Design and performance of rigid nanosize multimetallic cartwheel pincer compounds as Lewis-acid catalysts

Article abstract of DOI:10.1021/om0101689

Novel strategies for the preparation of rigid cartwheel pincer metal complexes have been developed. The aromatic backbone of these materials ensures a high rigidity, which is expected to be important for a high retention when these multimetallic nanosize complexes are applied as homogeneous catalysts in a nanomembrane reactor. The ligand precursors C₆[C₆H₃(CH₂Y)₂- 3,5]₆ (10, Y = NMe₂; 11, Y = SPh; 12, Y = PPh₂; 13, Y = pz = pyrazol-1-yl) have been prepared in high yields from the key intermediate C₆[C₆H₃ (CH₂Br)₂-3,5]₆ (9). The hexakis(pincer) palladium(II) complexes C₆[(PdX)-4-C₆H₂(CH₂Y)₂-3, 5]₆ (14, Y = SPh, L = Cl; 15, Y = PPh₂, L = Cl; 16, Y = pyrazol-1-yl, L = OAc; 17, Y = pyrazol-1-yl, L = Cl) have been prepared via direct electrophilic palladation of the corresponding ligands. The (tris)pincer ligand C₆H₃[Br-4-C₆H₃(CH₂ NMe₂)₂-3,5]₃-1,3,5 (20) was prepared via a triple-condensation reaction of 4-bromo-3,5-bis[(dimethylamino)methyl]acetophenone (19). Reaction of 20 with Pd(dba)₂ yielded the tripalladium complex C₆H₃[(PdBr)-4-C₆H₃(CH₂ NMe₂)₂-3,5]₃-1,3,5 (21). The crystal structure of 21 shows a propeller-like structure with D₃ symmetry and a fixed bromine-bromine distance of 17.4573(4) ?, approximately forming a triangle with a height of 15.2 ?. These nanosize cartwheel pincer metal complexes based on tridentate Y,C,Y′ pincer ligands have been used as homogeneous Lewis-acid catalysts. Moreover, the influence of the donor substituent Y on the catalytic activity of cationic mono-Y,C,Y′ Pd^II complexes as Lewis-acid catalysts in the double Michael reaction between methyl vinyl ketone and ethyl α-cyanoacetate, as a model reaction, has been investigated. It was found that cationic N,C,N′-type pincer complexes (1a, Y = NMe₂; 1b, Y = pz; 1c, Y = pz* = 3,5-dimethylpyrazol-1-yl; 23) were superior to the P,C,P′- and S,C,S′-pincer complexes (1d, Y = PPh₂-Le, Y = SPh). The nanosize cationic tri-N,C,N′ Pd^II complex 23 was found to have a catalytic activity per catalytic site in the double Michael reaction of the same order of magnitude as the monopincer analogue 1a (k = 279 × 10^-6 s^-1 for 1a vs k = 232 × 10^-6 s^-1 for 23). The combination of the nanosize dimensions, the catalytic activity, and the high thermal and air stability makes these complexes excellent candidates for application in a continuous process in a nanomembrane reactor.

Full text of DOI:10.1021/om0101689

Organometallics 2001, 20, 3159-3168
3159
Design a n d P er for m a n ce of Rigid Na n osize Mu ltim eta llic
Ca r tw h eel P in cer Com p ou n d s a s Lew is-Acid Ca ta lysts
Harm P. Dijkstra,† Michel D. Meijer,† J im Patel,‡ Rob Kreiter,†
Gerard P. M. van Klink,† Martin Lutz,§ Anthony L. Spek,§,| Allan J . Canty,‡ 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 March 1, 2001
Novel strategies for the preparation of rigid cartwheel pincer metal complexes have been
developed. The aromatic backbone of these materials ensures a high rigidity, which is
expected to be important for a high retention when these multimetallic nanosize complexes
are applied as homogeneous catalysts in a nanomembrane reactor. The ligand precursors
C6[C6H3(CH2Y)2-3,5]6 (10, Y ) NMe2; 11, Y ) SPh; 12, Y ) PPh2; 13, Y ) pz ) pyrazol-1-yl)
have been prepared in high yields from the key intermediate C6[C6H3(CH2Br)2-3,5]6 (9). The
hexakis(pincer) palladium(II) complexes C6[(PdX)-4-C6H2(CH2Y)2-3,5]6 (14, Y ) SPh, L )
Cl; 15, Y ) PPh2, L ) Cl; 16, Y ) pyrazol-1-yl, L ) OAc; 17, Y ) pyrazol-1-yl, L ) Cl) have
been prepared via direct electrophilic palladation of the corresponding ligands. The
(tris)pincer ligand C6H3[Br-4-C6H3(CH2NMe2)2-3,5]3-1,3,5 (20) was prepared via a triple-
condensation reaction of 4-bromo-3,5-bis[(dimethylamino)methyl]acetophenone (19). Reaction
of 20 with Pd(dba)2 yielded the tripalladium complex C6H3[(PdBr)-4-C6H3(CH2NMe2)2-3,5]3-
1,3,5 (21). The crystal structure of 21 shows a propeller-like structure with D3 symmetry
and a fixed bromine-bromine distance of 17.4573(4) Å, approximately forming a triangle
with a height of 15.2 Å. These nanosize cartwheel pincer metal complexes based on tridentate
Y,C,Y′ pincer ligands have been used as homogeneous Lewis-acid catalysts. Moreover, the
influence of the donor substituent Y on the catalytic activity of cationic mono-Y,C,Y′ PdII
complexes as Lewis-acid catalysts in the double Michael reaction between methyl vinyl ketone
and ethyl R-cyanoacetate, as a model reaction, has been investigated. It was found that
cationic N,C,N′-type pincer complexes (1a , Y ) NMe2; 1b, Y ) pz; 1c, Y ) pz* )
3,5-dimethylpyrazol-1-yl; 23) were superior to the P,C,P′- and S,C,S′-pincer complexes (1d ,
Y ) PPh2; 1e, Y ) SPh). The nanosize cationic tri-N,C,N′ PdII complex 23 was found to have
a catalytic activity per catalytic site in the double Michael reaction of the same order of
magnitude as the monopincer analogue 1a (k ) 279 × 10-6 s-1 for 1a vs k ) 232 × 10-6 s-1
for 23). The combination of the nanosize dimensions, the catalytic activity, and the high
thermal and air stability makes these complexes excellent candidates for application in a
continuous process in a nanomembrane reactor.
In tr od u ction
bearing multidentate ligands or ligand precursors. Their
design is usually such that the resulting multimetallic
system can easily be recovered for reuse after catalysis
from the product-containing solution.2 Recently, we and
others reported the development of nanosize multimetal
homogeneous catalysts, which were separable from the
reaction mixture by nanomembrane filtration.2d-g,j These
catalysts are based on metalated phosphine ligands,2d,e,g
P,O ligands,2f or tridentate Y,C,Y′ ligands2j (so-called
“pincer” ligands) immobilized on large organic frame-
works, e.g. carbosilane dendrimers.
Within the field of homogeneous catalysis there is
currently a great interest in the application of tailored/
engineered organic compounds as soluble support ma-
terials for anchored, catalytically active metal com-
plexes.1 These organic materials often have a periphery
* To whom correspondence should be addressed. Tel: +3130
2533120. Fax: +31302523615. E-mail: g.vankoten@chem.uu.nl.
† Debye Institute, Utrecht University.
‡ School of Chemistry, 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.
In organic synthesis, transition-metal complexes act-
ing as Lewis-acid catalysts have received considerable
attention in recent years.3-7 Tridentate Y,C,Y′ pincer
ligands in combination with group VIII metals (A;
(1) For a review on the application of metallodendrimers as homo-
geneous catalysts, see: Kreiter, R.; Kleij, A. W.; Klein Gebbink, R. J .
M.; van Koten, G. Topics in Current Chemistry, Dendrimers IV by Prof.
Dr. F. Vo¨gtle.
10.1021/om0101689 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/08/2001

3160 Organometallics, Vol. 20, No. 14, 2001
Dijkstra et al.
F igu r e 1.
F igu r e 2.
Figure 1) have been found to be active as homogeneous
Lewis-acid catalysts as well.8-10 Venanzi and Zhang
have reported on the use of chiral P,C,P′-type complexes
as catalysts in the aldol reaction between benzaldehydes
and methyl isocyanoacetate.8 Zhang has also reported
that the palladium complexes exhibit a higher activity
than the analogous platinum complexes in this reaction.
The use of a chiral palladated 1,3-bis(2-oxazolinyl)-
benzene complex in an aldol reaction, as well as in a
single and double Michael reaction, has been reported
by Stark et al.9 The same ligand on rhodium has been
used by Nishiyama and co-workers in the enantioselec-
tive allylation of aldehydes.10 Although palladated oxa-
zolinyl-based pincer complexes9 appear to be more active
in the aldol reaction than the corresponding P,C,P′
analogue,8b a detailed investigation into the influence
of the donor group Y on the catalyst activity has not
been reported thus far.
