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Journal Article
Pedras, B., H. M. Santos, L. Fernandes, B. Covelo, A. Tamayo, E. Bertolo, J. L. Capelo, T. Aviles, and C. Lodeiro. "Sensing metal ions with two new azomethine-thiophene pincer ligands (NSN): Fluorescence and MALDI-TOF-MS applications." Inorg Chem Commun. 10 (2007): 925-929. AbstractWebsite

The two new pincer azomethine-thiophene ligands (N,NE',N,NE')-N,N'-(thiophene-2,5-diylbis(methan-1-yl-1-ylidene))bis(naphathalen-2-ylmethanamine) (L1) and (E)-(4,6-dihydropyren-1-yl)-N-((5-((E)-(pyren-1-ylmethylimino)ethyl)thiophen-2-yl)methylene)methanamine (L2), their absorption, fluorescence and MALDI-TOF-MS spectroscopic studies are described. The two systems synthesised combine the emissive probes pyrene and naphthyl with the good chelating properties of a tridentate SN2 donor-set from a thiophene Schiff-base ligand. Both ligands gave analytically pure solid complexes with Ni(II) and Pd(II) salts. The bichromophoric pyrene derivative L2 presents two emission bands in solution, one corresponding to the monomer species and a red-shifted band attributable to the intramolecular excimer. Ni(II) and Pd(II) complexation affects the conformation in solution, increasing the monomer emission at the expense of the excimer band; this effect could be explored in metal ion sensing. System L1 behaves as a non emissive probe. In situ complexation reactions followed by MALDI-TOF-MS spectrometry without matrix support have also been performed; these experiments show that L1 could be a potential chemosensor for Ni(II) and Pd(11). (c) 2007 Elsevier B.V. All rights reserved.

Pinto, P., M. J. Calhorda, V. Felix, T. Aviles, and M. G. B. Drew. "Syntheses and crystal structures of polynuclear Cu(I) complexes containing the 1,1 '-bis(diphenylphosphino)-ferrocene ligand." Monatsh Chem. 131 (2000): 1253-1265. AbstractWebsite

The reaction between [Cu(NCMe)(4)][PF6] and 1,1'-bis-(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(mu -dppf)Cu(dppf)][PF6](2) (2), and [(dppf)Cu(mu -Cl)(2)Cu(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 PF6- 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 Fe, a significant Cu and Cl character, which is reflected in its electrochemical properties.

Agostinho, M., V. Rosa, T. Aviles, R. Welter, and P. Braunstein. "Synthesis and characterization of Co and Ni complexes stabilized by keto- and acetamide-derived P,O-type phosphine ligands." Dalton T (2009): 814-822. AbstractWebsite

The coordination properties of the beta-keto phosphine ligands R(2)PCH(2)C(O)Ph (HL(1), R = i-Pr; HL(2), R = Ph), of the new acetamide-derived phosphine ligand (i-Pr)(2)PNHC(O) Me (HL(3)) and of Ph(2)PNHC(O) Me (HL(4)) have been examined towards Ni(II) complexes. Comparisons are made between systems in which the PCH(2) function of the ketophosphine has been replaced with an isoelectronic PNH group in amide-derived ligands, or the PCH functionality of phosphinoenolates with a PN group in phosphinoiminolate complexes. Furthermore, ligands HL(2) and HL(4) reacted with [(eta(5)-C(5)H(5))CoI(2)(CO)] to afford the phosphine mono-adducts [(eta(5)-C(5)H(5))CoI(2){Ph(2)PCH(2)C(O)Ph}] (1) and [(eta(5)-C(5)H(5))CoI(2){Ph(2)PNHC(O)Me}] (3), respectively, which upon reaction with excess NEt(3) yielded the phosphinoenolate complex [(eta(5)-C(5)H(5))CoI{Ph(2)PCH (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Ph}] (2) and the phosphinoiminolate complex [(eta(5)-C(5)H(5))CoI{Ph(2)PN (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Me}] (4), respectively. The complexes cis-[Ni{(i-Pr)(2)PN (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Me}(2)] (6) and cis-[Ni{Ph(2)PN (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Me}(2)] (7) were obtained similarly from NiCl(2) and HL(3) and HL(4), respectively, in the presence of a base. The phosphinoenolate complex [Ni{(i-Pr)(2)PCH (center dot center dot center dot) under barC((center dot center dot center dot) under barO) Ph}(2)] (5) exists in ethanol as a mixture of the cis and trans isomers, in contrast to cis-[Ni{(Ph(2)PCH (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Ph}(2)], and the solid-state structure of the trans isomer of 5 was established by X-ray diffraction. The structures of the ligand HL3 and of the complexes 1, 3 in 3 center dot 3/2CH(2)Cl(2), 4, 6 and 7 have also been determined by X-ray diffraction and are compared with those of related complexes. Complexes 4, 6 and 7 contain a five-membered heteroatomic metallocyclic moiety, which is constituted by five different chemical elements. The structural consequences of the steric bulk of the P substituents and of the electronic characteristics of the P, O chelates are discussed.

