Reactivity studies of (η6-arene)ruthenium dimeric complexes towards pyrazoles: Isolation of amidines, bis pyrazoles and chloro bridged pyrazole complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.07.036

The complex [(η⁶-p-cymene)Ru(μ-Cl)Cl]₂ 1 reacts with pyrazole ligands (3a-g) in acetonitrile to afford the amidine derivatives of the type [(η⁶-p-cymene)Ru(L) (3,5-HRR′pz)](BF4)₂ (4a-f), where L = {HN = C(Me)3,5-RR′pz}; R, R′ = H (4a); H, CH₃, CH₆H₅ (4c); CH₃, C₆ H₅ (4d) OCH₃ (4e); and OC₂H₅ (4f), respectively. The ligand L is generated in situ through the condensation of 3,5-HRR′pz with acetonitrile under the influence of [(η⁶-p-cymene)RuCl₂]₂. The complex [(η⁶-C₆Me₆)Ru(μ-Cl)Cl] ₂ 2 reacts with pyrazole ligands in acetonitrile to yield bis-pyrazole derivatives such as [(η⁶-C₆ Me₆)Ru (3,5-HRR′pz)₂Cl](BF₄) (5a b), where R, R′ = H (5a); H, CH₃ (5b) as well as dimeric complexes of pyrazole substituted chloro bridged derivatives [{(η⁶-C₆Me₆)Ru(μ-Cl) (3,5-HRR′pz)}₂](BF₄)₂ (5c-g), where R, R′ = CH₃ (5c); C₆H₅ (5d); CH₃, C₆H₅ (5e); OCH₃ (5f); and OC₂H₅ (5g), respectively. These complexes were characterized by FT-IR and FT-NMR spectroscopy as well as analytical data. The molecular structures of representative complexes [(η⁶-C₆Me₆)Ru {3(5)-Hmpz}₂Cl]⁺ 5b, [(η⁶- C₆Me₆)Ru(μ-Cl)(3,5-Hdmpz)]₂ ²⁺ 5c and [(η⁶-C₆Me₆) Ru(μ-Cl){3(5)Me,5(3)Ph-Hpz}]₂²⁺ 5e were established by single crystal X-ray diffraction studies.

Full text of DOI:10.1016/j.jorganchem.2004.07.036

Journal of Organometallic Chemistry 689 (2004) 3265–3274
www.elsevier.com/locate/jorganchem
Reactivity studies of (g6-arene)ruthenium dimeric complexes towards
pyrazoles: isolation of amidines, bis pyrazoles and chloro bridged
pyrazole complexes
a
P. Govindaswamy , Yurij A. Mozharivskyj , Mohan Rao Kollipara
b
a,
*
a
Department of Chemistry, North-Eastern Hill University, Shillong 793022, India
Ames Laboratory, Iowa State University of Science and Technology, Ames, IA 50011, USA
b
Received 8 June 2004; accepted 22 July 2004
Available online 24 August 2004
Abstract
The complex [(g6-p-cymene)Ru(l-Cl)Cl]2 1 reacts with pyrazole ligands (3a–g) in acetonitrile to afford the amidine derivatives of
the type [(g6-p-cymene)Ru(L)(3,5-HRR0pz)](BF4)2 (4a–f), where L = {HN‚C(Me)3,5-RR0pz}; R, R0 = H (4a); H, CH3 (4b); C6H5
(4c); CH3, C6H5 (4d) OCH3 (4e); and OC2H5 (4f), respectively. The ligand L is generated in situ through the condensation of 3,5-
HRR0pz with acetonitrile under the influence of [(g6-p-cymene)RuCl2]2. The complex [(g6-C6Me6)Ru(l-Cl)Cl]2 2 reacts with pyr-
azole ligands in acetonitrile to yield bis-pyrazole derivatives such as [(g6-C6Me6)Ru (3,5-HRR0pz)2Cl](BF4) (5a–b), where R,
R0 = H (5a); H, CH3 (5b), as well as dimeric complexes of pyrazole substituted chloro bridged derivatives [{(g6-C6Me6)Ru(l-Cl)
(3,5-HRR0pz)}2](BF4)2 (5c–g), where R, R0 = CH3 (5c); C6H5 (5d); CH3, C6H5 (5e); OCH3 (5f); and OC2H5 (5g), respectively. These
1
complexes were characterized by FT-IR and FT-NMR spectroscopy as well as analytical data. The molecular structures of rep-
5c and [(g6-C6Me6)Ru(l-
resentative complexes [(g6-C6Me6)Ru{3(5)-Hmpz}2Cl]+ 5b, [(g6-C6Me6)Ru(l-Cl)(3,5-Hdmpz)]2
Cl){3(5)Me,5(3)Ph-Hpz}]2 5e were established by single crystal X-ray diffraction studies.
2+
2+
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: p-Cymene; Hexamethylbenzene; Pyrazoles; Amidine; Ruthenium
1. Introduction
catalytic processes such as olefin polymerization [2–5].
The g6-arene ligands are isoelectronic with g5-cyclopen-
tadienyl ligands and the syntheses of g6-arene complexes
are much easier than that of cyclopentadienyl com-
plexes. The three-legged piano stool structure of
arene–ruthenium(II) complexes have attracted interest
in recent years [6] due to their exhibition of catalytic
[7] and anticancer activities [8]. Recently, a lot of interest
has been given to these complexes due to the prepara-
tion of water-soluble arene–ruthenium complexes [9],
which exhibit antibiotic, antiviral and catalytic activity
such as the hydrogenation of bicarbonate in aqueous
solution [9].
In recent years, the coordination chemistry of che-
lated ligands containing mixed functionalities on transi-
tion metal centers has been an extremely active area of
research [1]. In particular, transition metal complexes
with a coordination group, which is p electron bonded
(like the cyclopentadienyl ligand) have attracted atten-
tion from the viewpoints of improving and elucidating
*
Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 255
0076.
E-mail addresses: kmrao@nehu.ac.in, mrkollipara@yahoo.com
(M.R. Kollipara).
1
Reactions between free nitriles and nucleophiles such
as amines, alcohols and water usually proceed in
In the case of amidine, the molecular structure of representative
complex was published in J. Coordination Chem. 56 (2003) 1085–1091.
