Reactions of [PdX2(dppm)] complexes with grignard reagents

Article abstract of DOI:10.1021/om970376u

Reactions of [PdX₂(dppm)] (X = Cl, Br) with a range of Grignard reagents have been investigated. Diorganopalladium complexes of the type [PdR₂(dppm)] were obtained in good yield with the bulky mesityl or trimethylsilylmethyl groups,

Full text of DOI:10.1021/om970376u

5096
Organometallics 1997, 16, 5096-5101
Rea ction s of [P d X2(d p p m )] Com p lexes w ith Gr ign a r d
Rea gen ts
Robert A. Stockland, J r., Gordon K. Anderson,* and Nigam P. Rath
Department of Chemistry, University of MissourisSt. Louis, 8001 Natural Bridge Road,
St. Louis, Missouri 63121
Received May 5, 1997X
Reactions of [PdX2(dppm)] (X ) Cl, Br) with a range of Grignard reagents have been
investigated. Diorganopalladium complexes of the type [PdR2(dppm)] were obtained in good
yield with the bulky mesityl or trimethylsilylmethyl groups, provided the reactions were
performed using high Grignard:Pd ratios in ether solution. With the smaller R groups Me,
Et, Bu, and CH2Ph, only the halide-bridged A-frame complexes [Pd2R2(µ-X)(µ-dppm)2]+ were
formed, irrespective of the reaction conditions. Mixtures of chloride- and bromide-bridged
complexes were produced when [PdCl2(dppm)] was treated with RMgBr, so [PdBr2(dppm)]
was used as the starting material in certain cases. The mesityl derivative [Pd2(C6H2Me3)2-
(µ-Br)(µ-dppm)2]+ could be obtained from the reaction of [PdBr2(dppm)] with 4 mol equiv of
C6H2Me3MgBr in CH2Cl2 solution, but with Me3SiCH2MgCl mixtures of monomeric and
dimeric complexes were obtained under these conditions. The A-frame complex [Pd2(CH2-
SiMe3)2(µ-Cl)(µ-dppm)2]+ was generated, however, by reaction of [Pd(CH2SiMe3)2(dppm)] with
1 mol equiv of HCl. The A-frames were isolated as their PF6- salts. They were characterized
by elemental analysis, NMR spectroscopy, and, in the case of [Pd2(C6H2Me3)2(µ-Br)(µ-dppm)2]-
PF6, X-ray crystallography. The molecular structure of the [Pd2(C6H2Me3)2(µ-Br)(µ-dppm)2]+
cation reveals that it adopts an elongated boat conformation, with the dppm CH2 groups
lying on the same side of the Pd2P4 framework as the bridging bromide. With the smaller
aryl Grignards PhMgBr, p-tolylMgBr, or o-tolylMgCl, the diarylpalladium species [PdAr2-
(dppm)] could be detected in solution at low temperatures but at ambient temperature
reductive coupling of the aryl groups occurred and the palladium(I) complexes [Pd2X2-
(µ-dppm)2] were formed.
In tr od u ction
Sn or MeMgBr, for example, cleanly produced the
halide-bridged methylpalladium cation [Pd2Me2(µ-X)(µ-
dppm)2]+. In contrast to this, reaction of the platinum
complex [PtCl2(dppm)] with MeLi has been reported to
give [PtMe2(dppm)],10,11 although with MeMgI the iodide-
bridged A-frame compound was obtained.12 Reactions
with EtMgBr or PhCH2MgBr gave the appropriate
dialkylplatinum complex, and treatment of [PtCl2-
(dppm)] with arylmagnesium bromides also produced
species of the type [PtAr2(dppm)].12 In this paper, we
report the reactions of [PdCl2(dppm)] or [PdBr2(dppm)]
with a range of Grignard reagents.
We have prepared a number of hydride-bridged pal-
ladium or platinum complexes of the type [M2R2(µ-H)-
(µ-dppm)2]PF6, including unsymmetrical diplatinum or
platinum-palladium species.1-4 In each case, the final
step was reduction of the corresponding halide-bridged
dimer. In the case of platinum, the cyclooctadiene
complexes [PtClR(cod)] proved to be convenient sources
of the chloride-bridged derivatives5 and several such
precursors are available.6 For palladium, however, only
the corresponding methyl7,8 and benzyl9 complexes are
known, stable materials. We investigated the use of
chloride-bridged arsine complexes of the type [Pd2R2(µ-
Cl)2(AsPh3)2],4 but these were also of limited stability,
and removal of triphenylarsine proved problematic in
certain cases. Thus, we decided to investigate the
reactions of [PdCl2(dppm)] with organometallic re-
agents, and we have reported4 that reactions with Me4-
Resu lts a n d Discu ssion
Rea ction s of [P d Cl2(d p p m )] w ith Excess RMgX
(R ) CH2SiMe3, C6H2Me3). Treatment of an ether
suspension of [PdCl2(dppm)] with 8 mol equiv of ((tri-
methylsilyl)methyl)magnesium chloride or mesitylmag-
nesium bromide resulted in quantitative formation of
the diorganopalladium complexes [PdR2(dppm)] (eq 1).
The complexes were isolated as analytically pure, air-
stable solids. They are soluble in most common organic
solvents but decompose slowly in halogenated solvents,
such as chloroform or CH2Cl2. Each compound exhibits
a single resonance at approximately -30 ppm in its 31P-
X Abstract published in Advance ACS Abstracts, October 15, 1997.
(1) Fallis, K. A.; Xu, C.; Anderson, G. K. Organometallics 1993, 12,
2243.
(2) Xu, C.; Anderson, G. K. Organometallics 1994, 13, 3981.
(3) Xu, C.; Anderson, G. K. Organometallics 1996, 15, 1760.
(4) Stockland, R. A., J r.; Anderson, G. K.; Rath, N. P. Inorg. Chim.
