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 (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 MgR 2 (R=CH 2 SiMe 3 ) affords [(THF) 3 Na(μ‐ IPr − ) MgR 2 (THF)] ( 2 ) [ IPr − =:C{[N(2,6‐ i Pr 2 C 6 H 3 )] 2 CHC] containing an anionic NHC ligand, whereas surprisingly sodium magnesiate [NaMgR 3 ] fails to deprotonate IPr affording instead the redistribution coordination adduct [ IPr 2 Na 2 MgR 4 ] ( 1 ). Compound 2 undergoes selective C2‐methylation when treated with MeOTf furnishing novel abnormal NHC complex [{ a IPr Me MgR 2 } 2 ] ( 3 ). Dissolving 3 in THF led to the dissociation of this complex into MgR 2 and a IPr Me with the latter isomerizing to the olefinic NHC IPr=CH 2 . 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 [ a IPr Me AuR] ( 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.