Synthesis and X-ray crystallographic characterization of (μ-(diphenylphosphino)phenyl-C2,P)palladium bromide. A novel tetranuclear metalated compound

Full text of DOI:10.1021/ic9702734

6472
Inorg. Chem. 1997, 36, 6472-6475
was refluxed for 10 min, giving a yellow-green solid and a yellow
Synthesis and X-ray Crystallographic
Characterization of
solution. After the solution was cooled, the solid was separated by
filtration and dissolved in a minimum amount of dichloromethane,
giving a yellow solution and a black residue, which was discarded.
Addition of acetone to the filtered solution resulted in the formation
of 1, a yellow powder, which was washed with acetone and dried in
vacuo (0.173 g, 0.097 mmol, 73% yield). Anal. Calcd for C72H56-
Br4P4Pd4: C, 48.30; H, 3.15. Found: C, 48.13; H, 2.04. 31P{1H} NMR
(CDCl3): δ 26.74 ppm.
[Pd{P(C6H4)(C6H5)2}Br(PCBr)] (2). To a suspension of 0.300 g
of Pd(dba)2 (0.52 mmol) in toluene (3 mL) was added PCBr (0.360 g,
1.05 mmol). The mixture was stirred at room temperature for 45 min.
During this time, a dark brown solution was formed, which was refluxed
for 10 min. The resulting yellow solution was filtered and evaporated
to dryness. The residue was extracted twice with 5 mL of acetone,
and the extracts were evaporated to dryness. Crystallization of the
residue from a dichloromethane-ethyl ether mixture gave pale yellow
crystals that were washed with ethyl ether and dried in vacuo, resulting
in the formation of 0.219 g of 2 as a cis/trans mixture of isomers (0.28
mmol, 53% yield). Anal. Calcd for C36H28Br2P2Pd: C, 54.82; H, 3.58.
Found: C, 55.56; H 3.56. 31P{1H} NMR (CDCl3): cis isomer δ 19.85
(Pa), -81.74 (Pb) ppm (2JP-P ) 12 Hz); trans isomer δ 26.73 (Pa),
-88.43 (Pb) ppm (2JP-P ) 460 Hz). Cis/trans ratio ) 0.80 from
integration of the signals in the 31P NMR spectrum.
Reaction of 2 and Pd(dba)2. To a solution of 0.150 g of 2 (0.20
mmol) in toluene (3 mL) was added Pd(dba)2 (0.109 g, 0.19 mmol).
The mixture was stirred at room temperature for 45 min and refluxed
for 10 min, giving a yellow solution and a dark solid. Further
crystallization of this solid from CH2Cl2-acetone gave 1 in the pure
form (0.080 g, 0.045 mmol, 48% yield).
Thermal Reaction of 2 in Toluene. A 0.100 g sample of 2 (0.13
mmol) (mixture of cis and trans isomers), dissolved in 5 mL of toluene,
was heated at 100 °C for 1 h. The 31P NMR spectrum of the solution
confirmed the presence of a substantial amount of free PCBr. The
solution was evaporated to dryness, and the residue was crystallized
from dichloromethane-acetone mixture, yielding 1 (0.022 g, 0.012
mmol, 37% yield).
(µ-(Diphenylphosphino)phenyl-C2,P)palladium
Bromide. A Novel Tetranuclear Metalated
Compound
Atta M. Aarif,† Francisco Estevan,‡
Abel Garc´ıa-Bernabe´,‡ Pascual Lahuerta,*,†,‡
Mercedes Sanau´,†,‡ and M. Angeles Ubeda‡
Department of Chemistry, University of Utah,
Salt Lake City, Utah 84112, and Departamento de
Qu´ımica Inorga´nica, Universitat de Vale`ncia,
46100 Burjassot-Valencia, Spain
ReceiVed March 6, 1997
Introduction
Transition metal compounds with bridging metalated ligands
are often restricted to compounds with metal-metal bonds.1
There are some examples of binuclear platinum(II) complexes
containing bridging o-C6H4PPh2 or o-C6H4P(Ph)CH2CH2P(Ph)2
ligands in which there is no formal metal-metal bond.2 Even
though a large number of cyclometalated palladium compounds
have been reported, palladium compounds with bridging meta-
lated phosphines are rare.3a,b A recent publication reports a
tetranuclear palladium(II) species with a metalated 2-[N-(1-
naphthylmethylidene)amino]benzenethiolate ligand (C,N,S). In
this compound, the Pd(C,N,S) fragments resulting from meta-
lation of the pendant side arm are bridged by the sulfur atoms.3c
We describe here the ability of a metalated ligand, [P(C6H4)Ph2]-
(PC), to exhibit chelating and bridging coordination modes in
a quite reversible way. We also describe the preparation and
characterization of a tetranuclear metalated palladium compound
with interesting structural features.
