Oxygen Reduction with a Bifunctional Iridium Dihydride Complex

Abstract

The iridium dihydride [Ir(H)2 (HPNP)](+) (PNP=N(CH2 CH2 PtBu2 )2 ) reacts with O2 to give the unusual, square-planar iridium(III) hydroxide [Ir(OH)(PNP)](+) and water. Regeneration of the dihydride with H2 closes a quasi-catalytic synthetic oxygen-reduction reaction (ORR) cycle that can be run several times. Experimental and computational examinations are in agreement with an oxygenation mechanism via rate-limiting O2 coordination followed by H-transfer at a single metal site, facilitated by the cooperating pincer ligand. Hence, the four electrons required for the ORR are stored within the two covalent MH bonds of a mononuclear metal complex.

Understanding the Synergistic Effects Observed When Using Tethered Dual Catalysts for Heat and Light Activated Catalysis

“…A possible explanation is that the Ir centre promotes the reaction between 1 O 2 and thioanisole either through IrÀ O 2 or IrÀ S coordination. It has been shown previously that iridium-dioxide species can be generated through reaction of an iridium complex with either singlet [57] or triplet oxygen, [58] and that these types of complexes can oxidise organic compounds. [59] As such, it is possible that dioxidebound analogues of the iridium based catalysts 2-5 form under our reaction conditions.…”

Dioxygen insertion into the gold(i)–hydride bond: spin orbit coupling effects in the spotlight for oxidative addition

“…The TS state optimized with SOC (red line) lies slightly lower in energy, and it is straightforward to obtain a free energy Δ G ≠ = 31.6 kcal mol –1 = Δ H ≠ – T *Δ S ≠ (298.15 K) = 22.5 – (–9.1) kcal mol –1 . Whereas the MECP approach has been recently applied to the study of O 2 addition to an iridium complex 28 and of Pd(0) oxidation through formation of a cyclic peroxo complex, 29 to the best of our knowledge the computation of such a ‘spin-forbidden’ adiabatic TS with a SOC Hamiltonian has never been done before. The frequency calculation reveals only one imaginary frequency, corresponding to the stretching of the Au–H and O–O bonds.…”

Reductive O2 Binding at a Dihydride Complex Leading to Redox Interconvertible μ-1,2-Peroxo and μ-1,2-Superoxo Dinickel(II) Intermediates

“…Using metal hydrides is an attractive strategy for storing the required electrons for reductive small molecule binding, as it circumvents the need for highly reduced metal ions. It is interesting to note that many transition metal hydride complexes, in particular for 4d and 5d metal ions such as Pd II , Pt IV , Rh III , or Ir III , react with dioxygen via insertion in the metal hydride bond to give hydroperoxo intermediates. However, this may involve a HX reductive elimination/O 2 oxidative addition sequence .…”