Supplementary Information – Rowan, A. E. et al.
S-1
Supplementary Information:
Pall Thordarson, Edward J. A. Bijsterveld, Alan E. Rowan* & Roeland J. M. Nolte,
Epoxidation of Polybutadiene by a Topologically-Linked Catalyst
Contents:
Synthesis of rotaxane Mn3
S-2
SEC analysis of rotaxane Mn3:
S-3
Mechanism for the conversion of PD to PE in a two-phase system
S-4
Binding of inhibitor viologen (V) in the cavity of Mn1
S-5
Estimation of the binding affinity of 4-tert-butylpyridine to Mn1
S-6
Calculation of inside and outside catalytic conversion
S-7
References
S-8
Supplementary Information – Rowan, A. E. et al.
S-2
Synthesis of rotaxane Mn3
O
=
n
n
61%
22%
O
n
n
4: R = OH
5: R = Cl
R i)
R
CN
17%
CN
n = 50-100
-
2 PF6
H3N
N
N Mn
N
N
O
O
O
2x
O
N
N
O
O
N
ii)
N
6
O
O
O
+
N
O
n
N
N
H
N O
N
CN
N
H
CN
n = 50-100
N
N
bipy2PD
Mn1
2x
O
iIi)
Br
7
N
N Mn
N
N
O
O O
N
O
O
N
N
O
O
N
N Mn
N
N
O
O
N
N O
N
O
N
H
O
CN
n
CN
n = 50-100
N
H
O
N
O OO
O
O
N
N
O
O
N
O
N O
N
Mn3
Scheme S1
Scheme S1. Reagents and conditions: i) Polymer 4 (Aldrich, Mn = 4200, PD = 1.8,
22% cis-1,4-polybutadiene, 61% trans-1,4-polybutadiene, 17% 1,2-polybutadiene),
excess SOCl2, CHCl3 solvent, reflux 3h, not isolated. ii) 5, excess 6, Et3N,
CH3CN/CHCl3 solvent, under Ar overnight, then ion-exchange with NH4PF6(aq)
followed by chromatography over silica (CHCl3/CH3OH/CH3NO2, 6:1:1, v/v/v)
giving bipy2PD in 71% yield. iii) 2 equiv. Mn1, 1 equiv. bipy2PD, excess 7, DMF
solvent at 90-100 C for 3-10 days, then ion-exchange with NH4PF6(aq). The product
was purified by repeated size-exclusion chromatography (Biobeads SX-1) using THF
as an eluent to give Mn3 in 43% yield, green solid. UV-vis (CHCl3/CH3CN 1:1 v/v):
269.5 [O.D. (g Mn3/dm3) 7.8], 341sh (2.1), 375.5 (2.8), 402.5sh (2.2), 480 (4.6), 585
(0.5), 617.0 (0.5), 753.0sh (0.05) nm. See also SEC data in Figure S1.
Supplementary Information – Rowan, A. E. et al.
S-3
SEC analysis of rotaxane Mn3
at 618 nm
at 254 nm
at 618 nm
at 618 nm
arb. intensity
Mn3
Bipy2PD
Mn1:bipy2PD:Mn1
Mn1
Elution time (min)
Figure S1. Analytical size-exclusion chromatography (SEC) of MnIII-porphyrin
compounds Mn1 and Mn3, bipy2PD, and the bipy2PD:Mn1 mixture. The
experiments were carried using a Shimatzu system (Mixed D-300 column
300x7.5mm, PL gel, 5 m) and THF as an eluent. The traces are normalized to
maximum intensity. The porphyrin compounds Mn1 and Mn3 were monitored at a
wavelength corresponding to a high-intensity Q-band (618 nm). The bipy2PD
polymer showed no significant absorption above 300 nm. The pseudo-rotaxane
mixtures Mn1:bipy2PD:Mn1 where monitored at the Q-band wavelength (618 nm) of
the porphyrins to investigate if the porphyrin stayed attached to the polymer on the
SEC-column, which turned out not to be the case.
Supplementary Information – Rowan, A. E. et al.
Mechanism for the conversion of PD to PE in a two-phase system
Figure S2. Schematic representation of how the conversion of PD to PE catalysed by
Mn1 in a dichloromethane-water (CH2Cl2/H2O) two phase system might proceed. The
PD is dissolved in CH2Cl2 and the catalyst is present at the interphase (as concluded
from monolayer experiments). Conversion of PD leads to hydrophilic PE which will
prefer to be located in the aqueous phase, leading to a net movement of the polymer as
indicated by the arrow.
S-4
Supplementary Information – Rowan, A. E. et al.
S-5
Binding of inhibitor viologen (V) in the cavity of Mn1
Viologens (N,N’-dialkyl 4,4’-substituted bipyridines) like V have a very high
affinity to Mn1.1,2 For instance, in 1:1 CHCl3/CH3CN (v/v) the association constant of
the complex between V to H212 (the free base analogue of Mn1) has been determined
to be Kass = 6 x105 M-1,2 and in 4:1 CHCl3/CH3CN (v/v) Kass = 3 x 107 M-1.3 From 1H
NMR data (both one- and two-dimensional) it was demonstrated that V binds within
the cavity of H21.2 Using NOESY NMR data as the basis, molecular modelling
studies showed the geometry of this complex to be as shown here in Figure S3b,S3c.
