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)PdCl 2 , or Pd(OAc) 2 resulted in the formation of (κ 2 -PNSiO(H))Pd(acac) ( 3 ), (κ 2 -PN(H)SiO(H))PdCl 2 ( 4 ), and (κ 3 -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 Me 3 SiOTf, yielding (κ 3 -PNSiO(H))PdOTf ( 6 ). Analogous treatment with Me 3 SiCl did not lead cleanly to the expected (κ 3 -PNSiO(H))PdCl ( 7 ), but instead ultimately to (κ 2 -PN(H)SiO(SiMe 3 ))PdCl 2 ( 8 ). The dianionic PNSiO ligand was accessed by reactions of 5 with base in the presence of pyridine or PMe 3 to give (κ 3 -PNSiO)Pd(py) ( 9 ) and (κ 3 -PNSiO)Pd(PMe 3 ) ( 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.