Zirconium Metal-Organic Frameworks Assembled from Pd and Pt PNNNP Pincer Complexes: Synthesis, Postsynthetic Modification, and Lewis Acid Catalysis

Article abstract of DOI:10.1021/acs.inorgchem.7b03063

Carboxylic acid-functionalized Pd and Pt P^NN^NP pincer complexes were used for the assembly of two porous Zr metal-organic frameworks (MOFs), 2-PdX and 2-PtX. Powder X-ray diffraction analysis shows that the new MOFs adopt cubic frame

Full text of DOI:10.1021/acs.inorgchem.7b03063

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Zirconium Metal−Organic Frameworks Assembled from Pd and Pt
PNNNP Pincer Complexes: Synthesis, Postsynthetic Modification, and
Lewis Acid Catalysis
Benjamin R. Reiner, Neil T. Mucha, Anna Rothstein, J. Sebastian Temme, Pu Duan,
Klaus Schmidt-Rohr, Bruce M. Foxman, and Casey R. Wade*,†,‡
†Department of Chemistry, Brandeis University, 415 South Street MS 015, Waltham, Massachusetts 02453, United States
S
* Supporting Information
ABSTRACT: Carboxylic acid-functionalized Pd and Pt PNNNP
pincer complexes were used for the assembly of two porous Zr
metal−organic frameworks (MOFs), 2-PdX and 2-PtX. Powder
X-ray diffraction analysis shows that the new MOFs adopt cubic
framework structures similar to the previously reported
Zr6O4(OH)4[(POCOP)PdX]3, [POCOP = 2,6-(OPAr2)2C6H3);
−
Ar = p-C6H4CO2 , X = Cl−, I−] (1-PdX). Elemental analysis
and spectroscopic characterization indicate the presence of
missing linker defects, and 2-PdX and 2-PtX were formulated
−
as Zr6O4(OH)4(OAc)2.4[M(PNNNP)X]2.4 [M = Pd, Pt; PNNNP = 2,6-(HNPAr2)2C5H3N; Ar = p-C6H4CO2 ; X = Cl−, I−].
Postsynthetic halide ligand exchange reactions were carried out by treating 2-PdX with Ag(O3SCF3) or NaI followed by
PhI(O2CCF3)2. The latter strategy proved to be more effective at activating the MOF for the catalytic intramolecular
hydroamination of an o-substituted alkynyl aniline, underscoring the advantage of using halide exchange reagents that produce
soluble byproducts.
Scheme 1. Synthesis and Framework Structure of 1-PdX
INTRODUCTION
Transition-metal complexes supported by arene-based diphos-
phine pincer ligands (PZEZP, Figure 1) have been found to
■
Figure 1. General structure of PZEZP pincer complexes.
than an analogous homogeneous Pd POCOP complex, and the
difference in activity was attributed to inhibition of catalyst
decomposition pathways in the MOF. Humphrey and cow-
orkers employed a similar design strategy to prepare a Co MOF
containing Pd PCCCP linkers and showed that the material
catalyze a wide range of organic transformations and small
molecule activation reactions.1−21 Much of the appeal and
success of PZEZP pincer ligand platforms arises from their
tunability and the stability conferred by chelation. We and
others have been interested in incorporating transition-metal
PZEZP complexes into porous metal−organic frameworks
(MOFs).22−25 In addition to offering ease of product separation
and recyclability, heterogenization of homogeneous catalysts
can potentially improve catalyst lifetime and activity via site
isolation or other immobilization effects. MOFs have attracted
considerable interest as heterogeneous catalyst platforms owing
to their well-defined structures, inherent porosity, and
amenability to functionalization.26−32
activates CO2 under mild conditions after Cl−/CH3 ligand
−
exchange at the Pd pincer sites.23 Stoddart, Farha, and
coworkers used solvent-assisted ligand incorporation to
immobilize Ir POCOP complexes within the mesoporous Zr
MOF NU-1000, and the resulting material was found to
catalyze the gas phase hydrogenation of ethylene.24
Although the identities of the central arene donor (E) and
phosphine linker groups (Z) can have a profound impact on
reactivity, PZEZP pincer complexes often exhibit similar
We recently reported the synthesis and characterization of a
Zr MOF, 1-PdX, assembled from a linker based on a Pd POCOP
pincer complex (Scheme 1).22 The MOF exhibits markedly
better catalytic activity for transfer hydrogenation of aldehydes
Received: December 4, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b03063
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molecular structures.9,33−35 This led us to consider that an
isostructural series of MOFs might be obtained using PZEZP
pincer metallolinkers with different arene donors, linker groups,
or even chelated metal species. To explore this possibility and
the scope of immobilization and site isolation effects, we have
been investigating the assembly of Zr MOFs from linkers based
on PNNNP pincer complexes. Herein, we report the synthesis
and characterization of two porous Zr MOFs, 2-PdX and 2-PtX,
constructed from Pd and Pt PNNNP pincer complexes. These
materials adopt the same cubic framework structure as 1-PdX,
providing initial evidence that the isoreticular principle can be
applied to pincer MOFs. In addition, postsynthetic halide
ligand exchange reactions at the Pd centers of 2-PdX were
investigated as a means of activating the MOF for Lewis acid-
catalyzed transformations. Silver salts are ubiquitous and
operationally simple halide abstraction agents, but precipitation
of insoluble AgX salts can potentially pollute a heterogeneous
catalyst. As a result, halide abstraction becomes uniquely
challenging in MOFs owing to the need for soluble byproducts
that can be easily separated from the heterogeneous catalyst.
We previously reported the use of PhI(TFA)2 (TFA =
O2CCF3) for I−/TFA− ligand exchange in 1-PdX and
considered this reagent to be advantageous because it produces
PhI and I2 as soluble byproducts.22 Herein, we further highlight
the efficacy of this strategy, demonstrating that Cl−/I− ligand
exchange in 2-PdX followed by reaction with PhITFA2 is
superior to treatment with AgOTf (OTf = O3SCF3) for
activating the MOF as a Lewis acid catalyst for intramolecular
hydroamination.
chloride analogues (Figures S9, S12, S18, S21). The H NMR
spectra of these complexes display all expected resonances.
1
tBu4L-PdI and Bu4L-PtI were deprotected by reaction with
t
trifluoroacetic acid (HTFA) in CH2Cl2 solution. The crude
products were then treated with pyridine (1.5 equiv) in acetone
solution, resulting in elimination of 1 equiv of HI and isolation
of the zwitterionic complexes H3L-MI. The 31P{1H} NMR
spectra of the H3L-MI complexes exhibit broadened resonances
centered at 69.9 and 63.2 ppm for M = Pd and Pt, respectively
(Figures S15 and S24). Single crystals of H3L-PdI were
obtained from a saturated methanol solution, and the X-ray
crystal structure supports deprotonation of one of the
carboxylate groups concomitant with loss of the outer sphere
I− to form the zwitterionic complex (Figure S1).
