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Enno Lork

Publications and source records attributed to Enno Lork.

18 recordsLinked to original sources
PubMed2006

Isomers of a dibismuthane, R2Bi-BiR2 [R = 2,6-(Me2NCH2)2C6H3], and unusual reactions with oxygen: formation of [R2Bi]2(O2) and R'R' 'Bi [R' = 2-(Me2NCH2)-6-{Me2N(O)CH2}C6H3; R' ' = 2-(Me2NCH2)-6-{O(O)C}C6H3].

R2Bi-BiR2 [1; R = 2,6-(Me2NCH2)2C6H3], a dibismuthane that exists in different forms in the crystalline state, reacts in air with the formation of the peroxide [R(2)Bi]2(O2) (2) and partial oxidation of the pendant (dimethylamino)methyl groups, yielding the mononuclear bismuth complex R'R' 'Bi (3) [R' = 2-(Me2NCH2)-6-{Me2N(O)CH2}C6H3; R' ' = 2-(Me2NCH2)-6-{O(O)C}C6H3].

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PubMed2005

Guanidinophosphazenes: design, synthesis, and basicity in THF and in the gas phase.

A principle for creating a new generation of nonionic superbases is presented. It is based on attachment of tetraalkylguanidino, 1,3-dimethylimidazolidine-2-imino, or bis(tetraalkylguanidino)carbimino groups to the phosphorus atom of the iminophosphorane group using tetramethylguanidine or easily available 1,3-dimethylimidazolidine-2-imine. Seven new nonionic superbasic phosphazene bases, tetramethylguanidino-substituted at the P atom, have been synthesized. Their base strengths are established in tetrahydrofuran (THF) solution by means of spectrophotometric titration and compared with those of eight reference superbases designed specially for this study, P2- and P4-iminophosphoranes. The gas-phase basicities of several guanidino- and N',N',N'',N''-tetramethylguanidino (tmg)-substituted phosphazenes and their cyclic analogues are calculated, and the crystal structures of (tmg)3P=N-t-Bu and (tmg)3P=N-t-Bu x HBF4 are determined. The enormous basicity-increasing effect of this principle is experimentally verified for the tetramethylguanidino groups in the THF medium: the basicity increase when moving from (dma)3P=N-t-Bu (pKalpha = 18.9) to (tmg)3P=N-t-Bu (pKalpha = 29.1) is 10 orders of magnitude. A significantly larger basicity increase (up to 20 powers of 10) is expected (based on the high-level density functional theory calculations) to accompany the similar gas-phase transfer between the (dma)3P=NH and (tmg)3P=NH bases. Far stronger basicities still are expected when, in the latter two compounds, all three dimethylamino (or tetramethylguanidino) fragments are replaced by methylated triguanide fragments, (tmg)2C=N-. The gas-phase basicity (around 300-310 kcal/mol) of the resulting base, [(tmg)2C=N-]3P=NH, having only one phosphorus atom, is predicted to exceed the basicity of (dma)3P=NH by more than 40 powers of 10 and to surpass also the basicity of the widely used commercial [(dma)3P=N]3P=N-t-Bu (t-BuP4) superbase.

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PubMed2005

[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl: a long-lived radical anion and its stable salts.

[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazole (1) is synthesized in 62% yield by fluoride ion-induced condensation of 3,4-difluoro-1,2,5-thiadiazole with (Me(3)SiN=)(2)S. The reversible electrochemical reduction of 1 leads to the long-lived [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion (2) and further to the dianion (3). The radical anion 2 is also obtained by the chemical reduction of the precursor 1 with t-BuOK in MeCN. The radical anion 2 is characterized by ESR spectroscopy in solution and in the crystalline state. The stable salts [K(18-crown-6)][2] and [K(18-crown-6)][2].MeCN (8 and 9, respectively) are isolated from the spontaneous decomposition of the [K(18-crown-6)][PhXNSN] (6, X = S; 7, X = Se) salts in MeCN solution followed by XRD characterization. The radical anion 2 acts as a bridging ligand in 8 and as chelating ligand in 9. The structural changes observed by XRD in going from 1 to 2 are explained by means of DFT/(U)B3LYP/6-311+G calculations.

