Synthesis, substitution kinetics, and electrochemistry of the first tetrathiafulvalene-containing beta-diketonato complexes of rhodium(I).
The synthesis of the first rhodium(I) cyclooctadiene complexes containing tetrathiafulvalene (TTF) groups substituted on a beta-diketonato ligand in either the methine position (3 position), [Rh(cod)(H(3)CCOC{S-TTF-(MeS)(3)}COCH(3))] (3), or terminal position (1 position), [Rh(cod){(Me(3)-TTF)COCHCOCH(3)}] (4), is reported. The effect of the beta-diketonato substitution position on the kinetics of substitution of the TTF-containing beta-diketonato ligand with 1,10-phenanthroline from 3 and 4 to give [Rh(cod)(phen)](+), as well as on the electrochemical properties of 3 and 4, was investigated. Second-order substitution rate constants, k(2), in methanol were found to be almost independent of the substitution position, with 4 (k(2) = 2.09 x 10(3) dm(3) mol(-1) s(-1)) reacting only about twice as fast as 3. An appreciable solvent pathway in the substitution mechanism was only observed for 4 with k(s) = 42 s(-1). A complete mechanism for both substitution reactions is proposed. The electrochemistry of 3 and 4 in CH(2)Cl(2)/0.10 mol dm(-3) [N((n)Bu)(4)][B(C(6)F(5))(4)] showed three redox processes. Two of these were electrochemically reversible and are associated with the redox-active TTF group. For 3, TTF-based formal reduction potentials, E degrees', were observed at 0.082 and 0.659 V vs Fc/Fc(+), respectively; 4 exhibited them at -0.172 and 0.703 V vs Fc/Fc(+) at a scan rate of 100 mV s(-1). A Rh(II)/Rh(I) redox couple was observed at E degrees' = 0.89 V for 3, after both TTF oxidations were completed, and at 0.51 V for 4; this is between the two TTF redox processes. The more difficult oxidation of the Rh(I) center of 3 indicates more effective electron-withdrawing from the Rh(I) center to the first-oxidized TTF(+) group at the methine position of the beta-diketonato ligand of 3(+) than to the terminal-substituted TTF(+) group in 4(+).
Fourie
Eleanor
E
Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, Republic of South Africa.
Swarts
Jannie C
JC
Lorcy
Dominique
D
Bellec
Nathalie
N
D004563:Electrochemistry; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*
D006571:Heterocyclic Compounds; D007659:Ketones; D009942:Organometallic Compounds; D012238:Rhodium; C063887:tetrathiafulvalene