Abstract
Three new complexes [Mo(η3-C3H5)Br(CO)2{iPrN=C(R)C5H4N}], where R = H (IMP = N-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls exo), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)3, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR, 13C- and 29Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the cis-cyclooctene and cis-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.
Highlights
N-isopropyl 2-iminomethylpyridine (i PrN=CHC5 H4 N, IMP) is an α-diimine ligand with lower symmetry than 2,20 -bipyridyl and, a promising candidate in the design of selective catalysts
Based on the N content, these results indicated that the loading of the Y-IMP ligand inside the pores of the different materials was found to be 0.59, 0.72, and 0.96 mmol·g−1, for the MCM-1, MCM-2, and MCM-3 materials, respectively
= N-isopropyl 2-iminomethylpyridine), was interesting since the two isomers of this seven-coordinate and pseudo-octahedral complex were for the first time found [44] in the crystal, and there was no particular disorder
Summary
N-isopropyl 2-iminomethylpyridine (i PrN=CHC5 H4 N, IMP) is an α-diimine ligand with lower symmetry than 2,20 -bipyridyl and, a promising candidate in the design of selective catalysts. Several authors have described the synthesis and characterization of complexes, such as [Mo(VI)O2 Cl2 (IMP)] [1], [Mo(II)(η3 -C3 H5 )Cl(CO) (R1 ,R2 -IMP)], or [Mo(0)(CO) (R1 ,R2 -IMP)], with several R1 and R2 groups (Scheme 1) [2,3]. A few crystal structures have been determined by X-ray diffraction for the latter. The [Mo(CO) (R1 ,R2 -IMP)] complexes with R1 = H, Me, Ph and R2 =. [Mo(CO) (IMP)] was immobilized in MCM-41 (MCM) with a spacer, and both the complex and the porous material were tested in the catalytic epoxidation of cis-cyclooctene [5].
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