Molecular Manipulations of a Utility Nitrogen–Heterocyclic Carbene by Sodium Magnesiate Complexes and Transmetallation Chemistry with Gold Complexes. Issue 41 (19th June 2018) - Hernán‐Gómez, Alberto
Abstract: 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=CH2 SiMe3 ) affords [(THF)3 Na(μ‐IPr − ) MgR2 (THF)] (2 ) [IPr − =:C{[N(2, 6‐ i Pr2 C6 H3 )]2 CHC] containing an anionic NHC ligand, whereas surprisingly sodium magnesiate [NaMgR3 ] fails to deprotonateIPr affording instead the redistribution coordination adduct [IPr 2 Na2 MgR4 ] (1 ). Compound2 undergoes selective C2‐methylation when treated with MeOTf furnishing novel abnormal NHC complex [{ a IPr Me MgR2 }2 ] (3 ). Dissolving3 in THF led to the dissociation of this complex into MgR2 and a IPr Me with the latter isomerizing to the olefinic NHCIPr=CH2 . The ability of2 and3 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 while3 can also transfer its abnormal NHC ligand to give5, in4 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. Abstract : Normal or abnormal, it's still gold ! Novel NHC stabilised Au I alkyl complexes have been accessed via a transmetallation approach based on a mixed Na/Mg platform containing an anionic NHC as a precursor.