Another 0.100 g sample of 2 (0.13 mmol) and 0.015 g of PCBr
(0.03 mmol), dissolved in 5 mL of toluene, were treated as described
above, yielding 1 (0.008 g, 0.004 mmol, 12% yield).
Synthesis of Compounds Pd{P(C6H4)(C6H5)2}Br(PR3). PR3 )
PPh3. To a suspension of 0.050 g (0.028 mmol) of 1, in 15 mL of
degassed CH2Cl2, was added 0.029 g (0.111 mmol) of PPh3. The
mixture changed from yellow to a pale yellow solution after 10 min.
The resulting solution was stirred at room temperature for 30 min and
evaporated to dryness. Crystallization of the residue from a 1:2 CH2-
Cl2-hexane mixture gave a pale yellow crystalline mixture of cis/trans-
Pd{P(C6H4)(C6H5)2}Br(PPh3) isomers 3 (0.067 g, 85% yield). Anal.
Calcd for C36H29BrP2Pd‚1/4CH2Cl2: C, 59.55; H, 4.07. Found: C,
59.33; H, 3.28. 1H NMR (CDCl3): δ 6.3 (aromatics, t, J ) 8 Hz), 6.8
(aromatics, t, J ) 7 Hz), 6.9-7.6 (aromatics, m), 7.7 (aromatics, t, J
) 8 Hz) and 8.0 (aromatics, dd, J ) 12 Hz, J ) 7 Hz), 5.3 ppm (CH2-
Cl2). 31P{1H} NMR (CDCl3): cis isomer δ 16.0 (Pa), -79.8 (Pb) ppm
Experimental Section
All reactions were carried out in argon atmosphere, using standard
Schlenk techniques. P(o-BrC6H4)Ph2 (PCBr) was purchased from
commercial sources (Organometallics). Solvents were degassed and
used without further purification. Pd(dba)2 [dba ) (C6H5)CHdCHsC-
(O)sCHdCH(C6H5)] was prepared by the literature procedure.4
Elemental analyses were performed by ICMA, University of Zaragoza.
NMR spectra were recorded in Bruker AC-200 and Varian Unity-400
spectrometers.
Preparation of Compounds. [Pd{P(C6H4)(C6H5)2}Br]4 (1). To
a suspension of 0.300 g of Pd(dba)2 (0.52 mmol) in toluene (3 mL)
was added PCBr (0.180 g, 0.52 mmol). The mixture was stirred at
room temperature for 45 min, and the resulting dark brown solution
(2JP-P ) 16 Hz); trans isomer δ 30.9 (Pa), -85.8 (Pb) ppm (2JP-P
462 Hz). Cis/trans ratio )0.30.
)
PR3 ) PCy3. To a suspension of 0.040 g of 1 (0.022 mmol) in 5
mL of CH2Cl2 was added PCy3 (0.025 g, 0.089 mmol). The mixture
was stirred at room temperature for 30 min, and the resulting pale
yellow solution was evaporated to dryness. Crystallization of the
residue from a CH2Cl2-hexane mixture gave a pale yellow compound,
trans-Pd{P(C6H4)(C6H5)2}Br(PCy3) (4) (0.051 g, 79% yield). Anal.
Calcd for C36H47BrP2Pd: C, 59.39; H, 6.51. Found: C, 59.41; H, 6.87.
1H NMR (CDCl3): δ 1.30 (cyclohexyl, m, 9H), 1.64 (cyclohexyl, d, J
) 12 Hz, 6H), 1.71 (cyclohexyl, d, J ) 12 Hz, 3H), 1.80 (cyclohexyl,
d, J ) 10 Hz, 6H), 2.05 (cyclohexyl, d, J ) 10 Hz, 6H), 2.52
(cyclohexyl, d, J ) 14 Hz, 3H), 7.20 (aromatics, m, 2H), 7.26
(aromatics, m, 2H), 7.41 (aromatics, m, 6H), 7.92 ppm (aromatics, dd,
J ) 11 Hz, J ) 8 Hz, 4H). 13C{1H} NMR: 26.43 (cyclohexyl, s),
27.63 (cyclohexyl, d, JC-P ) 10 Hz), 30.25 (cyclohexyl, s), 32.88
(cyclohexyl, d, JC-P ) 17 Hz), 125.47 (aromatics, d, JC-P ) 8 Hz),
128.69 (aromatics, dd, JC-P) 10 Hz, JC-P ) 5 Hz), 129.73 (aromatics,
† University of Utah.
