Heterolytic cleavage of dihydrogen by frustrated Lewis Pairs derived from α-(dimesitylphosphino)ferrocenes and B(C6F5) 3

Article abstract of DOI:10.1021/om800339c

Treatment of the α-dimethylamino[3]ferrocenophane system 3 with methyl iodide followed by dimesitylphosphine (Mes₂PH) gave the α-(dimesitylphosphino)[3]ferrocenophane 5. This forms a frustrated Lewis pair [5/8] with B(C₆F₅)₃ (8) that rapidly reacts with dihydrogen under ambient conditions to probably give the phosphonium cation/hydrido borate anion salt [5-H⁺/H-8^-]. This, however, is unstable under the applied reaction conditions with regard to replacement of the newly formed phosphonium leaving group at the ferrocenophane a-position for hydride from the [HB(C₆F₅)₃ ^-] counteranion to eventually yield the unfunctionalized [3]ferrocenophane product (10) and Mes₂PH· B(C ₆F₅)₃ (11) - both characterized by independent syntheses. Analogously, Ugi's amine (6) was converted to (1-(dimesitylphosphino) -ethyl)ferrocene (7). The frustrated pair [7/8] consumes dihydrogen under similar conditions to yield the reduction products ethylferrocene (14) and Mes₂PH · B(C₆F₅)₃ (11).

Full text of DOI:10.1021/om800339c

Organometallics 2008, 27, 5279–5284
5279
Heterolytic Cleavage of Dihydrogen by Frustrated Lewis Pairs
†
Derived from r-(Dimesitylphosphino)ferrocenes and B(C6F5)3
Dominique P. Huber,‡ Gerald Kehr,‡ Klaus Bergander,‡,§ Roland Fro¨hlich,‡,
Gerhard Erker,*,‡ Soichiro Tanino,‡,| Yasuhiro Ohki,| and Kazuyuki Tatsumi|
Organisch-Chemisches Institut der UniVersita¨t Mu¨nster, Corrensstrasse 40, 48149 Mu¨nster, Germany, and
Research Center for Materials Science, Nagoya UniVersity, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
ReceiVed April 16, 2008
Treatment of the R-dimethylamino[3]ferrocenophane system 3 with methyl iodide followed by
dimesitylphosphine (Mes2PH) gave the R-(dimesitylphosphino)[3]ferrocenophane 5. This forms a frustrated
Lewis pair [5/8] with B(C6F5)3 (8) that rapidly reacts with dihydrogen under ambient conditions to probably
give the phosphonium cation/hydrido borate anion salt [5-H+/H-8-]. This, however, is unstable under
the applied reaction conditions with regard to replacement of the newly formed phosphonium leaving
group at the ferrocenophane R-position for hydride from the [HB(C6F5)3-] counteranion to eventually
yield the unfunctionalized [3]ferrocenophane product (10) and Mes2PH · B(C6F5)3 (11)sboth characterized
by independent syntheses. Analogously, Ugi’s amine (6) was converted to (1-(dimesitylphosphino)-
ethyl)ferrocene (7). The frustrated pair [7/8] consumes dihydrogen under similar conditions to yield the
reduction products ethylferrocene (14) and Mes2PH · B(C6F5)3 (11).
metals (Fe-Fe, Fe-Ni) in special chemical environments to
utilize the reductive power of dihydrogen (H2 f 2H+ + 2e-).4,5
Quite recently, Stephan et al. discovered metal-free systems that
were able to split H2 by a non-self-quenching combination of a
bulky phosphine and a very electrophilic borane to give the
corresponding phosphonium/hydrido borate products (see Scheme
1, eq 1).6-9 It was later shown that some such “frustrated Lewis
pairs” were able to serve as catalysts for the hydrogenation of
bulky imines. Even some combinations of bulky imines or
nitriles with B(C6F5)3 showed H2-activation properties and led
to hydrogenation of these unsaturated organic products.6,7 We
had recently described the weakly internally coordinated
Introduction
Until recently catalytic dihydrogen activation had been a
domain of transition-metal chemistry. Homolytic or heterolytic
H2 cleavage and activation has been achieved by a variety of
bulk metals and/or by a great variety of molecular transition-
metal complexes.1-3 Even the natural H2-converting enzymes,
the hydrogenases, make use of the unique features of transition
* To whom correspondence should be addressed. E-mail: erker@
uni-muenster.de.
† Dedicated to Professor Klaus Kühlein on the occasion of his 70th
birthday.
‡ Universita¨t Mu¨nster.
§ NMR experiments.
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10.1021/om800339c CCC: $40.75
2008 American Chemical Society
Publication on Web 09/26/2008

5280 Organometallics, Vol. 27, No. 20, 2008
Huber et al.
Scheme 1
Scheme 2
frustrated phosphine/borane pair 1 and shown that it represents
one of the most active metal-free H2-activation systems reported
so far. The 1/2 system is an active hydrogenation catalyst for
enamines and bulky imines at room temperature10 (Scheme 1,
eq 1).
The ferrocene backbone has served as a very useful frame-
work for ligand design and synthesis in, for example, hydro-
genation catalysis.3 Therefore, it was tempting to synthesize and
investigate P/B pairs that involve these metallocene backbones
at the bulky phosphorus, the borane component, or both. We
here wish to report the syntheses of the (to our knowledge) first
examples of active frustrated pairs based on phosphine-
substituted ferrocenes and ferrocenophanes. These showed some
remarkable chemical behavior subsequent to fast heterolytic
dihydrogen activation and splitting. This noticeable reactivity
pattern of these new systems will be described below for two
examples.
