Synthesis, characterization, and reactivity of (π-allyl)palladium(II) wrap-around complexes with 1,3-dienes

Article abstract of DOI:10.1016/j.ica.2010.12.046

Synthesis of a series of cationic "wrap-around" complexes, η³-, η²- (CH₂-CH-CHR-CH ₂-CH₂-CHCHX) Pd(II)L⁺ (R = H, CH₃; X = H, Cl, CO₂Me; L = PPh₃, P(C₄H ₄N)₃), is described. These chelate complexes were prepared by exposure of π-allyl chloride dimers, (η³-(CH ₂-CX-CH₂)PdCl)₂, to either 1,3-butadiene or isoprene to yield π-allyl chloride dimers of the type (η³- CH₂CHCRCH₂CH₂CH = CH(X)PdCl)₂ which result from insertion of the diene into each π-allyl unit. Abstraction of chloride with either AgSbF₆ or NaB(Ar_F)₄ in the presence of L gives the cationic wrap-around complexes in high yields. Single crystal X-ray diffraction studies of 8a (R = -CH₃, X = -Cl, L = PPh₃) and 9a (R = -H, X = -Cl, L = PPh₃) show that Pd(II) adopts essentially a square planar geometry and the chelate arm occupies a syn orientation with respect to the allyl unit. Exposure of these wrap-around complexes to nitriles of differing basicities displaces the chelated alkene to varying extents and allows assessment of the relative strengths of chelation as a function of substituents, X and R. Initial rapid displacement of the chelated alkene yields a syn-π-allyl isomer which equilibrates with the anti-π-allyl isomer which cannot close to form a chelate. Treatment of 8b with 1,3-butadiene gives not polybutadiene but 2-chloro-4-methyl-1,E-4,6- heptatriene and 2-chloro-4-methyl-1,Z-4,6-heptatriene. Formation of these trienes is first-order in butadiene. This reaction serves as a model for chain-transfer in the polymerization of butadiene.

Full text of DOI:10.1016/j.ica.2010.12.046

Inorganica Chimica Acta 369 (2011) 150–158
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization, and reactivity of (
wrap-around complexes with 1,3-dienes
p-allyl)palladium(II)
Stephanie A. Urbin a, Tomislav Pintauer b, Peter White a, Maurice Brookhart a,
⇑
a Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
b Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA, USA
a r t i c l e i n f o
a b s t r a c t
3-,
g
2- (CH2–CH–CHR–CH2–CH2–CH@CHX)
Article history:
Available online 4 January 2011
Synthesis of a series of cationic ‘‘wrap-around’’ complexes,
g
Pd(II)L+ (R = H, CH3; X = H, Cl, CO2Me; L = PPh3, P(C4H4N)3), is described. These chelate complexes were
prepared by exposure of
prene to yield -allyl chloride dimers of the type (
from insertion of the diene into each -allyl unit. Abstraction of chloride with either AgSbF6 or NaB(ArF)4
p
-allyl chloride dimers, (
g
3-(CH2-CX-CH2)PdCl)2, to either 1,3-butadiene or iso-
3-CH2CHCRCH2CH2CH = CH(X)PdCl)2 which result
This manuscript is dedicated to our friend
and colleague, Prof. Robert Bergman, whose
remarkable insights, fortitude to tackle
tough problems, and experimental rigor
have led to numerous path-breaking
advances in organometallic and organic
chemistry.
p
g
p
in the presence of L gives the cationic wrap-around complexes in high yields. Single crystal X-ray diffrac-
tion studies of 8a (R = –CH3, X = –Cl, L = PPh3) and 9a (R = –H, X = –Cl, L = PPh3) show that Pd(II) adopts
essentially a square planar geometry and the chelate arm occupies a syn orientation with respect to
the allyl unit. Exposure of these wrap-around complexes to nitriles of differing basicities displaces the
chelated alkene to varying extents and allows assessment of the relative strengths of chelation as a func-
Keywords:
(p-Allyl)palladium(II)
pi-Allyl Pd(II)
Wrap-around complex
1,3-Diene insertion
tion of substituents, X and R. Initial rapid displacement of the chelated alkene yields a syn-
p-allyl isomer
which equilibrates with the anti- -allyl isomer which cannot close to form a chelate. Treatment of 8b
p
with 1,3-butadiene gives not polybutadiene but 2-chloro-4-methyl-1,E-4,6-heptatriene and 2-chloro-4-
methyl-1,Z-4,6-heptatriene. Formation of these trienes is first-order in butadiene. This reaction serves
as a model for chain-transfer in the polymerization of butadiene.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Akermark and Vitagliano showed that the cationic (
nyl)Pd(II) and (
3-neryl)Pd(II) complexes supported by acetonitrile
g
3-gera-
g
Allyl Pd(II) complexes containing a chelating olefinic group of
general structure A (‘‘wrap-around’’ complexes) have been formu-
lated as key intermediates in several reactions and have been iso-
lated and characterized by a number of groups. Complexes in
which n = 3 have been established as intermediates in the Pd(II)-
catalyzed telomerization of 1,3-butadiene (BD) in protic solvents
as well as in the Pd-catalyzed carbocyclization of 1-acetoxy-2,7-
dienes. In each case, complexes of type 1, in which the anion is
weakly coordinating (e.g. BF4ꢀ), have been isolated and shown to
be competent intermediates [1–3].
exist as an equilibrating mixture of three species as shown in
Scheme 1, with the ratio of wrap-around complex 2 to bis-nitrile
complexes 3-syn and 3-anti, dependent on the palladium to nitrile
ratio [3]. The g
3-neryl system possessing anti stereochemistry does
not form a chelate complex, and the authors propose the differing
propensities of these systems to form chelates may explain the dif-
fering regiochemistries of nucleophilic attack on the allyl moieties.
Nickel wrap-around complexes similar in structure to 1 have
played a role in Ni(II)-catalyzed diene polymerization reactions.
Taube has shown that ‘‘ligand-free’’ wraparound Ni(II) complexes
are highly reactive initiators for butadiene (BD) polymerization
[4]. We have previously spectroscopically observed (allyl)Ni
(g
4-butadiene)+, 4, at low temperatures and showed that this spe-
cies reacts rapidly with two equivalents of BD to generate a third
insertion, wrap-around complex 5 shown in Scheme 2 [5]. At high-
er temperatures, the third insertion product initiates polymeriza-
tion of BD and intermediates in the chain growth have been
identified [5,6].
Hughes and Powell studied the monomer/dimer equilibria
shown below and suggested that a wrap-around complex similar
to 7 may be involved in BD polymerization initiated by the nickel
dimer, [(allyl)Ni(O2CCF3)]2 (Scheme 3) [7].
⇑
Corresponding author.
