Synthesis, cyclization, and migration insertion oligomerization of CpFe(CO)2(CH2)3PPh2 in solution

Article abstract of DOI:10.1021/om4010516

Cyclopentadienyldicarbonyl[(diphenylphosphino)propyl]iron (CpFe(CO) ₂(CH₂)₃PPh₂, FpP), containing both Fp and phosphine groups, was synthesized as a difunctional monomer for migration insertion polymerization (M

Full text of DOI:10.1021/om4010516

Article
pubs.acs.org/Organometallics
Synthesis, Cyclization, and Migration Insertion Oligomerization of
CpFe(CO)2(CH2)3PPh2 in Solution
Kai Cao, Brian Tsang, Yibo Liu, Daniel Chelladural, William P. Power,* and Xiaosong Wang*
Department of Chemistry and Waterloo Institute for Nanotechnology (WIN), University of Waterloo, 200 University Avenue,
Waterloo, Canada N2L 3G1
S
* Supporting Information
ABSTRACT: Cyclopentadienyldicarbonyl[(diphenylphosphino)propyl]-
iron (CpFe(CO)2(CH2)3PPh2, FpP), containing both Fp and phosphine
groups, was synthesized as a difunctional monomer for migration insertion
polymerization (MIP). FpP underwent either intra- or intermolecular
reactions in solution. When a solution with low FpP concentration (ca.1%
by weight) was left at 25 °C, FpP was quantitatively converted to the five-
membered-ring species 1 via CO release. On the other hand, when a
solution at the same low concentration was heated to 70 °C in the dark, an
intramolecular migration insertion reaction was promoted, leading to a high
conversion of FpP (ca. 70%) to the six-membered cyclic Fp acyl derivatives
2. At the same temperature with an increase in the concentration of FpP to
10% by weight, intermolecular MIR became predominant (ca. 90%) with a
low yield of ring molecules (ca. 10%). Solution polymerization of FpP (ca.
20% by weight) was therefore performed at 70 °C, which generated both THF-soluble and -insoluble macromolecules via
intermolecular migration insertion reactions. The resulting macromolecules were fully characterized by using FT-IR, solution-
and solid-state 31P, and 13C NMR. The soluble macromolecules exhibit a molecular weight of ca. 4200 with a PDI value of ca.
1.24, as characterized by GPC. A kinetic study shows that the polymerization follows a step-growth mechanism.
nucleophilic ligands, e.g. phosphine (PR3), leads to air-stable
phosphine-coordinated acyl complexes as a result of MIR.34,35
By combining both Fp and phosphine groups into one
molecule via an alkyl spacer, difunctional A-B type monomers
of cyclopentadienyldicarbonyl[(diphenylphosphino)propyl]
iron (CpFe(CO)2(CH2)3PPh2, FpP) have been prepared.31
The monomers undergo MIP, leading to air-stable poly-
(cyclopentadienylcarbonyl[(diphenylphosphino)butanoyl]iron)
(P-FpP) with a molecular weight of up to 104.31 The
polymerization was performed in bulk in order to suppress
possible intramolecular cyclic reactions. In an effort to explore
solution MIP, we carried out the experiments to investigate
FpP solution reaction behavior. The reactions are performed
under conditions with varied FpP concentration and temper-
ature. The results indicate that the molecules in solvents
undergo both intramolecular cyclic reactions and intermolec-
ular MIR depending on the reaction conditions (Scheme 1). At
low concentration, two cyclic molecules have been produced at
either low or high temperature (1 and 2 in Scheme 1). On the
other hand, at relatively higher monomer concentration, an
intermolecular reaction of FpPs predominates (3 in Scheme 1).
As a result of this investigation, solution polymerization of FpP
with a monomer concentration of 20% was conducted at 70 °C,
resulting in both THF-soluble and insoluble PFpP.
