Here, we describe the successful application of novel glucofuranose‐derived 1,3‐diphosphites in the rhodium‐catalysed asymmetric hydroformylation of vinyl acetate, 2,5‐dihydrofuran and ...2,3‐dihydrofuran. In the hydroformylation of vinyl acetate, total regioselectivity and high ee (up to 73%) were obtained. When 2,3‐ and 2,5‐dihydrofuran were the substrates, total chemo‐ and regioselectivities were achieved together with ees up to 88%. These results correspond to the highest ee values reported to date in the asymmetric hydroformylation of these substrates. The HP‐NMR studies of the RhH(CO)2(L) species (L=15 and 17) demonstrated that both ligands coordinate to the Rh centre in an eq‐eq fashion. The complex RhH(CO)2(15) was detected as a single isomer with characteristic features of eq‐eq coordination. However, the broadening of the corresponding signals indicated that this species is rapidly interchanging in solution. In contrast, complex RhH(CO)2(17) was detected as a mixture of two conformational isomers at low temperature due to the greater flexibility of the monocyclic backbone of this ligand.
Palladium complexes bearing monodentate and bidentate phosphine ligands (1-7) were synthesised and used as catalyst precursors in the methoxycarbonylation of norbornene. The catalytic systems bearing ...ligands 1, 3 and 4 afforded excellent conversions (>99%) and selectivity of the ester (>99%). NMR investigations showed that using complex 1a as the precursor resulted in the protonated phosphine, 1-H(+), being formed under catalytic conditions and thus the addition of acid is not required for the activation of this system since the reaction involving the precursor with methanol under CO pressure produces 2 equivalents of HCl and leads to the formation of the active species. The protonation of ligand 4 under methoxycarbonylation conditions was also observed and the diprotonated diphosphine was isolated and characterised. This compound was tested as a ligand and acid source in a catalysis and provided excellent conversion and high selectivity to the ester.
Abstract
Here, we describe the successful application of novel glucofuranose‐derived 1,3‐diphosphites in the rhodium‐catalysed asymmetric hydroformylation of vinyl acetate, 2,5‐dihydrofuran and ...2,3‐dihydrofuran. In the hydroformylation of vinyl acetate, total regioselectivity and high
ee
(up to 73%) were obtained. When 2,3‐ and 2,5‐dihydrofuran were the substrates, total chemo‐ and regioselectivities were achieved together with
ee
s up to 88%. These results correspond to the highest
ee
values reported to date in the asymmetric hydroformylation of these substrates. The HP‐NMR studies of the RhH(CO)
2
(L) species (L=
15
and
17
) demonstrated that both ligands coordinate to the Rh centre in an
eq‐eq
fashion. The complex RhH(CO)
2
(
15
) was detected as a single isomer with characteristic features of
eq‐eq
coordination. However, the broadening of the corresponding signals indicated that this species is rapidly interchanging in solution. In contrast, complex RhH(CO)
2
(
17
) was detected as a mixture of two conformational isomers at low temperature due to the greater flexibility of the monocyclic backbone of this ligand.
New pyrene‐tagged imidazolium salts and their corresponding carboxylates were synthesised and the latter tested as organocatalysts in the cycloaddition of CO2 with epoxides. The best performing ...organocatalyst was then non‐covalently immobilised onto carbon materials (carbon nanotubes (CNTs), reduced graphene oxide (rGO) and carbon beads (CBs)) via π‐π stacking interactions and their activity and recoverability in the cycloaddition reaction were studied. The heterogenised catalyst onto reduced graphene oxide (4 a@rGO) was recycled several times although a loss of activity was observed. This catalyst was also used for the transformation of a series of epoxides under mild conditions.
Cooperative NHC‐based catalysis: New pyrene‐tagged imidazolium carboxylates non‐covalently immobilised onto carbon materials were synthesised and tested as organocatalysts in the cycloaddition of CO2 with epoxides. The heterogenised catalyst onto reduced graphene oxide (4 a@rGO) was recycled several times and used for the transformation of a series of epoxides under mild conditions.
•Metal complexes (Co, Fe, Mn) bearing ONO ligands are highly active catalysts in CO2/epoxide coupling reaction.•Synthetized catalysts were tested successfully in catalytic coupling of CO2 with ...propylene oxide using PPNCl as co-catalyst.•The catalytic conditions for the Mn complex were optimized and reach the TOF of 1600 h−1.
The use of carbon dioxide as feedstock in copolymerization reaction with epoxides has been ideally proposed as an alternative route to produce chemicals without the use of phosgene. One of the most appealing strategies is to use metal complexes as catalysts to form cyclic organic carbonates. These organic compounds are very interesting in industry due to their enormous scope of applications. In this paper, the use of catalytic systems based on sustainable, non-toxic and cheap metal complexes (Mn, Fe, Co) containing Schiff-base tridentate ONO ligands in the synthesis of propylene carbonate (PC) from carbon dioxide and propylene oxide (PO), are discussed. All complexes were tested successfully, affording cyclic carbonate in high productivities (3800 mol PC/mol cat) using a co-catalyst. Synthetized iron and manganese complexes have shown significantly higher activities compared with the activity showed by the new cobalt complexes. The catalytic conditions using the manganese (II) complex 2 were optimized and a TOF of 1600 h−1 was reached.
Abstract
In the present work, hollow PdAg-CeO
2
heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the ...first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO
2
counterpart in an additive manner. The PdAg-CeO
2
NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO
2
moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance.
Modular syntheses of functionalised, alkoxy‐tethered 1,3‐bis(2,4,6‐trimethylphenyl)imidazolium (IMes⋅H+) and 1,3‐bis(2,6‐diisopropylphenyl)imidazolium (IPr⋅H+) derivatives ...1,3‐bis(4‐alkyloxy‐2,4,6‐trimethylphenyl)imidazolium (IXyOR⋅H+) and 1,3‐bis(4‐alkyloxy‐2,6‐diisopropylphenyl)imidazolium (IPrOR⋅H+) are reported. A reliable synthesis of the key starting material 4‐amino‐3,5‐diisopropylphenol is also described. Etherification of hydroxy‐decorated ligand intermediates before formation of the imidazolium core and subsequent modification, or direct etherification of the versatile synthon IPrOH⋅HCl, allowed access to various linker types including triethoxysilyl, primary amino and norbornenyl, which are not accessible by other methods. An IPrOR–palladium(II) complex was prepared, and its catalytic activity was evaluated in challenging Buchwald–Hartwig aminations of aryl chlorides. This precatalyst displayed excellent activity and selectivity under mild reaction conditions, achieving in some cases a 10‐fold improvement in TOF relative to the IPr‐based version. An unexpected activity profile was observed wherein sterically demanding anilines were coupled more easily than those lacking ortho‐substitution.
A series of novel ONO ligands bearing an ionic pendant-armed (hereinafter indicated as ONONu, where Nu corresponds to an anionic nucleophile) were synthesized, characterized, and successfully ...coordinated to cobalt and manganese precursors. New air-stable cobalt (III) complexes (1-6) and manganese (II) complexes (7 and 8) were obtained and characterized. Single crystal X-ray diffraction analysis of the Co(III) compound 5 confirmed the presence of two quaternized ligands coordinated to the metal and iodide as counterion. These novel complexes were revealed to be active catalysts in the coupling reaction of carbon dioxide and propylene oxide (PO) in different degrees of success. Among these, the manganese complex 8 afforded the best results towards the formation of propylene carbonate (PC) with a productivity of 256 kg PC/(kg cat·h), achieving a TON of 4860.
PDF