The lack of understanding of the influence of the
donor substituent Y (Figure 1) on the activity of the
Lewis-acid catalyst impedes the rational design of
effective catalysts of the form A. For the design and
synthesis of nanosize homogeneous catalysts based on
pincer metal building blocks for organic reactions,
knowledge about this aspect is important. Thus, we
have undertaken such a study by varying Y in com-
plexes 1a -e (Figure 2) and investigated the catalytic
activity of these complexes in the double Michael
reaction between methyl vinyl ketone and ethyl R-cy-
anoacetate as a model reaction. While a direct compari-
son is not entirely valid, since the substituents attached
to the different donor atoms are not equivalent in all
cases (e.g. the pincer complex with Y ) NPh2 cannot be
prepared), this series can give a good indication of the
overall effect of the donor atom (N, P, or S) on the
activity of the catalyst. Furthermore, complexes 1b (Y
) pz ) pyrazol-1-yl) and 1c (Y ) pz* ) 3,5-dimeth-
ylpyrazol-1-yl) can also provide additional information
about the influence of the electron-donating methyl
groups on the activity of the Lewis-acid catalyst. In
addition, we report here the application of multipincer
complexes as nanosize homogeneous catalysts in the
same double Michael reaction. For this study, rigid
multipincer benzene complexes B2h and C (Figure 3)
were selected incorporating six and three palladated
pincer groups, respectively. An obvious difference be-
tween B and C is the lower degree of congestion about
the metal centers in the tripalladium cartwheel com-
plex. We expect that a high degree of rigidity in the
backbone of these nanosize catalysts is advisable for
optimal retention of such materials by nanomembrane
filters.
(2) (a) Knapen, J . W. J .; van der Made, A. W.; de Wilde, J . C.; van
Leeuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature
1994, 372, 659. (b) Kragl, U.; Dreisbach, C. Angew. Chem., Int. Ed.
Engl. 1996, 35, 642. (c) Reetz, M. T.; Lohmer, G.; Schwickardi, R.
Angew. Chem., Int. Ed. 1997, 36, 1526. (d) Giffels, G.; Beliczey, J .;
Felder, M.; Kragl, U. Tetrahedron: Asymmetry 1998, 9, 691. (e)
Brinkmann, N.; Giebel, D.; Lohmer, G.; Reetz, M. T.; Kragl, U. J . Catal.
1999, 183, 163. (f) Hovestad, N. J .; Eggeling, E. B.; Heidbu¨chel, H. J .;
J astrzebski, J . T. B. H.; Kragl. U.; Keim, W.; Vogt, D.; van Koten, G.
Angew. Chem., Int. Ed. 1999, 38, 1655. (g) De Groot, D.; Eggeling, E.
B.; de Wilde, J . C.; Kooijman, H.; van Haaren, R. J .; van der Made, A.
W.; Spek, A. L.; Vogt, D.; Reek, J . N. H.; Kamer, P. C. J .; van Leeuwen,
P. W. N. M. Chem. Commun. 1999, 1623. (h) Dijkstra, H. P.;
Steenwinkel, P.; Grove, D. M.; Lutz, M.; Spek, A. L.; van Koten, G.
Angew. Chem., Int. Ed. 1999, 38, 2186. (i) Albrecht, M.; Hovestad, N.
J .; Boersma, J .; van Koten, G. Chem. Eur. J . 2001, 7, 1289. (j) Kleij,
A. W.; Gossage, R. A.; Klein Gebbink, R. J . M.; Brinkman, N.; Reijerse,
E. J .; Kragl, U.; Lutz, M.; Spek, A. L.; van Koten, G. J . Am. Chem.
Soc. 2000, 122, 12112.
(3) (a) Mahrwald, R. Chem. Rev. 1999, 99, 1095 and references
therein. (b) Christoffers, J . Eur. J . Org. Chem. 1998, 1259 and
references therein. (c) Drury, W. J .; Ferraris, D.; Cox, C.; Young, B.;
Lectka, T. J . Am. Chem. Soc. 1998, 120, 11006.
(4) Diels-Alder Reactions: (a) Bruin, M. E.; Ku¨ndig, E. P. Chem.
Commun. 1998, 2635. (b) Kanemasa, S.; Oderaotoshi, Y.; Sakaguchi,
S.-I.; Yamamoto, H.; Tanaka, J .; Wada, E.; Curran, D. J . Am. Chem.
Soc. 1998, 120, 3074. (c) Schaus, S. E.; Brånalt, J .; J acobsen, E. N. J .
Org. Chem. 1998, 63, 403. (d) Davies, D. L.; Fawcett, J .; Garrat, S. A.;
Russell, D. R. Chem. Commun. 1997, 1351. (e) Evans, D. A.; Murry, J .
A.; von Matt, P.; Norcross, R. D.; Miller, S. J . Angew. Chem., Int. Ed.
Engl. 1995, 34, 798. (f) Ku¨ndig, E. P.; Bourdin, B.; Bernardinelli, G.
Angew. Chem., Int. Ed. Engl. 1994, 33, 1856. (g) Corey, E. J .; Imai,
N.; Zhang, H.-Y. J . Am. Chem. Soc. 1991, 113, 728.
(5) Aldol reactions: (a) Fujimura, O. J . Am. Chem. Soc. 1998, 120,
10032. (b) Evans, D. A.; MacMillan, D. W. C.; Campos, K. R. J . Am.
Chem. Soc. 1997, 119, 10859. (c) Yanagisawa, A.; Matsumoto, Y.;
Nakashima, H.; Asakawa, K.; Yamamoto, H. J . Am. Chem. Soc. 1997,
119, 9319. (d) Evans, D. A.; Murry, J . A.; Kozlowski, M. C. J . Am.
Chem. Soc. 1996, 118, 5814. (e) Mikami, K.; Matsukawa, S. J . Am.
Chem. Soc. 1994, 116, 4077.
Resu lts a n d Discu ssion
(6) Michael reactions: (a) Blacker, A. J .; Clarke, M. L.; Loft, M. S.;
Mahon, M. F.; Williams, J . M. J . Organometallics 1999, 18, 2867. (b)
Sawamura, M.; Hamashima, H.; Ito, Y. Tetrahedron 1994, 50, 4439.
(c) Evans, D. A.; Rovis, T.; Kozlowski, M. C.; Wade Downey, C.; Tedrow,
J . S. J . Am. Chem. Soc. 2000, 122, 9134.
(7) Alkylation reactions: (a) Ferraris, D.; Young, B.; Dudding, T.;
Lectka, T. J . Am. Chem. Soc. 1998, 120, 4548. (b) Yanagisawa, A.;
Nakashima, H.; Ishiba, A.; Yamamoto, H. J . Am. Chem. Soc. 1996,
118, 4723.
Syn th esis of Mon op in cer Com p lexes. Complexes
1a -e were prepared from the corresponding palladium
halide complexes 3a -e by reaction with silver tetrafluo-
roborate in wet acetone (Scheme 1).11-13 The palladium
chloride complex 3c was prepared via direct electrophilic
palladation, using Pd(OAc)2 in refluxing acetic acid,14
while complexes 3d ,e were prepared according to lit-
erature procedures.15
(8) (a) Gorla, F.; Togni, A.; Venanzi, L. M.; Albinati, A.; Lianza, F.
Organometallics 1994, 13, 1607. (b) Longmire, J . M.; Zhang, X.; Shang,
M. Organometallics 1998, 17, 4374.
Different routes were developed for the synthesis of
metalated hexakis(pincer)- and (tris)pincer-substituted
benzenes (B and C, respectively, Figure 3), which are
rigid nanosize molecules potentially suitable for recov-
(9) (a) Stark, M. A.; Richards, C. J . Tetrahedron Lett. 1997, 38, 5881.
(b) Stark, M. A.; J ones, G.; Richards, C. J . Organometallics 2000, 19,
1282.
(10) Motoyama, Y.; Narusawa, H.; Nishiyama, H. Chem. Commun.
1999, 131.

Rigid Nanosize Cartwheel Pincer Compounds
Organometallics, Vol. 20, No. 14, 2001 3161
niques. Therefore, we developed an improved route to
9, as outlined in Scheme 2, which involves the trimer-
ization of the bis(pincer)acetylene species 7 to hexakis-
[3,5-bis(methoxymethyl)phenyl]benzene (8), which can
easily be converted to 9.
Compound 7 was prepared in a one-pot Pd/Cu cata-
lyzed cross-coupling reaction starting from iodoarenes
6 and gaseous acetylene (Scheme 2).17 This procedure
afforded 7 in 90% overall yield, which is a significant
improvement over the four-step procedure reported
earlier (22% overall yield for 7).16
Conversion of the bis(pincer)acetylene 7 in two steps
to the key intermediate 9 and subsequent introduction
of the different donor substituents Y via nucleophilic
substitution reactions resulted in the formation of the
different hexakis(pincer) ligands 10-13 (Scheme 3).
Meta la tion of Hexa k is(p in cer ) Liga n d s. Direct
electrophilic palladation of dodecasulfide 11 and dode-
caphosphine 12 with a small excess of [Pd(MeCN)4]-
(BF4)2 in acetonitrile,18 followed by addition of LiCl, gave
the hexakis(chloropalladium) complexes 14 and 15 in
90 and 89% yields, respectively (Scheme 4). The reaction
time needed for complete metalation of 11 (3 h),
however, was considerably shorter than the time needed
for 12 (110 h). Thus far, the hexapalladium(II) complex
1
15 has been analyzed by H, 13C, and 31P NMR spec-
troscopy only; no product found to be pure by elemental
analysis has yet been obtained. The analogous dodeca-
sulfide 14 has been characterized by X-ray crystal-
lography, and its molecular structure showed a cart-
wheel-like structure with C3 symmetry and diametrically
opposed Pd-Pd separations of 15.340(2) Å.2h
F igu r e 3.