Acta 1997, 259, 173.
(5) Anderson, G. K.; Clark, H. C.; Davies, J . A. J . Organomet. Chem.
1981, 210, l35.
(6) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411.
(7) Rulke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(8) Ladipo, F. T.; Anderson, G. K. Organometallics 1994, 13, 303.
(9) Stockland, R. A., J r.; Anderson, G. K.; Rath, N. P.; Braddock-
Wilking, J .; Ellegood, J . C. Can. J . Chem. 1996, 74, 1990.
(10) Appleton, T. G.; Bennett, M. A.; Tompkins, B. J . Chem. Soc.,
Dalton Trans. 1976, 439.
(11) Cooper, S. J .; Brown, M. P.; Puddephatt, R. J . Inorg. Chem.
1981, 20, 1374.
(12) Hassan, F. S. M.; McEwan, D. M.; Pringle, P. G.; Shaw, B. L.
J . Chem. Soc., Dalton Trans. 1985, 1501.
S0276-7333(97)00376-2 CCC: $14.00 © 1997 American Chemical Society

Reactions of [PdX2(dppm)] Complexes
Organometallics, Vol. 16, No. 23, 1997 5097
when a large excess of Grignard is employed, the second
substitution cannot compete with A-frame formation.
Rea ction s of [P d Cl2(d p p m )] w ith RMgX (R ) Et,
Bu , CH2P h , CH2SiMe3, C6H2Me3). We have described
previously the reaction of [PdCl2(dppm)] with methyl-
magnesium bromide,4 although in that instance we did
not isolate the known halide-bridged A-frame complex
generated in situ, but allowed it to react with NaBH3-
CN to give the corresponding hydride-bridged cation
[Pd2Me2(µ-H)(µ-dppm)2]+. Analogous reactions with ca.
3 mol equiv of RMgBr (R ) Et, Bu, CH2Ph) in CH2Cl2
solution at -78 °C also gave halide-bridged A-frame
complexes of the type [Pd2R2(µ-X)(µ-dppm)2]+, which we
isolated as their PF6- salts after metathesis with NH4-
PF6 or TlPF6. When [PdCl2(dppm)] was treated with
these bromide-containing Grignard reagents, however,
mixtures of chloride- and bromide-bridged compounds
were obtained, so [PdBr2(dppm)] was used as the
starting material in these cases. Under such conditions,
reaction with RMgBr cleanly produced the bromide-
bridged A-frame species [Pd2R2(µ-Br)(µ-dppm)2]PF6 in
excellent yields (eq 2).
{1H} NMR spectrum, this negative chemical shift being
indicative of the presence of a four-membered chelate
ring.13 In each case, a simple triplet for the methylene
hydrogens of the dppm ligand is observed in the 1H
NMR spectrum, as expected for a symmetrical mono-
1
meric species. The H NMR spectrum of the (trimeth-
ylsilyl)methyl derivative also contains a singlet due to
the six equivalent methyl groups, a doublet of doublets
for the CH2 groups attached to palladium, and the
expected aromatic signals. The spectrum for [Pd(C6H2-
Me3)2(dppm)] shows two singlets in a 2:1 ratio for the
methyl groups and a single resonance for the aromatic
hydrogens of the mesityl groups, indicating that the
o-CH3 as well as the aromatic CH groups are magneti-
cally equivalent. No broadening of these signals oc-
curred as the temperature was lowered to 210 K in
CDCl3 solution. This indicates that the molecule is
already static at ambient temperature, the two mesityl
groups lying perpendicular to the square plane of the
molecule such that it represents a plane of symmetry.
The related platinum complexes [PtR2(dppm)] (R )
o-tolyl, 1-naphthyl) were found to exist as mixtures of
syn and anti forms at low temperatures, when rotation
about the PtsC bonds became slow on the NMR time
scale.12
Whereas treatment of [PdCl2(dppm)] with 8 mol equiv
of mesitylmagnesium bromide in ether produced [Pd-
(C6H2Me3)2(dppm)], reaction with 4 mol equiv of the
Grignard reagent in CH2Cl2 solution gave the halide-
bridged A-frame complex. (The Grignard reagent reacts
with the palladium complex more rapidly than with the
chlorinated solvent.) Again, a mixture of chloride- and
bromide-bridged species was formed, but with [PdBr2-
(dppm)] as the starting material the reaction produced
[Pd2(C6H2Me3)2(µ-Br)(µ-dppm)2]+ cleanly.
The reaction of [PdCl2(dppm)] with 8 mol equiv of
((trimethylsilyl)methyl)magnesium chloride in ether
gave [Pd(CH2SiMe3)2(dppm)], whereas when CH2Cl2
was used as the solvent mixtures of [Pd2(CH2SiMe3)2(µ-
Cl)(µ-dppm)2]+ and [Pd(CH2SiMe3)2(dppm)] were ob-
tained. The chloride-bridged A-frame was obtained,
however, by treating [Pd(CH2SiMe3)2(dppm)] with HCl
(generated in situ from acetyl chloride and methanol).
The monomeric complex [PdCl(CH2SiMe3)(dppm)] (δ(P)
-7.0 d, δ(P) -39.5 d, 2J (P,P) ) 70 Hz) was formed
initially, but this converted to the A-frame complex on
standing. The dimesitylpalladium complex also reacted
with HCl to give [PdCl(C6H2Me3)(dppm)] first (δ(P)
-23.3 d, δ(P) -44.7 d, 2J (P,P) ) 63 Hz), which dimerized
on standing in solution. As pointed out above, [Pd2(CH2-
CMe3)2(µ-Cl)(µ-dppm)2]+ could be observed in solution,
but we have been unable to isolate it in pure form.
