Reaccions de cicloaddició [2+2+2] catalitzades per Rh(I)

The development of new chemical processes and efficient catalysts for the formation of carbon-carbon bonds is an important topic in organic chemistry. In particular, the [2+2+2] cycloaddition reaction involving different insaturations mainly alkynes, alkenes and nitriles is a highly efficient synthetic tool that allows polysubstituted benzenic, cyclohexadienic and pyridinic compounds to be obtained in one reaction step and in an atom economy process, resulting in the simultaneous formation of three new bonds in the formed ring. In recent years, research to produce new catalysts that can work effectively in mild reaction conditions has attracted great interest, as has the use of these processes in the synthesis of products of potential biological interest. This doctoral thesis is based on the methodological study of the rhodium(I)-catalyzed [2+2+2] cycloaddition reaction.

Dissociation of water on oxygen-covered Rh{111}

The adsorption of water and coadsorption with oxygen on Rh{111} under ultrahigh vacuum conditions was studied using synchrotron-based photoemission and photoabsorption spectroscopy. Water adsorbs intact on the clean surface at temperatures below 154 K. Irradiation with x-rays, however, induces fast dissociation and the formation of a mixed OH+H(2)O layer indicating that the partially dissociated layer is thermodynamically more stable. Coadsorption of water and oxygen at a coverage below 0.3 monolayers has a similar effect, leading to the formation of a hydrogen-bonded network of water and hydroxyl molecules at a ratio of 3:2. The partially dissociated layers are more stable than chemisorbed intact water with the maximum desorption temperatures up to 30 K higher. For higher oxygen coverage, up to 0.5 monolayers, water does not dissociate and an intact water species is observed above 160 K, which is characterized by an O 1s binding energy 0.6 eV higher than that of chemisorbed water and a high desorption temperature similar to the partially dissociated layer. The extra stabilization is most likely due to hydrogen bonds with atomic oxygen.

New half-sandwich heterobimetallic CpMPt (M=Rh, Ir) dithiolato bridged complexes

Cationic heterobimetallic complexes 5–7 [(PPh3)2Pt(μ-edt)MClCp′)]BF4 (edt=−S(CH2)2S−; 5: M=Rh and Cp′=η5-C5H5; 6: M=Rh and Cp′=η5-C5Me5 and 7: M=Ir and Cp′=η5-C5Me5) were prepared by reaction of [Pt(edt)(PPh3)2] with [Cp′ClM(μ-Cl)2MClCp′] in THF in the presence of two equivalents of AgBF4. The crystalline structure of 5 was determined by X-ray diffraction methods. Cationic heterobimetallic complexes [(PPh3)2Pt(μ-S(CH2)2S)MClCp′)]BF4 (M=Rh, Ir) were prepared. The crystalline structure of [(PPh3)2Pt(μ-edt)RhClCp)]BF4 was determined by X-ray diffraction methods.

A synchrotron powder X-ray diffraction study of the skutterudite-related phases AB1.5Te1.5 (A=Co, Rh, Ir; B= Ge, Sn)

X-ray resonant scattering has been exploited to investigate the crystal structure of the AB1.5Te1.5 phases (A = Co, Rh, Ir; B = Ge, Sn). Analysis of the diffraction data reveals that CoGe1.5Te1.5 and ASn1.5Te1.5 adopt a rhombohedral skutterudite-related structure, containing diamond-shape B2Te2 rings, in which the B and Te atoms are ordered and trans to each other. Anion ordering is however incomplete, and with increasing the size of both cations and anions, the degree of anion ordering decreases. By contrast, the diffraction data of IrGe1.5Te1.5 are consistent with an almost statistical distribution of the anions over the available sites, although some ordered domains may be present. The thermoelectric properties of these materials are discussed in the light of these results.

Synthesis and characterisation of the anion-ordered tellurides MGeTe (M = Co, Rh)

The synthesis and structural characterisation, carried out using a combination of single-crystal and powder X-ray diffraction, of the materials MGeTe (M = Co, Rh) are described. These phases adopt an ordered α-NiAs2 structure, which can be considered intermediate between those of pyrite and marcasite. Electrical resistivity and Seebeck coefficient measurements, carried out over the temperature range 77 ≤ T/K ≤ 325, indicate that these materials are n-type semiconductors.

Structure and electrical transport properties of the ordered skutterudites MGe1.5S1.5 (M = Co, Rh, Ir)

High-resolution powder neutron diffraction data collected for the skutterudites MGe1.5S1.5 (M=Co, Rh, Ir) reveal that these materials adopt an ordered skutterudite structure (space group R3¯), in which the anions are ordered in layers perpendicular to the [111] direction. In this ordered structure, the anions form two-crystallographically distinct four-membered rings, with stoichiometry Ge2S2, in which the Ge and S atoms are trans to each other. The transport properties of these materials, which are p-type semiconductors, are discussed in the light of the structural results. The effect of iron substitution in CoGe1.5S1.5 has been investigated. While doping of CoGe1.5S1.5 has a marked effect on both the electrical resistivity and the Seebeck coefficient, these ternary skutterudites exhibit significantly higher electrical resistivities than their binary counterparts.

