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.

A unique phenomenon of regioisomerism in coordination chemistry was discovered: the reaction of a sterically hindered o-quinone annelated with a dithiete ring with Pddba 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.

o-Quinones are both well-studied and promising redox-active chelating ligands. There are plenty of interesting effects to be found on o-quinone-derived metallocomplexes, such as photo-thermo mechanical effect in solid phase and in solution, luminescence, SMM properties and so on. A combination o-quinone function with an additional coordination site or redox active fragment in the same molecule might sufficiently extend an assembling as well as functional capability of such ligand in complexes. In this paper, the authors focus on o-quinones decorated with additional non-dioxolene chelating coordination site or with electron donor redox active annelated fragments.

Regioselectivity in interaction of bifunctional o‐quinone annulated with dithiete cycle with tris(dibenzylideneacetone)dipalladium (Pd2dba3) in presence of bidentate phosphines was studied. Excluding the case of 1,2‐bis(diphenylphosphino)ethane (dppe) species, the formation of corresponding dithiolates with high yields was observed. Coordination of palladium to the dithiolene site of bifunctional ligand causes a distortion of the dioxolene site as well as significant decrease of its electron‐acceptor ability. The formation of both catecholate and dithiolate isomers, observed in case of reaction with dppe, might be interpreted as a consequence of kinetic factors.

No abstract