Synthetic and Structural Studies of 2-Acylmethyl-6-R-Difunctionalized

Article pubs.acs.org/IC

Synthetic and Structural Studies of 2‑Acylmethyl-6-RDifunctionalized Pyridine Ligand-Containing Iron Complexes Related to [Fe]-Hydrogenase Li-Cheng Song,*,†,‡ Kai-Kai Xu,†,‡ Xiao-Feng Han,†,‡ and Ji-Wei Zhang†,‡ †

Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, ‡Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin 300071, China S Supporting Information *

ABSTRACT: As active site models of [Fe]-hydrogenase, tridentate 2-acylmethyl-6-methoxymethoxy-difunctionalized pyridine-containing complexes η3-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(L1) (4, L1 = I; 5, SCN; 6, PhCS2) were prepared via the following multistep reactions: (i) etherification of 2-MeO2C-6-HOC5H3N with ClCH2OMe to give 2-MeO2C-6-MeOCH2OC5H3N (1), (ii) reduction of 1 with NaBH4 to give 2-HOCH2-6-MeOCH2OC5H3N (2), (iii) esterification of 2 with 4-toluenesulfonyl chloride to give 2-TsOCH2-6-MeOCH2OC5H3N (3), (iv) nucleophilic substitution of 3 with Na2Fe(CO)4 followed by treatment of the resulting Fe(0) intermediate Na[(2-CH2-6-MeOCH2OC5H3N)Fe(CO)4] (M1) with I2 to give complex 4, and (v) condensation of 4 with KSCN and PhCS2K to give complexes 5 and 6, respectively. In contrast to the preparation of complexes 4−6, bidentate 2-acylmethyl-6methoxymethoxy-difunctionalized pyridine-containing model complexes η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(I)(L2) (7, L2 = PPh3; 8, Cy-C6H11NC) and η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(L3) (9, L3 = 2-SC5H4N; 10, 8-SC9H6N) were prepared by ligand exchange reactions of 4 with PPh3, Cy-C6H11NC, 2-KSC5H4N, and 8-KSC9H6N, respectively. Particularly interesting is that the tridentate 2,6-bis(acylmethyl)pyridine- and 2-acylmethyl-6-arylthiomethylpyridine-containing model complexes η3-[2,6-(COCH2)2C5H3N]Fe(CO)2(L4) (11, L4 = PPh3; 12, CO) and η3-2-(COCH2-6-ArSCH2C5H3N)Fe(CO)2(ArS) (13, ArS = PhS; 14, 2-S-5-MeC4H2O) were obtained, unexpectedly, when 2,6-(TsOCH2)2C5H3N reacted with Na2Fe(CO)4 followed by treatment of the resulting mixture with ligands PPh3 and CO or disulfides (PhS)2 and (2-S-5MeC4H2O)2. Reactions of ligand precursors 3 and 2,6-(TsOCH2)2C5H3N with Na2Fe(CO)4 were monitored by in situ IR spectroscopy, and the possible pathways for producing complexes 4 and 11−14 via intermediates Na[(2-CH2-6MeOCH2OC5H3N)Fe(CO)4] (M1), Na[(2-CH2-6-TsOCH2C5H3N)Fe(CO)4] (M2), and (2-COCH2-6-CH2C5H3N)Fe(CO)3 (M3) are suggested. New compounds 1−14 were characterized by elemental analysis, spectroscopy, and, for some of them, X-ray crystallography.

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INTRODUCTION Hydrogenases are a class of natural metalloenzymes that catalyze H2 metabolism in a variety of microorganisms.1−4 According to the metal content in their active sites, hydrogenases are generally divided into three groups, namely, [FeFe]-hydrogenases,5,6 [NiFe]-hydrogenases,7,8 and [Fe]hydrogenase.9,10 [Fe]-hydrogenase is formally named H2forming methylenetetrahydromethanopterin dehydrogenase (Hmd), which was discovered 2 decades ago by Thauer and co-workers from Methanothermobacter marburgensis.11 This enzyme catalyzes the stereospecific reduction of methenyltetrahydromethanopterin (methenyl-H4MPT+) with H2 to form methylenetetrahydromethanopterin (methyleneH4MPT) and H+ (Scheme 1).9,12,13 Recent spectroscopic14−16 and, particularly, X-ray crystallographic17−19 studies revealed that the active site of [Fe]hydrogenase, in contrast to those of [FeFe]- and [NiFe]© XXXX American Chemical Society

Scheme 1. Heterolytic Cleavage of H2 Catalyzed by [Fe]Hydrogenase

Received: October 28, 2015

A

DOI: 10.1021/acs.inorgchem.5b02490 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Scheme 2. (a) Active Site of [Fe]-Hydrogenase and (b) Representatives of the Four Types of Models Reported in This Article

hydrogenases, has only a single Fe(II) center that is coordinated to a cysteine S atom, two cis-terminal CO ligands, a bidentate 2-acylmethyl-6-hydroxypyridine moiety, and an as yet unknown ligand, which is presumably a molecule of water (Scheme 2a). Because [Fe]-hydrogenase’s active site structure has been successfully elucidated, numerous model complexes of [Fe]hydrogenase have been prepared and structurally characterized.20−36 In recent years, we have prepared several series of 2acylmethyl-6-R (R = CH2OH, PhCO2CH2, OH, etc.)difunctionalized pyridine ligand-containing models for [Fe]hydrogenase by a novel method that involves nucleophilic substitution reactions of 2,6-disubstituted pyridine derivatives 2-TsOCH2-6-RC5H3N (Ts = 4-MeC6H4SO2) with Na2Fe(CO)4 followed by treatment of the resulting Fe(0) complex salts Na[(2-CH2-6-RC5H3N)Fe(CO)4] with the corresponding reagents.29,31−33 To further develop the synthetic methodology and new reactions used for preparing new types of [Fe]hydrogenase model complexes, particularly the 2-acylmethyl-6R-difunctionalized pyridine-containing [Fe]-hydrogenase models, we continued to study this synthetic method by reacting the 2-TsOCH2-6-MeOCH2O- and 2,6-bis(TsOCH2)-difunctionalized pyridine derivatives with Na2Fe(CO)4 followed by treatment of the resulting mixture with some appropriate reagents. Interestingly, this study led to the preparation and characterization of four new types of [Fe]-hydrogenase model complexes: one type with a tridentate acylmethyl(methoxymethoxy)pyridine ligand, another type with a bidentate acylmethyl(methoxymethoxy)pyridine ligand, the third type with a tridentate bis(acylmethyl)pyridine ligand, and the fourth type with a tridentate acylmethyl(arylthiomethyl)pyridine ligand (Scheme 2b). In addition, it is worth noting that for production of the third and fourth types of complexes a possible pathway has been suggested in which a novel 2-acylmethyl-6-methylenepyridine ligand-containing fourmembered ferracycle intermediate and its novel reactions with ligands PPh3 and CO or disulfides (PhS)2 and 2,2′-dithiobis(5methylfuran) (2-S-5-MeC4H2O)2 are involved. Herein, we report the interesting results obtained during this study.