Rosa, V., S. A. Carabineiro, T. Aviles, P. T. Gomes, R. Welter, J. M. Campos, and M. R. Ribeiro. "Synthesis, characterisation and solid state structures of alpha-diimine cobalt(II) complexes: Ethylene polymerisation tests." J Organomet Chem. 693 (2008): 769-775. AbstractWebsite

A series of cobalt(II) compounds of the type [CoX2(alpha-diimine)] were synthesised by direct reaction of anhydrous CoCl2 or CoI2 and the corresponding alpha-diimine ligand, in CH2Cl2: [CoI2(o,o',p-Me3C6H2-DAB)] ( 1), [ CoI2(o,o'-(Pr2C6H3)-Pr-i-DAB)] ( 2), ( where Ar-DAB = 1,4-bis(aryl)-2,3-dimethyl-1,4-diaza-1,3-butadiene), and [CoCl2(o,o',p-Me3C6H2- BIAN)] (3), [CoCl2(o,o'- (Pr2C6H3)-Pr-i-BIAN)] (4), and [CoI2(o,o'-(Pr2C6H3)-Pr-i-BIAN)] (5) (where Ar-BIAN = bis(aryl) acenaphthenequinonediimine). All compounds were characterised by elemental analyses, IR, mass spectrometry, and X-ray diffraction whenever possible. The crystal structures of compounds 2-4 showed, in all cases, distorted tetrahedral geometries about the Co, built by two halogen atoms and two nitrogen atoms of the alpha-diimine ligand. Compounds 3 and 4, as well as [ CoCl2(o,o',p-Me3C6H2-DAB)] (1a), and [ CoCl2( o,o'- (Pr2C6H3)-Pr-i- DAB)] (2a), were activated by methylaluminoxane (MAO) and tested as catalysts for ethylene polymerisation, showing low catalytic activities. Selected polyethylene ( PE) samples were characterised by H-1 and C-13 NMR and FT-IR spectroscopies, and by differential scanning calorimetry (DSC), revealing branching microstructures (2.5-5.5%). (c) 2007 Elsevier B. V. All rights reserved.

Rosa, V., P. J. Gonzalez, T. Aviles, P. T. Gomes, R. Welter, A. C. Rizzi, M. C. G. Passeggi, and CD Brondino. "Synthesis, solid-state structures, and EPR spectroscopic studies on polycrystalline and single-crystal samples of alpha-diimine cobalt(II) complexes." Eur J Inorg Chem (2006): 4761-4769. AbstractWebsite

