Unsolvated [KFl(SiPh3)]n (Fl = fluorenyl): A supramolecular chain structure assembled exclusively through K?C-π-bonding

Article abstract of DOI:10.1016/j.jorganchem.2010.11.037

Unsolvated potassium 9-triphenylsilylfluorenide, [KFl(SiPh ₃)]_n (3, Fl = fluorenyl), has been prepared in 89% yield by metalation of 9-fluorenyltriphenylsilane (2) with potassium hydride in toluene/THF and structurally characterized

Full text of DOI:10.1016/j.jorganchem.2010.11.037

Journal of Organometallic Chemistry 696 (2011) 1935e1938
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Unsolvated [KFl(SiPh3)]n (Fl ¼ fluorenyl): A supramolecular chain structure
assembled exclusively through K/Ce -bonding
p
,
Ahmad Zaeni a, Falk Olbrich b, Cristian G. Hrib c, Frank T. Edelmann c
*
a Chemistry Department, Haluoleo University, Kendari, Indonesia
b Institut für Anorganische und Angewandte Chemie der Universität Hamburg, D-20146 Hamburg, Germany
c Chemisches Institut der Otto-von-Guericke, Universität Magdeburg, D-39106 Magdeburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Unsolvated potassium 9-triphenylsilylfluorenide, [KFl(SiPh3)]n (3, Fl ¼ fluorenyl), has been prepared in
89% yield by metalation of 9-fluorenyltriphenylsilane (2) with potassium hydride in toluene/THF and
structurally characterized by X-ray diffraction. In the solid state, compound 3 comprises a linear chain
structure. Due to the absence of coordinating solvent molecules, supramolecular self-assembly occurs
Received 14 October 2010
Received in revised form
17 November 2010
Accepted 23 November 2010
solely via K/Cep-bonding.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Fluorene
Fluorenyl ligands
Silicon
Potassium
X-ray structure
1. Introduction
2. Results and discussion
Fluorenyl ligands (Fl) play an important role in the synthesis of
highly efficient Group 4 [1] and lanthanide [2] metallocene catalysts
for olefin polymerization. Such catalytically active metallocene
complexes are generally made by metathetical reactions between
Group 4 or rare-earth metal halides and the corresponding alkali
metal fluorenides. The solid state structures of alkali metal fluo-
renides have been the subject of detailed structural investigations in
recent years [3]. The vast majority of the structurally characterized
examples are solvated species containing coordinated Lewis bases
such as Et2O [3f], DME (1,2-dimethoxyethane) [3j], TMEDA
(N,N,N0,N0-tetramethylethylenediamine) [3b], PMDTA (N,N,N0,N00,
N00-pentamethyldiethylenetriamine) [3b,d] or 18-crown-6 [3i,j,m].
In contrast, the structures of unsolvated alkali metal fluorenides
have been studied to a much lesserextent. Notable are reports on the
solid-state structures of the unsubstituted base-free derivatives LiFl
[3g] and NaFl [3h]. We report here the synthesis and structural
characterization of the unsolvated potassium derivative of 9-fluo-
renyltriphenylsilane which in the solid state comprises an unusual
supramolecular chain structure assembled exclusively through
Scheme 1 illustrates the synthetic route leading to the title
compound potassium 9-triphenylsilylfluorenide, [KFl(SiPh3)]n (3).
The starting material, 9-fluorenyltriphenylsilane (2), was first
reported almost sixty years ago by Gilman and Miller [4a,b]. We
obtained compound 2 in high yield (82%) by a slight modification of
the original preparation [4a,b] via metalation of fluorene (1) with
n-butyllithium followed by treatment of the LiFl intermediate with
Ph3SiCl. In an earlier report, the anion of 2 had already been studied
in solution [4c]. It was generated by deprotonation of 2 with
CH3SOCHꢀ2 Kþ in DMSO-d6 and its 1H and 13C NMR spectra were
measured. In order to isolate a crystalline material, the deprotona-
tion reaction of 2 was carried out with the use of potassium hydride.
