Mario Martelli

Electrochemistry of coordination compounds: II. Electrochemical reduction of di-(1,2-bisdiphenylphos-phinoethane)M(I) chloride: A new route to hydrido di-(1,2-bisdiphenylphosphinoethane)M(I) (M=Rh, Ir)

Summary The electrochemical behaviour of di-(1,2-bisdiphenyl-phosphinoethane)M(I) chloride (M=Rh, Ir) has been investigated on the mercury electrode in acetonitrile. The reduction proceeds in both cases via a two-electron step leading to anionic complexes which react in the applied solvent forming the corresponding hydrides. This behaviour suggests a new route to hydrido complexes. A comparison is made with the chemical behaviour of the anionic d 10 M(−I) complexes previously reported and a tentative interpretation is proposed.

Electrochemistry of coordination compounds: XIII. Ruthenium(I) and ruthenium(0) complexes generated by electrochemical reduction of chlorodi-(1,3-bisdiphenylphosphinopropane)ruthenium(II)-hexafluorophosphate

Abstract The electrochemical reduction of chlorodi-(1,3-bisdiphenylphosphinopropane)ruthenium(II)hexafluorophosphate, [RuCl(DPP)2](PF6), has been studied on the mercury electrode in 1,2-dimethoxyethane +0.1 M TBAP. The polarogram shows two reversible one-electron waves corresponding to the formation of [RuCl(DPP)2] and [RuCl(DPP)2]. Both products are unstable and decay through a disproportionation pathway and a fast internal metalation via Cl− elimination with formation of HRu(C6H4PPh·CH2CH2 CH2·PPh2)(DPP), respectively. The hypothesis is put forward that the geometry of a metal-complex can be one of the factors which allow us to obtain d7 monomeric complexes by electrochemical methods.

Electrochemistry of coordination compounds—XI: The influence of the anionic ligand, X, on the polarographic behaviour of M(CO) (PPh3)2X (M = Rh, Ir)

Abstract This paper presents an investigation on effects of the nature of the anionic ligand, X, on the electrochemical reduction of M(CO) (PPh3)2X (M = Rh, Ir). The obtained half-wave potentials allow to define a kinetic scale of electron donor properties of the different anionic ligands, to which the ability to stabilize the dioxygen adduct is related.

Electrochemistry of coordination compounds

Abstract The electrochemical behaviour of d 8 organometallic rhodium and iridium complexes, M(R)(CO)(PPh 3 ) 2 (R = alkyl, aryl), has been investigated with a mercury electrode in acetonitrile. The reduction proceeds via a single two-electron step, no (or only small) differences in the reduction potential being noted between rhodium and iridium. The comparison with previous findings suggests that this unusual result is related to a specific influence of the organic ligand in promoting the reduction process in such a way that the actual redox molecular orbital can be mainly of ligand-orbital character. Since (i) specific medium effects could not be studied and (ii) studies of the effects of substituents in the benzene ring of some rhodium organometallic complexes were inconclusive, it was not possible to establish the pathways for the electron uptake.

Electrochemical preparation of d2 organometallic rhodium and iridium complexes

Abstract M(R)(CO)(PPh 3 ) 2 compounds (M = Rh, Ir; R = Me, p -tolyl, p -methoxyphenyl, C 6 F 5 , Ph 3 C and Ph) have been prepared by oxidative addition to a p 8 halogen or a d 10 anionic complex followed by electrochemical reduction.

Electrochemistry of coordination compounds: Part XIV. Polarographic behaviour of d8 ruthenium nitrosyl complexes

Abstract The voltammetric behaviour of the new complex, [Ru(NO)(Ph 2 PCH 2 CH 2 CH 2 PPh 2 ) 2 ] + , has been studied in 1,2-dimethoxyethane and the results compared with those obtained in the analogous reduction of [Ru(NO)(Ph 2 PCH 2 PPh 2 ) 2 ] + . The reduction proceeds in two reversible, one-electron steps. Stepwise reduction of these cationic complexes leads to two reversible, one-electron steps. Stepwise reduction of these cationic complexes leads to anionic complexes with formal oxidation number (−II) through the intermediate state which, in the case of Ph 2 PCH 2 CH 2 PPh 2 ligand, is unstable and decays via a disproportionation pathway. A reduction-oxidation mechanism accounting for the chemical and electrochemical results is proposed.

Electrochemistry of coordination compounds III. Electrochemical reduction of di-(cis-1,2-bisdiphenyl-phosphinoethylene) rhodium(I) chloride

Summary The electrochemical behaviour of di-( cis -1,2-bisdiphenylphosphinoethylene)-rhodium(I) chloride (Rh(VPP) 2 Cl) has been studied on the mercury electrode in acetonitrile-0.1 M TBAP. The reduction leads via a two electron step to [Rh(VPP) 2 ] − which reacts in this solvent to form RhH(VPP) 2 . The comparison between these results and those obtained in the electrochemical reduction of the saturated analogue Rh(DPE) 2 Cl suggests a higher π-aceptor character of VPP than DPE.

Electrochemistry of coordination compounds: IX. An approach to the kinetic study of the reversible addition of carbon monoxide to di-(1,2-bisdiphenylphosphinoethane)rhodium(I) perchlorate by cyclic voltammetry

Abstract The reversible addition of carbon monoxide to [Rh(DPE)2]+ has been studied by cyclic voltammetry. The greatest contribution of this technique is that the uptake and release of CO, occurring before electron transfer, can be characterized and their rates measured. The differences in the reversibility of the CO addition between this complex and the isoelectronic isostructural cobalt and iridium ones are compared. A suggestion is made on the possible relevance of kinetic factors in the release of the CO molecule.

Electrochemistry of coordination compounds: Part XVII. Electron transfer properties in nickel(II), palladium(II) and platinum(II) complexes with hybrid bidentate ligands containing phosphorus and nitrogen or sulfur donor atoms

Abstract The electrochemical behavior of a series of cationic complexes of general formula [M(L−L′)2]2+ (M=Ni, Pd, Pt; L−L′=Ph2PCH2CH2SEt, Ph2PCH2CH2SPh, Ph2PCH2CH2-2-Py) has been examined in 1,2-dichloroethane at the mercury electrode. The palladium and platinum complexes undergo irreversible two-electron reductions, while the nickel compounds are reduced in two reversible one-electron steps involving rare and stable Ni(I) derivatives. An interpretation based on the relevance of π-bonding in determining the electron transfer properties of these complexes is suggested.