Cationic Arylmanganese(II) Derivatives Occurring in Ion-Pair Forms with Tetraphenylborate Anions: Synthetic, Structural, and Magnetic Studies

We report a class of cationic manganese(II) aryl compounds stabilized by weak donor solvents or by interactions with the counteranion BPh4- to form ion-pair species. The parent compound used was Mn3Mes6 (1; Mes = 2,4,6-Me3C6H2), which can be synthesized on a large scale by a conventional method and conveniently used as starting material. Reaction of 1 with BPh3 in Et2O gave the cationic derivative [MesMn(OEt2)3]+BPh4- (2), containing a single Mn-C bond and three weakly bonded Et2O molecules. In order to avoid coordinating solvent, the reaction between 1 and BPh3 was then carried out in toluene. This reaction gave, depending on the reaction time and the BPh3/Mn ratio, the monomeric [MesMn(η3-Ph)2-BPh2] (3) and the dimeric [Ph2B(η2-Ph)2(μ-MnPh) 2(η2-Ph)2BPh2] (4) ion pairs. Temperature-dependent magnetic measurements showed that for 1 and 4 a strong antiferromagnetic coupling exists between the d5 ions brought about by the bridging aryl groups and/or the short Mn⋯Mn distance (2.851(2) Å, 1; 2.796(1) Å, 4). Such a coupling, much greater than that observed in several Mn(II)-Mn(II) dimers, has J values of 55.4 cm-1 (complex 4) and 40.4 cm-1 (complex 1). Crystallographic details: 1 is triclinic, space group P1, with a = 12.850(3) Å, b = 20.327(4) Å, c = 11.407(3) Å, α = 95.11(2)°, β = 114.00(2)°, γ = 98.77(2)°, Z = 2, and R = 0.052; 2 is triclinic, space group P1, with a = 11.237(2) Å, b = 19.035(2) Å, c = 10.991(1) Å, α = 99.30(1)°, β = 106.66(1)°, γ = 104.58(1)°, Z = 2, and R = 0.070; 3 is monoclinic, space group P21/n, with a = 10.070(1) Å, b = 15.901(1) Å, c = 20.876(2) Å, β = 101.94(1)°, Z = 4, and R = 0.054; 4 is monoclinic, space group P21/c, with a = 15.074(4) Å, b = 13.289(4) Å, c = 20.139(5) Å, β = 98.39(2)°, Z = 4, and R = 0.055.