CO-Induced Reductive Elimination of P(t-Bu)2H from the Platinum(II) Dinuclear Derivative Pt2[μ-P(t-Bu)2]2(H)2[P(t-Bu)2H]2, Affording Mononuclear Platinum(0) or Triangulo Triplatinum(I,I,II) Derivatives

Abstract

Carbon monoxide (1 atm) quantitatively converts the Pt(II) dinuclear derivative Pt2[μ-P(t-Bu)2]2(H)2[P(t-Bu)2H]2 (1) into the new PtI2PtII triangulo cluster Pt3[μ-P(t-Bu)2]3(H)(CO)2 (2). The 44e- species 2 was characterized by IR and multinuclear NMR spectroscopy and by a single-crystal X-ray diffraction study. Complex 2 is formed through the slow CO-induced reductive elimination of P(t-Bu)2H from 1, affording the intermediate mononuclear Pt(0) carbonyl derivative Pt[P(t-Bu)2H]2(CO)2 (4), which equilibrates with the carbonyl-bridged triangulo derivative Pt3[P(t-Bu)2H]3(μ-CO)3 (5); these are the main products under high pressures of CO. Two alternative mechanisms were examined for the subsequent formation of complex 2, the first being the rapid condensation of complex 4 with unreacted 1 while the second assumes 5 as the direct precursor of 2. Although the first mechanism cannot be conclusively rejected, the second seems the most appropriate, since under high pressures of CO/H2 complex 2 was shown to equilibrate with 5. In the presence of an excess of other phosphines, the carbonylation of 1 yields quantitatively the mononuclear monocarbonyl derivatives Pt(PR3)3(CO) (R3 = Ph3, Et3, t-Bu2H).