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.036

3266
P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
presence of Lewis acid or base [10]. Ruthenium-contain-
ing g5-cyclopentadienyl or g6-benzene ligands have
been the subject of active studies focusing on their use
in organic synthesis [11]. However, arene–ruthenium
compounds with coordinated nitriles react with the
nucleophiles without the help of a Lewis acid or base
[12] to form amidine complexes. McCleverty et al. [13]
and we reported [14] the condensation of acetonitrile
and pyrazole ligands bonded to an arene–ruthenium
[(g6-arene)RuCl2]2 to form amidine complexes. Only a
few other examples of formation of this type of amidine
derivatives in transition metal complexes with coordi-
nated nitriles have been reported [15]. During investiga-
tion of the reactivity studies of ruthenium(II) complex
with nucleophiles, such as pyrazoles are inserted to
the coordinated acetonitrile to give stable (g6-arene)-
ruthenium(II) amidine complexes of the form
[(g6-arene)Ru(L)(3,5-HRR0pz)][BF4]2, where L = 1-
methylcarbaldi- mino-3,5-subsituted pyrazoles.
J being given in Hz. Electrospray ionization mass spec-
tra were obtained in positive-ion mode with a Shimadzu
LCMS 2010 triple quadruple mass spectrometer.
2.2. Materials and methods
All chemicals used were of reagent grade. All reac-
tions were carried out in distilled and dried solvents. Ru-
Cl3 Æ 3H2O was purchased from Arora Matthey Ltd.,
and used as received. The ligands such as pyrazole
(Hpz) (3a) and 3-methylpyrazole (3-Hmpz) (3b) (from
Merck) were used as received. The precursor complexes
[{(g6-arene)Ru(l-Cl)Cl}2], {where g6-arene = p-cymene
(1) or hexamethylbenzene (2)} were prepared according
to the literature procedures [19,20]. We adopted the lit-
erature procedure to synthesize the ligands [21].
2.3. Preparation of ligands
Recently Faure et al. [16,17] reported the ability of
the cluster cation [H3Ru3(C6H6) (C6Me6)(O)]+ to effi-
ciently catalyze the hydrogenation of benzene to give
cyclohexane under biphasic conditions. In the search
for new building blocks for the synthesis of arene–ruthe-
nium clusters, we obtained mononuclear disubstituted
and chloro-bridged pyrazole complexes. The reaction
of complex 2 [(g6-C6Me6)Ru(l-Cl)Cl]2 with 3,5-disubsti-
tuted pyrazoles surprisingly yielded chloro bridged
pyrazole complexes of the type [(g6-C6Me6)2Ru2(l-Cl)2-
(3,5-RR0pz)2]. To the best of our knowledge, only cleav-
age of both terminal and bridged chloride ligands has
been reported so far [18].
2.3.1. dimethylpyrazole (3,5-Hdmpz) (3c)
Acetylacetone (2 ml) and excess of hydrazine hydrate
(ꢀ5 ml) were stirred for 15 min, whereby white solid pre-
cipitated out. The white solid was filtered and washed
with hexane and dried under vacuum (yield 83.33%).
The same method was used for the preparation of
other disubstituted pyrazoles taking the corresponding
diketones instead of acetyl acetone. In the case of 3f
and 3g, methanol (15 ml) was used as a solvent to dis-
solve the ketones (Table 1).
3. Preparation of compounds
Herein, we present the syntheses of the following
arene–ruthenium complexes – the amidine complexes,
the substituted bis(pyrazole) complexes and the chloro
bridged pyrazole complexes. The single-crystal X-ray
structure analyses of [(g6-C6Me6)Ru{3(5)-Hmpz}2
3.1. [(g6-p-cymene)Ru(Hpz)(L)](BF4)2 (4a) {L = HN
=C(Me)pz}
The following general procedure was used to synthe-
size the complexes 4a–4f.
(Cl)]+, [(g6-C6Me6)2Ru2(l-Cl)2(3,5-Hdmpz)2]2+
,
and
2+
[(g6-C6Me6)Ru(l-Cl){3(5) Me,5(3)Ph-Hpz}]2 are re-
ported as well.
A mixture of [{(g6-p-cymene)Ru(l-Cl)Cl}2] (0.163
mmol) and pyrazole ligand 3a–3g (1.141 mmol) in aceto-
nitrile (20 ml) were refluxed for 10–15 min, cooled to
room temperature and filtered. The yellow filtrate was
stirred for one hour and then NH4BF4 (1.141 mmol)
was added and stirred again for 15 min. The solvent
was removed under reduced pressure when an oily mass
separated out. The oily mass was dissolved in dichloro-
methane and then filtered. The solution was concen-
trated to 2 ml and excess hexane was added for
precipitation. The yellow compound was separated out
and dried under vacuum.
2. Experimental
2.1. Physical measurements
Elemental analysis was performed in a Perkin–Elmer-
2400 CHN/O analyzer. Infrared spectra were recorded
on a Perkin–Elmer-model 983 spectrophotometer with
the sample prepared as KBr pellets. Electronic spectra
were recorded on a Hitachi-300 spectrophotometer.
The 1H NMR and 13C {1H} NMR spectra were re-
corded in acetone-d6 and CDCl3 solvents with tetra-
methylsilane as internal standard and recorded on
Bruker AMX-400 (400 MHz) and Bruker ACF-300
(300 MHz) spectrometers, the coupling constants
4a: (Yield 52.56%). Elemental Anal. (%) for
C18H25RuN5B2F8: C, 38.88; H, 4.29; N, 11.94. Found:
C, 38.36; H, 4.02; N, 12.02%. IR (KBr pellets, cmꢁ1):
m
C–N)
(N–H) 3429 (s), 3104 (s) m(amidine C‚N) 1646 (s), m (pyrazole
1
1527 (s), m(B–F) 1062 (s). H NMR (acetone-d6, d):
1.11 & 1.23 (d, 6H, CHMe2), 2.04 (s, 3H, CH3), 2.75

P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
3267
Table 1
Ligand codes and IR data of ligands
Sl No.
