Carbon–Sulfur Bond Cleavage Reactions of Quinolyl-Substituted

Jun 1, 2017 - *M.H.: tel, +81-6-6605-2519; fax, +81-6-6605-2522; e-mail, ... of QT gave the sulfur-free diiron complex [Fe2{CHCHCHC(Q)}(CO)5], whereas...
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Carbon−Sulfur Bond Cleavage Reactions of Quinolyl-Substituted Thiophenes with Iron Carbonyls Takumi Matsunaga, Isamu Kinoshita, and Masakazu Hirotsu* Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan S Supporting Information *

ABSTRACT: Thermal reactions of quinolyl-substituted thiophenes (2-(8′-quinolyl)thiophene (QT), 2-methyl-5-(8′quinolyl)thiophene (MeQT), 2-(8′-quinolyl)-5(trimethylsilyl)thiophene (TMSQT)) with [Fe3(CO)12] gave the corresponding thiolate-bridged diiron complexes [Fe2(μLR)(CO)5] (R = H, Me, SiMe3), where LH, LMe, and LTMS are dianionic N,C,S-tridentate ligands (SC(R)CHCHC(Q)2−, Q = 8-quinolyl) formed by the oxidative addition of the C−S bond in QT, MeQT, and TMSQT, respectively. In contrast, the formation of photoreaction products of the quinolylsubstituted thiophenes with [Fe(CO)5] was dependent on the R group of the thiophene ring. The photoreaction of QT gave the sulfur-free diiron complex [Fe2{CHCHCHC(Q)}(CO)5], whereas the photoreactions of MeQT and TMSQT gave the thiolate-bridged triiron complex [Fe3(μ-LMe)(CO)8] and diiron complex [Fe2(μ-LTMS)(CO)5], respectively, as the major products. In the triiron complexes [Fe3(μ-LR)(CO)8], an Fe(CO)3 unit is bound to the C(R)CHCH moiety in the Smetallacycle of the diiron complexes [Fe2(μ-LR)(CO)5]. The difference in the photoreaction products is described on the basis of the reactivity of the thiolate complexes [Fe2(μ-LR)(CO)5] and [Fe3(μ-LR)(CO)8]. Although the photoreactions of the diiron complexes [Fe2(μ-LR)(CO)5] with [Fe(CO)5] produced the corresponding triiron complexes [Fe3(μ-LR)(CO)8], desulfurization leading to the formation of [Fe2{CHCHCHC(Q)}(CO)5] was predominant for R = H, and a fast conversion of the triiron complex to a CO elimination product was observed for R = SiMe3.

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INTRODUCTION Activation of a thioether group by transition-metal complexes is a useful method for functionalizing organosulfur compounds via cleavage of the carbon−sulfur bond.1,2 This method has been applied to catalytic reactions such as cross-coupling, alkyne insertion, cyclization, and borylation reactions.2−6 Recently, the functionalization of thiophenes, heterocyclic compounds containing a thioether group, via C−S cleavage was reported.7,8 This progress will stimulate further studies on the transformation of thiophene derivatives because the thiophene ring is a component of natural products, 9 phermaceuticals,10 and organic electronic materials.11 We have applied the C−S bond cleavage method mediated by transition-metal carbonyls to the development of functional thiolate complexes from dibenzothiophene (DBT) derivatives by introducing a coordinating N-donor group at the position adjacent to the C−S bond.12−15 Coordination of the N-donor group accelerates the cleavage of the proximal C−S bond, forming thiolate complexes with N,C,S-tridentate ligands.12−14 For example, the reactions of 4-(2′-pyridyl)dibenzothiophene (PyDBT) with iron carbonyls afford the C,S-bridged diiron complex [Fe2(μ-PyBPT)(CO)5], where PyBPT denotes a dianion of 3′-(2″-pyridyl)-1,1′-biphenyl-2-thiol (Scheme 1).13 Furthermore, the N,C,S-coordination of PyBPT suppresses successive C−S bond cleavage, leading to desulfurization.12,16 © XXXX American Chemical Society

Scheme 1. Reactions of PyDBT with Iron Carbonyls

Such a selective C−S cleavage is also crucial for the metalcatalyzed functionalization of thioether groups because the two C−S bonds can be activated. Introduction of substituents into thiolate-containing metallacycles, which cannot be achieved for the PyBPT complexes, is an advantage in the modification of S-metallacycle complexes. Therefore, monocyclic thiophenes were used as the ligand precursors in this study. In general, the C−S bonds of monocyclic thiophenes are more easily cleaved by transitionmetal complexes in comparison to those of polycyclic thiophenes such as DBT.17 However, the formed S-metallacycle undergoes desulfurization via the second C−S bond cleavage.18 Furthermore, the selectivity of the C−S bond cleavage depends Received: April 12, 2017

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DOI: 10.1021/acs.organomet.7b00280 Organometallics XXXX, XXX, XXX−XXX

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Organometallics on the substituents of the thiophene ring.19 Thus, the coordinating group is required to synthesize the desired thiolate complexes. Recently, C−S activation of thiophenes with an 8-quinolyl group was reported using [Pt(dippe)H]2 (dippe = 1,2bis(diisopropylphosphino)ethane), even though the quinoline N atom is not bound to Pt in the metal-insertion products.20 Herein, we report that the C−S bond cleavage of quinolylsubstituted thiophenes can be utilized to synthesize the iron complexes of N,C,S-tridentate ligands. The 8-quinolyl group is crucial for the stabilization of the formed thiolate complexes, and other substituents on the thiophene ring affect the reactivity of the S-metallacycle in the thiolate complexes.

23% yields, respectively, after the chromatographic purification and recrystallization of the crude products. Complexes 1b,c were characterized by NMR and IR spectroscopy, elemental analysis, and X-ray crystallography. The 1H resonances (C6D6) of 1b for CH in the S-metallacycle were observed at 6.04 (SCMeCHCH) and 5.08 ppm (SCMeCHCH): the upfield shift for CH adjacent to the quinolyl group is significant. These signals of 1c appear at 6.78 and 5.29 ppm. Three 13C{1H} resonances were observed in the carbonyl region: the five carbonyl ligands are attributed to the fluxional Fe(CO)3 moiety and two static carbonyl ligands. This suggests that their structures are similar to that of the diiron complex [Fe2(μ-PyBPT)(CO)5] (Schemes 1 and 2).13 The crystal structures of diiron complexes 1b,c are shown in Figure 2. Two Fe atoms are bound to five CO ligands and a

