Room-temperature carbon-sulfur bond activation by a reactive (dippe)Pd fragment

Article abstract of DOI:10.1021/acs.organomet.5b00194

The reactivity of [Pd(dippe)(μ-H)]₂ (1) and [(μ-dippe)Pd]₂ (2) (dippe = 1,2-bis(diisopropylphosphino)ethane) toward C-S bonds in thiophene derivatives and thioethers was investigated, which led to C-S bond activation products. The thiapalladacycles derived from thiophenic substrates were fully characterized by ¹H, ³¹P, and ¹³C NMR spectroscopy, elemental analysis, and X-ray diffraction. The stability of the C-S insertion products was probed by performing competition experiments which follow the thermodynamic stability order (dippe)Pd(κ²C,S-benzothiophene) (6) > (dippe)Pd(κ²C,S-dibenzothiophene) (8) > (dippe)Pd(κ²C,S-thiophene) (3). The reactivity of the thiapalladacycles with small molecules such as H₂, CO, and alkynes was investigated.

Full text of DOI:10.1021/acs.organomet.5b00194

Article
pubs.acs.org/Organometallics
Room-Temperature Carbon−Sulfur Bond Activation by a Reactive
(dippe)Pd Fragment
Lloyd Munjanja, William W. Brennessel, and William D. Jones*
Department of Chemistry, University of Rochester, P.O. Box 270216, 491, Rochester, New York 14627-0216, United States
S
* Supporting Information
ABSTRACT: The reactivity of [Pd(dippe)(μ-H)]2 (1) and [(μ-dippe)Pd]2
(2) (dippe = 1,2-bis(diisopropylphosphino)ethane) toward C−S bonds in
thiophene derivatives and thioethers was investigated, which led to C−S bond
activation products. The thiapalladacycles derived from thiophenic substrates
1
were fully characterized by H, 31P, and 13C NMR spectroscopy, elemental
analysis, and X-ray diffraction. The stability of the C−S insertion products was
probed by performing competition experiments which follow the thermodynamic stability order (dippe)Pd(κ2C,S-
benzothiophene) (6) > (dippe)Pd(κ2C,S-dibenzothiophene) (8) > (dippe)Pd(κ2C,S-thiophene) (3). The reactivity of the
thiapalladacycles with small molecules such as H2, CO, and alkynes was investigated.
article extends the study of reactivity of 1 toward various
thiophenic substrates.
INTRODUCTION
■
Interest in C−S bond activation has risen due to the
significance of hydrodesulfurization (HDS) in the petroleum
refining industry. HDS is the catalytic process for the removal
of sulfur from organosulfur compounds (organosulfur com-
pounds account for ∼5 wt % in petroleum) under 150−600 psi
of hydrogen at 300−450 °C.1 Current technologies of Ni/Mo
(or Mo/Co) heterogeneous catalysts reduce the sulfur content
of oil from 1−5% to ∼300 ppm in fuels.1 With new mandates
by the Environmental Protection Agency to reduce sulfur
content from transportation fuels to 10 ppm or lower,2 there is
a greater demand for the development of new catalysts that can
meet this new challenge. Consequently, homogeneous
transition-metal catalysts serve as models for C−S cleavage
by providing an understanding of how the thiophene substrates
react with the metal center to yield thiametallacycles.
We have previously reported the C−S activation of
thiophenes by a hydride-bridged nickel3 dimer and a
platinum−hydride dimer4 to form ring-opened thiophene
adducts. Work in our laboratory with [Ni(dippe)(μ-H)]2
(dippe = 1,2-bis(diisopropylphosphino)ethane) found that it
is possible to activate the carbon−sulfur bond in thiophene,
benzothiophene, dibenzothiophene, 4-methylbenzothiophene,
and other cyclic sulfur compounds to yield the corresponding
thianickelacycles. An analogous platinum complex, [(dippe)-
PtH]2, was found to activate thiophene over the course of 10
days at 70 °C. As part of our ongoing studies related to C−S
bond activation with group 10 metal complexes, we became
interested in studying the analogous dihydride palladium
complex 1 to compare its reactivity with nickel and platinum.
Garcia et al. have previously reported reactions of a variety of
substituted thiophenes with Pd(PEt3)3.5 [Pd(dippe)(μ-H)]2
(1) was first generated in situ by our group and has been
shown to react with thiophene to give 3 (eq 1), although both
reactant and product were found to be very unstable.4 This
RESULTS AND DISCUSSION
■
Preparation of the Palladium(I) Hydride Dimer 1 and
Dinuclear Pd(0) Species 2. We generated the bridging
hydrido complex [Pd(dippe)(μ-H)]2 (1) in situ from a
palladium-chloro precursor6 and sodium triethylborohydride.
Here we show that [Pd(dippe)(μ-H)]2 (1) and the dinuclear
Pd(0) species [(μ-dippe)Pd]2 (2)7 remain in an equilibrium
with a relative ratio of 9:1, respectively, when a suspension of
[(dippe)PdCl2] is treated with 2 equiv of NaHBEt3 in toluene
(Scheme 1). The 31P{1H} NMR spectrum shows two singlet
resonances, one at δ 61.3 which has been assigned to 1 and the
other resonance at δ 33.0 corresponding to [(μ-dippe)Pd]2 (2).
The 1H NMR spectrum (THF-d8) of the in situ solution shows
a quintet centered at δ −2.00 (JP−H = 40 Hz) assigned to 1,
indicative of hydride coupling to four equivalent phosphorus
atoms. Efforts to isolate 1 in pure form have so far been
unsuccessful, since this complex decomposes readily under
vacuum.
When a frozen toluene solution (−196 °C) containing a
mixture of 1 and 2 was subjected to freeze−pump−thaw degas,
2 was formed exclusively by the loss of H2 from 1.
Subsequently, addition of 1 atm of H2 to 2 establishes the
initial equilibrium between 1 and 2. We propose that the
Received: March 12, 2015
© XXXX American Chemical Society
A
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Scheme 1. Formation of [Pd(dippe)(μ-H)]2 (1) and [(μ-
Scheme 3. Trapping the 14-Electron (dippe)Pd0 Species A
dippe)Pd]2 (2) in Situ
corresponding C−S bond insertion adducts exclusively with the
complete disappearance of 1 and 2, as detailed in the following
section.
Reactivity of a Mixture Containing 1 and 2 with
Thiophenic Substrates. The reactivity of a mixture
containing 1 and 2 toward C−S activation was examined.
