Syntheses and characterization of arene ruthenium (II) complexes containing N,N′-donor Schiff base ligands. Crystal and molecular structure of [(η6-C6Me6)Ru (C5H4N-2-CH=N-C6H4-p-

Article abstract of DOI:10.1016/S0277-5387(02)01430-4

Reaction of [(η⁶-C₆Me₆)RuCl₂]₂ (1a) with N, N′-donor Schiff bases viz., para-substituted N-(2-pyridinylmethylene)phenylamines yielded complexes of the formulation [(η⁶-C₆Me₆

Full text of DOI:10.1016/S0277-5387(02)01430-4

Polyhedron 22 (2003) 605Á609
/
www.elsevier.com/locate/poly
Syntheses and characterization of arene ruthenium (II) complexes
containing N,N?-donor Schiff base ligands. Crystal and molecular
structure of [(h6-C6Me6)Ru(C5H4N-2-CHꢀ
/
Nꢁ
/
C6H4-p-NO2)]PF6
R. Lalrempuia a, Mohan Rao Kollipara a,*, Patrick J. Carroll b
a Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
Received 7 October 2002; accepted 9 December 2002
Abstract
Reaction of [(h6-C6Me6)RuCl2]2 (1a) with N,N?-donor Schiff bases viz., para-substituted N-(2-pyridinylmethylene)phenylamines
yielded complexes of the formulation [(h6-C6Me6)Ru(C5H4N-2-CHꢀ C6H4-p-X)Cl]ꢀ 2aÁ
Nꢁ e where C6Me6ꢁhexamethylbenzene,
Xꢁ
H (2a), CH3 (2b), OCH3 (2c), Cl (2d) and NO2 (2e). Reaction of 1a and [(h6-p-cymene)RuCl2]2 (1b) where p-cymeneꢁ
(CH3C6H4CH(CH3)2) with N-(2-pyridinylmethylene)cyclohexylamine (2-PC) yielded complexes of the type [(h6-arene)Ru(2-
PC)Cl]ꢀ (areneꢁ
C6Me6 (3a); p-cymene, (3b)) respectively. All these complexes were isolated as their PF6 salt. These complexes
were characterized by spectroscopic and analytical data. The molecular structure of [(h6-C6Me6)Ru(C5H4N-2-CHꢀ
NꢁC6H4-p-
/
/
/
/
/
/
/
/
/
NO2)Cl]PF6 2e has been determined by X-ray crystallography.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: p-Cymene; Hexamethylbenzene; N-(2-pyridinylmethylene)phenylamines; N-(2-pyridinylmethylene)cyclohexylamine; Schiff base;
Ruthenium
1. Introduction
complex
NO2)Cl]PF6 is also reported.
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
/
Nꢁ/C6H4-p-
Recent interest in half sandwich arene ruthenium
complexes arises from their use as catalysts [1] in organic
syntheses and also recent studies have shown that they
are found to inhibit cancer cell growth [2]. Moreover,
the photophysics, photochemistry and redox properties
of a,a?-diimines ruthenium [3] complexes have been
prolific areas of research over the past two decades.
There are few reports of arene ruthenium complexes
with a,a?-diimines [4] available in literature. Herein, we
would like to report the synthesis and characterization
of new cationic half sandwich ruthenium complexes of
N,N?-Schiff base ligands. The molecular structure of the
2. Experimental
All reactions were carried out in distilled and dried
solvents. Pyridine 2-carboxaldehyde (Fluka) was used as
received. All liquid aromatic amines were reagent grade
and were distilled prior to use and solid aromatic amines
1
were used as such. H NMR spectra were recorded in
CD3CN, CDCl3 and (CD3)2CO solvents with tetra-
methylsilane as an internal standard and recorded on a
Brucker ACF-300 MHz spectrometer. Infrared spectra
were taken on a Perkin-Elmer model 983 spectrophot-
ometer using KBr pellets. Elemental analysis was
performed in Perkin-Elmer-2400 CHNS/O analyser.
