Synthesis, characterization and catalytic application of iron complexes modified by monodentate phosphane ligands

Article abstract of DOI:10.1002/ejic.201100233

In the present study, the properties of new monodentate phosphane ligands with a N,N-diphenyl-1H-pyrrol-1-amine moiety have been investigated. The ligands are easily accessible by lithiation of N,N-diphenyl-1H-pyrrol-1-amine in the 2-position and by quenc

Full text of DOI:10.1002/ejic.201100233

SHORT COMMUNICATION
DOI: 10.1002/ejic.201100233
Synthesis, Characterization and Catalytic Application of Iron Complexes
Modified by Monodentate Phosphane Ligands
Michael Haberberger,[a] Elisabeth Irran,[b] and Stephan Enthaler*[a]
Keywords: Phosphanes / Monodentate ligands / Iron / Homogeneous catalysis
In the present study, the properties of new monodentate
phosphane ligands with a N,N-diphenyl-1H-pyrrol-1-amine
moiety have been investigated. The ligands are easily ac-
cessible by lithiation of N,N-diphenyl-1H-pyrrol-1-amine in
the 2-position and by quenching with phosphane chlorides
(2: R = tBu, 3: R = Ph). After characterization of the ligands,
their coordination to iron carbonyls has been studied. The
ligands coordinate through the phosphorus in a monodentate
fashion to the iron to realize complexes with the (L)Fe(CO)4
motif. Initial catalytic experiments have been performed; the
iron-catalyzed reduction of alkynes to alkenes with excellent
selectivities to the corresponding alkenes has been achieved.
Introduction
Results and Discussion
Synthesis of Phosphane Ligands
The advance of sustainable and more environmentally
friendly techniques for the synthesis of high-value products
is one of the central aims for industry as well as academia.[1]
In this regard, transition-metal-catalyzed reactions offer an
efficient and versatile approach and represent a key feature
for the advancement of “green chemistry”, specifically for
waste prevention, achieving high atom economy and advan-
tageous economics.[2] A current trend is the substitution of
expensive and toxic metals (e.g., Rh, Ir, Ru) by cheap, abun-
dant and less toxic metals.[3] Thus the use of biometals, e.g.
iron, is of great importance. Over the last years, special at-
tention was directed to iron catalysis.[4] Aside from the
choice of the metal, the influence of the surrounding li-
gands is of importance.[5] In this context, phosphane li-
gands have been demonstrated as useful tools, with respect
to catalyst activity and selectivity, in various iron-catalyzed
reduction protocols, e.g. C=O, amides, imines, alkynes.[6]
However, improvement of activity and selectivity still re-
mains a challenge. On the basis of our ongoing interest in
iron catalysis, we report herein the synthesis of easy access-
ible phosphanes, the synthesis and characterization of the
corresponding iron complexes and the application in re-
duction chemistry, i.e. the selective reduction of alkynes to
alkenes.[7]
Recently, various groups reported the synthesis and ap-
plication of 2-phosphanyl-1-arylpyrrole ligands (PAP li-
gands).[8,9] By selective lithiation in the 2-position of N-sub-
stituted pyrroles with nBuLi/tmeda (N,N,NЈ,NЈ-tetra-
methylethylenediamine) and subsequent reaction with
phosphane chlorides, electron-rich and sterically de-
manding ligands were accessed. The ligands have been
proven to be useful in the making of highly active catalysts
with transition metals and have been applied in numerous
catalytic transformations.[8,9] Further, the substituent con-
nected to the pyrrole nitrogen atom has a crucial influence
(electronic and steric) on catalysis. So far, most of the PAP
ligands are based on aryl substituents that form a N–C
bond. We were interested in knowing whether the carbon
group can be replaced by an amine functionality to generate
a N–N bond and allow a different electronic and steric situ-
ation. Furthermore, the amine-based group can be an ad-
ditional donor, which can coordinate to the metal centre.
On the basis of this concept, we developed a new type of
pyrrole–phosphane ligand. The overall synthesis of phos-
phanes 2 and 3 proceeds in two steps and starts with the
reaction of dimethoxytetrahydrofuran and N,N-diphenylhy-
drazine. Both compounds were heated at reflux in acetic
acid to yield N,N-diphenyl-1H-pyrrol-1-amine (1). After
[a] Technische Universität Berlin, Department of Chemistry,
Cluster of Excellence “Unifying Concepts in Catalysis”,
Straße des 17. Juni 135/C2, 10623 Berlin, Germany
Fax: +49-30-314-29732
E-mail: stephan.enthaler@tu-berlin.de
[b] Technische Universität Berlin, Department of Chemistry,
Straße des 17. Juni 135/C2, 10623 Berlin, Germany
Scheme 1. Synthesis of 2 and 3.
