Spectral, structural and DFT studies of platinum group metal 3,6-bis(2-pyridyl)-4-phenylpyridazine complexes and their ligand bonding modes

Article abstract of DOI:10.1016/j.jorganchem.2009.12.004

Reactions of 3,6-bis(2-pyridyl)-4-phenylpyridazine (L^ph) with [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = C₆H₆, p-ⁱPrC₆H₄Me and C₆Me₆), [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂, (M = Rh and Ir) and [(η⁵-Cp)Ru(PPh₃)₂Cl] (Cp = C₅H₅, C₅Me₅ and C₉H₇) afford mononuclear complexes of the type [(η⁶-arene)Ru(L^ph)Cl]PF₆, [(η⁵-C₅Me₅)M(L^ph)Cl]PF₆ and [(Cp)Ru(L^ph)(PPh₃)]PF₆ with different structural motifs depending on the π-acidity of the ligand, electronic properties of the central metal atom and nature of the co-ligands. Complexes [(η⁶-C₆H₆)Ru(L^ph)Cl]PF₆ 1, [(η⁶-p-ⁱPrC₆H₄Me)Ru(L^ph)Cl]PF₆ 2, [(η⁵-C₅Me₅)Ir(L^ph)Cl]PF₆ 5, [(η⁵-Cp)Ru(PPh₃)(L^ph)]PF₆, (Cp = C₅H₅, 6; C₅Me₅, 7; C₉H₇, 8) show the type-A binding mode (see text), while complexes [(η⁶-C₆Me₆)Ru(L^ph)Cl]PF₆ 3 and [(η⁵-C₅Me₅)Rh(L^ph)Cl]PF₆ 4 show the type-B binding mode (see text). These differences reflect the more electron-rich character of the [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂ and [(η⁵-C₅Me₅)Rh(μ-Cl)Cl]₂ complexes compared to the other starting precursor complexes. Binding modes of the ligand L^ph are determined by ¹H NMR spectroscopy, single-crystal X-ray analysis as well as evidence obtained from the solid-state structures and corroborated by density functional theory calculations. From the systems studied here, it is concluded that the electron density on the central metal atom of these complexes plays an important role in deciding the ligand binding sites.

Full text of DOI:10.1016/j.jorganchem.2009.12.004

Journal of Organometallic Chemistry 695 (2010) 707–716
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Spectral, structural and DFT studies of platinum group metal
3,6-bis(2-pyridyl)-4-phenylpyridazine complexes and their ligand bonding modes
Kota Thirumala Prasad a, Gajendra Gupta a, A.K. Chandra a, M. Phani Pavan b, Kollipara Mohan Rao a,
*
a Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b Department of Chemistry, University of Hyderabad, Hyderabad, India
a r t i c l e i n f o
a b s t r a c t
Reactions of 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph) with [(
g
6-arene)Ru(
5-Cp)Ru(PPh3)2Cl] (Cp = C5H5,
6-arene)Ru(Lph)Cl]PF6, [( 5-C5Me5)-
M(Lph)Cl]PF6 and [(Cp)Ru(Lph)(PPh3)]PF6 with different structural motifs depending on the
-acidity of
the ligand, electronic properties of the central metal atom and nature of the co-ligands. Complexes
[(
6-C6H6)Ru(Lph)Cl]PF6 1, [( 6-p-iPrC6H4Me)Ru(Lph)Cl]PF6 2, [( 5-C5Me5)Ir(Lph)Cl]PF6 5, [(g5
Cp)Ru(PPh3)(Lph)]PF6, (Cp = C5H5, 6; C5Me5, 7; C9H7, 8) show the type-A binding mode (see text), while
complexes [(
6-C6Me6)Ru(Lph)Cl]PF6 3 and [( 5-C5Me5)Rh(Lph)Cl]PF6 4 show the type-B binding mode
(see text). These differences reflect the more electron-rich character of the [( -Cl)Cl]2
6-C6Me6)Ru(
and [( -Cl)Cl]2 complexes compared to the other starting precursor complexes. Binding
5-C5Me5)Rh(
l-Cl)Cl]2 (arene = C6H6,
Article history:
p-iPrC6H4Me and C6Me6), [(
g
5-C5Me5)M(
l-Cl)Cl]2, (M = Rh and Ir) and [(
g
Received 18 November 2009
Received in revised form 2 December 2009
Accepted 8 December 2009
Available online 13 December 2009
C5Me5 and C9H7) afford mononuclear complexes of the type [(
g
g
p
g
g
g
-
Keywords:
Arene ligands
Pyridazine ligand
Platinum group metals
Ligand bonding modes
Density functional calculations
g
g
g
l
g
l
modes of the ligand Lph are determined by 1H NMR spectroscopy, single-crystal X-ray analysis as well
as evidence obtained from the solid-state structures and corroborated by density functional theory cal-
culations. From the systems studied here, it is concluded that the electron density on the central metal
atom of these complexes plays an important role in deciding the ligand binding sites.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
jugated bonds, the orientation of substituents and the scope for
manipulating ligand charge. In this regard, bridging polypyridyl li-
Polypyridyl complexes of platinum group metals are being con-
tinuously investigated because of their multiple applications in
fields of science including photophysics and photochemistry [1–
6], supramolecular chemistry [7], catalysis [8–13] and bioinorganic
gands (viz. 2,20-bipyrimidine (bpym), 2,3-bis(2-pyridyl)pyrazine
(bppz), 3,5-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz), 3,6-bis(2-pyri-
dyl)pyridazine (bppn), and 2,4,6-tris(2-pyridyl)-1,3,5-triazine li-
gands) have received much attention [27–33]. The wider family
of such ligands with 4- or 4,5-substituted pyridazine moieties
(viz., 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph) (Fig. 1) has been
relatively less studied. More recently, Constable and co-workers
published a few reports on silver(I) complexes [34–37] incorporat-
ing such ligands.
chemistry [14–19]. The organometallic complexes of
g
6-arene
ruthenium [20,21] and
g
5-half-sandwich complexes of rhodium
and iridium have attracted considerable current interest as poten-
tial anticancer agents (Dyson et al.) [14–19,22,23]. Another impor-
tant aspect, especially from the catalytic prospective, is the design
of Ru@O functional groups and analogues capable of reversibly
accepting multiple electrons and protons within a relatively small
potential range [24–26]. This capacity to modify the environment
in order to induce electronic as well as steric effects gives scope
for the design and fabrication of tailored catalysts for specific
reactions.
The properties of metal complexes largely depend on how the
nature of the bridging ligand mediates metal–metal interactions.
This role of bridging ligands is strongly influenced by factors such
as the acceptor and donor properties of coordination sites, the
length and rigidity of the spacers, the presence or absence of con-
Symmetrical 3,5-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz) and to a
lesser extent 3,6-bis(2-pyridyl)pyridazine (bppn) frequently bind
via any two of the four nitrogen atoms present (N1 and N2 or N3
and N4) on the pyridine and tetrazine/pyridazine moieties,
employing a bidentate j
2 bonding mode to coordinate with d6 me-
tal centers [38,39]. A phenyl substituent introduces a element of
asymmetry in the 3,6-bis(2-pyridyl)pyridazine (L) ligand moiety,
as shown by the 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph) li-
gand. This can bind to a metal via atoms N1 and N2 (type-A) or
atoms N3 and N4 (type-B) (see Fig. 2) in a bidentate j2 bonding
mode. The ligand is a four electron donor since the phenyl substi-
tuent creates differences in the electronic environment on the two
available binding sites. Apart from the above two possibilities
(type-A or type-B) (Fig. 2), a combination of the two types
* Corresponding author. Tel.: +91 364 272 2620; fax: +91 364 272 1010.
