Terphenyl(bisamino)phosphines: Electron-rich ligands for gold-catalysis

Article abstract of DOI:10.1039/d0dt02435j

Terphenyl(bisamino)phosphines have been identified as effective ligands in cationic gold(i) complexes for the hydroamination of acetylenes. These systems are related to Buchwald phosphines and their steric properties have been evaluated. Effective hydroamination was noted even at low catalyst loadings and a series of cationic gold(i) complexes has been structurally characterized clearly indicating stabilizing effects through gold-arene interactions.

Full text of DOI:10.1039/d0dt02435j

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DOI: 10.1039/D0DT02435J
Terphenyl(bisamino)phosphines: Electron-rich Ligands for Gold-
Catalysis
Jan-Erik Siewert,a André Schumann,a Malte Fischer,a Christoph Schmidt,a Tobias Taeufer,a and
Received 00th January 20xx,
Accepted 00th January 20xx
Christian Hering-Junghans*a
DOI: 10.1039/x0xx00000x
Terphenyl(bisamino)phosphines have been identified as effective
ligands in cationic gold(I) complexes for the hydroamination of
acetylenes. These systems are related to Buchwald phosphines and
their steric properties have been evaluated. Effective
hydroamination was noted even at low catalyst loadings and a
series of cationic gold(I) complexes has been structurally
characterized clearly indicating stabilizing effects through gold-
arene interactions.
This Work
R
P
Mes
Ar
Mes
R
R
N
R
H
P
R
NR2
NR2
N
R
H
R
R
N
P
P
R
R
R
R
AuCl
MLx
AuCl
AuCl
R
R
C
B
A
D
Figure 1. General metal complexes with Buchwald-type ligands (A), related gold
complexes from the literature (B, C), and synthetic targets of this study (D).
Transition metal catalysis is governed by the influence of
multiple factors; however, most crucial are the following three:
Metals, substrates and ligands.1 Among the plethora of ligands
used in transition metal catalysis phosphines have been
demonstrated to be an invaluable ligand class in a variety of
transformations. Buchwald and co-workers have developed the
so-called Buchwald-type phosphines, which have been shown
to occupy two coordination sites in low-valent Pd-complexes
(Figure 1, A).2-4 In addition to the P-Pd interaction an η1-Pd−Cipso
bonding interaction was found in the complex LPd(dba) (L = 2-
mode at gold is operational. This forces substrates into trans-
position of the ligand, which enhances its electronic effects.
Cationic gold complexes are well suited for the electrophilic
activation of alkynes and their subsequent functionalization
with a variety of nucleophiles.9-11 This preference for alkyne
activation has been attributed to the low LUMO energies of Au-
alkyne complexes, rendering them more electrophilic.12, 13 In
Au(I) catalysis a major drawback is the decay of the gold
catalyst, which results from reduction of the cationic gold
center to Au(0).14 It has been shown that in many of these
transformations electron-rich phosphine ligands outperform
their electron-deficient counterparts. For the intermolecular
amination of alkynes electron-rich phosphines with a 2-
biphenyl moiety are considered superior.15 Comparing the TEP-
values of common Buchwald-type phosphines show that they
(2´,6´-dimethoxybiphenyl)dicyclohexylphos-phine;
dba
=
dibenzylidene-acetone).5 The 2-biphenyl moiety in this ligand
class has allowed to achieve the challenging coupling of aryl
chlorides and extremely hindered aryl boronic acids in Suzuki-
Miyaura cross-coupling reactions. Since their initial synthesis
various Buchwald-type phosphines have been presented and
are now commercially available (e.g. JohnPhos).6
t
do not exceed the donor strength of simple Bu3P,8 and the
In order to access the electronic properties of phosphines
usually Tolman’s cone angle and/or electronic parameter (TPE)
are utilized, allowing to measure direct ligand metal
interactions.7, 8 In contrast to Pd-catalysis (with mostly square
planar complexes), in gold(I)-catalysis the linear coordination
prominent class of N-heterocyclic carbenes (NHCs) are stronger
σ-donor ligands (Figure 1).16 Dielmann and co-workers, as well
as Sundermayer et al. have recently pushed the electron-
donating ability of phosphines beyond their classical endpoint
through P-substitution with N-heterocyclic imines (NHIs)17 or
phosphazenes,18 respectively. In addition, the NHI-
functionalization allows the metal center to engage in
additional interaction with the aryl-substituents in the NNHC
position of the carbene (Figure 1, C).
-
aLeibniz-Institut für Katalyse e.V. Rostock
Albert-Einstein-Straße 29a, 18059 Rostock, Germany.
Terphenyl-groups, of the general formula 2,6-Ar2-C6H3, have
played a leading role in advancing the chemistry of low-valent
main group and transition metal species.19-23 A reagent
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: Synthesis and
characterization of compounds, NMR spectra, crystallographic, and computational
details. CIFs available from the CCDC, deposition numbers 2014543-2014551. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/x0xx00000x{[
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DOI: 10.1039/D0DT02435J
Scheme 1. Two synthetic routes towards terphenyl-substituted
bisaminophoshines 1a (R = Me) and 1b (R = Et).
Figure 2. POV-Ray depiction of the molecular structure of 1a (left) and 2a (right).
Ellipsoids are drawn at 50% probability, 150(2) K. All hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (°) of 1a (left): C1−P1
1.8591(14), P1–N1 1.6827(12), P1–N2 1.6850(13), P1–C1 1.8591(14); N2–P1–N1
107.79(6), N1–P1–C1 108.37(6), N2–P1–C1 97.87(6), C25–N1–C26 112.90(13),
C25–N1–P1 126.32(11), C26–N1–P1 118.37(11), C27–N2–C28 112.66(13), C27–
N2–P1 117.47(10), C28–N2–P1 126.48(10). 2a (right): P1–N2 1.657(4), P1–N1
1.659(4), P1–C1 1.846(4), P1–Au1 2.2366(11), Cl1–Au1 2.3017(14), C16–Au1
3.2839(33), C21–Au1 3.1008(43); N2–P1–N1 108.5(2), N2–P1–C1 113.3(2), N1–
P1–C1 99.33(19); C25–N1–C26 112.1(4), C25–N1–P1 118.2(3), C26–N1–P1
124.0(3), C27–N2–C28 112.5(4), C27–N2–P1 123.4(3), C28–N2–P1 123.5(3); Au1–
P1–C1–C2 -128.2(3).
commonly used to introduce the terphenyl moiety is Ter-Li (Ter
= 2,6-Mes2-C6H3),24 which can be treated with element halides
to access Ter-EXn species.17, 25, 26 In our hands treatment of Ter-
Li with PCl3 often resulted in trace amounts of Ter-H
contaminating the desired Ter-PCl2 product.27 Thus, we were
interested in a way to circumvent the formation of Ter-H.
Ragogna et al. have recently described the successful
preparation of [TerPS]2, a source of monomeric phosphinidine
sulfides.28 [TerPS]2 is synthesized by treating Ter-PCl2 with
S(SiMe3)2. In their study the authors outlined an alternative
route towards Ter-PCl2. Additionally, TerPH2 was shown to form
AuCl complexes in which stabilizing arene-interactions with one
of the flanking mesityl group are detected (Figure 1, B).29
In this contribution we describe the application of the TerPCl2
precursors TerP(NR2)2 [R = Me (1Me), Et (1Et)] as Buchwald-type
phosphine ligands in gold(I)-catalyzed hydroamination
reactions of terminal alkynes (Figure 1, D). The effect of the
amino groups was investigated on a theoretical basis and an
efficient tool for the estimation of the TEPNi-value is presented.
