Flexibility and Stability of Metal Coordination Macromolecules

Article abstract of DOI:10.1002/chem.201701133

The effect of chain structure on flexibility and stability of macromolecules containing weak P?Fe metal coordination bonds is studied. Migration insertion polymerization (MIP) of FpC_XFp (1) and PR₂C_YPR₂ (2) (Fp: CpFe(CO)₂; C_X and C_Y: alkyl spacers; P: phosphine; R: phenyl or isopropyl) generates P(1/2), in which the P?Fe and Fe?P bonds with opposite bonding direction are alternatively arranged in the backbone. On the other hand, P(FpC_XP) synthesized from AB-type monomers (FpC_XP) has P?Fe bonds arranged in the same direction. P(1/2) is more rigid and stable than P(FpC_XP), which is attributed to the chain conformation resulting from the P?Fe bonding direction. In addition, the longer spacers render P(1/2) relatively flexible; the phenyl substituents, as compared with the isopropyl groups, improves the rigidity, thermal, and solution stability of P(1/2). It is therefore possible to incorporate weak metal coordination bonds into macromolecules with improved stability and adjustable flexibility for material processing.

Full text of DOI:10.1002/chem.201701133

A Journal of
Accepted Article
Title: Flexibility and Stability of Metal Coordination Macromolecules
Authors: Xiao-Song Wang, Dapeng Liu, Diya Gen, Heyang Jiang, and
Nicholas Lanigan
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10.1002/chem.201701133
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Flexibility and Stability of Metal Coordination Macromolecules
Heyan Jiang,[a,b] Diya Geng,[a] Dapeng Liu,[a] Nicholas Lanigan,[a] and Xiaosong Wang*[a]
Dedication ((optional))
Abstract: The effect of chain structure on flexibility and stability of
the macromolecules containing weak P-Fe metal coordination bonds
is studied. Migration insertion polymerization (MIP) of FpCXFp (1)
and PR2CYPR2 (2) (Fp: CpFe(CO)2; CX and CY: alkyl spacers; P:
phosphine; R: phenyl or isopropyl) generates P(1/2), in which the P-
Fe and Fe-P bonds with opposite bonding direction are alternatively
arranged in the backbone. On the other hand, P(FpCXP) synthesized
from AB-type monomers (FpCXP) has P-Fe bonds arranged in the
same direction. P(1/2) is more rigid and stable than P(FpCXP), which
is attributed to the chain conformation resulting from the P-Fe
bonding direction. In addition, the longer spacers render P(1/2)
relatively flexible; the phenyl substituents, as compared with the
isopropyl groups, improves the rigidity, thermal and solution stability
of P(1/2). It is therefore possible to incorporate weak metal
coordination bonds into macromolecules with improved stability and
adjustable flexibility for material processing.
Nevertheless, the stability is sufficient for molecular weight
characterization,[19] material processing[22] and self-assembly.[21]
This marginal stability is also an opportunity for us to investigate
the effect of macromolecular structure on the stability of the
metal carbonyl polymers with P-Fe bonds. The resultant
knowledge is desirable for the design and creation of MCPs with
weak metal coordination bonds.
n
(CH2)x
P
Fe
(CH2)x
P
(CH2)x
P
Fe
Fe (CH2)x
OC CO
P
Fe
n-2
O
O
OC CO
CO
CO
x = 3 or 6
Scheme 1. Migration insertion polymerization (MIP) of FpCXP for P(FpCXP).
The backbone of P(FpP) with P-Fe coordination bonds
separated by aliphatic spacers is reminiscent of that for
polyamide known as nylon. It is well known that the properties of
nylon are related to the direction of amide bonds along the chain.
Nylon 66 with reversed direction of the amide bond between
each repeating unit favors more hydrogen bonding as compared
to nylon 6 prepared from caprolactam in a head-to-tail fashion.
