Synthesis and characterization of antiapicophilic arsoranes and related compounds

Article abstract of DOI:10.1021/ic3014893

Utilizing bulky bidentate ligand systems with C₂F₅ and n-C₃F₇ groups, antiapicophilic arsoranes (5b and 5c, respectively) were synthesized. A kinetic study on the isomerization of these arsoranes to their more stable isomers showed that the barriers increased in the order of CF₃ < C₂F₅ < n-C ₃F₇ in accord with their steric bulk. It was also revealed that the degree of freezing isomerization was larger for the change from CF₃ to C₂F₅ than from C₂F ₅ to n-C₃F₇, obvious from the differences in activation free energy at 363 K of 1.6 and 0.3 kcal mol^-1, respectively. X-ray structural analysis of several precursors of these two systems disclosed the unique structures of these compounds.

Full text of DOI:10.1021/ic3014893

Article
pubs.acs.org/IC
Synthesis and Characterization of Antiapicophilic Arsoranes and
Related Compounds
Xin-Dong Jiang,*,†,‡ Shiro Matsukawa,‡,§ Satoshi Kojima,‡ and Yohsuke Yamamoto*,‡
†The Key Laboratory for Special Functional Materials, Ministry of Education, Henan University, Kaifeng, 475-004, China
‡Department of Chemistry, Graduate School of Science, Hiroshima University,1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526,
Japan
§Department of Chemistry, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, 274-8510, Japan
S
* Supporting Information
ABSTRACT: Utilizing bulky bidentate ligand systems with
C2F5 and n-C3F7 groups, antiapicophilic arsoranes (5b and 5c,
respectively) were synthesized. A kinetic study on the
isomerization of these arsoranes to their more stable isomers
showed that the barriers increased in the order of CF3 < C2F5
< n-C3F7 in accord with their steric bulk. It was also revealed
that the degree of freezing isomerization was larger for the
change from CF3 to C2F5 than from C2F5 to n-C3F7, obvious
from the differences in activation free energy at 363 K of 1.6
and 0.3 kcal mol−1, respectively. X-ray structural analysis of
several precursors of these two systems disclosed the unique
structures of these compounds.
facile stereomutation usually interpreted by the Berry
pseudorotation (BPR) mechanism.46 The former is the
propensity for more electronegative and sterically less bulky
groups to prefer the apical sites, and the latter is a low-energy
nondissociative intramolecular site exchange process peculiar to
TBP molecules. An alternative mechanism called turnstile
rotation (TR) proposed by Ugi et al.47−50 has been calculated
to be higher in energy than BPR. Recently, Lammertsma
proposed that TR can be explained as a special combination of
BPRs.51
As for 10-P-5 compounds, using the Martin ligand (Figure 1,
A),13 we succeeded in freezing the BPR enough to isolate a
series of phosphoranes violating the apicophilicity concept with
an oxygen-equatorial carbon-apical configuration (O-equatori-
al).52−60 These phosphoranes are kinetically stabilized products
and can still be converted into their corresponding more stable
stereoisomers with a carbon-equatorial oxygen-apical config-
INTRODUCTION
■
Hypervalent compounds of the main group elements have been
attracting increasing interest by both experimental and
theoretical chemists for quite a while.1 Especially of note is
hypervalent phosphorus (phosphorane) chemistry,2−5 due to
its relevance to the phosphoryl transfer reaction in biological
systems,6−9 since formation or hydrolysis of biologically
relevant phosphorus compounds10−12 such as DNA or RNA
involves hypervalent13 10-P-514−16 phosphorus as intermediates
or transition states. Although hypervalent 10-As-5 arsenic
compounds (arsoranes) have been investigated to a lesser
extent, they are significant as intermediates in reactions of
arsonium ylides with carbonyl compounds to form olefins or
epoxides.17−26 Thus, to clarify the mechanism of such reactions,
comprehensive knowledge of the thermodynamic and kinetic
properties of the transient species would be needed, and in
turn, it is quite important to establish an understanding of the
difference in structure and reactivity of isomeric pentacoordi-
nate compounds.
Pentacoordinate compounds are known to adopt two
different structures: one is a trigonal bipyramid (TBP)
structure, and the other is a square pyramid (SP) structure,
and the former is generally preferred. The TBP structure
includes two distinct bonds: the apical bond and the equatorial
bond. The apical bond is described as a three-center-four-
electron (hypervalent) bond, whereas the equatorial bond is
described as an sp2 bond. The apical bond is comprised of two
sites positioned linearly with the center intersecting with the
equatorial plane perpendicularly. This structural characteristic
brings about two unique features, i.e., apicophilicity27−45 and
Figure 1. Reported bidentate ligands for freezing Berry pseudorotation
used in the present study.
Received: July 11, 2012
Published: September 26, 2012
© 2012 American Chemical Society
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Article
3F). Anal. Calcd for C20H13AsF12O2.5 (2a·0.5THF): C, 40.29; H, 2.20.
Found: C, 40.26; H, 2.10. 4a−Li: mp 102.0−103.0 °C (decomp.). 1H
uration (O-apical). Furthermore, we recently developed a new
bidentate ligand bearing two C2F5 groups (Figure 1, B), which
was more effective for freezing the BPR of the phosphoranes
than the Martin ligand.23,61−67 More recently, we also
developed an even more bulky bidentate ligand C bearing
two n-C3F7 groups, which had a larger capability to freeze the
BPR of phosphoranes (Figure 1, C).68 However, unlike the
situation with phosphorus chemistry, little is known about
hypervalent arsenic species (arsoranes), one reason being that
arsoranes often suffer from BPR faster than the corresponding
phosphoranes.69 For example, the activation free energy of
Ph2PF3 at its coalescence temperature (379 K) was determined
to be 18.7 kcal mol−1,70 whereas the single fluorine signal of
Ph2AsF3 observed at room temperature did not decoalesce even
at −90 °C.71 A theoretical study has shown the energy of BPR
for AsF5 (3.0 kcal mol−1) to be lower than that of PF5 (4.3 kcal
mol−1).72 As we have done for the phosphoranes, investigation
of each isolated stereoisomer of the arsoranes would lead to a
better understanding of the general and fundamental properties
of pentacoordinate arsoranes. Recently, we communicated our
preliminary studies on 10-As-5 compounds with ligands A and
B.64 Herein, we systematically report on the synthesis of O-
equatorial arsoranes and kinetic study of their pseudorotation
to the more stable O-apical isomers with the three ligands A−
C. In addition, the unique structures of a series of arsenic
species, including O-equatorial arsoranes, O-apical arsoranes, an
arsine, a tetracoordinate arsoranide, hydroxyarsoranes, and
iodoarsoranes, determined by crystallography are presented.
3
3
NMR (CDCl3): δ = 8.06 (d, JHH = 7.6 Hz, 2H), 7.60 (d, JHH = 7.6
3
4
Hz, 2H), 7.39 (td, JHH = 7.6 Hz, JHH = 1.2 Hz, 2H), 7.32 ppm (td,
3JHH = 7.6 Hz, 4JHH = 1.2 Hz, 2H). 19F NMR (CDCl3): δ = −73.8 (q,
4JFF = 8.6 Hz, 6F), −76.3 ppm (q, JFF = 8.6 Hz, 6F).
