Luminescent iridium(III) porphyrin complexes as near-infrared-emissive biological probes.

We report herein the design, synthesis and characterisation of a series of luminescent iridium(III) porphyrin complexes [Ir(ttp)(CHCHOH)] (Http = 5,10,15,20-tetra-4-tolylporphyrin) (1), [Ir(tpp-Ph-NO)(CO)Cl] (Htpp-Ph-NO = 5-(4-((4-nitrophenoxy)carbonyloxymethyl)phenyl)-10,15,20-triphenylporphyrin) (2), [Ir(tpp-COOMe)(Py)](Cl) (Htpp-COOMe = 5-(4-methoxycarbonylphenyl)-10,15,20-triphenylporphyrin; Py = pyridine) (3) and [Ir(tpp-COOH)(Py)](Cl) (Htpp-COOH = 5-(4-carboxylphenyl)-10,15,20-triphenylporphyrin) (4). All the complexes displayed long-lived near-infrared (NIR) emission attributed to an excited state of mixed triplet intraligand (IL) (π → π*) (porphyrin) and triplet metal-to-ligand charge transfer (MLCT) (dπ(Ir) → π*(porphyrin)) character. The cytotoxicity of the complexes toward HeLa cells was examined by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) assay.

A ratiometric fluorescent probe for real-time monitoring of intracellular glutathione fluctuations in response to cisplatin.

Real-time imaging of fluctuations in intracellular glutathione (GSH) concentrations is critical to understanding the mechanism of GSH-related cisplatin-resistance. Here, we describe a ratiometric fluorescence probe based on a reversible Michael addition reaction of GSH with the vinyl-functionalized boron-dipyrromethene (4,4-difluoro-4-bora-3,4-diaza--indacene or BODIPY) . The probe was applied for real-time monitoring of the fluctuations in GSH levels in cells under cisplatin treatment.

Regulation of an Ambient-Light-Induced Photocyclization Pathway (Norrish-Yang Versus 6π) by Substituent Choice.

Photocyclization, irrespective of whether multiple steps (e.g., Norrish-Yang cyclization) or a single concerted step (e.

Real-time monitoring of newly acidified organelles during autophagy enabled by reaction-based BODIPY dyes.

Real-time monitoring of newly acidified organelles during autophagy in living cells is highly desirable for a better understanding of intracellular degradative processes. Herein, we describe a reaction-based boron dipyrromethene (BODIPY) dye containing strongly electron-withdrawing diethyl 2-cyanoacrylate groups at the α-positions. The probe exhibits intense red fluorescence in acidic organelles or the acidified cytosol while exhibiting negligible fluorescence in other regions of the cell.

Iodine-catalysed transfer hydrogenation of a carbon-carbon σ-bond with water.

Iodine catalysed the transfer hydrogenation of a benzylic C-C σ-bond in [2.2]paracyclophane with water to yield 4,4'-dimethylbibenzyl. The C-C σ-bond was first cleaved by homolytic substitution with iodine radicals to produce a 4,4'-diiodomethylbibenzyl intermediate.

Hydrodebromination of allylic and benzylic bromides with water catalyzed by a rhodium porphyrin complex.

Hydrodebromination of allylic and benzylic bromides was successfully achieved by a rhodium porphyrin complex catalyst using water as the hydrogen source without a sacrificial reductant. Mechanistic investigations suggest that bromine atom abstraction via a rhodium porphyrin metalloradical operates to give the rhodium porphyrin alkyl species and the subsequent hydrolysis of the rhodium porphyrin alkyl species to a hydrocarbon product is a key step to harness the hydrogen from water.

Ligand effect on the rhodium porphyrin catalyzed hydrogenation of [2.2]paracyclophane with water: key bimetallic hydrogenation.

Rhodium porphyrin catalyzed hydrogenation of the aliphatic carbon-carbon σ-bond of [2.2]paracyclophane with water has been examined with a variety of tetraarylporphyrins and axial ligands. Mechanistic investigations show that Rh(ttp)H, which can be derived from the reaction of [Rh(ttp)] with water without a sacrificial reductant, plays an important role in promoting bimetallic reductive elimination to give the hydrogenation product.

