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
[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-β-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 ΔGcoal⧧ = 53.7 kJ mol–1. DFT calculations agreed with
an intrapyrazole proton transfer process assisted by two water molecules
(ΔG = 63.1 kJ mol–1). An
X-ray diffraction study on 4 indicated electron delocalization
in the iridapyrazole ring. The reaction of the irida-β-diketone
[IrHCl­{(PPh2(o-C6H4CO))2H}] (1) with H2NNRR′
in aprotic solvents gave irida-β-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))-κP,κO] (6) or [IrHCl­(PPh2(o-C6H4CO))­(PPh2(o-C6H4CN)-κP)­(NH2NHPh-κNH2)] (9) containing o-(diphenylphosphine)­benzonitrile
and phenylhydrazine, respectively. From a CH2Cl2/CH3OH solution of 9 kept at −18 °C,
single crystals of [IrHCl­(PPh2(o-C6H4CO))­(PPh2(o-C6H4CN)-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(PPh2(o-C6H4CO))2(NH2NH­(CH3)-κNH2)] (7). Single-crystal X-ray
diffraction analysis was performed on 6 and 7.