Properties and Reactivities of the Hydrido Ligands in Iridium Sulfido Clusters Relevant to Activation and Production of H2

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 ΔG_coal^⧧ = 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.

Phosphine, isocyanide, and alkyne reactivity at pentanuclear molybdenum/tungsten–iridium clusters

Trigonal-bipyramidal molybdenum/tungsten–iridium clusters undergo ligand substitution with isocyanides and triphenylphosphine, and react with alkynes with CC cleavage or triiridium-face-specific addition.

H-H and N-H bond cleavage of dihydrogen and ammonia with a bifunctional parent imido (NH)-bridged diiridium complex

Hydrogenation and protonation of parent imido complexes have attracted much attention in relation to industrial and biological nitrogen fixation. The present study reports the structure and properties of the highly unsaturated diiridium parent imido complex [(Cp*Ir)(2)(μ(2)-H)(μ(2)-NH)](+) derived from deprotonation of a parent amido complex. Because of the Lewis acid-Brønsted base bifunctional nature of the metal-NH bond, the parent imido complex promotes heterolysis of H(2) and deprotonative N-H cleavage of ammonia to afford the corresponding parent amido complexes under mild conditions.