Pyrazoles, 1,4-dihydroxy-, oxidation

Tetraazafulvalenes bearing two pyrazole subunits could be prepared by an original way. Tlius, treatment of benzylidene acetophenone with iso-pentylnitrite leads to an A, A -dihydroxy-bipyrazolyl-A, A -oxide, which in turn can be oxidized to TAF of type 100 (72CC961, 79JOC3211). Another type of oxidative dimerization was observed by the reaction of the electron-rich l-methyl-2,4-bis(dimethylamino)imidazole with silver salts (83TL3563). A bis-cation was isolated in 30% yield in the presence of sodium tetrafluo-roborate an unsymmetrical structure 101 was predicted from its NMR data (Scheme 40). 

Fig. II.1.16 (a) Structure of the binuclear ruthenium complex [ Ru(bipy)2 2( x-L)](PF6)2 (bipy = 2,2 -bipyridyl, L = l,4-dihydroxy-2,5-bis(pyrazol-l-yl)benzene dianion) and (b-d) voltammo-grams for the oxidation and reduction of [ Ru(bipy)2 2( Jl-L)](PF6)2 in dimethylsulphoxide (0.1 M NBU4PF6) at a 25 xm diameter platinum disc electrode employing (b) a scan rate of 2 V s (c) a scan rate of 20 mV s and (d) square-wave detection with frequency 50 Hz, amplitude 25 mV, step potential 5 mV...

Figure 9 Spectroelectrochemical oxidation of [Ru(bipy)2 (HL°)]+ (H2L0 = 1,4-dihydroxy-2,3-bis(pyrazol-1-yl)benzene) as a function of time between 0 and 20 min. Reprinted with permission from Keyes TE, Jayaweera PM, McGarvey JJ and Vos JG (1997) Journal of the Chemical Society, Dalton Transactions, 1627-1632.

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