A. Garypidou et al.
Inorganica Chimica Acta 518 (2021) 120254
attenuation constant for all samples. The pulse gradients (G) were
incremented from 5% to 95% of the maximum gradient strength and
were varied in 32 steps in a linear ramp. The time domain of all spectra is
32 K at t2 dimension and 32 increments at t1.
300 mg (0.5 mmol) of [Pd(ppy)(
μ
-Cl)]2, a solution (5 mL) of 232 mg
(1.1 mmol) 2,9-dimethyl-1,10-phenanthroline (ncp) in CH2Cl2 was
added. Upon addition, the color changed to dark yellow. The reaction
mixture was kept at room temperature for 24 h and then evaporated to
dryness under reduced pressure. The crude product was washed several
times with diethyl ether, dissolved in 2 mL of CH2Cl2 and allowed in
slow diffusion with vapors of diethyl ether. After a few days, light-
orange crystals appeared which were collected with filtration, washed
with diethyl ether (2 × 5 mL) and dried in vacuum over CaCl2. Yield:
61%. Anal. for C25H20ClN3Pd (cal.): C : 59.54% ; H : 4,00% ; N : 8,33%;
(found): C : 59.52%; H : 4.05%; N : 8.36%. HR-ESI-MS, positive (m/z):
found 468.0685, calc. 468.0687 for [C25H20N1306Pd]+. 1H NMR (500
MHz, 298 K, acetone‑d6, δ in ppm): ppyH6′, 9.83 (d, 1H); ncpH4H7, 8.50
(d, 2H); ppyH4′, 8.06 (t, 1H); ncpH5H6, 8.03 (s, 2H); ppyH3′, 7.98 (d,
1H); ncpH3H8, 7.80 (d, 2H); ppyH5′, 7.38 (t, 1H); ppyH5, 6.88 (t, 1H);
ppyH4, 6.52 (t, 1H); ppyH3, 5.60 (d,1H); ncpCH3, 3.12 (s, 6H).
The diffusion dimension was processed with Bruker Dynamics Center
software. The measured signal is the integral over the whole sample
volume and the NMR signal intensity is attenuated depending on the Δ, δ
and G values. This intensity change is described by the following
equation:
2g2δ2(Δꢀ δ)
I = I0eꢀ y
3
where I is the observed intensity, I0 the reference intensity (unten-
anted signal intensity), D the diffusion coefficient, γ the gyromagnetic
ratio of the observed nucleus, g the gradient strength, δ the length of the
gradient, and Δ the diffusion time.
According to the Stokes-Einstein equation [38], the diffusion coef-
ficient D and the hydrodynamic radius (rh) of a molecule are inversely
proportional.
[Pd(ppy)(bcp)Cl] (2): To a 25 mL solution of CH2Cl2 containing
300 mg (0.5 mmol) [Pd(ppy)(μ-Cl)]2, 401 mg (1.1 mmol) 2,9-dimethyl-
4,7-diphenyl-1,10-phenanthroline (bcp) dissolved in 10 mL CH2Cl2 was
added. After the addition the color of the solution turned from yellow to
dark orange. The reaction mixture was kept at room temperature for 24
h and then evaporated to dryness under reduced pressure forming an
orange solid. The product was washed several times with isopropyl
ether. Yield: 59%. Anal. for C37H28ClN3Pd (cal.): C : 67.69% ; H : 4.30% ;
N : 6.40%. (found): C : 67.78%; H : 4.27%; N : 6.34%. HR-ESI-MS,
positive (m/z): found 620.1323, calc. 620.1313 for [C37H28N1306Pd]+.
1H NMR (500 MHz, 298 K, acetone‑d6, δ in ppm) : ppyH6′, 9.89 (d, 1H);
ppyH4′, 8.08 (t, 1H); ppyH3′, 8.02 (d, 1H); bcpH5H6, 7.92 (s, 2H);
bcpH3H8, 7.76 (s, 2H); ppyH6, 7.66 (d, 1H); bcpHaHbHc, 7.63 (m,
10H); ppyH5′, 7.41 (t, 1H); ppyH5, 6.93 (t, 1H); ppyH4, 6.59 (t, 1H);
ppyH3, 5.83 (d, 1H); bcpCH3, 3.20 (s, 6H).
2.3. X-ray crystallography
Suitable single crystals covered with paratone-N oil were attached to
Hampton cryoloops and transferred to the goniometer head. X-ray
diffraction data were collected (ω-scans) with an Oxford Diffraction
Xcalibur-3 diffractometer using Cu Kα radiation (λ = 1.54184 Å). Data
were collected and processed by using the CRYSALIS CCD and RED
software [39] respectively. Empirical absorption corrections (multiscan
based on symmetry related measurements) were applied using CrysAlis
RED software. The structures were solved by direct methods using
SIR2014 [40] and refined on F2 using full-matrix least-squares with the
latest version of SHELXL [41]. All non-H atoms were refined aniso-
tropically and carbon-bound H-atoms were introduced at calculated
positions and allowed to ride on their parent atoms. Water hydrogen
atoms in (3) were located from difference Fourier maps and refined
isotropically using Shelx restraints. The refinement of the structure of
(4) was not without problems due to severe disordering of one of the
ligands and special details can be found in the deposited CIF file in
addition to full structural details. Geometric/crystallographic calcula-
tions were carried out using PLATON [42] and WINGX [43] packages;
graphics were prepared with X-Seed [44]. Details of X-Ray diffraction
data and refinement are presented in Table S1. CCDC 1972794,
1972495, 1972496 and 2012800 contain the supplementary crystallo-
graphic data for (1), (3) (4) and (8), respectively. These data can be
obtained free of charge from the Cambridge Crystallographic Data
[Pd(ppy)(ncp)Н O]PF6⋅0.5(CH3CH2)O (3): In 20 mL of acetone,
50 mg (0.1 mmol) of2(1) was dissolved and a solution containing 25 mg
(0.1 mmol) of AgPF6 in 2 mL of the same solvent was added dropwise.
