Synthesis, Structures, and Some Properties of Diiron Oxadiselenolate

Article pubs.acs.org/Organometallics

Synthesis, Structures, and Some Properties of Diiron Oxadiselenolate (ODSe) and Thiodiselenolate (TDSe) Complexes as Models for the Active Site of [FeFe]-Hydrogenases Li-Cheng Song,* Bin Gai, Zhan-Heng Feng, Zong-Qiang Du, Zhao-Jun Xie, Xiao-Jing Sun, and Hai-Bin Song Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China S Supporting Information *

ABSTRACT: Parent complexes (μ-ODSe)Fe2(CO)6 (A, ODSe = SeCH 2 OCH 2 Se) and (μ-TDSe)Fe 2 (CO) 6 (B, TDSe = SeCH2SCH2Se) could be prepared by oxidative addition of (HSeCH2)2X (X = O, S) with Fe3(CO)12. While reactions of A with 1 equiv of monophosphines in the presence of the decarbonylating agent Me3NO afforded the corresponding phosphine-monosubstituted complexes (μ-ODSe)Fe2(CO)5(L) (1, L = Ph3P; 2, L = Ph2POMe), the N-heterocyclic carbene (NHC)-monosubstituted complexes (μ-ODSe)Fe2(CO)5(L) (3, L = IMes; 4, L = IMes/Me) were prepared by reactions of the 1,3bis(mesityl)imidazolium salt IMes·HCl and 1-mesityl-3-methylimidazolium salt IMes/Me·HI with n-BuLi, followed by treatment of the corresponding NHC intermediates with A. The phosphinecontaining imidazolium salt IMes/CH2CH2PPh2·HCl reacted with A in the presence of Me3NO to give the imidazolium/ phosphine-monosubstituted complex (μ-ODSe)Fe2(CO)5(IMes/CH2CH2PPh2·HCl) (5), whereas it reacted with t-BuOK or n-BuLi, followed by treatment of A with the resulting intermediate NHC/phosphine or both the resulting NHC/phosphine and phosphine Ph 2 PCHCH 2 , to afford the corresponding NHC/phosphine-disubstituted complex [(μ-ODSe)Fe2(CO)5]2(IMes/CH2CH2PPh2) (6) and complex 6 along with (μ-ODSe)Fe2(CO)5(Ph2PCHCH2) (7), respectively. In addition, 7 could also be produced simply by reaction of 6 with n-BuLi. The phosphine-monosubstituted complexes (μTDSe)Fe2(CO)5(L) (8, L = Ph3P; 9, L = Ph2PH) were similarly prepared by reactions of B with 1 equiv of the corresponding monophosphines in the presence of Me3NO, whereas reaction of B with m-chloroperoxybenzoic acid afforded the corresponding bridgehead S atom-oxidized complex (μ-TDSeO)Fe2(CO)6 (10, TDSeO = SeCH2S(O)CH2Se). While complexes A/B and 1− 10 were structurally characterized, a comparative study on H2 production from HOAc catalyzed by parent complexes A/B and their sulfur analogues (μ-ODT)Fe2(CO)6/(μ-TDT)Fe2(CO)6 was carried out.

■

INTRODUCTION Hydrogenases are natural enzymes that can catalyze hydrogen metabolism in a broad range of prokaryotic and eukaryotic microorganisms.1 According to the metal content in the active site, hydrogenases are generally classified as [NiFe]-hydrogenases,2 [FeFe]-hydrogenases,3 and [Fe]-hydrogenases (Hmd).4 Recently, [FeFe]-hydrogenases (hereafter referred to as [FeFe]Hases) have attracted considerable attention, largely owing to their unusual structures and particularly their high catalytic ability for the production of “clean” and renewable hydrogen fuel.5 The X-ray crystallographic,6−9 FTIR spectroscopic,10−12 and theoretical13 studies revealed that the active site of [FeFe]Hases, the so-called H-cluster, is composed of a butterfly [Fe2S2] cluster with one of its iron atoms linked to a cubic [Fe4S4] cluster via the sulfur atom of a cysteinyl group; in addition, the two iron atoms in the butterfly cluster are bridged by a dithiolate cofactor (SCH2XCH2S; X = CH2, NH, or O) and coordinated by a given amount of CO and CN− ligands © 2013 American Chemical Society

(Figure 1). It is worthy of note that the dithiolate cofactor was originally assigned as a propanedithiolate (PDT, SCH2CH2CH2S)7 but later assigned as an azadithiolate (ADT, SCH2NHCH2S).8 Very recently, Lubitz and co-workers have presented 14N HYSCORE evidence to support the aforementioned assignment of an azadithiolate,14a whereas Szilagyi has suggested the dithiolate cofactor to be an

Figure 1. Basic structure of H-cluster (X = CH2, NH, or O). Received: April 10, 2013 Published: June 19, 2013 3673

dx.doi.org/10.1021/om400309j | Organometallics 2013, 32, 3673−3684

Organometallics

Article

The molecular structure of A was unequivocally confirmed by X-ray crystal diffraction analysis. The ORTEP view of A is depicted in Figure 2, whereas Table 1 lists its selected bond

oxadithiolate (ODT, SCH2OCH2S) by using an X-ray crystallographic refinement to close to atom resolution and the DFT optimizations.14b On the basis of successful structural elucidation regarding the H-cluster, a great number of biomimetic models have been prepared, such as those prepared by CO substitution reactions of the parent diiron all-carbonyl complexes (μ-PDT)Fe2(CO)6, (μ-ODT)Fe2(CO)6, (μ-TDT)Fe2(CO)6 (TDT = thiodithiolate = SCH2SCH2S), and (μ-PDSe)Fe2(CO)6 (PDSe = propanediselenolate = SeCH2CH2CH2Se) with various electron donors.15−25 It is worth pointing out that, although parent complex (μ-TDSe)Fe2(CO)6 (TDSe = thiodiselenolate = SeCH2SCH2Se) was recently prepared,26 there are no derivative to be reported, and particularly no parent complex (μ-ODSe)Fe 2 (CO) 6 (ODSe = oxadiselenolate = SeCH2OCH2Se) and its derivative have been reported, so far. Therefore, to further develop the biomimetic chemistry of [FeFe]Hases and to see some influences of the bridged chalcogen Se atoms and bridgedhead O/S atoms in such model complexes toward their structures and properties, we recently launched a study on the synthesis, structural characterization, and some properties of the ODSe- and TDSe-type models derived from their parent complexes (μ-ODSe)Fe2(CO)6 (A) and (μ-TDSe)Fe2(CO)6 (B). In this article we report the interesting results.

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

■

lengths and angles. Although the crystal structure of B was previously reported,26 we also determined the crystal structure of this complex that was prepared by our new method. While its ORTEP view is shown in Figure S1 (see the Supporting Information), the selected bond lengths and angles are given in Table S1 (see the Supporting Information). As shown in Figure 2 and Figure S1, complexes A and B contain an ODSe ligand and a TDSe ligand, respectively, each of which is bridged between two iron atoms with six carbonyls. Both Fe1 and Fe1A atoms in A and B adopt a slightly distorted square-pyramidal geometry, and the Fe1−Fe1A bond lengths in A and B (2.5599 Å for A and 2.5600 Å for B) are almost identical with that of their analogue (μ-PDSe)Fe2(CO)6 (2.556 Å),24 but much longer than the corresponding bond lengths of their analogues (μ-ODT)Fe2(CO)6 (2.5133 Å)31 and (μ-TDT)Fe2(CO)6 (2.5159 Å),32 apparently due to the larger size of the Se atom than the S atom. In addition, it is noteworthy that the bridgehead O4 atom in A and S1 atom in B are disordered (50%), which agrees very well with the solution 1H NMR spectra of A and B showing only one singlet at 4.46 and 3.29 ppm for their CH2 groups, respectively. Synthesis and Structural Characterization of Phosphine-Substituted ODSe-Type Model Complexes 1 and 2. We further found that the phosphine-monosubstituted ODSe-type models (μ-ODSe)Fe2(CO)5(L) (1, L = Ph3P; 2, L = Ph2POMe) could be prepared in 50% and 65% yields by treatment of A with an equimolar decarbonylating agent, Me3NO·2H2O,33 followed by treatment with the corresponding phosphines in MeCN at room temperature (Scheme 2). Complexes 1 and 2 were also characterized by elemental analysis and various spectroscopic methods. The IR spectra of 1 and 2 displayed three absorption bands in the range 2039− 1926 cm−1 for their terminal CO ligands. These νCO bands lie at much lower frequency compared to those (2065−1971 cm−1) of their parent complex A, due to CO substitution with the stronger electron-donating phosphine ligands.34 The 1H NMR spectra of 1 and 2 each showed two singlets in the region 3.50−4.18 ppm for the two chemically different protons in their

