Syntheses Structures and Photochemistry of Manganese Nitrosyls Derived from Designed Schiff Base Ligands: Potential NO Donors that can be Activated by Near-Infrared Light

摘要

Two manganese nitrosyls, namely [Mn(SBPy3)(NO)](ClO4)2 (>1) and [Mn(SBPy2Q)(NO)](ClO4)2 (>2) have been synthesized by using designed pentadentate Schiff base ligands N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-aldimine (SBPy3) and N,N-bis(2-pyridyl methyl)amine-N-ethyl-2-quinoline-2-aldimine (SBPy2Q). Reaction of NO(g) with [Mn(SBPy3)(MeOH)](ClO4)2 and [Mn(SBPy2Q)(EtOH)](ClO4)2 in MeCN affords >1 and >2 respectively in good yields. Narrow-width peaks in the ¹H NMR spectra and strong νNO at 1773 cm^-1 (of >1) and 1759 cm^-1 (of >2) confirm a strongly-coupled {low-spin Mn(II)-NO^• }formulation for both these {Mn-NO} nitrosyls. In MeCN, >1 exhibits two strong absorption bands with λmax at 500 and 720 nm. These bands red shifts to 550 and 785 nm in case of >2 due to substitution of the pyridyl-imine moiety of SBPy₃ with quinolyl-imine moiety in the SBPy₂Q ligand frame. Exposure of solutions >1 and >2 to near-infrared (NIR) light (780 nm, 5 mW) results in rapid bleaching of the orange and fuchsia solutions and free NO is detected in the solutions by an NO-sensitive electrode. The high quantum yield values (Φ) of >1 (0.580 ± 0.010, λ_irr = 550 nm, MeCN) and >2 (0.434 ± 0.010, λ_irr = 550 nm, MeCN) and in particular their sensitivity to NIR light of 800-950 nm range strongly suggest that these designed manganese nitrosyls could be used as NIR light-triggered NO donors.