Reversible CO Dissociation of Tricarbonyl Iodide [Fe]-Hydrogenase

Article pubs.acs.org/Organometallics

Reversible CO Dissociation of Tricarbonyl Iodide [Fe]-Hydrogenase Models Ligating Acylmethylpyridyl Ligands Bowen Hu,† Xiangyang Chen,‡,§ Dawei Gong,† Wen Cui,† Xinzheng Yang,*,‡ and Dafa Chen*,† †

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150001, People’s Republic of China ‡ Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China § University of Chinese Academy of Sciences, Beijing, People’s Republic of China S Supporting Information *

ABSTRACT: A combined experimental and computational investigation of the CO dissociation properties of three [Fe]hydrogenase models, [(2-CH2CO-6-HOC5H3N)Fe(CO)3I] (1), [(2-CH2CO-6-MeOC5H3N)Fe(CO)3I] (2), and [(2-CH2CO-6t-BuOC5H3N)Fe(CO)3I] (3), shows equilibria of tricarbonyl and dicarbonyl complexes in solution. In CH3CN, 1 transforms to the solvated product [(2-CH 2 CO-6-HOC 5 H 3 N)Fe(CO)2(CH3CN)I] (7). The reactivity of 2 with PPh3 was also explored, giving [(2-CH2CO-6-MeOC5H3N)Fe(CO)2(PPh3)I] (8) via one CO substitution by PPh3.

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INTRODUCTION Three wild types of hydrogenases, [FeFe]-, [NiFe]-, and [Fe]hydrogenases, have been identified and characterized.1−7 Different from the other two types of hydrogenases with two metal atoms, the active site of [Fe]-hydrogenase only contains one Fe atom, which is coordinated by two cis-COs, a cysteine sulfur atom (Cys 176), a labile water, and a bidentate acylmethylpyridinol ligand (Figure 1). [Fe]-hydrogenase can catalyze the activation of H2 in the presence of methenyltetrahydromethanopterin (methenyl-H4MPT+).8,9

Fe(CO)3I] (2) with [Fe]-hydrogenase apoenzyme, respectively.49 Interestingly, only the semisynthetic enzyme reconstituted from 1 is active. DFT calculations indicate the deprotonated 2-hydroxyl serves as an internal base, which reduces the energy barrier for H2 activation. On the basis of this mechanism, Hu et al. successfully synthesized the first functional small-molecule mimic of [Fe]-hydrogenase by introducing Et2PCH2N(Me)CH2PEt2, which could act as a proton acceptor, into complex 2.38 1, 2, and the similar complex [(2-CH2CO-6-t-BuOC5H3N)Fe(CO)3I] (3) are not only structural models of [Fe]hydrogenase but also important precursors for functional models. However, they are not very stable in solution, and all of them have unusual 1H NMR and IR spectra: the two signals of the −CH2− groups in the 1H NMR spectrum are always mirror-unsymmetrical to each other in those three complexes. For example, 3 shows two mutually unsymmetrical doublets at 5.42 and 4.29 ppm in CDCl3, with the latter signal sharper and taller than the former.31 In addition to three main absorptions of the CO ligands in their IR spectra, there is a weak peak at around 1970 cm−1; for example, 3 in CH2Cl2 shows three strong absorptions at 2088, 2040, and 2008 cm−1 and a weak absorption at 1973 cm−1.31,50 Those unusual phenomena prompted us to explore their physical and chemical insights, which might be helpful for synthesizing more stable and effective functional models. In this paper, we report a combined experimental and computational investigation of the reversible CO dissociation properties of these model complexes.

Figure 1. Active site of [Fe]-hydrogenase.

After the report of the X-ray crystal structure of [Fe]hydrogenase, a number of its structural models have been synthesized,10−38 and many efforts have been made to understand its catalytic mechanism.39−49 Shima and coworkers’ experimental study reveals that the 2-hydroxyl group in the pyridinol ligand participates in the reaction of [Fe]hydrogenase with isocyanides.41 Computational studies also suggest that the 2-hydroxyl group is essencial for H 2 activation.42−48 Recently, two semisynthetic enzymes were reconstituted from the model complexes [(2-CH2CO-6HOC5H3N)Fe(CO)3I] (1) and [(2-CH2CO-6-MeOC5H3N)© XXXX American Chemical Society

Received: June 28, 2016

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DOI: 10.1021/acs.organomet.6b00524 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

