Rhodium Complexes of 2,6-Bis(dialkylphosphinomethyl)pyridines: Improved C-H Activation, Expanded Reaction Scope, and Catalytic Direct Arylation

Article abstract of DOI:10.1021/acs.organomet.7b00532

The reactivity of (PNP)Rh(Ph) (PNP = 2,6-bis(dialkylphosphinomethyl)pyridine) toward a variety of electrophiles (Ar-I, ArCH₂Cl, O₂, I₂, B₂pin₂, and ArSO₃H) was explored, and several new modes of oxidative reactivity were observed. Substituting ^tBu₂P for ⁱPr₂P provided 100-fold rate enhancement toward C-H bond activation and addressed the previously reported challenge of N₂ inhibition. Studying the stoichiometric reactivity of (PNP)Rh complexes toward C-H cleavage and oxidative functionalization led to (PNP)Rh-catalyzed cross-coupling of aryl iodides with sp² and sp³ C-H bonds.

Full text of DOI:10.1021/acs.organomet.7b00532

Article
Cite This: Organometallics XXXX, XXX, XXX-XXX
pubs.acs.org/Organometallics
Rhodium Complexes of 2,6-Bis(dialkylphosphinomethyl)pyridines:
Improved C−H Activation, Expanded Reaction Scope, and Catalytic
Direct Arylation
Joseph J. Gair, Yehao Qiu, Natalie H. Chan, Alexander S. Filatov, and Jared C. Lewis*
Department of Chemistry, University of Chicago, Chicago Illinois 60637, United States
*
S Supporting Information
ABSTRACT: The reactivity of (PNP)Rh(Ph) (PNP = 2,6-
bis(dialkylphosphinomethyl)pyridine) toward a variety of
electrophiles (Ar−I, ArCH Cl, O , I , B pin , and ArSO H)
2
2
2
2
2
3
was explored, and several new modes of oxidative reactivity were
t
i
observed. Substituting Bu P for Pr P provided 100-fold rate
2
2
enhancement toward C−H bond activation and addressed the
previously reported challenge of N inhibition. Studying the
2
stoichiometric reactivity of (PNP)Rh complexes toward C−H
cleavage and oxidative functionalization led to (PNP)Rh-
2
3
catalyzed cross-coupling of aryl iodides with sp and sp C−H
bonds.
INTRODUCTION
given substrate without assistance from substrate directing
effects has been harnessed to control site selectivity via
molecular recognition elements in the secondary coordination
■
The ability to selectively functionalize C−H bonds is changing
the way chemists construct organic molecules by enabling the
use of new strategic disconnections and synthetic inputs.
12−16
1
−6
sphere.
Achieving this level of catalyst control for other
In
transformations first requires the development of catalysts that
are capable of functionalizing C−H bonds without assistance
from functional group directing effects. These catalysts could
then be integrated into scaffolds containing secondary sphere
particular, direct reaction of C−H bonds in organic substrates
can sidestep the need to install functional groups required for
conventional reactions. Most methods for selective C−H
functionalization, however, rely on directing effects of func-
tional groups, which act by facilitating activation of a particular
C−H bond on a given class of substrates (e.g., ortho to a Lewis
basic aromatic substituent). While this approach leads to
convenient predictability, it inherently limits the possibility of
functionalizing other sites in a molecule (e.g., meta to a Lewis
basic substituent on an aromatic substrate) without changing
the directing group. Directed strategies can also reduce
synthetic efficiency if the directing group is not desired in the
12−23
elements to control their selectivity.
Of course, fundamental studies on a number of stoichio-
metric, nondirected C−H activation reactions predate most
catalytic systems, and this much needed pursuit continues to
24−29
t
this day.
In one recent example, Bu(PNP)RhCl was
reported to cleave aromatic C−H bonds at room temperature
t
to generate the corresponding Bu(PNP)Rh(Ph) complex
30
(
1). We envisioned that this reaction could be exploited for
7
catalytic C−H functionalization if 1 could react with an oxidant
to give a functionalized arene and a rhodium complex capable
of subsequent C−H activation (Scheme 1). Moreover, since
final product and can be complicated by unwanted directing
8
effects of desired functional groups.
Methods that do not depend on functional group directing
effects to promote cleavage of a particular C−H bond (often
9
Scheme 1. Proposed Substrate Functionalization and
Catalyst Regeneration
termed “nondirected” in the literature), on the other hand, are
far less developed than the corresponding directed approaches.
Beyond the obvious practical reason that in the absence of
simplifying symmetry in a substrate nondirected reactions
10
afford product mixtures, metal complexes with sufficient
reactivity to activate a C−H bond under conditions that enable
catalytic turnover of the resulting organometallic intermediates
are remarkably rare. One notable exception in this regard is
iridium-catalyzed C−H borylation, which reliably functionalizes
aromatic C−H bonds distal to substituents with only minor
11
contributions from substituent directing effects. The ability of
such catalysts to functionalize multiple C−H bonds within a
Received: July 14, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00532
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
assistance from substrate directing effects was not required for
mild C−H cleavage, we hypothesized that a catalytic system
might afford the desired nondirected reactivity required for
designing catalysts that control site selectivity through
molecular recognition in the secondary coordination sphere.
has been studied on (PNP)Rh(Ar) complexes relevant to
37,38
32,35,36
aromatic C−H functionalization.
As such, progress
has been limited in developing catalytic methods for non-
directed C−H functionalization of simple arenes, i.e. by
coupling the nondirected C−H activation illustrated in Scheme
1
with the addition/elimination chemistry discussed above.
RESULTS AND DISCUSSION
Despite the impressive reactivity of Bu(PNP)RhCl toward C−
H bonds, we hypothesized that steric crowding about the metal
One notable exception in this regard is the recent stepwise
■
t
t
reaction of (PNP)Rh complexes with BuOK, H
, CO
, and p-
2
2
toluenesulfonic acid to give net carbonylation of benzene
t
31
36
center and the benzylic methylene in Bu(PNP) complexes
(catalytic reactions yielded 1.3 turnovers after 5 days). This
t
could be limiting reaction rates. Substituting the Bu
stepwise reactivity demonstrates the necessary steps for catalyst
turnover; however, it also illustrates a key challenge in
developing (PNP)Rh-catalyzed C−H functionalization: incom-
patibility between bases required for ligand deprotonation and
electrophiles required to cleave Rh−C bonds.
