New mononuclear ruthenium complexes of η5-cyclichydrocarbon containing azine ligands: Syntheses, spectral and structural studies

Article abstract of DOI:10.1016/j.jorganchem.2005.05.001

A series of mononuclear indenyl and pentamethylcyclopentadienyl ruthenium(II) complexes of formulation [(η⁵-L₃) Ru(PPh₃)(L₂)]X, (where L₃ = indenyl, pentamethylcyclopentadienyl; X = PF₆ or BF₄ and L ₂ = azine ligands) have been prepared by the reaction of [(η⁵-L₃)Ru(PPh₃)₂(CH ₃CN)]X with the appropriate azine ligands in methanol or dichloromethane/benzene mixture. The reaction of nitro substituted azine ligands with the complexes [(η⁵-L₃)Ru(PPh₃) ₂(CH₃CN)]X are solvent dependent. All these complexes were isolated as their PF₆ or BF₄ salts. The complexes were fully characterized with the help of microanalyses, FT-IR and NMR spectroscopy. The molecular structure of representative complexes 5c and 6a were established by single X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2005.05.001

Journal of Organometallic Chemistry 690 (2005) 3720–3729
www.elsevier.com/locate/jorganchem
New mononuclear ruthenium complexes of
g5-cyclichydrocarbon containing azine ligands:
Syntheses, spectral and structural studies
a
Keisham Sarjit Singh , Yurij A. Mozharivskyj ,
b
c
Carsten Tho¨ne , Mohan Rao Kollipara
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
c
Institut fu¨r Anorganische und Analytische Chemie der Tu, Hagenring 30, 38106 Braunschweig, Germany
Received 28 March 2005; received in revised form 28 April 2005; accepted 1 May 2005
Available online 21 June 2005
Abstract
series of mononuclear indenyl and pentamethylcyclopentadienyl ruthenium(II) complexes of formulation [(g5-
A
L3)Ru(PPh3)(L2)]X, (where L3 = indenyl, pentamethylcyclopentadienyl; X = PF6 or BF4 and L2 = azine ligands) have been prepared
by the reaction of [(g5-L3)Ru(PPh3)2(CH3CN)]X with the appropriate azine ligands in methanol or dichloromethane/benzene mix-
ture. The reaction of nitro substituted azine ligands with the complexes [(g5-L3)Ru(PPh3)2(CH3CN)]X are solvent dependent. All
these complexes were isolated as their PF6 or BF4 salts. The complexes were fully characterized with the help of microanalyses,
FT-IR and NMR spectroscopy. The molecular structure of representative complexes 5c and 6a were established by single X-ray
crystallography.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Indenyl; Pentamethylcyclopentadienyl; Pyridine-2-carboxaldehyde; 2-acetylpyridine; Azine; Ruthenium
1. Introduction
in both SN1 [7,8] and SN2 [7–11] substitution reactions,
compared with their cyclopentadienyl analogues. Recent
kinetic studies [7,10], indicate the relative ease of slip-
page of the indenyl ring from g5- to g3-coordination
during SN2 substitution reaction at 18-electron metal
centers. The relative ease of ring slippage for indenyl
vs. cyclopentadienyl ligands has generally been attrib-
uted to the rehybridization of indenyl p-system, which
involves an increase in the aromatic character of the
benzene ring [7–10]. The chemistry of the complexes
[Cp0Ru(PPh3)2Cl] (where, Cp0 = indenyl, Cp or Cp*)
are characterized by ready displacement of one triphe-
nylphosphine or one triphenylphosphine along with
chloride ion to yield neutral or cationic complexes [12].
Over the decades, syntheses of half sandwich complexes
containing N-donor ligands such as polypyridyl, azo
Half sandwich complexes of platinum group metals
have been proved to be extremely useful in stoicheomet-
ric and catalytic asymmetric syntheses and have there-
fore attracted much study [1–5]. Extensive studies on
chemistry of half sandwich ruthenium complexes of
cyclopentadienyl are known [6]. However the analogous
indenyl and pentamethylcyclopentadienyl complexes
have remained relatively unexplored. It is well known
that g5-indenyl complexes display enhanced reactivity
*
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).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.001

K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
3721
and SchiffÕs base have received considerable attention
due to their interesting photophysical, photochemical
properties and potential use in several fields viz., photo-
chemical molecular devices, in solar energy conversion,
as light sensitive probes in biological systems and as
photosensitizers in redox reaction, and catalytic proper-
ties [13].
in the study are shown in Scheme 1. The complexes were
1
characterized with the help of H and 31P {1H} NMR
spectroscopy. The structure of representative complexes
5c and 6a were established by single X-ray study.
2. Experimental
Literature survey reveals that most of the study on
indenyl and pentamethylcyclopentadienyl ruthenium
(II) complexes are centered on the reactivity study of
these complexes towards alkenes and alkynes [14,15].