The halide-bridged A-frame complexes are air-stable,
colorless to yellow or orange solids. The cations are
stable as their halide salts if kept below 0 °C, but they
are more stable as their hexafluorophosphate salts,
obtained by metathesis with NH4PF6 or TlPF6. They
have been characterized by NMR spectroscopy, elemen-
tal analysis, and, in the case of the mesityl derivative,
X-ray crystallography. The 31P{1H} NMR spectrum of
With smaller alkyl Grignards, the dialkylpalladium
complexes were not obtained but rather the A-frame
derivatives (vide infra). For example, addition of 8 mol
equiv of MeMgBr to [PdCl2(dppm)] gave only the
bromide-bridged A-frame complex [Pd2Me2(µ-Br)(µ-
dppm)2]+. With neopentylmagnesium chloride, mix-
tures of [Pd(CH2CMe3)2(dppm)] (δ(P) -23.8) and [Pd2-
(CH2CMe3)2(µ-Cl)(µ-dppm)2]+ (δ(H) 0.01 (s, 18H, CMe3),
2
1.00 (s, 4H, PdCH2), 4.31 (dq, 2H, J (H,H) ) 14.5 Hz,
2J (P,H) ) 3.5 Hz, PCH2P), 4.53 (dq, 2H, 2J (H,H) ) 14.5
2
Hz, J (P,H) ) 5 Hz, PCH2P); δ(P) 13.0) were obtained,
the former being favored at high Grignard to palladium
ratios, but the dialkylpalladium complex could not be
isolated in pure form. The diorganopalladium com-
plexes could be converted to the corresponding A-frames
by treatment with 1 mol equiv of HCl, generated in situ
from the reaction of acetyl chloride with methanol.
Evidently it is only with very bulky organic groups
that we have been able to isolate complexes of the type
[PdR2(dppm)], whereas with smaller R groups the
dimeric A-frame species is formed preferentially. Since
substitution of the chlorides by R groups must take
place in a stepwise manner, an intermediate species of
the form [PdClR(dppm)] would be generated. Which
product forms subsequently would depend on the rela-
tive rates of dimerization or reaction with a second
equivalent of the Grignard reagent. Whereas both
processes might be expected to be slower with bulky
groups, dimerization is apparently slowed to a greater
extent, allowing reaction with RMgX to proceed further,
at least when excess Grignard reagent is present. With
smaller R groups, dimerization is so rapid that even
(13) Garrou, P. E. Chem. Rev. 1981, 81, 229.

5098 Organometallics, Vol. 16, No. 23, 1997
Stockland et al.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [P d 2(C6H2Me3)2(µ-Br )-
(µ-d p p m )2]P F 6‚3CH2Cl2
Pd(1)-P(1)
Pd(1)-C(3)
Pd(2)-P(3)
Pd(2)-C(12)
2.340(2)
2.034(6)
2.350(2)
2.033(7)
Pd(1)-P(2)
Pd(1)-Br
Pd(2)-P(4)
Pd(2)-Br
2.330(2)
2.5273(8)
2.329(2)
2.5551(8)
P(1)-Pd(1)-P(2)
P(1)-Pd(1)-Br
P(2)-Pd(1)-Br
P(3)-Pd(2)-P(4)
P(3)-Pd(2)-Br
P(4)-Pd(2)-Br
Pd(1)-Br-Pd(2)
172.87(6)
93.09(5)
88.67(5)
170.30(6)
92.35(5)
90.73(5)
83.32(2)
P(1)-Pd(1)-C(3)
P(2)-Pd(1)-C(3)
C(3)-Pd(1)-Br
P(3)-Pd(2)-C(12)
P(4)-Pd(2)-C(12)
C(12)-Pd(2)-Br
89.2(2)
89.6(2)
174.9(2)
88.7(2)
90.3(2)
167.5(2)
of 83° through the bridging bromide. The eight-
membered Pd2P4C2 ring adopts an elongated boat
conformation, with the two CH2 groups and the bridging
bromide lying on opposite faces of the Pd2P4 plane. The
mesityl groups occupy terminal positions trans to the
bridging bromide, the C-Pd-Br angles being 174.9° and
167.5°. The mesityl rings lie almost perpendicular to
the Pd2P4 plane, presumably in order to minimize
repulsions between these rings and the phenyl rings of
the dppm ligands. This conformation is likely to persist
in solution also, since the o-methyl groups are magneti-
cally nonequivalent in the 1H NMR spectrum, indicating
that rotation about the Pd-C bonds is slow on the NMR
time scale at ambient temperature (vide supra).
F igu r e 1. Projection view of the molecular structure of
the [Pd2(C6H2Me3)2(µ-Br)(µ-dppm)2]+ cation showing the
atom-labeling scheme, with non-hydrogen atoms repre-
sented by 50% probability ellipsoids.
each complex exhibits a single resonance in the range
8-17 ppm, typical of bridging dppm. The 1H NMR
spectrum exhibits two doublets of quintets for the
methylene hydrogens of the dppm ligands (although
these overlap in the butyl case). This is due to the
presence of axial and equatorial environments for these
hydrogens, since inversion of the A-frame structure is
slow on the NMR time scale.14 Each hydrogen exhibits
coupling to the other of ca. 14 Hz and to the four
equivalent P atoms.
The solid state structures of a number of dipal-
ladium15-30 and diplatinum31-41 A-frame complexes
(15) Olmstead, M. M.; Hope, H.; Benner, L. S.; Balch, A. L. J . Am.
Chem. Soc. 1977, 99, 5502.
The ethyl, butyl, and (trimethylsilyl)methyl complexes
display the expected resonances due to the alkyl groups.
