Synthesis and characterization of cationic rhodium(I) dicarbonyl complexes

Article abstract of DOI:10.1016/j.ica.2010.12.005

Treatment of Rh(acac)(CO)₂ (acac = acetoacetonate) with perchloric acid followed by addition of an α-diimine (α-diimine = 1,4-bis(Ar)-2,3-dimethyl-1,4-diaza-1,3-butadiene, Ar = 3,5-dimethylphenyl, 1; 3,5-di-tert-butylphenyl, 2; and 3,4,5-trimet

Full text of DOI:10.1016/j.ica.2010.12.005

Inorganica Chimica Acta 367 (2011) 108–113
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and characterization of cationic rhodium(I) dicarbonyl complexes
⇑
James Kovach, 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:
Treatment of Rh(acac)(CO)2 (acac = acetoacetonate) with perchloric acid followed by addition of an a-dii-
Received 11 November 2010
Received in revised form 29 November 2010
Accepted 2 December 2010
Available online 9 December 2010
mine (
tert-butylphenyl, 2; and 3,4,5-trimethoxyphenyl, 3; phenyl, 4; and 4-chlorophenyl, 5) generates a series
of complexes of the type [Rh( -diimine)(CO)2][ClO4] 6–10 with varying electronic properties of the sup-
a-diimine = 1,4-bis(Ar)-2,3-dimethyl-1,4-diaza-1,3-butadiene, Ar = 3,5-dimethylphenyl, 1; 3,5-di-
a
porting diimine ligand. X-ray crystal structures have been determined for the a-diimine ligands 1–5, and
complexes 6, 8, and 10.
Keywords:
Ó 2010 Elsevier B.V. All rights reserved.
Rhodium compounds
Carbon monoxide
a-Diimine
1. Introduction
(acac = acetylacetonate) with perchloric acid in acetone generating
[Rh(acetone)2(CO)2][ClO4] in situ, and then addition of bipym to
displace the acetone ligands [43]. Similarly, we found that proton-
ation of the acac ligand of Rh(acac)(CO)2 with perchloric acid fol-
lowed by coordination the chelating diimines 1–5 (Fig. 1), led to
the formation of 6–10.
While these syntheses are similar, there are subtle but signifi-
cant differences that should be observed to ensure a clean product.
Specifically, the details of the order of addition, reaction time, stoi-
chiometry, and work-up procedures detailed in the experimental
section are very important to generate the pure complexes. For in-
stance, longer reaction times did not necessarily increase yield, but
often decreased purity. Workup procedures also differed: evapo-
rating the crude reaction solution to dryness, then washing with
non-polar solvents was sufficient to purify 7 and 9. This was not
the case for 8, which required a second purification step (crystalli-
zation) after the non-polar solvent wash. Non-polar solvent wash-
ing was not an appropriate purification method for 6 and 10; both
required crystallization by layering the crude reaction solution
with diethyl ether at ꢀ20 °C.
Rhodium carbonyl coordination complexes play an important
role in organic transformations, with two of the largest and most
important being hydroformylation [1–6] and the carbonylation of
methanol to acetic acid with [Rh(CO)2I2]ꢀ by Monsanto [3,7–9]. Ef-
forts to improve Monsanto’s acetic acid synthesis are ongoing, with
a considerable number of these catalysts being rhodium carbonyl
complexes [10–17]. Additionally, rhodium complexes with car-
bonyl ligands show catalytic activity towards carbonylative hydro-
silylation [18], reductive amination [19], isomerization [20–22]
polymerization [23,24], and reduction [25,26]. C–H activation of al-
kanes by the photodissociation of a CO ligand of the rhodium car-
bonyl complexes Rh(Cp)(CO)2 and Rh(Tp0)(CO)2 (Cp =
g
5-C5H5,
Tp0 = hydrotris(3,5-dimethylpyrazolyl)borate) are well understood
[27–31] and the reactive fragments: [Rh(Cp)(CO)] [32–39]
[Rh(Tp0)(CO)] [40], and [Rh( 5-C4H4P)(CO)] [41] have been investi-
g
gated by theoreticians. Extending the utility of C–H activation,
Shul’pin et al. showed how the rhodium carbonyl cluster Rh6(CO)16
(and to a lesser extent Rh2Cp2(CO)3 and Rh3(CpMe)3(CO)3) could C–
H activate and functionalize benzene to phenol with hydrogen per-
oxide [42].
