Pathway to a molecular calcium methyl

The dimeric β-diketiminato calcium hydride, [(BDI)CaH]2 (BDI = HC{(Me)CN-2,6-iPr2C6H3}2), reacts with ZnMe2 to afford the bimetallic calcium zincate complex, [(BDI)Ca(μ-CH3)2Zn(μ-H)]2, which subsequently undergoes an intramolecular reaction to effect the formation of [(BDI)CaMe]2, a notable omission from the homologous series of β-diketiminato alkylcalcium derivatives.

From alkaline earth to coinage metal carboranyls

The β-diketiminato calcium and magnesium complexes, [(BDI)MgnBu] and [(BDI)CaH]2 (BDI = HC{C(Me)NDipp}2; Dipp = 2,6-di-isopropylphenyl), react with ortho-carborane (o-C2B10H12) to provide the respective [(BDI)Ae(o-C2B10H11)] (Ae = Mg or Ca) complexes. While the lighter group 2 species is a monomer with magnesium in a distorted trigonal planar environment, the heavier analogue displays a puckered geometry at calcium in the solid state due to Ca⋯H-B intermolecular interactions. These secondary contacts are, however, readily disrupted upon addition of THF to provide the 4-coordinate monomer, [(BDI)Ca(THF)(o-C2B10H11)]. [(BDI)Mg(o-C2B10H11)] was reacted with [NHCIPrMCl] (NHCIPr = 1,3-bis(isopropyl)imidazol-2-ylidene; M = Cu, Ag, Au) to provide [NHCIPrM(o-C2B10H11)], rare C-bonded examples of coinage metal derivatives of unsubstituted (o-C2B10H11)- and confirming the alkaline earth compounds as viable reagents for the transmetalation of the carboranyl anion.

Molecular Main Group Metal Hydrides

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.

Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl

Although the nucleophilic alkylation of aromatics has recently been achieved with a variety of potent main group reagents, all of this reactivity is limited to a stoichiometric regime. We now report that the ytterbium(II) hydride, [BDIDippYbH]2 (BDIDipp = CH[C(CH3)NDipp]2, Dipp = 2,6-diisopropylphenyl), reacts with ethene and propene to provide the ytterbium(II) n-alkyls, [BDIDippYbR]2 (R = Et or Pr), both of which alkylate benzene at room temperature. Density functional theory (DFT) calculations indicate that this latter process operates through the nucleophilic (SN2) displacement of hydride, while the resultant regeneration of [BDIDippYbH]2 facilitates further reaction with ethene or propene and enables the direct catalytic (anti-Markovnikov) hydroarylation of both alkenes with a benzene C-H bond.

Organocalcium-mediated nucleophilic alkylation of benzene

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 n-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 the n-alkyl benzenes with regeneration of the calcium hydride. Density functional theory calculations implicate an unstabilized Meisenheimer complex in the C-H activation transition state.

β-Diketiminate calcium hydride complexes: the importance of solvent effects

A series of (DIPPnacnac)CaN(SiMe₃)₂·S complexes (DIPPnacnac = HC[C(Me)N(2,6-iPr-C₆H₃)]₂; S = solvent) could be obtained by the addition of S = THF, DME or N-Me-morpholine (Morph) to (DIPPnacnac)CaN(SiMe₃)₂·OEt₂ or (DIPPnacnac)CaN(SiMe₃)₂. Crystal structures for complexes with S = DME and Morph are compared to literature-known structures with S = none, THF or Et₂O. Bulkier and weaker Lewis bases like the tertiary amines Et₃N, TMEDA and DABCO did not interact with (DIPPnacnac)CaN(SiMe₃)₂. The reaction of (DIPPnacnac)CaN(SiMe₃)₂ with PhSiH₃ gave conversion to a calcium hydride complex that dismutated in (DIPPnacnac)₂Ca and CaH₂. The reaction of (DIPPnacnac)CaN(SiMe₃)₂·S with PhSiH₃ gave [(DIPPnacnac)CaH·S]₂ for S = THF, Et₂O or N-Me-morpholine (Morph). For S = DME, high reaction temperatures were needed and dismutation into (DIPPnacnac)₂Ca and CaH₂ was observed. Extensive NMR investigations (VT-NMR and PGSE) confirm the dimeric nature of [(DIPPnacnac)CaH·THF]₂ in aromatic solvents or in THF. Thermal decomposition of [(DIPPnacnac)CaH·THF]₂ (release of H₂ at 200 °C) is compared to that of Mg and Zn analogues. Weakly coordinating Et₂O in [(DIPPnacnac)CaH·OEt₂]₂ could be replaced by THF, Morph or DABCO but not with Et₃N. The addition of TMEDA led to the formation of CaH₂ and unidentified products. The addition of DME led to the decomposition of Et₂O and complex [(DIPPnacnac)CaOEt]₂ was obtained. Crystal structures of the following compounds are presented: (DIPPnacnac)CaN(SiMe₃)₂·S (S = Morph, DME), [(DIPPnacnac)CaH·S]₂ (S = Et₂O, Morph and DABCO) and [(DIPPnacnac)CaOEt]₂. Although bulky ligands have long been thought to be the key to the stabilization of calcium hydride complexes, the presence of a polar, strongly coordinating, co-solvent is also crucial.

Coordination of arenes and phosphines by charge separated alkaline earth cations

Generation of ‘naked’ β-diketiminato magnesium and calcium cations allows the isolation of benzene, toluene, 1,4-difluorobenzene and terminal phosphine adducts.

Synthesis, characterization and catalytic activity of rare-earth metal amides incorporating cyclohexyl bridged bis(β-diketiminato) ligands

The bridged bis(β-diketiminato) ligands supported rare-earth amides exhibited high catalytic activity towards the hydrophosphination of β-nitroalkene and α,β-unsaturated carbonyl derivatives with an excellent regioselectivity.