Ruthenium (II) β-diketimine as hydroamination catalyst, crystal structure and DFT computations

Article abstract of DOI:10.1007/s11243-021-00456-6

A new half-sandwich ruthenium (II) complex containing β-diketiminate ligand has been synthesized and used for hydroamination of acrylonitrile with aromatic and aliphatic amines. The catalytic activity of prepared complex was compared with a series of ruthenium complexes of β-diketiminate ligands, and the effect of electronic and steric properties of these ligands on catalytic activity of their complexes was investigated. Replacement of H atom in α position of β-diketiminate with (CF₃) as an electron-withdrawing group leads to decreasing the reaction yield, and on the other hand, electron-donating group (CH₃) has the opposite effect. In addition, crystal structure of [Ru(p-cymen)Cl(L^H,Cl)] was determined by single X-ray crystallography. Hirshfeld surface analysis has been performed to determine the dominate interactions in molecular crystal. Furthermore, density functional, QTAIM and energy calculations have been carried out, to get the detailed insight into electronic and bonding characteristics of titled compound.

Full text of DOI:10.1007/s11243-021-00456-6

Transition Metal Chemistry
https://doi.org/10.1007/s11243-021-00456-6
Ruthenium (II) β‑diketimine as hydroamination catalyst, crystal
structure and DFT computations
Sara Dindar · Ali Nemati Kharat1 · Barzin Safarkoopayeh · Alireza Abbasi
1
1
1
Received: 21 November 2020 / Accepted: 19 March 2021
©
The Author(s), under exclusive licence to Springer Nature Switzerland AG 2021
Abstract
A new half-sandwich ruthenium (II) complex containing β-diketiminate ligand has been synthesized and used for hydroami-
nation of acrylonitrile with aromatic and aliphatic amines. The catalytic activity of prepared complex was compared with a
series of ruthenium complexes of β-diketiminate ligands, and the eꢀect of electronic and steric properties of these ligands on
catalytic activity of their complexes was investigated. Replacement of H atom in α position of β-diketiminate with (CF ) as an
3
electron-withdrawing group leads to decreasing the reaction yield, and on the other hand, electron-donating group (CH ) has
3
H,Cl
the opposite eꢀect. In addition, crystal structure of [Ru(p-cymen)Cl(L )] was determined by single X-ray crystallography.
Hirshfeld surface analysis has been performed to determine the dominate interactions in molecular crystal. Furthermore,
density functional, QTAIM and energy calculations have been carried out, to get the detailed insight into electronic and
bonding characteristics of titled compound.
Introduction
addition of aniline to acetylene in the presence of mercury
II) chloride as the ꢁrst homogenous system for hydroamina-
(
Amines are commonly found as fundamental compounds
in the bulk and ꢁne chemical industry since they are widely
used in agrochemicals, dyes, natural products and pharma-
ceutically active compounds.[1]. Numerous methods have
been developed for synthesis of amines such as N-alkylation
of amines with alkyl and aryl halides, amination of carbonyl
compounds and amination of alcohols [2–5]. Addition of an
N–H group from a nucleophilic amine or ammonia directly
to a C–C multiple bond known as hydroamination reaction
has received extensive attention because of 100% atom-
eꢂcient process, broad availability and low-cost starting
materials [6]. Due to the thermodynamic characteristics of
this transformation (weakly exergonic and highly negative
entropy), using an applicable catalytic system is essential
tion of alkynes [16]. Subsequently, many catalytic systems
by transition metals, such as palladium, rhodium, nickel and
ruthenium have been shown to provide acceptable catalytic
activity [17–20]. Ruthenium complexes show strong activity
in coordination and activation of unsaturated C–C bonds, so
these complexes are used extensively as catalysts in some
transformations, such as oleꢁn metathesis, C–H activation
and hydrogenation [21–24]. Among these ruthenium com-
plexes, half-sandwich ruthenium (II) complexes coordinated
6
to η -arenes are well developed and have a wide range of
applications as catalyst precursors. Shibata et al. reported
the ꢁrst enantioselective hydroamination of styrene with sec-
ondary alkylamines in the presence of [Ru(benzene)Cl ] ,
2
2
in which the asymmetric anti-Markovnikov products were
[
7]. Various types of transition metal complexes, the lantha-
generated in moderate yields [25, 26].
nides, the alkaline earth metals and strong bases have been
utilized as the catalysts for hydroamination reactions [8–15].