RESULTS AND DISCUSSION Synthesis and Structural Characterization of Parent Complexes A and B. Although the parent TDSe-type model complex (μ-TDSe)Fe2(CO)6 (B) is known and was prepared by reaction of S(CH2SeCN)2 with Fe3(CO)12,26 its analogue, namely, the parent ODSe-type model complex (μ-ODSe)Fe2(CO)6 (A) still remains unknown, up to now. However, we recently found a new method by which both A and B could be prepared conveniently. This method involves oxidative addition of the corresponding diselenols HSeCH2XCH2SeH (X = O, S) with Fe3(CO)12 in THF at reflux in 45% and 68% yields, respectively (Scheme 1). Scheme 1

Complexes A and B prepared by this new method were fully characterized by elemental analysis, various spectroscopies, and X-ray crystallography. The IR spectra of A and B displayed three to four absorption bands in the range 2068−1971 cm−1 for their terminal CO ligands. The 1H NMR spectra of A and B showed a singlet at 4.46 and 3.29 ppm for the two chemically equivalent protons in their CH2 groups caused by fast folding of the six-membered FeSe2C2O and FeSe2C2S rings, respectively.27 In addition, the 13C{1H} NMR spectra of A and B displayed a singlet at 60.6 and 17.6 ppm for the carbon atoms in their two chemically equivalent CH2 groups, whereas the 77 Se{1H} NMR spectra of A and B showed a singlet at 76.0 and 184.4 ppm for their two chemically equivalent Se atoms,22,28−30 respectively. 3674


Organometallics

Article

Table 1. Selected Bond Lengths (Å) and Angles (deg) for A Se(1)−C(4) Se(1)−Fe(1A) Se(1)−Fe(1) Se(2)−C(5) Fe(1)−Se(1)−Fe(1A) Fe(1)−Se(2)−Fe(1A) Se(1)−Fe(1)−Se(2) Se(1)−Fe(1)−Fe(1A)

1.985(4) 2.3681(8) 2.3681(8) 1.984(4) 65.43(3) 65.41(3) 86.36(2) 57.283(16)

Fe(1)−Se(2) Se(2)−Fe(1A) Fe(1)−Fe(1A) C(4)−O(4) Se(2)−Fe(1)−Fe(1A) C(1)−Fe(1)−Se(1) C(5)−O(4)−C(4) O(4)−C(4)−Se(1)

2.3688(7) 2.3689(7) 2.5599(10) 1.406(5) 57.296(13) 101.34(9) 112.9(3) 115.4(3)

Scheme 2

CH2 groups, due to slowed folding of the six-membered FeSe2C2O ring.27 Furthermore, 2 exhibited an additional doublet at 3.59 ppm for its methoxy hydrogen atoms attached to the Ph2P group with a coupling constant 3JP−H = 10.4 Hz. While the 31P{1H} NMR spectra of 1 and 2 showed a singlet at 67.9 and 171.1 ppm for their P atoms, the 77Se{1H} NMR spectra displayed a singlet at 34.3 and 60.4 ppm for their two chemically equivalent Se atoms, respectively. The molecular structures of 1 and 2 are shown in Figures 3 and 4, whereas Table 2 lists their selected bond lengths and

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

make the H-cluster models.35−37 This is mainly owing to their stronger σ-donation with negligible π-accepting ability, as well as their greater electronic and steric tunability in comparison with phosphine ligands.38−40 We found that the NHCsubstituted ODSe-type model complexes (μ-ODSe)Fe2(CO)5(IMes) (3) and (μ-ODSe)Fe2(CO)5(IMes/Me) (4) could be prepared by treatment of A in THF at room temperature with the NHC ligands IMes and IMes/Me, which were generated in situ by reactions of their precursors 1,3bis(mesityl)imidazolium salt IMes·HCl and 1-mesity-3-methylimidazolium salt IMes/Me·HI with n-BuLi41 in 52% and 47% yields, respectively (Scheme 3). The IR spectra of 3 and 4 showed three strong absorption bands in the range 2028−1910 cm−1 for its terminal CO ligands. These νC≡O bands of 3 and 4, similar to those of their phosphine analogues 1 and 2, lie at much more lower frequency compared to that of their parent compound A. This is because the NHC ligands, as mentioned above, are stronger σ-donors than phosphines and particularly than the terminal CO ligand.38−40 The 1H NMR spectrum of 3 displayed one singlet at 7.20 ppm for its two chemically equivalent imidazole H atoms, whereas 4 showed two singlets at 6.88 and 7.14 ppm for its two chemically different imidazole H atoms. The 13C{1H} NMR spectra of 3 and 4 each exhibited one signal at 192.5 and 187.0 ppm for their carbene C atoms,42,43 respectively, whereas the 77Se{1H} NMR spectra of 3 and 4 showed a singlet at −10.2 and 383.6 ppm for their two chemically equivalent Se atoms, respectively. The X-ray crystallographic study (Figures 5 and 6, Table 3) revealed that complexes 3 and 4 both contain an ODSe ligand bridged between the two iron atoms in their butterfly [Fe2Se2] cluster cores. In addition, their NHC ligands IMes and IMes/Me are coordinated with one square-pyramidal iron atom in an apical position and trans to their bridgehead O6 atoms. The Fe1−Fe2 bond length of 3 (2.5745 Å) is very close to that of 4 (2.587 Å), but somewhat longer than the corresponding bond


angles. As can be seen in Figures 3 and 4, they are indeed the phosphine-substituted derivatives of parent complex A, in which the phosphine ligands Ph3P and Ph2POMe in 1 and 2 are all located in the apical positions of their two square-pyramidal iron atoms, respectively. In addition, the bridgehead O6 atoms of 1 and 2 are trans to their phosphine ligands in order to avoid the strong steric repulsion of the bulky ligand Ph3P or Ph2POMe with its bridgehead structure unit. The Fe1−Fe2 bond length of 1 (2.5572 Å) is slightly longer than that of 2 (2.5305 Å), but nearly the same as that of its analogue (μPDSe)Fe2(CO)5(PPh3) (2.5533 Å).24 Synthesis and Structural Characterization of NHCSubstituted ODSe-Type Model Complexes 3 and 4. In recent years, N-heterocyclic carbenes (NHC) have been extensively utilized as surrogates for phosphines in order to 3675


Organometallics

Article

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and 2 1 Se(1)−C(6) Se(1)−Fe(1) Se(1)−Fe(2) Fe(2)−P(1) Fe(1)−Se(1)−Fe(2) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(1)−Se(1) Se(2)−Fe(1)−Fe(2)

1.996(5) 2.3938(9) 2.4018(9) 2.2382(14) 64.45(3) 64.78(3) 85.71 (3) 57.50(3)

Se(1)−C(6) Se(1)−Fe(2) Se(1)−Fe(1) Se(2)−Fe(1) Fe(1)−Se(1)−Fe(2) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(1)−Se(1) Se(2)−Fe(1)−Fe(2)

1.987(4) 2.3827(9) 2.4067(10) 2.3819(9) 63.78(3) 64.14(3) 85.54 (3) 57.97(3)

Fe(2)−Se(2) Se(2)−Fe(1) Fe(1)−Fe(2) C(6)−O(6) Se(1)−Fe(1)−Fe(2) P(1)−Fe(2)−Se(2) P(1)−Fe(2)−Fe(1) Se(2)−Fe(2)−Fe(1)

2.3839(11) 2.3900(9) 2.5572(12) 1.401(6) 57.93(2) 103.30(5) 156.27(5) 57.73(4)

Se(2)−Fe(2) Fe(1)−Fe(2) Fe(2)−P(1) C(6)−O(6) Se(1)−Fe(1)−Fe(2) P(1)−Fe(2)−Se(1) P(1)−Fe(2)−Fe(1) Se(1)−Fe(2)−Fe(1)

2.3840(10) 2.5305(12) 2.1885(13) 1.406(5) 57.65(3) 102.50(5) 151.78(4) 58.57(3)

2

Scheme 3


Synthesis and Structural Characterization of Imidazolium Salt-Containing Phosphine-Substituted ODSeType Model Complex 5, NHC-Containing PhosphineDisubstituted ODSe-Type Model Complex 6, and Diphenyl(vinyl)phosphine-Substituted ODSe-Type Model Complex 7. We further found that the imidazolium salt-containing phosphine-substituted model complex (μODSe)Fe2(CO)5(IMes/CH2CH2PPh2·HCl) (5) could be prepared in 59% yield by the Me3NO-assisted CO substitution reaction of parent complex A with the phosphine-containing imidazolium salt IMes/CH2CH2PPh2·HCl in MeCN at room temperature (Scheme 4). More interestingly, the NHC/phosphine-disubstituted model complex [(μ-ODSe)Fe2(CO)5]2(IMes/CH2CH2PPh2) (6) was found to be prepared in 26% yield by treatment of the NHC-containing phosphine IMes/CH2CH2PPh2 (generated in situ by reaction of the imidazolium salt IMes/CH2CH2PPh2·HCl with tBuOK), whereas treatment of the imidazolium salt IMes/CH2CH2PPh2·HCl with n-BuLi under similar conditions afforded both the NHC/phosphine-disubstituted complex 6 and the Ph2P(CHCH2)-monosubstituted model complex (μODSe)Fe2(CO)5(Ph2PCHCH2) (7) in 14% and 19% yields, respectively. Presumably, the concomitant formation of both 6 and 7 in the latter case is because the imidazolium saltcontaining phosphine IMes/CH2CH2PPh2·HCl could undergo both HCl-elimination and β-elimination in the presence of n-BuLi to give the NHC IMes/CH2CH2PPh2 and phosphine Ph2P(CHCH2)


lengths of their analogues (μ-PDSe)Fe2(CO)5(IMes) (2.559 Å)24 and (μ-PDT)Fe2(CO)5(IMes) (2.525 Å)31 or (μ-PDT)Fe2(CO)5(IMe) (2.5333 Å).35 3676


