Synthesis and reactivity of neutral palladium(II) alkyl complexes that contain phosphinimine-arenesulfonate ligands

Article abstract of DOI:10.1021/om501262r

The synthesis and characterization of ortho-phosphiniminium-arenesulfonate zwitterions 1a-1d, the corresponding sodium salts 3a-3d, methyl(pyridine)palladium(II) complex 4a, and methyl(4-tert-butylpyridine)palladium(II) 5a-5d complexes are reported. Complex 4a suffers from limited solubility in aromatic hydrocarbons, while 5a-5d are soluble in benzene and toluene. Complex 5a forms a tridentate orthopalladated species 6a upon heating to 80 °C in toluene. Introduction of alkyl substituents on the phosphinimine phosphorus atom retards orthopalladation, and the (ⁿBu)₃P functionalized complex 5d does not undergo orthopalladation after heating at 80°C for 24 h. The Pd-C bond in the orthopalladated complex 6a is inert toward ethylene insertion. Complexes 5a-5d do not react with ethylene at 80°C and decompose to Pd⁰ and zwitterions 1a-1d.

Full text of DOI:10.1021/om501262r

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Neutral Palladium(II) Alkyl Complexes
that Contain Phosphinimine-Arenesulfonate Ligands
Christopher T. Burns,* Suisheng Shang, and Mark S. Mashuta
Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40292, United States
S
* Supporting Information
ABSTRACT: The synthesis and characterization of ortho-
phosphiniminium-arenesulfonate zwitterions 1a−1d, the cor-
responding sodium salts 3a−3d, methyl(pyridine)palladium-
(II) complex 4a, and methyl(4-tert-butylpyridine)palladium-
(II) 5a−5d complexes are reported. Complex 4a suffers from
limited solubility in aromatic hydrocarbons, while 5a−5d are
soluble in benzene and toluene. Complex 5a forms a tridentate
orthopalladated species 6a upon heating to 80 °C in toluene.
Introduction of alkyl substituents on the phosphinimine phosphorus atom retards orthopalladation, and the (nBu)3P
functionalized complex 5d does not undergo orthopalladation after heating at 80 °C for 24 h. The Pd−C bond in the
orthopalladated complex 6a is inert toward ethylene insertion. Complexes 5a−5d do not react with ethylene at 80 °C and
decompose to Pd0 and zwitterions 1a−1d.
branching.1,8 The molecular weight (MW) and polymerization
activity of the resulting polymers from these catalysts can be
INTRODUCTION
■
Insertion polymerization of ethylene and propylene by early
transition metal catalysts occurs on a vast scale.1 Late transition
tuned by incorporation of different substituents (R) on the P-
SO ligand9 and by varying the labile ligand (L) attached to
metal catalysts have also been studied for olefin polymerization
and oligomerization due to their different reactivity, branch
palladium,10 but are generally low compared to other catalysts.2
formation, and generally reduced oxophilic nature.2−5 This last
Several examples of cationic Pd complexes that are
structurally similar to (P-SO)PdMe(L) catalysts have been
feature is particularly important with regard to the insertion
generated by replacement of the sulfonate donor group.11
polymerization of functionalized olefins. Neutral palladium(II)
complexes incorporating anionic ortho-phosphino-arenesulfo-
These complexes, in general, react with ethylene to afford
oligomers, low-MW polymers, or dimers of ethylene. Less
explored are bidentate asymmetric donor ligands where the
phosphine functional group has been replaced with a stronger
donor group. The use of a stronger donor group in place of the
phosphine may provide enhanced electronic asymmetry and
lower metal electrophilicity, compared to the P-SO ligands,
while maintaining the neutral character of the palladium alkyl
complex. Nozaki reported the synthesis of a palladium alkyl
complex B, which contains an N-heterocyclic carbine (NHC)-
sulfonate ligand in which the NHC and sulfonate groups are
linked by a methylene spacer (Figure 1).12 Zhou and Jordan
reported Pd(II) alkyl complexes where the NHC-sulfonate
ligand contains a phenylene spacer (Figure 1, C).13 No reaction
with ethylene was observed for complexes of type C, while no
reactivity studies have been published for complex B. We are
investigating ortho-phosphinimine-arenesulfonate Pd(II) com-
plexes as catalysts in organometallic chemistry (Figure 1, D).
The modular nature of phosphinimine synthesis allows for the
creation of a diverse ligand library where steric and electronic
properties can be manipulated with ease.14 Neutral phosphini-
mines are stronger donors than phosphines due to potential
nate (P-SO) ligands (Figure 1, A) have received considerable
attention as versatile catalysts for ethylene polymerization to
highly linear polyethylene (PE)6 and the copolymerization of
ethylene with a variety of functionalized monomers.7 The
combination of strong (phosphine) and weak (sulfonate) σ-
donor groups in the P-SO ligand is thought to inhibit β-hydride
elimination, thus eliminating chain walking and polymer
Figure 1. Palladium complexes that contain chelating asymmetric
donor ligands incorporating a sulfonate group.
Received: December 10, 2014
Published: May 11, 2015
© 2015 American Chemical Society
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delocalization about the NP double bond.15 The steric
properties of phosphinimines are different than those of
phosphines since the steric bulk is slightly removed from the
metal center. Here, we describe the synthesis of several ortho-
phosphinimine-arenesulfonate ligands, their corresponding
neutral Pd(II) methyl complexes, studies of their dynamic
behavior, thermal stability/reactivity, and ethylene insertion
reactivity of these complexes.
pyridinium tetrafluoroborate as our H+ source and believed free
pyridine would be a competent nucleophile for the
deprotection reaction. The Staudinger reaction18 was combined
with the [Hpy][BF4]/pyridine deprotection sequence in a
single reaction flask, thus avoiding isolation of phosphinimine
sulfonate esters altogether.14 Azide 2 was reacted with Ph3P in
toluene at 25 °C for 6 h. After stirring for 6 h, the toluene was
removed under vacuum and the reaction residue was dissolved
in CH2Cl2. Excess pyridine and [Hpy][BF4] were added to the
CH2Cl2 solution, and the reaction was refluxed overnight. After
workup, the PN-SO zwitterion 1a was isolated in 70% yield
(Scheme 1) as a white solid. We applied our “one-pot”
synthesis to formation of PN-SO zwitterions 1b−1d using
Ph2PMe, PhP(nBu)2, and (nBu)3P, respectively. Zwitterions
1a−1d are air-stable and can be isolated using column
chromatography. In the case of the more electron-rich
phosphines, PhP(nBu)2 (1c) and (nBu)3P (1d), we found
that optimal yields were obtained by stirring the [Hpy][BF4]/
pyridine CH2Cl2 solution at 25 °C for 72 h (1c) and 48 h (1d)
instead of refluxing for 12 h. The 31P NMR chemical shifts for
1a−1d are consistent with values for phosphiniminium salts
observed in the literature.19
RESULTS AND DISCUSSION
■
PN-SO Zwitterions. On the basis of the synthesis of a chiral
ortho-imidazolium-benzenesulfonate reported by Hoveyda and
co-workers (Figure 2, E),16 we determined that the best route
Figure 2. Chiral ortho-imidazolium-benzenesulfonate and ortho-
phosphiniminium-benzenesulfonate.
(PN-SO)PdMe(py) Complexes. The reaction of zwitterion
1a with (cod)Pd(Me)Cl (cod = cyclooctadiene) in CD2Cl2 and
excess pyridine does not lead to the formation of CH4 and [κ2-
2-((C6H5)3PN)-5-CH3C6H3SO3]PdCl(py) as expected. In-
stead, unreacted 1a, free cyclooctadiene, and trans-Pd(py)2-
(Me)Cl were present in solution after 24 h. This is in contrast
to reactivity observed when phosphonium-sulfonate zwitterions
([P-SO]H; e.g., ligand in complex A) were reacted with
(cod)Pd(Me)Cl in the presence of pyridine to produce the
palladium chloride pyridine complexes [P-SO]PdCl(py).20 The
difference in reactivity observed for 1a and [P-SO]H was
attributed to the decreased acidity of zwitterion 1a. The pKa of
[P-SO]H zwitterions (≤2.7) is orders of magnitude lower than
the pKa of a protonated phosphinimine (∼10).6a,14,21
Zwitterion 1a is too weak an acid to facilitate methane
elimination from the Pd−Me bond of (cod)Pd(me)Cl to form
the desired [PN-SO]PdCl(py) complex. An alternative strategy
for the synthesis of neutral PN-SO palladium complexes had to
be explored.
PN-SO zwitterions 1a−1d were converted to their
corresponding sodium salts 3a−3d by deprotonation with
excess NaH in THF (Scheme 2). Sodium salt 3a reacted with
trans-Pd(py)2(Me)Cl in C6H6 to afford [κ2-2-((Ph)3PN)-5-
CH3C6H3SO3]PdMe(py) (4a) in 86% yield (Scheme 3).4a
Palladium complex 4a is insoluble in C6H6 (this along with
toluene are the desired solvents for polymerizations reactions),
so to separate 4a from NaCl generated during the reaction, the
to our nonsymmetric strong/weak σ-donor ortho-phosphini-
mine-arenesulfonate (PN-SO) zwitterions (Figure 2, F) was to
use commercially available 2-aminobenzenesulfonic acids.
