Synthesis and X-ray structures of the polycyclic dimers {[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ-NtBu) 2AsN(tBu)Li]2

Article abstract of DOI:10.1002/zaac.200700543

The metathesis of [PhB(μ-NtBu)₂]AsCl and tBuN(H)Li in 1:1 molar ratio in diethyl ether produced the amido derivative [PhB(μ-NtBu) ₂AsN(tBu)H] (1) in good yield. The lithiation of 1 with one equivalent of nBuLi afforded the lithium salt [PhB(μ-NtBu) ₂AsN(tBu)Li] (2a). Both 1 and 2a were characterized by multinuclear NMR spectroscopy. The crystal structure of 2a is comprised of a U-shaped, centrosymmetric dimer in which the monomeric [PhB(μ-NtBu)₂AsN(tBu) ]^-Li⁺ units are linked by Li-N interactions to give a six-rung ladder. Oxidation of 2a with one-half equivalent of I₂ in diethyl ether resulted in hydrogen abstraction from the solvent to give the dimeric lithium iodide adduct {[PhB(μ-NtBu)₂AsN(tBu)H]LiI} ₂ (1·LiI) with a central Li₂I₂ ring.

Full text of DOI:10.1002/zaac.200700543

DOI: 10.1002/zaac.200700543
Synthesis and X-ray Structures of the Polycyclic Dimers
{[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ-NtBu)2AsN(tBu)Li]2
Jari Konu and Tristram Chivers*
Calgary AB / Canada, University of Calgary, Department of Chemistry
Received October 5th, 2007; accepted December 15th, 2007.
Abstract. The metathesis of [PhB(μ-NtBu)2]AsCl and tBuN(H)Li
in 1:1 molar ratio in diethyl ether produced the amido derivative
[PhB(μ-NtBu)2AsN(tBu)H] (1) in good yield. The lithiation of 1
with one equivalent of nBuLi afforded the lithium salt [PhB(μ-
NtBu)2AsN(tBu)Li] (2a). Both 1 and 2a were characterized by
multinuclear NMR spectroscopy. The crystal structure of 2a is
comprised of a U-shaped, centrosymmetric dimer in which the
monomeric [PhB(μ-NtBu)2AsN(tBu)]ϪLiϩ units are linked by
Li-N interactions to give a six-rung ladder. Oxidation of 2a with
one-half equivalent of I2 in diethyl ether resulted in hydrogen ab-
straction from the solvent to give the dimeric lithium iodide adduct
{[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 (1·LiI) with a central Li2I2 ring.
Keywords: Arsenic; Boraamidinate; Lithium; Polycyclic com-
pounds; Crystal structures
Introduction
particular, to make a direct comparison of the arsenic
systems with the known phosphorus derivatives
[PhB(μ-NtBu)2PN(tBu)X] (X ϭ H, Li) [7]. In this context
we report herein (a) the synthesis and multinuclear
NMR spectroscopic characterization of the arsenic
boraamidinateamide [PhB(μ-NtBu)2AsN(tBu)H] (1) and
the lithium derivative [PhB(μ-NtBu)2AsN(tBu)Li] (2a)
and (b) the solid state structures of the polycyclic
dimers, {[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 (1·LiI) and
[PhB(μ-NtBu)2AsN(tBu)Li]2 (2a).
The dianionic boraamidinate (bam) ligand, [RB(NRЈ)2]2Ϫ
,
is formally isoelectronic with the extensively studied
monoanionic amidinate (am) ligand [RC(NRЈ)2]Ϫ. Recent
work on early main group and transition-metal complexes
has established that the 2Ϫ charge on the bam ligand results
in some interesting fundamental differences compared to
the behavior of the monoanionic am ligand [1Ϫ5]. We have
also reported the first examples of heavy Group 15 bora-
amidinates in which the versatile coordinating ability of the
bam ligand was highlighted [6]. In addition to the mono-
bams [PhB(μ-NtBu)2]MCl (M ϭ As, Sb, Bi) with a poten-
tially useful M-Cl reactive site, the unusual 2:3 bam com-
plexes, M2[PhB(μ-NtBu)2]3 (M ϭ Sb, Bi), displayed a un-
ique bonding arrangement in which two metal centers are
each N,NЈ-chelated by one bam ligand and the two
[M(bam)]ϩ units are bridged by the third [bam]2Ϫ ligand.