2.2. X-ray Crystallography
2. Results and discussion
The a-diimine ligands 1–5 were synthesized as described in the
Section 4. Evaporation of acetone or ethanol solutions produced
crystals suitable for structure determination. The data parameters
for these compounds are summarized in Table 1, with thermal
ellipsoid representations shown in Fig. 2. Average bond lengths
for 1–5 are typical, with N1–C1 = 1.28 Å, N1–C3 = 1.42 Å, C1–
C1A = 1.50 Å, and C1–C2 = 1.50 Å, and all molecules crystallize
with an anti conformation about the C1–C1A bond (Table 2). Rho-
dium complexes 6ꢁCDCl3, 8ꢁCDCl3, and 10 crystallized by layering a
2.1. General/synthesis
Oro synthesized [Rh(bipym)(CO)2][ClO4] (bipym = 2,20-bipyrim-
idine) by protonation of the acac ligand of Rh(acac)(CO)2
⇑
Corresponding author.
E-mail address: jones@chem.rochester.edu (W.D. Jones).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.12.005

J. Kovach et al. / Inorganica Chimica Acta 367 (2011) 108–113
109
R4
R3
R5
ClO4
1) HClO4, acetone, 25 oC, 0-30 min.
N
N
CO
CO
Rh(acac)(CO)2
Rh
R5
R3
R3
R4
N
N
R4
2)
R3
R5
R5
R4
acetone, 25 oC, 0.5-5 h
25 - 58 % Yield (Isolated)
6, R3 = R5 = CH3, R4 = H
7, R3 = R5 = C(CH3)3, R4 = H
8, R3 = R4 = R5 = OCH3
9, R3 = R4 = R5 = H
10, R3 = R5 = H, R4 = Cl
Fig. 1. Syntheses of 6–10.
Table 1
X-ray data parameter table of 1–5, 6ꢁCDCl3, 8ꢁCDCl3, 8ꢁC3H6O, and 10.
Parameter
1
2
3
4
5
6ꢁCDCl3
8ꢁCDCl3
8ꢁC3H6O
10
Empirical
formula
C
20H24N2
C32H48N2
C22H28N2O6 C16H16N2
C16H14Cl2N2 C23H24Cl4DN2O6Rh C25H28Cl4DN2O12Rh C27H34ClN2O13Rh C18H14Cl3N2O6Rh
Formula weight 292.41
Crystal system monoclinic
460.72
monoclinic
C2/c
35.129(4)
5.8999(7)
15.3407(19) 14.2004(8)
416.46
monoclinic
C2/c
32.0431(19) 5.4366(4)
4.6033(3) 8.6026(6)
236.31
orthorhombic monoclinic
Pbca
305.19
671.17
orthorhombic
Pbca
16.158(3)
12.6924(19)
795.22
orthorhombic
Cmc21
20.932(2)
13.2850(13)
11.5186(11)
90
90
90
3203.0(5)
4
732.92
orthorhombic
Cmc21
20.776(2)
13.2576(16)
11.3548(13)
90
90
90
3127.6(6)
4
563.57
orthorhombic
Cmcm
22.210(5)
13.152(3)
7.4991(16)
90
90
90
2190.5(8)
4
Space group
a (Å)
b (Å)
P21/n
P21/n
5.6857(4)
8.6145(6)
5.2793(3)
11.2707(6)
14.1803(8)
90
c (Å)
27.3962(18) 15.6359(12) 27.519(4)
a
(°)
90
90
95.807(1)
90
2083.9(2)
4
90
90
90
90
97.887(1)
90
90
90
90
b (°)
96.294(1)
90
838.66(8)
2
114.873(2)
90
2884.6(6)
4
c
(°)
V (Å3)
1281.29(15) 758.59(10)
4
5643.7(15)
8
Z
2
Goodness-of-fit 1.047
1.04
1.05
1.035
1.051
1.009
1.053
1.048
1.11
(GOF) on F2
Final R indices R1 = 0.0418 R1 = 0.0403 R1 = 0.0357 R1 = 0.0410
[I > 2 (I)] wR2 = 0.1192 wR2 = 0.1133 wR2 = 0.1037 wR2 = 0.1098 wR2 = 0.1054 wR2 = 0.0980
R1 = 0.0493 R1 = 0.0473 R1 = 0.0394 R1 = 0.0490 R1 = 0.0538 R1 = 0.1131
wR2 = 0.1263 wR2 = 0.1198 wR2 = 0.1078 wR2 = 0.1154 wR2 = 0.1152 wR2 = 0.1170
R1 = 0.0385 R1 = 0.0533
