Fabrizia Fabrizi de Biani

An efficient oxidative desulfurization process using terbium-polyoxometalate@MIL-101(Cr)

An efficient and recyclable oxidative desulfurization process (ODS) to remove the most refractory sulfur-compounds (dibenzothiophene, 1-benzothiophene and 4,6-dimethyldibenzothiophene) from fuel is reported. The ODS process was catalyzed by terbium-polyoxometalate [Tb(PW11O39)2]11− (Tb(PW11)2) and its composite Tb(PW11)2@MIL-101. The tetrabutylammonium (TBA) salt of Tb(PW11)2 was prepared and further incorporated in the porous metal–organic framework MIL-101(Cr). The TBA compound and its composite were characterized by various techniques (powder X-ray diffraction, FT-IR, FT-Raman, SEM and elemental analysis), and their electrochemical behavior was investigated, indicating that the structure of the polyoxometalate anion must be retained after immobilization. The studied ODS process was based on a biphasic system formed by a model oil with various refractor sulfur-compounds and an extracting solvent using H2O2 as the oxidant. Two main steps in the process were carefully investigated: the initial extraction and the oxidative catalytic stage. The optimization of the ODS process was performed by the analysis of the most suitable extracting solvent and also comparing the desulfurization performance of the homogeneous Tb(PW11)2 and the heterogeneous Tb(PW11)2@MIL-101 catalysts. Acetonitrile was selected as the best solvent because it allowed the highest desulfurization rate, conciliating good initial extraction and high catalytic performance. The presence of the porous catalyst Tb(PW11)2@MIL-101 seemed not to influence the initial extraction step; however, with this porous hybrid catalyst were obtained higher desulfurization rates during the catalytic stage. Remarkably, using Tb(PW11)2@MIL-101 and the oil–acetonitrile system complete desulfurization of oil was achieved only after 5 h. The recyclability of the solid catalyst was investigated for three consecutive ODS cycles and its stability was confirmed by several techniques.

Pressure- and Temperature-Induced Valence Tautomeric Interconversion in a o-Dioxolene Adduct of a Cobalt–Tetraazamacrocycle Complex

An electronic switch at the molecular level has been realized by using a class of ionic compounds of the formula [Co(L)(diox)]Y (L = tetraazamacrocyclic ligand, Y = mononegative anion). Such compounds undergo temperature- and pressure-induced intramolecular one-electron transfer equilibria. The transition temperature of interconversion varies with the nature of the counterions Y (Y = PF6, BPh4, I). Surprisingly the effect of the anion on the transition temperature is not only governed by its volume but also by its coulombic interaction.

SYNTHESIS, STRUCTURE AND ELECTROCHEMICAL STUDIES OF THE FIRST MIXED-METAL CLUSTERS WITH THE P-N-P ASSEMBLING LIGANDS (PH2P)2NH (DPPA), (PH2P)2N(CH3) ( DPPAM) AND (PH2P)2N(CH2)3SI(OET)3 (DPPASI)

