Ruthenium nitrosyls derived from tetradentate ligands containing carboxamido-N and phenolato-o donors: syntheses, structures, photolability, and time dependent density functional theory studies

Abstract

In order to examine the role(s) of designed ligands on the NO photolability of {Ru-NO}(6) nitrosyls, a set of three nitrosyls with ligands containing two carboxamide groups along with a varying number of phenolates have been synthesized. The nitrosyls namely, (NEt(4))(2)[(hybeb)Ru(NO)(OEt)] (1), (PPh(4))[(hypyb)Ru(NO)(OEt)] (2), and [(bpb)Ru(NO)(OEt)] (3) have been characterized by X-ray crystallography. Complexes 1-3 are diamagnetic, exhibit nu(NO) in the range 1780-1840 cm(-1) and rapidly release NO in solution upon exposure to low power UV light (7 mW/cm(2)). Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) calculations on 1-3 indicate considerable contribution of ligand orbitals in the MOs involved in transitions leading to NO photolability. The results of the theoretical studies match well with the experimental absorption spectra as well as the parameters for NO photorelease and provide insight into the transition(s) associated with loss of NO.

Figure 1

Tetradentate dicarboxamide ligands containing zero, one, or two phenolato-O donors

Figure 2

Anionic tetradentate dicarboxamido-N ligands with either pyridine- or quinoline-N donors

Figure 3

Thermal ellipsoid (probability level 50%) plot of [(hybeb)Ru(OEt)]^2- (anion of 1) with select atom-labeling. H atoms are omitted for the sake of clarity.

Figure 4

Thermal ellipsoid (probability level 50%) plot of [(hypyb)Ru(OEt)]⁻ (anion of 2) with select atom-labeling. H atoms are omitted for the sake of clarity.

Figure 5

Thermal ellipsoid (probability level 50%) plot of [(bpb)Ru(NO)(OEt] (3) with select atom-labeling. H atoms are omitted for the sake of clarity.

Figure 6

Electronic absorption spectra of 1 (dashed line), 2 (solid line), 3 (dotted line) in EtOH

Figure 7

Changes in the electronic absorption spectrum upon photolysis of 2 in MeCN following illumination with intervals of UV light. Inset: NO amperogram of 2 in H₂O upon illumination with UV light for time periods as indicated.

Figure 8

a) TDDFT calculated energy transitions and oscillator strengths (shown as vertical lines, red = major low energy transition), experimental (solid lines) and calculated (dashed lines) electronic absorption spectra. b) Calculated HOMO/LUMO energy diagram of complexes 1 (left), 2 (middle), and 3 (right). The most prominent MOs involved in the lowest energy transitions (labeled in red) and their diagrams are shown. Other orbitals involved in TDDFT calculated transitions are labeled in black.