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A bimetallic carbene complex architecture that incorporates a cyclopentadienyl-annulated imidazol-2-ylidene moiety is characterized. The ligand architecture enables direct electronic interaction between the pi- and sigma-bonded metals. A preliminary example of aqueous Suzuki coupling employing a metallocene-fused imidazol-2-ylidene-derived catalyst is described.

A new phenanthrene-fused N-heterocyclic carbene was generated and characterized in solution. The synthesis of air-stable Rh, Ir, and Ag complexes, supported by the new phenanthrene-fused imidazol-2-ylidene ligand, is described. Deprotonation of phenanthrene-fused imidazolium salt 4 in the presence of [M(COD)Cl] 2 (M ) Rh, Ir) afforded complexes 6 and 7 in excellent yields. The silver complex was obtained by reaction of 4 with Ag 2 O. The solid state molecular structures of these complexes have been determined by X-ray diffraction studies. The fluorescence emission spectra of 4, 6, and 7 are compared to that of phenanthrene.

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A zwitterionic ligand yields a trimetallic carbene complex (see structure), in which the metal centers are electronically coupled by a single ligand that employs both σ and π bonding. This imidazol‐2‐ylidene complex, derived from the imidazoliumcyclopentadienide zwitterion, reveals a carbene‐ligand architecture that allows the incorporation of multiple metal and/or main‐group element centers.

A range of carbene structures and their adducts with one another and with a selection of small-molecule electrophiles and nucleophiles were examined at the composite correlated molecular orbital theory G3MP2 level to explore ground-state "carbenic" structures, their stabilities, and reactivities. Differences between carbene general classification as a singlet electrophilic carbene or singlet nucleophilic carbene and their given reactivity are discussed. A key quantity is the carbon−carbon bond dissociation energy for carbene dimers or the carbene-adduct dissociation energy for other species. The carbene dimer bond dissociation energies span a wide range from 10 to 170 kcal/mol. The hydrogenation energies and singlet−triplet splitting were found to correlate best with the carbene's self-dimerization energy, whereas other descriptors do not. The proton and fluoride affinities of the carbenes alone prove inadequate for classifying reactivity among classes of carbenes. The self-dimerization bond dissociation energy, hydrogenation energy, and singlet−triplet splitting of various carbenes, despite sometimes large differences in proton affinity and other indicators of reactivity, provide usable metrics to correlate substantial amounts of thermodynamic and kinetic (reactivity) information regarding these structures.

Ein zwitterionischer Ligand bildet einen Trimetall‐Carbenkomplex (siehe Struktur), dessen Metallzentren durch den im σ‐ und π‐Modus bindenden Liganden elektronisch gekoppelt sind. Die Architektur des Carbenliganden ist entscheidend für den Einbau mehrerer Metall‐ und/oder Hauptgruppenelementzentren in diesem Imidazol‐2‐yliden‐Komplex.

The synthesis of bis[(3a,4,5,6,6a-η)-1,3,4,5,6-pentamethylcyclopenta[d]imidazo-2-thionoyl]iron(II) is reported. Structural determination of the unusual hetero-substituted metallocene by X-ray crystallographic analysis is described. Preliminary electrochemical studies reveal that oxidation and reduction potentials for the subject ferrocene lie midway between those of ferrocene and decamethylferrocene.