Structural features of lithio[3]ferrocenophane systems bearing stabilizing dimethylamino substituents

Article abstract of DOI:10.1021/om8001894

Treatment of the a-dimethylamino[3]ferrocenophane derivative 3 with n-butyllithium results in a directed o-metalation at the adjacent Cp ring of the ferrocene unit to selectively yield the (R*,R*,p-S*) diastereomer 4. Similarly, lithiation of rac-12 gives (R*,p-S*)-13. Both these compounds form mesc-type dimers in the crystal that feature a central C₂Li₂ four-membered-ring moiety. Compound 13 crystallizes with excess n-butyllithium to form a (13-n-BuLi) dimer that was also characterized by X-ray diffraction. Directed lithiation of the nonbridged ferrocene derivative l-(dimethylaminobenzyl)ferrocene (16) with tertbutyllithium resulted in an opposite stereoselectivity to yield (R*,p-R*)-17, which forms a chiral dimeric structure in the solid state, as was revealed by its X-ray crystal structure analysis.

Full text of DOI:10.1021/om8001894

3248
Organometallics 2008, 27, 3248–3253
Structural Features of Lithio[3]ferrocenophane Systems Bearing
Stabilizing Dimethylamino Substituents
Chao Chen, Roland Fröhlich,# Gerald Kehr, and Gerhard Erker*
Organisch-Chemisches Institut der UniVersität Münster, Corrensstrasse 40, 48149 Münster, Germany
ReceiVed February 28, 2008
Treatment of the R-dimethylamino[3]ferrocenophane derivative 3 with n-butyllithium results in a directed
o-metalation at the adjacent Cp ring of the ferrocene unit to selectively yield the (R*,R*,p-S*) diastereomer
4. Similarly, lithiation of rac-12 gives (R*,p-S*)-13. Both these compounds form meso-type dimers in
the crystal that feature a central C2Li2 four-membered-ring moiety. Compound 13 crystallizes with excess
n-butyllithium to form a (13 · n-BuLi) dimer that was also characterized by X-ray diffraction. Directed
lithiation of the nonbridged ferrocene derivative 1-(dimethylaminobenzyl)ferrocene (16) with tert-
butyllithium resulted in an opposite stereoselectivity to yield (R*,p-R*)-17, which forms a chiral dimeric
structure in the solid state, as was revealed by its X-ray crystal structure analysis.
Scheme 1
Introduction
Ferrocene-based ligand systems have played an increasingly
important role in homogeneous catalysis, especially in the
asymmetric formation of organic target molecules.1 Chelate
ligands such as Josiphos, Walphos, Ferriphos, and many more2
have consequently been used extensively in asymmetry catalysis,
especially in asymmetric catalytic hydrogenation and related
processes. We3 and others4 have contributed to this field by the
design and synthesis of various chiral [3]ferrocenophane-derived
chelate ligand systems. So far, the P,P-chelate ligands 1 and 2
(see Scheme 1) have shown an interesting performance as
components in palladium-catalyzed alternating CO/ethene5 or
asymmetricalternatingCO/propenecopolymerization,6respectively.
The synthesis of most of the ligands mentioned above and
many of their congeners at one stage involves a stereoselective-
directed lithiation step at the ferrocene nucleus. Analogous to
the corresponding arene lithiation chemistry7 this is usually
achieved in ferrocene chemistry by treatment of a precursor,
which features a suitably positioned pendant -OR or -NR2
substituent, with, for example, butyllithium. Li+ coordination
during the reaction then often very efficiently leads to highly
regioselective arene or ferrocene metalation.3,5,6 Quenching of
the resulting ferrocenyl lithium derivative with a suitable
electrophile (e.g., halogen, organic carbonyl, chlorophosphine
derivatives) then leads to the respective functionalized product.
Scheme 2 shows a typical example.
* Corresponding author. E-mail: erker@uni-muenster.de.
# X-ray crystal structure analyses.
(1) Togni, A.; Hayashi, T., Eds. Ferrocenes: Homogenous Catalysis,
Organic Synthesis, Materials Science; VCH: Weinheim, 1995. Togni, A.;
Dorta, R.; Kollner, C.; Pioda, G. Pure Appl. Chem. 1998, 70, 1477–1485.
Ojima, I., Ed. Catalytic Asymmetric Synthesis; Wiley-VCH: New York,
2000. Barbaro, P.; Bianchini, C.; Giambastiani, G.; Parisel, S. L. Coord.
Chem. ReV. 2004, 248, 2131–2150. Arraya´s, R. G.; Adrio, J.; Carretero,
J. C. Angew. Chem. 2006, 118, 7836–7878; Angew. Chem., Int. Ed. 2006,
45, 7674-7715.
(2) Togni, A.; Breutel, C.; Schnyder, A.; Spindler, F.; Landert, H.; Tijani,
A. J. Am. Chem. Soc. 1994, 116, 4062–4066. Ireland, T.; Grossheimann,
G.; Wieser-Jeunesse, C.; Knochel, P. Angew. Chem. 1999, 111, 3397–3400;
Angew. Chem., Int. Ed. 1999, 38, 3212-3215. Perea, J. J. A.; Lotz, M.;
Knochel, P. Tetrahedron: Asymmetry 1999, 10, 375–384. Sturm, T.;
Weissensteiner, W.; Spindler, F. AdV. Synth. Catal. 2003, 345, 160–164.
Lopez, F.; Harutyunyan, S. R.; Minnaard, A. J.; Feringa, B. L. J. Am. Chem.
Soc. 2004, 126, 12784–12785. Chen, W.; Mbafor, W.; Roberts, S. M.;
Whittall, J. J. Am. Chem. Soc. 2006, 128, 3922–3923. Chen, W.; McCor-
mack, P. J.; Mohammed, K.; Mbafor, W.; Roberts, S. M.; Whittall, J. Angew.
