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.

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.

Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. In this paper, we introduce a general method for the fabrication of metal sulfide nanoparticle/polymer films employing a low-cost and low temperature route compatible with large-scale device manufacturing. Our approach is based upon the controlled in situ thermal decomposition of a solution processable metal xanthate precursor complex in a semiconducting polymer film. To demonstrate the versatility of our method, we fabricate a CdS/P3HT nanocomposite film and show that the metal sulfide network inside the polymer film assists in the absorption of visible light and enables the achievement of high yields of charge photogeneration at the CdS/P3HT heterojunction. Photovoltaic devices based upon such nanocomposite films show solar light to electrical energy conversion efficiencies of 0.7% under full AM1.5 illumination and 1.2% under 10% incident power, demonstrating the potential of such nanocomposite films for low-cost photovoltaic devices.

Reaction of catalytic quantities of a β-diketiminato n-butylmagnesium complex with pinacol–borane in the presence of pyridine derivatives provides facile access to borylated dihydropyridines. The reaction is applicable to a wide range of monocyclic and fused-ring pyridine derivatives and catalytic turnover is proposed to occur through a well-defined sequence of Mg–H/pyridine dearomatization and Mg–N/B–H sigma bond metathesis steps.

The calcium-catalyzed intramolecular hydroamination of alkenes and alkynes is reported. The beta-diketiminato complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}-Ca{N(SiMe3)2}(THF)] affects catalytic cyclization of a range of aminoalkenes and aminoalkynes with activities that are broadly commensurate to those of established rare earth catalysts.

The -diketiminato complex [{HC(C(Me) 2 N-2,6-iPr 2 C 6 H 3 ) 2 }Ca{N(SiMe 3 ) 2 }(THF)] effects intermolecular hydrophosphination of a range of alkenes and alkynes. In behaVior reminiscent of lanthanocene(III) catalysis, a more electrophilic alkene is polymerized to phosphine-terminated macromolecules.Organophosphines, R 3 P, are an important class of compound widely employed in transition metal catalysis and organic synthesis. Hydrophosphination, the addition of the P-H bond of a primary or secondary phosphine to an unsaturated C-C bond, is a potentially powerful and, importantly, atom-efficient route to such compounds. 1 The transformation can be achieved under radical conditions or, alternatively, may be promoted by group 1, 2 late transition metal, 3 or lanthanide based catalysts. 4 On the basis of a proposed analogy between catalytic lanthanide and heavier group 2 metal centers, we have previously reported the -diketiminato-stabilized calcium amide 1 as an effective catalyst for the intramolecular hydroamination of aminoalkenes and aminoalkynes. 5 The reaction was postulated to occur by the generalized catalytic cycle outlined in Scheme 1, via (i) initiation of the precatalyst by a σ-bond metathesis (or protonolysis) of 1 with a primary amine to form a calcium primary amide, (ii) an intramolecular insertion of the alkene into the Ca-N bond, and (iii) the σ-bond metathesis of the resultant calcium alkyl with a further equivalent of amine to liberate the product and regenerate the active catalyst. On the basis of the numerous applications of lanthanide-based catalysts to the heterofunctionalization of unsaturated carboncarbon bonds, we speculated that the observed reactivity was not confined to the intramolecular hydroamination of alkenes and alkynes. Indeed, Harder has very recently shown that homoleptic benzyl alkaline earth complexes may act as precatalysts for the hydrosilylation of alkenes. 6 Lanthanocene catalysts of the form Cp* 2 LnX (X ) H, CH-(SiMe 3 ) 2 , Ln ) La, Sm, Y, Lu) have been applied to the intramolecular hydrophosphination/cyclization of a variety of phosphinoalkenes. 7 In this case, the reaction mechanism has been studied in depth and occurs via a pathway analogous to that depicted in Scheme 1. Both experimental and theoretical studies suggest that the σ-bond metathesis of the Ln-C bond of the intermediate is the rate-determining step (cf. Scheme 1, step iii). Furthermore, the intermolecular hydrophosphination of alkenes with such catalysts has not been achieved; rather, a lanthanocene phosphide mediated polymerization of ethylene has been reported. 8 Although divalent ytterbium catalysts have been applied to the intermolecular variant of this reaction, 4 the reaction mechanism in these cases is potentially complicated by reductive initiation.We now present a preliminary account of the application of 1 to the intermolecular hydrophosphination of unsaturated C-C bonds. In this regard it is noteworthy that limited evidence exists for both σ-bond metathesis and insertion steps requisi...

The heteroleptic magnesium alkyl complex [CH{C(Me)NAr}(2)Mg(n)Bu] (Ar = 2,6-(i)Pr(2)C(6)H(3)) is reported as a highly efficient pre-catalyst for the hydroboration of aldehydes and ketones with pinacolborane.

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.