Cyclopentadienyl (Cp) ligands are a cornerstone of coordination chemistry and transition-metal catalysis. Their tuning profoundly influences the chemical and biological reactivity, the induced selectivity, and the stability of the corresponding metal complexes. However, compared to phosphines for instance, the accessible chemical space of Cps is rather narrow, exhibiting major limitations regarding the nature, pattern, and number of Cp substituents. A second caveat concerns the absence of a coherent synthetic strategy, with the available approaches lacking generality, scalability, and operational simplicity. Moreover, a desirable decoupling of sterics from electronics in Cp synthesis - by providing an independent choice of the degree of substitution and the attached functionalities - remains an unresolved issue.
In this thesis, we disclose a unified strategy toward underexplored 1,2,3-trisubstituted cyclopentadienes (1,2,3-Cps) with precise control of each substituent. The versatility of this robust and diversity-oriented synthesis platform enabled installation of elusive functionalities and sterically distinct substituent patterns. In catalytic benchmark systems, the cobalt and rhodium complexes directly outperformed classical Cp ligands with respect to reactivity, regioselectivity, catalyst loading, and turnover number.
Regarding chiral cyclopentadienyl ligands (Cpx), past ligand design efforts have predominantly focused on on disubstituted Cpx and the incorporation of different chiral pool entities. Despite a very strong potential application space, the availability of highly tunable fully substituted analogs and a concise synthetic approach to access them remain unresolved issues.
In this optic, we disclose a modular and convergent strategy for the rapid assembly of pentasubstituted Cpx ligands (CpV) with extensive steric and electronic tunability of the CpV substituents. It leverages the developed 1,2,3-Cp platform in a one-step dialkylation strategy, incorporating a wide range of chiral bis-electrophiles. The combinatorial approach enables fast diversification of the ligand set, thereby lowering the upfront synthetic investment needed for catalyst screenings, which increases time and resource economy.
In asymmetric catalytic assessments, multiple CpV ligands directly outperformed their di- or trisubstituted Cpx counterparts with simultaneously improved yields, diastereo-, and enantioselectivities. Easily introduced substituent modifications prompt strong responses in reaction outcome, vastly expanding the performance boundaries in future asymmetric methodology development.
