Facile synthesis of rhodium and iridium complexes bearing a [PEP]-type ligand (E = Ge or Sn) via E–C bond cleavage

Abstract

Rhodium and iridium complexes bearing a tridentate [PEP] type ligand ([PEP] = {o-(Ph₂P)C₆H₄}₂E(Me); E = Ge or Sn) were synthesized through the phosphine exchange reaction accompanied by selective E–C bond cleavage. The ligand precursors {o-(Ph₂P)C₆H₄}₂EMe₂ (E = Ge or Sn) were readily obtained in excellent yields by treating {o-(Ph₂P)C₆H₄}₂Li with 0.5 equivalents of Me₂ECl₂. Tris(triphenylphosphine)rhodium(I) carbonyl hydride M(H)(CO)(PPh₃)₃ (M = Rh, Ir) cleaved one of the E–Me bonds of {o-(Ph₂P)C₆H₄}₂EMe₂ exclusively to afford the trigonal bipyramidal (TBP) complexes, [PEP]M(CO)(PPh₃). Square-planar rhodium complexes [PEP]Rh(PPh₃) were also prepared from the reactions of tetrakis(triphenylphosphine)rhodium(I) hydride Rh(H)(PPh₃)₄ with {o-(Ph₂P)C₆H₄}₂EMe₂. Further, the trans influence of group 14 elements E (E = Si, Ge, Sn) in [PEP]Rh(PPh₃) is discussed in terms of the ¹J_Rh–P coupling constants, indicating that E exhibited a stronger trans labilizing effect in the order Sn < Ge < Si.