Tripodal polyphosphine ligands as inductors of chelate ring-opening processes in mononuclear palladium(ii) and platinum(ii) compounds. The X-ray crystal structure of two derivatives containing dangling phosphorus

Abstract

The reaction of NP₃ (tris[2-(diphenylphosphino)ethyl]amine and PP₃ (tris[2-(diphenylphosphino)ethyl]phosphine) with the five-coordinate complexes [PdCl(NP₃)]Cl (1) and [MX(PP₃)]X [M = Pd: X = Cl(2), Br(3), I(4); M = Pt: X = Cl(5), Br(6), I(7)], respectively, followed by ³¹P{¹H}NMR when X = Cl, led to the formation of unprecedented four-coordinate halides in a 1 : 2 metal to ligand ratio, [M(AP₃)₂]X₂ [A = N, M = Pd: X = Cl(8); A = P, M = Pd: X = Cl(9), Br(10), I(11); A = P, M = Pt: X = Cl(12), Br(13), I (14)], containing reactive dangling phosphorus. Given the non characterised precursors [M(ONO₂)(PP₃)](NO₃)], the interaction between the heteronuclear species [MAg(NO₃)₃(PP₃)] [M = Pd(15), Pt(16)] and PP₃ was explored. It was found that the addition of 1 equivalent of phosphine afforded [MAg(NO₃)(PP₃)₂](NO₃)₂ [M = Pd(15*), Pt(16*)] containing Ag(I) bound to two dangling phosphorus while the reaction with 2 equivalents led to the complexes [M(PP₃)₂](NO₃)₂ [M = Pd (17), Pt (18)] in coexistence with [Ag₂(μ-PP₃)₂](NO₃)₂. The fate of Ag(I) on the reaction of the mixed metal compounds with excess PP₃ consisted of preventing dissociation, observed in solution for halides, and acting as an assistant for crystallization. Colourless single crystals of 18 and 10, studied by X-ray diffraction, were afforded by reaction of 16 with 4 equivalents of PP₃ and from solutions of 10 in chloroform coexisting with red crystals of 3, respectively. The structures revealed the presence of dications [M(PP₃)₂]²⁺ that show two five-membered chelate rings to M(II) in a square-planar arrangement and four uncoordinated phosphine arms with the counter anions being symmetrically placed at 4.431 (Br⁻) and 13.823 (NO₃⁻) Å from M(II) above and below its coordination, MP₄, plane. Complexes 9 and 12 were shown to undergo an interesting reactivity in solution versus group 11 monocations. The reactions consisted of conversions of the two five-membered chelate rings to M into three (structure I) or two (structure II) fused five-membered chelate rings, formation of species where Pt(II) retained its square-planar environment with the two dangling phosphine arms of each PP₃ bound to Cu(I) or Ag(I) (structure III) and complexes bearing distorted square-planar (P₂MCl₂) and presumably tetrahedral (AuP₄+ P₂AuCl₂) arrangements (structure IV). The processes with Ag(I) salts also gave mixtures of I+III (chloride and nitrate) or II+III (nitrate).