Abstract
Previous theoretical and experimental endeavors suggested that [Cu(C6H6)]+ prefers the η1/η2 mode over the η6 mode due to the augmented repulsion between the benzene ring and metal d-electrons. Nevertheless, the use of silylene as a neutral ligand has led to the isolation of the first monomeric copper cation, [{PhC(NtBu)2SiN(SiMe3)2}Cu(η6-C6H6)]+[SbF6]- (3), where a copper atom is bound to the benzene ring in an unsupported η6 fashion. However, the use of IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) in place of silylene results in the formation of [IPr·Cu(η2-C6H6)]+[SbF6]- (6), where the copper atom is bound to the benzene ring in the η2 mode. The discrepancy in hapticities is also reflected when hexamethylbenzene is employed as the arene ring. The silylene supported copper cation continues to bind in the η6 mode in 2 while the NHC copper cation displays an η3 bonding mode in 5. DFT calculations are carried out to understand how the use of silylene led to the η6 binding mode and why IPr afforded the η2 binding mode.
Highlights
Synthetic chemists o en nd fascination in isolating a compound that has been theoretically predicted as well as observed in the gas phase but never realized under laboratory conditions
To further test the relative in uence of steric repulsions and non-covalent interactions on the hapticity of the coordinated arenes we have carried out energy decomposition analysis (EDA) for 3 and 6 (Table 2), as well as for the hypothetical complex 60 in which the benzene is forced to be coordinated in an h6 mode
This study was undertaken to synthesize the rst copper cation bound to the benzene ring in an unsupported h6 mode
Summary
Synthetic chemists o en nd fascination in isolating a compound that has been theoretically predicted as well as observed in the gas phase but never realized under laboratory conditions. Single crystal X-ray studies on 5 and 6 indicated h3 and h2 coordination[12] of the Cu atom with the arene rings, respectively (Fig. 3) (please see S3 in the ESI† for the deduction of hapticities in 5 and 6).
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