4
[TBPY-5-12]-1-(1,1-dimethylethyl)-3,3,3′,3′-tetrakis-
(trifluoromethyl)-1λ5-1,1′(3H,3′H)-spirobi[2,1-benzoxarsole] (5a).
Under N2, t-BuLi (1.57 M n-pentane solution, 0.35 mL, 0.549
mmol) was added to a solution of 2a (101 mg, 0.181 mmol) in Et2O
(3.0 mL) at −78 °C. The mixture was then stirred for 1 h at room
temperature. I2 (139 mg, 0.549 mmol) was added at −78 °C, and the
mixture was stirred for 1 h at 0 °C. The reaction was quenched with
aqueous Na2S2O3 (2 × 20 mL). The mixture was extracted with Et2O
(2 × 50 mL), and the organic layer was washed with brine (2 × 30
mL) and dried over anhydrous MgSO4. After removing the solvents by
evaporation, the resulting crude mixture was separated by preparative
TLC (n-hexane:CH2Cl2 = 4:1) to afford 5a (56.5 mg, 0.0916 mmol,
50%) and 3a (21.5 mg, 0.0373 mmol, 21%) as white solids. Colorless
crystals of 5a and 3a suitable for X-ray analysis were obtained by
recrystallization from n-hexane/CH2Cl2. 5a: mp 130.0−130.8 °C
1
3
(decomp.). H NMR (CDCl3): δ = 7.92 (br d, JHH = 6.8 Hz, 2H),
7.84 (br d, 3JHH = 6.8 H, 2H), 7.60−7.67 (m, 4 H), 1.39 ppm (s, 9H).
19F NMR (CDCl3): δ = −73.6 (q, JFF = 8.6 Hz, 6F), −76.3 ppm (q,
4
4JFF = 8.6 Hz, 6F). Anal. Calcd for C22H17AsF12O2: C, 42.88; H, 2.78.
Found: C, 42.68; H, 2.38. 3a: mp 138.2−139.0 °C. 1H NMR (CDCl3):
δ = 8.36 (d, 3JHH = 7.2 Hz, 2H), 7.91 (br d, JHH = 7.2 Hz, 2H), 7.82
3
(td, 3JHH = 7.2 Hz, 4JHH = 1.4 Hz, 2H), 7.77 (td, 3JHH = 7.2 Hz, 4JHH
=
1.4 Hz, 2H), 3.33 ppm (s, 1H). 19F NMR (CDCl3): δ = −73.8 (q, 4JFF
4
= 8.6 Hz, 6F), −74.4 ppm (q, JFF = 8.6 Hz, 6F). Anal. Calcd for
C18H9AsF12O3: C, 37.52; H, 1.57. Found: C, 37.38; H, 1.30.
2-[3,3-Bis(1,1,2,2,2-pentafluoroethyl)-2,1-benzoxarsol-1(3H)-yl]-
α,α-bis(1,1,2,2,2-pentafluoroethyl)benzenemethanol (2b). Under
N2, 1,1,1,2,2,4,4,5,5,5-decafluoro-3-(2-bromophenyl)-3-pentanol (934
mg, 2.21 mmol) was added to a slurry of NaH (199 mg, 4.97 mmol) in
THF (3.0 mL) at 0 °C, and the mixture was stirred for 0.5 h at room
temperature. To the mixture cooled to −78 °C, t-BuLi (1.57 M n-
pentane solution, 2.90 mL, 4.55 mmol) was added, and the mixture
was stirred for 1 h at the same temperature. The mixture was then
transferred to a solution of AsCl3 (0.095 mL, 0.113 mmol) in THF
(3.0 mL) at −78 °C. The mixture was allowed to warm to room
temperature and stirred for 18 h. The reaction was quenched with
distilled water (2 × 50 mL). The mixture was extracted with ether (2
× 60 mL) and dried over anhydrous MgSO4. After removing the
solvents by evaporation, the resulting crude mixture was separated by
column chromatography (n-hexane:CH2Cl2 = 5:1) to afford 2b (215
mg, 0.384 mmol, 17%) containing 7% of hydroxyarsorane 3b and 4b−
Na (278.8 mg, 0.408 mmol, 18%) as white solids. Colorless crystals of
3b suitable for X-ray analysis were obtained by recrystallization of the
mixture from n-hexane/CH2Cl2. Colorless crystals of 4b−Na
MeOH·3H2O suitable for X-ray analysis were obtained by dissolving
the solid in n-hexane at −17 °C and adding a few drops of MeOH to
induce crystallization. Compound 2b was gradually oxidized in air to
give 3b; therefore, 2b was used in the following reaction without
further purification. Similarly, compound 4b−Na was oxidized in the
EXPERIMENTAL SECTION
■
General Procedures. Melting points were measured using a
1
Yanaco micromelting point apparatus and are uncorrected. H NMR
(400 MHz) and 19F NMR (376 MHz) spectra were recorded using a
1
JEOL EX-400 or a JEOL AL-400 spectrometer. H NMR chemical
shifts (δ) are given in ppm downfield from Me4Si, determined by
residual chloroform (δ = 7.26 ppm). 19F NMR chemical shifts (δ) are
given in ppm downfield from the external CFCl3. Elemental analyses
were performed using a Perkin-Elmer 2400 CHN elemental analyzer.
All reactions were carried out under N2. Tetrahydrofuran (THF) and
diethyl ether (Et2O) were freshly distilled from Na−benzophenone, n-
hexane was distilled from Na, and other solvents were distilled from
CaH2. Merck silica gel 60 was used for column chromatography.
2-[3,3-Bis(trifluoromethyl)-2,1-benzoxarsol-1(3H)-yl]-α,α-bis-
(trifluoromethyl)benzenemethanol (2a). Under N2, TMEDA (1.60
mL, 10.6 mmol) was added to n-BuLi (1.58 M n-hexane solution, 14.0
mL, 22.1 mmol) at room temperature, and the mixture was stirred for
20 min. 1,1,1,3,3,3-Hexafluoro-2-phenyl-2-propanol (1.70 mL, 10.1
mmol) in THF (1.0 mL) was then added at 0 °C, and the mixture was
stirred for 8 h at room temperature. The mixture was then transferred
to a solution of AsCl3 (0.42 mL, 5.0 mmol) in THF (5.0 mL) at −78
°C. The mixture was warmed to room temperature and stirred for 12
h. The reaction was quenched with distilled water (2 × 50 mL). The
mixture was extracted with ether (2 × 80 mL) and dried over
anhydrous MgSO4. After removing the solvents by evaporation, the
resulting crude mixture was subjected to recrystallization from n-
hexane to afford 2a (1.22 g, 2.18 mmol, 21%) as a white solid.
