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Synthesis of iron thienyl complexes
Inorganica Chimica Acta 358 (2005) 2602–2608 www.elsevier.com/locate/ica
Synthesis of iron thienyl complexes Marile´ Landman
a,*
, Mandy van Staden b, Helmar Go¨rls c, Simon Lotz
b,*
a
c
Department of Chemistry, University of South Africa, P.O. Box 392, Pretoria 0003, South Africa b Department of Chemistry, University of Pretoria, Pretoria 0002, South Africa Friedrich-Schiller-Universita¨t, Institut fu¨r Anorganische und Analytische Chemie, Lessingstrasse 8, D-07743 Jena, Germany Received 5 August 2004; accepted 6 March 2005 Available online 7 April 2005
Abstract Dimetallation of thiophene (TH2), bithiophene (BTH2) and 3,6-dimethyl[3,2-b]thienothiophene (TTH2) using a slight excess of butyl lithium, followed by the addition of [FeCp(CO)2I], resulted in the formation of [2,5-{FeCp(CO)2}2T], 1 and [2-{FeCp (CO)2}T]. The analogous reaction with bithiophene as precursor afforded similar products [2,2 0 -{FeCp(CO)2}2BT] 2 and [2-{FeCp (CO)2}BTH] 3. In addition to the expected mono- ([2-{FeCp(CO)2}-TTH] 4) and binuclear ([2,2 0 -{FeCp(CO)2}2-TT] 5) products, dimetallation of 3,6-dimethyl[3,2-b]thienothiophene and the subsequent reaction with [FeCp(CO)2I] yielded carbonyl inserted mono-([2-{FeCp(CO)2}C(O)-{TT}2H] 6) and binuclear ([2-{FeCp(CO)2}C(O)-{TT}2-2 0 -{FeCp(CO)2}] 7) carbon–carbon coupled products. The precursor [2,7-{SnMe3}2-TT] (8) was prepared and reacted with [FeCp(CO)(PEt3)I] in the presence of a palladium catalyst to afford [2-{FeCp(CO)(PEt3)}C(O)-{TT}2-2 0 -{SnMe3}] 10. 2005 Elsevier B.V. All rights reserved. Keywords: Thiophene derivatives; Iron; Binuclear complexes; Carbon–carbon coupling reactions
1. Introduction Five-membered heterocycles, in which transition metals are connected to the a-carbons of the heterocyclic ring, have not received much attention in the literature. Few of these complexes contain more than one metal fragment directly bonded to the heteroaromatic ring system. Complexes containing thiophene [1,2] or thiophene derivatives [3] are more abundant than other five-membered heteroarene metal complexes [4,5,2] because of their relevance as model compounds for desulfurization. Known metallocene complexes of the type (2-thienyl)2MCp2 include the transition metals Ti, Zr, Hf, Nb and W [6]. One of the initial preparations for mono-substituted arene complexes [7] included the reaction of Na [FeCp(CO)2] with halide substituted arene compounds *
Corresponding authors. Tel.: +27 12 4202800; fax: +27 12 3625297. E-mail address: [email protected] (S. Lotz).
0020-1693/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.03.022
at low temperatures and involved the nucleophilic displacement of the halide by [FeCp(CO)2]. Nesmeyanov employed this method in preparing iron complexes of the type [FeCp(CO)2R], with R = 2-thienyl, 2-furyl, 5methyl-2-furyl and 4,5-benzo-2-furyl. These complexes were synthesized by the reaction of Na[FeCp(CO)2] with 2-heteroaryl carbonyl chloride, followed by photochemical decarbonylation of these acyl complexes to yield the target products [8]. Rauchfuss et al. [9] prepared this same 2-[FeCp(CO)2]thienyl complex as part of a research study on the activation and desulfurization of thiophene and benzothiophene by iron carbonyls. Very few examples of disubstituted r,r-arene or -heteroarene complexes are known in the literature and several different methods [10–12] have been employed in an attempt to synthesize these complexes. Kotani et al. [13] prepared [Pt(PBu3)2(2-thienyl)2] as well as 2,5-thienylene-bridged diplatinum complexes. This study was extended to include bithiophene as
M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
bridging ligand. Synthesis of the 2-thienyl and 2,5thienylene platinum compounds was accomplished via a 2-trimethylstannylthiophene [4c] and a 2,5-bis(trimethylstannyl)thiophene [14] precursor. Nickel and palladium complexes were prepared in a similar fashion to the method employed by Mu¨ller and Brune [15] for the preparation of disubstituted phenyl platinum complexes. Evidence of metal–metal communication [16] through the phenyl conjugated ring system prompted further study of thiophene and similar compounds. From the literature work discussed, it is clear that the synthesis of iron carbonyl complexes with arene substituents is not straightforward. Several different methods have been employed for various different arenes and heteroarenes. These methods have been employed and evaluated in the syntheses of the novel iron complexes of different thiophene derivatives reported in this study. The reactivities of mono- and dilithiated thiophene derivatives with iron carbonyl compounds were investigated.
2. Results and discussion The first synthetic route employed in preparing the iron complexes with thiophene derivatives was the synthesis via lithiated intermediates, a similar method used by Lapinte et al. [17] in synthesizing compounds consisting of long carbon chains end-capped with FeCp(CO)2metal moieties. The thiophene ligands were dilithiated using n-butyl lithium and TMEDA in a hexane solution at elevated temperatures or in THF at low temperatures. Upon reaction of 2,5-dilithiated thiophene with FeCp (CO)2I, two products were isolated: firstly, the yellow [2-FeCp(CO)2TH] complex, previously prepared by Nesmeyanov et al. [8], and secondly the orange coloured [2,5-{FeCp(CO)2}2T] complex, 1. This product has been documented in a review article [18], but to our knowledge the spectroscopic data have not yet been published. Both complexes were formed in low yields and the disubstituted complex especially seemed to be very unstable. Similar products were formed in the reaction Me
S
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of dilithiated bithiophene. The orange-red [2,9-{FeCp (CO)2}2BT] complex, 2, and the yellow [2-FeCp (CO)2BTH] complex, 3, were isolated, but in this case the binuclear complex was found to be particularly stable. The analogous reaction using 3,6-dimethylthieno[3,2-b]thiophene afforded four products. Again the mono iron complex, 5, as well as the bis complex, 4, was yielded, but two more products, complexes 6 and 7, in which C–C coupling is observed, were formed. Fig. 1 shows the reaction of a bis iron complex 4 and a mono iron complex 5 to form complex 6 and the reaction between two bis iron complexes 4 to form complex 7. These C–C coupling reactions are facilitated by the formation of the iron dimer [FeCp(CO)2]2. It is assumed that the insertion of a carbonyl group stabilizes the molecule. This reaction was also performed using the metal complex MoCp(CO)2Cl, but no organometallic products were formed during the reaction Table 1. It was obvious from the yields of the reaction products that these reactions had not gone to completion. It was suggested that the reason for the low reactivity between the two reagents could be ascribed to the relative strength of the Fe–I bond. By substituting the iodine ligand for a more labile leaving group on the metal, a higher yield of target products was envisaged. Therefore, it was contemplated to repeat the reactions, but instead of reacting the lithiated species with FeCp(CO)2I, FeCp(CO)2(O3SCF3) was used, containing a triflate leaving group. This method, however, proved to be unsuccessful since only the mono iron complex was obtained for both ligands. A new approach towards the synthesis of disubstituted iron complexes of thiophene derivatives was decided on, based on the literature reports by Lo Sterzo et al. [19]. They recounted the preparation of rmetallaacetylides by palladium-catalyzed formation of metal–carbon bonds. The general procedure constitutes the coupling of halogen-containing transition metal moieties to mono- and bis[(trimethylstannyl) acetylides] in the presence of catalytic amounts of palladium. The 2,5-bis(trimethylstannyl)thiophene [14] and 2,7-bis(trimethylstannyl)-3,6-dimethylthieno[3,2-b]
H
(OC)2CpFe S Me
S
Me
CO
Me
S
2 FeCp(CO)2 I S
Me
+
2 n-BuLi
FeCp(CO)2 (OC)2CpFe
Me 5
Me
Fig. 1. Synthesis of complexes 4–7.
