Metal-Ligand Cooperation at Phosphine-Based Acceptor Pincer Ligands
Acceptor ligands, which predominantly withdraw electron density from a transition metal center, often engage in weak metal-ligand interactions. These can be stabilized by flanking the acceptor moiety with strongly binding phosphines in a pincer motif, aff
- PDF / 4,504,775 Bytes
- 45 Pages / 439.37 x 666.142 pts Page_size
- 25 Downloads / 226 Views
Metal-Ligand Cooperation at Phosphine-Based Acceptor Pincer Ligands Martine R. Tiddens and Marc-Etienne Moret
Contents 1 Introduction 2 σ-Acceptor Ligands 2.1 Ambiphilic Ligands and the Retrodative Bond Model 2.2 Metal-Ligand Cooperative Catalysis Employing d10 Complexes of the σ-Acceptor Ligand Diphosphinoborane 2.3 Metal-Ligand Cooperative Reactivity at Group 8 and 9 Complexes of the σ-Acceptor Ligand Diphospinoborane 3 π-Acceptor Ligands 3.1 Dewar-Chatt-Duncanson Model 3.2 Anchored Olefin-Metal Complexes: First Steps Towards Metal-Ligand Cooperativity 3.3 Metal-Ligand Cooperative Catalysis Induced by Side-On Coordination of a Ketone 3.4 Imine Side-On Coordination: Synthesis and Metal-Ligand Cooperative Reactivity 4 Concluding Remarks References
Abstract Acceptor ligands, which predominantly withdraw electron density from a transition metal center, often engage in weak metal-ligand interactions. These can be stabilized by flanking the acceptor moiety with strongly binding phosphines in a pincer motif, affording more robust complexes in which bond activation and/or bond-forming events can take place while preserving the integrity of the molecule as a whole. This contribution highlights recent developments in this area. Compounds incorporating a borane at the central position are discussed first, followed by compounds incorporating an electrophilic C ¼ E (E ¼ C, O, N) π-bond. In both cases, recent examples highlight the ability of these ligands to (1) respond to electronic changes at the metal by modifying their binding mode and (2) accept a
M. R. Tiddens and M.-E. Moret (*) Utrecht University, Organic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht, The Netherlands e-mail: [email protected]
M. R. Tiddens and M.-E. Moret
nucleophilic fragment (e.g., hydride) from substrate molecules. Applications of acceptor pincer ligands as cooperative catalysts are discussed. Keywords Acceptor ligands · Ambiphilic ligands · Bond activation · Cooperative catalysis · Metal-ligand cooperation · Pincer · π-Ligands
1 Introduction The great successes of homogeneous catalysts in terms of stability, activity, and selectivity can be attributed to one’s ability to precisely tune the properties of a transition metal (TM) center by means of ligand design. Traditionally, supporting ligands have been thought of as spectator ligands whose role was to tune the properties of a transition metal and thereby facilitate metal-centered bond activation of substrates. This paradigm is currently challenged by systems displaying metalligand cooperative reactivity, including (1) ligands facilitating bifunctional substrate activation [1–6], (2) redox-active ligands [7–14], and (3) ligands showing hemilabile coordination behavior [15–20]. Here, bond activation and/or bond-forming events involve strong interplay of the metal center and the cooperative ligand, facilitating reaction pathways that would be less accessible by using conventional homogenous catalyst. A prominent early example of catalysts incorporati
Data Loading...
