Conformational Isomerism in (p-RC6H4NC)2W(dppe)2: Substantial Structural Changes Resulting from Subtle Differences in the 
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- 作者：Nicole L. Wagner ; Frank E. Laib ; and Dennis W. Bennett
- 刊名：Journal of the American Chemical Society
- 出版年：2000
- 出版时间：November 8, 2000
- 年：2000
- 卷：122
- 期：44
- 页码：10856 - 10867
- 全文大小：298K
- 年卷期：v.122,no.44(November 8, 2000)
- ISSN：1520-5126
文摘
Bis(arylisocyanide) complexes of tungsten containing bulky bidentate aryl phosphine ligands adopteither cis or trans conformations, depending on the nature of the para-substituent group on the aryl isocyanideligand. Ab initio calculations on a series of ligands, p-RC6H4NC, indicate that the energy of the LUMO isdetermined by the electron-withdrawing/donating capabilities of the substituent group, which determine therelative 
-acidity of the ligand. Strong acids, which contain electron-withdrawing groups, tend to polarizesufficient charge density away from the metal center to effect the formation of the sterically less favorable,but electronically stabilized, cis conformer. Weaker acids, containing donor substituents, do not provideenough electronic stabilization to overcome steric repulsion, resulting in the adoption of trans geometry.(CNC6H4NC)W(dppe)2 exists as the cis conformer, as does (CNC6H2(CH3)2NC)W(dppe)2, while (CNC6(CH3)4NC)W(dppe)2, with increased steric bulk coupled with decreased -acidity, exists as the trans conformer.Theoretical and experimental studies indicate that the energy match between isocyanide ligands and the metalcenter can be modified significantly by the selection of various substituents and that relatively subtle variationsin the electronic structure of the ligands can have dramatic effects on the structures of the resulting complexes.
-acidity of the ligand. Strong acids, which contain electron-withdrawing groups, tend to polarizesufficient charge density away from the metal center to effect the formation of the sterically less favorable,but electronically stabilized, cis conformer. Weaker acids, containing donor substituents, do not provideenough electronic stabilization to overcome steric repulsion, resulting in the adoption of trans geometry.(CNC6H4NC)W(dppe)2 exists as the cis conformer, as does (CNC6H2(CH3)2NC)W(dppe)2, while (CNC6(CH3)4NC)W(dppe)2, with increased steric bulk coupled with decreased -acidity, exists as the trans conformer.Theoretical and experimental studies indicate that the energy match between isocyanide ligands and the metalcenter can be modified significantly by the selection of various substituents and that relatively subtle variationsin the electronic structure of the ligands can have dramatic effects on the structures of the resulting complexes.