Solvothermal reaction of the H3L-MI (M = Pd, Pt)
complexes with ZrCl4 in a 4/1 v/v mixture of N,N-
dimethylformamide (DMF) and acetic acid (AcOH) generates
2-PdX and 2-PtX as bright yellow and white microcrystalline
powders, respectively (Scheme 3). Notably, attempts to use the
Scheme 3. Synthesis of 2-PdX and 2-PtX
deprotected chloride derivatives (i.e., H3L-MCl) for MOF
synthesis resulted only in the formation of dark, amorphous
solids. A similar trend was previously observed for the synthesis
of Zr MOFs from H4[POCOP-PdX] (X = Cl, I) complexes.22
The contrasting behavior of the M−Cl and M−I complexes
likely reflects the difference in leaving group ability between Cl−
and I− ligands.37 The more strongly bound I− ligands ostensibly
act as protecting groups, suppressing ligand exchange and
subsequent decomposition processes under the solvothermal
reaction conditions.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of 2-PdX and 2-PtX.
t
The ligand Bu4L was prepared by the P−N coupling of
t
ClP(C6H4CO2 Bu)2 with 2,6-diaminopyridine in the presence
a
Scheme 2. Synthesis of Pincer Complexes H3L-MI.
The powder X-ray diffraction (PXRD) data show that 2-PdX
and 2-PtX are isostructural with 1-PdX (Figure 2). Full-pattern
decomposition of the data was performed using Pawley
refinement and provided cubic unit cell parameters of a =
16.76 and 16.81 Å for 2-PdX and 2-PtX, respectively (Tables S2
and S3 and Figures S2 and S3). 2-PdX and 2-PtX are both
stable under ambient conditions but experience loss of
crystallinity upon methanol solvent exchange followed by
drying in vacuo. Optimized workup conditions include washing
with DMF and acetone followed by soaking (ca. 16 h) in
acetone prior to drying under reduced pressure. Following this
procedure, samples of 2-PdX and 2-PtX were desolvated by
heating under reduced pressure (10−4 Torr) at 150 °C for 16 h.
N2 adsorption measurements (77 K) (Figure S4) gave
calculated Brunauer−Emmett−Teller (BET) surface areas of
922 and 726 m2 g−1 for 2-PdX and 2-PtX, respectively, which
are comparable to that previously observed for 1-PdX (1164 m2
g−1). Pore size distribution analyses for 1-PdX, 2-PdX, and 2-
PtX using the DFT method show similar major pore
distributions around 10−12 Å that are consistent with the
proposed structure (Figure S5). However, 2-PdX and 2-PtX
exhibit a broad distribution of larger pores in the 14−20 Å
range that could be attributable to the presence of missing
linker defects.
a
Conditions: (i) NEt3, toluene, 80 °C, 16 h; (ii) MCl2(cod), CH2Cl2,
16 h; (iii) NaI, acetone, 1.5 h; (iv) CF3CO2H, CH2Cl2, 16 h; (v)
pyridine, acetone, 0.5 h
of triethylamine (Scheme 2).36 The M−Cl pincer complexes,
tBu4L-MCl (M = Pd, Pt), were obtained by reaction of Bu4L
t
with an equimolar amount of the appropriate MCl2(cod) (cod
= 1,5-cyclooctadiene) metal precursor in CH2Cl2 solution.
Subsequent Cl−/I− exchange with NaI generated the pincer
complexes tBu4L-PdI and tBu4L-PtI. The 31P{1H} NMR spectra
t
of the Bu4L-MX (X = Cl, I) complexes exhibit a single
resonance in the 61−76 ppm range with the signals for the
Combustion analysis and inductively coupled plasma optical
emission spectrometry (ICP-OES) were used to determine the
tBu4L-MI complexes shifted slightly downfield relative to the
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Figure 3. Solid-state 31P NMR spectra of 2-PdX and 2-PtX with
magic-angle spinning (MAS) and total suppression of spinning
sidebands (TOSS).48 See Supporting Information for experimental
details.
bands could be clearly identified in the ATR−IR spectra of 2-
PdX and 2-PtX (Figure S52).
Samples of 2-PdX and 2-PtX were digested with a 3:1 v:v
mixture of trifluoroacetic acid (HTFA) and C6D6, and the
resulting solutions were analyzed by 31P and 1H NMR
spectroscopy and ESI-MS. The 31P{1H} NMR spectra each
exhibit two major signals appearing at 74.0 and 69.9 ppm for 2-
Figure 2. (a) PXRD patterns of 1-PdX, 2-PdX, and 2-PtX (Cu Kα
radiation, λ = 1.54 Å). (b) Defect-free framework structure of 2-MX.
(c) View of a portion of the framework showing ovoidal pores. Blue
octahedra represent [Zr6O4(OH)4]12+ building units.
PdX and 67.7 (1J195Pt−P = 1359.1 Hz) and 64.0 (1J195Pt−P
=
1394.4 Hz) ppm for 2-PtX (Figure 4). In both cases, the signals
compositions of desolvated samples of 2-PdX and 2-PtX. ICP-
OES provided Zr:M (M = Pd, Pt) ratios of 2.9:1 and 2.7:1 for
2-PdX and 2-PtX, respectively. These values reflect deficiencies
of Pd and Pt based on the formula expected from the
framework structure (Zr6O4(OH)4[MX(PNNNP)X]3) and are
likely the result of missing linker-type defects (vide infra).38−46
The elemental analysis data provide M:I:Cl molar ratios of
1:0.82:0.88 and 1:0.66:0.74 for 2-PdX and 2-PtX, respectively,
indicating that a significant amount of Cl− is introduced from
the use of ZrCl4 for the MOF synthesis. An overall 1:2 M:halide
ratio is expected if the halides provide charge balance of the
cationic pincer complexes. Consequently, the experimentally
determined ratios reflect the partial absence of charge balancing
outer sphere halides. We have not clearly identified the
remaining charge-balancing species, but it is possible that
acetate or deprotonated Zr6 SBUs may fulfill this role.47
2-PdX and 2-PtX were characterized by solid and solution
state NMR spectroscopy as well as electrospray mass
spectrometry (ESI-MS) to gain further insight into their
structure and composition. The solid-state 31P NMR spectra of
2-PdX and 2-PtX show broad, asymmetric signals centered at
72 and 67 ppm, respectively (Figure 3). The spectra also show
the presence of a minor species, giving rise to a signal around
25 ppm. The chemical shift of the minor species is in line with
that observed for the PNNNP pincer ligand in solution but could
also arise from a small amount of ligand decomposition.22
Although ligand decomposition is likely to result in the
presence of oxidized phosphine species, no PO stretching
Figure 4. 31P{1H} NMR spectra of acid digested samples of 2-PdX
(top) and 2-PtX (bottom).