INTRODUCTION
■
The convergence of organometallic and polymer chemistry has
led to the emergence of an interdisciplinary research field of
metal-containing polymers (MCPs).1−5 Many MCPs exhibit
interesting functions and self-assembly behavior, which render
them very promising as building blocks for modern
technologies.6−16 Taking advantage of the well-developed
organometallic chemistry, the synthesis of various metal-
containing polymerizable compounds for processable macro-
molecules has therefore become a demanding but challenging
research topic.17−23 This research is essential to extend the
scope of MCPs and will offer new opportunities for the future
of organometallic chemistry.24
Migration insertion reaction (MIR)25−27 is a well-studied
organometallic reaction and has been explored for the
coordination polymerization of a number of organic monomers,
including olefins,28 CO,29 and CO2,30 for stereocontrolled
organic polymers. Unlike previous reports which used metal
complexes as catalysts, we have developed migration insertion
polymerization (MIP), in which metal complexes acting as
monomers get involved in the construction of polymer
backbones. As a result, a new class of main-chain MCPs was
produced.31 The polymers are also of interest due to the
presence of metal-coordinated phosphorus, which may have
properties complementary to those of previously reported
phosphorus-containing polymers.32,33 It is well-known that the
reaction of alkyldicarbonylcyclopentadienyliron (FpR) with
Received: October 29, 2013
© XXXX American Chemical Society
A
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(Table S2, Supporting Information).37 Infrared spectroscopy of
the monomer shows characteristic peaks at 1952 and 2004
cm−1 (Figure 1b), which are representative of the terminal CO
groups in FpP.25 The 31P NMR spectrum reveals a signal at
−14.7 ppm, confirming the presence of the phosphine group
(Figure 1c).
Scheme 1. Solution Reactions of FpP in THF
1
The H NMR spectrum of FpP in DMSO-d6 (Figure 2a)
exhibits a strong resonance at 4.8 ppm, representing the Cp
RESULTS AND DISCUSSION
■
Synthesis and Characterization of FpP.
Cyclopentadienyldicarbonyl[(diphenylphophino)propyl]iron
(FpP) was synthesized via a reaction between (3-
chloropropyl)diphenylphosphine and potassium cyclopentadie-
nyldicarbonyliron.31 The yellow oil-like form of FpP was
produced most of the time, which rendered the crystallization
of FpP difficult. The possible reason is attributed to the light
sensitivity of Fp derivatives,36 which may create trace amounts
of impurities during the purification process. We therefore
performed the reaction and purification in the dark. As a result,
a yellow powder of FpP was obtained upon solvent
evaporation. The yellow powder can be crystallized from
hexane solution at −49 °C, resulting in single crystals suitable
for X-ray diffraction. X-ray diffraction shows that the molecules
crystallized in a monoclinic crystal system with space group
P21/c (Table S1, Supporting Information). As shown in Figure
1, the Fe is coordinated in a pseudo-octahedral three-legged
piano-stool fashion. The Fe−C8 bond distance is 2.066 Å, and
the C6−Fe−C7, C6−Fe−C8, and C7−Fe−C8 bond angles are
93.64, 85.84, and 87.29°, respectively. These structure
parameters are similar to those for other Fp derivatives
reported in the literature such as [(η5-C5H5)Fe(CO)2]2(CH2)4
1
1
Figure 2. H NMR of FpP in DMSO-d6 (a) and H−1H COSY in
C6D6 (b).
ring, and a broad resonance at 7.30−7.40 ppm, representing the
phenyl groups. The upfield peak at 1.46 ppm is assigned to the
protons α and β to Fe (a and b in Figure 2a), while the signal at
2.1 ppm is due to the protons adjacent to the phosphorus (c in
Figure 2a). The integration ratio of these two peaks is 2:1
(Figure 2a), which supports the assignment. 1H−1H 2D COSY
NMR of FpP in C6D6 was also performed and the spectrum is
illustrated in Figure 2b. As shown in the figure, the proton
signals for the propyl spacer are well separated in C6D6. The
chemical shift at 1.6 ppm represents the proton α to Fe. The
triplet at 2.2 ppm is due to the proton adjacent to phosphorus.
Multiple peaks at 1.8 ppm can be assigned to the protons β to
Fe. This assignment is confirmed by the 2D chemical shift
correlation map (Figure 2b). No cross peaks are observed for
the signals at 1.6 and 2.2 ppm, suggesting that they are
separated by the methylene in the middle of the propyl spacer.
