Cleavage and reassembly of trinuclear palladium clusters in reactions with an isocyanide ligand

Abstract

Reaction of the trinuclear cluster cation [Pd₃(µ₃-CO)(µ-dppm)₃]²⁺[dppm = bis(diphenylphosphino)-methane] with excess xylyl isocyanide, 2,6-Me₂C₆H₃NC, led to cleavage giving the binuclear palladium(I) complex cation [Pd₂(CNC₆H₃Me₂-2,6)₂(µ-dppm)₂]²⁺, and unidentified palladium(0) species. The 2,6-Me₂C₆H₃NC ligands in [Pd₂(CNC₆H₃Me₂-2,6)₂(µ-dppm)₂]²⁺ undergo rapid exchange with excess 2,6-Me₂C₆H₃NC and, at low temperature, an adduct is formed and identified spectroscopically as [Pd₂(CNC₆H₃Me₂-2,6)₂(µ-CNC₆H₃Me₂-2,6)(µ-dppm)₂]²⁺. A dppm ligand of [Pd₂(CNC₆H₃Me₂-2,6)₂(µ-dppm)₂]²⁺ is deprotonated and oxidized in the presence of an excess of dppm and oxygen to give [Pd₂(CNC₆H₃Me₂-2,6)₂{µ-Ph₂PCHPPh₂(O)-C,P}(µ-dppm)]⁺, which has been characterized by a structure determination {crystal data for the [PF₆]^–·Me₂CO salt: triclinic, space group P, a= 14.523(2), b= 22.448(4), c= 12.203(3)Å, α= 95.52(2), β= 110.98(2), γ= 108.21(1)°, Z= 2, R= 0.0563, R′= 0.0574}. Complex [Pd₂(CNC₆H₃Me₂-2,6)₂(µ-dppm)₂]²⁺ can react with the palladium(0) species, which is formed in the initial cluster cleavage reaction, by formal addition of Pd(CNC₆H₃Me₂-2,6)₂ to give the trinuclear A-frame cluster complex [Pd₂(CNC₆H₃Me₂-2,6)₂{µ-Pd(CNC₆H₃Me₂-2,6)₂}(µ-dppm)₂]²⁺, thus completing the fragmentation and reassembly of trinuclear clusters. This complex has been characterized by a structure determination {crystal data for the 2[PF₆]^–·0.5Me₂CO salt: orthorhombic, space group P2₁2₁2₁, a= 21.810(3), b= 21.879(4), c= 18.274(5)Å, Z= 4, R= 0.0566, R′= 0.0632}; in solution, it slowly loses Pd(CNC₆H₃Me₂-2,6)₂ to reform [Pd₂(CNC₆H₃Me₂-2,6)₂(µ-dppm)₂]²⁺