Synthesis and characterization of a stable non-cyclic bis(amino)arsenium cation

Article abstract of DOI:10.1139/cjc-2017-0420

The reaction of Li[Mes?NH] (1, Mes? = 2,4,6-tri-tert-butylphenyl) with aminoarsane Mes?N(H)AsCl₂ (2, Mes? = 2,4,6-t-Bu₃C₆H₂) at -80 °C resulted in the formation of bisamino(chloro)arsane (Mes?NH)₂AsCl (3Cl) by elimination of LiCl. 3Cl reacted with the Lewis acids such as AlCl₃, GaCl₃, and Ag[X] (X = AsF₆^-, OTf^-, BF₄^-; OTf = trifluoromethanesulfonate = OSO₂CF₃^-) upon chloride ion abstraction to give salts bearing the cation [(Mes?NH)₂As]⁺ (3[X]; X = AsF₆^-, OTf^-, BF₄^-, ECl₄; E = Al, Ga). 3⁺ represents the first NH-functionalized acyclic bis(amino)arsenium cation. The formation of the salts bearing 3⁺ could also be observed in the reaction of cyclo-1,3-diarsa-2,4-diazane [ClAs(μ-NMes?)]₂ (4) with Lewis acids (AlCl₃, GaCl₃) in the presence of proton sources in solution. All presented salts 3[X] were stable at room temperature and fully characterized.

Full text of DOI:10.1139/cjc-2017-0420

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Synthesis and Characterization of A Stable Non-cyclic
Bis(amino)arsenium Cation
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Marcus Kuprat,† Axel Schulz,†,‡,* Max Thomas,† and Alexander Villinger†
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†Institut für Chemie, Abteilung Anorganische Chemie, Universität Rostock, AlbertꢀEinsteinꢀStrasse 3a, 18059 Rostock, Germany
‡LeibnizꢀInstitut für Katalyse e.V. an der Universität Rostock, AlbertꢀEinsteinꢀStrasse 29a, 18059 Rostock, Germany
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Dedicated to Prof. Dr. Neil Burford
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Abstract:
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The reaction of Li[Mes*NH] (1, Mes * = 2,4,6ꢀtriꢀtertꢀbutylphenyl) with aminoarsane Mes*N(H)AsCl2 (2,
Mes* = 2,4,6ꢀtꢀBu3C6H2) at –80 °C resulted in the formation of bisamino(chloro)arsane (Mes*NH)2AsCl
–
(3Cl) by elimination of LiCl. 3Cl reacted with the Lewis acids such as AlCl3, GaCl3 and Ag[X] (X = AsF6 ,
–
–
OTf–, BF4 ; OTf = trifluoromethanesulfonate = OSO2CF3 ) upon chloride ion abstraction to give salts
bearing the cation [(Mes*NH)2As]+ (3[X]; X = AsF6 , OTf–, BF4 , ECl4; E = Al, Ga). 3+ represents the first
NHꢀfunctionalized acyclic bis(amino)arsenium cation. The formation of the salts bearing 3+ could also be
observed in the reaction of cycloꢀ1,3ꢀdiarsaꢀ2,4ꢀdiazane [ClAs(ꢀꢀNMes*)]2 (4) with Lewis acids (AlCl3,
GaCl3) in the presence of proton sources in solution. All presented salts 3[X] were stable at room
temperature and fully characterized.
–
–
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Keywords: arsenic, cation, bis(amino)arsenium cation, crystal structure

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Introduction
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In the last decades the possibility to generate dicoordinate nitrogen bound arsenic compounds was shown
not only for a series of amino(imino)arsanes (I, Scheme 1) but also for nonꢀcyclic and cyclic
bis(amino)arsenium ions (II, III).1–7 Furthermore, base stabilized mono8 and di cations of arsenic have been
reported.9
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Scheme 1. I: aminoiminoarsane, II: bis(amino)arsenium cation, III: (6π)ꢀdiazarsolium cation.
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As depicted in Scheme 2, for acyclic bis(amino)arsenium cations, at least three Lewis representations need
to be considered. The second resonance structure in Scheme 2 displays a divalent As atom with an
unsaturated cationic (six valence) electronꢀdeficit center and an empty pzꢀorbital. That is why in contrast to
species I, compounds such as II and III can be regarded as carbene analogues with respect to the
isoelectronic situation in the valence shell.
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Mes*
As
Mes*
Mes*
As
Mes*
Mes*
As
Mes*
N
N
N
N
N
N
H
H
H
H
H
H
GaCl4
GaCl4
GaCl4
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Scheme 2. Resonance structures of acyclic bis(amino)arsenium cations.
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While numerous acyclic diaminophosphenium ions are known,10 up to now only two structures of salts
with an acyclic diaminoarsenium cation [(R2N)2As]+ (R = SiMe3) were published in 2013.5 Contrarily,
cationic fourꢀ, fiveꢀ and sixꢀmembered cyclic bis(amino)arsenium salts have been known for years.6,7,11–13
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The phosphenium ion [(Mes*NH)2P]+ was synthesized by Burford et al. in the reaction of [Mes*NP]+ with
Mes*NH2 (supermesityl = Mes* = 2,4,6ꢀtꢀBu3C6H2).14 This reaction was described as a nucleophilic
addition of a N–H bond to the phosphadiazonium cation displaying a formal insertion of a NP unit into a N–

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H bond. Recently, we could isolate and characterize an arsadiazonium cation [Mes*NAs]+ allowing further
systematic investigations for the syntheses of dicoordinated arsenium ions [R2As]+.15
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We describe here the generation of the cation [(Mes*NH)2As]+ (3+) as [GaCl4]–ꢀsalt in the reaction of
–
[Mes*NAs]+[GaCl4 ] (5[GaCl4]) with Mes*NH2. For the direct syntheses of other salts bearing 3+, we
present a convenient synthetic protocol starting from (Mes*NH)2AsCl (3Cl), which can be considered as an
ideal precursor for salts of 3+, when treated with chloride ion abstracting Lewis acids. Furthermore, we
report on reactions of Mes*NAs+ꢀsalts with Lewis bases such as PnPh3 (Pn = P, As, Sb).
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Experimental
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General Information. All manipulations were carried out under oxygenꢀ and moistureꢀfree conditions
under argon atmosphere using standard Schlenk or drybox techniques.
Preparation of starting materials. All solvents were freshly distilled prior to use. Methylene dichloride
was purified according to a literature procedure,16 dried over P4O10, and distilled from CaH2. Diethylether
and toluene were dried over Na/benzophenone, nꢀhexane was dried over Na/benzophenone/tetraglyme. Nꢀ
butyllithium (2.5M solution in hexanes, Acros Organics) was used as received. GaCl3 (SigmaꢀAldrich) was
freshly sublimed prior to use. 1,3ꢀDichloroꢀ2,4ꢀbisꢀ(2,4,6ꢀtriꢀtertꢀbutylphenyl)cycloꢀ1,3ꢀdiarsaꢀ2,4ꢀdiazane
[Mes*NAsCl]2 (4) was prepared according to a literature procedure.12,15 This procedure includes the
synthesis of 1. 4ꢀDimethylaminopyridine (DMAP) was used as received. PPh3, AsPh3 and SbPh3 were
freshly sublimed prior to use.
X-ray: BRUKER Apex KappaꢀII CCD diffractometer using graphite monochromated Mo Kα radiation (λ =
0.71073).
NMR: BRUKER Avance 250, 300 and 500 NMR spectrometers. Spectra were referenced internally to
corresponding deuterated solvents (1H: δref (CDHCl2) = 5.31 ppm, within CD2Cl2, 13C: δref (CD2Cl2) =
54 ppm).
IR: NICOLET 380 FTꢀIR spectrometer (Smart Orbit ATR module).

