Stoichiometric reactivity relevant to the Mor-DalPhos/Pd-catalyzed cross-coupling of ammonia and 1-bromo-2-(phenylethynyl)benzene

Article abstract of DOI:10.1021/om201122q

While Mor-DalPhos/Pd precatalyst mixtures have in general proven to be highly effective for the monoarylation of ammonia employing a range of (hetero)aryl (pseudo)halide cross-coupling partners, we have observed previously that 1-bromo-2-(phenylethynyl)benzene (Ar*Br) is a challenging substrate for this catalyst system. We report herein on our efforts to examine some possible modes of catalyst inhibition by this substrate. Treatment of [CpPd(allyl)] with Mor-DalPhos in the presence of Ar*Br afforded [(κ²-P,N-Mor-DalPhos)Pd(Br)(Ar*)] (1; 85%), which was transformed into [(κ³-P,N,O-Mor-DalPhos)Pd(Ar*)] ⁺OTf^- (3; 83%) upon treatment with AgOTf. The characterization of 3 establishes the ability of the Mor-DalPhos ligand to adopt a κ³-P,N,O structure, which may influence the course of some Pd-catalyzed amination processes. While treatment of 1 with AgOTf in the presence of ammonia, or alternatively treatment of 3 with ammonia, resulted in the clean formation of [(κ²-P,N-Mor-DalPhos)Pd(NH ₃)(Ar*)]⁺OTf^- (2), our efforts to isolate this compound were thwarted by the facile loss of ammonia from 2 to give 3. Neither NMR spectroscopic nor X-ray crystallographic data obtained for 1 and 3 support the existence of significant Pd···alkyne interactions in these complexes. Treatment of the Pd(0) species [L ₂Pd(diphenylacetylene)] (L₂ = Mor-DalPhos, 4; L ₂ = CyPFtBu-JosiPhos, 5) with Ar*Br resulted in divergent behavior: while multiple phosphorus-containing products were observed in the case of 4, under analogous conditions 5 was transformed cleanly into [(κ²-P,P-JosiPhos)Pd(Br)(Ar*)] (6). The identification of 6 was facilitated via independent synthesis from Ar*Br, JosiPhos, and [CpPd(allyl)] (90%). These observations suggest that the inferior performance of Mor-DalPhos relative to JosiPhos in the arylation of ammonia using Ar*Br may be attributable in part to the inefficiency with which putative [(Mor-DalPhos)Pd(alkyne)] species re-enter the catalytic cycle via C-Br oxidative addition.

Full text of DOI:10.1021/om201122q

Article
pubs.acs.org/Organometallics
Stoichiometric Reactivity Relevant to the Mor-DalPhos/Pd-Catalyzed
Cross-Coupling of Ammonia and 1-Bromo-2-(phenylethynyl)benzene
Pamela G. Alsabeh,† Robert McDonald,‡ and Mark Stradiotto*,†
†Department of Chemistry, Dalhousie University, 6274 Coburg Road, P.O. Box 15000, Halifax, Nova Scotia, Canada B3H 4R2
‡X-ray Crystallography Laboratory, Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
S
* Supporting Information
ABSTRACT: While Mor-DalPhos/Pd precatalyst mixtures
have in general proven to be highly effective for the
monoarylation of ammonia employing a range of (hetero)aryl
(pseudo)halide cross-coupling partners, we have observed
previously that 1-bromo-2-(phenylethynyl)benzene (Ar*Br) is
a challenging substrate for this catalyst system. We report
herein on our efforts to examine some possible modes of
catalyst inhibition by this substrate. Treatment of [CpPd(allyl)] with Mor-DalPhos in the presence of Ar*Br afforded [(κ2-P,N-
Mor-DalPhos)Pd(Br)(Ar*)] (1; 85%), which was transformed into [(κ3-P,N,O-Mor-DalPhos)Pd(Ar*)]+OTf− (3; 83%) upon
treatment with AgOTf. The characterization of 3 establishes the ability of the Mor-DalPhos ligand to adopt a κ3-P,N,O structure,
which may influence the course of some Pd-catalyzed amination processes. While treatment of 1 with AgOTf in the presence of
ammonia, or alternatively treatment of 3 with ammonia, resulted in the clean formation of [(κ2-P,N-Mor-DalPhos)Pd(NH3)-
(Ar*)]+OTf− (2), our efforts to isolate this compound were thwarted by the facile loss of ammonia from 2 to give 3. Neither
NMR spectroscopic nor X-ray crystallographic data obtained for 1 and 3 support the existence of significant Pd···alkyne
interactions in these complexes. Treatment of the Pd(0) species [L2Pd(diphenylacetylene)] (L2 = Mor-DalPhos, 4; L2 =
CyPFtBu-JosiPhos, 5) with Ar*Br resulted in divergent behavior: while multiple phosphorus-containing products were observed
in the case of 4, under analogous conditions 5 was transformed cleanly into [(κ2-P,P-JosiPhos)Pd(Br)(Ar*)] (6). The
identification of 6 was facilitated via independent synthesis from Ar*Br, JosiPhos, and [CpPd(allyl)] (90%). These observations
suggest that the inferior performance of Mor-DalPhos relative to JosiPhos in the arylation of ammonia using Ar*Br may be
attributable in part to the inefficiency with which putative [(Mor-DalPhos)Pd(alkyne)] species re-enter the catalytic cycle via C−
Br oxidative addition.
