[L*Rh(NBD)Cl] (L* = Chiral Cyclic Monophosphonite): A Novel Class of Rhodium(I) Complexes and Their Evaluation in the Asymmetric Hydrosilylation of Ketones. Investigations of the Effects of Temperatur
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- 作者：Dieter Haag ; Jan Runsink ; and Hans-Dieter Scharf
- 刊名：Organometallics
- 出版年：1998
- 出版时间：February 2, 1998
- 年：1998
- 卷：17
- 期：3
- 页码：398 - 409
- 全文大小：324K
- 年卷期：v.17,no.3(February 2, 1998)
- ISSN：1520-6041
文摘
A series of new rhodium(I) complexes[L*Rh(NBD)Cl] (L* = chiral cyclic phosphonitewitha fused 1,4-dioxane or cyclobutane ring in the backbone) wassynthesized via the corresponding borane-phosphonite adducts. They turned out to be highlyactive catalysts inthe asymmetric hydrosilylation of ketones in a broad temperature range.Evaluation of thetemperature dependent measurements according to the Eyring formalismdisclosed anonlinear relationship between ln P (P = ratioof the enantiomeric product alcohols) andthe reciprocal of temperature marked by the occurrence of points ofinversion in the middletemperature region between -5 and 30 
C. These findingsindicate a complexly composedselection mechanism that is controlled by at least two relevant partialsteps. Furthermore,by comparison of different catalysts based on a 1,4-dioxane, acyclobutane, or a 1,3-dioxolanering in the backbone of L*, the conformational properties of the ligandbackbone were revealedto be a crucial feature determining not only the extent but also thedirection of chiralitytransfer, thus providing a versatile tool for the construction ofstereocomplementary ligands.Accordingly, by proper choice of the ligand backbone and thetemperature, fairly goodenantioselectivities in the hydrosilylation of rather different ketoneslike acetophenone (82%ee) and pivalophenone (86% ee) can be achieved.
C. These findingsindicate a complexly composedselection mechanism that is controlled by at least two relevant partialsteps. Furthermore,by comparison of different catalysts based on a 1,4-dioxane, acyclobutane, or a 1,3-dioxolanering in the backbone of L*, the conformational properties of the ligandbackbone were revealedto be a crucial feature determining not only the extent but also thedirection of chiralitytransfer, thus providing a versatile tool for the construction ofstereocomplementary ligands.Accordingly, by proper choice of the ligand backbone and thetemperature, fairly goodenantioselectivities in the hydrosilylation of rather different ketoneslike acetophenone (82%ee) and pivalophenone (86% ee) can be achieved.