E-mail address: mbrookhart@unc.edu (M. Brookhart).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.12.046

S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
151
Scheme 1. Displacement of g
2-olefin chelate by nitrile.
Scheme 4. Wrap-around Pd(II) complexes prepared.
Scheme 2. Ni(II) third insertion wrap-around complex 5.
The cationic, syn wrap-around complexes were characterized by
multinuclear NMR spectroscopy and elemental analyses (see Sec-
tion 4). The solid state structures of 8a and 9a were determined
by X-ray crystallography. ORTEP drawings for 8a and 9a are shown
in Figs. 1 and 2, respectively. The crystallographic information is
reported in Tables SI.1–SI.3 in the Supporting Information. The
X-ray structures confirm the syn geometry of the wrap-around
complexes and the g
2-binding of the chelating olefin arm and are
structurally similar to the geranyl chelate reported by Akermark
Scheme 3. Monomer/dimer equilibrium studied by Hughes et al. [7].
and Vitagliano, and also by Ciajolo [3,11].
Typical 1H NMR spectra for a selection of wrap-around com-
plexes are shown in Supporting Information (Fig. SI.1). The proton
spectra are similar to a wrap-around complex reported by Echavar-
ren and co-workers [12] and signal assignments are straightfor-
ward (these assignments appear in Section 4). Signals assigned to
We report here an investigation of simple Pd(II) wrap-around
complexes of type 1, with n = 2. These studies include the synthesis
and structural analysis of several simple derivatives of 1 and a
semi-quantitative analysis of the binding strength of the chelate
arm as a function of substituents on the alkene through analysis
of dynamic NMR spectra. Attempted use of these systems for diene
polymerization resulted in chain transfer and release of a 1,4,6-tri-
ene, suggesting that polymerization of dienes is not feasible with
the Pd systems in contrast to the Ni analogs.
the g
2-bound olefinic protons appear upfield of the chemical shift
of the corresponding free olefins, characteristic of an alkene–metal
interaction [13–15]. Additionally, low temperature NMR studies
(ꢀ90 °C) of each complex verified that there were no unexpected
fluxional processes occurring in these species.
2.2. Determination of olefin binding affinities by reaction of wrap-
around complexes with nitrile ligands
2. Results and discussion
2.1. Synthesis of and characterization of wrap-around complexes
The wrap-around complexes 8a–11a (Scheme 4) were synthe-
With the cationic palladium(II) wrap-around complexes in
hand, titration experiments were performed using various nitriles
to displace the
equilibrium between the wrap-around complexes and their nitrile
adducts provides relative binding strengths of the
2-olefins coor-
dinated to the metal in the wrap-around complexes. The effect of
varying the electronic properties of each
2-olefin, the phosphine
g
2-bound olefin. A quantitative assessment of the
sized starting with the [(g
3-H2CC(X)CH2)PdCl]2 dimer [8]. Func-
tional groups in the 2-position of the allyl unit (X = H, Cl,
COOMe) are readily incorporated by the use of the corresponding
2-substituted allyl chlorides. Selective insertion of a single diene
unit forms the corresponding dimeric complexes as a 50:50 mix-
ture of syn and anti isomers. The unsubstituted (X = H) syn/anti
isomers have been previously reported [9,10]. Subsequent halide
abstraction with NaB(ArF)4 or AgSbF6 at ꢀ78 °C and addition of a
phosphine ligand affords the cationic syn wrap-around complexes
in near quantitative yields (Scheme 5).
g
g
ligand, and the counterion were examined. The equilibrium con-
stants were quantified by monitoring the allylic, olefinic, and
methyl 1H NMR resonances and also the 31P NMR resonances.
These results reveal how readily the chelates open and thus may
offer insight into the ability of these wrap-around complexes to
react with less coordinating substrates.

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S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
Scheme 5. General synthetic route for Pd(II) wrap-around complexes.
Fig. 1. ORTEP diagram of 8a. Thermal ellipsoids drawn at 50% probability, SbFꢀ6 and
protons omitted for clarity. Selected bond lengths (Å): Pd(1)–C(7) 2.160(5),
Pd(1)–C(6) 2.183(5), Pd(1)–C(5) 2.275(5), Pd(1)–C(1) 2.294(5), Pd(1)–C(2),
2.340(5), C(1)–C(2) 1.369(8), C(5)–C(6) 1.420(8), C(6)–C(7) 1.403(8).
Fig. 2. ORTEP diagram of 9a. Thermal ellipsoids drawn at 50% probability, SbF6ꢀ
and protons omitted for clarity. Selected bond lengths (Å): Pd(1)–C(7) 2.129(7),
Pd(1)–C(6) 2.156(7), Pd(1)–C(5) 2.203(7), Pd(1)–C(1) 2.326(6), Pd(1)–C(2), 2.326(7),
C(1)–C(2) 1.342(10), C(5)–C(6) 1.373(12), C(6)–C(7) 1.417(11).
Upon addition of nitrile to the wrap-around complex A, the ni-
trile can displace the g
2-olefin to form the ‘‘open’’ complex B. Once
the wrap-around complex is open, it can undergo syn/anti isomer-
ization to form the open anti complex C, where the longer chain is
anti to the allylic proton (Hc) (Scheme 6).
computed from the weighted average resonance (see below). The
syn/anti isomerization from open syn complex B to anti-C, on the
other hand, is slow on the NMR time scale, and anti-C has a sepa-
rate, distinct Hc allylic resonance at 5.54 ppm. As more equivalents
of nitrile are added, more of the open complex B is formed, which
then in turn isomerizes to open complex C. At 1, 2, and 3 equiva-
lents of nitrile, the allylic resonance for C grows as more open com-
plex is formed and isomerized, until 8b is fully opened at five
equivalents of 3,5-bis(trifluoromethyl)benzonitrile. At long times,
the syn/anti ratio is constant and thermodynamically slightly
favors the syn form.
The opening/closing equilibria for these systems (interconver-
sion of A and B) are fast on the NMR time scale and therefore only
the time-averaged resonances are observed, whereas the syn/anti
isomerization is slow on the NMR time scale and the anti isomer
cannot form a stable wrap-around complex. This is clearly shown
by the olefinic, methyl, and allylic (Hc) resonances in the 1H NMR
spectra in Fig. 3, where 0, 1, 2, 3, and 5 equivalents of 3,5-bis(tri-
fluoromethyl)benzonitrile have been added to 8b. First, consider
the allylic central 1H signal, Hc. At zero equivalents of nitrile, 8b
is completely closed and Hc resonates at 6.19 ppm. Upon addition
of one equivalent of nitrile, the allylic resonance shifts upfield to
5.87 ppm, where this signal-averaged peak corresponds to 50:50
closed:open, or half A and half B. Subsequent additions of nitrile
shift the allylic resonance further upfield until, at five equivalents
of nitrile, 8b has fully converted from closed (A) to open (B) and
Hc resonates at 5.64 ppm. The equilibrium ratio of [A]:[B] can be
A similar phenomenon is observed with the olefinic resonances.
