Dialkyl(1,3-diarylimidazolin-2-ylidenamino)phosphines: Strongly Electron-Donating, Buchwald-Type Phosphines

Article abstract of DOI:10.1021/acs.organomet.8b00439

The synthesis and properties of a series of strongly electron-donating, sterically demanding dialkyl(1,3-diarylimidazolin-2-ylidenamino)phosphines (IAPs) are reported. Determination of the TEP values shows that the bulky IAPs are better donor ligands than

Full text of DOI:10.1021/acs.organomet.8b00439

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Dialkyl(1,3-diarylimidazolin-2-ylidenamino)phosphines: Strongly
Electron-Donating, Buchwald-Type Phosphines
Tim Witteler, Heidar Darmandeh, Paul Mehlmann, and Fabian Dielmann*
Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Correnstraße 30, 48149 Munster,
̈ ̈ ̈
̈ ̈
Germany
S
* Supporting Information
ABSTRACT: The synthesis and properties of a series of strongly
electron-donating, sterically demanding dialkyl(1,3-diarylimidazolin-2-
ylidenamino)phosphines (IAPs) are reported. Determination of the
TEP values shows that the bulky IAPs are better donor ligands than
classical N-heterocyclic carbenes. The steric profiles of the IAPs in
neutral and cationic gold(I) complexes were analyzed by X-ray
diffraction studies and computational methods, revealing similar
structural features to the Buchwald-type phosphines. The new
phosphines were tested in the gold-catalyzed hydroamination of
phenylacetylene with anilines.
workers.10 Although structural variations among the alkyl
INTRODUCTION
■
groups11 and the biaryl unit gave rise to a large library of
ligands with diverse sterical properties, to date the electron-
donating ability of the Buchwald-type phosphines11b,12 does
not exceed that of tBu3P,13 and N-heterocyclic carbenes
(NHCs) are stronger σ donor ligands (Figure 1).14
The efficiency of transition metal catalysts is often strongly
governed by the electronic and steric parameters of their
ancillary ligands. Among the various types of ligands, tertiary
phosphines (PR3) have the intriguing ability to profoundly
modulate the steric and electronic properties of metal
complexes to which they are bound, which makes them one
of the most versatile ligands to tune the activity, selectivity, and
stability of homogeneous metal catalysts.1 Buchwald’s
dialkylbiarylphosphines2 are a salient example of how subtle
structural variations among the substituents at phosphorus
create critical reactivity differences at the metal center, and
they have found applications in numerous fields of
homogeneous catalysis including palladium-catalyzed cross-
coupling reactions3 and gold(I)-catalyzed transformations.4
Characteristic design features of these monodentate phos-
phines are the strongly σ donating ability and the tunable steric
influence on the metal atom enabled by tailoring of the biaryl
unit. Thus, sterically demanding biaryl groups can facilitate the
formation of mono-phosphine complexes, while stabilizing the
low valent metal center through interaction with the π-
system5two structural features which have been shown to be
crucial, for instance, in Pd-catalyzed aromatic fluorination
reactions.3a,6 Examples for recent developments of Buchwald-
type phosphines include the introduction of a directing group
into the biaryl unit to trigger the antinucleophilic attack of
alkynes.7 Elegant methods for the derivatization of the biaryl
We recently reported an approach to expand the electron-
donating properties of phosphines beyond their classical
boundaries by directly attaching π-donor substituents, namely,
imidazolin-2-ylidenamino groups,15 to the phosphorus atom.16
Figure 1. An overview: TEP values of dialkyl imidazolin-2-
ylidenaminophosphines (IAPs) compared to dialkyl biaryl phos-
phines, PPh3, PtBu3, and classical NHC ligands.
unit were reported by Shi and co-workers via Rh-catalyzed CH
8
́
activation and by Cesar and co-workers using pyrimidinium
betaines as aryl group surrogates.9 Particularly, electron-
withdrawing cationic pyridiniophoshines with Buchwald-type
structural features were developed by Alcarazo and co-
Received: June 27, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Scheme 1. Synthesis of IAPs 3a−d and of [AuCl(IAP)] Complexes 4a−h
a
Reagents and conditions (yields): (a) KOtBu, toluene, −78 °C, and then TMSN3, 110 °C; (b) PCl(R1)2, THF; 3a (99%), 3b (99%), 3c (56%
conversion), 3d (99%); (c) [AuCl(tht)], THF, 21 °C, 4a−g (99%).