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RAMAN: BRUKER Vertex70 FTꢀIR with RAM II FTꢀRAMAN module, Nd:YAG laser (1064 nm) or
HORIBA Scientific LabRAM HR800 system, diode laser (785 nm, 100 mW), HeꢀNe laser (633 nm, 17
mW), frequency doubling Nd:YAG laser (532 nm, 50 mW).
MS: THERMO ELECTRON Finnigan MAT 95ꢀXP spectrometer.
CHN-Analysis: THERMO QUEST Flash EA 1112 analysator.
Melting points: STANFORD RESEARCH SYSTEMS EZꢀMelt, automated analysator, data uncorrected.
Heating rate 20 °C/min (clearingꢀpoints are reported).
DSC: METTLERꢀTOLEDO DSC 823e (Heating rate 5 °C/min)
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Synthesis of 3Cl
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To a solution of 2,4,6ꢀtriꢀtertꢀbutylaniline (Mes*NH2, 261 mg, 1.0 mmol) in Et2O (10 ml) nꢀButyllithium
(1.0 mmol) is added at room temperature and stirred for 1.5 hours. The reaction solution is added to a stirred
solution of AsCl3 (181 mg, 1.0 mmol) in Et2O (3 ml) at room temperature. The resulting rose suspension of
generated Mes*N(H)AsCl2 and LiCl is stirred for 30 minutes. The precipitated LiCl is separated by
filtration. Li[Mes*NH], obtained from reaction of Mes*NH2, (261 mg, 1.0 mmol) and nꢀButyllithium
(1.0 mmol) in Et2O (3 ml), is added to the filtrate at –80 °C over a period of 10 minutes. The solvent is
removed in vacuo at room temperature and the product extracted with 5 ml nꢀhexane. 3Cl is purified by reꢀ
crystallization from Et2O solution. Decomp. 115 °C. Anal. calc. % (found) for C36H60AsClN2 (631.25): C,
1
68.50 (66.28); H, 9.58 (9.17); N, 4.44 (4.41). H NMR (25°C, CD2Cl2, 300.13 MHz): δ = 1.29 (s, 18 H, pꢀ
C(CH3)3), 1.53 (s, 36 H, oꢀC(CH3)3), 5.57 (s, 2 H, NH), 7.33 (s, 4 H, CH). 13C{1H} NMR (25°C, CD2Cl2,
75.48 MHz): δ = 31.76 (s, pꢀC(CH3)3), 33.89 (s, oꢀC(CH3)3), 35.04 (s, pꢀC(CH3)3), 36.74 (s, oꢀC(CH3)3),
124.04 (s, CH, Ar), 137.88 (s, pꢀAr), 144.59 (s, oꢀAr), 145.32 (s, ipsoꢀAr). IR (ATR, 64 scans, cm−1): 3352
(m), 2959 (s), 2951 (s), 2903 (m), 2868 (m), 1597 (m), 1477 (m), 1463 (m), 1422 (s), 1392 (m), 1361 (s),
1304 (w), 1288 (m), 1241 (m), 1214 (s), 1200 (m), 1111 (s), 1022 (w), 933 (w), 922 (w), 912 (w), 878 (m),
828 (s), 816 (m), 780 (m), 750 (m), 732 (w), 667 (w), 649 (w), 629 (m), 594 (m), 568 (w), 546 (w). Raman
(460 mW, 25 °C, 150 scans, cm−1): 3088 (1), 2965 (10), 2909 (9), 2784 (1), 2712 (2), 1601 (5), 1461 (3),
1449 (4), 1430 (3), 1366 (1), 1345 (1), 1293 (3), 1256 (2), 1245 (2), 1225 (3), 1202 (4), 1183 (3), 1146 (3),
1119 (1), 1029 (1), 934 (3), 926 (3), 826 (4), 803 (1), 755 (2), 635 (2), 573 (3), 477 (1), 373 (2), 323 (1), 263

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(4), 149 (5), 113 (2), 87 (2). MS (CI pos. Isobutane): 262 [Mes*NH3]+, 334 [Mes*NAs]+, 595
[(Mes*NH)2As]+.
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Synthesis of 3[AlCl4]
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A) To a stirred colorless solution of 3Cl (0.124 mmol, 78 mg) in toluene (5 ml) powdered AlCl3
(0.124 mmol, 17 mg) is added at –80 °C. The color of the resulting solution alters to yellow within a few
minutes. The solution is warmed up to ambient temperatures and stirred for two hours resulting in a yellow
precipitate and a clear colorless supernatant which is removed by a syringe. The precipitate is washed with
toluene and dried in vacuo. 3[AlCl4] is obtained as a yellow powder (90 mg, 0.118 mmol, 95 %).
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B) To a stirred solution of 4, (0.118 mmol, 87 mg) in toluene (1 ml) a solution of AlCl3 (0.235 mmol,
31 mg) in toluene (8 ml) is added dropwise at –80 °C to give a clear orange solution. Crystals of 3[AlCl4]
are obtained by subsequent removal of solvent at –70 °C. The supernatant is removed by decantation.
3[AlCl4] is isolated as a yellow crystalline solid. Decomp. 156 °C. Anal. calc. % (found) for
1
C36H60AlAsCl4N2 (764.59): C, 56.55 (56.27); H, 7.91 (7.89); N, 3.66 (3.69). H NMR (25°C, CD2Cl2,
250.13 MHz): δ = 1.32 (s, 18 H, pꢀC(CH3)3), 1.57 (s, 36 H, oꢀC(CH3)3), 7.53 (s, 4 H, CH), 10.44 (s, 2 H,
NH). 13C{1H} NMR (25°C, CD2Cl2, 62.90 MHz): δ = 31.5 (s, pꢀC(CH3)3), 34.6 (s, oꢀC(CH3)3), 35.6 (s, pꢀ
C(CH3)3), 37.5 (s, oꢀC(CH3)3), 124.8 (s, CH, Ar), 131.4 (s, pꢀAr), 148.5 (s, oꢀAr), 152.5 (s, ipsoꢀAr). IR
(ATR, 64 scans, cm−1): 3236 (m), 3009 (w), 2956 (s), 2872 (m), 1600 (m), 1476 (m), 1463 (m), 1419 (m),
1395 (m), 1362 (m), 1294 (w), 1269 (m), 1243 (m), 1214 (s), 1181 (m), 1106 (s), 1025 (w), 938 (w), 926
(w), 912 (w), 881 (m), 852 (s), 820 (w), 798 (w), 779 (w), 762 (w), 666 (w), 648 (w), 634 (w), 627 (w), 582
(s). Raman (784 nm, lat10X, 25 °C, 4 sc/60 sec, cm−1): 2962 (2), 2929 (2), 2904 (2), 2870 (1), 2780 (1),
2708 (1), 1600 (3), 1468 (2), 1454 (2), 1422 (2), 1396 (1), 1363 (1), 1347 (2), 1289 (2), 1254 (1), 1243 (1),
1218 (4), 1186 (5), 1146 (4), 1117 (2), 1024 (1), 927 (2), 861 (10), 821 (6), 798 (5), 762 (3), 698 (4), 648
(2), 569 (3), 465 (2), 418 (1), 349 (3), 263 (2), 183 (2), 134 (6), 119 (6), 107 (7), 70 (10). MS (CI pos.
Isobutane): 206 [Mes*NH3
ꢀ
tBu]+, 262 [Mes*NH3]+. Crystals of 3[AlCl4] suitable for Xꢀray
crystallographic analysis are obtained by reꢀcrystallization from CH2Cl2.
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Synthesis of 3[GaCl4]