Sch em e 1a
Treatment of dodecapyrazole 13 with Pd(OAc)2 in
acetic acid resulted in the formation of C6[(PdOAc)-4-
C6H2(CH2pz)2-3,5]6 (16), which was isolated in 53%
yield. Reaction of 16 with LiCl gave the corresponding
hexakis(chloropalladium) complex 17, which upon reac-
tion with AgBF4 in wet acetone afforded the hexakis-
(aquapalladium) complex C6[{Pd(OH2)}-4-C6H2(CH2-
Pz)2-3,5]6 (18) in 70% yield (Scheme 4).
Complete palladation of hexakis(pincer) ligand 10 was
not feasible via direct electrophilic palladation. There-
fore, the palladium centers were introduced via a
lithiation-transmetalation method using t-BuLi as the
lithiation agent and PdCl2(SEt2)2 as the palladium
source. Although complete lithiation occurred, as shown
by a deuteration reaction with D2O and subsequent
analysis by 1H and 13C NMR spectroscopy, complete
palladation via this route also could not be achieved.
a
Conditions: (i) Pd(OAc)2, acetic acid, reflux, 18 h, followed
by LiCl, acetone, room temperature, 2 h; (ii) AgBF4, acetone/
water, room temperature, 1 h.
ery by nanomembrane filtration. Recently, we reported
the first synthesis of a fully palladated hexakis(pincer)
complex (B, M ) Pd, Y ) SPh, L ) Cl; Figure 3) and its
molecular geometry in the solid state.2h In this study,
the preparation of palladated hexakis(pincer) complexes
having a variety of different coordinative ligands and
the synthesis of novel tripalladated pincer complexes
have been carried out.
Syn th esis of Hexa k is(p in cer ) Com p ou n d s. The
various hexakis(pincer) ligands C6[C6H3(CH2Y)2-3,5]6
(10-13) can be prepared using dodecabromide C6-
[C6H3(CH2Br)2-3,5]6 (9) as the key synthetic intermedi-
ate. The synthesis of 9 was first reported by Ducheˆne
and Vo¨gtle,16 but this route involved a number of time-
consuming and expensive column chromatography tech-
(11) For the synthesis of 3a see: Alsters, P. L.; Baesjou, P. J .;
J anssen, M. D.; Kooijman, H.; Sicherer-Roetman, A.; Spek, A. L.; van
Koten, G. Organometallics 1992, 11, 4124.
(12) For the synthesis of 1b and 3b see: Canty, A. J .; Honeyman,
R. T.; Skelton, B. W.; White, A. H. J . Organomet. Chem. 1990, 389,
277.
(13) For the synthesis of 1a from 3a see: Grove, D. M.; van Koten,
G.; Louwen, J . N.; Noltes, J . G.; Spek, A. L.; Ubbels, H. J . C. J . J . Am.
Chem. Soc. 1984, 104, 6609.
(14) Hartshorn, C. M.; Steel, P. J . Organometallics 1998, 17, 3487.
(15) (a) For the synthesis of 3d see: Rimml, H.; Venanzi, L. M. J .
Organomet. Chem. 1983, 259, C6. (b) For the synthesis of 3e see:
Lucena, N.; Casabo, J .; Escriche, L.; Sanchez-Castello, G.; Teixidor,
F.; Kiveka¨s, R.; Sillanpa¨a¨, R. Polyhedron 1996, 15, 3009.
(16) Ducheˆne, K.-H.; Vo¨gtle, F. Synthesis 1986, 659.
(17) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 4467.
(18) Procedure reported by: (a) Loeb, S. J .; Shimizu, G. K. H. J .
Chem. Soc., Chem. Commun. 1993, 1396. (b) Kickham, J . E.; Loeb, S.
J . Inorg. Chem. 1994, 33, 4351.

3162 Organometallics, Vol. 20, No. 14, 2001
Sch em e 2. Syn th esis of C6[C6H3(CH2Br )2-3,5]6 (9) fr om 3,5-Dim eth yla n ilin ea
Dijkstra et al.
a
Conditions: (i) 25% H2SO4(aq), NaNO2(aq), -10 °C, 30 min, followed by KI(aq), -10 f 90 °C, 2 h; (ii) N-bromosuccinimide,
AIBN, MeOAc, reflux, hν, 12 h; (iii) NaOMe, MeOH, reflux, 18 h; (iv) HCtCH, [PdCl2(PPh3)2], CuI, Et2NH, 18 h, room temperature;
(v) [PdCl2(PhCN)2], benzene, reflux, 6 h; (vi) AcBr, BF3‚OEt2, CH2Cl2, reflux, 24 h.
Sch em e 3a
Sch em e 4. P a lla d a tion Rou tes for Va r iou s
C6(C6H3(CH2Y)2-3,5)6 Liga n d sa
a
Conditions: (i) HNMe2, CH2Cl2, room temperature, 3 h;
(ii) PhSH, K2CO3, DMF, room temperature, 18 h; (iii)
HPPh2‚BH3, n-BuLi, THF, -30 °C f room temperature, 18 h,
followed by HBF4‚OEt2, Et2O, room temperature, 2 h; (iv)
pyrazole, K, THF, reflux, 1.5 h, followed by addition of 9, THF,
reflux, 15 h.
On average, four to five pincer groups were palladated
by this method.
a
Conditions: (i) [Pd(NCMe)4](BF4)2, MeCN, reflux, 5-110
h, followed by LiCl, acetone, room temperature, 1 h; (ii)
Pd(OAc)2, AcOH, reflux, 15 h; (iii) LiCl, acetone, room tem-
perature, 15 h; (iv) AgBF4, acetone, room temperature, 3 h.
Syn th esis of Tr is(p in cer ) Com p ou n d s. The syn-
thesis of the tris(pincer) ligand C6H3[Br-4-C6H3(CH2-
NMe2)2-3,5]3-1,3,5 (20) started from substituted ace-
tophenone 19 (Scheme 5), prepared according to a
previous literature procedure.19 A triple condensation
reaction of 19 with tetrachlorosilane in ethanol afforded
20 in 70% yield.20 Palladation of this tris(pincer) ligand
was achieved via an oxidative addition reaction with Pd-
(dba)2, resulting in the formation of palladated tris-
(pincer) complex 21 in 70% yield. The corresponding
triplatinum(II) compound 22 was obtained in 73% yield
by reaction of 20 with [Pt(tol)2SEt2]2, a method previ-
ously reported.21 The neutral complex 21 can easily be
(19) Van de Kuil, L. A.; Luitjes, H.; Grove, D. M.; Zwikker, J . W.;
van der Linden, J . G. M.; Roelofsen, A. M.; J enneskens, L. W.; Drenth,
W.; van Koten, G. Organometallics 1994, 13, 471.
(20) Modification of a reported method was used: Elmorsy, S. S.;
Pelter, A.; Smith, K. Tetrahedron Lett. 1991, 32, 4175.
(21) Canty, A. J .; Patel, J .; Skelton, B. W.; White, A. H. J .
Organomet. Chem. 2000, 599, 195.

Rigid Nanosize Cartwheel Pincer Compounds
Organometallics, Vol. 20, No. 14, 2001 3163
Sch em e 5a
F igu r e 4. Displacement ellipsoid plot (50% probability
level) of 21. Symmetry operations: (i) 1 - y, x - y, z; (ii) 1
1
1
4
2
- x + y, 1 - x, z; (iii) /3 + y, -1/3 + x, /6z; (iv) /3 - x, /3
1
1
2
1
- x + y, /6 - z; (v) /3 + x - y, /3 - y, /6 - z.
of D3. The “pincer” systems are therefore tilted in the
same direction with respect to the central benzene ring
(twist angle 47.31°). The size of the molecule is probably
best defined by the fixed bromine-bromine distance of
17.4573(4) Å. If we approximate the molecular shape
as a triangle, the height of the triangle would be 15.2
Å. The molecules are stacked on top of each other in
the direction of the crystallographic c axis with six
molecules in one unit cell. We can thus roughly ap-
proximate the thickness of the molecule in the crystal
with c/6 ) 5.9 Å.
a
Conditions: (i) SiCl4, EtOH, reflux, 18 h; (ii) Pd(dba)2,
benzene, room temperature, 18 h; (iii) [Pt(tol)2SEt2]2, benzene,
reflux, 3 h; (iv) AgBF4, wet acetone, room temperature, 2 h.
Although these hexakis- and tris(pincer) complexes
have fairly low molecular weights, especially in com-
parison with dendrimers, the rigid structures result in
their true nanoparticle dimensions. These properties
make them appropriate catalysts for retention by na-
nomembrane filters.
Sch em e 6
Ca t a lysis. Complexes 1a -e were tested as Lewis-
acid catalysts in the double Michael reaction between
ethyl R-cyanoacetate and methyl vinyl ketone (Scheme
6) as a model reaction, and the results are summarized
in Table 1.
converted to the corresponding triionic aqua complex
23 in 76% yield by treatment with silver tetrafluorobo-
rate in wet acetone (Scheme 5).
