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Trimethylsilyl-substituted ligands as solubilizers of metal complexes in supercritical carbon dioxide

The SiMe3 group (TMS), introduced as a substituent at the cyclopentadienyl ligand, is found to magnify the solubility of the corresponding metal complexes in supercritical carbon dioxide (scCO2). This is verified from comparative solubility measurements of the species (η5-Me3SiC5H4)MoO2Cl, 1a, (η5-Me3SiC5H4)2ZrCl2, 2a, and (η5-Me3SiC5H4)Co(CO)I2·0.5(I2), 3a (newly synthesised), and of their unsubstituted precursors 1b–3b, respectively. In spite of the increased solubility, the chemical, structural and reactivity properties of the TMS derivatives are scarcely affected. Confirmation comes from a detailed study of the cobalt complex 3a that includes X-ray structural determination. The geometry is most similar to that of the precursor 3b while an apparently different Co–CO interaction is observed in the carboxylated analogue [(η5–PhCH2CO2C5H4)Co(CO)I2, 3c]. The problem is computationally tackled by using the DFT B3LYP method. The optimised geometries of the simplified models of 3a–3c are all very similar. In particular, the computed stretching frequency of the unique CO ligand is consistent with the insignificant influence of the TMS group while it suggests a reduced amount of metal back-donation in 3c. It is inferred that the TMS complexes 1a–3a, while having higher solubility in scCO2, maintain almost unaltered the electronic and chemical features of their parent compounds. In particular, the role of 1a–3a as catalysts, that is well documented for homogeneous solutions, remains unaltered in the very different scCO2 environment. The assumption is experimentally validated for 1a by performing with the latter two classic catalytic processes. The first process is the oxidation of PPh3 that is achieved by using molecular oxygen as an oxidant. The second example concerns the epoxidation of cyclohexene achieved in presence of tert-butyl hydroperoxide (TBHP).

Synthesis, X-ray structure, and theoretical studies of novel cationic mono-cyclopentadienyl complexes of Co(III): the orthometalation of trans-azobenzene

Abstract New cationic mono-cyclopentadienyl complexes of Co(III) containing mono or bidentate nitrogen donor ligands of general formula [Co(η5-C5H5)(PPh3)L2][BF4]2 (L=NC–CH3, 2, and NC–Ph, 3) or [Co(η5-C5H5)(PPh3)(L–L)][BF4]2, [L–L=2,2′-bisimidazole (H2biim) (4) and dipyridylamine [HN(NC5H5)2] (5) have been synthesised by the stoichiometric reaction of the Co(III) complex Co(η5-C5H5)(PPh3)I2 (1), with Ag[BF4] and the appropriate ligand in CH2Cl2. Under the same conditions and using trans-azobenzene as a ligand, an orthometalation reaction took place, giving the new compound [Co(η5-C5H5)(PPh3)(κ-C,κ-N–C6H4NNPh)][BF4] (6) in high yield. The structural characterisation of compounds 4 and 6, and of the starting compound Co(η5-C5H5)(PPh3)I2 (1) was done by single-crystal X-ray diffraction studies. DFT calculations ( adf program) were performed in order to understand the orthometallation reaction.

CpCo(CO)2-catalysed cyclotrimerisation of alkynes in supercritical carbon dioxide

Abstract The reactivity of mono-substituted HCCR (R=Ph, a ; CH 2 OH, b ; CH 2 CH 2 CH 2 CH 3 , c ) and di-substituted RCCR (R=CH 2 CH 3 , d ; CO 2 CH 3 , e ; Ph, f ) acetylenes was studied in supercritical carbon dioxide (scCO 2 ) using the easily available complex CpCo(CO) 2 as catalyst. The reaction of phenylacetylene produced a mixture of the isomeric cyclotrimers 1,3,5- ( 2a ) and 1,2,4-triphenylbenzene ( 2a′ ), in a 1:5 ratio, and traces of cobaltcyclopentadienone complexes CpCo(η 4 -C 4 H 2 [Ph] 2 CO) ( 6a , mixture of isomers). The possible product formed by the incorporation of CO 2 to alkynes, i.e. diphenylpyrone ( 7a ) was not observed. The reaction of the cobaltacyclopentadiene complex CpCo(1.4-σ-C 4 [Ph] 4 )(PPh) 3 ( 8f ), in scCO 2 , was performed. No insertion of CO 2 into the CoC σ-bond to form tetraphenylpyrone ( 7f ) by reductive elimination was observed, instead the cobaltcyclobutadiene complex CpCo(η 4 -C 4 [Ph] 4 ) ( 9f ) was formed. In the reactions with other alkynes, lower yields were obtained in general, except in the cyclotrimerisation of the highly activated alkyne, propargyl alcohol ( b ). Reaction of the non-activated alkynes, 1-hexyne ( c ) and 3-hexyne ( d ), produced complex mixtures of cobalt complexes in low yield in which the alkyne was coordinated to cobalt. Finally, the highly hindered diphenylacetylene ( f ) gave a mixture of the known complexes CpCo(η 4 -C 4 [Ph] 4 ) ( 9f ) and CpCo(η 4 -C 4 [Ph] 4 CO) ( 6f ) in agreement with the results observed in conventional organic solvents.