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M. Haberberger, E. Irran, S. Enthaler
SHORT COMMUNICATION
isolation, a selective lithiation in the 2-position of the pyr- (Scheme 2).[10] In the case of 6, suitable crystals for single-
role unit was performed with n-butyllithium in THF at 0 °C crystal X-ray diffraction analysis were obtained by slow
(Scheme 1).
cooling to room temperature and slow evaporation of the
Subsequently, chloro-di-tert-butylphosphane or chlorodi- solvent (see Figure 3), while the reaction of 2 with
phenylphosphane, respectively, were added to allow C–P Fe2(CO)9 was incomplete and only small amounts of the
bond formation. In the case of phosphane 3, lithiation was corresponding complex 5 was formed. In accordance with
performed in the presence of N,N,NЈ,NЈ-tetramethylethyl- other monodentate iron phosphane complexes reported in
enediamine (tmeda). The ligands were purified by either the literature, four carbonyl groups are attached to the iron
column chromatography (2) or crystallization in acetone centre.[11,12] For the carbonyl ligand in the trans position
(3). It is noteworthy that phenyl-substituted phosphane 3 is with respect to the phosphane ligand, a shorter Fe–C dis-
highly air- and moisture stable (Ͼ6 month), while phos- tance (1.768 Å) could be observed because of the trans-
phane 2 is easily oxidized. The molecular structure of com- effect of the phosphane ligand. The cis-positioned carbonyl
pound 2 is confirmed as the corresponding phosphane ox- ligands show almost equal Fe–C distances (1.784–1.794 Å).
ide (2-oxide) by X-ray crystallography and is depicted in The Fe–P bond length (2.248 Å) is shorter in contrast to
Figure 1. The N–N distance (1.392–1.394 Å) of 2-oxide and similar complexes in the literature. The bond angles be-
phosphane 3 (Figure 2) are quite similar. The phenyl groups tween the carbonyl ligands in the equatorial position
at the phosphorus atom of compound 3 are slightly dis- (116.06–122.18°) differ from the ideal angle of 120° because
torted compared to the tert-butyl groups of phosphane 2.
of steric hindrance of the phenyl groups at the phosphorus
and at the nitrogen atoms. In addition, the carbonyl ligand
in the axial position is nearly linearly coordinated (178.96°).
The large N2–Fe distance (4.025 Å) neglects the coordina-
tion of nitrogen to the iron centre. Attempts to force the
coordination of the nitrogen donor, by irradiation of the
complex with light or addition of Me3NO, failed so far. In
the case of complex 5, the IR spectra shows two strong
absorption bands at 1962 and 1929 cm–1, which can be at-
tributed to the carbonyl ligands coordinated equatorially
and axially to the iron, while for complex 6, two strong
bands at 1971 and 1938 cm–1 are observed. The signals in
the 1H NMR spectra for both compounds 5 and 6 are
broad, because of the properties of iron. In contrast, the
Figure 1. Molecular structure of 2-oxide. Hydrogen atoms are
omitted. Thermal ellipsoids are drawn at the 50% probability level.
Selected bond lengths [Å]: N1–N2 1.394(4), P1–O1 1.477(2), N3–
N4 1.392(4), P2–O2 1.488(2).
Scheme 2. Synthesis of iron phosphane complexes 5 and 6.
Figure 2. Molecular structure of 3. Hydrogen atoms are omitted.
Thermal ellipsoids are drawn at the 50% probability level. Selected
bond lengths [Å]: N1–N2 1.3919(18).
Synthesis of Iron Phosphane Complexes
Figure 3. Molecular structure of 6. Hydrogen atoms are omitted.
Thermal ellipsoids are drawn at the 50% probability level. Selected
bond lengths [Å]: Fe–C1 1.768(3), Fe–C 1.784(3)–1.794(3), Fe–P
Moreover, phosphanes 2 and 3 were treated with equi-
molar amounts of diiron nonacarbonyl in refluxing diethyl
ether to yield the corresponding iron complexes 5 and 6 2.2484(7).
