The Kumada-Tamao-Corriu Coupling Reaction Catalyzed by Rhodium-Aluminum Bimetallic Complexes.

Rhodium-aluminum bimetallic complexes catalyze the Kumada-Tamao-Corriu (KTC) cross-coupling reaction using arylmagnesium compounds that are generated from the corresponding aryl fluorides or chlorides in situ by these catalysts. This method allows the challenging KTC coupling reaction to be carried out using aryl fluorides as nucleophiles, which affords various biaryls.

Merging Pd0 /PdII Redox and PdII /PdII Non-redox Catalytic Cycles for the Allylarylation of Electron-Deficient Alkenes.

An allylarylation of electron-deficient alkenes with aryl boronates and allylic carbonates has been developed. This method allows access to a wide variety of carbon skeletons from readily available starting materials. Mechanistic studies indicate that this reaction is enabled by a cooperative catalysis based on merging Pd0 /PdII redox and PdII /PdII non-redox catalytic cycles.

Magnesiation of Aryl Fluorides Catalyzed by a Rhodium-Aluminum Complex.

We report the magnesiation of aryl fluorides catalyzed by an Al-Rh heterobimetallic complex. We show that the complex is highly reactive to cleave the C-F bonds across the polarized Al-Rh bond under mild conditions. The reaction allows the use of an easy-to-handle magnesium powder to generate a range of arylmagnesium reagents from aryl fluorides, which are conventionally inert to such metalation compared with other aryl halides.

Nickel-catalysed anti-Markovnikov hydroarylation of unactivated alkenes with unactivated arenes facilitated by non-covalent interactions.

Anti-Markovnikov additions to alkenes have been a longstanding goal of catalysis, and anti-Markovnikov addition of arenes to alkenes would produce alkylarenes that are distinct from those formed by acid-catalysed processes. Existing hydroarylations are either directed or occur with low reactivity and low regioselectivity for the n-alkylarene. Herein, we report the first undirected hydroarylation of unactivated alkenes with unactivated arenes that occurs with high regioselectivity for the anti-Markovnikov product. The reaction occurs with a nickel catalyst ligated by a highly sterically hindered N-heterocyclic carbene. Catalytically relevant arene- and alkene-bound nickel complexes have been characterized, and the rate-limiting step was shown to be reductive elimination to form the C-C bond. Density functional theory calculations, combined with second-generation absolutely localized molecular orbital energy decomposition analysis, suggest that the difference in activity between catalysts containing large and small carbenes results more from stabilizing intramolecular non-covalent interactions in the secondary coordination sphere than from steric hindrance.

Pd/NHC-catalyzed cross-coupling reactions of nitroarenes.

N-Heterocyclic carbene (NHC) ligands effective for the cross-coupling of nitroarenes were identified. A rational design of the NHC ligand structures enabled significant reduction of catalyst loadings compared with the previous system employing BrettPhos as a phosphine ligand. Experimental and theoretical studies to compare these ligands gave some insights into high activity of the newly developed NHC ligands.

Carboallylation of Electron-Deficient Alkenes with Organoboron Compounds and Allylic Carbonates by Cooperative Palladium/Copper Catalysis.

The aryl- and alkylallylation of electron-deficient alkenes was achieved by cooperative palladium/copper catalysis. The reaction affords various carbon skeletons from readily available alkenes, allylic carbonates, and organoboron compounds, whereby a variety of functional groups such as acetyl, alkoxycarbonyl, bromo, and cyano moieties are tolerated well.

Carboallylation of electron-deficient alkenes by palladium/copper catalysis.

A method for the carboallylation of electron-deficient alkenes with tetraorganosilicon reagents and allylic carbonates based on Pd/Cu catalysis has been developed. This method affords a wide range of structurally diverse carbon skeletons from readily available starting materials, and tolerates various functional groups.

Rhodium Complexes Bearing PAlP Pincer Ligands.

