Syntheses and spectroscopic studies of some pi-organometallic carbonyl complexes.

Chu, Chit-Kay (1974) Syntheses and spectroscopic studies of some pi-organometallic carbonyl complexes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The preparation and characterization of a series of new π-Mn(CO)₃ and πCr (CO)₃ complexes are discussed. The benzoylcyclopentadienylmanganese tricarbonyl derivatives obtained are generally yellow in colour and melt at temperatures between 50° - 100°. The corresponding π-CR(CO)₃ complexes are orange to red in colour and melt at higher temperatures. These complexes are stable in their solid state but decompose readily in solution. -- The infrared spectra of these complexes have been studied both in CCl₄ and in Nujol mulls. A C₃v local symmetry is assumed for the M(CO)₃ moieties and the electronic effects of aromatic substituents on the ν(CO) vibrations are explained by the M.O. model. The electronic effects of the substituents on one ring are transmitted to the other vie the ketonic carbonyl group as indicated by the corresponding shifts of the ketonic ν(CO) frequencies. The lower ν(CO) frequencies observed for the π-Cr(CO)₃ complexes are mainly due to the decrease of π-electron density on the benzene ring. -- The electronic absorption bands of these complexes have been tentatively assigned on the basis of their shifts with substituent changes and by the comparison of such bands with those of related complexes. -- NMR spectral studies show that the π-character of the aromatic ring is not reduced by the electron-with-drawing effect of the Cr(CO)₃ group is that in which the Cr atom is mainly bonded to the meta and substituent positions of the monosubstituted benzene ring. -- The delocalisation of the unpaired spin in radical anions of these complexes is well illustrated by their ESR spectra. These spectra have been simulated and the spin densities calculated using McConnell’s equation. Good agreement between experimental and theoretical spin densities has been obtained. Hyperfine splitting constants show that a substantial amount of the spin density is found on the manganese atom, and the para and ortho protons of the phenyl ring. No hyperfine lines have been observed for the meta or cyclopentadienyl protons. -- The mass spectra of these complexes show a fragmentation pattern in which the CO molecules are lost first. The ability of the ionic structures to undergo intramolecular rearrangement process is facilitated by the active participation of the metallic orbitals with the π-orbitals of the ligand. The stability of the ions is dependent on the ring substituents. Where the substituent is electron donating the ions are usually stabilized and vice versa. This is consistent with the view that the electron removed during ionization belongs to a molecular orbital very largely associated with the metal atom.

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