From Table 1 it is clear that pincer complexes based
on N,C,N′-type ligands (1a -c, 23, entries 1-3 and 6)
are the most active catalysts in this reaction. The P,C,P′
pincer complex 1e (entry 5) shows rather low activity,
while the reaction catalyzed by the S,C,S′ pincer com-
plex 1d (entry 4) is hardly faster than the blank reaction
(entry 7). It was also found that the catalytic activity of
1c was considerably higher than the activity of 1b
(entries 2 and 3, respectively). The only difference
between the two catalysts is that 1c contains two methyl
substituents in the pyrazolyl group (pz*), making 1c a
weaker Lewis acid than 1b. The effect of the methyl
group substitution can be seen by comparing the pKa
value of 1-Mepz (pKa ) 1.19) with that of 1,3,5-Me3pz
Brownish crystals of 21 suitable for a crystal structure
determination were obtained by slow diffusion of diethyl
ether into a concentrated solution of 21 in methylene
chloride. The molecular geometry of 21 shows a central
benzene ring substituted at the 1-, 3-, and 5-positions
with diorganoamine moieties each cyclopalladated at the
intraannular position between the CH2NMe2 groups
(Figure 4). This affords square-planar PdII centers with
a ligand environment comprised of tridentate N,C,N′
coordination by the organic moiety with a bromo ligand
trans to the metal-bonded aromatic carbon. Compound
21 crystallizes in the trigonal space group R3hc with the
molecule on a special position with crystallographic 32
symmetry. This leads to an exact molecular symmetry

3164 Organometallics, Vol. 20, No. 14, 2001
Dijkstra et al.
Ta ble 1. Ca ta lytic Activities of th e Va r iou s P in cer
Ca ta lysts in th e Dou ble Mich a el Rea ction betw een
Meth yl Vin yl Keton e a n d Eth yl r-Cya n oa ceta te
(pincer) complex 18 was also active in the double
Michael reaction, despite the fact that the catalyst did
not dissolve under the reaction conditions. These solu-
bility issues also explain the much lower activity of 18
relative to its monopincer analogue 1b. In contrast, the
catalytic activity of the soluble nanosize tricationic
catalyst 23 was found to be similar to that of its
monopincer analogue 1a .
As separation of the catalyst will be important in the
final catalytic process, we are currently investigating
to what extent nanosize pincer catalysts, such as 23,
are retained by nanomembranes. Preliminary results
have already shown that the platinum analogue 22
exhibits a retention of approximately 94% by the MPF-
60 membrane, which is quite efficient for such a small
molecule.23 For continuous processes, however, higher
retentions are needed. Thus, we are currently also
investigating the synthesis of larger nanosize pincer
complexes with rigid cores for use as homogeneous
catalysts in continuous nanomembrane reactor pro-
cesses.23
a
entry
catalyst
k (10-6 s-1
)
t1/2 (min)b
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
23
blank
279
134
348
4.18
9.48
232
3.78
41
86
33
2800
1200
50
3056
a
Determined by 1H NMR by comparison of the integration of
the CH2 protons of ethyl R-cyanoacetate to the combined integra-
tion of the ethyl ester CH2 protons of the reactant and product.
The reactions are first order in CN (CN ) ethyl R-cyanoacetate);
the rate constant k was determined by plotting -ln([CN/[CN]0)
b
versus time (in seconds). t1/2 ) ln 2/(60k).
(pKa ) 2.90).22 Thus, although 1c is a weaker Lewis acid
than 1b, it is the most active catalyst tested in this
series and also the most active catalyst of the pincer
type reported in the literature so far for this particular
reaction. Although the mechanism of this reaction is not
yet fully established, this probably means that not a
deprotonation step but rather the dissociation of the
product or an intermediate from the metal center
determines the rate of this reaction, as such a step is
expected to be faster for weaker Lewis acids.
Unfortunately, the hexakis(pincer) complex 18 is not
soluble under the reaction conditions used for the double
Michael reaction. Nevertheless, 18 did show catalytic
activity (70% after 22 h), despite the heterogeneous
nature of the reaction. Complex 23, on the other hand,
is soluble under the reaction conditions, and from Table
1 it is clear that the catalytic activity per palladium
center of tris(pincer) complex 23 is almost the same as
that of the corresponding monopincer analogue 1a (in
all reactions the total numbers of PdII centers were kept
equal). Although three catalytic sites are located in a
single catalyst particle, this has no significant influence
on the catalytic activity of the independent catalytic
sites. Thus, with the tris(pincer) systems we have a
system in hand which is soluble in common organic
solvents and is quite heat- and air-stable.
Exp er im en ta l Section
Solvents were purified and dried according to standard
procedures, stored under a nitrogen atmosphere, and freshly
distilled prior to use. NMR solvents were purchased and used
without further purification. The complexes 1b,12 3a ,11 3b,12
3d ,15a 3e,15b and [PdCl2(cod)]24 were prepared according to
literature procedures. All other reagents were purchased and
used without further purification. NMR spectra were recorded
with a Varian Unity Inova 400 WB spectrometer (1H NMR,
399.716 MHz; 13C NMR, 100.6 MHz), a Varian 300 spectrom-
eter (1H NMR, 300.1 MHz; 13C NMR, 75.5 MHz; 31P NMR,
121.5 MHz), or a Varian Gemini 200 spectrometer (1H NMR,
200.1 MHz; 13C NMR, 50.3 MHz; 31P NMR, 81.0 MHz).
Mikroanalyses were determined by either Dornis and Kolbe,
Microanalytisches Laboratorium, Mu¨lheim, Germany, or the
Central Science Laboratory, University of Tasmania.
Syn th esis of 1,3-Bis[(3,5-d im eth ylp yr a zol-1-yl)m eth yl]-
ben zen e (2c). To a stirred suspension of finely cut potassium
(1.12 g, 29.9 mmol) in THF (60 mL) under an argon atmos-
phere was added 3,5-dimethylpyrazole (2.88 g, 29.9 mmol). The
mixture was heated to reflux and maintained at this temper-
ature until beads of molten potassium were no longer evident
(∼3 h). The solution was cooled to ambient temperature, and
2,6-bis(bromomethyl)benzene (3.59 g, 13.6 mmol) was added
in one portion. The reaction mixture was allowed to stand at
reflux overnight, quenched by addition of water (0.1 mL), and
filtered and the solvent removed in vacuo. The product, 1,3-
(3,5-Me2pzCH2)2C6H4 (2c), was purified by distillation. Yield:
Con clu sion s
New routes have been developed for the synthesis of
rigid nanosize organometallic materials based on an
aromatic backbone. Hexametallic complexes 14-18 and
trimetallic complexes 21-23 have been prepared in good
yields and have been fully characterized (except for 15).
The molecular structure of 21 shows a propeller-like
structure with a molecular symmetry of D3 and a
bromine-bromine distance of 17.4573(4) Å.
The cationic N,C,N′ palladium(II) complexes are the
most active Lewis-acid catalysts of the pincer-type series
in the double Michael reaction between ethyl R-cyano-
acetate and methyl vinyl ketone reported thus far.
Comparison of the catalytic activities of 1b and 1c
demonstrates that the weaker Lewis acid (1c) gives a
higher activity in this particular reaction, which may
mean that dissociation of the product or an intermediate
from the metal center appears as a unique step in the
rate law of this reaction. Furthermore, the hexakis-
1
3.27 g (82%). Mp: 68-71 °C. H NMR (CDCl3, 300 MHz): δ
3
3
7.24 (t, J ) 7.7 Hz, 1H, Ar H), 6.94 (d, J ) 7.8 Hz, 2H, Ar
H), 6.76 (s, 1H, Ar H), 5.85 (s, 2H, H4-3,5-Me2pz), 5.18 (s,
4H, CH2), 2.25 (s, 6H, CH3), 2.12 (s, 6H, CH3). 13C NMR (CDCl3,
75 MHz): δ 147.5, 139.1, 137.9, 129.0, 125.5, 124.6, 105.5, 52.2,
13.4, 11.0. Anal. Calcd for C18H22N4: C, 73.44; H, 7.53; N,
19.03. Found: C, 73.25; H, 7.39; N, 19.10.
Syn th esis of 1-(Ch lor op a lla d iu m )-2,6-bis[(3,5-d im eth -
ylp yr a zol-1-yl)m eth yl]ben zen e (3c). A solution of Pd(OAc)2
(0.10 g, 0.45 mmol) and 2c (0.15 g, 0.49 mmol) in acetic acid
(23) Dijkstra, H. P.; Kruithof, K.; Ronde, N.; Vogt, D.; van Klink,
G. P. M.; van Koten, G. To be submitted for publication. SelRo
nanofiltration membranes (MPF-60) were purchased from Koch Mem-
brane Systems Inc., Du¨sseldorf, Germany; further product information
may be found at http://www.kochmembrane.com.
(24) Drew, D.; Doyle, J . R.; Shaver, A. G. Inorg. Synth. 1972, 13,
47.
(22) Canty, A. J .; Lee, C. V. Organometallics 1982, 1, 1063.

Rigid Nanosize Cartwheel Pincer Compounds
Organometallics, Vol. 20, No. 14, 2001 3165
(10 mL) was heated to 120 °C and maintained at this
temperature for 2 h. The solvent was removed by rotary
evaporation and the residue dissolved in CH2Cl2 (50 mL). The
resultant solution was washed with water (3 × 50 mL). The
solvent was removed by rotary evaporation and the product
dissolved in acetone (50 mL) along with LiCl (0.24 g). The
mixture was stirred overnight and then centrifuged and the
solution decanted to leave a tan solid. The product was washed
with water (20 mL), acetone (20 mL), and CH2Cl2 (5 mL) and
dried in vacuo. Yield: 0.18 g (90%). 1H NMR (CDCl3, 300
MHz): δ 6.39 (s, 3H, Ar H), 5.82 (s, 2, H4 3,5-Me2pz), 5.65 (d,
and were then dried with K2CO3. After filtration, the filtrate
was reduced in vacuo to leave a brown oily residue. This
residue was flame-distilled from solid KOH (10 g) to afford
C6H3I(Me)2-3,5 (4) as a light orange oil. Yield: 67.1 g (70%).
