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Dehydrogenation of LGeH by a Lewis N-Heterocyclic Carbene Borane Pair under the Formation of L ' Ge and its Reactions with B(C6F5)(3) and Trimethylsilyl Diazomethane: An Unprecedented Rearrangement of a Diazocompound to an Isonitrile
No full textHerein we report the dehydrogenation of LGeH (1) [L = CH{(CMe)(2,6-IPr2C6H3N)}(2)] by a frustrated Lewis NHC borane pair under the formation of an imidazolium borate salt (2) and the heterocyclic germylene L'Ge (3) [L' = CH{(C=CH2)(CMe)(2,6-IPr2C6H3N)(2)}]. The reaction of 3 with B(C6F5)(3) in toluene results in the formation of a zwitterion containing a germylene moiety, [B(C6F5)(3)L '' Ge] (4) [L '' = CH{(CCH2)(CMe)(2,6-iPr(2)C(6)H(3)N)(2)}], Subsequent treatment of 4 with 1 equiv of 1,3-di-tert-butylimidazol-2-ylidene (NHC) gives B(C6F5)(3)L"'Ge (5) [L"' = CH{(C=CH2)(CCH2B(C6F5)(3))(2,6-IPr2C6H3N)(2)}] under formation of the imidazolium cation, Moreover compound 3 reacts with trimethylsilyl diazomethane (N2CHSiMe3) to form the diazogermylene LGeC(N-2)SiMe3 (6) under C-H bond cleavage. Compound 6 slowly rearranges to the isonitriletrimethylsilyl germanium(II) amide LGeN(SiMe3)NC (6a). All compounds were characterized by microanalysis and multinuclear NMR spectroscopy. Compounds 4, 6, and 6a were unequivocally identified by single crystal X-ray structure analysis.Deutsche Forschungsgemeinschaf
Cleavage of a N-H Bond of Ammonia at Room Temperature by a Germylene
No full textThe reaction of LGeCl [1; L = CH{(CMe)(2,6-(i)Pr(2)C(6)H(3)N)}(2)] with 1,3-di-tert-butylimidazol-2-ylidene results in the formation of the germylene L'Ge [2; L' = CH{(C=CH(2))(CMe)(2,6-(i)Pr(2)C(6)H(3)N)(2)}]. 2 reacts with ammonia under N-H cleavage to give LGeNH(2) (3). This type of reaction can also be used to activate primary amines. 3 is characterized by microanalysis, multinuclear NMR spectroscopy, and X-ray structural analysis. The single-crystal X-ray structural analysis indicates 3 to be a monomer, and the germanium atom shows a trigonal-pyramidal environment with a stereochemically active lone pair.Deutsche Forschungsgemeinschaft; Gottinger Akademie der Wissenschafte
Transition metal complexes containing the S(NtBu)(4)(2-) tetraimidosulfate dianion
No full textThree novel metal complexes [(acac)(2)Cu-2(NtBu)(4)S] (3), (Li(thf)(4)](2)(I4Cd2(NtBu)(4)S] (4) and Rthf)(2)Li((SiMe3)(2)N}-1Zn(NtBu)(4)S] (5) are prepared from the intended transmetalation of the dilithium complex of N,N',N '' N ''' tetrakis(tert-butyptetraimidosulf ate Rthf)(4)Li-2(NtBu)(4)S] (1). The two lithium cations are replaced by either the cationic (acac)Cu(ii) moiety, the neutral 12Cd(ii) residue or only a single lithium cation is substituted by the cationic (Me3SO2NZn(ii) fragment. The complexes show two main results: first the S(NtBu)(4)(2-) tetrahedron can serve as a ligand to transition metals from the soft Cu(ii) to the harder Zn(ii) at opposite sides and second the S-N bond distances vary only marginally in response to the various metals and the four distances constantly sum up to 6.38(2) A. Hence the electropositive sulfur atom responds by internal shift to the metal-polarized negative charge at the outside of the S(NR)(4)(2-) tetrahedron.Danish National Research Foundation [DNRF93
Reaction of beta-diketiminate tin(II) dimethylamide LSnNMe2 [L = HC(CMeNAr)(2); Ar=2,6-iPr(2)C(6)H(3)] with ketones and alkynes
No full textThe reactions of stable beta-diketiminate tin(II) dimethylamide LSnNMe2 [L = HC(CMeNAr)(2); Ar = 2,6-iPr(2)C(6)H(3)] (1) with ketones and activated terminal alkynes are described. 1 reacts with 2-benzoylpyridine and 2,2,2-trifluoroacetophenone to give the tin(II)-alkoxides LSnOCPh(2-Py)NMe2 (2) and LSnOCPh(CF3)NMe2 (3), respectively, by nucleophilic addition of the dimethylamido group to the carbonyl moiety. Furthermore, the reaction of 1 with terminal alkynes (HCCCO2R, R = Me, Et) forms tin(II)-alkynyl LSnCCCO2R (R= Me, (4); R = Et, (5)) compounds under elimination of Me2NH rather than undergoing a nucleophilic addition reaction at the carbon - carbon triple bond. Compounds 2 - 5 were characterized by microanalysis and multinuclear NMR spectroscopy. Moreover, 2 and 5 could be crystallized and their constitutions were confirmed by X-ray structural analysis. 2 and 5 are monomers in the solid state and the metal atom shows a distorted trigonal-pyramidal coordination sphere.Deutsche Forschungsgemeinschaf
Low‐Temperature NMR and Crystal Structure Analyses of a Hemilabile Tin Complex
No full textThe reaction of SnCl2 with the Janus Head ligands Ph(2)PPic (1. Pic = 2-picolyl) and Ph2P(NSiMe3)Pic (2) led to the novel tin complexes [(Ph(2)PPic)Sn(Cl)][SnCl3] (4) and [(Cl2Sn{(NH)(Pic)PPh2}] THF (6). The hemiability of the Ph(2)PPic (1) ligand in 4 was investigated by low temperature Sn-119 and P-31 NMR studies. A remarkable equilibrium of two formal SnCl2 units with 1 could be revealed. Crystal structure analysis of 4 and 6 substantiated the understanding of the hemilabile behaviour of the presented Janus Head ligands
Coordination Site Selective <i>Janus Head</i> Ligands