Conductivity measurement was performed in Wayne
Kerr Automatic Precision Bridge B-905. The ligands
* Corresponding author. Tel.:
550486.
ꢀ
/
91-364-550041; fax:
ꢀ/91-364-
C5H4N-2-CHꢀ
/
Nꢁ
/
C6H4-p-X (where XꢁH, CH3,
/
E-mail addresses: mrkollipara@rediffmail.com, kmrao@nehu.ac.in
(M.R. Kollipara).
OCH3, Cl, NO2) and 2-PC were prepared according to
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(02)01430-4

606
R. Lalrempuia et al. / Polyhedron 22 (2003) 605Á609
/
the literature methods [5]. The precursor complexes
[(arene)RuCl2]2, areneꢁC6Me6 1a, p-cymene 1b were
prepared by known methods [6].
converged to R1ꢁ
reflections for which F ꢀ
/
0.0534 and wR2ꢁ
4s(F) and R1ꢁ
1.138 for all 5971 unique, non-zero
/
0.1332 for 5471
/
/
/
0.0592, wR2ꢁ
/
0.1378 and GOFꢁ
/
reflections and 350 variables1.
2.1. Preparation of [(h6-C6Me6)Ru(C5H4N-2-CHꢀ
C6H4-p-X)Cl]PF6 (2aÁe) (XꢁH, CH3, OCH3, Cl,
NO2)
/
Nꢁ
/
Table 1 shows cell information, data collection
parameters, and refinement data. Table 2 lists bond
distances and bond angles. Fig. 1 is an ORTEP [10]
representation of the molecule with 30% probability
thermal ellipsoids displayed.
/
/
These complexes were prepared using a general
procedure in which the mixture of [(h6-C6Me6)RuCl2]2
(0.15 mmol) and the ligand (0.30 mmol) in methanol (20
ml) were stirred at room temperature for 1 h. The
resulting solution was filtered and NH4PF6 (0.32 mmol)
was added to the clear solution. Then stirred at 0 8C
whereby orange compound precipitated for complexes
3. Results and discussion
The reaction of [(h6-arene)RuCl2]2 with neutral N,N?-
Schiff base ligands yielded complexes of the type 2 and 3
with XꢁCH3, Cl, NO2 which was collected and washed
/
in fairly good yield. The orangeÁred colored complexes
/
with water, methanol and finally with diethylether and
dried in vacuum.
of 2 are air stable while the dark brown complexes of 3
are slightly air sensitive. These complexes are insoluble
in water, chlorinated, alcohol and non-polar solvents
but soluble in other polar solvents. These complexes
exhibited 1:1 electrolyte system [11] in acetonitrile
For the complexes with XꢁH and OMe, the dark
/
brown solution was stirred for 2 h and the solvent was
removed under reduced pressure. The residue was
extracted with dichloromethane and filtered through
short silica column. The resulting solution was reduced
in volume to about 2 ml and hexane (15 ml) was added
to give red brown compound, which was recrystallized
from the mixture of acetone and hexane to give orange
solution (ꢁ
130 ohmꢂ1 cm2 molꢂ1).
/
Table 1
Summary of structure determination of compound [(h6-C6Me6)R-
u(C5H4N-2-CHꢀNꢁC6H4-p-NO2)]PF6 (2e)
/
/
crystals. Yield ranges from 70Á
/
80%.
Formula
RuC24H27N3PO2F6Cl
670.98
Formula weight
Crystal class
Space group
Z
2.2. Preparation of [(h6-arene)Ru(2-PC)Cl]PF6;
monoclinic
P21/n (#14)
4
areneꢁC6Me6 (3a), p-cymene (3b)
/
Cell constants
˚
The complexes were prepared in similar manner to
that of the preparation of 2 (XꢁH, OMe) where the
oily product obtained was washed several times with
a (A)
˚
10.65120(10)
11.71340(10)
21.7134(3)
98.1180(10)
2681.86(5)
8.13
/
b (A)
˚
c (A)
b (8)
hexane to gave dark brown solid in 65% yield.
