- Preparation, solution behavior, and solid-state structures of (1,3-R2C5H3)2UX2, where R Is CMe3 or SiMe3 and X is a one-electron ligand
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High-yield preparations of the uranium metallocenes [1,3-(Me3Si)2C5H3] 2UCl2 (Cp″2UCl2) and [1,3-(Me3C)2C5H3] 2UCl2 (Cp?2UCl2) have been developed from the reaction of UCl4 and the corresponding magnesocenes Cp″2Mg and Cp?2Mg in diethyl ether. The chloride ligands can be exchanged with either Me3SiBr or Me3Sil to give the uranium metallocene bromides or iodides. The fluorides were prepared by the reaction of BF3·OEt2 with Cp″2U(NMe)2, Cp?2U-(OMe)2, or Cp?2UMe2. The crystal structures of Cp″2UCl2, Cp?2UCl2, Cp″2UMe2, Cp?2UF2, and dimeric (Cp″2UF2)2 are reported. The idealized symmetry of the monomers Cp″2UX2 and Cp?2UCl2 is C2v when X is F, Cl, or Br and C2 when X is I or Me; in the dimer, the idealized symmetry is Ci. This preference is rationalized by intramolecular and intermolecular steric effects. The solution ring conformations and intramolecular exchange processes have been studied by variable-temperature 1H NMR spectroscopy. In all cases, the low-temperature limiting spectra are consistent with the idealized symmetry observed in the solid state.
- Lukens Jr., Wayne W.
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p. 1235 - 1246
(2008/10/08)
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- Gas-phase measurements of the kinetics of BF2(+)-induced polymerization of olefinic monomers
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The initial steps in the BF2(+)-induced polymerization of the monomers of ethylene, propylene, cis-2-butene, isobutene, and styrene have been observed in the gas phase at room temperature using the Selected-Ion Flow Tube (SIFT) technique.Rate constants and product distributions have been determined for the initiation of the polymerization in each case.All five initiation reactions were found to be rapid (k >/= 5.0*10-10 cm3 molecule-1 s-1).The primary product ions that propagate polymerization have been identified and sequential addition reactions have been followed in all five systems.For ethylene the energetics of the initial steps have been followed using ab initio molecular orbital theory.Reaction of BF2+ with the vapours of water and benzene have also been characterized. Key words: ion-induced polymerization; alkenes; kinetics; gas phase ion chemistry
- Forte, Leonard,Lien, Min H.,Hopkinson, Alan C.,Bohme, Diethard K.
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p. 1576 - 1583
(2007/10/02)
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