摘要:

AbstractOrganosilyl exchange reactions of the extremely electronrich and formally “antiaromatic” 1,4‐bis(trimethylsilyl)‐substituted 1,4‐dihydropyrazine1with Ph3SiCl or Me5Si2Cl yielded the new compounds2and3with triarylsilyl and disilanyl substituents. At δ = 4.53 in CDCl3compound3shows a particularly high‐field shifted1H‐NMR resonance for the 1,4‐dihydropyrazine protons. In contrast to the planar ring arrangement of 1,4‐bis(triisopropylsilyl)‐1,4‐dihydropyrazine4, the crystal structure determination of the 2,5‐dimethylated analogue5as obtained by reductive silylation exhibits a pronounced boat conformation of the heterocycle due to steric repulsion between the substituents, the closest H…H (CH3/ CH) contact being 211 pm. Despite the sizeable structural differences between4and5both compounds are reversibly oxidized at very negative potentials, at ‐0.90 and ‐0.85 V vs. Fc+/0, respectively, It appears that the electrochemical behavior of this class of compounds is determined ***primarly by the configuration at the nitrogen centers and less by the ring conformation. Compound4reacts with C60under EPR‐detectable electron exchange to afford4+*and C −*60. The radical cation4+*generated separately via oxidation with iodine was characterized by low‐temperature UV/Vis and ENDOR spectroscopy. An ENDOR spectrum revealing silylalkyl coupling was also obtained for the related radical cation of reversibly oxidizable 1,1′ ‐bis(tert‐buty

ISSN:0009-2940    

DOI:10.1002/cber.19951280802

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

Abstract9‐Borabicyclo[3.3.1]nonane (9‐BBNH) reacts with monocarboxylic acids to afford 9‐(acyloxy)‐9‐borabicyclo[3.3.1]nonanes which are dimers in the solid state as shown by X‐ray crystal structures of the benzoate and pivalate. More complex reactions were observed by allowing 9‐BBNH to react with dicarboxylic acids in THF or monoglyme. Thus, (9‐BBN)2oxalate3contains a fully delocalized oxalate unit with equal C‐O and B‐O bond lengths. Traces of water convert it into the tetrakis(9‐BBN) oxalate5. A rather unusual structure is veryfied by 9‐BBN 2,2‐dimethylmalonate7which according to its molecular structure is a tetramer featuring a 32‐membered ring system. In contrast, reactions of oxalic acid with thexylborane leads to reduction of the acid and formation of a bicyclic dioxaborolo‐dioxaborolane10. Several intermediates were detected by11B‐NMR spectroscopy as well as in reactions of BH3· THF or BH3· SMe2with oxalic acid. — It follows from the present study that (acyloxy)boranes derived from dicarboxylic acids are strong Lewis acids with an unexpe

ISSN:0009-2940    

DOI:10.1002/cber.19951280803

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractSelenium, SeCl4, and MCl4(M = Zr, Hf) react in a sealed evacuated glass ampoule at 130°C to afford red, moisture sensitive crystals of Se2+4(ZrCl2‐6) and Se2‐6(HfCl2‐6). The isotypic crystal structures (tetragonal,P42/ncm, Z= 4) consist of square‐planar Se2+4cations and slightly distorted octahedral MCl2‐6(M = Zr, Hf) anions. The ions are packed corresponding to the NaCl structure type with the centres of gravity of the Se4rings and the metal atoms of the MCl6octahedra in the Na and Cl positions. From Te, TeCl4, and HfCl4one obtains under similar conditions at 200°C Te2+4(HfCl2‐6) in form of dark violet crystals. The crystal structure (triclinic,P1, Z = 1) is built of nearly square‐planar Te2+4ions and octahedral HfCl2‐6ions. The packing of the ions corresponds to a rhombohedrally distorted Cs

ISSN:0009-2940    

DOI:10.1002/cber.19951280804

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractOptically pure 1,4‐bis(diphenylphosphanyl)‐2‐hydroxy‐butane (2) and its methyl ether1can be conveniently prepared by starting from chiral pool substances such as malic or L‐ascorbic acid. Different pathways to these compounds were elucidated. In one case an interesting migration of an acetalic OH‐protective group was observed. The reaction of the bisphosphanes with Rh1or PdIIgave uniform metal complexes. On the basis of X‐ray structural analysis, NMR and IR data it was concluded that in the investigated precatalysts of the type [Rh(COD)(bisphosphane)]BF4a coordination of the alkoxy or hydroxy oxygen to the metal does not take place. Nevertheless, significant differences in enantioselectivity and activity could be observed when several prochiral substrates were