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Scheme 3. Synthesis of Ligand Precursors 1−3

NaBH4 in refluxing THF/MeOH, precursor 2 was produced in 89% yield. Finally, ligand precursor 3 was prepared in 96% yield by esterification of 2 with 4-toluenesulfonyl chloride/KOH in THF from 0 °C to room temperature. Although ligand precursors 1 and 3 are air-stable white solids, precursor 2 is an air-stable colorless liquid. These new compounds were fully characterized by elemental analysis and IR, 1H NMR, and 13C{1H}NMR spectroscopies. For instance, the IR spectra of 1 and 2 showed one absorption band at 1721 or 3464 cm−1 for the ester carbonyl group of 1 and hydroxy group of 2, whereas complex 3 exhibited two bands at 1364 and 1177 cm−1 for its thiocarbonyl group. The 1H NMR spectra of 1−3 displayed one singlet in the range 3.48−3.55 ppm and one singlet from 5.41 to 5.60 ppm for the methyl and methylene groups in their MeOCH2O substituents, respectively. In addition, the 13C{1H}NMR spectra of 1−3 exhibited a signal at 165.5, 64.2, and 71.4 ppm for the carbonyl C atom of 1, hydroxymethyl C atom of 2, and methylene C atom attached to the TsO group of 3, respectively. Tridentate 2-acylmethyl-6-methoxymethoxypyridine-containing model complexes 4−6 could be prepared by the methods used to obtain the previously reported difunctionalized pyridine-containing iron complexes.29,31−33 Thus, as shown in Scheme 4, when ligand precursor 3 reacted with Na2Fe(CO)4 in MeCN at 0 °C followed by treatment of the resulting Fe(0) intermediate Na[(2-CH 2 -6-MeOCH 2 OC 5 H 3 N)Fe(CO) 4 ] (M1) with iodine, the tridentate difunctionalized pyridinecontaining Fe(II) model complex 4 was produced via an in situ CO migratory insertion reaction of intermediate M1 followed by coordination of an iodide ligand, pyridine N atom, and methoxy O atom in 46% yield. Furthermore, when complex 4 was treated with KSCN and PhCS2K in MeCN at room temperature, the tridentate difunctionalized pyridine-containing Fe(II) complexes 5 and 6 were prepared via nucleophilic substitution of iodide in 4 by anionic ligands NCS− and PhCS2− in 96 and 92% yields, respectively. To support the suggested pathway for the formation of iodide complex 4 by reaction of precursor ligand 3 with disodium salt Na2Fe(CO)4, we performed in situ IR spectroscopy (see the Supporting Information)29,37 to prove the existence of intermediate salt M1 (note that our attempts to isolate this intermediate salt were unsuccessful due to it being

RESULTS AND DISCUSSION

Synthesis and Characterization of Ligand Precursors 2-MeO 2 C-6-MeOCH 2 OC 5 H 3 N (1), 2-HOCH 2 -6-MeOCH2OC5H3N (2), and 2-TsOCH2-6-MeOCH2OC5H3N (3) and Tridentate 2-Acylmethyl-6-methoxymethoxypyridine-Containing Model Complexes η3-(2COCH2-6-MeOCH2OC5H3N)Fe(CO)2(L1) (4, L1 = I; 5, SCN; 6, PhCS2). In order to prepare model complexes 4−6, we first prepared their ligand precursors, 1−3. Ligand precursors 1−3 could be prepared conveniently by the synthetic methods shown in Scheme 3. Thus, when 2,6-disubstituted pyridine 2MeO2C-6-HOC5H3N was treated with ClCH2OMe in the presence of K2CO3/NaI and in refluxing acetone, precursor 1 was obtained in 69% yield. In addition, when 1 was treated with B


Article

Inorganic Chemistry

CH2CO groups and two doublets or one singlet at 5.29−5.65 ppm for their OCH2O groups, which was dependent upon whether the two H atoms in the CH2CO and OCH2O groups were diastereotopic under the determined conditions.29,38 The 13 C{1H}NMR spectra of 4−6 showed one signal at 252−264 ppm, which is typical of their acyl C atoms.29,38 The molecular structures of 4 and 5 were further confirmed by X-ray crystallography. ORTEP views of 4 and 5 are shown in Figures 2 and 3, respectively, and their selected bond lengths

Scheme 4. Synthesis of Model Complexes 4−6

highly unstable). As shown in the in situ IR spectra (Figure 1), when complex 3 was added to a MeCN solution of

Figure 2. ORTEP view of 4 with 30% probability level ellipsoids.

Figure 1. In situ IR spectra for the formation of 4 starting from 3 and Na2Fe(CO)4 via intermediate M1 in MeCN.

Na2Fe(CO)4, the original νCO absorption bands of Na2Fe(CO)4 at 1760 (vs), 1884 (m), and 1915 (w) cm−1 gradually decreased, and after ca. 10 min, they were completely replaced by a very strong band at 1880 cm−1 and a middle band at 1995 cm−1. This means that Na2Fe(CO)4 was totally consumed and that intermediate salt M1 was formed. The in situ IR spectra further showed that after addition of I2 (ca. 15 min) the aforementioned two νCO absorption bands disappeared and, instead, two middle bands at 2036 and 1976 cm−1 along with one weak band at 1675 cm−1 were generated. The three new bands can be attributed to the two terminal carbonyls and one acyl ligand for the newly formed complex 4. Model complexes 4 and 5 are air-stable yellow solids, whereas complex 6 is an air-stable brown solid. The three complexes were characterized by elemental analysis and various spectroscopic methods. For example, the IR spectra of 4−6 exhibited two strong absorption bands in the region 2045− 1962 cm−1 for their two terminal carbonyls and one strong absorption band in the range 1673−1658 cm−1 for the acyl groups ligated to their Fe(II) centers.29,38 The 1H NMR spectra of 4−6 displayed two doublets at 3.91−4.73 ppm for their


and angles are given in Table 1. As shown in Figures 2 and 3, complexes 4 and 5 indeed contain a tridentate 2-acylmethyl-6methoxymethoxy-difunctionalized pyridine ligand whose acylmethylpyridyl and methoxymethoxypyridyl moieties construct a five-membered ferracycle and a six-membered ferracycle with their iron(II) centers, respectively. The two terminal CO ligands of 4 and 5 reside in positions cis to their acyl ligands, whereas the iodide ligand in 4 and SCN ligand in 5 are located in positions trans to one of their two CO ligands. Particularly C


Article

Inorganic Chemistry Table 1. Selected Bond Lengths [Å] and Angles [deg] for 4 and 5 4 Fe(1)−I(1) Fe(1)−N(1) Fe(1)−C(3) C(1)−Fe(1)−C(2) C(3)−Fe(1)−O(5) C(4)−C(3)−Fe(1) N(1)−C(9)−O(4)

2.6601(6) 2.036(2) 1.909(3) 89.47(13) 173.38(10) 111.52(18) 119.9(2)

Fe(1)−C(4) Fe(1)−N(2) Fe(1)−N(1) C(1)−Fe(1)−C(2) C(1)−Fe(1)−N(2) C(2)−Fe(1)−N(1) C(4)−Fe(1)−N(1)

1.9257(19) 1.9603(17) 2.0190(16) 91.02(9) 177.63(8) 173.93(8) 85.18(8)

Fe(1)−O(5) O(3)−C(3) N (1)−C(5) C(2)−Fe(1)−N(1) N(1)−Fe(1)−O(5) C(1)−Fe(1)−I(1) C(9)−O(4)−C(10)

2.151(2) 1.217(3) 1.357(4) 174.53(12) 88.82(8) 171.36(9) 116.6(2)

Fe(1)−O(5) O(3)−C(4) N (1)− C(6) C(4)−Fe(1)−O(5) C(6)−N(1)−Fe(1) C(3)−N(2)−Fe(1) N(2)−C(3)−S(1)

2.1336(14) 1.2073(3) 1.361(2) 174.10(7) 113.67(13) 166.77(16) 178.63(19)

