Exo complex

Each of ()] -allyl)Fp, () -pentadienyl)Fp, and ( -cyclopentadienyl)Fp complexes undergo photolytic loss of CO to afford their respective Cp(CO)Fe( ) complexes. In both the cases of allyl and acyclic pentadienyl complexes, the -complexes are stable compounds, isolated as a mix-tme of exo and endo complexes, with the exo complex being more thermodynamically stable. In the pentadienyl case a significant amount of the ( -pentadienyl)FeCp complex is also isolated. In the case of ( -cyclopentadienyl)Fp complexes the -complexes are observable (again as an exolendo mixtme) only at 77 K, by IR spectroscopy. At room temperatme, only the ( -cyclopentadienyl)FeCp is realized. ... 

In the former insertion according to (b) yields the endo complex LXII, whereas in the latter direet attack of phenyl carbanion aecording to (a) produces the exo complex LXIV. However, palladium-diene complexes - and the iron complex LXV react with heteroatom nucleophiles according to path (a) even when the nucleophile is partly coordinated to the metal. Thus there is an intrinsic difference between heteroatom nucleophiles and simple carbanions in accordance with the division made in this section. 

The endo complex should be formed in y-CD. This complex, in which the probe is less exposed to the oxygen quenching, has a structure similar to that proposed in reference 139 for 26. The exo complex, in which the probe is more exposed to bulk water and to the action of foreign quenchers, should prevail in -CD. The increase of CD concentration should shift the structure of the complex from that shown in the figure to one in which the two... 

This reaction revealed several very interesting and unexpected (or curious) steps. The meehanistic explanation given by Castellani can be summarized in the following seheme. First, syn insertion of 1 to Ph-Pd-I affords the cis, exo complex 3. In this ease, syn f-H elimination to give phenylnorbomene is impossible due to the rigid trans configuration of the Pd atom and -hydrogen. The... 

In another context, the biaryl lactones could also be activated by a tf-coordination of a transition metal fragment which added an additional element of planar chirality to the system. For instance, coordination of a tricarbonyl chromium unit to the phenolic part of biaryl lactones delivered the corresponding jj -complex. The latter complex was configurationally unstable and existed as a mixture of the two atropodiastereomeric forms. From this equilibrium, the ring cleavage with sodium borohydride proceeded highly stereo-selectively, yielding the biaryl alcohol exo complex exclusively (Scheme 5.12). ... 

Complexation of metals to curved carbon n surfaces has attracted continuous interest since the discovery of fullerenes. So far, fullerenes have been found to act as an -coordination ligand to various transition metals from its eYO- r-surface [1, 2], Other coordination modes in exo complexes were reported in the modified fullerene it systems [3], such as buckyferrocene [4] Fe(CgoMe5)Cp (Cp = cyclopentadienyl). Fullerenes are also known to form the endohedral metal complexes to provide potential materials in carbon chemistry [5, 6], On the other hand, fullerene fragments, termed as n bowls (we use this term in the present chapter, whereas they have been also called open geodesic polyarenes [7] or buckybowls [8]), also possess curved carbon n surfaces, n Bowls have attracted interest in the science of nonplanar -conjugated carbon systems [9-14], From the viewpoint of coordination chemistry, such molecules are quite unique because they can provide not only a convex surface but also an open concave surface for binding (a schematic illustration is shown in Fig. 35.1), which was first addressed by the computational study of hemifullerene (C30H12) in 1993 [15],... 

In the analogous reaction of P-ionone with FejCCO), 1 h of sonolysis gave a 4 1 mixture of endo and exo complexes (Scheme 134). In contrast, Cais and Maoz report that the thermal reaction of the diene with Fe(CO)j leads to isolation of a 3 1 ratio of products in favour of the exo-isomer [278]. However, it should also be noted that the overall yield of the thermal reaction was only 21 %, that is a factor of three less than that obtained under sonolytic conditions. 

The only topological type in this small molecule area that has not been exploited extensively as a neutral ligand in supramolecular chemistry was the Class IV dendritic (cascade)-type architecture. Vogtle et al. introduced this fourth major small molecule architecture in the late 1970s in a single isolated communication [33]. These low molecular weight dendritic (cascade) molecules served as precursors to macromolecules, which are now recognized as dendrons, den-drimers, and hyperbranched polymers [34,35], Interest in the supramolecular aspects of dendritic systems has occurred only recently. As described earUer [36], they offer the potential for either endo or exo complexation and are the focus of this account. 

Cyclic Dienes. Ring opening of cis- and rrfl/is-2-phenylmethylene[3- Hi]-cyclopropane yields stereospecifically the trimethylenemethane complexes (82a, b), respectively the results are consistent with an allowed disrotatory ring opening, and are in agreement with frontier MO calculations. The exo-complex (83) and its enrfo-isomer have been prepared by reaction of the free... 

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