Cobalt Corroles with Bis‐Ammonia or Mono‐DMSO Axial Ligands. Electrochemical, Spectroscopic Characterizations and Ligand Binding Properties

Abstract

Four bis-ammonia ligated cobalt corroles and four mono-DMSO ligated cobalt corroles with different meso-aryl substituents on the macrocycle (A 2 B-and A 3 -corroles) were synthesized and investigated as to their electrochemical and spectroscopic properties under different solution conditions. The complexation energies of the investigated cobalt corroles were [a] Scheme 2. Structures of the investigated bis-ammonia and mono-DMSO meso-aryl cobalt corroles. dinated form of A 3 -and/or A 2 B-cobalt corroles) which will bind CO. Very recently, concentrations of CO as low as a few hundred ppb were measured by SAW sensors emphasizing the interest of such sensors for the detection of carbon monoxide. [4] Scheme 3. Synthesis of mono-DMSO and bis-NH 3 cobalt corroles.The eight cobalt corroles 1DMSO-4DMSO and 1NH 3 -4NH 3 were prepared according to the synthetic procedure shown in Scheme 3. The A 3 -and A 2 B-free-base corroles 1H-4H were synthesized according to published procedures described by Gryko and co-workers, [5] and metallated with Co(OAc) 2 in DMSO to give the cobalt complexes 1DMSO-4DMSO, each with a single DMSO molecule as axial ligand. These mono-DMSO adducts were then treated with an aqueous ammonia solution to give the bis-ammonia derivatives 1NH 3 -4NH 3 in 79-94 % yield. Spectroscopic Characterization1DMSO-4DMSO were measured at a concentration of 10 -3 M in both CH 2 Cl 2 and DMSO containing 0.1 M TBAP (Figure 2). In CH 2 Cl 2 the spectra are characterized by a Soret band at 379-387 nm and a single less intense band at 562-566 nm. There is also a shoulder on the Soret band at about 414-417 nm. These spectra are similar to previously reported UV/Vis spectra for a related series of mono-DMSO ligated cobalt nitrophenylcorroles under the same solution conditions. [3] Similar spectral patterns are seen for 2DMSO, 3DMSO and 4DMSO in the two solvents but this is not the case for 1DMSO as seen in Figure 2. The spectrum in CH 2 Cl 2 (Figure 2a) is assigned to the mono-DMSO adduct while in DMSO a mixture of the five-and six-coordinate derivatives are proposed to exist, the hexa-coordinate DMSO adduct having bands at 417, 442, 453 and 618 nm as described on the following pages. It should be noted that 1DMSO is the only cobalt corrole among the currently investigated compounds which possesses six electronwithdrawing substituents on the meso-phenyl rings, and this seems to facilitate the binding of a second DMSO molecule to the cobalt center of the neutral compound. Stronger pyridine binding constants were also earlier reported for cobalt corroles with electron-withdrawing substituents on the meso-phenyl rings. [3] UV/Visible spectra of the bis-ammonia complexes 1NH 3 -4NH 3 were also measured at a concentration of 1 × 10 -3 M un-Eur.(CO 2 MePh)Mes 2 CorCo(DMSO) (2DMSO): 88 % yield (211 mg). UV/ Visible (toluene, 1 % DMSO): λ max (ε × 10 -3 L·mol -1 cm -1 ) 383 (62.9), 563 (13.1) nm. 1 H NMR [500 MHz, CDCl 3 + NH 3 (g)]: δ = 8.98 (d,

Old Dog, New Tricks: Innocent, Five-coordinate Cyanocobalt Corroles

“…Although the same final [(Ar) 3 CorCo II ] − product is formed in both cases, the difference in thermodynamic half-wave potentials for the one-electron addition can be significant, varying by as much as 1.0 V depending on the type of axial ligand and specific Ar substituents. 38,48,58 One problem with elucidating the effect of axial coordination on the redox potentials of hexacoordinate cobalt corroles is the lability of the axial ligand(s) in solution, which results in a concentration-dependent complexation where one, or both, ligands dissociate in dilute solutions. In search of nonlabile coordinating ligands, we recently investigated the possible binding of anionic ligands to neutral cobalt triarylcorroles and found that 10 of the 11 investigated anionic ligands (PF 6 − , BF 4 − , HSO 4 − , ClO 4 − ,B r − ,I − ,C l − , OAc − ,F − , OTs − ) were unable to bind to the cobalt center of the neutral complex, with the only exception being CN − , where a stepwise formation of both mono-and bis-CN adducts was observed in solutions of CH 2 Cl 2 (eqs 3 and 4).…”

Selective and Additive‐Free Hydrogenation of Nitroarenes Mediated by a DMSO‐Tagged Molecular Cobalt Corrole Catalyst

“…With the intention to provide the cobalt central atom of complex 1 in a low oxidation state to foster the hydrogenation process, [12a] we conducted the nitrobenzene reduction in the presence of solid reducing agents such as Zn, Mn, and Mg. Rewardingly, the pertinent reaction also proceeded well without external reductants and moreover, the catalytic system did not benefit in any way from the addition of acids or bases (Table S4). If ammonia was added to a solution of 1 in ethanol, formation of the known bis(ammine) cobalt corrole complex was observed [25b] which, however, proved to be inactive in the target transformation. These experimental findings provided compelling reasons that the given Co‐catalyzed nitroarene hydrogenation is best performed without any additives.…”

Porous organic polymers based on cobalt corroles for carbon monoxide binding

“…Tetrakis(4-ethynylphenylmethane) 2, 55 corrole 1 59 and metallocorrole 3 37 were prepared according to previously published procedures. Additional information is given in the Supporting Information.…”

“…ammonia acting as a protecting group. 37 Interestingly, ammine ligands are sufficiently labile to be easily removed by gentle heating under vacuum to lead to the "active" tetracoordinated cobalt corroles without any bound ligand in apical position. Such square planar complex constitutes the active species of cobalt corroles for CO bonding on the metal center.…”

“…We have very recently addressed this problem and shown that cobalt corroles can be stabilized and easily isolated in air atmosphere without any degradation when the coordination sphere of the metal center is fulfilled with one or two labile axial ligands chosen between DMSO or ammonia, these latter acting as "protecting groups". 37 In addition, the binding properties of CO on metallocorroles is still poorly understood but is relevant with respect to the ubiquity of this gas in polluted air. Permanent porosity and stability are prerequisites for various applications of a material for gas separation or sensing.…”