Formation, characterization, structure and bonding analysis of the metal-carbon bond OM-(η6-C6H6) (M = Sc, Ti) complexes in solid matrix: Infrared spectroscopic and theoretical study

Article abstract of DOI:10.1016/j.jorganchem.2014.11.021

The reactions of ScO and TiO molecules with benzene have been studied in solid argon with infrared absorption spectroscopy combining with theoretical calculations. Laser-evaporation of bulk higher oxide targets prepared the scandium and titanium monoxide

Full text of DOI:10.1016/j.jorganchem.2014.11.021

Journal of Organometallic Chemistry 777 (2015) 25e30
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Formation, characterization, structure and bonding analysis of the
metalecarbon bond OM-(
matrix: Infrared spectroscopic and theoretical study
h
6-C6H6) (M ¼ Sc, Ti) complexes in solid
,
b
,
, b
Yanying Zhao a *, Yuchen Zhang a, Xin Liu a, Kexue Fan a, Xuming Zheng a
a Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, China
b Engineering Research Center for Eco-dyeing and Finishing of Textiles, Key Laboratory of Advanced Textiles Materials and Manufacture Technology,
Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of ScO and TiO molecules with benzene have been studied in solid argon with infrared
absorption spectroscopy combining with theoretical calculations. Laser-evaporation of bulk higher oxide
targets prepared the scandium and titanium monoxide molecules. The scandium and titanium monoxide
molecules reacted with benzene to form the typical transition metalecarbon bond (MCB) complexes,
Received 30 August 2014
Received in revised form
15 November 2014
Accepted 20 November 2014
Available online 28 November 2014
OM-(
h
6-C6H6) (M ¼ Sc, Ti), which have been identified on the basis of isotopic infrared studies and
density functional calculations. The theoretical calculation results illustrate the deformation of the planar
carbon skeleton of benzene takes place and the bond lengths of MeO are largely elongated upon OM-(h6
-
Keywords:
C6H6) (M ¼ Sc, Ti) complexes. The population results illustrate the OM-(
2A1 and 1A1 electronic ground state both with C2v symmetry arising from 2
and TiO reaction with benzene, respectively. The OSc-(
6-C6H6) and OTi-(
h
6-C6H6) are determined to have
OM-(h
6-C6H6) complexes
P
D
h
and 1 ꢀ of excited-state ScO
Transition metalecarbon bond
Matrix isolation infrared spectroscopy
Theoretical calculations
h
6-C6H6) are both stable depp
coordination compounds and can also not be photoisomerized by UV irradiation under low temperature
in solid argon matrix. Natural bond orbital analyses conclude that the OTi-(h
6-C6H6) system includes two
NBO analysis
equivalent TieC single bonds with strong binding bond energies.
© 2014 Elsevier B.V. All rights reserved.
Introduction
coordinated to benzene molecules are important in understanding
the elemental reaction mechanisms of many processes such as
catalysis, surface chemistry and material synthesis [3,4]. The
chemical reactivity of neutral transition metal atoms as well as
cations with benzenes has been extensively investigated and pro-
vided a wealth of insight concerning the reactivity of metal atoms
and cations [5e8]. Matrix isolation has proven to be a suitable tool
to form and isolate these metal-benzene complexes so that
chemical properties can be investigated by such means as electron
paramagnetic resonance (EPR), electronic absorption, Raman and
infrared spectroscopy [9e15]. The first-row transition metal ben-
zene M(C6H6) complexes have previously been assumed to have C6v
symmetry [16]. Only recently have theoretical calculations pre-
dicted that the planar carbon skeleton in these complexes might
deform in select electronic states [15,17], and even the ground
states of several M(C6H6) complexes have been predicted to have a
symmetry lower than C6v [18]. By contrast, interactions between
transition metal oxides and benzenes and the reactions of transi-
tion metal oxides, particularly neutral oxide molecules with ben-
zenes are relatively little known, in part because of the
Transition metals (TMs), because of their rich valence electrons,
large ionic radii and high positive charges, can have high coordi-
nation numbers without sacrificing the strength of interactions
with a ligand. The study of complexes of transition metals (TMs)
and reduced arenes have long been investigated because of their
fundamental importance and potential as multielectron reagents in
science and industry. Arenes are characteristic of outstanding sta-
bility due to their aromaticity, but the accessibility of both their
p
and p* orbitals allows them to serve as multielectron neutral or
anionic ligands [1,2]. As a consequence, arenes serve as excellent
ligands for TM complexes. As the simplest arene, benzene, could
shed light on the fundamental building blocks and also provides a
basic bonding understanding between the transition metals and
larger carbon molecules of TM-arenes. The complexes of TMs
* Corresponding author. Tel.: þ86 571 868 436 27.
E-mail address: yyzhao@zstu.edu.cn (Y. Zhao).
http://dx.doi.org/10.1016/j.jorganchem.2014.11.021
0022-328X/© 2014 Elsevier B.V. All rights reserved.

