Exploring the Influence of Phosphine Ligation on the Gold-Catalyzed Hydrohydrazination of Terminal Alkynes at Room Temperature

Article abstract of DOI:10.1021/acs.organomet.7b00373

The synthesis and/or NMR/X-ray characterization of a new series of (L)AuCl complexes is reported, featuring BippyPhos, AdJohnPhos, silyl ether based ligands including OTips-DalPhos, and PAd-DalPhos. These complexes, along with previously reported analogue

Full text of DOI:10.1021/acs.organomet.7b00373

Article
pubs.acs.org/Organometallics
Exploring the Influence of Phosphine Ligation on the Gold-Catalyzed
Hydrohydrazination of Terminal Alkynes at Room Temperature
Nicolas L. Rotta-Loria,† Alicia J. Chisholm,† Preston M. MacQueen,† Robert McDonald,‡
Michael J. Ferguson,‡ and Mark Stradiotto*,†
†Department of Chemistry, Dalhousie University, 6274 Coburg Road, P.O. Box 15000, Halifax, Nova Scotia B3H 4R2, Canada
‡X-Ray Crystallography Laboratory, Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
S
* Supporting Information
ABSTRACT: The synthesis and/or NMR/X-ray characterization of a new series of
(L)AuCl complexes is reported, featuring BippyPhos, AdJohnPhos, silyl ether based
ligands including OTips-DalPhos, and PAd-DalPhos. These complexes, along with
previously reported analogues featuring cataCXium-A, tBuJohnPhos, and Mor-
DalPhos, were screened as precatalysts using LiB(C6F5)4·2.5Et2O as an activator in
the hydrohydrazination of terminal aryl alkynes with hydrazine hydrate under
unprecedentedly mild conditions (25 °C, 1 mol % Au). The precatalyst
(cataCXium-A)AuCl proved to be particularly effective in such transformations,
demonstrating useful scope.
Scheme 1. Gold-Catalyzed Hydrohydrazination of Terminal
Alkynes with Hydrazine (X = Halide)
INTRODUCTION
■
Hydroamination and related additions of N−H bonds across
unsaturated substrates represents an attractive means of
preparing sought-after organic nitrogen compounds in an
atom-economical fashion.1 Given the particularly high
activation barrier associated with the direct addition of N−H
bonds to unactivated carbon−carbon multiple bonds of alkenes
and alkynes,2 the development of catalysts for such trans-
formations has emerged as an important goal in modern
synthetic chemistry. As a result, a diversity of hydroamination
catalyst classes, most notably organometallic variants, have
emerged over the past 20 years, enabling transformations of a
broad spectrum of substrates.1 Notwithstanding such progress,
hydrohydrazination reactions involving parent hydrazine, a
cheap and readily available reagent that is prepared and used on
an industrial scale,3 remain relatively unexplored. A number of
challenges associated with using hydrazine in this and other
metal-catalyzed transformations exist, including unwanted
metal reduction4 leading to potentially inactive aggregates.
Whereas hydrohydrazinations involving hydrazine/hydrazide
derivatives, including in the absence of a metal catalyst,5 have
been demonstrated in a variety of contexts,6 the first
transformation of this type using parent hydrazine was reported
only recently (Scheme 1). In their pioneering 2011 report,
Bertrand and co-workers7 employed a bulky cyclic (alkyl)-
aminocarbene-ligated Au(I) precatalyst in the hydrohydrazina-
tion of alkynes and allenes (typically ≥90 °C, 5 mol % Au).
