Synthesis of some [1,2-bis(alkoxycarbonyl)ethyl]ruthenium(II) complexes and their catalytic activities for cis-trans isomerization of dialkyl maleates

Abstract

The hydridoruthenium(1i) complex [RuCI(CO)H( PPh,),](1) reacted smoothly with dimethyl maleate and diethyl maleate at room temperature to give insertion products,(2; R = Me) and (3; R = Et), respectively. Complex (2) was also formed by reaction of (1 ) with dimethyl fumarate. Complexes (2) and (3) were converted into binuclear complexes [{hu[CH(CO,R)CH,C(b)OR](p-CI)(CO)(PPh,)},] (4; R = Me) and (5; R = Et), respectively, by heating above 100 "C. Complex (4) reacted with Na[BH(pz),] (pz = 1 -pyrazolyl) at ambient temperature to afford [Ru{CH(CO,Me)CH,CO,Me}(CO){BH(pz),)( PPh,)]. Complexes (I), (2), and ( 4) were found to catalyze cis-trans isomerization of dialkyl maleates above 100 "C. A kinetic study of the isomerization of dimethyl maleate revealed that the reaction rates were proportional to the concentrations of both the substrate and the catalyst, and that the ratio of the catalytic constants per ruthenium atom is about 1.6 : 1 .O: 0.36 for (1 ), (2), and (4), respectively, at 120 "C. Addition of PPh, to the catalyst accelerated the reaction rates. It is deduced that the

NaBr-Assisted Photoelectrochemical and Photochemical Integrated Process for Isomerization of Maleate Esters to Fumarate Esters

“…High selectivity for isomerization of the maleate esters can be obtained by electron transfer mediation owing to the redox reaction of NaBr under mild conditions. Conversely, the conventional thermochemical process provides low selectivity and energy efficiency accompanied by large amounts of toxic and harmful reagents, − while the enzyme-catalyzed process is expensive. ,, In the thermochemical process, Br 2 is often used in the maleate-to-fumarate isomerization through the Br radical-initiated radical chain reactions under illuminations and organic phase. − Br 2 is highly harmful and corrosive to human tissue, and it is highly reactive and instable, making handling and using it a difficult task. Furthermore, a molar amount of Br 2 produced through the halide exchange method requires an equivalent of more toxic Cl 2 as a strong oxidant, which is also produced by electrochemical process (see more details in the Supporting Information).…”