Treatment of 2 with KH in THF according to Scheme 1 directly
afforded the potassium fluorenide [KFl(SiPh3)]n (3) in 89% yield.
NMR spectra (1H and 13C) clearly showed the absence of coor-
dinated THF in the product despite the fact that the preparation had
been carried out in the presence of THF. Large, yellow-green X-ray
quality single-crystals of 3 were grown by carefully layering the
filtered reaction mixture with n-pentane and allowing the mixture
to stand undisturbed over a period of ca. 2 weeks. Crystal data and
structure refinement details are listed in Table 1, and selected bond
lengths and angles for 3 are summarized in Table 2. Fig. 1 depicts
the supramolecular chain structure of 3, while the coordination
environment around potassium is illustrated in Fig. 2.
K/Cep-bonding.
* Corresponding author. Tel.: þ49 391 6718327; fax: þ49 391 6712933.
E-mail address: frank.edelmann@ovgu.de (F.T. Edelmann).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.11.037

1936
A. Zaeni et al. / Journal of Organometallic Chemistry 696 (2011) 1935e1938
Table 2
n
1. BuLi / Et2O
Selected bond lengths [Å] and angles [ꢂ] for [KFl(SiPh3)]n (3). The compound (3)
crystallizes with 2 molecules in the asymmetric unit.
2. Ph3SiCl
KeC(1)
KeC(2)
3.014(3)
3.074(3)
3.141(3)
3.206(3)
3.221(3)
3.243(4)
3.256(4)
3.263(4)
3.274(3)
3.300(3)
3.301(3)
3.306(4)
3.328(4)
3.342(4)
3.374(4)
3.381(4)
3.391(5)
3.404(4)
3.462(4)
3.469(4)
1.814(3)
1.879(3)
1.881(3)
1.897(3)
K0eC(10)
3.010(3)
3.101(3)
3.107(3)
3.229(3)
3.238(3)
3.246(3)
3.265(3)
3.271(3)
3.292(3)
3.294(4)
3.298(3)
3.299(4)
3.329(4)
3.368(4)
3.369(3)
3.379(4)
3.416(3)
3.421(4)
3.438(4)
3.467(4)
1.818(3)
1.884(3)
1.885(3)
1.895(3)
K0eC(130)
K0eC(20)
H
SiPh3
1
KeC(13)
KeC(26)
KeC(25)
KeC(19)
KeC(24)
KeC(7)
KeC(14)
KeC(20)
KeC(8)
KeC(18)
KeC(15)
KeC(27)
KeC(23)
KeC(17)
KeC(16)
KeC(21)
KeC(22)
KeC(31)
SieC(1)#1
SieC(20)
SieC(14)
SieC(26)#1
K0eC(190)
K0eC(260)
K0eC(140)
K0eC(250)
K0eC(80)
2
KH
THF
- H2
K0eC(70)
K0eC(180)
K0eC(200)
K0eC(150)
K0eC(240)
K0eC(170)
K0eC(210)
K0eC(160)
K0eC(310)
K0eC(230)
K0eC(220)
K0eC(270)
Si’eC(10)
K
SiPh3
3
Scheme 1. Synthetic route to 9-fluorenyltriphenylsilane (2) and potassium 9-triphe-
nylsilylfluorenide, [KFl(SiPh3)]n (3).
Si’eC(200)#2
Si’eC(140)#2
Si’eC(260)
The X-ray structural analysis confirmed the presence of an
unsolvated potassium fluorenide. In the solid state, compound 3
comprises a linear chain structure of the type [KFl(SiPh3)]n. Due to
the absence of coordinating solvent molecules, supramolecular
C(1)#1eSieC(20)
C(1)#1eSieC(14)
C(20)eSieC(14)
C(1)#1eSieC(26)#1
C(20)eSieC(26)#1
C(14)eSieC(26)#1
114.78(15)
113.85(16)
100.39(14)
110.09(14)
108.16(15)
109.05(15)
C(10)eSi’eC(200)#2
C(10)eSi’eC(140)#2
C(200)#2eSi’eC(140)#2
C(10)eSi’eC(260)
C(200)#2eSi’eC(260)
C(140)#2eSi’eC(260)
114.00(15)
113.41(15)
100.16(14)
110.53(14)
109.85(14)
108.37(15)
self-assembly occurs solely via K/Cep-bonding. Such K/Cep-
bonding is not uncommon and has been found in very different
classes of potassium compounds containing aromatic ring systems.