However, indenyl or Cp* phosphine complexes contain-
ing N-based ligands of the type [Cp0Ru(PPh3)(LL)]+ are
virtually unknown except our group reported a few of
such complexes in the recent years [16,17]. We have pre-
viously described the syntheses of indenyl (ind) [16a] and
pentamethylcyclopentadienyl (Cp*) [16b] ruthenium (II)
complexes of bidentate N,N0 donor SchiffÕs base ligands.
However, our attempt to synthesize analogous complex
of sterically demanding multidentate tetra-2-pyridyl-
1,4-pyrazine (tppz) ligand were so far unsuccessful,
instead we isolated complexes of the type [(tppz)Ru-
(PPh3)2X] (where, X = CH3CN, Cl) resulted from the
displacement of indenyl or Cp* moiety by the tppz ligand
[18]. This observation suggest that the stability of indenyl
or Cp* ligands largely depend on the steric nature of the
incoming ligand. In general, reactions with sterically
demanding multidentate ligands displaced the organic
fragment viz., Cp* and indenyl from the complex. It is
well known that complexes of indenyl and Cp* are highly
reactive which are attributed to the ring slippage from g5-
to g3- and back to g5- of the indenyl ligand in the case of
indenyl complexes while electron rich nature of methyl
group is the entirely responsible in the Cp* complexes
[19]. The high reactivity of such complexes and labile nat-
ure of the indenyl or Cp* ligand poised practical difficul-
ties on the syntheses of their complexes containing
sterically multidentate N-base ligands.
All synthetic operations were performed in a nitrogen
atmosphere. Solvents were dried over appropriate drying
agents, and then distilled prior to use [21]. The ligands
were made by the condensation of pyridine-2-carboxal-
dehyde or 2-acetylpyridine with the appropriate hydra-
zine [22]. The starting materials, [(g5-C9H7)-
Ru(PPh3)2Cl] (1) [23] and [(g5-C5Me5)Ru(PPh3)2Cl] (2)
[15] were prepared following the literature methods while
the complexes [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6 (3)
[23] and [(g5-C5Me5)Ru(PPh3)2(CH3CN)]BF4 (4) [24]
were prepared by minor modifications of the literature
procedures as described below. The NMR spectra were
recorded on Bruker ACF-300 MHz and Bruker AMX-
400 MHz instruments with SiMe4 as an internal stan-
dard. Chemical shift for 31P resonances were referred
to 85% H3PO4. Infrared spectra were recorded as a
KBr pellets on a Perkin–Elmer model 983 spectrometer.
Electronic spectra were recorded on a Hitachi-U-2300
spectrophotometer in dichloromethane (ca. 10ꢀ4 M). Mi-
cro analytical data were obtained from Regional Sophis-
ticated Instrumentation Centre (RSIC) NEHU,
Shillong, using a Perkin–Elmer 2400 CHN/S analyzer.
2.1. Preparation of [(g5-C9H7)Ru(PPh3)2(CH3CN)]-
PF6 (3)
The complex [(g5-C9H7)Ru(PPh3)2Cl] (1) (100 mg,
0.128 mmol) and NH4PF6 (39 mg, 0.24 mmol) were re-
fluxed in 30 ml of acetonitrile for 2 h. During this time,
the solution turned yellow and white solid was ap-
peared. The solution was filtered to remove the white so-
lid. The filtrate was rotary evaporated to dryness and the
residue was dissolved in dichloromethane and filtered
into 50 ml of hexane, whereby the product precipitated
out as a yellow crystalline solid.
To the best of our knowledge indenyl and pentameth-
ylcyclopentadienyl ruthenium complexes of azine li-
gands have not been studied [20]. In continuation of
our study on the reaction of indenyl and pentamethylcy-
clopentadienyl complexes with various N-base ligands
herein, we described the syntheses of a series of indenyl
and pentamethylcyclopentadienyl ruthenium (II) com-
plexes with some azine ligands. The ligands involved
1H NMR (CDCl3, d): 2.3(s, 3H), 4.5 (d, 2H, indenyl),
4.7 (t, 1H, indenyl), 6.9–7.8 (m, 34H). NMR (dP,
CDCl3): 54.55.
2.2. Preparation of [(g5-C5Me5)Ru(PPh3)2(CH3CN)]-
BF4 (4)
NO
2
R
R
NO
2
N
N
N
N
NH
N
N
R
R
The complex was prepared in analogy to (3) as de-
scribed above using [(g5-C5Me5)Ru(PPh3)2Cl] (2) and
NH4BF4 instead of [(g5-C9H7)Ru(PPh3)2Cl] and
NH4PF6.
1H NMR (CDCl3, d): 1.32 (s, 15H, C5Me5), 2.17 (s, 3H,
CH3CN), 6.78–7.83 (m, 30 H). NMR (dP, CDCl3): 45.28.
R=H,2-Pyridyl-2,4-dinitro
phenyl Ketazine (pdk )
R= H, Bis (2-Pyridyl ) Ketazine (bpk )
R=Me,Bis (2-Pyridyl methyl ) ketazine (bpmk )
R= Me, 2-Pyridylmethyl-2,4-dinitro
phenyl Ketazine (pdmk )
Scheme 1.