1H NMR (C6D6, 200 MHz): δ 7.18 (s, 2H, Ar H), 6.57 (s, 1H,
Ar H), 1.90 (s, 6H, CH3). 13C NMR (C6D6, 50 MHz): δ 140.0,
135.4, 129.6, 94.9, 21.0.
Syn th esis of 3,5-Bis(br om om eth yl)iod oben zen e (5).
C6H3IMe2-3,5 (4; 55.0 g, 237 mmol), N-bromosuccinimide (95.0
g, 534 mmol), and AIBN (azobis(isobutyronitrile); 2.63 g, 16
mmol) were mixed in methyl acetate (400 mL). This mixture
was photolytically heated to reflux by irradiation of the flask
with a 100 W IR bulb for 12 h (no additional heating source
was used). The reaction mixture was then cooled to room
temperature, followed by evaporation of the volatiles. This
resulted in the formation of a solid residue, which was washed
with cold hexanes (0 °C, 2 × 200 mL) and subsequently
extracted with boiling hexanes (4 × 400 mL). The combined
hexanes extract was heated to reflux to redissolve all solids,
and the solution was cooled to room temperature over a period
of 18 h. Crystals of pure 5 that had formed during this time
were collected by filtration, washed with cold hexanes (0 °C,
2 × 200 mL), and dried in vacuo. Yield: 43.5 g (47%). Mp:
110-113 °C (lit.16 mp 112-114 °C). 1H NMR (CDCl3, 200
MHz): δ 7.67 (s, 2H, Ar H), 7.38 (s, 1H, Ar H), 4.38 (s, 4H,
CH2). 13C NMR (CDCl3, 50 MHz): δ 140.3, 137.8, 129.0, 94.4,
31.4.
3
3J ) 14.1 Hz, 2H, CH2), 4.90 (d, J ) 13.8 Hz, 2H, CH2), 2.65
(s, 6H, CH3), 2.34 (s, 6H, CH3). 13C NMR (CDCl3, 75 MHz): δ
152.3, 145.8, 140.0, 137.0, 125.0, 124.2, 107.0, 54.3, 15.5, 11.7.
Anal. Calcd for C18H21ClN4Pd: C, 49.67; H, 4.86; N, 12.87.
Found: C, 49.78; H, 4.92; N, 12.80.
Syn th esis of 1-(Aqu a p a lla d iu m )-2,6-bis[(3,5-d im eth -
ylp yr a zol-1-yl)m eth yl]ben zen e Tetr a flu or obor a te (1c).
To a stirred suspension of 3c (110 mg, 0.24 mmol) in acetone
(10 mL) was added a solution of AgBF4 (47 mg, 0.24 mmol) in
water (1.0 mL). The solution was stirred in the absence of light
for 10 min and then filtered through Celite. The solvent was
removed in vacuo and the residue extracted with acetone (15
mL). The solution was filtered, and a tan solid precipitated
on addition of diethyl ether. Yield: 80 mg (66%). 1H NMR
(acetone-d6, 300 MHz): δ 7.20 (d, 3J ) 7.5 Hz, 2H, Ar H), 7.03
3
(t, J ) 7.5 Hz, 1H, Ar H), 6.08 (s, 2H, H4 3,5-Me2pz), 5.68 (d,
3
3J ) 14.4 Hz, 2H, CH2), 5.40 (d, J ) 14.7 Hz, 2H, CH2), 2.50
Syn th esis of 3,5-Bis(m eth oxym eth yl)iod oben zen e (6).
Synthesis as described by Ducheˆne and Vo¨gtle16 using 5 (75.9
g, 194 mmol) as the starting material. Yield: 54.0 g (95%). 1H
NMR (CDCl3, 200 MHz): δ 7.58 (s, 2H, Ar H), 7.22 (s, 1H, Ar
H), 4.35 (s, 4H, CH2), 3.35 (s, 6H, OMe); 13C NMR (CDCl3, 50
MHz): δ 140.7, 135.6, 125.8, 94.5, 73.6, 58.4.
(s, 6H, CH3), 2.25 (bs, 6H, CH3). 13C NMR (acetone-d6, 75
MHz): δ 150.5, 142.6, 136.8, 126.1, 125.1, 106.8, 53.7, 12.9,
10.7. Anal. Calcd for C18H23BF4N4OPd: C, 42.84; H, 4.54; N,
11.10. Found: C, 42.71; H, 4.65; N, 10.98.
Syn th esis of 1-(Aqu a pa lla d iu m )-2,6-bis[(d ip h en ylp h os-
p h in o)m eth yl]ben zen e Tetr a flu or obor a te (1d ). AgBF4
(0.21 g, 1.1 mmol) dissolved in wet acetone (1 mL) was added
to a solution of 3d (0.68 g, 1.1 mmol) in wet acetone (15 mL).
This mixture was stirred in the absence of light at room
temperature for 1 h. Subsequently, the reaction mixture was
filtered and the filtrate was reduced to a volume of 10 mL.
Et2O (10 mL) was added, resulting in the precipitation of a
white solid, which was collected, washed with Et2O (2 × 10
mL), and dried in vacuo. Yield: 0.69 g (92%). 1H NMR (acetone-
d6, 200 MHz): δ 7.93-7.83 (m, 8H, Ar H), 7.72-7.63 (m, 12H,
Syn th esis of Bis[3,5-bis(m eth oxym eth yl)p h en yl]a cet-
ylen e (7). Solid [PdCl2(PPh3)2] (2.60 g, 3.7 mmol) and CuI (0.35
g, 1.85 mmol) were added to a stirring solution of 3,5-bis-
(methoxymethyl)iodobenzene (6; 54.0 g, 185 mmol) in Et2NH
(500 mL) at room temperature in a 1 L round-bottomed
Schlenk tube. After stirring of the reagents, a slow stream of
acetylene was passed through the stirred solution for 16 h at
room temperature. The color of the reaction mixture gradually
turned to dark red and after 16 h a two-phase system had
formed. After in vacuo evaporation of the volatiles, the residue
was extracted with hexanes (2 × 200 mL) and the combined
organic extracts were stored at -25 °C for 24 h. The precipi-
tated white solid which formed during this time was filtered
off, washed with cold hexanes (-25 °C, 100 mL) and dried in
vacuo to afford 7 as a white solid. Yield: 29.5 g (90%). Mp:
37-39 °C (lit.16 38-41 °C). 1H NMR (CDCl3, 200 MHz): δ 7.42
(s, 4H, Ar H), 7.28 (s, 2H, Ar H), 4.44 (s, 8H, CH2), 3.39 (s,
12H, OMe). 13C NMR (CDCl3, 50 MHz): δ 136.6, 129.9, 126.7,
123.4, 89.3, 74.1, 58.3.
2
4
Ar H), 7.28-7.17 (3H, Ar H), 4.24 (pseudo t, J P,H and J P,H
)
4.8 Hz, 4H, CH2). 31P NMR (acetone-d6): δ 47.9.
Syn th esis of 1-(Aqu a p a lla d iu m )-2,6-bis[(p h en ylsu lfi-
d o)m eth yl]ben zen e Tetr a flu or obor a te (1e). AgBF4 (0.21
g, 1.1 mmol) in wet acetone (1 mL) was added to a solution of
3e (0.51 g, 1.1 mmol) in wet acetone (15 mL). This mixture
was stirred in the absence of light at room temperature for 1
h. Subsequently, the reaction mixture was filtered and the
filtrate was reduced to a volume of 10 mL. Et2O (10 mL) was
added, resulting in the precipitation of a light yellow solid,
which was collected, washed with Et2O (2 × 10 mL), and dried
in vacuo. Yield: 0.55 g (94%). 1H NMR (acetone-d6, 200
MHz): δ 7.90-7.96 (m, 4H, Ar H), 7.52-7.59 (m, 6H, Ar H),
7.10-7.13 (m, 3H, Ar H), 4.91 (bs, 4H, CH2).
Syn th esis of Hexa k is[3,5-bis(m eth oxym eth yl)p h en yl]-
ben zen e (8). Synthesis was as described by Ducheˆne and
Vo¨gtle16 using 7 (27.3 g, 77.0 mmol) and [PdCl2(NCPh)2] (12.1
g, 47.3 mmol) in benzene (150 mL). The workup was performed
as follows: after evaporation of the volatiles, the solid residue
was extracted with boiling hexanes (3 × 250 mL). The
combined hexane extract was cooled to room temperature over
a period of 20 h after which pure 8 had separated from the
solution as colorless crystals, which were collected by filtration,
washed with hexanes (2 × 100 mL) and dried in vacuo. Yield:
Syn th esis of 3,5-Dim eth yliod oben zen e (4). A solution
of NaNO2 (30.0 g, 435 mmol) in H2O (100 mL) was added
dropwise over
a period of 15 min to a solution of 3,5-
dimethylaniline (50.0 g, 413 mmol) in aqueous H2SO4 (650 mL,
4.5 M) at -10 °C. The resulting reaction mixture was stirred
at -10 °C for an additional 15 min, after which a solution of
KI (80 g, 482 mmol) in H2O (100 mL) was slowly added over
a period of 5 min, while the temperature was maintained at
-10 °C. The reaction mixture was warmed and stirred for 2 h
each at 0, 20, and 90 °C. The resulting dark brown reaction
mixture was cooled to room temperature and subsequently
extracted with Et2O (3 × 200 mL). The combined organic
extracts were washed successively with aqueous Na2SO3 (100
mL, 1 M), aqueous NaOH (100 mL, 4 M), and brine (100 mL)
1
16.4 g (60%). H NMR (CDCl3, 200 MHz): δ 6.70 (s, 12H, Ar
H), 6.61 (s, 6H, Ar H), 3.99 (s, 24H, CH2), 2.83 (s, 36H, OMe).