R1 = 0.0322
wR2 = 0.0645
R1 = 0.0403
wR2 = 0.0675
R1 = 0.0336
wR2 = 0.0724
R1 = 0.0429
wR2 = 0.0767
R1 = 0.0436
wR2 = 0.0740
R1 = 0.1126
wR2 = 0.0936
r
R indices (all
data)
concentrated chloroform solution of the complex with pentane and
a second crystallization method was discovered for 8 by layering
an acetone solution with pentane crystallizing as 8ꢁC3H6O. The data
parameters for these compounds are summarized in Tables 1 and
3, with thermal ellipsoid representations shown in Fig. 3. The aver-
age Rh–CO bond length is 1.87 0.01 Å and the average Rh–N bond
length is 2.06 0.01 Å. When comparing the free diimine ligands 1,
3, 5 to the coordinated diimine complexes 6ꢁCDCl3, 8ꢁCDCl3,
8ꢁC3H6O, and 10, there is little elongation of the N@C bond1or elon-
gation of the backbone C(sp2)–C(sp2) bond2 observed.
9 are consistent with complexes in the form of monohydrates
7ꢁH2O, 8ꢁH2O, and 9ꢁH2O, respectively. It is difficult to provide di-
rect evidence for these monohydrate complexes explicitly; how-
ever hydrogen bonding of water to these oxygen rich complexes
is not unreasonable. It should be noted that 8 crystallizes with
either chloroform-d1 or acetone as 8ꢁCDCl3 or 8ꢁC3H6O, respec-
tively, forming solvent channels throughout the crystal lattice.
These solvent channels for both crystal systems are of similar size,
and exhibit similar behavior. Upon removal from the mother li-
quor, both crystallization systems very readily lose solvent from
the lattice, thus destroying the integrity of the crystal for analysis
by X-ray diffraction. It is proposed that upon removal of organic
solvent in the workup steps for 7, 8, and 9, water may be incorpo-
rated forming the respective monohydrates.
2.3. Other characterization
Compounds 1 and 6–10 show 1H NMR spectra that indicate pur-
ity. Combustion analyses for 1, 6, and 10 also indicate the isolation
of analytically pure compounds. Combustion analyses for 7, 8, and
3. Conclusion
We have outlined the synthesis and characterization of a series
of cationic rhodium(I) dicarbonyl complexes with a variety of dii-
mine ligands. Further investigation of the reactivity of these com-
plexes is underway.
1
Elongation of the N@C bond for 6ꢁCDCl3 = 0.001(1) and 0.004(4) Å, 8ꢁCDCl3 =
0.005(4) Å, 8ꢁC3H6O = 0.007(3) Å, and 10 = 0.004(4) Å.
2
Elongation of the backbone C(sp2)–C(sp2) bond for 6ꢁCDCl3 = 0.007(5) Å,
8ꢁCDCl3 = 0.017(5) Å, 8ꢁC3H6O = 0.010(7) Å, and 10 = 0.008(8) Å.

110
J. Kovach et al. / Inorganica Chimica Acta 367 (2011) 108–113
1
2
3
4
5
Fig. 2. Molecular structures of 1–5. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms were omitted for clarity. All molecules exhibit a crystallographic
inversion center at the midpoint of the C1–C1A bond.
Table 2
Selected bond lengths (Å) and torsion angles (°) of 1–5.