Single crystals of 5 suitable for X-ray crystal structure analysis
were obtained from cold pentane. Complex 5 features a typical
[3]ferrocenophane framework in the crystal. The Cp planes are
almost parallel to each other, with Fe-C(Cp) distances ranging
from 2.000(3) to 2.047(4) Å. The C3 bridge shows a typical
cycloalkane-like folded geometry with a strong structural
differentiation of pseudo-axial and -equatorial substituent posi-
tions. The (small) CH3 substituent at the bridge position C6
thus features a pseudo-axial arrangement, with the C6-C7
vector (1.515(4) Å) being almost oriented coplanar with the C1
to C5 Cp ring plane (see Figure 1). Consequently, the bulky
trans-Mes2P substituent at C9 is found in a pseudo-equatorial
orientation at the bridge (dihedral angles: C6-C8-C9-P1 )
174.5(2)°, C14-C10-C9-P1 ) -119.2(3)°). The coordination
geometry of the phosphorus center in 5 strongly deviates from
planarity, as expected. It features C-P-C bond angles of
102.0(1)° (C9-P1-C24), 114.1(1)° (C9-P1-C15), and 100.9(1)°
(C15-P1-C24).
Results and Discussion
The first synthesis was started from the R-(dimethylamino)[3]-
ferrocenophane system 3. This, in turn, was prepared by a
sequence starting from 1,1′-diacetylferrocene via a Mannich
reaction followed by catalytic hydrogenation, as previously
described by us in the literature.11 For this synthesis we only
employed the rac series. We started from a sample of 3 that
was highly enriched in the trans isomer (ca. 20:1). The tertiary
amine 3 was quaternized by treatment with methyl iodide (to
give 4) and then treated with dimesitylphosphine. The exchange
reaction apparently proceeded by means of the typical two-step
reaction mechanism, involving anchimeric assistance of the iron
In solution, compound 5 exhibits a set of a total of eight 13
C
12,13
center
to eventually yield the R-dimesitylphosphino-
NMR CH signals of the pair of C5H4 groups plus two
corresponding ipso-C resonances (δ 90.8 (s, C1), δ 89.6 (d,
2JPC ) 21.5 Hz, C10) and the typical 13C NMR resonances of
the disubstituted [3]ferrocenophane bridge (δ 18.6 (6-CH3), 26.8
(3JPC ) 12.9 Hz, C-6), 48.4 (2JPC ) 28.6 Hz, C-8), and 27.9
(1JPC ) 19.1 Hz, C-9)). As expected, the mesityl groups at the
stereogenic phosphorus center are diastereotopic, featuring pairs
of well-separated 1H NMR o- and p-methyl resonances and m-H
signals (for details see the Experimental Section). The 31P NMR
resonance of 5 is at δ -10.0 (in d6-benzene).
Analogously, we have converted (racemic) “Ugi’s amine”
(6)14 to the corresponding (1-(dimesitylphosphino)ethyl)ferro-
cene (7) by quaternization with MeI followed by the substitution
reaction by treatment with dimesitylphosphine (Mes2PH) in
acetonitrile (see Scheme 2). Compound 7 was also characterized
by X-ray diffraction (single crystals from pentane).
substituted [3]ferrocenophane derivate 5 (ca. 55%) (see Scheme
2).
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Heterolytic CleaVage of Dihydrogen
Organometallics, Vol. 27, No. 20, 2008 5281
Scheme 3
angle between the planes of the pair of mesityl substituents at
P1 (i.e., C31 to C36 vs C21 to C26) was found at 98.1°.
Mixing of the R-(dimesitylphosphino)[3]ferrocenophane (5)
with the strong boron Lewis acid B(C6F5)315 (8) in d6-benzene
did not result in any observed adduct formation.16 The absence
of any appreciable change of the NMR features of the
components in the ca. 1:1 mixture rendered 5/B(C6F5)3 (8) a
frustrated Lewis pair [5/8] (see Scheme 3). Consequently, the
5/B(C6F5)3 (8) mixture reacted rapidly with dihydrogen (1.8 bar)
at room temperature. After specific workup of the reaction
mixture (for details see the Experimental Section) we isolated
the [3]ferrocenophane derivate 10 in >70% yield. This specific
ferrocenophane product derived from the hydrogenation reaction
mixture was characterized by spectroscopy and by comparison
with a reference sample independently synthesized by LiAlH4/
AlCl3 reduction of the [3]ferrocenophanone 12,17 including an
X-ray crystal structure analysis. The product 10 features a very
typical set of NMR data (1H NMR: δ 2.09, 1.61 (9-H,H′), 1.76,
1.63 (8-H,H′), 1.87 (6-H), 1.12 (6-CH3)), including a set of 10
separate 13C(Cp) NMR resonances.
