Photoinduced formal gallylene transfer from gallium-bridged dimetallic complexes to 16-electron metal fragments

Article abstract of DOI:10.1021/om301148y

Photoirradiation of the mixtures of Cp′(dppe)FeGaM(CO)₅ (Cp′ = η⁵-C₅Me₅ (Cp), M = W (2), Cr (3); Cp′ = η⁵-C₅H₅ (Cp), M = W (5), Cr (6)) and Fe(CO)₅ in C₆D

Full text of DOI:10.1021/om301148y

Article
pubs.acs.org/Organometallics
Photoinduced Formal Gallylene Transfer from Gallium-Bridged
Dimetallic Complexes to 16-Electron Metal Fragments
Takako Muraoka, Hideaki Motohashi, Hiroki Tomura, and Keiji Ueno*
Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu 376-8515, Japan
S
* Supporting Information
ABSTRACT: Photoirradiation of the mixtures of Cp′(dppe)FeGaM(CO)5 (Cp′ = η5-
C5Me5 (Cp*), M = W (2), Cr (3); Cp′ = η5-C5H5 (Cp), M = W (5), Cr (6)) and
Fe(CO)5 in C6D6 caused formal gallylene transfer from 2, 3, 5, and 6 to the Fe(CO)4
fragment to afford the gallium-bridged diiron complexes Cp′(dppe)FeGaFe(CO)4 (Cp′
= Cp* (1), Cp (4)) in moderate yields. Gallylene transfers with Cp(dppe)FeGaFe-
(CO)4 (4) and M(CO)6 (M = W, Cr) also took place to produce 5 and 6, respectively;
however, that with Cp*(dppe)FeGaFe(CO)4 (1) and M(CO)6 did not proceed. Photoirradiation of 4 alone in toluene caused
CO dissociation and dimerization to afford the gallylene-bridged tetrametallic complex {μ-Cp(dppe)FeGa}2Fe2(CO)6(μ-CO)
(8). In contrast to 4, the Cp* analogue 1 gave no gallylene-bridged complex in a similar reaction.
synthesis and structure of the homodimetallic L′mMGaMLn
complexes (M = Fe, Pt, Ru).
INTRODUCTION
■
Over the past decade, there has been remarkable progress in
the investigation of the synthesis and structures of transition-
metal complexes with low-valent gallylene ligands RGa.1,2 The
isolation of the first base-free terminal gallylene complex
Ar*GaFe(CO)4 (Ar* = 2,6-(2,4,6-iPr3C6H2)2C6H3)3a stimu-
lated the research in this area.3,4 Recent development of
gallylene ligand precursors, such as Cp*Ga (Cp* = η5-
C5Me5),5,6 (Me3Si)3CGa,7,8 and gallium(I) N-heterocy-
cles,9,6m,t,10 has facilitated the preparation of gallylene
complexes by ligand substitution of labile ligands with the
gallylene ligand precursors.
We have investigated the synthesis and reactivity of gallium
atom bridged complexes Cp*(dppe)FeGaM(CO)n (dppe =
Ph2P(CH2)2PPh2; M(CO)n = Fe(CO)4 (1), W(CO)5 (2),
Cr(CO)5 (3)) and Cp*(dmpe)FeGaFe(CO)4 (dmpe =
Me2P(CH2)2PMe2).11 On the basis of the 18-electron rule,
these complexes can be recognized as gallylene complexes with
the metal fragment substituted gallylene ligand RGa (R =
Cp*(dppe)Fe, Cp*(dmpe)Fe) (Figure 1). However, since the
To date, synthetic routes for gallylene complexes RGaMLn
have been limited mainly to salt elimination between
dihalogallanes with dianionic metal fragments, halide abstrac-
tion from halogallyl complexes RXGaMLn, or ligand sub-
stitution with RGa ligands. Development of an alternative route
is important for obtaining a variety of RGaMLn complexes. In
this paper, we report the first photoinduced, formal gallylene
transfer reactions from the gallium-bridged complexes to metal
carbonyl fragments M(CO)n (M(CO)n = Fe(CO)4, W(CO)5,
Cr(CO)5). Related borylene transfer reactions from borylene
complexes (Me3Si)2NBM(CO)5 (M = Cr, Mo, W) and the
boron-bridged dimetallic complex Cp*(OC)2FeBCr(CO)5 to
16-electron transition-metal fragments M′Lm to afford RBM′Lm
complexes (R = (Me3Si)2N, Cp*(OC)2Fe) have already been
reported by Braunschweig’s group.14
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Cp-Substituted
Gallium-Bridged Dimetallic Complexes 4−6. We have
reported that gallium-bridged dimetal complexes with Cp*
substituents, Cp*(dppe)FeGaM(CO)n (M(CO)n = Fe(CO)4
(1), W(CO)5 (2), Cr(CO)5 (3)), are synthesized by the
reaction of the dichlorogallyliron complex Cp*(dppe)FeGaCl2
and the corresponding dianionic carbonylates K2[M(CO)n].11
The Cp analogues Cp(dppe)FeGaM(CO)n (Cp = η5-C5H5;
M(CO)n = Fe(CO)4 (4), W(CO)5 (5), Cr(CO)5 (6)) were
also obtained in moderate to high yields by the reactions of
Cp(dppe)FeGaCl2 (7) and K2[M(CO)n] in THF for several
hours (eq 1).