respective ClP(NR2)2 precursors. In the 1H NMR spectrum of 1a
and 1b two signals for the ortho and para CH3-groups of the
mesityl groups in a 2:1 ratio are observed. In 1a a dublet
corresponding to the two NMe2 groups is detected, indicating
C2 symmetry in solution. In 1b a complex multiplet is observed
for the methylene protons in the Et-groups of the NEt2-moiety,
and a triplet for the Me-groups. X-ray quality crystals of 1a and
1b were grown from saturated n-hexane solutions at 5 °C over
a period of 24 h. The phosphorus atoms show a coordination
environment deviating significantly from an ideal trigonal
pyramid [Σ(<P) (1a) 314.03°, (1b) 317.26°, cf. TerPMe231 309.0°,
32
TerPCl2 305.58°], which is further supported by NBO analysis
[wB97XD/6-31g(d,p) level of theory] showing
a 50/50
contribution of 3s and 3p orbitals for the lone pair (LP) on
phosphorus.33 The P−CTer bond lengths are [(1a) 1.8591(14),
(1b) 1.813(11) Å] indicative of P−C single bonds
[Σrcov(P−C) = 1.85 Å].34 The P−N distances [(1a) P1−N1
1.6981(11), P1−N2 1.6942(12) Å; (1b)P1−N1 1.6981(11), P1−N2
1.6942(12); cf. (Me3Si)2NPCl2 P−N 1.6468(8) Å]35 are contracted
[Σrcov(P−N) = 1.82 Å],34 hinting at partial double bond character
through interaction of the N-LPs with the other σ*(P−N) orbitals
as shown through 2nd order perturbation analysis using NBO
with stabilization energies for 1a of 14.5 and 10.2 and for 1b of
18.1 and 9.5 kcal/mol, respectively. The sum of angles at the N
in 1b deviate from the expected trigonal planar coordination
environment, and minimal pyramidalization is observed [Σ(<N1)
= 352.78°].
With the structural analysis of 1a and 1b in hand, the structural
resemblance with Buchwald’s dialkylbiarylphosphines became
evident. These are regarded as privileged ligands in various Pd-
and Au-catalyzed reactions. In analogy to the Buchwald systems
the 2,6-substitution pattern on the central aryl moiety of the
terphenyl-framework, affords a binding pocket about the
phosphorus that would allow for arene interactions of a
Results and discussion
Ragogna and co-workers have recently described a route
towards Ter-PCl2 through aminolysis of Ter-P(NEt2)2 with dry
HCl.28, 30 Consequently, we prepared Ter-P(NR2)2 [R = Me (1a),
Et (1b)] by treatment of isolated Ter-Li with ClP(NR2)2 (R = Me,
Et; an HCl-free P-source) in toluene at ambient temperature
(Scheme 1, reaction 1). In case of 1a, filtration over a celite-
padded frit and removal of the solvent resulted in the isolation
of an analytically pure colourless solid in 67% yield. For 1b, after
stirring for 1.5 h, the solvent was removed and the residue was
extracted with n-hexane, concentrated to incipient
crystallization and standing at 5 °C overnight afforded 1b as an
analytically pure colourless crystalline solid, in a moderate yield
of 40%. We found that consistently higher yields are obtained
by starting from Ter-I. Lithiation of Ter-I with 2.5 M nBuLi (in n-
hexane) in Et2O at 0 °C and subsequent treatment with
ClP(NR2)2 afforded 1a (79%) and 1b (89%) in good isolated yields
(Scheme 1, reaction 2). In addition, this synthetic approach can
be easily scaled and 1b was prepared on a multigram scale.
Ligands 1a and 1b are characterized by 31P NMR signals at 102.5
and 100.2 ppm, respectively, upfield- shifted compared to their
2 | Dalton Trans., 2020, 00, 1-11
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DOI: 10.1039/D0DT02435J
Mes
NR2
Mes
NR2
NR2
(Me2S)AuCl
P
NR2
P
- SMe2
toluene
rt
Au
Cl
2a
2b
)
R = Me ( ), Et (
AgOTf
- AgCl
Ag[X]
- AgCl
CH2Cl2
rt
D = MeCN, Py
rt
Mes
NR2
Mes
NR2
Figure 3. Steric maps of gold complexes 2a (left) and 2b (right).
In 2a and 2b there are close contacts between Au1 and one of
the flanking terphenyl groups [(2a) C21–Au1 3.1008(43); (2b)
C17–Au1 2.9707(20) Å], which is in contrast to the known
complex (TerPMe2)AuCl.29 This stabilizing arene-interaction was
further authenticated through an analysis of the electron
density of an optimized structure at the wB97XD/6-31g(d,p)
level of theory, using the AIM (Atoms in Molecules) approach.40
This showed a line critical point between Au and C21 (2a) and
C17 (2b) , respectively (see ESI for details),41 and supports the
notion that the mesityl group provide meaningful stabilization.
Using the SambVca 2.1 online application the steric properties
of ligands 1a and 1b were analysed (based on the molecular
structures of complexes 2).42 This showed percent buried
volumes (%Vbur) of 48.8% (1Me) and 55.4% (1Et), respectively.
The %Vbur describes how much volume of a sphere centered on
the metal (rsphere = 3.5 Å; dM−L = 2a 2.2366(11); 2b 2.2445(5) Å)
is occupied by the ligand. From the steric maps it is evident that
the flanking mesityl group takes up major space in the SW-
quadrant of the xy-plane perpendicular to the P−Au-axis (Figure
3), while the NMe2 groups occupy less space than the NEt2-
groups, which is clearly reflected in the NE, E and SE quadrants
of the steric maps. This is in the range of JohnPhos (50.9%),
however, exceeds the value of simple phosphines (PPh3 34.5%,
PtBu3 42.4%).43
In a next series of experiments, we investigated the formation
of cationic gold complexes. As an entry 2a and 2b were treated
with AgOTf in benzene and 31P NMR spectroscopy of the
reaction mixtures showed the formation of new species with
singlet resonance at 86.5 ppm and 78.9 ppm, respectively.
Interestingly, the 19F NMR spectrum showed a singlet at −76.6
ppm, which is in agreement with a covalently bound triflate
group (c.f. Ter[Me2(OTf)Si]N-Sb(Cl)Me δ(19F) = −76.95 ppm).35
After removal of AgCl by filtration, concentration to incipient
crystallization, and layering with n-hexane [TerP(NMe2)2]AuOTf
(3a) and [TerP(NEt2)2]AuOTf (3b) were afforded as colourless
solids in 64% and 49% isolated yield, respectively. X-Ray quality
crystals of 3b were obtained from a saturated CH2Cl2 solution
layered with n-hexane after standing at 5 °C for 24 h (Figure 4,
left). The Au−P distance is shorter than in 2a and 2b [(3b)
P1−Au1 2.2187(4) Å], hinting at a more positive Au-center. This
increase is further supported by two close contacts between
gold and one of the flanking mesityl groups [C7−Au1 3.0506(14),
C8−Au1 2.9955(13) Å]. Overall, the metrical parameters are
close to complexes 2a and 2b.
P
NR2
P
NR2
X
Au
O
Au
D
CF3
O
S
O
X = BF4 R = Me (4a)
X = BF4 R = Et (4b)
X = PF6 R = Me (5a)
3a
R = Me ( ), Et (
3b
)
Scheme 2. Synthesis of gold complexes 2 and transformation into 3 and donor-
stabilized complexes 4 and 5a.
coordinated metal with one of the flanking mesityl groups.
Similar systems based on redox-responsive terphenyl-
substituted phosphonites have been recently described by
Breher and co-workers.36 Jones et al. pushed this concept
further by introducing bisbiphenyl phosphines providing
enhanced stability for cationic gold centers.37 In addition, the
steric and electronic properties of related Ar2C6H3-PR2 systems
have been studied in detail.38, 39 Combination of 1a or 1b with
one equivalent of AuCl(SMe2) in CH2Cl2 under the exclusion of
light at room temperature for 1 h, subsequent concentration
and layering with n-hexane afforded 2a (67%) and 2b (91%) in
good to excellent isolated yields as colorless X-ray quality
crystals (Scheme 2). Upon coordination the P atom is minimally
shielded as shown by a 31P NMR shift of 96.7 ppm (2a) and 93.3
ppm (2b), respectively. This trend is also reflected in the
theoretic NMR shifts obtained from GIAO calculations on the
wB97XD/6-31g(d,p)/ECP60MWD level of theory.33 In the 1H
NMR spectrum both complexes show only two signals for the
Me-groups of the terphenyl-moiety, indicating free rotation
about the P−CTer axis on the NMR timescale at room
temperature. SXRD experiments revealed the expected arene-
interactions between the Au(I)-center and one of the ortho-
mesityl groups of the terphenyl moiety. Upon coordination to
AuCl the sum of angles at phosphorus increases [Σ(<P) (2a)
321.13°, (2b) 323.55°, cf. (TerPMe2)AuCl 318.33°]29 and the P−N
bonds are contracted by ca. 2% [(2a) P1−N1 1.659(4) Å, P1−N2
1.657(4) Å; (2b) P1−N1 1.6665(17) Å, P1−N2 1.6604(17) Å] when
compared with the free ligands 1a and 1b. The complexes show
a nearly linear P-Au-Cl arrangement with P−Au distances [(2a)
P1−Au1 2.2366(11); (2b) 2.2445(5) Å; cf. (TerPMe2)AuCl
2.2964(10) Å]29 in the expected range for phosphine gold
complexes.
