Synthesis and characterization of stable hypervalent carbon compounds (10-C-5) bearing a 2,6-bis(p-substituted phenyloxymethyl)benzene ligand

Article abstract of DOI:10.1021/ja043802t

X-ray analysis of bis(p-fluorophenyl)methyl cation bearing a 2,6-bis(p-tolyloxymethyl)benzene ligand showed a symmetrical structure (10-C-5) where the two C-O distances are identical, although the distance (2.690(4) A) is longer than those (2.43(1) and 2.

Full text of DOI:10.1021/ja043802t

Published on Web 04/02/2005
Synthesis and Characterization of Stable Hypervalent Carbon
Compounds (10-C-5) Bearing a 2,6-Bis(p-substituted
phenyloxymethyl)benzene Ligand
Kin-ya Akiba,*,‡ Yuji Moriyama,† Mitsuhiro Mizozoe,† Hideki Inohara,†
Takako Nishii,† Yohsuke Yamamoto,*,† Mao Minoura,† Daisuke Hashizume,§
Fujiko Iwasaki,§ Nozomi Takagi,| Kazuya Ishimura,| and Shigeru Nagase|
Contribution from the Department of Chemistry, Graduate School of Science,
Hiroshima UniVersity, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan,
AdVanced Research Center for Science and Engineering, Waseda UniVersity, 3-4-1 Ohkubo,
Shinjuku-ku, Tokyo 165-8555, Japan, Department of Applied Physics and Chemistry,
The UniVersity of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan,
and Department of Theoretical Molecular Science, Institute for Molecular Science, Myodaiji,
Okazaki 444-8585, Japan
Received November 30, 2004; E-mail: yyama@sci.hiroshima-u.ac.jp
Abstract: X-ray analysis of bis(p-fluorophenyl)methyl cation bearing a 2,6-bis(p-tolyloxymethyl)benzene
ligand showed a symmetrical structure (10-C-5) where the two C-O distances are identical, although the
distance (2.690(4) Å) is longer than those (2.43(1) and 2.45(1) Å) of 1,8-dimethoxy-9-dimethoxymethyl-
anthracene monocation, which was recently reported by us. However, X-ray analysis of the more stable
aromatic xanthylium cation with the same benzene ligand showed the tetracoordinate carbon structure
where only one of the two oxygen ligands is coordinated with the central carbon atom. These results clearly
indicate that the carbocations (10-C-5) bearing the sterically flexible benzene ligand were quite sensitive
to the electronic effect on the central carbon atom. The electron distribution analysis by accurate X-ray
measurements and the density functional calculation on the initially mentioned bis(p-fluorophenyl)methyl
cation clearly show that the central carbon atom and the two oxygen atoms are bonded even if the bond
is weak and ionic based on the small value of the electron density (F(r)) and the small positive Laplacian
2
value (∇ F(r)) at the bond critical points.
Introduction
compounds of these elements. In 1951, theoretical interpretation
of the structure of [I-I-I]-K+ and its analogues was proposed
The chemistry of hypervalent compounds has been acquiring
wider and deeper attention both by organic chemists and by
inorganic chemists as a new and rapidly developing area
between the two fields during the past 20 years.1 Especially,
during active experimental investigations on the organic chem-
istry of silicon,2 phosphorus,3 sulfur,4 and iodine,5 several new,
unique but fundamental features of structures and reaction
patterns have been found to commonly occur to the organic
on the basis of the three-center four-electron (3c-4e) bond using
molecular orbital theory.6a The three-center four-electron (3c-
4e) bond has been called a hypervalent bond and consists of an
apical bond of a pentacoordinate trigonal bipyramidal molecule
where a hypervalent bond is most typically seen.6b To experi-
mentally create a 3c-4e bond of pentacoordinate molecules, three
methods can be considered (Scheme 1): (i) add two free radicals
to coordinate with a pair of unshared electrons in a p orbital;
(ii) add two pairs of unshared electrons (nucleophiles) to
† Hiroshima University.
‡ Waseda University.
§ The University of Electro-Communications.
| Institute for Molecular Science.
(4) (a) Martin, J. C. Science 1983, 221, 509-514. (b) Drabowicz, J. In
Chemistry of HyperValent Compounds; Akiba, K.-y., Ed.; Wiley-VCH:
New York, 1999; Chapter 7, pp 211-240 and references therein. (c)
Furukawa, N.; Sato, S. In Chemistry of HyperValent Compounds; Akiba,
K.-y., Ed.; Wiley-VCH: New York, 1999; Chapter 8, pp 241-278 and
references therein. (d) Lentz, D.; Seppelt, K. In Chemistry of HyperValent
Compounds; Akiba, K.-y., Ed.; Wiley-VCH: New York, 1999; Chapter
10, pp 295-326 and references therein.
(1) (a) Akiba, K.-y. Chemistry of HyperValent Compounds; Wiley-VCH: New
York, 1999. (b) Block, E. Heteroatom Chemistry; VCH: New York, 1990.
(2) (a) Corriu, J. P. In Chemistry of HyperValent Compounds; Akiba, K.-y.,
Ed.; Wiley-VCH: New York, 1999; Chapter 4, pp 81-146 and references
therein. (b) Kira, M.; Zhang, L. C. In Chemistry of HyperValent Compounds;
Akiba, K.-y., Ed.; Wiley-VCH: New York, 1999; Chapter 5, pp 147-
169 and references therein.
(3) (a) Holmes, R. R. Pentacoordinated Phosphorus-Structure and Spectros-
copy; ACS Monograph 175, 176; American Chemical Society: Washington,
DC, 1980; Vols. 1, 2. (b) Corbridge, D. E. C. Phosphorus: An Outline of
Its Chemistry, Biochemistry, and Technology, 4th ed.; Elsevier: Amsterdam,
1990; Chapter 14, pp 1233-1256. (c) Burgada, R.; Setton, R. In The
Chemistry of Organophosphorus Compounds; Hartley, F. R., Ed.; Wiley-
Interscience: Chichester, 1994; Vol. 3, pp 185-272. (d) Kawashima, T.
In Chemistry of HyperValent Compounds; Akiba, K.-y., Ed.; Wiley-
VCH: New York, 1999; Chapter 6, pp 171-210 and references therein.
(5) (a) Zhdankin, V. V.; Stang, P. In Chemistry of HyperValent Compounds;
Akiba, K.-y., Ed.; Wiley-VCH: New York, 1999; Chapter 11, pp 327-
358 and references therein. (b) Ochiai, M. In Chemistry of HyperValent
Compounds; Akiba, K.-y., Ed.; Wiley-VCH: New York, 1999; Chapter
12, pp 359-388 and references therein. (c) Varvoglis, A. The Chemistry
of Polycoordinated Iodine; VCH: New York, 1992.
(6) (a) Pimentel, G. C. J. Chem. Phys. 1951, 19, 446. Hackand, R. J.; Rundle,
R. E. J. Am. Chem. Soc. 1951, 73, 4321. (b) Musher, J. I. Angew. Chem.,
Int. Ed. Engl. 1969, 8, 54-68.