R
C2
N1A C3A
C2A
C1 C1A
C3 N1
R
.
1
2
3
4
5
N1–C1
N1–C3
C1–C1A
C1–C2
1.2814(9)
1.4212(9)
1.5028(13)
1.5030(10)
1.2807(9)
1.2807(9)
1.2811(10)
1.4224(10)
1.5032(15)
1.5027(11)
1.2782(16)
1.4158(15)
1.502(2)
1.4236(8)
1.5028(12)
1.4997(10)
1.4203(8)
1.4987(13)
1.5035(10)
1.4970(16)
C3–N1–C1–C1A
175.82(7)
179.30(7)
177.64(7)
179.11(8)
178.41(13)
tories, Inc. and used as received. NMR spectra were recorded on a
Bruker 500 MHz or 400 MHz spectrometer. 13C NMR spectral
assignments were determined by comparing the 13C{1H} spectrum
to the corresponding 13C and 1H–13C HSQC spectra. C, H, N analysis
was obtained from the CENTC Elemental Analysis Facility at the
University of Rochester. Infrared spectra were obtained on a Shi-
madzu 8400S FTIR using an ATR attachment.
4. Experimental
4.1. General considerations
Rhodium(acetylacetonate)(CO)2 (Strem), formic acid (J.T. Baker,
90.5%). 2,3-butanedione (Alfa Aesar, 99%), 3,4,5-trimethoxyaniline
(Acros, 97%), 4-chloroaniline (Eastman) were used as received.
Acetone, aniline, hexane, and methanol were purchased from Mal-
linckrodt and used as received. Perchloric acid (70%), diethyl ether,
and pentane were purchased from Fisher and used as received. 3,5-
Dimethylaniline (98%) and 3,5-di-tert-butylaniline (98%) were pur-
chased from Aldrich and used as received. CDCl3 with 1% (vol:vol)
tetramethylsilane was purchased from Cambridge Isotope Labora-
4.2. Synthesis of 1,4-bis(3,5-dimethylphenyl)-2,3-dimethyl-1,4-diaza-
1,3-butadiene, 1
A 100 mL round bottom flask was loaded with 3,5-dimethyani-
line (5.936 g, 48.01 mmol), 2,3-butanedione (2.004 g, 23.04 mmol),

J. Kovach et al. / Inorganica Chimica Acta 367 (2011) 108–113
111
Fig. 3. Molecular structures of 6ꢁCDCl3, 8ꢁCDCl3, and 10. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms, perchlorate ions, and solvent molecules were
omitted for clarity.
and methanol (50 mL). Formic acid (0.4 mL) was added and the
reaction mixture was stirred at room temperature for 23 h. The
yellow precipitate was separated by filtration and then washed
with ꢀ30 °C MeOH (3 ꢂ 30 mL). Recrystallization from boiling
EtOH, washing with cold EtOH (0 °C, 3 ꢂ 30 mL), then cold pentane
(0 °C, 1 ꢂ 30 mL), and drying under vacuum afforded yellow crys-
tals (1.876 g, 28%, mp 141–142 °C). Crystals suitable for structure
determination were grown by evaporation of an acetone solution.
Anal. Calc. for C16H16N2: C, 82.14; H, 8.27; N, 9.58. Found: C,
4.3. Synthesis of 1,4-bis(3,5-di-tert-butylphenyl)-2,3-dimethyl-1,4-
diaza-1,3-butadiene, 2
Prepared according to the literature [44]. Crystals suitable for
structure determination were grown by evaporation of an acetone
solution.
4.4. Synthesis of 1,4-bis(3,4,5-trimethoxyphenyl)-2,3-dimethyl-1,4-
diaza-1,3-butadiene, 3
82.18; H, 8.30; N, 9.86%. IR (ATR) mC
@
N
1633 cmꢀ1 1H NMR
.
(400 MHz, CDCl3, 25 °C) d 6.76 (s, 2H, HAR), 6.42 (s, 4H, HAR), 2.34
(s, 12H, CH3), 2.15 (s, 6H, CH3). 13C{1H}NMR (125 MHz, CDCl3,
25 °C): d 167.9 (s, C), 151.0 (s, C), 138.6 (s, C), 125.3 (s, CH), 116.3
(s, CH), 21.3 (s, CH3), 15.3 (s, CH3).