Protection of the sulfonic acid group as an alkyl ester will
allow for the clean conversion of the 2-amino group to a
phosphinimine. Phosphinimines, while relatively air-stable,
decompose under the relatively harsh deprotection conditions
(acetic acid at 110 °C) used in the synthesis of E to form
Ph3PO and an amine. Other deprotection routes needed to
be explored.14,17
The ortho-phosphinimine-arenesulfonate zwitterions 1a−1d
were synthesized in good yields by a four-step sequence
(Scheme 1). 2-Azido-5-methylbenzenesulfonate propyl ester 2
can be prepared on a multigram scale.14
2-Amino-5-methylbenzenesulfonic acid was reacted with neat
ClSO3H to produce 2-amino-5-methylbenzenesulfonyl chlor-
ide, as shown in Scheme 1. 2-Amino-5-methylbenzene-sulfonyl
chloride was reacted with 1-propanol in the presence of 1,4-
diazabicyclo[2.2.2]octane (DABCO) to yield propyl-2-amino-
5-methylbenzenesulfonate.17 Azido sulfonate ester 2 was
synthesized via diazotization of the corresponding amine,
followed by reaction with sodium azide in water, and isolated as
an oil in 82% yield. Phosphinimine synthesis, phosphinimine
protonation, and propyl sulfonate ester deprotection can be
carried out in a single reaction vessel. We chose to use
Scheme 1
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Scheme 2
Scheme 3
Figure 3. ORTEP-328 diagram of 5a showing 50% ellipsoids. H atoms
are omitted for clarity. Key bond distances (Å) and angles (deg):
Pd(1)−C(35) 2.005(3); O(1)−Pd(1) 2.171(2); N(1)−Pd(1)
2.068(2); N(2)−Pd(1) 2.029(2); N(1)−P(1) 1.608(2); S(1)−O(1)
1.478(2); S(1)−O(2) 1.448(2); S(1)−O(3) 1.446(2); (C1)−C(6)
1.403(4); O(1)−Pd(1)−N(1) 88.63(8); O(1)−Pd(1)−N(2)
87.98(9); N(2)−Pd(1)−C(35) 90.38(11); C(35)−Pd(1)−N(1)
93.31(11).
solid was briefly dissolved in CH2Cl2 and separated by filtration
from the insoluble NaCl. Prolonged exposure of 4a to CH2Cl2
under ambient room light leads to homolytic cleavage of the
Pd−Me bond in 4a and eventual formation of a Pd−Cl bond
due to radical reactions between the methyl radical, the
palladium-based radical, and the chlorinated solvent. This
behavior has been seen before in neutral palladium methyl
complexes that contain strong donor ligands.22 To overcome
the benzene insolubility observed in complex 4a, we employed
4-tert-butylpyridine in place of pyridine to synthesize trans-
Pd(4-tBupy)2(Me)Cl.23 Use of pyridines with an alkyl
substituent para- to the pyridine nitrogen to increase a (P-
SO)Pd(II) based polymerization catalyst’s solubility in aromatic
solvents is known.24 The sodium salts 3a−3d were reacted with
trans-Pd(4-tBupy)2(Me)Cl in C6H6 to afford neutral PN-SO
Pd(II) methyl 4-tert-butylpyridine complexes 5a−5d in good
yield (Scheme 3). All four PN-SO Pd(II) methyl complexes
5a−5d are soluble in both benzene and toluene.
Molecular Structure of 5a. Crystals suitable for X-ray
crystallography were obtained by slow diffusion of pentane into
a benzene solution of 5a. The structure of the PN-SO Pd(II)
methyl 4-tert-butylpyridine complex 5a was determined by X-
ray diffraction, and an ORTEP diagram of the corresponding
structure is shown in Figure 3. The structure of 5a is similar to
those of (P-SO)PdMe(py) complexes.9a,25 In the structure of
5a, the geometry at Pd is square-planar and the methyl ligand is
cis to the phosphinimine. The [PN-SO]Pd chelate in 5a has a
distorted boat conformation with the Pd(1) atom displaced
0.613(6) Å out of the O(1)−C(1)−C(6) base plane. In 5a, the
sulfonate sulfur atom and phosphinimine nitrogen atom N(1)
are located at the bow and stern of the boat, respectively, with
sulfonate O(2) and P(1) of the phosphinimine located in axial
positions. The boat conformation of the [PN-SO]Pd chelate in
5a arranges sulfonate oxygens O(2) and O(3) away from the
metal center, which differs from [P-SO]Pd chelate rings where
one sulfonate oxygen atom points toward the Pd atom due to
the puckered conformation of the [P-SO]Pd chelate ring.9a,25
The P(1)−N(1) bond distance [1.608(2) Å] in 5a suggests a
1
degree of single bond character, which is supported by the H
NMR spectrum of 5a at 25 °C (see the discussion in next
section below). The P(1)−N(1) bond in 5a is shorter in length
versus the exocyclic phosphiniminium P−N bond found in
zwitterion 1a [1.6327(17) Å], which has a high degree of single
bond character.14 It is very similar in length to the P−N bond
observed in the free phosphinimine Ph3PNPh [1.603(3) Å]
but longer than the exoocyclic P−N bond found in the
dichloropalladium(II) phosphinimine-phosphine complex [κ2-
Ph3PN(CH2)3PPh2]PdCl2 [1.575(6) Å].26 It is shorter than
the exocyclic P−N bond observed in the dichloropalladium(II)
phosphinimine-imine complexes LMesPdCl2 (LMes = (Ph)3P
N(C6H4)C(Ph)(N(2,4,6-MeC6H2) [1.6267(16) Å] and
L
TolPdCl2 (LTol = (Ph)3PN(C6H4)C(Ph)(N(4-MeC6H4)
[1.615(5) Å].27 In addition, the Ph3P group on N(1) of the
coordinated phosphinimine in 5a is situated below the arene
ring plane of the 5-methylbenzenesulfonate fragment with a
C5−C6−N1−P1 torsion angle of 64.1(3)°, which is greater
than the corresponding torsion angle observed in zwitterion 1a
[39.2(3)°].14
Solution Structures of (PN-SO)PdMe(py) Complexes.
Compounds 4a, 5a−5d were characterized by H, 13C{1H},
1
and 31P{1H} and multidimensional NMR. The 31P{1H} NMR
chemical shifts for the phosphinimines in complexes 4a, 5a−5d
fall in the range of 30−45 ppm, which is consistent with values
for phosphinimines coordinated to Pd(II) observed in the
literature.15a,26b,27,29 The H NMR spectra of 4a and 5a−5d
1
contain one set of 5-CH3C6H3SO3, pyridine (4a), and 4-tert-
butylpyridine (5a−5d) resonances. The 1H−1H NOESY
spectra of 5a is consistent with placement of the palladium
methyl group cis to the phosphinimine and the 4-tert-
butylpyridine group trans. This is in agreement with the solid
state structure of 5a and structurally characterized (P-SO)Pd
alkyl complexes.9,25 The 1H−1H NOESY spectra of 4a and 5b−
5d show the same orientation of the methyl group and pyridine
ligand on palladium, as observed in 5a. The 1H NMR spectra of
4a and 5a at 25 °C show that the ortho-hydrogens of the
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phosphinimine phenyl rings are equivalent. Through-space
interactions between the Pd-Me group and the ortho-hydrogens
1
of the phosphinimine phenyl rings are observed in the H−1H
NOESY spectra for both 4a and 5a. This indicates a degree of
free rotation about the phosphinimine P−N bond in solution in
both 4a and 5a. Similar observations were made for complexes
5b−5d, indicating free rotation about the phosphinimine P−N
bond in our [PN-SO]PdMe(py) complexes.
Orthopalladation of 5a−5d. Complex 5a is soluble in
toluene-d8 and stable for days at 25 °C. Orthopalladation of
complex 5a can be thermally induced by heating 5a in toluene-
d8 at 80 °C for 6 h to produce CH4 (δ 0.17) and [κ3-2-
((C6H4)Ph2PN)-5-MeC6H3SO3]Pd(4-tBuPy) 6a (Scheme
4).
Scheme 4
Figure 4. ORTEP-328 diagram of 6a showing 50% ellipsoids. H atoms
are omitted for clarity. Key bond distances (Å) and angles (deg):
Pd(1)−C(9) 1.965(4); O(1)−Pd(1) 2.100(3); N(1)−Pd(1)
2.057(3); N(2)−Pd(1) 2.024(3); N(1)−P(1) 1.621(3); S(1)−O(1)
1.488(3); S(1)−O(2) 1.450(3); S(1)−O(3) 1.442(3); (C1)−C(6)
1.415(5); O(1)−Pd(1)−N(1) 91.68(10); O(1)−Pd(1)−N(2)
86.28(11); N(2)−Pd(1)−C(9) 93.76(14); C(9)−Pd(1)−N(1)
88.27(13).
with sulfonate oxygen O(2) pointed toward the Pd atom. The
P(1)−N(1) bond distance [1.621(3) Å] in 6a is longer in
length versus the phosphinimine P−N bond in 5a due to ring
strain associated with the newly formed five atom chelate ring
and indicates a high degree of single bond character. The
structure of 6a is similar to those of other orthopalladated
phosphinimine PdII complexes.27,30
Triphenylphosphine derived phosphinimines are known to
undergo orthopalladation reactions with Pd(OAc)2 in refluxing
CH2Cl2.30 Recently, it was shown that dichloropalladium(II)
phosphinimine-imine complexes LMesPdCl2 and LTolPdCl2
undergo reversible orthopalladation reactions when exposed
to sodium acetate at elevated temperatures, followed by HCl in
Et2O at 25 °C.27 The accepted mechanism for this reaction is
electrophilic substitution and thus may be catalyzed by the
presence of an electrophilic palladium center that has increased
Lewis acidity after homolysis of the Pd−Me bond of 5a.30 The
31P{1H} NMR spectrum of 6a shows a signal at 47 ppm
(CD2Cl2). This downfield shift is due to strain on phosphorus
caused by the 5-membered ring in 6a, which is characteristic of
When complex 5d, containing a (nBu)3P functionalized
phosphinimine, was heated under the same conditions as 5a, no
n
metalation of the butyl groups was observed after 6 h (based
on 31P{1H} NMR, Scheme 5). Even after 24 h at 80 °C, no
Scheme 5
orthopalladated phosphinimines.27,30 The H NMR spectrum
1
(CD2Cl2) of 6a shows sharp singlets at 1.38 and 2.16 ppm for
the 9 alkyl protons of the 4-tert-butylpyridine and the 3 tolyl
protons of the PN-SO orthopalladated ligand, respectively. The
aromatic protons of the coordinated 4-tert-butylpyridine appear
at two doublets as 8.81 and 7.48 ppm. The orthopalladated
phosphinimine phenyl ring of 6a displays 4 inequivalent signals
that are upfield of the two unreacted phosphinimine phenyl
rings. The 13C{1H} NMR spectrum (CD2Cl2) for 6a shows a
characteristic doublet for the orthopalladated carbon at 158.2
ppm (JCP = 20.0 Hz).
