2-phenyl derivatives, dimers structure

Spectroscopic investigations of the lithium derivatives of cyclohexanone (V-phenylimine indicate that it exists as a dimer in toluene and that as a better donor solvent, THF, is added, equilibrium with a monomeric structure is established. The monomer is favored at high THF concentrations.110 A crystal structure determination was done on the lithiated A-phenylimine of methyl r-butyl ketone, and it was found to be a dimeric structure with the lithium cation positioned above the nitrogen and closer to the phenyl ring than to the (3-carbon of the imine anion.111 The structure, which indicates substantial ionic character, is shown in Figure 1.6. 

Silver(I) complexes are known with the tris(pyrazolyl)borate [HB(pz)3] and the methyl, phenyl, bromo, or trifluoromethyl-substituted derivatives. The structure of the silver tri(pyrazolyl)borato species has been a puzzle since it was first reported.385,386 It was suggested that the structure could be oligomeric, but recently the crystal structure of the compound [Ag HB(3,5-Me2pz)3 ]2 shows that it has a dimeric structure387 where the silver(I) centers are tricoordinated by a bidentate arm of one ligand and a monodentate arm of the other ligand (29). The related complexes [Ag HB(4-Brpz)3 ]2, [Ag HB(4-Mepz)3 ]2, [Ag HB(3,5-Me2pz)3 ]2, [Ag HB(3-Mepz)3 ] , [Ag B(pz)4 ], and... 

In the solid state, 2,6-diphenylphenol has a monomeric structure with an intramolecular O-H—tt interaction to one of the ortho-phenyl substituents.143 Interestingly, the 2,6-diphenyl-4-nitrophenol derivative has a dimeric structure in the solid state with intermolecular, as well as intramolecular, O-H—77 interactions between ortho-phenyl substituents.144 The latter compound represented the first example of bifurcated OH—77 bonding (Fig. 28). 

The first examples of urea-containing dimeric capsules were discovered independently by Rebek and Bohmer [165,166]. These are based on calix[4]arene ethers, in which the lower rim ether units help to fix the calixarenes in a cone conformation via intramolecular interactions. Figure 60 shows the generic structure of such systems. Synthetically, the urea calixarenes are readily prepared. The calixarenes are first nitrated, followed by a reduction of these groups into amines. The urea derivatives are fixed to the upper rim by reaction of the p-amino calixarenes with isocyanates. Many systems were studied using differently substituted ureas which contain either short alkyl chains or simple phenyl derivatives. Studies also involved the changing of the lower rim ether substituents. 

The solvent-free phenyl derivatives of the heavier alkali metals have not been structurally characterized. Phenyl sodium dimers crystallize in the presence of donors such as, PMDTA and TMEDA. Using the bulky mesityl-substituted derivatives, a solvent-free arylsodium compound has been characterized [Na(C6H3Mes2-2,6)]2. ... 

Hilmersson and Davidsson studied by means of intensive NMR investigations a mixed 1 1 complex of n-BuLi and the Hthiated methoxyamine 6 (Scheme 1) in diethyl ether at -80°C [68]. A fluxional exchange between tetrameric and dimeric structures of the chiral Hthiated pyrrolidine 14 and -BuLi is apparent in diethyl ether solution [69]. With the Hthiated amine 15, a derivative of 6,75% ee of (S)-l-phenyl-l-pentanol was obtained in n-BuLi additions to PhCHO, using a ratio of 1.0 0.45 0.25 in diethyl ether at -116°C [37]. The N-methyl derivative gave only 2% ee, while the N-isopropyl derivative 16 yielded 82% ee under the same conditions. This demonstrates Ae crucial role of the N-isopropyl substituent in 16. Addition of dimethoxymethane increased the enantioselectivity of 16 to 91% ee of (S)-l-phenyl-l-pentanol. With Hthiated 16, enantioselectivities of up to 98.5% ee were achieved in butylations of aHphatic aldehydes [70]. Hilmersson demonstrated that the mixed Hthium amide/ -BuLi aggregate alkylates aldehydes faster than the pure -BuLi oHgomers, Eq. (2) [71]. 

The unsolvated dimer 89 can be obtained by recrystallization from pentane. A C2NgLi4 cage forms the core of the molecule. Each cage contains two essentially planar [C(NBu )3] dianions, linked by four lithium atoms. In contrast, the related phenyl derivative [Li2 C(NPh)3 ]2(thf)6, 153, forms an acyclic ladder-shaped structure similar to that of various lithium benzamidinates or diiminosulfinates [124]. 

---