Pyrazole cleavage of tris(3,5-dimethylpyrazolyl)borate with Ruthenium(II) complexes: Synthesis, structural characterization and DFT studies

Article abstract of DOI:10.1016/j.molstruc.2016.11.097

The reaction of [Ru(H)(Cl)(CO)(PPh₃)₃] (1) with KTp* (KTp* = Potassium tris(3,5-dimethylpyrazolyl)borate) in a refluxing toluene yields a mixture of [RuTp*(H)(CO)(PPh₃)] (2), [Ru(H)(Cl)(pz*H)(CO)(PPh₃)₂] (3), and [H(pz*)B(μ-pz*)₂B(pz*)H] (4) (pz*H = 3,5-dimethylpyrazole). The products (3) and (4) were obtained by the degradation of the scorpionate ligand, Tp*. These complexes were characterised by IR, ¹H NMR, UV, X-ray crystallography and DFT calculations.

Full text of DOI:10.1016/j.molstruc.2016.11.097

Journal of Molecular Structure 1133 (2017) 264e270
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Pyrazole cleavage of tris(3,5-dimethylpyrazolyl)borate with
Ruthenium(II) complexes: Synthesis, structural characterization and
DFT studies
Donkupar Kharbani, Debojit Kumar Deb, Ibaniewkor L. Mawnai, Sunshine D. Kurbah,
Biplab Sarkar, E.K. Rymmai*
Department of Chemistry, Centre for Advance Studies, North-Eastern Hill University, Shillong, 793022, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of [Ru(H)(Cl)(CO)(PPh3)3] (1) with KTp* (KTp* ¼ Potassium tris(3,5-dimethylpyrazolyl)
borate) in a refluxing toluene yields a mixture of [RuTp*(H)(CO)(PPh3)] (2), [Ru(H)(Cl)(pz*H)(CO)(PPh3)2]
Received 10 May 2016
Received in revised form
12 September 2016
Accepted 30 November 2016
Available online 1 December 2016
(3), and [H(pz*)B(
m
-pz*)2B(pz*)H] (4) (pz*H ¼ 3,5-dimethylpyrazole). The products (3) and (4) were
obtained by the degradation of the scorpionate ligand, Tp*. These complexes were characterised by IR, 1H
NMR, UV, X-ray crystallography and DFT calculations.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Poly(pyrazolyl)borate degradation
Pyrazaboles
Ruthenium(II)
Pnicogen bond
1. Introduction
In this paper, we describe the synthesis of scorpionate complex
[RuTp*(H)(CO)(PPh3)] (2) and investigate the mechanistic path-
Tris(3,5-dimethylpyrazolyl)borate (Tp*), a scorpionate ligand
containing an alkyl-substituent of parent tris(pyrazolyl)borate (Tp)
was introduced in 1966 by Trofimenko [1]. Since then, complexes
formed by these versatile scorpionate ligands have been reported
with almost every metal in the periodic table [2]. Many of these
complexes have been investigated and are widely employed in
various fields of chemistry such as catalysis, biomimetics, materials
science and radiopharmaceutics [3,4]. Changing the nature of
substituents on the pyrazolyl ring, especially those at the 3 position,
leads to stabilization of the complexes by steric control of the
interaction with the metal centres [5e7]. One interesting aspect of
these ligands is that they show various modes of coordination
which include ligand rearrangements or modifications [8,9]. Pol-
y(pyrazolyl)borates undergo some transformations in which they
give products containing pyrazole or pyrazolate derivatives, mainly
due to BeN bond cleavage [10]. Because of this degradation,
comparatively less work on the complexes containing well known
Trofimenko scorpionate ligands has been reported.
ways for the isolation of [Ru(H)(Cl)(pz*H)(CO)(PPh3)2] (3) and
[H(pz*)B( -pz*)2B(pz*)H] (4) from the reaction mixtures. The
analogous complex [RuTp(H)(CO)(PPh3)] reported in literature [11],
provides the route of synthesizing the new complex [RuTp*(H)(-
CO)(PPh3)] (2).
m
2. Experimental section
2.1. Materials and methods
All chemicals were reagent grade, and solvents were dried and
purified prior before use; toluene was distilled from sodium wire
and acetophenone. The complex [Ru(H)(Cl)(CO)(PPh3)3] (1) [12]
and KTp* ligand [13] were prepared according to literature
methods. All the reactions were carried out in standard Schlenk
technique under a dry and oxygen-free nitrogen atmosphere.
Infrared spectra were recorded on a Perkin-Elmer FTIR spectrom-
eter using KBr pellets and the 1H NMR spectra were recorded on
Brucker AVENCE II 400 MHz spectrometer using tetramethylsilane
as a reference. UVeVisible spectra were recorded on a Perkin-Elmer
Lamda 25 UVeVisible spectrophotometer.
* Corresponding author.
