Mixed-metal cluster chemistry IX: Alkylarylphosphine derivatives of [CpWIr₃(CO)₁₁] and X-ray crystal structure of [CpWIr₃(μ-CO)₃(CO)₇(PMe₂Ph)]

Reactions of [CpWIr₃(CO)₁₁] (1) with equimolar amounts of the bidentate alkylarylphosphines bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)methane (dppm) afford the substitution products [CpWIr₃(μ-L)(μ-CO)₃(CO)₆] [L=dppe (2), dppm (3)]. Reactions of 1 with stoichiometric amounts of the monodentate alkylarylphosphines PMePh₂ and PMe₂Ph afford the substitution products [CpWIr₃(μ-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 interconverting isomers resolvable at low temperatures. Variable temperature ³¹P- and ¹³C-NMR spectra for 2 and 3 enable structural assignment of the isomers, revealing a triiridium face spanned by bridging carbonyls, a diaxially-ligated diphosphine with (in the case of dppe) a flexible backbone, and an apical tungsten-coordinated cyclopentadienyl (Cp) ligand situated over differing WIr₂ faces in the configurations. ¹³C-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 tripodal rotation. A 'merry-go-round' of carbonyl ligands in the basal Ir(μ-CO)₃(CO)₃ plane occurs at a similar temperature to that of tripodal 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 bridging carbonyls, and that the iridium-bound PMe₂Ph ligates axially and the tungsten-bound Cp coordinates apically with respect to the triiridium face. Information from this crystal structure, ³¹P-NMR data, and comparison with analogous PPh₃- and PMe₃-ligated tungsten-triiridium clusters have been employed to suggest coordination geometries for the other isomers of 4-9. The geometries of the PMePh₂- and PMe₂Ph-derivatives 4-9 follow those of the previously reported PMe₃-derivatives, with the exception of the minor isomer [CpWIr₃(μ-CO)₃(CO)₅(PMePh₂)₃ ] (6b) which has an unprecedented triradial, apical substitution geometry.