Luciano Pandolfo

New coordination polymers based on the triangular [Cu3(μ3-OH)(μ-pz)3]2+ unit and unsaturated carboxylates

By reacting copper(II) acrylate with pyrazole (Hpz), two trinuclear copper derivatives [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(H2O)2(Hpz)], 1, and [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(CH3OH)], 2, are obtained, in water and methanol respectively, while copper(II) methacrylate affords [Cu3(mu3-OH)(mu-pz)3(CH2C(CH3)COO)2], 3, independently from the solvent used. In 1 and 2 two triangular trinuclear units are connected through acrylate bridges forming hexanuclear clusters that, in the case of 2 are further connected through double syn-syn carboxylate bridges, generating a 1-D coordination polymer. In the case of 3 a different 1-D coordination polymer is obtained by alternating syn-syn and syn-anti double carboxylate bridges connecting the trinuclear clusters. In all cases H-bonds contribute both to the stabilization of these arrangements and to the formation of more extended supramolecular networks. Compounds 1-3 are valuable catalysts in the peroxidative oxidation with aqueous H2O2, in MeCN at 25 degrees C, of cycloalkanes (i.e. cyclohexane and cyclopentane) to the corresponding ketones and alcohols (overall yield up to 36%, TON = 36), following a radical mechanism as shown by radical trap experiments, and the effects of various factors are studied. Electrochemical experiments show that the copper(II) centres are reduced to copper(I) and copper(0).

Functionalized ylides: new trends in organometallic chemistry

The coordination and organometallic chemistry of P- and As-carbonyl stabilized ylides is reviewed. As a general feature, the coordination chemistry of R3ECHCOR′-type (E=P, As) ligands appears to be dominated by C(ylide) metal coordination, although a few examples of O(ylide)-bound complexes are known. The factors addressing C(ylide)-vs. O(ylide)-coordination in Pt(II) and Pd(II) systems are examined. The Ni(II) complexes containing P,O-chelate ylide ligands are also discussed, with a special emphasis on their catalytic activity. The synthesis and reactivity of phosphonium functionalized isocyanides and their corresponding ylides, which provide a new route to metal coordinated indole systems, are described. Finally, the reactivity of Ph3PCCO towards metal substrates is summarized including the formation of ketenyl complexes.

Green and low temperature synthesis of nanocrystalline transition metal ferrites by simple wet chemistry routes

Crystalline and nanostructured cobalt (CoFe2O4), nickel (NiFe2O4), zinc (ZnFe2O4) and manganese (MnFe2O4) spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of coprecipitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining coprecipitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low temperature of 75 °C and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction (XRPD), while X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy (TEM) observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer (SQUID) revealing hard and soft ferrimagnetic behavior, respectively.

Magnetic Properties and Vapochromic Reversible Guest-Induced Transformation in a Bispyrazolato Copper(II) Polymer: an Experimental and Dispersion-Corrected Density Functional Theory Study

Dispersion-corrected density functional theory (DFT-D) calculations, Electron Spin Resonance spectroscopy (EPR), and variable temperature magnetic moment measurements were used to investigate the structure and the electronic/magnetic properties of bispyrazolato-copper(II) coordination polymer and of its hydration product. The Cu(II) ions are antiferromagnetically coupled through the sigma system of the pyrazolate rings in both compounds. Theoretical electron density maps reveal that water molecules interact simultaneously and to a comparable extent with two Cu(II) centers (through the electronegative O end) and two pyrazolate rings (through the partly positively charged H atoms), which is compatible with the observed internuclear distances. DFT-D calculations indicate that low kinetic barriers are involved in the rearrangement of the host structure.

The Organometallic Chemistry of Carbon Suboxide

Abstract Carbon suboxide, C3, O2, reacts with a great variety of organometallic compounds. With organo-silicon and aluminium compounds it reacts with the C˭O moiety, giving sililation and carboalumination reactions. Insertion reactions of C˭C are performed with compounds having M-H, M-OR, M-NR2, M-PR2 bonds (M ≠ Si, Al), giving mono-metal derivatives (ketenyl) or di-metal derivatives of acil groups (amides, esthers, phospides). The coordination of C˭O or C˭C to transition metal complexes, the formation of allenic compounds and the decarbonylation reactions allow the synthesis of a series of particular metal derivatives (ketenyl, ketenylidene and carbonyl complexes) which, in some cases, present a peculiar reactivity.