3722
K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
2.3. Preparation of new complexes
8.08 (s, 1H), 8.08 (d, 1H, 3J(HH) = 2.34), 7.69 (dt,
1H, J(HH) = 1.28, 4J(HH) = 12.8), 7.64 (dt, 1H,
3J(HH) = 1.84, 4J(HH) = 15.3), 7.49 (br, 1H), 7.43
(br, 1H), 6.84–7.36 (m, 15H), 1.45 (d, 15H,
4J(HP) = 1.18, (C5Me5)). NMR (dP, CDCl3): 46.92.
2.3.1. [(g5-C9H7)Ru(PPh3)(bpk)]PF6 (5a)
The complex [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6(1)
(100 mg, 0.107 mmol), the ligand bpk (50 mg,
0.22 mmol) and methanol (40 ml) were mixed in a
round bottom flask. The mixture was refluxed for 3 h
under nitrogen atmosphere, and the solution became
dark brown as the reaction proceeded. The solution
on evaporation to dryness by rotary evaporator affor-
ded a brown residue, which was purified by column
chromatography on silica gel using a dichlorometh-
ane-acetone (5:1, v/v) mixture as eluent. The solution
on subsequent concentrated to ca. 5 ml and addition
of excess hexane induce a dark brown solid. Yield:
70 mg, 78%.
IR (KBr, cmꢀ1): 1619, 1608 m(C@N), 1082 m
. Anal.
ðBF4Þ
Calc. for C40H40BF4N4PRu: C, 60.33; H, 5.02; N,
7.03. Found: C, 59.26; H, 4.98; N, 7.24%. UV–vis
(kmax, nm): 455.
2.3.4. [(g5-C5Me5)Ru(PPh3)(bpmk)]BF4 (5d)
This complex was prepared similar to (5b), except the
complex [(g5-C5Me5)Ru(PPh3)2(CH3CN)]BF4 (100 mg,
0.12 mmol) was used instead of complex 3 and refluxed
for 10 h. Following the same procedure as for complex
(5b), the complex (5d) was obtained as a light brown so-
lid. Yield: 66 mg, 72%.
3
NMR (dH,CDCl3): 9.80 (d, 1H, J(HH) = 5.14), 8.84
3
3
(d, 1H, J(HH) = 4.55), 8.12 (s, 1H) 8.09 (s, 1H), 8.02
NMR (dH, CDCl3): 9.04(d, 1H, J(HH) = 5.14), 8.76
(dt, 1H, 3J(HH) = 1.58, 4J(HH) = 7.5), 7.87 (dt, 1H,
unresolved), 6.69–7.33 (m, 23H), 5.26 (d, 2H,
3J(HH) = 2.38, indenyl), 4.73 (t, 1H, 3J(HH) = 2.53,
indenyl). NMR (dP, CDCl3): 55.84. IR (KBr, cmꢀ1):
1628, 1613 m(C@N), 844 m(PF6). UV–vis (kmax, nm): 456.
Anal. Calc. for C39H32N4P2F6Ru: C, 56.2; H, 3.8; N,
6.7. Found: C, 55.8; H, 3.6; N, 6.3%.
(d, 1H, 3J(HH) = 4.70), 8.67 (d, 1H, 3J(HH) = 5.21),
8.15 (d, 1H, 3J(HH) = 1.97), 7.93 (dt, 1H,
4
3J(HH) = 1.9, J(HH) = 15.9), 7.72 (br, 1H), 6.84–7.64
(m, 17H), 2.29 (s, 3H), 2.14 (s, 3H), 1.45 (d, 15H,
4J(HP) = 1.37, C5Me5). NMR (dP, CDCl3): 46.36. IR
. Anal. Calc.
(KBr, cmꢀ1): 1624, 1612 m(C@N), 1082 m
for C42H44BF4N4PRu: C, 61.19; H, 5.34; N, 6.79.
ðBF4Þ
Found: C, 60.37; H, 5.18; N, 6.28%. UV–vis (kmax
nm): 425.
,
2.3.2. Preparation of [(g5-C9H7)Ru(PPh3)(bpmk)]PF6
(5b)
The complex [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6 (1)
(100 mg, 0.107 mmol) and the ligand bpmk (63 mg,
0.26 mmol) were dissolved in minimum amount of
CH2Cl2 and benzene (40 ml) was added. The resulting
solution was heated to reflux for 10 h under nitrogen
atmosphere. The solution became light brown color as
reaction proceeded. A workup analogous with that of
5a afforded the product as light brown solid. Yield:
69 mg, 75%.
2.3.5. Preparation of [(g5-C9H7)Ru(PPh3)(pdk)]PF6
(6a)
The complex [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6
(100 mg, 0.12 mmol) and the ligand pdk (63 mg,
0.22 mmol) were dissolved in minimum amount of
dichloromethane (5 ml) and then benzene (40 ml) was
added. The resulting mixture was heated to reflux for
10 h under nitrogen atmosphere. The color of the solu-
tion progressively changed from yellow orange to dark
brown. After the mixture was cooled, the solvent was re-
moved by rotary evaporator. The brown residue was ex-
tracted with CH2Cl2 and purified by column
chromatography on silica gel using dichloromethane:
acetone (8:1, v/v) mixture as an eluent. The solution
was concentrated to ca. 5 ml and addition of excess hex-
ane gave the compound 6a as dark brown solid. The
brown solid was collected and washed with hexane.