Organometallics

Article

Table 3. Selected Bond Lengths (Å) and Angles (deg) for 3 and 4 3 Se(1)−C(6) Se(1)−Fe(1) Se(1)−Fe(2) Se(2)−Fe(1) Fe(2)−Se(1)−Fe(1) Fe(1)−Se(2)−Fe(2) Se(2)−Fe(1)−Se(1) Se(2)−Fe(1)−Fe(2)

1.968(7) 2.4016(12) 2.3861(11) 2.3905(12) 65.06(4) 65.13(3) 85.69 (4) 57.48(3)

Fe(1)−C(8) Se(1)−Fe(2) Se(2)−Fe(1) Se(2)−Fe(2) Se(2)−Fe(1)−Se(1) Se(2)−Fe(1)−Fe(2) Se(1)−Fe(1)−Fe(2) Se(1)−Fe(2)−Se(2)

1.980(11) 2.370(2) 2.383(2) 2.377(2) 85.82(8) 56.97(6) 56.70(7) 86.44(7)

Fe(2)−Se(2) Fe(2)−C(8) Fe(1)−Fe(2) C(8)−N(1) Se(1)−Fe(1)−Fe(2) Se(1)−Fe(2)−Se(2) Se(1)−Fe(2)−Fe(1) Se(2)−Fe(2)−Fe(1)

2.3926(11) 1.989(7) 2.5745(13) 1.405(8) 57.18(3) 85.98(4) 57.76(3) 57.39(3)

Se(1)−Fe(1) Fe(1)−Fe(2) C(8)−N(1) Se(1)−C(6) Se(1)−Fe(2)−Fe(1) Se(2)−Fe(2)−Fe(1) Fe(2)−Se(1)−Fe(1) Fe(2)−Se(2)−Fe(1)

2.392(2) 2.587(2) 1.364(12) 2.09(2) 57.49(6) 57.19(6) 65.81(7) 65.83(7)

4

Complexes 5−7 were characterized by elemental analysis, by spectroscopy, and particularly for 6 and 7 by X-ray crystsllography. The IR spectra of 5−7 showed three absorption bands in the range 2038−1920 cm−1 for their terminal carbonyls, whereas the 1H, 13C{1H}, and 31P{1H} NMR spectra of 5−7 displayed the corresponding signals for their organic groups, terminal carbonyls, and phosphorus atoms. Particularly noteworthy is that the 77Se{1H} NMR spectra of 5 and 7 showed one singlet at 29.4 and 46.2 ppm for their two chemically equivalent Se atoms, and the bridged double-butterfly [Fe2Se2] cluster complex 6 displayed two singlets at −11.1 and 35.6 ppm for its two pairs of chemically different Se atoms, respectively. Although the crystal structure of 5 was not determined due to lack of suitable single crystals, structures of both 6 and 7 were determined by X-ray crystal diffraction analyses. While the ORTEP views of 6 and 7 are shown in Figures 7 and 8, the selected bond lengths and angles are presented in Table 4. As

Scheme 4

(Scheme 5). However, it should be noted that the formation of 7 by direct β-elimination reaction from 6 could not be completely excluded, since our experiment proved that complex 7 could be produced in 47% yield by direct β-elimination reaction of 6 under the action of n-BuLi in THF at room temperature. Scheme 5

3677


Organometallics

Article

resulting mixture with 1 equiv of Ph3P and Ph2PH in 80% and 61% yields, respectively. In addition, the bridgehead sulfur atom-oxidized TDSe-type model complex (μ-TDSeO)Fe2(CO)6 (10) could be prepared by oxidation reaction of its parent complex B with m-chloroperoxybenzoic acid in CH2Cl2 from 0 °C to room temperature in 58% yield (Scheme 6). Complexes 8 and 9 were fully characterized by elemental analysis, spectroscopy, and X-ray diffraction analysis. The IR spectra of 8 and 9 displayed three to four absorption bands in the range 2038−1917 cm−1 for their terminal CO ligands, which is very close to that of the phosphine-substituted ODSetype model complexes 1 and 2. The 13C{1H} NMR spectra of 8 and 9 displayed signals in the region 209−213 ppm for their carbonyl C atoms, whereas the 31P{1H} NMR spectra of 8 and 9 showed a singlet at 68.4 and 43.3 ppm for their P atoms, respectively. In addition, the 77Se{1H} NMR spectra exhibited a singlet at 141.4 and 178.8 ppm for their two chemically equivalent Se atoms, respectively. The molecular structures of 8 and 9 are shown in Figures 9 and 10, whereas their selected bond lengths and angles are tabulated in Table 5. As shown in Figures 9 and 10, the structures of 8 and 9 are very similar to the phosphinesubstituted ODSe-type models 1 and 2; namely, their phosphine ligands Ph3P and Ph2PH occupy the apical positions of the square-pyramidal geometry of Fe1 and Fe2 atoms, respectively. In addition, the bridgehead S1 and S2 atoms are both trans to PPh3 and PPh2H. The Fe1−Fe2 bond length of 8 (2.5522 Å) is slightly longer than that of 9 (2.5325 Å), but much longer than that of its analogue (μ-TDT)Fe2(CO)5(PPh3) (2.5108 Å).44 The IR spectrum of complex 10, similar to that of its TDTtype model analogue,45 displayed three absorption bands in the range 2077−1982 cm−1 for their terminal CO ligands. The 1H NMR spectrum showed two doublets at 2.40 and 3.91 ppm for the two chemically different protons in their CH2 groups, owing to slowed folding of the six-membered FeSe2C2S ring.27 In addition, the 13C{1H} NMR spectrum of 10 displayed two signals at 207.1 and 207.3 for its carbonyl C atoms, whereas the 77 Se{1H} NMR spectrum showed a singlet at 221.7 ppm for its two chemically equivalent bridged Se atoms. The molecular structure of complex 10 (Figure 11, Table 5) is very similar to that of its analogue (μ-TDTO)Fe2(CO)6.45 The Fe1−Fe2 bond length of this molecule (2.5645 Å) is almost identical with that of its parent complex B (2.5600 Å), but much longer than that of its analogue (2.5127 Å)45 due to the larger size of the Se atom than the S atom. Finally, it should be noted that the O7 atom is located in the common equatorial position of the two fused six-membered rings, namely, the boatshaped Fe1Se1C7S1C8Se2 and the chair-shaped Fe2Se1C7S1C8Se2. In addition, the bond length of S1O7 is 1.493 Å, which is almost identical with that of its TDT-type model complex (1.500 Å).45 Comparative Study on Electrochemical and Electrocatalytic Behavior of Parent ODSe/TDSe-Type Models A/ B and Their Sulfur Analogues. The electrochemical and electrocatalytic properties of some H-cluster models were previously investigated by CV techniques.26,31,32,46−48 For accurate comparison, we determined the cyclic voltammograms and electrochemical data of parent models A/B and their sulfur analogues (μ-ODT)Fe2(CO)6/(μ-TDT)Fe2(CO)6 under the same conditions. While their cyclic voltammograms are shown in Figure 12, the electrochemical data are listed in Table 6. Both A and B display one quasi-reversible reduction, one



can be seen in Figure 7, complex 6 contains two diiron ODSe moieties, which are connected together through the NHC/ phosphine ligand IMes/CH2CH2PPh2. Particularly noteworthy is that the NHC and phosphine moieties in the NHC/phosphine ligand are located in the two apical positions of the squarepyramidal Fe2 and Fe4 atoms, respectively. Figure 8 shows that complex 7 is actually isostructural with complexes 1 and 2, in which its phosphine ligand Ph2PCH CH2 is located in the apical position of the square-pyramidal Fe2 atom and the bridgehead O6 atom is trans to the bulky phosphine ligand Ph2PCHCH2. Synthesis and Structural Characterization of Phosphine-Substituted TDSe-Type Model Complexes 8/9 and the Bridgehead Sulfur Atom-Oxidized TDSe-Type Model Complex 10. The phosphine-monosubstituted TDSetype models (μ-TDSe)Fe2(CO)5(L) (8, L = Ph3P; 9, L = Ph2PH) were found to be similarly prepared by treatment of their parent complex B with 1 equiv of Me3NO·2H2O in MeCN at room temperature, followed by treatment of the 3678


