The Synthesis, Structural Characterization and Conformational Analysis of (1,3-Bis(2-methyl-4-diethylaminophenyl)imidazolidin-2-ylidene)chloro(1, 5-cyclooctadiene)rhodium(I)

Article abstract of DOI:10.1515/znb-2005-0804

A four-coordinated Rh(I) complex with a new heterocyclic carbene ligand, functionalized by amino donor pendants, 4, was synthesized and characterized by elemental analyses, NMR and IR spectroscopy, and the molecular structure of the title compound has bee

Full text of DOI:10.1515/znb-2005-0804

The Synthesis, Structural Characterization and Conformational
Analysis of (1,3-Bis(2-methyl-4-diethylaminophenyl)imidazolidin-
2-ylidene)chloro(1,5-cyclooctadiene)rhodium(I)
Hasan Karabıyıka, Rafet Kılınc¸arslanb, Muhittin Aygu¨na, Bekir C¸ etinkayab, and
Orhan Bu¨yu¨kgu¨ngo¨rc
a Dokuz Eylu¨l University, Department of Physics, Fen Edebiyat Fakultesi, Fizik Bolumu,
˙
Kaynaklar Yerleskesi, 35160-Buca, Izmir, Turkey
b
˙
Ege University, Department of Chemistry, 35100- Bornova, Izmir, Turkey
c Ondokuz Mayıs University, Department of Physics, 55139-Kurupelit, Samsun, Turkey
Reprint requests to Dr. M. Aygu¨n. E-mail: muhittin.aygun@deu.edu.tr
Z. Naturforsch. 60b, 837 – 842 (2005); received July 5, 2004
A four-coordinated Rh(I) complex with a new heterocyclic carbene ligand, functionalized by
amino donor pendants, 4, was synthesized and characterized by elemental analyses, NMR and
IR spectroscopy, and the molecular structure of the title compound has been determined by X-
ray crystallography. Crystallographic data: monoclinic, P21/m, a = 7.9307(5), b = 25.0061(12),
◦
3
c = 8.0780(6) A, β = 101.366(6) , V = 1570.58(17) A , ρcalc = 1.3515(1) g cm−3, Z = 2. The
experimentally obtained structural parameters for compound 4 compare reasonably well with those
calculated at the semi-empirical ZINDO/1 level of theory carried out to elucidate conformational
flexibility and steric hindrances.
˚
˚
Key words: N-Heterocyclic Carbenes, Rhodium Complexes, Carbene Ligand, Crystal Structure,
ZINDO/1
Introduction
ylidene metal complex synthesis precludes the pres-
ence of many types of functional groups [17, 18]. As
a possible system for this research, we have chosen
4-diethylamino-2-methylphenyl as the N-substituent.
The presence of peripheral –NEt2 group is expected
to improve water solubility through quaternization of
this group.
The renaissance of metal complexes of N-hetero-
cyclic carbenes began after their use as alternatives
for phosphine complexes used in homogeneous catal-
ysis [1 – 5]. The use of CC-saturated imidazolidin-2-
ylidene ligands results in even higher catalytic activity.
Examples of such reactions include the Heck olefina-
tion of haloarenes [6], hydroformylation [6], the asym-
metric hydrosilylation of acetophenone [7, 8], hydro-
genation [9] and cyclopropanation of alkenes [10].
Experimental Section
Materials and methods
All manipulations were performed by using Schlenk-
type flasks under dry argon and standard high vacuum-
line techniques. The solvents were analytical grade and dis-
tilled after drying. NMR spectra were recorded at 297 K
on a Varian instrument at 400 MHz (1H), 100,56 MHz
The nature of the N-substituents of the carbene lig-
and has a pronounced effect upon the catalytic activity
of the complexes [10, 11]. On the other hand, biphasic
catalysis consisting of a water-phase containing cat-
alytic species and a non-miscible organic phase con-
tinues to attract interest in view of industrial applica-
tions [12]. For this purpose a number of attempts have
been made to introduce hydrophilic functional groups
on convenient ligands, mainly phosphines [12– 15].
Despite their similar catalytic behaviour, examples of
hydrophilic carbene complexes are rare [16, 17]. The
employment of highly reactive nucleophiles as well as
(
13C). Elemental analyses were carried out by the analyti-
cal service of TUBITAK with a Carlo Erba Strumentazione
Model 1106 apparatus. Crystallographic data from single
crystal X-ray diffraction have been collected with the STOE
IPDS2 diffractometer.
