Periodic trends in charge distribution for transition-metal complexes containing catecholate and semiquinone ligands. Synthetic, physical, and stereodynamic properties of the tris(3,5-di-tert-butylquinone) complexes of ruthenium and osmium
- Univ. of Colorado, Boulder (USA)
Tris(3,5-di-tert-butylbenzoquinone) complexes of Ru and Os have been synthesized in the interest of investigating periodic trends in charge distribution for tris(quinone) complexes of second- and third-row transition metals. Infrared spectra of the two complexes are similar but differ from spectra obtained on related semiquinone (Fe(DBSQ){sub 3}) and catecholate (Re(DBCat){sub 3}) complexes. Both complexes undergo two oxidation and two reduction reactions at similar potentials. Crystallographic characterization on the cis and trans isomers of Ru(DBQ){sub 3} and on trans-Os(DBQ){sub 3} at {minus}60{degree}C shows short M-O bond lengths, typical of complexes containing high oxidation state forms of Ru and Os. Ligand C-O bond lengths are found to be intermediate between semiquinone and catecholate values, with lengths that are more semiquinone-like for Ru(DBQ){sub 3} and more catecholate-like for Os(DBQ){sub 3}. This subtle difference in charge distribution between the second- and third-row metals appears to contribute to marked differences in the stereodynamic properties of the two complexes. Both are diamagnetic and show sharp NMR spectra at room temperature. Eight tert-butyl and eight ring proton resonances are observed for Ru(DBQ){sub 3} at room temperature, indicating the presence of stereochemically rigid cis and trans isomers. Two tert-butyl and two ring proton resonances are observed for Os(DBQ){sub 3} at room temperature. At {minus}85{degree}C eight tert-butyl and eight ring proton resonances appear as molecular rearrangement rates decrease on the NMR time scale. Analysis of the temperature dependence of the spectrum of Os(DBQ){sub 3} has indicated racemization by a trigonal twist mechanism at lower temperatures, with structural isomerization and racemization by a rhombic twist mechanism at higher temperatures.
- OSTI ID:
- 7123371
- Journal Information:
- Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 112:3; ISSN 0002-7863; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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AMINES
AROMATICS
CATECHOLAMINES
CHARGE DISTRIBUTION
COMPLEXES
CONFORMATIONAL CHANGES
DATA
DATA ANALYSIS
EXPERIMENTAL DATA
HYDROXY COMPOUNDS
INFORMATION
INFRARED SPECTRA
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OSMIUM COMPLEXES
PHENOLS
PHYSICAL PROPERTIES
POLYPHENOLS
QUINONES
RUTHENIUM COMPLEXES
SPECTRA
SYNTHESIS
TRANSITION ELEMENT COMPLEXES