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Iron Complexes Modified by Monodentate Phosphane Ligands
31P NMR spectra show sharp signals – the coordinated and of alkynes to alkenes.[12] However, an unsolved challenge
non-coordinated ligands can be determined conclusively. As must be addressed to the (E)/(Z)-selectivity to obtain one
expected, the signals for coordinated ligands are shifted to isomer exclusively. In accordance to earlier reports, diphen-
a lower field, 103.0 ppm for complex 5 (2: 1.3 ppm) and ylacetylene 7 was chosen as the model substrate. The pre-
55.3 ppm for complex 6 (3: –31.4 ppm).
catalyst was formed in situ by reacting 5 mol-% of diiron
nonacarbonyl with 10 mol-% of ligand 2 or 3 in THF. After
addition of the reducing reagent (EtO)3SiH, the reaction
mixture was stirred for 12 h at 60 °C (Table 1). The reaction
was then quenched under aqueous conditions. The best per-
formance for the formation of stilbene was found for the
catalyst containing ligand 3, with yields of Ͼ99% and a
(Z)-selectivity of 87%, while with ligand 2 a lower conver-
sion and a (Z)-selectivity of 72% was obtained. Further-
more, the isolated complex 6 was applied as a precatalyst.
However, a significant reduced yield and selectivity was ob-
served relative to the in situ approach. Probably, in the in
situ approach, complexes are formed along with 6, which
are catalytically active, which results in increased yields.
Unfortunately, the complexes are so far unidentified. More-
over, various substituted diphenylacetylenes have been re-
duced in the presence of Fe2(CO)9 and ligand 3, which re-
sults in the formation of the corresponding stilbenes in
good yield and selectivities. It should be noted that in all
cases, no over reduction was observed.
Reduction of Alkynes to Alkenes
With these new ligands and complexes in hand, we were
interested in the iron-catalyzed reduction of alkynes to al-
kenes, since alkenes have a wide range of applications in
industry as well as in academic research, e.g. as synthons
for bulk chemicals, pharmaceuticals, agrochemicals, poly-
mers, natural product synthesis and as key intermediates in
organic syntheses. Catalytic hydrogenation has been proven
to be a method of choice.[13] However, over reduction to
the corresponding alkanes often occurs, which reduces the
impact of this method.[14] An alternative to hydrogenation
is hydrosilylation, with the advantage of mild reaction con-
ditions and a straightforward process. The group of Chirik
applied well-defined iron complexes modified by tridentate
nitrogen ligands on the reduction of alkynes with silanes to
the corresponding alkenes at ambient temperature.[15] Re-
cently, we have reported the application of a robust and
easy-to-adopt iron-based catalyst for the selective reduction
Conclusions
Table 1. Iron-catalyzed reduction of alkynes.
In summary, we have presented the straightforward syn-
thesis of monodentate phosphanes based on the N,N-di-
phenyl-1H-pyrrol-1-amine scaffold. The corresponding iron
complexes have been obtained by reacting the phosphanes
with diiron nonacarbonyl in a molar ratio of 1:1. The de-
fined complexes consist of the structural motif LFe(CO)4.
The complexes have been applied as useful catalysts in the
reduction of alkynes to alkenes with good selectivities. Con-
trary to case for the isolated complex, the in situ approach
exhibited an increase in yield and selectivity. In future work,
the composition of the in situ catalyst will be studied to
understand the different behaviour.
Experimental Section
General: All manipulations with oxygen- and moisture-sensitive
compounds were performed under dinitrogen by using standard
1
Schlenk techniques. H and 13C NMR spectra were recorded on a
Bruker AFM 200 spectrometer (1H: 200.13 MHz; 13C: 50.32 MHz)
by using the proton signals of the deuterated solvents as reference.
IR spectra were recorded either on a Nicolet Series II Magna-IR-
System 750 FTR-IR or on a Perkin–Elmer Spectrum 100 FT-IR
spectrometer. Electron-impact mass spectra (EI-MS) were recorded
on a Finnigan MAT95S.
Safety Consideration: During our studies we used triethoxysilane
as reducing reagent without incident. However, Buchwald et al. re-
ported on difficulties when working with triethoxysilane.[16]
[a] Reaction conditions: Reactions were carried out with
0.036 mmol Fe2(CO)9 (5 mol-%), 0.072 mmol ligand, 0.72 mmol
substrate, 0.79 mmol (EtO)3SiH (1.1 equiv.), 2.0 mL THF, 12 h at
60 °C. [b] The conversion was determined by GC (30 m Rxi-5ms
column, 40–300 °C). For compound 7, dodecane was applied as
internal standard. [c] In brackets the isolated yield is stated. [d] The
isolated complex 6 was applied as pre-catalyst.