9
10.1021/ja043802t CCC: $30.25 © 2005 American Chemical Society
J. AM. CHEM. SOC. 2005, 127, 5893-5901
5893

A R T I C L E S
Akiba et al.
Scheme 1. Creation of a Three-Center Four-Electron (3c-4e) Bond of Pentacoordinate Molecules
Scheme 2. Synthesis of Carbocations Bearing 2,6-Bis(sulfur- or
selenium-substituted)methylbenzene
coordinate with a vacant p orbital; or (iii) add a pair of unshared
electrons to coordinate with the σ* orbital of an X-Z bond in
a cationic or neutral molecule. When X is a carbon, method
(iii) corresponds to the formation of the transition state (TS) of
the SN2 reaction.
Recently, we reported the first fully characterized pentaco-
ordinate hypervalent 10-C-57 carbon compound (1)8 and the 10-
B-5 boron compounds (2)9 bearing a sterically rigid 1,8-
dimethoxyanthracene ligand, which correspond to method (ii)
above. The X-ray results [the two O-C distances are almost
identical (2.43(1) and 2.45(1) Å) in 1, and the O-B distances
are 2.405(6) and 2.462(6) Å in 2 (X ) OMe)] and the hybrid
density functional theory (DFT) calculation of 1 and 2 clearly
showed the presence of an attractive interaction between the
central carbon (or the boron) atom and the oxygen atoms at the
1,8 positions, although the C(or B)-O bond is weak and ionic.8,9
The bonding nature of the central carbon (or the boron) atom
and the coordinating oxygen atoms bearing an anthracene ligand
will be discussed in a separate paper.9c
and the two O(p-Tol) groups in 15b-ClO4 was clarified by
electron-distribution analysis based on accurate X-ray measure-
ments and DFT calculation.
Instead of the sterically rigid anthracene derivatives, here we
report the synthesis and crystal structures of carbocations (3)
having a series of newly prepared 2,6-bis(substituted)methyl-
benzene ligands.10 Among the series, compounds 7a-7d
(Scheme 2) bearing two SMe, S(p-Tol) (p-Tol: p-CH3C6H4),
and SeMe groups showed unsymmetrical structures where only
one of the two sulfurs (or seleniums) coordinated with the central
carbon atom resulting in sulfonium (or selenonium) salts.
However, X-ray analysis of sterically flexible 15b-ClO4, 15c-
ClO4, and 15e-ClO4 bearing two O(p-Tol) groups and 16a-
ClO4, 16b-PF6, and 16d-PF6 bearing two O(p-CH3OC6H4)
groups (Scheme 5 and Table 2) showed symmetrical structures
where the two O-C distances are almost identical, although
the two O-C distances (2.6-2.9 Å) are even longer than those
of 1. The attractive O-C interaction between the central carbon
Figure 1. 1H and 13C NMR spectra of 7a-ClO4 at -40 °C (CD3CN).
Scheme 3. Bond Switching (Bell Clapper Rearrangement) in 7
(7) For N-X-L designation: X, central atom; N, formal valence-shell electrons
about an X; L, the number of ligands. Perkins, C. W.; Martin, J. C.;
Arduengo, A. J.; Lau, W.; Alegria, A.; Kochi, J. K. J. Am. Chem. Soc.
1980, 102, 7753.
(8) (a) Akiba, K.-y.; Yamashita, M.; Yamamoto, Y.; Nagase, S. J. Am. Chem.
Soc. 1999, 121, 10644. (b) Yamashita, M.; Kamura, K.; Yamamoto, Y.;
Akiba, K.-y. Chem.-Eur. J. 2003, 9, 3655-3659.
(9) (a) Yamashita, M.; Yamamoto, Y.; Akiba, K.-y.; Nagase, S. Angew. Chem.,
Int. Ed. 2000, 39, 4055-4058. (b) Yamashita, M.; Watanabe, K.;
Yamamoto, Y.; Akiba, K.-y. Chem. Lett. 2001, 1104-1105. (c) Yamashita,
M.; Yamamoto, Y.; Akiba, K.-y; Hashizume, D.; Iwasaki, F.; Takagi, N.;
Nagase, S. J. Am. Chem. Soc. 2005, 127, in press.
(10) (a) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750-
3781. (b) Albrecht, M.; Kochs, B. M.; Spek, A. L.; van Koten, G. J.
Organomet. Chem. 2001, 624, 271-286.
Table 1. Activation Parameters for the Bond Switching Process in
7
∆
Gq
∆
Hq
∆
Sq
Tc
298
solvent
(kcal/mol)
(kcal/mol)
(eu)
(K)
7a (TFPB)
7a (TFPB)
7b (ClO4)
7b (ClO4)a
7b (TFPB)
CD2Cl2
CD3CN
CD3CN
CD3CN
CD2Cl2
11.4
13.9
13.7
13.8
11.7
13.1 ( 0.1
15.3 ( 0.1
13.3 ( 0.1
12.8 ( 0.1
10.2 ( 0.2
5.6 ( 0.2
4.6 ( 0.2
-1.2 ( 0.1
-3.5 ( 0.2
-5.2 ( 0.6
259
303
297
311
249
a Based on 19F NMR.
9
5894 J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005

Hypervalent Carbon Compounds
A R T I C L E S
atom to give a sulfonium salt. The X-ray structure of 7c-ClO4
is shown in Figure 2 (bond distance: S1-C1 ) 1.973(8) Å,
S2-C1 ) 4.86(1) Å), and the structure of 7a-ClO4 (not shown)
was similar to that of 7c-ClO4.
Preparation of Oxygen Ligands and of the Corresponding
Carbocation Derivatives: Behaviors in Solution. The corre-
sponding OMe ligand (8) and the alcohol (9) were prepared by
similar procedures (Scheme 4), but demethylation and decom-
position took place after the treatment of 9 with perchloric acid
to give an unidentified mixture. Therefore, we prepared the
corresponding O(p-Tol) alcohols, 13a-13d, and O(p-MeOC6H4)
alcohols, 14a-14d. The corresponding cations, 15a-15c, 16a-
16d, could be prepared almost quantitatively by treatment with
perchloric acid (Scheme 5) (15d was very unstable and could
not be isolated). The cations were somewhat unstable at room
temperature (vide infra) in solution, but the dark green color
persisted up to 0 °C for several hours.
Figure 2. ORTEP drawing of 7c-ClO4.
Results and Discussion
Preparation of Sulfur and Selenium Ligands and of the
Corresponding Carbocation Derivatives: Observation of
Bond Switching Process. Sulfur and selenium ligands (5a-
5c) were prepared from the tribromide (4) in good yields
(Scheme 2). The corresponding lithium salt from 5 reacted with
benzophenone derivatives to give the corresponding alcohols
(6a-6d) (yield: 51-87% for 6a-6c and 14% for 6d, respec-
tively). Treatment of 6a-6d with perchloric acid gave the
corresponding cations, 7a-7d, as a perchlorate almost quanti-
tatively.
