Palladium complexes of a new phosphine-amido-siloxide pincer ligand with variable degrees of protonation

Abstract

This manuscript describes the preparation of a new PN(H)SiO(H) pincer-type ligand that is based on the diarylamine backbone and links together phosphine, amine, and silanol donor sites. Treatment of PN(H)SiO(H) with Pd(acac)2, (COD)PdCl2, or Pd(OAc)2 resulted in the formation of (κ2-PNSiO(H))Pd(acac) (3), (κ2-PN(H)SiO(H))PdCl2 (4), and (κ3-PNSiO(H))PdOAc (5), in which the supporting ligand displays different degrees of coordination and protonation. In complex 5, the PNSiO(H) ligand functions as a tridentate phosphine-amido-silanol pincer ligand, with additional strong hydrogen bonding between the silanol OH and one of the oxygens of the Pd-bound acetate. Complex 5 cleanly exchanged acetate for a triflate upon treatment with Me3SiOTf, yielding (κ3-PNSiO(H))PdOTf (6). Analogous treatment with Me3SiCl did not lead cleanly to the expected (κ3-PNSiO(H))PdCl (7), but instead ultimately to (κ2-PN(H)SiO(SiMe3))PdCl2 (8). The dianionic PNSiO ligand was accessed by reactions of 5 with base in the presence of pyridine or PMe3 to give (κ3-PNSiO)Pd(py) (9) and (κ3-PNSiO)Pd(PMe3) (10), respectively. Solid-state structures of 5 and 9 were established by single-crystal X-ray diffractometry and revealed square-planar geometry about Pd with tridentate coordination of the pincer ligand.