he development of synthetic protocols that utilize
ammonia as a synthon is attractive, given the low cost
Chart 1
T
and abundant nature of this reagent, and in terms of the
opportunities afforded by such synthetic methods with regard
to streamlining the synthesis of nitrogen-containing organic
molecules.1 However, despite the remarkable advances that
have been achieved in metal-catalyzed C−N bond-forming
reactions, including the emergence of the Pd-catalyzed cross-
coupling of amines and (hetero)aryl (pseudo)halides (i.e.,
Buchwald−Hartwig amination),2 the successful incorporation
of ammonia into synthetic protocols that are well-established
for other classes of amines has proven challenging.1 Indeed,
whereas Buchwald−Hartwig amination was established in
1995,3 the Pd-catalyzed arylation of ammonia has emerged
only recently.4−6
The successful development of Buchwald−Hartwig amina-
tion protocols that accommodate ammonia as a substrate can
be attributed largely to the identification of suitable ancillary
coligands that enable the synthesis of arylamines in high yield
and with useful selectivity (e.g., monoarylation vs polyarylation)
and substrate scope. In this vein, we have recently reported on
the development of Mor-DalPhos (Chart 1),5 which is a
broadly effective ligand for use in the selective Pd-catalyzed
monoarylation of challenging substrates, including ammonia,5
hydrazine,7 and acetone.8,9 In building on this chemistry, we
developed a previously unknown tandem ammonia cross-
coupling/cyclization protocol that enables the construction of
NH-indoles via arylation of ammonia by using 1-bromo-2-
(phenylethynyl)benzene (Ar*Br) and related derivatives.6
However, as part of this investigation, we noted that Mor-
DalPhos/Pd mixtures performed poorly under a range of
experimental conditions (e.g., 5 mol % of Pd, 3 equiv of KOtBu,
3 equiv of NH3, 90 °C, 18 h) involving the test substrate Ar*Br,
affording the desired 2-phenylindole product in less than 50%
Received: November 14, 2011
Published: January 19, 2012
© 2012 American Chemical Society
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yield. By comparison, we found that the use of the CyPFtBu
variant of JosiPhos (Chart 1), a ligand that has been shown by
Hartwig and co-workers to be highly effective for the arylation
of both amines2a,b,10 and ammonia,4a,c afforded a range of
ammonia-derived 2-arylindole products, as well as analogous
cross-coupling/cyclization products derived from methylamine
and hydrazine, in good to excellent yield.6 In an effort to shed
some light on the divergent behavior of Mor-DalPhos and
JosiPhos in this catalytic chemistry, we conducted a brief
stoichiometric reactivity survey relevant to the Mor-DalPhos/
Pd-catalyzed cross-coupling of ammonia and Ar*Br, including
selected comparisons to the analogous JosiPhos-based catalyst
system. We report herein on the results of these studies,
including the first observation of a κ3-P,N,O binding mode for
the Mor-DalPhos ligand.
Figure 1. ORTEP diagram of 1·CH2Cl2 shown with 50% ellipsoids. All
hydrogen atoms and the dichloromethane solvate have been omitted
for clarity. Selected interatomic distances (Å): Pd−P, 2.2681(7); Pd−
N, 2.232(2); Pd−Br, 2.5154(4); Pd−C11, 2.011(3); Pd···C17,
3.200(3); Pd···C18, 3.891(3).
RESULTS AND DISCUSSION
■
The oxidative addition of aryl halides to in situ generated (Mor-
DalPhos)Pd0 species has been shown to occur under mild
conditions, and the arylation of ammonia using this catalyst
system proceeds smoothly with ortho-substituted aryl halides
other than Ar*Br.5 Given these observations, we initially turned
our attention to examining the spectroscopic and structural
features of the product obtained from C−Br oxidative addition
of Ar*Br to (Mor-DalPhos)Pd0, in an effort to assess whether
alkyne coordination to Pd(II) in this putative catalytic
intermediate might underpin the relatively poor performance
of the Mor-DalPhos/Pd system with this substrate. Treatment
of [CpPd(allyl)] with Mor-DalPhos in the presence of Ar*Br in
THF solution afforded the desired oxidative addition product
[(κ2-P,N-Mor-DalPhos)Pd(Br)(Ar*)] (1) as an analytically
pure beige solid in 85% isolated yield (Scheme 1). Solution
the κ2-P,N nature of the Mor-DalPhos ligand, the trans
disposition of Br and P as well as that of C and N (in keeping
with the greater trans-directing abilities of P relative to N), and
the notably long Pd···alkyne contacts (3.200(3) and 3.891(3)
Å).
We have demonstrated previously that treatment of [(κ2-P,N-
Mor-DalPhos)Pd(Cl)(Ar)] (Ar = Ph, 4-MeOC6H4) with
AgOTf in the presence of 3 equiv of ammonia in a mixture
of dichloromethane and 1,4-dioxane affords isolable cationic
ammine complexes that resist loss of ammonia upon exposure
to vacuum.5 Under similar conditions 1 is transformed cleanly
into the analogous cationic ammine complex 2 (Scheme 1). In
monitoring the progress of the reaction by using 31P NMR
spectroscopic methods, the disappearance of 1 (56.3 ppm) is
accompanied by the clean formation of 2 (62.6 ppm); the
ammine ligand in 2 gives rise to a broad 1H NMR resonance at
2.82 ppm. However, efforts to isolate 2 via removal of the
reaction solvent in vacuo resulted in a decrease in the intensity
of the 31P NMR resonance associated with 2 and the
appearance of a single new phosphorus-containing species (3;
δ(31P) 80.0). We were successful in our efforts to generate 3
rationally via addition of AgOTf to 1 in the absence of
ammonia, and in turn 3 was isolated as an analytically pure dark
yellow solid in 83% isolated yield. Treatment of solutions of 3
with 3 equiv of ammonia resulted in the clean regeneration of
the ammine adduct 2 (31P NMR). The observed propensity of
2 to release ammonia differs from our previously reported [(κ2-
P,N-Mor-DalPhos)Pd(NH3)(Ar)]+OTf− (Ar = Ph, 4-
MeOC6H4) complexes5a phenomenon that we initially
envisioned might be attributable to the competitive binding
of the alkyne fragment to Pd, leading to 3. However, as in 1, the
frequencies of the 13C NMR resonances associated with the
alkyne carbons in 3 (93.7 and 90.1 ppm) are inconsistent with
the existence of significant Pd···alkyne interactions. The
crystallographic characterization of 3 is in keeping with this
assertion;11 an ORTEP12 diagram of this complex is presented
in Figure 2. The Pd···alkyne distances in 3 (3.148(4) and
3.790(4) Å), while statistically shorter than the related contacts
in 1, can still be viewed as being sufficiently long so as to
preclude significant Pd···alkyne bonding interactions. Rather,
the coordinative and electronic unsaturation that results from
the loss of ammonia in 2 is instead apparently compensated by
the Mor-DalPhos ligand adopting a tridentate κ3-P,N,O binding
Scheme 1
NMR spectroscopic characterization data support the identity
of 1 as being the expected square-planar complex, devoid of any
significant Pd···alkyne interactions. Indeed, the alkyne carbon
13C NMR chemical shifts observed for 1 (90.0 and 97.0 ppm)
are only very modestly downfield of those of the Ar*Br
precursor (88.0 and 93.9 ppm). The crystallographic character-
ization of 1 corroborates these solution NMR data;11 an
ORTEP12 diagram of 1 is presented in Figure 1, which confirms
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Scheme 2
Figure 2. ORTEP diagram of 3·OEt2 shown with 50% ellipsoids. All
hydrogen atoms, the diethyl ether solvate, and the triflate counteranion
have been omitted for clarity. Selected interatomic distances (Å): Pd−
P, 2.2264(7); Pd−N, 2.106(3); Pd−O, 2.246(2); Pd−C11, 1.997(3);
Pd···C17, 3.148(4); Pd···C18, 3.790(4).
