Cl HO X OH + 1 2 X = direct bond 3 X = CMe 2 O X O Cl Cl O X O O O 4, 5 2 O X O O O 6, 7 hn 8, 9 Fe + Fe + Fe + Fe + Fe + Cl Synthesis and structural characterization of cyclic aryl ethers Alaa S. Abd-El-Aziz,* a Christine R. de Denus, a Michael J. Zaworotko b and C. V. Krishnamohan Sharma b a Department of Chemistry, University of Winnipeg, Winnipeg, Manitoba, Canada, R3B 2E9 b Department of Chemistry, Saint Mary’s University, Halifax, Nova Scotia, Canada, B3H 3C3 The facile preparation of macrocyclic ethers is achieved using S N Ar reactions of (dichlorobenzene)CpFe + complexes with various dinucleophiles, followed by photolytic deme- tallation; X-ray crystallography gives unequivocal structural proof for one of these macrocycles. Cyclic polyethers are important synthetic targets owing to their selective complexation and chiral recognition. 1–3 Interest in these materials originates from the size and nature of their cavity, which dictates whether or not such materials are capable of binding with other compounds. 2 Although a great deal of attention has been directed toward the encapsulation abilities of supramolecules, there is a growing interest in the synthesis of cyclic aryl ethers. 3–5 These compounds are appealing since the rigidity and stability of their structures greatly reduces con- formational freedom which may allow chiral recognition or catalysis at high temperature or in hostile environments. 4a Mullins et al. reported that cyclic aryl ethers may be subjected to ring-opening polymerization to produce linear polyethers without the release of side-products. 4b Here, we report the synthesis of four new cyclic aryl ethers, and the crystal structure of 8 utilizing temporary complexation to the cyclopentadienyl- iron (CpFe + ) moiety. The molecular design and controlled synthesis of aromatic polyethers with pendant CpFe + moieties has been a focus of our recent research. The complexation of chloroarenes to the CpFe + moiety has allowed nucleophilic aromatic substitution (S N Ar) reactions to take place with a large number of dinucleophiles. 6 This methodology has enabled us to prepare a number of oligomeric ethers, thioethers and amines under very mild experimental conditions. Owing to the paucity of existing methods for the preparation of cyclic aryl ethers, we have been exploring new routes for the synthesis of such materials. A drawback of the existing methods is the need for electron withdrawing substitutents on the haloarene ring to promote the substitution reactions. 5 The ease of complexation and decom- plexation of the CpFe + to the arene systems shows the advantages of our methodology. The stepwise displacement of both chloro groups in [(h 6 -1,2-dichlorobenzene)(h 5 -cyclo- pentadienyl)]iron(ii) hexafluorophosphate 10 or [(h 6 -1,3-dichlorobenzene)(h 5 -cyclopentadienyl]iron(ii)hexa- fluorophosphate 1 with a variety of dinucleophiles has allowed for the facile preparation of macrocycles 8, 9, 17, and 18. To our knowledge there are few reports which outline the preparation of macrocyclic materials using S N Ar reactions of substituted chlorobenzenes activated by temporary complexation to a metal moiety. 7 The preparation of dibenzo crown ethers was achieved via the S N Ar reactions of (o-dichlorobenzene)- Cr(CO) 3 with diethylene glycol and bis(2-mercaptoethyl) ether. 7a A disadvantage of this particular synthetic method is the implementation of harsh reaction conditions in order to obtain the desired products in rather modest yields. Scheme 1 outlines the reaction sequence employed for the preparation of cyclic aryl ethers 8 and 9. The initial reaction of complex 1 and dinucleophile 2 or 3 in a 2 : 1 molar ratio was carried out in order to obtain the bimetallic complex (4 or 5) in high yield. The reaction of 4 or 5 with 2 in an equimolar ratio led to the formation of complexed cyclic aryl ethers 6 and 7 in yields of 86 and 89%, respectively. The rigid nature of these complexed macrocycles introduces both cis- and trans-orienta- tions of the CpFe + moieties attached to the arene ring. 8 The presence of two different cyclopentadienyl (Cp) resonances as well as a complex aromatic region in the 1 H NMR spectra indicated that there was a mixture of both cis and trans products present. Based on the integration of the respective Cp resonances, it was determined that for complex 6 the ratio was 3 : 1 while it was 1 : 1 for complex 7. The major structure was predicted to be trans based on previous findings. 8 Photolytic demetallation was implemented to allow for the recovery of the free organic macrocycles 8 or 9 in yields of 64 and 58%, respectively, which may be attributed to the poor solubility of these macrocyclic materials in most organic Scheme 1 Chem. Commun., 1998 265 Published on 01 January 1998. Downloaded on 13/08/2013 19:20:04. View Article Online / Journal Homepage / Table of Contents for this issue