Fluoroalkylation of a Methylplatinum(II) Complex under

Mar 28, 2017 - Organometallics , 2017, 36 (7), pp 1391–1397. DOI: 10.1021/acs.organomet.7b00098 ... Cite this:Organometallics 36, 7, 1391-1397 ...
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Fluoroalkylation of a Methylplatinum(II) Complex under Photoirradiation Yuji Suzaki, Minetada Kiho, and Kohtaro Osakada* Laboratory for Chemistry and Life Science, Institute of Innovative Research, R1-3, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan S Supporting Information *

ABSTRACT: The UV irradiation of a mixture of PtMe2(cod) (cod = 1,5cyclooctadiene) and n-C4F9I in a 1:12 molar ratio for 15 min produces Pt(nC4F9)2(cod) in 61% yield at room temperature. The reaction without irradiation, as reported previously, proceeds much more slowly; heating the mixture for 7 days at 50 °C forms PtMe(n-C4F9)(cod) in 9% yield and no Pt(n-C4F9)2(cod). Pt(n-C4F9)2(cod) is converted to complexes having chelating ligands, Pt(n-C4F9)2(L) (L = dppe (1,2-bis(diphenylphosphino)ethane), dppp (1,3-bis(diphenylphosphino)propane), bpy (2,2′-bipyridine)). The photoassisted fluoroalkylation of PtMe(n-C4F9)(cod) also affords Pt(nC4F9)2(cod), while the monomethylplatinum complexes PtMe(C6H4-4-F)(cod) and PtClMe(cod) react with n-C4F9I under photoirradiation to afford complexes with a perfluorobutyl ligand, Pt(n-C4F9)(C6H4-4-F)(cod) and PtCl(n-C4F9)(cod), respectively. The above reactions do not provide isolable Pt(IV) complexes, in contrast to the reactions of alkyl or fluoroalkyl iodides with diorganoplatinum(II) complexes having dinitrogen ligands. The mechanism of the fluoroalkylation of Pt(II) complexes under photoirradiation is discussed on the basis of the reaction products.

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INTRODUCTION Transition-metal complexes having an M−CF2− bond are regarded as intermediates in the fluoroalkylation of organic compounds as well as the functionalization and polymerization of fluoroethylenes.1−3 Hughes reported the introduction of fluorinated alkyl ligands into various transition metals, such as Co, Rh, Ir, Mo, and W, via the reactions of RF−I with lowvalent metal complexes as well as the chemical properties of the fluoroorganotransition metal complexes.4 Michelin extensively reviewed recent reports on Pt complexes having fluorinated alkyl ligands and phosphine ligands.5 The synthesis and reactions of the complexes as well as catalysis using the complexes were described in detail. Alkylplatinum complexes as well as fluoroarylplatinum complexes are mostly synthesized by the reactions of alkyl compounds of the nontransition elements Li, Mg, B, and Al with complexes having halogeno and pseudohalogeno ligands.6 Pt complexes with perfluoroalkyl ligands, however, are obtained by the addition of fluoroalkyl iodides to low-valent organoplatinum complexes. Clark reported the synthesis of Pt(CF3)2(cod) (cod = 1,5-cyclooctadiene) by the reaction of CF3I with PtMe2(cod) (Scheme 1A).7 The reaction requires 4 days to complete. A small amount of [PtMe3I]4 was also obtained, which was ascribed to the liberation of MeI from the initial Pt(IV) product and its oxidative addition to PtMe2(cod). A similar reaction yields the methyl(fluoroalkyl)platinum(II) complexes PtMeRF(L) (L = cod, nbd (norbornadiene), tmeda (N,N,N′,N′-tetramethylethylenediamine); RF = CF3, n-C3F7, i-C3F7, n-C4F9) and/or bis(fluoroalkyl)platinum complexes.8 The complexes have been employed as precursors of new fluoroalkyl platinum complexes © XXXX American Chemical Society

Scheme 1. Synthesis of (A) Pt(CF3)2(cod) and (B) Pt{(CF2)3}(cod)a

a

See refs 7 and 8f.

having various auxiliary ligands.9 Vicic reported that the reaction of I−C3F6−I with PtMe2(cod) at room temperature affords Pt(C3F6I)Me(cod) as the initial product, and further reaction for 36 h at 90 °C converts it into a platinacyclobutane, Pt(C3F6)(cod), via oxidative addition of the remaining C−I bond to the Pt(II) center and by the elimination of MeI (Scheme 1B).8f Thus, the stepwise substitution of Me ligands by the fluorinated alkyl group takes place in these reactions, and the second step is slower than the first step. The mechanism of the fluoroalkylation of the Pt(II)−diene complex was given in previous reports,7,8a,b but details of the reactions have not yet been clarified. Here, we report that the reaction of n-C 4F9 I with PtMe2(cod) is much smoother upon photoirradiation in Received: February 7, 2017

A

DOI: 10.1021/acs.organomet.7b00098 Organometallics XXXX, XXX, XXX−XXX

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Organometallics comparison to that in the dark and it is extended to the synthesis of new unsymmetrical Pt(II) complexes having a perfluoroalkyl ligand.