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RESULTS AND DISCUSSION Preparation of Quinolyl-Substituted Thiophenes. The three quinolyl-substituted thiophenes 2-(8′-quinolyl)thiophene (QT),20,21 2-methyl-5-(8′-quinolyl)thiophene (MeQT),22 and 2-(8′-quinolyl)-5-(trimethylsilyl)thiophene (TMSQT) were used as the precursors of N,C,S-tridentate ligands LH, LMe, and LTMS, respectively (Figure 1). QT and MeQT were

Figure 1. Quinolyl-substituted thiophenes (left) and N,C,S-tridentate ligands (right).

prepared by the palladium-catalyzed Suzuki−Miyaura crosscoupling reactions of 8-quinolineboronic acid with 2bromothiophene or 2-bromo-5-methylthiophene according to a reported procedure.20 The use of 2-bromo-5-(trimethylsilyl)thiophene in the coupling reaction resulted in a low yield of TMSQT (13%), and detrimethylsilylation leading to the formation of QT (30%) was observed.23 Therefore, trimethylsilylation of QT was carried out to improve the yield of TMSQT (41% from 8-quinolineboronic acid).24 Thermal Reactions of Quinolyl-Substituted Thiophenes with [Fe3(CO)12]. The reactions of 2-(8′-quinolyl)thiophene derivatives (QT, MeQT, TMSQT) with [Fe3(CO)12] in toluene at 80 °C afforded dark brown solutions containing the diiron complexes [Fe2(μ-LH)(CO)5] (1a), [Fe2(μ-LMe)(CO)5] (1b), and [Fe2(μ-LTMS)(CO)5] (1c) as the major products, respectively (Scheme 2). Although 1a was obtained as a mixture with a desulfurization product (vide infra), dark brown crystals of 1b,c were isolated in 20% and

Figure 2. ORTEP drawings of (a) 1b and (b) 1c with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

thiolate ligand formed by the oxidative addition of the C−S bond of MeQT or TMSQT. The C−S cleaved ligand bridges two Fe atoms through S and C atoms. The Fe(1) atom is bound to N, C, and S donor atoms to form a five-membered azametallacycle and a six-membered thiolate-containing metallacycle. An Fe(CO)3 unit is bound to the S-metallacycle through Fe−Fe, Fe−S, and two Fe−C bonds. Selected bond lengths and angles for 1b,c are given in Table 1. The geometrical parameters are quite similar to each other, indicating that the bulkier trimethylsilyl group does not affect the dinuclear structure. The geometrical parameters around Fe of 1b,c were compared with those of [Fe2(μ-PyBPT)(CO)5] and its analogues with the general formula of [Fe2(μ-L′)(CO)5], where L′ denotes the N,C,S-tridentate ligands derived from DBT derivatives.13,14 The Fe(1)−C(15) bond is ca. 0.05 Å longer than Fe(1)−C(14) because of the trans influence of the central C donor (C(4)) of the N,C,S-tridentate ligand. These

Scheme 2. Thermal Reactions of 2-(8′-Quinolyl)thiophene Derivatives with [Fe3(CO)12]

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Organometallics Table 1. Selected Bond Distances (Å) and Angles (deg) for 1b,c and 3a−c Fe(1)−S(1) Fe(1)−N(1) Fe(1)−C(4) Fe(1)−C(14) Fe(1)−C(15) Fe(1)−C(16) Fe(2)−S(1) Fe(2)−C(3) Fe(2)−C(4) Fe(3)−C(1) Fe(3)−C(2) Fe(3)−C(3) Fe(1)−Fe(2) Fe(2)−Fe(3) S(1)−C(1) C(1)−C(2) C(2)−C(3) C(3)−C(4) C(4)−Fe(1)−S(1) C(4)−Fe(1)−N(1) S(1)−Fe(1)−N(1) Fe(1)−S(1)−Fe(2) Fe(1)−C(4)−Fe(2)

1b

1c

3a

3b

3c

2.2377(13) 1.995(4) 1.937(4) 1.754(5) 1.807(5) 2.803(5) 2.2829(13) 2.147(4) 2.094(4)

2.2314(6) 1.9944(16) 1.940(2) 1.756(2) 1.810(2) 2.821(2) 2.2817(7) 2.140(2) 2.0975(19)

2.2102(6) 1.9956(17) 1.9999(19) 1.763(2) 1.818(2) 2.355(2) 2.2656(6)

2.2161(8) 1.9905(19) 1.994(2) 1.770(2) 1.814(2) 2.297(2) 2.2527(8)

2.2056(10) 1.993(3) 1.998(3) 1.767(3) 1.809(4) 2.352(3) 2.2453(10)

2.5604(10)

2.5615(6)

1.786(4) 1.321(6) 1.457(6) 1.425(6) 87.24(12) 83.43(16) 160.31(11) 68.99(4) 78.77(15)

1.798(2) 1.327(3) 1.482(3) 1.417(3) 87.25(6) 83.37(8) 160.69(5) 69.153(19) 78.64(7)

2.1052(19) 2.093(2) 2.034(2) 2.201(2) 2.5131(5) 2.7786(5) 1.772(2) 1.406(3) 1.406(3) 1.455(3) 85.66(6) 84.27(7) 163.23(5) 68.305(19) 75.45(7)

2.113(2) 2.135(2) 2.039(2) 2.162(2) 2.5007(6) 2.7624(7) 1.789(2) 1.409(3) 1.405(3) 1.455(3) 85.07(7) 83.95(8) 160.73(6) 68.05(2) 74.94(7)

2.118(3) 2.151(3) 2.041(3) 2.187(3) 2.5071(8) 2.7714(8) 1.784(3) 1.418(4) 1.412(4) 1.448(4) 85.24(9) 83.89(12) 160.77(8) 68.56(3) 75.00(11)

was isolated as black crystals (2.3% yield). Details of the characterization and structures of 2a and 3a are mentioned later. In the thermal reactions of QT, MeQT, and TMSQT with [Fe3(CO)12], the yield of 1a is lower than those of 1b,c, because of the side reactions including desulfurization. Desulfurization has been reported in the corresponding thermal reactions of monocyclic thiophenes without coordinating groups (C4H4S, 2-MeC4H3S, 2,5-Me2C4H2S), providing the ferroles [Fe2{C(R1)CHCHC(R2)}(CO)6] and the thiaferroles [Fe2{SC(R1)CHCHC(R2)}(CO)6] (R1 = R2 = H; R1 = Me, R2 = H; R1 = R2 = Me).18,25−27 It has been reported that heating a benzene solution of [Fe2{SC(Me)CHCHCH}(CO)6] (reflux, 21 h) results in 42% conversion and formation of the desulfurization product [Fe2{C(Me)CHCHCH}(CO)6].18 To compare the thermodynamic stability of 1b with that of [Fe2{SC(Me)CHCHCH}(CO)6], a C6D6 solution of 1b was heated at 80 °C for 23 h. 1H NMR measurements showed 10% conversion, mainly to MeQT (4%) (Figure S11 in the Supporting Information). These data indicate that the Smetallacycle is stabilized by the fused azametallacycle formed from the 8-quinolyl group. Furthermore, when 1a in toluene-d8 was heated at 80 °C for 7 h, desulfurization was not observed, in contrast to the desulfurization of the thiaferroles. However, heating of triiron complex 3a in toluene-d8 at 80 °C resulted in the formation of 2a (Figure S12 in the Supporting Information, 23 h: 2a, 25%; 3a, 55%); hence, 3a is a possible intermediate in the desulfurization reaction. Photoreactions of Quinolyl-Substituted Thiophenes with [Fe(CO)5]. Photoreactions of 2-(8′-quinolyl)thiophene derivatives (QT, MeQT, TMSQT) with [Fe(CO)5] also gave the C−S cleaved products. Formation of the major reaction products, however, was dependent on the R group adjacent to the S atom, as summarized in Scheme 3. The photoreaction of QT produced the desulfurization product 2a, whereas MeQT

