Ni-promoted syntheses of new 3,3′-dichloro-5,5′-bipyrazoles and poly(bipyrazole-5,5′-diyl)s and isolation of nickel complexes relevant to the syntheses

Reactions of 3,5-dichloropyrazoles and 3,3'-dichloro-5,5'-bipyrazoles with zerovalent nickel complex, Ni(0)L-m, have been studied. In cases of 3,5-dichloro-1,4-dimethylpyrazole and 3,5-dichloro-4-methoxycarbonyl-1-methylpyrazole, only the C(5)-C1 bond of the two C-C1 bonds reacts with Ni(0)L-m to afford novel bis(pyrazolyl)nickel(II) complexes with the intact C(3)-C1 bond in moderate yields. Treatment of the bis(pyrazolyl)nickel(II) complexes with H2SO4 gives the new dichloro monomers: 3,3'-dichloro-1,1',4,4'-tetramethyl-5,5' and its 4,4'-bis(methoxycarbonyl) analogue. These undergo dehalogenative polycondensation to give poly(1,1',4,4'-tetramethyl-5,5'-bipyrazole-3,3'-diyl) (6) and its 4,4'-bis(methoxycarbonyl) analogue (7), respectively. Polymer 6 is soluble in formic acid, and gives an intrinsic viscosity of 39 cm(3) g(-1) in formic acid, whereas polymer 7 is soluble in various organic solvents and has an M-n value of 8800 (M-w/M-n = 1.56) as estimated from GPC. They show photoluminescent peaks at the onset position of the respective pi-pi* absorption bands.