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RESULTS AND DISCUSSION The UV irradiation (Hg lamp) of a CDCl3 solution containing a mixture of PtMe2(cod) and n-C4F9I ([PtMe2(cod)]0 = 10 mM, [n-C4F9I]0 = 120 mM) produced Pt(n-C4F9)2(cod) in 61% yield after 15 min at 25 °C, as shown in eq 1. The reaction

Figure 2. Change in the concentrations of compounds in the reaction mixture of PtMe2(cod) and n-C4F9I (A) under UV irradiation (Hg lamp) at 0 °C and (B) without UV irradiation at 50 °C in the dark (Table 1, run 7): (◇) PtMe2(cod); (○) PtMe(n-C4F9)(cod); (+) PtMeI(cod); (●) Pt(n-C4F9)2(cod); (□) PtCl(n-C4F9)(cod); (■) PtI(n-C4F9)(cod); (×) an uncharacterized product (see ref 10).

in a 1:4 molar ratio for the same duration gave Pt(nC4F9)2(cod) and PtMe(n-C4F9)(cod) in 7% and 54% yields, respectively. The complex Pt(n-C4F9)2(cod) was converted to the chelate complexes Pt(n-C4F9)2(L) (L = dppe (1,2bis(diphenylphosphino)ethane), dppp (1,3-bis(diphenylphosphino)propane), bpy (2,2′-bipyridine)) upon the addition of these P,P and N,N ligands. Figure 1 depicts the molecular structure of Pt(n-C4F9)2(cod) and Pt(n-C4F9)2(dppp), both of which have common square-

spectrum of the reaction mixture contains signals corresponding to the above products and a minor signal that is attributed to PtI(n-C4F9)(cod) (δF −110.9). The reaction without UV irradiation at 50 °C (Figure 2B) occurred much more slowly, as mentioned in the previous report.7 The consumption of PtMe2(cod) required 12 h, and a mixture of PtMe(I)(cod) and PtMe(n-C4F9)(cod) was formed. Pt(n-C4F9)2(cod) was not observed even after 27 h. The ratio of the products Pt(n-C4F9)2(cod) and PtMe(nC4F9)(cod) under photoirradiation conditions was affected by the solvent used. The reaction in CD3CN gave Pt(nC4F9)2(cod) within 5 min via formation and consumption of PtMe(n-C4F9)(cod), while the reaction in C6D6 solvent formed PtMe(n-C4F9)(cod) as the main product after 5 min (Figure 3).

Figure 1. Crystal structures of (A) Pt(n-C4F9)2(cod) and (B) Pt(nC4F9)2(dppp). Hydrogen atoms are omitted.

planar structures. The bond lengths of Pt1−C1 and Pt1−C5 in Pt(n-C4F9)2(cod) (2.060(8), 2.060(8) Å) are shorter than those in Pt(n-C4F9)2(dppp) (2.109(4), 2.104(4) Å) owing to the larger trans effect of the phosphine ligand in comparison to that of the π-accepting olefin ligand. Pt(CF3)2(L) (L = C6H41,2-(PPh2(CHCH2))) was reported to contain Pt−CF3 bonds with different lengths, depending on the ligand trans to the CF3 group (2.082(6) Å (trans to P) and 2.032 Å (trans to vinyl)).9 The reaction was monitored by 1H and 19F{1H} NMR spectroscopy. Figure 2A shows the change in the concentrations of the compounds in the reaction mixture, under UVirradiated conditions, which was monitored by the 1H NMR spectra. The reaction mixture initially formed PtMe(n-C4F9)(cod) (δH 5.14 (JPtH = 23 Hz), 5.40 (JPtH = 18 Hz)) within 1 min, which was then converted into Pt(n-C4F9)2(cod) (δH 5.83 (JPtH = 19 Hz)) with generation of MeI (δH 2.16, 79% yield after 15 min).10 The amount of Pt(n-C4F9)2(cod) reached a maximum at 15 min, and further irradiation resulted in its conversion into an uncharacterized Pt complex (δH 5.21 and 6.03, δF −95.6). Since photoirradiation of the isolated Pt(nC4F9)2(cod) did not change the NMR spectrum, the product obtained by the prolonged reaction did not form via the simple photodecomposition of Pt(n-C4F9)2(cod). The 19F{1H} NMR

Figure 3. Change in the concentrations of compounds in the reaction mixture of PtMe2(cod) and n-C4F9I under UV irradiation (Hg lamp) at 0 °C in (A) CD3CN and (B) C6D6: (◇) PtMe2(cod); (○) PtMe(nC4F9)(cod); (●) Pt(n-C4F9)2(cod); (■) PtI(n-C4F9)(cod).

