DOI: 10.1021/cg100633w
Nitrate Ion Assisted Argentophilic Interactions as a Template for Solid State [2 þ 2] Photodimerization of Pyridyl Acrylic Acid, Its Methyl Ester, and Acryl Amide
2010, Vol. 10 3315–3320
Ramkinkar Santra and Kumar Biradha* Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India Received May 11, 2010; Revised Manuscript Received July 3, 2010
ABSTRACT: Ag 3 3 3 Ag interactions were shown to template [2 þ 2] photochemical reactions of unsymmetrically substituted olefin molecules, namely 4-pyridyl acrylic acid (1), 4-pyridyl acryl amide (2), and methyl ester of 4-pyridyl acrylic acid (3) in their Ag(I) complexes [Ag(1)2(NO3)] 3 MeOH (4); [Ag(2)2(NO3)] (5); and [Ag(3)2(NO3)] 3 MeOH (6). Nitrate ions were found to bridge these Ag 3 3 3 Ag interactions in two ways: as a discrete dimer in 4 and 5 and as a zigzag 1D-polymer in the case of 6. Irradiation of these complexes in UV/sunlight produced respective head-to-head dimers in nearly 100% yields, as supported by 1H NMR spectroscopy. In the case of 5, the transformation was shown to occur in single crystal to single crystal fashion by determining the crystal structure of partially irradiated materials of 5. Further, we have also found that the irradiation of mechanically grounded samples of AgNO3 with 2 or 3 produces a similar [2 þ 2] reaction, to result in respective head-to-head dimers in good yields. The wealth of knowledge on intermolecular interactions in the solid state is of immense help in engineering solid state reactions,1 in particular [2 þ 2] photodimerization of olefins containing different substitutions.2-4 In this regard, the use of small organic molecules which can clip the two olefins in the required geometry via hydrogen bonds is an elegant and very well explored strategy.3 Further, coordination bonds4 and exotic interactions such as halogen bonding2d were also shown to template these reactions. However, in most cases, the olefin is bis-pyridyl ethylene or containing symmetrical substitution on both ends of the olefin. The reactions of olefins containing unsymmetrical substitutions are rarely studied via template reactions.2g,h The resultant cyclobutane products from such hetero functional olefins (pyridine and some other functionality) have a potential to act as useful multidentate ligands for the construction of MOFs.5 In this communication we would like to report [2þ2] reactions of such unsymmetrical olefins, namely 4-pyridyl acrylic acid (1), 4-pyridyl acryl amide (2), and the methyl ester of 4-pyridyl acrylic acid (3) using Ag 3 3 3 Ag interactions as a template. The crystal structures of silver nitrate complexes of iso-nicotinamide suggested that Ag 3 3 3 Ag interactions could be a better template for the [2 þ 2] reactions in these compounds.6 Ag 3 3 3 Ag interactions, either ligand/anion supported or unsupported, are very well-known in the literature,7-12 but to date only two examples were reported in the literature for their utility in templating of [2 þ 2] photochemical reactions of olefins.10 Silver ions can exert argentophilic interactions even at distances little more than the sum of their van der Wall radii (3.44 A˚), maintaining the angular specificities.11 Thus, even a very weak argentophilic interaction can be expected to bring the double bonds within a reactive distance (