Scheme 4. Attempted Synthesis of a Cation (10) Bearing
2,6-Bismethoxymethylbenzene
In solutions of 7a-7d, two sets of signals for the sulfur
substituents, the methylene groups, and the meta carbons (or
protons) on the trisubstituted phenyl ring were observed at low
temperatures, although only one set of symmetrical signals was
observed at higher temperatures. For example, two sharp singlets
for the S-CH3 protons (δ 1.45, 2.25) and carbons (δ 11.9, 22.2)
in 1H and 13C NMR spectra were observed in 7a-ClO4 at -40
°C (CD3CN) (Figure 1), but coalescence took place at 30 °C in
1H NMR. At higher temperatures (100 °C), two sharp singlets
of the S-CH3 (δ 2.05) and S-CH2 protons (δ 4.02) were
observed for the same sample.
Scheme 5. Synthesis of Cations (15a-c and 16a-d) Bearing
2,6-Bis(p-substituted phenyloxymethyl)benzene
These results indicated that the ground state of the compounds
should be a tetracoordinated structure at the central carbon atom,
and the bond switching (bell clapper rearrangement) took place
as illustrated in Scheme 3. The activation free energies (∆Gq)
of the process for 7a-TFPB and 7d-TFPB [TFPB: tetrakis-
{3,5-bis(trifluoromethyl)phenyl}borate] were determined on the
basis of the simulation of the coalescence of the methyl signals.
The activation free energies (∆Gq) are shown in Table 1 together
with the coalescence temperature (Tc). The activation free
energies were almost the same in CD2Cl2 in the sulfur and
q
selenium ligand; thus, ∆G298 was 11.4 kcal/mol (Tc (coales-
1
cence temperature) ) 259 K in 400 MHz H NMR) for 7a-
In solutions of 15a-15c, two sets of signals were observed
only for the methylene group and the ortho and meta carbons
of the central carbon substituents (Ar2) at low temperatures,
although only one set of symmetrical signals including the meta
carbons (or protons) on the trisubstituted phenyl ring was
observed for other signals. Figure 3 shows the coalescence of
the two sets of signals for the ortho and meta carbons of the
central carbon substituents (Ar2: δ 130.2 and 131.4, 139.7, and
140.2) coalesced at -30 °C. These results are consistent with
the propeller inversion (Scheme 6) at the aryl substituents (Ar2)
in trityl cations as a similar inversion process was reported by
TFPB, and ∆G298q ) 11.7 kcal/mol (Tc ) 249 K) for 7d-TFPB.
It should be noted that 7a-ClO4 showed the same coalescence
temperature as 7a-TFPB. Therefore, the counteranion should
not be interacted with the cationic part. In polar CD3CN solution,
activation energies were higher by ca. 2.5 kcal/mol because of
the stabilization of the starting polarized onium structures.
Therefore, the pentacoordinated carbon structure (7q) should be
the transition state of the bond switching process.
Consistent with the NMR behavior in solution, the X-ray
crystal structures of 7a-ClO4 or 7c-ClO4 clearly show that only
one of the sulfur atoms is coordinated with the central carbon
9
J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005 5895

A R T I C L E S
Akiba et al.
Table 2. Distances of the Central Carbon Atom (C1) and the Donating Oxygen Atoms (O1 and O2) and the O1-C1-O2 Angles Revealed by
X-ray Analysis of 15b-ClO4, 15c-ClO4, 15e-ClO4, 15f-ClO4, 16a-ClO4, 16b-PF6, and 16d-PF6
15c-ClO4
(X Cl)
15b-ClO4
(X F)
16a-ClO4
(X H)
16b-PF6
(X F)
16b-PF6
15e-ClO4
(Z S)
15f-ClO4
(Z O)
distance (Å)
)
)
)
)
(X
)
OCH3)
)
)
C1-O1
2.671(4)
2.682(4)
2.690(4)
2.690(4)
2.705(2)
2.705(2)
2.718(5)
2.718(5)
2.77(1)
2.776(4)
2.617(4)
2.855(5)
2.827(4)
155.7(2)
165.0(2)
3.026(4)
4.23
C1-O2
2.78(1)
O1-C1-O2
161.9(1)
162.3(1)
158.9(2)
160.4(4)
159.1(4)
Figure 4. UV-vis spectra of 16a-16d.
Scheme 6. Propeller Inversion at the Aryl Substituents (Ar2) in
Trityl Cations
Figure 3. Variable-temperature 13C NMR (CD2Cl2) spectra of 15b-ClO4.
Coalescence of the ortho and meta carbons of p-fluorophenyl substituents.
Breslow et al.11b The barrier for inversion was ∆GTc ) 11.7
q
kcal/mol (Tc ) 249 K) in CD2Cl2.
(X: σ+p, Cl +0.07 (16c), H 0 (16a), F -0.11 (16b), CH3O
-0.78 (16d)), resulting in the smaller HOMO-LUMO energy
gap and the absorption shifted to the longer wavelength.
X-ray Crystallographic Analyses of Several Carbocations
Bearing O(p-Tol) or O(p-CH3OC6H4) Ligand: Electronic
Effects of the Aryl Substituents on the Central Carbon Atom
Affected the C-O Distance and the Structure. The crystals
of bis(p-fluorophenyl)[2,6-bis(p-methylphenyloxymethyl)phen-
yl]methyl perchlorate 15b-ClO4 suitable for X-ray analysis were
obtained after careful recrystallization from CH2Cl2 in a freezer.
X-ray structural analysis of 15b-ClO4 was carried out on the
basis of the centrosymmetric Pbcn group, showing that the
required two-fold axis passed through the central carbon and
the two carbon atoms at ipso and para positions in the
trisubstituted benzene ring. Figure 6 shows the ORTEP drawing
It is interesting to note that the cations 15a-15c and 16a-
16d are colored solids, and the UV-vis spectra of 16a-16d
(mostly purple solid) showed interesting behavior (Figure 4).
The wavelength of the absorption is shifted according to
electron-withdrawing substituents (X) attached to the aryl
substituents (p-XC6H4: Ar2 in Scheme 5). Based on the
calculated HOMO and LUMO orbitals in 15b-ClO4 (Figure 5),
the substituent effect of the Ar2 in 16 on the wavelength can be
explained by HOMO (hybrid of the π-electrons of the aryl
substituents (Ar1) and the lone pair electrons of the oxygen atom
of the ligand)-LUMO (hybrid of the empty p orbital of the
central carbon atom and the aryl group (Ar2)) interaction. The
energy of the LUMO orbital should be lowered by introducing
the electron-withdrawing substituents on Ar2 such as chlorine
(11) (a) Breslow, R.; Garratt, S.; Kaplan, L.; LaFollette, D. J. Am. Chem. Soc.
1968, 90, 4051-4055. (b) Breslow, R.; Kaplan, L.; LaFollette, D. J. Am.
Chem. Soc. 1968, 90, 4056-4064.
(12) (a) Becke, A. D. Phys. ReV. 1988, A38, 3098-3100, (b) Becke, A. D. J.
