Luca Labella

A facile synthesis of Zn4(μ4-O)(O2CNMe2)6

Abstract Zn4O(O2CNMe2)6 was synthesized from ZnO and [NH2Me2][O2CNMe2] in MeCN as solvent and characterized by spectroscopic and diffractometric methods.

Isolation and structural determination of two derivatives of the elusive carbamic acid

The dibenzyl-substituted carbamic acid (PhCH2)2NC(O)OH (1), its deprotonation product [(PhCH2)2NH2]- [(PhCH2)2NCO2] (2) and CoCl(NO)2[PhP(OCH2CH2)2NC(O)OH ]·2MeCOMe(3·2MeCOMe) are reported, the diffractometric study showing the carbamic acids 1 and 3 to be paired through hydrogen bonds.

Syntheses and reactions of ansa-[2,2-bis(η-cyclopentadienyl)propane]-tungsten and -molybdenum compounds

Reaction between [MCl4(dme)](M = W or Mo; dme = 1,2-dimethoxyethane) with Li2[C5H4CMe2C5H4] gave the ansa-bridged metallocene dichlorides [M{(η-C5H4)CMe2(η-C5H4)}Cl2](M = W or Mo). Treatment of these with LiAlH4 or ZnMe2 gave respectively the dihydrides [M{(η-C5H4)CMe2(η-C5H4)}H2](M = W or Mo) and the dimethyl derivatives [M{(η-C5H4)CMe2(η-C5H4)}Me2](M = W or Mo). Treatment of [W{(η-C5H4)CMe2(η-C5H4)}Me2] with HX (X = PhCO2 or NH3l) gave [W{(η-C5H4)CMe2(η-C5H4)}Me(Y)] with Y = PhCO2 or l, respectively. Both of these react with Na[AlH2(OCH2CH2OMe)2] giving the methylhydride [W{(η-C5H4)CMe2(η-C5H4)}Me(H)]. The latter is thermally stable in refluxing benzene. Ultraviolet photolysis of [Mo{(η-C5H4)CMe2(η-C5H4)}H2] in benzene gave the phenylhydride derivative [Mo{(η-C5H4)CMe2(η-C5H4)}Ph(H)]; the corresponding tungsten derivative [W{(η-C5H4)CMe2(η-C5H4)}H2] is not photosensitive. The crystal structures of [W{(η-C5H4)CMe2(η-C5H4)}Cl2], [W{(η-C5H4)CMe2(η-C5H4)}H2], (two modifications) and [Mo{(η-C5H4)CMe2(η-C5H4)}H2] have been determined by X-ray diffraction. The ansa-bridged bis(η-cyclopentadienyl) compounds show marked differences in reactivity compared to non-ansa analogues and this is discussed in terms of the modifications of the electronic structure as a consequence of the ansa bridge.

Synthesis, and crystal and molecular structures of the triflato and trifluoroacetato complexes of zinc, Zn(O3SCF3)2(DME)2 and [Zn(O2CCF3)2(DME)]n

Abstract Anhydrous Zn(O3SCF3)2 and Zn(O2CCX3)2, X=F, Cl, Br were obtained in substantially quantitative yields from ZnO (or ZnEt2 in the case of the bromide derivative) and a mixture of the corresponding acid and anhydride in heptane as medium. The reactions are rapid and moderately exothermic. Recrystallization of the triflate and trifluoroacetate complexes from dimethoxyethane (DME) produced single crystals of Zn(O3SCF3)2(DME)2 (1) and [Zn(O2CCF3)2(DME)]n (2) suitable for X-ray diffraction studies. In both compounds zinc is hexacoordinated with a pseudo-octahedral geometry. Compound 1 is constituted by mononuclear molecules with terminal monodentate O3SCF3 ligands in trans position. A polynuclear chain structure was found for 2 with zinc atoms joined alternatively by triple and single carboxylato bridges, and with bidentate terminal DME.

