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. 2025 May 28;44(11):1217-1226.
doi: 10.1021/acs.organomet.5c00172. eCollection 2025 Jun 9.

Synthesis, Characterization and Catalytic Activity of Iron, Cobalt and Nickel Complexes Bearing an N‑Heterocyclic Carbene-Based PCP Pincer Ligand

Tiago F C Cruz  1   2 , Daniel P Zobernig  1 , Berthold Stöger  3 , Ernst Pittenauer  4 , Karl Kirchner  1
Affiliations

Synthesis, Characterization and Catalytic Activity of Iron, Cobalt and Nickel Complexes Bearing an N‑Heterocyclic Carbene-Based PCP Pincer Ligand

Tiago F C Cruz et al. Organometallics. .

Abstract

Reactions of the bis-((R2phosphanyl)-methyl)-1H-benzo-[d]-imidazole-3-ium hexafluorophosphate precursors [(PCP-R)-H]-PF6 (R = iPr, Ph) with zerovalent precursors [Fe3(CO)12], [Co2(CO)8], [Ni-(COD)2] and [Ni-(PPh3)4], respectively, gave rise to the cationic iron, cobalt and nickel complexes [Fe-(PCP-iPr)-(CO)2H]-PF6 (1), [Co-(PCP-iPr)-(CO)2]-PF6 (2), [Co-(PCP-Ph)-(CO)2]-PF6 (3), [Ni-(PCP-iPr)-(cyclooct-4-en-1-yl)]-PF6 (4) and [Ni-(PCP-iPr)-H]-PF6 (5), by oxidative addition of the benzimidazolium CH bond in [(PCP-R)-H]-PF6. The complexes bearing the bidentate ligand 3-((diisopropylphosphanyl)-methyl)-1-methyl-1H-benzo-[d]-imidazolidene PC-iPr [Fe-(PC-iPr)-(CO)3] (6) and [Fe-(PC-iPr)-(CO)3H]-BF4 (7) were also synthesized. All complexes were characterized by NMR and FTIR spectroscopies, high resolution mass spectrometry and selected cases by single-crystal X-ray diffraction. Cobalt complexes 2 and 3 were catalytically active in the hydroboration of styrene with pinacolborane (HBPin) using 1 mol % of precatalyst and 2 mol % of KOtBu in THF at 70 °C for 18 h with yields of 87-93%. In addition, complex 2 also catalyzed the hydroboration of terminal alkenes in good yields (68-88%). Reaction of complex 2 with 5 equivs of HBPin and 2 equivs of KOtBu in THF gave rise to the cobalt-(I) hydride complex [Co-(κ2-(P,C)-PCP-iPr)-H-(CO)2] (8), indicating that the mechanism of the catalytic process follows a cobalt-(I) hydride pathway.

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Figures

1
1. Examples of PCP pincer complexes containing anionic (A–C) and neutral (D) donors.
1
1. Synthesis of PCP Iron, Cobalt and Nickel Complexes 1–5
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2. Synthesis of PC Iron Complexes 6 and 7
1
1
Single-crystal X-ray diffraction structures of complexes 1, 2, 4, 6 and 7, showing 50 or 30% probability ellipsoids. Most hydrogen atoms (except that of the hydride ligands when applicable) and the counteranions of the complexes (when applicable) were omitted and the iPr groups were presented in wireframe mode for clarity.
3
3. Reaction of Complex 2 With HBPin/KOtBu: Detection of the Hydride Complex 8
4
4. Mechanism for the Hydroboration of Alkenes Catalyzed by Complex 2/KOtBu
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References

    1. van Koten G.. Tuning the reactivity of metals held in a rigid lig-and environment. Pure Appl. Chem. 1989;61:1681–1694. doi: 10.1351/pac198961101681. Coining of the name “pincer”. - DOI

