Coligands Controlled Reactivities of Ruthenium(II) Precursors: Antiferromagnetically Coupled Ruthenium(III)-Phenoxyl versus Ruthenium(II)-Phenoxyl Forms.

The study disclosed that the reactivities of [Ru II (PPh 3 ) 3 Cl 2 ] and [Ru II (PPh 3 ) 3 (CO)(H)Cl] precursors toward a trimethoxyarylimino-phenol derivative are sensibly different. The former promotes methoxy demethylation reaction affording a [Phenolato-Ru III -Phenolato] unit, while the latter containing π-acidic CO and hydride as coligands leads to C-H activation reaction, generating a [Phenolato-Ru II -Aryl] unit. Notably, the oxidized analogues of these two forms produce antiferromagnetically coupled [Ru III -phenoxyl] and paramagnetic [Ru II -phenoxyl] forms, which exhibit diverse reactivities. Surprisingly, the magnetically coupled [Ru III -phenoxyl] form obtained from [Phenolato-Ru III -Phenolato] motif leads to coligand, PPh 3 oxidation and undergoes dimerization, making a Ru-Ru bond (2.599(2) Å), while the [Ru II -phenoxyl] form obtained from [Phenolato-Ru II -Aryl] motif leads to C-C coupling and H abstraction reactions. The coupling reaction affords a 4,4'-dibenzosemiquinonate anion radical complex, but the H-abstraction of the phenoxyl form gives a [Ru II -Phenol] complex. For comparison, [Ru II (IQ R 0 )] and [Ru II (ISQ R·- )] complexes were also isolated, where IQ R 0 and ISQ R·- are p -R- o -iminobenzoquinone and p -R- o -iminobenzosemiquinonate anion radicals. However, they fail to promote any bond-formation reaction. The molecular and electronic structures of the ruthenium (II/III) complexes were confirmed by single-crystal X-ray crystallography, EPR spectroscopy, and DFT calculations.