Probing intermetallic coupling in dinuclear N-heterocyclic carbene ruthenium(II) complexes

A series of bimetallic N-heterocyclic carbene (NHC) ruthenium(II) complexes were synthesized, which comprise two [RuCl₂(cymene)(NHC)] units that are interlinked via the NHC nitrogens by alkyl chains of different length. Electrochemical characterization revealed two mutually dependent oxidation processes for the complex with a methylene linker, indicating moderate intramolecular electronic coupling of the two metal centers (class II system). The degree of coupling decreases rapidly upon increasing the number of CH₂ units in the linker and provides essentially decoupled class I species when propylene or butylene linkers are used. Electrochemical analyses combined with structural investigations suggest a through-bond electronic coupling. Replacement of the alkyl linker with a p-phenylene group afforded cyclometalated complexes, which were considerably less stable. The electronic coupling in the methylene-linked complex and the relatively robust NHC–ruthenium bond may provide access to species that are switchable on the molecular scale

Bonding of imidazol-2-ylidene ligands in nickel complexes

The bonding of imidazol-2-ylidenes (H2Im) in a series of nickel complexes with seemingly different complex fragment group electronegativities, i.e., [Ni(H2Im)3], [Ni(H2Im)2], [Ni(H2Im)(CO)], [Ni(H2Im)(CO)2], and [Ni(H2Im)(CO)3], was analyzed. This series provides theoretical evidence that the bonding of imidazol-2-ylidene ligands to metal−complex fragments strongly depends on the nature of the ligand environment of the metal complex. An analysis of a series of isostructural complexes D2h- and D2d-M(H2Im)2 with different metals (M = Ni, Pd, Pt) reveals that the bonding also strongly depends on the metal used in the complex