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. 2020 Oct 7;142(40):17131-17139.
doi: 10.1021/jacs.0c07689. Epub 2020 Sep 22.

Facile H/D Exchange at (Hetero)Aromatic Hydrocarbons Catalyzed by a Stable Trans-Dihydride N-Heterocyclic Carbene (NHC) Iron Complex

Subhash Garhwal  1 , Alexander Kaushansky  1 , Natalia Fridman  1 , Linda J W Shimon  2 , Graham de Ruiter  1
Affiliations

Facile H/D Exchange at (Hetero)Aromatic Hydrocarbons Catalyzed by a Stable Trans-Dihydride N-Heterocyclic Carbene (NHC) Iron Complex

Subhash Garhwal et al. J Am Chem Soc. .

Abstract

Earth-abundant metal pincer complexes have played an important role in homogeneous catalysis during the last ten years. Yet, despite intense research efforts, the synthesis of iron PCcarbeneP pincer complexes has so far remained elusive. Here we report the synthesis of the first PCNHCP functionalized iron complex [(PCNHCP)FeCl2] (1) and the reactivity of the corresponding trans-dihydride iron(II) dinitrogen complex [(PCNHCP)Fe(H)2N2)] (2). Complex 2 is stable under an atmosphere of N2 and is highly active for hydrogen isotope exchange at (hetero)aromatic hydrocarbons under mild conditions (50 °C, N2). With benzene-d6 as the deuterium source, easily reducible functional groups such as esters and amides are well tolerated, contributing to the overall wide substrate scope (e.g., halides, ethers, and amines). DFT studies suggest a complex assisted σ-bond metathesis pathway for C(sp2)-H bond activation, which is further discussed in this study.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Selected examples of first-row transition-metal PCcarbeneP pincer complexes and the herein reported reactivity of [(PCNHCP)Fe(H)2N2)] (2).
Scheme 1
Scheme 1. Synthesis of PCNHCP Iron Complexes 1 and 2 and the Observed H/D Exchange in Benzene-d6
Figure 2
Figure 2
Solid state structures of [(PCNHCP)FeCl2] (1, left) and [(PCNHCP)Fe(H)2N2] (2, right). Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms (except H1 and H2) and cocrystallized solvent molecules are omitted for clarity.
Figure 3
Figure 3
Calculated free energy profiles (ΔH/ΔG) in kcal mol–1 and plausible mechanistic pathways for hydrogen isotope exchange (HIE) of 3 with benzene. Hydrogen atoms (except Hb) are omitted for clarity. For computational details, see the Supporting Information.
See this image and copyright information in PMC

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