Agostic bonds in cyclometalation

SummaryAlthough four-coordinate square-planar geometries, with a formally 16-electron counting, are absolutely dominant in isolated Pt(II) complexes, three-coordinate, 14-electron Pt(II) complexes are believed to be key intermediates in a number of platinum-mediated organometallic transformations. Although very few authenticated three-coordinate Pt(II) complexes have been characterized, a much larger number of complexes can be described as operationally three-coordinate in a kinetic sense. In these compounds, which we have called masked T-shaped complexes, the fourth position is occupied by a very weak ligand (agostic bond, solvent molecule or counteranion), which can be easily displaced. This review summarizes the structural features of the true and masked T-shaped Pt(II) complexes reported so far and describes synthetic strategies employed for their formation. Moreover, recent experimental and theoretical reports are analyzed, which suggest the involvement of such intermediates in reaction mechanisms, particularly C–H bond-activation processes.

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“…Cyclometalation processes, sometimes involving agostic situations [114], have been thoroughly reviewed recently [115]. …”

Section: Reviewmentioning

confidence: 99%

True and masked three-coordinate T-shaped platinum(II) intermediates

Ortuño¹,

Conejero²,

Lledós³

2013

Beilstein J. Org. Chem.

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“…Commonly, cyclometalation reactions with conventional substrates that have a γ carbon atom as the heteroatom proceed very easily via agnostic interactions with CH activation, as shown in Equation (1.1) [45]. Then, the metal atom is coordinated by the heteroatom and becomes the active center in the five-membered ring products.…”

Section: Introductionmentioning

confidence: 99%

Applications of Cyclometalation Five-Membered Ring Products and Intermediates as Catalytic Agents

Omae¹

2016

MRC

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The five-membered ring products and intermediates of cyclometalation reactions are very easily synthesized via donation from a hetero atom to a metal atom, which leads to the very high functionality of the product. This functionality is caused by the donation of the hetero atom and various types of metal atoms, halogen atom and other ligands such as alkanes, alkenes, alkynes, Cp, Cp*, aryl groups and heterocyclic compounds. These products have three types of catalytic applications: cyclometalation five-membered ring products as catalysts, cyclometalation five-membered ring intermediates as catalyst agents and cyclometalation five-membered ring intermediates with unconventional substrates and as catalyst actions. Because of the high functionality of these products, the applications of them have been increasing not only as the metathesis in the first and second generations of Hoveyda-Grubbs catalysts but also as in chiral reactions, crosscoupling reactions and polymerization reactions. The above cyclometalation products have been utilized for the production in many industrial fields such as pharmaceuticals, OLEDs, carbon dioxide utilizations, dye-sensitizer solar cells and sensors. We expect that these products would be used for the development of further new industrial products.

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“…[4][5][6][7] The choice of a specific term to underline the importance of the activation of the C-H bond proved to be remarkably appropriate. Indeed, thorough investigation of various catalytic processes further lead to the development of numerous reactions involving agostic interactions, such as the alkane oxidative addition, 8 C-H bond elimination, 9 transcyclometallation, 10 cyclometallation of benzoquinoline, 11 and Ziegler-Natta polymerization. 12,13 In processes such as cyclometallation using d-block transition metals, it was proposed that agostic interactions may play a decisive role.…”

Section: Introductionmentioning

confidence: 99%

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

Zins

Silvi

Alikhani

2015

Phys. Chem. Chem. Phys.

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Agostic bonding is of paramount importance in C-H bond activation processes. The reactivity of the σ C-H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X-H bond can indeed be described as "agostic" bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X-H bond is in agostic interaction with a metal center when the protonated X-H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X-Hagostic bond critical point with respect to that of X-Hfree well correlates with the lengthening of the agostic X-H bond distance as well as with the shift of the vibrational frequency associated with the νX-H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes.

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Agostic bonds in cyclometalation

Cited by 44 publications

References 130 publications

True and masked three-coordinate T-shaped platinum(II) intermediates

True and masked three-coordinate T-shaped platinum(II) intermediates

Applications of Cyclometalation Five-Membered Ring Products and Intermediates as Catalytic Agents

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

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