Reactivity of phosphido-bridged diplatinum complexes towards electrophiles: synthesis of new hydrides and related Pt2Cu and Pt2Ag clusters

Abstract

The doubly-bridged, dinuclear complex [Pt₂(μ-PPh₂)(μ-o-C₆H₄PPh₂)(PPh₃)₂] (1) reacts with electrophiles such as H⁺ or [M(PPh₃)]⁺ (M = Cu, Ag, Au) first at the metal–metal bond. This is supported by an X-ray diffraction study of [Pt₂{μ-Cu(PPh₃)}(μ-PPh₂)(μ-o-C₆H₄PPh₂)(PPh₃)₂]PF₆ (2) which reveals a Pt₂Cu triangular metal core and, unexpectedly, a bonding interaction between the Cu atom and the C_ipso of the orthometalated phenyl. This confers a tetrahedral-like geometry to the Cu atom. In the neutral complex [Pt₂{μ-AgOC(O)CF₃}(μ-PPh₂)(μ-o-C₆H₄PPh₂)(PPh₃)₂] (3), the silver atom is coordinated by the terminally bound trifluorocarboxylate anion. Reactions of 1 in a polar solvent with 2 equiv. of acid HA, where A is a weakly nucleophilic anion, afforded the dicationic solvento adducts [Pt₂(μ-H)(μ-PPh₂)(Solv)(PPh₃)₃]A₂ (5a, Solv = THF, A = PF₆; 5b, Solv = CH₂Cl₂, A = BF₄; 5c, Solv = acetone, A = BF₄) which result from rupture of the Pt–C σ bond and transformation of the cyclometalated bridging ligand into PPh₃. The coordinated solvent molecule is readily displaced by nucleophiles such as PO₂F₂⁻, CF₃SO₃⁻, Cl⁻ or Br⁻, thus forming monocationic complexes, 6–9, respectively. An X-ray diffraction study on [Pt₂(μ-H)(μ-PPh₂)(OPOF₂)(PPh₃)₃](PF₆)·0.5CH₂Cl₂ (6·0.5CH₂Cl₂) establishes that the OPOF₂ group is linked by one O atom to platinum, to our knowledge an unprecedented feature.