Synthesis, Structural Characterization, and Properties of Some

Jul 5, 2012 - Li-Cheng Song , Fei-Xian Luo , Bei-Bei Liu , Zhen-Chao Gu , and Hao Tan ... Li-Cheng Song , Bin Gai , Zhan-Heng Feng , Zong-Qiang Du ...
0 downloads 0 Views 694KB Size
Download PDF
Article pubs.acs.org/Organometallics

Synthesis, Structural Characterization, and Properties of Some Functionalized Phosphine-Containing Diiron Complexes As Models for the Active Site of [FeFe]-Hydrogenases Li-Cheng Song,* Liang-Xing Wang, Guo-Jun Jia, Qian-Li Li, and Jiang-Bo Ming Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China S Supporting Information *

ABSTRACT: The first phosphinobenzaldehyde- and phosphinoporphyrin-functionalized model complexes (1−4) have been synthesized and structurally characterized. Thus, reaction of diiron complex [(μ-SCH 2 ) 2 CH 2 ]Fe 2 (CO) 6 or [(μSCH2)2NC6H4CO2Me-p]Fe2(CO)6 with p-Ph2PC6H4CHO in the presence of Me3NO gave the phosphinobenzaldehyde-functionalized model complexes [(μSCH2)2CH2]Fe2(CO)5(p-Ph2PC6H4CHO) (1) and [(μ-SCH2)2NC6H4CO2Me-p]Fe2(CO)5(p-Ph2PC6H4CHO) (2) in 61% and 71% yields, respectively. Further reaction of 1 or 2 with PhCHO, pyrrole, and BF3·OEt2 followed by treatment with pchloranil resulted in formation of the phosphinoporphyrin-functionalized model complexes 5-{[(μ-SCH2)2CH2]Fe2(CO)5(p-Ph2PC6H4)}-10,15,20-triphenylporphyrin (3) and 5-{[(μ-SCH2)2NC6H4CO2Me-p]Fe2(CO)5(p-Ph2PC6H4)}-10,15,20-triphenylporphyrin (4) in 19% and 18% yields, respectively. While the new complexes 1−4 were characterized by elemental analysis and spectroscopy, the structures of 1, 3, and 4 were confirmed by X-ray crystallography. Particularly interesting is that complex 4 was found to be a catalyst for the photoinduced H2 production in the presence of the electron donor EtSH and the proton source HOAc.

■

INTRODUCTION [FeFe]-hydrogenases ([FeFe]Hases) are natural metalloenzymes that can catalyze the proton reduction to hydrogen at surprising rapidity in a variety of microbes.1 In recent years, [FeFe]Hases have received considerable attention, largely because of their unique structure and particularly their special function for production of hydrogen, an alternative “clean” energy source.2,3 The X-ray crystallographic4 and IR spectroscopic5 studies have revealed that the active site of [FeFe]Hases, the so-called H-cluster,6 mainly consists of a butterfly Fe2S2 cluster and a cubane-like Fe4S4 cluster, which are linked together through a cysteine S atom. In addition, the two iron atoms in the Fe2S2 cluster are coordinated by CO and CN− diatomic ligands and are bridged by a less defined dithiolate ligand. This dithiolate was recently suggested as an azadithiolate (ADT, SCH2NHCH2S) in which the bridgehead N atom plays an important role in the heterolytic cleavage or formation of hydrogen catalyzed by the natural enzymes7,8 (Scheme 1). To date, numerous H-cluster models have been prepared from the simple diiron all-carbonyl complexes such as (μ-PDT)Fe2(CO)6 (PDT = propanedithiolate), (μ-ADT)Fe2(CO)6, (μ-ODT)Fe 2 (CO)6 (ODT = oxadithiolate), (μ-TDT)Fe2(CO)6 (TDT = thiodithiolate), and (μ-PDS)Fe2(CO)6 (PDS = propanediselenolate) by CO substitution reactions with various electron donors such as CN−, R3P, RNC, and NHC ligands.9−21 This is because such simple dinuclear complexes are known to bear striking structural similarities to the H-cluster and the electron donors can make their iron © 2012 American Chemical Society

Scheme 1. Basic Structure of the H-Cluster Determined by Protein X-ray Crystallography

atoms more electron-rich and thus more easily accepting of a proton for catalytic H2 production. In this article, we will describe the synthesis, structural characterization, and some properties of the novel functionalized phosphine-containing model complexes in which two of them contain a benzaldehyde-functionalized phosphine and another two have a porphyrin-functionalized phosphine. It should be pointed out that the former two were mainly used in this article as precursors to prepare the latter two, and the latter two actually belong to light-driven-type models since they contain a photosensitizer porphyrin macrocycle.22−26 Received: May 15, 2012 Published: July 5, 2012 5081

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

■

Article

RESULTS AND DISCUSSION

Synthesis and Characterization of Model Complexes 1 and 2 with a Benzaldehyde-Functionalized Phosphine Ligand. We found that treatment of the PDT- and ADT-type model complexes [(μ-SCH 2 ) 2 CH 2 ]Fe 2 (CO) 6 and [(μSCH 2 ) 2 NC 6 H 4 CO 2 Me-p]Fe 2 (CO) 6 with 1 equiv of Me3NO·2H2O in CH2Cl2/MeCN at room temperature, followed by treatment with 1 equiv of p-Ph2PC6H4CHO, gave rise to the corresponding benzaldehyde-functionalized phosphine-substituted model complexes [(μ-SCH2)2CH2]Fe2(CO)5(p-Ph2PC6H4CHO) (1) and [(μSCH2)2NC6H4CO2Me-p]Fe2(CO)5(p-Ph2PC6H4CHO) (2) in 61% and 71% yields, respectively (Scheme 2). Scheme 2 Figure 1. ORTEP plot of 1 with 30% probability level ellipsoids.