The
nate upfield at 4.73 and 4.46 ppm. Upon addition of nitrile, these
olefinic protons shift downfield as the nitrile displaces the
2-ole-
g
2-bound olefinic protons in wrap-around complex 8b reso-
g
fin and resonate at 5.17 and 5.13 ppm when full conversion to B is
achieved. The olefinic peaks for the anti open isomer, C, resonate at
5.24 and 5.23 ppm, characteristic of resonances for an unbound

S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
153
Scheme 6. Titration of wrap-around complexes with nitrile.
Fig. 3. Allylic, olefinic, and methyl regions of the 1H NMR spectra for the titration of 8b with 3,5-bis(trifluoromethyl)benzonitrile in CD2Cl2.
olefin. Finally, the methyl resonances exhibit the same behavior
and resonate at 1.78 ppm for the completely closed complex A,
1.67 ppm for the completely open complex B, and 2.03 ppm for
the anti open isomerized complex C for the 3,5-bis(trifluoro-
methyl)benzonitrile adduct.
out at this temperature, as evidenced by the broad peaks, it is clear
that the resonance at room temperature is indeed a time-averaged
signal between open and closed complexes A and B.
The equilibrium constants determined by the titration experi-
ments (Keq1 for the closed/open equilibrium and Keq2 for the syn/
anti isomerization equilibrium) can be estimated by monitoring
the resonances and integrations of the allylic, olefinic, and methyl
peaks in the 1H NMR and the phosphorus peaks in the 31P NMR for
the titration experiments. Since the resonances for A and B are
averaged, a weighted distribution calculation is used to determine
the relative amounts of [A] and [B] (see Section 4). The concentra-
tion of C is easily determined since it is not rapidly equilibrating
with the other isomers and yields sharp signals. From this informa-
tion Keq1 and Keq2 were determined (Eq. (1)). Since Keq1 involves
Examination of the fast exchange between closed and open
complexes A and B was possible through analysis of variable tem-
perature 31P NMR spectra recorded upon addition of 5, 10, and 20
equivalents of benzonitrile to wrap-around complex 10a. When
five equivalents of benzonitrile were added to wrap-around com-
plex 10a, a roughly 50/50 mixture of open and closed species
was generated (Fig. 4). The phosphorus resonance at 28.1 ppm
(23 °C), assigned to C, shifts upfield slightly to 27.6 ppm upon cool-
ing to ꢀ80 °C. The second 31P NMR peak at 27.1 ppm at room tem-
perature, assigned to the time-averaged signal for A and B,
broadens upon cooling, and decoalesces at temperatures lower
than ꢀ70 °C into two separate peaks as the fast exchange between
A and B is frozen out. At ꢀ80 °C, the resonance for the open com-
plex of 10a (B) is shifted downfield to 28.0 ppm. Conversely, the
resonance for the closed wrap-around complex A shifts upfield to
26.7 ppm towards the original phosphorus shift for the completely
closed wrap-around 10a, which resonates at 26.6 ppm. While the
exchange between bound and free olefin is not completely frozen
competitive binding between the
lated to the binding strength of the
thermodynamic ratio between the syn and anti isomers.
g
2-olefin and the nitrile, it is re-
2-olefin. Keq2 represents the
g
½Bꢁ
½Cꢁ
½Bꢁ
Keq1
¼
;
Keq2
¼
ð1Þ
½Nitrileꢁ½Aꢁ
The titration experiments were repeated with two other ni-
triles, acetonitrile and benzonitrile, and the equilibrium constants
for the opening of the wrap-around complex (Keq1) as well as the

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S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
Table 1
Equilibrium constants determined by titration of wrap-around complexes with 3,5-
bis(trifluoromethyl)benzonitrile.
a
a
Entry
Wrap-around complex
Keq1 (Mꢀ1
)
Keq2
1
2
3
4
5
6
7
9a
11a
8a
8b
8c
230
180
120
100
150
<3
<0.05
0.5
0.4
0.6
0.5
10a
10b
N/A
N/A
<3
a
Equilibrium constants were calculated at 25 °C.
incorporates P(NC4H4)3, which is a better
p-acceptor that PPh3,
and shows a more weakly coordinated alkene arm relative to the
analogous PPh3 complex (entry 3). A small counterion effect was
observed, with the more coordinating counterion, SbFꢀ6 , exhibitinꢀg
a slightly larger equilibrium constant, Keq1, than that of B(ArF)4
(compare entries 3 and 4).
Once the wrap-around is in the open form, B,
r–p isomerization
yields the mixture of the syn and anti open chain products, B and C,
respectively. The ratio of syn and anti isomers is nearly unaffected
by the substituents on the olefin arm, the type of phosphine, or the
counterion. The syn/anti equilibrium (Keq2) for all of the wrap-
around complexes is essentially the same (ca. 0.5) and slightly fa-
vors the less sterically hindered syn isomer, with two exceptions.
Wrap-around complex 9a favors the syn species exclusively at
room temperature and no isomerization is observed. This is attrib-
uted to the absence of a methyl group in the three position of the
allyl unit and the high steric preference of a substituent for the syn
Fig. 4. Variable temperature 31P NMR spectra of 10a plus five equivalents of
benzonitrile in CD2Cl2.
position relative to the anti position. Additionally, the
g
2-olefin
arm in wrap-around complexes 10a and 10b were never displaced
by excess bis(trifluoromethyl)benzonitrile as the olefin is very
strongly bound to the metal and the nitrile is a weak ligand.
syn/anti isomerization (Keq2) were determined for all wrap-around
complexes. With these two strongly coordinating nitriles, acetoni-
trile and benzonitrile, wrap-around complexes bearing electron-
withdrawing groups on the chelating olefinic moieties (8a–8c,
9a, 11a) are completely opened after the addition of 62 equiva-
lents of nitrile, whereas wrap-around complexes bearing elec-
2.3. Attempted polymerization of isoprene and butadiene by wrap-
around catalysts
tron-donating groups (10a–10c) exhibit a smaller Keq1 of 3 Mꢀ1
.
