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Pure Appl. Chem., 2010, Vol. 82, No. 4, pp. 891-904

Published online 2010-03-13

Toward carbyne: Synthesis and stability of really long polyynes

Rik R. Tykwinski1,2*, Wesley Chalifoux1, Sara Eisler3, Andrea Lucotti4, Matteo Tommasini4, Daniele Fazzi5, Mirella Del Zoppo4 and Giuseppe Zerbi4

1 Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
2 Institute for Organic Chemistry, Friedrich-Alexander-University, Erlangen‑Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany
3 Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada
4 Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy
5 Center for NanoScience and Technology CNST IIT@PoliMi, via Pascoli 70/3, 20133 Milan, Italy

Abstract: Molecules composed of sp-hybridized carbon chains (polyynes) are the simplest of the known conjugated organic oligomers. In comparison to their counterparts such as polyacetylene and polydiacetylene, however, the formation of polyynes has traditionally posed a difficult synthetic challenge. In particular, there is no reliable method to form end-capped polyethynylene, and monodisperse polyynes have therefore been assembled. As a result, structure–property relationships for shorter polyynes have been relatively well established in recent years, while extension of these trends toward longer polyynes has remained a difficult task. Using the Fritsch–Buttenberg–Wiechell (FBW) rearrangement, the formation of diynes through decaynes has become possible and has provided a unique chance to explore the physical characteristics of conjugated polyyne chains. This paper highlights recent advances in the synthesis of extended polyynes, as well as interesting aspects of their NMR, Raman, and UV/vis spectroscopic analyses. These synthetic achievements offer the opportunity to predict some of the properties of the carbon allotrope carbyne. In particular, a set of X-ray crystallographic analyses of t-Bu end-capped polyynes (tBu[n]) shows a definitive experimental trend in reduced bond-length alternation (BLA).