Applying late transition metals for selective preparation
of amines by hydroamination reaction has been reported in
several research papers [6]. Kozlov in 1936 reported the
Among half-sandwich arene–ruthenium complexes, the
products containing dinitrogen ligands have been exten-
sively investigated and shown excellent activities in a wide
range of catalytic reactions, such as reduction of ketones
and imines, leading to secondary alcohols and amines [27].
The β-diketiminate ligands known as “nacnac” are chelating
bidentate ligands, with a framework according to Scheme 1,
which have gained considerable attention in stabilizing tran-
sition-metal complexes in regard of diverse coordinating
modes and tunable stereo-electronic features. Coordination
*
Ali Nemati Kharat
anemati@ut.ac.ir
1
School of Chemistry, College of Science, University
of Tehran, Tehran, Iran
Vol.:(0
1
123456789)
3

Transition Metal Chemistry
demonstrate that the structure of the complex is similar to
previously reported ruthenium (II) β-diketiminate complexes
[
35], as Ru(II) has three-coordinate piano-stool geometry.
Furthermore, to get insight into the electronic structure of
the complex, DFT and QTAIM (Quantum Theory of Atoms
in Molecules) calculations were carried out and the elec-
tronic structure of the title compound was investigated.
Computational details
Scheme 1 Typical β-diketiminate framework (nacnac ligands were
X,Y
X,Z
To get insight into the electronic structure of the com-
plex, density functional calculations were carried out with
ORCA.4.2.1, using the BP86 functional and the def2-TZVP
basis set [36]. The electronic structure of the title compound
was investigated by QTAIM (Quantum Theory of Atoms In
Molecules) using Multiwfn program [37].
speciꢁed as Lo and L
in text)
m
chemistry of nacnac ligands by the ꢁrst row transition metals
has been investigated comprehensively in comparison with
other d-block elements such as Rh, Ir, Pd, Pt and Ru, which
have been reported in some publications [28–32].
The half-sandwich arene–ruthenium complexes having
various β-diketiminate ligands developed by Phillips et al.
eꢂciently catalyze the addition of CCl or toluenesulfonyl
Experimental
4
chloride to styrene. Moreover, the eꢀects of electron-with-
drawing and electron-donating groups in the structure of
General
“
nacnac” (X symbols in Scheme 1) on catalyst activation
were investigated. Interestingly, the complexes with methyl
All reactions were performed under nitrogen atmosphere
using a nitrogen-ꢁlled glove box or standard Schlenk tech-
niques. All the chemicals and reagents used in this study
were purchased from Sigma-Aldrich and Strem Chemi-
cals and utilized without puriꢁcation. The solvents were
of analytical grade and purified prior to use based on
standard methods. [Ru(p-cymene)Cl ] , RuCl PPh , (Cp)
substituent on the β-diketiminate ligand were almost inactive
toward the addition of CCl to styrene, whereas those having
4
electron-withdrawing CF substituent showed appreciably
3
high activity [33]. Schreiber and co-workers prepared ruthe-
nium (II) complexes based on ꢃuorinated β-diketiminate
ligands and explored their catalytic applicability toward
Diels–Alder reactions. These were found to be robust Lewis
acid catalysts for the Diels–Alder reaction between α,β-
unsaturated aldehydes and dienes [34].
2
2
2
3
RuCl(PPh ) , RuH (CO)(PPh ) and RuCl(OAC)(PPh )
3
2
2
3 3
3 3
were prepared according to previously published methods
[38–41]. Ruthenium β-diketiminate complexes were used
in this study prepared by reported methods in Phillips group
[35, 42]. 1H NMR spectra data were recorded at room tem-
Herein, a new half-sandwich ruthenium (II) complex con-
taining β-diketiminate ligand has been synthesized as it was
shown in Scheme 2, and its catalytic activity in hydroami-
nation reactions of aromatic and aliphatic amines with
acrylonitrile was investigated. Catalytic activity of other
ruthenium complexes consisting of diꢀerent derivatives of
β-diketiminate ligands was compared to our prepared new
perature in CDCl on a Bruker AV III HD 400 MHz instru-
3
ment. Single-crystal X-ray diꢀraction data were collected
with a Bruker X8 APEX II CCD equipped with MoKα radia-
tion at room temperature. The course of the reactions was
monitored with a gas chromatograph (Agilent Technologies
7890A Instrument), equipped with a capillary column (HP-
5, 5% phenyl methyl siloxane, capillary 60.0 mm 9 250 mm
9 1.00 mm) and a ꢃame ionization detector (FID).
