Neutral pentacoordinate group 14 compounds with β-diketonato ligands

Article abstract of DOI:10.1021/om900779s

A stable neutral pentacoordinate germanium compound substituted with three CF₃ and a dibenzoylmethane ligand was synthesized. Single-crystal X-ray diffraction structure determination proves the presence of two crystallographically independent molecules in the asymmetric unit, one of them deviating somewhat from planarity. Density functional computations show the isolated molecule to be planar, while the computation of a molecule pair yielded a minimum, where the planarity of the two monomeric units differ from each other, with the resulting structure resembling the unit cell in the crystal. Bader analysis revealed this molecule pair to be bound together by hydrogen bonds. The stability of the pentacoordinate bond in this compound is about 23 kcal/mol at the B3LYP/6-31+G* (31 kcal/mol at the MP2/6-31+G*// B3LYP/6-31+G*) level. The stabilizing effect of the trifluoromethyl substituent on the pentacoordinate structure is comparable to that of the fluorine group. Computations on the analogous Si-containing systems reveal similar pentacoordinate structures, even though the relative stabilities of these structures are somewhat different for the two group 14 elements. For example, germanium substituted by three -OEt moieties forms a stable pentacoordinate structure with the acetylacetone (acac) ligand (explaining the role of acac as hydrolysis inhibitor of tetraethoxygermane), while the hypervalent bond of the silicon analogue is unstable at the B3LYP/6-31+G* level.

Full text of DOI:10.1021/om900779s

1100 Organometallics 2010, 29, 1100–1106
DOI: 10.1021/om900779s
Neutral Pentacoordinate Group 14 Compounds with β-Diketonato ligands
†
Petra Bombicz, Ilona Kovacs, Laszlo Nyulaszi,* Denes Szieberth, and Peter Terleczky
‡
,‡
‡
‡
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
†Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences,
H-1525 Budapest, POB 17, Hungary, and ‡Department of Inorganic and Analytical Chemistry,
ꢀ ꢀ
Budapest University of Technology and Economics, Szt Gellert ter 4, H-1521 Budapest, Hungary
Received September 7, 2009
A stable neutral pentacoordinate germanium compound substituted with three CF3 and a
dibenzoylmethane ligand was synthesized. Single-crystal X-ray diffraction structure determination
proves the presence of two crystallographically independent molecules in the asymmetric unit, one of
them deviating somewhat from planarity. Density functional computations show the isolated
molecule to be planar, while the computation of a molecule pair yielded a minimum, where the
planarity of the two monomeric units differ from each other, with the resulting structure resembling
the unit cell in the crystal. Bader analysis revealed this molecule pair to be bound together by
hydrogen bonds. The stability of the pentacoordinate bond in this compound is about 23 kcal/mol at
the B3LYP/6-31þG* (31 kcal/mol at the MP2/6-31þG*//B3LYP/6-31þG*) level. The stabilizing
effect of the trifluoromethyl substituent on the pentacoordinate structure is comparable to that of the
fluorine group. Computations on the analogous Si-containing systems reveal similar pentacoordi-
nate structures, even though the relative stabilities of these structures are somewhat different for the
two group 14 elements. For example, germanium substituted by three -OEt moieties forms a stable
pentacoordinate structure with the acetylacetone (acac) ligand (explaining the role of acac as
hydrolysis inhibitor of tetraethoxygermane), while the hypervalent bond of the silicon analogue is
unstable at the B3LYP/6-31þG* level.
Introduction
however, either are charged2 or are often described as
zwitterionic compounds.5-7 In many of the neutral com-
pounds the tetracoordinate group 14 element is loosely
complexed by an electron pair donor (among others, see
the works of Bassindale and Baukov),2h,8 as indicated by the
Hypervalent compounds with heavier group 14 elements
are known, the first examples of such silicon compounds
dating back to the beginning of the 19th century.1 These
compounds are also of contemporary interest (as shown by
the rapidly increasing number of publications2) due to their
reactivity. While many of these hypervalent systems are
hexacoordinate,1,3 pentacoordinate species are also known
and their enhanced stability with respect to the analogous
carbon compounds has recently been elegantly explained by
the different sizes of the central atoms (carbon and silicon).4
Most of the hypervalent silicon and germanium species,
8
˚
2.3-2.8 A interatomic distance; thus, the existence of five
equally bound moieties can be questioned. For example, in
the case of silatranes 1, with certain substituents a variation
of the SiN “bonding” distance from the equilibrium state by
(3) (a) Boudjouk, P.; Kloos, S. D.; Kim, B. K.; Page, M.; Thweatt, D.
J. Chem. Soc., Dalton Trans. 1998, 877–879. (b) Bolte, M.; Hensen, K.;
Spangenberg, B. J. Chem. Crystallogr. 2000, 30, 245–249. (c) Fester, G. W.;
Wagler, J.; Brendler, E.; Kroke, E. Eur. J. Inorg. Chem. 2008, 5020–5023.
€
(d) Fester, G. W.; Wagler, J.; Brendler, E.; Bohme, U.; Roewer, G.; Kroke, E.
*To whom correspondence should be addressed. E-mail: nyulaszi@
mail.bme.hu.
Chem. Eur. J. 2008, 14, 3164–3176. (e) Fester, G. W.; Wagler, J.; Brendler,
€
E.; Bohme, U.; Gerlach, D.; Kroke, E. J. Am. Chem. Soc. 2009, 131, 6855–
(1) (a) Gay-Lussac, J. L.; Thenard, L. J. Mem. Phys. Chim. Soc.
d’Arcueil 1809, 2, 317. (b) Davy, J. Philos. Trans. R. Soc. London 1812,
102, 352.
