Activation of SF5CF3 by the N-Heterocyclic Carbene SIMes

The greenhouse gas SF5CF3 was photochemically activated with SIMes (1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) to give 1,3-dimesityl-2,2-difluoroimidazolidine (SIMesF2), and 1,3-dimesitylimidazolidine-2-sulfide, as well as the trifluoromethylated carbene derivative 1,3-dimesityl-2-fluoro-2-trifluoromethylimidazolidine. CF3 radicals, as well as SF4, serve presumably as intermediates of the conversions. In addition, the photochemical activation of SF5CF3 was performed in the presence of triphenylphosphine. The formation of triphenyldifluorophosphorane and triphenylphosphine sulfide was observed.


Thermal Activation of SF 5 CF 3 with SIMes
Heating a 1:1 mixture of SIMes and SF 5 CF 3 at 90 • C for 190 min in toluene-d 8 led to the formation of 1,3-dimesityl-2-fluoro-2-trifluoromethylimidazolidine (1), SIMesF 2 (2) and 1,3-dimesitylimidazolidine-2-sulfide (3), with NMR yields of 18%, 31%, and 31% based on Molecules 2023, 28, 6693 2 of 10 the amount of SF 5 CF 3 (Scheme 1).The 19 F NMR spectrum (Figure 1) of the mixture shows a signal at δ = −55.8ppm for SIMesF 2 (2), which is consistent with the literature [15,28,29], as well as a doublet at δ = −76.3with a coupling constant 3 J FF of 4.2 Hz, and a quartet at δ = −83.1 with a coupling constant 3 J FF of 4.4 Hz for compound 1.The formation of 3 was further confirmed through comparing the 1 H NMR spectrum with the data reported in the literature [15].It was noted that traces of trifluoromethane were also observed according to the 19 F NMR spectrum.Heating the sample further for one hour led to a decrease in the amount of 1 and SIMesF 2 (2) and, instead, more trifluoromethane and trifluoromethaned 1 were observed.The latter can be formed due to the reaction of an intermediate CF 3 radical (see below) via hydrogen or deuterium atom transfer.Attempts to achieve a similar transformation in benzene gave the considerably lower amounts of 1, 2, and 3, possibly due to the lower reaction temperature, which was limited by the boiling point of benzene.
Molecules 2023, 28, x FOR PEER REVIEW 2 of 10 and 1,3-dimesitylimidazolidine-2-sulfide (3), with NMR yields of 18%, 31%, and 31% based on the amount of SF5CF3 (Scheme 1).The 19 F NMR spectrum (Figure 1) of the mixture shows a signal at δ = −55.8ppm for SIMesF2 (2), which is consistent with the literature [15,28,29], as well as a doublet at δ = −76.3with a coupling constant 3 JFF of 4.2 Hz, and a quartet at δ = −83.1 with a coupling constant 3 JFF of 4.4 Hz for compound 1.The formation of 3 was further confirmed through comparing the 1 H NMR spectrum with the data reported in the literature [15].It was noted that traces of trifluoromethane were also observed according to the 19