For the 1:2 Group 15 bam systems, both solvated complexes
(Et2O)LiM[PhB(μ-NtBu)2]2 (M ϭ As, Bi) and unsolvated
ladder structures LiM[PhB(μ-NtBu)2]2 (M ϭ As, Sb) were
observed; these complexes showed interesting fluxional be-
havior in solution (Berry pseudorotation) in the case of
M ϭ Sb, Bi [6].
Experimental Section
General procedures
All reactions and the manipulations of products were performed
under an argon atmosphere by using standard Schlenk techniques
or an inert atmosphere glove box. The compounds PhBCl2 (Ald-
rich, 97 %), AsCl3 (Alfa, 99 %), tBuNH2 (Aldrich, 99 %), iodine
(Aldrich, 99.8 %) and nBuLi (Aldrich, 2.5 M solution in hexanes)
were used as received. LiN(H)tBu was prepared by the addition of
nBuLi to a solution of tBuNH2 in n-hexane at Ϫ10 °C and its
purity was checked by 1H NMR spectroscopy. The compound
[PhB(μ-NtBu)2]AsCl [6] was prepared as described earlier. The
solvents n-hexane, toluene and Et2O were dried by distillation over
Na/benzophenone under an argon atmosphere prior to use.
Elemental analyses were performed by Analytical Services, Depart-
ment of Chemistry, University of Calgary.
The availability of the monofunctional reagent [PhB(μ-
NtBu)2]AsCl [6] provided an opportunity to investigate the
chemistry of the arsenic atom in bam complexes and, in
Spectroscopic methods
* Prof. Dr. T. Chivers
Department of Chemistry
University of Calgary
2500 University Drive N.W.
Calgary, Alberta T2N 1N4 / Canada
Fax: (ϩ)1-403-289-9488
1
7
The H, Li, 11B and 13C NMR spectra were obtained in d8-THF
at 23 °C on a Bruker DRX 400 spectrometer operating at 399.59,
155.30, 128.20 and 100.49 MHz, respectively. 1H and 13C spectra
are referenced to the solvent signal and the chemical shifts are re-
ported relative to (CH3)4Si. 7Li and 11B NMR spectra are refer-
enced externally and the chemical shifts are reported relative to a
E-mail: chivers@ucalgary.ca
Z. Anorg. Allg. Chem. 2008, 634, 875Ϫ879
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
875

J. Konu, T. Chivers
Table 1 Crystal structure data for 1·LiI and 2a.a)
1.0 M solution of LiCl in D2O and to a solution of BF3 ·Et2O in
C6D6, respectively.
1·LiI
2a
Formula
Mr
C36H66As2B2I2Li2N6
1022.09
C36H64As2B2Li2N6
766.27
Synthesis of [PhB(μ-NtBu)2AsN(tBu)H] (1)
Crystal size, mm
Crystal system
Space group
0.10 ϫ 0.08 ϫ 0.02
triclinic
P1
0.20 ϫ 0.16 ϫ 0.12
monoclinic
C2/c
10.404(2)
18.933(4)
21.030(4)
90.00
99.87(3)
90.00
4081(1)
4
1.247
1.669
1616
12, 22, 25
2.26-25.02
13086
3603
0.0876
A
mixture of [PhB(μ-NtBu)2]AsCl (0.597 g, 1.75 mmol) and
tBuN(H)Li (0.138 g, 1.75 mmol) was cooled to Ϫ80 °C and cold
diethyl ether (50 mL, Ϫ80 °C) was added via cannula. The reaction
mixture was stirred for 1/2 h at Ϫ80 °C and ca. 5 h at room tem-
perature. The precipitate of LiCl was removed by filtration and the
solvent was evaporated under vacuum to give 1 as a white powder
(0.514 g, 78 %). Anal. Calcd for C18H33AsBN3: C 57.31; H 8.82; N
11.14. Found: C 56.67; H 9.22; N 10.53 %.
1H NMR (d8-THF, 23 °C): δ 7.20-7.37 [m, 5H, C6H5], 3.20 [s, 1H, NH], 1.32
[s, 9H, C(CH3)3], 1.09 [s, 18H, C(CH3)3]. 13C{1H} NMR: δ 127.6-132.0
[C6H5], 52.6 [C(CH3)3], 52.2 [C(CH3)3], 33.8 [C(CH3)3], 33.7 [C(CH3)3]. 11B
NMR: δ 34.7.