Figure 1. Structures of complex 1 and bonding model A.
bridging gallium atom adopts sp hybridization with two empty
p orbitals, it can accept dπ electrons through π back-donation
from both metal fragments, Cp*(pp)Fe (pp = dppe, dmpe) and
Fe(CO)4. In fact, both Cp*(dppe)Fe−Ga and Ga−Fe(CO)4
bonds in 1 are markedly shorter than those observed for Ga−
Fe single bonds, indicating significant contribution of π back-
donation from both iron fragments to Ga. Thus, we have
proposed bonding model A for complex 1, as shown in Figure
1. Aldridge et al.12 and Fischer et al.13 have also investigated the
Characterization of complexes 4−6 was achieved by
1
spectroscopic methods as well as elemental analyses. The H,
Received: November 27, 2012
Published: January 15, 2013
© 2013 American Chemical Society
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Article
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Cp(dppe)FeGaW(CO)5·0.5(toluene) (5·0.5(toluene))
W−Ga
W−C1
W−C3
W−C5
Fe−P2
Fe−C33
Fe−C35
W−Ga−Fe
Ga−W−C2
Ga−W−C4
Ga−Fe−P1
P1−Fe−P2
W−C2−O2
W−C4−O4
2.5510(4)
2.001(4)
2.045(4)
2.033(4)
2.1532(9)
2.082(3)
2.102(4)
170.10(2)
92.14(11)
89.41(10)
85.00(3)
86.16(3)
175.9(3)
178.7(3)
Fe−Ga
W−C2
W−C4
Fe−P1
Fe−C32
Fe−C34
Fe−C36
Ga−W−C1
Ga−W−C3
Ga−W−C5
Ga−Fe−P2
W−C1−O1
W−C3−O3
W−C5−O5
2.2449(6)
2.033(4)
2.045(4)
2.1601(9)
2.098(3)
2.099(3)
2.105(4)
172.06(11)
81.23(10)
84.90(12)
91.76(3)
177.8(4)
178.9(3)
174.1(4)
13C, and 31P NMR spectra for complexes 4−6 were essentially
comparable to those observed for the corresponding Cp*
analogues 1−3 except for the Cp part. The ν(CO) data in the
IR spectra of complexes 4−6 are summarized in Table 1, in
Table 1. Comparison of ν(CO) Frequencies in Gallium-
Bridged Dimetal Complexes 1−6 and in Cp*GaM(CO)n and
Me3PM(CO)n Complexes (M(CO)n = Fe(CO)4, W(CO)5,
Cr(CO)5)
Fe−Ga and W−Ga bond lengths (2.2449(6) and 2.5510(4) Å,
respectively) are shorter than the corresponding usual single
bonds (Fe−Ga, 2.28−2.52 Å;2a,6l,17 W−Ga, 2.71−2.76 Å18) and
even shorter than those observed for Cp* analogue 2 (Fe−Ga,
2.2687(12) Å; W−Ga, 2.5861(8) Å).11d The shortening of Fe−
Ga and W−Ga bonds in complex 5 is attributable to the
alleviation of steric repulsion between Cp′ and CO ligands. In
the Cp* complex Cp*(dppe)FeGaW(CO)5 (2), the closest
interatomic distances between the Me carbon atom in Cp*
ligand and carbonyl oxygen in the W(CO)5 fragment (3.481(4)
and 3.520(4) Å) are within the sum of van der Waals radii (3.5
Å) of the Me group (2.0 Å) and oxygen (1.5 Å),11d while
relatively little steric repulsion is observed between the Cp ring
and W(CO)5 fragment in the Cp analogue Cp(dppe)FeGaW-
(CO)5 (5).
