New Oxypyridinate Paddlewheel Ligands for Alkane-Soluble, Sterically-Protected Ru2(II,III) and Ru2(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]. Functionafization 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 kappa(1)-axial CH2Cl2 (6-CH2Cl2) 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-C6D6). 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 PPh3 is observed upon room temperature photolysis in fluid solution.