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1.
Shapiro PJ Sinnema PJ Perrotin P Budzelaar PH Weihe H Twamley B Zehnder RA Nairn JJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(21):6212-6222
A detailed study of the thermal decomposition of the zwitterionic, ring-borylated ansa-chromocene hydrido carbonyl complex [Cr(CO)H{Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (2) is described. This complex is formed in the reaction between [Cr(CO){Me(4)C(2)(C(5)H(4))(2)}] (1) and B(C(6)F(5))(3) in toluene at -78 degrees C. Above -25 degrees C, 2 decomposes to a 50:50 mixture of the low-spin, 17e Cr(III) complexes [Cr(CO){Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (3b) and [Cr(CO){Me(4)C(2)(C(5)H(4))(2)}][HB(C(6)F(5))(3)] (4). Carbon monoxide elimination from 3 b generates high-spin, 15 e [Cr{Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (3a), which coordinates two other electron-donating ligands, such as xylyl isocyanide, PMe3, and PPh(2)Me to form the low-spin, 17 e electron complexes 3c, 3d, and 3e, respectively. High-spin, 15 e [Cr{Me(4)C(2)(C(5)H(4))(2)}][HB(C(6)F(5))(3)] (5) is generated by heating 3 b in toluene at 100 degrees C and periodically removing the evolved CO. Efforts to isolate more than a few X-ray quality crystals of 5 were thwarted by its tendency to form an insoluble precipitate (6) with the same molecular formula. Heating the solution of 5 at 120 degrees C results in its partial conversion (ca. 28 %) to 3a, thereby allowing the formation of 3a in yields as high as 74 % from the reaction between 1 and B(C(6)F(5))(3). The X-ray crystal structures of 3 b-e and 5 are described. Cyclic voltammetry measurements on 3 a-e reveal a dramatic reduction in the redox potentials of the complexes relative to their non-borylated analogues. DFT calculations show that this is due primarily to electrostatic stabilization of the oxidized species by the negatively charged borylate group. EPR and 19F NMR spectroscopy allow 3a to be distinguished from its Lewis base adducts 3 b-e and reveal the relative affinities of different Lewis bases for the chromium. 相似文献
2.
In the homopolymerisation of propene by the cyclopentadienyl‐amide titanium catalyst systems [η5,η1‐C5H4(CH2)2NR]TiCl2/MAO and [η5,η1‐C5H4(CH2)2NR]Ti(CH2Ph)2/B(C6F5)3 (R = tBu, iPr, Me), the catalyst with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl‐amide ancillary ligands, where larger amide substituents result in higher molecular weights. Based on the present information a hypothesis is formulated in which an increased cation‐anion interaction for the less sterically hindered catalyst is responsible for disfavouring chain transfer relative to chain growth. 相似文献
3.
Stefan Arndt Klaus Beckerle Kai C. Hultzsch Piet-Jan Sinnema Peter Voth Thomas P. Spaniol Jun Okuda 《Journal of molecular catalysis. A, Chemical》2002,190(1-2):215-223
In order to understand the nature of the putative cationic 12-electron species [M(η5:η1-C5R4SiMe2NR′)R″]+ of titanium catalysts supported by a linked amido-cyclopentadienyl ligand, several derivatives with different cyclopentadienyl C5R4 and amido substituents R′ were studied systematically. The use of tridentate variants (C5R4SiMe2NCH2CH2X)2− (C5R4=C5Me4, C5H4, C5H3tBu; X=OMe, SMe, NMe2) allowed the NMR spectroscopic observation of the titanium benzyl cations [Ti(η5:η1-C5Me4SiMe2NCH2CH2X)(CH2Ph)]+. Isoelectronic neutral rare earth metal complexes [Ln(η5:η1-C5R4SiMe2NR′)R″] can be expected to be active for polymerization. To arrive at neutral 12-electron hydride and alkyl species of the rare earth metals, we employed a lanthanide tris(alkyl) complex [Ln(CH2SiMe3)3(THF)2] (Ln=Y, Lu, Yb, Er, Tb), which allows the facile synthesis of the linked amido-cyclopentadienyl complex [Ln(η5:η1-C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)]. Hydrogenolysis of the linked amido-cyclopentadienyl alkyl complex leads to the dimeric hydrido complex [Ln(η5:η1-C5Me4SiMe2NCMe3)(THF)(μ-H)]2. These complexes are single-site, single-component catalysts for the polymerization of ethylene and a variety of polar monomers such as acrylates and acrylonitrile. Nonpolar monomers such as -olefins and styrene, in contrast, give isolable mono-insertion products which allow detailed studies of the initiation process. 相似文献
4.
5.
Sinnema PJ Shapiro PJ Foo DM Twamley B 《Journal of the American Chemical Society》2002,124(37):10996-10997
Ring borylation of [Me4C2(eta5-C5H4)2CrCO] by B(C6F5)3 affords the zwitterionic complex {Me4(eta5-C5H4)(eta5-C4H3B(C6F5)3)}CrH(CO) (1), the first structurally characterized bent-metallocene complex of Cr(4+). This species decomposes thermally to the zwitterionic species {Me4(eta5-C5H4)(eta5-C4H3B(C6F5)3)}Cr (2) and the ionic species [Me4C2(eta5-C5H4)2CrCO][HB(C6F5)3] (3). The molecular structure of 2 is also described. 相似文献
6.
The 400 MHz 1H NMR spectra of the cardiac antiarrhythmic, mexiletine, 1, have been studied with different chiral solvating agents (CSA) to obtain a very promising method for direct determination of enantiomeric excess (e.e.) with limited amounts of 1. The methods included the use of β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), α-methoxy-α-(trifluoromethyl)phenylacetic acid (MTPA), and 2,2,2-trifluoro-1-(9-anthryl)ethanol (TFAE). Use of TFAE in CDCl3 with the free base of 1 appeared to give the best results, with enantiomeric shift differences observed for the signals of the sidechain methyl, CH 3CH, and the aryl methyls. 相似文献
7.
8.
S. Sinnema R.J. Radwanski J.J.M. Franse D.B. de Mooij K.H.J. Buschow 《Journal of magnetism and magnetic materials》1984,44(3):333-341
Ternary tetragonal compounds of the composition R2Fe14B were observed for R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The lattice constants and the X-ray density of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 20 T. These latter measurements were made in two mutually perpendicular directions, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy was found to consist of contributions due to the Fe and rare-earth sublattice, respectively. 相似文献
9.
Sinnema PJ Nairn J Zehnder R Shapiro PJ Twamley B Blumenfeld A 《Chemical communications (Cambridge, England)》2004,(1):110-111
The first thermally robust and air stable bent-sandwich chromocene complex with chromium in the +4 oxidation state has been isolated and fully characterized. 相似文献
10.
A. Sinnema F. van Rantwijk A.J. de Koning A.M. van Wijk H. van Bekkum 《Tetrahedron》1976,32(18):2269-2272
Hexamethylbicyclo[2.2.0]hexanes underwent endo,exo isomerization (skeletal inversion) and stereoselective supra, antara cleavage at 140–250°. The kinetics were studied and the products isolated and identified. The reactions are discussed in terms of a common 1,4-π-bonded intermediate which evolves to the invertomer or opens conrotatorially to methyl-substituted hexadienes. 相似文献