Whereas these workers later established the utility of anti-Bredt
N-heterocyclic carbene (NHC) ligated Au(I) precatalysts in
room-temperature hydrohydrazinations of terminal alkyl-
substituted alkynes (5 mol % Au),8 efforts to extend this
room-temperature catalysis to terminal aryl alkynes were
unsuccessful. Notably, this substrate limitation was overcome
by Hashmi and co-workers9 in 2014. In employing appropri-
ately substituted saturated abnormal NHCs, these workers
achieved the first and only room-temperature hydrohydrazina-
tions of terminal aryl alkynes (5 mol % Au) and did so using
the more convenient reagent hydrazine hydrate,9 rather than
anhydrous hydrazine.7,8,10 A 2017 report by Mendoza-Espinosa
and co-workers11 focusing on mesoionic carbene ligation
revealed that Au(I) precatalysts outperform Au(III) species in
the hydrohydrazination of terminal aryl alkynes (80 °C, 3 mol
% Au).10 Computational analyses by Ujaque, Lledos
́
, and co-
Received: May 16, 2017
© XXXX American Chemical Society
A
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workers12 support a reaction pathway involving alkyne
activation by cationic (carbene)AuI species in alkyne hydro-
hydrazination chemistry employing parent hydrazine, thereby
reaffirming the importance of employing a halide abstraction
agent as a means of activating a neutral LAuX precatalyst (X =
halide).
Collectively, the aforementioned reports would appear to
suggest that carbene-based ancillary ligation is a prerequisite for
Au-catalyzed alkyne hydrohydrazination with hydrazine,
especially considering the poor performance of PPh3AuCl in
this chemistry.9 In combining our interests in ancillary ligand
design for Au-catalyzed alkyne hydroamination13 and in
developing synthetically useful transformations of parent
hydrazine,14 we sought to test this idea by exploring the
feasibility of employing phosphines in Au-catalyzed alkyne
hydrohydrazination with hydrazine, with the goal of expanding
our appreciation of the ancillary ligand structures that give rise
to efficient catalysts (Scheme 1). Herein we report the results
of our investigation, which establish (L6)AuCl (L6 =
cataCXium-A) as a state of the art precatalyst for such
hydrohydrazinations of terminal aryl alkynes (typically 25 °C, 1
mol % Au, using hydrazine hydrate).
Information) neither are unusual nor vary significantly, with
Au−P (2.23−2.26 Å), Au−Cl (2.28−2.30 Å), and nearly linear
P−Au−Cl linkages (170−179°) observed that are in agreement
with previously reported compounds, including the cataCXium-
A and Mor-DalPhos complexes C615 and C713 and (carbene)-
AuCl complexes8,10 that have been employed previously in
alkyne hydrohydrazination employing hydrazine. The Au−Au
distance (2.9700(3) Å) in C9 is within the common range
observed for aurophilic interactions.16
With a collection of phosphine-ligated Au(I) precatalysts in
hand (i.e., C1−C9), we conducted a competitive screen
involving the hydrohydrazination of phenylacetylene with
hydrazine hydrate to give 1, employing LiB(C6F5)4·2.5Et2O
as a halide abstraction agent under mild conditions (4 h, 25 °C,
1 mol % precatalyst; Scheme 3). While most of the precatalysts
surveyed afforded low consumption of the starting materials
and ≤20% conversion to 1, C5 and C6 both afforded high
conversion to the target hydrazine product, with C6 proving to
be marginally superior. The success of C5 and C6 in enabling
this reaction is noteworthy, given that Bertrand8 and Hashmi9
have each demonstrated the inability of otherwise effective
(carbene)AuCl complexes to catalyze such a transformation
under these mild conditions. Furthermore, the observation that
the Mor-DalPhos ligated precatalyst C7 is highly effective for
the stereoselective hydroamination of internal aryl alkynes with
dialkylamines13 but is ineffective for the test transformation
leading to 1 (Scheme 3) confirms that the ancillary ligand plays
an important role in determining the successful outcome of Au-
catalyzed hydroaminations in a substrate-dependent manner.
