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

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 Cipso 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.