a
complex
ν(CO) /cm−1
Cp*(dppe)FeGaFe(CO)4 (1)11a
Cp*(dppe)FeGaW(CO)5 (2)11d
Cp*(dppe)FeGaCr(CO)5 (3)11d
Cp(dppe)FeGaFe(CO)4 (4)
Cp(dppe)FeGaW(CO)5 (5)
Cp(dppe)FeGaCr(CO)5 (6)
1998, 1923, 1890, 1878
2033, 1940 (sh), 1905
2015, 1933 (sh), 1897
1996, 1918, 1890, 1879
2035, 1950 (sh), 1890
2017, 1943 (sh), 1890
2037, 1966, 1942
6a
Cp*GaFe(CO)4
3d
Cp*GaW(CO)5
2065, 1986, 1910
6a
Cp*GaCr(CO)5
2052, 1982, 1918, 1902
2043, 1967, 1932
16
Me3PFe(CO)4
17
Me3PW(CO)5
2070, 1946, 1936
17
Me3PCr(CO)5
2062, 1981, 1942
a
In KBr.
Photoinduced Gallylene Transfers with Cp*-Substi-
tuted Dimetallic Complexes Cp*(dppe)FeGaM(CO)n (M-
(CO)n = W(CO)5 (2), Cr(CO)5 (3), Fe(CO)4 (1)) and Fe(CO)5
or M(CO)6 (M = Cr, W). The results of photoinduced gallylene
transfer reactions are summarized in Table 3. A C6D6 solution
of the Fe−Ga−W dimetal complex Cp*(dppe)FeGaW(CO)5
(2) and pentacarbonyliron (Fe(CO)5) was irradiated at
addition to those observed for 1−3 and Cp*GaM(CO)n and
Me3PM(CO)n complexes. The ν(CO)s observed for complexes
4−6 were comparable to those for complexes 1−311 and
sufficiently red-shifted from those for Cp*GaM(CO)n and
Me3PM(CO)n complexes.3d,6b,15,16 These results indicate that
the Cp*(dppe)FeGa and Cp(dppe)FeGa ligands donate more
electron density to the M(CO)n fragment than the Cp*Ga and
PMe3 ligands.
1
ambient temperature, and the reaction was monitored by H
NMR spectroscopy. A new Cp* signal assignable to the diiron
complex Cp*(dppe)FeGaFe(CO)4 (1) appeared at 1.44 ppm
within 0.5 h. After irradiation for 3 h, complex 2 was completely
consumed and the yield of complex 1 reached 58% (entry 1 in
Table 3 and eq 2). No reaction occurred without irradiation.
Thus, the irradiation of 2 and Fe(CO)5 causes formal gallylene
transfer in which the gallylene ligand Cp*(dppe)FeGa migrates
to the Fe(CO)4 fragment to afford the gallium-bridged diiron
complex Cp*(dppe)FeGaFe(CO)4 (1). Complex 1 was also
obtained in 48% yield by the photochemical reaction of
Cp*(dppe)FeGaCr(CO)5 (3) and Fe(CO)5 in C6D6 (entry 2
in Table 3 and eq 2). In contrast to the gallylene transfer from
M(CO)5 (M = W, Cr) to the Fe(CO)4 moieties mentioned
above, no gallylene transfer took place in the photochemical
reaction of the diiron complex Cp*(dppe)FeGaFe(CO)4 (1)
and Cr(CO)6 or W(CO)6 at ambient temperature in C6D6 for
3 h (entry 3 or 4 in Table 3). Further photoirradiation of each
reaction mixture resulted in the formation of unidentified
precipitates. Thus, the photoinduced gallylene transfer
reactions affording the Cp*-substituted Fe−Ga−Fe complex
Cp*(dppe)FeGaFe(CO)4 (1) are more favorable than those
transforming complex 1 into 2 or 3.
X-ray crystal structural analysis of complex 5 (Figure 2 and
Table 2) revealed the almost linear Fe−Ga−W framework
(170.10(2)°), indicating sp hybridization of the Ga atom. The
Figure 2. ORTEP drawing of 5 with 50% probability ellipsoids.