bond lengths in the other phosphine-substituted derivatives of diiron all-carbonyl model complexes.29−32 Synthesis and Characterization of Model Complexes 3 and 4 with a Porphyrin-Functionalized Phosphine Ligand. Interestingly, complexes 3 and 4 could be prepared by the improved Lindsey method.33 Thus, treatment of the benzaldehyde-functionalized phosphine-containing model complexes 1 and 2 with benzaldehyde and pyrrole in a 1:3:4 molar ratio in the presence of catalyst BF3·OEt2, followed by treatment with the oxidant p-chloranil, afforded the corresponding porphyrin-functionalized phosphine-substituted model complexes 5-{[(μ-SCH 2 ) 2 CH 2 ]Fe 2 (CO) 5 (pPh2PC6H4)}-10,15,20-triphenylporphyrin (3) and 5-{[(μSCH2)2NC6H4CO2Me-p]Fe2(CO)5(p-Ph2PC6H4)}-10,15,20triphenylporphyrin (4) in 19% and 18% yields along with a given amount of tetraphenylporphyrin (H2TPP), respectively (Scheme 3). Complexes 3 and 4 are also air-stable solids, which were fully characterized by elemental analysis, spectroscopy, and X-ray crystal diffraction analysis. For instance, the IR spectra of 3 and 4 showed three absorption bands in the range 2044−1933 cm−1 for their terminal carbonyls and three absorption bands in the range 1660−1350 cm−1 for the skeletal vibrations of the pyrrole rings in their porphyrin macrocycle.34 In addition, the 1H NMR spectra of 3 and 4 exhibited one singlet at −2.93 and −2.80 ppm for their pyrrole NH groups, and the 31P{1H} NMR spectra of 3 and 4 showed a singlet at 66.04 and 65.60 ppm for their P atoms, respectively. The UV−vis absorption spectra and fluorescence emission spectra of 3 and 4, along with those of H2TPP (for comparison), were also dertermined. As shown in Figures 2 and 3, the UV−vis spectra of 3 and 4 display one Soret band at 418 nm in the near-UV region and four Q bands at 515−645 nm in the visible range.35 These Soret and Q bands are almost the same as those of H2TPP determined under the same conditions. In addition, as can be seen in Figures 4 and 5, complexes 3 and 4 exhibit two fluorescence emission bands at 650 and 716 nm. The two emission bands are also nearly the same as the corresponding bands of H2TPP under the same determined conditions, although their intensities are strongly quenched relative to those of the H2TPP bands, with a quenching efficiency, Q, of 70% and 61%, respectively. According to the previously reported similar cases,22,23 the remarkably decreased intensities of the two fluorescence

Complexes 1 and 2 are air-stable red solids, which were characterized by elemental analysis and IR, 1H NMR, and 31 1 P{ H} NMR spectroscopy. The IR spectra of 1 and 2 displayed one strong absorption band at ca. 1704 cm−1 for their formyl groups and three absorption bands in the range 2047− 1929 cm−1 for their terminal carbonyls. The three νCO absorption bands of 1 and 2 are much lower than those corresponding to their parent complexes,27,28 which is obviously due to the increased strength of the back-bonding between their iron atoms and the attached carbonyls caused by CO substitution with the stronger electron-donating phosphine ligand p-Ph2PC6H4CHO. In addition, the 1H NMR spectra of 1 and 2 exhibited a singlet at 10.06 and 10.07 ppm for their formyl groups, whereas the 31P{1H} NMR spectra of 1 and 2 showed a singlet at 67.09 and 66.63 ppm for their P atoms, respectively. The molecular structure of 1 was unambiguously confirmed by X-ray crystal diffraction analysis. While the ORTEP plot of 1 is presented in Figure 1, selected bond lengths and angles are listed in Table 1. Figure 1 shows that complex 1 contains a propanedithiolate ligand, which is bridged between the Fe(1) and Fe(2) atoms of the diiron subsite to form two fused six-membered rings of the chair-shaped Fe(1)S(1)C(8)C(7)C(6)S(2) and boat-shaped Fe(2)S(1)C(8)C(7)C(6)S(2). In addition, the benzaldehydefunctionalized phosphine ligand is shown to occupy the apical position of the square-pyramidal geometry of the Fe(2) atom and is cis to its bridgehead C(7) atom. While the C(27)−O(6) double-bond length is 1.209 Å, the Fe(2)−P(1) and Fe(1)− Fe(2) single-bond lengths are equal to 2.2538 and 2.5329 Å, which are very close to the corresponding Fe−P and Fe−Fe 5082

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

Article

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

2.2734(13) 2.2590(15) 1.833(4) 1.824(4) 84.45(5) 56.33(4) 67.93(3) 114.12(14)

Fe(1)−Fe(2) Fe(2)−S(1) Fe(2)−S(2) Fe(2)−P(1) C(8)−S(1)−Fe(1) C(15)−P(1)−Fe(2) C(9)−P(1)−Fe(2) C(21)−P(1)−Fe(2)

2.5329(11) 2.2731(16) 2.2747(15) 2.2538(13) 110.46(15) 119.74(13) 111.45(11) 116.93(12)

Scheme 3

Figure 2. UV−vis spectra of 3 and H2TPP in CH2Cl2 (5 × 10−6 M). The Soret band absorptions were normalized and the spectra were amplified 10-fold in the Q-band region.

