Neutral and cationic trimethylsilylmethyl complexes of indium

Article abstract of DOI:10.1021/om800562z

The trimethylsilylmethyl indium complex [In(CH₂-SiMe ₃)₃] (1) was studied by single-crystal X-ray structure analysis at low temperature and shown to be weakly associated as dimeric units with a long indium-carbon bond in the bridges. The bis(trimethylsilylmethyl) cation [In(CH₂SiMe₃)2(THF)3][B(C₆F ₅)₄] (2) was prepared by protonolysis of the neutral complex [In(CH₂SiMe₃)₃] with [NPhMe ₂H][B(C₆F₅)₄] in THF. Crystal structure analysis revealed that mononuclear 2 adopts a square-pyramidal geometry.

Full text of DOI:10.1021/om800562z

Organometallics 2008, 27, 4817–4820
4817
Notes
Neutral and Cationic Trimethylsilylmethyl Complexes of Indium
Ilja Peckermann, Dominique Robert, Ulli Englert, Thomas P. Spaniol, and Jun Okuda*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52074 Aachen, Germany
ReceiVed June 17, 2008
Table 1. Structural Features of Homoleptic Organoindium
Summary: The trimethylsilylmethyl indium complex [In(CH2-
SiMe3)3] (1) was studied by single-crystal X-ray structure
Compounds
degree of
∑
C-In-C
analysis at low temperature and shown to be weakly associated
as dimeric units with a long indium-carbon bond in the bridges.
The bis(trimethylsilylmethyl) cation [In(CH2SiMe3)2(THF)3]-
[B(C6F5)4] (2) was prepared by protonolysis of the neutral
complex [In(CH2SiMe3)3] with [NPhMe2H][B(C6F5)4] in THF.
Crystal structure analysis reVealed that mononuclear 2 adopts
a square-pyramidal geometry.
compound
[InMes3]
association
In · · · C (Å)
(deg)
ref
monomeric
359.9
7
[In{CH(SiMe3)2}3] monomeric
[In(CH2SiMe3)3] (1) dimeric
357.9
356.0
11
this
3.082(7)
work
[InMe3]
[InPh3]
tetrameric
3.11(4); 3.59(4)
358
360
15
16
17
infinite chain 3.07(2)
[In(CH2Ph)3]
[InCp3]
infinite chain 3.002(6); 3.081(7) a 356.3
infinite chain 2.466(8)/2.482(4) b 346.6/342.9 b 18
[IntBu3]
infinite chain 3.467(5)
359.6
19
Introduction
a First value for the In · · · ortho-C contact, second for the
In · · · meta-C contact. b First value from ref 18a, second from ref 18b.
Organoindium compounds, in particular allyl indium reagents,
are currently attracting interest as a new type of carbanionic
reagents with a reactivity profile distinct from that of conven-
tional polar organometallics based on main group elements.1,2
In the context of investigating cationic organyl complexes of
the rare-earth metals, we became interested in comparing the
Lewis acidity and electrophilicity of these elements vis-a`-vis
that of indium, which has an ionic radius (0.800 Å) similar to
that of the smaller rare-earth elements (Sc ) 0.745 Å; Lu )
0.861 Å; Y ) 0.900 Å).3 Compared with the lighter homologue
aluminum, indium shows a pronounced tendency to expand its
coordination sphere.4 While dimeric indium species are typically
encountered in heteroleptic derivatives with three-electron-donor
ligands in the bridges as in [{InMe2(µ-Ct CMe)}2],5 [{IntBu2(µ-
OEt)}2],6 or [{InMes2(µ-Cl)}2],7 Lewis base coordination leads
to discrete molecules with coordination number up to five, as
observed in the 10-electron species [In(CH2Ph)Cl2(THF)2]8 or
[In(η1-C5H5)Cl2(THF)2].9 Six-coordination is found in [InCl3-
(THF)3].10 Bulky organyl substituents such as mesityl C6H2Me3-
2,4,6 (Mes)7 and bis(trimethylsilyl)methyl CH(SiMe3)211 prevent
association in the solid state, giving monomeric species, whereas
with sterically less demanding ligands chain-like polymeric
structures in the solid state are formed (Table 1). In order to
compare the properties of the trimethylsilylmethyl ligand in
organorare-earth metal and organoaluminum chemistry,4,12 we
report here on the structure of previously reported [In(CH2-
SiMe3)3] (1) and the cation [In(CH2SiMe3)2(THF)3]-
[B(C6F5)4] (2) derived therefrom.