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Mes
NR2
NR2
P
AgX, light
(i)
Au
Cl
-AgCl
-"Au"
NR2
Cl
R2N
Ag
2a
2b
P
R = Me ( ), Et (
)
Mes
Mes
P
Ag
NR2
NR2
Cl
Mes
NR2
NR2
Figure 4. POV-Ray depiction of the molecular structure of 3b (left) and 4a (right).
Ellipsoids are drawn at 50% probability, 150(2) K. All hydrogen atoms in 4a have
been omitted for clarity. Selected bond lengths (Å) and angles (°) of 3b (left):
C1−P1 1.8632(14), P1–N1 1.6528(13), P1–N2 1.6580(13), P1–Au1 2.2187(4), P1–
O1 2.0948(11), C7−Au1 3.0506(14), C8−Au1 2.9955(13); N2–P1–N1 109.44(7), N1–
P1–C1 115.66(6), N2–P1–C1 100.83(6), C25–N1–C26 115.42(13), C27–N1–P1
123.76(11), C25–N1–P1 120.55(11), C29–N2–C31 115.62(12), C29–N2–P1
124.48(10), C31–N2–P1 119.79(10), O1–Au1–P1 174.42(4). 4a (right): P1–N2
1.6559(18), P1–N1 1.6588(19), P1–C1 1.837(2), P1–Au1 2.2376(5), Au1−N3
2.0431(18), C7–Au1 3.1364(23), C8–Au1 3.0504(24); N2–P1–N1 108.69(10), N2–
P1–C1 101.34(9), N1–P1–C1 113.57(10); C25–N1–C26 112.75(18), C25–N1–P1
122.20(15), C26–N1–P1 123.72(15), C27–N2–C28 112.48(18), C27–N2–P1
117.44(15), C28–N2–P1 125.49(15), N3–Au1P1 174.33(6), C29–N3–Au1 169.5(2);
Au1–P1–C1–C2 47.17(16).
P
AgCl
6a 6b
R = Me ( ), Et ( )
(ii)
CH2Cl2
1a
R = Me ( ), Et (
1b
)
Scheme 3. Serendipitous decomposition of cationic gold complexes into [(1)AgCl]2
dimeric complexes 6 (i) and their rational synthesis from L and AgCl (ii).
crystals that were identified as the neutral silver chloride
complex [(1a)AgCl]2 (6a). We therefore conclude that it is of the
utmost importance to carefully remove any traces of silver
chloride and work in the dark, when preparing cationic gold
complexes, as the formation of the respective ligand silver
chloride complexes might proceed unnoticed and influence
catalytic tests.44 6a and the related complex [(1b)AgCl]2 (6b)
were independently synthesized by combining 1 with AgCl in a
1:1 stoichiometry in CH2Cl2 and continued stirring for 16 h under
the exclusion of light afforded 6a and 6b as colourless air and
moisture stable crystalline solids (Scheme 3). In the 31P NMR
spectra 6a and 6b show two dublets due to coupling with the
To obtain an active catalyst for the hydroamination of alkynes
with anilines, 2a and 2b were treated with AgBF4 in CH3CN and
after filtration, an aliquot was taken for NMR analysis. In the 31
P
NMR spectrum new signals highfield-shifted at 89.7 (4a) and
84.4 ppm (4b), respectively, compared to the starting material
1
were detected. Broad resonances in the H NMR spectrum at
0.98 and 1.46 ppm, respectively, indicate a coordinated CH3CN
molecule, which is further supported by a 19F NMR shift for both
complexes of −150.2 ppm, showing a non-interacting [BF4]−
anion. Colourless X-ray quality crystals of 4a were obtained
from a saturated C6D6 solution and revealed the expected ion-
separated structure with a threefold disordered [BF4]− anion
(Figure 4, right). Additionally, we treated 2a with AgPF6 in
CH2Cl2, added an excess of pyridine and the mixture was stirred
overnight. Upon removal of the solvent and excess pyridine, X-
Ray quality crystals were obtained from a saturated CH2Cl2
solution layered with n-hexane. In analogy to complex 4a the
base adduct, pyridine in this case, of the cationic gold complex
two spin ½ silver isotopes (107Ag and 109Ag) at 99.3 (1J109Ag,P
=
862.3 Hz, 1J107Ag,P = 746.4 Hz) and 94.3 ppm (1J109Ag,P = 864.0 Hz,
1J107Ag,P = 748.9 Hz), respectively. X-ray quality crystals were
grown from saturated acetone solutions in air and 6a and 6b
(Figure 5) crystallize as centrosymmetric dimers.33
was obtained with
a
non-coordinating [PF6]− anion in
[TerP(NMe2)2Au(py)][PF6] (5a). In 4a and 5a the Au-P distances
are similar to complexes 2 [P1−Au1 (4a) 2.2376(5); (5a) 2.247(3)
Å; cf. (TerPMe2)AuCl 2.2964(10) Å] and two contacts with the
flanking mesityl group below 3.1 Å are detected in the base-
stabilized cations. Overall, the structural parameters clearly
show that the terphenyl structural motif gives rise to stabilizing
Au-arene interactions, which should prove beneficial in catalytic
trials, as was shown by Xu and co-workers in terms of complex
stability in intermolecular hydroamination reactions.15
Preparing complexes 3-5, sometimes the formation of a new
species characterized by a dublet of dublets in the 31P NMR
spectrum was noted. This species was only observed if AgCl was
not completely removed during filtration and when the solution
was kept in daylight. In one instance we obtained X-ray quality
Figure 5. POV-Ray depiction of the molecular structure of 6b. Ellipsoids are drawn
at 30% probability, 150(2) K. All hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (°): C1−P1 1.8652(18), P1–N1 1.6701(17),
P1–N2 1.6700(17), P1–Ag1 2.4038(6), Ag1–Cl1 2.5060(6), Ag1–Cl1’ 2.6120(6),
Ag1–Ag1’ 3.6518(7) Å; P1–Ag1–Cl1 135.850(19), Ag1–Cl1–Ag1‘ 91.017(18).
4 | Dalton Trans., 2020, 00, 1-11
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33
The molecular structures show a µ-Cl bridged dimer with a experimental TEP values was noted (Figure 6). Complexes
View Article Online
deltoid Ag2Cl2 core coordinated by two ligands 1a or 1b, were chosen to span from extrDeOmI:e1l0y.103e9/leDc0tDrTo0n2-4r3ic5hJ
respectively. The solid structures of 6a and 6b are closely phosphazenyl phosphines to electron-poor phosphines such as
related to that of [XPhosAg(µ-Cl)]2.45 Complexes with a (Ag-µ- PCl3 and PF3 giving a range of experimental TEPs from 2017.3 to
Cl)2 core comprising a single phosphine ligand on Ag are rare 2110.8 cm−1.7, 8, 17, 18, 32, 49, 50 A linear regression allowed to derive
and restricted to bulky monodentate phosphine ligands, such as the TEPNi values for ligands 1a and 1b of 2059.6 cm−1 and 2053.0
P(NC4H8NMe)3,46 Ph2P(CH2)PPh2C(H)C(O)C6H4Cl,47 and the cm−1, respectively. This is more electron rich than classical PPh3
simple P(Cy)3.48
and approaches the donor strength of IMes, while the more
To further characterize the electronic character of electron rich IAPs and phosphazenyl phosphines are not
terphenyl(bisamino)phosphine ligands DFT calculations were surpassed. Especially 1b is a stronger donor (based on TEPNi)
carried out to determine the theoretical TEP-value (TEPNi,theo) of than PtBu3 and falls in the range of newly developed YPhos
terphenyl(bisamino)phosphines 1. Therefore, the complexes ligands.51 2019 Carmona, Nicasio and co-workers described a
[(1a)∙Ni(CO)3] and [(1b)∙Ni(CO)3] were constructed in silico and series of nickel carbonyl complexes of dialkylterphenyl
their gas-phase structures were optimized at the BP86/def2SVP phosphines, and the A1 mode for [(TerPMe2)Ni(CO)3] was
level of theory and confirmed as minima by frequency detected at 2063 cm−1.39 This illustrates the influence of the
analyses.33
amino groups on phosphorus to render ligands 1a and 1b more
Of the resulting unscaled frequencies, the A1 symmetrical CO electron rich and thus as a class with superior donor properties
stretching mode was chosen for the evaluation of the donor for the gold-catalyzed hydroamination of alkynes.
