Periphery-palladated carbosilane dendrimers: Synthesis and reactivity of organopalladium(II) and -(IV) dendritic complexes. Crystal structure of [PdMe(C6H4(OCH2Ph)-4)(bpy)] (bpy = 2,2′-bipyridine)

Article abstract of DOI:10.1021/om9901269

A carbosilane dendrimer with 12 peripheral iodoarene groups, [Si{(CH₂)₃Si((CH₂)₃-SiMe ₂(C₆H₄CH₂OC₆H ₄I-4))₃}₄] (G₁-ArI, 9), and the corresponding G₀ model compound [Si-{(CH₂)₃SiMe₂(C₆H ₄CH₂OC₆H₄I-4)}₄] (G₀-ArI, 8) have been prepared from [Si{(CH₂)₃Si((CH₂)₃-SiMe ₂(C₆H₄CH₂Br))₃} ₄] (G₁-Br, 7) and the corresponding G₀ model compound [Si{(CH₂)₃SiMe₂-(C₆H ₄CH₂Br)}₄] (G₀-Br, 6). These dendritic species react with [Pd₂(dba)₃·dba/tmeda] (dba = dibenzylideneacetone, tmeda = N,N,N′,N′-tetramethylethylenediamine) to yield the periphery-palladated complexes [Si{(CH₂)₃SiMe₂(C₆H ₄CH₂O(C₆H₄-4)PdI(tmeda))} ₄] (G₀-ArPdI(tmeda), 10) and [Si{(CH₂)₃Si((CH₂)₃SiMe ₂(C₆H₄CH₂O(C₆H ₄-4)PdI(tmeda))3}4] (G₁-ArPdI(tmeda), 11). Complexes 10 and 11 react with LiMe and 2,2′-bipyridine (bpy) to yield the air-stable [Si-{(CH₂)₃SiMe₂(C₆H ₄CH₂OC₆H₄PdMe(bpy))}₄] (G₀-PdMe(bpy), 12) and [Si{(CH₂)₃Si((CH₂)₃-SiMe ₂(C₆H₄CH₂OC₆H ₄PdMe(bpy)))₃}₄] (G₁-ArPdMe(bpy), 13). Complexes 12 and 13 undergo oxidative addition with benzyl bromide to form species containing Pd(IV) centers. These complexes can undergo subsequent reductive elimination at ambient temperature involving both Me-Ar and Me-CH₂Ph coupling on decomposition. Iodoarenes that model the arms of carbosilane-based dendrimers have been synthesized, and procedures have been developed for maximizing yields of organopalladium(II) and -(IV) derivatives of the iodoarenes as part of a program directed toward the isolation and study of organopalladium functionalized dendrimers. The iodoarenes RC₆H₄(CH₂OC₆H ₄I-4′)-4 (R = H (1a), SiMe₃ (1b)) were obtained and found to undergo facile oxidative addition to [Pd₂(dba)₃·dba/tmeda] to form [PdI(Ar)-(tmeda)] (2a,b), which react with LiMe to form [PdMe(Ar)(tmeda)] (3a,b). Bpy displaces tmeda to form [PdMe(Ar)(bpy)] (4a,b), and the latter complexes undergo oxidative addition with benzyl bromide to form the complexes [PdBrMeAr(CH₂Ph)(bpy)] (5a,b). The palladium-(IV) complex 5a undergoes facile and clean reductive elimination at ambient temperature in CDCl₃ to form the coupling products Me-C₆H₄(OCH₂Ph)-4 (89%), PhCH₂-C₆H₄(OCH₂Ph)-4 (9%), and Me-CH₂Ph (2%). However, 5b undergoes more complex behavior to form Me-C₆H₄-(OCH₂C₆H ₄(SiMe₃)-4′)-4 (87%), Me-CH₂Ph (6%), and PhCH₂-CH₂Ph (7%) together with [PdBr₂(bpy)]. The complex [PdMe(C₆H₄(OCH₂Ph)-4)(bpy)] (4a) has been characterized by X-ray diffraction. The asymmetric unit contains two similar but crystallographically independent molecules. Each molecule has square-planar geometry for palladium with the aryl ring tilted by 76.2(4) and 67.1(3)° to the coordination plane, respectively. The crystal examined by X-ray diffraction exhibits significant substitutional disorder at one site: [PdX-(C₆H₄(OCH₂Ph)-4)(bpy)] (X = Me (71%), Cl (29%)).

Full text of DOI:10.1021/om9901269

2970
Organometallics 1999, 18, 2970-2980
P er ip h er y-P a lla d a ted Ca r bosila n e Den d r im er s:
Syn th esis a n d Rea ctivity of Or ga n op a lla d iu m (II) a n d
-(IV) Den d r itic Com p lexes. Cr ysta l Str u ctu r e of
[P d Me(C6H4(OCH2P h )-4)(bp y)] (bp y ) 2,2′-Bip yr id in e)
Neldes J . Hovestad,† J ason L. Hoare,‡ J ohann T. B. H. J astrzebski,†
Allan J . Canty,‡ Wilberth J . J . Smeets,§ Anthony L. Spek,§,| and
Gerard van Koten*,†
Debye Institute, Department of Metal-Mediated Synthesis, Utrecht University, Padualaan 8,
3584 CH Utrecht, The Netherlands, School of Chemistry, University of Tasmania, Hobart,
Tasmania, 7001 Australia, and Bijvoet Center for Biomolecular Research, Department of
Crystal and Structural Chemistry, Utrecht University, Padualaan 8,
3584 CH Utrecht, The Netherlands
Received February 22, 1999
A carbosilane dendrimer with 12 peripheral iodoarene groups, [Si{(CH2)3Si((CH2)3-
SiMe2(C6H4CH2OC6H4I-4))3}4] (G1-ArI, 9), and the corresponding G0 model compound [Si-
{(CH2)3SiMe2(C6H4CH2OC6H4I-4)}4] (G0-ArI, 8) have been prepared from [Si{(CH2)3Si((CH2)3-
SiMe2(C6H4CH2Br))3}4] (G1-Br, 7) and the corresponding G0 model compound [Si{(CH2)3SiMe2-
(C6H4CH2Br)}4] (G0-Br, 6). These dendritic species react with [Pd2(dba)3‚dba/tmeda] (dba )
dibenzylideneacetone, tmeda ) N,N,N′,N′-tetramethylethylenediamine) to yield the periphery-
palladated complexes [Si{(CH2)3SiMe2(C6H4CH2O(C6H4-4)PdI(tmeda))}4] (G0-ArPdI(tmeda),
10) and [Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2O(C6H4-4)PdI(tmeda))3}4] (G1-ArPdI(tmeda), 11).
Complexes 10 and 11 react with LiMe and 2,2′-bipyridine (bpy) to yield the air-stable [Si-
{(CH2)3SiMe2(C6H4CH2OC6H4PdMe(bpy))}4] (G0-PdMe(bpy), 12) and [Si{(CH2)3Si((CH2)3-
SiMe2(C6H4CH2OC6H4PdMe(bpy)))3}4] (G1-ArPdMe(bpy), 13). Complexes 12 and 13 undergo
oxidative addition with benzyl bromide to form species containing Pd(IV) centers. These
complexes can undergo subsequent reductive elimination at ambient temperature involving
both Me-Ar and Me-CH2Ph coupling on decomposition. Iodoarenes that model the arms of
carbosilane-based dendrimers have been synthesized, and procedures have been developed
for maximizing yields of organopalladium(II) and -(IV) derivatives of the iodoarenes as part
of a program directed toward the isolation and study of organopalladium functionalized
dendrimers. The iodoarenes RC6H4(CH2OC6H4I-4′)-4 (R ) H (1a ), SiMe3 (1b)) were obtained
and found to undergo facile oxidative addition to [Pd2(dba)3‚dba/tmeda] to form [PdI(Ar)-
(tmeda)] (2a ,b), which react with LiMe to form [PdMe(Ar)(tmeda)] (3a ,b). Bpy displaces
tmeda to form [PdMe(Ar)(bpy)] (4a ,b), and the latter complexes undergo oxidative addition
with benzyl bromide to form the complexes [PdBrMeAr(CH2Ph)(bpy)] (5a ,b). The palladium-
(IV) complex 5a undergoes facile and clean reductive elimination at ambient temperature
in CDCl3 to form the coupling products Me-C6H4(OCH2Ph)-4 (89%), PhCH2-C6H4(OCH2Ph)-4
(9%), and Me-CH2Ph (2%). However, 5b undergoes more complex behavior to form Me-C6H4-
(OCH2C6H4(SiMe3)-4′)-4 (87%), Me-CH2Ph (6%), and PhCH2-CH2Ph (7%) together with
[PdBr2(bpy)]. The complex [PdMe(C6H4(OCH2Ph)-4)(bpy)] (4a ) has been characterized by
X-ray diffraction. The asymmetric unit contains two similar but crystallographically
independent molecules. Each molecule has square-planar geometry for palladium with the
aryl ring tilted by 76.2(4) and 67.1(3)° to the coordination plane, respectively. The crystal
examined by X-ray diffraction exhibits significant substitutional disorder at one site: [PdX-
(C6H4(OCH2Ph)-4)(bpy)] (X ) Me (71%), Cl (29%)).
In tr od u ction
their precisely defined nanoscale, often globular, mo-
lecular structure. For example, exciting potential ap-
plications are being developed in areas such as micelle
mimicry, magnetic resonance imaging, immunodiag-
nostics, and targeted gene delivery.1-13 There also has
Dendrimers are currently generating enormous inter-
est in diverse areas of science and technology due to
* To whom correspondence should be addressed. Tel: +3130
2533120. Fax: +31302523615. E-mail: g.vankoten@chem.uu.nl.
† Debye Institute, Utrecht University.
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‡ University of Tasmania.
§ Bijvoet Center for Biomolecular Research, Utrecht University.
| Address correspondence pertaining to crystallographic studies to
this author. E-mail: A.L.Spek@chem.uu.nl.
