%0 Journal Article %1 Waldhoer.1996 %A Waldhoer, Eberhard %A Zulu, Mthembeni M. %A Zalis, Stanislav %A Kaim, Wolfgang. %D 1996 %J Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry %K arom complex complex;ESR complex;MO complex;UV electrophile electroredn heterocycle radical %N 6 %P 1197--1204 %T Coordination-induced switch between the singly occupied and the lowest unoccupied molecular orbitals in two methylviologen-derived chromophores %X The arom. heterocycles 2,7-diazapyrene (dap) and 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (4-bptz) each exhibit two very close-lying lowest unoccupied MOs (MOs) with very different character, viz., a methylviologen-like MO (b1u) and a quinonoid (dap) or tetrazine-localized MO (4-bptz) of au symmetry. Calcns. (HMO, semiempirical NDO type, ab initio) suggest that the orbital crossing between b1u and au and thus the character of the singly occupied MO in one-electron reduced compds. can be effected by removal of electron d. from the potentially coordinating pyridyl nitrogen centers. This suggestion was studied exptl. by coordination of electrophiles, either alkyl cations, R+, or neutral complex fragments, W(CO)5, to both pyridine N centers. Exptl. data from UV-VIS-NIR and esp. EPR spectroelectrochem. show that coordination of two neutral W(CO)5 fragments to dap is sufficient to cause a change from singly occupied au (in dap.bul.-) to singly occupied b1u in dapW(CO)52.bul.-. In contrast, the 4-bptz.bul.- radical system requires coordination of two electrophiles R+ (R = CH3, C2H5) in order to move b1u below au while the ditungsten(0) radical anion complex is still a 2Au species. on SciFinder(R)

@article{Waldhoer.1996, abstract = {The arom. heterocycles 2,7-diazapyrene (dap) and 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (4-bptz) each exhibit two very close-lying lowest unoccupied MOs (MOs) with very different character, viz., a methylviologen-like MO (b1u) and a quinonoid (dap) or tetrazine-localized MO (4-bptz) of au symmetry. Calcns. (HMO, semiempirical NDO type, ab initio) suggest that the orbital crossing between b1u and au and thus the character of the singly occupied MO in one-electron reduced compds. can be effected by removal of electron d. from the potentially coordinating pyridyl nitrogen centers. This suggestion was studied exptl. by coordination of electrophiles, either alkyl cations, R+, or neutral complex fragments, W(CO)5, to both pyridine N centers. Exptl. data from UV-VIS-NIR and esp. EPR spectroelectrochem. show that coordination of two neutral W(CO)5 fragments to dap is sufficient to cause a change from singly occupied au (in dap.bul.-) to singly occupied b1u in {dap[W(CO)5]2}.bul.-. In contrast, the 4-bptz.bul.- radical system requires coordination of two electrophiles R+ (R = CH3, C2H5) in order to move b1u below au while the ditungsten(0) radical anion complex is still a 2Au species. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Waldhoer, Eberhard and Zulu, Mthembeni M. and Zalis, Stanislav and Kaim, Wolfgang.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/25de97bd01452cbfd58bdebd5ee05a175/huebleriac}, interhash = {dd12f6b0aa6785d98b32ee053494d189}, intrahash = {5de97bd01452cbfd58bdebd5ee05a175}, issn = {0300-9580}, journal = {Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry}, keywords = {arom complex complex;ESR complex;MO complex;UV electrophile electroredn heterocycle radical}, number = 6, pages = {1197--1204}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {Coordination-induced switch between the singly occupied and the lowest unoccupied molecular orbitals in two methylviologen-derived chromophores}, year = 1996 }