The weakly coordinating 3,5-bis(trifluoromethyl)benzonitrile al-
lows comparison of the equilibrium constants of all wrap-around
complexes (Scheme 7 and Table 1). A larger equilibrium constant
(Keq1) signifies a greater preference for the open complex B, with
Polymerization of 1,3-butadiene (BD) and isoprene (IP) was at-
tempted using wrap-around complexes 8a–8c, 10a, 10c, and 11a as
initiators in methylene chloride at room temperature and 50 °C for
20 h. Unfortunately, these reactions proceeded with very low con-
versions (2–12%) and produce only short chain oligomers, suggest-
ing that the rate of chain transfer is likely comparable to or faster
than the rate of propagation. Initial 1H NMR spectroscopic investi-
gations of the reactivity of wrap-around complexes with BD and IP
at 25 °C showed decomposition of the catalyst via disproportion-
ation to form a catalytically inactive bisphosphine species and pal-
ladium black upon monitoring after 20 h. As such, a closer
examination of the reactivity with 1,3-dienes and the mechanism
of chain transfer was undertaken by low temperature NMR
spectoscopy.
the
indicative of a more weakly bound
g
2-olefin being displaced by nitrile. Therefore, a large Keq1 is
g
2-olefin. Likewise, a smaller
Keq1 indicates a more strongly bound olefin.
The binding affinity of the olefin was studied as a function of
substituent X, the phosphine ligand, and the counteranion. It was
found that electron-withdrawing groups (X = CO2Me, Cl, entries
1–5) weaken the binding affinity of the g
2-wrap-around olefin, rel-
ative to the unsubstituted (X = H) systems (entries 6 and 7). Vary-
ing the phosphine ligand from PPh3 to P(NC4H4)3 also slightly
influences the binding affinity of the olefin. Complex 8c (entry 5)
Scheme 7. Wrap-around equilibrium with 3,5-bis(trifluoromethyl)benzonitrile.

S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
155
Scheme 8. Chain transfer and trapping of the new Pd(II) complex.
2.4. Chain transfer with wrap-around catalysts
Table 2
Influence of [BD] on the rate of chain transfer for complex 8b.
Addition of butadiene to 8a or 8b in an in situ NMR experiment
resulted in chain transfer and formation of the triene 12 and trap-
Equivalents BD
Temperature (°C)
Rate (sꢀ1
)
5
10
20
ꢀ45
ꢀ45
ꢀ45
0.8 ꢂ 10ꢀ3
1.2 ꢂ 10ꢀ3
2.9 ꢂ 10ꢀ3
ping of one equivalent of BD to form a new crotyl
p-allyl palla-
dium(II) complex 13 at temperatures above ꢀ55 °C (Scheme 8).
The crotyl complex 13 could not be isolated due to the labile nature
of the solvent or diene in the fourth coordination site. However,
trapping with triphenylphosphine yielded the bisphosphine com-
plex 14, which has been independently synthesized to confirm
the 1H and 31P NMR spectral assignments of the in situ generated
species. The organic product was isolated by vacuum removal of
CD2Cl2 at ꢀ30 °C, extraction of the nonpolar triene product from
the residue by cyclohexane-d12, and then characterized by NMR
spectroscopy and mass spectrometry (see Section 4 for details).
The chain transfer organic product, 12, exists as a mixture of E
and Z isomers in a 2:1 ratio, respectively. Two characteristic allylic
peaks for each isomer resonate in the 1H NMR spectrum at d 6.65
and 5.48 for the E isomer, and at d 6.33 and 5.39 for the Z isomer.
Additionally, each isomer has a distinct resonance for the methyl
group, appearing at d 1.72 and 1.83 for the E and Z isomers,
respectively.
rate dependence on [BD] is observed for the chain transfer event.
This is in contrast to previous findings for -allyl Ni(II) systems,
where the rate of chain transfer in butadiene polymerization reac-
tions is independent of the concentration of diene [4].
These differences suggest that, while the
are highly active for BD and IP polymerization, the
systems suffer from a fast rate of chain transfer relative to the rate
of polymerization, resulting in dimerization or oligomerization of
BD and IP for the analogous Pd(II) systems.
p
p
-allyl Ni(II) systems
p-allyl Pd(II)
3. Summary
Syntheses and characterizations of several easily-tunable wrap-
around complexes 8a–8c, 9a, 10a–10c, and 11a have been
described (see Scheme 5). Single crystal X-ray structural determi-
nations of 8a and 8a reveal 16-electron
chelating olefin arm. The
The kinetics of this chain transfer process were studied by 1H
NMR spectroscopy. In a typical experiment, a screw-cap NMR tube
was charged with a methylene chloride-d2 solution of 8b and 5–20
equivalents of BD at ꢀ45 °C and monitored for 35 min. To deter-
mine the order in [BD], the observed rate constants for chain trans-
fer were measured over several diene concentrations while holding
the initial concentration of 8b constant. The results of these exper-
iments are shown in Fig. 5 and summarized in Table 2. A first-order
p-allyl complexes with a
g
2-chelating olefin arm can be displaced
by nitriles of varying strengths via titration of a solution of wrap-
around complex with various equivalents of nitriles. These titra-
tion experiments lend insight into the relative binding affinity of
the chelating olefin arm. Electron-withdrawing substituents on
the olefin (X = –COOMe, –Cl) allowed for facile displacement of
the
g
2-olefin by nitrile, whereas an unsubstituted vinyl group
10 equiv BD
was more strongly bound to the palladium center and could not
be effectively displaced by nitrile. Counterion and phosphine sub-
stituent effects were relatively minor and had very little influence
on the binding affinity of the olefin arm. Attempted catalytic poly-
merization of isoprene and 1,3-butadiene by wrap-around com-
plexes yielded short chain oligomers with very poor conversions
and catalyst decomposition. Low temperature NMR analysis shows
wrap-around 8b reacts with butadiene at ꢀ55 °C in what corre-
sponds to a chain transfer process to yield a triene and a methallyl
complex. This process was examined kinetically and found to be
first-order in [BD], in contrast to the zero-order butadiene depen-
dence of the chain transfer process found for polymerization of
0
0
500
1000
1500
-1
-2
-3
-4
-5
-6
-7
y = -0.0012x - 3.7549
R2 = 0.9975
time (sec)
butadiene by ligand-free (p-allyl)Ni(II) complexes. The fast rate
of chain transfer for these Pd(II) systems adequately explains the
Fig. 5. Kinetic plot of the disappearance of the wrap-around complex 8b over time
upon addition of 10 equivalents of 1,3-butadiene.
lack of polymerization activity for BD and IP.