Heterometallic triangular palladium–cobalt clusters stabilized by three bridging diphosphine ligands such as Ph 2 PNHPPh 2 (dppa), (Ph 2 P) 2 N(CH 3 ) (dppam), (Ph 2 P) 2 N(CH 2 ) 3 Si(OEt) 3 (dppaSi), or mixed ligand sets Ph 2 PCH 2 PPh 2 (dppm)/dppa, dppm/dppam or dppm/dppaSi have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of making possible their use in the sol–gel process (case of dppaSi). The crystal structure determination of [CoPd 2 ( μ 3 -CO) 2 ( μ -dppam) 3 ]PF 6 confirms the triangular arrangement of the metal core, with each edge bridged by a dppam ligand, although disorder problems prevent a detailed discussion of the bonding parameters. Different approaches are given to functionalize the heterometallic clusters: alkylation of the nitrogen atom of co-ordinated dppa ligands or introduction of a third bridging diphosphine in a precursor tetranuclear cluster containing only two bridging diphosphine ligands. In the latter case, it was found that their nature critically determined whether or not the reaction occurred. The diversity of bridging ligands allowed an investigation of their influence on the electrochemical properties of the clusters. By comparison with [CoPd 2 ( μ 3 -CO) 2 (CO) 2 ( μ -dppm) 2 ] + which contains only two assembling ligands, it is generally observed that trinuclear cationic CoPd 2 clusters containing three (identical or different) edge-bridging bidentate diphosphine ligands show increased redox flexibility. A notable stabilisation of the metal core is observed when three dppm ligands bridge the metal–metal bonds and [CoPd 2 ( μ 3 -CO) 2 ( μ -dppm) 3 ] reversibly undergoes either a single-step two-electron oxidation or two distinct one-electron reductions. Complexes with the other diphosphines exhibit similar redox behaviour, but the stability of their redox congeners depends upon the nature of the diphosphine: a lower redox aptitude is exhibited by the dppa and dppam derivatives [CoPd 2 ( μ 3 -CO) 2 ( μ -dppa) 3 ] + and [CoPd 2 ( μ 3 -CO) 2 ( μ -dppam) 3 ] + .

Isomerism and redox properties of 1-ferrocenyl1,3-butanedionate complexes

Abstract The ferrocenyl diketone [(C5H5)Fe(C5H4)COCH2COCH3] has been used to form neutral metal complexes of the 1-ferrocenyl-l,3-butanedionate ligand [(C5H5)Fe(C5H4)COCHCOH3]−: the aluminium complex of this ligand, [Al{(C5H5)Fe(C5H4)COCHCOCH3}3], has been characterised by 1H and 13C NMR as a 2:3 mixture of fac and mer isomers, having C3 and C1 molecular symmetry respectively. Electrochemical studies show that each peripheral 1-ferrocenyl-1,3-butanedionate ligand L of both MIIL2 (M = Co, Ni, Cu) and MIIIL3 (M = Al, Cr, Mn, Fe) complexes undergoes reversible one-electron oxidation at potential values essentially overlapping each other. This means that the central metal ions prevent any electronic communication between the two or three ferrocene fragments. In addition to these reversible ferrocene-centred oxidations, there are reversible one-electron reductions centred at M for MnL3 and FeL3 (but not for CrL3 or AIL3), but the metal-centre reductions of MIIL2 are irreversible owing to further reactions following reduction.

Experimental and TDDFT Characterization of the Light-Induced Cluster-to-Iron Charge Transfer in the (Ferrocenylethynyl)-Substituted Trinuclear Platinum Derivative [Pt3(μ-PBut2)3(CO)2(C≡C−Fc)]+

The reaction between Pt(3)(mu-PBu(t)(2))(3)(CO)(2)Cl (2) and ethynylferrocene, in the presence of catalytic amounts of CuI, gives Pt(3)(mu-PBu(t)(2))(3)(CO)(2)C[triple bond]CFc (1), characterized by X-ray crystallography and representing a rare example of the sigma-coordination of an alkynyl moiety to a cluster unit. In a dichloromethane (CH(2)Cl(2)) solution, compound 1 undergoes three consecutive one-electron oxidations, the first of which is assigned to the ferrocene-centered Fe(II)/Fe(III) redox couple. Spectroelectrochemistry, carried out on a solution of 1, shows the presence of a broad band in the near-IR region, growing after the electrochemical oxidation, preliminarily associated with a metal-to-metal charge transfer toward the Fe(III) ion of the ferrocenium unit. Density functional theory (DFT) has been employed to analyze the ground- and excited-state properties of 1 and 1(+), both in the gas phase and in a CH(2)Cl(2) solution. Vertical excitation energies have been computed by the B3LYP hybrid functional in the framework of the time-dependent DFT approach, and the polarizable continuum model has been used to assess the solvent effect. Our results show that taking into account the medium effects together with the choice of an appropriate molecular model is crucial to correctly reproducing the excitation spectra of such compounds. Indeed, the nature of the substituents on P atoms has been revealed to have a key role in the quality of the calculated spectra.

