Jamie Hicks

Hydrogenation is among the most widely used transformations in chemical synthesis, yet it typically relies on precious transition-metal catalysts, pressurised hydrogen gas and an excess of solvents. Here we report a solvent-free, transition-metal-free hydrogenation method based on mixtures of simple, commercially available calcium salts (CaH ₂ with Ca(OH) ₂ or CaCO ₃ ). Under mechanochemical conditions, calcium hydride reacts with calcium hydroxide or carbonate to generate H ₂ in situ, eliminating the need for an external hydrogen source. The system efficiently hydrogenates alkenes, alkynes and aromatic hydrocarbons, including tetrasubstituted alkenes and benzene. Mechanistic studies support reversible hydrocalciation at the calcium hydride surface followed by irreversible hydrogenolysis with in situ generated H ₂ . The method was demonstrated to be general, with the hydrogenation of 16 examples proceeding with an average of 74% yield, providing a safe, cheap and practical alternative to transition metal-catalysed hydrogenation of carbon-carbon multiple bonds.

Taking oxygen-free chemistry to the next level: the O -deletion reaction of diamidoarylether ligands coordinated to boron or aluminium is presented, affording 4,5-diaminofluorene compounds on a gram scale.

Anionic calcium alkyl complexes have been synthesised through the reduction of ethylene by an anionic calcium hydride. The alkyl complexes are demonstrated to be superbasic, rapidly deprotonating ethers below room temperature, leading to C─O bond cleavage. In reactions with benzene, selective 1,4‐metalation of benzene is observed, forming an inverse‐crown areneide complex. This transformation, previously inaccessible to calcium, proceeds via a stepwise mechanism, which can also be facilitated by co‐complexation with organometallic reagents such as tert ‐butyllithium and phenylpotassium.

Anionic calcium alkyl complexes have been synthesised through the reduction of ethylene by an anionic calcium hydride. The alkyl complexes are demonstrated to be superbasic, rapidly deprotonating ethers below room temperature, leading to C─O bond cleavage. In reactions with benzene, selective 1,4‐metalation of benzene is observed, forming an inverse‐crown areneide complex. This transformation, previously inaccessible to calcium, proceeds via a stepwise mechanism, which can also be facilitated by co‐complexation with organometallic reagents such as tert ‐butyllithium and phenylpotassium.

A highly nucleophilic aluminium( i ) anion is reported, showing exceptional reactivity and selectivity towards the C–H activation of arenes.

Benzene reduction by molecular complexes remains an important synthetic challenge, requiring harsh reaction conditions involving group I metals. Reductions of benzene, to date, typically result in a loss of aromaticity, although the benzene tetra-anion, a 10π-electron system, has been calculated to be stable and aromatic. Due to the lack of sufficiently potent reductants, four-electron reduction of benzene usually requires the use of group I metals. Here we demonstrate the four-electron reduction of benzene and some of its derivatives using a samarium(ii) alkyl reagent, with no requirement for group I metals. Whereas organosamarium(ii) typically reacts through one-electron processes, the compounds reported here feature a rare two-electron process. Combined experimental and computational results implicate a transient samarium(i) intermediate involved in this reduction process, which ultimately provides the benzene tetra-anion. The remarkably strong reducing power of this samarium(ii) alkyl implies a rich reactivity, providing scope for its application as a reducing agent.

A series of iron aluminyl complexes have been synthesised in good crystalline yields from reactions between bulky diamido aluminium iodide complexes and K[Fe(CO)₂Cp] in the solid state. The series of metal–metal bonded complexes have been characterised by X-ray crystallography and were investigated using density functional theory to probe the effects of ligand substitution on the Al–Fe bond.

The hypercoordinate [SiH₆]²⁻ anion is not stable in solution. Here, we report the room temperature, solution stable molecular [SiH₆]²⁻ complex, [{KCa(NON)(OEt₂)}₂][SiH₆] (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene)), where the [SiH₆]²⁻ anion is stabilised within a supramolecular assembly that mimics the solid‐state environment of the anion in the lattice of K₂SiH₆. Solution‐state reactivity of the complex towards carbon monoxide, benzaldehyde, azobenzene and acetonitrile is reported, yielding a range of reduction and C−C coupled products.

Using a flexible diamido framework, a bulky boron bromide has been prepared as a precusor to a boryl anion with an extremely wide N–B–N angle. Reduction of the compound with lithium metal resulted in intramolecular C–N bond activation and migration of an aryl group onto the boron centre. Reaction of the boron bromide with K[FeCp(CO)₂] resulted in nucleophilic reactivity of a carbonyl oxygen and the cooperative activation of CO.