Structural studies on substituted pentaruthenium carbido carbonyl clusters

摘要

The structures of [Ru5C(CO)(14)L], where L = P(4-C6H4OMe)(3), 2a, P(4-C6H4F)(3), 2b, and PCy3, 2c, and of [Ru5C(CO)(13)(etpb)(2)] (etpb = P(OCH2)(3)CEt)), 3, have been determined. The Ru-Ru and Ru-P bond distances of the [Ru5C(CO) L-15-n(n)] clusters, 2a, 2b,2c, 3, [Ru5C(CO)(14)(PPh3)], and [Ru5C(CO)(13)(PPh3)(2)], were analyzed and the results are compared with those reported elsewhere for the unsubstituted parent cluster, and for the clusters [Ru-3(CO)(12-n)L-n], n = 1 or 2. The Ru-5 clusters all maintain the square pyramidal arrangement of the parent cluster and the general arrangement of the ligands. The average Ru-Ru distances are remarkably constant but individual Ru-Ru distances vary widely. A clear feature is that the lengths of the Ru-Ru bonds in the basal plane that are cis to the axial Ru-P bonds are longer than any of the other Ru-Ru distances in all the [Ru5C(CO)(15-n)L-n] clusters except 3. The distance lengthens slightly with increasing cone angle of the substituent P-donor ligand but this effect may be at least partly due to crystal packing effects. The Ru-P distances in the Ru-5 and Ru-3 clusters increase significantly with increasing ligand cone angle and net electron donicity. The two effects cannot easily be separated due to the general correlation of the donicity and size of the P-donor ligands and both effects may apply. A distinctive feature of these changes in bond lengths is that they do not depend on whether n = 1 or 2, showing that the substituent effects are localized. The carbido atom out-of-plane distance increases in an approximately linear fashion with the basicity of the P-donor ligand. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 32]