The relative stabilities of PhE(NH-t-Bu)2 and PhE(μ-N-t-Bu)2EPh (E = As, Sb, and Bi): X-ray structures of {Li2[PhAs(N-t-Bu)2]}2 and PhE(μ-N-t-Bu)2EPh (E = Sb, Bi)

Article abstract of DOI:10.1139/v03-019

The reaction of PhECl₂ with 2 equiv of LiHN-t-Bu has been studied for the series E = As, Sb, and Bi to determine the effect of the phenyl group on subsequent amine condensation processes. For PhAsCl₂, the metathesis product PhAs(NH-t-Bu)₂ 4 was obtained as a colourless oil. Similar reactions involving PhECl₂, where E = Sb or Bi, yielded the cyclodipnict(III)azanes PhE(μ-N-t-Bu)₂EPh 5 (E = Sb) and 6 (E = Bi), respectively. Treatment of 4 with 2 equiv of n-BuLi produced the dilithium salt Li₂[PhAs(N-t-Bu)₂] 7a. Products 4, 5, 6, and 7a were characterized by ¹H, ⁷Li (7a), and ¹³C NMR spectra, while 5, 6, and 7a were also structurally characterized by X-ray crystallography. Compound 7a is dimeric in the solid state via intermolecular Li...N and η⁶-Li...Ph interactions. The cyclodipnict(III)azanes 5 and 6 have similar structures, with the exocyclic phenyl groups in trans positions relative to the E₂N₂ ring. This synthetic approach provides a new route to the four-membered rings RE(μ-N-t-Bu)₂ER (E = Sb, Bi) and the first example of a bis(organyl)cyclodibism(III)azane.

Full text of DOI:10.1139/v03-019

169
The relative stabilities of PhE(NH-t-Bu)2 and
PhE(␮-N-t-Bu)2EPh (E = As, Sb, and Bi): X-ray
structures of {Li2[PhAs(N-t-Bu)2]}2 and PhE(␮-N-t-
Bu)2EPh (E = Sb, Bi)
Glen G. Briand, Tristram Chivers, and Masood Parvez
Abstract: The reaction of PhECl2 with 2 equiv of LiHN-t-Bu has been studied for the series E = As, Sb, and Bi to
determine the effect of the phenyl group on subsequent amine condensation processes. For PhAsCl2, the metathesis
product PhAs(NH-t-Bu)2 4 was obtained as a colourless oil. Similar reactions involving PhECl2, where E = Sb or Bi,
yielded the cyclodipnict(III)azanes PhE(µ-N-t-Bu)2EPh 5 (E = Sb) and 6 (E = Bi), respectively. Treatment of 4 with 2
1
equiv of n-BuLi produced the dilithium salt Li2[PhAs(N-t-Bu)2] 7a. Products 4, 5, 6, and 7a were characterized by H,
7Li (7a), and 13C NMR spectra, while 5, 6, and 7a were also structurally characterized by X-ray crystallography. Com-
pound 7a is dimeric in the solid state via intermolecular Li···N and η6-Li···Ph interactions. The cyclodipnict(III)azanes
5 and 6 have similar structures, with the exocyclic phenyl groups in trans positions relative to the E2N2 ring. This syn-
thetic approach provides a new route to the four-membered rings RE(µ-N-t-Bu)2ER (E = Sb, Bi) and the first example
of a bis(organyl)cyclodibism(III)azane.
Key words: arsenic, antimony, bismuth, amides, imides.
Résumé : Afin de pouvoir déterminer l’effet du groupe phényle sur les processus subséquents de condensation de
l’amine, on a étudié la réaction de PhECl2 (E = As, Sb et Bi) avec deux équivalents de LiHN-t-Bu. Dans le cas du
PhAsCl2, le produit de dismutation, PhAs(NH-t-Bu)2 (4), a été obtenu sous la forme d’huile incolore. Les réactions
semblables de PhECl2 dans lesquelles E = Sb ou Bi conduisent respectivement aux cyclodipnict(III)azanes, PhE(µ-N-t-
Bu)2EPh (5, E = Sb) et (6, E = Bi). Le traitement du composé 4 avec deux équivalents de BuLi conduit à la formation
1
du sel dilithié Li2[PhAs(N-t-Bu)2] (7a). Les produits 4, 5, 6 et 7a ont été caractérisés par leurs spectres RMN du H et
7
du Li (7a) et des spectres RMN du 13C alors que les produits 5, 6 et 7a ont aussi été caractérisés par diffraction des
rayons X. À l’état solide, le composé 7a existe à l’état trimère par le biais d’interactions Li···N et η6-Li···Ph. Les cy-
clodipnict(III)azanes 5 et 6 ont des structures semblables avec des groupes phényles exocycliques en positions trans par
rapport au cycle E2N2. Cette approche fournit une nouvelle voie de synthèse vers les cycles à quatre chaînons RE(µ-N-
t-Bu)2ER (E = Sb, Bi) et le premier exemple d’une bis(organyl)cyclodibism(III)azane.
