Reactions of SnMe2-Bridged Bis (cyclopentadienes) with Iron

Mar 16, 2012 - ... Bis(cyclopentadienes) with Iron Pentacarbonyl: Migration of the SnMe2 Group ... the SnMe2 group undergoes a similar migration to pr...
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Reactions of SnMe2-Bridged Bis(cyclopentadienes) with Iron Pentacarbonyl: Migration of the SnMe2 Group Bolin Zhu,* Yuan Li, Yunfei Chen, and Wei Shi College of Chemistry and Tianjin Key Laboratory of Structure and Performance for Functional Molecule, Tianjin Normal University, Tianjin 300387, People’s Republic of China S Supporting Information *

ABSTRACT: In reactions of the singly bridged bis(cyclopentadiene) (SnMe2)(tBuC5H4)2 (1) or the doubly bridged bis(cyclopentadienes) (SiMe2)(SnMe2)(RC5H3)2 (R = H (2), R = tBu (3)) with Fe(CO)5 in refluxing xylene, the bridging SnMe2 group migrates from the ligand to the iron atoms to give compounds (5, 7, 9a,b) containing the Fe−Sn−Fe units, together with the corresponding destannylated products (6, 8, 10a,b); the bridging SiMe2 group (in 2 and 3) does not migrate. However, in the reaction of the doubly bridged ligand (GeMe2)(SnMe2)(C5H4)2 (4) with Fe(CO)5, the SnMe2 group undergoes a similar migration to produce the complex GeMe2[(η5-C5H4)Fe(CO)2]2SnMe2 (12), containing the Fe−Sn−Fe unit, both SnMe2 and GeMe2 groups migrate from the ligand to the iron atoms to yield the product [(GeMe2)(η5-C5H4)Fe(CO)2][(SnMe2)(η5-C5H4)Fe(CO)2] (11), containing one Fe−Ge bond and one Fe−Sn bond, or the SnMe2 group is cleaved to afford the destannylation product GeMe2[(η5C5H4)Fe(CO)]2(μ-CO)2 (13). The stability of complexes 5, 7, and 12 containing the Fe−Sn−Fe unit toward heat and light was also studied. The molecular structures of 9a,b, 11, and 12 were determined by X-ray diffraction.

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INTRODUCTION Reactions of EMe3-substituted cyclopentadiene ligands (type A) and EMe2-bridged bis(cyclopentadiene ligands) (types B and C) with transition-metal carbonyl complexes (especially group VIB and VIII metal carbonyls, such as Fe(CO)5, Ru3(CO)12, or M(CO)6 (M = Cr, Mo, W)), have been the subject of continuous interest by chemists in organometallic chemistry for several decades. In reactions of this type, the EMe3 group or the bridging EMe2 group on the ligand sometimes migrates from the Cp ring to the metal center or is completely removed from the ligand.

(C5H4)2(CMe2)(EMe2) (E = Si, Ge) (type C) with M(CO)6 (M = Mo, W) or Fe(CO)5 gave the corresponding desilylation or degermylation products,5,6 together with a structurally novel complex with an E−M bond (type D), which was accompanied by EMe2 group migration from the Cp ring to the transition metal. Generally, ruthenium analogues of type D could only be produced by photolysis of its metal complexes (SiMe2)[(C5R4)2Ru2(CO)4] (R = H, Me).7−9

Little chemistry of SnMe2-bridged ligands (types B and C) has been reported up to now, especially their reactions with transition-metal complexes. To the best of our knowledge, only a few synthetic and structural studies10−14 and several examples of their application to the preparation of early-transition-metal metallocenes have been reported.10−12 To develop a wider generality of the migration behavior of the EMe2 bridging group during reactions with transition-metal complexes, we extended the bridging group to SnMe2, selected four typical ligands (1−4, including types B and C; Chart 1), and explored their reactions with Fe(CO)5. Results of these studies are reported in this paper.

In the first example of this type of reaction, reported by Keppie and Lappert in 1969,1 C5H5-EMe3 (type A) was reacted with (MeCN)3M(CO)3 (E = Ge, Sn, M = Mo, W) or Fe(CO)5 (E = Sn). It was found that EMe3 (E = Ge, Sn) migrates to the metal atom to give (η5-C5H5)M(CO)n(EMe3) (M = Mo, W, n = 3; M = Fe, n = 2), while no migration was observed when the substituted group on the Cp ring was SiMe3.2 Later there were reports of desilylation and degermylation in reactions of EMe2bridged bis(cyclopentadiene) ligands (E = Si, Ge) with metal carbonyl complexes, 3 − 6 including the reactions of (C5H5)2SiMe2 (type B) with (EtCN)3M(CO)3 (M = Cr, Mo) to give only the corresponding desilylation products [(η5C5H5)M(CO)3]2.3 Also, reactions of doubly bridged ligands © 2012 American Chemical Society