Preparation of the title compound
A mixture of 1,3-bis(2-methyl-4-diethylaminophenyl)
electrophiles at different stages of the imidazolidin-2- imidazolinium chloride (0.37 g, 0.86 mmol) and [Rh(µ-
c
0932–0776 / 05 / 0800–0837 $ 06.00 ꢀ 2005 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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838
H. Karabıyık et al. · A Rhodium Complex with a New Heterocyclic Carbene Ligand
Fig. 1. Synthesis of 4. (i) Glyoxal, EtOH, RT; (ii) NaBH4, EtOH, 78 ◦C; (iii) CH(OEt)3, NH4Cl, 130 ◦C; (iv) [Rh(µ-OMe)(1,5-
COD)]2, 110 ◦C, PhMe.
Fig. 2. ORTEP3 drawing of the title compound showing the atomic numbering scheme for non-hydrogen atoms. Displacement
ellipsoids of non-H atoms are shown at the 30% probability level. [(i): x, y+3/2, z)
OMe)(1,5-COD)]2 (0.208 g, 0.43 mmol) in toluene (5 cm3) (d, CDCl3): d 214.80 (d, J = 47.26 Hz, Ccarb=Rh); 147.53,
was heated under reflux for 2 h. The solution was cooled 135.26, 131.87, 128.92, 113.25, 110.16 (Caren); 97.16 (d,
to room temperature and hexane (15 ml) was added. The J = 6.83 Hz, COD(CH=CH); 66.99 (d, J = 15.28 Hz,
solid was filtered off and recrystallized from CH2Cl2/Et2O COD(CH=CH); 52.8 (NCH2CH2N); 44.76 (NCH2CH3);
(1 cm3/3 cm3), filtered and dried. Yield: 0.360 g. (68%, 32.49 (COD(CH2)); 28.40 (COD(CH2)); 19.18 (2-CH3-
m. p.: 248 – 250 ◦C. Analysis for RhClC33H48N4: calcd. C6H3); 12.8 (NCH2CH3).
C 62.19, H 7.59, N 8.79) (found: C 62.23, H 7.76, N 8.83).
1H NMR (400 MHz, CDCl3): δ = 7.95 (d, J = 8.58 Hz,
2H, C6H3); 6.68 (dd, J = 8.77 Hz, 2H, C6H3); 6.53 (d,
J = 2.73, 2H, C6H3); 4.57 (s, 2H, CODvinyl); 3.96 (t,
J = 18.33 Hz, 2H, NCH2CH2); 3.84 (t, J = 18.33, 2H,
NCH2CH2); 3.42-3.37 (m, 8H, NCH2CH3); 3.06 (s, 2H,
CODvinyl); 2.32 (s, 6H, 2-(CH3)C6H3); 1.75 – 1.52 (m, 8H,
CODallyl); 1.2 (t, J = 14.04, 12H, NCH2CH3). 13C NMR
X-ray crystallography
Suitable crystals were obtained directly from the syn-
thesis as yellow needles. The structure was solved by the
Patterson method (SHELXS-97) [19] and refined by full-
matrix least squares techniques (SHELXL-97) [20]. Details
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H. Karabıyık et al. · A Rhodium Complex with a New Heterocyclic Carbene Ligand
839
Table 1. Crystal data and structure refinement details for the title compound.
Crystal data
Data collection
Diffractometer
Diff. meth.
Abs. corr. type
Intensity decay
Temperature [K]
θmin [◦]
Refinement
Unique reflections
Refined parameters
Chemical formula
Formula weight
Cryst. system
Space group
RhClC33H48N4
639.11
monoclinic
P21/m (No:11)
0.71073 (Mo-Kα )
7.9307(5)
25.0061(12)
8.0780(6)
101.366(6)
1570.58(17)
2/672
STOE IPDS2
rotation
integration
< 1%
293(2)
1.63
28.30
0.6713
3162
197
R (for all data)
0.0481
0.0826
0.0367
0.082
0.859
1
wR2 (for all data)
R1(Fo > 4σ(Fo))
wR2(Fo > 4σ(Fo))
GoF
˚
Wavelength [A]
˚
a [A]
b [A]
θmax [◦]
˚
˚
c [A]
Tmin
Tmax
Reflns. with (F > 4σ(Fo)) 2261
o
β [◦]
0.8675
Deepest hole (eA−3
)
)
−0.62
−3
˚
˚
3
˚
V [A ]
h, k, l ranges
Meas. frac.theta max. 0.996
Meas. frac.theta full
Method of abs. corr.
