TRICYCLOHEXYLPHOSPHINE-SUBSTITUTED VERSUS TRIPHENYLPHOSPHINE-SUBSTITUTED DERIVATIVES OF A FACE-BRIDGED TRIRUTHENIUM CARBONYL CLUSTER COMPLEX - A COMPARATIVE-STUDY OF THEIR SYNTHESIS, STRUCTURE, AND CATALYTIC ACTIVITY IN THE HOMOGENEOUS HYDROGENATION OF DIPHENYLACETYLENE

The face-bridged cluster complexes [Ru-3(mu-H)(mu 3-ampy)(CO)9] (1) an d [Ru-3(mu-H)(2)(mu(3)-ampy)(CO9)][BF4] (2) (Hampy = 2-amino-6-methylp yridine) react with tricyclohexylphosphine (PCy(3)) to give the respec tive monosubstituted derivatives [Ru-3(mu-H)(mu(3)-ampy)(CO)(8)(PCy(3) )] (3a) and [Ru-3(mu-H)(2)(mu(3)-ampy)(CO)(8)(PCy(3))][BF4] (4a). Prot onation of 3a with HBF4.OEt(2) affords 5a (an isomer of 4a); this comp lex can also be prepared by stirring 4a in THF at reflux temperature. Complex 3a is a catalytic precursor for the homogeneous hydrogenation of diphenylacetylene (80 degrees C, P(H-2) < 1 atm), but the reaction is very slow. The alkenyl-bridged compounds [Ru-3(mu(3)-ampy)(mu-PhC=C HPh)(CO)(7)(PCy(3))] (6a) and (mu-H)(2)(mu(3)-ampy)(mu-PhC=CHPh)(CO)(6 )(PCy(3))] (7a), which are intermediates in the catalytic hydrogenatio n reaction, have been prepared by the sequential reactions of complex 3a with diphenylacetylene and hydrogen. Ah compounds have been charact erized spectroscopically (IR, NMR). The structure of complex 6a has be en determined by X-ray diffraction methods: C45H51N2O7PRu3, triclinic, space group P $($) over bar$$ 1, a = 11.568(7) Angstrom, b = 11.684(2 ) Angstrom, c = 18.958(11) Angstrom, alpha = 81.34(3)degrees, beta = 7 5.84(6)degrees, gamma = 63.92(3)degrees, Z = 2. All results obtained a re compared to those previously determined for related cluster compoun ds containing PPh(3) instead of PCy(3).