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mutually unsymmetrical doublets for the −CH2− group. A similar phenomenon was discovered in a mixture of [(2CH2CO-6-MeOC5H3N)Fe(CO)2{S-(2-CF3-C6H4)}] and [(2CH2CO-6-MeOC5H3N)Fe(CO)3{S-(2-CF3-C6H4)}].30 Although the molecular formula and the configuration of two CO ligands of 6 can be confirmed, the exact structure of 6 is still unknown. The stabilities of five possible isomers have been examined through density functional theory (DFT) calculations. Figure 3 shows the calculated structures and their

RESULTS AND DISCUSSION CO Dissociation Properties of 1−3. The ν(CO) IR bands of complex 3 are similar in acetone and in CH2Cl2.31 When 3 was dissolved in acetone, it showed three strong absorptions and one weak absorption at 2086, 2036, and 2007 cm−1 and at 1969 cm−1, respectively (Figure 2a), and the

Figure 3. Structures and relative electronic energies of five possible isomers of 6.

relative electronic energies. Among all of these five structures, 6a with a vacant position trans to the carbonyl in the acylmethylpyridyl ligand is the most stable. 2 exhibits a similar dissociation property, evidenced by a weak absorption around 1970 cm−1 in its IR spectrum.50 By use of a procedure similar to the transformation of 3 to 6, parts of 2 were shown to convert to the dicarbonyl product 5 (Scheme 1), which was identified by IR spectra.50 The IR spectrum of 1 in acetone also has a weak peak at 1961 cm−1, and the ratio of the dicarbonyl complex [(2CH2CO-6-HOC5H3N)Fe(CO)2I] (4) to 1 increases in both CH3OH and THF (Figure S5 in the Supporting Information).50 We also tried to see if the ratio of 4 to 1 would increase in CH3CN in comparison to that in acetone. Unexpectedly, CO gas was formed immediately once 1 was dissolved in CH3CN, giving the p roduct [(2-CH 2 CO-6-HOC 5 H 3 N)Fe(CO)2(CH3CN)I] (7) (Scheme 2). The IR spectrum of 7

Figure 2. IR spectra: (a) 3 in acetone; (b) 3 in CH3CN; (c) 6 in acetone.

intensity ratio of the peak at 1969 cm−1 to that at 2086 cm−1 is about 1:6. When the solvent was changed to CH3CN, the ratio increased significantly to about 1:1 (Figure 2b). We then attempted to isolate the new complex in CH3CN. After the solution was dried under vacuum for 2 h, we surprisingly found that the IR spectrum of the residue in acetone had only two strong CO absorption bands with similar intensities at 2033 and 1969 cm−1 (Figure 2c), which indicates that the residue was mainly composed of the dicarbonyl complex 6 with two cisCOs. Interestingly, if this solution was left under N2 at room temperature for 24 h, most of 6 transferred back to 3. This means that the primary ligands in 3 and 6 are the same. Therefore, we propose that 6 has a molecular formula of [(2CH2CO-6-t-BuOC5H3N)Fe(CO)2I], and it is formed by the dissociation of one CO from 3 (Scheme 1). The selftransformation between 3 and 6 is quite similar to that of the [Fe]-hydrogenase models with thiolate ligands.30,31 This also explains the instability of 3 and the difficulty in isolating 6. Thus in fact, when 3 was dissolved in solution, it turned into a mixture of 3 and 6. Due to the fast transformation, the 1H NMR signals from the two species coalesced, resulting in two

Scheme 2. Reaction of 1 with CH3CN

Scheme 1. Equilibrium between Tricarbonyl Complexes and Dicarbonyl Complexes shows two ν(CO) absorptions at 2050 and 1996 cm−1 with almost the same intensities, which indicates the existence of two cis-COs (Figure 4). In fact, we previously reported the ν(CO) absorptions of 7 in CH3CN at 2068, 2050, and 1996 cm−1.31 We believe the peak at 2068 cm−1 belongs to some impurities in CH3CN. At that time the measured sample was in a very low concentration; therefore, the peak at 2068 cm−1 was relatively strong. We did not see the reaction between 1 and CH3CN in that study. Therefore, the previously reported 1H NMR B

DOI: 10.1021/acs.organomet.6b00524 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 3. Reaction of 2 with PPh3

at 69.6 ppm. 8 was further characterized by X-ray crystallography (Figure 6). The structure of 8 is similar to

