Solid-state and solution dynamics of the reversible loss of hydrogen from the iridium nonclassical polyhydride complexes IrClH2(PR3)2(H2) (R = Pri, Cy, But)

Article abstract of DOI:10.1021/ic00036a020

The complexes IrClH₂(PR₃)₂(H₂) (R = Prⁱ (1a), Cy (1b)) were generated through the reaction of the corresponding unsaturated dihydride complexes, IrClH₂(PR₃)₂ (R = Prⁱ (2a), Cy (2b)), with H₂ in solution or the solid state. The complexes were also prepared through treatment of THF solutions of IrCl₃-SH₂O and 2 equiv of phosphine with 2 equiv of sodium naphthalide under an atmosphere of hydrogen. The molecular structure of 1a·C₁₀H₈ was determined by a single-crystal X-ray diffraction study. Crystallographic data for 1a·C₁₀H₈: triclinic P1, Z = 2, a = 8.069 (3) A?, b = 13.822 (6) A?, c = 14.519 (5) A?, α = 82.56 (3)°, β = 82.34 (3)°, γ = 72.90 (3)°, V = 5170 (5) A?³; ρ_calcd = 1.737 g/cm³. Under an atmosphere of argon, 1a and 1b eliminate H₂ and convert back to the unsaturated complexes. Variable-temperature ¹H NMR studies of 1a and 1b in toluene-d₈ solution under 0.5 atm of H₂ show that they establish rapid equilibria with 2a and 2b, respectively, which are sensitive to hydrogen pressure and temperature. Similar studies of the more sterically hindered IrClH₂(PBu^t₃)₂ (2c) under 0.5 atm of H₂ show only indirect evidence of a much slower equilibrium with 1c, while low concentrations of 1c can be directly observed under 1 atm of H₂. The presence of dihydrogen ligands in 1a and 1b are indicated by their extremely facile exchange with free H₂ and by the respective minimum T₁ values for the ¹H NMR resonance due to the exchanging metal-bound hydrogens at 300 MHz of 22 and 27 ms, respectively. Variable-temperature ³¹P{¹H} NMR spectra of 1a dissolved in toluene-d₈ also demonstrate the interconversion of 1a and 2a. The metal bound hydrogens of 1a and 1b undergo D/H exchange in toluene-d₈, THF-d₈, and CD₂Cl₂ solutions. The reversible uptake of hydrogen by 2a in the solid state was studied through monitoring of M-H absorptions by FTIR spectroscopy. Comparison of the relative intensities of the M-H infrared absorptions of 1a and 2a with those observed for 1b and 2b in equilibrated samples under 1 atm of H₂ indicates that the equilibrium position lies much more toward the dihydrogen complex in the case of the PPRⁱ₃ derivative. Similar studies of the reaction of 2a with D₂ establish that the intramolecular exchange between the dihydrogen and hydride ligands of 1a occurs in the solid state.