Synthesis, Structures and Their Application in the Suzuki-Miyaura Cross Coupling Reaction

A series of novel palladium(ii) acetylacetonato complexes bearing mesoionic carbenes (MICs) have been synthesized and characterized. The synthesis of the complexes of type (MIC)Pd(acac)I (MIC = 1-mesityl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (1), 1,4-(2,4,6-methyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (2), 1,4-(2,6-diisopropyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (3); acac = acetylacetonato) via direct metalation starting from the corresponding triazolium iodides and palladium(ii) acetylacetonate is described herein. All complexes were characterized by 1H- and 13C-NMR spectroscopy and high resolution mass spectrometry. Additionally, two of the complexes were characterized by single crystal X-ray crystallography confirming a square- planar coordination geometry of the palladium(ii) center. A delocalized bonding situation was observed within the triazolylidene rings as well as for the acac ligand respectively. Complex 2 was found to be an efficient pre- catalyst for the Suzuki-Miyaura cross coupling reaction between aryl-bromides or -chlorides with phenylboronic acid. View Full-Tex

structural characterization of Pd(II) complexes and their catalytic properties

The exclusive formation of the 1,5-cycloaddition product between azides and alkynes is taken advantage of in generating the first examples of abnormal carbenes from these precursors. This new route provides unprecedented post- functionalization possibilities for such abnormal carbenes

electrochemical properties, electronic structures and catalysis

A mesoionic carbene with a ferrocene backbone is used as a metalloligand to generate the first example of their Fe–Au heterobimetallic complexes. The details of geometric and electronic structures in different redox states and preliminary catalytic results are presented

Structural Characterization and Catalytic Hydrosilylation Reactions

Two series of different Cu(I)-complexes of “click” derived mesoionic carbenes are reported. Halide complexes of the type (MIC)CuI (with MIC = 1,4-(2,6-diisopropyl)-phenyl-3-methyl-1,2,3-triazol-5-ylidene (for 1b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene (for 1c)) and cationic complexes of the general formula [Cu(MIC)2]X (with MIC =1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = CuI2− (for 2á), 1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2a), 1,4-(2,6-diisopropyl)phenyl-3-methyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2b), 1-benzyl-3-methyl-4-phenyl-1,2,3-triazol-5-ylidene, X = BF4− (for 2c)) have been prepared from CuI or [Cu(CH3CN)4](BF4) and the corresponding ligands, respectively. All complexes were characterized by elemental analysis and standard spectroscopic methods. Complexes 2á and 1b were studied by single-crystal X-ray diffraction analysis. Structural analysis revealed 2á to adopt a cationic form as [Cu(MIC)2](CuI2) and comparison of the NMR spectra of 2á and 2a confirmed this conformation in solution. In contrast, after crystallization complex 1b was found to adopt the desired neutral form. All complexes were tested for the reduction of cyclohexanone under hydrosilylation condition at elevated temperatures. These complexes were found to be efficient catalysts for this reaction. 2c was also found to catalyze this reaction at room temperature. Mechanistic studies have been carried out as well

Imidazolyl‐Substituted Benzo‐ and Naphthodithiophenes as Precursors for the Synthesis of Transient Open‐Shell Quinoids

The synthesis of three novel imidazolyl-substituted sulfur-containing heteroacenes is reported. These heteroacenes consisting of annelated benzo- and naphthothiophenes serve as precursors for the generation of open-shell quinoid heteroacenes by oxidation with alkaline ferric cyanide. Spectroscopic and computational experiments support the formation of reactive open-shell quinoids, which, however, quickly produce paramagnetic polymeric material

Influencing the coordination mode of tbta (tbta = tris[(1-benzyl- 1H-1,2,3-triazol-4-yl)methyl]amine) in dicobalt complexes through changes in metal oxidation states

The complexes [(tbta)Co(μ-CA-2H)Co(tbta)(CH3CN)](BF4)21 and [(tbta)Co(μ-OH)2Co(tbta)](BF4)42 (tbta = tris[(1-benzyl- 1H-1,2,3-triazol-4-yl)methyl]amine and CA = chloranilic acid) were synthesized and characterized by X-ray crystallography, SQUID magnetometry and NMR spectroscopy. The reactions to form these complexes deliver 1 as a paramagnetic species containing two high spin Co(II) centers, and 2 as a diamagnetic compound with two low spin Co(III) centers. Structural analysis shows that in 1 the capped-octahedral environment around the Co(II) centers is highly distorted with rather long bonds between the metal and donor atoms. The tbta ligand binds to the Co(II) centers through the three triazole nitrogen donor atoms in a facial form, with the Co–N(amine) distance of 2.494(2) Å acting as a capping bond to the octahedron. In the crystal an unusual observation of one acetonitrile molecule statistically occupying the coordination sites at both Co(II) centers is made. 1 displays a series of intermolecular C–HCl and π–π interactions leading to extended three- dimensional structures in the solid state. These interactions lead to the formation of voids and explain why only one acetonitrile molecule can be bound to the dinuclear complexes. In contrast to 1, the cobalt centers in 2 display a more regular octahedral environment with shorter cobalt–donor atom distances, as would be expected for a low spin Co(III) situation. The tbta ligand acts as a perfect tetradentate ligand in this case with the cobalt–N(amine) distance of 2.012(3) Å falling in the range of a normal bond. Thus, we present the rare instances where the ligand tbta has been observed to bind in a perfectly tetradentate fashion in its metal complexes. The room temperature magnetic moment of 6.30 μB for 1 shows values typical of two high spin Co(II) centers, and this value decreases at temperatures lower than 30 K indicating a weak antiferromagnetic coupling and zero field splitting. Mass spectrometric analysis of 2 provided evidence for the formation of an oxo- bridged dicobalt complex in the gas phase