Figure 4. IR spectrum of 7 in CH3CN.

spectrum of 1 in CD3CN belongs to 7 rather than 1. 7 only exists in CH3CN and cannot be isolated. It is interesting that only 1 shows reactivity with CH3CN. This suggests that, when the 2-hydroxyl group is replaced by other ligands, the reactivity of 1 might be quite different. We remeasured the 1H NMR spectrum of 1 in d6-acetone and found it exhibits three signals at 7.88, 7.25, and 7.04 ppm for the pyridyl ring and two doublets at 5.06 and 4.35 ppm for the diastereotopic methylene hydrogens. The two doublets of the −CH2− group are also not very symmetrical to each other.50 Similar to the case for 6, the exact structure of 7 cannot be determined from the current experimental data. Therefore, five isomers with two cis-COs, an iodide, and CH3CN ligand have been computationally examined. Their structures and relative electronic energies are shown in Figure 5. Among those five

Figure 6. Solid-state structure of 8. The thermal ellipsoids are displayed at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): Fe(1)−N(1), 2.038(3); Fe(1)−P(1), 2.2692(12); Fe(1)−C(7), 1.960(4); Fe(1)−C(27), 1.868(4); Fe(1)−C(28), 1.760(5); Fe(1)− I(1), 2.6849(7); C(7)−O(2), 1.222(5); C(27)−O(3), 1.127(4); C(28)−O(4), 1.146(5); C(27)−Fe(1)−C(28), 89.63(18); C(28)− Fe(1)−N(1), 170.65(17); C(7)−Fe(1)−N(1), 83.68(15); P(1)− Fe(1)−I(1), 172.57(4); C(7)−Fe(1)−C(27), 169.57(18).

that of the complex [(2-CH2CO-6-MeOCH2OC5H3N)Fe(CO)2(PPh3)I] reported by Song’s group.36 The Fe center is coordinated in a distorted-octahedral geometry. The C(28)− Fe(1)−N(1), P(1)−Fe(1)−I(1), and C(7)−Fe(1)−C(27) angles are 170.65(17), 172.57(4), and 169.57(18)°, respectively. The bidentate acylmethylpyridyl ligand coordinates with Fe via the pyridyl nitrogen and acyl carbon donors. The PPh3 ligand is trans to the iodide ligand. The two terminal CO groups are cis to each other. The IR spectrum shows two absorptions at 2022 and 1967 cm−1 for the terminal CO groups in the solid state, consistent with the existence of two cis-COs. A mixture of 2 and 5 was also treated with PPh3. The reaction was complete in about 5 min, much faster than that of 2, and also gave 8 in high yield. The results further confirm that 4−6 are dicarbonyl complexes.

Figure 5. Structures and relative electronic energies of possible isomers of 7.

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structures, 7b with an iodide trans to the carbonyl in the acylmethylpyridinol ligand is the most stable, while 7a with CH3CN trans to the carbonyl in the acylmethylpyridinol ligand is only 2.9 kcal/mol less stable than 7b. Reactions of 2 with PPh3. When 2 was treated with PPh3 in CH2Cl2 at room temperature, the reaction was complete in around 30 min and gave the product [(2-CH2CO-6-tMeOC5H3N)Fe(CO)2(PPh3)I] (8) (Scheme 3). The 1H NMR of 8 shows a triplet at 7.75 ppm and two doublets at 6.98 and 6.77 ppm for the pyridyl ring, a multiplet at 7.54−7.32 ppm for the PPh3 group, two doublets at 4.47 and 3.44 ppm for the methylene group, and a singlet at 3.79 ppm for the methoxyl group, respectively. The 31P NMR exhibits one signal

CONCLUSIONS In summary, the tricarbonyl [Fe]-hydrogenase models 1−3 exist in equilibria with dicarbonyl complexes 4−6 via reversible CO dissociation, which causes two mutually unsymmetrical doublets for the −CH2− group in each of their 1H NMR spectra and weak CO absorptions at around 1970 cm−1 in their IR spectra in solution. The CO dissociation might be part of the reason that 1−3 are not very stable in solution, and it suggests that when these kind of model are synthesized, the yields might be improved in the presence of external CO gas. DFT calculations suggest that the vacant positions are trans to C

