Magnetic HMS silica as a Support to Immobilization of Catalysts Based on Cationic Manganese Porphyrins

Abstract

The immobilization of cationic manganese porphyrins (MnP) over the surface of a magnetic hexagonal HMS silica (HMS‐Mag) produced a solid with high surface area and relatively homogeneous pores. Given the presence of the magnetite, the catalysts are easily recovered and reused without loss of mass. The MnP immobilization explored the strong interaction between the positive charges of the cationic MnP and the deprotonated Si‐OH groups on the surface of HMS‐Mag. Soret bands on the UV‐Vis spectra of the MnP‐loaded HMS‐Mag confirmed the presence of MnP on the prepared solids. The catalytic efficiency, robustness, and reusability of the prepared solids were investigated on cis‐cyclooctene and cyclohexane oxidations. The solids showed similar or higher catalytic efficiency than the corresponding MnP under homogeneous catalysis, with selectivity for cyclohexanol in cyclohexane oxidation. Additionally, the solid catalysts showed high resistance against deactivation, confirming the reusability capacity in at least five cycles of cyclooctene oxidation.

The Research on Porphyrins and Analogues in Brazil: A Small Review Covering Catalytic and other Applications since the Beginning at Universidade de São Paulo in Ribeirão Preto until the Joint Venture between Brazilian Researchers and Colleagues from Universidade de Aveiro, Portugal

“…This was probably caused by the relative arrangement of MnP2 with the β-pyrrolic bromine atoms inside the pores of SBA-15 in the SBA-Si-Mag support (Figure 12), in comparison to the arrangement of MnP1, which seemed to be immobilized on the surface of the support and showed selectivity to 2-and 3-hexanol. Although other metalloporphyrins have been immobilized on SBA-15 and other mesoporous silica solids (HMS, MCM-41), 85,86,[88][89][90][91]94 similar selectivity results were not reported before. This astonishing selectivity for position C-1 indicates that the immobilization of MnP2 inside the pores of SBA-Si-Mag produced a selective catalyst for the oxidation of the terminal carbon of n-hexane, which is another amazing example of a non-innocent support contribution to the unusual selectivity of solids resulting from immobilization of MPs.…”

“…In spite of all the different solids used as supports for the immobilization of metalloporphyrins (Table 1), there is an expectation that MPs organized as porous materials, either using a porous solid as support (e.g., macroporous LDH, mesoporous silicas or zeolites), [85][86][87][89][90][91]99,100,125 or integrated into porous structures, such as metal-organic frameworks (MOFs) 27,80,140,141,145,146,192,193 or porous organic polymers (e.g., PIM = polymers of intrinsic microporosity), 149,153 will have enhanced catalytic performance, mainly regarding the selectivity, relative to non-porous materials, since the confinement effect for reagents and/or products may lead to unusual and unexpected selectivities for the same reaction relative to a homogeneous environment.…”

“…These objectives have contributed to an increasing number of reports on the use of solids based on magnetic particles for various catalytic purposes. 86,87,[92][93][94][201][202][203][204] A solid support based on mesoporous SBA-15 silica (Santa Barbara Amorphous) 205 and magnetite particles (F 3 O 4 ) was prepared (named SBA-Si-Mag), and then two cationic MnPs (here named as MnP1, and MnP2) were immobilized on them, generating two solid catalysts (MnP1-SBA-Si-Mag and MnP2-SBA-Si-Mag, Figure 12). The third generation porphyrin MnP2 was used to search for the best efficiency of the cationic catalyst.…”

Magnetically recyclable nanocatalysts based on magnetite: an environmentally friendly and recyclable catalyst for esterification reactions

“…These particles appeared to be homogeneously dispersed in the sample when compared with the bright field image ( Fig. 6a) (Ucoski et al, 2017).…”

Recent Advances in Catalyzed Sequential Reactions and the Potential Use of Tetrapyrrolic Macrocycles as Catalysts

“…There are many reports of the preparation of solid catalysts via their immobilization onto inert and usually inorganic matrices, such as layered double hydroxides [ 10 ], mesoporous silica [ 11 , 12 ], titanium oxides [ 8 ], zeolites [ 13 ], magnetic particles [ 14 ], and many more [ 15 , 16 , 17 , 18 ], in order to recover the catalyst for reuse. In addition, catalyst immobilization on inert matrices can produce unusual activities and synergism between the interacting species [ 19 ].…”