Activated vs. pyrolytic carbon as support matrix for chemical functionalization: Efficient heterogeneous non-heme Mn(II) catalysts for alkene oxidation with H2O2
摘要:
Two types of heterogeneous catalytic materials, Mn-II-L(3)imid@Cox and Mn-II-L(3)imid@PCox, have been synthesized and compared by covalent grafting of a catalytically active [Mn-II-L(3)imid] complex on the surface of an oxidized activated carbon (Cox) and an oxidized pyrolytic carbon from recycled-tire char (PCox). Both hybrids are non-porous bearing graphitic layers intermixed with disordered sp(2)/sp(3) carbon units. Raman spectra show that (I-D/I-G)(activatedcarbon) > (I-D/I-G)(pyrolyticcarbon) revealing that oxidized activated carbon(Cox) is less graphitized than oxidized pyrolytic carbon (PCox). The Mn-II-L(3)imid@Cox and Mn-II-L(3)imid@PCox catalysts were evaluated for alkene oxidation with H2O2 in the presence of CH3COONH4. Both showed high selectivity towards epoxides and comparing the achieved yields and TONs, they appear equivalent. However, Mn-II-L(3)imid@PCox catalyst is kinetically faster than the Mn-II-L(3)imid@Cox (accomplishing the catalytic runs in 1.5 h vs. 5 h). Thus, despite the similarity in TONs Mn-II-L(3)imid@PCox achieved extremely higher TOFs vs. Mn-II-L(3)imid@Cox. Intriguingly, in terms of recyclability, Mn-II-L(3)imid@Cox could be reused for a 2th run showing a similar to 20% loss of its catalytic activity, while Mn-II-L(3)imid@PCox practically no recyclable. This phenomenon is discussed in a mechanistic context; interlinking oxidative destruction of the Mn-complex with high TOF5 for Mn-II-L(3)imid@PCox, while the low-TOFs of Mn-II-L(3)imid@Cox are preventive for the oxidative destruction of the Mn-complex. (C) 2016 Elsevier B.V. All rights reserved.
已经合成了仿生的三咪唑配体,在本文中称为L 3imid。已经评估了其与Mn(II)缔合形成的配合物对H 2 O 2催化烯烃环氧化的影响。Mn(II)/ L 3imid体系的催化效率显示出可以被乙酸铵打开,具有显着的有效性和对环氧化物的选择性。结合了具有席夫碱亚胺基和咪唑环结构特征的仿生配体L 3imid被认为与Mn(II)/ L 3imid系统的催化活性增强有关。
已经合成了仿生的三咪唑配体,在本文中称为L 3imid。已经评估了其与Mn(II)缔合形成的配合物对H 2 O 2催化烯烃环氧化的影响。Mn(II)/ L 3imid体系的催化效率显示出可以被乙酸铵打开,具有显着的有效性和对环氧化物的选择性。结合了具有席夫碱亚胺基和咪唑环结构特征的仿生配体L 3imid被认为与Mn(II)/ L 3imid系统的催化活性增强有关。