In light of the limitations imposed by the strong bases
required for ligand deprotonation, we sought to develop
complexes capable of C−H activation under milder conditions.
We envisioned that weakly coordinating anions could decrease
i
substituents on this ligand for Pr substituents could accelerate
both ligand deprotonation and C−H activation by reducing
steric clashes with bulky bases and arene substrates,
respectively. Consistent with this hypothesis, the calculated
barrier to C−H oxidative addition was lower for 5 than for 1
⧧
(
ΔΔG = 3.9 kcal/mol) (see section S1.2 in the Supporting
Information). In addition, decreased steric bulk could reduce
nitrogen inhibition by decreasing the ability of the environ-
3
0
ment about the metal center to differentiate between small
the pK of the benzylic methylene by generating a formally
a
(
N )- and medium-sized (C H ) ligands.
Indeed, when 5 mM solutions of 2 and 3 were treated with
.2 equivalents of potassium tert-butoxide ( BuOK) in side by
cationic Rh center to withdraw electron density from the
2
6
6
dearomatized ligand. Gratifyingly, the methanesulfonate (OMs)
t
i
1
complex Pr(PNP)Rh(OMs) (6) reacted with benzene in the
side reactions, complex 3 gave product formation at an initial
rate 100 times greater than that for 2 (101 and 0.95 μM/min,
respectively, Figure 1). The initial rate of starting material
presence of potassium 2,6-bis(tert-butyl)-4-methoxyphenolate
to give the corresponding phenyl complex in excellent yield
i
(97%), whereas Pr(PNP)Rh(Cl) was inert under these
conditions (Scheme 2).
Scheme 2. C−H Activation with Milder Base
39,40
Although weakly coordinating anions were previously
used on (PNP)Ir complexes to provide a coordination site for
Ph-H oxidative addition, we did not observe C−H activation
i
with Pr(PNP)Rh(OMs) in the absence of base. In contrast to
the methanesulfonate complex (6), 4-toluenesulfonate (OTs)
i
complex Pr(PNP)Rh(OTs) (7) reacted with the ortho C−H
bond of the weakly coordinating anion to give Rh(III) hydrido
i
t
Figure 1. Overlaid C−H activation reaction profiles for Pr and Bu
complexes 2 and 3.
arylsuflonate 8notably, the first direct observation of C−H
III
41
oxidative addition to afford a stable (PNP)Rh aryl hydride.
In contrast to the observed C−H activation via 7, complex 9
(generated in the presence of excess 4-toluenesulfonic acid) did
not undergo ortho metalation upon prolonged heating (Figure
2). The differential reactivity of 7 and 9 toward C−H activation
underscores a salient point. When (PNP)Rh(Ph) is function-
alized in the presence of excess arene and oxidant (Scheme 1),
the resulting (PNP)Rh(X) can access productive and
unproductive pathways: namely, C−H activation or further
reaction with electrophile to generate complexes incapable of
C−H activation. As such, a key challenge in developing (PNP)
Rh catalyzed C−H functionalization is finding electrophiles that
react readily with (PNP)Rh(Ph) to give (PNP)Rh(X) and react
negligibly with (PNP)Rh(X) relative to the rate of C−H
activation.
consumption (a lower bound for rate of ligand deprotonation)
was only 7-fold faster for complex 3 (113 vs 16 μM/min), and
no buildup of dearomatized intermediate (4) was observed
during the reaction of 3. These results suggest that substituting
t
i
Bu for Pr accelerates the overall reaction by a modest increase
in the rate of ligand deprotonation and a larger acceleration in
C−H cleavage. Surprisingly, the rate and maximum yield of
stoichiometric C−H activation revealed a strong dependence
on alkali-metal counterion (K > Na ≫ Li: see section S1.3 in
the Supporting Information).
Having improved the rate and yield of C−H activation, we
next investigated different methods to functionalize the
resulting metal−carbon bond in 5. Several reactions, including
oxidative addition (of Me-I and I ) and reductive elimination of
With this balance in mind, we sought to explore the reactivity
of (PNP)Rh(Ph) toward a variety of electrophiles both to
understand the basic reactivity of adducts of C−H activation
and to find reagents amenable to (PNP)Rh-catalyzed, non-
2
3
2−34
CH -X (X = Cl, Br, I, CN),
that could enable turnover of
have been observed at related (PNP)Rh phenyl and methyl
complexes. Notably, however, only a fraction of this reactivity
3
5
B
DOI: 10.1021/acs.organomet.7b00532
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Article
dimethyldibenzyl (Figure 3) rather than the desired reductive
elimination. In contrast, reaction of 5 with dimethylcarbonate
afforded alkylated arene (toluene) in good yield (76%), and
reaction with B pin at 140 °C afforded phenylboronic acid
2
2
pinacol ester in excellent yield (97%) (Figure 3A and section
S1.13 in the Supporting Information).
Previous studies on oxidative addition of aryl halides to
pincer complexes and on the stability of aryl halides to base led
43−46
us to pursue reactions of 5 with aryl iodides (Figure 3).
To
our delight, 5 reacted with aryl iodides at elevated temperature
(
(
120 °C) to yield the desired biaryl product and (PNP)Rh(I)
12) (Figure 3). Among the electrophiles assessed in Figure 3,
aryl iodides stood out as the least likely to undergo further,
unproductive addition to the organometallic product (PNP)-
Rh(X). To confirm this, we heated 12the product of the
reaction of 5 with aryl iodideswith excess iodobenzene
(Figure 3). After 40 h at 140 °C, only 4% of unproductive
oxidative addition product 13 was formed, as confirmed by
Figure 2. Reactivity of 5 with 4-toluenesulfonic acid and ORTEP
drawing of 8 with 50% thermal ellipsoids and all hydrogens except
Rh−H omitted for clarity.
directed C−H functionalization. A recent report of oxidative
addition of O to (PNP)Ir(Ph) suggested that 1 might react
2
42
with O to afford dearomatized Rh(III) hydroxo complex 10.
independent synthesis of 13 via reaction of 5 with I (Figure 3
and section S1.6 in the Supporting Information). Moreover,
2
2
Moreover, reductive elimination of phenol from 10 would
afford dearomatized complex 4 and thereby circumvent the
need for harsh exogenous bases. Complex 1 did indeed react
iodo complex 12 reacted with C D to give the desired adduct
6
6
5 (Figure 4). In contrast to the C−H activation reactions in
with O to give a dearomatized species consistent with complex
2
1
0 as the major product (Figure 3A). Precipitation of the crude
Figure 4. (A) ORTEP drawing of complex 12 with 50% thermal
ellipsoids (one of two conformers in the unit cell shown for clarity).