We report rhodium complexes bearing PAlP pincer ligands with an X-type aluminyl moiety. IR spectroscopy and single-crystal X-ray diffraction analysis of a carbonyl complex exhibit the considerable σ-donating ability of the aluminyl ligand, whose Lewis acidity is confirmed through coordination of pyridine to the aluminum center. The X-type PAlP-Rh complexes catalyze C2-selective monoalkylation of pyridine with alkenes.

Site-Selective Linear Alkylation of Anilides by Cooperative Nickel/Aluminum Catalysis.

We report meta- and para-selective linear alkylation reactions of anilides with alkenes by nickel/N-heterocyclic carbene (NHC) and aluminum catalysis. With a less bulky NHC, the alkylation reaction of N-methyl-N-phenylcyclohexanecarboxamides proceeded mainly at the meta position. In contrast, a bulky NHC ligand led to the para-selective alkylation of N-sec-alkyl anilides.

How to Control Inversion vs Retention Transmetalation between PdII-Phenyl and CuI-Alkyl Complexes: Theoretical Insight.

Transmetalation between Pd(Br)(PhA)(PCyp3)2 (Ph = phenyl, Cyp = cyclopentyl) and Cu(CaHMePhB)(NHC) (NHC = 1,3-bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene) is an important elementary step in recently reported catalytic cross-coupling reaction by Pd/Cu cooperative system. DFT study discloses that the transmetalation occurs with inversion of the stereochemistry of the CaHMePhB group. In its transition state, the CaHMePhB group has almost planar structure around the Ca atom. That planar geometry is stabilized by conjugation between the π* orbital of the PhB and the 2p orbital of the Ca. Another important factor is activation entropy (ΔS°‡); retention transmetalation occurs through Br-bridging transition state, which is less flexible than that of the inversion transmetalation because of the Br-bridging structure, leading to a smaller activation entropy in the retention transition state than in the inversion transition state. For CaHMeEt group, transmetalation occurs in a retention manner. In the planar CaHMeEt group of the inversion transition state, the Ca 2p orbital cannot find a conjugation partner because of the absence of π-electron system in the CaHMeEt. Transmetalation of CaHMe(CH═CH2) occurs in a retention manner because the vinyl π* is less effective for the conjugation with the Ca 2p because of its higher orbital energy than the Ph π*. The introduction of electron-withdrawing substituent on the PhB is favorable for inversion transmetalation. These results suggest that the stereochemistry of the Ca atom in transmetalation can be controlled by electronic effect of the CaHMeR (R = phenyl, vinyl, or alkyl) and sizes of the substituent and ligand.

C3-Selective alkenylation of N-acylindoles with unactivated internal alkynes by cooperative nickel/aluminium catalysis.

Highly regio- and stereoselective alkenylation of N-acylindoles with unactivated internal alkynes has been accomplished by cooperative nickel/aluminium catalysis to afford C3-alkenylated indoles. Coordination of the acyl moiety to a bulky aluminium-based Lewis acid plays a crucial role in the selective functionalization at the C3-position by electron-rich nickel(0) catalysis.

para-Selective C-H Borylation of (Hetero)Arenes by Cooperative Iridium/Aluminum Catalysis.

para-Selective C-H borylation of benzamides and pyridines has been achieved by cooperative iridium/aluminum catalysis. A combination of iridium catalysts commonly employed for arene C-H borylation and bulky aluminum-based Lewis acid catalysts provides an unprecedented strategy for controlling the regioselectivity of C-H borylation to give variously substituted (hetero)arylboronates, which are versatile synthetic intermediates for complex multi-substituted aromatic compounds.

para-Selective Alkylation of Benzamides and Aromatic Ketones by Cooperative Nickel/Aluminum Catalysis.

We report a method that ensures the selective alkylation of benzamides and aromatic ketones at the para-position via cooperative nickel/aluminum catalysis. Using a bulky catalyst/cocatalyst system allows reactions between benzamides and alkenes to afford the corresponding para-alkylated products. The origin of the high para-selectivity has also been investigated by density functional theory calculations.

