Investigation of the mechanism of C(sp3)-H bond cleavage in Pd(0)-catalyzed intramolecular alkane arylation adjacent to amides and sulfonamides.

The reactivity of C(sp(3))-H bonds adjacent to a nitrogen atom can be tuned to allow intramolecular alkane arylation under Pd(0) catalysis. Diminishing the Lewis basicity of the nitrogen lone pair is crucial for this catalytic activity. A range of N-methylamides and sulfonamides react exclusively at primary C(sp(3))-H bonds to afford the products of alkane arylation in good yields. The isolation of a Pd(II) reaction intermediate has enabled an evaluation of the reaction mechanism with a focus on the role of the bases in the C(sp(3))-H bond cleaving step. The results of these stoichiometric studies, together with kinetic isotope effect experiments, provide rare experimental support for a concerted metalation-deprotonation (CMD) transition state, which has previously been proposed in alkane C(sp(3))-H arylation. Moreover, DFT calculations have uncovered the additional role of the pivalate additive as a promoter of phosphine dissociation from the Pd(II) intermediate, enabling the CMD transition state. Finally, kinetic studies were performed, revealing the reaction rate expression and its relationship with the concentration of pivalate

An organometallic building block approach to produce a multidecker 4 f single-molecule magnet

An organometallic building block strategy was employed to investigate the magnetic properties of a LnIII organometallic single-ion magnet (SIM) and subsequent single-molecule magnet (SMM) after coupling two of the monomeric units. New homoleptic DyIIICOT″2 and LnIII2COT″3 (Ln = Gd, Dy) complexes have been synthesized. DFT calculations of the bimetallic DyIII complex indicate strong metal–ligand covalency and uneven donation to the DyIII ions by the terminal and internal COT″2– (cyclooctatetraenide) rings that correlate with the respective bond distances. Interestingly, the studies also point to a weak covalent interaction between the metal centers, despite a large separation. The ac susceptibility data indicates that both DyIIICOT″2 and DyIII2COT″3 act as an SIM and an SMM, respectively, with complex multiple relaxation mechanisms. Ab initio calculations reveal the direction of the magnetic anisotropic axis is not perpendicular to the planar COT″ rings for both DyIIICOT″2 and DyIII2COT″3 complexes due to the presence of trimethylsilyl groups on the COT″ rings. If these bulky groups are removed, the calculations predict reorientation of the anisotropic axis can be achieved

Orthogonal Palladium-Catalyzed Direct C−H Bond Arylation of Heteroaromatics with Aryl Halides

International audienceTransition metal‐catalyzed direct C−H bond functionalization of heterocycles with halo(het)arenes has received considerable attention as synthetic alternative to standard cross‐coupling reactions regarding step‐ and atom‐economy in the preparation of heteroarylmetals intermediates and better chemo‐selectivity towards standard organic functions such as aldehyde, ketone, ester, cyanide, and amide. An additional major and poorly highlighted interest of such methodology is its unparalleled ability to open the chemical space of functionalization of heterocycles towards challenging unprecedented sites. This Review gives an overview of the advances in challenging orthogonal direct C−H arylation of heterocycles related to the wide variety of catalytic C−H bond metalation processes, most of them evaluated by DFT calculations