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PubMed2004

Syntheses and chemistry of hypervalent cyclo-R4Sb4, cyclo-(RSbE)n[R = 2-(Me2NCH2)C6H4, E = O, S] and precursors.

The cyclostibane R(4)Sb(4)(1)(R = 2-(Me(2)NCH(2))C(6)H(4)) was synthesized by reduction of RSbCl(2) with Mg in THF or with Na in liquid NH(3). The reaction of 1 with [W(CO)(5)(THF)] gives the stibinidene complex RSb[W(CO)(5)](2)(2). RSbCl(2) and (RSbCl)(2)E [E = O (6), E = S (8)] react with KOH or Na(2)S in toluene/water to give the heterocycles (RSbE)(n)[E = O, n= 3 (3); E = S, n= 2 (4)]. The chalcogeno-bridged compounds of the type (RSbCl)(2)E [E = O (6), E = S (8)] were synthesized by reaction of RSbCl(2) with KOH or Na(2)S in toluene/water, but also by reaction of RSbCl(2) with the heterocycles (RSbE)(n). The compounds (RSbI)(2)O (7) and (RSbBr)(2)S (9) were prepared via halogen-exchange reactions between (RSbCl)(2)E and NaI (E = O) or KBr (E = S) or by reactions between RSbI(2) and KOH or RSbBr(2) and Na(2)S. The reaction of cyclo-(RSbS)(2) with W(CO)(5)(THF) in THF results in trapping of the cis isomer in cyclo-(RSbS)(2)[W(CO)(5)](5). The solution behaviour of the compounds was investigated by (1)H and (13)C NMR spectroscopy. The molecular structures of compounds 1-7 and 9 were determined by single-crystal X-ray diffraction.

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PubMed2004

Anionic triazine systems.

The synthesis of TAS+ C3N3F4- (1) (TAS+ = (Me2N)3S+) and the reactions of 1 with Me3SiOSiMe3 and Me3SiCF3 to give TAS+ C3N3F2O- (2) and TAS+[(NCF)(NCCF3)(NC(CF3)(2)]- (4) are reported. An isomer of 4, TAS+[(NCCF3)2(NCFCF3)]-, compound 6, was obtained by fluoride ion addition to (CF3CN)3. From the reactions with Me3SiNMe2 neutral fluoroamino triazines C3N3Fn(NMe2)(n-1) (n = 1, 2) were isolated. Possible reaction pathways are discussed, the X-ray structures of 1, 2, 4 and 6 were determined.

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PubMed2003

Syntheses, structures, and dynamic behavior of chiral racemic organoantimony and -bismuth compounds RR'SbCl, RR'BiCl, and RR'SbM [R = 2-(Me2NCH2)C6H4, R' = CH(Me3Si)2, M = H, Li, Na].