Insertion of palladium into the carbon−sulfur bonds was
achieved for most, but not all, of the substrates tested (Figure
1).
equilibrium between 1 and 2 is established via a reactive 14-
electron intermediate species, (dippe)Pd(0) (A) (Scheme 1).
Neither A nor dippe ligand was observed in the 31P{1H} NMR
spectrum even at low temperatures. 31P{1H} NMR spectra
taken over a course of several days indicated that the amounts
of 1 and 2 decreased as the concentration of two new
complexes increased. These complexes were identified as the
thermodynamically stable species 4 and 5, as judged by a singlet
at δ 45.5 and two multiplets at δ 49.5 and 54.8, respectively, in
the 31P{1H} NMR spectra (Scheme 2).8 The solution shows no
precipitate but is opaque brown.
Scheme 2. Formation of [(dippe)2Pd] (4) and
[Pd2(dippe)2(μ-dippe)] (5) from a Mixture of 1 and 2
Figure 1. Summary of complexes synthesized using a mixture
containing [Pd(dippe)(μ-H)]2 (1) and [(μ-dippe)Pd]2 (2). Reported
yields are isolated yields unless otherwise noted.
In support of the formation of the 14-electron intermediate
species A, Fink and co-workers observed the formation of the
mixed dimer (μ-dippe)(μ-dcpe)Pd after the dissolution of
equimolar amounts of [(μ-dippe)Pd]2 and [(μ-dcpe)Pd]2
(dcpe = 1,2-bis(dicyclohexylphosphino)ethane).7 Conse-
quently, treatment of a THF solution mixture of 1 and 2
with a slight excess of dippe ligand converts both complexes to
4, indicating that 1 and 2 in the above experiment interconvert
via A, which was trapped by the dippe ligand to give 4
exclusively as shown in Scheme 3. Palladium colloid is
presumably also formed in the reaction in Scheme 2, as the
opaque brown solution9 becomes transparent brown upon
stirring over elemental mercury.
Jones and co-workers showed previously that reduction of
[(dippe)PdCl2] in neat thiophene gave the C−S insertion
adduct 3.4 Similarly, the reaction of a solution containing a
mixture of 1 and 2 and an excess of benzothiophene at room
temperature afforded a white solid identified analytically and
spectroscopically as (dippe)Pd(κ2C,S-benzothiophene) (6). A
31P{1H} NMR spectrum of complex 6 shows a pair of doublets
at δ 73.5 and 66.7 with J = 26.2 Hz, consistent with a
mononuclear, asymmetric ring-opened structure. X-ray-quality
crystals were grown by layering a solution of 6 in CH2Cl2 (−30
°C) with hexanes (Figure 2). The geometry of 6 is slightly
distorted square planar. The dihedral angle between planes
Since both 1 and 2 plus H2 disproportionate in solution to
afford a coordinatively unsaturated nucleophile, A, addition of
an organosulfur compound to the solution instantly yields the
B
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Figure 3. ORTEP drawing of (dippe)Pd(κ2C,S-3-methylbenzothio-
phene) (7). Selected bond lengths (Å): Pd(1)−C(1), 2.059(3);
Pd(1)−P(1), 2.2805(11); Pd(1)−S(1), 2.2816(11); Pd(1)−P(2),
2.3262(11); S(1)−C(4), 1.764(4); C(1)−C(2), 1.307(5); C(2)−
C(3), 1.455(6); C(3)−C(4), 1.398(6). Selected bond angles (deg):
C(1)−Pd(1)−P(1), 90.67(10); C(1)−Pd(1)−S(1), 90.80(10); P(1)−
Pd(1)−S(1), 176.90(4); C(1)−Pd(1)−P(2), 175.98(10); P(1)−
Pd(1)−P(2), 85.59(4); S(1)−Pd(1)−P(2), 93.01(4).
Figure 2. ORTEP drawing of (dippe)Pd(κ2C,S-benzothiophene) (6).
Selected bond lengths (Å); Pd(1)−C(1), 2.032(3); Pd(1)−P(1),
2.2554(9); Pd(1)−S(1), 2.2793(8); Pd(1)−P(2), 2.3144(9); S(1)−
C(4), 1.734(3); C(1)−C(2), 1.321(4); C(2)−C(3), 1.454(4); C(3)−
C(4), 1.411(4). Selected bond angles (deg): C(1)−Pd(1)−P(1),
91.65(9); C(1)−Pd(1)−S(1), 93.58(9); P(1)−Pd(1)−S(1),
170.97(4); C(1)−Pd(1)−P(2), 173.47(10); P(1)−Pd(1)−P(2),
86.44(3); S(1)−Pd(1)−P(2), 89.14(3).
and NMR spectroscopic results were consistent with a
monomeric ring-opened structure. X-ray-quality crystals were
grown from a solution of 8 in THF at room temperature
(Figure 4). The metallacyclic complex 8 is highly distorted
P1−Pd−P2 and S1−Pd−C1 is 9.8(1)° and corresponds to a
slight fold as opposed to a twist. The Pd−P2 bond (2.3144(9)
Å) is slightly longer than the Pd−P1 bond (2.2554(9) Å),
which is characteristic of similar asymmetric (dippe)Pd
complexes.10,18 It is postulated that the Pd−P2 bond is longer
due to the trans effect of C(sp2) being much greater than that
of S. The bite angle for the chelating dippe ligand is 86.44(3)°,
comparable to that of complex 3 of 86.19(4)°,4 as well as to
those of other (dippe)Pd complexes.8,18,20 The metallacycle
complex 6 is square planar with an RMS deviation of 0.011 Å.
Similar to the carbon−sulfur activation chemistry of [(dippe)-
NiH]2,3 palladium inserts exclusively into the vinyl C−S bond
of benzothiophene in lieu of the aryl C−S bond.
