Visible-Light-Promoted Thiolation of Benzyl Chlorides with Thiosulfonates via a Photoactive Electron Donor-Acceptor Complex.

Visible-light-promoted thiolation of benzyl chlorides with thiosulfonates is disclosed via an electron donor-acceptor complex strategy. In addition to efficiently delivering a series of arylbenzylsulfide compounds, versatile thioglycosides were also successfully constructed by applying the metal- and photocatalyst-free protocol. Preliminary mechanistic studies suggest that a radical-radical coupling process was involved in this transformation.

Dual-Emissive Monoruthenium Complexes of N(CH3)-Bridged Ligand: Synthesis, Characterization, and Substituent Effect.

Three monoruthenium complexes 1(PF6)2-3(PF6)2 bearing an N(CH3)-bridged ligand have been synthesized and characterized. These complexes have a general formula of [Ru(bpy)2(L)](PF6)2, where L is a 2,5-di(N-methyl-N'-(pyrid-2-yl)amino)pyrazine (dapz) derivative with various substituents, and bpy is 2,2'-bipyridine. The photophysical and electrochemical properties of these compounds have been examined. The solid-state structure of complex 3(PF6)2 is studied by single-crystal X-ray analysis. These complexes show two well-separated emission bands centered at 451 and 646 nm (Δλmax = 195 nm) for 1(PF6)2, 465 and 627 nm (Δλmax = 162 nm) for 2(PF6)2, and 455 and 608 nm (Δλmax = 153 nm) for 3(PF6)2 in dilute acetonitrile solution, respectively. The emission maxima of the higher-energy emission bands of these complexes are similar, while the lower-energy emission bands are dependent on the electronic nature of substituents. These complexes display two consecutive redox couples owing to the stepwise oxidation of the N(CH3)-bridged ligand and ruthenium component. Moreover, these experimental observations are analyzed by computational investigation.

Nickel-Catalyzed Chemo- and Regioselective Benzylarylation of Unactivated Alkenes with o-Bromobenzyl Chlorides.

Chemo- and regioselectively nickel-catalyzed reductive benzylarylation of unactivated alkenes with o-bromobenzyl chlorides is disclosed herein, in which electrophiles participate through a single-component double-site approach. Moreover, its utility is underscored by the concise synthesis of bioactive Indane compounds and postreaction functionalizations leading to structurally diverse scaffolds. Preliminary mechanistic investigations suggest a radical chain reaction mechanism.

Dual-Emissive Tris-Heteroleptic Ruthenium Complexes: Tuning the DNA-Triggered Ratiometric Emission Response by Ancillary Ligands.

Three tris-heteroleptic mononuclear Ru(II) complexes with dual fluorescence and phosphorescence-[Ru(dpma)(bpy)(phen)]2+ (12+), [Ru(dpma)(bpy)(dppz)]2+ (22+), and [Ru(dpma)(phen)(dppz)]2+ (32+)-have been designed and used as ratiometric light-response probes for DNA, where dpma is di(pyrid-2-yl)(methyl)-amine, bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and dppz is dipyridophenazine, respectively. Single crystals of complex 2(PF6)2 have been obtained and studied by X-ray analysis. The interactions of these complexes with different DNAs are investigated by means of spectroscopic methods, viscosity measurements, and molecular modeling. In the presence of calf thymus DNA, complexes 2(PF6)2 and 3(PF6)2 show the emergence of a new lower-energy phosphorescence emission band; meanwhile, the higher-energy fluorescence emission band is essentially unchanged, functioning as an intrinsic internal reference. These two complexes exhibit stronger preference for calf thymus DNA over single-strand DNA (d(A)16 and d(C)16). In contrast, no binding interaction between 1(PF6)2 and calf thymus DNA is observed. The intrinsic binding constants (Kb) of 2(PF6)2 and 3(PF6)2 with calf thymus DNA are determined to be (1.4 ± 0.4) × 105 and (9.5 ± 0.15) × 104 M-1, respectively. In addition, these spectroscopic results are compared with those of the prototype complex [Ru(bpy)2(dppz)]2+ (42+), and density functional theory and time-dependent density functional theory calculations are employed to elucidate these experimental findings.

Ratiometric detection of amyloid-ß aggregation by a dual-emissive tris-heteroleptic ruthenium complex.

A dual-emissive tris-heteroleptic ruthenium complex is designed, synthesized and applied for the ratiometric photoluminescent detection of amyloid-ß (Aß) aggregation in both steady and transient states. The Aß aggregation is supported by transmission electron microscopy and confocal laser scanning microscopy analysis. In addition, molecular docking calculations have been performed to gain insights into the interaction mode between the ruthenium complex and Aß fibrils.