related derivatives may be attributable in part to the inefficiency
with which putative [(Mor-DalPhos)Pd(alkyne)] species re-
enter the catalytic cycle via Ar−X oxidative addition.
motif. On the basis of these observations, it appears that the
congestion imposed by the o-(phenylethynyl)phenyl ligand,
rather than the propensity of this fragment to engage in π-
bonding to Pd, may represent the primary factor leading to the
loss of ammonia and the formation of 3. It is unclear whether
cationic ammonia adducts analogous to 2, arising from the
displacement of (pseudo)halide (X) on Pd by ammonia in Ar−
X oxidative addition products such as 1, represent important
reactive intermediates in the Mor-DalPhos/Pd-catalyzed cross-
coupling of ammonia and Ar*Br or other aryl (pseudo)halides.
However, should such intermediates be accessible, the ability of
the Mor-DalPhos ligand to adopt a κ3-P,N,O binding motif in
response to the loss of ammonia promoted by the presence of a
sterically demanding Pd−Ar ligand (such as o-(phenylethynyl)-
phenyl) may contribute in part to the inferior catalytic
performance of the Mor-DalPhos/Pd catalyst system, relative
to catalysts featuring ligands that are not obviously capable of
tridentate coordination (e.g., JosiPhos).
In summary, we report herein on our efforts to identify
possible modes of Mor-DalPhos/Pd catalyst inhibition when
using 1-bromo-2-(phenylethynyl)benzene (Ar*Br) as a sub-
strate for the monoarylation of ammonia. In the course of these
studies we noted that neither the putative oxidative addition
product [(κ2-P,N-Mor-DalPhos)Pd(Br)(Ar*)] (1) nor the
corresponding product derived from bromide abstraction
using AgOTf [(κ3-P,N,O-Mor-DalPhos)Pd(Ar*)]+OTf− (3)
featured significant Pd···alkyne interactions in solution or the
solid state. These observations would appear to rule out
substrate inhibition arising from intramolecular alkyne
coordination to Pd following initial C−Br oxidative addition.
The characterization of 3 establishes for the first time the ability
of the Mor-DalPhos ligand to adopt a κ3-P,N,O structure, which
may play a role in Pd-catalyzed amination processes, especially
where the (pseudo)halide ligand is labile. We also observed that
whereas [(κ2-P,N-Mor-DalPhos)Pd(NH3)(Ph)]+OTf− is an
isolable complex that resists loss of ammonia upon prolonged
exposure to vacuum, the more facile loss of ammonia from [(κ2-
P,N-Mor-DalPhos)Pd(NH3)(Ar*)]+OTf− (2) to give 3 pre-
cluded the isolation of 2. It is feasible that the capacity of the
Mor-DalPhos ligand to adopt a κ3-P,N,O binding motif in
response to the loss of ammonia promoted by the sterically
demanding Pd−Ar* ligand could contribute to the challenges
encountered with this substrate when using the Mor-DalPhos/
Pd catalyst system. Finally, in contrast to the clean C−Br
oxidative addition of Ar*Br to [(JosiPhos)Pd-
(diphenylacetylene)] that was observed (giving 6), the
analogous chemistry involving [(Mor-DalPhos)Pd-
(diphenylacetylene)] afforded the target oxidative addition
product 1, accompanied by the generation of free Mor-DalPhos
and other unidentified phosphorus-containing species. These
observations suggest that the inefficiency with which putative
[(Mor-DalPhos)Pd(alkyne)] species re-enter the catalytic cycle
via C−Br oxidative addition may also contribute to the
observed inferior performance of Mor-DalPhos/Pd versus
JosiPhos/Pd catalyst systems in the Buchwald−Hartwig
amination of Ar*Br using ammonia.