Figure 3. UV−vis spectra of 4 and H2TPP in CH2Cl2 (5 × 10−6 M). The Soret band absorptions were normalized and the spectra were amplified 10-fold in the Q-band region.

emission bands of 3 and 4 relative to those of H2TPP could be attributed to the strong intramolecular electron transfer (ET) from the photoexcited state of the porphyrin macrocycle to the diiron subsite via the coordinatively bonded phosphine moiety. It should be noted that such an intramolecular ET is one of the important steps required for the proton reduction to hydrogen catalyzed by the natural enzymes.

To further confirm the molecular structures of 3 and 4, as well as to further understand the relationship between their structures and properties, the X-ray crystallographic studies of 3 and 4 were undertaken. While ORTEP plots of 3 and 4 are depicted in Figures 6 and 7, Table 2 lists their selected bond lengths and angles. The X-ray diffraction analysis of complex 3 revealed that (i) it contains a diiron-PDT moiety in which the six-membered 5083

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

Article

Figure 4. Fluorescence emission spectra (λex = 412 nm) of 3 and H2TPP in CH2Cl2 (5 × 10−6 M).

Figure 6. ORTEP plot of 3 with 30% probability level ellipsoids.

Figure 5. Fluorescence emission spectra (λex = 410 nm) of 4 and H2TPP in CH2Cl2 (5 × 10−6 M).

rings Fe(2)S(1)C(6)C(7)C(8)S(2) and Fe(1)S(1)C(6)C(7)C(8)S(2) adopt a chair conformation and a boat conformation, respectively; (ii) the porphyrin-functionalized phosphine ligand is connected to the Fe(1) atom of the diiron subsite and located in an apical position of the square-pyramidal geometry of the Fe(1) atom; (iii) the four benzene rings are twisted relative to the planar porphyrin macrocycle with a dihedral angle from 68.5° to 85.9° in order to minimize the steric repulsions between the two ortho-hydrogen atoms in each of the four phenyl groups with the two proximal pyrrole rings; and (iv) the Fe(1)−P(1) (2.2376 Å) and Fe(1)−Fe(2) (2.5074 Å) bond lengths are slightly shorter than the Fe(2)−P(1) and Fe(1)−Fe(2) bond lengths in its parent complex 1, whereas the C−N bond lengths in its pyrrole rings are almost the same (1.366−1.378 Å) and lie between those of normal single and double C−N bonds.36 Interestingly, in contrast to 3, the X-ray diffraction analysis of complex 4 indicated that (i) it contains a diiron-ADT moiety in which the boat-shaped ring Fe(1)S(1)C(10)N(1)C(9)S(2) is fused to a chair-shaped ring Fe(2)S(1)C(10)N(1)C(9)S(2) and the substituent p-MeO2C6H4 is attached to the N(1) atom via the common axial bond N(1)− C(6) of the aforementioned two six-membered rings; (ii) although complex 4 includes the same porphyrin-functionalized phosphine ligand as that of 3, it is coordinated to Fe(2) of the

Figure 7. ORTEP plot of 4 with 30% probability level ellipsoids.

diiron subsite and located in a basal position of the squarepyramidal Fe(2); and (iii) the four benzene rings around the porphyrin macrocycle of 4 are twisted with a smaller dihedral 5084

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

Article

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 3 and 4 Complex 3 Fe(1)−S(1) Fe(1)−S(2) S(1)−C(6) S(2)−C(8) S(1)−Fe(1)−S(2) S(1)−Fe(1)−Fe(2) Fe(1)−S(1)−Fe(2) C(8)−S(2)−Fe(1)

2.2605(10) 2.2659(10) 1.822(4) 1.840(4) 84.43(4) 56.60(3) 67.19(3) 114.61(13)

Fe(1)−S(1) Fe(1)−S(2) S(2)−C(9) S(1)−C(10) Fe(1)−Fe(2) S(2)−Fe(1)−S(1) S(2)−Fe(1)−Fe(2) S(1)−Fe(1)−Fe(2) Fe(2)−S(1)−Fe(1) C(9)−S(2)−Fe(1) C(9)−S(2)−Fe(2)

2.2716(17) 2.2542(17) 1.861(5) 1.848(5) 2.5434(12) 83.88(6) 56.16(4) 55.47(5) 68.39(5) 110.45(18) 113.54(19)

Fe(1)−Fe(2) Fe(2)−S(1) Fe(2)−S(2) Fe(1)−P(1) C(8)−S(2)−Fe(2) C(21)−P(1)−Fe(1) C(9)−P(1)−Fe(1) C(15)−P(1)−Fe(1)

2.5074(7) 2.2708(10) 2.2555(11) 2.2376(10) 109.35(15) 114.10(11) 112.31(12) 120.27(12)

Fe(2)−S(1) Fe(2)−S(2) Fe(2)−P(1) N(1)−C(6) O(2)−C(2) C(16)−P(1)−Fe(2) C(28)−P(1)−Fe(2) C(22)−P(1)−Fe(2) C(6)−N(1)−C(10) C(6)−N(1)−C(9) C(10)−N(1)−C(9)

2.2538(16) 2.2728(16) 2.2397(16) 1.401(7) 1.185(7) 113.25(17) 118.68(18) 116.51(18) 121.0(5) 123.3(5) 113.8(5)