6864. (f) Metz, S.; Burschka, C.; Tacke, R. Organometallics 2009, 28, 2311–
2317. (g) Kampfe, A.; Kroke, E.; Wagler, J. Eur. J. Inorg. Chem. 2009,
1027–1035. (h) Holloczki, O.; Nyulaszi, L. Organometallics 2009, 28,
4159–4164. (i) Arduengo, A. J., III; Jones, P. G.; Krafczyk, R.; Marshall,
W. J.; Schmutzler, R.; Thonnessen, H.Unpublished results, 1997. Jones, P. G.
Private communication to the Cambridge Crystallographic Database,
deposition number CCDC 611491. (j) Ghadwal, R. S.; Sen, S. S.; Roesky,
H. W.; Tavcar, G.; Merkel, S.; Stalke, D. Organometallics 2009, 28, 6374–
6377.
(4) Pierrefixe, S. C. A. H.; Guerra, C. F.; Bickelhaupt, F. M. Chem.
Eur. J. 2008, 14, 819–828.
(5) Tacke, R.; Bertermann, R.; Burschka, C.; Dragota, S. Angew.
Chem., Int. Ed. 2005, 44, 5292–5235.
(6) Troegel, D.; Burschka, C.; Riedel, S.; Kaupp, M.; Tacke, R.
(2) For reviews see: (a) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young,
J. C. Chem. Rev. 1993, 93, 1371–1448. (b) Holmes, R. R. Chem. Rev. 1996,
96, 927. (c) Corriu, R. J. P.; Querin, C.; Henner, B. J. L.; Wong Chi Man,
W. W. C. Organometallics 1988, 7, 237. (d) Negrebetsky, V. V.; Baukov, Yu.
I. Russ. Chem. Bull. 1997, 46, 1807–1831. (e) Tacke, R.; P€ulm, M.; Wagner,
B. Adv. Organomet. Chem. 1999, 44, 221–273. (f) Brook, M. A. Silicon in
Organic, Organometallic, and Polymer Chemistry; Wiley: New York,
2000; pp 97-114. (g) Tacke, R.; Seiler, O. In Silicon Chemistry: From
the Atom to Extended Systems; Jutzi, P., Schubert, U., Eds.; Wiley-VCH:
Weinheim, Germany, 2003; pp 324-337. (h) Kost, D.; Kalikhman, I. Adv.
Organomet. Chem. 2004, 50, 1–106. (i) Negrebetsky, V. V.; Tandura, S. N.;
Baukov, Yu. I. Russ. Chem. Rev. 2009, 78, 21–51. (j) Couzijn, E. P. A.;
Slootweg, J. C.; Ehlers, A. W.; Lammertsma, K. Z. Anorg. Allg. Chem.
2009, 635, 1273–1278.
Angew. Chem., Int. Ed. 2007, 46, 7001–7005.
(7) Theis, B.; Burschka, C.; Tacke, R. Chem. Eur. J. 2008, 14, 4618–
4630.
r
pubs.acs.org/Organometallics
Published on Web 02/05/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 5, 2010 1101
Scheme 1. Neutral Pentacoordinate Structures of Group
14 Elements
Scheme 2. Complexes of Interest for Silicon, Gallium, and
Germanium Formed with the acac Ligand
Scheme 3. Closed (Hypercoordinate) and Open Forms for the
Acetylacetonate Complexes (E:Si, Ge)
carbon atoms are attached to the central group 14 element
such as 5 (R0 = Me, Ph),15a 8,17 and 9 (R = Ph) are rare.18
The aim of the present work was to explore the possibilities
of stabilizing pentacoordinate silicon and germanium com-
pounds with at least three carbon substituents. We have
selected the bidentate acetylacetone (acac) ligand, which was
already used to form a neutral hexacoordinate19 as well as
hexacoordinate ionic20 complexes (10); furthermore, a Ga
complex with the acac ligand (11) was also reported21
(Scheme 2). Also, this ligand has been used to synthesize a
three-coordinate compound of germanium (12).22 Interest-
ingly, acetylacetonate is also used as an inhibitor in the
hydrolysis of tetraethoxygermane when forming GeO2 nano-
sheets,23 and we suspect that this behavior can be explained
by the formation of a stabilized pentacoordinate intermedi-
ate (see below).
˚
(0.25 A has resulted in an energy change of only 1.2 kcal/
mol,9 indicating the weakness of the hypervalent interaction.
The ligands of the group 14 elements in the few remaining
known neutral pentacoordinate systems are mainly electro-
negative groups (F, Cl, O, N), such as different amino and
phosphino complexes of SiX4 (X = F, Cl, Br)10 or 2,11 3,12
4
(R = Cl),13 4 (R = ONO2),14 5 (R0 = Cl),15 6 (X = F, Cl),3e
7,16 and real pentacoordinate compounds, where only three
This ligand system has a further advantage, since a direct
comparison of the relative energies of the opened (13o) and
closed forms (13h) provides an estimate for the stability of
the hypervalent bond in 13h (Scheme 3). It is worth noting
that in most of the stable pentacoordinate structures triden-
tate ligands were used for complexation.3g,12-14,24
(8) (a) Pongor, G.; Kolos, Zs.; Szalay, R.; Knausz, D. J. Mol. Struct.
(THEOCHEM) 2005, 714, 87–97. (b) Szalay, R; Pongor, G.; Harmat, V.;
Bocskei, Zs.; Knausz, D. J. Organomet. Chem. 2005, 690, 1498.
(c) Bassindale, A. R.; Borbaruah, M.; Glynn, S. J.; Parker, D. J.; Taylor,
P. G. J. Organomet. Chem. 2000, 606, 125–131. (d) Bassindale, A. R.;
Parker, D. J.; Taylor, P. G.; Auner, N.; Herrschaft, B. J. Organomet. Chem.
2003, 667, 66–72.