parameters. To fit the theoretical frequencies to experimental In order to evaluate the catalytic activity of complexes 4a and
values the υtheor.(CO) for eleven different complexes [LNi(CO)3] 4b in the hydroamination of aryl alkynes with anilines we first
were calculated and a linear dependency with respect to their
did a screening of the general reaction conditions, such as
catalyst loading, solvent, temperature and reaction time using
the phenylacetylene, p-toluidine pairing. Monitoring of the
hydroamination between phenylacetylene and p-toluidine with
2 mol% of 4a or 4b in MeCN at 60 °C via NMR spectroscopy
(1,3,5-(OMe)3-C6H3 as internal standard) showed that
conversion plateaued after ca. 6 h, we therefore decided to run
catalytic reactions overnight (ca. 16 h) to take into account
different sterics of the substrates to be used. Variation of the
catalyst loading revealed that no significant drop of conversion
occurs going from 2 mol% to 1 mol% and minimally worse
results were obtained with 0.5 mol%. Catalytic activity ceases
when only 0.1 mol% of 4a or 4b were used as catalyst.
Considering that in many gold-catalyzed transformations
catalyst loadings in excess of 5 mol% are present,9-11 this
catalyst system is competitive with known systems. To further
underline this, complex 4b was compared with
(Me2N)3P
N
N
P
Ph
P
Ph
P
P(NMe2)3
Ph
Ph
Ph
Ph
N
P
N
NMe2
NMe2
C
(Me2N)3P
L1
L2
Mes
Mes
N
iPr
tBu
Dip
Mes
Me
N
N
P
P
tBu
iPr
C
N
N
P
N
N
N
Me
Mes
Mes
Dip
L4
Mes
L5
L6
L3
Ph
Ph
NMe2
NMe2
H
H
F
F
Cl
Ph
P
Me2N
P
H
P
F
P
Cl
P
Cl
L10
L11
L8
L9
L7
[(JohnPhos)Au(CNMe)]BF4
using
the
p-toluidine
phenylacetylene pairing in MeCN at 80 °C and after 2 h GC yields
(vs. biphenyl as internal standard) in excess of 89 % and 84 %,
respectively, were recorded. In contrast, [(Ph3P)Au(NCMe)]BF4
only gave 12 % of the respective imine after 5 h under the same
conditions.33 In a next series of experiments, we changed the
solvent from MeCN to benzene and a minimal drop in
conversion was noted. We therefore chose MeCN for our
substrate scope. Lowering the temperature at optimized
conditions from 60 °C to 40 °C resulted in a consistent drop of
the isolated yield from 78% to 65%. We thus chose 60°C to
evaluate the substrate scope.
With the optimized parameters in hand we tested both,
different anilines and acetylenes (Scheme 4). To investigate the
influence of the steric bulk of the aniline, p-toluidine, Mes-NH2
(Mes = 2,4,6-Me3-C6H2)
and
Dip-NH2
(Dip
=
2,6-
diisopropylphenyl) were tested. Overall, 12 different derivatives
could be synthesized using different aryl-substituted alkynes. It
should be noted that the electron-rich alkynes 4-MeO- and
Figure 6. Diagram showing the correlation between experimental TEPNi-values of
selected complexes [LNi(CO)3] and their corresponding theoretical A1(CO) values
obtained at the BP86/def2SVP level of theory.
This journal is © The Royal Society of Chemistry 20xx
Dalton Trans., 2020, 00, 1-11 | 5
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R1
addition of p-toluidine to 4a. 7a was characterized by
View Article Online
R2
[(L)Au(NCMe)]BF4 (1 mol%)
N
31
multinuclear NMR spectroscopy, showinDgOaI: 10P.10N3M9/DR0DsiTg0n2a4l35aJt
93.8 ppm and a broad signal for the p-toluidine-NH2 at 4.5 ppm
in the 1H NMR spectrum. Using 1mol% of 7a as a catalyst for the
hydroamination of p-toluidine with phenylacetylene at 80 °C,
showed a yield of the desired imine of 72% (GC). This clearly
shows that electron rich ligands favour amine dissociation and
therefore enhance turnover even at low catalyst loadings.
H2NR2
+
MeCN, 16 h
60 °C
R1
iPr
L1 = 1a
L2 = 1b
N
N
N
N
iPr
tBu
L1: 73 %a
L2: 76 %a
L1: 97 %a
L2: 93 %a
L1: 71 %a
L2: 81 %a
L1: 98 %b
L2: 100 %b
Conclusions
iPr
Overall, we report the isolation, spectroscopic and structural
characterization of bulky terphenyl(bisamino)phosphines 1.
These Buchwald-type ligands with flanking mesityl groups have
been shown to possess attractive interactions between thegold
center and one of the flanking mesityl groups, as was
ascertained by determination of the molecular structures of a
series of gold complexes 2, 3, 4 and 5.The percent buried
volume of 1b amounts to ca. 55% and a linear fit of known TEP-
values with their respective gas phase structures (obtained by
DFT studies) revealed that particularly 1b can be classified as an
electron-rich phosphine and their application in the
intermolecular hydroamination of alkynes was tested.
Preparing catalyst solutions by chloride ion abstraction from 2
with AgX salts, sometimes the formation of the respective
dimeric Ag-complexes [(L)Ag-µ-Cl]2 6a and 6b was noted, which
were independently synthesized. This is another example that
AgCl contamination can result in erroneous catalyst screening
results. Screening of the catalytic reaction conditions showed
efficient hydroamination to take place at 60°C in MeCN with a
catalyst loading of 4 of 1 mol% and moderate to excellent yields
were achieved for bulky anilines such as Dip-NH2 and different
phenyl acetylene derivatives. No obvious difference in
performance between ligands 1a and 1b was noted. In
summary, terphenylbisaminophosphines meet the criteria of
N
N
N
N
iPr
tBu
tBu
F3C
F3C
L1: 35 %a
L2: 50 %a
L1: 77 %b
L2: 74 %b
L1: 87 %a
L2: 87 %a
L1: 94 %b
L2: 94 %b
iPr
iPr
N
N
N
N
iPr
iPr
F3C
MeO
MeO
MeO
L1: 99 %b
L2: 100 %b
L1: 73 %a
L2: 92 %a
L1: 77 %b
L2: 90 %b
L1: 94 %b
L2: 100 %b
O
NH2
[AuL1/2(MeCN)]BF4
MeCN, 16 h, 60 °C
+
R = tBu (91%)
silica gel
R
R
R = OMe (87%)
Scheme 4. Substrate scope of the gold-catalysed hydroamination of various aryl alkynes
with anilines of varying bulk. (adenotes isolated yields; bdenotes NMR yields, (MeO)3C6H3
as internal standard)
4-tBu-phenylacetylene could be converted into the respective
imines quantitively as determined by H NMR spectroscopy,
1
efficient
ligands
for
intermolecular
gold-catalyzed
using 1,3,5-(OMe)3-C6H3 as an internal standard. However,
attempts to isolate these electron-rich imines after column
chromatography on silica with n-Hex/EtOAc (4:1) as the eluent,
resulted in the isolation of the corresponding benzophenone
derivatives in good isolated yields (Scheme 4, bottom). The
isolated yields for the hydroamination of phenylacetylene are
generally good, with up to 97% yield for the reaction with Mes-
NH2. Interestingly, for F3C-C6H4-CCH with the yield increases
hydroamination reactions, as they combine strong donor
properties with the 2-biphenyl structural motif, which is needed
to enhance complex stability and dissociation of additives
during catalysis.