Cobalt compounds of the general formula [COX2(alpha-diimine)], where X = Cl or I and the alpha-diimines are 1,4-diaryl-2,3-dimethyl-1,4-diaza-1,3-butadiene (Ar-DAB) and bis(aryl)acenaphthenequinonediimine (Ar-BIAN) were synthesized by the direct reaction of the anhydrous cobalt salts CoCl2 or CoI2 and the corresponding alpha-diinline ligand in dried CH2Cl2. The synthesized compounds are [Co(Ph-DAB)Cl-2] (1a), [Co(o,o',p-Me3C6H2-DAB)Cl-2] (1b), and [Co(o,o'iPr(2)C(6)H(3)-DAB)Cl-2] (1c) with the ligands Ar-DAB, and also [Co(o,o',p-Me3C6H2-BIAN)I-2] (2'b) with the ligand Ar-BIAN. The crystal structures of all the compounds were solved by single-crystal X-ray diffraction. In all cases the cobalt atom is in a distorted tetrahedron, which is built up of two halide atoms and two nitrogen atoms of the alpha-dimune ligand. X-band EPR measurements of polycrystalline samples performed on compounds 1b, 1c, and 2'b indicate a high-spin Col, ion (S = 3/2) in an axially distorted environment. Single-crystal EPR experiments on compounds 1b and 1c allowed us to evaluate the orientation of the g tensor in the molecular frame. (c) Wiley-VCH Verlag GmbH & Co.

Aviles, T., A. Dinis, M. J. Calhorda, P. Pinto, V. Felix, and M. G. B. Drew. "Synthesis, X-ray structure, and theoretical studies of novel cationic mono-cylopentadienyl complexes of Co(III): the orthometalation of trans-azobenzene." J Organomet Chem. 625 (2001): 186-194. AbstractWebsite

New cationic mono-cyclopentadienyl complexes of Co(III) containing mono or bidentate nitrogen donor ligands of general formula [Co(eta (5)-C5H5)(PPh3)L-2][BF4](2) (L = NC-CH3, 2, and NC = Ph, 3) or [Co(eta (5)-C5H5)(PPh3)(L-L)[BF4](2), [L-L = 2,2 ' -bisimidazole (H(2)biim) (4) and dipyridylamine [HN(NC5H5)(2)] (5) have been synthesised by the stoichiometric reaction of the Co(III) complex Co(eta (5)-C5H5)(PPh3)I-2 (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 placet giving the new compound [Co(eta (5)-C5H5)(PPh3)(kappa -C,kappa -N-C6H4N=NPh)][BF4] (6) in high yield. The structural characterisation of compounds 4 and 6, and of the starting compound Co(eta (5)-C5H5)(PPh3)I-2 (1) was done by single-crystal X-ray diffraction studies. DFT calculations (ADF program) were performed in order to understand the orthometallation reaction. (C) 2001 Elsevier Science B.V. All rights reserved.

Aviles, T., A. Dinis, J. O. Goncalves, V. Felix, M. J. Calhorda, A. Prazeres, M. G. B. Drew, H. Alves, R. T. Henriques, V. da Gama, P. Zanello, and M. Fontani. "Synthesis, X-ray structures, electrochemistry, magnetic properties, and theoretical studies of the novel monomeric [CoI2(dppfO(2))] and polymeric chain [CoI2(mu-dppfO(2))(n)]." J Chem Soc Dalton (2002): 4595-4602. AbstractWebsite

The new compound [Co(eta(5)-C5H5)(dppf-P,P')I]I, 1, was synthesised by the stoichiometric reaction of the Co(III) complex [Co(eta(5)-C5H5)(CO)I-2], 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 (dppfO(2)) joining tetrahedral Co(II) units [CoI2(mu-dppfO(2))](n), 3. Attempts to obtain the polymeric chain 3 by the direct reaction of dppfO(2) with CoI2, in CH2Cl2, gave instead the monomeric compound [CoI2(dppfO(2))], 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(dppfO(2))] and [CoI2(mu-dppfO(2))](n) was studied, and the results are consistent with tetrahedral S = 3/2 Co-II, possessing a (4)A(2) ground state, and S = 0 Fe-II. In these compounds, Co-II negative zero field splittings were determined from an analysis of the magnetic susceptibility temperature dependence, with D/k = -13 and -14 K for CoI2(dppfO(2)) and [CoI2(mu-dppfO(2))](n), respectively. DFT calculations were performed in order to understand the electronic structure of [Co(eta(5)-C5H5)(dppf-P,P')I]I, 1, as well as that of the paramagnetic specie [CoI2(dppfO(2))], 4. The [CoI2(mu-dppfO(2))](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 [Co-III(eta(5)-C5H5)(dppf-P,P')I]I and by [Co(dppfO(2))I-2] is discussed.

