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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
Author(s) -
Sato Masaru,
Nagata Toru,
Tanemura Atsushi,
Fujihara Takashi,
Kumakura Shigekazu,
Unoura Kei
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200306004
Subject(s) - ruthenocene , redox , fulvene , chemistry , ferrocene , cyclic voltammetry , electron paramagnetic resonance , photochemistry , crystallography , medicinal chemistry , electrochemistry , inorganic chemistry , nuclear magnetic resonance , physics , electrode
Abstract 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 CHCH units as follows: RcRc (0.32 V)>RcCHCHRc (+0.09 V)>Rc(CHCH) 2 Rc (−0.06 V)>Rc(CHCH) 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, [(η 5 ‐C 5 Me 5 )Ru{μ 2 ‐η 6 :η 6 ‐C 5 H 4 CH(CHCH) n CHC 5 H 4 }Ru(η 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.