26
Y. Zhao et al. / Journal of Organometallic Chemistry 777 (2015) 25e30
experimental difficulty in making “pure” transition metal oxide
molecules for reaction studies.
ScO þ C6H6
Under controlled laser energy, laser evaporation of a Sc2O3
Transition metal oxides are widely used as catalysts and cata-
lytic support. The first row transition monoxide is the simplest
transition metal oxide. It provides an ideal starting point for un-
derstanding the interactions of transition metal oxides with ben-
zene. Recently are reported some transition metal monoxides
reacted with some small hydrocarbons such as CH4, C2H2, C2H4
[19e23], However, the reactions of transition metal oxide mole-
cules with benzene have received quite little attention. In the
present paper, we report the matrix isolation infrared spectra and
density functional theoretical results on the reaction products of
laser-ablated Sc2O3 and TiO2 bulk metal oxides and benzene in solid
argon, showing the experimental evidence for the OM (C6H6)
species, as the major reaction products.
target followed by condensation with pure argon formed ScO
(954.8 cmꢀ1 with a site absorption at 951.8 cmꢀ1) as the major
product with minor [ScO(Ar)5]þ (at 976.4 cmꢀ1), ScOꢀ(889.2 cmꢀ1),
and ScOꢀ2 (722.5 cmꢀ1) [32e34]. These absorptions show no obvious
change on annealing. Broadband irradiation almost destroyed the
ScOꢀ and ScO2ꢀ absorptions, slightly increased the [ScO(Ar)5]þ ab-
sorption at the expense of the ScO absorption. Distinct new product
absorptions are observed in the experiments when different con-
centration C6H6/Ar mixtures are used as the reagent gas. Fig. 1
shows the representative spectra in selected regions with a C6H6/
Ar sample (0.1% molar ratio). Besides the aforementioned scandium
oxide absorptions, a new absorption at 880.2 cmꢀ1 is observed on
sample deposition, as shown in Table 1. The new product absorp-
tion increased when annealing (trace bec), and markedly enhanced
when the matrix is annealed to 45 K (trace c). The 880.2 cmꢀ1
absorption also has no change when the matrix is irradiated by the
output of a high pressure mercury arc lamp without pass filter
Experimental methods and computational details
The experimental setup for pulsed laser-ablated and matrix
isolation Fourier transform infrared (FTIR) spectroscopy has been
described in detail previously [24]. Briefly, the Nd: YAG laser
fundamental (1064 nm, 20 Hz repetition rate and 8 ns pulse width)
was focused onto the rotating metal oxide targets (Sc2O3, TiO2). The
laser-ablated metal oxides were co-deposited with benzene in
excess argon onto the 12 K CsI window for 1e2 h at a rate of
3e5 mmol/h. The C6H6 sample was subjected to several liquid ni-
trogen freeze-pump-thaw cycles at 77 K before use. The C6H6/Ar
mixture of 0.05e0.2% volume was prepared in a stainless steel
vacuum tube using standard manometric technique. Isotopic C6D6
and 13C6H6 (ISOTEC, 99%) were used without further purification.
Infrared spectra were recorded on a Bruker IFS 113 V spectrometer
at 0.5 cmꢀ1 resolution between 4000 and 400 cmꢀ1 using a DTGS
detector. After the infrared spectrum of the initial deposition had
been recorded, the samples were warmed to the desired temper-
ature, quickly re-cooled, and the spectrum taken followed by
repetition of these steps using higher temperatures, and selected
samples were subjected to broadband photolysis using a high-
pressure mercury arc lamp.
Quantum chemical calculations were performed using the
Gaussian 09 program package [25]. The geometry optimized cal-
culations are performed at the level of density functional theory
(DFT) with the hybrid B3LYP method, which incorporates the
Becke's three-parameter functional (B3) with the Lee-Yang-Parr
(LYP) correlation functional [26,27]. The hybrid density functional
B3LYP has proven to be an accurate method for reproducing metal-
ligand bond lengths. The 6-311þþG(d, p) basis sets were used for
the C, O, H, Sc, Ti atoms [28,29]. The geometries were fully opti-
mized and the harmonic vibrational frequencies were calculated
with analytic second derivatives, and zero-point vibrational en-
ergies (ZPVE) were derived at the B3LYP level of theory. The
bonding characteristics were analyzed using natural bond orbital
(NBO) theory [30], which was achieved with the NBO 3.1 package as
implemented in Gaussian 09 suite of programs. The single point
energies of the structures optimized at the B3LYP level were
calculated at CCSD(T) (the coupled cluster level with single and
double excitations plus perturbative triple excitations) [31] using
the same basis. The used wave function has been already stabled.
(250 < l < 580 nm, trace d). There are no changes to be observed in
the benzene spectral regions.
TiO þ C6H6
Similar experiments are also performed using a bulk TiO2 target.
