Versatile reactivity of Pd-catalysts: mechanistic features of the mono-N-protected amino acid ligand and cesium-halide base in Pd-catalyzed C–H bond functionalization

Abstract

The widely used C-H functionalization strategies and some complexities in the Pd-catalyzed chemical transformations were analyzed. It was emphasized that in the course of catalysis various Pd-intermediates (including nano-scale Pd-clusters) could act as active catalysts. However, both identification of these catalytically active species and determination of factors controlling the overall catalytic process require more comprehensive and multi-disciplinary approaches. Recent joint computational and experimental approaches were instrumental in: (1) demonstrating that the addition of Pd(OAc)2 as a catalyst precursor to RSeH and RSH reagents forms the [Pd(SeR)2]n and [Pd(SR)2]n clusters, respectively, which show an unprecedented ability for selective synthesis of Markovnikov-type products starting with a mixture of reagents RSH/RSeH and acetylenic hydrocarbons; (2) predicting a valid mechanism of the amino acid ligand-assisted Pd(II)-catalyzed C-H activation that is shown to proceed via the formation of the catalytically active Pd(II) intermediate with a bidentately coordinated dianionic amino acid ligand; (3) demonstrating that the amino acid ligand plays crucial roles in the ligand-assisted Pd(II)-catalyzed C-H activation by acting as: (a) a weakly coordinating ligand to stabilize the desirable Pd(II)-precatalyst, (b) a soft proton donor and a bidentately coordinated dianionic ligand in the catalytically active Pd(II) intermediate, and (c) a proton acceptor accelerating the C-H deprotonation via the CMD mechanism; and (4) revealing the roles of the CsF base (and "cesium effect") in the Pd(0)/PCy3-catalyzed intermolecular arylation of the terminal β-C(sp(3))-H bond of aryl amide and predicting the unprecedented "Cs2-I-F cluster" assisted mechanism for this reaction.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…During the past several decades, many metals have been studied in catalytic activation and functionalization of carbon-hydrogen bonds. The reader is directed to selected recent examples with gold [123], cobalt [124][125][126] chromium [127], copper [128][129][130][131] iron [132][133][134][135], iridium [136], manganese [137][138][139], molybdenum [140], nickel [141], osmium [142][143][144][145][146][147][148], palladium [149][150][151], rhenium [152], rhodium [153,154], ruthenium [155,156], and vanadium [157,158].…”

Mechanistic Details of Pd(II)-Catalyzed C–H Iodination with Molecular I2: Oxidative Addition vs Electrophilic Cleavage

“…( Figure S5 and Table S2), (4) Molecular orbital (MO) analysis of I 2 and complex 2 ( Figure S6), (7) I 2 Oxidative Addition through the S N 2 pathway (Figures S7, S8 and S9), (8) Single point energies (Table S3), (9) PES starting from PdIOAc ( Figure S10), (10) Other redoxneutral iodination pathways ( Figure S11), (11) MO and NBO analysis of complex EC-3 ( Figure S12 and Tables S4 and S5), (12) Substrate effect C(sp2) vs. C(sp3) on EC-TS ( Figure S13 and S14), (13) Ring size and steric effects ( Figure S15), (14) EC FMO analysis and transition states (Table S4 and Figure S12), (15) Experimental Characterization and Spectra, (16) SI References, (17) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 …”

“…[10][11] Oxidation of the R-Pd(II) species to form a RPd(IV) intermediate (i.e.Pd(II)/Pd(IV) redox chemistry) is one of the accepted pathways for [RPd(II)]-mediated transformations. 12,13 The emergence of suitable oxidants and ligands allowing the isolation and characterization of relevant Pd(IV) species have provided significant support to the development of Pd(II)/Pd(IV) redox chemistry.…”

Theoretical studies of palladium-catalyzed cycloaddition of alkynyl aryl ethers and alkynes

“…Transition metal-catalyzed functionalization of C-H bonds is a rapidly growing field in synthetic organic chemistry and organometallic chemistry that enables efficient access to a wide variety of building blocks [1][2][3][4][5]. Much effort has naturally been devoted to developing more convenient and efficient strategies for catalytic C-H functionalization reactions.…”