Dominique de Montauzon

New chiral phosphorus-containing dendrimers with ferrocenes on the periphery

Four series of new chiral ferrocenyl dendrimers (up to the 11th generation) have been synthesised and fully characterised. Electrochemical studies have been carried out on these dendrimers. In every case, one single oxidation wave has been observed, corresponding to the independent oxidation of all the ferrocene groups to ferrocenium. The chiroptical properties of the different dendrimers have been studied: the molar rotation depends only on the number of stereogenic units, independently of the generation in all series of dendrimers.

First electrochemical investigation of the redox properties of DOPA-melanins by means of a carbon paste electrode

Abstract The electrochemical properties of eumelanins, a cutaneous pigment responsible for skin color, insoluble in any solvent, was studied by using a carbon paste electrode. Eumelanins synthesized by enzymatic oxidation of l -DOPA were included in the carbon paste. The concentration of melanins (10%) and the potential scan rate (10 −4 V s −1 ) were chosen in ranges for which there is a linear relationship between these parameters and the current peak intensity. In these thin-layer conditions, the voltammogram of eumelanins at pH 5.6 reveals two main peaks in oxidation at +460 and +525 mV versus SCE and in reduction at +20 and −355 mV versus SCE. No variation of peak potential was observed when the pH was varied in the range 2–8. An average of two electrons (three for the first oxidation scan) were exchanged in these redox processes whereas the number of subunits in one molecule of melanin was around 15 as found by MALDI mass spectroscopy experiments. These results support the assumption of an irregular organization of monomer units in the structure of melanins.

New phosphorus-containing dendrimers with ferrocenyl units in each layer

Abstract New phosphorus-containing dendrimers bearing ferrocenyl units within the branches were synthesised using a new 1,1’-disubstituted ferrocenyl building block. The structure of one of the synthetic intermediates was determined by X-ray analysis. In every case, one single oxidation was observed for each ferrocenic layer, corresponding to the independent oxidation of all ferrocenes within one layer to ferroceniums. The oxidation potential for a particular layer depends on substituents on ferrocenes, but not on their localisation within the dendrimers.

Carbide formation and simultaneous intramolecular carbide-ethylidyne coupling as the result of the reduction of trinuclear clusters containing the Fe3(CO)9(μ3-CCH3) unit

Abstract Reduction of Fe 3 (CO) 9 (μ 3 -CCH 3 )(μ 3 -COC 2 H 5 ) molecule with two equivalents of [Mn(CO) 5 ] − or treatment of the electrochemically generated [Fe 3 (CO) 10 (μ 3 -CCH 3 )] 2− with methanol gives the cluster anion [Fe 3 (CO) 9 (μ 3 Cue5fcCCH 3 )] − . Experiment with the 13 CO-enriched [Fe 3 (CO) 10 (μ 3 -CCH 3 )] − cluster shows that the [Fe 3 (CO) 9 (μ 3 Cue5fcCCH 3 )] − complex results from the coupling of a carbide, produced by carbon-oxygen breaking, with the μ 3 -ethylidyne ligand of the original cluster.

Electrochemical and theoretical study of the redox properties of transition metal complexes with {Pt2S2} cores

The oxidation processes undergone by the [Pt2(mu-S)2] core in [Pt2(P[intersection]P)2(mu-S)2](P[intersection]P = Ph2P(CH2)nPPh2, n= 2,3) complexes have been analysed on the basis of electrochemical measurements. The experimental results are indicative of two consecutive monoelectronic oxidations after which the [Pt2(mu-S)2] core evolves into [Pt2(mu-S2)]2+, containing a bridging disulfide ligand. However, the instability of the monoxidised [Pt2(P[intersection]P)2(mu-S)2]+ species formed initially, which converts into [Pt3(P[intersection]P)3(mu-S)2]2+, hampered the synthesis and characterisation of the mono and dioxidised species. These drawbacks have been surpassed by means of DFT calculations which have also allowed the elucidation of the structural features of the species obtained from the oxidation of [Pt2(P[intersection]P)2(mu-S)2] compounds. The calculated redox potentials corresponding to the oxidation processes are consistent with the experimental data obtained. In addition, calculations on the thermodynamics of possible processes following the degradation of [Pt2(P[intersection]P)2(mu-S)2]+ are fully consistent with the concomitant formation of monometallic [Pt(P[intersection]P)S2)] and trimetallic [Pt3(P[intersection]P)3(mu-S)2]2+ compounds. Extension of the theoretical study on the [Pt2Te2] core and comparisons with the results obtained for [Pt2S2] have given a more general picture of the behaviour of [Pt2X2](X = chalcogenide) cores subject to oxidation processes.