Results and Discussion
The trimethylsilylmethyl indium complex [In(CH2SiMe3)3]
(1) was synthesized according to the procedure previously
reported by Beachley et al. and isolated as a colorless oil.13
The solid state structure of [In(CH2SiMe3)3] (1), obtained from
single crystals grown in a microcapillary, revealed the presence
of a weakly associated dimer in the lattice with a distorted
trigonal-planar environment around the indium center (Figure
* Corresponding author. E-mail: jun.okuda@ac.rwth-aachen.de.
(1) For an overview of recent applications of indium organyls in organic
syntheses, see: Araki, S.; Hirashita, T. In ComprehensiVe Organometallic
Chemistry III; Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier: Oxford,
2007; Vol. 9, p 649.
(2) (a) Araki, S.; Hirashita, T. In Main Group Metals in Organic
Synthesis; Yamamoto, H., Oshima, K., Eds.; Wiley-VCH: Weinheim,
Germany, 2004; p 323. (b) Loh, T.-P. Science of Synthesis; Georg Thieme:
Stuttgart, Germany, 2004; Vol. 7, p 413.
(3) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751.
(4) (a) Kramer, M. U.; Robert, D.; Nakajima, Y.; Englert, U.; Spaniol,
T. P.; Okuda, J. Eur. J. Inorg. Chem. 2007, 665. (b) Atwood, D. A. Coord.
Chem. ReV. 1998, 176, 407.
(5) Fjeldberg, T.; Haaland, A.; Seip, R.; Weidlein, J. Acta Chem. Scand.
1981, 35A, 437.
(8) Kra¨uter, T.; Werner, B.; Neumu¨ller, B. Z. Naturforsch. 1996, 51b,
637.
(9) Visona`, P.; Benetollo, F.; Rossetto, G.; Zanella, P. Polyhedron 1996,
15, 1743.
(10) Wells, R. L.; Kher, S. S.; Baldwin, R. A.; White, P. S. Polyhedron
1994, 13, 2731.
(6) Bradley, D. C.; Frigo, D. M.; Hursthouse, M. B.; Hussain, B.
Organometallics 1988, 7, 1112.
(11) Carty, A. J.; Gynane, M. J. S.; Lappert, M. F.; Miles, S. J.; Singh,
A.; Taylor, N. J. Inorg. Chem. 1980, 19, 3637.
(12) (a) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347, 339. (b)
Zeimentz, P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV. 2006,
106, 2404.
(13) (a) Beachley, O. T.; Rusinko, R. N. Inorg. Chem. 1979, 18, 1966.
(b) Kopasz, J. P.; Hallock, R. B.; Beachley, O. T. Inorg. Synth. 1986, 24,
89.
(7) (a) Leman, J. T.; Barron, A. R. Organometallics 1989, 8, 2214. (b)
Schluter, R. D.; Cowley, A. H.; Atwood, D. A.; Jones, R. A.; Bond, M. R.;
Carrano, C. J. J. Am. Chem. Soc. 1993, 115, 2070. (c) Rossetto, G.; Brianese,
N.; Camporese, A.; Casellato, U.; Ossola, F.; Porchia, M.; Zanella, P.;
Graziani, R. Gazz. Chim. Ital. 1990, 120, 805. (d) Quillian, B.; Wang, Y.;
Wie, P.; Handy, A.; Robinson, G. H. J. Organomet. Chem. 2006, 691, 3765.
10.1021/om800562z CCC: $40.75
2008 American Chemical Society
Publication on Web 08/27/2008

4818 Organometallics, Vol. 27, No. 18, 2008
Notes
Scheme 1
plane (∑C-Al-C ) 343.3°).4 The deviation from planarity in 1
is however less pronounced. Conversely, the boron and gallium
analogues were found to be monomeric in the solid state.4
The In-C bond lengths in 1 ranging from 2.171(8) and
2.189(7) Å fall into the range of values observed in earlier
studies about the solid state structures of tri(alkyl) indium
compounds.7,11,15-19 As a result of the steric congestion induced
by the close contact between both molecules, the In-C5-Si2
angle (110.7(3)°) is significantly smaller compared to In-C1-Si1
(124.6(4)°) and In-C9-Si3 (121.3(4)°). The bond of the alkyl
group that shows a close interaction with the neighboring
molecule is slightly elongated (In1-C5 ) 2.189(7) Å). Simi-
larly, the C5-Si2 bond (1.870(7) Å) is slightly elongated (cf.