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S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
4.4. General numbering scheme
4. Experimental
4.1. General considerations
4.4.1. [Pd(IP-2Cl)PPh3][SbF6] (8a)
All reactions, unless otherwise stated, were conducted under an
atmosphere of dry, oxygen free argon using standard high-vacuum,
Schlenk, or drybox techniques. Argon was purified by passage
through columns of BASF R3-11 catalyst (Chemalog) and 4 Å
molecular sieves. Palladium catalysts were stored in an MBraun
glovebox at ꢀ35 °C to prevent thermal decomposition. 1H, 31P,
and 13C NMR spectra were recorded on a Bruker DRX 500 MHz or
a Bruker DRX 400 MHz spectrometer. Chemical shifts were refer-
enced relative to residual CHCl3 (d 7.24 for 1H) and CH(D)Cl2 (d
5.32 for 1H), CD2Cl2(d 53.8 for 13C), CDCl3 (d 77.0 for 13C). Assign-
ments were supported by 1H–13C HMQC, 1H–1H COSY, and NOESY
experiments. Elemental analyses were carried out by Atlantic
Microlab, Inc., of Norcross, GA. GPC analyses were performed in
HPLC grade tetrahydrofuran at 25 °C using a Waters Alliance HPLC
equipped with Waters Styragel HR2, HR4, and HR5 columns and a
Waters 410 refractive index detector. Molecular weights are re-
ported relative to polystyrene standards. The crystallographic
information for 1a and 2a is reported in Appendix A. The data
was obtained on a Bruker SMART APEX-2 X-ray diffractometer a
The general procedure was employed using [(IP-2-Cl-p-allyl)PdCl]2
(0.200 g, 0.460 mmol), triphenylphosphine (0.190 g, 0.74 mmol),
and silver hexafluoroantimonate (0.250 g, 0.74 mmol). Yield:
0.365 g (64%). 1H{31P} NMR (400 MHz, CD2Cl2, 25 °C): d 7.40–7.70
3
3
(m, 15H, PPh3), 6.24 (dd, JHHsyn = 13 Hz, JHHanti = 7.6 Hz, 1H, H3),
3
4.93 (s, 1H,
H10), 4.41 (s, 1H, H11), 4.04 (dd, JHH = 16 Hz,
3JHH = 12 Hz, JHH = 4.0 Hz, 1H, H8), 3.66–3.76 (m, 2H, H6+H2),
3.32–3.42 (m, 2H, H1+H7), 2.76 (m, 1H, H5), 1.87 (s, 3H, R4 = CH3).
31P{1H} NMR (160 MHz, CD2Cl2, 25 °C): d 28.7. 13C{1H} NMR
3
ꢀ173 °C using Mo K
a radiation.
3
(100 MHz, CD2Cl2, 25 °C): d 20.8 (d, JCP = 3.7 Hz, C4), 45.2 (s, C5),
4.2. Materials
49.3 (d, J = 5.0 Hz, C6), 61.3 (s, C1), 90.2 (s, C8), 116.0 (d, J = 3.7 Hz,
3
C2), 130.3 (d, C9), 129.9 (d, JCP = 10.8 Hz, PPh3), 132.1 (d,
All solvents were deoxygenated and dried by passage over col-
umns of activated alumina [16,17]. Isoprene and 1,3-butadiene
were purchased from Aldrich and purified by vacuum transfer
through 4 Å molecular sieves and stored over 4 Å molecular sieves
at ꢀ35 °C under argon. Methylene chloride-d2 and chloroform-d
were purchased from Cambridge Isotope Laboratories and stored
over 4 Å molecular sieves. NaB(ArF)4 was purchased from Boulder
Scientific. Allyl chloride, allyl bromide, AgSbF6, PdCl2, LiCl, and trip-
yrrolidinylphosphine were purchased from Aldrich and used as re-
ceived. Tripyrrolylphosphine was prepared according to literature
2
4JCP = 2.1 Hz, PPh3), 133.8 (d, JCP = 13.1 Hz, PPh3), 139.3 (d,
2JCP = 19.2 Hz, C3), 145.2 (s, C7). Anal. Calc. for C26H27PClPdSbF6
(748.12): C, 41.74; H, 3.65. Found: C, 42.15; H, 3.67%.
4.4.2. [Pd(IP-2Cl)PPh3][B(ArF)4] (8b)
The general procedure was employed using [(IP-2-Cl-p-allyl)
PdCl]2 (0.200 g, 0.460 mmol), triphenylphosphine (0.190 g,
0.74 mmol), and NaB(ArF)4 (0.620 g, 0.74 mmol). Yield: 0.698 g
(72%). 1H NMR (400 MHz, CD2Cl2, 25 °C): d 7.4–7.6 (m, 15H, PPh3),
3
3
methods [18]. The
p-allyl palladium halide dimers were synthe-
6.18 (dd, JHHsyn = 13.2 Hz, JHHanti = 7.4 Hz, 1H, H3), 1.79 (d,
4JHP = 5.2 Hz, 3H, R4 = CH3), 4.73 (s, 1H, H10), 4.46 (d, JHH = 5.6 Hz,
3
sized according to literature procedures [11].
3
3
1H, H11), 3.86 (td, JHH = 4.0 Hz, JHH = 13.8 Hz, 1H, H8), 3.70 (dd,
1H, H2), 3.68 (m, 1H, H7), 3.35 (dd, 2JHH = 2.4 Hz, 3JHH = 13.2 Hz, 1H,
H1), 3.34 (m, 1H, H6), 2.73 (m, 1H, H5). 31P{1H} NMR (160 MHz,
CD2Cl2, 25 °C): d 26.9. 13C{1H} NMR (126 MHz, CD2Cl2, 25 °C): d
4.3. (Allyl)Pd(II) complex synthesis
4.3.1. Synthesis of [(IP-2-Cl-p-allyl)PdCl]2
1
162.0 (q, JCB = 49.8 Hz, B(ArF)4 Cipso), 145.2 (s, C7), 138.2 (d, C3),
Under an argon atmosphere, [(2-Cl-
p-allyl)PdCl]2 (0.600 g,
2
135.2 (s, B(ArF)4 Co), 133.8 (d, JCP = 13.0 Hz, Ph3), 132.3 (d,
1.38 mmol) and excess isoprene (6.3 mL, 69.0 mmol) were dis-
solved in dry methylene chloride (40 mL). The solution was
allowed to stir for ca. 30 min at room temperature until one equiv-
alent of diene had inserted into the palladium-allyl bond as deter-
mined by 1H NMR analysis. The solvent was removed in vacuo to
yield the dimer as a yellow oil. The product was washed with
dry pentane (3 ꢂ 20 mL) to yield the product as an isolable powder.
Yield: 0.702 g (89%).
4JCP = 2.4 Hz, Ph3), 130.1 (d, C9), 129.9 (d, 3JCP = 10.8 Hz, Ph3), 129.2
2
(q, JCF = 31.5 Hz, B(ArF)4 Cm), 128.3, 126.1, 123.9, 121.8 (q,
1JCF = 272.9 Hz, B(ArF)4 CF3), 117.9 (B(ArF)4 Cp), 116.1 (s, C2), 90.3
(s, C8), 61.2 (s, C1), 49.2 (s, C6), 45.0 (s, C5), 20.8 (s, C4). Anal. Calc.
for C58H39PClPdB(ArF)4 (1375.62): C, 50.64; H, 2.86. Found: C,
50.61; H, 2.89%.
