Imprinting Chiral Information into Rigidified Dendrimers

Article abstract of DOI:10.1021/om0340387

Chiral, polymerizable P₂Pt(S-BINOL) metallodendrimers constructed of flexible benzyl ether repeat units were cross-linked/imprinted into highly porous and rigid organic polymers (methacrylate-based). Two meta-Cl substituents on the P-Ar portion of the metallomonomer reduced BINOL loss during polymer formation to levels that enabled site accessibility to be measured by the quantitation of S-BINOL cleavage (HCl) and BINOL/Br ₂BINOL exchange reactions. In general, the total site accessibility decreased as the generation number or steric bulk of the dendritic arms increased, which was offset by an increased effectiveness of the chiral imprint as the size of the dendritic arms increased. Thus polymerizable dendritic metallomonomers can be copolymerized into highly cross-linked organic polymers, and a memory for the absolute stereochemistry of the imprint ligand retained and used to affect the stereochemistry of reactions at the metal in the core.

Full text of DOI:10.1021/om0340387

4984
Organometallics 2003, 22, 4984-4998
Im p r in tin g Ch ir a l In for m a tion in to Rigid ified
Den d r im er s
J ennifer J . Becker and Michel R. Gagne´*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
Received J uly 14, 2003
Chiral, polymerizable P2Pt(S-BINOL) metallodendrimers constructed of flexible benzyl
ether repeat units were cross-linked/imprinted into highly porous and rigid organic polymers
(methacrylate-based). Two meta-Cl substituents on the P-Ar portion of the metallomonomer
reduced BINOL loss during polymer formation to levels that enabled site accessibility to be
measured by the quantitation of S-BINOL cleavage (HCl) and BINOL/Br2BINOL exchange
reactions. In general, the total site accessibility decreased as the generation number or steric
bulk of the dendritic arms increased, which was offset by an increased effectiveness of the
chiral imprint as the size of the dendritic arms increased. Thus polymerizable dendritic
metallomonomers can be copolymerized into highly cross-linked organic polymers, and a
memory for the absolute stereochemistry of the imprint ligand retained and used to affect
the stereochemistry of reactions at the metal in the core.
In tr od u ction
combining the properties of homo- and heterogeneous
catalysis to obtain catalysts with wholly new properties,
not available in either a purely homogeneous or het-
erogeneous catalyst formulation.
The heterogenization of “homogeneous” catalysts onto
solid supports1 (silica,2 alumina,3 polymers,4,5 etc.) has
long been seen as a methodology for combining the most
beneficial aspects of each catalyst type into a single
formulation. As a result, the primary focus of these
efforts has been on the development of highly selective
and/or stable catalysts with physical properties that
enable phase discrimination between the product and
catalyst. Strategies encompassing solid/liquid, solid/gas,
and liquid/liquid6,7 differentiation of products and cata-
lysts are the rule,8 although many recent sophisticated
approaches to reversible phase switching have been
developed.9 Much less effort has emerged, however, in
It was with the significant technical challenges em-
broiled in this caveat that we began to explore strategies
to synthesize “homogeneous” catalysts that operated
within the confines of an artificial, “well-defined” active
site that was composed of a solid phase material. In
particular we desired active site structures that con-
tained structural elements reminiscent of biological
active sites for the purpose of achieving chemical
reactivity not obtainable from a “normally” solvated
transition metal catalyst.
Molecular imprinting10 seemed like an ideal platform
for the synthesis of transition metal catalysts located
within the interior of a polymer-imprinted active site.
The imprinting process consists of the copolymerization
of organic or inorganic templates into highly cross-
linked organic polymers, their modification or excision
providing molecularly imprinted polymers (MIPs) that
retain chemical information (shape, functional group
display, etc.) related to the original template. While
most of the MIP efforts have been directed to analytical
applications, these techniques have more recently been
applied to problems in synthesis11 and catalysis.12
* Corresponding author.
(1) (a) For a thematic issue of Chemical Reviews on heterogenizing
catalysts see Issue 10: Chem. Rev. 2002, 102. (b) Cornils, B.; Hermann,
W. A. In Applied Homogeneous Catalysis with Organometallic Com-
pounds; Cornils, B., Hermann, W. A., Eds.; VCH Publishers: New
York, 1996; Vol. 2, Chapter 3.1.1.
(2) (a) Basset, J . M.; Niccolai, J . P. In Applied Homogeneous
Catalysis with Organometallic Compounds; Cornils, B., Hermann, W.
A., Eds.; VCH Publishers: New York, 1996; Vol. 2, pp 624-636. (b)
Pugin, B. J . Mol. Catal. A: Chem. 1996, 107, 273-279.
(3) Marks, T. J . Acc. Chem. Res. 1992, 25, 57-65.
(4) For reviews on soluble polymers as catalyst supports see: (a)
Dickerson, T. J .; Reed, N. N.; J anda, K. J . Chem. Rev. 2002, 102, 3325-
3344. (b) Bergbreiter, D. E. Chem. Rev. 2002, 102 3345-3384. (c)
Osburn, P. L.; Bergbreiter, D. E. Prog. Polym. Sci. 2001, 26, 2015-
2081.
(5) For examples of insoluble polymers as catalyst supports see:
Fan, Q.-H.; Li, Y.-M.; Chan, A. S. C. Chem. Rev. 2002, 102, 3385-
3466.
With regard to the synthesis of chiral active sites for
applications in asymmetric catalysis, we have previously
(6) For aqueous biphase catalysis see: (a) Kohlpaintner, C. W.;
Fischer, R. W.; Cornils, B. Appl. Catal., A 2001, 221, 219-225. (b)
Wachsen, O.; Himmler, K.; Cornils, B. Catal. Today 1998, 42, 373-
379.
(7) For fluorous biphase catalysis see: (a) Hope, E. G.; Stuart, A.
M. J . Fluorine Chem. 1999, 100, 75-83. (b) Horva´th, I. T. Acc. Chem.
Res. 1998, 31, 641-650. (c) Barthel-Rosa, L. P.; Gladysz, J . A. Coord.
Chem. Rev. 1999, 190-192, 587-605.
(8) Sheldon, R. A., van Bekkum, H., Eds. Fine Chemicals through
Heterogeneous Catalysis; Wiley-VCH: Weinheim, DE, 2001.
(9) Curran, D. P. Angew. Chem., Int. Ed. 1998, 37, 1174-1196.
(10) Sellergren, B., Ed. Molecularly Imprinted Polymers, Man-made
mimics of antibodies and their applications in analytical chemistry;
Elsevier: Amsterdam, 2001.
(11) Whitcombe, M. J .; Alexander, C.; Vulfson, E. N. Synlett 2000,
911-923.
(12) (a) Wulff, G. Chem. Rev. 2002, 102, 1-27. (b) Tada, M.;
Iwasawa, Y. J . Mol. Catal. A: Chem. 2003, 3953, 1-23. (c) Alexander,
C.; Davidson, L.; Hayes, W. Tetrahedron 2003, 59, 2025-2057. (d)
Severin, K. Curr. Opin. Chem. Biol. 2000, 4, 710-714. (e) Santora, B.
P.; Gagne´, M. R. Chem. Innovation 2000, 30, 22-29.
10.1021/om0340387 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/25/2003

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4985
Sch em e 1
conditions would significantly overcome the problem of
microscopic site heterogeneity.
A possible solution presented itself when we consid-
ered that only the interface between the cavity and the
bulk polymer might be consequential to site structure
and fidelity. By providing the metallomonomer with its
own interface to bulk polymer we hypothesized that
tailorable active sites with significantly enhanced struc-
tural and compositional homogeneity would be possible.
We imagined that a metallomonomer with polymer-
izable dendritic arms of relatively short length would
provide the means to such a controllable interface.20
Since each active site would contain the same degree of
dendritic foliage, they should be more chemically and
compositionally similar, at least in comparison to those
in normal MIPs. This protocol would differ from a
traditional MIP since the imprinting media would
actually be the rigidified dendrimer21 instead of the
cross-linked bulk polymer matrix.
This approach is conceptually similar to and was
stimulated by Zimmerman’s early work on cored, shell-
cross-linked dendrimers.22 More recently he has dem-
onstrated a significant advance to molecular imprinting
in that core removal leads to soluble “monomolecular”
imprinted dendrimers capable of molecular recogni-
tion.23,24 In the latter case, porphyrin core-based den-
drimers with peripheral alkene groups were subjected
to the Grubbs metathesis catalyst under high dilution
conditions, which provides the intramolecular cross-
links needed to zip-up the surface of the dendritic
sphere. Core removal provides soluble, monomolecular
imprints with eight carboxy groups converging at the
core of the dendrimer host, the organization of which
provides the means to differentiate pyridine-function-
alized porphyrins of various sizes and shapes.
Although Zimmerman’s work has convincingly shown
that size and functionality can be imprinted into soluble
dendrimers, our adaptation of the dendrimer imprinting
approach to asymmetric catalysis/molecular recognition
by metal-containing species required that chiral infor-
mation be imprinted into dendrimers, an accomplish-
ment that, to our knowledge, has not been reported.25
Thus, we report herein experiments designed to test the
hypothesis that dendrimers can be rigidified to imprint
chiral information and that this information can be used
to affect the stereochemical outcome of reactions at
metals located in the core.
As a first step to implementing our strategy for new
catalyst design, we synthesized metallomonomers with
polymerizable dendrons and examined the imprint
fidelity as a function of the generation number and
substitution pattern of the dendrimer arm. The arms
shown that copolymerizing chiral metallomonomers
such as 1 into highly cross-linked porous polymers
(∼95% cross-linking monomer) leads, after BINOL
removal, to P2Pt- sites capable of enantiomer recogni-
tion in BINOL rebinding.13 The chiral cavity generated
by BINOL removal enabled an otherwise achiral metal
to recognize the BINOL enantiomer that was originally
used to imprint the associated chiral cavity.14
Enantiomer ratios for BINOL recognition experiments
depended on several factors but reached as high as 97:3
in favor of the imprinted enantiomer. Obtaining such
high selectivities, however, required that many less
selective sites be poisoned, taking advantage of the fact
that the less selective sites were more reactive. The
obvious conclusion was that these MIPs were composed
of a complex distribution of sites that ranged from
completely encapsulated and inaccessible to entirely
solvent exposed (no chiral cavity), with every imaginable
combination in between. Scheme 1 depicts such a MIP
emphasizing the polydispersity of sites.
Although site heterogeneity15 is not necessarily det-
rimental to analytical applications,10 it seriously un-
dermines the goal of synthesizing well-defined (and
controllable) catalytic sites with associated shape and
functionality,16,17 since unselective hyperactive sites will
disproportionately contribute to product output or se-
lectivity (for example the surface site in Scheme 1 would
be unselective). Thus the goal of multi-turnover cataly-
sis puts a premium on eliminating heterogeneity in
general and surface sites in particular.18
Polymer matrix formation is a complex process that
begins with a 1:1 ratio of the monomer(s) to the
porogenic solvent and ends with a biphasic monolith:
a solvent-filled three-dimensional pore phase micro-
scopically intermixed with a cross-linked polymer.19
Unfortunately, given the complexity of this process, we
considered it unlikely that tweaking the polymerization
(13) Brunkan, N. M.; Gagne´, M. R. J . Am. Chem. Soc. 2000, 122,
6217-6225.
(14) For related case studies utilizing transition state analogues to
imprint cavities for metal catalysis see: (a) Polborn, K.; Severin, K.
Chem. Commun. 1999, 2481-2482. (b) Polborn, K.; Severin, K. Eur.
J . Inorg. Chem. 2000, 1687-1692.
(15) (a) Shimizu, K. D.; Umpleby, R. J ., II. Polym. Mater. Sci. Eng.
2003, 84, 847-848. (b) Umpleby, R. J ., II; Baxter, S. C.; Chen, Y.; Shah,
R. N.; Shimizu, K. D. Anal. Chem. 2001, 73, 4584-4591. (c) Umpleby,
R. J ., II; Bode, M.; Shimizu, K. D. Analyst 2000, 125, 1261-1265.
(16) Koh, J . H.; Larsen, A. O.; Gagne´, M. R. Organometallics 2002,
21, 7-9.
(20) Hecht, S.; Fre´chet, J . M. J . Angew. Chem., Int. Ed. 2001, 40,
75-91.
(21) For a review on heterogenizing catalysts with dendrimers see:
Heerbeek, R. V.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.; Reek, J .
N. H. Chem. Rev. 2002, 102, 3717-3756.
(22) (a) Shultz, L. G.; Zhao, Y.; Zimmerman, S. C. Angew. Chem.,
Int. Ed. 2001, 40, 1962-1966. (b) Wendland, M. S.; Zimmerman, S. C.
J . Am. Chem. Soc. 1999, 121, 1389-1390.
(17) For a complementary approach to metal site manipulation
see: (a) Sharma, A. C.; Borovik, A. S. J . Am. Chem. Soc. 2000, 122,
8946-8955. (b) Padden, K. M.; Krebs, J . F.; MacBeth, C. E.; Scarrow,
R. C.; Borovik, A. S. J . Am. Chem. Soc. 2001, 123, 1072-1079.
(18) Site isolation is typically well maintained, see: Krebs, J . F.;
Borovik, A. S. Chem. Commun. 1998, 553-554.
(23) Zimmerman, S. C.; Wendland, M. S.; Rakow, N. A.; Zharov, I.;
Suslick, K. S. Nature 2002, 418, 399-403.
(24) Mertz, E.; Zimmerman, S. C. J . Am. Chem. Soc. 2003, 125,
3424-3425.
(25) For a recent review on chiral dendrimers and their use in
sensing and asymmetric catalysis, see: Romagnoli, B.; Hayes, W. J .
Mater. Chem. 2002, 12, 767-799.
(19) Sherrington, D. C. Chem. Commun. 1998, 2275-2286.