Co-condensation of the species from laser evaporation of TiO2 with
pure argon at 12 K produced strong titanium monoxide and two
sites (990.3, 988.1 and 985.7 cmꢀ1) and dioxide absorptions
(
48TiO2: n1, 917.0 cmꢀ1 and n3, 946.9 cmꢀ1) [21,35]. In the experi-
ments of laser-ablated TiO2 target with 0.1% C6H6 in excess argon,
the band of TiO decreases on annealing and almost disappears at
44 K, while the bands in the TiO2 and benzene regions have no
obvious change to be observed. As shown in Fig. 2A new absorption
at 972.9 cmꢀ1 produces, and increases obviously when the sample
annealing to higher temperature (Fig. 2, trace bec). The 972.9 cmꢀ1
band makes no obvious change on subsequent broadband irradia-
tion (Fig. 2, trace d).
The experiments were repeated with the C6D6 and 13C6H6
samples. We failed in observing any changes in the benzene spec-
tral regions in all experiments. The new absorptions have the
similar behavior to the normal experiments in the same experi-
mental conditions. The small isotopic shifts are observed in new
absorptions, as shown in Table 1.
Results
Infrared spectra
Fig. 1. The infrared spectra in the SceO stretching region from laser-ablated Sc2O3 bulk
target with 0.1% C6H6 in excess argon. (a) 1 h deposition, and after annealing to (b)
35 K, (c) 45 K, (d) full-arc photolysis for 20 min.
The ScO and TiO monoxide reactants were prepared from laser
evaporation of bulk Sc2O3 and TiO2 targets.

Y. Zhao et al. / Journal of Organometallic Chemistry 777 (2015) 25e30
27
Table 1
Observed and calculated frequencies (cmꢀ1), and intensities (in parentheses, km/
mol) of MeO for the potential species.
12C6H6
13C6H6
C6D6
Assignment
Exptl. Calc.a
Exptl. Calc.a
Exptl. Calc.a
880.2 936.4(619) 880.2 937.6(561) 879.7 937.0(558) SceO stretching
of OSc-(
6-C6H6)
972.9 1018.9(483) 972.9 1018.4(480) 972.9 1017.4(464) TieO stretching
of OTi-(
6-C6H6)
h
h
a
The values in parentheses represent the IR intensities (km/mol).
Molecular structures and geometries
The possible geometries have been optimized for the MO, OM-
Fig. 3. Optimized C2v geometries of OM-(
(d, p) level with the zero point correction. The geometry parameters referred to
Table 2.
h
6-C6H6) (M ¼ Sc and Ti) at B3LYP/6-311þþG
(h
2-C6H6), OM-(
h
4-C6H6) and OM-(
h
6-C6H6) (M ¼ Sc, Ti) systems.
DFT calculation results indicate that the OM-(
C6H6) complexes will converged to the OM-(
The optimized geometry is shown in Fig. 3. Table 2 also lists the
optimized geometry parameters.
h -
2-C6H6) and OM-(h4
h
6-C6H6) (M ¼ Sc, Ti).
ground state geometry is singlet 1A1 state, which is 6.4 kcal/mol
lower in energy than triplet state 3A1 (see Supporting information).
These results indicate the ground state of the OTi-(h
6-C6H6) com-
OSc-(
The B3LYP/6-311þþG(d, p) predicts the OSc-(
to be a 2A1 ground state with a C2v symmetry, as shown in Fig. 3. The
OSc-(
6-C6H6) complex is predicted that the terminal of scandium
h
6-C6H6)
plex is 1A1 state with distortion benzene skeleton with two groups
of carbon atoms, in which two CeC bond lengths are 2.190 Å and
the other four one are 2.377 Å.
h
6-C6H6) complex
h
is coordinated to center of benzene plane and ScO is perpendicular
to the benzene plane. The two SceC bond lengths are 2.517 Å and
Discussions
the other four ones are 2.616 Å, as shown in Table 2. The OSc-(h6
-
C6H6) complex are composed of two shorter 0.010 Å and four longer
0.041 Å CeC bond lengths (1.385 and 1.436 Å) than ones in the C6H6
(1.395 Å) molecule. The SceO bond length is elongated 0.036 Å
from 1.659 (bond length of ScO) to 1.695 Å.
Assignment
The band at 880.2 cmꢀ1 is not observed in the experiments
when laser-evaporated Sc atoms were co-deposited with C6H6/Ar
mixture and Sc2O3 target with pure argon [34,35]. So the band at
880.2 cmꢀ1 is attributed to the OSc-( 6-C6H6) complex. The ab-
h
OTi-(
The geometry optimizations are carried on the singlet and
triplet spin states of the OTi-(
6-C6H6) complex. The OTi-( 6-C6H6)
complex is calculated to have two stable geometries without any
imaginary frequency. Similar to OSc-(
6-C6H6), the TiO on the ter-
h
6-C6H6)
sorption shows no carbon-13 isotopic shift with 13C6H6, and ex-
hibits very small (less than 1 cmꢀ1) deuterium isotopic shift with
C6D6. These experiments suggests that the 880.2 cmꢀ1 absorption is
h
h
due to the SceO stretching mode of a OSc-(h
6-C6H6) complex,
h
which is red-shifted 74.6 cmꢀ1 relative to the 954.8 cmꢀ1 of ScO
molecule. Table 1 lists the observed and calculated vibrational
frequencies of the product absorptions.
