Synthesis, Structures, and Photophysical Properties of Ruthenium(II) Quinolinolato Complexes

Reaction of [Ru^II(PR₃)₃Cl₂] with 2-methyl<b>-</b>8-quinolinolate (MeQ) in the presence of Et₃N in MeOH produced the neutral carbonyl hydrido complexes [Ru^II(MeQ)­(PR₃)₂(CO)­(H)] (R = Ph (<b>1</b>), MeC₆H₄ (<b>2</b>), MeOC₆H₄ (<b>3</b>)). An analogous reaction occurs between [Ru^II(PPh₃)₃Cl₂] and MeQH in ethanol to give [Ru^II(MeQ)­(PPh₃)₂(CO)­(CH₃)] (<b>4</b>). The carbonyl, hydride, and methyl ligands of these complexes are most likely derived from the decarbonylation of ROH. Reaction of [Ru^II(PPh₃)₃(CO)­(H)₂] with 5-substituted quinolinolato ligands (XQ, X = H, Cl, Ph) produced the neutral complexes [Ru^II(XQ)­(PPh₃)₂(CO)­(H)] (XQ = Q (<b>5</b>), ClQ (<b>6</b>), PhQ (<b>7</b>)). Treatment of <b>1</b> and <b>5</b>–<b>7</b> with excess KCN in MeOH following by metathesis with PPh₄Cl afforded PPh₄⁺ salts of the anionic carbonyl dicyano complexes [Ru^II(XQ)­(CO)­(CN)₂(PPh₃)]⁻ (XQ = MeQ (<b>8</b>), Q (<b>9</b>) ClQ (<b>10</b>), PhQ (<b>11</b>)). Under similar conditions, reaction of <b>1</b> with excess CyNC in the presence of NH₄PF₆ afforded [Ru^II(MeQ)­(CyNC)₂(CO)­(PPh₃)]⁺ (<b>12</b>). All complexes have been characterized by IR, ESI/MS, ¹H NMR and elemental analysis. The crystal structures of complexes <b>3</b>, <b>4</b>, <b>8</b>, and <b>12</b> have been determined by X-ray crystallography. The UV and emission spectra of these complexes have also been investigated. All complexes exhibit short-lived quinolinolate-based LC fluorescence in solution at room temperature and dual emissions derived from LC fluorescence and phosphorescence at 77 K glassy medium. These emissions are relatively insensitive to the nature of the ancillary ligands but are readily tunable by varying the substituents on the quinolinolato ligand

Synthesis, Structures, and Photophysical Properties of Ruthenium(II) Quinolinolato Complexes

Reaction of [Ru^II(PR₃)₃Cl₂] with 2-methyl<b>-</b>8-quinolinolate (MeQ) in the presence of Et₃N in MeOH produced the neutral carbonyl hydrido complexes [Ru^II(MeQ)­(PR₃)₂(CO)­(H)] (R = Ph (<b>1</b>), MeC₆H₄ (<b>2</b>), MeOC₆H₄ (<b>3</b>)). An analogous reaction occurs between [Ru^II(PPh₃)₃Cl₂] and MeQH in ethanol to give [Ru^II(MeQ)­(PPh₃)₂(CO)­(CH₃)] (<b>4</b>). The carbonyl, hydride, and methyl ligands of these complexes are most likely derived from the decarbonylation of ROH. Reaction of [Ru^II(PPh₃)₃(CO)­(H)₂] with 5-substituted quinolinolato ligands (XQ, X = H, Cl, Ph) produced the neutral complexes [Ru^II(XQ)­(PPh₃)₂(CO)­(H)] (XQ = Q (<b>5</b>), ClQ (<b>6</b>), PhQ (<b>7</b>)). Treatment of <b>1</b> and <b>5</b>–<b>7</b> with excess KCN in MeOH following by metathesis with PPh₄Cl afforded PPh₄⁺ salts of the anionic carbonyl dicyano complexes [Ru^II(XQ)­(CO)­(CN)₂(PPh₃)]⁻ (XQ = MeQ (<b>8</b>), Q (<b>9</b>) ClQ (<b>10</b>), PhQ (<b>11</b>)). Under similar conditions, reaction of <b>1</b> with excess CyNC in the presence of NH₄PF₆ afforded [Ru^II(MeQ)­(CyNC)₂(CO)­(PPh₃)]⁺ (<b>12</b>). All complexes have been characterized by IR, ESI/MS, ¹H NMR and elemental analysis. The crystal structures of complexes <b>3</b>, <b>4</b>, <b>8</b>, and <b>12</b> have been determined by X-ray crystallography. The UV and emission spectra of these complexes have also been investigated. All complexes exhibit short-lived quinolinolate-based LC fluorescence in solution at room temperature and dual emissions derived from LC fluorescence and phosphorescence at 77 K glassy medium. These emissions are relatively insensitive to the nature of the ancillary ligands but are readily tunable by varying the substituents on the quinolinolato ligand

Dual Homogeneous and Heterogeneous Pathways in Photo- and Electrocatalytic Hydrogen Evolution with Nickel(II) Catalysts Bearing Tetradentate Macrocyclic Ligands