Having discovered that the cataCXium-A ligated complex C6
is a capable precatalyst for the hydrohydrazination of
phenylacetylene with hydrazine hydrate under mild conditions
(4 h, 25 °C, 1 mol % Au), we then turned our attention to
examining the scope of reactivity (Scheme 4). A range of
substituted terminal aryl alkynes were accommodated success-
fully under these conditions; p-alkyl, -methoxy, and -halide
substituents were well tolerated and the desired product in each
case was generated in high yield (2−6, 87−98%). While the
presence of an o-amino group within the phenylacetylene
framework did somewhat inhibit conversion, the successful
formation of 8 (52%) was nonetheless achieved at room
temperature. Conversely, the p-trifluoromethyl-substituted
phenylacetylene substrate leading to 7 proved to be particularly
challenging, requiring more forcing conditions in order to
achieve suitable conversion (94%; 14 h, 90 °C, 5 mol % Au),
whereas by use of a saturated abnormal NHC ligand this
transformation was enabled under more mild conditions (71%;
7 h, 20 °C, 5 mol % Au).9 Attempts to employ 1-phenyl-2-
trimethylsilylacetylene in place of phenylacetylene afforded high
conversion (87%) to the desilylated product 1. Suitably high
conversion was also achieved when using 3-phenyl-1-propyne
leading to 9 (70%), or terminal (hetero)aryl alkynes based on
pyridine or thiophene, leading to 10 and 11 (98 and 75%,
respectively). Although not explored broadly, the ability of the
C6-based catalyst system to effect hydrohydrazinations of
internal alkynes was established in the transformation of
diphenylacetylene (14 h, 90 °C, 5 mol % Au), leading to 12
(83%).
RESULTS AND DISCUSSION
■
In selecting phosphines to employ in our survey, we envisioned
that sterically demanding ligands might work best in supporting
reactive, low-coordinate, cationic Au(I) centers, in part by
discouraging bimolecular decomposition. With this in mind, the
following ligands were chosen (Scheme 1): BippyPhos (L1);
tBuJohnPhos (L2); AdJohnPhos (L3); OTips-DalPhos (L4)
and the new variant L5; cataCXium-A (L6); Mor-DalPhos
(L7); PAd-DalPhos (L8). This set of ligands was chosen
intentionally to span monophosphines featuring or lacking a
secondary donor moiety (i.e., (hetero)aryl, O, N), as well as a
bisphosphine. From a practical perspective, L1−L8 are all air-
stable and, with the exception of L5, are commercially available.
Whereas (L2)AuCl (C2) and (L7)AuCl (C7) were obtained
from commercial sources, and (L3)AuCl (C3)13 and (L6)AuCl
(C6)15 were prepared using literature methods, the otherwise
new (L)AuCl complexes derived from L1 (C1), L4 (C4), L5
(C5), and L8 (C8) were prepared in high yield either by
displacement of dimethyl sulfide from AuCl(SMe2) or from
HAuCl4·H2O under reducing conditions (Scheme 2, see the
Experimental Section). The presence of two phosphorus atoms
in L8 was exploited in the preparation of the digold species
(L8)(AuCl)2 (C9).
Each of the new complexes reported herein was identified on
the basis of NMR and elemental analysis data, as well as single-
crystal X-ray diffraction data (Figure 1); X-ray data for C3 are
also provided. The metrical parameters found within the solid-
state structures of these complexes (Table S1 in the Supporting
a
Scheme 2. Synthesis of Gold Precatalysts
CONCLUSIONS
■
In summary, the results of a screening process involving a
crystallographically characterized series of phosphine-ligated
and LiB(C6F5)4·2.5Et2O-activated (L)AuCl precatalysts in the
a
Isolated percent yield of analytically pure material provided.
B
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Figure 1. Single-crystal X-ray structures of some gold precatalyst complexes featured in this hydrohydrazination survey, shown with 30% thermal
ellipsoids and with hydrogen atoms omitted for clarity.
the catalyst “tool box” for chemists who seek to apply this
methodology in chemical synthesis.
Scheme 3. Phosphine Ligand Screen in the Room-
Temperature, Gold-Catalyzed Hydrohydrazination of
Phenylacetylene at Low Catalyst Loadings
a
EXPERIMENTAL SECTION
■
General Considerations. Unless otherwise stated, all reactions
were set up inside a nitrogen-filled inert-atmosphere glovebox and
worked up in air using benchtop procedures. When they were used
within the glovebox, solvents were deoxygenated by sparging with
nitrogen gas followed by passage through a double-column solvent
purification system packed with alumina and copper-Q5 reactant
(toluene and benzene), or alumina (dichloromethane) and storage
over activated 4 Å molecular sieves. Ligands L417 and L818 and
complexes C313 and C615 were prepared using literature methods; L4
and L8 are also available from commercial sources. All other materials
including L1, C2, and C7 were used as received from commercial
sources. Column chromatography was carried out using neutral
Silicycle Siliaflash 60 silica (particle size 40−63 μm; 230−400 mesh).