Fe−C(carbonyl) parameters are similar to those of [Fe2(μL′)(CO)5]; therefore, the electron-donating ability of the central C donor atom is comparable to that of the DBT-derived ligand L′ in these diiron complexes.13,14 On the other hand, the π coordination of the S-metallacycle to Fe(2) is different between LR and L′. The Fe(2)−C(4) distances for 1b (2.094(4) Å) and 1c (2.0975(19) Å) are shorter than the corresponding distances for [Fe2(μ-L′)(CO)5] (2.139(5) 2.152(3) Å).13,14 The differences for Fe(2)−C(3) are more significant: 2.147(4) Å for 1b, 2.140(2) Å for 1c, and 2.337(2)2.444(3) Å for [Fe2(μ-L′)(CO)5]. These findings indicate the higher π-coordination ability of the S-metallacycles derived from the monocyclic thiophenes in comparison to that derived from DBT. In the case of the reaction of QT, two bands were observed in silica gel column chromatography. The first major band contained diiron complex 1a and desulfurization product [Fe2{CHCHCHC(Q)}(CO)5] (2a, Q = 8-quinolyl; Figure 3), which are difficult to separate from each other. Complex 1a

Figure 3. Side products in the thermal reaction of QT with [Fe3(CO)12]: desulfurization product 2a and triiron complex 3a.

was characterized by NMR spectroscopy (C6D6): the CH signals in the S-metallacycle were observed at 6.38 (SCHCHCH), 5.08 (SCHCHCH), and 4.68 (SCHCHCH) ppm. The yields determined by 1H NMR measurements were 9.6% for 1a and 1.5% for 2a. The second minor band contained the triiron complex [Fe3(μ-LH)(CO)8] (3a; Figure 3), which C

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Organometallics and TMSQT produced the triiron and diiron thiolate complexes, respectively.

The methyl derivative MeQT suppressed the desulfurization in the photoreaction with [Fe(CO)5]. A THF solution of MeQT and [Fe(CO)5] (2 equiv) was irradiated for 1 h. In the column chromatography, a dark brown band of the triiron complex [Fe3(μ-LMe)(CO)8] (3b) was observed in addition to an orange band of diiron complex 1b. Complexes 1b and 3b were isolated in 4% and 11% yields based on Fe, respectively. The 1H NMR spectrum of 3b in C6D6 showed an upfield shift for the CH group in the S-metallacycle at 5.83 (SCMeCHCH) and 4.25 (SCMeCHCH) ppm: the significant upfield shift for the CH group adjacent to the methyl groups is due to the coordination to the Fe(CO)3 fragment. In the 13C{1H} NMR spectrum (C6D6) of 3b, six CO signals were observed at room temperature, and an intense signal at 211.8 ppm was assigned to the fluxional CO ligands of the Fe(CO)3 unit. When 3 equiv of [Fe(CO)5] was treated under prolonged irradiation conditions, the yield of 3b increased to 42%. The precursor TMSQT has a more sterically demanding trimethylsilyl group as substituent R. The photoreaction of [Fe(CO)5] (2 equiv) with TMSQT predominantly produced diiron complex 1c, which was obtained in 26% yield after column chromatography and recrystallization. When the photoreaction was performed in the presence of 5 equiv of [Fe(CO)5], the triiron complex [Fe3(μ-LTMS)(CO)8] (3c) was obtained in addition to 1c. However, the yield of 3c was very low: 1c, 21%; 3c, 1%. Structures of Triiron Complexes 3a−c. In the photoreactions, we expected that the differences in the products are relevant to triiron complexes 3a−c, because the conversion of 3a to 2a was observed as described above. The crystal structures of 3a−c were determined by X-ray diffraction analysis (Figure 5 and Table 1). No significant difference, however, was observed between them. The C−S cleaved ligand LR bridges three Fe atoms. The Fe(1) atom is surrounded by the S, C, and N donor atoms of LR and three carbonyl ligands. The S-metallacycle is bound to Fe(2) through S and C(4) atoms and to Fe(3) through C(1), C(2), and C(3) atoms. Furthermore, Fe(2) is directly bound to Fe(1) and Fe(3) with Fe(1)−Fe(2)−Fe(3) angles of 104.181(19), 103.88(2), and 103.81(3)° for 3a−c, respectively. The Fe(1)−Fe(2) bond is ca. 0.26 Å shorter than Fe(2)−Fe(3). The Fe(1) and Fe(2) atoms are bridged by anionic S and C donors in addition to the semibridging carbonyl ligand. Thus, the formal oxidation states of Fe(1), Fe(2), and Fe(3) can be assigned to +1, +1, and 0, respectively. The six-membered ring of the S-metallacycle has a boat structure with Fe(1) and C(2) deviating from the least-squares plane (S(1), C(1), C(3), C(4)) at ca. 1.0 and 0.3 Å, respectively. For the S-metallacycle in 3a−c, the double-bond character of C(1)−C(2) and C(2)−C(3) is higher than that of C(3)−C(4). This is consistent with the π coordination of the C(1)C(2)C(3) moiety to Fe(3). The S-metallacycle derived from the monocyclic thiophenes can bind two Fe(CO)3 units owing to the delocalization of the π system irrespective of the R substituent. The binding of Fe(3) causes elongation of the Fe(1)−C(4) bond, while the S(1)−C(1) length remains unchanged. The Fe(3)−C(1) lengths and C(1)−Fe(3)− C(20) angles are slightly affected by the R substituent adjacent to the S atom: 2.093(2) Å and 94.91(9)° for 3a, 2.135(2) Å and 90.18(10)° for 3b, 2.151(3) Å and 98.64(14)° for 3c. Nevertheless, these differences cannot explain the influence of substituent R on the photoreactions.

