A Structural Strategy for Generating Rapid Electron-Transfer Kinetics in Copper(II/I) Systems

Abstract

Electron-transfer in low molecular weight copper(II/I) systems is generally accompanied by a large reorganization of the inner-coordination sphere. On the basis of recent kinetic studies involving Cu(II/I)-macrocyclic polythiaether complexes, it was hypothesized that forcing Cu(II) out of the macrocyclic cavity (i) decreases the changes in bond angles upon reduction and (ii) obviates any need for donor atom inversion. This should diminish the reorganizational barrier and, thereby, increase the electron self-exchange rate. This hypothesis has now been tested utilizing a somewhat soluble 12-membered macrocyclic tetrathiaether, oxathiane[12]aneS4 (L). Crystal structures of the CuIIL and CuIL complexes confirm that, whereas one Cu−S bond dissociates upon reduction, the remaining bond lengths and angles change only minimally. The free ligand, oxathiane[12]aneS4, C10H18OS4, crystallizes in the orthorhombic space group Pbca with Z = 8, a = 15.211(2) Å, b = 8.5113(9) Å, c = 20.548(3) Å. The CuIIL complex crystallizes as a 5-coordinate monomer with water as the apical ligand: [CuL(OH2)](ClO4)2·H2O, C10H22O11S4Cl2Cu, monoclinic P2(1)/c, Z = 4, a = 15.774(2) Å, b = 8.485(5) Å, c = 16.508(9) Å, β = 112.11(6)°. The CuIL complex crystallizes as a binuclear species: [(CuL)2NCCH3](ClO4)2·NCCH3, C24H42N2O10S8Cl2Cu2, in the triclinic space group P1̄ with Z = 4, a = 12.5917(2) Å, b = 13.0020(3) Å, c = 14.9285(3) Å, α = 68.356(1)°, β = 84.298(1)°, γ = 61.129(1)°. The kinetics of CuII/I(oxathiane[12]aneS4) reacting with four selected counter reagentstwo oxidants and two reductantsyield exceptionally large cross-reaction rate constants. Application of the Marcus cross relation yields calculated self-exchange rate constants ranging from 4 × 105 to 8 × 105 M-1 s-1 (median: 6 × 105 M-1 s-1) for this CuII/IL redox system at 25 °C, μ = 0.10. A comparable result of k 11 = (8.4 ± 0.8) × 105 M-1 s-1 has been obtained by NMR line-broadening measurements (at 25 °C, corrected to μ = 0.10). This is the largest self-exchange rate constant ever reported for a low molecular weight Cu(II/I) system. Thus, elimination of donor atom inversion coupled with a constrained inner sphere appears to represent a feasible approach for accelerating electron transfer in Cu(II/I) macrocyclic systems.

Chemistry of selenium/tellurium-containing Schiff base macrocycles

“…Also recent studies indicate polydentate Schiff base macrocycles with larger diameter often deviate from planarity upon metal complexation, taking a concave conformation which is the essence of a metallocavitand; (2) Schiff base macrocyclic ligands will be quite interesting with hard donors such as 'O' as they would be accessible for future encapsulation of both 'hard' and 'soft' transition metal centers, giving rise to heterobimetallic complexes possessing novel structures and reactivities which have potential applications in homogeneous and heterogeneous catalysis. Mixed N, O, S-donor crowns form an interesting class of compounds and have found use as selective extractants for soft metal cations [69] and as models for the active site of some enzymes [70]. (3) Synthesis of Schiff's base macrocycles containing Se-Se and Te-Te fragments will be interesting as organic diselenides/ ditellrides are useful synthetic reagents and intermediates for organic synthesis and also they are intermediates in a biologically important process involving glutathione peroxidase, a seleniumcontaining enzyme.…”

Efficient synthesis of novel 1,2,4-triazole fused acyclic and 21–28 membered macrocyclic and/or lariat macrocyclic oxaazathia crown compounds with potential antimicrobial activity

“…Conversion of this parent triazole into the corresponding acyclic 1,u-bis(triazoles) 17e25/macrocyclic crown compounds 43, 44/or lariat macrocycles 46, 47, 49 enhanced the inhibitory effect against one or more type of the test organisms. Thus, compared to compound 15, compounds 19, 21, 23 (at concentrations 2.5e5.0 mg/mL) showed higher inhibitory effect against Aspergillus fumigatus RCMB 002008 (1), compounds 18, 19e22, 46 (at concentrations 1.0e5.0 mg/mL) showed higher inhibitory effect against Penicillium italicum RCMB 001018 (1), compounds 17e19, 21, 23e25, 44, 46 (at concentrations 1e5.0 mg/mL) showed higher inhibitory effect against Syncephalastrum racemosum RCMB 016001, compounds 18, 20, 22, 23, 43, 46 (at concentrations 1.0e5.0 mg/mL) showed higher inhibitory effect against Candida albicans RCMB 005003,compounds 17,18,20,22,24,43,44, 47 (at concentrations 1.0e5.0 mg/mL) showed higher inhibitory effect against Staphylococcus aureus RCMB 106-001 (1), compounds 18, 43, 44 (at concentrations 2.5e5.0 mg/mL) showed higher inhibitory effect against Pseudomonas aeruginosa compounds 17,19,21,24,25,46,47,49 (at concentrations 1e5.0 mg/mL) showed higher inhibitory effect against Bacillus subtilis RCMB 101-001, compounds 21, 43, 44 showed higher inhibitory effect against Escherichia coli RCMB 103-001 (at concentrations 1.0e2.5 mg/mL). On the other hand, compounds 17, 23, 24, 44, 47, 49 (at concentration 5.0 mg/mL) exhibited lower inhibitory effect against Penicillium italicum RCMB 001018 (1), compounds 17e20, 23e25, 46, 47, 49 (at concentration 5.0 mg/mL) exhibited lower inhibitory effect against Escherichia coli RCMB 103-001, when compared to compound 15.…”

“…1,2-Bis[4-(2-hydroxybenzylideneamino)-5-(pyridin-3-yl)-4H-1,2,4-triazol-3-ylsulfanyl]ethane (25). Yield 571 mg (92%); colorless crystals, mp 244e246 C. IR: 3440 (br), 2929, 1604, 1450, 1267, 1032 ): d 3.59 (s, 4H, SCH 2 CH 2 ), 6.89 (t, 2H, J ¼ 7.8 Hz, ArH), 6.96 (d,2H,J ¼ 8.4 Hz,ArH),7.45 (m,2H,ArH), 7.53 (ddd, 2H, J H-5 pyrid.eH-2 pyrid.…”

“…Mixed N,O,S-donor crowns form an interesting class of compounds, which have found use as selective extractants for soft metal cations [24] and as models for the active sites of some enzymes [25].…”

Synthesis of mixed‐donor azaoxathia macrocyclic tetraamides, acyclic polyether di/and tetraamides and their C‐pivot lariat derivatives

“…Macrocycles containing nitrogen and/or sulfur donor atoms are of interest as they exhibit high affinities towards heavy transition metal ions and their selectivity is readily tunable by altering the composition of the donor-atom set and ring size [5,6]. Mixed N, O, and S-donor crowns, form an interesting class of compounds, which are used to selectively extract soft metal cations [7,8] and as models for the active sites of some enzymes [9]. Other changes involved the development of functional groups in the macrocyclic ring.…”