The reaction profile in CDCl3 (Figure 4) obtained by the ON-OFF switching of photoirradiation shows an initial increase in the concentration of PtMe(n-C4F9)(cod) with a decrease in the concentration of PtMe2(cod) followed by the formation of Pt(n-C4F9)2(cod). The reaction proceeded slowly without photoirradiation and resumed with the start of irradiation. The results of the reactions under various conditions are summarized in Table 1. The reaction in the presence of a radical inhibitor, butylated hydroxyltoluene (BHT) (run 3), resulted in the formation of Pt(n-C4F9)Me(cod) as the main product even under photoirradiation. The addition of cod (1.3 equiv with respect to Pt) retarded the reaction, although the B

DOI: 10.1021/acs.organomet.7b00098 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

yield after 6 h was 7% (run 9). The photoinitiated reaction of nC6F13I, having a longer fluoroalkyl chain, with PtMe2(cod) proceeded similarly to yield Pt(n-C6F13)2(cod) (run 10), while a similar reaction using i-C3F7I resulted in the formation of the methylplatinum(II) complex PtMe(i-C3F7)(cod) (run 11). The low reactivity of the secondary perfluoroalkyl group was reported also in the reaction without photoirradiation.8d Photoirradiation during reaction 1 enhanced the introduction of both the first and second perfluoroalkyl ligands into the Pt(II) center. We applied photoirradiation to the synthesis of unsymmetrical Pt(II) complexes, as mentioned below. The photoinduced perfluorobutylation of PtMeX(cod) (X = n-C4F9, C6H4-4-F, Cl) gave PtX(n-C4F9)(cod) (X = n-C4F9 (61%, NMR yield), C6H4-4-F (70%, isolated yield), Cl (68%, isolated yield)) (eq 2). n-C4F9I did not react with PtCl2(cod) under these conditions.

Figure 4. Profile of the reaction of PtMe2(cod) and n-C4F9I in CDCl3 under ON-OFF switching of photoirradiation showing concentrations of (i) Pt(n-C4F9)2(cod), (ii) PtMe(n-C4F9)(cod), (iii) PtMe(I)(cod), and (iv) PtMe2(cod).

Table 1. Reaction of Perfluoroalkyl Iodides RF-I with PtMe2(cod)a yield (%)b PtRF run

RF

1

n-C4F9

hν

2

n-C4F9c

hν

conditions

3

n-C4F9

hν, BHT

4

n-C4F9

hν, code

d

5

n-C4F9

hν, N(n-Bu4)I

6

n-C4F9

ambient light h

7

n-C4F9

dark

8 9 10 11

n-C4F9 n-C4F9 n-C6F13 i-C3F7

darki darkj hν hν

f

PtMeRF(cod)

temp, time

2(cod)

25 °C, 15 min 25 °C, 20 min 25 °C, 20 min 25 °C, 20 min 25 °C, 20 min 25 °C, 5 days 50 °C, 178 h 50 °C, 1 h 50 °C, 1 h 25 °C, 2 h 25 °C, 30 min

61

0

7

54

4

14

In reactions 1 and 2, the Me ligand of the Pt complex is substituted by the perfluorobutyl group of n-C4F9I, and the reaction should involve an intermediate Pt complex, having a high-valent Pt center and three Pt−C bonds. Scheme 2 depicts

21

42

Scheme 2

97

61g

0

0

9

0 0 58 0

quant 0 (7k) 0 78

a Conditions unless specified otherwise: [PtMe2(cod)]0 = 10 mM, [RFI]0 = 120 mM (12 equiv with respect to Pt), in CDCl3. A high-pressure Hg lamp was used for hν irradiation. bEstimated from 1H NMR. c[nC4F9]0 = 40 mM (4 equiv with respect to Pt). dButylated hydroxytoluene (BHT) 15 equiv with respect to PtMe2(cod). e1.3 equiv with respect to PtMe2(cod). f1.0 equiv with respect to PtMe2(cod). gIn CH2Cl2 (isolated yield). hIn air. iDegassed CDCl3 was used under Ar. jUnder O2. kYield after 6 h.