4986 Organometallics, Vol. 22, No. 24, 2003
Becker and Gagne´
Sch em e 2
were designed to emanate from the rear of the molecule
to the front reactive quadrants, and thus define an
active site.
able dendrons synthesized in this manner are collected
in Scheme 2.
Although literature precedence suggested that the
metallomonomers would be readily available, we had
concerns that the dendrimer arms would be entirely too
flexible to effectively imprint (and retain) subtle chiral
information. On the other hand, dendron rigidification
by copolymerization into a stiff polymer matrix should
provide a significant force to the arms; the balance of
those forces, flexible versus rigid, was not a priori
predictable. The results reported herein show that chiral
information can indeed be imprinted into these environ-
ments and this information utilized to affect the ster-
eochemistry of chemical reactions occurring at the metal
core of the active site.
Directly relevant to our current work are the benzyl
ether dendritic diphosphine ligands synthesized by
Tsuji26 and the polymerizable TADDOL-27 and BINOL-
based28 dendrimers of Seebach, which were copolymer-
ized and utilized in multi-recycle asymmetric catalysis.
Seebach’s polymerizable dendrimers seemed like the
perfect starting point and are based on the benzyl ether
repeat unit developed by Fre´chet.29
P la tin u m Com p lex Syn th esis. Coupling of these
dendrons to bis(dichlorophosphino)ethane was accom-
plished with a modified procedure of Tsuji.26 Activation
by metal/halogen exchange of the aryl bromides by
nBuLi (-78 °C, THF) followed by addition of CuCl and
bis(dichlorophosphino)ethane produced extremely oxy-
gen sensitive diphosphines (at least in the non-chlori-
nated cases) that could never be isolated without
extensive oxidation. Standard phosphine reduction and
protection protocols were incompatible with the periph-
eral vinyl groups, so the diphosphines were quenched
with (COD)PtCl2 prior to workup to produce the corre-
sponding P2PtCl2 precursors as foamy solids (Scheme
3). Although the exact role of CuCl in the P-C coupling
is unclear, its absence leads to numerous unidentifiable
minor phosphine species in the reaction mixture.31 By
1H NMR the main impurity present in the crude P2PtCl2
reaction mixture was debrominated dendron, which
could be removed with successive Et2O washes. The P2-
PtCl2 were first converted to P2PtCO3 intermediates
with Ag2CO3 and then directly to the desired enan-
tiopure P2Pt(S-BINOL) metallomonomers by the meth-
ods of Andrews32 (Scheme 3); each of the metallomono-
mers was a foamy, amorphous solid. The P2Pt(BINOL)
metallomonomers were purified from traces of excess
BINOL by washing with Et2O or precipitating with Et2O
Resu lts a n d Discu ssion
Den d r on Syn th esis. The polymerizable dendrons
used for metallomonomer synthesis were available
through standard convergent methods starting with
4-vinylbenzyl chloride, Seebach’s polymerizable genera-
tion one (G1) and generation two (G2) benzyl bromides,
or the tri-styryl-derivatized pyrogallols previously re-
ported by Kumar.30 The benzyl halides were coupled,
in good yields, to 4-bromophenol, 4-bromo-2-chlorophen-
ol, and 4-bromo-2,6-dichlorophenol (e.g., eq 1), with
Fre´chet’s optimized coupling conditions29 (K2CO3 and
18-crown-6 ether in refluxing acetone). The polymeriz-
(26) Balaji, B. S.; Obora, Y.; Ohara, D.; Koide, S.; Tsuji, Y. Organ-
ometallics 2001, 20, 5342-5350.
(27) Sellner, H.; Seebach, D. Angew. Chem., Int. Ed. 1999, 38, 1918-
1920.
(28) Sellner, H.; Faber, C.; Rheiner, P. B.; Seebach, D. Chem. Eur.
J . 2000, 6, 3692-3705.
(29) Hawker, C. J .; Fre´chet, J . M. J . J . Am. Chem. Soc. 1990, 112,
7638-7647.
(31) (a) Gelman, D.; J iang, L.; Buchwald, S. L. Org. Lett. 2003, 5,
2315-2318. (b) Tomori, H.; Fox, J . M.; Buchwald, S. L. J . Org. Chem.
2000, 65, 5334-5341.
(32) Andrews, M. A.; Gould, G. L.; Klooster, W. T.; Koenig, K. S.;
Voss, E. J . Inorg. Chem. 1996, 35, 5478-5483.
(30) For the synthesis of nonpolymerizable analogues see: Krish-
namoorthy, K.; Ambade, A. V.; Mishra, S. P.; Kanungo, M.; Contractor,
A. Q.; Kumar, A. Polymer 2002, 43, 6465-6470.

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4987
Sch em e 3
Sch em e 4
Sch em e 5
from a CH2Cl2 solution, which led to prepolymerization
materials that were free of unreacted dendron and
BINOL, although all traces of solvent could never be
removed from the foams.
The 31P NMR spectra of all metallomonomers display
a single resonance at ∼25 ppm(s) with couplings to
1
platinum of 3620-3690 Hz. The H NMR spectra are
generally broad (the higher the generation, the broader
the peaks) and are not diagnostic except for the vinyl
and benzyl regions (4.92-5.87 ppm). The meta-chloro
1
substituents significantly sharpen the H NMR spectra
of the metallomonomers, with the dichloro-substituted
dendrimers providing the sharpest spectra. The reduced
C2-symmetry of the BINOLates is observed as a splitting
of the peaks in the diagnostic vinyl and benzyl regions.
Although sections of the 1H NMR spectra are broad, free
BINOL and unreacted dendron can be clearly observed,
when present, providing additional confidence in the
purity of the metallomonomers used for polymer syn-
thesis.
Test P olym er iza tion s. The first polymers to be
made employed the “zero” (G0) and first-generation (G1)
non-chlorinated metallomonomers G0 and G1 (Scheme
4). The two polymers were synthesized using a standard
imprinting protocol (62 µmol Pt, ∼98 mol % ethylene
dimethacrylate (EDMA),33 1:1 by weight with ClPh, 1
mol % AIBN, 60 °C, 24 h), providing brown monolithic
polymers with a permanent pore structure and high
surface areas34 (Scheme 5). The product polymers were
manually broken into small pieces, Soxhlet extracted
with CH2Cl2 for 6 h to remove any residual high-boiling
chlorobenzene, and dried in vacuo for 12 h at 50 °C.
Quantitative HPLC analysis unexpectedly showed 20%
(G0) and 36% (G1) of the polymer’s BINOL content
being washed out prior to deliberate cleavage from the
metal. Since BINOL quantification is the indirect tool
used to measure site accessibility and fidelity (vide
infra), BINOL loss at this stage was intolerable.35
Numerous control experiments indicated that a simple
generation-dependent decomposition was not operative,
as thermolysis of G0 and G1 in chlorobenzene and ClPh/
EDMA mixtures showed them to be thermally stable
(by 31P NMR) to 120 °C. Hypothesizing that BINOL loss
was caused by or was accompanied by P2PtCl2 formation
during the polymerization, we also examined non-
chlorinated porogens. Using G0 as the test metal-
lomonomer, polymers were made with toluene and
o-difluorobenzene porogens; however, significant BINOL
loss was still observed (toluene, 21%; o-difluorobenzene,
19%). Moreover, a nonpolymerizable version of these
compounds, (tetra-4-methoxydppe)Pt(BINOL), 2, was
subjected to identical polymerization and Soxhlet ex-
traction conditions and was recovered intact after
polymer formation, suggesting that BINOL extrusion
is somehow related to the physical forces on the mol-
ecule generated by the growth and rigidification of the
polymer around the complex as it is incorporated into
the matrix. Apparently larger dendrimers are more
sensitive to these forces.
(33) This value varies with the MW of the dendritic comonomer.
The Pt-loading is constant in each experiment, however.
(34) Santora, B. P.; Gagne´, M. R.; Moloy, K. G.; Radu, N. S.
Macromolecules 2001, 34, 658-661.
(35) In contrast, polymers made with dppe 1 lost <1% of the Bu2-
BINOL prior to cleavage (see ref 13).

4988 Organometallics, Vol. 22, No. 24, 2003
Becker and Gagne´
Ta ble 1. %BINOL Loss d u r in g P olym er iza tion a
Ta ble 2. HCl Clea va ge a n d Rebin d in g Da ta for
Cl2-Su bstitu ted Den d r im er s
entry
polymer
%BINOL loss
∑(σp + σm)38
% Br2BINOLb
1
2
3
4
5
6
7
8
P -(G0)
P -(G1)
20
36
9
22
1
7
2
2
-0.27
-0.27
0.10
0.10
0.47
0.47
0.47
0.47
% BINOL
(% of BINOL
% ee
entry
polymer
HCl cleavagea
sites)c
Br2BINOLd
P -(G0-Cl)
P -(G1-Cl)
P -(G0-Cl2)
P -(G1-Cl2)
P -(G2-Cl2)
P -(G1t-Cl2)
1
2
3
4
P -(G0-Cl2)
P -(G1-Cl2)
P -(G2-Cl2)
P -(G1t-Cl2)
87
68
63
67
47 (54)
36 (53)
32 (51)
31 (46)
35
39
41
44
a
% of the total BINOL sites present in the polymer, uncorrected
a
b
Determined after 6 h Soxhlet wash with CH2Cl2.
for BINOL loss occurring prior to cleavage. Percentage of total
Pt sites that exchange BINOL for Br2BINOL. c Percentage of sites
capable of egressing BINOL (by HCl cleavage) that also exchange
Ch lor o-Ba sed Den d r im er s. To test a second hy-
pothesis that the higher electron density of the 4-ben-
zyloxy-substituted diphosphines (cf. 1) was contributing
to BINOL lability during polymer formation (also sup-
ported by the observation that these diphosphines are
extremely prone to oxidation), metallomonomers with
one and two meta-chloro substituents on each of the
P-Ar rings were prepared (Schemes 2-4). Polymer
formation with EDMA provided six new yellow poly-
mers.36
d
BINOL for Br2BINOL. % enantiomeric excess of the exchanged
Br2BINOL.
protonatively removed from the polymer. Treating the
yellow to brown BINOLate polymers with HCl liberated
the BINOL from the Pt site and presumably converted
the imprinted site to the yellow to colorless P2PtCl2
forms.39 The free BINOL was then removed from the
polymer matrix (Soxhlet washing with CH2Cl2 for 12
h) and quantified by HPLC.
Total active site accessibility was not surprisingly
generation dependent, as P -(G0-Cl2) showed a rela-
tively high accessibility (87% BINOL cleavage), whereas
BINOL cleavage occurred at only 68, 63, and 67% of the
platinum sites in P -(G1-Cl2), P -(G2-Cl2), and P -(G1t-
Cl2), respectively (Table 2). Since bleaching of the
polymers suggested complete reaction of the P2Pt-
(BINOL) unit with HCl (strong thermodynamic driving
force), the reduced recovery of BINOL was interpreted
as hindered egress of the large BINOL ligand either
directly from the active site or indirectly via constric-
tions in the solvent channels not allowing passage of
the large ligands.40 The significant drop in accessibility
between G0 and the relatively similar G1 and G2
polymers hinted at a genuine difference in the physical
structure of these sites; the G0 systems were not
expected to be very “dendritic” in character.
Several attempts to modify the rigidity of the matrix
to enable better access to the site and still maintain
BINOL memory were made. Replacing the EDMA
component of the monomers with a 75:25 mass ratio of
EDMA and MMA or a 1:1 mixture of EDMA and the
more flexible butyl-linked dimethacrylate (BDMA),41 in
P -(G1-Cl2), did not provide any accessibility differences.
The EDMA/MMA and EDMA/BDMA matrixes each led
to 5 and 9% BINOL loss during polymer formation and
HCl cleavages of 69 and 67%, respectively. Thus these
apparently more flexible supports do not provide the
anticipated higher accessibility, suggesting that site
accessibility may be more a function of the dendritic
interface to bulk polymer than the bulk matrix itself
(vide infra).
As Table 1 summarizes, two trends emerge, the first
being that BINOL loss is again generation dependent,
but more importantly that electron-withdrawing groups
provide enhancements in template stability. For ex-
ample in G1 metallomonomers, zero, one, and two meta
substituents lead to 36, 22, and 7% loss, respectively,
upon polymer formation (entries 2, 4, and 6). The trend
is identical in G0 metallomonomers, although the
absolute BINOL loss is lower. Unexpectedly, the single
G2 metallomonomer that was made loses less BINOL
than G1 (entries 6 and 7). In the meta,meta-Cl2 systems,
where BINOL loss is diminished [1, 7, 2, and 2% for
P -(G0-Cl2), P -(G1-Cl2), P -(G2-Cl2), and P -(G1t-Cl2),
respectively], only the G1 has >2% BINOL loss. Al-
though the reason(s) for BINOL loss is not known, it is
clear that both the local steric hindrance (generation
number) and phosphine basicity combine to create
instability during the polymerization process.37 Never-
theless, the enhanced stabilities provided by the meta,
meta-Cl2-modified templates solved a critical problem
and enabled careful studies to assess the recognition
properties of these imprinted polymers.
Since the weight percent of metallomonomer (constant
loading of 62 µmol Pt/g dry polymer) increased signifi-
cantly on progressing from G0 to G2, the accessible
Site Accessibility. The adopted standard for mea-
suring the absolute active site accessibility was the
amount of the BINOL imprinting ligand that could be
(38) Sigma for -OMe was used to simulate a benzyloxy substituent.
Harisch, C.; Leo, A.; Unger, S. H.; Kim, K. H.; Nikaitami, D.; Lien, E.
J . J . Med. Chem. 1973, 16, 1207-1216.
(39) P2PtCl2 complexes with two, one, and zero chlorine substituents
are off-white, pale yellow, and yellow-brown, respectively.
(40) Unpublished studies have shown that variations in ligand size
correlate in the expected way for ligand egress (larger ) more hindered
escape).
(36) Metallomonomers with two, one, and zero chlorine substituents
are yellow, yellow-brown, and brown, respectively.
(37) Consistent with a significant electronic contribution is the
observation that the G1 metallomonomer containing the less basic 6,6′-
Br2BINOL ligand loses only 20% Br2BINOL during polymer formation
(cf. 36%, entry 2). The pKa’s of 6-Br-2-naphthol and 2-naphthol are
16.2 and 17.1, respectively. Bordwell, F. G.; Cheng, J .-P. J . Am. Chem.
Soc. 1991, 113, 1736-1743.
(41) Wulff, G. In Polymeric Reagents and Catalysis; Ford, W. T., Ed.;
American Chemical Society: Washington, DC, 1986; pp 186-230.

