Multicomponent Porphyrin Assemblies as Functional Bidentate Phosphite Ligands for Regioselective Rhodium-Catalyzed Hydroformylation

Article abstract of DOI:10.1002/anie.200352525

Selectivity from a rigid sandwich-type complex: A supramolecular approach was used to prepare chelating ligands that give high selectivity for the linear aldehyde in the rhodium-catalyzed hydroformylation of 1-octene. The multicomponent assembly consists of two tris(zinc(II) porphyrin)-phosphite ligands (blue) and three ditopic templates (red) with the rhodium complex (green) in the middle of the structure.

Full text of DOI:10.1002/anie.200352525

Angewandte
Chemie
Supramolecular Catalysts
Multicomponent Porphyrin Assemblies as
Functional Bidentate Phosphite Ligands for
Regioselective Rhodium-Catalyzed
Hydroformylation**
Vincent F. Slagt, Piet W. N. M. van Leeuwen, and
Joost N. H. Reek*
Noncovalent synthesis of well-defined molecular structures of
nanometer dimensions has proven to be an attractive alter-
[
1]
native to covalent synthesis. Several examples of large and
[
2]
complex multicomponent assemblies have been reported,
and the number of medium-sized structures based on hydro-
[
1,3]
gen bonds as well as metal–ligand interactions is enormous.
The current challenge in this field comprises the translation of
these esthetically appealing structures into functional materi-
[
4]
als. Catalysis has been one of the longstanding proposed
[
5]
applications of supramolecular chemistry, and one of the
[
6]
more recent strategies involves the encapsulation of sub-
strates within self-assembled host molecules to invoke new
[*] Dr. J. N. H. Reek, V. F. Slagt, P. W. N. M. van Leeuwen
Institute of Molecular Chemistry
University of Amsterdam
Nieuwe Achtergracht 166, 1018 WV Amsterdam (The Netherlands)
Fax: (+31)-20-525-6422
E-mail: reek@science.uva.nl
[**] The NRSCC is kindly acknowledged for financial support.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2003, 42, 5619 –5623
DOI: 10.1002/anie.200352525
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5619

Communications
[
7]
reaction pathways. So far, however, only a few examples
exist that describe the modification of transition-metal
fitted with the equation for a complex with a 3:1 stoichiom-
etry assuming identical binding sites, with an average binding
[
8]
7
À1
catalysts by supramolecular encapsulation. Here we report
on a multicomponent porphyrin-based assembly that serves
as a bidentate ligand in a sandwich-type rhodium complex.
The bidentate ligand system held together by three bridging
ditopically coordinated template molecules shows a high
selectivity for the linear aldehyde in the rhodium-catalyzed
hydroformylation of 1-octene.
The tris(zinc(ii) porphyrin)phosphite ligand 1 was pre-
pared by the reaction of phosphorus trichloride with three
equivalents of 5-(3-hydroxyphenyl)-10,15,20-tris(phenyl)-
zinc(ii) porphyrin (see the Supporting Information). The
monomeric phosphite ligand 1 contains three zinc(ii) por-
phyrin moieties that can be used as anchoring points for the
formation of multicomponent assemblies. The phosphorus
donor atom of 1 does not coordinate to the zinc(ii) porphy-
constant calculated of 1.9 ” 10 m , which is typical for ditopic
[
9]
complexation. Interestingly, the ditopic binding is stronger
in the complex [Rh(acac)(1) ] than in the free ligand 1,
2
showing that the ditopic binding between two ligands of the
complex is preferred over ditopic binding within the ligand of
the complex.
To investigate the coordination properties of these new
multicomponent ligand assemblies, their rhodium carbonyl
hydride complexes were studied with high-pressure NMR
spectroscopy at various a/1 ratios (Figure 1). The NMR
experiments in [D ]-toluene under 20 bars of H /CO show
8
2
[
8a]
rins
and is therefore accessible for selective transition-
metal coordination to form the catalytically active complex.
We used 1,4-diazabicyclo[2.2.2]octane (dabco, a) as a ditopic
template ligand, since it has been shown previously to form
[
9]
strong, well-defined 1:2 complexes with zinc(ii) porphyrins,
and we applied quinuclidine (b) as a monotopic reference
template.
