Molecular Manipulations of a Utility Nitrogen–Heterocyclic Carbene by Sodium Magnesiate Complexes and Transmetallation Chemistry with Gold Complexes

• Published in: Chemistry : a European journal 2018-07, Vol.24 (41), p.10541-10549
• Main Authors: Hernán‐Gómez, Alberto, Uzelac, Marina, Baillie, Sharon E., Armstrong, David R., Kennedy, Alan R., Fuentes, M. Ángeles, Hevia, Eva
• Format: Article
• Language: English
• Subjects: Carbenes; Chemistry; cooperative effects; Gold; Ligands; Magnesium; Methylation; mixed metal; Molecular chains; N-heterocyclic carbenes; Nitrogen; Organic chemistry; Sodium; Structural analysis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201802008

Expanding the scope and applications of anionic N‐heterocyclic carbenes (NHCs), a novel series of magnesium NHC complexes is reported using a mixed sodium–magnesium approach. Sequential reactivity of classical imidazol‐ 2‐ylidene carbene IPr with NaR and MgR2 (R=CH2SiMe3) affords [(THF)3Na(μ‐IPr−)MgR2(THF)] (2) [IPr−=:C{[N(2,6‐iPr2C6H3)]2CHC] containing an anionic NHC ligand, whereas surprisingly sodium magnesiate [NaMgR3] fails to deprotonate IPr affording instead the redistribution coordination adduct [IPr2Na2MgR4] (1). Compound 2 undergoes selective C2‐methylation when treated with MeOTf furnishing novel abnormal NHC complex [{aIPrMeMgR2}2] (3). Dissolving 3 in THF led to the dissociation of this complex into MgR2 and aIPrMe with the latter isomerizing to the olefinic NHC IPr=CH2. The ability of 2 and 3 to transfer their anionic and abnormal NHC ligands, respectively to AuI metal fragments has been investigated allowing the isolation and structural characterization of [RAu(μ‐IPr−)MgR(THF)2] (4) and [aIPrMeAuR] (5) respectively. In both cases transfer of an alkyl R group is observed. However while 3 can also transfer its abnormal NHC ligand to give 5, in 4 the anionic NHC still remains coordinated to Mg via its C4 position, whereas the {AuR} fragment occupies the C2 position previously filled by a donor‐solvated {Na(THF)3}+ cation. Normal or abnormal, it's still gold! Novel NHC stabilised AuI alkyl complexes have been accessed via a transmetallation approach based on a mixed Na/Mg platform containing an anionic NHC as a precursor.