Dinucleating ligands based on functionalized oxalamides: Lability of Re(I) coordination with the phosphorus pendant arms

Abstract

The reactions of ortho-(thio)phosphorylated anilines with oxalyl chloride smoothly afforded new ditopic pincer ligands with an oxalamide core and phosphorus(V) pendant arms. The thiophosphoryl-functionalized oxalamide readily underwent direct cyclometalation under the action of Re(CO)5Br in the presence of a base, furnishing the expected ditopic Re(I) pincer complex. At the same time, its phosphoryl-containing counterpart, owing to the labile coordination of the PO groups, afforded a complicated mixture of products, which finally resulted in two binuclear complexes with either coordinated or uncoordinated phosphoryl arms. The structures of all the isolated complexes were elucidated using NMR and IR spectroscopy as well as X-ray diffraction analysis, which provided some insight into the mechanism of their formation. The results of the preliminary evaluation of cytotoxic properties of some of the Re(I) complexes are presented.