E-mail address: ekrymmai68@gmail.com (E.K. Rymmai).
http://dx.doi.org/10.1016/j.molstruc.2016.11.097
0022-2860/© 2016 Elsevier B.V. All rights reserved.

D. Kharbani et al. / Journal of Molecular Structure 1133 (2017) 264e270
265
2.2. Single crystal X-ray crystallography
filtered to obtain the clear solution. The solvent was removed under
reduced pressure to get a pale yellowish product. The product was
washed well with diethylether and recrystallized from toluene
leading to the deposition of pale yellowish crystals of (2), the or-
ange blocks of (3) and the white crystalline products of (4). Small
portion of samples were collected for spectroscopic analysis. A
single crystal suitable for X-ray for all the complexes was obtained
from toluene/ether solution. [RuTp*(H)(CO)(PPh3)] (2):IR (KBr,
pellet); 2518 cmꢀ1 (BeH), 2036 cmꢀ1 (RueH), 1912 cmꢀ1 (CO), 1H
Single crystals of the compounds were obtained by slow evap-
oration at room temperature. Single crystal X-ray data of the
compounds were measured at 291.8 K, employing X calibur, Eos,
Gemini diffractometer equipped with a monochromated Mo/K ra-
diation ((
l
¼ 0.71073 Å) source. Crys Alis PRO; Agilent, 2013 soft-
ware packages were used for data collection and reduction. The
structure of the complexes were solved by direct methods [14], and
refined by a full matrix least squares procedure based on F2 [14]
minimizing R ¼ S jj F0j - jFcjj / S jF0j, wR ¼ [S [w (F20 e Fc2)2] / S
(F20)2]1/2 and S ¼ [S [(F20 e F2c)2/ (n e p)]1/2. For structure solution and
refinements SHELXT-2014 and SHELX-2014 [15] were used in all
cases.
NMR (CDCl3, 400 MHz);
d
ꢀ12.03 (d, J(PH) ¼ 24 Hz, 1H, RuH), 1.36
(s, 3H, Tp*CH3), 1.69 (s, 3H, Tp*CH3), 1.85 (s, 3H, Tp*CH3), 2.14 (s, 3H,
Tp*CH3), 2.19 (s, 3H, Tp*CH3), 2.40 (s, 3H, Tp*CH3), 5.01 (s, 1H,
Tp*CH), 5.57 (s, 1H, Tp*CH), 5.61 (s, 1H, Tp*CH), 7.10e7.38 (m, 15H,
PPh3).
2.3. Computational methodology
3. Results and discussion
All calculations were carried out using the Gaussian 09 package
[16]. Full geometry optimizations of the complexes were performed
using the density functional theory (DFT) based B3LYP [17] method
along with the 6-31G(d,p) basis set for lighter atoms (H, B, C, N, P, Cl
and O) and LANL2DZ for the heavier atom (Ru). The 6-31G(d,p) is a
standard polarized basis set which adds d function on heavier
atoms and p function on lighter atoms while LANL2DZ is pseudo-
potential basis set mainly used for post-third row atoms. The
structures of the complexes (2, 3, and 4) were at the minima in the
potential energy surface by ensuring the absence of imaginary
frequencies. Natural Bond Orbital analysis (NBO) [18] has been
carried out to obtain the natural electronic configurations, charges
on the individual atoms and the d-orbital occupancies of the Ru
metal atom present in the complexes. Time-dependent density
functional theory (TDDFT) [19,20] with the B3LYP associated with
the polarizable continuum solvent-effect model (PCM) [21] was
performed to predict the UV spectra in dichloromethane solution.
GaussSum 2.2 [22] was used for the analysis of UVeVis spectra,
oscillator-strengths, HOMO-LUMO energy-gap, transitions be-
tween various states and the fractional contributions of various
groups to each molecular orbital. In addition, nucleus-independent
chemical shift (NICS) was performed on product (4) using the
gauge-invariant atomic orbital (GIAO) [23] approach. Since the ring
3.1. General
The complex [RuTp*(H)(CO)(PPh3)] (2) was synthesized by a
similar procedure for the synthesis of the less steric KTp complex as
reported by Ning-Yu Sun and Stephen J. Simpson [11]. Treatment of
[Ru(H)(Cl)(CO)(PPh3)3] (1) with 1 equivalent of KTp* in toluene for
24 h leads to the formation of mixture of complexes (2), (3) and (4)
(Scheme 1). These complexes have the same solubility in a range of
solvents and were separated by recrystallization from the reaction
mixture. The yellowish crystals of (2), orange blocks of complex (3)
and the white crystalline product of complex (4) were collected
manually which were sufficient for spectroscopic analysis. They
were structurally identified by combination of spectroscopic anal-
ysis such as IR and 1H NMR spectroscopy. In addition, the solid
structures of (2), (3) and (4) were determined by single crystal X-
ray diffraction.
