Catalytic activation of dioxygen by oximatocobalt(II) and oximatoiron(II) complexes for catecholase-mimetic oxidations of o-substituted phenols

Cobalt(II) Complexes with Substituted Salen‐Type Ligands and Their Dioxygen Affinity in N,N‐Dimethylformamide at Various Temperatures

“…In more detail, the analysis of the K py data leads to the following conclusions: (i) the order observed for group A complexes, K py (1) Ͼ K py (2) Ͼ K py (3) Ͼ K py (8), reflects the combined electronic and steric effects of an increasing number of methyl and tert-butyl groups, respectively, which increase the electron density and decrease the accessibility of the cobalt center; (ii) the order observed for group B complexes, K py (4) Ͼ K py (5) Ϸ K py (6) Ͼ K py (7), is due to the same sort of effects; (iii) the finding that K py (4) Ͼ K py (6) and K py (5) Ͼ K py (7) demonstrates the (probable) steric effect of two methyl groups on the CH 2 -C(CH 3 ) 2 bridge of 6 and 7, which reduce the accessibility of the cobalt; and (iv) the finding that K py (2) Ͼ K py (3), K py (4) Ͼ K py (5), and K py (6) Ͼ K py (7) can be ascribed to the combined electronic and steric substituent effects of the methyl group and tertbutyl group, respectively, in the para-and ortho-position to the phenolic oxygen.…”

“…As an example, Figure 1 shows the spectral changes associated with the stepwise titration of complex 3 with pyridine in toluene. The (A, [py]) data follow the relationship in Equation (6), which describes monoadduct formation according to Equation (2). The occurrence of a sharp isosbestic point indicates that there is no additional diadduct formation.…”

“…[5] Co(salen) and Co(acacen) can be classified as four-coordinate chelate Co II complexes with an N 2 O 2 set of donor atoms. As shown by the cobaloximes [6] and by Co II complexes with N 4 macrocyclic ligands [7] or with aliphatic N x and N/O chelate ligands, [8,9] an affinity of the cobalt center for dioxygen is also generated by planar N 4 donor systems. For all the O 2 -binding complexes CoL, where L is an N 2 O 2 -or N 4 -type ligand, it is generally found that the interaction of the cobalt with dioxygen is more or less favored by an additional base B (such as pyridine, for example) coordinated in one of the axial positions to form five-coordinate CoL·B.…”

Catechol oxidase and phenoxazinone synthase activity of a manganese(II) isoindoline complex

“…Functional models of catecholase have been extensively studied using copper [29][30][31][32][33][34][35][36][37][38][39], iron [40,41], cobalt [42], manganese [43][44][45], and zinc [37] complexes as catalysts, and free radical such as TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) [46] as initiator, but only a limited number of model systems has been reported in connection with the phenoxazinone synthase [47,48].…”

A functional phenoxazinone synthase model based on dioximatomanganese(II)

“…Important substrate groups have been phenol and catechol derivatives, which provide valuable mechanistic information on processes in living organisms and are sometimes also of synthetic utility. Catechol dioxygenases are involved in the metabolism of aromatic compounds and low-molecular iron complexes are intensively studied as models of the enzyme active center [2][3][4][5][6][7][8]. In addition to dioxygenase activity, enzymes and models also exhibit catecholase activity, a feature of biological importance.…”