5

noteworthy is that in 4 and 5 the acyl ligands are trans to an oxygen atom of the methoxymethoxy group. Such a geometric arrangement is very similar to that between an acyl ligand and the possibly coordinated H2O molecule in the natural [Fe]hydrogenase enzyme.17,18 Synthesis and Characterization of Bidentate 2Acylmethyl-6-methoxymethoxypyridine-Containing Model Complexes η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(I)(L2) (7, L2 = PPh3; 8, Cy-C6H11NC) and η2-(2COCH2-6-MeOCH2OC5H3N)Fe(CO)2(L3) (9, L3 = 2-SC5H4N; 10, 8-SC9H6N). Interestingly, in contrast to the preparation of tridentate 2-acylmethyl-6-methoxymethoxypyridine-containing complexes 5 and 6, bidentate 2-acylmethyl-6-methoxymethoxypyridine-containing model complexes 7 and 8 could be prepared by ligand exchange reactions of complex 4 with PPh3 and Cy-C6H11NC in CH2Cl2 at room temperature in 97 and 93% yields, respectively (Scheme 5). This is obviously due to the coordinated ether substituent OCH2OMe in 4 being a much weaker ligand than the terminal CO ligand. In addition, bidentate 2-acylmethyl-6-methoxymethoxypyridine-containing model complexes 9 and 10 could be obtained by a ligand exchange reaction of 4 with 2-KSC5H4N in CH2Cl2 or 8KSC9H6N in MeCN at room temperature via nucleophilic replacement of the iodide and OCH2OMe ligands in 4 by C5H4NS− and C9H6NS− ligands in 97 and 93% yields, respectively (Scheme 5). Apparently, models 9 and 10 are more natural models than 7 and 8 since the inorganic iodide ligands in 7 and 8 are replaced by organic S/N-containing ligands. Model complexes 7−10 are air-stable yellow solids. These new complexes were characterized by elemental analysis and various spectroscopic methods, and the structures of 7 and 9 were unequivocally confirmed by X-ray crystallography. Similar to model complexes 4−6, the IR spectra of 7−10 showed two strong absorption bands in the range 2034−1954 cm−1 for their two terminal carbonyls and one strong absorption band in the region 1652−1631 cm−1 for the acyl groups attached to their Fe(II) centers.29,38 The 1H NMR spectra of 7−10 displayed two doublets at 3.64−4.87 ppm for their CH2CO groups and two or one singlet at 4.66−5.59 ppm for their OCH2O groups,29,38 whereas the 13C{1H}NMR spectra showed one signal at 246−265 ppm, which is characteristic of their acyl C atoms.29,38


The X-ray crystallographic study (Figures 4 and 5 and Table 2) revealed that both 7 and 9 have a bidentate 2-acylmethyl-6methoxymethoxy-difunctionalized pyridine ligand, which constitutes a five-membered ferracycle with their iron(II) centers, acyl C atoms, and pyridine N atoms. The two terminal CO ligands in 7 and 9, like those in 4 and 5 as well as in the active site of [Fe]-hydrogenase, are located in positions cis to their acyl ligands. In addition, the PPh3 ligand in 7 is located in the position trans to the iodine atom and 9 has another ferracycle formed by coordination of the S and N atoms of the mercaptopyridinate ligand with its iron(II) center. Synthesis and Characterization of Tridentate 2,6Bis(acylmethyl)pyridine-Containing Model Complexes D


Article

Inorganic Chemistry

η3-[2,6-(COCH2)2C5H3N]Fe(CO)2(L4) (11, L4 = PPh3; 12, CO) and Tridentate 2-Acylmethyl-6-arylthiopyridine-Containing Model Complexes η3-(2-COCH2-6-ArSC5H3N)Fe(CO)2(ArS) (13, ArS = PhS; 14, 2-S-5-MeC4H2O). We further found that tridentate 2,6-bis(acylmethyl)pyridine- and 2acylmethyl-6-arythiomethylpyridine-containing complexes 11− 14 were unexpectedly produced in 48, 24, 77, and 47% yields, respectively, when 2,6-bis(TsOCH2)-disubstituted pyridine 2,6bis(TsOCH2)C5H3N reacted with Na2Fe(CO)4 in MeCN at 0 °C followed by treatment of the resulting mixture with ligands PPh3 and CO or with disulfides (PhS)2 and (2-S-5-MeC4H2O)2 (Scheme 6). As shown in Scheme 6, the formation of complexes 11−14 includes three major reaction steps. The first step involves intermolecular nucleophilic attack of the negatively charged Fe atom in Na2Fe(CO)4 at one of the two methylene C atoms in 2,6-(TsOCH2)2C5H3N to generate the intermediate Fe(0) complex salt M2. This step of the reaction is very similar to the above-mentioned reaction for the formation of intermediate M1 and the previously reported reactions of TsOCH2-containing pyridine derivatives 2-TsOCH2-6-RC5H3N with Na2Fe(CO)4 to give the corresponding Fe(0) complex salts.29,31−33 The second step includes intramolecular nucleophilic attack of the negatively charged Fe atom in M2 at the second TsO-attached methylene C atom followed by CO migratory insertion and pyridine N atom coordination to form the novel 2-acylmethyl6-methylenepyridine ligand-containing four-membered ferracycle M3. Interstingly, this type of reaction for the formation of intermediate M3 is unprecedented and might be expected to be reversible since the four-membered ferracycle in M3 is highly strained and thus easily opened by nucleophilic attack of the excess TsO− group produced via the first and second substitution reaction steps. The third step for the production of complexes 11 and 12 involves ring enlargement of the fourmembered ferracycle in M 3 via the migration of its pyridylmethyl group to the C atom of an adjacent CO group followed by coordination of the external PPh3 and CO ligands.39−41 The third step for the production of complexes 13 and 14 includes ring-opening of the four-membered ferracycle in M3 by a concerted addition of disulfide (PhS)2 or (2-S-5-MeC4H2O)2 across the Fe−CH2 bond (possibly involving a four-membered cyclic transition state formed by two S atoms, one Fe atom, and one C atom of the S−S and



Table 2. Selected Bond Lengths [Å] and Angles [deg] for 7 and 9 7 Fe(1)−C(2) Fe(1)−C(3) Fe(1)−N(1) P(1)−Fe(1)−I(1) C(24)−P(1)−Fe(1) C(1)−Fe(1)−N(1) Fe(1)−N(1)−C(5)

1.872(4) 1.948(3) 2.040(3) 174.96(6) 115.77(9) 170.07(13) 115.32(19)

Fe(1)−C(8) O(3)−C(8) C(3)−N(1) C(1)−Fe(1)−C(2) C(1)−Fe(1)−N(2) C(8)−Fe(1)−N(1) C(1)−Fe(1)−S(1)

1.9266(15) 1.2213(17) 1.3443(19) 91.72(7) 172.74(6) 160.69(6) 89.32(5)

Fe(1)−P(1) O(3)−C(3) Fe (1)− I(1) C(2)−Fe(1)−C(1) C(9)−N(1)−C(5) C(10)−O(5)−C(11) Fe(1)−C(3)−O(3)

2.2576(12) 1.217(3) 2.694(2) 89.68(16) 116.9(3) 112.7(3) 130.7(3)

Fe(1)−N(2) Fe(1)−N(1) Fe (1)−S(1) N(1)−Fe(1)−S(1) C(3)−N(1)−Fe(1) C(14)−N(2)−Fe(1) C(9)−C(8)−Fe(1)

2.0523(12) 2.0536(13) 2.3840(8) 69.54(4) 101.35(10) 128.52(10) 110.20(11)

9

E


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Inorganic Chemistry

and 2001 (w) cm−1 are very close to those corresponding to M1 and the previously reported analogues.29,32 (ii) The fact that intermediate M3 was not observed by situ IR spectroscopy is most likely due to the very small amount of it present in the equilibrium with a large amount of M2. However, if the reaction rates of M3 with the added PPh3/CO or disulfides (PhS)2/(2-S5-MeC4H2O)2 are fast enough, then complexes 11−14 could still be obtained in quite high yields through a simultaneously fast shift in the equilibrium to M3.42 (iii) Although the third step of the ring enlargement and ring-opening for producing 11−14 requires energy, this required energy could be compensated by the energy released from the conversion of the highly strained four-membered ferracycle-containing M3 to the five-membered ferracycle-containing products of 11−14. (iv) Although the suggested pathways for the production of 11−14 seem to be plausible, some mechanistic details still remain to be further studied in the future. Model complexes 11−14 are air-stable yellow solids and were characterized by elemental analysis and various spectroscopic techniques. The IR spectra of 11−14 displayed two absorption bands in the range 2039−1949 cm−1 for their terminal CO ligands and one absorption band at 1684−1614 cm−1 for their acyl groups.29,38 The 1H NMR spectra of 11−14 showed two doublets or one singlet at 3.10−4.21 ppm for their CH2CO groups, and 13 and 14 showed one singlet or two doublets at 4.53−5.03 ppm for their CH2S groups, which was dependent upon whether the two H atoms in the CH2CO or CH2S groups were diastereotopic under the determined conditions.29,38 The 13C{1H} NMR spectra of 11−14 exhibited one or two signals at 254−280 ppm for their acyl C atoms.29,38 The molecular structures of 11−13 were unambiguously confirmed by X-ray crystallographic study. The ORTEP views of 11−13 are depicted in Figures 7−9, respectively, and Table 3


