following organometallic complexes were studied as models of the coordination between metal atoms and different C(x)H(y) ligands: Co2Fe(CO)9(CCH2), Co2Ru(CO)9(CCH2), Os3(H)2(CO)9(CCH2) and Co2Fe(CO)9(CC(H)CH3) (eta3-eta2-vinylidene or mu3-eta2-methylvinylidene group); Fe2(C5H5)2(CO)3(CCH2) (mu2-eta1-vinylidene group); Os3(mu-H)(CO)9(CHCH2) (mu2-eta2-vinyl group); CH3Mn(CO)5 (eta1-methyl group); Os3(mu-H)2(CO)10(CH2) and Fe2(CO)9=8(CH2) (mu2-eta1-methylene group); Co3(CO)9(CH) (mu3-methyne group); Co3(CO)9(CCH3) (mu3-eta1-ethylidyne group); Os3(H)(CO)9(C2H) (mu3-eta2-acetylide group). The infrared frequencies and intensities associated with the main vibrational modes of the ligands (C=C and C-H stretchings, C-H deformations) were evaluated and compared with those of appropriate model molecules. Both the frequency and intensity data can be usefully correlated with structural parameters (e.g. C-C and C-H bond distances and HCH bond angles) and provide information on the charge distribution on the ligands. It is therefore possible to discuss the type of metal-ligand interaction and the balance between the sigma and pi contributions to the bond.