Search

An evidence for the formation of a rare meta-metalated inherently chiral calix[4]arene is described. Our strategy involved using a mesoionic carbene to direct C–H activation, but proved to form an unexpectedly unstable intermediate that was identified through high-resolution mass spectrometry. On route to our target, a new optimized method to mononitrocalix[4]arenes was developed, including optimized and high yielding transformations to azide and 1,2,3-triazole derivatives which may have application in other areas of research.

Mesoionic carbenes (MIC) of the 1,2,3-triazol-5-ylidene type are currently popular ligands in organometallic chemistry. Their use in main group chemistry has been rather limited. In this contribution we present mono- and di-MIC-boranes with MICs based on triazolylidenes. The synthesis involves in-situ deprotonation of the corresponding triazolium salts and their reaction with boranes to form the desired compounds. Whereas this reaction route worked well for all triazolium salts derived from the 1,4-regioisomer of the triazoles, for the methlyene-bridged bi-triazolium salt derived from a 1,5-substiuted triazole, we observed the unexpected decomposition of the bi-triazolium and the formation of a triazole-borane with a new N−B bond. All compounds were characterized via multinuclear NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction. Furthermore, the MIC-boranes were used as reducing agents for the reduction of the C=O of aldehydes to the corresponding alcohols.

We present herein anionic borate‐based bi‐mesoionic carbene compounds of the 1,2,3‐triazol‐4‐ylidene type that undergo C−N isomerization reactions. The isomerized compounds are excellent ligands for CoII centers. Strong agostic interactions with the “C−H”‐groups of the cyclohexyl substituents result in an unusual low‐spin square planar CoII complex, which is unreactive towards external substrates. Such agostic interactions are absent in the complex with phenyl substituents on the borate backbone. This complex displays a high‐spin tetrahedral CoII center, which is reactive towards external substrates including dioxygen. To the best of our knowledge, this is also the first investigation of agostic interactions through single‐crystal EPR spectroscopy. We conclusively show here that the structure and properties of these CoII complexes can be strongly influenced through interactions in the secondary coordination sphere. Additionally, we unravel a unique ligand rearrangement for these classes of anionic mesoionic carbene‐based ligands., C−N isomerization reactions on borate‐based anionic bi‐mesoionic carbene ligands are reported. The CoII complexes with these ligands display geometries, spin states, and reactivities that are controlled by agostic interactions in the secondary coordination sphere.

A novel complex featuring a mesoionic carbene [Fe2(CO)5(trz)(?-pdt)] (1) (trz = 1-phenyl-l,3-methyl,4-butyl-1,2,3-triazol-5-ylidene), was synthesized and spectroscopically and structurally characterized. The reductive behaviour of this compound in the presence and in the absence of acid (CH3CO2H) was examined by cyclic voltammetry (CV) that revealed the lack of efficient activity towards proton reduction.

A strong σ-donor mesoionic carbene ligand has been synthesized and applied to four different palladium-catalyzed cross-coupling transformations, proving the catalyst/medium compatibility and the increased activity of this system over previous reports in Deep Eutectic Solvent medium. Some cross-coupling processes could be carried out at room temperature and using aryl chlorides as starting materials. The possible implementation of multistep synthesis in eutectic mixtures has also been explored. The presence of palladium nanoparticles in the reaction media has been evaluated and correlated to the observed activity. This work was supported by the Spanish Ministerio de Economía, Industria y Competitividad (CTQ2015-66624-P and PGC2018-096616-B-I00) and the University of Alicante (VIGROB-316).

We demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by AuI and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au–C(alkyne) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom.

none 7 no Two phosphorescent Ir(III) complexes bearing a mesoionic carbene ligand based on 1,2,3-triazolylidene are obtained for the first time. A silver−iridium transmetalation of the in situ-generated mesoionic carbene affords the cationic dichloro complex [Ir(trizpy)2Cl2]+ (3, trizpy = 1-benzyl-3- methyl-4-(pyridin-2-yl)-1H-1,2,3-triazolylidene) that reacts with a bis-tetrazolate (b-trz) dianionic ligand to give [Ir(trizpy)2(b-trz)]+ (5). The new compounds are fully characterized by NMR spectroscopy and mass spectrometry, and the X-ray structure of 3 is determined. The electrochemical behavior is somewhat different compared to most standard cationic iridium complexes. The first oxidation process is shifted to substantially higher potential in both 3 and 5, due to peculiar and different ligand-induced effects in the two cases, which stabilize the highest occupied molecular orbital; reduction processes are centered on the mesoionic carbene ligands. Both compounds exhibit a mostly ligand-centered luminescence band in the blue-green spectral region, substantially stronger in the case of 5 versus 3, both in CH3CN solution and in poly(methyl methacrylate) matrix at room temperature. Optimized geometries, orbital energies, spin densities, and electronic transitions are determined via density functional theory calculations, which support a full rationalization of the electrochemical and photophysical behavior. This work paves the way for the development of Ir-based emitters with neutral mesoionic carbene ligands and anionic ancillary ligands, a new concept in the area of cationic Ir(III) complexes. none Baschieri, Andrea; Monti, Filippo; Matteucci, Elia; Mazzanti, Andrea; Barbieri, Andrea; Armaroli, Nicola; Sambri, Letizia Baschieri, Andrea; Monti, Filippo; Matteucci, Elia; Mazzanti, Andrea; Barbieri, Andrea; Armaroli, Nicola; Sambri, Letizia

(-) Menthol was converted to 1-menthyl-3-methyl-4-phenyltriazolium iodide and 1-neomethyl-3-methyl-4-phenyltriazolium iodide in four steps. These triazolium salts that are enantio pure but diastereo isomers, served as precursors for the synthesis of the corresponding enantio pure bis(1,2,3-triazol-5-ylidene)PdI2 complexes with menthyl and neomenthyl wing tip groups. The palladium complexes were synthesized in high yields using a recently developed mild method under base free and silver free conditions at ambient temperature. These triazolium salts also served as precursors for the synthesis of the corresponding enantio pure PEPPSI type (1,2,3-triazol-5-ylidene) (pyridine)PdI2 complexes. All the complexes were thoroughly characterized by spectroscopic and single crystal XRD data. The relative catalytic activities of these complexes were compared for Suzuki-Miyaura C-C coupling. � 2015 Elsevier B.V. All rights reserved.

A series of PEPPSI-type palladium(II) complexes was synthesized that contain 3-chloropyridine as an easily removable ligand and a triazolylidene as a strongly donating mesoionic spectator ligand. Catalytic tests in Suzuki–Miyaura cross-coupling reactions revealed the activity of these complexes towards aryl bromides and aryl chlorides at moderate temperatures (50 °C). However, the impact of steric shielding was the inverse of that observed with related normal Nheterocyclic carbenes (imidazol-2-ylidenes) and sterically congested mesityl substituents induced lower activity than small alkyl groups. Mechanistic investigations, including mercury poisoning experiments, TEM analyses, and ESI mass spectrometry, provide evidence for ligand dissociation and the formation of nanoparticles as a catalyst resting state. These heterogeneous particles provide a reservoir for soluble palladium atoms or clusters as operationally homogeneous catalysts for the arylation of aryl halides. Clearly, the substitution of a normal N-heterocyclic carbene for a more basic triazolylidene ligand in the precatalyst has a profound impact on the mode of action of the catalytic system. European Research Council Science Foundation Ireland