Alkyne coordination to (Mor-DalPhos)Pd0 species generated
following C−N reductive elimination13 involving the Ar*Br
substrate, the derived aniline prior to cyclization, and/or the
diphenylacetylene that is formed as a byproduct in catalysis
employing Mor-DalPhos/Pd6 might also inhibit the Mor-
DalPhos/Pd catalyst system. As such, we turned our attention
to examining the efficiency of C−Br oxidative addition of Ar*Br
to the [L2Pd(diphenylacetylene)] complexes 4 (L2 = Mor-
DalPhos) and 5 (L2 = JosiPhos) to give the Pd(II) products 1
and 6, respectively (Scheme 2). In monitoring the reaction of
the JosiPhos complex 5 with 1 equiv of Ar*Br in THF at room
temperature (over 48 h) or 65 °C (over 2.5 h), clean
conversion to the anticipated oxidative addition product 6 was
observed by use of 31P NMR methods.14 The identity of 6 was
confirmed via independent synthesis; the addition of Ar*Br to a
mixture of JosiPhos and [CpPd(allyl)] afforded 6 as an
analytically pure orange solid in 90% isolated yield. In contrast,
treatment of the Mor-DalPhos precursor 4 with Ar*Br under
analogous experimental conditions resulted in the consumption
of 4, along with the formation of multiple phosphorus-
containing species, including the target oxidative addition
product 1 and free Mor-DalPhos ligand. These observations
qualitatively suggest that the comparatively poor catalytic
performance of Mor-DalPhos/Pd mixtures, relative to the
JosiPhos-based catalyst, in the monoarylation of Ar*Br and
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were conducted
under dinitrogen within an inert-atmosphere glovebox, utilizing
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glassware that was oven-dried (130 °C) and evacuated while hot prior
to use. Pentane and dichloromethane were deoxygenated by sparging
with dinitrogen followed by passage through a double-column solvent
purification system purchased from MBraun Inc. equipped with either
one alumina-packed column and one column packed with copper-Q5
reactant (pentane) or two alumina-packed columns (dichloro-
methane). THF and diethyl ether were each dried over Na/
benzophenone followed by distillation under an atmosphere of
dinitrogen. Deuterated solvents (Cambridge Isotopes) were degassed
by using three repeated freeze−pump−thaw cycles and stored over 4 Å
molecular sieves for 24 h prior to use. All solvents were stored under
dinitrogen over activated 4 Å molecular sieves. Mor-DalPhos,5
[CpPd(allyl)],15 and 1-bromo-2-(phenylethynyl)benzene6 were pre-
pared according to literature procedures. Silver trifluoromethanesul-
fonate (Strem), CyPFtBu-JosiPhos (Solvias), diphenylacetylene
(Aldrich), and 0.5 M solutions of ammonia in 1,4-dioxane (Aldrich)
was added, and the vial was resealed with the cap. The resulting
mixture was stirred magnetically for 1 h at room temperature, during
which time a gray precipitate formed. 31P NMR analysis of the reaction
mixture indicated the consumption of 1 and complete conversion to a
single new phosphorus-containing species (2). The precipitate was
removed by filtration over Celite, the filtrate was triturated with
pentane (2 × 2 mL), and the mixture was concentrated to apparent
dryness, affording the desired product 2 as a yellow powder (50.5 mg
isolated) that was found to contain varying amounts of 1,4-dioxane
(ca. 0.75 equiv), as well as trace amounts of other solvents used in the
synthesis. Our efforts to obtain solvent-free samples of 2 for elemental
analysis were thwarted by the loss of the ammine ligand from 2 (to
1
give 3) upon prolonged exposure to vacuum. H NMR (CDCl3): δ
8.07 (dd, J = 8.4, 3.1 Hz, 1H, ArH), 7.87 (m, 1H, ArH), 7.70 (m, 1H,
ArH), 7.65 (d, J = 7.7 Hz, 1H, Pd-ArH), 7.46 (m, 1H, ArH), 7.38−
7.36 (m, 3H, Pd-ArH, Ph), 7.29−7.28 (m, 3H, Ph), 7.07 (td, J = 7.5,
1.3 Hz, 1H, Pd-ArH), 7.00 (m, 1H, Pd-ArH), 4.37 (m, 1H, morph
CH2), 4.13−4.07 (m, 3H, morph CH2), 3.96−3.89 (m, 2H, morph
CH2), 3.33 (m, 1H, morph CH2), 3.20 (m, 1H, morph CH2), 2.82 (br
s, 3H, NH3), 2.42−2.39 (m, 3H, 1-Ad CH2), 2.25−2.23 (m, 3H, 1-Ad
CH2), 2.10 (br s, 6H, 1-Ad CH/CH2), 1.88−1.69 (m, 15H, 1-Ad CH/
CH2), 1.60−1.58 (m, 3H, 1-Ad CH). 13C{1H} NMR (CDCl3): δ
160.9 (d, JPC = 12.8 Hz, aryl Cquat), 148.3 (Pd-aryl Cquat), 138.2 (Pd-
aryl CH), 135.9 (aryl CH), 133.8 (aryl CH), 133.0 (Pd-aryl CH),
131.0 (alkyne Ph CH), 129.4 (alkyne Ph Cquat), 128.8 (alkyne Ph
CH), 128.6 (aryl CH), 127.5 (alkyne Ph CH), 127.1 (m, aryl CH),
126.1 (d, JPC = 29.2 Hz, aryl Cquat), 124.6 (alkyne Ph CH), 123.3 (Pd−
Ar Cquat), 122.1 (aryl CH), 119.6 (aryl CH), 94.5 (alkyne), 90.3
(alkyne), 61.7 (morph CH2), 61.6 (morph CH2), 56.4 (morph CH2),
1
were used as received. H, 13C, and 31P NMR characterization data
were collected at 300 K on a Bruker AV-500 spectrometer operating at
500.1, 125.8, and 202.5 MHz (respectively), with chemical shifts
reported in parts per million downfield of SiMe4 (for 1H and 13C) and
85% H3PO4 in D2O (for 31P). Structural elucidation was enabled
1
1
1
through analysis of H−1H COSY, H−13C HSQC, H−13C HMBC,
and DEPTQ-135 data. In some cases, fewer than expected unique 13C
NMR resonances were observed, despite prolonged acquisition times,
and the OTf signals are not assigned. Elemental analyses were
performed by Canadian Microanalytical Service Ltd., Delta, BC
(Canada) and Midwest Microlab, LLC, Indianapolis, IN (USA).