Ligand
IR data (KBr pellets, cmꢁ1); m(NH) and m(pyrazole C–N)
3c
3d
3e
3f
3,5-Dimethylpyrazole
3,5-Hdmpz
3197 (m), 1593 (m)
3283 (m), 1606 (m)
3264 (m), 1606 (m)
3323 (m), 1600 (m)
3325 (m), 1597 (m)
3,5-Dimethoxypyrazole
3,5-Diethoxypyrazole
3,5-Diphenylpyrazole
3,5-HdMeopz
3,5-HdEtopz
3,5-HdPhpz
3g
3(5)Methyl 5(3)-phenylpyrazole
3(5)Me,t 5(3)PhHpz
(sep, 1H, CHMe2), 3.03 (s, 3H, CH3), 6.05 (d, 2H,
J = 6.08), 6.25 (d, 2H, J = 6.04), 6.58 (t, 1H, CH pz),
7.03 (t, 1H, CH pz), 7.80 (d, 1H, J = 3.24, CH pz),
8.71 (d, 1H, J = 3.08, CH pz), 8.91 (d, 1H, J = 1.88,
CH pz), 9.28 (d, 1H, 1.86, CH pz), 11.9 (s, 1H, NH),
12.3 (s, 1H, NH). 13C NMR (acetone-d6, d): 22.34,
23.14, 26.48,27.01 (CH3), 33.67 [CH-(CH3)2], 86.32,
87.08, 89.31, 90.79 (CH, cymene), 92.67, 107.28 (C, cym-
ene), 108.43, 110.61, 111.91, 112.89, 113.15 117.15 (pz),
156.23 (pz, NC–Me). UV–Vis (CH2Cl2): kmax = 416 nm.
(4d) [( g6-p-cymene)Ru{3(5)Me, 5(3)Ph-Hpz}(L)]
(BF4)2{L = HN=C(Me)Me, Phpz}. (Yield 60.15%)
Elemental Anal. (%) for C32H37RuN5B2F8: C, 50.15;
H, 4.86; N, 9.14. Found: C, 50.36; H, 5.64; N, 8.91%.
IR (KBr pellets, cmꢁ1): m(N–H)3423 (s), 3237 (s), m (amidine
1
C‚N)1639 (s), m(pyrazole C–N) 1573 (m), m(B–F) 1082 (s). H
NMR (acetone-d6, d): 1.03 & 106 (d, 6H), 1.96 (s, 3H),
2.09 (s, 3H), 2.35 (s, 3H), 2.87 (sep, 1H), 3.03 (s, 3H),
6.26 (d, 2H, J = 5.88), 6.42 (s, 1H), 6.53 (d, 2H,
J = 5.92), 6.77 (s, 1H), 7.21–7.84 (m, 10H), 11.51 (s,
1H), 11.76 (s, 1H). 13C NMR (acetone-d6, d): 15.17,
18.34, 22.05, 22.39, 22.76, 29.14 (CH3), 31.82 CH–
Me2, 80.24, 82.99, 84.19, 85.51 (CH, cymene), 88.79,
102.93 (C, cymene), 103.70, 106.97, 126.17, 126.58,
127.06, 127.97, 128.26, 128.92, 129.28, 129.85, 130.05,
131.54, 146.44, 149.18, (Ph, pz), 156.00 (NC–Me).
UV–Vis (CH2Cl2): kmax = 411 nm.
(4b)
[(g6-p-cymene)Ru{3(5)-Hmpz}(L)](BF4)2
{L = HN=C(Me)mpz}. (Yield 58.66%) Elemental Anal.
(%) for C20H29RuN5B2F8: C, 39.11; H, 4.75; N, 11.39.
Found: C, 38.95; H, 4.36; N, 11.06%. IR (KBr pellets,
cmꢁ1): m(N–H) 3317 (b), 3138 (s), m(amidine
1653
C‚N)
1
(m), m(pyrazole C–N) 1527 (m), m(B–F) 1076 (s). H NMR
(acetone-d6, d): 1.15 & 1.18(d, 6H, CHMe2), 2.20 (sep,
1H, CHMe2), 2.37 (s, 3H, CH3), 2.47 (s, 3H, CH3),
2.85 (s, 3H, CH3), 3.20 (s, 3H, CH3), 5.98 (d, 2H,
J = 6.12), 6.20 (d, 2H, J = 6.12), 7.03 (d, 1H, J = 3.12,
CH pz), 8.59 (d, 1H, J = 3.12, CH pz), 8.67 (d, 1H,
J = 3.08, CH pz), 9.13 (d, 1H, J = 2.00, CH pz), 11.80
(s, 1H, NH), 12.23 (s, 1H, NH). 13C NMR (acetone-
d6, d): 15.08, 18.21, 20.42, 22.44, 24.96, 26.46 (CH3),
33.59 [CH-(CH3)2], 86.94, 87.90, 88.29, 89.49 (CH, cym-
ene), 91.76, 94.22(C, cymene), 112.38, 112.86, 117.35,
118.32, 140.15, 149.56 (pz), 155.51 (NC–Me). UV–Vis
(CH2Cl2): kmax = 419.3 nm.
6
(4e) [(g -p-cymene)Ru(3 5-HdMeopz)(L)](BF4)2
{L = HN=C(Me)Meopz}. (Yield 55.26%). Elemental
Anal. (%) for C22H33RuO4N5B2F8: C, 37.41; H, 4.71;
N, 9.91. Found: C, 37.12; H, 4.93; N, 9.53%. IR (KBr
pellets, cmꢁ1): m(N–H) 3449 (b), 3198 (s), m(amidine
1
C‚N)1618 (s), m(pyrazole C–N) 1560 (s), m(B–F) 1083 (s). H
NMR (acetone-d6, d): 1.31 & 1.34(d, 6H, CHMe2),
2.19 (s, 3H, CH3), 2.82 (sep, 1H, CHMe2), 3.18 (s, 3H,
CH3), 3.33 (s, 1H, CH3), 3.41 (s, 1H, CH3), 3.48 (s,
1H, CH3), 3.58 (s, 1H, CH3), 5.65 (d, 2H, J = 5.80),
5.76 (s, 1H CHpz), 5.88 (d, 2H, J = 5.72), 5.97 (s, 1H,
CHpz), 9.22 (s, 1H, NH), 9.85 (s, 1H, NH). 13C NMR
(acetone-d6, d): 15.25, 18.32, 20.35, 26.91, 27.11, 27.28,
27.45, 28.42 (CH3), 34.02 [CH(CH3)2, 84.37, 84.64,
85.31, 86.24 (CH, cymene), 89.12, 101.87 (C, cymene),
106.75, 111.96, 114.12, 116.97, 119.42, 122.56 (pz),
158.15 (NC–Me). UV–Vis (CH2Cl2): kmax = 401 nm.
