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

Abstract

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.

Library of Fluorescent Polysulfonamides and Polyamide Synthesized by Iridium-Catalyzed Direct C–H Amidation Polymerization

“…In addition to directing groups ( D1 – D6 ) with which catalysis proceeded via intermediates of stable 5-membered iridacycles, directing groups ( D7 – D12 ) generating key intermediates of relatively less stable 6-membered iridacycles were also investigated (Scheme ). , As expected, the yield obtained with the tertiary amide, D7 , was very low, and D8 containing a 6-membered heterocycle also produced only 57% and 68% of the desired product at 25 and 50 °C, respectively (Scheme ). Unexpectedly, changing to D9 containing a 5-membered heterocycle to produce the intermediate of 6-membered iridacycle, greatly improved the yield to 99% contrarily to the earlier reports (Scheme ).…”

“…Unexpectedly, changing to D9 containing a 5-membered heterocycle to produce the intermediate of 6-membered iridacycle, greatly improved the yield to 99% contrarily to the earlier reports (Scheme ). , Furthermore, pyrrolidinone was another excellent directing group ( D10 ) to give the product in quantitative yield at 25 °C, whereas larger lactams, piperidone ( D11 ) and caprolactam ( D12 ), showed much lower reactivity at 25 °C (Scheme ). In short, these results suggest that even small changes in the structures of the directing groups could lead to huge changes in the efficiency of C–H amidation, regardless of whether the intermediates are 5- or 6-membered iridacycles.…”

Secondary Coordination Sphere Alkylation Promotes Cyclometalation

“… − Together, these points suggest that upon addition of n BuLi to 5 , one of the ( n Pr)­BCy 2 ( n Pr = propyl linker to phosphorus) groups is alkylated to form [Cy 2 B­( n Pr)­( n Bu)] − (either from an unobserved [Fe]–(CH 2 ) 3 CH 3 intermediate or from nucleophilic attack at boron by n BuLi) rearranging to cyclometalate [Fe], giving [ 10- n Bu 3 ] 3– , with concomitant release of LiCl and Cy 2 B­( n Bu) (Figures and ). Cyclometalation offers a route toward compounds bearing a metal–carbon bondthe subject of several review articles. − In the present instance, SCS incorporation is the main driver for this transformation, offering a route for [M]–C bond formation. Such [M]–C products have been used as precursors in catalysis and studied as starting points toward reactive chemical systems.…”

Four-membered C^N chelation in main-group organometallic chemistry

“…1 For example, the N → M bond allows a controlled nucleophilic attack at the metal centre. 2 Most of the well-studied examples of organometallic compounds where such intramolecular coordination has been utilized involve C^N five-membered rings. 3 Some of these organometallic complexes have found applications in catalysis, 2 as OLEDs, 4 as sensors, 2 in solar cells 2 and in bioimaging.…”

“…2 Most of the well-studied examples of organometallic compounds where such intramolecular coordination has been utilized involve C^N five-membered rings. 3 Some of these organometallic complexes have found applications in catalysis, 2 as OLEDs, 4 as sensors, 2 in solar cells 2 and in bioimaging. 5 Representative examples of metal complexes containing such five-membered C^N rings are shown in Scheme 1.…”