Yield: 73 mg, 75%.
3
NMR (dH,CDCl3): 9.48 (d, 1H, J(HH) = 5.8), 9.28
(d, 1H, J(HH) = 4.2), 8.59 (d, 1H, J(HH = 3.8) 4.12),
3
3
3
8.77(d, 1H, J(HH) = 4.12), 8.59(d, 1H, J(HH) = 3.8)
3
3
3
8.17(t, 1H, J(HH) = 4.9), 7.92 (t, 1H, J(HH) = 7.8),
3
3
7.62(t, 1H, J(HH) = 7.5), 7.52 (t, 1H, J(HH) = 4.32),
6.99–7.40 (m, 18H), 4.95 (d, 2H, 3J(HH) = 3.8), 4.47
3
(t, 1H, J(HH) = 2.9), 2.34 (s, 3H), 2.29 (s, 3H). NMR
(dP, CDCl3): 55.43. IR (KBr, cmꢀ1): 1633, 1620
m
(C@N), 844 m(PF6). Anal. Calc. for C41H36N4P2F6Ru:
C, 57.13; H, 4.18; N, 6.50. Found: C, 57.76; H, 4.36;
NMR (dH, CDCl3): 9.59 (s, 1H, NH), 8.85 (d, 1H,
3J(HH) = 3.92), 8.11(s, 1H), 7.99 (d, 1H, 3J(HH) =
4.7), 7.84 (dt, 1H, 3J(HH) = 1.5, 4J(HH) = 15), 7.58
(dt, 1H, 3J(HH) = 1.08, 4J(HH) = 12), 6.82–7.50 (m,
22H), 5.52 (d, 2H,3J(HH) = 3.6, indenyl) 4.71(t, 1H,
3J(HH) = 4.2, indenyl). NMR (dP, CDCl3): 47.82. IR
N, 6.13%. UV–visible (kmax, nm): 447.
2.3.3. [(g5-C5Me5)Ru(PPh3)(bpk)]BF4 (5c)
This complex was prepared in analogy to the prepa-
ration of (5a), except the complex [(g5-C5Me5)-
Ru(PPh3)2(CH3CN)]BF4 (4) was used instead of
complex (3).Yield: 68 mg, 76%.
(KBr, cmꢀ1): 1606 m(C@N)
masymðNO Þ, 844 m . UV–vis (kmax, nm): 423. Anal. Calc.
for C39H31F6N5O4P2Ru: C, 51.38; H, 3.40; N, 7.68.
,
1493 msymðNO Þ
, 1341
2
ðPF6Þ
2
3
NMR (dH, CDCl3): 8.93 (d, 1H, J(HH) = 6), 8.79
(d, 1H, 3J(HH) = 5.13), 8.36 (s, 1H), 8.16 (s, 1H),
Found: C, 51.86; H, 3.86; N, 7.25%.

K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
3723
2.3.6. Preparation of [(g5-C9H7)Ru(PPh3)(pdmk)]PF6
(6b)
The complex was prepared by analogy to that of 5b,
using the complex [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6
(100 mg, 0.11 mmol) and the ligand, pdmk (69 mg,
0.22 mmol) and isolated as light brown solid. Yield:
70 mg, 71%.
NMR (dH, CDCl3): (Signals for the minor isomer are
given in the parentheses). 10.42 (9.96) (s, 1H, NH), 9.33
(9.22) (d, 1H, 3.8, 3J(HH) = 2.44), 8.79* (d, 1H,
3J(HH) = 2.59), 8.41 (dt, 1H, J(HH) = 1.8, 4J(HH) =
11.46), 7.66–6.86* (m, 23H), 5.10 (4.99) (d, 2H,
3J(HH) = 4.32, 2.43, indenyl), 4.74 (4.50) (t, 1H, unre-
solved, indenyl), 2.62 (2.38) (s, 3H). *Signals for the min-
or isomer are obscured by the major isomer. NMR (dP,
CDCl3): 47.53. IR (KBr, cmꢀ1): 1613 m(C@N), 1513
were measured at 293(2) K for complex 5c and 133(2) K
for complex 6a respectively measured on a Smart Apex
with CCD detector and Bruker Smart 1000 CCD detec-
tor, respectively employing graphite monochromater
˚
using Mo Ka radiation (k = 0.71073 A). Intensity data
were corrected for Lorentz and polarization effects and
absorption correction was made using SAINT program
[25]. The structures were solved by direct methods
(SHELXS 97) [26] and refined by full matrix least squares
base on F2 using (SHELXL-97) [27]. The weighting scheme
used. W ¼ 1=½r2ðF o2Þ þ aP2 þ bPꢁ where P ¼ ðF 2oþ
2F 2cÞ=3. Non-hydrogen atoms were refined anisotropi-
cally and hydrogen atoms were refined using a ‘‘riding’’
model. Refinement converged at a final R = 0.0421 and
0.0352 for complex 5c and 6a, respectively, (for observed
data F), and wR2 = 0.1057 and 0.07909 for complex 5c
and 6a respectively, (for unique data F2).
masymðNO Þ, 1334 msymðNO Þ, 844 m
. Anal. Calc. for
C40H33F6N5O4P2Ru: C, 51.94; H, 3.57; N, 7.57. Found:
ðPF6Þ
2
2
C, 52.12; H, 3.86; N, 7.15%. UV–vis (kmax, nm): 418.