Chem. Phys. 1993, 98, 5648-5652, (c) Perdew, J. P.; Wang, Y. Phys. ReV.
1992, B45, 13244-13249.
9
5896 J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005

Hypervalent Carbon Compounds
A R T I C L E S
Scheme 7. Intramolecular Friedel-Crafts Reaction in 15g-ClO4
fluorenyl cation derivative, 15g-ClO4, could be observed up to
-20 °C, the dark green color disappeared at room temperature,
and the intramolecular Friedel-Crafts product 17 was obtained
(Scheme 7) almost quantitatively. The cyclopentadienyl cation
system is more unstable than the trityl cation system. The
structure of 17 was confirmed by X-ray analysis (not shown).
However, the more stable aromatic thioxanthylium cation 15e-
ClO4 and xanthylium cation 15f-ClO4 could be isolated without
any difficulty. X-ray analysis of 15e-ClO4 (Figure 7) showed
two independent molecules where the two C-O distances (first
molecule, 2.617(4), 2.827(4) Å; second molecule, 2.776(4),
2.855(5) Å) are significantly different in the two molecules,
indicating that the C-O interaction is very weak and the energy
difference between the two molecules is small. Here, the
thioxanthene ring is perfectly orthogonal to the substituted
benzene ring of the ligand. In addition, it is quite interesting to
note that the xanthene ring of 15f-ClO4 is tilted to the
uncoordinated arm and the central carbon looks like a tetraco-
ordinate, although the C1-O1 length (3.026(4) Å) of the
coordinated arm is quite long and is close to the sum of the
van der Waals radii (3.25 Å) (Figure 8). Selected C-O distances
and O-C-O angles are shown in Table 2. The aromatic
xanthylium cation should be more stable than the thioxanthylium
Figure 5. HOMO and LUMO orbitals of 15b (X ) F) calculated at the
B3PW91/6-31G(d) level.
Figure 6. ORTEP drawing of 15b-ClO4.
of a single molecule of 15b-ClO4. Because of the symmetry,
the bond distance between O1-C1 and O2-C1 is the same
(2.690(4) Å), which is even longer than those of the C-O
distances (2.43(1) and 2.45(1) Å) in 1 and is significantly longer
than that of a covalent C-O bond (1.43 Å),13 but it is still shorter
than the sum of the van der Waals radius (3.25 Å).13 The sum
of the angles (C2-C1-C4, C2-C1-C3, and C3-C1-C4) around
the central carbon is 360.0°, indicating that the carbon is planar
with sp2 hybridization. Moreover, both oxygens (O1 and O2)
are sp2; that is, the sum of the angles (C5-O1-C6, C1-O1-C6,
C1-O1-C5) around O1 is 360.0°. Because the sp2 lone pairs of
O1 and O2 should be directed toward the empty p-orbital of the
central carbocation, the geometry around the central carbon atom
C1 is TBP, which is only slightly distorted. The 2p orbitals of
O1 and O2 become parallel to the aromatic 6π system of the
substituted benzene ligand and are perpendicular to the hyper-
valent bond of O1-C1-O2.
+
cation, and this is exemplified by the Hammett σp values
(-0.60 for SMe, and -0.78 for OMe). The difference of C-O
attractive interaction between 15e-ClO4 and 15f-ClO4 is
consistent with the less-attractive interaction between the central
carbon and the oxygen atoms in 15f-ClO4 (xanthilium) than in
15e-ClO4 (thioxanthilium). The order of the C-O distance is
15c-ClO4 (X ) Cl) < 15b-ClO4 (X ) F) in the O(p-Tol) system
and 16a-ClO4 (X ) H) < 16b-ClO4 (X ) F) < 16c-ClO4 (X
) CH3O) in the O(p-CH3OC6H4) system. It also agrees with
+
the Hammett σp values of the substituents (Cl +0.07, H 0, F
-0.11, CH3O -0.78). It is noteworthy that the C-O distance
in 16b (p-CH3OC6H4 ligand) is almost the same as that in 15b
(p-tolyl ligand), because the two bond distances are within 3σ
of each other.
Electron Density Distribution Study in 15b-ClO4 Based
on the Accurate X-ray Analysis. The accurate X-ray measure-
ment of 15b-ClO4 was carried out by using a Spring-8 beam
line (see details in the Experimental Section). The structure and
the C-O distance (2.6822(4) Å) are well consistent with the
regular X-ray analysis described in Table 2 (2.690(4) Å). Figure
9 shows the static model map of 15b-ClO4 on the plane
intersecting the sp2 plane of C1 perpendicularly along the C1-
C4 bond.
The character of the O1-C1-O2 bond (Figure 6) is clearly
shown in the static model map. The topologies of deformation
electron densities of the bond are quite different from those of
the covalent bonds. As shown in Figure 9, the two lone pairs
on each O atom in the O(p-tolyl) group appear as an electron-
rich region (marked in blue) in the plane bisecting C6-O1-C5
To elucidate the property and the degree of interaction
between the central carbon atom and the two oxygen atoms in
15, several compounds were synthesized and were structurally
characterized for comparison. Although the formation of the
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann,
R. E., Jr.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniel, A. D.; Kudin,
S. K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.;
Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski,
J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-
Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.5;
Gaussian, Inc.: Pittsburgh, PA, 1998.
9
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A R T I C L E S
Akiba et al.
Figure 7. ORTEP drawing of 15e-ClO4.
Figure 8. ORTEP drawing of 15f-ClO4.
Figure 10. Bond paths of 15b-ClO4 between the central carbon and the
oxygen of the arm based on the accurate X-ray analysis.
on the O atom to the empty 2p orbital of the central carbon
atom, thus forming a three-center four-electron bond.
For the quantitative treatment of the characterization of the
bonds, topological analyses were performed. The bond paths
(shown as red lines) were found between the central carbon
and the oxygen of the arm as shown in Figure 10. The shapes
of the bond paths of the two bonds are identical. The bond
critical points on each bond path are closer to the central carbon
atom than the O atoms because of the polarities of the bonds.
3
The small electron density (F(r); 0.0170(4) e/ao ; ao ) 0.529177
2
5
Å) and the small positive Laplacian (∇ (r); 0.0486(1) e/ao )
value at the bond critical point indicate that the bond is weak
and polarized. These values are very similar to the values for
the C-O bond in our hypervalent five-coordinate carbon
Figure 9. Static model map of 15b-ClO4 based on the accurate X-ray
analysis. Positive and negative regions are shown as blue and red lines,
respectively, and zero contours are omitted.
compound (1) (F(r), 0.022 e/ao ; ∇ F(r), 0.080 e/ao ).8 The
difference between the present substituted benzene system and
the anthracene system, especially the decrease in the F(r) and
3
2
5
(C8-O2-C7). One of the two peaks is extended to the central
carbon atom. The hole of the 2p orbital appears as electron-
deficient regions (marked in red) at both sides of the sp2 plane
of the central carbon atom and has lobes extended perpendicular
to the plane. One of the two lone pairs in the sp3 orbital on
each O atom is directed to the empty 2p orbital of the central
carbon atom. Such geometry of the orbital clearly indicates that
the electrons are donated from the lone pairs in the sp3 orbital
2
∇ F(r) values, implies an even weaker bond in the present
substituted benzene system. Further investigation toward the
quantitative estimation of the attractive force is underway.
