IrI(η4-diene) precatalyst activation by strong bases: formation of an anionic IrIII tetrahydride: formation of an anionic IrIII tetrahydride

Paven Kisten, Eric Manoury, Agustí Lledós, Adrian C. Whitwood, Jason M. Lynam, John M. Slattery, Simon B. Duckett*, Rinaldo Poli*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The reaction between [IrCl(COD)]2 and dppe in a 1 : 2 ratio was investigated in detail under three different conditions. [IrCl(COD)(dppe)], 1, is formed at room temperature in the absence of base. In the presence of a strong base at room temperature, hydride complexes that retain the carbocyclic ligand in the coordination sphere are generated. In isopropanol, 1 is converted into [IrH(1,2,5,6-η22-COD)(dppe)] (2) on addition of KOtBu, with k12 = (1.11 ± 0.02) × 10−4 s−1, followed by reversible isomerisation to [IrH(1-κ-4,5,6-η3-C8H12)(dppe)] (3) with k23 = (3.4 ± 0.2) × 10−4 s−1 and k32 = (1.1 ± 0.3) × 10−5 s−1 to yield an equilibrium 5 : 95 mixture of 2 and 3. However, when no hydride source is present in the strong base (KOtBu in benzene or toluene), the COD ligand in 1 is deprotonated, followed by β-H elimination of an IrI-C8H11 intermediate, which leads to complex [IrH(1-κ-4,5,6-η3-C8H10)(dppe)] (4) selectively. This is followed by its reversible isomerisation to 5, which features a different relative orientation of the same ligands (k45 = (3.92 ± 0.11) × 10−4 s−1; k5-4 = (1.39 ± 0.12) × 10−4 s−1 in C6D6), to yield an equilibrated 32 : 68 mixture of 4 and 5. DFT calculations assisted in the full rationalization of the selectivity and mechanism of the reactions, yielding thermodynamic (equilibrium) and kinetic (isomerization barriers) parameters in excellent agreement with the experimental values. Finally, in the presence of KOtBu and isopropanol at 80 °C, 1 is transformed selectively to K[IrH4(dppe)] (6), a salt of an anionic tetrahydride complex of IrIII. This product is also selectively generated from 2, 3, 4 and 5 and H2 at room temperature, but only when a strong base is present. These results provide an insight into the catalytic action of [IrCl(COD)(LL)] complexes in the hydrogenation of polar substrates in the presence of a base.

Original languageEnglish
Article numberD2DT04036K
Pages (from-to)2495-2505
Number of pages11
JournalDalton Transactions
Issue number8
Publication statusPublished - 26 Jan 2023

Bibliographical note

Funding Information:
This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 860322, and was granted access to the resources of the CICT (Centre Interuniversitaire de Calcul de Toulouse, project CALMIP). We are also grateful to the CNRS (Centre National de la Recherche Scientifique) for additional funding and to S. M. Wahidur Rahaman for a few initial investigations. JML is funded through a Royal Society Industrial Research fellowship.

Publisher Copyright:
© 2023 The Royal Society of Chemistry.

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