E-mail address: mohanrao59@gmail.com (K. Mohan Rao).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.12.004

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K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
4
N
2. Results and discussion
N
3
N
N
2.1. Syntheses
2
N
N
The dinuclear arene ruthenium complexes [(g l-
6-arene)Ru(
1
N
N
Cl)Cl]2 (arene = C6H6, p-iPrC6H4Me and C6Me6) react with two
equivalents of 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph
) in
methanol, being stirred at room temperature in the presence of
NH4PF6 to form the mononuclear arene ruthenium complex cat-
ions [(
and [(
g g
6-C6H6)Ru(Lph)Cl]+ (1), [( 6-p-iPrC6H4Me)Ru(Lph)Cl]+ (2),
g
6-C6Me6)Ru(Lph)Cl]+ (3) (Scheme 1) and isolated as their
hexafluorophosphate salts. The metal atom bonds to the LPh ligand
through the N1 and N2 atoms in the type-A complexes 1 and 2,
while in the type-B complex 3 the metal bonds through the N3
and N4 atoms of the ligand.
L
Lph
Fig. 1. Unsubstituted 3,6-bis(2-pyridyl)pyridazine (L) and substituted 3,6-bis(2-
pyridl)-4-phenylpyridazine (Lph).
Similarly, reacting the dimeric chloro-bridged complexes [(g5
-
C5Me5)M(
leads to the formation of the mononuclear cationic complexes
[(
5-C5Me5)Rh(Lph)Cl]+ (4) and [( 5-C5Me5)Ir(Lph)Cl]+ (5) (Scheme
l
-Cl)Cl]2 (M = Rh, Ir) with the same Lph ligand at 50 °C
R
g
g
R
2), isolated as their hexafluorophosphate salts. The metal atom
bonds to the LPh ligand through the N3 and N4 atoms in the
type-B complex 4, while in the type-A complex 5 the metal bonds
via the N1 and N2 atoms of the ligand.
1
M
N
X
N
1
2
N
M
3
X
2
N
N
3
N
4
N
The
u(PPh3)2Cl] and [(
Lph ligand in ethanol at 60 °C to form the mononuclear complex
cations [(
5-C5H5)Ru(Lph)PPh3]+ (6), [( 5-C5Me5)Ru(Lph)PPh3]+ (7)
and [(
5-C9H7) Ru(Lph)PPh3]+ (8) (Scheme 3), isolated as their
complexes
[(
g
5-C5H5)Ru(PPh3)2Cl],
[(g
5-C5Me5)R-
4
N
g
5-C9H7)Ru(PPh3)2Cl] reacted with the same
g
g
g
type-A
Fig. 2. The two types of complexes [
type-B
hexafluorophosphate salts. In all these type-A complexes the metal
bonds through the N1 and N2 atoms of the ligand.
M(Lph)X]+ (M = Ru, Rh and Ir).
R
Complexes 1, 2 and 3 are orange-yellow, 4 and 5 are dark yel-
low, while 6, 7 and 8 are orange-brown in color. All are non-hygro-
scopic, air-stable solids soluble in acetonitrile and partially soluble
in dichloromethane, chloroform, methanol and acetone. All com-
plexes have been characterized on the basis of elemental analysis,
1H NMR, IR, UV–Visible spectroscopy and mass spectrometry.
The infrared spectra of complexes 1–8 exhibit a strong band in
(type-A + type-B) for the same compound is also possible, but not
treated in this research.
The reaction of 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph
)
with [(
g
6-arene)Ru(
l
-Cl)Cl]2 (arene = C6H6 and p-iPrC6H4Me),
[(
g
5-C5Me5)Ir(
l
-Cl)Cl]2 and [(
g
5-Cp)Ru(PPh3)2Cl] (Cp = C5H5,
the region 844–850 cmꢀ1, a typical
mP–F stretching band for the PF6
C5Me5 and C9H7) led to the formation of type-A mononuclear
complexes. Use of [( -Cl)Cl]2 and [(
g
6-C6Me6)Ru( 5-C5Me5)Rh(
l
g
l-
anions. Besides this, peaks were observed which correspond to the
phenyl, pyridyl and pyridazine rings (C@C and C@N moieties). The
mass spectra display peaks with m/z at 580, 525, 573, 554, 638,
743, 818 and 789, corresponding to the molecular ion M+ peaks
for complexes 1–8, respectively.
Cl)Cl]2 led to the formation of type-B complexes. The third possibil-
ity (combination of type-A and type-B) was not borne out in this
work. The nature of the bonding modes for the above complexes
was elucidated here through NMR and X-ray crystallography. In
addition to these studies, we have performed DFT calculations on
the complexes 2, 3, 4, 5 and 6 in order to better understand the nat-
ure of the bonding modes in the ruthenium, rhodium and iridium
2.2. NMR studies
complexes with Lph
.
To the best of our knowledge, there are yet no reports on half-
sandwich platinum group metal complexes with the Lph ligand.
The successful formation here of such mononuclear complexes
gives promise and scope for the development of metalla-ligands
or synthons based on organometallic systems. Another important
factor is the presence of a phenyl ring on the ligand backbone. In
the absence of this feature (viz., with the 3,6-bis(2-pyridyl)pyrida-
zine ligand), we were unable to obtain stable and acceptable yields
of both mononuclear as well as dinuclear complexes. Due to this,
some research groups had suspended further work on such sys-
tems, notably those striving to prepare water oxidation catalysts
using this ligand [40].
We here report the synthesis of eight new platinum group me-
tal complexes having arenes, Cp* and 3,6-bis(2-pyridyl)-4-phen-
ylpyridazine (Lph) as ligands, all characterized by IR, NMR, mass
spectrometry and UV/Visible spectroscopy. The complexes and free
ligands were also subjected to density functional theory (DFT) cal-
culations. Molecular structures of three representative complexes
(derived from X-ray crystal data) are presented as well.
The 1H NMR spectrum of the free (unbound) ligand Lph exhibits
resonances at d 8.80 (d, 6-H), 8.74 (d, 60-H), 8.67 (s, 9-H), 8.49 (d, 3-
H) 7.94 (td, 30,4-H), 7.80 (td, 40-H), 7.44 (m, Ph-H), 7.34 (dd, 5-H),
7.28 (dd, 50-H) in CDCl3. Upon coordination with metal atoms,
the 1H NMR spectrum of the Lph ligand protons exhibits two differ-
ent sets of resonances for the two different types of complexes. The
type-A complexes 1, 2, 5, 6, 7 and 8 show one type of spectral res-
onance (see Fig. 3), while the type-B complexes 3 and 4 show a dif-
ferent set of resonances (see Fig. 4) for the aromatic regions of the
ligand.
Type-A: The 1H NMR spectra of the Ru(II)Lph and Ir(III)Lph com-
plexes 1, 2 and 5–8 exhibit ten sets of resonances at ꢁd 9.54 (d, 6-
H), 8.76 (d, 60-H), 8.72 (d, 3-H), 8.21 (s, 9-H), 8.18 (td, 4-H), 7.57 (td,
40-H), 7.37 (td, 5-H), 7.30 (m, ph-H), 7.15 (td, 50-H) and 6.79 (d,
30-H) ppm for the protons of the Lph ligand in CD3CN-d3. The reso-
nances of the protons 6, 60, 3 and 4 of ligand Lph are shifted down-
field by d ꢁ 0.75, 0.10, 0.32 and 0.31, respectively with respect to
the free ligand. As an example, the NMR spectrum of the type-A
complex 6 is presented in Fig. 3.

K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
709
R
R
Ru
:
:
N
1
2
Cl
N
N
N
N
N
N
N
6
6
N
6
N
Ru
N
Cl
2
N
3
Scheme 1.
Rh
4
N
Cl
N
3
N
2
1
N
N
N
N
4
N
+
0
.
5
[
(
η
5
-
C
5 M
e
)
5
4
I
r
N
(
μ
-
C
l
)
3
C
l
]
2
N
N
2
Ir
Cl
1
N
5
Scheme 2.