Figure 1. View of the molecular geometry of 5. Selected bond
lengths (Å) and angles (deg) for 5: Fe-CCp ) 2.000(3)-2.047(4),
C1-C6 ) 1.535(4), C6-C7 ) 1.515(4), C6-C8 ) 1.549(4),
C8-C9 ) 1.546(4), C9-C10 ) 1.498(4), C9-P1 ) 1.899(3),
P1-C15 ) 1.862(3), P1-C24 ) 1.856(3); C1-C6-C7 ) 112.6(3),
C1-C6-C8 ) 113.5(2), C7-C6-C8 ) 112.2(3), C6-C8-C9 )
117.3(2), C8-C9-C10 ) 112.0(2), C8-C9-P1 ) 108.8(2),
C10-C9-P1 ) 106.2(2), C9-P1-C15 ) 114.1(1), C9-P1-C24
) 102.0(1), C15-P1-C24 ) 100.9(1).
In the crystal, compound 10 shows a typical [3]ferro-
cenophane geometry (see Figure 3) with Fe-C(Cp) bond lengths
in the range 2.013(4)-2.050(4) Å. The C3 bridge is again
strongly folded. However, in contrast to the structure of the
corresponding phosphino[3]ferrocenophane derivative 5 (see
above and Figure 1), the monosubstituted compound 10 shows
a conformational arrangement of the bridge that features the
CH3 substituent at C6 in a pseudo-equatorial orientation
(dihedral angles: C2-C1-C6-C7 ) 70.5(6)°, C2-C1-C6-C8
) -63.5(6)°, C1-C6-C8-C9 ) -56.7(7)°).
Figure 2. Molecular structure of 7. Selected bond lengths (Å) and
angles (deg): Fe-CCp ) 2.029(3)-2.061(3), C16-C15 ) 1.544(4),
C15-C10 ) 1.499(4), C15-P1 ) 1.887(3), P1-C21 ) 1.858(3),
P1-C31 ) 1.851(3); C16-C15-C10 ) 110.5(3), C16-C15-P1
) 108.7(2), C10-C15-P1 ) 105.7(2), C15-P1-C21 ) 113.3(2),
C15-P1-C31 ) 101.0(1), C21-P1-C31 ) 106.1(1).
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In the crystal complex 7 exhibits the typical ferrocene
framework, with Fe-C(Cp) bond lengths in a range between
2.029(3) and 2.061(3) Å (Figure 2). The 1-phosphinoethyl
substituent at a Cp ring features a conformation that has the
C-CH3 vector rotated ca. 30° out of the adjacent Cp ring plane
(dihedral angle C11-C10-C15-C16 ) -29.6(5)°). The very
bulky -PMes2 group is rotated away from the ferrocene core.
This anti substituent orientation is characterized by the dihedral
angles C11-C10-C15-P1 ) 87.8(3)° and C14-C10-C15-P1
) -89.5(3)°. The C10-C15-P1 angle amounts to 105.7(2)°
(C10-C15-C16 ) 110.5(3)°). The coordination geometry at
P1 is nonplanar (bond angles: C15-P1-C31 ) 101.0(1)°,
C15-P1-C21 ) 113.3(2)°, C21-P1-C31 ) 106.1(1)°). The
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2002, 2069. Jacobsen, H.; Guidotti, S.; Camurati, I.; Focante, F.; Angellini,
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5282 Organometallics, Vol. 27, No. 20, 2008
Huber et al.
Scheme 4
Scheme 5
Figure 3. Molecular structure of 10. Selected bond lengths (Å)
and angles (deg): Fe-CCp ) 2.013(4)-2.050(4), C1-C6 )
1.524(6), C6-C7 ) 1.498(6), C6-C8 ) 1.468(6), C8-C9 )
1.476(5), C9-C10 ) 1.505(6); C1-C6-C7 ) 111.5(4), C1-C6-C8
) 115.4(4), C7-C6-C8 ) 115.3(4), C6-C8-C9 ) 122.7(4),
C8-C9-C10 ) 116.7(4).
We then reacted the [5/8] frustrated pair with D2. After the
usual workup the corresponding monodeuterated [3]ferro-
cenophane derivative 10-D was isolated (90% yield). Again,
the composition of the product was characterized by spectros-
copy and by direct comparison with a reference sample (for
details see the Supporting Information), which in this case was
prepared by LiAlD4 reduction of the corresponding trans-R-
chloro[3]ferrocenophane derivative 13.19 From these combined
experiments it is likely that treatment of the [5/8] pair with
dideuterium has selectively resulted in the formation of the
trans-disubstituted [3]ferrocenophane derivative 10-D (see
Scheme 4).
The (1-(dimesitylphosphino)ethyl)ferrocene/B(C6F5)3 mixture
[7/8] was also treated with H2 (Scheme 5). It reacted at room
temperature and 1.1 bar of dihydrogen pressure. From the NMR
spectroscopic characterization of a reaction mixture in d8-toluene
formation of Mes2PH · B(C6F5)3 (11) was found. Workup of a
reaction mixture involving chromatography gave the product
ethylferrocene (14) in 57% yield (1H NMR δ 2.19 (q, 2H), 1.08
(t, 2JHH ) 7.5 Hz, 3H, CH2CH3); 13C NMR δ 69.2 (Cp), 91.6,
68.2, 67.9 (C5H4), 23.1, 15.5 (C2H5)). For comparison, com-
pound 14 was independently synthesized by reduction of the
corresponding ferrocenyl ethanol with Me2S · BH3.20 The frus-
trated pair [7/8] also reacts cleanly with D2 (12 h, 1.1 bar, room
temperature) under analogous conditions to give the monodeu-
terium-substituted ethylferrocene product 14-D, isolated in 51%
yield after chromatographic workup. It features a 1:1:1 triplet
at δ 22.7 of the Fe-CHD-CH3 carbon atom in the 13C NMR
spectrum in d6-benzene.
