Alexandre P. Umpierre

Turnover Numbers and Soluble Metal Nanoparticles

The catalytic activity expressed by turnover number (TON) and turnover frequency (TOF) in different fields of catalysis (enzymatic, homogeneous (single‐site), heterogeneous (multi‐site), and nanocatalysis (oligo‐site)) are usually estimated in slightly different ways and with slightly different, yet important meanings. For soluble metal nanoparticles, the ideal is to determine the TON by using the titrated number of active catalytic sites before the catalyst is inactivated. However, in the absence of reliable titration methods it is suggested that TON figures should always be reported as the number of moles of reactants consumed per mol of soluble metal catalyst, and that they should also be corrected by the number of exposed surface atoms by using the metal atom’s magic number approach. Moreover, it is strongly recommended that the TOF should be determined from the slope of plots of turnover numbers versus time, because in various cases the size and shape of the soluble nanoparticles might change dramatically during the reaction. As in organometallic catalysis, in the absence of TON vs. time data, the TOF should be estimated for low substrate conversions.

Pd(II)-dissolved in ionic liquids: a recyclable catalytic system for the selective biphasic hydrogenation of dienes to monoenes

Bis-acetilacetonato de paladio dissolvido no liquido ionico tetrafluoroborato de 1- n-butil-3metilimidazolio catalisa de forma seletiva a hidrogenacao de dienos conjugados e nao-conjugados (funcionalizados ou nao) as suas respectivas mono-olefinas. O sistema nao requer o uso de cosolventes orgânicos, sendo os produtos da reacao separados por simples decantacao ou destilacao. A fase ionica pode ser reutilizada ate 15 vezes sem perdas significativas na sua atividade catalitica e seletividade. Palladium acetylacetonate dissolved in 1- n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid catalyses the selective two-phase hydrogenation of conjugated and non-conjugated (functionalized and non-functionalized) dienes into the respective monoenes. The system does not require the use of organic solvents, the products are removed by simple decantation or distillation and the recovered ionic catalytic solution can be reused several times without any significant changes in its catalytic activity and selectivity.

Organo-zincate molten salts as immobilising agents for organometallic catalysis

The combination of 1-n-butyl-3-methylimidazolium chloride with ZnCl2 affords ionic mixtures with different melting point temperatures depending on the zinc molar fraction. RuCl2(PPh3)3 immobilised in the low melting mixture (60 °C) promotes the 1-hexene hydrogenation (turnover frequencies up to 44 min−1) and the recovered solid catalyst phase can be reused several times.

Selective hydrogenation of 1,3-butadiene by transition metal compounds immobilized in 1-butyl-3-methyl imidazolium room temperature ionic liquids

Os complexos [Co(acac) 2 ], [Co(acac) 3 ], [Fe(acac) 3 ] e [Ni(acac) 2 ] (acac = acetilacetonato) dissolvidos em tetrafluoroborato de 1-butil-3-metilimidazonio (1), trifluorometanosulfonato de 1butil-3-metilimidazolio (2) ou hexafluorofosfato de 1-butil-3-metilimidazolio (3), catalisam a hidrogenacao de 1,3-butadieno em butenos em sistema catalitico tipicamente bifasico. A conversao do 1,3-butadieno, a seletividade e a frequencia de rotacao (TOF) sao fortemente dependentes do metal de transicao e do liquido ionico. Para [Co(acac) 2 ] dissolvido em 1, estudos cineticos sugerem que a reacao ocorre no meio liquido ionico, com uma energia aparente de ativacao de of 33.8 kJ mol -1 . A solucao ionica do catalisador pode ser recuperada e reutilizada varias vezes sem mudancas perceptiveis na atividade e seletividade da reacao. The compounds [Co(acac) 2 ], [Co(acac) 3 ], [Fe(acac) 3 ] and [Ni(acac) 2 ] (acac = acetylacetonate) dissolved in 1-butyl-3-methyl imidazolium tetrafluoroborate (1), trifluoromethanesulphonate (2) or hexafluorophosphate (3) catalyze the reduction of 1,3-butadiene into butenes in a typical two-phase catalytic reaction. The 1,3-butadiene conversion, the selectivity and turnover frequencies (TOF) are strongly dependent on the nature of the transition metal catalyst precursor and the ionic liquid. For [Co(acac) 2 ] dissolved in 1, kinetic studies strongly suggest that the reaction takes place in the ionic solution bulk, having an apparent activation energy for the overall process of 33.8 kJ mol -1 . The recovered ionic catalyst solution can be reused several times without any significant changes on activity and selectivity.