Complex 4

angle, from 63.0° to 64.8°. However, the C−N bond lengths (1.361−1.378 Å) in the pyrrole rings of 4 are also nearly the same as those of 3 and lie between those of normal single and double C−N bonds.36 Finally, it should be noted that although some porphyrin-containing light-driven-type model complexes are known,22,24,25 complexes 3 and 4 are the first prepared and crystallographically characterized light-driven-type models containing a porphyrin-functionalized phosphine coordinated to an Fe atom of the diiron subsite. Photoinduced Hydrogen Production Catalyzed by LightDriven Model 4. The photoinduced catalytic systems for H2 production usually comprise four separate components: an electron donor, a photosensitizer, a catalyst, and a proton source.37−41 However, recently we reported a study on photoinduced H2 production by using a three-component system. This system consists of an electron donor, a proton source, and a light-driven model that has a photosensitizer tetraphenylporphyrin moiety covalently bonded to the bridgehead N atom of a simple ADT-type model for the active site of [FeFe]Hases.24 In order to examine if our light-driven models 3 and 4 could behave as photoactive catalysts to accomplish the expected H2 production, we chose 4 to constitute a threecomponent system with an electron donor and a proton source to carry out the expected H2 production experiments. It was found that H2 was indeed produced when a 500 W Hg lamp with a UV cutoff filter (λ >400 nm) irradiated a CH2Cl2 solution consisting of model 4, electron donor EtSH, and proton source HOAc (entry 1, Table 3). However, when the same experiment was carried out in the absence of EtSH or HOAc, only a trace amount of H2 was evolved (entries 2/3, Table 3), and no H2 could be detected when the experiment was run without light irradiation or in the absence of model 4 (entries 4/5, Table 3). It follows that the presence of electron donor EtSH, proton source HOAc, and light-driven model 4, as well as the light irradiation, are essential for such photoinduced H2 production. Figure 8 shows the time dependence of photoinduced H2 production. As can be seen in Figure 8, the H2 evolution is linearly increased during the first 10 min of

Table 3. Photocatalytic H2 Production Experiments in CH2Cl2 Solutions by Using EtSH as the Sacrificial Electron Donora entry photocatalyst 1 2 3 4 5 a

model model model model

4 4 4 4

electron donor

proton source

irradiation time (min)

EtSH EtSH

HOAc

20 20 20

EtSH EtSH

HOAc HOAc HOAc

20

TON 0.50 0.03 0.09 0 0

TONs are calculated based on model 4.

Figure 8. Time dependence of photoinduced H2 production from CH2Cl2 solutions (10 mL) consisting of EtSH (10 mM) and HOAc (10 mM) catalyzed by model 4 (0.1 mM).

irradiation and then increased very slowly, and finally the total 20 min irradiation produces 0.5 × 10−3 mmol of H2.

■

CONCLUSIONS We have prepared the first phosphinobenzaldehyde and phosphinoporphyrin ligand-containing H-cluster models 1−4 via convenient synthetic routes, and their structures are fully 5085

