Synthesis and structural characterization of (CH2)n-bridged indenyl-pyrazoles and their cyclopentadienyl nickel(II) complexes

A new class of (CH2)n-bridged indenyl-pyrazoles [4-{Ind-(CH2)n}-RR′PzH] (Ind = 1H-inden-3-yl, n = 1–3, RR′Pz = 3,5-disubstituted pyrazolato) were synthesized. Reactions of the indenyl-functionalized pyrazoles with nickelocene in refluxing toluene afforded trimetallic and dimetallic cyclopentadienyl nickel(II) complexes, i.e., [CpNi{4-(Ind-(CH2)n)-RR′Pz}2]2Ni and [CpNi{4-(Ind-(CH2)n)-RR′Pz}]2, depending on the steric hindrance from the 3,5-disubstituents on the pyrazolato rings. In the CpNi(II) complexes, pyrazolato ligands exhibit μ-η1:η1 coordination to the metal centers and the indenyl moieties demonstrate no interaction with the metals. All the indenyl-pyrazoles and their complexes were characterized by spectroscopic and analytical methods including X-ray crystallographic study.