Type-B: The 1H NMR spectra of the Ru(II) and Rh(III) complexes
6-C6Me6)Ru(Lph)Cl]+ (3) and [( 5-C5Me5)Rh(Lph)Cl]+ (4) exhibit
ruthenium complexes having the
g
6-p-iPrC6H4Me and
g
6-C6H6 co-
[(
g
g
ligands, where Ru–LPh bonding occurs in type-A fashion. Similar
results for other complexes (based on reactivity studies) were
observed earlier in our research group, where complexes contain-
ing the hexamethylbenzene co-ligand contrast clearly with those
eight sets of resonances at d = 8.91 (d, 60-H), 8.82 (d, 6-H), 8.67
(s, 9-H), 8.59 (d, 30-H), 8.04 (td, 40-H), 7.67-7.61 (m, 5 and ph-H),
7.53 (td, 4 and 50-H) and d = 8.91 (d, 60-H), 8.59 (d, 6-H), 8.41 (s,
9-H), 8.39 (d, 30-H), 8.19 (td, 40-H), 7.81 (m, 4 and 50-H), 7.68 (d,
3-H), 7.66–7.61 (m, 5 and ph-H) ppm in CDCl3 (Fig. 4a and b).
The resonances of protons 60, 9, 30 and 40 of the ligand are shifted
downfield by d ꢂ 0.17, 0.01, 0.55 and 0.21 ppm, respectively (with
respect to the corresponding free Lph protons) due to the inductive
effect of the metal [20]. The significant downfield shift of proton 9
of ligand Lph reveals the formation of type-B complexes as com-
pared to the previous type.
containing the
g g
6-p-iPrC6H4Me and 6-C6H6 ligands [41,42].
Furthermore, the aromatic regions of Lph ligand signals complex
2 exhibit a singlet at d = 2.28 for the methyl protons, a septet at
d = 2.82 for the CH proton of the isopropyl group, two doublets
for the diastereotopic methyl protons of the isopropyl group, and
likewise four doublets for the diastereotopic CH protons of the p-
cymene ligand. Complexes 1 and 3 exhibit a singlet for the protons
of the benzene ring and protons of the hexamethylbenzene at d
6.18 and 2.18, respectively. Complexes 4 and 5 exhibit a singlet
for the methyl protons of the pentamethylcyclopentadienyl ligand
at d 1.77 and 1.68, respectively. Complexes 6 and 7 exhibit a singlet
at d 4.91 and 2.03 for the protons of the cyclopentadienyl ligand
and the methyl protons of pentamethylcyclopentadienyl ligand,
We choose to distinguish the two types of complex on the basis
of NMR, and present the spectra of the type-B complexes 3 and 4
(Fig. 4a and b). This furnishes the evidence for the formation of
complex 3 with the type-B bonding mode in ruthenium complexes
having the hexamethylbenzene co-ligand. This is not the case with

710
K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
R
N
Ru
N
PPh3
N
N
+[(η5-Cp)Ru(PPh3)2Cl]
N
N
-Cl- , PPh3
N
N
R
=
6
7
8
Scheme 3.
Fig. 3. Aromatic region of the 1H NMR spectrum of complex 6 (type-A) in CDCl3.
respectively. Complex 8 exhibits three characteristic sets of signals
(multiplet, triplet and doublet) for the protons of the indenyl li-
gand. The protons of the triphenylphosphine ligand exhibit a mul-
tiplet at d 7.22–7.55. The 31P{1H} NMR spectra of complexes 6, 7,
and 8 show chemical shifts at d 46.12, 49.21, and 48.42, respec-
tively, which indicate that each metal atom is bonded with a single
triphenylphosphine ligand.
of the pyridine moiety and one nitrogen atom of the pyridazinyl
moiety. This could be due to the steric interactions of arene li-
gands, electronic factors, the nature of the co-ligands, the oxidation
state of the metal atom and the symmetry of the ligand. The nature
of these bonding modes is studied here by density functional the-
ory (see later). The molecular structures of complexes 2, 4 and 6
are shown in Figs. 5–7, respectively, with the bond lengths and an-
gles presented in Table 1.
In the mononuclear complexes 2, 4 and 6 the nitrogen-metal
distances (2.073, 2.120 and 2.086 Å) associated with the pyridyl li-
gand are slightly longer than the corresponding pyridazinyl ligand
nitrogen-metal distance (2.045, 2.084 and 2.076 Å). These are
comparable to those in the previously studied complexes
2.3. Molecular structures
The molecular structures of [(
6-p-iPrC6H4Me)Ru(Lph)Cl]+ (2),
g
5-C5Me5)Rh(Lph)Cl]+ (4) and [( 5-C5H5)Ru(Lph)(PPh3)]+ (6) have
g
[(g
been established by single-crystal X-ray analysis of their hexa-
fluorophosphate salts (Tables 1 and 2). The complexes show a typ-
ical piano-stool geometry with the metal center coordinated to the
arene ligand, to the chelating Lph ligand, and to a terminal chloride
in complexes 2 and 4, and triphenylphosphine in complex 6. The
metal atom is in an octahedral arrangement with the two cis-nitro-
gen atoms of the Lph ligand acting as a bidentate chelating ligand
through the two neighboring pyridyl and pyridazinyl nitrogen
atoms. In principle, in mononuclear complexes, tetradentate li-
gands such as L or Lph can coordinate to the metal center either
through the N1 and N2 atoms (type-A) or the N3 and N4 atoms
(type-B). It is fascinating to observe here that the crystal structures
of complexes 2 and 6 are found to be N1,N2-coordinated (type-A),
while the complex 4 is found to be N3,N4-coordinated (type-B) in a
five-membered ring chelating fashion involving the nitrogen atom
[(
g
6-p-iPrC6H4Me)RuCl(2,3-bis(2-pyridyl)
pyrazine)]BF4
[43],
[Rh2(L-H)(NBD)(
g
1-C7H7)(CH3OH)(CH3CN)](BF4)2 [44], and [(g6
-
p-iPrC6H4Me)Ru(2-(2-pyridyl)-1,8-naphthyridine)Cl]PF6 [45]. The
Rh–N distances (2.120(3) and 2.084(3) Å) in 4 are slightly longer
than the corresponding distances in complex 2 (2.073(3) and
2.045(2) Å) and complex 6 (2.076 and 2.086). The M–Cl bond
lengths [2.387(10) and 2.384(13)] show no significant differences
between values for the cations studied here and other reported val-
ues [46]. The N–M–N bond angles [76.1(11)° in 2 and 76.0(13)° in 4
are similar in value to that [76.2(2)°] observed in the complex
[(g6p-iPrC6H4Me)RuCl(2,3-bis(
In complex 2, the distance between the ruthenium atom and
the centroid of the
6-p-iPrC6H4Me ring is 1.693 Å. In complex 4,
the distance between the rhodium atom and the centroid of the
a
-pyridyl)quinoxaline)]+ [47].
g

K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
711
Fig. 4. Aromatic regions of the 1H NMR spectra of (a) complex 4; (b) complex 3 (type-B) in CDCl3.
Table 1
Selected bond lengths (Å) and bond angles (°) for complexes 2, 6 and 4.
Table 2
Complex
Complex
Complex 4
Crystallographic and structure refinement parameters for complexes 2, 4 and 6.
