Keggin-type Polyoxometalates [PW11O39MCl]5– with Noble Metals (M = Rh and Ir): Novel Synthetic Entries and ESI-MS Directed Reactivity Screening

A new synthetic entry to iridium Keggin-type polyoxometalate complexes from [PW11O39](7-) and K-3[IrCl6] under harsh conditions is reported. The complex [PW11O39IrCl](5-) (1(5-)) featuring an IrCl functionality was obtained in high yield and characterized by NMR spectroscopic and ESI-MS techniques. The presence of Li+ (3-4 M) is essential for a quantitative yield of 1(5-). The reactivities of 1(5-) and its rhodium analogue [PW11O39RhCl](5-) in ligand substitution at the noble metal site were studied. Thiocyanate coordination successfully yielded (Bu4N)(5)[PW11O39M(SCN)] [M = Rh (2a), Ir, (3a)]. In both cases, the SCN ligands are coordinated by sulfur atoms, according to C-13 NMR and IR spectroscopic data. Gas-phase fragmentation reactions of compounds 2a and 3a were also investigated by collision-induced dissociation (CID) experiments. Reaction of [PW11O39RhCl](5-) with NaN3 resulted in Cl- to OH- replacement accompanied by the liberation of the RhCl fragment, whereas 1(5-) proved unreactive with NaN3. Attempts to coordinate NO2- are adversely affected by competing noble metal excision with formation of free [PW11O39](7-).