Synthesis and Reactivity of Manganese(II) Complexes Containing N‑Heterocyclic Carbene Ligands

A series of manganese­(II) complexes containing aryl-substituted N-heterocyclic carbene (NHC) ligands have been synthesized and characterized. Chloride complexes of Mn­(II) containing the NHC ligands 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr) and 1,3-dimesitylimidazol-2-ylidene (IMes) were prepared in straightforward fashion by direct carbene addition to MnCl₂(THF)_1.6. These complexes exist as chloride-bridged dimers in solution of formula [Mn₂Cl₂(μ-Cl)₂(NHC)₂]. The monomeric complex [MnCl₂(IMes)₂] has also been prepared and structurally characterized, although NMR studies are consistent with facile dissociation of one of the IMes ligands in solution. [Mn₂Cl₂(μ-Cl)₂(IPr)₂] serves as a precursor to dimeric alkyl and aryl compounds of Mn­(II) including [Mn₂R₂(μ-Cl)₂(NHC)₂] (R = Bn, <i>o</i>-tolyl, and Ph) and the bridging methyl complex [Mn₂Me₂(μ-Me)₂(IPr)₂]. Stoichiometric reactions of these hydrocarbyl species with bromocyclohexane demonstrate that they are not chemically competent in C–C coupling reactions involving alkyl electrophiles