The orthopalladation of 5a to form 6a was scaled up using
toluene as the solvent. Complex 6a was isolated as a light
yellow solid in 74% yield. Crystals suitable for X-ray
crystallography were obtained by slow diffusion of pentane
into a benzene solution of 6a. The molecular structure of 6a
was determined by X-ray diffraction, and an ORTEP diagram of
the corresponding structure is shown in Figure 4. In the
structure of 6a, the geometry at Pd is slightly distorted square-
planar and the orthopalladated carbon atom is cis to the
phosphinimine nitrogen, forming a new five atom chelate ring.
The 4-tert-butylpyridine ligand occupies the remaining
coordination site on the Pd atom. There is a slight distortion
from trigonal-planar geometry observed for N(1). The [PN-
SO]Pd six atom chelate in 6a adopts a puckered conformation
n
metalation of the butyl groups was observed, although some
thermal decomposition of 5d had occurred, as indicated by the
presence of PN-SO zwitterion 1d (25% 1d, 31P{1H} NMR) in
solution. This shows that complex 5d is thermally robust and
that undesired metalation reactions can be prevented by use of
appropriate phosphines in our PN-SO ligands.
We have explored heating complexes 5b and 5c, which
contain Me(Ph)2P and PhP(nBu)2 functionalized phosphini-
1
mines, at 80 °C. The reactions were monitored by H and
31P{1H} NMR, and amounts of each species present were
determined by integration of the 31P{1H} NMR spectra with
Ph3PO as an internal standard. Complex 5b dramatically
inhibited orthopalladation but does not completely stop it, as
observed with 5d (Figure 5). After 6 h at 80 °C, only 14% of 5b
had undergone orthopalladation. After 24 h at 80 °C, 58% of 5b
had undergone orthopalladation. Similar results have been
reported for the inhibition of orthopalladation reactions by the
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under these conditions is not due to the inability of ethylene to
displace the coordinated 4-tert-butylpyridine ligand in com-
plexes 5a−5d. Shen and Jordan reported that (P-SO)PdMe(L)
complexes containing a para-substituted alkylpyridine (L = 4-
(5-nonyl)pyridine), instead of pyridine, are reactive toward the
insertion of ethylene under similar conditions.24
The Pd−C bond in the orthopalladated complex 6a is inert
toward ethylene insertion (Scheme 6). NMR analysis showed
no evidence for coordination or reaction between 6a and
ethylene (1 or 5 equiv) at 25 or 80 °C in toluene-d8. Similar
results were obtained when orthopalladated species derived
from dichloropalladium(II) phosphinimine-imine complexes
L
MesPdCl2 and LTolPdCl2 (LMes = (Ph)3PN(C6H4)C(Ph)(
N(2,4,6-MeC6H2); LTol = (Ph)3PN(C6H4)C(Ph)(N(4-
MeC6H4)) were exposed to 1-hexene.27
Figure 5. Comparison of thermal stability of complexes 5a−5d after 6
h at 80 °C.
SUMMARY
■
We have synthesized bidentate PN-SO zwitterions 1a−1d,
sodium salts 3a−3d, and their palladium(II) methylpyridine
complexes 4a, 5a−5d. Our [PN-SO]PdMe(py) complexes 5a−
5d were characterized in solution, and 5a was characterized in
the solid state as well. Complex 5a, when heated to 80 °C in
toluene, undergoes orthopalladation to form CH4 and 6a in
good yield. Complexes 5b−5d do not undergo orthopallada-
tion as readily as 5a with complex 5d, containing a (nBu)3P
derived phosphinimine, being stable at 80 °C for 24 h.
Complexes 5a−5d do not react with ethylene at 80 °C to
produce any products derived from ethylene insertion; instead,
zwitterions 1a−1d are isolated in each case. Orthopalladated
complex 6a is inert toward ethylene insertion.
Synthesis of the PN-SO zwitterions 1a−1d is modular and
allows for the creation of a diverse ligand library.14 Steric and
electronic properties can be manipulated with ease by simple
modification of the phosphine used in the Staudinger reaction.
We are currently expanding this research to include other
ligands and their corresponding transition metal complexes. We
are also exploring the versatility of our ligand system with
environmentally benign metals such as zinc and iron.
replacement of phenyl rings with methyl groups on
phosphorus.31 When compound 5c was heated at 80 °C for
6 h, 11% of 5c had undergone orthopalladation (Figure 5).
While this was consistent with the reactivity observed for 5b,
we also observed 21% of zwitterion 1c. After 24 h at 80 °C,
46% of 5c was still present in solution but no orthopalladated
product was observed. Instead, the amount of zwitterion 1c had
increased to 29% and three unknown phosphorus-containing
species totaling 25% were present. It is unclear at this time why
complex 5c ultimately decomposes to 1c instead of undergoing
orthopalladation upon heating to 80 °C.
Reaction of 5a−5d and 6a with Ethylene. In contrast to
[P-SO]PdR species, complexes 5a−5d do not react with
ethylene under catalytically relevant conditions.9a When
complexes 5a−5d were dissolved in toluene, exposed to
ethylene under polymerization conditions (75 psi) at 80 °C
for 6 h, no products from ethylene insertion reactions were
observed (Scheme 6). In each case, rapid Pd0 formation was
Scheme 6
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed under
nitrogen or vacuum using Schlenk or high-vacuum techniques or in a
nitrogen-filled drybox. Nitrogen was purified by passage through
columns containing activated molecular sieves and Q-5 oxygen
scavenger. Pentane, hexanes, toluene, benzene, and dichloromethane
were purified by passage through columns of activated 4 Å molecular
sieves. Diethyl ether and tetrahydrofuran were distilled from Na/
benzophenone ketyl. CDCl3 and CD2Cl2 were dried over CaH2,
degassed by freeze−pump−thaw cycles, and vacuum transferred to a
storage vessel. THF-d8 was distilled under nitrogen from sodium/
benzophenone ketyl, degassed, and stored under vacuum. Toluene-d8
was dried over sodium/benzophenone ketyl, degassed by freeze−
pump−thaw cycles, and vacuum transferred to a storage vessel. 1-
Propanol was distilled from I2/magnesium granules and stored under
nitrogen. PdCl2 (Pressure Chemical), PPh3 (Aldrich), PMePh2
(Aldrich), and P(nBu)3 (Alfa Aesar) were used as received. 2-
Amino-5-methylbenzenesulfonyl chloride,14 propyl-2-amino-5-methyl-
benzene sulfonate,14 2-((C6H5)3PNH)-5-CH3C6H3SO3 (1a),14 and
2-(CH3(C6H5)2PNH)-5-CH3C6H3SO3 (1b),14 pyridinium tetra-
fluoroborate,32 P(nBu)2Ph,33 trans-(py)2PdMeCl,21 and trans-
(4-tBupy)2PdMeCl21 were prepared as described in the literature. All
other reagents and solvents were purchased from Aldrich and used
without further purification.
observed once the reaction vessel had reached 80 °C. When the
reactions were worked up, the zwitterions 1a−1d were isolated
as the major phosphorus-containing species. In the case of 5a, a
small amount of the orthopalladated complex 6a was observed
by 31P{1H} NMR in the reaction residue. For the reaction of
ethylene with complexes 5b−5d, no orthopalladated products
were observed in any of these reactions. These results show
that decomposition of complexes 5a−5d is faster than reaction
with ethylene. We believe that the decomposition of 5a−5d
1H, 13C, and 31P NMR spectra were recorded in Teflon valve sealed
tubes on Varian 400 and 500 spectrometers at ambient probe
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Article
temperature unless otherwise indicated. 1H and 13C chemical shifts are
reported versus SiMe4 and were determined by reference to the
residual 1H and 13C solvent peaks. 31P chemical shifts were referenced
to external 85% aqueous H3PO4. Elemental analyses were performed
by Midwest Microlabs (Indianapolis, IN).