Results and Discussion
(9) Csonka, G. I.; Hencsei, P. J. Mol. Struct. (THEOCHEM) 1996,
362, 199–208.
In order to assess the stability of the pentacoordinate
system with different substituents at the group 14 element,
first we have carried out density functional computations
at the B3LYP/6-31þG* level (see Tables 1 and 2 for the
germanium and Tables S1 and S2 in the Supporting Informa-
tion for the silicon species, respectively). We have found
recently3h that this level of theory provides a conservative
estimate of the formation of hypercoordinate silicon-centered
systems with respect to experimental observations.3i,j,15a
As expected, the electronegative substituents stabilize the
(10) (a) Schnell, E. Monatsh. Chem. 1962, 93, 1136–1141. (b) B€urger,
€
H.; Sawodny, W.; Hofler, F. Monatsh. Chem. 1965, 96, 1437. (c) Beattie,
I. R. Q. Rev. Chem. Soc. 1963, 17, 382. (d) Beattie, I. R.; Ozin, G. A.
J. Chem. Soc. A 1970, 370.
(11) Kobayashi, J.; Kawaguchi, K.; Kawashima, T. J. Am. Chem.
Soc. 2004, 126, 1631–1638.
(12) Seiler, O.; Burschka, C.; Fenske, T.; Troegel, D.; Tacke, R.
Inorg. Chem. 2007, 46, 5419–5424.
(13) Metz, S.; Burschka, C.; Platte, D.; Tacke, R. Angew. Chem., Int.
Ed. 2007, 46, 7006–7009.
(14) Metz, S.; Burschka, C.; Tacke, R Organometallics 2008, 27,
6032–6034.
(15) (a) Kuhn, N.; Kratz, T.; Blaser, D.; Boese, R. Chem. Ber. 1995,
128, 245. (b) Bonette, F.; Kato, T.; Destarac, M.; Mignani, G.; Cossío, F. P.;
Baceiredo, A. Angew. Chem., Int. Ed. 2007, 46, 8632–8635. (c) Shipov,
A. G.; Kramarova, E. P.; Murasheva, T. P.; Negrebetsky, Vad. V.; Bylikin, S.
Yu.; Korlyukov, A. A.; Baukov, Yu. I. Russ. Chem. Bull., Int. Ed. 2005, 54,
2233–2234.
(16) Bylikin, S. Yu.; Shipov, A. G.; Kramarova, E. P.; Negrebetsky,
V. V.; Korlyukov, A. A.; Baukov, Yu. I.; Hursthouse, M. B.; Male, L.;
Bassindale, A .R.; Taylor, P. G. J. Organomet. Chem. 2009, 694, 244–
248.
(19) Dobrokhotova, Zh. V.; Koroteev, P. S.; Saushev, A. V.; Alek-
sandrov, G. G.; Novotortsev, V. M.; Nefedov, S. E.; Egorov, M. P. Russ.
Chem. Bull. 2003, 52, 1681–1687.
(20) West, R. J. Am. Chem. Soc. 1958, 80, 3246–3249.
(21) Beachley, O. T., Jr.; Gardinier, J. R.; Churchill, M. R. Organo-
metallics 2003, 22, 1145–1151.
(22) Stobart, S. R.; Churchill, M. R.; Hollander, F. J.; Youngs, W. J.
J. Chem. Soc., Chem. Commun. 1979, 911–912.
(17) Kano, N.; Goto, S.; Kawashima, T. Organometallics 2003, 22,
1152–1155.
(18) Liu, Y.; Steiner, S. A.; Spahn, C. W.; Guzei, I. A.; Toulokho-
(23) Adachi, M.; Nakagawa, K.; Sago, K.; Murataa, Y.; Nishikawab,
Y. Chem. Commun. 2005, 2381–2383.
(24) Seiler, O.; Burschka, C.; Metz, S.; Penka, M.; Tacke, R. Chem.
nova, I. S.; West, R. Organometallics 2007, 26, 1305–1307.
Eur. J. 2005, 11, 7379–7386.

1102 Organometallics, Vol. 29, No. 5, 2010
Bombicz et al.
˚
Table 1. B3LYP/6-31þG* Structural Data (in A) for the Hyper-
valent Germanium Species 13h (E = Ge) with Different R Groups
(R0 = H)a
bond distance. For the most stable pentacoordinate struc-
tures the axial E-O distance (see Ge-Oax in Table 1) is only
slightly longer than the equatorial distance (Ge-Oeq in
Table 1). It is also worth noting that the pairs of C-C and
C-O distances tend to equalize as the pentacoordinate
character of the silicon or germanium increases, indicating
delocalization along the OCCCO framework. Other acetyl-
acetonate complexes of gallium,21,25 chromium,26 and
lanthanides27 exhibit a similar bond equalization. According
to X-ray crystallographic studies the largest difference be-
R = H R = Me R = CF3 R = F R = Cl R = OEt
˚
tween C-O and C-C distances is 0.022 and 0.045 A for the
Ge-Oax 2.579
Ge-Oeq 1.854
2.744
1.883
1.307
1.237
1.372
1.438
þ1.4
2.189
1.848
1.309
1.255
1.371
1.418
-10.9
1.972 2.042
1.816 1.866
1.300 1.302
1.268 1.264
1.379 1.377
1.409 1.408
-20.5 -6.1
2.089
1.871
1.301
1.254
1.375
1.416
-7.5
Lu(III) and Dy(III) complexes,27 respectively, while the Ga
complex 11 is symmetrical.21
Oeq-C1
Oax-C3
C1-C2
C2-C3
1.312
1.237
1.368
1.438
Since the pentavalency is apparently related to the bonding
between the ring carbon atoms, further tuning of the strength
of the hypervalent bond should be possible by variation of
the substituents of the β-diketonato moiety. For the substit-
uents of the silicon (germanium) we have selected the CF3
group, which was shown to promote the formation of the
hypervalent structures efficiently. The results in Table 2 for
the germanium (in Table S2 in the Supporting Information
for the silicon) compounds show clearly that the phenyl
substitution increases further the stability of the pentaco-
ordinate structure. 13h (E = Ge, R = CF3, R0 = Ph) is more
