The silver complex of the tripodal N-heterocyclic carbene ligand TIME Me , [(TIME Me ) 2 Ag 3 ]-(PF 6 ) 3 (3), reacts with copper(I) bromide and (dimethyl sulfide)gold(I) chloride to yield the corresponding D 3 -symmetrical copper(I) and gold(I) complexes [(TIME Me ) 2 Cu 3 ](PF 6 ) 3 (4) and [(TIME Me ) 2 Au 3 ](PF 6 ) 3 (5). Single-crystal X-ray diffraction, spectroscopic, and computational studies of this series of metal NHC complexes are described. The group 11 metal complexes of the TIME Me ligand exhibit isostructural geometries, with three metal ions bridging two of the TIME Me ligands. Each metal ion is linearly coordinated to two carbene centers, with each of the carbenoid carbons stemming from a different ligand. Overall, the molecules possess D 3 symmetry. The electronic structure of these newly synthesized compounds was elucidated with the aid of DFT calculations. In contrast to the common assumption that NHCs are pure σ-donor ligands, our calculations reveal the existence of both σ-and π-type interactions between the metal ions and the carbenoid carbons. A study of the closely related D 2d -symmetrical species Pd(CN 2 Bu t 2 C 2 H 2 ) 2 (6) and the simplified D 2h -symmetrical model complexes M(IM Me C:) 2 (8-10; M ) Ag, Cu, Au) allowed for quantitative comparison of the two different types of bonding interactions. It was found that π-back-bonding interactions in these diaminocarbene model species contribute to approximately 15-30% of the complexes' overall orbital interaction energies.

The synthesis and spectroscopic characterization of the mononuclear uranium complex [((ArO)(3)tacn)U(III)(NCCH(3))] is reported. The uranium(III) complex reacts with organic azides to yield uranium(IV) azido as well as uranium(V) imido complexes, [((ArO)(3)tacn)U(IV)(N(3))] and [((ArO)(3)tacn)U(V)(NSi(CH(3))(3))]. Single-crystal X-ray diffraction, spectroscopic, and computational studies of this analogous series of uranium tris-aryloxide complexes supported by triazacyclononane are described. The hexadentate, tris-anionic ligand coordinates to the large uranium ion in unprecedented fashion, engendering coordinatively unsaturated and highly reactive uranium centers. The macrocyclic triazacyclononane tris-aryloxide derivative occupies six coordination sites, with the three aryloxide pendant arms forming a trigonal plane at the metal center. DFT quantum mechanic methods were applied to rationalize the reactivity and to elucidate the electronic structure of the newly synthesized compounds. It is shown that the deeply colored uranium(III) and uranium(V) species are stabilized via pi-bonding interaction, involving uranium f-orbitals and the axial acetonitrile and imido ligand, respectively. In contrast, the bonding in the colorless uranium(IV) azido complex is purely ionic in nature. The magnetism of the series of complexes with an [N3O3-N(ax)] core structure and oxidation states +III, +IV, and +V is discussed in context of the electronic structures.

A reactive low-valent uranium(III) complex supported by an aryloxide functionalised triazacyclononane has been synthesised and provides a platform for enhanced uranium reactivity.