Prepared according to the literature [44]. Crystals suitable for
structure determination were grown by evaporation of an acetone
solution.

112
J. Kovach et al. / Inorganica Chimica Acta 367 (2011) 108–113
Table 3
methyl-1,4-diaza-1,3-butadiene (89.1 mg, 0.193 mmol), and stir-
red vigorously for 5 h at 25 °C. The red solution was evaporated
to dryness and the resulting red solid was washed with hexane
(3 ꢂ 15 mL), pentane (3 ꢂ 15 mL), and diethyl ether (3 ꢂ 20 mL),
then dried under vacuum affording a red-orange solid (34.7 mg,
25%). Anal. Calc. for C34H48ClN2O6RhꢁH2O: C, 55.40; H, 6.84; N,
Selected bond lengths (Å) and angles (°) of 6ꢁCDCl3, 8ꢁCDCl3, 8ꢁC3H6O, and 10. Note:
the below drawing is provided for comparison purposes and may or may not
correspond to the actual atom numbering in the respective ORTEP diagrams.
C3 C4
N1 N2
X
3.80. Found: C, 55.82; H, 7.08; N, 3.80%. IR (ATR) mC
@
2100,
O
2051 cmꢀ1 1H NMR (400 MHz, CDCl3, 25 °C) d 7.38 (s, 2H, HAR),
.
X
Rh1
7.17 (s, 4H, HAR), 2.43 (s, 6H, –CH3), 1.35 (s, 36H, –C(CH3)3). 13C
1
C1
C2
NMR (125 MHz, CDCl3, 25 °C): d 182.4 (s, C), 181.8 (d, JC–
Rh = 70 Hz, CO), 153.4 (s, C), 148.6 (s, C), 122.1 (s, CHAR), 114.9 (s,
O1
O2
CHAR), 35.3 (s, C(CH3)3), 31.2 (s, C(CH3)3), 20.6 (s, CH3).
.
6ꢁCDCl3
8ꢁCDCl3
8ꢁC3H6O
10
1.859(5)
Rh1–C1
Rh1–C2
Rh1–N1
Rh1–N2
N1–C3
N2–C4
C3–C4
C1–O1
C2–O2
1.874(3)
1.879(3)
2.058(2)
2.062(2)
1.278(4)
1.284(4)
1.510(4)
1.130(4)
1.129(3)
92.08(13)
77.35(10)
1.872(3)
1.872(3)
2.062(2)
2.062(2)
1.286(3)
1.286(3)
1.516(4)
1.129(3)
1.129(3)
88.95(16)
77.39(11)
1.8648(17)
1.8649(17)
2.0663(13)
2.0663(13)
1.288(2)
1.288(2)
1.510(3)
1.135(2)
1.135(2)
4.9. Synthesis of [Rh(1,4-bis(3,4,5-trimethoxyphenyl)-2,3-dimethyl-
1,4-diaza-1,3-butadiene)(CO)2][ClO4], 8
1.859(5)
2.055(3)
2.055(3)
1.280(5)
1.280(5)
1.508(8)
1.133(6)
1.133(6)
91.7(3)
A 100 mL round bottom flask was loaded with, in this order:
Rh(acac)(CO)2 (50.3 mg, 0.195 mmol), acetone (6 mL), HClO4 (17
lL, 0.197 mmol), solid 1,4-bis(3,4,5-trimethoxyphenyl)-2,3-di-
methyl-1,4-diaza-1,3-butadiene (81.1 mg, 0.195 mmol), and stir-
red vigorously for 4.5 h at 25 °C. The red solution was evaporated
to dryness and the resulting red solid was washed with hexane
(3 ꢂ 15 mL), pentane (3 ꢂ 15 mL), and diethyl ether (3 ꢂ 20 mL),
then dried under vacuum affording a red solid (92.2 mg, 70%
(crude)). The complex was further purified by dissolving in acetone
(6 mL), layering with diethyl ether (15 mL), and cooling to ꢀ20 °C
forming red needles (42.2 mg, 32% (purified)). Crystals suitable
for structure determination were grown by layering a CDCl3 solu-
tion of 8 with pentane at 25 °C forming 8ꢁCDCl3, or by layering
an acetone solution with pentane at 25 °C forming 8ꢁC3H6O. Anal.
