Synthesis, structure and properties of cycloruthenated complexes: Crystal structure of mono-chloro-(η6-p-cymene)-{(phenylazo)phenyl}ruthenium(II)

Article abstract of DOI:10.1016/S0022-328X(99)00611-7

Two cycloruthenated complexes of formulation [(η⁶-p-cymene)RuCl(L)], where L = (phenylazo)phenyl (pap) (1a) and (4,4′-dimethyl)(phenylazo)phenyl (dmpap) (1b) were prepared from a transmetallation reaction involving [(η⁶-p-cymene)RuCl₂]₂ and [HgCl(L)] in refluxing CHCl₃ or MeOH. The molecular structure of [(η⁶-p-cymene)RuCl(pap)] (1a) has been determined by X-ray crystallography. The complex contains a η⁶-p-cymene group, a chloride and a bidentate C,N-donor orthometallated (phenylazo)phenyl ligand. The complexes have been characterized from NMR data. The orthometallated carbon appears near δ 188 ppm in the ¹³C-NMR in CDCl₃.

Full text of DOI:10.1016/S0022-328X(99)00611-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 596 (2000) 232–236
Note
Synthesis, structure and properties of cycloruthenated complexes:
crystal structure of
mono-chloro-(h6-p-cymene)-{(phenylazo)phenyl}ruthenium(II)
Rakesh K. Rath, Sudha G. Valavi, Kannappan Geetha, Akhil R. Chakravarty *
Department of Inorganic and Physical Chemistry, Indian Institute of Science, UGC Centre of Ad6anced Study, Bangalore 560012, India
Dedicated to Professor F. Albert Cotton on the occasion of his 70th birthday
Abstract
Two cycloruthenated complexes of formulation [(h6-p-cymene)RuCl(L)], where L=(phenylazo)phenyl (pap) (1a) and (4,4%-
dimethyl)(phenylazo)phenyl (dmpap) (1b) were prepared from a transmetallation reaction involving [(h6-p-cymene)RuCl2]2 and
[HgCl(L)] in refluxing CHCl3 or MeOH. The molecular structure of [(h6-p-cymene)RuCl(pap)] (1a) has been determined by X-ray
crystallography. The complex contains a h6-p-cymene group, a chloride and a bidentate C,N-donor orthometallated (phenyl-
azo)phenyl ligand. The complexes have been characterized from NMR data. The orthometallated carbon appears near l 188 ppm
in the 13C-NMR in CDCl3. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Arene-ruthenium; ortho-Metallation; Crystal structure; Azobenzene
Herein we report the synthesis, structure and properties
of [(h6-p-cymene)RuCl(L)], where L is bidentate chelat-
ing C,N-donor (phenylazo)phenyl (1a) or (4,4%-di-
methyl)(phenylazo)phenyl (1b) ligand. Complex 1a has
been structurally characterized.
1. Introduction
The half-sandwich (h6-arene)ruthenium(II) com-
plexes have drawn considerable current attention in
asymmetric transformation reactions and in the devel-
opment of the chemistry of optically active enantio-
selective catalytic systems [1–10]. The ancillary ligand
bonded to ruthenium plays a vital role in such catalytic
reactions. Earlier studies have shown that N,N- and
N,O-donor bidentate ligands are useful in the synthesis
of optically active diastereomeric complexes as well as
for asymmetric induction studies [11–15]. The chem-
istry of cycloruthenated (arene)ruthenium(II) complexes
are relatively scarce and only a few systems having
C,N-donor bidentate ligands have been explored in
diastereomeric reactions [3–6,14].
2. Results and discussion
The complexes of formulation [(h6-p-cymene)-
RuCl(L)] are prepared from a facile transmetallation
reaction involving [(h6-p-cymene)RuCl2]2 and the or-
thometallated mercury(II) complex HgCl(L) in chloro-
form or methanol [L, (phenylazo)phenyl, 1a or (4,4%-
dimethyl)-(phenylazo)phenyl, 1b]. The complexes are
fairly air stable in the solid state but are unstable in the
solution phase. Both the complexes are characterized
from elemental analysis and NMR spectral data. The
electronic spectra of the complexes show intense charge
transfer bands involving the azofunctionality and p-
cymene ligand near 450 nm in acetonitrile along with a
very strong band near 330 nm. A relatively weak visible
The present work stems from our interest to develop
the chemistry of (h6-arene)ruthenium complexes having
C,N-donor azobenzene and related ligand systems.
* Corresponding author.
E-mail address: arc@ipc.iisc.ernet.in (A.R. Chakravarty)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00611-7