The IR spectrum of complex (2) shows the nB-H band at
2518 cmꢀ1, indicating the presence of coordinated Tp* ligand when
compared to the stretching frequency of free KTp* which was
observed at 2437 cmꢀ1. Comparison of the nCO and nRu-H stretching
frequencies of complex (2) and its analogous complex (Table 1),
shows that when Tp is replaced by a stronger electron donating Tp*
ligand, both the metal-hydride
are enhanced in the metal complex (2). Since, the
s
-bond and metal-carbonyl bond
and type of
current due to the cyclic
p electron delocalization are induced by
s
p
the external magnetic field which is applied perpendicular to the
ring current, therefore the out of plane component of the NICSzz
tensor was evaluated using Multiwfn [24].
interactions are mostly occurring between the metal and the li-
gands, a general conclusion can be drawn that “substitution by a
stronger electron donating ligand to a transition metal complex
enhances the inherent bonding of the ligands to the metal centre”;
and the reverse must be true.
2.4. Synthesis of complexes (2), (3) and (4)
The 1H NMR spectrum of the complex (2) shows a doublet at
A mixture of [Ru(H)(Cl)(CO)(PPh3)3] (1) (0.5 g, 0.524 mmol) and
KTp* (0.17 g, 0.505 mmol) in toluene (40 ml) was refluxed for 24 h.
The mixture was then allowed to cool to the room temperature, and
d
ꢀ12.03 (J(PH) ¼ 24 Hz) due to the hydride ligand and indicates the
cis coupling with the phosphorus atom of the triphenylphosphine.
The complex (2) exhibits three singlet peaks in the range of
Scheme 1. Reaction of [Ru(H)(Cl)(CO)(PPh3)3] (1) with KTp*.

266
D. Kharbani et al. / Journal of Molecular Structure 1133 (2017) 264e270
Table 1
tris(3,5-dimethylpyrazolyl)borate, the monodentate ligands of tri-
phenylphosphine, carbon monoxide and a hydride forming an
octahedral geometry (Fig. 2). Table 2 shows the crystal data
refinement of the complex (2) and Table 3 compiles the selected
bond lengths, bond angles for the complexes and are comparable
with the theoretical data.
The nCO and nRu-H stretching frequencies of Complex (2) with its analogue [RuTp
(H)(CO)(PPh3)].
Complex
nCO (cmꢀ1
)
nRu-H (cmꢀ1
)
[RuTp(H)(CO)(PPh3)]
[RuTp*(H)(CO)(PPh3)] (2)
1922
1912
1985
2036
3.3. Geometry optimization
5.01e5.61 ppm for the three different chemical environments of
the protons at 4-positions of the pyrazole rings, consistent with the
rigid tridentate Tp* ligand. The IR and 1H NMR spectra of products
(3) and (4) are comparable to that of the reported values obtained
by the different synthetic routes [25,26].
The geometries of all the gas phase compounds (2e4) are
optimized at B3LYP level and no geometrical constraints are
applied during optimization. The input files of the complexes are
prepared from the crystallographic coordinates obtained from X-
ray measurements. The important bond-lengths and bond-angles
of these complexes are tabulated in Table 3. The calculated bond-
lengths and bond-angles are in good agreement with the experi-
mental single crystal X-ray data measurements.
The main interest of our work was to obtain complex (2), but
complex (3) formed by the usual pyrazole cleavage [27] was also
obtained. However, the formation of (3) in which pz*H ligand is
trans to CO (instead of H) may have a mechanistic significance
because the phosphine ligand replaced by pz*H from [Ru(H)(Cl)(-
CO)(PPh3)3] (1) was initially trans to H [28] (Scheme 1). Moreover,
Romero and co-workers [25] kept on obtaining complex (3) when
1-hydroxymethyl-3,5-dimethylpyrazole was treated with different
precursor complexes, such as, [RuCl2(PPh3)3], [Ru(Cl)(H)(PPh3)3]
and [Ru(H)(Cl)(CO)(PPh3)3]. The other two possible isomers of (3),
namely, (3a) and (3b) (Fig. 1) were not reported in the literature.
DFT based B3LYP calculations on (3), (3a) and (3b) were performed
and support the formation of (3) as (3a) and (3b) are higher in
energy by 3.77 and 23.83 kcal molꢀ1 respectively.
3.4. Atomic charge analysis
The atomic charge distributions on donor-acceptor atoms for
the complexes under investigation are obtained from the NBO
analysis and are tabulated in Table 4. Comparing the atomic
charges in Table 4, it can be seen that the electron charge density
on Ru(II) in their respective complexes is increased i.e., before
complexation the charge on Ruthenium is þ2, and after
complexation the charge of Ru in complexes (2) and (3)
are ꢀ0.803 and ꢀ1.158, respectively. This indicates that the li-
gands transfer their negative charges to the respective ruthenium
metal ion during formation of complexes i.e., for complex (2) the
electron charge density on hydride decreases from ꢀ1 to þ0.081
whereas for complex (3) the electron charge density on both hy-
dride and chloride decreases from ꢀ1 to þ0.104 and ꢀ0.544,
respectively. The increase in electron charge density of the Ru
metal ion in complexes (2) and (3) can also be understood from
the natural electronic configuration obtained from NBO analysis.
