Reactivity of a Palladacyclic Complex: A Monodentate Carbonate Complex and the Remarkable Selectivity and Mechanism of a Neophyl Rearrangement

Article abstract of DOI:10.1021/acs.organomet.7b00631

The ligand N(CH₂-2-C₅H₄N)₂(CH₂CH₂CH₂OH), L1, reacted with [Pd(CH₂CMe₂C₆H₄)(COD)] to give a new fluxional cycloneophyl organopalladium complex [Pd(CH₂CMe₂C₆H₄)(κ²-L1)], 1, which on attempted recrystallization from THF gave the monodentate carbonate complex [Pd(CO₃)(κ³-L1)], 2. Complex 2 was prepared in designed syntheses by reaction of [PdCl(κ³-L1)]⁺ with silver carbonate or by reaction of [Pd(OH)(κ³-L1)]⁺ with CO₂. Complex 1 reacted with aqueous CO₂ to give the cationic neophylpalladium complex [Pd(CH₂CMe₂C₆H₅)(κ³-L1)]⁺(HCO₃)^-, 6. Complex 6 reacts with hydrogen peroxide to give complex 2 with release of a mixture of organic products, the major one being 2-phenyl-2-butanol, PB. The formation of PB involves a neophyl rearrangement with the unprecedented preference for methyl over phenyl migration. A mechanistic basis for this unexpected reaction is proposed, involving β-carbon elimination at a palladium(IV) center.

Full text of DOI:10.1021/acs.organomet.7b00631

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX-XXX
Reactivity of a Palladacyclic Complex: A Monodentate Carbonate
Complex and the Remarkable Selectivity and Mechanism of a
Neophyl Rearrangement
Ava Behnia, Mahmood A. Fard, Johanna M. Blacquiere,* and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada
S
* Supporting Information
ABSTRACT: The ligand N(CH2-2-C5H4N)2(CH2CH2CH2OH), L1,
reacted with [Pd(CH2CMe2C6H4)(COD)] to give a new fluxional
“cycloneophyl” organopalladium complex [Pd(CH2CMe2C6H4)(κ2-
L1)], 1, which on attempted recrystallization from THF gave the
monodentate carbonate complex [Pd(CO3)(κ3-L1)], 2. Complex 2
was prepared in designed syntheses by reaction of [PdCl(κ3-L1)]+
with silver carbonate or by reaction of [Pd(OH)(κ3-L1)]+ with CO2.
Complex 1 reacted with aqueous CO2 to give the cationic
neophylpalladium complex [Pd(CH2CMe2C6H5)(κ3-L1)]+(HCO3)−,
6. Complex 6 reacts with hydrogen peroxide to give complex 2 with
release of a mixture of organic products, the major one being 2-
phenyl-2-butanol, PB. The formation of PB involves a neophyl rearrangement with the unprecedented preference for methyl
over phenyl migration. A mechanistic basis for this unexpected reaction is proposed, involving β-carbon elimination at a
palladium(IV) center.
toward oxidation by dioxygen or hydrogen peroxide, we have
studied the cycloneophylpalladium(II) complex with the ligand
HO(CH2)3N(CH2−2-py)2, L1, py = pyridyl.7 The ligand is
expected to bind to give [Pd(CH2CMe2C6H4)(κ2-L1)], 1, in
which L1 binds through the amine and one pyridyl group,
leaving one free pyridyl group to act in an analogous way as the
free nitrogen donor in C and a free hydroxyl group to act in an
analogous way as those in E and G (Scheme 1). Efforts to
isolate palladium(IV) complexes are ongoing, but this paper
reports two unexpected and interesting observations. The first
is that complex 1 can fix carbon dioxide from the air to give the
first example of a monodentate carbonate complex of
palladium(II), [Pd(κ1-CO3)(κ3-N,N′,N″-L1)], and the second
is that the reaction involves a unique type of the “neophyl
rearrangement”. Some background information to place these
observations in context is given below.
The fixation of CO2 from the air and conversion to useful
organic products are considerable challenges and the subjects of
much current research.8 One approach is to trap CO2 by
complexes of catalytically active metals, often to give carbonate
or carboxylate derivatives, followed by conversion to organic
derivatives. In this context, several carbonate and bicarbonate
complexes of palladium(II) are known, and they can often be
prepared by reactions involving CO2/H2O or carbonic acid.9−11
For example, J (Scheme 2) can be prepared from
corresponding dimethylpalladium(II) complex, I, by proto-
nolysis with CO2/H2O and can then undergo further loss of
INTRODUCTION
■
Catalytic oxidation of organic compounds using plentiful and
environmentally benign oxidants, such as H2O2 and O2, is
highly desirable.1 A major ongoing challenge in this field is to
improve oxidation selectivity and this is driving many
fundamental studies into the reactivity and mechanism of key
oxidation steps.1,2 Specifically, organopalladium(II) complexes
with hard nitrogen-donor ligands oxidize with H2O2 to give
reactive palladium(IV) intermediates that can undergo
reductive elimination with C−O bond formation.2 For example,
complex A, with the bulky MesNCCNMes (Mes =
mesityl) ligand, reacts with hydrogen peroxide to give the
product of oxygen atom insertion, B, probably by an oxidative
addition−reductive elimination sequence, whereas complex C,
with a potentially tridentate triazacyclononane ligand, gives
stable palladium(IV) complex D (Scheme 1).2 In related
organoplatinum chemistry, ligands with pendent hydroxyl
groups enhance reactivity toward oxidation by H2O2 or O2.
Thus, dimethylplatinum(II) complexes E and G are oxidized by
hydrogen peroxide and dioxygen, respectively, to give F and H
(Scheme 1).3 The proton-coupled electron transfer reactions,
which are possible with ligands of the type shown in Scheme 1,
have general significance in several areas of chemistry.4
The “cycloneophyl”, CH2CMe2C6H4, group (A−D, Scheme
1) has proven to be particularly valuable in studies of reactivity
and selectivity in organopalladium chemistry.2,5,6 The group is
ideally suited to assess selectivity as it contains both Pd−Csp3
and Pd−Csp2 bonds, and the C(Me)2 group prevents any
complicating β-hydride elimination pathways. In order to
further increase the reactivity of palladium(II) complexes
Received: August 18, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
However, to the best of our knowledge, no monodentate
carbonate complexes of palladium have been reported.
Scheme 1. Diverse Oxidation Reactivity Achieved with
Simple Diimine Ligand (A, B), Ligand with Pendent
Nitrogen Donor Group (C, D), and Ligands with Pendent
Alcohol or Phenol Group (E−H)
The neophyl rearrangement can be observed in reactions
involving either free radical or carbocation intermediates. In
free radical reactions, there is often a competition between
•
hydrogen abstraction by the primary radical PhCMe2CH2 to
give t-butylbenzene or rearrangement by phenyl group
•
migration to give PhCH2CMe2 , followed by disproportiona-
tion or dimerization of this rearranged radical.12,13 No products
that would arise from the radical MeCH2CMePh•, which would
be formed by methyl group migration in the primary neophyl
radical, were observed in this or subsequent studies.12,13
Similarly, in neophyl cations or incipient cations formed in
solvolysis reactions, phenyl migration always occurs to a greater
extent than does methyl migration.14 For example, formolysis
of neophyl tosylate occurred only 0.7% by methyl migration
(Scheme 3).14b Mechanisms involving radical or cationic
intermediates can be distinguished by the characteristic product
mixtures formed.12−14
Scheme 3. Neophyl Carbocation Rearrangement
Scheme 2. Some Known Carbonate and Bicarbonate
Complexes of Palladium(II)
Selective phenyl migration also occurs in the β-carbon
elimination from a cationic neophylpalladium(II) complex,15
though methyl migration can occur in neopentyl complexes, as
determined by mass spectrometry (Scheme 4).16,17 In contrast
to all of the above examples, the reactions reported in this
paper give organic products that are formed mostly by methyl
migration in the neophyl rearrangement, and the mechanistic
basis for this unique selectivity will be discussed.
