- On the regioselectivity of alkylation of the (trimethylsilyl) tetramethylcyclopentadienide anion. A new approach to the synthesis of 1,2,3,4-tetramethylfulvene
-
The regioselectivity of alkylation of lithium (trimethylsilyl) tetramethylcyclopentadienide C5Me4SiMe3 -Li+ was studied by 1H and 13C NMR spectroscopy using its reactions with MeI, MeOTs, ClCH2CH 2Br, and ClCH2CH2I in different solvents as representative examples. Sterically non-hindered MeI and MeOTs presumably attack the C atom bonded to the silyl group giving 1,2,3,4,5- pentamethylcyclopentadienylsilane. For bulkier alkyl halides, such as ClCH 2CH2Br and ClCH2CH2I, the regioselectivity of alkylation changes to form preferentially gem-dialkyl-substituted cyclopentadienes. The reaction of C5Me 4SiMe3 -Li+ with formaldehyde affords 1,2,3,4-tetramethylfulvene in a high yield, providing an alternative synthetic approach to a number of ω-functionalized peralkylated cyclopentadienes. The quantum-chemical calculations of the C5Me 4SiMe3 - anion by the RHF and DFT (RMPW1PW91) methods in the valence-split 6-311+G(d,p) basis set are in good agreement with the experimental data.
- Krut'ko,Borzov,Veksler
-
-
Read Online
- 29Si NMR Spectra of Silicon-Containing Uranium Complexes
-
29Si NMR spectra have been recorded for a series of uranium complexes containing silicon, and the data have been combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or oxidation state. Data on 52 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals that, although there is some overlap in the range of shifts of U4+ complexes versus U3+ complexes, in general U3+ species have shifts more negative than those of their U4+ analogues. The single U2+ example has the most negative shift of all at -322 ppm at 170 K. With only a few exceptions, U4+ complexes have shifts between 0 and -150 ppm (vs SiMe4), whereas U3+ complexes resonate between -120 and -250 ppm. The small data set on U5+ species exhibits a broad 250 ppm range centered near 40 ppm. The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion exhibit chemical shifts less negative than those of other types of ligands.
- Windorff, Cory J.,Evans, William J.
-
-
Read Online
- Structural analysis of zincocenes with substituted cyclopentadienyl rings
-
New zincocenes [ZnCp′2] (2-5) with substituted cyclopentadienyl ligands C5Me4H, C5Me 4tBu, C5Me4SiMe2tBu and C 5Me4SiMe3, respectively, have been prepared by the reaction of ZnCl2 with the appropriate Cp′-transfer reagent. For a comparative structural study, the known [Zn(C5H 4SiMe3)2] (1), has also been investigated, along with the mixed-ring zincocenes [Zn(C5Me5)(C 5Me4SiMe3)] (6) and [Zn(C5Me 5)(C5H4SiMe3)] (7), the last two obtained by conproportionation of [Zn(C5Me5),] with 5 or 1, as appropriate. All new compounds were characterised by NMR spectroscopy, and by X-ray methods, with the exception of 7, which yields a side-product (C) upon attempted crystallisation. Compounds 5 and 6 were also investigated by 13C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped-sandwich geometries. Compounds 5 and 6 have rigid, η5/ η1(σ) structures, in which the monohapto C 5Me4SiMe3 ligand is bound to zinc through the silyl-bearing carbon atom, forming a Zn-C bond of comparable strength to the Zn-Me bond in ZnMe2. Zincocene 5 has dynamic behaviour in solution, but a rigid η5/η1(σ) structure in the solid state, as revealed by 13C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η1-Cp′ group (Me and SiMe3) have permitted observation for the first time of the rigid η5/η1 solution structure. Iminoacyl compounds of composition [Zn(η5- C5Me4R)(η1-C(NXyl)C5Me 4R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl = 2,6-dimethylphenylisocyanide) have also been obtained and characterised.
- Fernandez, Rafael,Grirrane, Abdessamad,Resa, Irene,Rodriguez, Amor,Carmona, Ernesto,Alvarez, Eleuterio,Gutierrez-Puebla, Enrique,Monge, Angeles,Del Amo, Juan Miguel Lopez,Limbach, Hans-Heinrich,Lledos, Agusti,Maseras, Feliu,Del Rio, Diego
-
-
Read Online
- Producing polyolefin products
-
Catalyst systems and methods for making and using the same. A method of methylating a catalyst composition while substantially normalizing the entiomeric distribution is provided. The method includes slurrying the organometallic compound in dimethoxyethane (DME), and adding a solution of RMgBr in DME, wherein R is a methyl group or a benzyl group, and wherein the RMgBr is greater than about 2.3 equivalents relative to the organometallic compound. After the addition of the RMgBr, the slurry is mixed for at least about four hours. An alkylated organometallic is isolated, wherein the methylated species has a meso/rac ratio that is between about 0.9 and about 1.2.
- -
-
Page/Page column 40
(2018/04/20)
-
- Influence electronique et sterique du ligand tetramethylcyclopentadienyle sur les proprietes physiques et sur la reactivite de complexes du titane et du zirconium
-
The complexes (C5Me4H)2MR1R2 (M=Ti, Zr) and (C5Me4H)(C5H5)MR1R2 (M=Ti) have been prepared (R1=R2=Cl, CH3, C6H5, p-C6H4CH3, CO; R1=Cl, R2=CH3, C6H5, p-C6H4CH3).The NMR and IR spectra of these complexes indicate that C5Me4H exhibits an electron-donor effect more important than C5H5 and a little bit weaker than that of C5Me5.A structural investigation of the complex (C5Me4H)2Zr(C6H5)Cl and the study of the 1H or 13C dynamic NMR properties of the compounds (C5Me4H)2MR1R2 (M=Ti, Zr; R1=R2=C6H5, p-C6H4CH3; R1=Cl, Br, R2=C6H5, p-C6H4CH3) show clearly that C5Me4H has a steric effect intermediate between C5H5 and C5Me5.The steric or electronic effects of C5Me4H have been used to induce specific isomerization reactions of various alkenes by using (C5Me4H)2Ti(CH3)2 as catalyst. --- Key words: zirconium, titanium, tetramethylcyclopentadienyl, photo-assisted, isomerization.
- Courtot, P.,Pichon, R.,Salaun, J. Y.,Toupet, L.
-
p. 661 - 672
(2007/10/02)
-