2
6
Complex
2ꢃCHCl3
4
6
Bond distances
Ru–N1
Ru–N2
Ru–Cl1
Ru–centroid
(arene)
Chemical
formula
Crystal system
Space group
Crystal color and Orange block
shape
Crystal size
(mm3)
a (Å)
b (Å)
c (Å)
C31H29Cl4N4RuPF6 C30H29ClN4RhPF6 C43H34F6N4P2Ru
2.073(3)
2.045(3)
2.387(10) 2.308(10) Rh–Cl1
2.086(3)
2.076(3)
Rh–N4
Rh–N3
2.120(3)
2.084(3)
2.384(13)
1.789
Triclinic
Monoclinic
P21/n (no. 14)
Red block
Monoclinic
P2(1)/c
Red block
ꢀ
P1 (no. 2)
1.693
1.843
Rh–centroid (Cp*
ring)
C9–C10
C5–C6
N2–N3
1.483(5)
1.479(5)
1.334(4)
1.466(5)
1.490(6)
1.340(4)
C9–C10
C5–C6
N3–N4
1.471(5)
1.500(5)
1.330(4)
0.23 ꢄ 0.17 ꢄ 0.16 0.28 ꢄ 0.23 ꢄ 0.18 0.50 ꢄ 0.26 ꢄ 0.15
10.4283(19)
11.247(2)
15.491(3)
85.104(3)
81.287(3)
71.700(3)
1703.8(5)
2
9.244(3)
14.147(5)
23.425(8)
10.1059(2)
20.6495(4)
18.8735(4)
Bond angles
N1–Ru–N2
N1–Ru–Cl1
N2–Ru–Cl1
Ru1–N2–C9
Ru1–N2–N3
Ru1–N1–C10
76.11(11) 76.11(2)
N2–Rh–N3
N4–Rh–Cl1
N3–Rh–Cl1
Rh1–N3–C9
Rh1–N3–N2
Rh1–N4–C10
76.00(13)
83.50(10)
88.73(10)
117.99
120.35
116.03
83.91(9)
84.95(8)
119.83
117.16
117.61
95.75(9)
89.97(9)
118.9(3)
117.9(2)
116.7(2)
a
(°)
b (°)
95.900(6)
94.3950(10)
c
(°)
V (Å3)
Z
3047.4(18)
4
3926.97(14)
4
T (K)
173(2)
1.648
0.883
2.28 < h < 25.95
6597
173(2)
1.589
0.765
2.26 < h < 25.60
5963
293(2) K
1.495
0.546
1.46 < h < 28.29
9046
Dx (g/cm3)
g
5-C5Me5 ring is 1.789 Å, while the distance between the ruthe-
nium atom and the
5-C5H5 ring is 1.843 Å. These bond distances
are comparable to those in the related complex cations [(g6
p-iPrC6H4Me)Ru(pyNp)Cl]PF6, [( 5-C5Me5)Ir(pyNp)Cl]PF6 (PyNp =
2-(2-pyridyl)-1,8-naphthyridine) (1.68 and 1.79 Å) [45], [( 5-
C5Me5)RhCl(C5H4N–2CH@N–C6H4-p-Cl)]+ [48] and [Ru(g5
C5H5)(PPh3)(
2-paa)]+ and [Ru( 5-C5H5)( 1-dppm)( 2-paa)]+ [49].
l
(mmꢀ1
)
g
Scan range (°)
Unique
reflections
Reflections used 5719
[I > 2 (I)]
Rint
Final R indices
[I > 2
(I)]*
R indices (all
data)
Goodness-of-fit
(GOF)
-
g
g
4684
5505
r
-
0.0260
0.0452,
wR2 = 0.1264
0.0518,
wR2 = 0.1323
1.005
0.0426
0.0496,
wR2 = 0.1267
0.0642,
wR2 = 0.1355
1.068
0.0376
0.0568,
wR2 = 0.1560
0.1004,
wR2 = 0.1778
1.048
j
g
j
j
The solid state molecular structures of representative complexes
2, 4 and 6 are presented in Figs. 5–7, respectively.
r
2.4. Theoretical calculations
Max, min
D
q
0.864, ꢀ0.710
0.807, ꢀ0.543
0.953, ꢀ0.797
(e Åꢀ3
)
All calculations on the molecular species studied were carried
out using the B3LYP DFT method and different basis sets. All spe-
cies were subjected to full geometry optimization.
P
P
Structures were refined on F2o: wR2 = [ [w(Fo2 ꢀ Fc2)2]/ w(F2o)2]1/2
, where
*
P
w
ꢀ1 = [ (F2o) + (aP)2 + bP] and P = [max(Fo2, 0) + 2F2c ]/3.

712
K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
Fig. 7. Molecular structure of complex 6 at 35% probability level. Hydrogen atoms
and hexafluorophosphate anion have been omitted for clarity.
Fig. 5. Molecular structure of a complex 2 at 35% probability level. Hydrogen atoms,
chloroform molecule and hexafluorophosphate anion have been omitted for clarity.
syn LPh (Table S1). These values are very close to the experimental
values [34]. In terms of energy, anti L is 14.33 kcal/mol more stable
than syn L while anti Lph is 9.68 kcal/mol [Table S2 (Supplementary
material)] more stable than syn Lph. The coordinated Lph ligand in
complexes 2 and 4 is in the syn conformation.
The electronic charges on the nitrogen atoms in the anti Lph con-
formation reveal that atoms N3 and N4 have more negative charge
than atoms N1 and N2 (see Fig. SF1c). This suggests that presence
of the phenyl group affects the electronic charges on the four nitro-
gen atoms as well as the dihedral angles of the pyridine and pyrid-
azine rings, so that the N3–N4 (type-B) binding site is more
electron-rich than the N1–N2 (type-A) bonding site.
2.4.2. Structures of complexes
In order to gain further insight into the bonding modes in the
ruthenium, rhodium and iridium complexes, we have carried out
a detailed investigation using density functional theory. The key
findings are described in the following sections.
B3LYP/LanL2DZ calculations with full geometry optimization
were undertaken for the cationic species 2, 4 and 6 in both type-
A and type-B bonding modes as depicted in Fig. SF2 of the support-
ing information, where the crystal structure geometries provided
the starting input for optimization. The other species 3 and 5 were
subjected to calculation using appropriate modifications of the
geometries of 2, 4 and 6. The calculated geometrical parameters
of the above complexes [Table S3 (Supplementary material)] are
found to be in close agreement with the experimental values ob-
tained from X-ray crystallographic study (Table 1). From Table S3
of Supplementary material we can see that the positions of binding
have discernible effects on the stability and geometrical structure
of the complexes. Comparing the computed results of the parent
complexes 2, 3, 4, 5, 6 with the experimental data (see Table 1),
we find that the computed coordination bond lengths (Ru–N) are
shorter than the corresponding experimental value by 1–3%, the
largest differences being found for the metal–arene carbon dis-
tances [50]. Computed coordinated bond angles are wider by 2%
than those found experimentally. At the same time, the computed
mean bond lengths C–C(N) of the ligand skeletons of these com-
plexes are close to the general bond lengths. We thereby deduce
Fig. 6. Molecular structure of complex 4 at 35% probability level. Hydrogen atoms
and hexafluorophosphate anion have been omitted for clarity.
2.4.1. L and Lph ligand structures
We have performed DFT calculations using the B3LYP/6-31+G**
strategy to determine the effect of the phenyl substituent on the
nitrogen atoms of the central pyridazine and pyridine rings. Firstly,
both the ligands L and Lph in their free state were optimized in the
low-energy anti orientation [Fig. SF1a and c (Supplementary mate-
rial)]. Since these ligands occur in the syn conformer in complexes
2, 4 and 6, they were also optimized in the higher energy syn ori-
entation (Fig. SF1b and d). The anti conformer of L is planar but
the syn conformer is non-planar with the N–C–C–N dihedral being
83.8° [Table S1 (Supplementary material)]. On the other hand, both
anti and syn orientations of Lph are non-planar, due to the effect of
the phenyl substituent on the central pyridazine ring. The dihedral
angles N1–C2–C3–N2 and N3–C6–C7–N4 are, respectively, found
to be 141.3° and 179.2° for anti LPh, and ꢀ62.9° and ꢀ47.2° for

K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
713
that the structures obtained from these DFT calculations are
reliable.
of binding mode neither depends on the steric nature of the co-li-
gands nor on the oxidation state of the complex. However, the
optimized geometries of 4 and 5 reveal that size of the metal atom
does have a significant impact on choice of binding mode, where
the rhodium complex 4 favors the type-B bonding mode while
the iridium complex 5 favors the type-A bonding mode (substitu-
ents or co-ligands and oxidation state being the same). In addition
to the effect of the size of the metal atom, the nature of the co-li-
gand also has an impact on the choice of bonding mode because
complexes with less electron-rich donor co-ligands favor the
type-A bonding mode (1 and 2 and 5–8) while complexes having
more electron-rich donor co-ligands favor the type-B bonding
mode (3 and 4). These DFT results thus elucidate the effects of
the size of the metal atom, the nature of the co-ligands and various
electronic factors on the nature of bonding mode.
