Exclusive complexes

An investigation of the kinetics of formation of the Li+ and Ca2+ complexes of cryptand 2.1.1 using stopped-flow calorimetry suggests that complexation occurs initially at one face of the cryptand such that the metal is only partially enclosed (to yield an exclusive complex). Then follows rearrangement of this species to yield the more stable product, containing the metal ion inside the cryptand (the inclusive product) (Liesegang, 1981). X-ray diffraction studies have indeed demonstrated that exclusive complexes are able to be isolated for systems in which the metal is too large to readily occupy the cryptand cavity (Lincoln et al., 1986). 

An exclusion complex of this type has been identified by X-ray crystallography for the KNCS complex of the smaller [2.2.1]cryptand,454 ([2.2.1]cryptand = 73, n = 1, m = 1, / = 0). The cation occupies a site in the 18-membered ring provided by the ligand rather than in the central cavity and so resembles the coordination of potassium by 18-crown-6 (Figure 21a). In contrast, the smaller Na+ cation is of optimal size for the [2.2.1]cryptand and so an inclusion complex occurs with the cation inside the cage (Figure 21b).454 Binuclear inclusion complexes have not yet been isolated for bicyclic cryptands. 

Reaction of (30) with diethyl sodiomalonate gives exclusively complex (94), which can be demetal-lated to give the cyclohexenone derivative (95 Scheme 13) in good overall yield.27 A range of nucleophiles can be used, including cyanide, and keto ester enolates, giving, e.g. (96) or (97 Scheme 13), respectively. 

Base Proton Complexation Shifts The complexation shifts of certain nucleic acid base resonances of poly(dA-dT) on formation of the daunomycin neighbor exclusion complex reflect the shielding contribution due to the anthracycline ring less the contribution from one neighboring base pair which is displaced following intercalation. Thus, the adenosine H-2 resonance remains unperturbed (Figure 27) while the thymidine exchangeable H-3 proton... 

Different compounds which complex the fluoride anion were recently developed. Sapphyrine (1) is a porphyrin with 5 pyrrole rings, and when it is doubly protonated it can exclusively complex F in its cavity68. Similarly, Seppelt prepared the thermally stable salt 2 with a bulky cation where the fluoride can be completely desolvated, thus increasing its efficiency as a nucleophile and a base69. 

Treatment of the o-methyl diphenyl ether complex 58a with isobutyronitrile carbanion at —78 °C and then allowing the reaction mixture to warm up to room temperature affords the ipso complex 59a almost quantitatively. Ipso SNAr of the phenoxy group also occurs with acetonitrile, propionitrile, and alkoxycarbonyl carbanions (Scheme 28) [46]. Similarly, addition of isobutyronitrile carbanion to 2,3-dimethyl diphenyl ether complex 58b gives exclusively complex 59b under the same experimental conditions. 

The effect of the nature of the leaving group has been delineated in the case of 2,6-dimethylfluoro and chloro complexes. Complex 96a reacts with LiC(CH3)[S(CH2)3S] and CF3C02D to give exclusively complex 97a by a teie-meta SnAt [70], whereas complex 96b reacts with LiC(Ph)[S(CH2)3S] and CF3C02D to give deuterated complex 97b by a tele-para SNAr [72],... 

An interesting aspect of the bis(methyl)ruthenium complexes 33 is their tendency to allow hydride abstraction with (Ph3C)PF6. They lead to ethylene complexes 55 and 56 (46,47).The X-ray structure of 55 shows bond distances of 1.411(13) A for C=C and 1.50 A for Ru—H (46,47). The reaction probably proceeds via intermediates 53 and 54, although it was not established whether the transformation 33 - 53 involves a mono-electronic process as with WMe2(C5H5)2 (48). A similar reaction from the deuterated derivative 57 gives exclusively complex 58, configurationally... 

An interesting result reported recently by the same group of workers (70) relates to the discovery of two types of 1 1 caesium cryptates for cryptand C222. The possibility for the existence of an exclusive complex... 

Basic calixarenes of the type calix[n]arene have been complexed with with n ranging from 3 to 9, including 12, and can be either inclusion complexes or exclusion complexes (see Table 47). Inclusion complex have three or more phenolic-oxygen bonds with the uranium, essentially enclosing the metal entirely, and the exclusion complexes have three or less, leading to a less than perfect encircling of the metal. " ... 

