47-electron organometallic clusters derived by chemical and electrochemical oxidation of trihydrido(alkylidyne)triruthenium and -triosmium clusters. Ligand additivity in metal clusters

摘要

Cyclic voltammograms for H3Ru3(mu(3)-CX)(CO)(9-n)L-n (X = OMe, SEt, Me, Et, Ph, NMeBz, Br; L = PR3, AsPh3, SbPh3; n = 2, 3), H3Ru3(mu(3)-COMe)(CO)(6)(PPh3)(2)(L) (L = P(OMe)(3), CNCH2Ph), and H3Os3(mu 3-COMe)(CO)(7)(PPh3)(2) each display a quasi-reversible to reversible, one-electron oxidation followed by an irreversible to quasi-reversible, one-electron oxidation. The ligand and substituent effects upon the oxidation potential are analyzed as an example of ligand additivity in a cluster system; the oxidation potential of the alkylidyne cluster core is as sensitive to pi-donor substituent effects as are aromatic pi complexes such as CpFe(C5H4X) to substituents on the rings; and the dependence of the oxidation potential of the cluster upon ligand substitution on any given Ru atom is 37% of that expected for the oxidation of a monometallic complex. Reactions with 1 equiv of Ag+ or ferricenium give the 47-electron cations [H3Ru3(CX)(CO)(6)L-3](1+) (X = OMe; L-3 = (PPh3)(2)L'; L' = CO, PPh3, P(OMe)(3), CNCH2Ph; X = Ph, NMeBz, SEt, L = PPh3), characterized by EPR spectroscopy; the equilibrium between isomers H3Ru3(COMe)(CO)(6)(ax-PPh3)(2)(ax-and eq-PPh3)(0/1+) (ax = axial coordination, eq = equatorial coordination) favors the axial coordination for the 48-electron cluster (eq/ax = 0.15) and equatorial coordination for the 47-electron species (eq/ax = 6.4). The rate constant for ax-eq isomerization for the 47-electron species (6.5 s(-1)) is 4 orders of magnitude greater than that for the 48-electron species (2 x 10(-4) s(-1)). The 47-electron clusters have lifetimes which are correlated with the oxidation potentials of the precursors, ranging from seconds to many hours at room temperature. Slow decomposition of [H3Ru3(COMe)(CO)(6)L-3](1+) in the absence of added CO forms the new 46-electron clusters [H3Ru3(CO)(7)L-3](1+) (L = PPh3, AsPh3). [H3Ru3(COMe)(CO)(6)(PPh3)(3)](1+) does not react with CCl4 but does react with Lewis bases such as CO and acetonitrile. Disproportionation occurs with acetonitrile, chloride, and pyridine; the CO products are [HRu3(CO)(9)(PPh3)(3)](1+), [MePPh3](1+),and H3Ru3(COMe)(CO)(9-n)(PPh3)(n) (n = 1, 2). [References: 64]