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4989
Ta ble 3. Accessible Su r fa ce Ar ea (SA, N2 BET) a s a
F u n ction of Gen er a tion Nu m ber a t a
Meta llom on om er Loa d in g of 62 µm ol P t/g of
P olym er
containing 20 equiv of (()-Br2BINOL and 15 vol % H2O
at 60 °C for 12 h. Excess Br2BINOL and excised BINOL
were washed from the polymer by Soxhlet extraction
(CH2Cl2, 12 h). The polymer was then treated with HCl
to release the rebound Br2BINOL, which was collected
by Soxhlet extraction, and analyzed by chiral HPLC to
quantify the extent and the selectivity of the rebinding
reaction.
As Table 2 summarizes, the dendrimer-based metal-
lomonomers indeed lead to active sites capable of
recognizing the absolute sense of the originally im-
printed BINOL enantiomer; that is, otherwise achiral
dendrimers can be rigidified into supramolecular con-
formations that retain chiral information. Thus, P -(G0-
Cl2), P -(G1-Cl2), P -(G2-Cl2), and P -(G1t-Cl2) ex-
change the BINOL in 47, 36, 32, and 31% of their total
platinum sites for Br2BINOL, with enantioselectivities
of 35, 39, 41, and 44%, respectively (Table 2). This
ability to recognize the same absolute sense of a chiral
imprinting ligand represents the first reported case of
asymmetric dendrimer imprinting.
samplea
SA (m2/g) wt % comonomer comonomer MW
p EDMA
460
P -(3)
403
301
255
198
245
260
157
6.7
10.1
17.0
29.1
19.3
15.8
15.6
1038.1
1682.4
2633.5
4537.5
3165.4
2633.5
2633.5
P -(G0-Cl2)
P -(G1-Cl2)
P -(G2-Cl2)
P -(G1t-Cl2)
P -(G1-Cl2)b
P -(G1-Cl2)c
a
Surface area analyses were carried out after HCl cleavage
(Scheme 5). 75:25 EDMA/MMA. c 1:1 EDMA/BDMA.
b
Sch em e 6
Taken together the data show that as the size
(generation) of the dendritic metallomonomers in-
creases, fewer sites liberate BINOL for both HCl cleav-
age and Br2BINOL exchange. However, when the
number of sites exchanging BINOL for Br2BINOL is
normalized by the number of sites fundamentally
capable of egressing BINOL (as assessed by HCl cleav-
age), the exchange percentages are remarkably constant
from G0 to G2 (54, 53, and 51%, respectively), Table 2.
With regard to enantiomer recognition, the enantio-
selectivity for Br2BINOL recognition gradually increases
from G0 to G1 to G2 (35 f 39 f 41% ee), although just
as importantly, the absolute sense of recognition is the
same as that of the imprinting ligand (S). Thus the arms
of the dendrimer can indeed be rigidified by copolym-
erization into highly cross-linked polymers and chiral
information cast into the dendritic structure.
surface area of each polymer was measured by N2 BET.
These data are collected in Table 3 and show that the
bulk properties of the polymer indeed respond to the
change in cross-link density and/or the weight percent
of metallomonomer, with the higher generation metal-
lomonomers leading to diminished surface areas. Al-
though the differences are numerically significant, the
absolute surface areas are still relatively high, and it
does not seem likely that this drop is the source of the
change in site accessibility.
Site F id elity. To assess the chiral memory of the
imprinted dendrimer, an (S)-BINOL/(()-6,6′-Br2BINOL
(Br2BINOL) exchange reaction was developed (Scheme
6). This method proved capable of quantifying the extent
and selectivity of a ligand exchange reaction and thus
the ability of the dendrimer to recognize the originally
imprinted enantiomer of BINOL. Thermolysis of the
polymer with excess Br2BINOL exchanged those plati-
num sites able to accommodate the (presumably as-
sociative) ligand exchange. Removing the unreacted
Br2BINOL and excised BINOL, followed by HCl cleav-
age of all BINOL species present in the polymer and
quantification by chiral HPLC, provides a direct mea-
sure of the number of sites able to ligand exchange
(%Br2BINOL) along with their selectivity (% ee Br2-
BINOL) (Scheme 6). This procedure probes the ef-
ficiency of the chiral imprint in addition to providing
information on site distribution and selectivity in the
imprinted dendrimer.
From a synthetic perspective the observation that the
tris-styryl-terminated G1 metallomonomer (G1t-Cl2)
functioned slightly better (accessibility and selectivity)
than the G2-bis-styryl-terminated case is noteworthy,
since the synthetic difficulty on progressing from G1 to
G2 is significant, the G2 having a MW of ∼4500.42
A
three-dimensional model of the G1 pyrogallol metal-
lomonomer with S-BINOL is shown in Figure 1.
Site Hom ogen eity. As a tool to measure site homo-
geneity in MIPs, a comparison of BINOL/Br2BINOL
exchange reactions at 60 and 120 °C was performed.
Table 4 collects the data for the exchange reactions at
the two temperatures, organized to compare changes in
the number of sites to react and their respective
selectivities for the different dendritic metallomonomers
(entries 1-4). Not surprisingly the number of sites to
exchange the BINOL ligands increased at the higher
temperature, although the magnitude of the increase
was less than expected based on prior studies.13 The
increase in reactive sites on going from 60 to 120 °C
was only 1% for G0 and 6 and 7% for G1 and G2,
respectively. This similarity in site accessibility was not
observed in earlier phenol/BINOL exchange reactions.13
The initial exchange reactions were carried out at 60
°C in chlorobenzene (similar to the initial polymeriza-
tion conditions). In each rebinding experiment, the
polymer was suspended in a chlorobenzene solution
(42) Only the largest of the dendrimers likely approach bona fide
dendritic properties, see: Bosman, A. W.; J anssen, H. M.; Meijer, W.
W. Chem. Rev. 1999, 99, 1665-1688.

4990 Organometallics, Vol. 22, No. 24, 2003
Ta ble 4. BINOL/Br 2BINOL Exch a n ge Da ta
Becker and Gagne´
% Pt
(60 °C)
% ee
(60 °C)
% Pt
(120 °C)
% ee
(120 °C)
∆% Pt
(120-60 °C)
∆% ee
(120-60 °C)
entry
polymer
∆(∆∆Gq)a
1
2
3
4
5
P -(G0-Cl2)
P -(G1-Cl2)
P -(G2-Cl2)
P -(G1t-Cl2)
P -(3)b
47
36
32
31
33
35
39
41
44
51
48
42
39
37
51
44
41
50
50
71
1
6
7
6
18
9
2
9
6
20
0.25
0.14
0.28
0.23
0.64
a
b
∆∆Gq of kS/kR at s120 °C - ∆∆Gq of kS/kR at 60 °C. BINOL cleavage with HCl liberates 89% of available BINOL.
propenyldppe)Pt(S-BINOL) metallomonomer 3 was tested
under the identical BINOL/Br2BINOL exchange condi-
tions. At 60 °C, 33% of the total sites exchange BINOL
for Br2BINOL (the same as the G1-pyrogallol), with an
enantioselectivity of 51% (cf. 44% for G1t-Cl2), similar
to the best performing dendrimer. The biggest difference
between P -(3) and the dendritic polymer sites came at
120 °C. At this temperature the number of sites to
undergo ligand exchange and the enantioselectivity
increased significantly (+18% and +20% ee) compared
to the 60 °C results. In units of activation energy
differences, the change is even more noteworthy (∆-
(∆∆Gq) ) 0.64 kcal mol-1). Thus it appears that ad-
ditional superselective sites are accessible at high tem-
perature in P -(3) but not in the dendritic polymers.
These superselective sites provide the large boost in
selectivity for BINOL recognition at 120 °C; their
selectivity is consistent with the kinetic selectivity of
the most selective phenol/BINOL exchange previously
measured.13
These large changes in site reactivity and selectivity
suggest a broader diversity of reactive sites in the
traditional MIP experiment, highly selective sites being
accessible at high, but not moderate temperatures. In
contrast, the attenuated temperature-dependent changes
in reactivity/selectivity of the dendritic metallomono-
mers point to a significantly narrowed distribution in
the reactive sites. This higher uniformity, however,
comes at the expense of a subset of most selective sites
that is accessible/populated at high temperatures in
P -(3).
F igu r e 1. Space-filling representations (H atoms removed
for simplification) of the three representative local minima
from the Spartan MMFF94 Monte Carlo conformer analy-
sis of the non-styryl version of G1t -Cl2. A is the lowest
energy structure, while B and C are randomly chosen local
minima of nearly equal relative energy (see text). Light
green, Cl; dark green, BINOL carbons; red, O; pink, P;
yellow, Pt.
Like these other studies, however, the enantioselec-
tivities do increase at the higher temperatures, a
phenomenon that was previously interpreted as result-
ing from the accessibility of more hindered, more
selective sites at the higher temperatures. Apparently
some slightly more selective dendritic sites are acces-
sible at 120 °C, although the overall selectivity increases
are modest (2-9%, 0.14-0.28 kcal mol-1). In regard to
changes in site accessibility and selectivity, the pyro-
gallol-terminated metallodendrimer again performs
nearly identical to the more “expensive” G2 metal-
lomonomer.
Further complicating the overall picture of site ac-
cessibility is the increase with dendrimer generation in
the number of inaccessible sites (from HCl cleavage),
even though these higher generations have relatively
homogeneous reactive site distributions. Apparently two
types of sites are obtained from the imprinting of a
dendritic metallomonomer, one class that inadvertently
buries the template (makes it inaccessible) and another
class that is open, reactive, and homogeneous in nature
but only moderately selective. Increasing the size of the
dendritic periphery shifts the distribution of these sites
in an intuitively reasonable fashion (i.e., bulkier ) more
To provide a point of comparison to previously inves-
tigated nondendritic metallomonomers, the (tetraiso-

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4991
buried sites), but only subtly changes the selectivity of
the reactive sites. In the dendritic systems a site could
become buried either by complete encapsulation of the
core by the polymer or by a single dendrimer arm
blocking the egress of BINOL (vide infra). In contrast,
the more traditional metallomonomer leads to fewer
completely buried sites but, because of the site construc-
tion material (bulk amorphous polymer), generates a
continuous distribution of reactive sites, including the
selective high-temperature ones.
Our working hypothesis on the unusual behavior of
the metallodendrimers currently focuses on the many
conformational degrees of freedom available to the
flexible -CH2-O- linkage (C-O bond rotation is also
rapid).43 Depending on the solvent, these dendrimers
can adopt highly compact (arms folded in) or extended
structures.44 Polymerization of the former conformers
could easily lead to a subset of active sites with blocked
BINOL egress (by our definition an inaccessible site),
the folded in arm blocking the escape pathway for the
ligand. These notions of conformational-dependent be-
havior stimulated the computational studies detailed
below.
arms reaches below the BINOL fragment, while the
remainder stay pulled back (a fourth structure is shown
in the table of contents graphic of this issue).
Viewed as an ensemble of local minima, the display
of structural variability at a nearly isoenergetic point
is as impressive as it is sobering, especially considering
that imprinting into this array of structures is what
leads to the observed enantiomer selective rebinding
results. Clearly this media, while capable of rigidifica-
tion and imprinting, has its own unique challenges to
obtaining high-quality homogeneous imprints.
On the basis of this analysis, we hypothesize that
more rigid metallodendrimers, along with decreasing
the degrees of freedom accessible to the dendrimer arm
and providing a more uniform conformational ensemble,
should also adopt more extended structures that will
limit the number of buried sites; that is, stiffer dendrons
should keep the polymerizable ends on the exterior of
the metallomonomer. Future experiments aimed at
examining the response of reactivity/selectivity to in-
creases in the dendron chain rigidity will help to address
the issue of dendron conformations on site accessibility
and fidelity.
Mon te Ca r lo Sim u la tion s. To model/visualize the
accessible minimized structures available to these flex-
ible materials, a Monte Carlo simulation was carried
out on the dendritic portion of a non-styryl derivative
of G1t-Cl2 using Spartan MMFF94. The terminal
tribenzylated pyrrogallol unit was preminimized (after
conformational searching) and was not systematically
varied during the simulation, although it was allowed
to respond to minimization. The central metal fragment
was constrained to be square planar with 90° P-Pt-P,
P-Pt-O, and O-Pt-O bond angles. A total of ∼2300
different initial starting points were minimized and
examined with an eye to assessing the conformation
degrees of freedom accessible to a prepolymerization
complex. Because of the admittedly low-level calcula-
tion, the bottom 10 kcal mol-1 structures (∼65) were
each kept and inspected.
Figure 1 contains three of these structures, chosen
to represent the diversity of this set. Figure 1A (front
and side view) represents the lowest energy-minimized
structure. The dendritic arms adopt a gross C2 sym-
metric arrangement that is compact and contains in-
terligand π-stacks. The relevance of this lowest energy
structure to a complex process that involves the cross-
linking of this solvated structure into the matrix of a
highly rigidified polymer is dubious; however it provides
an informative visualization of the structure.
Su m m a r y
Polymerizable metallodendrimers constructed of a
flexible repeat unit can be cross-linked into highly
porous and rigid organic polymers to imprint chiral
information. This chiral information, temporally trapped
in the supramolecular conformations of the rigidified
dendritic arms, modifies the stereochemistry of reac-
tions occurring at the core of the dendrimers.
The effectiveness of the chiral imprint is dependent
on a number of factors. As the generation number (steric
bulk) increases, the total active site accessibility for
imprinting ligand removal and BINOL/Br2BINOL ex-
change reactions decrease, but the ability of the den-
drimer to imprint and retain chiral information in-
creases slightly. The number of reactive Pt sites only
slightly decreased from generation 1 to 2, and the
selectivities were remarkably constant (small ∆% ee)
over the range of accessible sites, at least when com-
pared to the more traditional P -3 metallomonomer
system (large ∆% ee).
Substitution patterns of the dendron were also im-
portant; chlorine substituents are necessary on the
P-Ar portion of the dendron to stabilize the complexes
to BINOL loss during polymer formation. Substitution
patterns at the periphery of the dendron also have an
affect on reactivity/selectivity; the first-generation py-
rogallol (tris-styryl-terminated) dendrimer has an ac-
cessibility and selectivity similar to those of the G2 bis-
styryl-terminated dendrimer.
Equally revealing are several of the other structures
present in the set of local minima (Figures 1B and 1C).
In the set of 65, the most compact was 1B, which
completely encapsulates the BINOL fragment from
behind and above and if polymerized with a similar
geometry would lead to a completely encapsulated
structure (no doubt a highly selective one). Figure 1C,
on the other hand, was more typical in that the dendritic
arms tended to be less compact, with arms jutting out
in seemingly random directions. In this case one of the
Exp er im en ta l Section
Gen er a l Meth od s. Racemic Br2BINOL,45 isopropenyld-
ppe,46 (COD)PtCl2,47 4-bromo-2,6-dichlorophenol,48 and benzyl
(45) Cram, D. J .; Sogah, G. D. Y. J . Am. Chem. Soc. 1979, 101,
3035-3042.
(46) Taylor, R. A.; Santora, B. P.; Gagne´, M. R. Org. Lett. 2000, 2,
1781-1783.
(43) Eliel, E. L.; Wilen, S. H.; Mander, L. N. Stereochemistry of
Organic Compounds; J ohn Wiley & Sons: New York, 1994.
(44) For a summary of extensive discussions on dendrimer end
localization, see ref 42.
(47) McDermott, J . X.; White, J . F.; Whitesides, G. M. J . Am. Chem.
Soc. 1976, 98, 6521-6527.
(48) Kısaku¨rek, D.; Aslan, A.; Isc¸i, H. Polymer 2000, 41, 5149-5155.

