New C₂‐Symmetric Diphosphite Ligands Derived from Carbohydrates: Effect of the Remote Stereocenters on Asymmetric Catalysis

Abstract

The synthesis of new modular chiral diphosphite ligands with C 2 -symmetry and carbohydrate backbone is reported. We also report here the synthesis of the corresponding rhodium complexes. All these species have been characterised in solution by NMR spectroscopy and in some cases in the solid state by X-ray diffraction. The solution structures of the hydridorhodiumcarbonyl species, where L = diphosphites 12a-14a, 12b, have been studied using high-pressure NMR spectroscopy. The configuration and substitution of the remote stereocentres in positions 2 and 5 of the tetrahydrofuran ring of the diphosphite ligands were observed to have a considerable influence on the results obtained in the rhodium-catalysed hydroformylation and hydrogenation reactions. Thus, the configuration of the major isomer obtained in the hydroformylation reaction may be controlled by changing the configuration of these stereocentres.

Chiral Diphosphite‐Modified Rhodium(0) Nanoparticles: Catalyst Reservoir for Styrene Hydroformylation

“…Rhodium nanoparticles were obtained by decomposition of two different rhodium precursors, [Rh(η 3 ‐C 3 H 5 ) 3 ]9 and [Rh(μ‐OMe)(cod)] 2 ,10 which were synthesised by following previously described methods. As a standard procedure, the decomposition of each rhodium organometallic precursor under an H 2 atmosphere (3 bar) was carried out in thf inside a Fischer–Porter bottle at room temperature and in the presence of the chosen ligand ( 1 11 or 2 ;12 Rh /L , 1:0.2; Scheme ) 6. The decomposition of both rhodium precursors took place in a similar way.…”

“…The use of carbohydrate‐derived diphosphites 1 and 2 as ligands in the hydroformylation of vinylarenes catalyzed by rhodium molecular complexes has been previously reported 11,12,17. As a result of the interesting results provided with these Rh/diphosphite systems we considered testing our diphosphite‐stabilized rhodium nanoparticles as catalysts in the hydroformylation reaction.…”

“…Solvents were purified by standard procedures. Ligands 1 11 and 2 12 were prepared by methods described previously. All other reagents were used as commercially available.…”

Hidroformilação: um Marco Histórico na Catálise Homogênea

“…No entanto, observa-se que a enantiosseletividade na reação de hidroformilação do estireno depende da configuração da ponte que une o grupo fosfina ao grupo fosfito, enquanto que o valor do excesso enantiomérico depende da combinação da quiralidade de ambos os fragmentos. A enantiosseletividade observada é, assim, maior quando a configuração das duas unidades binaftilo é oposta, tendo-se obtido valores de 94-95%, quando se utiliza o par R,S ou S, R, mas de apenas 25%, quando se utiliza o diastereoisomero R,R 18,48 Claver e seus colaboradores desenvolveram a síntese de avaliação catalítica de uma vasta família de difosfitos, contendo na sua estrutura derivados de açucares, tais como, D-(+)-xilose, D-(+)-glicose e D-glicosamina e BINOL ou H8BINOL (Esquema 9), sendo que a sua utilização como ligantes em reações de hidroformilação catalisada por complexos de ródio originando aldeídos com elevado excesso enantiomérico 49,50,51,52,53,54,55,56 .…”

Heteroatom‐Substituted Secondary Phosphine Oxides (HASPOs) as Decomposition Products and Preligands in Rhodium‐Catalysed Hydroformylation

“…[1,2] For example, ligands bearing the bulky O,O'-3,3'-di-tert-butyl-5,5'-dimethoxy-1,1'-biphenyl-2,2'-diyl phosphite subunit I (Scheme 2) have been extensively studied in technical hydroformylation reactions [12,13] and also in other metal-catalysed reactions. [14] Cleavage of the POÀR bond of I by hydrolysis gives HASPO 1 B.…”