The mesityl derivative exhibits three signals due to the
methyl groups and two aromatic CH resonances, indi-
cating that there is hindered rotation about the Pd-C
bonds. The benzyl derivative [Pd2(CH2Ph)2(µ-Br)(µ-
dppm)2]+ exhibits a broad singlet resonance at 2.89 ppm,
due to the benzyl methylene hydrogens. The aromatic
signals associated with the benzyl group appear at
unexpectedly low frequencies, namely, a doublet at 5.17
ppm due to the o-hydrogens, a triplet at 6.35 ppm due
to the m-hydrogens, and a further triplet of lower
intensity at 6.65 ppm due to the p-hydrogens. These
all appear at lower frequencies than the dppm aromatic
signals (7.2-7.8 ppm). Similar chemical shifts are
observed for the chloride-bridged complex, obtained from
the reaction of [PdCl(CH2Ph)(cod)]9 with dppm.
(16) Balch, A. L.; Benner, L. S.; Olmstead, M. M. Inorg. Chem. 1979,
18, 2996.
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1981, 52, 47.
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(19) Hanson, A. W.; McAlees, A. J .; Taylor, A. J . Chem. Soc., Perkin
Trans. I 1985, 441.
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R.; Nelson, D. A.; Lilga, M. A. Inorg. Chem. 1987, 26, 3622.
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Soc., Chem. Commun. 1988, 47.
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E.; Manning, M.; Anderson, O. P.; Stille, J . K. J . Am. Chem. Soc. 1988,
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180, 183.
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Acta 1993, 205, 15.
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Dalton Trans. 1994, 1283.
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13, 3664.
X-r ay Str u ctu r e Deter m in ation of [P d2(C6H2Me3)2-
(µ-Br )(µ-d p p m )2]P F 6‚3CH2Cl2. Crystals of the bro-
mide-bridged mesitylpalladium A-frame complex suit-
able for X-ray diffraction were obtained from CH2Cl2/
hexane solution. The crystal structure belongs to the
space group P1h. The lattice contains three molecules
of CH2Cl2 per [Pd2(C6H2Me3)2(µ-Br)(µ-dppm)2]PF6 unit.
The molecular structure of the cation is shown in Figure
1, and selected bond distances and angles are presented
in Table 1. There are no significant interactions be-
tween the cation, the anion, or the solvent molecules.
The molecule exhibits approximate square planar
geometry about each of the palladium atoms, with the
two planes being inclined toward each other at an angle
(28) Besenyei, G.; Parkanyi, L.; Simandi, L. I.; J ames, B. R. Inorg.
Chem. 1995, 34, 6118.
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Chem. Commun. 1997, 1143.
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Muir, K. W.; Puddephatt, R. J .; Thomson, M. A. J . Chem. Soc., Dalton
Trans. 1982, 299.
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R. J .; Treurnicht, I. Angew. Chem., Int. Ed. Engl. 1987, 26, 86.
(36) Hadj-Begheri, N.; Puddephatt, R. J .; Manojlovic-Muir, L.;
Stefanovic, A. J . Chem. Soc., Dalton Trans. 1990, 535.
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tallics 1992, 11, 795.
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1992, 31, 2979.
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1993, 12, 933.
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Chem. Soc. 1983, 105, 5642.

Reactions of [PdX2(dppm)] Complexes
Organometallics, Vol. 16, No. 23, 1997 5099
Sch em e 1
have been reported. A large majority of these adopt
elongated boat conformations, the exceptions being the
carbonyl-bridged dipalladium species [Pd2Cl2(µ-CO)-
(µ-dmpm)2]19 and [Pd2(OCOCF3)2(µ-CO)(µ-dppm)2]23 and
[Pt2Me2(µ-H)(µ-dppm)2]PF6,38 which exist in chair con-
formations. In each of the previously reported boat
structures, the CH2 groups of the bridging diphosphine
ligands lie on the same side of the M2P4 plane as the
group occupying the apex of the A-frame structure.
Thus, the present study represents the first example of
a boat conformation in which the terminal groups (the
mesityl groups here) and the dppm CH2 groups lie on
the same face of the dimer. Consideration of the
molecular structure reveals that two of the phenyl rings
of the dppm ligands and the mesityl ring on each side
of the A-frame lie almost parallel to each other, and this
π-stacking effect may be responsible for the conforma-
tion adopted in this case.
4)2(dppm)] (δ(P) -29.0), and treatment of [PdCl2(dppm)]
with 2-MeC6H4MgCl in toluene-d8 produced [Pd(C6H4-
Me-2)2(dppm)] (δ(P) -27.8). Again, in each case, a
number of species was formed when the solution was
allowed to warm to ambient temperature.
Rea ction s of [P d Cl2(d p p m )] w ith Ar MgX (Ar )
P h , 4-Tolyl, 2-Tolyl). When an ether suspension of
[PdCl2(dppm)] was treated with 1 mol equiv of phenyl-
magnesium bromide at ambient temperature, the mix-
ture turned dark red rapidly. After filtration of the
palladium-containing species and magnesium salts, the
ether was evaporated and the resulting solid was
identified by 1H NMR spectroscopy and GC-MS as
diphenyl. The palladium species was identified as the
palladium(I) complex [Pd2Br2(µ-dppm)2] (δ(P) -5.2),42
the terminal ligands being derived from the bromide in
the Grignard reagent used. The analogous reaction
with 4-tolylmagnesium bromide produced 4,4′-ditolyl
and [Pd2Br2(µ-dppm)2], whereas with o-tolylmagnesium
chloride the products were 2,2′-ditolyl and [Pd2Cl2-
(µ-dppm)2] (δ(P) -2.5),42 the organic products again
Although allowing the low-temperature reaction mix-
tures to warm to ambient temperature did not cleanly
produce the palladium(I) complexes found when the
reactions were performed at 25 °C, the detection of
[PdAr2(dppm)] at -78 °C strongly suggests that such
species are involved in the ambient-temperature reac-
tions also. We propose the sequence of events shown
in Scheme 1. The first step is reaction of [PdCl2(dppm)]
with the Grignard reagent to produce [PdAr2(dppm)].
