Digging the Sigma-Hole of Organoantimony Lewis Acids by Oxidation

Article abstract of DOI:10.1002/anie.201808551

The development of group 15 Lewis acids is an area of active investigation that has led to numerous advances in anion sensing and catalysis. While phosphorus has drawn considerable attention, emerging research shows that organoantimony(III) reagents may a

Full text of DOI:10.1002/anie.201808551

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Accepted Article
Title: Digging the sigma-hole of organoantimony Lewis acids by
oxidation
Authors: Mengxi Yang, Daniel Tofan, Chang-Hong Chen, Kevin
Michael Jack, and Francois Pierre Gabbai
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Digging the -hole of organoantimony Lewis acids by oxidation
Mengxi Yang, Daniel Tofan, Chang-Hong Chen, Kevin M. Jack, and François P. Gabbaï*
Abstract: The development of group 15 Lewis acids is an area of
active investigation that has led to numerous advances in anion
sensing and catalysis. While phosphorus has drawn considerable
attention, emerging research shows that organoantimony(III)
reagents may also act as potent Lewis acids. By comparing the
It is interesting to note that the Lewis acidity at antimony can
also be imparted through the use of perfluorinated ligands.
While SbPh3 (1) does not possess any notable Lewis acidity,
Matile et al. have shown recently that Sb(C6F5)3 (2) binds
chloride anions and catalyzes anion pairing reactions involving
organic chlorides (Figure 1).[10] This halide binding event again
illustrates the presence of low lying * orbitals which accept
density from a donor orbital located on the incoming anion. This
phenomenon can also be referred to as resulting from the
properties of SbPh3, Sb(C6F5)3, and SbArF with those of their
3
tetrachlorocatecholate analogs SbPh3Cat, Sb(C6F5)3Cat, and
SbArF Cat (Cat = o-O2C6Cl4, ArF = 3,5-(CF3)2C6H3), we now show
3
that the Lewis acidity of electron deficient organoantimony(III)
reagents can be readily enhanced by oxidation to the +V state as
verified by binding studies, organic reaction catalysis, and
computational studies. We rationalize these results by explaining
that oxidation of the antimony center leads to a lowering of the
accepting * orbital and a deeper carving of the associated -hole.
presence of
a a term that usually
so-called -hole,[11]
emphasizes the contribution of electrostatic forces to the
interaction (Figure 2).[12] In this paper, we show that oxidation of
antimony to the +V state can be used to carve the electrostatic
potential profile about the antimony atom, leading to a deeper -
hole. We also demonstrate that control over the depth of the -
hole impacts the affinity of antimony for incoming electron-rich
substrates and turns on catalysis.
The chemistry of group 15 Lewis acids is experiencing a surge
of activity that has led to a series of stimulating developments in
the area of phosphorus-mediated catalysis.[1] Antimony
derivatives, because of their intrinsically higher Lewis acidity,[2]
are also drawing considerable attention both in the areas of
small molecule activation and catalysis[3] as well as in anion
complexation.[4] Recent efforts in the chemistry of
organoantimony(III)[5] have established that derivatives such as
I[6] and II[7] readily bind halide anions (Figure 1) via donation into
the * orbital (Figure 2).[7] Based on the same principle, we also
found that antimony (III) halides could serve to promote
activation of transition metals either via direct interaction with the
metal (III)[8] or anion abstraction (IV)[9] (Figure 1).
Figure 2. Orbital and electrostatic origin of the Lewis acidity in antimony
derivatives. The intensification of the blue color illustrates an energy lowering
in the case of the LUMO and a greater positive charge development at
antimony in the case of the -hole.