For instance, before complexation the natural electronic config-
uration for Ru(II) cation is 4d(6.00) but after complexation the
natural electronic configurations for Ru metal ion in complexes (2)
and (3) are 5s(0.36) 4d(7.73) 5p(0.72) 5d(0.02) and 5s(0.39)
4d(7.94) 5p(0.55) 5d(0.02) 6p(0.29), respectively. For Ru(II) metal
The isolation of pyrazabole side product (4) was first reported by
Blosch [26] when KTp* was treated with Tungsten (VI) complexes.
The generation of pyrazabole from the poly(pyrazolyl)borate was
also proposed by Hill and co-workers [29] when bis(pyrazolyl)
borate was treated with [RuCl2(PPh3)3]. The tris(pyrazolyl)borate
ligand in the complex cleaves when there is one (i.e., bi-dentate k2
-
N,N mode) or two (i.e., mono-dentate k
1-N,N mode) pendant pyr-
azole nitrogen(s) left uncoordinated for sufficient amount of time
to facilitate the nucleophilic attack [30]. Based on the above ob-
servations and the isolation of the products (3) and (4) from the
reaction mixture, we are therefore tend to believe that the reaction
proceeds by the mechanisms as shown in Scheme 2a and b in which
exceptionally stable pyrazabole [31], is generated. The mechanism
for the formation of (3) remains unclear, however the following
scenarios are likely to happen: (i) Formation of an intermediate (A)
activates the nucleophilic attack at the boron centre with either the
free ligand (Scheme 2a) or with another intermediate (A) (Scheme
2b) to form the highly stable pyrazabole (4). (ii) Electronic and
steric effects promote the transformation of (B) to (3) because the
ion in the free state, the valence d-orbitals occupancy in each of
22
the dxy, dyz, and dxz orbitals is 2.0, whereas d
and d2z orbitals
x-y
remain unoccupied. This is because the energy of d and d2z or-
22
x-y
bitals is 0.1126 a.u. higher than the dxy, dyz, and dxzorbitals. On
complexation the occupancy of dxy, dyz, and dxz orbitals of Ru de-
22
creases (<2.0) and the d and dz2 orbitals get occupied as shown in
Ru(II) metal centre in (B) is bonded to relatively more
p-acid and
x-y
bulky phosphine ligands, hence replacing one PPh3 by Clꢀ to form
Table 5.
The total hyperconjugation to
lone-pairs of N5 and N3 atoms and their respective NeC bond pairs
of scorpionate ligand in complex (2) are 0.28 and 0.27 k cal molꢀ1
Also in complex (3) the total hyperconjugation to P1eC12and
P2eC19 from the lone-pair of N1 atom and its respective NeC
bond of pyrazole ligand are 0.58 kcal molꢀ1. These observations
s*P1eC16 and s*P1eC28 from the
(3) will be electronically and sterically favoured.
.
3.2. Molecular structure of complex (2)
s
*
s*
The single crystal X-ray analysis shows that the complex is
constructed from scorpionate ligand consisting of a tripodal
suggest that in complexes (2) and (3) there are P⋯N interactions
commonly known as pnicogen interactions.
PPh3
PPh3
PPh3
3.5. Infrared, NICSzz and electronic spectral analysis
H
N
NH
Cl
N
NH
Cl
H
N
NH
Ru
Ru
Ru
The theoretical harmonic frequencies was scaled by a factor of
0.961 as obtained from CCCB database for B3LYP/6-31G(d,p) level of
theory. Scaling of harmonic frequency is required to account for the
anharmonicity of the fundamental frequencies which can aid in
interpretation of experimental results from the theoretical calcu-
lated results. The theoretical IR vibrational frequencies are in
CO
H
Cl
OC
CO
PPh3
(3b)
PPh3
(3a)
PPh3
(3)
Fig. 1. The possible isomers of complex (3).

D. Kharbani et al. / Journal of Molecular Structure 1133 (2017) 264e270
267
Scheme 2. Suggested mechanisms for the formation of [Ru(H)(Cl)(pz*H)(CO)(PPh3)2] (3) and [H(pz*)B(m-pz*)2B(pz*)H] (4).
Fig. 2. Molecular structures of the complexes (2) and (3).
reasonable agreement with the experimental IR spectra. The band
observed at 2520 cmꢀ1(expt. value 2518 cmꢀ1) indicates the pres-
ence of nB-H moiety in complex (2). For complex (3) the band at
around 2520 cmꢀ1 was not observed which indicates the absence of
BeH moiety. Strong bands observed around 1938 cmꢀ1(expt. value
1912 cmꢀ1) and 1963 cmꢀ1 (expt. value 1934 cmꢀ1) correspond to
nCO stretching frequencies and medium bands observed around
1978 cmꢀ1(expt. value 2036 cmꢀ1) and 2020 cmꢀ1(expt. value
2086 cmꢀ1) correspond to nRu-H stretching frequencies for com-
plexes (2) and (3) respectively. NICS [32] is the computed value of
the negative magnetic shielding at some selected point in space,
generally at a ring or cage centre. Initially NICS(0)iso was introduced
by Paul Schleyer as a simple and efficient probe of aromaticity. But
this index was not a pure measure of
p-electron framework as s

268
D. Kharbani et al. / Journal of Molecular Structure 1133 (2017) 264e270
Table 2
Table 5
Crystallographic and structure refinement for Complex (2).
Calculated d orbital occupancy of the central metal atom in the complexes.
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
C
34H38N6BPORu
Complex (2)
Complex (3)
689.55
dxy
dxz
1.5758
1.6090
1.6832
1.3381
1.5273
dxy
dxz
1.7755
1.9456
1.7554
1.1413
1.3212
293.2(4)
Triclinic
P1
dyz
dyz
22
22
d
d
x-y
x-y
10.1479(9)
10.9974(8)
16.3933(13)
74.118(6)
76.264(7)
70.031(7)
1632.8(2)
2
dz2
dz2
b/Å
c/Å
ꢁ
ꢁ
ꢁ
/
a
b
g
/
/
Volume/Å3
Z
m
/mmꢀ1
0.566
Radiation
MoK
12303
7464/0/407
1.050
a
(
l
¼ 0.71073)
Reflections collected
Data/restraints/parameters
Goodness of fit on F2
Final R indexes [I ꢂ 2
s
(I)]
R1 ¼ 0.0322, wR2 ¼ 0.0745
Final R indexes [all data]
R1 ¼ 0.0420, wR2 ¼ 0.0797
Table 3
Selected bond lengths and bond angles for complexes (2) and (3).
Complex (2)
Complex(3)
Distance (Å)
Expt.
Calc.
Distance (Å)
Expt.
Calc.
Ru1eP1
Ru1eN3
Ru1eN1
Ru1eN5
Ru1eC34
Ru1eH
2.302(6)
2.268(18)
2.112(17)
2.182(17)
1.810(2)
1.546(2)
2.398
2.342
2.154
2.217
1.855
1.588
Ru1eP1
Ru1eP2
Ru1eN1
Ru1eCl1
Ru1eC37
Ru1eH
2.361(13)
2.359(13)
2.172(4)
2.565(17)
1.967(7)
1.935(3)
2.429
2.429
2.225
2.660
1.859
1.582
Angles (º)
Expt.
Calc.
Angles (º)
Expt.
Calc.
N3eRu1eP1
N1eRu1eP1
N1eRu1eN3
N3eRu1eN5
N5eRu1eP1
N3eRu1eH
C34eRu1eP1
C34eRu1eN3
C34eRu1eN1
C34eRu1eN5
N1eRu1eN5
N1eRu1eH
N5eRu1eH
C34eRu1eH
P1eRu1eH
101.63(5)
174.96(5)
81.91(7)
90.04(6)
95.18(5)
170.61(8)
89.44(8)
96.36(8)
93.75(9)
171.21(9)
81.89(7)
89.47(8)
84.94(8)
87.87(8)
86.75(8)
98.48
174.67
82.98
89.29
94.02
171.43
91.48
96.27
93.46
173.69
82.96
89.27
85.91
87.76
88.94
P1eRu1eCl1
P2eRu1eP1
P2eRu1eCl1
N1eRu1eP1
N1eRu1eP2
N1eRu1eCl1
N1eRu1eH
C37eRu1eP1
C37eRu1eP2
C37eRu1eCl1
C37eRu1eN1
C37eRu1eH
P1eRu1eH
90.35(5)
177.35(5)
92.25(5)
91.43(12)
88.26(12)
86.56(12)
85.64(10)
90.23(17)
89.72(17)
101.5(2)
90.25
178.80
90.26
89.48
89.48
85.74
87.06
89.66
89.67
99.87
174.39
87.33
89.68
89.68
172.80
Fig. 3. HOMO-LUMO energy gap of the complexes (2) and (3).
Table 6
Calculated individual energies (eV) along with the compositions (%) and character of
virtual orbitals of the complexes.
171.8(2)
86.10(10)
89.28(10)
88.09(10)
172.42(10)
Orbital
Energy (eV)
Complex (2)
Character
P2eRu1eH
Cl1eRu1eH
Composition (%)
Ru
CO
Tp*
H
PPh3
H-6
H-4
H-3
H-1
ꢀ6.41
ꢀ6.09
ꢀ6.01
ꢀ5.55
ꢀ5.21
ꢀ0.73
ꢀ0.53
ꢀ0.49
0.19
0
0
9
2
9
1
0
1
0
12
3
98
28
81
43
30
1
3
2
58
91
0
0
0
1
0
0
1
0
1
0
2
3
2
2
Tp*
60
14
46
65
2
7
5
13
4
Ru þ Tp*
contributions also influences the magnetic environments which
resulted in non-zero NICS(0)iso for nonaromatic rings. Eventually
NICS(1)iso which referred to total isotropic shielding value at a point
1 Å above the ring centre was developed. NICS(1)iso was therefore
Tp*
Ru þ Tp*
Ru þ Tp*
PPh3
PPh3
PPh3
HOMO (H)
LUMO (L)
Lþ1
4
96
88
93
16
2
free from any
s contributions but it was still based on the total
Lþ2
isotropic shielding values, rather than the contributions from the zz
Lþ6
Tp*
Tp*
Lþ12
1.24
Orbital
Energy (eV) Complex(3)
Composition (%)
Ru CO pz*H
Character
Table 4
Calculated NBO charges (in e) of the central metal atom and atoms coordinated to
the central metal atom in the complexes.
H
PPh3 Cl
Complex (2)
Complex (3)
H-4
H-3
H-2
H-1
ꢀ6.42
ꢀ6.21
ꢀ5.76
ꢀ5.68
18
22
40
0
4
4
3
6
30
2
0
1
3
1
0
0
0
0
0
1
0
2
45
67
25
1
11
78
93
57
33 PPh3 þ Cl
q (Ru1)
q (N1)
q (N3)
q (N5)
q (H)
ꢀ0.803
ꢀ0.208
ꢀ0.262
ꢀ0.240
þ0.081
þ0.754
þ1.292
q (Ru1)
q (Cl1)
q (H)
q (P1)
q (P2)
q (C37)
q (N1)
ꢀ1.158
ꢀ0.544
þ0.104
þ1.295
þ1.295
þ0.239
ꢀ0.239
0
0
PPh3 þ Ru
Ru þ pz*H þ PPh3
59 11
26 Ru þ Cl
30 Ru þ Cl
HOMO (H) ꢀ5.35
58
18
3
0
1
1
LUMO (L)
Lþ3
ꢀ0.84
ꢀ0.35
ꢀ0.02
1
0
2
PPh3
PPh3
PPh3 þ Ru
q (C34)
q (P1)
Lþ8
26 12

D. Kharbani et al. / Journal of Molecular Structure 1133 (2017) 264e270
269
Table 7
Calculated major orbital excitation contributions (%), dominant excitation character, oscillator strength (f), energy difference (in eV), theoretical wavelengths (
l
in nm) obtained
from electronic transitions analysis with TDDFT(B3LYP) method.
Major orbital excitation contributions (%)
Dominant excitation character
Oscillator strength (f)
Energy gap (eV)
Calc.
l(nm)
Expt l(nm)
Complex (2)
HOMO / L þ 1 (35%)
HOMO / LUMO (54%)
H-1 / LUMO (35%)
H-1 / L þ 2 (20%)
H-4 / LUMO (32%)
H-6/LUMO (36%)
H-6 / L þ 1 (39%)
H-3 / L þ 6 (31%)
H-1 / L þ 12 (33%)
Complex (3)
Ru/Tp* / PPh3 (MLCT/LLCT)
Ru/Tp* / PPh3 (MLCT/LLCT)
Ru/Tp* / PPh3(MLCT/LLCT)
Ru/Tp* / PPh3 (MLCT/LLCT)
Ru/Tp* / PPh3 (MLCT/LLCT)
Tp* / PPh3 (LLCT)
Tp* / PPh3 (LLCT)
Tp* / Tp* (ILCT)
Ru/Tp* / Tp*MLCT/ILCT)
0.0144
0.0295
0.0266
0.0238
0.0333
0.0248
0.0561
0.0257
0.1326
4.68
4.48
4.82
5.06
5.36
5.68
5.88
6.20
6.79
350
310
303
263
249
243
230
216
206
346
295
218
HOMO / LUMO(78%)
H-1 / LUMO (79%)
H-3 / LUMO (58%)
H-4 / L þ 3 (35%)
H-3 / L þ 8 (34%)
Ru/Cl / PPh3 (MLCT/LLCT)
Ru/Cl / PPh3 (MLCT/LLCT)
PPh3/Ru / PPh3 (ILCT/MLCT)
PPh3/Cl / PPh3 (ILCT/LLCT)
PPh3/Ru / PPh3 (ILCT/MLCT)
0.0319
0.1174
0.2548
0.0577
0.0536
4.51
4.84
5.37
6.07
6.19
358
314
267
222
217
340
280
212
component of the shielding tensor as ring current due to
p
electron
antiaromatic in nature. The antiromaticity of (4) is attributed to the
presence of electronegative nitrogen atoms in the ring which re-
sults in non-homogeneous electron distribution in the ring.
The HOMO-LUMO gap is the lowest energy electronic excitation
possible in a molecule. The energy of the HOMO-LUMO gap reveal
about what wavelengths the compound can absorb. The kinetic
stability, chemical reactivity and the colour of the transition metal
complexes in solution is governed by the HOMO-LUMO energy gap.
The Frontier Molecular Orbital diagrams of both the complexes (2)
delocalization which is induced by the external magnetic field
applied perpendicular (z direction) to the ring. Therefore NICS(1)zz
is more popularly used for aromaticity evaluations. Negative NICS
values denote aromaticity, positive NICS values denote anti-
aromaticity and small NICS value indicate non-aromaticity. For
NICS(0)zz, the ring critical point was selected for calculation. For
product(4) the NICS(0)zz and NICS(1)zz are found to be 24.21 ppm
and 5.52 ppm respectively, which indicate that complex (4) is
Fig. 4. The UV spectra of complexes (2) and (3) along with the TDDFT calculated UV spectra.

270
D. Kharbani et al. / Journal of Molecular Structure 1133 (2017) 264e270
and (3) and their energy-gaps are shown in Fig. 3. The HOMO-
LUMO energy gaps for the complexes (2) and (3) are 4.48 and
4.51 eV, respectively. The Mulliken population analysis used for
calculating the percentage contributions of various groups to each
molecular orbital (Table 6) suggests that for complex (2) the major
percentage of HOMO is located over the metal atom Ru and Tp*
whereas for complex (3), the major percentage of HOMO is located
over the metal atom Ru and Cl ligand. The LUMO of both complexes
(2) and (3) are located over the PPh3 ligands. Some of the selected
electronic transitions for complexes (2) and (3) based on oscillator
strengths were tabulated in Table 7.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.11.097.
References
[1] (a) S. Trofimenko, J. Am. Chem. Soc. 88 (1966) 1842e1844.
[2] (a) S. Trofimenko, Scorpionates, the Coordination Chemistry of Poly-
pyrazolylborate Ligands, Imperial College Press, London, 1999;
(b) S. Trofimenko, Chem. Rev. 93 (1993) 943e980;
For complex (2), the calculated absorption bands in the range of
350e249 nm corresponds to MLCT/LLCT charge transfers and the
dominant excitations leading to these charge transfers are
HOMO/Lþ1 (35%), HOMO/LUMO (54%), H-1/LUMO (35%), H-
1/Lþ2 (20%) and H-4/LUMO (32%). Other absorptions bands at
around 243 nm and 230 nm corresponds to LLCT charge transfer
whereas bands at 216 nm and 206 nm corresponds to ILCT and
MLCT/ILCTcharge transfers and the dominant excitations leading to
these charge transfers are H-6/LUMO (36%), H-6/Lþ1 (39%), H-
3/Lþ6 (31%) and H-1/Lþ12 (33%).
(c) S. Trofimenko, Polyhedron 23 (2004) 197e203.
[3] (a) N. Kitajima, W.B. Tolman, Prog. Inorg. Chem. 43 (1995) 419e531;
(b) N.A. Foley, J.P. Lee, Z. Ke, T.B. Gunnoe, T.R. Cundari, Acc. Chem. Res. 42
(2009) 585e597.
[4] G. Parkin, Adv. Inorg. Chem. 42 (1995) 291e393.
[5] H.D. Bari, M. Zimmer, Inorg. Chem. 43 (2004) 3344e3348.
[6] K. Niedenzu, S. Trofimenko, Top. Curr. Chem. 131 (1986) 1e37.
[7] A.L. Rheingold, R.L. Ostrander, B.S. Haggerty, S. Trofimenko, Inorg. Chem. 33
(1994) 3666e3676.
[8] J.M. White, V.W.L. Ng, D.C. Clarke, P.D. Smith, M.K. Taylor, Charles G. Young,
Inorg. Chim. Acta. 362 (2009) 4570e4577.
[9] (a) J.S. Figueroa, J.G. Melnick, G. Parkin, Inorg. Chem. 45 (2006) 7056;
(b) K. Pang, J.M. Tanski, G. Parkin, Chem. Commun. (2008) 1008e1010.
[10] S. Bieller, A. Haghiri, M. Bolte, J.W. Bats, M. Wagner, H. Lerner, Inorg. Chim.
Acta 359 (2006) 1559e1572.
[11] N.Y. Sun, S.J. Simpson, J. Organomet. Chem. 434 (1992) 341e349.
[12] N. Ahmad, J.J. Levison, S.D. Robinson, M.F. Uttley, Inorg. Synth. 15 (1974) 45.
[13] S. Trofimenko, J. Am. Chem. Soc. 89 (1967) 6288e6294.
[14] G.M. Sheldrick, Acta. Crystallogr. Sect. A Crystallogr. 64 (2008) 112.
[15] G.M. Sheldrick, SHELXL-97: Program for Crystal Structure Refinements, Uni-
versity of Gottingen, Gottingen, Germany, 1996.
For complex (3), the calculated absorption bands at 358 and 314
correspond to MLCT/LLCT charge transfers whereas bands at
267 nm, 222 nm and 217 nm corresponds to ILCT/MLCT, ILCT/LLCT
and ILCT/MLCT charge transfers and the dominant excitations
leading to these charge transfers are HOMO/LUMO (78%), H-
1/LUMO (79%), H-3/LUMO (58%), H-4/Lþ3 (35%) and H-
3/Lþ8 (34%) respectively. The UV spectra of complexes (2) and (3)
(Fig. 4) from TDDFT calculations show that main electronic transi-
tions obtained are in good agreement with the experimental
observations.
[16] M.J. Frisch, et al., GAUSSIAN 09, Revision C.01, Gaussian Inc, Walling-ford CT,
2009.
[17] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785e789.
[18] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899e926.
[19] M.E. Casida, J.M. Seminario (Eds.), Recent Developments and Applications in
Modern Density Functional Theory, Theoretical and Computational Chemistry,
vol. 4, Elsevier, 1996. Amsterdam.
4. Conclusion
[20] N.N. Matsuzawa, A. Ishitani, D.A. Dixon, T. Uda, J. Phys. Chem. A 105 (2001)
4953e4962.
The synthesis of new complex [RuTp*(H)(CO)(PPh3)] (2) was
described and the side products (3) and (4) were obtained by
pyrazole cleavage of KTp* ligand. There are several reasons that
may lead to the cleavage of BeN bond in poly(pyrazolyl)borate li-
gands, such as polarity of solvents, the presence of Lewis acids or
Bronsted acids, and the steric bulk of the peripheral ligands [33,34],
but the formation of stable pyrazaboles must be the main driving
force that leads to the degradation of the ligands. The substitution
by a stronger electron donating ligand to a metal complex increases
the inherent bonding of the ligands to the metal centre.
The experimental data of the complexes were in good agree-
ments with theoretical DFT calculations. The theoretical calcula-
tions show that there are pnicogen interactions in the complexes
(2) and (3).
[21] V. Barone, M. Cossi, J. Tomasi, J. Chem. Phys. 107 (1997) 3210e3221.
[22] N.M.O. Boyle, A.L. Tenderholt, K.M. Langner, J. Comput. Chem. 29 (2008)
839e845.
[23] P. Pulay, J.F. Hinton, K. Wolinski, Mathematical and physical sciences, in:
J.A. Tossel (Ed.), Nuclear Magnetic Shieldings and Molecular Structure,
NATOASI Series C, vol. 386, 1993 (Amsterdam: Kluwer).
[24] T. Lu, F. Chen, Multiwfn: a multifunctional wave function analyzer, J. Comp.
Chem. 33 (2012) 580e592.
[25] A. Romero, A. Vegas, A. Santos, A.M. Cuadro, J. Chem. Soc. Dalton Trans. (1987)
183e186.
[26] L.L. Blosch, A.S. Gamble, K. Abboud, J.M. Boncella, Organometallics 11 (1992)
2342e2344.
[27] (a) L.M. Caldwell, Adv. Organomet. Chem. 56 (2008) 1;
(b) M. Lail, K.A. Pittard, T.B. Gunnoe, Adv. Organomet. Chem. 56 (2008) 95;
(c) E. Becker, S. Pavlik, K. Kirchner, Adv. Organomet. Chem. 56 (2008) 155;
(d) I.R. Crossley, Adv. Organomet. Chem. 56 (2008) 199;
(e) F.A. Jalon, A. Otero, A. Rodriguez, J. Chem. Soc. Dalton Trans. (1995)
1629e1633.
[28] S.K. Seetharaman, M.C. Chung, U. Englich, K.R. Senge, M.B. Sponsler, Inorg.
Chem. 46 (2007) 561e567.
[29] R.J. Abernethy, A.F. Hill, M.K. Smith, A.C. Willis, Organometallics 28 (2009)
6152e6159.
Acknowledgements
[30] G. Bellachioma, G. Cardaci, V. Gramlich, A. Macchioni, F. Pieroniand,
L.M. Venanzi, J. Chem. Soc. Dalton Trans. (1998) 947e951.
[31] S. Trofimenko, J. Am. Chem. Soc. 89 (1967) 4948.
[32] H.F.B. Shaidaei, C.S. Wannere, C. Corminboeuf, R. Puchta, P.v.R. Schleyer, J. Org.
Lett. 8 (2006) 863e866.
[33] F. Yraola, F. Albericio, M. Corbella, M. Royo, Inorg. Chim. Acta 361 (2008)
2455e2461.
[34] C.J. Jones, J.A. McClevetty, A.S. Rothin, J. Chem. Soc. Dalton Trans. (1986)
109e111.
Donkupar Kharbani and Debojit Kumar Deb are thankful to the
UGC-RGNF-ST and UGC-Non-Net Fellowship, for financial support.
We acknowledge SAIF and DST-PURSE SCXRD of NEHU for collect-
ing NMR and X-ray analysis data. B. S. acknowledge DST (Grant No:
EMR/2015/002322) and FIST program and UGC., Govt. of India, New
Delhi for the CAS grant to the Department and Computer Centre,
NEHU for providing computational facilities.