RR'SbCl (1) and RR'BiCl (2) [R = 2-(Me(2)NCH(2))C(6)H(4), R' = CH(Me(3)Si)(2)] form by the reaction of R'ECl(2) (E = Sb, Bi) with RLi. The reaction of 1 with LiAlH(4) and metalation with n-BuLi gives RR'SbH (3) and RR'SbLi.2THF (4) (THF = tetrahydrofuran). Transmetalation of 4 with sodium tert-butoxide in the presence of TMEDA (TMEDA = tetramethylethylenediamine) leads to RR'SbNa.TMEDA (5). Structural analyses by (1)H NMR in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO with a variation of the temperature (1, 2, 4, and 5) and by single-crystal X-ray diffraction (1, 2, 4, and 5) revealed the intramolecular coordination of the pendant Me(2)N group on the pnicogen centers in 1 and 2 and on Li or Na in 4 or 5. The variable-temperature (1)H NMR spectra of the hydride 3 in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO show that the pyramidal configuration on antimony is stable up to 100 degrees C, whereas inversion at the nitrogen is not prevented by internal coordination even at -80 degrees C. The crystals of 1, 2, 4, and 5 consist of discrete molecules with the Sb and Bi atoms in an approximately Psi-trigonal-bipyramidal environment in the cases of 1 and 2 and in a pyramidal environment in the cases of 4 and 5. Crystal data for 1: triclinic, space group Ponemacr;, a = 7.243(4) A, b = 10.373(3) A, c = 15.396(5) A, alpha = 79.88 degrees, beta = 78.27 degrees, gamma = 71.480(10) degrees, V = 1066.2(7) A(3), Z = 2, R = 0.0614. 2: monoclinic, space group P2(1)/n, a = 10.665(2) A, b = 14.241(2) A, c = 14.058(2) A, beta = 90.100(10) degrees, V = 2135.1(6) A(3), Z = 4, R = 0.049. 4: monoclinic, space group P2(1)/n, a = 11.552(2) A, b = 16.518(3) A, c = 15.971(5) A, beta = 96.11(2) degrees, V = 3030.2(12) A(3), Z = 4, R = 0.0595. 5: monoclinic, space group P2(1)/n, a = 9.797(2) A, b = 24.991(5) A, c = 14.348(3) A, beta = 94.98(3) degrees, V = 3499.66(12) A(3), Z = 4, R = 0.0571. The dissociation of the intramolecular N-pnicogen bond and inversion at the nitrogen occurs when solutions of 1 or 2 in C(6)D(6) or C(6)D(5)CD(3) are heated above 25 or 30 degrees C. 1 and 3-5 are stable with respect to inversion of the configuration at the antimony in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO up to 160 degrees C. Bismuth inversion, probably via the edge mechanism, is observed in solutions of 2 in (CD(3))(2)SO at 45 degrees C but not in C(6)D(5)CD(3) below 125 degrees C.

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PubMed2003

Synthesis of a stibindolyl anion from trimesitylantimony and potassium.

2-(3',5'-Dimethylphenyl)-5,7-dimethylstibindolyl potassium-pmdeta (1) (pmdeta = pentamethyldiethylenetriamine) is obtained from trimesitylantimony, potassium and the amine ligand in tetrahydrofuran; crystals of 1 consist of stacks of (pmdeta)K+ ions and stibindolyl anions with alternating Sb-K and eta5-SbC4-K interactions.

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PubMed2002

Hexaalkylguanidinium and 2-(dialkylamino)-1,3-dimethylimidazolinium trimethyldifluorosiliconates and perfluoroalkoxides. Accidental isolation and molecular structure of [C(NMe2)3]+F-*6CH2Cl2.

Hexaalkylguanidinium and 2-(dialkylamino)-1,3-dimethylimidazolinium trimethyldifluorosiliconates, precursors for two stable hexaalkylguanidinium perfluoroalkoxides, were synthesized by treating commercially available bis(dialkylamino)difluoromethane derivatives with (dialkylamino)trimethylsilanes in aprotic media. With hexamethylguanidinium pentafluoroethoxide the introduction of the lipophilic and electronegative C2F5O group was straightforwardly achieved in the case of primary and secondary alkyl triflates to furnish the respective fluorinated ethers. The molecular structures of [(CH2NMe)2C(NEt2)]+[Me3SiF2]- and [C(NMe2)3]+F-*6CH2Cl2 were determined, showing in the latter case a fluoride anion octahedrally coordinated by six methylene chloride molecules via hydrogen bridges with a F...H distance of 205 pm (C...F distance 270.0(3) pm).

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PubMed2002

Tris(dimethylamino)oxosulfonium difluorotrimethylsilicate, (Me(2)N)(3)SO(+)Me(3)SiF(2)(-) (TAOS Fluoride).