stable by 23 kcal/mol than its isomer 13o (E = Ge, R = CF3,
R0 = Ph), and this energy difference can be considered as the
strength of the hypervalent bond. It is worth noting that at
the MP2/6-31þG*//B3LYP/6-31þG* level the energy dif-
ference between the closed and the opened forms is 31 kcal/
mol. The higher predicted stability of the hypervalent com-
pound at the MP2 level is in agreement with our previous
results.3h For the analogous silicon compound 13h (E = Si,
R = CF3, R0 = Ph) is more stable by 23.1 kcal/mol than 13o
(Table S2), the MP2/6-31þG*//B3LYP/6-31þG* stability
of the closed form being 23.6 kcal/mol. It is worth noting that
the energy difference between 9 (R = H) and its isomer with
one opened five-membered ring was considerably smaller
(8.2 and 13.5 kcal/mol at the HF/6-31G** and MP2/6-
31G** levels, respectively).28 Also, the computed energy
difference between an OacetylfSi coordinating rotamer of
XMe2SiCH2NAc2 (X = -OAc, -F, -Cl, -Br, -OCOCF3)
with respect to the opened form did not exceed 6 kcal/mol29
and the QCISD(T)/6-311G**//MP2/6-31G*þZPE stability
of amino complexes of different substituted silanes even with
the most electronegative substituents was less than 5.2 kcal/
mol.30
ΔE (kcal/ þ2.0
mol)
a The relative energies are given with respect to the open forms 13o
(E = Ge, R0 = H) in kcal/mol.
˚
Table 2. B3LYP/6-31þG* Structural Data (in A) for the Hyper-
valent Germanium Species 13h (E = Ge) with Different R0 Groups
(R = CF3)a
R0 = H
R0 = Ph (14)
R0 = CF3
R0 = CH3
Ge-Oax
Ge-Oeq
Oeq-C1
Oax-C3
C1-C2
C2-C3
ΔE (kcal/
mol)
2.189
1.848
1.309
1.255
1.371
1.418
-10.9
2.038
1.836
1.319
1.280
1.386
1.415
-23.1
2.353
1.826
1.312
1.234
1.369
1.439
-13.5
2.096
1.841
1.315
1.269
1.380
1.419
-16.9
a The relative energies are given with respect to the open forms 13o
(E = Ge, R = CF3) in kcal/mol.
pentacoordinate structure 13h, and with R = F the pen-
tacoordinate structure becomes more stable than the
open-chain isomer 13o. The hypercoordinate germanium
compounds have an enhanced relative stability with respect
to their silicone counterparts in most of the cases; for the
heavier analogue the hypercoordinate structure is more
stable even for R = Cl. Not only the easily hydrolyzable
halogens (note that with di-, tri-, and tetrachlorosilanes the
formation of hexacoordinate anionic species was reported20)
but also the CF3 group turns out to promote the formation of
the hypercoordinate structures in a manner comparable to
that of fluorine! The introduction of ethoxy moieties (R =
-OEt) on the germanium center also supports the penta-
valency; the relative stability of the hypercoordinate form is
7.5 kcal/mol. The stability of this pentacoordinate structure
explains the ability of the acac ligand to inhibit the hydrolysis
of tetraethoxygermane. Interestingly in the case of the
silicon-centered analogue the open chain isomer is more
stable (by 6.6 kcal/mol); accordingly, in the hydrolysis reac-
tion of tetraethoxysilane the acac ligand should be a less
effective inhibitor. The stability difference between the
opened and the closed forms correlates with the axial E-O
On the basis of the above theoretical results on the
synthesizability,31 14 (13h, E = Ge, R = CF3, R0 = Ph)
was prepared from (CF3)3GeI and dibenzoylmethane in
toluene at -40 °C in the presence of triethylamine as proton
acceptor (Scheme 4). The product was isolated after recrys-
tallization from toluene/hexane as moisture-sensitive yellow
(25) Beachley, O. T., Jr.; Gardinier, J. R.; Churchill, M. R. Organo-
metallics 2000, 19, 4544–4549.
(26) Sanada, T.; Suzuki, T.; Yoshida, T.; Kaizaki, S. Inorg. Chem.
1998, 37, 4712–4717.
(27) Fukuda, Y.; Nakao, A.; Hayashi, K. Dalton Trans. 2002, 527–
533.
(28) Minyaev, R. M.; Starikov, A. G. Russ. Chem. Bull. 1999, 48,
1225–1233.
(29) Belogolova, E. F.; Sidorkin, V. F. J. Mol. Struct.
(THEOCHEM) 2004, 668, 139–145.
(30) Anglada, J. M.; Bo, C.; Bofill, J. M.; Crehuet, R. J.; Poblet, M.
Organometallics 1999, 18, 5584.
(31) Hoffmann, R.; Schleyer, P. v. R.; Schaefer, H. F. Angew. Chem.,
Int. Ed. 2008, 47, 7164.

Article
Organometallics, Vol. 29, No. 5, 2010 1103
Figure 2. Structural overlay of the two molecules in the asym-
metric unit showing the conformational difference especially at
the Ge atoms. Molecule 14a is green, and molecule 14b is red.
Figure 1. Molecular structures and ORTEP32 representation of
the two crystallographically independent molecules of 14 found
in the asymmetric unit. The displacement ellipsoids are drawn at
the 50% probability level, and heteroatoms are shaded. The
upper molecule is 14a, and the lower molecule is 14b.