mmol) cooled to 0 °C was added a mixture of 4 mL of water, 4.1 mL
of HBF4 (48% aqueous solution), and 2 mL of EtOH (95%) precooled
to 0 °C (this and all other following manipulations in this reaction
were performed in air). After 20 min, a solution of NaNO2 (0.66g,
9.62 mmol) in water (5 mL) precooled to 0 °C was added dropwise
with vigorous stirring; an orange foam formed immediately during the
addition. After 20 min, the orange foam was filtered and washed with a
limited amount of 0 °C water (10 mL), 0 °C ethanol (10 mL), and 0
°C water (10 mL), affording an orange solid. Quickly after filtration,
the collected solid was added to a flask containing 5 mL of 0 °C water,
resulting in an orange suspension. With vigorous stirring, a 0 °C
solution of NaN3 (1.01 g, 15.57 mmol) in water (10 mL) was added
dropwise to the 0 °C orange suspension. An orange oil was observed
immediately on the surface. The mixture was stirred for 1 h at 0 °C
and 1.5 h at 25 °C. The orange oil had settled to the bottom. The
reaction mixture was extracted with Et2O (3 × 15 mL). The organic
layers were combined and dried over Na2SO4. The Na2SO4 was
filtered off, and the volatiles were removed under vacuum, yielding 2 as
Crystallographic Studies. Data for single crystal X-ray diffraction
studies were collected on an Agilent Technologies/Oxford Diffraction
Gemini CCD diffractometer at 100 K using MoKα radiation (0.71073
Å). Crystals of 5a were grown by slow diffusion from pentane/C6H6
and mounted on a 0.05 mm CryoLoop with Paratone oil for data
collection. C35H37N2O3PPdS: yellow prism, 0.23 × 0.14 × 0.13 mm3,
orthorhombic space group Pbcn, a = 17.86211(17) Å, b =
17.52994(15) Å, c = 21.0147(2) Å, V = 6580.15(11) Å3, Dcalc
=
1.419 mg/m3, Z = 8.34 The structure was solved by Patterson methods
and refined using the SHELXTL35,36 (v 6.14) suite of programs. All
nonhydrogen atoms were refined using anisotropic thermal parame-
ters. A 0.25 pentane molecule of solvation was found to be severely
disordered, and a suitable model could not be obtained during
refinement. Its contribution was subtracted from the data using the
program SQUEEZE.37 All hydrogen atoms were placed in their
geometrically generated positions and refined as a riding model.
Phenyl H’s were included as fixed contributions with U(H)iso = 1.2 ×
Ueq (attached C atom) while methyl groups were allowed to ride on
the attached C atom (the torsion angle which defines its orientation
was allowed to refine), and these atoms were assigned U(H)iso = 1.5
× Ueq (attached C atom). For 6867 reflections, I > 2σ(I) [R(int)
0.038] the final anisotropic full matrix least-squares refinement on F2
for 344 variables converged at R1 = 0.044 and wR2 = 0.096 with a
GOF of 1.07.34−36
1
a dark orange oil (2.00 g, 87%). H NMR (CDCl3): δ 7.72 (s, 1H, 3-
CH), 7.44 (d, J = 8.4, 1H, 5-CH), 7.20 (d, J = 8.4, 1H, 6-CH), 4.06 (t,
J = 6.4, 2H, CH2CH2CH3), 2.38 (s, 3H, 3-CH3C6H3), 1.71 (m, 2H,
CH2CH2CH3), 0.96 (t, J = 7.6, 3H, CH2CH2CH3).
2-((nBu)2PhPNH)-5-MeC6H3SO3 (1c). To a clear brown
solution of 2 (3.87 g, 15.2 mmol) in toluene (40 mL) in a 200 mL
Kjeldahl flask was added P(nBu)2Ph (4.1 mL, 16.7 mmol) dropwise at
25 °C. Effervescence was observed immediately after addition of
P(nBu)2Ph. The solution was stirred for 6 h and became a clear yellow
solution. Removal of the solvent under vacuum afforded a yellow
viscous material, which was redissolved with CH2Cl2 (40 mL). The
resulting clear yellow solution was transferred via cannula over to a
suspension of pyridinium tetrafluoroborate ([pyH][BF4]) (2.53 g, 15.2
mmol) in CH2Cl2 (40 mL). The Kjeldahl flask was rinsed with CH2Cl2
(40 mL), and the rinsing solution was transferred to the reaction flask
via cannula. Pyridine (1.9 mL, 22.75 mmol) was added to the white
suspension in CH2Cl2, and the reaction mixture was stirred at 25 °C
for 72 h. A clear pale brown solution was observed, and the volatiles
were removed under vacuum. The resulting viscous residue was
triturated with diethyl ether (3 × 60 mL), followed by filtration, to give
a brown residue. The residue was separated by column chromatog-
raphy using silica gel (150 g) and CHCl3. The residue was loaded onto
the column with CHCl3 and elution was begun (100 mL). The column
was eluted with CHCl3−MeOH 95:5 (500 mL) and CHCl3−MeOH
90:10 (1500 mL). The fractions (100 mL) were analyzed by UV−vis,
and those that contained the product were combined and dried under
vacuum, affording a white foam. The foam was treated with CH2Cl2
(40 mL) and diethyl ether (80 mL) to afford a white precipitate.
Filtration of the precipitate, followed by diethyl ether washes (3 × 20
mL), afforded 1c (1.54g, 23%) as a white powder. 1H NMR (CDCl3):
δ 9.51 (d, J = 9.6, 1H, NH), 7.95 (m, 2H, 2,6-CH of nBu2C6H5P), 7.81
Crystals of 6a grown by slow diffusion from pentane/C6H6 contain
three full occupancy benzene solvates. The first benzene solvate is
modeled with three full occupancy carbon atoms C35−C37 (the other
three solvate carbon atoms are generated by a center of symmetry).
The second benzene solvate was modeled with C40−C45 while the
third benzene solvate was modeled with C50−C54 (both share a
common atom C45), all atoms refined anisotropically at 0.5
occupancy. A center of symmetry generates the full occupancy solvent.
The disordered t-butyl pyridyl group was modeled as follows: Two sets
of four carbon atoms (C26a, C27a, C29a, and C30a) at 60%
occupancy, and (C26b, C27b, C29b, and C30b) at 40% occupancy in
addition to full occupancy N1 and C28 comprised the pyridyl portion
of the group. C32a−C34a (70% occupancy) and C32b−C34b (30%
occupancy) with a full occupancy C31 atom were used to model the
disordered t-butyl group. All atoms in 6a were refined anisotropically
except for the 30% disordered t-butyl group, which was refined
isotropically with restraints. C43H23N2O3PPdS·3C6H6: colorless prism,
0.21 × 0.05 × 0.01 mm3, triclinic space group P1, a = 9.3572(6) Å, b =
̅
11.8341(8) Å, c = 18.5228(14) Å, α = 87.010(6)°, β = 87.005(6)°, γ =
69.223(6)°, V = 1913.9(2) Å3, Dcalc = 1.362 mg/m3, Z = 2. For 8824
reflections, I > 2σ(I) [R(int) 0.062] the final anisotropic full matrix
least-squares refinement on F2 for 410 variables converged at R1 =
0.050 and wR2 = 0.107 with a GOF of 1.08. Crystallographic data for
the structural analysis has been deposited with the Cambridge
Crystallographic Data Centre, CCDC Nos. 1038502−1038503 for 5a
and 6a. Copies of this information may be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ
U.K. E-mail: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.
cam.ac.uk.
n
(s, 1H, 6-CH of −C6H3SO−), 7.72 (m, 1H, 4-CH of Bu2C6H5P),
6.86 6.86(dd, J = 8.0, 1.2, 1H, 4-CH of −C6H3SO3−), 6.36 (d, J = 8.0,
1H, 3-CH of −C6H3SO3−), 2.69 (m, 2H, CH2CH2CH2CH3), 2.59 (m,
2H, CH2CH2CH2CH3), 2.20 (s, 3H, 5-CH3 of −C6H3SO3−), 1.59 (m,
4H, CH2CH2CH2CH3), 1.39 (m, 4H, CH2CH2CH2CH3), 0.82 (t, J =
7.2, 6H, CH2CH2CH2CH3), 31P NMR (CDCl3): δ 46.0. 13C NMR
(CDCl3): δ 136.3 (d, JPC = 7.6), 135.0 (d, JPC = 3.1, para-CH of
nBu2C6H5P), 133.4, 132.1, 132.0 (d, JPC = 10.6, ortho-CH of
n
nBu2C6H5P), 130.8, 130.2 (d, JPC = 12.2, meta-CH of Bu2C6H5P),
129.5, 120.6(d, JPC = 91.9, ipso C of C6H5P), 117.8 (d, J = 3.0), 23.7,
23.5 (d, JPC = 14.0), 23.14, 22.9 (d, JPC = 4.6), 20.5, 13.2. Anal. Calcd
for C21H30NO3PS: C, 61.89; H, 7.42; N, 3.44. Found: C, 62.21; H,
7.25; N, 3.67.
All ligands and their precursors bear a sulfonated toluidine parent
structure which has an atom-labeling scheme as follows:
2-((nBu)3PNH)-5-MeC6H3SO3 (1d). To a 200 mL pear-shaped
flask containing a clear brown solution of 2 (2.95 g, 11.4 mmol) in
toluene (10 mL) chilled to 0 °C for 15 min was added a solution of
P(nBu)3 (2.42 g, 12.0 mmol) in toluene (30 mL) via cannula transfer
by aid of rinsing with toluene (10 mL), resulting in a yellow solution.
The mixture was allowed to return to 25 °C. Effervescence was
observed after addition of the P(nBu)3 solution. The yellow solution
was stirred for 6 h until no effervescence was observed. The solvent
2-N3-5-CH3C6H3SO3CH2CH2CH3 (2). The compound was synthe-
sized according to a modified literature procedure.14 To a flask
containing propyl-2-amino-5-methylbenzenesulfonate (2.10 g, 9.16
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was removed under vacuum to afford a yellow frothy solid. The solid
was dissolved in CH2Cl2 (20 mL). The yellow solution was transferred
via cannula to a 300 mL Kjeldahl flask containing a suspension of
[pyH][BF4] (1.92 g, 11.4 mmol) in CH2Cl2 (20 mL). The 200 mL
pear-shaped flask was rinsed with CH2Cl2 (3 × 20 mL), and the
rinsing solutions were transferred to the reaction flask via cannula.
