298
S. Biswas et al. / Journal of Molecular Structure 1099 (2015) 297e303
assignment of spectral bands and redox properties have been
interpreted by DFT and TDDFT calculations. We also report the
catalytic transfer hydrogenation of ketones with 2-propanol and
oxidation of alcohols with N‒methylmorpholine‒N‒oxide (NMO).
grade) at a flow rate of 30 mL/min. The injection volume of sample
was 2 L. The oxidation products were identified by GC co-injection
with authentic samples.
m
3 2 6
2.3. Preparation of [Rh(PPh )(L)Cl ](PF ) (1)
2
. Experimental
RhCl
solution of 2-(methylthio)-N-((pyridine-2-yl)methylene)benzen-
amine (L) (0.091 g, 0.395 mmol) and PPh (0.104 g, 0.385 mmol).
The reaction mixure was refluxed for 10 h under stirring condition.
The solvent was removed under reduced pressure using a rotary
evaporator. The red gummy mass was dissolved in minimum vol-
3 2
.3H O (0.10 g, 0.379 mmol) was added to an acetonitrile
2
.1. Materials
3
2
-(methylthio)-N-((pyridine-2-yl)methylene)benzenamine (L)
was prepared following the published procedure [35]. Pyridine-2-
carboxaldehyde and 2-aminothiophenol were purchased from
Sigma Aldrich, and used as received. All other chemicals and sol-
vents were of reagent grade and were used without further
purification.
ume of methanol and aqueous solution of NH
precipitate the product. The precipitate was filtered and washed
with cold water, finally dried in vacuuo over P 10. Yield was
4 6
PF was added to
4
O
0.197 g, 64%.
2 6 2 2
Anal. Calc. for C31H27Cl F N P RhS (1): C, 46.00; H, 3.36; N,
2
.2. Physical measurements
ꢀ1
3
y
.46%. Found: C, 45.87; H, 3.31; N, 3.40%. IR data (KBr, cm ): 1594
ꢀ
1
(C]N), 842
y(PF ). H NMR data (CDCl , ppm): 8.86 (1H, d,
6
3
Microanalyses (C, H, N) were performed using a PerkineElmer
J ¼ 4.2 Hz), 8.67 (1H, s), 8.41 (2H, d, J ¼ 8.0 Hz), 7.87 (1H, t,
CHN-2400 elemental analyzer. The electronic spectra were
measured on Lambda 750 Perkin Elmer spectrophotometer in
acetonitrile solution. The IR spectra were recorded on RX-1 Perkin
III
IV
J ¼ 8.1 Hz), 7.12e7.52 (20H, m), 2.89 (3H, s). E (Rh /Rh ): 1.07 V;
E
pc: ꢀ1.05 V.
ꢀ1
Elmer spectrophotometer in the spectral range 4000e400 cm
with the samples in the form of KBr pellets. Luminescence property
was measured using LS-55 Perkin Elmer fluorescence spectropho-
tometer at room temperature (298 K) in acetonitrile solution by
2
.4. Procedure for catalytic transfer hydrogenation
The ketone (1 mmol), KOH (2 mL of a 0.2 M solution in 2-
1
cm path length quartz cell. Fluorescence lifetimes were measured
3
propanol), and the complex (0.01 mmol dissolved in CH CN)
using a time-resolved spectrofluorometer from IBH, UK. The in-
strument uses a picoseconds diode laser (NanoLed-03, 370 nm) as
the excitation source and works on the principle of time-correlated
were added to 10 mL of 2-propanol, and the mixture was refluxed
for 4 h. 2-Propanol was removed on a rotary evaporator, and the
resulting semisolid was extracted with diethyl ether (5 ꢂ 10 mL).
The extract was passed through a short column of silica gel. The
column was washed with ~100 mL of diethyl ether. All the eluates
from the column were mixed, and the solvent from the mixture was
evaporated off on a rotary evaporator. The resulting residue was
dissolved in 2e3 mL of hexane and subjected to GC.
single photon counting [51]. The goodness of fit was evaluated by
2
c
criterion and visual inspection of the residuals of the fitted
1
3
function to the data. H NMR spectra were recorded in CDCl on
Bruker 300 MHz FT-NMR spectrometers in presence of TMS as in-
ternal standard. Cyclic voltammetric measurements were carried
out using a CH1 Electrochemical workstation. A platinum wire
working electrode, a platinum wire auxiliary electrode and Ag/AgCl
reference electrode were used in a standard three-electrode
2.5. Procedure for catalytic oxidation of alcohols with NMO
4 4
configuration. [nBu N][ClO ] was used as the supporting electro-
lyte and the scan rate used was 50 mV s in acetonitrile under
dinitrogen atmosphere. Powder X-ray diffractions were performed
ꢀ1
A solution of complex (0.01 mmol) in CH
to the mixture containing alcohol substrate (1 mmol), K
1.3 mmol), solid NMO (3 mmol) and molecular sieves. The reaction
mixture was refluxed for 3 h, and the solvent was then evaporated
under reduced pressure. The residue was then extracted with
diethyl ether (20 mL), concentrated to z 1 mL. The oxidized
product present in diethyl ether extract was analyzed by GC.
2
Cl
2
(25 mL) was added
2
CO
3
(
on a Bruker D8 instrument with Cu K
The luminescence quantum yield was determined using carba-
zole as reference with a known of 0.42 in MeCN. The complex
a radiation.
f
R
and the reference dye were excited at the same wavelength,
maintaining nearly equal absorbance (~0.1), and the emission
spectra were recorded. The area of the emission spectrum was in-
tegrated using the software available in the instrument and the
quantum yield is calculated according to the following equation:
2.6. Computational details
h
.
i
Full geometry optimization was carried out using the density
ꢀ
ꢁ
ꢂ
2
S
2
R
f =f ¼ ½A =A ꢁ ꢂ ðAbsÞ ðAbsÞS ꢂ h
h
S
R
S
R
R
functional theory method at the B3LYP level for the representative
complex 1a [52,53]. All elements except rhodium were assigned the
6-31G(d) basis set. The LANL2DZ basis set with effective core po-
tential was employed for the rhodium atom [54e56]. The vibra-
tional frequency calculation was performed to ensure that the
optimized geometry represents the local minima and there are only
positive eigenvalues. All calculations were performed with
Gaussian09 program package [57] with the aid of the GaussView
visualization program. Vertical electronic excitations based on
B3LYP optimized geometry were computed using the time-
dependent density functional theory (TDDFT) formalism [58e60]
in acetonitrile using conductor-like polarizable continuum model
(CPCM) [61e63]. GaussSum [64] was used to calculate the frac-
tional contributions of various groups to each molecular orbital.
here,
f
S
and
f
R
are the luminescence quantum yield of the sample
and A are the area under the
emission spectra of the sample and the reference respectively,
Abs) and (Abs) are the respective optical densities of the sample
and the reference solution at the wavelength of excitation, and
and are the values of refractive index for the respective solvent
used for the sample and reference.
and reference, respectively. A
S
R
(
S
R
h
S
h
R
The catalytic conversion yields were determined by GC instru-
ment equipped with a flame ionization detector (FID) using a HPe5
column of 30 m length, 0.53 mm diameter and 5.00
thickness. The column, injector and detector temperatures were
mm film
ꢃ
2
00, 250 and 250 C respectively. The carrier gas was N
2
(UHP