minal of Ti is perpendicular to the center of C6H6 skeleton, as shown
in Fig. 3. The B3LYP/6-311þþG(d, p) method determines that triplet
state (C6v symmetry with 3A1 electronic state) is higher 1.6 kcal/mol
than singlet state (C2v symmetry with 1A1). The more accurate
CCSD(T)//B3LYP/6-311þþG(d, p) calculated results illustrated the
To validate the experimental assignment and to investigate the
structure and bonding of the complex, density functional theory
calculations are performed on the OSc-(h
6-C6H6) complex. The
harmonic SceO stretching vibrational frequency is determined to
be 936.4 cmꢀ1 with 619 km/mol IR intensity. The other vibrational
modes are predicted to have much lower IR intensities than the
SceO stretching mode, and can not be observed due to weakness,
see Table 3. The SceO stretching mode is also calculated to exhibit
no carbon-13 shift and 0.6 cmꢀ1 deuterium shift, consistent with
the experimental observations. The SceO stretching mode is pre-
dicted to be red-shifted by about 63.1 cmꢀ1 with respect to the
Table 2
Calculated bond lengths (Å), dihedral angles (degree) and binding energies (in kcal/
mol) of ground MO and OM-(
h
6-C6H6) (M ¼ Sc, Ti) complexes.
DAa
Eb
b
rMeO
rMeC
rCeC
rCeH
OSc-(
OTi-(
h
6-C6H6(C2v
,
2A1) 1.695 2.616 1.436 1.084 169.7 16.7(17.6)
2.517 1.385 1.081
h
6-C6H6(C2v
,
1A1)
1.632 2.376 1.460 1.084 173.1 32.1(41.7)
2.190 1.380 1.080
The MeO bond lengths of ScO (2Sþ) and TiO (3
D
) are 1.659 and 1.612 Å.
a
Fig. 2. The infrared spectra in the 880e740 cmꢀ1 region from laser-ablated TiO2 bulk
target with 0.1% C6H6 in excess argon. (a) 1.5 h deposition, and after annealing to (b)
35 K, (c) 44 K, (d) full-arc photolysis for 20 min.
Refer to the distortion angle of benzene skeleton.
b
Binding energies with respect to C6H6 (1A1g) þ MO (2Sþ for ScO and 3
D for TiO),
the CCSD(T) values in parentheses, unit in kcal/mol.

28
Y. Zhao et al. / Journal of Organometallic Chemistry 777 (2015) 25e30
Table 3
Calculated energies (Hartrees), vibrational frequencies (cmꢀ1), modes and intensities (km/mol) of the OM-(
theory.
h
6-C6H6) (M ¼ ScTi) complexes at B3LYP/6-311þþ(d, p) level of
Species
OSc-(
Energya
Frequencies (intensity, mode)
3209.0(0, a1), 3205.7(3, b2), 3186.4(13, b1), 3182.9(1, a1), 3168.7(1, b2), 1591.2(36, a1), 1491.5(0, b1), 1449.5(1, b2)1375.8(0, a2),
h
6-C6H6) ꢀ1068.200768
(C2v
,
2A1)
(ꢀ1066.6034524) 1354.5(0, a2), 1328.3(48, b1), 1189.2(3, a1), 1168.6(1, b1), 1039.0(0, a2), 1030.2(0, b1), 1023.0(0, b2), 970.2(9, b2), 957.8(23, b2),
951.5(2, a1), 936.4(619, a1), 916.9(0, a2), 840.6(0, b1), 827.3(11, a1), 738.3(23, b2), 698.2(56, a1), 629.0(1, b2), 617.5(0, a2),
588.9(0, a1), 381.8(0, a2), 355.2(1, a1), 253.2(3, b2), 252.5(14, b1), 251.4(5, a1), 88.4(38, b2), 67.5(45, b1)
OTi-(
(C2v
h
6-C6H6) ꢀ1156.956237
3212.7(0, a1), 3210.1(4, b2), 3193.0(9, b1), 3190.2(1, a1), 3177.8(0, a2), 3176.6(0, b2), 1578.0(23, b2), 1494.9(10, b1), 1423.0(1, b1),
,
1A1)
(ꢀ1155.3136123) 1375.0(0, a2), 1375.0(0, a2), 1334.1(0, a2), 1301.5(78, b1), 1174.4(0, a1), 1153.4(0, b1), 1054.0(0, a2), 1032.9(0, b2), 1018.9(483, a1),
1003.5(1, b1), 977.0(2, b2), 948.4(0, a2), 937.7(8, a1), 936.8(34, b2), 839.8(18, a1), 833.0(0, b1), 772.8(22, b2), 755.7(36, a1),
630.1(2, b2), 614.4(0, a1), 614.1(0, a2), 389.9(0, a1), 388.9(11, b1), 364.0(0, b2), 335.8(0, a1), 320.5(0, a1), 135.6(15, b2), 105.8(22, b1)
a
The energies in parentheses represent for the CCSD(T)/6-311þþ(d, p) on B3LYP/6-311þþ(d, p) optimized geometries.
frequency of diatomic ScO calculated at the same level of theory,
comparably with the experimentally observed shift (74.6 cmꢀ1).