13C NMR of FpP in DMSO-d6 shows one peak at 217 ppm
representing the terminal CO group; signals due to phenyl and
Cp appeared at 128−139 and 85−86 ppm, respectively (Figure
S1, Supporting Information). The resonances due to the three
carbons in the propyl chain (a−c in Figure S1) are observed
upfield at 34.3, 32.5, and 5.1 ppm. 13C−1H HMQC 2D NMR
of FpP in C6D6 was performed to assign these signals (Figure
S1, Supporting Information). As shown in the figure, the cross
peaks indicate that the signals at 5.1, 34.3, and 32.5 ppm in 13
C
NMR are connected to protons a−c in the 1H NMR spectrum,
respectively. On the basis of this assignment, the one-, two-,
and three-bond 13C−31P coupling constants for these three
carbons (1JPC, JPC, and JPC) are 14, 15.3, and 11.4 Hz,
2
3
2
respectively (inset in Figure S1). We noticed that JPC is larger
1
than JPC, which is peculiar but is commonly observed for
phosphine compounds.38
Cyclization Reaction of FpP. Fp derivatives usually
undergo two types of reactions in the presence of phosphine:
(1) CO release followed by phosphine coordination36 and (2)
MIR at an elevated temperature.34 FpP containing both Fp and
phosphine groups is therefore expected to undergo cyclic
reactions under both conditions. When an FpP solution of low
Figure 1. Crystal structure (a) and FT-IR (b) and 31P NMR in
DMSO-d6 (c) of FpP.
B
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concentration (ca. 1% by weight) in THF was exposed to light
and left at room temperature for 7 days, over 99% of the FpP
was converted to the five-membered-ring species 1. On the
other hand, when the solution was heated to 70 °C in the dark,
the major product (ca. 70%) was the six-membered-ring species
2 via an intramolecular MIR.
To characterize 1 and 2, single crystals suitable for X-ray
crystallography were grown in hexane for 1 and in hexane/
DCM (4/1) mixed solvents for 2 at −49 °C. The X-ray analysis
(Figure 3) showed that both molecules crystallize in a
Table 1, for a compound with R being a bulky carborane cage
(C2B10H11),39 the P−Fe−C angles are much larger than those
Table 1. Comparison of Bond Angles and Distances for 1
and Its Acyclic Analogues
acyclic (η5-C5H5)Fe(CO)(PPh3)R
39
bond angle or distance
ring 1
R = Et36,40
R = C2B10H11
C(8)−Fe−C(6)
C(6)−Fe−P
C(8)−Fe−P
Fe−P
Fe−CO
Fe−C(R)
89.81(6)
93.60(5)
81.98(4)
2.1581(3)
1.729(4)
2.057(1)
92.76(7)
92.3(4)
96.4(3)
99.68(1)
2.271
90.61(5)
87.86 (5)
2.1699(4)
1.7291(17)
1.9601(16)
1.729(8)
2.093(6)
for a compound with R being Et (Table 1). Also as a result of
the steric effect, the Fe−P bond distance (2.271 Å) is much
longer in comparison to 2.1699(4) Å for the Et-substituted
analogue (Table 1).36 For the five-membered-ring species 1, the
C(8)−Fe−P angle (81.98(4)°) is obviously smaller than for the
acyclic analogues (Table 1), which may generate a certain
degree of ring strain. However, as a result of the ring
constraints, one can see that the P−Fe bond (2.1581(3) Å)
becomes much smaller in comparison to those in the acyclic
compounds (Table 1). This result suggests that the cyclic
bidentate ligand is able to introduce a strong P−Fe bond by
overcoming the phosphine steric effects. The Fe distances to
other ligands are comparable for both cyclic and acyclic
compounds (Table 1).
For Fp acetyl derivatives, it has been systemically studied and
demonstrated that the Fe−P bond length is related to the steric
effect of the alkylphosphine ligand.41 As shown in Table 2, by
Table 2. Comparison of Bond Angles and Distances for 2
and Its Acyclic Analogues
acyclic (η5-C5H5)Fe(CO)(PPhRR′)
C(O)R′
bond angle or
distance
ring 2
R = Ph; R′ = Bu43 R = Me; R′ = Me41
C(1)−Fe−C(6)
C(6)−Fe−P
C(1)−Fe−P
Fe−P
92.76(7)
90.61(5)
87.89(5)
2.169
92.1(4)
95.9(3)
91.3(3)
2.198
94.6(2)
92.9(1)
88.2(1)
2.180
Figure 3. Crystal structures for 1 (a) and 2 (b).
Fe−CO
1.729
1.723
1.725
Fe−C(O)R
1.960
1.992
1.948
monoclinic crystal system with space group P21/c (Table S1,
Supporting Information). Both Fe atoms in 1 and 2 assume a
pseudo-octahedral coordination geometry with the Cp ring
occupying three coordination sites (piano-stool configuration).
The torsion angles (Tables S3 and S4, Supporting Information)
indicate that all elements for the ring structures are not on the
same plane. The six-membered-ring species 2 adopts a
cyclohexane-like chair conformation, suggesting that low strain
energy is involved in the compound.