The 3,6-bis(2-pyridyl)-4-phenylpyridazine (Lph) ligand has two
bidentate binding sites, viz., the N1 and N2 atoms (type-A) and
the N3 and N4 atoms (type-B). In principle, the metal atom should
prefer the type-A mode (atoms N1 and N2), since the substituents
of the pyridazine ring (phenyl and pyridine rings) are meta with re-
spect to N2, and the dihedral angle N1–C2–C3–N2 for the anti con-
former of Lph (141.3°) is found to be less than the dihedral angle
N3–C6–C7–N4 (179.2°). On the other hand, for the type-B bonding
mode (at atoms N3 and N4), the substituents of the central pyrid-
azine ring (phenyl and pyridine rings) are, respectively, para and
meta with respect to N3. The dihedral angle N3–C6–C7–N4
(179.2°) is found to be noticeably greater than the dihedral angle
N1–C2–C3–N2 (141.3°) (see Table S3). These results suggest that
the metal atom prefers to bind through the N1 and N2 atoms
(type-A) rather than through the N3 and N4 atoms (type-B).
On the other hand, the Mulliken atomic charges on the N3 and
N4 atoms of ligand Lph are more negative than for the N1 and N2
atoms (see Fig. SF1c). This means that atoms N3 and N4 should
be better electron donors towards the metal center than atoms
N1 and N2, implying that formation of type-B complexes is more
favorable than type-A complexes. Interestingly, experimental re-
sults reveal that complexes 3 and 4 favor the type-B bonding mode
while all the other complexes favor the type-A mode. Possible rea-
sons could be the size of the metal atom, oxidation state of the
complex, symmetry of the ligand and nature of the substituents
on the metal atom.
2.5. UV/Visible spectroscopy
Electronic absorption spectral data of complexes 1–8 at 10ꢀ5 M
concentration in the range 290–600 nm are summarized in Table 3.
The spectra of these complexes are characterized by two main fea-
tures, viz., an intense ligand-localized or intra-ligand
tion in the ultraviolet region, and metal-to-ligand charge transfer
(MLCT) d
(M) ? p* (Lph ligand) bands in the visible region [51].
p ? p
* transi-
p
Since the low spin d6 configuration of the mononuclear complexes
provides filled orbitals of proper symmetry at the Ru(II), Rh(III) and
Ir(III) centers, these can interact with low lying p* orbitals of the
ligands. All these complexes show an intense band in the region
290–320 nm and a low-energy absorption band in the visible re-
gion 420–445 nm. In addition to these two absorption bands, an
additional low intensity band at 350 nm and a shoulder type band
The molecular structure of complex [(g
6-p-iPrC6H4Me)R-
u(Lph)Cl]+ 2 shows j2 type coordination in the type-A bonding
mode (see Fig. 6). This geometry was optimized for both type-A
and type-B bonding modes. The results reveal that the type-A bond-
ing mode is 1.25 kcal/mol more stable than type-B. Replacing
p-iPrC6H4Me of 2 with the more electron-rich hexamethylbenzene
Table 3
(C6Me6) ligand gives the complex 3 [(g
6-C6Me6)Ru(Lph)Cl]+. The
UV/Visible spectral data for selected complexes in acetonitrile at 298 K.
Complex no.
Complex
kmax (nm)/e
10ꢀ5 Mꢀ1 cmꢀ1
geometry of this complex was built up by modification of complex
2 in both conformations, being optimized at the B3LYP level with a
LanL2DZ basis set (Fig. SF2 3A and B). The results reveal that the
type-B structure is 0.96 kcal/mol more stable than the type-A struc-
ture. These trends suggest that the nature of the co-ligands impacts
on the bonding mode of the Lph ligand. Since the energy difference
between type-A and type-B [see Table S4 (Supplementary mate-
rial)] structures is quite low, packing and other environmental fac-
tors may affect preference of one form over the other. The
1
2
3
4
5
6
7
[(
[(
[(
[(
[(
[(
[(
g
g
g
g
g
g
g
6-C6H6)Ru(Lph)Cl]+
306 (0.47) 412
320 (0.65) 420
317 (0.61) 412
299 (0.49) 349 (0.15) 420
300 (0.51) 380 470
290 (0.61) 435(0.15)
294 (0.36) 445
6-p-iPrC6H4Me)Ru(Lph)Cl]+
6-C6Me6)Ru(Lph)Cl]+
5-C5Me5)Rh(Lph)Cl]+
5-C5Me5)Ir(Lph)Cl]+
5-C5H5)Ru(Lph)PPh3]+
5-C9H7)Ru(Lph)PPh3]+
molecular structure of [(g j
5-C5Me5)Rh(Lph)Cl]PF6 4 shows a 2 type
of coordination with the type-B bonding mode (see Fig. 6). The
geometry was optimized for both type-A and type-B bonding
modes (Fig. SF2 4A and B), where the results predict the type-A
structure as 0.95 kcal/mol less stable than the type-B structure.
Replacing rhodium in [(
g
5-C5Me5)Rh(Lph)Cl]PF6 4 with the larger
atom iridium gives [(
g
5-C5Me5)Ir(Lph)Cl]PF6 5, where the energy
of the type-A structure is 0.35 kcal/mol lower in energy than the
type-B structure (Fig. SF2 5A and B). This suggests that size of the
metal atom also has a significant effect on the preferred choice of
bonding mode.
In order to study the effect of steric interactions on the choice of
bonding mode, we replaced the p-iPrC6H4Me and chloride ligands
in complex 2 with the less electron-rich (but sterically free) cyclo-
pentadienyl ligand and the bulky triphenylphosphine ligand,
respectively, giving the complex 6. Calculated energies of the opti-
mized geometries (Fig. SF2 6A and B) reveal that the type-A struc-
ture of 6 is 1.96 kcal/mol more stable than the type-B structure.
This suggests that steric factors do not have much impact on the
choice of bonding mode (see Table S4).
In conclusion, the calculated energies of the optimized geome-
tries of complexes 2, 3, 4, 5 and 6 reveal that the preferred choice
Fig. 8. UV/Visible electronic spectra of complexes in acetonitrile at 298 K.

714
K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
at 280 nm for complexes 4 and 5, respectively are observed. The
(100%) [MꢀPF6]+, 573.6 (30%) [MꢀPF6ꢀCl]+. IR (KBr, cmꢀ1): m(P–F)
high intensity band in the UV region is assigned to inter- and in-
845; 558m.
tra-ligand
tion band in the visible region is assigned to metal-to-ligand
p–
p* transitions [52,53], while the low-energy absorp-
3.2. General procedure for preparation of mononuclear complexes 4
and 5
charge transfer (MLCT) (t2g
presented in Fig. 8.
–p
*). Spectra of these complexes are
A mixture of [(g l-Cl)Cl]2 (M = Rh, Ir) (0.07 mmol),
5-C5Me5)M(
ligand Lph (0.18 mmol) and 2.5 equivalents of NH4PF6 in dry meth-
anol (15 ml) was refluxed for 4 h. The reaction mixture was cooled
over-night at room temperature, during which time the crystalline
compound was formed. It was separated by filtration, washed with
cold methanol, diethyl ether and dried under vacuum.
