Heterotrinuclear Complexes with Palladium, Rhodium, and Iridium Ions Assembled by Conformational Switching of a Tetraphosphine Ligand around a Palladium Center

Abstract

Reaction of [PdCl2(cod)] with a tetraphosphine, meso-bis[((diphenylphosphino)methyl)phenylphosphino]methane (dpmppm), afforded the mononuclear PdII complexes [PdCl(dpmppm-κ3)]X (X = Cl (1a), PF6 (1b)); the pincer-type dpmppm ligand coordinates to the Pd atom with two outer and one inner phosphorus atom to form fused six- and four-membered chelate rings. The remaining inner phosphine is uncoordinated and readily reacts with [Cp*MCl2]2 to give the heterodimetallic complexes [PdCl(Cp*MCl2)(μ-dpmppm-κ3,κ1)]X (X = Cl, M = Rh (21a), Ir (21b); X = PF6, M = Rh (23a), Ir (23b)). Attachment of the second metal fragment to the uncoordinated phosphine caused a crucial conformational change of the six-membered chelate ring from a stable chair conformation to a twist-boat structure, which concomitantly destabilizes the four-membered ring for its opening reactions. Complexes 21 (X = Cl) were converted to [PdCl2(Cp*MCl2)(dpmppm═O)], in which the terminal P atom is dissociated and oxidized as Ph2P(═O)CH2P(Ph)CH2P(Ph)CH2PP...