Electron-Density Distribution Study in 15b-ClO4 by
Density Functional Calculation. The structure of 15b-ClO4
was optimized with hybrid density functional theory (DFT) at
9
5898 J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005

Hypervalent Carbon Compounds
A R T I C L E S
was added an CH3CN solution (120 mL) of 2,6-bis(bromomethyl)-
bromobenzene 4 (20.8 g, 60.7 mmol). The reaction mixture was heated
to reflux for 14 h. The crude oil was treated with saturated aqueous
NH4Cl, and the organic layer was distilled to give pure 5a (62.6 g,
63%) as a pale yellow oil. Compound 5a: bp 105-106 °C/0.3 Torr;
MS m/z 277 (M+). 1H NMR (CDCl3) δ 2.28 (s, 6H), 3.53 (s, 4H), 7.22
(t, 1H, J ) 8 Hz), 7.31 (d, 2H, J ) 8 Hz). 13C NMR (CDCl3) δ 45.3,
63.6, 126.3, 126.6, 129.0, 138.3.
General Procedures for Synthesis of 6. To a THF (10 mL) solution
of 5 (1 mmol) was added dropwise n-BuLi (1.05 mL, 1.20 M in hexane,
1.26 mmol) at -78 °C under Ar, and the solution was stirred for 1 h.
To the reaction mixture was added dropwise a THF (6 mL) solution of
a ketone (1 mmol) at -78 °C. The mixture was allowed to warm to
room temperature and was stirred for 3-6 h. The mixture was treated
with saturated aqueous NH4Cl. The crude product was purified by silica
gel chromatography or recycling HPLC.
Figure 11. Optimized structure of 15b-ClO4 at the B3PW91/6-31G(d)
level.
General Procedures for Synthesis of 7. To a solution of 6 (0.3
mmol) in diethyl ether (5 mL) were added a few drops of 70%
perchloric acid (0.25 mL, 0.4 mmol) under Ar at room temperature.
After the mixture was stirred for 2 h, the resulting precipitates were
washed with diethyl ether (5 mL × 3).
Diphenyl[2,6-bis(methylthiomethyl)phenyl]methyl Perchlorate
1
(7a-ClO4). Yield 80%, colorless crystals; mp 135-137 °C. H NMR
(CD3CN, -40 °C) δ 1.45 (s, 3H), 2.25 (s, 3H), 3.13 (s, 2H), 4.71 (d,
J ) 17 Hz, 1H), 5.01 (d, J ) 17 Hz, 1H), 7.40-7.70 (m, 13H). 13C
NMR (CD3CN, -40 °C) δ 11.9, 22.2, 32.2, 43.4, 85.6, 123.9, 126.7,
126.8, 127.0, 127.5, 127.9, 128.2, 128.3, 129.1, 132.9, 133.3, 134.5,
134.9. Anal. Calcd for C23H23ClO4S2: C, 59.66; H, 5.01. Found: C,
59.32; H, 4.88.
General Procedures for Synthesis of 13 and 14. To a THF (10
mL) solution of 11 or 12 (1 mmol) was added dropwise n-BuLi (1.05
mL, 1.20 M in n-hexane, 1.26 mmol) at -78 °C under Ar, and the
solution was stirred for 1 h. To the reaction mixture was added dropwise
a THF (5 mL) solution of a ketone (1 mmol) at -78 °C. The mixture
was allowed to warm to room temperature and was stirred for 3-6 h.
The mixture was treated with saturated aqueous NH4Cl. The crude
product was purified by silica gel chromatography or recycling HPLC.
Diphenyl[2,6-bis(p-methylphenoxymethyl)phenyl]methanol (13a).
Yield 58%, colorless crystals (recrystallized from n-hexane); mp 115.5-
117.0 °C. 1H NMR (CDCl3) δ 2.21 (s, 6H), 3.55 (s, 1H), 4.61 (s, 4H),
6.36 (d, 4H, J ) 8 Hz), 6.89 (d, 4H, J ) 8 Hz), 7.22 (s, 10H), 7.39 (t,
1H, J ) 8 Hz), 7.58 (d, 2H, J ) 8 Hz). Anal. Calcd for C35H32O3: C,
83.97; H, 6.44. Found: C, 84.12; H, 6.18.
Bis(p-fluorophenyl)[2,6-bis(p-methylphenoxymethyl)phenyl]-
methanol (13b). Yield 49%, colorless crystals (recrystallized from
n-hexane); mp 112.6-113.8 °C. 1H NMR (CDCl3) δ 2.23 (s, 6H), 3.91
(s, 1H), 4.59 (s, 4H), 6.39 (d, 4H, J ) 9 Hz), 6.93 (d, 4H, J ) 9 Hz),
6.98 (d, 4H, J ) 9 Hz), 7.26-7.29 (m, 4H), 7.39 (t, 1H, J ) 8 Hz),
7.59 (d, 2H, J ) 8 Hz). FAB(+)MS M+ 536.
Figure 12. Bond paths of 15b-ClO4 between the central carbon and the
oxygen of the arm calculated at the B3PW91/6-31G(d) level.
the B3PW91/6-31G(d) level,12 using the Gaussian 98 program.13
The basis sets employed were 6-31G(d)14 for C, O, F, and H.
The calculation indicates that the symmetrical C2 structure of
15b-ClO4 is the energy minimum (Figure 11). The two C-O
distances are almost identical (2.689 Å) to the experimental
distances (2.6822(4) Å). It should be noted that the bond paths
are also found between the central carbon atom and the two
oxygen atoms by the calculation (Figure 12), and the path is
well consistent with the one by detailed X-ray analysis previ-
3
ously described. In addition, the small F(r) value of 0.017 e/ao
2
and the small positive ∇ F(r) value of 0.052 e/ao5 calculated at
3
the bond critical points agree well with those of 0.0170(4) e/ao
and 0.0486(1) e/ao5 by the accurate X-ray analysis, respectively.
Conclusion
The present series of sterically flexible substituted benzenes
showed the sensitivity of the C-O interaction to the electronic
effect on the central carbocation, and this was exemplified by
the X-ray analysis of these compounds. The X-ray data represent
a series of stable pentacoordinate carbon structures, in which
the central carbon equally attracts the two apical ligands, to
varying extents. The remarkable coincidence of quantitative
values obtained by accurate X-ray analysis and DFT calculation
is certainly noteworthy here.