Organometallics

Article

Table 4. Selected Bond Lengths (Å) and Angles (deg) for 6 and 7 6 Se(1)−Fe(1) Se(2)−Fe(2) Se(3)−Fe(3) Fe(3)−Fe(4) Fe(1)−Se(1)−Fe(2) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(1)−Se(1) Se(4)−Fe(3)−Se(3)

2.3834(16) 2.3890(16) 2.3872(16) 2.5689(18) 65.41(5) 65.47(5) 86.06(6) 86.37(5)

Se(1)−C(6) Se(1)−Fe(2) Se(1)−Fe(1) Se(2)−Fe(2) Fe(2)−Se(1)−Fe(1) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(1)−Se(1) Se(1)−Fe(1)−Fe(2)

1.997(3) 2.3888(7) 2.3905(8) 2.3840(8) 64.54(3) 64.40(2) 85.18(3) 57.70(2)

Fe(4)−P(1) Fe(2)−C(15) Fe(1)−Fe(2) C(15)−N(1) Se(3)−Fe(3)−Fe(4) P(1)−Fe(4)−Fe(3) Se(1)−Fe(1)−Fe(2) Se(2)−Fe(2)−Se(1)

2.234(2) 2.004(8) 2.5830(18) 1.360(10) 57.40(5) 149.77(8) 57.56(4) 85.71(5)

Se(2)−Fe(1) Fe(1)−Fe(2) Fe(2)−P(1) C(20)−C(21) P(1)−Fe(2)−Se(2) Se(2)−Fe(2)−Se(1) P(1)−Fe(2)−Fe(1) C(20)−P(1)−Fe(2)

2.4043(7) 2.5518(7) 2.2324(9) 1.314(4) 100.87(3) 85.67(3) 154.54(3) 110.34(10)

7

Scheme 6


cathodically, consistent with the transition to a one-electron process).26 This is because the peak heights of A and B are close to that of the well-known one-electron oxidation of ferrocene under the same conditions (Figures S2 and S3, see the Supporting Information), and particularly the final Q values for A and B determined by controlled potential coulometry (CPC) are close to half that of the known two-electron reduction of dimer [CpFe(CO)2]2 (Figure S4, see the Supporting Information). In contrast to the first reductions, the oxidations of A and B displayed at 0.71 and 0.64 V are best classified as a two-electron process since their final Q values determined by CPC are close to that of the well-known twoelectron reduction of [CpFe(CO)2]2 (Figure S5, see the Supporting Information). It should be noted that the oxidation peak heights of A and B are much less than twice that of the one-electron oxidation of ferrocene under the same conditions (Figures S2 and S3, see the Supporting Information), presumably due to some of A and B being decomposed during their reduction processes. Actually, the cyclic voltammetric behavior of A/B is very similar to that of their sulfur analogues, except that the first reduction peaks of A and B are positively shifted by about 30 mV, indicating that the ODSe/TDSe-type models A/B are more easily reduced than their corresponding sulfur analogues. To compare the electrocatalytic activity of the aforementioned four models for H2 production, their cyclic voltammograms in the presence of acetic acid were also determined under


irreversible reduction, and one irreversible oxidation. The first reductions displayed at −1.55 V for A and −1.49 V for B could be assigned to a one-electron process (note that B was previously reported to show a two-electron reduction peak near −1.5 V at a scan rate of 100 mV/s; however, at fast scan rates the reduction peak intensity decreases and the position shifts 3679


Organometallics

Article

Table 5. Selected Bond Lengths (Å) and Angles (deg) for 8−10 8 Se(1)−C(6) Se(1)−Fe(2) Se(2)−Fe(1) Se(2)−Fe(2) Fe(1)−Se(1)−Fe(2) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(1)−Se(1) Se(2)−Fe(1)−Fe(2)

1.980(3) 2.3795(5) 2.3721(5) 2.3831(5) 64.454(15) 64.921(15) 86.610(16) 57.747(13)

Se(1)−C(6) Se(1)−Fe(1) Se(2)−Fe(1) Se(2)−Fe(2) Fe(1)−Se(1)−Fe(2) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(2)−Fe(1) Se(1)−Fe(1)−Fe(2)

1.987(8) 2.4009(15) 2.3764(16) 2.3771(16) 63.90(5) 64.38(5) 57.79(5) 57.73(4)

S(1)−O(7) Se(1)−Fe(2) Se(1)−Fe(1) Se(2)−Fe(2) Fe(1)−Se(1)−Fe(2) Fe(2)−Se(2)−Fe(1) Se(2)−Fe(2)−Se(1) Se(2)−Fe(1)−Se(1)

1.493(5) 2.3751(10) 2.3825(10) 2.3662(10) 65.23(3) 65.43(3) 88.29(3) 87.83(3)

Fe(1)−P(1) Se(1)−Fe(1) Fe(1)−Fe(2) C(6)−S(1) Se(1)−Fe(2)−Se(2) P(1)−Fe(1)−Se(2) P(1)−Fe(1)−Se(1) Se(1)−Fe(2)−Fe(1)

2.2433(7) 2.4063(5) 2.5522(5) 1.781(3) 86.972(16) 102.25(2) 110.63(2) 58.282(13)

Fe(2)−P(1) Fe(1)−C(2) Fe(1)−Fe(2) Fe(1)−C(1) Se(1)−Fe(2)−Fe(1) P(1)−Fe(2)−Se(2) Se(2)−Fe(1)−Se(1) P(1)−Fe(2)−Fe(1)

2.212(2) 1.767(10) 2.5325(18) 1.804(9) 58.36(5) 102.27(8) 87.76(5) 148.25(8)

Se(2)−Fe(1) S(1)−C(7) Fe(1)−Fe(2) Fe(1)−C(1) C(7)−S(1)−O(7) Se(2)−Fe(1)−Fe(2) Se(1)−Fe(1)−Fe(2) Se(1)−Fe(2)−Fe(1)

2.3787(10) 1.791(6) 2.5645(11) 1.810(6) 105.6(3) 57.05(3) 57.24(3) 57.52(3)

9

10

Figure 12. Cyclic voltammograms of A, B, (μ-ODT)Fe2(CO)6, and (μ-TDT)Fe2(CO)6 (1.0 mM) in 0.1 M n-Bu4NPF6/MeCN at a scan rate of 0.1 V·s−1.


Table 6. Electrochemical Data of A, B,26 (μODT)Fe2(CO)6,31 and (μ-TDT)Fe2(CO)626,32

the same conditions. While the cyclic voltammograms of A and B are shown in Figures 13 and 14, those of their sulfur analogues are depicted in Figures S6 and S7 (see the Supporting Information). As shown in Figures 13/14 and Figures S6/S7, when the first 2 mM HOAc was added, their first reduction peaks increased slightly, but did not continuously increase with subsequent addition of the acid. However, in contrast to this, when the first 2 mM HOAc was added, their second reduction peaks grew up considerably with continuous addition of the acid. Apparently, such observations are typical of the electrocatalytic proton reduction processes.26,31,32,46−48 When bulk electrolysis of a MeCN solution of A (0.33 mM) with excess HOAc (6.6 mM) was carried out at −2.14 V for 1

(μ-TDT)Fe2(CO)6 (μ-ODT)Fe2(CO)6 B A

Epc1/V

Epc2/V

Epa/V

−1.52 −1.58 −1.49 −1.55

−2.01 −2.10 −1.97 −2.06

0.76 0.83 0.64 0.71

h, a total of 15 F mol−1 passed, which corresponds to 7.5 turnovers. Under comparable conditions, the turnover numbers for bulk electrolysis of a MeCN solution of B, (μ-TDT)Fe2(CO)6, and (μ-ODT)Fe2(CO)6 are 6.4, 8.0, and 10, 3680


Organometallics

Article

catalytic activity of A and B is slightly lower than that of their sulfur analogues, respectively. Such observations reflect the influences of not only the bridgehead O/S atoms but also the bridged chalcogen S/Se atoms in model complexes A/B and their sulfur analogues.