Compound 4a−Li (1.47 g, 2.61 mmol, 26%) was obtained as a
colorless liquid from the filtrate. Colorless crystals of 2a·THF suitable
for X-ray analysis were obtained by further recrystallization from n-
hexane. Unfortunately only small crystals of low quality inevitably
containing THF could be obtained. However, the GOF value validates
our assignments. 2a: mp 148.0−149.0 °C (decomp.). 1H NMR
(CDCl3): δ = 8.32 (br s, 1H), 8.04 (br s, 1H), 7.77 (br s, 1H), 7.61 (s,
open air to slowly give 3b. 2b: 1H NMR (CDCl3): δ = 8.19 (d, 3JHH
=
3
3
7.8 Hz, 2H), 7.57 (br d, JHH = 7.8 Hz, 2H), 7.34 (td, JHH = 7.8 Hz,
4JHH = 1.2 Hz, 2H), 7.26 ppm (td, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz, 2H).
19F NMR (CDCl3): δ = −78.1 (t, 3JFF = 18.5 Hz, 6F), −78.22 (s, 3F),
2
−78.23 (s, 3F), −114.8 (s, 2F), −114.9 (s, 2F), −116.1 (dq, JF−F
=
=
3
2
4
282 Hz, JFF = 18.5 Hz, 2F), −119.3 ppm (dq, JFF = 282 Hz, JFF
18.5 Hz, 2F). 3b: mp 112.1−113.0 °C. 1H NMR (CDCl3): δ = 8.48−
8.46 (m, 2H), 7.90 (br s, 2H), 7.82−7.76 (m, 4H), 3.19 ppm (s, 1H).
19F NMR (CDCl3): δ = −78.3 (s, 6F), −78.8 (s, 6F), −115.5 (dm, 2JFF
2
= 285 Hz, 2F), −117.2 to −117.3 (m, 4F), −120.0 ppm (dm, JFF
=
285 Hz, 2F). Anal. Calcd for C22H9AsF20O3: C, 34.04; H, 1.17. Found:
1
2H), 7.47 (t, 3JHH = 7.6 Hz, 2H), 7.40 ppm (t, 3JHH = 7.6 Hz, 2H). 19
NMR (CDCl3): δ = −73.7 (q, 4JFF = 8.6 Hz, 3F), −73.9 (q, 4JFF = 8.6
F
C, 33.89; H, 0.81. 4b−Na: mp 109.1−109.9 °C (decomp.). H NMR
(CDCl3): δ = 8.05 (d, 3JHH = 7.6 Hz, 2H), 7.60 (d, 3JHH = 7.6 Hz, 2H),
7.38 (td, 3JHH = 7.6 Hz, 4JHH = 1.2 Hz, 2H), 7.32 ppm (td, 3JHH = 7.6
4
4
Hz, 3F), −76.2 (q, JFF = 8.2 Hz, 3F), −77.2 ppm (q, JFF = 8.2 Hz,
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Article
Hz, 4JHH = 1.2 Hz, 2H). 19F NMR (CDCl3): δ = −78.2 (s, 6F), −78.6
extracted with Et2O (2 × 50 mL), and the organic layer was washed
with brine (2 × 50 mL) and dried over anhydrous MgSO4. After
removing the solvents by evaporation, the resulting crude mixture was
separated by preparative TLC (n-hexane:CH2Cl2 = 4:1) to afford 5c
(15.8 mg, 0.0155 mmol, 5%), 3c (50.3 mg, 0.0512 mmol, 17%), and
6c (48.8 mg, 0.0449 mmol, 15%) as white solids and 1c−H2 (34.2 mg,
0.0769 mmol, 26%) as a colorless liquid. Colorless crystals of 5c and
6c suitable for X-ray analysis were obtained by recrystallization from n-
hexane/CH2Cl2. Unfortunately crystals of good quality could not be
obtained for 5c, and the R value was somewhat high. However, the
GOF value validates our assignments. 5c: mp 114.0−115.0 °C
2
(s, 6F), −115.0 (s, 4F), −118.0 (dm, JFF = 285.0 Hz, 2F), −120.0
2
ppm (dm, JFF = 285.0 Hz, 2F).
[TBPY-5-12]-1-(1,1-dimethylethyl)-3,3,3′,3′-tetrakis(1,1,2,2,2-pen-
tafluoroethyl)-1λ5-1,1′(3H,3′H)-spirobi[2,1-benzoxarsole] (5b).
Under N2, t-BuLi (1.57 M n-pentane solution, 0.30 mL, 0.471
mmol) was added to a solution of 2b (113 mg, 0.142 mmol) in Et2O
(3.0 mL) at −78 °C. The mixture was then stirred for 1 h at room
temperature. I2 (115 mg, 0.452 mmol) was added at −78 °C, and the
mixture was stirred for 1 h at 0 °C. The reaction was quenched with
aqueous Na2S2O3 (2 × 10 mL). The mixture was extracted with Et2O
(2 × 40 mL), and the organic layer was washed with brine (2 × 30
mL) and dried over anhydrous MgSO4. After removing the solvents by
evaporation, the resulting crude mixture was separated by preparative
TLC (n-hexane:CH2Cl2 = 4:1) to afford 5b (23.4 mg, 0.0287 mmol,
20%) as a white solid, followed by reversed-phase HPLC (MeCN) to
afford 3b (RT = 20 min: 7.7 mg, 0.0099 mmol, 7%) and 6b (RT = 31.6
min: 19.2 mg, 0.0217 mmol, 15%) as white solids. Colorless crystals of
5b and 6b suitable for X-ray analysis were obtained by recrystallization
from n-hexane/CH2Cl2. 5b: mp 148.3−149.1 °C (decomp.). 1H NMR
1
(decomp.). H NMR (CDCl3): δ = 7.99−7.97 (m, 2H), 7.83 (br s,
2H), 7.63−7.61 (m, 4H), 1.34 ppm (s, 9H). 19F NMR (CDCl3): δ =
−81.2 (t, 3JFF = 12.3 Hz, 6F), −81.5 (s, 6F), −109.0 (s, 4F), −111.6 (s,
4F), −120.4 (dq, 2JFF = 289.5 Hz, 3JFF = 12.3 Hz, 2F), −122.3 (dq, 2JFF
3
2
= 289.5 Hz, JFF = 12.3 Hz, 2F), −123.8 (d, JFF = 289.5 Hz, 2F),
−127.1 ppm (d, 2JFF = 289.5 Hz, 2F). Anal. Calcd for C30H17AsF28O2:
C, 35.45; H, 1.69. Found: C, 35.40; H, 1.44. 6c: mp 97.0−98.0 °C
1
(decomp.). H NMR (CDCl3): δ = 8.49−8.46 (m, 2H), 7.85 (br s,
2H), 7.74−7.44 ppm (m, 4H). 19F NMR (CDCl3): δ = −80.9 (s, 6F),
−81.5 (s, 6F), −110.5 (s, 4F), −111.3 (d, 2JFF = 288.3 Hz, 2F), −114.6
(d, 2JFF = 288.3 Hz, 2F), −119.8 (d, 2JFF = 288.3 Hz, 2F), −123.0, (d,
2JFF = 288.3 Hz, 2F), −124.6 (dm, 2JFF = 288.3 Hz, 2F), −125.9 ppm
3
(CDCl3): δ = 7.98−7.96 (m, 2H), 7.81 (br d, JHH = 6.8 H, 2H),
7.63−7.61 (m, 4H), 1.35 ppm (s, 9H). 19F NMR (CDCl3): δ = −78.4
(s, 6F), −78.5 (s, 6F), −113.1 (s, 4F), −114.2 (d, 2JFF = 286 Hz, 2F),
2
2
−115.9 ppm (d, JFF = 286 Hz, 2F). Anal. Calcd for C26H17AsF20O2:
(dm, JFF = 288.3 Hz, 2F). Spectral data of 3c were consistent with
C, 38.26; H, 2.10. Found: C, 38.34; H, 2.07. 6b: mp 155.0−155.5 °C.
those of the same product obtained as the product described above.