Attempts to react a mixture of 1 and 2 with 2-
methylbenzothiophene were unsuccessful, attributed to the
vinyl C−S bond being obstructed by the methyl group at the 2-
position. Theoretical studies carried out in our group on the
binding of platinum metal to thiophenes showed that π
coordination to the double bond adjacent to the C−S bond is
an essential step before insertion into the C−S bond.11
In contrast, when 3-methylbenzothiophene was subjected to
the same reaction conditions, C−S bond activation took place,
yielding a monomeric complex, 7, as shown by the X-ray
structure (Figure 3). A plausible explanation for this
observation is that for 3-methylbenzothiophene the methyl
substituent is positioned away from the palladium center,
thereby allowing π coordination to the double bond adjacent to
the C−S bond before C−S cleavage. However, no π complex
could be detected prior to product formation. Comparably to 6,
complex 7 is nearly square planar. The RMS deviation of the
metallacycle moiety is 0.015, indicating its planarity. The
dihedral angle between the planes P1−Pd−P2 and S1−Pd−C1
is 3.1(1)°. The trans effect (C(sp2) ≫ S) is also noticeable in
complex 7 by the inequivalent Pd−P bonds with Pd−P2 at
2.3262(11) Å being longer than Pd−P1 at 2.2805(11) Å.
The reaction of a mixture of 1 and 2 with dibenzothiophene
at room temperature led to the solid white product (dippe)-
Pd(κ2C,S-dibenzothiophene) (8) in 45 min. X-ray diffraction
Figure 4. ORTEP drawing of (dippe)Pd(κ2C,S-dibenzothiophene)
(8). Selected bond lengths (Å): Pd(1)−C(1), 2.069(7); Pd(1)−P(1),
2.271(2); Pd(1)−P(2), 2.319(2); Pd(1)−S(1), 2.353(2); S(1)−C(4),
1.766(8); C(1)−C(2), 1.376(10); C(2)−C(3), 1.498(10); C(3)−
C(4), 1.400(10); Selected bond angles (deg): C(1)−Pd(1)−P(1),
93.1(2); C(1)−Pd(1)−P(2), 178.3(2); P(1)−Pd(1)−P(2), 86.30(7);
C(1)−Pd(1)−S(1), 85.7(2); P(1)−Pd(1)−S(1), 169.65(7); P(2)−
Pd(1)−S(1), 94.56(7).
from planarity due to the rigidity of the biphenyl moiety, for
which the angle between the two biphenyl ring planes is
40.7(2)°. The trans effect (C(sp2) ≫ S) is again apparent by
the inequivalent Pd−P bonds: Pd−P1 at 2.271(2) Å and Pd−
P2 at 2.319(2) Å.
Solution and solid forms of complex 8 gradually decompose
within a couple of weeks to form 4 and 5 (+DBT) at room
temperature. In contrast to the chemistry of [(dippe)NiH]2,
C
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C−S activation of 4-methyldibenzothiophene and 4,6-dime-
thyldibenzothiophene with a mixture of of 1 and 2 were
unsuccessful. The fact that dibenzothiophene reacts indicates
that intermediate A can find access to the C−S bond that is
ultimately cleaved. It is somewhat surprising, therefore, that the
unhindered C−S bond of 4-methyldibenzothiophene does not
react.
A mixture of 1 and 2 instantly reacts with thianthrene and
thioxanthene at room temperature to give the C−S insertion
products (dippe)Pd(κ2C,S-thianthrene) (9) and (dippe)Pd-
(κ2C,S-thioxanthene) (10), respectively. Colorless crystals of
both 9 and 10 were grown by slow evaporation of a solution in
THF at −30 °C (Figures 5 and 6). Solutions of solid products 9
Figure 6. ORTEP drawing of (dippe)Pd(κ2C,S-thioxanthene) (10).
Selected bond lengths (Å): Pd(1)−C(1), 2.0525(13); Pd(1)−P(1),
2.2696(4); Pd(1)−P(2), 2.3332(4); Pd(1)−S(1), 2.3439(4); S(1)−
C(5), 1.7613(13); C(1)−C(2), 1.400(2); C(2)−C(3), 1.515(2);
C(3)−C(4), 1.506(2); C(4)−C(5), 1.4067(19). Selected bond angles
(deg): C(1)−Pd(1)−P(1), 89.19(4); C(1)−Pd(1)−P(2), 172.38(4);
P(1)−Pd(1)−P(2), 87.242(13); C(1)−Pd(1)−S(1), 97.14(4); P(1)−
Pd(1)−S(1), 165.921(13); P(2)−Pd(1)−S(1), 87.840(13); C(5)−
S(1)−Pd(1), 117.48(5).
Figure 5. ORTEP drawing of (dippe)Pd(κ2C,S-thianthrene) (9).
Selected bond lengths (Å); Pd(1)−C(1), 2.053(2); Pd(1)−P(1),
2.2471(6); Pd(1)−P(2), 2.3114(6); Pd(1)−S(1), 2.3530(6); S(1)−
C(4), 1.753(2); S(2)−C(3), 1.774(2); S(2)−C(2), 1.786(2); C(1)−
C(2), 1.384(3); C(3)−C(4), 1.412(3). Selected bond angles (deg):
C(1)−Pd(1)−P(1), 91.82(6); C(1)−Pd(1)−P(2), 177.43(6); P(1)−
Pd(1)−P(2), 86.86(2); C(1)−Pd(1)−S(1), 90.52(6); P(1)−Pd(1)−
S(1), 174.85(2); P(2)−Pd(1)−S(1), 90.63(2); C(4)−S(1)−Pd(1),
115.19(8).
Hz) started forming at the expense of 3. Within a few minutes 3
disappeared and 6 formed. Free thiophene was formed from
the decomposition of 3, as indicated by the 1H NMR spectrum.
This indicates that the benzothiophene adduct 6 is
thermodynamically more stable than the thiophene adduct 3
and that 3 is very labile. Alternatively, equimolar amounts of 3
and 6 were dissolved in THF and the reaction was monitored
by NMR spectroscopy. Complex 3 was observed to completely
decompose over 12 h, leaving 6 in solution in addition to free
thiophene.
and 10 are stable indefinitely in moisture and air. Both
structures show highly distorted metallacycles due to the ring-
bridging sulfur and methylene groups favoring twists of the
biphenyl ring planes of 80.69(6) and 83.23(5)° in 9 and 10,
respectively. The deviation from planarity at the metal center of
the planes P1−Pd−P2 and S1−Pd−C1 is 5.0(1)° for 9 and
14.19(4)° for 10. Similarly to the other palladium C−S
insertion products (6−8), the Pd−P2 bond is longer than the
Pd−P1 bond in both complexes 9 and 10 due to the C(sp2) ≫
S trans effect.