Chem. 2007, 119, 4219–4222; Angew. Chem., Int. Ed. 2007, 46, 4141-
4144. For some recent use of the Josiphos ligand see e.g.: Bercot, E. A.;
Rovis, T. J. Am. Chem. Soc. 2004, 126, 10248–10249. Hsiao, Y.; Rivera,
N. R.; Rosner, T.; Krska, S. W.; Njolito, E.; Wang, F.; Sun, Y.; Armstrong,
J. D., III; Grabowski, E. J. J.; Tillyer, R. D.; Spindler, F.; Malan, C. J. Am.
Chem. Soc. 2004, 126, 9918–9919. Lipshutz, B. H.; Servesko, J. M.; Taft,
B. R. J. Am. Chem. Soc. 2004, 126, 8352–8353. Walphos: Moran, W. J.;
Morken, J. P. Org. Lett. 2006, 8, 2413–2415. Ferriphos: Cho, Y.-h.; Zunic,
V.; Senboku, H.; Olsen, M.; Lautens, M. J. Am. Chem. Soc. 2006, 128,
6837–6846.
The respective ferrocenyl-Li systems, e.g., 4, and their
structural and chemical features, play a decisive role in this
chemistry. Since there were surprisingly few structural studies
(5) Liptau, P.; Seki, T.; Kehr, G.; Abele, A.; Fro¨hlich, R.; Erker, G.;
Grimme, S. Organometallics 2003, 22, 2226–2232.
(6) Liptau, P.; Tebben, L.; Kehr, G.; Fro¨hlich, R.; Erker, G.; Hollmann,
F.; Rieger, B. Eur. J. Org. Chem. 2005, 1909–1918.
(3) Liptau, P.; Knu¨ppel, S.; Kehr, G.; Kataeva, O.; Fro¨hlich, R.; Erker,
G. J. Organomet. Chem. 2001, 637, 621–630. Liptau, P.; Tebben, L.; Kehr,
G.; Wibbeling, B.; Fro¨hlich, R.; Erker, G. Eur. J. Inorg. Chem. 2003, 3590-
3600, 4261. Tebben, L.; Kehr, G.; Fro¨hlich, R.; Erker, G. Synthesis 2004,
1971–1976. Tebben, L.; Neumann, M.; Kehr, G.; Fro¨hlich, R.; Erker, G.;
Losi, S.; Zanello, P. Dalton Trans. 2006, 1715–1720. Nilewski, C.;
Neumann, M.; Tebben, L.; Fro¨hlich, R.; Kehr, G.; Erker, G. Synthesis 2006,
2191–2200.
(7) Jastrzebski, J. T. B. H.; van Koten, G.; Konijn, M.; Stam, C. H.
J. Am. Chem. Soc. 1982, 104, 5490–5491. Reich, H. J.; Gudmundsson, B.
J. Am. Chem. Soc. 1996, 118, 6074–6075. Reich, H. J.; Goldenberg, W. S.;
Gudmundsson, B.; Sanders, A. W.; Kulicke, K. J.; Simon, K.; Guzei, I. A.
J. Am. Chem. Soc. 2001, 123, 8067–8079. Kronenburg, C. M. P.; Rijnberg,
E.; Jastrzebski, J. T. B. H.; Kooijman, H.; Spek, A. L.; van Koten, G. Eur.
J. Org. Chem. 2004, 153–159. Arink, A. M.; Kronenburg, C. M. P.;
Jastrzebski, J. T. B. H.; Lutz, M.; Spek, A. L.; Gossage, R. A.; van Koten,
G. J. Am. Chem. Soc. 2004, 126, 16249–16258. Kronenburg, C. M. P.;
Rijnberg, E.; Jastrzebski, J. T. B. H.; Kooijman, H.; Lutz, M.; Spek, A. L.;
Gossage, R. A.; van Koten, G. Chem.-Eur. J. 2005, 11, 253–261.
(4) Sturm, T.; Weissensteiner, W. Organometallics 2002, 21, 1766–
1774. Cayuela, E.; Jalo´n, F. A.; Manzano, B. R.; Espino, G.; Weissensteiner,
W.; Mereiter, K. J. Am. Chem. Soc. 2004, 126, 7049–7062.
10.1021/om8001894 CCC: $40.75
2008 American Chemical Society
Publication on Web 05/29/2008

Structural Features of Lithio[3]ferrocenophane Systems
Organometallics, Vol. 27, No. 13, 2008 3249
ortho-positions often leads to bending of the CipsoLi2Cipso plane13
toward a nearly planar tetracoordinate carbon environment14–16 such
as 7 in Scheme 3. Alternatively, an unsymmetrical shifting of the
Li-positions may occur that ultimately leads to structures of the
type 8, which have been found in some higher or mixed aggregates
(see Scheme 3).17
Scheme 2
Combinations of these distortions may in some cases occur.18
We will see how the R-NMe2-substituted lithio[3]ferrocenophane
systems structurally behave in comparison to these ArLi
reference systems.
Scheme 3
Results and Discussion
Syntheses. The lithio[3]ferrocenophane system 4 (see Scheme
2) was obtained from a synthetic sequence previously reported by
us. 1,1′-Diacetylferrocene 919 was subjected to an intramolecular
Mannich condensation reaction to yield the unsaturated [3]ferro-
cenophane derivative 1020 (see Scheme 4). This was then catalyti-
cally hydrogenated (Pd/C, H2) to give a trans/cis mixture of the
saturated amino[3]ferrocenophane derivative 3. Recrystallization
followed by treatment with n-butyllithium eventually gave pure 4
(R*,R*,p-S* diastereomer) after crystallization from ether (70%).
of lithioferrocene-containing systems reported in the literature,8–10
we decided to investigate the structural properties of the
-NMe2-substituted lithio[3]ferrocenophane system (4) and some
related complexes.
(13) van Koten, G.; Noltes, J. G. J. Am. Chem. Soc. 1979, 101, 6593–
6599. Harder, S.; Boersma, J.; Brandsma, L.; Kanters, J. A.; Duisenberg,
A. J. M.; van Lenthe, J. H. Organometallics 1991, 10, 1623–1627. Harder,
S.; Brandsma, L.; Kanters, J. A.; Duisenberg, A.; van Lenthe, J. H. J.
Organomet. Chem. 1991, 420, 143–154. Harder, S.; Ekhart, P. F.; Brandsma,
L.; Kanters, J. A.; Duisenberg, A. J. M.; von Rague´ Schleyer, P.
Organometallics 1992, 11, 2623–2627. Pepels, A.; Gu¨nther, H.; Amoureux,
J.-P.; Fernande´z, C. J. Am. Chem. Soc. 2000, 122, 9858–9859. Gossage,
R. A.; Jastrzebski, J. T. B. H.; van Koten, G. Angew. Chem. 2005, 117,
1472–1478; Angew. Chem., Int. Ed. 2005, 44, 1448-1452.
Such systems might be compared with the preferred structural
arrangements of the underlying metal-free carbocyclic lithioarene
compounds, which often exhibit dimeric or higher aggregated
structures in the solid state. Ligand-free phenyllithium (6) features
an orthogonal dimeric structure in the crystal11 (see Scheme 3).
Several donor ligand-stabilized analogues feature similar struc-
tures,12 but such systems show a tendency toward two major
structural distortions. The attachment of donor substituents in the
(14) Chandrasekhar, J.; von Rague´ Schleyer, P. J. Chem. Soc., Chem.
Commun. 1981, 260–261. Harder, S.; Boersma, J.; Brandsma, L.; van
Heteren, A.; Kanters, J. A.; Bauer, W.; von Rague´ Schleyer, P. J. Am. Chem.
Soc. 1988, 110, 7802–7806. Markies, P. R.; Schat, G.; Villena, A.;
Akkerman, O. S.; Bickelhaupt, F.; Smeets, W. J. J.; Spek, A. L. J.
Organomet. Chem. 1991, 411, 291–302. Sorger, K.; Schleyer, P. v. R.;
Stalke, D. J. Chem. Soc., Chem. Commun. 1995, 2279–2280. Sorger, K.;
Schleyer, P. v. R.; Fleischer, R.; Stalke, D. J. Am. Chem. Soc. 1996, 118,
6924–6933. Jantzi, K. L.; Guzei, I. A.; Reich, H. J. Organometallics 2006,
25, 5390–5395.
(8) Lai, C.-K.; Naiini, A. A.; Brubaker, C. H., Jr Inorg. Chim. Acta
1989, 164, 205–210. Ahlberg, P.; Davidsson, O.; Hilmersson, G.; Lo¨-
wendahl, M.; Håkasson, M. J. Chem. Soc., Chem. Commun. 1994, 1573–
1574. Voigt, F.; Fischer, A.; Pietzsch, C.; Jacob, K. Z. Anorg. Allg. Chem.
2001, 627, 2337–2343.
(15) Hoffmann, R.; Alder, R. W.; Wilcox, C. F., Jr J. Am. Chem. Soc.
1970, 92, 4992–4993. Ro¨ttger, D.; Erker, G. Angew. Chem. 1997, 109, 840–
856; Angew. Chem., Int. Ed. Engl. 1997, 36, 812-827. Erker, G. Chem.
Soc. ReV. 1999, 28, 307–314. Erker, G.; Venne-Dunker, S.; Kehr, G.;
Kleigrewe, N.; Fro¨hlich, R.; Mueck-Lichtenfeld, C.; Grimme, S. Organo-
metallics 2004, 23, 4391–4395.
(9) Jacob, K.; Scha¨fer, M.; Steiner, A.; Sheldrick, G. M.; Edelmann,
F. T. J. Organomet. Chem. 1995, 487, C18–C20. Jacob, K.; Scholz, J.;
Pietzsch, C.; Edelmann, F. T. J. Organomet. Chem. 1995, 501, 71–77.
Bucaille, A.; Le Borgne, T.; Ephritikhine, M.; Daran, J.-C. Organometallics
2000, 19, 4912–4914.
(16) Frenking, G. Chem. Phys. Lett. 1984, 111, 529–532. Buchwald,
S. L.; Lucas, E. A.; Davis, W. M. J. Am. Chem. Soc. 1989, 111, 397–398.
Bosold, F.; Zulauf, P.; Marsch, M.; Harms, K.; Lohrenz, J.; Boche, G.
Angew. Chem. 1991, 103, 1497–1499; Angew. Chem., Int. Ed. Engl. 1991,
30, 1455-1457. Poumbga, C. N.; Be´nard, M.; Hyla-Kryspin, I. J. Am. Chem.
Soc. 1994, 116, 8259–8265.
(10) Seidel, N.; Jacob, K.; Fischer, A. K.; Pietzsch, C.; Zanello, P.;
Fontani, M. Eur. J. Inorg. Chem. 2001, 145–151. Henderson, K. W.;
Kennedy, A. R.; Mulvey, R. E.; O’Hara, C. T.; Rowlings, R. B. Chem.
Commun. 2001, 1678–1679.
(11) Thoennis, D.; Weiss, E. Chem. Ber. 1978, 111, 3157–3161.
Dinnebier, R. E.; Behrens, U.; Obricht, F. J. Am. Chem. Soc. 1998, 120,
1430–1433. Actually, [PhLi]n is a polymer of dimers in the crystal, which
shows both structural motifs, namely, σ-coordination to the single “carb-
anionic” aryl ipso-carbon atom to form the central Li2C2 four-membered
ring and coordination to the π-system of the next adjacent aryl group.
Although [(Et2O)LiPh]4 is a tetramer (see: Hope, H.; Power, P.P. J. Am.
Chem. Soc. 1983, 105, 5320-5324), the dimer like in [(TMEDA)LiPh]2 is
a leading structural motif in aryl lithiums, like the structures presented in
this paper. See e.g.: Stey, T.; Stalke, D. Lead structures in lithium organic
chemistry. In The Chemistry of Organolithium Compounds; Rappoport, Z.,
Marek, I., Eds.; John Wiley & Sons: Chichester, 2004; pp 47-120. See
also for a comparison: Dinnebier, R. E.; Behrens, U.; Obricht, F.
Organometallics 1997, 16, 3855–3858.
(17) Markies, P. R.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.; Smeets,
W. J. J.; Spek, A. L. Organometallics 1990, 9, 2243–2247. Waggoner,
K. M.; Power, P. P. Organometallics 1992, 11, 3209–3214. Ruhlandt-Senge,
K.; Ellison, J. J.; Wehmschulte, R. J.; Pauer, F.; Power, P. P. J. Am. Chem.
Soc. 1993, 115, 11353–11357.
(18) Arvidsson, P. I.; Ahlberg, P.; Hilmersson, G. Chem.-Eur. J. 1999,
5, 1348–1354. Goldfuss, B.; Khan, S. I.; Houk, K. N. Organometallics 1999,
18, 2927–2929.
(19) Woodward, R. B.; Rosenblum, M.; Whiting, M. C. J. Am. Chem.
Soc. 1952, 74, 3458–3459. Schwink, L.; Knochel, P. Chem.-Eur. J. 1998,
4, 950–968.
(20) Knu¨ppel, S.; Fro¨hlich, R.; Erker, G. J. Organomet. Chem. 1999,
586, 218–222. Knu¨ppel, S.; Fro¨hlich, R.; Erker, G. J. Organomet. Chem.
2000, 595, 308–312. See also: Knu¨ppel, S.; Erker, G.; Fro¨hlich, R. Angew.
Chem. 1999, 111, 2048–2051; Angew. Chem., Int. Ed. 1999, 38, 1923-
1926. Bai, S.-D.; Wei, X.-H.; Guo, J.-P.; Liu, D.-S.; Zhou, Z.-Y. Angew.
Chem. 1999, 111, 2051–2054; 1999, 38, 1926-1928. Knu¨ppel, S.; Wang,
C.; Kehr, G.; Fro¨hlich, R.; Erker, G. J. Organomet. Chem. 2005, 690, 14–
32.
(12) See also: Goldstein, M. J.; Wenzel, T. T. HelV. Chim. Acta 1984,
67, 2029–2036. Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1990,
112, 8008–8014. Markies, P. R.; Schat, G.; Akkerman, O. S.; Bickelhaupt,
F.; Smeets, W. J. J.; van der Sluis, P.; Spek, A. L. J. Organomet. Chem.
1990, 393, 315–331. Lenders, B.; Grove, D. M.; Smeets, W. J. J.; von der
Sluis, P.; Spek, A. L.; van Koten, G. Organometallics 1991, 10, 786–791.

3250 Organometallics, Vol. 27, No. 13, 2008
Chen et al.
Scheme 4
Scheme 5
Scheme 6
directed lithiation at the proximal position of the ferrocene C5H3
ring adjacent to the R-NMe2 substituent must lead to the
diastereomer of 4 with the relative configuration (R*,R*,p-S*).
In the crystal isolated dimers of 4 were found. Of the two
possible combinations we find only the meso-dimer (see Figure
1). It contains a pair of monomeric units of opposite relative
stereochemistry bridged by two lithium atoms. The lithium
atoms and their adjacent ferrocene ipso-carbon centers form a
central C2Li2 four-membered substructure. The dimeric structure
of meso-4 is constrained in the solid state by a crystallographic
center of symmetry.
The side view of the structure (see Figure 1, bottom) shows
that the central C2Li2 unit features a marked rhombohedral
distortion. One lithium atom is almost coplanar with its adjacent
C5H4 ring (Li1-C14: 2.144(3) Å; angle centroid Cp-C14-Li:
147.4°). The other lithium atom (Li1*-C14: 2.103(3) Å)
features a slightly shorter Li-C distance and is displaced out
of the C10-C14 plane (angle centroid Cp-C14-Li*: 135.2°)
toward the iron center [Li1 is 0.426 Å below the C10-C14
plane; Li1* is 1.407 Å above]. The Li1 · · · Li1* distance is
2.391(5) Å. The Li1* · · · Fe1 separation amounts to 2.853(2)
Å.
The adjacent amine nitrogen atom is coordinated to Li1
(Li1-N1: 2.067(3) Å). The resulting five-membered heterocycle
features an envelope-shaped conformation with the atoms Li1,
C14, C10, and C9 being oriented in one plane and N1 (the “tip
of the envelope”) out of the plane away from the central Fe
atom (angle C9-N1-Li1: 98.3(1)°; deviation of N1 from the
adjacent plane: 0.774 Å).
In the structure of the meso-4 dimer the two ferrocene units
are offset to each other by half a ferrocene unit, which is
determined by the specific combination of the positions of the
connecting lithium atoms. In the dimer the central C2Li2 plane
deviates markedly from the mean Cp planes of their adjacent
ferrocene units (angle between the C14, Li1, C14*, Li1* vs the
C10-C14 plane: 55.4°).
Complex 13 features a very similar dimeric structure in the
crystal (meso-13 dimer). It is composed at two chiral monomeric
subunits of opposite stereochemistry (i.e., R,p-S/S,p-R). Again,
the meso-dimer contains a rhombohedrally shaped central C2Li2
ring system that is rotated by ca. 55.7° from an orthogonal
arrangement with the adjacent Cp planes. The characteristic
individual bond lengths amount to 2.150(4) Å (Li1-C14) and
For a comparison we prepared the related R-dimethylamino[3]-
ferrocenophane (13). The sequence21 started with a Friedel-Crafts
reaction of ferrocene with acryloyl chloride to give 11. Reduc-
tive amination (dimethylamine/Ti(OiPr)4; NaBH4) then gave the
product (12). Its lithiation with 1 molar equiv of n-butyllithium
in ether followed by crystallization gave 13 in >70% yield (see
Scheme 5). Treatment of 12 with 2 molar equiv of n-BuLi under
similar conditions eventually gave large crystals of 13 · n-BuLi
in 60% yield.
Also for the purpose of structural comparison we prepared
the related unbridged (R-dimethylamino)lithioferrocene deriva-
tive (17). The corresponding starting material (16) was synthe-
sized according to a literature procedure22 (see Scheme 6). The
final lithiation step (t-BuLi in ether/pentane) furnished the
product (17), which crystallized with coordination of a molecule
of ether in the solid state.
Descriptions of Crystal Structures of the Lithiated
Ferrocenophane Compounds. The chirality centers in trans-3
are not independent of each other. Consequently, selective
(21) Rosenblum, M.; Banerjee, A. K.; Danieli, N.; Fish, R. W.; Schlatter,
V. J. Am. Chem. Soc. 1963, 85, 316–324. Dixneuf, P.; Dabard, R. Bull.
Soc. Chim. Fr. 1972, 7, 2838–47. Dixneuf, P.; Dabard, R. Bull. Soc. Chim.
Fr. 1972, 7, 2847–54. Turbitt, T. D.; Watts, W. E. J. Organomet. Chem.
1972, 46, 109–348. Cayuela, E. M.; Xiao, L.; Sturm, T.; Manzano, B. R.;
Jalon, F. A.; Weissensteiner, W. Tetrahedron: Asymmetry 2000, 11, 861–
869. Faux, N.; Razafimahefa, D.; Picart-Goetgheluck, S.; Brocard, J.
Tetrahedron: Asymmetry 2005, 16, 1189–1197.
(22) Fukuzawa, S.-i.; Fujimoto, K.; Komuro, Y.; Matsuzawa, H. Org.
Lett. 2002, 4, 707–709. Tappe, K.; Knochel, P. Tetrahedron: Asymmetry
2004, 15, 91–102.

Structural Features of Lithio[3]ferrocenophane Systems
Organometallics, Vol. 27, No. 13, 2008 3251
Figure 2. Projection of the structure of the meso-13 dimer (thermal
ellipsoids at the 50% level). Selected bond lengths (Å) and angles
(deg): Fe-CCp 2.001(2)-2.104(2), Fe-Li1* 2.882(3), C5-Li1*
2.647(4), C1-C6 1.503(3). C6-C8 1.534(3), C8-C9 1.544(3),
C9-C10 1.518(2), C9-N1 1.499(2), C9-Li1 2.717(4), C10-Li1
2.738(4), C14-Li1 2.150(4), C14-Li1* 2.105(4), N1-Li1 2.073(4);
C1-C6-C8 114.7(2), C6-C8-C9 115.3(2), C8-C9-C10 114.2(2),
C8-C9-N1 110.2(2), C10-C9-N1 106.7(2), C9-N1-Li1 97.7(1),
N1-Li1-C14
89.1(2),
C14-Li1-C14*111.7(2).
N1-Li1-C14*
136.9(2),
Figure 1. Two views of the molecular structure of the meso-4 dimer
in the crystal (thermal ellipsoids at the 50% level). Selected bond
lengths (Å) and angles (deg): Fe-CCp 2.006(1)-2.106(1), Fe-Li1*
2.853(2), C5-Li1* 2.638(3), C1-C6 1.508(2). C6-C7 1.529 (2).
C6-C8 1.543(2), C8-C9 1.549(2), C9-C10 1.519(2), C9-N1
1.501(2), C9-Li1 2.725(3), C10-Li1 2.739(3), C14-Li1 2.144(3),
C14-Li1* 2.103(3), N1-Li1 2.067(3); C1-C6-C7 112.1(1),
C1-C6-C8 112.8(1), C7-C6-C8 111.8(1), C6-C8-C9 116.3(1),
C8-C9-C10 114.1(1), C8-C9-N1 109.7(1), C10-C9-N1
107.0(1), C9-N1-Li1 98.3(1), N1-Li1-C14 89.2(1), N1-Li1-
C14* 137.0(1), C14-Li1-C14*111.5(1).
2.073(4) Å (Li1-N1). The internal chelate ring features bond
angles of 89.1(2)° (C14-Li1-N1), 97.7(1)° (Li1-N1-C9),
106.7(1)° (N1-C9-C10), 123.1(2)° (C9-C10-C14), and
96.9(2)° (C10-C14-Li1). The Li1 · · · Li1* distance in the meso-
13 dimer amounts to 2.388(7) Å.
Figure 3. View of the molecular structure of the 13 · n-BuLi dimer
(thermal ellipsoids at the 50% level). Selected bond lengths (Å)
and angles (deg): Fe-CCp 2.002(2)-2.094(2), C1-C6 1.495(3).
C6-C8 1.537(3), C8-C9 1.540(3), C9-C10 1.518(3), C9-N1
1.502(2), C9-Li2 2.781(4), C14-Li2 2.252(4), C14-Li2* 2.226(3),
N1-Li2 2.088(4), C14-Li1 2.136(4), C21-Li1 2.212(4), C21-Li1*
2.219(4), C21-Li2* 2.316(4); C1-C6-C8 114.0(2), C6-C8-C9
114.2(2),C8-C9-C10114.5(2),C8-C9-N1110.0(2),C10-C9-N1
107.5(1), C9-N1-Li2 100.3(1), N1-Li2-C14 88.4(2), N1-Li2-
C14* 122.4(2), C14-Li2-C14* 107.0(1).
The molecular structure of the n-butyllithium adduct [13 · n-
BuLi dimer] is markedly different. It contains molecular entities
that are comprised of two lithioferrocene (13) and two n-
butyllithium subunits. In this case the pair of [3]ferrocenophane
entities is of the same chirality [i.e., R*,p-S*,R*,p-S*]. In the
overall C2-symmetrical structure two lithium atoms (Li2, Li2*)
are bridging the ferrocene units such that they are both oriented
close to the adjacent C5H3 plane (C14-Li2: 2.252(4) Å, angle
Li2-C14-Li2*: 70.9(1)°). The angle between the Li1-C14-Li2
and C10-C14 planes amounts to 49.4°. Consequently, we note
a weak N1-Li2 (2.088(4) Å) interaction in this subunit. The
additional pair of lithium atoms brought in by the formal
addition of two n-butyllithium building blocks are oriented such
that the total of four alkali metal atoms form a tetrahedral Li4
cluster in the center of this molecular arrangement. It is
characterized by bond distances Li1-Li2 2.457(5) Å, Li1-Li1*
2.443(7) Å, Li2-Li2* 2.597(6) Å, and Li1-Li2* 2.547(5) Å.
The pair of n-butyl substituents is C2-symmetrically oriented
toward the outside. Their R-CH2 groups are bridging between
pairs of lithium atoms [Li1-C21*: 2.219(4) Å, Li2-C21*:
2.316(4) Å, angle Li1-C21*-Li2: 65.6(2)°].
The X-ray crystal structure analysis of rac-17 has revealed that
the directed lithiation of the open aminomethylferrocene precursor
16 has resulted in a different stereochemical result as compared to
the bridged R-amino[3]ferrocenophane systems (3). The latter
consistently led to the formation of lithioferrocenophanes with R*,p-
S* configuration [e.g., (R*,R*,p-S*)-4 or (R*,p-S*)-13], whereas

3252 Organometallics, Vol. 27, No. 13, 2008
Chen et al.
the rigid orientation of the -NMe2 substituent at the C3-bridge.
This relatively large group in all cases adopts a pseudoequatorial
position. It directs the attack of the organolithium base
selectively into the ferrocene ring position, which leads to the
formation of a single diastereoisomeric lithio[3]ferrocenophane
derivative with (R*,R*,p-S*) configuration. This was for the first
time directly observed in this study, by characterizing the
molecular structures of the respective products 4 and 13.
Quenching of the lithio[3]ferrocenophane (R*,R*,p-S*)-4 with
ClPR2 reagents had previously resulted in the formation of the
corresponding (R*,R*,p-R*)-5 derivatives: the change of p-S*
to p-R* results from a formal Cahn, Ingold, Prelog priority
reversal. In contrast, the nonbridged system (16) leads to a
different stereochemical result, again to the best of our
knowledge for the first time observed here directly. Here a
specific conformational control of the pendent -CHPh(NMe2)
substituent leads to the specific formation of the (R*,p-R*)-17
diastereomer at the ferrocenyllithium stage.
The results of our X-ray diffraction analyses of these lithium-
bridged dimers reveal some interesting structural arrangements.
The structures of the lithiated [3]ferrocenophanes (4, 13) feature
both a rotation of the central Li2C2 plane relative to the adjacent
Cp planes and a shifting of the lithium atoms. This can be
described as a combination of both the 6 f 7 and 6 f 8
distortions as they were schematically depicted in Scheme 3.
However, in both cases the overall structure is still reminiscent
of a regular (i.e., perpendicular) aryl lithium dimer structure.
The same is true for the 13 · n-BuLi dimer. In this case this
distorted bonding arrangement seems to be strongly stabilized
by the presence of the pair of added n-butyllithium units, which
gives rise to the formation of a central Li4 cluster inside the
supramolecular architecture.23
The structure of the 17 · 0.5Et2O dimer represents an interesting
borderline case between the structural extremes 6 and 7 sketched
in Scheme 3. Here the open architecture has apparently induced a
marked rotation of the Li-Li vector from an orthogonal arrange-
ment (reminiscent of 6) toward a more coplanar orientation. It
seems that a more flexible system may conformationally favor this
rather unusual planarized geometry, especially if that is stabilized
by the coordination of an additional ligand.
Figure 4. View of the molecular geometry of the 17 · 0.5Et2O dimer
(thermal ellipsoids at the 50% level). Selected bond lengths (Å)
and angles (deg): Fe-CCp 2.025(3)-2.111(2) [2.033(2)-2.119(2)],
C9-C10 1.515(2) [1.522(3)], C9-N1 1.500(2) [1.495(3)], C14-Li1A
2.234(4) [2.231(4)], C14-Li1B 2.119(4) [2.128(4)], N1-Li1
2.198(4) [2.059(4)], O33-Li1A 1.983(3); C10-C9-N1 108.6(1)
[110.1(2)], C9-N1-Li1 98.1(1) [103.7(2)], N1-Li1-C14 87.0(1)
[88.8(2)], N1-Li1-C14* 117.6(2) [124.3(2)], C14-Li1-
C14*108.8(1) [117.5(2)], N1A-Li1A-O33 112.0(2).
directed lithiation of 16 resulted in the formation of product 17
with a “like” configuration, i.e., (R*,p-R*)-17.
In the crystal we find isolated dimeric molecular entities of
17. Each dimer is composed of a pair of monomeric lithiocene
derivatives of the same chirality [i.e., R*,p-R*,R*,p-R*]. There
is an additional ether molecule present in each dimer. The
ferrocene moieties are connected by a pair of lithium atoms.
The bridging is unsymmetrical (bond lengths C14A-Li1A:
2.234(4) Å, C14A-Li1B: 2.119(4) Å, C14B-Li1B: 2.128(4)
Å, C14B-Li1A: 2.231(4) Å). The bond angles inside the central
C2Li2 four-membered ring amount to C14A-Li1A-C14B
108.8(1)°, C14B-Li1B-C14A 117.5(2)°, Li1A-C14B-Li1B
66.5(1)°, Li1A-C14A-Li1B 66.6(1)°. The angle between the
Li1A-C14A-Li1B plane and the adjacent C10A-C14A Cp
plane is 90.6°; the corresponding angle between the C10B-C14B
and Li1A-C14B-Li1B planes amounts to 38.4°. This places
the structure of the 17 dimer somewhere between the extremes
of 6 and 7 (see Scheme 3 and Figure 4).
Experimental Section
General Procedures. All experiments were carried out under a
dry argon atmosphere using standard Schlenk techniques or in a
glovebox. Solvents (including deuterated solvents used for NMR) were
dried and distilled prior to use. 1H and 13C spectra were recorded on
1
a Bruker AV300 or a Varian 600 Unity Plus spectrometer. H and
13C data were determined by 1D- (APT, TOCSY, NOE) and 2D-NMR
experiments (13C,1H GHSQC, 13C,1H GHMBC, and 1H,1H COSY).
Elemental analysis was performed on a Foss-Heraeus CHNO-Rapid.
The starting materials rac-trans-3,3 rac-12,21 and rac-1622 were
prepared according to the reported procedures.
X-ray Crystal Structure Analyses. Data sets were collected
with a Nonius KappaCCD diffractometer, equipped with a rotating
anode generator. Programs used: data collection COLLECT (Nonius
B.V., 1998), data reduction Denzo-SMN (Otwinowski, Z.; Minor,
W. Methods Enzymol. 1997, 276, 307-326), absorption correction
SORTAV (Blessing, R. H. Acta Crystallogr. 1995, A51, 33-37;
Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421-426) and Denzo
We note that lithium atom Li1A carries a coordinated diethyl
ether ligand (Li1A-O33: 1.983(3) Å). It is also weakly bonded
to the nitrogen center of the adjacent -NMe2 group (Li1A-N1A:
2.198(4)Å,anglesLi1A-N1A-C9A:98.1(1)°,N1A-Li1A-O33:
112.0(2)°). Lithium atom Li1B is coordinated only to its
neighboring dimethylamino nitrogen center (Li1B-N1B: 2.059(4)
Å).
(23) See for a comparison: Marsch, M.; Harms, K.; Lochmann, L.;
Boche, G. Angew. Chem., Int. Ed. Engl. 1990, 29, 308–309; Angew. Chem.
1990, 102, 334-336 [(n-BuLi)4(LiO-t-Bu)4]Davies, R. P.; Raithby, P. R.;
Snaith, R. Angew. Chem., Int. Ed. Engl. 1997, 36, 1215–1217; Angew. Chem.
1997, 109, 1261-1263 [(Et2O)4(n-BuLi)2{Ph(C6H4Li)NLi}2(LiNPh2)]
Some Conclusions
The stereochemistry of the directed lithiation of the R-dimeth-
ylamino[3]ferrocenophane systems 3 and 12 is determined by

Structural Features of Lithio[3]ferrocenophane Systems
Organometallics, Vol. 27, No. 13, 2008 3253
(Otwinowski, Z.; Borek, D.; Majewski, W.; Minor, W. Acta
Crystallogr. 2003, A59, 228-234), structure solution SHELXS-97
(Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473), structure
refinement SHELXL-97 (Sheldrick, G. M. Universita¨t Go¨ttingen,
1997; Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112-122),
graphics XP (BrukerAXS, 2000) and SCHAKAL (Keller, E.
Universita¨t Freiburg, 1997).
ature. Again the solution was cooled to -32 °C for crystallization.
Crystalline 13 · n-BuLi was isolated by decanting the solvent in a
glovebox (203 mg, 60%). A satisfactory result of element analysis
for this compound was not obtained due to its high sensitivity. 1H
NMR (600 MHz, d8-toluene, 298 K): δ -0.41(m)/-0.44 (br) (Σ
2H), 1.15 (pt, 3H), 1.72/1.92 (each m, each 1H), 1.76 (m, 2H) (Bu),
1.47 (s, 3H, NMe), 1.51/2.29 (each m, each 1H, 6-H), 1.93 (m,
1H, 9-H), 1.94/1.98 (each m, each 1H, 8-H), 2.02 (s, 3H, NMe),
3.82, 3.97, 4.25 (each m, each 1H, 11,12,13-H), 3.95, 3.96, 3.97,
4.00 (each m, each 1H, 2,3,4,5-H). 13C{1H} NMR (125 MHz, d8-
toluene, 298 K): δ 14.3, 32.7, 33.4, n.o. (Bu), 25.2 (C6), 39.5 (C8),
43.1 (NMe), 45.9 (NMe), 64.4, 67.5, 68.9, 71.8 (C2,3,4,5), 68.1
(C9), 71.4, 74.9, 78.1 (C11,12,13), 86.1 (C1), 98.2 (C10), n.o.
(C14).
X-ray crystal structure analysis for 13 · n-BuLi: formula
[C15H18FeLiN · LiC4H9]2, M ) 678.29, orange crystal 0.45 × 0.25
× 0.20 mm, a ) 21.6614(3) Å, b ) 10.6671(2) Å, c ) 19.0435(3)
Å, ꢀ ) 124.613(1)°, V ) 3621.46(10) Å3, Fcalc ) 1.244 g cm-3, µ
) 0.828 mm-1, empirical absorption correction (0.707 e T e
0.852), Z ) 4, monoclinic, space group C2/c (No. 15), λ ) 0.71073
Å, T ) 198 K, ω and ꢁ scans, 13 024 reflections collected ((h, (
k, ( l), [(sin θ)/λ] ) 0.66 Å-1, 4263 independent (Rint ) 0.048)
and 3394 observed reflections [I g 2σ(I)], 240 refined parameters,
R ) 0.037, wR2 ) 0.102, max. residual electron density 0.41
(-0.44) e Å-3, hydrogen atoms calculated and refined as riding
atoms.
Preparation of 17. A solution of 16 (320 mg, 1.0 mmol) in
ether (5 mL) was cooled with an ice-salt bath (ca. -20 °C). After
t-BuLi (0.6 mL, 1.5 M in pentane, 0.9 mmol) was added, the bath
was removed and the solution was kept without any agitation for
24 h. Big crystals of 17 (232 mg, 64%) were isolated by decanting
the solvent in a glovebox. NMR data were obtained by dissolving
the crystals at -78 °C and directly measured at -75 °C. At -5 °C
the detected compound rearranged to a complex mixture (see the
Supporting Information). Anal. Calcd for (C19H20FeLiN)2 · Et2O:
C 69.63, H 6.96, N 3.87. Found: C 69.39, H 6.91, N 3.86. 1H NMR
(600 MHz, d8-THF, 198 K): δ 1.92 (br, 6H, NMe2), 3.34 (br, 5H,
Cp), 3.76, 3.93. 3.95 (each br, each 1H, 11,12,13-H), 4.02 (br, 1H,
9-H), 7.17 (pt, 1H, p-Ph), 7.31 (pt, 2H, m-Ph), 7.58 (pd, 2H, o-Ph).
13C NMR (125 MHz, d8-THF, 198 K): δ 45.5 (br, NMe2), 67.7,
70.2, 76.5 (C11,12,13), 68.8 (Cp), 73.4 (C9), 99.0 (C10), 126.3
(p-Ph), 128.0 (m-Ph), 129.0 (o-Ph), 148.3 (i-Ph), n.o. (C14).
Preparation of Lithio[3]ferrocenophane 4. A solution of rac-
trans-3 (420 mg, 1.5 mmol) in diethyl ether (10 mL) was cooled
with an ice-salt bath (ca. -20 °C). After n-BuLi (1.6 mL, 1.6 M
in hexane, 3.2 mmol) was added, the cooling bath was removed
and the solution was kept without any agitation for 48 h. Big crystals
of 4 (300 mg, 70%) were isolated by decanting the solvent in a
glovebox. Anal. Calcd for C16H20FeLiN: C 66.47, H 6.97, N 4.84.
1
Found: C 65.49, H 7.08, N 4.51. H NMR (300 MHz, d8-THF,
3
2
298 K): δ 1.23 (d, J ) 7.4 Hz, 3H, 7-H), 2.06 (ddd, J ) 12.8
3
3
Hz, J ) 3.6, 2.1 Hz, 1H, 8-H), 2.22 (s, 6H, NMe2), 2.67 (dd, J
) 11.7, 2.1 Hz, 1H, 9-H), 2.76 (qt, J ) 7.4, 3.6 Hz, 1H, 6-H),
3
2
3
3.28 (ddd, J ) 12.8, J ) 11.9, 3.6 Hz, 1H, 8-H′), 3.74, 3.94,
3.95, 4.43 (each m, each 1H, 2,3,4,5-H), 3.90, 4.15 (each m, each
1H, 11,13-H), 3.98 (m, 1H, 12-H). 13C{1H} NMR (75 MHz, d8-
THF, 298 K): δ 17.5 (C7), 29.4 (C6), 45.8 (NMe2), 45.8 (C8), 64.6
(C9), 65.8, 67.1, 69.4, 72.2 (C2,3,4,5), 69.7 (C12), 74.4, 81.0
(C11,13), 90.1 (C10), 92.4 (C1), n.o. (C14).
