2,2'-Diphosphinotolanes and Their Multifaceted Reactivities: On the Edge Between [PCCP]-Pincer Ligands and P-Heterocyclic Carbenes

在本研究项目的范围内，将进行探索性研究，以揭示2，2‘-二膦戊烷及其配位化学。在初步实验中，发现这些体系表现出分叉的反应活性，分别受所用金属离子和前驱体的控制。一般来说，发散的反应途径可能导致刚性的[PCCP]-钳形络合物或PHC配位的物种(PHC=P-杂环卡宾)。为了能够控制和选择性地合成这些不同类型的络合物，需要对后来的发现进行深入分析。这一分析无疑代表了这一研究项目过程中要达到的最重要的里程碑之一。在[PCCP]-钳形支架的情况下，重点将集中在早期过渡金属络合物及其反应性上。由于简单的理论考虑表明，这种[PCCP]-钳形化合物非常适合于稳定M=E-和M≡E-基序(E=Cr2，NR和CR)，因此我们打算合成第4族、第5族和第6族亚烷基和亚烷基。接下来，将考察这些络合物在不同催化过程中的应用，例如烯烃或炔烃的歧化反应。然而，上述P-杂环卡宾似乎特别适合于合成后过渡金属络合物。在这方面，重点将放在选定的贵金属(Ru、Rh和Pd及其较重的同系物)上，因为它们的PHC-络合物在均相催化中具有广泛的应用前景(特别是催化转移氢化、烯烃歧化和烯丙基取代反应)。为了开发制备PCH-络合物的基本概念，还打算合成双-PHC-络合物。连续地，必须评估这些络合物在均相催化中的应用，这为进入完全未知的科学领域铺平了道路。

Within the bounds of this research project, exploratory studies are to be conducted in order to shine light on 2,2'-diphosphinotolanes and their coordination chemistry. In preliminary experiments, these systems were found to exhibit bifurcated reactivities, which are governed by the employed metal ions and precursors, respectively. In general, the divergent reaction pathways may either lead to rigid [PCCP]-pincer complexes or to PHC-coordinated species (PHC = P-heterocyclic carbene). To allow for a controlled and selective synthesis of these different types of complexes, an in-depth analysis of the later discovery is required. This analysis certainly represents one of the most important milestones to be reached over the course of this research project. In the case of [PCCP]-pincer scaffolds, the focus will be set on early transition metal complexes and on their reactivities. Given that simple theoretic considerations indicate that such [PCCP]-pincer complexes are well-suited for the stabilization of M=E- and M≡E-motifs (E = CR2, NR and CR), the synthesis of group 4, group 5 and group 6 alkylidenes and alkylidynes is intended. In turn, these complexes are to be examined with respect to their application in different catalytic processes, such as alkene or alkyne metathesis. The aforementioned P-heterocyclic carbenes, however, seem to be particularly well-suited for the synthesis of late transition metal complexes. In this context, the focus will be set on selected precious metals (Ruthenium, Rhodium and Palladium and their heavier homologs), as their PHC-complexes hold great promise for various applications in homogeneous catalysis (inter alia for catalytic transfer hydrogenations, alkene metathesis and allylic substitution reactions). To exploit the underlying concept for the preparation of PCH-complexes, the synthesis of bis-PHC-complexes is intended as well. Consecutively, these complexes have to be evaluated with respect to their applications in homogeneous catalysis, which paves the way for entering entirely uncharted scientific terrain.