3
V (A )
˚
m (cmꢂ1
)
2.3. Crystallographic analysis
Crystal size (mm)
)
0.42ꢃ/0.11ꢃ0.06
/
Dcalc (g cmꢂ3
F(000)
1.662
1352
X-ray quality crystals of complex 2e as PF6 salt, were
obtained by a diffusion technique in which diethylether
was carefully layered into acetonitrile solution of the
˚
0.71069A)
Radiation
Mo Ka (lꢁ
5.14Á54.96
130h 0
280
26 725
5971 (Rint
5471 (F ꢀ
/
2u 0/28 range (8)
/
hkl collected
ꢂ/
/
/
13; ꢂ140k 0
/
/
/
15; ꢂ
/
complex. An orangeÁred crystal was mounted on a glass
/
/
l
fiber with epoxy cement. X-ray intensity data were
collected on a Rigaku R-AXIS IIc area detector
No. reflections measured
No. unique reflections
No. observed reflections
ꢁ
4s)
/
0.0312)
/
employing graphite-monochromated Mo Ka radiation
No. reflections used in refine- 5971
ment
˚
0.71069 A) at a temperature of 293 K. The intensity
(lꢁ
/
data were corrected for Lorentz and polarization effects
and for absorption using REQAB [7]. The structure was
solved by direct methods (SIR92) [8]. Refinement was
No. parameters
R indices (F ꢀ4s)
R indices (all data)
350
R1ꢁ
/
/
0.0534, wR2ꢁ
/
0.1332
R1ꢁ
/
0.0592, wR2ꢁ
/
0.1378
by full-matrix least squares based on F2 using SHELXL
-
GOF
˚
Final difference peaks (e A
1.138
ꢂ3
)
ꢀ
/
0.659, ꢂ0.638
/
93 [9]. All reflections were used during refinement (F2’s
that were experimentally negative were replaced by F2ꢁ
/
2
0). The weighting scheme used was wꢁ
/
1/(s2(Fo )ꢀ
/
2
2
0.0693P2ꢀ
drogen atoms were refined anisotropically and hydrogen
/
2.5252P) where Pꢁ
/
(Fo ꢀ2Fc )/3. Non-hy-
/
1
R1 ꢁ
{aw(F2oꢂ
and pꢁthe number of parameters refined.
/
ajjFojꢂ
/
jFcjj/aFoj, wR2 ꢁ
/
{aw (F2oꢂ
/
F2c )2/aw (Fo2)2}1/2
the number of reflections
,
GOFꢁ
/
/
F2c)2/(nꢂ
/
p)}1/2, where nꢁ
/
atoms were refined using a ‘riding’ model. Refinement
/

R. Lalrempuia et al. / Polyhedron 22 (2003) 605Á
/
609
607
Table 2
Selected bond lengths (A) and angles (8) for [(h -C6Me6)Ru(C5H4N-2-CHꢀ
6
˚
/
Nꢁ/C6H4-p-NO2)]PF6 (2e)
Bond lengths
Bond angle
Ruꢁ
Ruꢁ
Ruꢁ
Ruꢁ
Ruꢁ
Ruꢁ
Ruꢁ
N3ꢁ
N3ꢁ
/
N1
2.099(3)
2.106(3)
2.250(3)
2.227(3)
2.225(4)
2.251(4)
2.190(3)
1.184(8)
1.207(8)
Ruꢁ
C13ꢁ
C14ꢁ
C15ꢁ
C16ꢁ
C17ꢁ
/
C13
2.204(3)
1.435(5)
1.395(6)
1.448(6)
1.410(6)
1.422(6)
1.288(4)
1.431(4)
N1ꢁ
N1ꢁ
N2ꢁ
C7ꢁ
C6ꢁ
C5ꢁ
C15ꢁ
C16ꢁ
N1ꢁRuꢁ
N2ꢁRuꢁ
O1ꢁN3ꢁ
O1ꢁN3ꢁ
O2ꢁN3ꢁ
/
Ruꢁ
Ruꢁ
Ruꢁ
/
N2
75.90(11)
96.13(13)
94.42(12)
126.5(2)
116.3(2)
116.2(2)
90.79(11)
92.52(12)
83.92((9)
85.84(8)
123.7(6)
118.9(6)
117.4(6)
/N2
/
C14
C15
C16
C17
C18
/
/
C18
C13
/
C14
C15
C16
C17
C18
O1
/
/
/
/
/
/
N2-Ru
N2ꢁRu
N1-Ru
/
/
/
/
/
/
/
/
N2ꢁ
/C6
/
Ruꢁ
/Cl
/
N2ꢁ
/
C7
/
Ruꢁ
/Cl
/O2
/
/
ꢁCl
/
/
/
C
/
/
O2
/
/
C10
/
/
C10
for methyl protons of hexamethylbenzene at around d
1.8 and 2.1, respectively and the peaks for the ligand
