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

A variety of novel magnesium complexes containing sp (alkynyl) or sp 2 (imido) hybridized ligands were synthesized utilizing both deprotonative and addition routes. Spectroscopic and structural analysis revealed 4, 5, and 6-coordinate complexes, both hetero- and homoleptic. 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 sp 2 and sp 3 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 sp 2 (imido) atoms. Specifically, we exploit the high acidity of terminal alkynes and diphenylacetonitrile to prepare tetra-solvated distorted octahedral complexes Mg(C≡CC 6 H 4 R- p ) 2 (THF) 4 (R = Me, CF 3 ) and Mg(N=C=CPh 2 ) 2 (THF) 4 starting from the commercial alkyl reagent MgBu 2 . Adopting a similar deprotonative strategy using benzophenoneimine Ph 2 C=NH affords the heteroleptic trinuclear complex Mg 3 (N=CPh 2 ) 4 n Bu 2 (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 Mg 3 (N=CPh 2 ) 6 (THF) 2 .