4.4.3. [Pd(IP-2Cl)P(NC4H4)3][SbF6] (8c)
4.3.2. General procedure for the synthesis of complexes 8a–8c
The general procedure was employed using [(IP-2-Cl-p-al-
Under an argon atmosphere, [(IP-2-Cl-
p
-allyl)PdCl]2 and two
lyl)PdCl]2 (0.150 g, 0.26 mmol), tripyrrolylphosphine (0.120 g,
0.53 mmol), and silver hexafluoroantimonate (0.180 g, 0.53 mmol).
Yield: 0.295 g (78%). 1H NMR (400 MHz, CD2Cl2, 25 °C): d 6.83 (s,
6H, P(NC4H4)3), 6.54 (s, 4H, P(NC4H4)3), 6.31 (m, 1H, H3), 1.92 (d,
equivalents triphenylphosphine were dissolved in dry methylene
chloride (20 mL) and the resulting yellow solution was stirred at
room temperature for 5 min. A solution of two equivalents silver
hexafluoroantimonate in 5 mL methylene chloride was then added
via cannula at ꢀ78 °C and the mixture was stirred for an additional
hour at this temperature before the solution was allowed to slowly
warm to room temperature. The resulting solution was filtered
through celite and the solvent evaporated in vacuo. The product
was washed with 3 ꢂ 10 mL of dry pentane and dried under
vacuum to yield a yellow powder.
3
4JHP = 7.2 Hz, 3H, R4 = CH3), 5.11 (s, 1H, H10), 4.43 (d, JHH = 6.8 Hz,
3
3
1H, H11), 3.96 (td, JHH = 12.8 Hz, JHH = 3.2 Hz, 1H, H8), 4.23 (dd,
3JHH = 7.6 Hz, JHH = 2.4 Hz, 1H, H2), 3.68 (m, 1H, H7), 3.67 (d,
2
3JHH = 12.8 Hz, 1H, H1), 3.28 (m, 1H, H6), 2.78 (m, 1H, H5), 1.96 (s,
3JHP = 7.2 Hz, 3H, R4 = CH3). 31P{1H} NMR (160 MHz, CD2Cl2,
25 °C): d 95.2. Anal. Calc. for C20H24PClN3PdSbF6 (714.79): C,
33.59; H, 3.39. Found: C, 33.66; H, 3.36%.

S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
157
4.4.4. [Pd(BD-2Cl)PPh3][SbF6] (9a)
The general procedure was employed using [(2-Cl-
4.4.8. [Pd(IP-2H)P(NC4H4)3][SbF6] (10c)
p
-allyl)
The general procedure was employed using AgSbF6 (0.274 g,
0.797 mmol). Yield: 0.360 g (66%). 1H NMR (300 MHz, CD2Cl2,
25 °C): d 6.83 (s, 6H, P(NC4H4)3), 6.54 (s, 4H, P(NC4H4)3), 6.71 (m,
PdCl]2 (2.63 mmol) and excess butadiene (6.22 g, 0.115 mol) to
form the isolable butadiene inserted palladium chloride dimer.
For the second step, [Pd(BD-2Cl)Cl]2 (0.100 g, 0.18 mmol), triphen-
ylphosphine (0.097 g, 0.37 mmol) and AgSbF6 (0.127 g, 0.37 mmol)
were used. Yield: 0.214 g (79%). 1H{31P} NMR (400 MHz, CD2Cl2,
1H, R9 = H), 6.48 (m, 1H, R9 = H), 6.40 (dd, 3JHHsyn = 16.8 Hz, 3JHHanti
=
7.5 Hz, 1H, H3), 4.71 (d, 3JHH = 16.8, 1H, H10), 4.44 (dd, 3JHH = 8.1 Hz,
3
3JHH = 8.1 Hz, 1H, H11), 4.12 (d, JHH = 7.5, 1H, H2), 3.53–3.40 (m,
3
3
25 °C): d 7.4–7.6 (m, 15H, PPh3), 6.34 (dt, JHHsyn = 12 Hz, JHHanti
=
peak overlap, 3H, H1+ H7+H8), 3.20 (m, 1H, H6), 2.74 (pt, 1H, H5),
1.82 (d, 3JHP = 7.2 Hz, 3H, R4 = CH3). 31P{1H} NMR (160 MHz, CD2Cl2,
25 °C): d 95.7.
3
3
6 Hz, 1H, H3), 6.04 (dt, JHH = 12 Hz, JHH = 4.0 Hz, 1H, R4 = H), 5.11
(s, 1H, H10), 4.48 (s, 1H, H11), 4.00 (td, 3JHH = 13.6 Hz, JHH = 4.4 Hz,
3
3
2
1H, H8), 3.73 (dd, JHH = 7.0 Hz, JHH = 2.0 Hz, 1H, H2), 3.51 (m, 1H,
3
H7), 3.45 (d, JHH = 12.8 Hz, 1H, H1), 3.26 (m, 1H, H6), 2.86 (m, 1H,
4.4.9. [Pd(IP-2COOMe)(PPh3)][SbF6] (11a)
H5). 31P{1H} NMR (160 MHz, CD2Cl2, 25 °C): d 26.4. Anal. Calc. for
C25H24PClPdSbF6 (733.08): C, 40.96; H, 3.31. Found: C, 41.01; H,
3.53%.
The general procedure was employed using [(2-COOMe-p-allyl)
PdCl]2 (0.200 g, 0.83 mmol), triphenylphosphine (0.436 g,
1.66 mmol) and AgSbF6 (0.571 g, 1.66 mmol). Yield: 0.795 g
(62%). 1H{31P} NMR (400 MHz, CD2Cl2, ꢀ40 °C): d 7.30–7.70 (m,
3
3
15H, PPh3), 6.28 (dd, JHHsyn = 13 Hz, JHHanti = 7.6 Hz, 1H, H3),
4.4.5. General procedure for the synthesis of complexes 10a–10c and
11a
3
5.11 (s, 1H, H10), 4.85 (s, 1H, H11), 3.84 (d, JHH = 7.4 Hz, 1H, H2),
3.66 (m, 1H, H8), 3.57 (s, 3H, R9 = COOCH3), 3.40–3.55 (m, 2H,
Under an argon atmosphere, [(p-allyl)PdBr]2 (0.200 g,
3
3
H7+H6), 3.12 (d, JHH = 12.8 Hz, 1H, H1), 2.61 (pt, JHH = 11 Hz, 1H,
H5), 1.78 (s, 3H, R4 = CH3). 31P{1H} NMR (160 MHz, CD2Cl2, 25 °C):
d 27.9. Anal. Calc. for C28H30O2PPdSbF6ꢃ2 CH2Cl2 (941.58): C,
38.26; H, 3.65. Found: C, 38.20; H, 3.68%
0.40 mmol) was dissolved in dry methylene chloride (20 mL) and
then an excess of isoprene (2.3 mL, 23.0 mmol) was added. The
solution was allowed to stir for 1–2 days until one equivalent of
diene had inserted into the palladium-allyl bond as monitored by
1H NMR spectroscopy. The solvent was removed in vacuo to yield
the dimer as a yellow oil which was not isolated but was carried
on directly to the next step. The dimer and triphenylphosphine
(0.209 g, 0.80 mmol) were dissolved in dry methylene chloride
(20 mL) and the resulting yellow solution was stirred at room tem-
perature for 5 min. Next, two equivalents silver hexafluoroantimo-
nate or NaB(ArF)4 were added at ꢀ78 °C and the mixture was
stirred for an additional hour before the solution was allowed to
slowly warm to room temperature. The resulting solution was fil-
tered through celite and the solvent evaporated in vacuo. The prod-
uct was washed with 3 ꢂ 10 mL of dry pentane and dried under
vacuum to yield a yellow powder.