Figure 4. Dynamic 19F NMR spectra of the Mes2PH · B(C6F5)3
adduct 11 (in d8-toluene).
Since the product 10 was free of phosphorus and was isolated
in high yield, we needed to identify the phosphorus-containing
coproduct. This was identified from the reaction mixture as the
Mes2PH · B(C6F5)3 adduct 11. The product 11 was characterized
by its very typical temperature-dependent NMR spectra (see
above) and by comparison with an authentic reference sample
independently prepared from Mes2PH and B(C6F5)3 (8). In one
experiment, the reference was actually added to the reaction
mixture to show its identity by NMR.
Product 11 shows rather uncharacteristic NMR spectra at
ambient temperature, featuring, for example, three broad 19F
NMR signals. Decreasing the monitoring temperature leads to
a rapid decoalescence, eventually resulting in a very charac-
teristic low-temperature 19F NMR spectrum that exhibits a total
of 14 separate resonances, namely six o-F, three p-F, and five
signals corresponding to six m-F atoms (one signal of double
intensity) of the three C6F5 groups at boron in the adduct 11
(see Figure 4). This indicates freezing of the conformational
equilibration of the L-B(C6F5)3 part of 11, probably due to a
chiral conformation.18 Consequently, the prochiral Mes2PH part
of the Mes2PH · B(C6F5)3 adduct 11 features dynamic 1H NMR
spectra: upon decreasing the monitoring temperature, we here
observe decoalescence of, for example, the mesityl m-H singlet
to eventually give a set of four separate 1H NMR resonances at
the limiting low-temperature situation.
Conclusions
This study shows that ferrocene and ferrocenophane deriva-
tives that bear very bulky dimesitylphosphino substituents at
the position R to the metallocene nuclei can readily be prepared.
These very bulky phosphines form frustrated Lewis pairs with
B(C6F5)3 (8). The systems [5/8] and [7/8] both cleave dihydro-
gen heterolytically under ambient conditions. It is likely that
the phosphonium cation/hydrido borate anion pairs [5-H+/
H-8-] and [7-H+/H-8-] are initially formed (see Scheme 3). It
appears that the R-Mes2PH+ substituent in these special cases
is a sufficiently good leaving group to make the systems
kinetically labile. Cleavage of the Mes2PH moiety from [5-H+],
(19) Neumann, M. Doctoral Dissertation, Universita¨t Mu¨nster, 2007.
(20) Kim, D.-H.; Ryu, E.-S.; Cho, C. S.; Shim, S. C.; Kim, H.-S.; Kim,
T.-J. Organometallics 2000, 19, 5784. Routaboul, L.; Chiffre, J.; Balavoine,
G. G. A.; Daran, J.-C.; Manoury, E. J. Organomet. Chem. 2001, 637-639,
364.
(18) Ahlers, W.; Temme, B.; Erker, G.; Fro¨hlich, R.; Fox, T. J.
Organomet. Chem. 1997, 527, 191. Vagedes, D.; Erker, G.; Kehr, G.;
Bergander, K.; Kataeva, O.; Fro¨hlich, R.; Grimme, S.; Mu¨ck-Lichtenfeld,
C. Dalton Trans. 2003, 1337.

Heterolytic CleaVage of Dihydrogen
Organometallics, Vol. 27, No. 20, 2008 5283
2.21, 2.03 (each m, each 1H, H-8), 2.10 (s, 3H, p-CH3Mes′), 1.98
(s, 3H, p-CH3Mes), 1.03 (d, JHH ) 7.2 Hz, 3H, H-7). 13C{1H} NMR
(C6D6, 151 MHz, 298 K): δ 143.3 (broad, d, JCP ) 15.6 Hz, o-Mes′),
143.0 (d, JCP ) 14.4 Hz, o-Mes), 137.9 (p-Mes′), 137.4 (p-Mes),
133.1 (broad, d, JCP ) 30.5 Hz, i-Mes′), 132.7 (d, JCP ) 25.7 Hz,
i-Mes), 130.5 (d, JCP ) 2.8 Hz, m-Mes′), 130.3 (d, JCP ) 2.8 Hz,
m-Mes), 90.8 (C-1), 89.6 (broad, d, JCP ) 21.5 Hz, C-10), 70.4 (d,
JCP ) 3.4 Hz, R), 68.6 (R), 68.6 (ꢀ), 68.3 (ꢀ) (C-11 to C-14), 69.5
(ꢀ), 69.2 (ꢀ), 68.5 (R), 67.8 (R) (C-2 to C-5), 48.4 (d, JCP ) 28.6
Hz, C-8), 27.9 (d, JCP ) 19.1 Hz, C-9), 26.8 (d, JCP ) 12.9 Hz,
C-6), 23.5 (d, JCP ) 13.8 Hz, o-CH3Mes), 23.1 (d, JCP ) 14.4 Hz,
o-CH3Mes′), 20.9 (p-CH3Mes′), 20.8 (p-CH3Mes), 18.6 (broad, C-7).