‡ Universitat de Vale`ncia.
(1) Cotton, F. A.; Walton, R. A. Multiple Bonds between Metal Atoms;
Clarendon Press: Oxford, 1993.
(2) (a) Arnold, D. P.; Bennet, M. A.; McLaughlin, G. M.; Robertson, G.
B.; Whittaker, M. J. J. Chem. Soc., Chem. Commun. 1983, 32. (b)
Bennet, M. A.; Berry, D. E.; Bhargava, S. K.; Ditzel, E.; Robertson,
G. B.; Willis, A. C. J. Chem. Soc., Chem. Commun. 1987, 1613. (c)
Bennett, M. A.; Bhargava, S. K.; Griffiths, K. D.; Robertson, G. B.;
Wickramasinghe, W. A.; Willis, A. C. Angew. Chem., Int. Ed. Engl.
1987, 26, 258.
(3) (a) Braunstein, P.; Matt, D.; Dusausoy, Y.; Fischer, J.; Mitschler, A.;
Ricard, L. J. Am. Chem. Soc. 1981, 103, 5115. (b) Braunstein, P.;
Fisher, J.; Matt, D.; Pfeffer, M. J. Am. Chem. Soc. 1984, 106, 410.
(c) Kawamoto, T.; Nagasawa, I.; Kuma, H.; Kushi, Y. Inorg.Chem.
1996, 35, 2427.
(4) Rettig, M. F.; Maitlis, P. M. Inorg. Synth. 1977, 17, 134.
S0020-1669(97)00273-5 CCC: $14.00 © 1997 American Chemical Society

Notes
Inorganic Chemistry, Vol. 36, No. 27, 1997 6473
Table 1. Crystallographic Data for [Pd{P(C6H4)(C6H5)2}Br]4
formula: C72H56Br4P4Pd4
fw: 1790.38
Dcalcd ) 1.804 g cm-3
T ) 289 K
space group: Fddd
cell dimensions (16 °C):
a ) 18.195(2) Å
b ) 20.873(3) Å
c ) 34.712(7) Å
V ) 13183.20 Å3
Z ) 8
diffractometer: CAD4
radiation: Mo KR (0.717 03 Å)
µ(Mo KR) ) 10.14 cm-1
Ra ) 0.0387
Rwb ) 0.0518
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) ∑||Fo| - |Fc||w1/2/∑|Fo|w1/2
.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) in
[Pd{P(C6H4)(C6H5)2}Br]4
Pd-Br
Pd-P′
2.505(1)
2.232(2)
Pd′-Br
Pd-Cl
2.567(1)
2.023(8)
Br-Pd-Br′
Br-Pd-Cl
Br′-Pd-Cl
85.25(3)
91.1(2)
171.0(2)
Br-Pd-P′
Br′-Pd-P′
P′-Pd-Cl
177.30(7)
95.81(6)
87.4(2)
Figure 1. ORTEP view of 1 with the atom labeling scheme. Hydrogens
are omitted for clarity.
s), 130.35 (aromatics, m), 130.62 (aromatics, d, JC-P ) 6 Hz), 131.02
(aromatics, d, JC-P ) 6Hz), 133.11 (aromatics, t, JC-P ) 7 Hz), 133.76
(aromatics, dd, JC-P ) 12 Hz, JC-P ) 2 Hz), 140.04 (aromatics, d,
JC-P ) 17 Hz), 148.12 ppm (aromatics, dd, JC-P ) 47 Hz, JC-P ) 4
Hz) . 31P{1H} NMR (CDCl3): δ 32.91 (Pa), -87.00 (Pb) ppm, (2JP-P
) 440 Hz).
Scheme 1
NMR Study of Pd(dba)(PCBr)2 in Solution. Samples of Pd(dba)-
(PCBr)2 were prepared in situ by reacting Pd(dba)2 and PCBr in toluene
in a 1:2 molar ratio and stirring the mixture at room temperature for
45 min. 31P NMR spectra were recorded at different temperatures in
the range from -55 to +25 °C. High-temperature spectra were
recorded in a separate experiment, using a new sample that was heated
at 45 °C for 30 min, and after the sample was allowed to equilibrate at
room temperature for 10 min, a new spectrum was recorded. The
experiment was repeated after heating at 55, 65, and 75 °C.