Similar to the ScO þ C6H6 systems, the experiment observations
imply the absorption at 972.9 cmꢀ1 produced in the 0.1% C6H6 in
argon at the expense of the TiO absorptions. This suggests that the
972.9 cmꢀ1 absorption should be assigned to TieO stretching vi-
CCSD(T)//B3LYP for OTi-(h
6-C6H6) because of the lack of proper
treatment for dispersive interactions with B3LYP method [36,37].
The reactions of ScO and TiO with C6H6 are exothermic 17.6 and
41.7 kcal/mol in energy. The complex absorptions increased on
annealing, indicating that the process maybe require no activation
energy. The binding energies are listed at the CCSD(T)//B3LYP/6-
311þþG(d, p) level, and the chemical reaction equation as follows:
bration of the OTi-(h
6-C6H6) complex. The band at 972.9 cmꢀ1 in-
crease greatly when the sample is annealed to higher temperature,
and is not observed in the Ti þ C6H6/Ar experiments and laser
ablated TiO2 in pure argon. During the process the TiO2 absorptions
conduct no obvious change. The 972.9 cmꢀ1 band shows no carbon-
13 and deuterium isotopic shift with 13C6H6 and C6D6, which also
illustrates that the band is due to the terminal TieO stretch vibra-
Natural bonding orbital analyses
As shown in Table 4, The natural bond orbital analysis display
the atomic natural charge transfer on every atoms for OM-(h6
-
C6H6) (M ¼ Sc, Ti) complexes. Comparing to isolated ScO and C6H6
molecule, the positive natural charges increase from 1.029 to 1.620
on Sc atom, and 0.204 to 0.224(0.229) on H atom, relatively, the
negative charges decrease from ꢀ0.204 to ꢀ0.268(0.425) on C atom
tional mode of the OTi-(h
6-C6H6) complex. The absorption at
990.3 cmꢀ1 has been attributed to the TieO stretching vibration
frequency of TiO molecule [35].
and ꢀ1.029 to ꢀ1.052 on O atom for ScO-(
for TiO-(
h
6-C6H6) complex. While
h
6-C6H6), the positive natural charges increase 0.541 on Ti
Density functional calculations support the above experimental
assignment. Table 3 lists the calculated vibration frequencies of
and 0.026 on H atom, the negative charge decrease average 0.070
on O and 0.126 on C atom. The natural orbital charges illustrate that
the charges make redistribution between benzene and metal
monoxides, which leads to the positive charges on metal and
hydrogen atoms become more positive, while the negative charges
on O and C atoms become more negative. The results indicate 0.568
and 0.601 electron transfer from the ScO and TiO unit to the C6H6
skeleton.
every mode on OTi-(
TieO stretching vibrational frequency is predicted at 1018.9 cmꢀ1 in
the 1A1 state of the OTi-( 6-C6H6) complex, which agrees well with
the experimental values (972.9 cmꢀ1). The predicted TieO
h
6-C6H6) complex. As shown in Table 3, the
h
stretching frequency of 1A1 OTi-( 6-C6H6) complex is red-shifted
h
23.4 cmꢀ1 when compared to that of free TiO molecule, which is
close to the experimental observed values (17.4 cmꢀ1). The results
indicate that the calculated isotopic frequencies display a small
shift and the modes in the benzene spectral regions are too weaker
to be observed experimentally.
The well-studied ScO molecule has been shown to have a 2Sþ
ground state with (core) (3
p
)4(9
s
)1(1
d
)0. A 2D is the first excited
0
state with an electronic configuration of (core) (3
[38].The 9
and 3dz2 orbitals of metal atom that is directed away from the O
p d s)
)4(1 )1(9
The reactions of ScO and TiO with C6H6 are exothermic on the
basis of the calculations of the binding energies between MO and
C6H6. Table 2 lists the calculated binding energies at B3LYP and
s
orbital of MO is primarily a non-bonding hybrid of 4s
atom. The 1d orbital is largely 3d orbital of the metal atom that is
CCSD(T)//B3LYP levels of theory. The binding energies for OSc-(h6
-
mainly non-bonding [39]. According to our calculations, the 2D
state lies 32.4 kcal/mol above the 2Sþ ground state at the B3LYP
level of theory. The ground state 3D of TiO with (core)
C6H6) calculated at the B3LYP level is a little smaller than that
calculated at CCSD(T)//B3LYP level, while it is much larger at
(3p d s
)4(1 )1(9 )1 electronic configuration has also been calculated to
Table 4
NBO atomic charges of the atoms and Wiberg bond indices (WBIs) in the NAO basis
for organometallic OM-(
h
6-C6H6) (M ¼ Sc, Ti) complexes from the B3LYP/6-311þþG
(d, p) level of theorya.