.
4.4.10. Characterization of the organic chain transfer product 12
Addition of 1,3-butadiene to 8a or 8b resulted in chain transfer
and formation of the organic product and a new palladium(II) allyl
complex (Scheme 8). The organic product was isolated by vacuum
removal of the solvent at ꢀ30 °C, dissolved in cyclohexane-d12, and
characterized by NMR and ESI+ mass spectrometry. The ratio of E–
4.4.6. [Pd(IP-2H)PPh3][SbF6] (10a)
The general procedure was employed using AgSbF6 (0.274 g,
0.80 mmol). Yield: 0.623 g (78%). 1H NMR (400 MHz, CD2Cl2,
3
25 °C): d 7.30–7.70 (m, 15H, PPh3), 6.24 (dd, JHHsyn = 12.8 Hz,
3JHHanti = 7.4 Hz, 1H, H3), 6.48 (m, 1H, R9 = H), 4.52 (d, JHH = 16.8,
3
Z
isomers was 2:1. Characterization of
E
isomer: 1H NMR
3
3
1H, H10), 4.34 (dd, JHH = 7.6 Hz, JHH = 7.7 Hz, 1H, H11), 3.59 (d,
3
3
(500 MHz, C6D12, 25 °C): d 6.65 (dd, JH3–H1 = 10.5 Hz, JH3–H2
=
3
3JHH = 7.4, 1H, H2), 3.30 (d, JHH = 12.8 Hz, 1H, H1), 3.26–3.39 (m,
17.5 Hz, 1H, H3), 5.48 (dd, JHH = 7.5 Hz, JHH = 7.5 Hz, 1H, H5),
3
3
2H, H7+H6), 3.15 (m, 1H, H8), 2.71 (pt, 1H, H5), 1.73 (d, 3JHP = 4.4 Hz,
3H, R4 = CH3). 31P{1H} NMR (160 MHz, CD2Cl2, 25 °C): d 26.6.
13C{1H} NMR (126 MHz, CD2Cl2, 25 °C): d 20.6 (s, C4), 42.1 (d,
J = 4.8 Hz, C6), 46.2 (s, C5), 61.1 (s, C1), 92.3 (s, C8), 116.4 (d,
5.10 (d, JHH = 17.5 Hz, 1H, H2), 5.08 (s, 1H, H8), 5.03 (s, 1H, H9),
3
4.94 (d, 3JHH = 10.5 Hz, 1H, H1), 3.11 (dd, 3JHH = 9.5 Hz, 3JHH = 9.5 Hz,
1H, H6+H7), 1.72 (s, 3H, CH34). Characterization of Z isomer: 1H
3
NMR (500 MHz, C6D12
,
25 °C):
d
6.33 (dd, JH3–H1 = 10.5 Hz,
3
2JCP = 3.7 Hz, C2), 129.8 (d, JCP = 10.6 Hz, PPh3), 130.6 (d,
3JH3–H2 = 17.5 Hz, 1H, H3), 5.39 (dd, JHH = 7.5 Hz, JHH = 7.5 Hz,
3
3
4
1JCP = 43.8 Hz, PPh3), 114.0 (d, JCP = 2.4 Hz, PPh3), 132.3 (s, C7),
1H, H5), 5.21 (d, JHH = 17.5 Hz, 1H, H2), 5.08 (s, 1H, H8), 5.03 (s,
3
2
2
133.7 (d, JCP = 13.0 Hz, PPh3), 140.1 (d, JCP = 19.9 Hz, C3). Anal.
Calc. for C26H28PPdSbF6 (712.65): C, 43.75; H, 3.96. Found: C,
43.56; H, 4.00%.
3
3
1H, H9), 5.00 (d, JHH = 10.5 Hz, 1H, H1), 3.11 (dd, JHH = 9.5 Hz,
3JHH = 9.5 Hz, 1H, H6+H7), 1.83 (s, 3H, CH34). ESI-MS (metha-
nol:cyclohexane (50:1), +ion scan, m/z): 142.1 Da (expected:
142.055 Da).
4.4.7. [Pd(IP-2H)PPh3][B(ArF)4] (10b)
The general procedure was employed using NaB(ArF)4 (0.706 g,
0.80 mmol). Yield: 0.936 g (64%). 1H NMR (400 MHz, CD2Cl2,
25 °C): d 7.30–7.70 (m, 15H, PPh3), 7.63 and 7.52 (s and s, 12H,
4.4.11. In situ generated methallyl phosphine complex 13
A
screw-cap NMR tube was charged with 8b (0.028 g,
0.021 mmol) dissolved in 500 L CD2Cl2. Two equivalents of 1,3-
l
3
3
B(ArF)4), 6.11 (dd, JHHsyn = 14.8 Hz, JHHanti = 7.4 Hz, 1H, H3), 6.36
butadiene were then added at low temperature. The chain transfer
reaction was monitored via 1H NMR for 50 min, at which point all
of the original starting wrap-around complex 8b had undergone
chain transfer and insertion of one equivalent of 1,3-butadiene
3
(m, 1H, R9 = H), 4.49 (d, JHH = 16.4 Hz, 1H, H10), 4.35 (dd,
2
3
3JHH = 7.6 Hz, 1H, H11), 3.59 (dd, JHH = 2.4 Hz, JHH = 7.4 Hz, 1H,
3
H2), 3.3 (m, 3H, H8+H7+H6), 3.11 (d, JHH = 14.8 Hz, 1H, H1), 2.64
(pt, 1H, H5), 1.69 (d, JHP = 4.4 Hz, 3H, R4 = CH3). 31P{1H} NMR
formed the (p-methallyl)Pd(triphenylphosphine)(solvent or diene)
3
(160 MHz, CD2Cl2, 25 °C): d 26.9. Anal. Calc. for C58H40PPdB(ArF)4
(1339.75): C, 51.94; H, 3.01. Found: C, 51.35; H, 2.89%.
complex 13. 1H NMR (400 MHz, CD2Cl2, ꢀ45 °C): d 7.50–7.30 (m,
15H, PPh3), 5.72 (m, Hc, 1H), 4.42 (m, H1, 1H), 3.97 (d, 3JHH = 4.8 Hz,

158
S.A. Urbin et al. / Inorganica Chimica Acta 369 (2011) 150–158
3
Hsyn, 1H), 2.83 (d, JHH = 12.4 Hz, Hanti, 1H), 1.98 (bs, CH3, 3H).