Gradually, the yellow reaction mixture turned to red solution with
some white solid still present. The reaction mixture was stirred for 1 h,
and the white solid disappeared. Pyridine (1.7 mL, 17.1 mmol) was
added to the reaction solution. The reaction was stirred at 25 °C for 48
h. The resulting brown solution was pumped down under vacuum,
giving a glutinous residue, which was treated with CH2Cl2 (15 mL)
and Et2O (75 mL). A brown oily insoluble precipitate was observed.
Decantation of the liquid layer afforded a gelatinous solid. Treatment
with Et2O (75 mL) and decantation of the ether layer were performed.
The resulting viscous solid was pumped down to a brown foam. The
frothy solid was separated by column chromatography using silica gel
(150g) and CHCl3. The column was eluted with CHCl3 (100 mL),
CHCl3−MeOH 98:2 (1500 mL), CHCl3−MeOH 95:5 (500 mL), and
CHCl3−MeOH 90:10 (500 mL). The fractions (100 mL) were
analyzed by UV−vis, and those that contained the product were
combined and dried under vacuum, affording a brown oil. The brown
oil was treated consequentially with CHCl3/Et2O (20 mL/80 mL),
hexane (30 mL), and benzene (3 × 30 mL) to give an off-white
precipitate (4.00 g). The resulting solid was washed with Et2O (2 × 50
mL), yielding 1d as a white powder (2.50 g, 57%). 1H NMR (DMSO-
d6): δ 8.63(d, J = 6.4, 1H, NH), 7.53 (s, 1H, 6-CH of −C6H3SO3−),
7.16 (d, J = 7.8, 1H, 4-CH of −C6H3SO3−), 7.09 (d, J = 7.8, 1H, 3-CH
of −C6H3SO3−), 2.51 (m, 6H, (CH3CH2CH2CH2)3PNH−), 2.30
( s , 3 H , 5 - C H 3 o f − C 6 H 3 S O 3 − ) , 1 . 5 3 ( m , 6 H ,
( C H 3 C H 2 C H 2 C H 2 ) 3 P  N H − ) , 1 . 4 2 ( m , 6 H ,
( C H 3 C H 2 C H 2 C H 2 ) 3 P  N H − ) , 0 . 9 0 ( m , 9 H ,
(CH3CH2CH2CH2)3PNH−). 31P NMR (DMSO-d6): δ 56.7. 13C
NMR (DMSO-d6): δ 140.8 (d, JPC = 5.4), 136.1, 131.0 (d, JPC = 4.7),
130.8, (d, JPC = 6), 130.6, (d, JPC = 5.4), 129.6 (d, JPC = 3.1), 128.7,
128.6 (d, JPC = 3.9), 127.2 (d, JPC = 7.0), 123.5 (d, JPC = 2.3), 29.9 (d,
JPC = 54.2), 20.4. Anal. Calcd for C19H34NO3PS: C, 58.89; H, 8.84; N,
3.61. Found: C, 58.77; H, 8.80; N, 3.36.
−C6H3SO3−), 6.20 (d, J = 8.0, 1H, 4-CH of −C6H3SO3−), 2.19 (d, J
= 13.2, 3H, MePN), 2.00 (s, 3H, 5-CH3 of −C6H3SO3). 31P NMR
(THF-d8): δ 10.2. 13C NMR (THF-d8): 147.0, 137.8, 132.3 (d, JPC
=
9.1), 131.3, 130.7, 129.5, 128.8 (d, JPC =166.2),128.3 (d, JPC = 11.2),
124.4, 123.1 (d, JPC = 12.2), 19.5, 15.4(d, JPC = 82.7). Anal. Calcd for
C20H19NNaO3PS: C, 58.96; H, 4.70; N, 3.44. Found: C, 58.76; H,
4.44; N, 3.06.
2-((nBu)2PhPN)-5-MeC6H3SO3Na (3c). To a flask loaded with
1c (1.54 g, 3.42 mmol) and NaH (0.12 g, 5.14 mmol) was added THF
(50 mL) while stirring. The turbid mixture was stirred for 4 h to give a
clear slightly yellow solution, which was filtered through dry Celite.
Removal of THF afforded a yellow solid, which was stirred in pentane
(40 mL) for 30 min. The resulting suspension was filtered off, and the
collected solid was washed with pentane (2 × 10 mL), yielding 3c
(1.47 g, 95%) as a pale yellow powder. 1H NMR (THF/benzene-d6): δ
7.71 (s, 1H, 6-CH of −C6H3SO3−), 7.71 (broad, 2H, 2,6-CH of
PhPN),7.59 (m, 4-CH of PhPN), 7.07 (broad, 2H, 3,5-CH of PhPN),
6.52 (bd, J = 8.0, 1H, 4-CH of −C6H3SO3−), 6.29 (bd, J = 8.0, 1H, 4-
CH of −C6H3SO3−), 2.20−2.50 (m, 4H, CH2CH2CH2CH3), 1.94(s,
3H, 5-CH3 of −C6H3SO3), 1.45(m, 4H, CH2CH2CH2CH3), 1.32(m,
4H, CH2CH2CH2CH3), 0.63 (t, J = 7.6, 6H, CH2CH2CH2CH3). 31P
NMR (THF-d8): δ 20.1. 13C NMR (THF-d8): 161.8, 151.7, 146.6(d,
JPC = 7.6), 143.8. 122.1,30.2, 26.3 (d, JPC = 61.5), 24.5(d, JPC = 41.5),
15.3. Anal. Calcd for C21H29NNaO3PS: C, 58.73; H, 6.81; N, 3.26.
Found: C, 58.70; H, 6.54; N, 3.44.
2-((nBu)3PN)-5-MeC6H3SO3Na (3d). To a flask loaded with 1d
(1.58 g, 3.68 mmol) and NaH (0.32 g, 5.52 mmol) was added THF
(50 mL) while stirring. The turbid mixture was stirred for 4 h to give a
clear slightly yellow solution, which was filtered through dry Celite.
Removal of THF afforded a yellow solid, which was stirred in pentane
(40 mL) for 30 min. The resulting suspension was filtered off, and the
collected solid was washed with pentane (2 × 10 mL), yielding 3d
(1.33 g, 89%) as a pale yellow powder. 1H NMR (THF-d8): δ 7.71 (s,
1H, 6-CH of −C6H3SO3−), 6.80 (dd, J = 8.0, 2.0, 1H, 4-CH of
−C6H3SO3−), 6.56 (dd, J = 8.0, 2.0, 1H, 4-CH of −C6H3SO3−),
2.17(s, 3H, 5-CH3 of −C6H3SO3), 2.00 (m, 6H, CH2CH2CH2CH3),
1.45(m, 6H, CH2CH2CH2CH3), 1.32 (m, 6H, CH2CH2CH2CH3),
0.83 (t, J = 7.6, 9H, CH2CH2CH2CH3). 31P NMR (THF-d8): δ 26.5.
13C NMR (THF-d8): 161.8, 151.7, 146.6(d, JPC = 7.6), 143.8.
122.1,30.2, 26.3 (d, JPC = 61.5), 24.5(d, JPC = 41.5), 15.3. Anal. Calcd
for C19H33NNaO3PS: C, 55.73; H, 8.12; N, 3.42. Found: C, 55.76; H,
7.96; N, 3.06.
2-((C6H5)3PN)-5-CH3C6H3SO3Na (3a). To a flask loaded with
1a (2.23 g, 5.00 mmol) and NaH (0.18 g, 7.50 mmol) was added THF
(60 mL) while stirring. The turbid mixture was stirred for 4 h to give a
clear, slightly yellow solution with a small amount of gray precipitate
present. The yellow solution was filtered through dry Celite on a
medium glass frit under N2, and the clear, yellow filtrate was collected.