Nanocrystalline Sb-doped SnO2 films modified with cyclometalated ruthenium complexes for two-step electrochromism.

Sb-Doped nanocrystalline SnO2 (SnO2:Sb) thin films functionalized with cyclometalated ruthenium complexes 1 or 2 on FTO conductive glasses have been prepared and characterized. These complexes contain a redox-active amine unit separated from the ruthenium ion by a phenyl or biphenyl linker, respectively, to modify the absorption wavelengths at different redox states. Near-infrared electrochromism of both films has been examined by oxidative spectroelectrochemical measurements and double-potential-step chronoamperometry. A contrast ratio (ΔT%) of 33% at 1070 nm and 63% at 696 nm has been achieved for the SnO2:Sb/1 film in two stepwise oxidation processes, respectively. The other film with complex 2 shows two-step electrochromism at 1310 and 806 nm with ΔT% of 36% and 76%, respectively. The response time of electrochromic switching is around a few seconds. Taking advantage of the good contrast ratio, the rapid response, and the long retention time of each oxidation state, these films have been successfully used to demonstrate surface-confined flip-flop memory functions with a high ON/OFF ratio.

Tuning the dual emissions of a monoruthenium complex with a dangling coordination site by solvents, O2, and metal ions.

A polypyridyl monoruthenium complex with a dangling coordination site shows dual fluorescence/phosphorescence emissions at room temperature. The emission properties can be modulated by multiple stimuli including solvents, O2, and metal ions.

Transition from a Metal-Localized Mixed-Valence Compound to a Fully Delocalized and Bridge-Biased Electrophore in a Ruthenium-Amine-Ruthenium Tricenter System.

A series of cyclometalated diruthenium complexes with a redox-active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one-electron-oxidized state can be either in the form of a weakly or strongly coupled mixed-valence diruthenium complex, a fully charge-delocalized three-center system, or a bridge-biased electrophore. This transition among different electronic forms was supported by electrochemistry, near-infrared absorption, electron paramagnetic resonance, and density functional theory analysis.

Reductive electropolymerization of bis-tridentate ruthenium complexes with 5,5''-divinyl-4'-tolyl-2,2':6',2''-terpyridine.

Four bis-tridentate ruthenium complexes with 5,5''-divinyl-4'-tolyl-2,2':6',2''-terpyridine (dvtpy) have been synthesized. Among them, 3(PF6) ([(dvtpy)Ru(Mebib)](PF6)) and 4(PF6) ([(dvtpy)Ru(dpb)](PF6)) are cyclometalated, and 5(PF6)2 ([(dvtpy)Ru(Mebip)](PF6)2) and 6(PF6)2 ([(dvtpy)Ru(tpy)](PF6)2) are noncyclometalated, where Mebib is 2-deprotonated-1,3-bis(N-methylbenzimidazolyl)benzene, dpb is 2-deprotonated-1,3-di(2-pyridyl)benzene, Mebip is 2,6-bis(N-methylbenzimidazolyl)pyridine, and tpy is 2,2':6',2''-terpyridine, respectively. Reductive electropolymerization of these complexes and copolymerization of 4(PF6) and 5(PF6)2 proceeded smoothly, both on glassy carbon and ITO glass electrodes, to afford stable metallopolymeric films with well-defined redox processes. On the basis of the monomer structures, electrochemical properties, and polymerization mechanism, the polymer chains of these materials are supposed to be composed of organic frameworks with the metal ions laterally chelated to the main backbones. The polymeric films on ITO surfaces display promising electrochromism in the visible region with good reversibility and moderate contrast ratio. Besides, the apparent diffusion constants of films of 3(PF6)­6(PF6)2 were measured by potential step chronoamperometry and the typical surface morphology of poly-5(PF6)2/ITO film was studied using SEM.

Substituent and solvent effects on the electrochemical properties and intervalence transfer in asymmetric mixed-valent complexes consisting of cyclometalated ruthenium and ferrocene.

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF6) (Fcdpb=2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene; L=2,6-bis-(N-methylbenzimidazolyl)-pyridine (Mebip), 2,2':6',2''-terpyridine (tpy), 4-nitro-2,2':6',2''-terpyridine (NO2tpy), and trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine (Me3tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH2Cl2, CH3NO2, CH3CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, ΔE(1/2)(E(1/2)(Ru(II/III))-E(1/2)(Fc(0/+))), decreased slightly with increasing solvent donocity. The mixed-valent states of these complexes have been generated by electrolysis and the resulting intervalence charge-transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, E(op), and ΔE(1/2) of four mixed-valent complexes in a given solvent.