RESULTS AND DISCUSSION
■
The complex [Pd(CH2CMe2C6H4)(κ2-N,N′-L1)], 1, was
prepared by ligand exchange from the corresponding 1,5-
cyclooctadiene complex [Pd(CH2CMe2C6H4)(COD)]2,5,6 and
the known ligand N,N-bis(pyrid-2-ylmethyl)-N-(3-
hydroxypropyl)amine, L1 (Scheme 5).7 Complex 1 was
thermally stable under dinitrogen atmosphere and was fully
1
characterized by H and 13C NMR spectroscopy, including
correlated 1H−1H COSY, 1H−1H NOESY, and 1H−13C
HSQC and HMBC NMR spectroscopy at both room
temperature and −30 °C, as well as by mass spectrometry
and IR spectroscopy. The IR spectra of free ligand L1 and
complex 1 show peaks due to ν(OH) centered at 3304 and
3285 cm−1, respectively. The MALDI-MS of 1 gave a parent
ion peak at m/z = 495.9 that matches well with the simulated
m/z value and isotope pattern for [1 + H]+.
methane to give bidentate carbonate complex K.9
Hydroxopalladium(II) complex L reacts with CO2 to give
monodentate bicarbonate complex M, which can eliminate
water to give binuclear bridging carbonate complex N.10
B
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 4. β-Phenyl or β-Methyl Elimination Reactions at
Palladium(II)
Figure 1. 1H NMR spectra (600 MHz, acetone-d6 solution) of
complex 1 at different temperatures.
separate peaks. Following precedents on the mechanisms of
substitution at palladium(II),18 it is likely that the exchange
between free and coordinated pyridyl groups occurs by way of
square pyramidal and trigonal bipyramidal intermediates, and
the trigonal bipyramidal intermediate 1* (which contains an
effective plane of symmetry) is able to collapse to 1a or 1b by
dissociation of one of the two pyridyl groups (Scheme 5). The
activation energy for fluxionality is estimated, using the Eyring
equation, as ΔG⧧ = 58 kJ mol−1 at 297 K.19a
Scheme 5. Synthesis of Complex 1 and the Proposed
Mechanism of Interconversion of Isomers 1a and 1b by Way
of 1*
In solution, complex 1 exists largely as one isomer, though
minor peaks in the low temperature NMR spectra might be due
1
to a minor isomer. A H−1H NOESY experiment was carried
out at −30 °C to check for the close interligand contacts
expected between H6a and H6 for isomer 1a or H6a and H9
for isomer 1b. However, no interligand correlations were
observed, perhaps as a result of the fluxionality, so it is
uncertain if the major isomer is 1a or 1b.
All attempts to crystallize 1 (dry solvent, inert atmosphere,
various solvents, and temperatures) were unsuccessful.
However, in one attempt, a solution of complex 1 in
tetrahydrofuran, which had not been dried or distilled, was
allowed to evaporate slowly in air and gave good crystals of a
compound which was structurally characterized as the
carbonate complex [Pd(κ1-O-CO3)(κ3-N,N′,N″-L1)], 2, in the
hydrated form [Pd(κ1-O-CO3)(κ3-N,N′,N″-L1)]·6H2O, 2a.
There were enough single crystals to obtain a 1H NMR
spectrum of complex 2, which was soluble in D2O. The NMR
spectrum was consistent with the observed structure, in which
both pyridyl groups are coordinated and the complex has
approximate Cs symmetry. However, there was insufficient
material to allow full characterization, and the mechanism by
which the organic CH2CMe2C6H4 ligand was replaced by
carbonate was obscure. Further research was clearly necessary.
In the first step, the independent synthesis of complex 2 was
carried out, as illustrated in Scheme 6. The reaction of ligand
L1 with palladium(II) chloride gave the cationic
chloropalladium(II) complex [PdCl(κ3-N,N′,N″-L1)]+, 3,
which was isolated as the tetrachloropalladate(II) salt [PdCl-
(κ3-N,N′,N″-L1)][PdCl4], 3a. The chloride salt [PdCl(κ3-
N,N′,N″-L1)]Cl, 3b, was prepared later. Complex 3a reacted
with excess silver carbonate to give complex 2 in good yield.
Alternatively, complex 3a reacted with silver triflate to give the
triflate complex 4, which reacted with potassium hydroxide to
It should be noted that complex 1 is asymmetric, so there are
two potential isomers 1a and 1b with the CH2Pd group trans to
the pyridine or amine donor, respectively. However, at room
temperature, the 1H NMR spectrum of 1 in (CD3)2CO
solution gave only singlet resonances for the CH2 and CMe2
groups of the organic CH2CMe2C6H4 ligand, while four
resonances for the C6H4 group were observed (Figure 1).
Only a single set of broad resonances was observed for the two
pyridylmethyl groups of coordinated ligand L1, suggesting that
the complex might exhibit fluxionality, and this was confirmed
by the NMR spectra at lower temperatures. At −30 °C, each
broad pyridyl resonance had split into two equal resonances.
Additionally, the broad CH2N resonance that integrates to four
protons (for H7a and H7b) had split into four overlapping
doublets in the region δ 4.1−4.4 (Figure 1). Similarly, the
CMe2 resonance of the organic ligand had split into two equal
resonances, while the CH2 resonance did not give resolved
C
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 6. Two Independent Syntheses of the Palladium(II)
Carbonate Complex 2
Figure 2. Isotope patterns for [2+K]+: (a) simulated and (b) observed
by MALDI MS using anthracene as the matrix.
give hydroxopalladium(II) complex 5, which could then
undergo further reaction with carbon dioxide to give 2. This
last synthesis is analogous to the route used to make other
bicarbonate or carbonate complexes of palladium(II) (Scheme
2)9−11 and provides a potential step in which CO2 from air
could give complex 2.
Complexes 2 (both 2a and a different crystalline form
[Pd(κ1-O-CO3)(κ3-N,N′,N″-L1)]·5H2O·MeOH, 2b) and 3b
were characterized by structure determination, and all
Figure 3. Structure of complex 3b, showing 30% probability ellipsoids.
Selected bond distances (Å): Pd(1)−N(1) 2.0170(8); Pd(1)−N(2)
2.0254(8); Pd(1)−N(3) 2.0107(8); Pd(1)−Cl(1) 2.3024(6).
1
complexes 2−5 were characterized spectroscopically. The H
and 13C NMR spectra were consistent with the complexes
having Cs symmetry, with equivalent 2-pyridylmethyl groups,
for which each CHaHb group appeared as an AB multiplet in
1
the H NMR spectra. The 13C NMR spectrum of complex 2
The molecular structures of complex 2 in solvates 2a and 2b
are shown in Figure 4. The ligand is bound in a similar way as
in complex 3, and all contain slightly distorted square planar
palladium(II) centers, with Houser’s parameter τ4 = 0.10, 0.09,
and 0.13 in 2a, 2b, and 3 respectively.21 The carbonate ligand is
oriented roughly perpendicular to the square plane of the
palladium(II) center and syn to the 3-hydroxypropyl group in
each case. The carbonate is clearly monodentate, and to the
best of our knowledge, this is the first example of a palladium
complex containing a carbonate ligand bound in this form. The
key to its formation is likely to be the use of a neutral pincer
ligand that both prevents carbonate chelation and gives a
neutral complex. With monodentate or bidentate coligands,
bidentate carbonate is usually preferred (K, Scheme 2), while
with anionic pincer ligands, the monodentate bicarbonate or
bridging carbonate (M and N, Scheme 2) is preferred.9−11 The
main difference between the molecular structures of 2a and 2b
is in the conformation of the 3-hydroxypropyl substituents, and
this is attributed to different hydrogen bonding in the two
solvates.
contained a resonance at δ = 166 for the carbonate carbon
atom, just outside the range δ = 159−164 reported for η2-
carbonate or η1-bicarbonate complexes of palladium(II).9−11
The infrared spectrum of complex 2 contained a strong band at
1316 cm−1, assigned to ν(CO) of the η1-carbonate ligand, at
considerably lower energy than the range of 1655−1700 cm−1
found for η2-carbonate complexes9−11,19b or 1600−1650 cm−1
found for η1-bicarbonate complexes,9,10 indicating that this
could be a useful criterion to distinguish between these bonding
modes. In the MALDI-MS of 2, using an anthracene matrix
containing KCl to aid ionization, the most abundant ion was
observed at m/z 462.8, corresponding to [2 + K]+ (Figure 2).