3. Experimental
All solvents were dried and distilled prior to use. 2-Cyanopyri-
dine and phenyl acetylene (Aldrich) were purchased and used as
received. The complexes [(
Me)Ru( -Cl)Cl]2, [(
6-C6Me6)Ru(
C5Me5)M( -Cl)Cl]2 (M = Rh, Ir) [57–59], [(
and [(
5-C9H7)Ru(PPh3)2Cl] [60,61] were prepared according to lit-
g
6-C6H6)Ru(
-Cl)Cl]2
l
-Cl)Cl]2, [(
[54–56],
5-C5H5)Ru(PPh3)2Cl]
g
6-p-iPrC6H4-
[(g5
l
g
l
-
3.2.1. [(g
5-C5Me5)Rh(Lph)Cl]PF6 (4)
l
g
Dark yellow color, yield 80 mg (77%): Anal. Calc. for
C30H29ClN4RhPF6 (728.9): C, 49.43; H, 4.01; N, 7.69. Found: C,
50.10; H, 3.99; N, 7.65%. 1H NMR (400 MHz, CDCl3, 25 °C):
d = 8.91 (d, 1H, JH–H = 8 Hz), 8.59 (d, 1H), 8.41 (s, 1H), 8.39 (d,
1H), 8.19 (td,1H), 7.81 (m, 2H), 7.68 (d, 1H), 7.66–7.61 (m, 5H),
7.40 (d, 1H), 1.77 (s, 15H, C5Me5) ppm. ESI-MS (m/z): 583.1
(100%) [MꢀPF6]+, 558.1 (23%) [MꢀPF6ꢀCl]+. IR (KBr, cmꢀ1): m(P–F)
845s; 558m.
g
erature methods. The ligand Lph was prepared by the Diels–Alder
reaction of 3,6-bis(2-pyridyl)tetrazine with phenyl acetylene
[62]. NMR spectra were recorded on an AMX-400 MHz spectrome-
ter. Infrared spectra were recorded as KBr pellets on a Perkin–El-
mer 983 spectrophotometer, while elemental analyses of the
complexes were performed on a Perkin–Elmer-2400 CHN/S ana-
lyzer. Mass spectra were obtained from Waters ZQ 4000 mass
spectrometer by the ESI method. Absorption spectra were obtained
at room temperature using a Perkin–Elmer Lambda 25 UV/Visible
spectrophotometer.
3.2.2. [(g
5-C5Me5)Ir(Lph)Cl]PF6 (5)
Dark yellow color, yield 70 mg (83%): Anal. Calc. for
C30H29ClN4IrPF6 (818.2): C, 44.04; H, 3.57; N, 6.85. Found: C,
44.10; H, 3.59; N, 6.79%. 1H NMR (400 MHz, CDCl3, 25 °C):
d = 9.30 (d, 1H, JH–H = 8 Hz), 8.88 (dd, 2H, JH–H = 6.8 Hz), 8.71 (s,
1H), 8.45 (td, 1H), 8.22 (td, 2H), 7.84 (td, 1H), 7.75 to 7.67 (m,
5H), 7.53 (d, 1H), 1.68 (s, 15H, C5Me5) ppm. ESI-MS (m/z): 673.3
(100%) [MꢀPF6]+, 638.1 (32%) [MꢀPF6ꢀCl]+. IR (KBr, cmꢀ1): m(P–F)
845s; 558m.
3.1. General procedure for preparation of mononuclear complexes 1–3
A
mixture
of
[(
g
6-arene)Ru(
l
-Cl)Cl]2
(arene = C6H6,
p-iPrC6H4Me and C6Me6) (0.07 mmol), ligand Lph (0.15 mmol) and
2.5 equivalents of NH4PF6 in dry methanol (15 ml) was stirred at
room temperature for 6 h. The precipitate was separated by filtra-
tion, washed with cold methanol, diethyl ether and dried under
vacuum.
3.3. General procedure for preparation of mononuclear complexes 6–8
A
mixture of [(Cp)Ru(PPh3)2Cl] (Cp = C5H5, C5Me5, C9H7)
(0.07 mmol), ligand Lph (0.08 mmol) and 1.5 equivalents of NH4PF6
in dry ethanol (15 ml) was refluxed for 14 h. The color changed
from a dark yellow to a dark red color. The reaction mixture was
cooled over-night at room temperature during which time the
crystalline compound was formed. Some of the crystals were found
suitable for X-ray crystal study. The product was separated by fil-
tration, washed with cold ethanol, diethyl ether and dried under
vacuum.
3.1.1. [(g
6-C6H6)Ru(Lph)Cl]PF6 (1)
Orange-yellow solid, yield 80 mg (89%): Anal. Calc. for
C26H20ClN4RuPF6 (669.5): C, 46.61; H, 3.01; N, 8.36. Found: C,
46.68; H, 3.18; N, 8.48%. 1H NMR (400 MHz, CD3CN, 25 °C):
d = 9.57 (d, 1H, JH–H = 5.58 Hz), 8.86 (d, 1H, JH–H = 8 Hz), 8.31 (s,
1H), 8.26 (d, 1H), 8.18 (td, 1H), 8.08 (td, 2H), 7.71 (td, 1H), 7.53–
7.51 (m, 5H), 7.25 (d, 1H), 6.18 (s, 6H, C6H6) ppm. ESI-MS (m/z):
525.1 (100%) [MꢀPF6]+, 489.1 (10%) [MꢀPF6ꢀCl]+. IR (KBr, cmꢀ1):
m(P–F) 844s; 558m.
3.3.1. [(g
5-C5H5)Ru(Lph)(PPh3)]PF6 (6)
Orange color, yield 60 mg (63%): Anal. Calc. for C43H34N4RuP2F6
(883.2): C, 58.14; H, 3.86; N, 6.31. Found: C, 58.11; H, 3.90; N,
6.59%. 1H NMR (400 MHz, CDCl3, d) 9.50 (d, 1H), 8.75 (d, 1H),
8.72 (d, 1H), 8.21 (s, 1H), 8.14 (td,1H), 7.57 (td, 1H), 7.37 (td,
1H), 7.30–7.20 (m, 20H),7.14 (td, 1H) 6.78 (d, 1H), 4.83 (s, 5H,
C5H5) ppm. 31P{1H} = 46.12 ppm. ESI-MS (m/z): 743.5 (100%)
[MꢀPF6]+. IR (KBr, cmꢀ1): m(P–F) 842s; 527m.
3.1.2. [(g
6-p-iPrC6H4Me)Ru(Lph)Cl]PF6 (2)
Dark orange solid, yield 80 mg (89%): Anal. Calc. for
C30H28ClN4RuPF6 (726.05): C, 49.63; H, 3.89; N, 7.72. Found: C,
50.08; H, 3.78; N, 7.95%. 1H NMR (400 MHz, CD3CN, 25 °C):
d = 9.42 (d, 1H, JH–H = 5.60 Hz), 8.78 (dd, 2H, JH–H = 8 Hz), 8.28 (s,
1H), 8.15(dt, 1H), 7.75 (td, 1H), 7.58–7.63 (m, 5H),7.43 (td, 2H),
7.20 (d, 1H, JH–H = 8 Hz), 6.04 (d, 1H), 6.01 (d, 1H), 5.85 (d, 1H),
5.81 (d, 1H), 2.82 (sept, 1H, CH(CH3)2), 2.28 (s, 3H, CH3), 1.18 (d,
3H, CH(CH3)2), 1.14 (d, 3H, CH(CH3)2) ppm. ESI-MS (m/z): 580.8
(100%) [MꢀPF6]+, 544.7 (20%) [MꢀPF6ꢀCl]+. IR (KBr, cmꢀ1): m(P–F)
842s; 558m.
3.3.2. [(g
5-C5Me5)Ru(Lph)(PPh3)]PF6 (7)
Orange color, yield 68 mg (60%): Anal. Calc. for C48H44N4RuP2F6
(953.38): C, 60.16; H, 4.63; N, 5.85. Found: C, 60.11; H, 4.69; N,
5.74%. 1H NMR (400 MHz, CDCl3, 25 °C): d = 9.07 (d, 1H), 8.89 (d,
1H), 8.81 (td, 1H), 8.25 (s, 1H), 8.17 (td, 1H), 7.51–7.12 (m, 23H),
6.76 (d, 1H), 4.90 (s, 5H, C5Me5) ppm. 31P{1H} = 45.25 ppm. ESI-
3.1.3. [(g
6-C6Me6)Ru(Lph)Cl]PF6 (3)
Orange-yellow solid, yield 80 mg (89%): Anal. Calc. for
C32H32ClN4RuPF6 (754.1): C, 50.97; H, 4.28; N, 7.43. Found: C,
51.08; H, 4.31; N, 7.29%. 1H NMR (400 MHz, CD3CN, 25 °C):
d = 8.91 (d, 1H, JH–H = 5.58 Hz), 8.82 (d, 1H, JH–H = 8 Hz), 8.67 (s,
1H), 8.59 (d, 1H, JH–H = 8 Hz), 8.04 (td, 1H), 7.67–7.61 (m, 7H),
7.53 (td, 2H), 2.18 (s, 18H, C6(Me)6) ppm. ESI-MS (m/z): 608.9
MS (m/z): 818.1 (100%) [MꢀPF6]+. IR (KBr, cmꢀ1):
m(PF) 844s; 527m.
