Heterobimetallische phosphanido-verbrückte Zweikern-Komplexe - Synthese von cis-rac-[(η-C5H4R)2Zr{μ-PH(2,4,6−iPr3C6H2)}2M(CO)4] (RMe,MCr,Mo; RH,MMo)

Heterobimetallic Phosphanido-bridged Dinuclear Complexes - Syntheses of cis-rac-[(η-C₅H₄R)₂Zr{μ-PH(2,4,6-ⁱPr₃C₆H₂)}₂M(CO)₄] (R?Me, M?Cr, Mo; R?H, M?Mo) The zirconocene bisphosphanido complexes [(η-C₅H₄R)₂Zr{PH(2,4,6-ⁱPr₃C₆H₂)}₂] (R?Me, H) react with [(NBD)M(CO)₄] (NBD?norbornadiene, M?Cr, Mo) to give only one diastereomer of the phosphanido-bridged heterobimetallic dinuclear complexes cis-rac-[(η-C₅H₄R)₂Zr{μ-PH(2,4,6-ⁱPr₃C₆H₂)}₂M(CO)₄] [R?Me, M?Cr ( 1 ), Mo ( 2 ); R?H, M?Mo ( 3 )]. However, no reaction was observed between [(η-C₅H₅)₂Zr{PH(2,4,6-^tBu₃ C₆H₂)}₂] and [Pt(PPh₃)₄]. 1—3 were characterised spectroscopically. For 1—3 , the presence of the racemic isomer was shown by NMR spectroscopy. No reaction was observed at room temperature for 3 and CS₂, (NO)BF₄, Me₃NO or PH(2,4,6-Me₃C₆H₂)₂. With Et₂AlH or PhC?CH decomposition of 3 was observed.     

Electron impact ionization of unstable enols: H2CCHOH,H2CC(OH)?CH3 and H2CC(OH)?C2H5

Ethenol, 2-hydroxypropene and 2-hydroxybutene-1 were prepared by low-pressure pyrolysis of cyclobutanol, 1-methylcyclobutanol and 1-ethylcyclobutanol, respectively. Mass spectra, ionization energies, appearance energies of metastable ions and kinetic energy releases were determined on a reverse Nier-Johnson double-focusing mass spectrometer. Mercury and CH₃ radicals from the pyrolysis of dimethylmercury were employed for calibration of the energy scale. The ionization energy of 2-hydroxybutene-1 is 8.55 ± 0.1 eV and the appearance energies of [C₂H₅CO]⁺ and [CH₃CO]⁺ from that molecule are 10.25 ± 0.1 and 10.40 ± 0.1 eV, respectively. Changes observed in metastable peak shapes for certain fragmentation reactions upon pyrolysis are discussed.     

The distonic ions HO+CHCH2C˙H2 and CH3C(O+H)CH2C˙H2

The distonic ions HO⁺?CHCH₂C^˙H₂ (1) and CH₃C(?O⁺H)CH₂C^˙H₂ (2) were directly generated, their decompositions characterized and their appearance energies determined by photoionization. Heats of formation derived from the appearance energies were 757 kJ mol^?1 for 1 and 692 kJ mol^?1 for 2. Deuterium labeling demonstrates that both ions decompose at low energies in the same ways as their isomers with the same skeletal structures, consistent with proposals that 1 and 2 are intermediates in the decompositions of those systems. Surprisingly, the values of the translational energy releases accompanying the formation of CH₃CO⁺ and C₂H₅CO⁺ from 2 appear to be inversely proportional to the available excess energy. The 1,2-H-shift RC(?O⁺H)CH₂C˙H₂ → RC(?O₊H)C˙HCH₃ is compared to the corresponding, non-occurring 1,2-H-shift in alkyl free radicals.     

Synthese,Strukturen und Reaktivität von [(2,4,6-Ph3C6H2)Te(μ2-O)X]2 (X  Br und I)

Synthesis, Structures, and Reactivity of [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)X]₂ (X ? Br, I) [(2,4,6-Ph₃C₆H₂)Te]₂ reacts with iodine affording the aryltellurenic halide (2,4,6-Ph₃C₆H₂)TeI, which is oxidized by oxygen to yield [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)I]₂. It crystallizes with two molecules of dichloromethane in the monoclinic space group P2₁/c with a unit cell of the dimensions a = 911.3(4); b = 1153.3(2); c = 2244.1(9) pm; β = 93.53(2)°, Z = 2). The analogues bromo compound [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)Br]₂ is obtained by the reaction of [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)I]₂ with NH₄Br. It crystallizes with two molecules of xylene in the monoclinic space group P2₁/n (a = 1067.5(5); b = 1018.4(4); c = 2486.5(8) pm; β = 101.71(2)°; Z = 2). Both compounds are built up by two (2,4,6-Ph₃C₆H₂)TeX units (X ? Br, I) which are linked by two oxgen bridges to form centrosymmetric molecules. The Te? O? Te angles are 102°. Distinct Te? O bond lengths have been found (191.4(2) and 208.6(2) pm in [(2,4,6-Ph₃C₆H₂)Te(μ₂-O)I]₂ and 189.8(4)/208.4(5 pm in the bromo compound).     

Structures and isomerizations of carbenoids H2CCCLiX (X  F,Cl)

Novel structures of H₂C?C?CLiX (X ? F, Cl) were determined using HF/STO-3G gradient method. Both of the carbenoids have two equilibrium structures, askew and linear forms, at the level of calculation. In the case X?F, the former is more stable, but in the case X=Cl, the latter is more stable. The frontier MOs are given and analyzed.     

Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (MTi,XCH3, MZr,XiBu) in copolymerization of ethylene with styrene

Catalytic activity of Me₂SiCp*N^tBuMX₂/(CPh₃)(B(C₆F₅)₄) [MTi, XCH₃ (1); MZr, X=ⁱBu (2)] systems in the ethylene/styrene (E/S) feed was examined. Experimental data revealed high activity for the catalytic system (1) for copolymerization ethylene with styrene, whereas the system with enhanced catalytic activity for ethylene homopolymerization (2) was temporarily blocked in the styrene presence yielding, even at high styrene content, homopolyethylene as the final product. Properties of thus obtained polymers were analyzed. Catalytic system (1) occurred very sensitive to S/E ratio in the comonomers feed. The 10‐fold acceleration for ethylene consumption was shown in two experimental sets conducted at S/E = 1.3 ratio, 1 bar, and 7.5 bar ethylene pressure, respectively. The consequent enhancement in S/E ratio resulted in slowing down both ethylene consumption and catalyst deactivation rates. Atactic polystyrene was formed at high styrene content with the catalyst (1). Catalytic system (1) allowed design of products with the highest styrene content (20 mol %) at low ethylene pressure, moderate temperature, and high S/E ratio. The apparent activation energy estimated from the initial rates of ethylene consumption was 54.6 kJ/mol. Analysis of apparent reactivity factors (r_E = 9 and r_S = 0.04; r_E × r_S = 0.4) and ¹³C‐NMR copolymer spectra revealed an alternating tendency of the comonomers for active center incorporation. DSC measurements showed considerable decrease of melting points and crystallinity even for copolymers with low styrene content. The catalyst produced relatively high–molecular weight copolymers (140–150 kg/mol) even at 80°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1083–1093, 1999