C1-Si1 1.850(8) Å and C9-Si3 1.843(8) Å), although the
significance of this comparison is limited by the rather high
standard uncertainties.
Figure 1. ORTEP view of [In(CH2SiMe3)3] (1). Displacement
ellipsoids are drawn at the 50% probability level. Selected bond
angles (Å) and angles (deg): In1-C1 2.171(8), In1-C5 2.189(7),
In1-C9 2.175(8), C1-Si1 1.850(8), C5-Si2 1.870(7), C9-Si3
1.843(8); C1-In1-C5 119.9(3), C5-In1-C9 116.2(3), C9-In1-C1
119.9(3),In1-C1-Si1124.6(4),In1-C5-Si2110.7(3),In1-C9-Si3
121.3(4).
Since cationic dialkyl complexes of the inherently Lewis
acidic group 3 and 13 metals are of interest,12,20 we have studied
the formation of the monocationic derivative of 1. Only few
cationic diorganoindium complexes have been reported so
far.21-23 The reaction of 1 with the strong Brønsted acid
[NPhMe2H][B(C6F5)4] in THF gave the bis(trimethylsilylmeth-
yl)indium(III) cation by protonolysis of one alkyl group and
abstraction of tetramethylsilane (Scheme 1). Weaker acids such
as [NEt3H][B(C6F5)3] failed to protonolyze 1.
The cationic complex 2 was isolated as colorless, thermally
robust crystals soluble in benzene. Variable-temperature 1H
NMR spectra suggest labile THF ligands. The charge-separated
Figure 2. ORTEP view of [In(CH2SiMe3)3] (1). Displacement
ellipsoids are drawn at the 50% probability level. Hydrogen atoms
are omitted for clarity. Selected interatomic distances (Å) and angles
(deg): In1 · · · In1′ 3.6668(14), In1-C5 2.189(7), In1 · · · C5′ 3.082(7);
In1-C5-In1′ 86.4(2), C5-In1-C5′ 93.6(2). Primed atoms are
related to unprimed atoms by the symmetry operation 1-x, 1-y,
1-z.
(15) (a) Amma, E. L.; Rundle, R. E. J. Am. Chem. Soc. 1958, 80, 4141.
(b) Vranka, R. G.; Amma, E. L. J. Am. Chem. Soc. 1967, 89, 3121. (c)
Blake, A. J.; Cradock, S. J. Chem. Soc., Dalton Trans. 1990, 2993. (d)
Lewinski, J.; Zachara, J.; Starowieyski, K. B.; Justyniak, I.; Lipkowski, J.;
Bury, W.; Kruk, P.; Wozniak, R. Organometallics 2005, 24, 4832.
(16) (a) Malone, J. F.; McDonald, W. S. Chem. Commun. 1969, 591.
(b) Malone, J. F.; McDonald, W. S. J. Chem. Soc. A 1970, 3362.
(17) Neumu¨ller, B. Z. Anorg. Allg. Chem. 1991, 592, 42.
1). In contrast to the perfect trigonal-planar geometry observed
in [InMes3] (∑C-In-C ) 359.9°),7 the sum of the angles around
the indium center in 1 (∑C-In-C ) 356.0°) presents a slight
deviation from planarity. Thus, the central atom is found
0.2527(6) Å above the plane subtended by the carbon atoms
C1, C5, and C9. Similarly, the indium center in [In{CH-
(SiMe3)2}3] is found 0.191 Å above the plane defined by the
(18) (a) Einstein, F. W. B.; Gilbert, M. M.; Tuck, D. G. Inorg. Chem.
1972, 11, 2832. (b) Beachley, O. T., Jr.; MacRae, D. J.; Kovalevsky, A. Y.;
Zhang, Y.; Li, X. Organometallics 2002, 21, 4632.
(19) (a) Uhl, W.; Emden, C. H.; Geisler, G.; Harms, K. Z. Anorg. Allg.
Chem. 2003, 629, 2157. (b) Cowley, A. R.; Downs, A. J.; Marchant, S.;
Macrae, V. A.; Taylor, R. A.; Parsons, S. Organometallics 2005, 24, 5702.