Terpyridines Functionalised with Ferrocenyl Groups of Different Redox Potential

2,2′:6′,2′′-Terpyridines bearing a substituent × in the 4′-position [3a: × = Fc–C≡C–p-C6H4; 3b: × = Fc#–C≡C–p-C6H4; Fc = (C5H5)Fe(C5H4), Fc# = (C5Me4H)Fe(C5Me4)] were prepared by Pd0-catalysed cross-coupling reactions. 3b was characterised by X-ray structure analysis. [(3a)RuCl2(DMSO)] (4a) and [(3b)RuCl2(DMSO)] (4b) were obtained by reaction of [RuCl2(DMSO)4] with 1 equivalent of 3a and 3b, respectively, while the analogous reaction with 2 equivalents afforded [(3a)2Ru][PF6]2 (5a) and [(3b)2Ru][PF6]2 (5b), respectively, after precipitation with aqueous [NH4][PF6]. Similarly, [(3a)Ru(tpy)][PF6]2 (6) was isolated from the reaction of 4a with 2,2′:6′,2′′-terpyridine (tpy). Compounds 3 and 5 were investigated by cyclic voltammetry, which revealed that the introduction of eight methyl groups leads to the expected cathodic shift of the E0′ values of ca. 0.44 V for the ferrocenyl-centered redox processes.

Electron‐Sink Behaviour of the Carbonylnickel Clusters [Ni32C6(CO)36]6– and [Ni38C6(CO)42]6–: Synthesis and Characterization of the Anions [Ni32C6(CO)36]n– (n = 5–10) and [Ni38C6(CO)42]n– (n = 5–9) and Crystal Structure of [PPh3Me]6[Ni32C6(CO)36] · 4 MeCN

The hexacarbide clusters [H6–nNi38C6(CO)42]n− (n = 3, 4, 5, or 6) have been directly obtained from the reaction of [Ni6(CO)12]2– with C3Cl6, whereas the related anions, [H6–nNi32C6(CO)36]n− (n = 5 or 6), have been obtained by degradation under carbon monoxide of [Ni38C6(CO)42]6–, or upon thermal treatment at ca. 110 °C of [Ni10C2(CO)16]2– salts. The compound [PPh3Me]6[Ni32C6(CO)36] ·4 MeCN is triclinic, space group P&1macr; (No 2), with a = 15.974(3), b = 17.474(3), c = 18.200(4) A, α = 61.37(2), β = 69.31(2), γ = 72.35(2)° and Z = 1; final R = 0.033. The structure of [Ni32C6(CO)36]6– has an idealised Oh symmetry and is based on a truncated octahedral Ni32C6 framework, with all edges spanned by bridging carbonyl groups. The six interstitial carbide atoms are lodged in square-antiprismatic cavities. The overall geometry of the Ni32C6 core is very similar to that found previously in [HNi38C6(CO)42]5–, and shows very close interatomic separations. Both [Ni32C6(CO)36]6– and [H6–nNi38C6(CO)42]n− (n = 5 or 6) display electron-sink behaviour. Thus, they have been chemically and electrochemically reduced to their corresponding [Ni32C6(CO)36]n− (n = 7–10), [Ni38C6(CO)42]n− (n = 7–9) and [HNi38C6(CO)42]n− (n = 6–8) derivatives, and several of the involved redox changes show features of electrochemical reversibility. In contrast, both [Ni32C6(CO)36]6– and [H6–nNi38C6(CO)42]n− (n = 5 or 6) support only one partially reversible oxidation step. Their different behaviour upon protonation or oxidation is an indirect, but unambiguous, proof of the hydride nature of [HNi32C6(CO)36]5– and [H6–nNi38C6(CO)42]n− (n = 3, 4, or 5), which could not be validated by 1H-NMR spectroscopy.