R.K. Rath et al. / Journal of Organometallic Chemistry 596 (2000) 232–236
233
Table 1
band is observed in the range 575–597 nm. The com-
,
Bond lengths (A) and bond angles (°) for 1a with estimated S.D.s in
plexes are redox active and show an irreversible
azo bond reduction at −1.15 V and an irreversible
oxidation process at 0.9 V vs. SCE in MeCN–0.1 M
TBAP.
parentheses (CO, the centroid of the h6-arene ring)
Bond lengths
Ru1–C2
Ru1–C3
Ru1–C4
Ru1–C5
Ru1–C6
Ru1–C7
C2–C3
C3–C4
C4–C5
C5–C6
C6–C7
C11–C12
2.344(4)
2.217(4)
2.193(5)
2.169(4)
2.154(5)
2.321(4)
1.429(6)
1.383(6)
1.427(6)
1.411(7)
1.421(6)
1.397(7)
1.389(7)
1.377(8)
1.735(2)
Ru1–Cl1
Ru1–C11
Ru1–N1
C5–C8
C8–C9
C8–C10
C1–C2
C2–C7
N1–C17
N1–N2
N2–C16
C11–C16
C14–C15
C15–C16
2.393(1)
2.005(4)
2.041(4)
1.508(6)
1.523(6)
1.524(7)
1.503(6)
1.379(6)
1.435(6)
1.279(5)
1.380(6)
1.400(7)
1.365(9)
1.400(7)
The 1H-NMR data suggest a 1:1 ratio of the p-
cymene and the azophenyl ligands in 1a and 1b. The
arene ligand displays a singlet for the methyl, two
doublets and a septet for the CHMe2 in the range l
0–3 ppm. The arene ring protons appear within l 5–7
ppm. The appearance of two doublets for the two
methyls of the CHMe2 moiety could be due to the
diastereotropic nature of the methyl groups. The spec-
tral features in the range l 7–9 ppm are due to the
chelating (phenylazo)phenyl ligand. The orthometal-
lated phenyl group in 1b shows a singlet at 8.22 ppm.
The four doublets in the ranges 7.0–7.3 and 8.0–8.1
ppm are assignable to the aryl group protons of the
bidentate ligand. The methyl groups of the ligand ap-
pear as two singlets near l 2.5 ppm. The 13C-NMR
C12–C13
C13–C14
Ru1–CO
Bond angles
Cl1–Ru1–N1
Cl1–Ru1–CO
N1–Ru1–CO
Ru1–N1–C17
N1–N2–C16
C11–C16–N2
C14–C15–C16
C12–C13–C14
N1–C17–C18
C5–C8–C9
C9–C8–C10
C2–C3–C4
C3–C4–C5
C5–C6–C7
C6–C5–C8
89.4(1)
125.2(4)
132.2(3)
124.0(3)
111.1(4)
117.4(4)
118.6(6)
121.3(6)
120.5(5)
108.7(4)
111.4(5)
122.0(4)
121.0(5)
122.3(4)
123.4(4)
Cl1–Ru1–C11
N1–Ru1–C11
C11–Ru1–CO
Ru1–N1–N2
Ru1–C11–C16
N2–C16–C15
C13–C14–C15
C11–C12–C13
N1–C17–C22
C5–C8–C10
C1–C2–C3
86.6(1)
75.8(2)
130.8(6)
121.4(4)
114.2(4)
119.2(6)
119.9(6)
121.1(5)
119.1(4)
114.0(5)
120.7(4)
121.6(5)
116.1(4)
120.5(5)
C1–C2–C7
C4–C5–C6
C4–C5–C8
spectra of the complexes show the M–C s-bond for-
mation. This characteristic signal is observed at l 188.0
ppm for 1a (Fig. 1) and l 188.7 ppm for 1b. The
13C-NMR spectral features of 1a and 1b are essentially
same. The NMR data are consistent with those re-
ported for related pap and 4,4%-dmpap complexes
[15,16]. The assignments of the protons in 1a have been
made unambiguously from the 2D-NMR correlation
spectra in CDCl3–TMS and the crystal-structure data.
The complex [(h6-p-cymene)RuCl(pap)] (1a) has
been structurally characterized by X-ray crystallogra-
phy. An ORTEP [17] view of the complex is shown in
Fig. 2. Selected bond distances and bond angles are
given in Table 1. The coordination geometry of the
metal center is essentially octahedral with the h6-p-
cymene ring carbons occupying one face of the octahe-
dron. The remaining sites are occupied by a chloride
Fig. 1. 13C-NMR spectrum of 1a in CDCl3 (S, solvent peak).
and
a
bidentate chelating C,N-donor (phenyl-
azo)phenyl ligand. The Ru–C (arene) distances vary
,
considerably from 2.154 to 2.334 A [18,19]. The
Ru(1)–C(11) bond of 2.005(4)° is marginally shorter
than the similar Ru–C s-bond distances reported in
related (h6-p-cymene)ruthenium complexes [4].
Fig. 2. ORTEP drawing giving 50% probability thermal ellipsoids and
the atom labeling scheme of [(h6-p-cymene)RuCl(pap)] (1a).

