Stable Mg²⁺ Dication Weakly Stabilized/Coordinated in Solution: Synthesis, Structure, Reactivity, and Use in...

Area of Science:

• Organometallic Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Development of stable, soluble magnesium complexes is crucial for advancing homogeneous catalysis.
• Weakly coordinating anions are key to stabilizing reactive metal centers.
• Understanding cation-anion interactions is vital for predicting reactivity.

Purpose of the Study:

• To synthesize and characterize the first soluble and stable Mg(II) dication stabilized by carborane anions.
• To investigate the catalytic activity of this novel magnesium complex in various organic transformations.
• To elucidate the structure-activity relationship by comparing with a related ammoniododecaborate salt.

Main Methods:

• Synthesis of Mg[HexCB11Cl11]2 via reaction of Mg(nBu)2 with [Ph3C][HexCB11Cl11].
• Solid-state structural analysis and solution-state experimental studies.
• Classical molecular dynamics simulations (cMD) to probe cation-anion interactions.
• Catalytic testing for polymerization, hydrosilylation, hydrogenation, and CO2 reduction.

Main Results:

• Successfully synthesized and characterized the stable Mg(II) dication complex, Mg[HexCB11Cl11]2 (1).
• Experimental and computational data confirmed retained cation-anion association in solution due to Mg's high electrophilicity.
• Complex 1 demonstrated catalytic activity in 1-hexene polymerization, alkyne coordination, alkene/alkyne hydrosilylation, CO2 hydrosilylation to methane, transfer hydrogenation, and imine hydrogenation.
• A comparative study showed Mg[(nBu)3NB12H4Cl7]2 (2), with a more basic anion, exhibited lower Lewis acidity and reduced reactivity.

Conclusions:

• The novel Mg(II) dication stabilized by [HexCB11Cl11]- anions represents a significant advancement in magnesium chemistry.
• The complex exhibits versatile catalytic properties, driven by the balance of Mg electrophilicity and weak anion interactions.
• This work opens new avenues for utilizing magnesium complexes as efficient and tunable catalysts in organic synthesis.