The lithiation of 2‐(aminomethyl)pyridine and the subsequent reaction with ClSiMe2tBu yields (tert‐butyldimethylsilyl)(2‐pyridylmethyl)amine (1). The metalation of 1 with dimethylzinc gives colorless dimeric methylzinc 2‐pyridylmethyl(tert‐butyldimethylsilyl)amide (2), which crystallizes in the triclinic space group P1¯. The solvent‐free thermal decomposition of 2 at 150 °C leads to the evolution of methane, the precipitation of zinc metal and the formation of amine 1, bis(methylzinc)—1,2‐dipyridyl‐1,2‐bis(tert‐butyldimethylsilylamido)ethane (3), and bis[(tert‐butyldimethylsilyl)(2‐pyridylmethyl)amido]zinc (4). Compound 3 can be obtained in good yield by reacting 2 with dimethylzinc at elevated temperatures in toluene. During this reaction, zinc metal precipitates and methane is evolved. The C−C coupling product 3 crystallizes in the tetragonal space group I41cd. The lithiation of 1 and the subsequent metathesis reaction with anhydrous ZnCl2 yields complex 4 almost quantitatively.
The weak neutral current (Z-boson exchange) [1][2][3] between electrons and nucleons (quarks) introduces a small energy difference (DE PV ) between enantiomers of a chiral molecule owing to parity violation (P-odd effects). [4,5] There have been several attempts to measure the parity-violation (PV) difference between enantiomers, [6][7] however, such effects are estimated to be of the order of a few millihertz [8][9][10] for currently known molecules, and several orders of magnitude too low for the present ability of high-resolution spectroscopy. Here we report relativistic calculations of PV effects for several chiral compounds that contain a heavy-metal center; shifts in DE PV of up to 4.8 10 À14 au (300 Hz) are recorded for such compounds as [(h 5 -C 5 H 5 )Re(CO)(NO)I], which can easily be prepared. The high DE PV value is an indication that future P-odd experiments for chiral molecules should be directed towards heavy-transition-metal complexes.Since the creation of the unified electroweak theory by Weinberg, Salam, and Glashow, the investigation of PV effects has become one of the most exciting areas in particle physics. [1][2][3] Precise measurements of PV in atoms are now accurate enough for the standard model to be tested successfully.[11] Electroweak theory also predicts a small energy difference (DE PV ) between pairs of enantiomers, and thus a breakdown of mirror-image symmetry. The search for such effects currently involves vibrational, [5,[12][13][14] NMR, [15,16] electronic, [17,18] and Mössbauer [6,19] spectroscopy, electric-field optical activity, [20] and preferred crystallization.[21] Most notably, Chardonnet and co-workers performed a saturation spectroscopy experiment for CHFClBr in the 9.3 mm spectral range using a tunable CO 2 laser that provided a spectral purity of 6 Hz. [12] They obtained Dn PV = n RÀ Àn S+ = 9.4 AE 5.1 AE 12.7 Hz between the two enantiomers, where the first value of uncertainty is derived from statistical error and the second is determined by systematic effects. More recently, the same group reduced these uncertainties and obtained Dn PV = À4.2 AE 0.6 AE 1.6 Hz.[22] Thus the search for the breakdown of mirror-image symmetry in chiral molecules remains one of the most challenging tasks in molecular chemistry and physics.It is a nontrivial issue to find chiral compounds suitable for high-resolution spectroscopic measurements of parity nonconservation effects.[23] P-odd effects scale approximately like Z n (n % 5; Z = nuclear charge of the atom), [24] which limits the choice to heavy-element-containing compounds. Furthermore, in accordance with the single-center theorem of Hegstroem, the substance should contain more than one heavy element (either as ligands or chiral centers).[25] A detailed analysis of P-odd effects, with respect to the environment around a center of chirality, has been given by Faglioni and Lazzeretti.[26] Very recently they also proposed the hypothetical molecule [BiHFX] (X = Br, I) as a suitable candidate with PV effects, with the Dn PV value of the i...
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-
The zincation of triisopropylsilylamine with dimethyl-and diethylzinc yields dimeric methylzinc (1) and ethylzinc triisopropylsilylamide (2). Complex 1 crystallizes in the monoclinic space group P2 1 /n, 2 in P2 1 /c. The reaction of dimethylzinc with adamantylamine gives [(THF)ZnMe][(AdNH 2 )ZnMe][m-N(H)Ad] 2 (3) which crystallizes in the monoclinic space group P2 1 /n. All these compounds have central Zn 2 N 2 cycles. Contrary to 1 and 2 with triply coordinated metal centers, the zinc atoms in 3 show a distorted tetrahedral coordination sphere due to the contact to the neutral coligands THF and adamantylamine.
The trinuclear title compound, C74H88Cl2N4P4- Si4Zn3, is derived from a geminally substituted carbdianion. The central zinc atom shows a nearly linear coordination geometry with very short Zn- C bond lengths (average 191 pm). The peripheral metal centers of the chlorozinc moieties are chelated by the phosphanimine donors and hence are triply coordinated, thus forming a six-membered CP2N2Zn ring with Zn-N distances of 195 pm (average).
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