It often occurs when the central potassium ion is sterically unsat-
urated and in need of increasing its formal coordination number
Symmetry transformations used to generate equivalent atoms: #1 - x ꢀ 1, y, z #2 -
x þ 1, y, z.
[5]. Three different
potassium ion, involving all three phenyl rings of the triphenylsilyl
substituent. On one side, the ligand is
5-bonded to potassium via
the formally anionic central cyclopentadienyl moiety of the fluo-
renyl system with KeC(1) being the shortest distance (3.014(3) Å).
On the same side, the coordination is complemented by an allyl-like
p-systems are coordinated to the central
h
3-interaction with one of the phenyl rings. Supramolecular self-
assembly into a polymeric linear chain structure (Fig. 1) is accom-
plished through h6
-interactions with two phenyl rings of
neighboring triphenylsilylfluorenyl groups. Thus the unique overall
coordination of the [Fl(SiPh3)]ꢀ anions can be best described as
h3 h5 h6 6-bridging. The KeC distances differ significantly, falling
h
ep
m
-
:
: :h
in the range of 3.010(3) (KeC(1))e3.469(4) (KeC(31)) Å, but are still
in the normal range reported earlier for solvated potassium fluo-
Table 1
Crystal data and structure refinement for [KFl(SiPh3)]n ꢁ 05. toluene (3).
renides [3] and various other potassium compounds involving
interactions with aromatic rings [5].
p-
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
zabah
C69H54K2Si2
1017.50 g/mol
133(2) K
0.71073 Å
Triclinic
Notably, the crystal structure of 3 differs largely from those of
the unsubstituted base-free derivatives LiFl [3g] and NaFl [3h]. The
crystal lattice of the parent lithium fluorenide is built up of subunits
in which two lithium ions are encapsulated by two nearly planar
and parallel arranged carbanions, whereas solvent-free fluo-
renylsodium forms the salt-like structure Na2[NaFl3], containing
the novel trigonal [NaFl3]2ꢀ anion [3h]. In contrast, the crystal
structure of 3 comprises the supramolecular [KFl(SiPh3)]n chains.
As illustrated in Fig. 3, these polymeric chains are found in a parallel
alignment without leaving any larger pores in the crystal lattice.
In summarizing the results reported here, unsolvated potassium
9-triphenylsilylfluorenide, [KFl(SiPh3)]n (3, Fl ¼ fluorenyl), is readily
Pꢀ1
Unit cell dimensions
a ¼ 7.9070(5) Å
b ¼ 9.4621(6) Å
c ¼ 37.571(2) Å
2608.3(3) Å3
2
a
b
g
¼ 92.100(3)ꢂ
¼ 90.576(3)ꢂ
¼ 111.749(3)ꢂ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
1.296 mg/m3
0.272 mmꢀ1
1068
0.35 ꢁ 0.15 ꢁ 0.07 mm3
1.08e26.37ꢂ
ꢀ9 ꢃ h ꢃ 9, ꢀ11 ꢃ k ꢃ 11,
ꢀ46 ꢃ l ꢃ 46
Reflections collected
23374
Independent reflections
Completeness to theta ¼ 26.37ꢂ
Absorption correction
10570 [R(int) ¼ 0.0582]
99.4%
None
Refinement method
Full-matrix least-squares on F2
10570/114/697
Data/restraints/parameters
Goodness-of-fit on F2
1.087
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 ¼ 0.0676,wR2 ¼ 0.1328
R1 ¼ 0.0983,wR2 ¼ 0.1432
0.475 and ꢀ0.430 e Åꢀ3
Fig. 1. ORTEP view of the supramolecular chain structure of [KFl(SiPh3)]n (3) with
thermal ellipsoids at the 50% probability level (H atoms are not shown for clarity).