a possible mechanism for the reaction via a neutral Pt(IV) intermediate. The oxidative addition of RFI to PtMe2(cod) generates a Pt(IV) complex, PtMe2(RF)(I)(cod), having RF and I ligands at the trans positions of the octahedral metal center (Scheme 2i). The reductive elimination of MeI from the Pt(IV) intermediate affords a Pt(II) complex having perfluoroalkyl and methyl ligands (Scheme 2ii). In fact, PtMe(C4F9)(cod) is obtained as the main product of reaction 1. The reductive elimination of ethane from the same intermediate (Scheme 2iii) would give PtRF(I)(cod), which is observed in a tiny amount in reaction 1. The oxidative addition of MeI, formed as shown in Scheme 2ii, to PtMe2(cod) produces PtMe(I)(cod) via the Pt(IV) intermediate (Scheme 2iv). Alkyl iodide and fluoroalkyl iodide were reported to cause oxidative addition to diorganoplatinum(II) complexes with dinitrogen ligands and to afford stable Pt(IV) complexes having

formation of Pt(n-C4F9)2(cod) was not inhibited (run 4). The reaction in the presence of N(n-Bu)4I (run 5) gives Pt(nC4F9)Me(cod) in high yield (>97%) after 20 min and a small amount of Pt(n-C4F9)2(cod) ( CH3−I > CF3−I. Thus, the results of the photopromoted reaction of perfluoroalkyl iodide with PtMe2(cod) are not consistent with Scheme 2, which involves the Pt(IV) intermediate and reductive elimination of MeI from it. Studies on the oxidative addition of perfluoroalkyl halides to late-transition-metal complexes having a cyclopentadienyl (Cp) ligand suggested the presence of the fluorocarbanion mechanism and radical mechanism, depending on the substrates and metal centers.4 The pathway by the former mechanism forms the cationic iodo complex of the metal as the initial product, while that by the latter yields the cationic perfluoroalkyl complex. Scheme 3 shows a possible mechanism of reaction 1 based on the radical pathway of the oxidative addition. A single electron transfer (SET) process of a mixture of PtMe2(cod) and RFI generates the corresponding radical pair (Scheme 3i), and activation of the C−I bond followed by

addition of the perfluoroalkyl radical forms the cationic Pt(IV) complex having two Pt−Me bonds and a Pt−RF bond. Activation of the former bond by iodo anion would form the methyl(perfluoroalkyl)platinum(II) complex (Scheme 3iii). Generation of reactive species by an SET process was proposed for various organic and inorganic reactions, including the initiation of oxidative addition of perfluoroalkyl iodide to PtMe2(phen) (phen = 1,10-phenanthroline).12a It is not clear whether PtMe2(cod) and perfluoroalkyl iodide undergoes the reaction initiated by SET because the cod ligand is much less donating and has no π conjugation. Application of the above mechanism to fluoroalkylation in reactions 1 and 2 needs to assume activation of a Pt−Me bond by iodo anion, although similar reactions were not common. Addition of N(n-Bu4)I to the reaction mixture did not enhance formation of Pt(nC4F9)2(cod) (Table 1, run 5), although the step in Scheme 3iii could be promoted by the addition of I−. Thus, clear evidence to support the reaction via pathways in Scheme 3 were not obtained from the results. The significant retardation of the reaction by addition of the radical inhibitor BHT and the presence of an oxygen atmosphere (Table 1, runs 3 and 9) suggests a radical mechanism for the fluoroalkylation under photoirradiation. It is known that photoirradiation of perfluoroalkyl iodides causes homolysis of the C−I bond of R F I to generate the perfluoroalkyl radical RF• and I• upon photoirradiation.16 Scheme 4 summarizes the mechanism based on the free radical Scheme 4

generated under the conditions. Perfluoroalkyl radical is formed under the photoirradiation (Scheme 4i). The formed perfluoroalkyl radical reacts with PtMe2(cod) to yield Pt(III) complex, [PtMe2RF(cod)] (Scheme 4ii). The iodine radical activates a Pt−Me bond that is weaker than the Pt−RF bond, and abstracts Me ligand of the Pt(III) intermediate to afford PtMeRF(cod) and MeI (Scheme 4iii). At present, clear evidence to support either of the proposed mechanisms has not been obtained, but significant acceleration of the photoirradiation suggests the probability of Scheme 3 and/or Scheme 4. The fluoroalkylation of PtMe2(cod) without photoirradiation occurs much more slowly but yields the same products as those of the reaction under photoirradiation; PtMeRF(cod) is obtained as the initial product of the reaction under UV irradiation, but as the final product of a much slower thermal reaction. The bis(perfluoroalkyl)platinum complex PtRF2(cod) was not obtained from the thermal reaction due to the low reactivity of R F I with PtMeR F (cod) and/or reductive elimination of MeI from PtMeRF2I(cod) formed in the reaction of RFI wit PtMeRF(cod). The generation of the perfluoroalkyl radical (Scheme 4) cannot be expected without irradiation, which suggests the occurrence of the radical-promoted