4. Results and discussion
2.3.7. Preparation of [(g5-C5Me5)Ru(PPh3)(pdk)]BF4
(6c)
The reaction of [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6
(3) or [(g5-C5Me5)Ru(PPh3)2(CH3CN)]BF4 (4) with the
azine ligands viz., bpk or bpmk in refluxing methanol
or dichloromethane/benzene mixture gives mononuclear
complexes (5a–5d) in good yield (72–78%) as the only
product irrespective of the stoicheometric ratios
(Scheme 2). Although some dinuclear complexes of sim-
ilar ligands were reported in arene ruthenium(II) cases
[20], our attempt to synthesize dinuclear complexes of
indenyl and pentamethylcyclopentadienyl were unsuc-
cessful probably due to the presence of satirically
demanding triphenylphosphine ligand. In similar man-
ner, the reaction of complex (3) or (4) with pdk or pdmk
in refluxing dichloromethane/benzene mixture leads to
the formation of the complexes (6a–6d) in good yield.
The complexes were purified by column chromatogra-
phy technique and obtained in 70–75% yield (Scheme
2). However, use of refluxing methanol as the reaction
medium in the preparation of these complexes (6a–6d)
afforded a green compound. Spectroscopic data suggest
that the green compound could be ambiguously a
decomposed product as evident from the absence of
the characteristic signals of indenyl and Cp* ligand in
the proton NMR spectrum. The exact structure of the
compound is yet not known, the investigation is under
progress. All these complexes (6a–6d) are air stable in
solid state and soluble in chlorinated solvents. They
have been characterized by microanalyses, infrared
and NMR (1H, 31P {1H}) spectroscopy (details are given
in Section 2) and X-ray diffraction study for representa-
tive complexes 5c and 6a have been carried out.
This complex was prepared by following the same
procedure as (6a) except the complex [(g5-C5Me5)R-
u(PPh3)2(CH3CN)]BF4 (4) was used in place of [(g5-
C9H7)Ru(PPh3)2(CH3CN)]PF6 (3). Yield: 69 mg, 70%.
NMR (dH, CDCl3): 9.62 (s, 1H, NH), 8.91 (d, 1H,
3
3J(HH) = 4.8), 8.54 (s, 1H) 8.31 (dt, 1H, J(HH) = 1.9,
4J(HH) = 9.8), 8.12 (dt, 1H, 3J(HH) = 4.2, 4J(HH) =
6.2), 6.92–7.94 (m, 19H), 1.36 (s, 15H, C5Me5). NMR
(dP, CDCl3): 42.74. IR (KBr, cmꢀ1): 1623 m(C@N), 1497
masymðNO Þ, 1348 msymðNO Þ. Anal. Calc. for C40H39BF4-
2
2
N5PRu: C, 55.04; H, 4.47; N, 8.02. Found: C, 54.21;
H, 4.86; N, 7.89%. UV–vis (kmax, nm): 416.
2.3.8. Preparation of [(g5-C5Me5)Ru(PPh3)(pdmk)]-
BF4 (6d)
The same procedure as (6b) was adopted except the
complex [(g5-C5Me5)Ru(PPh3)2(CH3CN)]BF4 was used
in place of [(g5-C9H7)Ru(PPh3)2(CH3CN)]PF6. Yield:
73 mg, 74%.
NMR (dH, CDCl3): 9.24 (s, 1H, NH), 8.52 (d, 1H,
3
3J(HH) = 3.8), 8.23 (t, 1H, J(HH) = 4.3), 8.12 (t, 1H,
3J(HH) = 3.8), 6.89–7.84 (m, 19H), 2.34 (s, 3H),1.34
(d, 15H, 4J(HP) = 1.23, C5Me5). NMR (dP, CDCl3):
42. 63. IR (KBr, cmꢀ1): 1625 m(C@N), 1491 masymðNO Þ
,
2
1348 msymðNO Þ. Anal. Calc. for C41H41BF4N5PRu: C,
55.52; H, 4.62; N, 7.90. Found: C, 54.98; H, 5.06; N,
2
7.28%. UV–vis (kmax, nm): 433.
