Unprecedented metallapyrazoles [IrH2{Ph2P(o-C6H4)CNNHC(o-C6H4)PPh2}] (3) and [IrHCl{Ph2P(o-C6H4)CNNHC(o-C6H4)PPh2}] (4) were obtained by the reaction of the irida-beta-ketoimine [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNNH2))H}] (2) in MeOH heated at reflux in the presence and absence of KOH, respectively. In solution, iridapyrazole 3 undergoes a dynamic process due to prototropic tautomerism with an experimental barrier for the exchange of Delta G(coal)(double dagger) = 53.7 kJ mol(-1). DFT calculations agreed with an intrapyrazole proton transfer process assisted by two water molecules (Delta G = 63.1 kJ mol(-1)). An X-ray diffraction study on 4 indicated electron delocalization in the iridapyrazole ring. The reaction of the irida-beta-diketone [IrHCl{(PPh2(o-C6H4CO))(2)H}] (1) with H2NNRR' in aprotic solvents gave irida-beta-ketoimines [IrHCl{(PPh2(o-C6H4CO))(PPh2(o-C6H4CNNRR'))H}] (R = R' = Me (5); R = H, R' = Ph (8)), which can undergo N-N bond cleavage to afford the acyl-amide complex [IrHCl(PPh2(o-C6H4CO))(PPh2(o-C6H4C(O)N(CH3)(2)))-kappa P,kappa O] (6) or [IrHCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CN)-kappa P)(NH2NHPh-kappa NH2)] (9) containing o-(diphenylphosphine)benzonitrile and phenylhydrazine, respectively. From a CH2Cl2/CH3OH solution of 9 kept at -18 degrees C, single crystals of [IrHCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CN)-kappa P))(HN-NPh-kappa NH)] (10) containing o-(diphenylphosphine)benzonitrile and phenyldiazene were formed, as shown by X-ray diffraction. The reaction of 1 with methylhydrazine in methanol gave the hydrazine complex [IrCl(PPh2(o-C6H4CO))(2)(NH2NH(CH3)-kappa NH2)] (7). Single-crystal X-ray diffraction analysis was performed on 6 and 7.