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10.1021/om9901269 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 07/08/1999

Periphery-Palladated Carbosilane Dendrimers
Organometallics, Vol. 18, No. 16, 1999 2971
been an explosive interest in the chemistry of dendrim-
ers incorporating transition metals into their structure,
as part of the dendrimeric skeleton14-26 and/or as
peripheral functionalization.27-42 Periphery-functional-
ized dendrimers have immense potential in areas such
as organic synthesis and homogeneous catalysis, where
well-defined and easily accessible reaction sites (or their
precursors) are essential. Furthermore, their nanoscale
macromolecular architecture should allow simple re-
moval of the catalytic species from product streams.
Recently an organonickel dendrimer containing 12
nickel atoms σ-bonded to the peripheral carbon atoms
of a carbosilane dendrimer was shown to be catalytically
F igu r e 1.
active for the Kharasch addition of polyhalogenoalkanes
to carbon-carbon double bonds.29
The development of organopalladium(IV) chemistry
is also a relatively recent phenomenon,43,44 and the
observed or suspected intermediacy of Pd(IV) complexes
in various stoichiometric and catalytic organic trans-
formations has generated numerous studies aimed at
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reactions. Interesting examples of selectivity in C-C
bond formation in reductive elimination from triorga-
nopalladium(IV) complexes have been documented.43-54
For complexes containing structurally simple organic
groups, [PdIVMeAr(CH2Ph)(N∼N)], exclusive Ar-Me
bond formation has been observed when the bidentate
nitrogen donor is 2,2′-bipyridine (bpy) with less selectiv-
ity observed for the more rigid 1,10-phenanthroline
(phen).52,54 This has been ascribed to the increased
rigidity of phen, hindering the necessary rearrange-
ment(s) of organic groups at the Pd(IV) center and/or
the formation of other transition states.
Recently, we have prepared carbosilane dendrimers
with terminal iodoarene functionality, derived from
polyols, and incorporating an ester group.55 These
dendrimers were functionalized with organopalladium
groups at their periphery, via the oxidative addition of
the C-I bond to Pd(0). However, as determined by
studies on a model compound, the ester function in the
molecule appeared to prevent the transmetalation of the
complex to a diorganopalladium(II) complex. The emerg-
ing importance of organopalladium(IV) complexes has
prompted us to attempt the synthesis of dendrimers
containing organo groups that are expected to be both
ideal for palladium functionalization and transmetala-
tion and suitable for incorporation as part of the
dendrimer synthesis prior to palladium functionaliza-
tion. In view of recent work showing that transmeta-
lation is possible when there is a methoxy substituent
on the aryl group of [PdI(Ar)(tmeda)],54 we report here
the synthesis of a carbosilane dendrimer with peripheral
functionality identical with those of 1a ,b (see Figure 1)
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2972 Organometallics, Vol. 18, No. 16, 1999
Hovestad et al.
and developed the organopalladium chemistry of 1a ,b
as model chemistry for the incorporation of palladium
into the dendrimer.
Groups 1a ,b are suitable periphery groups, since
iodoarenes undergo facile oxidative addition reactions
with palladium(0) substrates (eq 1)54,56,57 and there is
an emerging synthetic chemistry for carbosilane-based
dendrimers.8,25,28,29,32 These studies were undertaken to
(C6H4(OCH2Ph)-4)(tmeda)] (2a ). The reaction of 1b with
[Pd2(dba)3‚dba/tmeda] occurred in 95% yield in benzene
at 8 °C and in 50% yield in benzene at room temperature
to give [PdI(C6H4(OCH2C6H4SiMe3-4′)-4)(tmeda)] (2b).
Reaction of excess LiMe with the arylpalladium iodide
complexes 2a ,b gave the methyl(aryl)palladium(II) com-
plexes 3a ,b without formation of metallic palladium.
Due to the intrinsic thermal instability of 3a ,b (slow
decomposition occurs even at -30 °C in solution) these
1
compounds were only characterized by H and 13C{1H}
spectroscopy (see Experimental Section). However, sub-
sequent exchange of the tmeda ligand by bpy afforded
in quantitative yield the corresponding bpy analogues
4a ,b respectively, which are temperature- and air-stable
and have been fully characterized.
The oxidative addition of benzyl bromide to acetone
solutions of 4a ,b was performed at 0 °C, and isolation
of the triorgano-Pd(IV) complexes (5a ,b; see eq 2) as
white powders was carried out at low temperature by
means of a dry ice cooled microfilter.
determine the most efficient reaction conditions for
periphery palladation of dendrimers containing terminal
ArI moieties, since (at least near) quantitative reactions
are required in practical dendrimer syntheses to mini-
mize laborious purification procedures. To assess the
impact of the increase in steric bulk around the pal-
ladium center, X-ray crystallographic studies were
undertaken on one such Pd(II) complex. Of particular
interest in this study was the effect of the large para
substituents on the synthesis and structure of Pd(II) and
Pd(IV) complexes, including selectivity in reductive
elimination compared with smaller methoxy substitu-
ents already studied,54 since this should be expected to
give useful information toward developing dendrimer
chemistry containing Pd-C σ-bonds. Studies of the
model chemistry indicated suitable conditions for the
synthesis of a periphery-palladated dendrimer, followed
by a NMR investigation of the formation and decompo-
sition of Pd(IV) centers at the periphery of a dendrimer.
Resu lts
Once isolated, the Pd(IV) complexes could be handled
for short periods in the solid state at 0 °C. In the absence
of X-ray crystallographic data, the structures of the Pd-
(IV) complexes have been assigned the configuration as
shown in eq 2 from comparison of spectra with earlier
1H and 13C{1H} NMR spectroscopic studies of related
complexes. These have shown that the chemical shift
of PdIVMe resonances in the 1H NMR spectrum depends
on the position of the methyl group relative to nitrogen
and halogen, with Me trans to N appearing at low-field
(∼2.3 ppm) and Me trans to X (X ) Br, I) at higher field
(∼1.7 ppm).52 For complexes [PdXMe(Ph)(CH2Ph)(bpy)]
(X ) Br, I), 13C{1H} NMR spectroscopic studies have
shown that the CH2Ph and X groups are most likely
mutually trans.52 Small-scale NMR studies have shown
that the oxidative addition of organohalides to [PdMe2-
(bpy)] is quantitative,47,48,58 although the Pd(IV) com-
plexes thus formed are generally isolated in moderate
yield (52-71%). The results presented herein indicate
that it is possible to isolate these thermally unstable
organopalladium(IV) complexes of bpy in higher yield
(∼80%).
Syn th esis a n d Rea ctivity of P a lla d iu m (II) a n d
-(IV) Com p lexes. In the preparation of completely
functionalized organopalladium dendrimers, it is crucial
to develop experimental procedures which prevent the
formation of metallic palladium wherever possible. The
synthetic procedure for the preparation of phenylpal-
ladium(II) compounds, developed by de Graaf et al.,56,57
shown to be useful for substituted iodoarenes54 and used
in the preparation of palladated dendrimers,55 was
successfully modified to give high-yield preparations of
new arylpalladium(II) complexes from 1a ,b. Palladium-
(IV) complexes were prepared by oxidative addition of
benzyl bromide to an acetone solution of these Pd(II)
precursors.
The reaction of [Pd2(dba)3‚dba/tmeda] with ArI is
typically performed at 50 °C in benzene and 80 °C in
tetrahydrofuran. However, reduced temperatures were
necessary for the reaction of [Pd2(dba)3‚dba/tmeda] with
1a ,b in order to prevent extensive decomposition to
metallic palladium. Thus, the reaction of 1a with [Pd2-
(dba)3‚dba/tmeda] occurred quantitatively at room tem-
perature in benzene and in 95% yield in tetrahydrofuran
at room temperature to give the tmeda complex [PdI-
Red u ctive Elim in a tion fr om P d (IV) Com p lexes.
The Pd(IV) complexes decompose cleanly in CDCl3 to
give Pd(II) complexes and no metallic palladium. While
organic group coupling is predominantly between Ar
and Me groups, it is exclusive for neither of the Pd(IV)
complexes. For 5a the reductive elimination products
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Periphery-Palladated Carbosilane Dendrimers
Organometallics, Vol. 18, No. 16, 1999 2973
Ta ble 1. Cr ysta l Da ta a n d Deta ils of th e
Str u ctu r e Deter m in a tion of
arise from Me-Ar, Ar-CH2Ph, and Me-CH2Ph coupling,
in 89%, 9%, and 2% yields, respectively (eq 3). For
P d Me(C6H4(OCH2P h )-4)(bip y) (4a )
empirical formula
C24H22N2OPd‚C24-xH22-3x
-
N2OPdClx (x ) 0.289)
fw
927.64
cryst syst
space group
a, b, c, (Å)
triclinic
P1h (No. 2)
10.6985(8), 11.8973(8),
17.5225(14)
R, â, γ (deg)
Vcalcd (Å3)
Z
103.495(6), 92.797(6), 114.671(8)
1943.6(3)
2
1.585
941
9.9
Dcalcd (g/cm3)
F(000) (e)
complex 5b the decomposition products arise from Me-
Ar, PhCH2-Br, and Me-CH2Ph coupling in 92%, 3%,
and 3% yields, respectively. For this complex 2% of the
organic products were identified by GC-MS as the
PhCH2-CH2Ph coupling product (vide infra).
Earlier studies of selectivity in reductive elimination
from related triorganopalladium(IV) complexes have
used integration of signals in 1H NMR spectra to
determine the ratios of products.52,54 In this study,
although the corresponding organopalladium(II) com-
plexes were observable in the 1H NMR spectra, their
precipitation in the NMR tube rendered unsuitable the
use of NMR integration. In these cases stoichiometry
was determined by GC-MS analysis of NMR samples
after complete disappearance of Pd(IV) signals and silica
gel chromatography to remove Pd(II) products.