moiety appeared in the range of d 7Á9. The methine
/
proton of 2 and 3 appear at around d 8.4 and 8.8,
respectively. This proton resonated in the same range of
corresponding p-cymene compounds [4b]. The a-proton
of the pyridine ring of complex 3 showed a up field shift
of about d 0.3 in comparison to complex 2 due to the
cyclohexyl group. 1H NMR spectrum of complex 3b
suggests the presence of h6-p-cymene and 2-PC in 1:1
ratio. The protons of isopropyl group of the h6-p-
cymene ligand appear as two sets of doublets at around
d 1.16 due to the loss of planarity of the benzene ring
because of steric nature of the ligand (Fig. 2) [12]. Septet
at d 2.70 was observed for single proton of isopropyl
group. The benzene ring protons of p-cymene appeared
Fig. 1. ORTEP view of the complex [(h6-C6Me6)Ru(C5H4N-2-CHꢀ
C6H4-p-NO2)] 2e showing 30% probability thermal ellipsoids with
/
Nꢁ
/
atom numbering scheme. PF6 omitted for clarity.
as two doublets and a triplet in the range of d 5.92Á6.23,
/
[(h6-C6Me6)RuCl2]2 ꢀ2(C5H4N-2-CH.N*C6H4-p-X)
respectively due to long range coupling with isopropyl-
1
proton. H NMR spectrum of complex 3b is shown in
Fig. 2.
0 [(h6-C6Me6)Ru(C5H4N-2-CH.N
*C6H4-p-X)Cl]PF6
Electronic spectra of these complexes in acetonitrile
exhibited bands in the range of 340Á400 nm (Table 4).
/
These low-energy absorption were assigned to Ru (dp)
to ligand (p*) metal to ligand charge transfer (MLCT)
transition.
(X.H; CH3; OCH3; Cl; NO2 (2a-e))
[(h6-arene)RuCl2]2 ꢀ2(C5H4N-2-CH.N*C6H11)
0 [(h6-arene)Ru(C5H4N-2-CH.N*C6H11)Cl]PF6
areneꢁ(h6-C6Me6) (3a); p-cymene (3b)
The complex [(h6-C6Me6)Ru(C5H4N-2-CHꢀ
/
Nꢁ
/
C6H4-p-NO2)]PF6 (2e) has been structurally character-
ized by X-ray crystallography. An ORTEP view of the
complex is shown in Fig. 1. The complex 2e exist as half
sandwich complex with the arene ring occupying three
facial sites. The ruthenium atom is p bonded to the
These complexes are characterized by elemental
1
analysis, IR and H NMR spectral data (Table 3). All
these complexes gave satisfactory analytical data. IR
spectra of the complexes showed medium intensity
hexamethylbenzene ligand with an average Ruꢁ
/
C dis-
bands in the range of 1600Á
the benzene ring. Complex 2e has showed characteristic
1488 cmꢂ1 similar to the
/
1400, 770Á
557 cmꢂ1 for
/
˚
tance 2.22 A similar to that observed in related
hexamethylbenzene ruthenium complexes [13]. The dis-
tance between ruthenium and the chloride ligand is 2.39
IR bands for nNO at 1526Á
/
2
˚
A. In addition to being bonded to the arene and the
chloride ligands, the ruthenium atom is also directly
coordinated to two nitrogen atoms of the Schiff base
range observed for nNO of other reported compounds.