UV/Vis spectroscopic titrations in toluene were per-
formed to study the binding of ditopic template a to ligand
1
(Scheme 1). The titration curve representing the binding of
a to 1 shows two distinct inflection points, indicating that
there are two different binding sites (see the Supporting
Information). These binding modes likely consist of a ditopi-
cally bound species I corresponding to the inflection point at
[
10]
a/1 = 1, and monotopically bound dabco II,
as was also
[
9a]
found for other flexible trimeric porphyrin systems. The
binding constants obtained from curve fitting (K = 1.1 ”
0 m and K = 5.5 ” 10 m ) are in line with the expected
[
11]
I
7
À1
5
À1
1
II
values for these two different binding modes. As expected, the
[
12]
curve for the titration of complex [Rh(acac)(1)2] with a
shows one inflection point only, indicating that all dabco
molecules are bound in a similar ditopic fashion (see the
Supporting Information). The stoichiometry of the supra-
1
Figure 1. H NMR spectra (hydride region) of rhodium catalyst assem-
blies of tris(zinc(ii) porphyrin)phosphite 1 and various amounts of
dabco a under high pressure.
molecular complex formed (a/[Rh(acac)(1) ] = 3/1) is in line
2
with the proposed structure 2. The titration curve could be
Scheme 1. Representation of the formation of a multicomponent assembly from ligand 1, template a (=dabco), and a transition-metal catalyst M.
P=monodentate phosphorus ligand.
5
620
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 5619 –5623

Angewandte
Chemie
that monomeric tris(zinc(ii) porphyrin)phosphite 1 in the
hydroformylation. In addition, the selectivity decreased
(TOF = 3.4 ” 10 and l/b = 1.9) and the amount of 2-octene
formed increased. Likely, the more bulky ligand assembly
3
presence of a rhodium precursor forms the hydridorhodium-
3
1
1
(
biscarbonyl)diphosphite complex; P{ H} NMR spectro-
scopy shows the formation a doublet (d = 148.0 ppm, JRh-P
=
1(b)3 leads to monophosphite rhodium complexes, which
explains the increase in activity and decreases in selectivity.
[
15]
2
32 Hz), and a rhodium hydride signal A (d = À9.3 ppm,
1
[13]
J
= 9 Hz) appears as a triplet in the H NMR spectrum.
Interestingly, the rhodium catalyst based on assembly 2,
[Rh(CO) H(1 a )], shows a high selectivity (l/b = 15.1) and a
H-P
The gradual addition of dabco a (a/1 = 0–0.75) to this
2
2 3
complex resulted in a decrease of intensity of A and the
formation of a new rhodium complex with hydride signal B
lower activity, which is characteristic for bidentate chelating
[
14]
ligand systems. This shows that the multicomponent ligand
assembly based on noncovalent interactions acts as a chelat-
(
d = À9.4 ppm). This shows that under these conditions two
catalyst systems are in slow exchange on the NMR timescale
300 MHz, 298 K), which suggests the ditopic complexation of
dabco. This is substantiated by the chemical shift of the bound
[
16]
ing bisphosphite! Surprisingly, lowering the temperature to
(
308C resulted in an even more selective catalyst, and the l/b
[
17]
ratio increased to 22.8,
suggesting that the assembled
[
9]
dabco at À4.9 ppm. The addition of more dabco (a/1 = 1–
supramolecular catalyst system 2 is more stable at lower
temperatures; this is explained by the stronger binding of the
nitrogen donor atoms of the template to the zinc(ii) porphyrin
1
.5) resulted in the rise of a new distinct rhodium hydride
signal C (d = À9.54 ppm) that is in slow exchange with B. At
the a/1 ratio of 1.5, C is the only hydride signal present and is
therefore likely that of the proposed structure 2. In this highly
symmetrical complex the phosphites are fixed in space by the
complexation of three ditopic templates. Increasing the
concentration to an excess of dabco resulted in a gradual
small upfield shift of hydride signal C, finally giving hydride
signal D (d = À9.6 ppm, a/1 = 3). This shows that complex 2 is
in fast exchange on the NMR timescale with another
assembly in which some of the dabco templates are mono-
topically bound to the zinc(ii) porphyrin, indicating that
assembly 2 is not stable in the presence of excess dabco.
The rhodium catalysts based on the assemblies consisting
of phosphite 1 and either ditopic dabco a or monotopic
quinuclidine b were studied in the rhodium-catalyzed hydro-
[
18]
moieties.
