Synthesis and X-ray crystallographic characterization of substituted aryl imines

Article abstract of DOI:10.1016/j.molstruc.2011.02.027

We report the synthesis of α-diimine 1,4-bis(2,5-di-tert-butylphenyl) -2,3-dimethyl-1,4-diaza-1,3-butadiene, 1, and α-iminoketones 2-[(3,5-xylyl)imino]acenaphthylen-1-one, 4, and 2-[(4-chlorophenyl)imino] acenaphthylen-1-one, 5, all of which have been cha

Full text of DOI:10.1016/j.molstruc.2011.02.027

Journal of Molecular Structure 992 (2011) 33–38
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and X-ray crystallographic characterization of substituted aryl imines
⇑
James Kovach, Maria Peralta, William W. Brennessel, William D. Jones
Department of Chemistry, University of Rochester, Rochester, NY 14627, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 January 2011
Received in revised form 11 February 2011
Accepted 12 February 2011
Available online 17 February 2011
We report the synthesis of
a-diimine 1,4-bis(2,5-di-tert-butylphenyl)-2,3-dimethyl-1,4-diaza-1,3-buta-
diene, 1, and
imino]acenaphthylen-1-one, 5, all of which have been characterized by 1H NMR, 13C NMR, IR, and
X-ray crystallography. Also, we report the previously unknown X-ray crystal structures of -diimines
Ar-BIAN (Ar-BIAN = bis(arylimino)acenaphthene; Ar = 3,5-xylyl, 2; Ar = 4-chlorophenyl, 3) and -iminok-
a-iminoketones 2-[(3,5-xylyl)imino]acenaphthylen-1-one, 4, and 2-[(4-chlorophenyl)-
a
a
etone 2-[(2,6-xylyl)imino]acenaphthylen-1-one, 6. In solution, 4 and 5 show fluxional behavior observed
with variable temperature 1H NMR in DMSO-d6 which is attributed to isomerization between the E and Z
form of the imine.
Keywords:
Schiff base
a-Diimine
Ó 2011 Elsevier B.V. All rights reserved.
a-Iminoketone
BIAN
Isomerization
1. Introduction
formic acid (Baker, 90.5%) were used as received. CDCl3 with 1%
TMS (vol:vol) added was purchased from Cambridge Isotope Labo-
Imines (also known as Schiff bases) represent a large and rich
area in chemistry [1–4]. When -diimines are used as donor-li-
ratories, Inc. and used as received. C, H, N analysis for 1 and 5 was
obtained from the University of Illinois Microanalysis Laboratory.
C, H, N analysis for 4 was obtained from the CENTC Elemental Anal-
ysis Facility at the University of Rochester. Infrared spectra were
obtained on a Shimadzu 8400S FTIR using an ATR attachment.
NMR data were obtained on a Bruker 400 or 500 MHz NMR spec-
a
gands forming d8 square planar coordination complexes, reactions
including ethylene dimerization [5], ethylene oligomerization [6],
ethylene polymerization [7–11], propylene polymerization [12],
2-butene polymerization [13], butadiene polymerization [14], CO
and vinyl arene copolymerization generating atactic polyketones
[15], and the CAH activation of methane [16] and benzene [17]
are observed. Specifically, transition metal catalysts containing
trometer. Mass spectral data were obtained on
LCMS-2010 with an electrospray ion source.
a Shimadzu
coordinated a-diimine 3 have been used for the synthesis of epox-
ides [18], N-arylpyrroles [19], hetero-Diels–Alder adducts [19], ani-
line from the reduction of nitrobenzene [20], and allylic amines
2.2. 1,4-bis(2,5-di-tert-butylphenyl)-2,3-dimethyl-1,4-diaza-1,3-
butadiene (1)
[19,21]. Coordination of
that can polymerize norbornene [22]. Additionally, complexes con-
taining -iminoketones have been shown to polymerize olefins
[23] and phenylacetylene [24]. A schematic representation of com-
pounds 1–6 investigated in this study is shown in Fig. 1.
a-diimine 2 to nickel(II) gives a catalyst
A 100 mL round bottom flask was loaded with 2,5-di-tert-butyl-
aniline (1.451 g, 6.99 mmol), 2,3-butanedione (313 mg, 3.60
mmol), formic acid (0.06 mL, 1.44 mmol), and methanol (40 mL).