Photolytic Activation of SF5CF3 with SIMes
When a mixture of SF5CF3 and 6.7 equivalents of SIMes was irradiated at 311 nm in benzene-d6 for 3 h, the formation of 62% of 1, and 105% of 2 and 3 was observed, as well as 1% of α,α,α-trifluorotoluene-d5 (Scheme 2).All yields are NMR yields based on the amount of SF5CF3.Further irradiation for 16 h led to the hydrolysis of 2 by adventitious water, to give a urea derivative and HF.The generation of 4 could then be due to the presence of HF.Compound 4 and the thiourea product 3 were observed in a ratio of 4:7.In addition, as described below, the trifluoromethylation of C6D6 will result in the generation of DF.DF can subsequently lead an FDF − derivative of 4. Compound 4 shows a singlet at −65.68 ppm in the 19 F NMR spectrum for the CF3 group and a broad signal at -169.40 ppm, indicating the presence of an FHF -anion.The presence of the cation was also Molecules 2023, 28, x FOR PEER REVIEW 2 of 10 and 1,3-dimesitylimidazolidine-2-sulfide (3), with NMR yields of 18%, 31%, and 31% based on the amount of SF5CF3 (Scheme 1).The 19 F NMR spectrum (Figure 1) of the mixture shows a signal at δ = −55.8ppm for SIMesF2 (2), which is consistent with the literature [15,28,29], as well as a doublet at δ = −76.3with a coupling constant 3 JFF of 4.2 Hz, and a quartet at δ = −83.1 with a coupling constant 3 JFF of 4.4 Hz for compound 1.The formation of 3 was further confirmed through comparing the 1 H NMR spectrum with the data reported in the literature [15].It was noted that traces of trifluoromethane were also observed according to the 19 F NMR spectrum.Heating the sample further for one hour led to a decrease in the amount of 1 and SIMesF2 (2) and, instead, more trifluoromethane and trifluoromethane-d1 were observed.The latter can be formed due to the reaction of an intermediate CF3 radical (see below) via hydrogen or deuterium atom transfer.Attempts to achieve a similar transformation in benzene gave the considerably lower amounts of 1, 2, and 3, possibly due to the lower reaction temperature, which was limited by the boiling point of benzene.

Photolytic Activation of SF5CF3 with SIMes
When a mixture of SF5CF3 and 6.7 equivalents of SIMes was irradiated at 311 nm in benzene-d6 for 3 h, the formation of 62% of 1, and 105% of 2 and 3 was observed, as well as 1% of α,α,α-trifluorotoluene-d5 (Scheme 2).All yields are NMR yields based on the amount of SF5CF3.Further irradiation for 16 h led to the hydrolysis of 2 by adventitious water, to give a urea derivative and HF.The generation of 4 could then be due to the presence of HF.Compound 4 and the thiourea product 3 were observed in a ratio of 4:7.In addition, as described below, the trifluoromethylation of C6D6 will result in the generation of DF.DF can subsequently lead an FDF − derivative of 4. Compound 4 shows a singlet at −65.68 ppm in the 19 F NMR spectrum for the CF3 group and a broad signal at -169.40 ppm, indicating the presence of an FHF -anion.The presence of the cation was also

Photolytic Activation of SF 5 CF 3 with SIMes
When a mixture of SF 5 CF 3 and 6.7 equivalents of SIMes was irradiated at 311 nm in benzene-d 6 for 3 h, the formation of 62% of 1, and 105% of 2 and 3 was observed, as well as 1% of α,α,α-trifluorotoluene-d 5 (Scheme 2).All yields are NMR yields based on the amount of SF 5 CF 3. Further irradiation for 16 h led to the hydrolysis of 2 by adventitious water, to give a urea derivative and HF.The generation of 4 could then be due to the presence of HF.Compound 4 and the thiourea product 3 were observed in a ratio of 4:7.In addition, as described below, the trifluoromethylation of C 6 D 6 will result in the generation of DF.DF can subsequently lead an FDF − derivative of 4. Compound 4 shows a singlet at −65.68 ppm in the 19 F NMR spectrum for the CF 3 group and a broad signal at −169.40 ppm, indicating the presence of an FHF − anion.The presence of the cation was also confirmed via ESI-MS.Independently synthesized 1,3-dimesityl-2-trifluoromethylimidazolinium tetrafluoroborate showed the same signal in the 19 F NMR spectrum.The formation of α,α,α-trifluorotoluened 5 with a yield of 22% (based on SF 5 CF 3 ) was confirmed via 19 F NMR spectroscopy and GC-MS.The irradiation of a benzene-d 6 solution of SF 5 CF 3 at 311 nm for 168 h without the presence of SIMes gave α,α,α-trifluorotoluene-d 5 with a yield of 2% only.With toluene-d 8 as a solvent, the photochemical activation of SF 5 CF 3 with SIMes led to the formation of CD 3 C 6 D 5 CF 3 , although the reaction is not selective, and small amounts for unknown products can be detected in the 19 F NMR spectrum.Trifluoromethylation proceeded at the ortho (9%, NMR yield based on the consumption of SF 5 CF 3 ) and para (5%) position of toluene-d 8, but also at the meta position (4%) [22,30,31].
confirmed via ESI-MS.Independently synthesized 1,3-dimesityl-2-trifluoromethylimidazolinium tetrafluoroborate showed the same signal in the 19 F NMR spectrum.The formation of α,α,α-trifluorotoluene-d5 with a yield of 22% (based on SF5CF3) was confirmed via 19 F NMR spectroscopy and GC-MS.The irradiation of a benzene-d6 solution of SF5CF3 at 311 nm for 168 h without the presence of SIMes gave α,α,α-trifluorotoluene-d5 with a yield of 2% only.With toluene-d8 as a solvent, the photochemical activation of SF5CF3 with SIMes led to the formation of CD3C6D5CF3, although the reaction is not selective, and small amounts for unknown products can be detected in the 19 F NMR spectrum.Trifluoromethylation proceeded at the ortho (9%, NMR yield based on the consumption of SF5CF3) and para (5%) position of toluene-d8, but also at the meta position (4%) [22,30,31].
Scheme 2. The irradiation of SIMes and SF5CF3 in C6D6 at 311 nm (the NMR yields are based on the amount of SF5CF3).

