Angular Distortions at Benzylic Carbons Due to Intramolecular Polarization-Induced Metal鈥揂rene Interactions: A Case Study with Open-Shell Chromium(II) NHC Complexes
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- 作者：Andreas A. Danopoulos ; Kirill Yu. Monakhov ; Vincent Robert ; Pierre Braunstein ; Roberto Pattacini ; Susana Conde-Guada帽o ; Martin Hanton ; Robert P. Tooze
- 刊名：Organometallics
- 出版年：2013
- 出版时间：March 25, 2013
- 年：2013
- 卷：32
- 期：6
- 页码：1842-1850
- 全文大小：432K
- 年卷期：v.32,no.6(March 25, 2013)
- ISSN：1520-6041
文摘
The synthesis and full characterization of the unprecedented open-shell Cr(II) benzyl organometallic complexes [Cr(NHC)2(benzyl)2] (2) and [Cr(NHC*)(benzyl)2] (3) (NHC = N,N鈥?diisopropylimidazol-2-ylidene; NHC* = N,N鈥?bis(2,6-diisopropylphenyl)imidazol-2-ylidene) from [Cr(benzyl)3(THF)3] and [CrCl2(THF)2]/[Mg(benzyl)2], respectively, uncovered unusually acute angles (93掳 in 2 and 76掳 in 3) at the sp3 benzylic C of the coordinated benzyl ligands. Detailed theoretical analyses (DFT and CASPT2) of the four- and three-coordinate Cr(II) species were performed to elucidate the physical origin of the benzyl bending and led to the recognition of a noncovalent, intramolecular polarization-induced metal鈥揳rene (PIMA) interaction as being responsible for it. The energetic contribution from a single PIMA interaction is estimated to be ca. 50 kJ/mol. A comparison with the origin of the angular distortions in the d0 [Zr(benzyl)4] complex will also be presented. Sharing the common origin of an induced-dipole charge density scheme with intermolecular anion鈭捪€ interactions, the intramolecular PIMA interaction concept involving a transition metal unpaired d electron and arene鈭捪€ orbitals can be viewed as an extension of intermolecular anion鈭捪€ interactions and leads to remarkable quantitative prediction of the observed structural distortions. PIMA interactions may manifest themselves in diverse structural and dynamic phenomena and have broad implications in chemical sciences.