Carbon-dispersed Pt-Rh nanoparticles for ethanol electro-oxidation. Effect of the crystallite size and of temperature

This work presents results of studies of carbon-dispersed Pt-Rh (1:1) nanoparticles as electrocatalysts for the ethanol electro-oxidation. The influences of the crystallite size and the cell temperature on the yields of CO2, acetaldehyde and acetic acid are investigated. Metal nanoparticles were prepared by two different routes: (1) impregnation on carbon powder followed by thermal reduction on hydrogen atmosphere and (2) chemical reduction of the precursor salts. The surface active area and the electrochemical activity of the electrocatalysts were estimated by CO stripping and cyclic voltammetry in the absence and in the presence of ethanol, respectively. Reaction intermediates and products were analyzed by in situ Fourier Transform Infra-Red Spectroscopy (FTIR) and Differential Electrochemical Mass Spectrometry (DEMS). The electrochemical stripping of CO and the electrochemical ethanol oxidation were slightly faster on the Pt-Rh electrocatalysts compared to Pt/C. Also, in situ FTIR spectra and DEMS measurements evidenced that the CO2/acetaldehyde and the CO2/acetic acid ratios are higher for the Pt-Rh/C materials in relation to Pt/C. This was ascribed to the activation of the C-C bond breaking by Rh, this being more prominent for the materials with smaller crystallite sizes. (C) 2008 Elsevier B.V. All rights reserved.

Electrocatalysis of ethanol oxidation on Pt monolayers deposited on carbon-supported Ru and Rh nanoparticles

Pt monolayers deposited on carbon- supported Ru and Rh nanoparticles were investigated as electrocatalysts for ethanol oxidation. Electronic features of the Pt monolayers were studied by in situ XANES (X-ray absorption near-edge structure). The electrochemical activity was investigated by cyclic voltammetry and cronoamperometric experiments. Spectroscopic and electrochemical results were compared to those obtained on carbon-supported Pt-Ru and Pt-Rh alloys, and Pt E-TEK. XAS results indicate a modification of the Pt 5d band due to geometric and electronic interactions with the Ru ant Rh substrates, but the effect of withdrawing electrons from Pt is less pronounced in relation to that for the corresponding alloys. Electrochemical stripping of adsorbed CO, which is one of the intermediates, and the currents for the oxidation of ethanol show faster kinetics on the Pt monolayer deposited on Ru nanoparticles, and an activity that exceeds that of conventional catalysts with much larger amounts of platinum. (c) 2007 Elsevier B.V. All rights reserved.

Ethanol electro-oxidation on carbon-supported Pt-Ru, Pt-Rh and Pt-Ru-Rh nanoparticles

This work investigates the effects of carbon-supported Pt, Pt-Ru, Pt-Rh and Pt-Ru-Rh alloy electrocatalysts oil the yields of CO2 and acetic acid as electro-oxidation products of ethanol. Electronic and structural features of these metal alloys were studied by in situ X-ray absorption spectroscopy (XAS). The electrochemical activity was investigated by polarization experiments and the reaction intermediates and products were analyzed by in situ Fourier Transform Infra-Red Spectroscopy (FTIR). Electrochemical stripping of CO. which is one of the adsorbed intermediates, presented a faster oxidation kinetics on the Pt-Ru electrocatalyst, and similar rates of reaction on Pt-Rh and Pt. The electrochemical current of ethanol oxidation showed a higher value and the onset potential was less positive oil Pt-Ru. However, in situ FTIR spectra evidenced that the CO2/acetic acid ratio is higher for the materials with Rh, mainly at lower potentials. These results indicate that the Ru atoms act mainly by providing oxygenated species for the oxidation of ethanol intermediates, and point out ail important role of Rh on the C-C bond dissociation. (C) 2007 Elsevier Ltd. All rights reserved.

Methane conversion reactions on Ni catalysts promoted with Rh: Influence of support

Ni catalysts supported on gamma-Al(2)O(3) and Mg(Al)O were prepared with and without Rh as a promoter and tested in the reforming of methane in the presence of excess methane, simulating a model biogas. The effects of adding synthetic air on the methane conversion and the formation of carbon were assessed. The catalysts were characterized by X-ray spectroscopy (EDS), surface area (BET), X-ray diffraction (XRD), Temperature-programmed reduction (TPR), X-ray absorption near-edge structure (XANES) and XPD. The results showed that in catalysts without Rh, the Ni interacts strongly with the supports, showing high reduction temperatures in TPR tests. The addition of Rh increased the amount of reducible Ni and facilitated the reduction of the species interacting strongly with the support. In the catalytic tests, the samples promoted with Rh suffered higher carbon deposition. The in situ XPD suggested that on the support gamma-Al(2)O(3), the presence of Rh probably led to a segregation of Ni species with time on stream, leading to carbon deposition. On the support MgAlO, the presence of Rh improved the dispersion of Ni, by reducing the Ni(0) crystallite size, suggesting that in this case the carbon deposition was due to a favoring of CH(4) decomposition by Rh. (C) 2011 Elsevier B.V. All rights reserved.

