Journal of Organometallic Chemistry 587 (1999) 176 – 180
Reactivity of [Et
4N]
2[MeSb{Fe(CO)
4}
3] toward HOAc and
[Cu(MeCN)
4]BF
4: formation of [Et
4N][Me(OAc)Sb{Fe(CO)
4}
2] and
[MeSb{Fe(CO)
4}{Fe
2(CO)
8}]
Minghuey Shieh
a,*, Li-Fang Ho
a, Jiann-Jang Cherng
a, Chuen-Her Ueng
a,
Shie-Ming Peng
b, Gene-Hsiang Lee
caDepartment of Chemistry, National Taiwan Normal Uni6ersity, Taipei116, Taiwan, ROC bDepartment of Chemistry, National Taiwan Uni6ersity, Taipei107, Taiwan, ROC
cInstrumentation Center, National Taiwan Uni6ersity, Taipei107, Taiwan, ROC
Received 16 March 1999; received in revised form 18 May 1999
Abstract
Reactions of the tetrahedral methylantimony complex [Et4N]2[MeSb{Fe(CO)4}3] with HOAc and [Cu(MeCN)4][BF4] were investigated. While the reaction of [Et4N]2[MeSb{Fe(CO)4}3] with HOAc forms the substituted complex [Et4 N][Me(OAc)-Sb{Fe(CO)4}2] ([Et4N][I]), the treatment with [Cu(MeCN)4][BF4] forms the oxidized product [MeSb{Fe(CO)4}{Fe2(CO)8}] (II). The structures of [Et4N][I] and II are determined by single-crystal X-ray diffraction. [Et4N][I] crystallizes in the orthorhombic space group Pna21with a = 16.627(4), b = 9.411(3), c = 17.347(4) A, , V=2714(1) A,3, and Z = 4. The crystals of II are triclinic, space group P1( with a=9.335(1), b=10.313(3), c=10.372(1) A,, a=97.46(1), b=93.63(1), g=94.65(1)°, V=984.0 (3) A,3, and
Z = 2. Cluster I is an OAc group substituted product which displays a tetrahedral metal core with the central antimony atom
bonded to two Fe(CO)4fragments, one Me group, and one OAc moiety. Compound II is the two-electron oxidized product of [Et4N]2[MeSb{Fe(CO)4}3] where one FeFe bond is formed upon the addition of [Cu(MeCN)4][BF4]. The results are compared with those of the analogous bismuth system and the role of the main group elements is discussed as well. © 1999 Elsevier Science S.A. All rights reserved.
Keywords:Antimony; Carbonyl; Iron; X-ray diffraction
1. Introduction
Main group-transition metal carbonyl clusters attract extensive attention due to their interesting bonding modes and reactivity patterns [1]. To understand the reactivity of metal clusters, their reactions towards acids [1] and oxidants such as [Cu(MeCN)4]BF4 [1,2]
have been well documented. Recent study has shown that the role of the main group elements has significant influence on the reactivity of the mixed main group-transition metal clusters [3]. We have been interested in the interaction of main group-transition metal clusters with organic moieties and have investigated the alkyla-tions of the tetrahedral clusters [Et4N]3[E{Fe(CO)4}4]
(E = Bi, Sb) with a series of alkyl halides [4]. The monoalkylated products [Et4N]2[RE{Fe(CO)4}3] (E =
Bi, Sb) were obtained from these reactions. In the bismuth system, treatments of [Et4N]2[RBi{Fe(CO)4}3] with HCl (aq.) yielded the decomposed products; how-ever, the reaction with the mild acid HOAc led to the cyclic complexes [RBiFe(CO)4]2. On the other hand, the reactions of [Et4N]2[RBi{Fe(CO)4}3] with
[Cu(Me-CN)4][BF4] underwent severe bond breakage to give the
decomposition products as well [4b]. To probe the effect of HOAc and [Cu(MeCN)4][BF4] and the role of
the main group element in these reactions, we further investigated the reactions of the analogous monoalky-lated antimony cluster [Et4N]2[MeSb{Fe(CO)4}3] with
HOAc and [Cu(MeCN)4][BF4], which are compared
with the outcome of the BiFe system. * Corresponding author. Fax: + 886-2-29324249.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 2 - 3 2 8 X ( 9 9 ) 0 0 2 9 1 - 0
2. Experimental
2.1. General methods
All reactions were performed under an atmosphere of pure nitrogen using standard Schlenk techniques [5]. Solvents were purified, dried, and distilled under nitro-gen prior to use. The compound [Et4N]2
[Me-Sb{Fe(CO)4}3] was prepared according to the published
method [4c]. IR spectra were recorded on a Perkin – Elmer Paragon 500 spectrometer as solutions in CaF2 cells. The 1H- and 13C-NMR spectra were taken on a
Jeol 400 (400 MHz) instrument. Elemental analyses were performed on a Perkin – Elmer 2400 analyzer at the NSC Regional Instrumental Center at National Taiwan University, Taipei, Taiwan.