Although only 1 mol equiv of the Grignard was added,
the low solubility of [PdCl2(dppm)] in ether (or in CD2-
Cl2 or toluene-d8 at low temperatures) would ensure
that the ArMgX:Pd ratio in solution was high. This
would allow rapid replacement of the second halide
before dimerization of [PdClAr(dppm)] to give the A-
frame complex [Pd2Ar2(µ-X)(µ-dppm)2]+ could occur.
Reductive elimination of the diaryl would produce the
highly reactive palladium(0) species [Pd(dppm)], which
would react with another molecule of [PdCl2(dppm)] to
generate the palladium(I) complex [Pd2X2(µ-dppm)2] (X
) Cl or Br, depending on the Grignard reagent em-
ployed).
1
being identified by their H NMR and GC-MS data (eq
3).
Reductive eliminations from diorganopalladium(II)
and -platinum(II) complexes are well-known. With aryl
substituents, stable palladium complexes of the type cis-
[Pd(C6X5)2L2] (X ) F, Cl) have been reported, but the
corresponding cis-[PdPh2L2] species are unknown.43 The
strongly electron-withdrawing nature of the pentafluo-
rophenyl groups enhances the stability of their com-
plexes. In the present instance, we have been unable
to distinguish between the rates of reductive elimination
for the three different aryl groups, phenyl, 4-tolyl, and
2-tolyl, each reaction being rapid at ambient tempera-
ture. When Ar ) mesityl, however, the dimesitylpal-
ladium complex could be isolated and reductive elimi-
nation did not occur. Reductive elimination from cis-
diarylplatinum(II) complexes proceeds by a concerted
mechanism,44 and it has been shown that the two aryl
groups must lie perpendicular to the square plane in
When the reaction of [PdCl2(dppm)] with PhMgBr was
carried out at -78 °C in CD2Cl2 solution ([PdCl2(dppm)]
is only slightly soluble at this temperature), a single
resonance was observed in the 31P{1H} NMR spectrum
at -31.1 ppm. This is shifted to higher frequency than
the signal observed for the starting material (δ(P) -53.2)
and is very close to that found for [Pd(C6H2Me3)2(dppm)]
(vide supra). Thus, we have assigned this resonance to
[PdPh2(dppm)]. When the solution was allowed to warm
to ambient temperature, a further reaction took place
and several phosphorus-containing species were formed.
The corresponding low-temperature reaction with
4-MeC6H4MgBr in CD2Cl2 solution gave [Pd(C6H4Me-
(43) Canty, A. J . In Comprehensive Organometallic Chemistry II;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
Oxford 1995; Vol. 9, p 225-290.
(44) Braterman, P. S.; Cross, R. J .; Young, G. B. J . Chem. Soc.,
Dalton Trans. 1977, 1892.
(40) Yam, V. W.; Chan, L.-P.; Lai, T.-F. Organometallics 1993, 12,
2197.
(41) Toronto, D. V.; Balch, A. L. Inorg. Chem. 1994, 33, 6132.
(42) Hunt, C. T.; Balch, A. L. Inorg. Chem. 1982, 21, 1641.

5100 Organometallics, Vol. 16, No. 23, 1997
Stockland et al.
order that elimination may occur.45 When the aryl
groups are mesityl groups, they will indeed both lie
perpendicular to the plane but they must be oriented
at 90° to each other in the product dimesityl,46 and this
will inhibit the reductive elimination process.
) 8 Hz, PCH2P), 6.91 (s, 4H, C6H2Me3), 6.95-7.3 (m, 20H,
PPh2). 31P{H} NMR: δ(P) -30.6 (s).
P r ep a r a tion of [P d 2(CH2SiMe3)2(µ-Cl)(µ-d p p m )2]P F 6.
[PdCl2(dppm)] (0.200 g, 0.356 mmol) was suspended in ether
(30 mL) at ambient temperature. Me3SiCH2MgCl (2.85 mL
of a 1.0 M ether solution) was added by syringe. The yellow
solution was stirred for 30 min, then methanol (0.5 mL) was
added to quench the excess Grignard reagent. Acetyl chloride
(0.71 mL of a 0.5 M solution in toluene) was added by syringe,
and the solution was stirred for 10 min. The solvents were
removed in vacuo, and the resulting solid was dried overnight.
The solid was extracted with CH2Cl2 (30 mL), and this solution
was treated with NH4PF6 (0.202g, 1.23 mmol) in methanol (2.0
mL). The mixture was stirred at ambient temperature for 30
min, then the solvent was removed in vacuo. The resulting
solid was dried, then washed with ether and hexane at -78
°C. Finally, it was extracted with CH2Cl2 (30 mL). The
solution was filtered, then the solvent was evaporated. The
solid was recrystallized from CH2Cl2/hexane at 0 °C to give
the product as a pale yellow solid (0.209 g, 88%). Anal. Calcd
for C58H66ClF6P5Pd2Si2: C, 52.09; H, 4.93. Found: C, 51.85;
H, 5.00. 1H NMR (acetone-d6): δ(H) -0.95 (s, 18H, SiMe3),
1.04 (m, 4H, CH2SiMe3), 3.98 (dq, 2H, 2J (H,H) ) 14 Hz, 2J (P,H)
Su m m a r y
With the bulky organic groups mesityl and (trimeth-
ylsilyl)methyl, the reactions of [PdX2(dppm)] (X ) Cl, Br)
proceed to give the diorganopalladium species [PdR2-
(dppm)]. In contrast, with smaller alkyl groups, the
halide-bridged A-frame complexes [Pd2R2(µ-X)(µ-dppm)2]+
(R ) Me, Et, Bu, CH2Ph) are formed. The nature of
the products obtained depends on the relative rates of
reaction of [PdXR(dppm)] with further Grignard reagent
to produce [PdR2(dppm)] or with a second molecule of
[PdXR(dppm)] to produce the dimer. With smaller aryl
groups, the diarylpalladium species are formed, but they
undergo rapid reductive elimination at ambient tem-
perature to produce the diaryl and the palladium(I)
complex [Pd2X2(µ-dppm)2].
