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Reactions of a series of unsymmetrically substituted N-heterocyclic carbene ligands with Ru3(CO)12afforded a variety of mononuclear (1, 2), trinuclear (3, 4, 5, and 5′), and tetranuclear (6, 7) ruthenium complexes via intramolecular ruthenium-mediated sp2and sp3C–H bond activations. Complexes 6and 7include an octahedral cluster skeleton consisting of four ruthenium atoms and two metalated carbon atoms. The formation of this type of ruthenium clusters is proposed to involve the initial C–C double-bond migration and subsequent sp2C–H bond activations. All new complexes were fully characterized, and the molecular structures of 1, 2, 5, 6, and 7were determined by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

The electronic structures and photophysical properties of eight Pt-complexes with different N-heterocyclic carbene ligands and potential to serve as light emitting diode materials were investigated by density functional theory and time-dependent density functional theory, employing the BP86 functional for geometry optimisations, SAOP potential for excited state calculations and all-electron TZ2P basis set throughout. Non-radiative and radiative decay rate constants were determined for each system through analyses of the geometric relaxations, d-orbital splitting and spin–orbit couplings at the optimised S0and T1geometries. Three Pt-systems bound to two N-heterocyclic carbenes were shown to be nonemissive, while a fourth was shown to be emissive from the T1excited state. Similar T1-initated emission was observed for three other Pt-systems investigated, each bound to four N-heterocyclic carbenes, while a fourth similarly tetra-ligated system showed T2-initation of emission. The results highlight the coupling of ligand-identity to photophysical properties and more importantly, the potential for rational optimisation and tuning of emission wavelengths and phosphorescent efficiencies. Encouragingly, two of the tetra-N-heterocyclic carbene ligated systems show strong potential to serve as highly-efficient blue and green light emitting materials, respectively. [ABSTRACT FROM AUTHOR]

Thermal treatment of indenyl-functionalized imidazolium salts and N-heterocyclic carbenes with Ru3(CO)12gave different products. The normal mononuclear metal complexes (2a, 2b) were obtained viadirect reaction of indenyl-functionalized imidazolium salts (1a, 1b) with Ru3(CO)12. Unexpected intramolecular C–H activated products (3a, 3b, 4a, 4b) were obtained viathermal treatment of corresponding indenyl-functionalized N-heterocyclic carbenes. All complexes were determined by 1H NMR, 13C NMR, IR spectra and elemental analysis. The molecular structures of 2b, 3a, 3band 4bwere determined by X-ray diffraction. [ABSTRACT FROM AUTHOR]

The intramolecular sp2and sp3C–H activated products, as well as the monometalated products, based on the “(p-cymene)Ru(NHC)” framework were synthesised by treatment of a series of NHCs (1-R-3-methylimidazol-2-ylidene [R = Ph (1), Bn (2), t-Bu (3), i-Pr (4), Mes (5), Cy (6)] and 1,3-bis(isopropyl)imidazol-2-ylidene (7)) with [(p-cymene)RuCl2]2under mild conditions. A new NHC precursor (1-tert-butyl-3-phenyl-4,5-dihydro-imidazol-2-ylidene) was also designed to compare the reactivity of sp2C–H and sp3C–H bonds upon cyclometalation, and only the sp3C–H activated product (8) was observed. The factors that possibly determine the selectivity of intramolecular sp2or sp3C–H activation are elucidated by a series of experiments. In the cases where activation of both sp2C–H and sp3C–H is possible, steric factors overrode the others to dominate the regioselectivity of activation. All complexes were characterised by 1H NMR, 13C NMR and HRMS spectra. The molecular structures of 1, 3, 5, 6, 7, and 8were confirmed by X-ray diffraction. [ABSTRACT FROM AUTHOR]

Carbenes are known for their ability to abstract HCl from hydrochlorosilanes to form carbene hydrochloride adducts. In contrast, the Si-H bond insertion products RSiCl2(cAACH) (2, 4, 6, and 8) have been formed in the reaction of RSiHCl2 [R = Ar(SiMe3)N (1), Cp* (3), PhC(NtBu)2 (5), Cl (7); Ar = 2,6-iPr2C6H3] with a cyclic alkyl(amino) carbene (cAAC:) irrespective of the steric demand of the R group. The new products have been characterized by various analytical tools including X-ray crystallography, electron ionization mass spectrometry, and NMR spectroscopy. Theoretical investigations have also been performed to understand why cAAC prefers insertion into the Si-H bond rather than the dehydrohalogenation pathway. [ABSTRACT FROM AUTHOR]