(20) (a) For a recent overview of cationic aluminum complexes, see:
Saito, S. In ComprehensiVe Organometallic Chemistry III; Mingos, D. M. P.,
Crabtree, R. H., Eds.; Elsevier: Oxford, 2007; Vol. 9, p 283. (b) For a recent
overview of cationic gallium and indium complexes, see: Schulz, S. In
ComprehensiVe Organometallic Chemistry III; Mingos, D. M. P., Crabtree,
R. H.,Eds.; Elsevier: Oxford, 2007; Vol. 3, p 297.
three carbon atoms directly bound to the metal (∑C-In-C
)
357.9°).11 In 1, a weak interaction of each indium atom with a
carbon atom of a neighboring molecule [In1 · · · C5′ ) 3.082(7)
Å] in the solid state leads to formation of a dimeric structure
(Figure 2). This short interaction represents the only contact
involving interatomic distances significantly shorter than the sum
of the van der Waals radii.14 The dimeric nature of 1 is
reminiscent of that of its aluminum congener [Al(CH2SiMe3)3],
where the metal is situated 0.4748(6) Å above the C1-C2-C3
(21) (a) Neumu¨ller, B.; Gahlmann, F. J. Organomet. Chem. 1991, 414,
271. (b) Gahlmann, F.; Neumu¨ller, B. Z. Anorg. Allg. Chem. 1994, 620,
847.
(22) Hoffmann, K.; Weiss, E. J. Organomet. Chem. 1973, 50, 17.
(23) (a) Korolev, A. V.; Delpech, F.; Dagorne, S.; Guzei, I. A.; Jordan,
R. F. Organometallics 2001, 20, 3367. (b) Delpech, F.; Guzei, I. A.; Jordan,
R. F. Organometallics 2002, 21, 1167. (c) Robson, D. A.; Bylikin, S. Y.;
Cantuel, M.; Male, N. A. H.; Rees, L. H.; Mountford, P.; Schro¨der, M.
J. Chem. Soc., Dalton Trans. 2001, 157. (d) Hausen, H. D.; Mertz, K.;
Weidlein, J.; Schwarz, W. J. Organomet. Chem. 1975, 93, 291. (e) Cowley,
A. R.; Downs, A. J.; Marchant, S.; Macrae, V. A.; Taylor, R. A.; Parsons,
S. Organometallics 2005, 24, 5702.
(14) The CSD database suggests a value of 1.93 Å for the van der Waals
radius of indium, see: (a) Bondi, A. J. Phys. Chem. 1964, 68, 441. PLATON
uses the even larger value of 2.43 Å, see: (b) Spek, A. L. J. Appl.
Crystallogr. 2003, 36, 7. Carbon is commonly associated with a contact
radius of 1.70 Å, see refs 14a and b and (c) Allen, F. Acta Crystallogr.
Sect. B 2002, 58, 380.
(24) Hallock, R. B.; Beachley, O. T., Jr.; Li, Y.-J.; Sanders, W. M.;
Churchill, M. R.; Hunter, W. E.; Atwood, J. L. Inorg. Chem. 1983, 22,
3683.

Notes
Organometallics, Vol. 27, No. 18, 2008 4819
Table 3. Crystal Data and Convergence Results for [In(CH2SiMe3)3]
(1) and [In(CH2SiMe3)2(THF)3][B(C6F5)4] (2)
1
2
empirical formula
Mr (g mol-1
C12H33InSi3
376.47
C20H46InO3Si2,C24BF20
1184.62
)
cryst size (mm)
cryst color and habit
cryst syst
space group
a (Å)
0.5 × 0.3 × 0.3 0.43 × 0.34 × 0.23
colorless rod
triclinic
colorless block
monoclinic
P2/c
j
P1
10.353(3)
10.358(3)
10.386(2)
74.22(2)
77.787(19)
67.66(2)
984.0(4)
2
25.692(3)
10.8489(13)
18.007(2)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
104.287(2)
Figure 3. ORTEP view of the cationic part of one of the two
independent ion pairs in [In(CH2SiMe3)2(THF)3][B(C6F5)4] (2).
Displacement ellipsoids are drawn at the 30% probability level.
Hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): In1-C1 2.136(11), In1-O1 2.425(7); C1-In1-C1′
159.0(6),C1-In1-O2100.5(3),O1-In1-O1′158.3(4),O1-In1-O2
79.15(18).