3.3.3. [(g
5-C9H7)Ru(Lph)(PPh3)]PF6 (8)
Yellowish brown color, yield 70 mg (83%): Anal. Calc. for
C47H36N4RuP2F6 (933.3): C, 60.16; H, 3.87; N, 5.97. Found: C,
60.11; H, 3.89; N, 5.99%. 1H NMR (400 MHz, CDCl3, 25 °C):

K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
715
[6] M. Yanagida, L.P. Singh, K. Sayama, K. Hara, R. Katoh, A. Islam, H. Sugihara, H.
Arakawa, M.K. Nazeeruddin, M. Grätzel, J. Chem. Soc., Dalton Trans. 16 (2000)
2817–2822.
[7] P.R. Ashton, R. Ballardini, V. Balzani, A. Credi, K.R. Dress, E. Ishow, C.J. Clevelaan,
O. Kosian, J.A. Preece, N. Spencer, J.F. Stoddart, M. Venturi, S. Wenger, Chem.
Eur. J. 6 (2008) 3558–3574.
d = 9.68 (d, 1H), 8.76 (d, 1H), 8.69 (d, 1H), 8.20 (s, 1H), 8.12 (td, 2H),
7.94 (td, 2H) 7.63 (td, 1H), 7.22–7.55 (m, 24H, 4Ph), 4.87(t, 1H),
4.71 (d, 2H) ppm. 31P{1H} = 48.42 ppm. ESI-MS (m/z): 789.4
(100%) [MꢀPF6]+. IR (KBr, cmꢀ1): m(P–F) 841s; 548m.
[8] F. Hanasaka, K.-I. Fujita, R. Yamaguchi, Organometallics 24 (2005) 3422–3433.
[9] M.S. El-Shahawi, A.F. Shoair, Spectrochim. Acta, Part A 60 (2004) 121–127.
[10] R. Noyori, S. Hashigushi, Acc. Chem. Res. 30 (1997) 97–102. and reference
therein.
[11] S.-I. Murahashi, H. Takaya, T. Naota, Pure Appl. Chem. 74 (2002) 19–23.
[12] U.J. Jauregui-Haja, M. Dessoudeix, P. Kalck, M. Wilhelm, H. Delmas, Catal.
Today 66 (2001) 297.
3.4. Single-crystal X-ray structure analyses
X-ray quality crystals of the complex 2. CHCl3 were obtained by
the slow diffusion of diethyl ether into a chloroform solution of 2,
while the crystals of 4 and 6 were obtained from slow evaporation
of their reaction mixtures. The data were measured using a Bruker
[13] C.A. Sandoval, T. Ohkuma, N. Utsumi, K. Tsutsumi, K. Murata, R. Noyori, Chem.
Asian J. 1–2 (2006) 102–110.
[14] P.J. Dyson, G. Sava, Dalton Trans. (2006) 1929–1933.
[15] W.H. Ang, P.J. Dyson, Eur. J. Inorg. Chem. (2006) 4003–4018.
[16] A.F.A. Peacock, A. Habtemariam, R. Fernandez, V. Walland, F.P.A. Fabbiani, S.
Parsons, R.E. Aird, D.I. Jodrell, P.J. Sadler, J. Am. Chem. Soc. 128 (2006) 1739–
1748.
[17] A. Habtemariam, M. Melchart, R. Fernandez, S. Parsons, I.D.H. Oswald, A. Par-
kin, F.P.A. Fabbiani, J.E. Davidson, A. Dawson, R.E. Aird, D.I. Jodrell, P.J. Sadler, J.
Med. Chem. 49 (2006) 6858–6868.
[18] M. Melchart, A. Habtemariam, O. Novakova, S.A. Moggach, F.P.A. Fabbiani, S.
Parsons, V. Brabec, P.J. Sadler, Inorg. Chem. 46 (2007) 8950–8962.
[19] C. Scolaro, A. Bergamo, L. Brescacin, R. Delfino, M. Cocchietto, G. Laurenczy, T.J.
Geldbach, G. Sava, P.J. Dyson, J. Med. Chem. 48 (2005) 4161–4171.
[20] E. Hilllard, A. Vessieres, F. Le Bideau, D. Plazuk, D. Spera, M. Huche, G. Jaouen,
Chem. Med. Chem. 1 (2006) 551–559.
SMART CCD diffractometer using Mo K
a graphite monochromated
radiation ( = 0.71073 Å). The structures were solved by direct
a
methods using the program SHELXS-97 [63]. Refinement and all fur-
ther calculations were carried out using SHELXL-97 [64]. Hydrogen
atoms were included at the calculated positions and treated as rid-
ing atoms using the SHELXL default parameters. The non-H atoms
were refined anisotropically, using weighted full-matrix least-
squares on F2. Crystallographic details are summarized in Table
2. Figs. 5–7 were drawn with ORTEP [65], representing the struc-
tures of complexes 2, 4 and 6, respectively.
ˇ
ˇ
[21] M. Auzias, B. Therrien, G. Süess-Fink, P.P. Štepnicka, W.H. Ang, P.J. Dyson,
Inorg. Chem. 47 (2008) 578–583.
3.5. Theoretical calculations
[22] M.A. Scharwitz, I. Ott, Y. Geldmacher, R. Gust, W.S. Sheldrick, J. Organomet.
Chem. 693 (2008) 2299–2309.
[23] S.K. Singh, S. Joshi, A.R. Singh, J.K. Saxena, D.S. Pandey, Inorg. Chem. 46 (2007)
10869–10876.
[24] M. Haga, M.M. Ali, H. Maegawa, K. Nozaki, A. Yoshimura, T. Ohno, Coord. Chem.
Rev. 94 (1994) 99–118.
[25] M. Haga, M.M. Ali, R. Arakava, Angew. Chem. Int., Ed. Engl. 35 (1996) 76–78.
[26] S. Baitalik, U. Florke, K. Nag, Inorg. Chem. 38 (1999) 3296–3308.
[27] N. Gupta, N. Grover, G.A. Neyhart, P. Singh, H.H. Thorp, Inorg. Chem. 32 (1993)
310–316.
Density functional theory (DFT) [66] calculations were under-
taken for the ligands L and Lph as well as for the complexes [(g6
-
-
p-iPrC6H4Me)Ru(Lph)Cl]+,
C5Me5)Ir(Lph)Cl]+, [
[(
g
5-C5Me5)Rh(Lph)Cl]+,
[(g5
g
5-C5H5)Ru(Lph)(PPh3)]+ in both the binding
modes (type-A and type-B). Full geometry optimization was carried
out with the use of the B3LYP [Becke three-parameter exchange
functional (B3) and the Lee–Yang–Parr correlation functional
(LYP)] method [67,68] together with the 6-31+G** and LanL2DZ
[69–71] basis sets for ligands and for complexes, respectively. Star-
ing atomic coordinates for the cationic complexes (2, 4 and 6) were
taken from the single-crystal X-ray structures. All computations
were performed with the GAUSSIAN 03 package [72]. Frequency cal-
culations were performed to determine whether the optimized
geometries were minima on the potential energy surface.
[28] B.L. Schottel, H.T. Chifotides, M. Shatruk, A. Chouai, L.M. Pe´rez, J. Bacsa, K.R.
