MIXED-METAL CLUSTER CHEMISTRY IX - ALKYLARYLPHOSPHINE DERIVATIVES OF [CPWIR3(CO)(11)] AND X-RAY CRYSTAL-STRUCTURE OF [CPWIR3(MU-CO)(3)(CO)(7)(PME2PH)](2)

Reactions of [CpWIr3(CO)(11)] (1) with equimolar amounts of the bident ate alkylarylphosphines bis(diphenylphosphino)ethane (dppe) and bis(di phenylphosphino)methane (dppm) afford the substitution products [CpWIr 3(mu-L)(mu-CO)(3)(CO)(6)] [L=dppe (2), dppm (3)]. Reactions of 1 with stoichiometric amounts of the monodentate alkylarylphosphines PMePh2 a nd PMe2Ph afford the substitution products [CpWIr3(mu-CO)(3)(CO)(8-n)( L)(n)] [L = PMePh2, n = 1 (4), 2 (5), 3 (6); L = PMe2Ph, n = 1 (7), 2 (8), 3 (9)]. The clusters 2-8 are fluxional in solution, with the inte rconverting isomers resolvable at low temperatures. Variable temperatu re P-31- and C-13-NMR spectra for 2 and 3 enable structural assignment of the isomers, revealing a triiridium face spanned by bridging carbo nyls, a diaxially-ligated diphosphine with (in the case of dppe) a fle xible backbone, and an apical tungsten-coordinated cyclopentadienyl (C p) ligand situated over differing WIr2 faces in the configurations. C- 13-NMR exchange spectroscopy (EXSY) spectra reveal that these isomers interconvert by tripodal rotation at the apical CpW(CO)(2), resolvable (in the case of 3) into a 'waggling' of the CpW(CO)(2) group over the non-diphosphine ligated WIr2 faces before the onset of complete tripo dal rotation. A 'merry-go-round' of carbonyl ligands in the basal Ir(m u-CO)(3)(CO)(3) plane occurs at a similar temperature to that of tripo dal rotation for 3, but at a higher temperature for 2. For 2, flexing of the diphosphine backbone is the highest energy process observed. A structural study of one isomer of 7, namely 7a, reveals that the three edges of the triiridium face of the tetrahedral core are spanned by b ridging carbonyls, and that the iridium-bound PMe2Ph ligates axially a nd the tungsten-bound Cp coordinates apically with respect to the trii ridium face. Information from this crystal structure, P-31-NMR data, a nd comparison with analogous PPh3- and PMe3-ligated tungsten-triiridiu m clusters have been employed to suggest coordination geometries for t he other isomers of 4-9. The geometries of the PMePh2- and PMe2Ph-deri vatives 4-9 follow those of the previously reported PMe3-derivatives, with the exception of the minor isomer [CpWIr3(mu-CO)(3)(CO)(5)(PMePh2 )(3)] (6b) which has an unprecedented triradial, apical substitution g eometry. (C) 1998 Elsevier Science S.A. All rights reserved.