appear in ∼3:1 ratio, which was reproducible over several
1
samples. The H NMR spectra of the digested samples also
clearly show two sets of resonances consistent with the
presence of two distinct pincer complexes (Figures S28 and
S30). The solid and solution state NMR data for the MOFs
closely resemble those obtained for the H3L-MCl and H3L-MI
complexes in solution, indicating that the pincer complex
linkers remain intact both within the MOF and in solution after
acid digestion. ESI-MS analysis confirmed the identity of the
species present in the digested solution as the M−I and M−Cl
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pincer complexes. The mass spectrum of 2-PdX shows two
major parent ions with m/z = 795 and 886 amu that are
assigned to H4[L-PdCl]+ and H4[L-PdI]+, respectively (Figure
S39). Similarly, H4[L-PtCl]+ (m/z = 883 amu) and H4[L-PtI]+
(m/z = 975 amu) were observed to be the major parent ions
present in the mass spectrum of 2-PtX (Figure S40). Together,
these data support mixed occupancy of the M-coordinated
halide.
Scheme 4. Postsynthetic Halide Ligand Exchange Reactions
of 2-PdX
In addition to the resonances assigned to the pincer
1
complexes, the H NMR spectra of digested samples of 2-
PdX and 2-PtX display signals attributable to acetic acid
(HOAc) at 1.86 ppm (Figures S28 and S30). Because
desolvated samples were used for digestion, HOAc is not
likely to be present as a pore-occluding guest molecule but
rather incorporated into the framework structure as OAc−.
Assignment of framework bound acetate is further supported by
quantitative solid-state 13C NMR spectra of 2-PdX and 2-PtX
that show signals consistent with acetate groups at 22 and 179
ppm (Figure S37). The CH3 resonances at 22 ppm exhibit
significant line broadening and partial dipolar dephasing that is
in contrast to the sharp signal of a highly mobile species,
assigned to residual acetone, at 30 ppm. These characteristics
confirm the solid-like behavior of the OAc− species in the
1
MOF. Integration of the solution-state H and solid-state 13C
NMR spectra provides H4[L-MX]+:OAc ratios of ∼1:1 for both
MOF samples. These data combined with the Zr:M ratios
determined by ICP-OES analysis suggest that the empirical
formulas of 2-PdX and 2-PtX are best given as
{Zr6O4(OH)4(OAc)2.4[L-MX]2.4}Y2.4. The presence of OAc−
or other modulator-derived anions often signals the presence of
missing linker defects in Zr MOFs.38−42 It seems likely that 2-
PdX and 2-PtX retain the same framework structure as 1-PdX
but contain a larger number of disordered missing linker
defects. However, given the level of uncertainty associated with
structure determination from powder X-ray diffraction data, we
cannot rule out the possibility of alternate framework
structures. Efforts to obtain samples suitable for single crystal
X-ray diffraction have not yet been successful.
Postsynthetic Halide Ligand Exchange. Exchange of
halide ligands for more weakly coordinating anions is often
necessary to activate homogeneous organometallic complexes
for catalysis. We previously observed that treatment of 1-PdX
with PhI(TFA)2 facilitates I−/TFA− ligand exchange, activating
the MOF for transfer hydrogenation catalysis.22 This halide
exchange strategy is advantageous because it produces PhI and
I2 as soluble byproducts that can be easily separated from the
MOF. Consequently, we sought to determine if a similar
approach could be used for halide ligand exchange in 2-PdX.
In our initial screening, 2-PdX was treated with a solution of
PhI(TFA)2 in MeCN and washed copiously with MeCN
(Scheme 4). 31P{1H} NMR analysis of the acid-digested
product indicated that the H4[L-PdCl]+ pincer complex was the
major species in solution (Figure 5). This result is consistent
with oxidative exchange of I− for TFA− followed by
coordination of the outer sphere Cl− ions that remain present
in 2-PdX. To circumvent the formation of Pd−Cl species, we
subjected 2-PdX to a Cl−/I− ligand exchange reaction prior to
treatment with PhI(TFA)2. Accordingly, 2-PdI was generated
by treating 2-PdX with an aqueous solution of NaI. The
31P{1H} NMR spectrum of an acid-digested sample of 2-PdI
Figure 5. 31P{1H} NMR spectra of digested samples of 2-PdX, 2-PdI,
2-PdX + PhI(TFA)2, 2-PdTFA, and 2-PdOTf/AgOTf.
pincer complex and indicate quantitative Cl−/I− exchange.
Moreover, the ESI-MS spectrum of the digested product
contains a major signal corresponding to the H4[L-PdI]+ parent
ion at m/z = 886 (Figure S41). Next, 2-PdI was treated with a
CH2Cl2 solution of PhI(TFA)2 (4 equiv per Pd), and after 24 h,
the supernatant solution had turned a pink color, signaling the
formation of I2. The 31P{1H} NMR spectrum of an acid-
digested sample of the resulting material, 2-PdTFA, features
two singlets centered at 74.0 and 71.1 ppm that appear in a ∼
1:1 ratio. The downfield signal is consistent with the presence
of unreacted H4[L-PdI]+ species, while the chemical shift of the
new resonance at 71.1 ppm closely matches that observed for
1
t
exhibits a single major resonance at 74.0 ppm, and the H
the analogous homogeneous complex, Bu4L-PdTFA, in the
NMR spectrum displays a single set of well-resolved signals
same solvent mixture (Figure S43). Consequently, the data
(Figure S32). The spectra match those expected for the Pd−I
indicate ∼50% conversion of the Pd−I sites to Pd−TFA.
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Efforts to increase conversion by resubjecting the product to
PhI(TFA)2/CH2Cl2 solutions were largely unsuccessful. After
the second treatment, only a faint color change was observed
for the reaction supernatant, and 31P NMR analysis showed no
significant changes in the Pd−I:Pd−TFA product ratio (Figure
S44).
reflect the presence of Pd−OTf species in solution. Never-
theless, the appearance of crystalline AgI and AgCl in the
PXRD patterns of 2-PdX/AgOTf indicates that AgOTf
facilitates some degree of X−/OTf− halide exchange.
