Berylliant! Interaction of a well‐defined adduct of MeBeH and an N‐heterocyclic carbene (NHC) with PhSiH3 results in complete rupture of the heterocycle, and activation of the NHC through effective BeH2 insertion into a CN bond of the heterocycle (see scheme; Ar=2,6‐diisopropylphenyl, IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene).

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.

High-de-hydride! A straightforward reaction between a magnesium silylamido/N-heterocyclic carbene adduct and phenylsilane provides a {Mg(4)H(6)} cluster molecule that may be regarded as a combination of two magnesium dihydride and two magnesium monohydride moieties.

No abstract

Addition of the N-heterocyclic carbene (NHC), 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene (IPr), to equimolar quantities of group 1 and group 2 bis(trimethylsilyl)amides results in the isolation of charge separated species, [M(IPr)(2)](+)[M'{N(SiMe(3))(2)}(3)](-) (M = Li, Na, K; M' = Mg, Ca, Sr, Ba). Although these systems were found to be prone to the separation of oily, most likely liquid clathrate, materials, either slow cooling or careful diffusion of the less polar solvent hexane into toluene solutions yielded nine crystalline heterobimetallic complexes in which the coordination sphere of the cationic group 1 center was found by X-ray diffraction analysis to be provided by two IPr ligands. These derivatives are the first examples of any compounds in which coordination at the central alkali metal cation is provided exclusively by NHC ligands and, for the cases where M = Na, are the first instances of any type in which an NHC ligand is bound to sodium. The anionic group 2-containing component of each compound was found to comprise three bis(trimethylsilyl)amido ligands coordinated in an approximately trigonal array about the divalent metal center. The bonding within the unusual cationic components of the compounds has been investigated by density functional theoretical (DFT) methods. Natural Bond Orbital (NBO) analyses have revealed that the coordination is provided by donation of the sp-hydridized IPr lone pair into the valence s-orbital of the alkali metal cation and are consistent with weaker binding, and consequently more labile solution behavior, as group 1 is descended.