New Oxypyridinate Paddlewheel Ligands for Alkane-Soluble, Sterically-Protected Ru 2 (II,III) and Ru 2 (II,II) Complexes.

The paddlewheel complex Ru ₂ (chp) ₄ Cl (1-Cl, chp = 6-chloro-2-oxypyridinate), upon reduction with Zn, has been previously shown to dimerize to [Ru ₂ (chp) ₄ ] ₂ (2), blocking further chemistry at the Ru ₂ (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 Ru ₂ (II,II) paddlewheel complexes Ru ₂ (dbchp) ₄ (3) and Ru ₂ (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 κ ¹ -axial adduct in CH ₂ Cl ₂ (6-CH ₂ Cl ₂ ) and showing evidence of an axial interaction with n-decane. The first example of an axially free Ru ₂ (II,II) complex with a ³ A ground state is observed upon crystallization of 6 from benzene (6-C ₆ D ₆ ). Complex 6 is accessed via Zn reduction of Ru ₂ (dsichp) ₄ Cl (4-Cl), which along with Ru ₂ (dsichp) ₄ N ₃ (4-N ₃ ), show similar structural and electronic properties to their non-TMS-substituted analogues, 1-Cl and 1-N ₃ . Photolysis of 4-N ₃ in frozen solution generates Ru ₂ (dsichp) ₄ N (5); no N atom transfer to PPh ₃ is observed upon room temperature photolysis in fluid solution.