Ringenberg Mark R, Wittkamp Florian, Apfel Ulf-Peter, Kaim Wolfgang
Universität Stuttgart, Institut für Anorganische Chemie , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
Inorganic Chemistry 1/Bioinorganic Chemistry, Ruhr-University Bochum , Universitätsstrasse 150, D-44780 Bochum, Germany.
Inorg Chem. 2017 Jul 3;56(13):7501-7511. doi: 10.1021/acs.inorgchem.7b00957. Epub 2017 Jun 9.
The tricarbonyliron (TCFe) complexes Fe(CO)(dppf) and Fe(CO)(dppp), where dppf = 1,1'-bis(diphenylphosphino)ferrocene and dppp = 1,3-bis(diphenylphosphino)propane, exhibit redox activity that induces configurational isomerization. The presence of the ferrocenyl (Fc) group stabilizes higher oxidized forms of TCFe. Using spectroelectrochemistry (IR, UV-vis, Mössbauer, and EPR) and computational analysis, we can show that the Fc in the backbone of the dppf ligand tends to form a weak dative bond to the electrophilic TCFe and TCFe species. The open shell TCFe intermediate was stabilized by the distribution of spin between the two Fe centers (Fc and TCFe), whereas lacking the Fc moiety resulted in highly reactive TCFe species. The [Fe(CO)(dppf)] cation adopts two possible configurations, square-pyramidal (without an Fe-Fe interaction) and trigonal-bipyramidal (containing an Fe-Fe interaction). The two configurations are in equilibrium with the trigonal-bipyramidal configuration being enthalpically favored (ΔH = -7 kJ mol). There is an entropic penalty (ΔS = -20 J mol) due to tilting of the Cp (cyclopentadienide) rings of the dppf moieties by ∼8°. Additionally, the terminal iron hydride [FeH(CO)(dppf)]BF was formed by protonation with a strong acid (HBF·EtO).
三羰基铁（TCFe）配合物Fe(CO)(dppf)和Fe(CO)(dppp)，其中dppf = 1,1'-双（二苯基膦基）二茂铁，dppp = 1,3-双（二苯基膦基）丙烷，表现出能引发构型异构化的氧化还原活性。二茂铁基（Fc）基团的存在稳定了TCFe的更高氧化态。通过光谱电化学（红外、紫外可见、穆斯堡尔和电子顺磁共振）以及计算分析，我们可以表明dppf配体主链中的Fc倾向于与亲电的TCFe和TCFe物种形成弱配位键。开壳层TCFe中间体通过两个铁中心（Fc和TCFe）之间的自旋分布得以稳定，而缺少Fc部分则导致高活性的TCFe物种。[Fe(CO)(dppf)]阳离子有两种可能的构型，四方锥（无Fe-Fe相互作用）和三角双锥（含有Fe-Fe相互作用）。这两种构型处于平衡状态，三角双锥构型在焓上更有利（ΔH = -7 kJ/mol）。由于dppf部分的Cp（环戊二烯基）环倾斜约8°，存在熵罚（ΔS = -20 J/mol）。此外，末端氢化铁[FeH(CO)(dppf)]BF是通过用强酸（HBF₄·Et₂O）质子化形成的。
