Three-component 1D and 2D metal phosphonates: structural variability, topological analysis and catalytic hydrocarboxylation of alkanes

Herein, we report the use of diphosphonate building blocks and chelating auxiliary N, N-ligands to generate novel polymeric architectures. Specifically, we report new 1D and 2D coordination polymers incorporating three components: transition metal ions (Co2+, Cu2+, Mn2+ or Zn2+), diphosphonate ligands (methanediphosphonate, MDPA, or 1,2-ethanediphosphonate, EDPA) and N, N-heterocyclic chelators (1,10phenanthroline, phen, or 2,2'-bipyridine, bpy). Six compounds were isolated under mild synthesis (ambient temperature) conditions: [Cu-2(phen)(2)(EDPA)(2)(H2O)(4)](infinity) (1), [Co(phen)(EDPA)(H2O)(2)]infinity (1a), {[Cu(phen)(MDPA)]center dot H2O]}(infinity) (2), [Mn(bpy)(EDPA)(H2O)(2)](infinity) (3), [Zn(bpy)(EDPA)]infinity N (4), and, lastly, a discrete Ni2+ molecular derivative [Ni(phen)(H2O)(4)](EDPA) (5). Synthetic details, crystal structures, and intermolecular interactions (p-p stacking and hydrogen bonding) in 1-5 are discussed. Topological analyses and classification of the underlying metal-organic networks in 1-4 were performed, revealing the uninodal 1D chains with the 2C1 topology in 1-3 and the binodal 2D layers with the 3,4L13 topology in 4. In 1-3 and 5, multiple hydrogen bonds lead to the extension of the structures to give 3D H-bonded nets with the seh-4,6-C2/c topology in 1 and 3, 2D H-bonded layers with the 3,5L52 topology in 2, and a 3D H-bonded net with the 6,6T1 topology in 5. The catalytic activity of compounds 1 and 1a was evaluated in a single-step hydrocarboxylation of cyclic and linear C-5-C-8 alkanes to furnish the carboxylic acids with one more carbon atom. These reactions proceed in the presence of CO, K2S2O8, and H2O at 60 degrees C in MeCN/H2O medium. Compound 1 showed higher activity than 1a and was studied in detail. Substrate scope was investigated, revealing that cyclohexane and n-pentane are the most reactive among the cyclic and linear C-5-C-8 alkanes, and resulting in the total yields of carboxylic acids (based on substrate) of up to 43 and 36%, respectively. In the case of cycloalkane substrates, only one cycloalkanecarboxylic acid is produced, whereas a series of isomeric monocarboxylic acids is generated when using linear alkanes; an increased regioselectivity at the C(2) position of the hydrocarbon chain was also observed.