Spectral data for 1c−H2 were consistent with those described in our
reported paper.68
1H NMR (CDCl3): δ = 8.49 (d, 3JHH = 5.6 Hz, 2H), 7.91 (br d, 3JHH
=
3
4
5.6 Hz, 2H), 7.79 (td, JHH = 5.6 Hz, JHH = 1.5 Hz, 2H), 7.75 ppm
(td, 3JHH = 5.6 Hz, 4JHH = 1.5 Hz, 2H). 19F NMR (CDCl3): δ = −78.4
(s, 6F), −78.8 (t, 3JFF = 19.5 Hz, 6F), −112.4 (d, 2JFF = 287.9 Hz, 2F),
[TBPY-5-12]-1-(1,1-dimethylethyl)-3,3,3′,3′-tetrakis(1,1,2,2,3,3,3-
heptafluoroproyl)-1λ5-1,1′(3H,3′H)-spirobi[2,1-benzoxarsole] (7c).
A solution of 5c (14.2 mg, 0. 0139 mmol) in toluene (3.0 mL) was
heated at 105 °C for 12 h. After concentration in vacuo, the residue
was separated by column chromatography (n-hexane:CH2Cl2 = 4:1) to
afford 7c (14.0 mg, 0.0137 mmol, 98%) as a white solid. Colorless
crystals of 7c suitable for X-ray analysis were obtained by
2
3
2
−115.6 (dq, JFF = 287.9 Hz, JFF = 19.5 Hz, 2F), −116.0 (dq, JFF
=
3
2
287.9 Hz, JFF = 19.5 Hz, 2F), −120.4 ppm (d, JFF = 287.9 Hz, 2F).
Anal. Calcd for C22H8AsF20IO3: C, 29.82; H, 0.91. Found: C, 29.88; H,
0.67.
2-[3,3-Bis(1,1,2,2,3,3,3-heptafluoropropyl)-2,1-benzoxarsol-
1(3H)-yl]-α,α-bis(1,1,2,2,3,3,3-heptafluoropropyl)benzenemethanol
(2c). Under N2, 1,1,1,2,2,3,3,5,5,6,6,7,7,7-tetradecafluoro-4- (2-bromo-
phenyl)-4-heptanol (1.78 g, 3.40 mmol) was added to a slurry of NaH
(340.8 mg, 8.52 mmol) in THF (5.0 mL) at 0 °C, and the mixture was
stirred for 0.5 h at room temperature. To the mixture cooled to −78
°C, t-BuLi (1.57 M n-pentane solution, 4.60 mL, 7.22 mmol) was
added, and the mixture was stirred for 1 h at the same temperature.
The mixture was then transferred to a solution of AsCl3 (0.145 mL,
0.172 mmol) in THF (5.0 mL) at −78 °C. The mixture was allowed to
warm to room temperature and stirred for 12 h. The reaction was
quenched with distilled water (2 × 80 mL). The mixture was extracted
with ether (2 × 100 mL) and dried over anhydrous MgSO4. After
removing the solvents by evaporation, the resulting crude mixture was
subjected to recrystallization from n-hexane to afford a mixture of
1
recrystallization from n-hexane/CH2Cl2. 7c: H NMR (CDCl3): δ =
8.39−8.37 (m, 2H), 7.78 (br s, 2H), 7.65−7.62 (m, 4H), 1.29 ppm (s,
9H). 19F NMR (CDCl3): δ = −81.2 (s, 6F), −81.5 (s, 6F), −108.9 (br
d, 2JFF = 293.2 Hz, 2F), −109.9 (br d, 2JFF = 293.2 Hz, 2F), −110.7 (d,
2JFF = 293.2 Hz, 2F), −112.7 (d, 2JFF = 293.2 Hz, 4F), −123.1 (d, 2JFF
= 293.2 Hz, 4F), −124.6 ppm (d, 2JFF = 293.2 Hz, 2F). Anal. Calcd for
C30H17AsF28O2: C, 35.45; H, 1.69. Found: C, 35.36; H, 1.64.
X-ray Crystal Structure Determinations of Arsenic Com-
pounds. Crystals suitable for X-ray structural determination were
mounted on a Mac Science DIP2030 imaging plate diffractometer and
irradiated with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å) for data collection. Unit cell parameters were determined
by separately autoindexing several images in each data set using the
DENZO program (MAC Science).73 For each data set, the rotation
images were collected in 3° increments with a total rotation of 180°
about the φ axis. Data were processed using SCALEPACK. Structures
were solved by a direct method with the SHELX-97 program.74
Refinement on F2 was carried out using full-matrix least-squares by the
SHELX-97 program.74 All non-hydrogen atoms were refined using the
anisotropic thermal parameters. Hydrogen atoms were included in the
refinement along with the isotropic thermal parameters. Crystal data
and structure refinements of these arsenic species are listed in Tables
1−4.
1
three compounds (2c:3c:4c−Na = 22:51:27 by H and 19F NMR).
The mixture was then subjected to recrystallization from n-hexane/
CH2Cl2 to afford 3c (0.624 g, 0.64 mmol, 19%) as a white solid.
Colorless crystals of 3c suitable for X-ray analysis were obtained by
further recrystallization from n-hexane/CH2Cl2. 3c: mp 110.0−111.0
1
3
°C (decomp.). H NMR (CDCl3): δ = 8.45 (d, JHH = 7.2 Hz, 2H),
7.92 (br d, 3JHH = 7.2 Hz, 2H), 7.02 (td, 3JHH = 7.2 Hz, 4JHH = 1.5 Hz,
3
4
2H), 7.76 (td, JHH = 7.2 Hz, JHH = 1.5 Hz, 2H), 3.21 ppm (s, 1H).
19F NMR (CDCl3): δ = −80.9 (s, 6F), −81.4 (s, 6F), −111.2 (d, 2JFF
=
=
=
=
2
2
291.6 Hz, 2F), −112.1 (d, JFF = 291.6 Hz, 2F), −114.4 (d, JFF
2
2
291.6 Hz, 2F), −115.2 (d, JFF = 291.6 Hz, 2F), −120.2 (d, JFF
RESULTS AND DISCUSSION
2
2
■
291.6 Hz, 2F), −123.1 (d, JFF = 291.6 Hz, 2F), −124.1 (d, JFF
2
291.6 Hz, 2F), −125.6 ppm (d, JFF = 291.6 Hz, 2F). Anal. Calcd for
Synthesis of Arsines. Arsines 2, along with hydroxyarsor-
anes 3 and arsoranides 4, were prepared by treatment of AsCl3
with 2-fold amounts of the corresponding bidentate ligands 1
(Scheme 1).75 Compound 2a showed four distinct fluorine
signals corresponding to the CF3 groups in the 19F NMR
spectrum (δ = −73.7, −73.9, −76.2, and −77.2 ppm at 25 °C),
C26H9AsF28O2: C, 31.99; H, 0.93. Found: C, 31.73; H, 1.20.