Mots clés : arsenic, antimoine, bismuth, amides, imides.
[Traduit par la Rédaction] Briand et al. 174
Introduction
proton after initial E—N bond formation. Reactions involv-
ing primary amines and PCl3 do not afford tris(amino)pnic-
tines P(NHR)3; rather, further amine elimination occurs to
yield [cyclodiphosph(III)azanes] 1, 2, cyclic systems (ClPNR)3,
P4(NR)6 cages, or other condensation products, depending
on the choice of amine substituent and reaction stoichio-
metry (2, 3). Although there have been fewer such studies
involving ECl3 (E = As, Sb, Bi), similar condensation reac-
tions are observed (4–12).
Pnicogen(III) compounds of secondary amines have been
employed extensively as reagents for the preparation of com-
pounds containing other functional groups (1). Homoleptic
species E(NR2)3 (E = P, As, Sb, Bi) are synthesized via sim-
ple metathesis reactions of a pnicogen(III) halide with the
appropriate amine or alkali metal amide. Analogous studies
involving primary amines, on the other hand, have proven to
be less predictable as a result of the remaining acidic amino
Received 16 October 2002. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 3 March 2003.
G.G. Briand, T. Chivers,1 and M. Parvez. Department of
Chemistry, The University of Calgary, Calgary, AB T2N
1N4, Canada.
1Corresponding author (e-mail: chivers@ucalgary.ca).
Can. J. Chem. 81: 169–174 (2003)
doi: 10.1139/V03-019
© 2003 NRC Canada

170
Can. J. Chem. Vol. 81, 2003
In contrast to reactions involving PCl3, metathesis prod-
(5.140 g, 17.35 mmol, 66%). NMR data (thf-d8): 1H NMR δ:
1.25 (s, 18 H, N-t-Bu), 1.85 (s, 2 H, NH), 7.21–7.25 (m, 1
H, AsPh-p), 7.28–7.32 (m, 2H, AsPh-o), 7.69–7.72 (m, 2 H,
AsPh-m). 13C NMR δ: 33.7 (NCMe3), 52.5 (NCMe3), 128.9
(AsPh), 129.0 (AsPh), 131.6 (AsPh), 150.1 (AsPh).
ucts of H2N-t-Bu and RPCl2 (R = Ph, Me, -t-Bu, C5Me5)
yield RP(NH-t-Bu)2 rather than the condensation products 3
(E = P) (6c, 13). The intermediates RP(NH-t-Bu)Cl (R = Me,
t-Bu) are also isolable, given the appropriate reaction
stoichiometry (14). Similar observations have been made for
reactions of H2N-t-Bu and RAsCl2, which yield RAs(NH-t-
Bu)2 and RAsCl(NH-t-Bu) with formation of minor amounts
of 3 (E = As; R′ = t-Bu) (15). To our knowledge, related
studies involving RECl2 (E = Sb, Bi) have not been reported.
They are of interest in determining the effect of the pnicogen
organyl substituent on condensation processes in these sys-
tems. We now report the results of an investigation of the re-
action between LiNH-t-Bu and PhECl2 for the series E = As,
Sb, and Bi, which gives the metathesis product 4 for arsenic
and the condensation products 5 and 6 for antimony and bis-
muth, respectively. Further, we describe the metallation of 4
to give 7a, and the solid-state structures of 5, 6, and 7a.