For [(dippe)Ni] adducts, the thiophene and the benzothio-
phene C−S insertion products were in equilibrium with Keq
≈
110 (eq 3).3 On the other hand, (PEt3)2Pt(κ2C,S-benzothio-
phene) was found to be 10 times more stable than the
corresponding (PEt3)2Pt(κ2C,S-thiophene).12
The reactivity of the Pd(dippe) fragment A with thiophenic
substrates occurs rapidly at room temperature. This can be
compared with the reactions of Pd(PEt3)3 with thiophenes,
which requires heating to 70 °C for 10 min to 3 h.5
Relative Thermodynamic Stabilities of the Thiapalla-
dacycles Derived from Thiophene, Benzothiophene,
and Dibenzothiophene. The reaction of (dippe)Pd(κ2C,S-
thiophene) (3) with 1 equiv of benzothiophene in THF was
probed (eq 2). Initially 31P{1H} NMR spectroscopy showed a
pair of doublets: δ 74.59 and 67.10 (J = 25.5 Hz), attributed to
3. However, with the addition of benzothiophene, 6 with a pair
of doublets at δ 73.52 (d, J = 26.2 Hz) and δ 66.86 (d, J = 26.2
In a separate experiment, the reaction of (dippe)Pd(κ2C,S-
dibenzothiophene) (8) with 1 equiv of benzothiophene in THF
affords 6 and free dibenzothiophene in 12 h (eq 4). Initially,
31P{1H} NMR spectroscopy showed two pairs of doublets at δ
71.86 (d, J = 19.4 Hz) and δ 68.60 (d, J = 19.4 Hz), attributed
to 8. In 12 h the initial set of doublets was replaced by another
pair of doublet resonances at δ 73.52 (d, J = 26.2 Hz) and δ
66.86 (d, J = 26.2 Hz) for 6. Free dibenzothiophene was
D
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benzothiophene from 6 was observed, with the formation of a
thermally stable palladium complex, 11 (eq 6). The reaction
1
observed in the H NMR spectrum. This result establishes the
stability of 6 in comparison to 8. In addition, this shows that
reaction of a mixture of 1 and 2 with dibenzothiophene to form
8 is reversible but that 8 loses dibenzothiophene more slowly
than 3 loses thiophene.
In another related experiment equimolar amounts of 3 and 8
were mixed together in THF and the reaction was monitored
by NMR spectroscopy over the course of 1 h. Complete
decomposition of 3 was observed with formation of free
thiophene. Complex 8 remains in solution. Alternatively,
adding 1 equiv of dibenzothiophene to a solution of 3 results
in complete formation of 8 along with free thiophene after 1 h.
This observation establishes that complex 8 is more
thermodynamically stable than complex 3 in solution (eq 5).
was monitored by 31P{1H} NMR spectroscopy over 8 h.
Disappearance of the pair of doublet resonances at δ 73.52 (d, J
= 26.2 Hz) and δ 66.86 (d, J = 26.2 Hz) for 6 was seen with
simultaneous growth of a singlet at δ 66.5 for complex 1116 (eq
1
6). Free benzothiophene was observed by H NMR spectros-
copy. Similar palladium18 and nickel19 complexes with π-
coordinating alkynes have been reported in the literature.
Attempts to carbonylate complex 6 at 1 atm of CO to
functionalize benzothiophene to 2H-thiochromen-2-one were
not successful. Instead, the reaction yielded a thermodynami-
cally stable dicarbonyl palladium complex, (dippe)Pd(CO)2
(12),20 (eq 7) and free benzothiophene. A plausible
In light of these experimental results, the thermodynamic
stability of the thiapalladacycles was established as 6 ≫ 8 > 3. A
similar trend was seen by Garcia and co-workers in their C−S
activation studies of thiophene, benzothiophene, and dibenzo-
thiophene using tris(triethylphosphine)platinum(0).12 Studies
with [Ni(dippe)(μ-H)]2 in our group also show a related
trend.3
Reactivity of 6 with Small Molecules. Since complex 6
was the most reluctant to reductively eliminate benzothio-
phene, its reactivity with small molecules was studied. In our
search to model HDS processes we have discovered that
thiametallacycles formed from the insertion of metals such as
rhodium or iridium1,13 and platinum12 into benzothiophenes
usually react with H2 to give 2-ethylthiophenol,14 2,3-
dihydrobenzothiophene,15 or ethylbenzene.16 We decided to
carry out similar experiments with H2 to probe HDS with
complex 6. The disappearance of complex 6 was observed in
the 31P{1H} NMR spectrum when 6 was treated with H2 at 1−
5 atm, with simultaneous generation of the decomposition
products 4 and 5. No other intermediates were observed by
spectroscopy. 1H NMR spectroscopy showed no signals due to
benzothiophene hydrogenation or desulfurization products.
Spectroscopic data showed the formation of free benzothio-
phene.
explanation for this observation would be that the nucleophilic
intermediate fragment A would be more likely to bind strongly
to carbon monoxide via back-donation, hence favoring 12
instead of a carbonylated benzothiapalladacycle.
Reaction of a Mixture of 1 and 2 with Ph2S. Although
C−S bonds of thioethers are relatively weak, their reactions
with transition metals have been less commonly studied.
Recently, we reported C−S insertions into aryl, vinyl, and allyl
sp2 and sp3 carbon centers of thioethers using [(dippe)Pt-
(NBE)] (NBE = norbornene) as a source of platinum(0).21
Reactions with [(dippe)Pt(NBE)] were done under relatively
harsh conditions with temperatures >100 °C and long reaction
times in contrast to the observations in this study with a
mixture of 1 and 2. Addition of excess diphenyl sulfide to a
mixture of 1 and 2 formed a light yellow solid, the C−S
insertion adduct 13, which shows a characteristic pair of
doublet resonances in the 31P{1H} NMR spectrum at δ 61.4
and 59.4 with J = 19.6 Hz. Complex 13 is stable indefinitely
under an inert atmosphere at room temperature and was
unchanged after heating at 80 °C in C6D6 for more than 8 h.
Acyclic palladium complexes derived from the C−S
activation of thioethers were more responsive to CO insertions
than the cyclic palladium complexes derived from activation of
thiophenes. A plausible explanation for this observation is that
there may be a thermodynamically unfavorable insertion of CO
in the cyclic complexes due to either the introduction of ring
strain or a decrease in aromaticity, both of which would be
absent upon CO insertion in the acyclic complexes. Hence,
treatment of (dippe)Pd(SPh)(Ph) (13) with 1 atm of CO for
12 h affords new palladium complexes in solution. Complex 13
in either benzene or THF converted to four major phosphorus-
containing products that were observed in the 31P{1H} NMR
spectrum. The products were identified by NMR spectroscopy
and X-ray diffraction as (dippe)Pd(SPh)2 (14), (dippe)Pd-
(SPh)(COPh) (15), 12, and 4 (eq 8).