The decomposition of [PdBrMe{C6H4(OCH2Ph)-4}-
(CH2Ph)(bpy)] (5a ) was also examined in the presence
of PhCH2Br, and products different from those of eq 3
were detected. Although Me-Ar (87%) and Me-CH2-
Ph (6%) were detected as for eq 3, PhCH2-CH2Ph (7%)
was also observed and an orange crystalline precipitate
of [PdBr2(bpy)] was formed. No palladium metal was
formed.
Ligh t-In d u ced Decom p osition of Dior ga n op a l-
la d iu m (II) bp y Com p lexes 4a ,b. To test the robust-
ness of the Pd(II) moiety and both the Si-C and C-O
bonds present in the molecules, solid-state and solution
decomposition studies were undertaken. After exposure
to light at ambient temperature for 1 week, bright
yellow samples of 4a ,b became dark brown, and GC-
MS analysis of a diethyl ether extract of the solid
residues revealed the presence of Me-Ar coupling
products only, i.e., Me-C6H4(OCH2Ph)-4 and Me-C6H4-
(OCH2C6H4(SiMe3)-4′)-4 for 4a ,b, respectively. Thus, the
solid-state decomposition of the organopalladium(II)
complexes reported here occurs via a reductive elimina-
tion process. Chlorine incorporation into the molecule
occurred during recrystallization from CDCl3, either via
direct reaction of the Pd(II) complex with CDCl3 or with
DCl/HCl present in CDCl3. An acetone solution of 4a
decomposed over 1 week to yield orange crystals, which
were analyzed by X-ray crystallography. The crystals
contain both the starting material 4a and [PdCl-
(C6H4(OCH2Ph)-4)(bpy)] (vide infra).
Str u ctu r a l Stu d y of Cr ysta ls Obta in ed d u r in g
Decom p osition of 4a . The crystal examined has two
independent molecules in the asymmetric unit. Crystal-
lographic data and related bond length and angles are
presented in Tables 1 and 2. One of these is [PdMe-
(C6H4(OCH2Ph)-4)(bpy)] (4a ) (molecule 1) (Figure 2),
and the other (“molecule 2”) is substantially disordered
such that 29% of the molecules are [PdCl(C6H4(OCH2-
Ph)-4)(bpy)] instead of the methylpalladium(II) complex.
µ(Mo KR) (cm-1
cryst size (mm)
temp (K)
radiation, Mo KR (graphite
monochromated) (Å)
)
0.05 × 0.08 × 0.63
150
0.710 73
θmin, θmax (deg)
1.2, 25.0
ω
0.86 + 0.35 tan θ
3, no decay
-12 to +13; -15 to +13;
-22 to +22
12 298, 6837
4062
scan type
scan (deg)
ref rflns
data set
total, unique no of data
no. of obsd data (I > 2.0σ(I))
N
ref, Npar
6837, 553
R, Rw, S
0.0592, 0.1356, 1.00
w ) 1/(σ2(Fo2) + (0.0516P)2)
0.00, 0.00
weighting scheme
max, av shift/error
min, max resd intensity (e/Å3) -1.20, 0.87
“Molecule 2” has bond lengths and angles similar to
those of molecule 1 (Table 1), and the geometry at
palladium is very similar to that reported for the two
polymorphs of [PdMePh(bpy)].57,59
The conformation of the arylpalladium(II) group is of
particular interest, as it provides one indication of the
possible geometry to be obtained in periphery-palladated
carbosilane dendrimers. The aryl group bonded to
palladium forms dihedral angles of 76.2(4)° (molecule
1) and 67.1(3)° (“molecule 2”) with the “PdC2N2” mean
planes, compared to 78.7(2)° in one polymorph of [Pd-
MePh(bpy)]57 and 65.7(11), 70.7(10), 75.3(11), and 75.7-
(12)° in the four independent molecules in a second
polymorph of [PdMePh(bpy)].59 The variation in the
values between the two molecules in the crystal is
reflected also in dihedral angles between the phenyl
rings in each [PdC6H4OCH2C6H5] unit (54.3(4)° (mol-
ecule 1), 67.9(4)° (“molecule 2”)) and in the torsion
angles between the outer phenyl ring and the “OCCipso
”
group (-179.2(7)° (molecule 1), 172.0(6)° (“molecule 2”)).
Syn t h esis a n d Ch a r a ct er iza t ion of G0-Ar I a n d
G1-Ar I. The dendritic alkyl bromide intermediates 6
and 7 were synthesized in high (80%) or moderate (55%)
overall yields by starting from the corresponding poly-
1
ols.60 The H NMR spectra show an AA′BB′ pattern for
the aromatic protons on the disubstituted benzene ring
of 6 and 7 in the range 7.4-7.6 ppm. Benzylic protons
appear at 4.49 and 4.46 ppm, respectively. The meth-
ylene protons appear for G0 (24) and G1 (72) as three
well-resolved resonances. The 13C{1H} NMR spectra
show characteristic signals for the benzylic carbon at
34.1 and 33.8 ppm. Only two of the inner core methylene
(59) Spek, A. L.; J anssen, M. D.; Markies, B. A.; van Koten, G. Acta
Crystallogr., Sect. C 1996, 52, 868.
(60) Hovestad, N. J .; J astrzebski, J . T. B. H.; van Koten, G. Polym.
Mater. Sci. Eng. 1999, 80, 53.

2974 Organometallics, Vol. 18, No. 16, 1999
Hovestad et al.
Sch em e 1a
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) a n d Oth er Da ta for th e Or d er ed a n d
Disor d er ed Molecu les of
[P d Me(C6H4(OCH2P h )-4)(bp y)] (4a )
ordered (n ) 1)a
disordered (n ) 2)b
Bond Distances
2.121(8)
Pd(n)-C(11n)
Pd(n)-C(12n)
Pd(n)-N(1n)
Pd(n)-N(2n)
Pd(2)-Cl(1)
2.01(3)c
1.996(8)
2.123(7)
2.122(7)
2.38(2)c
1.971(9)
2.111(7)
2.120(8)
Bond Angles
85.0(3)
C(11n)-Pd(n)-C(12n)
C(11n)-Pd(n)-N(1n)
C(11n)-Pd(n)-N(2n)
C(12n)-Pd(n)-N(1n)
C(12n)-Pd(n)-N(2n)
N(1n)-Pd-N(2n)
87.3(10)
175.0(10)
98.2(10)
97.7(3)
174.2(3)
76.9(3)
178.4(3)
101.3(3)
96.3(3)
171.6(3)
77.5(3)
Pd(n)-C(12n)-C(13n)
Pd(n)-C(12n)-C(17n)
Pd(n)-N(1n)-C(1n)
Pd(n)-N(1n)-C(5n)
Pd(n)-N(2n)-C(6n)
Pd(n)-N(2n)-C(10n)
Cl(1)-Pd(2)-C(122)
Cl(1)-Pd(2)-N(12)
Cl(1)-Pd(2)-N(22)
118.0(6)
126.4(6)
125.8(6)
116.2(5)
115.5(5)
127.1(7)
121.0(6)
124.0(6)
126.1(6)
115.9(5)
115.7(6)
126.7(6)
88.5(6)
173.2(6)
96.8(6)
Deviations from the “PdC2N2” mean plane (in Å; ø2 ) 254):
Pd(1),-0.0404(7); C(111), 0.057(8); C(121), -0.060(8); N(11), 0.064(7);
N(21), -0.059(7). The mean planes of pyridine rings containing
N(11), N(21), and the phenyl ring bound to palladium form
dihedral angles of 4.0(3), 10.8(4), and 76.2(4)° with the “PdC2N2”
mean plane. The phenyl ring bonded to palladium forms dihedral
angles of 1.6(8), 2.1(8), and 89.9(4)° with “C(151),O(11),C(181)”,
a
a
Reagents and conditions: (i) 4.1 equiv of CBr4, 4.1 equiv
of PPh3, THF, room temperature, 24 h; (ii) HOC6H4I-4, K2CO3,
acetone, room temperature, 24 h.
b
“O(11),C(181),C(191)”, and the other phenyl ring plane. Devia-
tions from the “PdC2N2” mean plane (in Å; ø2 ) 9.4): Pd(2),
0.015(1); C(112), 0.03(3); C(122), -0.023(8); N(12), 0.028(7); N(22),
-0.024(7). The mean planes of pyridine rings containing N(12),
N(22), and the phenyl ring bound to palladium form dihedral
angles of 3.5(6), 6.0(6), and 65.9(6)° with the “PdC2N2” mean
plane. The phenyl ring bonded to palladium forms dihedral
angles of 7.3(7), 9.0(8), and 67.9(4)° with “C(152),O(12),C(182)”,
“O(12),C(182),C(192)”, and the other phenyl ring plane. c Occu-
pancies for C(11n) and Cl(1) were refined as 0.71 and 0.29,
respectively.
Sch em e 2a
F igu r e 2. ORTEP drawing (50% probability level) of
[PdMe(C6H4(OCH2Ph)-4)(bpy)] (4a ) (molecule 1).
carbons of G1 are visible, and the third resonance occurs
together with resonances of one of the outer methylene
carbons. MALDI-TOF-MS spectra of G0-Br and G1-Br
show signals at m/z 1127.8 and 3644.6 corresponding
to [G0-Br + 1Na]+ (calcd 1127.1) and [G1-Br + 1Ag]+
(calcd 3644.4), respectively. A solution of sodium acetate
in THF was added to the sample of G0-Br, and a solution
of silver(I) trifluoroacetate in THF was added to the
sample of G1-Br in order to improve the peak resolution.
The iodides 8 and 9 were readily obtained from the
bromides 6 and 7 and were synthesized in high overall
yield (68% and 75%; Schemes 1 and 2). They exhibited
NMR resonances with integrations as expected: two
AA′BB′ patterns (aryl) and 24 G0 and 72 G1 “outer”
a
Reagents and conditions: (i/ ii) procedures similar to those
used for the synthesis of 8 in Scheme 1.
methylene protons as three well-resolved resonances.