complex in this reaction. A suitable crystal of prepared
H,Cl
[
Ru(p-cymen)Cl(L )] complex (complex (1)) was stud-
ied by single-crystal X-ray diꢀraction technique. Results
nBuLi
Scheme 2 Synthesis route for preparation of the β-diketiminato-(η6-arene)–Ru(II) Complex (1)
1
3

Transition Metal Chemistry
Catalyst preparation
General procedure for the hydroamination
Synthesis of β‑diketiminate ligand LH,Cl
The autoclave was charged with catalyst [Ru(p-cymen)
Cl(LH,Cl)] (0.05 mmol), amine (5 mmol), acrylonitrile
(6 mmol) and 1.5 ml toluene as solvent. 0.04 g K CO used
4
.5gr (28 mmol), 2,6-dichloroaniline was added to a solution
2
3
of 1 ml (13.75 mmol) malondialdehyde in 70 ml toluene.
The mixture was heated, and then (0.1 g) p-toluenesulfonic
acid was added. Afterwards, the reaction was reꢃuxed for
as base. The autoclave was ꢃushed with argon for 5 min,
and then it was stirred at 100 °C (Scheme 3). After 20 h, the
autoclave was cooled to room temperature and the products
were analyzed by gas chromatography (GC). Conversions
were calculated for acrylonitrile using n-decane as standard.
2
4 h to achieve a clear light yellow solution. Then, solvent
was removed under vacuum to get a solid residue. It was
dissolved in 40 ml diethyl ether and then quenched with
saturated sodium bicarbonate (30 ml), and it was stirred for
1
h at room temperature. Organic layer was separated and
Result and discussion
dried over Na SO , diethyl ether was removed by rotary
2
4
evaporator, and remaining solid was dried in oven. 1H
Applying acrylate as an activated oleꢁn in mild condition
catalytic hydroamination reaction in the presence of transi-
tion metal complexes was reported by diꢀerent groups of
researchers and provided excellent activity. In this work,
hydroamination reaction of acrylonitrile with a range of
aliphatic amines and aniline in the presence of catalytic
NMR (500 MHz, CDCl3) δ(ppm): 11.84 (d, 1H, NH), 7.36
(
t, H,), 6.89 (d, 2H, α–CH), 6.26 (t, 2H, Ar–p–H) 4.88 (t,
1
H, β–CH).
Synthesis of Ruthenium β‑diketiminate complex
Ru(p‑cymen)Cl(LH,Cl)]
[
amount of half-sandwich ruthenium β-diketiminate complex
H,Cl
[
Ru(p-cymen)Cl(L )] was carried out with selectivity up
Cl,H
A 0.2 g (0.54 mmol) portion of L
was added to a dried
to 99%. As it can be observed from Table 1, the presence of
ruthenium complexes as a catalyst has a signiꢁcant impact
on the reaction yield, especially when complexes with a free
coordination site on metal center have been used.
2
5-mL Schlenk ꢃask under inert conditions. A 20 ml dried
and nitrogen-saturated THF was added. The solution was
cooled in an ice bath for 10 min, and then 0.5 ml of a 1.6 M
n-BuLi was added dropwise and the color of the solution
changed immediately to yellow. The reaction was stirred at
ice bath for 2 h and at room temperature overnight after-
wards. Volatile components were removed in vacuum, leav-
ing a bright yellow solid.
Among the selected catalysts, four-coordinated complex
(1) (entry 3) and [RuCl (p-cymen)] complex (entry 4)
2
2
Table 1 Hydroamination of acrylonitrile with aniline in the presence
of diꢀerent ruthenium catalysts
Cl,H
In glove box, 0.2 g (0.45 mmol) of L .Li(THF) was
No
Catalyst
Conversion
Selectivityb
dissolved in dried and degassed dichloromethane, and
then this suspension was added dropwise to a solution of
a
(
%)
1
2
3
4
5
6
7
8
No Catalyst
RuCl ·xH O
10
30
98
87
55
70
35
29
–
7
0 mg (0.5 equiv.) of [RuCl (p-cymen)] in 10 ml CH Cl .