Selective Aliphatic Carbon-Carbon Bond Activation by Rhodium Porphyrin Complexes.

The carbon-carbon bond activation of organic molecules with transition metal complexes is an attractive transformation. These reactions form transition metal-carbon bonded intermediates, which contribute to fundamental understanding in organometallic chemistry. Alternatively, the metal-carbon bond in these intermediates can be further functionalized to construct new carbon-(hetero)atom bonds.

Rational Design of Emissive NIR-Absorbing Chromophores: Rh(III) Porphyrin-Aza-BODIPY Conjugates with Orthogonal Metal-Carbon Bonds.

The facile synthesis of Group 9 Rh(III) porphyrin-aza-BODIPY conjugates that are linked through an orthogonal Rh-C(aryl) bond is reported. The conjugates combine the advantages of the near-IR (NIR) absorption and intense fluorescence of aza-BODIPY dyes with the long-lived triplet states of transition metal rhodium porphyrins. Only one emission peak centered at about 720 nm is observed, irrespective of the excitation wavelength, demonstrating that the conjugates act as unique molecules rather than as dyads.

Room temperature carbon(CO)-carbon(α) bond activation of ketones by rhodium(ii) porphyrins with water.

The mild and selective aliphatic C(CO)-C(α) bond activation (CCA) of ketones was successfully achieved at room temperature using rhodium(ii) porphyrins in the presence of H2O. Rh(II)(tmp) (tmp = tetrakismesitylporphyrinate dianion) disproportionates in H2O to generate the highly reactive intermediate Rh(III)(tmp)(OH) for cleaving the C-C bond of ketone, giving up to 90% of Rh(III)(tmp)(COR) and the corresponding oxidized carbonyl product in up to 76% yield within 10 min. Substrate scopes cover aliphatic as well as aromatic ketones.

User-friendly aerobic reductive alkylation of iridium(III) porphyrin chloride with potassium hydroxide: scope and mechanism.

Alkylation of iridium 5,10,15,20-tetrakistolylporphyrinato carbonyl chloride, Ir(ttp)Cl(CO) (1), with 1°, 2° alkyl halides was achieved to give (ttp)Ir-alkyls in good yields under air and water compatible conditions by utilizing KOH as the cheap reducing agent. The reaction rate followed the order: RCl < RBr < RI (R = alkyl), and suggests an SN2 pathway by [Ir(I)(ttp)](-). Ir(ttp)-adamantyl was obtained under N2 when 1-bromoadamantane was utilized, which could only undergo bromine atom transfer pathway.

Base-promoted aryl-bromine bond cleavage with cobalt(II) porphyrins via a halogen atom transfer mechanism.

Aryl-bromine bonds are successfully cleaved by cobalt(II) porphyrins in basic media to give Co(por)Ar (por = porphyrin) in good yields. Mechanistic studies suggested that the aryl-bromine bond is cleaved through a halogen atom transfer mechanism, which is different from the aryl-halogen bond cleavage mechanism with other group 9 metalloporphyrins.

Catalytic carbon-carbon σ-bond hydrogenation with water catalyzed by rhodium porphyrins.

The catalytic carbon-carbon σ-bond activation and hydrogenation of [2.2]paracyclophane with water in a neutral reaction medium is demonstrated. The hydrogen from water is transferred to the hydrocarbon to furnish hydrogen enrichment in good yields.

Metalloradical-catalyzed rearrangement of cycloheptatrienyl to benzyl.

Rh(ttp)(C(7)H(7)) rearranged to give Rh(ttp)(CH(2)Ph) quantitatively at 120 °C in 12 d (ttp = 5,10,15,20-tetratolylporphyrinato dianion). This process is 10(10) faster than for the organic analogue. Mechanistic investigation suggests that a Rh(II)(ttp)-catalyzed pathway is operating.

Mechanistic studies of the reaction of Ir(III) porphyrin hydride with 2,2,6,6-tetramethylpiperidine-1-oxyl to an unsupported Ir-Ir porphyrin dimer.