Catalytic Studies. Indoles are common motifs in natural
products and pharmaceuticals.49,50 They can be efficiently
assembled using a variety of strategies, including Lewis acid-
catalyzed intramolecular cyclization of o-alkynyl substituted
anilines.51 Moreover, Pd and Pt PNP pincer complexes have
found success as Lewis acid catalysts for intramolecular
hydrofunctionalization reactions.52−59 In most cases, these
catalysts are activated by exchanging halide ligands for more
weakly coordinating anions. These considerations prompted us
to compare the catalytic activity of the Pd PNNNP MOFs
activated with PhI(TFA)2 and AgOTf for intramolecular
hydroamination reactions. 2-(Butyn-1-yl)aniline (3) was
chosen as a benchmark substrate, and catalytic reactions were
carried out in 1,4-dioxane at 95 °C with 5 mol % catalyst based
on Pd (Table 1). Product yields were determined by
The precipitation of highly insoluble AgX byproducts makes
silver-based reagents convenient for halide abstraction reactions
involving soluble organometallic complexes. However, these
reagents are potentially problematic for use with MOFs because
the solid AgX cannot be easily separated. Considering the
ubiquity of silver-based precatalyst activation, we wanted to
investigate the effectiveness of silver salts for halide exchange in
2-PdX. A suspension of 2-PdX in MeCN was treated with
AgOTf (OTf− = O3SCF3 ) and heated at 60 °C for 12 h to
−
generate 2-PdX/AgOTf. PXRD analysis confirms that 2-PdX/
AgOTf retains crystallinity after the reaction. However, the
pattern also contains peaks corresponding to crystalline AgCl
and AgI (Figure 6), and these byproducts could not be
1
integration of the H NMR spectra.
a,b
Table 1. Hydroamination of o-Alkynyl Aniline 3
c
entry
catalyst
2-PdX
% yield 4
% yield 5
TON
1
2
3
4
5
6
7
8
9
77
40
69
35
93
48
<5
19
10
17
9
2-PdI
2-PdX/AgOTf
2-PdI/AgOTf
2-PdTFA
trace
5
23
12
<1
19
10
2-PdTFA (run 2)
2-PdPMe3
tBu4L-PdOTf
tBu4L-PdTFA
d
94
52
a
Reaction conditions: substrate (0.1 mmol), catalyst (0.005 mmol Pd),
b
1
1,4-dioxane, 95 °C, 12 h. Yields were determined by H NMR with
respect to an internal standard (hexamethylbenzene). Turnover
c
numbers (TON) were calculated per Pd using the empirical formula
d
for 2-PdX that accounts for missing linker defects. Reaction time was
1 h.
Under the catalytic conditions, 2-PdX and 2-PdI afforded 2-
ethylindole 4 in 77 and 40% yield, respectively (entries 1 and
2), after 12 h. 2-PdX exhibits remarkably good catalytic activity
despite the presence of I− and Cl− ligands. The lower catalytic
activity observed for 2-PdI is consistent with the presence of
only the less labile I− ligands. To our surprise, 2-PdX/AgOTf
furnished 4 in slightly lower yield (69%) than 2-PdX. For
comparison, a sample of 2-PdI/AgOTf was prepared by treating
2-PdI with AgOTf and found to deliver 4 in 35% yield under
the same catalytic conditions. The similar catalytic activities of
2-PdX/AgOTf and 2-PdI/AgOTf to the parent MOFs 2-PdX
and 2-PdI provide further support that AgOTf is not effective
for X−/OTf− exchange at the Pd−X sites within these materials.
Thus, formation of the AgX species observed by PXRD analysis
should be the result of exchange of only the outer sphere halide
counterions. Moreover, the slight decrease in catalytic activity
of the AgOTf-treated MOFs compared to 2-PdX and 2-PdI
may be attributed to pore occlusion by the insoluble AgX
Figure 6. PXRD patterns of 2-PdX, 2-PdI, 2-PdTFA, and 2-PdX/
AgOTf (Cu Kα, λ = 1.54 Å).
removed by washing with common organic solvents. The
31P{1H} NMR spectrum of an acid-digested sample of 2-PdX/
AgOTf (CF3CO2H:C6D6, 3:1 v:v) exhibits two major
resonances at 69.9 and 74.0 ppm (Figure 5). These resonances
closely resemble those expected for the Pd−Cl and Pd−I
species, albeit appearing in a different ratio (Pd−Cl:Pd−I ≈
5.7:1) than was observed for 2-PdX (∼1:3). The homogeneous
complex tBu4L-PdOTf was prepared by reaction of tBu4L-PdCl
with AgOTf in MeCN solution and observed to give rise to a
31P{1H} NMR signal at 75.5 ppm in the CF3CO2H:C6D6
solvent mixture (Figure S42). Thus, the 31P{1H} NMR
spectrum of the digested sample of 2-PdX/AgOTf does not
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species. 2-PdTFA proved to be the most active of the MOF
catalysts, generating indole 4 in 93% yield (entry 5). The large
difference in catalytic activity between 2-PdI/AgOTf and 2-
PdTFA clearly illustrates the superiority of PhITFA2 as an
activating reagent. However, 2-PdTFA exhibits only modestly
better activity than 2-PdX and significantly diminished activity
upon attempted recycling (entry 6). Trace amounts of
trifluoroacetamide 5 were also observed in the catalytic
reactions employing 2-PdTFA. The consumption of TFA
anions and a proton of unknown origin in this off-cycle reaction
pathway may lead to catalyst deactivation and account for the
modest activity and poor recyclability of 2-PdTFA. This notion
is further supported by a marked difference in catalytic activity
between the homogeneous complexes tBu4L-PdOTf and tBu4L-
PdTFA (vide infra).
CONCLUSIONS
■
Carboxylate-functionalized Pd and Pt PNNNP pincer complexes
were used for the assembly of porous Zr MOFs 2-PdX and 2-
PtX. PXRD analysis shows that both MOFs adopt a cubic
framework structure and are isostructural to the previously
reported 1-PdX. This result is perhaps not surprising given the
structural similarities between the PNNNP and POCOP pincer
ligand frameworks, but heralds the ability to synthesize
isoreticular or multivariate MOFs using PZEZP pincer
complexes. Despite similar solvothermal synthesis conditions,
spectroscopic characterization and elemental analysis indicate
that 2-PdX and 2-PtX contain a larger number of missing linker
defects than 1-PdX and are best formulated as
{Zr6O4(OH)4(OAc)2.4[PNNNP-MX]2.4}Y2.4 (X/Y = Cl, I).