Synthesis of 1. A vial was charged with a magnetic stir bar, Mor-
DalPhos (112.1 mg, 0.242 mmol), [CpPd(allyl)] (55.3 mg, 0.260
mmol), 1-bromo-2-(phenylethynyl)benzene (186.5 mg, 0.725 mmol),
and THF (2 mL). The vial containing the resulting red-brown reaction
mixture was sealed with a PTFE-lined cap, removed from the
glovebox, and heated at 65 °C for 16 h under the influence of magnetic
stirring, at which time the consumption of Mor-DalPhos and the clean
formation of 1 was confirmed by use of 31P NMR methods. The
resulting slurry was concentrated to dryness in vacuo, washed with
diethyl ether (5 × 2 mL) until the washings remained colorless, and
dried in vacuo to afford 1 as an analytically pure beige powder in 85%
isolated yield (169.1 mg, 0.204 mmol). Anal. Calcd for
C44H51BrNOPPd: C, 63.89; H, 6.21; N, 1.69. Found: C, 63.62; H,
6.19; N, 1.41. Crystals suitable for single-crystal X-ray diffraction
analysis were obtained from vapor diffusion of diethyl ether into a
56.0 (morph CH2), 43.4 (d, JPC = 16.2 Hz, 1-Ad Cquat), 42.8 (d, JPC
=
14.7 Hz, 1-Ad Cquat), 41.3 (1-Ad CH2), 39.6 (1-Ad CH2), 36.3 (1-Ad
CH2), 35.9 (1-Ad CH2), 28.7−28.5 (m, 1-Ad CH). 31P{1H} NMR
(CDCl3): δ 62.6.
Synthesis of 3. In a vial containing a magnetic stir bar, 1 (100.0
mg, 0.121 mmol), and CH2Cl2 (3 mL) was added silver
trifluoromethanesulfonate (34.2 mg, 0.133 mmol), and the resulting
mixture was stirred magnetically for 1 h at room temperature, at which
time complete consumption of 1 and conversion to a new product (3)
was confirmed by use of 31P NMR. The reaction mixture was filtered,
and the resulting filtrate was concentrated and dried in vacuo to afford
a green-yellow solid. The solid was washed with diethyl ether (4 × 2
mL) to afford 3 as a dark yellow powder in 83% yield (89.5 mg, 0.100
mmol). Anal. Calcd for C45H51F3NO4PPdS: C, 60.30; H, 5.74; N, 1.56.
Found: C, 60.55; H, 5.66; N, 1.49. Crystals suitable for X-ray
diffraction analysis were obtained from vapor diffusion of diethyl ether
into a dichloromethane solution of 3. 1H NMR (CDCl3): δ 8.12 (dd, J
= 8.5, 3.5 Hz, 1H, ArH), 7.81 (t, J = 7.5 Hz, 1H, ArH), 7.75 (m, 1H,
ArH), 7.61 (m, 1H, Pd-ArH), 7.56 (m, 1H, ArH), 7.44 (m, 1H, Pd-
ArH), 7.37−7.34 (m, 2H, alkyne Ph), 7.31−7.29 (m, 3H, alkyne Ph),
7.14−7.09 (m, 2H, Pd-ArH), 4.82 (br s, 1H, morph CH2), 4.69 (br s,
1H, morph CH2), 4.23−4.19 (m, 2H, morph CH2), 3.98 (br s, 1H,
morph CH2), 3.86 (br s, 1H, morph CH2), 3.60 (br s, 2H, morph
CH2), 2.42−2.27 (m, 6H, 1-Ad CH2), 2.13 (br s, 6H, 1-Ad CH2/CH),
1.97−1.71 (m, 15H, 1-Ad CH2/CH), 1.61−1.58 (m, 3H, 1-Ad CH2).
13C{1H} NMR (CDCl3): δ 153.8 (m, aryl Cquat), 148.8 (Pd-aryl Cquat),
136.6 (Pd-aryl CH), 135.6 (aryl CH), 134.2 (aryl CH), 133.2 (Pd-aryl
CH), 130.6 (alkyne Ph CH), 129.7 (Pd-aryl Cquat), 128.8−128.4 (aryl
CH and Cquat), 126.8 (d, JPC = 7.5 Hz, aryl CH), 126.5 (Pd-aryl CH),
124.7 (Pd-aryl CH), 122.9 (alkyne Ph Cquat), 121.7 (aryl CH), 119.2
(aryl CH), 93.7 (alkyne Cquat), 90.1 (alkyne Cquat), 70.3 (m, morph
CH2), 55.3 (morph CH2), 54.8 (morph CH2), 43.9 (d, JPC = 16.4 Hz,
1-Ad Cquat), 43.5 (d, JPC = 15.1 Hz, 1-Ad Cquat), 41.2 (1-Ad CH2), 40.0
(1-Ad CH2), 36.0 (1-Ad CH2), 35.6 (1-Ad CH2), 28.6−28.4 (m, 1-Ad
CH). 31P{1H} NMR (CDCl3): δ 80.0.
1
concentrated dichloromethane solution of 1. H NMR (CDCl3): δ
8.18 (dd, J = 8.0, 2.5 Hz, 1H, ArH), 7.87 (m, 1H, ArH), 7.61 (m, 1H,
ArH), 7.56 (d, J = 8.0 Hz, 1H, Pd-ArH), 7.46−7.44 (m, 2H, alkyne
Ph), 7.36 (m, 1H, ArH), 7.28 (m, 1H, Pd-ArH), 7.24−7.18 (m, 3H,
alkyne Ph), 6.97 (m, 1H, Pd-ArH), 6.84 (m, 1H, Pd-ArH), 5.50 (m,
1H, morph CH2), 5.40 (m, 1H, morph CH2), 4.22 (m, 1H, morph
CH2), 3.99−3.92 (m, 2H, morph CH2), 3.85 (m, 1H, morph CH2),
3.10 (m, 1H, morph CH2), 2.91 (m, 1H, morph CH2), 2.48−2.45 (m,
3H, 1-Ad CH2), 2.27−2.26 (m, 3H, 1-Ad CH2), 2.13−2.05 (m, 6H, 1-
Ad CH/CH2), 1.89−1.75 (15H, 1-Ad CH/CH2), 1.59−1.56 (m, 3H,
1-Ad CH). 13C{1H} NMR (CDCl3): δ 160.3 (d, JPC = 12.6 Hz, aryl
Cquat), 145.4 (d, JPC = 5.0 Hz, Pd-aryl Cquat), 138.7 (Pd-aryl CH),
136.0 (aryl CH), 132.5 (aryl CH), 131.6 (Pd-aryl CH), 131.3 (alkyne
Ph Cquat), 131.1 (alkyne Ph CH), 128.8 (d, JPC = 7.5 Hz, aryl CH),
128.2 (alkyne Ph CH), 127.5 (alkyne Ph CH), 127.4 (d, JPC = 27.7 Hz,
aryl Cquat), 126.1 (Pd-aryl CH), 126.0 (d, JPC = 5.0 Hz, aryl CH), 125.0
(Pd-aryl Cquat), 122.7 (Pd-aryl CH), 97.0 (alkyne), 90.0 (alkyne), 62.2
(morph CH2), 61.7 (morph CH2), 56.4 (morph CH2), 55.2 (morph
CH2), 43.4 (1-Ad Cquat), 43.3 (d, JPC = 25.2 Hz, 1-Ad Cquat), 41.3 (1-
Ad CH2), 39.3 (1-Ad CH2), 36.3 (1-Ad CH2), 36.0 (1-Ad CH2),
28.8−28.6 (m, 1-Ad CH2). 31P{1H} NMR (CDCl3): δ 56.3.
