Reactivity of a tantalum-lithium alkylidene supported by an anionic triazacyclononane ligand

Nickel-Catalyzed Anionic Cross-Coupling Reaction of Lithium Sulfonimidoyl Alkylidene Carbenoids With Organolithiums

The mechanistic platform for a novel nickel0 -catalyzed anionic cross-coupling reaction (ACCR) of lithium sulfonimidoyl alkylidene carbenoids (metalloalkenyl sulfoximines) with organometallic reagents is reported herein, affording substituted alkenylmetals and lithium sulfinamides. The Ni0 -catalyzed ACCR of three different types of metalloalkenyl sulfoximines, including acyclic, axially chiral and exocyclic derivatives, with sp2 organolithiums and sp2 and sp3 Grignard reagents has been studied. The ACCR of metalloalkenyl sulfoximines with PhLi in the presence of the Ni0 -catalyst and precatalyst Ni(PPh3 )2 Cl2 afforded alkenyllithiums, under inversion of configuration at the C atom and complete retention at the S atom. In a combination of experimental and DFT studies, we propose a catalytic cycle of the Ni0 -catalyzed ACCR of lithioalkenyl sulfoximines. Computational studies reveal two distinctive pathways of the ACCR, depending on whether a phosphine or 1,5-cyclooctadiene (COD) is the ligand of the Ni atom. They rectify the underlying importance of forming the key Ni0 -vinylidene intermediate through an indispensable electron-rich Ni0 -center coordinated by phosphine ligands. Fundamentally, we present a mechanistic study in controlling the diastereoselectivity of the alkenyllithium formation via the key lithium sulfinamide coordinated Ni0 -vinylidene complex, which consequently avoids an unselective formation of an alkylidene carbene Ni-complex and ultimately racemic alkenyllithium.

Lability of Ta–NHC adducts as a synthetic route towards heterobimetallic Ta/Rh complexes

This work highlights the reactivity of Ta–NHC adducts and the aptitude of the NHC motif to transfer from Ta to Rh which is used with profit as an efficient synthetic route to access early/late heterobimetallic complexes.

Titanium Carbene Complexes Stabilized by Alkali Metal Amides

Facile α-H elimination from tetrakis(trimethylsilylmethyl)titanium precursors to give adducts of (alkylidene)bis(alkyl)titanium complexes is induced by light alkali metal amides of the NNNN-type macrocyclic anionic ligand Me₃ TACD [(Me₃ TACD)H=1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane]. In the crystal, the alkali metal interacts with the carbene carbon atom or with the CH₂ group of the trimethylsilymethyl ligand. The nucleophilic character of the carbene carbon atom was shown by the reaction with benzophenone and terminal acetylenes.

The formation, reactivity and interconversion of novel small eta(1)- and eta(3)-triazacyclononane complexes of rhodium(I) and rhodium(III)

We have successfully synthesised and characterised a number of eta(1)- and eta(3)-triazacyclononane Rh(I) and Rh(III) derivatives. By using different reaction conditions, we have been able to convert one of the eta(1)-triazacyclononane complexes to an eta(3)-derivative. Also, we have observed a rare example of an addition of an organic fragment to a metal bound ligand to form a quaternary carbon centre.