Consequently, nylon 66 has higher melting temperature, higher
crystallinity, and lower permeability, etc.[23]
Inspired by this well-known organic system, P(1/2) was
synthesized from MIP of FpCXFp (1) (CX = alkyl spacers, X = 3
or 6) and PR2CYPR2 (2) (R = phenyl or isopropyl, CY = alkyl
spacers, Y = 3 or 6) (Scheme 2). P(1/2) backbones contain
reversely directed P-Fe and Fe-P bonds along the chain. The
thermal and solution properties of P(1/2) were studied and
compared with those for P(FpCXP) macromolecules with P-Fe
bonds arranged in the same direction (Scheme 1).
Introduction
Although various metal containing polymers (MCPs) have been
created,[1-8] It remains difficult in the synthesis of main-chain
MCPs,[6, 9-10] particularly those containing relatively weak metal
coordination bonds.[11-13] To overcome this difficulty, it is
necessary to explore backbone structure-correlated physical
properties, particularly thermal- and solution stability, but rarely
reported.
Among various reported MCPs, the physical properties of
polyferrocenylsilane (PFS) as a function of its chemical structure
have been thoroughly investigated.[14] The resultant knowledge
has prompted the creative applications of PFS polymers as
unique building blocks for functional materials and
supramolecular science.[15-18] On the other hand, the structure-
correlated properties of other MCPs, e.g. metal carbonyl
polymers, containing relatively weak metal coordination bonds
are rarely investigated.[11-13]
R
P
R
R
P
R
n
n
+
Fe (CH2)X Fe
(CH2)Y
2
CO
CO
OC
OC
1
Migration insertion polymerization (MIP) of FpP (Fp
=
R
R
P
R
R
R
P
R
CpFe(CO)2, P = phosphine) derivatives, AB-type monomers, has
generated P(FpP) that is a main chain MCP containing P-Fe
coordination bonds (Scheme 1).[19-20] P(FpP) solids and
aggregated colloids in water are air-stable,[21] whereas, in a good
solvent, such as THF, P(FpP) decomposes in a few days.[19]
Fe
P
R
(CH2)Y
(CH2)X Fe
O
OC
Fe
P
R
Fe
(CH2)Y
(CH2)X
n-1
O
O
CO
CO
CO
CO
3
2a: Y = 3, R = phenyl;
2b: Y = 6, R = phenyl;
2c: Y = 3, R = isopropyl
1a: X = 3;
1b: X = 6
Scheme 2. Migration insertion polymerization (MIP) of 1 and 2 for P(1/2).
[a]
[b]
Dr. H. Jiang, D. Geng, D. Liu, N. Lanigan, Prof. X. Wang
Department of Chemistry, Waterloo Institute for Nanotechnology,
University of Waterloo, Waterloo, ON, N2L 3G1, Canada
E-mail: xiaosong.wang@uwaterloo.ca
Chongqing Key Laboratory of Catalysis and Functional Organic
Molecules, Chongqing Technology and Business University,
Chongqing 400067, PR China.
The manuscript is organized in two sections: 1) Following the
synthesis and characterization of P(1/2) macromolecules, their
structure-correlated properties are discussed; 2) The effect of P-
Fe bonding directions on the properties of P(FpP) and P(1/2)
macromolecules are evaluated and discussed. The work
illustrates that the relatively weak P-Fe coordination bonds can
be incorporated into MCPs with adjustable flexibility and
enhanced stability.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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Results and Discussion
particularly for the P(1/2) with a larger Mn (entry 1, 3, 5, 6 in
Table 1). We reported before that the Mn for P(FpP) measured
by GPC coincidently matched that estimated by 1H NMR end
group analysis.[19, 20] It implies that the chain for P(1/2) has a
higher degree of contraction resulting in a relatively smaller
hydrodynamic volume as compared with P(FpP) chains.
As shown in Table 1, when the polymerization of 1a/2a is
prolonged from 20 h (entry 1) to 80 h (entry 2), there is no
substantial increase in Mn. However, the PDI narrows from 1.80
to 1.35 (entries 1, 2). This result can be rationalized by the steric
effect. The end groups in the oligomers are relatively reactive for
the growth, while the growth of larger molecules ceases due to
the steric hindrance. Consequently, a longer polymerization time
levels the Mn off resulting in a narrow PDI (entry 2). Similar
phenomenon was also observed for other systems.