Garcia and co-workers12 have concluded that HDS reactions
in platinum systems are promoted by the use of hydridic agents.
With this knowledge we explored the use of various hydride
sources to achieve HDS with the palladium system. Et3SiH,
NaBH4, and LiAlH4 were reacted with 6, but unfortunately
none of these produced any HDS products, as evidenced by
NMR spectroscopy and GC-MS. Only free benzothiophene
was observed in these studies.
Palladacycles have since been known to insert alkynes17 into
the Pd−C(sp2) and Pd−C(sp3) bonds. We investigated
thiapallacycle alkyne insertion by the reaction of 6 with 1
equiv of diphenylacetylene. Complete reductive elimination of
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evaporation from a THF solution showed a cocrystallized
mixture of 15 and 14 (∼7:1, respectively) (Figure 7). The two
monodentate ligand sites were each modeled as a disorder of
ligands SPh and C(O)Ph (0.79:0.21 and 0.33:0.67, for the
two sites, respectively).
In addition to the Pd-containing products, formation of the
organic thioester product S-phenyl benzothioate (6%) as well
as the reductive elimination product of 13 diphenyl sulfide
1
(3%) was observed in the H NMR spectrum. This reaction
shows the success of carbonylation of thioethers to thioesters
using palladium, although in a very inefficient fashion. Similar
carbonylation reactions of thioethers have been shown by
Hillhouse and co-workers using [(2,2-bipyridine)Ni(1,5-cyclo-
octadiene)].22
The mixture of the complexes in eq 8 could not be separated
1
by any method attempted, and the H NMR spectra were too
complicated to assign the resonances to individual species. The
31P{1H} NMR (C6D6) spectrum of the products in eq 8
revealed the presence of previously independently synthesized
4 and 12; thus, we decided to independently synthesize
complexes 14 and 15 for comparison.
Addition of an excess of diphenyl disulfide to a mixture of 1
and 2 afforded a yellow solid with a singlet resonance at δ 85.0
in the 31P{1H} NMR (C6D6) spectrum (eq 9), matching the
data for 14 in eq 8.
Figure 7. ORTEP drawings of (dippe)Pd(SPh)2 (14) (top) and
(dippe)Pd(SPh)(COPh) (15) (bottom) Selected bond lengths (Å):
Pd(1)−C(7), 2.046(3); Pd(1)−C(7′), 2.051(7); Pd(1)−P(1),
2.2883(4); Pd(1)−P(2), 2.3362(4); Pd(1)−S(1′), 2.3876(14);
Pd(1)−S(1), 2.4038(6).
Complex 15 was independently synthesized from the C−S
bond activation of S-phenyl benzothioate by a mixture of 1 and
2 to form a yellow solid containing 15 and 14 coproduced in a
4:1 ratio, respectively (eq 10). Solid-state IR spectroscopy
CONCLUSIONS
■
In summary, we have synthesized and characterized C−S
activation adducts of benzothiophene, dibenzothiophene, 3-
methylbenzothiophene, thianthrene, thioxanthene, diphenyl
sulfide, and S-phenyl benzothioate using the reactive proposed
intermediate (dippe)Pd0 (A). The thermodynamic stability of
the thiapalladacycles has been studied via competition experi-
ments to show that (dippe)Pd(κ2C,S-benzothiophene) (6) is
much more stable than (dippe)Pd(κ2C,S-dibenzothiophene)
(8) and (dippe)Pd(κ2C,S-thiophene) (3). Activation of the C−
S bond of the thioether diphenyl sulfide to yield (dippe)Pd-
(SPh)(Ph) (13) was explored. Carbonylation of complex 13
produced a mixture of complexes: (dippe)Pd(SPh)2 (14),
(dippe)Pd(SPh)(COPh) (15), (dippe)Pd(CO)2 (12), and
(dippe)2Pd (4) but most importantly the carbonylated organic
product S-phenyl benzothioate in low yield.
showed that the carbonyl stretch in complex 15 appears at 1604
cm−1, which differs from the free S-phenyl benzothioate
carbonyl stretch at 1663 cm−1.
Attempts to separate 14 and 15 were unsuccessful. X-ray-
quality crystals grown from the yellow solid by slow
F
DOI: 10.1021/acs.organomet.5b00194
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
tube, and the reaction was monitored by NMR spectroscopy over the
course of 12 h. Initially, 31P NMR spectroscopy showed two sets of
pairs of doublets at δ 73.52 (d, J = 26.2 Hz) and 66.86 (d, J = 26.2 Hz)
attributed to 6 and at δ 71.86 (d, J = 19.4 Hz) and 68.60 (d, J = 19.4
Hz) for 8, respectively. In the course of 12 h, 8 gradually disappeared,
leaving behind 6 and free dibenzothiophene in solution. Complex 4
was also observed in the 31P{1H} NMR spectrum.
EXPERIMENTAL SECTION
■
General Procedures. All operations and routine manipulations
were performed under a nitrogen atmosphere, either on a high-vacuum
line using modified Schlenk techniques or in a Vacuum Atmospheres
Corp. Dri-Lab. Benzene-d6 and THF-d8 were purchased from
Cambridge Isotope Laboratories, Inc. Prior to use, benzene-d6 and
THF-d8 were distilled under vacuum from a dark purple solution of
benzophenone ketyl and stored in an ampule with a Teflon valve.
CD2Cl2 was dried with CaH2 and stored over molecular sieves. THF
and toluene were distilled from dark purple solutions of
benzophenone ketyl and stored over molecular sieves in an ampule
with a Teflon valve. Thiophene (99+%) was purchased from Sigma-
Aldrich Co. and dried under CaCl2. (CH3CN)2PdCl2, benzothio-
phene, dibenzothiophene, 3-methylbenzothiophene, 2-methyldibenzo-
thiophene, thioxanthene, thianthrene, diphenyl disulfide, and diphenyl
sulfide were purchased from Sigma-Aldrich Co. and used without
further purification. S-Phenyl benzothioate23 and dippe7 ligand were
synthesized via the reported literature procedures.
Establishing the Relationship between (dippe)Pd(κ2C,S-
thiophene) (3) and (dippe)Pd(κ2C,S-dibenzothiophene) (8).
