Regioselective Reactions of 1,3-Diynes with the Titanocene Vinylidene Fragment [Cp*2Ti=C=CH2]. Crystal and Molecular Structure of Cp*2TiC(C![]()
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- 作者：Rü ; diger Beckhaus ; Javier Sang ; Ulli Englert ; and Uwe Bö ; hme
- 刊名：Organometallics
- 出版年：1996
- 出版时间：October 29, 1996
- 年：1996
- 卷：15
- 期：22
- 页码：4731 - 4736
- 全文大小：216K
- 年卷期：v.15,no.22(October 29, 1996)
- ISSN：1520-6041
文摘
The titanocene vinylidene intermediate[Cp*2Ti=C=CH2] (6)(Cp*: C5(CH3)5), formedbyethene or methane elimination fromCp*2TiCH2CH2C=CH2(5) andCp*2Ti(CH=CH2)(CH3)(7), respectively, reacts with 1,3-diynes RC
C-CCR (R= Me (13a), Ph (13b), SiMe3(13c),CMe3 (13d)) by a [2 + 2]-cycloaddition,giving metallacyclobutenesCp*2TiC(CCR)=CRC=CH2(9a-d). Using the unsymmetrical 1,3-diyneRCCCCR1 (R = CMe3, R1 =SiMe3 (13e)), a9:1 mixture of the metallacyclobutenesCp*2TiC(CCR)=CR1C=CH2(9e) and Cp*2TiC(CCR1)=CRC=CH2 (9e')is formed. In all cases, exclusive formation of oneregioisomerexhibiting the CCR substituent in the 
chars/alpha.gif" BORDER=0>-position of themetallacycle is observed. Theregioselectivity of the formation of 9 is attributed to thepolarity of the CC bond as well asthe stereochemical conditions, proven by ab initiocalculations at the Hartree-Fock (HF)level of theory with the 3-21G(*) standard basis set and molecularmodeling. The X-raystructure of 9c is presented. Subsequent reactions of9 with an excess of the titanoceneintermediate 6, to form binuclear metallacycles, are notobserved.
C-CCR (R= Me (13a), Ph (13b), SiMe3(13c),CMe3 (13d)) by a [2 + 2]-cycloaddition,giving metallacyclobutenesCp*2TiC(CCR)=CRC=CH2(9a-d). Using the unsymmetrical 1,3-diyneRCCCCR1 (R = CMe3, R1 =SiMe3 (13e)), a9:1 mixture of the metallacyclobutenesCp*2TiC(CCR)=CR1C=CH2(9e) and Cp*2TiC(CCR1)=CRC=CH2 (9e')is formed. In all cases, exclusive formation of oneregioisomerexhibiting the CCR substituent in the chars/alpha.gif" BORDER=0>-position of themetallacycle is observed. Theregioselectivity of the formation of 9 is attributed to thepolarity of the CC bond as well asthe stereochemical conditions, proven by ab initiocalculations at the Hartree-Fock (HF)level of theory with the 3-21G(*) standard basis set and molecularmodeling. The X-raystructure of 9c is presented. Subsequent reactions of9 with an excess of the titanoceneintermediate 6, to form binuclear metallacycles, are notobserved.