Redox‐Neutral Coupling between Two C(sp 3 )−H Bonds Enabled by 1,4‐Palladium Shift for the Synthesis of Fused Heterocycles

Remote Construction of N-Heterocycles via 1,4-Palladium Shift-Mediated Double C-H Activation

In the past years, Pd⁰‐catalyzed C(sp³)−H activation provided efficient and step‐economical methods to synthesize carbo‐ and heterocycles via direct C(sp²)−C(sp³) bond formation. We report herein that a 1,4‐Pd shift allows access to N‐heterocycles which are difficult to build via a direct reaction. It is shown that o‐bromo‐N‐methylanilines undergo a 1,4‐Pd shift at the N‐methyl group, followed by intramolecular trapping by C(sp²)−H or C(sp³)−H activation at another nitrogen substituent and remote C−C bond formation to generate biologically relevant isoindolines and β‐lactams. The product selectivity is influenced by the employed ligand, with NHCs favoring the product of remote C−C coupling against products arising from direct C−C coupling and N‐demethylation.

Large Isotope Effects in Organometallic Chemistry

The kinetic isotope effect (KIE) is key to understanding reaction mechanisms in many areas of chemistry and chemical biology, including organometallic chemistry. This ratio of rate constants, k_H /k_D , typically falls between 1-7. However, KIEs up to 105 have been reported, and can even be so large that reactivity with deuterium is unobserved. We collect here examples of large KIEs across organometallic chemistry, in catalytic and stoichiometric reactions, along with their mechanistic interpretations. Large KIEs occur in proton transfer reactions such as protonation of organometallic complexes and clusters, protonolysis of metal-carbon bonds, and dihydrogen reactivity. C-H activation reactions with large KIEs occur with late and early transition metals, photogenerated intermediates, and abstraction by metal-oxo complexes. We categorize the mechanistic interpretations of large KIEs into the following three types: (a) proton tunneling, (b) compound effects from multiple steps, and (c) semi-classical effects on a single step. This comprehensive collection of large KIEs in organometallics provides context for future mechanistic interpretation.

Palladium-Catalyzed Synthesis of Benzophenanthrosilines by C-H/C-H Coupling through 1,4-Palladium Migration/Alkene Stereoisomerization

A new and efficient synthesis of 8H-benzo[e]phenanthro[1,10-bc]silines from 2-((2-(arylethynyl)aryl)silyl)aryl triflates under palladium catalysis has been developed. The reaction mechanism was experimentally investigated and a catalytic cycle involving C-H/C-H coupling through a new mode of 1,4-palladium migration with concomitant alkene stereoisomerization is proposed.

Divergent Synthesis of Vinyl-, Benzyl-, and Borylsilanes: Aryl to Alkyl 1,5-Palladium Migration/Coupling Sequences

Organosilicon compounds have been extensively utilized both in industry and academia. Studies on the syntheses of diverse organosilanes is highly appealing. Through-space metal/hydrogen shifts allow functionalization of C-H bonds at a remote site, which are otherwise difficult to achieve. However, until now, an aryl to alkyl 1,5-palladium migration process seems to have not been presented. Reported herein is the remote olefination, arylation, and borylation of a methyl group on silicon to access diverse vinyl-, benzyl-, and borylsilanes, constituting a unique C(sp³ )-H transformation based on a 1,5-palladium migration process.