Hydrogen atoms are omitted for clarity.
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Article
spectroscopy. In both reactions, a new Cp signal (4.26 ppm)
assignable to the unidentified complex B appeared just after the
irradiation and reached 19 and 28% yield upon 60 and 10 min
irradiation, respectively. The complex B was completely
consumed within 2 h to give mixtures of 4 and 5 (entries 5
and 7 in Table 3). These results imply that complex B is a
common intermediate for Cp(dppe)FeGa transfer between
W(CO)5 and Fe(CO)4. At present, we have not managed to
isolate and identify complex B. However, since the same
complex B was also formed by the reaction of Cp(dppe)-
FeGaFe(CO)4 (4) and W(CO)5(thf)19 in THF at 25 °C for 2
h, we assume the complex B to be the gallylene-bridged
heterometallic complex [(OC)4Fe{μ-Cp(dppe)FeGa}W-
(CO)5]. The proposed structure of B is also supported by
the fact that the borylene-bridged dimetallic complex
[(OC)5W{μ-BN(SiMe3)2}Co(CO)Cp] has been reported by
Braunschweig et al. as the intermediate for the photoinduced
borylene transfer reaction between (OC)5WBN(SiMe3)2 and
Cp(OC)2Co.14b
Table 3. Photoinduced Gallylene Transfer Reactions of Ga-
Bridged Dimetallic Complexes 1−6
substrate
t
entry
1
(h)
product (yield (%))
Cp*(dppe)Fe-
GaW(CO)5
(2)
Fe(CO)5
Fe(CO)5
3
1 (58)
1 (48)
2
3
Cp*(dppe)Fe-
GaCr(CO)5
(3)
3
3
Cp*(dppe)FeGa- W(CO)6
Fe(CO)4 (1)
2 (0), 1 (80)
4
5
1
Cr(CO)6
Fe(CO)5
3
2
3 (0), 1 (88)
4 (25), 5 (44)
Cp(dppe)Fe-
GaW(CO)5
(5)
Synthesis and Characterization of a Tetrairon Com-
plex with Two Bridging Gallylene Ligands, 8. Photolysis
of the Cp-substituted diiron complex Cp(dppe)FeGaFe(CO)4
(4) in toluene for 72 h resulted in the formation of {μ-
Cp(dppe)FeGa}2Fe2(CO)6(μ-CO) (8) in 28% yield (Scheme
1). In contrast to the case for the Cp complex, no Cp*-
6
Cp(dppe)Fe-
GaCr(CO)5
(6)
Fe(CO)5
1
4 (33), 6 (18)
5 (45), 4 (30)
7
8
Cp(dppe)FeGa-
Fe(CO)4 (4)
W(CO)6
Cr(CO)6
2
2
4
6 (20), 4 (42), {μ-Cp(dppe)
FeGa}2Fe2(CO)6(μ-CO) (8, 15)
Scheme 1
Photoinduced Gallylene Transfers with Cp-Substi-
tuted Dimetallic Complexes Cp(dppe)FeGaM(CO)n (M-
(CO)n = W(CO)5 (5), Cr(CO)5 (6), Fe(CO)4 (4)) and Fe(CO)5
or M(CO)6 (M = Cr, W). Irradiations of Cp-substituted Ga-
bridged dimetallic complexes 4−6 with Fe(CO)5 or M(CO)6
(M = W, Cr) also caused gallylene transfer reactions but gave a
mixture of the starting substrates and the newly formed
complexes (entries 5−8 in Table 3) For example, the reaction
of Cp(dppe)FeGaW(CO)5 (5) with Fe(CO)5 in C6D6 gave a
mixture of Cp(dppe)FeGaFe(CO)4 (4) (25%) and 5 (44%)
(entry 5 in Table 3). In the photoinduced reaction of
Cp(dppe)FeGaFe(CO)4 (4) and Cr(CO)6 (entry 8 in Table
3), the tetrairon complex {μ-Cp(dppe)FeGa}2Fe2(CO)6(μ-
CO) (8) (15%) was also formed in addition to Cp(dppe)-
FeGaCr(CO)5 (6) (20%) and 4 (42%) after 2 h. This reaction
mixture remained unchanged even after an additional 4 h of
irradiation. This result implies that complex 8 is not an
intermediate for gallylene transfer. Complex 8 was independ-
ently prepared by the photochemical reaction of complex 4 in
toluene (vide infra).
substituted analogue of 8 was obtained by photolysis of
Cp*(dppe)FeGaFe(CO)4 (1) in toluene. Instead, a trace
amount of the hydride complex Cp*(dppe)FeH (9) was
formed via cleavage of the Cp*(dppe)Fe−Ga bond and
abstraction of H from toluene (Scheme 1).11c These results
suggest that the steric bulk of Cp* ligand in complex 1
hampered the formation of the gallylene-bridged complex.
