Calix[4]arene based monophosphites, identification of three conformations and their use in the rhodium-catalysed hydroformylation of 1-octene

Eight monodentate phosphites (2-9) based on the calix[4]arene backbone were synthesised following two synthetic routes. Out of six conformations only three were actually formed under the applied reaction conditions. X-Ray ana lysis of two conformers (4 and 5) provided insight into the 3-dimensional s tructure of two of these conformations. The three conformations were charac terised by H-1, C-13 and P-31 NMR spectroscopy. NMR experiments showed that several of the phosphites are flexible showing fluxional behaviour of the molecular backbone in solution, but no interconversion between the differen t conformers was observed. The conformation of the product in the phosphite synthesis is determined at the point where the phosphorus atom is linked t o two hydroxyl groups of the calix[4]arene (phosphorus amidite). Such an in termediate phosphorus amidite (12) was isolated in the synthesis of 4 and 5 . Phosphites 3-6, 8 and 9 were tested in rhodium-catalysed hydroformylation . Differences in rate can be correlated to the conformation of the ligand.