Synthesis, Characterization, and Electrochemical Behavior of (5,10,15-Tri-X-phenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III) Triphenylphosphine Complexes, Where X = p-OCH3, p-CH3, p-Cl, m-Cl, o-Cl, m-F, or o-F

Abstract

PC)Co(PPh3), where X = /7-OCH3, p-CH3, p-C 1, m-Cl, m-F, o-Cl, o-F, or H, were synthesized and characterized in nonaqueous media using electrochemical, spectroelectrochemical, and EPR techniques. The o-Cl derivative exists as different atropisomers in solution, and a thermal interconversion between them was achieved at 338 K in toluene. Activation parameters (AS*, AH*) for interconversion between the atropisomers were obtained from NMR measurements and were similar in magnitude to values reported for ortho-substituted tetraphenylporphyrin derivatives. Formation constants for pyridine binding to the pentacoordinated cobalt(III) corroles in benzene were obtained from UV-visible spectrophotometric measurements and ranged between 20 and 193 M-1, with the exact value depending upon the specific electron-donating or electron-withdrawing group on the three phenyl rings of the complex. The redox potentials of (OMTXPC)Co(PPh3) also shift with the nature of the phenyl ring substituents, and linear ffee-energy relationships are observed. Each cobalt(III) derivative undergoes two oneelectron reductions, the first of which involves a Co(IH)/Co(II) conversion and concomitant loss of the bound PPI13 ligand. Four one-electron oxidations are also observed for the investigated compounds, and this contrasts with the oxidative properties of related cobalt(II) porphyrins which undergo a maximum of three one-electron oxidations under similar solution conditions. The first one-electron oxidation of each cobalt(III) corrole is metalcentered and results in formation of a Co(IV) corrole as ascertained by EPR spectroscopic characterization of the electrogenerated species.

Synthesis and Structural Characterization of a Novel Covalently-Bound Corrole Dimer

“…(4) ± (7)]. OD 0 is the calculated absorption that would have been obtained if there was no dissociation of 4 (e(4) 108 000 m À1 cm À1 ) to 5 and OD is the experimental value at given K diss [py] [5]/ [4] (4) [5] [py] (OD 0 À OD)/(e(5) À e(4)) DOD/De …”

“…The latter observation is analogous to previous findings with triphenylphosphine-coordinated cobalt complexes of other corroles. [6] Based on the analysis of Kadish and co-workers, [5] we assign the first reduction of 2 to a Co III /Co II couple and the irreversibility of the process to dissociation of triphenylphosphine from the cobalt(ii) complex ([Co(tpfc)PPh 3 ] À 3 [Co(tpfc)] À PPh 3 ). The first oxidation (E 1/2 0.58 V) and second reduction (E 1/2 À 1.25 V) processes are also reversible for the bis-pyridine complex 4.…”

“…While Conlon et al have reported a substitution reaction as to form monoamine cobalt(iii) corroles, [4a] Adamian et al analyzed their results as simple addition of the amines to the vacant coordination site of [Co(cor)PPh 3 ]. [5] Using a different synthetic route, Murakami et al have isolated both a fourcoordinate cobalt(iii) corrole and its mono-pyridine adduct and shown that the six-coordinate bis-pyridine adduct is only formed in solutions that contain excess pyridine. [4b] Another aspect that has been intensively investigated with cobalt corroles is their electrochemistry, [6] with the clear conclusion that in the absence of coordinated PPh 3 their oxidation process is irreversible.…”

High-valent transition metal corrolazines

“…These square planar complexes were also observed to be paramagnetic, and were formulated as containing a high-spin Co III ion. A number of other Co III corroles have been characterized crystallographically as 5-coordinate compounds with axial PPh 3 ligands of the structure Co III (b-R 8 -meso-Ar-corrolate)(PPh 3 ) (R = H, Ar = Ph [48,49]; R = Me, Ar = Ph [50]; R = Me, Ar = 4-Cl-Ph [51]) and as the 6-coordinate bis-pyridine complex Co III (TETPC)(py) 2 (TETPC, 7,8,12,13-tetraethyl-2,3,17,18-tetraphenylcorrolate) [52]. All of these compounds are diamagnetic, as expected for low-spin Co III .…”

“…In situ EPR measurements on the electrochemical oxidation product of Co III (OMTPC)(PPh 3 ) (OMTPC = b-octamethyl-meso-triphenylcorrolate) gave a spectrum with rhombic symmetry (g 1 = $2.14, g 2 = 2.002, and g 3 = $1.89), and a 10 G splitting of the central line (by the I = 1/2 31 P nucleus). The authors concluded that this complex contained a Co IV ion rather than a Co III p-cation radical [51]. Despite the limited number of isolable Co IV corroles, electrochemical oxidation of a wide range of Co III corroles indicate that higher-valent species are readily accessible, however this oxidation may be occurring at the macrocycle rather than at the metal center [38,48,51,52,65].…”