STRUCTURE AND REACTIVITY OF THE ZERO-VALENT RUTHENIUM COMPLEX RU(1,2-BIS(DIPHENYLPHOSPHINO)ETHANE)(CO)(3) AND THE DICATIONIC RUTHENIUM DIMER 2(1,2-BIS(DIPHENYLPHOSPHINO)ETHANE)(2)(CO)(6)](2+)

The structure of Ru(dppe)(CO)(3) was characterized by single crystal X -ray diffraction [monoclinic crystal system, space group P2(1)/n, a=12 .2353(2) Angstrom, b=16.0803(3) Angstrom, c=14.2451(3) Angstrom, beta= 111.109(1)degrees, V=2614.62(9) Angstrom(3), Z=4] and found to be inte rmediate between trigonal bipyramidal and square pyramidal. One electr on oxidation of Ru(dppe)(CO)(3) using [(eta(5)-C5H5)(2)Fe][PF6] produc ed [Ru-2(dppe)(2)(CO)(6)][PF6](2). The dicationic complex was fully ch aracterized by solution spectroscopic methods and by single crystal X- ray diffraction [trigonal crystal system, space group P3(1)21, a=20.56 6(2) Angstrom, c=13.871(2) Angstrom, V=5080.7(8) Angstrom(3), Z=3] and found to have a dimeric structure with two octahedral units sharing a common apex via a Ru(I)-Ru(I) single bond. One octahedral unit is rot ated approximately 45 degrees relative to the other, and the chelating phosphine ligand occupies sites cis and trans to the Ru(I)-Ru(I) bond . All of the carbonyl ligands were found to be terminal. The dimer was fluxional in solution and line-shape analysis of the P-31{H-1} and C- 13{H-1} variable-temperature NMR spectra was used to investigate the e xchange mechanism and evaluate the rate constants. The mechanism invol ved an intramolecular, two-site exchange involving pairwise bridging c arbonyls and had activation parameters of 11.8 +/- 0.15 kcal mol(-1) a nd -6.7 +/- 0.6 eu for Delta H double dagger and Delta S double dagger respectively. The dimer exhibited similar thermal and photochemical r eactivity patterns; disproportionation occurred in CH3CN and halogen a tom abstraction occurred in halogenated solvents. (C) 1998 Elsevier Sc ience S.A. All rights reserved.