Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 90. Synthesis of the complexes [W2M2(µ-CO)(µ-CMe)(µ3-CMe)(µ-PPh2)2(CO)3(η-C5H5)2](M = Rh or Ir) and related tetra- and penta-nuclear metal compounds; interconversion of ketenyl and λ5-phospha-alkyne ligands bridging tungsten–rhodium bonds

Abstract

The reaction between [Ir2(µ-PPh2)2(cod)2](cod = cyclo-octa-1,5-diene) and [W(CMe)(CO)2(η-C5H5)] in refluxing thf (tetrahydrofuran) affords the tetranuclear mixed-metal compound [W2Ir2(µ-CO)(µ-CMe)(µ-CMe)(µ-PPh2)2(CO)3(η-C5H5)2]. The pathway by which this complex is formed has been modelled by a series of reactions involving rhodium-tungsten species. Thus [W2Rh2(µ-CO)(µ3-CMe){µ-C(Me)C(O)}(µ-PPh2)2(CO)2(η-C5H5)2] reacts rapidly with CO to yield [W2Rh2(µ-CO)(µ3-CMe){µ-C(Me)C(O)}(µ-PPh2)2(CO)3(η-C5H5)2]. In refluxing thf the latter compound initially isomerises to give [W2Rh2(µ-CO)2(µ3-CMe){µ- C(Me)PPh2}(µ-PPh2)(CO)3(η-C5H5)2], which on further heating loses CO and affords [W2Rh2(µ-CO)(µ-CMe)(µ3-CMe)(µ-PPh2)2(CO)2(η-C5H5)2]. In an extension of these interconversions the pentanuclear metal cluster compound [W3Rh2(µ-CO)3(µ-CMe)(µ3-CMe){µ-C(Me)PPh2}(µ-PPh2)(CO)2(η-C5H5)3] on refluxing in thf for several hours also releases CO to give [W3Rh2(µ-CO)2(µ-CMe)2(µ3-CMe)(µ-PPh2)2(CO)2(η-C5H5)3]. The new compounds were characterised by their 1H, 13C-{1H}, and 31P-{1H} n.m.r. spectra.