Terphenyls structure

Using related chemistry, we have found these repetitive couplings to be facile and have used aromatic diboronic acids83 to generate simple terphenyl structures on solid support.84 We used gel-phase fluorine NMR spectroscopy85 to observe the incorporation of the appropriate groups (Scheme 34) in repeated palladium-catalyzed reactions at slightly elevated temperature (55°C). This unoptimized two-step process was complete in essentially 24 h. 

Figure 5.3 Recyclable hypervalent iodine reagents based on the frameworks of 1,3,5,7-tetraphenyladamantane (65-67), tetraphenylmethane (69-71), biphenyl (structures 73 and 74) and terphenyl (structure 76).

PCT are prepared by direct anhydrous chlorination of terphenyl, as for PCB. Commercial grades are similarly mixtures of isomers the possible number is very large, as the terphenyl structure itself has 3 isomeric forms (o-. m. and p-). (Fig. 1). The grade normally used is Aroclor 5460 (or its Kanechlor equivalent), which contains ca. 60% chlorine it is often sold in admixture with PCB grades. Basic properties are summarised in Table 3. 

The frequently used starting material Li(TMEDA)[PhC(NSiMe3)2] was found to be monomeric in the solid state. Monomeric molecular structures were also established for lithium amidinates containing very bulky terphenyl or triptycenyl... 

To our knowledge, the crystal structure of only one mesogenic terphenyl compound has been described in the literature up to now [81]. The chemical... 

Fig. 12. Chemical structure of the mesogenic 4-cyano-4 -n-pentyl-p-terphenyl (T15)...

Structure of 4-cyano-4 -n-pentyl-p-terphenyl (T15) is shown in Fig. 12. This compound, first prepared by Gray et al. [82], exhibits a nematic phase with a wide temperature range. 

A first milestone was the development of a novel intramolecular Diels-Alder cyclization of terphenyl monomers 38 and 41, containing both 4-phenylbuta-dienyl and styryl functions. The formation of the [4-1-2] cyclization adducts 39 and 42 is followed by a simple aromatization of the cyclohexene moieties [59]. In this way, the phenylated, two-dimensional arylene structures, 40 and 43,... 

Pt(en)(N03)2] and [Pt(OTf)2L2] (L = mono- or 1/2 bidentate tertiary phosphine) or dinuclear complexes of the type [Pt2(OTf)2(/i-monodentate tertiary phosphine cr-aryl = 4, -biphenyl, / -terphenyL 4,4 -benzophenone, etc.) other structural motifs employing platinum(II) have also been reported.2 0 The addition of bridging, multidentate N-donor ligands of various shapes and sizes to the labile complexes in a suitable solvent system has afforded several classes of discrete, plat-inum(II)-containing polygons, polyhedra, and catenanes. 

With solubility as one of the principal problems to obtain structural information, the introduction of lipophilic ligands has been particularly successful, as shown impressively with the silyl substituted [CH(SiMe3)2] and [C(SiMe3)3] ligands.20 Steric bulk has also been applied successfully to reduce the tendency toward aggregation. This has been vividly demonstrated by recent chemistry utilizing terphenyl ligands.21... 

Biphenyl, terphenyl, and quaterphenyl all have room-temperature structures that behave similarly, and also all have low-temperature phases in which only one conformer is present. The torsion angle about the central C-C bond in biphenyl is estimated to be about 10° in the low-temperature form, which is appreciably less than that in the gas phase. In the case of terphenyl, it has been established (41) that the room-temperature structure is disordered each molecule librates in a double-well potential, with the barrier height being about 0.6 kcal/ mol. In the low-temperature form the molecule is stabilized in one of the two minima of the well, and has its terminal rings rotated in the same sense, so that the molecule conserves its center of symmetry. This alternation of rotations between adjacent rings is found (42) also in the low-temperature form of quaterphenyl and results in the molecule being noncentric (even though the crystal structure has a center of symmetry). 

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