Synthesis, characterization and properties of P(1/2). 1 and 2
were synthesized[24-26] and used as AA and BB-type monomers
for MIP (Scheme 2). Upon the polymerization, the oil-like
monomers turned to reddish brown solids, which were dissolved
in THF and subsequently precipitated in hexane generating
yellow powders. The resultant P(1/2) is soluble in a broad range
of organic solvents, including THF, CH2Cl2, toluene and stable
up to more than 10 days in non-chlorinated solvents (Figure S1).
In CHCl3 and CH2Cl2, P(1/2) decomposes in one and three days,
respectively (Figure S1). (P(1a/2c) and P(1b/2c)) with isopropyl
phosphine groups are less stable than those with phenyl
phosphine (P(1a/2a), P(1a/2b), P(1b/2a), P(1b/2b)) (Figure S2).
This difference suggests that the stability of P(1/2) is not simply
a result of the steric impediment around the Fe-P unit, because
the isopropyl substituent is much more sterically demanding
than the phenyl group. The nature of rigid aromatic structure
with a quadrupole moment may also account for the improved
stability of P(1/2) with phenyl groups.
Table 1. Molecular weights and thermal properties for P(1/2) prepared from
migration insertion polymerization of 1 and 2.[a]
Entry
Monomers
Yield
(%)
82
Mn(GPC[b]/NMR[c]
Kg/Mole
11.3/18.4
14.0/-
)
PDI
Tdec
(°C)
187
-
Tg
(°C)
133
-
1
2[d]
3
1a/2a
1a/2a
1a/2b
1a/2c
1b/2a
1b/2b
1b/2c
1.80
1.35
1.62
1.71
1.53
2.13
1.95
NMR and IR analyses indicate that P(1/2) contains the same
metal coordination units as P(FpP) polymerized from FpP, AB-
type monomers. The spectra for P(1a/2a) are illustrated in
Figure 1. As shown in the figure, the 31P NMR spectrum shows
one signal at 74 ppm due to the coordinated phosphine (Figure
1a) and the 1H NMR spectrum displays a resonance at 4.19 ppm
due to the Cp in Fp acyl units (Figure 1b). The appearance of
these two signals suggests that the polymer contains phosphine-
coordinated Fp acyl building structures resulted from the MIP.[19-
93
64
7.2/12.1
2.9/3.7
182
169
189
182
160
105
86
4
79
5
75
12.8/23.1
4.4/7.7
111
98
6
65
7
55
2.2/2.4
45
[a]
[d]
[b]
Polymerization was performed for 20 h and
80 h in THF at 70 °C,
Mn
relatively to polystyrene standards, [c] Mn estimated from 1H NMR end group
20]
The presence of terminal and acyl CO groups are confirmed
analysis.
by IR spectrum that displays two absorptions at 1911 and 1602
cm−1 (Figure S3a).[19-20] Correspondingly, 13C NMR spectrum
reveals two signals at 220 ppm and 274 ppm due to the CO
group[20] (Figure S3b). A weak signal at 34 ppm due to the
oxidized phosphine is observed in the 31P NMR spectrum
(Figure 1a), suggesting that the product contains an
uncoordinated phosphine end group.[20] 1H NMR spectrum also
reveals a weak signal at 4.68 ppm due to the Cp in Fp end
group (Figure 1b).[27] The number average molecular weight (Mn)
for P(1/2) is therefore calculated via end-group analysis and
listed in Table 1.
The effect of monomer structure on Mn of P(1/2) obtained
under the same conditions is discussed. As shown in Table 1,
both P(1a/2c) and P(1b/2c) have a very low Mn (entries 4, 7),
which is rationalized by the larger steric effect of 2c with
isopropyl groups. The length of the spacers in the monomers
also significantly influences the Mn. For example, the Mn for
P(1a/2a) with propyl spacers (entry 1) is obviously larger than
that for P(1b/2b) with hexyl spacers (entry 6). We have found
this relationship in our previous research. MIP of FpC6P with a
hexyl spacer only generated P(FpC6P) oligomers;[29] while
P(FpC3P) with a relatively larger Mn was produced under the
same conditions.[19] The flexible backbone resulting from the
longer spacer may reduce the possibility for the end groups to
encounter each other for intermolecular metal coordination
reactions.