31P{1H} NMR (C6D6, 162 MHz, 298 K): δ -10.0 (ν1/2 ) 3 Hz,
ca. 4% probably cis isomer). Anal. Calcd for C32H37FeP: C, 75.59;
H, 7.33. Found: C, 75.63; H, 7.27. X-ray crystal structure analysis
of 5: formula C32H37FeP, Mr ) 508.44, yellow crystal 0.35 × 0.10
× 0.10 mm, a ) 15.4990(2) Å, b ) 15.2570(2) Å, c ) 22.8414(3)
probably assisted by the iron neighboring group followed by
nucleophilic hydride attachment from the [H-8-] counteranion,
is likely to be the favored pathway of a subsequent reaction in
this system following the initial H2 activation process. The
observed regio- and stereochemical outcome12,13 of the respec-
tive experiments employing D2 instead of the H2 supports this
description of reaction sequence observed here. A similar
reaction mode was observed starting from the [7/8] frustrated
Lewis pair. We conclude that these specific ferrocene or
ferrocenophane moieties at a bulky phosphine are compatible
with rapid heterolytic dihydrogen activation and cleavage by
frustrated Lewis pairs. We have seen that the positioning of
the phosphine substituent at a substitution-sensitive position of
the metallocene framework might lead to specific subsequent
reactivities. Electronic or steric stabilization of this situation
must be considered in order to produce sufficiently persistent
systems which might be of interest to allow for a subsequent
intermolecular utilization of the H2-derived reduction equivalents.
Å, V ) 5401.27(12) Å3, Fcalcd ) 1.250 g cm-3, µ ) 0.636 mm-1
,
empirical absorption correction (0.808 e T e 0.939), Z ) 8,
orthorhombic, space group Pbca (No. 61), λ ) 0.710 73 Å, T )
223 K, ω and ꢁ scans, 40 084 reflections collected ((h, (k, (l),
(sin θ)/λ ) 0.66 Å-1, 6424 independent (Rint ) 0.090) and 3895
observed reflections (I g 2σ(I)), 314 refined parameters, R1 )
0.053, wR2 ) 0.146, maximum (minimum) residual electron density
0.68 (-0.45) e Å-3, hydrogen atoms calculated and refined as riding
atoms.
Experimental Section
General Procedures. All manipulations involving air-sensitive
materials were carried out using standard Schlenk type glassware
(or a glovebox) under an atmosphere of argon. Solvents were dried
with the procedure reported by Grubbs21 or were distilled from
appropriate drying agents. The amines 3 and 6 and the borane 8
were prepared as reported.11,13,15 NMR spectra were recorded on
AC 200, AV 300, DPX300, and AV400 spectrometers from Bruker,
INOVA 500 and UnityPlus 600 spectrometers from Varian, and
JNM-ECP500 and ECA600 spectrometers from JEOL. NMR
assignments were made by various 2D NMR measurements. For
the X-ray crystal structure analyses, data sets were collected with
a Nonius KappaCCD diffractometer, equipped with a rotating anode
generator. Programs used are as follows: data collection, COLLECT
(Nonius BV, 1998); data reduction, Denzo-SMN;22 absorption
correction, SORTAV23 and Denzo;24 structure solution, SHELXS-
97;25 structure refinement, SHELXL-97 (G. M. Sheldrick, Univer-
sita¨t Go¨ttingen, 1997); graphics, XP (BrukerAXS, 2000).
Preparation of the rac-r-(Dimesitylphosphino)[3]ferroceno-
phane System (5). Amine 3 (0.70 g, 2.47 mmol, trans:cis ) 20:1)
was dissolved in acetonitrile (20 mL) and cooled (0 °C) before
MeI (1.5 mL, 0.024 mol) was added dropwise. After 10 min, the
reaction mixture was warmed to room temperature and stirred (2
h). Removal of the solvent and drying (0.5 h, high vacuum) gave
the ammonium iodide 4. Dimesitylphosphine (0.60 g, 2.20 mmol)
and acetonitrile (20 mL) were added, and the mixture was kept
overnight at 65 °C. Diethyl ether was added at room temperature.
After filtration, the solvent was evaporated from the filtrate.
Chloroform was added, a precipitate was filtered off, the solvent
was removed in vacuo, and the residue was chromatographed
(cyclohexane) to give product 5. The product was then crystallized
from pentane and obtained in pure form with a trans:cis ratio of
about 15:1 (0.67 g, 54% yield). Crystals suitable for the X-ray
crystal structure analysis were obtained from cold pentane. 1H NMR
(C6D6, 600 MHz, 298 K): δ 6.76 (d, JHP ) 1.9 Hz, 2H, HMes′),
6.61 (d, JHP ) 2.0 Hz, 2H, HMes), 4.42 (R), 3.93 (ꢀ), 3.89 (ꢀ),
3.80 (R), (each m, each 1H, H-11 to H-14), 4.00 (2H, ꢀ), 3.98
(1H, R), 3.97 (1H, R) (each m, H-2 to H-5), 3.95 (m, 1H, H-9),
2.61 (s, 6H, o-CH3Mes′), 2.56 (m, 1H, H-6), 2.52 (s, 6H, o-CH3Mes),
Preparation of rac-(1-(Dimesitylphosphino)ethyl)ferrocene (7).