Benzylic protons appear as singlets at 4.99 and 4.94
ppm, respectively. The 13C{1H} NMR spectra show
characteristic signals for C-I at 83.4 and the benzylic
carbon at 70.4 ppm for both 8 and 9. The MALDI-TOF-
MS spectra of G0-ArI and G1-ArI show signals at m/z

Periphery-Palladated Carbosilane Dendrimers
Organometallics, Vol. 18, No. 16, 1999 2975
F igu r e 3. G1-ArPdMe(bpy) (13).
1772.9 and 5323.2, corresponding to [G0-ArI + 1Ag]
(calcd 1772.1) and [G1-ArI + 1Ag] (calcd 5324.6), re-
spectively.
without formation of metallic palladium. However, due
to their thermal instability in the solid state, the ligand
exchange reactions were performed as soon as possible
after drying and solvent exchange procedures. These
complexes were synthesized in 63% (12) and 51% (13)
overall yields (Figure 3 and Schemes 3 and 4). The Pd-
Rea ction s of G0-Ar I a n d G1-Ar I w ith [P d 2(d ba )3‚
d ba /tm ed a ]: Syn th esis a n d Ch a r a cter iza tion of
Com p lexes. The oxidative addition of substituted den-
dritic iodoarenes to Pd(0) proceeded very well. These
complexes were synthesized in 88% (10) and 33% (11)
overall yield. The complexes exhibited NMR resonances
with integrations as expected. The most characteristic
feature of the 13C{1H} NMR spectra is the lack of a
signal at approximately 100 ppm, arrising from C-I in
G0-ArI and G1-ArI, indicating, in conjunction with the
“clean” AA′BB′ pattern in the 1H NMR spectra, complete
palladation. The MALDI-TOF-MS spectra of [G0-ArPdI-
(tmeda)] and [G1-ArPdI(tmeda)] show signals at m/z
2582.1 and 7927.1, corresponding to [G0-ArPdI(tmeda)
+ 1Na] (calcd 2583.3) and [G1-ArPI(tmeda) + 1Na]
(calcd 7928.1), respectively.
1
Me resonance in H NMR appear at 0.38 and 0.37 ppm,
respectively, and appear in 13C{1H} NMR at -3.8 and
-3.7 ppm, respectively. The MALDI-TOF-MS spectra
of G0-ArPdMe(bpy) and G1-ArPdMe(tbpy) show signals
at m/z 2379.8 and 7147.9, corresponding to [G0-ArPdMe-
(bpy) + Ag] (calcd 2380.4) and [G1-ArPdMe(bpy) + Ag]
(calcd 7149.7), respectively.
P a lla d iu m (IV)-Den d r im er Ch em istr y. The model
Pd(IV) complexes 5a ,b have low stability, and it was
considered unlikely that it would be possible to isolate
Pd(IV) complexes with the G0 and G1 skeletons. Thus,
the reactions of [G0-ArPdMe(bpy)] (12) and [G1-ArPdMe-
(bpy)] (13) with benzyl bromide were examined initially
by 1H NMR spectroscopy, and as a result of this
examination the isolation of complexes was not at-
tempted. Complexes 12 and 13 are slightly soluble in
(CD3)2CO and CDCl3. The latter solvent was used to
Rea ction s of [G0-Ar P d I(tm ed a )] a n d [G1-Ar P d I-
(tm ed a )] w ith LiMe a n d bp y: Syn th esis a n d Ch a r -
a cter iza tion of Com p lexes. Reaction of excess LiMe
with 10 and 11 gave the diorganopalladium complexes

2976 Organometallics, Vol. 18, No. 16, 1999
Hovestad et al.
Sch em e 3a
Sch em e 4a
a
Reagents and conditions: (i) procedures similar to those
used for the synthesis of 12 in Scheme 3.
of benzyl bromide with 12 and 13 could not be deter-
mined, Pd(IV) centers were detected and the occurrence
of Me-Ar and Me-CH2Ph coupling is consistent with
formation of Pd(IV) centers.
Discu ssion
The organoiodides 1a ,b may be successfully converted
into organopalladium(II) and -(IV) complexes, and the
methyl(aryl)benzylpalladium(IV) complexes so obtained
have a fac-PdC3 configuration. The decomposition be-
havior of the Pd(IV) complexes [PdBrMe(C6H4(O-
CH2C6H4R-4′)-4)(CH2Ph)(bpy)] 5a (R ) H) and 5b (R )
SiMe3) differs from that of related complexes reported
earlier. Thus, in contrast to the reaction of eq 3,
[PdBrMe(C6H4R-4)(CH2Ph)(bpy)] (R ) H, OMe) give
exclusively [PdBr(CH2Ph)(bpy)] and Me-Ph.54 The de-
crease in selectivity in reductive elimination for 5a (see
eq 3) compared with that of other [PdBrMeAr(CH2Ph)-
(bpy)] complexes is not as large as that observed for
analogous complexes where the bidentate nitrogen
donor ligand is 1,10-phenanthroline (phen), where up
to 20% of the observed reductive elimination products
arise from Ar-CH2Ph coupling.54 Thermodynamic fac-
tors have been suggested as the main determinants in
selectivity in C-C bond formation during reductive
elimination from [PdBrMe2(CH2Ph)(L2)] (L2 ) bpy,
phen),45 and the selectivity observed for structurally
simple [PdBrMe(Ar)(CH2Ph)(bpy)] complexes is consis-
tent with this proposal, since the Ar-Me bond has
higher energy than those of Ar-CH2Ph and Me-CH2-
Ph. The difference in selectivity exhibited by the phen
complexes has been ascribed to kinetic factors, predomi-
nantly the expected requirement for axial/equatorial
orientation of the ligands to be coupled,61 which requires
a
Reagents and conditions: (i) 4 Pd(dba)2, 4 tmeda, benzene,
0 °C, 1 h; (ii) 4 LiMe, Et2O/THF; 4 bpy, benzene, room
temperature.
characterize Pd(IV) model complexes formed in the
reaction with benzyl bromide and to study their decom-
position. When solutions of 12 and 13 with excess benzyl
bromide were warmed from -20 °C, reaction was
detected at -10 °C. Complex spectra were obtained,
containing broad resonances for the cloudy solutions,
which become more yellow with time. Resonances could
be attributed to PdIVCH2Ph groups (Ha, Hb for the
benzylic group at 3.60 and 3.89 ppm and H3,5, H2,6 for
the phenyl group at 6.70 and 6.48 ppm) on comparison
with spectra of the model complexes 5a ,b in the same
solvent. The PdIVCH2Ph resonances decreased as the
reaction was monitored, and a broad resonance at 2.38
ppm, which appeared soon after reaction commenced,
continued to increase in intensity and could be readily
attributed to “4-MeC6H4”. GC-MS analysis revealed the
presence of Me-CH2Ph and PhCH2-CH2Ph. Bibenzyl
formation is consistent with the observation (see above)
that reaction of the model Pd(II) complex 5a with excess
benzyl bromide results in the formation of 7% PhCH2-
CH2Ph. Thus, although the stoichiometry of reductive
elimination from Pd(IV) centers generated on reaction
(61) Byers, P. K.; Canty, A. J .; Crespo, M.; Puddephatt, R. J .; Scott,
J . D. Organometallics 1988, 7, 1363.

Periphery-Palladated Carbosilane Dendrimers
Organometallics, Vol. 18, No. 16, 1999 2977
isomerization from configuration 5a ,b to allow Me-Ar
coupling. The increased difficulty in achieving this
orientation from the (assumed) cationic intermediate
formed on dissociation of bromide when phen is present,
compared with more flexible bpy, is believed to account
for the lowering in selectivity.54 In the present case,
where the more flexible bpy ligand is present, it is likely
that the decrease in selectivity results from more
hindered motion around an (assumed) intermediate
cationic Pd(IV) center due to the dramatic increase in
steric bulk of the Ar group.
For complex 5b (R ) SiMe3), which decomposes
differently from 5a (R ) H), to give Me-Ar (92%), Me-
CH2Ph (3%), PhCH2-Br (3%), and PhCH2-CH2Ph (2%),
other processes appear to be occurring together with
reductive elimination. The formation of PhCH2-Br
implies that the oxidative addition of PhCH2-Br to Pd-
(II) may be reversible. There are few examples of
reversible oxidative addition in similar systems, and
they appear to be limited to [PdIMe3(L2)] (L2 ) bis(p-
tolylimino)acenaphthene)53 and [PtIMe3(dppe)].62 The
formation of PhCH2-CH2Ph indicates the occurrence of
complex decomposition mechanism(s), and similar ob-
servations have been reported for the reaction of PhCH2-
Br with [PdMe2(PPh3)2], where a Pd(IV) intermediate
was not detected spectroscopically.63
Exp er im en ta l Section
Gen er a l Com m en ts. All syntheses were performed under
an inert atmosphere using standard Schlenk techniques.
Solvents were purified according to standard procedures and
freshly distilled before use. Model compounds IC6H4(OCH2-
Ph)-4 (1a )64 and Me3SiC6H4(CH2Br)-465 were prepared by a
literature procedure, and the dendrimeric silane polyolic
precursors [Si{(CH2)3SiMe2(C6H4CH2OH-4)}4] (G0-OH) and [Si-
{(CH2)3Si((CH2)3SiMe2(C6H4CH2OH))3}4] (G1-OH) were pre-
pared as previously reported.60 Melting points were determined
using a Bu¨chi melting point apparatus and are uncorrected.