Mechanisms for the Activation of SF5CF3
Compound 1 was then investigated regarding its ability to transfer a CF3 group to aromatics.Thus, the reaction mixture of 1, SIMesF2 (2) and 3 in C6D6, obtained for the thermal SF5CF3 activation, (Scheme 1) was degassed under a vacuum to remove any excess of SF5CF3 and irradiated afterwards at 311 nm.No formation of α,α,α-trifluorotoluene-d5 was observed.This suggests that 1 is not capable of transferring a CF3 group to aromatics.However, as mentioned above, the formation of compound 1 resembles a process known in the literature for the photochemical activation of SF6 by N-heterocyclic carbenes, which is initiated by an electron transfer [15,28].Thus, a SET (single-electron transfer) after carbene excitation to SF5CF3 can be proposed to give a carbene radical cation and SF5CF3 - radical anion (Scheme 3).The formation of an N-heterocyclic carbene radical cation as an intermediate has been proposed by Severin et al. in their discussion of the reaction between SIMes and [Ph3C][B(C6F5)4] to yield [SIMes-C6H5-CPh2] + at −40 °C [32,33].The SF5CF3 − radical anion will then decompose to give SF5 − and a CF3 radical.The latter transformation is consistent with low-temperature electron attachment experiments [27,34,35].The formed CF3 radical recombines with the SIMes radical cation to form 5 bearing an SF5 - anion.The SF5 − anion can convert into SF4 and 6 [24,36,37].Compound 6 then reacts to give the observed compound 1 via the nucleophilic attack of the fluoride.SF4 reacts further, yielding SIMesF2 (2) and the thiourea derivative 3, as was shown in independent experiments [15].For the thermal activation of SF5CF3, a comparable transformation can be imagined, although electron transfer can be hampered by a kinetic barrier.In this regard, an incipient transition state or pre-interaction of the nucleophilic carbene with SF5CF3 seems to be conceivable [8,23,38,39].It should be noted that an ion flow tube study shows that OH − reacts with SF5CF3, yielding CF3OH and SF5 − [40].As mentioned above, DF can be formed in association with the photochemical trifluoromethylation of the aromatic compounds.For this process, initially a cyclohexadienyl radical via reaction with a CF3 radical with C6D6 might be generated [22,30,[41][42][43].The cyclohexadienyl radical can Scheme 2. The irradiation of SIMes and SF 5 CF 3 in C 6 D 6 at 311 nm (the NMR yields are based on the amount of SF 5 CF 3 ).