Natural charges
Bond order
M
O
Cb
Hb
MeO MeCb CeCb CeHb
OSc-(
OTi-(
h
6-C6H6)
1.620 ꢀ1.052 ꢀ0.268 þ0.224 1.579 0.059 1.539 0.915
ꢀ0.425 þ0.229
0.129 1.260 0.917
h
6-C6H6) þ1.361 ꢀ0.760 ꢀ0.253 þ0.228 1.879 0.164 1.571 0.912
ꢀ0.484 þ0.234
0.486 1.177 0.914
The natural atomic charges: C6H6: C is ꢀ0.204 and H is þ0.204. ScO: Sc is þ1.029 and
O is ꢀ1.029. TiO: Ti is þ0.830 and O is ꢀ0.830.
The bond orders: ScO: 1.688; TiO: 1.899; CeC and CeH of C6H6: 1.438 and 0.927.
a
The results listed are for the electronic ground state of the species.
Including two different types of carbon or hydrogen atoms, upper value referred
b
to four equal atoms, below value referred to two equal atoms.
Fig. 4. HOMO and LUMO orbital of OM-(
h
6-C6H6) (M ¼ Sc and Ti) complexes.

Y. Zhao et al. / Journal of Organometallic Chemistry 777 (2015) 25e30
29
Table 5
Natural electron configuration on atom for organometallic OM-(
h
6-C6H6) (M ¼ Sc, Ti) complexes from NBO population at B3LYP/6-311þþG (d, p) level of theorya.
OSc-(
6-C6H6)
h
OTi-(h
6-C6H6)
Sc
O
[Core]4S(0.04)3d(0.78)4d(0.02)5p(0.01)
[Core]2S(0.96)2p(2.55)4s(0.01)
[Core]2S(0.48)2p(1.66)4p(0.01)
[Core]2S(0.49)2p(1.85)4p(0.01)
1S(0.39)
[Core]3d(2.52)4p(0.33)5S(0.10)4d(0.02)
[Core]2S(1.82)2p(4.80)
[Core]2S(0.96)2p(3.25)4p(0.01)
[Core]2S(0.98)2p(3.45)4p(0.02)
1S(0.77)
Cb
Hb
1S(0.38)
1S(0.76)
The natural electron configuration of C6H6: C is [Core]2S(0.95)2p(3.23)4p(0.01) and H is 1S(0.79).
ScO:Sc: [Core]4S(0.89)3d(0.57)4p(0.03) and O is [Core]2S(0.98)2p(2.51)3S(0.04).
TiO: [Core]4S(0.86)3d(1.75)4p(0.03) and O is [Core]2S(0.97)2p(2.37)3S(0.02).
a
The results listed are for the electronic ground state of the species.
Including two different types of carbon or hydrogen atoms, upper value referred to four equal bonds, below value referred to two equal bonds.
b
be 17.0 kcal/mol lower in energy than its singlet state 1Sꢀ with
annealing allowed the C6H6 molecule diffuse, and the reaction
products formed between metal monoxide and benzene have been
isolated and characterized in argon matrix by infrared spectroscopy
0
(core) (3
p
)4(1
d
)2(9
s
)
electronic configuration at CCSD(T)//B3LYP/
6-311þþG(d, p) level (See Supporting information).
The bonding in the OM-(
h
6-C6H6) complex is different from
and DFT theoretical calculations. The OM-(
h
6-C6H6) (M ¼ Sc, Ti)
those of the dinitrogen and acetylene [23,40], the interactions with
complexes produced spontaneously on annealing without any
activation energy. Broadband photolysis can't destroy the com-
plexes due to their strong MeC bonds. The density functional
2D ScO are dominated by the synergic donations of filled orbitals of
C2H2 and N2. The empty 9
for donation from the C2H2 and N2 fragment. The singly occupied 1
molecular orbital of 2D ScO is the back-donation orbital, it can
interact with the anti-bonding orbitals of N2 and C2H2 in side-
s orbital is the primary acceptor orbital
d
theoretical calculations show that the OM-(h
6-C6H6) complexes
have a 2A1 ground state for Sc and 1A1 ground state for Ti both with
the deformation of the planar carbon skeleton of benzene (C2v). The
CCSD(T) binding energies imply the strong metal-carbon bonds
p
1
bonding geometry. However, the benzene has a A1g ground state
with …(3e1u)4(1a2u)2(3e2g)4(1e1g)41e2u0 electronic configuration.
