Generation and characterization of [(P)M-(X)-Co(TMPA)]n+ assemblies; P = Porphyrinate, M = FeIII and CoIII, X = O2-, OH-, O2(2-), and TMPA = tris(2-pyridylmethyl)amine

Abstract

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 mu-oxo, micro-hydroxo, and micro-peroxo (micro-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 mu-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; angleFe-O-Co = 171.6 degrees and d(Fe...Co) = 3.58 A. Complex 1 was further characterized by UV-vis (lambdamax = 437 (Soret) and 557 nm), 1H NMR [delta 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 (microeff = 3.1), and superconducting quantum interference device (SQUID) susceptometry (J = -114 cm-1, S = 1). The micro-hydroxo analogue [(F8TPP)FeIII-(OH)-CoII(TMPA)]+ (2) [UV-vis lambdamax = 567 nm; delta 78 ppm (pyrrole-H); Evans NMR microeff = 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 micro-peroxo species, a dicobalt micro-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 degrees C [UV-vis lambdamax = 435 (Soret), 548, and 583 (weak) nm; silent EPR spectrum; diamagnetic NMR spectrum]. The oxygenation/deoxygenation equilibrium is reversible; warming solutions of 3 releases approximately 1 equiv of O2 and the reduced complexes are reformed.