No full textThe deprotonation of PhP(CH(2)Py)(2) (Py = 2-pyridyl) (1) leads to a Joints head ligand, in which one coordination site is provided by the two carbanionic CH bridges, while the two ring nitrogen atoms and the phosphorus atom supply the second site. This coordination pattern is displayed in the metal complexes [(Et(2)O)(3)Li(2){C(H)Py}(2)PPh](2) (2) and [{(SiMe(3))(2)NSn}(2){C(H)Py}(2)PPh] (3). In accordance with the different size of the metal moieties, 2 is a dimeric compound, while 3 forms a monomeric complex. The comparison of the solid-state structures of 2 and 3 displays a distinct response of the bonding of the deprotonated ligands toward the various metal atoms. Detailed NMR experiments show that the tin complex 3 has identical structures in both solution and the solid state.DNRF; Center of Materials Crystallography (CMC
Synthesis of Tetrasubstituted Alkenes through a Palladium-Catalyzed Domino Carbopalladation/C-H-Activation Reaction
No full textHelical tetrasubstituted alkenes (7) were obtained in a highly efficient way through a palladium-catalyzed domino-carbopalladation/CH-activation reaction of propargylic alcohols 6 in good to excellent yields. Electron-withdrawing- and electron-donating substituents can be introduced onto the upper and lower aromatic rings. The substrates (6) for the domino process were synthesized by addition of the lithiated alkyne (20) to various aldehydes (19); moreover, the substrates were accessible enantioselectively (in 95?% ee) by reduction of the corresponding ketone using the Noyori procedure
Coordination Abilities of Di-2-picolylphenylphosphane Judged on the Basis of Charge Density Investigations
No full textThe hindered reactivity of [PhP(CH2Py)(2)LiCl](2) (2) compared to the coordination behavior of the lithium chloride free ligand PhP(CH2Py)(2) (Py = 2-pyridyl) (1) could be elucidated by means of experimental electron density studies. According to the successful synthesis of metal complexes containing the dianionic Janus Head ligand [PhP(CHPy)(2)](2-), the formation and the coordination pattern of the monoanionic ligand [PhP{C(H)Py}(CH2Py)](-) was examined. The reaction of ligand 1 with n-butyllithium/PMDETA and the superbase n-butyllithium/NaOtBu, respectively, led to the alkali metal complexes [(PMDETA)Li{C(H)Py}P(CH2Py)Ph] (5) and [(PyCH2)PhP{C(H)Py}Na(Et2O)](2) (6)
A Germanium(II) Hydride as an Effective Reagent for Hydrogermylation Reactions
No full textHerein we report on the reactivity of the stable germanium(II) hydride LGeH (L = CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) (2), which contains a low-valent germanium atom. 2 is prepared from the corresponding germanium(II) chloride LGeCl (1) using H3Al center dot NMe3 or K[HB(iBu)(3)] in toluene. The reaction of 2 with carbon dioxide in toluene at room temperature affords a germanium(II) ester of formic acid, LGe-O-C(O)H (3), which is formed by insertion of the carbon dioxide into the germylene hydrogen bond. 2 also reacts with alkynes at room temperature to give the first germanium(II)-substituted alkenes (4, 5, and 6). These two reaction types have in common the fact that the hydrogen and germylene from LGeH are transferred to an unsaturated bond: the carbon-oxygen double bond (C=O) in the former case and the carbon-carbon triple bond (C C) in the latter. Moreover, the reaction of 2 with elemental sulfur in toluene at room temperature leads to the germanium dithiocarboxylic acid analogue LGe(S)SH (7). Compound 7 is formed by the unprecedented insertion of elemental sulfur into the germylene hydrogen bond and oxidative addition of elemental sulfur to the germanium(II) atom. This leads to the formal conversion of the GeH hydride to a SH proton. Compounds 3-7 were investigated by microanalysis, multinuclear NMR spectroscopy, and single-crystal X-ray structural analyses.Deutsche Forschungsgemeinschaft; Gottinger Akademie der Wissenschafte
Oxidative Addition Versus Substitution Reactions of Group 14 Dialkylamino Metalylenes with Pentafluoropyridine
No full textDiallcylamino compounds of group 14 elements (Si, Ge, Sn) in the +2 oxidation state supported by benzamidinate ligands were synthesized and treated with pentafluoropyridine. Two different modes of reactivity were observed, depending on the metal atom and the basicity of the substituent at the metal. Pentafluoropyridine undergoes oxidative addition reaction at the Si(II) and Ge(II) atoms whereas at the Sn(II) atom substitution of the NMe2 group by the para fluorine of pentafluoropyridine occurs. The C F bond activation by the lone pair of germanium is the first report of this kind. The Sn(II) fluoride obtained has an elongated Sn F bond length and can be used as a good fluorinating agent. The compounds were characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray structural analysis. Single crystal X-ray structural analysis of the tin fluoride shows an asymmetric dimer with weak Sn(II)(F) (F)Sn(II) interactions.Center for Materials Crystallography (CMC); Land Niedersachse
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