RESUMEN
A unique phenomenon of regioisomerism in coordination chemistry was discovered: the reaction of a sterically hindered o-quinone annelated with a dithiete ring with Pd2dba3 in the presence of 1,2-bis(diphenylphosphino)ethane (dppe) gave a mixture of two regioisomers: catecholate 3Cat and dithiolate 3Dit. Both isomers were isolated in crystalline form and characterized by NMR, IR and X-ray diffractometry studies. DFT calculations reveal that the 3Dit species is more thermodynamically stable than the isomer 3Cat. Isomerization of 3Cat to 3Dit in solution was observed.
RESUMEN
An unusual reactivity of sterically hindered o-quinones with an annelated dithiete ring towards coordination at a dithiolene site has been discovered. New Pd and Pt dithiolate complexes have been synthesized. The reaction proceeds regioselectively, and the quinone site of the parent ligand is not affected even while using an excess of the metal complex. Both Pt and Pd complexes display a square planar surrounding for the metal ion and have very similar NMR, IR and UV/Vis spectra. Surprisingly, being coordinated at the dithiolene site to the metal, the ligand exhibits activity like an o-quinone, it could be reduced with different metals resulting in the corresponding o-semiquinonates which were confirmed by EPR spectroscopy. It was shown that an unpaired electron exhibits HFC with the phosphorus nuclei of phosphine ligands coordinated to the metal ions at the dithiolene site of the molecule.
RESUMEN
New four-, five- and six-coordinated cyclometallated o-semiquinonato palladium complexes were obtained and characterized in solution by EPR. Interaction of square-planar azaphenyl palladium semiquinonate with mono and bidentate phosphane donors leads to formation of five- and six-coordinated adducts. Typical values of HFC constants on apical and basal phosphorouses are observed for such compounds. In one case the reversible addition of tri-phenyl-phosphane was observed. The coordination mode of pincer ligand (bi- or tridentate) in o-semiquinonato pincer complexes depends on the nature of linker between coordinating group and pincer aryl ring. In the case of CH(2) linker five coordinated complexes are formed. The "swing" and "fan" oscillations are observed for these compounds. Complexes with -O- linker are the first examples of compounds with bidentate bonded phosphorous-based pincer ligand. Most of complexes are unstable and decompose during some hours. Only the application of o-semiquinones as spin labels and using the EPR technique made possible to observe and interpret their structure.
RESUMEN
The number of dicarbonyl-o-semiquinonato (o-iminosemiquinonato) rhodium complexes was isolated and characterized. Some reactions of these compounds with tertiary phosphines (substitution, addition) were studied by EPR in solution using o-semiquinones (o-iminosemiquinones) as spin labels.