The synthesis and structure of [Zn(TEMPO)2]2 and [Zn(µ-H)(µ(2)-η(1):η(1)-TEMPO)]6.

The commercially available radical TEMPO (2,2,6,6-tetramethylpiperidin-1-yloxy) reacts with [ZnCp*2] (1) to yield the homoleptic compound [Zn(TEMPO)2]2 (2) through coupling of two Cp* radicals. Compound 1 reacts with H2 to afford the hydride complex [Zn(µ-H)(µ(2)-η(1)-η(1)-TEMPO)]6 (3) featuring a planar Zn6H6 ring in the solid state. Preliminary data suggest that the formation of 3 proceeds via a radical mechanism.

Zincocene and dizincocene N-heterocyclic carbene complexes and catalytic hydrogenation of imines and ketones.

The N-heterocyclic carbene (NHC) adducts Zn(Cp(R))(2) (NHC)] (Cp(R) =C(5)HMe(4), C(5)H(4) SiMe(3); NHC=ItBu, IDipp (Dipp=2,6-diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*(2)] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh(2))(2) (aItBu)](2) was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated Zn(I) adducts [Zn(2)Cp*(2) (NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of (13)C NMR spectroscopic and X-ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp*(2)] with H(2) to give [Zn(2)Cp*(2)] is discussed.

Allyl strontium compounds: synthesis, molecular structure and properties.

The synthesis and attempted isolation of neutral bis(allyl)strontium [Sr(C(3)H(5))(2)] (1) resulted in the isolation of potassium tris(allyl)strontiate K[Sr(C(3)H(5))(3)] (2). In situ generated 1 shows a pronounced Brønsted basicity, inducing polymerisation of THF. Ate complex 2 crystallises as [K(THF)(2){Sr(C(3)H(5))(3)}(THF)](∞) (2·(THF)(3)). The salt-like solid state structure of 2·(THF)(3) comprises a two-dimensional network of (µ(2)-η(3):η(3)-C(3)H(5))(-) bridged potassium and strontium centres. Synthesis of allyl complexes 1 and 2 utilised SrI(2), [Sr(TMDS)(2)] (3) (TMDS = tetramethyldisilazanide), and [Sr(HMDS)(2)] (HMDS = hexamethyldisilazanide) as strontium precursors. The solid state structure of previously reported [Sr(TMDS)(2)] (3) was established by X-ray single crystal analysis as a dissymmetric dimer of [Sr(2)(TMDS)(4)(THF)(3)] (3·(THF)(3)) with multiple Si-HSr agostic interactions. The presence of ether ligands (THF, 18-crown-6) influenced the Si-HSr resonances in the NMR spectra of the amido complex 3.

Calcium-mediated dearomatization, C-H bond activation, and allylation of alkylated and benzannulated pyridine derivatives.

A facile and general synthetic pathway for the production of dearomatized, allylated, and C-H bond activated pyridine derivatives is presented. Reaction of the corresponding derivative with the previously reported reagent bis(allyl)calcium, [Ca(C(3)H(5))(2)] (1), cleanly affords the product in high yield. The range of N-heterocyclic compounds studied comprised 2-picoline (2), 4-picoline (3), 2,6-lutidine (4), 4-tert-butylpyridine (5), 2,2'-bipyridine (6), acridine (7), quinoline (8), and isoquinoline (9). Depending on the substitution pattern of the pyridine derivative, either carbometalation or C-H bond activation products are obtained. In the absence of methyl groups ortho or para to the nitrogen atom, carbometalation leads to dearomatized products. C(sp(3))-H bond activation occurs at ortho and para situated methyl groups. Steric shielding of the 4-position in pyridine yields the ring-metalated product through C(sp(2))-H bond activation instead. The isolated compounds [Ca(2-CH(2)-C(5)H(4)N)(2)(THF)] (2b⋅(THF)), [Ca(4-CH(2)-C(5)H(4)N)(2)(THF)(2)] (3b⋅(THF)(2)), [Ca(2-CH(2)-C(5)H(3)N-6-CH(3))(2)(THF)(n)] (4b⋅(THF)(n); n=0, 0.75), [Ca{2-C(5)H(3)N-4-C(CH(3))(3)}(2)(THF)(2)] (5c⋅(THF)(2)), [Ca{4,4'-(C(3)H(5))(2)-(C(10)H(8)N(2))}(THF)] (6a⋅(THF)), [Ca(NC(13) H(9)-9-C(3)H(5))(2)(THF)] (7a⋅(THF)), [Ca(4-C(3) H(5)-C(9) H(7)N)(2)(THF)] (8b⋅(THF)), and [Ca(1-C(3)H(5)-C(9)H(7) N)(2)(THF)(3)] (9a⋅(THF)(3)) have been characterized by NMR spectroscopy and metal analysis. 9a⋅(THF)(4) and 4b⋅(THF)(3) were additionally characterized in the solid state by X-ray diffraction experiments. 4b⋅(THF)(3) shows an aza-allyl coordination mode in the solid state. Based on the results, mechanistic aspects are discussed in the context of previous findings.