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

Article

71%), mp 170−172 °C. Anal. Calcd for C34H26Fe2NO8PS2: C, 52.13; H, 3.35; N, 1.79. Found: C, 52.11; H, 3.34; N, 1.75. IR (KBr disk): νCO 2047 (vs), 1985 (vs), 1937 (s); νCO 1705 (s) cm−1. 1H NMR (400 MHz, CDCl3): 3.06 (br s, 2H, 2SCHH), 3.86 (s, 3H, OCH3), 4.13, 4.16 (2s, 2H, 2SCHH), 6.57, 6.59 (2s, 2H, 2o-H of NC6H4), 7.50 (s, 6H, 2p-H of P(C6H5)2, 4m-H of P(C6H5)2), 7.73 (br s, 4H, 4o-H of P(C6H5)2), 7.88−7.93 (m, 6H, 2m-H of NC6H4, C6H4CHO), 10.07 (s, 1H, CHO) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 66.63 (s) ppm. Preparation of 5-{[(μ-SCH2)2CH2]Fe2(CO)5(p-Ph2P C6H4)}10,15,20-Triphenylporphyrin (3). The mixture of 1 (547 mg, 0.84 mmol), PhCHO (0.25 mL, 2.52 mmol), pyrrole (0.23 mL, 3.36 mmol), and BF3·OEt2 (0.043 mL, 0.34 mmol) in CH2Cl2 (340 mL) was stirred in the dark at room temperature for 16 h to give a brownred solution. After p-chloranil (826 mg, 3.36 mmol) was added and the new mixture was refluxed for 2 h, solvents were removed under reduced pressure and the residue was subjected to flash column chromatography (Al2O3, CH2Cl2). The eluate was reduced to a suitable volume for TLC separation (CH2Cl2/petroleum ether, 1:1). From the first purple band, H2TPP (90 mg, 17%) was obtained as a purple solid, which was identified by comparison of its IR and 1H NMR spectra with those of the authentic sample.34,47 From the second purple-red band, complex 3 was obtained as a purple-red solid (180 mg, 19%), mp 184 °C (dec). Anal. Calcd for C64H45Fe2N4O5PS2: C, 66.45; H, 3.92, N, 4.84. Found: C, 66.42; H, 3.98; N, 4.81. IR (KBr disk): νNH 3316 (m); νCO 2043 (vs), 1981 (vs), 1933 (s); νpyrrole ring 1558 (m), 1473 (m), 1350 (m) cm−1. 1H NMR (400 MHz, DMSOd6): −2.93 (s, 2H, 2NH), 1.32−1.71 (m, 4H, CHHCH2CHH), 1.96− 2.01 (m, 2H, CHHCH2CHH), 7.63−7.66 (m, 2H, 2p-H of P(C6H5)2), 7.70−7.73 (m, 4H, 4m-H of P(C6H5)2), 7.82, 7.84 (2s, 9H, 6m-H of 3C6H5, 3p-H of 3C6H5 in porphyrin) 7.92−7.98 (m, 6H, 2o-H of PC6H4, 4o-H of P(C6H5)2), 8.21, 8.22 (2s, 6H, 6o-H of 3C6H5 in porphyrin), 8.40, 8.42 (2s, 2H, 2m-H of PC6H4), 8.83, 8.86 (2s, 8H, 8CH of pyrrole rings) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 66.04 (s) ppm. UV−vis (CH2Cl2): λmax (log ε) 418 (4.69), 515 (3.36), 550 (3.01), 589 (2.80), 645 (2.67) nm. Preparation of 5-{[(μ-SCH2 ) 2 NC 6H 4 CO 2Me-p]Fe 2 (CO)5 (pPh2PC6H4)}-10,15,20-Triphenylporphyrin (4). A solution of 2 (525 mg, 0.67 mmol), PhCHO (0.20 mL, 2.01 mmol), pyrrole (0.19 mL, 2.68 mmol), and BF3·OEt2 (0.034 mL, 0.27 mmol) in CH2Cl2 (268 mL) was stirred in the dark at room temperature for 16 h to give a brown-red solution. To this solution was added p-chloranil (659 mg, 2.68 mmol), and the new mixture was heated at reflux for 2 h to give a brown-black solution. Then, the same workup as for 3 afforded H2TPP (74 mg, 18%) and complex 4 as a purple-red solid (145 mg, 17%), mp 172 °C (dec). Anal. Calced for C71H50Fe2N5O7PS2: C, 66.00; H, 3.90; N, 5.42. Found: C, 66.13; H, 3.64; N, 5.47. IR (KBr disk): νNH 3316 (m); νCO 2044 (vs), 1984 (vs), 1938 (s); νCO 1714 (s); νpyrrole ring 1660 (m), 1474 (m), 1351 (m) cm−1. 1H NMR (400 MHz, CDCl3): −2.80 (s, 2H, 2NH), 3.26 (br s, 2H, 2SCHH), 3.87 (s, 3H, OCH3), 4.28, 4.31(2s, 2H, 2SCHH), 6.66, 6.68 (2s, 2H, 2o-H of NC6H4), 7.60, 7.61 (2s, 6H, 4m-H of P(C6H5)2, 2p-H of P(C6H5)2), 7.75, 7.77 (2s, 9H, 6m-H of 3C6H5, 3p-H of 3C6H5 in porphyrin), 7.92, 7.94 (2s, 2H, 2m-H of NC6H4), 7.99−8.03 (m, 4H, 4o-H of P(C6H5)2), 8.08−8.13 (m, 2H, 2o-H of PC6H4), 8.19, 8.22 (2s, 6H, 6o-H of 3C6H5 in porphyrin), 8.30, 8.32 (2s, 2H, 2m-H of PC6H4), 8.81, 8.85 (2s, 8H, 8CH of pyrrole rings) ppm. 31P{1H} NMR (162 MHz, CDCl3, 85% H3PO4): 65.60 (s) ppm. UV−vis (CH2Cl2): λmax (log ε) 418 (4.63), 515 (3.30), 549 (2.97), 589 (2.78), 645 (2.66) nm. Photoinduced H2 Production Catalyzed by Light-Driven Model 4. A 30 mL Schlenk flask fitted with a N2 inlet tube, a serum cap, a magnetic stir-bar, and a water-cooling jacket was charged with model 4 (1.29 mg, 0.001 mmol), EtSH (7 μL, 0.1 mmol), HOAc (6 μL, 0.1 mmol), and CH2Cl2 (10 mL). While stirring, the resulting solution was thoroughly deoxygenated by bubbling with nitrogen and then was irradiated through a Pyrex glass filter (λ > 400 nm) using a 500 W Hg lamp at about 25 °C (controlled by the cooling jacket). The purpose of using such a UV cutoff filter is to obtain visible light and to avoid decomposition of EtSH.35 During the photoinduced catalysis, the evolved H2 was withdrawn periodically using a gastight syringe,

characterized by combustion analysis, various spectroscopies, and X-ray crystallography. It is shown that the phosphinobenzaldehyde-functionalized model complexes 1 and 2 can be prepared by the Me3NO-promoted CO substitution reactions of diiron complex [(μ-SCH 2 ) 2 CH 2 ]Fe 2 (CO) 6 or [(μSCH2)2NC6H4CO2Me-p]Fe2(CO)6 with p-Ph2PC6H4CHO, whereas the improved Lindsey’s cyclization reaction of 1 or 2 with PhCHO, pyrrole, and BF3·OEt2 followed by treatment with p-chloranil gives rise to the phosphinoporphyrin-functionalized model complexes 3 and 4, respectively. It is interesting to note that the phosphinobenzaldehyde and phosphinoporphyrin ligands in 1 and 3 have been proved by X-ray crystallography to coordinate to their square-pyramidal Fe atoms in an apical position, whereas the phosphinoporphyrin ligand in 4 is coordinated to its square-pyramidal Fe atom in a basal position in order to minimize the strong steric repulsion between the Nsubstituent p-MeO2CC6H4 and the bulky phosphinoporphyrin ligand. In addition, light-driven model 4 is found to be a catalyst for the photoinduced H2 production, although its catalytic efficiency is considerably low. Further studies on improvement of the photocatalytic activity of model 4 by replacement of its terminal carbonyls with other ligands10,11 and/or by coordination of its porphyrin macrocycle with various metal cations42,43 will be carried out in this laboratory.

