Coordination chemistry and X-ray studies with novel sterically constrained diphosphonite ligands

The coordination of two novel, sterically constrained diphosphonite ligands towards different palladium, platinum and rhodium precursors has been studied. Complexes of this hitherto unexplored class of diphosphonites, based on rigid xanthene backbones, have been characterized by X-ray crystallography as well as by NMR and IR spectroscopy. A short and concise overview is given on the scarce literature on phosphonite related chemistry. Structural differences in the complexes obtained due to steric influences of the ligands are discussed. Ligand 1, bearing 2-tert-butylphenolate groups, led to orthometallated complexes cis-[MCl{1-κ3C,P,P}] (M = Pd, Pt) and to trans-[RhCl(CO)(1)]. These complexes were compared with those formed with ligand 2, bearing 2,2′-dioxo-3,3′-di-tert-butyl-5,5′-dimethoxy-1,1′-biphenyl groups, preventing orthometallation. The complexes trans-{PdCl2(2)], cis-[PtCl2(2)] and trans-[RhCl(CO)(2)] were structurally characterized. Valuable data were collected on chemical shifts, Pt–P coupling constants, as well as CO stretch frequencies of Rh–CO complexes as important tools for structural characterization of such complexes.