[TBPY-5-12]-1-(1,1-dimethylethyl)-3,3,3′,3′-tetrakis(1,1,2,2,3,3,3-
heptafluoroproyl)-1λ5-1,1′(3H,3′H)-spirobi[2,1-benzoxarsole] (5c).
Under N2, t-BuLi (1.57 M n-pentane solution, 0.60 mL, 0.471
mmol) was added to a solution of 2c (286.7 mg, 0.298 mmol) in Et2O
(5.0 mL) at −78 °C. The mixture was then stirred for 1 h at room
temperature. I2 (218.6 mg, 0.861 mmol) was added at −78 °C, and the
mixture was stirred for 1 h at room temperature. The reaction was
quenched with aqueous Na2S2O3 (2 × 60 mL). The mixture was
1
and the two aromatic rings were equivalently observed by H
NMR. This indicates that compound 2a is a trivalent arsine in
the solution state, and it is in clear contrast to the phosphorus
10998
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Inorganic Chemistry
Article
analogue which exists as a pentacoordinate hydrophosphorane
with an equatorial P−H bond.76,77 Although 2a was stable to
air, 2b and 2c were gradually oxidized in the open air to give
the corresponding hydroxyarsoranes 3b and 3c, respectively.
The arsoranides 4 were easily separated from 2 by
recrystallization (n-hexane) or TLC (n-hexane/CH2Cl2).67
Compound 4a-Li bearing the Martin ligand (A) was very
stable to water or air,75 but 4b−Na and 4c−Na showed
instability and slowly gave 3b and 3c, respectively.
Table 1. Crystal and Refinement Data for 2a·THF, 3a, and
3b
2a·THF
3a
3b
formula
Mw
C22H17AsF12O3
632.27
C18H9AsF12O3
576.17
C22H9AsF20O3
776.21
cryst syst
space group
color
triclinic
P-1
triclinic
monoclinic
P21/c
P-1
colorless
plate
colorless
plate
colorless
plate
habit
Structure of Arsenic Species. The unique trivalent
structure of 2a·THF was confirmed by X-ray crystallography
(Figure 2), in which the interatomic distances As1···O1 and
As1−O2 of 2a THF were 2.465 and 1.890 Å, respectively. The
As1···O1 distance was significantly shorter than the sum of the
van der Waals radii for arsenic and oxygen (3.37 Å) by 0.91 Å,78
suggesting that there is interaction between As1 and O1.
Hydroxyarsorane 3a was obtained as one of the byproducts in
the following synthesis of the O-equatorial arsorane 5a. The
ORTEP diagrams for 3a, 3b, and 3c are shown in Figure 3.
Selected bond lengths and angles are summarized in Table 5.
The apical bond angles O1−As1−O2 of 3 (179.03(9)° for 3a,
179.20(10)° for 3b, and 178.12(9)° for 3c) are nearly of the
ideal value of 180°, and the sums of the equatorial angles (C1−
As1−C2, C2−As1−O3, and O3−As1−C1) for 3a, 3b, and 3c
are 360°, 360°, and 359.99°, respectively, thus indicating that
one of the byproduct compounds 3 with a hydroxyl group as a
monodentate ligand at the equatorial site takes on nearly ideal
trigonal-bipyramidal (TBP) structures. Colorless crystals for
4b−Na·MeOH·3H2O suitable for X-ray crystallography were
obtained by dissolving the solid in n-hexane and adding a few
drops of methanol to induce crystallization, Figure 4. Selected
bond lengths and angles are summarized in Table 6. The C1−
As1−C2 angle of 4b−Na·MeOH·3H2O (107.37°) is expanded
by 6.5° compared with that of the CF3 analog 4a−Et4N
(100.9°) reported by our group.75 This is in good agreement
with the trend observed for analogous 10-Sb-4 compounds in
which the corresponding angles are 110.3° for the C2F5
derivative67 and 103.6° for the CF3 derivative.66 This should
be due to steric repulsion between the endo-C2F5 group and the
equatorial aromatic ring of the other bidentate. Other structural
parameters for 4a−Et4N and 4b−Na MeOH·3H2O around the
arsenic atom were very similar. The O1−As1−O2 angles of
4b−Na·MeOH·3H2O and 4a−Et4N are 168.39° and 169.0°,
respectively, and thus distorted from the ideal value of 180° to
some extent. Analysis of the D angles (61.01° and 68.1°,
respectively) according to the method of Seppelt indicate that
the structures should be classified as trigonal bipyramids and
not square pyramids.79
a, Å
8.7080(8)
10.9580(10)
13.7650(4)
75.472(3)
76.821(4)
73.579(10)
1202.0(2)
2
11.5340(2)
12.6580(2)
15.0050(2)
67.2910(10)
87.6990(10)
88.6520(10)
2019.16(5)
4
13.4940(4)
8.2620(2)
23.4950(7)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
97.2910(1)
90
2598.22(13)
4
D
calcd, g cm−3
1.747
1.895
1.984
abs. coeff., mm−1
1.531
1.812
1.479
F(000)
628
1128
1512
radiation, λ, Å
T, K
Mo Kα, 0.71073 Mo Kα, 0.71073 Mo Kα, 0.71073
293(2)
293(2)
298(2)
data, collected
+h, k,
l
+h, k,
l
+h, +k,
l
data/restraints/
params
3866/0/344
8827/0/615
5610/0/416
R1 [I > 2σ(I)]
wR2 (all data)
GOF
0.1832
0.4798
1.093
0.0455
0.1309
1.086
0.0471
0.1394
1.143
CCDC No.
886009
886010
886011
Table 2. Crystal and Refinement Data for 3c, 4b−
Na·MeOH·3H2O, and 5a
4b−
3c
Na·MeOH·3H2O
5a
formula
Mw
C26H9AsF28O3
976.25
C23H18AsF20O6Na C22H17AsF12O2
868.28
616.28
monoclinic
P21/c
cryst syst
space group
color
triclinic
monoclinic
P21/c
P-1
colorless
plate
colorless
plate
colorless
plate
habit
a, Å
9.8340(2)
12.6640(3)
13.9860(2)
75.133(2)
69.4430(10)
77.5720(10)
1561.14(5)
2
10.5860(2)
27.3010(6)
11.1630(3)
90
8.3040(3)
16.0250(7)
17.9010(10)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
109.3920(10)
90
99.950(2)
90
3043.17(12)
4
2346.28(19)
4
Synthesis of the O-Equatorial Arsoranes. In order to
prepare antiapicophilic arsoranes, we chose the tert-butyl group
as the monodentate ligand since it was the most effective ligand
for slowing isomerization of the series of O-equatorial
phosphoranes to their corresponding O-apical isomers.52,53
The antiapicophilic arsoranes 5 could then be synthesized from
the corresponding arsines 2, utilizing our reported method for
synthesis of O-equatorial spirophosphoranes using I2 as the
oxidizing agent (Scheme 2).53 Byproducts in the reactions were
hydroxyarsoranes 3, iodoarsoranes 6 (6b and 6c), and the
protonated bidentate ligand 1c−H2.68 Interestingly, the
iodoarsoranes 6 were stable enough to bear aqueous workup
and chromatographic treatment. These are rare examples of
water-stable iodoarsoranes. In contrast, for the CF3 system 6a
was not obtained, suggesting that it is highly unstable to water.
