1,2,3-Triazole-derived mesoionic biscarbenes bridged by a pyridylene group were synthesized and their structures were determined. Bulky substituents on the carbene rings stabilized the carbenes, which enabled their crystal structures to be determined. As implied by DFT calculations and the experimen-

A dinuclear copper(i) complex bearing a mesoionic carbene ligand has been prepared from the corresponding silver analogue and its structure determined spectroscopically. The results revealed that two Cu(i) halide salt molecules were bound to the carbon atoms of the pyridine-bridged bis(triazolylidene) moieties rather than the pyridine. Cyclic voltammogram measurements revealed that the two Cu(i) centres underwent a stepwise oxidation, suggesting that both the triazolylidene rings of the ligand could be on the same expanded π-conjugated system. The catalytic hydroboration of styrene derivatives with bis(pinacolato)diborane in the presence of this complex allowed for the β-selective formation of the corresponding alkylboronate esters.

structure of pyridine-bridged 1,2,3-triazol-5-ylidene (3a, 3b), which are prepared from the corresponding bis(1,2,3-triazole) (1a, 1b) as the starting material, via the methylated bis(1,2,3-triazolium) salts (2a, 2b). The compounds 2a and 2b are easily reduced to form 3a and 3b, respectively, in good yields (Scheme 2) [23]. They are rare examples of the isolated MIC. The X-ray crystallography and DFT calculations of 3a indicated its characteristic amphiphilic nature; because it has an expanded π-conjugated plane including one pyridine and two carbene rings, the stabilized π*-orbital easily accept a single unpaired electron to form anionic radical species in part, despite the fact that carbene carbons are strong σ-donor [24]. Here, we successfully synthesized and determined the tridentate MIC complex of iron. Unexpectedly, even if stoichiometric amount of the carbene ligand was added to iron halides, two molecules of the carbene coordinated to form dicationic homoleptic iron complex 4 with stepwise liberation of two halide anions from iron halides. Materials and Methods All experiments were carried out under an inert gas atmosphere using standard Schlenk techniques and a glove box (MBraun UniLab) unless otherwise noted. THF, toluene, hexane, and benzene-d 6 were distilled from benzophenone ketyl and stored under a nitrogen atmosphere. Organic reagents used for coupling reactions were distilled just before use. The starting materials, 2,6-bisacetylpyridine [25] and 2-azido-2,6-diisopropylbenzene [26] were prepared according to the literature. 1 H NMR (400 MHz) and 13 C NMR (100 MHz) spectra were recorded on a Bruker AVANCE III HD 400 MHz spectrometer at room temperature in CDCl 3 or acetonitrile-d 3. Chemical shifts (δ) were recorded in ppm from the internal standard. IR spectra were recorded in cm-1 on a PERKIN ELMER Spectrum Two spectrometer equipped with a universal diamond ATR.

Iron complexes bearing 1,2,3-triazol-5-ylidene were synthesized and applied to reaction with hydrosilane and homogeneous catalytic hydrosilylation of aromatic aldehydes. Addition of a free carbene to a solution of FeBr2(CO)4 yielded...