The structure of complex 3b is shown in Figure 3 and
confirms that L1 acts as a tridentate ligand binding through the
three nitrogen donors to give a square planar cationic
palladium(II) complex. The bond length Pd−N(2) for the
amine donor is slightly longer than those to the pyridine
donors, and the distances are unexceptional.20 The hydroxyl
group is not coordinated but is hydrogen bonded to both the
chloride anion and a water molecule in 3b. Complex 3b forms
an interesting supramolecular polymeric structure formed by
hydrogen bonding between the CH2OH group, chloride anion
and two water molecules, as illustrated in Figure S40.
Both complexes 2a and 2b give complex three-dimensional
network structures by hydrogen bonding involving the
carbonate ligands, the 3-hydroxypropyl groups, and water
molecules. Figure 5 shows a small part of these networks in
D
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 5. Structures of dimer units of (above) complex 2a and
(below) complex 2b formed by hydrogen bonding, showing 25%
thermal ellipsoids.
Scheme 7. Conversion of Complex 1 to 2 by Way of
Complex 6 and the Distribution of Organic Products
Figure 4. Molecular structures of complexes (a) 2a and (b) 2b,
showing 30% probability ellipsoids. Selected bond distances (Å) and
angles (deg): 2a, Pd(1)−N(1) 2.003(9); Pd(1)−N(2) 2.007(8);
Pd(1)−N(3) 2.007(9); Pd(1)−O(2) 2.012(7); C(16)−O(2)
1.221(13); C(16)−O(4) 1.352(13); C(16)−O(3) 1.258(12);
N(1)−Pd(1)−N(2) 84.27(3); N(2)−Pd(1)−N(3) 82.99(3); N(3)−
Pd(1)−O(2) 97.06(3); O(2)−Pd(1)−N(1) 95.52(3); 2b, Pd(1)−
N(1) 2.006(2); Pd(1)−N(2) 2.017(2); Pd(1)−N(3) 2.015(2);
Pd(1)−O(2) 2.020(2); C(16)−O(2) 1.325(3); C(16)−O(4)
1.285(3); C(16)−O(3) 1.256(3); N(1)−Pd(1)−N(2) 83.46(9);
N(2)−Pd(1)−N(3) 84.00(9); N(3)−Pd(1)−O(2) 96.49(8); O(2)−
Pd(1)−N(1) 96.10(8).
which dimer units can be identified. In complex 2a, there is
direct pairwise intermolecular H-bonding between the
carbonate and alcohol groups, with O(1)···O(4A) = O(1A)···
O(4) = 2.67 Å, while pairs of water molecules also bridge
between carbonate ligands, with O(3)···O(5) = O(3A)···O(5A)
= 2.71 Å and O(3)···O(5a) = O(3a)···O(5) = 2.80 Å. In
complex 2b, a water molecule O(2W) bridges between each
carbonate and alcohol group, with O(1)···O(2WA) = O(1A)···
O(2W) = 2.74 Å and O(3)···O(2W) = O(3a)···O(2WA) =
2.70 Å.
Having proved the structure of unusual carbonate complex 2,
the remaining challenge was to determine how it was formed
from complex 1. It seemed possible that this could involve
reaction of 1 with some combination of water, dioxygen, and
carbon dioxide. No reaction occurred when a solution of
complex 1 in dry tetrahydrofuran was stirred under CO2, O2, or
a combination of the two. However, a reaction did occur when
a solution of 1 in wet tetrahydrofuran was stirred under an
atmosphere of CO2 to give cationic neophylpalladium(II)
spectrum of 6 showed the resonances expected for the ligand in
κ3-N,N′,N″-L1 bonding mode, similar to those for complexes 2-
5 and also peaks typical for the neophylpalladium group.2,5,6 In
particular, the phenyl group gave three resonances in a 2:2:1
intensity ratio for the o-, m-, and p-H atoms. When the similar
reaction was carried out in D2O, the corresponding complex 6-
d was formed (Scheme 7), in which the phenyl group contained
1
one deuterium atom in the ortho position, as shown by the H
and 2H NMR spectra (Figure 6). In particular, the ortho
1
complex 6 as the bicarbonate salt (Scheme 7). The H NMR
resonance in the 1H NMR integrated as a single proton, and the
E
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
phenyl migration, but the present reaction occurs with 65%
methyl migration and only 14% phenyl migration. A
mechanism involving either a free neophyl carbocation or
radical intermediate can therefore be eliminated based on the
observed organic product distribution.12−14 The rearrangement
is therefore proposed to occur within the coordination sphere
of the palladium center, probably after oxidation of complex 6
by hydrogen peroxide.
Two possible routes to major products 2 and PhMeEtCOH,
PB, are shown in Scheme 8, both involving β-methyl
Scheme 8. Possible Mechanisms of Reaction of 6 with H2O2
a
To Give 2
Figure 6. NMR spectra of complex 6-d in D2O solution: (a) 2H NMR
1
spectrum and (b) H NMR spectrum.
2H NMR showed the presence of an ortho-D atom. In the
infrared spectrum of complex 6, a strong band was observed at
ν(CO) = 1611 cm−1, which is in the range for the bicarbonate
ion (1610−1655 cm−1).19b The formation of 6 from 1 involves
selective protonolysis of the aryl-palladium bond by carbonic
acid,5,6 but further protonolysis of the Pd-neophyl group from 6
did not occur under these conditions. An attempt to
recrystallize complex 6 from chloroform led to decomposition
to give chloro complex 3b (Figure 3). The reaction of 6 with
DCl in D2O solution also gave complex 3b along with
PhCMe2CH2D. Finally, it was hypothesized that peroxide
impurity in the tetrahydrofuran solvent might have been
involved in the original synthesis of complex 2, so a reaction of
complex 6 in aqueous solution with hydrogen peroxide was
carried out. This reaction did indeed give complex 2 in good
yield.
The complex mixture of organic products from the reaction
of complex 6 in D2O solution with H2O2 was analyzed after
extraction into CDCl3 by a combination of GC-MS and H
a
1
Ligand L1 is drawn as NNN for simplicity. The favored mechanism
involves concerted β-Me elimination and nucleophilic OH− attack
followed by C−C reductive elimination (O → S → 5). The disfavored
mechanism involves β-Me elimination, alkene insertion and C−O
reductive elimination (O → Q → R → 5).
NMR spectroscopy.22 The major organic products were
identified as PhMeEtCOH (2-phenyl-2-butanol, PB, 51%),
trans-PhMeCCHMe (trans-2-phenyl-2-butene, 9%), and
PhEtCCH2 (2-phenyl-1-butene, 5%), which are products
expected for hydrolysis of a neophyl cation after methyl group
migration (compare Schemes 3 and 7),14 PhCH2CMe2OH (2-
benzyl-2-propanol, BP, 10%) and PhCH2MeCCH2 (2-
benzyl-1-propene, 4%), which are products expected for
hydrolysis of a neophyl cation after phenyl group migration
(Schemes 3 and 7),14 and t-BuPh (t-butylbenzene, 6%), which
is the product expected from protonolysis of the neophyl group
from 6 without rearrangement. Together, these products
account for 85% of the neophyl groups originally present in
the reagent 6. No neophyl dimers were detected, which would
be expected if neophyl radical intermediates were involved.12,13
Also absent was the alcohol PhMe2CCH2OH, which would be
formed by hydrolysis of the neophyl cation without rearrange-
ment. Although the nature of the products is as expected for a
neophyl cation intermediate, the selectivity is dramatically
different. Thus, the reaction of Scheme 3, with neophyl
rearrangement, occurs with <1% methyl migration and >99%
elimination as a key step. Hydrogen peroxide often gives
trans oxidative addition by a polar mechanism.1,3,23 In reaction
with complex 6 this would give dicationic hydroxopalladium-
(IV) intermediate O,1,3 and then octahedral palladium(IV)
complex P. However, if hydroxide coordination to give P does
not occur, then β-methyl elimination from O might occur to
give alkene complex Q,15−17 which could undergo alkene
insertion in the opposite sense to give PhMeEtCPd(IV)
intermediate R. Reductive elimination with C−OH bond
formation could then give organic product PB and complex
5, which would be expected to react easily with the bicarbonate
anion to give observed product 2. There are several difficulties
with this mechanism. Alkene complexes of palladium(IV) are
unknown, and dicationic complex Q is likely to be at high
energy. Isomerization of primary alkyl complex O to tertiary
alkyl complex R is also likely to be unfavorable. Finally,
F
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
reductive elimination with alkyl C−O bond formation usually
occurs by external nucleophilic attack at carbon, and this will be
difficult with a bulky tertiary alkyl group, as in R.4,24 Perhaps
more likely is that the β-methyl elimination occurs in concert
with hydroxide addition to give S and that S undergoes
reductive elimination with C−C bond formation to give 5 and
PB (Scheme 8). The minor alcohol product PhCH2CMe2OH
(2-benzyl-2-propanol, BP) would be formed by an analogous
sequence of reactions if the first intermediate O underwent β-
phenyl instead of β-methyl elimination. The challenge is to
understand why β-methyl elimination is dominant, when the
closest precedent from palladium(II) chemistry would predict
selective β-phenyl elimination (Scheme 4).2,24
expected, octahedral palladium(IV) complex P, which is
predicted to have hydrogen bonding between the CH2OH
and adjacent PdOH group, is calculated to be most stable,
though it was not observed. One feature that may be
particularly significant is that the predicted conformation of
the neophyl group in 6 and O has π-stacking between the
phenyl group and one of the 2-pyridyl groups with one methyl
group oriented toward the palladium center. In order to form
potential product P, the neophyl group has to reorient in order
to allow access of the hydroxide ion to palladium (Figure 8).