(4f) [(g6-p-cymene)Ru(3 5-HdEtopz)(L)](BF4)2
{L = HN=C(Me)Etopz}. (Yield 56.87%). Elemental
Anal. (%) for C26H41RuN5O4B2F8: C, 41.00; H, 5.42;
N, 9.19. Found: C, 41.32; H, 4.97; N, 8.94%. IR (KBr
pellets, cmꢁ1): m(N–H) 3448 (b), 3272 (s), m(amidine C‚N)
(4c)
[(g6-p-cymene)Ru(3,5-HdPhpz)(L)](BF4)2
{L = HN=C(Me)dPhpz}. (Yield 56.94%) Elemental
Anal. (%) for C42H41RuN5B2F8: C, 56.65; H, 4.64; N,
7.86. Found: C, 56.33; H, 4.85; N, 7.53%. IR (KBr pel-
lets, cmꢁ1): m(N–H) 3449 (s), 3177 (s), m(amidine C‚N) 1653
1
(m), m(pyrazole C–N) 1566 (s), m(B–F) 1082 (s). H NMR
(acetone-d6, d): 1.08, & 1.12 (d, 6H, CHMe2), 2.21 (s,
3H, CH3), 2.30 (s, 3H, CH3), 2.71 (sep, 1H, CHMe2),
5.85 (d, 2H, J = 6.13), 6.01 (d, 2H, J = 8.28), 7.0–7.6
(m, 20H, Ph), 7.64 (s, 1H, CHpz), 7.90 (s, 1H, CH pz),
10.53 (s, 1H, NH), 11.13 (s, 1H, NH). 13C NMR (ace-
tone-d6, d): 17.89, 20.47, 21.28, 21.87 (CH3), 28.99
(CH–Me2), 79.95, 80.23, 82.14, 84.91 (CH, cymene),
87.46, 96.35 (C, cymene), 113.41, 125.29, 125.46,
125.78, 126.02, 126.34, 126.94, 127.82, 128.38, 128.75,
128.87, 128.94, 129.13, 129.47, 129.86, 130.09, 130.24,
130.87, 131.07, 131.78, 143.85, 148.40 (Ph, pz), 153.92
(NC–Me). UV–Vis (CH2Cl2): kmax = 413 nm.
1618(s), m(pyrazole
1560 (s), m(B–F) 1082 (s). 1H
C–N)
NMR (acetone-d6, d): d 1.32, & 1.35 (d, 6H, CHMe2),
1.49 (s, 3H, CH3), 2.18 (t, 3H, CH3), 2.20 (t, 3H,
CH3), 2.22 (s, 3H, CH3), 2.23 (t, 3H, CH3), 2.29 (t,
3H, CH3), 2.40 (sep, 1H CHMe2), 3.34 (q, 2H, CH2),
3.49 (q, 2H, CH2), 3.53, (q, 2H, CH2), 3.63 (q, 2H,
CH2), 5.73 (s, 1H, CHpz), 5.84 (s, 1H, CHpz), 5.98 (d,

3268
P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
2H, J = 6.38), 6.15 (d, 2H, J = 6.12), 9.01 (s, 1H, NH),
9.78 (s, 1H, NH). UV–Vis (CH2Cl2): kmax = 408 nm.
10H, Ph), 11.79 (s, 2H, NH). UV–Vis (CH2Cl2):
k
max = 317 nm.
5f[(g6-C6Me6)Ru(l-Cl)(3,5-HdMeopz)]2(BF4)2.
(Yield 57.36%). Elemental Anal. (%) for C34H52Ru2-
3.2. [(g6-C6Me6)Ru(Hpz)2(Cl)]BF4 (5a)
N4O4Cl2B2F8: C, 39.74; H, 5.10; N, 5.45. Found: C,
39.55; H, 5.31; N, 5.68%. IR (KBr pellets, cmꢁ1): m(N–
The following general procedure was used to synthe-
size the complexes 5a–5g.
1
3211 (s), m(pyrazole C–N) 1540 (m), m(B–F) 1082 (s). H
H)
A
mixture of [{(g6-C6Me6)Ru(l-Cl)Cl}2] (0.149
NMR (CDCl3,d): 2.10 (s, 36H, HMB), 3.82 (s, 6H,
CH3), 3.42 (s, 6H, CH3), 5.46 (s, 2H, CHpz), 10.18 (s,
2H, NH). UV–Vis (CH2Cl2): kmax = 398 nm.
mmol), pyrazole ligand (1.047 mmol) and NH4BF4
(1.047 mmol) were refluxed in acetonitrile (20 ml) for
30 min, cooled to room temperature and then filtered
for removing NH4Cl. The yellow filtrate was concen-
trated under reduced pressure. The oily mass was dis-
solved in dichloro-methane and filtered. The filtrate
was concentrated to 2 ml and excess of hexane was
added for precipitation. The yellow compounds were
centrifuged and dried under vacuum.
5g [(g6-C6Me6)Ru(l-Cl)(3, 5-HdEtopz)]2(BF4)2.
(Yield 53.69%). Elemental Anal. (%) for C38H60Ru2-
N4O4Cl2B2F8: C, 42.12; H, 5.58; N, 5.17. Found: C,
42.28; H, 5.42; N, 5.31%. IR (KBr pellets, cmꢁ1): m(N–
1
3230 (b), m(pyrazole C–N) 1543 (m), m(B–F) 1082 (s). H
H)
NMR (CDCl3, d): 2.12 (s, 36H, HMB), 1.88 (t, 6H,
CH3), 1.98 (t, 6H, CH3), 3.25 (q, 4H, CH2), 3.49 (q,
4H, CH2), 5.48 (s, 2H, CHpz), 9.57 (b, 2H, NH). UV–
Vis (CH2Cl2): kmax = 398 nm.