2
2
) 4 Hz, PCH2P), 4.45 (dq, 2H, J (H,H) ) 14 Hz, J (P,H) ) 5
Hz, PCH2P), 7.5-7.9 (m, 40H, PPh2). 31P{1H}NMR: δ(P) 13.5
(s).
Exp er im en ta l Section
P r ep a r a tion of [P d2(C6H2Me3)2(µ-Br )(µ-d p p m )2]P F 6. To
a CH2Cl2 solution of [PdBr2(dppm)] (0.200 g, 0.307 mmol) was
added Me3C6H2MgBr (1.23 mL of a 1.0 M solution in ether).
The yellow solution was stirred for 30 min, then methanol (2.0
mL) was added by syringe. The mixture was stirred for an
additional 1 h, then the solvent was removed in vacuo. The
resulting solid was dried, then extracted with CH2Cl2 and
treated with NH4PF6 (0.20 g, 1.23 mmol) in methanol (1.0 mL).
After 1 h, the solvent was evaporated, and the solid was dried,
washed with ether and hexane, and extracted with CH2Cl2 (5.0
mL). The resulting solution was passed through a short
column of neutral alumina, eluting with CH2Cl2 (40 mL). The
solvent was removed in vacuo, leaving the product as a
colorless solid (0.187 g, 84%). Crystals suitable for an X-ray
diffraction study were obtained from a CH2Cl2/hexane solution
at 0 °C. 1H NMR (CDCl3): δ(H) 1.79, 2.42, 2.58 (s, 9H,
C6H2Me3), 3.83 (dq, 2H, 2J (H,H) ) 14 Hz, 2J (P,H) ) 4.5 Hz,
PCH2P), 4.35 (dq, 2H, 2J (H,H) ) 14 Hz, 2J (P,H) ) 4.5 Hz,
PCH2P), 5.85, 5.97 (s, 2H, C6H2Me3), 6.8-7.8 (m, 40H, PPh2).
31P{1H} NMR: δ(P) 8.6 (s).
All reactions were carried out under an atmosphere of argon.
[PdCl2(dppm)] was prepared by reaction of [PdCl2(cod)] with
dppm, and [PdBr2(dppm)] (δ(P) -56.3) was generated by
stirring an acetone solution of [PdCl2(dppm)] with excess LiBr
for 24 h at ambient temperature. Grignard reagents were
purchased from Aldrich. 1H and 31P{1H} NMR spectra were
recorded on a Varian Unity plus 300 or Bruker ARX-500
spectrometer. Chemical shifts are relative to the residual
solvent resonance or external H3PO4, respectively, positive
shifts representing deshielding. The following abbreviations
are used: s ) singlet, t ) triplet, q ) quintet, sx ) sextet, m
) multiplet. GC-MS data were obtained on a Hewlett-Packard
5988 instrument. Microanalyses were performed by Atlantic
Microlab, Inc, Norcross, GA.
P r ep a r a tion of [P d (CH2SiMe3)2(d p p m )]. [PdCl2(dppm)]
(0.100 g, 0.178 mmol) was suspended in ether (5 mL) at
ambient temperature. Me3SiCH2MgCl (1.42 mL of a 1.0 M
solution) was added by syringe. The solution was stirred for
20 min. Methanol (0.5 mL) was added to quench the excess
Grignard reagent. The solvents were removed, and the solid
was dried in vacuo. The solid was washed with ether and
hexane at -78 °C. The residue was then extracted with CH2-
Cl2 (30 mL) and filtered. The solvent was removed to leave
the product as a pale yellow solid (0.108 g, 91%). Anal. Calcd
for C33H44P2PdSi2: C, 59.55; H, 6.61. Found: C, 59.38; H, 6.55.
1H NMR (CDCl3): δ(H) -0.15 (s, 18H, SiMe3), 0.70 (dd, 4H,
3J (P,H) ) 12, 10 Hz, CH2SiMe3), 3.81 (t, 2H, 1J (P,H) ) 7.5
Hz, PCH2P), 7.2-7.6 (m, 20H, PPh2). 31P{H} NMR: δ(P)
-27.0 (s).
P r ep a r a tion of [P d (C6H2Me3-2,4,6)2(d p p m )]. [PdCl2-
(dppm)] (0.200 g, 0.356 mmol) was added to an ether solution
of Me3C6H2MgBr (2.85 mL of a 1.0 M solution). The suspen-
sion was stirred for 20 min, then methanol (0.4 mL) was added,
and the solvent was removed in vacuo. The orange residue
was extracted with CH2Cl2 and filtered, then the CH2Cl2 was
evaporated, and the residue was washed with ether and
hexane. The solid was dissolved in benzene and passed
through a Florisil column, eluting with benzene (50 mL). The
benzene was removed in vacuo to leave the product as a
colorless solid (0.217 g, 84%). Anal. Calcd for C43H44P2Pd: C,
70.80; H, 6.04. Found: C, 70.72; H, 6.13. 1H NMR (C6D6):
δ(H) 2.31 (s, 6H, p-Me), 2.79 (s, 12H, o-Me), 3.59 (t, 2H, 2J (P,H)
P r ep a r a tion of [P d 2(CH2P h )2(µ-Br )(µ-d p p m )2]P F 6.