4-Ethynylpyridine as bridging moiety in mixed Ru/Re complexes

Two ruthenium(II) 4-ethynylpyridine-hydride complexes bearing one Lewis-basic nitrogen atom as coordination site, namely trans-Ru(dppe)2H(CCpy-4) (1) and trans-Ru(dppm)2H(CCpy-4) (2) (dppe=1,2-bis(diphenylphosphino) ethane, dppm=1,2-bis(diphenylphosphino) methane) and Ru(dmpe)2(CCpy-4)2 (3) (dmpe=1,2-bis(dimethylphosphino) ethane) with two nitrogen donor atoms were applied to synthesize the heterobimetallic mixed Ru/Re complexes 4–7. The X-ray crystal structure of the binuclear complex [Re(CO)3(t-bu2bipy)Ru(dppe)2(CCpy-4)H] [OS(O)2CF3] (t-bu2bipy=4, 4′-di (t-butyl)-2,2′-bipyridine, (7)) has been determined. Besides the usual characterization (IR, NMR, UV/Vis, EA) of the compounds 1–7, thermogravimmetry (TG) and cyclovoltammetry (CV) of selected complexes were measured in order to study the interaction between the organometallic building blocks. The existence of long-range Ru⋯Re interactions has been observed.

Synthesis, Structure, and Spectroscopic Characterization of [H8−nRh22(CO)35]n− (n = 4, 5) and [H2Rh13(CO)24{Cu(MeCN)}2]− Clusters: Assessment of CV and DPV As Techniques to Circumstantiate the Presence of Elusive Hydride Atoms

The previously ill-characterized [H(x)Rh(22)(CO)(35)](4-/5-) carbonyl cluster has been obtained as a byproduct of the synthesis of [H(3)Rh(13)(CO)(24)](2-) and effectively separated by metathesis of their sodium salts with [NEt(4)]Cl. Although the yields are modest and never exceed 10-15% (based on Rh), this procedure affords spectroscopically pure [H(3)Rh(22)(CO)(35)](5-) anion. Formation of the latter in mixture with other Rh clusters was also observed by electrospray ionization-mass spectrometry (ESI-MS) in the oxidation of [H(2)Rh(13)(CO)(24)](3-) with Cu(2+) salts. The recovery of further amounts of [H(3)Rh(22)(CO)(35)](5-) was hampered by too similar solubility of the salts composing the mixture. Conversely, the reaction in CH(3)CN of [H(2)Rh(13)(CO)(24)](3-) with [Cu(MeCN)(4)](+)[BF(4)](-) leads to the [H(2)Rh(13)(CO)(24){Cu(MeCN)}(2)](-) bimetallic cluster. The X-ray crystal structures of [H(4)Rh(22)(CO)(35)](4-), [H(3)Rh(22)(CO)(35)](5-), and [H(2)Rh(13)(CO)(24){Cu(MeCN)}(2)](-) are reported. From a formal point of view, the metal frame of the former two species can be derived by interpenetration along two orthogonal axes of two moieties displaying the structure of the latter. The availability of [H(8-n)Rh(22)(CO)(35)](n-) salts prompted their detailed chemical, spectroscopic, and electrochemical characterization. The presence of hydride atoms has been directly proved both by ESI-MS and (1)H NMR. Moreover, both [H(4)Rh(22)(CO)(35)](4-) and [H(3)Rh(22)(CO)(35)](5-) undergo distinctive electrochemically reversible redox changes. This allows to assess electrochemical studies as indisputable though circumstantial evidence of the presence of (1)H NMR-silent hydride atoms in isostructural anions of different charge.

A molecular wire incorporating a robust hexanuclear platinum cluster

Reaction of [Pt(6)(CO)(4)(P(t)Bu(2))(4)Cl(2)] with excess HS(CH(2))(4)SH in Et(2)NH gave highly stable [Pt(6)(CO)(4)(P(t)Bu(2))(4){S(CH(2))(4)SH}(2)], which adsorbs unchanged onto gold surfaces. This permitted the fabrication and electrical characterisation of gold|molecule|gold junctions involving a well-defined metal carbonyl cluster compound.