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Methyl-substituted cyclopentadienyl ligands: influence on the properties of titanocene chloro(ethyl)aluminates

1988; Elsevier BV; Volume: 347; Issue: 1-2 Linguagem: Inglês

10.1016/0022-328x(88)80272-9

1872-8561

Karel Mach, Vojtěch Varga,

Organometallic Complex Synthesis and Catalysis

Abstract The binuclear complexes C p2TiCl2AlCl2−xEtx ( C p = Cp, MeCp, Me3Cp, Me4Cp and Me5Cp; x = 0–2) were prepared from C p2TiCl2 by reduction with ethylaluminium compounds EtxAlCl3−x (x = 1–3) and/or from C p2TiCl by addition of aluminium compounds EtxAlCl3−x (x = 0–2). The reductive method did not yield the complexes (Me5Cp)2Ti(AlCl4) and (Me5Cp)2Ti(AlCl3Et) and gave only low yields of complexes containing 3 or 4 Me groups in the C p ligand and no or one Et group in the aluminate ligand. All these complexes were prepared by the addition method except (Me4Cp)2Ti(AlCl4) which reacted rapidly with exces AlCl3 to give (Me4Cp)Ti(AlCl4)2. On going from the Cp to Me3Cp binuclear complexes the electronic effect of the Me groups decreased the rate of their formation in the reduction reaction, shifted their λmax(d−d) to shorter wavelengths, increased their g-value and the aA1 coupling constant and decreased the aTi)7/2) coupling constant. It was suggested that the steric effect was responsible for a considerable deviation from these correlations in the Me5Cp complexes, showing an extremely low g-value and λmax (d−d) at very long wavelengths.