Fe−CH2 bonds), followed by displacement of one CO ligand in M3 with the resulting arylthiomethyl groups. Finally, it should be noted that (i) we have employed in situ IR spectroscopy to monitor the reaction course of 2,6(TsOCH2)2C5H3N with Na2Fe(CO)4 (see the Supporting Information). As a result, as shown in Figure 6, after ca. 10 min of the studied reaction, the three νCO absorption bands for Na2Fe(CO)4 at 1760 (vs), 1885 (m), and 1916 (w) cm−1 completely disappeared and, instead, two new νCO bands at 1884 (vs) and 2001 (w) cm−1 emerged. This means that intermediate M2 was formed since the two bands at 1884 (vs)


lists their bond lengths and angles. Figures 7 and 8 indicate that complexes 11 and 12 indeed contain a tridentate 2,6bis(acylmethyl)pyridine ligand, which forms two five-membered ferracycles with their iron(II) centers. Both acylmethyl ligands in 11 and 12 are trans to each other. Similar to 11 and 12, complex 13 (Figure 9) includes a tridentate 2-acylmethyl-6phenylthiomethylpyridine ligand, which constructs two five-

Figure 6. Monitoring the reaction course of 2,6-(TsOCH2)2C5H3N with Na2Fe(CO)4 in MeCN by in situ IR spectroscopy. F


Article

Inorganic Chemistry Table 3. Selected Bond Lengths [Å] and Angles [deg] for 11−13 11 Fe(1)−C(2) Fe(1)−C(1) Fe(1)−N(1) C(2)−Fe(1)−C(1) C(2)−Fe(1)−N(1) C(1)−Fe(1)−N(1) N(1)−Fe(1)−C(3)

1.7565(18) 1.7901(18) 1.9721(14) 89.94(8) 175.02(7) 91.50(7) 81.99(6)

Fe(1)−C(2) Fe(1)−C(3) Fe(1)−C(1) C(2)−Fe(1)−C(3) C(2)−Fe(1)−C(1) C(3)−Fe(1)−C(1) C(2)−Fe(1)−N(1)

1.7713(17) 1.8092(16) 1.8206(16) 89.80(7) 90.56(7) 170.71(6) 173.69(6)

Fe(1)−P(1) Fe(1)−C(11) C(5)− N(1) N(1)−Fe(1)−C(11) N(1)−Fe(1)−P(1) C(11)−Fe(1)−P(1) C(9)−N(1)−C(5)

2.2902(7) 2.0103(17) 1.354(2) 103.02(7) 91.33(4) 89.42(5) 120.77(15)

Fe(1)−N(1) Fe(1)−C(4) Fe(1)− C(12) N(1)−Fe(1)−C(1) N(1)−Fe(1)−C(12) N(1)−Fe(1)−C(4) C(6)−N(1)−Fe(1)

1.9660(13) 2.0260(16) 2.0129(16) 90.73(6) 96.80(6) 82.62(6) 119.33(10)

Fe(1)−N(1) Fe(1)−S(2) Fe(1)−S(1) N(1)−Fe(1)−S(2) S(1)−Fe(1)−S(2) N(9)−N(1)−C(5) C(11)−S(1)−Fe(1)

1.9766(13) 2.3592(5) 2.3832(6) 88.57(4) 85.273(18) 119.48(13) 107.76(5)

12

13 Fe(1)−C(2) Fe(1)−C(1) Fe(1)−C(3) C(1)−Fe(1)−C(2) C(1)−Fe(1)−C(3) C(1)−Fe(1)−N(1) C(2)−Fe(1)−S(2)

1.7767(17) 1.7793(17) 1.9340(16) 90.74(7) 86.60(7) 94.87(6) 85.77(5)

methoxymethoxypyridine, the second type includes complexes 7−10, each having a bidentate 2-acylmethyl-6-methoxymethoxypyridine, the third type includes complexes 11 and 12, each having a tridentate 2,6-bis(acylmethyl)pyridine, and the fourth type includes complexes 13 and 14, each having a tridentate 2acylmethyl-6-arylthiomethylpyridine. Although complex 4 was prepared by a nucleophilic substitution reaction of 2,6disubstituted pyridine derivative 3 with Na2Fe(CO)4 followed by treatment of the resulting Fe(0) intermediate M1 with I2, complexes 5 and 6 were prepared by condensation reactions of 4 with KSCN and PhCS2K. However, in contrast to the preparation of 4−6, complexes 7−10 were prepared by ligand exchange reactions of complex 4 with PPh3, Cy-C6H11NC, 2KSC5H4N, and 8-KSC9H6N, respectively. Particularly interesting is that complexes 11−14 were produced unexpectedly by treatment of 2,6-disubstituted pyridine derivative 2,6(TsOCH2)2C5H3N with Na2Fe(CO)4 followed by treatment of the resulting mixture with ligands PPh3 and CO as well as with disulfides (PhS)2 and (2-S-5-MeC4H2O)2. We have suggested the possible pathways for the formation of complexes 11−14. The first step in the suggested pathways involves i n t e r mo l e c u l a r n u c l e o p h i l i c s u b s t i t u t i o n o f 2 , 6 (TsOCH2)2C5H3N with Na2Fe(CO)4 to give intermediate M2. The second step involves intramolecular nucleophilic substitution of M2 followed by CO migratory insertion and pyridine N atom coordination to afford intermediate M3. The third step for the formation of complexes 11 and 12 involves ring enlargement of the four-membered ferracycle in M3 via CO migratory insertion of M3 followed by coordination of the external PPh3 and CO ligands. The third step for the formation of complexes 13 and 14 involves ring-opening of the fourmembered ferracycle in M3 by addition of the two arylthio groups in disulfides (PhS)2 and (2-S-5-C4H2O)2 followed by displacement of one CO ligand with the resulting arylthiomethyl groups. X-ray crystallographic studies of the four types of model complexes 4, 5, 7, 9, and 11−13 confirm that (i) the


membered ferracycles with its iron(II) center. While the acylmethyl ligand is trans to the phenylthiomethyl ligand, the phenylthio ligand is trans to one of the two terminal CO ligands. In addition, the two terminal CO ligands in 13, like those in complexes 4, 5, 7, and 9 as well as in the active site of [Fe]-hydrogenase, are located in positions cis to its acylmethyl ligand.