NMR spectra were recorded at 300 K and referenced internally to the
solvent employed. Splitting patterns are indicated as follows: br, broad;
s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. All coupling
constants (J) are reported in hertz (Hz). In some cases fewer than
expected independent 13C NMR resonances were observed despite
prolonged acquisition times. Mass spectra were obtained using ion trap
(ESI) instruments operating in positive mode, and GC data were
obtained on an instrument equipped with a SGE BP-5 column (30 m,
0.25 mm i.d.).
a
1
Estimated percent conversion to 1 stated on the basis of H NMR
data using trimethoxybenzene as an internal standard, and isolated
percent yield given in parentheses.
hydrohydrazination of terminal aryl alkynes with hydrazine
hydrate establish (L6)AuCl (L6 = cataCXium-A) as being
highly effective for these reactions. The ability of (L6)AuCl to
effect such transformations under mild conditions (25 °C, 1
mol % Au) distinguishes this precatalyst from previously
reported precatalysts for alkyne hydrohydrazination with
unsubstituted hydrazine, which are exclusively of the type
(carbene)AuCl and operate under somewhat more forcing
conditions (>80 °C and/or 5 mol % Au). In addition to
establishing for the first time the beneficial role of appropriately
configured phosphine ancillary ligands in Au-catalyzed alkyne
hydrohydrazination chemistry, we view our results as expanding
Synthesis of L5. A method directly analogous to that employed in
the preparation of OTips-DalPhos (L4)17 was used, whereby
ClSi(OtBu)3 was used in place of ClSi(iPr)3. The crude product was
purified by column chromatography using a 1/100 (EtOAc/hexanes)
C
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dichloromethane solution of C1. 1H NMR (500 MHz, CDCl3): δ 8.11
(d, J = 2.1 Hz, 1H, PyrH), 7.74−7.72 (m, 2H, ArH), 7.55−7.53 (m,
2H, ArH), 7.39−7.36 (m, 3H, ArH), 7.35−7.27 (m, 4H, ArH), 7.23−
7.16 (m, 4H, Ar−H), 6.79 (d, J = 2.1 Hz, 1H, PyrH), 0.90 (d, J = 16.6
Hz, 9H, tBu), 0.79 (d, J = 16.5 Hz, 9H, tBu). 13C{1H} NMR (125.8
MHz, CDCl3): δ 149.4, 141.5, 140.2, 140.1, 133.0−126.0 (overlapping
signals), 120.0, 114.7, 37.3 (overlapping signals), 29.5 (overlapping
signals). 31P{1H} NMR (202.4 MHz, CDCl3): δ 48.2. Anal. Calcd for
C32H35AuClN4P: C, 52.01; H, 4.77; N, 7.58. Found: C, 51.87; H, 4.62;
N 7.68.
Scheme 4. Substrate Scope for the C6-Catalyzed
Hydrohydrazination of Alkynes
a
Compound C4. The title complex was synthesized via GP2 from L4
and was isolated as a white solid in 91% yield. A single crystal suitable
for X-ray diffraction was obtained via vapor diffusion of pentane into a
1
dichloromethane solution of C4. H NMR (500 MHz, CDCl3): δ
7.73−7.68 (m, 1H, ArH), 7.38−7.28 (m, 1H, ArH), 7.03−6.96 (m,
2H, ArH), 2.23−2.19 (m, 12H, AdH), 2.02 (s, 6H, AdH), 1.85−1.80
(m, 3H, CH(CH3)2), 1.71 (s, 12H, AdH), 1.20−1.18 (m, 18H,
CH(CH3)2). 13C{1H} NMR (125.8 MHz, CDCl3): δ 135.3, 132.1,
120.0, 118.8 (d, JCP = 12.6 Hz), 112.9, 42.5−42.0 (overlapping
signals), 36.3, 28.5 (d, JCP = 16.4 Hz), 18.2, 13.6. 31P{1H} NMR
(202.4 MHz, CDCl3): δ 51.1. Anal. Calcd for C35H55AuClOPSi: C,
53.65; H, 7.08; N, 0. Found: C, 53.49; H, 7.17; N < 0.5.