Scheme 3

D

DOI: 10.1021/acs.organomet.7b00098 Organometallics XXXX, XXX, XXX−XXX

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Organometallics reactions in Scheme 3 C4F9)(cod) in a minor simultaneous occurrence of RF−I and reductive photoirradiation.8

NMR (376 MHz, CDCl3, room temperature): δ −126.5 (CF2), −113.2 (CF2), −88.4 (PtCF2, JPtF = 392 Hz), −81.3 (CF3). Anal. Calcd for C16H12F18Pt: C, 25.92; H, 1.63; F, 46.13. Found: C, 25.43; H, 1.35; F, 43.43. HR-ESI-MS: calcd for C16H11F18Pt ([M − H]−) 740.0217, found 740.0244. Method B: Synthesis under UV Irradiation (Hg Lamp). n-C4F9I (200 μL, 428 mg, 1.2 mmol) was added to a CHCl3 (1.0 mL) solution of PtMe2(cod) (33.5 mg, 0.105 mmol) in a Schlenk flask, located 5 cm away from the lamp, and stirred at room temperature for 40 min under irradiation with a high-pressure Hg lamp. The solvent was removed under reduced pressure to yield the crude product as a yellow solid, which was purified by silica gel column chromatography (eluent hexane/AcOEt 4/1, Rf = 0.38) to yield Pt(n-C4F9)2(cod) as a white solid (16.9 mg, 0.023 mmol, 23%). Synthesis of Pt(n-C6F13)2(cod). A CH2Cl2 (1.0 mL) solution of PtMe2(cod) (32.4 mg, 0.097 mmol) was added to n-C6F13I (260 μL, 516 mg, 1.16 mmol) in a Schlenk flask and stirred at room temperature for 90 min under irradiation with a high-pressure Hg lamp. The solvent was removed under reduced pressure to yield the crude product as a yellow solid, which was purified by silica gel column chromatography (eluent hexane/AcOEt 4/1, Rf = 0.36) to yield Pt(nC6F13)2(cod) as a white solid (40.7 mg, 0.043 mmol, 44%). 1H NMR (400 MHz, CDCl3, room temperature): δ 2.54−2.61 (m, 8H, CH2), 5.83 (s, 4H, CH, JPtH = 36 Hz). 13C{1H} NMR (100 MHz, CDCl3, room temperature): δ 28.9 (CH2), 111.6 (CH). Fluorocarbons were not detected. 19F{1H} NMR (376 MHz, CDCl3, room temperature): δ −126.5 (CF2), −123.0 (CF2), −122.4 (CF2), −88.1 (CF2, JPtF = 391 Hz), −81.2 (CF3). Anal. Calcd for C20H12F26Pt: C, 25.52; H, 1.28; F, 52.47. Found: C, 25.01; H, 1.19; F, 53.22. HR-ESI-MS: calcd for C20H11F26Pt ([M − H]−) 940.0090, found 940.0103. Synthesis of Pt(n-C4F9)2(dppe). A CH2Cl2 solution (5.0 mL) of Pt(n-C4F9)2(cod) (30.5 mg, 0.041 mmol) was added to dppe (1,2bis(diphenylphosphino)ethane; 19.4 mg, 0.049 mmol) in a Schlenk flask and stirred at room temperature for 22 h. The solvent was removed under reduced pressure to yield the crude product as a white solid. Recrystallization from CH 2 Cl 2 /hexanes yielded Pt(nC4F9)2(dppe) as a white solid (31.5 mg, 0.031 mmol, 74%). 