Synthesis and Structural Characterization of a Series of Mono-O-(diphenylphosphinobenzyl)calix[6]arenes with and without tert-Butyl Moieties at the Upper Rim

Synthesis and characterization of a series of mono-O-(diphenylphosphinobenzyl)calix[6]arenes are presented. The two types of calix[6]arene moieties were prepared: 1 (with tert-butyl groups at the upper rim) and 2 (without the tert-butyl groups). With regard to the position of a phosphorus atom, the diphenylphosphino group was introduced onto the ortho, meta, or para positions with the benzyl ether moiety. These phosphines as well as their oxides were fully characterized by elemental analysis, NMR measurements, and HR-ESI-MS. The NMR study indicated that 1 had a cone conformation whereas 2 was very flexible in solution. These phosphines were found to be effective ligands in Rh-catalyzed hydroformylation.