Polymeric ladderanes; structural characterization and their application in synthetic organic chemistry
2014-05-09T12:44:32Z (GMT) by
A range of copper(I) alkynyl ladder polymers have been prepared via a simple single step microwave reaction at 100 °C for 2 minutes, using copper hydroxyacetate (Cu2(OH)3Ac.H2O) as the copper source, all with yields in excess of 80 %. A variety of functional groups were chosen ranging from a simple aromatic phenol ring, substituted aromatic groups, groups with a long carbon chain, and an example of 2 alkynyl units in one chain. The polymeric structure of these materials has been elucidated by powder X-ray diffraction, the results of which confirm that by changing the R groups on the copper ladder chains the structure of the ladder itself is altered to accommodate the variety of sizes and shapes. This was further detailed using a series of methyl substituted phenyl rings as the R group (ortho, meta and para), which were further examined by solid state NMR, and Raman spectroscopy. The raman data confirmed that the copper copper distance in the ladder backbone varied based on the side group present. The NMR results suggest that not only are there variations to copper backbone, but also there are different possible positions for the aromatic group to stack in based on the substitution on the aromatic ring. All data collected indicates the crystallinity of the polymer is strongly affected by the choice of alkyne. The range of ladder polymers has been used to catalyse a series of dipolar cycloaddition reactions of terminal alkynes and organic azides, with the aim to obtain additional mechanistic information on the alkyne-azide click reactions. These reactions were carried out using a simple microwave method requiring an excess of alkyne (1.5 eq) to azide (1 eq), using 10 mol% of the ladder polymer as catalyst for 10 minutes at 100 °C. These conditions were then modified slightly to allow for on water catalysis of the click reactions using copper(I) alkynyl ladder polymers. Triazole products were obtained in excellent yields ranging from approximately 60 -95%. Using similar conditions it was also possible to introduce an iodo group to the triazole product when starting with iodoacetylene rather than a terminal alkyne, with only slightly reduced yields of 50-70%. Flow chemistry was briefly tested and was shown to be a viable option for the synthesis of 1,2,3-traizoles using copper(I) alkynyl ladder polymer catalysts. The support material copper on carbon was investigated for comparison with the copper(I) alkynyl ladder polymers. The support material was found to actually be a composition of copper hydroxynitrate, a layered material capable of forming copper(I) ladder polymers, and carbon. A series of these materials were made using different supports using the same method as carbon, and all resulted in a mixture of copper hydroxynitrate and support material. An impurity was discovered in specific carbon batches (depending on the carbon preparation method) and was identified as libethenite (copper hydroxyphosphate). A series of click reactions were carried out using these copper hydroxynitrate/carbon mixtures and excellent yields of 80-90% were obtained, the impurity libethenite was also tested but found to not catalyse the click reaction.