Removal of THF afforded a yellow solid, which was stirred in pentane
(40 mL) for 30 min. The resulting suspension was filtered off onto a
medium glass frit under N2, and the collected solid was washed with
pentane (2 × 10 mL), yielding 3a (2.09 g, 89%) as a pale yellow
[κ2-2-((C6H5)3PN)-5-CH3C6H3SO3]Pd(NC5H5)(CH3) (4a). A
flask containing 3a (0.23 g, 0.5 mmol) and trans-bis(pyridine)-
palladium(II) methyl chloride (trans-(py)2PdMeCl) (0.16 g, 0.5
mmol) was charged with benzene (30 mL) while stirring under N2
at 25 °C. Shortly after the addition of C6H6, the clear faint green
solution turned turbid. The reaction was stirred for 2 h under N2 at 25
°C, resulting in an off-white suspension. The precipitate was collected
onto a layer of dry Celite and washed with benzene (2 × 10 mL). The
collected solid was light green. The solid was dissolved and washed
down into a flask with CH2Cl2 (3 × 20 mL). Evaporation of the filtrate
afforded a yellow residue, which was further treated with Et2O (20
mL) to give a white suspension. The suspension was filtered and
washed with Et2O (2 × 10 mL), yielding 4a (0.28 g, 86%) as an off-
white solid. 1H NMR (CDCl3): δ 8.38 (dd, J = 6.8, 1.6, 2H, 2,6-CH of
(C5H5N)Pd), 8.00 (m, 6H, 2,6-CH of (C6H5)3PN−), 7.77 (s, 1H,
6-CH), 7.65 (tt, J = 8.0, 1.6, 1H, 4-CH of Pd(NC5H5), 7.58 (m, 3H, 4-
CH of (C6H5)3PN−), 7.48 (m, 6H, 3,5-CH of (C6H5)3PN−),
7.18 (m, 1H, 4-CH of Pd(NC5H5)), 6.89 (dd, J = 8.0, 2.0, 1H, 4-CH),
6.96 (dd, J = 7.6, 2.0, 1H, 3-CH), 2.18 (s, 3H, 5-CH3), 0.16 (s, 3H,
PdCH3). 31P NMR (CDCl3): δ 31.6. 13C NMR (CDCl3): δ 152.0,
143.1, 142.0 (d, JPC = 9.9), 137.1, 134.6 (d, JPC = 9.8, ortho-CH of
(C6H5)3PN−), 132.6 (d, JPC = 2.2, para-CH of (C6H5)3PN−),
132.3, 130.4, 129.4, 128.5 (d, JPC = 100.9, ipso C of (C6H5)3PN−),
1
powder. H NMR (THF-d8): δ 7.99 (m, 6H, 2,6-CH of (C6H5)3P
N−), 7.73 (bs, 1H, 6-CH of −C6H3SO3−), 7.23−7.48 (m, 9H, 3,5-CH
of (C6H5)3PN− and 4-CH of (C6H5)3PN−), 6.52 (d, J = 7.5, 1H,
4-CH of −C6H3SO3−), 6.34 (d, J = 7.5, 1H, 3-CH of −C6H3SO3−),
2.03 (s, 3H, 5-CH3 of −C6H3SO3−).13C NMR (THF-d8):146.4 (2-C),
138.0 (d, JPC = 22.0, 1-C), 133.0 (d, JPC = 9.9, ortho-CH of
(C6H5)3PN−), 132.0 (d, JPC = 98.7, ipso C of (C6H5)3PN), 130.8
(para-CH of (C6H5)3PN−), 129.6 (overlapping of 4- and 6-C),
128.2 (d, JPC = 12.2, meta-CH of (C6H5)3PN−), 123.9 (5-C), 122.0
(3-C), 19.7 (5-CH3). 31P NMR (THF-d8): δ −1.64. Anal. Calcd for
C25H21NNaO3PS: C, 63.96; H, 4.51; N, 2.98. Found: C, 63.76; H,
4.55; N, 2.66.
2-(CH3(C6H5)2PN)-5-MeC6H3SO3Na (3b). To a flask loaded
with 1b (1.00 g, 2.60 mmol) and NaH (94 mg, 3.90 mmol) was added
THF (50 mL) while stirring. The turbid mixture was stirred for 4 h to
give a clear slightly yellow solution, which was filtered through dry
Celite. Removal of THF afforded a yellow solid, which was stirred in
pentane (40 mL) for 30 min. The resulting suspension was filtered off,
and the collected solid was washed with pentane (2 × 10 mL), yielding
3b (0.97 g, 91%) as a pale yellow powder. 1H NMR (THF-d8): δ 7.85
(m, 4H, 2, 6-CH of Ph2PN),7.67 (s, 1H, 6-CH of −C6H3SO3−),
7.20−7.41 (m, 6H, 3,4,5-CH of Ph2PN), 6.44 (d, J = 8.0, 1H, 4-CH of
128.2 (d, JPC = 11.6, meta-CH of (C6H5)3PN−), 126.5 (d, JPC
=
4.5), 124.7, 20.6, −4.4. Anal. Calcd for C31H29N2O3PPdS: C, 57.24; H,
4.52; N, 4.33. Found: C, 57.18; H, 4.56; N, 4.20.
[κ2-2-((C6H5)3PN)-5-CH3C6H3SO3]Pd(4-(CH3)3CC5H5N)(CH3)
(5a). A flask containing 3a (0.23 g, 0.5 mmol) and trans-bis(4-tert-
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butylpyridine)palladium(II) methyl chloride (trans-(4-tBupy)2-
PdMeCl) (0.21 g, 0.5 mmol) was charged with benzene (30 mL)
while stirring under N2 at 25 °C. Shortly after the addition of C6H6,
the clear faint green solution turned to a clear yellow solution. The
reaction was stirred for 2 h under N2 at 25 °C, resulting in a clear
yellow solution. The yellow solution was filtered through dry Celite
along with 2 × 10 mL benzene rinses. Evaporation of the filtrate
afforded a yellow solid residue, which was further treated with benzene
(10 mL) and pentane (30 mL) to give a light yellow precipitate. The
precipitate was filtered onto a medium glass frit and washed with
pentane (3 × 10 mL), yielding 5a (0.28 g, 80%) as a faint yellow-green
solid. Crystals of 5a suitable for X-ray diffraction were obtained by
9H, 4-(CH3)3C(C5H4N))Pd), 0.94 (3H, CH2CH2CH2CH3), 0.78
(3H, CH2CH2CH2CH3), 0.47 (s, 3H, PdCH3). 31P NMR (CDCl3): δ
39.9. 13C NMR (CDCl3): 161.8, 151.2, 143.1, 142.8 (d, JPC = 8.3),
132.4, 132.1 (d, JPC = 9.6), 130.9, 130.2, 129.5, 128.7 (d, JPC = 11.4),
126.7 (d, JPC = 3.0), 122.0, 34.8, 30.1, 26.9 (d, JPC = 69.0), 26.08 (d,
JPC = 60.0), 24.8, 23.9, 20.6, 13.4(d, JPC = 18.2), −6.8. Anal. Calcd for
C31H45N2O3PPdS: C, 56.15; H, 6.84; N, 4.22. Found: C, 56.44; H,
6.89; N, 4.17.
[κ2-2-((nBu)3PN)-5-MeC6H3SO3]Pd(4-(CH3)3CC5H5N)Me (5d).
A flask containing 3d (0.32 g, 0.75 mmol) and trans-(4-tBupy)2-
PdMeCl (0.43 g, 0.75 mmol) was charged with benzene (30 mL)
while stirring. Shortly, an initially observed clear faint green solution
turned to a clear yellow solution. The reaction proceeded for 2 h,
resulting in a clear yellow solution. The yellow solution was filtered
through dry Celite along with 2 × 10 mL benzene rinsing. Evaporation
of the filtrate afforded a yellow solid residue, which was further treated
with pentane (30 mL) to give a yellow precipitate. The precipitate was
filtered onto a medium glass frit and washed with pentane (3 × 10
mL), yielding 5d (0.36 g, 74%) as a yellow solid. 1H NMR (CD2Cl2):
8.39 (dd, J = 4.8, 1.6, 2H, 2,6-CH of (4-(CH3)3CC5H4N)Pd), 7.71 (s,
1H, 6-CH of −C6H3SO3−), 7.29 (d, J = 4.8, 1.6, 2H, 3,5-CH of (4-
(CH3)3C(C5H4N))Pd), 7.04 (dd, J = 8.0, 2.0, 1H, 4-CH of
−C6H3SO3−), 2.31(s, 3H, 5-CH3 of −C6H3SO3−), 2.21 (m, 3H, Ha
of CH2CH2CH2CH3), 2.02(m, 3H, Hb of CH2CH2CH2CH3), 1.83 (m,
3H, Ha of CH2CH2CH2CH3), 1.67(m, 3H, Hb of CH2CH2CH2CH3),
1.44(m, 6H, CH2CH2CH2CH3), 1.26 (s, 9H, 4-(CH3)3C(C5H4N))-
Pd), 0.95 (t, J = 7.6, 9H, CH2CH2CH2CH3), 0.62 (s, 3H, PdMe). 31P
NMR (CD2Cl2): δ 44.8. 13C NMR (CD2Cl2): 162.2, 151.0, 131.0,
128.6,127.6, 122.1, 34.8, 29.9, 12.9 (d, JPC = 60.7), 24.5(d, JPC = 56.4),
24.1, 20.4, 13.3, −8.0. Anal. Calcd for C29H49N2O3PPdS: C, 54.16; H,
7.68; N, 4.36. Found: C, 54.24; H, 7.89; N, 4.35.
1
diffusion of pentane into a C6H6 solution of 5a at 25 °C. H NMR
(CDCl3): δ 8.24 (dd, J = 5.2, 1.6, 2H, 2,6-CH of (CH3)3C(C5H5N)-
Pd), 8.03 (m, 6H, 2,6-CH of (C6H5)3PN−), 7.76 (s, 1H, 6-CH),
7.58 (m, 3H, 4-CH of (C6H5)3PN−), 7.14 (dd, J = 5.2, 1.6, 2H, 3,5-
CH of 4-(CH3)3C(C5H5N)Pd), 6.89 (dd, J = 8.0, 2.0, 1H, 4-CH), 6.95
(dd, J = 8.0, 2.0, 1H, 3-CH), 2.19 (s, 3H, 5-CH3), 1.24 (s, 9H, 4-
(CH3)3C(C5H5N)Pd), 0.15 (s, 3H, CH3Pd). 31P NMR (CDCl3): δ
31.3. 13C NMR (CDCl3): δ 162.4, 152.3, 144.0, 142.8 (d, JPC = 9.9),
135.5 (d, JPC = 9.8, ortho-CH of (C6H5)3PN−), 133.4(para-CH of
(C6H5)3PN−), 133.1, 131.2, 130.2, 130.4 (d, JPC = 101.0, ipso C of
(C6H5)3PN−), 129.1(d, JPC = 12.1, meta-CH of (C6H5)3PN−),
127.3, 122.7, 35.7, 34.0, 21.5, −4.0. Anal. Calcd for C35H37N2O3PPdS:
C, 59.79; H, 5.30; N, 3.98. Found: C, 59.44; H, 5.49; N, 3.71.
