Comparative study of the catalytic activity of the complexes Cp*RuCl(PAr3)2 [Ar = -C6H5 and 4-CF3-C6H4] in the ATRP of styrene

Abstract

A polimerização do estireno por ATRP foi conduzida usando os complexos Cp*RuCl(PPh 3 ) 2 , e Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 como catalisadores, a fim de avaliar a influência das propriedades eletrônicas dos ligantes fosfinas na velocidade e controle da polimerização. Os dados cinéticos para polimerizações realizadas com Cp*RuCl(PPh 3 ) 2 , mostram que os pesos moleculares aumentam linearmente com a conversão, com uma eficiência média de iniciação, de 0,77. Os pesos moleculares obtidos no estudo cinético com Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 também aumentam com a conversão, mas mostram um marcado desvio abaixo dos pesos moleculares teóricos. Este comportamento foi explicado pela oxidação gradual, irreversível do catalisador Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 , como confirmado pela espectroscopia de RMN de 31 P. O catalisador Cp*RuCl(PPh 3 ) 2 promove a polimerização com uma velocidade maior do que usando Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 , o que é consistente com as melhores propriedades de doação de elétrons de PPh 3 versus P(4-CF 3 −C 6 H 4 ) 3 . Estudos preliminares da polimerização do estireno com ATRP em CO 2 supercrítico mostram que somente o catalisador Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 , com ligantes fluorados, é ativo.Styrene polymerization by ATRP was conducted independently using the complexes Cp*RuCl(PPh 3 ) 2 , and Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 as catalysts, in order to evaluate the influence of the electronic properties of the phosphine ligands on the rate and control of the polymerization. The kinetic data for polymerizations carried out with Cp*RuCl(PPh 3 ) 2 , show that molecular weights increase linearly with conversion with an average initiation efficiency of 0.77. The molecular weights obtained in the kinetic study with Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 also increase with conversion but show a marked deviation below the theoretical molecular weights. This behavior was explained by the gradual, irreversible, oxidation of catalyst Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 as confirmed by 31 P-NMR spectroscopy. Catalyst Cp*RuCl(PPh 3 ) 2 promotes the polymerization with a rate of polymerization higher than that obtained using Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 ; this is consistent with the better electron donating properties of PPh 3 versus P(4-CF 3 −C 6 H 4 ) 3 . Preliminary studies of styrene polymerization by ATRP in supercritical CO 2 , shows that only catalyst Cp*RuCl[P(4-CF 3 −C 6 H 4 ) 3 ] 2 , with fluorinated ligands, was active.Keywords: atom transfer radical polymerization (ATRP), half sandwich ruthenium catalysts, styrene polymerization, supercritical carbon dioxide IntroductionHalf sandwich organometallic complexes containing transition metal from group 8 (Fe 1,2 and Ru 3-10 ) are an important group of catalysts in the polymerization of vinyl monomers by ATRP. The reversible, one electron oxidation-reduction that these complexes experience during controlled radical polymerization, promotes the establishment of a dynamic equilibrium between active and dormant species, with equilibrium con...

Atom transfer radical polymerization by [RuCl2(PPh3)2(amine)] catalysts: Cyclic amines as tuner of reactivity

“…Comparison between the reactivity of complexes 1, 2, and 3 and the electrochemical data suggests that the efficiency of using these types of complexes seems to be induced by steric factors; however, electronic effects should also be considered. Furthermore, from studies with [RuCl 2 (PPh 3 ) 3 ] and other Ru complexes, the activities of the amine-Ru complexes 1, 2, and 3 were higher [19,22,26,35,[49][50][51][52][53], and this fact can be associated with the amines as ancillary ligands, which are not discoordinated over the reaction.…”