%0 Journal Article %1 Matheis.1994 %A Matheis, Walter %A Poppe, Juergen %A Kaim, Wolfgang %A Zalis, Stanislav. %D 1994 %J Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry %K AM1 bipyrazinium;MNDO bipyridazinium;ENDOR bipyridinium bipyrimidinium cation complex diquaternized heteroarom heteroarom;electrochem radical;ESR radical;metal redox %N 9 %P 1923--1928 %T Diquaternized heterocycles with strong electronic coupling between a metal-chelating site and a methylviologen-type redox function: EPR/ENDOR detected coordination of metal ions and complexes by radical cation intermediates %X Calcd. (MNDO, AM1) and exptl. results from electrochem. and EPR/ENDOR spectroscopy are reported for diquaternized heterocyclic systems I2+/.bul.+/0, II2+/.bul.+/0, and III2+/.bul.+/0, which exhibit simultaneously features of the methylviologen two-step redox system and an a-diimine chelate site for metal coordination. While metal-free species IIn+ and IIIn+ could not be synthesized as pure compds., the diazamethylviologen system In+, a hybrid structure between MVn+ and 2,2'-bipyridine, was studied esp. as the radical cation intermediate (n = 1) in the presence of potentially coordinating electrophiles such as Zn2+, Cu+, Inn+, Tl+, Mo(CO)4, [Re(CO)3(PPh3)]+ or [Ru(bpy)2]2+. The different character of the metal centers in terms of charge, ligand preference and the ability to back-donate electrons into the singly occupied p* orbital of the cationic radical ligand det. the variable extent of ion-pair assocn. via EPR/ENDOR-detectable spin transfer. System IIn+, which can be described as a 3,3'-coupled N-methylpyrazinium dimer, could be isolated only in coordinated form, bound to [Ru(bpy)2]2+ or Re(CO)3Cl, both complexes showing a rather irreversible second redn. due to the nonclassical (non-Kekule) electronic structure as predicted from the calcns. for II0 and III0. [on SciFinder(R)]

@article{Matheis.1994, abstract = {Calcd. (MNDO, AM1) and exptl. results from electrochem. and EPR/ENDOR spectroscopy are reported for diquaternized heterocyclic systems I2+/.bul.+/0, II2+/.bul.+/0, and III2+/.bul.+/0, which exhibit simultaneously features of the methylviologen two-step redox system and an \textgreek{a}-diimine chelate site for metal coordination. While metal-free species IIn+ and IIIn+ could not be synthesized as pure compds., the diazamethylviologen system In+, a hybrid structure between MVn+ and 2,2'-bipyridine, was studied esp. as the radical cation intermediate (n = 1) in the presence of potentially coordinating electrophiles such as Zn2+, Cu+, Inn+, Tl+, Mo(CO)4, [Re(CO)3(PPh3)]+ or [Ru(bpy)2]2+. The different character of the metal centers in terms of charge, ligand preference and the ability to back-donate electrons into the singly occupied \textgreek{p}* orbital of the cationic radical ligand det. the variable extent of ion-pair assocn. via EPR/ENDOR-detectable spin transfer. System IIn+, which can be described as a 3,3'-coupled N-methylpyrazinium dimer, could be isolated only in coordinated form, bound to [Ru(bpy)2]2+ or Re(CO)3Cl, both complexes showing a rather irreversible second redn. due to the nonclassical (non-Kekule) electronic structure as predicted from the calcns. for II0 and III0. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Matheis, Walter and Poppe, Juergen and Kaim, Wolfgang and Zalis, Stanislav.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/22300a2109c7cf79ceaa8f202c996ac0a/huebleriac}, interhash = {5f1b49609e28496ad14da24a0434488e}, intrahash = {2300a2109c7cf79ceaa8f202c996ac0a}, issn = {0300-9580}, journal = {Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry}, keywords = {AM1 bipyrazinium;MNDO bipyridazinium;ENDOR bipyridinium bipyrimidinium cation complex diquaternized heteroarom heteroarom;electrochem radical;ESR radical;metal redox}, number = 9, pages = {1923--1928}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {Diquaternized heterocycles with strong electronic coupling between a metal-chelating site and a methylviologen-type redox function: EPR/ENDOR detected coordination of metal ions and complexes by radical cation intermediates}, year = 1994 }