Platinum(0)-mediated C–O bond activation of ethers via an S_N2 mechanism

Abstract

A computational study of the C(methyl)-O bond activation of fluorinated aryl methyl ethers by a platinum(0) complex Pt(PCyp) (Cyp = cyclopentyl) (N. A. Jasim, R. N. Perutz, B. Procacci and A. C. Whitwood, Chem. Commun., 2014, 50, 3914) demonstrates that the reaction proceeds via an S2 mechanism. Nucleophilic attack of Pt(0) generates an ion pair consisting of a T-shaped platinum cation with an agostic interaction with a cyclopentyl group and a fluoroaryloxy anion. This ion-pair is converted to a 4-coordinate Pt(ii) product trans-[PtMe(OAr)(PCyp)]. Structure-reactivity correlations are fully consistent with this mechanism. The Gibbs energy of activation is calculated to be substantially higher for aryl methyl ethers without fluorine substituents and higher still for alkyl methyl ethers. These conclusions are in accord with the experimental results. Further support was obtained in an experimental study of the reaction of Pt(PCy) with 2,3,5,6-tetrafluoro-4-allyloxypyridine yielding the salt of the Pt(η-allyl) cation and the tetrafluoropyridinolate anion [Pt(PCy)(η-allyl)][OCNF]. The calculated activation energy for this reaction is significantly lower than that for fluorinated aryl methyl ethers.

Alumination of Aryl Methyl Ethers: Switching Between Sp2 and Sp3 C–O Bond Functionalisation with Pd-Catalysis

“…The non-catalysed reaction of 1 with 2a was presumed to occur by an SN2 mechanism in which 1 act as an aluminium-centered nucleophile. 31,32 DFT calculations using the M06L functional and a hybrid basis-set support the proposal that such a mechanism is feasible (Figure 3a). SN2 attack occurs via TS-1 with a DG ‡ = 34.1 kcal mol -1 .…”

Oriented External Electric Fields and Ionic Additives Elicit Catalysis and Mechanistic Crossover in Oxidative Addition Reactions

“…The above discussion regarding the concerted mechanism gave us the impression that alkyl electrophiles remain almost inert to an external electric field. However, our computations show that unlike in the case of aryl electrophiles, alkyl electrophiles can undergo a facile S N 2-type mechanism for activation of the CH 3 –X bond. , In the field-free case, an S N 2-type mechanism is not possible due to the special electronic structure of the catalyst that possesses a σ-hole at the metal center (Figure a). However, when the field is switched on, the σ-hole on the catalyst is filled (Figure b) and the metal center is now nucleophilic enough to attack the CH 3 –X bond from the backside, leading to an S N 2-type TS.…”

Unconventional mechanism and selectivity of the Pd-catalyzed C–H bond lactonization in aromatic carboxylic acid

“…The next step of the reaction is the C–O bond formation from the Pd(II)-complex 6 . Previous experimental and computational studies have demonstrated a complexity of the C–O bond formation from the Pd(II), Pt(IV), and Pd(IV)-complexes 46 – 53 . In 2001, Goldberg and coworkers concluded that the C(sp 3 )–O bond formation from the Pt(IV)-complex, likely, involves the OR – dissociation and following nucleophilic addition 46 .…”