Atom-economic access to cationic magnesium complexes

Cationic alkaline-earth complexes attract interest for their enhanced Lewis acidity and reactivity compared with their neutral counterparts. Synthetic protocols to these complexes generally utilize expensive specialized reagents in reactions generating multiple by-products. We have studied a simple ligand transfer approach to these complexes using (NacNac)MgR and ER3 (NacNac = β-diketiminate anion; E = group 13 element; R = aryl/amido anion) which demonstrates high atom economy, opening up the ability to target these species in a more sustainable manner. The success of this methodology is dependent on the identity of the group 13 element with the heavier elements facilitating faster ligand exchange. Furthermore, while this reaction is successful with aromatic ligands such as phenyl and pyrrolyl, the secondary amide piperidide (pip) fails to transfer, which we attribute to the stronger 3-centre-4-electron dimerization interaction of Al2(pip)6

Atom-efficient synthesis of a benchmark electrolyte for magnesium battery applications

The benchmark magnesium electrolyte, [Mg2Cl3]+ [AlPh4]−, can be prepared in a 100% atom-economic fashion by a ligand exchange reaction between AlCl3 and two molar equivalents of MgPh2. NMR and vibrational spectroscopy indicate that the reported approach results in a simpler ionic composition than the more widely adopted synthesis route of combining PhMgCl with AlCl3. Electrochemical performance has been validated by polarisation tests and cyclic voltammetry, which demonstrate excellent stability of electrolytes produced via this atom-efficient approach

New developments in main group chemistry for application in modern battery technology

The first results chapter discusses results unrelated to magnesium batteries, however, the techniques used were similar to those utilised in other results chapter. Arylmethyl anions allow alkali-metals to bind in a σ-fashion to the lateral carbanionic centre or a π-fashion to the aryl ring or in between these extremities, with the trend towards π bonding increasing on descending group 1. Here we review known alkali metal structures of diphenylmethane, fluorene, 2-benzylpyridine and 4-benzylpyridine. Next, we synthesise Li, Na, K monomers of these diarylmethyls using polydentate donors PMDETA or Me6TREN to remove competing oligomerizing interactions, studying the effect that two aromatic rings has on negative charge (de)localisation via NMR spectroscopy, X-ray crystallographic analysis and DFT studies. For magnesium batteries, the ‘All Phenyl Complex’ (APC) has been shown to be one of the foremost electrolyte complexes, with the active species considered to be [Mg2Cl3·6THF]+[AlPh4]-. Originally synthesised through the reaction of PhMgCl and AlCl3 in THF, this hasshown to be a low atom economic route and instead an alternative method of combining Ph2Mg and half an equivalent of AlCl3 has been shown to yield the same active species but with a higher atom economy. Based on this knowledge, a range of R2Mg species have been developed and further reacted with AlCl3 to produce an array of [Mg2Cl3·6THF]+[AlR4]- complexes which could potentially be superior electrolytes. These have been analysed through X-ray crystallography and NMR spectroscopy and have been tested electrochemically, with DFT calculations also performed where appropriate.The first results chapter discusses results unrelated to magnesium batteries, however, the techniques used were similar to those utilised in other results chapter. Arylmethyl anions allow alkali-metals to bind in a σ-fashion to the lateral carbanionic centre or a π-fashion to the aryl ring or in between these extremities, with the trend towards π bonding increasing on descending group 1. Here we review known alkali metal structures of diphenylmethane, fluorene, 2-benzylpyridine and 4-benzylpyridine. Next, we synthesise Li, Na, K monomers of these diarylmethyls using polydentate donors PMDETA or Me6TREN to remove competing oligomerizing interactions, studying the effect that two aromatic rings has on negative charge (de)localisation via NMR spectroscopy, X-ray crystallographic analysis and DFT studies. For magnesium batteries, the ‘All Phenyl Complex’ (APC) has been shown to be one of the foremost electrolyte complexes, with the active species considered to be [Mg2Cl3·6THF]+[AlPh4]-. Originally synthesised through the reaction of PhMgCl and AlCl3 in THF, this hasshown to be a low atom economic route and instead an alternative method of combining Ph2Mg and half an equivalent of AlCl3 has been shown to yield the same active species but with a higher atom economy. Based on this knowledge, a range of R2Mg species have been developed and further reacted with AlCl3 to produce an array of [Mg2Cl3·6THF]+[AlR4]- complexes which could potentially be superior electrolytes. These have been analysed through X-ray crystallography and NMR spectroscopy and have been tested electrochemically, with DFT calculations also performed where appropriate

Sigma/pi bonding preferences of solvated alkali-metal cations to ditopic arylmethyl anions

Arylmethyl anions allow alkali-metals to bind in a σ-fashion to the lateral carbanionic centre or a π-fashion to the aryl ring or in between these extremities, with the trend towards π bonding increasing on descending group 1. Here we review known alkali metal structures of diphenylmethane, fluorene, 2-benzylpyridine and 4-benzylpyridine. Next, we synthesise Li, Na, K monomers of these diarylmethyls using polydentate donors PMDETA or Me 6TREN to remove competing oligomerizing interactions, studying the effect that two aromatic rings has on negative charge (de)localisation via NMR, X-ray crystallographic and DFT studies. Diphenylmethyl and fluorenyl anions maintain C(H)−M interactions regardless of alkali-metal, although the adjacent arene carbons engage in interactions with larger alkali-metals. Introducing a nitrogen atom into the ring (at the 2- or 4-position) encourages relocalisation of negative charge away from the deprotonated carbon and onto nitrogen. Phenyl(2-pyridyl)methyl moves from an enamide formation at one extremity (lithium) to an aza-allyl formation at the other extremity (potassium), while C- or N-coordination modes become energetically viable for Na and K phenyl(4-pyridyl)methyl complexes