The thermal properties of P(1/2) was analyzed using DSC and
TGA. Within the range of Mn achievable by MIP, the variation of
Tg as a function of Mn is negligible. For example, we observed
that P(FpC3P) molecules with degree of polymerization (DP) of 7
Figure 1. (a) 31P NMR, (b) 1H NMR (CDCl3) spectra for P(1a/2a).
Figure 1. (a) 31P and (b) 1H NMR spectra for P(1a/2a)
o
and 20 have the same Tg of 99 C.[19, 20] So the difference in Tg
for P(1/2) as listed in Table 1 is attributed to the variation in
chemical structure. In general, the polymers with phenyl groups
and shorter spacers, such as P(1a/2a), are more rigid with a
higher Tg. The onset of decomposition temperature (Tdec) for
P(1/2) is in the range from 160-190 C (Table 1 and Figure S5),
which is 40-70 oC higher than the Tdec for Fp acyl small
The Mn of P(1/2) relative to polystyrene (PSt) standards was
also characterized by GPC. By comparing the Mn measured by
GPC with those estimated from the end group analysis, it
appears that the GPC analysis underestimates the Mn,
o
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molecules,[31-32] As shown in Table 1, the substituent groups on
the phosphorus influence the thermal stability more than the
spacers. The Tdec for P(1a/2c) and P(1b/2c) containing isopropyl
To test this speculation, we examined the solution stability of
P(1a/2a) in THF using 31P NMR and GPC. After exposing to air
for 20 days, the 31P NMR spectrum (Figure 2a) shows no
change in the signals. GPC analysis further indicates that there
is no degradation of the sample and the Mn remains unchanged
(Figure 2c). 30 days later, the 31P NMR spectrum displays
multiple signals in addition to those due to the original P(1a/2a),
suggesting the occurrence of the decomposition. So P(1a/2a) is
stable for at least 20 days in THF. In contrast, P(FpC3P) in THF,
as we have reported before, decomposed resulting in
precipitates in a few days.[19] The 31P NMR of the supernatant
shows weak signals (Figure 2b) corresponding to the
decomposed fragments with low molecular weight as indicated
by GPC analysis (Figure 2c). Similarly, P(1b/2b) also has a
higher solution stability than P(FpC6P) (Figure S6).
o
o
phosphine groups is ca. 160 C and 169 C (entries 4 and 7),
o
respectively, while the Tdec is in the range between 180 C and
190 oC for all the polymers with phenyl phosphine groups
(entries 1, 3, 5, 6). The effect of the spacer length on the Tdec for
these polymers (entry 1, 3, 5, 6) is within 10 oC.
The effect of P-Fe bonding direction along the chain.
P(1a/2a)/P(FpC3P) and P(1b/2b)/P(FpC6P) are two pairs of
macromolecules with three and six carbon atoms in the spacers,
respectively. Although the macromolecules for each pair have
the same chemical composition, the direction of P-Fe
coordination along the backbone is different in
a way
reminiscent of the amide bonds in nylon 66 and nylon 6. This
difference in the backbone structure affects the thermal
properties of the macromolecules. As shown in Table 1, the Tg
P(1a/2a)
PFpC3P
a)
b)
o
for the former polymer in the pairs is 133 C (P(1a/2a)) and 98
oC (P(1b/2b)), respectively. The corresponding counterpart has
a
Tg of 99 oC (P(FpC3P))[19] and 68 oC (P(FpC6P)),[29]
o
respectively. This difference in Tg (ca. 30 C) suggests that the
reversed direction of P-Fe bond between each repeating unit
renders P(1a/2a) and P(1b/2b) more rigid. As the Tdec is
compared, P(1a/2a) (187 oC) and P(1b/2b) (182 oC) are
relatively stable than P(FpC3P) (180 oC)[19] and P(FpC6P) (170
oC),[29] respectively. The enhanced thermal stability for P(1/2)
may be related to the chain conformation resulting from the
metal coordination direction in the backbone.