2 2 2 2
28
95
85
50
60
28
25
The reaction mixture was stirred overnight, then precipi-
tated LiCl was removed by ꢁltration, and the solvent was
removed in vacuum. After drying under vacuum, a dark red
solid was obtained (Scheme 2). Crystals suitable for X-ray
diꢀraction analysis were grown in the mixture of dichlo-
romethane and pentane in −30 °C. 1H NMR (500 MHz,
3
2
[Ru(p-cymen)Cl(LH,Cl)]
[Ru(p-cymene)Cl2]2
RuCl (PPh )
2
3 3
(Cp)RuCl(PPh3)2
RuCl(OAC)(PPh3)3
RuH (CO)(PPh )
3 3
CDCl ) δ(ppm): 7.37 (t, 4H, Ar–m–H), 7.63 (d, 2H, α–CH),
2
3
7
.15 (d, 2H, Ar–p–H), 5.71 (t, 1H, β–CH), 2.76 (m, 1H,
Acrylonitrile (6 mmol), aniline (5 mmol), catalyst (3 mol%), K CO
2
3
p-cymene iPr–(CH)) 1.70 (s, 1H, p-cymene CH ), 1.17 (d,
(0.05 mmol), toluene (1 ml), T=100 °C, 20 h.
3
a
6
H, p-cymene iPr–(CH ) ).
Data were determined by GC, and conversions were calculated for
3
2
acrylonitrile using n-decane as standard,
b
Selectivity is measured for Markovnikov product (Scheme 3)
Scheme 3 Hydroamination of
acrylonitrile with aniline
1
3

Transition Metal Chemistry
showed signiꢁcant activity by conversion of 98% and 87%,
respectively. Moreover, six-coordinated [RuH (CO)(PPh ) ]
It seems the larger CH substituent on Y-position of ligand
3
as it is shown in Scheme 1, making a barrier for active site of
2
3 3
(
entry 8) and [RuCl(OAC)(PPh ) ] (entry 7) complexes
complex, and thus a lower rate of reaction was observed for
3
3
CH3,CH3
showed less activity in the reaction conditions. It is pro-
posed that the low reactivity of such saturated metal com-
plexes is caused by an energy-consuming preliminary ligand
dissociation.
[Ru(C H )Cl(L
O
)] (entry 3) in comparison to H sub-
6
6
CH3,H
stituent in complex [RuCl(L
)] (entry 2). No signiꢁcant
distinction in catalytic activity was observed when substitu-
ent on the ꢃanking aryl groups (Z) changes from 3,5-dime-
thyl to triꢃuoromethyl (entry 5 and 6), so these complexes
showed similar activity.
Reaching acceptable activity from [Ru(p-cymen)
H,Cl
Cl(L )] complex (1), the eꢀect of ligand architecture was
investigated on catalytic activity by testing diꢀerent ruthe-
nium nacnac complexes which have electron-withdrawing
group (CF ) or electron-donating group (CH ) in their
Solvent as one of the important factors can aꢀect the con-
version and chemo-selectivity of hydroamination reaction
(Table 3). Therefore, applying diꢀerent solvents from polar,
nonpolar, protic and aprotic was studied when complex (1)
was used as a catalyst. Employing toluene as a nonpolar
aprotic solvent, the higher yield was detected in comparison
to polar aprotic solvents. The lower conversion in such sol-
vent like DMF and acetonitrile is due to coordination of the
solvent to Ru center and blocks the active catalytic sites of
the complex. Using n-butanol as a solvent is not applicable
due to the forming of some by-products from the N-alkyla-
tion reaction of amine in the presence of ruthenium catalyst.
