Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Abstract

In this perspective, we highlight the recent development of metallation protocols of non-polar unsaturated molecules for the generation of organo-alkaline earth metal compounds and their applications in chemical synthesis and catalysis.

Constrained Geometry ansa‐Half‐Sandwich Complexes of Magnesium – Versatile s‐Block Catalysts

“…In general, hydroelementation reactions are of great interest for a variety of reasons, including the synthetically straight forward possibility to incorporate functional group across different unsaturated chemical bonds, combined with their high atom economy. One of the most popular hydroelementation reactions are hydroborations, for which different magnesium‐based catalysts have been reported in the past [14,33–38] . Accordingly, we probed the possibility of using ansa ‐half‐sandwich complexes 1 a – d as catalysts for hydroboration reactions of alkynes, nitriles and imines with pinacolborane (Scheme 4; Table 3).…”

“…One of the most popular hydroelementation reactions are hydroborations, for which different magnesium-based catalysts have been reported in the past. [14,[33][34][35][36][37][38] Accordingly, we probed the possibility of using ansa-half-sandwich complexes 1 a-d as catalysts for hydroboration reactions of alkynes, nitriles and imines with pinacolborane (Scheme 4; Table 3).…”

“…[25,[30][31][32] Furthermore, magnesium-based catalysts have also been employed in hydroelementation reactions, pioneered by the groups of Hill, Harder, Sadow and others. [15,33] For example, magnesiumcatalyzed hydroborations are a well-established area [14,[33][34][35][36][37][38] as is the important reaction type of hydroamination, such as intramolecular ring-closing hydroamination for the preparation of Nheterocycles. [13,[39][40][41][42][43][44][45][46][47] Furthermore, interest in atom-economical CÀ C bond formation in organic chemistry has increased.…”

Generation of Allylmagnesium Reagents by Hydromagnesiation of 2‐Aryl‐1,3‐dienes

“…Semi‐hydrogenation of 1,3‐dienes via hydrometallation by a molecular calcium hydride [6] or a potassium hydride‐magnesium amide system [7] under pressurized hydrogen atmosphere was reported. We recently disclosed unique hydridic reactivity of magnesium hydride (MgH 2 ) that can be generated in situ by counter ion metathesis between sodium hydride (NaH) and magnesium iodide (MgI 2 ) in tetrahydrofuran (THF), toward non‐polar π‐conjugate systems such as arylalkynes and 1,3‐enynes [8–10] . For example, regioselective hydromagnesiation of 1,3‐enynes is promoted to generate allenyl/propargylmagnesium species (Scheme 1B).…”

Regioselective C–H Alkylation of Aromatic Ethers with Alkenes by a Half-Sandwich Calcium Catalyst

“…Recently, calcium-based efficient catalysts have been intrigued by many scientists as they can be used in a variety of organic transformations to replace the expensive transition metal catalysts, mainly due to their earth-abundant, nontoxic, environmentally benign, and biocompatible nature. Molecular calcium alkyl complexes have served as precatalysts in a wide range of catalytic reactions including hydrogenation, hydrofunctionalization, and dehydrogenative couplings but have not been applied to the catalytic C–H alkylation of arenes.…”