Through comparison with previously reported data for
acyclic analogues, we discovered that the formation of the cyclic
structures appears to counteract the steric effect of phosphine
ligands, leading to shorter P−Fe bonds. For Fp derivatives, Fe
offers limited space to accommodate CO, phosphine, and one
anionic ligand of R− on the three coordination sites. The size of
the phosphine and R groups will therefore influence their bond
distances to Fe and bond angles. For example, as shown in
using dimethylphenylphosphine to replace the commonly used
triphenylphosphine, the shortest Fe−P bond (2.180 Å) for this
type of compound had been reported (Table 2).41 However, via
the formation of the cyclic Fp acyl derivative 2, the bond can be
further strengthened, leading to an even shorter P−Fe bond
length of 2.169 Å. A similar bond length was also reported for a
five-membered-ring Fp acetyl derivative.42
31P NMR spectra for 1 and 2 are shown in Figure S2
(Supporting Information). As shown in the figure, compounds
1 and 2 exhibit a single peak at 109 and 70 ppm, respectively.
These characteristic peaks can therefore be used as indicative
1
for the formation of the rings. H NMR spectroscopy for 1 is
illustrated in Figure 4a, in which the Cp signal appears at 4.2
ppm. This peak undergoes a 0.6 ppm upfield shift in
comparison to that in FpP as a result of the coordination of
phosphorus to Fe. The occurrence of the coordination created
C
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1
Figure 4. H NMR (a) and 13C−1H HMBC 2D NMR (b) for 1 in
CDCl3.
1
an asymmetric Fe unit, which significantly complicated the H
1
Figure 5. H NMR (a) and 13C−1H HMBC 2D NMR (b) for 2 in
NMR spectrum of the molecule (Figure 4a). As shown in the
figure, multiple chemical shifts are observed at 7.8−7.1 and
2.50−1.30 ppm, accounting for phenyl groups and the propyl
spacer, respectively. To resolve the upfield peaks, 13C NMR and
13C−1H HMQC 2D NMR were performed. In 13C NMR, the
signals due to the three propyl carbons appear at 36, 31, and 12
ppm, which can be respectively assigned to the carbon adjacent
to phosphorus25 the carbons β and α to Fe on the basis of the
degree of the C−P coupling effect. Hydrogen to carbon
connectivities are subsequently determined from the cross
peaks in the 2D NMR spectrum. Consequently, chemical shifts
at 2.5 and 2.3 ppm can be assigned to protons α to phosphorus
(c in Figure 4b), the peaks at 2.0 ppm are due to the proton α
to iron (a in Figure 4b), and β protons appear at 2.1 and 1.3
ppm. (b in Figure 4b).
Similar to the case for 1, compound 2 also displays multiple
peaks appearing upfield due to the propyl spacer. From 13C
NMR, C−P coupling with JPC = 32.4 Hz was only observed for
the signal at 29 ppm, and no coupling effect was observed for
the other two signals. Therefore, the chemical shift at 29 ppm is
assigned to the carbon adjacent to phosphorus (c in Figure 5b).
The carbon α to the acyl group appears at 68 ppm (a in Figure
5b), which is consistent with previous literature data.25 The
signal at 21 ppm is attributed to the carbon β to the acyl group
(c in Figure 5b). Subsequently, the proton peaks are assigned
via the cross peaks appearing in the 2D NMR (Figure 5b).
Effect of Concentration and Temperature on the FpP
Solution Reaction. On the basis of the above investigation,
possible products produced from the FpP solution reaction can
be analyzed by using 31P NMR. A representative spectrum is
illustrated in Figure 6. As shown in the figure, after the solution
was heated at 40 °C for 6 h, both 1 and 2 were formed, as
indicated by the signals at 109 and 70 ppm, respectively. The
CDCl3.
chemical shift at −14.7 ppm is attributed to unreacted FpP. In
addition, two signals at 72.8 and −13.6 ppm due to
coordinated25 and uncoordinated phosphorus are observed.
The appearance of these two peaks with an intensity ratio of
close to 1:1 strongly suggests the formation of FpP dimers.
Taking advantage of the well-resolved chemical shifts for all
products of intra- and intermolecular reactions, we further
investigated solution reactions of FpP with varied concentration
and temperature.
By a comparison of integration ratios, the relative
conversions of FpP each species can be extracted. The resulting
data for all reaction conditions are illustrated in Table 3.