Compound C5. The title complex was synthesized via GP2 from L5
and was isolated as a white solid in 90% yield. A single crystal suitable
for X-ray diffraction was obtained via vapor diffusion of pentane into a
a
Following GP3 or GP4 (see the Experimental Section) with
estimated conversion to product stated on the basis of 1H NMR
data using trimethoxybenzene as an internal standard. Reaction
employing 1-phenyl-2-trimethylsilylacetylene in place of phenyl-
1
dichloromethane solution of C5. H NMR (500 MHz, CDCl3): δ
b
8.56−8.51 (m, 1H, ArH), 7.56−7.54 (m, 1H, ArH), 7.43−7.40 (m,
1H, ArH), 7.06 (t, J = 7.5 Hz, 1H, ArH), 2.34−2.32 (br m, 6H, AdH),
2.21 (br s, 6H, AdH), 2.02 (br s, 6H, AdH), 1.75−1.69 (br m, 12H,
AdH), 1.40 (s, 27H, OtBu). 13C{1H} NMR (125.8 MHz, CDCl3): δ
156.1, 146.4 (d, JCP = 23.9 Hz), 132.9, 121.2 (d, JCP = 14.4 Hz), 120.6
(d, JCP = 4.7 Hz), 116.0 (d, JCP = 41.5 Hz), 74.9, 42.1 (d, JCP = 23.9
Hz), 41.8, 36.5, 31.9, 28.9 (d, JCP = 10.3 Hz). 31P{1H} NMR (202.4
MHz, CDCl3): δ 97.4. Anal. Calcd for C38H61AuClO4PSi: C, 52.26; H,
7.04; N, 0. Found: C, 52.31; H, 7.44; N, <0.5.
Compound C8. The title complex was synthesized via GP1 from L8
and was isolated as a white solid in 96% yield. A single crystal suitable
for X-ray diffraction was obtained via vapor diffusion of diethyl ether
into a dichloromethane solution of C8. The NMR spectra of L8 and
derived complexes are rendered complex due to a combination of
second order phenomena and dynamic behavior involving the chiral
phosphaadamantyl cage (CgP)/P(o-tolyl)2 moiety.18 1H NMR
(CD2Cl2, 500 MHz): 8.62−8.58 (m, 1H, ArH), 7.65−7.62 (m, 1H,
ArH), 7.55−7.52 (m, 1H, ArH), 7.37−7.31 (m, 4H, ArH), 7.28−7.25
(m, 1H, ArH), 7.16−7.11 (m, 2H, ArH), 6.75 (m, 2H, ArH), 2.90−
2.88 (m, 1H, CgPH), 2.63 (br, 3H, CgPH), 2.33 (s, 3H, CgPH or
ArCH3), 2.12−1.84 (m, 4H, CgPH), 1.57 (s, 2H, CgPH), 1.45 (s, 4H,
CgPH), 1.31 (s, 3H, CgPH or ArCH3), 0.94−0.89 (m, 2H, CgPH).
31P{1H} NMR (CD2Cl2, 202.4 MHz): 9.22 (d, JPP = 207 Hz), 4.92 (d,
JPP = 207 Hz). Anal. Calcd for C30H34AuClO3P2: C, 48.87; H, 4.65; N,
0. Found: C, 48.61; H, 4.73; N < 0.5.
Compound C9. The title complex was synthesized via GP1 from L8
(using 2 equiv of AuCl(SMe2)) and was isolated as a yellow solid in
97% yield. A single crystal suitable for X-ray diffraction was obtained
via vapor diffusion of diethyl ether into a dichloromethane solution of
C9. The NMR spectra of L8 and derived complexes are rendered
complex due to a combination of second order phenomena and
dynamic behavior involving the chiral phosphaadamantyl cage (CgP)/
P(o-tolyl)2 moiety.18 1H NMR (CD2Cl2, 500 MHz): 8.89−8.85 (m,
1H, ArH), 7.82−7.78 (m, 1H, ArH), 7.60−7.55 (m, 3H, ArH), 7.54−
7.51 (m, 1H, ArH), 7.47−7.45 (m, 1H, ArH), 7.29−7.26 (m, 1H,
ArH), 7.22−7.15 (m, 2H, ArH), 6.95−6.91 (m, 1H, ArH), 6.38−6.33
(m, 1H, ArH), 2.89−2.88 (m, 3H, CgPH), 2.80 (s, 3H, CgPH), 2.35−
2.32 (m, 1H, CgPH), 2.05−1.90 (m, 5H, CgPH), 1.60−1.56 (m, 4H,
CgPH and/or ArCH3), 1.49−1.43 (m, 6H, CgPH and ArCH3).