3. Structure analysis and refinement
The IR-spectra of the complexes showed absorption
bands in the region of 1606–1633 cmꢀ1 corresponding
to the mC@N stretching frequency of the ligands. The
complexes 5a–5d exhibits two absorption bands, one at
X-ray quality crystals of both the complexes 5c and 6a
were grown by slow diffusion of hexane into dichloro-
methane solution of 5c and 6a. The X-ray intensity data

3724
K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
X
R
(ii)
Ru
N
Ph P
N
N
3
N
X
R
=indenyl, R=H, X =PF6(5a );
R= Me, X=PF6 (5b)
(i)
6
Ru
Cl
3
Ru
CH CN
3
Ph P
3
=Cp*,R= H, X=BF4(5c );
R= Me, X= BF4 (5d )
PPh
PPh
Ph P
3
3
7
1
3
7a
X
2
indenyl =
(iii)
5
3a
Ru
4
PPh
3
NO
2
N
NH
N
Cp* =
R
=indenyl, R=H, X=PF6 (6a );
R= Me, X=PF6 (6b )
NO
2
(i) CH3CN, NH4BF4 orNH4PF6
(ii) bpk or pbmk, MeOH or
CH2Cl2 / C6H6
=Cp*, R = H, X = BF4 (6c)
R= Me, X = BF4 (6d)
(iii) pdk or pdmk, CH2Cl2 / C6 H6
Scheme 2.
a lower frequency which could be assignable to the coor-
dinated mC@N while other at a little higher frequency
assignable to the uncoordinated mC@N frequency. The
spectra also contained absorption bands for the PF6
and BF4 counter anions at 844 and 1082 cmꢀ1, respec-
tively. A strong band was observed in the IR spectra
of the complexes 6a–6d in the region 1491–1513 cmꢀ1
4.47–4.74 [J(HH) = 2.9–4.2 Hz], respectively (occasion-
ally as two unresolved multiplets). However, the reverse
was observed in the indenyl ruthenium allenylidene and
SchiffÕs base complexes [14b,16a]. The up field shift of
H2 proton could be due to the slight distortion towards
g3-mode in these complexes. The distortion towards g3
mode leads to the greater localization of electron around
H2 and consequently the proton is well shielded as com-
pared to the protons of H1, 3. Further, the proton NMR
spectra of these complexes exhibit a doublet at d 8.52–
8.93 in the cases of Cp* complexes while at a lower field
strength in the range of d 9.22–9.80 in the case of indenyl
complexes which are assignable to the ortho protons of
the pyridine of the ligand. The complexes (6a–6d) dis-
play the signals for NH proton of the ligand. In the inde-
nyl complexes this NH proton were observed at down
field region at d 9.59 and 10.42 as compared to Cp*
complexes where the resonance were observed at d
9.32 and 9.24, respectively. The proton NMR spectra
of all these complexes exhibit a multiplet resonance in
the range of d 6.69–7.94 corresponding to the protons
of arene and triphenylphosphine ligands. The proton
NMR spectra of representative complexes 5a and 6b
are shown in Fig. 1.
corresponding to the mNO (asymmetric stretching vibra-
2
tion) while for the symmetric stretching vibration the
band is observed in the region 1334–1348 cmꢀ1. The
proton NMR spectra of these complexes showed the res-
onances for the indenyl and Cp* ligands, apart from the
signals for the coordinated azine ligand and
triphenylphosphine.
The spectra of the Cp* complexes showed resonance
for the methyl protons of the Cp* ligand as singlet and
occasionally doublet as previously found in other Cp*
complexes [15,16b] in the range of d 1.35–1.45. The dou-
blet observed could be due to the coupling of the proton
of the methyl group with the phosphorous atom of the
triphenylphosphine. As have been observed in some
other indenyl complexes [14a], in the proton NMR spec-
tra of the indenyl complexes, the resonances for the H1, 3
protons was found to be shift in the up field region rel-
ative to the H2 proton, where the protons of H1,3 ob-
served as a doublet in the range of d 4.95–5.52
[J(HH) = 2.1–3.8 Hz] and that of H2 in the range of d
The complexes may exhibit diasteriomerism, but all
efforts to separate the diasteriomers were unsuccessful
in our working condition. However, the existence of

K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
3725
Fig. 1. 1H NMR spectrum of (a) complex 5a (b) complex 6b.
diasteriomers has been supported by the ill resolved
NMR data. The complex (6b) exhibit diasteriomers in
the ratio 1:1.7. Except complex (6b), in the respective
spectra of the complexes, signals for the minor diasteri-
omers is hidden or not well resolved, therefore, we are
unable to make precise interpretation of the different sig-
nals. In this communication, except (6b), in the rest of
the complexes we have taken into account only for the
major isomers. In the spectrum of complex 6b the major
isomer resonances appeared in the downfield region with
comparison to the minor isomer. The 31P {1H} spectra
of the indenyl complexes (5a) and (5b) appeared in the
down field region at d 55.84 and 55.43, respectively as
compared to the analogous Cp* complexes (6a) and
(6b) where the resonance appeared at d 47.8 and 47.5,
respectively. The most remarkable features of the 31P
{1H} NMR spectra is the up field shift of the resonances
of the nitro substituted azine complexes in both indenyl
and Cp* complexes relative to the starting precursor
complexes 3 and 4. The signals for the indenyl com-
plexes (6a) and (6b) are observed at d 47.8 and 47.5 while
for the Cp* complexes (6c) and (6d) at d 42.74 and 42.63,
respectively. The UV–visible spectra of the complexes in
CH2Cl2 at ca. 10ꢀ4 M showed absorption band in the
range of 416–456 nm. This low energy band is assignable
to metal to ligand charge transfer transition (MLCT),
[Ru(dp)–L(pp)] (Fig. 2).