Synthesis of N,N-diphenyl-1H-pyrrol-1-amine: 1,1-Diphenylhydraz-
ine (0.11 mol) was dissolved in 1,4-dioxane at room temperature.
Dimethoxytetrahydrofuran (0.14 mol) was added, followed by ace-
tic acid (100 mL). The solution was stirred and heated at reflux for
Eur. J. Inorg. Chem. 2011, 2797–2802
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2799

M. Haberberger, E. Irran, S. Enthaler
SHORT COMMUNICATION
12 h, during which the colour changed to deep brown. After cool-
ing to room temperature, dichloromethane was added, and the
solution was filtered through a plug of silica. The solvent was re-
moved in vacuo to yield a black oily residue, which was purified
by vacuum distillation to give off-white crystals. Yield: 15.2 g
(59%). M.p. 58 °C (off-white crystals). B.p. 138–140 °C (1 mbar).
1H NMR (200 MHz, CDCl3, 25 °C): δ = 6.24 (t, J = 2.31 Hz, 2 H,
pyrrole), 6.86 (t, J = 2.31 Hz, 2 H, pyrrole), 6.94–7.07 (m, 6 H,
C6H5), 7.23–7.34 (m, 4 H, C6H5) ppm. 13C NMR (50 MHz, CDCl3,
25 °C): δ = 107.6, 119.1, 120.6, 123.1, 129.2, 130.6, 146.1 ppm. IR
m/z = 395 [M+ + 1 H]. HRMS calcd. for [C24H31N2OP + H]
395.22468; found 395.22321.
Synthesis of N,N-Diphenyl-1H-pyrrol-1-amine-2-diphenylphosphane
(3): A solution of N,N-diphenyl-1H-pyrrol-1-amine (17.8 mmol) in
dry THF (50 mL) was stirred under an atmosphere of dinitrogen.
The mixture was cooled to 0 °C, and, in a sequence, n-butyllithium
[20.5 mmol (1.2 equiv.), 1.6 m in n-hexane] and N,N-tetramethyleth-
ylenediamine (17.1 mmol) were added dropwise by syringe. The
solution was stirred for additional 2 h at 0 °C, followed by addition
of chlorodiphenylphosphane (17.8 mmol) and stirring at room tem-
perature for 8 h. After refluxing for 3 h, the solvent was removed
in vacuo. The residue was dissolved in toluene (100 mL) and fil-
tered. The solvent was removed, and the residue dissolved in ace-
tone in air. After several days, colourless crystals appeared. The
crystals were removed by filtration and dried in vacuo. Yield: 6.2 g
(KBr): ν = 3400 (w), 3027 (w), 1942 (w), 1727 (w), 1591 (s), 1495
˜
(s), 1330 (m), 1313 (m), 1295 (m), 1195 (w), 1180 (w), 1156 (w),
1069 (m), 1061 (m), 997 (w), 973 (m), 890 (w), 747 (s), 717 (s), 691
(s), 643 (m), 507 (w) cm–1. MS (ESI): m/z = 235 [M+ + 1 H]. HRMS
calcd. for [C16H14N2 + H] 235.12298; found 235.12223.