Sequential treatment of 2-PdX with NaI and PhI(TFA)2
generates 2-PdI and 2-PdTFA, respectively. The MOFs cleanly
disassemble in trifluoroacetic acid, allowing for product
characterization by solution state NMR and ESI-MS analysis.
These analyses show complete Cl−/I− ligand exchange in 2-PdI
and ∼50% conversion of the Pd−I sites to Pd−TFA in 2-
PdTFA. The reaction of 2-PdX with AgOTf results in the
formation of crystalline AgI and AgCl, but spectroscopic data
suggest that X−/OTf− ligand exchange does not occur at the
Pd−X sites. 2-PdTFA displays better catalytic activity than 2-
PdI/AgOTf for the intramolecular hydroamination of 2-(butyn-
1-yl)aniline, confirming that oxidative ligand exchange is a more
effective means of activating the MOF-immobilized Pd species.
2-PdTFA also outperformed the homogeneous analogue tBu4L-
Given the evidence for a large number of defect sites in 2-
PdX, we sought to confirm that the Pd pincer sites are
responsible for the observed catalysis. We hypothesized that the
strongly donating L-type ligand PMe3 should selectively
coordinate and block access to the Pd sites, shutting down
the contribution of these sites to the observed catalysis.
Consequently, 2-PdPMe3 was synthesized by soaking 2-PdX in
a MeCN solution of PMe3. After washing, the 31P{1H} NMR
spectrum of an acid-digested sample features a doublet and
triplet resonance in a 2:1 ratio centered at 78.1 and δ −9.7 ppm
(1J31P−P = 25.7 Hz), respectively, that are assigned to H4[L-
Pd(PMe3)]2+ species (Figure S35). Signals attributed to H4[L-
PdI]+ (74.0 ppm) and [HPMe3]+ (−2.90 ppm) also appear in a
∼1:1 ratio. The presence of the latter species indicates either
incomplete conversion (∼75%) of the Pd−I sites to Pd−PMe3
or PMe3 ligand dissociation induced by the strongly acidic
digestion procedure. Regardless, 2-PdPMe3 delivered only trace
amounts of 4 under the catalytic conditions (entry 7),
substantiating that the Pd pincer sites are primarily responsible
for catalysis. Similarly, catalytic reactions carried out in the
presence of UiO−67 or absence of any catalyst showed no
appreciable formation of the desired indole product.
t
PdTFA but is a less active catalyst than Bu4L-PdOTf. These
results point to a detrimental effect of the trifluoroacetate
ligands/anions on the Lewis acid catalytic activity of the Pd
PNNNP complexes. Current studies are focused on developing
new strategies to carry out halide ligand exchange with less
basic and more weakly coordinating anions as well as expanding
the scope of MOFs assembled from PZEZP pincer complexes.
EXPERIMENTAL SECTION
■
The catalytic activities of the homogeneous complexes tBu4L-
General Considerations. ZrCl4 (Sigma-Aldrich), N,N-dimethyl-
formamide (DMF, 99.9%, EMD), and glacial acetic acid (Macron)
used for synthetic preparations were used as received unless otherwise
noted. ClP(C6H5-COOtBu)2,22 PdCl2(cod), PtCl2(cod),61 and butynyl
aniline 362 were prepared as described in the literature. All other
solvents and reagents were purchased from commercial suppliers and
used as received. Routine powder X-ray diffraction patterns for phase
identification were collected on a Rigaku Miniflex 600 diffractometer
using Nickel-filtered Cu Kα radiation (λ = 1.5418 Å). High-resolution
synchrotron PXRD data were collected at 295 K using beamline 11-
BM at the Advanced Photon Source (APS, Argonne National
Laboratory, Argonne, IL) using an average wavelength of 0.414536
Å. Nitrogen adsorption isotherms were measured at 77 K (liquid
nitrogen bath) using a Micromeritics 3Flex Surface Characterization
Analyzer. Prior to analysis, samples (100−200 mg) were heated under
reduced pressure until the outgas rate was less than 2 mTorr/min.
Inductively coupled plasma atomic emission spectroscopy (ICP-AES)
measurements were performed by Robertson Microlit Laboratories
(Ledgewood, NJ). Elemental microanalyses were performed by
Atlantic Microlab (Norcross, GA) or Robertson Microlit Laboratories
(Ledgewood, NJ). ESI-MS experiments were performed using a
Micromass ZQ4000 single quadrupole mass detector.
t
PdOTf and Bu4L-PdTFA were also investigated (Table 1,
t
entries 8 and 9). Bu4L-PdOTf was markedly superior to 2-
PdTFA, generating indole 4 in 94% yield after 1 h, while tBu4L-
PdTFA furnished 4 in only 52% yield after 12 h. Similar to 2-
PdTFA, a stoichiometric amount (∼5%) of trifluoroacetamide
5 was identified as a side product in the reaction employing
tBu4L-PdTFA. Thus, we surmise that consumption of TFA− via
the formation of 5 leads to catalyst deactivation and is
t
responsible for the poor activity of Bu4L-PdTFA and lack of
recyclability of 2-PdTFA. Further studies are necessary to
elucidate the mechanism of catalyst deactivation, but we
hypothesize that the process stems from the greater basicity of
TFA− versus OTf− and may involve deprotonation of the NH
linker groups of the PNNNP ligand. This hypothesis would
suggest that a more active and recyclable pincer MOF catalyst
could be obtained by oxidative halide ligand exchange with a
less basic anion such as OTf−. However, attempts to carry out
oxidative I−/OTf− exchange using in situ-generated PhI(OTf)2
have been unsuccessful thus far, resulting in materials that suffer
significant losses in crystallinity and exhibit poor catalytic
activity. We believe this to be a limitation of the ill-defined
nature of PhI(OTf)2, which is usually generated in situ from
PhI(O2CCH3)2 and Me3SiOTf.60
Solution-state NMR spectra were measured using either a Varian
Inova or MR 400 MHz spectrometer (101 MHz operating frequency
for 13C, 162 MHz operating frequency for 31P, and 376 MHz operating
frequency for 19F). For H and 13C{1H} NMR spectra, the solvent
1
resonance was referenced as an internal standard. For 31P{1H} NMR
spectra, 85% H3PO4 was used as an external standard (0 ppm). For 19
F
F
DOI: 10.1021/acs.inorgchem.7b03063
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
NMR spectra, 1% CF3COOH was used as an external standard
afford the desired product as an orange solid (1.248 g, 96%). 1H NMR
(400 MHz, CDCl3): δ 9.60 (s, 2H, NH), 8.09−7.99 (m, 16H,
1
(−76.55 ppm). Solvent-suppressed H NMR spectra were collected
using the WET1D sequence with default parameters.63 Solid-state
NMR experiments were performed on a Bruker (Billerica, MA) DSX-
benzoate Ar−H), 7.40 (t, JH−H = 7.5 Hz, 1H, pyridine Ar−H), 7.30
3
3
t
(d, JH−H = 8.2 Hz, 2H, pyridine Ar−H), 1.53 (s, 36H, Bu). 13C{1H}
NMR (101 MHz, CDCl3): δ 164.4 (s, 4C, CO2), 159.7 (t, JC−P = 7.2
Hz, 2C, Ar), 142.6 (s, C, Ar), 136.0 (s, 4C, Ar), 133.44 (t, JC−P = 8.0
Hz, 8C, Ar), 133.40 (t, JC−P = 29.4 Hz, 4C, Ar), 130.0 (t, JC−P = 6.1
Hz, 8C, Ar), 102.3 (br, 2C, Ar), 82.1 (s, 4C, C(CH3)3), 28.2 (s,12C,
C(CH3)3). 31P{1H} NMR (162.0 MHz, CDCl3): δ 75.6 (s). Anal.