X-ray crystal structure analysis (Figure 3 and Table 4)
revealed that the structure of 8 resembles that observed for {μ-
(Me3Si)3SiGa}2Fe2(CO)6(μ-CO) (10).20 Both complexes
contain a Fe2(CO)6 skeleton with one bridging CO and two
bridging gallylene ligands. The Fe1−Fe2 distance (2.6914(10)
Å) in 8 is comparable to that observed for 10 (2.6804(8) Å).
The Fe−Ga bond lengths in bridging gallylene fragments
(average 2.499(1) Å) in 8 are sufficiently longer than those
observed for 10 (average 2.389(1) Å) and {μ-
(Me3Si)3SiGa}3Fe2(CO)6 (average 2.382(1) Å)20 and are
within the range of usual Fe−Ga single bonds in (μ-
gallylene)iron complexes (2.31−2.52 Å).10n,12a,b,17a,21 Terminal
Fe−Ga lengths (Fe3−Ga1 = 2.3246(7) Å and Fe4−Ga2 =
2.3352(9) Å) are also within the range for usual Fe−Ga single
bonds (2.28−2.52 Å).2a,6l,17
Mechanistic Consideration of Photoinduced Gally-
lene Transfers from Ga-Bridged Dimetallic Complexes.
To obtain information on the reaction mechanism for the
photoinduced gallylene transfer, the photochemical reactions of
Cp(dppe)FeGaW(CO)5 (5) and Fe(CO)5 and of Cp(dppe)-
1
FeGaFe(CO)4 (4) and W(CO)6 were monitored by H NMR
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ketyl followed by distillation under a nitrogen atmosphere before use.
Benzene-d6 was distilled from a potassium mirror under vacuum and
stored on 4 Å molecular sieves. Dichloromethane-d2 was used as
received. 1,2-Bis(diphenylphosphino)ethane (dppe) was recrystallized
from EtOH. Fe(CO)5, W(CO)6, and Cr(CO)6 were used as received.
NMR spectra were recorded on a JEOL JNM-AL300 or a JEOL
JNM-AL500 Fourier transform spectrometer at room temperature. IR
spectra were recorded on a JASCO FT/IR-600 Plus spectrometer at
room temperature. Elemental analyses were performed by the
Microanalytical Center, Gunma University, or the Institute for
Materials Chemistry and Engineering, Kyushu University. Photolysis
was carried out by using an Ushio UV-452 450 W medium-pressure
Hg lamp placed in a water-cooled quartz jacket immersed in a water
bath (4 °C) and a Pyrex reaction vessel.
Figure 3. ORTEP drawing of 8 with 50% probability ellipsoids.
Hydrogen atoms are omitted for clarity.
