ABSTRACT
In the course of our studies toward the development of new heterogeneous conditions for better controlling regioselectivity in organic reactions, we investigated the application of sol-gel immobilized organometallic catalyst for regioselective hydroaminomethylation of vinylarenes with aniline or nitroarene derivatives in an aqueous microemulsion. By immobilization of 6 mol % [Rh(cod)Cl]2 within a hydrophobic silica sol-gel matrix we were able to perform efficient hydroaminomethylation under mild conditions and isolate 2-arylpropylamines with high regioselectivity. The regioselectivity of the reaction was found to be mainly dependent on the hydrophobicity of the catalyst support. It is also significantly affected by the electronic nature of the substrates, by the reaction temperature, and by syngas pressure. The heterogenized catalyst can be reused for several times.
Subject(s)
Gels/chemistry , Propylamines/chemistry , Rhodium/chemistry , Silica Gel/chemistry , Vinyl Compounds/chemistry , Catalysis , MethylationABSTRACT
Terminal aromatic alkynes are converted rapidly into ketones in a regioselective manner by treatment of their microemulsions with 0.33 M mineral acid between 80 and 140 °C. Internal and aliphatic acetylenes are likewise hydrated, but require longer reaction periods. The products are easily isolated from the reaction mixtures by phase separation. Replacement of H2 O by D2 O leads to the formation of trideuteriomethyl ketones.
Subject(s)
Alkynes/chemistry , Lewis Acids/chemistry , Water/chemistry , Catalysis , Emulsions , Green Chemistry TechnologyABSTRACT
[reaction: see text] Schiff bases of aromatic aldehydes and anilines that fail to react with triethylaluminum are smoothly alkylated at room temperature in the presence of lanthanide catalysts. The alkylation takes place selectively at the vinylic carbon atom.
Subject(s)
Aluminum/chemistry , Lanthanoid Series Elements/chemistry , Organometallic Compounds/chemistry , Alkylation , Benzaldehydes/chemical synthesis , Benzaldehydes/chemistry , Catalysis , Molecular Structure , Organometallic Compounds/chemical synthesisABSTRACT
[reaction: see text] Silica sol-gel encaged PdCl(2)(PPh(3))(2) is a recyclable catalyst for the Heck vinylation of aryl iodides. It is possible to couple the Heck reaction with photocyclization in a one-pot process.
ABSTRACT
A facile three-phase transport process is described that allows to carry out catalytic reactions in water, whereby all components are hydrophobic. According to this process a hydrophobic substrate is microemulsified in water and subjected to an organometallic catalyst, which is entrapped within a partially hydrophobized sol-gel matrix. The surfactant molecules, which carry the hydrophobic substrate, adsorb/desorb reversibly on the surface of the sol-gel matrix breaking the micellar structure, spilling their substrate load into the porous medium that contains the catalyst. A catalytic reaction then takes place within the ceramic material to form the desired products that are extracted by the desorbing surfactant, carrying the emulsified product back into the solution. The method is general and versatile and has been demonstrated with the catalytic hydrogenations of alkenes, alkynes, aromatic C=C bonds, and nitro and cyano groups.
ABSTRACT
We extend our sol-gel methodology of one-pot sequences of reactions with opposing reagents to an enzyme/metal-complex pair. Sol-gel entrapped lipase and sol-gel entrapped RhCl[P(C(6)H(5))(3)](3) or Rh(2)Co(2)(CO)(12) were used for one-pot esterification and C-C double bond hydrogenation reactions, leading to saturated esters in good yields. When only the enzyme is entrapped, the homogeneous catalysts quench its activity and poison it. Thus, when 10-undecenoic acid and 1-pentanol were subjected in one pot to the entrapped lipase and to homogeneously dissolved RhCl[P(C(6)H(5))(3)](3) under hydrogen pressure, only 7% of the saturated 1-pentyl undecanoate was obtained. The yield jumped 6.5-fold when both the enzyme and the catalyst were immobilized separately in silica sol-gel matrixes. Similar one-pot esterifications and hydrogenations by sol-gel entrapped lipase and heterogenized rhodium complexes were carried out successfully with the saturated nonoic, undecanoic, and lauric acids together with several saturated and unsaturated alcohols. The use of (S)-(-)-2-methylbutanol afforded an optically pure ester. The heterogenized lipase is capable of inducing asymmetry during esterification with a prochiral alcohol. Both the entrapped lipase and the immobilized rhodium catalysts can be recovered simply by filtration and recycled in further runs without loss of catalytic activity.
Subject(s)
Enzymes, Immobilized/chemistry , Esters/chemical synthesis , Lipase/chemistry , Organometallic Compounds/chemistry , Rhodium/chemistry , Alcohols/chemistry , Carboxylic Acids/chemistry , Catalysis , Gels/chemistry , Lipase/metabolismABSTRACT
Sodium tetraalkynylaluminates (1-4), prepared from NaAlH4 and terminal alkynes, cross-couple with aryl bromides in the presence of Pd(0) and Pd(II) catalysts. The reactions take place in boiling THF or DME. The process is applicable to both homo- and heterocyclic aryl bromides and can be used for conversion of polybromo compounds into polyalkynes. The reactions are high yielding and selective, free of undesired homocoupling and hydrogenolysis processes. The reagents selectively react with the ring-bound bromine atoms but do not affect chloro, cyano, triflate, or ester functions.
ABSTRACT
Treatment of PtCl(4) with CO at 40-110 degrees C forms a powerful alkyne hydration catalyst that operates both under homogeneous conditions in wet THF and under phase-transfer conditions in (CHCl(2))(2)/H(2)O in the presence of tricaprylmethylammonium chloride (Aliquat 336). Complex HPtCl(CO)(2) is regarded as the active hydration catalyst. It is assumed to be formed by initial transformation of PtCl(4) to H(2)[Pt(3)(CO)(6)](n) (n = 5, 6) followed by reaction with HCl (generated by decomposition of the starting platinum salt).
