Chapter 2 - Siloles: Part 2: Silaindenes (Benzosiloles) and Silafluorenes (Dibenzosiloles): Synthesis, Characterization, and Applications

Abstract

Abstract The preparation of benzannulated siloles including silaindenes (benzosiloles) and silafluorenes (dibenzosiloles) reported during the period 1996 through 2010 is reviewed. As is the case for nonannulated siloles, tolan and related systems were the precursors of choice in the traditional route to silaindenes, through formation of a dilithio reagent. More recently, transition metal-catalyzed reactions of various silyl-substituted dienes and ene-ynes have been introduced as is also the case for condensation of 2-silylphenylboronic acid with alkynes. Formation of ladder oligomers and polymers with ladder segments related to silaindene is included. The traditional route to silafluorenes involved starting with o , o ′-dibromobiphenyl followed by formation of the dilithio reagent and then quenching with chlorosilanes. Several extensions of this approach have been made through development of new biphenyl precursors with multiple halogen substituents that then have produced substituents at the benzo-positions of the silafluorene that are useful for further chemical elaboration of the basic core. The traditional route through dilithio reagents has been supplemented by new transition metal-catalyzed processes involving a variety of precursors in addition to a Friedel–Crafts route to silafluorenes. Reactions at both the silicon center and involving C–X substituents on the carbon framework are summarized. Compounds related to silafluorenes such as silicon-bridged benzene-heteroarenes and silicon-bridged bithiophenes that exhibit a commonality in the synthetic methods to silafluorenes are discussed. Silafluorenes and dithienosiloles have played a role in the formation of oligomers as well as homopolymers and copolymers. Silafluorenes and dithienosiloles have been employed in electronic devices particularly in photovoltaic cells, white light-emitting diodes and bulk heterojunction solar cells and field effect transistors. The characterization methods reported for monomers and polymers are tabulated as well as applications in device construction when reported.