1H NMR (400 MHz, CDCl3, room temperature): δ 2.09 (m, CH2, 4H), 7.44−7.48 (m, C6H5, 8H), 7.51−7.55 (m, C6H5, 4H), 7.66−7.71 (m, C6H5, 8H). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 29.7, 128.7, 128.7 (JPC = 11 Hz), 129.2 (JPC = 50 Hz), 131.4, 133.7 (JPC = 11 Hz). 19F{1H} NMR (376 MHz, CDCl3, room temperature): δ −126.5 (CF2), −113.6 (CF2), −82.1 (CF2, JPtF = 356 Hz), −81.6 (CF3). Anal. Calcd for C34H24F18P2Pt(H2O)0.5: C, 39.24; H, 2.42; F, 32.86. Found: C, 39.06; H, 2.39; F, 32.69. Synthesis of Pt(n-C4F9)2(dppp). A CH2Cl2 solution (5.0 mL) of Pt(n-C4F9)2(cod) (29.9 mg, 0.040 mmol) was added to dppp (1,3bis(diphenylphosphino)propane; 20.4 mg, 0.049 mmol) in a Schlenk flask and stirred at room temperature for 2 h. The solvent was removed under reduced pressure to yield the crude product as a white solid. Recrystallization from CH 2 Cl 2 /hexanes yielded Pt(nC4F9)2(dppp) as a white solid (33.0 mg, 0.032 mmol, 78%). 1H NMR (400 MHz, CDCl3, room temperature): δ 1.73−1.86 (m, CH2, 2H), 2.27−2.31 (m, CH2, 4H), 7.43−7.46 (m, C6H5, 8H), 7.48−7.51 (m, C6H5, 4H), 7.63−7.67 (m, C6H5, 8H). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 18.1, 23.5, 128.5 (m), 130.9 (m), 133.3 (m). 19F{1H} NMR (376 MHz, CDCl3, room temperature): δ −126.6 (CF2), −113.0 (CF2), −82.8 (CF2, JPtF = 332 Hz), −81.6 (CF3). Anal. Calcd for C35H26F18P2Pt: C, 40.12; H, 2.51. Found: C, 39.97; H, 2.34. Synthesis of Pt(n-C4F9)2(bpy). A MeCN (4.0 mL)/CHCl3 (1.0 mL) solution of Pt(n-C4F9)2(cod) (30.9 mg, 0.042 mmol) was added to bpy (2,2′-bipyridine) (7.6 mg, 0.049 mmol) in a Schlenk flask and stirred at 60 °C for 2 h. The solvent was removed under reduced pressure to yield the crude product as a yellow solid, which was purified by aluminum oxide chromatography (eluent hexane/AcOEt 2/3, Rf = 0.17) to yield Pt(n-C4F9)2(bpy) as a yellow solid (28.0 mg, 0.035 mmol, 85%). The compound gradually decomposed on standing in CDCl3. 1H NMR (400 MHz, CD3CN, room temperature): δ 7.70 (m, 2H), 8.26 (m, 2H), 8.37 (m, 2H), 9.01 (m, 2H). 13C{1H} NMR (125 MHz, CD3CN, room temperature): δ 124.7, 128.0, 141.7, 153.5,