5a: (Yield 58.13%). Elemental Anal. (%) for
C18H26RuN4ClBF4: C, 41.43; H, 5.02; N, 10.73. Found:
C, 41.71; H, 4.89; N, 10.57%. IR (KBr pellets, cmꢁ1):
m(N–H) 3138 (s), m(pyrazole C–N) 1527 (s), m(B–F) 1082 (s).
1H NMR (CDCl3, d): 2.06 (s, 18H, HMB), 6.74 (t,
2H), 6.41 (d, 2H, J = 3.12), 8.07 (d, 2H, 3.23), 11.70
(s, 2H, NH). UV–Vis (CH2Cl2): kmax = 407.4 nm.
5b [(g6-C6Me6)Ru{3(5)-Hmpz}2(Cl)]BF4. (Yield
52.54%). Elemental Anal. (%) for C20H30RuN4ClBF4:
C, 44.01; H, 4.80; N, 10.26. Found: C, 44.41; H, 4.58;
N, 10.13%. IR (KBr pellets, cmꢁ1): m(N–H) 3283 (s), m (pyr-
4. Crystallographic investigations
The single-crystal structure analysis of amidine com-
plex
[(g6-p-cymene)Ru{HN‚C(Me)3,5-dmpz}(3,5-
Hdmpz)]2+ has been published previously [14] by us.
X-ray quality crystals of the complexes 5b and 5c were
grown by slow diffusion of hexane into dichloromethane
solution and the complex 5e was grown in CDCl3 solu-
tion. A yellow crystal of complex 5b and an orange crys-
tals of complex 5c and 5e were mounted on a Bruker
Apex CCD diffractometer in a full reciprocal sphere
equipped with CCD detector and used for data collec-
tion. X-ray intensity data were collected with graphite
monochromated Mo Ka radiation at 293(2) K, with
0.3ꢁ scans in x scan in mode and 10 s per frame. The
intensity data were corrected for Lorentz and polariza-
tion effects. The absorption correction was done using
the SAINT program [22]. A summary of crystal data,
data collection parameters and convergence results is
compiled in Table 2. An empirical absorption correction
was made by modeling a transmission surface by spher-
ical harmonics employing equivalent reflections with
I > 3 r (I) (program SADABS) [23]. The structure was
solved by direct methods [24]. All the non-hydrogen
atoms were refined anisotropically using the full-matrix,
least-squares technique on F2 using the SHELXL-97 soft-
ware [25]. All the hydrogen atoms were found from dif-
ference Fourier synthesis after four cycles of anisotropic
refinement and as the ‘‘riding’’ model. Figs. 1–4 are the
ORTEP [26] representations of the molecules with 50%
(Fig. 1 is 30%) probability thermal ellipsoids displayed.
Refinement converged at final R1 values of 0.0546,
0.0564 and 0.0480 (for observed data F) for 5b, 5c and
5e, respectively.
1
azole C–N) 1573 (s), m(B–F) 1069 (s). H NMR (acetone-d6,
d): 2.08 (s, 18H, HMB), 2.82 (s, 6H, CH3); 6.27 (d, 2H,
J = 2.87, CHpz), 7.89 (d, 2H, J = 3.04, CHpz), 11.83
(NH, 2H). UV–Vis (CH2Cl2): kmax = 439.9 nm.
5c[(g6-C6Me6)Ru(l-Cl)(3,5-Hdmpz)]2(BF4)2. (Yield
60.03%). Elemental Anal. (%) for C34H52Ru2N5Cl2B2F8:
C, 42.38; H, 5.44; N, 5.81. Found: C, 42.11; H,
5.62; N, 5.72%. IR (KBr pellets, cmꢁ1): m(N–H) 3204
1
(s), m(pyrazole C–N) 1573 (m), m(B–F) 1082 (s). H NMR
(CDCl3, d): 2.20 (s, 36H, HMB), 2.82 (s, CH3, 6H),
2.90 (s, CH3, 6H), 6.35 (s, 2H, CHpz), 11.42 (NH,
2H). MS (ESI): m/z 877 (M+). UV–Vis (CH2Cl2):
k
max = 416.10 nm.
5d[(g6-C6Me6)Ru(l-Cl)(3, 5-HdPhpz)]2(BF4)2.
(Yield 54.23%) Elemental Anal. (%) for C54H60Ru2
N4Cl2B2F8: C, 53.52; H, 4.99; N, 4.62. Found: C,
53.95; H, 5.02; N, 4.68%. IR (KBr pellets, cmꢁ1):
m(N–H) 3197 (s), m(pyrazole
1566 (s), m(B–F) 1082
C–N)
(s). 1H NMR (acetone-d6, d): 2.80 (s, 36H, HMB),
5.29 (s, 2H, CHpz), 8.24–7.09 (m, 20H, Ph), 11.78
(NH, 2H). UV–Vis (CH2Cl2): kmax = 417.93 nm.
5e [(g6-C6Me6)Ru(l-Cl){3(5)Me, 5(3)Ph-Hpz}]2
(BF4)2. (Yield 57.14%). Elemental Anal. (%) for
C44H56Ru2N4Cl2B2F8: C, 48.59; H, 5.19; N, 5.15.
Found: C, 48.64; H, 5.39; N, 5.25%. IR (KBr pellets,
cmꢁ1): m(N–H) 3302 (s), m(pyrazole
1082 (s). H NMR (CDCl3, d): 2.51 (s, 6H, CH3), 2.79
(s, 36H, HMB), 6.41 (s, 2H, CHpz), 7.37–7.38 (m,
1573 (m), m(B–F)
C–N)
1

P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
3269
Table 2
Crystal data and structure refinement for complexes 5b, 5c and 5e
Formula
Mr
C20H30BClF4N4Ru
549.81
293 (2)
C34H52B2Cl2F8N4Ru2
963.46
293 (2)
C44H48B2Cl2F8N4Ru2
1079.52
293 (2)
T (K)
˚
Wavelength (A)
Crystal system
Space group
0.71073
Monoclinic
P21/c
0.71073
Monoclinic
P21/n
0.71073
Triclinic
ꢀ
P1
Unit cell dimensions
˚
a (A)
˚
9.8188(5)
13.7982(7)
17.8018(9)
90
9.5865(7)
14.6210(11)
14.4797(11)
90
10.3196 (17)
14.823 (3)
15.199 (3)
86.838(3)
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
102.543 (1)
90
94.313 (1)
90
81.107 (3)
84.585(3)
2284.8(7)
3
˚
V (A)
2354.3(2)
4
2023.8(3)
4
Z
2
Crystal size (mm3)
Dcalc (g cmꢁ3)
F(000)
0.12 · 0.09 · 0.08
1.551
1120
0.3 · 0.2 · 0.2
1.581
976
0.06 · 0.05 · 0.03
1.569
1088
h (ꢁ)
1.88–28.27.