Influencing the coordination mode of tbta (tbta = tris[(1-benzyl- 1H-1,2,3-triazol-4-yl)methyl]amine) in dicobalt complexes through changes in metal oxidation states

The complexes [(tbta)Co(μ-CA-2H)Co(tbta)(CH3CN)](BF4)21 and [(tbta)Co(μ-OH)2Co(tbta)](BF4)42 (tbta = tris[(1-benzyl- 1H-1,2,3-triazol-4-yl)methyl]amine and CA = chloranilic acid) were synthesized and characterized by X-ray crystallography, SQUID magnetometry and NMR spectroscopy. The reactions to form these complexes deliver 1 as a paramagnetic species containing two high spin Co(II) centers, and 2 as a diamagnetic compound with two low spin Co(III) centers. Structural analysis shows that in 1 the capped-octahedral environment around the Co(II) centers is highly distorted with rather long bonds between the metal and donor atoms. The tbta ligand binds to the Co(II) centers through the three triazole nitrogen donor atoms in a facial form, with the Co–N(amine) distance of 2.494(2) Å acting as a capping bond to the octahedron. In the crystal an unusual observation of one acetonitrile molecule statistically occupying the coordination sites at both Co(II) centers is made. 1 displays a series of intermolecular C–HCl and π–π interactions leading to extended three- dimensional structures in the solid state. These interactions lead to the formation of voids and explain why only one acetonitrile molecule can be bound to the dinuclear complexes. In contrast to 1, the cobalt centers in 2 display a more regular octahedral environment with shorter cobalt–donor atom distances, as would be expected for a low spin Co(III) situation. The tbta ligand acts as a perfect tetradentate ligand in this case with the cobalt–N(amine) distance of 2.012(3) Å falling in the range of a normal bond. Thus, we present the rare instances where the ligand tbta has been observed to bind in a perfectly tetradentate fashion in its metal complexes. The room temperature magnetic moment of 6.30 μB for 1 shows values typical of two high spin Co(II) centers, and this value decreases at temperatures lower than 30 K indicating a weak antiferromagnetic coupling and zero field splitting. Mass spectrometric analysis of 2 provided evidence for the formation of an oxo- bridged dicobalt complex in the gas phase

Catalytic oxygenation of sp3 “C-H” bonds with Ir(III) complexes of chelating triazoles and mesoionic carbenes

Cp*-Ir(III) complexes with additional chelating ligands are known active pre- catalysts for the oxygenation of C–H bonds. We present here eight examples of such complexes where the denticity of the chelating ligands has been varied from the well-known 2,2′-bpy through pyridyl-triazole, bi-triazole to ligands containing pyridyl-triazolylidene, triazolyl-triazolylidene and bi- triazolylidenes. Additionally, we also compare the catalytic results to complexes containing chelating cyclometallated ligands with additional triazole or triazolylidene donors. Single crystal X-ray structural data are presented for all the new complexes that contain one or more triazolylidene donors of the mesoionic carbene type. We present the first example of a metal complex containing a chelating triazole-triazolylidene ligand. The results of the catalytic screening show that complexes containing unsymmetrical donors of the pyridyl-triazole or pyridyl-triazolylidene types are the most potent pre- catalysts for the C–H oxygenation of cyclooctane in the presence of either m-CPBA or NaIO4 as a sacrificial oxidant. These pre-catalysts can also be used to oxygenate C–H bonds in other substrates such as fluorene and ethyl benzene. The most potent pre-catalysts presented here work with a lower catalyst loading and under milder conditions while delivering better product yields in comparison with related literature known Ir(III) pre-catalysts. These results thus point to the potential of ligands with unsymmetrical donors obtained through the click reaction in oxidation catalysis

(Electro)catalytic C-C bond formation reaction with a redox-active cobalt complex

Cooperativity between cobalt and non-innocent ligands in electron transfer processes has been utilized for (electro)catalytic C–C bond formation reactions

Half-Sandwich Ir(III) and Os(II) Complexes of Pyridyl-Mesoionic Carbenes as Potential Anticancer Agents

A series of cationic chlorido arene-iridium(III) and arene-osmium(II) complexes with bidentate pyridyl functionalized mesoionic carbenes (MIC) of the 1,2,3-triazol-5-ylidene type have been prepared. The variations in the ligand structures include the position of the pyridyl substituent relative to the triazolylidene ring (N-wingtip vs C-wingtip), phenyl versus ethyl substituents, and incorporation of several functional groups at the phenyl substituents. Five complexes have been characterized by X-ray structural analysis. All complexes, including osmium(II) and ruthenium(II) analogues having a pyrimidyl in place of the pyridyl group, have been studied for their cytotoxic activity on a human cervical carcinoma HeLa cell line. Two of the compounds, Ir5 and Ir9, were the most cytotoxic with IC50 values of 7.33 μM and 2.01 μM, respectively. Examination of their cytotoxic effect on different cell lines revealed that they preferentially kill cancer over normal cells. The Ir5 and Ir9 compounds arrested cells in G2 and induced a dose-dependent increase in SubG0/G1 cell population. Apoptosis, as the primary mode of cell death, was confirmed by Annexin V/PI staining, detection of cleaved PARP, and caspases 3 and 7 activity upon treatment of HeLa cells with both compounds. The higher toxicity of Ir9 is probably due to its increased accumulation in the cells compared to Ir5. The role of glutathione (GSH) in the protection of cells against Ir5 and Ir9 cytotoxicity was confirmed by pretreatment of cells either with buthionine sulfoximine (inhibitor of GSH synthesis) or N-acetyl-cysteine (precursor in GSH synthesis)