or Scheme 4. Formation of PtI(namount in Figure 2B may suggest of the reaction via oxidative addition elimination of ethane even under

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CONCLUSION The fluoroalkylation of a methylplatinum(II) complex bearing a cod ligand upon the addition of an n-perfluoroalkyl iodide is significantly enhanced by UV irradiation. UV irradiation was therefore employed to synthesize an unsymmetrical Pt(II) complex having a perfluoroalkyl ligand. The thermal reaction results in the monofluoroalkylation of platinum(II) complexes even after a longer reaction period. Electron transfer from the complex to fluoroalkyl iodide, giving a radical species or direct photoassisted formation of n-perfluoroalkyl radicals from nperfluoroalkyl iodides, is responsible for the perfluoroalkylation of the methylplatinum(II) complexes.17

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EXPERIMENTAL SECTION

General Considerations. PtCl2(cod), PtMe2(cod), and PtClMe(cod) were prepared via literature methods.8a,18 The solvents and chemicals were commercially available. 1H, 13C{1H}, and 19F{1H} NMR spectra were recorded on Bruker Biospin Avance III spectrometers. 1,3,5-Tris(trifluoromethyl)benzene (δ −63.5) was added as an internal standard for 19F{1H} NMR measurements. ESIMS were determined with a Bruker microTOF II spectrometer (eluent acetone). Elemental analyses were carried out with a LECO CHNS932 or Yamaco MT-5 CHN autorecorder. X-ray crystal structure analyses of the obtained orange crystals were performed with a Rigaku AFC-10R Saturn CCD diffractometer or Bruker SMART APEXII ULTRA/CCD diffractometer with graphite-monochromated Mo Kα radiation. Calculations and analyses were carried out using the program package Crystal Structure for Windows19 and Mercury.20 Crystal structure calculations of Pt(n-C4F9)2(cod) had the issue of disorder of a carbon of the cod ligand, and structural parameters of the atoms within the ligand may contain errors because of it. Synthesis of Pt(C6H4-4-F)Me(cod). (C6H4-4-F)MgBr (1.0 M, 800 μL, 0.80 mmol) was added to an Et2O (30 mL) solution of PtClMe(cod) (125 mg, 0.35 mmol) at 0 °C, and the mixture was stirred for 6 h and warmed to room temperature. The reaction mixture was quenched by addition of NH4Cl(aq). The reaction mixture was washed with H2O, and the organic phase was dried over anhydrous MgSO4. The solvent was removed under reduced pressure to yield the crude product as a pale yellow solid, which was purified by silica gel column chromatography (eluent hexane/AcOEt 1/4, Rf = 0.42) to yield Pt(C6H4-4-F)Me(cod) as a white solid (92.4 mg, 0.22 mmol, 71%). 1H NMR (400 MHz, CDCl3, room temperature): δ 0.81 (s, CH3, 3H, JPtH = 82 Hz), 2.34−2.49 (m, CH2, 8H), 4.82 (s, CH, 2H, JPtH = 38 Hz), 5.08 (s, CH, 2H, JPtH = 40 Hz), 6.85 (m, m-C6H4, 2H), 7.22 (m, o-C6H4, 2H). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 6.68 (Me, JPtC = 760 Hz), 29.7 (CH2), 30.1 (CH2), 101.9 (m, CH), 114.3 (m, CH), 135.0 (C6H4), 152.1 (C6H4), 159.1 (C6H4), 160.9 (C6H4). 19F{1H} NMR (376 MHz, CDCl3, room temperature): δ −122.5 (s, JPtF = 12 Hz). Anal. Calcd for C15H19FPt: C, 43.58; H, 4.52; F, 4.60. Found: C, 43.61; H, 4.52; F, 4.38. Synthesis of Pt(n-C4F9)2(cod). Method A: Synthesis under Ambient Light. n-C4F9I (600 μL, 3.6 mmol) was added to a CH2Cl2 (5.0 mL) solution of PtMe2(cod) (99 mg, 0.30 mmol) and stirred at room temperature for 5 days under ambient light. The solvent was removed under reduced pressure to yield the crude product as a pale yellow solid, which was purified by silica gel column chromatography (eluent hexane/AcOEt 4/1, Rf = 0.38) to yield Pt(n-C4F9)2(cod) as a white solid (138 mg, 0.186 mmol, 61%). 1H NMR (400 MHz, CDCl3, room temperature): δ 2.53−2.61 (m, 8H, CH2), 5.82 (s d, 4H, CH, JPtH = 38 Hz). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 28.9 (CH2), 111.7 (CH). Fluorocarbons were not detected. 19F{1H} E

