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The past decade has witnessed some remarkable advances in our appreciation of the structural and reaction chemistry of the heavier alkaline earth (Ae = Mg, Ca, Sr, Ba) elements. Derived from complexes of these metals in their immutable +2 oxidation state, a broad and widely applicable catalytic chemistry has also emerged, driven by considerations of cost and inherent low toxicity. The considerable adjustments incurred to ionic radius and resultant cation charge density also provide reactivity with significant mechanistic and kinetic variability as group 2 is descended. In an attempt to place these advances in the broader context of contemporary main group element chemistry, this review focusses on the developing state of the art in both multiple bond heterofunctionalisation and cross coupling catalysis. We review specific advances in alkene and alkyne hydroamination and hydrophosphination catalysis and related extensions of this reactivity that allow the synthesis of a wide variety of acyclic and heterocyclic small molecules. The use of heavier alkaline earth hydride derivatives as pre-catalysts and intermediates in multiple bond hydrogenation, hydrosilylation and hydroboration is also described along with the emergence of these and related reagents in a variety of dehydrocoupling processes that allow that facile catalytic construction of Si-C, Si-N and B-N bonds.

Magnesium and calcium hydrido-tris(pentafluorophenyl)borate derivatives catalyse the completely selective reductive hydroboration of CO2 with pinacolborane (HBpin) to provide the methanol equivalent, CH3OBpin.

Both homo- and heteroleptic alkyl and amide complexes of the Group 2 elements Mg and Ca are shown to be active for the catalytic dehydrocoupling of Me(2)NH.BH(3). Reactions of either magnesium dialkyls or the beta-diketiminate complex [HC{(Me)CN(Dipp)}(2)MgnBu] with four or two equivalents of Me(2)NHBH(3), respectively, produce compounds containing the [H(3)BNMe(2)BH(2)Me(2)N](-) ion, which coordinates to the magnesium centers through Mg-N and Mg...HB interactions in both the solution and solid states. Thermolysis of these compounds at 60 degrees C produces the cyclic product [(H(2)BNMe(2))(2)] and, it is proposed, magnesium hydrido species by an unprecedented delta-hydride elimination process. Calcium-based species, although less reactive than their magnesium-based counterparts, are found to engage in similar dehydrocoupling reactivity and to produce a similar distribution of products under thermally promoted catalytic conditions. A mechanism for these observations is presented that involves initial production and insertion of H(2)B=NMe(2) into polarized M-N bonds as the major B-N bond-forming step. The efficacy of this insertion and subsequent beta- or delta-hydride elimination steps is proposed to be dependent upon the charge density and polarizing capability of the participating Group 2 center, providing a rationale for the observed differences in reactivity between magnesium and calcium.

A β-diketiminato n-butylmagnesium complex is presented as a selective precatalyst for the reductive hydroboration of organic nitriles with pinacolborane (HBpin).

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This article provides a comprehensive overview of piezo-and ferro-electric materials based on organic molecules and organic-inorganic hybrids for mechanical energy harvesting. Molecular (organic and organic-inorganic hybrid) piezo-and ferroelectric materials exhibit significant advantages over traditional materials due to their simple solution-phase synthesis, light-weight nature, thermal stability, mechanical flexibility, high Curie temperature, and attractive piezo-and ferroelectric properties. However, the design and understanding of piezo-and ferroelectricity in organic and organic-inorganic hybrid materials for piezoelectric energy harvesting applications is less well developed. This review describes the fundamental characterization of piezo-and ferroelectricity for a range of recently reported organic and organic-inorganic hybrid materials. The limits of traditional piezoelectric harvesting materials are outlined, followed by an overview of the piezo-and ferroelectric properties of organic and organic-inorganic hybrid materials, and their composites, for mechanical energy harvesting. An extensive description of peptide-based and other biomolecular piezo-and ferroelectric materials as a biofriendly alternative to current materials is also provided. Finally, current limitations and future perspectives in this emerging area of research are highlighted. This perspective aims to guide chemists, materials scientists, and engineers in the design of practically useful organic and organic-inorganic hybrid piezo-and ferroelectric materials and composites for mechanical energy harvesting.

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.