New bisphosphinites from pamoic acid

Reaction of PhPCl2 with pamoic acid in a 2:1 molar ratio gives a bisphosphinite 5 as a conformational mixture of 5a and 5b which show different solubility in THF and Et2O. The less soluble biaxial conformer 5a was isolated spectrally pure, while it is very difficult to get pure biequatorial 5b without contamination of 5a. Oxidation of 5a with hydrogen peroxide/elemental sulfur or selenium gave the corresponding chalcogenides. The conformational features of the compounds were revealed by X-ray crystallography. In addition, two examples of complexes of 5a were prepared, the chelate complex [PtCl2{(5a)-P, P'}] and the bis-rhodium bridging complex from [RhCl2Cp*](2) dimer.