New hydridoirida-beta-diketones [IrH{(PPh2(o-C6H4CO))(2)H}(CO)]ClO4 2 and [IrH{(PPh2(o-C6H4CO))(2)H}(olefin)]BF4 (olefin = C2H4, 5; 1-hexene, 10) have been prepared. These complexes may afford new diacylhydridoiridium(III) derivatives. In chloroform solution, complex 2 is in equilibrium with the deprotonated diacylhydride trans-[IrH(PPh2(o-C6H4CO))(2)(CO)] complex 3. In DMSO, deprotonation cl, 2 occurs to yield the kinetically favored product 3, which isomerizes to the thermodynamically favored complex cis-[IrH(PPh2(o-C6H4CO))(2)(CO)] 4. Reprotonation of 4 with HBF4 in chlorinated solvents gives the cation in 2. In coordinating solvents such as dimethyl sulfoxide or acetonitrile, complex 5 undergoes displacement of ethylene to afford [IrH{(PPh2(o-C6H4CO))(2)H}(L)]BF4 (L = DMSO, 7; CH3CN, 9). Complexes 5 and 7 undergo deprotonation by NEt3 to give the corresponding diacylhydrides. The ethylene complex gives only trans-[IrH(PPh2(o-C6H4CO))(2)(C2H4)] 6, while the dimethyl sulfoxide derivative affords a mixture of trans- and cis-[IrH(PPh2(o-C6H4CO))(2)(DMSO)] 8. Complex 10 shows inhibited alkene rotation around the Ir-olefin axis, All of the complexes were fully characterized spectroscopically. Single-crystal X-ray diffraction analysis was performed on complexes 3, 4, and 9. The C-13 NMR and X-ray data point to a carbenoid character in the carbon atoms bonded to iridium in the irida-beta-diketone fragment, so that it can be considered as an acyl(hydroxycarbene) moiety.