Mechanistic Studies of Single-Step Styrene Production Using a Rhodium(I) Catalyst

Abstract

The direct and single-step conversion of benzene, ethylene, and a Cu(II) oxidant to styrene using the Rh(I) catalyst (DAB)Rh(TFA)(η-CH) [DAB = N,N'-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] has been reported to give quantitative yields (with Cu(II) as the limiting reagent) and selectivity combined with turnover numbers >800. This report details mechanistic studies of this catalytic process using a combined experimental and computational approach. Examining catalysis with the complex (DAB)Rh(OAc)(η-CH) shows that the reaction rate has a dependence on catalyst concentration between first- and half-order that varies with both temperature and ethylene concentration, a first-order dependence on ethylene concentration with saturation at higher concentrations of ethylene, and a zero-order dependence on the concentration of Cu(II) oxidant. The kinetic isotope effect was found to vary linearly with the order in (DAB)Rh(OAc)(η-CH), exhibiting no KIE when [Rh] was in the half-order regime, and a k/k value of 6.7(6) when [Rh] was in the first-order regime. From these combined experimental and computational studies, competing pathways, which involve all monomeric Rh intermediates and a binuclear Rh intermediate in the other case, are proposed.

Oxidative Hydrophenylation of Ethylene Using a Cationic Ru(II) Catalyst: Styrene Production with Ethylene as the Oxidant

“…We recently reported that Rh catalyst precursors efficiently catalyze oxidative olefin hydroarylation with Cu(II) oxidants to form alkenyl arene . Thus, we attempted to improve catalysis using 4 by adding external oxidants.…”

“…The complex [(MeOTTM)Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph][BAr′ 4 ] produces 53 TON of styrene under 40 psig of ethylene at 150 °C, and the selectivity toward styrene production increases when higher ethylene pressures are used. The work reported herein is unique in its direct use of ethylene, a reactant, as the oxidant for this process whereas previously disclosed work by our group and that of Milstein and co‐workers utilized copper(II) salts or O 2 as oxidant. The reduced ethylene, to form ethane, can in principle be easily recycled to ethylene.…”

Oxidative Alkenylation of Arenes Using Supported Rh Materials: Evidence that Active Catalysts are Formed by Rh Leaching

“…Recently, we reported Rh‐catalyzed arene alkenylation to directly synthesize styrene and 1‐aryl alkenes using molecular catalysts in homogeneous processes [13,14,36–41] . Based on the mechanistic studies, our initial proposed catalytic cycle involves (Scheme 3): a) Rh‐carboxylate assisted arene C−H activation, b) ethylene coordination and insertion into a Rh‐aryl bond, c) β‐hydride elimination, and d) alkenyl arene dissociation and oxidation of a Rh−H intermediate with CuX 2 (X=carboxylate) to regenerate the starting catalyst.…”

Compósitos de poliestireno expandido reciclado com solvente biodegradável e plastificado com glicerol para impressão 3D: processamento e caracterizações.

“…A pureza do benzeno deve ser mais elevada, cerca de 99% e é importante que a presença de enxofre não exceda 0,1%. (11,12,15) As razões entre as massas molares do etileno e do benzeno devem ser controladas para evitar a produção do polietilbenzeno, normalmente são produzidos 41% em massa de etilbenzeno com pureza superior a 99%, 8% de polietilbenzeno e 51% do benzeno é inalterada. (12,16) Durante a reação, o alumínio, presente nas impurezas do etileno e do benzeno, e o cloro, proveniente do cloreto de etilo, reagem formando o cloreto de alumínio.…”

“…Apresenta ponto de ebulição sob 145,2°C e o volume de contração na polimerização é de 17%. (11,12,15,16,21) Visto o processo de preparação do monômero de estireno e algumas de suas propriedades, o tópico 2.2 apresentará a polimerização do estireno para obtenção do PS.…”