We have attempted to model the potential intermediates and
products arising from the unique neophyl rearrangement
(Scheme 8). No minimum could be found for the potential
alkene intermediate [Pd(OH)Me(CH2CMePh)L1]2+OH−,
Q, or the analogous product of β-phenyl elimination,
[Pd(OH)Ph(CH2CMe2)L1]2+OH−, Q*. The best structures
found resembled carbocations containing the Pd-CH2−
COMPUTATIONAL STUDIES
■
Several problems in the above study could not be solved
experimentally, so DFT calculations (BP functional, scalar
correction for relativity) were carried out to provide additional
insight. The calculated structures for complexes 1a and 1b are
shown in Figure 7. Complex 1b is calculated to be more stable
than 1a by 7 kJ mol−1, so it is tentatively assigned as the
dominant isomer of complex 1 (Scheme 5).
CMePh+ or Pd-CH2−CMe2 units in Q and Q*, respectively,
+
and were at high energy. Consistent with the arguments above,
the potential route involving β-methyl elimination and alkene
insertion to give intermediates Q and R is considered to be
improbable. Figure 9 shows the calculated structures of the
Figure 7. Calculated structures and relative energies of isomers 1a and
1b.
The modeling of the potential oxidative addition of hydrogen
peroxide to complex 6 is shown in Figure 8. Complex O
contains PdOH, CH2OH and OH− groups but the structure is
predicted to have hydrogen bonding involving all of them.25 As
Figure 9. Predicted structures and relative energies of complexes O, S,
S*, and 5.
potential intermediates [Pd(OH)Me(CH2−CMePhOH)L1]+,
S, and the analogous product of β-phenyl elimination,
[Pd(OH)Ph(CH2−CMe2OH)L1]+, S*, for the alternative
mechanism involving concerted β-carbon elimination/hydrox-
ide addition. The formation of S or S* and subsequent
reductive elimination with C−C bond formation (probably
after a ligand dissociation step)2,26 to form the alcohol PB
(Scheme 8) or BP are favorable, so this route is considered
likely. However, these limited calculations do not explain the
observed selectivity since the product of phenyl migration S* is
calculated to be more stable than that of methyl migration S,
Figure 8. Calculated structures and relative energies of 6, O, and P.
G
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and so the usual dominance of phenyl migration in neophyl
(perhaps present in the original synthesis as an impurity in the
tetrahydrofuran solvent). This oxidation step is followed rapidly
by formation of complex 2 with release of a mixture of organic
products, the major one being 2-phenyl-2-butanol, PB. The
formation of PB involves a neophyl rearrangement with the
unprecedented preference for methyl over phenyl migration. A
possible mechanistic basis for this unexpected reaction is
proposed, involving β-carbon elimination at a palladium(IV)
center.
rearrangements or β-carbon elimination, based on the better
bridging ability of the phenyl group, might be predicted.14,15
A
possible explanation is that the initial oxidation step to give O,
in which a methyl group is oriented close to palladium (Figure
9), is rate-determining and that methyl group migration occurs
somewhat faster than the rotation about the neophyl-palladium
bond that is needed to orient the phenyl group close to the
vacant site, as required for phenyl group migration. Rotation of
the neophyl group will be slowed by steric effects and also
electronic effects, since the phenyl/pyridine π-stacking
attraction will be lost on rotation. We know of no precedents
for β-elimination at palladium(IV), but there are examples of
remote methyl group migration to platinum(IV) from
methylboron or methylsilicon groups, often initiated by
nucleophilic attack by hydroxide at boron or silicon.17,24
The observed structures of complex 2 exhibit complex
hydrogen bonding motifs (Figure 5). The complex is
formulated as a neutral carbonate complex, in which the
carbonate group is hydrogen bonded to water and, in 2a, to the
alcohol substituent. The hydrogen atoms were not refined in
the structure determinations, and calculations on some model
compounds were carried out to probe the nature of these
hydrogen bonding interactions. In the three cases studied
(Figure 10), an unsymmetrical hydrogen bond O−H···O is
EXPERIMENTAL SECTION
■
General Procedures. Reactions were carried out in air, unless
otherwise specified. For those reactions that were conducted under a
nitrogen atmosphere, standard Schlenk or glovebox techniques were
used. All solvents used for air- and moisture-sensitive reactions were
purified using an Innovative Technologies 400−5 Solvent Purification
System (SPS) and were stored over activated 4 Å molecular sieves.
NMR spectra were recorded at 298 K using a Varian 600 MHz
1
spectrometer (13C at 150.7 MHz). H and 13C chemical shifts are
reported relative to TMS. Complete assignments were aided by the
1
1
1
use of H−1H gCOSY, H−1H NOESY, H−13C{1H} HSQC, and
1H−13C{1H} HMBC experiments and are reported using the labeling
scheme in Figures 1 and 6 and in the Supporting Information. For 2H
2
NMR experiments, H chemical shifts were referenced externally to
the H peak of D2O (δ(2H) = 4.63 ppm). Aqueous 30% H2O2 was
2
degassed by bubbling N2 through for 10 min. Complexes
[PdCl2(COD)], [Pd(CH2CMe2C6H4)(COD)], and the ligand, N,N-
bis(pyrid-2-ylmethyl)-N-(2-hydroxyethyl)amine, L1, were synthesized
according to the literature procedures.2,5−7 NMR for L1 in CDCl3:
δ(1H) = 8.55 (d, 2H, 3J(H5H6) = 5 Hz, H6), 7.63 (t, 2H, 3J(H3H4) =
3J(H4H5) = 8 Hz, H4), 7.40 (d, 2H, 3J(H3H4) = 8 Hz, H3), 7.16 (dd,
3
2H, J(H4H5) = 8 Hz, 5 Hz, H5), 3.81 (s, 4H, CH2N), 3.73 (t, 2H,
3
3J(HH) = 6 Hz, CH2O), 2.76 (t, 2H, J(HH) = 6 Hz, CH2N), 1.79
(quin, 2H, 3J(HH) = 6 Hz, CH2). The chemical shifts reported for L1
in ref 7 are correct, but many of the coupling constants are not.
Elemental analyses were performed by Laboratoire d’Analyze
́
́ ́ ́
Elementaire del’Universite de Montreal and Canadian Microanalytical
Service, Ltd. MALDI-TOF mass spectra were collected using an AB
Sciex 5800 TOF/TOF mass spectrometer using pyrene or anthracene
as the matrix in a 20:1 matrix/substrate molar ratio. Organic products
were analyzed using a Shimadzu GCMS-QP2010 Ultra GC with a DB-
5 column. Infrared spectra were collected by using a PerkinElmer
UATR TWO FTIR spectrometer.