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Organometallics

h at room temperature, and then the solvent was dried under vacuum for 2 h. The residue was solubilized in CH2Cl2 (5 mL), and the IR was recorded again immediately (Figure S4a in the Supporting Information). In comparison with the IR spectrum of 2 (Figure S4b), parts of 2 were shown to convert to 5. IR for 5 (νCO, CH2Cl2, cm−1): 2038 (s), 1973 (s). Equilibrium Studies of 1 with 4. Complex 1 (5.0 mg, 0.012 mmol) was dissolved in acetone (5 mL), and the IR was recorded (Figure S5a in the Supporting Information), showing that the main species is 1. However, when the solvent was changed to THF or CH3OH, the ratio of 4 to 1 increased (Figure S5b,c). When the solvent was evaporated, decomposition occurred. IR for 4 (νCO, CH3OH, cm−1): 2038 (s), 1972 (s). IR for 4 (νCO, THF, cm−1): 2034 (s), 1961 (s). Reaction of 1 with CH3CN. Complex 1 (5.0 mg, 0.012 mmol) was dissolved in CH3CN (5 mL), and a gas formed immediately, giving the dicarbonyl product 7, which was identified by IR spectroscopy. The 1H NMR of 7 has been reported in our previous report (Figure S7 in the Supporting Information),31 while that of 1 has not been reported (Figure S8 in the Supporting Information). 1 H NMR for 1 (400.13 MHz, d6-acetone): 7.88 (t, J = 8.0 Hz, 1H), 7.25 (d, J = 8.0 Hz, 1H), 7.04 (d, J = 8.0 Hz, 1H), 5.06 (d, J = 20.0 Hz, 1H), 4.35 (d, J = 20.0 Hz, 1H). IR for 7 (νCO, CH3CN, cm−1): 2050 (s), 1996 (s). Reaction of 2 with PPh3. PPh3 (38.0 mg, 0.145 mmol) was added to a solution of 2 (50.0 mg, 0.120 mmol) in CH2Cl2 (10 mL) with stirring at room temperature. After 30 min, the solvent was evaporated. The solid residue was washed with hexane (20 mL) and recrystallized from CH2Cl2/hexane to afford 8 (70.0 mg, 0.108 mmol; yield 90%) as a yellow solid. 1 H NMR (400.13 MHz, d6-acetone): 7.75 (t, J = 8.0 Hz, 1H), 7.54− 7.32 (m, 15H), 6.98 (d, J = 8.0 Hz, 1H), 6.77 (d, J = 8.0 Hz, 1H), 4.47 (d, J = 22.0 Hz, 1H), 3.79 (s, 3H), 3.44 (d, J = 22.0 Hz, 1H) ppm. 31P NMR (162 MHz, d6-acetone): 69.6 ppm. IR (νCO, KBr, cm−1): 2022 (s), 1967 (s). Anal. Calcd for C28H23FeINO4P: C, 51.64; H, 3.56; N, 2.15. Found: C, 51.80; H, 3.43, N, 2.12. Reaction of a Mixture of 2 and 5 with PPh3. Complex 2 (50.0 mg, 0.120 mmol)) was dissolved in CH3CN (20 mL), the solution was stirred for 1 h at room temperature, and then the solvent was dried under vacuum for 2 h. The residue was solublized in CH2Cl2 (10 mL), and PPh3 (38.0 mg, 0.145 mmol) was then added to the solution. After 5 min, the solvent was evaporated. The solid residue was washed with hexane (20 mL) and recrystallized from CH2Cl2/hexane to afford 8 (65.0 mg, 0.100 mmol; yield 83%).

the acylmethylpyridyl ligand in complexes 4−6, which is reasonable because the open positions of the similar fivecoordinate models with thiolate ligands30,31 and the H2-binding position of [Fe]-hydrogenase are all trans to the acylmethylpyridyl derivatives.9 PPh3 could replace one CO in complex 2 to form 8. Different from the case for 2 and 3, complex 1 could react with CH3CN to form the solvated product 7. This indicates that the reactivity is quite different when a 2-hydroxyl group is replaced by other ligands, which is important for the design of H2-related catalysts.51−56 Unlike 1−3 that exist as a mixture of tricarbonyl and dicarbonyl complexes, 7 is in a pure form in CH3CN, as confirmed by its −CH2− 1H NMR signals, which are mutually symmetrical to each other, with mirrorsymmetrical shapes and the same height.

