Pd(II) and Pt(II) complexes with mixed phosphorus-oxygen donor ligands

Article abstract of DOI:10.1016/S0277-5387(97)00483-X

A series of new complexes have been synthesized from reactions of [M(NCCH₃)₄][BF₄]₂ (M = Pd, Pt) with the mixed donor ligand tris(2,4,6-trimethoxyphenyl) phosphine (TMPP). Reaction of [Pd(NCCH₃)₄][BF₄]₂ with two equivalents of TMPP in acetone produces the ether-phosphine complex [Pd(TMPP)₂][BF₄]₂, 1. In this molecule the Pd atom is situated at the center of a pseudo-octahedron, with the phosphorus atoms in a cis orientation. The complex was also characterized by infrared, electronic, and NMR spectroscopies as well as by cyclic voltammetry. Reaction of [Pd(NCCH₃)₄][BF₄]₂ with four equivalents of TMPP in acetone yields the neutral phosphino-phenoxide compound Pd(TMPP-O)₂, 2, where TMPP-O is the demethylated form of TMPP. ¹H and ³¹P{¹H} NMR studies of 2 support the assignment of a solution structure that involves free rotation of the uncoordinated phenyl rings of the TMPP ligands. Reaction of [Pt(NCCH₃)₄][BF₄]₂ with two equivalents of TMPP in acetonitrile yields [PT(NCCH₃)₂(TMPP)₂][BF₄] ₂, 3. Structural and spectroscopic data for 3 indicate that free rotation of the arene rings in solution is restricted due to steric influences of the two CH₃CN co-ligands. Reaction of PtCl₂(NCCH₃)₂ with two equivalents of TMPP in acetone or reaction of [Pt(NCCH₃)₄][BF₄]₂ with four equivalents of TMPP in acetone gives Pt(TMPP-O)₂, 4. Reaction of PtCl₂(NCCH₃)₂ with two equivalents of TMPP in tetrahydrofuran yields the neutral compound PtCl(TMPP)(TMPP-O), 5. Although suitable single crystals were not obtained, the structure of compound 5 was deduced from infrared and NMR spectroscopies to be a square planar molecule with one neutral TMPP ligand coordinated in an η¹ fashion and a demethylated TMPP group bound as an η²-P,O ligand where the phosphorus atoms are trans and the other two coordination sites are occupied by a phenoxide oxygen and a Cl atom.