1
(83%). H NMR (200 MHz, CDCl3, 25 °C): δ = 6.80–7.30 (m, 21
Synthesis of N,N-Diphenyl-1H-pyrrol-1-amine-2-di-tert-butylphos-
H), 6.28–6.36 (m, 1 H), 6.02–6.09 (m, 1 H) ppm. 13C NMR
(50 MHz, CDCl3, 25 °C): δ = 145.9, 136.8, 136.7, 133.7, 133.3,
130.6, 129.0, 128.4, 128.2, 128.1, 124.8 (d, J = 1.66 Hz), 123.0,
119.4 (d, J = 1.28 Hz), 116.5 (d, J = 2.47 Hz), 109.2 (d, J = 1.07 Hz)
ppm. 31P NMR (50 MHz, CDCl3, 25 °C): δ = –31.4 ppm. IR
phane (2):
A
solution of N,N-diphenyl-1H-pyrrol-1-amine
(19.6 mmol) in dry THF (50 mL) was stirred under an atmosphere
of dinitrogen. The mixture was cooled to 0 °C, and n-butyllithium
[23.6 mmol (1.2 equiv.), 1.6 m in n-hexane] was added dropwise by
syringe. The solution was stirred for additional 2 h at 0 °C, followed
by the addition of di-tert-butylchlorophosphane (19.99 mmol) and
stirring at room temperature for 8 h. After refluxing for 3 h, the
solvent was removed in vacuo. The residue was dissolved in toluene
(100 mL) and filtered. The solvent was removed, and, after drying,
a white powder was obtained. Yield: 5.1 g (69%). 1H NMR
(200 MHz, C6D6, 25 °C): δ = 6.65–7.20 (m, 11 H), 6.48–6.54 (m, 1
H), 6.23–6.29 (m, 1 H), 1.03 (s, 9 H, tBu), 0.97 (s, 9 H, tBu) ppm.
13C NMR (50 MHz, C6D6, 25 °C): δ = 146.8, 129.4, 128.7, 124.6,
123.0, 122.8, 119.2, 115.7, 115.6, 108.4, 107.9, 32.6, 32.2, 30.5,
30.2 ppm. 31P NMR (50 MHz, C6D6, 25 °C): δ = 1.3 ppm. IR
(KBr): ν = 3435 (m), 3112 (m), 3093 (m), 3068 (m), 3050 (s), 3009
˜
(m), 2627 (w), 2346 (w), 1948 (w), 1888 (w), 1809 (w), 1743 (w),
1676 (w), 1587 (s), 1533 (m), 1492 (s), 1460 (s), 1432 (s), 1395 (m),
1329 (s), 1306 (s), 1281 (s), 1211 (m), 1191 (s), 1156 (m), 1120 (m),
1095 (m), 1079 (m), 1069 (m), 1027 (m), 1007 (m), 998 (m), 909
(w), 876 (m), 849 (w), 837 (m), 807 (m), 760 (s), 727 (s), 695 (s),
654 (m), 628 (m), 594 (w), 571 (w), 523 (s), 502 (s), 487 (m), 458
(w) cm–1. MS (ESI): m/z = 419 [M+ + 1 H]. HRMS calcd. for
[C28H23N2P + H] 419.16716; found 419.16548.
General Synthesis of Iron Phosphane Complexes: A solution of the
corresponding phosphane ligand (761 μmol) and diironnonacarb-
onyl (761 μmol) in diethyl ether (30 mL) was heated at reflux for
1–2 h. The solution was allowed to cool to room temperature. The
volatiles were removed in vacuo to yield a brown foam. The prod-
ucts were purified by extraction and filtration through a pad of
aluminium oxide. Coloured crystals were obtained by crystalli-
zation from diethyl ether.
(KBr): ν = 3395 (w), 3133 (w), 3067 (w), 2939 (m), 2862 (m), 1939
˜
(w), 1744 (w), 1590 (s), 1493 (s), 1456 (s), 1414 (m), 1361 (m), 1274
(s), 1209 (m), 1174 (m), 1097 (m), 1074 (m), 1028 (m), 1008 (m),
930 (w), 884 (w), 808 (w), 799 (w), 749 (s), 723 (s), 691 (s), 634 (m),
590 (w), 572 (w), 525 (w), 489 (w), 460 (w) cm–1. MS (ESI): m/z =
379 [M+ + 1 H]. HRMS calcd. for [C24H31N2P + H] 379.22976;
found 379.22839.
Synthesis of N,N-Diphenyl-1H-pyrrol-1-amine-2-di-tert-butylphos-
phane Oxide (2-oxide): A solution of N,N-diphenyl-1H-pyrrol-1-
amine (19.6 mmol) in dry THF (50 mL) was stirred under an atmo-
sphere of dinitrogen. The mixture was cooled to 0 °C, and, in a
sequence, n-butyllithium [23.6 mmol (1.2 equiv.), 1.6 m in n-hexane]
and N,N-tetramethylethylenediamine (19.6 mmol) were added
dropwise by syringe. The solution was stirred for additional 2 h
at 0 °C, followed by the addition of di-tert-butylchlorophosphane
(19.99 mmol) and stirring at room temperature for 8 h. After re-
fluxing for 3 h, the solvent was removed in vacuo. The residue was
dissolved in toluene (100 mL) and filtered. The volume was reduced
to ca. 50 mL, and ethyl acetate was added in air. After several days,
colourless crystals appeared. The crystals were removed by fil-
tration and dried in vacuo. Yield: 7.3 g (95%). 1H NMR (200 MHz,
CDCl3, 25 °C): δ = 6.90–7.29 (m, 11 H, C6H5), 6.53–6.59 (m, 1 H,
pyrrol), 6.34–6.39 (m, 1 H, pyrrol), 1.15 (s, 9 H, tBu), 1.08 (s, 9 H,
tBu) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 146.1, 130.9,
128.6, 128.5, 128.4, 122.6, 119.9, 116.6, 116.3, 107.7, 107.5, 38.1,
36.8, 26.3 ppm. 31P NMR (50 MHz, CDCl3, 25 °C): δ = 48.7 ppm.