In this case, aniline takes part in another catalyst cycle and
3
3
structure. The monoanionic β-diketiminate ligand provided
a robust framework with relatively strong donating proper-
ties by bidentate coordination around the metal center. The
electronic and steric eꢀect of ligand on metal can be easily
tuned by a substituted group on its backbone. Normally, the
electronic properties of ligand are aꢀected by group on α
position (X) and the steric properties of ligand can be con-
trolled by substitutes on ortho position of ꢃanking aryl rings
(
Y) (Scheme 1). To investigate such electronic and steric
eꢀects on catalytic activity of β-diketiminate derivatives
complexes, a series of these complexes were synthesized
according to the instruction that was reported previously [34,
3
5, 42], and their catalytic activity was compared to a new
H,Cl
Table 3 Eꢀect of diꢀerent solvents on hydroamination of acryloni-
[
Ru(p-cymen)Cl(L )] complex (1) that was prepared in
trile with aniline
this article. As it can be observed from Table 2, these series
of complexes show diꢀerent catalytic activities in reaction
No
Solvent
Conversion (%)a Selectivityb
H,Cl
condition. In the case of applying [Ru(p-cymen)Cl(L )]
1
2
3
4
5
6
7
DMF
50
45
20
98
87
50
50
88
90
–
96
95
83
87
complex (1), it is proved to be highly eꢂcient as a catalyst
Acetonitrile
N-butanol
Toluene
THF
Dioxane
No Solvent
for the hydroamination in comparison to other mentioned
CF3,CH3
β-diketiminate complexes. The [Ru(C H )Cl(L
)],
6
6
which carries the electron-withdrawing CF X-substituent
3
group, showed signiꢁcantly less activity. In contrast, the
presence of electron-donating CH group in this position
3
leads to higher catalytic activity of complex [Ru(C H )
6
6
CH3,CH3
Acrylonitrile (6 mmol), aniline (5 mmol), complex (1) (3 mol%),
K CO (0.05 mmol), solvent (1 ml), T=100 °C, 20 h. a Data were
Cl(L
)] (entry 3). However, the existence of hydrogen
O
2
3
in the same place has a moderate electron-donating eꢀect
and shows high activity (entry 2). The steric features of
ligand also have inꢃuence on catalytic activity of complex.
determined by GC, and conversions were calculated for acrylonitrile
using n-decane as standard b Selectivity is measured for Marko-
vnikov product (Scheme 3)
Table 2 Hydroamination of
acrylonitrile with aniline in
the presence of ruthenium
β-diketiminate complexes
Selectivityb
No
Complex
X
Y
Z
Conversion
a
(
%)
1
2
3
4
5
6
[Ru(p-cymen)Cl(LH,Cl)]
H
Cl
H
CH3
CH3
H
H
H
H
H
CH3
CF3
98
90
83
45
80
79
95
93
92
90
90
88
CH3,H
[RuCl(L
)]
CH3
CH3
CF3
CH3
CH3
CH3,CH3
CF3,CH3
[Ru(C H )Cl(L
)]
)]
)]
6
6
O
O
m
[Ru(C H )Cl(L
6
6
CH3,CH3
[Ru(C H )Cl(L
6
6
[Ru(C H )Cl(L CH3,CF3)]
H
6
6
m
Acrylonitrile (6 mmol), aniline (5 mmol), catalyst (3 mol%), K CO (0.05 mmol), toluene (1 ml),
2
3
T=100 °C, 20 h. a Data were determined by GC, and conversions were calculated for acrylonitrile using
n-decane as standard b Selectivity is measured for Markovnikov product (scheme 3)
1
3

Transition Metal Chemistry
as a consequence conversion of styrene in the hydroamina-
tion reaction decreases [43] (Table 4).
aliphatic amines show higher activity than aniline in
hydroamination. The best results were obtained for primary
amine (Table 5, entries 1–5). In comparison to primary alky-
lamines, secondary derivatives showed less activity, which is
due to their higher nucleophilic property, as they coordinate
more strongly to the metal, and their transfer to the carbon
center is more diꢂcult. In addition, the electrostatic repul-
sion between π-electrons of alkyne and more electron-rich
secondary amines leads to greater steric eꢀect.
There are numerous possibilities for the reaction pathway;
one proposed mechanism is N–H bond activation. In the ꢁrst
step of this pathway, the N–H bond of amine binds to a coor-
dinatively unsaturated ruthenium center giving the (amido)
ruthenium hydride (Scheme 4). Then, alkene coordinates
to the ruthenium center to form complex (2), followed by
intramolecular nucleophilic attack of the nitrogen lone pair
to the coordinated carbon–carbon double bond. Reductive
elimination of alkylamido (3) would give the product (4) and
reproduce the coordinatively unsaturated ruthenium center
Crystal structure
[
44].
