Irida-β-ketoimines Derived from Hydrazines To Afford Metallapyrazoles or N-N Bond Cleavage: A Missing Metallacycle Disclosed by a Theoretical and Experimental Study.

Unprecedented metallapyrazoles [IrH{PhP(o-CH)CNNHC(o-CH)PPh}] (3) and [IrHCl{PhP(o-CH)CNNHC(o-CH)PPh}] (4) were obtained by the reaction of the irida-β-ketoimine [IrHCl{(PPh(o-CHCO))(PPh(o-CHCNNH))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 ΔG = 53.7 kJ mol. DFT calculations agreed with an intrapyrazole proton transfer process assisted by two water molecules (ΔG = 63.1 kJ mol). An X-ray diffraction study on 4 indicated electron delocalization in the iridapyrazole ring. The reaction of the irida-β-diketone [IrHCl{(PPh(o-CHCO))H}] (1) with HNNRR' in aprotic solvents gave irida-β-ketoimines [IrHCl{(PPh(o-CHCO))(PPh(o-CHCNNRR'))H}] (R = R' = Me (5); R = H, R' = Ph (8)), which can undergo N-N bond cleavage to afford the acyl-amide complex [IrHCl(PPh(o-CHCO))(PPh(o-CHC(O)N(CH)))-κP,κO] (6) or [IrHCl(PPh(o-CHCO))(PPh(o-CHCN)-κP)(NHNHPh-κNH)] (9) containing o-(diphenylphosphine)benzonitrile and phenylhydrazine, respectively. From a CHCl/CHOH solution of 9 kept at -18 °C, single crystals of [IrHCl(PPh(o-CHCO))(PPh(o-CHCN)-κP))(HN═NPh-κNH)] (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(PPh(o-CHCO))(NHNH(CH)-κNH)] (7). Single-crystal X-ray diffraction analysis was performed on 6 and 7.