X-ray Structure Determination. Yellow prisms were grown by
vapor diffusion of acetone in a solution of 1 in CH2Cl2. A summary
of the fundamental crystal data is given in Table 1. Cell constants
were obtained from 25 reflections (4 < 2θ < 50°). Space group was
obtained from systematic absences and subsequent least-squares refine-
ment. The structure was solved by standard heavy atom techniques
with the Molen/Vax package.5 Non-hydrogen atoms were refined with
anisotropic thermal parameters. The hydrogen atom positions were
calculated and added to the structure factor calculations but were not
refined. Scattering factors and ∆f ′ and ∆f ′′ values were taken from
the literature.6 Selected bond lengths (Å) and angles (deg) are given
in Table 2.
across the metalated ligands are considerably shorter (Pd‚‚‚Pd′
3.09 Å) than those across the Pd2Br2 bridge (Pd‚‚‚Pd′′ 3.64 Å).
The bromine bridges are not symmetric: Pd-Br 2.505(1) and
Pd-Br′ 2.567(1) Å. This trend in Pd-Br distances is consistent
with the trans influences of PR3 and σ-aryl.
Results and Discussion
The reaction of the orthohalogenated phosphine PCBr and
Pd(dba)2 (1:1 molar ratio) results in the formation of the
tetranuclear palladium compound 1 in high yield (Scheme 1,
reaction i). This compound can be described as a palladium-
(II) species resulting from insertion of the palladium(0) into
the C-Br bond of the phosphine.
The structure of 1 (Figure 1), determined by X-ray diffraction,
consists of a parallelogram of four palladium atoms, with
alternate sides bridged either by two orthometalated phosphines
or by two bromides. The metalated phosphines are in a head-
to-tail arrangement. Each palladium has a square planar
coordination, bound to one carbon, one phosphorus, and two
bromines. The distances between nonbonded palladium atoms
Several examples of tetranuclear palladium compounds have
been described in the literature.7 The arrangement of the
palladium atoms seems to be very much dependent on the nature
of the auxiliary ligands. Particularly in those compounds with
palladium in oxidation state II, the metal atoms can have a
distorted tetrahedral arrangement,7a-c a butterfly shape,7g or a
square arrangement with different bridging ligands conecting
the metal atoms in a pairwise manner.7i-k The palladium-
palladium distances are significantly longer for the palladium-
(II) compounds, consistent with the existence of only weak
metal-metal interactions. To our knowledge, there is only one
species, Na2[Pd4(µ-Cl)4(µ-pcp)2(pcpH)2], with a similar structure
(Figure 2A). In this compound, the four palladium atoms are
bridged by chlorines and PCP (methylenebis(phosphinic aci-
date)) ligands.7k The nonbonded Pd‚‚‚Pd distances across the
bridging pcp and pcpH ligands are considerably longer (3.332
Å) than the analogous distances in 1 across the metalated
(5) Frenz, B. A. The Enraf-Nonius CAD4 SDP. A real-time System for
Concurrent X-Ray Data Collection and Crystal Structure Determina-
tion. Computing and Crystallography; Delft University Press: Delft,
Holland, 1978; pp 64-71.
(6) Cromer, D. T.; Waber, J. T. International Tables for X-Ray Crystal-
lography; Kynoch Press: Birmingham, U.K., 1974, Vol. IV, pp 72-
98, 149-150; Tables 2.2B and 2.3.1.

6474 Inorganic Chemistry, Vol. 36, No. 27, 1997
Notes
It was noticeable that, even in the presence of an excess of
PCBr, 1 was obtained in moderate or low yield. This is due to
the equilibrium reaction shown in Scheme 1 involving 1, 2, and
free PCBr ligand. The occurrence of reaction iv has been
confirmed by 31P NMR spectroscopy as 2, in halogenated
solvents, slowly forms 1, leaving PCBr in solution. At room
temperature, this rearrangement is very slow, and it is only
noticeable after 7 h, but it is fast in boiling 1,2-dichloroethane
(bp 83 °C). This equilibrium can be minimized by adding free
PCBr to the solution.
Figure 2. Metal arrangements observed for tetranuclear palladium
compounds: (A) planar and (B) tetrahedral.
The reverse reaction (reaction iii) can be completed only after
long standing of 1 and PCBr in solution at room temperature.