R
S
O
S
C S
(OC)2CpFe S
S
Me
4
Me
R=H 6 Me R = FeCp(CO)2 7 + [FeCp(CO)2]2
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Table 1 Spectroscopic data for 1–10 Complex 1 2 3
4 5 6
1
13
H NMR data (d/ppm in CDCl3)
4.95 (s, 10H, Cp), 6.83 (s, 2H, H3) 4.96 (s, 10H, Cp), 6.64 (d, 2H, H4, J = 2.3), 6.96 (d, 2H, H3, J = 1.8) 4.98 (s, 5H, Cp), 6.93 (t, 1H, H8, J = 4.4), 6.98 (s, br, 1H, H4), 7.05 (t, 1H, H7, J = 4.4), 7.11 (s, br, 1H, H9), 7.24 (s, br, 1H, H3) 2.27 (d, 3H, Me, J = 1.0 Hz), 2.31 (s, 3H, Me), 5.01 (s, 5H, Cp), 6.68 (q, 1H, H7, J = 1.0) 2.25 (s, 6H, Me3 and Me6), 4.95 (s, 10H, Cp) 2.33 (s, 3H, Me), 2.36 (s, 3H, Me), 2.54 (s, 3H, Me), 2.55 (s, 3H, Me), 5.00 (s, 5H, Cp), 7.13 (s, 1H, H13)
7
2.34b (s, 6H, Me9 and Me12), 2.52 (s, 6H, Me3 and Me6), 5.02 (s, 10H, Cp)
8
0.40 (d, 18H, SnMe3, J = 55.8), 2.37 (s, 6H, Me)
9
2.34 (s, 3H, Me6), 2.38 (s, 3H, Me3), 6.93 (s, 1H, H7), 0.42 (d, 9H, SnMe3, J = 56.1)
10
0.05 (d, 9H, SnMe3, J = 56.8), 0.84 (t, 9H, P(CH2CH3)3, J = 6.3 Hz), 1.23 (m, 6 H, P(CH2CH3)3), s2.32 (s, 3H, Me12), 2.36 (s, 3H, Me9), 2.57 (s, 3H, Me6), 2.61 (s, 3H, Me3)
a b
IR dataa (m/cm1 in CH2Cl2)
C NMR data (d/ppm in CDCl3)
85.5 (Cp), 140.7 (C3), 150.0 (C2), 215.2 (Fe(CO)2) 86.1 (Cp), 139.3 (C3), 124.5 (C4), 214.8 (Fe(CO)2)
2025 (s), 1972 (vs) 2028 (s), 1976 (vs)
84.7 (Cp), 138.2 (C3), 120.7 (C4), 124.8 (C7), 126.5 (C8), 121.4 (C9), 213.2 (Fe(CO)2)
2034 (s), 1987 (vs)
14.8 (Me), 17.3 (Me), 85.8 (Cp), 129.6 (C7), 136.3 (C6), 142.8 (C3) 145.8 (C2), 214.4 (Fe(CO)2) 17.2 (Me), 85.8 (Cp), 214.2 (Fe(CO)2) 14.6 (Me), 15.2 (Me), 15.7 (Me), 17.3 (Me), 85.9 (Cp), 125.3 (C12), 130.4 (C13), 132.1 (C9), 135.9 (C6), 136.7 (C3), 213.9 (Fe(CO)2), 255.2 (C@O) 14.1 (Me), 14.7 (Me), 15.6 (Me), 17.4 (Me), 85.7 (Cp), 213.7 (Fe(CO)2), 254.8 (C@O)
2026 (s), 1974 (vs) 2023 (s), 1972 (vs) 2029 (s), 1978 (vs) 1655 (C@O) 2053 (s), 2028 (s), 2007 (vs), 1978 (vs) 1656 (C@O)
8.33 (SnMe3), 16.4 (Me), 134.9 (C4), 136.5 (C6), 147.6 (C2) 8.25 (SnMe3), 14.7 (Me), 16.3 (Me), 122.1 (C6), 130.1 (C7), 134.7 (C5), 136.8 (C3), 142.4 (C4), 145.4 (C2) 1941 (vs)
Carbonyl region. Overlap of signals occurs, broad bands observed.
fragment. Other products were also observed, but unfortunately their yields were too low to be able to isolate and characterize. Complexes 1–10 were characterized spectroscopically using infrared and NMR spectroscopy as well as mass spectrometry. Recording of 13C NMR spectra proved to be problematic, since the complexes were unstable at room temperature and even more so in solution. Decomposition occurred in several cases and made the unambiguous assignment of resonance peaks impossible in several cases. Nearly all the carbons in the structures of the complexes are quaternary carbons. It was interesting to note that the thiophene
thiophene (8) were prepared in order to apply this method to our ligand systems. The mono-substituted compound, 2-(trimethylstannyl)-3,6-dimethylthieno [3,2-b] thiophene 9, formed as a byproduct in the preparation of 8. The planned synthetic route for preparation of the iron complexes is outlined in Fig. 2. After completion of the reactions for both ligands, it was only possible to isolate and characterize one product, 10, formed in the reaction of FeCp(CO)(PEt3)I with 2,7-bis(trimethylstannyl)-3,6-dimethylthieno[3,2-b]thiophene (8). This product was formed similar to the formation of complexes 6 and 7 by the substitution of one of the trimethylstannyl groups by an iron metal
Me
S SnMe3 +
Me3Sn S 8
2 FeCp(CO)(PEt3)I
Me Pd catalyst Me
Me
S
S FeCp(CO)(PEt3)
Me
S
O
(Et3P)(OC)CpFe S
Me
(Et3P)(OC)CpFe
SnMe3
S
C S
10 Me
Fig. 2. Formation of C–C coupled bisthienothiophene iron complex.
Me
M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
complexes were seemingly more stable than their 3,6dimethylthieno[3,2-b]thiophene counterparts, which is contrary to the trend observed for carbene complexes of these thiophene derivatives where the complexes with the condensed rings were more stable than the analogous thiophene complexes [20]. Pauson et al. [21] suggested that the Fe–Carene bond is stabilized by the effect of the condensed ring. This same effect was observed by Nesmeyanov et al. [8], who observed the stability of the [2-{FeCp(CO)2}benzofuryl] complex compared to the iron complexes containing fivemembered heterocyclic ligands. Suitable crystals for X-ray diffraction studies were obtained for 8, which crystallized as colourless cubic crystals, from a dichloromethane/hexane (1:1) solution. For 4 a quartet splitting pattern is found for the proton on the 7-position. This is due to long-range coupling with the methyl protons on the 6-position. For this methyl group a doublet is observed, instead of the expected singlet and the coupling constant of 1.0 Hz is calculated, correlating well with other four-band couplings observed in the literature [22]. The 1H NMR spectrum of 7 is affected by the coordination of a second metal moiety in that broad, undefined peaks are observed compared to the high resolution of the mononuclear complex. Interesting to note is the stability of 7 even though the second metal fragment is directly bonded to the ring system and carbonyl insertion did not take place to stabilize this metal moiety. Previously, it was shown in our laboratories that a second manganese alkyl bond is stabilized by a carbonyl group inserted into the manganese alkyl bond on the other side of a conjugated spacer [23]. Doublets are observed on the 1H NMR spectra of 8, 9 and 10 for the methyl protons of the trimethylstannyl groups. These doublets are ascribed to coupling of these protons with the Sn nucleus. A large coupling constant is observed for this coupling, which corresponds well with the literature values [24].
2605
Fig. 3. Ball-and-stick plot of 8.
The tin atom is in a pseudotetrahedral environment, evident from the bond angles around the Sn atom. The bond angles of C(7)–Sn–C(6) 109.9(2), C(7)–Sn– C(1) 112.3(2), C(6)–Sn–C(1) 107.0(1), C(7)–Sn–C(5) 110.1(2), C(6)–Sn–C(5) 111.4(2) and C(1)–Sn–C(5) 105.9(2) are marginally different from the normal value of 109 for tetrahedral arrangements. The Sn–C(thienyl) ˚ ) as those recorded for bond length is the same (2.15(1) A the same bonds in [Sn(thienyl)4] [25] and the analogous ˚ ). These distances are similar [Sn(phenyl)4] [26] (2.14(1) A ˚ found for Sn– to the average bond length of 2.14 A C(Me) bonds. 2.2. Conclusion This study has shown that lithiated thiophene derivatives in combination with iron metal precursors afford complex reaction mixtures leading to various products in low yields. Furthermore, many of the intermediates are unstable and the observation of products resulting from carbon–carbon coupling reactions, facilitated by the CpFe(CO)L fragment, is of interest.