The resulting imidazolin-2-ylidenaminophosphines (IAPs)
have been utilized in the Suzuki−Miyaura cross-coupling
reactions of nonactivated aryl chlorides and for the
nucleophilic activation of CO2,17 SO2,18 and SF6.19 With the
intention to develop strongly electron-donating phosphines
with Buchwald-type structural parameters, we herein report the
synthesis and properties of a series of sterically demanding
IAPs and explore their performance in Au-catalyzed hydro-
amination reactions.
metal complexes. IAPs 3a−d are air sensitive and must be
handled under inert conditions. They are soluble in THF,
toluene, and aliphatic solvents. Owing to their high basicity,17a
they rapidly decompose in alcohols, CHCl3, or CH2Cl2. The
31P NMR signals of the phosphorus atoms appear in a range
between 59.4 and 74.5 ppm (Table 1). The molecular
Table 1. 31P NMR Chemical Shifts (ppm) of IAPs and Their
Corresponding [Au(IAP)Cl] Complexes
IAP
δ
31P
complex
δ
31P
RESULTS AND DISCUSSION
■
3a
3b
3c
3d
3e16
3f16
58.3
59.4
74.5
74.0
60.0
73.1
4a
4b
4c
4d
4e
4f
69.6
69.4
80.2
78.9
66.4
44.1
To explore the influence of the substitution around the
phosphorus atom, the phosphines 3a−g depicted in Scheme 1
were selected. Phosphines 3a−e bear two alkyl substituents
(iPr or tBu) and one 1,3-diarylimidazolin-2-ylidenamino
substituent [aryl = mesityl (Mes) or 2,6-diisopropylphenyl
(Dipp)] at the phosphorus atom. We reasoned that the
imidazole-aryl fragment would have similar steric properties to
the biaryl moiety of the Buchwald-type ligands. Finally, to
permit comparison, the phosphines 3f,16 3g,17b 3h,17b and P(2-
biphenyl)tBu2 (JohnPhos)20 were included in our investiga-
tions.
Synthesis of IAPs 3a−d. Phosphines 3a−d were prepared
in a two-step synthesis starting from the imidazolium salts
following the reported procedure for 3e.16 After deprotonation
of the imidazolium salts, the free NHCs were treated with
trimethylsilyl azide. Prolonged heating to 110 °C gave the
imines 2a,21 2b,22 and 2c21 upon N2 elimination in very good
yields. The IAPs were obtained as crystalline, white to off-
white solids in quantitative yield from the reaction of imines
2a−c with dialkylchlorophosphines PR2Cl via elimination of
TMSCl. For phosphine 3c, the steric bulk conferred by the tBu
and Dipp groups seemed to impede full conversion and the
mixture of 2c and 3c was used for the subsequent synthesis of
structure of 3b and 3d was confirmed by X-ray crystal
structure analyses (Figure 2). As expected for Buchwald-type
phosphines, the lone pairs of the phosphorus atoms are
pointing toward the aryl substituent, which may result from the
minimization of the steric repulsion between the aryl
substituents and the alkyl groups at the phosphorus atom.
Electron Donor Property. The Tolman electronic
parameter (TEP)13 of phosphines 3a−d was determined by
measuring the infrared A1 CO stretching frequencies of the
nickel complexes [Ni(CO)3(3a−d)] in dichloromethane using
FT-IR spectroscopy (Table 2). IAPs 3a−e display TEP values
in the range of 2053.0−2044.4 cm−1, significantly lower than
that of PtBu3 (2056.1 cm−1)13 and JohnPhos (2056.1 cm−1).
The contribution of the imidazolin-2-ylidenamino substituents
to the overall electron-donating ability of the phosphines
increases with their ability to stabilize a positive charge in the
imidazole backbone (NsIDipp < NIDipp < NIMes). As a
B
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(2.232−2.251 Å) and Au−Cl (2.310−2.319 Å) bonds lengths,
except for 4f, showing an elongated Au−Cl bond of 2.359 Å,
which may result from the higher donor strength of 4f.
Remarkably, two distinct conformations were found for the
imidazolin-2-ylidenamino substituents (Scheme 2): In con-
former A, one aryl group is directed toward the gold atom,
whereas, in conformer B, both aryl groups are pointing toward
the alkyl substituents at phosphorus. The Au···C distances to
the aryl rings (4a: 3.256 Å, 4d: 3.155 Å) are slightly below the
sum of their van der Waals radii (3.36 Å). Buchwald-type
phosphines typically adopt an orientation in which the second
aryl group of the biaryl moiety faces toward the metal atom
similar to A, which allows stabilizing metal−arene interactions,
with the metal being closest to the ipso carbon. This
orientation can be fixed by substituents at the first phenyl
ring in the ortho position to the dialkylphosphino moiety.3d For
our IAPs, the orientation of the imidazolin-2-ylidenamino
group seems to be governed by the steric repulsion between
the aryl groups at the imidazoline-N atoms and the alkyl
substituents at the phosphorus atom. With increasing steric
bulk of the alkyl groups at the P atom, the CPC angle is
enlarged (104° with iPr, 113° with tBu), which should stabilize
conformer A with respect to B. This, in turn, explains why both
orientations are found among complexes 4a, 4b, and 4e,
containing the smaller iPr substituents.
Figure 2. Solid-state structures of 3b (left) and 3d (right). Hydrogen
atoms omitted for clarity. Only one part of the disordered NPtBu2
moiety in 3d is depicted. Ellipsoids are displayed at 50% probability.
Selected bond lengths [Å] and angles [deg]: 3b: P−N1 1.7083(9),
N1−C1 1.2882(13), P−N1−C1 128.05(8), N1−C1−N2 122.37(9),
N1−C1−N3 133.85(9). 3d: P−N1 1.686(2), N1−C1 1.315(3), P−
N1−C1 124.83(12), N1−C1−N2 114.54(10), N1−C1−N2′
141.40(12).
