Kinetic Element Effect for Atropisomerization of an Organometallic Complex of the Misdirected Ligand 1,1'-Biisoquinoline
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- 作者：Michael T. Ashby ; Susan S. Alguindigue ; and Masood A. Khan
- 刊名：Organometallics
- 出版年：2000
- 出版时间：February 21, 2000
- 年：2000
- 卷：19
- 期：4
- 页码：547 - 552
- 全文大小：135K
- 年卷期：v.19,no.4(February 21, 2000)
- ISSN：1520-6041
文摘
The quinoline moieties of the metal-bound 
2-1,1'-biisoquinoline ligand of (6-benzene)(
/
-1,1'-biisoquinoline)halometal(II) hexafluorophosphate (metal = ruthenium, osmium; halo= chloro, iodo; 1(M = Ru, Os; X = Cl, I)) are stereotopic. The rates of atropisomerization ofthe /-1,1'-biisoquinoline ligand, measured by spin-labeling NMR methods, indicate theenergy barrier is higher for 1(Ru) than 1(Os); e.g., 
H
[1(M = Ru, X = Cl)] = 77.3(2) andH[1(M = Os, X = Cl)] = 71.2(2) kJ mol-1. Since the crystal structures of 1(M = Ru, X =Cl) and 1(M = Os, X = Cl) reveal comparable metric parameters, steric factors associatedwith atropisomerization of the 1,1'-biisoquinoline ligand, essentially the deformation of the1,1'-binaphthylene skeleton that is necessary to pass H8 and H8' past one another, arepresumably equivalent for the Ru and Os derivatives. Assuming that normal bond energiesare greater for the third-row transition metal than for second-row transition metals, weconclude the difference in reactivity can be attributed to electronic factors-the 
-donororbitals and 
-acceptor orbitals of the 1,1-biisoquinoline ligand are misdirected in the groundstate but redirected in the syn transition state of atropisomerization. Thus, an inverserelationship between the kinetic and thermodynamic stabilities of 1 is observed for themisdirected 
[directed] misdirected (MDM) isomerization of 1 (the more thermodynamically stable bond is more reactive). Atropisomerization of 1 represents only the secondexample of such an inverse free-energy relationship for a thermodynamically controlledreaction, and it contrasts with the regular relationship that has been found for theatropisomerization of related directed [misdirected] directed (DMD) systems.
2-1,1'-biisoquinoline ligand of (6-benzene)(/-1,1'-biisoquinoline)halometal(II) hexafluorophosphate (metal = ruthenium, osmium; halo= chloro, iodo; 1(M = Ru, Os; X = Cl, I)) are stereotopic. The rates of atropisomerization ofthe /-1,1'-biisoquinoline ligand, measured by spin-labeling NMR methods, indicate theenergy barrier is higher for 1(Ru) than 1(Os); e.g., H[1(M = Ru, X = Cl)] = 77.3(2) andH[1(M = Os, X = Cl)] = 71.2(2) kJ mol-1. Since the crystal structures of 1(M = Ru, X =Cl) and 1(M = Os, X = Cl) reveal comparable metric parameters, steric factors associatedwith atropisomerization of the 1,1'-biisoquinoline ligand, essentially the deformation of the1,1'-binaphthylene skeleton that is necessary to pass H8 and H8' past one another, arepresumably equivalent for the Ru and Os derivatives. Assuming that normal bond energiesare greater for the third-row transition metal than for second-row transition metals, weconclude the difference in reactivity can be attributed to electronic factors-the -donororbitals and -acceptor orbitals of the 1,1-biisoquinoline ligand are misdirected in the groundstate but redirected in the syn transition state of atropisomerization. Thus, an inverserelationship between the kinetic and thermodynamic stabilities of 1 is observed for themisdirected [directed] misdirected (MDM) isomerization of 1 (the more thermodynamically stable bond is more reactive). Atropisomerization of 1 represents only the secondexample of such an inverse free-energy relationship for a thermodynamically controlledreaction, and it contrasts with the regular relationship that has been found for theatropisomerization of related directed [misdirected] directed (DMD) systems.