Stoichiometric Studies on the Carbonylative Trifluoromethylation of Aryl Pd(II) Complexes using TMSCF₃ as the Trifluoromethyl Source

Abstract

We have performed a series of stoichiometric studies in order to identify viable steps for a hypothetical catalytic cycle for the palladium-mediated carbonylative coupling of an aryl bromide with TMSCF3. Our work revealed that benzoyl Pd­(II) complexes bearing Xantphos or tBu3P as the phosphine ligands, which are generated from the corresponding PdII(Ph)Br complexes exposed to stoichiometric 13CO from 13COgen, were unable to undergo transmetalation and reductive elimination to trifluoroacetophenone. Instead, in the presence of base and additional CO, these organometallic complexes readily underwent reductive elimination to the acid fluoride. Attempts to determine whether the acid fluoride could represent an intermediate for acetophenone production were unrewarding. Only in the presence of a boronic ester did we observe some formation of the desired product, although the efficiency of transformation was still low. Finally, we investigated the reactivity of four phosphine-ligated PdII(Ph)­CF3 complexes (Xantphos, DtBPF, tBu3P, and triphenylphosphine) with carbon monoxide. With the exception of the tBu3P-ligated complex, all other metal complexes led to the facile formation of trifluoroacetophenone. We also determined in the case of triphenylphosphine that CO insertion occurred into the Pd–Ar bond, as trapping of this complex with n-hexylamine led to the formation of n-hexylbenzamide.

Palladium‐Catalyzed Chlorocarbonylation of Aryl (Pseudo)Halides Through In Situ Generation of Carbon Monoxide

“…We assigned this peak to the carbonyl carbon of 10 that couples to the ligand phosphorous atoms.Its chemical shift is very similar to related acyl complexes of Xantphos-ligated palladium(II). [32] Long range correlation in the 1 H- 13 CHMBC spectrum between the carbon peak at d = 225.8 ppm and ap roton signal, identified as aC H 2 group,c onfirms the identity of this deshielded carbon signal as the carbonyl group of acyl complex 10.Unfortunately,this complex was found to be less stable than the related complex reported by Skrydstrup [31] and rapidly decomposed at room temperature.Wecould identify the decomposition product of 10 as (Xantphos)PdCl 2 by comparing the spectroscopic data to the data of an authentic sample.…”

Versatile Palladium-Catalyzed Approach to Acyl Fluorides and Carbonylations by Combining Visible Light- and Ligand-Driven Operations

“…Stoichiometric studies offer insight into the reductive elimination step. Grushin and Skrydstrup have previously noted that in situ -generated palladium­(aroyl)­fluoride complexes undergo thermal reductive elimination with PPh 3 and Xantphos ligands, respectively . In the case of Xantphos, the reaction requires 70 °C.…”

Theoretical study for evaluating and discovering organic hydride compounds as novel trifluoromethylation reagents

“…Trifluoromethylation reaction is an important branch of organic fluorine chemistry, 1–5 and the design and discovery of new trifluoromethylation reagents have always been a research hotspot. 6–8 At present, important progress has been made in the discovery and application of trifluoromethylation reagents. 1–9 All trifluoromethylation reagents 1,2 could be reasonably divided into nucleophilic trifluoromethylation reagents, 10,11 electrophilic trifluoromethylation reagents 12–16 and free radical trifluoromethylation reagents 17–21 according to their reaction mechanisms.…”

“…6–8 At present, important progress has been made in the discovery and application of trifluoromethylation reagents. 1–9 All trifluoromethylation reagents 1,2 could be reasonably divided into nucleophilic trifluoromethylation reagents, 10,11 electrophilic trifluoromethylation reagents 12–16 and free radical trifluoromethylation reagents 17–21 according to their reaction mechanisms. Generally, nucleophilic trifluoromethyl reagents and electrophilic trifluoromethyl reagents need to be activated by light, catalysts or single electron donors/acceptors to generate key active free radical intermediates to provide ˙CF 3 (Scheme 1); 9–16 in fact, only a few examples are available as + CF 3 or − CF 3 transfer mechanisms.…”