Synthesis of Cp(dppe)FeGaCl2 (7). A toluene solution (60 mL)
of Cp(OC)2FeGaCl2 (0.485 g, 1.53 × 10−3 mol) and 1,2-
bis(diphenylphosphino)ethane (dppe; 0.605 g, 1.52 × 10−3 mol)
was irradiated for 25 h at ambient temperature. The reaction mixture
was concentrated to ca. 20 mL and cooled to −30 °C to afford orange
crystals of Cp(dppe)FeGaCl2 (7; 0.634 g, 9.74 × 10−4 mol) in 64%
yield. 1H NMR (300 MHz, C6D6): δ/ppm 7.66−6.93 (m, 20H, PPh),
4.20 (s, 5H, C5H5), 2.82 (m, 2H, PCH2CH2P), 2.19 (m, 2H,
PCH2CH2P). 13C{1H} NMR (125.7 MHz, C6D6): δ/ppm 143.5−
127.8 (m, PPh), 77.4 (s, C5H5), 30.1 (m, PCH2). 31P{1H} NMR
(121.5 MHz, C6D6): δ/ppm 105.3 (s, dppe). Anal. Calcd for
7·(toluene) (C38H37Cl2FeGaP2): C, 60.68; H, 4.96. Found: C, 60.96;
H, 5.14.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for {μ-
Cp(dppe)FeGa}2Fe2(CO)6(μ-CO)·2CH2Cl2 (8·2CH2Cl2)
Fe1−Fe2
Fe1−Ga2
Fe1−C2
Fe1−C4
Fe2−Ga2
Fe2−C5
Fe2−C7
Fe3−P1
2.6914(10)
2.4670(12)
1.717(4)
Fe1−Ga1
Fe1−C1
Fe1−C3
Fe2−Ga1
Fe2−C1
Fe2−C6
Fe3−Ga1
Fe3−P2
Fe4−P3
2.4509(9)
2.056(4)
1.882(4)
1.739(4)
2.5677(12)
1.892(4)
2.5104(11)
1.703(4)
1.817(4)
1.831(4)
2.3246(7)
2.2911(16)
2.2840(15)
2.0580(15)
2.3352(9)
2.0681(14)
59.69(4)
Synthesis of Cp(dppe)FeGaFe(CO)4 (4). To a THF (15 mL)
solution of Cp(dppe)FeGaCl2 (7; 0.407 g, 6.17 × 10−4 mol) was
added a THF suspension (10 mL) of K2[Fe(CO)4]24a (0.155 g, 6.21 ×
10−4 mol) with vigorous stirring. The resultant mixture was stirred for
5 h at 25 °C and then filtered through a glass filter. After removal of
volatiles from the filtrate in vacuo, the residue was washed with hexane
(5 mL) to give orange crystals of Cp(dppe)FeGaFe(CO)4 (4; 0.389 g,
Fe4−Ga2
Fe4−P4
Fe2−Fe1−Ga1
Ga1−Fe1−Ga2
Fe1−Fe2−Ga2
Ga1−Fe3−P1
P1−Fe3−P2
Ga2−Fe4−P4
Fe1−Ga1−Fe2
Fe2−Ga1−Fe3
Fe1−Ga2−Fe4
Fe1−C1−Fe2
Fe2−Fe1−Ga2
Fe1−Fe2−Ga1
Ga1−Fe2−Ga2
Ga1−Fe3−P2
Ga2−Fe4−P3
P3−Fe4−P4
Fe1−Ga1−Fe3
Fe1−Ga2−Fe2
Fe2−Ga2−Fe4
58.05(3)
55.49(3)
97.80(4)
90.94(4)
90.34(4)
82.88(5)
153.56(3)
65.46(3)
157.14(3)
102.18(4)
56.49(4)
94.95(5)
1
5.14 × 10−4 mol) in 83% yield. H NMR (300 MHz, C6D6): δ/ppm
85.52(5)
7.61−6.89 (m, 20H, PPh), 4.04 (s, 5H, C5H5), 2.17 (m, 2H,
PCH2CH2P), 1.99 (m, 2H, PCH2CH2P). 13C{1H} NMR (125.7 MHz,
C6D6): δ/ppm 218.2 (CO), 139.8−127.4 (m, PPh), 75.3 (s, C5H5),
30.9 (m, PCH2). 31P{1H} NMR (121.5 MHz, C6D6): δ/ppm 96.2 (s,
dppe). IR (KBr): ν/cm−1 1996, 1918, 1890, 1879 (νCO). Anal. Calcd
for C35H29Fe2GaO4P2: C, 55.53; H, 3.86. Found: C, 55.57; H, 4.12.
Synthesis of Cp(dppe)FeGaW(CO)5 (5). To a THF suspension
(60 mL) of K2[W(CO)5]24b (1.82 × 10−3 mol) was added a THF
solution (40 mL) of Cp(dppe)FeGaCl2 (7; 0.430 g, 6.51 × 10−4 mol)
at −80 °C with vigorous stirring. The resultant mixture was stirred for
2 h at −80 °C, 1 h at 0 °C, and then 4 h at 25 °C. After removal of
volatiles from the reaction mixture in vacuo, the residue was extracted
with toluene (100 mL). The extract was filtered through a Celite pad
on a Schlenk filter. The volatiles were removed from the filtrate in
vacuo. The residue was dissolved in a mixture of THF (5 mL) and
hexane (5 mL) and cooled to −35 °C to give orange crystals of
Cp(dppe)FeGaW(CO)5 (5; 0.284 g, 3.12 × 10−4 mol) in 48% yield.
