Synthesis of diphenylphosphine palladium complexes

Article abstract of DOI:10.1016/S0020-1693(98)00269-2

The synthesis of Pd(PPh₂H)₂Cl₂ is achieved by reaction of Pd(PhCN)₂Cl₂ with PPh₂H in toluene at room temperature. Pd(PPh₂H)₂Cl₂ spontaneously transforms int

Full text of DOI:10.1016/S0020-1693(98)00269-2

Inorganica Chimica Acta 284 (1999) 116±118
Note
Synthesis of diphenylphosphine palladium complexes
Roberto Giannandrea, Piero Mastrorilli, Cosimo Francesco Nobile*
Istituto di Chimica del Politecnico and Centro C.N.R. M.I.S.O., trav. 200 Re David, 4 I-70126 Bari, Italy
Received 2 May 1998
Abstract
The synthesis of Pd(PPh2H)2Cl2 is achieved by reaction of Pd(PhCN)2Cl2 with PPh2H in toluene at room temperature. Pd(PPh2H)2Cl2
spontaneously transforms into [PdCl(m-PPh2)(PPh2H)]2 when let in solution and affords Pd(PPh2H)4 when treated with two equivalents of
PPh2H in ethanol. # 1999 Elsevier Science S.A. All rights reserved.
Keywords: Diphenylphosphine complexes; Dinuclear complexes; Palladium complexes
1. Introduction
group metals we here describe the synthesis, the character-
isation and the reactivity of PdCl2(PPh2H)2 (5).
The reaction of palladium salts with diphenylphosphine
has been described for the ®rst time by Issleib and Wenschuh
[1] who suggested, on the basis of elemental analyses and of
molecular weight measurements, complex 1 as the only
product.
2. Experimental
2.1. Materials and apparatus
All manipulations were carried out under a pure dinitro-
gen atmosphere, using freshly distilled and oxygen-free
solvents.
Diphenylphosphine was purchased from Strem. Samples
for melting point determinations were sealed in capillary
tubes under nitrogen. IR spectra were recorded on a Perkin
Elmer 883 spectrometer. The UV±Vis spectra in solution
were recorded on a Kontron Uvikon 942 spectrophotometer.
Elemental analyses were carried out by using a Carlo Erba
Elemental analyser mod. EA 1108. The NMR spectra were
recorded on a Varian XL200 or on a Bruker AM400 spectro-
meter at 297 K, 31P shifts being measured with respect to
external 85% H3PO4. Simulated NMR spectra were calcu-
lated using the WINDAISY program. GC/MS analyses of
the reaction solutions were performed using a HP 5890
chromatograph (30 m SE30 column) coupled with a mass
selective detector HP 5970B, 70 eV.
Further studies conducted by Hayter, showed that, depend-
ing on reaction conditions, PdCl2 or Na2PdCl4 react with
PPh2H to form two different complexes, 2 and 3 [2].
Complex 2 was the same compound described as 1 by
Issleib and reformulated as phosphido-bridged (instead that
chloro-bridged) by Hayter. Complex 3 was successively
recognised as the zerovalent Pd(PPh2H)4 species 4 [3].
From both studies stems the conclusion that
PdCl2(PPh2H)2 is unstable and not isolable at the purity
state. In the paper of Hayter, however, there is a mention to
an unstable intermediate complex whose colour and decom-
position behaviour indicate as PdCl2(PPh2H)2. In the course
of our studies on secondary phosphine complexes of VIII
2.2. Dichlorobis(diphenylphosphino)palladium(II) (5)
2.2.1. From PdCl2(PhCN)2
A toluene solution of PPh2H (1.94 g, 10.4 mmol in 10 ml)
was added dropwise to a toluene solution of PdCl2(PhCN)2
(2.0 g, 5.2 mmol in 30 ml) under stirring. The stirring was
*Corresponding author. Tel.: +39-80-5460608; fax: +39-80-5460611.
0020-1693/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(98)00269-2