Triphenylphosphine-substituted N,N-di-iso-propylcarbamate of ruthenium(II) and its reactions with carbon monoxide

Abstract Chloride displacement from RuCl 2 (PPh 3 ) 3 by NH i Pr 2 /CO 2 in toluene as medium gave the N , N -di- iso -propylcarbamato derivative Ru(O 2 CN i Pr 2 ) 2 (PPh 3 ) 2 , ( 1 ), whose X-ray crystal structure determination showed the mononuclear compound to contain hexacoordinated ruthenium bonded to bidentate carbamato and to cis -arranged tertiary phosphine groups in a distorted octahedral geometry. Carbonylation at room temperature rapidly converted 1 to the monocarbonyl derivative Ru(O 2 CN i Pr 2 ) 2 (PPh 3 ) 2 (CO) ( 2 ), presumably containing a monodentate carbamato group, the dicarbonyl compound Ru(O 2 CN i Pr 2 ) 2 (PPh 3 ) 2 (CO) 2 ( 3 ) being formed over longer reaction times. X-ray diffraction data showed 3 to contain hexacoordinate ruthenium(II) with monodentate carbamato groups trans to the carbonyl groups and with trans -arranged triphenylphosphine groups. Controlled hydrolysis of 3 yielded the dicarbonyl-carbonato complex Ru(O 3 C)(PPh 3 ) 2 (CO) 2 ·H 2 O ( 4 ), crystallographically established to contain a bidentate carbonato group, trans triphenylphosphine ligands and water hydrogen-bonded to the carbonato ligand.

Nanostructured Copper Oxide on Silica–Zirconia Mixed Oxides by Chemical Implantation

N,N-Dialkylcarbamato complexes of copper(II), [Cu(O(2)CNR(2))(2)] (R = All = allyl, C(3)H(5); iPr, CH(CH(3))(2)) were prepared with the aim of functionalizing silica and nanostructured silica-zirconia matrices. The mixed matrices for the grafting reactions were prepared by copolymerizing MAPTMS (methacryloxypropyltrimethoxysilane), the precursor for the silica matrix, with the zirconium tetranuclear derivative [Zr(4)O(2)(OMc)(12)] (OMc = methacrylate), the precursor for the zirconia nanoparticles. Suspension of the silica and silica-zirconia matrices in a solution of the copper dialkylcarbamate led to the functionalization of the respective substrates. The composition, microstructure, morphology, and physicochemical nature of the copper species grafted on the matrices were investigated by FTIR, X-ray photoelectron spectroscopy (XPS), EPR, X-ray absorption spectroscopy (XAS), XRD, TEM, and dinitrogen adsorption. The effect of selected experimental parameters (the nature of the copper precursor and of the matrix, grafting time, thermal treatment) on the grafting reaction was investigated. The Cu/Si ratio is increased by increasing the grafting time and the ZrO(2)-SiO(2) matrix is more reactive to attack by the carbamato complexes than either prepared or commercial SiO(2). After functionalization of the matrix, thermal treatment yielded nanostructured copper(II) oxide clusters, average diameter 12-15 nm, uniformly supported on the silica and on the silica-zirconia matrices.

Reaction of a tetranuclear N,N-di-iso-propylcarbamato complex of cerium(III) with dioxygen: synthesis and X-ray characterization of both the oxidation product and its precursor

Abstract The tetranuclear N,N-di-iso-propylcarbamato complex of cerium(III) Ce 4 ( O 2 CN i Pr 2 ) 12 , 1, has been synthesized and its crystal structure solved through X-ray diffraction methods. The oxidation of the cerium(III) complex by dioxygen produces the μ3-oxo tetranuclear cerium(IV) derivative Ce 4 ( μ 3 - O ) 2 ( O 2 CN i Pr 2 ) 12 , 2, which has been characterised by single crystal X-ray diffractometry. Structural rearrangements on going from the cerium(III) derivative to the corresponding cerium(IV) product have been established. This is the first case of a μ-oxo-carbamato complex being obtained by oxygenation, whereby product and precursor maintain the basic structural features.