■

EXPERIMENTAL SECTION

General Comments. All reactions were performed using standard Schlenk and vacuum-line techniques under an atmosphere of highly purified N2. Dichloromethane was distilled over CaH2 under N2. Acetonitrile was distilled once from P2O5 and then from CaH2 under N2. Me3NO·2H2O, EtSH, HOAc, BF3·OEt2, benzaldehyde, and 2,3,5,6-tetrachlorobenzoquinone (p-chloranil) were availably commercially and used as received. Pyrrole was freshly distilled before use. H2TPP,44 [(μ-SCH2)2CH2]Fe2(CO)6,45 p-Ph2PC6H4CHO,46 and [(μSCH2)2NC6H4CO2Me-p]Fe2(CO)628 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 and 31P{1H} NMR spectra were recorded on a Varian Mercury Plus 400 NMR spectrometer or a Bruker Avance 300 NMR spectometer. Elemental analyses were performed on an Elementar Vario EL analyzer. Melting points were determined on a Yanaco MP-500 apparatus and were uncorrected. Preparation of [(μ-SCH2)2CH2]Fe2(CO)5(p-Ph2PC6H4CHO) (1). To the red solution of [(μ-SCH2)2CH2]Fe2(CO)6 (405 mg, 1.05 mmol) in CH2Cl2 (10 mL) was added a solution of Me3NO·2H2O (116 mg, 1.05 mmol) in MeCN (10 mL), and then the mixture was stirred at room temperature for about 20 min until its color turned dark brown. After a CH2Cl2 (10 mL) solution of p-Ph2PC6H4CHO (305 mg, 1.05 mmol) was added and the new mixture was stirred for an additional 1 h, solvents were removed at reduced pressure and the residue was subjected to TLC separation by using acetone/petroleum ether (1:3 v/v) as eluent to give 1 as a red solid (412 mg, 61%), mp 158−160 °C. Anal. Calcd for C27H21Fe2O6PS2: C, 50.03; H, 3.27. Found: C, 50.08; H, 3.44. IR (KBr disk): νCO 2046 (vs), 1986 (vs), 1929 (s); ν CO 1703 (s) cm−1. 1H NMR (300 MHz, DMSO-d6): 1.05−1.47 (m, 4H, CHHCH 2 CHH), 1.76−1.82 (m, 2H, CHHCH2CHH), 7.58−7.65 (m, 10H, 2C6H5), 7.74−7.80 (m, 2H, 2 m-H of C6H4CHO), 8.05, 8.07 (2s, 2H, 2 o-H of C6H4CHO), 10.06 (s, 1H, CHO) ppm. 31P{1H} NMR (121 MHz, CDCl3, 85% H3PO4): 67.09 (s) ppm. Preparation of [(μ-SCH 2 ) 2 NC 6 H 4 CO 2 Me-p]Fe 2 (CO) 5 (pPh2PC6H4CHO) (2). The same procedure was followed as for 1, except that [(μ-SCH2)2NC6H4CO2Me-p]Fe2(CO)6 (440 mg, 0.84 mmol), Me3NO·2H2O (93 mg, 0.84 mmol), and p-Ph2PC6H4CHO (245 mg, 0.84 mmol) were utilized and by using acetone/petroleum ether (1:3 v/v) as eluent. 2 was separated as a red solid (471 mg, 5086

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

Article

Table 4. Crystal Data and Structural Refinement Details for 1, 3, and 4 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) 2θmax/deg no. of rflns no. of indep rflns index ranges

goodness of fit R Rw largest diff peak and hole/e Å−3

1

3

4

C27H21Fe2O6PS2 648.23 monoclinic P21/c 8.523(5) 17.128(9) 18.972(11) 90 95.871(5) 90 2755(3) 4 1.563 1.303 1320 55.76 25 473 6554 −10 ≤ h ≤ 11 −22 ≤ k ≤ 22 −24 ≤ l ≤ 24 0.940 0.0539 0.1463 0.318/−0.589

C64H45Fe2N4O5PS2·2CH2Cl2 1326.68 monoclinic P21/c 15.0944(6) 8.8897(3) 46.427(2) 90 97.235(2) 90 6180.1(4) 4 1.426 0.789 2720 55.78 48 749 14 228 −19 ≤ h ≤ 19 −11 ≤ k ≤ 11 −61 ≤ l ≤ 60 1.120 0.0734 0.1683 0.980/−1.037