31P{1H} NMR (CD2Cl2, 202.4 MHz): 9.10 (d, JPP = 51 Hz), 4.47 (d,
c
acetylene. Isolated yield of the derived diazine (3′ or 11′; see the
d
Supporting Information). Employing 5 mol % each of C6 and
LiB(C6F5)4·2.5Et2O, 90 °C, 14 h, with isolated yield stated for 12.
eluent system to afford the target product as a white powder (90%).
1H NMR (500 MHz, CDCl3): δ 7.66−7.65 (m, 1H, ArH), 7.27−7.24
(m, 1H, ArH), 7.23−7.19 (m, 1H, ArH), 6.91−6.88 (m, 1H, ArH),
1.98−1.96 (m, 6H, AdH), 1.87−1.86 (m, 12H, AdH), 1.65 (s, 12H,
AdH), 1.37 (s, 27H, tBuH). 13C{1H} NMR (125.8 MHz, CDCl3): δ
160.4 (d, JCP = 22.6 Hz), 137.1, 129.4, 124.6 (d, JCP = 27 Hz), 119.4,
119.2, 73.6, 42.0 (d, JCP = 14 Hz), 37.3, 37.0, 36.8, 31.5, 29.0 (d, JCP
=
8.7 Hz). 31P{1H} NMR (202.4 MHz, CDCl3): δ 11.7. HRMS: m/z
ESI+ found 641.4149 [M + H]+, calculated for C38H62O4PSi 641.4155.
General Procedure for the Synthesis of Au Complexes
(GP1). In air, a 100 mL round-bottom Schlenk flask was charged with
a magnetic stir bar, phosphine ligand (0.41 mmol), and dichloro-
methane (30 mL). To this mixture was added a mixture of
AuCl(SMe2) (0.41 mmol, 120.8 mg) in dichloromethane (50 mL).
The reaction vessel was covered in Al foil to circumvent light-induced
decomposition and was connected to a Schlenk apparatus. The
headspace of the reaction flask was evacuated briefly and back-filled
with nitrogen gas, and magnetic stirring was initiated. After 2 h, the
reaction mixture was concentrated in vacuo. In air, the resulting
residue was washed with acetone (2 × 10 mL) and was dried in vacuo
to afford the target product.
General Procedure for the Synthesis of Au Complexes
(GP2). Under a nitrogen atmosphere, a 50 mL round-bottom Schlenk
flask was charged with a magnetic stir bar, HAuCl4·H2O (1.45 mmol,
0.492 g), and water (1.5 mL), and magnetic stirring was initiated. To
this mixture was added dropwise 2,2′-thiodiethanol (4.4 mmol) over
the course of 0.5 h, during which time the solution changed from an
orange-yellow emulsion to clear and colorless. The Schlenk flask was
then opened, and against a counterflow of nitrogen the phosphine
ligand (1.45 mmol) was added in a single portion, followed by the
addition of ethanol (4.5 mL). The Schlenk flask was then resealed
under nitrogen, and magnetic stirring was continued for 3 h. The
resulting mixture was then filtered in air and was washed with acetone
(2 × 15 mL), diethyl ether (15 mL), and pentane (15 mL). The
remaining solid was then dried in vacuo to afford the target product.
