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

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 : XVI. New mixed 1,2-bis(diphenylphosphino)ethaneacetonitrile or -carbon monoxide iron(II), iron(I) and iron(0) complexes

The new iron compound, trans-[Fe(DPE)₂(MeCN)₂] (ClO₄)₂ (DPE=PPh₂CH₂CH₂PPh₂), has been prepared and investigated electrochemically. In acetonitrile the complex shows two reduction steps, consistent with the formation of the stable iron(I) species, [Fe(DPE)₂(MeCN)]⁺ and the rather labile π-bonded acetonitrile adduct, Fe(DPE)₂(π-MeCN), respectively. Acetonitrile substitution by carbon monoxide leads to formation of the carbonylated species, which have been characterized, and examined by electrochemical techniques. A significant feature is that trans-[Fe(CO)₂(DPE)₂]²⁺, unlike trans-[Fe(DPE)₂(MeCN)₂]²⁺, takes up two electrons in a single process, the unstable d⁷ intermediate undergoing a fast disproportionation. A tentative interpretation of this behaviour is suggested.     

Heteropolymetallic complexes of 1,1′-bis (diphenylphosphino)ferrocene,dppf. VIII. X-ray crystal structure of copper(I) dimer [(μ-dppf)(Cu(dppf))2](ClO4)2 1

The dimeric Cu(I) complex [(-dppf)(Cu(dppf))₂](ClO₄)₂, where dppf is Fe((n⁵-C₅H₄)P-(C₆H₅)₂)₂, has been characterized by single-crystal X-ray crystallography. The complex crystallizes in the triclinic space groupP1 (no. 2) with unit cell parametersa=21.852(5),b=18.063(5),c=14.867(5)Å, =114.32(3), =109.87(3), =82.84(3)°. The structure was refined toR=5.40% based on 5562 observed reflections. Two crystallographically independent, structurally equivalent, units were observed in the structure. The structure consists of the centrosymmetric dimeric [(-dppf) (Cu(dppf))₂]²⁺ cations and ClO^4/– anions. The copper atoms are three-coordinate being trigonally bonded to one chelating and one bridging ligand. The P-Cu-P bond angles for the chelating dppf ligand are 111.1(2)° and 111.3(2)°, while the P-Cu-P angles linking different dppf molecules range from 123.9(2) to 124.2(2)°. Cu-P bond distances fall within normal ranges lying between 2.265(5) and 2.285(4)Å, with the values for the chelating dppf being slightly larger than those observed for the bridging ligand. The cyclopentadienyl rings are exactly staggered and parallel, and the P atoms 180° opposed in the bridging dppf, while the rings maintain an approximately staggered configuration and are inclined by 1.6° to each other with the P atoms being 39.5° apart in the chelating ligand. A steric control of the stereochemistry of the monomer fragment of the dimer complex is suggested.Presented at the XXVIII International Conference on Coordination Compounds, Gera, FRG, 1990; see Abstracts No. 6-31.     

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

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.     

Homoleptic complexes of cobalt(0) and nickel(0,I) with 1,1'-bis(diphenylphosphino)ferrocene (dppf): synthesis and characterization

Reduction of Co(dppf)Cl2 with 2 equiv of sodium naphthalenide in THF, in the presence of dppf, affords the homoleptic complex Co(dppf)2, 1, isolated in 65% yield as a brick red solid, extremely air sensitive. In solution, under inert atmosphere, 1 slowly decomposes into Co and dppf, following a first-order kinetic law (t1/2 = 21 h at 22 degrees C). Similarly to the Rh and Ir congeners, 1 undergoes a one-electron reversible reduction to [Co(dppf)2]-. Attempts to obtain this d10 species by chemical as well as electrochemical reduction of 1 lead to the hydride HCo(dppf)2, 2, as the only product that can be isolated. Reduction of Ni(dppf)Cl2 with sodium in the presence of dppf and catalytic amounts of naphthalene affords Ni(dppf)2, 3, isolated in 60% yield as a yellow air stable solid. The stoichiometric oxidation of 3 with [FeCp2]PF6 forms the d9 complex [Ni(dppf)2]PF6, 4, which represents the second example of a structurally characterized Ni(I) complex stabilized by phosphines. A single-crystal X-ray analysis shows for the metal a distorted tetrahedral environment with a dihedral angle defined by the planes containing the atoms P(1), Ni, P(2) and P(3), Ni, P(4) of 78.2 degrees and remarkably long Ni-P bond distances (2.342(3)-2.394(3) A). The EPR spectroscopic properties of 1 (at 106 K in THF) and 4 (at 7 K in 2-methyl-THF) have been examined and g tensor values measured (1, gx = 2.008, gy = 2.182, gz = 2.326; 4, gx = 2.098, gy = 2.113, gz = 2.332). A linear dependence between the hyperfine constants and the Ni-P bond distances has been evidenced. Finally, the change with time of the EPR spectrum of 4 indicates that it very slowly releases dppf.     

Electrochemistry of coordination compounds: Part XVIII. Electrochemical behaviour of d8 iron and osmium nitrosyl complexes a comparison with their ruthenium analogue

A detailed study of the electrochemical behaviour of the d⁸ complexes [Fe(NO)(Ph₂PCH₂CH₂PPh₂)₂]⁺ and [Os(NO)(Ph₂PCH₂CH₂PPh₂)₂]⁺, with emphasis on the properties of the reduced species, has been made and the results compared with those obtained in the reduction of the corresponding ruthenium derivative. the reduction proceeds in two reversible one-electron steps leading to d¹⁰ anionic complexes through an intermediate which, in the case of iron, is labile towards the loss of one phosphorus ligand. A tentative interpretation of this behaviour is suggested.     

Preparation and characterization of close-packed nanostructured sol–gel ceria thin films prepared using cerium-sec-butoxide as precursor

Polycrystalline, close-packed, homogeneous nanostructured ceria thin films were prepared by sol–gel process via dip-coating technique on soda-lime glass and (100)-oriented Si substrates. To produce the films, a sol was prepared using, as precursor, a home made cerium sec-butoxide dissolved in secondary butanol. The chemical composition, the microstructural/morphological characteristics and the optical properties of the coatings were investigated in detail. The experimental results clearly demonstrate that the ceria films are nanocrystalline (CeO₂, cubic phase \textFm[`3]\textm {\text{Fm}}\bar{3}{\text{m}} ) with an average grain size of about 2–3 nm for the samples grown on glass and of about 4–5 nm for the samples grown on silicon. The analyses of ceria layers grown on silicon show that the ceria coatings are free from organic residues and that a Si-oxide layer is formed at the film/substrate interface. The optical results evidence a red shift of the energy gap of about 0.5 eV that can be ascribed to conversion of relevant Ce⁴⁺ sites to Ce³⁺ sites and a consequent creation of oxygen vacancy at the surface of the ceria grains.