Synthesis and Characterization of Homo- and Heterodinuclear Complexes Containing the N3M(μ2-SR)3MN3 Core (M = Fe, Co, Ni)

A novel amine-thiolate ligand, H3 3·6HCl (N,N ‘ ,N ‘ ‘-tris-[2-thio-3-aminomethyl-5-tert-butylbenzyl]-1,1,1-tris(aminomethyl)ethane), has been synthesized and used in the preparation of dinuclear complexes of Fe, Co, and Ni. The nonadentate N6S3 ligand H3 3 is formally derived from the symmetric tridentate N2S ligand H1 1 (2,6-bis(aminomethyl)-4-tert-butylthiophenol). It provides two dissimilar octahedral N3S3 and N‘3S3 coordination sites to give complexes with a central N3M(μ 2-SR)3MN‘3 core structure (N and N‘ denote primary and secondary amine nitrogen atoms, respectively). The complexes of H3 3 exist as dinuclear [MII 2(3)]+, [MIIIMII(3)]2+, or [MIII 2(3)]3+ species which are all accessible by chemical or electrochemical reduction/oxidation. The following complexes were isolated as microcrystalline solids: [CoIII 2(3)][ClO4]3 (4b), [NiIIINiII(3)][BPh4]2 (5b), and [FeIIIFeII(3)][BPh4]2 (6b). The chemical and physicochemical properties of the respective species are very similar to those of Fe, Co, and Ni complexes of H1 1, [M2(1)3] n + (M = Co, n = 3, (4a); M = Ni, n = 2 (5a); M = Fe, n = 2 (6a)), and support the formulation of 4b−6b as discrete dinuclear species with a central N3M(μ 2-SR)3MN‘3 core. NMR spectra of diamagnetic cobalt complexes 4a and 4b reveal the complexes to be C 3 h and C 3 symmetric, respectively, in the solution state. The crystal structure determination of [CoIII 2(1)3][Fe(CN)6]·7MeOH·3H2O (4c) (monoclinic, space group C2/c, a = 28.037(2) Å, b = 17.861(1) Å, c = 25.727(2) Å, β = 90.24(1)°, and Z = 8) reveals 4c to consist of dinuclear [CoIII 2(1)3]3+ trications featuring two fac-octahedral N3CoIII(SR)3 units bridged at the thiolate sulfur atoms. Compound 4c represents the first structurally characterized MIII 2 complex of H1 1. The ability of H3 3 to form heterodinuclear complexes is demonstrated with the synthesis of [CoIIINiII(3)][BPh4]2 (7) and its linkage isomer [NiIICoIII(3)][BPh4]2 (8). All complexes undergo two electrochemically and chemically reversible one-electron-transfer reactions which convert the respective [M2(3)] n + species. For MIII 2/MIIIMII (E 1 1/2) and MIIIMII/MII 2 (E 2 1/2): −0.40 V, −0.84 V (M = Co), +0.49 V, +0.05 V (M = Ni), +0.21 V, −0.33 V (M = Fe) vs SCE. Heterodinuclear complexes 7 and 8 also give rise to two consecutive one-electron-transfer processes at E 1 1/2 (NiIII/II) and E 2 1/2 (CoIII/II): +0.55 V, −0.71 V (for 7) and +0.60 V, −0.86 V (for 8), respectively. Comparison of the electrochemical