Stepwise Reduction at Magnesium and Beryllium: Cooperative Effects of Carbenes with Redox Non-Innocent α-Diimines

Lucas A Freeman; Jacob E Walley; Akachukwu D Obi; Guocang Wang; Diane A Dickie; Andrew Molino; David J D Wilson; Robert J Gilliard Jr

doi:10.1021/acs.inorgchem.9b01058

Stepwise Reduction at Magnesium and Beryllium: Cooperative Effects of Carbenes with Redox Non-Innocent α-Diimines

Inorg Chem. 2019 Aug 19;58(16):10554-10568. doi: 10.1021/acs.inorgchem.9b01058. Epub 2019 May 24.

Authors

Lucas A Freeman¹, Jacob E Walley¹, Akachukwu D Obi¹, Guocang Wang¹, Diane A Dickie¹, Andrew Molino², David J D Wilson², Robert J Gilliard Jr¹

Affiliations

¹ Department of Chemistry , University of Virginia , 409 McCormick Road , PO Box 400319, Charlottesville , Virginia 22904 , United States.
² Department of Chemistry and Physics, La Trobe Institute for Molecular Science , La Trobe University , Bundoora , Victoria 3083 , Australia.

PMID: 31124671
DOI: 10.1021/acs.inorgchem.9b01058

Abstract

In the past two decades, the organometallic chemistry of the alkaline earth elements has experienced a renaissance due in part to developments in ligand stabilization strategies. In order to expand the scope of redox chemistry known for magnesium and beryllium, we have synthesized a set of reduced magnesium and beryllium complexes and compared their resulting structural and electronic properties. The carbene-coordinated alkaline earth-halides, (^Et2CAAC)MgBr₂ (1), (SIPr)MgBr₂ (2), (^Et2CAAC)BeCl₂ (3), and (SIPr)BeCl₂ (4) [^Et2CAAC = diethyl cyclic(alkyl)(amino) carbene; SIPr = 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazole-2-ylidene] were combined with an α-diimine [2,2-bipyridine (bpy) or bis(2,6-diisopropylphenyl)-1,4-diazabutadiene (^DippDAB)] and the appropriate stoichiometric amount of potassium graphite to form singly- and doubly-reduced compounds (^Et2CAAC)MgBr(^DippDAB) (5), (^Et2CAAC)MgBr(bpy) (6), (^Et2CAAC)Mg(^DippDAB) (7), (^Et2CAAC)Be(bpy) (8), and (SIPr)Be(bpy) (9). The doubly-reduced compounds 7-9 exhibit substantial π-bonding interactions across the diimine core, metal center, and π-acidic carbene. Each complex was fully characterized by UV-vis, FT-IR, X-ray crystallography, ¹H, ¹³C, and ⁹Be NMR, or EPR where applicable. We use these compounds to highlight the differences in the organometallic chemistry of the lightest alkaline earth metals, magnesium and beryllium, in an otherwise identical chemical environment.