Electron transfer across multiple hydrogen bonds: the case of ureapyrimidinedione-substituted vinyl ruthenium and osmium complexes.
J Am Chem Soc
; 131(13): 4892-903, 2009 Apr 08.
Article
em En
| MEDLINE
| ID: mdl-19278253
ABSTRACT
Ruthenium and osmium complexes 2a,b and 3a,b featuring the N-4,6-dioxo-5,5-dibutyl- or the N-4,6-dioxo-5,5-di-(2-propenyl)-1,4,5,6-tetrahydropyrimidin-2-yl-N'(4-ethenylphenyl)-urea ligand dimerize by a self-complementary quadruply hydrogen-bonding donor/donor/acceptor/acceptor (DDAA) motif. We provide evidence that the dimeric structures are maintained in nonpolar solvents and in 0.1 M NBu(4)PF(6)/CH(2)Cl(2) supporting electrolyte solution. All complexes are reversibly oxidized in two consecutive two-electron oxidations (DeltaE(1/2) approximately = 500 mV) without any discernible potential splitting for the oxidation of the individual hydrogen-bridged redox active moieties. IR and UV/vis/NIR spectroelectrochemistry show a one-step conversion of the neutral to the dication without any discernible features of an intermediate monooxidized radical cation. Oxidation-induced IR changes of the NH and CO groups that are involved in hydrogen bonding are restricted to the styryl-bonded urea NH function. IR band assignments are aided by quantum chemical calculations. Our experimental findings clearly show that, at least in the present systems, the ureapyrimidinedione (Upy) DDAA hydrogen-bonding motif does not support electron transfer. The apparent reason is that neither of the hydrogen-bonding functionalities contributes to the occupied frontier levels. This results in nearly degenerate pairs of MOs representing the in-phase and out-of-phase combinations of the individual monomeric building blocks.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Osmio
/
Pirimidinonas
/
Rutênio
/
Ureia
/
Cristalografia por Raios X
Idioma:
En
Revista:
J Am Chem Soc
Ano de publicação:
2009
Tipo de documento:
Article
País de afiliação:
Alemanha