Synthesis and Reactivity of Phosphine-Quinolinolato Rhodium Complexes: Intermediacy of Vinylidene and (Amino)carbene Complexes in the Catalytic Hydroamination of Terminal Alkynes

Rhodium-Catalyzed Anti-Markovnikov Hydroamination of Aliphatic and Aromatic Terminal Alkynes with Aliphatic Primary Amines

Anti-Markovnikov hydroamination of both aliphatic and aromatic terminal alkynes with primary amines was achieved using an 8-quinolinolato rhodium catalyst to form aldimines and enamines in high yields. This catalytic system realized high functional group tolerance including hydroxy, bromo, cyano, and thioester groups.

2:1 versus 1:1 Coupling of Alkylacetylenes with Secondary Amines: Selectivity Switching in 8-Quinolinolato Rhodium Catalysis

Both 2:1 and 1:1 couplings of alkylacetylenes with secondary amines were achieved using 8-quinolinolato rhodium catalysts and CsF. The 2:1/1:1 selectivity was switched by choosing the reaction solvent. In DMA, an unprecedented 2:1 coupling reaction of alkylacetylenes with amines proceeded to give 2-aminodiene products. One-pot 2:1 coupling/reduction provided rapid access to various allylamines, while one-pot coupling/hydrolysis gave enones as products. In toluene, anti-Markovnikov hydroamination occurred under relatively mild conditions to give 1:1 coupling products.

DFT calculations bring insight to internal alkyne-to-vinylidene transformations at rhodium PNP- and PONOP-pincer complexes

Through DFT calculations, the equilibrium between Rh–alkyne and Rh–vinylidene species of PXNXP pincer ligated Rh cationic complexes is shown to be tuned by the P–Rh–P bite angle, which in turn is dictated by the nature of the X moiety of the pincer ligand.

Carbon-Carbon Bond Formation via Catalytically Generated Aminocarbene Complexes: Rhodium-Catalyzed Hydroaminative Cyclization of Enynes with Secondary Amines

We report a hydroaminative cyclization of enynes using phosphine-quinolinolato rhodium catalysts. The hydroaminative cyclization of 2-vinylphenylacetylene derivatives with secondary amines gives 2-aminoindenes in good yields. The reaction is considered to proceed through carbon-carbon bond formation on a catalytically generated aminocarbene ligand.

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

With their mechanistic novelty and various modalities of reactivity, transition metal unsaturated carbene (alkenylidene) complexes have emerged as versatile intermediates for new reaction discovery. In particular, the past decade has witnessed remarkable advances in the chemistry of metal vinylidenes and allenylidenes, leading to the evolution of a diverse array of new catalytic transformations that are mechanistically distinct from those developed in the previous two decades. This review aims to provide a survey of the recent achievements in the development of organic reactions that make use of transition metal alkenylidenes as catalytic intermediates and their applications to organic synthesis.