4992 Organometallics, Vol. 22, No. 24, 2003
Becker and Gagne´
Ch a r t 1
bromides28 were synthesized according to literature proce-
dures. All chemicals were purchased from Aldrich except 1,2-
bis(dichlorophosphino)ethane (Strem) and S-BINOL (Kankyo
Kagaku Center Co., Ltd., J apan). The platinum complexes P2-
PtCl2, P2PtCO3, and P2PtBINOL were synthesized by proce-
dures similar to those published for dppe analogues.32,49
Chlorobenzene was distilled from P2O5 and freeze-pump-
thaw degassed before use as a porogen, but was used as
received in rebinding experiments. 2,2′-Azobis(isobutyro)nitrile
(AIBN) was recrystallized from MeOH, dried in vacuo, and
stored under N2 at -35 °C. EDMA was washed twice with
aqueous 1 M NaOH and once with brine to remove inhibitor,
dried over MgSO4, filtered, distilled (105 °C/1 mmHg), freeze-
pump-thaw degassed, and stored under N2 at -35 °C. CuCl
was used as received and stored under N2. Polymerizations
were performed in an MBraun LabMaster 100 glovebox.
Reactions performed under Ar were carried out using standard
Schlenk techniques.
NMR spectra were recorded on either a Bruker Avance 300
or a Bruker Avance 400 spectrometer. Chemical shifts are
reported in ppm and referenced to residual solvent peaks (1H
and 13C NMR) or to an external standard (85% H3PO4, 31P
NMR). Microanalysis data are reported for those complexes
that were well-behaved solids. Most of the dendritic compounds
were foamy solids or of a honey-like consistency that precluded
complete solvent removal.
HPLC analysis was performed on a Hewlett-Packard Series
1100 instrument, using a Daicel Chiralcel OD-H column (95%
hexanes/5% EtOH, 0.8 mL/min flow rate). HPLC chromato-
grams were recorded at wavelengths of 254, 278, 289, and 333
nm and compared to calibration curves to determine analyte
concentration. G0-Br .50 4-Vinylbenzyl chloride (3.26 mL, 23.1
mmol), 4-bromophenol (4.00 g, 23.1 mmol), K2CO3 (3.83 mg,
27.71 mmol), 18-crown-6 ether (581.8 mg, 2.20 mmol), and
tetrabutylammonium iodide (474.0 mg, 1.28 mmol) were
combined in 66 mL of dry THF and heated to reflux for 16 h.
The reaction mixture was cooled to room temperature and
filtered through Celite, eluting with THF. The solvent was
evaporated to an off-white solid and precipitated from EtOAc/
petroleum ether to yield 6.01 g (90%) of a waxy solid. 1H NMR
(400 MHz, CDCl3): δ 7.37 (m, 6 H), 6.84 (m, 2 H), 6.72 (dd, J
) 10.8, 17.6 Hz, 1 H), 5.76 (d, J ) 17.6 Hz, 1 H), 5.26 (d, J )
10.8 Hz, 1 H), 5.01 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ
157.6, 137.4, 136.3, 136.0, 132.3, 127.6, 126.4, 116.7, 114.2,
113.1, 69.9. Anal. Calcd for C15H13BrO: C, 62.30; H, 4.53.
Found: C, 62.38; H, 4.41.
(G0)P tCl2. G0-Br (993.4 mg, 3.44 mmol) was dissolved in
30 mL of THF. The solution was cooled to -78 °C, and a freshly
titrated 2.5 M solution of nBuLi in hexanes (1.37 mL, 3.43
mmol) was added dropwise. After stirring at -78 °C for 1 h,
CuCl (372.0 mg, 3.76 mmol) was added, and the reaction
mixture was stirred for an additional 15 min, followed by
addition of 1,2-bis(dichlorophosphino)ethane (1.42 mL of a
0.6024 M solution in THF, 0.855 mmol). The resulting reaction
mixture was stirred at -78 °C under Ar for 24 h. The solution
was then transferred via cannula to a solution of 321.3 mg
(0.859 mmol) of (COD)PtCl2 in 20 mL of CH2Cl2. After stirring
for 1 h at room temperature, the volatiles were removed in
vacuo. The dark yellow residue was taken up in CH2Cl2 and
filtered through Celite to remove any salts. Evaporation of the
solvent followed by Et2O wash of the residue, to remove any
uncoupled dendron, resulted in (G0)P tCl2. 31P NMR (162
1
MHz, CD2Cl2): δ 40.4 (J P-Pt ) 3650 Hz). H NMR (400 MHz,
CD2Cl2): δ 7.56 (dd, J ) 8.8, 11.6 Hz, 8 H), 7.43 (dd, J ) 8.0,
21.2 Hz, 16 H), 7.07 (d, J ) 7.2 Hz, 8 H), 6.74 (dd, J ) 10.8,
17.6 Hz, 4 H), 5.78 (d, J ) 18.0 Hz, 4 H), 5.27 (d, J ) 11.2 Hz,
4 H), 5.11 (s, 8 H), 2.22 (m, 4 H).
(G0)P tCO3. (G0)P tCl2 (1.0248 g, 0.859 mmol) was dissolved
in 50 mL of wet CH2Cl2. Ag2CO3 (867.3 mg, 3.146 mmol) was
added and the reaction mixture stirred at room temperature,
protected from light. After 8 h, the reaction was complete by
31P NMR, and the reaction mixture was filtered through Celite
to remove AgCl. The solvent was removed in vacuo to afford
732.2 mg (72%) of a dark brown powder, which was taken on
without further purification to the next step. 31P NMR (162
(49) (a) Gugger, P.; Limmer, S. O.; Watson, A. A.; Willis, A. C.; Wild,
S. B. Inorg. Chem. 1993, 32, 5692-5696. (b) Brunkan, N. M.; White,
P. S.; Gagne´, M. R. Angew. Chem., Int. Ed. 1998, 37, 1579-1582.
(50) Cramer, E.; Percec, V. J . Poly Sci., A: Polym. Chem. 1990, 28,
3029-46.
1
MHz, CD2Cl2): δ 30.1 (J P-Pt ) 3522 Hz). H NMR (400 MHz,
CD2Cl2): δ 7.75 (dd, J ) 8.8, 11.6 Hz, 8 H), 7.39 (m, 16 H),
7.01 (d, J ) 7.2 Hz, 8 H), 6.71 (dd, J ) 10.4, 17.6 Hz, 4 H),