Bis(p-chlorophenyl)[2,6-bis(p-methylphenoxymethyl)phenyl]-
methanol (13c). Yield 53%, colorless crystals (recrystallized from
1
n-hexane); mp 46.7-48.2 °C. H NMR (CDCl3) δ 2.33 (s, 6H), 4.06
(s, 1H), 4.57 (s, 4H), 6.38 (d, 4H, J ) 8 Hz), 6.93 (d, 4H, J ) 8 Hz),
7.22 (s, 8H), 7.39 (t, 1H, J ) 8 Hz), 7.58 (d, 2H, J ) 8 Hz). 13C NMR
(CDCl3) δ 20.45, 69.62, 82.51, 114.20, 128.06, 128.31, 129.17, 129.60,
129.87, 130.04, 130.27, 133.69, 136.70, 142.61, 144.52, 155.59, 181.21.
FAB(+)MS 568, 551, 461, 443, 353. Anal. Calcd for C35H30Cl2O3: C,
73.81; H, 5.31. Found: C, 73.86; H, 5.22
Diphenyl[2,6-bis(p-methoxyphenoxymethyl)phenyl]methanol (14a).
1
Yield 65%. H NMR (CDCl3) δ 3.64 (s, 1H), 3.71 (s, 6H), 4.59 (s,
Experimental Section
4H), 6.40 (d, 4H, J ) 9 Hz), 6.65 (d, 4H, J ) 9 Hz), 7.31 (s, 10H),
7.37 (t, 1H, J ) 8 Hz), 7.61 (d, 2H, J ) 8 Hz). Anal. Calcd for
C35H32O5: C, 78.93; H, 6.06. Found: C, 78.66; H, 5.95.
Bis(p-fluorophenyl)[2,6-bis(p-methoxyphenoxymethyl)phenyl]-
methanol (14b). Yield 67%, pale yellow solid; mp 38.2-39.0 °C. 1H
NMR (CDCl3) δ 3.72 (s, 6H), 4.03 (s, 1H), 4.57 (s, 4H), 6.43 (d, 4H,
Synthesis of 2,6-Bis(methylthiomethyl)bromobenzene (5a). To a
500 mL round-bottom flask fitted with a reflux condenser was added
aqueous sodium methanethiolate (15%, 280 g, 660 mmol), and then
(14) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.;
DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654-3665.
9
J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005 5899

A R T I C L E S
Akiba et al.
J ) 9 Hz), 6.68 (d, 4H, J ) 9 Hz), 6.94-6.98 (m, 4H), 7.26-7.28 (m,
4H), 7.40 (t, 1H, J ) 8 Hz), 7.59 (d, 2H, J ) 8 Hz). Anal. Calcd for
C35H30F2O5: C, 73.93; H, 5.32. Found: C, 73.76; H, 5.25.
(s, 4H), 6.03 (d, 4H, J ) 9 Hz), 6.59 (d, 4H, J ) 9 Hz), 7.20-7.80
(br, 6H), 7.60-7.90 (br, 2H), 7.67 (d, 2H, J ) 8 Hz), 7.83 (t, 1H, J )
8 Hz). UV-vis (CH2Cl2, -15 °C) λ(ꢀmax) 600.5 (287), 467.0 (3184),
335 (687), 290 (537). Anal. Calcd for C35H29F8O4P: C, 60.35; H, 4.20.
Found: C, 60.03; H, 3.84.
Bis(p-chlororophenyl)[2,6-bis(p-methoxyphenoxymethyl)phenyl]-
methanol (14c). Yield 50%, pale yellow solid; mp 45-49 °C. 1H NMR
(CDCl3) δ 3.73 (s, 6H), 4.17 (s, 1H), 4.56 (s, 4H), 6.42 (d, 4H, J ) 9
Hz), 6.69 (d, 4H, J ) 9 Hz), 7.23 (s, 8H), 7.41 (t, 1H, J ) 8 Hz), 7.59
(d, 2H, J ) 8 Hz). Anal. Calcd for C35H30Cl2O5: C, 69.89; H, 5.03.
Found: C, 69.50; H, 4.66.
Bis(p-chlorophenyl)[2,6-bis(p-methoxyphenoxymethyl)phenyl]-
methyl hexafluorophosphate (16c-PF6). mp 116.5-117.8 °C. (re-
crystallized from CH2Cl2/Et2O). 1H NMR (CD2Cl2) δ 3.70 (s, 6H), 4.49
(s, 4H), 6.10 (d, 4H, J ) 9 Hz), 6.63 (d, 4H, J ) 9 Hz), 7.42 (br, 4H),
7.57 (br, 4H), 7.70 (br, 2H), 7.85 (br, 1H). UV-vis (CH2Cl2, -15 °C)
λ(ꢀmax) 715.0 (359), 458.0 (3312), 350.5 (1093), 341.5 (1033), 290.5
(703). Anal. Calcd for C35H29Cl2F6O4P + 0.5CH2Cl2: C, 55.23; H,
3.92. Found: C, 55.52; H, 3.44.
Bis(p-methoxyphenyl)[2,6-bis(p-methoxyphenoxymethyl)phenyl]-
methanol (14d). Yield 40%. 1H NMR (CDCl3) δ 3.56 (s, 1H), 3.69 (s,
6H), 3.75 (s, 6H), 4.61 (s, 4H), 6.43 (d, 4H, J ) 9 Hz), 6.65 (d, 4H,
J ) 9 Hz), 6.79 (d, 4H, J ) 9 Hz), 7.19 (d, 4H, J ) 9 Hz), 7.34 (t, 1H,
Bis(p-methoxyphenyl)[2,6-bis(p-methoxyphenoxymethyl)phenyl]-
methyl Hexafluorophosphate (16d-PF6). mp 144.0-146.0 °C. (re-
crystallized from CH2Cl2/Et2O). 1H NMR (CD2Cl2) δ 3.68 (s, 6H), 4.08
(s, 6H), 4.47 (s, 4H), 6.21 (d, 4H, J ) 9 Hz), 6.63 (d, 4H, J ) 9 Hz),
7.05 (d, 4H, J ) 9 Hz), 7.48 (d, 4H, J ) 9 Hz), 7.66 (d, 2H, J ) 9
Hz), 7.76 (d, 4H, J ) 9 Hz). UV-vis (CH2Cl2, -15 °C) λ(ꢀmax) 715.0
(359), 458.0 (3312), 350.5 (1093), 341.5 (1033), 290.5 (703). Anal.
Calcd for C37H35F6O6P: C, 61.67; H, 4.90. Found: C, 61.80; H, 4.23.
J ) 8 Hz), 7.59 (d, 2H, J ) 8 Hz). Anal. Calcd for C37H36O7
benzene: C, 76.99; H, 6.31. Found: C, 77.01; H, 6.20.
+
General Procedures for Synthesis of 15 and 16. To a solution of
13 or 14 (0.07 mmol) in CH2Cl2 (2.5 mL) were added a few drops of
70% perchloric acid under Ar at -15 °C. After the mixture was stirred
for 1 h, the additional CH2Cl2 (10 mL) was added slowly, and the
reaction mixture was passed through a column of anhydrous Na2SO4
to remove excess perchloric acid and water under Ar while keeping
the column at the same temperature. The solvent was deliberately
removed by Ar flow at -20 °C to precipitate the desired perchlorate
salts of carbenium cation as purple plates.