No significant cluster cleavage (<10%) is observed after boiling
in 1,2-dichloroethane for 2 h. However, 2 readily reacts with
1 equiv of Pd(dba)2 (reaction v), to give 1 as the major reaction
product.
Figure 3. Schematic structure for 2-cis and 2-trans isomers.
These results suggest that substantial Pd-P dissociation
occurs in 2 at high temperature. However, we do not have any
evidence of a dinuclear species such as (PC)Pd(µ2-Br)2Pd(PC)
formed in solution from the “Pd(PC)Br” fragments resulting
from Pd-P dissociation in 2. If such a species is formed in
solution, it probably undergoes rearrangement of the metalated
ligand from chelating to bridging coordinated mode to generate
1.
phosphine ligand (3.09 Å). To our knowledge, 1 is the first
example of a palladium compound with bridging metalated
phosphines. It is interesting to compare the structure of 1 with
that of [PdCl(ArNNNAr)]4 (ArNNNAr ) 1,3-di(p-tolyl)-
triazenide).7c In this case, the palladium atoms adopt a distorted
tetrahedral arrangement (Figure 2B) rather than a square
arrangement. The factors that control these structural details
are not clear at this time.
The tetranuclear unit of 1 is readily cleaved by other
phosphines of different cone angles allowing the isolation of
the mononuclear species Pd(PC)BrP (P ) PPh3 (3), PCy3 (4))
in high yield (reaction vi). Based on the 31P NMR spectra, we
consider these compounds structurally similar to 2 (see Experi-
mental Section). In the case of PCy3, only the trans isomer is
formed, but some isomerisation to the cis isomer (up to 20%)
is observed after 24 h in dichloromethane at room temperature.
The 13C NMR spectrum of a freshly prepared sample of 4 gave
the 10 expected signals for the metalated phosphine in the
chemical shift range of 125-149 ppm. The DEPT spectrum
allow us to assign the signal at 131.02 ppm to the carbon bonded
to the palladium. For 3, a cis/trans isomeric ratio close to 0.3
is observed.
The Chemical Reaction. We have monitored the reaction
of Pd(dba)2 and PCBr, looking for some intermediates that might
give information about the mechanistic aspects of the metalation
process. After stirring a mixture of PCBr and Pd(dba)2 (2:1
P:Pd molar ratio) in toluene at room temperature, a dark brown
solution is formed. The reaction is completed in about 30-40
min according to the 31P{1H}NMR data. The resulting solution
exhibits two resonances of equal intensity at 29.2 and 24.8 ppm.
Similar spectroscopic results have been reported for Pd(dba)-
(PPh3)2 isolated from the reaction of Pd(dba)2 and PPh3.10 Based
on these results, we assume that Pd(dba)(PCBr)2 is formed in
solution before the metalation reaction occurs. This is also the
only P-containing complex in solution when Pd(dba)2 and PCBr
are mixed in a 1:1 or 1:3 molar ratio.
If Pd(dba)2 is reacted with an excess of the orthohalogenated
phosphine PCBr (P:Pd molar ratio 2 or higher), 2 is the main
reaction product, but 1 is still formed in low yield (<15%)
(Scheme 1, reaction ii). The 31P NMR spectrum of 2 shows
two blocks of signals of equal intensity and is consistent with
the formula Pd(η2-PC)Br(η1-PCBr) for 2. The high-field signals
at ca. -80 ppm, characteristic of a four-atoms M-P-C-C
metallocycle,8 are assigned to the metalated phosphine, and the
signals at ca. 20 ppm are assigned to the η1-PCBr ligand. The
2
observed JP-P coupling constants of 12 and 460 Hz indicate
that 2 is present as a mixture of two isomers, 2-cis and 2-trans
(Figure 3), with a cis/trans ratio of 0.80. It is generally accepted
that the arrangement of a phosphine trans to an aryl group is
much less favorable than the cis arrangement in palladium(II)
compounds.9 In this context, the observation of the 2-cis isomer
as a result of a thermal reaction is remarkable.
(7) Palladium tetramers in a tetrahedral arrangement: (a)Yang, H.; Khan,
M. A.; Nicholas, K. M. J. Chem. Soc., Chem. Commun. 1992, 210.
(b) Sembiring, S. B.; Colbran, S. B.; Craig, D. C.; Scudder, M. L. J.