31P{1H} NMR (160 MHz, CD2Cl2, ꢀ45 °C): d 27.7 (bs, PPh3).
and the observed signal averaged peak (closed M open) were re-
corded, Eq. (2) was employed to determine the fraction of the
closed (A) and open (B + C) complexes. The concentration of closed
and open was then determined by multiplying the respective frac-
tion by the total palladium(II) concentration, calculated from the
initial moles of palladium(II) wrap-around complex added over
the total solution volume and taking into account the added nitrile.
From the total open concentration [B + C], the concentrations of B
and C were calculated from their respective integrals. With all
these known values, the equilibria constants Keq1 and Keq2 were
determined.
4.4.12. In situ generated methallyl bisphosphine complex 14
screw-cap NMR tube was charged with 8b (0.028 g,
0.021 mmol) dissolved in 500 L CD2Cl2. Two equivalents of 1,3-
butadiene were added at low temperature, and the chain transfer
reaction was monitored at ꢀ20 °C via 1H NMR for 50 min, at which
point all of the original starting wrap-around complex 8b had
undergone chain transfer and formed the (p-methallyl)Pd(triphen-
ylphosphine)(solvent or diene) complex 13. Then, one equivalent
A
l
of triphenylphosphine (5.5 mg, 0.021 mmol) was added via syringe
dobs ¼ ð1:00 ꢀ FopenÞAclosed þ ðFopenÞBopen
to the solution to form the (p-methallyl)Pd(PPh3)2 complex 14.
Only the major isomer was observed. 1H NMR (400 MHz, CD2Cl2,
25 °C): d 7.50–7.10 (m, 30H, PPh3), 5.63 (m, Hc, 1H), 4.26 (m, H1,
h
i h
i
Fopen
¼
dobs ꢀ Aclosed = Bopen ꢀ Aclosed
ð2Þ
3
1H), 3.53 (dd, JHH = 6.4 Hz, JHP = 6.4 Hz, Hsyn
,
1H), 3.21 (dd,
3JHH = 10.4 Hz, JHP = 10.4 Hz, Hanti, 1H), 1.05 (m, CH3, 3H). 31P{1H}
NMR (160 MHz, CD2Cl2, 25 °C): d 26.4 (d, JPP = 40.7 Hz, PPh3),
25.5 (d, JPP = 40.7 Hz, PPh3).
2
2
A
closed = d for starting complex or d when completely closed
(olefin is g2 bound to form the wrap-around); Bopen = d when the
complex is completely ‘‘open’’; Fopen = fraction of complex (out of
1.00 total) that is ‘‘open’’.
4.4.13. Synthesis of methallyl bisphosphine complex 14
In a Schlenk tube under an argon atmosphere, [(p-methal-
lyl)PdCl]2 (0.100 g, 0.254 mmol) and four equivalents of triphenyl-
phosphine (0.266 g, 1.02 mmol) were dissolved in dry methylene
chloride (20 mL) and then cooled in a dry ice/isopropyl alcohol
bath to ꢀ78 °C. A solution of two equivalents silver hexafluoroan-
timonate (0.150 g, 0.440 mmol) in 5 mL methylene chloride was
then added dropwise at ꢀ78 °C and the mixture was stirred for
ca. 30 min at low temperature before the solution was allowed to
warm slowly to room temperature. The resulting solution was can-
nula filtered and the solvent evaporated in vacuo. The product was
washed with 3 ꢂ 10 mL of pentane and dried under vacuum to
yield the product as a yellow powder. Yield: 0.375 g (80%). The ra-
tio of major (syn) to minor (anti) product was 12:1. Characteriza-
tion of major (syn) isomer: 1H NMR (400 MHz, CD2Cl2, 25 °C): d
7.50–7.10 (m, 30H, PPh3), 5.63 (m, Hc, 1H), 4.26 (m, H1, 1H), 3.53
Acknowledgments
We thank the National Science Foundation (CHE-0615794 and
CHE-1010170) for financial support for this work. We also appreci-
ate helpful discussions with Dr. Marc Walter and Dr. Abby
O’Connor.
Appendix A. Supplementary material
CCDC 804318 and 804319 contains the supplementary crystal-
lographic data for structures 8a and 9a, respectively. These data
can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.12.046.
3
3
(dd, JHH = 6.4 Hz, JHP = 6.4 Hz, Hsyn, 1H), 3.21 (dd, JHH = 10.4 Hz,
JHP = 10.4 Hz, Hanti, 1H), 1.05 (m, CH3, 3H). Characterization of min-
or (anti) isomer: 1H NMR (400 MHz, CD2Cl2, 25 °C): d 7.50–7.10 (m,
30H, PPh3), 5.63 (m, Hc, 1H, overlap with major isomer), 4.79 (m,
H1, 1H), 4.21 (dd, Hsyn, 1H), 3.21 (dd, Hanti, 1H, overlap with major
isomer), 1.05 (m, CH3, 3H, overlap with major isomer). 31P{1H}
NMR (160 MHz, CD2Cl2, 25 °C): d 26.4 (d, 2JPP = 40.7 Hz, PPh3, major
References
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2
isomer), 25.5 (d, JPP = 40.7 Hz, PPh3, major isomer), 25.1 (d,
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2
2JPP = 39.6 Hz, PPh3, minor isomer), 24.2 (d, JPP = 39.6 Hz, PPh3,
minor isomer).
4.4.14. General procedure for titration experiments
A screw-cap NMR tube was charged with ca. 10.0 mg of the
wrap-around complexes 8a–8c, 9a, 10a–10c, and 11a dissolved
in 500
sphere. NMR spectra were taken after 0, 1, 2, 3, 4, 5, 10, 15, 20,
25, 30, 35, and 40 equivalents of nitrile were added via a 10
lL of deuterated methylene chloride under inert atmo-
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lL
gas tight syringe at room temperature; a typical series of spectra
are shown in Section 2. Chemical shifts for H3, R4 = Me, and the
vinylic protons, H10 and H11, were monitored and recorded. The
first equilibrium (K1, as described by text) was fast on the NMR
time scale and thus the resonance monitored (typically the allylic
peak, H3) was an average of that for A and B. Once the chemical
shifts of the fully closed complex (A), the fully open complex (B),
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1354.