X-ray Crystallographic Analysis of 7c-ClO4, 15b-ClO4, 15c-ClO4,
15e-ClO4, 15f-ClO4, 16a-ClO4, 16b-PF6, and 16d-PF6. X-ray data,
except experimental electron distribution analysis, were collected on a
Mac Science DIP2030 imaging plate equipped with graphite-mono-
chromated Mo KR radiation (λ ) 0.71073 Å). The unit cell parameters
were determined by autoindexing several images in each data set
separately with the program DENZO. For each data set, rotation images
were collected in 3° increments with a total rotation of 180° about φ.
Data were processed by SCALEPACK. The structures were solved
using the teXsan system and were refined by full-matrix least-squares
and refined by full-matrix least-squares. The programs DENZO and
SCALEPACK are available from Mac Science Co., Z. Otwinowski,
University of Texas, Southwestern Medical Center. The program teXsan
is available from Rigaku Co. All crystallographic data (excluding
structure factors) for the compounds reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre (all data
have a supplementary publication number). A copy of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax, (+44)1223-336-033; e-mail, deposit@
ccdc.cam.ac.uk).
Diphenyl[2,6-bis(p-methylphenyloxymethyl)phenyl]methyl Per-
chlorate (15a-ClO4). 1H NMR (CDCl3) δ 2.21 (s, 6H), 4.45 (brs, 4H),
5.99 (d, 4H, J ) 8 Hz), 6.82 (d, 4H, J ) 8 Hz), 7.5-7.7 (m, 11H, J
) 9 Hz), 8.15 (d, 2H, J ) 8 Hz).
Bis(p-fluorophenyl)[2,6-bis(p-methylphenyloxymethyl)phenyl]-
methyl Perchlorate (15b-ClO4). mp 114.9-115.6 °C (dec) (recrystal-
1
lized from CH2Cl2/Et2O). H NMR (CD2Cl2) δ 2.22 (s, 6H), 4.51 (br,
4H), 6.04 (d, 4H, J ) 8 Hz), 6.90 (d, 4H, J ) 8 Hz), 7.30 (br, 4H),
7.59 (br, 4H), 7.71 (d, 2H, J ) 8 Hz), 7.87 (t, 1H, J ) 8 Hz). Anal.
Calcd for C35H29ClF2O6 + 0.5CH2Cl2: C, 64.36; H, 4.72. Found: C,
64.64; H, 4.28.
Bis(p-chlorophenyl)[2,6-bis(p-methylphenyloxymethyl)phenyl]-
methyl Perchlorate (15c-ClO4). mp 97.6-100.4 °C (dec) (recrystal-
1
lized from CH2Cl2/Et2O). H NMR (CD2Cl2) δ 2.22 (s, 6H), 4.51 (br,
4H), 6.04 (d, 4H, J ) 8 Hz), 6.90 (d, 4H, J ) 8 Hz), 7.30 (br, 4H),
7.59 (br, 4H), 7.71 (d, 2H, J ) 8 Hz), 7.87 (t, 1H, J ) 8 Hz). 13C
NMR (CD2Cl2, -15 °C) δ 20.32, 66.23, 112.12, 129.25, 129.93, 130.46
(br), 131.28 (br), 132.38, 134.39, 134.60, 135.50, 139.07, 140.04 (br),
7c-ClO4 (deposited as CCDC-251373): C35H31O4S2Cl, 615.20,
monoclinic, P21/n, pale yellow, a ) 14.4590(9) Å, b ) 11.522(1) Å,
c ) 19.651(2) Å, â ) 109.542(5)°, V ) 3085.2(4) Å3, 298 K, Z ) 4,
R ) 0.1059, GOF ) 1.882.
15b-ClO4 (deposited as CCDC-251374): C35H29O6F2Cl, 619.06,
orthorhombic, Pbcn, red purple, a ) 11.8900(6) Å, b ) 14.0860(4) Å,
c ) 17.8700(9) Å, V ) 2992.9(2) Å3, 298 K, Z ) 4, R ) 0.0649, GOF
) 1.364.
140.61 (br), 152.56, 153.68, 211.88. UV-vis (CH2Cl2, -15 °C) λ(ꢀmax
)
623.0 (266), 460.5 (2364), 351.5 (692), 337.5 (679), 267.5 (591). Anal.
Calcd for C35H29Cl3O6 + 0.5CH2Cl2: C, 62.02; H, 4.55. Found: C,
61.94; H, 4.22.
9-[2,6-Bis(p-methylphenoxymethyl)phenyl]thioxanthylium Per-
1
chlorate (15e-ClO4). H NMR (CDCl3) δ 2.08 (s, 6H), 4.62 (s, 4H),
5.69 (d, 4H, J ) 9 Hz), 6.62 (d, 4H, J ) 9 Hz), 7.73-7.85 (m, 5H),
7.93 (d, 2H, J ) 9 Hz), 8.19-8.23 (m, 2H), 8.60 (d, 2H, J ) 9 Hz).
15c-ClO4 (deposited as CCDC-251375): C35H29O6Cl3, 651.97,
orthorhombic, Pna21, brown purple, a ) 18.4610(5) Å, b ) 13.9050-
(3) Å, c ) 12.3370(7) Å, V ) 3166.9(1) Å3, 298 K, Z ) 4, R ) 0.0580,
GOF ) 1.327.
9-[2,6-Bis(p-methylphenoxymethyl)phenyl]xanthylium Perchlo-
1
rate (15f-ClO4). H NMR (CDCl3) δ 2.09 (s, 6H), 4.80 (s, 4H), 5.71
(d, 4H, J ) 9 Hz), 6.64 (d, 4H, J ) 9 Hz), 7.69-7.84 (m, 7H), 8.18
(d, 2H, J ) 9 Hz), 8.38-8.42 (m, 2H).
15e-ClO4 (deposited as CCDC-251376): C35H29O6SCl, 613.12,
triclinic, P1h, purple, a ) 11.5140(2) Å, b ) 15.3280(5) Å, c ) 18.5310-
(6) Å, R ) 78.168(1)°, â ) 78.935(2)°, γ ) 79.867(2)°, V ) 3109.6-
(2) Å3, 200 K, Z ) 4, R ) 0.0908, GOF ) 1.658.
15f-ClO4 (deposited as CCDC-251377): C35H29O7Cl, 597.06, tri-
clinic, P1h, purple, a ) 11.335(2) Å, b ) 11.064(2) Å, c ) 13.066(1)
Å, R ) 101.128(9)°, â ) 102.83(1)°, γ ) 102.734(5)°, V ) 1507.14-
(4) Å3, 200 K, Z ) 4, R ) 0.1063, GOF ) 1.583.
16a-ClO4 (deposited as CCDC-251378): C35H31O8Cl3, 615.08,
monoclinic, C2/c, purple, a ) 15.062(8) Å, b ) 20.078(1) Å, c )
11.4130(4) Å, â ) 114.277(3)°, V ) 3146.2(3) Å3, 298 K, Z ) 4, R )
0.0788, GOF ) 1.664.