[Pd2(dba)3‚dba] was prepared as reported.66 All other reagents
were obtained from Acros, unless otherwise indicated. 1H and
13C{1H} NMR spectra were recorded at 200 and 50 MHz,
respectively, using a Bruker AC200 spectometer, or at 300 and
75 MHz, respectively, using a Bruker AC300 spectrometer, at
room temperature unless otherwise indicated. Chemical shifts
are reported relative to Me4Si. GC-MS analyses were per-
formed on a Unicam Automass instrument, using electron
impact (EI, 70 eV). Microanalyses were performed by Dornis
und Kolbe Microanalytical Laboratories, Mulheim a.d. Ruhr,
Germany, and the Central Science Laboratory, University of
Tasmania. MALDI-TOF-MS spectra were acquired using a
Voyager-DE BioSpectrometry Workstation (PerSeptive Bio-
systems Inc., Framingham, MA) mass spectrometer equipped
with a nitrogen laser emitting at 337 nm. The instrument was
operated in the linear mode at an accelerating voltage in the
range 23 000-25 000 V. External calibration was performed
using insulin (bovine), and detection was done by means of a
linear detector and a digitizing oscilloscope operating at 500
MHz. Sample solutions with ∼30 mg/mL in THF were used,
and the matrix was 3,5-dihydroxybenzoic acid in THF (36 mg/
mL). A solution of sodium acetate in THF or a solution of
silver(I) trifluoroacetate in THF was added to the sample in
order to improve the peak resolution. The sample solution (0.2
µL) and the matrix solution (0.2 µL) were combined and placed
on a gold MALDI target and analyzed after evaporation of the
solvents.
Although Pd(IV) centers could be generated at the
periphery of [G0-ArPdMe(bpy)] and of the dendrimer
[G1-ArPdMe(bpy)], decomposition at the temperature
required for synthesis indicated that it is most unlikely
that a fully palladated Pd(IV) dendrimer could be
isolated.
Con clu d in g Rem a r k s
Procedures for all steps in the preparation of the
methyl(aryl)palladium(II) and methyl(aryl)benzylpal-
ladium(IV) model complexes for periphery palladated
carbosilane dendrimers have been optimized, and struc-
tural studies provide potential configurations for the
aryl benzyl ether fragment of a dendrimer arm bonded
to ‘PdIIMe(bpy)′. The wide variation in the conformations
of the′[Pd(C6H4OCH2Ph)]′ group in molecules 1 and 2
in the crystal obtained on partial decomposition of 4a ,
illustrated by torsion and dihedral angles, indicate that
there may considerable flexibility in these parameters
in dendrimers containing palladated fragments of this
type.
Syn th esis of th e Mod el Com p ou n d . Me3SiC6H4(CH2O-
(C6H4I-4′)-4) (1b). To a solution of Me3SiC6H4(CH2Br)-4 (2.17
g, 8.88 mmol) in 50 mL of acetone were added 4-iodophenol
(1.95 g, 8.88 mmol) and K2CO3 (3 g). The resulting mixture
was stirred at reflux temperature overnight, following which
the volatiles were removed in vacuo and the product partioned
between CH2Cl2 and water. The aqueous layer was washed (3
× 20 mL) with CH2Cl2, and the combined organic extracts were
dried over Na2SO4. Removal of the solvent in vacuo gave a
brown oil which solidified upon standing and which was
purified by column chromatography (silica gel, 25 × 2 cm,
eluent CH2Cl2) to give a white waxy solid in 52% yield. Melting
point: 71 °C. Anal. Calcd for C16H19IOSi (MW ) 382.3): C,
1
50.27; H, 5.01. Found: C, 50.34; H, 4.96. H NMR (CDCl3): δ
Although Pd(IV) complexes of bpy are thermally
unstable, they have been isolated here in high yield, and
in situ studies show that the oxidative addition of model
organohalides to palladium(II) is quantitative and that
decomposition of the unstable complexes can be studied
by NMR and GC-MS. Application of this approach to
[G0-ArPdMe(bpy)] (12) and the palladated dendrimer
[G1-ArPdMe(bpy)] (13) shows that the Pd(IV) centers
can be generated at the periphery of dendrimers, that
the complexes decompose at the same temperature as
those required for their formation, rendering isolation
extremely difficult, and that (at least) both Me-Ar and
Me-CH2Ph coupling occurs from the Pd(IV) centers.
7.59 m (4H, Si-C6H4, 2H, and O-C6H4-I, 2H, ortho to I,
overlapping), 7.40 (d, J ) 7.9 Hz, 2H, Si-C6H4, 2H), 6.76 d (2H,
J ) 7.2 Hz, O-C6H4-I, 2H, ortho to O), 5.03 s (2H, CH2), 0.29
s (9H, SiMe3). 13C{1H} NMR (CDCl3): δ 158.7 (O-C6H4-I,
O-Cipso), 140.5 ((SiMe3)-C6H4CH2, SiMe3-Cipso), 138.3 (O-C6H4-
I, ortho to I), 137.0 ((SiMe3)-C6H4CH2, CH2-Cipso), 133.7 ((SiMe3)-
C6H4-CH2, ortho to SiMe3), 126.8 ((SiMe3)-C6H4-CH2, ortho to
CH2), 117.3 (O-C6H4-I, ortho to O), 83.1 (O-C6H4-I, I-Cipso), 70.1
(Ph-CH2), -1.07 (SiMe3).
Syn th esis of th e Mod el Or ga n op a lla d iu m Com p lexes.
[P d I(C6H4(OCH2P h )-4)(tm ed a )] (2a ). To a stirred solution
of [Pd2(dba)3‚dba] (0.67 g, 1.2 mmol) in benzene (100 mL) was
added tmeda (0.22 mL, 1.4 mmol) and 1a (0.36 g, 1.2 mmol).
The resulting solution was stirred at room temperature for 1
(62) Goldberg, K. I.; Yan, J . Y.; Breitung, E. M. J . Am. Chem. Soc.
1995, 117, 6889.
(64) Cativiela, C.; Serrano, J . L.; Zurbano, M. J . Org. Chem. 1995,
60, 3074.
(63) de Graaf, W.; Boersma, J .; van Koten, G. Organometallics 1990,
9, 1479.
(65) J acob, L. A.; Chen, B.-L.; Stec, D. Synthesis 1993, 6, 611.
(66) Rettig, M. F.; Maitlis, P. M. Inorg. Synth. 1971, 134.

2978 Organometallics, Vol. 18, No. 16, 1999
Hovestad et al.
h, during which time the color changed from deep purple to
yellow. The solution was filtered and the solvent removed in
vacuo to give a yellow residue, which was washed with 3 × 10
mL of diethyl ether/pentane (1:1). The remaining yellow solid
was collected by centriguation and dried in vacuo. Yield: 100%.
The complex is stable in air and was recrystallized from CH2-
Cl2/pentane at -20 °C to give orange cubes. Melting point: 131
°C dec. Anal. Calcd for C19H27IN2OPd (MW ) 532.8): C, 42.84;
J ) 4.37 Hz, bpy H6′), 7.96 m (4H, bpy), 7.55 m and 7.39 m
(9H, overlapping bpy, Ph and C6H4), 6.90 d (2H, J ) 8.48 Hz,
C6H4 o- to O), 5.07 s (2H, CH2), 0.60 s (3H, PdMe). 13C{1H}
NMR (CDCl3): δ 155.3 (bpy), 155.2 (bpy), 154.1 (C6H4O, Cipso),
150.7 (C6H4Pd, Cipso), 150.3 (bpy), 148.4 (bpy), 138.13, 138.08,
137.6, 128.5, 128.4, 127.7, 127.6, 126.1, 125.8, 121.6, 121.2
(aromatics), 113.9 (C6H4O, o to O), 69.9 (CH2), -4.0 (PdMe).
[P dMe(C6H4(OCH2C6H4SiMe3-4′)-4)(bp y)] (4b). This com-
pound was prepared as described for 4a . Anal. Calcd for
1
H, 5.11; N, 5.26. Found: C, 42.77; H, 5.17; N, 5.19. H NMR
(CDCl3): δ 7.36 m (5H, CH2Ph aromatic protons), 7.11 (d, J )
8.4 Hz, 2H, C6H4 o to Pd), 6.70 d (2H, J ) 8.4 Hz, C6H4 o to
O), 4.95 s (2H, CH2Ph), 2.70 m (2H, tmeda, CH2), 2.68 s (6H,
NMe2), 2.58 m (2H, tmeda, CH2), 2.33 s (6H, NMe2). 13C{1H}
NMR (CDCl3): δ 155.93, 137.78, 136.12, 132.22, 128.46,
127.71, 127.63, 113.69 (aromatics), 70.04 (CH2Ph), 62.11
(N(CH3)2), 58.30 (N(CH3)2), 49.90 and 49.76 (tmeda CH2).
[P dI(C6H4(OCH2C6H4SiMe3-4′)-4)(tm eda)] (2b). This com-
pound was prepared in the same manner as 2a , except that
the benzene solution of [Pd2(dba)3‚dba] was cooled in an ice/
water bath before addition of 1b and tmeda. The complex was
isolated as an air- and temperature-stable orange crystalline
solid in 95% yield. The complex may be recrystallized from
CH2Cl2/pentane at -20 °C. Melting point: 140 °C dec. Anal.
Calcd for C22H35IN2OSiPd (MW ) 605.0): C. 43.68; H. 5.83;
C
27H30N2OPdSi‚H2O (MW ) 551.1): C, 58.85; H, 5.85; N, 5.08.
1
Found: C, 58.94; H, 5.38; N, 5.35. H NMR (CDCl3): δ 8.87 d
(1H, J ) 5.3 Hz, bpy H6), 8.37 d (1H, J ) 4.7 Hz, bpy H6′),
7.94 m, 7.49 m, 7.30 m and 6.86 d (14H, bpy, C6H4O & C6H4Si
overlapping), 5.05 s (2H, CH2), 0.59 s (3H, PdMe), 0.28 s (9H,
SiMe3). 13C{1H} NMR (CDCl3): δ 155.3, 155.2, 154.2, 150.7,
150.3, 148.4, 139.7, 138.7, 138.1, 137.6, 136.4, 133.5, 127.0,
126.1, 125.9, 121.6, 121.2, 113.9 (aromatics), 69.9 (CH2), -1.1
(SiMe3), -4.0 (PdMe). The presence of water in the sample is
1
apparent in the H NMR spectrum and arises from the rapid
synthesis of this compound from 3b (vide supra).
