Design, synthesis, and structural aspects of chalcogen-substituted pyridine dicarboxamide donors and their reactions Naveen Kumar, a Marilyn Daisy Milton, a Jai Deo Singh, a, * Shailesh Upreti a and Raymond J. Butcher b a Department of Chemistry, Indian Institute of Technology Delhi (IITD), Hauz Khas, New Delhi 110 016, India b Department of Chemistry, Howard University, Washington, DC 20059, USA Received 13 September 2005; revised 19 November 2005; accepted 1 December 2005 Available online 20 December 2005 Respectfully dedicated in honor of Professor Bal Krishan Puri on the occasion of his superannuation and 62nd birthday Abstract—The design and synthesis of a new family of potentially pentadentate N 3 Se 2 or N 3 Te 2 type donors bearing a 2,6-disub- stituted pyridine dicarboxamide moiety as the central fragment [–NH–C(@O)–pyridine–C(@O)–NH–] functionalized with chalcogen as additional donors in the appended arms of the pyridine ring through the alkyl spacers and their potential applications and reac- tivity toward d 8 and d 10 metal ions have been demonstrated. Ó 2005 Elsevier Ltd. All rights reserved. The design, synthesis, and study of organic host mole- cules that can accommodate cationic, neutral, or anionic guests is a thriving field of research 1–5 with increasing emphasis on the use of a combination of dynamic coor- dination chemistry and hydrogen bonding to allow more efficient syntheses of host molecules through self-assem- bly. 6,7 Intimately, organic carboxamides have proved to be spectacular ligands in self-assembly processes through hydrogen bonding and have also shown rele- vance to biological systems. 8 It has been established that the protonated forms of these species prefer the syn–syn conformation because of electrostatic interactions between the amide (NH) protons and the pyridine nitrogen. The presence of ÔexoÕ amide carbonyl oxygen (C@O) atoms that can act as hydrogen bond acceptors, present two favorable N–HÁÁÁN and C–HÁÁÁO electrostatic interactions (Chart 1a and b). 9 Consequently, the known patterns of hydro- gen bonding of the amide functionality make the systems useful building blocks for supramolecular architectures. For example, oligoamides have been designed such that can fold to give single or double heli- ces as well as other supramolecular assemblies. 8 In addi- tion, amide-linked catenanes, rotaxanes, and knots have been prepared by template synthesis. 10 Cyclic peptides N N O O H H N NH HN O O H H N N O O H H M N NH HN O O H H M 2+ (a) (b) (c) (d) X = het Chart 1. eroatom donors; such as N, P, O, or S; ( ) = alkyl or aryl spacers X X X X X ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) X X X N N 0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2005.12.004 Keywords:d 8 and d 10 metal ions; Dicarboxamide linkage; N 3 Se 2 /N 3 Te 2 donors; Pd(II) complex. * Corresponding author. Tel.: +91 11 26596455/26591512; fax: +91 11 26862037; e-mail: jaideo@chemistry.iitd.ernet.in Tetrahedron Letters 47 (2006) 885–889 Tetrahedron Letters