Chiral teleinduction in the polymerization of isocyanides David B. Amabilino a, * , Elena Ramos a , Jose ´-Luis Serrano b, * , Teresa Sierra b , Jaume Veciana a, * a Institut de Cie `ncia de Materials de Barcelona (CSIC), Campus Universitari de Bellaterra, 08193 Cerdanyola del Valle `s, Catalonia, Spain b Instituto de Ciencia de Materiales de Arago ´n (CSIC), Universidad de Zaragoza, 50009 Zaragoza, Spain Received 5 October 2004; received in revised form 18 November 2004; accepted 18 November 2004 Available online 11 January 2005 Abstract The effect of the length, constitution and conformation of rod-like spacers between an isocyanide group and a chiral substituent on the diastereoselectivity of the polymerization of these monomers has been studied. The chiral induction has been monitored using circular dichroism spectroscopy as well as polarimetry, and the polymers have also been characterized using NMR, gel permeation chromatography, and MALDI-TOF mass spectrometry. Of the different spacers that have been studied, the benzoate moiety is the most efficient in propagating the chiral information from stereogenic center to the polymer backbone. Remarkably, when this moiety is included in a spacer which separates the stereogenic center from the reactive carbon atom in the monomer by 21 A ˚ an appreciable induction of activity is still observed in the resulting polymer. q 2004 Elsevier Ltd. All rights reserved. Keywords: Chirality induction; Circular dichroism; Diastereoselectivity 1. Introduction The mechanisms by which chirality is transmitted over large distances are intriguing and important in a number of research areas [1–9]. Three general types of chiral induction exist: (i) during the formation of covalent bonds in which stereoelectronic and steric effects determine the enantio- or diastereo-selectivity kinetically [10–13]; (ii) in the devel- opment of non-covalent interactions in chiral aggregates wherein non-covalent interactions determine the thermo- dynamically most stable assembly [14–22] and; (iii) processes in which the enantio- or diastereo-selectivity of the formation of covalent bonds is influenced by non- covalent bonds [23–29]. It is in this latter group that non- covalent interactions can lead to a kinetically stable product by chiral induction over a large distance, or chiral teleinduction. When either enantiomer of 1A (Scheme 1), in which a stereogenic center is separated from an isocyanide moiety by a phenyl benzoate spacer, is polymerized a significant diastereoselectivity in the formation of the chiral backbone of the poly(isocyanide) 2A is recorded [30,31]. This chiral induction takes place over a distance of approximately 16 A ˚ through the phenyl benzoate group between the isocyanide moiety and the asymmetrically-substituted carbon atom. Because of this long-range effect, we refer to it as teleinduction. The phenomenon is subject to odd–even effects, as observed by the alternating helicities of the polymer backbone when the stereogenic center is moved sequentially down the aliphatic chain. Unlike other chiral polymers which display equilibria [32–37], the poly(iso- cyanide)s [38–48] of type 2A have atropoisomeric helical conformations generated during their synthesis with the aid of non-covalent interactions and which are kinetically stable with respect to changes in temperature and solvent [31]. They can even be forced to adopt other chiral conformations by kinetic trapping using appropriate co-monomers [49,50]. The observation of diastereoselectvity over such a long monomer 1A raises a number of interesting questions, such as: How does the diastereoselectivity vary with changes in (i) the length of the rod-like spacer; (ii) the rigidity of the spacer and; (iii) the conformation of the rod-like spacer? These questions are fundamental in order to formulate a hypothesis which explains the unusual chiral induction 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.11.113 Polymer 46 (2005) 1507–1521 www.elsevier.com/locate/polymer * Corresponding authors. Tel.: C34 935801853; fax: C34 935805729. E-mail addresses: amabilino@icmab.es (D.B. Amabilino), joseluis@ posta.unizar.es (J.-L. Serrano), vecianaj@ icmab.es (J. Veciana).