R. Giannandrea et al. / Inorganica Chimica Acta 284 (1999) 116±118
117
prolonged for about 2 h at room temperature causing the
precipitation of a yellow solid which was ®ltered, washed
with toluene and dried under vacuum. (2.8 g, yield 98%).
The compound is air stable in the solid state but sensitive
in solution, soluble in CH2Cl2 and slightly soluble in
aromatic solvents. Anal. calc. for C24H22Cl2P2Pd: C, 52.44;
H, 4.03; P, 11.27; Cl, 12.9; Pd, 19.36. Found: C, 52.12; H,
4.10; P, 11.12; Cl, 12.7; Pd, 19.30%. M.p. ˆ 1908C
(decompn).
in 6 ml) causing the immediate formation of a red±brown
solution that slowly lightened. After 1 day, the reaction
solution became pale yellow and a grey±orange solid
formed which was isolated by ®ltration, washed with etha-
nol and dried under vacuum.
UV±Vis (dichloromethane, 3.9 Â 10 5 mol dm 3): ꢀmax
(nm) ˆ 230 (ꢁ (dm3 mol 1 cm 1) ˆ 47 400), 330 (sh), 390
(8900), 520 (4050).
IR (nujol mull): ꢂmax (cm 1) ˆ 2267 (m, PH stretching),
1580 (vs), 1568 (s), 1431 (vs), 1376 (s), 1304 (s), 1175 (s),
1155 (s), 1090 (vs), 1065 (s), 1024 (s), 999 (s), 930 (s), 911
(vs), 898 (vs), 852 (m), 823 (vs), 745 (vs), 730 (vs), 694 (vs),
497 (vs), 459 (s), 428 (s), 409 (vs), 305 (m). ꢃ 31PfHg in
CD2Cl2: 18.1 (s); ꢃ 1H in CD2Cl2: 5.65 (d, JPH ˆ 285 Hz,
4H), 7.0±7.8 (m, 40H).
UV±Vis (dichloromethane, 1.4 Â 10 5 mol dm 3): ꢀmax
(nm) ˆ 228 (ꢁ (dm3 mol 1 cm 1) ˆ 79 500), 267 (53 000),
333 (13 500). IR (nujol mull): ꢂmax (cm 1) ˆ 2345 (m, PH
stretching), 1480 (vs), 1458 (vs), 1434 (vs), 1376 (s), 1332
(m), 1101 (vs), 1068 (s), 1026 (s), 996 (vs), 739 (vs), 689
(vs), 502 (vs), 472 (s), 453 (s), 288 (s). ꢃ 31P{H} in CDCl3:
1
7.41 (s). ꢃ H in CDCl3: 6.13 (d, JPHˆ404 Hz, 2H), 7.05±
7.80 (m, 20H).
3. Results and discussion
2.2.2. From H2PdCl4
PdCl2 (0.39 g, 2.2 mmol) was dissolved in HCl 37%
(7.0 ml) and the resulting dark red solution was diluted
with 10 ml of ethanol. To this solution, 8.0 ml of an ethanol
solution containing 0.82 g of PPh2H (4.4 mmol) was added,
causing the precipitation of a yellow solid which was
®ltered, washed with water and dried under vacuum
(obtained 1.1 g, yield 91%).
The idea followed to succeed in isolating PdCl2(PPh2H)2
was to avoid to carry out the synthesis at temperature higher
than room temperature (r.t.) or in protic solvents. Therefore,
a toluene solution of PdCl2(PhCN)2 was added to a toluene
solution of PPh2H at r.t. affording immediately a yellow
solid insoluble in aromatic solvents whose elemental ana-
lysis and spectroscopic features indicate it as PdCl2-
(PPh2H)2. The complex is yellow, soluble in halogenated
solvents, inde®nitely stable in the solid state but slowly
decomposes in solution. Its proton decoupled 31P NMR
spectrum consists of a singlet at 7.5 ppm, whereas the
coupled spectrum gives a doublet centred at 7.5 ppm with
2.3. Trans-dichlorobis(ꢄ-diphenylphosphide)
bis(diphenylphosphine)dipalladium(II) (2)
PdCl2(PPh2H)2 (200 mg, 0.36 mmol) was suspended in
8 ml of ethanol under vigorous stirring. After 5 h the solvent
was evaporated and the residue was dissolved in 8 ml of
fresh ethanol. This operation was repeated three times until
the ethanol phase resulted neutral at the litmus paper test.
After the last evaporation 5 ml of water was added to the
residue affording a pale orange solid, which was ®ltered,
washed with water, and dried under vacuum (obtained
175 mg, yield 95%).
1
JPH of 420 Hz. The resonance of the P±H in the H NMR
spectrum falls at 6.13 ppm and shows the expected coupling
constant with the phosphorus atom. The electronic spectrum
(see Section 2) is consistent with a monomeric square
planar structure, common in this kind of complexes.
The immediate precipitation of PdCl2(PPh2H)2 from the
reaction medium is observed also when PPh2H is added to
PdCl2 solution in ethanol/HCl 1.
When a CD2Cl2 solution of PdCl2(PPh2H)2 was left to
stand overnight, the initially clean 31P NMR spectrum
became complicated for the presence of new peaks in the
region of coordinated phosphines and of bridging phos-
phides substantiating the formation of the dimeric species
trans-[PdCl(m-PPh2)(PPh2H)]2 (2). Spectrum simulation
gave the parameters reported in the experimental part.
The high ®eld resonance of the bridging diphenylpho-
sphides (ꢃ ˆ 132.7 ppm) rules out the presence of a
Pd±Pd bond [4] whereas the appearance of an AA0XX0
UV±Vis (dichloromethane, 1.1 Â 10 5 mol dm 3): ꢀmax
(nm) ˆ 229 (ꢁ (dm3 mol 1 cm 1) ˆ 73 500), 327 (26 300),
377 (sh).
IR (nujol mull): ꢂmax (cm 1) ˆ 2348 (m, PH stretching),
1582 (m), 1571 (m), 1376 (s), 1307 (m), 1184 (m), 1160 (m),
1095 (s), 1069 (m), 1026 (s), 1998 (s), 1907 (s), 848 (vs),
739 (vs), 690 (vs), 503 (vs), 462 (vs), 410 (s), 288 (s).
ꢃ
31P{H} in CDCl3: 2.8 (m, terminal phosphines),
0
0
132.7 (m, bridging phosphides); JAX ˆ JA X ˆ 423.8 Hz;
0
0
0
0
JAX ˆ JA X ˆ 26.0 Hz; JXX ˆ 262.0 Hz; JAA
ˆ
3.0 Hz.
ꢃ 1H in CDCl3: 4.98 (dm, JPHˆ356 Hz, 2H), 7.00±7.80 (m,
40H).
1 Hayter reported in Ref. 2 [PdCl(m-PPh2)(PPh2H)]2 as the only product
of the reaction of H2PdCl4 with two equivalents PPh2H after crystal-
lisation from ethanol. Our study demonstrates that the dinuclear complex
[PdCl(m-PPh2)(PPh2H)]2 found by Hayter after crystallisation derives
from reaction of the initially formed PdCl2(PPh2H)2 when dissolved in
ethanol.
2.4. Tetrakis(diphenylphosphine)palladium(0) (4)
Diphenylphosphine (298 mg, 1.6 mmol) was added to an
ethanol suspension of PdCl2(PPh2H)2 (180 mg, 0.33 mmol