To probe the effect of oxidation on antimony acceptors, we
decided to compare the properties of SbPh3 (1), Sb(C6F5)3 (2),
and SbArF3 (3) with those of their tetrachlorocatecholate analogs
SbPh3Cat (4), Sb(C6F5)3Cat (5), and SbArF Cat (6) (Cat = o-
3
O2C6Cl4, ArF = 3,5-(CF3)2C6H3) (Figure 3). While most of these
compounds have been described previously,[3c,4c,13] 6 was
prepared by reaction of 3 with o-chloranil and its structure was
verified by X-ray crystallography.[14] We note in passing that the
use of the electron deficient tetrachlorocatecholate ligands in 5
and 6 is necessary to stabilize the +V oxidation state of these
compounds.
Figure 1. Selected examples of antimony(III) compounds acting as Lewis
acids.
[*]
M. Yang, D. Tofan, C.-H. Chen, K. M. Jack, Prof. Dr. F. P. Gabbaï
Department of Chemistry, Texas A&M University
College Station, TX 77843 (USA)
E-mail: francois@tamu.edu
Homepage: http://www.chem.tamu.edu/rgroup/gabbai/
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201808551
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Figure 3. Antimony-based Lewis acids studied in this work.
With these compounds at our disposal, we decided to test their
reactivity toward simple Lewis bases. For the purpose of this
study, we chose to benchmark the Lewis acidity of these
compounds against triphenylphosphine oxide, a base known to
coordinate to antimony (V) compounds.[3c] Using 1H and 19F
NMR spectroscopy, we found that 1, 2, and 3 do not interact to
any measurable extent with Ph3PO in CDCl3. By contrast, the 1H,
31P and 19F NMR spectra of stiboranes 4, 5 and 6 undergo
drastic changes upon addition of Ph3PO. In the case of 4, we
observed that the 1:1 adduct Ph3POSbPh3Cat is in rapid
Figure 4. a) Spectral changes in the 31P NMR spectra of Ph3PO (1.47 × 10-2
M) in CDCl3 observed upon incremental addition of SbPh3Cat (4). b) The
experimental and the calculated 1:1 binding isotherm for 4 and Ph3PO based
on the 31P NMR chemical shifts. The data were fitted with K = 120 ± 20 M-1,
(Ph3PO) = 29.8 ppm, (Ph3POSbPh3Cat) = 33.6 ppm. c) Spectral changes
observed in the UV-Vis absorption spectra of Sb(C6F5)3Cat (5) (5.34 × 10-4 M)
upon addition of Ph3PO (5.10 × 10-2 M) in CHCl3. d) The experimental and the
calculated 1:1 binding isotherm for 5 and Ph3PO based on the UV-vis
absorbance at 410 nm. The data were fitted with K = 3 (± 0.8) × 104 M-1, (5) =
382 M-1cm-1, (Ph3POSb(C6F5)3Cat) = 275 M-1cm-1.
equilibrium with
4 and Ph3PO at NMR concentrations.
Although stibines 2 and 3 remain unchanged in the presence of
Ph3PO, formation of adducts appear to take place in hexanes, a
solvent of lower polarity. Addition of stibine 2 and 3 to a solution
of Ph3PO in hexanes triggers a downfield shift of the 31P NMR
signal from 23.4 ppm to 28.5 ppm in the case of 2 and 28.4 ppm
in the case of 3. Crystals of Ph3PO→Sb(C6F5)3 were obtained by
cooling a pet ether (40-60) solution to −20°C, comfirming the
molecular structure of the proposed adduct.[14] The crystal
structure of Ph3PO→Sb(C6F5)3 confirms the presence of an
interaction between the antimony center and the oxygen of the
phosphine oxide in the solid state. The oxygen atom is
positioned trans to the C1 carbon atom (∠O1-Sb-C1 = 164.8°)
suggesting alignment of an oxygen lone pair with the -hole or
* orbital of the Sb-C1 bond. The Sb1-O1 distance of 2.628(4) Å
is well within the sum of the van der Waals radii of the two
Incremental addition of 4 to a solution of Ph3PO induces a
progressive downfield shift of the 31P NMR resonance consistent
with increasing concentrations of the 1:1 adduct. Treatment of
this titration data affords a binding constant (K) of 120 ± 20 M-1.
(Figure 4) Unlike 4, the fluorinated stiboranes 5 and 6 form 1:1
adducts with the Ph3PO (Ph3POSb(C6F5)3Cat and
Ph3POSbArF Cat, respectively) with no evidence of
3
dissociation or exchange at NMR concentrations. Since the 31P
NMR chemical shift of Ph3PO is equal to 29.6 ppm, that
measured for the adducts (41.5 ppm for 5 and 40.0 ppm for 6)
suggests a substantial polarization of the P=O functionality upon
coordination to antimony. UV-vis titration experiments carried
out by adding incremental amounts of Ph3PO to CHCl3 solutions
of 5 or 6 afford 1:1 binding isotherms that could be fitted with K =
3 (± 0.8) × 104 M-1 for 5 and K = 3 (± 1) × 105 M-1 for 6 (Figure 4
and Figure S8). These binding constants are one to two orders
of magnitude higher than that measured for 4. This
enhancement in Lewis acidity can be attributed to the
fluorination of the aryl rings and their resulting electron-
withdrawing properties. The higher Lewis acidity measured for 6
corroborates fluoride ion affinity (FIA) trends computed by
Krossing who found that BArF3 (471 kJ/mol) has a higher fluoride
anion affinity than B(C6F5)3 (444 kJ/mol).[15] Given that the 31P
NMR shift of Ph3POSb(C6F5)3Cat is more downfield than that
elements (RvdW(Sb,O)
= , consistent with the
3.97 Å)[17]
presence of a secondary interaction. These structural results
constitute the first crystallographic verification that Sb(C6F5)3 is a
pnictogen bond donor[11b,11c] or an antimony(III) Lewis acid.
These structural results are corroborated by a natural bond
orbital (NBO) analysis[18] of the adduct. This analysis describes
the Sb-O linkage as
a
lp(O)→*(Sb-C) donor-acceptor
interaction of Edel = 15.6 kcal/mol (Figure 5). This adduct also
appears to also be stabilized by an arene-perfluoroarene
interaction involving the phenyl ring containing C31 and the
pentafluorophenyl ring containing C13 and whose centroids are
separated by 3.58 Å. The presence of this interaction indicates
that 2 also possesses -acidic properties.
of Ph3POSbArF Cat, these UV-vis titration results indicate that
3
Lewis acidity measurements based on the simple measurement
of the 31P NMR chemical shift of a coordinated phosphine oxide
can be inaccurate.[16] A more general conclusion of these
experiments is that the Lewis acidity of stibines is readily
enhanced by oxidization with ortho-chloranil.
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4
5
6
398*
485*
497*
-1.62
-2.65
-2.68
*Isomers are present of the fluoride adducts of 4-6. The values reported here
are based on the most thermally stable isomer. See SI for further details.
The next step of our study was to determine whether these
derivatives can be used to catalyze organic transformations, and
whether the Lewis acidity trend derived from the above titration
experiments and calculations could also be reflected kinetically
(Scheme 1). We first tested these compounds as catalysts for
the transfer hydrogenation reaction known to occur between
Hantzsch ester and N-benzylideneaniline.[19] This reaction was
carried out in CDCl3, with a 5 mol% catalyst loading. We found
that the most Lewis acidic perfluorinated stiboranes 5 and 6
afforded an almost quantitative yield of the amine product after
10 min while 1 was essentially inactive. The non-fluorinated
stiborane 4 proved to be significantly less active than 5 and 6,
leading to a 29% yield after 10 min. This yield is in fact
comparable to that obtained with the perfluorinated stibines 2
and 3. A comparable trend was found when these antinomy
derivatives were used for the hydrogenation of quinoline using
Hantzsch ester, with 5 and 6 displaying the highest performance
(80% and 60%, respectively). We also probed the use of these
compounds as catalysts for the formation of N-benzhydryl
acetamide by reaction of diphenylbromomethane with
acetonitrile and water.[20] Consistent with the trend established in
the transfer hydrogenation reactions, the perfluorinated
stiboranes showed the highest activity; however, the difference
in reactivity observed with the fluorinated stibines, in particular 2,
was a lot less pronounced. We also note that the reaction
catalyzed by the non-fluorinated derivatives 1 and 4 showed
accumulation of the hydrolysis product diphenylmethanol.
Altogether, the catalytic activity of these antimony compounds
correlates well with their experimentally-determined Lewis
acidity as well as with the computed LUMO energy. A last
important point of discussion concerns the unusually elevated
activity of 2 in all three reactions, and especially in the Ritter-like
reaction involving diphenylbromomethane. Given that the
antimony-centered Lewis acidity in 2 is much lower than that in 5
and 6, we believe that the commendable performance of this
stibine results in part from the -acidic properties of the C6F5
substituents, as seen in the structure of Ph3PO→Sb(C6F5)3. We
speculate that these -acidic properties help acidify the
electrophilic reagents involved in these reactions thus
augmenting the catalytic properties of this simple fluorinated
stibine.[21]
Figure 5. Left: The structure of Ph3PO→Sb(C6F5)3 in the crystal. Thermal
ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and angles (deg): Sb1-O1 = 2.628(4),
P1-O1-Sb1 = 161.2(2), O1-Sb1-C1 = 164.8(2). Right: Principal lp(O)→*(Sb-
C) NBO donor-acceptor interactions found in the adduct. Isovalue = 0.05.
Figure 6. Electrostatic potential map (isovalue = 0.05) and LUMO contour plot
(isovalue = 0.05) of 2 (a, b) and 5 (c, d).
We propose that the higher Lewis acidity observed for the
stiboranes results from a deepening of the -hole and a lowering
of the antimony-centered * orbitals upon oxidation of the
antimony atom (Figure 2). Such effects are illustrated in Figure 6
for 2 and 5. Comparison of the electrostatic potential maps of
these two compounds show a greater development of positive
character at the antimony center of 5 illustrating the above
mentioned deepening of the -hole. We also note that while
both compounds feature directional * orbitals, that of 5 (-2.65
eV) is significantly lower in energy than that of 2 (-1.76 eV), in
line with its higher Lewis acidity. As shown in Table 1, a lowering
of the LUMO energy is also observed upon conversion of 1 into
4, and
3 into 6. Using fluoride ion affinity (FIA) as a
computational probe of Lewis acidity, our calculations reveal that
oxidation of the stibines into their corresponding stiboranes
raises their FIA by 110-150 kJ/mol.
Scheme 1. Transfer hydrogenation of N-benzylideneaniline and quinoline, and
Ritter-like reactions showing yields when compounds 1-6 are used as
catalysts.
Table 1. Calculated gas phase fluoride ion affinities and LUMO energies of the
Lewis acids.
Compound
FIA (kJ/mol)
LUMO (eV)
1
2
3
248
374
365
-0.55
-1.76
-1.90
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Conflict of interest
The authors declare no conflict of interest.
Keywords: antimony • Lewis acids • -hole • transfer
hydrogenation • molecular recognition
[1]
a) N. L. Dunn, M. Ha, A. T. Radosevich, J. Am. Chem. Soc. 2012, 134,
11330-11333; b) J. Cui, Y. Li, R. Ganguly, A. Inthirarajah, H. Hirao, R.
Kinjo, J. Am. Chem. Soc. 2014, 136, 16764-16767; c) M. Perez, C. B.
Caputo, R. Dobrovetsky, D. W. Stephan, Proc. Natl. Acad. Sci. U.S.A.
2014, 111, 10917-10921; d) M. H. Holthausen, J. M. Bayne, I. Mallov, R.
Dobrovetsky, D. W. Stephan, J. Am. Chem. Soc. 2015, 137, 7298-
7301; e) M. Perez, Z.-W. Qu, C. B. Caputo, V. Podgorny, L. J. Hounjet,
A. Hansen, R. Dobrovetsky, S. Grimme, D. W. Stephan, Chem. Eur. J
2015, 21, 6491-6500; f) K. D. Reichl, N. L. Dunn, N. J. Fastuca, A. T.
Radosevich, J. Am. Chem. Soc. 2015, 137, 5292-5295; g) W. Zhao, P.
K. Yan, A. T. Radosevich, J. Am. Chem. Soc. 2015, 137, 616-619; h) M.
R. Adams, C. H. Tien, R. McDonald, A. W. H. Speed, Angew. Chem. Int.
Ed. 2017, 56, 16660-16663; Angew. Chem. 2017, 129, 16887-16890; i)
G. Micheal, F. C. M., S. S. H., B. Johannes, N. Martin, G. Dietrich,
Chem. Eur. J. 2017, 23, 11560-11569; j) D. W. Stephan, Angew. Chem.
Int. Ed. 2017, 56, 5984-5992; Angew. Chem. 2017, 129, 6078-6086; k)
T. Hynes, E. N. Welsh, R. McDonald, M. J. Ferguson, A. W. H. Speed,
Organometallics 2018, 37, 841-844; l) B. Rao, C. C. Chong, R. Kinjo, J.
Am. Chem. Soc. 2018, 140, 652-656.
The results presented herein show that the Lewis acidity of
pnictogen bond donor based on organoantimony is notably
enhanced by oxidation to the +V state, a conclusion that
parallels that drawn in the case of iodine(III) halogen bond
donors.[22] Our analyses indicate that this Lewis acidity increase
originates from a lowering of the antimony centered * orbital as
well as a deepening of the -hole. These two effects, which
respectively capture the covalent and electrostatic nature of the
interaction formed between the antimony Lewis acid and the
incoming Lewis base, are manifested in the binding constants
obtained when these organoantimony compounds complex with
Ph3PO. The same effects also readily enhance their catalytic
properties in transfer hydrogenation and Ritter-like reactions
when the antimony is in the +V state. Finally, the work described
herein illustrates the duality that connects the orbital-based and
-hole-based descriptors of Lewis acidity in a way that mirrors
the continuum existing between covalent and ionic bonding
extremes.
[2]
[3]
a) A. P. M. Robertson, N. Burford, R. McDonald, M. J. Ferguson,
Angew. Chem. Int. Ed. 2014, 53, 3480-3483; Angew. Chem. 2014, 126,
3548-3551; b) A. P. M. Robertson, S. S. Chitnis, H. A. Jenkins, R.
McDonald, M. J. Ferguson, N. Burford, Chem. Eur. J. 2015, 21, 7902-
7913; c) S. S. Chitnis, A. P. M. Robertson, N. Burford, B. O. Patrick, R.
McDonald, M. J. Ferguson, Chem. Sci. 2015, 6, 6545-6555.
a) B. Pan, F. P. Gabbaï, J. Am. Chem. Soc. 2014, 136, 9564-9567; b)
N. Li, R. Qiu, X. Zhang, Y. Chen, S.-F. Yin, X. Xu, Tetrahedron 2015,
71, 4275-4281; c) D. Tofan, F. P. Gabbaï, Chem. Sci. 2016, 7, 6768-
6778; d) R. Arias-Ugarte, D. Devarajan, R. M. Mushinski, T. W. Hudnall,
Dalton Trans. 2016, 45, 11150-11161; e) M. Hirai, J. Cho, F. P. Gabbaï,
Chem. Eur. J. 2016, 22, 6537-6541; f) R. Arias-Ugarte, T. W. Hudnall,
Green Chemistry 2017, 19, 1990-1998; g) S. S. Chitnis, H. A. Sparkes,
V. T. Annibale, N. E. Pridmore, A. M. Oliver, I. Manners, Angew. Chem.
Int. Ed. 2017, 56, 9536-9540; Angew. Chem. 2017, 129, 9664-9668; h)
M. Yang, F. P. Gabbaï, Inorg. Chem. 2017, 56, 8644-8650; i) M. Yang,
N. Pati, G. Belanger-Chabot, M. Hirai, F. P. Gabbai, Dalton Trans. 2018.
a) I.-S. Ke, J. S. Jones, F. P. Gabbaï, Angew. Chem. Int. Ed. 2014, 53,
2633-2637; Angew. Chem. 2014, 126, 2671-2675; b) M. Hirai, F. P.
Gabbaï, Chem. Sci. 2014, 5, 1886-1893; c) M. Hirai, F. P. Gabbaï,
Angew. Chem. Int. Ed. 2015, 54, 1205-1209; Angew. Chem. 2015, 127,
1221–1225; d) M. Hirai, M. Myahkostupov, F. N. Castellano, F. P.
Gabbaï, Organometallics 2016, 35, 1854-1860; e) J. S. Jones, F. P.
Gabbaï, Acc. Chem. Res. 2016, 49, 857-867; f) A. M. Christianson, F. P.
Gabbaï, Chem. Commun. 2017, 53, 2471-2474; g) C.-H. Chen, F. P.
Gabbaï, Angew. Chem. Int. Ed. 2017, 56, 1799-1804; Angew. Chem.
2017, 129, 1825-1830; h) A. Kumar, M. Yang, M. Kim, F. P. Gabbaï, M.
H. Lee, Organometallics 2017, 36, 4901-4907; i) A. M. Christianson, E.
Rivard, F. P. Gabbaï, Organometallics 2017, 36, 2670-2676; j) J. S.
Jones, C. R. Wade, M. Yang, F. P. Gabbaï, Dalton Trans. 2017, 46,
5598-5604.
[4]
Experimental Section
The experimental procedures are provided in the Supplemental
Information.
Acknowledgements
Acknowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund for partial support
of this research (Grant 56871-ND3). We also acknowledge
support from the Welch Foundation (Grant A-1423) and Texas
A&M University (Arthur E. Martell Chair of Chemistry and
Laboratory for Molecular Simulation). We thank Dr. J. Stuart
Jones, Dr. Masato Hirai, Nilanjana Pati, and Mazarine Laurent
for their constructive input to the chemistry.
[5]
a) K. Ohkata, S. Takemoto, M. Ohnishi, K.-Y. Akiba, Tetrahedron Lett.
1989, 30, 4841-4844; b) C. J. Carmalt, A. H. Cowley, R. D. Culp, R. A.
Jones, S. Kamepalli, N. C. Norman, Inorg. Chem. 1997, 36, 2770-2776.
J. Qiu, B. Song, X. Li, A. F. Cozzolino, PCCP 2018, 20, 46-50.
[6]
[7]
[8]
[9]
A. M. Christianson, F. P. Gabbaï, Organometallics 2017, 36, 3013-3015.
̈
H. Yang, F. P. Gabbaı, J. Am. Chem. Soc. 2015, 137, 13425-13432.
J. S. Jones, F. P. Gabbaï, Chem. Eur. J. 2017, 23, 1136-1144.
[10] S. Benz, A. I. Poblador-Bahamonde, N. Low-Ders, S. Matile, Angew.
Chem. Int. Ed. 2018, 57, 5408-5412; Angew. Chem. 2018, 130, 5506-
5510.
This article is protected by copyright. All rights reserved.

10.1002/anie.201808551
Angewandte Chemie International Edition
COMMUNICATION
[11] a) T. Clark, M. Hennemann, S. Murray Jane, P. Politzer, J. Mol. Model.
2007, 13, 291-296J. Mol. Model; b) J. S. Murray, P. Lane, P. Politzer,
Int. J. Quantum Chem. 2007, 107, 2286-2292Int. J. Quantum Chem; c)
J. Schmauck, M. Breugst, Org. Biomol. Chem. 2017, 15, 8037-8045; d)
J. Y. C. Lim, P. D. Beer, Chem 2018, 4, 731-783.
[19] a) S. Benz, J. López-Andarias, J. Mareda, N. Sakai, S. Matile, Angew.
Chem. Int. Ed. 2017, 56, 812-815; Angew. Chem. 2017, 129, 830–833;
b) S. Benz, J. Mareda, C. Besnard, N. Sakai, S. Matile, Chem. Sci.
2017, 8, 8164-8169; c) T. Itoh, K. Nagata, M. Miyazaki, H. Ishikawa, A.
Kurihara, A. Ohsawa, Tetrahedron 2004, 60, 6649-6655.
[12] D. J. Pascoe, K. B. Ling, S. L. Cockroft, J. Am. Chem. Soc. 2017, 139,
15160-15167.
[20] a) S. M. Walter, F. Kniep, E. Herdtweck, S. M. Huber, Angew. Chem.
Int. Ed. 2011, 50, 7187-7191; Angew. Chem. 2011, 123, 7325-7329; b)
P. Wonner, L. Vogel, M. Duser, L. Gomes, F. Kniep, B. Mallick, D. B.
Werz, S. M. Huber, Angew. Chem. Int. Ed. 2017, 56, 12009-12012;
Angew. Chem. 2017, 129, 12172–12176.
[13] a) M. Fild, O. Glemser, G. Christoph, Angew. Chem. 1964, 76, 953-
953; b) M. M. Sidky, M. R. Maharan, W. M. Abdu, Phosphorus and
Sulfur and the Related Elements 1983, 15, 129-135; c) S. Yasuike, K.
Nakata, W. Qin, M. Matsumura, N. Kakusawa, J. Kurita, J. Organomet.
Chem. 2015, 788, 9-16.
[21] a) Y. Zhao, C. Beuchat, Y. Domoto, J. Gajewy, A. Wilson, J. Mareda, N.
Sakai, S. Matile, J. Am. Chem. Soc. 2014, 136, 2101-2111; b) T. Lu, S.
E. Wheeler, Org. Lett. 2014, 16, 3268-3271.
[14] CCDC 1857184 (6) and 1857185 (Ph3PO → Sb(C6F5)3) contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[22] a) F. Heinen, E. Engelage, A. Dreger, R. Weiss, S. M. Huber, Angew.
Chem. Int. Ed. 2018, 57, 3830-3833; Angew. Chem. 2018, 130, 3892-
3896; b) T. L. Seidl, D. R. Stuart, J. Org. Chem. 2017, 82, 11765-11771.
[15] I. Krossing, I. Raabe, Angew. Chem. Int. Ed. 2004, 43, 2066-2090;
Angew. Chem. 2004, 116, 2116-2142.
[16] M. A. Beckett, D. S. Brassington, S. J. Coles, M. B. Hursthouse, Inorg.
Chem. Commun. 2000, 3, 530-533.
[17] S. Alvarez, Dalton Trans. 2013, 42, 8617-8636.
[18] E. D. Glendening, J. K. Badenhoop, A. E. Reed, J. E. Carpenter, J. A.
Bohmann, C. M. Morales, F. Weinhold, NBO 5.9, Theoretical Chemistry
Institute, University of Wisconsin, Madison, WI, 2011.
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10.1002/anie.201808551
Angewandte Chemie International Edition
COMMUNICATION
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COMMUNICATION
Taking a dig at the -hole!
Oxidation of organoantimony
derivatives from the +III to the +V
state leads to a more pronounced
-hole on antimony making these
main group compounds better
pnictogen bond donors or better
Lewis acids. These results, which
can be rationalized using orbital-
based arguments, define a new
strategy for tuning the magnitude of
pnictogen bonding with applications
in catalysis.
Mengxi Yang, Daniel Tofan, Chang-
Hong Chen, Kevin M. Jack, and
François P. Gabbaï*
Page No. – Page No.
Digging the -hole of organo-
antimony Lewis acids via
oxidation
This article is protected by copyright. All rights reserved.