A. Zaeni et al. / Journal of Organometallic Chemistry 696 (2011) 1935e1938
1937
Fig. 2. Coordination environment around potassium in [KFl(SiPh3)]n (3).
accessible in high yield (89%) by metalation of 9-fluorenyl-
triphenylsilane (2) with potassium hydride in toluene/THF. X-ray
diffraction revealed a linear chain structure in the solid state. Due to
the absence of coordinating solvent molecules, supramolecular
self-assembly occurs solely via K/Cep-bonding. Compound 3 can
be expected to be a useful precursor for the synthesis of transition
metal complexes containing the triphenylsilylfluorenyl ligand.
Fig. 3. Parallel alignment of the supramolecular chains of [KFl(SiPh3)]n (3) in the
crystal structure.
3. Experimental section
3.1. General procedures
1 h. The reaction mixture was carefully hydrolyzed with cold water
(ca. 100 mL) and the organic phase was separated and dried over
MgSO4. Filtration and evaporation to dryness followed by rinsing
with n-pentane (3 ꢁ 50 mL) afforded 2 as a colorless solid in 82%
yield (27.9 g). M.p. 184 ꢂC. Analysis (C31H24Si, Mw ¼ 424.61 g/mol):
C 88.00 (calcd. 87.69), H 5.50 (5.70) %. IR (KBr): nmax 3435 (w br),
3066 (w), 3049 (w), 3001 (w), 2929 (w), 2851 (w), 2361 (vw), 1951
(vw br), 1907 (vw br), 1588 (8w), 1569 (w), 1484 (w), 1474 (w), 1442
(s), 1427 (vs), 1334 (w), 1303 (w), 1186 (w), 1178 (m), 1156 (w), 1107
(vs),1028 (m), 997 (m), 888 (w), 825 (w), 778 (vs), 736 (vs), 698 (vs),
The reactions were conducted in flame-dried glassware under
an inert atmosphere of dry argon employing standard Schlenk and
glovebox techniques. All solvents were distilled from sodium/
benzophenone under nitrogen atmosphere prior to use. All glass-
ware was oven-dried at 140 ꢂC for at least 24 h, assembled while
hot, and cooled under vacuum prior to use. The starting materials
fluorene and Ph3SiCl were purchased from commercial suppliers
and used as received. Potassium hydride (Aldrich) was freed from
mineral oil by washing with n-pentane under argon, dried in
vacuum and stored in the dry-box. NMR spectra were recorded in
THF-d8 or C6D6 solutions on a Bruker DPX 400 spectrometer at
25 ꢂC. Chemical shifts were referenced to TMS. Microanalyses were
performed using a Leco CHNS 923 apparatus. The intensity data of 3
were collected on a Bruker CDD SMART diffractometer with Mo Ka
radiation. The data were collected with the Bruker SMART [6]
620 (m), 580 (m), 519 (vs), 495 (s), 485 (s), 447 (m), 424 (m) cmꢀ1
.
1H and 13C NMR (THF-d8) were in excellent agreement with those
reported in the literature [4c].
3.3. Synthesis of potassium 9-triphenylsilylfluorenide, [KFl(SiPh3)]n
(3)
program using
u-scans. The space group was determined with
Bruker SAINT [6] program. The structure was solved by direct
methods (SHELXS-97) and refined by full-matrix least-squares
methods on F2 using SHELXL-97 [7].
To a suspension of KH (0.1 g, 2.5 mmol) in THF (10 mL) was
added a solution of 2 (1.06 g, 2.5 mmol) in THF/toluene (1:1, 20 mL)
and the mixture was stirred for 2 h at 80 ꢂC, causing gas evolution
(H2) and the development of an orange color. The solution was
filtered through a thin layer of Celite filter aid, and the clear orange
filtrate was carefully layered with n-pentane (15 mL) and left to
stand undisturbed for 2 weeks. During that time large, yellow-
green crystals grew, which were isolated by decanting the liquid
and drying in an argon stream. The resulting crystals of the toluene
solvate were directly suitable for X-ray diffraction. Thorough drying
in vacuo afforded the toluene-free material as an orange powder.