3. Experimental 3.1. General
2.1. Structural studies A single X-ray determination confirmed the structure of 8. Selected bond lengths and angles are given in Table 2. Fig. 3 represents a ball-and-stick plot of this structure. Table 2 Selected bond lengths and angles of 8 8
bond ˚) lengths (A
8
bond angles ()
Sn–C(1) S(1)–C(1) C(1)–C(2) C(2)–C(3) C(2)–C(4) C(3)–C(3)#1 C(3)–S(1)#1
2.152(3) 1.757(3) 1.369(5) 1.438(5) 1.513(5) 1.395(7) 1.730(4)
C(3)#1–S(1)–C(1) C(2)–C(1)–S(1) C(1)–C(2)–C(3) C(3)#1–C(3)–C(2)
92.50(16) 111.8(2) 111.3(3) 114.7(4)
All reactions and manipulations were performed under an inert atmosphere using standard Schlenk-tube techniques [27]. Solvents were dried by the usual procedures [28] and distilled under nitrogen prior to use. The starting materials thiophene, bithiophene and n-BuLi as well as the palladium catalyst Pd(CH3CN)2Cl2 were obtained from Aldrich and thiophene was purified as described in the literature [29]. The compounds 3,6-dimethylthieno[3,2-b]thiophene [30], [FeCp(CO)2I] [31], [FeCp(CO)(PEt3)I] [32,33] and [2,5-bis(SnMe3)thiophene][14] were synthesized according to the known literature methods. Column chromatography was performed on silica gel (0.063–0.200 mm) on columns that were cooled by circulating cold isopropanol (20 C) through column jackets. The solvents used for column chromatography were dichloromethane:hexane mixtures
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in varying ratios, unless stated otherwise. NMR spectra were recorded in CDCl3 as solvent on a Bruker AC-300 spectrometer with reference to the deuterium signal CDCl3. 1H and 13C NMR spectra were measured at 300.133 and 75.469 MHz, respectively. Infrared spectra were recorded as CH2Cl2 solutions on a BOMEM Michelson-100 FT spectrophotometer. Mass spectra were recorded on a Perkin–Elmer RMU-6H instrument operating at 70 eV. Melting points were recorded in capillaries on a Gallenkamp hot-stage apparatus and are uncorrected. 3.2. Synthesis of the metal complexes 3.2.1. Synthesis of [2,5-{FeCp(CO)2}2T] (1) Dilithiation of thiophene was accomplished by adding 17.0 ml (27.3 mmol) of n-butyl lithium and 3.7 ml (24.8 mmol) of TMEDA to a solution of 0.99 ml (12.4 mmol) of thiophene in 50 ml of hexane and refluxing the mixture for 30 min. The reaction mixture was cooled to 0 C, 30 ml of THF was added and cooled further to 20 C. 6.9 g (22.7 mmol) of FeCp(CO)2I was added with vigorous stirring and maintained for a further 2 h while the temperature was allowed to gradually raise until room temperature was reached. After filtration through silica gel and sodium sulfate, the solvent was removed under reduced pressure and the residue purified using column chromatography. Four bands were distinguished on the column. The first yellow band was identified as the mono iron complex previously synthesized by Nesmeyanov et al. [8]. The second brown product was the starting compound FeCp(CO)2I. The third red band was isolated and identified to be the iron dimer complex [FeCp(CO)]2. The fourth orange compound was characterized as the bis iron complex [2,5-{FeCp (CO)2}2T] (1). This compound is very polar and could only be collected by using pure dichloromethane as eluent. 1: Anal. Calc. for Fe2C18H12O4S: C, 49.58; H, 2.77. Found: C, 49.87; H, 2.91%. Yield: 1.13 g (21%), MS (EI): m/z 435.8 (50) [M+]; 407.8 (44) [M+ CO]; 379.8 (98) [M+ 2CO]; 351.8 (20) [M+ 3CO]; 323.8 (96) [M+ 4CO]; 258.8 (56) [M+ 4CO Cp]; 193.9 (19) [M+ 4CO 2Cp]; 83.0 (26) [M+ 4CO 2Cp 2Fe]. 3.2.2. Synthesis of iron complexes 2 and 3 Bithiophene (0.83 g, 5 mmol) was dissolved in 50 ml of tetrahydrofuran at 90 C under argon gas. The clear solution was stirred while 1.5 ml (10 mmol) of TMEDA was added, followed by the dropwise addition of 6.4 ml (10 mmol) of n-butyl lithium. The solution was stirred for 5 min after the additions and then allowed to warm to 50 C. Stirring was continued for a further 15 min at this temperature, during which time the colour of the solution changed from clear to milky yellow. The
solution was cooled to 80 C and stirred while [FeCp (CO)2I] (3.0 g, 10 mmol) was added. The mixture was stirred for 1 h at this temperature, allowed to warm up to room temperature and stirred for another hour. The solution turned bright red. The solvent was removed under reduced pressure and replaced with dichloromethane. The reaction mixture was filtered through silica gel using dichloromethane as solvent that resulted in the formation of a thick layer of orange solid on the top of the filter. The orange product was identified as [2,5-{FeCp (CO)2}2BT] 2. Crystallization from a 1:1 hexane:dichloromethane mixture yielded very flat, orange air-stable platelets. The remainder of the product mixture was separated by column chromatography. [2-FeCp(CO)2BTH] 3 was removed from the column as a yellow fraction with a 1:1 hexane:dichloromethane mixture as eluent. It was highly unstable and decomposed rapidly in solution. 2: Anal. Calc. for Fe2C22H14O4S2: C, 50.99; H, 2.72. Found: C, 51.21; H, 2.91%. Yield: 2.31 g (89%); MS (EI): m/z 517.9 (22) [M+]; 490.0 (6) [M+ CO]; 462.0 (76) [M+ 2CO]; 406.0 (100) [M+ 4CO]; 340.0 (5) [M+ 2CO Cp]; 274.0 (2) [M+ 4CO 2Cp]. 3: Anal. Calc. for FeC15H10O2S2: C, 52.64; H, 2.95. Found: C, 52.81; H, 3.11%. Yield: 0.13 g (8%); MS (EI): m/z 342.0 (32) [M+]; 314.0 (29) [M+ CO]; 285.9 (94) [M+ 2CO]; 219.2 (25) [M+ 2CO Cp]. 3.2.3. Synthesis of iron complexes 4, 5, 6 and 7 Dimetallation of 3,6-dimethylthieno[3,2-b]thiophene was accomplished by dissolving 0.337 g (2.0 mmol) of the ligand in 30 ml of dry ether and adding 1.4 ml (2.2 mmol) of n-butyl lithium while cooling the mixture on an ice bath. The mixture was stirred for 2 h at this temperature and for a further 30 min at room temperature. The reaction mixture was cooled to 40 C after which 0.6 g (2.0 mmol) of [FeCp(CO)2I] was added. The reaction was stirred for 15 min at this temperature and for a further 2 h at room temperature. Filtration through silica gel and the subsequent evaporation of the solvent in vacuo afforded a brown residue. Six products were isolated using column chromatography. The first product isolated was unreacted HTTH, yield: 0.03 g (8%). The second yellow product was characterized as the mono iron complex [2-FeCp(CO)2TTH] 4. The third brown product was identified as the iron starting material [FeCp(CO)2I], yield: 0.16 g (27%). The following two range-yellow products were found to be ([2-{FeCp (CO)2}C(O)-{TT}2H] 6) and ([2-{FeCp(CO)2}C(O){TT}2-2 0 -{FeCp(CO)2}] 7), which were isolated with yields of 0.17 g (16%) and 0.16 g (11%), respectively. The sixth orange product ([2,2 0 -{FeCp(CO)2}2-TT] 5) was isolated using dichloromethane as eluent. This product was characterized as the bis-iron complex. 4: Anal. Calc. for FeC15H12O2S2: C, 52.33; H, 3.49. Found: C, 52.51; H, 3.61%. Yield: 0.13 g (19%); MS (EI): m/z 343.9 (42) [M+]; 316.0 (14) [M+ CO]; 287.9