(B) ORTEP drawing of complex 5 with 50% thermal ellipsoids. (C)
C−H activation with complex 12 and functionalization of C−H
activation adduct 5 with 4-fluoroiodobenzene.
Figure 1, which were conducted in sealed tubes with evacuated
head space to reduce N inhibition, C−H activation with
2
complex 12 was conducted under an N atmosphere, indicating
2
that isopropyl ligand substitution effectively resolved the
Figure 3. (A) Reactivity of C−H activation products 1 and 5 with
various electrophiles. (B) ORTEP drawings of 10, 11, and 13 with
problem of N inhibition. C−H activation with complex 12,
2
5
0% thermal ellipsoids and hydrogens removed for clarity, except OH.
coupled with the reaction of 5 with aryl iodides as shown in
Figure 4, demonstrates the feasibility of steps in the desired
cycle outlined in Scheme 1.
reaction mixture with pentane afforded single crystals of
complex 10 suitable for X-ray diffraction (Figure 3B), but
attempts to purify and isolate complex 10 in bulk were not
successful. Moreover, reductive elimination of phenol from the
crude mixture was not observed with prolonged heating. In an
attempt to lower the barrier to reductive elimination, we next
With an improved complex for rhodium-mediated C−H
activation (3) in hand and a deeper understanding of the
reactivity of C−H activation adducts 1 and 5 in mind, we
sought to establish whether these complexes were capable of
catalytic C−H functionalization of simple arenes. Gratifyingly,
complex 3 catalyzed direct C−H arylation of benzene with a
variety of aryl iodides (Figure 5A). Control reactions revealed
that in the absence of rhodium catalyst there is a minor
background reaction (reported parenthetically for each
reaction).
explored the reactivity of 5 with C −X electrophiles. When 5
sp3
was treated with p-tolylbenzyl chloride, an intermediate
consistent with the desired oxidative addition product was
1
observed by H NMR (see section S1.5 in the Supporting
Information) but disproportionated to complex 11 and 4,4′-
C
DOI: 10.1021/acs.organomet.7b00532
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Organometallics
Article
Figure 6. (A) Control reactions with alternative precatalysts and
TEMPO additive. (B) Extracted ion GCMS chromatograms of toluene
3
reaction mixtures showing no sp functionalization in the absence of
rhodium.
(
PF )consistent with metal-centered reactivity see section
6
S1.8 in the Supporting Information).
2
The sp selectivity in rhodium-catalyzed direct arylation is
most consistent with previously reported radical-based
47
arylations (Figure 5B). Notably, reactions in the presence
or absence of rhodium catalyst had similar sp selectivity. This
Figure 5. (A) Direct arylation of benzene with various aryl iodides,
with yields given in boldface and yields of background reactions given
in parentheses. (B) Direct arylation of various arenes with 4-
iodoanisole, with yields given in boldface and yields of background
reactions given in parentheses.
2
finding could indicate that the rhodium complexes studied
herein catalyze C−H functionalization by initiating or
accelerating the background reaction, which has been proposed
4
7,49
to proceed through radical intermediates (Figure 6B).
On
3
the other hand, the sp C−H functionalization observed for
toluene, anisole, p-xylene, and mesitylene was not observed in
the BuOK-mediated background reaction, indicating that the
Complex 3 also catalyzes arylation of several simple arenes
with moderate electronic and steric variation (Figure 5B).
Importantly, this system enables functionalization of all C−H
bonds (ortho, meta, para, benzylic, and methoxy) in each
substrate tested with only minor contributions from substituent
directing effects. As noted above, the design of catalysts which
can override functional group directing effects and electronic
bias to give catalyst-controlled selectivity first requires the
development of catalystslike those described abovethat do
not require particular functional groups to promote C−H
functionalization.
t
rhodium catalyst enables access to pathways that are not
accessible to the active species in the background reaction
(Figure 6B).
CONCLUSION
■
Overall, we harnessed the ability of the (PNP)Rh platform to
mediate nondirected C−H activation and translated this
reactivity into a catalytic system capable of functionalizing a
variety of C−H bonds. This was enabled by the fact that this
complex does not require directing groups to enable C−H
activation. This was achieved by a ligand modification to
dramatically enhance the rate of C−H activation and an
expanded understanding of the stoichiometric reactivity of the
C−H activation complex (PNP)Rh(Ph) with a variety of
electrophiles. Moreover, we found that key drawbacks to the
Given reports of direct arylation reactions using aryl iodides
t
in the presence of BuOK and an organic catalyst, control
t
reactions were conducted to compare the yield of BuOK-
mediated benzene arylation in the presence of no additives, 5
i
i
mol % of Pr(PNP)Rh(Cl), or 5 mol % of the Pr(PNP) ligand
Figure 6A, entries 2, 4, and 5). These reactions revealed
(
comparable and dramatically reduced yields under the last two
(
PNP)Rh platform (nitrogen inhibition and dependence on
conditions relative to the first, indicating that the reaction is not
47
strong base) were readily mitigated by simple modifications
(smaller phosphines and weakly coordinating anions, respec-
tively). The resulting catalytic method, like others based on the
catalyzed by demetalated ligand alone. Whereas organo-
catalytic transformations of this type show no activity in the
48
presence of a catalytic radical trap (TEMPO), the (PNP)Rh-
catalyzed reaction maintained substantial activity under the
same conditions (Figure 6A, entry 3). Notably, the less
hindered complexes (3 and 5) were much more efficient
50,51
PNP platform that emerged from stoichiometric reactions,
sheds new light on the reactivity of the (PNP)Rh platform in
3
the form of unexpected sp functionalization and potential
t
precatalysts than bulkier complexes 2 and Bu(PNP)Ir(coe)-
catalysis of radical-based transformations.
