2-phenyl derivatives, dimers

Imines 268 (Ar = phenyl, p-anisyl, p-chloro-phenyl) are dimerized on heating in aprotic solvents to give the yellow tetraphenyl p-benzoquinone imines 267 and (or) their reduction products, the colorless p-phenylene diamine derivatives 270ss ... 

The radical (21a) in dichloromethane at 22°C gave a structureless signal ( = 2.041 G). In the solid state, (21a) is dimeric and diamagnetic with residual spin density 0.01% (see Section 4.21.3.1) <92CC1265>. The phenyl derivative (21b) also gave a broad unresolved signal g = 2.0394 G). Loss... 

A similar spiro-fused starting material was prepared to study the thermolysis of a 1,3-dioxane analog. As found for the dithia compound (cf. Section 8.11.6.3.1), a carbene-derived dimer was formed as the major detectible product (20%) <2002TL1927>. Other products, such as tricycle 185, have been identified in subsequent studies <2004CJC1769>. However, phenyl substitution at G-4 provided completely different thermolysis products, probably via formation of an open-chain bis-radical. Thus, 3-phenyl-7-butyrolactone and, after CO2 extrusion, phenylcyclo-propane are the major reaction products (Scheme 58) <2002CJC1187>. 

Chapman and Breslow synthesized zinc(II) complexes of monomer and dimers derived from 1,4,7-triazacyclododecane with phenyl 48 and 4,4 -biphenyl linkers 49 (55). They were examined as catalysts for the hydrolysis of 4-nitrophenyl phosphate (NP2 ) and bis(4-nitrophenyl) phosphate (BNP ) in 20% (v/v) DMSO at 55°C. On the basis of the comparison of the pseudo-first-order rate constants, the dinuclear zinc(II) complexes 48 with 1,3-phenyl and 1,4-phenyl linkers are ca. 5 times more efficient than monomer or 49 in the hydrolysis of NP2, leading to the conclusion that the two zinc(II) ions are simultaneously involved in the hydrolysis, as in the enzyme alkaline phosphatase. For the hydrolysis of BNP, a longer dimer 49 is ca. six times more effective than 1,3-phenyl-linked dimer 48 and monomers. 

Alkylgallium halides have been prepared by halogen alkyl exchange and were found to be dimers in the vapor (61, 78). The phenyl derivatives have been found to be dimeric in solution and it has been suggested that internal coordination takes place through halogen bridges. 

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. 

Stability of the compounds 86 varies dramatically with the nitrogen substituent. Methyl and phenyl derivatives (86 R = Me or Ph) are moderately stable crystalline solids—often hydrated (87 or 88 X = OH). The 2,4-dinitrophenyl derivative [86 R = CeH3(N02)2, R = H] is less stable but can be isolated as orange prisms (mp 112°C) It readily rearranges to the diaryl ether 96 (mp 128°C) with which it was originally confused.The monomeric 5-nitro-2-pyridyl derivative is similarly unstable and in solution dimerizes giving adduct The 4,6-di-... 

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. ... 

Bis[cyclopentadienyldicarbonyliron] and diaryl ditelluriums in refluxing benzene reacted to initinally form cyclopentadienyidicarbonylarenetellurolatoiron compounds. On prolonged heating, these compounds dimerized with loss of a carbonyl ligand . The dinuclear complexes exist in two isomeric forms. The crystals of the 4-ethoxy phenyl derivative were separated by hand into the two isomers . 

---