Carbon–Hydrogen Bond Stannylation and Alkylation Catalyzed by Nitrogen-Donor-Supported Nickel Complexes: Intermediates with Ni–Sn Bonds and Catalytic Carbostannylation of Ethylene with Organostannanes

Development of Axially Chiral Pyridylidene Amine Ligands and their Application in Pd-Catalyzed Enantioselective Allylic Substitution

A series of novel axially chiral pyridylidene amine (PYE) ligands has been developed, and their catalytic capability has been demonstrated in various highly efficient and enantioselective Pd-catalyzed asymmetric allylic substitutions. A density-functional theory (DFT) study explains the preferential enantiocontrol in the key transition states of the axially chiral PYE ligand-promoted Pd-catalyzed allylic alkylation.

Copper-catalyzed arylstannylation of arynes in a sequence

Diverse ortho-stannylbiaryls and teraryls have been synthesized by copper-catalyzed arylstannylation of arynes, in which the single or dual insertion of arynes into arylstannanes is precisely controllable by simply changing the equivalence of the aryne precursors employed.

A mesoionic nitrogen-donor ligand: structure, iridium coordination, and catalytic effects

A first example of a mesoionic ligand with a nitrogen coordination site was prepared by a simple and robust synthesis and is shown to have excellent properties for promoting iridium-catalyzed water oxidation.

Enhanced Catalytic Activity of Iridium(III) Complexes by Facile Modification of C,N-Bidentate Chelating Pyridylideneamide Ligands

A set of aryl-substituted pyridylideneamide (PYA) ligands with variable donor properties owing to a pronounced zwitterionic and a neutral diene-type resonance structure were used as electronically flexible ligands at a pentamethylcyclopentadienyl (Cp*) iridium center. The straightforward synthesis of this type of ligand allows for an easy incorporation of donor substituents such as methoxy groups in different positions of the phenyl ring of the C,N-bidentate chelating PYA. These modifications considerably enhance the catalytic activity of the coordinated iridium center toward the catalytic aerobic transfer hydrogenation of carbonyls and imines as well as the hydrosilylation of phenylacetylene. Moreover, these PYA iridium complexes catalyze the base-free transfer hydrogenation of aldehydes, and to a lesser extent also of ketones. Under standard transfer hydrogenation conditions including base, aldehydes are rapidly oxidized to carboxylic acids rather than reduced to the corresponding alcohol, as is observed under base-free conditions.

Nickel-catalyzed borylation of arenes and indoles via C-H bond cleavage

The first nickel-catalyzed method for the borylation of carbon-hydrogen bonds in arenes and indoles is described. The use of an N-heterocyclic carbene ligand is essential for an efficient reaction, with an N-cyclohexyl-substituted derivative being optimal. This method is readily applied to the gram scale synthesis of 2-borylindole.

Nickel complexes for catalytic C-H bond functionalization

The direct catalytic functionalization of traditionally unreactive C-H bonds is an atom-economic transformation that has become increasingly important and commonplace in synthetic applications. In general, 2(nd) and 3(rd) row transition metal complexes are used as catalysts in these reactions, whereas the less costly and more abundant 1(st) row metal complexes have limited utility. This Perspective article summarizes progress from our laboratory towards understanding the fundamental issues that complicate the use of Ni complexes for catalytic C-H bond functionalization, as well as approaches to overcoming these limitations. In practice it is found that Ni complexes can functionalize C-H bonds by processes that, to date, have not been observed with the heavier metals. An example is provided by the catalytic stannylation of C-H bonds with tributylvinyltin, Bu3SnCH=CH2, which produces ethylene as a by-product.