Generation of 2. A vial was charged with a magnetic stir bar, 1
(44.2 mg, 0.0534 mmol), and CH2Cl2 (2 mL). The vial was sealed
with a PTFE-lined cap equipped with a septum and transferred out of
the glovebox, and NH3 (0.5 M in 1,4-dioxane, 0.321 mL, 0.160 mmol)
was added via syringe. The solution was stirred briefly and then was
transferred back into the glovebox, at which point the cap was
removed, silver trifluoromethanesulfonate (15.1 mg, 0.0588 mmol)
Generation of 4. A vial charged with a magnetic stir bar, Mor-
DalPhos (75.0 mg, 0.162 mmol), [CpPd(allyl)] (36.1 mg, 0.170
mmol), diphenylacetylene (31.7 mg, 0178 mmol), and THF (1.8 mL)
was removed from the glovebox and heated at 65 °C for 2−4 h, under
the influence of magnetic stirring and with monitoring by use of 31P
NMR techniques. When the consumption of Mor-DalPhos and the
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Organometallics
Article
formation of 4 was observed, the reaction mixture was then
concentrated to dryness in vacuo and the resulting residue was
washed with cold pentane (5 × 2 mL, precooled to −30 °C) and dried
in vacuo to afford the desired product 4 as a light brown powder (41.2
mg isolated). Our efforts to obtain 4 in analytically pure form were
thwarted by the propensity of this material to retain fractional amounts
CH), 131.9 (d, JPC = 5.7 Hz, Pd-aryl CH), 131.8 (alkyne Ph CH),
129.7 (Pd-aryl Cquat), 128.2 (alkyne Ph CH), 128.1 (Pd-aryl CH),
127.6 (alkyne Ph CH), 125.5 (alkyne Ph Cquat), 122.8 (Pd-aryl CH),
97.4 (dd, JPC = 14.2, 6.9 Hz, Cp Cquat), 95.2 (alkyne), 89.6 (alkyne),
73.2 (dd, JPC = 27.5, 10.8 Hz, Cp Cquat), 72.8 (Cp CH), 69.6 (C5H5),
69.3 (d, JPC = 7.4 Hz, Cp CH), 68.3 (d, JPC = 5.3 Hz, Cp CH), 42.6 (d,
JPC = 22.4 Hz, Cy), 38.8 (CMe3), 37.3 (CMe3), 33.5 (d, JPC = 31.5 Hz,
Cy), 32.4 (d, JPC = 4.3 Hz, CHMe), 32.0 (CMe3), 31.1 (d, JPC = 3.9
Hz, CMe3), 29.7 (Cy), 28.3 (Cy), 27.7 (d, JPC = 8.3 Hz, Cy), 27.2 (d,
JPC = 11.1 Hz, Cy), 27.0 (d, JPC = 14.3 Hz, Cy), 26.6 (Cy), 17.9 (d, JPC
= 6.2 Hz, CHMe). 31P{1H} NMR (CDCl3): δ 73.2 (d, JPP = 34.4 Hz),
17.3 (d, JPP = 34.5 Hz).
1
of solvent, despite prolonged exposure to vacuum. H NMR (THF-
d8): δ 7.93−7.90 (m, 2H, ArH), 7.54 (t, J = 7.0 Hz, 1H, ArH), 7.34−
7.33 (m, 5H, ArH), 7.18−7.15 (m, 4H, ArH), 7.03−7.00 (m, 2H,
ArH), 5.28−5.24 (m, 2H, morph CH2), 3.78−3.76 (m, 2H, morph
CH2), 3.15−3.10 (m, 2H, morph CH2), 2.70−2.68 (m, 2H, morph
CH2), 2.12−2.10 (m, 6H, 1-Ad CH2), 1.92−1.89 (m, 6H, 1-Ad CH2),
1.81 (br s, 6H, 1-Ad CH), 1.63 (br s, 12H, 1-Ad CH2). 13C{1H} NMR
(THF-d8): δ 161.8 (d, JPC = 18.9 Hz, aryl Cquat), 136.6 (aryl CH),
133.0 (d, JPC = 15.1 Hz, aryl Cquat), 131.7 (aryl CH), 128.3 (alkyne Ph
CH), 128.1 (alkyne Ph CH), 126.7 (aryl CH), 126.2 (d, JPC = 5.1 Hz,
aryl CH), 124.6 (alkyne Ph CH), 68.3 (morph CH2), 58.9 (morph
CH2), 42.1 (d, JPC = 6.3 Hz, 1-Ad CH2), 39.3 (d, JPC = 5.0 Hz, 1-Ad
Cquat), 37.4 (1-Ad CH2), 29.7 (d, JPC = 9.2 Hz, 1-Ad CH). 31P{1H}
NMR (THF-d8): δ 60.3.
