Pyrazole mononuclear derivatives

The corresponding pyrazole mononuclear derivatives [AuCl(pzH)] have been prepared with the same ligands (Figure 7.41) [38]. Only the monosubstituted non-mesomorphic pyrazole leads to a liquid crystal, not the disubstituted mesomorphic ligand. The complex displays a SmA mesophase on cooling to 69.2 °C, although this is mixed with some crystallization. Moreover, this derivative is luminescent at 77 in the solid state. In addition, the corresponding trinuclear and mononuclear derivatives, namely [ Au(pz) 3] and [Au(Hpz)2]+, which could be expected to be liquid crystals are non-mesomorphic. 

Reactions of the metallocene derivatives of molybdenum with pyrazole lead to the mononuclear complexes of the type 22. Structure 22 shows that it cannot be used as a ligand for the preparation of dinuclear complexes owing to geometric constraints [80JOM( 197)291 83JOM(253)53]. In acetone, an unusual complex 23 is formed [83JOM(253)53]. The bidentate ligand is the product of the reaction of pyrazole and acetone. 

The interest for pyrazolate complexes containing the pz group as a mono-dentate ligand arises because of their recognized usefulness in the synthesis of dinuclear and trinuclear heterometallic derivatives. The mononuclear complex... 

Polynuclear Copper(l) Catalysts. Apart from mononuclear copper-catalyzed cyclopropanation, more recently polynuclear copper catalysts have been demonstrated to give characteristic diastereoselectivity. [Cu(dtbpz)]4, derived from 3,5-di-tert-butylpyrazole, gave high transicis ratio of 88 12 with slyrene and nonbulky EDA (19). In contrast, trinuclear triangular complexes, [Cu3( i3-OH)()u-pz)s(MeCOO)(MeO)(Hpz)] (Hpz = pyrazole), gave the same cyclopropanes in cis selectivity (trans cis = 38 62) (20). 

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