Dynamic Behavior of Chiral Sulfonimidoyl-Substituted Allyl and Alkyl (Dimethylamino)titanium(IV) Complexes: Metallotropic Shift, Reversible 
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- 作者：Hans-Joachim Gais ; Peter R. Bruns ; Gerhard Raabe ; Rü ; diger Hainz ; Marcel Schleusner ; Jan Runsink ; and Gadamsetti S. Babu
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：May 11, 2005
- 年：2005
- 卷：127
- 期：18
- 页码：6617 - 6631
- 全文大小：340K
- 年卷期：v.127,no.18(May 11, 2005)
- ISSN：1520-5126
文摘
Variable-temperature 1H and 13C NMR spectroscopy of the sulfonimidoyl-substituted allyltitanium(IV) complexes E-1a-c and Z-1a-c, which carry diethylamino groups at the Ti atom, revealed a fast1,3-C,N-shift of the Ti atom, leading to an equilibrium between the epimeric C
-titanium allyl complexes Aand C and the N-titanium allyl aminosulfoxonium ylide B. Based on these findings a model for the reactionsof E-1a-c and Z-1a-c with aldehydes is proposed, which features regio- and diastereoselective reactionsof the N-titanium ylide B at the -position and the C-titanium complex A at the 
-position. Model ab initiocalculations of the methylene and allyl (dimethylamino)sulfoxonium ylides 10 and 14, respectively, revealedshort C-S bonds, a stabilization by both electrostatic interaction and negative hyperconjugation, and alow C-S rotational barrier. The ylides preferentially adopt C-S and C-N conformations in which thelone pair orbital at the C atom is periplanar to the S=O bond and that at the N atom periplanar to theC-Ph bond. Variable-temperature NMR spectroscopy of the sulfonimidoyl-substituted alkyltitanium(IV)complex 16, which carries diethylamino groups at the Ti atom, revealed a dynamic behavior leading to acomplete topomerization of all four methylene hydrogens of the C-ethyl groups. Two fast processes areheld responsible for the topomerization of the hydrogens of 16. The first one is a reversible intramolecular
-hydride elimination/alkene-Ti-H insertion with the intermediate formation of a complex between(Et2N)TiH and a 1-alkenyl sulfoximine, and the second one consists of a reversible 1,3-C,N-shift of the Tiatom in combination with a C-S bond rotation. Interestingly, the room-temperature NMR spectra of thecorresponding sulfonimidoyl-substituted alkyltitanium(IV) complex 17, which carries isopropoxy groups atthe Ti atom, give no indication of a similar dynamic behavior of this complex.
-titanium allyl complexes Aand C and the N-titanium allyl aminosulfoxonium ylide B. Based on these findings a model for the reactionsof E-1a-c and Z-1a-c with aldehydes is proposed, which features regio- and diastereoselective reactionsof the N-titanium ylide B at the -position and the C-titanium complex A at the -position. Model ab initiocalculations of the methylene and allyl (dimethylamino)sulfoxonium ylides 10 and 14, respectively, revealedshort C-S bonds, a stabilization by both electrostatic interaction and negative hyperconjugation, and alow C-S rotational barrier. The ylides preferentially adopt C-S and C-N conformations in which thelone pair orbital at the C atom is periplanar to the S=O bond and that at the N atom periplanar to theC-Ph bond. Variable-temperature NMR spectroscopy of the sulfonimidoyl-substituted alkyltitanium(IV)complex 16, which carries diethylamino groups at the Ti atom, revealed a dynamic behavior leading to acomplete topomerization of all four methylene hydrogens of the C-ethyl groups. Two fast processes areheld responsible for the topomerization of the hydrogens of 16. The first one is a reversible intramolecular-hydride elimination/alkene-Ti-H insertion with the intermediate formation of a complex between(Et2N)TiH and a 1-alkenyl sulfoximine, and the second one consists of a reversible 1,3-C,N-shift of the Tiatom in combination with a C-S bond rotation. Interestingly, the room-temperature NMR spectra of thecorresponding sulfonimidoyl-substituted alkyltitanium(IV) complex 17, which carries isopropoxy groups atthe Ti atom, give no indication of a similar dynamic behavior of this complex.