The solution was vigorously stirred at room temperature for
22 h. The reaction mixture was filtered producing a yellow precip-
itate that was washed with methanol (3 ꢀ 10 mL) and dried under
vacuum affording 705 mg (44%) of a yellow powder. Crystals suit-
able for structure determination were grown by evaporation of an
acetone solution at 25 °C (mp 196–197 °C). IR (ATR) mC=N 1632
cmꢁ1 Anal. Calcd for C32H48N2: C, 83.42; H, 10.50; N, 6.08. Found:
C, 83.45; H, 10.72; N, 6.26. 1H NMR (400 MHz, CDCl3, 25 °C): d 7.39
(d, J = 8 Hz, 2 H), 7.14 (dd, 3J = 8 Hz, 4J = 2 Hz, 2 H), 6.57 (d, 4J = 2 Hz,
2 H), 2.27 (s, 6 H), 1.40 (s, 18 H), 1.37 (s, 18 H). 13C NMR (125 MHz,
CDCl3, 25 °C): d 166.9 (s, C), 149.2 (s, C), 148.9 (s, C), 136.5 (s, C),
126.1 (s, CH), 120.7 (s, CH), 116.6 (s, CH), 34.7 (s, C), 34.3 (s, C),
31.3 (s, C(CH3)3), 29.6 (s, C(CH3)3), 16.4 (s, CH3). MS (ESI - MeCN):
m/z = 461 [M]+.
a
2. Experimental
2.1. Materials and instrumentation
Acenaphthenequinone, 3,5-dimethylaniline (98%), 2,6-dimeth-
ylaniline (99%) and 2,5-di-tert-butylaniline (99%) were purchased
from Aldrich and used as received. Methanol (Mallinckrodt), 4-
chloroaniline (Eastman), 2,3-butanedione (Alfa Aesar, 99%), and
⇑
Corresponding author. Tel.: +1 585 275 5493; fax: +1 585 276 0205.
E-mail address: jones@chem.rochester.edu (W.D. Jones).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.02.027

34
J. Kovach et al. / Journal of Molecular Structure 992 (2011) 33–38
Fig. 1.
a-diimines 1–3 and a-iminoketones 4–6.
2.3. 3,5-xylyl-BIAN (2)
2.5. 2-[(3,5-xylyl)imino]acenaphthylen-1-one (4)
Synthesis of this compound was reported previously by
A 100 mL round bottom flask was loaded with acenaphthen-
Ragaini [25]. Synthesis of 2 was accomplished by refluxing 3,5-
equinone (100.6 mg, 0.552 mmol). A formic acid (10 lL, 0.24
dimethylaniline and acenaphthenequinone in toluene with
a
mmol)/methanol (10 mL) solution was added and the contents
stirred vigorously. A 3,5-dimethylaniline (71.6 mg, 0.579 mmol)/
methanol (20 mL) solution was added and the contents were re-
fluxed for 18 h. The red product solution precipitated an orange so-
lid upon cooling to ꢁ20 °C. The precipitate was separated by
filtration, washed with pentane (5 ꢀ 15 mL), and dried under vac-
uum at 112 °C for 21 h affording 36.3 mg (23%) of an orange pow-
der. Crystals suitable for structure determination were grown by
evaporation of an acetone solution at 25 °C (mp = 180 °C (de-
catalytic amount of p-toluenesulfonic acid using a Dean–Stark
trap. Crystals suitable for structure determination were grown by
slow evaporation of a pentane and chloroform solution (5:1) at
ꢁ20 °C.