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4993
5.77 (dd, J ) 0.4, 17.6 Hz, 4 H), 5.26 (dd, J ) 0.4, 10.4 Hz, 4
H), 5.04 (s, 8 H), 2.38 (m, 4 H).
1.3114 g (86%) of a dark brown powder, which was taken on
without further purification to the next step. 31P NMR (162
MHz, CD2Cl2): δ 30.4 (J P-Pt ) 3532 Hz). H NMR (400 MHz,
CD2Cl2): δ 7.74 (dd, J ) 8.4, 11.2 Hz, 4 H), 7.45-6.55 (series
of multiplets, 64 H), 5.78 (m, 8 H), 5.26 (m, 8 H), 5.04-4.95
(overlapping singlets, 24 H), 2.25 (m, 4 H).
1
(G0)P t(S-BINOL). (G0)P tCO3 (732.2 mg, 0.619 mmol) and
S-BINOL (187.4 mg, 0.655 mmol) were dissolved in 40 mL of
CH2Cl2. After 4 h the reaction was complete by 31P NMR, and
the solvent was removed in vacuo. The brown solid was washed
three times with Et2O to remove free BINOL. After drying in
vacuo the brown product was obtained in 94% yield (822.4 mg).
(G1)P t(S-BINOL). (G1)P tCO3 (1.3114 g, 0.614 mmol) and
S-BINOL (176.8 mg, 0.617 mmol) were dissolved in 40 mL of
CH2Cl2. After 3 h the reaction was complete by 31P NMR, and
the solvent was removed in vacuo. The dark brown solid was
washed three times with Et2O to remove free BINOL. After
drying in vacuo the dark brown product was obtained in 79%
yield (1.1492 g). 31P NMR (121.5 MHz, CD2Cl2): δ 26.7 (J P-Pt
1
31P NMR (121.5 MHz, CD2Cl2): δ 26.3 (J P-Pt ) 3660 Hz). H
NMR (300 MHz, CD2Cl2): δ 7.88 (m, 4 H), 7.75 (m, 4 H), 7.46
(m, 20 H), 7.29 (t, J ) 9.3 Hz, 2 H), 7.15 (t, J ) 14.7 Hz, 2 H),
7.02 (m, 8 H), 6.82 (m, 6 H), 6.58 (d, J ) 8.7 Hz, 2 H), 5.84
(dd, J ) 18.0, 19.8 Hz, 4 H), 5.33 (m, 4 H), 5.15 (s, 4 H), 4.98
(s, 4 H), 2.12 (m, 4 H). 13C NMR (75.5 MHz, CD2Cl2): δ 162.5,
161.9, 153.8, 138.0, 137.8, 136.7, 136.4, 136.3, 135.8, 135.7,
135.2, 134.5, 129.2, 128.9, 128.2, 128.1, 127.6, 126.8, 126.7,
126.1, 125.4, 125.0, 124.7, 121.4, 120.5, 118.2, 115.8, 115.6,
114.5, 114.4, 70.2, 70.1, 27.5.
P -(G0). Metallomonomer (G0)P t(S-BINOL) (137.4 mg,
97.69 µmol), AIBN (12.9 mg, 78.56 µmol), EDMA (1368.5 mg,
6904 µmol), and chlorobenzene (1497.4 mg) were combined in
a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, brown polymer. After Soxhlet extraction
with CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h,
1.4772 g of P -(G0) (62.56 µmol of Pt/g of polymer) was
obtained.
1
) 3687 Hz). H NMR (300 MHz, CD2Cl2): δ 7.89-7.67 (m, 8
H), 7.56-6.56 (series of multiplets, 72 H), 5.80 (m, 8 H), 5.29
(m, 8 H), 5.11-4.94 (overlapping singlets, 24 H), 2.12 (m, 4
H). 13C NMR (75.5 MHz, CD2Cl2): δ 162.3, 161.9, 160.6, 160.5,
153.6, 139.3, 139.2, 137.8, 137.7, 136.8, 136.7, 135.8, 135.7,
135.2, 134.3, 132.6, 130.5, 129.4, 129.0, 128.7, 128.2, 128.1,
126.7, 136.6, 124.9, 123.5, 121.4, 120.5, 118.8, 118.1, 115.8,
115.6, 114.3, 114.2, 113.4, 106.8, 106.7, 101.9, 70.3, 70.2, 70.1,
27.6.
P -(G1). Metallomonomer (G1)P t(S-BINOL) (229.4 mg,
97.22 µmol), AIBN (11.8 mg, 71.95 µmol), EDMA (1267.2 mg,
6393 µmol), and chlorobenzene (1.4996 g) were combined in a
20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, dark brown polymer. After Soxhlet extrac-
tion with CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h,
1.4748 g of P -(G1) (62.67 µmol of Pt/g of polymer) was
obtained.
G0-Cl-Br . 4-Vinylbenzyl chloride (580 µL, 4.12 mmol),
4-bromo-2-chlorophenol (867.0 mg, 4.15 mmol), K2CO3 (874.9
mg, 6.33 mmol), 18-crown-6 ether (222.1 mg, 0.840 mmol), and
tetrabutylammonium iodide (78.3 mg, 0.212 mmol) were
combined in 30 mL of dry acetone and heated to reflux for 16
h. The reaction mixture was cooled to room temperature and
filtered. The filtrate was evaporated and the resulting residue
taken up in Et2O, extracted twice with H2O, dried over MgSO4,
filtered, and evaporated to a white solid. After purification
through a plug of silica gel (1:1 hexanes/EtOAc) 1.1876 g (89%)
of a waxy white solid was obtained. 1H NMR (400 MHz,
CDCl3): δ 7.51 (d, J ) 2.5 Hz, 1 H), 7.40 (m, 4 H), 7.26 (dd, J
) 2.4, 8.7 Hz, 1 H), 6.79 (d, J ) 8.8 Hz, 1 H), 6.72 (dd, J )
10.8, 17.6 Hz, 1 H), 5.76 (d, J ) 17.6 Hz, 1 H), 5.27 (d, J )
10.8, 1 H), 5.09 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ 153.3,
137.4, 136.3, 135.4, 132.7, 130.4, 127.3, 126.4, 124.3, 115.2,
114.2, 112.9, 70.7. Anal. Calcd for C15H12BrClO: C, 55.67; H,
3.74. Found: C, 55.70; H, 3.69.
(G0-Cl)P tCl2. G0-Cl-Br (493.7 mg, 1.526 mmol) was dis-
solved in 20 mL of THF. The solution was cooled to -78 °C,
and a freshly titrated 2.5 M solution of nBuLi in hexanes (600
µL, 1.500 mmol) was added dropwise. After stirring at -78
°C for 1 h, CuCl (193.6 mg, 1.956 mmol) was added and the
reaction mixture was stirred for an additional 15 min, followed
by addition of 1,2-bis(dichlorophosphino)ethane (630 µL of a
0.6024 M solution in THF, 0.3795 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The
solution was then transferred via cannula to a solution of 142.5
mg (0.381 mmol) of (COD)PtCl2 in 20 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The yellow residue was taken up in CH2-
Cl2 and filtered through Celite to remove any salts. Evapora-
tion of the solvent followed by Et2O wash of the residue, to
remove any uncoupled dendron, resulted in 564.1 mg (99%)
of (G0-Cl)P tCl2. 31P NMR (162 MHz, CD2Cl2): δ 39.1 (J P-Pt
) 3633 Hz). 1H NMR (400 MHz, CD2Cl2): δ 7.80 (m, 4 H),
7.71 (dd, J ) 2.0, 11.6 Hz, 4 H), 7.43 (m, 16 H), 7.12 (dd, J )
2.0, 11.6 Hz, 4 H), 6.75 (dd, J ) 10.8, 17.6 Hz, 4 H), 5.79 (d, J
) 17.6 Hz, 4 H), 5.28 (d, J ) 10.8 Hz, 4 H), 5.20 (s, 8 H), 2.28
(m, 4 H).
G1-Br . G1-benzyl bromide (3.0017 g, 6.88 mmol),28 4-bro-
mophenol (1.2549 g, 7.25 mmol), K2CO3 (1.9999 g, 14.46 mmol),
18-crown-6 ether (387.4 mg, 1.46 mmol), and tetrabutylam-
monium iodide (138.8 mg, 0.376 mmol) were combined in 50
mL of dry acetone and heated to reflux for 17 h. The reaction
mixture was cooled to room temperature and filtered. The
filtrate was evaporated and the resulting residue taken up in
Et2O, extracted twice with H2O, dried over MgSO4, filtered,
and evaporated to a yellow oil. After purification by column
chromatography (silica gel, 5:1 hexanes/EtOAc) 3.374 g (93%)
1
of an extremely viscous oil was obtained. H NMR (400 MHz,
CDCl3): δ 7.39 (m, 10 H), 6.80 (m, 2 H), 6.72 (dd, J ) 10.8,
17.6 Hz, 2 H), 6.63 (d, J ) 2.0 Hz, 2 H), 6.54 (t, J ) 2.4 Hz, 1
H), 5.76 (dd, J ) 0.4, 17.6 Hz, 2 H), 5.26 (d, J ) 10.8, 2 H),
5.01 (s, 4 H), 4.95 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ
160.1, 157.7, 139.0, 137.4, 136.4, 136.2, 132.2, 127.7, 126.4,
116.7, 114.1, 113.1, 106.2, 101.6, 70.0, 69.8.
(G1)P tCl2. G1-Br (1.5227 g, 2.88 mmol) was dissolved in
30 mL of THF. The solution was cooled to -78 °C, and a freshly
titrated 2.5 M solution of nBuLi in hexanes (1.15 mL, 2.875
mmol) was added dropwise. After stirring at -78 °C for 1 h,
CuCl (320.0 mg, 3.23 mmol) was added, and the reaction
mixture was stirred for an additional 15 min, followed by
addition of 1,2-bis(dichlorophosphino)ethane (1.18 mL of a
0.6024 M solution in THF, 0.7108 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The
solution was then transferred via cannula to a solution of 266.3
mg (0.7117 mmol) of (COD)PtCl2 in 20 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The brown residue was taken up in CH2Cl2
and filtered through Celite to remove any salts. Evaporation
of the solvent followed by Et2O wash of the residue, to remove
any uncoupled dendron, resulted in 1.5281 g (98%) of (G1)-
P tCl2. 31P NMR (162 MHz, CD2Cl2): δ 40.4 (J P-Pt ) 3665 Hz).
1H NMR (400 MHz, CD2Cl2): δ 7.75 (dd, J ) 8.8, 11.6 Hz, 4
H), 7.44-6.56 (series of multiplets, 64 H), 5.77 (m, 8 H), 5.26
(m, 8 H), 5.08-4.98 (overlapping singlets, 24 H), 2.48 (m, 4
H).
(G1)P tCO3. (G1)P tCl2 (1.5281 g, 0.712 mmol) was dissolved
in 50 mL of wet CH2Cl2. Ag2CO3 (710.5 mg, 2.577 mmol) was
added and the reaction mixture stirred at room temperature,
protected from light. After 8 h, the reaction was complete by
31P NMR, and the reaction mixture was filtered through Celite
to remove AgCl. The solvent was removed in vacuo to afford

