Abstract:DFT studies on Pd-catalyzed C(sp3)–H activation of aliphatic amines have been performed using the B3LYP functional. The rate- and regio-determining step of the catalytic cycle is deprotonation of the Cmethyl–H bond through a six-membered cyclopalladation transition state.
“…The Pd(II) source for C–H activation is modelled as monomeric PdCl 2 , as studied previously for Pd-based bond activations [ 44 ]. The use of monomeric PdCl 2 is analogous to the use of monomeric Pd(OAc) 2 , or even the less computationally expensive Pd(η 2 -O 2 CH) 2 [ 45 ], which are often used in calculations, instead of Pd 3 (OAc) 6 [ 46 ]. Scheme 5.…”
The SCN ligand 2-{3-[(methylsulfanyl)methyl]phenyl}pyridine, 1, has been synthesized starting from an initial Suzuki–Miyaura (SM) coupling between 3-((hydroxymethyl)phenyl)boronic acid and 2-bromopyridine. The C–H activation of 1 with in situ formed Pd(MeCN)4(BF4)2 has been studied and leads to a mixture of palladacycles, which were characterized by X-ray crystallography. The monomeric palladacycle LPdCl 6, where L-H = 1, has been synthesized, and tested in SM couplings of aryl bromides, where it showed moderate activity. Density functional theory and the atoms in molecules (AIM) method have been used to investigate the formation and bonding of 6, revealing a difference in the nature of the Pd–S and Pd–N bonds. It was found that S-coordination to the metal in the rate determining C–H bond activation step leads to better stabilization of the Pd(II) centre (by 13–28 kJ mol−1) than with N-coordination. This is attributed to the electron donating ability of the donor atoms determined by Bader charges. The AIM analysis also revealed that the Pd–N bonds are stronger than the Pd–S bonds influencing the stability of key intermediates in the palladacycle formation reaction pathway.
“…The Pd(II) source for C–H activation is modelled as monomeric PdCl 2 , as studied previously for Pd-based bond activations [ 44 ]. The use of monomeric PdCl 2 is analogous to the use of monomeric Pd(OAc) 2 , or even the less computationally expensive Pd(η 2 -O 2 CH) 2 [ 45 ], which are often used in calculations, instead of Pd 3 (OAc) 6 [ 46 ]. Scheme 5.…”
The SCN ligand 2-{3-[(methylsulfanyl)methyl]phenyl}pyridine, 1, has been synthesized starting from an initial Suzuki–Miyaura (SM) coupling between 3-((hydroxymethyl)phenyl)boronic acid and 2-bromopyridine. The C–H activation of 1 with in situ formed Pd(MeCN)4(BF4)2 has been studied and leads to a mixture of palladacycles, which were characterized by X-ray crystallography. The monomeric palladacycle LPdCl 6, where L-H = 1, has been synthesized, and tested in SM couplings of aryl bromides, where it showed moderate activity. Density functional theory and the atoms in molecules (AIM) method have been used to investigate the formation and bonding of 6, revealing a difference in the nature of the Pd–S and Pd–N bonds. It was found that S-coordination to the metal in the rate determining C–H bond activation step leads to better stabilization of the Pd(II) centre (by 13–28 kJ mol−1) than with N-coordination. This is attributed to the electron donating ability of the donor atoms determined by Bader charges. The AIM analysis also revealed that the Pd–N bonds are stronger than the Pd–S bonds influencing the stability of key intermediates in the palladacycle formation reaction pathway.
“…[57] The failure to acetoxylate 4,4-diethyl-2,2-dimethyloxazolidine [Equation (37)] "is possibly a reflection of the reduced steric hindrance around the nitrogen atom that precludes effective ligand dissociation from the palladium centre". [58] Scheme 9. Treatment of 9A with PhI(OAc) 2 afforded acetate 9C, via the putative Pd IV intermediate 9D.…”
Section: Aliphatic Aminesmentioning
confidence: 99%
“…The regioselective acetoxylation of 2-(tert-butyl)-3,8-dimethylquinazolin-4(3H)-one, which occurred quasi-exclusively at the tert-butyl group [Equations (58) and (59)], shows that, under the reaction conditions, the reaction of the C(sp 3 )-H bond of a benzylic methyl group is not favored over that of an unactivated tert-butyl group. This is consistent with the proposed mechanism, [70] which involves an η 1 -benzylpalladium species of type 13A, rather than an η 3 -benzylpalladium species, as an intermediate for the acetoxylation of the benzylic methyl substituent (Scheme 13).…”
Section: Quinazolinonesmentioning
confidence: 99%
“…This is consistent with the proposed mechanism, [70] which involves an η 1 -benzylpalladium species of type 13A, rather than an η 3 -benzylpalladium species, as an intermediate for the acetoxylation of the benzylic methyl substituent (Scheme 13). γ-C(sp 3 )-acetoxylation rather than γ-C(sp 2 )-acetoxylation of 2-phenyl-3,8-dimethylquinazolin-4(3H)-one [Equation (58)] is also remarkable. The acetoxylated product originates from reductive elimination of Pd(OAc) 2 (path a) or S N 2 attack by an external acetate ion (path b).…”
This review summarizes Pd‐catalyzed procedures leading to single C–O bonds from aliphatic C–H bonds of substrates bearing heteroatomic groups. Coordination of the latter to PdII species favors the activation of a C(sp3)–H bond and controls the regioselectivity, leading to a palladacycle as intermediate. Either PdII–Pd0 or PdII–PdIV redox catalytic cycles, possibly with a PdIII intermediate, might be involved, depending on the directing group and the oxidant.
“…The recent advances in computational techniques offer tools to understand and rationalize more complex transformations, such as dehydrogenation reactions of alkanes . Notably, a comprehensive mechanism of the C–H bond cleavage step by the concerted metalation–deprotonation (CMD) pathway has been demonstrated to play an important role in homogeneous catalytic systems …”
The past decade has seen the development of a new reactivity concept, exploiting the ubiquity of C−H bonds. The direct activation of this bond type brings forth a straightforward way for the derivatization of organic molecules. Consequently, the design of metal catalyzed C−H bond functionalization reactions has become a flourishing area in organic synthesis. Thus, this review focuses on molecular transformation of "unactivated" C(sp 3 )−H and C(sp 2 )−H bonds present in feedstock and readily available hydrocarbons into valuable chemicals by nanoparticle-leveraged C−H activation, resulting in more sustainable approaches for industrial applications. The distinctive reactivity properties of these nanoentities lead to remarkable reactivity specificities depending on the type of surface sites and the structure dynamics, directly impacting the process selectivity.
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