Synthesis and Redox Behavior of Ruthenocene-Terminated Oligoenes: Characteristic and Stable Two-Electron Redox System and Lower Potential Shift of the Two-Electron Oxidation Wave with Elongating Conjugation

Ruthenocene-terminated butadienes and hexatrienes were prepared by the Wittig reaction of 3-ruthenocenyl-2-propenals with ruthenocenylmethylphosphonium salts and the Mukaiyama coupling of the propenals, respectively. Cyclic voltammetry of these complexes indicated that they were involved in a stable two-electron redox process. The oxidation potentials for ruthenocene-terminated oligoenes shifted progressively to lower potential with the increasing CH==CH units as follows: Rc--Rc (0.32 V)>RcCH==CHRc (+0.09 V)>Rc(CH==CH)(2)Rc (-0.06 V)>Rc(CH==CH)(3)Rc (-0.07 V), (Rc=ruthenocene). The tendency is in remarkable contrast to that in the successive one-electron redox process. These complexes were chemically oxidized to give stable crystalline solids, whose structures were confirmed by NMR spectroscopy and X-ray analysis to be oligoene analogues of a bis(fulvene) complex, for example, [(eta(5)-C(5)Me(5))Ru[mu(2)-eta(6):eta(6)-C(5)H(4)CH(CH==CH)(n)CHC(5)H(4)]Ru(eta(5)-C(5)Me(5))](2+) (n=1 or 2). The DFT calculation of the two-electron-oxidized species reproduced well the fulvene-complex structure for the ruthenocene moieties. Since both the neutral and oxidized species are stable and chemically reversible, this redox system may be serviceable as a two-electron version of the ferrocene one-electron redox system.

The stable inner salt 2,2-dimorpholino-2-ethylium-1-dithioate

The title compound, C(10)H(16)N(2)O(2)S(2), is considered to maintain an inner-salt structure in the crystal, where the planes of the carbenium and the thiocarboxylate moieties are nearly perpendicular to each other [77 (2) degrees ], and the backbone C-C bond length [N(2)C-CS(2) 1.510 (2) A] is significantly shorter than a normal C-C single-bond length.

Self-assembly of a porphyrin array via the molecular recognition approach: synthesis and properties of a cyclic zinc(II) porphyrin trimer based on coordination and hydrogen bonding

Self-assembly of [5-(pyrazol-4-yl)-10,20-bis(p-tolyl)-15- (2-ethoxycarbonylphenyl)porphyrinato]-zinc(II) (1), designed to have both a coordination site and a hydrogen bonding site, leads to a stable cyclic trimer array where coordination of the pyrazole nitrogen to the zinc(II) ion as well as hydrogen bonding between carbonyl oxygen and pyrazole NH holds each zinc(II) porphyrin. The recognition event for pyrazole has been confirmed preliminarily in the model studies using [5-(2-ethoxycarbonylphenyl)tris(p-tolyl)porphyrinato]-zinc(II) (3). The zinc(II) porphyrin 3 has large affinity for pyrazole due to the hydrogen bond between pyrazole and the 2-ethoxycarbonyl group in addition to the coordination bonding accompanied by the conformational change of the ethoxycarbonyl group in the coordination process. The (1)H NMR, IR, and UV-vis spectra of 1 and its ESI-MS and VPO measurements have revealed the cyclic trimer structure with an overall association constant of 6.0 x 10(13) M(-2) at 22 degrees C. The contribution of the hydrogen bond to the total free energy change in trimer formation is estimated to be 7.5 kcal/mol based on a reference trimer system without a hydrogen bonding site. The trimer geometry causes characteristic exitonic interaction between porphyrin units to yield a broad Soret band which is deconvoluted into four components by UV-vis and MCD spectral analyses. Electrochemical measurements have shown that only the first ring-oxidation process proceeds stepwise in the trimer.