To obtain more information on the performance of the
various catalyst assemblies we studied the rhodium-catalyzed
hydroformylation of 1-octene at 408C using various a/1 ratios;
the results are displayed in Figure 2. The catalyst shows a
gradual decrease in activity at increasing a/1 ratios (Fig-
ure 2a). Bidentate chelating phosphorus ligands typically
show lower activity in the rhodium-catalyzed hydroformyla-
tion, and the decrease thus confirms the assembly of a
bidentate chelating ligand system in situ. Interestingly, the
[
14]
formylation of 1-octene (Scheme 2, Table 1). The mono-
meric tris(zinc(ii) porphyrin)phosphite 1 yields a rhodium
catalyst with an activity and regioselectivity that is typical of
rhodium bisphosphite complexes (turnover frequency
3
(
TOF) = 2.0 ” 10 and ratio of linear to branched aldehyde
[
14]
products (l/b) = 2.5). In the presence of three equivalents of
monotopic ligand b, 1 is transformed into the bulkier system
1
(b) , which is even more active in the rhodium-catalyzed
3
Scheme 2. Rhodium-catalyzed hydroformylation of alkenes.
Table 1: Hydroformylation of 1-octene with rhodium catalysts based on
tris(zinc(ii) porphyrin)phosphite assemblies with various template
[
a]
ligands.
[
b]
[b]
[c]
[d]
[e]
Ligand
Template
T [8C]
TOF
l/b
2-Octene [%]
3
3
3
1
1
1
1
–
b
a
a
80
80
80
30
2.0”10
3.4”10
1.1”10
25
2.5
1.9
15.1
22.8
10.6
16.1
11.9
10.3
À1
[
a] [Rh(acac)(CO) ]=0.084 mmolL in toluene, pressure=20 bar (CO/
2
À1
H =1/1), 1-octene/rhodium=5160. [b] [1]=2.1 mmolL
,
[b]=
2
À1
À1
6
.3 mmolL
quency=(molaldehyde)(molRh)
h (808C) or 17 h (308C). [d] l/b=ratio of linear to branched oxidation
,
[a]=3.1 mmolL
.
[c] TOF=average turnover fre-
Figure 2. The activity (a, TOF) and selectivity (b, l/b ratio) of the rho-
dium complexes based on the assemblies formed from tris(zinc(ii)
porphyrin)phosphite 1 and various amounts of dabco a in the rho-
dium-catalyzed hydroformylation of 1-octene.
À1 À1
h
. The reaction was stopped after
1
product. [e] Amount of isomerization based on converted 1-octene.
Angew. Chem. Int. Ed. 2003, 42, 5619 –5623
www.angewandte.org
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5621

Communications
activity remains the same upon the addition of more than
.8 equiv of a to 1 (even up to 4.5 equiv), indicating that in this
region the catalysis is dominated by self-assembled chelating
ligands. The decrease in activity observed in the presence of
small amounts of a confirms that dabco is ditopically bound
between two porphyrins of different ligands.
The selectivity of the reaction is very sensitive to the a/1
ratio, and only around a/1 = 1.5 does the catalyst assembly
give high selectivity for the linear aldehyde (Figure 2b).
Apparently, the sandwich-type complex must have three
bridging dabco molecules to be highly selective. The selec-
tivity is likely associated with the rigidity of the assembly
formed. If there is a shortage of dabco, the sandwich assembly
has only one or two bridging dabco units, and in the presence
of excess dabco the binding of a fourth dabco will compete
with the third ditopically bound dabco molecule. In both
situations this leads to less rigid chelate assemblies and lower
selectivities.
c) J. L. Atwood, L. J. Barbour, M. J. Hardie, C. L. Raston,
Coord. Chem. Rev. 2001, 222, 3; d) G. F. Swiegers, T. J. Malefe-
tse, Chem. Rev. 2000, 100, 3483; e) M. Albrecht, Chem. Rev.
0
2001, 101, 3457; f) S. Leininger, B. Olenyuk, P. J. Stang, Chem.
Rev. 2000, 100, 853; g) B. J. Holliday, C. A. Mirkin, Angew.
Chem. 2001, 113, 2076; Angew. Chem. Int. Ed. 2001, 40, 2022.
4] a) D. N. Reinhoudt, M. Crego-Calama, Science, 2002, 295, 2403;
b) O. Ikkala, G. ten Brinke, Science, 2002, 295, 2407; c) G. R.
Desiraju, Nature, 2001, 412, 397; c) R. F. Service, Science 2001
293, 782.
[5] For reviews see: a) J. K. M. Sanders, Chem. Eur. J. 1998, 4, 1378;
b) P. D. Beer, P. A. Gale, Angew. Chem. 2001, 113, 502; Angew.
Chem. Int. Ed. 2001, 40, 486; c) M. C. Feiters, in Compr.