234
R.K. Rath et al. / Journal of Organometallic Chemistry 596 (2000) 232–236
In summary, we have synthesized new (arene)-
[umax, nm (m, l mol−1 cm−1)]: 597 (525), 455 (3350),
332 (11400), 270 (10410). H-NMR [CDCl3, 200 MHz,
l in ppm, J in Hz]: 8.29 (1H, m, H12), 8.18 (3H, m,
H15,18,22), 7.50 (3H, m, H19–21), 7.18 (2H, m, H13,14),
1
ruthenium(II) complexes having C,N-donor bidentate
(phenylazo)phenyl and (4,4%-dimethyl)(phenylazo)-
phenyl ligands. The complexes with a labile binding
site are suitable for stereochemical investigations in
chloride substitution reactions and for reactions di-
rected to the Ru–C s-bond.
3
3
5.69 (1H, d, JHH=6.5, H4), 5.54 (1H, d, JHH=6.1,
3
3
H7), 5.16 (1H, d, JHH=6.5, H3), 5.06 (1H, d, JHH
=
6.0, H6), 2.27 (1H, sp, 3JHH=7.0, H8), 2.11 (3H, s,
3
H1A–C), 0.90 (3H, d, JHH=7.0, H9A–C), 0.73 (3H, d,
3JHH=7.0, H10A–C) (s, singlet; d, doublet; sp, septet;
m, complex multiplet pattern). The hydrogen atom
numbering scheme is same as the carbon atom label-
ing scheme shown in Fig. 2. 13C-NMR [CDCl3, 100.61
MHz; l, ppm]: 188.05 (C11), 163.58, 158.16 (C16,17),
3. Experimental
All reactions were carried out in dry solvent under a
dinitrogen atmosphere. Azobenzene, azotoluene and
their mercury compounds were synthesized following
literature procedures [20,21]. The precursor complex
139.23, 130.52, 129.72, 128.23, 123.56, 122.98 (C12–15
,
C18–22), 106.14, 103.19, 95.58, 92.52, 86.43, 86.13
(C2–7), 30.79 (C1), 22.64, 21.19 (C9,10), 18.79 (C8).
[(h6-p-cymene)RuCl2]2 was made by
a
reported
method [22]. All chemicals were of reagent grade and
used as such.
3.2. Synthesis of [(p6-p-cymene)RuCl(4,4%-dmpap)]
Elemental analysis was performed on a Perkin–
Elmer 2400 CHN analyzer. The 1H- and 13C-{1H}-
NMR spectra were recorded on Bruker 200 MHz
and Bruker DRX 400 (carbon channel 100.6 MHz)
spectrometers, respectively. Tetramethylsilane (TMS)
was used as a standard (l 0.0 ppm). Electronic spectra
were recorded on a Hitachi U-3400 spectrophotome-
ter. Cyclic voltammetric measurements were performed
A
mixture of 0.3 g
(0.49 mmol) of [(h6-p-
cymene)RuCl2]2 and 0.45 g (1.01 mmol) of ClHg-
(dmpap) was stirred for 28 h in refluxing methanol.
The resulting solution was filtered through Celite and
the solvent was evaporated to isolate the solid, which
was then dissolved in 5 ml of CHCl3. Addition of cold
n-hexane gave a crystalline solid of 1b (0.4 g). The
solid was washed with cold hexane and dried in
vacuum. Anal. Found: C, 60.20; H, 5.41; N, 5.92.
C24H27N2ClRu requires: C, 60.06; H, 5.63; N, 5.84%.
UV–vis data in MeCN [umax, nm (m, l mol−1 cm−1)]:
using
a PAR model 253 Versastat potentiostat/
galvanostat with EG&G electrochemical software op-
erating on WINDOWS 95. In the three-electrode
configuration, a platinum button, a platinum wire,
and a saturated calomel electrode (SCE) were used
as working, auxiliary and reference electrodes, re-
1
577 (564), 451 (2160), 340 (13800). H-NMR [CDCl3,
200 MHz, l in ppm, J in Hz]: 8.23 (1H, s, H12),
3
spectively. In the measurements, 0.1
M
(Bun4N)-
8.11 (1H, d, 3JHH=8.0, H15), 8.02 (2H, d, JHH
=
3
ClO4 (TBAP) in acetonitrile solvent was used as a
supporting electrolyte. The measurements were made
at 25°C and the data were uncorrected for junction
potentials. Ferrocene was used as standard to verify
the potential observed against the SCE. The FeII/FeIII
couple of ferrocene was observed at 0.43 V (versus
SCE).
8.0, H18,22), 7.29 (2H, d, JHH=8.0, H19,21), 7.06 (1H,
d, 3JHH=8.0, H14), 5.69, 5.64, 5.29, 5.10 (4H, 4d,
3JHH=6.0, H3,4,6,7), 2.50 (3H, s, Me–C13), 2.47 (3H, s,
Me–C20), 2.23 (1H, sp, H8), 2.15 (3H, s, H1A–C),
0.86,0.72 (2×3H, 2d, JHH=6.8, H9A–C, H10A–C). 13C-
3
NMR [CDCl3, 100.61 MHz; l, ppm] 188.68 (C11),
162.50, 156.68 (C16,17), 141.06, 140.50, 130.70, 129.48,
126.12, 125.70, 123.63 (C12–15, C18–22), 106.41, 103.27,
96.21, 92.68, 87.24, 86.68 (C2–7), 31.52, 31.00 (C1,
3.1. Synthesis of [(p6-p-cymene)RuCl(pap)] (1a)
C
(C8).
6
H3–C13), 23.33, 22.90, 21.91 (C9,10, C
6 H3–C20), 19.54
A
mixture of 0.3 g
(0.49 mmol) of [(h6-p-
cymene)RuCl2]2 and 0.42 g (1.01 mmol) of ClHg(pap)
in 30 ml of CHCl3 was stirred for 48 h under refluxing
condition. The resulting dark red solution was filtered,
reduced to a volume of 5 ml and chromatographed on
a neutral alumina column in CHCl3. The major light
green band was collected using CHCl3 as an eluant
and a solid was obtained on evaporation of the sol-
vent. The complex was subsequently crystallized from
an acetone–toluene (1:1, v/v) mixture giving 0.27 g of
the product as dark orange crystals. Anal. Found: C,
58.28; H, 5.10; N, 6.50; C22H23N2ClRu requires: C,
58.47; H, 5.10; N, 6.20%. UV–vis data in MeCN
3.3. X-ray structure determination of 1a
Orange needles of 1a were obtained by cooling
a solution of the complex in acetone–toluene mixture
(1:1, v/v) at −5°C. Unit cell dimensions were ob-
tained on an Enraf–Nonius CAD4 diffractometer
equipped with graphite monochromated Mo–Ka radi-
,
ation (u=0.7107 A) using a crystal of approximate
dimension 0.32×0.13×0.49 mm3. Intensities of reflec-
tions (−105h510; 05k518; 05l517) within the
range 4°52q551° were measured in a ꢀ/2q scan

