Manganese(III) aryls of stoichiometry Mn(Mes)X2(PMe3)2 (Mes = 2,4,6-trimethylphenyl) can be prepared by the reaction of MnX2 (X = Cl, Br, I) with 1/2 equiv of Mg(Mes)2(thf)2 in the presence of PMe3 followed by oxidation with O2. The X-ray crystal structure of Mn(Mes)Br2(PMe3)2 reveals a trigonal-bipyramidal geometry with the phosphines in the axial sites and the mesityl and halide ligands in the equatorial plane: Mn-C = 2.089 (8) Å, Mn-P = 2.426 (3) Å, Mn-Br = 2.497 (2) Å. The intermediates present in solution prior to oxidation with O2 have been identified by EPR spectroscopy as manganese(II) monomesityl complexes of stoichiometry Mn(Mes)X(PMe3)2 or [Mn(Mes)X2(PMe3)−]. Addition of a further 1/2 equiv of Mg(Mes)2(thf)2 to the monomesityl intermediates gives the manganese(II) diaryl species Mn(Mes)2(PMe3)2, which has been isolated as a crystalline material. Attempts to prepare MnIII aryls directly from Mn(acac)3 lead instead to MnII products such as the o-tolyl complex [Li(tmed)2]2[Mn(o-C6H4Me)4]. Similarly, treatment of Mn(acac)3 with sodium cyclopentadienide leads to the formation of MnII products and not to the manganese(III) species NaMnCp4 as previously claimed. Crystal data (Mo Kδ, λ = 0.71073 Å) for Mn-(Mes)Br2(PMe3)2: space group P21/n with a = 8.956 (3) Å, b = 25.228 (8) Å, c = 9.472 (3) Å, β = 100.29 (3)°, V = 2106 (1) Å3, Z = 4, T = 299 K, RF = 0.050, and RwF = 0.048 for 182 variables and 1835 data.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry