Ferrocenylhydridoborates: Synthesis, structural characterization, and application to the preparation of ferrocenylborane polymers

Article abstract of DOI:10.1021/ja906575s

Mono- and ditopic lithium ferrocenylhydridoborates Li[FcBH₃] (2) and Li₂[H₃B-fc-BH₃] (4) have been synthesized from FcB(OMe)₂/(MeO)₂B-fc-B(OMe)₂ and Li[AlH₄] (Fc = fer

Full text of DOI:10.1021/ja906575s

Published on Web 10/16/2009
Ferrocenylhydridoborates: Synthesis, Structural
Characterization, and Application to the Preparation of
Ferrocenylborane Polymers
Matthias Scheibitz,† Haiyan Li,‡ Jan Schnorr,† Alejandro Sa´nchez Perucha,†
Michael Bolte,† Hans-Wolfram Lerner,† Frieder Ja¨kle,*,‡ and Matthias Wagner*,†
Institut fu¨r Anorganische und Analytische Chemie, Johann Wolfgang Goethe-UniVersita¨t
Frankfurt, Max-Von-Laue-Strasse 7, D-60438 Frankfurt am Main, Germany, and Department of
Chemistry, Rutgers UniVersity Newark, 73 Warren Street, Newark, New Jersey 07102
Received August 4, 2009; E-mail: matthias.wagner@chemie.uni-frankfurt.de; fjaekle@rutgers.edu
Abstract: Mono- and ditopic lithium ferrocenylhydridoborates Li[FcBH3] (2) and Li2[H3B-fc-BH3] (4) have
been synthesized from FcB(OMe)2/(MeO)2B-fc-B(OMe)2 and Li[AlH4] (Fc ) ferrocenyl; fc ) 1,1′-
ferrocenylene). X-ray quality crystals were grown from OEt2. Depending on the amount of Li+-coordinated
solvent molecules, dimeric (2(OEt2)2) or tetrameric (2(OEt2)) aggregates are observed in the solid state.
The ditopic derivative 4 crystallizes as two different macrocyclic dimers (4(OEt2)5 and 4(OEt2)6) in the unit
cell. Each of the four aggregates is held together mainly by RBH3-η2-Li bonds. Addition of Me3SiCl to 2 or
4 generates the corresponding boranes FcBH2 (5) and H2B-fc-BH2 (6), which can be trapped by adduct
formation with NMe2Et or SMe2. In contrast, when OEt2 is present as the sole Lewis basic donor, no stable
ether adducts are obtained, but condensation takes place leading to Fc2BH (10) and the novel borane
polymer [-fcB(H)-]n (9), respectively. In situ generation of FcBH2 (5) in the presence of cyclohexene gives
Fc2BCy and BCy3 but no FcBCy2, thereby indicating that 5 undergoes condensation to 10 more quickly
than hydroboration of an internal olefin can occur (Cy ) cyclohexyl). Fc2BH (10) was further studied as a
model system for the optimization of modification reactions of polymer [-fcB(H)-]n (9). Hydroboration of
PhCCH or tBuCCH with 10 proceeds smoothly and quantitatively to give the corresponding vinylboranes
Fc2B(CHdCHR) (11Ph, R ) Ph; 11tBu, R ) tBu), which were fully characterized. In a similar manner, the
polymeric borane 9 was successfully transformed into ferrocenylborane polymers [-fcB(CHdCHR)-]n (12Ph
,
R ) Ph; 12tBu, R ) tBu) that contain vinyl groups attached to boron. The structures of polymers 12 were
confirmed by NMR and IR spectroscopy and mass spectrometry. The MALDI-TOF spectra of 12Ph and
12tBu showed patterns of equidistant peaks with peak separations that are consistent with the masses of
the expected repeating units of each of the polymers. The absorption maxima in the UV-vis spectra of
polymers 12 are significantly red-shifted in comparison to the dimeric model systems 11.
structure of Be[BH4]27), a use as building blocks for coordination
polymers and low-dimensional solids can be envisaged.
Introduction
Tetrahydridoborate, diborane, and borane-Lewis base adducts
are abundant reducing agents in preparative chemistry.1 The
[BH4]- ion has also been employed as ligand for a wide range
of (transition) metal ions.2,3 In the latter context, the tendency
of [BH4]- to form unusual covalent complexes that are volatile
and/or soluble in unpolar solvents makes metal tetrahydroborates
valuable precursors for the deposition of metal boride thin
films.4-6 Moreover, given that [BH4]- ions have a propensity
to adopt bridging positions between metal ions (cf. the polymeric
However, it soon became apparent that replacement of
hydrogen atoms in [BH4]- or B2H6 by organic substituents
greatly expands the range of applications, because the organic
moiety in mono- and diorganylhydridoborates/boranes serves
as an important set-screw for tuning their chemical properties.
For example, compared to diborane, compounds such as
thexylborane or 9-borabicyclo[3.3.1]nonane show a greatly
enhanced regioselectivity in the hydroboration of olefins. Chiral
derivatives like diisopinocampheylborane proved to be efficient
reagents in asymmetric synthesis.8 Also in the case of metal
hydridoborate complexes, the presence of organyl groups should
result in a modulation of the M · · ·HB interaction(s) with impact
on structural9 and reactivity patterns.10-15
† Johann Wolfgang Goethe-Universita¨t Frankfurt.
‡ Rutgers University Newark.
(1) Pelter, A.; Smith, K.; Brown, H. C. Borane Reagents; Academic Press:
London, 1988.
(2) Marks, T. J.; Kolb, J. R. Chem. ReV. 1977, 77, 263–293.
(3) Ephritikhine, M. Chem. ReV. 1997, 97, 2193–2242.
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Chem. Soc. 1988, 110, 1643–1644.
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(8) Ramachandran, P. V.; Brown, H. C. Organoboranes for Syntheses;
ACS Symposium Series 783; American Chemical Society: Washing-
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Mater. 2007, 19, 3802–3807.
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9
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J. AM. CHEM. SOC. 2009, 131, 16319–16329 16319

A R T I C L E S
Scheibitz et al.
Scheme 1. Synthesis of Mono- and Ditopic
Ferrocenylhydridoborates 2 and 4a
Figure 1. π-Conjugated polymers synthesized by hydroboration polym-
erization (I) and condensation polymerization (II).
In view of this rich chemistry, our groups became interested
in the development of new classes of organylhydridoborates and
organylboranes with a special focus on the following targets:
(1) derivatives [OM-BH3]- and OM-BH2(Do) with organome-
tallic substituents OM (Do ) Lewis basic donor) and (2) ditopic
species [H3B-OM′-BH3]2- and (Do)H2B-OM′-BH2(Do), in
which two hydridoborate/borane functionalities are connected
by an organometallic linker OM′.
a Reagents and conditions: (i) 1 equiv of Li[AlH4], OEt2, -78 °C f rt.
(ii) 2 equiv of Li[AlH4], OEt2, -78 °C f rt.
The aimed-for hydridoborates [OM-BH3]- and [H3B-OM′-
BH3]2- not only are expected to serve as ideal starting materials
for the synthesis of the corresponding boranes but also could
function as interesting ligand molecules, because coordination
to appropriate metal ions Mx+ should provide access to novel
oligonuclear aggregates LnM[OM-BH3]m and supramolecular
materials {Mn[H3B-OM′-BH3]m}∞ in which classical Werner-
type complexes are combined with organometallic moieties.
Such compounds would have unique structural properties and
may serve as precursors of metal- and boron-containing
ceramics.
the π-conjugated polymer backbone and metal-centered orbitals
can be achieved.21
As an alternative to the hydroboration polymerization ap-
proach, we have recently developed a condensation polymeri-
zation protocol leading to boron-bridged polyferrocenes II
(Figure 1) via the reaction of 1,1′-bis(dibromoboryl)ferrocene
with triethylsilane.22 Experimental22,24 as well as theoretical22
evidence indicates the initial formation of B(Br)H-containing
intermediates, which then undergo polycondensation with
liberation of B2H6. Polymeric materials may therefore be
obtained by either hydroboration or condensation polymerization
of compounds OM-BH2(Do) and (Do)H2B-OM′-BH2(Do), and
to find suitable conditions for these processes is an intriguing
challenge.
This paper describes the synthesis of trihydridoborates
Li[FcBH3] and Li2[H3B-fc-BH3], which contain ferrocenyl (Fc)
and 1,1′-ferrocenylene (fc), respectively, as organometallic
moieties. We will first focus on their solid-state structures to
obtain insight into the coordination properties of the anions. In
a subsequent step, we will transform these compounds into
donor adducts FcBH2(Do) and (Do)H2B-fc-BH2(Do) and study
the competition between hydroboration and condensation in the
presence of suitable olefinic substrates. The last section is then
concerned with the application of selected ditopic boranes
(Do)H2B-fc-BH2(Do) to the development of new ferrocene- and
boron-containing polymers.
Our interest in boranes OM-BH2(Do) and (Do)H2B-OM′-
BH2(Do) in turn is driven by their potential as precursors to
polymeric materials. Chujo et al. have established the hydrobo-
ration polymerization of (hetero)aromatic diynes as a powerful
tool for the preparation of boron-doped π-conjugated macro-
molecules with useful optoelectronic properties (cf. I, Figure
1).16-19 Although a broad selection of diynes has already been
employed in this reaction, the boron component has remained
so far restricted mainly to mesityl- and tripylborane (I with R
) 2,4,6-trimethylphenyl or 2,4,6-tri-isopropylphenyl). More
recently, our groups have reported on the successful use of the
difunctional borane reagent 9,10-dihydro-9,10-diboraanthracene
in the hydroboration polymerization of 1,4-dialkynylbenzenes.20
Going one step further, we reasoned that mono- and ditopic
organometallic hydroboration reagents could significantly broaden
the scope of I-type materials if an electronic interaction between
Results and Discussion
The target compounds 2, 4, 5(Do), and 6(Do)2 are shown in
Schemes 1 and 2. Ferrocene was chosen as the organometallic
moiety, because it is easy to borylate, diamagnetic, chemically
robust, and electrochemically well-behaved.25,26 As trapping
reagents for the ferrocenylboranes 5 and 6, we tested three Lewis
basic donors (Do ) NMe2Et, SMe2, OEt2) of significantly
(10) Kot, W. K.; Edelstein, N. M.; Zalkin, A. Inorg. Chem. 1987, 26, 1339–
1341.
(11) Sun, Y.; Spence, R. E. v. H.; Piers, W. E.; Parvez, M.; Yap, G. P. A.
J. Am. Chem. Soc. 1997, 119, 5132–5143.
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L. R.; Zaworotko, M. J. Organometallics 1998, 17, 2459–2469.
(13) Chen, X.; Liu, F.-C.; Plecˇnik, C. E.; Liu, S.; Du, B.; Meyers, E. A.;
Shore, S. G. Organometallics 2004, 23, 2100–2106.
(14) Ding, E.; Du, B.; Meyers, E. A.; Shore, S. G.; Yousufuddin, M.; Bau,
R.; McIntyre, G. J. Inorg. Chem. 2005, 44, 2459–2464.
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Trans. 2008, 3599–3604.
(21) Organoboron π-conjugated polymers including Ru-, Pd-, and Pt-alkynyl
complexes have been reported: (a) Matsumi, N.; Chujo, Y.; Lavastre,
O.; Dixneuf, P. H. Organometallics 2001, 20, 2425–2427. (b)
Matsumoto, F.; Matsumi, N.; Chujo, Y. Polym. Bull. 2001, 46, 257–
262.
(16) Matsumi, N.; Naka, K.; Chujo, Y. J. Am. Chem. Soc. 1998, 120, 5112–
5113.
(22) Heilmann, J. B.; Scheibitz, M.; Qin, Y.; Sundararaman, A.; Ja¨kle, F.;
Kretz, T.; Bolte, M.; Lerner, H.-W.; Holthausen, M. C.; Wagner, M.
Angew. Chem., Int. Ed. 2006, 45, 920–925.
(17) Matsumi, N.; Miyata, M.; Chujo, Y. Macromolecules 1999, 32, 4467–
4469.
(18) Miyata, M.; Chujo, Y. Polym. Bull. 2003, 51, 9–16.
(19) Matsumi, N.; Chujo, Y. Polym. J. 2008, 40, 77–89.
(20) Lorbach, A.; Bolte, M.; Li, H.; Lerner, H.-W.; Holthausen, M. C.;
Ja¨kle, F.; Wagner, M. Angew. Chem., Int. Ed. 2009, 48, 4584–4588.
(23) Scheibitz, M.; Bats, J. W.; Bolte, M.; Lerner, H.-W.; Wagner, M.
Organometallics 2004, 23, 940–942.
(24) Heilmann, J. B.; Qin, Y.; Ja¨kle, F.; Lerner, H.-W.; Wagner, M. Inorg.
Chim. Acta 2006, 359, 4802–4806.
9
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Ferrocenylhydridoborates
A R T I C L E S
Scheme 2. Synthesis of Mono- and Ditopic Ferrocenylborane
a
Adducts 5(NMe2Et), 5(SMe2), 6(NMe2Et)2, 6(SMe2)2
a Reagents and conditions: (i) 5(NMe2Et), excess Me3SiCl/excess
NMe2Et, OEt2, -78 °C f rt; 5(SMe2), excess Me3SiCl, SMe2, -78 °C f
rt. (ii) 6(NMe2Et)2, excess Me3SiCl/excess NMe2Et, OEt2, -78 °C f rt;
6(SMe2)2, excess Me3SiCl, SMe2, -78 °C f rt.
different donor strengths in order to explore the stability limits
of the resulting adducts with respect to the aforementioned
condensation reaction.
Ferrocenylhydridoborate Precursors. The ferrocenyl- and
1,1′-ferrocenylenehydridoborates 2 and 4 were prepared from
the readily available boronic esters 125 and 325 by treatment
with 1 and 2 equiv of Li[AlH4], respectively (Scheme 1). The
structures of 2 and 4 were confirmed by multinuclear NMR
spectroscopy and single crystal X-ray diffraction.
The 11B NMR spectra (THF-d8) of 2 and 4 show quartets at
-30.6 ppm (1JBH ) 77.1 Hz) and -33.7 ppm (1JBH ) 79.2 Hz),
1
respectively, which collapse into singlets in the H-decoupled
mode. Both chemical shift values are in reasonable agreement
with those of other monoorganylhydridoborates (e.g., Li[Ph-
BH3], -26.4 ppm (1JBH ) 76.0 Hz)27). In the corresponding
1H NMR spectra, the hydride ions of the BH3 substituents give
rise to quartets (2, δ(1H) ) 0.86; 4, δ(1H) ) 0.75) due to
coupling with the 11B nucleus (I ) 3/2, natural abundance
80%).28 In the case of 2, 11B-coupling is also observed for all
carbon atoms of the substituted cyclopentadienyl ring
(δ(13C){1H} ) 67.2 (q, JCB ) 2.9 Hz), 75.1 (q, JCB ) 3.4 Hz),
92.4 (q, 1JCB ) 59.4 Hz)), whereas in the spectrum of 4, 11B-13C
coupling is only resolved for the ipso carbon resonance
Figure 2. Molecular structures of 2(OEt2)2 (top) and 2(OEt2) (bottom) in
the solid state; hydrogen atoms attached to carbon and Li+-coordinated OEt2
molecules have been omitted for clarity. Selected bond lengths (Å),
atom· · ·atom distances (Å), and angles (deg): 2(OEt2)2 B(1)-C(1) 1.597(4),
B(1)· · ·Li(1) 2.511(6), B(1) · · ·Li(1A) 2.455(6), Li(1) · · ·Li(1A) 3.274(10);
B(1)-Li(1)-B(1A) 97.5(2), Li(1)-B(1)-Li(1A) 82.5(2). Symmetry trans-
formation used to generate equivalent atoms: A -x + 1, -y + 1, -z + 1.
2(OEt2) B(1)-C(11) 1.598(4), B(2)-C(31) 1.590(4), B(1) · · ·Li(1) 2.536(5),
B(1)· · ·Li(2) 2.579(6), B(1) · · ·Li(2A) 2.553(5), B(2) · · ·Li(1) 2.274(6),
B(2)· · ·Li(2) 2.514(6), Li(1) · · ·Li(2) 3.044(7), Li(2) · · ·Li(2A) 3.543(9);
B(1)-Li(1)-B(2) 104.9(2), B(1)-Li(2)-B(2) 97.1(2), B(1)-Li(2)-B(1A)
92.7(2),Li(1)-B(1)-Li(2)73.0(2),Li(1)-B(2)-Li(2)78.8(2),Li(2)-B(1)-Li(2A)
87.3(2). Symmetry transformation used to generate equivalent atoms: A
-x + 1, -y + 1, - z + 2.
1
(δ(13C){1H} ) 87.8 (q, JCB ) 54.3 Hz)).
Compound 2 crystallizes from OEt2 with 2 equiv of Li+-
coordinated solvent molecules (2(OEt2)2), whereas recrystalli-
zation of 2(OEt2)2 from pentane at -30 °C leads to the
monoether adduct 2(OEt2). Crystals of the dilithium salt 4 were
also obtained from ethereal solutions. Details of the X-ray crystal
structure analyses of 2(OEt2)2, 2(OEt2), and 4(OEt2)2.67, are
compiled in Table 1S in Supporting Information.
ions and two negatively charged trihydridoborate substituents
(Figure 2 top). The corresponding distances between the Li+
ions and the boron atoms are B(1) · · ·Li(1) ) 2.511(6) Å and
B(1)· · ·Li(1A) ) 2.455(6) Å. Using Edelstein’s correlation29
of metal-boron distances as a measure of the denticity of a
trihydridoborate group, values of 1.6 ( 0.1 and 1.36 ( 0.06 Å
are estimated for the ionic radii of bidentate and tridentate
trihydridoborate ligands, respectively. Thus, B · · ·Li distances
of about 2.50 and 2.26 Å can be expected for RBH3-η2-Li and
RBH3-η3-Li coordination modes (ionic radii of Li+ ) 0.90 Å
(CN 6), 0.73 (CN 4)30). This leads to the conclusion that the
The crystal lattice of 2(OEt2)2 consists of centrosymmetric
dimers that are held together by interactions between two Li+
(25) Scheibitz, M.; Bolte, M.; Bats, J. W.; Lerner, H.-W.; Nowik, I.; Herber,
R. H.; Krapp, A.; Lein, M.; Holthausen, M. C.; Wagner, M. Chem.
Eur. J. 2005, 11, 584–603.
(26) Togni, A.; Hayashi, T. Ferrocenes; VCH: Weinheim, 1995.
(27) Singaram, B.; Cole, T. E.; Brown, H. C. Organometallics 1984, 3,
774–777.
(29) Edelstein, N. Inorg. Chem. 1981, 20, 297–299.
(28) Mason, J. Multinuclear NMR; Plenum Press: New York, 1987.
(30) Shannon, R. D. Acta Crystallogr. 1976, A32, 751–767.
9
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A R T I C L E S
Scheibitz et al.
trihydridoborate substituents in 2(OEt2)2 act as bidentate ligands
and that one H atom at each [FcBH3]- moiety is shared between
two Li+ ions. The coordination sphere of each Li+ ion is
completed by two OEt2 ligands (not shown in Figure 2; cf.
Figure 1S in Supporting Information for a complete plot of
2(OEt2)2).
Recrystallization of 2(OEt2)2 from pentane results in a
different crystal structure, 2(OEt2), in which each Li+ ion bears
only one OEt2 ligand (Figure 2 bottom, OEt2 ligands not shown;
cf. Figure 2S in Supporting Information for a complete plot of
2(OEt2)). In turn, this leads to a higher degree of aggregation
so that 2(OEt2) forms centrosymmetric tetramers in the solid
state. The short B(2)· · ·Li(1) distance of 2.274(6) Å indicates
a B(2)H3-η3-Li(1) binding mode. All other B · · ·Li distances fall
in the narrow range between 2.514(6) Å-2.579(6) Å, in accord
with bidentate coordination of the corresponding trihydridobo-
rate ligands. A closer inspection of the solid-state structure of
2(OEt2) reveals the following relationship with 2(OEt2)2: the
arrangement of the subunits Fe(1)/B(1), Li(2), Fe(1A)/B(1A),
and Li(2A) in 2(OEt2) closely resembles the dimeric aggregates
of 2(OEt2)2. As a substitute for the missing OEt2 ligand,
[FcB(2)H3]- binds to Li(2); the associated Li(1)+ ion adopts a
bridging position between B(1) and B(2). We note a further
short contact between Li(1) and the ipso carbon atom of the
Fe(1) ferrocene molecule (Li(1)-C(11) ) 2.453(5) Å), which
points toward a weak cyclopentadienyl-Li+ π-interaction.31,32
The crystal lattice of 4(OEt2)2.67 consists of two different
kinds of dimeric entities: dimer(1) contains 5 OEt2 ligands and
possesses C1 symmetry (Figure 3 top; OEt2 ligands not shown),
whereas the centrosymmetric dimer(2) has 6 OEt2 ligands
coordinated to its Li+ cations (Figure 3 bottom; OEt2 ligands
not shown; cf. Figure 3S in Supporting Information for a
complete plot of 4(OEt2)2.67).
The peripheral alkali metal atoms, Li(1) and Li(2), of dimer(1)
are located at bridging positions between the two [fc(BH3)2]2-
units. Each of these Li+ ions coordinates to both its hydridobo-
rate ligands in an η2-mode (range of B · · ·Li distances ) 2.48(1)
Å-2.61(1) Å) and, in addition, bears two OEt2 donors. In
contrast, the internal Li(4)+ ion is devoid of OEt2 ligands but
establishes close contacts to all four hydridoborate substituents
of the dimer.
Judging by the corresponding B · · ·Li distances, both B(3)H3
(2.44(1) Å) and B(4)H3 (2.43(1) Å) fragments act as bidentate
ligands, while B(1)H3 (2.67(1) Å) and B(2)H3 (2.68(1) Å) are
approaching monodentate binding modes. A highly unusual
coordination environment is observed for Li(3): apart from
binding one OEt2 ligand, it interacts with B(1)H3 (2.52(1) Å)
and B(2)H3 (2.515(9) Å) and apparently also with the Fe(1)
atom (Fe(1) · · ·Li(3) 2.653(9) Å). For geometric reasons, the
denticity of B(1)H3 and B(2)H3 cannot exceed the number of
1, even though the short B · · ·Li distances would suggest an
η2-mode. Comparably short Fe · · ·Li distances as in dimer(1)
have previously been observed for the lithium salt of a
[1.1]diborataferrocenophane, which contains one Li+ ion at the
center of its macrocyclic structure (in this case, the Fe· · ·Li
distances amount to 2.706(5) and 2.720(6) Å).33-35
Figure 3. Molecular structure of 4(OEt2)2.67 in the solid state; hydrogen
atoms attached to carbon and Li+-coordinated OEt2 molecules have been
omitted for clarity. (Top) dimer(1); (bottom) dimer(2). Selected bond lengths
(Å) and atom· · ·atom distances (Å): Dimer(1) B(1)-C(11) 1.586(8),
B(2)-C(21) 1.584(8), B(3)-C(31) 1.556(8), B(4)-C(41) 1.579(8),
B(1)· · ·Li(1) 2.61(1), B(1)· · ·Li(3) 2.52(1), B(1)· · ·Li(4) 2.67(1), B(2)· · ·Li(2)
2.58(1), B(2) · · ·Li(3) 2.515(9), B(2) · · ·Li(4) 2.68(1), B(3) · · ·Li(1) 2.54(1),
B(3) · · ·Li(4) 2.44(1), B(4) · · ·Li(2) 2.48(1), B(4) · · ·Li(4) 2.43(1), Fe(1) · · ·Li(3)
2.653(9); Dimer(2) B(5)-C(51) 1.579(7), B(6)-C(61) 1.594(7), B(5) · · ·Li(5)
2.516(9), B(5)· · ·Li(5A) 2.59(1), B(5) · · ·Li(6) 2.77(1), B(6) · · ·Li(5) 2.51(1),
B(6)· · ·Li(6A) 2.41(1).
Dimer(2) of 4(OEt2)2.67 possesses a centrosymmetric struc-
ture. Similar to dimer(1), we find two peripheral (Li(6), Li(6A);
two OEt2 ligands) and two internal (Li(5), Li(5A); one OEt2
ligand) Li+ ions. In contrast to dimer(1), each Li+ ion contributes
to connecting two [fc(BH3)2]2- moieties. Almost all BH3-Li
interactions in dimer(2) are mediated through bidentate bonding
modes; the only exception is B(5)H3-Li(6) [B(5A)H3-Li(6A)],
which is better described as an η1-coordination (2.77(1) Å).
Moreover, it is worth mentioning that the solid-state structure
of dimer(2) is strikingly similar to the structure of 1,1′-
(34) Rodr´ıguez-Otero, J.; Cabaleiro-Lago, E. M.; Pen˜a-Gallego, A.;
Montero-Campillo, M. M. Tetrahedron 2009, 65, 2368–2371.
(35) The interaction of ferrocene with Li+ in the gas phase has been studied
theoretically: Irigoras, A; Mercero, J. M.; Silanes, I.; Ugalde, J. M.
J. Am. Chem. Soc. 2001, 123, 5040–5043. Two minima have been
located on the energy surface. In the lower energy structure, the lithium
cation is η5-coordinated on top of one of the cyclopentadienyl rings
(cf. Li(1) in 2(OEt2)). The second minimum structure has the Li+ ion
bonded laterally to the iron atom (Fe · · ·Li ) 2.4 Å), which is
reminiscent of the situation in dimer(1). Selected related structures of
ferrocenyl-Li+ complexes exhibiting short Fe · · ·Li contacts or fer-
rocene-Li+ π-contacts are described in the following references:(a)
Walczak, M.; Walczak, K.; Mink, R.; Rausch, M. D.; Stucky, G. J. Am.
Chem. Soc. 1978, 100, 6382–6388. (b) Butler, I. R.; Cullen, W. R.;
Reglinski, J.; Rettig, S. J. J. Organomet. Chem. 1983, 249, 183–194.
(c) Sa¨nger, I; Heilmann, J. B.; Bolte, M; Lerner, H.-W.; Wagner, M.
Chem. Commun. 2006, 2027–2029. (d) Kaufmann, L.; Vitze, H.; Bolte,
M.; Lerner, H.-W.; Wagner, M. Organometallics 2007, 26, 1771–
1776.
(31) Haghiri Ilkhechi, A.; Scheibitz, M.; Bolte, M.; Lerner, H.-W.; Wagner,
M. Polyhedron 2004, 23, 2597–2604.
(32) Haghiri Ilkhechi, A.; Mercero, J. M.; Silanes, I.; Bolte, M.; Scheibitz,
M.; Lerner, H.-W.; Ugalde, J. M.; Wagner, M. J. Am. Chem. Soc.
2005, 127, 10656–10666.
(33) Scheibitz, M.; Winter, R. F.; Bolte, M.; Lerner, H.-W.; Wagner, M.
Angew. Chem., Int. Ed. 2003, 42, 924–927.
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Ferrocenylhydridoborates
A R T I C L E S
Figure 4. Molecular structure of 6(NMe2Et)2 in the solid state (50%
probability ellipsoids). Selected bond lengths (Å), bond angles (deg), and
torsion angles (deg): B(1)-N(1) 1.668(12), B(1)-C(11) 1.621(13);
N(1)-B(1)-C(11) 111.1(6); N(1)-B(1)-C(11)-C(12) -91.6(10).
Figure 5. Superposition of the molecular structures of the two crystallo-
graphically independent molecules of 5(SMe2); hydrogen atoms attached
to carbon have been omitted for clarity. Selected bond lengths (Å), bond
angles (deg), and torsion angles (deg): 5(SMe2)A B(1)-S(1) 1.991(11),
B(1)-C(11) 1.600(16); S(1)-B(1)-C(11) 107.6(7); S(1)-B(1)-C(11)-C(12)
94.0(12), C(1)-S(1)-B(1)-C(11) 177.7(6), C(2)-S(1)-B(1)-C(11) 73.8(6);
5(SMe2)BB(1A)-S(1A)1.953(11),B(1A)-C(11A)1.560(18);S(1A)-B(1A)-C(11A)
105.7(6);S(1A)-B(1A)-C(11A)-C(12A)91.7(11),C(1A)-S(1A)-B(1A)-C(11A)
-74.8(7), C(2A)-S(1A)-B(1A)-C(11A) -176.8(7).
dilithioferrocene when crystallized from THF (i.e.,
Li4(thf)6[fc2]).36
All [fc(BH3)2]2- ligands in dimer(1) and dimer(2) adopt
eclipsed conformations with both BH3 substituents pointing into
the same direction (range of B-COG-COG′-B′ angles )
4.2-15.9°; COG/COG′ ) centroids of the two cyclopentadienyl
rings of Fe(C5H4)2). The alternative anti conformation with
B-COG-COG′-B′ angles of around 180°, which would
ultimately lead to coordination polymers, is apparently energeti-
cally less favorable than the dimeric arrangement with its high
charge concentration.
N(1)-B(1)-C(11)-C(12) ) -91.6(10)). The B(1)-N(1) )
1.668(12) Å bond length is virtually the same as in the
monotopic congener 5(NMe2Et) (1.655(7) Å23).
Competition of Condensation and Adduct Formation. We
next studied the formation of borane adducts from the hydri-
doborate species. Abstraction of one hydride ion from 2 by
means of Me3SiCl (which is in turn transformed into Me3SiH)
generates the free ferrocenylborane FcBH2, which spontaneously
undergoes condensation to form Fc2BH (cf. 10, Scheme 5) and
B2H6.23 If, however, hydride elimination is carried out in the
presence of NMe2Et, FcBH2 can be trapped as the B-N adduct
FcBH2(NMe2Et), 5(NMe2Et).23 Using a similar procedure, the
corresponding bis-adduct 6(NMe2Et)2 was obtained from
4(OEt2)2.67 and excess Me3SiCl in OEt2/NMe2Et (Scheme 2).
X-ray quality crystals of 6(NMe2Et)2 were grown from a
saturated solution in heptane/toluene (1:1) at -30 °C; details
of the X-ray crystal structure analysis are provided in Table 2S
in Supporting Information. Compound 6(NMe2Et)2 represents
one of very few structurally characterized ditopic organo-
boranes.20,37-40 The most closely related other example is the
diborylmethane-TMEDA adduct Me3SiC(H)(BH2)2(NMe2CH2-
CH2NMe2), which forms an unusual seven-membered hetero-
cycle.40 The molecular structure of 6(NMe2Et)2 is centrosym-
metric with the borane substituents pointing into opposite
directions (Figure 4). The B-N vectors are almost perpendicular
to the planes of the cyclopentadienyl rings (torsion angle
To explore whether the weaker B-S adducts FcBH2(SMe2)
and (Me2S)H2B-fc-BH2(SMe2) could also be isolated, we treated
2(OEt2) and 4(OEt2)2.67 with excess Me3SiCl in dry SMe2 as
the solvent. We were indeed able to synthesize and fully
characterize the target compounds 5(SMe2) and 6(SMe2)2
(Scheme 2). The 11B NMR spectrum (SMe2-d6) of the ferroce-
nylborane-SMe2 adduct 5(SMe2) is characterized by a triplet at
-10.1 ppm (1JBH ) 101.5 Hz). The corresponding signal of
6(SMe2)2 (δ(11B) ) -7.8) possesses a width at half height of
h1/2 ) 300 Hz; 11B-1H coupling is not resolved. The 11B NMR
resonances for both SMe2 adducts appear at somewhat higher
field compared to the amine adducts (5(NMe2Et), -3.4 ppm
(tr, JBH ) 92.3 Hz);23 6(NMe2Et)2, -2.8 ppm (nr, h1/2 ) 290
1
Hz); C6D6). All 1H and 13C{1H}NMR data of 5(SMe2),
6(SMe2)2, and 6(NMe2Et)2 are fully in accord with the proposed
structures and therefore do not merit further discussion.
5(SMe2) crystallizes from SMe2 with two crystallographically
independent molecules in the asymmetric unit (5(SMe2)A,
5(SMe2)B; see Table 2S in Supporting Information for details
of the X-ray crystal structure). The major difference between
5(SMe2)A and 5(SMe2)B lies in the orientation of the two methyl
groups relative to the ferrocenyl fragment (cf. Figure 5 for a
superposition of 5(SMe2)A and 5(SMe2)B; an ORTEP plot of
5(SMe2)A is shown in Figure 4S in Supporting Information).
To a first approximation, 5(SMe2)A and 5(SMe2)B are mirror
images of each other. Upon detailed examination, however, it
becomes evident that the conformations of the two ferrocenyl
substituents are different, namely, eclipsed in 5(SMe2)A, but
staggered in 5(SMe2)B. The B-S bond lengths of 5(SMe2)
amount to 1.991(11) and 1.953(11) Å. The only other structur-
(36) Sa´nchez Perucha, A.; Heilmann-Brohl, J.; Bolte, M.; Lerner, H.-W.;
Wagner, M. Organometallics 2008, 27, 6170–6177.
(37) Yalpani, M.; Boese, R.; Ko¨ster, R. Chem. Ber. 1987, 120, 607–610.
(38) Baker, R. T.; Ovenall, D. W.; Harlow, R. L.; Westcott, S. A.; Taylor,
N. J.; Marder, T. B. Organometallics 1990, 9, 3028–3030.
(39) Paetzold, P.; Englert, U.; Finger, R.; Schmitz, T.; Tapper, A.;
Ziembinski, R. Z. Anorg. Allg. Chem. 2004, 630, 508–518.
(40) Zheng, C.; Hosmane, N. S. Acta Crystallogr. 1999, C55, 2107–2109.
9
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A R T I C L E S
Scheibitz et al.
Scheme 3. Preparation of Cyclohexyldi(ferrocenyl)borane 7 and
Tricyclohexylborane 8 by Reaction of the Ferrocenylhydridoborate
2 with Me3SiCl in the Presence of Cyclohexenea
NMR studies of 6(NMe2Et)2 in C6D6 solution did not show any
indication of polymerization of the ditopic borane at room
temperature (rt). We then studied the possible thermal polym-
erization in the solid state by thermogravimetric analysis. A
multistep profile was observed (cf. Figure 7S in Supporting
Information); the first step with an onset at ca. 125 °C leads to
ca. 7% weight loss, followed by a distinct second step with ca.
30% further weight loss occurring over the temperature range
from 130 to 300 °C. These two processes likely correspond to
loss of the amine ligands and possibly formation of a polymeric
species similar to 9 with concomitant liberation of borane.
Above 300 °C, slow further degradation is observed with the
residual weight at 800 °C amounting to ca. 25% of the initial
sample weight. The latter observation would be consistent with
formation of a ceramic material from a polymeric species.43
However, although the results indicate that a polymeric species
may be formed upon thermolysis of 6(NMe2Et)2, we reasoned
that use of a weaker donor should promote the polymerization
process and ultimately allow for rt polymerization to occur.
Indeed, we found that both 5(SMe2) and 6(SMe2)2 slowly
undergo condensation even in SMe2 solutions. On a preparative
scale, we treated the precursor 4 in SMe2 with Me3SiCl, thereby
generating the diadduct 6(SMe2)2 as described above, which
was expected to polymerize slowly and in a very controlled
manner. After a reaction time of 7 d (the reaction rate can be
increased by diluting the SMe2 with CH2Cl2), the mixture was
worked up, the crude product was reprecipitated from CH2Cl2
into hexane, and dried under reduced pressure. The polymeric
borane 9 was obtained as a pale red, air-sensitive powdery solid.
However, based on its 1H NMR data, the product was
contaminated with small quantities of BH3(SMe2), which were
surprisingly difficult to remove completely. However, we found
that 9 could be easily prepared by treatment of 4 with Me3SiCl
in OEt2 and simple evaporation of the mixture to dryness after
completion of the condensation. All further studies (vide infra)
were carried out on samples synthesized via this reaction
protocol.
a Reagents and conditions: (i) excess Me3SiCl/excess C6H10, OEt2, -78
°C f rt.
Scheme 4. Synthesis of Boron-Bridged Polyferrocene 9a
a Reagents and conditions: (i) excess Me3SiCl, Me2S, -78 °C f rt.
ally characterized SMe2 adduct of a monoorganylborane is the
dimeric species (MeSCH2BH2)2.41 This six-membered hetero-
cycle possesses B-S bond lengths of 1.951(2) Å, which
compare nicely with the values determined for 5(SMe2).
When instead of SMe2, OEt2 was used as reaction solvent,
we were not able to isolate or even detect the respective adducts
FcBH2(OEt2) and (Et2O)H2B-fc-BH2(OEt2) but rather observed
spontaneous condensation to Fc2BH (10) and [-fcB(H)-]n (9;
vide infra).
Competition of Condensation and Hydroboration. The suc-
cessful isolation of compounds 5(Do) and 6(Do)2 clearly shows
that FcBH2 and H2B-fc-BH2 more readily undergo B-NMe2Et
and B-SMe2 (but not B-OEt2) adduct formation than condensa-
tion to Fc2BH (10) and [-fcB(H)-]n (9). This result immediately
raises the question whether FcBH2 could also be trapped by
hydroboration before substituent scrambling occurs. To answer
this question, we treated a solution of 2(OEt2) and 8 equiv of
cyclohexene in OEt2 with excess Me3SiCl (Scheme 3). After
workup, the hydroboration product (7) of Fc2BH was isolated
in almost 65% yield. The structure of 7 was confirmed by
multinuclear NMR (δ(11Β) ) 66.2) and single crystal X-ray
crystallography (Figure 5S in Supporting Information). We also
obtained crystals of B(Cy)3 (8; Cy ) cyclohexyl, Figure 6S in
Supporting Information), which apparently forms by reaction
of the second condensation product, B2H6, with cyclohexene.
On the other hand, there was no indication for the presence of
FcB(Cy)2, and we therefore conclude that the rate of condensa-
tion of FcBH2 to Fc2BH is much higher than that of hydrobo-
ration of an internal cis-olefin by FcBH2.42
Hydroboration
of
Diferrocenylborane
and
Poly-
(ferrocenylborane). To develop a clean, high-yielding reaction
protocol for transformation of the primary polymer 9 into more
stable and better soluble macromolecules, we first screened
several carbonyl compounds, alkenes, and alkynes in the
hydroboration reaction with the dinuclear model compound
Fc2BH (10; Scheme 5). Phenylacetylene and tert-butylacetylene
turned out to be the reagents of choice, because they gave the
corresponding di(ferrocenyl)vinylboranes 11Ph and 11tBu in
virtually quantitative yield (NMR spectroscopic control; cf.
1
Figure 8S in Supporting Information for a H NMR spectrum
recorded on the crude reaction mixture of 10 and tBuCCH).
Typical of triorganylboranes,44 the vinylboranes 11Ph and 11tBu
generate low-field signals at 56.7 ppm (11Ph) and 57.2 ppm
(11tBu) in their 11B{1H} NMR spectra. The chemical composition
of the molecules (i.e., ferrocenyl/vinyl ) 2:1) is confirmed by
3
the proton integral ratios of the organyl substituents. JHH
Condensation Polymerization. 6(NMe2Et)2 was first exam-
ined as a potential precursor for the formation of a ferroce-
nylborane polymer, [-fcB(H)-]n (9; Scheme 4), via condensation
polymerization. For this process to occur efficiently, the amine
donor needs to reversibly dissociate from the borane moieties.
coupling constants of about 18 Hz within the vinyl moieties of
11Ph and 11tBu point toward trans arrangements of the vinyl
protons, which is in line with the expected cis addition of
boranes to alkynes.
(43) Manners, I. Science 2001, 294, 1664–1666.
(41) No¨th, H.; Sedlak, D. Chem. Ber. 1983, 116, 1479–1486.
(42) Cyclohexene was used in this experiment to circumvent potential
regioselectivity issues. It should be noted, however, that the reactivity
of a terminal alkene can be higher than that of cyclohexene.
(44) No¨th, H.; Wrackmeyer, B. Nuclear magnetic resonance spectroscopy
of boron compounds. In NMR Basic Principles and Progress; Diehl,
P., Fluck, E., Kosfeld, R., Eds.; Springer: Berlin, Heidelberg, New
York, 1978.
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Ferrocenylhydridoborates
A R T I C L E S
Scheme 5. Hydroboration of PhCCH or tBuCCH with
Ferrocenylborane 10 and Polymer 9a
Figure 6. (a) MALDI-TOF mass spectrum of polymer 12Ph acquired in
(+) ion reflector mode. The different series are indicated as A, B, C, and
D; the numbers of the individual peaks correspond to the number of
repeating units. (b) Expansion of the mass range from 690 to 890 Da and
comparison of the peak patterns with those calculated assuming a 10000:1
resolving power.
a Reagents and conditions: (i) 11Ph, 1 equiv of PhCCH, toluene, rt; 11tBu
,
excess tBuCCH, hexane, 35 °C, ultrasonication. (ii) 12Ph, excess PhCCH,
toluene, 50 °C; 12tBu, excess tBuCCH, toluene, ultrasonication at rt and 50
°C.
NMR spectroscopic investigations into the stability of 11Ph
and 11tBu toward oxygen and moisture were carried out by
exposing C6D6 solutions of the compounds to air. Under these
conditions, only 5% of 11Ph was left after 4 h, whereas the
relative amount of 11tBu with respect to all decomposition
products was about 90% after 4 h and still 45% after 25 h,
suggesting that a reasonably stable polymeric derivative of 9
should be accessible by hydroboration with tert-butylacetylene.
We performed hydroborations with polymer 9, which was
generated in situ from 4, using both PhCCH and tBuCCH.
Suspensions of 9 were prepared in toluene, the respective alkyne
was added at rt, and the mixtures were heated to 50 °C
(application of ultrasound increases the reaction rate). The
products were obtained as reddish solids upon evaporation of
the solvents, washed with hexanes and reprecipitated from
CH2Cl2 (12Ph) or toluene (12tBu) into hexane. Successful
hydroboration was confirmed by IR and NMR spectroscopy.
The individual NMR assignments were established by
comparison of the data for the polymers with those of the model
systems 11Ph and 11tBu, for which C,H-COSY was used to
unequivocally assign all resonances. Polymers 12Ph and 12tBu
show broad signals attributable to the 1,1′-ferrocenylene moieties
(ca. 4.2-4.7 ppm) as well as the phenyl (12Ph, 6.9-7.6 ppm)
and tert-butyl groups (12tBu, 0.9-1.1 ppm). Most importantly,
a new set of vinyl resonances was observed at 6.2, 6.6 ppm for
12tBu, in the same region as for the model compound 11tBu (6.32,
6.70 ppm). For polymer 12Ph, the vinyl protons overlap with
the aromatic protons in the region from 6.9-7.6 ppm, as is the
case for dimer 11Ph (7.24, 7.53 ppm). The generation of olefinic
groups at the polymer side chains was further confirmed by the
presence of intense CdC stretching bands at 1611 cm-1 (12Ph)
and 1623 cm-1 (12tBu), which lie in the typical range of
alkenylboranes45 (cf. 11Ph, 1608 cm-1; 11tBu, 1604 cm-1).
Polymer Characterization. Our attempts at determining the
molecular weight of the polymers by gel permeation chroma-
tography (GPC) analysis in THF did not provide any tangible
results, presumably due to the sensitivity of 12Ph and 12tBu
toward air and moisture. The polymers were then subjected to
dynamic light scattering in toluene solution under a nitrogen
atmosphere. However, the scattering intensity was too weak to
determine a reliable average hydrodynamic radius (Rh), which
suggests that the polymer chain lengths are relatively short and
the number average molecular weight (Mn) is e5000.46 This
result is consistent with prior studies on the related polymer
[-fcB(Mes)-]n, which was shown by GPC with in-line multiangle
laser light scattering detection (GPC-MALLS) to have a Mn of
5160.22
To confirm the polymer structure and to examine the polymer
end groups, we studied both polymers 12Ph and 12tBu by high
resolution MALDI-TOF mass spectrometry in (+) ion reflector
mode. The spectrum of 12Ph shows a complex pattern with
multiple series of peaks (Figure 6).
Importantly, for each of the independent series in 12Ph the
mass difference between peaks correlates well with that expected
for the repeating unit of [fcB(CHdCHPh)] (C18H15B1Fe1, 298
Da). The same is true for the spectrum of 12tBu (cf. Figure 9S
in Supporting Information), in which the peak separation
corresponds to the expected repeating unit of [fcB(CHdCHtBu)]
(C16H19B1Fe1, 278 Da). In the following, the different peak series
are discussed in more detail for the Ph derivative 12Ph; very
similar results were also obtained for 12tBu
.
Most of the major peak series can be assigned with confidence
by comparison of the individual peak patterns with those
calculated assuming a 10 000:1 resolving power. We find that
the series labeled as A2-A6 in Figure 6 with peak maxima of
712.33, 1010.44, 1307.55, 1606.66, and 1903.78 fits reasonably
welltopolymersoftheformula{(PhCHdCH)HB-[fcB(CHdCHPh)]n-
H}+ (n)2-6),thussuggestingthepresenceof[BH(CHdCHPh)]
(46) Berenbaum, A.; Braunschweig, H.; Dirk, R.; Englert, U.; Green, J. C.;
Ja¨kle, F.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2000, 122,
5765–5774.
(45) Zweifel, G.; Clark, G. M.; Leung, T.; Whitney, C. C. J. Organomet.
Chem. 1976, 117, 303–312.
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J. AM. CHEM. SOC. VOL. 131, NO. 44, 2009 16325

A R T I C L E S
Scheibitz et al.
Figure 7. Thermogravimetric analysis plots of 12Ph and 12tBu
.
moieties at both chain ends. Series B2-B4 with peak maxima
at 814.39, 1112.50, and 1410.62 closely matches the peak
positions expected for polymers in which one of the chain ends
underwent a second hydroboration reaction, i.e., {(PhCHdCH)2B-
[fcB(CHdCHPh)]n-H}+ (n ) 2-4). The third series that is
labeled as C4-C8 with peak maxima at 1206.49, 1503.60,
1801.71, 2099.82, and 2397.89 is likely also related to series A
(n ) 4-8), but one of the boron centers along the polymer
chain has not undergone hydroboration, i.e. an additional BH
functionality remains. Finally, the peaks labeled as D3 (895.36)
and D4 (1194.46) are tentatively attributed to polymers in which
there is a monoborylated ferrocenyl moiety (C10H9Fe) at one
chain end, while the other chain end features a [BH(CHdCHPh)]
group, i.e., {H-[fcB(CHdCHPh)]n-H}+.
The thermal stability of polymers 12Ph and 12tBu was
examined by thermogravimetric analysis (Figure 7). The onset
of degradation of polymer [-fcB(CHdCHPh)-]n (12Ph) was
determined by TGA under nitrogen to be ca. 185 °C (5% weight
loss). A multistep degradation process was observed over the
temperature range from 160 to 550 °C and the residual weight
at 800 °C was 18%. A similar profile was also observed for
[-fcB(CHdCHtBu)-]n (12tBu) with an onset of degradation of
160 °C (5% weight loss) and a residual weight of 28% at 800
°C. The thermal stability of both polymers is somewhat lower
than that of the mesityl-substituted derivative [-fcB(Mes)-]n,
which showed a single-step weight loss of 72%, with an
inflection point at 403 °C, and gave a brown ceramic material
in 28% yield.22 The different behavior may be related to the
higher stability of mesitylboranes in comparison to vinylborane
derivatives.47
Electronic Structure of Polymers and Model Systems. One
of the key questions with regard to the electronic properties of
polymers derived from 9 is whether a conformation is possible
that allows for efficient π-conjugation of the ferrocenes via the
empty p-orbital of the boron bridge. In this context, the model
compounds 11Ph and 11tBu were further investigated by X-ray
crystallography. Details of the X-ray crystal structure analyses
of 11Ph and 11tBu are included into Table 3S in Supporting
Information, and the structure plots are displayed in Figure 8.
Both molecules contain a trigonal-planar boron center and the
two ferrocenyl substituents adopt an anti conformation with
respect to the C(1)B(1)C(11)C(31) plane. Most importantly, an
inspection of the dihedral angles between the C5H4 rings and
the C(1)B(1)C(11)C(31) plane reveals values of 12.3°/21.1° for
11Ph and of about 17° for 11tBu, which is an ideal precondition
for substantial π-electron delocalization. Interestingly, the related
dihedral angle spanned by the plane of the olefinic double bond
Figure 8. Molecular structures of 11Ph (top) and 11tBu (bottom) in the solid
state (30% and 50% probability ellipsoids, respectively). Selected bond
lengths (Å), bond angles (deg), torsion angles (deg), and dihedral angles
(deg) for 11Ph: B(1)-C(1) 1.575(9), B(1)-C(11) 1.551(7), B(1)-C(31)
1.552(6),C(1)-C(2)1.340(17);C(1)-B(1)-C(11)111.5(4),C(1)-B(1)-C(31)
122.4(4),C(11)-B(1)-C(31)126.0(4),B(1)-C(1)-C(2)124.3(9),C(1)-C(2)-C(3)
124.2(9); C(2)-C(1)-B(1)-C(11) -123.1(6), C(2)-C(1)-B(1)-C(31)
60.8(7); B(1)C(1)C(2)//C(1)B(1)C(11)C(31) 58.7, C(11) to C(15) ring//
C(1)B(1)C(11)C(31) 21.1, C(31) to C(35) ring//C(1)B(1)C(11)C(31) 12.3.
For 11tBu: B(1)-C(1) 1.576(2), B(1)-C(11) 1.562(2), B(1)-C(31) 1.562(2),
C(1)-C(2) 1.340(2); C(1)-B(1)-C(11) 120.8(1), C(1)-B(1)-C(31) 116.4(1),
C(11)-B(1)-C(31) 122.9(1), B(1)-C(1)-C(2) 126.0(2), C(1)-C(2)-C(3)
129.2(2); C(2)-C(1)-B(1)-C(11) -33.8(2), C(2)-C(1)-B(1)-C(31)
148.2(2); B(1)C(1)C(2)//C(1)B(1)C(11)C(31) 32.7, C(11) to C(15) ring//
C(1)B(1)C(11)C(31) 17.2, C(31) to C(35) ring//C(1)B(1)C(11)C(31) 17.1.
(i.e., B(1)C(1)C(2)) and C(1)B(1)C(11)C(31) is only 32.7° for
11tBu (58.7° for 11Ph), most likely in order to minimize
unfavorable steric interactions.
Consistent with these findings, the longest wavelength
absorption maxima in the UV-vis spectra in toluene show
distinct bathochromic shifts for the polymers (12Ph, λmax ) 495
nm; 12tBu, λmax ) 482 nm) in comparison to the dimeric model
systems (11Ph, λmax ) 484 nm; 11tBu, λmax ) 472 nm),
accompanied by distinct tailing to longer wavelengths (cf.
Figure 10S in Supporting Information).
Conclusion
This paper reports on the first examples of mono- and ditopic
trihydridoborates and -boranes with organometallic substituents,
i.e., Li[FcBH3] (2; Fc ) ferrocenyl), Li2[H3B-fc-BH3] (4; fc )
(47) Entwistle, C. D.; Marder, T. B. Angew. Chem., Int. Ed. 2002, 41, 2927–
2931.
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Ferrocenylhydridoborates
A R T I C L E S
1,1′-ferrocenylene), FcBH2 (5), and H2B-fc-BH2 (6). The
hydridoborate salts 2 and 4 not only serve as precursors for 5
and 6 but also are potentially useful ligands for the generation
of inorganic/organometallic hybrid compounds. Especially the
ditopic species [H3B-fc-BH3]2- holds great promise in this
respect, because its anionic groups are connected by a flexible
ferrocenylene hinge that allows an anti conformation of the
donor sites, which should lead to coordination polymers, as well
as a syn conformation, which should lead to metalla-macro-
cycles. A crystal structure analysis of the ether solvate of the
lithium salt 4 revealed several structural peculiarities: (i)
macrocyclic dimers are formed, in which four Li+ ions and two
iron atoms are brought into close proximity; (ii) some of the
Li+ ions adopt bridging positions between the two [Cp-BH3]-
ligands of the same Fe(II) center, which is reminiscent of an
ansa-ferrocene motif; and (iii) the solid-state structure of 4 is
strikingly similar to the structure of the THF-solvate of 1,1′-
dilithioferrocene.36
The ferrocenylboranes FcBH2 (5) and H2B-fc-BH2 (6) can
be isolated and fully characterized only as donor adducts
FcBH2(Do) (5(Do)) and (Do)H2B-fc-BH2(Do) (6(Do)2; Do )
NMe2Et, SMe2). In the absence of suitable Lewis bases, 5 and
6 tend to undergo a condensation reaction leading to Fc2BH
(10) and the polymer [-fcB(H)-]n (9), respectively, with con-
comitant liberation of B2H6. This condensation is much faster
than the hydroboration of internal olefins as demonstrated in a
competition experiment, in which FcBH2 (5) was generated in
the presence of excess cyclohexene. In this experiment, Fc2BCy
was formed as the major ferrocene-containing product (con-
densation pathway, 2 FcBH2 + excess cyclohexene f Fc2BCy
+ BCy3, as opposed to hydroboration pathway, FcBH2 + excess
cyclohexene f FcBCy2).
to apply this new method also to the development of other
organic and organometallic polymeric materials.
Experimental Methods
General Remarks. All reactions were carried out under a
nitrogen atmosphere using Schlenk tube techniques. Reaction
solvents were either freshly distilled under argon from Na/Pb alloy
(alkanes) and Na/benzophenone (toluene, C6D6, OEt2, THF-d8) or
dried over molecular sieves (4 Å; CH3CN, CDCl3, CH2Cl2, SMe2,
SMe2-d6) prior to use. NMR: Bruker AM 250, Avance 300, Avance
400, and Varian 500. Chemical shifts are referenced to residual
solvent signals (1H, 13C{1H}) or external BF3 ·OEt2 (11B{1H}).
Abbreviations: s ) singlet, d ) doublet, tr ) triplet, vtr ) virtual
triplet, q ) quartet, m ) multiplet, br ) broad, no ) signal not
observed, nr ) signal not resolved, Ph ) phenyl. FcB(OMe)2 (1),25
fc(B(OMe)2)2 (3),25 and Fc2BH (10)23 were synthesized following
literature procedures.
Synthesis of Li[FcBH3] (2). A solution of Li[AlH4] in OEt2 (1
M; 10.6 mL, 10.6 mmol) was added dropwise with stirring at -78
°C to a solution of 1 (2.72 g, 10.55 mmol) in OEt2 (20 mL). After
30 min, the mixture was allowed to warm to rt and stirred for 1 h.
The insolubles were collected on a frit (G4) and washed with OEt2
(3 × 10 mL). The volume of the filtrate was slowly reduced under
vacuum, whereupon large yellow crystals of Li(OEt2)2[FcBH3]
(2(OEt2)2) formed, which were suitable for X-ray crystallography.
Crystals of the monoether adduct Li(OEt2)[FcBH3] (2(OEt2)) were
grown from a saturated solution of 2(OEt2)2 in pentane at -30 °C.
1
Yield of 2(OEt2)2: 2.83 g (76%). H NMR (400.1 MHz, THF-d8,
300 K): δ 0.86 (q, 1JBH ) 77.1 Hz, 3H; BH3), 3.75 (nr, 4H; C5H4),
3.81 (s, 5H; C5H5). 13C{1H} NMR (62.9 MHz, THF-d8, 300 K): δ
67.2 (q, JCB ) 2.9 Hz; C5H4), 68.3 (C5H5), 75.1 (q, JCB ) 3.4 Hz;
C5H4), 92.4 (q, 1JCB ) 59.4 Hz; CB). 11B NMR (128.4 MHz, THF-
d8, 300 K): δ -30.6 (q, 1JBH ) 77.1 Hz). Elemental analysis calcd
(%) for C18H32BFeLiO2 (354.04): C 61.07, H 9.11. Found: C 60.51;
H 8.98.
The novel polymer [-fcB(H)-]n (9), which is obtained upon
spontaneous condensation of 6, is interesting in its own right,
as it represents a rare example of a polymeric material with
multiple reactive borane groups.48 We exploited the ability of
these borane functionalities to undergo hydroboration reactions
for the preparation of new boron-bridged polyferrocenes. Indeed,
treatment of 9 with the alkynes PhCCH and tBuCCH leads to
smooth conversion to vinylborane polymers [-fcB(CHdCHR)]n
(12Ph, R ) Ph; 12tBu, R ) tBu). The polymer structures were
confirmed by NMR and IR spectroscopy, as well as MALDI-
TOF mass spectrometry. Interestingly, extended delocalization
via the boron empty p-orbitals is suggested by distinctly red-
shifted absorption maxima in the UV-vis spectra of the
polymers compared to the dinuclear model compounds
Fc2B(CHdCHR) (11Ph, R ) Ph; 11tBu, R ) tBu). Favorable
electronic delocalization is also consistent with the structural
features deduced from the X-ray structure of the dimeric species
11Ph and 11tBu, in which the C5H4 rings are almost coplanar to
the planes defined by the boron atom and the attached carbon
substituents.
Synthesis of Li2[fc(BH3)2] (4). A solution of Li[AlH4] in OEt2
(1 M; 11.0 mL, 11.0 mmol) was added dropwise with stirring at
-78 °C to a solution of 3 (1.81 g, 5.49 mmol) in OEt2 (20 mL).
After 30 min, the mixture was allowed to warm to rt and stirred
for 1 h. The insolubles were collected on a frit (G4) and washed
with OEt2 (4 × 15 mL). The volume of the filtrate was slowly
reduced under vacuum, whereupon large yellow crystals of
Li2(OEt2)2.67[fc(BH3)2] (4(OEt2)2.67) formed, which were suitable
1
for X-ray crystallography. Yield of 4(OEt2)2.67: 1.70 g (73%). H
1
NMR (400.1 MHz, THF-d8, 300 K): δ 0.75 (q, JBH ) 79.2 Hz,
6H; BH3), 3.51, 3.75 (2 × nr, 2 × 4H; C5H4). 13C{1H} NMR (62.9
1
MHz, THF-d8, 303 K): δ 68.0, 74.4 (C5H4), 87.8 (q, JCB ) 54.3
Hz; CB). 11B NMR (128.4 MHz, THF-d8, 300 K): δ -33.7 (q,
1JBH
)
79.2 Hz). Elemental analysis calcd (%) for
C
41.33H81.33B4Fe2Li4O5.33 (846.43): C 58.65, H 9.68. Found: C 58.18;
H 9.50.
Synthesis of FcBH2(SMe2) (5(SMe2)). Me3SiCl (0.50 mL,
0.43 g, 3.95 mmol) in SMe2 (5 mL) was added dropwise with
stirring at -78 °C to a solution of 2(OEt2) (0.190 g, 0.68 mmol)
in SMe2 (5 mL). After 30 min, the mixture was allowed to warm
to 0 °C, then stirred for 1 h, warmed to rt, and filtered over a frit
(G4). The volume of the filtrate was reduced to 2 mL, and the
remaining solution was stored at -30 °C for 3 d, whereupon
5(SMe2) crystallized in the form of long orange needles, which
were suitable for X-ray crystallography. Yield: 0.148 g (84%). 1H
NMR (250.1 MHz, SMe2-d6, 297 K): δ 2.05 (s, 6H; CH3), 2.60
(br, 2H; BH2), 3.93 (nr, 2H; C5H4), 3.99 (s, 5H; C5H5), 4.07 (nr,
2H; C5H4). 13C{1H} NMR (62.9 MHz, SMe2-d6, 297 K): δ 18.0
(CH3), 68.2 (C5H5), 69.7, 75.4 (C5H4), no (CB). 11B NMR (128.4
With this work we have established a viable pathway to
electronically interesting boron-containing metallopolymers,
which complements the ring-opening polymerization of boron-
bridged ferrocenophanes46,49 and the condensation polymeri-
zation of fc(BBr2)2 with HSiEt3.22 The primary polymer obtained
in our new approach, i.e., [-fcB(H)-]n, can be functionalized by
a broad variety of derivatization reactions. Work is in progress
1
MHz, SMe2-d6, 297 K): δ -10.1 (tr, JBH ) 101.5 Hz).
Synthesis of fc(BH2(SMe2))2 (6(SMe2)2). Me3SiCl (0.50 mL,
0.43 g, 3.95 mmol) in SMe2 (5 mL) was added dropwise with
stirring at -78 °C to a solution of 4(OEt2)2.67 (0.265 g, 0.63 mmol)
in SMe2 (10 mL). After 30 min, the mixture was allowed to warm
(48) Doshi, A.; Ja¨kle, F. Main Group Chem. 2006, 5, 309–318.
(49) Braunschweig, H.; Dirk, R.; Mu¨ller, M.; Nguyen, P.; Resendes, R.;
Gates, D. P.; Manners, I. Angew. Chem., Int. Ed. Engl. 1997, 36, 2338–
2340.
9
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A R T I C L E S
Scheibitz et al.
to 0 °C, then stirred for 1 h, warmed to rt, and filtered over a frit
(G4). The volume of the filtrate was reduced to 3 mL, and the
remaining solution was stored at -30 °C for 3 d, whereupon
6(SMe2)2 precipitated as yellow microcrystalline solid. Yield: 0.191
g (91%). 1H NMR (250.1 MHz, SMe2-d6, 297 K): δ 2.05 (s, 12H;
CH3), 2.54 (br, 4H; BH2), 3.80, 3.96 (2 × nr, 2 × 4H; C5H4).
13C{1H} NMR (62.9 MHz, SMe2-d6, 297 K): δ 18.0 (CH3), 70.2,
75.4 (C5H4), no (CB). 11B NMR (128.4 MHz, SMe2-d6, 297 K): δ
-7.8 (nr, h1/2 ) 300 Hz).
Synthesis of Fc2B(CHdCHtBu) (11tBu). Neat tBuCCH (0.25
mL, 0.17 g, 2.05 mmol) was added via syringe to a stirred
suspension of 10 (0.310 g, 0.81 mmol) in hexane (40 mL). After
the mixture had been heated to 35 °C in an ultrasonic bath for 3 h,
all volatiles were removed under vacuum. Recrystallization of the
crude material from hot H3CCN (7.5 mL) gave red X-ray quality
1
crystals of 11tBu. Yield: 0.366 g (97%). H NMR (250.1 MHz,
CDCl3, 300 K): δ 1.17 (s, 9H; CH3), 4.06 (s, 10H; C5H5), 4.59 (nr,
8H; C5H4), 6.32, 6.70 (2 × d, 3JHH ) 18.1 Hz, 2 × 1H; C2H2). 1H
NMR (300.0 MHz, C6D6, 300 K): δ 1.16 (s, 9H; CH3), 4.00 (s,
10H; C5H5), 4.47, 4.66 (2 × vtr, 2 × 4H; C5H4), 6.54, 6.84 (2 ×
Synthesis of fc(BH2(NMe2Et))2 (6(NMe2Et)2). Me3SiCl (1.5 mL,
1.28 g, 11.74 mmol) in OEt2 (5 mL) was added dropwise with
stirring at -78 °C to a solution of 4(OEt2)2.67 (0.412 g, 0.97 mmol)
and NMe2Et (1.00 mL, 0.68 g, 9.30 mmol) in OEt2 (20 mL). After
30 min, the mixture was allowed to warm to 0 °C, then stirred for
1 h, warmed to rt, and filtered over a frit (G4). The volume of the
filtrate was reduced to 5 mL, and the remaining solution was stored
at -30 °C for 24 h, whereupon 6(NMe2Et)2 precipitated as yellow
microcrystalline solid. Yield: 0.318 g (92%). X-ray quality crystals
were grown from a saturated solution of 6(NMe2Et)2 in heptane/
3
d, JHH ) 18.1 Hz, 2 × 1H; C2H2). 13C{1H} NMR (75.5 MHz,
C6D6, 300 K): δ 29.6 (CH3), 35.1 (C(CH3)3), 69.4 (C5H5), 73.9,
76.7 (C5H4), 128.8, 159.7 (C2H2), no (CB). 11B NMR (96.3 MHz,
C6D6, 300 K): δ 57.2 (h1/2 ) 500 Hz). IR (cm-1): 1604 (CdC-
tBu). UV-vis (nm): λmax(0.1 mM, toluene) ) 359, 472. Elemental
analysis calcd (%) for C26H29BFe2 (464.00): C 67.30, H 6.30. Found:
C 67.16; H 6.35.
Synthesis of [-fcB(H)-]n (9). Me3SiCl (0.50 mL, 0.43 g, 3.95
mmol) in SMe2 (5 mL) was added dropwise with stirring at -78
°C to a solution of 4(OEt2)2.67 (0.239 g, 0.56 mmol) in SMe2 (10
mL). After 30 min, the mixture was allowed to warm to 0 °C, stirred
for 1 h at this temperature, warmed to rt, and then filtered over a
frit (G4). The filtrate was stirred for 7 d at rt, whereupon it adopted
a deep red color. The volatiles were driven off under reduced
pressure, CH2Cl2 (5 mL) was added to the solid residue, and small
quantities of insoluble material were removed by filtration. The
filtrate was added dropwise to hexane (10 mL), whereupon 9
precipitated as pale red solid that was collected on a frit and washed
with hexane (3 × 5 mL). The isolated product was dried under
1
toluene (1:1) at -30 °C. H NMR (250.1 MHz, C6D6, 300 K): δ
0.58 (tr, 3JHH ) 7.3 Hz, 6H; CH2CH3), 1.86 (s, 12H; NCH3), 2.31
3
(q, JHH ) 7.3 Hz, 4H; CH2CH3), 2.88 (very br, 4H; BH2), 4.41
(m, 8H; C5H4). 13C{1H} NMR (62.9 MHz, C6D6, 300 K): δ 8.2
(CH2CH3), 47.2 (NCH3), 55.7 (CH2CH3), 70.5, 76.8 (C5H4), no
(CB). 11B NMR (128.4 MHz, C6D6, 303 K): δ -2.8 (nr, h1/2
)
290 Hz). Elemental analysis calcd (%) for C18H34B2FeN2 (355.94):
C 60.74, H 9.63. Found: C 60.55; H 9.61.
Synthesis of Fc2BCy (7) and BCy3 (8). Me3SiCl (0.50 mL,
0.43 g, 3.95 mmol) in OEt2 (5 mL) was added dropwise with stirring
at -78 °C to a solution of 2(OEt2) (0.130 g, 0.46 mmol) and
cyclohexene (0.39 mL, 0.32 g, 3.90 mmol) in OEt2 (5 mL). The
mixture was allowed to warm to rt, stirred for 1 h, and filtered
over a frit (G4). The insolubles were washed with OEt2 (2 × 5
mL), and the combined organic phases evaporated to dryness under
vacuum. The solid residue was dissolved in a minimum amount of
warm heptane, and the solution was stored at -30 °C, whereupon
dark orange colored crystals of 7 precipitated during a time span
of 12 h. Yield of 7: 0.068 g (64%). Colorless needles of 8 were
obtained by storing the mother liquid at -30 °C for several days.
Analytical data of 7: 1H NMR (250.1 MHz, C6D6, 300 K): δ
1.22-2.11 (m, 11H; C6H11), 4.01 (s, 10H; C5H5), 4.43, 4.64 (2 ×
nr, 2 × 4H; C5H4). 13C{1H} NMR (62.9 MHz, C6D6, 300 K): δ
27.8, 29.0, 31.1 (C6H11), 69.0 (C5H5), 73.5, 76.8 (C5H4), no (CB).
11B NMR (128.4 MHz, C6D6, 300 K): δ 66.2 (h1/2 ) 390 Hz).
Elemental analysis calcd (%) for C26H29BFe2 (464.00): C 67.30, H
6.30. Found: C 67.00; H 6.18. Analytical data of 8: 1H NMR (250.1
MHz, C6D6, 300 K): δ 1.00-2.07 (m, 33H; C6H11). 13C{1H} NMR
1
vacuum overnight. Yield: 0.070 g (64%). H NMR (250.1 MHz,
CDCl3, 300 K): δ 4.0-4.2 (∼ 0.7H; chain termini, C5H5), 4.2-4.5,
4.5-4.7 (2 × very br, 2 × 4H; C5H4) 5.7 (very br, 1H; BH).
13C{1H} NMR (100.6 MHz, CDCl3, 300 K): δ 67.0-70.5 (very
br; chain termini, C5H5), 71.4-79.1 (very br; C5H4), no (CB). 11
B
NMR (128.4 MHz, CDCl3, 300 K): δ 51.6 (h1/2 ) 1200 Hz). IR
(cm-1): 2360, 2341 (B-H).
Synthesis of [-fcB(CHdCHPh)-]n (12tPh). Neat Me3SiCl (1.30
mL, 1.11 g, 10.22 mmol) was added via syringe at -78 °C to a
stirred solution of 4(OEt2)2.67 (0.515 g, 1.21 mmol) in OEt2 (30
mL). The mixture was first stirred for 1 h and then allowed to warm
to rt. Volatiles were removed under vacuum and the residue was
treated with a solution of PhCCH (0.60 mL, 0.56 g, 5.48 mmol) in
toluene (30 mL). The resulting mixture was heated to 50 °C for
8 h. After filtration, the filtrate was evaporated to dryness under
vacuo and the solid residue was washed with hexane (3 × 10 mL)
to remove unreacted PhCCH. The reddish solid obtained was
dissolved in a minimum amount of CH2Cl2 and precipitated into
hexane. Yield: 0.24 g (66%). 1H NMR (500 MHz, CDCl3): δ
4.2-4.7 (br, 8H; C5H4), 6.9-7.6 (br, 7H; C6H5, C2H2). IR (cm-1):
1611 (CdC-Ph). UV-vis (nm): λmax(0.1 mM, toluene) ) 378, 495
(shoulder).
(62.9 MHz, C6D6, 300 K): δ 26.9, 27.4, 27.7 (C6H11), no (CB). 11
NMR (128.4 MHz, C6D6, 300 K): δ 81.8 (h1/2 ) 530 Hz).
B
Synthesis of Fc2B(CHdCHPh) (11Ph). Neat PhCCH (0.11 mL,
0.10 g, 1.00 mmol) was added via syringe to a stirred solution of
10 (0.377 g, 0.99 mmol) in toluene (40 mL). After the mixture had
been stirred for 24 h at rt, all volatiles were removed at 50 °C
under vacuum. Recrystallization of the crude material from H3CCN
(25 mL) gave dark red X-ray quality crystals of 11Ph. Yield: 0.198
Synthesis of [-fcB(CHdCHtBu)-]n (12tBu). Neat Me3SiCl (0.60
mL, 0.51 g, 4.70 mmol) was added via syringe at -78 °C to a
stirred solution of 4(OEt2)2.67 (0.224 g, 0.53 mmol) in OEt2 (15
mL). The mixture was first stirred for 1 h and then allowed to warm
to rt. Volatiles were removed under vacuum and the residue was
treated with a solution of tBuCCH (0.35 mL, 0.23 g, 2.85 mmol)
in toluene (15 mL). The resulting mixture was stirred at rt for 2 h,
it was then ultrasonicated for 3 h at rt, and for 4 h at 50 °C. After
filtration, the filtrate was evaporated to dryness under vacuum. The
residue was dissolved in a minimum amount of toluene and
precipitated into hexane. Yield: 0.062 (42%). 1H NMR (500 MHz,
CDCl3): δ 0.9-1.1 (br, 9H; tBu), 4.2-4.7 (br, 8H; C5H4), 6.2, 6.6
(br, 2H; C2H2). IR (cm-1): 1623 (CdC-tBu). UV-vis (nm): λmax(0.1
mM, toluene) ) 362, 482 (shoulder).
1
g (41%). H NMR (250.1 MHz, CDCl3, 300 K): δ 4.10 (s, 10H;
3
C5H5), 4.66 (nr, 8H; C5H4), 7.24 (d, JHH ) 18.1 Hz, 1H; C2H2),
3
7.36 (m, 1H; Ph-Hp), 7.42 (vtr, 2H; Ph-Hm), 7.53 (d, JHH ) 18.1
Hz, 1H; C2H2), 7.65 (d, 3JHH ) 7.3 Hz, 2H; Ph-Ho). 1H NMR (300.0
MHz, C6D6, 300 K): δ 4.00 (s, 10H; C5H5), 4.49, 4.69 (2 × vtr, 2
× 4H; C5H4), 7.13 (m, 1H; Ph-Hp), 7.22 (vtr, 2H; Ph-Hm), 7.43 (d,
3
3JHH ) 18.2 Hz, 1H; C2H2), 7.59 (d, JHH ) 7.4 Hz, 2H; Ph-Ho),
3
7.73 (d, JHH ) 18.2 Hz, 1H; C2H2). 13C{1H} NMR (75.5 MHz,
CDCl3, 300 K): δ 69.1 (C5H5), 73.7, 76.3 (C5H4), 126.9 (Ph-Co),
128.2 (Ph-Cp), 128.7 (Ph-Cm), 134.0, 144.8 (C2H2), no (Ph-Ci,
CB). 11B NMR (96.3 MHz, CDCl3, 300 K): δ 56.7 (h1/2 ) 500
Hz). IR (cm-1): 1608 (CdC-Ph). UV-vis (nm): λmax(0.1 mM,
toluene) ) 380, 484. Elemental analysis calcd (%) for C28H25BFe2
(483.99): C 69.48, H 5.21. Found: C 69.08; H 5.28.
Crystal Structure Analyses. Crystals of 2(OEt2)2, 2(OEt2),
4(OEt2)2.67, 5(SMe2), 6(NMe2Et)2, 11Ph, and 11tBu were measured
on a STOE IPDS-II diffractometer with graphite-monochromated
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16328 J. AM. CHEM. SOC. VOL. 131, NO. 44, 2009

Ferrocenylhydridoborates
A R T I C L E S
Mo KR radiation. An empirical absorption correction with program
PLATON50 was performed for all structures. The structures were
solved by direct methods using the program SHELXS51 and refined
with full-matrix least-squares on F2 using the program
SHELXL97.52 Hydrogen atoms were placed on ideal positions and
refined with fixed isotropic displacement parameters using a riding
model. One ether molecule in 4(OEt2)2.67 is disordered over two
sites with occupation factors 0.52(1) and 0.48(1). 5(SMe2) was a
racemic twin with a ratio of the twin components of 0.50(8):0.50(8).
In 11Ph, the atoms C(1) and C(2) constituting the olefinic bond are
disordered over two positions with occupancy factors of 0.74(2)
and 0.26(2). CCDC reference numbers: 740781 (2(OEt2)2), 740782
(2(OEt2)), 740783 (4(OEt2)2.67), 740784 (5(SMe2)), 740785
(6(NMe2Et)2), 740789 (11Ph), 740786 (11tBu).
sample plate inside a glovebox. Peptides were used for calibration
(Des-Arg-Bradykinin (904.4681), Angiotensin I (1296.6853), Glu-
Fibrinopeptide B (1570.6774), ACTH (clip 1-17) (2093.0867),
ACTH (clip 18-39) (2465.1989), ACTH (clip 7-38) (3657.9294)
with R-hydroxy-4-cyanocinnamic acid as the matrix).
Acknowledgment. M.W. is grateful to the Deutsche Forsch-
ungsgemeinschaft (DFG) and the Fonds der Chemischen Industrie
(FCI) for financial support. F.J. thanks the Alexander von Humboldt
Foundation for a Friedrich Wilhelm Bessel Research Award. M.S.
has been financially supported by a Ph.D. grant of the Fonds der
Chemischen Industrie (FCI) and the Bundesministerium fu¨r Bildung
und Forschung (BMBF).
Thermal Analyses of Polymers. Thermogravimetric analysis
(TGA) was performed under N2 atmosphere using a Perkin-Elmer
Pyris 1 system with ca. 4-5 mg of polymer at a heating rate of 20
°C/min from 30 to 800 °C.
Mass Spectrometry of Polymers. MALDI-TOF measurements
were performed on an Applied Biosystems 4700 (12Ph) or 4800
(12tBu) Proteomics Analyzer in (+) ion reflectron mode with delayed
extraction. Benzo[a]pyrene was used as the matrix (20 mg/mL in
toluene). Samples were prepared in toluene (10 mg/mL), mixed
with the matrix in a 1:10 ratio, and then spotted on the wells of a
Supporting Information Available: Crystallographic data for
all structurally characterized compounds in tabular form;
ORTEP-plots of 2(OEt2)2, 2(OEt2), 4(OEt2)2.67, and 5(SMe2)A;
ORTEP plots and a compilation of selected bond lengths and
angles of 7 and 8; cif files of all structures determined by X-ray
crystallography; thermogravimetric analysis plot of 6(NMe2Et)2;
1H NMR spectrum of the crude product of the hydroboration
of tBuCCH with Fc2BH (10); MALDI-TOF mass spectrum of
polymer 12tBu; comparison of the UV-vis spectra of 11Ph/12Ph
and 11tBu/12tBu. This material is available free of charge via the
Internet at http://pubs.acs.org.
(50) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.
(51) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467–473.
(52) Sheldrick, G. M. SHELXL-97. A Program for the Refinement of Crystal
Structures; Universita¨t Go¨ttingen: Go¨ttingen, 1997.
JA906575S
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