2.4. 4-chlorophenyl-BIAN (3)
Synthesis of this compound was reported previously by Valenti
and Calhorda [18] using Elsevier’s method [27]. Synthesis of 3 was
accomplished by refluxing 4-chloroaniline and acenaphthenequi-
none in toluene with a catalytic amount of glacial acetic acid using
a Dean–Stark trap. Crystals suitable for structure determination
were grown by evaporation of a CDCl3 solution at 25 °C.
comp)). IR (ATR) mC=O 1718 cmꢁ1 mC=N 1652 cmꢁ1. Anal. Calcd for
,
C20H15NO: C, 84.19; H, 5.30; N, 4.91. Found: C, 83.82; H, 5.19; N,
5.05. Major isomer: 1H NMR (400 MHz, CDCl3, 25 °C): d 8.17 (d,
3J = 8 Hz, 1 H), 8.16 (d, 3J = 7 Hz, 1 H), 8.00 (d, 3J = 8 Hz, 1 H), 7.81
(t, 3J = 8 Hz, 1 H), 7.46 (t, 3J = 8 Hz, 1 H), 7.04 (d, J = 7 Hz, 1 H),
Fig. 2. Synthesis of 1, 4, and 5.

J. Kovach et al. / Journal of Molecular Structure 992 (2011) 33–38
35
2.6. 2-[(4-chlorophenyl)imino]acenaphthylen-1-one (5)
A 100 mL round bottom flask was loaded with acenaphthen-
equinone (100.5 mg, 0.552 mmol). A formic acid (10 L, 0.24
l
mmol)/methanol (10 mL) solution was added and the contents
stirred vigorously. A 4-chloroaniline (77.0 mg, 0.604 mmol)/meth-
anol (20 mL) solution was added and the contents were refluxed
for 18 h, then cooled to 0 °C. The orange precipitate was separated
by filtration, washed with pentane (5 ꢀ 15 mL), and dried under
vacuum at 114 °C for 21 h affording 67.1 mg (42%) of an orange
powder. Crystals suitable for structure determiniation were grown
by evaporation of an acetone solution at 25 °C (mp = 230 °C (de-
Fig. 3. Solution dynamics of 4 and 5.
comp)). IR (ATR) mC=O 1729 cmꢁ1 mC=N 1656 cmꢁ1. Anal. Calcd for
,
C18H10ClNO: C, 74.11; H, 3.46; N, 4.80. Found: C, 74.01; H, 3.34;
N, 4.77. Major isomer: 1H NMR (400 MHz, CDCl3, 25 °C): d 8.20
(d, 3J = 8 Hz, 1 H), 8.18 (d, 3J = 7 Hz, 1 H), 8.04 (d, 3J = 8 Hz, 1 H),
7.84 (t, 3J = 8 Hz, 1 H), 7.49 (t, 3J = 8 Hz, 1 H), 7.45 (d, 3J = 8 Hz, 2
H), 7.08 (d, 3J = 7 Hz, 1 H), 7.05 (d, 3J = 8 Hz, 2 H). 13C NMR
(125 MHz, CDCl3, 25 °C): d 189.4 (s, C), 159.7 (s, C), 149.0 (s, C),
143.6 (s, C), 132.2 (s, CH), 131.0 (s, C), 130.6 (s, C), 130.5 (s, C),
6.92 (s, 1 H), 6.70 (s, 2 H), 2.36 (s, 6 H). 13C NMR (125 MHz, CDCl3,
25 °C): d 189.8 (s, C), 159.0 (s, C), 150.7 (s, C), 143.4 (s, C), 139.0 (s,
C), 132.0 (s, CH), 131.0 (s, C), 130.6 (s, C), 129.1 (s, CH), 128.1 (s,
CH), 127.9 (s, CH), 126.9 (s, C), 126.7 (s, CH), 123.7 (s, CH), 122.1
(s, CH), 115.5 (s, CH), 21.4 (s, CH3). MS (ESI – MeCN): m/z = 286
[M + H]+.
Table 1
Summary of crystallographic data for 1–6.