γ (deg)
V (Å3)
4863.9(10)
4
Z
Dcalc (g · cm-3
T (K)
)
1.271
1.618
213(2)
130(2)
µ(Mo KR) (mm-1
F(000)
)
1.366
0.651
392
2384
θ range (deg)
2.05-26.01
0.82-22.76
Table 2. Selected Indium-Carbon Distances in Ionic Organoindium
no. of reflns collected
8000
40 604
Compounds
no. of reflns obsd [I > 2σ(I)] 2828
no. of indep reflns (Rint 3855 (0.0841)
5867
)
6560 (0.0638)
6560/0/648
1.191
0.0812, 0.2065
0.0876, 0.2094
compound
[In(iPr)2(THF)2][BF4]
[In(Mes)2][BF4]
[In(CH2SiMe3)2(THF)3][B(C6F5)4] (2) 2.136(11), 2.133(10) this work
In-C (Å)
2.128(6)
2.130(10)
ref
21a
21b
no. of data/restraints/params 3855/0/154
goodness-of-fit on F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
1.077
0.0634, 0.1311
0.0970, 0.1384
[K][InMe4]
[K][In(CH2SiMe3)4]
2.239(3)
2.236(4), 2.234(4),
2.235(4), 2.251(4)
22
24
largest diff in peak and
0.986 and -0.836 2.403 and -1.618
hole (e · Å-3
)
dried over CaH2, distilled, and degassed prior to use. Anhydrous
InCl3 (ABCR) and [NPhMe2H][B(C6F5)4] (Boulder Scientific) were
used as received. All other chemicals were commercially available
and used after appropriate purification. NMR spectra were recorded
on a Bruker DRX 400 spectrometer (1H 400.1 MHz, 13C 100.6
MHz) or on a Varian Unity 500 spectrometer (1H, 499.6 MHz;
13C, 125.6 MHz; 11B, 160.3 MHz; 19F, 376.4 MHz) at room
temperature unless otherwise stated. All chemical shifts are given
in ppm. Chemical shifts for 1H and 13C NMR spectra were
referenced internally using the residual solvent resonances and
reported relative to SiMe4. 11B NMR spectra were referenced
externally to a 1 M solution of NaBH4 in D2O. 19F NMR spectra
were referenced externally to neat CFCl3.
[In(CH2SiMe3)3] (1). This compound was synthesized according
to the published procedure13 and isolated as a colorless liquid in 74%
yield; mp -42 °C. 1H NMR (CD2Cl2): δ -0.37 (s, 3 × 2 H, InCH2),
0.01 (s, 3 × 9 H, Si(CH3)3). 1H NMR (200 MHz, THF-d8): δ -0.50
(s, 3 × 2 H, InCH2), 0.01 (s, 3 × 9 H, Si(CH3)3). 13C{1H} NMR
(CD2Cl2): δ 2.47 (Si(CH3)3), 10.79 (InCH2).
ion pair crystallized in the monoclinic space group P2/c (No.
13) with the indium center as well as the oxygen atom O2 on
a crystallographic C2 axis and two independent molecular cations
within the unit cell (Figure 3). The indium atom is coordinated
to two σ-bound alkyl groups and three oxygen atoms of the
THF molecules in a square-pyramidal geometry, in which the
O2 oxygen atom occupies the axial position. Selected In-C
bond lengths of ionic indium(III) complexes are compiled in
Table 2. The values of 2.230(3)-2.239(3) Å in tetrahedral
indates are ca. 0.1 Å larger than in the cationic indium organyls
with distances of 2.13 Å, which is attributed to the positive
charge on the metal atom. The apical THF ligands in 2 are
stronger coordinated than the basal THF ligands. As expected,
the cationic complexes show shorter In-C bond lengths.
The In-O bond lengths to the basal THF ligands in 2
(2.425(7) and 2.458(7) Å) are ca. 0.2 Å longer than the
equatorial THF ligands in the octahedral [InCl3(THF)3] complex
(2.235(10) and 2.223(11) Å).10 The distances to the apical THF
ligands in 2 (2.223(12) and 2.253(10) Å) are similar to the bond
length of indium to the axial THF ligand (2.304(9) Å) in
[InCl3(THF)3].10
[In(CH2SiMe3)2(THF)3][B(C6F5)4] (2). To
a solution of
[In(CH2SiMe3)3] (200 mg, 512 µmol) in 3 mL of THF was added
a solution of [NPhMe2H][B(C6F5)4] (416 mg, 512 µmol) in 3 mL
of THF, and the mixture was stirred at 60 °C for 17 h. After
removing the solvent in Vacuo, the white precipitate was repeatedly
washed with pentane and dried under reduced pressure to give 550
mg (503 µmol) of a colorless solid; yield 95%; mp 157-158 °C.
