Regular and Inverse Secondary Kinetic Enthalpy Effects (KHE) for the Rate of Inversion of Thioether and 1,1'-Biisoquinoline Complexes of Ruthenium and Osmium
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- 作者：Michael T. Ashby ; Susan S. Alguindigue ; Justin D. Schwane ; and Tad A. Daniel
- 刊名：Inorganic Chemistry
- 出版年：2001
- 出版时间：December 17, 2001
- 年：2001
- 卷：40
- 期：26
- 页码：6643 - 6650
- 全文大小：107K
- 年卷期：v.40,no.26(December 17, 2001)
- ISSN：1520-510X
文摘
Thioether complexes with the formula 
/
-chloro(thioether)bis(2,2'-bipyridine)metal(II) (M = Ru, Os; thioether= dimethyl sulfide (3a+), diethyl sulfide (3b+), and tetrahydrothiophene (3c+)) have been synthesized. The ratesof inversion at the sulfur atom of the thioether ligands have been measured by spin-inversion transfer and line-shape NMR methods. In every case, the ruthenium derivative exhibits a faster inversion frequency at a giventemperature than the corresponding osmium derivative. In contrast, similar complexes with the formula chloro(
/
-1,1'-biisoquinoline)(2,2':6',2"-terpyridine)metal(II), 4(M=Ru,Os)+, undergo atropisomerization of themisdirected 1,1'-biisoquinoline (1,1'-biiq) ligand with rates that are faster for osmium than ruthenium. As a resultof the lanthanide contraction effect and the similar metric parameters associated with the structures of second-row and third-row transition metal derivatives, steric factors associated with the isomerizations are presumablysimilar for the Ru and Os derivatives of these compounds. Since third-row transition metal complexes tend tohave larger bond dissociation enthalpies (BDE) than their second-row congeners, we conclude the difference inreactivities of 3(M=Ru)+ versus 3(M=Os)+ and 4(M=Ru)+ versus 4(M=Os)+ are attributed to electronic effects.For 3, the S3p lone pair of the thioether, the principal 
donor orbital, is orthogonal to the metal acceptororbital in the transition state of inversion at sulfur and the S 3s orbital is an ineffective donor. Thus, a regularrelationship between the kinetic and thermodynamic stabilities of 3(M=Ru)+ and 3(M=Os)+ is observed for thedirected 
[misdirected]
directed (DMD) isomerization (the more thermodynamically stable bond is lessreactive). In contrast, atropisomerization of 4+ involves redirecting (strengthening) the M-N bonds of themisdirected 1,1'-biiq ligand in the transition state. Therefore, an inverse relationship between the kinetic andthermodynamic stabilities of 4(M=Ru)+ and 4(M=Os)+ is observed for the misdirected [directed] misdirected (MDM) isomerization (the more thermodynamically stable bond is more reactive). The rates obtainedfor 4+ are consistent with the rates of atropisomerization of /-(/-1,1'-biisoquinoline)bis(2,2'-bipyridine)metal(II), 1(M=Ru,Os)2+, and (
6-benzene) /-(/-1,1'-biisoquinoline)halometal(II), 2(M=Ru,Os;halo=Cl,I)+,that we reported previously. We term the relative rates of reaction of second-row versus third-row transitionmetal derivatives kinetic element effects (KEE = ksecond/kthird). While the KEE appears to be generally usefulwhen comparing reactions of isostructural species (e.g. the relative rates of 1(M=Ru)2+, 1(M=Os)2+, and 1(M=Ir)3+), different temperature dependencies of reactions prevent the comparison of related reactions betweenspecies that have different structures (e.g., the 1,1'-biiq atropisomerization reactions of 1(M=Ru,Os)2+ versus2(M=Ru,Os;halo=Cl,I)+ versus 4(M=Ru,Os)+). This problem is overcome by comparing entropies of activationand kinetic enthalpy effects (KHE = Hthird/Hsecond). For a given class of 1,1'-biiq complexes, we observe astructure/reactivity relationship between H and the torsional twist of the 1,1'-biiq ligands that are measured inthe solid state.
/-chloro(thioether)bis(2,2'-bipyridine)metal(II) (M = Ru, Os; thioether= dimethyl sulfide (3a+), diethyl sulfide (3b+), and tetrahydrothiophene (3c+)) have been synthesized. The ratesof inversion at the sulfur atom of the thioether ligands have been measured by spin-inversion transfer and line-shape NMR methods. In every case, the ruthenium derivative exhibits a faster inversion frequency at a giventemperature than the corresponding osmium derivative. In contrast, similar complexes with the formula chloro(/-1,1'-biisoquinoline)(2,2':6',2"-terpyridine)metal(II), 4(M=Ru,Os)+, undergo atropisomerization of themisdirected 1,1'-biisoquinoline (1,1'-biiq) ligand with rates that are faster for osmium than ruthenium. As a resultof the lanthanide contraction effect and the similar metric parameters associated with the structures of second-row and third-row transition metal derivatives, steric factors associated with the isomerizations are presumablysimilar for the Ru and Os derivatives of these compounds. Since third-row transition metal complexes tend tohave larger bond dissociation enthalpies (BDE) than their second-row congeners, we conclude the difference inreactivities of 3(M=Ru)+ versus 3(M=Os)+ and 4(M=Ru)+ versus 4(M=Os)+ are attributed to electronic effects.For 3, the S3p lone pair of the thioether, the principal donor orbital, is orthogonal to the metal acceptororbital in the transition state of inversion at sulfur and the S 3s orbital is an ineffective donor. Thus, a regularrelationship between the kinetic and thermodynamic stabilities of 3(M=Ru)+ and 3(M=Os)+ is observed for thedirected [misdirected] directed (DMD) isomerization (the more thermodynamically stable bond is lessreactive). In contrast, atropisomerization of 4+ involves redirecting (strengthening) the M-N bonds of themisdirected 1,1'-biiq ligand in the transition state. Therefore, an inverse relationship between the kinetic andthermodynamic stabilities of 4(M=Ru)+ and 4(M=Os)+ is observed for the misdirected [directed] misdirected (MDM) isomerization (the more thermodynamically stable bond is more reactive). The rates obtainedfor 4+ are consistent with the rates of atropisomerization of /-(/-1,1'-biisoquinoline)bis(2,2'-bipyridine)metal(II), 1(M=Ru,Os)2+, and (6-benzene) /-(/-1,1'-biisoquinoline)halometal(II), 2(M=Ru,Os;halo=Cl,I)+,that we reported previously. We term the relative rates of reaction of second-row versus third-row transitionmetal derivatives kinetic element effects (KEE = ksecond/kthird). While the KEE appears to be generally usefulwhen comparing reactions of isostructural species (e.g. the relative rates of 1(M=Ru)2+, 1(M=Os)2+, and 1(M=Ir)3+), different temperature dependencies of reactions prevent the comparison of related reactions betweenspecies that have different structures (e.g., the 1,1'-biiq atropisomerization reactions of 1(M=Ru,Os)2+ versus2(M=Ru,Os;halo=Cl,I)+ versus 4(M=Ru,Os)+). This problem is overcome by comparing entropies of activationand kinetic enthalpy effects (KHE = Hthird/Hsecond). For a given class of 1,1'-biiq complexes, we observe astructure/reactivity relationship between H and the torsional twist of the 1,1'-biiq ligands that are measured inthe solid state.