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Synthesis and reactivity of low-oxidation-state alkaline earth metal complexes

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Abstract

The synthesis of molecules that feature main-group elements in unusual oxidation states and coordination environments is a primary pursuit of main-group chemistry. The p-block elements saw early success towards this goal, and dozens of compounds that contain subvalent p-block metals, semi-metals and non-metals are now known. The development of reliable syntheses for these compounds made it possible to study them in detail, which expanded our understanding of bonding and electronic structure and served as the foundation from which catalysis mediated by main-group elements has emerged. For the group 2 elements, isolating reduced compounds has been a synthetic challenge that has spurred exciting progress in the synthesis of reduced alkaline earth compounds. The past two decades has seen the isolation of stable Be(0), Be(I), Mg(0), Mg(I) and Ca(I) compounds, along with studies of their reactivity profiles. In this Review, we overview the chemistry of isolated low-valent species with a focus on comparing newly discovered chemical trends and features among the different elements in the group. Finally, we discuss future directions and challenges for the field.

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Fig. 1: Overview of atomic trends in the alkaline earth group.
Fig. 2: Overview of molecular Be redox chemistry.
Fig. 3: Overview of bond activation mediated by Be and other stand-alone Be reactions.
Fig. 4: The synthesis and reactivity of Mg(I) dimers.
Fig. 5: The chemistry of the first Mg(0) complexes.
Fig. 6: Relevant Ca redox chemistry and the reactivity of low-valent Ca intermediates with dinitrogen.

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Acknowledgements

We are grateful to the University of Virginia for support of the Gilliard Research Group’s projects on alkaline earth metal chemistry. A special thanks is also extended to Gilliard Group members past and present, collaborators and other main-group teams that continue to advance alkaline earth metal chemistry.

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  1. Department of Chemistry, University of Virginia, Charlottesville, VA, USA

    Lucas A. Freeman, Jacob E. Walley & Robert J. Gilliard Jr

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  1. Lucas A. Freeman
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  2. Jacob E. Walley
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  3. Robert J. Gilliard Jr
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L.A.F. and J.E.W. wrote the review; R.J.G. directed the preparation and revision of the review.

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Correspondence to Robert J. Gilliard Jr.

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Nature Synthesis thanks Conor Pranckevicius and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Alison Stoddart, in collaboration with the Nature Synthesis team.

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Freeman, L.A., Walley, J.E. & Gilliard, R.J. Synthesis and reactivity of low-oxidation-state alkaline earth metal complexes. Nat. Synth 1, 439–448 (2022). https://doi.org/10.1038/s44160-022-00077-6

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