[Pd(CH2CMe2C6H4)(κ2-N,N′-L1)], 1. Under N2, a solution of N,N-
bis(pyrid-2-ylmethyl)-N-(2-hydroxypropyl)amine, L1, (0.148 g, 0.577
mmol) in dry THF (15 mL) was added to a stirred solution of
[Pd(CH2CMe2C6H4)(COD)] (0.200 g, 0.577 mmol) in dry THF (50
mL) cooled to −65 °C. The mixture was stirred and slowly warmed to
room temperature over 4 h. Upon removal of the solvent under
reduced pressure, a brown oil was formed which was washed with
hexane (20 mL) and cold ether (10 mL). The oil was dried under
vacuum, to give 1 (0.237 g, 0.477 mmol, 83%). NMR in (CD3)2CO at
25 °C: δ(1H) = 8.50 (br, 2H, H6a, H6b), 7.7−7.8 (m, 4H, H3a, H3b,
H4a, H4b), 7.29 (m, 2H, H5a, H5b), 7.19 (m, 1H, H6), 6.78 (m, 1H,
H4), 6.73 (m, 1H, H5), 6.67 (d, 1H, 3J(H3H4) = 7 Hz, H3), 4.18 (br,
Figure 10. Calculated hydrogen bonded structures for complex 2. In
the O−H···O units, the shorter OH distance is to the oxygen of water
or alcohol, and the longer distance is to the oxygen of carbonate.
predicted with the longer distance to the carbonate oxygen
atom. This is the expected pattern given the relative base
strengths of RO−, OH−, and CO32− and supports the proposed
formulation of complex 2 as the first monodentate carbonate
complex of palladium(II).
3
4H, H7a, H7b), 3.53 (t, 2H, J(H8aH9a) = 5 Hz, H8a), 2.88 (t, 2H,
3J(H9aH10a) = 8 Hz, H10a), 2.31 (m, 2H, H9a), 2.02 (s, 2H, H9),
1.31 (s, 6H, H8, H8′). δ(13C) = 167.89 (C2), 159.62 (C1), 157.46
(C2a, C2b), 148.81 (C6a, C6b), 136.71 (C4a, C4b), 134.44 (C5),
124.87 (C3a, C3b), 123.31 (C6), 123.06 (C5a, C5b), 121.97 (C4),
121.10 (C3), 62.71 (C7a, C7b), 59.89 (C10a), 55.32 (C8a), 47.11
(C7), 43.59 (C9), 33.42 (C8, C8′), 30.70 (C9a). NMR in (CD3)2CO
at −20 °C: δ(1H) = 8.64 (1H, H6a or H6b), 8.46 (1H, H6a or H6b),
7.78 (1H, H4a or H4b), 7.75 (1H, H4a or H4b), 7.67−7.66 (2H, H3a
and H3b), 7.36 (1H, H5a or H5b), 7.31 (1H, H5a or H5b), 7.19 (1H,
H6), 6.78 (1H, H4), 6.73 (1H, H5), 6.67 (1H, H3), 4.11−4.32 (4H,
H7a, H7a′, H7b, H7b′), 3.4−3.6 (2H, H8a, H8a′), 2.7−2.8 (2H,
H10a, H10a′), 2.36 (1H, H9a or H9a′), 2.31 (1H, H9a or H9a′), 2.05
CONCLUSIONS
■
A palladium(II) complex 2 containing a monodentate
carbonate ligand was first prepared serendipitously, by fixation
of carbon dioxide from air during an attempt to recrystallize a
new fluxional “cycloneophyl” complex, 1.1−4 The reaction is
shown to occur in two steps. The first involves protonolysis by
H2O/CO2 of the arylpalladium bond of 1 to give a cationic
neophylpalladium complex with a bicarbonate anion. The
second step involves oxidation of this complex by peroxide
H
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(1H, H9 or H9′), 1.96 (1H, H9 or H9′), 1.31 (3H, H8 or H8′), 1.27
(3H, H8 or H8′). MALDI MS (pyrene matrix): Calcd for
[Pd(CH2CMe2C6H4)L1]•+: m/z 495.9. Observed: m/z 495.9. IR:
ν(O−H) 3285 cm−1. Recrystallization from unpurified THF led to
decomposition, with formation of crystals of 2a, whose 1H NMR
spectrum was identical to that of 2, reported below.
3J(H4aH5a) = 3J(H5aH6a) = 7 Hz, H5a), 7.50 (d, 2H, 3J(H5aH6a) =
7 Hz, H6a), 7.46 (m, 2H, H4a), 5.12 (m, 2H, H7a or H7a′), 4.28 (m,
2H, H7a or H7a′), 3.39 (t, 3J(H9aH10a) = 6 Hz, 2H, H10a), 2.88 (m,
2H, H8a), 1.79 (m, 2H, H9a). δ(13C) = 163.48 (C2a), 148.51 (C3a),
141.56 (C5a), 124.59 (C4a), 124.80 (C6a), 67.35 (C7a), 60.14 (C8a),
58.50 (C10a), 30.20 (C9a). MALDI MS (Pyrene matrix): Calcd for
[PdL1]+: m/z 363.75. Observed: m/z 363.75. IR ν(O−H) 3533 cm−1.
[Pd(CH2CMe2Ph)(κ3-N,N′,N′′-L1)][HCO3], 6. Under N2, degassed
water (1.90 mL) was added to a dry and degassed THF solution (3
mL) of complex 1 (0.055 g, 0.11 mmol). The solution was stirred
under an atmosphere of carbon dioxide for 2 h; then, the solvent was
evaporated under vacuum to give 2 as a yellow powder (0.053 g, 0.096
mmol, 88%). NMR in D2O: δ(1H) = 8.04 (d, 2H, 3J(H5aH6a) = 5 Hz,
[Pd(CO3)(κ3-N,N′,N′′-L1)], 2. In a darkened flask, to an aqueous
solution (3 mL) of 3 (0.040 mg, 0.038 mmol) was added silver
carbonate (0.031 mg, 0.11 mmol) in water (4 mL) with stirring. After
17 h, the reaction mixture was centrifuged to separate silver chloride
and palladium salt as precipitates. The solvent was evaporated from the
resultant yellow solution under vacuum to give 2 as an air-stable,
yellow solid (0.040 mg, 0.094 mmol, 83%). NMR in D2O: δ(1H) =
8.17 (d, 2H, 3J(H5aH6a) = 6 Hz, H6a), 8.13 (dd, 2H, 3J(H5aH6a) = 6
3
H6a), 7.73 (t, 2H, 3J(H3aH4a) = J(H4aH5a) = 8 Hz, H4a), 7.38 (d,
3
3
2H, 3J(HH) = 8 Hz, H2, H6), 7.27 (d, 2H, 3J(H3aH4a) = 8 Hz, H3a),
Hz, J(H4aH5a) = 7 Hz, H5a), 7.63 (d, 2H, J(H3aH4a) = 7 Hz,
H3a), 7.58 (t, 2H, 3J(H3aH4a) = 3J(H4aH5a) = 7 Hz, H4a), 5.30 (d,
2H, 2J(H7aH7a′) = 16 Hz, H7a or H7a′), 4.43 (d, 2H, 2J(H7aH7a′) =
16 Hz, H7a or H7a′), 3.55 (m, 2H, H10a), 3.09 (m, 2H, H8a), 2.02
(m, 2H, H9a). δ(13C) = 166.85 (carbonate), 163.26 (C2a), 148.50
(C6a), 141.41 (C5a), 124.80 (C4a), 122.86 (C3a), 67.50 (C7a), 60.47
(C10a), 58.57 (C8a), 30.20 (C9a). MALDI MS (Anthracene matrix):
Calcd for [Pd(CO3)L1 + K]+: m/z = 462.8. Obsd: m/z = 462.8. IR
ν(O−H) 3341 cm−1, ν(C−O) 1316 cm−1. Anal. Calcd for
C32H40N6O8Pd2·5H2O: C, 40.90; H, 5.36; N, 8.94. Found: C, 41.07;
H, 5.07; N 8.92. Yellow crystals suitable for single-crystal X-ray
crystallographic analysis were grown by the slow evaporation of an
aqueous solution of 2 at room temperature.
