Inverse crown molecules

The donor-firee sodium magnesiate complexes with general formula [Na4Mg2(TMP)6(arene-di-ide)] (arene-di-ide = 2,5-C6H30Me in 54 3,5-C6H3NMe2 in 55 and 3,5-C6H3Me in 56 Fig. 35) are representative examples of inverse crown complexes. Those complexes are coined inverse crowns in view of their topological but inverse relation to conventional crown ethers in 

The three complexes 54—56 exhibit similar structural features, two Mg and four sodium cations within a 12-atom metal-TMP host ring, where the Mg cations anchor the corresponding guest arene-di-ide with four Na cations Jt-bonding in pairs to each metaUated C position. However, as expected, the structures of 2,5- (54) and 3,5-dimetallated arene (55 and 56) are subdy different due to the different metalation regioselectivities of the guest substrates. 

Another example of a sodium magnesium inverse crovm is the naphthalen-l,4-diide containing [ Na4Mg2(TMP)4(TTHP)2(l,4-CioH6) ] 57 (where TTHP is 2,2,6-trimethyl-l,2,3,4-tetrahydropyridide) (Fig. 36). 

It is obtained by reacting naphthalene with the aforementioned solvent-free sodium magnesium template base [Na4Mg2(TMP)6( Bu)2]- ° Prior to this result, using conventional alkyllithium or alkali metal bimetallic bases naphthalene, had only been regioselective metalated at the 2-position  

Na4Mg2N6 ring resembles that in 54 however, two of the TMP ligands have been transformed into TTHP (2,2,6-trimethyl-l,2,3,4-tetrahydropyridide) Hgand, formally by the loss of methane. 

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Hydride encapsulation in inverse crown molecules has also been observed. The reaction of NaBu, MgBu2 and three equivalents of HNPr 2 led to [Na2Mg2(NPr 2)4(p-H)2] " which... 

A remarkable series of inverse crown compounds featuring organic guest moieties encapsulated within host-like macrocyclic rings composed of sodium/potassium and magnesium ions together with anionic amide groups, such as TMP- (TMPH = 2,2,6,6-tetramethylpiperidine) and Pr NT (Pr NII = diisopropylamine), have been synthesized and characterized. Table 12.8.1 lists some examples of this class of inverse crown molecules. 

Molecular structures of two centrosymmetric inverse crown molecules containing organic cores ... 

Fig. 38). In this complex, benzene has been converted to a 1,4-dianion. Comparing this complex to compounds like 57, it seems that the addition of TMEDA has resulted in the formation of a molecule akin to an open inverse crown molecule (with the extrusion of neutral NaTMP). The TMEDA ligands chelate to the Na cations. 

This arrangement can be considered an inverse crown molecule, so named as it is essentially antithetical with respect to traditional crown ethers such as 18-crown-6 [(CH2CH20)6] which involve a Lewis basic ring which can encapsulate a Lewis acidic cation such as K". A similar product is obtained upon substituting the substrate toluene with benzene, that is, a 12-atom inverse crown containing a para-dimetalated benzenediide host (CgH4 ). Naphthalene can likewise be doubly deprotonated at the 1 and 4 positions [86]. 

Fig. 37 Molecular structures of Na/Mg left) and K/Mg (right) TMP inverse crowns with one (Cglli) " and six (QHs) guest molecules, respectively...

The guest molecules in the 1 2 [18]crown-6 2,4-dinitroaniline complex 21) are related by an inversion center (Fig. 13) 23). Both hydrogen atoms of the amine are involved in bifurcated hydrogen bonds. 

Figure 10. Solvation of twelve 18C6 crowns "diluted" in dry versus humid [BMI][PF6] solutions. Typical snapshots of die "first shell" solvent molecules and radial distribution functions "RDFs" around the center of the crown 18C6 BMI (bold), 18C6 F (dotted), 18C6 P (plain) and Sr OH2 (inversed ordinate).

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