3.2. Modified synthesis of 9-fluorenyltriphenylsilane (2) [4c]
To a solution of fluorene (13.5 g, 80 mmol) in diethyl ether
(200 mL) was added at ꢀ30 ꢂC a 1.6 M solution of n-butyllithium in
n-hexane (50 mL, 80 mmol). The mixture was allowed to warm to
room temperature and was stirred for 12 h. After filtration, solid
Ph3SiCl (23.6 g, 80 mmol) was added and stirring was continued for

1938
A. Zaeni et al. / Journal of Organometallic Chemistry 696 (2011) 1935e1938
Yield: 1.03 g (89%). M.p. ca. 150 ꢂC (dec.). Analysis (C31H23KSi,
Mw ¼ 462.70 g/mol): C 80.93 (calcd. 80.47), H 5.06 (5.01)%. IR (KBr):
nmax 3437 (vw br), 3066 (w), 3017 (w), 2922 (vw), 1961 (vw br),
1905 (vw br), 1845 (vw br), 1715 (w), 1611 (w), 1601 (w), 1589 (w),
1571 (w), 1479 (w), 1453 (m), 1428 (vs), 1325 (m), 1296 (s), 1261 (w),
1217 (m), 1184 (m), 1150 (m), 1118 (vs), 1028 (m), 1014 (m), 996 (m),
976 (m), 920 (w), 738 (s), 726 (s), 712 (vs), 700 (vs), 517 (vs), 445
(c) E. Kirillov, A.K. Dash, A.-S. Rodrigues, J.-F. Carpentier, C. R. Chim. 9 (2006)
1151.
[3] (a) S. Buchholz, K. Harms, M. Marsch, W. Massa, G. Boche, Angew. Chem. Int. Ed.
Engl. 101 (1989) 57;
(b) S. Corbelin, J. Kopf, E. Weiß, Chem. Ber. 124 (1991) 2417;
(c) C. Janiak, Chem. Ber. 126 (1993) 1603;
(d) D. Hoffmann, F. Hampel, P. von R. Schleyer, J. Organomet. Chem. 456
(1993) 13;
(e) H. Viebrock, D. Abeln, E. Weiß, Z. Naturforsch. B49 (1994) 89;
(f) M. Könemann, G. Erker, R. Fröhlich, E.-U. Würthwein, J. Am. Chem. Soc.
119 (1997) 11155;
(g) C. Üffing, R. Köppe, H. Schnöckel, Organometallics 17 (1998) 3512;
(h) R.E. Dinnebier, S. Neander, U. Behrens, F. Olbrich, Organometallics 18
(1999) 2915;
(i) S. Neander, F.E. Tio, R. Buschmann, U. Behrens, F. Olbrich, J. Organomet.
Chem. 582 (1999) 58;
(j) S. Neander, U. Behrens, F. Olbrich, J. Organomet. Chem. 604 (2000) 59;
(k) T. Kahler, U. Behrens, S. Neander, F. Olbrich, J. Organomet. Chem. 649
(2002) 50;
(m). 1H NMR (DMSO-d6, 400.1 MHz, 25 ꢂC):
d
¼ 7.89 (d, 2H, H-4 and
H-6), 7.59 (m, 11H, H-1, H-8 þ C6H5), 7.29 (m, 6H, C6H5), 7.19 (t, 2H,
H-2 and H-7), 7.18 (dd, 2H, H-3 and H-6) ppm. 13C NMR (DMSO-d6,
100.6 MHz, 25 ꢂC):
d
¼ 142.83 (C-10 and C-13), 141.10 (C-11 and
C-12), 134.80 (m-C6H5), 134.11 (ipso-C6H5), 128.84 (p-C6H5), 128.26
(C-2 and C-7), 128.15 (C-3 and C-5), 126.73 (C-8), 126.55 (C-1),
125.11 (o-C6H5), 119.92 (C-4), 76.88 (C-9) ppm.