Preparation of PhSb(µ-N-t-Bu)2SbPh, 5
A slurry of LiHN-t-Bu (2.108 g, 26.67 mmol) in diethyl
ether (20 mL) was added dropwise to a solution of PhSbCl2
(3.597 g, 13.33 mmol) in diethyl ether (5 mL) at 0°C to give
a cloudy yellow mixture, which was allowed to warm to
23°C. After 18 h, the solvent was removed under vacuum.
Hexane (20 mL) was added, and the mixture was centri-
fuged. The supernatant was decanted, and the solvent was
removed under vacuum to give 5 as a yellow-orange oil
(3.071 g, 5.69 mmol, 85%). The oily product crystallized on
1
standing at 23°C for 1 day. NMR data (thf-d8): H NMR δ:
1.26 (s, 18 H, N-t-Bu), 7.25–7.31 (m, 6 H, SbPh-p/o), 7.54–
7.72 (m, 4 H, SbPh-m). 13C NMR δ: 35.1 (NCMe3), 52.4
(NCMe3), 128.9 (SbPh), 129.2 (129.3) (SbPh), 134.1
(135.2) (SbPh). Anal. calcd. for C20H28N2Sb2 (%): C 44.49,
H 5.23, N 5.19; found: C 43.95, H 4.81, N 5.42.
Preparation of PhBi(µ-N-t-Bu)2BiPh, 6
A slurry of LiHN-t-Bu (0.100 g, 1.27 mmol) in diethyl
ether (5 mL) was added dropwise to a solution of
[PhBiCl2(thf)] (0.272 g, 0.633 mmol) in diethyl ether (5 mL)
at 0°C to give a cloudy orange mixture, which was allowed
to warm to 23°C. After 3 h, the solvent was removed under
vacuum. After addition of hexane (5 mL), the mixture was
centrifuged, and the supernatant was decanted and concen-
trated to 1 mL. After 2 days, red crystals of 6 were collected
(0.040 g, 0.056 mmol, 18%). NMR data (thf-d8): 1H NMR δ:
0.66 (s, 18 H, N-t-Bu), 7.33 (m, 2 H, BiPh-p), 7.64 (m, 4 H,
BiPh-o), 8.78 (m, 4 H, BiPh-m). 13C NMR δ: 35.5 (NCMe3),
55.1 (NCMe3), 128.8 (BiPh), 131.3 (BiPh), 136.7 (BiPh).
Anal. calcd. for C20H28Bi2N2 (%): C 33.62, H 3.95, N 3.92;
found: C 33.84, H 4.03, N 4.17.
Experimental section
Reagents and general procedures
Solvents were dried and distilled over Na/benzophenone
prior to use: diethyl ether and n-hexane. Phenylarsonic acid,
triphenylantimony, and thionyl chloride were used as re-
ceived from Aldrich. Antimony(III) chloride, triphenylbis-
muth, and bismuth(III) chloride were used as received from
Strem. PhAsCl2 (16), PhSbCl2 (17), [PhBiCl2(thf)](18), and
LiHN-t-Bu (19) were prepared according to literature proce-
dures (thf = tetrahydrofuran). Compound 4 has been re-
ported previously, but was prepared via a different route and
characterized by elemental analysis only (15a).
Preparation of Li2[PhAs(N-t-Bu)2], 7a
A solution of 2.5 M n-BuLi in hexanes (8.10 mL,
20.28 mmol) was added dropwise to a solution of PhAs(NH-
t-Bu)2 (3.003 g, 10.14 mmol) in diethyl ether (30 mL) at 0°C
to give a cloudy yellow mixture, which was allowed to warm
to 23°C. After 5 h, the solvent was removed under vacuum.
The resulting product was washed with n-hexane (3 × 5 mL)
to give 7a as a white powder (2.002 g, 6.50 mmol, 64%). X-
ray quality crystals were grown from diethyl ether – hexane
Instrumentation
7
1H, 13C, 31P, and Li NMR spectra were recorded on a
Bruker DRX 400 NMR spectrometer at 298 K. Chemical
shifts are reported relative to Me4Si in C6D6 (1H and 13C),
85% H3PO4 in D2O (31P), and 1 M LiCl in D2O (7Li). Ele-
mental analyses were provided by the Analytical Services
Laboratory, Department of Chemistry, University of Calgary.
