No abstract

The rhodium(I) and iridium(I) complexes 3a-6a contain the hemilabile Cp-quinoline chelate ligands 1 and 2, respectively, where the hard nitrogen donor does not displace the good acceptor ligand ethylene. After irradiation with visible light, intensely colored complexes are obtained, where the N-donor coordinates to the metal centers. Depending on the metal atom and on the substitution pattern at the Cp rings, the mono-ethene complex with N-metal coordination can be observed spectroscopically (e.g., 3b) or C-H addition products are probable intermediates. The iridium complex 6a is able to activate the aliphatic C-H bond in cyclohexane. With the rhodium complex 5a as the precatalyst, catalytic H/D exchange reactions have been performed with olefinic substrates. With linear R-olefins a fast doublebond isomerization dominates. The hemilabile ligands stabilize the catalytically active metal complexes without suppressing their activity significantly.

Nucleophilic addition of 8-lithioquinoline to the Cp 2 Co + cation leads to the formation of η 4 -(8-quinolylcyclopentadiene)(η 5 -cyclopentadienyl)cobalt(I) (7). Oxidative decomplexation with FeCl 3 liberates the quinolyl-substituted cyclopentadiene derivative 2a, which is stable at low temperature only. Deprotonation by strong bases such as NaH or KH leads to the alkali metal quinolyl cyclopentadienide salts, which are used as precursors for the synthesis of the corresponding Ti, Cr, and Al complexes. Whereas after its activation the aluminum compound 13 does not yield an olefin polymerization catalyst, the chromium(III) complex 12 reacts with methylaluminoxane (MAO) to give a highly active catalyst for the polymerization of ethylene.

A series of three organochromium­(III) complexes, based on a quinoline-substituted cyclopentadienyl ring coordinated to a CrCl2 moietyC5Me4(C9NH6)­CrCl2 (1), C5Ph4(C9NH6)­CrCl2 (2), and C5Me4(C11NH10)­CrCl2 (3)has been investigated by EPR spectroscopy, including high-frequency and -field EPR (HFEPR) as well as by 1H NMR. Complex 3 is new and has higher solubility than 1 and 2, which could potentially improve its activity as an alkene polymerization precatalyst, an application that has already been documented for 1 and 2. The HFEPR studies show that 1–3 exhibit zero-field splitting (zfs) that is unusually large for Cr­(III) (3d3, S = 3/2), as given by the axial zfs parameter D ≥ ∼3 cm–1. The zfs determined here for 1 is in good agreement with previous theoretical studies of this complex by other workers, which were made in the absence of any knowledge of the experimental data. Such a “blind” comparison of theory and experiment is very rare. The NMR spectra of 3 are fully analyzed using the zfs data and clearly show the dominant contribution of Fermi contact shifts, now that the pseudocontact (dipolar) shifts can be accurately determined. The results show the power of integrated magnetic resonance (EPR and NMR) spectroscopy combined with theoretical calculations in understanding the subtleties of electronic structure of the paramagnetic organometallic complex, in this case with S > 1/2, which could then be related to chemical reactivity or magnetic properties.

Bis(ethene) complexes of rhodium(I) and iridium(I) with 8-quinolylcyclopentadienyl ligands (Cp Q and Cp Q *) were oxidized by a photochemically induced reaction with chlorinecontaining solvents or by treatment with iodine. Upon this oxidation, the quinoline ring rotates and the N donor coordinates to the metal centers. Substitution of the halogenido ligands through acetato groups leads to highly soluble derivatives, in which the acetate moiety acts as a monodentate or