Experimental
with the steric demand of the respective aniline and up to 92% General methods
of the respective Dip-substituted imine were isolated. In
All reactions were performed under oxygen- and moisture-free
general, we observed that the isolated yields are usually over
70% and nearly independent of whether 1a or 1b were used as
a ligand. In summary, ligands of the type 1 represent a potent
class of electron-rich Buchwald-type phosphines, which have
proven to be efficient in stabilizing gold(I) complexes for the
intramolecular hydroamination of alkynes. It is known that in
the presence of amines the corresponding amine complexes
[LAu(H2N-R)]X form and inhibit coordination of the alkyne to the
metal. In the presence of a strongly donating ligand, amine
dissociation should be more favourable.52 We therefore
independently synthesized [(1a)Au(NH2-p-Tol)]BF4 (7a) by
conditions under an inert atmosphere of argon using standard
Schlenk techniques or an inert atmosphere glovebox (MBraun
LABstar ECO). Acetonitrile, diethylether, toluene, n-hexane and
dichloromethane were purified with the Grubbs-type column
system “Pure Solve MD-5” and dispensed into thick-walled
Schlenk bombs equipped with Young-type Teflon valve
stopcocks and stored under an atmosphere of argon prior to
use. Benzene was refluxed over Na/benzophenone and freshly
distilled prior to use. Dichloromethane was additionally
refluxed over CaH2 and freshly distilled prior to use Acetonitrile
was additionally stored over molecular sieves (4 Å, 4-8 mesh)
6 | Dalton Trans., 2020, 00, 1-11
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Dalton Transactions
Full Paper
prior to use. C6D6 was refluxed over Na and freshly distilled prior ClP(NMe2)2 (0.930 g, 6.016 mmol, 1.05 eq.) in Et2O (10 mL) was
View Article Online
DOI: 10.1039/D0DT02435J
to use. CDCl3 was refluxed over P4O10 and distilled prior to use. added dropwise at −78 °C. The reaction mixture was slowly
CD2Cl2 was refluxed over P4O10 and distilled onto CaH2 and was warmed to ambient temperature and stirred overnight.
refluxed again and then distilled prior to use.
Afterwards, the solvent was removed under reduced pressure
2,6-Mes2-C6H3-I (Ter-I),53 2,6-Mes2-C6H3-Li (Ter-Li),24 and and the remaining white powder was extracted with toluene
ClP(NEt2)254 have been reported previously and were prepared (65 mL) and filtered using a G4 frit, packed with celite. The
according to modified literature procedures. n-BuLi (2.5 M in n- volume of the clear filtrate was reduced to ca. 4 mL and the flask
hexane, ACROS), ClP(NMe2)2 (99%, Alfa Aesar), AuCl(SMe2) was placed in the freezer (−30 °C) for 48 h. This resulted in clear
(>97%, TCI), AgPF6 (98%, TCI), AgSO3CF3 (≥99%, Sigma Aldrich), colorless blocks of TerP(NMe2)2 (1a, 1.940 g, 4.485 mmol, 79%).
3
AgCl (99 %, Sigma Aldrich), JohnPhos (97%, Sigma Aldrich), PPh3 1H NMR (300 MHz, C6D6): δ = 7.12 (td, JHH = 7.2 Hz,
3
4
(95%, Sigma Aldrich) and AgBF4 (98%, Sigma Aldrich) were 5JHH = 0.7 Hz, 1H, p-C6H3), 6.90 (dd, JHH = 7.2 Hz, JPH = 2.7 Hz,
stored under an argon atmosphere and used as received. 2H, m-C6H3), 6.89 (s (br), 4H, m-CH-Mes), 2.24 (s, 6H, Ar-CH3),
DippNH2 (ABCR, 90%) and MesNH2 (98% Alfa Aesar) were 2.22 (s, 12H, Ar-CH3), 2.21 (d, 3JPH = 8.6 Hz, 12H, NCH3). 13C{1H}
distilled prior to use. Acetylenes PhCCH (98%, Sigma Aldrich), 4- NMR (75 MHz, CDCl3): δ = 144.1, 140.5, 140.4, 135.6 (d, JCP
=
OMe-C6H4-CCH (97 %, Sigma Aldrich), 4-CF3-C6H4-CCH (97% 27.7 Hz), 130.5, 127.8, 127.7, 42.4 (d, 2JCP = 19.5 Hz), 21.4 (d, 5JPC
Sigma Aldrich) and 4-tBu-C6H4-CCH (96%, Acros Organics) were = 5.0 Hz), 21.2. 31P{1H} NMR (122 MHz, C6D6): δ = 103.42. IR
recondensed, degassed three times and stored over sieves (4 Å) (ATR, 32 scans, cm-1): v = 2967 (w), 2915 (w), 2855 (m), 2827
prior to use. Pyridine (99.8%, Sigma Aldrich) was refluxed over (m), 2785 (m), 1608 (w), 1558 (w), 1478 (w), 1443 (m), 1375 (w),
KOH, distilled and stored over molecular sieves (3 Å) prior to 1267 (m), 1197(m), 1059 (w), 979 (m), 964 (s), 848 (s), 809 (m),
use.
773 (m), 755(m), 719 (w), 672 (s), 646 (m), 576 (m), 561 (m), 550
1H, 13C{1H}of , 11B, 19F{1H} and 31P{1H} NMR spectra were (m), 534 (w), 452 (m), 409 (m). MS (ESI-TOF): expected
recorded on BRUKER AV300, AV400 or Fourier300 m/z = 433.2773, found: m/z = 433.2767. EA: calc.: C 77.74, H
spectrometers. All 1H NMR and 13C NMR spectra are referenced 8.62, N6.48, found: C 77.39, H 8.54, N 6.08%.
using the chemical shifts of residual proton solvent resonances
(benzene-d6: δH 7.16, δC 128.06; chloroform-d: δH 7.26, δC Synthesis of TerP(NEt2)2 (1b)
77.16; dichloromethane-d2: δH 5.32, δC 53.84). Chemical shifts
From Ter-Li: Terphenyllithium (0.465 g, 1.428 mmol) was
suspended in toluene (15 mL) and the yellowish suspension was
cooled to −78°C. To this suspension ClP(NEt2)2 (0.360 g,
1.571 mmol) in toluene (5 mL) was added dropwise over a
are reported in ppm (δ) relative to tetramethylsilane. The
31P{1H} NMR spectra were referenced to external 85% H3PO4
and the 19F NMR spectra to CFCl3 as external standard. IR
spectra were recorded in ATR mode on a Bruker Alpha II IR
period of 5 min. The cooling bath was removed, and the mixture
spectrometer under an atmosphere of argon. Elemental
was allowed to warm to ambient temperature over a period of
analysis was done using a Leco Tru Spec elemental analyzer.
1 h. Subsequently, toluene was removed using an external
Melting points were determined on a Mettler-Toledo MP 70
solvent trap, resulting in a yellowish pasty material, which was
then extracted with n-hexane (20 mL) and filtered using a celite-
apparatus. Melting points are uncorrected and were measured
in sealed capillaries under an Ar atmosphere. Mass spectra
padded frit (G4). The filtrate was then concentrated to incipient
were recorded on
a MAT 95XP Thermo Fisher mass
crystallization (ca. 2 mL) and placed in the fridge (ca. 5 °C) for 72
h. This resulted in colorless, X-ray quality blocks of TerP(NEt2)2
(1b, 0.273 g, 0.568 mmol, 40%).
spectrometer in electrospray ionization mode.