Transition-metal-mediated activation of arylisocyanates in supercritical carbon dioxide

Abstract The reactivity of arylisocyanates in supercritical carbon dioxide (scCO 2 ) was studied using the easily available complexes CpCo(CO) 2 , CpCoPPh 3 Me 2 and Ni(cod) 2 as catalysts. A study of the solubility of the catalysts in scCO 2 was undertaken in all cases. The complex CpCo(CO) 2 is very soluble, 1.7×10 −1 mol kg −1 , while CpCoPPh 3 Me 2 has a lower solubility, 7.2×10 −3 mol kg −1 , and Ni(cod) 2 is insoluble in scCO 2 . For comparison purposes, the reactions were performed in parallel in scCO 2 , using toluene as a solvent and just with the neat liquid arylisocyanate. Reactions in scCO 2 either do not take place at all, when CpCo(CO) 2 is used as catalyst, or occur with low yields affording the trimer of the corresponding arylisocyanate when CpCoPPh 3 Me 2 or Ni(cod) 2 act as catalysts. No incorporation of CO 2 into the organic substrate was observed. Better conversions to triarylisocyanate were obtained when the reactions were performed by direct mixture of the liquid arylisocyanate ArNCO (Ar=Ph, p -CH 3 C 6 H 4 , p -CH 3 OC 6 H 4 ) and the catalyst. Using toluene as a solvent, the yields of the trimers were lower than those obtained in neat arylisocyanate, and in some cases they were not formed at all. For instance in the reaction of CpCo(CO) 2 and tolylisocyanate either under stoichiometric or catalytic conditions the trimer is not obtained, instead the compound H 2 R 3 N 3 C 2 O 2 (R=CH 3 C 6 H 4 ), was isolated in low yield. In the reaction of Ni(cod) 2 /PPh 3 with phenylisocyanate, the trimer was formed but in low yield. The lower yields of the trimers observed when the reactions were performed in scCO 2 or in toluene, compared to that observed in neat arylisocyanates, indicates that the decrease in reactivity is due to a decrease in concentration.

Synthesis, X-ray structures, electrochemistry, magnetic properties, and theoretical studies of the novel monomeric [CoI2(dppfO2)] and polymeric chain [CoI2(μ-dppfO2)n]

The new compound [Co(η5-C5H5)(dppf-P,P′)I]I, 1, was synthesised by the stoichiometric reaction of the Co(III) complex [Co(η5-C5H5)(CO)I2], 2, with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in CH2Cl2, and was characterised by multinuclear NMR spectroscopy. Exposure to air of THF or CH2Cl2 solutions of compound 1 gave, in an unexpected way, a polymeric chain comprising bridging 1,1′-bis(oxodiphenylphosphoranyl)ferrocene (dppfO2) joining tetrahedral Co(II) units [CoI2(μ-dppfO2)]n, 3. Attempts to obtain the polymeric chain 3 by the direct reaction of dppfO2 with CoI2, in CH2Cl2, gave instead the monomeric compound [CoI2(dppfO2)], 4, in which dppfO2 is coordinated in a chelating mode. The structural characterisation of compounds 2, 3, and 4 was carried out by single crystal X-ray diffraction studies. The magnetic behaviour of [CoI2(dppfO2)] and [CoI2(μ-dppfO2)]n was studied, and the results are consistent with tetrahedral S = 3/2 CoII, possessing a 4A2 ground state, and S = 0 FeII. In these compounds, CoII negative zero field splittings were determined from an analysis of the magnetic susceptibility temperature dependence, with D/k = −13 and −14 K for CoI2(dppfO2) and [CoI2(μ-dppfO2)]n, respectively. DFT calculations were performed in order to understand the electronic structure of [Co(η5-C5H5)(dppf-P,P′)I]I, 1, as well as that of the paramagnetic specie [CoI2(dppfO2)], 4. The [CoI2(μ-dppfO2)]n chain was also analysed and found to behave very similarly to the monomeric iodine derivative 4. The calculations showed the unpaired electrons to be localized on the Co(II) centre in all these species. The rather complicated electrochemical behaviour exhibited by the dppf complex [CoIII(η5-C5H5)(dppf-P,P′)I]I and by [Co(dppfO2)I2] is discussed.