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EXPERIMENTAL SECTION

Chemicals and Reagents. All manipulations were carried out under an inert N2(g) atmosphere using a Schlenk line. Solvents were distilled from appropriate drying agents under N2 before use. All reagents were purchased from commercial sources. Liquid compounds were degassed by standard freeze−pump−thaw procedures prior to use. Complexes 1−3 were prepared as described previously.26,31 Physical Methods. The 1H and 31P NMR spectra were recorded on a Bruker Avance 400 spectrometer. 1H NMR chemical shifts were referenced to residual solvent as determined relative to Me4Si (δ 0 ppm). The 31P{1H} chemical shifts were reported in ppm relative to external 85% H3PO4. IR spectra were recorded on a Nicolet iS5 FT-IR spectrometer. Elemental analyses were performed on a PerkinElmer 240C analyzer. X-ray diffraction studies were carried out with an Agilent CrysAlisPro X-ray single-crystal diffractometer. Data collections were performed using four-circle kappa diffractometers equipped with CCD detectors. Data were reduced and then corrected for absorption.57 Solution, refinement, and geometrical calculations for all crystal structures were performed by SHELXTL.58 Computational Details. All DFT calculations were performed by using the Gaussian 09 suite of programs59 for the M06 functional60 in conjugation with the all-electron 6-31++G(d,p) basis set61 for C, H, N, and O atoms. The Stuttgart relativistic effective core potential basis sets ECP10MDF and ECP46MDF were used for Fe and I, respectively.62,63 All structures were optimized in acetonitrile by using the integral equation formalism polarizable continuum model (IEFPCM)64 with SMD radii and cavity-dispersion-solvent-structure terms.65 Thermal corrections were calculated within the harmonic potential approximation on optimized structures at T = 298.15 K and 1 atm pressure. The calculated structures were verified to have no imaginary frequency (IF) for all structures. Equilibrium Studies of 3 with 6. Complex 3 (10.0 mg, 0.022 mmol) was dissolved in CH3CN (5 mL), and the IR was recorded (Figure S1 in the Supporting Information), showing a mixture of 3 and 6. The solution was stirred for 1 h at room temperature, and then the solvent was dried under vacuum for 2 h. The residue was solubilized in acetone (5 mL), and the IR was recorded again immediately (Figure S2a in the Supporting Information). From the IR spectrum, 3 almost completely converted into 6. The solution was then left under an N2 atmosphere at room temperature. The IR spectra were recorded again after 1 and 3 h, respectively (Figure S2b,c), indicating that most of 6 converted back to 3. Pure 6 and a satisfactory 1H NMR spectrum of 6 could not be obtained because of the equilibrium. When a small amount of 6 was dissolved in d6-acetone, after 24 h at room temperature, the 1H NMR showed that most of 6 changed back to 3 (Figure S6 in the Supporting Information). If 3 was dissolved in acetone rather than CH3CN, after the solution was stirred for 1 h and dried under vacuum for 2 h, the IR spectrum in acetone showed a mixture of 3 and 6 (Figure S3 in the Supporting Information). IR for 6 (νCO, acetone, cm−1): 2033 (s), 1969 (s). Equilibrium Studies of 2 with 5. Complex 2 (10.0 mg, 0.024 mmol) was dissolved in CH3CN (5 mL), the solution was stirred for 1

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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.6b00524.

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IR and NMR data (PDF) X-ray crystallographic data for 8 (CIF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail for X.Y.: [email protected]. *E-mail for D.C.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21302028 to D.C., 21201049 to B.H., and 21373228 to X.Y.). X.Y. acknowledges financial support from the “100-Talent Program” of the Chinese Academy of D

DOI: 10.1021/acs.organomet.6b00524 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Sciences. B.H. acknowledges financial support from the China Postdoctoral Science foundation (2016M591519).

