Electrocatalytic hydrogenation on a rhodium complex—polypyrrole film electrode: Effect of the polymeric environment on the selectivity of the catalyst

Synthesis of the Novel 4,4’- and 6,6’- Dihydroxamic - 2,2’-Bipyridines and Improved Routes to 4,4’- and 6,6’- Substituted 2,2’-Bipyridines and Mono-N-Oxide-2,2’-Bipyridine

“…Introduction 2,2'-Bipyridinyls continue to attract attention as important ligands of great interest for chelation of transition metals 1 due to their ability to form very stable complexes with many cations and to their remarkable anti-tumoral [2][3][4][5] , catalytic 6 , electrocatalytic 7,8 and photochemical 9 properties. Nevertheless, the methods available for the synthesis of new or even well-known symmetrical and unsymmetrical derivatives of 2,2'-bipyridines are usually not practical, and present low yields.…”

Molecular Electrocatalytic Hydrogenation of Carbonyls and Dehydrogenation of Alcohols

“…Pioneering work in the field of Molecular Electrocatalytic Carbonyl Hydrogenation (MECH) was performed in the early 1990s by Moutet et al using rhodium complexes (Scheme 1). [18] In these early reports the link between activity of transfer hydrogenation (TH) catalysts and the possibility to activate them electrochemically was established. [17,18] It was possible to reduce the polymerized Rh(III) precatalysts by two electrons to yield stable Rh(I)-species.…”

“…[18] In these early reports the link between activity of transfer hydrogenation (TH) catalysts and the possibility to activate them electrochemically was established. [17,18] It was possible to reduce the polymerized Rh(III) precatalysts by two electrons to yield stable Rh(I)-species. At potentials slightly negative of the Rh(III)/Rh(I) couple, the so-generated species 2 is active for the 2e À reduction of cyclohexanone to cyclohexanol (Scheme 1).…”

“…However, in the presence of unsaturations, hydrogenation of the C=C double bonds is favored. [18] Mechanistically, it is proposed that the reaction of Rh(I) intermediate with a proton source (e. g. water) forms a cationic Rh(III) hydride, responsible for the reduction of the substrates. [29] Modifications of the ligands led to remarkable turnover numbers (TON, as high as 5300) without loss in selectivity (Scheme 1, complex 1 and 4, Table 1 entry 3 and 4).…”

Álcoois quirais: métodos químicos e catalíticos de obtenção por redução assimétrica

“…As aplicações de complexos de ródio em eletrocatálise têm sido muito investigadas por Moutet e colaboradores e, apesar da maior parte das investigações não se referir à eletrocatálise assimétrica enantiosseletiva, têm-se excelentes resultados de diastereosseletividade. Oliveira e Moutet 85,86 relataram a hidrogenação eficiente da carvona e de algumas cicloexanonas substituídas sobre eletrodos de carbono modificados por filmes poliméricos, obtidos pela eletropolimerização oxidativa do complexo [Rh III (L 1 ) 2 (Cl) 2 ][BF 4 ] onde têm-se ligantes bipirídinicos pirrol-substituídos para a eletropolimerização através do anel pirrólico e a formação de um eletrodo modificado recoberto pelo filme formado. Uma diferença marcante de seletividade foi encontrada na hidrogenação de substratos volumosos sobre o cátodo catalítico, quando se compara sua hidrogenação catalítica ou eletrocatalítica com complexos similares usados em meio homogêneo.…”