c)
P(FpCXP) (X = 3, 6) with P-Fe bonds arranged in the same
direction along the chain is expected to have a more regular
structure. Dynamic simulation has indicated that P(FpCXP)
backbones are fully extended into a linear helical conformation
in THF.[30] P(1/2) with opposite direction of P-Fe bonds between
each coordination unit may adopt a non-linear conformation
(Scheme 3). The less ordered chain conformation may reduce
the possibility for the relatively weak metal coordination bonds to
interact with the external media (Scheme 3), which is a possible
reason for the improved stability of P(1/2).
Figure 2. Time-resolved 31P NMR spectra (a) for the THF solution (2 mg mL−1
)
of P(1a/2a); (b) and P(FpC3P); (c) GPC curves for P(1a/2a) after aging in THF
for 20 days and for P(FpC3P) after aging in THF for 10 days.
If the stability is indeed caused by the chain conformation,
photo- and oxidant-induced degradation behavior should be
different. Photons can penetrate through the solution and
polymers for the degradation reaction regardless of the chain
conformation. Figure 3 and S7 illustrate the time-resolved 31P
NMR spectra for the solutions of P(1/2) and P(FpCXP) in THF
exposed to an LED light (wavelength: 400–410 nm). As shown
in the figures, the degradation behavior for both P(1/2) and
P(FpCXP) is similar. After 10 minutes, the intensity for the peak
due to the main chain coordinated phosphine at 74 ppm
obviously decreases. One hour later, this signal is barely visible
suggesting that all macromolecules decompose.
PFpC3P
P(1a/2a)
=
Fe
(CH2)3
P
O
CO
=
Fe
Fe
(CH2)3
O
CO
O
CO
=
P
(CH2)3
P
Scheme 3. Schematic representation of the chain conformation for P(FpC3P)
and P(1a/2a).
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macromolecules, has a similar CD profile (Figure 5 C and 5d). It
is therefore reasonable to think that the chiral structure of the
metal coordination units in the backbone is responsible for the
CD signal and the intensity of the signal for the solutions with the
same concentration can be an indicative of the stereoregularity
of the backbones. By comparing P(FpC3P) and P(FpC6P) with
P(1a/2a) and P(1b/2b) respectively, the intensities of the CD
signals for the former polymers are higher, suggesting that
P(FpCXP) (X = 3, 6) has a higher ordered chain conformation
than P(1/2). This preliminary data illustrate that the directions of
metal coordination bonds along the chain affects the chain
conformation and is a factor adjusting the stability of the
macromolecules with weak Fe-P metal coordination bonds.
P(1a/2a)
PFpC3P
b)
a)
Figure 3. Time-resolved 31P NMR spectra for (a) P(1a/2a) and (b) P(FpC3P) in
THF (5 mg mL−1) irradiated by LED light (wavelength = 400–410 nm).
The time-resolved 31P NMR spectra for P(1a/2a) and P(FpC3P)
in the presence of H2O2 are illustrated in Figure 4. As shown in
Figure 4a, although the intensity for the signal due to the
oxidized phosphine increases slowly over a day, substantial
amount of the coordinated phosphine in P(1a/2a) with chemical
shift at 74 ppm remains. Not until the fourth day do we start to
observe the precipitates (Figure S8). On the other hand,
P(FpC3P) in the presence of H2O2 decomposes and generates
precipitates in three hours (Figure S8). Consequently, the 31P
NMR of the solution shows a weak signal due to the coordinated
phosphine at 74 ppm (Figure 4b). The 31P NMR spectra also
indicate that P(1b/2b), as compared with P(FpC6P), are more
resistant to H2O2 (Figure S9). This difference in the resistance
can be attributed to the conformation of chains. The linear
helical structure of PFpCXP backbone[30] expels the iron
coordination units towards the solvent and therefore enhances
the interaction between H2O2 and the metal coordination units.
In contrast, the metal coordination units in P(1/2) may be
embedded within the less regular chains, which reduces the
possibility to react with H2O2 and thus enhances the stability.