1H NMR (300 MHz, C6D6): δ/ppm 7.67 (m, 4H, PPh), 7.39 (m, 4H,
PPh), 7.24 (m, 2H, PPh), 7.05−6.93 (m, 10H, PPh), 4.05 (s, 5H,
C5H5), 2.02 (m, 2H, PCH2CH2P), 1.83 (m, 2H, PCH2CH2P).
13C{1H} NMR (125.7 MHz, C6D6): δ/ppm 204.5 (s, trans-CO, 1JW−C
92.89(5)
64.81(2)
141.53(3)
136.54(3)
85.85(15)
1
The H NMR spectrum of complex 8 shows a Cp signal at
4.24 ppm and multiplet signals corresponding to CH2 and Ph
groups of the dppe ligand at 2.5−3.0 and 6.9−7.7 ppm,
respectively. In the 13C{1H} NMR spectrum at 292 K, the
signals assignable to terminal and bridging CO were not
observable, indicating rapid exchange between terminal and
bridging CO ligands in solution. The existence of terminal and
bridging CO ligands is spectroscopically identified in the IR
spectrum; four terminal and one bridging ν(CO)s are observed
at 1985, 1948, 1906, and 1889 cm−1 and at 1763 cm−1,
respectively. These absorptions are red-shifted from those
observed for 1020 (2026, 1999, 1971, 1962, 1948, 1920, and
22
1784 cm−1) and Fe2(CO)9 (2080, 2034, and 1828 cm−1).
1
= 160.4 Hz), 202.0 (s, cis-CO, JW−C = 122.8 Hz), 143.0−127.8 (m,
This result indicates that strong electron donation takes place
from Cp(dppe)FeGa to the diiron fragment and, therefore,
strong π back-donation from the iron atoms to the CO ligands.
PPh), 75.8 (s, C5H5), 30.8 (m, PCH2). 31P{1H} NMR (121.5 MHz,
C6D6): δ/ppm 94.9 (s, dppe). IR (KBr): ν/cm−1 2035, 1950, 1890
(νCO). Anal. Calcd for C36H29FeGaO5P2W: C, 47.36; H, 3.20. Found:
C, 46.92; H, 3.33.
EXPERIMENTAL SECTION
Synthesis of Cp(dppe)FeGaCr(CO)5 (6). Complex 6 was
synthesized in a manner similar to that described in the synthesis of
Cp(dppe)FeGaW(CO)5 (5) using Cp(dppe)FeGaCl2 (7; 0.450 g,
6.82 × 10−4 mol) and K2[Cr(CO)5]24c (1.90 × 10−3 mol). Orange
crystals of Cp(dppe)FeCr(CO)5 (6; 0.286 g, 3.66 × 10−4 mol) were
■
General Procedures. All manipulations were performed using
standard Schlenk tube techniques under nitrogen, vacuum line
techniques, or a drybox under nitrogen. Syntheses of Cp-
(OC)2FeGaCl2,23 Cp*(dppe)FeGaFe(CO)4 (1),11a Cp*(dppe)-
FeGaW(CO)5 (2),11d and Cp*(dppe)FeGaCr(CO)5 (3)11d were
reported previously. K2[Fe(CO)4]24a and K2[M(CO)5] (M = W,
Cr)24b,c were synthesized by the literature procedures. Toluene,
hexane, and THF were dried by refluxing over sodium benzophenone
1
obtained in 56% yield. H NMR (300 MHz, C6D6): δ/ppm 7.73 (m,
4H, PPh), 7.40 (m, 4H, PPh), 7.25 (m, 2H, PPh), 6.99−6.91 (m, 10H,
PPh), 4.12 (s, 5H, C5H5), 2.07 (m, 2H, PCH2CH2P), 1.88 (m, 2H,
PCH2CH2P). 13C{1H} NMR (125.7 MHz, C6D6): δ/ppm 226.8
646
dx.doi.org/10.1021/om301148y | Organometallics 2013, 32, 643−648

Organometallics
Article
(trans-CO), 221.1 (cis-CO), 142.8−127.8 (m, PPh), 75.7 (s, C5H5),
Joint Research Center for Materials and Devices (Institute for
Materials Chemistry and Engineering, Kyushu University)”.