X-ray crystal structure analysis for 4: formula C16H20FeLiN, M
) 289.12, orange crystal 0.55 × 0.25 × 0.25 mm, a ) 7.5675(1) Å,
b ) 9.2846(2) Å, c ) 10.4913(2) Å, R ) 106.946(1), ꢀ ) 98.020(1)°,
γ ) 102.853(2)°, V ) 670.75(2) Å3, Fcalc ) 1.432 g cm-3, µ ) 1.106
mm-1, empirical absorption correction (0.582 e T e 0.770), Z ) 2,
j
triclinic, space group P1 (No. 2), λ ) 0.71073 Å, T ) 198 K, ω and
ꢁ scans, 6967 reflections collected ((h, ( k, ( l), [(sin θ)/λ] ) 0.67
Å-1, 3227 independent (Rint ) 0.034) and 3069 observed reflections
[I g 2σ(I)], 175 refined parameters, R ) 0.026, wR2 ) 0.070, max.
residual electron density 0.36 (-0.45) e Å-3, hydrogen atoms
calculated and refined as riding atoms.
Preparation of Lithio[3]ferrocenophane 13. A solution of rac-
12 (270 mg, 1.0 mmol) in ether (5 mL) was cooled with an ice-salt
bath (ca. -20 °C). After n-BuLi (0.6 mL, 1.6 M in hexane, 0.96
mmol) was added, the bath was removed and the solution was kept
without any agitation for 48 h. Big crystals of 13 were isolated by
decanting the solvent in a glovebox (198 mg, 72%). Anal. Calcd
for C15H18FeLiN: C 65.49, H 6.60, N 5.09. Found: C 64.61, H
6.65, N 4.87. 1H NMR (300 MHz, d8-THF, 298): δ 1.88 (td, 2J )
X-ray crystal structure analysis for 17 · 0.5Et2O: formula
(C19H20FeLiN)2*C4H10O, M ) 724.42, orange crystal 0.30 × 0.25
× 0.20 mm, a ) 10.9229(1) Å, b ) 12.9582(2) Å, c ) 13.9885(2)
Å, R ) 75.410(1)°, ꢀ ) 84.683(1)°, γ ) 83.606(1)°, V )
1899.88(4) Å3, Fcalc ) 1.266 g cm-3, µ ) 0.797 mm-1, empirical
absorption correction (0.796 e T e 0.857), Z ) 2, triclinic, space
3
14.0, J ) 14.0, 2.3 Hz, 1H, 6-H), 2.13 (br m, 1H, H-8), 2.23 (s,
3
2
6H, NMe2), 2.45 (dd, J ) 11.0, 1.5 Hz, 1H, 9-H), 2.51 (dt, J )
3
14.0, J ) 3.4 Hz, 1H, 6-H′), 3.10 (br m, 1H, 8-H′), 3.71, 3.87,
3.95, 4.40 (each br, each 1H, 2,3,4,5-H), 3.93, 3.99, 4.16 (each br,
each 1H, 11,12,13-H). 13C{1H} NMR (75.0 MHz, d8-THF, 298
K): δ 27.6 (C6), 38.8 (C8), 45.7(NMe2), 65.9, 69.7, 70.4, 71.6
(C2,3,4,5), 70.0, 74.8, 80.9 (C11,12,13), 72.2 (C9), 87.6 (C1), 89.8
(C10), n.o. (C14).
j
group P1 (No. 2), λ ) 0.71073 Å, T ) 198 K, ω and ꢁ scans,
20 005 reflections collected ((h, ( k, ( l), [(sin θ)/λ] ) 0.66 Å-1
,
8977 independent (Rint ) 0.054) and 7248 observed reflections [I
g 2σ(I)], 448 refined parameters, R ) 0.040, wR2 ) 0.104, max.
residual electron density 0.42 (-0.59) e Å-3, hydrogen atoms
calculated and refined as riding atoms.
X-ray crystal structure analysis for 13: formula C15H18FeLiN,
M ) 275.10, orange crystal 0.30 × 0.15 × 0.10 mm, a ) 7.4443(1)
Å, b ) 9.2993(2) Å, c ) 9.9602(3) Å, R ) 95.318(1)°, ꢀ )
108.510(1)°, γ ) 102.226(2)°, V ) 629.43(2) Å3, Fcalc ) 1.451 g cm-3
,
µ ) 1.174 mm-1, empirical absorption correction (0.720 e T e 0.892),
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft, the Fonds der Chemischen Indus-
trie, and the Alexander von Humboldt-Stiftung (For-
schungsstipendium to C.C.) is gratefully acknowledged. We
thank the reviewers for helpful and interesting comments.
j
Z ) 2, triclinic, space group P1 (No. 2), λ ) 0.71073 Å, T ) 198 K,
ω and ꢁ scans, 5795 reflections collected ((h, ( k, ( l), [(sin θ)/λ]
) 0.67 Å-1, 3013 independent (Rint ) 0.039) and 2587 observed
reflections [I g 2σ(I)], 165 refined parameters, R ) 0.034, wR2 )
0.080, max. residual electron density 0.46 (-0.41) e Å-3, hydrogen
atoms calculated and refined as riding atoms.
Supporting Information Available: Details of the X-ray crystal
structure analyses and additional experimental and spectroscopic
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
Preparation of Lithio[3]ferrocenophane 13 · n-BuLi. A solu-
tion of rac-12 (270 mg, 1.0 mmol) in ether (5 mL) was cooled
with an ice-salt bath (ca. -20 °C). After n-BuLi (1.3 mL, 1.6 M
in hexane, 2.08 mmol) was added, the bath was removed and the
solution was kept without any agitation for 48 h at room temper-
OM8001894