Photo-assisted formation of a chelating diphos ligand from PPh3 and a cyclometallated [P(C6H4)(C6H5)]- ligand. Crystal structure of Pd{η2-o-[P(C6H5)2] 2(C6H4)}Br2

Article abstract of DOI:10.1016/S0022-328X(99)00673-7

The cyclometallated palladium compound, Pd[η²-(C₆H₄)P(C₆H ₅)₂]Br[P(C₆H₅)₃] (1), in the solid state by action of light, evolves to give Pd{η₂-0-[P(C₆H₅)₂] ₂(C₆H₄)}Br₂ (2). This compound contains the diphosphine, 0-[P(C₆H₅)]₂(C₆H₄), as chelated ligand that is formed by a couple reaction of the metallated ligand η²-[(C₆H₄)P(C₆H ₅)₂]^- and the coordinated arylphosphine. A study by NMR spectroscopy confirms that the 0-phenylene bridge in the diphosphine ligand in 2 comes from the metallated phosphine ligand in 1.

Full text of DOI:10.1016/S0022-328X(99)00673-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 596 (2000) 248–251
Note
Photo-assisted formation of a chelating diphos ligand from PPh3
and a cyclometallated [P(C6H4)(C6H5)2]− ligand. Crystal structure
of Pd{h2-o-[P(C6H5)2]2(C6H4)}Br2
Francisco Estevan, Abel Garc´ıa-Bernabe´, Pascual Lahuerta *, Mercedes Sanau´,
M. Angeles Ubeda, Jose´ R. Gala´n-Mascaro´s
Departament de Qu´ımica Inorga`nica, Uni6ersitat de Vale`ncia, E-46100 Burjassot, Valencia, Spain
Received 12 August 1999; received in revised form 27 October 1999
Dedicated to Professor F.A. Cotton on his 70th birthday
Abstract
The cyclometallated palladium compound, Pd[h2-(C6H4)P(C6H5)2]Br[P(C6H5)3] (1), in the solid state by action of light, evolves
to give Pd{h2-o-[P(C6H5)2]2(C6H4)}Br2 (2). This compound contains the diphosphine, o-[P(C6H5)2]2(C6H4), as chelated ligand that
is formed by a couple reaction of the metallated ligand h2-[(C6H4)P(C6H5)2]− and the coordinated arylphosphine. A study by
NMR spectroscopy confirms that the o-phenylene bridge in the diphosphine ligand in 2 comes from the metallated phosphine
ligand in 1. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Palladium; Cyclometallation; PꢀC bond breaking
rigidity [3] associated with a sterically congested situa-
tion due to the bulkiness of the auxiliary ligand P,
usually a triarylphosphine. An observation supporting
this interpretation was that compounds of type I with
small-size phosphines as PMe3 or PMe2Ph are not
stable and undergo evolution to form dinuclear species
of type II, {Pd[m-(C6H4)P(C6H5)2]Br[P]}2 (Scheme 1)
[2]. In this transformation the metallated ligand rear-
ranges from chelating to bridging coordination mode.
The reverse process, from bridging to chelating mode,
seems to be very favorable for compounds with bulky
phosphines [1,2].
1. Introduction
In recent papers [1,2] we have described the synthesis
and characterization of new palladium(II) compounds
of general formula cis,trans-Pd[h2-(C6H4)P(C6H5)2]-
Br[P] that contain a metallated phosphine ligand
[(C6H4)P(C6H5)2]−, (PC), forming a four-atom metallo-
cycle (type I in Scheme 1). The stability of these com-
pounds was related to the concept of geometrical
We report in this paper additional results concerning
the reactivity of the cyclometallated compound mixture,
cis,trans-Pd[h2-(C6H4)P(C6H5)2]Br[P(C6H5)3] (1). These
compounds in the solid state slowly form, among other
unidentified species, the compound Pd{h2-o-[P-
(C6H5)2]2(C6H4)}Br2 (2). This reaction, which is pro-
moted by light, involves coupling of the metallated
ligand PC and the coordinated triphenylphosphine.
Scheme 1.
* Corresponding author.