As shown in Fig. S3, the highest occupied molecular orbitals,
included in the OM-(
analysis concludes that the strong MeC bonds are formed in the
OM-(
6-C6H6) complexes, which leads to the weaker MeO and CeH
h
6-C6H6) complexes. The density population
HOMO, HOMO ꢀ 1 and HOMO ꢀ 4, are the
The lowest unoccupied molecular orbitals, LUMO and LUMO þ 1,
are anti-bonding in character. According to the frontier molecular
orbital theory, the 9 orbital of metal monoxides is the primary
acceptor orbital for donation from the pHOMOꢀ4 filled orbital of
benzene fragment. The singly occupied 1 molecular orbital is the
p
bonding in character.
h
bonds. The results indicate that TieC bond become much stronger
than SceC bonds. The natural charge transfer illustrates that the
p
s
organometallic OM-(
h
6-C6H6) (M ¼ Sc, Ti) complexes are equivalent
to MOþ cation binding with C6Hꢀ6 anion. Natural orbital analyses
d
verify two TieC single bonds are characteristic of 1, 3-metal-carbon
back-donation orbital. It can interact with the pHOMO and pHOMOꢀ1
orbitals of C6H6 in perpendicular bonding geometry. The electrons
on 1d molecular orbital of MO would feedback to the virtual pLUMO
bonds (1, 3-MC bonds) in the OTi-(h
6-C6H6) system, which is
inspiring us further to investigate the arenes and phenyl derivatives
including metal-carbon bonds.
(1e2u) orbital of C6H6. The interactions between MO and C6H6 are
dominated by the donation and back-donation toward C6H6. Fig. 4
Acknowledgment
shows the bonding orbitals for OM-(
h
6-C6H6) (M ¼ Sc and Ti)
complexes.
We gratefully acknowledge finical support from National Nat-
ural Science Foundation of China (Grants Nos. 21273202, 21473162
and 21033002), National Basic Research Program of China
(2013CB834604), and the Project Grants 521 Talents Cultivation of
Zhejiang Sci-Tech University. We are also grateful to support from
Zhejiang Provincial Top Key Academic Discipline of Chemical En-
gineering and Technology of Zhejiang Sci-Tech University. Kind
thanks for significant beneficial discussions with Prof. Mingfei Zhou
in Fudan University.
Table 4 lists the bond orders of OM-(h
6-C6H6) complexes ob-
tained using Wiberg bond indices [41]. The WBIs of MeC imply the
obvious bonding interactions, and TieC (WBI: 0.164 and 0.486)
bond is stronger than SceC (WBI: 0.059 and 0.129). The decrease of
Wiberg bond indices on MeO and CeH indicate that the MeO and
CeH bonds of OM-(
isolated MO and C6H6. WBIs on CeC bond also show that four CeC
h
6-C6H6) complexes become weaker than the
bonds are strengthened and two are weakened for OM-(
complexes.
h
6-C6H6)
Natural electron configuration on atom illustrated that the OSc-
Appendix A. Supplementary data
(h h D)
6-C6H6) and OTi-( 6-C6H6) species are formed by excited ScO(2
and TiO (1Sꢀ) reaction with benzene. As shown in Table 5, the
electron configurations are [Core]4s(0.04)3d(0.78)4d(0.02)5p(0.01)
for Sc and [Core]3d(2.52)4p(0.33)5s(0.10)4d(0.02) for Ti in the OM-
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.11.021.
(h
6-C6H6) complexes. The NBO search finds the two TieC single
References
bonds (NBOs 9, 16) and two TieC antibonds (NBOs 244, 251) in OTi-
(h
6-C6H6) system, which exhibits a typical dpep*p orbital interaction
[1] M.N. Bochkarev, Chem. Rev. 102 (2002) 2089.
characteristic of 1, 3-metal-carbon bond (1, 3-MC bond) [42].
[2] W.L. Huang, S.I. Khan, P.L. Diaconescu, J. Am. Chem. Soc. 133 (2011) 10410.
[3] A. Nakajima, K. Kaya, J. Phys. Chem. A 104 (2000) 176.
[4] A. Brückner, Chem. Commun. 19 (2001) 2122.
[5] Transition metal atom reactions in the gas phase, see, for example: J.J. Carroll,
K.L. Haug, J.C. Weisshaar, M.R.A. Blomberg, P.E.M. Siegbahn, M. Svensson
J. Phys. Chem. 99 (1995) 13955.
[6] Petra A.M. van Koppen, M.T. Bowers, C.L. Haynes, P.B. Armentrout, J. Am.
Chem. Soc. 120 (1998) 5704.
[7] J.J. Carroll, J.C. Weisshaar, J. Phys. Chem. 100 (1996) 12355.
Conclusions
Laser-ablated Sc2O3 and TiO2 bulk metal oxides co-deposited
with benzene in excess argon to form scandium monoxide and ti-
tanium dioxide and monoxide as the primary products. Sample

30
Y. Zhao et al. / Journal of Organometallic Chemistry 777 (2015) 25e30
[8] T.D. Jaeger, M.A. Duncan, J. Phys. Chem. A 109 (2005) 3311.