In the OSF(4)/Me(2)NSiMe(3) system besides the long known Me(2)NS(O)F(3) only the trisubstituted derivative is isolated as (Me(2)N)(3)SO(+)Me(3)SiF(2)(-) (3). Similar to (Me(2)N)(3)S(+)Me(3)SiF(2)(-) compound 3 is an excellent fluoride ion donor. With AsF(5) and HF the corresponding hexafluoroarsenate (Me(2)N)(3)SO(+)AsF(6)(-) (4) and the hydrogen bifluoride (Me(2)N)(3)SO(+)HF(2)(-) (5) are formed in almost quantitative yield. X-ray structure determinations of 3-5 surprisingly showed two different types of structures for the cation. In 3 and 5 this cation has C(3) symmetry, while in the hexafluoroarsenate 4 a (Me(2)N)(3)S(+)-like structure with C(s)() symmetry is determined. The experimental results for (Me(2)N)(3)SO(+) and (Me(2)N)(3)S(+) are compared with theoretical calculations for these cations and their isoelectronic neutral counterparts, the phosphorus amides (Me(2)N)(3)PO and (Me(2)N)(3)P, respectively.

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PubMed2002

Lithium fluoroarylamidinates: syntheses, structures, and reactions.

Lithium fluoroarylamidinates [(Ar(F)C(NSiMe(3))(2)Li)(n).xD] (Ar(F) = 4-CF(3)C(6)H(4), n = 2, D = OEt(2), x = 1 (2a); n = 1, D = TMEDA, x = 1 (4a); Ar(F) = 2-FC(6)H(4), n = 2, D = OEt(2), x = 1 (2b); Ar(F) = 4-FC(6)H(4), n = 2, D = OEt(2), x = 2 (2c); Ar(F) = 2,6-F(2)C(6)H(3), n = 2, D = OEt(2), x = 1 (2d); n = 2, D = 2,6-F(2)C(6)H(3)CN, x = 2 (3d); Ar(F) = C(6)F(5), n= 2, D = OEt(2), x = 1 (2e), n = 1, D = TMEDA, x = 1 (4e); n = 1, x = 2, D = OEt(2) (5e); D = THF (6e)) were prepared by the well-known method from LiN(SiMe(3))(2) and the corresponding nitrile in diethyl ether or by addition of the appropriate donor D to the respective diethyl ether complexes. Depending on the substituents at the aryl group and on the donors D, three different types of structures were confirmed by X-ray crystallography. Hydrolysis of 2e gave C(6)F(5)C(NSiMe(3))N(H)SiMe(3) (7e) and C(6)F(5)C(NH)N(H)SiMe(3) (8e). The lithium fluoroarylamidinates 2a-2d react with Me(3)SiCl to give the corresponding tris(trimethylsilyl)fluoroarylamidines Ar(F)C(NSiMe(3))N(SiMe(3))(2) (9a-9d). Attempts to prepare C(6)F(5)C(NSiMe(3))N(SiMe(3))(2) from 2e and Me(3)SiCl failed; however, the unprecedented cage [[C(6)F(5)C(NSiMe(3))(2)Li](4)LiF] (10e) in which a fluoride center is surrounded by a distorted trigonal bipyramid of five Li atoms was obtained from this reaction.

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PubMed2002

The anti-inflammatory triterpenoid methyl 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oate methanol solvate hydrate.

The title compound, C(32)H(43)NO(4) x CH(4)O x H(2)O, has a nearly planar cyano-enone A ring in an otherwise normal oleanane triterpenoid. Rings A, B and C are non-chairs, but rings D and E adopt essentially cyclohexane chair conformations. The structure clearly establishes the C-D-E ring stereochemistry as trans-syn-cis, as predicted from a nuclear Overhauser effect (NOE) NMR measurement.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2002

A novel type of formation of zwitterionic compounds, containing two phosphorus atoms of opposite charge and different coordination number.

The oxidation of bis[bis(dialkylamino)phosphinyl]methane 1 with 5,5,5-trifluoro-4-(trifluoromethyl)penta-3-en-2-one 2 unexpectedly gave zwitterionic compound 7 which according to X-ray analysis contains two phosphorus atoms of opposite charge and different coordination number (lambda 4P(+); lambda 6P(-)) with a direct P-H bond at the hexacordinated phosphorus.