Scheme 4. Preparation of Compound 14
Figure 3. Crystal packing diagram from the b crystallographic
axis showing the alternating layers of the two conformationally
different molecules. Molecule 14a is green, and molecule 14b is
red.
crystals with a yield of 74%. Well formed, pale yellow, prism-
shaped single crystals of 14 suitable for X-ray diffraction
study were obtained by recrystallization from diethyl ether at
-30 °C. The diffraction measurement was performed at
100(2) K. Despite the disordered CF3 groups it was possible
to refine the structure to 6.09%. Hydrogen atoms were found
on the difference Fourier map.
There are two chemically identical but crystallographically
different molecules in the asymmetric unit (Figure 1; crystal
data and details of the structure determination are given in
the Supporting Information).
˚
˚
moieties (C116-H116 F251 = 0.950 A, 2.550 A, 3.384(9)
3 3 3
˚
˚
˚
A, 147.0° and C216-H216 F = 153 0.950 A, 2.470 A,
3.361(5) A, 156.00°). The molecules are arranged in the
3 3 3
˚
crystal forming alternating layers of the phenyl rings and
the terminal trifluoromethyl groups along the a crystallo-
graphic axis (Figure 3). The phenyl moieties are not close
enough to each other to have a significant π π interaction
3 3 3
˚
(C111-C116 and C231-C236 at 3.736(2) A, C131-C136
˚
and C211-C216 at 3.811(2) A) because the three terminal
The two crystallographically independent molecules differ
in their conformation. The six-membered -O-C-C-C-
O-Ge- rings have a mostly delocalized electron system (see
also below) shown by the distribution of the bond lengths
(Table 3). However, the Ge atom is out of plane of the other
CF3 groups act as spacers. Some of the terminal CF3 groups
have enough free space available in the crystal to be dis-
ordered with site occupation factors of 0.670 around C16,
0.6307 around C25, and 0.926 around C26.
The X-ray structure is in good agreement with the com-
puted results (Table 2). The Ge atom remains in the plane in
the computed structure for the isolated molecule of 14.
Attempts to locate a nonplanar minimum on the B3LYP/
6-31þG* potential energy surface (starting an optimization
from the structure obtained by X-ray crystallography) has
failed; only the planar structure was obtained for 14 with
different optimization strategies.
˚
five atoms of the ring by 0.588 A in molecule 14a, while Ge
remains in the plane in molecule 14b (the distance between
˚
Ge and the -O-C-C-C-O- plane is 0.023 A). The two
molecules are shown superimposed in Figure 2 to visualize
the conformational difference. The packing arrangement
highlighting the molecules of two different conformations
is presented in Figure 3.
There is no classic hydrogen bond in the crystal structure.
Two weak C-H F interactions exist only between the two
Since our attempts at optimizing a nonplanar structure for
14 have failed, we have tried a different approach with the
3 3 3

1104 Organometallics, Vol. 29, No. 5, 2010
Bombicz et al.
Table 3. Important Interatomic Distances and Angles of Molecule 14a (Ge out of Plane) and Molecule 14b (Ge in Plane)
measured
computeda
measured
computeda
˚
Bond Distances (A)
Ge1-O11
Ge1-O12
O11-C11
O12-C13
C11-C12
C12-C13
1.841(3)
1.964(3)
1.323(5)
1.293(5)
1.377(6)
1.400(6)
1.854
2.035
1.319
1.284
1.385
1.413
Ge2-O21
1.828(3)
1.967(3)
1.328(4)
1.283(4)
1.372(6)
1.402(5)
1.845
2.042
1.318
1.279
1.385
1.415
Ge2-O22
O21-C21
O22-C23
C21-C22
C22-C23
Bond Angles (deg)
O11-Ge1-O12
Ge1-O11-C11
Ge1-O12-C13
O11-C11-C12
O12-C13-C12
C11-C12-C13
87.6(1)
85.9
O21-Ge2-O22
Ge2-O21-C21
Ge2-O22-C23
O21-C21-C22
O22-C23-C22
C21-C22-C23
88.2(1)
86.6
128.4(2)
126.0(2)
123.5(4)
122.1(4)
122.7(4)
133.0
129.3
123.5
122.7
122.6
132.2(2)
130.7(3)
123.3(4)
121.6(3)
123.6(4)
133.9
129.9
123.9
122.7
122.8
Dihedral Angles (deg)
Ge1-O11-C11-C12
16.0(6)
-14.4
Ge2-O21-C21-C22
-2.3(6)
3.6
a Computation refers to the geometric parameters of the optimized “molecule pair” structure.
3
˚
aim of describing the effects responsible for nonplanarity.
We have carried out a B3LYP/6-31G* geometry optimiza-
tion for a molecule pair of 14, starting from the solid-state
geometry in the crystal (Figure 2). In the optimized structure
one of the Ge atoms indeed remained significantly displaced
from the six-membered ring (see Table 3), while the deviation
from planarity was much less in case of the second molecule.
To understand the nature of the interaction, the analysis of
the B3LYP/6-31þG* electron density for the two molecular
assemblies (14a and 13b) at the geometry of the crystal
structure was carried out by the method developed by
Bader.33 This analysis revealed 11 bond critical points of
low electron density (ranging from 0.003 to 0.006 au), all
Table 4. Computed Electron Densities (in au/A ) and Their Lap-
lacians for the Open and Hypervalent Forms of 13 (R = CF3, R0 =
Ph, E = Si, Ge)
E = Si
electron
E = Ge
electron
species
bond
density
Laplacian
density
Laplacian
13h
O-Eax
O-Eeq
C-Eax
C-Eeq
O-E
0.0795
0.1040
0.1062
0.1096
0.1315
0.1156
-0.0884
-0.1619
-0.0430
-0.0411
-0.2563
-0.0465
0.0755
0.1137
0.1117
0.1185
0.1321
0.1248
-0.0605
-0.1395
-0.0256
-0.0236
-0.1673
-0.0294
13o
C-E
corresponding to F H interactions. These weak nonclas-
note that for the hitherto investigated hypercoordinate Si
complexes large positive Laplacians were reported,3e,29,30,34
which were considered a consequence of ionic interactions.