[P d Br Me(C6H4(OCH2P h )-4)(CH2P h )(bp y)] (5a ). To an
acetone solution of 4a (60.8 mg, 0.13 mmol) at 0 °C was added
10 equiv of PhCH2Br, and the resulting solution was stirred
for 30 min and then cooled to -30 °C for 5 h, during which
time a white precipitate had formed. The solid was collected
by filtration at ∼-40 °C and washed with cold (-30 °C) ether
until PhCH2Br was not detected in the washings by GC-MS.
The compound was dried in vacuo at 0 °C. Yield: 89%. 1H NMR
(263 K, CDCl3): δ 8.68 d (1H, J ) 5.9 Hz, bpy H6), 8.32 d (1H,
J ) 5.0 Hz, bpy H6′), 8.05 d (1H, J ) 8.1 Hz, bpy), 7.94 d (1H,
J ) 8.1 Hz, bpy), 7.84 t (1H, J ) 7.6 Hz, bpy), 7.78 b (2H,
bpy), 7.68 t (1H, J ) 7.5 Hz, bpy), 7.46 m (6H, PhCH2O, H2,3,5,6
and C6H4Pd o to Pd overlapping), 7.22 t (1H, J ) 6.8 Hz,
PhCH2O, H4), 6.99 d (2H, J ) 8.5 Hz, C6H4O o to O), 6.77 t
(1H, J ) 7.3 Hz, PdCH2Ph, H4), 6.59 t (2H, J ) 7.2 Hz,
PdCH2Ph, H3,5), 6.39 b (2H, PdCH2Ph, H2,6), 5.10 s (2H, OCH2-
Ph), 3.83 d (1H, J ) 7.2 Hz, PdCHaHbPh), 3.69 d (1H, J ) 7.2
Hz, PdCHaHbPh), 2.35 s (3H, PdMe).
[P d Br Me{C6H4(OCH2C6H4(SiMe3)-4′)-4)(CH2P h )(bp y)]
(5b). This compound was prepared as for 5a above. Yield: 87%.
1H NMR (263 K, CDCl3): δ 8.71 d (1H, J ) 5.3 Hz, bpy H6),
8.35 d (1H, J ) 5.0 Hz, bpy H6′), 8.07 d (1H, J ) 8.0 Hz, bpy),
7.92 m (2H, bpy), 7.76 m (3H, bpy & C6H4Pd o to Pd
overlapping), 7.60 d (2H, J ) 7.8 Hz, C6H4Si), 7.49 d (2H, J )
7.5 Hz, C6H4Si), 7.45 t (1H, J ) 6.5 Hz, bpy), 7.26 t (1H, J )
6.7 Hz, bpy), 6.98 d (2H, J ) 8.6 Hz, C6H4O o to O), 6.79 t
(1H, J ) 7.5 Hz, PdCH2Ph, H4), 6.61 t (2H, J ) 7.3 Hz,
PdCH2Ph, H3,5), 6.43 b (2H, PdCH2Ph, H2,6), 5.10 s (2H, OCH2-
Ph), 3.84 d (1H, J ) 7.2 Hz, PdCHaHbPh), 3.69 d (1H, J ) 7.2
Hz, PdCHaHbPh), 2.36 s (3H, PdMe), 0.28 s (9H, SiMe3).
1
N. 4.63. Found: C, 43.42; H, 5.73; N, 4.71. H NMR (CDCl3):
δ 7.52 d (2H, J ) 7.8 Hz, SiMe3-C6H4), 7.39 d (2H, J ) 7.8 Hz,
SiMe3-C6H4), 7.11 d (2H, J ) 8.5 Hz, C6H4Pd o to Pd), 6.71 d
(2H, J ) 8.4 Hz, C6H4O, o to O), 4.94 s (2H, OCH2), 2.76-2.54
m and 2.68 s (10H, tmeda CH2 and NMe2), 2.34 s (6H, NMe2),
0.26 s (9H, SiMe3). 13C{1H} NMR (CDCl3): δ 156.1 (C6H4O,
C
ipso), 139.8 (C6H4Pd, Cipso), 138.3 (C6H4CH2, Cipso), 136.1 (C6H4-
Pd, o to Pd), 133.5 (C6H4CH2), 132.1 (C6H4Si, Cipso), 127.0 (C6H4-
CH2), 113.9 (C6H4O, o to O), 70.0 (CH2), 62.1 (NMe2), 58.3
(NMe2), 49.9 & 49.8 (tmeda CH2), -1.1 (SiMe3).
[P d Me(C6H4(OCH2P h )-4)(tm ed a )] (3a ). The white com-
plex (MW ) 420.9) was obtained in 93% yield using the
reported procedure for MePhPdII complexes.48 The complex is
insufficiently stable for microanalysis. However, it was suf-
1
ficiently characterized by H and 13C{1H} NMR spectroscopy,
and afterward it was converted to complex 4a by ligand
exchange. 1H NMR (CDCl3, 253 K): δ 7.39 m (7H, Ph and C6H4
Pd o to Pd, overlapping), 6.75 d (2H, J ) 8.1 Hz, C6H4O o to
O), 4.96 s (2H, CH2), 2.59 m (4H, tmeda, CH2), 2.52 s, (6H,
NMe2), 2.30 s (6H, NMe2), -0.08 s (3H, Pd-Me). 13C{1H} NMR
(CDCl3, 253 K): δ 154.6 (C6H4O, Cipso), 150.6 (C6H4Pd, Cipso),
137.9 (PhCH2, Cipso), 137.4 (C6H4Pd, o to Pd), 128.6 (PhCH2),
128.0 (PhCH2), 127.8 (PhCH2), 113.0 (C6H4O, o to O), 69.5
(CH2), 59.9 (NMe2), 59.3 (NMe2), 48.6 (tmeda, CH2), -8.2 (Pd-
Me).
[P d Me(C6H4(OCH2C6H4(SiMe3)-4′)-4)(tm ed a )] (3b). This
complex was synthesized as described for 3a , in 97% yield,
and is a white, thermally unstable compound (MW ) 493.1).
1H NMR (CDCl3, 253 K): δ 7.56 d (2H, AA′BB′, J ) 7.8 Hz,
C6H4Si), 7.46 d (2H, AA′BB′, J ) 7.7 Hz, C6H4Si), 7.36 d (2H,
AA′BB′, J ) 8.2 Hz, C6H4Pd, o to Pd), 6.77 d (2H, AA′BB′, J )
8.1 Hz, C6H4O o- to O), 4.96 s (2H, CH2), 2.57 m (4H, tmeda,
CH2), 2.52 s, (6H, NMe2), 2.31 s (6H, NMe2), 0.27 s (9H, SiMe3),
-0.08 s (3H, PdMe). 13C{1H} NMR (CDCl3, 253 K): δ 154.6
(C6H4O, Cipso), 150.6 (C6H4Pd, Cipso), 139.9 (C6H4Si, Cipso), 138.4
(C6H4CH2, Cipso), 137.4 (C6H4Pd, o to Pd), 133.7 (C6H4Si, o to
Si), 127.3 (C6H4CH2, o to CH2), 112.9 (C6H4O, o-to O), 69.4
(CH2), 59.9 (NMe2), 59.3 (NMe2), 48.6 (tmeda, CH2), -0.94
(SiMe3), -8.2 (PdMe).
2
Syn th esis of G0-Br a n d G1-Br . G0-Br Si{(CH )3SiMe2-
(C6H4-4)CH2Br }4 (6). To a solution of G0-OH (0.84 g, 0.98
mmol) in THF (20 mL) were added PPh3 (1.61 g, 6.15 mmol)
and, in small portions, CBr4 (2.04 g, 6.15 mmol). The mixture
was stirred at room temperature for 17 h and filtered, and
the solvent was removed in vacuo. The residue was dissolved
in DCM and the solution chromatographed on silica gel (DCM
eluent). The product was obtained as a pale yellow oil in 80%
yield. Anal. Calcd for C48H72Br4Si5 (MW ) 1109.2): C, 51.98;
H, 6.54; Si, 12.66. Found: C, 52.13; H, 6.63; Si, 12.61. 1H NMR
(CDCl3): δ 7.48 (d, J ) 8.1 Hz, 8H, ArH, 7.37 (d, J ) 8.1 Hz,
8H, ArH), 4.49 (s, 8H, ArCH2), 1.30 (m, 8H, SiCH2CH2), 0.78
(t, J ) 8.1 Hz, 8H, CH2SiAr), 0.50 (t, J ) 8.1 Hz, 8H, CH2-
SiCH2), 0.24 (s, 24H, Si(CH3)2Ar). 13C{1H} NMR (CDCl3): δ
140.9 (4C, Ar, C-Si), 138.6 (4C, Ar, C-CH2), 134.5 (8C, Ar, C o
to Si), 128.7 (8C, Ar, C o to CH2), 34.1 (4C, ArCH2), 21.0 (4C,
CH2SiAr), 19.0 (4C, CH2CH2SiAr), 17.9 (4C, SiCH2CH2CH2),
-2.4 (SiCH3)2Ar). MALDI-TOF-MS: m/z 1127.8 [G0-ArCH2-
Br + 1Na]+ (calcd 1127.1).
[P d Me(C6H4(OCH2P h )-4)(bp y)] (4a ). The bright yellow
air- and temperature-stable complex was obtained in quantita-
tive yield using the reported procedure for MePhPdII com-
plexes.54 This complex is light-sensitive, decomposing to
metallic palladium after approximately 2 days when stored
in the light. Anal. Calcd for C24H22N2OPd (MW ) 460.9): C,
1
62.55; H, 4.81; N, 6.08. Found: C, 62.38; H, 4.80; N, 5.94. H
G1-Br , Si{(CH 2)3Si((CH 2)3SiMe2(C6H 4CH 2Br -4))3}4 (7).