Calc. for C24H28ClN2O12RhꢁH2O: C, 41.60; H, 4.36; N, 4.04. Found:
C1–Rh1–C2
N1–Rh1–N2
88.31(10)
77.17(7)
76.96(19)
4.5. Synthesis of 1,4-diphenyl-2,3-dimethyl-1,4-diaza-1,3-butadiene,
4
Prepared by a modified literature procedure [45]. Crystals suit-
able for structure determination were grown by evaporation of an
acetone solution.
C, 41.33; H, 4.52; N, 4.06%. IR (ATR) mC
@ .
2091, 2034 cmꢀ1 1H
O
4.6. Synthesis of 1,4-bis(4-chlorophenyl)-2,3-dimethyl-1,4-diaza-1,3-
butadiene, 5
NMR (400 MHz, CDCl3, 25 °C) d 6.61 (s, 4H, HARYL), 3.91 (s, 12H, –
OCH3), 3.88 (s, 6H, –OCH3), 2.43 (s, 6H, –CH3). 13C NMR
(125 MHz, CDCl3, 25 °C): d 182.8 (s, C), 181.6 (d, JC–Rh = 70 Hz,
Rh–CO), 154.4 (s, C), 144.6, (s, C), 137.5 (s, C), 97.6 (s, CH), 61.1
(s, OCH3), 56.6 (s, OCH3), 20.7 (s, CH3).
Prepared by a modified literature procedure [46]. Crystals suit-
able for structure determination were grown dissolving in boiling
ethanol and cooling to 25 °C.
4.10. Synthesis of [Rh(1,4-diphenyl-2,3-dimethyl-1,4-diaza-1,3-
butadiene)(CO)2][ClO4], 9
4.7. Synthesis of [Rh(1,4-bis(3,5-dimethylphenyl)-2,3-dimethyl-1,4-
diaza-1,3-butadiene)(CO)2][ClO4], 6
A 25 mL round bottom flask was loaded with, in this order:
Rh(acac)(CO)2 (49.9 mg, 0.193 mmol), acetone (10 mL), and HClO4
A 50 mL round bottom flask was loaded with, in this order:
Rh(acac)(CO)2 (50.0 mg, 0.194 mmol), acetone (12 mL), HClO4 (16
(20
lL, 0.232 mmol), and stirred vigorously for 30 min at 25 °C.
lL, 0.186 mmol), solid 1,4-bis(3,5-dimethylphenyl)-2,3-dimethyl-
1,4-Diphenyl-2,3-dimethyl-1,4-diaza-1,3-butadiene
(45.9 mg,
1,4-diaza-1,3-butadiene (56.8 mg, 0.194 mmol), and stirred vigor-
ously for 30 min at 25 °C. Diethyl ether (35 mL) was added to the
resulting red solution, and cooled to ꢀ20 °C overnight to crystal-
lize. The product was separated by filtration, washed with diethyl
ether (3 ꢂ 10 mL), and dried under vacuum affording red needles
(33.7 mg, 33%). Crystals suitable for structure determination were
grown by layering a CDCl3 solution of 6 with pentane at 25 °C crys-
tallizing as 6ꢁCDCl3. Anal. Calc. for C22H24ClN2O6Rh: C, 47.97; H,
0.194 mmol) dissolved in acetone (6 mL) was added and stirred
vigorously for 3 h at 25 °C. The dark red solution was evaporated
to dryness and the resulting dark red solid was washed with hex-
ane (5 ꢂ 15 mL) and pentane (5 ꢂ 15 mL), then dried under vac-
uum affording a dark red (maroon) solid (55.5 mg, 58%). Anal.
Calc. for C18H16ClN2O6RhꢁH2O: C, 42.17; H, 3.54; N, 5.46. Found:
C, 41.74; H, 3.17; N, 5.57%. IR (ATR) mC
@ .