Figure 5. Circular dichroism (CD) spectra of (a) P(FpC3P)20 and P(1a/2a)14
with the same concentration of Fe ([Fe] = 2.47 x 10-3 μM); (b) P(FpC6P)14 and
P(1b/2b)5 with the same concentration of of Fe ([Fe] = 2.24 x 10-3 μM) (c)
FpC6 in THF ([Fe] = 1.91 x 10-3 μM).
Conclusions
a)
b)
Migration insertion polymerization (MIP) of ditopic Fp derivatives,
FpCXFp (1) and bi-functional phosphine, PR2CYPR2 (2) has
generated P(1/2). The backbone of P(1/2) is constructed from
the alternative P-Fe and Fe-P coordination bonds with opposite
bonding directions. In contrast, P(FpCXP) contains P-Fe bonds
in the same direction along the chain. P(1/2) is more rigid and
stable than P(FpCXP), which is rationalized by the less ordered
chain conformation of P(1/2) resulting from the opposite
direction of the metal coordination bonds along the chain. In
addition, the flexibility and stability of P(1/2) can be adjusted by
the length of aliphatic organic spacers and the substituents on
the phosphorus centres. It is therefore possible to incorporate
weak metal-coordination bonds into MCPs for processing
materials by adjusting the coordination direction along the chain
and the chemical structure of organic ligands.
P(1a/2a)
PFpC3P
Figure 4. Time-resolved 31P NMR spectra for (a) P(1a/2a) and (b) P(FpC3P) in
THF (10 mg mL−1) in the presence of H2O2 (30 %).
The macromolecules are constructed from the same metal
coordination units that are chiral at the Fe center, so circular
dichroism (CD) experiments may be able to probe the difference
in the chain conformation. THF solutions of P(1a/2a), P(1b/2b),
P(FpCXP) (X = 3 and 6) were examined. As shown in Figure 5a
and 5b, all the solutions show positive CD signals. Fp heptanoyl
compound (FpC6), representing the Fe coordination units in the
Experimental Section
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Materials and instrumentation. THF was freshly distilled under nitrogen
10 h at 24 oC and then heated to reflux for 30 min. After cooling,
deoxygenated water (25 ml) was added and subsequently the organic
layer was separated. The water layer was extracted with ether. The
combined organic solution was then dried over magnesium sulfate for a
few hours. After filtration, the organic solvents were removed in vacuo.
The residue was distilled in vacuo yielding the diphosphine as a colorless
liquid, 7.1 g (81%), b.p. 95-98°C / 0.01 mmHg. 1H NMR (CDCl3): 1.69-
1.65 ppm (m, 4H, CH(CH3)2), 1.44-1.42 ppm (m, 4H, CH2P), 1.22-1.00
ppm (m, 26H, CH2CH2CH2, CH(CH3)2). 31P NMR (CDCl3): 3.83 ppm(s)
(1H and 31P NMR spectra is illustrated in Figure S11).
from
Na-benzophenone.
Sodium
(Na),
potassium
(Fp2),
(K),
1,3-
cyclopentadienylirondicarbonyl
Bis(diphenylphosphino)propane,
dimer
1,6-Bis(diphenylphosphino)hexane,
diisopropylphosphine, n-butyllithium, 1,3-dichloropropane and 1,6-
dichlorohexane were purchased from Strem Chemicals Inc.
Benzophenone was purchased from Fisher Scientific. P(FpCXP) (X = 3 or
6) was prepared according to literature.[20, 29] All chemicals were used as
received unless otherwise indicated.
The molecular weights and molecular weight distributions (Mw/Mn) for
P(1/2) macromolecules were characterized by GPC using PSt standards.
THF was used as the eluent at a flow rate of 1.0 mL min-1. 1H, 31P, and
Migration
insertion
polymerization:
Migration
insertion
polymerization 1 and 2 was performed in THF solution (20 wt%) at 70 °C.
Samples were withdrawn for 31P NMR analysis during the polymerization.
