In the palladium-catalyzed allylic alkylation of
(E)-3-substituted-2-propenyl acetates (1),
1-substituted-2-propenyl acetates (2), and 1- or 3-deuterio-2-cyclohexenyl
acetate (5), which proceeds through 1,3-unsymmetrically substituted π-allylpalladium intermediates, selective
substitution at the position originally
substituted with acetate was observed by use of a sterically bulky
monodentate phosphine ligand,
2-(diphenylphosphino)-2‘-methoxy-1,1‘-binaphthyl (MeO-MOP).
Studies of the structure of π-allylpalladium
complexes generated by mixing
[PdCl(π-cyclohexenyl)]2 with 1 or 2 equiv of
MeO-MOP (L*) revealed that
cationic bisphosphine complex
[Pd(L*)2(π-cyclohexenyl)]+Cl-
is not formed even in the presence of excess
ligand but neutral monophosphine complex
PdCl(L*)(π-cyclohexenyl) (11) is formed, leaving
excess ligand
free, and that the exchange of the coordination site of Cl and L* in
11 is much slower than that in
triphenylphosphine complex
PdCl(PPh3)(π-cyclohexenyl) (13).
The slow exchange can rationalize the retention
of regiochemistry in the allylic alkylation catalyzed by
palladium/MeO-MOP complex.
Der idealen Alkoholoxidation einen Schritt näher: Die katalytische Oxidation von Alkoholen in Wasser mit O2 unter Atmosphärendruck wurde mit Pd‐Nanokatalysatoren erreicht, die in einem amphiphilen Harz dispergiert sind (siehe Schema). Dieses Katalysatorsystem vereint in sich hohe katalytische Aktivität (bedingt durch die große Oberfläche der Nanopartikel) und Reaktivität in wässrigem Medium (dank der Amphiphilie der polymeren Matrix).
Asymmetric hydrosilylation of simple terminal alkenes (RCH=CH2) with trichlorosilane at 40 °C in the presence of 1 × 10−3 or 1 × 10−4 molar amounts of palladium catalyst prepared in situ from [PdCl(η3-C3H5)]2 and (S)-2-diphenylphosphino-2′-methoxy-1,1′-binaphthyl ((S)-MeO-MOP) proceeded with unusual regioselectivity and with high enantioselectivity to give high yields of 2-(trichlorosilyl)alkanes together with a minor amount of 1-(trichlorosilyl)alkanes. Optically active alcohols, RCH(OH)CH3, were obtained by oxidation of the carbon–silicon bond. Regioselectivities for forming 2-silylalkanes over 1-silylalkanes and enantiomeric purities of alcohols are as follows: R = n-C4H9: 89/11, 94% ee (R). R = n-C6H13: 93/7 95% ee (R). R = n-C10H21: 94/6, 95% ee (R). R = PhCH2CH2: 81/19, 97% ee (S). R = PhCH2CH2CH2: 80/20, 92% ee (R). R = cyclo-C6H11: 66/34, 96% ee (R). A similar hydrosilylation of 1-alkenes, 4-pentenyl benzoate and 1,5-heptadiene gave corresponding 2-alkanols of 90% ee and 87% ee, respectively, the ester carbonyl and the internal double bond remaining intact.
An amphiphilic polystyrene-polyethylene glycol (PS-PEG) resin-supported ruthenium complex was designed and prepared. The polymeric Ru complex was found to promote the transition metal-catalyzed atom transfer radical addition of halogenated compounds to olefins, the Kharasch reaction, in water under heterogeneous as well as AIBN-free conditions with a high level of atom economy to meet green chemical requirements.
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