D
DOI: 10.1021/acs.organomet.7b00532
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3JHH = 7.0 Hz), 12H, PrCH
i
). P{ H} NMR (202 MHz, C
31
1
D
): δ
EXPERIMENTAL SECTION
3
6
6
■
2
13
1
4
1
1
7.88 (d, J = 148.8 Hz, 2P). C{ H} NMR (126 MHz, C D ): δ
RhP
6
6
General Methods. Unless otherwise noted, all reactions and
manipulations were performed under a circulating nitrogen atmos-
phere in an Innovative Technologies glovebox or using standard
Schlenk techniques with dried and degassed solvents. As noted
2
3
65.03 (vtd, J = 6.3, J = 1.1 Hz, ortho pyr), 129.76 (s, para pyr),
PC
RhC
3
4
19.38 (vtd, J = 5.3, J
CH ), 34.49 (vtd, J = 6.7, J = 1.5 Hz, PCH ), 24.25 (vtd, J =
= 1.2 Hz, meta pyr), 38.74 (s, OMs-
RhC
PC
RhC
1
2
1
3
PC
2
PC
2
i
2
i
9
(
.6, J = 1.0 Hz, PrCH), 19.23 (vt, J = 3.9 Hz, PrCH ), 17.70 (s
5
2
31
31
RhC PC 3
previously, due to strong P− P coupling in the pincer ligand,
i
br), PrCH ). Anal. Calcd for C H NO SP Rh: C, 44.70; H, 7.13;
1
13
3 20 38 3 2
many H and C signals appear as virtual triplets (vt) and are reported
N, 2.61. Found: C, 46.57; H, 7.52; N, 2.78. Material prepared by this
method gave carbon analysis outside the range viewed as establishing
analytical purity (Δ1.87%). Elemental analysis and graphical H, P,
and C NMR data are provided to illustrate the degree of purity of the
bulk material obtained by this method without additional purification.
Pr(PNP)Rh(OTs) (7). In a J. Young tube was placed a stock solution
of 5 in C D (14 μmol, 583 μL, 24 mM, 1 equiv) which also contained
mesitylene (4.66 μmol, 8 mM) as an internal standard. To this
solution was added a stock solution in C D of 4-toluenesulfonic acid
14 μmol, 93.3 mM, 150 μL). The mixture was immediately capped,
shaken, and analyzed by H NMR, which revealed conversion to 7
3
1
1
as such with the apparent coupling constant noted. In P{ H}
experiments the sweep width of the decoupling channel is insufficient
1
31
1
to simultaneously decouple aliphatic and hydridic H resonances: as
13
such, 31P{ H} spectra of rhodium hydrides include coupling to Rh−H.
1
5
3
i
Literature procedures were used to prepare [Rh(coe) (Cl)] , Pr-
i
2
2
5
4
i
51
t
55
i
33
t
(
(
PNP), pyrr- Pr(PNP), Bu(PNP), Pr(PNP)Rh(Cl) (3), Bu-
56 37
t
6
6
PNP)Rh(Cl) (2), Bu(PNP)Rh(Ph) (2), potassium 2,6-bis(tert-
butyl)-4-methoxyphenolate, and Bu(PNP)Ir(coe)(PF ).
5
7
t
39
6
i
6
6
Synthesis and Characterization. Pr(PNP)Rh(Ph) (5). A 500 mL
round-bottom flask was charged with 3 (4.778 g, 10 mmol, 1 equiv), a
stir bar, and 100 mL of THF. To the deep red, stirred solution was
added phenylmagnesium chloride in THF (10.4 mmol, 4.55 mL, 2.2
M, 1.04 equiv). Reaction progress was monitored by 31P NMR of 50
μL aliquots dissolved in 500 μL of C D . After 43 h, all of the starting
(
1
with concomitant elimination of benzene as the major products.
However, during the first 6 min of the reaction, an intermediate was
observed with 1H and 31P NMR spectra consistent with metal-
6
6
centered protonation (see the Supporting Information) specifically
material had been consumed and the solvent was removed under
reduced pressure. To remove any residual THF, the dark solid mixture
was suspended in 10 mL of toluene and concentrated in vacuo. The
mixture was extracted with refluxing pentane (40 mL) which was
filtered over a medium frit into a warm side-arm flask. The mixture of
product and magnesium salts in the original reaction vessel was
extracted six times in this manner while the collection flask was gently
warmed to prevent precipitation. Over the course of the extractions
approximately half of the pentane evaporated to give a concentrated
solution of 5 in warm pentane. The filtrate was transferred to a 200
mL jar, sealed, cooled to room temperature, and transferred to a −35
1
1
31
a rhodium hydride resonance (δ −18.94, m by H NMR, d by H{ P}
1
i
NMR, J
= 19.0 Hz) and broken symmetry of the PCH and Pr
RhH
2
resonances. After 12 h at 21 °C the reaction had gone to 98% of the
desired product by 1H NMR with respect to mesitylene internal
standard. The reaction mixture was poured into a 1 dram vial,
concentrated under reduced pressure, and suspended in 1 mL of
pentane. After 12 h at −35 °C the supernatant was removed by pipet
to afford 5.8 mg (68% yield) of complex 7. The precipitated material
contains several minor (PNP)Rh impurities and is estimated to be
0% pure as determined by integration of the P NMR spectrum. H
NMR (500 MHz, C D ): δ 8.17 (d, J = 7.9 Hz, 2H, OTs CH), 6.91
31
1
8
3
6
6
HH
°
3
C freezer. After 48 h at −35 °C the supernatant was decanted to give
.66 g (70% yield) of large black-red crystals of complex 5. Single
crystals suitable for X-ray diffraction were grown by slow evaporation
3
3
(
6