Equimolar amounts of 3 (15 mg, 0.033 mmol) and 8 (17 mg, 0.033
mmol) were dissolved in 0.6 mL of THF-d8 in a J. Young NMR tube,
and then the reaction was monitored by 31P NMR spectroscopy over
the course of 12 h. Complex 8 remained in solution while 3
decomposed to form free thiophene and complex 4.
General Procedure for the Synthesis of the C−S Insertion
Products. Under a nitrogen atmosphere, NaHBEt3 (91 μL of 1 M
solution in toluene, 0.091 mmol) was added slowly to a stirred
suspension of [(dippe)PdCl2] (20 mg, 0.046 mmol) in 0.5 mL of
toluene and 4 equiv of substrate. The resulting dark red solution was
stirred for 30−45 min and then filtered through Celite on a fine glass
frit. The solvent was evaporated under vacuum overnight to yield C−S
insertion products. The products were washed with 6 mL of either
hexane or pentane.
1
All H and 13C NMR spectra were collected on either a Bruker
Avance 400 or Avance 500 MHz spectrometer. All chemical shifts were
reported in ppm (δ) relative to tetramethylsilane and referenced to the
chemical shifts of residual solvent resonances (C6HD5, δ 7.16 or
1
(dippe)Pd(κ2C,S-benzothiophene) (6). Complex 6 was synthesized
(7.5 mg, 32%) using 4 equiv of benzothiophene (24 mg, 0.18 mmol).
1H NMR (400 MHz, THF-d8): δ 7.66 (d, J = 7.8 Hz, 1H), 7.57−7.26
128.0). While H chemical shifts are given to three decimal places
( 0.4 Hz), these values can vary slightly with concentration and
temperature. 13C shifts are given to two decimal places ( 1 Hz).
31P{1H} NMR spectra were referenced relative to external H3PO4.
Elemental analysis was performed by the University of Rochester using
a PerkinElmer 2400 Series II elemental analyzer in CHN mode. GC-
MS spectra were recorded on a Shimadzu QP2010 GCMS instrument.
Infrared spectra were recorded in the solid state on a Thermo
Scientific Nicolet 4700 FT-IR spectrometer equipped with a smart
orbit diamond attenuated total reflectance (ATR) accessory.
Establishing the Equilibrium between Pd(dippe)(μ-H)]2 (1)
and [(μ-dippe)Pd]2 (2). NaHBEt3 (45.4 μL of 1 M solution in
toluene) was added slowly to a stirred suspension of [(dippe)PdCl2]
(10 mg, 22.7 μmol) to give a dark red solution. Two singlet resonances
were observed at δ 61.3 (1) and 33.1 (2) in a ratio of 9:1 in the
31P{1H} NMR spectrum. (The same ratio was seen in C6H6 or THF
(m, 2H), 7.11 (d, J = 7.6 Hz, 1H), 6.82 (dt, J = 38.1, 7.1 Hz, 2H),
2.60−2.24 (m, 4H), 2.11−1.79 (m, 4H), 1.40−1.13 (m, 24H).
13C{1H} NMR (126 MHz, THF-d8): δ 138.91 (s), 138.04 (s), 135.87
(d, J = 9.1 Hz), 131.38 (s), 130.50 (s), 129.78 (d, J = 10.3 Hz), 124.11
(s), 119.62 (s), 22.71−22.29 (m), 20.35−19.45 (m), 18.86 (d, J = 5.0
Hz), 18.60 (d, J = 5.1 Hz), 17.66 (s), 17.39 (s), 13.41 (s). 31P{1H}
NMR (162 MHz, THF-d8): δ 73.52 (d, J = 26.2 Hz), 66.86 (d, J = 26.2
Hz) Anal. Calcd (found) for C22H38PdP2S·0.3CH2Cl2: C, 50.68
(50.43); H, 7.36 (7.34).
(dippe)Pd(κ2C,S-3-methylbenzothiophene) (7). Complex 7 (20%
NMR yield) could not be isolated in pure form by any method
attempted. 13C and 1H NMR spectra could not be obtained. However,
31P{1H} NMR spectroscopy showed the presence of 7 (major
product) and complexes 2, 4, and 5 as minor products. Surprisingly,
the oily reddish brown product formed crystals, which were confirmed
by X-ray diffraction as 7 (see the Supporting Information for X-ray
diffraction details). 31P{1H} NMR (162 MHz, THF-d8, 25 °C): δ
70.20 (d, J = 26.3 Hz), 65.31 (d, J = 26.3 Hz).
solvent.) After freeze/pump/thaw degassing of the solution, 1
gradually disappeared as 2 grew in. New chemical shifts were also
observed as minor decomposition products, identified as [Pd(dippe)2]
(4) and [Pd2(dippe)2(μ-dippe)] (5), which show a singlet resonance
at δ 45.5 and two multiplets at δ 49.5 and 54.8, respectively. Addition
of H2 (1 atm) to a solution of 2 resulted in 1 gradually growing back,
establishing the equilibrium ratio between 1 and 2 of 9:1, respectively.
Establishing the Relationship between (dippe)Pd(κ2C,S-
thiophene) (3) and (dippe)Pd(κ2C,S-benzothiophene) (6).
Equimolar amounts of 3 (15 mg, 0.033 mmol) and 6 (17 mg, 0.033
mmol) were dissolved in 0.6 mL of THF-d8, and the reaction was
monitored via 31P{1H} NMR spectroscopy. Initially two sets of pairs of
doublets were observed in the 31P{1H} NMR spectrum: one at δ 74.59
and δ 67.10 (J = 25.5 Hz) attributed to 3 and another set at δ 73.52 (d,
J = 26.2 Hz) and δ 66.86 (d, J = 26.2 Hz) for 6. The dark red solution
mixture was monitored for 12 h, over which time 3 decomposed,
leaving behind 6 as the only C−S activated product and free
thiophene. It was also observed that the concentration of 4 increased
(singlet at δ 46.03 in the 31P{1H} NMR spectrum) throughout the
experiment. Alternatively, a solution of 3 (15 mg, 0.033 mmol) was
dissolved in 0.6 mL THF-d8 and 1 equiv of benzothiophene (4.4 mg,
0.033 mmol) was introduced. Within a few minutes the complete
disappearance of resonances for 3 and the growth of a pair of doublets
at δ 73.52 (d, J = 26.2 Hz) and δ 66.86 (d, J = 26.2 Hz) for 6 was
observed via 31P{1H} NMR spectroscopy. Complex 4 was also
observed in the 31P{1H} NMR spectrum. Free thiophene was formed
from the decomposition of 3.