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A) To a stirred solution of 3Cl (0.182 mmol, 115 mg) in toluene (3 ml) a solution of GaCl3 (0.182 mmol,
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32 mg) in toluene (2 ml) is added dropwise at room temperature and stirred for one hour resulting in a
yellow precipitate and a clear colorless supernatant which is removed by a syringe. The precipitate is
washed with toluene and dried in vacuo. 3[GaCl4] is obtained as a yellow powder (138 mg, 0.171 mmol,
94 %).
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B) To a stirred solution of 4 (0.087 mmol, 64 mg) in toluene (2 ml) a solution of GaCl3 (0.173 mmol,
31 mg) in toluene (1 ml) is added dropwise at –80 °C, followed by dropwise addition of 2,4,6ꢀtriꢀtertꢀ
butylaniline (Mes*NH2, 44 mg, 0.170 mmol) in toluene (2 ml). The reaction mixture is warmed to room
temperature and stirred for two hours. Removal of solvent, washing with toluene and drying in vacuo yields
3[GaCl4] as a yellow powder (65 mg, 0.081 mmol, 92 %). Decomp. 135 °C. Anal. calc. % (found) for
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C36H60AsCl4GaN2 (807.33): C, 53.56 (52.69); H, 7.49 (7.02); N, 3.47 (3.42). H NMR (25°C, CD2Cl2,
300.13 MHz): δ = 1.32 (s, 18 H, pꢀC(CH3)3), 1.57 (s, 36 H, oꢀC(CH3)3), 7.53 (s, 4 H, CH), 10.50 (s, 2 H,
NH). 13C{1H} NMR (25°C, CD2Cl2, 75.48 MHz): δ = 31.51 (s, pꢀC(CH3)3), 34.62 (s, oꢀC(CH3)3), 35.63 (s,
pꢀC(CH3)3), 37.50 (s, oꢀC(CH3)3), 124.80 (s, CH, Ar), 131.42 (s, pꢀAr), 148.43 (s, oꢀAr), 152.48 (s, ipsoꢀAr).
IR (ATR, 64 scans, cm−1): 3231 (m), 3009 (m), 2956 (s), 2872 (m), 1600 (m), 1475 (m), 1471 (m), 1463
(m), 1418 (m), 1395 (m), 1362 (m), 1294 (w), 1269 (w), 1243 (m), 1213 (s), 1180 (m), 1105 (s), 1025 (w),
938 (w), 926 (w), 912 (w), 881 (m), 851 (s), 820 (w), 798 (w), 779 (w), 762 (w), 666 (w), 647 (w), 634 (w),
627 (w), 581 (m), 543 (w). Raman (460 mW, 25 °C, 150 scans, cm−1): 3237 (1), 3129 (1), 3109 (1), 2971
(10), 2911 (9), 2785 (2), 2712 (2), 1603 (7), 1470 (4), 1457 (3), 1451 (3), 1426 (3), 1399 (2), 1366 (2), 1351
(3), 1293 (3), 1256 (2), 1246 (2), 1221 (5), 1189 (8), 1148 (6), 1119 (3), 1030 (1), 930 (3), 865 (9), 824 (7),
801 (5), 782 (1), 764 (3), 701 (4), 651 (2), 573 (4), 469 (1), 421 (1), 350 (6), 265 (2), 155 (2), 132 (5), 114
(4), 111 (4). MS (CI pos. Isobutane): 262 [Mes*NH3]+, 334 [Mes*NAs]+, 595 [(Mes*NH)2As]+. Crystals of
3[GaCl4] suitable for Xꢀray crystallographic analysis are obtained by reꢀcrystallization from a CH2Cl2
solution of 3[GaCl4].
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Synthesis of 3[OTf] • toluene
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A) To a stirred colorless solution of 3Cl (78 mg, 0.124 mmol) in CH2Cl2 (5 ml) powdered Ag[OTf]
(0.124 mmol, 32 mg) is added at −80 °C. The color of the resulting solution alters to yellow within a few

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minutes. The solution is warmed up to room temperature under stirring within one hour. Afterwards, the
solution is stirred for another hour resulting in a colorless precipitate and a clear orange supernatant. After
filtration (F4) and removal of the solvent in vacuo 3[OTf] is obtained as a yellow powder (87 mg, 0.117
mmol, 94 %).
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B) To a stirred solution of 4 (0.134 mmol, 99 mg) in toluene (6 ml) powdered Ag[OTf] (0.284 mmol,
73 mg) is added at –80 °C. The resulting orange suspension is warmed to room temperature over a period of
one hour and is then filtered (F4), resulting in a yellow solution. Subsequent, the solution is cooled to –
80 °C again and a solution of PPh3 (0.402 mmol, 105 mg) in toluene (3 ml) is added under stirring. The
reaction solution is warmed to room temperature and stirred for two hours resulting in a colorless solid and a
clear orange supernatant. The solid is separated from the liquid by filtration. The filtrate is concentrated and
cooled to 5 °C. Crystals of 3[OTf] · toluene are obtained by storage of the solution at 5 °C for some hours.
Crystals of [Ag(PPh3)3][OTf] · 2 CH2Cl2 (9) suitable for Xꢀray crystallographic analysis are obtained by reꢀ
crystallization of the colorless solid from a CH2Cl2 solution. Decomp. 165 °C. Anal. calc. % (found) for
1
C37H60AsF3N2O3S (744.87): C, 59.66 (56.97); H, 8.12 (7.74); N, 3.76 (3.67). H NMR (25°C, CD2Cl2,
250.13 MHz): δ = 1.32 (s, 18 H, pꢀC(CH3)3), 1.56 (s, 36 H, oꢀC(CH3)3), 7.52 (s, 4 H, CH), 11.93 (s, 2 H,
NH). 13C{1H} NMR (25°C, CD2Cl2, 62.90 MHz): δ = 31.6 (s, pꢀC(CH3)3), 34.3 (s, oꢀC(CH3)3), 35.6 (s, pꢀ
C(CH3)3), 37.4 (s, oꢀC(CH3)3), 124.4 (s, CH, Ar), 132.4 (s, pꢀAr), 148.5 (s, oꢀAr), 151.7 (s, ipsoꢀAr). IR
(ATR, 32 scans, cm−1): 2958 (s), 2872 (m), 1599 (m), 1478 (w), 1464 (m), 1456 (w), 1435 (w), 1423 (w),
1397 (m), 1362 (m), 1292 (m), 1269 (m), 1242 (m), 1219 (m), 1209 (s), 1162 (m), 1155 (m), 1108 (m), 1022
(s), 930 (w), 914 (w), 880 (m), 855 (m), 806 (m) 757 (w), 707 (w), 633 (s), 574 (m). Raman (784 nm,
lat10X, 25 °C, 5 sc/40 sec, cm−1): 3024 (1), 2970 (2), 2911 (2), 2875 (1), 1600 (3), 1473 (1), 1455 (1), 1442
(2), 1425 (3), 1397 (1), 1365 (1), 1345 (1), 1292 (2), 1244 (1), 1221 (4), 1191 (4), 1148 (4), 1120 (2), 1022
(3), 930 (2), 917 (2), 867 (10), 824 (7), 804 (5), 785 (1), 763 (3), 756 (3), 705 (4), 648 (2), 573 (3), 471 (1),
436 (1), 423 (1), 386 (1), 347 (1), 313 (1), 268 (1), 134 (6), 110 (9), 71 (9). MS (CI pos. Isobutane): 206
t
[Mes*NH3 ꢀ Bu]+, 244 [Mes* ꢀ 2H]+, 246 [Mes*]+, 262 [Mes*NH3]+. Crystals of 3[OTf] ⋅ toluene suitable
for Xꢀray crystallographic analysis are obtained by reꢀcrystallization from toluene.

