Molecular manipulations of a utility nitrogen-heterocyclic carbene by sodium magnesiate complexes and transmetallation chemistry with gold complexes

Expanding the scope and applications of anionic N‐heterocyclic carbenes (NCHs), 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 Au(I) 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.