E-mail address: pascual.lahuerta@uv.es (P. Lahuerta)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00673-7

F. Este6an et al. / Journal of Organometallic Chemistry 596 (2000) 248–251
249
reaction mixture a new species named as 2d was iso-
lated. The 31P{1H} spectrum of 2d showed only one
1
signal at 64.1 ppm. The H-NMR spectrum showed the
same four groups of signals at 7.42, 7.50, 7.58 and 7.76
ppm but in this case the relative intensities were 4:2:4:4
The fact that the signal at 7.58 ppm assigned to the
four protons in the bridging o-phenylene group was still
present in 2d supports that this fragment comes from
the metallated phosphine ligand [(C6H4)P(C6H5)2]− and
not from the coordinated triphenylphosphine. Conse-
quently, compound 2d was formulated as Pd[h2-
(C6H5)2P(C6H4)P(C6D5)2]Br2.
Scheme 2.
2. Results and discussion
When the compound Pd[h2-(C6H4)P(C6H5)2]Br[P(p-
CH3C6H4)3] (4) was similarly irradiated, a new com-
pound, 5 was obtained. The 31P{1H}-NMR spectrum
showed a typical AB system (lA=64.3, lB=63.9 ppm,
The cyclometallated compound cis,trans-Pd[h2-
(C6H4)P(C6H5)2]Br[P(C6H5)3] (1) is readily available
from the reaction of the tetranuclear compound {Pd[m2-
(C6H4)P(C6H5)2]Br}4 [1] with stoichiometric amounts of
triphenylphosphine. In solution, this compound is
present as a mixture of cis and trans isomers in equi-
librium. We have observed that 1 in the solid state and
exposed to light slowly changed from pale yellow to an
orange color. Simultaneously in the 31P-NMR spectrum
1
2JPꢀP=16 Hz) and the H- and 13C-NMR spectra con-
firmed the presence of only one type of CH3 in the
molecule. These data confirm that also in the formation
of compound 5, the whole PC ligand was incorporated
to form the bidentate ligand. Consequently compound
5 was formulated as Pd[h2-(C6H5)2P(C6H4)P(p-CH3-
C6H4)2]Br2.
The nature of the other product or products resulting
from this reaction is not clear to us yet. Additional
studies will be performed oriented to investigate this
point and also further mechanistic details of this partic-
ular reaction.
two new doublet signals at 42.6 and 53.4 ppm (JPꢀP%
=
27 Hz) and one new singlet at 64.2 ppm appeared with
increasing intensity. After long irradiation (ca. 5 days)
the evolution was completed and from this reaction
mixture, we were able to isolate single crystals of a
product of formula Pd{h2-o-[P(C6H5)2]2(C6H4)}Br2 (2),
confirmed by X-ray methods. Compound 2 was also
synthesized by reaction of o-[P(C6H5)2]2(C6H4) with
PdCl2 and NaCl; the Pd{h2-o-[P(C6H5)2]2(C6H4)}Cl2
(3) obtained, easily exchanged the halogen ligand by
reaction with Bu4NBr in excess to give 2. The 1H-NMR
spectrum of 2 shows signals centered at 7.42, 7.50, 7.58
and 7.76 ppm of relative intensities 8:4:4:8. From
the COSY spectrum we can assign these signals to
protons of the compound and we observe that the
signal at 7.58 ppm corresponds to four protons of the
o-phenylene bridge and the other three signals are due
to the protons of terminal phenyl rings. Compounds 2
and 3 had been prepared previously from [PdCl4]2−
[4].
2.1. The crystal structure
The structure of 2 (Fig. 1) was determined by X-ray
diffraction, and corresponds to the Pd[h2-(C6H5)2-
We have confirmed that light irradiation is necessary
to produce the chemical reaction of the process. The
formation of 2 is remarkable because it takes place in
the solid state at room temperature and it involves PꢀC
bond cleavage and bond formation as well as extensive
ligand rearrangement (Scheme 2). We have performed
two independent experiments to conclude that the o-
[P(C6H5)2]2(C6H4) ligand is formed by coupling of the
metallated PC group and one ‘P(C6H5)2’ group from
the triphenylphosphine. The first of these experiments
consisted of irradiating the compound Pd[h2-
(C6H4)P(C6H5)2]Br[P(C6D5)3] (1d) in the same condi-
tions already described for 1. From the resulting
Fig. 1. ORTEP drawing of compound Pd{h2-o-[P(C6H5)2]2(C6H4)}Br2.
