Reductive cyclotrimerization of CO and isonitriles with a highly reactive CaI synthon

Thum S, Mai J, Schmidt M, Langer J, Harder S (2025)

Publication Type: Journal article

Publication year: 2025

Journal

DOI: 10.1039/d5sc02829a

Abstract

Whereas the small molecule activation with β-diketiminate (BDI)Mg^I complexes of type (BDI)Mg-Mg(BDI) is extensively investigated, lack of similar Ca^I reagents prevents studies on Ca^I reactivity. Herein, we report on small molecule activation with dinitrogen complexes of type (BDI)Ca(N2)Ca(BDI) which acts as Ca^I synthon by release of N2 and two electrons. Reaction of [(BDI*)Ca(THP)]2(N2) with CO led to formation of a deltate product with the cyclic C3O3²⁻ dianion (1); BDI* = HC[C(Me)N(DIPeP)]2 (DIPeP = 2,6-(Et2CH)-phenyl) and THP = tetrahydropyran. Reaction with the isonitrile CyN 00000000000000000 00000000000000000 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 01111111111111110 00000000000000000 00000000000000000 00000000000000000 C gave as the major product a complex with the triimino deltate C3(NCy)3²⁻ dianion (2) which is unstable in solution. Isolation of the side-product (BDI*)2Ca·(CN-Cy) (3) indicates dynamic ligand exchange and Schlenk equilibria. Variation of the isonitrile reagent led to isolation of (BDI*)2Ca·(CN-R) (4: R = xylyl, 5: R = tBu). Crystal structures and NMR studies in solution are discussed for complexes 1-5. We also report an extensive DFT study on the reductive trimerization of MeN C with this Ca^I synthon. The key intermediate (BDI)Ca(MeNC)Ca(BDI) contains dianionic MeNC²⁻. Contrary to expectation, C-C coupling does not proceed by nucleophilic attack at a second MeNC reagent. Electron transfer results in two bridging MeNC˙⁻ radical anions. This rare singlet diradicaloid reacts further by radical coupling to [MeNC-CNMe]²⁻. Differences with Mg^I reactivity are discussed.

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How to cite

APA:

Thum, S., Mai, J., Schmidt, M., Langer, J., & Harder, S. (2025). Reductive cyclotrimerization of CO and isonitriles with a highly reactive CaI synthon. Chemical Science. https://doi.org/10.1039/d5sc02829a

MLA:

Thum, Stefan, et al. "Reductive cyclotrimerization of CO and isonitriles with a highly reactive CaI synthon." Chemical Science (2025).

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