2.2. Reaction of [Et4N]2[MeSb{Fe(CO)4}4]with HOAc
To a sample of 0.792 g (0.879 mmol) of [Et4N]2[MeSb{Fe(CO)4}3] was added 5.0 ml of HOAc.
The mixed solution was stirred and heated in an oil bath at 50°C for 65 h. The solution was filtered and HOAc was then removed under vacuum, and the residue was then washed with hexanes and extracted with ether. The ether extract was recrystallized with ether/hexanes to give 0.21 g (0.317 mmol) of a yellowish orange product [Et4N][Me(OAc)Sb{Fe(CO)4}2] ([Et4
N]-[I]) (36%). IR (nCO, MeCN): 2040 m, 2017 s, 1930 vs,
br cm− 1. 1H-NMR (400 MHz, DMSO-d
6, 298 K): d
1.61 (s, 3H), 1.73 (s, 3H) (chemical shifts not given for [Et4N]+). Anal. Calc. for [Et
4
N][Me(OAc)Sb{Fe-(CO)4}2]: C, 34.48; H, 3.96; N, 2.12. Found: C, 34.35; H, 3.75; N, 2.05%.
2.3. Reaction of [Et4N]2[MeSb{Fe(CO)4}4] with [Cu(MeCN)4][BF4]
To a solution of 0.630 g (0.70 mmol) of [Et4N]2[MeSb{Fe(CO)4}3] in 30 ml of THF was added
0.458 g (1.46 mmol) of [Cu(MeCN)4][BF4]. The mixed
solution was stirred at room temperature for 63 h. The solution was filtered, the solvent was removed under vacuum, and the residue was then extracted with hex-anes. The hexanes extract was chromatographed using hexanes as eluent to give the greenish brown product which was recrystallized with ether/hexanes to give 0.11 g (0.17 mmol) of yellowish orange complex [MeSb{Fe(CO)4}{Fe2(CO)8}] (II) (25%). IR (nCO,
hex-anes): 2106 m, 2061 s, 2039 s, 2028 s, 2010 w, sh, 1975 w, 1944 m, br cm− 1.1H-NMR (400 MHz, CDCl
3, 298
K): d 2.34 (s, 3H). 13C-NMR (100 MHz, CDCl 3, 298
K): d 6.37, 206.3, 213.4. Anal. Calc. for [MeSb{Fe-(CO)4}{Fe2(CO)8}]: C, 24.38; H, 0.47. Found: C, 24.52;
H, 0.48. M.p. 104°C (dec.).
2.4. X-ray structural characterization of complexes [Et4N][I] and II
A summary of selected crystallographic data for [Et4N][I] and II is given in Table 1. All crystals were mounted on glass fibers with Epoxy cement. Data collection was carried out on a Nonius CAD4 diffrac-tometer using graphite-monochromated Mo – Ka radia-tion at 25°C. Ac scan absorption correction was made [6]. Data reduction and structural refinement were per-formed using the NRCC-SDP-VAX packages [7], and atomic scattering factors were taken from the Interna-tional Tables for X-ray Crystallography [8].
