Copper–arene complex tamed by silylene

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Ligand selection unleashes first monomeric [Cu(η⁶-C₆H₆)]⁺ complex

Study to synthesise the first copper cation bound to a benzene ring in an unsupported h6 mode

Source: © Royal Society of Chemistry

Left: Scientists have made the first monomeric copper cation where a copper atom is bound to a benzene ring in an unsupported η6 fashion. Right: Previous studies have suggested that group 11 metal–arene complexes strongly prefer the η2 binding mode

Inorganic chemists working in Spain and India have isolated the first unsupported example of a monomeric copper cation where the copper atom bonds to a benzene ring in the η⁶ bonding mode.

All previous research has suggested that the η¹/ η²bonding modes are overwhelmingly preferred due to repulsion between the central metal d-orbitals and the benzene ring. While tethered examples of the η⁶mode were known, the ability to isolate a monomeric [Cu(η⁶-C₆H₆)]⁺complex was thought to be highly questionable.

Inspired by recent work on silylene–copper bromide complex, [{PhC(NtBu)2 }Si{N(SiMe₃)₂ }]2Cu₂Br₂, a team led by Santiago Alverez, Jorge Echeverría and Shabana Khan at the University of Barcelona and IISER Pune, used increased back donation from the neutral ligand to access [{PhC(NtBu)2SiN(SiMe₃)2 }Cu(η⁶ - C₆H₆ )]⁺[SbF6 ]^–.

Through further experimental study with other ligands and DFT, they found that to favour the η⁶ mode, the co-ordinating ligands had to have π-acceptor characteristics, with a third row donor atom – to minimise steric repulsions – and a small cone angle.