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SUMMARY AND CONCLUSIONS We have prepared four new types of [Fe]-hydrogenase model complexes by various synthetic methods. The first type includes complexes 4−6, each having a tridentate 2-acylmethyl-6G


Article

Inorganic Chemistry

Figure 9. ORTEP view of 13 with 30% probability level ellipsoids. a reflux condenser topped with a nitrogen inlet tube was charged with 2-MeO2C-6-HOC5H3N (4.59 g, 30.0 mmol) and acetone (250 mL). To the acetone solution were added chloromethyl methyl ether (2.51 mL, 33.0 mmol), potassium carbonate (20.70 g, 150 mmol), and sodium iodide (0.45 g, 3.0 mmol). After the mixture was stirred and refluxed for 10 h, most of the solvent (about 2/3 in volume) was removed on a rotary evaporator. To the remaining mixture was added water (200 mL), and it was then extracted twice with dichloromethane (2 × 100 mL). After the combined extracts were washed twice with water (2 × 100 mL), the separated organic phase was dried over anhydrous magnesium sulfate. The drying agent and solvent were removed to give a residue, which was subjected to fluorescence TLC (neutral alumina) separation using ethyl acetate/petroleum ether (1:3, v/v) as the eluent. From the main band, 1 (4.06 g, 69%) was obtained as a white solid. mp 64−65 °C. Anal. Calcd for C9H11NO4: C, 54.82; H, 5.62; N, 7.10. Found: C, 54.99; H, 5.46; N, 7.01. IR (KBr disk): νCO 1721 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 3.55 (s, 3H, OCH3), 3.95 (s, 3H, CO2CH3), 5.60 (s, 2H, OCH2O), 6.99−7.02 (m, 1H, 4-H of C5H3N), 7.72−7.77 (m, 2H, 3,5-H of C5H3N) ppm. 13 C{1H} NMR (100 MHz, CDCl3): 52.7 (OCH3), 57.4 (CO2CH3), 92.3 (OCH2O), 115.3, 119.4, 139.7, 145.5, 162.4 (C5H3N), 165.5 (CO2CH3) ppm. Preparation of 2-HOCH2-6-MeOCH2OC5H3N (2). To a stirred solution of 1 (4.06 g, 30.0 mmol) in THF (180 mL) was added NaBH4 (4.71 g, 124 mmol). After the mixture was heated to reflux, methanol (35 mL) was added dropwise by syringe (note that the addition of methanol caused rapid effervescence of the mixture). The new mixture was stirred and refluxed for an additional 1 h, and it was then cooled to room temperature and quenched with a saturated aqueous solution of ammonium (50 mL). After water (100 mL) was added, the mixture was extracted with methylene chloride (3 × 100 mL). The combined extracts were washed with water (2 × 100 mL) and dried over anhydrous magnesium sulfate. Removal of the drying agent and solvent afforded 2 (3.09 g, 89%) as a colorless liquid. Anal. Calcd for C8H11NO3: C, 56.80; H, 6.55; N, 8.28. Found: C, 56.68; H, 6.49; N, 8.31. IR (KBr disk): νOH 3464 (m) cm−1. 1H NMR (400 MHz, CDCl3): 3.52 (s, 3H, OCH3), 3.55 (s, 1H, OH), 4.70 (s, 2H, CH2OH), 5.52 (s, 2H, OCH2O), 6.71 (d, J = 8.0 Hz, 1H, 3-H of C5H3N), 6.91 (d, J = 7.6 Hz, 1H, 5-H of C5H3N), 7.61 (t, J = 7.6 Hz, 1H, 4-H of C5H3N) ppm. 13C{1H} NMR (100 MHz, CDCl3): 57.0 (OCH3), 64.2 (CH2OH), 91.9 (OCH2O), 109.4, 113.9, 139.8, 157.4, 162.2 (C5H3N) ppm. Preparation of 2-TsOCH2-6-MeOCH 2OC5H3N (3). While stirring, a solution of 2 (3.09 g, 18.3 mmol) in THF (140 mL) was cooled to 0 °C; then, KOH (5.12 g, 91.2 mmol), 10 drops of H2O (in order to increase the solubility of KOH in THF), and 4-

tridentate 2-acylmethyl-6-methoxymethoxy-difunctionalized pyridine ligand present in complexes 4 and 5 is ligated to their Fe(II) centers to form a five-membered ferracycle and a six-membered ferracycle, (ii) the bidentate 2-acylmethyl-6methoxymethoxy-difunctionalized pyridine present in complexes 7 and 9 is ligated to their Fe(II) centers to generate a five-membered ferracycle, (iii) the tridentate 2,6-bis(acylmethyl)- and 2-acylmethyl-6-phenylthiomethyl-difunctionalized pyridine ligands present in complexes 11−13 are ligated to their Fe(II) centers to constitute two five-membered ferracycles, (iv) the two terminal CO ligands in complexes 4, 5, 9, and 13, like those in the active site of [Fe]-hydrgenase, are located in positions cis to their acyl ligands, and (v) one of the two CO ligands in 4 and 5 is trans to an oxygen atom of the methoxymethoxy functionality. Such a geometric arrangement is very similar to that between an acyl ligand and the possibly coordinated H2O molecule in the natural [Fe]-hydrogenase enzyme.

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EXPERIMENTAL SECTION

General Comments. All reactions were carried out under an atmosphere of highly purified nitrogen by using standard Schlenk and vacuum line techniques. Fe(CO)5 and CO gas should be handled in a well-ventilated hood since they are highly toxic, and Na2Fe(CO)4·(1,4dioxane)1.5 must be kept under a dry inert atmosphere at all times since it is very pyrophoric. Tetrahydrofuran (THF) and 1,4-dioxane were distilled from Na/benzophenone ketyl under nitrogen. Acetonitrile and dichloromethane were purified by distillation once from P2O5 and then over CaH2. MeOCH2Cl, 4-MeC6H4SO2Cl (TsCl), 2-mercaptopyridine, KSCN, NaBH4, PPh3, Cy-C6H11NC, (PhS)2, (2-S-5-MeC4H2O)2, and some other materials were available commercially and used without further purification. Na2Fe(CO)4·(1,4dioxane)1.5,43 2-MeO2C-6-HOC5H3N,44 PhCS2K,45 8-KSC9H6N,46 and 2,6-(TsOCH2)2C5H3N47 were prepared according to published procedures. 1H, 13C{1H}, 31P{1H} NMR spectra were obtained on a Bruker Avance 400 NMR spectrometer. Solid IR spectra were recorded on a Bruker Vector 22 or Bruker Tensor 27 FT-IR spectrometer, whereas in situ IR spectra were taken on a ReactIR iC10 analyzer. Elemental analyses were performed on an Elementar Vario EL analyzer. Melting points were determined on a SGW X-4 microscopic melting point apparatus and are uncorrected. Preparation of 2-MeO2C-6-MeOCH2OC5H3N (1). A 500 mL, three-necked flask fitted with a magnetic stir bar, two serum caps, and H