20 h later, the solution was cooled to 24 oC. The crude product was
dissolved in a minimum of THF, and then precipitated in hexane. The
precipitate was collected and dried under vacuum at room temperature
overnight yielding a bright yellow powder. P(1a/2a): 1H NMR (CDCl3):
7.30-7.25 ppm (C6H5), 4.68 ppm (end group Cp, C5H5), 4.19 ppm (main
chain Cp, C5H5), 2.50-2.35 ppm (COCH2), 1.84-1.09 ppm (CH2CH2CH2,
CH2PFe). 31P NMR (CDCl3): 74.1 ppm (backbone PFe) and 34.1 ppm
(oxidized end group PPh2O). FTIR: 1911 cm−1 (terminal CO stretch) and
1602 cm−1 (acyl CO stretching). P(1a/2b): 1H NMR (CDCl3): 7.42-7.25
ppm (C6H5), 4.68 ppm (end group Cp, C5H5), 4.31 ppm (main chain Cp,
C5H5), 2.66-2.25 ppm (COCH2), 1.55-1.18 ppm (CH2CH2CH2,
CH2CH2CH2CH2CH2CH2, CH2PFe). 31P NMR (CDCl3): 74.0 ppm
(backbone PFe), −13.5 ppm (end group PPh2), and 34.9 ppm (oxidized
end group PPh2O). FTIR: 1910 cm−1 (terminal CO stretch) and 1602 cm−1
(acyl CO stretching). P(1a/2c) 1H NMR (CDCl3): 4.71 ppm (end group Cp,
C5H5), 4.53 ppm (main chain Cp, C5H5), 2.99-2.72 ppm (COCH2), 2.17-
1.11 ppm (CH2CH2CH2, CH(CH3)2, CH2PFe). 31P NMR (CDCl3): 77.8
ppm (backbone PFe) and 54.5 ppm (oxidized end group P(isopropyl)2O).
FTIR: 1911 cm−1 (terminal CO stretch) and 1601 cm−1 (acyl CO
stretching). P(1b/2a): 1H NMR (CDCl3): 7.28-7.25 ppm (C6H5), 4.69 ppm
(end group Cp, C5H5), 4.19 ppm (main chain Cp, C5H5), 2.66-2.37 ppm
(COCH2), 2.12-0.91 ppm (CH2CH2CH2, CH2CH2CH2CH2CH2CH2,
CH2PFe). 31P NMR (CDCl3): 73.9 ppm (backbone PFe), −14.3 ppm (end
group PPh2), and 34.1 ppm (oxidized end group PPh2O). FTIR: 1910
cm−1 (terminal CO stretch) and 1601 cm−1 (acyl CO stretching). P(1b/2b):
1H NMR (CDCl3): 7.44-7.30 ppm (C6H5), 4.68 ppm (end group Cp, C5H5),
4.33 ppm (main chain Cp, C5H5), 2.80-2.40 ppm (COCH2), 2.30-0.99
ppm (CH2CH2CH2CH2CH2CH2, CH2PFe). 31P NMR (CDCl3): 73.9 ppm
(backbone PFe) and 34.9 ppm (oxidized end group PPh2O). FTIR: 1908
cm−1 (terminal CO stretch) and 1605 cm−1 (acyl CO stretching). P(1b/2c):
1H NMR (CDCl3): 4.70 ppm (end group Cp, C5H5), 4.53 ppm (main chain
Cp, C5H5), 3.02-2.86 ppm (COCH2), 2.16-1.16 ppm (CH2CH2CH2,
CH2CH2CH2CH2CH2CH2, CH(CH3)2, CH2PFe). 31P NMR (CDCl3): 77.7
ppm (backbone PFe) and 54.6 ppm (oxidized end group P(isopropyl)2O).
FTIR: 1909 cm−1 (terminal CO stretch) and 1602 cm−1 (acyl CO
stretching).
13C NMR spectra were obtained on
spectrometer at ambient temperature using appropriate solvents. NMR
samples were prepared under dry nitrogen atmosphere unless
a Bruker-300 (300 MHz)
a
otherwise indicated. Fourier transform infrared (FT-IR) spectra were
recorded using a Perkin Elmer Spectrum RX I FT-IR system. The
samples were ground with KBr and then pressed into transparent pellets.