The O-Ge-C apical angles in the two molecules are close
to each other: 173.4(1)° in molecule 14a and 172.7(2)° in the
planar molecule 14b. We have investigated computationally
the structure with two equatorial Ge-O bonds, which was
10.1 kcal/mol less stable than 14 at the B3LYP/6-31þG*
level, while at the MP2/6-31þG*//B3LYP/6-31þG* level an
even smaller value (4.1 kcal/mol) was obtained. This has
turned out to be a first-order saddle point, which according
to an IRC study connects the two (energetically identical)
stereoisomeric forms of 14. This low-energy transition struc-
ture allows a facile interconversion of the two structures in
solution and indicates a dynamic NMR behavior. Never-
theless, the NMR spectral characteristics at -70 °C did not
show any change, in accordance with the low barrier (note
the MP2 results).
3 3 3
sical hydrogen bonds are likely to be responsible for the
special structural features observed in the crystal structure.
For the two oxygens attached to Ge, one is in an apical
˚
position, exhibiting a bond length of 1.964 (1.967) A, while
the other one is in an equatorial position, with a bond length
˚
of 1.841 (1.828) A (the data in parentheses refer to the
nonplanar molecule 14b). The difference is in agreement
with the usual lengthening of the apical bonds in trigonal-
bipyramidal molecules. For a better understanding of the
bonding situation around the germanium (silicon) core, the
electron density of 13o and 13h (R = CF3, R0 = Ph, E = Si,
Ge) was analyzed by the Bader method.33 The results are
summarized in Table 4. The C-E electron densities at the
critical points are similar for both the opened (13o) and
closed (13h) forms; furthermore, the values for the axial and
equatorial bonds differ only slightly. Among the O-E bonds
the one in the opened form exhibits the largest density at the
bond critical point, with the relative weakness of the axial
bond reflected by the smallest density. This observation is in
accordance with the length of the respective bonds given in
Tables 2 and S2). The (small) negative Laplacian values
indicate that all of the five bonds around germanium and
silicon have (polarized) covalent character. It is interesting to
The 19F NMR spectrum of 14 shows only a singlet for all
fluorine atoms at -56.57 ppm, a slight high-field shift
compared to the signals of (CF3)GeI (-53.38 ppm). In the
1H NMR spectrum a singlet appears for the H atom in the
(34) (a) Gordon, M. S.; Carroll, M. T.; Jensen, J. H.; Davis, L.;
Burggruf, L. W.; Guidry, R. M. Organometallics 1991, 10, 2657.
(b) Lyssenko, K. A.; Korlyukov, A. A.; Antipin, M. Yu.; Knyazev, S. P.;
Kirin, V. N.; Alexeev, N. V.; Chernyshev, E. A. Mendeleev Commun. 2000,
88. (c) Korlyukov, A. A.; Lyssenko, K. A.; Antipin, M. Yu.; Kirin, V. N.;
Chernyshev, E. A.; Knyazev, S. P. Inorg. Chem. 2002, 41, 5043–5051.
(d) Kocher, N.; Henn, J.; Gostevskii, B.; Kost, D.; Kalikhman, I.; Engels, B.;
Stalke, D. J. Am. Chem. Soc. 2004, 126, 5563–5568.
(32) Molecular Graphics, ORTEP, PLATON: Spek, A. L. J. Appl.
Crystallogr., 2003, 36, 7-13.
(33) (a) Bader, R. W. F.; Slee, T. S .; Cremer, D.; Kraka, E. J. Am.
Chem. Soc. 1983, 105, 5061. (b) Bader, R. W. F. Acc. Chem. Res. 1985,
18, 9.

Article
Organometallics, Vol. 29, No. 5, 2010 1105
C11(C12H)C13 framework at 6.42 ppm (for the labeling, see
Figure 1). In the 13C NMR spectrum only a small downfield
shift is observed for the C(CH)C framework (δCdΟ 187.42
ppm, δCH 95.35 ppm) in comparison to the signals of
dibenzoylmethane (δCdΟ 186.55, δCH 93.77 ppm). The re-
sonance of the CF3 groups appears as a septet of a quartet at
130.75 ppm. All these NMR data are in full accordance with
the low barrier interconversion of two identical but nonsym-
metric structures, obtained from the computations.
The six-membered -O-C-C-C-O-Ge- ring has an
apparently highly delocalized electron system according to
the single-crystal structural bond lengths, as also concluded
from the computed results (see above). This might suggest
that the six-membered ring can be aromatic, considering that
the Ge center contributes with 0 electrons to the 6-π-electron
system. Hyperconjugate aromatic systems with different
atoms without formal pz orbitals (carbon,35 phosphorus36)
are known, their aromaticity depending on the electron
donor or acceptor properties of the substituents on the
saturated center.35 Nevertheless, the GeO bond lengths in
14 do not show double-bond character, and also the B3LYP/
6-31þG* NICS(0) and NICS(1) values (þ3.7 and þ0.9 ppm,
respectively) indicate that no aromaticity is present in the
investigated system. Also, the frontier MOs are π orbitals
located mainly at the OCCCO fragment without any sig-
nificant involvement of Ge. The related silicon compound
13h (E = Si, R = CF3, R0 = Ph) exhibits aromaticity
measures similar to those of 14.
triethylamine, and C6D6 were dried over sodium/benzophe-
none. Dibenzoylmethane was dried in vacuo at room tempera-
ture for 2 h before use. (CF3)3GeI was purchased from Aldrich
Chemical Co. and used as received.