Cobalt/Mercury Carbide Clusters Based on Trigonal-Prismatic or Octahedral Co6C Skeletons − X-ray Crystal Structure of (NEt4)2[Co6C(CO)12{HgW(CO)3Cp}2]

The anionic transition metal clusters (NEt4)[Co6C(CO)x{HgM}] [M = W(CO)3Cp, Mo(CO)3Cp, Fe(CO)2Cp, Co(CO)4, Mn(CO)5] (x = 13 or 15) have been obtained by reaction of the corresponding octahedral (x = 13) or trigonal-prismatic (x = 15) cobalt carbido carbonyl clusters with the mercury derivatives ClHgM. Metal skeleton rearrangements and some redox processes have been found to be induced by varying both the temperature and the solvent, resulting in new compounds containing tetra- or hexacoordinated mercury atoms.

Synthesis, characterization and electrochemical studies of the heterometallic diclusters [{Fe2(μ-CO)(CO)6(μ-PPh2)Au}2(diphosphine)] (diphosphine=dppm, dppip, dppe, dppp)

Abstract Treatment of [(ClAu)2(diphosphine)] {diphosphine=bis(diphenylphosphino)methane (dppm), bis(diphenylphosphino)isopropane (dppip), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp)} with two equivalents of the anion [Fe2(μ-CO)(CO)6(μ-PPh2)]− in the presence of TlBF4 gives the new heterometallic diclusters [{Fe2(μ-CO)(CO)6(μ-PPh2)Au}2(diphosphine)] that have been isolated and characterized. Their 31P-NMR spectra show different patterns as a function of the diphosphine ligand. The electrochemical behavior of these compounds has been investigated and compared with that of the mono- [Fe2(μ-CO)(CO)6(μ-PPh2)(μ-AuPPh3)] and tricluster [{Fe2(μ-CO)(CO)6(μ-PPh2)Au}3(triphos)] derivatives.

Synthesis, characterization and solution studies on heteronuclear iron–copper clusters containing diphosphine ligands: crystal structure of the dicluster [{Fe2(μ-CO)(CO)6(μ-PPh2)Cu}2(dppp)]

Abstract Treatment of dichloromethane solutions of the di-iron compound [NEt 4 ][Fe 2 (CO) 6 (μ-CO)(μ-PPh 2 )] with one equivalent of [Cu(NCCH 3 ) 4 ]BF 4 at low temperatures, followed by the addition of half of an equivalent of diphosphine ligand (diphosphine=bis(diphenylphosphino)methane (dppm), bis(diphenylphosphino)isopropane (dppip), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp) and 1,4-bis(diphenylphosphino)butane), produces high yields of the mixed-metal dicluster compounds [{Fe 2 (μ-CO)(CO) 6 (μ-PPh 2 )Cu} 2 (diphosphine)]. The molecular structure of the dppp derivative has been determined by X-ray crystallography. For a 1:1:1 molar ratio of the reagents, complex mixtures have been obtained and studied by variable-temperature 31 P-NMR spectroscopy.

ELECTROCHEMICAL STUDIES OF MN3HGM (M = MO, W, MN, FE OR CO) AND MN3AU CLUSTER ANIONS

Abstract The electrochemical behaviour of compounds of the type (PPh4)[Mn3(CO)12(μ3-H)(μ-Hgm)][m = Mo(CO)3Cp(1), W(CO)3 Cp (2), Mn(CO)5 (3), Fe(CO)2 Cp (4) or Co(CO)4 (5)] and the [PPh4]+ salts of the anions [{Mn3(CO)12(μ3-H}2Hg]2− (6), [{Mn3(CO)12(μ3-H)Au} 2(dppe)]2− (7) and [{Mn3(CO)12( μ 3 - H ) Au } n ( triphos)(AuCl) 3−n ] n− [n = 1 ( 8 ), 2( 9 ), 3( 10 )] has heen investigated at Pt (or Au) electrodes in CH2Cl2 or THF by means of cyclic voltammetry and coulometry. All the compounds undergo a quasi-reversible oxidation and an irreversible reduction. The electrons involved in both oxidation and reduction are delocalized mainly onto the metal fragments, Mn3Hg and Mn3Au, and the slight changes in the redox potential throughout the series of compounds are explained in terms of the nucleophilicity of the metal fragments, m. In the series of gold clusters a weak electronic interaction has been observed between the metal units through the triphosphine.