Scheme 3. Photoreactions of 2-(8′-Quinolyl)thiophene Derivatives with [Fe(CO)5]

The photoreaction of QT with [Fe(CO)5] (2 equiv) was conducted in THF with a high-pressure mercury lamp, producing a dark brown solution containing the sulfur-free compound 2a as the major product. Silica gel column chromatography and recrystallization gave black crystals, containing 2a and small amounts of byproducts. Pure 2a was isolated by using 5 equiv of [Fe(CO)5] in 18% yield. The 1H signals (C6D6) for CH protons originating from the thiophene ring at 6.11, 5.77, and 5.72 ppm and the coupling constants are similar to those of the 1,3-butadiene-1,4-diyl diiron carbonyl complex [Fe2(C4H4)(CO)6].27 Single-crystal X-ray analysis of 2a proved that QT is desulfurized to form a 1-(8′-quinolyl)-1,3-butadiene-1,4-diyl ligand. The sulfur-free ligand is bound to Fe(1) as a C,C,Ntridentate ligand, forming two five-membered metallacycles (Figure 4 and Table 2). The C,C-chelated metallacycle is bound to the Fe(CO)3 unit, constructing the diiron carbonyl complex with an Fe−Fe bond. The coordination mode of the 1,3-butadiene-1,4-diyl moiety in 2a is similar to that of [Fe2(C4H4)(CO)6]: Fe(2) is almost equally bound to C(1)− C(4), and the C−C bonds are comparable to each other.27

Figure 4. ORTEP drawing of 2a with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity. D

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Organometallics Table 2. Selected Bond Distances (Å) and Angles (deg) for 2a Fe(1)−N(1) Fe(1)−C(4) Fe(1)−C(15) Fe(2)−C(1) Fe(2)−C(3) Fe(2)−C(16) C(1)−C(2) C(3)−C(4) C(4)−Fe(1)−C(1) C(1)−Fe(1)−N(1) Fe(1)−C(4)−Fe(2)

2.017(2) 1.936(2) 1.795(3) 2.097(2) 2.121(2) 1.801(3) 1.414(3) 1.412(3) 80.80(10) 160.60(9) 76.08(8)

Fe(1)−C(1) Fe(1)−C(14) Fe(1)−C(16) Fe(2)−C(2) Fe(2)−C(4) Fe(1)−Fe(2) C(2)−C(3) C(4)−Fe(1)−N(1) Fe(1)−C(1)−Fe(2)

1.928(3) 1.747(3) 2.384(3) 2.113(2) 2.119(2) 2.5027(8) 1.414(3) 81.99(9) 76.75(9)

Figure 5. ORTEP drawings of (a) 3a, (b) 3b, and (c) 3c with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

Photoreactions of Diiron Complexes 1a−c with [Fe(CO)5]. Triiron complexes 3a−c are probably produced by the addition of an Fe(CO)3 fragment to diiron complexes 1a− c. Therefore, the photoreactions of 1a−c with [Fe(CO)5] in C6D6 were carried out. A 7:1 mixture of 1a and 2a in C6D6 obtained by the thermal reaction described above was irradiated with a high-pressure mercury lamp in the presence of [Fe(CO)5]. During the photoreaction, formation of 3a and increase in the yield of 2a were observed along with some unidentified byproducts (Figure S13 in the Supporting Information). Finally, 2a became the major product (Scheme 4). Since the photolysis of 1a (as a

Information). The signals of 1b decreased and those of triiron complex 3b increased with the reaction time. Thus, 1b is an intermediate for the formation of 3b in the photoreaction of MeQT with [Fe(CO)5] (Scheme 4), even though the formation of MeQT and unidentified products was also observed. In the case of 1c, it was readily consumed in the photoreaction, and the formation of 3c and its fast conversion to a new complex, 4c, which showed a 1H NMR spectrum similar to that of 3c, were observed (Figures S10 and S15 in the Supporting Information). To confirm the formation of the final product 4c from the photoreaction of 1c via 3c, the photolysis of 3c in C6D6 was investigated by 1H NMR spectroscopy (Figure S10 in the Supporting Information). After 1 h of irradiation, 3c was completely converted to 4c. The product was crystallized from toluene−n-hexane. Single-crystal X-ray structure analysis of 4c revealed that a CO ligand dissociates from 3c to form the triiron complex [Fe3(μ-LTMS)(CO)7] (Scheme 5, Figure 6, and

Scheme 4. Photoreactions of Diiron Complexes with [Fe(CO)5]

Scheme 5. Photolysis of 3c

Table 3). The LTMS ligand is coordinated to Fe(1) through the N, C, and S donor atoms. The central C atom of LTMS is further bound to Fe(2) and Fe(3). The Fe(1)−Fe(2) and Fe(1)− Fe(3) distances (2.4921(9), 2.5653(9) Å) indicate direct metal−metal bonds. The Fe(1) and Fe(2) atoms are bridged by the thiolate S atom and a carbonyl ligand, as observed in the

mixture with 2a) and 3a did not show desulfurization, a reactive iron carbonyl complex such as [Fe(CO)4(solvent)] is crucial to the second C−S cleavage, leading to the desulfurization of QT. A C6D6 solution of diiron complex 1b and [Fe(CO)5] (1 equiv) was irradiated for 8 h, and the reaction was monitored by 1H NMR spectroscopy (Figure S14 in the Supporting E

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CONCLUSIONS In the reactions of quinolyl-substituted thiophenes with iron carbonyls, the iron atom was selectively inserted into the C−S bond proximal to the quinolyl group. The thermal reactions with [Fe3(CO)12] produced the diiron complexes [Fe2(μLR)(CO)5] as the major products; they are stabilized by the formation of two fused metallacycles. The thiolate-containing metallacycle in the diiron complexes further reacts with the iron carbonyl fragments; thus, formation of the photoreaction products with [Fe(CO)5] depends on the substituent R. The desulfurization was observed for QT (R = H), and MeQT (R = Me) and TMSQT (R = SiMe3) gave the triiron complex [Fe3(μ-LMe)(CO)8] and the diiron complex [Fe2(μ-LTMS)(CO)5], respectively. A possible mechanism for the second C− S bond cleavage leading to the desulfurization of QT involves a η2-C,S coordination mode of the thiolate C−S moiety, which is effectively prevented by the methyl or trimethylsilyl group proximal to S. These findings facilitate appropriate designs of synthetic routes and catalytic processes for thiophene-based materials via C−S bond cleavage.

Figure 6. ORTEP drawing of 4c with thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.

