Síntese, caracterização e estudos cinéticos da isomerização de compostos de Ru(II) contendo ligantes (X-bipy) ( X=-H, -NO2, -Me, - COOH, -SMe, O=SMe, -Cl, -OMe).
Resumo
The synthesis of coordination compounds containing bipyridine
derivative ligands and the influence of the substituent groups on the physical and
chemical properties were studied in this work.
Mixed compounds of the type [RuCl2(P P)(X bipy)] were
synthesized, where X - bipy represents the bipyridine derivatives and P - P =
triphenylphosphine (PPh3)2, 1,4-bis(diphenilphosphino)butane (dppb). The
characterization of the compounds showed that the isomer formed in solution is
dependent on the phosphine used. The isomer of the compounds containing the
triphenylphosphine exhibited a structure where the phosphine groups are mutually in
trans position. For the biphosphine compounds, dppb is trans to N-heterocyclic
ligand. The spectroscopic and electrochemical properties of the compounds showed
dependence with substituent group of the bipyridine. It was observed a linear
correlation of the pKa values of the X-bipy ligands with the redox potential of the
complexes. The decrease of the pKa value with the increase in the electronwithdrawing
ability of the X groups makes the ligand less basic. This effect enhances
the π-backbonding interactions, which implies in the energy decrease of the MLCT
transitions and in the redox potential increase of the metal center.
For the [RuCl2(dppb)(X-bipy)] complexes, the isomerization reactions
under light incidence were monitored by electronic spectroscopy or differential pulse
voltammetry. The photolysis study of the compound with the 2,2'-bipyridine ligand
allowed the assignment of the field ligand state for its photochemical activity. The
kinetic data supplied the assignment of a twist mechanism for the isomerization
process. It was observed an increase in the rate constant value for this process with
the increase pka values of the ligand.
The reactivity of the compound [RuCl2(COD)]n, COD is 1,5-
cyclooctadiene ligand, with the substituted bipyridine was studied in order to obtain
compounds containing different compositions with changes in reaction conditions.
Compounds of the type [RuCl2(COD)(X-bipy)], for X = H and Me, were obtained and
characterized by microanalysis, hydrogen nuclear magnetic resonance (RMN) and
electrochemical techniques. The reactions with other bipyiridines resulted in mixtures
of compounds of hard purification, needing a more systematic studies for the correct
attribution of their composition and structures. Tris(diimine)ruthenium complexes,
[Ru(X-bipy)3](PF6)2 with X = H, Me, MeO, MeS, were obtained and characterized by
microanalysis, hydrogen nuclear magnetic resonance and electrochemical
techniques.
With substituent groups containing sulfur atom, MeS and MeSO,
polinuclear complexes were obtained. The [RuCl2(P-P)(MeS-bipy)][(µ)-RuCl2(P-P)],
[RuCl2(CO)(PPh3)2]2[(µ) RuCl2(dppb)(MeS-bipy)] and {[RuCl2(dppb)]3[(µ)-Ru(MeSObipy)
3]}(PF6)2 compounds were synthesized and characterized by spectroscopic and
electrochemical techniques. An interesting electronic conducting mechanism was
observed. The sulfur atom is believed to withdraw electron density of the metallic
center by backdonation interaction transferring to the pyridine ring which, by being
more basic, transfer part of this density to the second metallic center.