Tunability of the MIIMIII/MII2 and MIII2/MIIMIII (M = Mn, Co) couples in bis-μ-O,O′-carboxylato-μ-OR bridged complexes

Abstract

A comparison of the electrochemical properties of a series of dinuclear complexes [M(2)(L)(RCO(2))(2)](+) with M = Mn or Co, L = 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp(-)) or 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato (bpbp(-)) and R = H, CH(3), CF(3) or 3,4-dimethoxybenzoate demonstrates: (i) The electron-withdrawing sulfonyl groups in the backbone of bpsmp(-) stabilize the [M(2)(bpsmp)(RCO(2))(2)](+) complexes in their M(II)(2) oxidation state compared to their [M(2)(bpbp)(RCO(2))(2)](+) analogues. Manganese complexes are stabilised by approximately 550 mV and cobalt complexes by 650 mV. (ii) The auxiliary bridging carboxylato ligands further attenuate the metal-based redox chemistry. Substitution of two acetato for two trifluoroacetato ligands shifts redox couples by 300-400 mV. Within the working potential window, reversible or quasi-reversible M(II)M(III)↔ M(II)(2) processes range from 0.31 to 1.41 V for the [Co(2)(L)(RCO(2))(2)](+/2+) complexes and from 0.54 to 1.41 V for the [Mn(2)(L)(RCO(2))(2)](+/2+) complexes versus Ag/AgCl for E(M(II)M(III)/M(II)(2)). The extreme limits are defined by the complexes [M(2)(bpbp)(CH(3)CO(2))(2)](+) and [M(2)(bpsmp)(CF(3)CO(2))(2)](+) for both metal ions. Thus, tuning the ligand field in these dinuclear complexes makes possible a range of around 0.9 V and 1.49 V for the one-electron E(M(II)M(III)/M(II)(2)) couple of the Mn and Co complexes, respectively. The second one-electron process, M(II)M(III)↔ M(III)(2) was also observed in some cases. The lowest potential recorded for the E°(M(III)(2)/M(II)M(III)) couple was 0.63 V for [Co(2)(bpbp)(CH(3)CO(2))(2)](2+) and the highest measurable potential was 2.23 V versus Ag/AgCl for [Co(2)(bpsmp)(CF(3)CO(2))(2)](2+).

Formation of a Metal-to-Nitrogen Bond of Normal Length by a Neutral Sufonamide Group within a Tridentate Ligand. A New Approach to Radiopharmaceutical Bioconjugation

“…Fewer than twenty complexes are known in which tertiary sulfonamides have been shown to bind to metals; 26-33 in all of these reported compounds the sulfonamide N is positioned advantageously by ligand rings. The evidence for angles close to 109.5° (Table 2) clearly indicates that binding to Re I results in sp 2 -to-sp 3 re-hybridization of the tertiary sulfonamide nitrogen.…”

“…Likewise, for complexes with other metals and differing widely in the ligands and geometries, values of 0.38–0.51 Å are typically found. 26,27,32,33 In contrast, for complexes in which the sulfonamide nitrogen is not bound, the out-of-the-plane distances in reported structures typically range from 0.06–0.125 Å. 26,27 …”

“…In almost all cases, the metal-bound tertiary sulfonamide nitrogen and the donors of the adjacent chelate rings occupy the face of an octahedron 26,28,33 or have a similar arrangement in complexes with other geometries. 29,30 In other words, these three N-donor atoms and the metal atom typically do not define a common plane.…”

“…Indeed, these are among the very few crystallographically characterized complexes containing tertiary sulfonamide N donors with any metal. 26-33 In previously reported sulfonamide complexes, the bound sulfonamide is either constrained within a ring system or has elongated bonds. 26-33 …”

High Turnover Catalase Activity of a Mixed‐Valence MnIIMnIII Complex with Terminal Carboxylate Donors

“…Table 1). 9a,12,15a This emphasizes the stabilization of higher oxidation states that is achieved upon introduction of anionic (hard) donors in the coordination sphere of the metal atom. Dubois et al10 observed lowering of oxidation potentials by ca 300 mV in di(μ‐oxo)Mn 2 complexes based on derivatives of the tripodal ligand tris(picolyl)amine, upon replacement of one pyridyl donor moiety by a carboxylate.…”