[κ2-2-(Me(C6H5)2PN)-5-MeC6H3SO3]Pd(4-(CH3)3CC5H5N)Me
(5b). A flask containing 3b (0.20 g, 0.5 mmol) and trans-
(4-tBupy)2PdMeCl (0.21 g, 0.5 mmol) was charged with benzene
(30 mL) while stirring. Shortly, an initially observed clear pale green
solution turned to a clear yellow solution. The reaction proceeded for
2 h, resulting in a clear yellow solution. The yellow solution was
filtered through dry Celite along with 2 × 10 mL benzene rinsing.
Evaporation of the filtrate afforded a yellow solid residue, which was
further treated with pentane (30 mL) to give a yellow precipitate. The
precipitate was filtered onto a medium glass frit and washed with
pentane (3 × 10 mL), yielding 5b (0.26 g, 95%) as a faint yellow-green
solid. 1H NMR (CD2Cl2): 8.24 (m, 2H, 2,6-CH of -(C6H5)2PN−),
8.21 (d, J = 5.2, 2H, 2,6-CH of (4-(CH3)3CC5H4N)Pd), 7.95 (m, 2H,
2,6-CH of -(C6H5)2PN−), 7.75 (s, 1H, 6-CH of −C6H3SO3−), 7.67
(m, 2H, 4-CH of −(C6H5)2PN−), 7.60 (m, 4H, 3,5-CH of
-(C6H5)2PN−), 7.23 (d, J = 5.2, 2H, 3,5-CH of (4-(CH3)3C-
(C5H4N))Pd), 6.88 (dd, J = 8.0, 2.0, 1H, 4-CH of −C6H3SO3−), 6.78
(dd, J = 8.0, 2.0, 1H, 3-CH of −C6H3SO3−), 2.35 (d, JPH = 13.2, 3H,
−CH3PN−), 2.26 (s, 3H, 5-CH3 of −C6H3SO3−), 1.26 (s, 9H, 4-
(CH3)3C(C5H4N))Pd), 0.27 (s, 3H, PdCH3). 31P NMR (CD2Cl2): δ
34.5. 13C NMR (CD2Cl2): 162.0, 151.2, 143.6, 142.5 (d, JPC = 9.1),
Generation of [κ3-2-((C6H4)Ph2PN)-5-MeC6H3SO3]Pd(4-
(CH3)3CC5H5N) 6a. A valved NMR tube was charged with 5a (3.0
mg, 4.2 μmol), and toluene-d8 (0.5 mL) was added via vacuum transfer
at −196 °C. After the NMR tube was flushed with N2, the valved
NMR tube was sealed and warmed to 25 °C and shaken until the solid
1
dissolved. H and 31P{1H} NMR at 25 °C spectra established that 5a
was the only species present in solution. The solution was heated to 80
1
°C for 6 h, and the solution was cooled to 25 °C. H and 31P{1H}
NMR spectra were recorded at 25 °C and showed complete
1
conversion of 5a to 6a. H NMR (toluene-d8): δ 8.54 (d, J = 6.8,
2H, 2,6-CH of 4-tBuPy), 8.44 (s, 1H, 6-CH of −C6H3SO3−), 7.90 (m,
4H, 2,6-CH of −Ph2PN−), 7.60−7.78 (m, 20H), 6.95−7.22 (m,
45H), 6.70−6.85 (m, 3H), 6.55 (d, J = 6.8, 2H, 3,5-CH of 4-tBuPy),
t
6.50 (d, J = 6.0, 6.38 (s, 2H), 1.89 (s, 3H, 5-Me), 0.84 (s, 9H, Bu),
0.18 (s, 0.83H, CH4). 31P NMR (toluene-d8): δ 50.2.
[κ3-2-((C6H4)Ph2PN)-5-MeC6H3SO3]Pd(4-(CH3)3CC5H5N) 6a.
A flask containing 5a (0.20 g, 0.28 mmol) was charged with toluene
(20 mL) and stirred. The clear faint yellow solution was heated to 80
°C for 15 h. The resulting clear yellow solution was filtered through
dry Celite along with 2 × 10 mL toluene rinsing. Evaporation of the
filtrate afforded a yellow solid residue, which was further treated with
pentane (30 mL) to give a yellow precipitate. The precipitate was
filtered onto a medium glass frit and washed with pentane (3 × 10
mL), yielding 6a (0.14 g, 74%) as a yellow solid. Crystals of 6a suitable
for X-ray diffraction were obtained by diffusion of pentane into a C6H6
solution of 6a at 25 °C. 1H NMR (CD2Cl2): 8.21 (d, J = 4.8, 2H, 2,6-
CH of 4-(CH3)3CC5H4N), 7.97 (m, 4H, 2,6-CH of -(C6H5)2PN−),
7.69 (m, 3H, 4-CH of −(C6H5)2PN−), 7.57 (m, 4H, m, 3H, 3,5-
CH of -(C6H5)2PN−), 7.47 (d, J = 4.8, 2H, 3,5-CH of 4-
(CH3)3CC5H4N), 7.24 (m, 1H, −C6H4−); 7.17 (m, 1H −C6H4−);
7.04 (m, 2H, −C6H4− and 6-CH of −C6H3SO3−), 6.62 (dd, J = 8.4,
2.0, 1H, 4-CH of −C6H3SO3−), 6.42 (dd, J = 8.4, 2.0, 1H, 3-CH of
−C6H3SO3−), 6.36 (m, 1H, −C6H4−); 2.16 (s, 3H, 5-CH3 of
−C6H3SO3−), 1.38 (s, 9H, 4-(CH3)3C(C5H4N))Pd). 31P{1H} NMR
(CD2Cl2): δ 47.0. 13C NMR (CD2Cl2): 162.0, 158.2 (JCP = 20.0).
133.4 (d, JPC = 10.6), 133.0 (d, JPC = 9.9), 132.7, 132.6, 131.7 (d, JPC
=
109.3), 131.0 (d, JPC = 2.3), 129.6 (d, JPC = 91.8), 128.8, 128.8 (d, JPC
= 11.4), 128.5 (d, JPC = 12.9), 126.3 (d, JPC = 5.3), 122.0, 34.8, 29.9,
20.4, 14.2 (d, JPC = 68.3), −6.0. Anal. Calcd for C32H41N2O3PPdS: C,
57.27; H, 6.16; N, 4.17. Found: C, 57.44; H, 5.89; N, 4.01.
[κ2-2-((nBu)2PhPN)-5-MeC6H3SO3]Pd(4-(CH3)3CC5H5N)Me
(5c). A flask containing 3c (0.75 g, 1.75 mmol) and trans-
(4-tBupy)2PdMeCl (0.21 g, 0.43 mmol) was charged with benzene
(30 mL) while stirring. Shortly, an initially observed clear greenish
solution turned to a clear yellowish solution. The reaction proceeded
for 2 h, resulting in a clear yellow solution. The yellow solution was
filtered through dry Celite along with 2 × 10 mL benzene rinsing.
Evaporation of the filtrate afforded a yellow solid residue, which was
further treated with pentane (30 mL) to give a yellow precipitate. The
precipitate was filtered onto a medium glass frit and washed with
pentane (3 × 10 mL), yielding 5c (0.54 g, 47%) as a light yellow-green
1
solid. H NMR (CDCl3): 8.34 (d, J = 6.4, 2H, 2,6-CH of 4-tBuPy),
7.97 (m, 2H, 2,6-CH of PhPN), 7.88 (s, 1H, 6-CH of −C6H3SO3−),
7.45−7.62 (m, 3H, 3,4,5-CH of −PhPN−), 7.18 (d, J = 6.4, 2H, 3,5-
CH of 4-tBuPy), 6.89 (dd, J = 8.0, 2.0, 1H, 4-CH of −C6H3SO3−),
6.72 (dd, J = 8.0, 2.0, 1H, 3-CH of −C6H3SO3−), 2.60 (m, 2H,
CH2CH2CH2CH3), 2.46 (m, 2H, CH2CH2CH2CH3), 2.26 (s, 3H, 5-
CH3 of −C6H3SO3−), 2.06(m, 2H, CH2CH2CH2CH3), 1.70 (m, 2H,
CH2CH2CH2CH3), 1.45−1.60 (m, 4H, CH2CH2CH2CH3), 1.26 (s,
151.2, 143.6, 142.5 (d, JPC = 9.1), 133.4 (d, JPC = 10.6), 133.0 (d, JPC
9.9), 132.7, 132.6, 131.7 (d, JPC = 109.3), 131.0 (d, JPC = 2.3),130.0,
129.6 (d, JPC = 91.8), 128.8, 128.8 (d, JPC = 11.4), 128.5 (d, JPC
=
=
12.9), 127.2, 126.3 (d, JPC = 5.3), 122.0, 34.8, 29.9, 20.4. Anal. Calcd
1851
DOI: 10.1021/om501262r
Organometallics 2015, 34, 1844−1854

Organometallics
Article
for C34H33N2O3PPdS: C, 59.43; H, 8.84; N, 4.08. Found: C, 59.44; H,
8.89; N, 4.17.
demand. The reaction mixture was initially a pale yellow but turned
black as the temperature reached 80 °C, indicating the formation of
Pd0. The reaction was terminated by venting the reaction vessel and
addition of excess methanol (50−100 mL), and the solution was
filtered through a plug of silica gel to give a solution that was clear and
colorless. The solvent was removed, and the reaction residue was
Generation of 6a in the Presence of Ph3PO. A valved NMR
tube was loaded with 5a (3.0 mg, 4.2 μmol) and Ph3PO (3.0 mg, 10.8
μmol). Toluene-d8 (0.5 mL) was added via vacuum transfer at −196
°C. After the NMR tube was flushed with N2, the valved NMR tube
was sealed, warmed to 25 °C, and shaken until the solids dissolved. 1H
and 31P{1H} NMR spectra established that 5a was the only species
present in solution. The solution was heated to 80 °C for 6 h. 1H and
31P{1H} NMR spectra were obtained. 31P{1H} NMR spectra
established that 5a was completely converted to 6a. 1H NMR
(toluene-d8): δ 8.56 (d, J = 6.8, 2 H, 2,6-CH of 4-tBuPy), 8.41(s, 1H,
6-CH of −C6H3SO3−), 7.89 (m, 4H, 2,6-CH of −Ph2PN−), 7.60−
7.78 (m, 14H), 6.95−7.22 (m, 40H), 6.70−6.80 (m, 3H), 6.53 (d, J =
1
analyzed by H and 31P{1H} NMR. 31P{1H} NMR (CDCl3): δ 43.9
(6a, 4%), 31.3 (1a, 96%).