Table 3. Selected Bond Distances (Å) and Angles (deg) for 4c Fe(1)−S(1) Fe(1)−N(1) Fe(1)−C(4) Fe(1)−C(14) Fe(1)−C(15) Fe(1)−C(16) Fe(2)−S(1) Fe(2)−C(4) Fe(2)−C(16) Fe(2)−C(3) Fe(3)−C(1) Fe(3)−C(2) Fe(3)−C(3) Fe(3)−C(4) Fe(3)−C(14) S(1)−C(1) C(1)−C(2) C(2)−C(3) C(3)−C(4) Fe(1)−Fe(2) Fe(1)−Fe(3) S(1)−Fe(1)−N(1) C(14)−Fe(1)−C(16) Fe(2)−Fe(1)−Fe(3)

Article

Aa

Ba

2.2228(13) 1.994(3) 2.017(4) 1.992(5) 1.788(5) 2.098(4) 2.2614(13) 2.092(4) 1.857(5) 2.558(4) 2.159(4) 2.082(5) 2.142(4) 2.122(4) 1.945(5) 1.787(4) 1.413(6) 1.416(6) 1.438(6) 2.4921(9) 2.5653(9) 168.11(10) 171.48(19) 93.33(3)

2.2235(13) 1.996(4) 2.021(4) 2.062(4) 1.782(5) 2.061(4) 2.2581(13) 2.107(4) 1.860(4) 2.551(4) 2.169(4) 2.082(4) 2.154(4) 2.107(4) 1.944(4) 1.794(4) 1.410(6) 1.412(6) 1.455(6) 2.4877(9) 2.5841(9) 168.81(11) 172.83(17) 93.24(3)

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EXPERIMENTAL SECTION

General Procedures. All manipulations were performed using a glovebox under an atmosphere of oxygen-free dry nitrogen or standard Schlenk techniques under a nitrogen atmosphere. Dried solvents and [Fe(CO) 5] were purchased from Kanto Chemical Co., Inc. [Fe3(CO)12] was purchased from Sigma-Aldrich Co. LLC. 8Quinolineboronic acid was purchased from Wako Pure Chemical Industries, Ltd. 2-Bromothiophene, 2-bromo-5-methylthiophene, and chlorotrimethylsilane were purchased from Tokyo Chemical Industry Co., Ltd. 2-Bromo-5-(trimethylsilyl)thiophene was prepared according to a literature procedure.24 2-(8′-Quinolyl)thiophene (QT)20,21 and 2methyl-5-(8′-quinolyl)thiophene (MeQT)22 were prepared according to literature procedures. Chromatographic separation of the products was performed under an ambient atmosphere. NMR spectra were recorded on a JEOL Lambda 300, a Bruker AVANCE 300, a Bruker AVANCE 400, or a Bruker AVANCE 600 FT-NMR spectrometer at room temperature. IR spectra were recorded on a JASCO FT/IR-4600 instrument by the KBr pellet method. Elemental analyses were performed by the Analytical Research Service Center at Osaka City University on J-Science JM10 or Fisons EA1108 elemental analyzers. Photolysis was carried out using a 450 W high-pressure Hg lamp (Ushio UM-452) placed in a water-cooled quartz jacket. 2-(8′-Quinolyl)-5-(trimethylsilyl)thiophene (TMSQT). Method A. A solution of 2-bromo-5-(trimethylsilyl)thiophene (244 mg, 1.0 mmol) and K2CO3 (415 mg, 3.0 mmol) in N,N-dimethylformamide (5.0 mL) and water (2.0 mL) was placed in a flask. The solution was bubbled with N2 gas for 20 min, and then [Pd(PPh3)4] (57 mg, 0.049 mmol) and 8-quinolineboronic acid (166 mg, 0.96 mmol) were added. The mixture was heated at 90 °C for 4 h and then cooled. Dichloromethane (10 mL) and water (10 mL) were added to separate the organic and aqueous layers. The organic layer was washed with water three times. The aqueous phase was extracted with a small amount of CH2Cl2. The combined organic extract was washed with a saturated aqueous NaCl solution and dried over MgSO4. After the solvent was evaporated, the resulting orange oil was purified by silica gel column chromatography (n-hexane/ethyl acetate, 9/1) to afford a pale yellow oil (35 mg, 13%). Method B. A solution of diisopropylamine (700 μL, 5.0 mmol) in THF (20 mL) was cooled to −78 °C. A 1.6 M solution of nbutyllithium (2.8 mL, 4.5 mmol) in n-hexane was added dropwise. The solution was warmed to 0 °C for 10 min and then cooled to −78 °C. A solution of QT (720 mg, 3.4 mmol) in THF (15 mL) was added dropwise, and then the solution was warmed to 0 °C for 10 min to give a yellow solution. After the temperature was lowered to −78 °C, chlorotrimethylsilane (140 μL, 1.1 mmol) was added, and the solution was warmed to room temperature for 40 min to give a red solution. A

a

There are two independent molecules, A and B, in an asymmetric unit, and A is displayed in Figure 6.

original triiron complex 3c, and Fe(3) lies on the thiolatecontaining metallacycle with a bridging carbonyl and two terminal carbonyl ligands. The arrangement of the three Fe atoms in 4c is quite different from that of 3c: the Fe atoms are bound on both sides of the S-metallacycle plane in 4c, and the Fe−Fe−Fe angle of 4c is smaller than that of 3c. Probably, the removal of CO induces the intramolecular rearrangement of the Fe atoms without breaking the Fe−Fe bond. In contrast to 3c, the methyl derivative 3b was tolerant to the photolysis in C6D6. Therefore, the low yield of 3c in the photoreaction of TMSQT with [Fe(CO)5] can be attributed to the fast conversion of 3c into 4c, even though the reason for the difference in the CO dissociation process between 3b and 3c is not clear. F