Article

Inorganic Chemistry

d6): 56.7 (OCH3), 62.7 (CH2CO), 95.3 (OCH2O), 107.7, 115.5, 123.3, 128.3, 133.3, 141.3, 143.0, 161.2, 164.7 (C5H3N, C6H5), 211.5, 211.8 (CO), 247.7 (SCS), 263.4 (CH2CO) ppm. Preparation of η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(I)(PPh3) (7). The same procedure as that for 5 was followed but PPh3 (0.079 g, 0.3 mmol) and CH2Cl2 (10 mL) were employed instead of KSCN and MeCN, respectively. From the major yellow band, 7 (0.199 g, 97%) was obtained as a yellow solid. mp 61 °C (dec). Anal. Calcd for C29H25FeINO5P: C, 51.13; H, 3.70; N, 2.06. Found: C, 50.98; H, 3.39; N, 2.08. IR (KBr disk): νCO 2022 (vs), 1967 (vs); νCO 1631 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 3.41 (s, 3H, OCH3), 4.05 (d, J = 21.2 Hz, 1H of CH2CO), 4.37 (d, J = 21.2 Hz, 1H of CH2CO), 5.05 (d, J = 7.0 Hz, 1H of OCH2O), 5.27 (d, J = 7.0 Hz, 1H of OCH2O), 6.89 (d, J = 8.0 Hz, 1H, 3-H of C5H3N), 6.98 (d, J = 7.2 Hz, 1H, 5-H of C5H3N), 7.38−7.46 (m, 15H, 3C6H5), 7.72 (t, J = 7.8 Hz, 1H, 4-H of C5H3N) ppm. 31P{1H} NMR (162 MHz, acetone-d6, H3PO4): 69.0 (s, PPh3) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 56.5 (OCH3), 66.7 (CH2CO), 94.4 (OCH2O), 106.6, 115.7, 128.4, 128.7, 130.5, 133.1, 133.2, 140.3, 162.0, 164.0 (C6H5, C5H3N), 210.2, 218.7 (CO), 260.9 (CH2CO) ppm. Preparation of η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(I)(CNC6H11-Cy) (8). The same procedure as that for 5 was followed except that cyclohexyl isocyanide (0.033 g, 0.3 mmol) and CH2Cl2 (10 mL) were used in place of KSCN and MeCN, respectively. From the major yellow band, 8 (0.137 g, 93%) was obtained as a yellow solid. mp 84 °C (dec). Anal. Calcd for C18H21FeIN2O5: C, 40.94; H, 4.01; N, 5.30. Found: C, 40.91; H, 4.12; N, 5.29. IR (KBr disk): νCN 2180 (s); νCO 2034 (vs), 1978 (vs); νCO 1652 (s) cm−1. 1H NMR (400 MHz, d6-DMSO): 1.40−1.86 (m, 10H, 5CH2 of C6H11 group), 3.49 (s, 3H, OCH3), 4.16 (d, J = 20.8 Hz, 1H of CH2CO), 4.87 (d, J = 20.8 Hz, 1H of CH2CO), 4.34 (s, 1H, CH of C6H11 group), 5.52 (d, J = 6.8 Hz, 1H of OCH2O), 5.59 (d, J = 6.8 Hz, 1H of OCH2O), 7.11 (d, J = 8.4 Hz, 1H, 3-H of C5H3N), 7.27 (d, J = 7.2 Hz, 1H, 5-H of C5H3N), 7.95 (t, J = 7.8 Hz, 1H, 4-H of C5H3N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 22.3, 24.8, 32.1, 54.0 (CH2 of C6H11 group), 56.3 (OCH3), 67.7 (CH2CO), 94.7 (OCH2O), 106.9, 115.5, 141.0, 162.0, 164.7 (C5H3N), 151.3 (CH of C6H11 group), 213.7, 214.2 (CO), 264.1 (CH2CO) ppm. Preparation of η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(2SC5H4N) (9). The same procedure as that for 5 was followed but 2KSC5H4N (0.045 g, 0.3 mmol) was employed instead of KSCN. From the major yellow band, 9 (0.122 g, 93%) was obtained as a yellow solid. mp 108 °C (dec). Anal. Calcd for C16H14FeN2O5S: C, 47.78; H, 3.51; N, 6.96. Found: C, 47.55; H, 3.51; N, 6.81. IR (KBr disk): νCO 2023 (vs), 1959 (vs); νCO 1651 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 3.14 (s, 3H, OCH3), 3.64 (d, J = 19.2 Hz, 1H of CH2CO), 4.39 (d, J = 19.2 Hz, 1H of CH2CO), 5.18 (s, 2H, OCH2O), 6.55 (d, J = 8.0 Hz, 1H, 3-H of SC5H4N), 6.81 (t, J = 6.2 Hz, 1H, 5-H of SC5H4N), 6.89 (d, J = 8.4 Hz, 1H, 3-H of C5H3N), 7.14 (d, J = 7.2 Hz, 1H, 5-H of C5H3N), 7.24 (t, J = 7.6 Hz, 1H; 4-H of SC5H4N), 7.76 (t, J = 7.8 Hz, 1H, 4-H of C5H3N), 8.19 (d, J = 5.2 Hz, 1H, 6-H of SC5H4N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 56.9 (OCH3), 64.4 (CH2CO), 95.4 (OCH2O), 107.8, 116.5, 118.0, 125.1, 136.2, 142.0, 152.8, 161.9, 165.6, 176.2 (C5H3N, SC5H4N), 211.2, 214.9 (CO), 264.8 (CH2CO) ppm. Preparation of η2-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(8SC9H6N) (10). The same procedure as that for 5 was followed except that 8-KSC9H6N (0.060 g, 0.3 mmol) was used in place of KSCN. From the major yellow band, 10 (0.127 g, 94%) was obtained as a yellow solid. mp 126 °C (dec). Anal. Calcd for C20H16FeN2O5S: C, 53.11; H, 3.57; N, 6.19. Found: C, 52.93; H, 3.63; N, 6.10. IR (KBr disk): νCO 2018 (vs), 1954 (vs); νCO 1647 (s) cm −1. 1H NMR (400 MHz, acetone-d6): 2.75 (s, 3H, OCH3), 3.92 (d, J = 19.8 Hz, 1H of CH2CO), 4.36 (d, J = 19.8 Hz, 1H of CH2CO), 4.66 (d, J = 7.2 Hz, 1H of OCH2O), 4.77 (d, J = 7.2 Hz, 1H of OCH2O), 6.78 (d, J = 8.4 Hz, 1H, 3-H of C5H3N), 7.25 (d, J = 7.2 Hz, 1H, 5-H of C5H3N), 7.30 (t, J = 7.6 Hz, 1H, 6-H of C9H6N), 7.44 (d, J = 8.0 Hz, 1H, 7-H of C9H6N), 7.64 (d, J = 7.2 Hz, 1H, 5-H of C9H6N), 7.70 (s, 1H, 3-H of C9H6N), 7.83 (t, J = 7.8 Hz, 1H, 4-H of C5H3N), 8.42 (d, J = 8.0 Hz, 1H; 4-H of C9H6N), 9.66 (d, J = 4.4 Hz, 1H, 2-H of C9H6N) ppm.

