Keggin-type polyoxometalates [PW11O39MCl] 5- with noble metals (M = Rh and Ir): Novel synthetic entries and ESI-MS directed reactivity screening

Abstract

A new synthetic entry to iridium Keggin-type polyoxometalate complexes from [PW11O39]7- and K3[IrCl 6] under harsh conditions is reported. The complex [PW 11O39IrCl]5- (15-) 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 15-. The reactivities of 15- and its rhodium analogue [PW11O39RhCl]5- in ligand substitution at the noble metal site were studied. Thiocyanate coordination successfully yielded (Bu4N)5[PW11O 39M(SCN)] [M = Rh (2a), Ir, (3a)]. In both cases, the SCN ligands are coordinated by sulfur atoms, according to 13C 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 NaN 3 resulted in Cl- to OH- replacement accompanied by the liberation of the RhCl fragment, whereas 15- proved unreactive with NaN3. Attempts to coordinate NO 2- are adversely affected by competing noble metal excision with formation of free [PW11O39]7-. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.