Generation of 5. A vial was charged with a magnetic stir bar,
JosiPhos (56.0 mg, 0.101 mmol), [CpPd(allyl)] (22.5 mg, 0.106
mmol), diphenylacetylene (19.7 mg, 0.111 mmol), and THF (1.2 mL).
The vial containing the resulting red-brown reaction mixture was
sealed with a PTFE-lined cap and was removed from the glovebox and
heated at 65 °C for 2 h, at which time complete conversion to the
desired product (5) was confirmed by use of 31P NMR methods. The
resulting red solution was concentrated to dryness in vacuo, washed
with cold pentane (3 × 2 mL, precooled to −30 °C), and dried in
vacuo to afford an orange powder (64.5 mg isolated). Although we
have thus far not been able to isolate 5 in analytically pure form, due to
the presence of minor unidentified impurities, the NMR character-
ization data obtained from this material are consistent with the target
complex (5, >90% pure on the basis of 31P NMR data); as such, the
crude material obtained was used without further purification. 1H
NMR (THF-d8): δ 7.22−7.20 (m, 2H, Ph), 7.16−7.13 (m, 2H, Ph),
7.09−7.04 (m, 4H, Ph), 6.99 (m, 1H, Ph), 6.89 (m, 1H, Ph), 4.66 (br
s, 1H, Cp CH), 4.52 (br s, 1H, Cp CH), 4.32 (br s, 1H, Cp CH), 4.22
(s, 5H, C5H5), 3.16 (m, 1H, CHMe), 2.50 (m, 1H, Cy), 2.22 (m, 1H,
Cy), 1.98−0.85 (m, 41H, Cy, *CH3, CMe3). 13C NMR (THF-d8): δ
141.5 (m, Ph Cquat), 140.4 (m, Ph Cquat), 128.4 (Ph CH), 128.1 (Ph
CH), 127.9 (Ph CH), 127.8 (Ph CH), 124.7 (d, JPC = 70.4 Hz,
alkyne), 124.6 (Ph CH), 124.0 (Ph CH), 122.3 (d, JPC = 64.1 Hz,
alkyne), 98.0 (dd, JPC = 18.9, 7.5 Hz, Cp Cquat), 75.9 (m, Cp Cquat),
73.3 (Cp CH), 70.0 (m, Cp CH), 69.8 (C5H5), 68.0 (d, JPC = 3.8 Hz,
Cp CH), 39.1 (d, JPC = 13.8 Hz, Cy), 37.8 (CMe3), 36.2 (CMe3), 35.5
(dd, JPC = 16.4, 4.3 Hz, Cy), 35.2 (m, CHMe), 32.1 (d, JPC = 7.8 Hz,
Cy), 31.8 (d, JPC = 8.3 Hz, CMe3), 31.6 (d, JPC = 8.2 Hz, CMe3), 30.6
(Cy), 30.0 (d, JPC = 8.2 Hz, Cy), 28.6−27.2 (m, Cy), 17.7 (d, JPC = 5.3
Hz, CHMe). 31P{1H} NMR (THF-d8): δ 85.7 (d, JPP = 8.1 Hz), 22.4
(d, JPP = 6.1 Hz).
Crystallographic Solution and Refinement Details. Crystallo-
graphic data were obtained at 173( 2) K on a Bruker D8/APEX II
CCD diffractometer using graphite-monochromated Mo Kα (λ =
0.710 73 Å) radiation, employing samples that were mounted in inert
oil and transferred to a cold gas stream on the diffractometer.
Programs for diffractometer operation, data collection, and data
reduction (including SAINT) were supplied by Bruker. Gaussian
integration (face-indexed) was employed as the absorption correction
method for 1·CH2Cl2. The crystal of 3·OEt2 used for data collection
was found to display nonmerohedral twinning; as such, multiscan
(TWINABS) was employed as the absorption correction method.
Both components of the twin were indexed with the program
CELL_NOW (Bruker AXS Inc., Madison, WI, 2004). The second
twin component can be related to the first component by a 3.2°
rotation about the [1,−0.35,−0.14] axis in real space and about the
[−0.71,1/2,1] axis in reciprocal space. Integrated intensities for the
reflections from the two components were written into a SHELXL-97
HKLF 5 reflection file with the data integration program SAINT
(version 7.68A), using all reflection data (exactly overlapped, partially
overlapped and nonoverlapped). The refined value of the twin fraction
(SHELXL-97 BASF parameter) was 0.3651(11). The structures were
solved by use of a Patterson search/structure expansion and refined by
use of full-matrix least-squares procedures (on F2) with R1 based on
2
2
2
2
Fo ≥ 2σ(Fo ) and wR2 based on Fo ≥ −3σ(Fo ). Anisotropic
displacement parameters were employed for all the non-hydrogen
atoms. Disorder involving the triflate counteranion in 3·OEt2 was
identified during the solution process. As a result, the distances within
the disordered triflate ion were restrained as follows: (a) the S1A−
C91A and S1B−C91B distances were constrained to be equal (within
0.03 Å); (b) the F91B−C91B, F92B−C91B, and F93B−C91B
distances were constrained to be equal (within 0.03 Å). All hydrogen
atoms were added at calculated positions and refined by use of a riding
model employing isotropic displacement parameters based on the
isotropic displacement parameter of the attached atom. In the case of
1·CH2Cl2, which crystallizes in the chiral space group P212121, the
near-zero final refined value of the Flack16 absolute structure
parameter (0.021(6)) confirmed that the correct absolute config-
uration had been implemented. Additional crystallographic informa-
tion is provided in the Supporting Information.
Synthesis of 6. A vial was charged with a magnetic stirbar,
JosiPhos (55.5 mg, 0.100 mmol), [CpPd(allyl)] (22.3 mg, 0.105
mmol), 1-bromo-2-(phenylethynyl)benzene (51.4 mg, 0.200 mmol),
and THF (1 mL). The vial containing the resulting red-brown mixture
was sealed with a PTFE-lined cap, removed from the glovebox, and
heated at 65 °C for 16 h, at which time complete conversion to the
desired product (6) was confirmed by use of 31P NMR methods. The
resulting orange slurry was concentrated to dryness in vacuo, washed
with Et2O (10 × 2 mL) until the washings remained colorless, and
dried in vacuo to afford 6 as an orange powder in 90% yield (82.7 mg,
0.090 mmol). Anal. Calcd for C46H61P2FeBrPd: C, 60.16; H, 6.70.