Mechanisms for the Activation of SF 5 CF 3
Compound 1 was then investigated regarding its ability to transfer a CF 3 group to aromatics.Thus, the reaction mixture of 1, SIMesF 2 (2) and 3 in C 6 D 6 , obtained for the thermal SF 5 CF 3 activation, (Scheme 1) was degassed under a vacuum to remove any excess of SF 5 CF 3 and irradiated afterwards at 311 nm.No formation of α,α,α-trifluorotoluene-d 5 was observed.This suggests that 1 is not capable of transferring a CF 3 group to aromatics.However, as mentioned above, the formation of compound 1 resembles a process known in the literature for the photochemical activation of SF 6 by N-heterocyclic carbenes, which is initiated by an electron transfer [15,28].Thus, a SET (single-electron transfer) after carbene excitation to SF 5 CF 3 can be proposed to give a carbene radical cation and SF 5 CF − and a CF 3 radical.The latter transformation is consistent with low-temperature electron attachment experiments [27,34,35].The formed CF 3 radical recombines with the SIMes radical cation to form 5 bearing an SF 5 − anion.The SF 5 − anion can convert into SF 4 and 6 [24,36,37].Compound 6 then reacts to give the observed compound 1 via the nucleophilic attack of the fluoride.SF 4 reacts further, yielding SIMesF 2 (2) and the thiourea derivative 3, as was shown in independent experiments [15].For the thermal activation of SF 5 CF 3 , a comparable transformation can be imagined, although electron transfer can be hampered by a kinetic barrier.In this regard, an incipient transition state or pre-interaction of the nucleophilic carbene with SF 5 CF 3 seems to be conceivable [8,23,38,39].It should be noted that an ion flow tube study shows that OH − reacts with SF 5 CF 3 , yielding CF 3 OH and SF 5 − [40].As mentioned above, DF can be formed in association with the photochemical trifluoromethylation of the aromatic compounds.For this process, initially a cyclohexadienyl radical via reaction with a CF 3 radical with C 6 D 6 might be generated [22,30,[41][42][43].The cyclohexadienyl radical can then transfer an electron to the SIMes radical cation, giving a cyclohexadienyl cation.The latter reacts with a fluoride, which stems from SF 5 − , and forms α,α,α-trifluorotoluene-d 5 , as well as DF.
then transfer an electron to the SIMes radical cation, giving a cyclohexadienyl cation.The latter reacts with a fluoride, which stems from SF5 − , and forms α,α,α-trifluorotoluene-d5, as well as DF.
Scheme 3. The proposed mechanism for the activation of SF5CF3 with SIMes in benzene-d6.
To confirm the presence of radical intermediates, TEMPO (2,2,6,6-tetramethylpiperidinyloxy) was added to a mixture of SIMes and SF5CF3 in C6D6.After 5 h of irradiation at 311 nm, signals for SIMesF2 (2) and TEMPO-CF3 (8) [44] in a ratio of 1:1 were observed in the 19 F NMR spectrum (Scheme 4).The presence of the thiourea derivative 3 was confirmed via 1 H NMR spectroscopy, as well as via GC-MS.It should be noted that the addition of TEMPO to the reaction of SF5CF3 with SIMes under non-photolytic conditions did not show the formation of TEMPO-CF3, which indicates that no CF3 radicals were formed.
Furthermore, 1,1-diphenylethylene was used as an additional trapping reagent for the CF3 radical.After irradiation at 311 nm for 4 h, the trifluoromethylated olefin 9 (0.5% based on the amount of 1,1-diphenylethylene), and the trifluoroalkane 10 (0.6% based on the amount of 1,1-diphenylethylene) were observed in a ratio of 2:3, as well as SIMesF2 2 (25% based on the amount of SIMes), 1 (10% based on the amount of SIMes), and the thiourea derivative 3, among traces of other compounds, such as trifluoromethane (Scheme 4).Mechanistically, the CF3 radical reacts with 1,1-diphenylethylene, and a trifluoromethylbenzyl radical is formed.Two molecules of the latter can generate the olefin 9 and the alkane 10 via hydrogen atom transfer.The formation of trifluoromethane can be explained by HAT from the trifluoromethylbenzyl radical to also yield 9. To confirm the presence of radical intermediates, TEMPO (2,2,6,6-tetramethylpiperidin yloxy) was added to a mixture of SIMes and SF 5 CF 3 in C 6 D 6 .After 5 h of irradiation at 311 nm, signals for SIMesF 2 (2) and TEMPO-CF 3 (8) [44] in a ratio of 1:1 were observed in the 19 F NMR spectrum (Scheme 4).The presence of the thiourea derivative 3 was confirmed via 1 H NMR spectroscopy, as well as via GC-MS.It should be noted that the addition of TEMPO to the reaction of SF 5 CF 3 with SIMes under non-photolytic conditions did not show the formation of TEMPO-CF 3 , which indicates that no CF 3 radicals were formed.Scheme 3. The proposed mechanism for the activation of SF5CF3 with SIMes in benzene-d6.
To confirm the presence of radical intermediates, TEMPO (2,2,6,6-tetramethylpiperidinyloxy) was added to a mixture of SIMes and SF5CF3 in C6D6.After 5 h of irradiation at 311 nm, signals for SIMesF2 (2) and TEMPO-CF3 (8) [44] in a ratio of 1:1 were observed in the 19 F NMR spectrum (Scheme 4).The presence of the thiourea derivative 3 was confirmed via 1 H NMR spectroscopy, as well as via GC-MS.It should be noted that the addition of TEMPO to the reaction of SF5CF3 with SIMes under non-photolytic conditions did not show the formation of TEMPO-CF3, which indicates that no CF3 radicals were formed.
Furthermore, 1,1-diphenylethylene was used as an additional trapping reagent for the CF3 radical.After irradiation at 311 nm for 4 h, the trifluoromethylated olefin 9 (0.5% based on the amount of 1,1-diphenylethylene), and the trifluoroalkane 10 (0.6% based on the amount of 1,1-diphenylethylene) were observed in a ratio of 2:3, as well as SIMesF2 2 (25% based on the amount of SIMes), 1 (10% based on the amount of SIMes), and the thiourea derivative 3, among traces of other compounds, such as trifluoromethane (Scheme 4).Mechanistically, the CF3 radical reacts with 1,1-diphenylethylene, and a trifluoromethylbenzyl radical is formed.Two molecules of the latter can generate the olefin 9 and the alkane 10 via hydrogen atom transfer.The formation of trifluoromethane can be explained by HAT from the trifluoromethylbenzyl radical to also yield 9.  Furthermore, 1,1-diphenylethylene was used as an additional trapping reagent for the CF 3 radical.After irradiation at 311 nm for 4 h, the trifluoromethylated olefin 9 (0.5% based on the amount of 1,1-diphenylethylene), and the trifluoroalkane 10 (0.6% based on the amount of 1,1-diphenylethylene) were observed in a ratio of 2:3, as well as SIMesF 2 2 (25% based on the amount of SIMes), 1 (10% based on the amount of SIMes), and the thiourea derivative 3, among traces of other compounds, such as trifluoromethane (Scheme 4).Mechanistically, the CF 3 radical reacts with 1,1-diphenylethylene, and a trifluoromethylbenzyl radical is formed.Two molecules of the latter can generate the olefin 9 and the alkane 10 via hydrogen atom transfer.The formation of trifluoromethane can be explained by HAT from the trifluoromethylbenzyl radical to also yield 9.