NMR (CDCl3): δ 8.88 d (1H, J ) 5.12 Hz, bpy H6), 8.38 d (1H,
The synthetic procedure is identical with that described for 6,

Periphery-Palladated Carbosilane Dendrimers
Organometallics, Vol. 18, No. 16, 1999 2979
starting from G1-OH (1.22 g, 0.44 mmol) in tetrahydrofuran
(20 mL) and PPh3 (2.12 g, 8.12 mmol) and in small portions
CBr4 (2.68 g, 8.08 mmol). A pale yellow oil was obtained.
C, 45.11; H, 5.99; N, 4.38. Found: C, 45.05; H, 5.94; N, 4.28.
1H NMR (CDCl3): δ 7.55 (d, J ) 7.6 Hz, 8H, ArH), 7.37 (d, J
) 8.0 Hz, 8H, ArH), 7.11 (d, J ) 8.5 Hz, 8H, ArH, o to Pd)),
6.70 (d, J ) 8.3 Hz, 8H, Ph, o to O), 4.90 (s, 8H, ArCH2), 2.76-
2.57 m and 2.67 s (10H, tmeda CH2 and N(CH3)2), 2.29 s (6H,
N(CH3)2)), 1.29 (m, 8H, SiCH2CH2), 0.76 (t, J ) 7.8 Hz, 8H,
CH2SiAr), 0.49 (t, J ) 7.6 Hz, 8H, CH2SiCH2), 0.22 (s, 24H,
Si(CH3.)2Ar. 13C{1H} NMR (CDCl3): δ 156.5 (4C, Ar, C-O),
139.7 (4C, Ar, C-Pd), 138.6 (4C, Ar, C-CH2), 136.6 (8C, Ar, C
o to Pd), 134.2 (8C, Ar, C o to Si), 132.7 (4C, Ar, C-Si), 127.5
(8C, Ar, C o to CH2), 114.3 (8C, Ar, C o to O), 70.4 (4C, ArCH2),
62.6 (N(CH3)2), 58.8 (N(CH3)2), 50.4 and 50.3 (tmeda CH2), 21.0
(4C, CH2SiAr), 19.0 (4C, CH2CH2SiAr), 17.9 (4C, SiCH2CH2-
CH2), -2.3 (Si(CH3)2). MALDI-TOF-MS: m/z 2582.1 [G0-ArPdI-
(tmeda) + 1Na]]+ (calcd 2583.3).
[G1-Ar P dI(tm eda)], [Si{(CH2)3Si((CH2)3SiMe2C6H4CH2O-
(C6H4-4)P d I-(tm ed a ))3}4] (11). This compound was prepared
in the same manner as 2a , starting from [Pd2(dba)3‚dba] (79.4
mg, 0.14 mmol), tmeda (26 µL, 0.17 mmol), and G1-ArI (9; 60.0
mg, 0.012 mmol) in benzene (50 mL), except that the benzene
solution of [Pd2(dba)3‚dba] was cooled to 8 °C by an ice/water
bath before addition of 9 and tmeda. The compound was
isolated as an air- and temperature-stable beige crystalline
solid in 33% yield. Melting point: 181 °C dec. Anal. Calcd for
Yield: 0.85 g, 0.24 mmol, 55%. Anal. Calcd for C156H240Br12
-
Si17 (3552.0): C, 52.75; H, 6.81; Si, 13.44. Found: C, 52.96; H,
6.79; Si, 13.59. 1H NMR (CDCl3, 298 K): δ 7.44 (d, J ) 7.8
Hz, 24H, ArH), 7.29 (d, J ) 7.6 Hz, 24H, ArH), 4.44 (s, 24H,
ArCH2), 1.32 (m, 24H CH2CH2SiAr), 1.27 (m, 8H, CH2-
SiCH2CH2CH2SiCH2), 0.79 (t, J ) 7.7 Hz, 24H, CH2SiAr), 0.53
(m, 40H, CH2SiCH2), 0.21 (s, 72H, Si(CH3)2Ar). 13C{1H} NMR
(CDCl3, 298 K): δ 140.9 (12C, Ar, C-Si), 138.8 (12C, Ar, C-CH2),
134.6 (24C, Ar, C o to Si), 128.5 (24C, Ar C o to CH2), 34.9
(24C, ArCH2), 20.8 (12C, CH2SiAr), 18.9 (16C, CH2CH2SiAr
and CH2SiCH2CH2CH2SiCH2), 18.4 (4C, CH2SiCH2CH2CH2-
SiCH2), 18.1 (4C, CH2SiCH2CH2CH2SiCH2), 17.7 (12C, CH2-
SiCH2CH2CH2SiAr), -2.7 (24C, Si(CH3)2Ar). MALDI-TOF-
MS: m/z 3644.6 [G1-Br + 1Ag]+ (calcd 3644.4).
2
Syn th esis of G0-Ar I a n d G1-Ar I. G0-Ar I, Si{(CH )3SiMe2-
(C6H4CH2OC6H4I-4)}4 (8). To a solution of G0-Br (6; 0.56 g,
0.51 mmol) in acetone (50 mL) were added 4-iodophenol (0.45
g, 2.05 mmol) and K2CO3 (0.35 g, 2.53 mmol), and the mixture
was stirred at reflux for 17 h. After removal of the solvent in
vacuo, the residue was extracted with DCM/water. The organic
layer was washed with water and dried over Na2SO4. The
volume was reduced, and the sample was chromatographed
on silica gel (DCM eluent). The product was obtained as a very
viscous, colorless oil, in 68% yield. Anal. Calcd for C72H88I4O4-
Si5 (1665.5): C, 51.92; H, 5.33; Si, 8.43. Found: C, 52.05; H,
5.41; Si, 8.52. 1H NMR (CDCl3): δ 7.55 (d, J ) 8.9 Hz, 8H,
ArH o to I), 7.50 (d, J ) 8.2 Hz, 8H, ArH), 7.37 (d, J ) 7.6 Hz,
8H, ArH), 6.74 (d, J ) 8.7 Hz, 8H, Ph, o to O), 4.99 (s, 8H,
ArCH2), 1.31 (m, 8H, SiCH2CH2), 0.78 (t, J ) 8.1 Hz, 8H, CH2-
SiAr), 0.50 (t, J ) 8.2 Hz, 8H, CH2SiCH2), 0.24 (s, 24H, Si-
(CH3)2Ar. 13C{1H} NMR (CDCl3): δ 159.1 (4C, Ar, C-O), 140.3
(4C, Ar, C-CH2), 138.7 (8C, Ar, C o to I), 137.4 (4C, Ar, C-Si),
134.3 (8C, Ar, C o to Si), 127.3 (8C, Ar, C o to CH2), 117.7 (8C,
Ar, C o to O), 83.5 (4C, Ar, C-I), 70.5 (4C, ArCH2), 21.0 (4C,
CH2SiAr), 19.0 (4C, CH2CH2SiAr), 17.9 (4C, SiCH2CH2CH2),
-2.4 (Si(CH3)2). MALDI-TOF-MS: m/z 1772.9 [G0-ArI + 1Ag]+
(calcd 1772.1).
C
300H480I12N24O12Pd12Si17 (MW ) 7892.66): C, 45.65; H, 6.13;
1
N, 4.26. Found: C, 45.72; H, 6.08; N, 4.31. H NMR (CDCl3):
δ 7.55 (d, J ) 7.6 Hz, 8H, ArH), 7.37 (d, J ) 8.0 Hz, 8H, ArH),
7.11 (d, J ) 8.5 Hz, 8H, ArH, o to Pd)), 6.70 (d, J ) 8.3 Hz,
8H, Ph, o to O), 4.90 (s, 8H, ArCH2), 2.76-2.57 m and 2.67 s
(10H, tmeda CH2 and N(CH3)2), 2.29 s (6H, N(CH3)2)), 1.29
(m, 8H, SiCH2CH2), 0.76 (t, J ) 7.8 Hz, 8H, CH2SiAr), 0.49 (t,
J ) 7.6 Hz, 8H, CH2SiCH2), 0.22 (s, 24H, Si(CH3)2Ar. 13C{1H}
NMR (CDCl3): δ 156.5 (4C, Ar, C-O), 139.7 (4C, Ar, C-Pd),
138.6 (4C, Ar, C-CH2), 136.6 (8C, Ar, C o to Pd), 134.2 (8C,
Ar, C o to Si), 132.7 (4C, Ar, C-Si), 127.5 (8C, Ar, C o to CH2),
114.3 (8C, Ar, C o to O), 70.4 (4C, ArCH2), 62.6 (N(CH3)2), 58.8
(N(CH3)2), 50.4 & 50.3 (tmeda CH2), 20.8 (12C, CH2SiAr), 18.9
(16C, CH2CH2SiAr and CH2SiCH2CH2CH2SiCH2), 18.4 (4C,
CH2SiCH2CH2CH2SiCH2), 18.1 (4C, CH2SiCH2CH2CH2SiCH2),
17.7 (12C, CH2SiCH2CH2CH2SiAr), -2.3 (Si(CH3)2). MALDI-
TOF-MS: m/z 7927.1 [G1-ArPdI(tmeda) + 1Na]]+ (calcd 7928.1).