1
5: (Reaction time: 1 d, deep red solid). H NMR (200 MHz, C6D6,
25 °C): δ = 7.40–5.80 (m), 4.91 (br. s), 1.88 (br. s), 1.00 (s) ppm.
31P NMR (50 MHz, C D , 25 °C): δ = 103.0 ppm. IR (KBr): ν =
˜
6
6
2968 (w), 2940 (w), 2894 (w), 2862 (w), 2348 (w), 2042 (m), 2000
(w), 1962 (s), 1929 (s), 1590 (m), 1494 (s), 1458 (w), 1391 (w), 1362
(w), 1312 (w), 1275 (w), 1175 (w), 1075 (w), 1028 (w), 809 (w), 750
(m), 724 (m), 693 (m), 635 (w), 490 (w) cm–1. MS (70 eV, EI): m/z
(%) = 490 (Ͻ1) [5 – 2ϫ CO], 462 (Ͻ1) [5 – 3ϫ CO], 434 (Ͻ1) [5 –
4ϫ CO], 378 (44), [5 – Fe(CO)4], 321 (16), 265 (46), 234 (19), 168
(100), 98 (18), (Molpeak was not detectable).
6: (Reaction time: 1 h, deep red crystals obtained from diethyl
ether). M.p. 167 °C. 1H NMR (200 MHz, CDCl3, 25 °C): δ = 8.20–
5.77 (m), 1.23 (s), 0.81 (s) ppm. 31P NMR (50 MHz, CDCl3, 25 °C):
δ = 55.3 ppm. IR (KBr): ν = 3114 (w), 3064 (w), 2049 (s), 1971 (s),
˜
1930 (s), 1588 (m), 1492 (m), 1458 (w), 1437 (m), 1257 (m), 1210
(w), 1184 (w), 1095 (m), 1079 (m), 761 (m), 752 (m), 736 (m), 693
(m), 626 (s), 563 (w), 543 (w), 534 (w), 505 (m) cm–1. MS (70 eV,
EI): m/z (%) = 502 (40) [6 – 3ϫ CO], 474 (100) [6 – 4ϫ CO], 418
(18) [6 – Fe(CO)4], 172 (33), (Molpeak was not detectable).
IR (KBr): ν = 3430 (m), 3112 (w), 3082 (w), 3027 (w), 2963 (m),
˜
2871 (m), 1728 (m), 1590 (m), 1496 (s), 1474 (m), 1460 (m), 1404 Single-Crystal X-ray Structure Determination: Crystals were each
(m), 1387 (m), 1364 (m) 1331 (m), 1308 (m), 1279 (m), 1221 (m), mounted on a glass capillary in perfluorinated oil and measured in
1197 (m), 1165 (s), 1121 (m), 1094 (m), 1081 (m), 1039 (m), 1017 a cold N2 flow. The data were collected by using an Oxford Diffrac-
(m), 931 (w), 874 (w), 811 (m), 762 (m), 742 (m), 701, 690 (m), 665 tion Xcalibur S Sapphire at 150(2) K (Mo-Kα radiation, λ =
(m), 646 (m), 538 (w), 523 (w), 488 (w), 473 (m) cm–1. MS (ESI): 0.71073 Å). The structures were solved by direct methods and re-
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Iron Complexes Modified by Monodentate Phosphane Ligands
fined on F2 with the SHELX-97 software package.[17] The positions
of the hydrogen atoms were calculated and considered isotropically
according to a riding model. CCDC-815979, -815980 and -815981
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
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R. M. Bullock, Angew. Chem. 2007, 119, 7504–7507; Angew.