1H NMR data of compl2exes 2 suggests a 1:1 ratio of the
1
hexamethylbenzene and Schiff base ligands. H NMR
spectra of the complexes 2 and 3a display sharp singlet
˚
ligand with an average distance of 2.10 A. The bite angle

608
R. Lalrempuia et al. / Polyhedron 22 (2003) 605Á609
/
Table 3
IR and 1H NMR data of the complexes 2a
/
e and 3a
/
b
Á
Á
Complex IR bands (KBr pellets, cmꢂ1
)
1H NMR, d (ppm) (Schiff base)
H NMR, d (ppm) (Arene)
2a
b
1590 (nCꢁN) 844 (nP ꢁF
1586 (nCꢁN) 844 (nP ꢁF
1589 (nCꢁN) 839 (nP ꢁF
1589 (nCꢁN) 843 (nP ꢁF
)
)
)
)
9.16 (d, 1H, 3), 8.80 (s, 1H), 8.34 (m, 2H), 7.96 (m, 1H),
7.85 (d, 2H), 7.63 (m, 2H)
1.87 (s, 18 H)
8.90 (d, 1H, 3), 8.41 (s, 1H), 8.11 (m, 2H), 7.77 (t, 1H),
7.59 (d, 2H), 7.50 (d, 2H), 2.44 (s, 3H)
8.89 (d, 1H, 3), 8.39 (s, 1H), 8.10 (m, 2H), 7.75 (t, 1H),
7.62 (d, 1H), 7.13 (d, 1H), 3.98 (s, 3H)
8.92 (m, 1H, 3), 8.46 (s, 1H), 8.12 (m, 2H), 7.79 (t, 1H),
7.69-7.58 (m, 4H)
1.87 (s, 18 H)
1.88 (s, 18H)
1.86 (s, 18H)
1.93 (s, 18H)
2.14 (s, 18H)
c
d
e
1584 (nCꢁN) 836 (nPꢁF
)
8.96 (m, 1H), 8.53 (s, 1H), 8.45 (m, 2H), 8.17 (m, 2H),
7.92-7.83 (m, 4H)
3aa
3ba
1597 (nCꢁN) 840 (nP ꢁF
)
9.43 (d, 1H, 6), 8.74 (s, 1H), 8.42 (d, 1H), 7.99 (m, 2H),
7.65 (m, 1H), 2.00-1.24 (m)
9.54 (d, 1H, 6), 8.86 (s, 1H), 8.29-8.24 (m, 2H), 7.81 (t, 1H, 6), 6.23 (dd, 2H, 6), 5.92 (t, 2H, 6), 2.70
1598 (nCꢁN) 838 (nPꢁF
)
1.95-1.98 (m)
(sp, 1H), 2.28 (s, 3H), 1.14 (dd, 6H, 6)
1H NMR of complexes taken in CD3CN.
a
In (CD3)2CO, s, singlet; d, doublet; t, triplet; m, multiplet.
The average Cꢁ
/
C bond lengths in the hexamethyl-
˚
benzene ring is 1.421 A with alternate short and long
Table 4
MLCT absorption at room temperature
bond lengths where C(13)ꢁ
C(14)ꢁC(15) bonds are shorter than the C(13)ꢁ
C(15)ꢁC(16) and C(17)ꢁC(18) which could be due to
the loss of planarity of the hexamethylbenzene ring. The
alternate bond lengths are indicative of a contribution
from the cyclohexatriene resonance structure to the
overall resonance hybrid [14].