Activation of SF 5 CF 3 with Triphenylphosphine
The described reactivity of SIMes was compared with that of PPh 3 .Thus, the photolysis of PPh 3 and SF 5 CF 3 at 353 nm led to the formation of 11 with a yield of 10%, and 12 with a yield of 28% (based on the amount of PPh 3 , see Scheme 5).α,α,α-Trifluorotoluene-d 5 was formed, as well.Additionally, traces of F 3 PPh 2 , Ph 2 PF 4 − , and O=PPh 2 F were observed, according to the 19 F NMR spectra [45].In contrast to the described reactivity with SIMes, the generation of a phosphorane containing a CF 3 group was not observed.The products were identified via 31 P NMR, 19 F NMR spectroscopy, as well as ESI-MS, and the data are consistent with compounds known in the literature [23].Irradiation at a wavelength of 375 nm led to the formation of only small amounts of phosphorane 12, and only traces of α,α,α-trifluorotoluene-d 5 .No thermal activation of SF 5 CF 3 in toluene-d 8 could be achieved via heating the reaction solution at 100 • C for 9 h.Notably, Buß et al. reported on the thermal activation of SF 6 using strongly basic phosphines [8], but could not observe the thermal activation of SF 6 with PPh 3 , due to the lower nucleophilicity of the latter [23].