(dippe)Pd(κ2C,S-dibenzothiophene) (8). Complex 8 was synthe-
sized (7.6 mg, 30%) using 4 equiv of dibenzothiophene (33 mg, 0.18
mmol). 1H NMR (500 MHz, CD2Cl2): δ 8.20 (br, s, 2H), 7.88 (br, s,
2H), 7.49 (br, s, J = 2.6 Hz, 4H), 2.50−2.27 (m, 4H), 2.01−1.87 (m,
2H), 1.72−1.59 (m, 2H), 1.40−1.11 (m, 24H). 13C{1H} NMR (126
MHz, CD2Cl2): δ 139.95 (s), 136.07 (s), 127.34 (s), 124.98 (s),
123.33 (s), 122.15 (s), 26.69 (d, J = 26.7 Hz), 25.27 (d, J = 17.7 Hz),
24.81−24.34 (m), 20.40−19.84 (m), 19.09−18.46 (m). 31P{1H} NMR
(162 MHz, THF-d8, 25 °C): δ 71.86 (d, J = 19.4 Hz). 68.60 (d, J =
19.4 Hz) Anal. Calcd (found) for C26H40PdP2S: C, 56.47 (56.24); H,
7.29 (7.21).
(dippe)Pd(thianthrene) (9). Complex 9 was synthesized (15.7 mg,
59%) using 4 equiv of thianthrene (39 mg, 0.18 mmol). 1H NMR (500
MHz, THF-d8): δ 7.42 (d, J = 7.5 Hz, 1H), 7.33 (d, J = 7.7 Hz, 1H),
7.16−7.04 (m, 2H), 6.86 (t, J = 6.6 Hz, 1H), 6.70 (dt, J = 31.1, 7.1 Hz,
2H), 6.57 (t, J = 6.9 Hz, 1H), 2.62−2.32 (m, 3H), 2.21−1.76 (m, 5H),
1.45 (dd, J = 17.3, 7.1 Hz, 3H), 1.39−1.28 (m, 9H), 1.28−1.18 (m,
6H), 1.15 (dd, J = 10.7, 7.0 Hz, 3H), 0.39 (dd, J = 14.5, 6.9 Hz, 3H).
13C{1H} NMR (126 MHz, THF-d8): δ 165.67 (d, J = 4.4 Hz), 164.61
(d, J = 4.4 Hz), 153.33 (s), 144.75 (s), 137.67 (s), 134.79 (s), 134.60
(d, J = 8.8 Hz), 134.21 (s), 133.36 (d, J = 7.0 Hz), 128.03 (d, J = 7.9
Hz), 127.75 (s), 120.65 (s), 27.54 (d, J = 24.3 Hz), 26.36 (d, J = 19.1
Hz), 24.10−23.55 (m), 22.45 (d, J = 22.4 Hz), 21.39 (d, J = 6.2 Hz),
20.59 (s), 20.46 (d, J = 4.8 Hz), 20.32 (d, J = 5.3 Hz), 20.06 (d, J = 6.0
Hz), 19.60 (d, J = 4.0 Hz), 18.95 (s), 18.40 (s), 17.16 (s), 16.02 (d, J =
6.6 Hz). 31P{1H} NMR (162 MHz, THF-d8, 25 °C): δ 74.37 (d, J =
Establishing the Relationship between (dippe)Pd(κ2C,S-
dibenzothiophene) (8) and (dippe)Pd(κ2C,S-benzothiophene)
(6). Equimolar amounts of (dippe)Pd(κ2C,S-dibenzothiophene) (15
mg, 0.027 mmol) and (dippe)Pd(κ2C,S-benzothiophene) (14 mg,
0.027 mmol) were dissolved in 0.6 mL of THF-d8 in a J. Young NMR
G
DOI: 10.1021/acs.organomet.5b00194
Organometallics XXXX, XXX, XXX−XXX

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Article
25.9 Hz), 67.60 (d, J = 25.9 Hz). Anal. Calcd (found) for
C26H40PdP2S2·0.25C6D6: C, 54.63 (55.24); H, 6.92 (6.38).
the tips of thin glass optical fibers and mounted on a Bruker SMART
CCD platform diffractometer for data collection.24 For each crystal a
preliminary set of cell constants and an orientation matrix were
calculated from reflections harvested from three orthogonal wedges of
reciprocal space. Full data collections were carried out using Mo Kα
radiation (0.71073 Å, graphite monochromator) with frame times
ranging from 25 to 60 s and at a detector distance of approximately 4
cm. Randomly oriented regions of reciprocal space were surveyed: four
to six major sections of frames were collected with 0.50° steps in ω at
four to six different φ settings and a detector position of −38° in 2θ.
The intensity data were corrected for absorption.25 Final cell constants
were calculated from the xyz centroids of approximately 4000 strong
reflections from the actual data collections after integration.26
(dippe)Pd(thioxanthene) (10). Complex 10 was synthesized (11.9
mg, 46%) with 4 equiv of thioxanthene (36 mg, 0.18 mmol). 1H NMR
(400 MHz, THF-d8): δ 7.22 (d, J = 7.6 Hz, 1H), 7.12 (t, J = 7.0 Hz,
1H), 6.99 (d, J = 7.3 Hz, 1H), 6.92−6.87 (m, 1H), 6.74−6.58 (m,
4H), 4.53 (d, J = 11.2 Hz, 1H), 3.65 (d, J = 11.1 Hz, 1H), 2.69−2.07
(m, 4H), 2.00−1.77 (m, 4H), 1.52−1.21 (m, 18H), 1.14 (dd, J = 10.5,
7.0 Hz, 3H), 0.30 (dd, J = 14.4, 7.0 Hz, 3H). 13C{1H} NMR (126
MHz, THF-d8): δ 154.24 (d, J = 4.3 Hz), 148.29 (d, J = 4.7 Hz),
144.77 (d, J = 8.3 Hz), 142.28 (s), 137.82 (d, J = 8.1 Hz), 134.37 (d, J
= 8.3 Hz), 128.15 (s), 126.80 (d, J = 7.6 Hz), 125.98 (s), 124.64 (d, J
= 6.7 Hz), 123.94 (s), 121.66 (s), 49.99 (s), 27.66 (d, J = 25.0 Hz),
24.09 (t, J = 22.0 Hz), 21.60 (dd, J = 38.2, 12.9 Hz), 20.62−20.03 (m),
19.53 (s), 18.50 (s), 16.87 (s), 16.22 (d, J = 6.8 Hz). 31P{1H} NMR
(162 MHz, THF-d8): δ 70.53 (d, J = 22.8 Hz), 64.16 (d, J = 22.9 Hz)
Anal. Calcd (found) for C27H42PdP2S: C, 57.19 (57.35); H, 7.47
(7.54).