d, J = 7.8 Hz, 2H, pyr meta), 6.85 (t, J = 7.6 Hz, 1H, pyr para),
HH HH
3
.28 (d, J = 7.6 Hz, 2H, OTs CH), 2.43 (m, 4H, PCH ), 2.27 (m,
HH 2
1
31
3
i
(
septet by H{ P} J = 7.0 Hz), 4H, PrCH), 1.97 (s, 3H, OTs
HH
1
of pentane from the supernatant solution at −35 °C. H NMR (500
1
31
3
i
CH ), 1.56 (m, (doublet by H{ P} J = 7.0 Hz), 12H, PrCH ),
1.02 (m, (doublet by H{ P} J = 6.9 Hz) 12H, PrCH ). P{ H}
NMR (202 MHz, C D ): δ 48.41 (d, J
3
HH
3
3
3
MHz, C D ): δ 7.94 (d, J = 7.6 Hz, 2H, Rh-Ph ortho), 7.21 (t, J
1
31
3
i
31
1
6
6
HH
HH
HH 3
3
=
(
2
(
7.4 Hz, 2H, Rh-Ph meta), 7.01 (t, J = 7.6 Hz, 1H, pyr-para), 6.93
1
13
1
HH
= 147.8 Hz). C{ H}
RhP
6
6
3
t, J = 7.1 Hz, 1H, Rh-Ph para), 6.51 (d, J = 7.6 Hz, 2H, pyr-meta),
2
3
HH
NMR (126 MHz, C D ): δ 165.10 (vtd, J = 6.4 Hz, J = 1.1 Hz,
6 6 PC RhC
3
i
.72 (vt, J = 3.3 Hz, 4H, PCH ), 1.91 (m, 4H, Pr CH), 1.14 (m,
PH 2
pyr ortho), 143.74 (s, OTs quaternary), 138.48 (s, OTs quaternary),
130.04 (s, pyr para), 128.21 (s,OTs CH), 126.65 (s, OTs CH), 119.49
(vtd, J = 5.4, J = 0.9 Hz, pyr meta), 34.48 (vtd, J = 6.9, J
1
31
3
i
doublet by H{ P} J = 7.1 Hz), 12H, PrCH ), 1.04 (m, (doublet
HH 3
1
31
3
i
31
1
by H{ P} J = 6.9 Hz), 12H, PrCH ). P{ H} NMR (202 MHz,
3
4
1
2
HH
3
=
PC
RhC
PC
PC
1
13
1
1
i
C D ): δ 42.64 (d, J
= 168.8 Hz). C{ H} NMR (126 MHz,
PC
6
6
RhP
1.4 Hz, PCH ), 24.26 (vt, J = 9.5 Hz, PrCH), 20.74 (s, OTs CH ),
2
P
C
3
2
1
2
i
i
C D ): δ 167.64 (vtd, J = 13.5, J
32.3 Hz, Rh-Ph C ipso),
6
6
RhC
19.32 (vt, J = 3.9 Hz, PrCH ), 17.70 (s, PrCH ).
PC 3 3
Pr(PNP)Rh(H)(OTs) (8). In a J. Young tube was placed a stock
solution of 5 in C D (14 μmol, 583 μL, 24 mM, 1 equiv) which also
contained mesitylene (4.66 μmol, 8 mM) as an internal standard. To
this solution was added a stock solution in C D of 4-toluenesulfonic
acid (14 μmol, 93.3 mM, 150 μL). The mixture was immediately
capped, shaken, and analyzed by H NMR, which revealed conversion
to 7 with concomitant elimination of benzene as the major products.
After 12 h, the reaction had gone to complete conversion to complex
7. The reaction mixture was heated to 100 °C for 12 h, during which
time a white solid precipitated from the reaction mixture. The
suspension was transferred to a 1 dram vial and the supernatant
removed by pipet. The precipitate was washed with diethyl ether and
dried under vacuum to give 8.1 mg (94% yield) of 8 as an off-white
precipitate. H NMR (500 MHz, CD Cl ): δ 7.68 (t, J = 7.7 Hz,
1H, pyr para), 7.34 (d, J = 7.6 Hz, 1H, pyr ortho), 7.23 (s, 1H,
HH
OTs), 7.19 (d, J = 7.8 Hz, 1H, OTs), 6.71 (d, J = 7.7 Hz, 1H,
OTs), 3.73 (d br, J = 16.2 Hz, 2H, PCH ), 3.49 (d br, J = 16.2
2
2
3
i
1
3
61.20 (dvt, J = 1.4, J = 6.6 Hz, pyr C-ortho), 141.11 (vt, J
=
RhC
PC
PC
.1 Hz, Rh-Ph C ortho), 130.35 (s, pyr C-para), 124.79 (m, Rh-Ph C
6
6
3
5
meta), 119.13 (vt, J = 4.6 Hz, pyr C meta), 118.13 (vt, J = 1.3
PC
PC
1
2
Hz, Rh-Ph C para), 37.03 (vt, J = 5.9 Hz, PCH ), 24.15 (dvt, J
PC
2
RhC
6
6
1
i
2
i
=
(
2
2.9, J = 8.9 Hz, Pr CH), 18.85 (vt, J = 3.6 Hz, Pr CH ), 17.77
PC PC 3
i
1
m, Pr CH ). Anal. Calcd for C H NP Rh: C, 57.81; H, 7.76; N,
3
25 40
2
.70. Found: C, 58.99; H, 8.02; N, 2.57. Material prepared by this
method gave carbon analysis outside the range viewed as establishing
analytical purity (Δ1.81%). Elemental analysis and graphical H, P,
and 13C NMR data are provided to illustrate the degree of purity of the
bulk material obtained by this method without additional purification.
1
31
i
Pr(PNP)Rh(OMs) (6). A J. Young tube was charged with 5 (100 mg,
.192 mmol, 1 equiv) and 500 μL of C D . To the blackish solution
0
6 6
1
3
was added 12.5 μL of methanesulfonic acid. The tube was capped,
2 2 HH
1
31
2
shaken, and analyzed by H and P NMR within 5 min of mixing. The
reaction was monitored 1 h later, which revealed no further reaction.
The contents of the J. Young tube were poured into 10 mL of stirring
pentane in a 20 mL scintillation vial at −35 °C to give an orange-red
precipitate. The precipitate settled to the bottom of the vial overnight
at −35 °C, at which time the supernatant was decanted to give 97.2
3
3
HH
HH
2
2
HH
2
HH
i
i
Hz, 2H, PCH ), 2.93 (m, 2H, PrCH), 2.24 (m, 5H, PrCH′
2
1
31
3
overlapped with OTs-CH ), 1.10 (m, (doublet by H{ P} J = 7.1
3
HH
i
i
i
Hz), 6H, PrCH ), 1.05 (m, 12H, PrCH ), 0.86 (m, 6H, PrCH ),
−18.65 (vtd, J = 12.7, J = 32.4 Hz, 1H, Rh−H). P{ H} NMR
(202 MHz, CD Cl ): δ 58.55 (td, J = 12.7, J
C{ H} NMR (126 MHz, CD Cl ): δ 161.42 (m, pyr ortho), 145.57
(s, OTs quaternary), 143.46 (m, OTs CH), 137.84 (s, pyr para),
137.08 (s, OTs quaternary), 129.80 (m, Rh−C), 124.82 (s, OTs CH),
3
3
3
1
2
1
31
1
mg (95% yield) of complex 6. H NMR (500 MHz, C D ): δ 6.79 (t,
6
6
HP
HRh
3
3
2 1
JHH = 7.4 Hz, 1H, pyr para), 6.22 (d, J = 7.7 Hz, 2H, pyr meta),
= 109.2 Hz).