DOI: 10.1021/acs.organomet.7b00098 Organometallics XXXX, XXX, XXX−XXX

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Organometallics 157.4. 19F{1H} NMR (376 MHz, CD3CN, room temperature): δ −126.1, −113.6, −89.5 (JPtF = 382 Hz), −81.6. HR-ESI-MS: calcd for C18H8F18N2PtCF3CO2 ([M + CF3COO]−) 901.9895, found 901.9877. Synthesis of Pt(n-C4F9)(C6H4-4-F)(cod). n-C4F9I (200 μL, 248 mg, 0.72 mmol) was added to a CH2Cl2 (3.0 mL) solution of PtMe(C6H4-4-F)(cod) (23.9 mg, 0.058 mmol) in a Schlenk flask and stirred at room temperature for 20 min under irradiation with a highpressure Hg lamp. The solvent was removed under reduced pressure to yield the crude product as a pale yellow solid, which was purified by silica gel column chromatography (eluent hexane/AcOEt 4/1, Rf = 0.28) to yield Pt(n-C4F9)(C6H4-4-F)(cod) as a white solid (25.1 mg, 0.043 mmol, 70%). 1H NMR (400 MHz, CDCl3, room temperature): δ 2.50−2.61 (m, 8H, CH2), 5.05 (s, 2H, CH, JPtH = 44 Hz), 5.67 (s d, 2H, CH, JPtH = 36 Hz), 6.83 (m, m-C6H4, 2H), 7.18 (m, o-C6H4, 2H). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 29.0 (CH2), 29.7 (CH2), 107.7 (CH, JPtC = 26 Hz), 114.3 (CH, JPtC = 18 Hz), 134.9 (C6H4), 141.9 (C6H4), 159.3 (C6H4), 161.2 (C6H4). 19 1 F{ H} NMR (376 MHz, CDCl3, room temperature): δ −126.0 (CF2), −121.8 (C6H4), −115.9 (CF2), −94.1 (CF2, JPtF = 29 Hz), −81.4 (CF3). Anal. Calcd for C18H16F10Pt: C, 35.02; H, 2.61; F, 30.77. Found: C, 34.68; H, 2.69; F, 28.78. Synthesis of Pt(n-C4F9)Cl(cod). n-C4F9I (241 μL, 497 mg, 1.44 mmol) was added to a CH2Cl2 (5.0 mL) solution of PtMeCl(cod) (39.5 mg, 0.11 mmol) in a Schlenk flask and stirred at room temperature for 100 min under irradiation with a high-pressure Hg lamp. The solvent was removed under reduced pressure to yield the crude product as a pale yellow solid, which was purified by silica gel column chromatography (eluent hexane/AcOEt 3/2, Rf = 0.25) to yield Pt(n-C4F9)Cl(cod) as a white solid (42.6 mg, 0.076 mmol, 68%). 1 H NMR (400 MHz, CDCl3, room temperature): δ 2.33−2.75 (m, 8H, CH2), 5.20 (s, 2H, CH, JPtH = 68 Hz), 5.93 (s d, 2H, CH, JPtH = 36 Hz). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 27.9 (CH2), 31.5 (CH2), 93.0 (CH), 117.9 (CH). 19F{1H} NMR (376 MHz, CDCl3, room temperature): δ −126.1 (CF2), −114.4 (CF2), −89.6 (CF2, JPtF = 324 MHz), −81.3 (CF3). HR-ESIMS: calcd for C12H11 F9PtCl ([M − H]−) 556.0049, found 556.0021. Synthesis of Pt(n-C4F9)I(cod). An acetone solution (1.0 mL) of NaI (6.5 mg, 0.043 mmol) was added to an acetone (3.0 mL) solution of Pt(n-C4F9)Cl(cod) (20.4 mg, 0.036 mmol) in a Schlenk flask and stirred at room temperature for 1 h. The white precipitate that formed was removed by filtration. The solvent was removed under reduced pressure to give the crude product, which was washed with water to yield Pt(n-C4F9)I(cod) as a white solid (17.5 mg, 0.027 mmol, 74%). 1 H NMR (400 MHz, CDCl3, room temperature): δ 1.97−2.20 (m, 4H, CH2), 2.36−2.58 (m, 8H, CH2), 5.42 (s, 2H, = CH, JPtH = 66 Hz), 5.97 (s d, 2H, CH, JPtH = 40 Hz). 13C{1H} NMR (125 MHz, CDCl3, room temperature): δ 28.9 (CH2), 31.1 (CH2), 98.6 (CH), 114.9 (CH). 19F{1H} NMR (376 MHz, CDCl3, room temperature): δ −126.0 (CF2), −110.9 (CF2), −81.3 (CF3), −80.9 (CF2, JPtF = 324 Hz). HR-ESI-MS: calcd for C12H11 F9PtI ([M − H]−) 647.9405, found 647.9390. Monitoring of the Reaction of n-C4F9I with PtMe2(cod). A CDCl 3 (1.0 mL) solution of PtMe 2 (cod) (0.01 mmol) ([PtMe2(cod)]0 = 10 mM) was added to n-C4F9I (0.12 mmol, 12 equiv) and 1,3,5-tris(trifluoromethyl)benzene (δF −63.5) used as an internal standard. The reaction was carried out in an NMR tube (diameter 4.9 mm; Pyrex), sealed with a rubber septum, located 5 cm away from the lamp. The reaction was monitored by 1H NMR and 19 1 F{ H} NMR spectroscopy. The irradiation time was regarded as the reaction time in this experiment.

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bridge Crystallographic Data Centre as supplementary publication nos. CCDC 1529379 and 1529380, respectively. NMR and UV spectra for the reaction mixtures and for some of the compounds prepared (PDF) Crystallographic data of Pt(n-C4F9)2(cod) and Pt(nC4F9)2(dppp) (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for K.O.: [email protected]. ORCID

Kohtaro Osakada: 0000-0003-0538-9978 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank our colleagues at the Center for Advanced Materials Analysis of our institute, Tokyo Institute of Technology, for HR-ESI-MS measurements, elemental analysis, and X-ray and NMR data. This work was supported by a Grant-in-Aid for Scientific Research for Young Scientists from the Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 25810059).

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00098. Crystallographic data of Pt(n-C4F9)2(cod) and Pt(n-C4F9)2(dppp) have also been deposited with the CamF

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DOI: 10.1021/acs.organomet.7b00098 Organometallics XXXX, XXX, XXX−XXX