118
R. Giannandrea et al. / Inorganica Chimica Acta 284 (1999) 116±118
with HCl (acidimetric and argentimetric analysis) and
diphenylphosphineoxide (GC/MS analysis). The solid
was characterised as Pd(PPh2H)4 (4) and its formation
can be accounted for as the result of a redox process between
the palladium and the free phosphine according to Eq. (2):
PdCl2ꢀPPh2H† ‡ 3PPh2H ‡ H2O
2
! PdꢀPPh2H† ‡ 2HCl ‡ OPPh2H
(2)
4
The behaviour of PdCl2±diphenylphosphine complexes is
summarised in Scheme 1.
Scheme 1.
spectrum (instead of an ABX2 one) substantiates the trans-
geometry. The transformation of 5 into 2 (Eq. (1)) occurs
with concomitant evolution of HCl every time the mono-
meric complex 5 is dissolved in the organic solvents, the rate
of the reaction increasing with the polarity of the medium.
The synthesis of 2 can thus be achieved in quantitative yield
by repeated cycles of dissolution of 5 in ethanol and
evaporation under vacuum of the resulting solution contain-
ing HCl.
Acknowledgements
We thank the Italian CNR and MURST for ®nancial
support.
References
[1] K. Issleib, E. Wenschuh, Z. Anorg. Allg. Chem. 305 (1960)
15.
2PdCl2ꢀPPh2H†2!ꢀtrans-‰PdClꢀm-PPh2†ꢀPPh2H†Š ‡2HCl
(1)
2
[2] R.G. Hayter, J. Am. Chem. Soc. 84 (1962) 3046.
[3] C.W. Weston, G.W. Bailey, J.H. Nelson, H.B. Jonassen, J. Inorg.
Nucl. Chem. 34 (1972) 1752.
The reaction of 5 with excess diphenylphosphine in ethanol
gave rise to a slow formation of a grey±orange solid along
[4] K.R. Dixon, A.D. Rattray, Inorg. Chem. 5 (1978) 1099.