Experimental and Theoretical Investigation of Z-E Alkene Isomerization in [(Cy3P)2Cl2Ru]2(
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- 作者：Xiang Niu ; Lakshmi Gopal ; Michael P. Masingale ; Dale A. Braden ; Bruce S. Hudson ; and Michael B. Sponsler
- 刊名：Organometallics
- 出版年：2000
- 出版时间：February 21, 2000
- 年：2000
- 卷：19
- 期：4
- 页码：649 - 660
- 全文大小：346K
- 年卷期：v.19,no.4(February 21, 2000)
- ISSN：1520-6041
文摘
The conjugated diruthenium bisalkylidene complex [(Cy3P)2Cl2Ru]2(
-CHCH=CHCH) (1,an inseparable 10:1 mixture of E and Z alkene isomers 1E and 1Z) and the separate E andZ isomers of the monoruthenium alkylidene complexes (Cy3P)2Cl2Ru=CHCH=CHCH=CH2(2E and 2Z) and (Cy3P)2Cl2Ru=CHCH=CHCH3 (3E and 3Z) have each been synthesizedthrough the stoichiometric reaction of olefin metathesis catalysts. Each pair of isomersundergo Z-E isomerization, though the isomerization rates and their dependencies on excessalkene and PCy3 are very different. Isomerization in 1 is the fastest, with 
H
= 100 ± 5kJ/mol and S = 67 ± 3 J/(mol K) (1Z to 1E) or 49 ± 3 J/(mol K) (1E to 1Z) as determinedby dynamic NMR, giving t1/2 = 11 s for the approach to equilibrium at 25 
C. The rate ofthis isomerization shows no phosphine dependence. Isomerizations of 2Z and 3Z are slower(t1/2 = 5-20 h), but the former is promoted by PCy3, while the latter is inhibited. In thepresence of (Z)-1,3,5-hexatriene, the isomerization of 2Z is much slower, while theisomerization of 3Z is accelerated by (Z)-1,3-pentadiene. Density functional calculations wereperformed to help interpret these results and elucidate which of several possible isomerizationmechanisms operates in each case.
-CHCH=CHCH) (1,an inseparable 10:1 mixture of E and Z alkene isomers 1E and 1Z) and the separate E andZ isomers of the monoruthenium alkylidene complexes (Cy3P)2Cl2Ru=CHCH=CHCH=CH2(2E and 2Z) and (Cy3P)2Cl2Ru=CHCH=CHCH3 (3E and 3Z) have each been synthesizedthrough the stoichiometric reaction of olefin metathesis catalysts. Each pair of isomersundergo Z-E isomerization, though the isomerization rates and their dependencies on excessalkene and PCy3 are very different. Isomerization in 1 is the fastest, with H = 100 ± 5kJ/mol and S = 67 ± 3 J/(mol K) (1Z to 1E) or 49 ± 3 J/(mol K) (1E to 1Z) as determinedby dynamic NMR, giving t1/2 = 11 s for the approach to equilibrium at 25 C. The rate ofthis isomerization shows no phosphine dependence. Isomerizations of 2Z and 3Z are slower(t1/2 = 5-20 h), but the former is promoted by PCy3, while the latter is inhibited. In thepresence of (Z)-1,3,5-hexatriene, the isomerization of 2Z is much slower, while theisomerization of 3Z is accelerated by (Z)-1,3-pentadiene. Density functional calculations wereperformed to help interpret these results and elucidate which of several possible isomerizationmechanisms operates in each case.