A
CH2Cl2 solution (30 mL) of [PdBr2(dppm)] (0.200 g, 0.307
mmol) was cooled to -78 °C and treated with PhCH2MgBr (1.0
mL of a 1.0 M ether solution). The solution was stirred for 3
h at -78 °C, then methanol (1.0 mL) was added, and the
solution was allowed to warm slowly to 0 °C. The solvents
were removed at 0 °C. The resulting solid was dried, then
extracted with CH2Cl2 and treated with NH4PF6 (0.20 g, 1.23
mmol) in methanol (1.0 mL). The mixture was maintained at
0 °C for 1 h, then the solvents were removed, and the solid
was dried in vacuo. The solid was washed with ether, hexane,
and warm benzene, then extracted with CH2Cl2 and filtered.
The solvent was evaporated, and the residue was crystallized
from a CH2Cl2/hexane solution at 0 °C, yielding the product
as a yellow powder (0.190 g, 89%). Anal. Calcd for C64H58Br-
F6P5Pd2: C, 55.31; H, 4.18. Found: C, 55.87; H, 4.33. 1H NMR
(CDCl3): δ(H) 2.89 (br s, 4H, CH2C6H5), 3.68 (dq, 2H, 2J (H,H)
2
2
) 14 Hz, J (P,H) ) 3.5 Hz, PCH2P), 4.39 (dq, 2H, J (H,H) )
14 Hz, 2J (P,H) ) 5 Hz, PCH2P), 5.17 (d, 4H, 3J (H,H) ) 7.5
Hz, CH2C6H5 o-hydrogens), 6.35 (t, 4H, 3J (H,H) ) 7.5 Hz,
CH2C6H5, m-hydrogens), 6.65 (t, 2H, 3J (H,H) ) 7.5 Hz,
CH2C6H5, p-hydrogens), 7.2-7.8 (m, 40H, PPh2). 31P{1H}
NMR: δ(P) 10.2 (s).
P r ep a r a tion of [P d 2Et2(µ-Br )(µ-d p p m )2]P F 6. To a CH2-
Cl2 solution (30 mL) of [PdBr2(dppm)] (0.200 g, 0.307 mmol)
maintained at -78 °C was added EtMgBr (1.0 mL of a 1.0 M
(45) Brune, H. A.; Hupfer, E.; Schmidtberg, G.; Baur, A. J . Orga-
nomet. Chem. 1992, 424, 225.
(46) Fro¨hlich, R.; Musso, H. Chem. Ber. 1985, 118, 4649.

Reactions of [PdX2(dppm)] Complexes
Organometallics, Vol. 16, No. 23, 1997 5101
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for [P d 2(C6H2Me3)2(µ-Br )(µ-d p p m )2]P F 6‚3CH2Cl2
ether solution) by syringe. The solution was stirred for 4 h,
then methanol (1.0 mL) was added, and the solution was
allowed to warm slowly to 0 °C. The solvent was removed at
0 °C, and the residue was extracted with CH2Cl2. To the CH2-
Cl2 solution was added NH4PF6 (0.20 g, 1.23 mmol) in
methanol (1.0 mL). The mixture was stirred at 0 °C for 30
min, then the solvent was removed in vacuo. The resulting
solid was dried, washed with ether and hexane, then extracted
with CH2Cl2 (5 mL). This solution was passed through a
column of neutral alumina, eluting with CH2Cl2 (50 mL). The
solvent was evaporated, leaving the product as an orange
powder (0.146 g, 75%). Anal. Calcd for C54H54BrF6P5Pd2: C,
51.29; H, 4.27. Found: C, 51.44; H, 4.30. 1H NMR (CDCl3):
δ(H) -0.03 (m, 6H, CH2CH3), 1.69 (m, 4H, CH2CH3), 3.74 (dq,
cryst syst
space group, Z
a (Å)
b (Å)
c (Å)
triclinic
P1h, 2
15.0482(2)
16.2499(2)
17.7349(2)
84.254(1)
66.663(1)
64.989(1)
3596.72(8)
1.569
R (deg)
â (deg)
γ (deg)
V (Å3)
density (g/cm-3
)
temperature (K)
θ range (deg)
203(2)
1.62-27.0
15 636 (0.051)
0.0673, 0.1806
0.1121, 0.2153
1.034
no. of indep reflns (Rint
)
R(F), Rw(F2)(F2 > 2.0 σ(F2))
R(F), Rw(F2) (all data)
goodness of fit on F2
2
2
2H, J (H,H) ) 14 Hz, J (P,H) ) 4 Hz, PCH2P), 4.28 (dq, 2H,
2J (H,H) ) 14 Hz, 2J (P,H) ) 5.5 Hz, PCH2P), 7.1-8.1 (m, 40H,
PPh2). 31P{1H} NMR: δ(P) 16.8 (s).
P r ep a r a tion of [P d 2Bu 2(µ-Br )(µ-d p p m )2]P F 6. n-BuMg-
Br (1.0 mL of a 1.0 M ether solution) was added to a CH2Cl2
solution (5.0 mL) of [PdBr2(dppm)] (0.200 g, 0.307 mmol) at
-78 °C. After 4 h, methanol (1.0 mL) was added and the
solution was allowed to warm slowly to 0 °C. The solvent was
removed at this temperature, and the residue was extracted
with acetone and treated with TlPF6 (0.0645 g, 0.184 mmol).