Synthesis of TerP(NMe2)2 (1a)
From Ter-I: Ter-I (2.500 g, 5.677 mmol) was suspended in Et2O
From Ter-Li: Terphenyllithium (0.994 g, 3.106 mmol) was and cooled to −78 °C and n-BuLi (2.49 mL, 2.5 M, 1.1 eq.) is
suspended in toluene (80 mL) and the yellowish suspension was added dropwise. The yellowish solution is allowed to warm to
cooled to −78 °C. ClP(NMe2)2 (0.479 g, 3.106 mmol) in toluene ambient temperatures over a period of 1 h and stirred for an
(5 mL) was added dropwise over a period of 5 min. The cooling additional 30 minutes. Then ClP(NEt2)2 (1.311 g, 6.245 mmol,
bath was removed, and the mixture was allowed to warm to 1.1 eq.) in Et2O (10 mL) was added dropwise at −78 °C. The
ambient temperature over a period of 1 h. The resulting white reaction mixture was slowly warmed to ambient temperature
suspension was filtered using a celite-padded frit. The filtrate and was further stirred overnight. Afterwards the volatiles were
was then concentrated to incipient crystallization (ca. 5 mL) and evaporated, n-hexane (70 mL) was added to the solid yellow
placed in the fridge (ca. 5 °C) for 72 h. This resulted in clear residue and the mixture was then filtered using a G4 frit packed
colorless blocks of TerP(NMe2)2 (1a, 0.898 g, 2.078 mmol, 67%). with celite. The volume of the clear filtrate was reduced to ca. 4
X-Ray quality crystals were obtained from a saturated n-hexane mL and the flask was placed in the freezer (−30 °C) for 48 h. This
solution at 5°C after 24 h.
resulted in the deposition of colorless, crystalline blocks, which
From Ter-I: Ter-I (2.500g, 5.677 mmol) was suspended in Et2O were washed with 5 mL of cold n-hexane (−30 °C). TerP(NEt2)2
and cooled to −78 °C and n-BuLi (2.49 mL, 2.5 M, 1.1 eq.) was (1b, 2.472 g, 5.150 mmol, 89%).
3
5
added dropwise over a period of 5 min. The yellowish solution 1H NMR (300 MHz, C6D6): δ = 7.10 (td, JHH = 7.1 Hz, JHP = 0.6
4
was allowed to warm to ambient temperatures over a period of Hz, 1H, p-C6H3), 6.89 (d, JHH = 0.7 Hz, 4H, m-Mes), 6.84 (dd,
1 h and was then stirred for an additional 30 min. Subsequently, 3JHH = 7.1 Hz, 4JPH = 2.6 Hz, 2H, m-C6H3), 2.83-2.46 (m, 8H, NCH2),
This journal is © The Royal Society of Chemistry 20xx
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2.26 (s, 12H, Ar-CH3), 2.24 (s, 6H, Ar-CH3), 0.84 (t, 3JHH = 7.1 Hz,
View Article Online
DOI: 10.1039/D0DT02435J
12H, NCH2CH3). 13C{1H} NMR (75 MHz, C6D6): δ = 144.7 (d, Synthesis of TerP(NMe2)2AuOTf (3a)
JCP =18.38 Hz), 142.1 (d, JCP =34.7 Hz), 141.2 (d, JCP = 3.41 Hz),
In a round-bottomed flask TerP(NMe2)2AuCl (66.5 mg, 0.100
mmol) and AgOTf (25.7 mg, 0.100 mmol) are suspended in 5 mL
benzene under the exclusion of light. The solution was stirred
at room temperature for 2 h and subsequently filtered using a
filter canula. The volume of the filtrate was reduced to ca. 1 mL,
layered with n-hexane (4 mL) and placed in the fridge (5 °C, 72
h). This resulted in the deposition of TerP(NMe)2)2AuOTf (50.1
mg, 0.064 mmol, 64%) as an amorphous powder.
136.2 (d, JCP = 1.33 Hz), 135.7, 130.9, 128.6, 127.98, 45.8 (d, 2JCP
5
3
= 20.4 Hz), 22.0 (d, JCP = 5.5 Hz), 21.2, 15.6 (d, JCP = 4.1 Hz).
31P{1H} NMR (122 MHz, C6D6): δ = 100.24. IR (ATR, 32 scans, cm-
1): v = 2963 (m), 2913 (m), 2864 (m), 2835 (w), 2726 (w), 1610
(w), 1559 (w), 1443 (m), 1371(m), 1327 (w), 1293 (w), 1277 (w),
1189 (m), 1180 (s), 1117 (w), 1074 (w), 1026 (m), 1014 (s), 907
(m), 850 (s), 804 (m), 787 (m), 750 (m), 718 (w), 664 (m), 636
(m), 577 (w), 559 (w), 551 (w), 535 (w), 491 (w), 473 (m), 437
(m). MS (ESI-TOF): expected m/z = 489.3398, found:
m/z = 489.3394, EA: calc.: C 78.65, H 9.28, N 5.73, found: C
78.49, H 9.10, N 5.51%.
3
5
1H NMR (300 MHz, C6D6): δ = 6.95 (td, JHH = 7.6 Hz, JPH = 1.7
Hz, 1H, p-C6H3), 6.91 – 6.82 (m, 4H, m-Mes), 6.62 (dd, 3JHH = 7.6
Hz, 4JPH = 4.3 Hz, 2H, m-C6H3), 2.28 (s, 6H, Ar-CH3), 1.89 (s, 12H,
Ar-CH3), 1.84 (d, JPH = 11.3 Hz, 12H, NCH3). 19F{1H} NMR (282
MHz, C6D6): −76.8. 31P{1H} NMR (122 MHz, C6D6): δ = 86.5.
X-Ray quality crystals of this compound could not be grown.
3
Synthesis of TerP(NMe2)2AuCl (2a)
TerP(NMe2)2 (0.130 g, 0.30 mmol) and ClAu(SMe2) (0.110 g, CHN and MS were not obtained for this compound.
0.30 mmol) were dissolved in dichloromethane (5 mL) under
the exclusion of light (wrap flask with tin foil) and stirred at Synthesis of TerP(NEt2)2AuOTf (3b)
ambient temperature for 1 h. Subsequently, the volume of the
reaction mixture was reduced to ca. 1 mL, layered with n-
hexane (3-5 mL) and placed in the fridge (ca. 5 °C) for 72 h. This
In a round-bottomed flask TerP(NEt2)2AuCl (0.100 g, 0.140
mmol) and AgOTf (0.036 mg, 0.140 mmol) are suspended in
CH2Cl2 (5 mL) and the mixture stirred under the exclusion of
resulted in the deposition of colorless, X-ray quality crystals of
light at room temperature for 1 h. Afterwards the mixture is
[{TerP(NMe2)2}AuCl] (2a, 0.130 g, 0.20 mmol, 66%).
filtered using a filter canula. The volume of the filtrate is
reduced to ca. 1 mL, layered with n-hexane (4 mL) and placed in
the fridge (5 °C, 72 h). This resulted in the deposition of
colorless, X-ray quality crystals of TerP(NEt)2)2AuOTf (0.054 g,
1H NMR (300 MHz, CDCl3): δ = 7.51 (td, 3JHH = 7.1 Hz, 5JHP = 1.6
3
Hz, 1H, p-C6H3), 7.04 (dd, JHH = 7.6 Hz, 4JPH = 4.0 Hz, 2H, m-
6
C6H3), 6.89 (d, JPH = 0.7 Hz, 4H, m-Mes), 2.34 (s, 12H, Ar-CH3),
2.31 (s, 6H, Ar-CH3), 2.06 (s, 12H, NCH3). 13C NMR (75 MHz,
0.069 mmol, 49%).
CDCl3): δ = 145.8 (d, JCP = 12.1 Hz), 138.5 (d, JCP = 5.3 Hz), 137.2
1H NMR (300 MHz, C6D6): δ = 7.02-6.94 (m, 1H, p-C6H3), 6.92 (s,
3
4
, 135.6, 132.0 (d, JCP = 8.4 Hz), 131.4 (d, JCP = 2.0 Hz), 129.0,
41.2 (d, 2JCP = 9.1 Hz), 21.9, 21.2. 31P{1H} NMR (122 MHz, CDCl3):
δ = 96.94. MS (ESI-TOF): expected m/z = 629.2360, found: m/z
= 629.2368. EA: calc.: C 50.57, H 5.61, N 4.21, found: C 50.67, H
5.61, N 4.24%.
