Valence electronic structure of bis(pyrazolyl)-bridged iridium dicarbonyl dimers. Electronic effects of 3,5-dimethylpyrazolyl substitution on metal-metal interactions

Journal Article · Wed Nov 30 00:00:00 EST 1988 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00297a030· OSTI ID:5975272

Lichtenberger, D L; Copenhaver, A S; Gray, H B; Marshall, J L; Hopkins, M D

The He I valence photoelectron spectra of (Ir(/mu/-pyrazolyl)(CO)/sub 2/)/sub 2/, (Ir(/mu/-3-methylpyrazolyl)(CO)/sub 2/)/sub 2/, and (Ir(/mu/-3,5-dimethylpyrazolyl)(CO)/sub 2/)/sub 2/ have been obtained. These complexes may be viewed as two square-planar d/sup 8/ iridium centers held together by two bridging pyrazolyl ligands to form a six-membered Ir-(N-N)/sub 2/-Ir ring. The ring is in a boat conformation with the iridium atoms positioned at the bow and stern such that interaction is possible between the filled d/sub z/sup 2// orbitals from each metal center. The 3,5-dimethylpyrazolyl complex is active as a hydrogenation catalysts while the other related complexes are not. It is found here that there is substantial interaction between the d/sub z/sup 2// atomic orbitals of the two iridium centers, and the ionization corresponding to the Ir-Ir antibonding d/sub z/sup 2//-d/sub z/sup 2// interaction is the lowest energy ionization band of these complexes. This ionization is cleanly separated from the other ionizations of the complexes. Of particular interest is the broad and unusual asymmetry found in the band profile of the initial ionization. The energy of the first ionization band is very sensitive to the methyl substitutions on the pyrazolyl groups. The sensitivity of this ionization to methyl substitution (and in turn the change in reaction chemistry between these complexes) is due more to the electronic inductive effects of the methyl group substitutions than to changes in geometry and splitting of the bonding and antibonding combinations of the metal d/sub z/sup 2// orbitals. 28 refs., 7 figs., 7 tabs.

• Research Organization: Univ. of Arizona, Tucson (USA)
• DOE Contract Number: AC02-80ER10746
• OSTI ID: 5975272
• Journal Information: Inorg. Chem.; (United States), Vol. 27:24
• Country of Publication: United States
• Language: English

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