13C NMR (CDCl3, 50 MHz): δ 140.4, 139.6, 136.6, 130.0, 124.3,
73.8, 56.8.
Syn th esis of Hexa k is[3,5-bis(br om om eth yl)p h en yl]-
ben zen e (9). Synthesis was as described by Ducheˆne and
Vo¨gtle16 using 8 (16.4 g, 15.4 mmol), BF3‚Et2O (80 mL, 635
mmol), and acetyl bromide (55 mL, 740 mmol) in CH2Cl2 (1200
mL). The workup was performed as follows: the reaction

3166 Organometallics, Vol. 20, No. 14, 2001
Dijkstra et al.
mixture was cooled with an ice bath and aqueous Na2CO3
(25%, 400 mL) was slowly added. After complete addition the
mixture was stirred for 15 min at room temperature. The CH2-
Cl2 layer was then collected, dried with MgSO4, filtered, and
concentrated to ca. 300 mL. Hexane was slowly added to the
resulting solution, resulting in the separation of pure hexa-
substituted benzene 9 as white crystals. The crystals were
collected by filtration, washed with hexanes (2 × 100 mL), and
dried in vacuo. Yield: 23.5 g (93%). 1H NMR (CDCl3, 200
MHz): δ 6.90 (s, 6H, Ar H), 6.83 (s, 12H, Ar H), 4.17 (s, 24H,
CH2). 13C NMR (CDCl3, 50 MHz): δ 140.4, 139.4, 137.6, 131.9,
127.1, 32.9.
at -70 °C. The temperature was allowed to rise to room
temperature, and stirring was continued for 2 h. Next, this
solution was added to a solution of 9 (0.50 g, 0.30 mmol) in
THF (30 mL) at -40 °C. The temperature was allowed to rise
to room temperature, and the mixture was stirred for another
18 h. All volatiles were evaporated, CH2Cl2 (75 mL) was added,
and this mixture was washed with H2O (3 × 50 mL) and dried
over MgSO4. The CH2Cl2 was evaporated, and the white solid
was washed with hot EtOH (2 × 50 mL) and hexanes (3 × 50
mL) and dried in vacuo to give 12‚12BH3 as a white air-stable
1
powder. Yield: 0.87 g (94%). H NMR (toluene-d8, 300 MHz):
3
δ 8.17 (pseudo t, 3J H,H and J P,H ) 9 Hz, 24H, o-H Ar-P), 7.87
3
3
(pseudo t, J H,H and J P,H ) 9 Hz, 24H, o-H Ar-P), 7.42-7.15
Syn th esis of Hexa k is{3,5-bis[(d im eth yla m in o)m eth yl]-
p h en yl}ben zen e (10). Neat HNMe2 (10 mL, 150 mmol) was
added in one portion to a solution of 9 (1.65 g, 1.00 mmol) in
CH2Cl2 (100 mL) at 0 °C. The reaction mixture was warmed
to room temperature over a period of 1 h and was stirred for
an additional 3 h. Aqueous NaOH (40 mL, 4 M, 160 mmol)
was then added, the CH2Cl2 layer was collected, and the water
layer was extracted with Et2O (4 × 50 mL). The combined
organic fraction was washed with saturated aqueous NaCl (50
mL), dried with MgSO4 and filtered. Evaporation of the filtrate
in vacuo afforded crude 10 as a pale yellow solid, mp 51-54
°C. Pure 10 was obtained by recrystallization of the corre-
sponding HBF4 salt, [C6{C6H3(CH2N(H)Me2)2-3,5}6](BF4)12 (10′),
which was prepared by addition of aqueous HBF4 (35%, excess)
to a solution of crude 10 in H2O (20 mL). Addition of MeOH
(150 mL) followed by warming of the mixture to ca. 60 °C
afforded a clear solution, from which upon cooling to room
temperature analytically pure white crystals (mp 161-163 °C)
of the dodecakis(tetrafluoroborate) salt 10′ separated. The
crystals were filtered off, washed with MeOH (2 × 30 mL) and
dried in vacuo. Dissolution of crystalline 10′ in H2O afforded
a clear solution which was neutralized with aqueous NaOH
(2 M, excess), followed by extraction of the desired product 10
with CH2Cl2 (3 × 60 mL). The combined CH2Cl2 extracts were
dried with MgSO4, filtered, and evaporated in vacuo to afford
pure 10. Yield: 0.96 g (79%).
(m, 72H, Ar H), 6.55 (s, 12H, Ar H), 6.21 (s, 6H, Ar H), 4.07
and 3.39 (pseudo t, ABX, 2J H,H and J P,H ) 12.5 Hz, 24H, CH2),
2
1.61 (br s, 36H, BH3). 13C NMR (CDCl3, 75 MHz): δ 32.38 (d,
1J P,C ) 34.0 Hz), 128.4-140.5 (9 different Ar-C). 31P NMR
(CDCl3, 121 MHz): δ 17.78. Anal. Calcd for C198H198P12B12: C,
77.23; H, 6.48; P, 12.07; B, 4.21. Found: C, 77.17; H, 6.64; P,
11.95; B, 4.16.
Rem ova l of BH3 fr om 12‚12BH3. HBF4‚OEt2 (1.98 mL,
6.60 mmol) was added dropwise to a solution of 12‚12BH3 (0.31
g, 0.10 mmol) in CH2Cl2 (25 mL) at 0-5 °C. The temperature
was allowed to rise to room temperature, and stirring was
continued for 2 h. Next, a saturated NaHCO3(aq) solution (50
mL) was added dropwise at 0 °C, resulting in considerable gas
evolution. After complete addition the reaction mixture was
stirred for 1 h at room temperature. The organic layer was
collected, the water layer was washed with CH2Cl2 (2 × 25
mL), and the combined organic layer was dried (MgSO4). After
evaporation of all volatiles 12 was obtained as a white solid
in quantitative yield. This product was used without further
purification. 1H NMR (C6D6, 200 MHz): δ 7.29-6.94 (m, 72H),
6.13 (s, 6H), 3.21 (br s, 24H). 13C NMR (C6D6, 50 MHz): δ 139.6
1
2
(d, J P,C ) 11.3 Hz), 136.4, 133.2 (d, J P,C ) 12.1 Hz), 128 4,
128.3, 128.2, 127.9, 127.6, 36.3. 31P NMR (C6D6, 54 MHz): δ
-7.95 (s).
Syn t h esis of H exa k is{3,5-b is[(p yr a zol-1-yl)m et h yl]-
p h en yl}ben zen e (13). To a stirred suspension of finely cut
potassium (0.16 g, 4.18 mmol) in dry THF (40 mL) was added
pyrazole (0.30 g, 4.36 mmol). The mixture was heated to reflux
and maintained at this temperature until the beads of molten
potassium were no longer evident ((1 h). The resulting white
suspension was cooled to ambient temperature, and 9 (0.50 g,
0.30 mmol) was added in one portion. The reaction mixture
was heated at reflux for 15 h and then quenched by addition
of H2O (0.1 mL) and filtered; the solvent was removed in vacuo.
The product was dissolved in CH2Cl2 (20 mL), the mixture was
filtered, and the filtrate was reduced to ∼1 mL. The product
precipitated as a white solid on addition of Et2O and was
finally crystallized from CH2Cl2/Et2O, giving 13 as small white
1
10: H NMR (C6D6, 200 MHz) δ 6.97 (s, 6H, Ar H), 6.94 (s,
12H, Ar H), 3.10 (s, 24H, CH2), 1.98 (s, 72H, Me); 13C NMR
(C6D6, 50 MHz): δ 141.3, 140.5, 137.9, 131.5, 126.9, 64.5, 45.4.
10′: 1H NMR (D2O, 300 MHz) δ 7.37 (s, 12H, Ar H), 7.17 (s,
6H, Ar H), 4.05 (s, 24H, CH2), 2.46 (s, 72H, HNMe2); 13C NMR
(D2O, 75 MHz) δ 141.8, 138.7, 134.9, 130.9, 130.6, 59.1, 41.9.
Anal. Calcd for C78H126B12F48N12 (10′): C, 41.21; H, 5.59; N,
7.39. Found: C, 41.19; H, 5.55; N, 7.35.
Syn th esis of Hexa k is{3,5-bis[(p h en ylsu lfid o)m eth yl]-
p h en yl}ben zen e (11). Thiophenol (2.5 mL, 24.4 mmol) was
added in one portion to a solution of 9 (1.65 g, 1.00 mmol) in
degassed DMF (50 mL) under nitrogen at room temperature.
Solid K2CO3 (7.9 g, 50 mmol) was added and the resulting
mixture was stirred for 48 h at 50 °C. The volatiles were
evaporated in vacuo and the residue was extracted with CH2-
Cl2 (3 × 50 mL). The combined organic fraction was washed
with brine (50 mL), dried with MgSO4 and filtered. Evapora-
tion of the filtrate in vacuo afforded crude 11 as a pale yellow
waxy solid. The hexasubstituted benzene 11 was purified by
slow diffusion of pentane into a concentrated solution of crude
11 in CH2Cl2. This resulted in the formation of off-white
crystals, which were collected by filtration, washed with
1
crystals. Yield: 0.40 g (89%). H NMR (CDCl3, 300 MHz): δ
7.46 (d, 12H, 3J ) 1.80 Hz, pz-H3), 6.80 (d, 12H, 3J ) 2.10,
pz-H5), 6.65 (s, 6H, Ar H), 6.38 (s, 12H, Ar H), 6.15 (t, 12H,
pz-H4), 4.84 (s, 24H, CH2). 13C NMR (CDCl3, 75 MHz):
δ
140.46, 139.28, 135.97, 130.05, 128.95, 125.20, 105.78, 55.09.
