No abstract

Keywords: Amides / CϪC coupling / Magnesium / Metalations / Metallacycles / Pyridyl ligands / Tin / ZincThe zincation of (2-pyridylmethyl)(triisopropylsilyl)amine (1) gives dimeric methylzinc (2-pyridylmethyl)(triisopropylsilyl)-amide (2). Further addition of dimethylzinc to a toluene solution of 2 at raised temperatures yields the C−C coupling product [1,2-dipyridyl-1,2-bis(triisopropylsilylamido)ethane]-bis(methylzinc) (3). Heating of molten 2, or UV irradiation of 2, results in the formation of 3 and zinc bis[(2-pyridylmethyl)-(triisopropylsilyl)amide] (4). The reaction between the zinc dihalide complexes of 1 [5a (X = Cl) and 5b (X = Br)] and methyllithium yields the C−C coupling product 3 and the heteroleptic complex 2, observed by NMR spectroscopy. During this reaction, zinc metal precipitates. The magnesiation of 1 with dibutylmagnesium gives magnesium bis[(2-pyridylmethyl)(triisopropylsilyl)amide] (6) in a quantitative yield. Subsequent addition of dimethylmagnesium results in a dismutation reaction and the formation of heteroleptic methylmagnesium (2-pyridylmethyl)(triisopropylsilyl)amide (7). Treatment of 1 with dimethylmagnesium also gives 7. This complex slowly undergoes an intramolecular metalation during which dark red single crystals of (tetrahydrofuran)-magnesium 2-(triisopropylsilylamidomethylidene)-1-azacyclohexa-3,5-dien-1-ide (8) precipitate. In this compound the aromaticity of the pyridyl fragment is abolished. The magnesiation of (tert-butyldimethylsilyl)(2-pyridylmethyl)amine (I) proceeds quantitatively to give methylmagnesium (tert-bu-

Red tetragallanediide Na 2 Ga 4 R* 4 •2THF was prepared by reduction of the monogallane R*GaCl 2 •THF in heptane or the tetrahedro-tetragallane R* 4 Ga 4 in benzene/tetrahydrofuran (THF) with sodium at 100 °C. Potassium worked analogously as a reduction agent. As an intermediate of the dehalogenation of R*GaCl 2 •THF, the orange digallane R* 2 Ga 2 Cl 2 and the dark violet tetrahedrane R* 4 Ga 4 were formed. The extreme air-and moisture-sensitive Na 2 Ga 4 R* 4 •2THF was stable against Me 3 SiCl, but reacted with oxygen under formation of R* 4 Ga 4 , and with GaBr under formation of sev-

No abstract

The equimolar reaction of calcium bis[bis(trimethylsilyl)amide] with 2,2,6,6‐tetramethylheptane‐3,5‐dione (Htmhd) in THF yields liquid mononuclear [Ca(tmhd){N(SiMe3)2}(THF)3] (1). A similar reaction in toluene with a stoichiometric ratio of 2:3 gives the dinuclear complex [{(THF)Ca}2(tmhd)2(µ‐tmhd){µ‐N(SiMe3)2}] (2). The calcium atoms of these complexes are in a distorted octahedral environment. In 2 the complex consists of two octahedra connected by a common face of one nitrogen base and two oxygen atoms; the bridging Ca−N bond lengths are extremely large. The metalation of the tetradentate Jacobsen reagent with calcium bis[bis(trimethylsilyl)amide] in 1,2‐dimethoxyethane (DME) gives the corresponding calcium complex 3, nearly quantitatively, as its DME adduct. The calcium atom is in an unusual trigonal prismatic coordination sphere. The metathesis reaction of 3 with tin(II) chloride yields the corresponding yellow tin(II) complex with the metal atom in a distorted square‐pyramidal environment. Complexes 2 and 3 show catalytic reactivity in the ring‐opening polymerization of cyclic esters such as lactones and lactides. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)