The 1H, 13C, and 19F NMR spectra were recorded on a Bruker
Avance 300 spectrometer operating at 300.1, 75.5, and 282.4 MHz,
respectively, using deuterated solvent (C6D6) as an internal lock
and TMS (1H, 13C) or CFCl3 (19F) as the external standard.
Melting points were taken on a Boetius micro melting point
apparatus and were uncorrected. Infrared spectra were recorded
on a Zeiss Specord IR 75 spectrometer, operating in the region
of 4000-400 cm-1. IR samples were prepared using Nujol.
High-resolution mass spectra were measured on a Varian
MAT 8200 mass spectrometer. Elemental analysis determina-
tion was performed with an Elementar Vario EL analyzer.
Synthesis of 14. A solution of (CF3)3GeI (0.813 g, 2.0 mmol) in
toluene (10 mL) was added dropwise to a solution of dibenzoyl-
methane (0.448 g, 2.0 mmol) and triethylamine (0.35 mL,
2.5 mmol) in toluene (10 mL) at -40 °C with stirring over a
1 h period. The reaction mixture was warmed slowly to room
temperature and stirred for a further 3 h and then filtered.
Removal of volatile materials from the filtrate in vacuo afforded
a yellow solid. Recrystallization of the residue from toluene/
hexane at -30 °C yielded the product (0.74 g, 74%) as yellow
crystals, mp 111-113 °C. Crystals of X-ray quality were grown
from diethyl ether at -30 °C. Anal. Calcd for C18H11F9O2Ge: C,
42.99; H, 2.20. Found: C, 43.08; H, 2.10. 1H NMR (benzene-d6):
δ 6.42 (s, 1H, CH), 6.92-6.99 (m, 4H, Ph), 7.06-7.12 (m, 2H,
Ph), 7.64-7.71 (m, 4H, Ph) ppm. 13C{1H} NMR (benzene-d6): δ
95.35 (CH), 128.51 (Ph), 128.98 (Ph), 130.75 (qua, 1JCF = 342.4
Hz, sep, 3JCF = 6.6 Hz, CF3), 134.04 (Ph), 134.70 (Ph), 187.42
(CO) ppm. 19F NMR (benzene-d6): δ -56.57 ppm. IR (cm-1):
1600 m, 1584 m, 1529 m, 1456 s. EI-MS: m/z 434.986 68 (calcd
for C17H11O2F674Ge 434.987 50) 27.82%, 432.985 10 (calcd for
C17H11O2F672Ge 432.988 40) 20.47%, 430.979 55 (calcd for
C17H11O2F670Ge 430.990 57) 15.05%, [Mþ - CF3].
Conclusions
The bidentate acac ligand and especially its phenyl deri-
vative (dibenzoylmethane) is efficient in complexing Si- and
Ge-centered molecules, resulting in neutral pentacoordinate
structures. The stabilizing effect of the CF3 substituents at
silicon or germanium is comparable to that of fluorine. With
three trifluoromethyl and a bidentate dibenzoylmethane
ligand a pentacoordinate germanium-centered molecule
could be synthesized and characterized by X-ray crystallo-
graphy. The resulting structure exhibited somewhat different
GeO bond lengths, in agreement with the apical and equa-
torial arrangement of the two oxygens, while the OCCCO
unit exhibits significant delocalization. The stability of the
pentacoordinate bond was estimated as 23 kcal/mol, in
comparison to the opened isomer. The Laplacians at the
bond critical points around the silicon or germanium
center indicate polarized covalent bonding. For the tris-
(triethoxygermene) center the pentacoordinate complex is
stable, while in the case of the silyl analogue the open-chain
tetracoordinate system is favored.
Data for the X-ray structure are as follows. Crystal data:
C18H11F9GeO2, formula weight 502.86, yellow, prism, size 0.75 ꢀ
0.60 ꢀ 0.25 mm, monoclinic crystal system, space group P21/c,
˚
˚
˚
a = 19.612(4) A, b = 14.042(3) A, c = 13.579(3) A, R = 90.00°,
o
3
˚
β = 105.02(3) , γ = 90.00°, V = 3611.8(12) A , T = 100(2) K,
Z = 8, F(000) = 1984, Dx =1.850 Mg m-3, μ = 1.799 mm-1. A
crystal was mounted on a loop. Cell parameters were deter-
mined by least-squares of the setting angles of 19 570 (2.9612 e
θ e 35.8470°) reflections. Intensity data were collected on a
Rigaku RAxis Rapid diffractometer (graphite monochroma-
˚
tor; Mo KR radiation, λ = 0.710 73 A) at 100(2) K in the range
3.09 e θ e 25.00°. A total of 84 243 reflections were collected,
of which 6351 were unique (R(int) = 0.1146, R(σ) = 0.0489);
6021 reflections were obtained with I > 2σ(I). Completeness to
2θ: 0.997. A numerical absorption correction was applied to
the data (the minimum and maximum transmission factors
were 0.3456 and 0.6619). The structure was solved by direct
methods (SHELXS-97).37 Neutral atomic scattering factors
and anomalous scattering factors were taken from ref 38.
Anisotropic full-matrix least-squares refinement (SHELXL-
97)39,40 on F2 for all non-hydrogen atoms yielded R1 = 0.0609
and wR2 = 0.1695 for 6021 (I > 2σ(I)) and R1 = 0.0656
and wR2 = 0.1755 for all (6351) intensity data (goodness of
fit 1.102; maximum and mean shift/esd 0.105 and 0.004;
extinction coefficient 0.0005(3)). The extinction coefficient
Experimental Section
General Considerations. All manipulations were performed in
flame- or oven-dried glassware under a dry nitrogen atmosphere
using standard Schlenk techniques. Toluene, diethyl ether,
(35) (a) Nyulaszi, L.; Schleyer, P. v. R. J. Am. Chem. Soc. 1999, 121,
6872–6875. (b) Wiberg, K. B.; Marquez, M. J. Am. Chem. Soc. 1998, 120,
2932–38.
