Generation and Characterization of [(P)M−(X)−Co(TMPA)]<i>ⁿ</i>⁺ Assemblies; P = Porphyrinate, M = Fe^III and Co^III, X = O^2-, OH^-, O₂^2-, and TMPA = Tris(2-pyridylmethyl)amine

With the established chemistry of bridged [(porphyrinate)FeIII−X−CuII(ligand)]n+ [X = O2- (oxo), OH- (hydroxo), O22- (peroxo)] complexes, we investigated the effect of cobalt ion substitution for copper or copper and iron. Thus, in this report, the generation and characterization of new μ-oxo, μ-hydroxo, and μ-peroxo (μ-X) assemblies of [(porphyrinate)MIII−X−CoII/III(TMPA)]n+ assemblies is described, where M = FeIII or CoIII and TMPA = tris(2-pyridylmethyl)amine. The μ-oxo complex [(F8TPP)FeIII−O−CoII(TMPA)]+ (1, F8TPP = tetrakis(2,6-difluorphenyl)porphyrinate) was isolated by an acid−base self-assembly reaction of a 1:1 mixture of (F8TPP)FeIII−OH and [CoII(TMPA)(MeCN)]2+ upon addition of triethylamine. The crystal structure of 1·2C4H10O proved the presence of an unsupported Fe−O−Co moiety; ∠Fe−O−Co = 171.6° and d(Fe···Co) = 3.58 Å. Complex 1 was further characterized by UV−vis (λmax = 437 (Soret) and 557 nm), 1H NMR [δ 40.6 (pyrrole-H), 8.8 and 8.7 (m-phenyl-H), 8.0 (p-phenyl-H), 4.4 (PY-4H), 2.6 (PY-3H), 1.0 (PY-5H), −1.1 (PY-6H), and −2.7 (TMPA−CH2−) ppm], electrospray ionization (ESI) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric methods, Evans method NMR (μeff = 3.1), and superconducting quantum interference device (SQUID) susceptometry (J = −114 cm-1, S = 1). The μ-hydroxo analogue [(F8TPP)FeIII−(OH)−CoII(TMPA)]+ (2) [UV−vis λmax = 567 nm; δ 78 ppm (pyrrole-H); Evans NMR μeff = 3.7] was generated by addition of 1 equiv of triflic acid to 1. The protonation is completely reversible, and 1 is regenerated from 2 by addition of triethylamine. While (F8TPP)FeII/[CoII(TMPA)(MeCN)]2+/O2 chemistry does not lead to a stable μ-peroxo species, a dicobalt μ-peroxo complex [(TPP)CoIII−(O22-)−CoIII(TMPA)]2+ (3, TPP = meso-tetraphenylporphyrinate) forms from a reaction of O2 with a 1:1 mixture of the CoII precursor components at −80 °C [UV−vis λmax = 435 (Soret), 548, and 583 (weak) nm; silent EPR spectrum; diamagnetic NMR spectrum]. The oxygenation/deoxygenation equilibrium is reversible; warming solutions of 3 releases ∼1 equiv of O2 and the reduced complexes are reformed.