Parameter
1
2ꢂ2CHCl3
3ꢂ1.5CDCl3
4
5
6
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
32H48N2
C30H26Cl6N2
627.23
Monoclinic
P21/n
9.7806(16)
19.289(3)
15.827(3)
90
93.150(2)
90
C25.5H14Cl6.5D1.5N2
581.83
Monoclinic
P21/c
26.661(5)
8.9992(18)
22.749(5)
90
113.149(3)
90
C20H15NO
285.33
Triclinic
C18H10ClNO
291.72
Triclinic
C20H15NO
285.33
Triclinic
460.72
Triclinic
P-1
P-1
P-1
P-1
6.3859(4)
9.8772(7)
12.1637(8)
89.846(1)
78.495(1)
74.660(1)
724.00(8)
1
8.2804(6)
8.5977(6)
11.0163(8)
95.550(1)
94.390(1)
111.317(1)
721.90(9)
2
6.8246(13)
9.0659(17)
10.721(2)
92.818(3)
90.832(3)
96.062(3)
658.7(2)
2
8.0450(9)
8.4663(10)
12.3511(14)
74.012(2)
84.002(2)
61.948(2)
713.39(14)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
2981.4(9)
4
1.095
5018.8(17)
8
1.066
Z
Goodness-of-fit, F2
1.037
1.031
1.079
1.044
Final R indices [I > 2sigma(I)]
R1 = 0.0507
wR2 = 0.1231
R1 = 0.0799
wR2 = 0.1386
R1 = 0.0549
wR2 = 0.1233
R1 = 0.0922
wR2 = 0.1384
R1 = 0.0478
wR2 = 0.1167
R1 = 0.0623
wR2 = 0.1226
R1 = 0.0504
wR2 = 0.1383
R1 = 0.0628
wR2 = 0.1484
R1 = 0.0391
wR2 = 0.1086
R1 = 0.0505
wR2 = 0.1134
R1 = 0.0473
wR2 = 0.1320
R1 = 0.0578
wR2 = 0.1436
R indices (all data)
Fig. 4. Crystal packing diagram of 3 and 6 showing intermolecular p-stacking. Thermal ellipsoids were drawn at 50% probability level. Atom labels were removed for clarity.

36
J. Kovach et al. / Journal of Molecular Structure 992 (2011) 33–38
129.6 (s, CH), 129.5 (s, CH), 128.3 (s, CH), 127.9 (s, CH), 126.5 (s, C),
123.6 (s, CH), 122.4 (s, CH), 119.7 (s, CH). MS (ESI - MeCN): m/
z = 292 [M]+.
suitable for structure determination were grown by slow evapora-
tion of a pentane and chloroform solution (4:1) at ꢁ30 °C.
2.7. 2-[(2,6-xylyl)imino]acenaphthylen-1-one (6)
3. Results and discussion
Synthesis of this compound was reported previously by Carney
[26]. Synthesis of 6 was accomplished by refluxing 2,6-dimethyl-
aniline and acenaphthenequinone in toluene with a catalytic
amount of p-toluenesulfonic acid using a Dean–Stark trap. Crystals
3.1. Synthesis and NMR characterization
The syntheses of 1, 4, and 5 outlined in this paper lead to pre-
cipitates that can be easily separated by a filtration step in high
Fig. 5. Molecular structure of 1–6 with thermal ellipsoids drawn at 50%. Hydrogen atoms were omitted for clarity.

J. Kovach et al. / Journal of Molecular Structure 992 (2011) 33–38
37
Table 2
Selected bond lengths of 1–6 (Å).