(36) (a) Nyulaszi, L.; Veszpremi, T. J. Phys. Chem. 1996, 100, 6456–
6462. (b) Goeller, A.; Heydt, H.; Clark, T. J. Org. Chem. 1996, 61, 5840–
5846. (c) Goeller, A.; Clark, T. J. Mol. Model. 2000, 6, 133–149. (d) Wang,
(37) Sheldrick, G. M. SHELXS-97 Program for Crystal Structure
€
€
Solution; University of Gottingen, Gottingen, Germany, 1997.
(38) International Tables for X-ray Crystallography; Wilson, A. J. C.,
Ed.; Kluwer Academic: Dordrecht, The Netherlands, 1992; Vol C,
pp 193-199, 500-502, 219-222.
€
Z. X.; Schleyer, P. v. R. Helv. Chim. Acta 2001, 84, 1578–1600. (e) Benko,
(39) Sheldrick, G. M. SHELXS-97 Program for the Refinement of
€
€
Z.; Nyulaszi, L. Aromatic Phosphorus Heterocycles in Aromaticity in
Heterocyclic Compounds; Krygowsky, T. M., Cyransky, M. K., Vol. Eds.;
Springer: New York, 2009; Topics in Heterocyclic Chemistry 19, pp 27-81.
Crystal Structures; University of Gottingen, Gottingen, Germany, 1997.
(40) Barbour, L. J. X-Seed - A software tool for supramolecular
crystallography. J. Supramol. Chem. 2001, 1, 189–191.

1106 Organometallics, Vol. 29, No. 5, 2010
Bombicz et al.
expression is
obtained. Transition state structures (one negative eigenva-
lue of the second derivative matrix) were verified by subse-
quent optimizing after changing the geometry along the
single imaginary frequency. In some cases (see text) further
MP2/6-31þG*//B3LYP/6-31þG* calculations were carried
out. For the visualization of the optimized molecules, the
Molden program43 and the Mercury program were used.44
Bader analysis33 was preformed using the AIM2000 soft-
ware.45
-1=4
3
2
ꢁ
Fc ¼ kFc½1 þ 0:001Fc λ =sin ð2θÞꢂ
The number of parameters is 623. The maximum and
minimum residual electron densities in the final difference
map was 1.672 and -1.047 e/A . They can be found close to
the Ge centers.
The weighting scheme applied was
3
˚
Acknowledgment. Financial support from the Hungar-
ian Scientific Foundation OTKA T 049258 is gratefully
acknowledged. A diffractometer purchase grant from
the National Office for Research and Technology (MU-
00338/2003) is gratefully acknowledged.
2
w ¼ 1=½σ2ðFo Þ þ ð0:1166PÞ þ 2:5390Pꢂ
2
where
2
2
P ¼ ðFo þ 2Fc Þ=3
Hydrogen atomic positions were located in difference maps.
Hydrogen atoms were included in structure factor calculations,
but they were not refined.
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication number CCDC 746174.
Calculations. The structures were fully optimized at the
B3LYP41 functional with the 6-31þG* basis set, while the
“dimer” of 14 was calculated at the B3LYP/6-31þG*//
B3LYP/6-31G* level using the Gaussian 03 program pack-
age.42 Subsequent calculation of the second derivatives was
carried out to characterize the nature of the stationary points
Supporting Information Available:
Figure S1, giving the
B3LYP/6-31þg* optimized structure of 14 (14b), Table S1,
˚
giving the B3LYP/6-31þG* structural data (in A) for the
hypervalent silicon species 13h (E = Si) with different R
groups (R0 = H), Table S2, giving B3LYP/6-31þG* structural
˚
data (in A) for the hypervalent silicon 13h (E = Si, R = CF3)
with different R0 groups, Tables S3-S40, giving optimized
structures in Cartesian coordinate format with total energies,
Table S41, giving crystal data and details of the structure
determination for 14a and 14b, Table S42, giving final coordi-
nates and equivalent isotropic displacement parameters of the
non-hydrogen atoms for 14a and 14b, Table S43, giving
hydrogen atom positions and isotropic displacement para-
meters for 14a and 14b, Table S44, giving (an)isotropic dis-
placement parameters for 14a and 14b, Table S45, giving bond
(41) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
˚
distances (A) for 14a and 14b, Table S46, giving bond angles
(deg) for 14a and 14b, Table S47, giving torsion angles (deg) for
(42) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.;. Montgomery, J. A; Vreven, T., Jr.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakr-
zewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.,
Wallingford, CT, 2004.
˚
14a and 14b, Table S48, giving contact distances (A) for 14a
˚
and 14b, Table S49, giving hydrogen bonds (A, deg) for 14a
and 14b, and a CIF file, giving the structure of 14. This material
is available free of charge via the Internet at http://pubs.acs.org.
(43) Schaftenaar, G.; Noordik, J. H. Molden: a pre- and post-
processing program for molecular and electronic structures. J. Com-
put.-Aided Mol. Design 2000, 14, 123–134.
(44) Macrae, C. F.; , Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.;
McCabe, P.; Pidcock, E.; L. Rodriguez-Monge Taylor, R.; , J. van de
Streek Wood, P. A. Mercury CSD 2.0-New Features for the Visualiza-
tion and Investigation of Crystal Structures. J. Appl. Crystallogr., 2008,
41, 466-470(DOI: 10.1107/S0021889807067908).
€
€
(45) Biegler-Konig, F.; Schonbohm, J.; Bayles, D. J. Comput. Chem.
2001, 22, 545–559.