Activation of SF5CF3 with Triphenylphosphine
The described reactivity of SIMes was compared with that of PPh3.Thus, the photolysis of PPh3 and SF5CF3 at 353 nm led to the formation of 11 with a yield of 10%, and 12 with a yield of 28% (based on the amount of PPh3, see Scheme 5).α,α,α-Trifluorotoluene-d5 was formed, as well.Additionally, traces of F3PPh2, Ph2PF4 − , and O=PPh2F were observed, according to the 19 F NMR spectra [45].In contrast to the described reactivity with SIMes, the generation of a phosphorane containing a CF3 group was not observed.The products were identified via 31 P NMR, 19 F NMR spectroscopy, as well as ESI-MS, and the data are consistent with compounds known in the literature [23].Irradiation at a wavelength of 375 nm led to the formation of only small amounts of phosphorane 12, and only traces of α,α,α-trifluorotoluene-d5. No thermal activation of SF5CF3 in toluene-d8 could be achieved via heating the reaction solution at 100 °C for 9 h.Notably, Buß et al. reported on the thermal activation of SF6 using strongly basic phosphines [8], but could not observe the thermal activation of SF6 with PPh3, due to the lower nucleophilicity of the latter [23].A possible mechanism involves SET from the phosphine to the SF5CF3, resulting in the formation of a SF5CF3 − radical anion and a PPh3 + radical cation (Scheme 6).The SF5CF3 radical anion then decomposes to give a CF3 radical and a SF5 − anion [27,34,35]

General Instruments, Methods, and Materials
All reactions were performed under an argon atmosphere, to exclude air and moisture.Chemicals were stored in an argon-filled glass apparatus, using the standard Schlenk-technique.SIMes was synthesized from 1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-1-ium tetrafluoroborate, KOtBu, and NaH, all of which were heated at night under a vacuum prior to use.TEMPO, SF5CF3, and PPh3 were purchased from commercial sources, and used without further purification.1,1-Diphenylethylene was stored over a molecular sieve (3 Å) before use.Toluene-d8, C6D6, and THF-d8 were stored over Solvona ® .All solvents were distilled and degassed prior to use, and stored under argon over  [23].

Activation of SF5CF3 with Triphenylphosphine
The described reactivity of SIMes was compared with that of PPh3.Thus, the photolysis of PPh3 and SF5CF3 at 353 nm led to the formation of 11 with a yield of 10%, and 12 with a yield of 28% (based on the amount of PPh3, see Scheme 5).α,α,α-Trifluorotoluene-d5 was formed, as well.Additionally, traces of F3PPh2, Ph2PF4 − , and O=PPh2F were observed, according to the 19 F NMR spectra [45].In contrast to the described reactivity with SIMes, the generation of a phosphorane containing a CF3 group was not observed.The products were identified via 31 P NMR, 19 F NMR spectroscopy, as well as ESI-MS, and the data are consistent with compounds known in the literature [23].Irradiation at a wavelength of 375 nm led to the formation of only small amounts of phosphorane 12, and only traces of α,α,α-trifluorotoluene-d5. No thermal activation of SF5CF3 in toluene-d8 could be achieved via heating the reaction solution at 100 °C for 9 h.Notably, Buß et al. reported on the thermal activation of SF6 using strongly basic phosphines [8], but could not observe the thermal activation of SF6 with PPh3, due to the lower nucleophilicity of the latter [23].A possible mechanism involves SET from the phosphine to the SF5CF3, resulting in the formation of a SF5CF3 − radical anion and a PPh3 + radical cation (Scheme 6).The SF5CF3 radical anion then decomposes to give a CF3 radical and a SF5 − anion [27,34,35]

