Cyanosilylation of Aromatic Aldehydes by Cationic Ruthenium(II) Complexes of Benzimidazole-Derived O‑Functionalized N‑Heterocyclic Carbenes at Ambient Temperature under Solvent-Free Conditions

A series of ruthenium complexes,
namely, [{1-(N-R1-2-acetamido)-3-(R2)-benzimidazol-2-ylidine}­Ru­(p-cymene)­Cl]­Cl,
where {R1 = 2,6-(i-Pr)2C6H3, R2 = i-Pr (1c); R1 = 2,6-(i-Pr)2C6H3, R2 = Et (2c);
R1 = 2,4,6-(CH3)3C6H2, R2 = Et (3c)}, of benzimidazole-derived
N/O-functionalized N-heterocyclic carbene ligands successfully carried
out the cyanosilylation reaction of aromatic aldehydes and heteroaryl
aldehydes with trimethylsilyl cyanide, providing good to excellent
yields (ca. 60–95%) at room temperature under solvent-free
condition. The ruthenium (1–3)c complexes were synthesized from the silver (1–3)b analogues in ca. 67–80%
yields. The silver (1–3)b complexes exhibited an argentophilic d10···d10 interaction in
its dinuclear macrometallacyclic motif, as observed by a short Ag···Ag
contact of 3.1894(3) Å in single-crystal X-ray diffraction studies
for a representative silver complex 2b and also in photoluminescence
studies that showed characteristic emission band(s) at ca. 534–536
nm in the CHCl3 solution and at ca. 482–487 and
530–533 nm in the solid state.