3
3
7.12 (dd, 2H, J(H5aH6a) = 5 Hz, J(H4aH5a) = 8 Hz, H5a), 6.80
3
3
(m, 2H, H3, H5), 6.58 (t, 1H, J(H3H4) = J(H4H5) = 7 Hz, H4),
4.52 (d, 2H, 2J(H7aH7a′) = 15 Hz, H7a or H7a′), 4.02 (d, 2H,
2J(H7aH7a′) = 15 Hz, H7a or H7a′), 3.15 (t, 2H, J(H9aH10a) = 6
3
Hz, H10a), 2.49 (m, 2H, H8a), 1.82 (s, 2H, H9), 1.29 (m, 2H, H9a),
1.19 (s, 6H, H8). δ(13C) = 163.84 (C2a), 160.08 (bicarbonate),
151.11 (C1), 149.33 (C6a), 139.52 (C4a), 127.66 (C3, C5), 125.70
(C2, C6), 125.28 (C4), 124.12 (C5a), 123.22 (C3a), 63.71 (C7a),
58.88 (C10a), 54.62 (C8a), 48.91 (C9), 41.46 (C7), 29.92 (C8), 29.25
(C9a). HRMS (ESI-TOF): Calcd for [Pd(CH2CMe2Ph)(L1)]: m/z
496.15801. Observed: m/z 496.16280. IR: ν(O−H) 3209 cm−1, ν(C−
O) 1606 cm−1. Anal. Calcd for C26H33N3O4Pd: C, 55.97; H, 5.96; N,
7.53. Found: C, 55.62; H, 5.93; N, 7.03. For the sample used for the
2H NMR experiment, degassed water was replaced with degassed D2O,
while the rest of the reaction conditions were unchanged. NMR in
H2O: δ(2H) = 7.4 (br, D2). Attempted recrystallization of 6 from
CHCl3 gave crystals of [PdCl(κ3-N,N′,N′′-L1)]Cl·2H2O, 3b, identi-
fied by structure determination.
[PdCl(κ3-N,N′,N′′-L1)]2[PdCl4], 3a. To a stirred solution of
[PdCl2(COD)] (0.300 g, 1.05 mmol) in acetone (50 mL) was
added an acetone solution (20 mL) of L1 (0.180 g, 0.700 mmol). A
brown precipitate was observed after 15 min. The mixture was stirred
for 2 more hours. The precipitate was then collected by vacuum
filtration and washed with acetone (3 × 5 mL) and dried under
vacuum, to give 3 as an air-stable solid (0.322 g, 0.307 mmol, 88%).
Reaction of Complex 6 with H2O2. H2O2 (0.137 mL, 30%
aqueous solution, 15 equiv) was added to a solution of complex 6
(0.055 g, 0.098 mmol) in D2O (1.2 mL) while vigorously stirring. The
solution was stirred for 3 min, then extracted with CDCl3 (1.5 mL).
3
NMR in CD3OD: δ(1H) = 8.72 (d, 2H, J(HH) = 6 Hz, H6a), 8.15
3
3
(dd, 2H, J(HH) = 6 Hz, 7 Hz, H5a), 7.69 (d, 2H, J(HH) = 7 Hz,
3
2
H3a), 7.57 (t, 2H, J(HH) = 7 Hz, H4a), 5.42 (d, 2H, J(HH) = 15
Hz, H7a or H7a′), 4.52 (d, 2H, 2J(HH) = 15 Hz, H7a or H7a′), 3.52
(t, 2H, 3J(HH) = 5 Hz, H10a), 3.17 (m, 2H, H8a), 1.92 (m, 2H, H9a).
δ(13C) = 164.86 (C2a), 150.58 (C6a), 141.32 (C5a), 124.73 (C4a),
122.93 (C3a), 67.30 (C7a), 60.92 (C8a), 58.22 (C10a), 30.70 (C9a).
HRMS (ESI-TOF): Calcd for [C15H19ClN3OPd]+: m/z = 398.025139.
Observed: m/z = 398.02504. IR: ν(O−H) 3380 cm−1. Anal. Calcd for
C30H38Cl6N6O2Pd3: C, 34.43; H, 3.66; N, 8.03. Found: C, 34.03; H,
3.70; N 7.79. Crystals were obtained by slow evaporation of a solution
of 3 in methanol at room temperature, and the connectivity was
established (Figure S39, CCDC 1570681), though disorder of the
[PdCl4]2− unit and associated water solvate molecules did not allow
full refinement.
1
The D2O layer was shown to contain complex 2 (84%) by H NMR
1
spectroscopy. The organic layer was analyzed by GC-MS and by H
NMR, using 1,3,5-trimethoxybenzene as internal standard. The major
product was identified as PhMeEtCOH, PB. Yield 51%. NMR in
CDCl3: δ(1H) = 7.43 (2H, Ho), 7.32 (2H, Hm), 7.25 (1H, Hp), 1.75−
1.85 (m, 2H, MeCHaHb), 1.50 (s, 3H, CCH3), 0.75 (t, 3H, J = 7 Hz,
CH2CH3).22a MS: Calcd for C10H14O: m/z = 150.11. Found: m/z =
150.10. Other organic products were identified and analyzed similarly.
All yields are an average of two runs.trans-2-Phenyl-2-butene (9%):
NMR: δ(1H) = 7.41−7.20 (m, 5H, ArH); 5.90 (br, 1H, CCH); 2.06
(br, 3H, Ar−C−CH3); 1.82 (br, 3H, CCCH3).22b MS: Calcd for
C10H12: m/z = 132.20. Found: m/z = 132.10. 2-Phenyl-1-butene (5%):
NMR: δ(1H) = 7.41−7.22 (m, 5H, ArH), 5.26 (br, 1H, CH2), 5.04
(br, 1H, CH2), 2.50 (q, 2H, CH2), 1.09 (t, 3H, CH3).22c MS: Calcd
for C10H12: m/z = 132.20. Found: m/z = 132.24. 2-Benzyl-2-propanol
(10%): NMR: δ(1H) = 7.45−7.03 (m, 5H, ArH), 2.74 (s, 2H, CH2),
1.2 (s, 6H, CH3).22d MS: Calcd for C10H14O: m/z = 150.11. Found:
m/z = 150.05. 2-Benzyl-1-propene (4%): NMR: δ(1H) = 7.28−7.16
(m, 5H, ArH), 4.80 (s, 1H, CHH), 4.72 (s, 1H, CHH), 3.30 (s,
2H, CH2), 1.66 (s, 3H, CH3).22e MS: Calcd for C10H12: m/z = 132.20.
Found: m/z = 132.10. t-Butylbenzene (6%): NMR: δ(1H) = 7.01−
7.46 (m, ArH), 1.31 (s, (CH3)3).22f MS: Calcd for C10H14: m/z =
134.21. Found: m/z = 134.17. The t-butylbenzene-d1 formed from 6
and DCl in D2O gave MS: Calcd for C10H13D: m/z = 135.12. Found:
m/z = 135.10.
[Pd(OTf)(κ3-N,N′,N′′-L1)](OTf), 4. In a darkened flask, an aqueous
solution (2 mL) of silver triflate (0.058 mg, 0.228 mmol) was added to
a solution of 3 (0.040 mg, 0.038 mmol) in water (5 mL). The mixture
was stirred for 20 min, then centrifuged to separate insoluble material.
The solvent was evaporated under vacuum from the light brown
solution to give 4 in 82% yield (0.083 mg, 0.062 mmol). NMR in
3
D2O: δ(1H) = 8.04 (m, 4H, H5a, H6a), 7.53 (d, 2H, J(HH) = 8 Hz,
3
3
H3a), 7.47 (t, 2H, J(HH) = 8 Hz, H4a), 5.52 (d, 2H, J(HH) = 15
Hz, H7a or H7a′), 4.32 (d, 2H, 3J(HH) = 15 Hz, H7a or H7a′), 3.41
(t, 3J(HH) = 6 Hz, 2H, H10a), 3.00 (m, 2H, H8a), 1.87 (m, 2H, H9a).
δ(13C) = 163.13 (C2a), 148.70 (C5a), 142.18 (C6a), 124.96 (C4a),
123.07 (C3a), 118.49 (CF3), 68.61 (C7a), 61.53 (C8a), 58.33 (C10a),
30.15 (C9a); δ(19F) −78.96. HRMS (ESI-TOF): Calcd for
[C16H19F3N3O4PdS]+: m/z = 512.00832. Observed: m/z =
512.00854. IR: ν(O−H) 3303 cm−1.
X-ray Structure Determinations.27 Data Collection and
Processing. A crystal was mounted on a Mitegen polyimide
micromount with a small amount of Paratone N oil. All X-ray
measurements were made using a Bruker Kappa Axis Apex2
diffractometer at a temperature of 110 K. The frame integration was
performed using SAINT, and the resulting raw data was scaled and
absorption corrected using a multiscan averaging of symmetry
equivalent data using SADABS.