D
calcd, g cm−3
2.077
1.895
1.745
abs. coeff.,
1.289
1.293
1.563
mm−1
F(000)
948
1712
1224
radiation, λ, Å
T, K
Mo Kα, 0.71073 Mo Kα, 0.71073
Mo Kα, 0.71073
173(2)
173(2)
173(2)
data, collected
+h, k,
l
+h, +k,
l
+h, +k,
l
data/restraints/ 6884/0/524
params
6079/0/462
4781/0/337
R1 [I > 2σ(I)]
wR2 (all data)
GOF
0.0521
0.1519
1.069
0.0467
0.1517
1.120
0.0508
0.1425
1.145
CCDC No.
886012
886013
639282
10999
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Inorganic Chemistry
Article
Table 3. Crystal and Refinement Data for 5b, 5c, 6b, and 6c
5b
5c
6b
6c
formula
Mw
C26H17AsF20O2
816.32
C30H17AsF28O2
1016.36
C22H8AsF20IO2
886.10
C26H8AsF28IO2
1086.14
monoclinic
C2/c
cryst syst
space group
color
monoclinic
P21/c
triclinic
orthorhombic
Pbcn
P-1
colorless
plate
colorless
plate
colorless
plate
colorless
plate
habit
a, Å
12.714(2)
13.013(2)
18.608(2)
90
9.4410(2)
10.7300(3)
18.2820(6)
105.0530(10)
100.9890(10)
94.4480(10)
1739.82(8)
2
18.5530(4)
8.8470(2)
16.8740(2)
90
22.9310(4)
15.0300(3)
9.6610(3)
90
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
109.1290(10)
90
90
100.717(1)
90
90
2908.6(7)
4
2769.67(9)
4
3271.61(13)
4
D
calcd, g cm−3
1.864
1.940
2.125
2.205
abs. coeff., mm−1
1.324
1.159
2.499
2.172
F(000)
1608
996
1688
2072
radiation, λ, Å
T, K
Mo Kα, 0.71073
173(2)
Mo Kα, 0.71073
173(2)
Mo Kα, 0.71073
298(2)
Mo Kα, 0.71073
200(2)
data, collected
data/restraints/params
R1 [I > 2σ(I)]
wR2 (all data)
GOF
+h, +k,
l
+h, k,
l
+h, k,
l
+h, +k,
l
6597/0/437
0.0605
7701/0/555
0.1153
3203/0/218
0.0559
3755/0/264
0.0413
0.1706
0.3577
0.2138
0.1326
1.071
1.135
1.121
1.257
CCDC No.
639283
886014
886015
886016
converted into the corresponding O-apical isomers 7 when
heated in solution (Scheme 3), the O-equatorial arsoranes were
proven to be kinetically stabilized and thermodynamically
unstable species. In other words, these are isolable arsoranes
with antiapicophilicity which still may undergo stereomutation
to their corresponding more stable stereoisomers.
Table 4. Crystal and Refinement Data for 7a, 7b, and 7c
7a
7b
7c
formula
Mw
C22H17AsF12O2
616.28
C26H17AsF20O2
816.32
C30H17AsF28O2
1016.36
triclinic
P-1
cryst syst
space group
color
orthorhombic
P212121
colorless
plate
triclinic
P-1
Structure of the Pentacoordinate Arsoranes. Solid-
state structures of the O-equatorial spiroarsoranes 5 (5a, 5b,
and 5c) and the O-apical spiroarsoranes 7 (7a, 7b, and 7c)
were confirmed by X-ray crystallographic analysis. ORTEP
diagrams for the O-equatorial and O-apical arsoranes are shown
in Figure 5. Selected bond lengths and angles are summarized
in Table 7. For the O-equatorial isomers, the bond distances of
As1−O1 (1.962(2) Å for 5a, 1.978(2) Å for 5b, and 1.961(6) Å
for 5c) and As1−C2 (1.978(4) Å for 5a, 1.986(3) Å for 5b, and
1.997(9) Å for 5c) are longer than As1−O2 (1.828(3) Å for 5a,
1.817(2) Å for 5b, and 1.827(7) Å for 5c) and As1−C1
(1.954(4) Å for 5a, 1.936(3) Å for 5b, and 1.966(10) Å for 5c),
respectively. This implies that the former two correspond to
apical bonds, while the latter two are equatorial bonds,
indicating that 5 are essentially of TBP structure. It is noted
that the apical bond angles O1−As1−C2 are distorted from the
ideal value of 180° with a larger displacement for 5a (162.07°)
than 5b (164.55°) and 5c (164.2°). The same goes for the
equatorial angle O2−As1−C1 comprising the two bidentates,
with that for 5a (123.86°) being larger than those of 5b
(116.80°) and 5c (118.6°). Furthermore, the differences
between the apical and the equatorial distances for the same
atom combinations for 5a (As−O, 0.13 Å; As−C, 0.02 Å) are
smaller than those for 5b (As−O, 0.16 Å; As−C, 0.05 Å) and
5c (As−O, 0.14 Å; As−C, 0.03 Å). These structural features
indicate that the distortion of 5a toward the RP (rectangular
pyramid) geometry along the Berry coordinate is slightly
greater than those of 5b and 5c. The lower degree of distortion
colorless
plate
colorless
plate
habit
a, Å
11.6890(2)
12.0290(2)
16.6230(3)
90
10.5300(2)
11.9040(3)
12.7020(4)
76.8420(10)
74.5350(10)
78.0960(10)
1476.16(7)
2
10.5400(1)
12.1040(2)
16.1730(3)
81.835(1)
72.973(1)
66.741(1)
1811.70(5)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
90
90
2337.31(7)
4
D
calcd, g cm−3
1.751
1.837
1.863
abs. coeff., mm−1
1.569
1.304
1.113
F(000)
1224
804
996
radiation, λ, Å
T, K
Mo Kα, 0.71073 Mo Kα, 0.71073 Mo Kα, 0.71073
173(2)
173(2)
200(2)
data, collected
+h, +k, +l
3129/0/334
+h, k,
l
+h, k,
l
data/restraints/
params
6527/0/445
8031/0/553
R1 [I > 2σ(I)]
wR2 (all data)
GOF
0.0435
0.1427
1.101
0.0509
0.1817
1.194
0.0409
0.1378
1.164
CCDC No.