1
2
31.1 (dd, JP−C = 29.4 Hz, JP−C = 8.9 Hz, PCH2). 31P{1H} NMR
(121.5 MHz, C6D6): δ/ppm 96.3 (s, dppe). IR (KBr): ν/cm−1 2017,
1943, 1890 (νCO). Anal. Calcd for C36H29CrFeGaO5P2: C, 55.35; H,
3.74. Found: C, 54.92; H, 3.96.
REFERENCES
■
(1) Whitmire, K. H. In Comprehensive Organometallic Chemistry III;
Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier: Amsterdam, 2007;
Vol. 3, Chapter 3.08, p 343.
General Procedure for the Photoinduced Gallylene Transfer
with Gallium-Bridged Dimetal Complexes and M(CO)n. In a
NMR sample tube with a Teflon vacuum valve, a C6D6 solution (0.5
mL) of Cp*(dppe)FeGaW(CO)5 (2; 4.6 mg, 5.0 × 10−6 mol) and
Fe(CO)5 (0.7 μL, 5 × 10−6 mol) was irradiated at ambient
temperature. During the irradiation, the reaction mixture changed
from yellow to orange. After 2.5 h, the gallium-bridged diiron complex
Cp*(dppe)FeGaFe(CO)4 (1) was formed in 58% NMR yield with the
complete consumption of 2.
Synthesis of {μ-Cp(dppe)FeGa}2Fe2(CO)6(μ-CO) (8). A degassed
toluene solution (40 mL) of Cp(dppe)FeGaFe(CO)4 (4; 0.389 g, 5.14
× 10−4 mol) was irradiated at 25 °C for 72 h. The reaction mixture was
degassed periodically utilizing freeze−pump−thaw cycles during the
photolysis. The reaction mixture was filtered through a glass filter. The
filtrate was concentrated to 15 mL and cooled to −30 °C to give red-
orange crystals of {μ-Cp(dppe)FeGa}2Fe2(CO)6(μ-CO) (8; 0.217 g,
1.50 × 10−4 mol) in 28% yield. 1H NMR (300 MHz, CD2Cl2): δ/ppm
7.70−6.93 (m, 40H, PPh), 4.24 (s, 10H, C5H5), 2.99 (m, 4H,
PCH2CH2P), 2.58 (m, 4H, PCH2CH2P). 13C{1H} NMR (125.7 MHz,
CD2Cl2): δ/ppm 144.0−125.7 (m, PPh), 76.3 (s, C5H5), 30.2 (m,
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(KBr): ν/cm−1 1985, 1948, 1906, 1889, 1763 (νCO). Anal. Calcd for
8·0.5(toluene) (C72.5H62Fe4Ga2O7P4): C, 56.84; H, 4.08. Found: C,
56.53; H, 3.96.
X-ray Crystal Structure Determination of Cp(dppe)FeGaW-
(CO)5·0.5(toluene) (5·0.5(toluene)) and {μ-Cp(dppe)-
FeGa}2Fe2(CO)6(μ-CO)·2CH2Cl2 (8·2CH2Cl2). A single crystal
suitable for X-ray crystal structure determination was mounted on a
glass fiber. The intensity data were collected on a Rigaku RAXIS-IV
imaging plate diffractometer with graphite-monochromated Mo Kα
radiation at 150 K. Crystallographic data for 5·0.5(toluene) and
8·2CH2Cl2 are given in Tables S-1 and S-5, respectively, in the
Supporting Information. The structure was solved by direct and
Fourier transform methods using SHELX-97.25 All non-hydrogen
atoms were refined by full-matrix least-squares techniques with
anisotropic displacement parameters based on F2 with all reflections.
All hydrogen atoms were placed at their geometrically calculated
positions and refined riding on the corresponding carbon atoms with
isotropic thermal parameters. The final residue R1 and the weighted
wR2 were 0.0307 and 0.0728 in 5·0.5(toluene) and 0.0524 and 0.1229
in 8·2CH2Cl2, respectively.
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■
S
* Supporting Information
Tables, figures, and CIF files giving details of structure
determinations and crystallographic data for complexes 5 and
8. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Tel and fax: +81-277-30-1260. E-mail: ueno@gunma-u.ac.jp.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by Grants-in-Aid for Scientific
Research (Nos. 23550066 and 24750053) and the “Element
Innovation” Project from the Ministry of Education, Culture,
Sports, Science and Technology of Japan. This work was
performed under the cooperative research program “Network
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