Methyl iodide (2.60 mL, 41.8 mmol) was added at 0 °C to a solution
of (1-(dimethylamino)ethyl)ferrocene (6; 1.54 g, 5.99 mmol) in
acetonitrile (30 mL). After stirring (2 h, 0-5 °C), the volatiles were
removed in vacuo. The resulting yellow solid was dissolved in
acetonitrile (50 mL), and dimesitylphosphine (1.62 g, 5.99 mmol)
was added. After the mixture was stirred (24 h, 60 °C), the volatiles
were removed in vacuo and the crude product was recrystallized
from pentane. Phosphine 7 was isolated as orange crystals (0.97 g,
33% yield). Crystals suitable for X-ray analysis were obtained from
cold pentane. 1H NMR (C6D6, 600 MHz, 298 K): δ 6.72 (d, JHP
)
2.1 Hz, 2H, Mes), 6.65 (d, JHP ) 2.2 Hz, 2H, Mes′), 4.17 (qd, JHH
) 7.1, JHP ) 4.4 Hz, 1H, CH), 4.13, 3.87, 3.71, 3.57 (each m,
each 1H, C5H4), 4.00 (s, 5H, Cp), 2.48 (s, 6H, o-CH3Mes), 2.38 (s,
6H, o-CH3Mes′), 2.09 (s, 3H, p-CH3Mes′), 2.04 (s, 3H, p-CH3Mes),
1.65 (dd, JHP ) 17.3 Hz, JHH ) 6.8 Hz, 3H, CH3). 13C{1H} NMR
(C6D6, 151 MHz, 298 K): δ 144.6 (d, JCP ) 14.5 Hz, o-Mes′),
143.0 (d, JCP ) 14.5 Hz, o-Mes), 138.5 (s, p-Mes′), 137.7 (s,
p-Mes), 133.3 (d, JCP ) 33.9 Hz, i-Mes), 133.0 (d, JCP ) 25.3 Hz,
i-Mes′), 131.3 (d, JCP ) 1.6 Hz, m-Mes), 130.4 (d, JCP ) 3.2 Hz,
m-Mes′), 92.8 (d, JCP ) 18.6 Hz, C-10), 70.0 (d, JCP ) 3.2 Hz, R),
68.0 (d, JCP ) 5.7 Hz, R), 67.8 (s, ꢀ), 67.5 (s, ꢀ) (C-11 to C14),
69.2 (s, C-1 to C-5), 30.1 (d, JCP ) 17.6 Hz, CH), 23.6 (d, JCP
)
14.6 Hz), 23.5 (d, JCP ) 14.6 Hz) (o-CH3Mes, o-CH3Mes′), 21.4 (s,
p-CH3Mes′), 21.2 (s, p-CH3Mes), 20.4 (d, JCP ) 29.9 Hz, CH3).
31P{1H} NMR (C6D6, 243 MHz, 298 K): δ -3.7 (q, broad, JPH
)
15.8 Hz). Anal. Calcd for C30H35FeP: C, 74.69; H, 7.31. Found: C,
74.71; H, 7.39. X-ray crystal structure analysis of 7: formula
C30H35FeP, Mr ) 482.40, yellow crystal 0.35 × 0.20 × 0.10 mm,
a ) 7.4493(2) Å, b ) 12.5125(3) Å, c ) 14.4119(4) Å, R )
71.541(2)°, ꢀ ) 85.738(1)°, γ ) 77.417(1)°, V ) 1243.59(6) Å3,
Fcalcd ) 1.288 g cm-3, µ ) 0.686 mm-1, empirical absorption
j
correction (0.795 e T e 0.935), Z ) 2, triclinic, space group P1
(No. 2), λ ) 0.710 73 Å, T ) 223 K, ω and ꢁ scans, 10 460
reflections collected ((h, (k, (l), (sin θ)/λ ) 0.66 Å-1, 5746
independent (Rint ) 0.055) and 3323 observed reflections (I g
2σ(I)), 296 refined parameters, R1 ) 0.059, wR2 ) 0.149,
(21) Pangborn, A. B.; Giradello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(22) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(23) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. Blessing, R. H.
J. Appl. Crystallogr. 1997, 30, 421.
(24) Otwinowski, Z.; Borek, D.; Majewski, W.; Minor, W. Acta
Crystallogr. 2003, A59, 228.
(25) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
maximum (minimum) residual electron density 0.65 (-0.59) e Å-3
,
hydrogen atoms calculated and refined as riding atoms.
1,1′-[Butane-1,3-diyl]ferrocene (10). From 5. Phosphine deriva-
tive 5 (27.0 mg, 0.053 mmol) was dissolved in C6D6 (1.5 mL) in

5284 Organometallics, Vol. 27, No. 20, 2008
Huber et al.
the glovebox before borane 8 (30.0 mg, 0.059 mmol) was added.
