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，以阐明2,2'-二膦烷及其配位化学。在初步实验中，发现这些体系表现出分岔反应，分别由所使用的金属离子和前体控制。一般来说，不同的反应途径可能导致刚性[PCCP]-钳形配合物或PHC-配位物质（PHC = p -杂环碳）。为了控制和选择性地合成这些不同类型的复合物，需要对后来的发现进行深入分析。这个分析无疑是这个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，重点将放在早期过渡金属配合物及其反应性上。考虑到简单的理论考虑表明，这种[PCCP]-钳形配合物非常适合M=E-和M≡E基序（E = CR2， NR和CR）的稳定，打算合成第4，第5和第6族烷基烯和烷基炔。反过来，这些配合物在不同催化过程中的应用，如烯烃或炔的复分解，将被检查。然而，前面提到的p杂环碳烯似乎特别适合于合成晚期过渡金属配合物。在这方面，重点将放在选定的贵金属（钌、铑和钯及其较重的同系物）上，因为它们的phc配合物在均相催化（特别是催化转移加氢、烯烃复分解和烯丙基取代反应）方面的各种应用前景很大。为了开发pch -配合物制备的基本概念，也打算合成双phc -配合物。随后，这些配合物必须根据其在均相催化中的应用进行评估，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.