DNA templated nanowires of a pentynyl-modified poly2-(2-thienyl)-pyrrole undergo functionalisation via"click chemistry" and retain their 1D-nanostructure and conductive properties.
The μ‐η2:η2‐peroxodicopper(II) core found in the oxy forms of the active sites of type III dicopper proteins have been a key target for bioinorganic model studies. Here, it is shown that simple bis(oxazoline)s (BOXs), which are classified among the so‐called “privileged ligands”, provide a suitable scaffold for supporting such biomimetic copper/dioxygen chemistry. Three derivatives R,HBOX‐Me2 (R = H, Me, tBu) with different backbone substituents have been used. Their bis(oxazoline)‐copper(I) complexes bind dioxygen to yield biomimetic μ‐η2:η2‐peroxodicopper(II) species. O2 can be reversibly released upon an increase in temperature. Their formation kinetics have been studied under cryo‐stopped‐flow conditions for the tBu derivative, giving activation parameters ΔH‡on = (2.27 ± 0.18) kcal mol–1, ΔS‡on = (–46.3 ± 0.8) cal K–1 mol–1 for the binding event and ΔH‡off = (11.7 ± 1.9) kcal mol–1, ΔS‡off = (–16.1 ± 8.2) cal K–1 mol–1 for the release of O2, as well as thermodynamic parameters ΔH° = (–10.0 ± 1.7) kcal mol–1 and ΔS° = (–32.7 ± 7.4) cal K–1 mol–1 for this equilibrium. The μ‐η2:η2‐peroxodicopper(II) complexes have been isolated as surprisingly stable solids and investigated in depth by a variety of methods, both in solution and in the solid state. Resonance Raman spectroscopy revealed a characteristic isotope‐sensitive stretch $\tilde {\nu}$O–O = 731–742 cm–1 (Δ[18O2] ≈ –39 cm–1) and an intense feature around 280 cm–1 diagnostic for the fundamental symmetric Cu2O2 core vibration. A slight butterfly‐shape of the Cu2O2 core has been derived from EXAFS data and DFT calculations. SQUID magnetic data evidenced strong antiferromagnetic coupled CuII2 (–2J ≥ 1000 cm–1). Thermal degradation in solution yields bis(hydroxo)‐bridged [(tBu,HBOX‐Me2)(L)Cu(OH)]2(PF6)2 (L = H2O, MeCN or THF); whereas in the case of H,HBOX‐Me2, ligand oxygenation has been detected. Preliminary reactivity studies with the substrate 2,4‐di‐tert‐butylphenol indicate the formation of the C–C coupling product 3,3′,5,5′‐tetra‐tert‐butyl‐2,2′‐biphenol, whereas ortho‐hydroxylation was not observed. The copper(I) complex [(tBu,HBOX‐Me2)Cu(MeCN)]PF6 as well as two dicopper(II) complexes [(L)(tBu,HBOX‐Me2)Cu(OH)]2(PF6)2 have been characterised by single‐crystal X‐ray diffraction. Considering the vast number of known BOX derivatives, a rich and versatile Cu/O2 chemistry based on this platform is anticipated.
Key peroxido and bis(μ-oxido) Cu2/O2 intermediates can be interconverted by peripheral (de)protonation events on the ligand backbone.
Bis(oxazoline)s (BOXs) are a privileged ligand class and have found widespread use in catalysis. Herein, the tautomerism of selected BOX ligands was evidenced by X‐ray diffractometry as well as by NMR and IR spectroscopy and supported by DFT calculations. In CDCl3 solution at room temperature, the new 1,1‐bis(4,4‐dimethyl‐1,3‐oxazolin‐2‐yl)‐1‐phenylmethane (Ph,HBOX‐Me2) ligand is present as a 1:1 mixture of the diimine and iminoenamine tautomers. Thermodynamic and kinetic data for the tautomeric equilibrium were determined, which allowed comparison with related bidentate ligand classes. The other BOXs studied, H,HBOX‐Me2, Me,HBOX‐Me2, and tBu,HBOX‐Me2, are largely present in the diimine form under similar conditions. IR spectroscopy was identified as a valuable tool for detecting the presence of the iminoenamine form as a minor component.
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