Structures of [Et4N][I] and II. The orange crystal of
[Et4N][I] chosen for diffraction measurement was ca.
0.10 × 0.45 × 0.55 mm, and brown crystal II had di-mensions 0.50 × 0.20 × 0.15 mm. Cell parameters were obtained from 25 reflections with 2u angle in the range 19.00 – 26.10° for [Et4N][I], and 23.38°B2uB32.48° for
II. A total of 1867 reflections with I\2.0s(I) for
[Et4N][I] (3060 reflections with I\2.5s(I) for II) were
used in the refinement. The structures were solved by the heavy atom method and refined by least-squares cycles. All the non-hydrogen atoms were refined with anisotropic temperature factors. Full-matrix least-squares refinement led to convergence with R = 3.3 and
Rw = 3.1% for [Et4N][I], and with R = 2.7 and Rw =
2.9% for II. Table 1
Crystallographic data for [Et4N][Me(OAc)Sb{Fe(CO)4}2] ([Et4N][I])
and [MeSb{Fe(CO)4}{Fe2(CO)8}] (II)
[Et4N][I] II C19H26Fe2NO10Sb C13H3Fe3O12Sb Empirical formula 641.69 640.44 Formula weight Orthorhombic
Crystal system Triclinic
Space group Pna21 P1(
16.627(4) a (A, ) 9.335(1) 10.313(3) 9.411(3) b (A, ) 17.347(4) c (A, ) 10.372(1) a (°) 97.46(1) b (°) 93.63(1) g (°) 94.65(1) 2714(1) V (A,3) 984.0(3) 4 Z 2 1.570 Dcalc(Mg m−3) 2.162 49.5 Absorption coefficient 20.826 (cm−1)
Diffractometer Nonius (CAD4) Nonius (CAD4) Radiation (l) (Mo–Ka) 0.7107 0.7107 (A, ) 25 25 Temperature (°C) 0.44/1.00 0.78/1.00 Tmin/Tmax Residuals, Ra, Rwa 0.033, 0.031 0.027, 0.029
aThe functions minimized during least-squares cycles were R =
Table 2
Selected bond distances (A, ) and bond angles (°) for [Et4N][Me(OAc)Sb{Fe(CO)4}2] ([Et4N][I])
Bond distances SbFe(1) 2.509(2) SbFe(2) 2.505(2) SbC(9) 2.151(8) SbO(9) 2.077(6) C(10)O(10) 1.34 (1) 1.19 (1) C(10)O(9) Bond angles
Fe(1)SbFe(2) 131.55(5) Fe(1)SbC(9) 106.2(2) Fe(2)SbC(9)
107.4(2) 107.2(2)
Fe(1)SbO(9)
Fe(2)SbO(9) 108.0(2) Fe(2)SbC(9) 107.2(2)
tion of the OAc-substituted tetrahedral complex [Et4N][Me(OAc)Sb{Fe(CO)4}2] ([Et4N][I]) instead of forming the corresponding antimony cyclic complex [MeSb{Fe(CO)4}]2.
In the bismuth case, the formation of
[RBi{Fe(CO)4}]2 is proposed to result from the
dimer-ization of RBi{Fe(CO)}4 derived from
[RBi{Fe-(CO)4}3]2 −. This study indicates that, in the antimony
case, the OAc− group behaves more importantly as a
nucleophile toward the central antimony atom, pre-sumably in the + 5 oxidation state, to replace one Fe(CO)4 group to form cluster I. This difference is
intriguing and could be attributed to the stronger SbO versus BiO bond, which results in the formation of the four-coordinated antimony product I in the Sb case rather than undergoing further fragmentation and dimerization to give the ring complex as in the Bi system. The result may suggest that the OAc− might
ligate to the bismuth atom in the BiFe system to form the reactive species [R(OAc)Bi{Fe(CO)4}2]− followed
by acetate removal, BiFe bond breakage, and dimer-ization to give the cyclic complexes.