PRh
HH
2
2
PH
3
13
1
2
.76 (s, 3H, OMs-CH ), 2.39 (vt, J = 3.5 Hz, 4H, PCH ), 2.28 (m
2 2
3
PH
2
1
31
3
i
(
septet by H{ P} J = 7.0 Hz), 4H, PrCH), 1.55 (m, (doublet by
H{ P} J = 7.0 Hz), 12H, PrCH ), 1.03 (m, (doublet by H{ P}
HH
1
31
3
i
1
31
HH
3
E
DOI: 10.1021/acs.organomet.7b00532
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
93.7 Hz). 13C{ H} NMR (126 MHz, CD Cl ): δ 160.88 (vt, J = 3.2
1
2
1
22.14 (s, OTs CH), 120.34 (vt, J = 4.1 Hz, pyr meta), 38.02 (vt,
PC
2 2 PC
1
1
i
1
2
JPC = 9.7 Hz, PCH ), 23.54 (vt, J = 10.0 Hz, PrCH), 22.82 (vt,
Hz, pyr ortho), 144.11 (vtd, J = 8.6, J = 24.8 Hz, Rh-Ph ipso),
RhC PC
139.98 (vtd, JPC = 2.4, JRhC= 0.7 Hz, Rh-Ph ortho), 137.86 (s, pyr
para), 125.05 (s, Rh-Ph meta), 121.47 (s, Rh-Ph para), 120.78 (vt, J
4.4 Hz, pyr meta), 40.28 (vt, J = 11.4 Hz, PCH ), 24.00 (vtd, J
10.5, J = 1.1 Hz, PrCH), 19.08 (s, PrCH ), 18.67 (s, PrCH ).
Anal. Calcd for C H NP RhCl : C, 50.86; H, 6.38; N, 2.37. Found:
C, 51.93; H, 6.57; N, 2.28. Material prepared by this method gave
carbon analysis outside the range viewed as establishing analytical
2
PC
1J = 13.8 Hz, PrCH), 20.99 (s, OTs-CH ), 18.75 (m, PrCH ),
i
i
3
2
PC
3
3
3
i
i
i
1
8.51 (s br, PrCH ), 17.73 (s br, PrCH ), 17.16 (s br, PrCH ). Anal.
PC
3
3
3
1
1
=
=
Calcd for C H NO SP Rh: C, 50.90; H, 6.90; N, 2.28. Found: C,
PC 2
PC
26
42
3
2
2
i
i
i
51.i09; H, 6.94; N, 2.22.
RhC
3
3
Pr(PNP)Rh(H)(OTs) (9). In a J. Young tube was placed a stock
solution of 5 in C D (14 μmol, 583 μL, 24 mM, 1 equiv) which also
contained mesitylene (4.66 μmol, 8 mM) as an internal standard. To
this solution was added a stock solution in C D of 4-toluenesulfonic
25 40
2
2
2
6
6
1
31
13
purity (Δ1.07%). Elemental analysis and graphical H, P, and
NMR data are provided to illustrate the degree of purity of the bulk
material obtained by this method without additional purification.
C
6
6
acid (28 μmol, 93.3 mM, 300 μL). The mixture was immediately
1
capped, shaken, and analyzed by H NMR, which revealed complete
i
Pr(PNP)Rh(I) (12). In a 20 mL glass vial charged with a stir bar was
conversion to 9 with concomitant elimination of benzene as the major
products. The reaction was monitored again 1 h later and revealed no
further reaction. The reaction mixture was transferred to a 1 dram vial,
concentrated in vacuo, washed with pentane, and dried under vacuum
to give 8.6 mg (78% yield) of 9 as an off-white precipitate. H NMR
500 MHz, C D ): δ 8.12 (d, J = 8.0 Hz, 2H, OTs), 8.07 (d, J
.1 Hz, 2H, OTs), 7.03 (t, J = 7.7 Hz, 1H, pyr para), 6.87 (d, J
7.8 Hz, 2H, OTs), 6.83 (d, J = 8.0 Hz, 2H, OTs), 6.62 (d, J
.7 Hz, 2H, pyr meta), 4.49 (vtd, J = 4.4, J = 17.0 Hz, 2H,
PCH ), 3.30 (m, (septet by H{ P} J = 7.2 Hz), 2H, PrCH), 2.77
vtd, J = 3.5, J = 17.1 Hz, 2H, PCH ), 2.20 (m, (septet by
H{ P} J = 7.1 Hz), 2H, PrCH), 1.94 (s, 3H, OTs-CH ), 1.92 (s,
H, OTs-CH ), 1.55 (m, (doublet by H{ P} J = 7.2 Hz), 6H,
PrCH ), 1.47 (m, (doublet by H{ P} J = 7.0 Hz), 6H, PrCH ),
placed 0.5 mL of an acetone solution of iPr(PNP)Rh(Cl) (72 mg, 0.15
mmol, 1 equiv) and 0.6 mL of an acetone solution of NaI (45 mg, 0.30
mmol, 2 equiv). After the mixture was stirred at room temperature for
10 min, P NMR analysis indicated complete consumption of
Pr(PNP)Rh(Cl). The acetone solvent was removed by vacuum. The
remaining solids were suspended in a minimal amount of benzene and
syringe filtered. The filtrate was then concentrated and transferred to a
small vial. Vapor diffusion of pentane was used to crystallize the
product, iPr(PNP)Rh(I). H NMR (500 MHz, C D ): δ 6.98 (t, J
7.8 Hz, 1H, pyr para), 6.4 (d, J = 7.69 Hz, 2H, pyr meta), 2.47
31
1
i
3
3
(
8
=
7
=
HH
=
6
6
HH
HH
3
3
HH
3
3
HH
HH
3
2
HP HH
1
3
1
31
3
i
6
6
HH
2
HH
3
3
2
=
(
HH
HP
HH
2
2
1
31
3
1
31
3
i
(vt, J = 3.5 Hz, 4H, PCH ), 2.18 (m, (septet by H{ P} J = 6.9
PH 2 HH
HH
3
i
1
31
3
1
31
3
Hz), 4H, PrCH), 1.52 (m, (doublet by H{ P} J = 7.0 Hz), 12H,
PrCH ), 0.97 (m, (doublet by H{ P} J = 6.9 Hz), 12H, PrCH ).
