Synthesis and Redox Behavior of Wurster Blue Cyclophanes

Takemura, Hiroyuki; Takehara, Kô; Ata, Masafumi

doi:10.1002/ejoc.200400289

Cited by 17 publications

(12 citation statements)

References 41 publications

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“…These two redox processes for 1 – 3 would correspond to the stepwise ligand‐centered oxidation of each of the two facing polymethyl‐substituted para‐ phenylenediamidate bridges. Hence, the resulting dicopper(II)/π radical and diradical species are the metallacyclic analogues of forms I and II from the N , N ′, N ′′, N ′′′‐tetramethyltetraza[7.7]paracyclophane, which shows similar values of the formal potentials to those of 3 ( E 1 =+0.08 and E 2 =+0.69 V vs. SCE) 6a. The observed linear decrease of the E 1 values according to 1 > 2 > 3 indicates that the oxidation of the polymethyl‐substituted para ‐phenylenediamidate bridge is favored as the number of electron‐donating methyl substituents increases (Figure 5).…”

Section: Resultsmentioning

confidence: 96%

Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers

Ferrando‐Soria

Castellano

Ruiz-Garcı́a

et al. 2013

Chemistry A European J

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Double-stranded anionic dinuclear copper(II) metallacyclic complexes of the paracyclophane type [Cu2L2](4-) have been prepared by the Cu(II)-mediated self-assembly of different para-phenylenebis(oxamato) bridging ligands with either zero-, one-, or four-electron-donating methyl substituents (L=N,N'-para-phenylenebis(oxamate) (ppba; 1), 2-methyl- N,N'-para-phenylenebis(oxamate) (Meppba; 2), and 2,3,5,6-tetramethyl- N,N'-para-phenylenebis(oxamate) (Me4ppba; 3)). These complexes have been isolated as their tetra-n-butylammonium (1 a-3 a), lithium(I) (1 b-3 b), and tetraphenylphosphonium salts (1 c-3 c). The X-ray crystal structures of 1 a and 3 c show a parallel-displaced π-stacked conformation with a smaller deviation from perpendicularity between the two benzene rings and the basal planes of the square planar Cu(II) ions when increasing the number of methyl substituents (average dihedral angles (ϕ) of 58.72(7) and 73.67(5)° for 1 a and 3 c, respectively). Variable-temperature (2.0-300 K) magnetic-susceptibility measurements show an overall increase of the intramolecular antiferromagnetic coupling with the number of methyl substituents onto the para-phenylene spacers (-J=75-95, 100-124, and 128-144 cm(-1) for 1 a-c, 2 a-c, and 3 a-c, respectively; H=-JS1×S2). Cyclic voltammetry (CV) measurements show a reversible one-electron oxidation of the double polymethyl-substituted para-phenylenediamidate bridging skeleton at a relatively low formal potential that decreases with the number of methyl substituents (E1=+0.33, +0.24, and +0.15 V vs. SCE for 1-3, respectively). The monooxidized dicopper(II) π-radical cation species 3' prepared by the chemical oxidation of 3 with bromine exhibits intense metal-to-ligand charge-transfer (MLCT) transitions in the visible and near-IR (λmax=595 and 875 nm, respectively) regions together with a rhombic EPR signal with a seven-line splitting pattern due to hyperfine coupling with the nuclear spin of the two Cu(II) ions. Density functional (DF) calculations for 3' evidence a characteristic iminoquinonoid-type short-long-short alternating sequence of C-N and C-C bonds for both tetramethyl-para-phenylenediamidate bridges and a large amount of spin density of negative sign mainly delocalized along each of the four benzene C atoms directly attached to the amidate N atoms, which is in agreement with a fully delocalized π-stacked monoradical ligand description. Hence, the spins of the two Cu(II) ions (SCu=1/2) that are antiparallel aligned in 3 (OFF state) become parallel in 3' (ON state). Further developments may be then envisaged for this new permethylated dicopper(II) paracyclophane with a redox noninnocent ligand as a prototype for molecular magnetic electroswitch.

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Section: Resultsmentioning

confidence: 96%

Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers

Ferrando‐Soria

Castellano

Ruiz-Garcı́a

et al. 2013

Chemistry A European J

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“…This paper reports on oxidized Me3C , Et3C , and iPr3C , which have been studied as both radical cations and diradical dications. Oxidation of Me3C and Me5C was studied earlier by Takemura and co-workers . They concluded that Me3C + could not be obtained and found that Me3C 2+ is diamagnetic but Me5C 2+ is paramagnetic.…”

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confidence: 96%

Alkylated Trimethylene-Bridged Bis(p-Phenylenediamines)

Nelsen

Schultz

et al. 2008

J. Am. Chem. Soc.

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One and two electron oxidation of N,N',N'',N'''-tetramethyl-1,5,12,16-tetraaza[5,5]paracyclophane (Me3C), a bis-trimethylene bridged bis-p-phenylene diamine (PD), and its ethyl and isopropyl analogues are discussed. The monocation and dication are both stable, as demonstrated by optical studies that show they are in equilibrium in solution, with an especially small difference in first and second oxidation potentials for Me3C in MeCN (+23 to -20 mV, measured by simulation of the optical spectrum and of the cyclic voltammogram, respectively). The monocations have charge localized in one PD unit and show a Hush-type mixed valence transition between their PD0 and PD.+ groups. The dications Me3C2+ and Et3C2+ have optical spectra that appear to show large splittings between their PD.+ groups and have a weak ESR spectrum, and 1H NMR data show that the former is a ground-state singlet. iPr3C2+ has a very different optical spectrum and exhibits a triplet ESR spectrum at 120 K. X-ray crystal structures show that for Me3C0 the N(CH2)3N units on each side are in doubly anti (aa) conformations that put the aryl rings as far apart as possible, but Me3C2+ has doubly gg N(CH2)3N trimethylene bridges and both N,N and C,C distances between the PD.+ groups that are significantly below van der Walls contact. In contrast, iPr3C0 is in a doubly ag conformation, and its diradical dication is suggested to be a triplet because it does not attain the doubly gg conformation.

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“…Although produced oxidatively, most of the diamines 1a-h prepared in this work were sensitive to oxidation. 9,13 This was not surprising in view of the applications for diamines 1a-h as antioxidants and it implied the need for careful work-up to minimise discrepancies between conversions and isolated yields. When necessary, to limit the extent of decomposition, products were isolated as their dihydrochloride salts from organic solutions of the diamines 1a-h, which mainly were low melting point solids.…”

Section: Resultsmentioning

confidence: 99%

“…p-Phenylenediamines (1) are useful stabilisers for polymers, particularly as antioxidants and antiozonants for rubbers. 4 They also serve as synthetic starting materials for flavins, 5 bis-Tro ¨ger's bases, 6 rod-like oligomers, rotaxanes, 7 redox-active macrocycles [8][9][10] and ladder polymers. 11 Published routes to 1 often involve multiple steps, [11][12][13][14][15][16][17] including protection and deprotection, that introduce two additional manipulations and lower the atom economy.…”

Section: Introductionmentioning

confidence: 99%