■

EXPERIMENTAL SECTION

General Comments. All reactions were carried out using standard Schlenk and vacuum-line techniques under an atmosphere of highly purified nitrogen. THF was purified by distillation under N2 from sodium/benzophenone ketyl, whereas dichloromethane was distilled over CaH2 and acetonitrile was distilled once from P2O5 and then from CaH2 under N2. Me3NO·2H2O, n-BuLi (2.5 M in hexane), Ph3P, t-BuOK, and m-chloroperoxybenzoic acid were available commercially and used as received. Fe 3 (CO) 12 , 49 Ph 2 PH, 50 Ph 2 POMe, 51 (HSeCH2)2X (X = O, S),52 1,3-bis(mesityl)imidazolium chloride (IMes·HCl),53 1-mesityl-3-methylimidazolium iodide (IMes/Me·HI),41 and 3-(2-diphenylphosphanylethyl)-1-(2,4,6-trimethylphenyl)-3H-imidazol-1-ium chloride (IMes/CH2CH2PPh2·HCl)54 were prepared according to the published procedures. Preparative TLC was carried out on glass plates (26 × 20 × 0.25 cm) coated with silica gel H (10−40 μm). IR spectra were recorded on a Bruker Vector 22 infrared spectrophotometer. 1H (13C, 31P, 77Se) NMR spectra were obtained on a Bruker Avance 300 or 400 NMR spectrometer. 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 (μ-ODSe)Fe2(CO)6 (A) and (μ-TDSe)Fe2(CO)6 (B). A 50 mL, three-necked flask equipped with a serum cap, a magnetic stirbar, and a nitrogen inlet tube was charged with Fe3(CO)12 (0.504 g, 1.0 mmol), (HSeCH2)2O (0.224 g, 1.10 mmol), and THF (20 mL). After the mixture was stirred at reflux for 1 h, solvent was removed at reduced pressure, and then the residue was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 1:10) as eluent. From the main orange-red band, A (0.217 g, 45%) was obtained as a red solid, mp 109−112 °C. Anal. Calcd for C8H4Fe2O7Se2: C, 19.95; H, 0.84. Found: C, 19.92; H, 0.93. IR (KBr disk): νCO 2065 (m), 2022 (s), 1999 (vs), 1971 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 4.46 (s, 4H, 2CH2) ppm. 13C{1H} NMR (100 MHz, CDCl3): 60.6 (s, CH2), 207.2 (s, CO) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 76.0 (s) ppm. When (HSeCH2)2S (0.242 g, 1.10 mmol) was used instead of (HSeCH2)2O, B (0.337 g, 68%) was obtained as a red solid, mp 118− 120 °C. Anal. Calcd for C8H4Fe2O6SSe2: C, 19.30; H, 0.81. Found: C, 19.34; H, 1.05. IR (KBr disk): νCO 2068 (s), 1989 (vs), 1972 (vs) cm−1. 1H NMR (300 MHz, CDCl3): 3.29 (s, 4H, 2CH2) ppm. 13 C{1H} NMR (100 MHz, CDCl3): 17.6 (s, CH2), 207.8 (s, CO) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 184.4 (s) ppm. Preparation of (μ-ODSe)Fe2(CO)5(L) (1, L = Ph3P; 2, L = Ph2POMe). The same equipped flask as described above was charged with A (0.241 g, 0.50 mmol), Me3NO·2H2O (0.056 g, 0.50 mmol), and MeCN (30 mL). The mixture was stirred at room temperature for about 15 min, and then Ph3P (0.131 g, 0.50 mmol) was added. After the new mixture was stirred at this temperature for 0.5 h, solvent was removed under vacuum to give a residue, which was subjected to TLC separation by using CH2Cl2/petroleum ether (v/v = 1:4) as eluent. From the main red band, 1 (0.180 g, 50%) was obtained as a red solid, mp 180 °C (dec). Anal. Calcd for C25H19Fe2O6PSe2: C, 41.94; H, 2.67. Found: C, 42.19; H, 2.76. IR (KBr disk): νCO 2038 (vs), 1976 (vs), 1926 (m) cm−1. 1H NMR (400 MHz, CDCl3): 3.50 (brs, 2H, CHHOCHH), 4.05 (brs, 2H, CHHOCHH), 7.44, 7.73 (2s, 15H, 3C6H5) ppm. 13C{1H} NMR (100 MHz, CDCl3): 59.8 (s, CH2), 128.4, 128.5, 130.1, 133.4, 133.5, 136.7, 137.1 (7s, C6H5), 210.0, 212.8 (2s, CO) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 67.9 (s) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 34.3 (s) ppm. When Ph2POMe (0.108 g, 0.50 mmol) was utilized in place of Ph3P, 2 (0.219 g, 65%) was obtained as a red solid, mp 101−102 °C. Anal. Calcd for C20H17Fe2O7PSe2: C, 35.86; H, 2.56. Found: C, 35.95;

Figure 13. Cyclic voltammograms of A (1.0 mM) with HOAc (0−10 mM) in 0.1 M n-Bu4NPF6/MeCN at a scan rate of 0.1 V·s−1.

Figure 14. Cyclic voltammograms of B (1.0 mM) with HOAc (0−10 mM) in 0.1 M n-Bu4NPF6/MeCN at a scan rate of 0.1 V·s−1.

respectively. This implies that the catalytic activity of A and its sulfur analogue (μ-ODT)Fe2(CO)6 is slightly higher than that of B and its sulfur analogue (μ-TDT)Fe2(CO)6, respectively. However, the catalytic activity of A and B is slightly lower than that of their sulfur analogues, respectively. Apparently, the former reflects the influence of the bridgehead O/S atoms in A/B and their sulfur analogues, whereas the latter reflects the influence of the bridged chalcogen S/Se atoms in these model complexes.

■

CONCLUSIONS The parent ODSe- and TDSe-type model complexes A and B have been prepared by a simple and convenient method, which includes the oxidative addition of diselenols (HSeCH2)2X (X = O, S) with Fe3(CO)12. Further CO substitution reactions of A and B with various phosphine and NHC ligands gave the corresponding substituted complexes 1−9, whereas the oxidation reaction of B with m-chloroperoxybenzoic acid afforded the bridgehead S atom-oxidized product 10. The Xray crystallographic studies reveal that the phosphine and NHC ligands in complexes 1−4 and 6−9 are all located in the apical positions of their square-pyramidal Fe atoms, whereas the O atom attached to the bridgehead S atom in complex 10 resides in the common equatorial position of the two fused sixmembered rings, namely, the boat-shaped Fe1Se1C7S1C8Se2 and the chair-shaped Fe2Se1C7S1C8Se2. A comparative study on H2 production from HOAc indicates that the catalytic activity of A and its sulfur analogue is slightly higher than that of B and its sulfur analogue, respectively. In addition, the 3681