Calcd for C49H57I2N3O8P2Pd: C, 47.53; H, 4.64; N, 3.39; Found: C,
47.57; H, 4.79; N, 3.45;
1
400 spectrometer at a resonance frequency of 400 MHz for H and
162 MHz for 31P and 100 MHz for 13C using a MAS probe in double-
resonance mode. See Supporting Information for additional details.
Synthesis of tBu4L. Under an inert atmosphere, a 100 mL Schlenk
flask was charged with 2,6-diaminopyridine (0.156 g, 1.43 mmol),
triethylamine (0.360 g, 3.56 mmol), and toluene (25 mL). The
reaction mixture was cooled to 0 °C, and a solution of ClP-
(C6H4COOtBu)2 (1.344 g, 3.19 mmol) in toluene (20 mL) was added
dropwise. The flask was then sealed and heated at 80 °C for 16 h. After
cooling, the pale yellow solution was filtered, and the solvent was
removed under reduced pressure. The resulting sticky yellow powder
was recrystallized with toluene:pentane (1:4) to give the desired
product as a white microcrystalline powder (1.04 g, 1.18 mmol, 83%).
31P{1H} NMR (162.0 MHz, CDCl3): δ 25.4 (s). 1H NMR (400 MHz,
CDCl3): δ 7.95 (d, J = 7.7 Hz, 8H), 7.46 (t, J = 7.6 Hz, 8H), 7.34 (t, J
= 8.0 Hz, 1H), 6.44 (d, J = 7.8 Hz, 2H), 4.99 (d, J = 7.6 Hz, 2H), 1.58
(s, 36H). 13C{1H} NMR (101 MHz, CDCl3): δ 165.4 (s, 4C, CO2),
157.2 (d, J = 20.5 Hz, 2C, Py2,6), 144.4 (d, J = 14.4 Hz, 4C, Ph), 140.0
(s, C, Py4), 133.0 (s, 4C, Ph4), 131.1 (d, 8C, J = 21.0 Hz, Ph2,6), 129.5
(d, 8C, J = 6.6 Hz, Ph3,5), 99.9 (d, 2C, J = 14.4 Hz, 2C, Py3,5), 81.4 (s,
4C, C(CH3)3), 28.3 (s, 12C, C(CH3)3). 31P{1H} NMR (162.0 MHz,
CDCl3): δ 25.4 (s). Anal. Calcd for C49H57N3O8P2: C, 67.04; H, 6.54;
N, 4.79; Found: C, 67.30; H, 6.55; N, 4.83.
Synthesis of tBu4L-PtI. The compound was prepared from tBu4L-
PtCl (0.863 g, 0.754 mmol) following the same procedure used for
tBu4L-PdI. The reaction yielded 0.951 g (95%) of Bu4L-PtI as a
t
1
reddish-orange solid. H NMR (400 MHz, CDCl3): δ 10.09 (s, 2H),
3
8.09−7.99 (m, 16H, benzoate Ar−H), 7.42 (t, JH−H = 7.7 Hz, 1H,
pyridine Ar−H), 7.31 (d, 3JH−H = 8.0 Hz, 2H, pyridine Ar−H), 1.53 (s,
36H, Bu). 13C{1H} NMR (101 MHz, CDCl3): δ 164.4 (s, 4C, CO2),
t
159.6 (t, JC−P = 6.6 Hz, 2C, Ar), 141.7 (s, C, Ar), 136.0 (s, 4C, Ar),
133.6 (t, JC−P = 7.8 Hz, 8C, Ar), 133.1 (t, JC−P = 33.9 Hz, 4C, Ar),
129.9 (t, JC−P = 6.3 Hz, 8C, Ar), 101.8 (br, 2C, Ar), 82.1 (s, 4C,
C(CH3)3), 28.2 (s, 12C, C(CH3)3). 31P{1H} NMR (162.0 MHz,
1
CDCl3): δ 68.1 (d, JPt−P = 2682.8 Hz). Anal. Calcd for
C49H57I2N3O8P2Pt: C, 44.36; H, 4.33; N, 3.17; Found: C, 44.31; H,
4.52; N, 3.14.
Synthesis of H3L-PdI. Trifluoroacetic acid (1 mL) was added to a
t
solution of Bu4L-PdI (0.542 g, 0.438 mmol) in CH2Cl2 (5 mL),
t
Synthesis of Bu4L-PdCl. A solution of PdCl2(cod) (0.164 g,
resulting in a color change of the solution from ruby to dark purple.
The solution was stirred for 16 h at room temperature before
removing the solvent using a rotary evaporator. Deionized water (12
mL) was added, resulting in precipitation of a bright orange solid. The
solid was collected by vacuum filtration and washed with deionized
water (3 × 5 mL) and CHCl3 (∼20 mL). The solid was dried under
reduced pressure to afford 0.393 g of the crude product (H4[L-PdI]I).
