Organomagnesium chemistry
[13] Although Grignard reagents were discovered and commonly used in 1900s, the corresponding fluoride RMgF was not synthesized until 1970, plausibly because of the difficulty in breaking the strong C-F bond.
[16][17] Grignard reagents forms dimers in solutions, and the R and X groups are exchanged between magnesium centers, enabling the Schlenk equilibrium between RMgX and MgR2 and MgX2.
Recent ab initio molecular dynamics computations[18][19] have shown that the formation of such dimers is crucial for explaining the reactivity of Grignard reagents.
[27][28] Unlike beryllium,[30][31] calcium, strontium, and barium,[32] no homoleptic carbonyl complex of magnesium has been found, probably because it lacks available (n-1)d orbitals, and it has low covalency.
However, [Mg(O3)2(CO)2] which contains ozonide anion (O3−) was identified when condensing atomic magnesium, oxygen and carbon monoxide in solid argon matrix.
[29] The compound shows increased C-O stretching frequency at 2188.9 cm−1, compared to free carbon monoxide (2143 cm−1), indicating little back-bonding from magnesium to the carbonyl.
[36] Since NHCs are better σ donors than ethers like THF,[37] it provides a scaffold for cationic molecular magnesium complexes, for it is categorized as neutral L-type ligand.
In 2019, Dagorne and co-workers reported the first cationic alkyl magnesium supported by NHC ligand, [LMgMe(THF)2]+ BPh4− (L = IMes, IPr).
[48] Dicyclopentadienyl (Cp) magnesium or magnesocene (Cp2Mg) was first characterized in 1954 by Wilkinson and Cotton,[50] and later crystal structure analysis[51][52] shows that it features a 5-fold symmetry with two η5-cyclopentadienyl ligands.
[55] However, because of lacking (n-1)d orbitals and back bonding,[56] the Mg-Cp interaction is weak, enabling cyclopentadienyl magnesium complexes to serve as Cp− precursor.
[69] In [(Dipp-NacNac)Mg(H2C=CEt2)][B(C6F5)4], Mg is closer to the terminal methylene with Mg-C distance of 2.338(2) Å, and the longer Mg-C distance is 2.944(5) Å. DFT calculations and AIM analysis[64][69][70] suggested that the Mg-alkene interaction is less covalent and should be mainly described as ion-induced dipole interactions, and the large asymmetry in the 2-ethylbutene complex should be attributed to charge distribution on the two sp2 carbon atoms.
The slightly longer Mg-C distance compared to Cp2Mg indicates a weaker donor ability of the boratabenzene, likely due to a more dispersed electron density among six instead of five atoms.
The luminescence properties of magnesium compounds have been studied since the pioneering work by Chandrasekhar and co-workers in 2005, where a phosphorus-based tris-hydrazone complex of Mg(II) was synthesized and determined to have an intense fluorescence emission peak at 442 nm in dichloromethane solution.
[72] In 2018, Roesky and co-workers developed a diamidophosphine ligand, with the ligated dimagnesium(II) compound having a fluorescence quantum yield of 34% in the solution.
[78] The first molecular Mg(I) compound, which contains a Mg-Mg bond, was synthesized by Jones, Stasch, and co-workers in 2007, from potassium metal reduction of Nacnac or priso ligand supported magnesium halide.
The first Mg(0) compound was reported in 2021 by Harder and co-workers, by reducing a similar Nacnac chelated in a harsher condition using newly prepared Na/NaCl.
