10.1002/ejic.201900060
European Journal of Inorganic Chemistry
COMMUNICATION
The complex was also characterized by electrospray
ionization time-of-flight mass spectrometry (ESI-TOF MS) (Figure
4). The main signals were identified as follows (m/z): 1311.1725
spectrum of the complex in this solvent, which suggests that all
the PPh3 ligands are equally distributed in an ideal tetrahedron
around the Pd center. Similar spectra were observed in methanol-
d4 (Figure S3), except in the 1H NMR spectrum of Pd(PPh3)4,
where the triplets from the ortho and meta protons overlapped at
ca. 7.35 ppm.
[2Pd+PPh3+3OPPh3+H]+;
677.0973
[Pd+2OPPh3+CH3]+;
631.0924 [M-2PPh3+H]+; 579.1624 [2OPPh3+Na]+; 339.1298
[PPh3+C6H5]+; and 301.0775 [OPPh3+Na]+; where M corresponds
to Pd(PPh3)4 (calc. 1154.2680). These data agree well with data
reported in the literature for palladium complexes with PPh3
ligands.[33-35] All peaks corresponding to fragment ions containing
the metal atom showed the isotopic distribution of Pd.[36]
Particularly, the distribution pattern of the peak centered at
1311.1725 evidenced the presence of 2 Pd atoms in the form of
dinuclear clusters as described elsewhere,[33] while the other
peaks corresponded to monoatomic Pd species. On the other
hand, it is worth to mention the presence of triphenylphosphine
oxide species (OPPh3) after the ionization process, being
associated afterwards with monoatomic Pd units as successfully
deduced from the rest of the peaks found (see Table S1 in SI). All
the peaks were assigned with errors <6.2 ppm.
Further characterization based on attenuated total reflection
(ATR-FTIR) spectroscopy can be found in SI.
Conclusions
In this paper, we present a greener, cheaper, and more
straightforward synthesis of the Pd(PPh3)4 complex than that
previously described in the literature. The method does not use
highly toxic reagents, and gives an excellent yield. Thus, it could
also reasonably be used on a larger scale. This complex is very
widely used in catalysis, so we expect that many groups may use
this procedure for in-house preparation of this catalyst. This would
lead to significant economic savings for the scientific community.
The complex has been fully characterized using different
spectroscopic and spectrometric techniques to demonstrate the
success of this new protocol: UV-Vis characterization allowed us
to calculate the molar extinction coefficient; ATR-FTIR
demonstrated the energy changes of the PPh3 units after the
formation of the metal complex (see the SI); PXRD helped us to
evaluate the stability of the complex after different treatments;
ESI-MS confirmed the molecular weight and Pd isotope
distribution; and 1H, 13C, and 31P NMR spectroscopy were used to
probe the effect of PPh3 coordination on the chemical shifts in
different media.
6x105
5x105
4x105
3x105
1,0x106
8,0x105
6,0x105
4,0x105
2,0x105
0,0
2x105
1x105
0
200 400 600 800 1000 1200 1400
1300
1305
1310
m/z
1315
1320
m/z
2,0x105
1,5x105
1,0x105
1,0x106
8,0x105
6,0x105
4,0x105
5,0x104
2,0x105
0,0
338
0,0
620
339
340
m/z
341
342
640
660
m/z
680
700
Experimental Section
Figure 4. ESI-TOF MS spectrum in the range 200
some amplifications of different regions: 1300
corresponding to the peak [2Pd+PPh3+3OPPh3+H]+); 620
corresponding to the mono-Pd peaks [Pd+2OPPh3+CH3]+ and [M-
2PPh3+H]+); 338 442 (bottom, left, corresponding to the peak [PPh3+C6H5]+).
̶
1400 (m/z) (top, left) and
1320 (top, right,
700 (bottom, right,
̶
Pd(OAc)2 (6.05 g, 27 mmol) and PPh3 (34.73 g, 132 mmol) were
dissolved in anhydrous DMSO (250 mL) in a 500 mL two-necked
round bottom flask. This mixture was stirred under a continuous
Ar flow at 150 °C. On the other hand, ascorbic acid (AA, 17.65 g,
100 mmol) was dissolved in DMSO (50 mL) under sonication and
then added via syringe to the previous mixture. Stirring and
heating were stopped after 15 min and crystallization started at
70 °C. After reaching room temperature, crystals were rapidly
filtered, under argon, in a sintered glass filter (nº 4), washed with
EtOH (×3) and Et2O (×3) until no color was observed in the filtrate.
The yellow crystals obtained (25.88 g; 83% yield) were dried
under vacuum overnight, protected from light with aluminum foil,
and stored afterwards at 4 °C. Elemental analysis confirmed the
composition of the complex: 73.08% C, 4.90% H, 10.12% P and
8.61% Pd (calc.: 74.84% C, 5.23% H, 10.72% P and 9.21% Pd).
̶
̶
Note the presence of the isotopic distribution pattern of Pd with the exception
of the last signal (339.1298).
Finally, 1H, 13C, and 31P nuclear magnetic resonance (NMR)
spectra were acquired in different solvents to fully characterize
the synthesized complex.[37] CDCl3 is not the best deuterated
solvent to use to assign the structure of this complex, at least at
room temperature, as decomposition of the metal complex seem
to occur. Protic polar solvents seem to be more convenient for the
1
characterization, allowing the integration of the signals in the H
NMR spectra. In 1H NMR spectrum of PPh3 in DMSO-d6 (Figure
5), signals due to the meta and para protons appear together at
7.39 ppm, while the ortho protons can be identified at 7.24 ppm.
In the 31P NMR spectrum, PPh3 can be observed at –7 ppm. For
Pd(PPh3)4, three triplets were observed in the 1H NMR spectrum
corresponding to the ortho, meta, and –para protons at 7.24, 7.31,
and 7.42 ppm, respectively. Three signals were observed in this
case for the Pd(PPh3)4 complex in the 13C NMR spectrum at 128,
131, and 133 ppm,[38] as well as a single peak at 33 ppm in the
31P NMR spectrum. No other broad signals were seen in the
Supporting Information (see footnote on the first page of this article):
detailed characterization and spectra of all compounds reported in the
manuscript can be found in the Supporting Information.
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