Monochromator
−10 → 10, 0 → 33, 0 → 10
Highest peak (eA
0.81
Z/F(000)
Mean shift / esd
Max. shift / esd
Max. shift
0.0020
0.0140
0.0010
ρcalc [g cm−3
]
1.352
6.57
0.60×0.53×0.22
0.993
Psi-scan
plane graphite
µ (Mo-Kα ) [cm−1
]
Crystal size (mm)
Table 2. Atomic fractional coordinates and equivalent
There is half an independent molecule in the asymmetric
unit.
isotropic displacement parameters of the atoms in the asym-
2
˚
metric unit (in A with ESDs in parentheses). Ueq is defined
as one third of the trace of the orthogonalized U tensor.
ij
Computational details
˚
Ueq [A]
Atom
x
y
z
The initial molecular structure obtained from the X-
ray crystallographic study was optimized by ZINDO/1 [22]
semi-empirical quantum mechanical calculations at the spin-
Restricted Hartree-Fock (RHF) level [23, 24] without any
symmetry constraints. ZINDO/1 has been parameterized to
generate geometries of molecules including transition met-
als. The optimized geometry was obtained by the applica-
Rh1
Cl1
N1
N2
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13B
0.34683(5)
0.52785(14) 1/4
1/4
0.35422(4) 0.0365(1)
0.14913(14) 0.0502(4)
0.2493(4)
0.0635(3)
0.1098(3)
−0.0008(4)
0.0483(5)
0.2030(4)
0.3120(4)
0.2642(4)
−0.1718(5)
0.1675(6)
0.0369(7)
0.3833(6)
0.5562(6)
0.2021(4)
0.306(2)
−0.00732(10) 0.2432(4)
0.0766(13)
0.0404(8)
0.0391(10)
0.0496(11)
0.0588(13)
0.0530(11)
0.20680(8)
0.15220(10)
0.11912(12)
0.06641(12)
0.04564(11)
0.08011(11)
0.13261(11)
0.13802(14)
0.0884(3)
0.1321(4)
0.1985(4)
0.2336(5)
0.2072(4)
0.1428(4)
0.1057(4)
0.2298(6)
0.0488(11) tion of the sequential conjugate gradient method, called the
0.0430(10)
0.0762(14)
0.0905
Polak-Ribiere [25] and Eigenvector Following [26] optimiza-
tion algorithm with a convergence limit of 0.01 kcal/mol and
−0.03953(17) 0.3596(6)
˚
an RMS gradient of 0.05 kcal/A mol. The semi-empirical cal-
−0.0705(2)
0.2673(8)
0.140(3)
0.0674(15)
0.095(2)
culations were carried out using the HyperChem 6.0 pro-
gram package [27]. After geometry optimization, to obtain
the molecular energy profile versus the selected torsion an-
gle [T(C17-N2-C1-C6)], this torsion angle was varied from
−180◦ to +180◦ in steps of 10◦, and the energy profile of
the molecule was obtained by single point calculations on
the computed potential energy surface. Probability-weighted
coordinates of C13, which is disordered in the crystal, were
used in the computations.
−0.03279(15) 0.1747(6)
−0.02982(18) 0.2867(6)
0.22236(14)
0.1772(9)
0.1997(10)
0.18904(17)
0.22284(12)
1/4
0.5260(4)
0.636(3)
0.685(3)
0.6766(5)
0.5537(4)
0.1658(5)
0.0630(12)
0.071(5)
0.072(5)
0.0880(17)
0.0553(11)
0.0342(11)
0.0556(11)
C13A 0.307(2)
C14
C15
C16
0.4875(6)
0.5604(4)
0.1422(5)
C17 −0.0707(5)
0.21965(13) −0.0596(5)
of the crystal data∗, parameters for data collection, the so-
lution and refinement procedures are given in Table 1. All
non-hydrogen atoms were anisotropically refined and an ex-
tinction correction (extinct. coeff. = 0.00746) was applied
in the refinement process. Scattering factors were taken
from International Tables for X-ray Crystallography [21].
Results and Discussion
The key intermediates 1 – 3 were obtained readily by
the condensation of 2-methyl-4-diethyla-minoaniline
with glyoxal. The resulting Schiff base 1 underwent
a smooth reduction providing the ethylenediamine 2
which was converted to the corresponding imidazolin-
ium chloride by treatment with CH(OEt)3 in the pres-
ence of NH4Cl. Next, the salt 3 was deprotonated in
situ with [Rh(µ-OMe)(1,5-COD)]2 to afford the de-
sired complex 4.
∗CCDC 243199 contains the supplementary crystallographic
data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data request/cif, by emailing
data request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336033.