R.K. Rath et al. / Journal of Organometallic Chemistry 596 (2000) 232–236
235
Calcutta) for the elemental analysis data and the Alex-
ander von Humboldt Foundation in Germany for the
donation of an electroanalytical system.
mode. Out of 3537 unique reflections, 2571 data with
I]2|(I) were used for the refinement of the structure.
The intensity data were corrected for Lorentz and
polarization effects. Crystal data: C22H23N2ClRu,
Mr=451.94, monoclinic, P21/a, a=8.806(3), b=
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920, v(Mo–Ka)=9.22 cm−1, T=293(2) K.
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(F2o+2F2c)/3, a=0.0233 and b=2.13 using 235
parameters for 2571 reflections [R indices (all data):
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−0.48 e A−3. The goodness-of-fit on F2 was 1.121.
,
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Crystallographic data (atomic coordinates, bond
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structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre,
CCDC no. 134995. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Acknowledgements
This work was supported by the Council of Scien-
tific and Industrial Research, New Delhi. We are
grateful to Professor P.S. Zacharias and Dr S. Pal
(Central University, Hyderabad) for providing the X-
ray data set. We thank Professor N. Roy Chaudhuri
(Indian Association for the Cultivation of Science,

236
R.K. Rath et al. / Journal of Organometallic Chemistry 596 (2000) 232–236
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