The reactivity of new (1,5-cyclooctadiene)rhodium acylpyrazolonates towards N- and P-donor ligands: X-ray structures of [Rh(1,5-COD)Qs], [Rh(1,5-COD)(phen)]Qs·0.5H2O (HQs=1-phenyl-3-methyl-4-(2-thenoyl)-pyrazol-5-one) and [Rh(1,5-COD)Br]2

Complexes [Rh(1,5-COD)(Q)] have been prepared by the reaction between [Rh(1,5-COD)Cl]2 (1,5-COD=1,5-cyclooctadiene) and HQ (where HQ=1-phenyl-3-methyl-4-R-pyrazol-5-one: R=2-thenoyl (HQs), 2-furanoyl (HQo) or tert-butylacetyl (HQT). [Rh(1,5-COD)(Q)] react with N2-donor ligands such as 1,10-phenanthroline (phen) or 2,2-bipyridyl (bipy) yielding ionic compounds [Rh(1,5-COD)(N2-donor)]Q. The substitutional lability of 1,5-COD in [Rh(1,5-COD)(Q)] versus mono- and di-organophosphine ligands was also investigated. In all cases 1,5-COD has been displaced. Reaction with two equivalents of PPh3 gave, upon oxidation of the Rh(I) centre, [Rh(PPh3)2(O2)(Q)] species containing a η2-peroxo-group. Reaction of [Rh(1,5-COD)(Q)] with the chelating P2-donor 1,2-bis(diphenylphosphino)ethane (dppe) or 4,4′-bis(diphenylphosphino)ferrocene (dppf) yields the peroxo Rh(III) compounds [Rh(dppe)2O2]QT and [Rh(dppf)O2(Qs)] or Rh(I) species [Rh(dppf-O2)(QT)] containing the diphosphine in the oxidised form. Finally the reaction between [Rh(1,5-COD)(Q)] and allylbromide yields the well-known [Rh(1,5-COD)Br]2. All complexes have been characterised by analytical and spectral data (IR, 1H and 31P{1H}-NMR spectra). The crystal structures of [Rh(1,5-COD)(Qs)], [Rh(1,5-COD)(phen)]Qs and [Rh(1,5-COD)Br]2, all containing a Rh(I) atom in a square coordinate environment, are also reported.