Received: November 17, 2011 Published: March 16, 2012 3035

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Chart 1

Scheme 2

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its structure. In this reaction, the bridging SiMe2 group stayed between two Cp rings, while the SnMe2 group migrated twice to give the final product 7, just as it did in the reaction of singly bridged ligand 1 with Fe(CO)5 (Scheme 1). Thus, in the reactions of doubly bridged bis(cyclopentadienes) with transition-metal carbonyls, the bridging SnMe2 group shows a different migration behavior and/or activity than the SiMe2 group; the latter either did not migrate in the presence of the other bridging SnMe2 group or participated in only a single migration to give a complex with a Fe−Si bond (type D compound) in the reaction of Fe(CO)5 with doubly bridged (CMe2)(SiMe2)(C5H4)2, in which the other bridging group is the inert CMe2.6 This difference in reactivity may be attributed to the stronger C−Si bond energy, which results in a lower migration ability. 8 was assigned as the destannylated product (SiMe2)[(η5-C5H4)Fe(CO)]2(μ-CO)2, on the basis of its previously reported 1H NMR and IR spectra.18 Reaction of (SiMe2)(SnMe2)(tBuC5H3)2 (3) with Fe(CO)5. To shed some light on the SnMe2 group migration mechanism, the tBu-substituted doubly bridged ligand 3 was synthesized and the reaction of 3 with Fe(CO)5 was studied. This reaction of ligand 3 with Fe(CO)5 in refluxing xylene afforded the two yellow crystalline solids 9a (6% yield) and 9b (13% yield), together with the two dark red crystalline solids 10a (11% yield) and 10b (15% yield) (Scheme 3). Complex 9a was isolated as air-stable yellow crystals. Its 1H NMR spectrum shows three peaks at δ 4.91, 4.89, and 4.78 for the protons in each cyclopentadienyl ring and a singlet at δ 1.26 for the protons in the tBu group. In addition, it exhibits two singlets at 0.34 and 0.33 ppm for the different CH3 protons in the SiMe2 group and two singlets at 0.62 and 0.56 ppm for the different CH3 protons in the SnMe2 group. The IR spectrum of 9a contains four strong ν(CO) bands in the range of 1980− 1909 cm−1, corresponding to the terminal CO ligands. These analytical data are fully compatible with the structure of 9a revealed by X-ray crystallography (Figure 1), in which two tBu groups adopt a meso configuration. Complex 9b was also obtained as air-stable yellow crystals. The 1H NMR spectrum shows three peaks at δ 4.97, 4.84, and 4.59 for the protons in each cyclopentadienyl ring and a singlet at δ 1.29 for the protons in the tBu group. However, it exhibits only one singlet at 0.34 ppm for all protons in the SiMe2 group and one singlet at 0.56 ppm for all protons in the SnMe2 group. Its IR spectrum also contains four strong ν(CO) bands in the range of 1976− 1906 cm−1, which are consistent with the terminal CO ligands. Single-crystal X-ray diffraction confirmed the molecular structure of 9b as an isomer of 9a, in which two tBu groups adopt a rac configuration (Figure 2). The production of rac-9 strongly suggests that the SnMe2 group migrates in two separate steps, not in a concerted way. A plausible mechanism is tentatively suggested in Scheme 4, which may be considered to proceed in the following way. (i) Two Fe(CO)3 moieties coordinate to two Cp rings from the same or opposite sides of the doubly bridged ligand to give an intermediate containing two (η4-tBuC5H3)Fe(CO)3 moieties. The similar intermediate

RESULTS AND DISCUSSION Reaction of (SnMe2)(tBuC5H4)2 (1) with Fe(CO)5. The reaction of ligand 1 with Fe(CO)5 in refluxing xylene afforded the yellow solid 5 (37% yield), together with the dark red solid 6 (12% yield) (Scheme 1). The IR spectrum of 5 exhibits only Scheme 1

terminal carbonyl bands (1960, 1914 cm−1). The 1H NMR spectrum of 5 displays two cyclopentadienyl proton peaks at 4.64 and 4.55 ppm, which are shifted to higher field than those in ligand 1 (5.88 and 5.54 ppm in C6D6); this may suggest that the cyclopentadienyl rings are η5 coordinated by iron atoms. In addition, 5 also shows a singlet for tBu protons at 1.27 ppm and a singlet for SnMe2 protons at 0.60 ppm. The chemical shift for the SnMe2 protons is more than 0.8 ppm lower than that in ligand 1 (−0.21 ppm for SnMe2 in C6D6),10 which suggests that the SnMe2 group may no longer be located between the Cp rings but may indicate a compound that contains an Fe−Sn−Fe structure. Namely, the complex [(η 5 - t BuC 5 H 4 )Fe(CO)2]2SnMe2 (5) was produced instead of the normal product (SnMe2)[(η5-tBuC5H3)Fe(CO)]2(μ-CO)2, containing an Fe−Fe bond. Compound 6 was assigned as the destannylated product [(η5-tBuC5H4)Fe(CO)]2(μ-CO)2, on the basis of its 1H NMR and IR spectra.15 Generally, compounds containing the M−Sn−M unit (M = Fe, Ru, Mo, W) are synthesized by the reaction of [(η5C5H5)M(CO)n]− (M = Fe, or Mo) with R2SnCl216 or by insertion of SnCl2 into the metal−metal bond of binuclear complexes such as (EMe2)[(η5-tBuC5H3)M(CO)]2(μ-CO)2 (E = Si, Ge; M = Fe, Ru).17 This paper reports for the first time that a compound with an M−Sn−M structure can be synthesized directly from the reaction of a SnMe2-bridged ligand with transition-metal carbonyls. Reaction of (SiMe2)(SnMe2)(C5H4)2 (2) with Fe(CO)5. We have previously reported the reactions of doubly bridged bis(cyclopentadienes) (CMe2)(EMe2)(C5H4)2 (E = Si, Ge) with Fe(CO)5,5,6 The bridging EMe2 group migrated to give a novel complex which contains an M−E bond (type D). In order to gain a deeper understanding of the migration of the bridging SnMe2 group and to make a comparison with that of the SiMe2 group, the (SiMe2)(SnMe2) doubly bridged ligand 2 was synthesized and its reaction with Fe(CO)5 was studied. The reaction of ligand 2 with Fe(CO)5 in refluxing xylene afforded the yellow solid 7 (32% yield), together with the dark red solid 8 (12% yield) (Scheme 2). After its 1H NMR and IR spectra were compared with reported data,17b the structure of compound 7 was identified as (SiMe 2 )[(η 5 -C 5 H 4 )Fe(CO)2]2SnMe2, which also contains an Fe−Sn−Fe moiety in 3036