Organometallics

Article

H, 2.59. IR (KBr disk): νCO 2039 (vs), 1976 (vs), 1927 (m) cm−1. 1 H NMR (400 MHz, CDCl3): 3.59 (d, 3H, 3JP−H = 10.4 Hz, CH3), 3.90 (brs, 2H, CHHOCHH), 4.18 (brs, 2H, CHHOCHH), 7.46, 7.80 (2s, 10H, 2C6H5) ppm. 13C{1H} NMR (100 MHz, CDCl3): 53.2 (s, CH3), 60.1 (s, CH2), 128.4, 128.5, 130.8, 131.1, 131.2 (5s, o,m,p-C of C6H5), 140.1 (d, 1JP−C = 43.0 Hz, ipso-C of C6H5), 210.2 (s, Fe(CO)3), 213.2 (d, 2JP−C = 12.11 Hz, PFe(CO)2) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 171.1 (s) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 60.4 (s) ppm. Preparation of (μ-ODSe)Fe2(CO)5(L) (3, L = IMes; 4, L = IMes/Me). To a stirred suspension of the imidazolium salt IMes·HCl (0.341 g, 1.00 mmol) in THF (15 mL) was dropwise added n-BuLi (0.40 mL, 1.00 mmol) by a syringe to give a yellowish solution. After the solution was stirred at room temperature for an additional 20 min, it was filtered under anaerobic conditions through a Celite-packed column and eluted with THF (10 mL) to give a filtrate containing the air-sensitive free carbene IMes. To this filtrate was added A (0.096 g, 0.20 mmol), and the new mixture was stirred at room temperature for 2 h. The resulting brown-red solution was evaporated to dryness under vacuum, and then the residue was subjected to TLC separation using CH2Cl2/ petroleum ether (v/v = 1:4) as eluent. From the main red band, 3 (0.078 g, 52%) was obtained as a red solid, mp 90 °C (dec). Anal. Calcd for C28H28Fe2N2O6Se2: C, 44.36; H, 3.72; N, 3.70. Found: C, 44.31; H, 3.81; N, 3.47. IR (KBr disk): νCO 2027 (vs), 1962 (vs), 1910 (m) cm−1. 1H NMR (400 MHz, CDCl3): 2.19 (s, 12H, 4o-CH3 of 2C6H2), 2.36 (s, 6H, 2p-CH3 of 2C6H2), 3.91−4.01 (m, 4H, 2CH2), 7.02 (s, 4H, 4m-H of 2C6H2), 7.20 (s, 2H, NCHCHN) ppm. 13 C{1H} NMR (100 MHz, CDCl3): 17.5 (s, o-CH3 of C6H2), 20.1 (s, p-CH3 of C6H2), 60.0 (s, CH2), 123.8 (s, NCHCHN), 128.3, 135.2, 136.9, 138.2 (4s, C6H2), 192.5 (s, NCN), 209.6, 212.0 (2s, CO) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): −10.2 (s) ppm. When the imidazolium salt IMes/Me·HI was used instead of IMes·HCl, 4 was obtained as a red solid (0.061 g, 47%), mp 131 °C (dec). Anal. Calcd for C20H20Fe2N2O6Se2: C, 36.73; H, 3.08; N, 4.28. Found: C, 36.52; H, 3.17; N, 4.17. IR (KBr disk): νC≡O 2028 (vs), 1964 (vs), 1910 (s) cm−1. 1H NMR (300 MHz, CDCl3): 2.12 (s, 6H, 2o-CH3 of C6H2), 2.37 (s, 3H, p-CH3 of C6H2), 4.02 (s, 3H, NCH3), 4.21 (s, 4H, 2CH2), 6.88 (s, 1H, CH3NCHCHNC6H2), 7.03 (s, 2H, 2m-H of C6H2), 7.14 (s, 1H, CH3NCHCHNC6H2) ppm. 13C{1H} NMR (100 MHz, CDCl3): 17.8 (s, o-CH3 of C6H2), 20.2 (s, p-CH3 of C6H2), 39.3 (s, NCH3), 59.8 (s, CH2), 122.9, 122.99, 123.1, 123.4, 123.3 (5s, NCHCHN), 128.2, 128.2, 128.3, 135.1, 136.2, 136.2, 138.2 (7s, C6H2), 187.0 (s, NCN), 210.6, 210.8, 215.0 (3s, CO) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 383.6 (s) ppm. Preparation of (μ-ODSe)Fe2(CO)5(IMes/CH2CH2PPh2·HCl) (5). To a stirred solution of A (0.241 g, 0.50 mmol) in MeCN (30 mL) was added Me3NO·2H2O (0.056 g, 0.50 mmol). After the mixture was stirred at room temperature for about 10 min, the imidazolium salt IMes/CH2CH2PPh2·HCl (0.217 g, 0.5 mmol) was added, and then the new mixture was stirred at room temperature for another 20 min. Volatiles were removed under vacuum, and then the residue was subjected to TLC separation using CH2Cl2 as eluent. From the main red band, 5 (0.260 g, 59%) was obtained as a red solid, mp 110−102 °C. Anal. Calcd for C33H32ClFe2N2O6PSe2: C, 44.60; H, 3.63; N, 3.15. Found: C, 44.36; H, 3.76; N, 3.19. IR (KBr disk): νCO 2038 (vs), 1975 (vs), 1922 (s) cm−1. 1H NMR (400 MHz, CDCl3): 2.10 (s, 6H, 2o-CH3 of C6H2), 2.38 (s, 3H, p-CH3 of C6H2), 3.58 (d, 2H, J = 6.4 Hz, PCH2), 4.07 (s, 4H, 2SeCH2), 4.87 (brs, 2H, NCH2), 7.03 (s, 2H, 2m-H of C 6 H 2 ), 7.15 (s, 1H, CH 2 NCHCHNC 6 H 2 ), 7.25 (s, 1H, CH2NCHCHNC6H2), 7.53, 7.94 (2brs, 10H, 2C6H5), 10.83 (s, 1H, NCHN) ppm. 13C{1H} NMR (100 MHz, CDCl3): 17.7 (s, o-CH3 of C6H2), 21.0 (s, p-CH3 of C6H2), 35.8 (d, 1JP−C = 21.4 Hz, PCH2CH2N), 46.84 (s, PCH2CH2N), 57.8, 60.9 (2s, SeCH2), 122.5, 123.5 (2s, NCHCHN), 128.9, 129.0, 129.8, 130.6, 132.4, 132.5, 134.1, 136.7, 137.1, 138.9, 141.2 (11s, C6H2, C6H5), 209.6, 213.6 (2s, CO) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 55.3 (s) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 29.4 (s) ppm. Preparation of [(μ-ODSe)Fe2(CO)5]2(IMes/CH2CH2PPh2) (6). To a stirred suspension of the imidazolium salt IMes/CH2CH2PPh2·HCl (0.217 g, 0.50 mmol) in THF (15 mL) was added t-BuOK (0.062 g, 0.55

mmol) to give a pinkish solution. After the solution was stirred at room temperature for 10 min, A (0.241 g, 0.50 mmol) was added, and then the new mixture was stirred at room temperature for 4 h. After removal of the solvent at reduced pressure, the residue was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 1:4) as eluent. From the main red band, 6 (0.167 g, 26%) was obtained as a dark red solid, mp 144−146 °C. Anal. Calcd for C40H35Fe4N2O12PSe4: C, 36.79; H, 2.70; N, 2.15. Found: C, 36.55; H, 2.75; N, 2.10. IR (KBr disk): νCO 2033 (s), 1963 (vs), 1920 (m) cm−1. 1H NMR (400 MHz, CDCl3): 2.06 (s, 6H, 2o-CH3 of C6H2), 2.34 (s, 3H, p-CH3 of C6H2), 3.26 (brs, 2H, PCH2), 3.88−4.21 (m, 8H, 4SeCH2), 4.95 (brs, 2H, NCH2), 6.98 (brs, 4H, 2m-H of C6H2, NCHCHN), 7.48, 7.82 (2brs, 10H, 2C6H5) ppm. 13C{1H} NMR (100 MHz, CDCl3): 18.6 (s, o-CH3 of C6H2), 21.2 (s, p-CH3 of C6H2), 37.31 (d, 1JP−C = 22.3 Hz, PCH2CH2N), 48.26 (d, 2JP−C = 8.3 Hz, PCH2CH2N), 60.7, 61.4 (2s, SeCH2), 122.3, 125.0 (2s, NCHCHN), 128.9, 129.0, 129.4, 130.7, 132.5, 132.6, 135.8, 137.0, 137.3, 139.3 (10s, C6H2, C6H5), 209.5, 210.5, 214.0, 214.5 (4s, CO) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 54.2 (s) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): −11.1 (brs, CNHCFeSe), 35.6 (brs, PFeSe) ppm. Preparation of [(μ-ODSe)Fe2(CO)5]2(IMes/CH2CH2PPh2) (6) and (μODSe)Fe2(CO)5(Ph2PCHCH2) (7). The same procedure as for the preparation of 6 was followed, except that n-BuLi (0.22 mL, 0.55 mmol) was used in place of t-BuOK. From the second brown-black band and the first red band, 6 (0.093 g, 14%) and 7 (0.064 g, 19%) were obtained as a dark red solid and a purple-red solid, respectively. 7: mp 121−122 °C. Anal. Calcd for C21H17Fe2O6PSe2: C, 37.87; H, 2.57. Found: C, 37.56; H, 2.65. IR (KBr disk): νCO 2037 (vs), 1972 (vs), 1925 (s) cm−1. 1H NMR (400 MHz, CDCl3): 3.85 (d, 2H, J = 5.2 Hz, CHHSeCHH), 4.07(d, 2H, J = 8.4 Hz, CHHSeCHH), 5.51− 5.61, 5.95−6.08 (2m, 2H, CHCH2), 6.80−6.93 (m, 1H, CH CH2), 7.45, 7.72 (2brs, 10H, 2C6H5) ppm. 13C{1H} NMR (100 MHz, CDCl3): 60.2 (SeCH2), 128.5, 128.6, 129.1, 130.2, 133.0, 133.1, 135.9, 136.4, 136.8, 137.2 (10s, C6H5, CHCH2), 210.1, 213.2 (2s, CO) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 59.2 (s) ppm. 77 Se{1H} NMR (76 MHz, CDCl3, Me2Se): 46.2 (s) ppm. 7 could also be prepared by the following method: To a stirred solution of 6 (0.444 g, 0.50 mmol) in THF (15 mL) was dropwise added n-BuLi (0.22 mL, 0.55 mmol) by a syringe at room temperature. After the mixture was stirred at this temperature for 4 h, solvent was removed at reduced pressure, and then the residue was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 1:4) as eluent. From the main red band, 7 (0.156 g, 47%) was obtained as a purplered solid. Preparation of (μ-TDSe)Fe2(CO)5(L) (8, L = Ph3P; 9, L = Ph2PH). A 50 mL, three-necked flask fitted with a serum cap, a magnetic stirbar, and a nitrogen inlet tube was charged with B (0.249 g, 0.50 mmol), Me3NO·2H2O (0.056 g, 0.50 mmol), and MeCN (10 mL). After the mixture was stirred at room temperature for 15 min, Ph3P (0.131 g, 0.50 mmol) was added, and then the new mixture continued to be stirred for an additional 0.5 h. Solvent was removed at reduced pressure to leave a residue, which was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 1:5) as eluent. From the main red band, 8 (0.293 g, 80%) was obtained as a red solid, mp 177 °C (dec). Anal. Calcd for C25H19Fe2O5PSSe2: C, 41.02; H, 2.62. Found: C, 41.04; H, 2.53. IR (KBr disk): νCO 2037 (m), 1972 (vs), 1952 (m), 1917 (s) cm−1. 1H NMR (400 MHz, CDCl3): 2.32 (d, J = 12.0 Hz, CHHSCHH), 2.85 (d, J = 12.0 Hz, CHHSCHH), 7.44, 7.74 (2s, 15H, 3C6H5) ppm. 13C{1H} NMR (100 MHz, CDCl3): 14.7 (s, CH2), 128.5 (d, 3JP−C = 9.5 Hz, m-C of C6H5), 130.2 (s, p-C of C6H5), 133.6 (d, 2JP−C = 10.9 Hz, o-C of C6H5), 136.2 (d, 1JP−C = 39.8 Hz, ipso-C of C6H5), 209.8 (s, Fe(CO)3), 212.0 (d, 2JP−C = 8.9 Hz, PFe(CO)2) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 68.4 (s) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 141.4 (s) ppm. When Ph2PH (0.10 mL, 0.50 mmol) was used instead of Ph3P, 9 (0.220 g, 67%) was obtained as a red solid, mp 78−79 °C. Anal. Calcd for C19H15Fe2O5PSSe2: C, 34.79; H, 2.30. Found: C, 34.58; H, 2.36. IR (KBr disk): νCO 2038 (s), 1980 (vs), 1930 (m) cm−1. 1H NMR (400 MHz, CDCl3): 3.00 (d, J = 12.4 Hz, CHHSCHH), 3.11 (d, J = 13.2 3682