A series of nickel­(II) complexes bearing tetradentate macrocyclic N₄, N₃S, and N₃P ligands were synthesized, and their photocatalytic activity toward proton reduction has been investigated by using [Ir­(dF­(CF₃)­ppy)₂(dmbpy)]­PF₆ (dF­(CF₃)­ppy = 2-(2,4-difluorophenyl)-5-trifluoromethyl­pyridine and dmbpy = 4,4′-dimethyl-2,2′-dipyridyl) as the photosensitizer and triethylamine (TEA) as the sacrificial reductant. The complex [Ni­(L4)]²⁺ (L4 = 2,12-dimethyl-7-phenyl-3,11,17-triaza-7-phospha-bicyclo­[11,3,1]­heptadeca-1(17),13,15-triene), which bears a phosphorus donor atom, shows the highest efficiency with TON up to 5000 under optimized conditions, while the tetraaza macrocyclic nickel complexes [Ni­(L1)]²⁺ and [Ni­(L2)]²⁺ (L1 = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo­[11.3.l]­heptadeca-1(17),2,11,13,15-pentaene; L2 = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo­[11.3.l]­heptadeca-1(17),13,15-triene) show lower photocatalytic activities. Transient UV–vis absorption and spectroelectrochemical experiments show that Ni­(II) is reduced to Ni­(I) under photocatalytic conditions. However, dynamic light scattering and mercury poisoning experiments suggest that the Ni­(I) is further reduced to Ni(0) nanoparticles which are the real catalysts for H₂ production. Electrocatalytic proton reduction by [Ni­(L4)]²⁺ has also been investigated. In this case, the electrochemical behavior is consistent with a homogeneous pathway, and no Ni nanoparticles were observed on the electrode surface during the first few hours of electrolysis. However, on prolonged electrolysis for >17 h, nickel-based nanoparticles were observed on the electrode surface, which are active catalysts for H₂ production

Light-Driven Reduction of CO₂ to CO in Water with a Cobalt Molecular Catalyst and an Organic Sensitizer

We report an efficient visible light-driven CO2 reduction system that functions in water and without any noble metal nor rare materials. Using the cobalt complex [Co(qpy)(OH2)2]2+ (1, qpy = 2,2′:6′,2″:6″,2‴-quaterpyridine) as a catalyst, an organic triazatriangulenium (TATA+) salt as the photosensitizer (PS), BIH + TEOA (BIH = 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole and TEOA = triethanolamine) as the sacrificial reductant (SD), CO and formate were first produced with a total TON >3700 upon irradiation in CO2-saturated CH3CN solution with visible light. Upon the addition of a weak Brönsted acid (water), catalysis was enhanced and directed toward CO production (19,000 TON, 93% selectivity). The photocatalytic system was further shown to function in pure water as a solvent. High metrics with a TON for CO of 2600 and 94% selectivity were obtained using TEA (triethylamine) as the SD

Slow Magnetic Relaxation in a Series of Mononuclear 8‑Coordinate Fe(II) and Co(II) Complexes

A series of homoleptic mononuclear 8-coordinate Fe^II and Co^II compounds, [Fe^II(<b>L</b>^<b>2</b>)₂]­(ClO₄)₂ (<b>2</b>), [Fe^II(<b>L</b>^<b>3</b>)₂]­(ClO₄)₂ (<b>3</b>), [Fe^II(<b>L</b>^<b>4</b>)₂]­(ClO₄)₂ (<b>4</b>), [Co^II(<b>L</b>^<b>1</b>)₂]­(ClO₄)₂ (<b>5</b>), [Co^II(<b>L</b>^<b>2</b>)₂]­(ClO₄)₂ (<b>6</b>), [Co^II(<b>L</b>^<b>3</b>)₂]­(ClO₄)₂ (<b>7</b>), and [Co^II(<b>L</b>^<b>4</b>)₂]­(ClO₄)₂ (<b>8</b>) (<b>L</b>^<b>1</b> and <b>L</b>^<b>2</b> are 2,9-dialkylcarboxylate-1,10-phenanthroline ligands; <b>L</b>^<b>3</b> and <b>L</b>^<b>4</b> are 6,6′-dialkylcarboxylate-2,2′-bipyridine ligands), have been obtained, and their crystal structures have been determined by X-ray crystallography. The metal center in all of these compounds has an oversaturated coordination number of 8, which is completed by two neutral homoleptic tetradentate ligands and is unconventional in 3d-metal compounds. These compounds are further characterized by electronic spectroscopy, cyclic voltammetry (CV), and magnetic measurements. CV measurements of these complexes in MeCN solution exhibit rich redox properties. Magnetic measurements on these compounds demonstrate that the observed single-ion magnetic (SIM) behavior in the previously reported [Fe^II(<b>L</b><b>¹</b>)₂]­(ClO₄)₂ (<b>1</b>) is not a contingent case, since all of the 8-coordinate compounds <b>2</b>–<b>8</b> exhibit interesting slow magnetic relaxation under applied direct current fields