Polynorbornene-Based Double-Stranded Ladderphanes with Cubane, Cuneane, Tricyclooctadiene, and Cyclooctatetraene Linkers Nai-Hua Yeh, Chih-Wei Chen, Shern-Long Lee, Hung-Jen Wu, Chun-hsien Chen,* and Tien-Yau Luh* Department of Chemistry, National Taiwan University, Taipei, Taiwan 106 * S Supporting Information ABSTRACT: Double-stranded ladderphanes 2, 3, and 5 having cubane, cuneane, and cyclooctatetraene linkers are synthesized by ring-opening metathesis polymerization (ROMP) of the correspond- ing bisnorbornene monomers 10, 11, and 13, respectively. Attempts to polymerize the corresponding tricyclooctadiene-linked bisnorbor- nene 12 are not successful, starting monomer being recovered. Polymer with this tricyclic diene linker 4 is obtained from the rhodium-catalyzed isomerization of 2. The scanning tunneling microscopic (STM) image of 2 shows an ordered pattern on the graphite surface by self-assembly. ■ INTRODUCTION Cubane represents one of the most fascinating molecules not only for its unique structural feature but also for other potential applications. 1 Cubane skeleton, although highly strained, exhibits extraordinary stability under various conditions. Incorporation of cubane moiety into oligomers and polymers has been sporadically explored. 2-6 Thus, [n]cubylcubanes and oligocubyl rods are synthesized from the treatment of diiodocubane or diiodooligocubyl with tert-butyllithium. 1b,2 Polymerization of bishomoallylcubane by cross-metathesis gives the corresponding oligomers with six to seven repeat units. 3 In addition to polyamides 4 and polyacrylates, 5 cubane-containing polynorbornenes are obtained by the ring-opening metathesis polymerization (ROMP) of the corresponding diastereomeric mixture of exo- and endo-norbornene esters. 6 Incorporation of valence isomers of cubane (such as substituted cuneane or tricycle[4.2.0.0 2,5 ]octadiene) other than a cyclooctatetraene derivative 5 into a polymer has not been explored. We recently reported a series of symmetrical 7 and unsym- metrical 8 double-stranded polynorbornene-based ladderphanes 1 having a range of different rigid aromatic or organometallic linkers. 9 Related disulfide-based ladderphanes have recently been disclosed. 10 Like a DNA molecule, the aromatic linkers in these ladderphanes are cofacially aligned, and the correspond- ing single-stranded polynorbornenes can undergo replication generating a daughter polymer. 7-9 Each of the monomeric unit in 1 spans about 5-6 Å. 7-9,11 The smallest possible dimensions of cylindrical 1,4-disubstituted cubane derivatives and related substituted C 8 H 6 -valence isomers such as cuneane, syn- tricycle[4.2.0.0 2,5 ]octadiene, or cyclooctatetraene are no more than 3.8 Å. 12 It is envisaged that a cubane derivative and related valence isomers can fit into this space and, therefore, could be used as linkers for double-stranded ladderphanes. In this paper, we wish to report the synthesis and characterization of a range of double-stranded polybisnorbornenes 2-5 using cubane and its valence isomers as linkers. ■ RESULTS AND DISCUSSION Cubanedicarbinol 6 was synthesized according to literature procedures. 13 Reduction of dimethyl 2,6-cuneanedicarboxylate 7 12c,14 by LAH gave 75% yield of 8. Diol 6 was allowed to react with acid chloride 9b in the presence of Et 3 N to afford the corresponding monomer 10 in 73% yield (Scheme 1). In a similar manner, monomer 11 was prepared. Treatment of 10 with 5 mol % [Rh(NBD)Cl] 2 in CHCl 3 -toluene at rt gave the corresponding tricyclooctadiene derivative 12 in 75% yield. 15 When the reaction was carried at refluxing temperature, cyclooctatetraene-linked bisnorbornene 13 was obtained in 70% yield (Scheme 1). 5,15b ROMP of 10 with 20 mol % of the first generation of the Grubbs catalyst (G-I) gave the corresponding polymer 2 in Received: January 4, 2012 Revised: March 2, 2012 Published: March 13, 2012 Article pubs.acs.org/Macromolecules © 2012 American Chemical Society 2662 dx.doi.org/10.1021/ma300027k | Macromolecules 2012, 45, 2662-2667