Can a Formally Zwitterionic Rhodium(I) Complex Emulate the Charge Density of a Cationic Rhodium(I) Complex? A Combined Synchrotron X-ray and Theoretical Charge-Density Study

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• 作者：El-Eulmi Bendeif ; Ch茅rif F. Matta ; Mark Stradiotto ; Pierre Fertey ; Claude Lecomte
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：March 19, 2012
• 年：2012
• 卷：51
• 期：6
• 页码：3754-3769
• 全文大小：816K
• 年卷期：v.51,no.6(March 19, 2012)
• ISSN：1520-510X

文摘

The molecular electron densities of structurally related cationic ([(魏²-3-PⁱPr₂-2-NMe₂-indene)Rh(COD)](CF₃SO₃), [1c](CF₃SO₃)) and formally zwitterionic ([(魏²-3-PⁱPr₂-2-NMe₂-indenide)Rh(COD)], 1z) complexes were accurately determined using synchrotron bright-source X-ray radiation at 30 K followed by multipolar refinement (COD = 畏⁴-1,5-cyclooctadiene). The densities were also obtained from density functional theory calculations with a large, locally dense basis set. A 28-electron ([Ar]3d¹⁰) core of the Rh atom was modeled by an effective core potential to obtain a density that was then augmented with relativistic cores according to the Keith鈥揊risch approximation. Calculations were performed at the experimental geometry and after vacuum-phase geometry optimization starting from the experimental geometry. Experimental and calculated geometries and electron-density distributions show that the electron density and electronic structure in the region of the Rh center are not significantly altered by protonation of the aromatic ring and that formal removal of CF₃SO₃H from [1c](CF₃SO₃) affords a complex 1z possessing substantial zwitterionic character (with a charge separation of ca. 0.9 electronic charge) featuring a negatively charged aromatic indenide framework. Further, the molecular electrostatic potentials of 1c and 1z exhibit similar topography around the metal, despite being drastically different in the vicinity of the indene or indenide portion of the cation (1c) and zwitterion (1z), respectively. Collectively, these observations obtained from high-level experimental and theoretical electron-density analysis confirm, for the first time, that appropriately designed zwitterionic complexes can effectively emulate the charge distribution found within ubiquitous cationic platinum-group metal catalyst complexes, in keeping with recent catalytic investigations.