Magnesium 4, 5, and 6 coordinate complexes with ligands bound via sp or sp2 hybridized atoms

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Rae, Annabel and Kennedy, Alan R. and Robertson, Stuart D. (2025) Magnesium 4, 5, and 6 coordinate complexes with ligands bound via sp or sp2 hybridized atoms. Polyhedron, 266. 117257. ISSN 0277-5387 (https://doi.org/10.1016/j.poly.2024.117257)

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Abstract

As a metallic element of high natural abundance, magnesium finds a wide range of uses in both stoichiometric and more recently catalytic applications. This often takes advantage of the basic or nucleophilic properties of its compounds or their ability to co-complex with other organometallic compounds. However, the homoleptic chemistry of Mg(II) is heavily skewed towards alkyl and aryl ligands bound via sp2 and sp3 hybridized atoms. Here, we report our combined NMR spectroscopic and X-ray crystallographic study into much rarer alternative THF solvates of homoleptic magnesium complexes using ligands which bind via sp (alkynyl) and sp2 (imido) atoms. Specifically, we exploit the high acidity of terminal alkynes and diphenylacetonitrile to prepare tetra-solvated distorted octahedral complexes Mg(C≡CC6H4R-p)2(THF)4 (R = Me, CF3) and Mg(N=C=CPh2)2(THF)4 starting from the commercial alkyl reagent MgBu2. Adopting a similar deprotonative strategy using benzophenoneimine Ph2C=NH affords the heteroleptic trinuclear complex Mg3(N=CPh2)4nBu2(THF)2 with distorted tetrahedral Mg centres. Related imidomagnesium halide complexes can be accessed either by deprotonation of the imine with a Grignard reagent, or nucleophilic addition of a Grignard reagent to a nitrile, but these unusual five-coordinate complexes are unresponsive to a 1,4-dioxane induced Schlenk equilibrium shift. Employing a higher reflux temperature switching from a THF to a toluene medium permits access to the THF solvate of a homoleptic imido complex which also possesses a trinuclear constitution in Mg3(N=CPh2)6(THF)2.

ORCID iDs

Rae, Annabel, Kennedy, Alan R. and Robertson, Stuart D. ORCID logoORCID: https://orcid.org/0000-0002-9330-8770;
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