Five ruthenium catalysts described herein facilitate self-sensitized carbon dioxide reduction to form carbon monoxide with a ruthenium catalytic center. These catalysts include four new and one previously reported CNC pincer complexes featuring a pyridinol derived N-donor and N-heterocyclic carbene (NHC) C-donors derived from imidazole or benzimidazole. The complexes have been characterized fully by spectroscopic and analytic methods, including X-ray crystallography. Introduction of a 2,2′-bipyridine (bipy) coligand and phenyl groups on the NHC ligand was necessary for rapid catalysis. [(CNC)­Ru­(bipy)­(CH3CN)]­(OTf)2 is among the most active and durable photocatalysts in the literature for CO2 reduction without an external photosensitizer. The role of the structure of this complex in catalysis is discussed, including the importance of the pincer’s phenyl wingtips, the bipyridyl ligand, and a weakly coordinating monodentate ligand.

The first example of a CNC pincer ligand with a central pyridinol ligand is reported in a nickel(ii) complex. This metal complex can be protonated or deprotonated reversibly in situ to switch on or off the photocatalytic performance towards CO2 reduction. The O- substituent appears essential for catalysis.

Ruthenium complexes bearing protic diimine ligands are cytotoxic to certain cancer cells upon irradiation with blue light. Previously reported complexes of the type [(N,N)2Ru­(6,6′-dhbp)]­Cl2 with 6,6′-dhbp = 6,6′-dihydroxybipyridine and N,N = 2,2′-bipyridine (bipy) (1 A ), 1,10-phenanthroline (phen) (2 A ), and 2,3-dihydro-[1,4]­dioxino­[2,3-f]­[1,10]­phenanthroline (dop) (3 A ) show EC50 values as low as 4 μM (for 3 A ) vs breast cancer cells upon blue light irradiation (Inorg. Chem.20177519). Herein, subscript A denotes the acidic form of the complex bearing OH groups, and B denotes the basic form bearing O– groups. This photocytotoxicity was originally attributed to photodissociation, but recent results suggest that singlet oxygen formation is a more plausible cause of photocytotoxicity. In particular, bulky methoxy substituents enhance photodissociation but these complexes are nontoxic (Dalton Trans201815685). Cellular studies are presented herein that show the formation of reactive oxygen species (ROS) and apoptosis indicators upon treatment of cells with complex 3 A and blue light. Singlet oxygen sensor green (SOSG) shows the formation of 1O2 in cell culture for cells treated with 3 A and blue light. At physiological pH, complexes 1 A -3 A are deprotonated to form 1 B -3 B in situ. Quantum yields for 1O2 (ϕΔ) are 0.87 and 0.48 for 2 B and 3 B , respectively, and these are an order of magnitude higher than the quantum yields for 2 A and 3 A . The values for ϕΔ show an increase with 6,6′-dhbp derived substituents as follows: OMe < OH < O–. TD-DFT studies show that the presence of a low lying triplet metal-centered (3MC) state favors photodissociation and disfavors 1O2 formation for 2 A and 3 A (OH groups). However, upon deprotonation (O– groups), the 3MLCT state is accessible and can readily lead to 1O2 formation, but the dissociative 3MC state is energetically inaccessible. The changes to the energy of the 3MLCT state upon deprotonation have been confirmed by steady state luminescence experiments on 1 A -3 A and their basic analogs, 1 B -3 B . This energy landscape favors 1O2 formation for 2 B and 3 B and leads to enhanced toxicity for these complexes under physiological conditions. The ability to convert readily from OH to O– groups allowed us to investigate an electronic change that is not accompanied by steric changes in this fundamental study.

2.6-Dialkyl-phenols exhibit little steric hindrance on reaction with phosphoryl chloride unless the alkyl substituent is bulky (i.e. t-butyl). Where bulky substituents are present reaction with phosphoryl chloride occurs only in the presence of Friedel-Crafts type catalysts after either a dealkylation or a rearrangement of the ortho-placed alkyl groups, followed by U-phosphorylation, has occurred. DIALKYLANILINES react with phosphoryl chloride and phosphorus trichloride by C-phosphorylation a t the @ava-position both in the presence specific Friedel-Crafts type catalysts to give mixtures of products containing from One to three phosphorust Present address:

We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)2Ru(n,n′‐dhbp)]Cl2 with n = 6 and 4 in 1A and 2A, respectively). Full characterization data are reported for 1A and 2A and single crystal X‐ray diffraction for 1A. Both 1A and 2A are diprotic acids. We have studied 1A, 1B, 2A, and 2B (B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy 3MLCT states relative to the acidic forms. Complexes 1A and 2A produce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC50 light values as low as 0.50 μM with PI values as high as >200 vs. MCF7. Computational studies were used to predict the energies of the 3MLCT and 3MC states. An inaccessible 3MC state for 2B suggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible 3MLCT state for 1O2 generation explains the excellent photocytotoxicity of 2.

No abstract

The absorption spectra of benzoic acid and some of its simple esters have been determined in various concentrations in polar and non-polar solvents. Changes in solvents and concentrations affect the fine structure of the curves more than the wave lengths and intensities of the maxima and the conclusions are therefore based primarily on variations in fine structure.The spectral changes are discussed in terms of dimerization, bonding with the solvent and ionization.

Nine new polycyclic aromatic BN-1,2-azaborine analogues containing the N-BOH moiety were synthesized using a convenient two-step, one-pot procedure. Characterization of the prepared compounds show the luminescence wavelength and the quantum yields of the azaborines were tunable by controlling the power and location of the donor and acceptor substituents on the chromophore. UV-visible spectroscopy and density functional theory (DFT) computations revealed that the addition of electron-donating moieties to the isoindolinone hemisphere raised the energy of the HOMO, resulting in the reduction of the HOMO-LUMO gap. The addition of an electron-accepting moiety to the isoindolinone hemisphere and an electron-donating group to the boronic acid hemisphere decreased the HOMO-LUMO gap considerably, leading to emission properties from partial intramolecular charge transfer (ICT) states. The combined effect of an acceptor on the isoindolinone side and a donor on the boronic acid side (strong acceptor-π-donor) gave the most red-shifted absorption. The polycyclic aromatic BN-1,2-azaborines emitted strong fluorescence in solution and in the solid-state with the largest red-shifted emission at 640 nm and a Stokes shift of Δλ = 218 nm, or Δν = 8070 cm.