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(37) Durgaprasad, G.; Xie, Z.-L.; Rose, M. J. Inorg. Chem. 2016, 55, 386−389. (38) Xu, T.; Yin, C.-J. M.; Wodrich, M. D.; Mazza, S.; Schultz, K. M.; Scopelliti, R.; Hu, X. J. Am. Chem. Soc. 2016, 138, 3270−3273. (39) Hiromoto, T.; Warkentin, E.; Moll, J.; Ermler, U.; Shima, S. Angew. Chem., Int. Ed. 2009, 48, 6457−6460. (40) Shima, S.; Vogt, S.; Göbels, A.; Bill, E. Angew. Chem., Int. Ed. 2010, 49, 9917−9921. (41) Tamura, H.; Salomone-Stagni, M.; Fujishiro, T.; Warkentin, E.; Meyer-Klaucke, W.; Ermler, U.; Shima, S. Angew. Chem., Int. Ed. 2013, 52, 9656−9659. (42) Yang, X.; Hall, M. B. J. Am. Chem. Soc. 2008, 130, 14036− 14037. (43) Yang, X.; Hall, M. B. J. Am. Chem. Soc. 2009, 131, 10901− 10908. (44) Dey, A. J. Am. Chem. Soc. 2010, 132, 13892−13901. (45) Finkelmann, A. R.; Stiebritz, M. T.; Reiher, M. J. Phys. Chem. B 2013, 117, 4806−4817. (46) Wodrich, M. D.; Hu, X. Eur. J. Inorg. Chem. 2013, 2013, 3993− 3999. (47) Murray, K. A.; Wodrich, M. D.; Hu, X.; Corminboeuf, C. Chem. - Eur. J. 2015, 21, 3987−3996. (48) Hedegård, E. D.; Kongsted, J.; Ryde, U. Angew. Chem., Int. Ed. 2015, 54, 6246−6250. (49) Shima, S.; Chen, D.; Xu, T.; Wodrich, M. D.; Fujishiro, T.; Schultz, K. M.; Kahnt, J.; Ataka, K.; Hu, X. Nat. Chem. 2015, 7, 995− 1002. (50) See the Supporting Information. (51) Moore, C. M.; Szymczak, N. K. Chem. Commun. 2013, 49, 400− 402. (52) Moore, C. M.; Dahl, E. W.; Szymczak, N. K. Curr. Opin. Chem. Biol. 2015, 25, 9−17. (53) Geri, J. B.; Szymczak, N. K. J. Am. Chem. Soc. 2015, 137, 12808− 12814. (54) Yang, X. Chem. Commun. 2015, 51, 13098−13101. (55) Shi, J.; Hu, B.; Gong, D.; Shang, S.; Hou, G.; Chen, D. Dalton Trans. 2016, 45, 4828−4834. (56) Moore, C. M.; Bark, B.; Szymczak, N. K. ACS Catal. 2016, 6, 1981−1990. (57) Blessing, R. H. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995, 51, 33−38. (58) Sheldrick, G. M. SHELXTL release 6.1.4 ed.; Bruker AXS Inc., Madison, WI 53719, USA, 2003. (59) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision C.01; Gaussian, Inc., Wallingford, CT, USA, 2009. (60) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241. (61) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865−3868. (62) Martin, J. M. L.; Sundermann, A. J. Chem. Phys. 2001, 114, 3408−3420. (63) Andrae, D.; Häußermann, U.; Dolg, M.; Stoll, H.; Preuß, H. Theor. Chim. Acta 1990, 77, 123−141. (64) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105, 2999−3094.

