HIGH-NUCLEARITY RUTHENIUM CARBONYL CLUSTER CHEMISTRY - VII - SYNTHESIS, NMR-STUDIES, ELECTROCHEMISTRY AND X-RAY CRYSTAL-STRUCTURE OF [PPN] [RU-8(MU(8)-P)(CO)(22)](2)

The reaction between [Ru-3(mu-H)(mu-NC5H4)(CO)(10)] and chloridiphenyl phosphine in refluxing chlorobenzene, followed by metathesis with bis( triphenylphosphoranylidene)ammonium chloride ([PPN]Cl), affords [PPN][ Ru-8(mu(8)-P)(CO)(22)] (1) in around 30% yield. P-31-NMR solution spec tra are consistent with the presence of at least two isomers of the cl uster anion, presumably due to differing carbonyl distributions; the c hemical shifts for these configurations (600-800 ppm downfield of H3PO 4) are consistent with a highly deshielded interstitial phosphorus ato m. An X-ray structural study of one isomer of 1 reveals that the phosp horus atom occupies an interstitial square antiprismatic site defined by the eight ruthenium atoms, with two bridging carbonyl ligands on op posite faces spanning interplanar Ru-Ru bonds, and twenty terminal car bonyl ligands completing the ligand set. The solid state P-31-NMR spec trum of the crystallographically-identified isomer reveals a signal at 596.1 ppm assigned to the square antiprismatic interstitial phosphoru s atom. Formal electron counting suggests that 1 has four electrons le ss than expected using Wade's rules. The reductive electrochemistry of 1 has been examined by cyclic voltammetry, and reveals the presence o f two one-electron and one two-electron reduction waves, an uptake of four electrons in total, consistent with the cluster's theoretical ele ctron deficiency in the resting state. (C) 1998 Elsevier Science S.A. All rights reserved.