Parker Gemma L, Lau Samantha, Leforestier Baptiste, Chaplin Adrian B
Department of Chemistry University of Warwick Gibbet Hill Road CV4 7AL Coventry UK.
Eur J Inorg Chem. 2019 Sep 8;2019(33):3791-3798. doi: 10.1002/ejic.201900727. Epub 2019 Aug 23.
Metal carbonyls are commonly employed probes for quantifying the donor properties of monodentate ligands. With a view to extending this methodology to -tridentate "pincer" ligands, the spectroscopic properties [ν(CO), , ] of rhodium(I) and rhodium(III) carbonyl complexes of the form [Rh(pincer)(CO)][BAr ] and [Rh(pincer)Cl(CO)][BAr ] have been critically analysed for four pyridyl-based pincer ligands, with two flanking oxazoline (NNN), phosphine (PNP), or N-heterocyclic carbene (CNC) donors. Our investigations indicate that the carbonyl bands of the rhodium(I) complexes are the most diagnostic, with frequencies discernibly decreasing in the order NNN > PNP > CNC. To gain deeper insight, a DFT-based energy decomposition analysis was performed and identified important bonding differences associated with the conformation of the pincer backbone, which clouds straightforward interpretation of the experimental IR data. A correlation between the difference in carbonyl stretching frequencies Δν(CO) and calculated thermodynamics of the Rh/Rh redox pairs was identified and could prove to be a useful mechanistic tool.
金属羰基化合物通常用作定量单齿配体给体性质的探针。为了将这种方法扩展到三齿“钳形”配体，对四种基于吡啶的钳形配体（带有两个侧翼恶唑啉（NNN）、膦（PNP）或N-杂环卡宾（CNC）给体）的[Rh(钳形)(CO)][BAr]和[Rh(钳形)Cl(CO)][BAr]形式的铑（I）和铑（III）羰基配合物的光谱性质[ν(CO)、 、 ]进行了严格分析。我们的研究表明，铑（I）配合物的羰基谱带最具诊断性，频率按NNN > PNP > CNC的顺序明显降低。为了获得更深入的见解，进行了基于密度泛函理论（DFT）的能量分解分析，并确定了与钳形主链构象相关的重要键合差异，这使得对实验红外数据的直接解释变得模糊。羰基伸缩频率差Δν(CO)与铑/铑氧化还原对的计算热力学之间的相关性被确定，这可能被证明是一种有用的机理工具。