4H, m-Mes), 6.62 (dd, 2H, m-C6H3), 2.63-2.44 (m, 8H, NCH2),
2.31 (s, 6H, Ar-CH3), 2.02 (s, 12H, Ar-CH3), 0.76 (t, 3JPH = 7.1 Hz,
12H, NCH2CH3) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ = 146.28
(d, JCP = 12.4 Hz), 139.18 (d, JCP = 5.8 Hz), 138.13, 136.23, 133.12
(d, JCP = 8.6 Hz), 132.25 (d, JCP = 2.4 Hz), 129.5, 128.7, 44.5 (d, J
= 9.6 Hz), 22.3, 21.3, 15.1. 19F{1H} NMR (376 MHz, CD2Cl2):
δ = −76.62 ppm. 31P{1H} NMR (162 MHz, CD2Cl2): δ = 78.89 ppm.
Synthesis of TerP(NEt2)2AuCl (2b)
TerP(NEt2)2 (0.960 g, 2.000 mmol) and ClAu(SMe2) (0.600 g, MS (ESI-TOF): expected m/z
=
834.2506, found:
2.000 mmol) were dissolved in dichloromethane (20 mL) under m/z = TerP(NEt2)2Au 685.2980, AuOTf 345.1763. EA: calc.: C
the exclusion of light (wrap flask with tin foil) and stirred at 47.48, H 5.43, N 3.36, S 3.84, found: C 47.02, H 5.69, N 3.38, S
ambient temperature for 1 h. The solvent was removed in 3.89%.
vacuo, resulting in an off-white solid of TerP(NEt2)2AuCl (2b,
1.313 g, 1.821 mmol, 91%). X-ray quality crystals were obtained Synthesis of [TerP(NMe2)2Au-MeCN]BF4 (4a)
from layering a saturated CH2Cl2 solution with n-hexane (5 °C
Complex 2a (0.030 g, 0.045 mmol) and AgBF4 (0.009 g, 0.045
mmol) combined in a round-bottomed flask, dissolved in
acetontrile (2.5 mL) and stirred under exclusion of light for 30
for 72 h).
1H NMR (300 MHz, C6D6): δ = 6.99 (t (br), 3JHH = 7.5, 1H, p-C6H3),
3
4
6.95 (m, 4H, m-Mes), 6.66 (dd, JHH = 7.5, JPH = 3.9 Hz, 2H,
m-C6H3), 2.59 (q, 3JHH = 7.1 Hz, 4H, NCH2), 2.56 (q, 3JHH = 7.1 Hz,
4H, NCH2), 2.30 (s, 6H, Ar-CH3), 2.09 (s, 12H, Ar-CH3), 0.77 (t,
3JHH = 7.1 Hz, 12H, NCH2CH3). 13C{1H} NMR (101 MHz, C6D6):
δ = 146.1 (d, JCP = 12.1 Hz), 139.6 (d, JCP = 5.2 Hz), 137.4, 135.7,
134.3, 132.4 (d, JCP = 8.0 Hz), 130.9 (d, JCP = 2.1 Hz), 129.7, 44.7
min at room temperature. The solution was then filtered using
a canula fitted with a glass microfiber filter. This mixture was
then dried and extracted with benzene-d6 and filtered into an
NMR-tube equipped with a J-young-type screw cap. X-ray
quality crystals of [TerP(NMe2)2Au-MeCN]BF4 (4a) were
obtained upon standing at room temperature for 48 h.
3
4
(d, JCP = 10.0 Hz), 22.4 , 21.3, 15.3 (d, JCP = 1.9 Hz). 31P{1H}
NMR (122 MHz, C6D6): δ = 93.26. MS (ESI-TOF): expected
m/z = 743.2571, found: m/z = 743.2574. EA: calc.: C 53.30, H
6.29, N 3.88, found: C 53.26, H 6.25, N 3.64. MP (° C): dec. >160
°C.
1H NMR (300 MHz, C6D6) δ = 6.97 (td, 3JHH = 7.6 Hz, 5JPH = 1.7 Hz,
3
1H, p-C6H3), 6.88 (s, 4H, m-Mes), 6.62 (dd, JHH = 7.6 Hz,
3
4JPH = 4.2 Hz, 2H, m-C6H3), 2.27 (s, 6H, Ar-CH3), 2.12 (d, JPH
=
11.3 Hz, 12H, NMe2), 1.93 (s, 12H, Ar-CH3), 0.98 (s, 3H, CH3CN).
8 | Dalton Trans., 2020, 00, 1-11
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19F{1H} NMR (282 MHz, C6D6): −150.24 ppm. 31P{1H} NMR (122 Crystals suitable for single-crystal X-ray diffrVaiecwtiAornticlewOnelirnee
DOI: 10.1039/D0DT02435J
MHz, C6D6): δ = 89.7 ppm.
obtained by slow evaporation of a solution of 6a in acetone.
1H NMR (300 MHz, CDCl3, 298 K): d = 2.04 (s, 24H, o-CH3C6H3),
2.25 (s, 12H, N(CH3)2), 2.28 (s, 12H, N(CH3)2), 2.34 (s, 12H,
p-CH3C6H3), 6.99-7.00 (m, 8H, CHMes), 7.00-7.03 (m, 4H,
m-CHArylP), 7.47-7.51 (m, 2H, p-CHArylP) ppm. 13C{1H} NMR
(75 MHz, CDCl3, 298 K): d = 21.2 (p-CH3C6H3), 21.55 (o-CH3C6H3),
13C NMR, CHN and MS were not obtained for this compound.
Synthesis of [TerP(NEt2)2Au-MeCN]BF4 (4b)
Complex 2b (0.032 g, 0.045 mmol) and AgBF4 (0.009 g, 0.045
mmol) combined in a round-bottomed flask, dissolved in
acetontrile (2.5 mL) and stirred under exclusion of light for 30
min at room temperature. The solution was then filtered using
a canula fitted with a glass microfiber filter. This mixture was
then dried and extracted with benzene-d6 and filtered into an
NMR-tube equipped with a J-young-type screw cap.
2
21.57 (o-CH3C6H3), 41.78 (d, JP,C = 13.5 Hz, N(CH3)2), 41.80 (d,
2JP,C = 13.7 Hz, N(CH3)2), 129.2 (CHMes), 130.9 (p-CHArylP), 131.4
3
(d, JP,C = 5.8 Hz, m-CHArylP), 133.7 (m, Cq,ArylP), 135.2
3
(o-Cq,MesC6H3), 137.4 (p-Cq,MesC6H3), 138.0 (d, JP,C = 6.1 Hz,
Cq,Mes), 144.5 (d, JC,P = 15.3 Hz, o-Cq,ArylP) ppm. 31P{1H} NMR
2
1
1
(122 MHz, CDCl3, 298 K): d = 99.3 (dd, JAg,P = 862.3 Hz, JAg,P
=
1H NMR (300 MHz, C6D6) δ = 6.99 (td, 3JHH = 7.6 Hz, 5JPH = 1.7 Hz,
1H, p-C6H3), 6.94 (s, 4H, m-Mes), 6.60 (dd, JHH = 7.6 Hz,
746.4 Hz) ppm. MS (ESI-TOF): expected: m/z = 1113.3184 [M-
Cl]+; found: m/z = 1113.3202. EA: calculated: C 58.40, H 6.48, N
4.86; found: C 58.56, H 6.96, N 4.34%.
3
4JPH = 4.0 Hz, 2H, m-C6H3), 2.67-2.52 (m, 8H, NCH2CH3) 2.41 (s,
6H, Ar-CH3), 2.01 (s, 12H, Ar-CH3), 1.46 (s, 3H, CH3CN), 0.80 (t,
3JHH = 7.1 Hz, 12H, NCH2CH3). 19F{1H} NMR (282 MHz, C6D6):
−150.22 ppm. 31P{1H} NMR (122 MHz, C6D6): δ = 84.4 ppm.
Single crystal X-ray analysis, 13C NMR, CHN and MS were not
obtained for this compound.