Organometallics

Article

Notes

Hz, CHHSCHH), 6.73 (d, J = 358.8 Hz, 1H, PH), 7.44, 7.75 (2brs, 10H, 2C6H5) ppm. 13C{1H} NMR (100 MHz, CDCl3): 16.3 (s, CH2), 128.9 (d, 3JP−C = 9.7 Hz, m-C of C6H5), 130.3 (s, p-C of C6H5), 132.2 (d, 2JP−C = 9.8 Hz, o-C of C6H5), 133.8 (d, 1JP−C = 43.1 Hz, ipso-C of C6H5), 209.7 (s, Fe(CO)3), 212.5 (d, 2JP−C = 8.2 Hz, PFe(CO)2) ppm. 31 1 P{ H} NMR (162 MHz, CDCl3, 85% H3PO4): 43.3 (s) ppm. 77 Se{1H} NMR (76 MHz, CDCl3, Me2Se): 178.8 (s) ppm. Preparation of (μ-TDSeO)Fe2(CO)6 (10). To a stirred red solution of B (0.125 g, 0.25 mmol) in CH2Cl2 (20 mL) was added 3-chloroperoxybenzoic acid (0.076 g, 0.50 mmol), and then the mixture was cooled to about 0 °C by an ice/water bath. After the mixture was stirred at this temperature for 15 min and at room pemperature for 12 h, volatiles were removed under vacuum, and then the residue was subjected to TLC separation using CH2Cl2 as eluent. From the main orange-red band, 10 (0.072 g, 56%) was obtained as a red solid, mp 110−112 °C. Anal. Calcd for C8H4Fe2O7SSe2: C, 18.70; H, 0.78. Found: C, 18.99; H, 0.95. IR (KBr disk): νCO 2077 (s), 2038 (s), 1982 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 2.40 (d, 2H, J = 9.2 Hz, CHHSCHH), 3.91 (d, 2H, J = 9.2 Hz, CHHSCHH) ppm. 13 C{1H} NMR (100 MHz, CDCl3): 30.1 (s, CH2), 207.1, 207.3 (2s, CO) ppm. 77Se{1H} NMR (76 MHz, CDCl3, Me2Se): 221.7 (s) ppm. X-ray Structure Determinations of A, B, 1−4, and 6−10. Single crystals suitable for X-ray diffraction analyses were grown by slow evaporation of the CH2Cl2/hexane solutions of 1, 9, and 10 and an Et2O solution of 2 at −5 °C, a slow evaporation of the CHCl3/ hexane solutions of 6 and 7 at −10 °C, and a slow diffusion of CH2Cl2 to petroleum solutions of A, B, 3, 4, and 8 at −20 °C. All the single crystals were mounted on a Rigaku MM-007 (rotating anode) diffractometer equipped with a Saturn 70 CCD or Saturn 724 CCD. Data were collected at 113 or 293 K using a confocal monochromator with Mo Kα radiation (λ = 0.71073 or 0.71075 Å) in the ω−ϕ scanning mode. Data collection, reduction, and absorption correction were performed with the CRYSTALCLEAR program.55 The structures were solved by direct methods using the SHELXS-97 program56 and refined by full-matrix least-squares techniques (SHELXL-97)57 on F2. Hydrogen atoms were located by using the geometric method. Details of crystal data, data collections, and structure refinements are summarized in Tables S2−S5 (see the Supporting Information). Electrochemical and Electrocatalytic Experiments. A solution of 0.1 M n-Bu4NPF6 in MeCN (Fisher Chemicals, HPLC grade) was used as electrolyte in each of the electrochemical and electrocatalytic experiments. The electrolyte solutions were degassed by bubbling with N2 for at least 10 min before measurements. The measurements were made using a BAS Epsilon potentiostat. All voltammograms were obtained in a three-electrode cell with a 3 mm diameter glassy carbon working electrode, a platinum counter electrode, and a Ag/Ag+ (0.01 M AgNO3/0.1 M n-Bu4NPF6 in MeCN) reference electrode under an atmosphere of nitrogen. The working electrode was polished with 0.05 μm alumina paste and sonicated in water for 10 min. Bulk electrolyses were run on a vitreous carbon rod (A = 2.9 cm2) in a twocompartment, gastight, H-type electrolysis cell containing ca. 25 mL of MeCN. All potentials are quoted against the Fc/Fc+ potential. Gas chromatography was performed with a GC-2014 Shimadzu gas chromatograph under isothermal conditions with nitrogen as a carrier gas and a thermal conductivity detector.

■

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We are grateful to 973 (2011CB935902), the National Natural Science Foundation of China (21132001, 21272122), and Tianjin Co-Innovation Center of Chemical Science and Engineering for financial support.

■

ASSOCIATED CONTENT

S Supporting Information *

Full tables of crystal data, atomic coordinates and thermal parameters, and bond lengths and angles for A, B, 1−4, and 6− 10 as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org.

