An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

Abstract

A silsesquioxane cage polymer functionalized with eight chloropropyl arms (1, T 8 -PrCl) reacted with 2,2′dipyridiylamine (DPA) to afford a new derivative with eight pendant linear chains (2, T 8 -Pr-DPA). Further reaction with [Mo(η 3 -C 3 H 5 )Br(CO) 2 (NCMe) 2 ] afforded another derivative containing three molybdenum units (3, T 8 -Pr-DPA-Mo), after substitution of the two nitrile ligands in each complex. These are the first silsesquioxane species containing DPA and the Mo(η 3 -C 3 H 5 )Br(CO) 2 fragment. The three materials were characterized by 1 H, 13 C, 29 Si, and 95 Mo NMR, FTIR, XRD, and elemental analysis, and T 8 -PrCl (1) was also structurally characterized by single-crystal X-ray diffraction. It was identified as a lowtemperature polymorph of this material. Elemental analysis indicated that all Cl atoms in the parent material T 8 -PrCl (1) were substituted by the deprotonated DPA group in T 8 -Pr-DPA (2). However, only three [Mo(η 3 -C 3 H 5 )Br(CO) 2 (DPA)] units were detected in T 8 -Pr-DPA-Mo (3). A comprehensive NMR study, complemented with DFT calculations, was carried out in order to detect the effect of Mo coordination on the cage silicon and on the protons and carbons of the propyl chain, but no significant effects were observed. Both 1 H and 29 Si chemical shifts vary upon introducing DPA but remain the same after reaction with the Mo(II) precursor. The 95 Mo NMR data reveal that the metal is not sensitive to the cage. The catalytic activity of 3 was tested as a precursor in the epoxidation of cyclooctene and styrene in the presence of TBHP. Despite the high selectivity toward the epoxides, the conversion and turnover frequencies were low, reflecting the behavior of the [Mo(η 3 -C 3 H 5 )Br(CO) 2 (DPA)] complex.

Molybdenum(II) catalyst precursors in olefin oxidation reactions

“…It has also been attached to a in a polyhedral oligomeric silsesquioxane [49] without any noticeable change, even though the NH group disappeared in the process (Scheme 5).…”

Synthesis, characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

“…The oligomeric catalyst POSS‐ATC‐[W(CO) 3 Br 2 ] was investigated in the epoxidation of 1‐octene, cyclooctene, limonene, cis ‐3‐hexen‐1‐ol, trans ‐3‐hexen‐1‐ol and styrene, using TBHP as oxidant at 55 °C under air atmosphere. The reactions were performed in a condenser with magnetic stirring and, to prevent the evaporation of the dichloromethane, a condenser was used . In each case, the container was loaded with the catalyst, substrate and TBHP as oxidant in a ratio of 1:100:200 in mmol% …”

“…The reactions were performed in a condenser with magnetic stirring and, to prevent the evaporation of the dichloromethane, a condenser was used . In each case, the container was loaded with the catalyst, substrate and TBHP as oxidant in a ratio of 1:100:200 in mmol% …”

“…Molybdenum and tungsten are well‐known catalysts and have been widely investigated. In general, epoxides can be prepared by the reaction of olefins with tert ‐butyl hydroperoxide (TBHP), catalyzed by transition metal complexes . Many POSS catalysts have been employed in epoxidation of olefins .…”

“…The catalyst used in the present work has shown a superior conversion (72%) using the same solvent. Dias Filho et al employed an oligosilsesquioxane cage functionalized with molybdenum(II) for epoxidation of cyclooctene and styrene in the presence of TBHP. The results showed a conversion of 59% for cyclooctene and 36% for styrene.…”