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Scheme 3

(steps ii′ and iii′) to give the final product meso-9. The similar SnMe3 migration has even been observed in the reactions of C5H5-EMe3 with (MeCN)3M(CO)3 (E = Ge, Sn; M = Mo, W) or Fe(CO)5 (E = Sn), which afforded the products (η5C5H5)M(CO)n(EMe3) (M = Mo, W, n = 3; M = Fe, n = 2) containing an M−E bond.1 However, if two Fe(CO)3 moieties are on opposite sides, (ii) one Sn−C bond is cleaved and the SnMe2 group migrates first from one Cp ring to an iron atom and then (iii) the other Sn−C is cleaved and a rotation of one Cp ring about the Si−C bond is required to form another Fe− Sn bond to afford rac-9. However, an alternative pathway to form meso-9 and rac-9 could not be ruled out: namely, both meso-9 and rac-9 are formed from the same intermediate cis(SiMe2)(SnMe2)[(η4‑tBuC5H3)Fe(CO)3]2. Similarly, meso-9 can be generated directly from two successive migrations of the SnMe2 group, while a facile silatropic 1,5-shift of the SiMe2 group on the cyclopentadienyl ring before the SnMe2 group migrates from the rings to the Fe atoms would lead to product rac-9. Similar situations of the reversible (simultaneous) 1,5silatropic shift have been observed in the interconversion of isomers of the doubly bridged bis(cyclopentadienyl) ligand (CMe2)(SiMe2)(C5H4)214 and in the rac−meso interchange of the doubly SiMe2 bridged titanocene (SiMe2)2[η5-C5H-3(CHMe2)-5-Me]2TiCl2.20 meso-10 and rac-10 were assigned as the destannylated products meso- and rac-(SiMe2)[(η5-tBuC5H3)Fe(CO)]2(μ-CO)2, on the basis of their 1H NMR and IR spectra, in comparison with reported data.21 The molecular structure of 9a is presented in Figure 1. The molecule consists of two [(η5-tBuC5H3)Fe(CO)2] moieties linked by one SiMe2 bridge and one SnMe2 bridge. It has a perfect symmetry plane passing through the Si and Sn atoms and the center of the Fe(1)−Fe(1A) bond; the six-membered ring Si(1)−C(1)−Fe(1)−Sn(1)−Fe(1A)−C(1A) constituting the molecular framework adopts a chair conformation. The Sn−Fe bond distance is 2.5719(4) Å, which is longer than that in its analogue (GeMe2)[(η5-C5H4)Fe(CO)2]2SnCl2 (2.49 Å)17a but is almost equal to that in the nonbridged analogue [(η5-C5H5)Fe(CO)2]2SnMe2 (2.60 Å).16d The steric requirements of the two [(η5-tBuC5H3)Fe(CO)2] fragments impose a significant distortion from tetrahedral coordination for the tin atom, as reflected in the large Fe(1)−Sn(1)−Fe(1A) angle of 118.341(17)°, which results in a diminished C(14)−Sn(1)− C(15) angle of 101.69(18)°. These angles are close to those (123 and 104°) in the nonbridged analogue [(η5-C5H5)Fe(CO)2]2SnMe2.16d The molecular structure of 9b is presented in Figure 2. It has an approximate C2 axis passing through the Si and Sn atoms, and the six-membered ring Si(1)−C(1)−Fe(1)−Sn(1)− Fe(2)−C(12) constituting the molecular framework adopts a

Figure 1. ORTEP diagram of meso-SiMe 2 [(η 5 - t BuC 5 H 3 )Fe(CO)2]2SnMe2 (9a). Thermal ellipsoids are shown at the 30% level. Selected bond lengths (Å) and angles (deg): Sn(1)−Fe(1) = 2.5719(4), Sn(1)−C(14) = 2.170(4), Sn(1)−C(15) = 2.171(4), Si(1)−C(1) = 1.863(2), Si(1)−C(10) = 1.861(4), Si(1)−C(11) = 1.855(4); Fe(1)−Sn(1)−Fe(1A) = 118.341(17), C(14)−Sn(1)− C(15) = 101.69(18), C(1)−Si(1)−C(1A) = 111.02(14), C(10)− Si(1)−C(11) = 109.6(2), Fe(1)−C(12)−O(1) = 178.4(3), Fe(1)− C(13)−O(2) = 177.6(3), Cp−Cp fold angle 25.2, Cp(centroid)− Fe(1)−Sn(1) = 124.0, Cp(centroid)−Fe(1)···Fe(2)−-Cp(centroid) = 0.

(η4-C5H6)Fe(CO)3 has even been mentioned in the reaction of cyclopentadiene with Fe(CO)5.19 If approach is from the same side, the SnMe2 group could undergo two successive migrations Scheme 4

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Complex 11 was isolated as air-stable yellow crystals. Its IR spectrum exhibits only terminal carbonyl bands (1972, 1926, 1910 cm−1). The 1H NMR spectrum of 11 displays four cyclopentadienyl proton peaks at 5.03, 5.00, 4.94, and 4.91 ppm, a singlet for the GeMe2 protons at 0.55 ppm, and a singlet for the SnMe2 protons at 0.44 ppm. The SnMe2 protons are about 0.15 ppm upfield compared with those of the SnMe2 protons in typical compounds (0.60 ppm in 7, 0.56 and 0.62 ppm in 9a, and 0.56 ppm in 9b) containing the Fe−Sn−Fe unit. All these spectroscopic data are fully compatible with the molecular structure of 11 revealed by X-ray diffraction analysis (Figure 3). Complex 12 was also the air-stable yellow crystals. The IR spectrum of 12 exhibits only terminal carbonyl bands (1976, 1952, 1922, 1912 cm−1), which is consistent with those (1996, 1975, 1941, 1927 cm−1) of an analogous complex (CH2)[(η5-C5H4)Fe(CO)2]2SnPh2.16b The 1H NMR spectrum displays two cyclopentadienyl proton peaks at 5.08, 4.89 ppm, a singlet for the GeMe2 protons at 0.51 ppm, and a singlet for the SnMe2 protons at 0.60 ppm, which is exactly the same chemical shift for SnMe2 protons in typical compounds containing the Fe−Sn−Fe unit. An X-ray diffraction analysis confirmed the structure of 12 as GeMe2[(η5-C5H4)Fe(CO)2]2SnMe2 (Figure 4). 13 was assigned as the destannylated product GeMe2[(η5C5H4)Fe(CO)]2(μ-CO)2, on the basis of its 1H NMR and IR spectra as compared with reported data for this compound.17a The production of 11 strongly suggests that there was competitive migration between the SnMe2 and GeMe2 groups. A plausible mechanism was tentatively suggested in Scheme 6.

