Dye-Tethered Ruthenium Nitrosyls Containing Planar Dicarboxamide Tetradentate N4 Ligands: Effects of In-Plane Ligand Twist on NO Photolability

Abstract

To examine the steric effects of the in-plane ligands in dye-sensitized {RuNO}(6) nitrosyls on their NO photolability, two new ligands, namely, 1,2-Bis(pyridine-2-carboxamido)-4,5-dimethoxybenzene (H(2)(OMe)(2)bpb) and 1,2-Bis(Isoquinoline-1-carboxamido)-4,5-dimethoxybenzene (H(2)(OMe)(2)IQ1, H's are dissociable carboxamide protons) have been designed and synthesized. The syntheses and spectroscopic properties of {RuNO}(6) nitrosyls derived from these two ligands, namely, [((OMe)(2)bpb)Ru(NO)(Cl)] (4-Cl), [((OMe)(2)IQ1)Ru(NO)(Cl)] (5-Cl), [((OMe)(2)bpb)Ru(NO)(Resf)] (4-Resf), and [((OMe)(2)IQ1)Ru(NO)(Resf)] (5-Resf), are reported. The structures of 5-Cl, 4-Resf, and 5-Resf have been determined by X-ray crystallography. Removal of the in-plane ligand twist in the quinoline-based R(2)bQb(2-) ligand frame (because of steric interactions between the extended quinoline ring systems) in both R(2)bpb(2-) and R(2)IQ1(2-) (pyridine and 1-isoquinoline rings, respectively, instead of quinoline rings in the equatorial plane) results in enhanced solution stability, as well as higher quantum yield values for NO photorelease upon exposure to 500 nm light. Both dye-tethered {RuNO}(6) nitrosyls 4-Resf and 5-Resf exhibit greater sensitivity to visible light compared to the chloro-bound species 4-Cl and 5-Cl. In addition, the dye-tethered nitrosyls are fluorescent and hence can be used as trackable NO donors in cellular studies.

A new photoactivable NO‐releasing {Ru−NO}6 ruthenium nitrosyl complex with a tetradentate ligand containing aniline and pyridine moieties

“…Φ NO was determined to be 0.19-0.34 depending on the solvents (Table 2). The observed Φ NO values of Ru-(EPBP)(NO)Cl are greater than those obtained from most of the previously reported mononuclear {RuNO} 6 complexes (SI, Table S3), [12,22,26,27,31,[46][47][48][49][50][51][52] and almost the highest among those of the nuetral {RuÀ NO} 6 complexes, indicating that the EPBP 2À ligand provides an effective platform forming RuNO complexes useful for NO-photoreleasing. The negatively charged and strong σ-donating EPBP 2À ligand might benifit the high quantum yields by both stabilizing the photoproducts and interfering with NO recombination.…”

“…Those lengths are in accordance with the reported values found in the RuNO complexes with the {RuNO} 6 electron configurations. [7,[18][19][20][21][22][23][24][25][26][27][28][29] The arrangement of RuÀ NÀ O is close to linearity with the bond angle of 170.5(5)°. This bond angle and the observed NO stretching vibration (ν NO ) at 1850 cm À 1 (SI, Figure S1(A)) indicate that the electronic structure of the complex can be assigned to Ru(II)-(NO + ).…”

Transition‐Metal Nitrosyls for Photocontrolled Nitric Oxide Delivery

“…Previous studies of the photochemical behavior of the salen ruthenium nitrosyls [Ru(salen)(Cl)(NO)] and [Ru(salen)(NO)(H 2 O)] {H 2 ‐salen = N , N′ ‐bis(salicylaldehyde)ethylenediimine} revealed that the quantum yields for release of NO under UV light irradiation (355 nm) were small, and the compounds were eventually converted into the corresponding solvated products . Mascharak and co‐workers have systematically investigated the dicarboxamide tetradentate ligands with ruthenium nitrosyls for some years , .…”

Photo-Controlled Release of NO and CO with Inorganic and Organometallic Complexes

“…Having more carboxamide groups resulted in a higher bathochromic effect, higher quantum yields, and a better stability under physiological conditions [90,107,108]. An example is the tetradentate anionic ligand bpb -containing two carboxamide groups (H 2 bpb = 1,2-bis(pyridine-2-carboxamido)benzene) from which they prepared the ruthenium complexes Ru(bpb)(NO)(X) Interestingly, the more sterically crowded Ru((OMe) 2 bQb)(NO)(Cl) (Figure 11) is less photoactive than the isoquinoline analog Ru((OMe) 2 IQ1)(NO)(Cl) [32] …”