Montilla, F., E. Clara, T. Aviles, T. Casimiro, A. A. Ricardo, and M. N. da Ponte. "Transition-metal-mediated activation of arylisocyanates in supercritical carbon dioxide." J Organomet Chem. 626 (2001): 227-232. AbstractWebsite

The reactivity of arylisocyanates in supercritical carbon dioxide (scCO(2)) was studied using the easily available complexes CpCo(CO)(2), CpCoPPh3Me2 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 x 10(-1) mol kg(-1), while CpCoPPh3Me2 has a lower solubility, 7.2 x 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), is used as catalyst, or occur with low yields affording the trimer of the corresponding arylisocyanate when CpCoPPh3Me2 or Ni(cod)(2) act as catalysts. No incorporation of CO2 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-CH3C6H4, p-CH3OC6H4) 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), and tolylisocyanate either under stoichiometric or catalytic conditions the trimer is not obtained, instead the compound H2R3N3C2O2 (R = CH3C6H4), was isolated in low yield. In the reaction of Ni(cod)(2)/PPh3 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. (C) 2001 Elsevier Science B.V. All rights reserved.

Montilla, F., V. Rosa, C. Prevett, T. Aviles, M. N. da Ponte, D. Masi, and C. Mealli. "Trimethylsilyl-substituted ligands as solubilizers of metal complexes in supercritical carbon dioxide." Dalton T (2003): 2170-2176. AbstractWebsite

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 (scCO(2)). This is verified from comparative solubility measurements of the species (eta(5)-Me-3 SiC5H4)MoO2 Cl, 1a, (eta(5)-Me3SiC5H4)(2)ZrCl2, 2a, and (eta(5)-Me3SiC5H4)Co(CO)I-2.0.5(I-2), 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 [(eta(5)-PhCH2CO2C5H4)Co(CO) I-2, 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 scCO(2) 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).

Vitor Rosa, Sara Realista, Ana Mourato, Luisa Maria Abrantes, Joao Henriques, Maria Jose Calhorda, Teresa Aviles, Michael G. B. Drew, and Vitor Felix. "{1,1 `-Bis(diphenylphosphino)ferrocene bridging two mono(cyclopentadienyl) cobalt moieties: Synthesis, structure, electrochemistry and DFT studies}." {JOURNAL OF ORGANOMETALLIC CHEMISTRY}. {712} (2012): {52-56}. Abstract

{Reaction of {[}Co(eta(5)-C5H5)(CO)(2)], 1, with 1,1'-bis(diphenylphosphino)ferrocene (dppf) yields the new trinuclear complex {[}Co(eta(5)-C5H5)(CO)](2)(mu-dppf), 2, which was structurally characterised by single crystal X-ray diffraction and showed two Co(eta(5)-C5H5)(CO) moieties covalently linked by a dppf bridge. Electrochemical studies in dichloromethane revealed that both Co(I) and Fe(II) in the precursors were oxidized to Co(II)/Co(III) and Fe(III), respectively. On the other hand, in 2 the two first oxidation waves were assigned to Co, the Fe(II) centre requiring a higher potential than in free dppf. DFT calculations showed that the HOMOs of 2 were localised in the Co fragments, owing to the destabilisation of the Co(eta(5)-C5H5)(CO) orbitals after binding dppf. (C) 2012 Elsevier B.V. All rights reserved.}