toluenesulfonyl chloride (4.70 g, 24.7 mmol) were added. After stirring at 0 °C for 1 h, the mixture was warmed to room temperature and then stirred at this temperature for 2 h. To this mixture was added water (100 mL), and the mixture was then extracted with dichloromethane (3 × 100 mL). After the extracts were washed with water (2 × 100 mL), the organic phase was dried over anhydrous magnesium sulfate. After the drying agent and solvent were removed, 3 (5.69 g, 96%) was obtained as a white solid. mp 52−53 °C. Anal. Calcd for C15H17NSO5: C, 55.71; H, 5.30; N, 4.33. Found: C, 55.63; H, 5.17; N, 4.15. IR (KBr disk): νSO 1364 (s), 1177 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 2.43 (s, 3H, CH3C6H4), 3.48 (s, 3H, OCH3), 5.01 (s, 2H, CH2OSO2), 5.41 (s, 2H, OCH2O), 6.70 (d, J = 8.4 Hz, 1H, 3-H of C5H3N), 6.99 (d, J = 7.2 Hz, 1H, 5-H of C5H3N), 7.33 (d, J = 7.8 Hz, 2H, 3,5-H of C6H4), 7.58 (t, J = 7.8 Hz, 1H, 4-H of C5H3N), 7.81 (d, J = 7.8 Hz, 2H, 2,6-H of C6H4) ppm. 13C{1H} NMR (100 MHz, CDCl3): 21.6 (CH3), 57.2 (OCH3), 71.4 (CH2OSO2), 91.8 (OCH2O), 110.9, 115.4, 128.1, 129.9, 132.9, 139.8, 145.0, 151.3, 162.2 (C6H4, C5H3N) ppm. Preparation of η3-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(I) (4). A suspension of Na2Fe(CO)4·(1,4-dioxane)1.5 (0.346 g, 1.0 mmol) in MeCN (20 mL) was cooled to 0 °C, and 3 (0.323 g, 1.0 mmol) was added. After the mixture was stirred at this temperature for 0.5 h, I2 (0.254 g, 1.0 mmol) was added, and the new mixture continued to be stirred at 0 °C for an additional 0.5 h to give a brown-yellow solution. The solvent was evaporated at reduced pressure, leaving a residue that was subjected to column chromatography (silica gel). Petroleum ether/acetone (2:1, v/v) eluted a major yellow band, from which 4 (0.194 g, 46%) was obtained as a yellow solid. mp 96 °C (dec). Anal. Calcd for C11H10FeINO5: C, 31.54; H, 2.41; N, 3.34. Found: C, 31.61; H, 2.29; N, 3.42. IR (KBr disk): νCO 2031 (vs), 1962 (vs); νCO 1666 (vs) cm−1. 1H NMR (400 MHz, acetone-d6): 3.96 (s, 3H, OCH3), 4.14 (d, J = 19.4 Hz, 1H of CH2CO), 4.56 (d, J = 19.4 Hz, 1H of CH2CO), 5.31 (d, J = 6.8 Hz, 1H of OCH2O), 5.65 (d, J = 6.8 Hz, 1H of OCH2O), 7.15 (d, J = 7.2 Hz, 1H, 3-H of C5H3N), 7.48 (d, J = 6.4 Hz, 1H, 5-H of C5H3N), 8.07 (t, J = 7.4 Hz, 1H, 4-H of C5H3N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 63.2 (OCH3), 65.3 (CH2CO), 96.2 (OCH2O), 114.4, 118.7, 143.0, 160.4, 166.9 (C5H3N), 210.4, 213.8 (CO), 255.7 (CH2CO) ppm. Preparation of η3-(2-COCH2-6-MeOCH2OC5H3N)Fe(CO)2(NCS) (5). To a stirred solution of 4 (0.126 g, 0.3 mmol) in MeCN (20 mL) was added KSCN (0.030 g, 0.3 mmol), and the mixture was then stirred at room temperature for 1 h to give a yellow solution. After the solvent was removed, the residue was subjected to column chromatography (silica gel) under anaerobic conditions. Elution with petroleum ether/acetone (4:1, v/v) developed a major yellow band, from which 5 (0.100 g, 96%) was obtained as a yellow solid. mp 87 °C (dec). Anal. Calcd for C12H10FeN2O5S: C, 41.16; H, 2.88; N, 8.00. Found: C, 41.19; H, 3.05; N, 8.05. IR (KBr disk): νNCS 2098 (s), νCO 2045 (s), 1981 (s); νCO 1673 (vs) cm−1. 1H NMR (400 MHz, acetone-d6): 3.96 (s, 3H, OCH3), 4.16 (d, J = 20.0 Hz, 1H of CH2CO), 4.48 (d, J = 20.0 Hz, 1H of CH2CO), 5.29 (d, J = 7.4 Hz, 1H of OCH2O), 5.48 (d, J = 7.4 Hz, 1H of OCH2O), 7.20 (d, J = 8.4 Hz, 1H, 3-H of C5H3N), 7.53 (d, J = 7.6 Hz, 1H, 5-H of C5H3N), 8.14 (t, J = 8.0 Hz, 1H, 4-H of C5H3N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 59.5 (OCH3), 63.0 (CH2CO), 96.2 (OCH2O), 141.3 (NCS), 113.6, 117.9, 142.6, 159.2, 166.1 (C5H3N), 205.6, 207.2 (C O), 252.8 (CH2CO) ppm. Preparation of η 3 -(2-COCH 2 -6-MeOCH 2 OC 5 H 3 N)Fe(CO)2(S2CPh) (6). The same procedure as that for 5 was followed except that PhCS2K (0.058 g, 0.3 mmol) was utilized in place of KSCN. From the major brown band, 6 (0.133 g, 92%) was obtained as a brown solid. mp 82 °C (dec). Anal. Calcd for C18H15FeNO5S2: C, 48.55; H, 3.40; N, 3.15. Found: C, 48.76; H, 3.19; N, 3.21. IR (KBr disk): νCO 2029 (vs), 1972 (vs); νCO 1658 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 3.59 (s, 3H, OCH3), 3.91(d, J = 19.8 Hz, 1H of CH2CO), 4.73 (d, J = 19.8 Hz, 1H of CH2CO), 5.54 (s, 2H, OCH2O), 7.15 (d, J = 8.0 Hz, 1H, 3-H of C5H3N), 7.33 (d, J = 6.8 Hz, 1H, 5-H of C5H3N), 7.44 (t, J = 7.0 Hz, 2H, m-H of C6H5), 7.62 (t, J = 6.8 Hz, 1H, p-H of C6H5), 7.95 (t, J = 7.6 Hz, 1H, 4-H of C5H3N), 8.09 (d, J = 7.2 Hz, 2H, o-H of C6H5) ppm. 13C{1H} NMR (100 MHz, acetoneI


Article

Inorganic Chemistry Table 4. Crystal Data and Structure Refinement Details for 4, 5, 7, and 9 mol formula mol wt cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc/g·cm−3 abs coeff/mm−1 F(000) index ranges

no. of reflns no. of ind reflns 2θmax/deg R Rw goodness of fit largest diff peak, hole/e Å−3

4

5

7

9

C11H10FeINO5 418.95 orthorhombic Pbca 12.149(2) 13.696(3) 16.327(3) 90 90 90 2716.8(9) 8 2.049 3.397 1616 −13 ≤ h ≤ 15 −16 ≤ k ≤ 18 −21 ≤ l ≤ 20 19 543 3228 55.76 0.0323 0.0647 1.169 1.598/−1.794

C12H10FeN2O5S 350.13 monoclinic P21/c 9.0498(17) 7.2069(14) 21.894(4) 90 91.65(3) 90 1427.4(5) 4 1.629 1.224 712 −11 ≤ h ≤ 11 −9 ≤ k ≤ 7 −28 ≤ l ≤ 28 12 689 3355 55.80 0.0319 0.0742 1.075 0.367/−0.478

C29H25FeIO5P·CH2Cl2 766.15 triclinic P1̅ 9.0675(18) 10.729(2) 16.273(3) 76.18(3) 85.14(3) 89.20(3) 1531.7(5) 2 1.661 1.767 764 −11 ≤ h ≤ 11 −13 ≤ k ≤ 13 −21 ≤ l ≤ 21 15 712 7207 55.82 0.0359 0.0877 1.024 0.591/−0.806

C16H14FeN2O5S 402.20 orthorhombic P212121 10.514(3) 11.132(3) 14.619(5) 90 90 90 1711.1(9) 4 1.561 1.032 824 −12 ≤ h ≤ 13 −14 ≤ k≤ 14 −18 ≤ l ≤ 1 16 685 4082 55.78 0.0200 0.0399 1.039 0.210/−0.367

mmol) in MeCN (50 mL) was cooled to 0 °C, and 2,6(TsOCH2)2C5H3N (0.460 g, 1.0 mmol) was added. After the mixture was stirred at this temperature for 0.5 h, (PhS)2 (0.218 g, 1.0 mmol) was added and the new mixture was stirred at room temperature for an additional 1 h to give a brown solution. After volatiles were removed at reduced pressure, the residue was subjected to column chromatography (silica gel). Elution with CH2Cl2/acetone (v/v = 10:1) developed a major yellow band, from which 13 (0.354 g, 77%) was obtained as a yellow solid. mp 147−148 °C. Anal. Calcd for C22H17FeNO3S2: C, 57.03; H, 3.70; N, 3.02. Found: C, 56.98; H, 3.74; N, 3.10. IR (KBr disk): νCO 2016 (vs), 1956 (vs); νCO 1658 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 3.86 (d, J = 21.2 Hz, 1H of CH2CO), 4.14 (d, J = 21.2 Hz, 1H of CH2CO), 5.03 (s, 2H, CH2S), 6.90−7.94 (m, 13H, 2C6H5, C5H3N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 44.7 (CH2S), 64.7 (CH2CO), 120.5, 121.1, 124.4, 127.3, 127.4, 128.3, 129.8, 135.4, 138.6, 143.2, 158.6, 160.7 (C6H5, C5H3N), 206.3, 212.8 (CO), 255.1 (CH2CO) ppm. Preparation of η3-[2-COCH2-6-(2-S-5-MeC4H2O)C5H3N]Fe(CO)2(2-S-5-MeC4H2O) (14). To the same mixture prepared from Na2Fe(CO)4·(1,4-dioxane)1.5 and 2,6-(TsOCH2)2C5H3N in MeCN as described above was added (2-S-5-MeC4H2O)2 (0.226 g, 1.0 mmol), and the new mixture was then stirred at room temperature for 1 h to give a brown solution. The same workup as that for the preparation of 13 gave complex 14 (0.221 g, 47%) as a yellow solid. mp 136 °C (dec). Anal. Calcd for C20H17FeNO5S2: C, 50.97; H, 3.64; N, 2.97. Found: C, 50.81; H, 3.40; N, 3.15. IR (KBr disk): νCO 2016 (vs), 1956 (vs); νCO 1662 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 1.94, 2.25 (2s, 6H, 2CH3), 3.89 (d, J = 20.8 Hz, 1H of CH2CO), 4.07 (d, J = 20.8 Hz, 1H of CH2CO), 4.53 (d, J = 17.0 Hz, 1H of CH2S), 4.88 (d, J = 17.0 Hz, 1H of CH2S), 5.61, 6.33, 6.93, 7.38 (4s, 4H, 2C4H2O), 7.40−7.84 (m, 3H, C5H3N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 10.6, 10.8 (CH3), 46.9 (CH2S), 64.3 (CH2CO), 110.6, 111.7, 114.4, 114.6, 117.0, 119.9, 120.3, 137.9, 141.8, 152.1, 153.1, 157.9, 160.4 (C4H2O, C5H3N), 206.3, 212.5 (CO), 254.1 (CH2CO) ppm. X-ray Crystal Structure Determinations of 4, 5, 7, 9, and 11− 13. Single crystals of 4, 5, 7, 9, and 11−13 suitable for X-ray diffraction analysis were grown by slow diffusion of hexane into their