Reaction of Ethylene with 5b in Toluene. In a glovebox, the
bottle was charged with (PN-SO)PdMe(py) complex 5b (10.3 mg,
0.018 mmol) and sealed. The bottle was removed from the glovebox
and attached to a stainless steel double-manifold vacuum/ethylene
line. The nitrogen atmosphere was removed by vacuum, and the bottle
was flushed with ethylene (5 atm). The bottle was vented to decrease
the ethylene pressure to 1 atm, and toluene (20 mL) was added by
syringe. The bottle was sealed, and the ethylene pressure was
immediately increased to the experimental pressure (5 atm). The
solution was stirred at 25 °C for 10 min, warmed to 80 °C, and stirred
for 6 h. The pressure was kept constant by feeding ethylene on
demand. The reaction mixture was initially a pale yellow but turned
black as the temperature reached 80 °C, indicating the formation of
Pd0. The reaction was terminated by venting the reaction vessel and
addition of excess methanol (50−100 mL), and the solution was
filtered through a plug of silica gel to give a solution that was clear and
colorless. The solvent was removed, and the reaction residue was
t
6.8, 3H), 6.37 (s, 2H), 1.90 (s, 3H, 5-Me), 0.85 (s, 9H, Bu), 0.18 (s,
0.58H, CH4). 31P NMR (toluene-d8): δ 50.2 (5a), 28.7 (Ph3PO).
Attempted Orthopalladation of 5b in the Presence of
Ph3PO. A valved NMR tube was loaded with 5b (5 mg, 7.1 μmol) and
Ph3PO (3.0 mg, 10.8 μmol). Toluene-d8 (0.5 mL) was added via
vacuum transfer at −196 °C. After the NMR tube was flushed with N2,
the tube was sealed, warmed to 25 °C, and shaken until the solids
1
dissolved. H and 31P{1H} NMR spectra established that 5b was the
only species present in solution. The solution was heated to 80 °C for
6 and 24 h. 1H and 31P{1H} NMR spectra were obtained for each time
interval. Integration of the 31P{1H} NMR spectrum established that,
after 6 h at 80 °C, 14% of 5b had undergone orthopalladation. After 24
h at 80 °C, integration of the 31P{1H} NMR spectrum established that
58% of 5b had undergone orthopalladation.
1
analyzed by H and 31P{1H} NMR. 31P{1H} NMR (CDCl3): δ 39.1
(1b).
Attempted Orthopalladation of 5c in the Presence of
Ph3PO. A valved NMR tube was loaded with 5c (7 mg, 10.5 μmol)
and Ph3PO (3.0 mg, 10.8 μmol). Toluene-d8 (0.5 mL) was added via
vacuum transfer at −196 °C. After the NMR tube was flushed with N2,
the tube was sealed, warmed to 25 °C, and shaken until the solids
Reaction of Ethylene with 5c in Toluene. In a glovebox, the
bottle was charged with (PN-SO)PdMe(py) complex 5c (10.5 mg,
0.015 mmol) and sealed. The bottle was removed from the glovebox
and attached to a stainless steel double-manifold vacuum/ethylene
line. The nitrogen atmosphere was removed by vacuum, and the bottle
was flushed with ethylene (5 atm). The bottle was vented to decrease
the ethylene pressure to 1 atm, and toluene (20 mL) was added by
syringe. The bottle was sealed, and the ethylene pressure was
immediately increased to the experimental pressure (5 atm). The
solution was stirred at 25 °C for 10 min, warmed to 80 °C, and stirred
for 6 h. The pressure was kept constant by feeding ethylene on
demand. The reaction mixture was initially a pale yellow but turned
black as the temperature reached 80 °C, indicating the formation of
Pd0. The reaction was terminated by venting the reaction vessel and
addition of excess methanol (50−100 mL), and the solution was
filtered through a plug of silica gel to give a solution that was clear and
colorless. The solvent was removed, and the reaction residue was
1
dissolved. H and 31P{1H} NMR spectra established that 5c was the
only species present in solution. The solution was heated to 80 °C for
6 and 24 h. 1H and 31P{1H} NMR spectra were obtained for each time
interval. Integration of the 31P{1H} NMR spectrum established that,
after 6 h at 80 °C, 11% of the orthopalladated product derived from 5c
was present along with 24% of zwitterion 1c. After 24 h at 80 °C,
integration of the 31P{1H} NMR spectrum established that 46% of 5c
was present in solution along with 29% of 1c and three unknown
phosphorus-containing species totaling 25%.
Attempted Orthopalladation of [κ2-2-((nBu)3PN)-5-
MeC6H3SO3]Pd(4-(CH3)3CC5H5N)Me (5d) in the Presence of
Ph3PO. A valved NMR tube was loaded with 5d (5 mg, 7.8 μmol)
and Ph3PO (3.0 mg, 10.8 μmol), and toluene-d8 (0.5 mL) was added
via vacuum transfer at −196 °C. After the NMR tube was flushed with
N2, the tube was sealed, warmed to 25 °C, and shaken until the solids
1
analyzed by H and 31P{1H} NMR. 31P{1H} NMR (CDCl3): δ 45.5
1
dissolved. H and 31P{1H} NMR spectra established that 5d was the
(1c).
only species present in solution. The solution was heated to 80 °C for
6 and 24 h. 1H and 31P{1H} NMR spectra were obtained for each time
interval. Integration of the 31P{1H} NMR spectrum established that,
after 6 h at 80 °C, 5d was the only species present in solution. After 24
h at 80 °C, integration of the 31P{1H} NMR spectrum established that
76% of 5d was present in solution along with 24% of zwitterion 1d.
Reaction of Ethylene with 5a−5d in Toluene. The following
general procedure was used. Polymerizations were performed in a 200
mL glass bottle equipped with a magnetic stir bar, a stainless steel
pressure head with inlet and outlet needle valves, a septum-capped ball
valve for injections, a check valve for safety, and a pressure gauge. In a
glovebox, the bottle was charged with (PN-SO)PdMe(py) complex 5a
(10.3 mg, 0.015 mmol) and sealed. The bottle was removed from the
glovebox and attached to a stainless steel double-manifold vacuum/
ethylene line. The nitrogen atmosphere was removed by vacuum, and
the bottle was flushed with ethylene (5 atm). The bottle was vented to
decrease the ethylene pressure to 1 atm, and toluene (20 mL) was
added by syringe. The bottle was sealed, and the ethylene pressure was
immediately increased to the experimental pressure (5 atm). The
solution was stirred at 25 °C for 10 min, warmed to 80 °C, and stirred
for 6 h. The pressure was kept constant by feeding ethylene on
Reaction of Ethylene with 5d in Toluene. In a glovebox, the
bottle was charged with (PN-SO)PdMe(py) complex 5d (10.5 mg,
0.017 mmol) and sealed. The bottle was removed from the glovebox
and attached to a stainless steel double-manifold vacuum/ethylene
line. The nitrogen atmosphere was removed by vacuum, and the bottle
was flushed with ethylene (5 atm). The bottle was vented to decrease
the ethylene pressure to 1 atm, and toluene (20 mL) was added by
syringe. The bottle was sealed, and the ethylene pressure was
immediately increased to the experimental pressure (5 atm). The
solution was stirred at 25 °C for 10 min, warmed to 80 °C, and stirred
for 6 h. The pressure was kept constant by feeding ethylene on
demand. The reaction mixture was initially a pale yellow but turned
black as the temperature reached 80 °C, indicating the formation of
Pd0. The reaction was terminated by venting the reaction vessel and
addition of excess methanol (50−100 mL), and the solution was
filtered through a plug of silica gel to give a solution that was clear and
colorless. The solvent was removed, and the reaction residue was
1
analyzed by H and 31P{1H} NMR. 31P{1H} NMR (CDCl3): δ 56.6
(1d).
1852
DOI: 10.1021/om501262r
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Organometallics
Article
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ASSOCIATED CONTENT
■
S
* Supporting Information
1H, 31P, and 13C NMR spectra of compounds. The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/om501262r.
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
■
We thank the donors of the American Chemical Society
Petroleum Research Fund (50401-DN13) and the University of
Louisville for generously supporting this research. M.S.M.
thanks the Department of Defense (W81XWH) from the
Telemedicine and Advanced Technology Research Center of
the U.S. Army, the Department of Energy (DEFG02-
08CH11538), and the Kentucky Research Challenge Trust
Fund for the upgrades of our X-ray facilities.
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