Reaction of {HC(CMeNAr)2}Li (Ar = 2,6-i-Pr2C6H3) with indium monochloride to yield the In-In bonded dimer [{HC(CMeNAr)2}InCl]2 and the hydroxide [{HC(CMeNAr)2}InCl(μ-OH)]2

Article abstract of DOI:10.1016/S0277-5387(01)01033-6

The reaction of the sterically encumbered lithium β- diketiminate {HC(CMeNAr)₂}Li (Ar = 2,6-i-Pr₂C₆H₃) with InCl in THF at approximately -78 °C yielded In metal and [{HC(CMeNAr)₂}InCl]₂ (1) as well as minor amounts of the hydroxide [{HC(CMeNAr)₂}In(Cl)(μ-OH)]₂, 2. The compounds 1 and 2 were characterized by ¹H, ¹³C NMR, IR spectroscopy and X-ray crystallography. The centrosymmetric structure of 1 features an In-In bond that is 2.8343(7) A? long which is well within the known range of In-In single bond distances. The metal β-diketiminate ring (i.e. C₃N₂In) is folded along the NN vector and features an out of plane deviation by the indium of 0.8953 A? and a dihedral angle between the C₃N₂ and InN₂ arrays of 145.8°. This can be attributed to steric effects of the Ar groups on the β-diketiminiate ligand. The structure of the hydroxide derivative 2 is a dimer in which the indiums are bridged by hydroxides to afford a planar In₂O₂ core with an average In-O distance of 2.13(2) A?. Attempted reduction of the dihalide compounds {HC(CMeNAr)₂}InX₂ (X = Cl, I) with sodium or potassium led to the formation of metallic indium and the free β-aminoimine (Ar)NC(Me₂)CHC(Me₂)N(Ar)H rather than the desired In(I) species, {HC(CMeNAr)₂}In:.

Full text of DOI:10.1016/S0277-5387(01)01033-6

Polyhedron 21 (2002) 525–529
www.elsevier.com/locate/poly
Reaction of {HC(CMeNAr)2}Li (Ar=2,6-i-Pr2C6H3) with indium
monochloride to yield the InꢀIn bonded dimer
[{HC(CMeNAr)2}InCl]2 and the hydroxide
[{HC(CMeNAr)2}InCl(m-OH)]2
Matthias Stender, Philip P. Power *
Department of Chemistry, Uni6ersity of California Da6is, One Shields A6enue, Da6is, CA 95616, USA
Received 17 August 2001; accepted 27 November 2001
Abstract
The reaction of the sterically encumbered lithium b-diketiminate {HC(CMeNAr)2}Li (Ar=2,6-i-Pr2C6H3) with InCl in THF at
approximately −78 °C yielded In metal and [{HC(CMeNAr)2}InCl]2 (1) as well as minor amounts of the hydroxide
1
[{HC(CMeNAr)2}In(Cl)(m-OH)]2, 2. The compounds 1 and 2 were characterized by H, 13C NMR, IR spectroscopy and X-ray
,
crystallography. The centrosymmetric structure of 1 features an InꢀIn bond that is 2.8343(7) A long which is well within the
known range of InꢀIn single bond distances. The metal b-diketiminate ring (i.e. C3N2In) is folded along the N···N vector and
,
features an out of plane deviation by the indium of 0.8953 A and a dihedral angle between the C3N2 and InN2 arrays of 145.8°.
This can be attributed to steric effects of the Ar groups on the b-diketiminiate ligand. The structure of the hydroxide derivative
2 is a dimer in which the indiums are bridged by hydroxides to afford a planar In2O2 core with an average InꢀO distance of
,
2.13(2) A. Attempted reduction of the dihalide compounds {HC(CMeNAr)2}InX2 (X=Cl, I) with sodium or potassium led to the
formation of metallic indium and the free b-aminoimine (Ar)NC(Me2)CHC(Me2)N(Ar)H rather than the desired In(I) species,
{HC(CMeNAr)2}In:. © 2002 Elsevier Science Ltd. All rights reserved.
Keywords: b-Diketiminate; Low valent indium; Bulky ligands; Metal–metal bonds
known, although there is widespread interest in In(I)
compounds as evidenced by the growing number of
organometallic [5–7] and related derivatives [7,8] of
In(I) that have been synthesized. Almost all of the
organoindium(I) compounds are associated in the solid
state. However, the trispyrazolylborate complexes
HB(pz)3In (pz=3-phenylpyrazolyl [7], 3,5-di-tert-
butylpyrazolyl [8a], 3-tert-butylpyrazolyl [8b], 3,5-
(CF3)2-pyrazolyl [8b,8c]), in which the In atom is
coordinated by three N donors, are monomeric in the
solid state. There is only one example of a monomeric,
organometallic In(I) species in the literature and this
species involves the bulky m-terphenyl group ꢀC6H3-
2,6-Trip2 (Trip=ꢀC6H2-2,4,6-i-Pr3) [9]. This ligand
shows a steric resemblance to the bulkyl b-diketiminate
[HC(CMeNAr)2]− (Ar=2,6-i-Pr2C6H3) [10]. Due to
the very rich chemistry already displayed by the
monomeric M(I) species [HC(CMeNAr)2]M: (M=Al,
Ga) [11–14] it is of interest to synthesize the In ana-
1. Introduction
Recent years have witnessed an impressive revival of
interest in bidentate, b-diketiminate ligands which have
been known for more than four decades [1]. Much of
the recent work has focused on more sterically encum-
bered derivatives that feature bulky substituents at the
nitrogens. These ligands have proved to be very useful
in a variety of roˆles including the stabilization of low
coordinate, low valent main Group 13 metal complexes
[2–4]. Through the use of the ligand [HC(CMeNAr)2]−
(Ar=2,6-i-Pr2C6H3) the unusual, two-coordinate,
monomeric M(I) species [HC(CMeNAr)2]M: (M=Al
[3], Ga [4]), which are analogous to carbenes, have been
stabilized. The corresponding In(I) species are un-
* Corresponding author. Tel.: +1-530-752-6913; fax: +1-530-752-
8995.
E-mail address: pppower@ucdavis.edu (P.P. Power).
0277-5387/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)01033-6

526
M. Stender, P.P. Power / Polyhedron 21 (2002) 525–529
logue and explore its chemistry. We now report that the
reaction of {HC(CMeNAr)2}Li with InCl leads not to
the expected monomeric {HC(CMeNAr)2}In analogue
but to disproportionation reactions that yield the unex-
pected InꢀIn bonded species [{HC(CMeNAr)2}InCl]2
(1) and the hydroxo complex [{HC(CMeNAr)2}InCl(m-
OH)]2 (2).
cold hexane (40 ml, ca. −10 °C). The solution was
allowed to come to ambient temperature where the
dark precipitate which had formed (indium metal and
lithium chloride) was allowed to settle. The amber
supernatant solution was then filtered through celite.
Concentration under reduced pressure produced a low
yield of large colorless needles which were collected
after ca. 8 h in a ca. 4 °C refrigerator. These were
identified as the hydroxide derivative 2. Yield: 0.05 g,
0.037 mmol, 15%, melting point (decomposition) m.p.
2. Experimental
1
(dec.)\100 °C. H NMR (400 MHz, C6D6): l 7.2–7.1
(m, 12H, Ph), 4.63 (s, 2H, g-CH), 3.31 (sept, 8H,
J=6.8 Hz, CHMe2), 1.48 (s, 12H, Me), 1.25 (d, 24H,
J=6.8 Hz, CHMe2), 1.10 (d, 24H, J=6.8 Hz,
CHMe2), 0.93 (s, broad, 2H, OH); 13C NMR (C6D6): d
(ppm)=159.2 (CN), 142.7, 141.3, 125.8, 123.6 (Ph),
94.2 (g-C), 28.6 (CHMe2), 24.4 (CHMe2), 23.4
(CHMe2), 20.7 (Me); IR (Nujol): w (cm−1)=3660
(wOH). The supernatant solution was decanted and
concentrated under reduced pressure to incipient crys-
tallization (ca. 30 ml). Storage for 30 h in a ca. 4 °C
refrigerator yielded the product 1 as colorless crystals.
2.1. Synthesis
2.1.1. General procedures
All manipulations were carried out using modified
Schlenk techniques under an atmosphere of N2 or in a
Vacuum Atmospheres HE-43 drybox. All solvents were
distilled from Na–K alloy and degassed three times
before use. The compound {HC(CMeNAr)2}H (Ar=
C6H3-2,6-i-Pr2) was prepared as previously described
[10]. InCl (99.99%) was purchased commercially and
used as received.
1
Yield: 0.23 g, 0.20 mmol, 16%, m.p. 155–157 °C. H
NMR (400 MHz, C6D6): d 7.2–7.0 (m, 12H, Ph), 4.73
(s, 2H, g-CH), 3.33 (sept, 8H, J=6.8 Hz, CHMe2),
1.58 (s, 12H, Me), 1.35 (d, 24H, J=6.8 Hz, CHMe2),
1.21 (d, 24H, J=6.8 Hz, CHMe2); 13C NMR (C6D6): l
(ppm)=171.8 (CN), 144.5, 138.0, 124.8 (Ph), 98.1 (g-
C), 28.3 (CHMe2), 25.8 (CHMe2), 25.2 (CHMe2), 24.6
(Me).
The attempted reduction of the dihalides
{HC(CMeNAr)2}InX2 (X=Cl, I) with finely divided
potassium in toluene resulted in the precipitation of In
metal at room temperature (r.t.).
2.2. [{HC(CMeNAr)2}InCl]2 (1) and
[{HC(CMeNAr)2}InCl(v-OH]2 (2)
A solution of {HC(CMeNAr)2}Li in THF (generated
by reaction of 1.06 g of {HC(CMeNAr)2}H and 1.6 ml
of 1.6 M n-BuLi in 20 ml of THF with cooling in an ice
bath) was added dropwise to a suspension of InCl (0.42
g, 2.79 mol) in THF (30 ml) with rapid stirring and
cooling in a dry ice acetone bath. The reaction mixture
was stirred for 2 h and then allowed to come to
approximately −10 °C (ice–NaCl bath). After stirring
for an additional 1 h the solvents were removed under
reduced pressure. The solid residue was extracted with
2.3. X-ray data collection
X-ray quality crystals of 1 or 2 were removed from
the Schlenk tube and immediately covered with a layer
of hydrocarbon oil. A suitable crystal was selected,
attached to a glass fiber and placed in the cold temper-
ature N2-stream as previously described [15]. The data
were collected near 90 K using a Bruker SMART 1000
Table 1
Data collection parameters for 1 and 2
1·hexane
2·2PhMe
C72H100Cl2In2N4O2
1354.13
monoclinic
P21/c
101.440(2)
13.6314(17)
13.6336(17)
18.915(2)
3445.3(7)
2
Formula
C64H96Cl2In2N4
1222.98
monoclinic
P21/c
102.051(2)
13.5411(10)
13.3095(10)
17.2363(13)
3038.0(4)
2
,
diffractometer and Mo Ka (u=0.71073 A) radiation.
Formula weight
Crystal system
Space group
i (°)
The SHELXTL version 5.03 program package was used
for the structure solutions and refinements [16]. Ab-
sorption corrections were applied using the SADABS
program [17]. The structures were solved by direct
methods and refined by full matrix, least-squares proce-
dures. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included in the refinement
at calculated positions using a riding model included in
the SHELXTL program package. Some details of the
data collection and refinement are given in Table 1.
Selected bond distances and angles for 1 and 2 are
provided in Table 2.
,
a (A)
,
b (A)
,
c (A)
3
,
V (A )
Z
v(Mo Ka) (mm−1
)
0.888
90(2)
0.0650
0.1117
0.792
90(2)
0.0260
0.0648
T (K)
R1
wR2
R1=SꢀꢀF0ꢀ−ꢀFcꢀꢀ/ꢀF0ꢀ. wR2=[Sꢀ(F02−Fc2)2S[ꢀ(F02]]1/2
.

M. Stender, P.P. Power / Polyhedron 21 (2002) 525–529
527
Table 2
Selected bond lengths (A) and angles (°) for 1 and 2
[18] that the reaction of the aza alkyl lithium compound
PhC{(Me3Si)2C}{N(SiMe3)}Li with InBr afforded the
,
InꢀIn
bonded
dimer
[PhC{C(SiMe3)2}{N-
1
2
(SiMe3)2}InBr]2. This reaction is significant in that the
uninegative, bidentate nature of this ligand is related to
the b-diketiminate {HC(CMeNAr)2}−. Other examples
of disproportionation reactions of various lithium
amide ligands with indium(I) halides to afford InꢀIn
bonded products are also known [19,20].
Bond lengths
In(1)ꢀN(1)
In(1)ꢀN(2)
In(1)ꢀCl(1)
In(1)ꢀIn(1A)
N(1)ꢀC(1)
N(2)ꢀC(3)
C(1)ꢀC(2)
C(2)ꢀC(3)
2.169(4)
2.172(4)
2.4142(14) In(1)ꢀCl(1)
2.8342(7)
1.335(7)
1.347(7)
1.389(7)
1.392(7)
In(1)ꢀN(1)
In(1)ꢀN(2)
2.1654(12)
2.1874(12)
2.3876(4)
2.1148(11)
2.1534(11)
1.3343(19)
1.3325(19)
1.407(2)
In(1)ꢀO(1)
In(1)ꢀO(1A)
N(1)ꢀC(1)
N(2)ꢀC(3)
C(1)ꢀC(2)
C(2)ꢀC(3)
3.2. Structures
1.401(2)
The structure of 1 is illustrated in Fig. 1. Selected
bond distances and angles are provided in Table 2. The
structure possesses a center of symmetry at the mid-
point of the InꢀIn bond. The indiums are four-coordi-
nate with a very distorted tetrahedral geometry at the
Bond angles
N(1)ꢀIn(1)ꢀN(2)
N(1)ꢀIn(1)ꢀCl(1)
N(2)ꢀIn(1)ꢀCl(1)
N(1)ꢀIn(1)ꢀIn(1A)
N(2)ꢀIn(1)ꢀIn(1A)
87.85(16) N(1)ꢀIn(1)ꢀN(2)
99.39(12) N(1)ꢀIn(1)ꢀCl(1)
99.81(11) N(2)ꢀIn(1)ꢀCl(2)
126.60(11) O(1)ꢀIn(1)ꢀO(1A)
126.75(11) O(1)ꢀIn(1)ꢀN(1)
87.26(5)
106.12(4)
103.91(3)
71.47(5)
145.70(5)
94.48(5)
,
metals. The InꢀIn distance is 2.8334(7) A which may be
Cl(1)ꢀIn(1)ꢀIn(1A) 110.59(4)
O(1)ꢀIn(1)ꢀN(2)
In(1)ꢀO(1)ꢀIn(1A) 108.53(5)
N(1)ꢀC(1)ꢀC(2)
C(1)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀN(2)
regarded as a typical one since it falls in the middle of
N(1)ꢀC(1)ꢀC(2)
C(1)ꢀC(2)ꢀC(3)
C(2)ꢀC(3)ꢀN(2)
125.8(3)
128.5(5)
125.9(5)
,
the currently known range (2.696(2)–2.922(1) A [21,22])
124.66(13)
129.27(14)
124.72(14)
for neutral molecular InꢀIn singly bonded species. The
,
InꢀN distances, av. 2.171(2) A, are marginally longer
,
than the 2.111(3)–2.147(1) A range observed in the
{HC(CMeNAr)2}InX2 (X=Cl or I) [2], but they are
,
3. Discussion
shorter than the average distance of 2.197(4) A in
{HC(CMeNAr)2}InMe2 [2]. The variation in these dis-
tances illustrates the influence of coligands on the effec-
tive ionic radius of indium. More electronegative
co-ligands contract the radius, whereas more elec-
tropositive ligands expand it; hence the longer InꢀN
distances in {HC(CMeNAr)2}InMe2. The C3N2 ring
fragment of the b-diketiminate ligand has planar ge-
ometry and the CꢀC and CꢀN distances are symmetric
indicating delocalization of the negative charge. How-
ever, the C3N2In ring is folded along the N···N vector
such that there is a dihedral angle of 145.8° between the
3.1. Synthesis
The compounds 1 and 2 were both obtained by the
addition of {HC(CMeNAr)2}Li, generated in THF, to
a suspension of InCl in THF with cooling in an approx-
imately −78 °C dry ice acetone bath. None of the
expected product {HC(CMeNAr)2}In: was isolated
from the reaction under these conditions. This was to
some extent surprising since the aluminum(I) and galli-
um(I) analogues of this putative indium species were
already known [3,4]. Furthermore, the one coordinate
indium derivative of the ꢀC6H3-2,6-Trip2 (Trip=C6H2-
2,4,6-i-Pr3) group, which bears a close steric resem-
blance to the {HC(CMeNAr)2} ligand, was already
characterized [9]. Moreover 2,6-Trip2H3C6In: was syn-
thesized by the direct reaction of the lithiated terphenyl
ligand with InCl in THF under almost identical condi-
tions to those described in this paper. In view of the
fact that indium metal, lithium chloride and free ligand
were produced during the course of the attempted
synthesis of {HC(CMeNAr)2}In:, it seems probable
that disproportionation and ligand redistribution reac-
tions occur to give the observed product 1 in 16% yield.
Small amounts of the hydroxo-bridged species 2 were
also obtained in much lower yield. The latter species is
probably the result of moisture contamination and it is
possible to carry out the reaction to generate negligible
amounts of 2 by using extremely strict anaerobic and
anhydrous procedures. In spite of the unanticipated
nature of the product 1, it has been recently reported
,
InN2 and C3N2 planes. The indium atom lies 0.895 A
from the extended C3N2 plane. This folding is similar to
that reported in {HC(CMeNAr)2}InMe2 but it is higher
than that seen in the halide derivatives. Another feature
Fig. 1. Thermal ellipsoid plot (30%) of 1. H atoms are not shown.

528
M. Stender, P.P. Power / Polyhedron 21 (2002) 525–529
known to be stable. The existence of this compound
and the aluminum and gallium species
{HC(CMeNAr)}M: (M=Al [3] or Ga [4]) strongly
suggest that {HC(CMeNAr)}In: should be obtainable
under different reaction conditions.
5. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC nos. 169219 and 169220 for com-
pounds 1 and 2. Copies of this information may be
obtained from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44-1233-336-033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://www.
ccdc.cam.ac.uk).
Fig. 2. Thermal ellipsoid plot (30%) of 2. H atoms are not shown.
of the structure of 1 is the narrow NꢀInꢀN angle and
this is similar to those reported for the halide and
methyl derivatives [2] which all have NꢀInꢀN angles
that are less than 90°. The InꢀCl bond length is
2.4142(14) A which is very similar to the 2.4174(9) A in
the tropoiminate complex (Me2ATI)2InCl [23] and
Acknowledgements
We are grateful to the National Science Foundation
and the Petroleum Research Fund administered by the
American Chemical Society for financial support.
,
,
,
slightly longer than the average of 2.396(3) A in
{HC(CMeNAr)2}InCl2 [2] although the accuracy of the
latter distance is reduced by the presence of bromine
contaminant.
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a crystallographically required planarity for the In2O2
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angles at indium and oxygen. The two InꢀO distances
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the sterically related species 2,6-Trip2H3C6In: [9] is

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