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Organometallics 0.6 M aqueous HCl solution (21 mL) was added. The resulting yellow solution was extracted with diethyl ether (10 mL × 3). The combined extract was washed with an aqueous solution of Na2CO3 and brine and dried over MgSO4. The solution was filtered and evaporated to give a green oil. The crude oil was purified by silica gel column chromatography (dichloromethane/n-hexane, 1/1) to give a yellow oil (574 mg, 59%). 1 H NMR (300 MHz, CDCl3): δ 9.04 (dd, 3J = 4.2 Hz, 4J = 1.8 Hz, 1H, 2-Q), 8.19 (dd, 3J = 8.3 Hz, 4J = 1.8 Hz, 1H, 4-Q), 8.05 (dd, 3J = 7.3 Hz, 4J = 1.4 Hz, 1H, 7-Q), 7.84 (d, 3J = 3.5 Hz, 1H, 3-T), 7.75 (dd, 3 J = 8.2 Hz, 4J = 1.4 Hz, 1H, 5-Q), 7.56 (dd, 3J = 8.2 Hz, 3J = 7.3 Hz, 1H, 6-Q), 7.45 (dd, 3J = 8.3 Hz, 3J = 4.2 Hz, 1H, 3-Q), 7.32 (d, 3J = 3.5 Hz, 1H, 4-T), 0.38 (s, 9H, SiMe3). 13C{1H} NMR (75.5 MHz, CDCl3): δ 149.7 (2-Q), 145.2, 144.8, 142.6, 136.3, 133.9, 133.2, 128.8, 128.39, 128.34, 127.2, 126.4, 121.1, 0.05 (SiMe3). Anal. Calcd for C16H17NSSi: C, 67.79; H, 6.04; N, 4.94. Found: C, 67.84; H, 6.12; N, 4.93. Thermal Reaction of QT with [Fe3(CO)12]. A dark green solution of [Fe3(CO)12] (252 mg, 0.50 mmol) and QT (106 mg, 0.50 mmol) in toluene (20 mL) was heated at 80 °C for 9 h. Volatiles of the resulting dark brown solution were removed under reduced pressure. The crude sample was purified by silica gel column chromatography (n-hexane/dichloromethane, 4/1). After the first green band was eluted, the second dark brown band was collected and evaporated to dryness. The orange residue was recrystallized by layering a toluene solution with n-hexane at −30 °C to afford dark brown crystals containing [Fe2(μ-LH)(CO)5] (1a) and [Fe2{CHCHCHC(Q)}(CO)5] (2a) in a 6.5:1 ratio (25.6 mg; 1a, 9.6%; 2a, 1.5%). Anal. Calcd for (C18H9Fe2NO5S)0.87(C18H9Fe2NO5)0.13: C, 47.13; H, 1.98; N, 3.05. Found: C, 47.38; H, 2.08; N, 3.04. The third dark yellow band was collected and evaporated to dryness. The residue was recrystallized by layering a THF solution with n-hexane at −30 °C to afford black crystals of [Fe3(μ-LH)(CO)8] (3a) (7.1 mg, 2.3%). Data for 1a are as follows. 1H NMR (300 MHz, C6D6): δ 8.79 (dd, br, 3J = 5.1 Hz, 4J = 1.3 Hz, 1H, 2-Q), 7.32 (m, 1H, 7-Q), 7.08 (dd, 3J = 8.3 Hz, 4J = 1.3 Hz, 1H, 4-Q), 7.01−6.92 (m, 2H, 5-Q, 6-Q), 6.38 (dd, 3J = 6.4, 5.6 Hz, 1H, SCHCHCH), 6.21 (dd, 3J = 8.3, 5.1 Hz, 1H, 3-Q), 5.08 (d, 3J = 5.6 Hz, 1H, SCHCHCH), 4.68 (d, 3J = 6.4 Hz, 1H, SCHCHCH). 13C{1H} NMR (100.6 MHz, C6D6): δ 217.4 (CO), 212.4 (CO), 211.4 (CO), 190.1 (QCFe), 156.5, 153.9, 153.2, 147.5, 144.6, 136.4, 126.1, 122.3, 120.2, 117.4, 77.9 (SCHCHCH). Data for 3a are as follows. 1H NMR (400 MHz, C6D6): δ 8.68 (dd, 3J = 5.1 Hz, 4 J = 1.3 Hz, 1H, 2-Q), 7.31 (dd, 3J = 7.3 Hz, 4J = 0.9 Hz, 1H, 7-Q), 6.99 (dd, 3J = 8.1 Hz, 3J = 7.3 Hz, 1H, 6-Q), 6.97 (dd, 3J = 8.2 Hz, 4J = 1.3 Hz, 1H, 4-Q), 6.70 (dd, 3J = 8.1 Hz, 4J = 0.9 Hz, 1H, 5-Q), 6.14 (dd, 3J = 8.2, 5.1 Hz, 1H, 3-Q), 5.95 (d, 3J = 6.3 Hz, 1H, SCHCHCH), 4.36 (dd, 3J = 6.3, 5.6 Hz, 1H, SCHCHCH), 3.06 (d, 3J = 5.6 Hz, 1H, SCHCHCH). 13C{1H} NMR (100.6 MHz, CDCl3): δ 232.3 (μ-CO), 216.5 (CO), 213.0 (CO), 211.6 (CO), 211.2 (Fe(CO)3), 209.7 (CO), 158.8, 155.7, 149.3, 137.5, 128.5, 128.3, 123.9, 123.7, 122.8, 120.9, 88.7 (SCHCHCH), 76.1 (SCHCHCH), 51.6 (SCHCHCH). Anal. Calcd for C21H9Fe3NO8S·0.1THF: C, 42.13; H, 1.62; N, 2.30. Found: C, 42.36; H, 1.89; N, 2.28. IR (KBr): νCO/cm−1 2051, 2001, 1992, 1957, 1944, 1884. [Fe2(μ-LMe)(CO)5] (1b). A solution of [Fe3(CO)12] (252 mg, 0.50 mmol) and MeQT (113 mg, 0.50 mmol) in toluene (20 mL) was heated at 80 °C for 9 h. The solution changed from dark green to dark brown. The reaction solution was filtered and evaporated to give a dark brown solid. The crude product was purified by silica gel column chromatography (dichloromethane/n-hexane, 2/1) to give a dark brown solid. The solid was washed with n-hexane and recrystallized by layering a toluene solution with n-hexane to give dark brown crystals (49 mg, 20%). 1H NMR (300 MHz, C6D6): δ 8.79 (dd, 3J = 5.1 Hz, 4J = 1.4 Hz, 1H, 2-Q), 7.35 (m, 1H, 7-Q), 7.09 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H, 4-Q), 7.01−6.94 (m, 2H, 5-Q, 6-Q), 6.20 (dd, 3J = 8.3 Hz, 4J = 5.1 Hz, 1H, 3-Q), 6.04 (dq, 3J = 5.5 Hz, 4J = 1.6 Hz, 1H, SCMeCHCH), 5.08 (d, 3J = 5.5 Hz, 1H, SCMeCHCH), 1.41 (d, 4J = 1.6 Hz, 3H, CH3). 13C{1H} NMR (75.5 MHz, C6D6): δ 217.8 (CO), 212.6 (CO), 211.6 (Fe(CO)3), 188.3 (QCFe), 156.4 (2-Q), 153.9, 153.2, 137.6, 136.4, 131.5, 126.0, 122.3, 117.3, 76.5 (SCMeCHCH),