C71H52Fe2N5O7PS2 1293.97 triclinic P1̅ 12.102(2) 14.449(3) 17.298(3) 78.937(5) 85.694(6) 86.281(5) 2956.2(9) 2 1.454 0.651 1336 54.00 30 573 10 413 −14 ≤ h ≤ 14 −17≤ k ≤ 17 −20 ≤ l ≤ 20 1.050 0.0742 0.1455 0.648/−0.524

which was analyzed by gas chromatography on a Shimadazu GC-2014 instrument with a thermal conductivity detector and a carbon molecular sieve column (3 mm × 2.0 m) and N2 as the carrier gas. The total amount of H2 produced during 20 min irradiation is 0.5 × 10−3 mmol. X-ray Structure Determinations of 1, 3, and 4. Single crystals of 1, 3, and 4 suitable for X-ray diffraction analyses were grown by slow evaporation of a CH2Cl2 solution of 1 and a slow diffusion of MeOH to CH2Cl2 solution of 3 or 4 at room temperature. A single crystal of 1, 3, or 4 was mounted on a Rigaku MM-007 (rotating anode) diffractometer equipped with a Saturn 70CCD. Data were collected at room temperature for 1 and 113 K for 3 and 4, using a confocal monochromator with Mo Kα radiation (λ = 0.71070 Å) in the ω−ϕ scanning mode. Data collection, reduction, and absorption correction were performed with the CRYSTALCLEAR program.48 The 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. Details of crystal data, data collections, and structure refinements are summarized in Table 4.

■

ACKNOWLEDGMENTS

■

REFERENCES

We are grateful to the National Natural Science Foundation of China (21132001, 20972073), 973 (2011CB935902), and the Tianjin Natural Science Foundation (09JCZDJC27900) for financial support.

(1) (a) Adams, M. W. W.; Stiefel, E. I. Science 1998, 282, 1842. (b) Cammack, R. Nature 1999, 397, 214. (2) (a) Evans, D. J.; Pickett, C. J. Chem. Soc. Rev. 2003, 32, 268. (b) Song, L.-C. Acc. Chem. Res. 2005, 38, 21. (c) Lubitz, W.; Tumas, W. Chem. Rev. 2007, 107, 3900. (3) (a) Graetzel, M. Acc. Chem. Res. 1981, 14, 376. (b) Bard, A. J.; Fox, M. A. Acc. Chem. Res. 1995, 28, 141. (c) Alper, J. Science 2003, 299, 1686. (4) (a) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C. Science 1998, 282, 1853. (b) Nicolet, Y.; Piras, C.; Legrand, P.; Hatchikian, E. C.; Fontecilla-Camps, J. C. Structure 1999, 7, 13. (c) 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. (d) Lemon, B. J.; Peters, J. W. Biochemistry 1999, 38, 12969. (5) (a) Pierik, A. J.; Hulstein, M.; Hagen, W. R.; Albracht, S. P. J. Eur. J. Biochem. 1998, 258, 572. (b) De Lacey, A. L.; Stadler, C.; Cavazza, C.; Hatchikian, E. C.; Fernandez, V. M. J. Am. Chem. Soc. 2000, 122, 11232. (c) Chen, Z.; Lemon, B. J.; Huang, S.; Swartz, D. J.; Peters, J. W.; Bagley, K. A. Biochemistry 2002, 41, 2036. (6) Adams, M. W. W. Biochim. Biophys. Acta 1990, 1020, 115. (7) Nicolet, Y.; Lemon, B. J.; Fontecilla-Camps, J. C.; Peters, J. W. Trends Biochem. Sci. 2000, 25, 138. (8) Fan, H.; Hail, M. B. J. Am. Chem. Soc. 2001, 123, 3828. (9) (a) Gloaguen, F.; Lawrence, J. D.; Schmidt, M.; Wilson, S. R.; Rauchfuss, T. B. J. Am. Chem. Soc. 2001, 123, 12518. (b) Liu, T.; Darensbourg, M. Y. J. Am. Chem. Soc. 2007, 129, 7008. (c) Liu, Y.-C.; Lee, C.-H.; Lee, G.-H.; Chiang, M.-H. Eur. J. Inorg. Chem. 2011, 1155. (10) Nehring, J. L.; Heinekey, D. M. Inorg. Chem. 2003, 42, 4288.

ASSOCIATED CONTENT

S Supporting Information *

Full tables of crystal data, atomic coordinates and thermal parameters, and bond lengths and angles for 1, 3, and 4 as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org.

■

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. 5087

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088

Organometallics

Article

(43) Okura, I. Coord. Chem. Rev. 1985, 68, 53. (44) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldamcher, J.; Assour, J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476. (45) Seyferth, D.; Henderson, R. S.; Song, L.-C. J. Organomet. Chem. 1980, 192, C1. (46) Wang, Y.; Lai, C. W.; Kwong, F. Y.; Jia, W.; Chan, K. S. Tetrahedron 2004, 60, 9433. (47) Bookser, B. C.; Bruice, T. C. J. Am. Chem. Soc. 1991, 113, 4208. (48) CRYSTALCLEAR 1.3.6; Rigaku and Rigaku/MSC: The Woodlands, TX, USA, 2005. (49) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure Solution; University of Göttingen: Germany, 1997. (50) Sheldrick, G. M. SHELXL97, A Program for Crystal Structure Refinement; University of Göttingen: Germany, 1997.