Chem. Soc., Dalton Trans. 1995, 3731. (c) Cuevas, J. V.; Garc´ıa-
Herbosa, G.; Mun˜oz M. A.; Hickman S. W.; Orpen, A. G.; Connelly,
N. G. J. Chem. Soc., Dalton Trans. 1995, 4127. (d) Mednikov, E. G.;
Eremenko, N. K.; Gubin, S. P.; Slovokhotov, Y. L.; Struchkov, Y. T.
J. Organomet. Chem. 1982, 239, 401. (e) Vargaftik, M. N.; Stromnova,
T. A.; Khodashova, T. A.; Porai-Koshits, M. A.; Moiseev, I. I. Koord.
Khim. 1981, 7, 132; Chem. Abstr. 1981, 94, 113637x. Palladium
tetramers in a nido structure: (f) Dubrowski, J.; Kriege-Simondsen,
J. C.; Feltham, R. D. J. Am.Chem. Soc. 1980, 102, 2089. Palladium
tetramers in a “butterfly” shape: (g) Uso´n, R.; Gimeno, J.; Oro, L.
A.; Martinez. J. M.; Cabeza, J. A. J. Chem. Soc., Dalton Trans. 1983,
1729. Palladium tetramers in a square arrangement: (h) Moiseev, I.;
Stromnova, T. A.; Vargaftik, M. N.; Mazo, G.; Kuz’mina, L. G.;
Struchkov, Y. T. J. Chem. Soc., Chem. Commun., 1978, 27. (i)
Mimoun, H.; Charpentier, R.; Mitschler, A.; Fischer, J.; Weiss, R. J.
Am. Chem. Soc. 1980, 103, 1047. (j) Bombieri, G.; Bruno, G.;
Cusumano, M.; Guglielmo, G. Acta Crystallogr., Sect. C. Cryst. Struct.
Commun. 1984, C40, 409. (k) King, C.; Roundhill, D. M.; Fronczek,
F. R. Inorg. Chem. 1987, 26, 4288. (l) Braunstein, P.; Luke, M. A.;
Tiripicchio, A.; Tiripicchio-Camellini, M. Angew. Chem., Int. Ed.
Engl. 1987, 26, 768. (m) Maekawa, M.; Munakata, M.; Kuroda-Sowa,
T.; Goto, T. Inorg. Chim. Acta 1995, 239, 159. (n) Alonso, E.; Fornie´s,
J.; Fortun˜o, C.; Martin, A.; Rosair, G. M.; Welch, A. J. Inorg. Chem.
1997, 36, 4426.
We have obtained some variable temperature 31P{1H} NMR
spectra of Pd(dba)(PCBr)2 in toluene solution. The two
resonances, already broad at room temperature, become broader
at higher temperature and collapse to a single resonance at ca.
70 °C. Addition of 1 equimolar amount of free PCBr did not
produce any significant modification of the line shape of the
spectra. At 75 °C, the metalation reaction is completed in 5 h,
(9) (a) Arlen, C.; Pfeffer, M.; Bars, O.; Le Borgne, G. J. Chem. Soc.,
Dalton Trans. 1986, 359. (b) Vicente, J.; Arcas, A.; Bautista, D.;
Tiripicchio, A.; Tiripicchio Camellini, M. New J. Chem. 1996, 20,
345.
(10) Herrmann, W. A.; Thiel, W. R.; Brossmer, C.; Ofele, K.; Priemeier,
T. J. Organomet.Chem. 1993, 461, 51.
(8) (a) Barcelo´, F.; Lahuerta, P.; Ubeda, M. A.; Foces-Foces, C.; Cano,
F. H.; Mart´ınez-Ripoll, M. J. Organomet. Chem. 1986, 301, 375. (b)
Besteiro, J.; Lahuerta, P.; Sanau´, M.; Solana, I.; Cotton, F. A.; Llusar,
R.; Schwotzer, W. Polyhedron 1988, 7, 87.

Notes
Inorganic Chemistry, Vol. 36, No. 27, 1997 6475
and signals due to 1, 2, and free PCBr are observed in the
31P{1H}NMR spectrum. No other resonances due to intermedi-
ate species were observed.
y Ciencia (Spain) for two visiting faculty fellowships (P.L. and
M.S.).
Supporting Information Available: Tables giving details of the
crystal structure determination, bond distances and angles, and refined
and calculated atomic coordinates and anisotropic thermal parameters
(6 pages). Ordering information is given on any current masthead page.
Acknowledgment. We thank the Direccio´n General de
Investigacio´n Cient´ıfica y Te´cnica (DGICYT) for financial
support (Project PB94-0988) and the Ministerio de Educacio´n
IC9702734