A Modular Approach to Asymmetric Mg(I) Complexes Using a Unique Cyclopentadienyl Mg(I) Complex

The first Mg^I complexes with non-N ligands have been isolated and were fully characterized. Reaction of [(BDI*)MgNa]₂ (III) with MgCp*₂ gave quantitative conversion to (BDI*)MgMgCp* (1); BDI* = HC[tBuC = N(DIPeP)]₂, DIPeP = 2,6-Et₂CH-phenyl) and Cp* = pentamethylcyclopentadienyl. A similar reaction with CaCp*₂ did not give (BDI*)MgCaCp* but led to insertion of the formal Mg° centre in the benzylic C─H bond, an oxidative addition that resulted in a mixed Mg/Ca hydride complex. The Cp* ligand in the unique (BDI*)MgMgCp* complex can be exchanged by addition of LM (M = Li, Na, K) complexes, resulting in formation of (BDI*)MgMgL and insoluble (Cp*M)_n. This modular approach worked for Cp*/N(SiMe₃)₂ exchange but not for the substitution of Cp* by P(SiMe₃)₂ or other PR₂ ligands. Reaction of (BDI*)MgMgCp* with a bulky NaOAr reagent led to quantitative formation of (BDI*)MgMgOAr·THF, a first Mg^I complex stabilized with an aryloxide ligand. All products have been fully characterized by X-ray diffraction and NMR methods. A computational study gives insight in the thermodynamics of formation and electronic structures.