[Pd(OH)(κ3-N,N′,N′′-L1)](OH), 5. To a solution of 4 (0.05 mg,
0.037 mmol) in water (10 mL) was added an aqueous solution (3 mL)
of KOH (0.008 mg, 0.151 mmol) while stirring. After 20 min, the
reaction mixture was centrifuged. The light brown solution was dried
under vacuum to give a brown powder in 85% yield (0.025 mg, 0.060
mmol). NMR in D2O: δ(1H) = 8.13 (m, 2H, H3a), 8.00 (t, 2H,
I
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Structure Solution and Refinement. The structures were solved by
using the SHELXT program. All non-hydrogen atoms were obtained
from the initial solution. The hydrogen atoms were introduced at
idealized positions and were allowed to ride on the parent atom. The
structural model was fit to the data using full matrix least-squares based
on F2. The calculated structure factors included corrections for
anomalous dispersion from the usual tabulation. The structure was
refined using the SHELXL-2014 program from the SHELX suite of
crystallographic software.27 Details are given in Table S1 and in
CCDC 1570679−1570682.
DFT Calculations. DFT calculations were carried out for gas phase
structures by using the Amsterdam Density Functional program based
on the BP functional, with double-ζ basis set and first-order scalar
relativistic corrections.28 Minima were confirmed by vibrational
analysis; transition states were not determined. Details are given in
the Supporting Information.
A.; Boyle, P. D.; Blacquiere, J. M.; Puddephatt, R. J. Organometallics
2016, 35, 2645−2654.
(3) (a) Thompson, K. A.; Kadwell, C.; Boyle, P. D.; Puddephatt, R. J.
J. Organomet. Chem. 2017, 829, 22−30. (b) Moustafa, M. E.; Boyle, P.
D.; Puddephatt, R. J. Chem. Commun. 2015, 51, 10334−10336.
(4) (a) Warren, J. J.; Tronic, T. A.; Mayer, J. M. Chem. Rev. 2010,
110, 6961−7001. (b) Weinberg, D. R.; Gagliardi, C. J.; Hull, J. F.;
Murphy, C. F.; Kent, C. A.; Westlake, B. C.; Paul, A.; Ess, D. H.;
McCafferty, D. G.; Meyer, T. J. Chem. Rev. 2012, 112, 4016−4093.
(c) Hammes-Schiffer, S. J. Am. Chem. Soc. 2015, 137, 8860−8871.
(d) Lubitz, W.; Ogata, H.; Rudiger, O.; Reijerse, E. Chem. Rev. 2014,
114, 4081−4148.
(5) (a) Cam
Carmona, E. Angew. Chem., Int. Ed. 1999, 38, 147−151. (b) Cam
J.; Palma, P.; Carmona, E. Coord. Chem. Rev. 1999, 193−195, 207−
281. (c) Campora, J.; Palma, P.; del Río, D.; Carmona, E.; Graiff, C.;
́
pora, J.; Lop
́
ez, J. A.; Palma, P.; Valerga, P.; Spillner, E.;
́
pora,
́
Tiripicchio, A. Organometallics 2003, 22, 3345−3347. (d) Behnia, A.;
Boyle, P. D.; Fard, M. A.; Blacquiere, J. M.; Puddephatt, R. J. Dalton
Trans. 2016, 45, 19485−19490.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00631.
■
S
́
(6) (a) Pendleton, I. M.; Perez-Temprano, M. H.; Sanford, M. S.;
Zimmerman, P. M. J. Am. Chem. Soc. 2016, 138, 6049−6060.
(b) Perez-Temprano, M. H.; Racowski, J. M.; Kampf, J. W.; Sanford,
́
M. S. J. Am. Chem. Soc. 2014, 136, 4097−4100. (c) Canty, A. J.;
Ariafard, A.; Camasso, N. M.; Higgs, A. T.; Yates, B. F.; Sanford, M. S.
Dalton Trans. 2017, 46, 3742−3748.
(7) Sundaravel, K.; Sankaralingam, M.; Suresh, E.; Palaniandavar, M.
Dalton Trans. 2011, 40, 8444−8458.
Spectra and structures of the complexes; summary of X-
ray data for complexes 2a, 2b, and 3b (PDF)
Atomic coordinates of calculated structures (XYZ)
Accession Codes
(8) (a) Appel, A. M.; Bercaw, J. E.; Bocarsly, A. B.; Dobbek, H.;
DuBois, D. L.; Dupuis, M.; Ferry, J. G.; Fujita, E.; Hille, R.; Kenis, P. J.
A.; Kerfeld, C. A.; Morris, R. H.; Peden, C. H. F.; Portis, A. R.;
Ragsdale, S. W.; Rauchfuss, T. B.; Reek, J. N. H.; Seefeldt, L. C.;
Thauer, R. K.; Waldrop, G. L. Chem. Rev. 2013, 113, 6621−6658.
(b) Omae, I. Curr. Org. Chem. 2016, 20, 953−962. (c) Omae, I. Coord.
Chem. Rev. 2012, 256, 1384−1405. (d) Yu, D.; Teong, S. P.; Zhang, Y.
Coord. Chem. Rev. 2015, 293−294, 279−291. (e) Johnson, M. T.;
Wendt, O. F. J. Organomet. Chem. 2014, 751, 213−220. (f) Lau, K.-C.;
Petro, B. J.; Bontemps, S.; Jordan, R. F. Organometallics 2013, 32,
6895−6898.
CCDC 1570679−1570682 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: johanna.blacquiere@uwo.ca.
*E-mail: pudd@uwo.ca.
■
(9) Ariyananda, P. W. G.; Yap, G. P. A.; Rosenthal, J. Dalton Trans.
2012, 41, 7977−7983.
ORCID
(10) (a) Pushkar, J.; Wendt, O. F. Inorg. Chim. Acta 2004, 357,
1295−1298. (b) Johansson, R.; Wendt, O. F. Organometallics 2007, 26,
2426−2430. (c) Mousa, A. H.; Fleckhaus, A.; Kondrashov, M.; Wendt,
O. F. J. Organomet. Chem. 2017, 845, 157−164.
Richard J. Puddephatt: 0000-0002-9846-3075
Notes
The authors declare no competing financial interest.
(11) (a) Fulmer, G. R.; Kaminsky, W.; Kemp, R. A.; Goldberg, K. I.
Organometallics 2011, 30, 1627−1636. (b) Smoll, K. A.; Kaminsky, W.;
Goldberg, K. I. Organometallics 2017, 36, 1213−1216. (c) Ortiz, D.;
Blug, M.; Le Goff, X.-F.; Le Floch, P.; Mezailles, N.; Maitre, P.
Organometallics 2012, 31, 5975−5978. (d) Ruiz, J.; Martinez, M. T.;
Florenciano, F.; Rodriguez, V.; Lopez, G.; Perez, J.; Chaloner, P. A.;
Hitchcock, P. B. Inorg. Chem. 2003, 42, 3650−3661. (e) Crutchley, R.
J.; Powell, J.; Faggiani, R.; Lock, C. J. L. Inorg. Chim. Acta 1977, 24,
L15−L16. (f) Ozawa, F.; Son, T.; Ebina, S.; Osakada, K.; Yamamoto,
A. Organometallics 1992, 11, 171−176. (g) Amatore, C.; Gamez, S.;
Jutand, A.; Meyer, G.; Moreno-Manas, M.; Morral, L.; Pleixats, R.
Chem. - Eur. J. 2000, 6, 3372−3376.
ACKNOWLEDGMENTS
We thank the NSERC (Canada) for financial support.
■
REFERENCES
■
(1) (a) Punniyamurthy, T.; Velusamy, S.; Iqbal, J. Chem. Rev. 2005,
105, 2329−2364. (b) Shi, Z.; Zhang, C.; Tang, C.; Jiao, N. Chem. Soc.
Rev. 2012, 41, 3381−3430. (c) Stahl, S. S. Science 2005, 309, 1824−
1826. (d) Shteinman, A. A. J. Mol. Catal. A: Chem. 2017, 426, 305−
315. (e) Gunsalus, N. J.; Koppaka, A.; Park, S. H.; Bischof, S. M.;
Hashiguchi, B. G.; Periana, R. A. Chem. Rev. 2017, 117, 8521−8573.
