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

Abstract

Abstract Reactions of 3,5-dichloropyrazoles and 3,3′-dichloro-5,5′-bipyrazoles with zerovalent nickel complex, Ni(0)Lm, have been studied. In cases of 3,5-dichloro-1,4-dimethylpyrazole and 3,5-dichloro-4-methoxycarbonyl-1-methylpyrazole, only the C(5)–Cl bond of the two C–Cl bonds reacts with Ni(0)Lm to afford novel bis(pyrazolyl)nickel(II) complexes with the intact C(3)–Cl 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′-bipyrazole 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 cm3 g−1 in formic acid, whereas polymer 7 is soluble in various organic solvents and has an Mn value of 8800 (Mw/Mn = 1.56) as estimated from GPC. They show photoluminescent peaks at the onset position of the respective π–π* absorption bands.