Metallocene, zeolite synthesis

Probably the first report on the use of a metaUocene in zeolite synthesis dates back more than ten years [124]. In the past few years, however, essentially two groups reported on the influence (i.e. structure directing properties) of cobalt metallocene compounds in the synthesis of zeolites and zeolite-like materials [e.g. 125-128]. In none of these studies had a new framework topology been synthesized. However, very recently Balkus and coworkers reported the synthesis of the first fourteen-membered ring zeolite, which they called UTD-1 (University of Texas at Dallas No. 1) [129-132]. UTD-1 was synthesized with a quite unusual template, viz. with bis(pentamethyl-cyclopentadienyl)cobalt(III) hydroxide [129-132]. Both the essentially pure-silica version and high-silica derivatives have been prepared. A typical synthesis of the all-silica version com-... 

The synthesis of phthallocyanines in zeolite Y has been the subject of several publications [52-58]. The different procedures are represented in Scheme 3. In principle, dicyanobenzene is reacted under inert conditions with transition metal zeolites. The latter can be prepared either via ion exchange, or via carbonyl or metallocene impregnation. 

K.J. Balkus, Jr., C.D. Hargis, and R. Szostak, Synthesis and Characterization of Zeolites Prepared using Metallocene Templates. Proceedings of 12th International Zeolite Conference, Materials Research Society, Warrendale, PA, 1999, 1931-1935. 

The in-s rtu synthesis of metalio-phthalocyanines in zeolites can be done via three distinct literature procedures (Scheme 1). The required amount of a given transition metal is brought into the zeolite via a simple ion exchange (procedure A), through adsorption of a TM-carbonyl (B) or a metallocene (C). After removal of the respective TM ligands (water, CO and cyclopentadiene, respectively), 1,2-dicyanobenzene (DCB) is adsorbed onto the TM-zeolite and the mixture heated to form the MePc compiex. Rnally, the sample has to be purified in such a way that oniv occiuded MePc complex remains in the zeolite. The association of DCB with the supercage TM ions in Y zeolite, are schematically shown in Fig. 3. 

The development of new or improved processes in catalysis and adsorption were in many cases induced by the development of new catalytic materials and adsorbents. In this context, the synthesis of new aluminosilicates is a continuing challenge in zeolite science. The present review, discussing the synthesis principles of selected more recent zeoUtes, has shown that there is still much room for innovation in this field. It can be expected that by the use of new classes of templates (one recent example is that of the metallocenes) new structures wiU be synthesized in the future. Moreover, with the availability of more and more sophisticated tools for modelling zeolite and template structures and their interactions, it will probably be possible to tailor templates for a given (or a theoretical) zeolite structure. Finally, beside the exploration of new templates and new reaction compositions, the influence of the synthesis conditions on the products should not be overlooked, e.g. changing the reaction parameters from subcriti-cal to supercritical conditions could well have an influence on the materials which are formed. 

The various strategies for preparation of zeolite encapsulated phthalocyanine complexes have largely involved the condensation of dicyanobenzene (DCB) around an intrazeolite metal ion to form the MPc complex. The efficiency of this template synthesis depends on the nature and location of the intrazeolite metal ion to be complexed. For example, metals have been introduced to the zeolite by ion exchange (7-13), metal carbonyls (14-19) and metallocene complexes (2-5,19-21) prior to reaction with DCB. Some of the advantages and disadvantages of these methods have been detailed by Jacobs (2). However, there are several problems that are inherent to the template synthesis in general. Often there is incomplete... 

---