G1Ar I, Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2OC6H4I-4))3}4
(9). The synthetic procedure is identical with that described
for 8, starting from G1-Br (7; 80.0 mg, 23 µmol), 4-iodophenol
(60.0 mg, 0.27 mmol), and K2CO3 (45.0 mg, 0.32 mmol) in
acetone (15 mL). A pale yellow oil was obtained. Yield: 80 mg,
16 µmol, 75%. Anal. Calcd for C228H288I12O12Si17 (MW )
5221.1): C, 52.45; H, 5.56; Si, 9.14. Found: C, 52.63; H, 5.54;
[G0-Ar P d Me(bp y)], [Si{(CH2)3SiMe2(C6H4CH2O(C6H4-4)-
P d Me-(bp y))}4] (12). This compound was prepared in the
same manner as 4a , starting from [G0-ArPdI(tmeda)] (10; 130
mg, 5.1 × 10-5 mol), LiMe (0.3 mL, 0.48 mmol, 1.6 M solution
in Et2O), and bpy (40 mg, 0.26 mmol) in Et2O/thf (50 mL). The
compound was isolated as an air- and temperature-stable
yellow crystalline solid in 63% yield. Melting point: 112 °C
dec. 1H NMR (CDCl3): δ 8.89 bs (1H, bpy H6), 8.36 bs (1H,
bpy H6′), 8.02 m, 7.52 m, 7.30 m (14H, bpy, C6H4Si overlap-
ping), 6.89 d (2H, J ) 7.8 Hz, C6H4O), 5.03 s (2H, CH2), 1.30
(m, 8H, SiCH2CH2), 0.80 (t, J ) 7.8 Hz, 8H, CH2SiAr), 0.59 s
(12H, PdMe), 0.49 (m, 8H, CH2SiCH2), 0.26 (s, 24H, Si(CH3.)2-
Ar). 13C{1H} NMR (CDCl3): δ 155.5, 155.3, 154.0, 150.9, 150.3,
148.4, 139.7, 138.7, 138.2, 137.6, 136.4, 133.9, 127.2, 126.4,
126.0, 121.7, 121.3, 112.1 (aromatics), 70.1 (CH2), 20.8 (4C,
CH2SiAr), 18.8 (4C, CH2CH2SiAr), 17.7 (4C, SiCH2CH2CH2),
-2.5 (Si(CH3)2). -3.8 (PdMe). MALDI-TOF-MS: m/z 2379.8
[G0-ArPdMe(bpy) + Ag]+ (calcd 2380.4).
1
Si, 9.26. H NMR (CDCl3, 298 K): δ 7.52 (d, J ) 9.0 Hz, 24H,
ArH o to I), 7.48 (d, J ) 8.5 Hz, 24H, ArH), 7.33 (d, J ) 7.4
Hz, 24H, ArH), 6.70 (d, J ) 7.7 Hz, 8H, Ph, o to O), 4.94 (s,
24H, ArCH2), 1.29 (m, 24H CH2CH2SiAr), 1.27 (m, 8H, CH2-
SiCH2CH2CH2SiCH2), 0.79 (m, 24H, CH2SiAr), 0.53 (m, 40H,
CH2SiCH2), 0.21 (s, 72H, Si(CH3)2Ar). 13C{1H} NMR (CDCl3,
298 K): δ 159.1 (12C, Ar, C-O), 140.2 (12C, Ar, C-CH2), 138.7
(24C, Ar, C o to I), 137.4 (12C, Ar, C-Si), 134.3 (24C, Ar, C o
to Si), 127.3 (24C, Ar, C o to CH2), 117.7 (24C, Ar, C o to O),
83.5 (12C, Ar, C-I), 70.4 (24C, ArCH2), 20.9 (12C, CH2SiAr),
18.9 (16C, CH2CH2SiAr and CH2SiCH2CH2CH2SiCH2), 18.5
(4C, CH2SiCH2CH2CH2SiCH2), 18.2 (4C, CH2SiCH2CH2CH2-
SiCH2), 17.8 (12C, CH2SiCH2CH2CH2SiAr), -2.3 (24C, Si-
(CH3)2Ar). MALDI-TOF-MS: m/z 5323.2 [G1-ArI + 1Ag]+ (calcd
5324.6).
[G1-Ar P dMe(bpy)], [Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2O-
(C6H4-4)P d -Me(bp y)))3}4] (13). This compound was prepared
in the same manner as 12, starting from [G1-ArPdI(tmeda)]
(11; 90 mg, 1.3 × 10-5 mol), LiMe (0.2 mL, 0.32 mmol, 1.6 M
solution in Et2O), and bpy (50 mg, 0.32 mmol) in Et2O/thf (50
mL). The compound was isolated as an air- and temperature-
stable yellow crystalline solid in 51% yield. Melting point: 128
Syn th esis of P a lla d a ted G0 a n d G1. [G0-Ar P d I(tm ed a )],
[Si{(CH 2)3SiMe2(C6H 4CH 2O(C6H 4-4)P d I(t m ed a ))}4] (10).
This compound was prepared in the same manner as 2a ,
starting from [Pd2(dba)3‚dba] (0.43 g, 0.75 mmol), tmeda (0.14
mL, 0.93 mmol), and G0-ArI (8; 0.31 g, 0.19 mmol) in benzene
(70 mL), except that the benzene solution of Pd2(dba)3‚dba was
cooled to 8 °C by an ice/water bath before addition of 8 and
tmeda. The compound was isolated as an air- and temperature-
stable beige crystalline solid in 88% yield. Melting point: 162
°C dec. Anal. Calcd for C96H152I4N8O4Pd4Si5 (MW ) 2556.1):
1
°C dec. H NMR (CDCl3): δ 8.89 bs (1H, bpy H6), 8.36 bs (1H,
bpy H6′), 8.02 m, 7.52 m, 7.30 m (14H, bpy, C6H4Si overlap-
ping), 6.89 d (2H, J ) 7.8 Hz, C6H4O), 5.05 s (2H, CH2), 1.29
(m, 24H, CH2CH2SiAr), 1.27 (m, 8H, CH2SiCH2CH2CH2SiCH2),
0.79 (m, 24H, CH2SiAr), 0.59 s (36H, PdMe), 0.53 (m, 40H,

2980 Organometallics, Vol. 18, No. 16, 1999
Hovestad et al.
CH2SiCH2), 0.21 (s, 72H, Si(CH3)2Ar). 13C{1H} NMR (CDCl3):
δ 155.5, 155.1, 154.4, 150.2, 150.0, 148.3, 139.5, 138.6, 138.0,
137.8, 136.4, 133.5, 126.8, 126.0, 125.5, 121.3, 121.2, 113.7
(aromatics), 69.5 (CH2), 20.9 (12C, CH2SiAr), 19.0 (12C, CH2-
CH2SiAr) (CH2SiCH2CH2CH2SiCH2, CH2SiCH2CH2CH2SiCH2,
and CH2SiCH2CH2CH2SiCH2 not visible), 17.7 (12C, CH2-
SiCH2CH2CH2SiAr), -2.3 (24C, Si(CH3)2Ar), -3.7 (PdMe).
MALDI-TOF-MS: m/z 7147.9 [G1-ArPdMe(bpy) + Ag]+ (calcd
7149.7).
automated Patterson techniques using DIRDIF70 and refined
on F2 by full-matrix least squares (SHELXL-96).71 Both
crystallographically independent molecules show partial sub-
stitution by chlorine on the Pd-bonded methyl site. One of them
was refined with a disorder model that was refined to a Cl to
CH3 ratio of 0.29:0.71. The second disorder form was only
minor and was ignored. Hydrogen atoms were taken into
account at calculated positions riding on their carrier atoms.
The highest residual features in the final difference map were
near Pd. Neutral atom scattering factors were taken from ref
72. Geometrical calculations and the ORTEP illustration were
done with PLATON.69
Red u ctive Elim in a tion fr om P d (IV) Mod el Com p lexes.
The Pd(IV) complexes were dissolved in CDCl3 at -10 °C, and
their 1H NMR spectra were recorded. As the solutions were
warmed to 25 °C, decomposition was monitored by 1H NMR
spectroscopy. When resonances due to the Pd(IV) complex had
disappeared entirely, the samples were chromatographed on
silica gel in a Pasteur pipet column and eluted with diethyl
Ack n ow led gm en t. This work was supported by the
Council for Chemical Sciences of The Netherlands
Organization for Scientific Research (CW-NWO) and the
Dutch Technology Foundation (STW) with financial aid
from Gist-brocades. Dr. J . Verweij (Gist-brocades) and
Prof. dr. J . G. de Vries (DSM) are kindly acknowledged
for their stimulating discussions. Financial support for
visits by J .L.H. (University of Tasmania, Utrecht Uni-
versity) and A.J .C. (Netherlands Institute for Catalysis,
NIOK) is gratefully acknowledged.
1
ether. The eluent was analyzed by GC-MS. H NMR spectra
were analyzed by comparison with reference spectra, as
previously reported.52,54
Red u ctive Elim in a tion fr om in situ P r ep a r ed Den -
d r itic P d (IV) Com p lexes. The dendritic palladium com-
plexes 12 and 13 were dissolved in CDCl3 at -20 °C, followed
by addition of excess benzyl bromide. The temperature was
then slowly increased until reductive elimination was ob-
served. The organic layer from the NMR tube was analyzed
by GC-MS.
Su p p or tin g In for m a tion Ava ila ble: Listings of atom
coordinates, thermal parameters, hydrogen atom parameters,
and ligand geometry for the complexes (14 pages). This
material is available free of charge via the Internet at
http://pubs.acs.org.
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for 4a . A transparent yellow needle-shaped
crystal was glued to the tip of a Lindemann glass capillary
(inert oil technique) and transferred into the cold nitrogen
stream of an Enraf-Nonius CAD4T diffractometer on a rotating
anode. Accurate unit-cell parameters were derived from the
setting angles of 25 reflections (SET4 method).67 Crystal data
and details of the structure determination are presented in
Table 1. An empirical correction for absorption was done with
the DIFABS technique68 as implemented in PLATON69 (cor-
rection range 0.738-1.264). The structure was solved with
OM9901269
(68) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
(69) Spek, A. L. Acta Crystallogr., Sect. A 1983, A46, C-34.
(70) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Grande, S.; Gould, R. O.; Smits, J . M. M.; Smykkalla, C. The
DIRDIF program system: Technical Report of the Crystallographic
Laboratory; University of Nijmegen, Nijmegen, The Netherlands.
(71) Sheldrick, G. M. SHELXL96: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1996.
(72) Wilson, A. J . C., Ed. International Tables for Crystallography;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C.
(67) de Boer, J . L.; Duisenberg, A. J . M. Acta Crystallogr., Sect. A
1984, 40, C-410.