It has been shown that most metal clusters can be oxidized by [Cu(MeCN)4]BF4 to cause metalmetal
bond formation or metalvertex loss to give rise to the oxidized products. However, the extent of oxidation is mainly dependent on the nature of the metalmetal bonds [2]. In the bismuth case, the monoalkylated bismuth compounds [Et4N]2[RBi{Fe(CO)4}3] with
[Cu(MeCN)4]BF4induced severe bond breakage/forma-tion to give the decomposed complexes [4b]. In this study, if [Et4N]2[MeSb{Fe(CO)4}3] was treated with
two equivalents of [Cu(MeCN)4]BF4, one FeFe bond was formed to give the tetrahedral neutral complex [MeSb{Fe(CO)4}{Fe2(CO)8}] (II). Compound II is
ob-viously the two-electron oxidized product of the tetra-hedral dianionic compound [Et4N]2[MeSb{Fe(CO)4}3].
Again, the differing outcomes could be ascribed to the stronger SbR and SbFe bonds compared with those in bismuth system due to the smaller size of Sb versus Bi.
Table 3
Selected bond distances (A, ) and bond angles (°) for [MeSb{Fe(CO)4}{Fe2(CO)8}] (II)
Bond distances 2.5543(9) 2.549(1) SbFe(1) SbFe(2) 2.162 (5) 2.5160(9) SbFe(3) SbC(13) 2.847(1) Fe(1)Fe(2) Bond angles 67.83(3)
Fe(1)SbFe(2) Fe(1)SbFe(3) 130.18(3) 110.0(2) Fe(2)SbFe(3)
Fe(1)SbC(13) 127.78(3)
112.0(2) Fe(3)SbC(13)
Fe(2)SbC(13) 105.2(2)
The selected distances and angles of [Et4N][I] and II
are given in Tables 2 and 3, respectively.
3. Results and discussion
3.1. Reaction of [Et4N]2[MeSb{Fe(CO)4}3]with HOAc
and [Cu(MeCN)4]BF4
The previous study showed that the monoalkylated bismuth complexes [Et4N]2[RBi{Fe(CO)4}3] formed the
cyclic products [RBi{Fe(CO)4}]2 when treated with
HOAc (R = Et, Pr, Bu); and in the Me case, the corresponding cyclic compound was also formed pre-sumably via the methylbismuth complex [4b]. The func-tion of HOAc is of interest because there is no acetate ligand incorporated into these clusters, which are in contrast to those of Ru3(CO)12 with carboxylic acids RCO2H (R = H, Me, or Et) [9] and other related diruthenium-based metal carbonyls [10]. According to the products from the BiFeCO system, HOAc acts more like an oxidizing agent to induce the cluster fragmentation and reformation. However, an interest-ing question arises if HOAc ever ligates to the BiFe clusters in the course of the reaction. To attempt to answer this question, we decided to treat the analogous complex [Et4N]2[MeSb{Fe(CO)4}3] with HOAc due to
the similar chemical property of Sb and Bi in some cases [1,4c]. This reaction, however, led to the
forma-distances (2.460 – 2.715 A, ) [11,13,14] and are compared to those found in other structurally characterized anti-mony complexes such as [ClSb{Fe(CO)2Cp}3]22 + (2.539
A, , average) [15] and [Cl2Sb{Fe(CO)2Cp}2]+ (2.440 A, ,
average) [16].
