136668-00-3Relevant academic research and scientific papers
Ligand Redox Noninnocence in [CoIII(TAML)]0/- Complexes Affects Nitrene Formation
De Bruin, Bas,Oudsen, Jean-Pierre H.,Rietdijk, Niels R.,Siegler, Maxime A.,Tepaske, Martijn A.,Tromp, Moniek,Van Der Vlugt, Jarl Ivar,Van Leest, Nicolaas P.,Venderbosch, Bas
, p. 552 - 563 (2020)
The redox noninnocence of the TAML scaffold in cobalt-TAML (tetra-amido macrocyclic ligand) complexes has been under debate since 2006. In this work, we demonstrate with a variety of spectroscopic measurements that the TAML backbone in the anionic complex [CoIII(TAMLred)]- is truly redox noninnocent and that one-electron oxidation affords [CoIII(TAMLsq)]. Multireference (CASSCF) calculations show that the electronic structure of [CoIII(TAMLsq)] is best described as an intermediate spin (S = 1) cobalt(III) center that is antiferromagnetically coupled to a ligand-centered radical, affording an overall doublet (S = 1/2) ground-state. Reaction of the cobalt(III)-TAML complexes with PhINNs as a nitrene precursor leads to TAML-centered oxidation and produces nitrene radical complexes without oxidation of the metal ion. The ligand redox state (TAMLred or TAMLsq) determines whether mono-or bis-nitrene radical complexes are formed. Reaction of [CoIII(TAMLsq)] or [CoIII(TAMLred)]- with PhINNs results in the formation of [CoIII(TAMLq)(Na￠Ns)] and [CoIII(TAMLq)(Na￠Ns)2]-, respectively. Herein, ligand-to-substrate single-electron transfer results in one-electron-reduced Fischer-type nitrene radicals (Na￠Ns-) that are intermediates in catalytic nitrene transfer to styrene. These nitrene radical species were characterized by EPR, XANES, and UV-vis spectroscopy, high-resolution mass spectrometry, magnetic moment measurements, and supporting CASSCF calculations.
Redox-Active Ligand Assisted Multielectron Catalysis: A Case of CoIII Complex as Water Oxidation Catalyst
Du, Hao-Yi,Chen, Si-Cong,Su, Xiao-Jun,Jiao, Lei,Zhang, Ming-Tian
, p. 1557 - 1565 (2018)
Water oxidation is the key step in both natural and artificial photosynthesis to capture solar energy for fuel production. The design of highly efficient and stable molecular catalysts for water oxidation based on nonprecious metals is still a great challenge. In this article, the electrocatalytic oxidation of water by Na[(L4-)CoIII], where L is a substituted tetraamido macrocyclic ligand, was investigated in aqueous solution (pH 7.0). We found that Na[(L4-)CoIII] is a stable and efficient homogeneous catalyst for electrocatalytic water oxidation with 380 mV onset overpotential in 0.1 M phosphate buffer (pH 7.0). Both ligand- and metal-centered redox features are involved in the catalytic cycle. In this cycle, Na[(L4-)CoIII] was first oxidized to [(L2-)CoIIIOH] via a ligand-centered proton-coupled electron transfer process in the presence of water. After further losing an electron and a proton, the resting state, [(L2-)CoIIIOH], was converted to [(L2-)CoIV=O]. Density functional theory (DFT) calculations at the B3LYP-D3(BJ)/6-311++G(2df,2p)//B3LYP/6-31+G(d,p) level of theory confirmed the proposed catalytic cycle. According to both experimental and DFT results, phosphate-assisted water nucleophilic attack to [(L2-)CoIV=O] played a key role in O-O bond formation.
Synthesis and characterization of Co(iii) amidoamine complexes: Influence of substituents of the ligand on catalytic cyclic carbonate synthesis from epoxide and carbon dioxide
Ramidi, Punnamchandar,Gerasimchuk, Nikolay,Gartia, Yashraj,Felton, Charlette M.,Ghosh, Anindya
supporting information, p. 13151 - 13160 (2013/09/12)
A series of amidoamine ligands (1) and their cobalt(iii) complexes (2) were synthesized and characterized by various spectroscopic techniques including 1H-NMR and X-ray crystallographic techniques. X-ray crystallography shows that one of the complexes, 2a, forms a chiral coordination polymer due to bridge formation with Li+ associated with the complex, although the ligand is achiral. Complex 2 was employed for catalytic synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2) in a solvent free condition. A strong influence of the substituents on the ligand 1 was revealed by the varied activity of complex 2. The presence of electron withdrawing groups such as chloro (2b) and nitro (2c) increases the Lewis acidity of the catalyst, which, in turn, enhances the catalytic activity of 2. An electron withdrawing group containing complexes (2b and 2c) showed exceptionally high catalytic activity with a turnover frequency (TOF) of 662 and 602 h-1 respectively at 130°C and 300 psig CO2 pressure. On the other hand, our studies indicate that a catalyst with an electron releasing group (2d) showed relatively lower activity with a TOF of 488 h-1 under similar reaction conditions. Our results show that cobalt(iii) complexes follow the reactivity order of 2d 2a 2c 2b.
Stable highly oxidizing cobalt complexes of macrocyclic ligands
Collins, Terrence J.,Powell, Richard D.,Slebodnick, Carla,Uffelman, Erich S.
, p. 8419 - 8425 (2007/10/02)
The first crystallographically characterized neutral square-planar complex of cobalt in an oxidation state higher than 2+, Co(η44-1), is reported. Structural data for this new class of compounds indicate that the macrocycle in Co(η4-1) is Equation Presented X = Cl, Co(η4-1) X = H, Co(η4-2) X = MeO, Co(η4-3) noninnocent; however, EPR data in toluene at 5.9 K (S = 1/2; g1 = 2.558, g2 = 2.170, g3 = 2.017; A2 ≈ 15 G) show that the metal center is the primary reisdence site of the unpaired electron. Co(η4-1) is a stable, yet potent, oxidant which is soluble in benzene and slightly soluble in pentane. The Co(η4-1)/[CoIII(η4-1)]- couple is reversible and found at 0.550 V vs Fc+/Fc in CH2Cl2 (ca. 1.26 V vs NHE). Co(η4-1) slowly oxidized water, yielding H[CoIII(η4-1)], which may also be prepared by the reaction of [CoIII(η4-1)]- with HBF4. Both the redox and the acid/base chemistries of [CoIII(η4-1)]- are reversible. Electrochemical and EPR data are also presented for Co(η4-2) and Co(η4-3).