2,3-Di(2-pyridyl)-5-phenylpyrazine: a NN-CNN-type bridging ligand for dinuclear transition-metal complexes.

A new bridging ligand, 2,3-di(2-pyridyl)-5-phenylpyrazine (dpppzH), has been synthesized. This ligand was designed so that it could bind two metals through a NN-CNN-type coordination mode. The reaction of dpppzH with cis-[(bpy)2RuCl2] (bpy = 2,2'-bipyridine) affords monoruthenium complex [(bpy)2Ru(dpppzH)](2+) (1(2+)) in 64 % yield, in which dpppzH behaves as a NN bidentate ligand. The asymmetric biruthenium complex [(bpy)2Ru(dpppz)Ru(Mebip)](3+) (2(3+)) was prepared from complex 1(2+) and [(Mebip)RuCl3] (Mebip = bis(N-methylbenzimidazolyl)pyridine), in which one hydrogen atom on the phenyl ring of dpppzH is lost and the bridging ligand binds to the second ruthenium atom in a CNN tridentate fashion. In addition, the RuPt heterobimetallic complex [(bpy)2Ru(dpppz)Pt(C≡CPh)](2+) (4(2+)) has been prepared from complex 1(2+), in which the bridging ligand binds to the platinum atom through a CNN binding mode. The electronic properties of these complexes have been probed by using electrochemical and spectroscopic techniques and studied by theoretical calculations. Complex 1(2+) is emissive at room temperature, with an emission λmax = 695 nm. No emission was detected for complex 2(3+) at room temperature in MeCN, whereas complex 4(2+) displayed an emission at about 750 nm. The emission properties of these complexes are compared to those of previously reported Ru and RuPt bimetallic complexes with a related ligand, 2,3-di(2-pyridyl)-5,6-diphenylpyrazine.

Asymmetric mixed-valence complexes that consist of cyclometalated ruthenium and ferrocene: synthesis, characterization, and electronic-coupling studies.

Three bis-tridentate ferrocene-containing cyclometalated ruthenium complexes, [(Fcdpb)Ru(tpy)](+) (1(+)), [(Fctpy)Ru(dpb)](+) (2(+)), and [(Fcdpb)Ru(Fctpy)](+) (3(+)), have been prepared and characterized, where Fcdpb is the 2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene, tpy is 2,2':6',2"-terpyridine, dpb is the 2-deprotonated form of 1,3-di(2-pyridyl)benzene, and Fctpy is 4'-ferrocenyl-2,2':6',2"-terpyridine. Single crystals of compounds 2(+) and 3(+) have been studied by X-ray analysis. Complexes 1(+) and 2(+) displayed two anodic redox waves, whilst three well-separated redox couples were observed for compound 3(+). A combined experimental and computational study suggested that the ferrocene unit on the Fcdpb moiety in compounds 1(+) and 3(+) was oxidized first. In contrast, the order of the oxidation of ruthenium and ferrocene in complex 2(+) was reversed. Metal-to-metal-charge-transfer transitions (MM'CT) have been observed for the singly oxidized states 1(2+), 2(2+), and 3(2+) in the near-infrared region. Hush analysis showed that the metal-metal electronic couplings in compounds 1(2+) and 3(2+) were much stronger than those in compound 2(2+).

Cyclometalated ruthenium oligomers with 2,3-di(2-pyridyl)-5,6-diphenylpyrazine: a combined experimental, computational, and comparison study with noncyclometalated analogous.

Recent investigations on polypyridine transition-metal complexes as potential molecular wires have provided new impetus for these long-studied and well-established systems. Using bridging ligands 2,3-di(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz), a tetrametallic cyclometalated ruthenium complex has been prepared and characterized, with each metal having one Ru-C bond. The electronic properties of this complex and two known monoruthenium and diruthenium complexes with dpdpz (DPDPZ series) were probed by electrochemical and spectroscopic techniques and compared to the previously reported tppz-based noncyclometalated ruthenium complexes (TPPZ series). The frontier orbital energy levels and electronic structures of the two series have been characterized by density functional theory (DFT) calculations. In accordance with the experimental results, these studies suggest that the DPDPZ series oligomers generally have a narrower energy gap relative to the TPPZ series. In addition, the large energy density of states in longer oligomers suggests the possibility of band-type conduction. The DPDPZ series exhibits red-shifted light absorption with enhanced intensity relative to the TPPZ series congeners. Time-dependent DFT computations have been performed to rationalize the electronic absorption of the DPDPZ series. Oxidative spectroelectrochemical measurements of the DPDPZ tetrametallic complex indicate the presence of intervalence charge-transfer transitions among ruthenium sites.

A bis(terpyridine)ruthenium complex with three redox-active amine sites: electrochemical, optical, and computational studies.

