Phenyl group aggregations

The patent literature covers many pyridazine derivatives claimed as blood platelet aggregation inhibitors and antithrombotic agents. The interest has been focused mainly on 6-aryl-4,5-dihydro-3(2//)-pyridazinones. In these compounds the aryl substituent has been varied within a wide range. Thus, dihydro-pyridazinones bearing a substituted or heterocycle-fused phenyl group at C-6 (60, R R2,R3 = H, alkyl Ar = substituted Ph) [34, 110-112,205-233] as well as various heteroaryl substituted congeners (61, R1, R2, R3 = H, alkyl Ar = pyridyl, thienyl, pyrrolyl, pyrazolyl) [234-241] have been prepared in search of novel antithrombotics. 

Figures 20.4.4(a) and 20.4.4(b) illustrate the crystal structure of the 1 1 complex of tetraphenylmethane and carbon tetrabromide. The nodes comprise C(C6H5)4 and CBr4 molecules, and the each linking rod is the weak interaction between a Br atom and a phenyl group. The hexamethylenetetramine-like structural unit is outlined by broken lines. Figures 20.4.4(c) and 20.4.4(d) show the crystal structure of tetrakis(4-bromophenyl)methane, which has a distorted diamondoid network based on the hexamethylenetetramine building unit. If the synthon composed of the aggregation of four Br atoms is considered as a node, then two kinds of nodes (Br4 synthon and quatenary C atom) are connected by rods consisting of p-phenylene moeities.

Direct reaction of soluble polymers that contain phenyl groups, for example, polystyrene, with chromium atoms leads to polymers crosslinked with bis(benzene)chromium. Oxidation leads to aggregates of Cr203 imbedded with the polymer. 

Metal complexes of TPPMS and TPPTS have amphophilic character because of the presence of both hydrophilic sulfonate groups and hydro-phobic phenyl groups in the ligand structure. This feature allows the complex to transfer readily between the aqueous and organic phases in a biphasic system. Furthermore, these complexes can aggregate to form micelles, or surface-active compounds. This property may be a particularly important one when the properties and selectivities of catalysts formed by such phosphines are being considered (130). 

The activation effect was really observed in random screening of chiral ligand/ activator combinations. Enantioselectivity of the reaction is also increased by matched eombination of diol ligands and nitrogen activators. The replacement of 3- and 3 -positions with bulky phenyl groups, 3,3 -diphenyl-l,l -bi-2-naphthol (L ), may further prevent the aggregation of binolato-Zn and increase the enantioselectivity, because of their steric demand to provide (S)-l-phenylpropanol in up to 65% ee and quantitative yields. 

---