Encapsulated Organometallic Complexes

Even if the metal cation exchanged zeolite is not dehydrated, the introduction of the ligand or its precursors frequently requires thermal treatment, which can redistribute the cations within the zeolite. Not all metal ions will become com-plexed and their presence can complicate the characterization of the materials as well as the interpretations of catalytic reactions. In principle, the uncomplexed metal ions should be removed by back-extraction. Unfortunately, however, this is a requirement more frequently honored in the breach, rather than the observance. 

A similar reservation applies to the need to remove ligand precursors or byproducts from the support. This is a particular issue in relation to intrazeolite com-plexation reactions in which the corresponding homogeneous synthesis is less than quantitative. Another difficulty relates to estabUshing the efficacy of ligand synthesis within a zeoUte. Thus, for example, although several reports of the syntheses of metal porphyrin complexes within zeolites have appeared, the ligands are, in fact, domed porphodimethenes (diameter -14 A), or protoporphyrins [138, 

A more subtle compUcation is that the complexation of free Ugands, H L, by deprotonation will alter the zeoUte acidity. 

With these caveats, then, the following is intended to illustrate the synthetic strategies to encapsulate complexes, rather than to comprehensively cover the field, which has been the subject of several reviews [140-142]. 

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The encapsulation of reactive organometallic complexes is not restricted to the anionic [Ga4(L13)6]12- cages. Thus, Fujita and coworkers were able to generate the coordinatively unsaturated complex [Cp Mn(CO)2] (Cp = C5H4Me) within a self-assembled [M Le] coordination cage 28 (Fig. 20) (132). Photoirradiation of solid 27 gave complex 28, the crystal structure of which confirms the presence of the unsaturated pyramidal [CpMn(CO)2] fragment. The direct observation of such intermediates is... 

These complexes are structural examples of cage organometallic complexes in which the metal is completely surrounded by the fullerene. Typically, complexes containing encapsulated metals are prepared by laser-induced vapor phase reactions between carbon and the metals. These compounds contain central metal cations surrounded by a fulleride, a fullerene that has been reduced. 

The majority of the molecnles that have been encapsulated in SWCNTs inclnde fullerene-type molecnles [38,68]. The non-fnllerene-type molecnles, based on transition metals, that have been shown to be encapsulated in CNTs are two organometallic complexes, the cobaltocene and ethylcobaltocene and a zinc phenylporphyrin [38,68,69]. The nature of the [CoCp2]-CNT interaction appeared to be more complex than pure van der Waals forces. The presence... 

The first bisphosphine calixarenes that have been used in catalysis are di(amide)-phosphine hybrids calix[4]ar-ene. Reaction of [RhCl(norbornadiene)]2 with these calixarene derivatives gave an organometallic complex whose norbornadiene-rhodium moiety lies above the cavity defined by the four substituents of the calixarene and between the two amide functionalities. This complex was applied in the hydroformylation reaction of styrene. The rather low reaction rate observed (7.5 turnovers per Rh per hour) has been attributed to a partial encapsulation of the metal center preventing the approach of the substrate. Indeed, the metal center may be viewed as located in a hemispherical ligand environment. 

Organic-modified clinoptilolite 22-P-12 22-P-15 Organometallic complexes, encapsulated... 

As presented in the previous section, the chiral self-assembled M4L6 supramolecular tetrahedron can encapsulate a variety of tetra-alkyl ammonium guests and presents high configurational stability. Raymond, Bergman and coworkers, used the tetrahedral [Ga4(23)6] (5.32) (H4(23) = l,5-bis(2,3-dihydroxybenzamido)naphthalene) (Figure 5.11) as a host to encapsulate reactive cationic organometallic complexes and studied some catalytic transformations within the chiral environment of the cavity of the supramolecular tetrahedron. 

Cso peapods, C50 encapsulated inside a CNT, were first produced and observed during CNT synthesis by pulsed laser vaporization [150]. Nowadays the synthesis of encapsulated fullerenes [151], endohedral fullerenes [71,151-156] and volatile organometallic complexes of fullerenes [157] within the CNTs is mainly achieved by vapor phase filling technique, consisting in heating at the... 

The in vitro effect of the organometallic complexes alone or encapsulated in Me- -CD was investigated using the hormone-independent breast cancer cell lines MDA-MB-231 after 4 days of culture to assess whether or not the inclusion of 4 or 6 into the CD affected their bioavailability. The corresponding results are reported in Fig. 47.19 [49]. 

The encapsulation of classical and organometallic transition-metal complexes to yield molecules of the type complex in a complex is a very attractive research area. A variety of inclusion complexes of this type has been reported. Of relevance for this review are reports on the encapsulation of coordinatively unsaturated transition-metal complexes inside self-assembled coordination cages (120), cyclodextrins (121,122), and cucurbiturils (123). 

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