After being stirred for 20 min, the solvent was removed in
vacuo and the residue was washed with ether and hexane. The
residue was extracted with CH2Cl2, and the solution was
filtered and evaporated to dryness to leave the product as a
yellow powder (0.160 g, 79%). Anal. Calcd for C58H62BrF6P5-
Pd2: C, 52.71; H, 4.70. Found: C, 52.47; H, 4.73. 1H NMR
(acetone-d6): δ(H) 0.02 (t, 6H, 3J (H,H) ) 7 Hz, CH2CH2-
CH2CH3), 0.21 (sx, 4H, 3J (H,H) ) 7 Hz, CH2CH2CH2CH3), 0.37
X-ray diffractometer using graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å) equipped with a sealed tube X-ray
source (50 kV × 40 mA) at 203 K. Preliminary unit cell
constants were determined with a set of 45 narrow frame (0.3°
in $) scans. A total of 5554 frames of intensity data were
collected, with a counting time of 10 s/frame at a crystal to
detector distance of 4.930 cm. The double-pass method of
scanning was used to exclude any noise. The collected frames
were integrated using an orientation matrix determined from
the narrow frame scans. The SMART software package47 was
used for data collection as well as frame integration. Analysis
of the integrated data did not show any decay. Final cell
constants were determined by a global refinement of x,y,z
centroids of 8192 reflections (θ < 19.0°). An empirical absorp-
tion correction was applied using SADABS48 based on the Laue
symmetry using 47 740 equivalent reflections (Tmax/Tmin ) 0.84/
0.61, Rint ) 8.6% and 5.9% before and after absorption
correction).
3
(q, 4H, J (H,H) ) 8 Hz, CH2CH2CH2CH3), 1.65 (m, 4H, CH2-
CH2CH2CH3), 4.38 (m, 4H, PCH2P), 7.2-8.1 (m, 40H, PPh2).
31P{1H} NMR: δ(P) 17.2 (s).
Rea ction s of [P d Cl2(d p p m )] w ith Ar MgX. (a ) Rea c-
tion s a t Am bien t Tem p er a tu r e. [PdCl2(dppm)] (0.100 g,
0.178 mmol) was suspended in ether (30 mL) at ambient
temperature. A solution of ArMgX (0.18 mL of a 1.0 M ether
solution; ArMgX ) PhMgBr, (4-tolyl)MgBr, (2-tolyl)MgCl) was
added by syringe. The yellow mixture turned dark red
immediately. After the mixture was stirred for 15 min, the
solution was filtered to remove the palladium-containing
products and magnesium salts and the solvent was evaporated.
Analysis of the filtered material by NMR spectroscopy revealed
the presence of [Pd2Cl2(µ-dppm)2] (δ(H) 4.17 (q, J (P,H) ) 4 Hz,
CH2), 7.1-7.6 (m, PPh2); δ(P) -2.5) or [Pd2Br2(µ-dppm)2] (δ-
(H) 4.15 (q, J (P,H) ) 4 Hz, CH2), 7.2-7.4 (m, PPh2); δ(P) -5.2).
The organic products obtained by solvent removal were identi-
fied as the diaryls by GC-MS (diphenyl, m/z 154 (p+, 100); 2,2′-
ditolyl, m/z 182 (p+, 100); 4,4′-ditolyl, m/z 182 (p+, 100)) and
1H NMR spectroscopy (2,2′-ditolyl, 2.04 (s, 6H, CH3), 7.09 (d,
2H, 3J (H,H) ) 7 Hz, C6H4Me), 7.18-7.26 (m, 6H, C6H4Me);
4,4′-ditolyl, 2.30 (s, 6H, CH3), 7.4-7.7 (m, 8H, C6H4Me)).
(b) Rea ction s a t Low Tem p er a tu r e. To a CD2Cl2 solu-
tion (0.5 mL) of [PdCl2(dppm)] (0.010 g, 0.018 mmol) was added
1 mol equiv of PhMgBr (0.017 mL of a 1.0 M ether solution)
at -78 °C. The 31P{1H} NMR spectrum at 200 K exhibited a
singlet resonance at -31.1 ppm, attributed to [PdPh2(dppm)].
Warming this solution to ambient temperature resulted in
formation of a large number of species, many of which remain
unidentified.
Structure solution and refinement were carried out using
the SHELXTL-PLUS (5.03) software package.49 The structure
was solved by Patterson methods and refined successfully in
the space group P1h. Full-matrix least-squares refinement was
2
carried out by minimizing ∑w(Fo - Fc2)2. The non-hydrogen
atoms were refined anisotropically to convergence. The hy-
drogen atoms were treated using appropriate riding models
(AFIX m3). The final residual values were R(F) ) 11.2% and
Rw(F2) ) 21.5%, s )1.03 for all data. Crystal data and
structure refinement parameters are given in Table 2.
Ack n ow led gm en t. Thanks are expressed to the
National Science Foundation (Grant No. CHE-9508228)
for support of this work, J ohnson Matthey Aesar/Alfa
for a generous loan of palladium salts, the National
Science Foundation (Grant Nos. CHE-9318696 and
9309690), the U.S. Department of Energy (Grant No.
DE-FG02-92CH10499) and the University of Missouri
Research Board for instrumentation grants.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and anisotropic displacement coefficients for the
non-hydrogen atoms, positional and isotropic displacement
coefficients for the hydrogen atoms, and a complete list of bond
distances and angles (14 pages). Ordering information is given
on any current masthead page.
Analogous reactions with (2-tolyl)MgCl or (4-tolyl)MgBr at
-78 °C yielded [Pd(2-tolyl)2(dppm)] (δ(P) -29.0 (CD2Cl2)) or
[Pd(4-tolyl)2(dppm)] (δ(P) -27.8 (toluene-d8)).
OM970376U
X-r a y Str u ctu r e Deter m in a tion of [P d 2(C6H2Me3)2(µ-
Br )(µ-d p p m )2]P F 6. A crystal of dimensions 0.42 × 0.22 ×
0.12 mm was mounted on a glass fiber in random orientation.
Preliminary examination and data collection were performed
using a Siemens SMART CCD detector system single-crystal
(47) Siemens Analytical X-ray Division, Madison, WI, 1994.
(48) Sheldrick, G. M. 1996, Unpublished work; based on the method
described in Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33.
(49) Sheldrick, G. M. Siemens Analytical X-ray Division, Madison,
WI 1995.