Ralte Lalrempuia

Synthesis, photo-, and electrochemistry of ruthenium bis(bipyridine) complexes comprising a N-heterocyclic carbene ligand.

Analogues of [Ru(bpy)3](2+) were prepared in which one pyridine ligand site is substituted by a N-heterocyclic carbene (NHC) ligand, that is, either by an imidazolylidene with a variable wingtip group R (R = Me, 3a; R = Et, 3b; R = iPr, 3c), or by a benzimidazolylidene (Me wingtip group, 3d), or by a 1,2,3-triazolylidene (Me wingtip group, 3e). All complexes were characterized spectroscopically, photophysically, and electrochemically. An increase of the size of the wingtip groups from Me to Et or iPr groups distorts the octahedral geometry (NMR spectroscopy) and curtails the reversibility of the ruthenium oxidation. NHC ligands with methyl wingtip groups display reversible ruthenium oxidation at a potential that reflects the donor properties of the NHC ligand (triazolylidene > imidazolylidene > benzimidazolylidene). The most attractive properties were measured for the triazolylidene ruthenium complex 3e, featuring the smallest gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the series (2.41 eV), a slightly red-shifted absorption profile, and reasonable excited-state lifetime (188 ns) when compared to [Ru(bpy)3](2+). These features demonstrate the potential utility of triazolylidene ruthenium complexes as photosensitizers for solar energy conversion.

Reactivity of Ir–NSiN Complexes: Ir‐Catalyzed Dehydrogenative Silylation of Carboxylic Acids

This work describes the results from the studies on the potential of [Ir(μ‐Cl)(cod)]2 (cod=1,5‐cyclooctadiene) as metallic precursor for the preparation of Ir(NSiN) complexes (NSiN=fac‐bis‐(pyridine‐2‐yloxy)methylsilyl). The reaction of [Ir(μ‐Cl)(cod)]2 with bis‐(pyridine‐2‐yloxy)methylsilane enabled the synthesis of [Ir(H)(Cl)(NSiN)(η2‐cod)] with an uncommon η2‐coordination mode for the cod ligand. The application of Ir–NSiN species as catalysts precursors for the dehydrogenative silylation of carboxylic acids was also explored. The outcomes from these catalytic studies revealed a clear influence of the ancillary ligand on the catalytic activity of Ir–NSiN species. Thus, whereas [Ir(H)(CF3SO3)(NSiN)(coe)] shows poor catalytic activity, the related complex [Ir(H)(CF3CO2)(NSiN)(coe)] with a trifluoroacetate ligand was demonstrated to be a highly active catalyst precursor.