The hydrogenphosphate complex of (1,5-cyclooctadiene)iridium(I), {[Bu4N][(1,5-COD)Ir · HPO4]}n: synthesis, spectroscopic characterization, and ES-MS of a new, preferred precursor to HPO42− and Bu4N+ stabilized Ir(0)n nanoclusters

The synthesis and characterization of a previously unknown, rare organometallic–phosphate complex, {[Bu4N][(1,5-COD)Ir · HPO4]}n (1), is described. Characterization of 1 was accomplished by elemental analysis, electrospray mass spectrometry (ES-MS), and 1H and 13C NMR which established the symmetry of the product as at least C2 or Cs. The ES-MS reveals an interesting, Ir(I) to Ir(III) oxidative process with intense peaks displaying the 191Ir/193Ir isotopic distribution patterns expected for the fragments [(1,5-COD)IrIII(HPO4)2]−, [(C8H11)2(IrIII)2(PO4)(HPO4)(H2O)]−, and [(C8H11)2(IrIII)2(PO4)(HPO4)(H2O)2]−. These fragments, in turn, provide evidence for a structure with two HPO42− groups attached to a single Ir, for example ring structures (of at least such C2 or Cs symmetry) such as {[Bu4N][(1,5-COD)Ir · HPO4]}2. Complex 1 is significant since it is known to be the preferred, compositionally precise precursor to the prototype example of a recently discovered class of novel, HPO42− and Bu4N+ stabilized nanoclusters, (Bu4N)2n2n+[Ir(0)n · (HPO4)n]2n−. Such nanoclusters are being extended, via their analogous hydrogenphosphate-organometallic precursors (1,5-COD)M+ or 2+/HPO42− (M=Rh(I), Ru(II), Pt(II)) to their corresponding, catalytically active [M(0)n · (HPO4)n]2n− nanoclusters.