13

C{1H} NMR (100 MHz, acetone-d6): 55.4 (OCH3), 64.8 (CH2CO), 93.6 (OCH2O), 106.7, 115.8, 119.8, 122.0, 127.2, 129.3, 130.1, 138.0, 140.7, 150.4, 152.3, 154.8, 160.8, 165.7 (C5H3N, C9H6N), 208. 4, 213.8 (CO), 263.4 (CH2CO) ppm. Preparation of η3-[2,6-(COCH2)2C5H3N]Fe(CO)2(PPh3) (11). A suspension of Na2Fe(CO)4·(1,4-dioxane)1.5 (0.346 g, 1.0 mmol) in MeCN (50 mL) was cooled to 0 °C, and 2,6-(TsOCH2)2C5H3N (0.460 g, 1.0 mmol) was added. After the mixture was stirred at this temperature for 0.5 h, PPh3 (0.262 g, 1.0 mmol) was added and the new mixture was stirred at room temperature for an additional 1 h to give a brown solution. After volatiles were removed at reduced pressure, the residue was subjected to column chromatography (silica gel). Elution with CH2Cl2/acetone (v/v = 20:1) developed a major yellow band, from which 11 (0.258 g, 48%) was obtained as a yellow solid. mp 155 °C (dec). Anal. Calcd for C29H22FeNO4P: C, 65.07; H, 4.14; N, 2.62. Found: C, 65.20; H, 4.19; N, 2.81. IR (KBr disk): νCO 2006 (vs), 1949 (s); νCO 1614 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 3.10 (d, J = 21.2 Hz, 2H of 2CH2CO), 3.59 (d, J = 21.2 Hz, 2H of 2CH2CO), 7.32−7.81 (m, 18H, C6H5, C5H3N) ppm. 31P {1H} NMR (162 MHz, acetone-d6, H3PO4): 42.6 (s, PPh3) ppm. 13 C{1H} NMR (100 MHz, acetone-d6): 66.6 (CH2CO), 120.1, 128.3, 128.4, 130.4, 131.8, 132.2, 133.5, 133.6, 137.1, 161.7 (C6H5, C5H3N), 209.5, 209.8, 214.7, 215.0 (CO), 278.9, 279.1 (CH2CO) ppm. Preparation of η3-[2,6-(COCH2)2C5H3N]Fe(CO)3 (12). The same mixture prepared from Na2Fe(CO)4·(1,4-dioxane)1.5 and 2,6(TsOCH2)2C5H3N in MeCN as described above was stirred and bubbled with carbon monoxide at room temperature for 1 h to give a brown solution. After the same workup as that for the preparation of 11, complex 12 (0.073 g, 24%) was obtained as a yellow solid. mp 165 °C (dec). Anal. Calcd for C12H7FeNO5: C, 47.88; H, 2.34; N, 4.65. Found: C, 48.13; H, 2.62; N, 4.92. IR (KBr disk): νCO 2039 (vs), 1972 (vs); νCO 1684 (s) cm−1. 1H NMR (400 MHz, acetone-d6): 4.21 (s, 4H, 2CH2CO), 7.72 (s, 2H, 3-H and 5-H of C5H3N), 8.06 (t, J = 7.8 Hz, 1H, 4-H of C5H3N) ppm. 13C{1H} NMR (100 MHz, acetone-d6): 68.9 (CH2CO), 121.6, 139.6, 162.8 (C5H3N), 207.5, 210.0 (CO), 265.8 (CH2CO) ppm. Preparation of η3-(2-COCH2-6-PhSCH2C5H3N)Fe(CO)2(PhS) (13). A suspension of Na2Fe(CO)4·(1,4-dioxane)1.5 (0.346 g, 1.0 J


Article

Inorganic Chemistry Table 5. Crystal Data and Structure Refinement Details for 11−13 mol formula mol wt cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc/g·cm−3 abs coeff/mm−1 F(000) index ranges

no. of reflns no. of ind reflns 2θmax/deg R Rw goodness of fit largest diff peak, hole/e Å−3

11

12

13

C29H22FeNO4P·CH2Cl2 620.22 monoclinic P21/c 9.694(3) 16.045(4) 18.325(5) 90 101.322(3) 90 2794.8(13) 4 1.474 0.825 1272 −12 ≤ h ≤ 12 −20 ≤ k ≤ 21 −24 ≤ l ≤ 24 32 724 6688 55.86 0.0329 0.0865 1.058 0.819/−0.446

C12H7FeNO5 301.04 monoclinic P21/n 10.750(5) 8.546(3) 12.793(5) 90 96.989(8) 90 1166.5(9) 4 1.714 1.308 608 −14 ≤ h ≤ 13 −11 ≤ k ≤ 11 −16 ≤ l ≤ 16 11 625 2779 55.82 0.0240 0.0651 1.025 0.248/−0.423

C22H17FeNO3S2·CH2Cl2 548.26 monoclinic P21/c 8.8635(18) 26.586(5) 10.356(2) 90 108.507(2) 90 2314.1(8) 4 1.574 1.090 1120 −11 ≤ h ≤ 11 −34 ≤ k ≤ 32 −13 ≤ l ≤ 13 24 024 5509 55.74 0.0293 0.0712 1.045 0.382/−0.463

CH2Cl2 solutions at −4 or 0 °C. Each of the single crystals was mounted on a Rigaku MM-007 (rotating anode) diffractometer equipped with a Saturn 70 CCD. Data were collected using a confocal monochromator with Mo Kα radiation (λ = 0.71073 Å) in the ω-2θ scanning mode at 113 K. Data collection, reduction, and absorption correction were performed using the CRYSTALCLEAR program.48 All structures were solved by direct methods using the SHELXS-97 program49 and refined by full-matrix least-squares techniques (SHELXL-97)50 on F2. Hydrogen atoms were located by using the geometric method. Crystal data, data collection, and structure refinement details are summarized in Tables 4 and 5.

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and the National Natural Science Foundation of China (21132001, 21272122, and 21472095) for financial support of this work.

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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.inorgchem.5b02490. In situ IR monitoring experiments for the formation of complex 4 and the reaction course of 2,6(TsOCH2)2C5H3N with Na2Fe(CO)4; NMR/IR spectra of representative complexes 6, 9, 11, and 13 (PDF) Full tables of crystal data, atomic coordinates and thermal parameters, and bond lengths and angles for 4, 5, 7, 9, and 11−13 (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Ministry of Science and Technology of China (973 programs 2014CB845604 and 2011CB935902) K


Article

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