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PubMed1999

Syntheses and Structures of Bis(azole)difluorosulfuranes.

Bis(imidazole)sulfur difluoride (4), bis(pyrazole)sulfur difluoride (6), and bis(1,2,4-triazole)sulfur difluoride (8) are formed in the reactions of N-(trimethylsilyl)imidazole, N-(trimethylsilyl)pyrazole, and 1-(trimethylsilyl)-1,2,4-triazole with SF(4), in high yield. The ring systems in these three molecules occupy equatorial positions in the pseudo-trigonal-bipyramidal coordination sphere of the central sulfur atoms. The angles between the planes of the ring substituents and the FSF axis for 4 and 6 are in the range 23.6-35.3 degrees, and in 8 the triazole rings are almost parallel (deviation 1.7 degrees ). The interaction between the heterocyclic substituents and the sulfur centers and their influence on the axial and equatorial bonds is discussed.

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PubMed1996

Hydroxoundecahydro-closo-dodecaborate(2-) as a Nucleophile. Preparation and Structural Characterization of O-Alkyl and O-Acyl Derivatives of Hydroxoundecahydro-closo-dodecaborate(2-).

The syntheses, solid state structures, and spectral properties of O-alkyl and O-acyl derivatives of hydroxoundecahydro-closo-dodecaborate(2-), 1, are described. Alkylation of 1 with ethyl iodide was achieved in dimethyl sulfoxide using potassium hydroxide as a base, leading to [N(n-C(4)H(9))(4)](2)[CH(3)CH(2)O-B(12)H(11)(2-)], 2, bis(tetrabutylammonium) ethoxyundecahydro-closo-dodecaborate(2-) [monoclinic P2(1)/n, a = 1192.4(9) pm, b = 1253.9(4) pm, c = 3049.1(10) pm, beta = 92.69(4) degrees, Z = 4, R1 = 0.0693, wR(2) = 0.1517]. Alkylation with 1,5-dibromopentane afforded the cyclic oxonium salt [PPN][C(5)H(10)O-B(12)H(11)(1-)], 3, (&mgr;-nitrido)bis(triphenylphosphorus)(1+) tetrahydropyrane-undecahydro-closo-dodecaborate(1-) [monoclinic P2(1)/c, a = 1938.1(2) pm, b = 1329.7(10) pm, c = 1944.0(2) pm, beta = 108.82(10) degrees, Z = 4, R1 = 0.0484, wR(2) = 0.0833]. Acylation of 1 in acetonitrile with acyl chlorides in the presence of pyridine yielded [N(n-C(4)H(9))(4)](2)[C(6)H(5)CO(2)-B(12)H(11)(2-)], 4, bis(tetrabutylammonium) undecahydrobenzoyl-closo-dodecaborate(2-) [monoclinic P2(1)/c, a = 1812.0(4) pm, b = 1711.9(3) pm, c = 1685.0(3) pm, beta = 114.03(3) degrees, Z = 4, R1 = 0.0915, wR(2) = 0.2093], and [N(n-C(4)H(9))(4)](2)[CH(3)CO(2)-B(12)H(11)(2-)], 5, bis(tetrabutylammonium) acetoxyundecahydro-closo-dodecaborate(2-) [monoclinic P2(1)/n, a = 1190.5(2) pm, b = 1243.0(10) pm, c = 3078.4(4) pm, beta = 92.76(10) degrees, Z = 4, R1 = 0.0642, wR(2) = 0.1462]. All crystal structures showed distortion of the pseudoicosahedral geometry of the boron cluster. The boron-oxygen distances varied from 144.2(5) pm for 2, 148.5(3) pm for 5, 149.4(12) pm for 4, to 152.8(4) pm for 3. The 3-fold coordinated oxygen of oxonium salt 3 is nearly planar.

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