[26] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[9] M.P. Andrews, S.M. Mattar, G.A. Ozin, J. Phys. Chem. 90 (1986) 744.
[10] M.P. Andrews, H.X. Huber, S.M. Mattar, D.F. McIntosh, G.A. Ozin, J. Am. Chem.
Soc. 105 (1983) 6170.
[27] C. Lee, E. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[28] (a) A.D. McLean, G.S. Chandler, J. Chem. Phys. 72 (1980) 5639;
(b) R. Krishnan, J.S. Binkley, R. Seeger, J.A. Pople, J. Chem. Phys. 72 (1980) 650.
[29] D. Andrae, U. Haussermann, M. Dolg, H. Stoll, H. Preuss, Theor. Chim. Acta. 77
(1990) 123.
ꢀ
[11] K. Bechamp, M. Levesque, H. Joly, L. Manceron, J. Phys. Chem. A 110 (2006)
6023.
[12] A. McCamley, R.N. Perutz, J. Phys. Chem. 95 (1991) 2738.
[13] B.R. Sohnlein, S.G. Li, D.S. Yang, J. Chem. Phys. 123 (2005) 214306.
[14] K. Judai, K. Sera, S. Amatsutsumi, K. Yagi, T. Yasuike, S. Yabushita, A. Nakajima,
K. Kaya, Chem. Phys. Lett. 334 (2001) 277.
[15] (a) L. Manceron, L. Andrews, J. Am. Chem. Soc. 110 (1988) 3840;
(b) J.T. Lyon, L. Andrews, J. Phys. Chem. A 109 (2005) 431.
[16] F. Rabilloud, J. Chem. Phys. 122 (2005) 134303.
[30] NBO version 3.1 A.E. Reed, J.E. Carpenter, F. Weinhold, J. Chem. Phys. 83
(1985) 735.
[31] J.A. Pople, M.H. Gordon, K. Raghavachari, J. Chem. Phys. 87 (1987) 5968.
[32] G.V. Chertihin, L. Andrews, M. Rosi, C.W. Bauschlicher Jr., J. Phys. Chem. A 101
(1997) 9085.
[33] Y.Y. Zhao, Y. Gong, M.H. Chen, C.F. Ding, M.F. Zhou, J. Phys. Chem. A 109 (2005)
11765.
[17] J.T. Lyon, L. Andrews, J. Phys. Chem. A 110 (2006) 7806.
[18] (a) A.K. Kandalam, B.K. Rao, P. Jena, R. Pandey, J. Chem. Phys. 120 (2004)
10414;
[34] Y.Y. Zhao, G.J. Wang, M.H. Chen, M.F. Zhou, J. Phys. Chem. A 109 (2005) 6621.
[35] G.V. Chertihin, L. Andrews, J. Phys. Chem. 99 (1995) 6356.
[36] Y. Ono, T. Taketsugu, Chem. Phys. Lett. 385 (2004) 85.
[37] M. Dolg, J. Chem. Inf. Comput. Sci. 41 (2001) 18.
[38] K.P. Huber, G. Herzberg, Constants of Diatomic Molecules, Van Nostrand-
Reinhold, New York, 1979.
[39] J. Zhuang, Z.H. Li, K.N. Fan, M.F. Zhou, J. Phys. Chem. A 116 (2012) 3388.
[40] M.F. Zhou, G.J. Wang, Y.Y. Zhao, M.H. Chen, C.F. Ding, J. Phys. Chem. A 109
(2005) 5079.
(b) B.R. Sohnlein, S. Li, D.-S. Yang, J. Chem. Phys. 123 (2005) 214306.
[19] M.H. Chen, Z.G. Huang, M.F. Zhou, Chem. Phys. 384 (2004) 165.
[20] G.J. Wang, S.X. Lai, M.H. Chen, M.F. Zhou, J. Phys. Chem. 109 (2005) 9514.
[21] G.J. Wang, Y. Gong, M.H. Chen, M.F. Zhou, J. Am. Chem. Soc. 127 (2006) 6780.
[22] G.J. Wang, M.H. Chen, M.F. Zhou, J. Phys. Chem. A 108 (2004) 11273.
[23] G.J. Wang, M.H. Chen, Y.Y. Zhao, M.F. Zhou, Chem. Phys. 322 (2006) 354.
[24] (a) M.F. Zhou, L. Andrews, C.W. Bauschlicher Jr., Chem. Rev. 101 (1999) 1931;
(b) Y. Gong, M.F. Zhou, L. Andrews, Chem. Rev. 109 (2009) 6765.
[25] M.J. Frisch, et al., Gaussian 09, Revision A.02, Gaussian, Inc., Wallingford, CT,
2009.
[41] K.B. Wiberg, Tetrahedron 24 (1968) 1083.
[42] G. Frenking, C.H. Suresh, Organometallics 31 (2012) 7171e7180.