Diphosphine ligand substitution in H4Ru4(CO)12: X-ray diffraction structures and reactivity studies of the cluster compounds H4Ru4(CO)10(P–P) [where P–P–(Z)–Ph2PCH–CHPPh2, bpcd

Abstract

The tetraruthenium cluster H4Ru4(CO)12 (1) has been studied for its reactivity with the unsaturated diphosphine ligands (Z)–Ph2PCH–CHPPh2 and 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) under thermal, near-UV photolysis, and Me3NO-assisted activation. All three cluster activation methods promote loss of CO and furnish the anticipated substitution products H4Ru4(CO)10[(Z)–Ph2PCH–CHPPh2] (2) and H4Ru4(CO)10(bpcd) (3) that possess a chelating diphosphine ligand. Clusters 2 and 3 have been characterized in solution by IR and NMR spectroscopies, and these data are discussed with respect to the crystallographically determined structure for both new cluster compounds. The 31P NMR spectral data and the solid-state structures confirm the presence of a chelating diphosphine ligand in clusters 2 and 3. Cluster 2 crystallizes in the monoclinic space P21/c, a=11.768(6) A, b=18.521(9) A, c=20.48(1) A, β=102.291(8)°, V=4361(4) A3, Z=4, and d calc=1.726 Mg/m3; R=0.0225, R w=0.0491 for 6798 reflections with I > 2σ(I). The four bridging hydrides were located in H4Ru4(CO)10[(Z)–Ph2PCH–CHPPh2] and their adopted positions are discussed relative to the solution 1H NMR spectrum. H4Ru4(CO)10(bpcd) crystallizes in the orthorhombic space Pbca, a=19.072(3) A, b=20.169(3) A, c=22.774(3) A, V=8760(2) A3, Z=8, and d calc=1.870 Mg/m3; R=0.0428, R w=0.0896 for 10296 reflections with I > 2σ(I). Sealed NMR tubes containing clusters 2 and 3 were found to be exceeding stable towards near-UV light and temperatures up to ca. 125 °C. The surprisingly robust behavior of 2 and 3 is contrasted with the related cluster Ru3(CO)10(bpcd) that undergoes fragmentation to the donor-acceptor compound Ru2(CO)6(bpcd) and the phosphido-bridged compound Ru2(CO)6(μ–PPh2)[μ–C–C(PPh2)C(O)CH2C(O)] under mild conditions. The electrochemical properties of each substituted cluster have been investigated by cyclic voltammetry, and our findings are discussed with respect to the reported electrochemical data on the parent cluster H4Ru4(CO)12.