General Instruments, Methods, and Materials
All reactions were performed under an argon atmosphere, to exclude air and moisture.Chemicals were stored in an argon-filled glass apparatus, using the standard Schlenk-technique.SIMes was synthesized from 1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-1-ium tetrafluoroborate, KOtBu, and NaH, all of which were heated at night under a vacuum prior to use.TEMPO, SF5CF3, and PPh3 were purchased from commercial sources, and used without further purification.1,1-Diphenylethylene was stored over a molecular sieve (3 Å) before use.Toluene-d8, C6D6, and THF-d8 were stored over Solvona ® .All solvents were distilled and degassed prior to use, and stored under argon over Scheme 6.The proposed mechanism for the activation of SF 5 CF 3 with triphenylphosphine.

General Instruments, Methods, and Materials
All reactions were performed under an argon atmosphere, to exclude air and moisture.Chemicals were stored in an argon-filled glass apparatus, using the standard Schlenktechnique.SIMes was synthesized from 1,3-Bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-1-ium tetrafluoroborate, KOtBu, and NaH, all of which were heated at night under a vacuum prior to use.TEMPO, SF 5 CF 3 , and PPh 3 were purchased from commercial sources, and used without further purification.1,1-Diphenylethylene was stored over a molecular sieve (3 Å) before use.Toluene-d 8 , C 6 D 6 , and THF-d 8 were stored over Solvona ® .All solvents were distilled and degassed prior to use, and stored under argon over molecular sieves (3 Å).As the light source, an LED lamp with a peak wavelength of 375 nm from Innotas Produktions GmbH (Zittau, Germany) was used, as well as a photo Multirays reactor (Helios Italquartz, Cambiago, Italy) equipped with ten light sources (15 W), with an emission maximum of 311 nm or 353 nm.The NMR spectra were recorded at room temperature with a Bruker AV III 300 or Bruker DPX 300 spectrometer (Ettlingen, Germany).The chemical shifts in the 1 H and 13 C{ 1 H} NMR spectra were calibrated to the residual solvent signal of the deuterated solvents.The 1 H NMR spectra were referenced as C 6 D 5 H: δ = 7.16 ppm; toluene-d 7 : δ = 6.97 ppm; CHD 2 CN: δ = 1.94 ppm, and CHDCl 2 : δ = 5.32 ppm.The 13 C{ 1 H} NMR spectra were referenced as C 6 D 6 : δ = 128.06ppm; toluene-d 8 : δ = 20.43 ppm; CD 3 CN: δ = 1.32 ppm and CD 2 Cl 2 : δ = 53.84ppm.The 19 F NMR spectra were referenced externally to CFCl 3 at δ = 0.0 ppm.As an internal standard for the quantification, 1-fluoropentane was used with δ of −217.6 ppm in the 19 F NMR spectrum.GC-MS measurements were conducted using an Agilent 6890N gas chromatograph with a capillary column (Agilent 19091S-433 Hewlett-Packard 5 MS: 30 m length, 0.25 mm inside diameter, 0.25 µm film thickness) and an Agilent 5973 Network mass selective detector.Helium (0.74 bar, 1.2 mL/min, 40 cm/s) was used as the carrier gas.The electron impact ionization was carried out with an ionization voltage of 70 eV.Mass spectra were measured with a Micromass Q-Tof-2 instrument, with a Linden LIFDI source (Linden CMS GmbH, Weyhe, Germany).ESI-MS spectra were recorded using an ADVION EXPRESSION CMS spectrometer, as an eluent CD 3 CN was used, and the sample was directly injected into the instruments.The data were analyzed using ADVION DATA EXPRESS Version 6.0.11.3.Caution: in some experiments, traces of HF were generated.Immediate access to procedures in case of contact with HF-containing solutions must be available.