It is well-known that Fp derivatives can readily release CO
ligand and the reaction is light sensitive.36 On the other hand,
MIR requires a relatively higher temperature.34 As a result,
intramolecular cyclization via CO release was the major
reaction when the reaction was performed at room temper-
ature, leading to 1 in a yield of over 90% (entries 1 and 2 in
Table 3). Particularly, when THF was used as solvent (entry 2
in Table 3), 1 was produced almost exclusively. When the
temperature was increased to 40 and 70 °C, MIR was
promoted, leading to a significant amount of products
produced from either intra- or intermolecular MIR (entries 3
and 4 in Table 3). The higher the temperature, the more MIR
product. When the reaction temperature was kept at 70 °C, the
percentage of intermolecular products increased from 46.3 to
70.4 and 89.6% (entries 5−7 in Table 3) by carrying out the
reaction with a concentration of FpP at 2%, 5% and 10%,
respectively. On the basis of this investigation, migration
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Figure 6. 31P NMR spectrum for the reaction solution of FpP in 1/1 THF/hexane (1% by weight, 40 °C, 6 h).
Table 3. 31P NMR Analysis of Reaction Mixtures of FpP Solutions
a
rel conversion (%)
entry
solvent
temp (°C)
concentration (wt %)
time
1
2
3
1
2
3
4
5
6
7
hexane
THF
THF
THF
THF
THF
THF
25
25
40
70
70
70
70
1.0
1.0
1.0
1.0
2.0
5.0
10
7 days
7 days
6 h
93.5
99.8
76.0
51.8
13
2.8
0.1
3.7
0.08
12.8
36.8
40.7
21
11.2
4 h
11.40
46.3
70.4
89.6
4 h
4 h
8.6
4 h
5.0
5.4
a
1 and 2 represent intramolecular cyclic complexes, while 3 represents intermolecular MIP products, as shown in Scheme 1.
Figure 7. Solid-state 31P NMR (a), solid-state 13C NMR (b), and FT-IR (c) for the insoluble materials produced from solution MIP of FpP.
insertion polymerization of FpP is possible if an FpP solution
with a high concentration is heated at an elevated temperature.
Solution Polymerization. Solution polymerization of FpP
in THF with concentration of ca. 20% by weight was performed
at 70 °C. After the solution was heated for 1 h, it was noticed
that there was insoluble material produced and suspended in
the solution. The insoluble fraction was separated from the
THF solution via centrifugation at the end of the polymer-
ization. The clear supernatant was then added dropwise into
hexane, yielding pale yellow precipitates. The weight ratio of
these two fractions (insoluble to soluble products) is ca. 30:70.
The THF-insoluble fraction also appears to be the same color
E
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and looks similar to the THF-soluble products. The insoluble
polymers were characterized by using solid-state 31P NMR and
13C NMR. As shown in Figure 7a, 31P NMR reveals two peaks
at 73 and 37.8 ppm along with multiple spinning sidebands.
These two peaks can be assigned to the main-chain coordinated
phosphorus and the oxidized phosphine end group. The solid-
state 13C NMR spectrum is illustrated in Figure 7b. As shown
in the figure, the signals for the phenyl group appear at 125−
130 ppm; the peaks between 85 and 88 ppm are assigned to the
Cp ring. The resonance signal at 67 ppm is due to the carbon
next to the acyl group. The two peaks at 32 and 36 ppm, due to
C−P coupling, arise from the carbon adjacent to the
phosphorus. The carbon in the middle of the spacer appears
at 20 ppm. All of these assignments are similar to the
corresponding signals in the solution 13C NMR of THF-soluble
PFpP. However, the chemical shift for the carbonyl groups is
Figure 9. 13C−1H HMQC 2D NMR for PFpP.
1
invisible due to weak H−13C cross-polarization for carbonyl
diastereotopic. Expanded 13C NMR indicates that there are
double peaks at 29 ppm due to C−P coupling (c in Figure 9),
suggesting that this carbon is adjacent to the phosphorus. In
contrast, the peak at 20 ppm (b in Figure 9) is a singlet,
indicating a weak C−P coupling effect. Therefore, the peak at
20 ppm can be assigned to the carbon β to the iron center.
From the cross peaks observed in Figure 9, the signal at 1.9−
carbon. FT-IR was then used for the characterization. As shown
in Figure 7c, two peaks at 1898 and 1597 cm−1 are observed,
which correspond to the terminal carbonyl and migrated
carbonyl groups, respectively.31 The existence of these two
types of carbonyl groups suggests that the insoluble materials
are the products resulting from migratory insertion reactions.
The reason for the formation of insoluble PFpP is a matter for
further research.