Diphenyl[2,6-bis(p-methoxyphenoxymethyl)phenyl]methyl Per-
chlorate (16a-ClO4). mp 108.0-109.0 °C (recrystallized from CH2-
Cl2/Et2O). 1H NMR (CD2Cl2) δ 3.68 (s, 6H), 4.44 (s, 4H), 6.04 (d, 4H,
J ) 9 Hz), 6.59 (d, 4H, J ) 9 Hz), 7.35-7.75 (br, 10H), 7.60-7.90
(br, 1H), 8.05-8.22 (br, 2H). UV-vis (CH2Cl2, -15 °C) λ(ꢀmax) 677.0
(331), 426.5 (1814), 330 (729), 291 (516). Anal. Calcd for C35H31-
ClO8: C, 68.23; H, 5.24. Found: C, 67.96; H, 4.92.
Bis(p-fluorophenyl)[2,6-bis(p-methoxyphenoxymethyl)phenyl]-
methyl Hexafluorophosphate (16b-PF6). mp 128.0-129.0 °C. (re-
crystallized from CH2Cl2/Et2O). 1H NMR (CD2Cl2) δ 3.66 (s, 6H), 4.42
9
5900 J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005

Hypervalent Carbon Compounds
A R T I C L E S
16b-PF6 (deposited as CCDC-251379): C35H31O8Cl3, 696.57, orthor-
hombic, Pbcn, purple, a ) 12.7300(5) Å, b ) 14.06090(6) Å, c )
17.6890(7) Å, V ) 3289.7(2) Å3, 298 K, Z ) 4, R ) 0.1548, GOF )
2.521.
package.20 The refinement was carried out against 11 095 independent
reflections of sin θ/λ e 1.0 Å-1 with I > 0 based on F2. At the first
stage of the refinements, atomic coordinates and Uij of non-hydrogen
atoms were fixed on those of the high order refinement, and the Uiso
values of the hydrogen atoms were fixed on those of the conventional
refinements based on reflections with sin θ/ λ e 0.65 Å-1. The
population parameters, Pv, Plm(, of non-hydrogen atoms and scale were
refined. Levels of multipoles were raised stepwise up to hexadecapole
for the non-hydrogen atoms. At the second stage, anisotropic and
isotropic temperature factors were refined for non-hydrogen and
hydrogen atoms, respectively, followed by the spherical Hartree-Fock
radial screening parameter, κ. At the third stage, the Pv, Plm(, and scale
were refined. The levels of multipoles were raised to the hexadecapole
for non-hydrogen atoms and to the dipole along the bonds for hydrogen
atoms in the same manner at the final stage. After those refinements,
the second and third strategies were repeated twice, and finally the Pv,
16d-PF6 (deposited as CCDC-251380): C37H35O6F6P, 720.64,
monoclinic, P21/n, red purple, a ) 13.5070(4) Å, b ) 17.866(1) Å, c
) 14.6090(9) Å, â ) 91.321(3)°, V ) 3524.4(3) Å3, 298 K, Z ) 4, R
) 0.1616, GOF ) 2.584.
Accurate X-ray Analysis of 15b-ClO4. A single crystal of 15b-
ClO4 having well-developed crystal faces, 0.24 × 0.21 × 0.10 mm,
was selected for measurement. Diffraction data were collected on an
automated imaging plate Weissenberg camera, MacScience DIP-LABO,
on BL04B2 beam line at SPring-815 using 37.8 keV (0.3282 Å) radiation
with an oscillation method at 100 K. Sixty frames were measured with
an oscillation angle of 4° and an interval of 3° to ensure a total
oscillation angle of 180°. Bragg spots on the imaging plates were
integrated up to sin θ/λ ) 1.0 Å-1 with the program DENZO and scaled
and averaged with the program SCALEPACK. Partial reflections were
omitted. Lorentz and polarization corrections were applied during the
scaling process. Absorption correction was not applied due to the low
absorbability of the specimen. Measured and independent reflections,
Rint, and completeness were 108928, 11503, 0.03, and 0.94, respectively.
Plm(, κ, coordinates, and temperature factors and scale were refined.
The number of parameters in the final cycle of the refinements was
852. A molecule electroneutrality constraint was applied through all
of the refinements. Crystal data: orthorhombic, space group Pbcn, a
) 11.853(1) Å, b ) 14.003(1) Å, c ) 17.725(1) Å, V ) 2942.0(4) Å3,
Z ) 4, DX ) 1.398 g cm-3, R(F) ) 0.0281 (for 11 095 reflections
with I > 0).
The structure was solved by a direct method and refined using
independent 3348 reflections with sin θ/λ e 0.65 Å-1 with the programs
SIR9716 and SHELXL97,17 respectively. Following the refinements,
high-order refinements were carried out using all 8823 independent
reflections with sin θ/λ g 0.60 Å-1 with the program SHELXL97. The
positions of the hydrogen atoms were constrained to have C-H
distances of 1.083 and 1.066 Å for aromatic and methyl groups,
respectively.18 Refinements of the multipole expansion method using
the Hansen-Coppens multipole formalism19 and topological analyses
based on the resulting parameters were performed with the XD
Acknowledgment. This work was supported by a Grant-in-
Aid for Scientific Research (Nos. 09239103, 11166248,
11304044) from the Ministry of Education, Science, Sports, and
Culture of the Japanese Government. Measurement of diffraction
data for electron density analysis of 15b-ClO4 was carried out
at SPring-8 under project number 2001A-0229-ND-np.
Supporting Information Available: Preparation of com-
pounds and tables of crystal data, structure solution and
refinement, atomic coordinates, anisotropic thermal parameters,
and bond distances and angles. This material is available free
of charge via the Internet at http://pubs.acs.org.
(15) Ozeki, T.; Kusaka, K.; Honma, N.; Nakamura, Y.; Nakamura, S.; Oike,
S.; Yasuda, N.; Imura, H.; Uekusa, H.; Isshiki, M.; Katayama, C.; Ohashi,
Y. Chem. Lett. 2001, 804.
(16) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Cryst. 1999, 32, 115.
(17) Sheldrick, G. M. SHELX-97, Program for the Analysis of Crystal Structures;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(18) Wilson, A. J. C. International Tables for Crystallography Kluwer Academic
Publishers: Dordrecht, 1992; Vol. C.
JA043802T
(19) (a) Coppens, P. X-ray Charge Densities and Chemical Bonding; Oxford
University Press: New York, 1997. (b) Hansen, N. K.; Coppens, P. Acta
Crystallogr., Sect. A 1978, 34, 909.
(20) Koritsanszky, T.; Howard, S.; Su, Z.; Mallinson, P. R.; Richter, T.; Hansen,
N. K. XD-a Computer Program Package for Multipole Refinement and
Analysis of Electron Densities from Diffraction Data; 2003.
9
J. AM. CHEM. SOC. VOL. 127, NO. 16, 2005 5901