Holzhacker Christian, Stöger Berthold, Carvalho Maria Deus, Ferreira Liliana P, Pittenauer Ernst, Allmaier Günter, Veiros Luis F, Realista Sara, Gil Adrià, Calhorda Maria José, Müller Danny, Kirchner Karl
Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria.
Dalton Trans. 2015 Aug 7;44(29):13071-86. doi: 10.1039/c5dt00832h.
Treatment of anhydrous FeX2 (X = Cl, Br) with 1 equiv. of the asymmetric chiral PNP pincer ligands PNP-R,TAD (R = iPr, tBu) with an R,R-TADDOL (TAD) moiety afforded complexes of the general formula [Fe(PNP)X2]. In the solid state these complexes adopt a tetrahedral geometry with the PNP ligand coordinated in κ(2)P,N-fashion, as shown by X-ray crystallography and Mössbauer spectroscopy. Magnetization studies led to a magnetic moment very close to 4.9μB reflecting the expected four unpaired d-electrons (quintet ground state). In solution there are equilibria between [Fe(κ(3)P,N,P-PNP-R,TAD)X2] and [Fe(κ(2)P,N-PNP-R,TAD)X2] complexes, i.e., the PNP-R,TAD ligand is hemilabile. At -50 °C these equilibria are slow and signals of the non-coordinated P-TAD arm of the κ(2)P,N-PNP-R,TAD ligand can be detected by (31)P{(1)H} NMR spectroscopy. Addition of BH3 to a solution of [Fe(PNP-iPr,TAD)Cl2] leads to selective boronation of the pendant P-TAD arm shifting the equilibrium towards the four-coordinate complex [Fe(κ(2)P,N-PNP-iPr,TAD(BH3))Cl2]. DFT calculations corroborate the existence of equilibria between four- and five-coordinated complexes. Addition of CO to [Fe(PNP-iPr,TAD)X2] in solution yields the diamagnetic octahedral complexes trans-[Fe(κ(3)P,N,P-PNP-iPr,TAD)(CO)X2], which react further with Ag(+) salts in the presence of CO to give the cationic complexes trans-Fe(κ(3)P,N,P-PNP-iPr,TAD)(CO)2X. CO addition most likely takes place at the five coordinate complex [Fe(κ(3)P,N,P-PNP-iPr,TAD)X2]. The mechanism for the CO addition was also investigated by DFT and the most favorable path obtained corresponds to the rearrangement of the pincer ligand first from a κ(2)P,N- to a κ(3)P,N,P-coordination mode followed by CO coordination to [Fe(κ(3)P,N,P-PNP-iPr,TAD)X2]. Complexes bearing tBu substituents do not react with CO. Moreover, in the solid state none of the tetrahedral complexes are able to bind CO.
用1当量的带有R,R - TADDOL（TAD）部分的不对称手性PNP钳形配体PNP - R,TAD（R =异丙基，叔丁基）处理无水FeX₂（X = Cl，Br），得到通式为[Fe(PNP)X₂]的配合物。X射线晶体学和穆斯堡尔光谱表明，在固态下这些配合物采用四面体几何构型，PNP配体以κ(2)P,N方式配位。磁化研究得出的磁矩非常接近4.9μB，反映出预期的四个未成对d电子（五重态基态）。在溶液中，[Fe(κ(3)P,N,P - PNP - R,TAD)X₂]和[Fe(κ(2)P,N - PNP - R,TAD)X₂]配合物之间存在平衡，即PNP - R,TAD配体是半不稳定的。在 - 50°C时，这些平衡较慢，通过(³¹)P{(¹)H}核磁共振光谱可以检测到κ(2)P,N - PNP - R,TAD配体未配位的P - TAD臂的信号。向[Fe(PNP -异丙基,TAD)Cl₂]溶液中加入BH₃会导致侧链P - TAD臂的选择性硼化，使平衡向四配位配合物[Fe(κ(2)P,N - PNP -异丙基,TAD(BH₃))Cl₂]移动。密度泛函理论计算证实了四配位和五配位配合物之间平衡的存在。在溶液中向[Fe(PNP -异丙基,TAD)X₂]中加入CO会生成抗磁性八面体配合物反式 - [Fe(κ(3)P,N,P - PNP -异丙基,TAD)(CO)X₂]，在CO存在下，它会与Ag⁺盐进一步反应生成阳离子配合物反式 - Fe(κ(3)P,N,P - PNP -异丙基,TAD)(CO)₂X。CO的加入最有可能发生在五配位配合物[Fe(κ(3)P,N,P - PNP -异丙基,TAD)X₂]上。还通过密度泛函理论研究了CO加入的机理，得到的最有利途径是钳形配体首先从κ(2)P,N -配位模式重排为κ(3)P,N,P -配位模式，然后CO与[Fe(κ(3)P,N,P - PNP -异丙基,TAD)X₂]配位。带有叔丁基取代基的配合物不与CO反应。此外，在固态下，没有一种四面体配合物能够结合CO。
