Di- and trinuclear complexes of palladium with a triphosphine ligand, bis(diphenylphosphinomethyl)phenylphosphine

Abstract

Reaction of [Pd 2(RNC) 6](PF 6) 2 with dpmp (2 equiv.) generated dipalladium complexes, [Pd 2(dpmp) 2(RNC) 2](PF 6) 2 ( 1), in good yields, where R = 2,6-xylyl (Xyl) and 2,4,6-mesityl (Mes), Complex 1a (R = Xyl) was characterized by X-ray crystallography to have a metal-metal bonded dinuclear structure (Pd−Pd = 2.607(2) Å) without bridging ligand. The dpmp ligand chelates to the metal through only the terminal phosphorus atoms. Complex 1a in acetonitrile easily lost one isocyanide ligand and was transformed into a dpmp-bridged dipalladium complex, anti-[Pd 2(μ-dpmp) 2(XylNC)] (PF 6) 2 · CH 3CN (( 2a)CH 3CN). The dinuclear core of 2a consists of a three- and a four-coordinate Pd atom bridged by two dpmp ligands (Pd−Pd = 2.702(1) Å). Complex la was restored by treatment of 2a with an excess of XylNC. When compound 1 was treated with zero-valent palladium complex [Pd 3(RNC) 6], A-frame trinuclear complex, A-frame-[Pd 3(μ-dpmp) 2(RNC) 2](PF 6) 2 ( 4), was obtained. The trimer 4 was also prepared by the reaction of [Pd 3(RNC) 8](PF 6) 2 with dpmp (2 equiv.) via a linear dpmp-bridged trimer, linear-[Pd 3(μ-dpmp) 2(RNC) 2](PF 6) 2 ( 3). Complex 4a (R = Xyl) was analyzed by X-ray crystallography to be a trinuclear A-frame structure joined by two Pd−Pd σ-bonds (Pd−Pd = 2.592(2) Å, Pd−Pd−Pd = 79.19(8)°). The two dpmp ligands doubly bridge between the three metal atoms. Whereas, complex 4 was thermally and chemically stable, complex 3a (R = Xyl) reacted with I 2 to lead to a trinuclear Pd(II) complex, [{PdI 2(dpmp) 2)2PdI 2] ( 5), which was characterized by an X-ray analysis. The two cis-PdI 2(dpmp) units were joined by trans-PdI 2 fragment without metal-metal bonds.