Crystals were grown from a THF/pentane solution at -30 °C within
one week. 1H NMR (THF-d8): δ 0.14 (s, 2 × 9 H, Si(CH3)3), 0.15
(s, 2 × 2 H, InCH2), 1.78 (m, 2 × 4 H, ꢀ-THF), 3.62 (m, 2 × 4 H,
R-THF). 13C{1H} NMR (THF-d8): δ 0.0 (InCH2SiCH3), 3.7
(InCH2SiCH3), 23.1 (ꢀ-THF), 65.1 (R-THF), 126.6 (br, Ph-1), 134.4
In summary, we have structurally characterized the parent
neutral tris(trimethylsilylmethyl)indium [In(CH2SiMe3)3] (1)
along with the bis(trimethylsilylmethyl) cation [In(CH2SiMe3)2-
(THF)3][B(C6F5)4] (2) and illustrated the tendency to higher
coordination number for the trivalent indium center. This is in
agreement with previously studied organoindium cations sta-
bilized by noncoordinating anions.23
Experimental Section
1
1
(d, JCF ) 230 Hz, Ph-4), 135.9 (Ph-3), 147.1 (d, JCF ) 264 Hz,
Ph-2). 11B{1H} NMR (THF-d8): δ -16.6. 19F NMR (THF-d8): δ
-168.8, -165.1, -132.8. 1H NMR (toluene-d8, -60 °C): δ -0.47
(s, 2 × 2 H, InCH2), -0.02 (s, 2 × 9 H, Si(CH3)2), 1.29 (br, 3 ×
4 H, ꢀ-THF), 3.31 (br, 3 × 4 H, R-THF). 1H NMR (toluene-d8, 60
°C): δ -0.23 (s, 2 × 2 H, InCH2), -0.08 (s, 2 × 9 H, (SiCH3)2),
1.40 (m, 3 × 4 H, ꢀ-THF), 3.36 (m, 3 × 4 H, R-THF). Anal. Calcd
General Considerations. All operations were performed under
an inert atmosphere of argon using standard Schlenk-line or
glovebox techniques. THF and pentane were distilled from sodium
benzophenone ketyl and sodium benzophenone ketyl triglyme,
respectively. Deuterated THF and toluene were dried over sodium,
distilled, and degassed prior to use; deuterated dichloromethane was

4820 Organometallics, Vol. 27, No. 18, 2008
Notes
for C44H46BF20InO3Si2: C, 44.61; H, 3.91; In 9.69. Found: C, 44.69;
H, 3.88; In, 9.49.
multiscan method as implemented in PLATON.25 The structures
were solved by direct methods and refined against all F2 data.26
Hydrogen atoms were treated as riding in idealized geometry. For
the graphical representation, the program ORTEP was used as
implemented in the program system WinGX.27 The data for CCDC
reference numbers 690488 (1) and 690487 (2) can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Crystal Structure Determination of 1 and 2. In view of the
low melting point, a single crystal of compound 1 was directly
grown on a NONIUS CAD4 diffractometer. A capillary containing
ca. 2 µL of the compound was exposed in appropriate geometry
(ꢁ ) 90°) to a cold stream of N2; the sample completely solidified.
The temperature of the gas stream was gradually increased to the
melting point, retaining only a small fraction of solid in the tip of
the capillary. Slow cooling resulted in a crystalline sample. The
procedure was repeated until a single crystal of satisfactory quality
was obtained; its diffraction pattern was directly registered on the
CAD4 diffractometer. X-ray diffraction measurement of 2 was
performed on a Bruker AXS diffractometer. Due to the low crystal
quality and the resulting low diffraction intensities at higher θ
angles, the measurement of 2 was performed only up to a maximum
θ value of 22.8°. Crystal data and convergence results are given in
Table 3. Intensity data for 2 were corrected for absorption by the
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie for
financial support.
Supporting Information Available: Crystallographic data for
1 and 2 as a CIF file. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM800562Z
(25) Spek, A. L. PLATON, A multipurpose crystallographic tool; Utrecht
University: Utrecht, The Netherlands, 2001.
(26) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(27) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.