Rhodium(I) and Iridium(I) Complexes of the Conformationally Rigid IBioxMe4 Ligand: Computational and Experimental Studies of Unusually Tilted NHC Coordination Geometries

详细信息    查看全文

• 作者：Jan-Niclas Luy ; Simone A. Hauser ; Adrian B. Chaplin ; Ralf Tonner
• 刊名：Organometallics
• 出版年：2015
• 出版时间：October 26, 2015
• 年：2015
• 卷：34
• 期：20
• 页码：5099-5112
• 全文大小：982K
• ISSN：1520-6041

文摘

Computational methods have been used to analyze distorted coordination geometries in a coherent range of known and new rhodium(I) and iridium(I) complexes containing bioxazoline-based NHC ligands (IBiox). Such distortions are readily placed in context of the literature through measurement of the Cnt(NHC)鈥揅b>NCNb>鈥揗 angle (螛b>NHCb>; Cnt = ring centroid). On the basis of restricted potential energy calculations using cis-[M(IBioxMeb>4b>)(CO)b>2b>Cl] (<b>M1b>; M = Rh, Ir), in-plane (yawing) tilting of the NHC was found to incur significantly steeper energetic penalties than orthogonal out-of-plane (pitching) movement, which is characterized by noticeably flat potential energy surfaces. Energy decomposition analysis (EDA) of the ground-state and pitched structures of <b>M1b> indicated only minor differences in bonding characteristics. In contrast, yawing of the NHC ligand is associated with a significant increase in Pauli repulsion (i.e., sterics) and reduction in M鈫扤HC 蟺 back donation, but is counteracted by supplemental stabilizing bonding interactions only possible due to the closer proximity of the methyl substituents with the metal and ancillary ligands. Aided by this analysis, comparison with a range of carefully selected model systems and EDA, distorted coordination modes in trans-[M(IBioxMeb>4b>)b>2b>(COE)Cl] (<b>M2b>; M = Rh, Ir) and [M(IBioxMeb>4b>)b>3b>]⁺ (<b>M3b>; M = Rh, Ir) have been rationalized. Steric interactions were identified as the major contributing factor and are associated with a high degree of NHC pitching. In the case of <b>Rh3b>, weak agostic interactions also contribute to the distortions, particularly with respect to NHC yawing, and are notable for increasing the bond dissociation energy of the distorted ligands. Supplementing the computational analysis, an analogue of the formally 14 VE Rh(I) species <b>Rh3b> bearing the cyclohexyl-functionalized IBiox6 ligand ([Rh(IBiox6)b>3b>]⁺, <b>Rh3-Cyb>) was prepared and found to exhibit an exceptionally distorted NHC ligand (螛b>NHCb> = 155.7(2)掳) in the solid state.