(l) S. Neander, J. Kornich, F. Olbrich, J. Organomet. Chem. 656 (2002) 89;
(m) U. Behrens, S. May, F. Olbrich, Z. Kristallogr. - New Cryst. Struct. 222
(2007) 307;
Acknowledgements
(n) A. Zaeni, F. Olbrich, A. Fischer, F.T. Edelmann, J. Organomet. Chem. 693
(2008) 3791.
This work was financially supported by the Otto-von-Guericke-
Universität Magdeburg. A.Z. thanks the DAAD (Deutscher Akade-
mischer Austauschdienst) for a Ph.D. scholarship.
[4] (a) L.S. Miller, Iowa State College, J. Sci. 26 (1952) 249;
(b) H. Gilman, A.G. Brook, L.S. Miller, J. Am. Chem. Soc. 75 (1953) 3757;
(c) S. Zhang, X.-M. Zhang, F.G. Bordwell, J. Am. Chem. Soc. 117 (1995) 602;
(d) N. Karakostas, S. Naumov, M.G. Siskos, A.K. Zarkadis, R. Hermann, O. Brede,
J. Phys. Chem. A109 (2005) 11679.
[5] Selected recent references: (a) D.L. Clark, G.B. Deacon, T. Feng, R.V. Hollis,
B.L. Scott, B.W. Skelton, J.G. Watkin, A.H. White, Chem. Commun. (1996) 1729;
(b) S. Chadwick, U. Englich, K. Ruhlandt-Senge, Organometallics 16 (1997)
5792;
Appendix A. Supplementary material
CCDC 795641 (3) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
(c) R.P.K. Babu, K. Aparna, R. McDonald, R.G. Cavell, Organometallics 20 (2001)
1451;
(d) T.J. Boyle, N.L. Andrews, M.A. Rodriguez, C. Campana, T. Yiu, Inorg. Chem. 42
(2003) 5357;
(e) C.S. Weinert, P.E. Fanwick, I.P. Rothwell, Inorg. Chem. 42 (2003) 6089;
(f) M.T. Gamer, P.W. Roesky, Organometallics 23 (2004) 5540;
(g) M.L. Cole, L.T. Higham, P.C. Junk, K.M. Proctor, J.L. Scott, C.R. Strauss, Inorg.
Chim. Acta 358 (2005) 3159;
(h) S. Bieller, M. Bolte, H.-W. Lerner, M. Wagner, Z. Anorg. Allg. Chem. 632
(2006) 319.
References
[1] Reviews: (a) I.A. Lobanova, V.I. Zdanovich, Usp. Khim. 57 (1988) 1688;
(b) H.G. Alt, E. Samuel, Chem. Soc. Rev. 27 (1998) 323;
(c) T. Cuenca, P. Royo, Coord. Chem. Rev. 193e195 (1999) 447;
(d) H.G. Alt, Synth. Methods Organomet. Inorg. Chem. 10 (2002) 167;
(e) W. Kaminsky, O. Sperber, R. Werner, Coord. Chem. Rev. 250 (2006) 110;
(f) S. Prashar, A. Antinolo, A. Otero, Coord. Chem. Rev. 2450 (2006) 133;
(g) J. Schellenberg, Prog. Polym. Sci. 34 (2009) 688.
[6] Bruker, SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA,
1998.
[7] (a) G.M. Sheldrick, SHELXL-97 Program for Crystal Structure Refinement.
Universität Göttingen, Germany, 1997;
(b) G.M. Sheldrick, SHELXS-97 Program for Crystal Structure Solution.
Universität Göttingen, Germany, 1997.
[2] Reviews: (a) C.-T. Qian, C.-J. Zhu, Chin. J. Chem. Eng. 20 (2002) 519;
(b) E. Kirillov, J.-Y. Saillard, J.-F. Carpentier, Coord. Chem. Rev. 249 (2005) 1221;