Figure 2. ORTEP diagram of rac-SiMe 2 [(η 5 - t BuC 5 H 3 )Fe(CO)2]2SnMe2 (9b). Thermal ellipsoids are shown at the 30% level. Selected bond lengths (Å) and angles (deg): Sn(1)−Fe(1) = 2.5660(8), Sn(1)−Fe(2) = 2.5828(9), Sn(1)−C(21) = 2.164(6), Sn(1)−C(22) = 2.147(8), Si(1)−C(1) = 1.866(6), Si(1)−C(12) = 1.863(6), Si(1)−C(10) = 1.826(7), Si(1)−C(11) = 1.857(6); Fe(1)− Sn(1)−Fe(2) = 114.9(3), C(21)−Sn(1)−C(22) = 103.8(3), C(1)− Si(1)−C(12) = 113.8(2), C(10)−Si(1)−C(11) = 112.3(4), Fe(1)− C(23)−O(1) = 178.8(7), Fe(1)−C(24)−O(2) = 178.6(6), Fe(2)− C(25)−O(3) = 178.5(6), Fe(2)−C(26)−O(4) = 176.8(7), Cp-Cp fold angle 94.1, Cp(centroid)−Fe(1)−Sn(1) = 118.2, Cp(centroid)− Fe(2)−Sn(1) = 121.0, Cp(centroid)−Fe(1)···Fe(2)−Cp(centroid) = 85.7.

twisted-boat conformation. The mean Sn−Fe bond distance (2.57 Å) is almost equal to that in 9a (2.5719(4) Å) and the nonbridged analogue [(η5-C5H5)Fe(CO)2]2SnMe2 (2.60 Å). The steric requirements of the two [(η5-tBuC5H3)Fe(CO)2] fragments impose a significant distortion from tetrahedral coordination on the tin atom, as reflected by the large Fe(1)− Sn(1)−Fe(2) angle of 114.93(3)°; this results in a diminished C(21)−Sn(1)−C(22) angle of 103.8(3)°. These angles are somewhat close to those (118.341(17) and 101.69(18)°) in 9a, and those (123 and 104°) in the nonbridged analogue [(η5C5H5)Fe(CO)2]2SnMe2.16d The two [(η5-tBuC5H3)Fe(CO)2] fragments linked by one SiMe2 bridge are arranged almost perpendicular to each other, as indicated by the dihedral angle of 94.1° between the Cp ring planes; the torsion angle of Cp(centroid)−Fe(1)···Fe(2)−Cp(centroid) (85.7°) shows that 9b adopts a completely twisted conformation. Reaction of (GeMe2)(SnMe2)(C5H4)2 (4) with Fe(CO)5. Since the migration ability of the bridging SiMe2 group is not as competitive as that of SnMe2, as indicated by the reactions of the (SiMe2)(SnMe2) doubly bridged ligands 2 and 3 with Fe(CO)5, we turned our attention to the synthesis of the (GeMe2)(SnMe2) doubly bridged bis(cyclopentadiene) 4 and expected to see competitive migration of the bridging GeMe2 and SnMe2 groups in its reaction with Fe(CO)5. The reaction of ligand 4 with Fe(CO)5 in refluxing xylene afforded the two yellow crystalline solids 11 (31% yield) and 12 (25% yield), together with one dark red solid, 13 (9% yield) (Scheme 5).

Scheme 6

It is somewhat similar to that in Scheme 4. It is only different in the final step, when the two Fe(CO)3 moieties are on opposite sides: (ii) the SnMe2 group migrates first from the Cp ring to Fe to give an intermediate containing an Fe−Sn bond, then in the next step (iii) the GeMe2 group moves from the Cp ring to

Scheme 5

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its tin analogue (2.539(1) Å for [SnMe 2 (η5-C5H4)Fe(CO)2]2).23 The molecular structure of 12 is presented in Figure 4. It has an approximate C2 axis passing through the Ge and Sn atoms,

the other Fe instead of the SnMe2 group, which is most likely due to its competitive migration ability and steric favor. Migration of the GeMe2 group could avoid the rotation of the Cp ring, to give the stable six-membered ring product 11. Generally, compounds exhibiting structures similar to 11 ([(EMe2)(η5-C5H4)M(CO)2][(E′Me2)(η5-C5H4)M(CO)2], E, E′ = Si, Ge, Sn; M = Fe, Ru) are synthesized from the thermal rearrangement of (EMe2EMe2)[(η5-C5H4)M(CO)]2(μ-CO)222 or by the unexpected addition of 1 equiv of base to [(η5C5H5)Fe(CO)2]2SnMe2.23 Here we report for the first time that this type of compound can be synthesized directly from a doubly bridged bis(cyclopentadiene) ligand (ligand 4) with Fe(CO)5. Combining all of the results described above, it is concluded that the migration ability/activity of bridging groups in doubly bridged bis(cyclopentadienyl) ligands decreases in the order SnMe2 > GeMe2 > SiMe2 in their reactions with transition-metal carbonyl complexes. The molecular structure of 11 is presented in Figure 3. The molecule of 11 consists of one [GeMe2(η5-C5H4)Fe(CO)2]

