@article { ISI:000362436800075, title = {Mono- and binuclear palladacycles via regioselective C-H bond activation: syntheses, mechanistic insights and catalytic activity in direct arylation of azoles}, journal = {RSC Advances}, volume = {5}, number = {99}, year = {2015}, month = {SEP}, pages = {81502-81514}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

{Regioselective C-H bond palladation of the hybrid pincer-type ligands, 3-R2PO-C6H4-1-(CH2NPr2)-Pr-i [(POCNiPr2)-P-R2-H; R = Ph (1a)

}, issn = {2046-2069}, doi = {10.1039/c5ra18289a}, author = {Pandey, Dilip K. and Khake, Shrikant M. and Gonnade, Rajesh G. and Punji, Benudhar} } @article {42739, title = {Mechanistic insights into pincer-ligated palladium-catalyzed arylation of azoles with aryl Iodides: evidence of a Pd-II-Pd-IV-Pd-II pathway}, journal = {Organometallics}, volume = {35}, year = {2016}, month = {MAR}, pages = {875{\textendash}886}, abstract = {

Pincer-based (R2POCNR'2)PdCl complexes along with CuI cocatalyst catalyze the arylation of azoles with aryl iodides to give the 2-arylated azole products. Herein, we report an extensive mechanistic investigation for the direct arylation of azoles involving a well-defined and highly efficient (iPr2POCNEt2)PdCl (2a) catalyst, which emphasizes a rare PdII{\textendash}PdIV{\textendash}PdII redox catalytic pathway. Kinetic studies and deuterium labeling experiments indicate that the C{\textendash}H bond cleavage on azoles occurs via two distinct routes in a reversible manner. Controlled reactivity of the catalyst 2a underlines the iodo derivative (iPr2POCNEt2)PdI (3a) to be the resting state of the catalyst. The intermediate species (iPr2POCNEt2)Pd-benzothiazolyl (4a) has been isolated and structurally characterized. A determination of reaction rates of compound 4a with electronically different aryl iodides has revealed the kinetic significance of the oxidative addition of the C(sp2){\textendash}X electrophile, aryl iodide, to complex 4a. Furthermore, the reactivity behavior of 4a suggests that the arylation of benzothiazole proceeds via an oxidative addition/reductive elimination pathway involving a (iPr2POCNEt2)PdIV(benzothiazolyl)(Ar)I species, which is strongly supported by DFT calculations.

}, doi = {10.1021/acs.organomet.6b00003}, author = {Khake, Shrikant M. and Jagtap, Rahul A. and Dangat, Yuvraj B. and Gonnade, Rajesh G. and Vanka, Kumar and Punji, Benudhar} } @article {44620, title = {Mechanism of nickel(II)-catalyzed C(2)-H alkynylation of indoles with alkynyl bromide}, journal = {Organometallics}, volume = {37}, year = {2018}, month = {JUL}, pages = {2037-2045}, abstract = {

The nickel system (THF)(2)NiBr2/phen has recently been shown as an efficient catalyst for the C-H bond alkynylation of diverse heteroarenes with (triisopropylsilyl)alkynyl bromide via monodentate chelation assistance. Herein, we report an extensive mechanistic investigation for the direct alkynylation of indoles involving the well-defined nickel catalyst, which features a coordinative insertion pathway of alkynyl bromide with the Ni(II) catalyst. Catalytic relevant nickel complexes, (phen)NiCl2 (5), (phen)(2)NiCl2 (6) and [(phen)(3)Ni].NiCl4 (7) were isolated, and the complexes 6 and 7 were structurally characterized. Well-defined complexes were as competent as the in situ generated catalyst system (THF)(2)NiBr2/phen for the alkynylation of indoles. Various controlled studies and reactivity experiments were performed to understand the probable pathway for the alkynylation reaction. Kinetics analysis highlights that the complex (phen)NiX2 acts as a precatalyst, and the involvement of substrate indole and LiO{\textquoteright}Bu are essential for the generation of the active catalyst. Deuterium labeling and kinetic studies suggest that the process involving C-H cleavage and carbo-nickelation of indole is a crucial rate influencing step. Reactivity study of various alkynyl compounds with nickel-species highlights a migratory insertion route for the reaction. DFT calculations firmly support the experimental findings and suggest the coordinative insertion pathway of alkynyl bromide rather than oxidative addition toward the nickel(II) center.

}, issn = {0276-7333}, doi = {10.1021/acs.organomet.8b00177}, author = {Khake, Shrikant M. and Jain, Shailja and Patel, Ulhas N. and Gonnade, Rajesh G. and Vanka, Kumar and Punji, Benudhar} }