M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
(100) [M+ 2CO]; 222.9 (7) [M+ 2CO Cp]; 167.0 (33) [M+ 2CO Cp Fe]. 5: Anal. Calc. for Fe2C22H16O4S2: C, 50.80; H, 3.10. Found: C, 50.96; H, 3.23%. Yield: 0.12 g (12%). 6: Anal. Calc. for FeC24H18O3S4: C, 53.53; H, 3.37. Found: C, 53.69; H, 3.51%. Yield: 0.17 g (16%); MS (EI): m/z 538.2 (36) [M+]; 510.2 (4) [M+ CO]; 482.1 (100) [M+ 2CO]; 454.1 (8) [M+ 3CO]; 389.1 (2) [M+ 3CO Cp]. 7: Anal. Calc. for Fe2C31H22O5S4: C, 52.11; H, 3.10. Found: C, 52.36; H, 3.21%. Yield: 0.16 g (11%); MS (EI): m/z 573.9 (9) [M+ 5CO]; 509.3 (22) [M+ 5CO Cp]; 443.2 (70) [M+ 5CO 2Cp]. 3.2.4. Synthesis of tin compounds 8 and 9 About 0.67 g (4.0 mmol) of DMTT was dissolved in 50 ml of hexane. 1.2 ml (8.0 mmol) of TMEDA and 5.5 ml (8.8 mmol) of n-butyl lithium were added at room temperature. The mixture was refluxed for 45 min and then cooled to 0 C. Lithium chloride precipitated as a white solid. The solution containing the dilithiated species was cooled to 40 C and 1.594 g (8.0 mmol) of SnMe3Cl was added. The mixture was stirred at this temperature for 15 min and a further two hours at room temperature. The solvent was removed in vacuo. 100 ml of water was added to the residue and extracted with three 30 ml portions of diethyl ether. The ether extracts were combined, dried over sodium sulfate and filtered. After evaporation of the solvent, the residue was washed with hexane after which an oily residue remained. All the hexane extracts were combined, the solution was concentrated and the product left to crystallize. Compound 8 ([2,2 0 -{SnMe3}2-TT]) crystallized as colourless, cubic crystals from this solution. The oily residue left in the initial flask was distilled and ([2-SnMe3-TTH] 9) was afforded as a colourless oil. 8: Anal. Calc. for Sn2C14H24S2: C, 34.06; H, 4.90. Found: C, 34.21; H, 5.01%. Yield: 1.50 g (76%); MS (EI): m/z 494.5 (45) [M+]; 479.5 (100) [M+ Me]; 449.4 (25) [M+ 3Me]; 419.3 (11) [M+ 5Me]; 404.2 (6) [M+ 6Me]. 9: Anal. Calc. for SnC11H15S2: C, 40.03; H, 4.58. Found: C, 40.20; H, 4.66%. Yield: 0.28 g (21%); MS (EI): m/z 333.5 (38) [M+]; 317.5 (93) [M+ Me]; 302.4 (30) [M+ 2Me]; 287.3 (9) [M+ 3Me]; 169.0 (100) [M+ 3Me Sn]. 3.2.5. Synthesis of iron complex 10 Precursor 8 (0.99 g; 2.0 mmol) and [FeCp(CO)(PEt3)I] (1.6 g; 4.0 mmol) were dissolved in 20 ml of DMF. The palladium catalyst Pd(CH3CN)2Cl2 (0.025 g; 0.1 mmol) was added to the solution and the mixture was stirred for 12 h at room temperature. [2-{FeCp (CO)(PEt3)}C(O)-{TT}2-2 0 -{SnMe3}] (10) was isolated using column chromatography, after collecting the green iron starting material.
2607
10: Anal. Calc. for FeSnC27H26O3S4: C, 46.67; H, 3.74. Found: C, 46.82; H, 3.91%. Yield: 0.37 g (24%). No M+ was observed. 3.3. Crystal structure determination The intensity data for the compound were collected at 90 C on a Nonius KappaCCD diffractometer, using graphite-monochromated Mo Ka radiation. Data were corrected for Lorentz and polarization effects, but not for absorption [34,35]. The structure was solved by direct methods (SHELXS) [36] and refined by full-matrix least squares techniques against F 2o (SHELXL-97) [37]. The hydrogen atoms of the structure were included at calculated positions with fixed thermal parameters. All non-hydrogen atoms were refined anisotropically. XP (SIEMENS Analytical X-ray Instruments, Inc.) was used for structure representations. Experimental details are given in Table 3. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary material Publication No. CCDC – 246551 (8). Copies of the data can be Table 3 Crystal data and structure refinement for 8 8 Empirical formula Formula weight Temperature (K) ˚) Wavelength (A Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z Dcalc (Mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm3) h Range for data collection () Index ranges
Reflections collected Independent reflections [Rint] Completeness to theta = 23.29 (%) Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Extinction coefficient Largest difference in peak ˚ 3) and hole (e A
C14H24S2Sn2 493.83 183(2) 0.71073 monoclinic P2(1)/c 13.8225(6) 6.6183(3) 11.3821(3) 90 113.642(3) 90 953.86(6) 2 1.719 2.822 480 0.40 · 0.32 · 0.20 3.58–23.29 15 6 h 6 15, 0 6 k 6 7, 12 6 l 6 12 2339 1320 [0.0336] 95.7 full-matrix least-squares on F2 1320/0/83 0.973 R1 = 0.0279, wR2 = 0.0843 R1 = 0.0287, wR2 = 0.0851 0.024(3) 1.051 and 0.391
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M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK [Fax: (+44) 1223336-033; E-mail: [email protected]]. Acknowledgements We thank Mr. E. Palmer for the NMR measurements and the National Research Foundation, Pretoria (Grant Gun No. 2053930) for financial assistance.
References [1] P.R. Stafford, T.B. Rauchfuss, S.R. Wilson, Inorg. Chem. 34 (1995) 5220. [2] A.N. Nesmeyanov, K.N. Anisimov, N.E. Kolobova, Izv. Akad. Nauk SSSR, Ser. Khim. 1356 (1964) 2247. [3] M.D. Rauch, T.R. Criswell, A.K. Ignatovicz, J. Organomet. Chem. 13 (1968) 419. [4] (a) S. Komiya, S. Ozaki, A. Shibue, J. Chem. Soc., Chem. Commun. (1986) 1555; (b) C. Eaborn, K.J. Kevin, A. Pidcock, J. Chem. Soc., Dalton Trans. (1978) 357; (c) J. Mu¨ller, C. Friedrich, J. Organomet. Chem. 377 (1989) C27. [5] G. Erker, R. Petrenz, C. Kru¨ger, F. Lutz, A. Weiss, S. Werner, Organometallics 11 (1992) 1646. [6] V.A. Knizhnikov, Yu.A. OlÕdekop, J. Gen. Chem. USSR (Engl. Transl.) 55 (1985) 1385. [7] A.D Hunter, R. Chukwu, B.D. Santarsiero, S.G. Bott, J.L. Atwood, J. Organomet. Chem. 526 (1996) 1. [8] A.N. Nesmeyanov, N.E. Kolobova, L.V. Goncharenko, K.N. Anisimov, Izv. Akad. Nauk SSSR, Ser. Khim. 1 (1976) 153. [9] A.E. Ogilvy, M. Draganjac, T.B. Rauchfuss, S.R. Wilson, Organometallics 7 (1988) 1171. [10] K.R. Aris, J.M. Brown, K.A. Taylor, J. Chem. Soc., Dalton Trans. (1974) 2222. [11] M.J. Robertson, C.J. White, R.J. Angelici, J. Am. Chem. Soc. 116 (1994) 5190. [12] J. Kiesewetter, G. Poignant, V. Guerchais, J. Organomet. Chem. 595 (2000) 81. [13] S. Kotani, K. Shiina, K. Sonogashira, J. Organomet. Chem. 429 (1992) 403.