This geometry has been recently validated by X-ray crystal structure of the complex
between H21 and the N,N’-dihydroxyethyl derivative of viologen V.4
a
b
N
ON O
O
O
N
N
N
M N
N
O
O
N
N
c
O
ON
O
Figure 3S. a) Schematic representation of the complex between Mn1 and V. b) Sideon view of the Mn1:V complex (wire-frame model). c) Edge-on view of the complex
(space-filling model).
Supplementary Information – Rowan, A. E. et al.
Estimation of the binding affinity of 4-tert-butylpyridine to Mn1
In order to quantify to what extent the “outside” mechanism contributes to the
epoxidation reaction catalysed by Mn1 in the presence of the ligand 4-tertbutylpyridine (tbpy), it is necessary to estimate the strength of association between
tbpy and Mn1. We measured the association constant (Kass) of the Mn1:tbpy
complex by UV-vis titration. Unfortunately, the binding of tbpy to Mn1 (and in
general of pyridine ligands to MnIII porphyrins5) causes only a very small shift of the
Q-bands (0.5-1 nm) and no detectable shift of the Soret-band. The association
constant was found to be Kass = 60 M-1,6 about ca. 10 times lower than the association
constant of the corresponding zinc(II) porphyrin2 (Zn1) complex Zn1:tbpy which can
be measured accurately (Kass = 625 M-1). Assuming Kass = 60 M-1, it can be calculated
that under the catalysis conditions used for the experiments in Table 1, entries 1-4
(500 equiv. tbpy per Mn1), only 3% of the porphyrin Mn1 does not have bound
tbpy.
S-6
Supplementary Information – Rowan, A. E. et al.
Calculation of inside and outside catalytic conversions
N
O
O O
N
O
O
N
N
N
M N
N
O
O
O
O
N
O
N O
N
Catalyst Mn4 (chemical structure without axial ligand (left) and schematic structure
with axial ligand (right)) is a fully blocked rotaxane analogue of Mn1, which was
used as a control to calibrate the percentage of epoxidation on the outside of Mn1.
This catalyst was synthesized by the coupling of 7 (see scheme S-1) with 4,4
bipyridine in the presence of Mn1.1
a) Calculation of inside and outside conversion for the Mn1-PD system.
A control experiment with Mn4 was carried out using conditions identical to those
reported in Table 1, entry 5, and in the presence of tbpy. The measured turnover
number/h was 3 ±0.5. Since this catalyst can only carry out epoxidations on the
outside, it can be calculated from the relative turnover numbers/h that for Mn1-PD
(15, see entry 5, Table 1), 80% of the polymer epoxidation occurs on the inside of the
catalyst Mn1.
b) Calculation of inside and outside conversion for the Mn1-bipyPD system.
From rate data
A control experiment with Mn4 was carried out, using conditions identical to those
reported in Table 1, entry 6, and in the presence of tbpy. The measured turnover
number/h was 4 ±0.5. By comparison with the turnover number/h for Mn1bipyPD (7,
see entry 6, Table 1), it can be calculated that 45% of the polymer epoxidation occurs
on the inside of the catalyst Mn1.
From product analysis
The percentage inside reaction for Mn1-bipyPD can also be calculated by a weighted
comparison of the percentage cis and trans epoxide formed by Mn1, Mn2 (100%
conversion outside) and Mn3 (100% conversion inside) and the percentage cis-trans
alkene in the starting polymer. Using this approach a value of 55% conversion inside
Mn1 is obtained.
In a separate experiment using the conditions described in Table 1, entry 8, a fivefold
excess of the polymer substrate bipy2PD was added to Mn3. In this experiment no
additional polymer conversion was observed (within experimental error), indicating
that at the given concentrations, no significant intermolecular catalysis occurs.
S-7
Supplementary Information – Rowan, A. E. et al.
References:
1.
Rowan, A. E., Aarts, P. P. M. & Koutstaal, K. W. M. Novel porphyrinviologen rotaxanes. Chem. Commun., 611-612 (1998).
2.
Elemans, J. A. A. W. et al. Porphyrin clips derived from diphenylglycoluril.
Synthesis, conformational analysis, and binding properties. J. Org. Chem. 64, 70097016 (1999).
3.
Thordarson, P. et al. Highly negative homotropic allosteric binding of
viologens in a double-cavity porphyrin. J. Am. Chem. Soc. 125, 1186-1187 (2003).
4.
Rowan, A. E. et al., unpublished results.
5.
Yuan, L-C. & Bruice, T. C. Influence of nitrogen base ligation and hydrogen
bonding on the rate constant of oxygen transfer from percarboxylic acids and alkyl
hydroperoxides (meso-tetraphenylporphinato)manganese(III) chloride. J. Am. Chem.
Soc. 108, 1643-1650 (1986).
6.
Tabata, M. & Nishimoto, J. In The Porphyrin Handbook, Vol. 9, Database of
Redox Potentials and Binding Constants (eds Kadish, K. M., Smith, K. M. & Guilard,
R.) 221-417 (Academic Press, San Diego, 2000).
S-8