¯
˚
a, A
10.598(2)
10.758(2)
13.087(3)
92.74(3)
111.28(4)
118.55(3)
1175.8(8)
1
1.443
2.763
512
12, 12, 15
2.24-25.03
7956
4128
0.0323
˚
b, A
˚
c, A
Ͱ, deg
β, deg
γ, deg
3
˚
V, A
Z
Dcalcd, g cmϪ3
μ(MoKα), cmϪ1
F(000), e
hkl range
° range, deg
Refl. measured
Refl. unique
Rint
Synthesis of [PhB(μ-NtBu)2AsN(tBu)Li] (2a)
Param. refined
Reflns [I>2σ (I)]
230
3235
0.0326
0.0742
1.052
0.58 and Ϫ0.48
217
2672
0.0556
0.1300
1.048
0.96 and Ϫ1.16
A solution of 1 (0.660 g, 1.75 mmol) in n-hexane (30 mL) was
cooled to Ϫ80 °C and 0.70 mL of nBuLi (2.5 M in hexanes,
1.75 mmol) was added via syringe. The reaction mixture was stirred
for 1/2 h at Ϫ80 °C and 15 h at room temperature. Solvent was eva-
porated and the resulting off-white powder was washed with cold
n-hexane (ca. 5 mL) giving 2a as a white powder (0.490 g, 73 %).
Anal. Calcd for C18H32AsBLiN3: C 56.43; H 8.42; N 10.97. Found:
C 55.47; H 8.15; N 9.72 %. X-ray quality crystals of 2a were ob-
tained from n-hexane in 6 d at 5 °C.
b)
R1 [I>2σ (I)]
c)
wR2 (all data)
GoF on F2
Ϫ3
˚
Δρfin (max/min), e A
a)
λ (MoKα) ϭ 0.71073 A b) R1 ϭ ΣʈFoΗ Ϫ ΗFcʈ/ΣΗFoΗ
˚
c) wR2 ϭ [Σw(Fo2-Fc2)2/ΣwFo
] .
4 1/2
atoms with anisotropic thermal parameters, the hydrogen atoms
1H NMR (d8-THF, 23 °C): δ 7.11-7.38 [m, 5H, C6H5], 1.29 [s, 9H, C(CH3)3],
1.09 [s, 18H, C(CH3)3]. 13C{1H} NMR: δ 126.7-132.7 [C6H5], 54.7 [C(CH3)3],
52.6 [C(CH3)3], 37.6 [C(CH3)3], 33.9 [C(CH3)3]. 7Li NMR: δ 1.01. 11B NMR:
δ 34.2.
bonded to carbons were placed in calculated positions [C-H ϭ
˚
˚
0.98 A for C(CH3)3 and 0.95 A for phenyl hydrogens]. The isotropic
thermal parameters of these atoms were fixed at 1.2 times to that
of the corresponding carbon for phenyl hydrogens, and 1.5 times
for C(CH3)3. In the final refinement, the hydrogen atoms were
riding on their respective carbon atoms. Crystallographic data are
summarized in Table 1. CCDC-667032 and CCDC-667033 contain
the supplementary crystallographic data for compounds 1·LiI
and 2a. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
dataϪrequest/cif.
Oxidation of [PhB(μ-NtBu)2AsN(tBu)Li] (2a) with I2
A solution of 2a (0.268 g, 0.70 mmol) in diethyl ether (30 mL) was
cooled to Ϫ80 °C and a solution of I2 (0.089 g, 0.35 mmol) in di-
ethyl ether (30 mL) was added via cannula. The reaction mixture
was stirred for 1/2 h at Ϫ80 °C and 2 h at room temperature. Solvent
was evaporated under vacuum and the resulting off-white powder
was washed with cold n-hexane (ca. 10 mL) giving a white powder
(0.289 g, 81 %, calculated as a 1:1 mixture of 1 and LiI). X-ray
quality crystals of 1·LiI were obtained from toluene in 1 d at 23 °C.
1H NMR (THF-d8, 23 °C): δ 7.17-7.39 [m, 5H, C6H5], 3.21 [s, 1H, NH], 1.34
[s, 9H, C(CH3)3], 1.10 [s, 18H, C(CH3)3]. 13C{1H} NMR: δ 127.6-132.0
[C6H5], 52.6 [C(CH3)3], 52.2 [C(CH3)3], 33.8 [C(CH3)3], 33.7 [C(CH3)3]. 7Li
NMR: δ 0.79. 11B NMR: δ 34.6.
Results and Discussion
Synthesis and characterization of [PhB(μ-
NtBu)2AsN(tBu)X] (1, X ؍ H; 2a, X ؍ Li)
The reaction of [PhB(μ-NtBu)2]AsCl with tBuN(H)Li in di-
ethyl ether produces [PhB(μ-NtBu)2AsN(tBu)H] (1) as an
analytically pure, white powder in ca. 80 % yield (eq. 1).
1
X-ray structure determination
The H NMR spectrum of 1 shows a singlet at 3.20 ppm
for the NH hydrogen and two singlets at 1.32 and 1.09 ppm
with relative intensities 1:2 for the exocyclic N(H)tBu and
endocyclic NtBu groups, respectively. The 11B NMR spec-
trum of 1 exhibits a single resonance at 34.7 ppm.
Crystals of {[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 (1·LiI) and [PhB(μ-
NtBu)2AsN(tBu)Li]2 (2a) were coated with Paratone 8277 oil and
mounted on a glass fiber. Diffraction data were collected on a
Nonius KappaCCD diffractometer using monochromated MoKα
˚
radiation (λ ϭ 0.71073 A) at Ϫ100 °C. The data sets were corrected
[PhB(μ-NtBu)2]AsCl ϩ tBuN(H)Li Ǟ
[PhB(μ-NtBu)2AsN(tBu)H] ϩ LiCl (1)
(1)
for Lorentz and polarization effects, and empirical absorption cor-
rection was applied to the net intensities. The structures were solved
by direct methods using SHELXS-97 [8] and refined using
SHELXL-97 [9]. In the structure of 1·LiI, the NH hydrogen atom
was located from the difference Fourier map and refined normally.
After the full-matrix least-squares refinement of the non-hydrogen
The treatment of 1 with one equivalent of nBuLi is ac-
companied by the disappearance of the NH resonance in
876
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Z. Anorg. Allg. Chem. 2008, 875Ϫ879

The Polycyclic Dimers {[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ-NtBu)2AsN(tBu)Li]2
the 1H NMR spectrum, which now exhibits two singlets for
A similar structure has been reported for the phos-
NtBu groups at 1.29 and 1.09 ppm in a 1:2 intensity ratio.
A single resonance is observed in the Li NMR spectrum
at 1.01 ppm, consistent with the formation of the lithium
derivative [PhB(μ-NtBu)2AsN(tBu)Li] (2a) (eq. (2)).
phorus-containing analogue, [PhB(μ-NtBu)2PN(tBu)Li]2
(2b) [7]. Significantly, the bam ligands in 2a adopt a cisoid
arrangement with respect to the central Li2N2 ring giving a
U-shaped structure, whereas a transoid conformation re-
sulting in an S-shaped arrangement is observed for 2b
(Scheme 1). This difference can be explained in the context
of the laddering principle for describing the oligomeric
structures of alkali metal amides [10]. In cases where lad-
dering is limited to dimerization by bulky substituents, a
transoid geometry is most often observed [11], although ex-
ceptions have been noted [12]. The pentacyclic structures of
2a and 2b may be considered as six-rung ladders formed by
the dimerization of a lithium amide in which one of the
substituents on nitrogen is a (bam)E (E ϭ P, As) unit. In
view of the shorter P-N compared to As-N bonds, the
transoid geometry in 2b may be preferred in order to mini-
mize interactions between tert-butyl groups attached to the
first and sixth rungs of the ladder. We note, however, that
the curvature of the cisoid arrangement in 2a is small so
that these steric interactions are limited.
7
[PhB(μ-NtBu)2AsN(tBu)H] ϩ nBuLi Ǟ
[PhB(μ-NtBu)2AsN(tBu)Li] ϩ nBuH (2)
(1)
(2a)
The crystal structure of 2a with the atomic numbering
scheme is depicted in Figure 1, and the pertinent bond par-
ameters are summarized in Table 2. The structure is com-
prised of a centrosymmetric dimer in which monomeric
[PhB(μ-NtBu)2AsN(tBu)]ϪLiϩ units are formed by N,NЈ-
chelation of the anion to the Liϩ cation through the amide
nitrogen and one of the bam nitrogens. These units are
linked by Li-N interactions to give a six-rung ladder with
one three-coordinate and two four-coordinate nitrogens in
each half of the molecule.
Scheme 1 The cisoid and transoid conformations observed for 2a
and 2b, respectively.
Figure 1 Crystal structure of [PhB(μ-NtBu)2AsN(tBu)Li]2 (2a)
with the atomic numbering scheme. Hydrogen atoms have been
omitted for clarity. a Symmetry operation: Ϫx, y, 1.5Ϫz.
The As-N bond length to the exocyclic amide nitrogen in
2a is ca. 0.15 A shorter than the As-N bonds to the bam
˚
ligand suggesting a stronger electrostatic interaction be-
tween As1 and N3. The As-N bond to the three-coordinate
nitrogen atom (N2) in the bam ligand is unusually long
˚
Table 2 Selected bond lengths/A and angles/° in {[PhB(μ-NtBu)2-
AsN(tBu)H]LiI}2 (1·LiI) and [PhB(μ-NtBu)2AsN(tBu)Li]2 (2a)
˚
˚
(1.923(4) A), cf. 1.789(3) A in LiAs[PhB(μ-NtBu)2];
˚
1.845(2) and 1.876(2) A in (Et2O)LiAs[PhB(μ-NtBu)2] [6],
1·LiI
2a
1·LiI
2a
˚
and only ca. 0.03 A shorter than the As-N bond to the four-
˚
Distances
As1-N1
As1-N2
As1-N3
B1-N1
coordinate nitrogen (N1). The disparity of ca. 0.08 A in the
1.917(3) 1.958(4)
1.870(3) 1.923(4)
1.858(3) 1.787(4)
1.481(6) 1.481(7)
1.427(6) 1.403(6)
Li1-N1
Li1-N3
Li1-N3a)
Li1-I1
2.195(7) 2.071(10)
2.145(7) 2.031(9)
B-N bond lengths is, however, fairly typical for the bam
ligand when three- and four-coordinate nitrogen atoms are
present [1, 6]. The three Li-N interactions in 2a are almost
equal in length, and those involving the amide nitrogen
(Li1-N3, Li1-N3a) are comparable to the values reported
for the phosphorus analogue 2b [7]. Curiously, the differ-
ence in conformation results in a shorter Li-N interaction
Ϫ
2.056(10)
2.682(7)
2.767(7)
Ϫ
Ϫ
B1-N2
Li1-I1b)
Angles
N1-As1-N2
N1-As1-N3
73.5(1)
96.2(1)
71.2(2)
99.2(2)
N1-Li1-N3
N1-Li1-I1
80.7(2) 88.1(4)
127.4(3)
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
N2-As1-N3 101.9(2) 106.3(2)
N1-Li1-I1b) 117.5(3)
N1-B1-N2
B1-N1-As1
B1-N2-As1
Li1-N1-As1
Li1-N3-As1
102.3(3) 103.0(4)
N3-Li1-I1
N3-Li1-I1b)
I1-Li1-I1b)
Li1-I1-Li1b)
128.4(3)
87.2(3)
102.5(2)
77.5(2)
˚
(by ca. 0.10 A) to the four-coordinate nitrogen in the bam
89.2(2)
92.8(3)
89.9(2)
93.1(2)
89.5(3)
93.2(3)
82.8(3)
88.3(3)
ligand (N1) in 2a than the corresponding distance in 2b
˚
(2.171(3) A) [7]. All four-membered rings (AsBN2, AsLiN2,
Li2N2) in 2a are notably non-planar with torsion angles in
the range 8.7-15.3°.
Symmetry operations: a) Ϫx, y, 1.5Ϫz b) 1Ϫx, 2Ϫy, 1Ϫz.
Z. Anorg. Allg. Chem. 2008, 875Ϫ879
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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877

J. Konu, T. Chivers
Oxidation of 2a with I2; crystal structure of
{[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 (1·LiI)
In an attempt to produce the neutral aminyl radical [PhB(μ-
NtBu)2AsN(tBu)]и, the reaction of 2a with one-half equiva-
lent of I2 was performed in diethyl ether at Ϫ80 °C (eq. (3)).
After the addition of iodine a clear, colorless solution was
observed; there was no indication of the intermediate for-
mation of a colored paramagnetic species. Subsequent re-
moval of the solvent gave a white powder.
1
[PhB(μ-NtBu)2AsN(tBu)Li] ϩ /2 I2 Ǟ
[PhB(μ-NtBu)2AsN(tBu)] ϩ LiI (3)
(2a)
1H NMR spectrum of the product measured in d8-THF
revealed three singlets at 3.21, 1.34 and 1.10 ppm in a rela-
tive ratio of 1:9:18, in addition to the characteristic reson-
ances for the phenyl group. The 13C{1H} NMR spectrum
showed two signals at 52.6 and 52.2 ppm for the α-carbons
and two resonances at 33.8 and 33.7 ppm for the methyl
carbons of the NtBu-groups. Single resonances were ob-
7
served at 34.6 and 0.79 ppm in the 11B and Li NMR spec-
tra, respectively. The similarity of these resonances with
those observed for 1, specifically the presence of the signal
at 3.21 ppm with an intensity of 1 relative to the intensities
1
of 9 and 18 observed for the two NtBu signals in the H
NMR spectrum, suggests the presence of an N-H func-
tionality, which may be explained by the formation of 1
due to hydrogen abstraction from the solvent. The single
resonance in the Li NMR spectrum is attributed to the
lithium iodide by-product.
Figure
2
(a) Crystal structure of {[PhB(μ-NtBu)2AsN-
7
(tBu)H]LiI}2 (1·LiI), and (b) the pentacyclic (NBNAsNHLiI)2-
core in 1·LiI with the atomic numbering scheme. Hydrogen atoms
bonded to carbons have been omitted for clarity. a Symmetry ope-
ration: 1Ϫx, 2Ϫy, 1Ϫz.
The white powder was recrystallized from toluene. An
X-ray crystal structure determination confirmed the forma-
tion of 1 and revealed that LiI is incorporated in the struc-
ture to give an adduct in which 1 is N,NЈ-chelated to the
Liϩ cation through the exocyclic N(H)tBu group and one
of the bam nitrogens; iodide counterions bridge two mono-
meric units to give a centrosymmetric dimer (Figure 2a).
The overall structure is pentacyclic with a central Li2I2 ring
which is tilted by ca. 76° with respect to the neighboring
LiAsN2 rings. The bam ligands in 1·LiI adopt a trans ar-
rangement with respect to the planar Li2I2 ring (Figure 2b).
A number of complexes in which LiI is entrapped in ladder
[13] or cubic [14] structures have been reported. The most
relevant examples for comparison with the structure of
1·LiI are the dimeric adducts [(2,6-dimethylpyridine)LiI]2
[15] and [(2-pyridyl-CH2N(H)SitBuMe2)LiI]2 [16], both of
which contain central Li2I2 rings with four-coordinate Liϩ
ions.
pounds (Table 2). The As-N bond to the exocyclic amide
nitrogen in 1·LiI is equal in length with the As-N bond to
the three-coordinate nitrogen in the bam ligand in 1·LiI.
The As1-N3 bond length is, however, considerably longer
˚
(by 0.07 A) than the corresponding bond in 2a. The anal-
ogous disparity in the P-N bond lengths is less pronounced
in the phosphorus derivatives, [PhB(μ-NtBu)2PN(tBu)X]
(X ϭ H, Li) [7], in which the hydrogen-containing com-
pound is monomeric. The difference in As-N bond lengths
between 1·LiI and 2a is, however, an indication of weaken-
ing of the electrostatic interaction between As1 and N3 as
a result of the N-H bond formation in 1·LiI.
The Li···N interactions in 1·LiI are expectedly weaker
˚
(by ca. 0.12 A) than the corresponding contacts in 2a due
to the strong Liϩ···IϪ connections in 1·LiI. Consistently
˚
In order to provide a context for a comparison of metri-
cal parameters, the structure of 1·LiI can be related to that
of 2a by the formal addition of HI to each of the monomer
units. The protonation of N3/N3a in 2a results in cleavage
of the Li1-N3/N3a bonds. The As-N bonds in the bam
with 2a, the Li···N contact to the bam nitrogen is ca. 0.05 A
longer than the analogous interaction to the amide nitrogen
in 1·LiI. The difference in Li···N interactions is also re-
flected in the inequality of 0.08 A in the Li···I contacts
[2.682(7) vs. 2.767(7) A], cf. 2.754(5) and 2.783(5) A in
[(2-pyridyl-CH2N(H)SitBuMe2)LiI]2 [16].
˚
˚
˚
˚
ligand in 1·LiI are ca. 0.05 A shorter than in the lithium
derivative 2a, whereas no significant difference can be ob-
served in the B-N bond lengths between the two com-
Shortening of the As-N bonds in 1·LiI compared to 2a
expectedly results in ca. 2.3° wider N-As-N angle, whereas
878
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 875Ϫ879

The Polycyclic Dimers {[PhB(μ-NtBu)2AsN(tBu)H]LiI}2 and [PhB(μ-NtBu)2AsN(tBu)Li]2
[3] T. Chivers, C. Fedorchuk, G. Schatte, M. Parvez, Inorg. Chem.
2003, 42, 2084Ϫ2093.
[4] T. Chivers, D. J. Eisler, C. Fedorchuk, G. Schatte, H. M.
the remaining bond angles within the bam ligands are equal
within estimated standard deviation. Similarly, lengthening
of the As1-N3 bond and Li···N interactions in 1·LiI affords
narrower N-As1-N3 and N1-Li1-N3 angles compared to
2a. The four-coordinate Liϩ cation shows significant distor-
tion from tetrahedral geometry with the angles in the wide
range of 80.7(2)Ϫ128.4(3)°. The planar Li2I2 four-mem-
bered ring exhibits considerable deviation from ideal square
with the bond angles of 77.5(2) and 102.5(2)° for Li-I-Li
and I-Li-I, respectively, cf. 76.2(2) and 103.8(2)° for [(2-pyr-
idyl-CH2N(H)SitBuMe2)LiI]2 [16].
In an attempt to prevent the formation of 1 in the one-
electron oxidation of 2a (eq. 3), the reaction was repeated
in the hydrogen-free solvent CS2 at Ϫ80 °C. At room tem-
perature, a red solution was obtained, but no EPR signal
could be detected. Recrystallization attempts from CS2
failed and the product decomposed in organic solvents, e.g.
benzene, to give 1 and a number of unidentified com-
pounds.
´
Tuononen, R. T. Boere, Chem. Commun. 2005, 3930Ϫ3932.
[5] T. Chivers, D. J. Eisler, C. Fedorchuk, G. Schatte, H. M.
´
Tuononen, R. T. Boere, Inorg. Chem. 2006, 45, 2119Ϫ2131.
[6] J. Konu, M. S. Balakrishna, T. Chivers, T. W. Swaddle, Inorg.
Chem. 2007, 46, 2627Ϫ2636.
[7] T. Chivers, C. Fedorchuk, G. Schatte, J. K. Brask, Can. J.
Chem. 2002, 80, 821Ϫ831.
[8] G. M. Sheldrick, SHELXS-97, Program for Crystal Structure
Determination, University of Göttingen, Göttingen (Ger-
many) 1997.
[9] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen, Göttingen (Germany)
1997.
[10] a) A. Downard, T. Chivers, Eur. J. Inorg. Chem. 2001,
2193Ϫ2201; b) R. E. Mulvey, Chem. Soc. Rev. 1998, 339Ϫ346.
[11] M. Beswick, D. S. Wright, in Comprehensive Organometallic
Chemistry II, Vol.1 (Ed.: C. Housecroft), Pergamon, Oxford,
1995, p. 9.
[12] W. Clegg, K. W. Henderson, L. Horsburgh, F. Mackenzie, R.
E. Mulvey, Eur. J. Inorg. Chem. 1998, 1, 53Ϫ56.
[13] T. Chivers, A. Downard, M. Parvez, Inorg. Chem. 1999, 38,
4347Ϫ4353.
[14] a) P. A. van der Schaaf, M. P. Hogerheided, D. M. Grove, A.
L. Spek, G. van Koten, J. Chem. Soc. Chem. Commun. 1992,
1703Ϫ1705; b) R. Fleischer, S. Freitag, D. Stalke, J. Chem.
Soc. Dalton Trans. 1998, 193Ϫ198.
Acknowledgements. The authors gratefully acknowledge financial
support from the Natural Sciences and Engineering Research
Council (Canada).
References
[1] For a recent review, see C. Fedorchuk, M. Copsey, T. Chivers,
Coord. Chem. Rev. 2007, 251, 897Ϫ924.
[15] C. L. Raston, C. R. Whitaker, A. H. White, Inorg. Chem. 1989,
28, 163Ϫ165.
[2] D. R. Manke, D. G. Nocera, Inorg. Chem. 2003, 42,
4431Ϫ4436.
[16] M. Westerhausen, A. N. Kneifel, P. Mayer, Z. Anorg. Allg.
Chem. 2006, 632, 634Ϫ638.
Z. Anorg. Allg. Chem. 2008, 875Ϫ879
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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