Compound C1. The title complex was synthesized via GP2 from L1
and was isolated as a white solid in 88% yield. A single crystal suitable
for X-ray diffraction was obtained via vapor diffusion of pentane into a
JPP = 51 Hz). Anal. Calcd for C30H34Au2Cl2O3P2: C, 37.15; H, 3.54; N,
0. Found: C, 37.33; H, 3.72; N, <0.5.
General Catalytic Procedure for the Formation of Imines
from Terminal Alkynes (GP3). Unless specified otherwise in the
D
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text, C6 (0.002 mmol) and LiB(C6F5)4·2.5Et2O (0.002 mmol) were
placed as a stock solution in C6D6 (200 μL total delivered) in a screw-
capped vial containing alkyne (0.2 mmol), hydrazine hydrate (0.24
mmol), C6D6 (400 μL), and a small magnetic stir bar. The vial was
sealed with a cap containing a PTFE septum, removed from the
glovebox, and placed in a temperature-controlled aluminum heating
block set at 25 °C, and vigorous magnetic stirring was initiated for 4 h.
General Catalytic Procedure for the Formation of Imines
from Internal Alkynes (GP4). Unless specified otherwise in the text,
C6 (0.02 mmol), LiB(C6F5)4·2.5Et2O (0.02 mmol), alkyne (0.4
mmol), hydrazine hydrate (0.48 mmol), and benzene (1.2 mL) were
placed in a screw-capped vial containing a small magnetic stir bar. The
vial was sealed with a cap containing a PTFE septum, removed from
the glovebox, and placed in a temperature-controlled aluminum
heating block set at 90 °C, and vigorous magnetic stirring was initiated
for 16 h.
Workup Method A (Purification via Chromatography). Upon
completion following GP3 or GP4, the reaction vial was cooled to
room temperature (if needed). The reaction mixture was filtered
through a Celite/silica plug and washed with dichloromethane (3 × 20
mL). From the collected eluent, the solvent was removed in vacuo via
rotary evaporation and the compound was purified by flash column
chromatography on silica gel.
AUTHOR INFORMATION
Corresponding Author
*E-mail for M.S.: mark.stradiotto@dal.ca.
ORCID
Robert McDonald: 0000-0002-4065-6181
Michael J. Ferguson: 0000-0002-5221-4401
Mark Stradiotto: 0000-0002-6913-5160
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the Natural Sciences and Engineering
Research Council of Canada (Discovery Grant RGPIN-2014-
04807 and I2I Grant I2IPJ/485197-2015), the Killam Trusts,
and Dalhousie University for their support of this work. Dr.
Michael Lumsden (NMR-3, Dalhousie) is thanked for ongoing
technical assistance in the acquisition of NMR data, and Mr.
Xiao Feng (Maritime Mass Spectrometry Laboratories,
Dalhousie) is thanked for technical assistance in the acquisition
of mass spectrometric data.
Workup Method B (Procedure for the Preparation of
Samples for NMR Quantification). Upon completion following
GP3 or GP4, the reaction vial was removed from the heating block and
cooled to 4 °C, whereby an internal standard of trimethoxybenzene
(0.04 mmol) was added to the reaction mixture. The reaction mixture
was then filtered through Celite, and the eluent was collected and
subjected to NMR analysis, with yields of product reported relative to
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1
the internal standard on the basis of integrated H NMR signals.
Crystallographic Solution and Refinement Details. Crystallo-
graphic data were obtained between 193 and 213 K on a Bruker D8/
APEX II CCD diffractometer equipped with a CCD area detector
using graphite-monochromated Mo Kα (α = 0.71073 Å) or Cu Kα (α
= 1.54178 Å) radiation employing a sample that was mounted in inert
oil and transferred to a cold gas stream on the diffractometer. Data
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(Gaussian integration; face-indexed) were each performed. Structure
solution by using direct methods, Patterson methods, or intrinsic
phasing was carried out, followed by least-squares refinement on F2.
All non-hydrogen atoms were refined with anisotropic displacement
parameters, while 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. Additional information is contained
in the deposited CIFs (CCDC 1550225−1550228, 1550230−
1550231).
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ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00373.
Complete characterization data for catalytic reaction
products, including NMR spectra, and selected tabulated
crystallographic data (PDF)
Accession Codes
CCDC 1550225−1550228 and 1550230−1550231 contain the
supplementary 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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DOI: 10.1021/acs.organomet.7b00373
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Organometallics
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