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, o-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.