639284
639285
886017
This distinction is a good indication that the steric environment
around the arsenic atom of 6b and 6c is much more hindered
than that of 6a. In addition, the O-equatorial arsoranes 5 could
also be synthesized from the corresponding arsoranides 4-Na.67
Since the O-equatorial arsoranes 5 were quantitatively
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Inorganic Chemistry
Article
Scheme 1. Synthesis of Tricoordinate Arsine 2
Table 5. Selected Bond Lengths (Angstroms) and Angles
(degrees) for 3a−c
3a
3b
3c
As1−O1
As1−O2
1.893(2)
1.855(2)
1.906(2)
1.875(2)
1.905(2)
1.874(2)
As1−O3
1.739(2)
1.737(2)
1.743(2)
As1−C1
1.907(3)
1.917(3)
1.912(3)
As1−C2
1.906(3)
1.913(3)
1.912(3)
O1−As1−O2
O1−As1−O3
O1−As1−C1
O1−As1−C2
O2−As1−O3
O2−As1−C1
O2−As1−C2
C1−As1−C2
C1−As1−O3
C2−As1−O3
179.03(9)
90.31(11)
85.90(12)
93.80(12)
89.37(11)
93.45(12)
87.16(12)
126.98(13)
118.83(12)
114.19(12)
179.20(10)
91.44(11)
85.53(12)
92.68(12)
88.66(12)
95.15(13)
86.55(12)
131.03(16)
114.85(14)
114.12(15)
178.12(9)
91.69(10)
85.68(11)
91.85(11)
89.53(10)
95.14(11)
86.34(11)
130.83(13)
113.42(12)
115.74(12)
Figure 2. ORTEP diagram of 2a·THF showing thermal ellipsoids at
the 30% probability level. Hydrogen atoms other than that of the
hydroxy group are omitted for clarity. Selected bond lengths
(Angstroms) and angles (degrees) for 2a: As1···O1, 2.465; As1−O2,
1.890(15); As1−C1, 2.02(2); As1−C2, 1.91(2); O2−As1−C1,
95.8(9); O2−As1−C2, 85.5(8); C1−As1−C2, 99.1(9).
latter. Thus, the observed distortion in the arsorane system
could be due to the larger bidentate ring strain imposed due to
the larger atom radius of the arsenic atom. In the O-apical
arsoranes 7 (7a, 7b, and 7c), the apical bond angles O1−As1−
O2 (170.82(14)° for 7a, 166.09(12)° for 7b, and 166.66(8)°
for 7c) are distorted from the ideal value of 180°, compared
with those of 3 with a hydroxyl group as the equatorial
monodentate (179.03(9)° for 3a, 179.20(10)° for 3b, and
178.12(9)° for 3c) but to a lesser degree than their
of 5b and 5c could be due to steric repulsion between the two
nearest C2F5/n-C3F7 groups within the molecules. For
analogous antiapicophilic phosphoranes with the t-Bu group
as the monodentate, the structural differences between the
CF352 and the C2F561 compounds were found to be small, with,
for instance, the apical bond angle being 169.5(1)° and
169.76(9)° and the angle between the bidentates being
120.7(2)° and 118.02(9)°, respectively, for the former and
Figure 3. ORTEP diagrams of 3a−c showing thermal ellipsoids at the 30% probability level. Hydrogen atoms other than that of the hydroxy group
are omitted for clarity.
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Inorganic Chemistry
Article
Scheme 3. Isomerization of O-Equatorial Arsoranes to Their
O-Apical Arsoranes
2.529(4) Å for 6b and 2.5090(5) Å for 6c.80 The other bonds
and angles of the iodoarsoranes were very similar to those of
our previously reported O-apical arsoranes.23
Kinetic Study. Kinetic measurements for isomerization of 5
to 7 were performed in p-tert-butyltoluene over the temper-
ature range of 60−80 °C for 5a to 7a, 85−105 °C for 5b to 7b,
and 95−115 °C for 5c to 7c by monitoring the change in the
integrals of the 19F NMR signals of the trifluoromethyl groups
(Table 8). Eyring plots of the rates showed good linearity for all
three temperatures (Figure 7). The activation parameters
derived from the plots for the CF3 derivatives (5a to 7a) are
Figure 4. ORTEP diagram of 4b−Na·MeOH·3H2O showing thermal
ellipsoids at the 30% probability level. Hydrogen atoms other than that
of the hydroxy group are omitted for clarity.
Table 6. Selected Bond Lengths (Angstroms) and Angles
(degrees) for 4b−Na·MeOH·3H2O
4a−Et4N75
4b−Na·MeOH·3H2O
ΔH⧧ = 26.0 0.3 kcal mol−1, ΔS⧧ = −2.1 0.8 e.u., ΔG⧧
=
363
26.8 kcal mol−1, those for the C2F5 derivatives (5b to 7b) are
ΔH⧧ = 28.2 0.7 kcal mol−1, ΔS⧧ = −0.6 2.0 e.u., ΔG⧧
As1−O1
As1−O2
As1−C1
As1−C2
O1−As1−O2
O1−As1−C1
O1−As1−C2
O2−As1−C1
O2−As1−C2
C1−As1−C2
2.011(4)
2.064(4)
1.947(6)
1.975(6)
169.0(2)
82.0(2)
2.071(2)
2.053(2)
=
363
28.4 kcal mol−1, and those for the n-C3F7 derivatives (5c to 7c)
1.968(3)
are ΔH⧧ = 28.6
0.6 kcal mol−1, ΔS⧧ = −0.3
1.6 e.u.,
1.970(3)
ΔG⧧ = 28.7 kcal mol−1 (Table 8, Figure 7). The activation
168.39(7)
81.04(11)
92.05(10)
91.81(10)
81.30(10)
107.37(11)
363
entropies (ΔS⧧) for all three were about the same with near
zero values. The difference in activation free energy for
isomerization of 5a and 5b was 1.6 (28.4−26.8) kcal mol−1,
indicating that increasing steric effects by changing CF3 to C2F5
was highly effective for slowing down BPR. A comparison of
the rates of isomerization of 5b and 5c at the same temperature
(95, 100, and 115 °C) shows that the isomerization rate for 5c
has been reduced to about one-half. Therefore, it could be said
that the steric effect of the n-C3F7 group is unnegligible. This
difference in rate corresponds to a difference in activation free
energy of 0.3 (28.7 − 28.4) kcal mol−1. Thus, the substituent
effect upon changing from C2F5 to n-C3F7 was not as significant
as that for the change from CF3 to C2F5. This is understandable
by considering the global maximum of the whole stereo-
mutation process, which could be approximated as the highest
energy intermediate where one of the bidentates occupies
diequatorial sites, as shown in Figure 8.49,50,52−69 It would be
easy to imagine that the terminal CF3 groups of the C3F7
91.8(2)
91.8(2)
80.5(2)
100.9(3)
corresponding O-equatorial isomers. The C1−As1−C2 angles
of 7b (132.19°) and 7c (131.19°) are widened by 7° compared
with that of 7a (124.4°), probably due again to the steric
differences of the ligands. Notable is that the structural
parameters about the central arsenic atom are practically the
same between 7b and 7c, although the conformations of the
fluorinated carbon groups are different. Thus, distinct structural
differences were observed between corresponding isomers of
the CF3 and C2F5 series, whereas the changes between the C2F5
and C3F7 derivatives were not as obvious. The structures of
iodoarsoranes 6b and 6c were confirmed by X-ray crystallog-
raphy (Figure 6). The equatorial bond lengths of As1−I1 were
Scheme 2. Synthesis of O-Equatorial Arsoranes
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Figure 5. ORTEP diagrams of 5a−c and 7a−c showing thermal ellipsoids at the 30% probability level. Hydrogen atoms are omitted for clarity.
