CLUSTER CHEMISTRY .71. ISOMERIZATION OF A PENTANUCLEAR RUTHENIUM CLUSTER BY ELIMINATION OF PHENYLPHOSPHINIDENE FROM A TERTIARY PHOSPHINE - X-RAY STRUCTURE OF RU5 (MU-5-C2PH)(MU-4-PPH)(MU-PPH2)(CO)13

Reactions of Ru5(mu-5-C2PPh2)(mu-PPh2)(CO)13 (1) in oxirane gave an isomer of 1, Ru5(mu-5-C2Ph)(mu-4-PPh)(mu-PPh2)(CO)13, which has been formed by formal elimination of PPh from the C2PPh2 ligand in 1 to the cluster, with concomitant cleavage of an Ru-Ru bond. The rhomboidal Ru4 core interacts with a C2Ph ligand to give a trigonal prismatic C2Ru4 arrangement, of which a triangular face is capped by the fifth Ru atom and a square face by the PPh group; the Ru5 skeleton has an envelope conformation. Notable is the short bond (1.965(6) angstrom) from the acetylide C-alpha to the edgebridging Ru atom, indicating some carbenic character for this carbon.