Encouraged by the results obtained with aniline, our
The complex is air stable and soluble in most organic sol-
vents. Suitable crystals of complex are obtained from mix-
ture of dichloromethane and pentane in −30 °C. Ortep view
of complex is illustrated in Fig. 1, and the structure of com-
plex is similar to previously reported ruthenium (II) com-
plexes of β-diketiminate [35]. The complex crystallized in
the monoclinic space group P2(1)/c with four molecules in
the unit cell. Single-crystal structure of this complex con-
ꢁrmed three-coordinate piano-stool geometry for Ru(II),
with the ruthenium atom π-bonded to the p-cymene ring
with an average Ru–C distance of 1.697 Å. The ruthenium
atom is also directly coordinated to both nitrogen atoms of
β-diketiminate ligand with a normal distance of 2.119 and
2.121 Å.
attention turned to aliphatic amines, and as it was expected,
Table 4 Catalytic hydroamination of diꢀerent amines with acryloni-
trile
No
Amine
Conversion
Selectivitya
b
(
%)
1
2
3
4
5
6
7
Cyclohexylamine
Hexylamine
Octylamine
Butylamine
Phenylethylamine
Morpholine
96
99
99
99
98
85
82
99
99
99
99
99
96
97
Diethylamine
Ru-Cl distances average is about 2.441 A° and is in agree-
ment with the values reported for similar structure being the
Acrylonitrile (6 mmol), amine (5 mmol), [Ru(cymene)Cl ]
6
2
2
η -arene–Ru fragment in the CSD and similar structure. The
(
3 mol%), dope (0.02 mmol), K CO (0.05 mmol), toluene (1 ml),
2 3
complex folds along the N–N vector and the angle between
T=100 °C, 20 h.
a
the C H plane and the N1–C2–C11–C8–N2 plane is 83.8°.
6 6
Data were determined by GC, and conversions were calculated for
acrylonitrile using n-decane as standard
It seems that steric conꢃict between ortho-chloro N-aryl
substituent and metal pushes the metal center out of the
b
Selectivity is measured for Markovnikov product (scheme 3)
Scheme 4 Proposed mechanism
for hydroamination of acry-
lonitrile with aniline leading to
Markovnikov product
1
3

Transition Metal Chemistry
Table 5 Crystallographic and structure reꢁnements data of complex
Ru(p-cymen)Cl(LH,Cl)]
β-diketiminate ligand plane. Some weak hydrogen bonds
exist in the structure, stabilizing the packing of the complex;
hydrogen bonds exist between the C–H bond in the ꢃank-
ing aryl groups and chloride ion of bonded to ruthenium
[
Formula
Fw
C25 H Cl N Ru
23 5 2
629.77
ii
ii
i
center in the next molecule [C(18) –H(18) …Cl(1) ]=2.704
A°, i=x, y, z, ii=1+x, y, z with an angle of 151.67 assem-
bling a two-dimensional network. Furthermore, every
asymmetric unit interacts with each other along b axis,
λ/Å
T/K
0.71073
100
crystal system
space group
Monoclinic
P12 /c
1
i
via signiꢁcant C–H···π interaction between [C(1)–H(1) …
a/Å
b/Å
c/Å
α/˚
9.6509(5)
15.2380(8)
16.7019(8)
90
93.167(2)
90
iii
C
(C12–C21) ]=2.879 A°, iii=1−x, −1/2+y, 1.5–z.
centroid
Crystallographic data for complex are listed in Table 5.
Geometry optimization and quantum theory
of atom in molecules
β/˚
γ/˚
V/Å3
2452.4(2)
1.076
Dcalc/Mg.m−3
Full geometry optimization has been done using BP86 func-
tional and the def2-TZVP basis sets. Geometry optimiza-
tion was started from the single-crystal X-ray experimental
atomic positions. Bond lengths and angles are in good agree-
ment with their corresponding values from X-ray structural
data. Figure 2 shows the superimposition of the calculated
Z
4
μ (mm−1)
1.202
F(000)
1264.0
56.56
2
θ (˚)
R (int)
0.0533
1.027
0.0283
0.0625
2,011,092
(
DFT) and X-ray structure for the titled compound. It is
GOOF
a
notable that benzene ring positions are slightly diꢀerent.
The QTAIM approach is repeatedly used for the bond-
ing situation between the atoms [45, 46]. Here, this method
is used in order to gain insight into binding characteristics
of titled complex. QTAIM reveals interesting facts about
hapticity and inter molecular interactions in titled complex.
R (I>2σ(I))
1
b
wR (I>2σ(I))
2
CCDC No
a
R =Σ||F |—|F ||/Σ|F |.