1
2.2 ppm in H NMR can be assigned to the proton on the
The molecular weight of the THF-soluble fraction was
determined by GPC. As illustrated in Figure 8a, the GPC curve
carbon adjacent to PPh2, while the peak at 0.9−1.3 ppm is due
to the protons β to the iron center.
During the polymerization, samples were withdrawn at
certain intervals and used for 31P NMR analysis. 31P NMR
spectra are compared in Figure 10. Signal at −14.7 ppm is due
to the monomers (P0 in Figure 10a).31 The chain end
coordinated phosphorus for dimers and other species with DP
more than 2 can be distinguished in the 31P NMR. As
illustrated in the Figure, signal at 72.8 ppm can be assigned to
dimers (P1 in Figure 10a) and that at 72.6 ppm is due to PFpP
with DP larger than 2 (P2 in Figure 10a). As shown in the
Figure, with the progress of the polymerization, the peak at
−14.7 ppm gradually decreased, which is accompanied by
increased intensities for the peaks due to coordinated backbone
phosphorus suggesting polymerization occurred (Figure S3).
As shown in Figure 10b, dimers were preferentially formed as
indicated by the appearance of the signal at 72.8 ppm when the
solution was heated for 30 min. These dimers converted to
longer chains over time as indicated by increased intensities for
the peaks at 72.6 ppm (Figure 10b) and the peaks around 74
ppm due to the backbone phosphorus (Figure S3). As
expected, the monomer consumption is much faster than the
step-growth of the dimers. After polymerization for 5 h,
although over 90% of FpP was consumed, 50% of the
coordinated products are dimers as estimated from the
integration ratio between the signals at 72.8 and 72.6 ppm.
Small amount of dimers (16.6%) still remained in the solution
even all monomers were consumed after 19 h (Figure 10b).
The NMR analysis indicates that the polymerization follows a
typical step-growth mechanism.
Figure 8. GPC curve for PFpP (a) and 1H NMR of PFpP in DMSO-d6
produced via solution polymerization of FpP in THF (b).
exhibits a molecular weight of 4200 g/mol with a PDI value of
1
1.24. The polymer structure was characterized using H NMR
(Figure 8b). In 1H NMR, the chemical shifts at 7.8−7.1 and 4.3
ppm represent the phenyl groups and Cp rings in each Fp acyl
repeat unit. The integration ratio of these two peaks is 1:2,
which is in agreement with the expected structure. The signal at
4.8 ppm represents the Cp ring for the Fp end group of the
polymer. Intensities of the chemical shifts for Cp at 4.3 and 4.8
ppm are compared for end group analysis, suggesting that the
polymer has a DP value of 11. The molecular weight estimated
from the analysis is ca. 4400, which is in agreement with the
GPC results. Chemical shifts for the propyl spacer appeared
between 0.8 and 2.7 ppm.
CONCLUSION
■
Cyclcopentadienyldicarbonyl[(diphenylphosphino)propyl]iron
(FpP) was synthesized and fully characterized. In solution, FpP
undergoes both intra- and intermolecular reactions depending
on the conditions. Reactions with lower FpP concentration (ca.
1% by weight) at 25 °C favor the formation of five-membered
rings via CO release, while at a higher temperature (70 °C),
13C−1H HMQC 2D NMR was performed to assign the
signal for the propyl spacer. The correlation map shows that the
1
signals at 2.8 and 2.3 ppm in H NMR connect to the same
peak at 66 ppm due to the acyl group in 13C NMR (a in Figure
9), suggesting that the two protons from C(O)CH2 are
F
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Figure 10. Chemical structures for FpP, FpP dimer and PFpP with DP larger than 2 (P0, P1, P2 respectively correspond to phosphorus in FpP,
coordinated phosphorus in FpP dimer and terminal repeat unit of PFpP with DP larger than 2) (a); Intensities for chemical shifts in the 31P NMR at
−14.7 ppm (P0), 72.6 ppm (P1) and 72.8 ppm (P2) as a function of polymerization time (b).
decoupling with magic angle spinning was employed. The relaxation
time and spinning rate were 20 s and 5.2 kHz, respectively. The hpdec
program was used. A total of 2 K scans was accumulated. Chemical
shifts were determined with respect to the external signal for
ammonium dihydrogen phosphate at 0.81 ppm.
Fourier transform infrared spectroscopy (FT-IR) was carried out as
Nujol mulls between KBr plates using a Perkin-Elmer Spectrum RX I
FT-IR system.