Immediately a white precipitate was formed which was removed with
centrifugation. Afterwards, 2 mL of H2O was added to the remaining
clear solution and the mixture was kept at 6 ◦C. After overnight cooling,
a yellow precipitate appeared which was filtered off, washed with
diethyl ether and re-dissolved in 2 mL of acetone. Addition of diethyl
ether, by slow vapor diffusion, formed bright yellow crystals which were
collected, washed with diethyl ether (2 × 5 mL) and dried in vacuum
over CaCl2. Yield: 50%. Anal. for C27H27O2N3Pd (cal.): C : 60.96% ; H :
5.12% ; N : 7.90%; (found): C : 60.98%; H : 5.14%; N : 7.86%. HR-ESI-
MS, positive (m/z): found 468.0685, calc. 468.0687 for
[C25H20N3106Pd]+. 1H NMR (500 MHz, 298 K, acetone‑d6, δ in ppm):
ppyH6′, 8.90 (d, 1H); ncpH4H7, 8.67 (d, 2H); ppyH4′, 8.21 (t, 1H);
ncpH5H6, 8.14 (s, 2H); ppyH3′, 8.13 (d, 1H); ncpH3H8, 7.95 (d, 2H);
ppyH6, 7.63 (d, 1H); ppyH5′, 7.55 (t, 1H); ppyH5, 6.98 (t, 1H); ppyH4,
6.58 (d,1H); ppyH3, 5.45 (d,1H); ncpCH3, 3.21 (s, 6H).
2.4. Hydroxylation of 2-phenylpyridine
The conditions of the hydroxylation reaction were optimized as
following: temperature was 120 ◦C, reaction time was 12 h and each
complex was about 0.20 eq of 2-ppy.
{[Pd(ppy)(ncp)]2(
μ-Cl)}PF6 (4): 300 mg (0.5 mmol) of [Pd(ppy)
(
μ-Cl)]2 was dissolved in 25 mL of CH2Cl2 and a solution containing 232
mg (1.1 mmol) of 2,9-dimethyl-1,10-phenanthroline (ncp) was added.
After a few minutes a solution of 326 mg (2 mmol) of NH4PF6 in 10 mL
CH2Cl2 was added. The reaction mixture was stirred at room tempera-
ture for 24 h, filtered off from the unreacted materials and evaporated to
dryness under reduced pressure. The crude product was washed several
times with water, dried and dissolved in 3 mL of CH2Cl2. After the slow
diffusion of diethyl ether vapors, light orange crystals precipitated
which were collected with filtration, washed with diethyl ether (2 × 5
In a typical experiment 25 μL (0.17 mmol) of 2-phenylpyridine, 0.75
mL of N-methyl-2-pyrrolidone (NMP) and 0.034 mmol complex (16–20
mg) were added to an open vial. The mixture was heated at 120 ◦C for
12 h and cooled at room temperature, while a microcrystalline precip-
itate was formed. An aliquot of 150
μL of the remaining solution was
added to an NMR tube containing 500
μ
L of aceton-d6. The 1H NMR
spectrum of the sample shows two different set of peaks corresponding
to 2-phenyl-pyridine and the hydroxylation product, 2-(pyridin-2-yl)
phenol (ppy-OH). The percentage of ppy-OH was determined from the
integrals of selected 1H NMR peaks.
mL) and dried in vacuum over CaCl2. Yield
: 61%. Anal. for
C
50H40ClF6N6PPd2 (cal.): C : 53.71% ; H : 3.61% ; N : 7.52%; (found): C :
53.78%; H : 3.58%; N : 7.48%. HR-ESI-MS, positive (m/z): found
468.0685, calc. 468.0687 for [C25H20N1306Pd]+; found, 973.1055, calc.
973.1071 for[C50H40ClN6Pd]+. ΛМ(acetone) = 173 S cm2 molꢀ 1 . 1H NMR
(500 MHz, 298 K, acetone‑d6, δ in ppm): ppyH6′, 9.27 (d, 1H); ncpH4H7,
8.43 (d, 2H); ppyH4′, 8.11 (t, 1H); ppyH3′, 8.03 (d, 1H); ncpH5H6, 7.97
2.5. Synthesis of the complexes
[Pd(ppy)(ncp)Cl] (1): To a solution of CH2Cl2 (10 mL) containing
3