Anal. Calcd for C90H78N24: C, 72.27; H, 5.26; N, 22.47. Found:
C, 72.35; H, 5.28; N, 22.36.
Syn t h esis of H exa k is{4-(ch lor op a lla d iu m )-3,5-b is-
[(p h en ylsu lfid o)m eth yl]p h en yl}ben zen e (14). A solution
of [Pd(NCMe)4](BF4)2 (1.41 g, 3.2 mmol) in degassed MeCN
(10 mL) was added over a period of 2 min to a solution of the
hexasubstituted benzene C6{C6H3(CH2SPh)2-3,5}6 (11; 1.0 g,
0.50 mmol) in degassed MeCN (40 mL). A red-brown solution
formed immediately and was heated at reflux for 5 h. The
resulting solution was evaporated to ∼15 mL, and Et2O (50
mL) was slowly added. This resulted in the precipitation of
[C6({Pd(NCMe)}C6H2(CH2SPh)2-3,5)6](BF4)6 as a pale yellow
solid, which was collected, washed with Et2O, and dried in
vacuo. Yield: 1.56 g. Subsequently, this solid was dissolved
in MeCN (80 mL), and LiCl (large excess) was added in one
1
pentane (50 mL), and dried in vacuo. Yield: 1.66 g (83%). H
NMR (CDCl3, 300 MHz): δ 7.22-7.10 (m, 60H, Ar H), 6.96 (s,
12H, Ar H), 6.64 (s, 6H, Ar H), 3.67 (s, 24H, CH2). 13C NMR
(CDCl3, 75 MHz): δ 146.1, 140.9, 139.8, 137.2, 136.0, 130.8,
128.8, 126.9, 125.9, 38.4. MALDI-TOF-MS: m/z 1999.78 ([M]+,
calcd 2000.97), 1891.49 ([M - SPh]+, calcd 1891.80), 1781.47
([M - 2 SPh]+, calcd 1782.63). Anal. Calcd for C126H102S12: C,
75.63; H, 5.14; S, 19.23. Found: C, 75.85; H, 5.29; S, 19.23.
Syn t h esis of H exa k is{3,5-b is[(d ip h en ylp h osp h in o)-
m eth yl]p h en yl}ben zen e (12). n-BuLi (3.62 mL, 5.79 mmol)
was added to HPPh2‚BH3 (1.08 g, 5.40 mmol) in THF (30 mL)

Rigid Nanosize Cartwheel Pincer Compounds
Organometallics, Vol. 20, No. 14, 2001 3167
portion. This resulted in a suspension which was stirred for
an additional 15 h. Subsequently, the solid material was
filtered off and washed with H2O (100 mL) and Et2O (2 × 100
mL), giving a yellow solid. This solid was dissolved in DMSO
(80 mL), and THF (140 mL) was added, resulting in a white
precipitate. This procedure was repeated three times, and the
solid was collected and dried in vacuo, affording 14 as a light
yellow solid. Yield: 1.28 g (90%). Yellow crystals suitable for
X-ray analysis were obtained by suspension of 14 in toluene
and addition of CH2Cl2 until all solids were dissolved, followed
by slow evaporation of the solvent in air.2h 1H NMR (DMSO-
d6, 200 MHz): δ 7.60-7.56 (m, 24H, Ar H), 7.44-7.31 (m, 36H,
Ar H), 6.33 (s, 12H, Ar H), 4.20 (br s, 24H, CH2). 13C NMR
(DMSO-d6, 50 MHz): δ 161.06, 148.22, 139.38, 136.80, 132.09,
130.60, 130.28, 130.20, 125.65, 49.76. MALDI-TOF-MS: m/z
NMR data were obtained and the product was derivatized as
the corresponding aqua complex 18.
Syn th esis of Hexa k is{4-(a qu a p a lla d iu m )-3,5-bis[(p yr a -
zol-1-yl)m eth yl]p h en yl}ben zen e Hexa k is(tetr a flu or obo-
r a te) (18). A solution of AgBF4 (82 mg, 0.42 mmol) in H2O
(0.5 mL) was added to a stirred suspension of 17 (0.16 g, 70
mmol) in acetone (50 mL). The solution was stirred in the
absence of light for 1 h. The solvent was removed in vacuo,
the residue was extracted with acetone (50 mL), and the
product 18 was precipitated as a white-tan powder on addition
1
of Et2O. Yield: 0.17 g (89%). H NMR (acetone-d6, 300 MHz):
3
δ 8.10 (d, J H,H ) 2.10 Hz, 12H, pz H), 7.53 (s, 12H, pz H),
6.81 (s, 12H, Ar H), 6.49 (t, 12H, pz H), 5.18 (s, 24H, CH2). 13
C
NMR (acetone-d6, 75 MHz): δ 141.34, 137.59, 132.94, 129.19,
107.01, 56.52. Anal. Calcd for C90H84B6F24N24O6Pd6: C, 39.21;
H, 3.07; N, 12.19. Found: C, 39.06; H, 3.17; N, 12.11.
2811.52 ([M - Cl]+, calcd. 2810.71). Anal. Calcd for C126H96
-
Cl6Pd6S12: C, 53.26; H, 3.48; S, 13.37. Found: C, 53.17; H,
3.40; S, 13.52.
Syn th esis of 1,3,5-Tr is{4-br om o-3,5-bis[(d im eth yla m i-
n o)m eth yl]p h en yl}ben zen e (20). A modification of a litera-
ture procedure was used.20 To a stirred solution of 4-bromo-
3,5-bis[(dimethylamino)methyl]acetophenone (1.3 g, 8.7 mmol)
in dry ethanol (20 mL) was added tetrachlorosilane (5.0 mL,
43.6 mmol) at 0 °C. The reaction mixture was heated to reflux
and kept at that temperature for 16 h. The reaction mixture
(a white suspension) was cooled to room temperature, and
aqueous HCl (25 mL, 4 M) was added, resulting in a brown
solution. This layer was washed with CH2Cl2 (2 × 50 mL), and
an NaOH solution (4 M) was added until a pH of 13-14 was
reached. Next, the aqueous layer was extracted with CH2Cl2
(3 × 50 mL) and the combined organic fractions were dried
over Mg2SO4. All volatiles were evaporated in vacuo, affording
a white sponge. The product was purified by recrystallization
Syn th esis of Hexa k is{4-(ch lor op a lla d iu m )-3,5-bis[(d i-
p h en ylp h osp h in o)m et h yl]p h en yl}b en zen e (15). [Pd(N-
CMe)4](BF4)2 (0.16 g, 0.38 mmol) dissolved in degassed MeCN
(5 mL) was added to a suspension of 12 (0.18 g, 63 mmol) in
degassed MeCN (15 mL), immediately resulting in a yellow
solution. This mixture was heated at reflux for 110 h and then
cooled to room temperature. The mixture was filtered over
Celite and washed with MeCN (20 mL), and the filtrate was
concentrated to ∼5 mL. Subsequently, Et2O (10 mL) was
added, resulting in a yellow precipitate, which was collected,
washed with Et2O (2 × 15 mL), and dried in vacuo. Yield: 0.25
g. The yellow solid was dissolved in acetone (15 mL), and LiCl
(54 mg, 1.26 mmol) dissolved in H2O (1 mL) was added. This
mixture was stirred for 1 h at room temperature, resulting in
the precipitation of a yellow solid. This solid was collected,
washed with H2O (2 × 15 mL), acetone (3 × 20 mL), and Et2O
(3 × 20 mL), and dried in vacuo, affording a brownish solid.
Yield: 0.21 g (89%). 1H NMR (CDCl3, 200 MHz): δ 7.90-6.97
(br m, 120H, Ar H), 6.45 (br s, 12H, Ar H), 3.16 (br s, 24H,
CH2). 13C NMR (CDCl3, 75 MHz): δ 128.5-146.1 (9 different
Ar C), 41.7. 31P NMR (CDCl3, 81 MHz): δ 34.29.
Syn t h esis of H exa k is{4-(a cet a t op a lla d iu m )-3,5-b is-
[(p yr a zol-1-yl)m eth yl]p h en yl}ben zen e (16). A solution of
Pd(OAc)2 (0.34 g, 1.53 mmol) and 13 (0.36 g, 0.24 mmol) in
AcOH (20 mL) was heated to 120 °C and maintained at this
temperature for 3 h. The resulting brown solution was cooled
to ambient temperature. Dropwise addition of Et2O eventually
produced a precipitate. The mixture was centrifuged and the
solution decanted. Et2O was added a second time until a
precipitate formed, and the mixture was again centrifuged and
decanted. Et2O (100 mL) was added to the resultant pale
brown solution, and the product precipitated as a tan solid.
The solution was decanted and the product immediately
washed with Et2O (2 × 50 mL) and then dried in vacuo,
affording 16 as an off-white solid. Yield: 0.32 g (53%). 1H NMR
(CDCl3, 300 MHz): δ 7.86 (br s, 12H, pz H), 7.15 (br s, 12H,
pz H), 6.49 (br s, 12H, pz H), 6.12 (s, 12H, Ar H), 4.54 (br s,
24H, CH2), 2.02 (s, 18H, CH3CO). 13C NMR (CDCl3, 75 MHz):
δ 142.28, 135.10, 130.92, 129.14, 107.30, 57.81. Anal. Calcd
for C102H90N24O12Pd6: C, 49.35; H, 3.65; N, 13.54. Found: C,
49.09; H, 3.75; N, 13.38.