Figure 4. ORTEP diagram of GeMe2[(η5-C5H4)Fe(CO)2]2SnMe2 (12). Thermal ellipsoids are shown at the 30% level. Selected bond lengths (Å) and angles (deg): Sn(1)−Fe(1) = 2.5826(6), Sn(1)− Fe(2) = 2.5661(6), Sn(1)−C(15) = 2.161(3), Sn(1)−C(16) = 2.171(3), Ge(1)−C(1) = 1.950(3), Ge(1)−C(8) = 1.935(3), Ge(1)−C(6) = 1.941(3), Ge(1)−C(7) = 1.935(3); Fe(1)−Sn(1)− Fe(2) = 115.172(15), C(15)−Sn(1)−C(16) = 102.70(13), C(1)− Ge(1)−C(8) = 112.25(12), C(6)−Ge(1)−C(7) = 113.33(16), Fe(1)−C(13)−O(1) = 178.8(3), Fe(1)−C(14)−O(2) = 178.4(3), Fe(2)−C(17)−O(3) = 179.0(3), Fe(2)−C(18)−O(4) = 177.6(3), Cp−Cp fold angle 96.0, Cp(centroid)−Fe(1)−Sn(1) = 121.7, Cp(centroid)−Fe(2)−Sn(1) = 122.0, Cp(centroid)−Fe(1)···Fe(2)− Cp(centroid) = 82.5. Figure 3. ORTEP diagram of [(GeMe2)(η5-C5H4)Fe(CO)2][(SnMe2)(η5-C5H4)Fe(CO)2] (11). Thermal ellipsoids are shown at the 30% level. Selected bond lengths (Å) and angles (deg): Ge(1)− Fe(1) = 2.470(4), Ge(1)−C(1A) = 2.052(4), Ge(1)−C(8) = 2.042(4), Ge(1)−C(9) = 2.044(4), Sn(1A)−Fe(1A) = 2.443(2), Sn(1A)−C(1) = 2.073(3), Sn(1A)−C(8A) = 2.050(3), Sn(1A)− C(9A) = 2.047(3); Fe(1)−Ge(1)−C(1A) = 111.39(12), C(8)− Ge(1)−C(9) = 109.39(17), C(1)−Sn(1A)−Fe(1A) = 111.69(10), C(8A)−Sn(1A)−C(9A) = 108.94(15), Sn(1A)−C(1)−Fe(1) = 130.51(12), C(1)−Fe(1)−Ge(1) = 100.77(9), Fe(1)−C(6)−O(1) = 179.2(2), Fe(1)−C(7)−O(2) = 177.7(3), Cp−Cp fold angle 0.0.

and the six-membered ring Ge(1)−C(1)−Fe(1)−Sn(1)− Fe(2)−C(8) constituting the molecular framework adopts a twisted-boat conformation. The mean Sn−Fe bond distance of 2.574 Å is almost equal to those in 9a (2.5719(4) Å), 9b (2.5744 Å), and the nonbridged analogue [(η5-C5H5)Fe(CO)2]2SnMe2 (2.60 Å). The steric demand of the two [(η5C5H4)Fe(CO)2] fragments imposes a significant distortion from tetrahedral coordination on the tin atom, as reflected by the large Fe(1)−Sn(1)−Fe(2) angle of 115.172(15)° and the resulting small C(15)−Sn(1)−C(16) angle of 102.70(13)°, which are almost equal to those (118.341(17) and 101.69(18) °) in 9a and those (114.9(3) and 103.8(3)°) in 9b; this means there is no significant steric effect of the two substituted tBu groups on the molecular structure. The two [(η5-C5H4)Fe(CO)2] fragments linked by one GeMe2 bridge are arranged almost perpendicular to each other, which is evident in the dihedral angle of 96.0° between the Cp ring planes and the torsion angle of Cp(centroid)−Fe(1)···Fe(2)−Cp(centroid) (82.5°), indicating that 12 adopts a completely twisted conformation. Photolysis of Complexes 5, 7, and 12. We considered whether the destannylated products (6, 8, and 13) might be the thermolysis products from the corresponding Fe−Sn−Fe

moiety and one [SnMe2(η5-C5H4)Fe(CO)2] moiety linked to each other by Ge−Fe and Sn−Fe bonds. Like many analogues ([GeMe 2 (η 5 -C 5 H 4 )Fe(CO) 2 ] 2 , 22c [GeMe 2 (η 5 -C 5 Me 4 )Fe(CO)2]2,22c [SnMe2(η5-C5H4)Fe(CO)2]223), 11 has Ci symmetry. The six-membered ring Fe(1)−Ge(1)−C(1A)−Fe(1A)−Sn(1A)−C(1), constituting its molecular framework, adopts a stable chair conformation. The Fe−Ge bond distance (2.470(4) Å) is slightly longer than those in the germanium analogues (2.379(2) Å for [GeMe2(η5-C5H4)Fe(CO)2]2, 2.401(1) and 2.395(1) Å for [GeMe2(η5-C5Me4)Fe(CO)2]2), while the Fe−Sn bond distance (2.443(2) Å) is shorter than in 3039