Selected distances are PdꢀP2=2.213(2), PdꢀP1=2.2366(19), Pdꢀ
Br1=2.4607(10), PdꢀBr2=2.4734(10), P1ꢀC21=1.804(8), P2ꢀC41=
1.800(8) A. Selected angles are P2ꢀPdꢀP1=87.03(7), P2ꢀPdꢀBr1=
176.62(6), P1ꢀPdꢀBr1=89.68(6), P2ꢀPdꢀBr2=88.97(6), P1ꢀPdꢀ
Br2=175.57(6), Br1ꢀPdꢀBr2=94.35(4)°.
,

250
F. Este6an et al. / Journal of Organometallic Chemistry 596 (2000) 248–251
P(C6H4)P(C6H5)2]Br2 compound. The palladium is
bounded to two bromines and two phosphorus atoms
of the diphosphine, (C6H5)2P(C6H4)P(C6H5)2, in a
square planar coordination. The PdꢀP distances are
resulting red–brown solution was filtered and 0.051 g
(0.114 mmol) of o-[P(C6H5)2]2(C6H4) were added, pre-
cipitating a light yellow solid which was filtered after
30 min of stirring. The solid was recrystallized from
a CH2Cl2–ethanol solution giving Pd{h2-o-[P(C6H5)2]2-
(C6H4)}Cl2, (0.064 g, 91% yield). Anal. Calc. for
C30H24Cl2P2Pd: C, 57.76; H, 3.88. Found: C, 57.20;
,
2.237(2) and 2.213(2) A and the PꢀPdꢀP angle,
87.01(7)° has a value between the observed ones in
similar compounds with diphosphines that contain a
central o-phenylene group with ortho substituents,
(83.4(3)–87.79(4)°) [5].
1
H, 3.61%. H-NMR (CDCl3): 7.46 ppm (m, 8H), 7.54
ppm (m, 4H), 7.65 ppm (m, 4H) and 7.80 ppm (dd,
J=11, J=9 Hz, 8H). 31P{1H}-NMR (CDCl3), 64.4
ppm.
3. Experimental
3.1.3. Pd[p2-o-(C6H5)2P(C6H4)P(C6D5)2]Br2 (2d)
All reactions were carried out in an argon atmo-
sphere, using standard Schlenk techniques. PdCl2,
NaCl, o-[P(C6H5)2]2(C6H4), P(C6H5)3, P(C6D5)3 and
P(p-CH3C6H4)3 were purchased from commercial
sources. Solvents were degassed and used without fur-
ther purification. Cis,trans-Pd[h2-(C6H4)P(C6H5)2]Br[P-
A 0.080 g (0.110 mmol) sample of a mixture of
cis,trans-Pd[h2-(C6H4)P(C6H5)2]Br[P(C6D5)3] (1d) was
suspended in 3 ml of CH2Cl2 and the same procedure
described for compound 2 was followed. A 0.034 g
sample of Pd[h2-o-(C6H5)2P(C6H4)P(C6D5)2]Br2 (2d)
1
was obtained (85%). H-NMR (CDCl3): 7.42 ppm (t,
(C6H5)3]
(1),
cis,trans-Pd[h2-(C6H4)P(C6H5)2]Br[P-
J=6 Hz, 4H, H meta to P in phenyl rings), 7.50 ppm
(m, 2H, H para to P in phenyl rings), 7.58 ppm (m, 4H,
o-phenylene bridge) and 7.76 ppm (dd, J=12, J=8
Hz, 4H, H ortho to P in phenyl rings). 31P{1H}-NMR
(CDCl3), 64.2 ppm (pseudotriplet).
(C6D5)3] (1d) and cis,trans-Pd[h2-(C6H4)P(C6H5)2]-
Br [P(p-CH3C6H5)3] (4) were prepared by the literature
procedures [1,2]. Elemental analyses were performed by
Servicio de Microanalisis Elemental, Universidad Com-
plutense de Madrid. NMR spectra were recorded on
Bruker AC-200 and Varian Unity-400 spectrometers.