[14] C. Van Pham, R.S. Macomber, H.B. Mark, H. Zimmer, J. Org. Chem. 49 (1984) 5250. [15] W.D. Mu¨ller, H.A. Brune, Chem. Ber. 119 (1986) 759. [16] U. Bayer, H.A. Brune, Z. Naturforsch. Teil B 38 (1983) 632. [17] F. Coat, C. Lapinte, Organometallics 15 (1996) 477. [18] T.B. Rauchfuss, Prog. Inorg. Chem. 39 (1991) 259. [19] (a) E. Viola, C. Lo Sterzo, F. Trezzi, Organometallics 15 (1996) 4352; (b) E. Viola, C. Lo Sterzo, R. Crescenzi, G. Frachey, J. Organomet. Chem. 493 (1995) C9. [20] M. Landman, H. Go¨rls, S. Lotz, Z. Anorg. Allg. Chem. 628 (2002) 2037. [21] P.L. Pauson, A.R. Quazi, B.W. Rockett, J. Organomet. Chem. 7 (1967) 325. [22] M. Hesse, H. Meier, B. Zeeh, Spektroskopische Metoden in Der Organische Chemie, Georg Thieme Verlag, Stuttgart, 1984. [23] T.A. Waldbach, P.H. van Rooyen, S. Lotz, Organometallics 12 (1993) 4250. [24] H. Friebolin, Basic One- and Two-dimensional NMR Spectroscopy, VCH Verlag, Weinheim, 1993, 104. [25] A. Karipides, A.T. Reed, D.A. Haller, F. Hayes, Acta Cryst. B 33 (1977) 950. [26] V.K. Belsky, A.A. Simonenko, V.O. Reikhsfeld, L.E. Saratov, J. Organomet. Chem. 244 (1983) 125. [27] D.F. Shriver, M.A. Drezdzon, The Manipulation of Air-sensitive Compounds, second ed., Wiley, New York, 1980. [28] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Laboratory Chemicals, second ed., Pergamon, New York, 1980. [29] G.H. Spies, R.J. Angelici, Organometallics 6 (1987) 1897. [30] K.S. Choi, K. Sawada, H. Dong, M. Hoshino, J. Nakayama, Heterocycles 38 (1994) 143. [31] R.B. King, F.G.A. Stone, Inorg.Synth. 7 (1963) 110. [32] P.M. Treichel, D.A. Komar, J. Organomet. Chem. 206 (1981) 77. [33] C. Moreno, M. Macazaga, R. Medina, D.H. Farrar, S. Delgado, Organometallics 17 (1998) 3733. [34] COLLECT, Data Collection Software, Nonius B.V., Netherlands, 1998. [35] Z. Otwinowski, W. Minor, Processing of X-ray diffraction data collected in oscillation mode, in: C.W. Carter, R.M. Sweet (Eds.), Methods in Enzymology, Macromolecular Crystallography, Part A, vol. 276, Academic Press, 1997, pp. 307–326. [36] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467. [37] G.M. Sheldrick, SHELXL-97 (Release 97-2), University of Go¨ttingen, Germany, 1997.
Synthesis of iron thienyl complexes Marile´ Landman
a,*
, Mandy van Staden b, Helmar Go¨rls c, Simon Lotz
b,*
a
c
Department of Chemistry, University of South Africa, P.O. Box 392, Pretoria 0003, South Africa b Department of Chemistry, University of Pretoria, Pretoria 0002, South Africa Friedrich-Schiller-Universita¨t, Institut fu¨r Anorganische und Analytische Chemie, Lessingstrasse 8, D-07743 Jena, Germany Received 5 August 2004; accepted 6 March 2005 Available online 7 April 2005
Abstract Dimetallation of thiophene (TH2), bithiophene (BTH2) and 3,6-dimethyl[3,2-b]thienothiophene (TTH2) using a slight excess of butyl lithium, followed by the addition of [FeCp(CO)2I], resulted in the formation of [2,5-{FeCp(CO)2}2T], 1 and [2-{FeCp (CO)2}T]. The analogous reaction with bithiophene as precursor afforded similar products [2,2 0 -{FeCp(CO)2}2BT] 2 and [2-{FeCp (CO)2}BTH] 3. In addition to the expected mono- ([2-{FeCp(CO)2}-TTH] 4) and binuclear ([2,2 0 -{FeCp(CO)2}2-TT] 5) products, dimetallation of 3,6-dimethyl[3,2-b]thienothiophene and the subsequent reaction with [FeCp(CO)2I] yielded carbonyl inserted mono-([2-{FeCp(CO)2}C(O)-{TT}2H] 6) and binuclear ([2-{FeCp(CO)2}C(O)-{TT}2-2 0 -{FeCp(CO)2}] 7) carbon–carbon coupled products. The precursor [2,7-{SnMe3}2-TT] (8) was prepared and reacted with [FeCp(CO)(PEt3)I] in the presence of a palladium catalyst to afford [2-{FeCp(CO)(PEt3)}C(O)-{TT}2-2 0 -{SnMe3}] 10. 2005 Elsevier B.V. All rights reserved. Keywords: Thiophene derivatives; Iron; Binuclear complexes; Carbon–carbon coupling reactions
1. Introduction Five-membered heterocycles, in which transition metals are connected to the a-carbons of the heterocyclic ring, have not received much attention in the literature. Few of these complexes contain more than one metal fragment directly bonded to the heteroaromatic ring system. Complexes containing thiophene [1,2] or thiophene derivatives [3] are more abundant than other five-membered heteroarene metal complexes [4,5,2] because of their relevance as model compounds for desulfurization. Known metallocene complexes of the type (2-thienyl)2MCp2 include the transition metals Ti, Zr, Hf, Nb and W [6]. One of the initial preparations for mono-substituted arene complexes [7] included the reaction of Na [FeCp(CO)2] with halide substituted arene compounds *
Corresponding authors. Tel.: +27 12 4202800; fax: +27 12 3625297. E-mail address: [email protected] (S. Lotz).
0020-1693/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.03.022
at low temperatures and involved the nucleophilic displacement of the halide by [FeCp(CO)2]. Nesmeyanov employed this method in preparing iron complexes of the type [FeCp(CO)2R], with R = 2-thienyl, 2-furyl, 5methyl-2-furyl and 4,5-benzo-2-furyl. These complexes were synthesized by the reaction of Na[FeCp(CO)2] with 2-heteroaryl carbonyl chloride, followed by photochemical decarbonylation of these acyl complexes to yield the target products [8]. Rauchfuss et al. [9] prepared this same 2-[FeCp(CO)2]thienyl complex as part of a research study on the activation and desulfurization of thiophene and benzothiophene by iron carbonyls. Very few examples of disubstituted r,r-arene or -heteroarene complexes are known in the literature and several different methods [10–12] have been employed in an attempt to synthesize these complexes. Kotani et al. [13] prepared [Pt(PBu3)2(2-thienyl)2] as well as 2,5-thienylene-bridged diplatinum complexes. This study was extended to include bithiophene as
M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
bridging ligand. Synthesis of the 2-thienyl and 2,5thienylene platinum compounds was accomplished via a 2-trimethylstannylthiophene [4c] and a 2,5-bis(trimethylstannyl)thiophene [14] precursor. Nickel and palladium complexes were prepared in a similar fashion to the method employed by Mu¨ller and Brune [15] for the preparation of disubstituted phenyl platinum complexes. Evidence of metal–metal communication [16] through the phenyl conjugated ring system prompted further study of thiophene and similar compounds. From the literature work discussed, it is clear that the synthesis of iron carbonyl complexes with arene substituents is not straightforward. Several different methods have been employed for various different arenes and heteroarenes. These methods have been employed and evaluated in the syntheses of the novel iron complexes of different thiophene derivatives reported in this study. The reactivities of mono- and dilithiated thiophene derivatives with iron carbonyl compounds were investigated.