ISSN:0009-2940    

DOI:10.1002/cber.19951280805

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electronic structure of the recently synthesized complex5obtained by the reaction of Cp2Ti(PMe3)(tBu‐CP) with (Et2BH)2was analyzed by means of molecular orbital (MO) calculations. The methods applied were the extended Hückel and the ab initio Hartree‐Fock procedures. The highest occupied MOs were derived from molecular fragments. The geometrical parameters calculated for a simplified model (6) are close to those obtained from an X‐ray investigation of5. The analysis of the results shows a strong donor‐acceptor interaction between the P‐B ó bond and the Ti center. The phosphorus lone pair is not involved

ISSN:0009-2940    

DOI:10.1002/cber.19951280806

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractFour drugs whose actions have a relation to the status of zinccontaining species in the human body were used as ligands in zinc complexes. Captopril (H2Cap) forms the compound [ZnCap] (1) presumed to be a coordination polymer with O and S coordination. Isoniazid, in the presence of zinc salts, is converted to 1,2‐diisonicotinoyl hydrazide (H2Nih) which forms polymeric [Zn(Nih)NH3] (2) with trigonal‐bipyramidal ZnO2N3coordination. Nalidixic acid (HNal) and zinc perchlorate yield [Zn(HNal)2(H2O)2](ClO4)2· 2 H2O (3) containing zinc in an octahedral ZnO6environment. Mercaptopurine (H2Mer), in the presence of ammonia, forms [Zn(Mer)(NH3)2].H2O (4) which is a coordination polymer containing tetrahedral ZnN4units. The structures of [Zn(Nih)NH3], [Zn(HNal)2(H2O)2](ClO4)2.2 H2O, and [Zn(Mer)(NH3)2].2 H2O were determined diffractometric

ISSN:0009-2940    

DOI:10.1002/cber.19951280807

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThree different thiazoline derivatives or their tautomeric mercaptoethylamine derivatives were used for the preparation of zinc complexes containing S,N ligands. 2‐(2‐pyridyl)‐3‐(2‐pyridylmethyl)‐1,3‐thiazolidine (PPMT) could not be opened reductively but acted as a tridentate nitrogen ligand in (PPMT)ZnX2(1a, b, X = Br, NO3). The thiazolidine tautomer N‐(2‐mercaptoethyl)salicylideneimine (MESIH2) yielded polymeric (MESI)Zn (2) and, after oxidation, monomeric (MESI)2Zn (3) containing a disulfide unit. The 2‐aryl‐benzo‐1,3‐thiazoline tautomers N‐(2‐mercaptophenyl)‐p‐fluoroben‐zylideneimine (MPFBH) and N‐(2‐mercaptophenyl)‐p‐meth‐oxybenzylideneimine (MPMBH) underwent reaction with diethyl zinc resulting in the unstable L.Zn‐Et complexes4aandb, which are probably dimeric and the stable 2:1 complex (MPFB)2Zn (5). The structures of3and5were determined and were found to exhibit distorted tetrahed

ISSN:0009-2940    

DOI:10.1002/cber.19951280808

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractVarious aromatic nitriles were used for the preparation of the nitrile‐capped clusters Fe3(CO)9(μ3‐η2‐RCN) (2) by reaction with Fe3(CO)12under hydrogen. Electron‐rich nitriles decrease, electron‐poor nitriles increase the thermal stability of clusters2. With CN‐substituted pyridines only traces of clusters2could be obtained. CO replacement in Fe3(CO)9(PhCN) (2a) by isonitriles also causes a lowering of the stability. Conversely, more stable products were obtained by substitution reaction with trimethyl phosphite. One PPh3and two dppm derivatives were also obtained. The structure of Fe3(CO)8‐P(OMe)3(μ3‐η2‐PhC

ISSN:0009-2940    

DOI:10.1002/cber.19951280809

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

Abstract13C,6Li HOESY Measurements were developed and performed for the first time on the13C‐labeled benzyllithium compound1.1D NOE difference,1H,6Li HOESY, and spin lattice relaxation measurements were used to obtain information on the position of the lithium, ion in solutio

ISSN:0009-2940    

DOI:10.1002/cber.19951280810

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe molecular structure of 1‐trifluoromethylthio‐1,2,2‐trifluoroethene, CF3SC(F) = CF2, was determined by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The S—CF3bond is oriented nearly perpendicular to the ethene plane with Φ(C = C‐S‐C) = 96.9(12)°. This orientation implies that the p‐shaped sulfur lone pair is perpendicular to the ethene π orbitals. The following skeletal bond lengths (rain Å) and angles (χ α in °) were obtained (error limits are 30 values): C = C = 1.302(19) Å, C(sp2)—S = 1.719(9) Å, SC(sp3) = 1.820(10) Å, C  CS = 120.0(9)°, and CSC  101.7(7)°. The experimental geometric parameters were reproduce

ISSN:0009-2940    

DOI:10.1002/cber.19951280811

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY