Crystal structure of dimerized 1,3-diisopropyl carbodiimide

Article abstract of DOI:10.1007/s10870-010-9892-6

A crystal structure of dimerized 1,3-diisopropyl carbodiimide (CDI) has been obtained and its synthesis through a reaction of CDI with aluminum chloride (AlCl₃) has been studied. It possesses space group P2₁/c, with a = 9.352(5), b = 7.956(4), c = 11.405(6) A and β = 112.465(5)°. It has been observed that this reaction is catalytic with respect to AlCl₃. Kinetic studies of the dimer show that its decomposition into CDI is first order with respect to the dimer. The reactivity of the dimer with metals has been investigated through reactions with methyl lithium and alane. The thermal stability of the dimer has been investigated by thermal gravimetric analysis and differential scanning calorimetry.

Full text of DOI:10.1007/s10870-010-9892-6

J Chem Crystallogr (2011) 41:375–378
DOI 10.1007/s10870-010-9892-6
ORIGINAL PAPER
Crystal Structure of Dimerized 1,3-Diisopropyl Carbodiimide
Peter George Gordon
Se a´ n Thomas Barry
•
Glenn P. A. Yap
•
Received: 4 May 2010 / Accepted: 3 September 2010 / Published online: 17 September 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A crystal structure of dimerized 1,3-diisopropyl
carbodiimide (CDI) has been obtained and its synthesis
through a reaction of CDI with aluminum chloride (AlCl3)
carbodiimide insertion over aluminum compounds, pro-
posing the mechanism illustrated in Scheme 1 [3]. Alu-
minum is often used as a starting point with new ligands
due to its availability, ease of use and strong acidic nature.
Compound 1 was first observed as a byproduct of our
investigations; subsequent examination of its utility in the
synthesis of volatile metal-bearing precursors showed little
promise but an investigation of its synthesis and thermol-
ysis was performed to extend our understanding of alu-
minum-carbodiimide interactions. Previous work on the
synthesis of carbodiimide dimers is scarce but has been
performed employing alkylating agents such as dimethyl
sulphate in the absence of solvent at room temperature [4]
and by a tandem aza-Wittig/[2 ? 2] cycloaddition of car-
bodiimides employing bis(iminophosphoranes) [5, 6].
has been studied. It possesses space group P2 /c, with
1
˚
a = 9.352(5), b = 7.956(4), c = 11.405(6) A and b =
1
12.465(5)°. It has been observed that this reaction is
catalytic with respect to AlCl . Kinetic studies of the dimer
3
show that its decomposition into CDI is first order with
respect to the dimer. The reactivity of the dimer with
metals has been investigated through reactions with methyl
lithium and alane. The thermal stability of the dimer has
been investigated by thermal gravimetric analysis and
differential scanning calorimetry.
Keywords Carbodiimide Á Crystal structure Á Aluminum
chloride
Experimental
Introduction
A single crystal was mounted on a thin glass fiber using
viscous oil and then cooled to the data collection temper-
ature. Data were collected on a Bruker AX SMART 1k
CCD diffractometer using 0.3° x-scans at 0, 90, and 180°
in F. Unit-cell parameters were determined from 60 data
frames collected at different sections of the Ewald sphere.
Semiempirical absorption corrections based on equivalent
reflections were applied. The structures were solved by
direct methods, completed with difference Fourier syn-
theses, and refined with full-matrix least-squares proce-
dures based on F2. All non-hydrogen atoms were refined
with anisotropic displacement parameters. All hydrogen
atoms were treated as idealized contributions. All scatter-
ing factors and anomalous dispersion factors are contained
in the SHELXTL 6.12 program library. CIF has been
submitted under CCDC 775576.
Our interest in carbodiimides stem from their use in the
synthesis of amidinates and guanidinates as ligands for
metal centres; these compounds are then evaluated as
potential vapour phase precursors for chemical vapour
deposition (CVD) and atomic layer deposition (ALD)
processes of aluminum oxide [1, 2]. We have also per-
formed theoretical and synthetic investigations of
P. G. Gordon Á S. T. Barry (&)
Department of Chemistry, Carleton University, 1125 Colonel By
Drive, Ottawa, ON K1S 5B6, Canada
e-mail: sbarry@ccs.carleton.ca
G. P. A. Yap
Department of Chemistry and Biochemistry, University of
Delaware, 236 Brown Laboratory, Newark, DE 19716, USA
123

3
76
J Chem Crystallogr (2011) 41:375–378
Scheme 1 Carbodiimide insertion mechanism [3]
General Procedures
All manipulations were performed in a glovebox under N2
atmosphere. The 1,3-diisopropyl carbodiimide (CDI), alu-
minum chloride (AlCl ), and all anhydrous grade solvents
3
Fig. 1 Molecular diagram and atomic labelling scheme of 1.
Hydrogen atoms have been omitted for clarity, and the thermal
ellipsoids are shown at 30% probability
1
were purchased from Aldrich and used as received. The H
NMR spectra were recorded on a Bruker AMX 300 spec-
trometer at ambient probe temperature, using the residual
protons in the deuterated solvent for reference. The deu-
terated benzene was purchased from Aldrich and used as
received.
which is comparable to similar structures [6–8]. The het-
erocycle is planar with a slightly smaller angle between the
C–N–C bonds (88.25°) as compared to the N–C–N angles
(91.75°). The exocyclic moieties show deviations from
ideal geometries partly due to the strain of the heterocycle
and partly due to steric repulsion induced on one another.
The sum of angles around N2 (328.74°) show a mild
deviation from ideal pyramidilization. The sum of angles
around C4 (359.5°) similarly show a very slight deviation
from the ideal planar structure. This is further highlighted
by the torsion angle C1–N1–C4–N2A of 1.60°, clearly
demonstrating that the N1–C4 double bond is not co-planar
with the ring (Tables 1, 2, 3).
Compound 1
1
,3-Diisopropyl carbodiimide (5.762 g, 45.7 mmol) was
added to a solution of hexanes (15 mL), ether (5 mL) and
AlCl (2.030 g, 15.2 mmol) in a round bottom pressure
3
vessel. The resulting clear yellow solution was stirred
rapidly and refluxed for 3 days at 120 °C. The resulting
upper yellow liquid phase was decanted and kept at
-
30 °C until crystals of 1 were formed and collected.
Hexane was added to the vessel containing the lower red
viscous liquid phase and stirred overnight for additional
With respect to the synthesis of 1, it was found that the
reaction of CDI with AlCl was catalytic with respect to
1
extraction (5.04 mm, 22.1%). H NMR (300 MHz, C D ):
6
6
3
d 3.76 (sept, 2H, C=NCH(Me) ), 3.61 (sept, 2H,
NCH(Me) ), 1.30 (d, 12H, C=NCH(CH ) ), 1.20 (d, 12H,
2 3 2
AlCl3 and would not proceed at temperatures below
120 °C. Similar catalytic and non-catalytic activity of
aluminum species with carbodiimides has been shown
previously [7, 9, 10]. Analysis of the red viscous product
2
NCH(CH ) ).
2
3
1
by H NMR was inconclusive, but these data in addition to
Results and Discussion
the viscosity of the liquid suggest that it may consist of
higher order oligomers of CDI.
A molecular diagram of 1 is given in Fig. 1. The strained
heterocycle is the most interesting feature and it dominates
the structure. The C–N distances in the heterocycle are
The dissociation kinetics of 1 were studied via a sealed
thick-walled NMR tube thermolysis experiment. The tube
was heated using an oil bath held at 150 °C for the duration
1
˚
essentially equivalent with an average length of 1.427 A,
of the rate study and removed for H spectrum acquisition
1
23

J Chem Crystallogr (2011) 41:375–378
377
Table 1 Crystal data summary
Table 3 Selected geometrical parameters
˚
(A, deg)
CCDC no.
775576
Compound
Empirical formula
Formula weight (g/mol)
Colour/shape
16 28 4
C H N
N2–C4
1.4252(14)
1.2508(16)
1.4766(15)
91.75(9)
252.4
N1–C4
Colourless/plate
120(2)
N2–C5
Temperature (K)
Crystal system
N2–C4–N2A
C4–N2–C4A
C4–N2–C5
C5–N2–C4A
N1–C4–N2
N1–C4–N2A
C1–N1–C4–N2A
C5–N2–C4–N1
Monoclinic
88.25(9)
Space group
1
P2 /c
123.03(9)
125.46(9)
130.05(10)
138.16(10)
1.6(2)
Unit cell dimensions
˚
a (A)
9.352(5)
7.956(4)
11.405(6)
112.465(5)
784.2(7)
2
˚
b (A)
˚
c (A)
b (°)
Volume (A )
45.59(17)
3
˚
Z
Density (kg/L)
1.07
-
1
)
Absorption coefficient (mm
Diffractometer
0.07
Bruker AXS APEX
8282
Reflections collected
h range for data collection (°)
Limiting indices
2.36–28.27
-12 B h B 11, -10
B k B 10, -15 B l B 14
Independent reflections
Reflections with I [ 2r(I)
Number of parameters
1813
1554
82
2
Goodness-of-fit on F
1.049
Table 2 Nonhydrogen fractional atomic coordinates and equivalent
isotropic thermal parameters
Fig. 2 Thermolytic dissociation of 1 at 150 °C
x
y
z
U (eq)
integration of the dimer peaks to the sum of the dimer and
CDI peaks was plotted against time, resulting in a smooth
curve showing 1 being depleted as the CDI was formed.
A linear relationship was found by taking the natural
logarithm of the ratio as a function of time, showing that
this is a straightforward first-order dissociation with respect
to 1, as shown in Fig. 2. The rate constant k is found from
the slope of the ln[compound 1] vs. time curve to be
C1
C2
C3
C4
C5
C6
C7
N1
N2
0.32853(13)
0.34692(15)
0.48546(14)
0.11062(13)
0.05934(13)
0.18098(15)
0.11329(16)
0.25174(11)
0.01376(10)
-0.17084(14)
-0.19161(16)
-0.17012(16)
-0.00906(13)
0.24890(14)
0.36649(15)
0.16162(17)
-0.01045(11)
0.12637(11)
0.67633(11)
0.81381(11)
0.66552(12)
0.55736(10)
0.41433(10)
0.50201(12)
0.32009(12)
0.62593(9)
0.49095(8)
0.0213(3)
0.0275(3)
0.0272(3)
0.0175(3)
0.0203(3)
0.0285(3)
0.0302(3)
0.0207(2)
0.0178(2)
-
6 -1
3.036 9 10
s . From this the half-life of dissociation
can be calculated as 63.4 h.
only. As the initial concentration of 1 dissociated into CDI,
a comparison of the integration of their respective peaks at
roughly 24-hour intervals was made, and checked against
the integration of the native deuterated benzene and the
peaks from adventitious ether. The peaks associated with
both 1 and CDI that were used for this comparison were the
isopropyl group doublets at 1.29 and 1.04 ppm, respec-
tively. These peaks were chosen for their sharpness,
intensity, and separation from other peaks. The ratio of the
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