title: Copper(II) complexes of 3,4,5-trisubstituted pyrazolates: in situ formation of pyrazole rings from different carbon centers.
abstract: The synthesis and characterization of two pyrazolate-bridged dicopper(II) complexes, [Cu(2)(L(1))(2)(H(2)O)(2)](ClO(4))(2) (1, HL(1)=3,5-dipyridyl-4-(2-keto-pyridyl)pyrazole) and [Cu(2)(L(2))(2)(H(2)O)(2)](ClO(4))(2) (2, HL(2)=3,5-dipyridyl-4-benzoylpyrazole), are discussed. These copper(II) complexes are formed from the reactions between pyridine-2-aldehyde, 2-acetylpyridine (for compound 1) or acetophenone (for compound 2), and hydrazine hydrate with copper(II) perchlorate hydrate under ambient conditions. The single-crystal X-ray structure of compound 1·2H(2)O establishes the formation of a pyrazole ring from three different carbon centers through C-C bond-forming reactions, mediated by copper(II) ions. The free pyrazoles (HL(1) and HL(2)) are isolated from their corresponding copper(II) complexes and are characterized by using various analytical and spectroscopic techniques. A mechanism for the pyrazole-ring synthesis that proceeds through C-C bond-forming reactions is proposed and supported by theoretical calculations.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2 A and 2 B Raja S. C. Mullick Road, Jadavpur, Kolkata-700032, India.
authors.forename: Oindrila
authors.initials: O
authors.lastname: Das
authors.forename: Tanmay
authors.initials: T
authors.lastname: Malakar
authors.forename: Arghya
authors.initials: A
authors.lastname: Mandal
authors.forename: Ankan
authors.initials: A
authors.lastname: Paul
authors.forename: Tapan Kanti
authors.initials: TK
authors.lastname: Paine