Lapointe Sébastien, Duari Prakash, Gessner Viktoria H
Faculty of Chemistry and Biochemistry, Chair of Inorganic Chemistry II, Ruhr University Bochum Universitätsstr. 150 44801 Bochum Germany
Chem Sci. 2023 Mar 13;14(14):3816-3825. doi: 10.1039/d2sc06759e. eCollection 2023 Apr 5.
Control of the metal ligand interaction by changes in the ligand protonation state is vital to many catalytic transformations based on metal-ligand cooperativity. Herein, we report on the coordination chemistry of a new PC(H)N pincer ligand with a central ylide as donor site, which through deprotonation to the corresponding yldiide changes from a neutral L-type ligand to an anionic LX-type PCN ligand. The isolation of a series of rhodium complexes showed that the strong donor ability of the neutral ylide PC(H)N is further increased upon deprotonation, as evidenced by one of the lowest reported CO stretching frequencies in complex [(PCN)Rh(CO)] (2) compared to other known rhodium carbonyl complexes. DFT calculations revealed that the high donor ability mostly results from the antibonding interaction of the p orbital at the ylide with the d orbital at rhodium, which enhances the backdonation into the π* orbital of the CO ligand. This unique interaction results in a rather long metal-carbon bond, but still a strong activation of the CO ligand in order to minimize repulsion between the filled orbitals at the rhodium and the ylide ligand. Accordingly, CO by phosphine replacement leads to a strong deviation from the square-planar geometry in the analogous phosphine complexes [(PCN)Rh(PR)] and an unusual reactivity with small alkyl halides, which upon oxidative addition add to the CO ligand, before inserting into the P-C bond in the pincer ligand. These results demonstrate the unique donor strength of yldiide ligands and their potential in the activation of strong bonds.
通过改变配体质子化状态来控制金属-配体相互作用对于许多基于金属-配体协同作用的催化转化至关重要。在此，我们报道了一种新型PC(H)N钳形配体的配位化学，该配体以中心叶立德作为供体位点，通过去质子化形成相应的叶立德二负离子，其从一个中性L型配体转变为一个阴离子LX型PCN配体。一系列铑配合物的分离表明，中性叶立德PC(H)N的强供体能力在去质子化后进一步增强，这一点通过配合物[(PCN)Rh(CO)] (2)中报道的最低CO伸缩频率之一与其他已知铑羰基配合物相比得到证明。密度泛函理论计算表明，高供体能力主要源于叶立德上p轨道与铑上d轨道的反键相互作用，这增强了向CO配体π*轨道的反馈π键作用。这种独特的相互作用导致了相当长的金属-碳键，但仍然对CO配体有很强的活化作用，以便使铑上的填充轨道与叶立德配体之间的排斥最小化。因此，在类似的膦配合物[(PCN)Rh(PR)]中，用膦取代CO会导致与平面正方形几何结构有很大偏差，并且与小烷基卤化物有异常的反应性，小烷基卤化物在氧化加成后加到CO配体上，然后再插入钳形配体的P-C键中。这些结果证明了叶立德二负离子配体独特的供体强度及其在活化强键方面的潜力。
