Infrared Spectra of CX₃–AuCl and CX₂–AuCl₂ Generated in Reactions of Laser-Ablated Gold Atoms with Chlorofluoromethanes and Carbon Tetrachloride

Laser-ablated gold atoms have been reacted with CF₃Cl, ¹³CF₃Cl, CF₂Cl₂, CFCl₃, CCl₄, and ¹³CCl₄ in excess argon during condensation, and the CX₃–AuCl (X = F, Cl) insertion products are generated. In the reactions of CFCl₃ and CCl₄ the methylidene complexes (CXCl–AuCl₂) are also produced, and CFCl–AuCl₂ is interconvertible with the insertion product CFCl₂–AuCl upon photolysis. The tetrachloroauric insertion and methylidene complexes are energetically comparable and also structurally close to each other. These products reveal that C–Cl insertion by Au readily occurs, consistent with our previous Au investigations, and subsequent X migration also follows in case the methylidene is energetically reachable. The C–Au bonds of the insertion and methylidene complexes are comparable, unlike those of the previously studied transition-metal systems, and NBO results also show that the methylidene C–Au bond (B3LYP computed 2.04 Å) is a effectively a single bond. Evidently the gold atom with filled 5d and 4f orbitals cannot accommodate a π system for a methylidene-like complex without larger stabilizing/conjugating ligands on carbon.