Exploring the Chemistry of Ruthenium Complexes with a Bidentate Barbiturate‐Imidazo[1,5‐a]pyridinylidene Ligand
A novel reactivity of 5‐barbiturate imidazo[1,5‐a]pyridinium 1⋅H with [Ru(2‐methylallyl)2(COD)] was explored which led to the formation of an uncommon, zwitterionic complex [Ru(1’)(1⋅H)], composed of the NHC ligand 1’, cyclometallated at one ortho‐methyl position of the N‐mesityl substituent, and the zwitterionic precursor 1⋅H. Barbiturate moieties coordinate either through a η3 mode or through coordination of the anionic oxygen atom to ensure the coordination saturation and stability to the complex. The addition of pivalic acid results in the protonolysis of the Ru‐Calkyl bond and demetallation of the N‐mesityl, while triphenylphosphine and pyridine are able to displace the rather labile 1⋅H ligand. Attempts to incorporate an alkylidene fragment from these complexes led to the isolation of a rare complex 7 bearing an alkylidene tethered to a η5‐cyclopentadienyl ligand formed by phenylacetylene tetramerization.