2. Results and discussion The first synthetic route employed in preparing the iron complexes with thiophene derivatives was the synthesis via lithiated intermediates, a similar method used by Lapinte et al. [17] in synthesizing compounds consisting of long carbon chains end-capped with FeCp(CO)2metal moieties. The thiophene ligands were dilithiated using n-butyl lithium and TMEDA in a hexane solution at elevated temperatures or in THF at low temperatures. Upon reaction of 2,5-dilithiated thiophene with FeCp (CO)2I, two products were isolated: firstly, the yellow [2-FeCp(CO)2TH] complex, previously prepared by Nesmeyanov et al. [8], and secondly the orange coloured [2,5-{FeCp(CO)2}2T] complex, 1. This product has been documented in a review article [18], but to our knowledge the spectroscopic data have not yet been published. Both complexes were formed in low yields and the disubstituted complex especially seemed to be very unstable. Similar products were formed in the reaction Me
S
2603
of dilithiated bithiophene. The orange-red [2,9-{FeCp (CO)2}2BT] complex, 2, and the yellow [2-FeCp (CO)2BTH] complex, 3, were isolated, but in this case the binuclear complex was found to be particularly stable. The analogous reaction using 3,6-dimethylthieno[3,2-b]thiophene afforded four products. Again the mono iron complex, 5, as well as the bis complex, 4, was yielded, but two more products, complexes 6 and 7, in which C–C coupling is observed, were formed. Fig. 1 shows the reaction of a bis iron complex 4 and a mono iron complex 5 to form complex 6 and the reaction between two bis iron complexes 4 to form complex 7. These C–C coupling reactions are facilitated by the formation of the iron dimer [FeCp(CO)2]2. It is assumed that the insertion of a carbonyl group stabilizes the molecule. This reaction was also performed using the metal complex MoCp(CO)2Cl, but no organometallic products were formed during the reaction Table 1. It was obvious from the yields of the reaction products that these reactions had not gone to completion. It was suggested that the reason for the low reactivity between the two reagents could be ascribed to the relative strength of the Fe–I bond. By substituting the iodine ligand for a more labile leaving group on the metal, a higher yield of target products was envisaged. Therefore, it was contemplated to repeat the reactions, but instead of reacting the lithiated species with FeCp(CO)2I, FeCp(CO)2(O3SCF3) was used, containing a triflate leaving group. This method, however, proved to be unsuccessful since only the mono iron complex was obtained for both ligands. A new approach towards the synthesis of disubstituted iron complexes of thiophene derivatives was decided on, based on the literature reports by Lo Sterzo et al. [19]. They recounted the preparation of rmetallaacetylides by palladium-catalyzed formation of metal–carbon bonds. The general procedure constitutes the coupling of halogen-containing transition metal moieties to mono- and bis[(trimethylstannyl) acetylides] in the presence of catalytic amounts of palladium. The 2,5-bis(trimethylstannyl)thiophene [14] and 2,7-bis(trimethylstannyl)-3,6-dimethylthieno[3,2-b]
H
(OC)2CpFe S Me
S
Me
CO
Me
S
2 FeCp(CO)2 I S
Me
+
2 n-BuLi
FeCp(CO)2 (OC)2CpFe
Me 5
Me
Fig. 1. Synthesis of complexes 4–7.
R
S
O
S
C S
(OC)2CpFe S
S
Me
4
Me
R=H 6 Me R = FeCp(CO)2 7 + [FeCp(CO)2]2
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M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
Table 1 Spectroscopic data for 1–10 Complex 1 2 3
4 5 6
1
13
H NMR data (d/ppm in CDCl3)
4.95 (s, 10H, Cp), 6.83 (s, 2H, H3) 4.96 (s, 10H, Cp), 6.64 (d, 2H, H4, J = 2.3), 6.96 (d, 2H, H3, J = 1.8) 4.98 (s, 5H, Cp), 6.93 (t, 1H, H8, J = 4.4), 6.98 (s, br, 1H, H4), 7.05 (t, 1H, H7, J = 4.4), 7.11 (s, br, 1H, H9), 7.24 (s, br, 1H, H3) 2.27 (d, 3H, Me, J = 1.0 Hz), 2.31 (s, 3H, Me), 5.01 (s, 5H, Cp), 6.68 (q, 1H, H7, J = 1.0) 2.25 (s, 6H, Me3 and Me6), 4.95 (s, 10H, Cp) 2.33 (s, 3H, Me), 2.36 (s, 3H, Me), 2.54 (s, 3H, Me), 2.55 (s, 3H, Me), 5.00 (s, 5H, Cp), 7.13 (s, 1H, H13)
7
2.34b (s, 6H, Me9 and Me12), 2.52 (s, 6H, Me3 and Me6), 5.02 (s, 10H, Cp)
8
0.40 (d, 18H, SnMe3, J = 55.8), 2.37 (s, 6H, Me)
9
2.34 (s, 3H, Me6), 2.38 (s, 3H, Me3), 6.93 (s, 1H, H7), 0.42 (d, 9H, SnMe3, J = 56.1)
10
0.05 (d, 9H, SnMe3, J = 56.8), 0.84 (t, 9H, P(CH2CH3)3, J = 6.3 Hz), 1.23 (m, 6 H, P(CH2CH3)3), s2.32 (s, 3H, Me12), 2.36 (s, 3H, Me9), 2.57 (s, 3H, Me6), 2.61 (s, 3H, Me3)
a b
IR dataa (m/cm1 in CH2Cl2)
C NMR data (d/ppm in CDCl3)
85.5 (Cp), 140.7 (C3), 150.0 (C2), 215.2 (Fe(CO)2) 86.1 (Cp), 139.3 (C3), 124.5 (C4), 214.8 (Fe(CO)2)
2025 (s), 1972 (vs) 2028 (s), 1976 (vs)
84.7 (Cp), 138.2 (C3), 120.7 (C4), 124.8 (C7), 126.5 (C8), 121.4 (C9), 213.2 (Fe(CO)2)
2034 (s), 1987 (vs)
14.8 (Me), 17.3 (Me), 85.8 (Cp), 129.6 (C7), 136.3 (C6), 142.8 (C3) 145.8 (C2), 214.4 (Fe(CO)2) 17.2 (Me), 85.8 (Cp), 214.2 (Fe(CO)2) 14.6 (Me), 15.2 (Me), 15.7 (Me), 17.3 (Me), 85.9 (Cp), 125.3 (C12), 130.4 (C13), 132.1 (C9), 135.9 (C6), 136.7 (C3), 213.9 (Fe(CO)2), 255.2 (C@O) 14.1 (Me), 14.7 (Me), 15.6 (Me), 17.4 (Me), 85.7 (Cp), 213.7 (Fe(CO)2), 254.8 (C@O)
2026 (s), 1974 (vs) 2023 (s), 1972 (vs) 2029 (s), 1978 (vs) 1655 (C@O) 2053 (s), 2028 (s), 2007 (vs), 1978 (vs) 1656 (C@O)
8.33 (SnMe3), 16.4 (Me), 134.9 (C4), 136.5 (C6), 147.6 (C2) 8.25 (SnMe3), 14.7 (Me), 16.3 (Me), 122.1 (C6), 130.1 (C7), 134.7 (C5), 136.8 (C3), 142.4 (C4), 145.4 (C2) 1941 (vs)
Carbonyl region. Overlap of signals occurs, broad bands observed.
fragment. Other products were also observed, but unfortunately their yields were too low to be able to isolate and characterize. Complexes 1–10 were characterized spectroscopically using infrared and NMR spectroscopy as well as mass spectrometry. Recording of 13C NMR spectra proved to be problematic, since the complexes were unstable at room temperature and even more so in solution. Decomposition occurred in several cases and made the unambiguous assignment of resonance peaks impossible in several cases. Nearly all the carbons in the structures of the complexes are quaternary carbons. It was interesting to note that the thiophene
thiophene (8) were prepared in order to apply this method to our ligand systems. The mono-substituted compound, 2-(trimethylstannyl)-3,6-dimethylthieno [3,2-b] thiophene 9, formed as a byproduct in the preparation of 8. The planned synthetic route for preparation of the iron complexes is outlined in Fig. 2. After completion of the reactions for both ligands, it was only possible to isolate and characterize one product, 10, formed in the reaction of FeCp(CO)(PEt3)I with 2,7-bis(trimethylstannyl)-3,6-dimethylthieno[3,2-b]thiophene (8). This product was formed similar to the formation of complexes 6 and 7 by the substitution of one of the trimethylstannyl groups by an iron metal
Me
S SnMe3 +
Me3Sn S 8
2 FeCp(CO)(PEt3)I
Me Pd catalyst Me
Me
S
S FeCp(CO)(PEt3)
Me
S
O
(Et3P)(OC)CpFe S
Me
(Et3P)(OC)CpFe
SnMe3
S
C S
10 Me
Fig. 2. Formation of C–C coupled bisthienothiophene iron complex.
