The N-alkyphosphine-substituted benzimidazoles 5 (R = methylenedicyclohexylphosphine), 7 (R = ethylene-di(tBu)phosphine), and 8 (R = ethylenedicyclohexylphosphine) have been prepared. The benzimidazoles react with [RhCl(COE)2]2 in the presence of tertiary phosphines under formal tautomerization of the benzimidazole and chelating coordination of the resulting bidentate NH,NR-NHC/phosphine ligand (P∧C) to give complexes [RhCl(P∧C)PR3] [6]–[9]. Depending on the steric demand of the PR3, the phosphines of the P∧C ligands, and on the spacer linking the benzimidazole ring nitrogen atom to the alkylphosphine, complexes with cis-P,P and trans-P,P geometry have been obtained and crystallographically characterized.

Phosphorescent PtII complexes featuring pincer luminophores of 2,6‐bis(1,2,4‐triazolyl)pyridine (H2L1) and 2,6‐bis(pyrazolyl)pyridine (H2L3) with a bulky adamantyl or tolyl substituent (H2L4) are systematically compared, and their structural features are correlated with their photophysical properties. The combination with 4‐amylpyridine (Py), triphenylphosphine (P) or benzimidazol‐2‐ylidene (N‐heterocyclic carbene, NHC) donors as monodentate ancillary ligands gave a series of highly luminescent triplet emitters with variable aggregation properties. The molecular structures of four of these complexes, namely, Pt‐L1‐P, Pt‐L1‐NHC, Pt‐L3‐P, and Pt‐L4‐P were garnered from single‐crystal X‐ray diffraction analysis. The coordination complexes displayed green phosphorescence in solution and in the solid state. In doped poly(methyl methacrylate) (PMMA) matrices, most of the complexes exhibited high phosphorescence quantum yields, which reached 59 % for Pt‐L3‐P. A comparative analysis between the spectroscopic data and the computed parameters derived from time‐dependent density functional theory (TD‐DFT) calculations suggests that the emission originates from metal‐perturbed ligand‐centered excited triplet states (3MP‐LC). The radiationless deactivation rate constants of the emissive states can be correlated with the aggregation properties derived from the substitution pattern at the tridentate luminophores and the ancillary ligands, whereas the radiative rate constants are determined by the electronic structures of the complexes. We found that PtII complexes containing pyrazolate donors showed an enhanced charge‐transfer character in the excited state, whereas bulky adamantyl moieties and triphenylphosphine ancillary ligands suppress bimolecular aggregation and quenching phenomena.

A new series of ruthenium(II) carbonyl complexes with benzene-based CCC-pincer bis-(carbene) ligands, [((R)CCC(R))Ru(CO)2(X)](0/+) and [((R)CCC(R))Ru(CO)(NN)](+) ((R)CCC(R) = 2,6-bis-(1-alkylimidazolylidene)benzene, R = Me or (n)Bu; X = I, Br, CH3CN, or 6-(aminomethyl)pyridine (ampy); NN = 2·CH3CN, or chelating ampy or bipyridine), was synthesized and fully characterized. X-Ray structure determinations revealed that these eight complexes have pseudo-octahedral configurations around the ruthenium center with the pincer ligand occupying three meridional sites. These complexes prove to be efficient precatalysts demonstrating very good activity and reusability for the transfer hydrogenation of ketones.

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