New sterically-hindered o-quinones annelated with metal-dithiolates: regiospecificity in oxidative addition reactions of a bifacial ligand to the Pd and Pt complexes

Abstract

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.

PdII(P‐P) Derivatives of o‐Quinone Annulated with Dithiete Cycle: Electrochemical Properties and Coordination Regioisomerism

“…Until now electrochemical studies were reported for similar systems with monodentate phosphine ligands only. [14] CV measurements indicate that compounds 4-10 undergo three transformations upon reduction. The first and the second transitions are ligand-centered, and they can be attributed to the subsequent formation of o-semiquinonate radical-anion and catecholate dianion species (Scheme 5).…”

Preparation and reactivity of benzo‐1,2‐dichalcogenete derivatives and their bis(triphenylphosphine)platinum complexes

“…Kuropatov et al reported the platinum complex of benzo‐1,2‐dithiete [6c,9]. We also prepared the dinuclear palladium complex upon treatment of benzo‐1,2‐diselenete 2c with tetrakis(triphenylphosphine)palladium [8].…”

Functionalized o-Quinones: Concepts, Achievements and Prospects

“…Binding at the dithiolate coordination site is preferable for the soft Lewis acids and vice versa. Group 10 zero-valent metal tetrakis (triphenylphosphine) complexes M(PPh 3 ) 4 (M = Pd, Pt) selectively react towards dithiolene site of the ligand 68 with formation of 71 and 72 mononuclear adducts (Scheme 31) [43].…”

“…Binding at the dithiolate coordination site is preferable for the soft Lewis acids and vice versa. Group 10 zero-valent metal tetrakis (triphenylphosphine) complexes M(PPh3)4 (M = Pd, Pt) selectively react towards dithiolene site of the ligand 68 with formation of 71 and 72 mononuclear adducts (Scheme 31) [43]. According to the cyclic voltammetry data, coordination of a metal fragment on the dithiolene site significantly decreases the first reduction potential of free dioxolene site from −0.42 V (68) to −0.90 V (71) and −0.80 V (72).…”

“…According to the cyclic voltammetry data, coordination of a metal fragment on the dithiolene site significantly decreases the first reduction potential of free dioxolene site from −0.42 V (68) to −0.90 V (71) and −0.80 V (72). Nevertheless, such mononuclear complex still might be regarded as an o-quinone equivalent and can be reduced by many one-electron agents to give corresponding heterobimetallic complexes (Scheme 32) [43]. Reaction of 68 with two-electron reducing agents results in catecholate or dithiolate derivatives depending on the Lewis acidity of the metal ion.…”