Synthesis of [TerP(NEt2)2AgCl]2 (6b)
AgCl (0.147 g, 1.023 mmol) and TerP(NEt2)2 (0.500 g,
1.023 mmol) were dissolved in 15 mL of dichloromethane under
the exclusion of light (wrap flask with tin foil) and the reaction
mixture was stirred for 16 h at room temperature which was
accompanied by precipitation of slight amounts of solid
material. After canula filtration all volatile components were
removed under vacuum, the residue was washed with n-hexane
(2×5 mL) and dried under vacuum to yield 6b 0.546 g
(0.422 mmol; 83%) as a colorless solid. Crystals suitable for
single-crystal X-ray diffraction were obtained by slow
evaporation of a solution of 6b in acetone.
Synthesis of [TerP(NMe2)2Au-py]PF6 (5a)
TerP(NMe2)2AuCl (0.066 g, 0.1 mmol) and AgPF6 (0.025 g,
0.1 mmol) were dissolved in 5 mL dichloromethane. 10 µL
pyridine was added to the solution and stirred overnight. After
canula filtration the clear solution is reduced to 1 mL, layered
with 5 mL n-hexane and placed in the freezer (−70 °C) for 4 h.
The solvent was removed and the resulting colorless crystals of
[TerP(NMe2)2Au-py]PF6 (0.062 gg, 0.088 mmol, 88%) were dried
in vacuo.
1H NMR (300 MHz, CDCl3, 298 K): d = 0.91 (t, 3JH,H = 7.1 Hz, 24H,
NCH2CH3), 2.10 (s, 24H, o-CH3C6H3), 2.36 (s, 12H, p-CH3C6H3),
2.54-2.79 (m, 16H, NCH2CH3), 6.94-6.97 (m, 4H, m-CHArylP),
7.00-7.01 (m, 8H, CHMes), 7.44-7.48 (m, 2H, p-CHArylP) ppm.
1H NMR (300 MHz,CD2Cl2) δ = 8.15-8.10 (m, 3H, p,m-CH-py),
7.73-7.68 (m, 2H, o-CH-py), 7.67-7.58 (m, 1H, p-CH-Ph), 7.09
1
1
(dd, JHH = 7.6 Hz, JHP = 4.2 Hz, 2H, m-CH-Ph), 6.88 (s, 4H,
m-CH-Ph), 2.40 (s, 6H, NCH3), 2.36 (s, 6H, NCH3), 2.14 (s, 6H, Ar-
CH3), 2.07 (s, 6H, Ar-CH3). 13C NMR (75 MHz, CD2Cl2): δ = 150.95
3
13C{1H} NMR (75 MHz, CDCl3, 298 K): d = 15.1 (d, JP,C = 2.7 Hz,
NCH2CH3) 21.3 (p-CH3C6H3), 21.83 (o-CH3C6H3), 21.84
(o-CH3C6H3), 45.0 (d, JP,C = 17.0 Hz, NCH2CH3), 129.6 (CHMes),
130.6 (p-CHArylP), 131.8 (d, JP,C = 5.5 Hz, m-CHArylP), 133.9 (m,
2
, 146.30 , 146.13 , 142.04 , 138.97 (d, JCP = 5.8 Hz), 137.78 ,
136.82 , 132.76 (d, JCP = 8.8 Hz), 129.26 , 127.10 , 40.81 (d, JCP
8.7 Hz), 22.00 , 21.15. 19F NMR (282 MHz, CD2Cl2): δ = −73.38 (d,
J = 707.6 Hz). 31P NMR (122 MHz, CD2Cl2): δ = 91.49, −144.45
(septet, 1JP-F = 707.6 Hz).
Sufficient CHN analyses for this compound were not obtained,
despite crystals showing no impurities on the basis of H NMR
spectroscopy.33
2
=
3
Cq,ArylP), 135.2 (o-Cq,MesC6H3), 137.7 (p-Cq,MesC6H3), 138.8 (d,
3JP,C = 6.3 Hz, Cq,Mes), 144.5 (m, o-Cq,ArylP) ppm. 31P{1H} NMR
1
(122 MHz, CDCl3, 298 K): d = 94.3 (dd, JAg,P = 864.0 Hz,
1JAg,P = 748.9 Hz) ppm. MS (ESI-TOF): expected: m/z = 1227.4428
[M-Cl]+; found: m/z = 1227.4449. EA: calculated: C 60.81, H
7.18, N 4.43; found: C 60.83, H 7.74, N 4.28 %.
1
Synthesis of [TerP(NMe2)2AgCl]2 (6a)
Synthesis of [TerP(NMe2)2Au(H2N-p-Me-C6H4]2 (7a)
AgCl (0.019 g, 0.129 mmol) and TerP(NMe2)2 (0.056 g,
0.129 mmol) were dissolved in 5 mL of dichloromethane under
the exclusion of light (wrap flask with tin foil) and the reaction
mixture was stirred for 16 h at room temperature, which was
accompanied by precipitation of slight amounts of solid
material. After canula filtration all volatile components were
removed under vacuum, the residue was washed with small
amounts of n-hexane (2×2 mL) and dried under vacuum to yield
6a 0.046 g (0.040 mmol; 62%) as a colorless solid.
Complex 2a (0.100 g, 0.150 mmol) and AgBF4 (0.031 g, 0.159
mmol) were combined in a round-bottomed flask, dissolved in
acetontrile (5 mL) and stirred under exclusion of light for 30 min
at room temperature. The solution was then filtered using a
canula fitted with a glass microfiber filter. To the filtrate p-
toluidene (0.020 g, 0.186 mmol) was added, resulting in the
formation of a white precipitate. The supernatant solution was
removed by canula filtration and the residual off-white solid
triturated with n-pentane and dried in vacuo. This afforded
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5.
6.
T. E. Barder, S. D. Walker, J. R. Martinelli and S. L.
View Article Online
[TerP(NMe2)2Au(H2N-p-Me-C6H4] (7a, 0.095 g, 0.113 mmol,
75%) as a greyish powder.
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1H NMR (300 MHz, CCl3) δ = 7.55 (td, 3JHH = 7.6 Hz, 5JPH = 1.7 Hz,
1H, p-C6H3), 7.09-7.00 (m, 4H, m-C6H3, p-Tol), 6.88 (d, br
3JHH = 8.4 Hz, 2H, p-Tol), 4.50 (br, 2H, p-Tol -NH2), 2.32 (s, 6H, Ar-
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The complex [Au(L)Cl] (0.045 mmol, 1 equiv; L = 1a, 1b) and
AgBF4 (0.045 mmol, 1 equiv) were dissolved in MeCN (2.5 mL)
and stirred under exclusion of light for 30 min at room
temperature and the solution was then filtered using a filter
canula fitted with a glass microfiber filter. This 0.018 M solution
was used as a stock solution. Acetylenes (0.455 mmol) and aryl
amines (0.503 mmol) were weighed in a glovebox and were
dissolved in 1.75 mL MeCN in a vial fitted with a septum screw
cap. Afterwards 0.25 mL of the respective catalyst standard
solutions of was added and stirred for 16 h at 60 °C. The NMR
yields were determined by 1H NMR spectroscopy as an average
of two runs using 1,3,5-MeO-C6H3 as an internal standard. The
characteristic singlet of the CH3 group of the imines that
appears around 2.3 ppm was used for the integration. For the
isolated yields, the products were purified by column
chromatography on silica gel. Spectroscopic data is provided in
the ESI.33
15.
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19.
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24.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
C. H.-J. thanks Prof. M. Beller for his support, the European
Union for funding (H2020-MSCA-IF-2017 792177), the Max
Buchner-Foundation for a Scientific Fellowship and support by
an Exploration Grant of the Boehringer Ingelheim Foundation
(BIS) is acknowledged. We thank our technical and analytical
staff for assistance, especially Dr. Anke Spannenberg for her
support regarding X-ray analysis. Dr. Alexander Villinger is
acknowledged for assistance with the X-ray analysis of 4a. Dr.
Jonas Bresien is kindly acknowledged for help with vibrational
spectroscopy and fruitful discussions on DFT calculations.
29.
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31.
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Experimental, computanional, and details on the X-ray
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Synopsis
Simple terphenyl(bisamino)phosphines are strong
donors and can be utilized as ligands in Au(I)-catalyzed
intramolecular hydroamination of alyknes.
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