1
at –15°C. NMR data (thf-d8): H NMR δ: 1.04 (s, 18 H, N-t-
Bu), 6.95 (t, 1 H, AsPh-p), 7.06 (t, 2 H, AsPh-o), 7.60 (d, 2
H, AsPh-m). 13C NMR δ: 38.2 (NCMe3), 53.5 (NCMe3),
Preparation of PhAs(NH-t-Bu)2, 4
A slurry of LiHN-t-Bu (4.134 g, 52.29 mmol) in diethyl
ether (40 mL) was added dropwise to a solution of PhAsCl2
(5.828 g, 26.14 mmol) in diethyl ether (15 mL) at –90°C to
give a cloudy white mixture. The mixture was allowed to
warm to 23°C, and after 18 h, the solvent was removed un-
der vacuum. Hexane (30 mL) was added and the mixture
was centrifuged. The supernatant was decanted and the sol-
vent removed under vacuum to give 4 as a yellow oil, which
was distilled (10–3 mm, ~80°C) to give a colourless oil
7
126.0, (AsPh), 127.5 (AsPh), 131.1 (AsPh). Li NMR δ:
1.92, 2.41. Anal. calcd. for C14H23AsLi2N2 (%): C 54.57, H
7.52, N 9.09; found: C 55.83, H 7.44, N 8.98.
X-ray structural analyses
Crystals of 5, 6, and 7a were coated with oil (Paratone
8277, Exxon) and mounted on glass fibres. Measurements
were made on a Nonius KappaCCD diffractometer using
© 2003 NRC Canada

Briand et al.
171
Table 1. Crystallographic data for 5, 6, and 7a.
5
6
7a
Empirical formula
C20H28N2Sb2
C20H28Bi2N2
C14H23AsLi2N2
Formula mass
Space group
a (Å)
b (Å)
c (Å)
539.94
P21/c
6.6067(2)
20.1293(6)
8.4739(3)
90
106.475(2)
90
1080.66(6)
2
714.40
P21/c
9.0544(3)
9.3725(2)
12.6567(5)
90
92.641(1)
90
1072.94(6)
2
308.14
P1
9.0354(1)
10.1088(2)
10.6036(3)
87.9151(9)
67.968(1)
64.324(1)
799.86(3)
2
α (°)
β (°)
γ (°)
V (Å3)
Z
F(000)
Dcalcd(g cm–3)
528
1.659
656
2.211
320
1.279
µ (mm–1)
T (K)
2.50
16.4
2.11
170(2)
0.71069
0.048
0.111
2
170(2)
0.71073
0.024
0.059
2
170(2)
0.71073
0.027
0.066
λ (Å)
a
R1
a
wR2
aR1 = (Σ||Fo| – |Fc||)/(Σ|Fo|) for (Fo > 2σ(Fo )), [I > 2 σ(I)]; wR2 = {[Σw(Fo – Fc2)2]/[Σw(Fo )2]}1/2 (all data).
2
2
monochromated Mo Kα radiation. Crystallographic data are
summarized in Table 1.2
of impurities. The absence of the condensation product 3
(E = As, R = R′ = t-Bu) represents an improvement on the
existing synthesis of 4 (15a). The identity of 4 was estab-
lished by 1H and 13C NMR spectra and by metallation with 2
equiv of n-butyllithium to yield the dilithium salt
Li2[PhAs(N-t-Bu)2] 7a (R = Ph), cf., the formation of
Li2[PhP(N-t-Bu)2] 7b from PhP(NH-t-Bu)2 (13a). The re-
sulting colourless crystals were of sufficient quality to allow
a definitive characterization via X-ray crystallographic anal-
ysis (vide infra). Wright and co-workers have recently de-
scribed extensive studies of the formation of the [As(N-t-
Bu)3]3– trianion by the reaction of As(NMe2)3 (1 equiv) with
a mixture of t-BuNH2 and t-BuNHLi (3:3 equiv) (24). Al-
though the formation of As(NH-t-Bu)3 is implied in this syn-
thesis, this intermediate was not isolated. The authors
propose a facile condensation to produce the cyclo-
diars(III)azane, t-BuN(H)As(µ-N-t-Bu)2AsN(H)-t-Bu (3, E =
As, R = R′ = t-Bu) to explain this observation (24).
Data were measured using ω and ϕ scans. The crystals
showed no sign of decay during data collection, and no de-
cay correction was employed. Cell constants were obtained
from the refinement (20) of 2330 (5), 2208 (6), or 3484 (7a)
reflections in the range 1 < φ < 27.5°. The space groups for
5 and 6 were uniquely determined from the systematic ab-
sences. The data were corrected for Lorentz and polarization
effects and for absorption using the multiscan method (20).
The structures were solved using direct methods (21) and
expanded using Fourier techniques (22) (SHELXL97) (23).
The nonhydrogen atoms were refined anisotropically. Hy-
drogen atoms were included at geometrically idealized posi-
tions and were not refined.
The Sb atom in 5 was disordered over two sites, Sb1 and
Sb2, with occupancy factors 0.574(1) and 0.426(1), respec-
tively. The t-Bu group exhibited rotational disorder wherein
the methyl C atoms were located over two sites each with
site occupancy factors 0.83(1) and 0.17(1). The disorder in
the phenyl ring was also apparent from the large thermal dis-
placement parameters of its carbon atoms.
The reaction of PhSbCl2 with 2 equiv of LiHN-t-Bu yields
a yellow-orange oil after removal of the solvent. The oil
crystallizes after 1 day at 23°C, and it was identified by
CHN analyses and NMR spectra as the condensation product
PhSb(µ-N-t-Bu)2SbPh 5. Compound 5 was obtained in 85%
1
yield and the H and 13C NMR spectra of the unpurified ma-
Results and discussion
terial indicated a single product. For PhBiCl2, the corre-
sponding reaction proceeds in a similar manner but, in this
case, the crude product was isolated as a solid. Crystals were
obtained from n-hexane and characterized as PhBi(µ-N-t-
Synthetic and NMR studies
The treatment of PhAsCl2 with 2 equiv of LiHN-t-Bu in
diethyl ether yields PhAs(NH-t-Bu)2 4 in ca. 65% yield, as a
1
1
colourless oil, after vacuum distillation. H and 13C NMR
Bu)2BiPh 6. The H NMR spectrum of the reaction mixture
spectra of the unpurified material show that primarily one
product is formed in this reaction with very minor amounts
exhibits three N-t-Bu resonances at δ 0.66, 1.01, and 1.07,
with approximate relative intensities 1:2:1, in addition to a
2 Supplementary data may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC
188507(7a), 188508(5), and 188509(6) contain the supplementary data for this paper. These data can be obtained, free of charge, via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, U.K.; fax
+44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2003 NRC Canada

172
Can. J. Chem. Vol. 81, 2003
Fig. 1. ORTEP diagram of 5 showing the two disordered mole-
cules (30% probability ellipsoids). Symmetry transformations
used to generate equivalent atoms: –x + 1, –y, –z + 1.
complex set of overlapping Ph resonances. The trans-isomer
of 6 was isolated in ca. 20% yield and shown to be attribut-
able to the resonance at δ 0.66. It is tentatively proposed that
one of the other products is the cis-isomer of 6, but attempts
to isolate this component by fractional crystallization were
unsuccessful. A candidate for the second unidentified prod-
uct is the monosubstituted derivative PhBi(Cl)(NH-t-Bu).
However, when the reaction was carried out in a 1:1
stoichiometry, no resonances were observed at δ 0.66, 1.01,
1
or 1.07 in the H NMR spectrum. Resonances attributable to
the N-t-Bu groups of an unidentified product appeared at δ
1.70 and 1.88.
+ 2 LiNH-t-Bu
[1]
PhECl2 −2LiCl → PhE(NH-t-Bu)2
(E = Sb,Bi)
− t-BuNH2
→1/2 PhE(µ-N-t-Bu)2EPh
5,E = Sb
6,E = Bi
1
For both 5 and 6, the H NMR spectra of the pure prod-
ucts show resonances for N-t-Bu and Ph groups in the ratio
1:1, suggesting that a condensation reaction has occurred
(eq. [1]). Previous routes to bis(organyl)cyclodis-
tib(III)azanes 3 (E = Sb; R = Me, t-Bu) involve metathesis
reactions between the organolithium reagents and ClSb(µ-N-
t-Bu)2SbCl (2, E = Sb, R = t-Bu), which is prepared from
SbCl3 and Li(Me3Si)N-t-Bu (24a, 24b). Bismuth analogues
of 3 (E = Bi) have not been reported, nor have the dichloro
derivatives 2 (E = Bi). The reaction of organyldihalopnic-
tines and lithiated primary amides thus represents a novel
synthetic route to these cyclodipnict(III)azanes.
Fig. 2. ORTEP diagram of 6 (30% probability ellipsoids). Sym-
metry transformations used to generate equivalent atoms: –x, –y,
–z + 1.
X-ray structural analyses
ORTEP diagrams of 5 and 6 are shown in Figs. 1 and 2,
respectively. The X-ray structure analyses of 5 and 6 con-
firm the formation of condensation products. In both struc-
tures, the exocyclic Ph groups are in a trans arrangement
with respect to the E2N2 ring. In the case of 5, there is a
static disorder in the Sb atom over two positions, giving two
unique molecules (Fig. 1). In one molecule, Sb(1) is bound
to C(5) of the phenyl ring and N(1) of the N-t-Bu group,
giving a trans-PhSb(µ-N-t-Bu)2SbPh structure, as a result of
inversion symmetry. The second molecule shows Sb(2)
bound to C(6) of the phenyl ring, as well as N(1) of the N-t-
Bu group, giving an Sb2N2 ring that also has a trans-PhSb(µ-
N-t-Bu)2SbPh structure. The Sb—N and Sb—N* interac-
tions are quite different in one molecule, but not in the other
(Sb(1)—N(1) = 1.988(4) Å, Sb(1)—N(1*) = 2.063(4) Å;
Sb(2)—N(1) = 2.019(4) Å, Sb(2)—N(1*) = 2.034(4) Å).
However, the average Sb—N bond distances are similar for
the two molecules (|Sb(1)—N| = 2.02(4) Å; |Sb(2)—N| =
2.027(8) Å), while the Sb—Cphenyl bond distances are signif-
icantly different (Sb(1)—C(5) = 2.169(5) Å; Sb(2)—C(6) =
2.234(7) Å). The structural parameters for 5 and 6 are com-
pared in Table 2. As expected, bond lengths to the bismuth
centre in 6 are longer than those to the antimony centres
(Bi—C = 2.285(4) Å vs. Sb—C = 2.169(5) and 2.234(7) Å;
Bi—N = 2.163(3) and 2.167(3) Å vs. Sb—N = 1.988(4)–
2.063(4) Å), and the bond angles at the bismuth centre are
considerably smaller than those at antimony. These observa-
tions can be attributed to the larger covalent radius of Bi(III)
vs. Sb(III).
Only one example of a bis(organyl)cyclodistib(III)azane
has been structurally characterized, i.e., trans-t-BuSb(µ-N-t-
Bu)2Sb-t-Bu 8 (25). Comparison of the bond angles and
Sb—Nring bond distances in 5 and 8 show all values to be in
the same range. The Sb—C bond distances in 5 are shorter
than those of 8 (2.252(6) Å), presumably as a result of sp2
rather than sp3 hybridization of carbon. Comparison with
other analogues shows that the bond angles at antimony in 5
are greater than those in [(RHN)Sb(µ-NR)2(NHR)] (R = 2,6-
Me2C6H3) 9 (8), while the Sb—Nring bond distances are in
© 2003 NRC Canada

Briand et al.
173
Table 3. Selected bond lengths (Å) and bond angles (°) for 7a
Table 2. Selected bond lengths (Å) and bond angles (°) for 5
and 6.
(E = As) and 7b (E = P).
5
6
7a
7ba
Bond lengths (Å)
E(1)—C(5)
E(1)—N(1)
E(1)—N(1*)
E(2)—C(6)
Bond lengths (Å)
E(1)—C(9)
E(1)—N(1)
E(1)—N(2)
Li(1)—N(1)
Li(1)—N(2*)
Li(2)—N(1)
Li(2)—N(2)
Li(2)—Cphenyl
Bond angles (°)
C(9)-E(1)-N(1)
C(9)-E(1)-N(2)
N(1)-E(1)-N(2)
2.169(5)
1.988(4)
2.063(4)
2.234(7)
2.019(4)
2.034(4)
2.285(4)
2.167(3)
2.163(3)
2.004(2)
1.853(2)
1.850(2)
1.916(4)
1.920(4)
2.015(4)
2.011(4)
2.624(4)–2.752(4)
1.867(3)
1.693(2)
1.686(3)
1.918(5)
1.928(6)
2.027(6)
2.017(5)
2.618(6)–2.750(6)
E(2)—N(1)
E(2)—N(1*)
Bond angles (°)
C(5)-E(1)-N(1)
C(5)-E(1)-N(1*)
N(1)-E(1)-N(1*)
E(1)-N(1)-E(1*)
C(6)-E(2)-N(1)
C(6)-E(2)-N(1*)
N(1)-E(2)-N(1*)
E(1)-N(1)-E(1*)
103.7(2)
103.3(2)
77.7(2)
102.3(2)
104.9(3)
104.3(2)
77.7(2)
93.4(1)
102.2(1)
78.7(1)
97.21(7)
97.32(7)
97.15(7)
99.8(1)
100.8(1)
102.8(1)
101.3(1)
aValues for one of two unique molecules (13a).
102.3(2)
the structures of 7a and 7b involve the longer E—C and (or)
E—N bond distances and the smaller bond angles at the
pnicogen center in 7a (see Table 3), both of which are a re-
sult of the larger covalent radius of As(III) vs. P(III). For
comparison with the unsolvated structure of 7a, crystalliza-
tion of 7a from THF produces the trisolvated monomer
{(THF)3Li2[PhAs(N-t-Bu)3]} in which the [PhAs(N-t-
Bu)2]2– ligand is N,N′ chelated to both Li+ ions. Each Li+ ion
is further coordinated by one terminal and one bridging THF
molecule (26).
Fig. 3. ORTEP diagram of 7a (R = Ph; methyl carbon atoms of
t-Bu groups are removed for clarity; 30% probability ellipsoids).
Symmetry transformations used to generate equivalent atoms:
–x + 1, –y, –z + 2.
Conclusions
The reaction of PhECl2 with 2 equiv of LiHN-t-Bu has
been studied for comparison with previous work on the anal-
ogous phosphorus systems, which yield bis(amido)organyl-
phosphines. These reactions result in the formation of
PhAs(NH-t-Bu)2 in the case of arsenic, while a subsequent
condensation reaction to afford the trans-cyclodipnict(III)az-
anes PhE(µ-N-t-Bu)2EPh is observed for both the antimony
and bismuth systems. This synthetic route represents a novel
pathway to RE(µ-NR′)2ER (E = Sb, Bi) species, including
the first example of a bismuth analogue. The metallation of
PhAs(NH-t-Bu)2 with Li-n-Bu produces a dimeric dilithiated
derivative that is isostructural with the phosphorus analogue.
same range. As 6 is the first structurally characterized exam-
ple of a bis(organyl)cyclodibism(III)azane, RBi(µ-NR′)2BiR,
no direct structural comparisons can be made. However,
comparison with [(RHN)Bi(µ-NR)2(NHR)] (R = 2,6-i-
Pr2C6H3) 10, the only reported analogue (9), shows the bond
angles in 6 to be larger, while the Bi—Nring bond distances
are similar. The larger bond angles for 5 and 6 are
counterintuitive given the steric bulk of the substituted
phenyl substituents in 9 and 10, respectively.
An ORTEP diagram of 7a is depicted in Fig. 3. The com-
plex 7a is isostructural with 7b, reported previously (13a),
and the metrical parameters are compared in Table 3. The
structure shows the pnicogen atom bound to a phenyl carbon
atom and two tert-butylamido nitrogen atoms in a pyramidal
arrangement. One of the lithium atoms (Li(2)) is symmetri-
cally chelated by the ligand in an N,N′ manner (Li(2)—N(1) =
2.015(4) Å; Li(2)—N(1) = 2.011(4) Å), while the second
lithium atom (Li(1)) is bound to one nitrogen atom (N(1))
only (1.916(4) Å). The resulting moiety dimerizes via a
short Li(1)—N(2*) interaction (1.920(4) Å) and an η6-
Li···Ph* interaction (Li(2)—C∗phenyl = 2.624(4)–2.752(4) Å)
to the second molecule. The most significant differences in
Acknowledgments
We thank Dr. Gabriele Schatte, Dorothy Fox, Qiao Wu,
and Dr. Raghav Yamdagni for assistance in collecting NMR
data and the Natural Sciences and Engineering Research
Council of Canada (NSERC) for funding.
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