Top Organomet Chem (2021) 68: 25–70
https://doi.org/10.1007/3418_2020_70
# Springer Nature Switzerland AG 2020
Published online: 1 December 2020
Metal-Ligand Cooperation
at Phosphine-Based Acceptor Pincer
Ligands
Martine R. Tiddens and Marc-Etienne Moret
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 σ-Acceptor Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.1 Ambiphilic Ligands and the Retrodative Bond Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 Metal-Ligand Cooperative Catalysis Employing d
10 Complexes of the σ-Acceptor
Ligand Diphosphinoborane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3 Metal-Ligand Cooperative Reactivity at Group 8 and 9 Complexes of the σ-Acceptor
Ligand Diphospinoborane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3 π-Acceptor Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1 Dewar-Chatt-Duncanson Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2 Anchored Olefin-Metal Complexes: First Steps Towards Metal-Ligand
Cooperativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3 Metal-Ligand Cooperative Catalysis Induced by Side-On Coordination of a Ketone . . . 49
3.4 Imine Side-On Coordination: Synthesis and Metal-Ligand Cooperative Reactivity . . . 59
4 Concluding Remarks . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . 62
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
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: M.Moret@uu.nl
https://doi.org/10.1007/3418_2020_70
# Springer Nature Switzerland AG 2020
Published online: 1 December 2020
Metal-Ligand Cooperation
at Phosphine-Based Acceptor Pincer
Ligands
Martine R. Tiddens and Marc-Etienne Moret
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 σ-Acceptor Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.1 Ambiphilic Ligands and the Retrodative Bond Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 Metal-Ligand Cooperative Catalysis Employing d
10 Complexes of the σ-Acceptor
Ligand Diphosphinoborane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3 Metal-Ligand Cooperative Reactivity at Group 8 and 9 Complexes of the σ-Acceptor
Ligand Diphospinoborane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3 π-Acceptor Ligands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1 Dewar-Chatt-Duncanson Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.2 Anchored Olefin-Metal Complexes: First Steps Towards Metal-Ligand
Cooperativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3 Metal-Ligand Cooperative Catalysis Induced by Side-On Coordination of a Ketone . . . 49
3.4 Imine Side-On Coordination: Synthesis and Metal-Ligand Cooperative Reactivity . . . 59
4 Concluding Remarks . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . 62
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
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: M.Moret@uu.nl