The first X-ray crystal structures of mono- and dipyridoimidazolinylidenes are presented, and the size of the carbene N-C-N angles discussed and correlated with the 13C NMR chemical shifts.

Keywords: Catalysis / Cyclic voltammetry / Fluorescence / Heterocycles / Substituent effects 3-Acceptor-substituted and 3,7-bisacceptor-substituted phenothiazines can be synthesized in moderate to excellent yields through Suzuki cross-coupling reactions between phenothiazin-3-yl pinacolyl boronates or phenothiazin-3,7-diyl bis(pinacolyl boronates) and electron-deficient (hetero)aryl halides. The electronic properties of (hetero)aryl-substituted N-methyl phenothiazines (UV/Vis absorption, fluorescence, redox potentials) can be correlated with the computed energies of the frontier molecular orbitals. Nitro-substituted de-

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Starting from the in situ generated free carbenes dipyrido[1,2-c;2′,1′-e]imidazolin-6-ylidene (dipiy) and 2,10-di-tert-butyldipyrido[1,2-c;2′,1′-e]imidazolin-6-ylidene (dipiy tBu), the synthesis of the new carbene complexes [RhCl(COD)(dipiy)] and [RhCl(COD)(dipiy tBu)] can be achieved. Upon chloride abstraction and coordination of phosphine, a very active precursor for the catalytic hydrosilylation of ketones is formed. The reaction was also followed by NMR spectroscopy. In addition the respective CuI(dipiy tBu) complex was synthesized and fully characterized. X-ray structure analysis reveals this compound to be a trimer [CuI(dipiy tBu)]3 with two Cu−Cu bonds in the solid state. However, unlike the imidazolinylidene analogues, this complex and in situ prepared CuX(dipiy) complexes (X = I, Cl) were found to be inactive in the hydrosilylation of ketones.