ASSOCIATED CONTENT
* Supporting Information
CIF files giving single-crystal X-ray diffraction data for
1·CH2Cl2 and 3·OEt2. This material is available free of charge
via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*Fax: 1-902-494-1310. Tel: 1-902-494-7190. E-mail: mark.
stradiotto@dal.ca.
■
1
Found: C, 59.87; H, 6.66. H NMR (CDCl3): δ 7.53−7.51 (m, 2H,
Ph), 7.39−7.31 (m, 4H, Ph, Pd-ArH), 7.17 (d, J = 7.6 Hz, 1H, Pd-
ArH), 7.09 (m, 1H, Pd-ArH), 6.85 (t, J = 7.3 Hz, 1H, Pd-ArH), 4.95
(s, 1H, Cp CH), 4.50 (br s, 1H, Cp CH), 4.45 (m, 1H, Cp CH), 4.25
(s, 5H, C5H5), 3.15 (m, 1H, CHMe), 2.67 (m, 1H, Cy), 2.54 (m, 1H,
Cy), 2.46−2.31 (m, 3H, Cy), 2.08 (m, 1H, Cy), 1.91−1.77 (m, 10H,
Cy, CHMe), 1.72−1.09 (m, 27H, Cy, CMe3). 13C{1H} NMR
(CDCl3): δ 160.3 (d, JPC = 118.0 Hz, Pd-aryl Cquat), 138.0 (Pd-aryl
ACKNOWLEDGMENTS
■
We thank the NSERC of Canada (including a Discovery Grant
for M.S. and a Postgraduate Scholarship for P.G.A.), the Killam
Trusts, and Dalhousie University for their generous support of
this work. Dr. Michael Lumsden (NMR-3, Dalhousie) is
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(13) We do not anticipate that the diminished performance of the
Mor-DalPhos/Pd catalyst system in the monoarylation of ammonia
when using Ar*Br in comparison to (for example) PhBr is attributable
to the C−N reductive elimination step, given that the more sterically
demanding Ar* group should promote reductive elimination in a
putative intermediate of the type [(κ2-P,N-Mor-DalPhos)Pd(NH2)
(aryl)]. Nonetheless, we are currently conducting an in-depth kinetic
study regarding the Mor-DalPhos/Pd catalyzed monoarylation of
ammonia with (hetero)aryl (pseudo)halides, including analyses of the
rates of C−X oxidative addition and C−N reductive elimination; we
will report on these studies elsewhere.
(14) Compound 6 was formed as a single isomer on the basis of
NMR spectroscopic data. The stereochemistry assigned for 6 is given
by analogy with the crystallographically characterized analogue [(κ2-
P,P-JosiPhos)Pd(Br)(Ph)], which features Br trans to the PCy2 group:
Roy, A. H.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 8704.
(15) Mitchell, E. A.; Baird, M. C. Organometallics 2007, 26, 5230.
(16) (a) Flack, H. D. Acta Crystallogr. 1983, A39, 876. (b) Flack, H.
D.; Bernardinelli, G. Acta Crystallogr. 1999, A55, 908. (c) Flack, H. D.;
Bernardinelli, G. J. Appl. Crystallogr. 2000, 33, 1143.
thanked for technical assistance in the acquisition of NMR data.
Solvias is thanked for a gift of JosiPhos.
REFERENCES
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2009, 15, 4528. (e) Lundgren, R. J.; Sappong-Kumankumah, A.;
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(11) (a) Selected crystallographic data for 1·CH2Cl2: empirical
formula, C45H53BrCl2NOPPd; formula weight, 912.06; crystal
dimensions (mm3), 0.48 × 0.17 × 0.09; crystal system, orthorhombic;
space group, P212121; a (Å), 10.9036(3); b (Å), 14.6554(4); c (Å),
25.5143(6); V (Å3), 4077.10(18); Z, 4; ρcalcd (g cm−3), 1.486; μ
(mm−1), 1.641; 2θ limit (deg), 55.02 with −14 ≤ h ≤ 14, −19 ≤ k ≤
19, −33 ≤ l ≤ 33; total data collected, 37 022; independent reflections,
9345; Rint = 0.0198; observed reflections, 9018; range of transmission,
2
0.8610−0.5088; data/restraints/parameters, 9345/0/478; R1 (Fo
≥
2σ(Fo )), 0.0282; wR2 (Fo2 ≥ 3σ(Fo )), 0.0849; goodness of fit, 1.076;
largest peak, hole (e Å−3), 1.108, −0.753. (b) Selected crystallographic
data for 3·OEt2: empirical formula, C49H61F3NO5PSPd; formula
weight, 970.42; crystal dimensions (mm3), 0.47 × 0.38 × 0.14; crystal
system, monoclinic; space group, P21/n; a (Å), 10.7231(8); b (Å),
16.1892(12); c (Å), 26.826(2); β (deg), 105.5094(9); V (Å3),
4487.4(6); Z, 4; ρcalcd (g cm−3), 1.436; μ (mm−1), 0.556; 2θ limit
(deg), 55.40 with −13 ≤ h ≤ 13, −0 ≤ k ≤ 21, 0 ≤ l ≤ 34; total data
collected, 11 664; independent reflections, 11 664; observed reflec-
tions, 10 624; range of transmission, 0.9252−0.7812; Ddata/
2
2
2
2
restraints/parameters, 11 664/4/583; R1 (Fo ≥ 2σ(Fo )), 0.0481;
wR2 (Fo2 ≥ 3σ(Fo )), 0.1239; goodness of fit, 1.145; largest peak, hole
2
(e Å−3), 1.992, −0.790.
(12) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
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dx.doi.org/10.1021/om201122q | Organometallics 2012, 31, 1049−1054