Two ruthenium complexes, [Ru(NN)(ttpy)](2+) and [Ru(NN)(daatpy)](2+), have been designed and prepared, where NN is bis(amine) ligand 4'-tolyl-5,5"-bis(di-p-anisylamino)-2,2':6',2"-terpyridine, ttpy is 4'-tolyl-2,2':6',2"-terpyridine, and daatpy is 4'-di-p-anisylamino-2,2':6',2"-terpyridine. Complex [Ru(NN)(daatpy)](2+) contains three redox-active amine groups and has been characterized by single-crystal X-ray analysis. These two complexes display much-enhanced light absorption capabilities with respect to the prototype compound [Ru(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine), which has been rationalized on the basis of time-dependent density functional theory calculations. Electrochemical and optical studies showed that there was little electronic coupling between two amine sites in complex [Ru(NN)(ttpy)](2+). On the other hand, a ligand-to-ligand (N → N'(•+)) charge-transfer band has been observed at 1430 nm for singly and doubly oxidized forms of [Ru(NN)(daatpy)](2+), and an electronic coupling parameter of 1000 cm(-1) was derived using the Hush formula. This band is interpreted as a charge transfer from the neutral amine of the daatpy ligand to oxidized aminium units in the NN ligand.

Near-infrared absorbing and emitting Ru(II)-Pt(II) heterodimetallic complexes of dpdpz (dpdpz = 2,3-di(2-pyridyl)-5,6-diphenylpyrazine).

The reaction of 2,3-di(2-pyridyl)-5,6-diphenylpyrazine (dpdpz) with K(2)PtCl(4) in a mixture of acetonitrile and water afforded mono-Pt complex (dpdpz)PtCl(2)4 in good yield, with two lateral pyridine nitrogen atoms binding to the metal center. Two types of Ru(II)-Pt(II) heterodimetallic complexes bridged by dpdpz, namely, [(bpy)(2)Ru(dpdpz)Pt(C≡CC(6)H(4)R)](2+) (7-9, R = H, NMe(2), or Cl, respectively) and [(tpy)Ru(dpdpz)Pt(C≡CPh)] (+) (12), were then designed and prepared, where bpy = 2,2'-bipyridine and tpy = 2,2';6',2''-terpyridine. In both cases, the platinum atom binds to dpdpz with a C(∧)N(∧)N tridentate mode. However, the coordination of the ruthenium atom with dpdpz could either be noncyclometalated (N(∧)N bidentate) or cyclometalated (C(∧)N(∧)N tridentate). The electronic properties of these complexes were subsequently studied and compared by spectroscopic and electrochemical analyses and theoretical calculations. These complexes exhibit substantial absorption in the visible to NIR (near-infrared) region because of mixed MLCT (metal-to-ligand-charge-tranfer) transitions from both the ruthenium and the platinum centers. Complexes 7 and 9 were found to emit NIR light with higher quantum yields than those of the mono-Ru complex [(bpy)(2)Ru(dpdpz)](2+) (5) and bis-Ru complex [(bpy)(2)Ru(dpdpz)Ru(bpy)(2)](4+) (13). However, no emission was detected from complex 8 or 12 at room temperature in acetonitrile.

Mononuclear and dinuclear ruthenium complexes of 2,3-Di-2-pyridyl-5,6-diphenylpyrazine: synthesis and spectroscopic and electrochemical studies.

Reported here are a new bridging ligand, 2,3-di-2-pyridyl-5,6-diphenylpyrazine (dpdpz), and its complexation with one or two ruthenium atoms. This ligand was designed so that it could bind to metal species in either a N(∧)N bidentate fashion or a C(∧)N(∧)N tridentate mode to form a metallacycle. The reaction between dpdpz and (tpy)RuCl3 (tpy = 2,2':6',2''-terpyridine) afforded C(∧)N(∧)N-type mono- and dinuclear cyclometalated complexes in moderate yields. On the other hand, N(∧)N-type mono- and dinuclear noncyclometalated complexes could be isolated from the reaction of dpdpz with (bpy)2RuCl2 (bpy = 2,2'-bipyridine). An asymmetric diruthenium complex, bridged by dpdpz, was prepared with one ruthenium atom cyclometalated and another one noncyclometalated. The electronic properties of these complexes were probed by electrochemical and spectroscopic techniques. They exhibited multiple reversible redox processes. However, the formal potentials and electrochemical energy gap are greatly dependent on the binding nature and number of ruthenium atoms. As indicated by electrochemical and spectroelectrochemical studies, diruthenium complexes bridged by dpdpz exhibited electronic coupling between the two metal centers. A comparison of the electronic absorption and emission properties of these complexes is also presented.