20154
1.98–28.26.
17308
1.38–17.57.
7398
Reflections collected
Independent reflections
Completeness to h
5532 [Rint = 0.0232]
28.27ꢁ–94.8%
0.825
4748 [Rint = 0.0346]
28.26ꢁ–94.6%
0.945
2910 [Rint = 0.0431]
17.57ꢁ–99.2%
0.847
l (Mo K a) (mmꢁ1
)
Data/parameters
Goodness-of-fit on F2
R1(I > 2I), wR2
5532/0/274
1.065
4748/0/223
1.022
2910/0/505
1.068
0.0546, 0.1571
0.0615, 0.1647
1.636 and ꢁ0.914
0.0564, 0.1411
0.0754, 0.1531
0.967 and ꢁ0.890
0.0466, 0.1149
0.0713, 0.1332
0.840 and ꢁ0.383
R1, R2 (all data)
Largest different
peak and hole (e A
ꢁ3
˚
)
Fig. 1. ORTEP diagram14 of complex [(g6-p-cymene)Ru{NH‚
C(Me)3,5-dmpz}(3,5-Hdmpz)](BF4)2 Æ H2O with 30% probability ther-
mal ellipsoids. Hydrogens and BF4 are omitted for clarity of the figure.
Fig. 2. ORTEP diagram of the complex 5b with 50% probability
thermal ellipsoids. Hydrogens and BF4 are omitted for clarity of the
˚
figure. Selected bond lengths (A) and bond angles (ꢁ). Bond lengths
(A): Ru–N(21) 2.116(3); Ru–N(31) 2.123(3); Ru–Cl 2.3979(10); N(31)–
˚
˚
˚
Selected bond lengths (A) and bond angles (ꢁ). Bond lengths (A):
Ru(1)–N(4) 2.132(6); Ru(1)–N(1) 2.092(5); Ru(1)–N(3) 2.045(6); N(3)–
C(16) 1.262(7); N(1)–N(2) 1.382(7); N(2)–C(16) 1.389(7). Bond angles
(ꢁ): N(1)–Ru(1)–N(4) 83.6(2); N(3)–Ru(1)–N(4) 87.5(2); N(3)–Ru(1)–
N(1) 74.3(2).
N(32) 1.338(5); N(31)–C(35) 1.328(5); N(21)–N(22) 1.366(5); N(21)–
C(25) 1.326(5); Ru–C*1.685 *Ruthenium to centroid of HMB. Bond
angles (ꢁ): N(31)–Ru–N(21) 88.06(13); N(31)–Ru–Cl 85.34(9); N(21)–
Ru–Cl 85.8 (1).

3270
P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
H
N
O
O
N
.
+
H2NNH2 H2O
R
R
R'
R'
R, R' = CH (3c)
3
= OCH (3d)
3
= OC H (3e)
2
5
= C H (3f)
6
5
= CH , C H (3g)
3
6 5
Scheme 1.
to the mN–H group of the ligands and strong bands at
around 1600 cmꢁ1 due to the mC–N of the pyrazoles.
5.2. Amidine complexes
The reaction of complex 1 with an excess of substi-
tuted pyrazole ligands 3 in acetonitrile, followed by
addition of NH4BF4, resulted the formation of yellow
Fig. 3. Molecular structure of the complex 5c. All the hydrogens and
˚
BF4 are omitted for clarity of the figure. Selected bond lengths (A) and
˚
bond angles (ꢁ). Bond lengths (A): Ru–N(1) 2.107(2); Ru–Cl (A)
2.4475(12); Ru–Cl 2.4390(12); N(1)–C(23) 1.4200; N(1)–N(2) 1.4200;
Ru–C* 1.684 *Ruthenium to centroid of HMB. Bond angles (ꢁ): N(1)–
Ru–Cl 86.47(9) N(1)–Ru–Cl(A) 87.44(9) Cl–Ru–Cl(A) 80.82(4) Ru–
Cl–Ru(A) 99.18(4).
colored and air-stable complexes of the type 4
(Scheme 2) by the chloride bridge cleavage of complex
1. In these complexes, the ruthenium atom is coordi-
nated to p-cymene, which occupies three coordinate
sites, the rest being occupied by the nitrogenꢀs of ami-
dine and pyrazole. The overall complex shows the pia-
no-stool structure [27] (Fig. 1). The micro-analytical
data suggested that the air-stable complexes obtained
have the composition [(g6-p-cymene)Ru{HN‚C(Me)
(3,5-RR0pz)}(3,5-HRR0 pz)](BF4)2. The in situ forma-
tion of the ligand 1-methylcarbaldimino-3,5-substituted
pyrazole presumably takes place by condensation of
3,5-substituted pyrazole with acetonitrile, as activated
by the complex 1.
5. Results and discussion
5.1. Preparation of ligands
The ligands 3c–3g were synthesized by condensation
of representative diketones with excess of hydrazine hy-
drate to afford 3,5-disubstituted pyrazole ligands
(Scheme 1). The IR spectra of these ligands (Table 1)
show strong bands in the range 3325–3197 cmꢁ1 due
Fig. 4. ORTEP diagram of the complex 5e (isomer B) with 50% probability thermal ellipsoids. Hydrogens and BF4 are omitted for clarity of the
˚
˚
figure. Selected bond lengths (A) and bond angles (ꢁ). Bond lengths (A): Ru(B)–C* 1.669 Ru(B)–N(31B) 2.103(7); Ru(B)–Cl(B) 2.423(3); Ru(B)–
Cl(B0) 2.436(3); N(31B)–C(35B) 1.4200; N(31B)–N(32B) 1.4200 *Ruthenium to centroid of HMB. Bond angles (ꢁ): N(31B)–Ru(B)–Cl(B) 85.5(2);
N(31B)–Ru(B)–Cl(B0) 88.2(2); Cl(B)–Ru(B)–Cl(B0) 81.18(11).