    1. For reviews on pincer complexes, see:

    2. Gossage R. A., van de Kuil L. A., van Koten G.. Di-aminoarylnickel­(II) “Pincer” Complexes: Mechanistic Considerations in the Kharasch Addition Reaction, Controlled Polymerization, and Dendrimeric Transition Metal Catalysts. Acc. Chem. Res. 1998;31:423–431. doi: 10.1021/ar970221i. - DOI
    3. Albrecht M., van Koten G.. Platinum Group Organometallics Based on “Pincer” Complexes: Sensors, Switches, and Catalysts. Angew. Chem., Int. Ed. 2001;40:3750–3781. doi: 10.1002/1521-3773(20011015)40:20<3750::AID-ANIE3750>3.0.CO;2-6. - DOI - PubMed
    4. van der Boom M. E., Milstein D.. Cyclometalated Phosphine-Based Pincer Complexes: Mechanistic Insight in Catalysis, Coordination, and Bond Activation. Chem. Rev. 2003;103:1759–1792. doi: 10.1021/cr960118r. - DOI - PubMed
    5. Singleton J. T.. The uses of pincer complexes in organic synthesis. Tetrahedron. 2003;59:1837–1857. doi: 10.1016/S0040-4020(02)01511-9. - DOI
    6. Liang L. C.. Metal complexes of chelating diarylamido phosphine ligands. Coord. Chem. Rev. 2006;250:1152–1177. doi: 10.1016/j.ccr.2006.01.001. - DOI
    7. The Chemistry of Pincer Compounds; Morales-Morales, D. , Jensen, C. M. , Eds.; Elsevier: Amsterdam, 2007.
    8. Nishiyama H.. Synthesis and use of bisoxazolinyl-phenyl pincers. Chem. Soc. Rev. 2007;36:1133–1141. doi: 10.1039/b605991k. - DOI - PubMed
    9. Benito-Garagorri D., Kirchner K.. Modularly Designed Transition Metal PNP and PCP Pincer Complexes based on Aminophosphines: Synthesis and Catalytic Applications. Acc. Chem. Res. 2008;41:201–213. doi: 10.1021/ar700129q. - DOI - PubMed
    10. Choi J., MacArthur A. H., Brookhart M., Goldman A. S.. Dehydrogenation and Related Reactions Catalyzed by Iridium Pincer Complexes. Chem. Rev. 2011;111:1761–1779. doi: 10.1021/cr1003503. - DOI - PubMed
    11. Selander N., Szabo K. J.. Catalysis by Palladium Pincer Complexes. Chem. Rev. 2011;111:2048–2076. doi: 10.1021/cr1002112. - DOI - PubMed
    12. Schneider S., Meiners J., Askevold B.. Cooperative Aliphatic PNP Amido Pincer Ligands – Versatile Building Blocks for Coordination Chemistry and Catalysis. Eur. J. Inorg. Chem. 2012;2012:412–429. doi: 10.1002/ejic.201100880. - DOI
    13. van Koten, G. ; Milstein, D. . Topics in Organometallic Chemistry, in Organometallic Pincer Chemistry; Springer: Berlin, 2013; Vol. 40.
    14. Szabo, K. J. ; Wendt, O. F. . Pincer and Pincer-type Complexes: Applications in Organic Synthesis and Catalysis; Wiley-VCH: Weinheim, Germany, 2014.
    15. Asay M., Morales-Morales D.. Non-symmetric pincer ligands: complexes and applications in catalysis. Dalton Trans. 2015;44:17432–17447. doi: 10.1039/C5DT02295A. - DOI - PubMed
    16. Murugesan S., Kirchner K.. Non-precious metal complexes with an anionic PCP pincer architecture. Dalton Trans. 2016;45:416–439. doi: 10.1039/C5DT03778F. - DOI - PubMed
    1. Martínez-Prieto L. M., Melero C., del Río D., Palma P., Cámpora J., Álvarez E.. Synthesis and Reactivity of Nickel and Palladium Fluoride Complexes with PCP Pincer Ligands. NMR-Based Assessment of Electron-Donating Properties of Fluoride and Other Monoanionic Ligands. Organometallics. 2012;31:1425–1438. doi: 10.1021/om2009793. - DOI
    2. Dauth A., Gellrich U., Diskin-Posner Y., Ben-David Y., Milstein D.. The Ferraquinone–Ferrahydroquinone Couple: Combining Quinonic and Metal-Based Reactivity. J. Am. Chem. Soc. 2017;139:2799–2807. doi: 10.1021/jacs.6b13050. - DOI - PMC - PubMed
    1. Himmelbauer D., Mastalir M., Stöger B., Veiros L. F., Pignitter M., Somoza V., Kirchner K.. Iron PCP Pincer Complexes in Three Oxidation States: Reversible Ligand Protonation To Afford an Fe(0) Complex with an Agostic C–H Arene Bond. Inorg. Chem. 2018;57:7925–7931. doi: 10.1021/acs.inorgchem.8b01018. - DOI - PubMed
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