Me
M. Landman et al. / Inorganica Chimica Acta 358 (2005) 2602–2608
complexes were seemingly more stable than their 3,6dimethylthieno[3,2-b]thiophene counterparts, which is contrary to the trend observed for carbene complexes of these thiophene derivatives where the complexes with the condensed rings were more stable than the analogous thiophene complexes [20]. Pauson et al. [21] suggested that the Fe–Carene bond is stabilized by the effect of the condensed ring. This same effect was observed by Nesmeyanov et al. [8], who observed the stability of the [2-{FeCp(CO)2}benzofuryl] complex compared to the iron complexes containing fivemembered heterocyclic ligands. Suitable crystals for X-ray diffraction studies were obtained for 8, which crystallized as colourless cubic crystals, from a dichloromethane/hexane (1:1) solution. For 4 a quartet splitting pattern is found for the proton on the 7-position. This is due to long-range coupling with the methyl protons on the 6-position. For this methyl group a doublet is observed, instead of the expected singlet and the coupling constant of 1.0 Hz is calculated, correlating well with other four-band couplings observed in the literature [22]. The 1H NMR spectrum of 7 is affected by the coordination of a second metal moiety in that broad, undefined peaks are observed compared to the high resolution of the mononuclear complex. Interesting to note is the stability of 7 even though the second metal fragment is directly bonded to the ring system and carbonyl insertion did not take place to stabilize this metal moiety. Previously, it was shown in our laboratories that a second manganese alkyl bond is stabilized by a carbonyl group inserted into the manganese alkyl bond on the other side of a conjugated spacer [23]. Doublets are observed on the 1H NMR spectra of 8, 9 and 10 for the methyl protons of the trimethylstannyl groups. These doublets are ascribed to coupling of these protons with the Sn nucleus. A large coupling constant is observed for this coupling, which corresponds well with the literature values [24].
2605
Fig. 3. Ball-and-stick plot of 8.
The tin atom is in a pseudotetrahedral environment, evident from the bond angles around the Sn atom. The bond angles of C(7)–Sn–C(6) 109.9(2), C(7)–Sn– C(1) 112.3(2), C(6)–Sn–C(1) 107.0(1), C(7)–Sn–C(5) 110.1(2), C(6)–Sn–C(5) 111.4(2) and C(1)–Sn–C(5) 105.9(2) are marginally different from the normal value of 109 for tetrahedral arrangements. The Sn–C(thienyl) ˚ ) as those recorded for bond length is the same (2.15(1) A the same bonds in [Sn(thienyl)4] [25] and the analogous ˚ ). These distances are similar [Sn(phenyl)4] [26] (2.14(1) A ˚ found for Sn– to the average bond length of 2.14 A C(Me) bonds. 2.2. Conclusion This study has shown that lithiated thiophene derivatives in combination with iron metal precursors afford complex reaction mixtures leading to various products in low yields. Furthermore, many of the intermediates are unstable and the observation of products resulting from carbon–carbon coupling reactions, facilitated by the CpFe(CO)L fragment, is of interest.
3. Experimental 3.1. General
2.1. Structural studies A single X-ray determination confirmed the structure of 8. Selected bond lengths and angles are given in Table 2. Fig. 3 represents a ball-and-stick plot of this structure. Table 2 Selected bond lengths and angles of 8 8
bond ˚) lengths (A
8
bond angles ()
Sn–C(1) S(1)–C(1) C(1)–C(2) C(2)–C(3) C(2)–C(4) C(3)–C(3)#1 C(3)–S(1)#1
2.152(3) 1.757(3) 1.369(5) 1.438(5) 1.513(5) 1.395(7) 1.730(4)
C(3)#1–S(1)–C(1) C(2)–C(1)–S(1) C(1)–C(2)–C(3) C(3)#1–C(3)–C(2)
92.50(16) 111.8(2) 111.3(3) 114.7(4)
All reactions and manipulations were performed under an inert atmosphere using standard Schlenk-tube techniques [27]. Solvents were dried by the usual procedures [28] and distilled under nitrogen prior to use. The starting materials thiophene, bithiophene and n-BuLi as well as the palladium catalyst Pd(CH3CN)2Cl2 were obtained from Aldrich and thiophene was purified as described in the literature [29]. The compounds 3,6-dimethylthieno[3,2-b]thiophene [30], [FeCp(CO)2I] [31], [FeCp(CO)(PEt3)I] [32,33] and [2,5-bis(SnMe3)thiophene][14] were synthesized according to the known literature methods. Column chromatography was performed on silica gel (0.063–0.200 mm) on columns that were cooled by circulating cold isopropanol (20 C) through column jackets. The solvents used for column chromatography were dichloromethane:hexane mixtures
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in varying ratios, unless stated otherwise. NMR spectra were recorded in CDCl3 as solvent on a Bruker AC-300 spectrometer with reference to the deuterium signal CDCl3. 1H and 13C NMR spectra were measured at 300.133 and 75.469 MHz, respectively. Infrared spectra were recorded as CH2Cl2 solutions on a BOMEM Michelson-100 FT spectrophotometer. Mass spectra were recorded on a Perkin–Elmer RMU-6H instrument operating at 70 eV. Melting points were recorded in capillaries on a Gallenkamp hot-stage apparatus and are uncorrected. 3.2. Synthesis of the metal complexes 3.2.1. Synthesis of [2,5-{FeCp(CO)2}2T] (1) Dilithiation of thiophene was accomplished by adding 17.0 ml (27.3 mmol) of n-butyl lithium and 3.7 ml (24.8 mmol) of TMEDA to a solution of 0.99 ml (12.4 mmol) of thiophene in 50 ml of hexane and refluxing the mixture for 30 min. The reaction mixture was cooled to 0 C, 30 ml of THF was added and cooled further to 20 C. 6.9 g (22.7 mmol) of FeCp(CO)2I was added with vigorous stirring and maintained for a further 2 h while the temperature was allowed to gradually raise until room temperature was reached. After filtration through silica gel and sodium sulfate, the solvent was removed under reduced pressure and the residue purified using column chromatography. Four bands were distinguished on the column. The first yellow band was identified as the mono iron complex previously synthesized by Nesmeyanov et al. [8]. The second brown product was the starting compound FeCp(CO)2I. The third red band was isolated and identified to be the iron dimer complex [FeCp(CO)]2. The fourth orange compound was characterized as the bis iron complex [2,5-{FeCp (CO)2}2T] (1). This compound is very polar and could only be collected by using pure dichloromethane as eluent. 1: Anal. Calc. for Fe2C18H12O4S: C, 49.58; H, 2.77. Found: C, 49.87; H, 2.91%. Yield: 1.13 g (21%), MS (EI): m/z 435.8 (50) [M+]; 407.8 (44) [M+ CO]; 379.8 (98) [M+ 2CO]; 351.8 (20) [M+ 3CO]; 323.8 (96) [M+ 4CO]; 258.8 (56) [M+ 4CO Cp]; 193.9 (19) [M+ 4CO 2Cp]; 83.0 (26) [M+ 4CO 2Cp 2Fe]. 3.2.2. Synthesis of iron complexes 2 and 3 Bithiophene (0.83 g, 5 mmol) was dissolved in 50 ml of tetrahydrofuran at 90 C under argon gas. The clear solution was stirred while 1.5 ml (10 mmol) of TMEDA was added, followed by the dropwise addition of 6.4 ml (10 mmol) of n-butyl lithium. The solution was stirred for 5 min after the additions and then allowed to warm to 50 C. Stirring was continued for a further 15 min at this temperature, during which time the colour of the solution changed from clear to milky yellow. The