(dippe)Pd(Ph)(SPh) (13). Complex 13 was synthesized (10.5 mg,
41%) with 4 equiv of diphenyl sulfide (30.1 μL, 0.18 mmol). 1H NMR
(400 MHz, C6D6): δ 7.60 (d, J = 7.2 Hz, 2H), 7.51 (t, J = 7.2 Hz, 2H),
7.04−6.83 (m, 6H), 2.10 (td, J = 14.6, 7.2 Hz, 2H), 1.75 (td, J = 14.5,
7.2 Hz, 2H), 1.37 (dd, J = 16.0, 7.2 Hz, 8H), 0.91 (dd, J = 13.0, 7.0 Hz,
8H), 0.73 (dd, J = 15.6, 7.1 Hz, 12H). 13C{1H} NMR (126 MHz,
C6D6): δ 162.55 (dd, J = 122.6, 7.9 Hz), 146.93−146.76 (m), 138.72
(s), 136.12 (s), 127.29 (s), 127.20 (s), 122.64 (s), 25.20 (d, J = 3.7
Hz), 25.05 (d, J = 10.1 Hz), 23.75 (t, J = 21.8 Hz), 20.30 (t, J = 17.6
Hz), 20.12 (d, J = 5.0 Hz), 19.22 (d, J = 3.2 Hz), 18.77 (s), 17.91 (s)
31P{1H} NMR (162 MHz, C6D6): δ 61.38 (d, J = 19.9 Hz), 59.35 (d, J
= 19.6 Hz). Anal. Calcd (found) for C26H42PdP2S: C, 56.26 (56.45);
H, 7.63 (7.65).
Structures were solved using SIR201127 and refined using SHELXL-
2014.28 Space groups were determined on the basis of systematic
absences, intensity statistics, or both. Direct-methods solutions were
calculated, which provided most non-hydrogen atoms from the E map.
Full-matrix least-squares/difference Fourier cycles were performed
which located the remaining non-hydrogen atoms. All non-hydrogen
atoms were refined with anisotropic displacement parameters. All
hydrogen atoms were placed in ideal positions and refined as riding
atoms with relative isotropic displacement parameters. Full-matrix
least-squares refinements on F2 were run to convergence.
In structures with multiple molecules in the asymmetric unit, only
one is shown in the figures and referred to in the discussions because
either the second independent molecule was disordered or the two
independent molecules were metrically identical. Full details for each
structure can be found in the Supporting Information.
ASSOCIATED CONTENT
* Supporting Information
■
S
(dippe)Pd(SPh)2 (14). Complex 14 was synthesized (15.2 mg, 56%)
with 4 equiv of diphenyl disulfide (39 mg, 0.18 mmol). 1H NMR (400
MHz, CD2Cl2): δ 7.30 (d, J = 7.3 Hz, 4H), 6.86 (m, 6H), 2.57 (s, 4H),
1.89 (m, 4H), 1.28 (m, 24H). 13C{1H} NMR (126 MHz, CD2Cl2)
δ146.64 (s), 134.24 (s), 127.17 (s), 122.08 (s), 26.77 (d, J = 24.7 Hz),
22.85−22.09 (m), 20.42 (s), 18.88 (s). 31P{1H} NMR (162 MHz,
CD2Cl2): δ 82.08 (s). Anal. Calcd (found) for C26H42PdP2S2: C, 53.19
(52.08); H, 7.21 (6.58).
Tables, figures, and CIF files giving crystallographic informa-
tion, including data collection parameters, bond lengths,
fractional atomic coordinates, and anisotropic thermal param-
eters, for complexes 6−10, 14, 15, and (dippe)Pd(Cl)2 (CCDC
deposition nos. 1050732−1050738 and 1052414) and NMR
spectra for new products. This material is available free of
charge via the Internet at http://pubs.acs.org.
(dippe)Pd(SPh)(COPh)(15). A 4 equiv amount of S-phenyl
benzothioate (39 mg, 0.18 mmol) was used. The aromatic region of
the 1H NMR and 31P{1H} NMR spectra of the yellow solid confirmed
AUTHOR INFORMATION
Corresponding Author
*E-mail for W.D.J.: william.jones@rochester.edu.
■
1
coproduction of 15 (81%) and 14 (19%). The H NMR spectrum’s
aliphatic region was difficult to characterize due to the presence of
dippe ligand resonances from both complexes 14 and 15 (see the
Supporting Information for spectra). 1H NMR (aromatic region) of 15
(400 MHz, THF-d8): δ 7.84 (d, J = 6.3 Hz, 2H), 7.14 (d, J = 7.2 Hz,
3H), 7.04 (d, J = 7.7 Hz, 2H), 6.54 (d, J = 7.3 Hz, 3H). 13C NMR (126
MHz, CD2Cl2): δ 146.40 (dd, J = 7.7, 2.8 Hz), 145.99−145.52 (m),
135.01 (s), 130.82 (s), 129.81 (s), 127.88 (s), 127.11 (s), 122.52 (s),
25.10 (d, J = 14.1 Hz), 23.33 (t, J = 22.8 Hz), 19.87 (d, J = 5.7 Hz),
19.74−19.49 (m), 18.79 (s). 31P{1H} NMR (162 MHz, THF-d8): δ
65.09 (d, J = 31.1 Hz), 58.36 (d, J = 31.0 Hz). The missing CO
resonance of 15 in the 13C{1H} NMR spectrum was confirmed by IR
(ATR, cm−1): νCO(stretch) 1604, differing from the carbonyl resonance
of free S-phenyl benzothioate at 1663 cm−1.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The National Science Foundation (NSF Grant CHE-1360985)
for their support of this work. This paper is dedicated to the
memory of Gregory L. Hillhouse, a giant in group 10
organometallic chemistry.
REFERENCES
■
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Carbonylation of Complex 13. A J. Young NMR tube was
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DOI: 10.1021/acs.organomet.5b00194
Organometallics XXXX, XXX, XXX−XXX