REFERENCES

(1) Shima, S.; Thauer, R. K. Chem. Rec. 2007, 7, 37−46. (2) Stiebritz, M. T.; Reiher, M. Chem. Sci. 2012, 3, 1739−1751. (3) Lubitz, W.; Ogata, H.; Rüdiger, O.; Reijerse, E. Chem. Rev. 2014, 114, 4081−4148. (4) Pulukkody, R.; Darensbourg, M. Y. Acc. Chem. Res. 2015, 48, 2049−2058. (5) Rauchfuss, T. B. Acc. Chem. Res. 2015, 48, 2107−2116. (6) Wombwell, C.; Caputo, C. A.; Reisner, E. Acc. Chem. Res. 2015, 48, 2858−2865. (7) Xu, T.; Chen, D.; Hu, X. Coord. Chem. Rev. 2015, 303, 32−41. (8) Shima, S.; Pilak, O.; Vogt, S.; Schick, M.; Stagni, M. S.; MeyerKlaucke, W.; Warkentin, E.; Thauer, R. K.; Ermler, U. Science 2008, 321, 572−575. (9) Hiromoto, T.; Ataka, K.; Pilak, O.; Vogt, S.; Stagni, M. S.; MeyerKlaucke, W.; Warkentin, E.; Thauer, R. K.; Shima, S.; Ermler, U. FEBS Lett. 2009, 583, 585−590. (10) Tard, C.; Pickett, C. J. Chem. Rev. 2009, 109, 2245−2274. (11) Wright, J. A.; Turrell, P. J.; Pickett, C. J. Organometallics 2010, 29, 6146−6156. (12) Corr, M. J.; Murphy, J. A. Chem. Soc. Rev. 2011, 40, 2279−2292. (13) Dey, S.; Das, P. K.; Dey, A. Coord. Chem. Rev. 2013, 257, 42−63. (14) Schultz, K. M.; Chen, D.; Hu, X. Chem. - Asian J. 2013, 8, 1068− 1075. (15) Royer, A. M.; Rauchfuss, T. B.; Gray, D. L. Organometallics 2009, 28, 3618−3620. (16) Royer, A. M.; Salomone-Stagni, M.; Rauchfuss, T. B.; MeyerKlaucke, W. J. Am. Chem. Soc. 2010, 132, 16997−17003. (17) Li, B.; Liu, T.; Popescu, C. V.; Bilko, A.; Darensbourg, M. Y. Inorg. Chem. 2009, 48, 11283−11289. (18) Liu, T.; Li, B.; Popescu, C. V.; Bilko, A.; Perez, L. M.; Hall, M. B.; Darensbourg, M. Y. Chem. - Eur. J. 2010, 16, 3083−3089. (19) Tanino, S.; Ohki, Y.; Tatsumi, K. Chem. - Asian J. 2010, 5, 1962−1964. (20) Turrell, P. J.; Wright, J. A.; Peck, J. N. T.; Oganesyan, V. S.; Pickett, C. J. Angew. Chem., Int. Ed. 2010, 49, 7508−7511. (21) Turrell, P. J.; Hill, A. D.; Ibrahim, S. K.; Wright, J. A.; Pickett, C. J. Dalton Trans. 2013, 42, 8140−8146. (22) Kalz, K. F.; Brinkmeier, A.; Dechert, S.; Mata, R. A.; Meyer, F. J. Am. Chem. Soc. 2014, 136, 16626−16634. (23) Obrist, B. V.; Chen, D.; Ahrens, A.; Schunemann, V.; Scopelliti, R.; Hu, X. Inorg. Chem. 2009, 48, 3514−3516. (24) Chen, D.; Scopelliti, R.; Hu, X. J. Am. Chem. Soc. 2010, 132, 928−929. (25) Chen, D.; Scopelliti, R.; Hu, X. Angew. Chem., Int. Ed. 2010, 49, 7512−7515. (26) Chen, D.; Scopelliti, R.; Hu, X. Angew. Chem., Int. Ed. 2011, 50, 5671−5673. (27) Chen, D.; Ahrens-Botzong, A.; Schuemann, V.; Scopelliti, R.; Hu, X. Inorg. Chem. 2011, 50, 5249−5257. (28) Chen, D.; Scopelliti, R.; Hu, X. Angew. Chem., Int. Ed. 2012, 51, 1919−1921. (29) Hu, B.; Chen, D.; Hu, X. Chem. - Eur. J. 2012, 18, 11528− 11530. (30) Hu, B.; Chen, D.; Hu, X. Chem. - Eur. J. 2013, 19, 6221−6224. (31) Hu, B.; Chen, D.; Hu, X. Chem. - Eur. J. 2014, 20, 1677−1682. (32) Song, L.-C.; Zhao, G.-Y.; Xie, Z.-J.; Zhang, J.-W. Organometallics 2013, 32, 2509−2512. (33) Song, L.-C.; Hu, F.-Q.; Zhao, G.-Y.; Zhang, J.-W.; Zhang, W.-W. Organometallics 2014, 33, 6614−6622. (34) Song, L.-C.; Xie, Z.-J.; Wang, M.-M.; Zhao, G.-Y.; Song, H.-B. Inorg. Chem. 2012, 51, 7466−7468. (35) Song, L.-C.; Hu, F.-Q.; Wang, M.-M.; Xie, Z.-J.; Xu, K.-K.; Song, H.-B. Dalton Trans. 2014, 43, 8062−8071. (36) Song, L.-C.; Xu, K.-K.; Han, X.-F.; Zhang, J.-W. Inorg. Chem. 2016, 55, 1258−1269. E

DOI: 10.1021/acs.organomet.6b00524 Organometallics XXXX, XXX, XXX−XXX

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Organometallics (65) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B 2009, 113, 6378−6396.

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DOI: 10.1021/acs.organomet.6b00524 Organometallics XXXX, XXX, XXX−XXX