2086, 2040 cmꢀ1 1H
O
NMR (400 MHz, CDCl3, 25 °C) d 7.44 (t, J = 8 Hz, 4H), 7.38 (d,
J = 8 Hz, 4H), 7.32 (t, J = 7 Hz, 2H), 2.37 (s, 6H). 13C NMR
(125 MHz, CDCl3, 25 °C) d 183.5 (s, C), 181.8 (d, JC-Rh = 70 Hz, Rh–
CO), 149.1 (s, C), 130.0 (s,CH), 128.3 (s, CH), 120.6 (s, CH), 20.5 (s,
CH3).
4.39; N, 5.08. Found: C, 47.76; H, 4.32; N, 5.04%. IR (ATR) mC
@
O
2093, 2040 cmꢀ1 1H NMR (400 MHz, CDCl3, 25 °C) d 6.98 (s, 2H,
.
CH), 6.92 (s, 4H, CH), 2.38 (s, 6H, CH3), 2.37 (s, 12H, CH3). 13C
1
NMR (125 MHz, CDCl3, 25 °C): d 182.6 (s, C), 181.7 (d, JC–
Rh = 70 Hz, CO), 148.9 (s, C), 140.3 (s, C), 130.1 (s, CH), 117.7 (s,
CH), 21.3 (s, CH3), 20.6 (s, CH3).
4.11. Synthesis of [Rh(1,4-bis(4-chlorophenyl)-2,3-dimethyl-1,4-
diaza-1,3-butadiene)(CO)2][ClO4], 10
4.8. Synthesis of [Rh(1,4-bis(3,5-di-tert-butylphenyl)-2,3-dimethyl-
1,4-diaza-1,3-butadiene)(CO)2][ClO4], 7
A 100 mL round bottom flask was loaded with, in this order:
Rh(acac)(CO)2 (50.1 mg, 0.194 mmol), acetone (6 mL), HClO4
A 100 mL round bottom flask was loaded with, in this order:
Rh(acac)(CO)2 (49.9 mg, 0.193 mmol), acetone (6 mL), HClO4
(17 lL, 0.197 mmol), solid 1,4-bis(4-chlorophenyl)-2,3-dimethyl-
1,4-diaza-1,3-butadiene (59.4 mg, 0.195 mmol), and stirred vigor-
(17
lL, 0.197 mmol), solid 1,4-bis(3,5-di-tert-butylphenyl)-2,3-di-
ously for 30 min at 25 °C. Diethyl ether (50 mL) was added to the

J. Kovach et al. / Inorganica Chimica Acta 367 (2011) 108–113
113
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resulting red solution, and cooled to ꢀ20 °C overnight. The precip-
itate was separated by filtration, washed with diethyl ether
(3 ꢂ 20 mL), and dried under vacuum affording
a red solid
(39.5 mg, 36%). Crystals suitable for structure determination were
grown by layering a CDCl3 solution with pentane at 25 °C. Anal.
Calc. for C18H14Cl3N2O6Rh: C, 38.36; H, 2.50; N, 4.97. Found: C,
37.98; H, 2.53; N, 4.95%. IR (ATR) mC
@ .
2094, 2046 cmꢀ1 1H NMR
O
(400 MHz, CDCl3, 25 °C): d 7.49 (d, J = 8 Hz, 4H), 7.33 (d, J = 8 Hz,
4H), 2.38 (s, 6H). 13C NMR (125 MHz, CDCl3, 25 °C): d 183.9 (s, C),
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Acknowledgments
This work was financially supported by the NSF through the
Center for Enabling New Technologies through Catalysis (CENTC)
CHE-0650456. The Center for Enabling New Technologies through
Catalysis (CENTC) Elemental Analysis Facility is also acknowledged
for use of its analytical facility.
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Appendix A. Supplementary material
CCDC 799909–799917 contain the supplementary crystallo-
graphic data for 1–5, 6ꢁCDCl3, 8ꢁCDCl3, 8ꢁC3H6 O, and 10. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic 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.ica.2010.12.005.
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