1
o
c
o
b
2
2 2
2
½
wR2 = [Σ(w(F —F ) )/Σw(F )2]
o
c
o
6
It can be seen that the central Ru is η and there are seven
intermolecular Cl···H electrostatic interactions. Selected
Fig. 1 Ortep view of complex
1), [Ru(cymene)Cl(β-
diketiminate)] for 50% ellipsoid
(
1
3

Transition Metal Chemistry
Fig. 2 Atom-by-atom superimposition of the DFT-optimized compound on the X-ray structure
Table 6 Bond critical point
electron densities (ρ), their
∇2ρ
Bond
Bond length Exp
Bond length Opt
ρ
ε
Mayer B.O
2
Laplacian, (∇ ρ), ellipticities (ε)
Ru –C
2.182 (2)
2.195 (2)
2.224 (2)
2.217 (2)
2.207 (2)
2.241 (2)
3.699 (2)
3.536 (2)
3.610 (2)
2.9433 (6)
2.8592 (6)
2.7993 (5)
3.6440 (6)
3.0036 (6)
3.4717 (6)
2.9517 (6)
2.193
2.206
2.244
2.220
2.191
2.266
3.996
3.529
3.539
2.898
2.950
2.765
3.522
2.989
3.318
3.056
0.088
0.082
0.083
0.079
0.084
0.081
0.002
0.008
0.007
0.007
0.008
0.010
0.003
0.007
0.003
0.008
0.224
0.268
0.214
0.258
0.218
0.241
0.008
0.021
0.025
0.027
0.025
0.033
0.010
0.026
0.009
0.029
0.66
0.55
1.11
1.19
0.66
0.67
0.21
0.03
0.09
0.59
0.65
0.19
0.23
0.58
0.20
0.68
0.57
0.46
0.45
0.43
0.56
0.33
1
9
and Mayer bond order
Ru –C
1
17
37
19
13
16
Ru –C
1
Ru –C
1
Ru –C
1
Ru –C
1
Cl ···Cl
5
4
3
6
Cl ···Cl
2
Cl ···Cl
2
C –H ···Cl
0.011
0.038
0.051
0.003
0.039
0.006
0.033
3
0
31
4
5
2
6
6
3
3
C –H ···Cl
3
0
33
C –H ···Cl
4
9
50
C –H ···Cl
4
9
50
C –H ···Cl
1
9
20
C –H ···Cl
4
7
48
C –H ···Cl
1
7
18
optimized geometric and QTAIM parameters are shown in
Table 6 and Fig. 3.
Hirshfeld surface calculation
In order to gain better insight into the intermolecular inter-
action of molecular crystals, Hirshfeld surface [49, 50] and
the related 2D ꢁngerprint [51, 52] plot together with inter-
molecular interaction energies were calculated using Crystal
Explorer [53]. Hirshfeld surface shows that the dominant
interaction in the solid phase is two sets of Cl···H interac-
tions between Cl connected to metal center and the C-H
from neighboring molecule benzene ring (Figs. 5 and 6).
Frontier molecular orbitals
The frontier molecular orbitals (HOMO and LUMO) can
reveal many properties of a compound. The iso-density
plots for the HOMOs and LUMOs orbitals are shown in
Fig. 4. It can be seen that HOMO is mainly localized on the
metal atom and the ligand, while the LUMO is most on the
benzene rings. By using HOMO and LUMO energy values
for the molecule, electronegativity and chemical hardness
can be calculated as follows: χ= [(I + A)/2] (electronega-
tivity), Ƞ = [(I−A)/2] (chemical hardness) where I and A
The Hirshfeld surfaces mapped with d
for the complex
norm
and respected ꢁngerprint plot are demonstrated in Fig. 7.
The dominant interaction in the complex is Cl·H can be
seen in the Hirshfeld surface as the bright red areas. Inter-
molecular interaction energies for a 3.8 Å cluster are sum-
marized in Table 8 and Fig. 6. Results suggest that the inter-
molecular interactions are of weak to moderate nature.
are ionization potential and electron aꢂnity; I = −E
HOMO
and A=−E
Table 7.
, respectively [47, 48], and are reported in
LUMO
1
3

Transition Metal Chemistry
Fig. 3 QTAIM molecular graph
together with ball and stick
Fig. 4 View of Frontier molecular orbitals LUMO (left) and HOMO (right)
Table 7 Orbital energies,
appear as distinct spikes in the 2D, the ꢁngerprint (Fig. 6).