Chem. Int. Ed. 2007, 46, 7360–7363.
¯
Compound 2-Oxide: Triclinic; space group P1; a = 9.6130(6), b =
12.7465(5), c = 22.6180(10) Å; α = 95.731(4)°, β = 99.133(4)°, γ =
110.383(5)°; V = 2528.7(2) Å3; Z = 2; ρcalcd. = 1.157 mgm–3; ab-
sorption coefficient 0.130 mm–1; F(000) 948; reflections collected:
19886; independent reflections: 8882 [Rint = 0.0579]; completeness
to θ = 25.00° (99.7%); max. and min. transmission 0.9770 and
0.9524; goodness-of-fit on F2 1.058; final R indices [IϾ2σ(I)]: R1
= 0.0784, wR2 = 0.1553; R indices (all data): R1 = 0.1435, wR2 =
0.1754; largest diff. peak and hole 0.470 and –0.354 eÅ–3.
[3]
[4]
¯
Compound 3: Triclinic; space group P1; a = 10.0533(4), b =
10.9260(5), c = 11.2871(5) Å; α = 111.201(4)°, β = 100.956(4)°, γ
= 101.463(4)°; V = 1085.29(8) Å3; Z = 2; ρcalcd. = 1.281 mgm–3;
absorption coefficient 0.145 mm–1; F(000) 440; reflections col-
lected: 9345; independent reflections: 3806 [Rint = 0.0219]; com-
pleteness to θ = 25.00° (99.8%); max. and min. transmission:
0.9565 and 0.9004; goodness-of-fit on F2 1.021; final R indices [I
Ͼ 2 σ (I)]: R1 = 0.0363, wR2 = 0.0765; R indices (all data): R1 =
0.0468, wR2 = 0.0797; largest diff. peak and hole 0.239 and
–0.280 eÅ–3.
[5]
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Compound 6: Monoclinic; space group P21/n; a = 16.3557(7), b =
10.8043(4), c = 17.0356(8) Å; α = 90°, β = 110.408(5)°, γ = 90°; V
= 2821.4(2) Å3; Z = 4; ρcalcd. = 1.380 mgm–3; absorption coefficient
0.631 mm–1; F(000) 1208; reflections collected: 10889; independent
reflections: 4956 [Rint = 0.0346]; completeness to θ = 25.00°
(99.7%); max. and min. transmission: 0.8789 and 0.7775; goodness-
of-fit on F2 0.940; final R indices [I Ͼ 2 σ (I)]: R1 = 0.0372, wR2
= 0.0688; R indices (all data): R1 = 0.0585, wR2 = 0.0722; largest
diff. peak and hole 0.273 and –0.346 eÅ–3.
General Procedure for the Reduction of Alkynes: A pressure tube
was charged with diiron nonacarbonyl (0.036 mmol, 5.0 mol-%)
and the corresponding ligand (0.072 mmol, 10 mol-%). The com-
pounds were dissolved in freshly distilled tetrahydrofuran (2.0 mL).
To this solution diphenylacetylene (0.72 mmol) and (EtO)3SiH
(0.79 mmol) were added by syringe. The reaction mixture was
stirred in a preheated oil bath at 60 °C for 12 h. The mixture was
cooled down in an ice bath and was treated with dodecane (10 μL)
as GC standard (for GC analysis) and aqueous sodium hydroxide
solution (1.0 mL) with stirring. The reaction mixture was stirred
for 60 min at room temperature and was then extracted with diethyl
ether (2ϫ10.0 mL). The combined organic layers were washed with
brine, dried with anhydrous Na2SO4 and filtered, and an aliquot
was removed for GC analysis (30 m Rxi-5ms column, 40–300 °C).
The obtained analytical data for all products are in agreement with
literature reports.[18]
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Acknowledgments
This work was supported by the Cluster of Excellence “Unifying
Concepts in Catalysis” (sponsored by the Deutsche Forschungsge-
meinschaft and administered by the Technische Universität Berlin).
The author thanks Prof. Dr. Matthias Drieß (Technische Uni-
versität Berlin) for general discussion. Paula Nixdorf (Technische
Universität Berlin) is acknowledged for analytical support.
Eur. J. Inorg. Chem. 2011, 2797–2802
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2801

M. Haberberger, E. Irran, S. Enthaler
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Received: March 7, 2011
Published Online: May 17, 2011
2802
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 2797–2802