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840
H. Karabıyık et al. · A Rhodium Complex with a New Heterocyclic Carbene Ligand
Elemental analyses and NMR spectra were in agree-
ment with the proposed structure. The clearest spectro-
scopic evidence identifying 4 as a carbene complex is
the appearance of a highly deshielded 13C NMR dou-
blet for Ccarb at 214.80 ppm (JRhC = 47.3 Hz). The
IR spectrum of 4 shows a strong band at 1520 cm−1
attributable to ν(CN2). The absorption bands in the
1400– 1600 cm−1 regions arise from the skeletal vi-
brations of the aromatic rings of the ligand.
A thermal ellipsoid drawing of compound 4 is
shown in Fig. 2 [28]. Fractional atomic coordinates and
equivalent isotropic displacement parameters for the
non-hydrogen atoms are listed in Table 2. Single crys-
tal X-ray diffraction analysis confirmed the monomeric
structure of 4. Several features of this structure, includ-
ing the planar geometry around the Rh atom and the
Fig. 3. Molecular packing diagram of the unit cell.
˚
short N-Ccarb distances (∼ 1.34 A), are consistent with
a carbene complex structure. Rh1, Cl1 and C16 atoms
have special positions (y = 1/4). No chiral centers are
found in the molecule, which has two-fold symme-
try on the mid points of the C12-C12i and C15-C15i
bonds. Rh1, Cl1 and C16 are located on the mirror
plane and the whole molecule has mirror plane through
the Rh1-C16 bond. Weighted average ring bond dis-
tances in the cyclooctadiene and carbene rings are
˚
1.4395 and 1.3908 A, respectively. The COD ring ex-
hibits a boat conformation with the Rh-CCOD distances
˚
ranging from 1.994(4) to 2.203(4) A. The bond dis-
tances Rh1-C12 and Rh1-C12i are shorter than Rh1-
C15 and Rh1-C15i. These results agree with the liter-
ature values [29, 30]. Bond distances between C and
Fig. 4. Calculated energy profile from ZINDO/1 of the title
molecule versus the torsion angle T(C17-N2-C1-C6).
i
˚
N atoms in the N-heterocyclic carbene ring have con- rine atom from the plane Rh-C12-C12 is 0.045(1) A,
siderable differences. Although both C16-N2 and C17- and the deviation of Ccarbene from the plane Rh-C15-
i
i
˚
˚
N2 are single bonds, C16-N2 [1.339(3) A] is shorter C15 is 0.005(3) A. When midpoints of C12-C12 and
than the others. Similar arguments can be proposed C15-C15i are considered, it can be stated that the title
for the C17i-N2i and C16-N2i bonds. The theoretical
compound is a cis isomer. These midpoints, the chlo-
studies indicate that the stability of these carbenes is rine atom and Ccarbene exhibit a slight distortion from
due to electron donation from the nitrogen lone pairs exact planarity at the rhodium atom. The coordination
into the formally vacant p(π) orbital of the carbene geometry about the rhodium center is approximately
carbon [31]. Indeed, excess charge located on the car- square-planar, as expected for a 16 e¯ Rh(I) complex.
bene carbon atom linked to rhodium is relatively higher Throughout the refinement process, C13 was treated
than on other carbon atoms in the molecule, whereas as disordered. C13 is located in C13A and C13B posi-
excess charges located on the nitrogen atoms in the tions with probabilities of 48.2% and 51.8%. There is
carbene ring are lower than on other nitrogen atoms weak π-π stacking [symm. code: −x, −y, −z] among
in the molecule (see Fig. 5). The Cl-Rh-Ccarbene angle 2-methyl-4-diethylaminophenylrings (centroid, Cg16)
of 88.89(12)◦ is in consistence with this type of com- in the crystal. The distance between the ring centroids
˚
pounds in the literatures [1, 2, 6, 16, 32 – 34]. The dihe- is 5.9731(18) A, and two C-H... π interactions are also
dral angle between planes defined by Rh-C12-C12i and found in the structure. For the C9---H23b... Cg16 in-
Rh-C15-C15i is 87.3(3)◦. The deviation of the chlo- teraction [sym. code: −x, −y, −z], the H23b... Cg16,
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H. Karabıyık et al. · A Rhodium Complex with a New Heterocyclic Carbene Ligand
841
◦
˚
Table 3. A comparison of selected bond distances [A], bond angles and torsion angles [ ] from the X-ray crystallographic
study and the ZINDO/1 semi-empirical method.