Cmpd
1
C(3)–N(1)
N(1)–C(1)
C(1)–C(2)
C(1)–C(1A)
1.498(2)
C(1A)–C(2A)
1.4991(17)
C(1A)–N(1A)
1.2854(14)
N(1A)–C(3A)
1.4183(14)
1.4183(14)
1.2854(14)
1.4991(17)
Cmpd
2
3
C(13)–N(1)
1.423(3)
1.412(3)
N(1)–C(1)
1.274(3)
1.272(3)
C(1)–C(10)
1.476(3)
1.478(3)
C(1)–C(2)
1.526(3)
1.529(3)
C(2)–C(3)
1.480(3)
1.478(3)
C(2)–N(2)
1.273(3)
1.272(3)
N(2)–C(19)
1.426(3)
1.414(3)
Cmpd
C(13)–N(1)
1.4163(14)
1.4215(15)
1.4215(9)
N(1)–C(1)
1.2763(14)
1.2742(15)
1.2777(9)
C(1)–C(10)
1.4811(14)
1.4825(16)
1.4782(10)
C(1)–C(2)
C(2)–C(3)
C(2)–O(1)
1.2217(13)
1.2131(14)
1.2149(9)
4
5
6
1.5411(15)
1.5463(16)
1.5437(10)
1.4762(15)
1.4817(16)
1.4767(10)
purity with no further purification necessary (Fig. 2). The synthesis
procedures reported in the literature for -diimines 2 and 3 in-
volve the in situ complexation to ZnCl2 forming Zn(Ar-BIAN)Cl2,
followed by the liberation of the Ar-BIAN ligand by addition of a
zinc precipitating agent [18,25,27]. We were able to synthesize
acenaphthenequinone (Fig. 5). The
average C1-C2 bond length of 1.54 Å which is slightly longer than
the corresponding -dimines 2 and 3, and all of which are longer
than the C1AC1A bonds of 1 which measures 1.50 Å (Table 2). Con-
versely, the N1AC1 bond is slightly longer in 1 than the acenaph-
thene derived imines 2–6. There is experimentally no difference
in bond length between N1 and the ipso carbon of the aryl ring
among the imines, with an average bond length of 1.42 Å.
a-iminoketones 4–6 have an
a
a
a-diimines 2 and 3 without the use of ZnCl2 by simply refluxing
a toluene solution of 2:1 aniline: acenaphthenequinone with an
acid catalyst while removing water using a Dean–Stark trap. By
changing to a lower boiling solvent (methanol), reducing the ani-
line: acenaphthenequinone ratio (1:1), and not removing any by-
4. Conclusion
product water, the analogous
a-iminoketones were isolated as 4
and 5.
We have shown the synthesis and characterization of new
substituted aryl imines 1, 4, and 5 and compared structural charac-
terization to previously known aryl imines 2, 3, and 6. Iminoke-
tones 4 and 5 showed dynamic solution state behavior that
equilibrates to one isomer at elevated temperature.
The 1H NMR spectrum of 1 shows that the chemical shift of the
backbone methyl groups occurs at d 2.27 which is slightly upfield
from that of 2,3-butanedione at d 2.33 ppm [28]. Similarly, the
chemical shifts of the tert-butyl groups of
1 (d 1.40 and
1.37 ppm) were comparable to the resonances for the tert-butyl
groups of 2,5-di-tert-butylaniline (d 1.42 and 1.29 ppm) [29]. The
room temperature 1H NMR spectrum of both 4 and 5 show a major
and a minor species present in CDCl3; however, a variable temper-
ature 1H NMR experiment in CDCl3 gave little insight into the solu-
tion state dynamics of these compounds. When compounds 4 and
5 were each dissolved in DMSO-d6, coalescence was observed at
approximately 115 °C and a single species was observed above this
temperature. Cooling back to room temperature reproduced the
original spectrum in both cases, suggesting the presence of an
equilibrium in solution. We assign these two species as the E and
Z isomers of the imine, which are present in a (E:Z) ratio of approx-
imately 13:1 for 4 and 8:1 for 5 at room temperature in CDCl3
(Fig. 3). This ratio is comparable to what was observed by Ragaini
for asymmetric Ar,Ar0-BIAN ligands which had solution state
(E,E:E,Z) ratios of 7:1 [30], 8:1 [15], and 10:1 [30]. A preference
for the (E,Z) isomer was observed in the solid state for bis(1-naph-
thylimino)acenaphthene by Avilés [31], and R-BIAN (R = tert-butyl
or 1-adamantyl) by Cowley [32].
Acknowledgements
This work was financially supported by the NSF through the
Center for Enabling New Technologies through Catalysis (CENTC,
CHE-0650456), the CENTC Elemental Analysis Facility at the Uni-
versity of Rochester, and NSF REU funding.
Appendix A. Supplementary material
NMR data for 1, 4, and 5. CCDC 806882-806887 contain the sup-
plementary crystallographic data for 1–6. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.molstruc.2011.02.027.
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