モリブドバナドリン酸塩／酸素系を利用した不飽和炭化水素類の酢酸パラジウム (Ii) による酸化反応

Abstract

Molybdovanadophosphoric acids (HPMoV) and their salts (NPMoV) partly substituted with an ammonium cation are efficient reoxidation systems for the Pd(OAc)2-catalyzed oxidation of alkenes and arenes with molecular oxygen. Acetoxylation of various cycloalkenes to 3-acetoxy-1-cycloalkenes was performed in good yields by the Pd(OAc)2/NPMoV/O2 system combined with hydroquinone. Oxidation of cyclohexene and styrene to the corresponding ketones by the same catalytic system in a mixed solvent of ethanol and water formed cyclohexanone and acetophenone, respectively, in fair to good yields. Monosubstituted alkenes such as ethyl acrylate and acrylonitrile underwent acetalization by this catalytic system to give the corresponding acetals in quantitative yields. Wacker-type oxidation of long-chain terminal alkenes by the present catalytic system was successfully achieved in the presence of a small amount of chloride ion. For example, oxidation of 1-octene formed 2-octanone (83%) as the major product, and the formation of undesired 3-octanone was less than 1%. The regioselectivity and yield of ketones were improved by dropwise addition of alkenes to the reaction system. The Pd(OAc)2/NPMoV/O2 system also acts as a good oxidation system for the carbomethoxylation of alkenes. Cyclopentene was carbomethoxylated under a mixture of CO (0.5 MPa) and air (0.5 MPa) to give dimethyl cis-1,2-and cis-1,3-cyclopentanedicarboxylates in good yields. Oxidative coupling reaction of benzene to biphenyl was performed by Pd(OAc)2 combined with HPMoV under dioxygen at 90°C. The best turn-over number of Pd(OAc)2 reached 109 and the yield of biphenyl was 14.3% based on the benzene used.

Palladium-Catalyzed Intermolecular Oxidative Amination of Alkenes with Amines, Using Molecular Oxygen as Terminal Oxidant

“…With regard to the Pd catalyst used in this reaction, PdCl 2 (PhCN) 2 gave the best result (90% yield), whereas the use of Pd(OAc) 2 and Pd(acac) 2 , which showed high activities in our previously reported Pd(II)/HPMoV/O 2 [44][45][46][47][48][49][50][51][52] and Pd(II)/NPMoV/O 2 [53][54][55][56] catalytic systems, gave only 7-14% of the desired products 3. Catalyst possessing less acidic counter ion such as PdCl 2 (PhCN) 2 is preferable to avoid over-coordination of the aniline nitrogen to Pd center.…”

“…Alternatively, complexes of molybdovanadophosphate ((NH 4 ) 5 H 4 PMo 6 V 6 O 40 nH 2 O:NPMoV), in which ammonium cations partly replace the acidic groups in HPMoV, have also been used as efficient reoxidation co-catalysts for the Pd(II)-catalyzed oxidation of alkenes [53,54]; this is a better reoxidation catalyst for oxidative coupling with more basic amines. We reported that a Pd(II)/NPMoV/O 2 or Pd(II)/NPMoV/HQ/O 2 (HQ: hydroquinone) system showed effective catalytic activity for acetoxylation and acetalization of olefins under mild conditions [53,54].…”

“…We reported that a Pd(II)/NPMoV/O 2 or Pd(II)/NPMoV/HQ/O 2 (HQ: hydroquinone) system showed effective catalytic activity for acetoxylation and acetalization of olefins under mild conditions [53,54]. The Pd(II)/NPMoV/O 2 catalytic system has been extended to Wacker-type oxidations and carbomethoxylation of olefins [55,56].…”

Heterogeneous alkenylation of aromatics under oxygen

“…Promising results were also reported with heteropolyoxometalates as co-catalysts [14,15,[17][18][19]. While there is considerable effort focused on designing highly active homogeneous systems, there are no reports on heterogeneous catalysts.…”

“…With the air or dioxygen TON up to 121 were obtained [14,15]. Such systems produce water as the only by-product (Scheme 1) but the reoxidation is more challenging.…”