Arylboration of 1-Arylalkenes by Cooperative Nickel/Copper Catalysis.

A method for the arylboration of 1-arylalkenes with bis(pinacolato)diboron and aryl chlorides or tosylates by cooperative Ni/Cu catalysis has been developed, which affords 2-boryl-1,1-diarylalkanes in high regio- and stereoselectivity. Under the applied conditions, this method is tolerant toward various functional groups, including silyl ether, alkoxycarbonyl, and aminocarbonyl moieties.

Reductive Cross-Coupling of Conjugated Arylalkenes and Aryl Bromides with Hydrosilanes by Cooperative Palladium/Copper Catalysis.

A method for the reductive cross-coupling of conjugated arylalkenes and aryl bromides with hydrosilanes by cooperative palladium/copper catalysis was developed, thus resulting in the highly regioselective formation of various 1,1-diarylalkanes, including a biologically active molecule. Under the applied reaction conditions, high levels of functional-group tolerance were observed, and the reductive cross-coupling of internal alkynes with aryl bromides afforded trisubstituted alkenes.

Anti-Markovnikov hydroheteroarylation of unactivated alkenes with indoles, pyrroles, benzofurans, and furans catalyzed by a nickel-N-heterocyclic carbene system.

We report the catalytic addition of C-H bonds at the C2 position of heteroarenes, including pyrroles, indoles, benzofurans, and furans, to unactivated terminal and internal alkenes. The reaction is catalyzed by a combination of Ni(COD)2 and a sterically hindered, electron-rich N-heterocyclic carbene ligand or its analogous Ni(NHC)(arene) complex. The reaction is highly selective for anti-Markovnikov addition to α-olefins, as well as for the formation of linear alkylheteroarenes from internal alkenes. The reaction occurs with substrates containing ketones, esters, amides, boronate esters, silyl ethers, sulfonamides, acetals, and free amines.

Copper-catalyzed borylative allyl-allyl coupling reaction.

Borylative allyl-allyl coupling using allenes, bis(pinacolato)diboron, and allyl phosphates has been developed in the presence of a copper catalyst bearing an N-heterocyclic carbene ligand. The reaction affords boryl-substituted 1,5-diene derivatives in good to high yields with high regioselectivity and Z selectivity.

Arylboration of alkenes by cooperative palladium/copper catalysis.

Arylboration of vinylarenes and methyl crotonate with aryl halides and bis(pinacolato)diboron by cooperative Pd/Cu catalysis has been developed, giving 2-boryl-1,1-diarylethanes and an α-aryl-ß-boryl ester in a regioselective manner. The reaction is compatible with a variety of functionalities and amenable to be scaled-up to a gram scale with no detriment to the yield. A short synthesis of the biologically active compound CDP840 was performed using the present reaction as a key step.

Intramolecular aminocyanation of alkenes by cooperative palladium/boron catalysis.

A cooperative palladium/triorganoboron catalyst to accomplish the intramolecular aminocyanation of alkenes through the cleavage of N-CN bonds is reported. 4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) is found to be crucial as a ligand for palladium to effectively catalyze the transformation with high chemo- and regioselectivity. A range of substituted indolines and pyrrolidines with both tetra- or trisubstituted carbon and cyano functionalities are readily furnished by the newly developed cyanofunctionalization reaction. A preliminary example of enantioselective aminocyanation is also described.

Copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron: efficient synthesis of 2-boryl 1,3-butadienes.

Something solid to build on: 2-Boryl 1,3-butadienes with various substitution patterns were formed in good to high yields in a copper-catalyzed borylation of α-alkoxy allenes with bis(pinacolato)diboron (see scheme; Bn=benzyl, pin=pinacolate, L is an N-heterocyclic carbene ligand). The products were found to be useful intermediates for the synthesis of cyclic vinyl boranes, α,ß-unsaturated ketones, and functionalized multisubstituted dienes.