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Organometallics

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Reaction of (SnMe2)(tBuC5H4)2 (1) with Fe(CO)5. A solution of 0.35 g (0.89 mmol) of (SnMe2)(tBuC5H4)2 and 0.25 mL (1.90 mmol) of Fe(CO)5 in 20 mL of xylene was refluxed for 16 h. After removal of solvent, the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent. The first band (yellow) afforded 5 (202 mg, 37% yield) as a yellow solid. The second band (red) gave 6 (50 mg, 12% yield) as brown crystals. Data for 5 are as follows. Anal. Calcd for C24H32Fe2O4Sn: C, 46.88; H, 5.25. Found: C, 46.67; H, 5.18. 1 H NMR (CDCl3): δ 4.64 (m, 4H, Cp H), 4.55 (m, 4H, Cp H), 1.27 (s, 18H, tBu H), 0.60 (s, 2J(1H−119Sn) = 17.4 Hz, 6H, Sn−Me). IR (νCO, cm−1): 1960 (s), 1914 (s). Reaction of (SiMe2)(SnMe2)(C5H4)2 (2) with Fe(CO)5. A solution of 0.50 g (1.49 mmol) of (SiMe2)(SnMe2)(C5H4)2 and 0.50 mL (3.80 mmol) of Fe(CO)5 in 20 mL of xylene was refluxed for 18 h. After removal of solvent the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent. The first band (yellow) afforded 7 (268 mg, 32%) as orange crystals. The second band (red) gave 8 (75 mg, 12%) as brown crystals. Data for 7 are as follows. Anal. Calcd for C18H20Fe2O4SiSn: C, 38.69; H, 3.61. Found: C, 38.48; H, 3.66. 1H NMR (CDCl3): δ 5.10 (m, 4H, Cp H), 4.91 (m, 4H, Cp H), 0.60 (s, 2J(1H−119Sn) = 18.6 Hz, 6H, Sn−Me), 0.36 (s, 6H, Si−Me). IR (νCO, cm−1): 1980 (s), 1961 (s), 1925 (s), 1899 (s). Reaction of (SiMe2)(SnMe2)(tBuC5H3)2 (3) with Fe(CO)5. A solution of 0.50 g (1.10 mmol) of (SiMe2)(SnMe2)(tBuC5H3)2 and 0.40 mL (3.00 mmol) of Fe(CO)5 in 20 mL of xylene was refluxed for 16 h. After removal of solvent the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent. The first band (yellow) afforded 9b (98 mg, 13%) as orange crystals. The second band (yellow) afforded 9a (46 mg, 6%) as orange crystals. The third band (yellow) afforded 10b (87 mg, 15%) as brown crystals. The fourth band (yellow) afforded 10a (64 mg, 11%) as brown crystals. Data for 9a are as follows. Anal. Calcd for C26H36Fe2O4SiSn: C, 46.54; H, 5.41. Found: C, 46.61; H, 5.52. 1H NMR (CDCl3): δ 4.91 (m, 2H, Cp H), 4.89 (m, 2H, Cp H), 4.78 (m, 2H, Cp H), 1.26 (s, 18H, tBu H), 0.62 (s, 2J1H- 119Sn = 18.3 Hz, 3H, Sn−Me), 0.56 (s, 2J(1H−119Sn) = 17.7 Hz, 3H, Sn−Me), 0.34 (s, 3H, Si−Me), 0.33 (s, 3H, Si−Me). IR (νCO, cm−1): 1980 (s), 1955 (s), 1928 (s), 1909 (s). Data for 9b are as follows. Anal. Calcd for C26H36Fe2O4SiSn: C, 46.54; H, 5.41. Found: C, 46.45; H, 5.38. 1H NMR (CDCl3): δ 4.97 (m, 2H, Cp H), 4.84 (m, 2H, Cp H), 4.59 (m, 2H, Cp H), 1.29 (s, 18H, tBu H), 0.56 (s, 2J(1H−119Sn) = 18.6 Hz, 6H, Sn−Me), 0.34 (s, 6H, Si−Me). IR (νCO, cm−1): 1976 (s), 1956 (s), 1915 (s), 1906 (s). Reaction of (GeMe2)(SnMe2)(C5H4)2 (4) with Fe(CO)5. A solution of 0.50 g (1.32 mmol) of (GeMe2)(SnMe2)(C5H4)2 and 0.50 mL (3.80 mmol) of Fe(CO)5 in 20 mL of xylene was refluxed for 22 h. After removal of solvent the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent. The first band (yellow) afforded 11 (245 mg, 31%) as yellow crystals. The second band (yellow) afforded 12 (200 mg, 25%) as orange crystals. The third band (red) gave 13 (55 mg, 9%) as brown crystals. Data for 11 are as follows. Anal. Calcd for C18H20Fe2GeO4Sn: C, 35.83; H, 3.34. Found: C, 35.71; H, 3.26. 1H NMR (CDCl3): δ 5.03 (m, 2H, Cp H), 5.00 (m, 2H, Cp H), 4.94 (m, 2H, Cp H), 4.91 (m, 2H, Cp H), 0.55 (s, 6H, Ge−Me), 0.44 (s, 2J(1H−119Sn) = 23.4 Hz, 6H, Sn−Me),. IR (νCO, cm−1): 1972 (s), 1926 (s), 1910 (s). Data for 12 are as follows. Anal. Calcd for C18H20Fe2GeO4Sn: C, 35.83; H, 3.34. Found: C, 35.77; H, 3.41. 1H NMR (CDCl3): δ 5.08 (m, 4H, Cp H), 4.89 (m, 4H, Cp H), 0.60 (s, 2J(1H−119Sn) = 18.6 Hz, 6H, Sn−Me), 0.51 (s, 6H, Ge−Me). IR (νCO, cm−1): 1976 (s), 1952 (s), 1922 (s), 1912 (s). Photolysis of Complexes 5, 7, and 12. A 50 mg (0.08 mmol) sample of [(η5-tBu(C5H4)Fe(CO)2]2SnMe2 (5) in 5 mL of THF was photolyzed with UV light for 30 min. The solvent was pumped off from the resulting red solution, and the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent; the only band (red) gave 6 (30 mg, 79%) as brown crystals. A 50 mg (0.09 mmol) sample of SiMe2[(η5-C5H4)Fe(CO)2]2SnMe2 (7) in 5 mL of THF was photolyzed for 30 min. Solvent was pumped off from the resulting red solution, and the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent; the only band (red) gave 8 (23 mg, 63%) as brown crystals.

