Tuneable reactivity with PPh3 and SnX2 of four- and five-coordinate Pd(ii) and Pt(ii) complexes containing polyphosphines

Abstract

The reactivity of the unusual d⁸ trigonal-bipyramidal systems [MX(PP₃)]X (X = Cl: M = Pd(1a), Pt(2a); X = Br: M = Pd(3a), Pt(4a); X = I: M = Pd(5a), Pt(6a); PP₃ = tris[2-(diphenylphosphino)ethyl]phosphine) in CHCl₃–CH₃OH, the square-pyramidal compounds [MCl(NP₃)]Cl (M = Pd(7a); Pt(8a); NP₃ = tris[2-(diphenylphosphino)ethyl]amine) in CD₃OD–DMF and the distorted square-planar mononuclear [MX(PNP)]X (M = Pd: X = Cl(10a); M = Pt: X = I(10b); PNP = bis[2-(diphenylphosphino)ethyl]amine) and the heteronuclear [PdAu₂X₄(PP₃)] [X = I(9a), Cl(14a), Br(15a)] and [MAuX₂(PP₃)]X [M = Pd: X = Cl(16a); M = Pt: X = Cl(17a), Br(18a)] species in CDCl₃ with PPh₃ + SnX₂ has been explored to establish the factors that influence the nature of the products. With the mononuclear precursors the course of the reaction is strongly dependent on the tripodal or linear arrangement of the polydentate ligand and in the former case on the halogen. Thus, while for chlorides (1a–2a, 7a–8a) and bromides (3a–4a) the reaction led to the trigonal-bipyramidal compounds [M(SnCl₃)(AP₃)][SnCl₃] [A = P: M = Pd(1), Pt(2); A = N: M = Pd(7), Pt(8)], [MBr(PP₃)][SnBr₃] [M = Pd(4), Pt(6)] containing M–Sn and M–Br bonds, respectively, for iodides (5a–6a) resulted in the unknown neutral square-planar compounds [MI₂(PP(PO)₂)(SnI₂)₂] [M = Pd(9) and Pt(10)] bearing two dangling PO–SnI₂ units and P₂MI₂ environments. However, complexes of the type [PtCl(PP₂PO)X]X′ [X = SnCl₂, X′ = [SnCl₃]⁻(11)] and [M(PP(PO)₂)₂X₄]X′₂ [X = SnCl₂, X′ = [SnCl₃]⁻: M = Pd(12), Pt(13)] showing PO–SnCl₂ arms were obtained by direct reaction of [PtCl(PP₂PO)]Cl (11a) and [M(PP(PO)₂)₂]Cl₂ [M = Pd(12a), Pt(13a)] with SnCl₂ in CH₃OH. Although complex 9 was also prepared by interaction of the heteronuclear iodide 9a with PPh₃ + SnI₂ in CDCl₃, the use of the neutral and ionic heteronuclear chlorides and bromides (14a–18a) as starting materials afforded the distorted square-planar ionic systems [MAuX′(PP₃)(PPh₃)][SnX₃]₂ [M = Pd: X = Cl, X′ = SnCl₃⁻(14); X = Br, X′ = SnBr₃⁻(15); M = Pt: X = Cl, X′ = SnCl₃⁻(17); X = Br, X′ = SnBr₃⁻(18)] containing M–SnX₃ and P–Au–PPh₃ functionalities. It was found that these reactions where the heteronuclear species are the precursors proceed via the trigonal-bipyramidal halides not only with X = Cl and Br(1a–4a) but also I(5a). When the precursors were 10a and 10b the reaction occurred with formation of [Pd(PNP)(PPh₃)][SnCl₃]₂ (23) and [Pt(PNP)(PPh₃)][SnCl₂I]₂ (24) showing M–PPh₃ units and trihalostannato counter anions.