ZWITTERIONIC SPECIES FROM TRIISOPROPYLPHOSPHINE AND 2-CYANOACRYLATES: SYNTHESIS, STRUCTURE AND PROPERTIES

Abstract

Triisopropylphosphine reacts with 2-cyanoacrylates with formation of the P-zwitterionic species 2a and 2b. The reaction of 2b with trimethylsilyltriflate, in the presence of traces of water, leads to the phosphonium triflate 3. 2b is alkylated at the carbon atom with methyl iodide with formation of the phosphonium iodide 4. The initially formed adducts of the zwitterionic species 2a and 2b with tosyl azide and with tosyl isocyanate are thermodynamically unstable. In the first case, the final products of the reaction are tosyl iminotriisopropylphosphine imide 6 and 2-cyanoacrylate polymers. In the second case, the reaction leads to the zwitterionic product 8, and, in the presence of traces of water, to the molecular complexes 9a and 9b. The reaction of the zwitterionic species 2a and 2b with methylisocyanate proceeds in an unusual way, resulting in the formation of the zwitterionic species 12a and 12b, as a result of the insertion of methylisocyanate into the C[sbnd]C bond of the starting zwitterionic adducts. The identity and structure of all the new products were established by elemental analysis, IR spectroscopy, ¹H-, ¹³C-, and ³¹P-NMR spectroscopy, as well as by single-crystal X-ray structure analyses for 2b, 8, 9a and 12b. The structures of 2b, 9a and 12b are closely similar as regards the molecular backbone. In all four structures there is evidence for some delocalisation of negative charge to the C(:O) and CN group.

Key Words:

• Triisopropylphosphine
• 2-cyanoacrylates
• zwitterionic species
• isocyanates
• rearrangement
• X-ray crystal structures