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

The doubly-bridged, dinuclear complex [Pt-2(mu-PPh2)(mu-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 [Pt-2{mu-Cu(PPh3)}(mu-PPh2)(mu-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 [Pt-2{mu-AgOC(O)CF3}(mu-PPh2)(mu-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 [Pt-2(mu-H)(mu-PPh2)(Solv)(PPh3)(3)]A(2) (5a, Solv = THF, A = PF6; 5b, Solv = CH2Cl2, A = BF4; 5c, Solv = acetone, A = BF4) which result from rupture of the Pt-C sigma 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 [Pt-2(mu-H)(mu-PPh2)(OPOF2)(PPh3)(3)](PF6).0.5CH(2)Cl(2) (6.0.5CH(2)Cl(2)) establishes that the OPOF2 group is linked by one O atom to platinum, to our knowledge an unprecedented feature.