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Synthesis of 3[BF4] • toluene
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A) To a stirred colorless solution of 3Cl (78 mg, 0.124 mmol) in CH2Cl2 (5 ml) powdered Ag[BF4]
(0.124 mmol, 24 mg) is added at −80 °C. The color of the resulting solution alters to yellow within a few
minutes. The solution is warmed up to room temperature and stirred for two hours resulting in a colorless
precipitate and a clear orange supernatant. After filtration (F4) and removing of solvent in vacuo 3[BF4] is
obtained as an orange liquid. The product can be obtained as a yellow powder from a nꢀhexane solution
(77 mg, 0.113 mmol, 91 %).
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B) To a stirred solution of 4 (0.108 mmol, 80 mg) in CH2Cl2 (5 ml) powdered Ag[BF4] (0.216 mmol,
42 mg) was added at –80 °C resulting in a deep red solution that was stirred for 30 minutes. Afterwards the
reaction solution was warmed to room temperature at which the color of the solution changed to yellow. The
colorless precipitate is separated from the liquid by filtration (F4). Subsequently, the solvent was removed
under reduced pressure and the product extracted with nꢀhexane. Mp. 144 °C. Anal. calc. % (found) for
1
C36H60AsBF4N2 (682.6): C, 63.34 (62.34); H, 8.86 (8.81); N, 4.10 (4.42). H NMR (25°C, CD2Cl2, 250.13
MHz): δ = 1.32 (s, 18 H, pꢀC(CH3)3), 1.55 (s, 36 H, oꢀC(CH3)3), 7.52 (s, 4 H, CH), 11.21 (s, 2 H, NH).
11B{1H} NMR (25°C, CD2Cl2, 80.25 MHz): δ = −0.81. 13C{1H} NMR (25°C, CD2Cl2, 62.90 MHz): δ = 31.5
(s, pꢀC(CH3)3), 34.3 (s, oꢀC(CH3)3), 35.6 (s, pꢀC(CH3)3), 37.4 (s, oꢀC(CH3)3), 124.5 (s, CH, Ar), 132.1 (s, pꢀ
Ar), 148.5 (s, oꢀAr), 151.9 (s, ipsoꢀAr). IR (ATR, 32 scans, cm−1): 3232 (m), 3162 (m), 3007 (m), 2960 (s),
2910 (m), 2872 (m), 1596 (m), 1477 (m), 1471 (m), 1464 (m), 1456 (w), 1435 (w), 1421 (m), 1397 (m),
1363 (m), 1288 (w), 1269 (w), 1241 (m), 1211 (m), 1180 (m), 1134 (s), 1104 (s), 1070 (s), 1028 (w), 941
(s), 913 (m), 883 (m), 850 (s), 819 (w), 784 (w), 759 (m), 673 (m), 667 (m), 648 (m), 617 (w), 602 (w), 569
(w). Raman (784 nm, lat10X, 25 °C, 6 sc/30 sec, cm−1): 2974 (1), 2907 (1), 1598 (2), 1468 (1), 1445 (1),
1423 (2), 1398 (1), 1367 (1), 1289 (2), 1243 (1), 1216 (2), 1188 (3), 1144 (3), 1117 (2), 1023 (1), 926 (1),
915 (2), 859 (10), 823 (5), 806 (4), 786 (1), 762 (3), 709 (2), 649 (1), 572 (2), 470 (1), 436 (1), 422 (1), 368
t
(1), 354 (1), 260 (1), 135 (4), 108 (5), 71 (7). MS (CI pos. Isobutane): 206 [Mes*NH3 ꢀ Bu]+, 262
[Mes*NH3]+. Crystals of 3[BF4] ⋅ toluene suitable for Xꢀray crystallographic analysis are obtained by reꢀ
crystallization from a toluene solution of 3[BF4].

Page 10 of 29
203
Synthesis of 3[AsF6] • 2 CH2Cl2
204
205
206
207
208
To a stirred solution of Ag[AsF6] (0.55 mmol, 0.163 g) in CH2Cl2 (5 ml), a yellow solution of 4
(0.5 mmol, 0.370 g) in CH2Cl2 (3 ml), is added dropwise at –90 °C over a period of five minutes. The
resulting red suspension is warmed to –50 °C over a period of one hour and filtered (F4). The solution is
slowly cooled to –80 °C, resulting in the deposition of orange crystals. The supernatant was removed by
decantation and the residue was dried in vacuo which yields 3[AsF6] ⋅ 2 CH2Cl2 as an orange crystalline
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
solid. Decomp. 127 °C. Anal. calc. % (found) for 3[AsF6] ⋅ CH2Cl2 (C37H62As2Cl2F6N2 (869.64): C, 51.10
1
(51.81); H, 7.19 (7.36); N, 3.22 (3.73). H NMR (25°C, CD2Cl2, 300.13MHz): δ = 1.33 (s, 18 H, pꢀ
C(CH3)3), 1.56 (s, 36 H, oꢀC(CH3)3), 7.53 (s, 4 H, mꢀCH), 10.49 (s, 2 H, NH). 13C{1H} NMR (25°C,
CD2Cl2, 75.5MHz): δ = 31.5 (s, pꢀC(CH3)3), 34.3 (s, oꢀC(CH3)3), 35.6 (s, pꢀC(CH3)3), 37.5 (s, oꢀC(CH3)3),
124.7 (s, CH, Ar), 131.7 (s, pꢀAr), 148.6 (s, oꢀAr), 152.3 (s, ipsoꢀAr). 19F{1H} NMR (25°C, CD2Cl2,
282.4MHz): δ = 61 (s, broad). IR (ATR, 32 scans, cm−1): 3272 (w), 2959 (m), 2873 (w), 1597 (w), 1470
(w), 1455 (w), 1434 (w), 1417 (w), 1396 (w), 1362 (m), 1297 (w), 1269 (w), 1242 (w), 1211 (m), 1178 (w),
1144 (w), 1104 (m), 1025 (w), 927 (w), 913 (w), 881 (m), 854 (m), 847 (m), 820 (w), 802 (m), 787 (w), 762
(w), 693 (s), 670 (s), 650 (m), 608 (m), 595 (m). Raman (50 mW, 25 °C, 402 scans, cm–1): 2968 (10), 2913
(10), 2789 (2), 2760 (12), 2714 (2), 1601 (7), 1469 (3), 1448 (4), 1416 (3), 1399 (3), 1367 (2), 1292 (3),
1248 (3), 1224 (7), 1193 (6), 1149 (5), 1121 (2), 1030 (1), 930 (2), 870 (4), 826 (5), 802 (2), 766 (1), 754
(1), 698 (2), 679 (2), 648 (1), 632 (1), 573 (3), 476 (1), 430 (1), 415 (1), 392 (1), 369 (2), 324 (3), 284 (2),
261 (2), 149 (5). MS (FAB+, Cs, 20keV, pꢀNBA matrix): 262 [Mes*ꢀNH3]+, 334 [Mes*ꢀNAs]+. Crystals of
3[AsF6] ⋅ 2 CH2Cl2 suitable for Xꢀray crystallographic analysis are obtained directly from the reaction
solution of 3[AsF6].
224
Synthesis of 7
225
226
227
228
229
To a stirred solution of 5 (0.216 mmol, 138 mg) in toluene (5 ml) a solution of SbPh3 (0.216 mmol, 76 mg)
in toluene (3 ml) was added dropwise at –60 °C. The obtained deep red solution was warmed to room
temperature. The reaction solution was concentrated under reduced pressure and stored for some hours
resulting in the deposition of crystals of 7 (110 mg, 0.188 mmol, 87 %). Mp. 164 °C. Anal. calc. % (found)
1
for C24H34AsCl3GaN (587.54): C, 49.06 (51.06); H, 5.83 (5.42); N, 2.38 (1.98). H NMR (25°C, CD2Cl2,

Page 11 of 29
230
231
232
233
234
235
236
237
300.13 MHz): δ = 1.33 (s, 9 H, C6(CH3)3), 1.60 (s, 9 H, C4(CH3)3), 1.66 (s, 9 H, C2(CH3)3), 7.39ꢀ7.47 (m, 5
H, Ar), 7.54 (s, 2 H, CH). 13C{1H} NMR (25°C, CD2Cl2, 75.48 MHz): δ = 31.58 (C15(CH3)3), 33.42
(C4(CH3)3), 35.27 (C15), 36.33 (C7(CH3)3), 37.07 (C11), 37.98 (C7), 50.38 (C6), 125.27 (C3, C5), 130.05
(pꢀPh), 130.99 (mꢀPh), 133.54 (C4), 133.81 (oꢀPh), 138.87 (C19), 146.77 (C2), 149.77 (C1). Due to the high
sensitivity of 7 against air and moisture no effective purification for further analytics of 7 is possible.
Crystals of 7 suitable for Xꢀray crystallographic analysis can only be obtained directly from the reaction
solution of 7.
238
Results and Discussion:
239
240
241
242
243
244
245
246
247
248
249
In solution, dimeric [ClAs(ꢀꢀNMes*)]2 (4) readily monomerized to give Mes*NAsCl. The reaction with
GaCl3 resulted in the formation of the arsadiazonium salt [Mes*N≡As][GaCl4] (5[GaCl4]).15 However, in
cases of long time storage of 5[GaCl4] in solutions of toluene or CH2Cl2 the slow formation of
[(Mes*NH)2As][GaCl4] (3[GaCl4]) could be observed. A similar reaction sequence was observed when 4
was treated with AlCl3 yielding salt 3[AlCl4]. These results indicated the presence of proton sources e.g.
HCl in solution or the slow generation of protons in these reactions (Scheme 3). Already Burford et al.
described the formation of [(Mes*NH)2P][GaCl4] in the reaction of [Mes*N≡P][GaCl4] with Mes*NH2.14
Analogously, we treated 5[GaCl4] with Mes*NH2 affording quantitatively 3[GaCl4] (Scheme 3). To explain
the formation of salts bearing the 3+ ion starting from 4 or 5+ in the presence of Lewis acids we studied
possible proton sources along the synthesis of the starting materials. The generation of starting material 4
was achieved by elimination of NEt3⋅HCl from Mes*N(H)AsCl2 (2) upon addition of NEt3. Despite several
purification steps for 4 most likely small amounts of HCl still remain e.g. as NEt3⋅HCl salt. It is also known
that CH2Cl2 slowly decomposes in the presence of Lewis acids or light generating HCl. Therefore, we
believe that storage of dissolved 5[GaCl4] for longer periods led to the reaction of 5+ with two equivalents of
250
251
252
253
254
255
HCl yielding GaCl3, AsCl3 and Mes*NH2 which reacted in a subsequent reaction with a further equivalent of
5+ to give 3[GaCl4] (Scheme 3). A similar slow decomposition of 4 can be assumed generating free
Mes*NH2.

Page 12 of 29
H
H
+ 2 HCl
Mes*
N
As
5[GaCl4]
GaCl4
Mes*
N
- AsCl3
ꢀ GaCl3
GaCl4
Mes*
N
As
Mes*
As
Mes*
GaCl4
N
N
H
H
3[GaCl4]
256
257
258
Scheme 3. Proposed reaction pathway of the formation of 3[GaCl4] in the reaction of 5+ with HCl.
259
260
261
262
263
264
265
266
267
268
We have already demonstrated that the chloride abstraction in (TerNH)2PCl by Lewis acids such as GaCl3
or several silver salts led to the formation of salts containing the cation [(TerNH)2P]+.17 Analogously, it was
shown by Gudat and coꢀworkers that the reaction of 2ꢀchloroꢀ1,3,2ꢀdiazarsolene with GaCl3 gave species III
as [GaCl4]– salt (Scheme 1, R = Mes).7 During the course of our work we tried to receive salts containing 3+
by treatment of (Mes*NH)2AsCl (3Cl) with different Lewis acids. Since 3Cl has not been described in
literature yet, it was necessary to find first synthetic access to this molecule, which proved to be rather
difficult. For this reason, we studied the reaction of LiN(H)Mes* with AsCl3 (Scheme 4). On the basis of 1H
NMR spectroscopic data we found that 1 reacted with AsCl3 in a molar ratio of 3:1 at ambient temperature
affording deeply red colored crystals of amino(imino)arsane Mes*N(H)AsNMes* (6) and Mes*NH2 in
accord with observations by Lappert et al. in 1986.1
H
H
H
AsCl3
Mes*
As
Mes*
Mes*
N
3
N
N
+
Mes*
N
Li
ꢀ 3 LiCl
H
1
6
269
270
Scheme 4. Reaction of 1 with AsCl3 in a molar ratio of 3:1.
271
272
273
274
It is noteworthy that Burford et al. obtained the aminoarsane 2 in 19 % yield in the reaction of 1 with an
excess of AsCl3 in Et2O at room temperature (Scheme 5).18 Interestingly, the reactions of three equivalents
of 1 with the heavy Pn(III)ꢀhalides resulted in a quantitative amination finally yielding Pn[N(H)Mes*]3 (Pn
= Sb, Bi).19

Page 13 of 29
AsCl3
H
Li
H
(excess)
Mes*
N
Mes*
N
ꢀ LiCl
AsCl2
1
2
275
18
276
Scheme 5. Reaction of 1 with an excess of AsCl3 according to Burford et al.
277
278
The dropwise addition of a solution of AsCl3 to a solution of Li[Mes*NH] (1) in Et2O at
–80 °C did not only yield 6 and Mes*NH2 but additionally 3Cl by elimination of LiCl (Scheme 6).
Cl
H
2 AsCl3
H
H
Mes*
As
Mes*
Mes*
N
5
N
N
+
Mes*
N
Li
ꢀ 5 LiCl
H
H
1
3Cl
Mes*
As
Mes*
+
N
N
H
6
279
280
Scheme 6. Observed products for the dropwise addition of AsCl3 to 1.
tBu
tBu
N
Cl
As
+
SiMe3
AsCl2
tBu
tBu
tBu
N
Li
N
N
ꢀ LiCl
Me3Si
tBu
281
282
283
Scheme 7. Synthesis of bisamino(chloro)arsane (tBu)2NAs(Cl)N(tBu)SiMe3 according to Scherer et al.20
284
285
286
287
288
On the basis of NMR spectroscopic investigations Scherer et al. reported on the stoichiometric reaction of
amino(dichloro)arsane R2NAsCl2 with Li[N(R)SiMe3] which resulted in the formation of the
t
bisamino(chloro)arsane R2NAs(Cl)N(R)SiMe3 (R = Bu) (Scheme 7).20 Accordingly, in the analogous
reaction a solution of 2 was added in stoichiometric amounts to a solution of 1 in Et2O at –80 °C (Scheme 8)
and pure 3Cl could be obtained after reꢀcrystallization in rather good yields (ca. 80 %).

Page 14 of 29
H
Li
Cl
Mes*
N
H
Li
H
AsCl3
Mes*
As
Mes*
1
Mes*
N
Mes*
N
N
N
ꢀ LiCl
ꢀ LiCl
AsCl2
H
H
1
3Cl
2
289
290
291
Scheme 8. Synthesis of 3Cl in a twoꢀstep synthesis.
H
H
+ AsCl3
Mes*
N
Mes*
N
Li
ꢀ LiCl
AsCl2
1
2
H
Li
ꢀ LiCl
Mes*
N
1
H
Cl
As
Mes*
N
1
Mes*
Mes*
Li
N
N
As
Mes*
Mes*
N
N
H
6
ꢀ LiCl
H
H
H
3Cl
Mes*
N
292
H
293
294
Scheme 9. Reaction pathway for the formation of 6 resulting from the addition of 1 and AsCl3 in a molar ratio of 3:1.
295
296
297
298
299
To summarize these results, an excess of AsCl3 resulted in the formation of 2, while an excess of 1 led to
formation of 6 and Mes*NH2 as shown in Scheme 9 . Obviously in the latter case, 1 induced upon contact
(
)
with 3Cl an indirect “HClꢀelimination” in the final step by formation of LiCl and Mes*NH2. As a
consequence, for a successful generation of 3Cl there had to be neither an excess of AsCl3 nor an excess of 1
during the course of reaction. A twoꢀstep synthesis as shown in Scheme 8 was found to give the best results.
300
301
302
Subsequently, 3Cl was treated with the Lewis acids AlCl3 and GaCl3, affording the salts 3[AlCl4] and
3[GaCl4] with yields over 90%. Furthermore, 3Cl was treated with the silver salts Ag[OTf] and Ag[BF4]
(Scheme 10). After extraction from precipitated silver chloride the solvates 3[OTf] ⋅ toluene and

Page 15 of 29
303
304
305
306
307
3[BF4] ⋅ toluene could be obtained from toluene solution also with yields over 90 %. In contrast, the
silylaminoarsane [(Me3Si)2N]2AsCl reacted with Ag[OTf] to give the cycloꢀ1,3ꢀdiarsaꢀ2,4ꢀdiazane
[(Me3Si)2NAsꢀꢁꢀNSiMe3]2 by elimination of Me3SiOTf.5 In the reaction of 3Cl with Ag[AsF6], surprisingly
a quantitative conversion of 3Cl to Mes*NH2 was detected by 1H NMR spectroscopy, presumably due to the
presence of HF in solution.
308
+ ECl3
[(Mes*NH)2As][ECl4]
(Mes*NH)2AsCl
3[ECl4]
3Cl
+ AgX
ꢀ AgCl
[(Mes*NH)2As][X]
(Mes*NH)2AsCl
3[X]
3Cl
309
310
Scheme 10. Top: Reaction of 3Cl with ECl3 (E = Al, Ga). Bottom: Reaction of 3Cl with AgX (X = OTf–, BF4 ).
–
311
312
313
314
315
316
In a next series of experiments we were interested in the reactivity of [Mes*N≡As][GaCl4] (5[GaCl4])
towards classical Lewis bases such as pyridine or triphenylpnictanes of the type PnPh3 (Pn = P, As, Sb) and
to compare these results with those of the lighter phosphorus congener reported by Burford et al.21–24 The
reaction of 5[GaCl4] with DMAP (4ꢀdimethylaminopyridine) at –80 °C yielded monomeric Mes*NAsCl and
DMAP⋅GaCl3 adduct. A similar reaction was found when 5[GaCl4] was treated with PPh3 at –80 °C
317
318
affording also the chloroiminoarsane along with the Ph3P⋅GaCl3 adduct (Scheme 7). Contrarily, treatment of
5[GaCl4] with AsPh3 at –80 °C resulted in a product mixture containing also Mes*NAsCl and Ph3As⋅GaCl3
besides arsonium salt [tBuAsPh3][GaCl4] ⋅ toluene (8) and 3[GaCl4] which could be coꢀcrystallized both as
main products in moderate yields (~40 %). The formation of an iminodiarsenium salt
[Mes*NAsAsPh3][GaCl4] could not be observed. A further unexpected molecule could be isolated from the
reaction of 5[GaCl4] with SbPh3 which yielded after formal elimination of ClSbPh2 a fourꢀmembered ring
with an innerꢀcyclic AsꢀNꢀbond, stabilized as GaCl3 adduct (7, Scheme 11).
319
320
321
322
323

Page 16 of 29
Mes*
Cl
N
As
+
DMAP
GaCl3
tBu
Mes*
Cl
+ DMAP
N
As
GaCl3
+ PPh3
+ SbPh3
N
+
Mes*
N
As
ꢀ ClSbPh2
As
Ph
P
GaCl4
tBu
Ph
5
tBu
Ph
GaCl3
Ph
7
+ AsPh3
Mes*
Cl
Mes*
As
Mes*
+
N
N
N
As
H
H
GaCl4
3[GaCl4]
Ph
Ph
tBu
+
+
Ph As
Ph As
GaCl3
Ph
Ph
GaCl4
8
324
325
326
Scheme 11. Summary of the obtained product mixtures in the reactions of 5[GaCl4] with DMAP and PnPh3 (Pn = P,
As, Sb).
327
328
329
330
331
332
To summarize these findings, on the one hand the stability of the formed adducts by release of one
chloride ion from the gallate anion involving the formation of a covalent As–Cl bond in Mes*NAsCl seemed
to be the driving force of the reactions in case of DMAP and PPh3. As already mentioned above, utilization
of 5[GaCl4] also led to the introduction of amounts of HCl into the reaction systems, which we unfortunately
could not avoid. While Mes*NAsCl seemed to be stable in the presence of traces of HCl, 5[GaCl4]

Page 17 of 29
333
immediately showed decomposition. DMAP⋅GaCl3 and Ph3P⋅GaCl3 can be regarded as chemically and
334
335
336
337
338
339
340
thermodynamically robust species. In contrast to the latter, adduct formation of Ph3As⋅GaCl3 seemed not to
be favored since the formation of several other products were observed at the same time (Scheme 7). In case
of SbPh3 formation of Ph3Sb⋅GaCl3 was not observed indicating a smaller Lewis basic character leading to a
different reaction channel (Ph transfer to arsenic) with the formation of Ph2SbCl and 7. On the other hand, it
was shown for the chosen reaction systems, that no formation of DMAP adducts of the arsadiazonium ion
occurred as well as no formation of phosphinoarsenium or arsinoarsenium ions as observed for the lighter
phosphorus congener (Scheme 12).14,24,25
341
342
343
344
We also tried to react in situ generated Mes*NAsCl with Ag[B(C6F5)4], however, only a complex product
mixture was obtained. Thus, we carried out the same reaction in the presence of SbPh3 in the hope to quench
[Mes*NAsꢀSbPh3]+, which did not work. Again a complex mixture was obtained, from which we were able
to crystallize [Ag(SbPh3)4][B(C6F5)4] (9).
DMAP
2 DMAP
Mes*
N
P
OTf
Mes*
N
P
OTf
DMAP
Ar
Ar
R
P
R
R
P
R
N
N
R
P
An
R
P
An
N
N
Ar
Ar
345
346
347
Scheme 12. Top: Reaction of Mes*NPOTf with DMAP reported by Burford et al.24 Bottom: Synthesis of a
bis(arylamino)phosphinophosphenium salt with R = Me, Ar = 2,6ꢀ(CHMe2)2C6H3; An = OTf.25
348
349
350
351
Interestingly, when 5[GaCl4] was treated with AsPh3 at –80 °C the beginning formation of the product
mixture obviously served as a proton providing medium because of the detected fast formation of 3[GaCl4]
after warming up the reaction solution. For this reaction, a similar reaction sequence as depicted in Scheme

Page 18 of 29
352
353
3 can be assumed. Thus, two general reaction channels for the formation of 3[GaCl4] are possible with either
3Cl or 4 as starting materials.
354
355
356
357
In comparison to the synthesis of 3[GaCl4] starting from 4, the reaction of 4 with Ag[AsF6] yielded
3[AsF6]. Again small amounts of HF or HCl within the reaction system are inevitable. It is known that the
reaction of 4 with Ag[OTf] resulted in the formation of cyclic [Mes*NꢀꢀꢀAsOTf]2 by elimination of silver
halide.26
358
359
360
361
362
363
364
365
366
Burford et al. explored the electrophilic character of the phosphadiazonium ion [Mes*N≡P]+, e.g. they
were able to isolate and fully characterize the iminophosphinphosphonium salt [Mes*NPPPh3][OTf]
obtained when Mes*NPOTf was treated with PPh3.14 To compare the reactivity of 5+ towards PPh3 with the
results of the Burford group, additionally, the reaction of [Mes*NꢀꢀꢀAsOTf]2 with PPh3 was explored. The
main product of this reaction was the formation of 3[OTf] indicating ringꢀopening upon attack of the base
PPh3. As side product, solvated [Ag(PPh3)3][OTf] (10) was isolated in low quantities and fully
characterized. Keeping in mind that [Mes*NꢀꢀꢀAsOTf]2 was prepared by silver halide elimination it was not
surprising that dissolved Ag+ salts can easily form solvated [Ag(PPh3)3][OTf], which was first described in
2000 by Laguna.27
367
368
369
370
The reaction of 4 with Ag[BF4] proved that among other products the formation of 3[BF4] also occurred.
Scheme 13 summarizes the two general synthetic methods to obtain salts of 3, either starting from 3Cl by
chloride elimination with Lewis acids (i) or starting from 4 in the reaction with Lewis acids in the presence
of proton sources (ii).
i
ii
(Mes*NH)2AsCl
[(Mes*NH)2As][An]
[Mes*NAsCl]2
3[An]
4
3Cl
371
372
373
374
Scheme 13. Synthetic methods to obtain salts of 3. Reaction with halides of group 13: (i) ECl3, An = ECl4, E = Al, Ga;
(ii) ECl3/ 2 HCl, An = ECl4, E = Al, Ga. Reaction with silver salts: (i) Ag[OTf], An = OTf, Ag[BF4], An = BF4; (ii) 2
Ag[OTf]/ PPh3/ 2 HCl, An = OTf; 2 Ag[BF4]/ 2 HX, X = F or Cl, An = BF4; 2 Ag[AsF6]/ 2 HX, X = F or Cl, An = AsF6.
375

Page 19 of 29
376
377
378
379
380
381
382
383
384
Since in case of route (ii) always the formation of product mixtures was found, reaction channel (i) is to be
preferred when preparing 3Cl. All presented salts of 3 were thermally stable and could be stored unlimited at
room temperature under inert conditions. They decomposed at temperatures between 127 °C
(3[AsF6] ⋅ 2 CH2Cl2) and 165 °C (3[OTf] ⋅ toluene). The As–Cl stretching mode for 3Cl could be detected in
the Raman spectrum at 323 cm–1 (cf. 326 cm–1 for [(Me3Si)2N]2AsCl). A significant feature of all described
1
salts of 3 is their pronounced lowꢀfield shift of the NHꢀresonance in the H NMR spectra depending of the
cationic character. While in 3Cl a polarized As–Cl bond was found (N–H: δ[1H] = 5.57), all 3[X] (X =
AlCl4, GaCl4, BF4, OTf, AsF6) salts form ion pairs and hence their N–H resonance was detected in the lowꢀ
field range between 10.44 for 3[AlCl4] and 11.93 ppm for 3[OTf] (see Table 1).
385

Page 20 of 29
Table 1: 1H NMR shifts [ppm] in CD2Cl2 for 3[X] (X = AlCl4, GaCl4, BF4, OTf, AsF6) and for comparison Mes*NH2 and
386
387
2.
3Cl
1.29
1.53
7.33
5.57
3[AlCl4] 3[GaCl4]
3[BF4]
1.32
3[OTf]
1.32
3[AsF6] Mes*NH2
2
pꢀC(CH3)3
1.32
1.57
1.32
1.57
1.33
1.56
1.27
1.45
7.19
4.01
1.28
1.49
7.36
5.83
oꢀC(CH3)3
CH,Ar
NH
1.55
1.56
7.53
7.53
7.52
7.52
7.53
10.44
10.50
11.21
11.93
10.49
388
389
390
391

Page 21 of 29
392
393
394
Figure 1. ORTEP drawing of the molecular structures of 3[X] (X = BF4, AlCl4, GaCl4, AsF6, OTf) in the crystal. Thermal
ellipsoids drawn with 50% probability at 173 K. Only Nꢀbonded hydrogen atoms are depicted for clarity. Selected bond
length and angles are listed in Table 2
.
395
396
397
398
399
All characterized 3+ cations (Figure 1) exhibit similar metrical parameters which are summarized in Table
2. The shortest distances between the arsenic centers and the anions are around 3.6 Å in all structures,
indicating rather weak cation···anion interactions and similar coordination behavior of all used anions. One
of the electronegative atoms of the anion is positioned in such a way that it fits into the pocket formed by the
two Mes* substituents directing towards the opened N–As–N unit. Therefore, N–H⋅⋅⋅X interactions can be
assumed. This arrangement and the N–H⋅⋅⋅X interactions are comparable with those found for the analogous
[(TerNH)2P]+ salts.17
400
401
402
403
3[AlCl4] and 3[GaCl4] crystallized solvent free, whereas compounds 3[OTf], 3[BF4] and 3[AsF6]
crystallized as the monoꢀsolvates 3[OTf] toluene and the diꢀsolvate 3[AsF6]
⋅
toluene, 3[BF4]
⋅
⋅ 2 CH2Cl2.
404
405
406
407
The toluene molecules in 3[OTf] toluene and 3[BF4] ⋅ toluene adopt comparable positions above the
⋅
angulated N–As–N unit. It is important to note that in both structures the As centers and the centroids (Ct) of
the toluene rings are not arranged on a crystallographic slide axis in the crystal. The shortest distances
As⋅⋅⋅Ct are 3.161 Å in 3[OTf]
⋅ toluene and 3.302 Å in 3[BF4] ⋅ toluene stabilizing these salts by weak
408
409
410
411
interactions (Σr
vdW(As⋅⋅⋅C) = 3.55 Å).28 Moreover, these η6ꢀinteractions confirm the electrophilic character
of the As center and pack its coordination sphere so that it is effectively protected against nucleophilic attack
what is quite favorable for longꢀtime storage. Such Mentschutkinꢀtype complexes of arsenic halides are
already known in the literature.29,30
412
413
414
415
416
417
418
The most prominent structural feature is the bent N–As–N unit (99ꢀ100°) with rather short As–N bond
lengths between 1.748 and 1.757Å clearly indicating double bond character (Σ
rcov(As–N) = 1.92 Å,
Σ
r
cov(As=N) = 1.74 Å).31 The first compound bearing an As=N double bond (1.714(7) and 1.745(7) Å) was
N,N’ꢀbis(2,4,6ꢀtriꢀtertꢀbutylphenyl)aminoꢀiminoarsane, reported by Lappert et al. in 1986.1 Moreover
cationic diazarsenium (1.763ꢀ1.814 Å)5 and neutral tetrazaarsole (1.784 ꢀ 1.805 Å)32 heterocycles containing
partial AsꢀN double bonds are known. Recently, neutral triazarsoles heterocycles were synthesized either by
insertion of isonitriles into arsatriazanediyls [As(ꢀꢀNTer)2N] (Ter = 2,6ꢀbis(2,4,6ꢀtrimethylphenyl)phenyl,

Page 22 of 29
419
420
1.875 Å)33 and by making use of a [3+2] cycloaddition reaction between an organic azide and an arsaalkyne
(1.839 Å).34
421
Table 2: Selected parameters (distances [Å], angles [°]) for derivatives of 3[X] (X = BF4, AlCl4, GaCl4, AsF6, OTf).
3[AlCl4]
1.757(3)
1.453(4)
99.5(2)
125.1(2)
359.1
3[GaCl4]
1.750(2)
1.461(3)
99.6(1)
125.7(2)
359.5
3[OTf]
3[BF4]
3[AsF6]
1.748(2)
1.456(3)
100.0(1)
123.9(2)
359.6
N–As(*)
C–N(*)
1.760(5)
1.444(7)
100.6(2)
119.6(4)
359.1
1.750(3)
1.453(4)
99.1(1)
123.9(2)
359.7
N–As–N`
As–N–C(*)
Σ(∡N1)
Σ(∡N2)
359.1
359.5
360.0
360.1
360.2
As+⋅⋅⋅X–
3.633
3.624
3.539
3.637
3.659
422
423
(*) average values
Table 3: Crystallographic details of the structures of 3[X] (X = BF4, AlCl4, GaCl4, AsF6, OTf) and 7.
3[AlCl4]
3[GaCl4]
3[OTf] ⋅ toluene
3[BF4] ⋅ toluene 3[AsF6] ⋅ 2 CH2Cl2
7
Chem. Formula
C36H60AlAsCl4N2
C36H60AsCl4GaN2 C44H68AsF3N2O3S C43H68AsBF4N2 C38H64As2Cl4F6N2 C24H34AsCl3GaN
Form. Wght. [g molꢀ1] 764.56
807.30
yellow
836.98
yellow
774.72
yellow
954.55
orange
monoclinic
P21/n
587.51
yellow
Colour
Cryst. system
Space group
a [Å]
yellow
monoclinic
C2/c
monoclinic
C2/c
orthorhombic
P212121
10.6600(5)
11.4046(5)
37.459(2)
90.00
monoclinic
P21/n
monoclinic
P21/n
24.945(1)
10.0767(5)
16.3057(9)
90.00
24.9686(7)
10.0804(3)
16.3100(4)
90.00
10.0267(3)
24.5792(8)
17.6919(5)
90.00
10.3463(2)
24.6479(5)
18.1301(4)
90.00
9.7496(3)
18.9671(5)
14.7660(4)
90.00
b [Å]
c [Å]
α [°]
β [°]
93.000(4)
90.00
92.793(2)
90.00
90.00
92.337(2)
90.00
92.460(1)
90.00
95.991(1)
90.00
γ [°]
90.00
V [Å3]
4093.0(4)
4
4100.2(2)
4
4554.0(4)
4
4356.5(2)
4
4619.2(2)
4
2715.6(1)
4
Z
ρcalc. [g cmꢀ3]
ꢀ [mmꢀ1]
λMoKα [Å]
T [K]
1.241
1.308
1.221
1.181
1.373
1.437
1.139
1.758
0.842
0.827
1.730
2.529
0.71073
173(2)
0.71073
173(2)
0.71073
173(2)
0.71073
203(2)
0.71073
173(2)
0.71073
173(2)
Measured reflections 20489
30858
35975
94859
60716
68291
Independent
4698
6248
7919
10952
10606
7216
reflections

Page 23 of 29
Reflections with I >
2σ(I)
2814
3942
4341
6255
7346
5078
Rint.
0.1087
1616
0.0802
1688
0.1255
1784
0.0841
1656
0.0364
1976
0.0627
1200
F(000)
R1 (R [F2 > 2σ(F2)])
wR2 (F2)
0.0532
0.1162
1.008
0.0442
0.0930
0.998
0.0598
0.1103
1.002
0.0603
0.1278
1.094
0.0417
0.1063
1.016
0.0386
0.0898
1.072
GooF
Parameters
CCDC #
212
213
510
573
527
280
1572163
1572160
1572161
1572162
1572159
1572157
424
425

Page 24 of 29
426
427
428
429
430
Figure 2. ORTEP drawing of the molecular structure of 7 in the crystal. Thermal ellipsoids drawn with 50% probability
at 173 K. Hydrogen atoms are omitted for clarity. Selected bond length [Å] and angles [°]: As–N 1.958(2), N–C1
1.309(3), C1–C6 1.500(3), As–C6 2.038(2), As–C19 1.937(3), N–Ga 1.951(2); N–As–C19 98.5(1), C1–N–Ga
145.5(2), C6–As–N–C1 6.8(1).
431
432
433
434
435
436
437
438
439
440
7 represents a rare example of a fourꢀmembered heterocycle consisting of As, N and two Cꢀatoms (Figure
2).35,36 Yellow needles of 7 crystallized in the monoclinic space group P21/n with four molecules per unit
cell. As depicted in Figure 2, the fourꢀmembered ring is almost planar with a maximum deviation from
planarity of 6.8° (∡(C6–As–N–C1)), while the sixꢀmembered condensed ring is stronger distorted from
planarity (21.2°). Both rings are arranged almost orthogonally to each other (∡(N–As–C6–C5) = 117.6°).
The C1–N bond with 1.309(3) Å displays some double bond character (cf. Σrcov(N–C) = 1.46 Å, Σrcov(N=C)
= 1.27 Å),31 whereas the As–N (1.958(2) Å), As–C6 (2.038(2) Å) and C6–C1 (1.500(3) Å) distances can be
regarded as classical single bonds. The Ga–N donorꢀacceptor bond with 1.951(2) Å lies in the expected
range (Σrcov(N–Ga) = 1.95 Å).31
441

Page 25 of 29
442
443
444
Figure 3. ORTEP drawing of the molecular structure of 6 and 8 in the crystal. Thermal ellipsoids drawn with 50%
probability at 173 K. Hydrogen atoms are omitted for clarity. Selected bond length [Å] and angles [°] are listed in
Tables S8 and Table S10.
445
446
447
448
449
450
451
Compound 6 crystallized in the orthorhombic space group P212121 with for units per cell (Figure 3). The
bent NꢀAsꢀN (99.0(1)°) moiety displayed rather short NꢀAs bonds (1.733(2), 1.752(2) Å) in accord with the
situation found for species 3[X] (vide infra, Table 2). Compound 8 crystallized in the triclinic space group
ꢀ
P1 with two formula units per cell (Figure 3). The molecular structure of the cation featured a distorted
tetrahedral environment around the central arsenic atom with two distinctly different As–C bonds (As–CPh
1.911(3)ꢀ1.920(3) Å vs. As–CtBu 1.985(3) Å). There are no significant cation···anion interactions.
452
453
454
455
Figure 4. ORTEP drawing of the molecular structure of 9 and 10 in the crystal. Thermal ellipsoids drawn with 50%
probability at 173 K. Hydrogen atoms are omitted for clarity. Selected bond length [Å] and angles [°] are listed in
Tables S11 and Table S12.
456
ꢀ
457
458
459
460
Both silver salts 9 and 10 crystallized in the triclinic space group P1 with two formula units per cell (Figure
4). While 9 displayed a Ag+ ion surrounded by four SbPh3 ligands (Ag–Sb: between 2.692 – 2.700 Å, cf.
Σrcov(Ag–Sb) = 2.68 Å),31 thus exhibiting a slightly distorted tetrahedral coordination environment, silver
salt 10 is only surrounded by three neutral PPh3 ligands (Ag–P: between 2.482 – 2.512 Å, cf. Σrcov(Ag–P) =

Page 26 of 29
–
461
462
2.39 Å)31 but one oxygen atom of the CF3ꢀSO3 anion is also rather close with 2.657(2) Å, cf. Σrcov(Ag–O) =
1.91 Å31 vs. ΣrvdW(AgꢂꢂꢂO) = 3.24 Å,28 hence the coordination is best described by a [3+1] mode.
463
464
465

Page 27 of 29
466
Conclusion:
467
468
469
470
471
472
473
474
In conclusion, the library of salts with dicoordinated arsenium cations [R2As]+ has been expanded by a
series of acyclic bis(amino)arsenium salts. Additionally, the reactivity of the arsadiazonium ion
[Mes*N≡As]+ towards protons has been explored as well as its Lewis acidic character towards classical
Lewis bases such as PnPh3 (Pn = P, As, Sb). A highꢀyielding synthetic protocols to obtain room temperature
stable salts of acyclic NHꢀfunctionalized bis(amino)arsenium cation [(Mes*NH)2As]+ is reported. These new
salts represent an interesting building block for the synthesis of low coordinated electrophilic arsenic
centers.
475
476
TOC Graphic
477
478
479
480
481
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