Molecular weights and molecular distributions, Mw/Mn, were
characterized by GPC at room temperature with THF as eluent at a
flow rate of 1.0 mL/min on a system consisting of a Waters 510 HPLC
pump, Jordi DVB mixed-bed linear columns (500 mm × 10 mm,
molecular weight range 102−107), and a Waters 410 differential
refractometer detector. Calibration parameters were obtained using
standard polystyrene samples.
Single crystals suitable for X-ray diffraction analysis were mounted
onto the tips of glass fibers with a thick oil and transferred immediately
into the cold nitrogen gas stream of the diffractometer cryostat. X-ray
data were collected using Mo Kα radiation at 200 K on a Bruker
Kappa APEX II System (Madison, WI, USA). Structures were solved
using direct methods and refined by full-matrix least squares on F2
using the APEX2 package (v2012.4.0).
MIR was promoted, generating six-membered rings as major
products when the FpP concentration was low. Intermolecular
MIR was promoted by increasing the FpP concentration.
Polymerization of FpP in a highly concentrated solution (20%
by weight) was therefore performed at 70 °C, leading to both
THF-soluble and -insoluble polymers. Both soluble and
insoluble polymers appear similar in color. The soluble
polymers have Mn values of ca. 4200 with a PDI value of
1.24 as characterized by GPC. FT-TR and solid-state NMR
analysis of the insoluble products indicates that they were also
generated via migration insertion polymerization. These
comprehensive studies of FpP chemical reactions in solution
offer valuable fundamental knowledge required for further
exploration of the newly developed MIP.
EXPERIMENTAL SECTION
■
Materials and Instrumentation. All experiments were performed
under an atmosphere of dry nitrogen using either standard Schlenk
techniques or a glovebox unless otherwise indicated. THF was freshly
distilled under nitrogen from Na/benzophenone. Hexane was
degassed with dry nitrogen. Toluene was dried with molecular sieves
before use. Sodium (Na), 1-bromo-3-chloropropane, and potassium
(K) were purchased from Sigma-Aldrich. Cyclopentadienyliron
dicarbonyl dimer (Fp2) was purchased from Strem Chemicals Inc.
Chlorodiphenylphosphine was purchased from Tokyo Chemical
Industry (TCI). Benzophenone was purchased from Fisher Scientific.
All chemicals were used as received unless otherwise indicated.
1H, 31P, and 13C NMR and heteronuclear multiple quantum
coherence (HMQC) and correlation spectroscopy (COSY) spectra
were obtained on a Bruker Avance 300 (1H, 300 MHz; 31P, 120 MHz;
13C, 75 MHz) spectrometer at ambient temperature using the
appropriate solvents. NMR samples were prepared under an
atmosphere of dry nitrogen unless otherwise indicated.
Synthesis of Sodium Diphenylphosphide (Ph2PNa). Ph2PNa
was prepared by heating sodium and ClPPh2 at 40 °C for 3 days. The
resulting orange solution was directly used for further reactions. 31P
NMR (THF): −23 ppm.
Synthesis of 3-Chloropropyldiphenylphosphine. A 250 mL
Schlenk flask was charged with a solution of BrCH2CH2CH2Cl (7.87
g, 5.0 × 10−2 mol) in dry THF (50 mL). To this solution was added
Ph2PNa (0.5 M in THF solution; 60 mL, 3.0 × 10−2 mol) dropwise at
0 °C. The mixture was then warmed to room temperature and stirred
overnight. After the reaction, the solvent and excess BrCH2CH2CH2Cl
were removed at 60 °C for ca. 2 h under vacuum. The residue was
dissolved in a minimum amount of hexane and the solution filtered
through a silica gel column. Hexane was then removed under vacuum
1
Solid-state 13C NMR was performed on a Bruker Avance 500 (13C,
125 MHz) spectrometer at ambient temperature with cross-polar-
ization and magic angle spinning. The contact time and spinning rate
were 2 ms and 6.1 kHz, respectively. The pulse program cpramp was
used. A total of 2 K scans was collected. The low-frequency 13C signal
at 29.5 ppm from admantane was used as an external reference to
determine the chemical shifts.
at room temperature, yielding a colorless oil (5.52 g, 70% yield). H
NMR (CDCl3): 7.45 and 7.35 (d, 10 H, aromatic protons), 3.60 (t,
2H, CH2Cl), 2.20 (t, 2H, CH2P), 1.92 ppm (m, CH2CH2CH2). 31
NMR: −14.7 ppm.