/
C(18), C(16)ꢁ
/
C(17) and
Complexa
lmax, nm
/
/C(14),
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
[(h6-C6Me6)Ru(C5H4N-2-CHꢀ
[(h6-p-Cymene)Ru(C5H4N-2-CHꢀ
/
Nꢁ
Nꢁ
Nꢁ
Nꢁ
Nꢁ
Nꢁ
/
C6H4-p-H)Cl]PF6
C6H4-p-CH3)Cl]PF6
C6H4-p-OCH3)Cl]PF6
C6H4-p-Cl)Cl]PF6
C6H4-p-NO2)Cl]PF6
C6H11)Cl]PF6
374
366
360
374
400
342
340
/
/
/
/
/
/
/
/
/
/
/
/
/
NꢁC6H11)Cl]PF6
/
4. Conclusions
of the chelating ligand is 75.90(11)8 not very different
from other related complexes [4b]. Notably, the phenyl
and pyridyl ring of the Schiff base are not coplanar.
Reactions of [(arene)RuCl2]2 (areneꢁhexamethyl-
benzene, p-cymene) with Schiff bases viz. para-substi-
tuted N-(2-pyridinylmethylene)phenylamines and N-(2-
/
Fig. 2. 1H NMR spectrum of complex [(h6-p-cymene)Ru(C5H4N-2-CHꢀ
/
NꢁC6H11)]PF6 (3b).
/

R. Lalrempuia et al. / Polyhedron 22 (2003) 605Á
/
609
609
Von Zelewsky, Coord. Chem. Rev. 84 (1988) 85;
pyridinylmethylene)cyclohexylamine yielded mononuc-
lear cationic complexes. The molecular structure of the
representative complex 2e has been determined by single
crystal X-ray diffraction analysis.
(c) K.R. Barqawi, Z. Murtaza, T.J. Meyer, J. Phys. Chem. 95
(1991) 47;
(d) J.R. Shaw, R.T. Webb, R.H. Schmehl, J. Am. Chem. Soc. 112
(1990) 1117;
(e) J.V. Caspar, T.J. Meyer, J. Am. Chem. Soc. 105 (1983) 5583;
(f) G.H. Allen, R.P. White, D.P. Rillema, T.J. Meyer, J. Am.
Chem. Soc. 106 (1984) 2613.
5. Supplementary material
[4] (a) D.N. Lee, H.J. Park, D.H. Kim, S.W. Lee, S.J. Park, B.H.
Kim, W.Y. Lee, Bull. Korean Chem. Soc. 23 (2002) 13;
(b) S.K. Mandal, A.R. Chakravarty, Polyhedron 11 (1992) 823;
(c) D.R. Robertson, I.W. Robertson, T.A. Stephenson, J.
Organomet. Chem. 202 (1980) 309;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre (CCDC), CCDC No. 193369 for complex
2e. Copies of the information may be obtained free of
charge from the director, CCDC, 12 Union Road,
(d) D.R. Robertson, T.A. Stephenson, J. Organomet. Chem. 142
(1977) C31;
(e) R.H. Crabtree, A.J. Pearman, J. Organomet. Chem. 141 (1977)
325;
Cambridge, CB2 1EZ, UK (fax: ꢀ44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk.
/
(f) Z. Shirin, R. Mukherjee, J.F. Richardson, R.M. Buchanan, J.
Chem. Soc., Dalton Trans. (1994) 465.
[5] (a) R.N. Dominey, B. Hauser, J. Hubbard, J. Dunham, Inorg.
Chem. 30 (1991) 4754;
(b) E.V. Dose, L.J. Wilson, Inorg. Chem. 17 (1978) 2660.
[6] (a) M.A. Bennett, T.N. Huang, T.W. Matheson, A.K. Smith,
Inorg. Synth. 21 (1985) 75;
Acknowledgements
KMR thanks the DST (DST SERC: SP/S1/F-22/98),
New Delhi for financial support.
(b) M.A. Bennett, T.W. Matheson, G.B. Robertson, A.K. Smith,
P.A. Tucker, Inorg. Chem. 10 (1980) 1014.
[7] REQAB4: R.A. Jacobsen, Private Communication, 1994.
[8] A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C.
Giacovazzo, A. Guagliardi, G. Polidoro, J. Appl. Cryst. 27
(1994) 435 (SIR92).
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