LED light (wavelength 400–410 nm, Super Bright LEDs Inc.) was used as
the light source for the photo-degradation experiments. Differential
scanning calorimetry (DSC) data were recorded using a Q10 DSC (TA
Instruments) under a flow of N2 (50 mL min−1). Samples (ca. 5 mg) were
enclosed in aluminum pans, with an empty aluminum pan as the
reference. The measurements were performed by heating the samples
from −50 °C to 155 °C (ramp: 10 °C min−1). The thermal history was
removed by a cycle of heating the samples to 155 °C (ramp: 10 °C min−1
)
and then cooling back to −50 °C (ramp: 10 °C min−1). Thermal
gravimetric analysis (TGA) was carried out on a TGA Q50 under N2 at a
heating rate of 10 °C min−1. Samples were dried under vacuum at
ambient temperature prior to the measurements. Circular dichroism (CD)
spectra were recorded on a Jasco J720 spectrometer (Japan) at 25 °C
under N2. THF solutions of the samples (1 mg mL-1) in a cell with 1.0 cm
path length were prepared for the experiments.
Synthesis. All experiments were performed under an atmosphere of
dry nitrogen using standard Schlenk techniques unless otherwise
indicated. FpCXFp (1)[24] and PR2CYPR2, R = isopropyl (2c) were
synthesized according to the literature.[25-26] PR2CYPR2, R = phenyl (2a,
2b) is commercially available;
Synthesis of 1: 1 was prepared via a reaction of Cl(CH2)XCl (X = 3, 6)
with K[CpFe(CO)2]. A typical experiment process is briefly described.
Cl(CH2)3Cl (0.64 g, 5.70 mmol) was added dropwise to a THF solution of
K[CpFe(CO)2] (2.5 g, 11.4 mmol). The reaction mixture was stirred for 15
h at 24 oC and then heated to reflux for 6-8 h. Afterwards, the reaction
was cooled to 24 oC and the solvent was removed under a reduced
pressure. The residue was extracted with dichloromethane (50 cm3). The
resulting solution was filtered and the solvent was removed under
reduced pressure leaving a brown oil. Addition of hexane (20 cm3) to the
oil and cooling in fridge caused a rapid formation of yellow crystals.
Recrystallization of these crystals from hexane yielding the required
products as yellow plates. FpC3Fp: yield 54%. 1H NMR (CDCl3): 4.72
ppm (s, 10H, C5H5), 1.46-1.45 ppm (m, 6H, CH2CH2CH2); FT-IR (Nujol
mull): 2006 and 1944 cm−1 (terminal CO stretching); FpC6Fp: yield 45%.
1H NMR (CDCl3): 4.73 ppm (s, 10H, C5H5), 1.54-1.32 ppm (m, 12H,
CH2CH2CH2CH2CH2CH2) FT-IR (Nujol mull): 2006 and 1946 cm−1
(terminal CO stretching) (1H NMR spectra is illustrated in Figure S10).
Acknowledgements
The Natural Sciences and Engineering Research Council of
Canada (NSERC) and the University of Waterloo are
acknowledged for financial support. Heyan Jiang is grateful for
the financial support of Chongqing Technology and Business
University, National Natural Science Foundation of China (no.
21201184), Natural Science Foundation Project of CQ (no.
cstc2014jcyjA10105) and Ministry of Education of Chongqing
(no. KJ1400601).
Synthesis of 2c: A typical process for the synthesis of 2c is described.
To an ice-cooling suspension of lithium diisopropylphosphide in ether/n-
hexane prepared from diisopropylphosphine (7.7 g, 65 mmol) and n-
butyllithium (1.6 M, 67 mmol), 1,3-dichloropropane (3.5 g, 31 mmol) was
added slowly in the period of 10 min. The resulting mixture was stirred for
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Weak metal coordination bonds can
be connected into macromolecules
with varied flexibility, higher thermal
and solution stability
Heyan Jiang, Diya Geng, Dapeng Liu,
Nicholas Lanigan, and Xiaosong Wang*
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Flexibility and Stability of Metal
Coordination Macromolecules
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