Mono(cyclopentadienyl)molybdenum chemistry: hydrido-, halogeno-, allylic, and butadiene derivatives of [1,2-bis(diphenylphosphino)ethane](η-cyclopentadienyl)molybdenum and related compounds

The new compounds [Mo(η-C5H5)2L2][PF6]2, [Mo(η-C5H5)(η3-C5H7)(dppe)], [Mo(η-C5H5)L2Cl3], [Mo(η-C5H5)(dppe)H3], [Mo(η-C5H5)(dppe) Br3]·C6H5Me, [Mo(η-C5H5)2(NCMe)2][PF6]2, [Mo(η-C5H5)2(dppm)H][PF6], [Mo(η-C5H5)(dppm)Cl][PF6]·0.5CH2Cl2, and [Mo(η-C5H5)(exo-H-C5H5)(dppm)][PF6]·CH2Cl2[L2= 1,2-bis (diphenylphosphino)ethane (dppe) or bis(diphenylphosphino)methane (dppm)] have been prepared. The trihydride [Mo(η-C5H5)(dppe)H3] reacts with butadiene giving [Mo(η-C5H5)(dppe)(η3-C3H4Me)].

Imine Ligands Based on Ferrocene: Synthesis, Structural and Mössbauer Characterization and Evaluation as Chromogenic and Electrochemical Sensors for Hg+2

The compounds 1-naphthyliminoferrocene, 1, and 2-methyl-1-naphthyliminoferrocene, 2, were prepared by the reaction of ferrocenecarboxaldehyde and the corresponding amine, 1-naphthylamine and 2-methyl-1-naphthylamine with one drop of pyrrolidine as the catalyst, in CH2Cl2, under an inert atmosphere. The compounds were fully characterized by elemental analyses, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF), FT-IR, 1H and 13C NMR as well as two-dimensional, NOESY, COSY and HSQC, NMR spectroscopy. Mossbauer spectroscopic studies were performed to characterize iron species in both compounds. The solid-state molecular structures of compounds 1 and 2 were determined by single crystal X-ray diffraction. Analysis of the electrochemical behaviour of complexes 1 and 2 was performed by cyclic and square wave voltammetry. Compounds 1 and 2 were tested as chromogenic and electrochemical sensors for Hg2+.

A Novel Infinite 1-D Chain of Silver(I) Bridged by trans-Azobenzene

The self-assembly of Ag[BF4] with trans-azobenzene in dichloromethane yields a new coordination polymer ([Ag(μ-trans-azobenzene)H20][BF4]) n which was characterized by X-ray single crystal diffraction. The crystal consists of 1-D zigzag cationic chains made up from [Ag(H20)]+ units linked by trans-azobenzene bridges and BF 4 − anions. Hydrogen bonding interactions between the chains and BF 4 − anions occur via intermolecular C−H…F and O−H…F contacts, and the crystal displays a 2-D supramolecular structure.

Syntheses and Crystal Structures of Polynuclear Cu(I) Complexes Containing the 1,1'-Bis­ (diphenylphosphino )-ferrocene Ligand

The reaction between [Cu(NCMe)4][PF6] and l,l′-bis-5-(diphenylphosphino)-ferrocene (dppf) in several ratios, solvents, and conditions led to the synthesis and structural characterization of the Cu(I) complexes [Cu(dppf)(Odppf][PF6] (1), [(dppf)Cu(μ-dppf)Cu(dppf)][PF6]2 (2), and [(dppf)Cu(μ-Cl)2Cu(dppf)] (3). Although 1 and the cation in 2 were known, the first was structurally characterized for the first time, exhibiting a significant asymmetry in the coordination sphere of Cu(I) owing to the presence of oxygen. In 2, the P F 6 − anion led to an interesting crystal packing with large open channels containing water. Finally, DFT calculations on a model of 3 showed that its HOMO exhibits, besides Fc, a significant Cu and Cl character, which is reflected in its electrochemical properties.