complexes (5, 7, and 12); however, when a xylene solution of 5, 7, or 12 was heated under reflux for 24 h, no product was observed by TLC monitoring except for the starting complex. This suggests that complexes 6, 8, and 13 were formed by an independent pathway during the reaction but not from the corresponding Fe−Sn−Fe complexes. Also, we were curious about the stability of Fe−Sn−Fe complexes (5, 7, and 12) upon photolysis with UV radiation. A sample of 5, 7, or 12 in toluene was photolyzed for 1 h, the solvent was pumped off from the resulting red solution, and the corresponding destannylated product (6, 8, or 13) was obtained (37−79% yield) (Schemes 7 Scheme 7

Scheme 8

and 8); this is consistent with the situation described in the photolysis of their nonbridged analogue [(η5-C5H5)Fe(CO)2]2SnMe2 with a medium-pressure Hg lamp, which also afforded the destannylated product [(η5-C5H4)Fe(CO)2]2.24

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CONCLUSION Reactions of the singly bridged bis(cyclopentadiene) (SnMe2)(tBuC5H4)2 (1) or doubly bridged bis(cyclopentadienes) (EMe2)(SnMe2)(RC5H3)2 (2, 3 (E = Si), 4 (E = Ge)) with Fe(CO)5 in refluxing xylene were studied. The bridging SnMe2 group in the ligands generally migrated twice to give compounds 5, 7, 9a,b and 12 with the Fe−Sn−Fe structural feature, together with the corresponding destannylated products 6, 8, 10a,b, and 13. Only for the reaction of ligand 4 with Fe(CO)5 was a product (11) obtained in which both the SnMe2 and GeMe2 groups migrated. The migrating abilities of bridging groups EMe2 (E = Sn, Ge, Si) were compared, and a plausible stepwise migration mechanism was proposed, while the destannylation mechanism still remains unclear. More detailed mechanistic studies of EMe2 (E = Sn, Ge, Si) group migration and an extension of the research from Fe(CO)5 to other transition-metal carbonyls are in progress.

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EXPERIMENTAL SECTION

General Considerations. Schlenk and vacuum line techniques were employed for all manipulations. All solvents were distilled from appropriate drying agents under argon prior to use. 1H NMR spectra were recorded on a Bruker AV300 instrument. IR spectra were recorded as KBr disks on a Nicolet 560 ESP FTIR spectrometer. Elemental analyses were performed on a Perkin−Elmer 240C analyzer. Photolyses were conducted with a 250 W high-pressure Hg lamp in an ice−water bath. Ligands 1−4 were prepared by literature methods.10−12,14,25 3040

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Organometallics

Article

Table 1. Crystal Data and Summary of X-ray Data Collection for 9a,b, 11, and 12 formula fw T (K) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ (μm−1) F(000) cryst size (mm) max 2θ (deg) no. of rflns collected no. of indep rflns/Rint no. of params goodness of fit on F2 R1, wR2 (I > 2σ(I)) R1, wR2 (all data) largest diff peak, hole (e Å−3)

9a

9b

11

12

C52H72Fe4O8Si2Sn2 1342.06 296(2) orthorhombic Pnma 12.3105(13) 18.709(2) 12.5383(13) 90 90 90 2887.8(5) 2 1.543 1.919 1360 0.15 × 0.14 × 0.13 50 13 973 2626/0.0261 170 1.035 0.0215, 0.0542 0.0252, 0.0572 0.361, −0.620

C52H72Fe4O8Si2Sn2 1342.06 296(2) triclinic P1̅ 10.2768(12) 10.9217(13) 15.2369(19) 71.693(2) 76.019(2) 68.965(2) 1499.3(3) 1 1.486 1.848 680 0.17 × 0.16 × 0.14 50.02 7434 5135/0.0168 317 1.075 0.0340, 0.0762 0.0479, 0.1053 0.714, −0.789

C18H20Fe2GeO4Sn 603.32 296(2) monoclinic C2/c 18.851(3) 8.6931(13) 13.460(2) 90 106.384(2) 90 2116.2(6) 4 1.894 3.935 1176 0.18 × 0.17 × 0.16 50 5255 1866/0.013 128 1.056 0.0159, 0.0397 0.0180, 0.0408 0.226, −0.186

C18H20Fe2GeO4Sn 603.32 296(2) monoclinic P21 9.1782(19) 12.419(3) 9.2376(19) 90 93.203(3) 90 1051.3(4) 2 1.906 3.961 588 0.18 × 0.17 × 0.16 49.98 5365 3109/0.0117 239 1.051 0.0135, 0.0302 0.0140, 0.0304 0.206, −0.258

A 50 mg (0.08 mmol) sample of GeMe 2 [(η 5 -C 5 H 4 )Fe(CO)2]2SnMe2 (12) in 5 mL of THF was photolyzed for 30 min. Solvent was pumped off from the resulting red solution, and the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2 as eluent; the only band (red) gave 13 (14 mg, 37%) as brown crystals. Crystallographic Studies. Single crystals of complexes 9a,b, 11, and 12 suitable for X-ray diffraction were obtained by crystallization from hexane/CH2Cl2. Data collection was performed on a Bruker SMART 1000, using graphite-monochromated Mo Kα radiation (ω− 2θ scans, λ = 0.710 73 Å). Semiempirical absorption corrections were applied for all complexes. The structures were solved by direct methods and refined by full-matrix least squares. All calculations were using the SHELXTL-97 program system. The crystal data and a summary of X-ray data collection are presented in Table 1.

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Ministry, and the Talent Fund Projects for Introduced Scholar in Tianjin Normal University (No. 5RL088).