P{ H} NMR (202 MHz, C D ): δ 50.40 (d, J = 139.4 Hz).
C{ H} NMR (126 MHz, C D ): δ 163.29 (vt, J = 7.0 Hz, pyr
ortho), 129.45 (s, pyr para), 119.69 (vt, JCP = 6.1 Hz, pyr meta),
36.57 (vt, JPC = 6.0 Hz, PCH
19.35 (t, JPC = 3.2 Hz, Pr CH
elemental analysis was not obtained for complex 12. Graphical H, P,
and 13C NMR data are provided to illustrate the degree of purity of the
bulk material obtained by this method; however, the possible presence
of residual sodium iodide cannot be excluded.
Pr(PNP)Rh(Ph)(I) (13). In a J. Young tube was placed a stock
solution of 5 in C D (14 μmol, 500 μL, 28 mM, 1 equiv) which also
contained mesitylene (4.0 μmol, 8 mM) as an internal standard. The
solution was diluted with 100 μL of C D . To this solution was added
a stock solution of iodine in C D (14 μmol, 140 mM, 100 μL). The
mixture was immediately capped, shaken, and analyzed by H NMR,
which revealed complete consumption of starting material, major
conversion to 13, and an additional species with a H NMR spectrum
consistent with the trans isomer of 13 ( P{ H} NMR δ 27.94 ppm, d,
JPRh = 94.2 Hz). After 90 min the mixture had undergone complete
conversion to 13 in 98% yield by H NMR with respect to 1,3,5-
trimethoxybenzene internal standard. The reaction mixture was
transferred to a 1 dram vial, concentrated in vacuo, washed with
pentane, and dried under vacuum to give 9.4 mg (87% yield) of 13 as
an orange solid. H NMR (500 MHz, CD Cl ): δ 8.86 (d br, J
7.0 Hz, 1H, Ph ortho), 7.76 (t, J = 7.7 Hz, 1H, pyr para), 7.45 (d,
JHH = 7.7 Hz, 2H, pyr meta), 6.94 (t br, J = 7.3 Hz, 1H, Ph meta),
.89 (t, J = 6.9 Hz, 1H, Ph para), 6.70 (t br, J = 7.1 Hz, 1H, Ph
HH HH
meta), 5.59 (d br, J = 7.3 Hz, 1H, Ph ortho), 4.28 (vtd, J = 4.3,
JHH = 17.2 Hz, 2H, PCH), 3.79 (m, (septet by H{ P} J = 7.3
3
HH
3
HH
i
1
31
3
i
i
1
31
3
i
3
HH
3
3
HH
3
3
1
1
1
1
1
31
3
i
1
(
1
.29 (m, (doublet by H{ P} J = 7.2 Hz), 6H, PrCH ), 0.88 (m,
6
6
RhP
HH
3
3
1
2
1
31
3
i
2
doublet by H{ P} J = 6.8 Hz), 6H, PrCH ), −18.97 (vtd, J
=
6
6
CP
HH
3
HP
1
31
1
3
0.2, J
= 19.5 Hz, 1H, Rh−H). P{ H} NMR (202 MHz, C D ):
HRh
6
6
2
1
13
1
1
i
δ 49.85 (dd, J = 9.1, J 100.6 Hz, 2P). C{ H} NMR (126 MHz,
2
), 24.18 (vt,
1
J
PC = 10.5 Hz, Pr CH),
PH
PRh
2
2
i
i
C D ): δ 167.06 (vt br, J = 4.5 Hz, pyr ortho), 141.32 (s, OTs
quaternary), 139.47 (s, OTs quaternary), 137.71 (s, pyr para), 128.52
s br, OTs CH), 128.47 (s, OTs CH), 126.63 (s, OTs CH), 126.33 (s
br, OTs CH), 120.59 (vt, J = 5.5 Hz, pyr meta), 36.01 (vt, J
.4 Hz, PCH ), 25.87 (vt, J = 12.7 Hz, PrCH), 25.49 (vt, J
1.0 Hz, PrCH), 20.72 (br, 2xOTs-CH ), 19.03 (vt, J = 2.0 Hz,
PrCH ), 18.64 (br, PrCH ),18.17 (br, PrCH ), 17.86 (br, PrCH ).
Anal. Calcd for C H NO S P Rh: C, 50.44; H, 6.41; N, 1.78. Found:
3
), 17.58 (s br, Pr CH
3
). Suitable
6
6
CP
1
31
(
3
1
=
=
CP
CP
1
i
1
9
2
CP
CP
i
i
2
1
2
3
CP
i
i
i
i
6
6
3
3
3
3
33
50
6 2 2
C, 50.72; H, 6.49; N, 1.78.