Chemical shifts (l) are given in ppm, relative to TMS
(1H, 13C), or 85% H3PO4 aqueous solution (31P). Cou-
pling constants (J) are given in Hz.
3.1.4. Pd[p2-o-(C6H5)2P(C6H4)P(p-CH3C6H4)2]Br2 (5)
A 0.095 g (0.126 mmol) sample of a mixture of
cis,trans-Pd[h2-(C6H4)P(C6H5)2]BrP(p-CH3C6H4)3 (4)
was suspended in 3 ml of CH2Cl2 and the same proce-
dure described for compound 2 was followed, giving
0.021 g of Pd[h2-o-(C6H5)2P(C6H4)P(p-CH3C6H4)2]Br2
(45%). Anal. Calc. for C32H28Br2P2Pd: C, 51.89; H,
3.1. Preparation of compounds
3.1.1. Pd{p2-o-[P(C6H5)2]2(C6H4)}Br2 (2)
3.51. Found: C, 51.50; H, 3.51%. H-NMR (CDCl3):
1
A
suspension of 0.150
g
of cis,trans-Pd[h2-
2.36 ppm (CH3, s, 6H), 6.8–8.0 ppm (aromatics, m,
22H). 13C{1H}-NMR (CDCl3): 21.6 ppm (CH3, s),
127–136 ppm (aromatics, m), 143 ppm (aromatics, s).
31P{1H}-NMR (CDCl3): lA=64.2, lB=63.9 ppm
(2JPꢀP%=16 Hz).
(C6H4)P(C6H5)2]Br[P(C6H5)3] (0.211 mmol) in CH2Cl2
extended in a Petri plate was irradiated with light from
an Osram-200 bulb for 5 days. In a few minutes CH2Cl2
was evaporated and during the total process the com-
pound evolved from a pale yellow solid to a brown one.
The brown solid was dissolved in 2 ml of CH2Cl2, and
10 ml of ethyl ether was added. The solution was
maintained at −20°C for 2 days, crystallizing a light
yellow solid that was filtered off and washed with ether
(0.044 g, 59% yield). Anal. Calc. for C30H24Br2P2Pd: C,
3.2. X-ray structure determination
An Enraf–Nonius CAD4 diffractometer was em-
ployed for data collection on compound 2. The struc-
ture was solved by direct methods using the SIR92
program, followed by Fourier synthesis and refined on
F2 for all reflections except for 308 with very negative
1
50.56; H, 3.39. Found: C, 49.87; H, 3.71%. H-NMR
(CDCl3): 7.42 ppm (t, J=6 Hz, 8H, H meta to P in
phenyl rings), 7.50 ppm (m, 4H, H para to P in phenyl
rings), 7.58 ppm (aromatics, m, 4H, o-phenylene
bridge) and 7.76 ppm (dd, J=12, J=8 Hz, 8H, H
ortho to P in phenyl rings). 31P{1H}-NMR (CDCl3),
64.2 ppm.
F2 or flagged for potential systematic errors (SHELXL
-
93). All non-H atoms were refined anisotropically. Yel-
low monocrystals were grown in CH2Cl2–hexane.
Pd[P2C30H24]Br2: crystal size: 0.2×0.25×0.3 mm3,
M=712.65, monoclinic, space group P21/n (c14) with
,
a=9.9307(7), b=15.170(3), c=18.459(2) A, i=
3.1.2. Pd{p2-o-[P(C6H5)2]2(C6H4)}Cl2 (3)
A 0.020 g (0.113 mmol) sample of PdCl2 and 0.014 g
(0.240 mmol) of NaCl were suspended in 5 ml of
ethanol and stirred at room temperature for 12 h. The
97.611(7)°, V=2756.3(7) A and Z=4 (Dcalc=1.717 g
3
,
cm−3
; Mo–Ka radiation u=0.71069 A), giving
,
R(F)=0.058 and Rw(F2)=0.159 by using 4821 ob-
served reflections with I\2|(I).

F. Este6an et al. / Journal of Organometallic Chemistry 596 (2000) 248–251
251
4. Supplementary material
References
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cation.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 133153 for compound 2.
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Acknowledgements
We thank the European Community (EC) for finan-
cial support (Project TMR Network ERBFMRXCT
60091).
.