New [Cp*M(Q)Cl] complexes (M = Rh or Ir, Cp* = pentamethylcyclopentadienyl, HQ = 1-phenyl-3-methyl-4R(C=O)-pyrazol-5-one in general, in detail HQ(Me), R = CH3; HQ(Et), R = CH2CH3; HQ(Piv), R = CH2-C(CH3)3; HQ(Bn), R = CH2-(C6H5); HQ(S), R = CH-(C6H5)(2)) have been synthesized from the reaction Of [CP*MCl2](2) with the sodium salt, NaQ, of the appropriate HQ proligand. Crystal structure determinations for a representative selection of these [Cp*M(Q)Cl] compounds show a pseudo-octahedral metal environment with the Q ligand bonded in the O,O'-chelating form. In each case, two enantiomers (S-M) and (R-M) arise, differing only in the metal chirality. The reaction of [Cp*Rh(Q(Bn))Cl] with MgCH3Br produces only halide exchange with the formation of [Cp*Rh(Q(Bn))Br], The [Cp*Rh(O)Cl] complexes react with PPh3 in dichloromethane yielding the adducts Cp*Rh(O)Cl/PPh3 (1:1) which exist in solution in two different isomeric forms. The interaction of [Cp*Rh(Q(Me))CI] with AgNO3 in MeCN allows generation of [Cp*Rh(QMe)(MeCN)]NO(3)center dot 3H(2)O, Whereas the reaction of [Cp*Rh(Q(Me))Cl] with AgClO4 in the same solvent yields both [Cp*Rh(Q(Me))(H2O)]ClO4 and [Cp*Rh(Cl)(H2O)(2)]ClO4; the H2O molecules derive from the not-rigorously anhydrous solvents or silver salts.