The solid was suspended in acetone (5 mL), and a solution of pyridine
(0.032 g, 0.405 mmol) in acetone (2 mL) was added, resulting in a
color change of the supernatant from ruby to bright orange. The
solution was stirred for 30 min at room temperature. The mixture was
centrifuged, and the supernatant was decanted. The solid was washed
successively with acetone (3 × 5 mL) and then water (∼20 mL) until
no color persisted in the filtrate. The resulting bright orange solid was
dried under vacuum to afford H3[L-PdI] (0.284 g, 0.321 mmol, 86%
0.575 mmol) in CH2Cl2 (3 mL) was added to a stirring solution of
tBu4L (0.505 g, 0.575 mmol) in CH2Cl2 (8 mL). The reaction was
stirred at room temperature for 4 h under an inert atmosphere before
the volatiles were removed under reduced pressure. The resulting
orange residue was triturated with a small amount of pentane (3 mL),
resulting in formation of a bright yellow solid. The solid was collected
by filtration, washed with pentane (3 × 3 mL), and dried under
t
1
reduced pressure to yield Bu4L-PdCl (0.574 g, 95% yield). H NMR
(400 MHz, CDCl3): δ 11.17 (s, 2H, NH), δ 8.10 (dd, 3JH−P = 14.2 Hz,
3JH−H = 6.4 Hz, 8H, benzoate Ar−H), 7.92 (d, JH−H = 8.1 Hz, 8H,
3
3
benzoate Ar−H), 7.18 (t, JH−H = 6.4 Hz, 1H, pyridine Ar−H), 7.11
(d, JH−H = 7.8 Hz, 2H, pyridine Ar−H), 1.50 (s, 36H, Bu). 13C{1H}
NMR (101 MHz, CDCl3): δ 164.3 (s, 4C, CO2), 160.9 (t, JC−P = 7.7
Hz, 2C, Ar), 142.6 (s, C, Ar), 135.5 (s, 4C, Ar), 134.0 (t, JC−P = 28.6
Hz, 4C, Ar), 132.2 (t, JC−P = 8.1 Hz, 8C, Ar), 130.0 (t, JC−P = 6.1 Hz,
8C, Ar), 102.2 (br, 2C, Ar), 81.9 (s, 4C, C(CH3)3), 28.2 (s, 12C,
C(CH3)3). 31P{1H} NMR (162.0 MHz, CDCl3): δ 67.8 (s). Anal.
Calcd for C49H57Cl2N3O8P2Pd: C, 55.77; H, 5.44; N, 3.98; Found: C,
55.96; H, 5.61; N, 3.79.
3
t
1
yield). H NMR (400 MHz, DMSO): δ 12.71 (br, 2H, NH), 8.07 (d,
3
3JH−H = 7.8 Hz, 8H, benzoate Ar−H), δ 7.94 (dd, JH−P = 12.9 Hz,
3
3JH−H = 6.1 Hz, 8H, benzoate Ar−H), 7.41 (t, JH−H = 7.7 Hz, 1H,
3
pyridine Ar−H), 6.28 (d, JH−H = 7.2 Hz, 2H, pyridine Ar−H).
13C{1H} NMR (101 MHz, DMSO): δ 166.7 (s, 4C, CO2), 162.9 (br,
2C, Ar), 141.8 (br, C, Ar), 136.4 (br, 4C, Ar), 134.3 (br, 8C, Ar),
132.5 (dd, JC−P = 13.0 Hz, JC−P = 6.4 Hz, 4C, Ar), 129.5 (t, JC−P = 5.4
Hz, 8C, Ar), 98.8 (br, 2C, Ar). 31P{1H} NMR (162.0 MHz, DMSO): δ
69.9 (s). Anal. Calcd for H3L-PdI·(H2O); C33H26IN3O9P2Pd: C,
43.85; H, 2.90; N, 4.65; Found: C, 44.18; H, 3.07; N, 4.55.
Synthesis of tBu4L-PtCl. The compound was prepared from
PtCl2(cod) (0.277 g, 0.740 mmol) and Bu4L (0.656 g, 0.747 mmol)
following the same procedure used for Bu4L-PdCl. The reaction
yielded 0.806 g (0.705 mmol, 95%) of Bu4L-PtCl as a bright yellow
t
t
t
1
solid. H NMR (400 MHz, CDCl3): δ 11.57 (s, 2H, NH), 8.10 (dd,
3JH−P = 13.8 Hz, 3JH−H = 6.8 Hz, 8H, benzoate Ar−H), 7.95 (d, 3JH−H
= 7.9 Hz, 8H, benzoate Ar−H), 7.08 (m, br, 3H, pyridine Ar−H), 1.51
t
Synthesis of H3L-PtI. The compound was prepared from Bu4L-
PtI (0.748 g) following the same procedure used for H3L-PdI. The
(s, 36H, Bu). 13C{1H} NMR (101 MHz, CDCl3): δ 164.4 (s, 4C,
reaction yielded 0.454 g (90%) of H3L-PtI as an orange solid. H
t
1
3
CO2), 160.7 (t, JC−P = 6.9 Hz, 2C, Ar), 141.5 (s, C, Ar), 135.6 (s, 4C,
Ar), 134.2 (t, JC−P = 33.1 Hz, 4C, Ar), 132.4 (t, JC−P = 8.0 Hz, 8C, Ar),
130.0 (t, JC−P = 6.3 Hz, 8C, Ar), 101.6 (br, 2C, Ar), 82.0 (s, 4C,
C(CH3)3), 28.2 (s, 12C, C(CH3)3). 31P{1H} NMR (162.0 MHz,
NMR (400 MHz, DMSO): δ 12.23 (br, 2H, NH), δ 8.09 (d, JH−H
=
3
3
7.8 Hz, 8H, benzoate Ar−H), 7.93 (dd, JH−P = 13.4, JH−H = 6.1 Hz,
3
8H, benzoate Ar−H), 7.47 (t, JH−H = 7.8 Hz, 1H, pyridine Ar−H),
6.34 (d, JH−H = 7.5 Hz, 2H, pyridine Ar−H). 13C{1H} NMR (101
3
1
CDCl3): δ 61.9 (d, JPt−P = 2770 Hz). Anal. Calcd for
MHz, DMSO): δ 166.6 (s, 4C, CO2), 140.8 (s, C, Ar), 134.2 (s, 4C,
3
C49H57Cl2N3O8P2Pt: C, 51.45; H, 5.02; N, 3.67; Found: C, 51.39;
Ar), 137.0 (t, JC−P = 36.8 Hz, 4C, Ar), 132.5 (t, JC−P = 7.1 Hz, 8C,
H, 5.06; N, 3.54.