5. Crystal structures determination
The crystal structures determination were carried out
for the representative complexes 5c and 6a. The perspec-
tive views of each complex including atom numbering
schemes are shown in Figs. 3 and 4. Details of crystallo-
graphic data collection parameters are summarized in
Table 1. Selected bond lengths and bond angles are
listed in Tables 2 and 3.
The complex 5c crystallize in the space group P1.
There are two independent molecules, A and B in the tri-
clinic unit cell which are mirror images to each other. The
geometry around the ruthenium atom can be regarded as
distorted octahedral with the Cp* ligand occupying three
facile coordination sites, p-bonded to the metal in g5-
fashion, while the remaining coordination positions are
occupied by the P-atom of PPh3 and N-atoms of the coor-
dinated azine ligand. The centroid bond distance between
˚
the ruthenium and ring carbons is 1.853 A (molecule A)

3726
K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
Fig. 2. UV–visible spectra of complex 5a and 5c. UV–visible spectrum of complex 5a in CH2Cl2. UV–visible spectrum of complex 5c in CH2Cl2.
˚
and 1.852 A (molecule B) which are comparable to that
observed in the related Cp* complex [16b]. Interestingly,
all the C–C bond lengths in the five member ring are
˚
equal to 1.4200 A, which suggests a considerable delocal-
ization of p-electron in the ring. The Ru–P bond length
˚
2.344(2) A is comparable to that found in related Ru–
˚
PPh3 complex (2.3593(7) A) [16b] but longer to that of
complex 6a and other indenyl ruthenium complexes.
The higher value of Ru–P bond distance in Cp* com-
plexes could be due to the bulkiness of the Cp* ligand.
Further, five member ring is planar as evident by the
nearly equal bond distances between the ruthenium atom
and the ring carbons. The bpk ligand is coordinated by
two N-atoms giving rise to the formation of five member
metallacycle. The five member metallacycle is being pla-
Fig.
3. Molecular
structure
of
complex
[(g5-C5Me5)Ru-
(PPh3)(C5H4N–CH@N–N@CH–C5H4N)]BF4 (5c) with 50% probable
thermal ellipsoids. Hydrogen atoms and BF4 ion have been omitted for
clarity.
narity with that of the Cp* ligand and they are in cis posi-
tion with respect to each other while the uncoordinated
pyridyl ring is slightly twisted out of the plane. The bite
angle of the chelating ligand N(1A)–Ru–N(22A) is
75.9(2)ꢁ which is very close to that found in the other re-
lated complex [16b]. The C@N bond length of the coor-
˚
dinated nitrogen, N(1A)–C(1A) (1.270 (13) A) is longer
than that of the uncoordinated C@N, N(2A)–C(2A)
˚
(1.210 (12) A) which could be due to the back donation
of electron from metal to p* orbital of the ligand.
The complex 6a crystallize in the Pca21 space group.
As in complex 5c the unit cell contains two independent
cations and anions (molecules 1 and 2). The centroid
bond distance between ruthenium and ring carbons for
the two molecules are Ru1–C9H7 (1.8571(12)) and
˚
Ru2–C9H7 (1.8530(12)) A, respectively. The indenyl li-
gand in the complex is bonded to g5-fashion and dis-
plays the asymmetric coordination generally observed
with this ligand [28]. The indenyl ligand exhibits a pro-
nounced ‘‘slip-fold’’ (D) distortion [29] relative to a pla-
Fig. 4. Molecular structure of complex [(g5-C9H7)Ru(PPh3){C5H4N–
CH@N–NH–C6H3(NO2)2}]PF6 (6a) showing with 50% probable
thermal ellipsoids. Hydrogen atoms and PF6 ion have been omitted
for clarity.