The amount of Cl ··· H/ H···Cl interactions comprises 22.7%
of the Hirshfeld surfaces.
B3P86 Def2-TZVP
chemical hardness, chemical
softness and electronegativity
of complex [Ru(p-cymen)
E HOMO (eV)
E LUMO (eV)
−4.35
−2.41
−1.94
3.38
0.14
0.97
H,Cl
Cl(L )]
∆
E HOMO–LUMO
Chemical hardness (ƞ)
Chemical softness (S)
Electronegativity (χ)
Conclusion
In this report, a new half-sandwich ruthenium (II) complex
containing β-diketiminate ligand has been synthesized and
it is found to eꢂciently catalyze the hydroamination of
acrylonitrile with both anilines and aliphatic amines. The
activity of complex was compared by a series of ruthenium
β-diketiminate complexes, and it was shown that the elec-
tronic and steric environment of ligand have direct eꢀect on
Two-dimensional ꢁngerprint plots quantitatively summa-
rize the nature and type of intermolecular contacts experi-
enced by the molecules in the crystal. The Cl ··· H/ H···Cl,
H ··· H/ H···H and C ··· H/ H···C intermolecular interactions
1
3

Transition Metal Chemistry
Fig. 5 The three-dimensional
Hirshfeld surface mapped with
d
showing the intermolecu-
norm
lar interactions
Fig. 6 3.8 Å radius cluster
activity of catalysts. The crystal structure of [Ru(p-cymen)
is 6 and Cl···H is most dominant interaction in the titled
compound. Comparative study of both experimental and
theoretical values reveals that structural conformations are
almost the same.
H,Cl
Cl(L )] was determined by X-ray crystallographic analy-
sis. DFT calculations together with QTAIM and Hirshfeld
surfaces analysis reveal the Hapticity of the benzene ring
1
3

Transition Metal Chemistry
Fig. 7 Two-dimensional ꢁngerprint plots a all b Cl…H c H…H d C…H
Table 8 Intermolecular
N
Symop
R*
Electron Density
E_ele
E_pol
E_dis
E_rep
E_tot
interaction energies (kJ/mol) for
a 3.8 Å cluster
1
2
1
1
0
0
1
1
0
−x, −y, −z
−x, y+1/2, −z+1/2
x, y, z
x, −y+1/2, z+1/2
−x, −y, −z
−x, y+1/2, −z+1/2
x, −y+1/2, z+1/2
−x, −y, −z
10.33
9.69
9.65
13.40
10.99
8.46
9.61
9.65
9.46
HF/3−21G
HF/3−21G
HF/3−21G
HF/3−21G
HF/3−21G
HF/3−21G
HF/3−21G
HF/3−21G
HF/3−21G
−18.1
−24.0
−23.1
1.0
−5.2
−12.1
−0.1
−4.1
−3.5
−9.8
−11.7
−12.6
−0.3
−1.7
−3.4
−2.7
−1.2
−2.1
−38.9
−24.3
−36.0
−3.3
−35.8
−64.2
−21.1
−38.8
−27.9
25.7
13.5
29.8
0.1
15.0
36.8
14.2
14.9
14.1
−39.1
−43.0
−40.0
−2.1
−26.5
−42.6
−9.4
−27.9
−18.6
−x, −y, −z
1
3

Transition Metal Chemistry
2
2
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55:168–173
5. Kumar P, Gupta RK, Pandey DS (2014) Chem Soc Rev
Supplementary data
3
CCDC number 2011092 contains the supplementary crystal-
lographic data for C H Cl N Ru complex. These data can
4
3:707–733
26. Otsuka M, Yokoyama H, Endo K, Shibata T (2012) Org Biomol
Chem 10:3815–3818
2
5
23
5
2
be obtained free of charge via http://www.ccdc.cam.ac.uk, or
from the Cambridge Crystallographic Data Center, 12 Union
Road, Cambridge CB2 1EZ, UK; Fax:+44 1223 336 033;
or E-mail: deposit@ccdc.cam.ac.uk.
2
2
2
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lics 24:6250–6259
support from Iran National Science Foundation (INSF).
Compliance with ethical standards
3
3. Phillips AD, Thommes K, Scopelliti R, Gandolꢁ C, Albrecht
M, Severin K, Schreiber DF, Dyson PJ (2011) Organometallics
30:6119–6132
Conflict of interest The authors declare that they have no conꢃict of
interest.
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