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(1) Keppie, S. A.; Lappert, M. F. J. Organomet. Chem. 1969, 19, P5. (2) Abel, E. W.; Moorhouse, S. J. Organomet. Chem. 1971, 28, 211. (3) Heck, J.; Kriebisch, K.-A.; Mellinghoff, H. Chem. Ber. 1988, 121, 1753. (4) Xu, S.; Xie, W.; Zhou, X.; Wang, J.; Chen, H; Guo, H.; Miao, F. Chem. J. Chin. Univ. 1996, 17, 1065. (5) Wang, B.; Zhu, B; Xu, S.; Zhou, X. Organometallics 2003, 22, 4842. (6) Wang, B.; Zhu, B.; Zhang, J.; Xu, S.; Zhou, X.; Weng, L. Organometallics 2003, 22, 5543. (7) Fox, T.; Burger, P. Eur. J. Inorg. Chem. 2001, 795. (8) Bitterwolf, T. E.; Shade, J. E.; Hansen, J. A.; Rheingold, A. L. J. Organomet. Chem. 1996, 514, 13. (9) Bitterwolf, T. E.; Leonard, M. B.; Horine, P. A.; Shade, J. E.; Rheingold, A. L.; Staley, D. J.; Yap, G. P. A. J. Organomet. Chem. 1996, 512, 11. (10) Gómez-Ruiz, S.; Prashar, S.; Fajardo, M.; Antiñolo, A.; Otero, A. J. Organomet. Chem. 2007, 692, 3057. (11) Hüttenhofer, M.; Prosenc, M.-H.; Rief, U.; Schaper, F.; Brintzinger, H.-H. Organometallics 1996, 15, 4816. (12) Nifant’ev, I. E.; Borzov, M. V.; Churakov, A. V.; Mkoyan, S. G.; Atovmyan, L. O. Organometallics 1992, 11, 3942. (13) Nifant’ev, I. E.; Borzov, M. V.; Ivchenko, P. V.; Yarnykh, V. L.; Ustynyuk, Y. A. Organometallics 1992, 11, 3462. (14) Nifant’ev, I. E.; Yarnykh, V. L.; Borzov, M. V.; Mazurchik, B. A.; Mstyslavsky, V. I.; Roznyatovsky, V. A.; Ustynyuk, Y. A. Organometallics 1991, 10, 3739. (15) (a) du Plooy, K. E.; Marais, C. F.; Carlton, L.; Hunter, R.; Boeyens, J. C. A.; Coville, N. J. Inorg. Chem. 1989, 28, 3855. (b) Reynoud, J.-F.; Leblanc, J.-C.; Moise, C. Organometallics 1985, 4, 1059. (16) (a) Braunschweig, H.; Dörfler, R.; Mager, J.; Radacki, K.; Seeler, F. J. Organomet. Chem. 2009, 694, 1134. (b) McArdle, P.; O’Neill, L.;

ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic details for complexes 9a,b, 11, and 12. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Fax: 86-22-23766532. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We sincerely thank Prof. Robert J. Angelici for improving the English for this article. We also gratefully acknowledge financial support from the National Natural Science Foundation of China (No. 21002069), the Scientific Research Foundation for Returned Overseas Chinese Scholars, the State Education 3041

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Cunningham, D. Inorg. Chim. Acta 1999, 291, 252. (c) McArdle, P.; O’Neill, L.; Cunningham, D.; Manning, A. R. J. Organomet. Chem. 1996, 524, 289. (d) Bir’yukov, B. P.; Struchkov, Y. T.; Anisimov, K. N.; Kolobova, N. E.; Skripkin, V. V. Chem. Commun. 1968, 159. (e) O’Connor, J. E.; Corey, E. R. Inorg. Chem. 1967, 6, 968. (f) Patil, H. R. H.; Graham, W. A. G. Inorg. Chem. 1966, 5, 1401. (17) (a) Zhang, Y.; Xu, S.; Tian, G.; Zhang, W.; Zhou, X. J. Organomet. Chem. 1997, 544, 43. (b) Hua, W.; Zhou, X.; Xu, S.; Wang, R.; Wang, H. Chem. J. Chin. Univ. 1995, 16, 387. (c) Bonati, F.; Wilkinson, G. J. Chem. Soc. 1964, 179. (18) Wegner, P. A.; Uski, U. A.; Kiester, R. P.; Dabestani, S.; Day, V. W. J. Am. Chem. Soc. 1977, 99, 4846. (19) (a) Kochhar, R. K.; Pittit, R. J. Organomet. Chem. 1966, 6, 272. (b) Whitesides, T. H.; Shelly, J. J. Organomet. Chem. 1975, 92, 215. (20) Miyake, S.; Henling, L. M.; Bercaw, J. E. Organometallics 1998, 17, 5528. (21) Zhang, Y.; Xu, S.; Tian, G.; Zhou, X.; Sun, J. J. Organomet. Chem. 1998, 553, 149. (22) (a) Sun, H.; Xu, S.; Zhou, X.; Wang, H.; Yao, X. J. Organomet. Chem. 1993, 444, C41. (b) Zhang, Y.; Xu, S.; Zhou, X. Organometallics 1997, 16, 6017. (c) Xie, W.; Wang, B.; Dai, X.; Xu, S.; Zhou, X. Organometallics 1998, 17, 5406. (d) Sun, H.; Pan, Y.; Huang, X.; Guo, Z.; Zhang, Z.; Zhang, H.; Li, J.; Wang, F. Organometallics 2006, 25, 133. (e) Chen, D.; Guo, J.; Xu, S.; Song, H.; Wang, B. Organometallics 2007, 26, 4212 and references therein.. (23) Sharma, S.; Cervantes, J.; Mata-Mata, J. L.; Brun, M.-C.; Cervantes-Lee, F.; Pannell, K. H. Organometallics 1995, 14, 4269. (24) Triplett, K.; Curtis, M. D. Inorg. Chem. 1976, 15, 431. (25) Zhu, B., Li, Y.; Shi, W.; Chen, Y. Submitted for publication.

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