Oligomerization of an ansa-ferrocene with pyrazabole bridge

Abstract

Ansa-ferrocenes with pyrazabole bridges are chemically robust entities and therefore suitable building blocks for the synthesis of rigid-rod polymers that combine redox-active Fe(II) centers and beltene-like  faces. The specific monomers we developed bear OEt groups at both tetracoordinated boron atoms (for solubility reasons) and ethynyl substituents at the 4-positions of the two pyrazole rings. Polymerization was accomplished by a condensation reaction with 1,4-diiodobenzene using a Sonogashira-Hagihara-type protocol. Thereby, oligomers with a number-average molecular weight of Mn = 7.6 kDa and dispersity of Ð = 1.55 were obtained, suggesting an average chain length of about 14 repeating units based on gel permeation chromatography (GPC) analysis in THF relative to narrow polystyrene standards. The molecular-weight determination was complemented by MALDI-TOF mass spectrometry and (heteronuclear) NMR spectroscopy to verify the intact pyrazabole monomer repeat units and the nature of the end-groups. The oligomers were further characterized by UV−vis spectroscopy and cyclic voltammetry, which demonstrated the successful synthesis of a new class of redox-active materials.

Synthesis, Structure, and Properties of Monodispersed and Highly Luminescent Organoborane Oligomers

“…Dithienooxadiborepine was chosen because it has high luminous efficiency and is easy to modify, 23a and ACID and NICS calculations have revealed additional stabilization through aromaticity for the dithienodiborepin PAHs. 23b Using Sonogashira coupling 24 and Glaser oxidative coupling reactions carried out under mild conditions, several ethynyl-linked or butadiynyl-linked organoborane oligomers were prepared successfully (Chart 1 and Scheme 1). It was found that the presence of hexyl substituents has a great impact on the structures and properties of the compounds.…”

Poly(ferrocenylene iminoborane): an inorganic–organic hybrid polymer comprising a backbone of moderately interacting ferrocenes

“…6 Several attempts have also been made to incorporate tricoordinate (sp 2 -hybridized) boron atoms into the bridging position of polyferrocenes. 7–10 The synthesis of aminoboranediyl-bridged polyferrocenes, PFB N , was first pursued by Manners and Braunschweig and co-workers via thermal ring-opening polymerization (ROP) of strained 1-amino-1-bora-[1]ferrocenophanes. 7 Recently, Müller and co-workers resumed these studies, resulting in soluble derivatives of this kind by using solubilizing alkyl groups at the ferrocene moieties (R′′).…”