Crown ethers. U -crown ether chemistry has been extensively studied due to the wide variey of complexes that can be formed. Uranyl can form both inclusion and exclusion complexes with both hetero- and homocrown ethers. Exclusion complexes can form bonds to other metals in the crown ether cavity directly or via hydrogen bonds to crown ether oxygens. The nature of complexation is dependent on the chemical environment. 

The hydrogenation of y-tocotrienyl acetate, a vitamin E precursor [43], is a striking example demonstrating the potential of these catalysts. With complex 27 all three double bonds in the side chain were reduced with very high enantio- and diastereoselectivity to give the natural (R,R,R)-isomer of y-tocotrienyl acetate almost exclusively. Complexes... 

In the [2.2.2] complex with cesium, the Cs" ". .. O distances are somewhat smaller than the corresponding sum of the Van-der-Waals radius of oxygen and the ionic radius of Cs", as was similarly observed in the Cs" complex of nonactin (see Chap. 3). This indicates that the cation presses heavily on the ligand. In fact, it was concluded from Cs-NMR data that in solution, [2.2.2] forms an exclusive complex with Cs" ", i.e. the metal ion does not occupy the central ligand cavity but is only partly... 

An exclusive complex of this type was actually found also in the crystalline state for the KNCS complex of the smaller [2.2.1] cryptand From molecular models, the cavity radius of this ligand was estimated to be 1.1 A which is too small for potassium to enter. As a result, occupies a site in the 18-membered ring rather than in the central cavity (see Fig. 38), thus resembling the coordination of K" by [18]crown-6. Additionally, the potassium ion is bonded to the isocyanate anion whereas anions are generally not coordinating to alkali metal ions in inclusive cryptates. 

Calixarenes fully functionalized at the lower rim with ether groups show a weak affinity for alkali metal ions. The case of the tetramethyl ether of /7-T rT-butylcalix[4]arene (13) is quite interesting, since it is conformationally mobile, and can adapt its conformation to different metal ions. The Na+ ion is exclusively complexed by the cone isomer, while Cs is preferentially bound by the partial cone isomer. 

Fedin and coworkers [102,103] have isolated a number of distinct species within CB[n] nanoreactors. For example, they identified a previously unrecognized hydronium di-cation in a solid-state complex with CB[6] [102]. Instead of the commonly recognized H7 O3 monocation (essentially a proton coordinated by three water molecules), they observed a cyclic H14 OJ species, stabilized and templated by a set of five hydrogen bonds to the CB[6] portal carbonyls, forming an exclusion complex. In another report, they showed that the trans form of the metal complex [Co(en)2Cl2r (en = ethylenediamine) was selectively encapsulated in CB[8] from a mixture of cis and trans complexes [103]. Furthermore, the trans complex was thermally stabilized in the CB[8] nanoreactor. This shows the potential utility of CB[n] nanoreactors to select specific reactant isomers for subsequent selective reactions. 

Mass spectrometric analysis of rhFSH N-glycans produced in CHO cells showed exclusively complex structures with more or less sialylated and... 

Flows of gases in isotropic media. Although we have considered liquids (with m = 0) exclusively, complex variables ideas readily extend to steady-state compressible gases. Consider the flow of a gas in homogeneous, isotropic media, following Discussion 4-2. Equations 4-17 and 4-18 suggest that... 

Shoren et al. [66] suggest that EAA somehow interferes with starch accessibility to micro-organisms and their hydrolytic enzymes. Amylose in starch forms V-type exclusion complexes with EAA that make it highly resistant to starch-hydrolyzing enzymes [66, 67]. 

Interestingly, complex 21 underwent essentially instantaneous deutera-tion, which was already complete during the NMR sample preparation. Isotope exchange involved the heterocyclic proton at C4 exclusively. Complex 23 was less reactive and H/D exchange occurred first at the C2-bound CHj group (one hour). Subsequent deuteration of the heterocyclic carbon C4 position was significantly slower and required two days to reach completion. These observations point to a more electrophilic character of the triazolylidene heterocycle (fast reactivity towards OH"), while the imidazolylidene is rather nucleophilic (fast reaction with H ), hence highlighting a remarkable difference between the two types of abnormal carbene. 

Inokuma, S., Xakezawa, M., Satoh, H., Nakamura, Y., Sasaki, X, and Nishimura, J., Efficient and selective synthesis of crownopaddlanes possessing two cyclobutane rings and exclusive complexation of lithium,/. Org. Chem., 63, 5791, 1998. 

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