After short evacuation, dihydrogen pressure (1.8 bar) was applied
(4 h) and the reaction mixture was stirred overnight. Residual 5
was oxidized by treatment with sulfur (2 h) to allow a convenient
subsequent chromatographic separation. Chromatography (silica gel,
pentane) gave 10 (9.30 mg, 73% yield). 1H NMR (C6D6, 300 MHz,
298 K): δ 4.05 (2H), 4.00 (2H), 3.92 (1H), 3.89 (2H), 3.86 (1H)
(each m, C5H4), 2.08 (1H), 1.86 (1H), 1.73 (1H), 1.62 (2H) (each
m, CH2CH2CH), 1.12 (d, JHH ) 7.0 Hz, 3H, Me). 13C{1H} NMR
(C6D6, 75 MHz, 298 K): δ 90.3 (C-1), 86.9 (C-10), 70.9, 70.2,
69.0, 68.9, 68.5, 68.1, 67.9, 66.2 (C5H4), 44.2, 30.6, 24.0
(CH2CH2CH), 21.3 (Me).
From Ketone 12. Ketone 12 (248 mg, 0.98 mmol) was added to
LiAlH4 (214 mg, 6.50 mmol) in Et2O (50 mL). AlCl3 (1.56 g, 1.17
mmol) was added before the reaction mixture was refluxed (40 °C,
5 h). After addition of ethyl acetate (wet), MeOH (wet), and H2O,
extraction (THF), drying (MgSO4), filtration, evaporation, and
chromatography (pentane), product 10 was obtained (0.22 g, 94%).
1H NMR (C6D6, 600 MHz, 298 K): δ 4.04, 3.99, 3.88, 3.88 (each
m, each 1H, H-2 to H-5), 4.03, 3.98, 3.92, 3.85 (each m, each 1H,
H-11 to H-14), 2.09 (m, 1H, H-9), 1.87 (m, 1H, H-6), 1.76 (m,
Dimesitylphosphine-Tris(pentafluorophenyl)borane Adduct (11).
Tris(pentafluorophenyl)borane (8; 479 mg, 0.94 mmol) was sus-
pended in pentane (40 mL), and dimesitylphosphine (254 mg, 0.94
mmol) was dissolved in pentane (6 mL). The phosphine solution
was then added to the borane solution at room temperature via
cannula, which resulted in the formation of a white suspension.
Stirring at room temperature (2 h) gave an almost clear solution,
which was filtered and reduced to about 25% of the original volume.
Cooling overnight (-20 °C) resulted in the precipitation of the white
solid 11, which was then stored at -20 °C (0.70 g, 92% yield). 1H
NMR (d8-toluene, 600 MHz, 233 K): δ 7.50 (d, broad, JHP ) 404
Hz, 1H, PH), 6.33, 6.23, 6.13, 5.92 (each broad, each 1H, m-Mes),
2.18 (3H), 1.81 (9H), 1.60 (3H), 0.81 (3H) (each s, each broad,
o-CH3Mes, p-CH3Mes). 31P NMR (d8-toluene, 243 MHz, 233 K): δ
-44.7 (ν1/2 ) 120 Hz). 19F NMR (d8-toluene, 564 MHz, 233 K):
δ -119.0, -129.4 (each 1F, o-F), -155.0 (1F, p-F), -162.1, 163.7
(each 1F, m-F) (each broad, C6F5), -126.0a, -128.1 (each 1F, o-F),
-154.4 (1F, p-F), -160.5, -163.2 (each 1F, m-F) (each broad,
C6F5), -126.9a, -128.6 (each 1F, o-F), -155.6 (1F, p-F), -162.8,
-163.2 (each 1F, m-F) (each broad, C6F5) (the superscript “a”
indicates that there is no relative assignment).
1-Ethylferrocene (14). From 7. Phosphine 7 (68 mg, 0.14 mmol)
and tris(pentafluorophenyl)borane (8; 71 mg, 0.14 mmol) were
dissolved in C6D6 (1.0 mL), and the mixture was stirred under a
hydrogen atmosphere (1.1 bar) for 12 h. The resulting reaction
mixture was analyzed by NMR. Isolation of product 14 (17 mg,
57% yield) as a yellow oil was achieved by chromatography of
the reaction mixture (pentane). 1H NMR (C6D6, 600 MHz, 298 K):
δ 3.99 (s, 5H, Cp), 3.95 (s, 4H, C5H4), 2.19 (q, JHH ) 7.5 Hz, 2H,
CH2CH3), 1.08 (t, JHH ) 7.5 Hz, 3H, CH2CH3). 13C{1H} NMR
(C6D6, 151 MHz, 298 K): δ 91.6 (C-1), 69.2 (Cp), 68.2, 67.9 (C5H4),
23.0 (CH2), 15.5 (CH3).
From Alcohol. Borane-dimethyl sulfide complex (0.10 mL, 0.98
mmol) was added to a solution of 1-(1-hydroxyethyl)ferrocene (200
mg, 0.87 mmol) in THF (10 mL). The solution was stirred at 50
°C for 1 h. After removal of the volatiles in vacuo, the crude product
was purified by chromatography (pentane). Ethylferrocene (14) was
obtained as an orange oil (113 mg, 61%).