Terceirização no setor de RH: estudo de casos em empresas do setor mecânico

Este trabalho procura investigar se a terceirização de alguns subsistemas de Recursos Humanos (RH), de empresas do setor metal-mecânico do Rio Grande do Sul, possibilita maior desenvolvimento e crescimento para as organizações e os funcionários. Contextualizou-se o tema, quando se abordou a flexibilização como resposta à globalização dos mercados, a terceirização, como ferramenta da flexibilização e aspectos referentes ao novo papel de RH e a terceirização neste setor. A pesquisa é de natureza quantitativa/qualitativa. Desenvolve-se inicialmente um levantamento de dados para identificar quais as empresas do setor metal-mecânico e associadas ao SINMETAL estão adotando a estratégia de terceirização no setor de RH. Posteriormente, a partir dos resultados da etapa de levantamento de dados, escolheram-se duas empresas fabricantes de autopeças para desenvolver os estudos de casos. Os dados foram coletados através de entrevistas semi-estruturadas e análise documental, como forma de conhecer a estratégia de terceirização utilizada nos subsistemas de RH e os resultados que as empresas obtiveram. Observou-se que as duas empresas apresentam diferentes métodos para manterem-se competitivas no mercado. A primeira focaliza sua gestão no envolvimento de seus funcionários, investindo em formação e treinamento e estimulando empregos duradouros. A segunda mostra-se mais voltada a medidas de curto prazo, privilegiando o enxugamento da estrutura, redução de custos e a manutenção da certificação ISO/QS. Quanto à terceirização no setor de RH, ambas utilizam-se no subsistema de recrutamento e seleção, diferenciando-se na forma de implantação do processo. A primeira montou um “serviço de psicologia” terceirizado, na própria empresa. A segunda empresa estudada, terceiriza o serviço de recrutamento e seleção por meio de consultorias, estabelecendo apenas uma relação de fornecedor de serviços. Conclui-se que a terceirização no setor de RH é uma estratégia, basicamente utilizada para o subsistema de recrutamento e seleção, que acarreta insegurança e instabilidade nas relação de trabalho, mas dependendo da forma como é empregada pode oportunizar o desenvolvimento de um trabalho especializado, agregando valor tanto para o profissional como para a empresa cliente.

Avaliação de resultados em RH: análise dos métodos propostos na literatura acadêmica

A avaliação de resultados em RH tem sido proposta por diversos autores nos últimos anos. As propostas diferem quanto à forma de mensuração da contribuição da área para o desempenho da organização e quanto ao conteúdo do que se propõe, efetivamente, mensurar. Essas divergências refletem, em grande medida, as premissas adotadas em relação ao papel que a área desempenha (ou deveria desempenhar). Esses métodos de avaliação e mensuração são também alvo de inúmeras críticas (Pfeffer, 1997). Levando-se em conta a diversidade de propostas para a avaliação e mensuração, as observações de Pfeffer (1997) e a escassez de trabalhos sobre o tema na literatura brasileira, este trabalho faz um levantamento e análise das propostas encontradas na literatura para avaliação e mensuração de resultados da área de RH.

Análise bibliométrica da produção científica brasileira de RH na década de 1990 - um mapeamento a partir das citações dos artigos publicados no ENANPAD

Neste artigo, é usada análise bibliométrica para entender a influência de autores e instituições na produção acadêmica em Recursos Humanos no Brasil na década de 90, bem como para mapear o comportamento de auto-citações e citações à própria instituição dos autores que produziram no período. O estudo levantou, nos 290 artigos de RH publicados na década de 90 (1991 a 2000) nos anais do Enanpad, a constituição, origem e padrão de interrelação de todas as citações, autores e instituições que publicaram e foram citados na área. No total, analisaram-se os padrões bibliométricos de 5814 citações, que compreendiam 342 autores, advindos de 51 instituições. Os resultados mostram uma área com alto índice de auto-citação e endogenia, e com uma elevada incidência de citação de jornais, revistas e autores estrangeiros e não acadêmicos; revelam também que Maria Tereza Fleury (FEA/USP) foi a acadêmica mais citada; que a USP, UFMG, UFRGS e a FGV-EAESP (nessa ordem) são as instituições com os autores mais citados; que a RAE é o veículo nacional mais referenciado no campo; e que alguns autores e instituições que publicaram no período têm elevada propensão à auto-citação e à consulta predominante a autores de sua própria instituição. O artigo termina oferecendo ao campo sugestões para desenvolvimento e debate, a partir dos seus resultados e sua comparação com trabalhos anteriores analisando a mesma base amostral.