P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
3271
Cl
H
N
Cl
Cl
N
CH CN
3
(BF )
4 2
H
N
Ru
H
N
C
CH
3
Ru
+
R
NH BF
4
Ru
Cl
4
R'
R
N
N
N
R'
R'
R
complex 1
R, R' = H (4a)
= H, CH (4b)
3
= C H (4c)
6
5
= CH C H (4d)
3,
6
5
OCH (4e)
=
3
= OC H (4f)
2
5
Scheme 2.
The formation of the amidine complex is confirmed
by the appearance of the m(amidine C–N) band in the range
conveniently monitored by the peak ratio in the 1H
NMR spectra and by elemental analyses. The infrared
spectra of these complexes show a strong band in the
range of 3283–3138 cmꢁ1 due to the mN–H mode of the
pyrazole ligands [30]. In addition, the IR spectra contain
strong bands at 1573–1527 cmꢁ1 due to the mC–N mode
of the pyrazole ligands, and a strong band at 1082
1
around 1653–1618 cmꢁ1 of the IR spectrum. The H
NMR spectra of the complexes (4a–f) exhibit doublets
for the methyl protons of the isopropyl group due to
diasteriotopic nature of isopropyl group because ruthe-
nium is at chiral center due to attachment four different
ligands. A septet at the range 2.5–3 ppm is observed for
the isopropyl proton. The two doublets observed at 5–6
ppm correspond to the aromatic p-cymene ring CH pro-
tons. The NH protons of amidine and the substituted
pyrazole ligands give peaks in the range 9.01–12.30
ppm. The 13C {1H} NMR spectrum also exhibits appro-
priate signals. The methyl carbons exhibit signals in the
ranges between 15 and 30 ppm. The methyl carbons of
the isopropyl group appear around 29–34 ppm, while
the cymene carbons appear in the ranges between 82
and 107 ppm. The carbons of the arene group are thus
similar to those in other similar reported compounds
[28]. The carbons of the pyrazole and phenyl groups
(CH, C-RR0, Ph) give peaks in the range 103–149
ppm, while, the C-atom of the incorporated acetonitrile,
NC-Me appears at around 153–158 ppm. We had earlier
confirmed the final structure of a representative complex
of this kind through X-ray crystal studies [14]. The
electronic spectra of complexes 4 in dichloromethane
feature a UV–Vis pattern similar to that seen for
the analogous RuII polypyridyl complexes [29] and
arising from the metal–to–ligand charge transfer. The
RuII(d t2g) to ligand p* transition appears at around
401–420 nm.
1
cmꢁ1 due to the mB–F mode of the BF4 group. The H
NMR spectra of these complexes exhibit a strong peak
at 2.06–2.08 ppm for hexamethylbenzene, which is
slightly shifted downfield in comparison to the starting
complex 2, which exhibits it at 2.02 ppm. The resonance
of the N–H proton of the pyrazole ligands is observed as
a singlet in the range 11.70–11.83 ppm in these com-
plexes. The complex 5a exhibits two doublets at 6.41
and 8.07 ppm, and one triplet at 6.74 ppm due to the
protons of the coordinated pyrazole ligand. The com-
plex 5b exhibits two doublets at 7.89 and 6.27 ppm,
respectively, for the ring protons of pyrazole and one
singlet at 2.82 ppm for the methyl group. The electronic
spectra of these complexes in dichloromethane exhibit
bands at 407 and 440 nm. These low-energy absorptions
are assigned to the RuII (dp) to ligand (p*) metal-to-lig-
and charge transfer (MLCT) transition. The structure of
the complex 5b is shown in Fig. 2.
5.4. Chloro bridged pyrazole complexes
The reaction of the complex 2 with 3,5-disubstituted
pyrazole ligands (3c–g) in acetonitrile resulted in the for-
mation of yellow colored and air-stable dimeric chloro
bridged pyrazole complexes of the type 5c–g (Scheme 3)
by substitution of the terminal chloride ligand. The simi-
lar reaction in the case of complex 1 invariably yielded
amidine complexes. When using 3,5-disubstituted pyraz-
ole ligands, only terminal N-coordinated pyrazole com-
plexes are formed with the bridged chloride ligands
instead of the expected monomeric or amidine
5.3. Monomeric complexes
The reaction of complex 2 with an excess of pyrazole
3a and the 3,5-dimethyl-pyrazole ligand 3b in acetonit-
rile gave the mononuclear complexes 5a and 5b (Scheme
3). The formation of these complexes 5a and 5b were

3272
P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
H
N
(BF )
4
Ru
Cl
N
R
H
N
N
R
R, R' = H (5a)
R'
R'
= H, CH (5b)
3
Cl
3a-g
CH CN
Cl
Cl
3
Ru
Ru
Cl
NH BF
4
4
R
N
H
N
R'
complex 2
Cl
Cl
(BF )
4 2
Ru
Ru
H
N
N
R'
R
R, R' = CH (5c)
3
= C H (5d)
6 5
= CH , C H (5e)
3
6 5
= OCH (5f)
3
= OC H (5g)
2 5
Scheme 3.
compounds. This suggests that bridged chloride ligands
of complex 2 are cleaved in the first step, either by aceto-
nitrile or by the pyrazole. Evidently for complexes (5c–g),
coordination of the second pyrazole in the presumed
monomeric intermediate [RuCl2(arene)(pz)]+ is slow
compared with re-formation of the chloro bridge, possi-
bly because of the greater steric bulk and electron-donat-
ing ability of C6Me6 relative to those of p-cymene. The
formation of complexes 5c–g is conformed by peak inte-
gration on the 1H NMR spectra. The IR spectra of chloro
bridged pyrazole complexes show a strong band at
around 1573–1540 cmꢁ1 due to mC–N mode present in
the coordinated pyrazole ligands.
6. Molecular structures
The single-crystal structure of the corresponding ami-
dine complex (Fig. 1) has been published previously [14].