Ar), 129.5 (t, JC−P = 5.7 Hz, 8C, Ar), 97.9 (s, 2C, Ar). 31P{1H} NMR
(162.0 MHz, DMSO): δ 63.2 (d, 1JPt−P = 2561.4 Hz). Anal. Calcd for
H3(PNNNP)PtI; C33H24IN3O8P2Pt: C, 40.67; H, 2.48; N, 4.31;
Found: C, 40.57; H, 2.67; N, 4.26.
t
t
Synthesis of Bu4L-PdI. A solution of Bu4L-PdCl (1.105 g, 1.05
mmol) in acetone (8 mL) was treated with a solution of NaI (0.317 g,
2.12 mmol) in acetone (1 mL). Immediate formation of NaCl was
observed, and the reaction was allowed to stir at room temperature for
1 h. The solvent was removed under reduced pressure, and the dark
red residue was extracted with CH2Cl2 (5 mL) and filtered through a
0.45 μm PTFE syringe filter. The filtrate was concentrated in vacuo to
Synthesis of 2-PdX and 2-PtX. Anhydrous ZrCl4 (0.030 g, 0.129
mmol) was suspended in acetic acid (1.6 mL) and DMF (4.4 mL) in a
20 mL screw-top scintillation vial. A solution of H3L-PdI or H3L-PtI
(0.043 mmol) in DMF (2 mL) was added, and the vial was sealed with
G
DOI: 10.1021/acs.inorgchem.7b03063
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Teflon-lined screw-top cap (Qorpak CAP-00554). The reaction
mixture was sonicated for 5 min to ensure complete dissolution of
the solids. The vial was then placed in a programmable oven at room
temperature and heated to 120 °C for 16 h. After reaching room
temperature, the solvent was decanted from the precipitated solid. The
solid was washed with DMF (3 × 15 mL) and acetone (3 × 10 mL)
and dried in vacuo (0.01 Torr) at room temperature for 2 h to afford
0.035 g of product. 2-PdX: 31P{1H} NMR (162.0 MHz, 3/1 v/v
CF3COOH/C6D6): δ 74.0 (s); 69.9 (s). Anal. Calcd for
{Zr6O4(OH)4[PdClC33H21N3O8P2]2.4(CH3COO)2.4}I2.4; C, 34.68; H,
2.16; N, 3.37; I, 10.18; Cl, 2.84, Zr, 17.68; Pd, 8.54; Found: C, 32.70;
H, 2.47; N, 3.11; I, 6.54; Cl, 1.95; Zr, 16.60; Pd, 6.68. 2-PtX: 31P{1H}
NMR (162.0 MHz, 3/1 v/v CF3COOH/C6D6): δ 67.7 (1JPt−P = 2719
Spectroscopic (NMR, IR) and ESI-MS data and
crystallographic data collection and refinement details
for H3L-PdI (PDF)
Accession Codes
CCDC 1587001 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, by emailing 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.
Hz,); 64.0 (1 JP t − P
= 2790 Hz,). Anal. Calcd for
AUTHOR INFORMATION
Corresponding Author
*E-mail: wade.521@osu.edu.
■
Zr6O4(OH)4[PtClC33H21N3O8P2]2.4(CH3COO)2.4}I2.4; C, 32.14; H,
2.00; N, 3.12; I, 9.43; Cl, 2.64; Zr, 16.95; Pt, 14.50; Found: C, 32.05;
H, 2.27; N, 3.49; I, 5.19; Cl, 1.62; Zr, 15.32; Pt, 12.11.
Synthesis of 2-PdI. A solution of NaI (0.098 g, 0.655 mmol) in
deionized water (5 mL) was added to a suspension of 2-PdX (0.160 g)
in deionized water (5 mL) in a 20 mL scintillation vial. The vial was
sealed and placed in an oven at 60 °C for 2 h. After cooling, the
mixture was centrifuged, and the supernatant was decanted. A fresh
solution of NaI (0.098 g, 0.655 mmol) in deionized water (5 mL) was
added, and the reaction was again heated at 60 °C for 2 h. The solid
was collected by centrifugation and washed successively with water (3
× 10 mL) and acetone (3 × 10 mL) and dried briefly in vacuo to
afford 2-PdI as a yellow microcrystalline powder (0.150 g). 31P{1H}
NMR (162.0 MHz, 3/1 v/v CF3COOH/C6D6): δ 74.0 (s).
ORCID
Klaus Schmidt-Rohr: 0000-0002-3188-4828
Bruce M. Foxman: 0000-0001-5707-8341
Casey R. Wade: 0000-0002-7044-9749
Present Address
‡C.R.W.: Department of Chemistry and Biochemistry, The
Ohio State University, Columbus, Ohio 43210, United States.
Notes
The authors declare no competing financial interest.
Synthesis of 2-PdTFA. In a N2-filled glovebox, solution of
PhITFA2 (0.026 g, 0.06 mmol) in CH2Cl2 (1 mL) was added to a
suspension of 2-PdI (0.050 g) in CH2Cl2 (5 mL) in a 20 mL
scintillation vial. The vial was sealed and left gently stirring at room
temperature. After 12 h, the reaction mixture was centrifuged, and the
pink purple supernatant was decanted. The solid was washed with
CH2Cl2 (3 × 5 mL) and dried briefly in vacuo. 2-PdTFA was isolated
as a pale yellow, microcrystalline powder (0.050 mg). 31P{1H} NMR
(162.0 MHz, 3/1 v/v CF3COOH/C6D6): δ 74.0 (s); 71.1 (s).
Reaction of 2-PdX and 2-PdI with AgOTf. In a N2-filled
glovebox, a solution of AgOTf (0.023 g, 0.090 mmol) in MeCN (1
mL) was added to a suspension of 2-PdX or 2-PdI (0.050 g) in MeCN
(5 mL) in a 20 mL scintillation vial. The vial was sealed and left gently
stirring at 60 °C. After 12 h, the reaction mixture was centrifuged, and
the supernatant was decanted. The solid was washed with MeCN (3 ×
5 mL) and dried briefly in vacuo. 2-PdX/AgOTf and 2-PdI/AgOTf
were isolated as yellow microcrystalline powders (0.050 g).
ACKNOWLEDGMENTS
■
Acknowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund (Grant 55281-
DNI-3) for support of this research. Use of the Advanced
Photon Source at Argonne National Laboratory was supported
by the U.S. Department of Energy (DOE) Office of Science
under Contract DE-AC02-06CH11357.
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2009, 131, 14168−14169.
+
1
Pd(PMe3)]2+) 74.0 (s, H4[L-PdI]+); 2.9 (s, HPMe3 ); −9.7 (t, JP−P
= 25.7 Hz, H4[L-Pd(PMe3)]2+).
General Procedure for Intramolecular Hydroamination
Reactions. In a N2-filled glovebox, a vial was charged with 3 (0.1
mmol), 5 mol % catalyst, 1,4-dioxane (0.4 mL), C6D6 (0.1 mL), and a
known amount of hexamethylbenzene (0.02−0.04 mmol) as an
internal standard. The reaction mixture was transferred to an NMR
tube and heated at 95 °C for 12 h. The product yields were
1
determined by H NMR spectroscopy.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b03063.
H
DOI: 10.1021/acs.inorgchem.7b03063
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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