1
from hexane at -30 °C. Yield: 0.79 g (70%). H NMR (CDCl3,
200 MHz): δ 7.78 (s, 3H, Ar H), 7.67 (s, 6H, Ar H), 3.66 (s,
12H, CH2), 2.35 (s, 26H, CH3). 13C NMR (CDCl3, 75 MHz): δ
141.9, 140.0, 139.5, 128.7, 126.8, 125.9, 64.4, 46.0. MALDI-
TOF-MS: m/z 884.7 ([M + H]+, calcd 883.2). Anal. Calcd for
C
42H57Br3N6: C, 56.96; H, 6.49; N, 9.49. Found: C, 56.82; H,
6.56; N, 9.44.
Syn t h esis of 1,3,5-Tr is{4-(b r om op a lla d iu m )-3,5-b is-
[(d im eth yla m in o)m eth yl]p h en yl}ben zen e (21). Ligand 20
(0.65 g, 0.73 mmol) and Pd(dba)2 (1.39 g, 2.40 mmol) were
dissolved in benzene (100 mL) and stirred at room temperature
for 20 h. All volatiles were evaporated in vacuo, THF (100 mL)
was added, and stirring was continued for 1 h, affording a
black precipitate. The mixture was filtered through Celite, and
the filtrate was evaporated to dryness. The remaining solid
was dissolved in CH2Cl2 (10 mL), and Et2O (50 mL) was added,
yielding a yellow solid. This procedure was repeated three
times, resulting in a light yellow solid. Yield: 0.63 g (72%).
Analytically pure brownish crystals were obtained by slow
diffusion of Et2O into a concentrated solution of the product
1
in CH2Cl2. H NMR (CDCl3, 200 MHz): δ 7.53 (s, 3H, Ar H),
7.06 (s, 6H, Ar H), 4.06 (s, 12H, CH2), 3.01, (s, 36H, CH3). 13C
NMR (CDCl3, 75 MHz): δ 157.4, 145.8, 142.9, 138.4, 124.6,
119.1, 74.8, 54.1. MALDI-TOF-MS: m/z 1128.6 ([M - Br]+,
calcd 1128.0). Anal. Calcd for C42H57Br3N6Pd3: C, 41.87; H,
4.77; N, 6.97. Found: C, 42.03; H, 4.72; N, 6.88.
Syn t h esis of 1,3,5-Tr is{4-b r om op la t in u m -3,5-b is[(d i-
m eth yla m in o)-m eth yl]p h en yl}ben zen e (22): Ligand 20
(0.60 g, 0.69 mmol) and [Pt(tol)2SEt2]2 were mixed in benzene
(50 mL), and this mixture was refluxed for 3 h, resulting in a
yellow precipitate. The reaction mixture was cooled to room
temperature, and all volatiles were evaporated. Next, the
yellow solid was extracted with CH2Cl2 (20 mL) and Et2O was
added, yielding a yellow precipitate. This yellow solid was
collected, washed with Et2O (3 × 20 mL) and dried in vacuo.
Syn th esis of Hexakis{4-(ch lor opalladiu m )-3,5-bis[(pyr a-
zol-1-yl)m eth yl]p h en yl}ben zen e (17). A solution of 16 (0.10
g, 40 mmol) was prepared by dissolution of the complex in
acetone (30 mL) and addition of H2O (3 mL). LiCl (17 mg, 0.4
mmol) was added to this solution, and the mixture was stirred
at ambient temperature for 15 h. After this time a brown
precipitate had formed, the mixture was centrifuged, and the
solution was decanted. The solid residue was washed with H2O
(50 mL), acetone (50 mL), and Et2O (50 mL) and then dried in
vacuo, giving 17 as a brown solid. Yield: 70 mg (74%). Because
the product was insoluble in common organic solvents, no
Yield: 0.74 g (73%). 1H NMR (CDCl3, 200 MHz): δ 7.59 (s,
3
3H, Ar H), 7.11 (s, 6H, Ar H), 4.09 (s, J Pt, ) 22.0 Hz, 12H,
H
CH2), 3.16 (s, J Pt,H ) 18.0 Hz, 36H, CH3). 13C NMR (CDCl3,
3
50 MHz): δ 146.32, 144.13, 143.56, 137.24, 123.91, 118.79,

3168 Organometallics, Vol. 20, No. 14, 2001
Dijkstra et al.
77.72, 55.93. Anal. Calcd for C42H57Br3N6Pt3: C, 34.29; H, 3.91;
N, 5.71. Found: C, 34.38; H, 3.82; N, 5.66.
factors 0.34-0.39). The structure was solved with Patterson
methods (DIRDIF97)27 and refined with SHELXL9728 against
F2 values of all reflections. Non-hydrogen atoms were refined
freely with anisotropic displacement parameters. Hydrogen
atoms were refined as rigid groups. The crystal structure
contains large isolated voids at the crystallographic origin and
its five symmetry-related positions (193 Å3/void, 1162 Å3/unit
cell) filled with disordered dichloromethane and diethyl ether
molecules. Their contribution to the structure factors was
secured by back-Fourier transformation (program PLATON,26
CALC SQUEEZE, 473 e/unit cell). There were 85 refined
parameters, with no restraints. R values (I > 2σ(I)): R1 )
0.0281, wR2 ) 0.0670. R values (all reflections): R1 ) 0.0288,
wR2 ) 0.0674. GOF ) 1.125. The rest electron density was
between -0.47 and 0.71 e/Å3. Molecular illustration, structure
checking, and calculations were performed with the PLATON
package.26
Syn th esis of 1,3,5-Tr is{4-(a qu a p a lla d iu m )-3,5-bis[(d i-
m eth yla m in o)m eth yl]p h en yl}ben zen e Tr is(tetr a flu or o-
bor a te) (23). To a solution of 21 in wet acetone (20 mL) was
added AgBF4 (0.20 g, 1.0 mmol) in water (1 mL). This mixture
was stirred for 30 min at room temperature and then filtered
over Celite. The filtrate was concentrated, and the product was
extracted into acetone (20 mL). Upon slow addition of Et2O
(20 mL) a white precipitate was formed, which was collected
and was dried in vacuo. Yield: 0.26 g (76%). 1H NMR (acetone-
d6, 200 MHz): δ 7.72 (s, 3H, Ar H), 7.32 (s, 6H, Ar H), 4.23 (s,
12H, CH2), 2.89 (s, 36H, CH3). 13C NMR (acetone-d6, 75
MHz): δ 150.94, 146.28, 142.89, 138.79, 124.26, 119.46, 73.62,
51.78. Anal. Calcd for C42H63B3F12N6O3Pd3: C, 39.42; H, 4.96;
N, 6.57. Found: C, 39.64; H, 5.20; N, 6.42.
Typ ica l Ca ta lytic Exp er im en t. Ethyl R-cyanoacetate
(0.17 mL, 1.6 mmol), methyl vinyl ketone (0.40 mL, 4.8 mmol),
diisopropylethylamine (28 µL, 0.16 mmol), and 1a (3.2 mg, 8
µmol, 0.5 mol %) were dissolved in CH2Cl2 (5 mL), and the
mixture was stirred at room temperature. The reaction
mixture was sampled (100 µL) at regular intervals, and the
samples were worked up by evaporating all solvent and methyl
vinyl ketone with a gentle stream of nitrogen. The conversion
in the worked up samples was determined by 1H NMR
spectroscopy. Conversions obtained were confirmed by GC-MS
analysis of the reaction mixture. All reactions which were
complete within 22 h were repeated and isolated yields
obtained by bulb-to-bulb distillation. For all reactions yields
were found to be between 85 and 100%.
Ack n ow led gm en t. This work was supported in part
(H.P.D., M.D.M., M.L., A.L.S.) by the Council for
Chemical Sciences of The Netherlands Organization for
Scientific Research (CW-NWO) and in part (J .P., A.J .C.)
by the Australian Research Council. Dr. B. S. Williams
(Utrecht University) is kindly acknowledged for stimu-
lating discussions and critical comments.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data and structure refinement details, positional and
thermal parameters, and bond distances and angles for 21.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Cr ysta l Str u ctu r e Deter m in a tion of 21. Crystal data are
as follows: C42H57Br3N6Pd3 + solvent, fw ) 1204.87,25 yellow
block, 0.30 × 0.30 × 0.24 mm3, trigonal, R3hc (No. 167), a ) b
) 15.6134(2) Å, c ) 35.2061(5) Å, V ) 7432.64(17) Å3, Z ) 6,
F ) 1.615 g/cm3. A total of 32 401 reflections were measured
on a Nonius Kappa CCD diffractometer with a rotating anode
(λ ) 0.710 73 Å) at a temperature of 150(2) K. Of these, 1874
reflections were unique (Rint ) 0.062).25 The absorption cor-
rection was based on multiple measured reflections (program
OM0101689
(26) Spek, A. L. PLATON: A Multipurpose Crystallographic Tool;
Utrecht University, The Netherlands, 2000.
(27) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF97 Program System, Technical Report of the Crystallography
Laboratory; University of Nijmegen, Nijmegen, The Netherlands, 1997.
(28) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
PLATON,26 routine MULABS, µ ) 3.53 mm-1 25 transmission
,
(25) Derived values do not contain the contribution of the disordered
solvent.