The FeSbFe angle (131.55(5)°) in cluster I is greater than the corresponding angles in [Me2
Sb-{Fe(CO)4}2]− (123.95(4)°) and [MeISb{Fe(CO)4}2]−
(122.20(7)°) [4c,11b]. This is caused by the less steric hindrance of the OAc group than the Me or I fragment because in cluster I the OAc group is almost perpendic-ular to the FeSbFe plane. For the monosubstituted SbFe clusters, the average Fe(1)SbFe(2) angle (128.98°) in II is significantly greater than that in [MeSb{Fe(CO)4}3]2 − (114.43°). This is attributable to
the existence of an Fe2(CO)8 moiety that contains an
FeFe bond. Moreover, cluster II is structurally related to the previously reported cluster [SbFe4(CO)16]− [14a],
in which the tetrahedral Sb atom is bonded to two Fe(CO)4 fragments and the Fe2(CO)8 moiety. The acute FeSbFe angle (with FeFe bond) in II (67.83(3)°) is greater than the corresponding angle of
Fig. 1.ORTEPdiagram showing the structure and atom labeling for I.
Fig. 2.ORTEPdiagram showing the structure and atom labeling for II.
3.2. Structures of complexes [Et4N][I] and II
As shown in Figs. 1 and 2, the antimony atoms in the clusters I and II are in the distorted tetrahedral envi-ronment. This type of structure is seen in some SbFe carbonyl clusters [4c,11] and clusters I and II provide the new additions to this family. For comparison, the average FeSbFe angle (without FeFe bonds), the SbFe distance, and the SbC length of the related tetrahedral clusters are listed in Table 4. As shown in Table 4, the SbC lengths are close to the sum of single bond covalent radii (2.2 A, ) [12] and compared well with those in the related clusters [4c]. The SbFe distances in
I and II are in the range of other known SbFe(CO)4
Table 4
Comparison of the average FeSbFe angle (without FeFe bonds) and the average SbFe and SbC distances in the related clusters SbC (A,)
SbFe (A,) FeSbFe angle (°)
Compounds Ref.
[Et4N]3[Sb{Fe(CO)4}4] 109.56 2.666 – [11a]
2.614
114.43 2.160(7)
[Et4N]2[MeSb{Fe(CO)4}3] [4c]
123.95(4) 2.53 [4c]
[Et4N][Me2Sb{Fe(CO)4}2] 2.146
– [11b]
[PPN][MeISb{Fe(CO)4}2] 122.20(7) 2.508 (1)
[Me4N][SbFe4(CO)16] 113.13 2.603 – [14a]
131.55(5) This work [Et4N][I] 2.507 2.151(8) This work 2.162(5) 2.540 128.98 II
[SbFe4(CO)16]− (62.09(3)°) due to the smaller steric
hindrance of the methyl group than the Fe(CO)4group.
Finally, in cluster I, the acetato ligand OAc binds to the Sb atom in theh1-fashion and this type of bonding
mode is less seen than the commonly observedh2-OAc
in the diruthenium complexes such as [Ru2(CO) 4-(m-O2CR)(DPPM)2]+, [Ru2(CO)4(m-O2CR)(DPPE)2]+,
[Ru2(m-Pz%)(m-O2CMe)(CO)4(HPz%)2], and [Ru2(
m-Pz%)(m-O2CMe)(CO)4(PPh3)2] [10]. It is noted that the
C(10)O(10) distance (1.19(1) A,) is significantly shorter than that (1.34 (1) A, ) of C(10)O(9), the one involving bonding to Sb, due to the chelating effect.
4. Summary
The reaction of [Et4N]2[MeSb{Fe(CO)4}3] with HOAc forms the OAc substituted cluster I while treat-ment with [Cu(MeCN)4]BF4 produces cluster II. These results are somewhat different from those of the corre-sponding reactions in the BiFe system due to the smaller size and larger basicity of the antimony versus the bismuth atom.
5. Supplementary material
Additional crystallographic data of [Et4N][I] and II
are available from the authors.
Acknowledgements
We thank the National Science Council of the Re-public of China for financial support (NSC87-2113-M-003-001).
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