4994 Organometallics, Vol. 22, No. 24, 2003
Becker and Gagne´
(G0-Cl)P tCO3. (G0-Cl)P tCl2 (564.1 mg, 0.4238 mmol) was
dissolved in 20 mL of wet CH2Cl2. Ag2CO3 (463.2 mg, 1.679
mmol) was added and the reaction mixture stirred at room
temperature, protected from light. After 4 h, the reaction was
complete by 31P NMR, and the reaction mixture was filtered
through Celite to remove AgCl. The solvent was removed in
vacuo to afford 475.6 mg (85%) of a dark yellow powder, which
was taken on without further purification to the next step.
31P NMR (162 MHz, CD2Cl2): δ 31.1 (J P-Pt ) 3528 Hz). 1H
NMR (400 MHz, CD2Cl2): δ 7.80 (m, 4 H), 7.71 (dd, J ) 1.6,
11.2 Hz, 4 H), 7.43 (m, 16 H), 7.05 (dd, J ) 2.0, 8.8 Hz, 4 H),
6.72 (dd, J ) 8.0, 11.2 Hz, 4 H), 5.77 (dd, J ) 0.4, 17.6 Hz, 4
H), 5.27 (d, J ) 10.8 Hz, 4 H), 5.12 (s, 8 H), 2.45 (m, 4 H).
(G0-Cl)P t (S-BINOL). (G0-Cl)P t CO3 (475.6 mg, 0.360
mmol) and S-BINOL (103.4 mg, 0.362 mmol) were dissolved
in 20 mL of CH2Cl2. After 4 h the reaction was complete by
31P NMR, and the solvent was removed in vacuo. The dark
yellow solid was washed three times with Et2O to remove free
BINOL. After drying in vacuo the dark yellow product was
obtained in 91% yield (504.5 mg). 31P NMR (121.5 MHz, CD2-
remove any uncoupled dendron, resulted in 929.1 mg (83%)
of (G1-Cl)P tCl2. 31P NMR (162 MHz, CD2Cl2): δ 39.8 (J P-Pt
) 3631 Hz). 1H NMR (400 MHz, CD2Cl2): δ 7.79 (m, 8 H),
7.45-7.14 (m, 32 H), 7.10 (d, J ) 8.4 Hz, 4 H), 6.77-6.59 (m,
20 H), 5.78 (d, J ) 17.6 Hz, 8 H), 5.25 (d, J ) 10.8 Hz, 8 H),
5.13 (s, 8 H), 5.09 (s, 16 H), 2.31 (m, 4 H).
(G1-Cl)P tCO3. (G1-Cl)P tCl2 (929.1 mg, 0.407 mmol) was
dissolved in 30 mL of wet CH2Cl2. Ag2CO3 (425.2 mg, 1.542
mmol) was added and the reaction mixture stirred at room
temperature, protected from light. After 4 h, the reaction was
complete by 31P NMR, and the reaction mixture was filtered
through Celite to remove AgCl. The solvent was removed in
vacuo to afford 877.2 mg (95%) of a dark yellow powder, which
was taken on without further purification to the next step.
31P NMR (162 MHz, CD2Cl2): δ 31.2 (J P-Pt ) 3531 Hz). 1H
NMR (400 MHz, CD2Cl2): δ 7.79 (t, J ) 11.2 Hz, 4 H), 7.69 (d,
J ) 9.6 Hz, 4 H), 7.40 (m, 32 H), 7.06 (d, J ) 8.0 Hz, 4 H),
6.76-6.56 (m, 20 H), 5.77 (d, J ) 17.6 Hz, 8 H), 5.26 (d, J )
10.8 Hz, 8 H), 5.10 (s, 8 H), 5.01 (s, 16 H), 2.39 (m, 4 H).
(G1-Cl)P t (S-BINOL). (G1-Cl)P t CO3 (877.2 mg, 0.386
mmol) and S-BINOL (112.6 mg, 0.394 mmol) were dissolved
in 30 mL of CH2Cl2. After 4 h the reaction was complete by
31P NMR, and the solvent was removed in vacuo. The dark
yellow solid was washed three times with Et2O to remove free
BINOL. After drying in vacuo the dark yellow product was
obtained in 93% yield (900.6 mg). 31P NMR (121.5 MHz, CD2-
1
Cl2): δ 25.1 (J P-Pt ) 3644 Hz). H NMR (300 MHz, CD2Cl2):
δ 8.01 (m, 2 H), 7.75 (m, 8 H), 7.55 (m, 10 H), 7.42 (m, 8 H),
7.16 (t, J ) 6.9 Hz, 2 H), 6.99 (m, 6 H), 6.88 (d, J ) 9.6 Hz, 2
H), 6.77 (m, 6 H), 5.83 (m, 4 H), 5.33 (m, 4 H), 5.23 (s, 4 H),
5.04 (s, 4 H), 2.13 (m, 4 H). 13C NMR (75.5 MHz, CD2Cl2): δ
162.0, 157.5, 157.4, 138.1, 138.0, 136.6, 135.8, 135.6, 135.0,
134.9, 134.5, 134.4, 132.9, 129.2, 129.1, 128.4, 128.0, 127.9,
127.8, 127.1, 126.9, 126.7, 125.9, 125.4, 124.9, 124.3, 124.0,
121.6, 120.9, 119.0, 114.7, 114.6, 114.5, 114.1, 71.1, 71.0, 27.1.
P -(G0-Cl). Metallomonomer (G0-Cl)P t(S-BINOL) (76.2
mg, 49.30 µmol), AIBN (5.7 mg, 34.7 µmol), EDMA (677.5 mg,
3418 µmol), and chlorobenzene (768.5 mg) were combined in
a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, yellow polymer. After Soxhlet extraction
with CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h,
724.9 mg of P -(G0-Cl) (63.09 µmol of Pt/g of polymer) was
obtained.
1
Cl2): δ 25.5 (J P-Pt ) 3666 Hz). H NMR (300 MHz, CD2Cl2):
δ 8.08 (m, 2 H), 7.80-7.60 (m, 8 H), 7.44-7.17 (m, 38 H), 7.02
(m, 6 H), 6.79-6.57 (m, 22 H), 5.81 (d, J ) 14.4 Hz, 8 H), 5.30
(m, 8 H), 5.18-5.02 (overlapping singlets, 24 H), 2.19 (m, 4
H). 13C NMR (75.5 MHz, CD2Cl2): δ 161.7, 160.5, 160.4, 157.3,
157.2, 153.6, 138.6, 138.5, 137.8, 137.7, 136.7, 135.8, 135.3,
134.9, 134.6, 134.4, 132.8, 130.6, 130.4, 129.3, 129.1, 128.5,
128.2, 128.1, 127.9, 126.7, 126.6, 125.8, 125.4, 124.9, 124.4,
124.0, 123.4, 121.7, 120.8, 118.9, 114.3, 114.2, 113.6, 106.5,
106.4, 102.1, 71.1, 70.9, 70.1, 70.0, 27.2.
P -(G1-Cl). Metallomonomer (G1-Cl)P t(S-BINOL) (163.0
mg, 65.33 µmol), AIBN (7.0 mg, 42.6 µmol), EDMA (837.3 mg,
4224 µmol), and chlorobenzene (999.5 mg) were combined in
a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, dark yellow polymer. After Soxhlet extrac-
tion with CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h,
947.4 mg of P -(G1-Cl) (63.04 µmol of Pt/g of polymer) was
obtained.
G1-Cl-Br . G1-benzyl bromide (1.7400 g, 3.99 mmol),28
4-bromo-2-chlorophenol (844.7 mg, 4.07 mmol), K2CO3 (860.5
mg, 6.23 mmol), 18-crown-6 ether (220.9 mg, 0.836 mmol), and
tetrabutylammonium iodide (90.1 mg, 0.244 mmol) were
combined in 40 mL of dry acetone and heated to reflux for 21
h. The reaction mixture was cooled to room temperature and
filtered. The filtrate was evaporated and the resulting residue
taken up in Et2O, extracted twice with H2O, dried over MgSO4,
filtered, and evaporated to a pale yellow oil. After purification
by column chromatography (silica gel, 2:1 hexanes/EtOAc)
1.8939 g (85%) of an extremely viscous oil was obtained. 1H
NMR (400 MHz, CDCl3): δ 7.49 (d, J ) 2.4 Hz, 1 H), 7.36 (m,
8 H), 7.21 (d, J ) 2.0 Hz, 2 H), 6.72 (m, 2 H), 6.64 (d, J ) 1.6
Hz, 2 H), 6.54 (br s, 1 H), 5.75 (d, J ) 17.6 Hz, 2 H), 5.25 (d,
J ) 10.8 Hz, 2 H), 5.04 (s, 2 H), 5.01 (s, 4 H). 13C NMR (100
MHz, CDCl3): δ 160.1, 153.3, 138.5, 137.3, 136.4, 136.2, 132.7,
130.4, 127.7, 126.4, 124.3, 115.2, 114.1, 112.9, 105.8, 101.7,
70.7, 69.8.
G0-Cl2-Br . 4-Vinylbenzyl chloride (600 µL, 4.26 mmol),
4-bromo-2,6-dichlorophenol (1.0429 g, 4.29 mmol), K2CO3
(890.3 mg, 6.44 mmol), 18-crown-6 ether (234.7 mg, 0.888
mmol), and tetrabutylammonium iodide (80.8 mg, 0.219 mmol)
were combined in 30 mL of dry acetone and heated to reflux
for 16 h. The reaction mixture was cooled to room temperature
and filtered. The filtrate was evaporated and the resulting
residue taken up in Et2O, extracted twice with H2O, dried over
MgSO4, filtered, and evaporated to a white solid. After
purification through a plug of silica gel (1:1 hexanes/EtOAc)
1
1.3471 g (88%) of a waxy white solid was obtained. H NMR
(400 MHz, CDCl3): δ 7.44 (m, 6 H), 6.72 (dd, J ) 10.8, 17.6
Hz, 1 H), 5.77 (dd, J ) 0.8, 17.6 Hz, 1 H), 5.27 (dd, J ) 0.4,
10.8, 1 H), 5.00 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ 150.5,
137.8, 136.4, 135.3, 131.6, 130.6, 128.7, 126.3, 116.6, 114.3,
74.8. Anal. Calcd for C15H11BrCl2O: C, 50.32; H, 3.10. Found:
C, 50.36; H, 2.94.
(G1-Cl)P tCl2. G1-Cl-Br (1.0993 g, 1.958 mmol) was dis-
solved in 25 mL of THF. The solution was cooled to -78 °C,
and a freshly titrated 2.33 M solution of nBuLi in hexanes (850
µL, 1.981 mmol) was added dropwise. After stirring at -78
°C for 1 h, CuCl (215.8 mg, 2.180 mmol) was added and the
reaction mixture was stirred for an additional 15 min, followed
by addition of 1,2-bis(dichlorophosphino)ethane (800 µL of a
0.6024 M solution in THF, 0.4819 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The
solution was then transferred via cannula to a solution of 181.3
mg (0.4845 mmol) of (COD)PtCl2 in 20 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The yellow residue was taken up in CH2-
Cl2 and filtered through Celite to remove any salts. Evapora-
tion of the solvent followed by Et2O wash of the residue, to
(G0-Cl2)P tCl2. G0-Cl2-Br (494.2 mg, 1.377 mmol) was
dissolved in 20 mL of THF. The solution was cooled to -78
n
°C, and a freshly titrated 2.5 M solution of BuLi in hexanes
(550 µL, 1.375 mmol) was added dropwise. After stirring at
-78 °C for 1 h, CuCl (162.5 mg, 1.642 mmol) was added and
the reaction mixture was stirred for an additional 15 min,
followed by addition of 1,2-bis(dichlorophosphino)ethane (570
µL of a 0.6024 M solution in THF, 0.3434 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4995
solution was then transferred via cannula to a solution of 128.7
mg (0.344 mmol) of (COD)PtCl2 in 20 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The yellow residue was taken up in CH2-
Cl2 and filtered through Celite to remove any salts. Evapora-
tion of the solvent followed by Et2O wash of the residue, to
remove any uncoupled dendron, resulted in 488.0 mg (97%)
of (G0-Cl2)P tCl2. 31P NMR (162 MHz, CD2Cl2): δ 40.0 (J P-Pt
126.3, 116.6, 114.0, 107.2, 102.1, 74.6, 69.7. Anal. Calcd for
C31H25BrCl2O3: C, 62.44; H, 4.23. Found: C, 62.49; H, 4.24.
(G1-Cl2)P tCl2. G1-Cl2-Br (1.0054 g, 1.687 mmol) was
dissolved in 20 mL of THF. The solution was cooled to -78
°C, and a freshly titrated 2.33 M solution of nBuLi in hexanes
(725 µL, 1.689 mmol) was added dropwise. After stirring at
-78 °C for 1 h, CuCl (196.1 mg, 1.981 mmol) was added and
the reaction mixture was stirred for an additional 15 min,
followed by addition of 1,2-bis(dichlorophosphino)ethane (700
µL of a 0.6024 M solution in THF, 0.4217 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The
solution was then transferred via cannula to a solution of 158.8
mg (0.4244 mmol) of (COD)PtCl2 in 20 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The yellow residue was taken up in CH2-
Cl2 and filtered through Celite to remove any salts. Evapora-
tion of the solvent followed by Et2O wash of the residue, to
remove any uncoupled dendron, resulted in 876.4 mg (86%)
of (G1-Cl2)P tCl2. 31P NMR (162 MHz, CD2Cl2): δ 40.7 (J P-Pt
1
) 3605 Hz). H NMR (400 MHz, CD2Cl2): δ 7.82 (d, J ) 12.0
Hz, 8 H), 7.49 (m, 16 H), 6.75 (dd, J ) 10.8, 17.6 Hz, 4 H),
5.80 (dd, J ) 0.4, 17.6 Hz, 4 H), 5.29 (dd, J ) 0.4, 10.8 Hz, 4
H), 5.13 (s, 8 H), 2.39 (m, 4 H).
(G0-Cl2)P tCO3. (G0-Cl2)P tCl2 (488.0 mg, 0.332 mmol) was
dissolved in 20 mL of wet CH2Cl2. Ag2CO3 (384.5 mg, 1.395
mmol) was added and the reaction mixture stirred at room
temperature, protected from light. After 4 h, the reaction was
complete by 31P NMR, and the reaction mixture was filtered
through Celite to remove AgCl. The solvent was removed in
vacuo to afford 460.7 mg (95%) of a dark yellow powder, which
was taken on without further purification to the next step.
31P NMR (162 MHz, CD2Cl2): δ 33.3 (J P-Pt ) 3530 Hz). 1H
NMR (400 MHz, CD2Cl2): δ 7.86 (d, J ) 12.4 Hz, 8 H), 7.44
(m, 16 H), 6.73 (dd, J ) 10.8, 17.6 Hz, 4 H), 5.78 (d, J ) 17.6
Hz, 4 H), 5.27 (d, J ) 10.8 Hz, 4 H), 5.05 (s, 8 H), 2.66 (m, 4
H).
1
) 3616 Hz). H NMR (400 MHz, CD2Cl2): δ 7.88 (d, J ) 12.0
Hz, 8 H), 7.43 (m, 32 H), 6.82 (d, J ) 2.0 Hz, 8 H), 6.76 (dd, J
) 11.2, 17.6 Hz, 8 H), 6.64 (s, 4 H), 5.80 (d, J ) 17.6 Hz, 8 H),
5.28 (d, J ) 10.8 Hz, 8 H), 5.07 (br s, 24 H), 2.42 (m, 4 H).
(G1-Cl2)P tCO3. (G1-Cl2)P tCl2 (876.4 mg, 0.362 mmol) was
dissolved in 30 mL of wet CH2Cl2. Ag2CO3 (380.3 mg, 1.379
mmol) was added and the reaction mixture stirred at room
temperature, protected from light. After 4 h, the reaction was
complete by 31P NMR, and the reaction mixture was filtered
through Celite to remove AgCl. The solvent was removed in
vacuo to afford 779.8 mg (89%) of a dark yellow powder, which
was taken on without further purification to the next step.
31P NMR (162 MHz, CD2Cl2): δ 33.3 (J P-Pt ) 3523 Hz). 1H
NMR (400 MHz, CD2Cl2): δ 7.86 (d, J ) 12.0 Hz, 8 H), 7.42
(m, 32 H), 6.77 (d, J ) 2.4 Hz, 8 H), 6.72 (m, 8 H), 6.59 (t, J )
2.0 Hz, 4 H), 5.78 (dd, J ) 0.8, 17.6 Hz, 8 H), 5.26 (dd, J )
0.8, 10.8 Hz, 8 H), 5.03 (br s, 24 H), 2.60 (m, 4 H).
(G0-Cl2)P t(S-BINOL). (G0-Cl2)P tCO3 (460.7 mg, 0.316
mmol) and S-BINOL (91.0 mg, 0.318 mmol) were dissolved in
20 mL of CH2Cl2. After 8 h the reaction was complete by 31P
NMR, and the solvent was removed in vacuo. The yellow solid
was washed three times with Et2O to remove free BINOL.
After drying in vacuo the yellow product was obtained in 85%
yield (450.6 mg). 31P NMR (121.5 MHz, CD2Cl2): δ 25.0 (J P-Pt
1
) 3611 Hz). H NMR (300 MHz, CD2Cl2): δ 7.89 (dd, J ) 4.8,
12.0 Hz, 8 H), 7.80 (d, J ) 8.0 Hz, 2 H), 7.72 (d, J ) 8.8 Hz, 2
H), 7.55 (m, 8 H), 7.44 (m, 8 H), 7.18 (t, J ) 6.8 Hz, 2 H), 7.06
(t, J ) 8.4 Hz, 2 H), 6.98 (d, J ) 8.8 Hz, 2 H), 6.92 (d, J ) 8.4
Hz, 2 H), 6.77 (m, 4 H), 5.81 (dd, J ) 17.6, 25.6 Hz, 4 H), 5.25
(dd, J ) 10.8, 21.6 Hz, 4 H), 5.22 (s, 4 H), 5.03 (d, J ) 2.0 Hz,
4 H), 2.45 (m, 2 H), 2.10 (m, 2 H). 13C NMR (75.5 MHz, CD2-
Cl2): δ 161.1, 155.2, 154.9, 138.5, 138.3, 136.7, 135.9, 135.7,
135.6, 134.6, 133.2, 131.5, 131.4, 129.4, 129.2, 128.2, 128.1,
126.7, 126.6, 125.4, 125.3, 125.2, 124.8, 124.0, 122.0, 114.8,
114.6, 75.7, 75.5, 26.7.51
(G1-Cl2)P t(S-BINOL). (G1-Cl2)P tCO3 (779.8 mg, 0.324
mmol) and S-BINOL (94.0 mg, 0.329 mmol) were dissolved in
30 mL of CH2Cl2. After 8 h the reaction was complete by 31P
NMR, and the solvent was removed in vacuo. The dark yellow
solid was washed three times with Et2O to remove free BINOL.
After drying in vacuo the dark yellow product was obtained
in 95% yield (791.0 mg). 31P NMR (121.5 MHz, CD2Cl2): δ 25.0
1
(J P-Pt ) 3613 Hz). H NMR (300 MHz, CD2Cl2): δ 7.94 (dd, J
P -(G0-Cl2). Metallomonomer (G0-Cl2)P t(S-BINOL) (84.9
mg, 50.46 µmol), AIBN (5.5 mg, 33.49 µmol), EDMA (669.1
mg, 3376 µmol), and chlorobenzene (752.9 mg) were combined
in a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, yellow polymer. After Soxhlet extraction
with CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h,
726.7 mg of P -(G0-Cl2) (64.66 µmol of Pt/g of polymer) was
obtained.
G1-Cl2-Br . G1-benzyl bromide (1.7870 g, 4.10 mmol),28
4-bromo-2,6-dichlorophenol (1.0167 g, 4.18 mmol), K2CO3
(926.1 mg, 6.70 mmol), 18-crown-6 ether (223.1 mg, 0.844
mmol), and tetrabutylammonium iodide (94.6 mg, 0.256 mmol)
were combined in 40 mL of dry acetone and heated to reflux
for 21 h. The reaction mixture was cooled to room temperature
and filtered. The filtrate was evaporated and the resulting
residue taken up in Et2O, extracted twice with H2O, dried over
MgSO4, filtered, and evaporated to a white solid. After
purification by column chromatography (silica gel, 2:1 hexanes/
EtOAc) 2.4114 g (98%) of a waxy white powder was obtained.
1H NMR (400 MHz, CDCl3): δ 7.44 (m, 10 H), 6.83 (d, J ) 2.0
Hz, 2 H), 6.76 (dd, J ) 10.8, 17.6 Hz, 1 H), 6.64 (t, J ) 2.0 Hz,
2 H), 5.80 (dd, J ) 0.4, 17.6 Hz, 2 H), 5.30 (d, J ) 10.8 Hz, 2
H), 5.06 (s, 4 H), 4.97 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ
159.9, 150.3, 138.1, 137.2, 136.3, 136.2, 131.5, 130.5, 127.6,
) 6.4, 11.6 Hz, 8 H), 7.79 (dd, J ) 8.0, 22.8 Hz, 4 H), 7.43 (m,
32 H), 7.20 (t, J ) 7.2 Hz, 4 H), 7.08 (t, J ) 7.2 Hz, 2 H), 7.03
(d, J ) 8.8 Hz, 2 H), 6.96 (d, J ) 8.8 Hz, 2 H), 6.89 (d, J ) 2.0
Hz, 2 H), 6.74 (m, 14 H), 6.60 (br s, 2 H), 5.80 (dd, J ) 8.4,
17.6 Hz, 8 H), 5.29 (dd, J ) 6.8, 10.8 Hz, 8 H), 5.17 (s, 4 H),
5.12 (s, 8 H), 5.04 (s, 8 H), 4.97 (s, 4 H), 2.45 (m, 2 H), 2.11 (br
s, 2 H). 13C NMR (75.5 MHz, CD2Cl2): δ 161.0, 160.3, 160.2,
155.1, 154.8, 138.4, 138.3, 137.6, 137.5, 136.7, 136.6, 125.8,
134.5, 133.1, 131.4, 131.3, 129.6, 129.3, 128.6, 128.1, 128.0,
127.8, 127.2, 126.6, 126.5, 125.3, 125.1, 124.8, 124.7, 123.9,
122.0, 114.2, 114.1, 107.8, 107.6, 102.5, 102.4, 75.6, 75.4, 10.2,
70.1, 26.6.51
P -(G1-Cl2). Metallomonomer (G1-Cl2)P t(S-BINOL) (170.8
mg, 64.87 µmol), AIBN (7.8 mg, 47.50 µmol), EDMA (831.3
mg, 4194 µmol), and chlorobenzene (1.0065 g) were combined
in a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, dark yellow polymer. After Soxhlet extrac-
tion with CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h,
971.4 mg of P -(G1-Cl2) (62.49 µmol of Pt/g of polymer) was
obtained.
G2-Cl2-Br . G2-benzyl bromide (2.6155 g, 2.87 mmol),28
4-bromo-2,6-dichlorophenol (714.0 mg, 2.94 mmol), K2CO3
(729.9 mg, 5.28 mmol), 18-crown-6 ether (154.8 mg, 0.586
mmol), and tetrabutylammonium iodide (57.9 mg, 0.157 mmol)
were combined in 60 mL of dry acetone and heated to reflux
for 21 h. The reaction mixture was cooled to room temperature
(51) Not all aromatic 13C resonances were observed.