— Bond distances —
X-ray
1.518(5)
1.471(5)
1.339(3)
1.994(4)
2.085(3)
2.202(3)
2.3965(12)
1.382(5)
— Bond angles —
X-ray
— Torsion angles —
X-ray
ZINDO/1
1.473
1.414
1.337
1.887
2.047
2.068
2.284
1.345
1.341
1.450
ZINDO/1
ZINDO/1
−24.05
109.09
C17-C17i
N2-C17
N2-C16
Rh1-C16
Rh1-C12
Rh1-C15
Rh1-Cl1
C12-C12i
C15-C15i
Cl1-Rh1-C16
Cl1-Rh1-C15
88.89(12) 98.15
91.53(9)
C15-Rh1-C12-C13B
C15-Rh1-C12-C12
−27.2(9)
106.2(2)
135.8(9)
−90.73(18) −88.93
i
85.65
Cl1-Rh1-C12 160.61(10) 162.77
C12-Rh1-C15 81.70(12) 88.20
C12-Rh1-C16 92.06(14) 83.15
C16-Rh1-C12-C13B
137.93
i
C16-Rh1-C12-C12
i
C12-Rh1-C12-C13B −133.4(9)
−133.14
−59.86
−150.05
89.59
i
C15-Rh1-C16 162.03(8) 162.24
C15-Rh1-C12-C13
Cl1-Rh1-C15-C14
−61.3(9)
−148.5(2)
90.50(18)
13.2(2)
i
N2-C16-N2
107.5(3)
110.17
110.23
104.63
122.38
122.79
116.18
117.35
115.98
i
C16-N2-C17 113.5(2)
Cl1-Rh1-C15-C15
1.358(4)
N2-C17-C17i 102.6(3)
C12-Rh1-C15-C14
10.08
i
C12-C13A/B 1.50(2)/1.57(2)
C13A/B-C14 1.471(18)/1.443(18) 1.464
C1-C2-C7
N2-C1-C2
N1-C8-C9
C8-N1-C10
122.5(3)
120.7(2)
109.7(4)
116.9(3)
C12-Rh1-C15-C15
−107.7(2)
−110.28
i
C12-Rh1-C15-C14
50.2(2)
46.64
i
C14-C15
N2-C1
N1-C4
1.503(5)
1.440(3)
1.390(4)
1.452
1.406
1.391
C15 -Rh1-C15-C14
121.0(3)
88.3(3)
111.1(3)
120.36
92.10
106.48
Cl1-Rh1-C16-N2
i
N1-C10-C11 113.9(4)
C12-Rh1-C16-N2
Fig. 5. Calculated excess charges on the non-hydrogen atoms by ZINDO/1 method.
Table 4. Calculated parameters of the optimized title com-
pound.
the same C9... Cg distance, C9---H23c... Cg16 [sym.
code: −x, −y, −z], the H23c... Cg16 distances and the
◦
˚
C9---H23c... Cg16 angle are 3.2244 A and 107.78 re-
spectively.
Total energy [kcal/mol]
Total energy (a.u.)
−208320.373
−331.973
Binding energy [kcal/mol]
Isolated atomic energy [kcal/mol]
Electronic energy [kcal/mol]
Core-core interaction [kcal/mol]
Heat of formation [kcal/mol]
Molecular point group
−27666.488
−180653.885
−1944804.692
1736484.318
−18912.232
Although the optimized geometry of the molecule
is in C1 molecular point symmetry group, the crystal-
lographic structure is in CS point symmetry group. Ex-
cept for this difference, no considerable difference is
found in the study. Some geometrical parameters ob-
tained by the different methods are compared in Ta-
ble 3, and energy parameters are given in Table 4.The
calculated energy profile from ZINDO/1 versus the tor-
sion angle T(C17-N2-C1-C6) is given in Fig. 4. In this
profile, the prominent peak near to 0◦ is due to steric
hindrance between the methyl group linked to C2 and
the COD ring, especially the rhodium atom. The other
C
1
Point charge dipole (debye)
sp hybrid dipole (debye)
pd hybrid dipole (debye)
Total dipole (debye)
6.922
2.752
0.069
9.486
C9... Cg16 distances and the C9---◦H23b... Cg angle
˚
are 3.1718, 3.634(6) A and 111.46 , respectively. In
the related interaction for the ring 2, which has also
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842
H. Karabıyık et al. · A Rhodium Complex with a New Heterocyclic Carbene Ligand
peaks are also primarily due to the rhodium atom and
COD, not due to the position or orientation of the chlo-
rine atom.
˙
¨
¨
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