1H, H-8), 1.63 (dm, JHH ) 11.2 Hz, 1H, H8′), 1.61 (dm, JHH
)
11.2 Hz, 1H, H-9′), 1.12 (d, JHH ) 7.0 Hz, 3H, H-7). 13C{1H}
NMR (C6D6, 151 MHz, 298 K): δ 90.5 (C-1), 86.8 (C-10), 71.0,
69.1, 68.5, 68.0 (C-11 to C-14), 70.2, 69.0, 68.1, 66.2 (C-2 to C-5),
44.2 (C-8), 30.6 (C-6), 24.1 (C-9), 21.3 (C-7). Anal. Calcd for
C14H16Fe: C, 70.03; H, 6.72. Found: C, 69.93; H, 6.68. X-ray crystal
structure analysis of 10: formula C14H16Fe, Mr ) 240.12, yellow
crystal 0.30 × 0.20 × 0.02 mm, a ) 9.8523(4) Å, b ) 7.6564(3),
Å, c ) 15.4974(7) Å, ꢀ ) 106.337(2)°, V ) 1121.82(8) Å3, Fcalcd
) 1.422 g cm-3, µ ) 1.305 mm-1, empirical absorption correction
(0.696 e T e 0.974), Z ) 4, monoclinic, space group P21/n (No.
14), λ ) 0.710 73 Å, T ) 223 K, ω and ꢁ scans, 6062 reflections
collected ((h, (k, (l), (sin θ)/λ ) 0.62 Å-1, 2282 independent
(Rint ) 0.072) and 1268 observed reflections (I g 2σ(I)), 137 refined
parameters, R1 ) 0.049, wR2 ) 0.115, maximum (minimum)
residual electron density 0.58 (-0.35) e Å-3, hydrogen atoms
calculated and refined as riding atoms.
1-Deuterioethylferrocene (14-D). Phosphine 7 (100 mg, 0.21
mmol) and borane 8 (105 mg, 0.21 mmol) were dissolved in C6D6
(1.0 mL) and stirred under a dideuterium atmosphere (12 h, ca.
1.1 bar). The resulting solution was analyzed by NMR. Chroma-
tography (pentane) gave the product 14-D (22 mg, 51% yield) as
a yellow oil. Reaction mixture at room temperature: 1H NMR (C6D6,
600 MHz, 298 K) δ 3.99 (s, 5H, Cp), 3.95 (s, 4H, C5H4), 2.18 (qt
(1:1:1), JHH ) 7.6 Hz, JHD ) 2.2 Hz, 1H, CHD), 1.07 (dt (1:1:1),
JHH ) 7.6 Hz, JHD ) 1.0 Hz, 3H, CH3); 2H NMR (C6D6, 92 MHz,
298 K) δ 2.15 (dq, JHD ) 2.2 Hz, 1.1 Hz, 1D, CHDCH3); 13C{1H}
NMR (C6D6, 151 MHz, 298 K) δ 91.5 (C-1), 69.2 (Cp), 68.2, 67.9
(C5H4), 22.7 (CDH), 15.4 (CH3).
1,1′-[1-Deuteriobutane-1,3-diyl]ferrocene (10-D). From 5. Phos-
phine 5 (47.8 mg, 0.094 mmol) was dissolved in C6D6 (2 mL) before
borane 8 (50.0 mg, 0.098 mmol) was added. After short evacuation,
dideuterium pressure (1.8 bar) was applied (10 min), the vessel
was closed, and the mixture was stirred overnight. After the reaction
mixture was treated with excess S8, stirred overnight, and chro-
matographed (pentane), the product 10-D (18 mg, 96% yield) was
1
obtained. H NMR (C6D6, 600 MHz, 298 K): δ 4.04, 3.99, 3.88,
3.88 (each m, each 1H, H-2 to H-5), 4.03, 3.98, 3.92, 3.86 (each
m, each 1H, H-11 to H14), 2.07 (dm, JHH ) 6.3 Hz, 1H, H-9),
1.86 (dqd, JHH ) 9.9, 7.0, 2.8 Hz, 1H, H-6), 1.75 (ddd, JHH
)
13.5, 6.3, 2.8 Hz, 1H, H-8), 1.62 (dm, JHH ) 13.5 Hz, 1H, H-8),
1.11 (d, JHH ) 7.0 Hz, 3H, H-7). 13C{1H} NMR (C6D6, 151 MHz,
298 K): δ 90.4 (C-1), 86.9 (C-10), 70.9, 69.0, 68.5, 67.9 (C-11 to
C-14), 70.2, 68.9, 68.0, 66.2 (C-2 to C-5), 44.1 (C-8), 30.5 (C-6),
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft (IRTG Mu¨nster-Nagoya “Complex
Functional Systems in Chemistry”) and the Fonds der
Chemischen Industrie is gratefully acknowledged. We thank
the BASF AG for a gift of solvents.
2
23.7 (t(1:1:1), JCD ) 19.5 Hz, C-9), 21.3 (C-7). H NMR (C6H6,
77 MHz, 298 K): δ 1.55 (broad, D-9).
From Chloride 13. A suspension of LiAlD4 (86 mg, 2.05 mmol)
in Et2O (5 mL) was added to a solution of 13 (224 mg, 0.82 mmol)
in Et2O (10 mL) at 0 °C. After stirring of the mixture overnight at
room temperature, addition of H2O and NaHCO3 (saturated
aqueous), extraction with Et2O, drying (MgSO4), filtration, evapora-
tion, and chromatography (pentane), the product 10-D was obtained
(162 mg, 82% yield). Anal. Calcd for C14H15DFe: C, 69.73; H,
7.11. Found: C, 70.52; H, 6.96.
Supporting Information Available: Text and figures giving
details of the characterization of the compounds, including com-
parison with the separately prepared reference systems, and CIF
files giving crystal data for 5, 7, and 10. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM800339C