˚
nar, the value being 0.1045 A which is comparable to
that found in other indenyl complexes [16a]. The g5-
indenyl ligand is distorted from planar, such that the

K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
3727
Table 1
Summary of structure determination of complex 5c and complex 6a
Empirical formula
C40H40BF4N4PRu
C39H31F6N5O4P2Ru
Formula weight
Temperature (K)
˚
Wavelength (A)
795.61
293(2)
0.71073
Triclinic
P1
910.70
133(2)
0.71073
Orthorhombic
Pca21
Crystal system
Space group
Unit cell dimensions
˚
a (A)
9.3834(5)
11.2553(6)
34.395(3)
11.2596(8)
19.3674(14)
90ꢁ
˚
b (A)
˚
c (A)
17.7894(10)
95.5400(10)
a (ꢁ)
b (ꢁ)
c (ꢁ)
92.8020(10)
93.9930(10)
1862.55(18)
3
˚
Volume (A )
7500.5(9)
8
1.613
Z
2
1.419
Density (calculated) (mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
0.518
816
0.583
3680
Crystal size (mm3)
h range for data collection
Index ranges
0.25 · 0.35 · 0.40
1.82–28.30ꢁ
0.31 · 0.28 · 0.19
1.18–30.04ꢁ
ꢀ11 6 h 6 12, ꢀ14 6 k 6 14, ꢀ22 6 l 6 22
ꢀ48 6 h 6 48, ꢀ15 6 k 6 15, ꢀ27 6 l 6 27
Reflections collected
Independent reflections
Completeness to theta
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices
16,404
147,107
21,929 [R(int) = 0.0656]
30.00ꢁ, 100.0%
14,630 [R(int) = 0.0122]
=28.30ꢁ, 91.4%
Full-matrix least-squares on F2
14,630/3/744
21,929/1/1035
1.051
R1 = 0.0352,
1.036
R1 = 0.0421
[I>2sigma(I)]
wR2 = 0.1057
R1 = 0.0481, wR2 = 0.1110
0.0(7)
wR2 = 0.0709
R1 = 0.0519, wR2 = 0.0774
ꢀ0.003(12)
R indices (all data)
Absolute structure parameter
Largest different peak and hole (e A
ꢀ3
˚
)
0.848 and ꢀ0.471
0.865 and ꢀ0.410
Table 2
The asymmetric metal carbon bond distance is due to
the slipping of ruthenium across the g5- to g3-coordina-
tion [28]. Although indenyl ligand is g5-bonded to the
metal atom, the structure shows a slight distortion of
the five member ring from planarity [30]. In contrast,
the benzo ring of the indenyl ligand is planar and show
significant localization of double bond at the C(1)–C(2)
˚
Selected bond lengths (A) and angles (ꢁ) of complex 5c
Bond lengths
RuA–C*
˚
1.853 A
RuA–N(1A)
RuA–N(22A)
RuA–P(1A)
N(1A)–N(2A)
N(1A)–C(1A)
N(2A)–C(2A)
2.073(7)
2.084(2)
2.344(2)
1.402(10)
1.270(13)
1.210(12)
˚
˚
(1.357(5) A), C(3)–C(4) (1.371(5) A) as previously found
for other indenyl complexes [14a,14b,16a,17a]. Both
these bond lengths are significantly shorter than those
Bond angles
˚
˚
N(1A)–RuA–N(22A)
N(1A)–RuA–P(1A)
N(22A)–RuA–P(1A)
C(1A)–N(1A)–N(2A)
C(1A)–N(1A)–RuA
N(2A)–C(2A)–C(31A)
75.9(2)
89.6(2)
of other three bonds viz. C(2)–C(3) (1.399(6) A), C(1)–
˚
C(9) (1.420(4) A), and C(5)–C(4) (1.419(4) A) in the
benzo ring. On the other hand, there is a delocalization
of p-electrons in the five member ring as evident from
the nearly equal bond lengths between the C–C bond
distances of the five member ring, the bond lengths falls
90.34(8)
117.7(8)
118.2(6)
122.8(9)
C* = Centroid of C(11A), C(12A), C(13A), C(14A), C(15A).
˚
within the range of 1.422(4)–1.444(4) A. The Ru1–P1
˚
bond distance 2.2902(7) A is comparable to that of other
Ru1–C bond distances of bridging carbon atoms Ru1–
related indenyl ruthenium complexes [16a,17a], but little
shorter than that of the complex 5c and other
Cp* complexes [16b]. The molecule exhibits the well
known pseudo-octahedral piano-stool geometry. The
inter ligand angles P(1)–Ru1–N(1), P(1)–Ru1–N(2),
N(1)–Ru1–N(2) and those between centroid and the legs
˚
C(5) (2.2902(7)) and Ru1–C(9) (2.285(3)) A are longer
than those to the ‘‘allylic’’ carbons Ru1–C(6)
˚
(2.188(3)), Ru1–C(7) (2.171(3)), Ru1–C(82.183(3)) A.
The asymmetric Ru–C bond lengths are also observed
in other indenyl ruthenium complexes [14,16a,17a].

3728
K.S. Singh et al. / Journal of Organometallic Chemistry 690 (2005) 3720–3729
Table 3
(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.2005.05.001.
˚
Selected bond lengths (A) and bond angles (ꢁ) of the complex 6a
including hydrogen bond
Bond lengths
Ru1–C**
1.8571(12)
2.097(2)
2.052(2)
2.2902(7)
1.407(3)
1.304(3)
1.433(4)
1.424(4)
1.422(4)
2.2902(7)
2.188(3)
2.171(3)
2.183(3)
2.285(3)
1.442(4)
1.444((4)
2.596(3)
Ru1–N(1)
Ru1–N(2)
Ru1–P(1)
References
N(2)–N(10)
N(2)–C(10)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
Ru1–C(5)
Ru1–C(6)
Ru1–C(7)
Ru1–C(8)
Ru1–C(9)
C(8)–C(9)
C(9)–C(5)
N(10)–H(0A)ꢂ ꢂ ꢂO(2)
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Appendix A. Supplementary data
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CCDC No. 266104 for complex 6a. Copies of this infor-
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CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
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