Ligand substitution of the redox-active diphosphine 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the alkynyl-bridged cluster Ru 3(CO) 9( μ2-H)( μ3- ν2-CC tBu). Synthesis, X-ray structure and electrochemical properties of Ru 3(CO) 7( μ2-H)( μ3- ν2-CC tBu) (bpcd)

Abstract

The alkynyl-bridged triruthenium cluster Ru 3(CO) 99 μ 2-H( μ 3- ν 2-C tBu) ( 1) reacts with the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3,-dione (bpcd) in the presence of Me 3NO to afford the new cluster Ru 3(CO) 7( μ 2-H)( μ 3- ν 2-CC tBu)(bpcd) ( 2) in 76% yield. The diphosphine ligand in 2 is bound at the unique ruthenium atom in a chelating fashion, and is the first example of a cluster-coordinated bpcd ligand. Cluster 2 has been characterized in solution by IR and NMR ( 1H and 31P) spectroscopy and in the solid state by X-ray diffraction analysis. Ru 3(CO) 7( μ 3- ν 2-CC tBu)(bpcd), as the CH 2Cl 2 solvate, crystallizes in the monoclinic space group P2 1/c: α = 21.190(1), b = 12.345(1) A ̊ , c = 17.272(1) A ̊ , β = 95.075(5)°, V = 4500.5(5) A ̊ , 3, Z = 4, d calc = 1.667 g cm −3; R = 0.399, R w = 0.0432 for 3255 observed reflections. The redox properties of 2 were explored by cyclic voltammetry, which revealed the presence of a reversible one-electron reduction process (bpcd based) and an irreversible oxidation (metal based). The nature of the HOMO and LUMO in 2 has been examined by carrying out extended Hückel MO calculations on the model cluster Ru 3(CO) 7( μ 2-H)( μ 3- ν 2-CCHH 4-bpcd), and the results are discussed with respect to the observed electrochemistry. The propensity of cluster 2 to undergo P-C bond cleavage is discussed in the light of other diphosphine ligand work.