20.4 (CH3). Anal. Calcd for C19H11Fe2NO5S: C, 47.84; H, 2.32; N, 2.94. Found: C, 47.58; H, 2.55; N, 2.94. IR (KBr): νCO/cm−1 2033, 2003, 1973, 1942, 1933, 1902. [Fe2(μ-LTMS)(CO)5] (1c). Method A. A solution of [Fe3(CO)12] (206 mg, 0.41 mmol) and TMSQT (104 mg, 0.37 mmol) in toluene (20 mL) was heated at 80 °C for 9 h. The solution changed from green to orange. Volatiles were removed under reduced pressure. The crude was purified by silica gel column chromatography (dichloromethane/n-hexane, 2/1) to give an orange solid. The solid was recrystallized from toluene/n-hexane to give orange crystals (46 mg, 23%). Method B. A quartz glass sample tube with a Teflon valve was charged with TMSQT (48 mg, 0.17 mmol), [Fe(CO)5] (69 mg, 0.55 mmol), and THF (10 mL). The solution was irradiated with a highpressure Hg lamp for 12 h, during which time the solution was degassed three times by the freeze−pump−thaw method every 3 h. The solution changed from yellow to dark brown. The solvent was removed under reduced pressure. The crude sample was purified by silica gel column chromatography (n-hexane/dichloromethane, 2/1). The orange band was collected and evaporated to give an orange crystalline solid. The solid was recrystallized from toluene/n-hexane to give orange crystals (24 mg, 26%). 1 H NMR (300 MHz, C6D6): δ 8.82 (dd, 3J = 5.1 Hz, 4J = 1.4 Hz, 1H), 7.44 (m, 1H, 7-Q), 7.11 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H, 4-Q), 7.04−6.97 (m, 2H, 5-Q, 6-Q), 6.78 (d, 3J = 5.5 Hz, 1H, SCSiMe3CHCH), 6.22 (dd, 3J = 8.3 Hz, 4J = 5.1 Hz, 1H, 3-Q), 5.29 (d, 3J = 5.5 Hz, 1H, SCSiMe3CHCH), 0.07 (s, 9H, SiMe3). 13C{1H} NMR (75.5 MHz, C6D6): δ 217.6 (CO), 212.5 (CO), 211.6 (Fe(CO)3), 188.8 (QCFe), 156.4, 153.8, 153.5, 152.6, 136.4, 133.5, 126.2, 122.4, 117.3, 80.1 (SCSiMe3CHCH), − 1.9 (SiMe3). Anal. Calcd for C21H17Fe2NO5SSi: C, 47.13; H, 3.20; N, 2.62. Found: C, 47.42; H, 3.30; N, 2.57. IR (KBr): νCO/cm−1 2035, 1989, 1978, 1944, 1927, 1919, 1901. [Fe2{CHCHCHC(Q)}(CO)5] (2a). A quartz glass sample tube with a Teflon valve was charged with QT (108 mg, 0.51 mmol), [Fe(CO)5] (493 mg, 2.5 mmol), and THF (20 mL). The yellow solution was degassed by the freeze−pump−thaw method. The solution was irradiated with a high-pressure Hg lamp for 8 h, during which time the solution was degassed every 3 h. Volatiles of the resulting dark brown solution were removed under reduced pressure. The crude sample was purified by silica gel column chromatography (dichloromethane/nhexane, 2/1). The red band was collected and concentrated. The resulting solid was recrystallized by layering a toluene solution with nhexane at −30 °C to afford 2a as red needle crystals (40 mg, 18%). 1 H NMR (300 MHz, C6D6): δ 8.80 (dd, 3J = 4.9 Hz, 4J = 1.4 Hz, 1H, 2-Q), 7.17 (m, 1H, 7-Q), 7.02 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H, 4Q), 6.92−6.83 (m, 2H, 5-Q, 6-Q), 6.27 (dd, 3J = 8.3 Hz, 3J = 4.9 Hz, 1H, 3-Q), 6.11 (t, 3J = 4J = 2.3 Hz, 1H, FeCHCHCH), 5.77, 5.72 (dd, dd, 3J = 5.1 Hz, 3J = 4J = 2.3 Hz, 2H, FeCHCHCH). 13C{1H} NMR (75.5 MHz, C6D6): δ 216.6 (Fe(CO)3), 214.3 (CO), 211.2 (CO), 168.8 (QCFe), 154.7, 153.4, 147.4, 144.6, 135.8, 127.6, 126.3, 122.6, 120.6, 113.7, 98.0. Anal. Calcd for C18H9Fe2NO5: C, 50.17; H, 2.10; N, 3.25. Found: C, 49.71; H, 2.21; N, 3.23. IR (KBr): νCO/cm−1 2026, 1993, 1971, 1925, 1903. [Fe3(μ-LMe)(CO)8] (3b). A quartz glass sample tube with a Teflon valve was charged with MeQT (217 mg, 0.96 mmol), [Fe(CO)5] (560 mg, 2.9 mmol), and THF (15 mL). The yellow solution was degassed by three freeze−pump−thaw cycles. The solution was irradiated with a high-pressure Hg lamp for 9 h, during which time the solution was degassed every 3 h. After the solvent was removed under reduced pressure, the crude product was purified by silica gel column chromatography (dichloromethane/n-hexane, 4/1). The green band was collected, evaporated, and recrystallized from toluene/n-hexane. The resulting black needle crystals were collected by decantation and washed with a small amount of cold n-hexane (245 mg, 42%). 1 H NMR (300 MHz, C6D6): δ 8.69 (dd, 3J = 5.1 Hz, 4J = 1.4 Hz, 1H, 2-Q), 7.35 (dd, 3J = 7.4 Hz, 4J = 1.0 Hz, 1H, 7-Q), 7.00 (dd, 3J = 8.1 Hz, 3J = 7.4 Hz, 1H, 6-Q), 6.99 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H, 4Q), 6.71 (dd, 3J = 8.1 Hz, 4J = 1.0 Hz, 1H, 5-Q), 6.15 (dd, 3J = 8.3 Hz, 3 J = 5.1 Hz, 1H, 3-Q), 5.83 (d, 3J = 6.5 Hz, 1H, SCMeCHCH), 4.25 G