6
6
i
Pr(PNP)Rh(Ph)(Cl) (11). In a J. Young tube was placed a stock
solution of 5 in C D (6.8 μmol, 200 μL, 35 mM, 1 equiv) which also
contained 1,3,5-trimethoxybenzene (1.4 μmol, 7 mM) as an internal
standard. The solution was diluted with 250 μL of C D . To this
solution was added a stock solution in C D6 of 4-methylbenzyl
6 6
2
1
6
6
1
6
6
31
1
6
1
chloride (20.4 μmol, 204 mM, 100 μL, 3 equiv). The mixture was
1
1
31
immediately capped, shaken, and analyzed by H and P NMR, which
revealed complete consumption of 5, major conversion to 11 and 4,4′-
dimethylbibenzyl, and an additional (PNP)Rh product consistent with
oxidative addition of benzyl chloride (see section S1.5 in the
1
3
i
=
Supporting Information for spectra: broken symmetry about Pr and
2
2
HH
3
1
1
31
2
PCH , Rh-CH (δ 4.20 (m by H, d by H{ P} J = 2.4 Hz),
HH
2
2
RhH
3
3
3
1
1
1
P{ H} (δ 34.35, d, J = 113.0 Hz)). After 5 h, the concentration of
the intermediate had decreased and a yellow precipitate (11) began to
form. The solution was heated to 80 °C for 12 h, which gave a 74%
HH
RhP
3
3
6
3
2
HH
HP
2
1
31
3
1
yield of 11 and 95% of 4,4′-dimethylbibenzyl by H NMR with respect
HH
i
2
2
to trimethoxybenzene internal standard. The product mixture was
transferred to a 1 dram vial, and dichloromethane was added dropwise
until the yellow precipitate dissolved. This mixture was layered with
diethyl ether, which afforded yellow single crystals of 11 suitable for X-
ray diffraction. The supernatant of the crystallization mixture was
analyzed by GCMS, which revealed a single organic product with a
Hz), 2H, PrCH), 3.63 (vtd, JHP = 4.0, JHH = 17.2 Hz, 2H, PCH), 2.02
1
31
3
i
(m, (septet by H{ P} JHH = 7.2 Hz) 2H, PrCH), 1.69 (m, (doublet
1
31
3
i
by H{ P} JHH = 7.4 Hz), 6H, PrCH ), 1.49 (m, (doublet by
3
1
31
3
i
1
31
H{ P} JHH = 7.3 Hz), 6H, PrCH ), 1.18 (m, (doublet by H{ P}
3
3JHH = 7.3 Hz), 6H, PrCH
i
), 1.13 (m, (doublet by H{ P} JHH = 7.3
Hz), 6H, PrCH ). P{ H} NMR (202 MHz, CD Cl ): δ 33.56 (d,
1
31
3
3
i
31
13
1
3
2
2
1
1
1
mass consistent with 4,4′-dimethylbibenzyl. H NMR (500 MHz,
CD Cl ): δ 8.06 (d, J = 7.8 Hz, 2H, Rh-Ph ortho), 7.71 (t, J
.7 Hz, 1H, pyr para), 7.39 (d, JHH = 7.4 Hz, 2H, pyr meta), 6.89 (t,
JHH = 7.3 Hz, 2H, Rh-Ph meta), 6.83 (t, J = 7.0 Hz, 1H, Rh-Ph
para), 3.92 (vt, J = 4.2 Hz, 4H, PCH ), 2.89 (m, (septet by H{ P}
JHH = 7.3 Hz), 4H, PrCH), 1.32 (m, (doublet by H{ P} J = 7.2
Hz), 12H, PrCH ), 1.05 (m, (doublet by H{ P} J = 7.3 Hz),
2H, PrCH ). P{ H} NMR (202 MHz, CD Cl ): δ 37.02 (d, J
JRhP = 96.1 Hz). C{ H} NMR (126 MHz, CD Cl ): δ 163.19 (vt,
2
2
3
3
4J = 4.1 Hz, pyr ortho), 145.78 (br, Ph ortho), 145.00 (vtd, J
2
=
=
2
2
HH
HH
PC
PC
3
1
7
8.8, J
= 30.5 Hz, Ph ipso), 137.59 (s, pyr para), 132.16 (br, Ph
ortho), 127.30 (br, Ph meta), 127.07 (br, Ph meta), 123.24 (s, Ph
para), 122.21 (vtd, J = 5.1, J = 0.8 Hz, pyr meta), 41.76 (vt, J
= 10.9 Hz, PCH ), 30.99 (vt, J = 11.7 Hz, PrCH), 26.45 (vtd, J
RhC 3
PrCH ), 19.48 (br, PrCH ), 18.77 (br, PrCH ). Graphical H, P,
RhC
3
3
HH
2
1
31
3
4
1
PC
2
PC RhC
PC
3
i
1
31
3
1
i
1
HH
2
PC
PC
i
1
31
3
2
i
i
= 11.1 Hz, J
= 1.9 Hz, PrCH), 21.33 (br, PrCH ), 20.28 (br,
3
HH
i
31
1
1
i
i
i
1
31
1
=
3
2
2
RhP
3
3
3
F
DOI: 10.1021/acs.organomet.7b00532
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
and 13C NMR data are provided to illustrate the degree of degree of
purity of the bulk material obtained by this method; however, the
possible presence of residual iodine cannot be excluded.
(12) Kuninobu, Y.; Ida, H.; Nishi, M.; Kanai, M. Nat. Chem. 2015, 7
(9), 712.
(13) Davis, H. J.; Mihai, M. T.; Phipps, R. J. J. Am. Chem. Soc. 2016,
1
38 (39), 12759.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00532.
(14) Li, H. L.; Kuninobu, Y.; Kanai, M. Angew. Chem. 2017, 129 (6),
■
1
517.
*
S
(
15) Hoque, M. E.; Bisht, R.; Haldar, C.; Chattopadhyay, B. J. Am.
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(
(
General and synthetic procedures (PDF)
Coordinates of calculated structures (XYZ)
(
1
(
Accession Codes
CCDC 1564239−1564244 and 1572210 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or 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.
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AUTHOR INFORMATION
Corresponding Author
E-mail for J.C.L.: jaredlewis@uchicago.edu.
■
*
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(
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ORCID
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929.
Jared C. Lewis: 0000-0003-2800-8330
Notes
The authors declare no competing financial interest.
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(
7
(
ACKNOWLEDGMENTS
■
We thank Michael D. Roy for preliminary synthesis and
Brandon E. Haines and Jonathan H. Skone for helpful
discussions. This work was supported by the NSF under the
CCI Center for Selective C−H Functionalization (CCHF,
CHE-1205646). J.J.G. was supported by an NSF predoctoral
fellowship (DGE-1144082). This work was completed in part
with resources provided by the University of Chicago Research
Computing Center. Use of the Advanced Photon Source, an
Office of Science User Facility operated for the U.S.
Department of Energy (DOE) Office of Science by Argonne
National Laboratory, was supported by the U.S. DOE under
contract No. DE-AC02-06miltCH11357. ChemMatCARS
Sector 15 is principally supported by the Divisions of
Chemistry (CHE) and Materials Research (DMR), National
Science Foundation, under grant number NSF/CHE-1346572.
Use of the PILATUS3 X CdTe 1 M detector is supported by
the National Science Foundation under grant number NSF/
DMR-1531283.
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