Activation of SF 5 CF 3 with SIMes by Heating
A PFA tube was filled with SIMes (0.016 g, 0.0525 mmol) and 1-fluoropentane (6 µL, 0.0525 mmol) as an internal standard.The tube was attached to a steel line, and C 6 D 6 (0.4 mL) was condensed into the PFA tube.After the solvent was degassed, SF 5 CF 3 (175 mbar, 0.0525 mmol) was condensed into the PFA tube, which was then flame-sealed under a vacuum.The reaction mixture was heated at 90 • C for 3 h.Compound 1 was detected with a yield of 18%, 2 was detected with a yield of 31%, and 3 was detected with a yield of 31%.All yields are NMR yields (internal standard: 1-fluoropentane) based on SF 5 CF 3 .
Reaction products 1, 2, and 3 were degassed (freed of SF 5 CF 3 ) and irradiated at 311 nm in the photochemical reactor at 311 nm.After irradiation for 16 h, no trifluoromethylated solvent was observed.

Photochemical Activation of SF 5 CF 3 with SIMes
A PFA tube was filled with SIMes (0.032 g, 0.105 mmol) and 1-fluoropentane (6 µL, 0.0525 mmol) as an internal standard.The tube was attached to a steel line, and C 6 D 6 (0.4 mL) was condensed on top.After the solvent was degassed, SF 5 CF 3 (87 mbar, 0.026 mmol, 1 eq) was condensed into the solution, and the PFA tube was flame-sealed under a vacuum.The reaction mixture was irradiated in a UV reactor (311 nm) at room temperature for 16 h.

Scheme 4 .Scheme 3 .
Scheme 4. Experiments to trap CF3 radicals (a) via the addition of TEMPO, and (b) via the addition of 1,1-diphenylethylene (* NMR yield based on the amount of 1,1-diphenylethylene, ** NMR yield based on the amount of SIMes).

Scheme 4 .
Scheme 4. Experiments to trap CF3 radicals (a) via the addition of TEMPO, and (b) via the addition of 1,1-diphenylethylene (* NMR yield based on the amount of 1,1-diphenylethylene, ** NMR yield based on the amount of SIMes).

Scheme 4 .
Scheme 4. Experiments to trap CF 3 radicals (a) via the addition of TEMPO, and (b) via the addition of 1,1-diphenylethylene (* NMR yield based on the amount of 1,1-diphenylethylene, ** NMR yield based on the amount of SIMes).

Scheme 5 .
Scheme 5.The reduction of SF5CF3 with triphenylphosphine (* based on the amount of PPh3).

Scheme 6 .
Scheme 6.The proposed mechanism for the activation of SF5CF3 with triphenylphosphine.

Scheme 5 .
Scheme 5.The reduction of SF 5 CF 3 with triphenylphosphine (* based on the amount of PPh 3 ).A possible mechanism involves SET from the phosphine to the SF 5 CF 3 , resulting in the formation of a SF 5 CF 3 − radical anion and a PPh 3 + radical cation (Scheme 6).The SF 5 CF 3 radical anion then decomposes to give a CF 3 radical and a SF 5 − anion [27,34,35].The latter can either decompose to fluoride and SF 4 , or give a Ph 3 PF radical via reaction with PPh 3 + .PPh 3 reacts with SF 4 , yielding F 2 PPh 3 and SPPh 3. The generated Ph 3 PF might become further fluorinated via intermediate sulfur fluorides or SF 4 , to yield PPh 3 F 2. The CF 3 radical reacts with the solvent C 6 D 6 , yielding α,α,α-trifluorotoluene-d 5 and, presumably, DF, possibly via the re-oxidation of a cyclohexadienyl radical cation with PPh 3 + , and subsequent deprotonation with fluoride .It should be noted that Dielmann et al. also proposed, for the photochemical activation of SF 6 with triphenylphosphine, a mechanism based on DFT calculations, in which an electron is initially transferred from a π orbital of an arene moiety of PPh 3 to the delocalized σ* orbital of SF 6 [23].

Scheme 5 .
Scheme 5.The reduction of SF5CF3 with triphenylphosphine (* based on the amount of PPh3).

Scheme 6 .
Scheme 6.The proposed mechanism for the activation of SF5CF3 with triphenylphosphine.