DOI: 10.1021/acs.organomet.7b00280 Organometallics XXXX, XXX, XXX−XXX

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Organometallics (dd, 3J = 6.5 Hz, 1H, SCMeCHCH), 1.43 (s, 3H, CH3). 13C{1H} NMR (75.5 MHz, C6D6): δ 232.5 (μ-CO), 217.3 (CO), 213.9 (CO), 212.0 (CO), 211.8 (Fe(CO)3), 210.4 (CO), 158.8, 155.8, 149.3, 137.0, 124.0, 123.7, 122.6, 122.1, 85.9 (SCMeCHCH), 79.2 (SCMeCHCH), 68.7 (SCMeCHCH), 28.4 (CH3). Anal. Calcd for C22H11Fe3NO8S: C, 42.83; H, 1.80; N, 2.27. Found: C, 42.80; H, 1.95; N, 2.29. IR (KBr): νCO/cm−1 2048, 1991 (br), 1953, 1939, 1905. Photoreaction of TMSQT with [Fe(CO)5]. A quartz glass sample tube with a Teflon valve was charged with TMSQT (88 mg, 0.31 mmol), [Fe(CO)5] (312 mg, 1.6 mmol), and THF (20 mL). The yellow solution was degassed by three freeze−pump−thaw cycles. The solution was irradiated with a high-pressure Hg lamp for 23.5 h, during which time the solution was degassed five times. The dark brown solution was dried under reduced pressure. The crude sample was purified by silica gel column chromatography (n-hexane/dichloromethane, 4/1) to give orange and dark green bands. Each band was collected and recrystallized from toluene/n-hexane to give orange cubic crystals of 2c (34.6 mg, 21%) and black plate crystals of [Fe3(μLTMS)(CO)8] (3c) (2.4 mg, 1%), respectively. Data for 3c are as follows. 1H NMR (400 MHz, C6D6): δ 8.72 (dd, 3 J = 5.1 Hz, 4J = 1.2 Hz, 1H, 2-Q), 7.43 (dd, 3J = 7.4 Hz, 4J = 0.7 Hz, 1H, 7-Q), 7.05 (dd, 3J = 8.1, 7.4 Hz, 1H, 6-Q), 7.00 (dd, 3J = 8.3 Hz, 4J = 1.2 Hz, 1H, 4-Q), 6.74 (dd, 3J = 8.1 Hz, 4J = 0.7 Hz, 1H, 5-Q), 6.28 (d, 3J = 6.5 Hz, 1H, SC(SiMe3)CHCH), 6.16 (dd, 3J = 8.3, 5.1 Hz, 1H, 3-Q), 4.74 (d, 3J = 6.5 Hz, 1H, SC(SiMe3)CHCH), 0.13 (s, 9H, SiMe3). 13C{1H} NMR (151 MHz, C6D6): δ 232.7 (μ-CO), 217.3 (CO), 213.5 (CO), 212.0 (Fe(CO)3), 211.4 (CO), 210.3 (CO), 159.3, 155.7, 149.2, 137.0, 128.3, 123.8, 123.7, 122.6, 122.1, 91.3 (SC(SiMe3)CHCH), 81.1 (SC(SiMe3)CHCH), 58.1 (SC(SiMe3)CHCH), −1.7 (SiMe3). IR (KBr): νCO/cm−1 2047, 1990, 1982, 1941, 1931, 1899. Photolysis of 3c. An NMR tube with a Teflon valve was charged with a C6D6 solution of 3c. The solution was irradiated with a highpressure Hg lamp. In the 1H NMR spectra, 3c was completely converted to [Fe3(μ-LTMS)(CO)7] (4c) within 1 h, and no further change was observed after an additional 3 h. After removal of C6D6, the residue was recrystallized from toluene/n-hexane to give black crystals of 4c. Data for 4c are as follows. 1H NMR (300 MHz, C6D6): δ 8.71 (dd, 3 J = 5.1 Hz, 4J = 1.3 Hz, 1H, 2-Q), 7.46 (d, 3J = 7.4 Hz, 4J = 0.9 Hz, 1H, 7-Q), 7.11 (dd, 3J = 8.1, 7.4 Hz, 1H, 6-Q), 6.95 (dd, 3J = 8.3 Hz, 4J = 1.3 Hz, 1H, 4-Q), 6.89 (dd, 3J = 8.1 Hz, 4J = 0.9 Hz, 5-Q), 6.28 (d, 3J = 5.8 Hz, 1H, SC(SiMe3)CHCH), 6.13 (dd, 3J = 8.3, 5.1 Hz, 1H, 3Q), 4.76 (d, 3J = 5.8 Hz, 1H, SC(SiMe3)CHCH), 0.10 (s, 9H, SiMe3). Stability of Iron Complexes. An NMR tube with a Teflon valve was charged with 1b (4.4 mg, 0.009 mmol), mesitylene (1 μL) as an internal standard, and C6D6 (0.5 mL). The solution was heated at 80 °C, and 1H NMR measurements were performed. After heating for 23 h, the yields of 1b and MeQT were 90% and 4%, respectively. In a similar reaction of 3a in toluene-d8, the yields of 2a and 3a were 25% and 55%, respectively (80 °C, 23 h). Photoreactions of Diiron Complexes with [Fe(CO)5]. An NMR tube with a Teflon valve was charged with 1b or 1c, [Fe(CO)5] (1 equiv), mesitylene, and C6D6. The solution was irradiated with a highpressure Hg lamp, and 1H NMR measurements were performed every 2 h. In the NMR experiments of 1a, a C6D6 solution containing a 7:1 mixture of 1a and 2a was used for the photoreaction, and [Fe(CO)5] (1 equiv) was added every 2 h. X-ray Crystal Structure Determination of 1b,c, 2a, 3a−c, and 4c. Diffraction data were collected on a Rigaku AFC11/Saturn 724+ CCD diffractometer. The data were processed and corrected for Lorentz and polarization effects using the CrystalClear software package.28 The analyses were carried out using the WinGX software.29 Absorption corrections were applied using the Multi Scan method. The structures were solved using direct methods (SIR9730) and refined by full-matrix least squares on F2 using SHELXL-2013.31 Crystallographic data are summarized in Tables S1−S3 in the Supporting Information. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms in 4c, except for the H atoms of the S-metallacycle, were placed in calculated positions with C−

H(aromatic) = 0.95 Å and C−H(methyl) = 0.98 Å and refined using a riding model with Uiso(H) = 1.2Ueq(C) and 1.5Ueq(C), respectively. Methyl H atoms in 1b and in a toluene molecule found for 3b were also treated using the riding model. Other H atoms were found in a difference Fourier map and refined isotropically.

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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.7b00280. NMR data for all new compounds and crystallographic data for 1b,c, 2a, 3a−c, and 4c (PDF) Accession Codes

CCDC 1551270−1551276 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*M.H.: tel, +81-6-6605-2519; fax, +81-6-6605-2522; e-mail, [email protected]. ORCID

Masakazu Hirotsu: 0000-0001-9010-1945 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Professor Hiroshi Nakajima of Osaka City University for valuable discussions and encouragement. This work was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) for Scientific Research (C) (No. 16K05729).

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REFERENCES

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DOI: 10.1021/acs.organomet.7b00280 Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.7b00280 Organometallics XXXX, XXX, XXX−XXX