Single crystal X-ray structure determinations were car-
ried out for complexes 5b, 5c and 5e for confirmation
of the formulation. Crystals of complexes 5b and 5c
were grown by slow diffusion of hexane into dichloro-
methane, while complex 5e was grown from dueterated
chloroform solution. The ruthenium atom is coordi-
nated to two molecules of the 3-methylpyrazole ligand
through its ring nitrogen atom, one chloride ligand
and one HMB molecule through g6 fashion in the com-
plex 5b, whereas in the cases of complex 5c and 5e, each
ruthenium atom is coordinated to two bridged chloride
ligands, one nitrogen atom of 3,5-dimethylpyrzole,
3(5)methyl-5(3)-phenylpyrazole ligands and one mole-
cule of hexamethylbenzene ligand. The geometry around
the metal atom can be regarded as distorted octahedral
if the g6-hexamethyl–benzene group is assumed to occu-
py three facial coordinated positions.
The complex [(g6-C6Me6)Ru{3(5)-Hmpz}2Cl]BF45b
crystallizes in the monoclinic space group P21/c (Fig. 2).
In HMB, three of the Ru–C bond lengths, viz., those
involving the C(11), C(13) and (16) are longer (2.212(4),
2.216(4) and 2.210(4) A) than the other three bonds
involving the C(12), C(14) and C(15) carbon atoms
˚
(2.198(4), 2.189(5) and 2.190(4) A). The average Ru–C
˚
distance is 2.202 A, whereas the distance between the
˚
ruthenium atom and the centroid of the ring is 1.685 A
at the axis x = 0.4391, y = 0.2239 and z = 0.1377. These
bond lengths are closely related to those in other reported
1
The H NMR spectra of complexes 5c–g display a
sharp singlet for the methyl protons of hexamethylben-
zene at around 2.1–2.8 ppm, while the peaks for the ligand
moiety of the CH of pyrazole group appear in the range of
5.3–6.4 ppm. The NH proton of these complexes exhibits
at around 9.6–11.8 ppm. The mass spectrum of the repre-
sentative complex 5c exhibits a molecular ion peak at
around 877 (M+). This molecular ion peak suggests that
the complex is dimeric even in solution. Steric factors play
a major role instead of electronic factors in the formation
of these complexes. The bulky group ligands such as
HMB and 3,5-disubstituted pyrazole ligands exert steric
constraints to form these types of complexes instead of
complexes of the type 5a–b or 4a–f. The electronic spectra
of these complexes in dichloromethane exhibits bands in
the range of 317–418 nm due to the Ru (dp) to ligand
(p*) metal-to-ligand charge transfer (MLCT) transition.
The ORTEP diagrams of the complexes 5c and 5e are
shown in Figs. 3 and 4, respectively.
˚

P. Govindaswamy et al. / Journal of Organometallic Chemistry 689 (2004) 3265–3274
3273
complexes [27]. The Ru–N bond lengths involving 3-
other related complexes [34]. The Ru–Cl bond lengths
˚
methylpyrazole are 2.116(3) and 2.123(3) A, respectively,
well in accord with the literature values [29]. The Ru–Cl
˚
are 2.4390 A (in 5c) and 2.422(3) A (in 5e), which are
˚
within the range observed in reported complexes [35].
˚
bond length is 2.3979(10) A, which is within the usual
˚
range of Ru–Cl bond distances (2.39 A) [31]. The geome-
try of the complex is octahedral with a piano-stool struc-
ture, and is marked by the nearly 90ꢁ value for the bond
angles between the non-hexamethylbenzene ligands
N(31)–Ru–N(21) (88.06(13ꢁ)), N(31)–Ru–Cl (85.34
(9ꢁ)), and N(21)–Ru–Cl (85.80(10ꢁ)) at the metal centre
[32].
7. Conclusions
It is interesting to observe the differences between the
two complexes 1 and 2, where complex 1 gives the ami-
dine complexes, while complex 2 gives disubstituted pyr-
azole complexes and chloro bridged pyrazole complexes
depend on the bulkiness of the ligand. With increase in
the ligand bulk, one can isolate the chloro bridged
disubstituted pyrazole complexes from complex 2. This
is a clear indication that the steric factors of the ligands
play a major role in the formation of these complexes.
The molecular geometries of the dimeric cationic
complexes 5c and 5e, which crystallize in the monoclinic
ꢀ
and triclinic space groups P21/n and P1, are shown in
Figs. 3 and 4. The ruthenium atom is p-bonded to the
hexamethylbenzene ligand with the distances between
ruthenium and the centroid of the six membered hexa-
˚
˚
methylbenzene rings equal to 1.684 A and 1.669 A, fall-
ing within the range found in other hexamethylbenzene
ruthenium complexes [33]. An interesting feature of
these crystal structures is their centrosymmetry, i.e.,
the two monomers are related to each other by an inver-
sion center (Ci). In the case of complex 5e, however, two
isomers A and B exist in the solid state, both being cen-
trosymmetric. In isomer A, the phenyl ring and the pyr-
azole ring attached to it are coplanner, but in isomer B
they are slightly twisted with respect to each other. The
isomer B is represented in Fig. 4. The monomers of com-
plexes A and B are mirror images of each other (iso-
mers) due to the different bond lengths between the
Ru atom and two Cl atoms (i.e., Ru(A)–Cl(A) are
Acknowledgements
K.M.R. and P.G. thank the Sophisticated Instru-
ments Facility (SIF), Indian Institute of Science, Banga-
lore, for providing the NMR facility. We thank Prof.
R.H. Duncan Lyngdoh for help in preparing the manu-
script. We also thank for the referees for helpful
suggestions.
Appendix A. Supplementary material
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre (CCDC), CCDC No. 236402 for complex 5b,
CCDC No. 236403 for complex 5c, and CCDC No.
236404 for complex 5e. 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). Supplementary
data associated with this article can be found, in the on-
line version at doi:10.1016/j.jorganchem.2004.07.036.
˚
2.423(3) and 2.448(3) A), and thus, different bond
strengths, it is possible to break dimer A and B into
monomers (Fig. 5). In solution, though, the two isomers
are indistinguishable due to free rotation.
The Ru–N bond lengths in both the complexes
˚
˚
(2.107(2)) A for complex 5c, and 2.101(7) A for complex
5e are comparable to that of Ru–N bond lengths in
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