P
Synthesis of FpP..44,45 A solution of Ph2PCH2CH2CH2Cl (1.01 g,
3.8 × 10−3 mol) in THF (5 mL) was added dropwise to an orange
suspension of FpK46 (1.00 g, 4.6 × 10−3 mol) in THF (25 mL) at 0
°C. The reaction flask was wrapped with aluminum foil in order to
exclude light. The mixture was stirred at room temperature for 2 h.
Solid-state 31P NMR spectra were recorded on a Bruker Avance 500
(31P, 202 MHz) spectrometer at ambient temperature. High-power
G
dx.doi.org/10.1021/om4010516 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
The THF was then removed under vacuum, and degassed hexane was
added to dissolve the crude product. The hexane solution was
transferred using a cannula into another Schlenk flask. After removing
solvent, an oil-like crude product was obtained. The oil was then
dissolved in a minimum amount of hexane/DCM (4/1, v/v) and the
solution filtered on a short silica gel column to remove dimers which
were formed during the reaction. The bright yellow solution was
collected, and solvents were subsequently removed under vacuum,
generating a bright yellow powder. The yellow powder was crystallized
from hexane at −49 °C to yield yellow crystals. Yield: 1.1 g (60%) 1H
NMR (DMSO-d6): 7.35 (t, 4 H, ortho C6H5), 7.32 (m, 6 H, para,
meta C6H5), 4.87 (s, 5H, C5H5), 2.07 (2H, PCH2), 1.46 ppm (4H,
FeCH2CH2). 1H NMR (C6D6): 7.61 (t, 4 H, ortho C6H5), 7.20 (m, 6
H, para, meta C6H5), 4.03 (s, 5H, C5H5),47 2.25 (t, 2H, PCH2), 1.80
(m, 2H, CH2CH2CH2), 1.64 ppm (t, 2H, Fe−CH2). 31P NMR
CH2CO); 31P NMR (CDCl3) 73.4, 72.3, and −13.6 ppm; FT-IR
1910 (terminal CO stretch), 1600 cm−1 (ketonic CO stretch).
ASSOCIATED CONTENT
■
S
* Supporting Information
Tables, figures, and CIF files giving crystal data for compounds
FpP, 1, and 2 (CCDC nos. 963926−963928) and 13C NMR
1
13C− H HMQC 2D NMR, and 31P NMR. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: bill.power@uwaterloo.ca (W.P.P.); xiaosong.wang@
uwaterloo.ca (X.W.).
(DMSO-d6): −14.7 ppm. 31P NMR (C6D6): −14.4 ppm. 13C NMR
2
(DMSO-d6): 5 (FpCH2,, 3JPC = 11.4 Hz), 32.5 (CH2CH2P(Ph)2, JPC
=
1
Notes
15.3 Hz), 34.3 (CH2P(Ph)2, JPC = 14 Hz), 87 (C5H4), 129, 132, 139
(Ph), 218 ppm (FeCO).44 FT-IR (Nujol mull): 2004 and 1952
cm−1 (terminal CO stretching).
The authors declare no competing financial interest.
Synthesis of Cyclopentadienyl(carbonyl)[3-(diphenylphos-
phanyl-κP)prop-1-yl]iron (1) from FpP. FpP was dissolved in THF
(concentration 10 mg/mL) and stirred at room temperature for 7 days
at room temperature. THF was subsequently removed under vacuum,
yielding an orange oil. The orange oil was chromatographed on a silica
gel column with hexane/ethyl acetate (10/1 v/v) as eluent. The yellow
band was collected, and the solvent was removed under high vacuum,
yielding an orange oil. The resulting oil was recrystallized from a
minimum amount of hexane at −49 °C. Yield: 70%. 1H NMR
(CDCl3): 7.76, 7.49, 7.33, and 7.15 (10H, C6H5), 4.21 (s, 5H, C5H5),
2.50 (m, 1H, PCH2), 2.30 (m, 1H, PCH2), 2.10 , (m, 1H,
CH2CH2CH2), 1.30 (m, 1H, CH2CH2CH2), 2.0 ppm (m, 2H,
FeCH2). 13C NMR (CDCl3): 36 (d, PCH2,1JPC3 = 31.2 Hz), 31 (d,
ACKNOWLEDGMENTS
■
X.W. is grateful for the financial support of the NSERC of
Canada and the University of Waterloo.
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CH2CH2CH2, JPC = 12.8 Hz), 12 (d, FeCH2, JPC = 10.9 Hz). 82.6
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