A square-planar Pt(II) complex with a pyridine-based pincer-type N-heterocyclic carbene ligand, [PtII(C∧N∧C)(Cl)]Cl (C∧N∧C = 2,6-bis(1-butylimidazol-2-ylidenyl)pyridine), was synthesized as a new type of emitter and structurally characterized. The complex shows aquachromic photoluminescence in the solid state upon hydration and dehydration.

A pyridine-based pincer-type N-heterocyclic carbene complex of Pt(II), [Pt(II)(mesC∧N∧C)CO](PF6)2 (mesC∧N∧C = 2,6-bis(1-mestylimidazol-2-ylidenyl)pyridine), displays size-selective vapochromic behavior upon exposure to small molecules with donor atoms. An acetone adduct showing a weak interaction between acetone and a CO ligand is also structurally determined.

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The methylenebis(N-alkylimidazolium) halides are converted to dialkylbiimidazoles by cuprous oxide with concurrent C−N bond cleavage and C−C bond formation. This unusual C−N bond cleavage is proposed to involve a Cu(I)−NHC (N-heterocyclic carbene) complex. The reaction is unique, as it involves C−H bond activation, C−N bond cleavage, and C−C bond formation.

Platinum complexes featuring pyridine bis-N-heterocyclic-imidazol-2-ylidene/-mesoionic-triazol-5-ylidene donors as pincer ligands and chloro (-Cl), acetonitrile (-NCCH3) or cyano (-CN) groups as auxiliary ligands are prepared as highly strained organometallic phosphors. X-ray structures of four of these complexes confirm a distorted square planar geometry, where the pincer ligand and its mesityl wingtips occur in a twisted conformation to each other. Electrochemical and photophysical characterization have been carried out and the experimental results are interpreted with the aid of density functional theory calculations. Emission responses of complexes under exposure to different vapors and mechanical shear are reported. Notably, the platinum complex featuring pyridine bis-imidazol-2-ylidene and a weakly donating acetonitrile auxiliary ligand exhibited strong aquachromic and mechanochromic emission responses, showing color changes from sky blue to green or yellow-green.

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Pd(II) complexes [PdBr(A-κ(3)CNC)]Br (1) and [PdBr(B-κ(3)CNC)]Br (2) with new CNC pincer-type ligands derived from 1,2,4-triazolin-5-ylidenes have been synthesized and characterized by multinuclei NMR spectroscopies, ESI mass spectrometry and X-ray diffraction analysis. The more soluble complex 1 proved to be an efficient pre-catalyst in copper- and amine-free Sonogashira reaction with high turnover numbers. The potential for recycling of the catalyst was also demonstrated.

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