New Oxypyridinate Paddlewheel Ligands for Alkane-Soluble, Sterically-Protected Ru₂(II,III) and Ru₂(II,II) Complexes

The paddlewheel complex Ru₂(chp)₄Cl (1-Cl, chp = 6-chloro-2-oxypyridinate), upon reduction with Zn, has been previously shown to dimerize to [Ru₂(chp)₄]₂ (2), blocking further chemistry at the Ru₂(II,II) axial site [ Inorg. Chem. 2015 , 54 , 8571 - 8589 ]. Functionalization of the chp ligand at the 3 and 5 positions with either bromine (dbchpH = 3,5-dibromo-6-chloro-2-pyridone) or trimethylsilyl (TMS) groups (dsichpH = 6-chloro-3,5-bis(trimethylsilyl)-2-pyridone) allows for the preparation of the Ru₂(II,II) paddlewheel complexes Ru₂(dbchp)₄ (3) and Ru₂(dsichp)₄ (6), respectively, neither of which shows evidence of dimerization. Though the utilization of 3 is limited due to insolubility, complex 6 is soluble even in typically non-coordinating solvents, forming a stable κ¹-axial adduct in CH₂Cl₂ (6-CH₂Cl₂) and showing evidence of an axial interaction with n-decane. The first example of an axially free Ru₂(II,II) complex with a ³A ground state is observed upon crystallization of 6 from benzene (6-C₆D₆). Complex 6 is accessed via Zn reduction of Ru₂(dsichp)₄Cl (4-Cl), which along with Ru₂(dsichp)₄N₃ (4-N₃), show similar structural and electronic properties to their non-TMS-substituted analogues, 1-Cl and 1-N₃. Photolysis of 4-N₃ in frozen solution generates Ru₂(dsichp)₄N (5); no N atom transfer to PPh₃ is observed upon room temperature photolysis in fluid solution.