Dunbar, J. Am. Chem. Soc. 128 (2006) 5895–5902.
[29] P. Ceroni, F. Paolucci, S. Roffia, S. Serroni, S. Campagna, A.J. Bard, Inorg. Chem.
37 (1998) 2829–2832.
[30] A.K.V. Kasack, R. Reinhardt, S. Torsten, T. Scheiring, S. Zalis, J. Fiedler, W. Kaim,
Dalton Trans. (1999) 575–582.
[31] N. Komatsuzaki, R. Katoh, Y. Himeda, H. Sugihara, H. Arakawa, K. Kasuga, J.
Chem. Soc., Dalton Trans. (2000) 2045–2053.
[32] C. Metcalfe, S. Spey, J.A. Thomas, Dalton Trans. (2002) 4732–4739.
[33] P.A. Anderson, F.R. Keene, T.J. Meyer, J.A. Moss, G.F. Strouse, J.A. Treadway,
Dalton Trans. (2002) 3820–3831.
[34] E.C. Constable, C.E. Housecroft, M. Neuburger, S. Reymann, S. Schaffner, Eur. J.
Org. Chem. (2008) 1597–1607.
Acknowledgements
[35] E.C. Constable, C.E. Housecroft, M. Neuburger, S. Reymann, S. Schaffner, Eur. J.
Inorg. Chem. (2008) 3540–3548.
[36] E.C. Constable, C.E. Housecroft, B.M. Kariuki, N. Kelly, C.B. Smith, Inorg. Chem.
Commun. 5 (2002) 199–202.
[37] E.C. Constable, C.E. Housecroft, B.M. Kariuki, M. Neuburger, C.B. Smith, Aust. J.
Chem. 56 (2003) 653–655.
[38] N. Singh, D.S. Pandey, J. Organomet. Chem. 689 (2004) 1821–1834.
[39] S. Ghumaan, B. Sarkar, S. Patra, K. Parimal, J.V. Slageren, J. Fiedler, W. Kaim,
G.K. Lahiri, J. Chem. Soc., Dalton Trans. (2005) 706–712.
[40] Z. Deng, H.-W. Tseng, R. Zong, D. Wang, R.P. Thummel, Inorg. Chem. 47 (2008)
1835–1848.
K.M. Rao gratefully acknowledges the Department of Science
and Technology, New Delhi, for financial support (Sanction Order
No. SR/S1/IC-11/2004). We thank the Sophisticated Instruments
Facility, Indian Institute of Science, Bangalore, for providing the
NMR facility. Thanks are due to Professor R.H. Duncan Lyngdoh
for help in preparing this manuscript.
Appendix A. Supplementary data
[41] P. Govindaswamy, Y.A. Mozharivskyj, K.M. Rao, J. Organomet. Chem. 689
(2004) 3265–3274.
[42] P. Govindaswamy, P.J. Carroll, Y.A. Mozharivskyj, K.M. Rao, J. Organomet.
Chem. 690 (2005) 885–894.
[43] A. Singh, N. Singh, D.S. Pandey, J. Orgnomet. Chem. 642 (2002) 48–57.
[44] R. Dorta, L. Konstantinovski, L.J.W. Shimon, Y. Ben-David, D. Milstein, Eur. J.
Inorg. Chem. (2003) 70–76.
[45] K.T. Prasad, B. Therrien, K.M. Rao, J. Organomet. Chem. 693 (2008) 3049–3056.
[46] B. Therrien, C. Said-Mohamed, G. Suss-Fink, Inorg. Chim. Acta 361 (2008)
2601–2608.
[47] R. Lalrempuia, K.M. Rao, Polyhedron 22 (2003) 3155–3160.
[48] P. Govindaswamy, Y.A. Mozharivskyj, K.M. Rao, Polyhedron 24 (2005) 1710–
1716.
CCDC 739572, 739570 and 739571 contain the supplementary
crystallographic data for 2ꢃCHCl3, 4 and 6. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.jorganchem.2009.12.004.
References
[49] K. Pachhunga, B. Therrien, K.A. Kreisel, G.P.A. Yap, K.M. Rao, Polyhedron 26
(2007) 3638–3644.
[50] J.G. Małecki, R. Kruszynski, M. Jaworska, P. Lodowski, Z. Mazurak, J.
Organomet. Chem. 693 (2008) 1096–1108.
[1] M.H. Keefe, K.D. Benkstein, J.T. Hupp, Coord. Chem. Rev. 205 (2008) 201–228.
[2] D.S. Tyson, C.R. Luman, X. Zhou, F.N. Castellano, Inorg. Chem. 40 (2001) 4063–
4071.
[3] J.F. Endicott, H.B. Schlegel, Md.J. Uddin, D.S. Seniveratne, Coord. Chem. Rev. 229
(2002) 95–106.
[4] W.R. Browne, R. Hage, J.G. Vos, Coord. Chem. Rev. 250 (2006) 1653–1668.
[5] M.T. Indelli, C. Chiorboli, F. Scandola, Top. Curr. Chem. 80 (2007) 215.
[51] E. Binamira-Soriaga, N.L. Keder, W.C. Kaska, Inorg. Chem. 29 (1990) 3167–
3171.
[52] C.S. Arau´ jo, M.G.B. Drew, V. Fe´lix, L. Jack, J. Madureira, M. Newell, S. Roche, T.M.
Santos, J.A. Thomas, L. Yellowlees, Inorg. Chem. 41 (2002) 2250–2259.

716
K. Thirumala Prasad et al. / Journal of Organometallic Chemistry 695 (2010) 707–716
[53] H. Deng, J. Li, K.C. Zheng, Y. Yang, H. Chao, L.N. Ji, Inorg. Chim. Acta 358 (2005)
3430–3440.
[54] M.A. Bennett, T.N. Huang, T.W. Matheson, A.K. Smith, Inorg. Synth. 21 (1982)
74–81.
[67] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652.
[68] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–789.
[69] A.D. Becke, J. Chem. Phys. 98 (1993) 1372.
[70] A. Gorling, Phys. Rev. A 54 (1996) 3912–3915.
[55] M.A. Bennett, T.W. Matheson, G.B. Robertson, A.K. Smith, P.A. Tucker, Inorg.
Chem. 19 (1980) 1014–1021.
[71] L. Tan, S. Zhang, X. Liu, Y. Chen, X. Liu, J. Organomet. Chem. 693 (2008) 3387–
3395.
[56] M.A. Bennett, A.K. Smith, J. Chem. Soc., Dalton Trans. (1974) 233–241.
[57] J.W. Kang, K. Moseley, P.M. Maitlis, J. Am. Chem. Soc. 91 (1969) 5970–5977.
[58] R.G. Ball, W.A.G. Graham, D.M. Heinekey, J.K. Hoyano, A.D. McMaster, B.M.
Mattson, S.T. Michel, Inorg. Chem. 29 (1990) 2023–2025.
[59] C. White, A. Yates, P.M. Maitlis, Inorg. Synth. 29 (1992) 228.
[60] M.I. Bruce, N.J. Windsor, Aust. J. Chem. 30 (1977) 1601–1604.
[61] G. Consiglio, F. Morandini, Chem. Rev. 87 (1987) 761–778.
[62] W.A. Butte, F. Case, J. Org. Chem. 26 (1961) 4690–4692.
[63] G.M. Sheldrick, Acta Crystallogr., Sect.A 46 (1990) 467–473.
[64] G.M. Sheldrich, SHELXS-97 and SHELXL-97, University of Göttingen, Göttingen,
Germany, 1999.
[72] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
J.A. Montgomery, T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.H. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian,
J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A.
Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels,
M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman,
J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W.
Chen, M.W. Wong, C. Gonzalez, J.A. Pople, GAUSSIAN 03, Revision E.01, Gaussian,
Inc., Pittsburgh, PA, 2003.
[65] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565–566.
[66] R.G. Parr, W. Yang, Density Functional Theory of Atoms and Molecules, Oxford
University Press, New York, 1989.