4996 Organometallics, Vol. 22, No. 24, 2003
Becker and Gagne´
Ch a r t 2
and filtered. The filtrate was evaporated and the resulting
residue taken up in CH2Cl2, extracted twice with H2O, dried
over MgSO4, filtered, and evaporated to a white foamy solid.
After purification by column chromatography (silica gel, 2:1
CH2Cl2/hexanes) 2.885 g (94%) of a white foam was obtained.
1H NMR (400 MHz, CDCl3): δ 7.41 (m, 18 H), 6.78 (m, 10 H),
6.64 (t, J ) 2.1 Hz, 1 H), 6.61 (t, J ) 2.1 Hz, 2 H), 5.80 (d, J
) 17.7 Hz, 4 H), 5.30 (d, J ) 11.1 Hz, 4 H), 5.04 (s, 8 H), 5.03
(s, 4 H), 4.97 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ 160.2,
160.0, 150.5, 139.4, 138.3, 137.4, 136.5, 136.4, 131.7, 130.7,
127.7, 126.5, 116.8, 114.2, 107.4, 106.4, 102.3, 101.7, 75.0, 70.1,
69.9.
(G2-Cl2)P tCl2. G2-Cl2-Br (2.6348 g, 2.46 mmol) was dis-
solved in 50 mL of THF. The solution was cooled to -78 °C
and a freshly titrated 2.5 M solution of nBuLi in hexanes (985
µL, 2.46 mmol) was added dropwise. After stirring at -78 °C
for 1 h, CuCl (286.4 mg, 2.89 mmol) was added and the
reaction mixture was stirred for an additional 15 min, followed
by addition of 1,2-bis(dichlorophosphino)ethane (1019 µL of a
0.6024 M solution in THF, 0.6138 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The
solution was then transferred via cannula to a solution of 231.9
mg (0.6198 mmol) of (COD)PtCl2 in 40 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The yellow-brown residue was taken up in
CH2Cl2 and filtered through Celite to remove any salts.
Evaporation of the solvent resulted in 2.6972 g (102%) of crude
(G2-Cl2)P tCl2, which was carried on without purification. 1H
NMR analysis showed product along with uncoupled G2-
dendron; however only one phosphorus-containing species was
present. 31P NMR (162 MHz, CD2Cl2): δ 40.6 (J P-Pt ) 3600
Hz). 1H NMR (400 MHz, CD2Cl2): δ 7.84 (d, J ) 12.0 Hz, 8
H), 7.39 (m, 64 H), 6.81-6.56 (series of multiplets, 52 H), 5.77
(d, J ) 17.6 Hz, 16 H), 5.26 (d, J ) 10.8 Hz, 16 H), 5.02 (m, 56
H), 2.35 (m, 4 H).
) 12.0, 13.8 Hz, 8 H), 7.74 (t, J ) 9.3 Hz, 4 H), 7.38 (m, 70 H),
7.01 (d, J ) 8.7 Hz, 2 H), 6.87 (m, 4 H), 6.82-6.64 (series of
multiplets, 36 H), 6.54 (m, 12 H), 5.76 (d, J ) 17.7 Hz, 16 H),
5.25 (d, J ) 10.8 Hz, 16 H), 5.01 (m, 56 H), 2.34 (m, 2 H), 2.02
(m, 2 H). 13C NMR (75.5 MHz, CD2Cl2): δ 161.1, 160.5, 160.4,
160.3, 160.2, 158.7, 158.1, 155.2, 154.8, 141.2, 139.8, 138.5,
138.4, 137.6, 136.8, 136.7, 136.2, 135.9, 135.5, 134.7, 133.1,
131.6, 131.4, 129.4, 128.8, 128.7, 128.5, 128.1, 127.8, 127.4,
126.7, 125.7, 125.3, 125.0, 124.8, 124.0, 122.1, 120.7, 114.3,
107.9, 107.7, 106.7, 106.6, 102.5, 101.8, 100.7, 75.7, 75.5, 70.3,
70.2, 70.1, 66.0, 26.6.
P -(G2-Cl2). Metallomonomer (G2-Cl2)P t(S-BINOL) (295.9
mg, 65.21 µmol), AIBN (5.6 mg, 34.10 µmol), EDMA (714.2
mg, 3603 µmol), and chlorobenzene (1.0063 g) were combined
in a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, yellow-brown polymer. After Soxhlet ex-
traction with CH2Cl2 for 6 h and drying in vacuo at 50 °C for
12 h, 975.9 mg of P -(G2-Cl2) (62.41 µmol of Pt/g of polymer)
was obtained. G1t-CO2Me. 4-Vinylbenzyl chloride (12.0 mL,
85.15 mmol), methyl 3,4,5-trihydroxybenzoate (5.0067 g, 27.19
mmol), K2CO3 (15.76 g, 113.60 mmol), 18-crown-6 ether (2.1707
g, 8.21 mmol), and tetrabutylammonium iodide (1.0185 g, 2.76
mmol) were combined in 200 mL of dry acetone and heated to
reflux for 42 h. The reaction mixture was cooled to room
temperature and filtered. The filtrate was evaporated and the
resulting residue taken up in CH2Cl2, extracted twice with
H2O, dried over MgSO4, and filtered; the solvent evaporated
to a pale pink solid to produce 12.93 g of G1t-CO2Me (89%),
which was carried on without purification to the next step.
1H NMR (400 MHz, CDCl3): δ 7.41-7.24 (m, 14 H), 6.70 (m,
3 H), 5.73 (m, 3 H), 5.24 (m, 3 H), 5.09 (s, 4 H), 5.08 (s, 2 H),
3.86 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ 166.5, 152.4,
142.1, 137.3, 137.2, 136.9, 136.5, 136.3, 136.0, 128.7, 127.7,
126.3, 125.9, 125.3, 114.0, 113.8, 108.9, 70.8, 70.5, 52.2.
G1t-OH. G1t-CO2Me (14.02 g, 26.37 mmol) was dissolved
in 200 mL of THF and slowly added to 1.54 g (40.58 mmol) of
LiAlH4 in 60 mL of THF at 0 °C. After warming to room
temperature and stirring overnight the reaction was quenched
with H2O and extracted with Et2O. The organic layer was dried
over MgSO4, filtered, and evaporated to a pink solid. After
precipitation from CH2Cl2/hexanes, 8.07 g (61%) of G1t-OH,
which was carried on without purification to the next step,
was obtained. 1H NMR (400 MHz, CDCl3): δ 7.40-7.24 (m,
12 H), 6.75-6.53 (m, 5 H), 5.74 (m, 3 H), 5.23 (m, 3 H), 5.06
(s, 4 H), 5.02 (s, 2 H), 5.54 (d, J ) 4.8 Hz, 2 H). 13C NMR (100
MHz, CDCl3): δ 152.8, 137.5, 137.4, 137.2, 137.0, 136.6, 136.5,
136.4, 128.8, 127.6, 126.3, 126.0, 114.0, 113.7, 106.2, 74.9, 70.8,
65.3.51
(G2-Cl2)P tCO3. (G2-Cl2)P tCl2 (2.6972 g, 0.6238 mmol) was
dissolved in 30 mL of wet CH2Cl2. Ag2CO3 (633.5 mg, 2.298
mmol) was added and the reaction mixture stirred at room
temperature, protected from light. After 7 h, the reaction was
complete by 31P NMR, and the reaction mixture was filtered
through Celite to remove AgCl. The solvent was removed in
vacuo to afford 2.4355 g (91%) of a yellow-brown powder, which
was taken on without further purification to the next step.
31P NMR (162 MHz, CD2Cl2): δ 33.0 (J P-Pt ) 3526 Hz). 1H
NMR (400 MHz, CD2Cl2): δ 7.80 (d, J ) 12.0 Hz, 8 H), 7.39
(m, 64 H), 6.82-6.66 (series of multiplets, 36 H), 6.60-6.55
(m, 16 H), 5.76 (d, J ) 17.6 Hz, 16 H), 5.25 (d, J ) 10.8 Hz, 16
H), 5.01 (m, 56 H), 2.37 (m, 4 H).
(G2-Cl2)P t(S-BINOL). (G2-Cl2)P tCO3 (2.4355 mg, 0.5647
mmol) and S-BINOL (164.5 mg, 0.5752 mmol) were dissolved
in 40 mL of CH2Cl2. After 6 h the reaction was complete by
31P NMR, and the solvent was removed in vacuo. The yellow-
brown solid was taken up in CH2Cl2 and precipitated with Et2O
three times to remove free BINOL and uncoupled G2-dendron.
After drying in vacuo the yellow-brown product was obtained
in 75% yield (1.9324 g). 31P NMR (121.5 MHz, CD2Cl2): δ 25.0
G1t-Br . G1t-OH (8.07 g, 16.01 mmol) was dissolved in 30
mL of THF and cooled to 0 °C. CBr4 (8.02 g, 24.18 mmol) was
added followed by 6.31 g (24.06 mmol) of PPh3. The reaction
was stirred at 0 °C for 30 min and then warmed to room
temperature and stirred overnight. H2O was added and the
reaction mixture extracted with Et2O. The organic layer was
dried over MgSO4, filtered, and evaporated to a yellow solid.
After purification by column chromatography (silica gel, 2:1
1
(J P-Pt ) 3628 Hz). H NMR (300 MHz, CD2Cl2): δ 7.90 (dd, J