■

REFERENCES

(1) (a) Cammack, R. Nature 1999, 397, 214. (b) Adams, M. W. W.; Stiefel, E. I. Science 1998, 282, 1842. (c) Nicolet, Y.; Cavazza, C.; Fontecilla-Camps, J. C. J. Inorg. Biochem. 2002, 91, 1. (2) (a) Volbeda, A.; Fontecilla-Camps, J. C. Dalton Trans. 2003, 4030. (b) Garcin, E.; Vernede, X.; Hatchikian, E. C.; Volbeda, A.; Frey, M.; Fontecilla-Camps, J. C. Structure 1999, 7, 557. (c) Albracht, S. P. J. Biochim. Biophys. Acta 1994, 1188, 167. (3) (a) Nicolet, Y.; Lemon, B. J.; Fontecilla-Camps, J. C.; Peters, J. W. Trends Biochem. Sci. 2000, 25, 138. (b) Peters, J. W. Curr. Opin. Struct. Biol. 1999, 9, 670. (c) Adams, M. W. W. Biochim. Biophys. Acta 1990, 1020, 115. (d) Fontecilla-Camps, J. C.; Frey, M.; Garcin, E.; Hatchikian, C.; Montet, Y.; Piras, C.; Vernède, X.; Volbeda, A. Biochimie 1997, 79, 661. (4) (a) Shima, S.; Thauer, R. K. Chem. Rec. 2007, 7, 37. (b) Dey, S.; Das, P. K.; Dey, A. Coord. Chem. Rev. 2013, 257, 42. (5) (a) Alper, J. Science 2003, 299, 1686. (b) Lubitz, W.; Tumas, W. Chem. Rev. 2007, 107, 3900. (6) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C. Science 1998, 282, 1853. (7) Nicolet, Y.; Piras, C.; Legrand, P.; Hatchikian, C. E.; FontecillaCamps, J. C. Structure 1999, 7, 13. (8) Nicolet, Y.; De Lacey, A. L.; Vernède, X.; Fernandez, V. M.; Hatchikian, E. C.; Fontecilla-Camps, J. C. J. Am. Chem. Soc. 2001, 123, 1596. (9) Lemon, B. J.; Peters, J. W. Biochemistry 1999, 38, 12969. (10) Pierik, A. J.; Hulstein, M.; Hagen, W. R.; Albracht, S. P. Eur. J. Biochem. 1998, 258, 572. (11) De Lacey, A. L.; Stadler, C.; Cavazza, C.; Hatchikian, E. C.; Fernandez, V. M. J. Am. Chem. Soc. 2000, 122, 11232. (12) Chen, Z.; Lemon, B. J.; Huang, S.; Swartz, D. J.; Peters, J. W.; Bagley, K. A. Biochemistry 2002, 41, 2036. (13) Fan, H.-J.; Hall, M. B. J. Am. Chem. Soc. 2001, 123, 3828. (14) (a) Silakov, A.; Wenk, B.; Reijerse, E.; Lubitz, W. Phys. Chem. Chem. Phys. 2009, 11, 6592. (b) Pandey, A. S.; Harris, T. V.; Giles, L. J.; Peters, J. W.; Szilagyi, R. K. J. Am. Chem. Soc. 2008, 130, 4533. (15) For reviews, see for example: (a) Tard, C.; Pickett, C. J. Chem. Rev. 2009, 109, 2245. (b) Fontecilla-Camps, J. C.; Volbeda, A.; Cavazza, C.; Nicolet, Y. Chem. Rev. 2007, 107, 4273. (16) Barton, B. E.; Rauchfuss, T. B. Inorg. Chem. 2008, 47, 2261. (17) Cheah, M. H.; Tard, C.; Borg, S. J.; Liu, X.-M.; Ibrahim, S. K.; Pickett, C. J.; Best, S. P. J. Am. Chem. Soc. 2007, 129, 11085. (18) Wright, R. J.; Lim, C.; Tilley, T. D. Chem.−Eur. J. 2009, 15, 8518. (19) Eilers, G.; Schwartz, L.; Stein, M.; Zampella, G.; De Gioia, L.; Ott, S.; Lomoth, R. Chem.−Eur. J. 2007, 13, 7075. (20) (a) Song, L.-C.; Li, C.-G.; Gao, J.; Yin, B.-S.; Luo, X.; Zhang, X.G.; Bao, H.-L.; Hu, Q.-M. Inorg. Chem. 2008, 47, 4545. (b) Song, L.C.; Liu, X.-F.; Ming, J.-B; Ge, J.-H; Xie, Z.-J.; Hu, Q.-M. Organometallics 2010, 29, 610. (21) (a) Song, L.-C.; Wang, L.-X.; Jia, G.-J.; Li, Q.-L.; Ming, J.-B. Organometallics 2012, 31, 5081. (b) Song, L.-C.; Gao, W.; Luo, X.; Wang, Z.-X.; Sun, X.-J.; Song, H.-B. Organometallics 2012, 31, 3324. (22) (a) Harb, M. K.; Niksch, T.; Windhager, J.; Görls, H.; Holze, R.; Lockett, L. T.; Okumura, N.; Evans, D. H.; Glass, R. S; Lichtenberger, D. L.; El-khateeb, M.; Weigand, W. Organometallics 2009, 28, 1039. (b) Harb, M. K.; Windhager, J.; Daraosheh, A.; Görls, H.; Lockett, L. T.; Okumura, N.; Evans, D. H.; Glass, R. S.; Lichtenberger, D. L.; Elkhateeb, M.; Weigand, W. Eur. J. Inorg. Chem. 2009, 3414. (c) Harb,

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 3683


Organometallics

Article

M. K.; Apfel, U.-P.; Sakamoto, T.; El-khateeb, M.; Weigand, W. Eur. J. Inorg. Chem. 2011, 986. (23) Gao, S.; Fan, J.; Sun, S.; Peng, X.; Zhao, X.; Hou, J. Dalton Trans. 2008, 2128. (24) Song, L.-C.; Gai, B.; Wang, H.-T.; Hu, Q.-M. J. Inorg. Biochem. 2009, 103, 805. (25) (a) Song, L.-C.; Gao, W.; Feng, C.-P; Wang, D.-F.; Hu, Q.-M. Organometallics 2009, 28, 6121. (b) Gao, W.; Song, L.-C.; Yin, B.-S.; Zan, H.-N.; Wang, D.-F.; Song, H.-B. Organometallics 2011, 30, 4097. (26) Harb, M. K.; Windhager, J.; Niksch, T.; Görls, H.; Sakamoto, T.; Smith, E. R.; Glass, R. S.; Lichtenberger, D. L.; Evans, D. H.; Elkhateeb, M.; Weigand, W. Tetrahedron 2012, 68, 10592. (27) Lawrence, J. D.; Li, H.; Rauchfuss, T. B.; Bénard, M.; Rohmer, M.-M. Angew. Chem., Int. Ed. 2001, 40, 1768. (28) Mathur, P.; Hossain, M. M.; Umbarkar, S.; Satyanarayana, C. V. V; Taval, S. S.; Puranik, V. G. Organometallics 1995, 14, 959. (29) Van Hal, J. W.; Whitmire, K. H. Organometallics 1998, 17, 5197. (30) Song, L.-C.; Zeng, G.-H.; Mei, S.-Z.; Lou, S.-X.; Hu, Q.-M. Organometallics 2006, 25, 3468. (31) Song, L.-C.; Yang, Z.-Y.; Bian, H.-Z.; Liu, Y.; Wang, H.-T.; Liu, X.-F.; Hu, Q.-M. Organometallics 2005, 24, 6126. (32) Song, L.-C.; Yang, Z.-Y.; Hua, Y.-J.; Wang, H.-T.; Liu, Y.; Hu, Q.-M. Organometallics 2007, 26, 2106. (33) Shen, J.-K.; Gao, Y.-C.; Shi, Q.-Z.; Basolo, F. Coord. Chem. Rev. 1993, 128, 69. (34) Collman, J. P.; Hegedus, L. S.; Norton, J. R. Finke, R. G. Principles and Applications of Organotransition Metal Chemistry, 2nd ed.; University Science Books: Mill Valley, CA, 1987. (35) Capon, J.-F.; Hassnaoui, S. E.; Gloaguen, F.; Schollhammer, P.; Talarmin, J. Organometallics 2005, 24, 2020. (36) Tye, J. W.; Lee, J.; Wang, H.-W.; Mejia-Rodriguez, R.; Reibenspies, J. H.; Hall, M. B.; Darensbourg, M. Y. Inorg. Chem. 2005, 44, 5550. (37) Liu, T.; Darensbourg, M. Y. J. Am. Chem. Soc. 2007, 129, 7008. (38) Herrmann, W. A.; Schütz, J.; Frey, G. D.; Herdtweck, E. Organometallics 2006, 25, 2437. (39) Mercs, L.; Labat, G.; Neels, A.; Ehlers, A.; Albrecht, M. Organometallics 2006, 25, 5648. (40) Viciano, M.; Mas-Marzá, E.; Sanaú, M.; Peris, E. Organometallics 2006, 25, 3063. (41) Arduengo, A. J., III; Rasika Dias, H. V.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1992, 114, 5530. (42) Song, L.-C.; Luo, X.; Wang, Y.-Z.; Gai, B.; Hu, Q.-M. J. Organomet. Chem. 2009, 694, 103. (43) Buchgraber, P.; Toupet, L.; Guerchais, V. Organometallics 2003, 22, 5144. (44) Song, L.-C.; Li, Q.-S.; Yang, Z.-Y.; Hua, Y.-J.; Bian, H.-Z.; Hu, Q.-M. Eur. J. Inorg. Chem. 2010, 1119. (45) Windhager, J.; Seidel, R. A.; Apfel, U.-P.; Görls, H.; Linti, G.; Weigand, W. Chem. Biodiversity 2008, 5, 2023. (46) (a) Chong, D.; Georgakaki, I. P.; Mejia-Rodriguez, R.; SanabriaChinchilla, J.; Soriaga, M. P.; Darensbourg, M. Y. Dalton Trans. 2003, 4158. (b) Borg, S. J.; Behrsing, T.; Best, S. P.; Razavet, M.; Liu, X.; Pickett, C. J. J. Am. Chem. Soc. 2004, 126, 16988. (47) Windhager, J.; Rudolph, M.; Bräutigam, S.; Görls, H.; Weigand, W. Eur. J. Inorg. Chem. 2007, 2748. (48) Capon, J.-F.; Gloaguen, F.; Pétillon, F. Y.; Schollhammer, P.; Talarmin, J. Coord. Chem. Rev. 2009, 253, 1476. (49) King, R. B. Organometallic Syntheses, Transition-Metal Compounds; Academic Press: New York, 1965; Vol. 1, p 95. (50) Kuchen, W.; Buchwald, H. Chem. Ber. 1958, 91, 2871. (51) Colle, K. S.; Lewis, E. S. J. Org. Chem. 1978, 43, 571. (52) Schmidt, M.; Hoffmann, G. G. Chem. Ber. 1979, 112, 2190. (53) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R.; Craig, H. A.; Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55, 14523. (54) Lee, H. M.; Chiu, P. L.; Zeng, J. Y. Inorg. Chim. Acta 2004, 357, 4313.

(55) CrystalClear and Crystalstructure; Rigaku and Rigaku Americas: The Woodlands, TX, 2007. (56) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure Solution; University of Göttingen: Germany, 1997. (57) Sheldrick, G. M. SHELXL97, A Program for Crystal Structure Refinement; University of Göttingen: Germany, 1997.

3684


Synthesis, Structures, and Some Properties of Diiron Oxadiselenolate

Recommend Documents