Supramol. Chem., Vol. 10, Elsevier, Oxford 1996, 267; d) R.
Breslow, S. D. Dong, Chem. Rev. 1998, 98, 1997; e) K. Takahashi,
Chem. Rev. 1998, 98, 2013; f) W. B. Motherwell, M. J. Bingham,
Y. Six, Tetrahedron, 2001, 57, 4663; g) M. T. Reetz, Top Catal.
1997, 4, 187; h) Y. Murakami, J.-I Kikuchi, Y. Hisaeda, O.
Hayashida, Chem. Rev. 1996, 96, 721.
[
[6] a) R. Wyler, J. de Mendoza, J. Rebek Jr., Angew. Chem. 1993,
105, 1820; Angew. Chem. Int. Ed. Engl. 1993, 32, 1699; b) M.
In conclusion, a new supramolecular approach is pre-
sented for the preparation of self-organized transition-metal
catalyst systems. The multicomponent assembly of two
Morgan, J. Rebek Jr., Chem. Rev. 1997, 97, 1647 – 1668; c) J.
Rebek Jr., Chem. Soc. Rev. 1996, 25, 255 – 264; d) J. Rebek Jr.,
Chem. Commun. 2000, 637 – 643; e) F. Hof, S. L. Craig, C.
Nuckolls, J. Rebek Jr. , Angew. Chem. 2002, 114, 1556; Angew.
Chem. Int. Ed. 2002, 41, 1488; f) A. Jasat, J. C. Sherman, Chem.
Rev. 1999, 99, 931; g) L. R. MacGillivray, J. L. Atwood, Angew.
Chem. 1999, 111, 1080; Angew. Chem. Int. Ed. 1999, 38, 1018;
h) C. J. Jones, Chem. Soc. Rev. 1998, 27, 289.
(
zinc(ii) porphyrin)phosphite ligands 1 and three ditopic
dabco ligands into the sandwich-type structure 2 leads to a
supramolecular chelating bidentate ligand. This chelate effect
was responsible for the high selectivity for the linear aldehyde
in the rhodium-catalyzed hydroformylation of 1-octene. The
selectivity is very sensitive to the a/1 ratio used, and we
showed that three bridging dabco ligands are required for
high selectivity. This novel supramolecular approach for the
preparation of chelating ligands has proven to be successful,
and the regioselectivity and activity in the hydroformylation
observed for the catalyst assembly ranks it among the best
[
7] a) J. Kang, J. Rebek Jr., Nature, 1997, 385, 50; b) J. Kang, G.
Hilmersson, J. Santamaria, J. Rebek Jr., J. Am. Chem. Soc. 1998,
120, 3650; c) J. Kang, J. Santamaria, G. Hilmersson, J. Rebek Jr.,
J. Am. Chem. Soc. 1998, 120, 7389; d) M. Yoshizawa, T.
Kusukawa, M. Fujita, S. Sakamoto, K. Yamaguchi, J. Am.
Chem. Soc. 2001, 123, 10454; e) M. Yoshizawa, Y. Takeyama, T.
Okano, M. Fujita, J. Am. Chem. Soc. 2003, 125, 3243; f) M.
Yoshizawa, Y. Takeyama, T. Kusukawa, M. Fujita, Angew.
Chem. 2002, 114, 1403; Angew. Chem. Int. Ed., 2002, 41, 1347;
g) R. Warmuth, J. L. Kerdelhue, S. S. Carrera, K. J. Langenwal-
ter, N. Brown, Angew. Chem. 2002, 114, 102; Angew. Chem. Int.
Ed., 2002, 41, 96.
[
19]
systems at present.
Experimental Section
For the synthesis of tris(5-(phenyl-2-yl)-10,15,20-tris(phenyl)zinc(ii)
porphyrin)phosphite 1 and further experimental details, see the
Supporting Information.
[
8] a) V. F. Slagt, J. N. H. Reek, P. C. J. Kamer, P. W. N. M. van -
Leeuwen, Angew. Chem. 2001, 113, 4401; Angew. Chem. Int. Ed.
2001, 40, 4271; b) G. A. Morris, S. T. Nguyen, J. T. Hupp, J. Mol.
Catal. A: Chem. 2001, 174, 15; c) M. L. Merlau, M. Del.
Pilar Meija, S. T. Nguyen, J. T. Hupp, Angew. Chem. 2001, 113,
Received: July 31, 2003 [Z52525]
4
369; Angew. Chem. Int. Ed. 2001, 40, 4239.
Keywords: homogenous catalysis · hydroformylation ·
porphyrinoids · self-assembly · supramolecular chemistry
.