The behaviour of [Pt(η3‐allyl)XP(C6H5)3] complexes in electrospray ionization conditions compared with those achieved by other ionization methods

Three Pt(II) η3-allylic compounds, [Pt(η3-allyl)XP(C6H5)3] (X = Cl, Br, I) have been studied under electrospray ionization (ESI) conditions. Unexpected behaviour, such as the complete lack of either [M]+. or [MH]+ ions, the formation of complexes with the solvent and bis-triphenylphosphino-containing species, was observed. To rationalize such results, a series of parallel measurements on the same compounds have been performed under electron impact, fast-atom bombardment and field ionization conditions. The data so obtained suggest that molecular species are not produced by ESI, probably due to the action of strong electric fields and collisionally induced decompositions occurring in different regions of the instrument. Complexes with the solvent originate through gas-phase ion–molecule reactions, while the bis-triphenylphosphino-containing species are formed by reaction of ions with triphenylphosphine formed by thermal decomposition inside the heated capillary line, just after the electrospray ionization source.

The organometallic chemistry of Ph3PCCO.: A route to metal-substituted ketenes

Abstract Ketenylidenetriphenylphosphorane, Ph 3 PCCO ( 1 ), presents, at a first glance, the characteristics of both ylides and ketenes, but its behavior is that typical of ylides, undergoing electrophilic attacks on the ylidic carbon that transform 1 into a ‘true’ ketene having PPh 3 as one substituent. Here we review the synthesis, the chemical–physical properties as well as the reactivity of these compounds, with a particular emphasis on the interaction with transition metal complexes. With this compound it has always been observed that the ylidic carbon of 1 binds to coordinatively unsaturated metals, which act as electrophiles, forming η 1 -ketenyl derivatives that can also be viewed as stabilized metal-substituted ketenes. Perspectives for the synthesis of other metal-substituted ketenes and developments on their study are also presented.

Reactivity of carbon suboxide toward As and P stabilized ylides. Crystal and molecular structure of CH2{C(=O) [C(=AsPh3) (COOMe)]}2

Abstract The reactions of carbon suboxide, C3O2, with a series of stabilized triphenylarsoranes, Ph3As=CHX (X = CN, COOMe, COMe, COPh, COC6H4-p-OMe), yield two different kinds of cmpounds. When X = CN, COOMe the reaction proceeds in a 2:1 ratio (ylide: C3C2) yielding open-chain maloni bis-ylidic compounds (1a,b) whereas in the cases of X = COMe, COPh, COC6H4-p-OME only 1:1 cyclic zwitterionic compounds (2a-c) are obtained. The crystal structure of the bis-ylidic compound 1b has been determined. The crystalas are monoclinic, space group C2/c with a = 19.296(8), b = 10.179(5), c = 19.743(8) A , β = 97.3(1)°, Z = 4 . The molecular parameters are consistent with an important contribution of the dipolar form −OC=CAs+. Carbon suboxide has been reactde also with Ph3P=CHX (X = COC6H4-p-OMe, COOMe) giving the cyclic zwitterionic compounds 3 when X = COC6H4-p-OME, whereas when X = COOMe a mixture of products has been obtained.

Carbon suboxide polymers

Abstract On the basis of pyrolysis and hydrolysis measurements, we propose for the polymers of carbon suboxide (prepared with cationic, anionic and radical initiators) a structure consisting of condensed rings of α and γ-pyrone units. On thermolysis the polymer gives CO and CO2 as the sole gaseous species, with a characteristic thermal spectral pattern. By titration with bases, at least two types of acid sites have been found: they are to be ascribed to α and γ-pyrones with different hydrolysis rates. Measurements of molecular weight by VPO, in water, on the polypyranonic derivative show 6–8 monomeric units per chain.

Reaction of ketenylidenetriphenylphosphorane, Ph3PCCO, with water: formation of methyltriphenylphosphonium hydrogencarbonate

Abstract The reaction of the oxocumulene ylide ketenylidenetriphenylphosphorane, Ph3PCCO (1), with an excess of water in THF yields a white microcrystalline solid, methyltriphenylphosphonium hydrogencarbonate, which contains one molecule of crystallization water, [Ph3MeP]CO3H·H2O (2). Compound 2 was characterized by IR, multinuclear NMR and ESI mass spectra. The chemical constitution was confirmed by X-ray crystal analysis. On heating, compound 2 decomposes giving CO2, H2O, C6H6 and Ph2MePO.