Imprinting Chiral Information into Dendrimers
Organometallics, Vol. 22, No. 24, 2003 4997
CH2Cl2/hexanes f 1:1 CH2Cl2/hexanes) 4.03 g (33%) of a waxy
white solid was obtained. 1H NMR (400 MHz, CDCl3): δ 7.41-
7.24 (m, 12 H), 6.76-6.66 (m, 5 H), 5.75 (m, 3 H), 5.25 (m, 3
H), 5.07 (s, 4 H), 5.02 (s, 2 H), 4.39 (s, 2 H). 13C NMR (100
MHz, CDCl3): δ 152.8, 138.5, 137.3, 137.2, 137.1, 136.6, 136.4,
136.3, 133.1, 128.37, 127.6, 126.3, 136.0, 114.1, 113.7, 108.7,
74.9, 71.0, 34.2.
161.1, 155.2, 154.9, 153.3, 153.1, 138.8, 138.6, 137.9, 137.8,
137.7, 137.6, 137.5, 137.0, 136.8, 125.9, 134.7, 133.2, 132.3,
131.8, 131.7, 131.6, 131.4, 130.0, 129.4, 129.3, 129.1, 129.0,
128.2, 128.1, 127.3, 126.7, 126.6, 126.4, 126.3, 125.8, 125.5,
125.4, 125.0, 124.9, 124.0, 122.2, 114.3, 114.2, 114.0, 113.9,
108.3, 108.2, 76.0, 75.9, 75.2, 75.1, 71.3, 71.2, 26.8.51
P -(G1t-Cl2). Metallomonomer (G1t-Cl2)P t(S-BINOL) (158.0
mg, 49.91 µmol), AIBN (6.5 mg, 39.6 µmol), EDMA (662.0 mg,
3340 µmol), and chlorobenzene (819.5 mg) were combined in
a 20 mL scintillation vial under N2 and sealed with a Teflon-
lined cap. The vial was heated to 60 °C for 24 h, yielding a
hard, transparent, yellow-brown polymer. After Soxhlet ex-
traction with CH2Cl2 for 6 h and drying in vacuo at 50 °C for
12 h, 791.4 mg of P -(G1t-Cl2) (58.73 µmol of Pt/g of polymer)
was obtained.
G1t-Cl2-Br . G1t-Br (1.9965 g, 3.52 mmol), 4-bromo-2,6-
dichlorophenol (873.9 mg, 3.60 mmol), K2CO3 (1.0724 g, 7.76
mmol), 18-crown-6 ether (191.4 mg, 0.724 mmol), and tetrabu-
tylammonium iodide (67.1 mg, 0.182 mmol) were combined in
50 mL of dry acetone and heated to reflux for 21 h. The
reaction mixture was cooled to room temperature and filtered.
The filtrate was evaporated and the resulting residue taken
up in CH2Cl2, extracted twice with H2O, dried over MgSO4,
filtered, and evaporated to a white solid. After purification by
column chromatography (silica gel, 3:1 CH2Cl2/hexanes) 2.3923
g (93%) of a foamy white solid was obtained. 1H NMR (400
MHz, CDCl3): δ 7.43-7.24 (m, 14 H), 6.78-6.66 (m, 5 H), 5.74
(m, 3 H), 5.24 (m, 3 H), 5.09 (s, 4 H), 5.04 (s, 2 H), 4.88 (s, 2
H). 13C NMR (100 MHz, CDCl3): δ 152.8, 150.3, 138.5, 137.3,
137.2, 137.1, 136.7, 136.5, 136.4, 131.6, 131.3, 130.6, 128.8,
127.6, 126.3, 126.0, 116.6, 114.0, 113.7, 108.2, 75.1, 74.9, 71.0.
Anal. Calcd for C40H33BrCl2O4: C, 65.95; H, 4.57. Found: C,
65.71; H, 4.54.
(Isop r op en yld p p e)P tCl2. Isopropenyldppe (1.0446 g, 1.87
mmol) in 20 mL of CH2Cl2 was slowly added to a solution of
(COD)PtCl2 (703.6 mg, 1.88 mmol) in 25 mL of CH2Cl2. After
stirring for 30 min the volatiles were removed in vacuo, and
the white solid was recrystallized from CH2Cl2/hexanes to
afford 638.3 mg (41%) of (isopropenyldppe)PtCl2. 31P NMR
1
(121.5 MHz, CDCl3): δ 40.4 (J P-Pt ) 3622 Hz). H NMR (300
MHz, CDCl3): δ 7.80 (dd, J ) 8.1, 12.0 Hz, 8 H), 7.52 (dd, J )
2.1, 8.4 Hz, 8 H), 5.43 (s, 4 H), 5.18 (s, 4 H), 2.31 (m, 4 H),
2.13 (m, 12 H).
(G1t-Cl2)P tCl2. G1t-Cl2-Br (951.3 mg, 1.31 mmol) was
dissolved in 25 mL of THF. The solution was cooled to -78
(Isop r op en yld p p e)P t(S-BINOL) (3). S-BINOL (104.2 mg,
0.364 mmol) and NaOtBu (71.5 mg, 0.744 mmol) were dissolved
in 5 mL of 1:1 THF and toluene. After stirring for 30 min the
solution was transferred via cannula to a suspension of 299.8
mg (0.364 mmol) of (isopropenyldppe)PtCl2 in 60 mL of
chlorobenzene. The reaction mixture immediately turned
yellow and after 1 h of stirring became homogeneous. The
volatiles were removed in vacuo and the yellow solid triterated
three times with 20 mL of dry toluene to remove residual tert-
butyl alcohol. CH2Cl2 (50 mL) was added and filtered to remove
the NaCl byproduct. Recrystallization from CH2Cl2/Et2O af-
forded 256.9 mg (68%) of yellow crystals. 31P NMR (121.5 MHz,
n
°C, and a freshly titrated 2.5 M solution of BuLi in hexanes
(522.5 µL, 1.31 mmol) was added dropwise. After stirring at
-78 °C for 1 h, CuCl (160.0 mg, 1.62 mmol) was added and
the reaction mixture was stirred for an additional 15 min,
followed by addition of 1,2-bis(dichlorophosphino)ethane (540
µL of a 0.6024 M solution in THF, 0.3253 mmol). The resulting
reaction mixture was stirred at -78 °C under Ar for 24 h. The
solution was then transferred via cannula to a solution of 121.7
mg (0.3253 mmol) of (COD)PtCl2 in 40 mL of CH2Cl2. After
stirring for 1 h at room temperature, the volatiles were
removed in vacuo. The yellow-brown residue was taken up in
CH2Cl2 and filtered through Celite to remove any salts.
Evaporation of the solvent resulted in 887.8 mg (92%) of crude
1
CD2Cl2): δ 26.9 (J P-Pt ) 3638 Hz); H NMR (300 MHz, CD2-
Cl2): δ 7.90 (dd, J ) 8.4, 11.1 Hz, 4 H), 7.77 (m, 6 H), 7.55 (m,
10 H), 7.10 (m, 2 H), 6.96 (m, 2 H), 6.81 (d, J ) 8.4 Hz, 2 H),
6.63 (d, J ) 8.7 Hz, 2 H), 6.54 (br. s, 2 H), 5.42 (br s, 2 H),
5.28 (br s, 2 H), 5.16 (br s, 2 H), 2.20 (m, 10 H), 2.10 (s, 6 H).
13C NMR (75.5 MHz, CD2Cl2): δ 162.6, 145.2, 144.9, 142.8,
135.8, 134.2, 133.2, 128.9, 127.9, 127.7, 127.5, 126.4, 126.2,
126.1, 125.7, 125.3, 125.0, 124.7, 121.4, 115.0, 114.7, 27.2, 21.8,
21.6.51 Anal. Calcd for C58H52O2P2Pt: C, 67.11; H, 5.05.
Found: C, 67.04; H, 5.05.
(G1t-Cl2)P tCl2, which was carried on without purification. 31
P
1
NMR (162 MHz, CD2Cl2): δ 41.0 (J P-Pt ) 3609 Hz). H NMR
(400 MHz, CD2Cl2): δ 7.96 (d, J ) 16.0 Hz, 4 H), 7.55-7.38
(m, 52 H), 6.96 (s, 8 H), 6.81 (m, 12 H), 5.85 (m, 12 H), 5.33
(m, 12 H), 5.16 (s, 16 H), 5.13-5.01 (m, 16 H), 2.53 (m, 4 H).
(G1t-Cl2)P tCO3. (G1t-Cl2)P tCl2 (877.8 mg, 0.301 mmol)
was dissolved in 30 mL of wet CH2Cl2. Ag2CO3 (450.0 mg, 1.63
mmol) was added and the reaction mixture stirred at room
temperature, protected from light. After 4 h, the reaction was
complete by 31P NMR, and the reaction mixture was filtered
through Celite to remove AgCl. The solvent was removed in
vacuo to afford 714.1 mg (81%) of a yellow-brown powder,
which was taken on without further purification to the next
step. 31P NMR (162 MHz, CD2Cl2): δ 34.7 (J P-Pt ) 3526 Hz).
1H NMR (400 MHz, CD2Cl2): δ 8.16 (d, J ) 11.2 Hz, 4 H),
7.63-7.54 (m, 52 H), 7.09 (d, J ) 16.0 Hz, 8 H), 6.96 (m, 12
H), 6.00 (m, 12 H), 5.48 (br s, 12 H), 5.33-5.19 (m, 32 H), 2.91
(m, 4 H).
d p p e P olym er (P -3). Metallomonomer 3 (100.5 mg, 96.81
µmol), AIBN (12.0 mg, 73.08 µmol), EDMA (1397.4 mg, 7050
µmol), and chlorobenzene (1.5033 g) were combined in a 20
mL scintillation vial under N2 and sealed with a Teflon-lined
cap. The vial was heated to 60 °C for 24 h, yielding a hard,
transparent, yellow polymer. After Soxhlet extraction with
CH2Cl2 for 6 h and drying in vacuo at 50 °C for 12 h, 1.49 g of
P -3 (62.34 µmol of Pt/g of polymer) was obtained.
Typ ica l HCl Clea va ge Exp er im en t. P -(G1-Cl2) (245.5
mg, 15.34 µmol of Pt) was suspended in 20 mL of CH2Cl2, and
10 drops of concentrated HCl(aq) was added. After 6 h of
stirring at room temperature, the polymer was filtered from
solution through a glass Soxhlet thimble. The filtrate was used
for Soxhlet extraction for 12 h. The solvent was removed in
(G1t-Cl2)P t(S-BINOL). (G1t-Cl2)P tCO3 (714.1 mg, 0.2428
mmol) and S-BINOL (71.4 mg, 0.2497 mmol) were dissolved
in 40 mL of CH2Cl2. After 4.5 h the reaction was complete by
31P NMR, and the solvent was removed in vacuo. The yellow-
brown solid was taken up in CH2Cl2 and precipitated with Et2O
three times to remove free BINOL and uncoupled G2-dendron.
After drying in vacuo the yellow-brown product was obtained
in 73% yield (562.1 mg). 31P NMR (121.5 MHz, CD2Cl2): δ 25.2
i
vacuo, and the residue was dissolved in 1.931 mL of PrOH.
Quantitative HPLC analysis revealed that S-BINOL was
removed from 67% of the Pt sites (22.4 min (S-BINOL)).
Typ ica l Rebin d in g Exp er im en t. P -(G1-Cl2) (309.4 mg,
19.33 µmol of Pt), rac-Br2BINOL (149.2 mg, 336.0 µmol), 3 mL
of chlorobenzene, and 0.5 mL of water were added to a Schlenk
tube under argon. The tube was sealed and placed in a 60 °C
oil bath. After stirring at 60 °C for 12 h, the polymer was
filtered from the hot solution through a glass Soxhlet thimble
and extracted with the filtrate and additional CH2Cl2 for 12
1
(J P-Pt ) 3619 Hz). H NMR (300 MHz, CD2Cl2): δ 7.97 (dd, J
) 4.2, 11.7 Hz, 6 H), 7.83 (dd, J ) 7.8, 15.6 Hz, 4 H), 7.52-
7.37 (m, 52 H), 7.15-6.71 (series of multiplets, 26 H), 5.81 (m,
12 H), 5.31 (m, 12 H), 5.21-4.92 (overlapping singlets, 32 H),
2.51 (m, 2 H), 2.18 (m, 2 H). 13C NMR (75.5 MHz, CD2Cl2): δ

4998 Organometallics, Vol. 22, No. 24, 2003
Becker and Gagne´
h. The polymer was dried for 1 h under vacuum, then
suspended in 20 mL of CH2Cl2, and 10 drops of concentrated
HCl(aq) was added. After 6 h of stirring at room temperature,
the polymer was again filtered from solution through a glass
Soxhlet thimble. The filtrate was used for Soxhlet extraction
for 16 h. The solvent was removed in vacuo and the residue
was dissolved in a known amount of PrOH for quantitative
chiral HPLC analysis (22.4 min (S-BINOL), 27.7 min (S-Br2-
BINOL), 38.6 min (R-Br2BINOL)).
of chlorobenzene, and 0.5 mL of water were added to a Schlenk
tube under argon. The tube was sealed and placed in a 60 °C
oil bath. After stirring at 60 °C for 12 h, the polymer was
filtered from the hot solution through a glass Soxhlet thimble
and extracted with the filtrate and additional CH2Cl2 for 12
h. The polymer was dried for 1 h under vacuum, then
suspended in 20 mL of CH2Cl2, and 10 drops of concentrated
HCl(aq) was added. After 6 h of stirring at room temperature,
the polymer was again filtered from solution through a glass
Soxhlet thimble. The filtrate was used for Soxhlet extraction
for 16 h. The solvent was removed in vacuo, and the residue
i
Su r fa ce Ar ea . Dinitrogen adsorption/desorption measure-
ments were performed at 77.3 K on a Quantrachrome model
Autosorb-1 porosimiter. Samples were degassed at 26 °C for
8 or 16 h prior to data collection. Surface area measurements
utilized a six-point adsorption isotherm collected over 0.05-
0.30 p/p0 and were analyzed via the BET method.52 Reported
surface area values are reported on the adsorption isotherm.
Typ ica l HCl Clea va ge Exp er im en t. P -(G1-Cl2) (245.5
mg, 15.34 µmol of Pt) was suspended in 20 mL of CH2Cl2, and
10 drops of concentrated HCl(aq) was added. After 6 h of
stirring at room temperature, the polymer was filtered from
solution through a glass Soxhlet thimble. The filtrate was used
for Soxhlet extraction for 12 h. The solvent was removed in
i
was dissolved in a known volume of PrOH for quantitative
chiral HPLC analysis (Daicel Chiralcel OD-H column (95%
hexanes/5% EtOH, 0.8 mL/min flow rate), 22.4 min (S-BINOL),
27.7 min (S-Br2BINOL), 38.6 min (R-Br2BINOL)).
Ack n ow led gm en t. We wish to thank Ms. Lori Van
Orden, who prepared G0-Br as part of an undergradu-
ate research project, the generous support of the Na-
tional Science Foundation (CHE-0075717 and CHE-
0315203), and Prof. Wenbin Lin (UNC-CH) for access
to his surface area instrument. M.R.G. is a Camille-
Dreyfus Teacher Scholar.
i
vacuo, and the residue was dissolved in 1.931 mL of PrOH.
Quantitative HPLC analysis revealed that S-BINOL was
removed from 67% of the Pt sites (22.4 min (S-BINOL)).
Typ ica l Rebin d in g Exp er im en t. P -(G1-Cl2) (309.4 mg,
19.33 µmol of Pt), rac-Br2BINOL (149.2 mg, 336.0 µmol), 3 mL
Su p p or tin g In for m a tion Ava ila ble: HCl cleavage and
rebinding data for the non-chlorinated and mono-chlorinated
metallodendrimers. This material is available free of charge
via the Internet at http://pubs.acs.org.
(52) Brunauer, S.; Emmett, P. H.; Teller, E. J . Am. Chem. Soc. 1951,
73, 373-380.
OM0340387