[9] a) N. Bampos, V. Marvaud, J. K. M. Sanders, Chem. Eur. J. 1998,
4, 335; b) C. C. Mak, N. Bampos, J. K. M. Sanders, Angew. Chem.
1
998, 110, 3169; Angew. Chem. Int. Ed. 1998, 37, 3020; c) C. C.
Mak, N. Bampos, S. L. Darling, M. Montalti, L. Prodi, J. K. M.
Sanders, J. Org. Chem. 2001, 66, 4476; d) C. A. Hunter, M. N.
Meah, J. K. M. Sanders, J. Am. Chem. Soc. 1990, 112, 5773;
e) C. A. Hunter, M. N. Meah, J. K. M. Sanders, J. Am. Chem.
Soc. 1990, 112, 5780.
[
1] L. J. Prins, D. N. Reinhoudt, P. Timmerman, Angew. Chem. 2001,
13, 2446; Angew. Chem. Int. Ed. 2001, 40, 2382.
1
[
2] a) B. Olenyuk, J. A. Whiteford, A. Fechtenkötter, P. J. Stang,
Nature 1999, 398, 796; b) M. Fujita, N. Fujita, K. Ogura, K.
Yamaguchi, Nature 1999, 400, 52; c) L. J. Prins, J. Huskens, F.
de Jong, P. Timmerman, D. N. Reinhoudt, Nature 1999, 398, 498;
d) N. Takeda, K. Umemoto, K. Yamaguchi, M. Fujita, Nature
[
[
10] At these concentrations the formation of larger assemblies is
unlikely, and indeed the spectroscopic data did not indicate
formation of such species.
11] We have analyzed the titration curves with a fitting program
developed by Hunter et al.: A. P. Bisson, C. A. Hunter, J. Carlos,
K. Young, Chem. Eur. J. 1998, 4, 845.
1
999, 398, 794; e) K. A. Jolliffe, P. Timmerman, D. N. Reinhoudt,
Angew. Chem. 1999, 111, 983; Angew. Chem. Int. Ed. 1999, 38,
33; f) L. R. MacGillivray, J. L. Atwood, Nature 1997, 389, 469;
g) L. J. Prins, F. de Jong, P. Timmerman, D. N. Reinhoudt, Nature
000, 408, 181.
9
[12] This complex was prepared in situ by mixing [Rh(acac)(CO)
with (zinc(ii) porphyrin)phosphite 1 in a 1:2 ratio.
]
2
2
[
3] a) J.-M. Lehn in Supramolecular Chemistry: Concepts and
Perspectives, VCH, Weinheim, 1995; b) M. Ortega Lorenzo,
C. J. Baddeley, C. Muryn, R. Raval, Nature 2000, 404, 376;
[13] These signals are similar to those found for other phosphite
rhodium complexes: a) G. J. H. Buisman, E. Vos, P. C. J. Kamer,
P. W. N. M. van Leeuwen, J. Chem. Soc. Dalton Trans. 1995, 409;
5
622
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 5619 –5623

Angewandte
Chemie
b) A. van Rooy, P. C. J. Kamer, P. W. N. M. van Leeuwen, Orga-
nometallics 1996, 15, 835.
[
[
[
14] P. W. N. M. van Leeuwen, C. Claver, in Rhodium-catalyzed
Hydroformylation, Kluwer, Dordrecht, 2000.
15] A. van Rooy, P. C. J. Kamer, P. W. N. M. van Leeuwen, Organo-
metallics 1996, 15, 835.
16] During the preparation of this manuscript a chelating bisphos-
phane based on hydrogen bonds yielding highly selective
hydroformylation catalysts was reported: B. Breit, W. Seiche, J.
Am. Chem. Soc. 2003, 125, 6608.
[
17] Usually the l/b ratio decreases at lower temperatures: a) R.
Lazzaroni, R. Settambolo, G. Uccello-Barretta, A. Caiazzo,
Organometallics 1996, 15, 4657; b) C. Botteghi, L. Cazzolato, M.
Marchetti, S. Paganelli, J. Org. Chem. 1995, 60, 6612.
18] G. Szintay, A. Horvath, Inorg. Chim. Acta 2000, 310, 175.
19] S. C. van der Slot, J. Duran, J. Luten, P. C. J. Kamer, P. W. N. M.
van Leeuwen, Organometallics 2002, 21, 3873.
[
[
Angew. Chem. Int. Ed. 2003, 42, 5619 –5623
www.angewandte.org
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5623