solution was cooled to 80 C and stirred while [FeCp (CO)2I] (3.0 g, 10 mmol) was added. The mixture was stirred for 1 h at this temperature, allowed to warm up to room temperature and stirred for another hour. The solution turned bright red. The solvent was removed under reduced pressure and replaced with dichloromethane. The reaction mixture was filtered through silica gel using dichloromethane as solvent that resulted in the formation of a thick layer of orange solid on the top of the filter. The orange product was identified as [2,5-{FeCp (CO)2}2BT] 2. Crystallization from a 1:1 hexane:dichloromethane mixture yielded very flat, orange air-stable platelets. The remainder of the product mixture was separated by column chromatography. [2-FeCp(CO)2BTH] 3 was removed from the column as a yellow fraction with a 1:1 hexane:dichloromethane mixture as eluent. It was highly unstable and decomposed rapidly in solution. 2: Anal. Calc. for Fe2C22H14O4S2: C, 50.99; H, 2.72. Found: C, 51.21; H, 2.91%. Yield: 2.31 g (89%); MS (EI): m/z 517.9 (22) [M+]; 490.0 (6) [M+ CO]; 462.0 (76) [M+ 2CO]; 406.0 (100) [M+ 4CO]; 340.0 (5) [M+ 2CO Cp]; 274.0 (2) [M+ 4CO 2Cp]. 3: Anal. Calc. for FeC15H10O2S2: C, 52.64; H, 2.95. Found: C, 52.81; H, 3.11%. Yield: 0.13 g (8%); MS (EI): m/z 342.0 (32) [M+]; 314.0 (29) [M+ CO]; 285.9 (94) [M+ 2CO]; 219.2 (25) [M+ 2CO Cp]. 3.2.3. Synthesis of iron complexes 4, 5, 6 and 7 Dimetallation of 3,6-dimethylthieno[3,2-b]thiophene was accomplished by dissolving 0.337 g (2.0 mmol) of the ligand in 30 ml of dry ether and adding 1.4 ml (2.2 mmol) of n-butyl lithium while cooling the mixture on an ice bath. The mixture was stirred for 2 h at this temperature and for a further 30 min at room temperature. The reaction mixture was cooled to 40 C after which 0.6 g (2.0 mmol) of [FeCp(CO)2I] was added. The reaction was stirred for 15 min at this temperature and for a further 2 h at room temperature. Filtration through silica gel and the subsequent evaporation of the solvent in vacuo afforded a brown residue. Six products were isolated using column chromatography. The first product isolated was unreacted HTTH, yield: 0.03 g (8%). The second yellow product was characterized as the mono iron complex [2-FeCp(CO)2TTH] 4. The third brown product was identified as the iron starting material [FeCp(CO)2I], yield: 0.16 g (27%). The following two range-yellow products were found to be ([2-{FeCp (CO)2}C(O)-{TT}2H] 6) and ([2-{FeCp(CO)2}C(O){TT}2-2 0 -{FeCp(CO)2}] 7), which were isolated with yields of 0.17 g (16%) and 0.16 g (11%), respectively. The sixth orange product ([2,2 0 -{FeCp(CO)2}2-TT] 5) was isolated using dichloromethane as eluent. This product was characterized as the bis-iron complex. 4: Anal. Calc. for FeC15H12O2S2: C, 52.33; H, 3.49. Found: C, 52.51; H, 3.61%. Yield: 0.13 g (19%); MS (EI): m/z 343.9 (42) [M+]; 316.0 (14) [M+ CO]; 287.9
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(100) [M+ 2CO]; 222.9 (7) [M+ 2CO Cp]; 167.0 (33) [M+ 2CO Cp Fe]. 5: Anal. Calc. for Fe2C22H16O4S2: C, 50.80; H, 3.10. Found: C, 50.96; H, 3.23%. Yield: 0.12 g (12%). 6: Anal. Calc. for FeC24H18O3S4: C, 53.53; H, 3.37. Found: C, 53.69; H, 3.51%. Yield: 0.17 g (16%); MS (EI): m/z 538.2 (36) [M+]; 510.2 (4) [M+ CO]; 482.1 (100) [M+ 2CO]; 454.1 (8) [M+ 3CO]; 389.1 (2) [M+ 3CO Cp]. 7: Anal. Calc. for Fe2C31H22O5S4: C, 52.11; H, 3.10. Found: C, 52.36; H, 3.21%. Yield: 0.16 g (11%); MS (EI): m/z 573.9 (9) [M+ 5CO]; 509.3 (22) [M+ 5CO Cp]; 443.2 (70) [M+ 5CO 2Cp]. 3.2.4. Synthesis of tin compounds 8 and 9 About 0.67 g (4.0 mmol) of DMTT was dissolved in 50 ml of hexane. 1.2 ml (8.0 mmol) of TMEDA and 5.5 ml (8.8 mmol) of n-butyl lithium were added at room temperature. The mixture was refluxed for 45 min and then cooled to 0 C. Lithium chloride precipitated as a white solid. The solution containing the dilithiated species was cooled to 40 C and 1.594 g (8.0 mmol) of SnMe3Cl was added. The mixture was stirred at this temperature for 15 min and a further two hours at room temperature. The solvent was removed in vacuo. 100 ml of water was added to the residue and extracted with three 30 ml portions of diethyl ether. The ether extracts were combined, dried over sodium sulfate and filtered. After evaporation of the solvent, the residue was washed with hexane after which an oily residue remained. All the hexane extracts were combined, the solution was concentrated and the product left to crystallize. Compound 8 ([2,2 0 -{SnMe3}2-TT]) crystallized as colourless, cubic crystals from this solution. The oily residue left in the initial flask was distilled and ([2-SnMe3-TTH] 9) was afforded as a colourless oil. 8: Anal. Calc. for Sn2C14H24S2: C, 34.06; H, 4.90. Found: C, 34.21; H, 5.01%. Yield: 1.50 g (76%); MS (EI): m/z 494.5 (45) [M+]; 479.5 (100) [M+ Me]; 449.4 (25) [M+ 3Me]; 419.3 (11) [M+ 5Me]; 404.2 (6) [M+ 6Me]. 9: Anal. Calc. for SnC11H15S2: C, 40.03; H, 4.58. Found: C, 40.20; H, 4.66%. Yield: 0.28 g (21%); MS (EI): m/z 333.5 (38) [M+]; 317.5 (93) [M+ Me]; 302.4 (30) [M+ 2Me]; 287.3 (9) [M+ 3Me]; 169.0 (100) [M+ 3Me Sn]. 3.2.5. Synthesis of iron complex 10 Precursor 8 (0.99 g; 2.0 mmol) and [FeCp(CO)(PEt3)I] (1.6 g; 4.0 mmol) were dissolved in 20 ml of DMF. The palladium catalyst Pd(CH3CN)2Cl2 (0.025 g; 0.1 mmol) was added to the solution and the mixture was stirred for 12 h at room temperature. [2-{FeCp (CO)(PEt3)}C(O)-{TT}2-2 0 -{SnMe3}] (10) was isolated using column chromatography, after collecting the green iron starting material.
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10: Anal. Calc. for FeSnC27H26O3S4: C, 46.67; H, 3.74. Found: C, 46.82; H, 3.91%. Yield: 0.37 g (24%). No M+ was observed. 3.3. Crystal structure determination The intensity data for the compound were collected at 90 C on a Nonius KappaCCD diffractometer, using graphite-monochromated Mo Ka radiation. Data were corrected for Lorentz and polarization effects, but not for absorption [34,35]. The structure was solved by direct methods (SHELXS) [36] and refined by full-matrix least squares techniques against F 2o (SHELXL-97) [37]. The hydrogen atoms of the structure were included at calculated positions with fixed thermal parameters. All non-hydrogen atoms were refined anisotropically. XP (SIEMENS Analytical X-ray Instruments, Inc.) was used for structure representations. Experimental details are given in Table 3. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary material Publication No. CCDC – 246551 (8). Copies of the data can be Table 3 Crystal data and structure refinement for 8 8 Empirical formula Formula weight Temperature (K) ˚) Wavelength (A Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z Dcalc (Mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm3) h Range for data collection () Index ranges
Reflections collected Independent reflections [Rint] Completeness to theta = 23.29 (%) Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Extinction coefficient Largest difference in peak ˚ 3) and hole (e A
C14H24S2Sn2 493.83 183(2) 0.71073 monoclinic P2(1)/c 13.8225(6) 6.6183(3) 11.3821(3) 90 113.642(3) 90 953.86(6) 2 1.719 2.822 480 0.40 · 0.32 · 0.20 3.58–23.29 15 6 h 6 15, 0 6 k 6 7, 12 6 l 6 12 2339 1320 [0.0336] 95.7 full-matrix least-squares on F2 1320/0/83 0.973 R1 = 0.0279, wR2 = 0.0843 R1 = 0.0287, wR2 = 0.0851 0.024(3) 1.051 and 0.391
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obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK [Fax: (+44) 1223336-033; E-mail: [email protected]]. Acknowledgements We thank Mr. E. Palmer for the NMR measurements and the National Research Foundation, Pretoria (Grant Gun No. 2053930) for financial assistance.
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