Reaction of hydrido[5,10,15,20-tetrakis(p-tolyl)porphyrinato]iridium(III) (Ir(ttp)H) (1) with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (2) at room temperature gave a 90% yield of the unsupported iridium(II) porphyrin dimer, Ir(II)(2)(ttp)(2) (3). Kinetic measurements revealed that the oxidation followed overall second-order kinetics: rate = k[Ir(ttp)H][TEMPO], k(25 °C) = 6.65 × 10(-4) M(-1).

Metalloradical-catalyzed aliphatic carbon-carbon activation of cyclooctane.

The aliphatic carbon-carbon activation of c-octane was achieved via the addition of Rh(ttp)H to give Rh(ttp)(n-octyl) in good yield under mild reaction conditions. The aliphatic carbon-carbon activation was Rh(II)(ttp)-catalyzed and was very sensitive to porphyrin sterics.

Carbon-carbon bond activation of 2,2,6,6-tetramethyl-piperidine-1-oxyl by a Rh(II) metalloradical: a combined experimental and theoretical study.

Competitive major carbon-carbon bond activation (CCA) and minor carbon-hydrogen bond activation (CHA) channels are identified in the reaction between rhodium(II) meso-tetramesitylporphyrin [Rh(II)(tmp)] (1) and 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) (2). The CCA and CHA pathways lead to formation of [Rh(III)(tmp)Me] (3) and [Rh(III)(tmp)H] (5), respectively. In the presence of excess TEMPO, [Rh(II)(tmp)] is regenerated from [Rh(III)(tmp)H] with formation of 2,2,6,6-tetramethyl-piperidine-1-ol (TEMPOH) (4) via a subsequent hydrogen atom abstraction pathway.

Rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction.

An interesting rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction was developed. A chiral atropisomeric dipyridyldiphosphane ligand was found to be highly effective in this system. This operationally simple protocol allows both catalyst and reactants to be handled under air without precautions.

An active ferrocenyl triarylphosphine for palladium-catalyzed Suzuki-Miyaura cross-coupling of aryl halides.

Pd-catalyzed Suzuki-Miyaura reaction of aryl chlorides was accomplished through the use of an active ferrocene-based triarylphosphine ligand. This air- and moisture-stable ligand was found to be effective for the cross-coupling of aryl halides at room temperature to 115 degrees C.

A simple and highly efficient P,O-type ligand for Suzuki-Miyaura cross-coupling of aryl halides.

A simple and efficient hemilabile-type phosphine ligand, found to be highly effective in Suzuki-Miyaura cross-coupling of aryl chlorides with generally low Pd-catalyst loading (0.05%), was prepared in one step based on an economically attractive approach from commercially available benzamide starting material.

A new atropisomeric P,N ligand for rhodium-catalyzed asymmetric hydroboration.

A new optically active and large dihedral angle atropisomeric P,N ligand, pyphos, which contains a tertiary phosphine and pyridine moiety, was prepared and resolved through diastereomeric complexation with chiral palladium amine complexes. The hexafluorophosphate salt of the diastereomers were found to be separable by fractional recyrstallization, while the corresponding chloride salt did not. [Rh(COD)pyphos]PF(6) complex was synthesized by metalation of pyphos with [Rh(COD)Cl](2) followed by anion exchange with NH(4)PF(6) in excellent yield, and the target rhodium complex was characterized by single-crystal X-ray crystallography.

Synthesis of beta-Linked Diporphyrins and Their Homo- and Hetero-Bimetallic Complexes.

beta-Meta- and -para-linked diporphyrins have been synthesized from two complementary routes using Suzuki cross-coupling and Adler condensation. Porphyrin boronate 6 cross couples with beta-monobromoporphyrin 2 to give unsymmetrically substituted porphyrin dimer 7c in high yield, and Adler condensation of beta-formylphenyltetraphenylporphyrins 9b,c with aryl aldehydes yields electronically tunable diporphyrins 7a-e. The homo- and hetero-bimetallic complexes 11a-c have been synthesized.

Base and Cation Effects on the Suzuki Cross-Coupling of Bulky Arylboronic Acid with Halopyridines: Synthesis of Pyridylphenols.

Strong base and large size cation have been shown to accelerate the rate and the yield of Suzuki coupling of a sterically bulky boronic acid with halopyridines in DME for the synthesis of pyridylphenols.