(f) Wu, W.; Jiang, H. Acc. Chem. Res. 2012, 45, 1736−1748.
(g) Campbell, A. N.; Stahl, S. S. Acc. Chem. Res. 2012, 45, 851−863.
(h) Gligorich, K. M.; Sigman, M. S. Chem. Commun. 2009, 3854−
3867. (i) Sigman, M. S.; Jensen, D. R. Acc. Chem. Res. 2006, 39, 221−
229. (j) Zhang, Y.-H.; Yu, J.-Q. J. Am. Chem. Soc. 2009, 131, 14654−
14655. (k) Huang, J.; Li, J.; Zheng, J.; Wu, W.; Hu, W.; Ouyang, L.;
Jiang, H. Org. Lett. 2017, 19, 3354−3357. (l) Scheuermann, M. L.;
Goldberg, K. I. Chem. - Eur. J. 2014, 20, 14556−14568.
(m) Vedernikov, A. N. Acc. Chem. Res. 2012, 45, 803−813.
(12) Urry, W. H.; Kharasch, M. S. J. Am. Chem. Soc. 1944, 66, 1438−
1440.
(13) (a) Seubold, F. H., Jr. J. Am. Chem. Soc. 1953, 75, 2532−2533.
(b) Wilt, J. W.; Pawlikowski, W. W., Jr. J. Org. Chem. 1975, 40, 3641−
3644. (c) Burton, A.; Ingold, K. U.; Walton, J. C. J. Org. Chem. 1996,
61, 3778−3782. (d) Weber, M.; Fischer, H. J. Am. Chem. Soc. 1999,
121, 7381−7388. (e) Chen, Z.-M.; Zhang, X.-M.; Tu, Y.-Q. Chem. Soc.
Rev. 2015, 44, 5220−5245.
(14) (a) Heck, R.; Winstein, S. J. Am. Chem. Soc. 1957, 79, 3432−
3438. (b) Saunders, W. H., Jr.; Paine, R. H. J. Am. Chem. Soc. 1961, 83,
882. (c) Shubin, V. G. Top. Curr. Chem. 1984, 116/117, 267−341.
(2) (a) Khusnutdinova, J. R.; Rath, N. P.; Mirica, L. M. J. Am. Chem.
Soc. 2012, 134, 2414−2422. (b) Qu, F.; Khusnutdinova, J. R.; Rath, N.
P.; Mirica, L. M. Chem. Commun. 2014, 50, 3036−3039. (c) Behnia,
J
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(15) Campora, J.; Gutierrez-Puebla, E.; Lopez, J. A.; Monge, A.;
Palma, P.; del Rio, D.; Carmona, E. Angew. Chem., Int. Ed. 2001, 40,
3641.
(16) Zhugralin, A. R.; Kobylianskii, I. J.; Chen, P. Organometallics
2015, 34, 1301−1306.
(17) O’Reilly, M. E.; Dutta, S.; Veige, A. S. Chem. Rev. 2016, 116,
8105−8145.
(18) (a) Langford, C. H.; Gray, H. B. Ligand Substitution Processes;
Benjamin: New York, 1965. (b) Banerjee, P. Coord. Chem. Rev. 1999,
190-192, 19−28.
(19) (a) Sandstrom, J. Dynamic NMR Spectroscopy; Academic Press:
London, 1982. (b) Nakamoto, K. Infrared and Raman Spectra of
Inorganic and Coordination Compounds, 5th ed.; Wiley-Interscience:
New York, 1997.
(20) (a) Seubert, K.; Bohme, D.; Kosters, J.; Shen, W.-Z.; Freisinger,
E.; Muller, J. Z. Anorg. Allg. Chem. 2012, 638, 1761−1767. (b) Nagy,
Z.; Fabian, I.; Benyei, A.; Sovago, I. J. Inorg. Biochem. 2003, 94, 291−
299. (c) Kim, S.; Kim, D.; Song, Y.; Lee, H.-J.; Lee, H. Aust. J. Chem.
2014, 67, 953−961. (d) Petersen, A. R.; White, A. J. P.; Britovsek, G. J.
P. Dalton Trans. 2016, 45, 14520−14523. (e) McSkimming, A.;
Diachenko, V.; London, R.; Olrich, K.; Onie, C. J.; Bhadbhade, M. M.;
Bucknall, M. P.; Read, R. W.; Colbran, S. B. Chem. - Eur. J. 2014, 20,
11445−11456. (f) Mandapati, P.; Giesbrecht, P. K.; Davis, R. L.;
Herbert, D. E. Inorg. Chem. 2017, 56, 3674−3685.
(21) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955−
964.
(22) (a) Lynch, J. E.; Eliel, E. L. J. Am. Chem. Soc. 1984, 106, 2943−
2948. (b) Nave, S.; Sonawane, R. P.; Elford, T. G.; Aggarwal, V. K. J.
Am. Chem. Soc. 2010, 132, 17096−17098. (c) Movahhed, S.; Westphal,
J.; Dindarog
7381−7384. (d) Fernan
Gonzalez, R. R. J. Org. Chem. 2009, 74, 3913−3918. (e) Alacid, E.;
Naj
̆
́
́
́
́
era, C. Org. Lett. 2008, 10, 5011−5014. (f) Terao, J.; Nakamura,
M.; Kambe, N. Chem. Commun. 2009, 6011−6013.
(23) (a) Thorshaug, K.; Fjeldahl, I.; Romming, C.; Tilset, M. Dalton
Trans. 2003, 4051−4056. (b) Aye, K.-T.; Vittal, J. J.; Puddephatt, R. J.
J. Chem. Soc., Dalton Trans. 1993, 1835−1839.
(24) (a) Smythe, N. A.; Grice, K. A.; Williams, B. S.; Goldberg, K. I.
Organometallics 2009, 28, 277−288. (b) Desnoyer, A. N.; Love, J. A.
Chem. Soc. Rev. 2017, 46, 197−238. (c) Sberegaeva, A. V.; Zavalij, P.
Y.; Vedernikov, A. N. J. Am. Chem. Soc. 2016, 138, 1446−1455.
(d) Pal, S.; Vedernikov, A. N. Dalton Trans. 2012, 41, 8116−8122.
(e) Safa, M.; Jennings, M. C.; Puddephatt, R. J. Organometallics 2012,
31, 3539−3550. (f) Mitton, S. J.; McDonald, R.; Turculet, L.
Polyhedron 2013, 52, 750−754.
(25) The structures of 6, O, and P in the presence of aqueous
hydrogen peroxide will certainly involve hydrogen bonding to solvent
molecules, and the structures and relative energies shown in Figure 8
will consequently be modified. We do not claim that the 3-
hydroxypropyl group plays a critical role in this reaction, and
preliminary results indicate that the chemistry is similar with the
corresponding ligand having a 3-methoxypropyl substituent.
(26) (a) Byers, P. K.; Canty, A. J.; Crespo, M.; Puddephatt, R. J.;
Scott, J. D. Organometallics 1988, 7, 1363−1367. (b) Hyvl, J.;
Roithova, J. Org. Lett. 2014, 16, 200−203. (d) Tang, F. Z.; Zhang, Y.;
Rath, N. P.; Mirica, L. M. Organometallics 2012, 31, 6690−6696.
(e) Xu, L.-M.; Li, B.-J.; Yang, Z.; Shi, Z.-J. Chem. Soc. Rev. 2010, 39,
712−733. (f) Racowski, J. M.; Dick, A. R.; Sanford, M. S. J. Am. Chem.
Soc. 2009, 131, 10974−10983.
(27) (a) SAINT, version 2013.8; Bruker-AXS: Madison, WI, 2013.
(b) SADABS, version 2012.1; Bruker-AXS: Madison, WI, 2012.
(c) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3.
(d) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3.
(28) (a) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; van
Gisbergen, S.; Guerra, C. F.; Snijders, J. G.; Ziegler, T. J. Comput.
Chem. 2001, 22, 931−967. (b) Becke, A. Phys. Rev. A: At., Mol., Opt.
Phys. 1988, 38, 3098−3100.
K
DOI: 10.1021/acs.organomet.7b00631
Organometallics XXXX, XXX, XXX−XXX