N,N-dialkylcarbamato metal complexes, molecular inorganic precursors to functionalized inorganic matrices

Abstract The relatively new class of the N,N-dialkylcarbamato metal complexes, of general formula [M(O2CNR2)n]m, n and m being the oxidation number of the central metal atom M and the nuclearity of the system, is reviewed with particular attention to compounds of Main Group elements (particularly tin, silicon and aluminium), and of transition d- and f-metals. Synthetic procedures and structural properties of the homoleptic compounds (i.e., compounds in which the set of anionic ligands is constituted by the monoanionic O2CNR2(−) ligand exclusively) are reported, also in relation to the results obtained by other research groups in this area. The reactivity of these systems is reported in connection with: (a) homoleptic derivatives; (b) non-homoleptic N,N-dialkylcarbamato complexes; (c) controlled hydrolysis of the homoleptic precursors to μ-oxo derivatives; (d) N,N-dialkylcarbamato complexes as reactive species towards surface hydroxyl groups, whereby Si–O–M linkages can be formed; (e) exhaustive hydrolysis of the N,N-dialkylcarbamato complexes; (f) metal N,N-dialkylcarbamato complexes as reactive intermediates to organic products. The literature references to papers originated from this research group can be found in the web site of the University of Pisa ( http://www.dcci.unipi.it/∼facal/ICA-BIB.htm ).

Smart Grafting of Lanthanides onto Silica via N,N-Dialkylcarbamato Complexes.

The grafting and the postgrafting functionalization of lanthanide ions on commercial amorphous silica have been herein carried out by using as a precursor the terbium N,N-dibutylcarbamato derivative [Tb(O2CNBu2)3]. The reaction of the complex with the surface silanols involved only a fraction of the carbamato ligands. The following protolytic substitution of the residual carbamato ligands was carried out by exploiting the Brønsteds acidity of the β-diketone dibenzoylmethane (Hdbm), in view of the antenna effect of the β-diketonato groups, which are commonly used in lanthanide photoluminescence studies. The reaction proceeded at room temperature in a clean and easy way affording the introduction of the chosen functionality in the lanthanide coordination sphere. The same procedure has been followed by using as a precursor the X-ray characterized heterometallic N,N-dibutylcarbamato complex [NH2Bu2]2[Ln4(CO3)(O2CNBu2)12] (Ln = Eu, Tb, Tm). In both cases, X-ray photoelectron spectroscopy evidenced the chemical implantation of the lanthanide ions on the silica surface, and photoluminescence studies pointed out the potentiality of the proposed synthetic approach in the preparation of highly luminescent materials.

Preparation of N,N-Dialkylcarbamato Lanthanide Complexes by Extraction of Lanthanide Ions from Aqueous Solution into Hydrocarbons

Lanthanides are easily extracted as N,N-dibutylcarbamato complexes from aqueous solutions of their chlorides into heptane solutions of dibutylamine saturated with CO2. The products are recovered in high yields and are soluble in hydrocarbons. The derivatives [Ln(O2CNBu2)3]n [Ln = Nd (1), Eu (2), Tb (3)], [NH2Bu2]2[Ln4(CO3)(O2CNBu2)12] [Ln = Tb (4), Sm (5), Eu (6)], and [Sm4(CO3)(O2CNBu2)10], 7, have thus been obtained. The crystal and molecular structure of 4 has been solved; the samarium and europium complexes 5 and 6 were found to be isostructural. Mass spectra of the complexes 1-3, 4, and 7 (in MeCN/toluene) reveal that equilibria are present in solution. Compound 2 has been reacted in toluene with NHBz2 in the presence of CO2 affording [NH2Bz2][Eu(O2CNBz2)4], 8, through a ligand exchange process. By thermal treatment, 8 afforded [Eu(O2CNBz2)3]n, 9. With a similar procedure [Sm(O2CNBz2)3]n, 10, was obtained from 5. According to the photoluminescence study carried out on solid samples of 2, 4, 5, 7, and 8, the metal centered f-f transitions represent the only effective way to induce lanthanide luminescence in these complexes.