The electrophilic aromatic substitution of a C-H bond of benzene is one of the archetypal transformations of organic chemistry. In contrast, the electron-rich π-system of benzene is highly resistant to reactions with electron-rich and negatively charged organic nucleophiles. Here, we report that this previously insurmountable electronic repulsion may be overcome through the use of sufficiently potent organocalcium nucleophiles. Calcium -alkyl derivatives-synthesized by reaction of ethene, but-1-ene, and hex-1-ene with a dimeric calcium hydride-react with protio and deutero benzene at 60°C through nucleophilic substitution of an aromatic C-D/H bond. These reactions produce thealkyl benzenes with regeneration of the calcium hydride. Density functional theory calculations implicate an unstabilized Meisenheimer complex in the C-H activation transition state.

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12−16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

A seven‐membered N,N′‐heterocyclic potassium alumanyl nucleophile is introduced and utilised in the metathetical synthesis of Mg−Al and Ca−Al bonded derivatives. Both species have been characterised by experimental and theoretical means, allowing a rationalisation of the greater reactivity of the heavier group 2 species implied by an initial assay of their reactivity.

Abstractβ‐Diketiminato (BDI) calcium alkyl derivatives undergo hydrogenolysis with H2 to regenerate [(BDI)CaH]2, allowing the catalytic hydrogenation of a wide range of 1‐alkenes and norbornene under very mild conditions (2 bar H2, 298 K). The reactions are deduced to take place with the retention of the dimeric structures of the calcium hydrido‐alkyl and alkyl intermediates via a well‐defined sequence of Ca−H/C=C insertion and Ca−C hydrogenation events. This latter deduction is strongly supported by DFT calculations (B3PW91) performed on the 1‐hexene/H2 system, which also indicates that the hydrogenation transition states display features which discriminate them from a classical σ‐bond metathesis mechanism. In particular, NBO analysis identifies a strong second order interaction between the filled α‐methylene sp3 orbital of the n‐hexyl chain and the σ* orbital of the H2 molecule, signifying that the H−H bond is broken by what is effectively the nucleophilic displacement of hydride by the organic substituent.

Dehydrocoupling reactions between the boranes HBpin and 9-borabicyclo[3.3.1]nonane and a range of amines and anilines ensue under very mild reaction conditions in the presence of a simple β-diketiminato magnesium n-butyl precatalyst. The facility of the reactions is suggested to be a function of the Lewis acidity of the borane substrate, and is dictated by resultant pre-equilibria between, and the relative stability of, magnesium hydride and borohydride intermediates during the course of the catalysis.