(11) Capon, J.-F.; Hassnaoui, S. E.; Gloaguen, F.; Schollhammer, P.; Talarmin, J. Organometallics 2005, 24, 2020. (12) (a) Lawrence, J. D.; Li, H.; Rauchfuss, T. B. Angew. Chem., Int. Ed. 2001, 40, 1768. (b) Song, L.-C.; Ge, J.-H.; Zhang, X.-G.; Liu, Y.; Hu, Q.-M. Eur. J. Inorg. Chem. 2006, 3204. (c) Schwartz, L.; Eilers, G.; Eriksson, L.; Gogoll, A.; Lomoth, R.; Ott, S. Chem. Commun. 2006, 520. (13) Song, L.-C.; Yang, Z.-Y.; Bian, H.-Z.; Wang, H.-T.; Liu, Y.; Liu, X.-F.; Hu, Q.-M. Organometallics 2005, 24, 6126. (14) Jablonskytė, A.; Wright, J. A.; Pickett, C. J. Eur. J. Inorg. Chem. 2011, 1033. (15) Song, L.-C.; Yang, Z.-Y.; Hua, Y.-J.; Wang, H.-T.; Liu, Y.; Hu, Q.-M. Organometallics 2007, 26, 2106. (16) Song, L.-C.; Gai, B.; Wang, H.-T.; Hu, Q.-M. J. Inorg. Biochem. 2009, 103, 805. (17) Daraosheh, A. Q.; Harb, M. K.; Windhager, J.; Görls, H.; EIkhateeb, M.; Weigand, W. Organometallics 2009, 28, 6275. (18) Harb, M. K.; Windhager, J.; Daraosheh, A.; Görls, H.; Lockett, L. T.; Okumura, N.; Evans, D. H.; Glass, R. S.; Lichtenberger, D. L.; EI-khateeb, M.; Weigand, W. Eur. J. Inorg. Chem. 2009, 3414. (19) Harb, M. K.; Apfel, U.-P.; Sakamoto, T.; EI-khateeb, M.; Weigand, W. Eur. J. Inorg. Chem. 2011, 986. (20) Windhager, J.; Görls, H.; Petzold, H.; Mloston, G.; Linti, G.; Weigand, W. Eur. J. Inorg. Chem. 2007, 4462. (21) Si, G.; Wang, W.-G.; Wang, H.-Y.; Tung, C.-H.; Wu, L.-Z. Inorg. Chem. 2008, 47, 8101. (22) Song, L.-C.; Tang, M.-Y.; Su, F.-H.; Hu, Q.-M. Angew. Chem., Int. Ed. 2006, 45, 1130. (23) Song, L.-C.; Tang, M.-Y.; Mei, S.-Z.; Huang, J.-H.; Hu, Q.-M. Organometallics 2007, 26, 1575. (24) Song, L.-C.; Wang, L.-X.; Tang, M.-Y.; Li, C.-G.; Song, H.-B.; Hu, Q.-M. Organometallics 2009, 28, 3834. (25) Kluwer, A. M.; Kapre, R.; Hartl, F.; Lutz, M.; Spek, A. L.; Brouwer, A. M.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 10460. (26) Samuel, A. P. S.; Co, D. T.; Stern, C. L.; Wasielewski, M. R. J. Am. Chem. Soc. 2010, 132, 8813. (27) Lyon, E. J.; Georgakaki, I. P.; Reibenspies, J. H.; Darensbourg, M. Y. Angew. Chem., Int. Ed. 1999, 38, 3178. (28) Song, L.-C.; Ge, J.-H.; Liu, X.-F.; Zhao, L.-Q.; Hu, Q.-M. J. Organomet. Chem. 2006, 691, 5701. (29) Song, L.-C.; Li, C.-G.; Gao, J.; Yin, B.-S.; Luo, X.; Zhang, X.-G.; Bao, H.-L.; Hu, Q.-M. J. Inorg. Biochem. 2008, 102, 1973. (30) Song, L.-C.; Ge, J.-H.; Zhang, X.-G.; Liu, Y.; Hu, Q.-M. Eur. J. Inorg. Chem. 2006, 3204. (31) Huo, F.; Huo, J.; Chen, G.; Guo, D.; Peng, X. Eur. J. Inorg. Chem. 2010, 3942. (32) Wen, N.; Xu, F.; Feng, Y.; Du, S. J. Inorg. Biochem. 2011, 105, 1123. (33) Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.; Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827. (34) Thomas, D. W.; Martell, A. E. J. Am. Chem. Soc. 1959, 81, 5111. (35) Shaw, J. L.; Garrison, S. A.; Alemán, E. A.; Ziegler, C. J.; Modarelli, D. A. J. Org. Chem. 2004, 69, 7423. (36) (a) Silvers, S. J.; Tulinsky, A. J. Am. Chem. Soc. 1967, 89, 3331. (b) Sessler, J. L.; Johnson, M. R.; Creager, S. E.; Fettinger, J. C.; Ibers, J. A. J. Am. Chem. Soc. 1990, 112, 9310. (37) Ozawa, H; Haga, M.; Sakai, K. J. Am. Chem. Soc. 2006, 128, 4926. (38) Rau, S.; Walther, D.; Vos, J. G. Dalton Trans. 2007, 915. (39) Fihri, A.; Artero, V.; Razavet, M.; Baffert, C.; Leibl, W.; Fontecave, M. Angew. Chem., Int. Ed. 2008, 47, 564. (40) Rosenthal, J.; Bachman, J.; Dempsey, J. L.; Esswein, A. J.; Gray, T. G.; Hodgkiss, J. M.; Manke, D. R.; Luckett, T. D.; Pistorio, B. J.; Veige, A. S.; Nocera, D. G. Coord. Chem. Rev. 2005, 249, 1316. (41) Amao, Y.; Tomonou, Y.; Ishikawa, Y.; Okura, I. Int. J. Hydrogen Energy 2002, 27, 621. (42) Darwent, J. R.; Douglas, P.; Harriman, A.; Porter, G.; Richoux, M.-C. Coord. Chem. Rev. 1982, 44, 83. 5088

dx.doi.org/10.1021/om300418z | Organometallics 2012, 31, 5081−5088