Table 7. Selected Bond Lengths (Angstroms) and Angles (degrees) for 5a−7c
5a64
5b64
5c
7a64
7b64
7c
As1−O1
As1−O2
As1−C1
As1−C2
1.962(2)
1.828(3)
1.978(2)
1.817(2)
1.961(6)
1.827(7)
1.966(10)
1.997(9)
2.039(10)
80.2(3)
1.931(3)
1.923(3)
1.934(3)
1.937(3)
1.9305(18)
1.9221(18)
1.924(2)
1.954(4)
1.936(3)
1.938(4)
1.928(4)
1.978(4)
1.986(3)
1.934(4)
1.929(4)
1.931(2)
As1−C3
2.006(4)
2.014(3)
2.005(4)
1.996(4)
1.998(2)
O1−As1−O2
O1−As1−C1
O1−As1−C2
O1−As1−C3
O2−As1−C1
O2−As1−C2
O2−As1−C3
C1−As1−C2
C1−As1−C3
C2−As1−C3
78.59(11)
83.02(14)
162.07(14)
91.46(16)
123.86(15)
85.15(14)
113.55(16)
100.13(17)
119.53(17)
102.02(17)
82.28(10)
82.71(12)
164.55(13)
89.64(13)
116.80(12)
84.99(13)
118.59(14)
99.99(15)
121.65(15)
101.55(15)
170.82(14)
83.82(17)
91.42(18)
93.45(16)
91.66(17)
84.53(17)
95.72(16)
124.4(2)
166.09(12)
83.79(14)
91.61(14)
98.80(16)
89.49(14)
83.89(14)
95.09(16)
132.19(16)
116.60(18)
111.14(19)
166.66(8)
83.66(9)
83.0(4)
164.2(4)
89.8(4)
91.33(9)
95.64(10)
90.21(9)
118.6(4)
84.8(4)
83.80(9)
117.4(4)
100.1(4)
121.2(4)
101.4(4)
97.67(10)
131.19(10)
113.80(10)
115.01(10)
116.96(18)
118.58(18)
groups are too far away to impose significant steric effects in the
vicinity of the central As atom. A comparison with
phosphoranes shows that the activation free energies for the
arsoranes (ΔG⧧363) are much lower than those for the
corresponding t-Bu-substituted phosphoranes where the
activation Gibbs free energy was calculated to be 31.1 kcal
mol−1 for the CF3 system53 and estimated to be ca. 38 kcal
mol−1 for the C2F5 system.61,64 This is in accordance with the
generally easier stereomutation for lower elements in the same
group of the periodic table.69 The differences in activation free
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Figure 7. Eyring plot for stereomutation of 5 to 7: (circle) 5a to 7a;
(square) 5b to 7b; (star) 5c to 7c.
Figure 6. ORTEP diagrams of 6b and 6c showing thermal ellipsoids at
the 30% probability level. Selected bond lengths (Angstroms) and
angles (degrees) for 6b: As1−O1, 1.891(2); As1−O2, 1.891(2); As1−
C1, 1.919(3); As1−C2, 1.919(3); As1−I1, 2.529(4); O1−As1−O2,
168.75(16); O1−As1−C1, 85.41(13); O1−As1−C2, 90.70(13); O1−
As1−I1, 95.62(8); O2−As1−C1, 90.70(13); O2−As1−C2, 85.41(13);
O2−As1−I1, 95.62(8); C1−As1−C2, 139.5(2); C1−As1−I1,
110.25(12); C2−As1−I1, 110.25(12). Selected bond lengths (Ang-
stroms) and angles (degrees) for 6c: As1−O1, 1.898(2); As1−O2,
1.898(2); As1−C1, 1.922(3); As1−C2, 1.922(3); As1−I1, 2.5090(5);
O1−As1−O2, 170.62(13); O1−As1−C1, 85.50(10); O1−As1−C2,
90.86(10); O1−As1−I1, 94.69(6); O2−As1−C1, 90.86(10); O2−
As1−C2, 85.50(10); O2−As1−I1, 94.69(6); C1−As1−C2,
134.29(17); C1−As1−I1, 112.85(8); C2−As1−I1, 112.85(8).
energy between the CF3 and the C2F5 groups, 7 (38 − 31.1)
kcal mol−1 for the phosphoranes and 1.6 (28.4 − 26.8) kcal
mol−1 for the arsoranes, indicate that the arsoranes are less
prone to steric hindrance.
CONCLUSIONS
■
In summary, by utilizing bulky bidentate ligand systems with
C2F5 and n-C3F7 groups, new antiapicophilic arsoranes (5b and
5c, respectively) could be synthesized. Both compounds were
characterized by X-ray structural analysis. These antiapicophilic
arsoranes isomerized to their more stable isomers (7b and 7c,
respectively) upon heating, and a kinetic study on this process
Figure 8. Energy diagram for isomerization of O-equatorial arsoranes
to O-apical isomers.
showed that the barriers increased in the order of CF3 < C2F5 <
n-C3F7. This proves that increasing steric hindrance is a
a
Table 8. Kinetic Parameters
process
T [K]
k [s−1
]
ΔH⧧ [kcal mol−1
]
ΔS⧧ [e.u.]
−2.1 0.8
ΔG⧧ [kcal mol−1
]
363
333
338
343
348
353
358
363
368
373
378
368
373
378
383
388
(1.78 0.02) × 10−5
(3.34 0.01) × 10−5
(6.01 0.02) × 10−5
(10.3 0.09) × 10−5
(17.6 0.20) × 10−5
(3.08 0.05) × 10−5
(5.47 0.11) × 10−5
(8.90 0.19) × 10−5
(16.7 0.36) × 10−5
(26.1 0.32) × 10−5
(5.69 0.15) × 10−5
(9.61 0.21) × 10−5
(16.2 0.04) × 10−5
(28.8 0.06) × 10−5
(44.1 0.10) × 10−5
5a → 7a
26.0 0.3
26.8
28.4
28.7
5b → 7b
5c → 7c
28.2 0.7
−0.6 2.0
28.6 0.6
−0.32 1.56
a
Error is given as the standard deviation.
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ASSOCIATED CONTENT
* Supporting Information
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X-ray crystallography details and CIF files of compounds
2a·THF, 3a, 3b, 3c, 4b−Na·MeOH·3H2O, 5c, 6b, 6c, and 7c.
This material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: xdjiang@henu.edu.cn; yyama@sci.hiroshima-u.ac.jp.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful to Central Glass Co., Ltd., for the
generous gift of hexafluorocumyl alcohol. This research was
supported by the Grant-in-Aid for Scientific Research on
Priority Areas (No. 17350021) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan and the
National Natural Science Foundation of China (20872026).
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