Metal-Ligand Cooperativity of Phosphorus-Containing Pincer Systems
A metal-bound phosphorus atom can actively participate in various organometallic reactions as an electron reservoir and/or a group transfer site, because a phosphorus atom can adopt several distinct forms such as cationic phosphenium, anionic phosphide, n
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Metal-Ligand Cooperativity of Phosphorus-Containing Pincer Systems Seji Kim, Yeong-Eun Kim, and Yunho Lee
Contents 1 Introduction 2 Electron and Proton Transfer Between Metal and Phosphorus 3 C-group Transfer Reactions of a M-P Moiety 4 O-(S-)group Transfer Reactions of a M-P Moiety 5 N-group Transfer Reactions of a M-P Moiety 6 Conclusion References
Abstract A metal-bound phosphorus atom can actively participate in various organometallic reactions as an electron reservoir and/or a group transfer site, because a phosphorus atom can adopt several distinct forms such as cationic phosphenium, anionic phosphide, neutral phosphine, or a phosphinyl radical, thus making it more versatile. Furthermore, the ability of the phosphorus atom to have various oxidation states promotes the phosphorus atom to be cooperatively engaged in the reaction occurring at a metal center. By using such properties of phosphorus, metal-ligand cooperative (MLC) reactions occurring at a P-M moiety embedded in several transition metal pincer systems are discussed in this chapter. Keywords Group transfer · Metal-ligand cooperativity · Phosphorus · Pincer ligand · Redox active
S. Kim, Y.-E. Kim, and Y. Lee (*) Department of Chemistry, Seoul National University, Seoul, South Korea e-mail: [email protected]
S. Kim et al.
1 Introduction Phosphorus-containing ligands have been widely utilized in various organometallic reactions and transition metal catalyses. The profound impact of various tertiary phosphines as a neutral donor has been well-recognized, due to their excellent character, versatile enough to play important roles in transition metal catalytic processes, such as hydrogenation, hydroformylation, and polymerization. To control the electronic and steric properties of phosphorus-containing ligands, various substituents have been synthetically incorporated. An electronic factor can be easily managed by employing alkyl and aryl groups, as well as heteroatoms to give a P-E bond (E ¼ O, N, or Si). A steric property nicely defined by “cone angle” suggested by Tolman in 1970 [1] can be controlled by utilizing substituents of different sizes. With their relative ease of synthetic preparation, various alkyl and aryl groups have been employed to control the steric and electronic properties of transition metal complexes, which allows to achieve high stereoselectivity. Their advantageous effects have been well perceived from a wide range of organometallic studies. One of the advantages of working with phosphorus-containing organometallic complexes is the convenience of using 31P nuclear magnetic resonance (NMR) spectroscopy. Having the phosphorus nuclear spin of ½ with high sensitivity, its NMR spectroscopic data can be conveniently collected and utilized not only to characterize various diamagnetic species but also to study kinetics in order to obtain a mechanistic understanding of organometallic reactions [2]. Various mono- and multidentate ligands having phosphorus atom(s) as a donor moiety have been synthesized and widely employed. In particula
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