The steric influence of the phosphine on the gold atom was
further analyzed by calculation of the percent buried volume
(%Vbur),25 a sterical parameter defined as the amount of the
volume of a sphere centered on the metal atom occupied by
atoms of a ligand (Table 3). Examination of these data reveals
that all phosphines (3a, 3b, 3d, 3e) are relatively bulky; the %
Table 2. TEP Values (cm−1) of IAPs 3a−h and Commonly
Used Phosphines and NHCs for Comparison
ligand
TEP
ligand
TEP
a
P(NsIDipp)iPr2 (3a)
P(NIDipp)iPr2 (3b)
P(NIDipp)tBu2 (3c)
P(NIMes)tBu2 (3d)
2053.0
2050.6
2047.8
2044.4
2047.8
2047.5
P(NIMes)2iPr (3f)
2038.6
2038.6
2056.1
2056.1
2068.9
2051.5
b
P(NIiPr)2iPr (3h)
V
bur is in the range of 49.1−58.6% similar to that of JohnPhos
c
PtBu3
d
(50.9%) but much larger than that of PPh3 (29.9%). The
values also confirm that the steric protection of the metal atom
is more pronounced if the phosphine adopts conformation A.
In complex 4f, the gold atom is surrounded by two mesityl
groups, leading to the largest value (64.5%) in this series.
Computational Studies. DFT calculations at the B3LYP-
D3BJ/def2-TZVP level of theory were used to shed light on
the relative stability of the two conformers A and B (Table 4).
For the [Au(IAP)Cl] complexes, the energy difference
between the optimized structures of conformers A and B are
in the range of +10.1 to −21.1 kJ/mol. As expected, conformer
A is more stable for those complexes, which contain bulky tBu
groups at the P atom (4c, 4d), in particular combined with the
flat mesityl substituents at the imidazole-N atoms (4d). In
contrast, conformer B is energetically favored for the
complexes with iPr groups at the P atom and Dipp groups at
the imidazole-N atoms. Worthy of note, for the cationic
gold(I) complexes [Au(IAP)]+, conformer A is significantly
lower in energy (−13.0 to −68.8 kJ/mol), indicating that
metal−arene interactions may indeed stabilize intermediate
low-coordinated complexes containing IAPs ligands (cf.
Figures S58−S67).
JohnPhos
a
c
P(NIMes)iPr2 (3e)
PPh3
b
e
P(NIiPr)iPr2 (3g)
IPr
a
b
c
TEP values from ref 27. TEP values from ref 17b. TEP values from
d
e
ref 13. TEP values calculated according to ref 13. TEP values from
ref 24.
consequence, the IAPs containing NIDipp or NIMes
substituents are stronger donors than classical N-heterocyclic
carbenes (cf. Figure 1).23
Synthesis of [Au(IAP)Cl] Complexes. The IAP ligands
3a−e were reacted with [Au(tht)Cl] in THF at room
temperature for 1 h (Scheme 1), which resulted in the clean
substitution of the tetrahydrothiophene (tht) ligand to form
the corresponding complexes [Au(IAP)Cl] (4a−e) as white
solids. The complexes can be handled in air and are soluble in
polar solvents such as THF, CHCl3, CH2Cl2, and acetonitrile.
The 31P NMR chemical shifts for the dialkyl phosphine
complexes 4a−e appear in a range between 66.4 and 78.9 ppm
(Table 1) and are generally shifted to higher frequency
compared to the corresponding free phosphine. The 31P NMR
signal of complex 4f (44.1 ppm) appears at lower frequency
compared to 3f (73.1 ppm).
Single crystals suitable for X-ray diffraction analysis of 4a,
4b, and 4d−f were obtained by diffusion of n-hexane into a
solution of the gold complex in CH2Cl2 or benzene. The
molecular structures are depicted in Figure 3, and selected
bond lengths and angles are given in Table 3. Unfortunately,
attempts to crystallize complex 4c failed. As expected, the gold
atom adopts a linear coordination sphere with similar Au−P
Synthesis of Cationic [Au(IAP)L]+X− Complexes. Our
attempts to synthesize cationic gold complexes from the
reaction of 4d with 1 equiv of silver triflate (AgOTf) in
CH2Cl2 gave complex 5 (Scheme 3). The incomplete halide
abstraction is a known problem in gold chemistry.26 The 31P
NMR spectrum of the reaction mixture shows a broad signal at
75.7 ppm (4d: 78.9 ppm), indicating dynamic behavior in
solution. To generate an isolable cationic mono gold complex,
pyridine was used as ancillary ligand. Treatment of 4d with
C
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 3. Solid-state structures of complexesFigure 4a, 4b, and 4d−f. Hydrogen atoms are omitted for clarity. Ellipsoids are displayed at 50%
probability.
Table 3. Buried Volume (%Vbur, r = 3.5 Å, d = 2.2 Å, Bondi Radii Scaled by 1.17),25 Selected Bond Lengths (Å), and Bond
Angles (deg) of the Solid-State Structures of Complexes 4a, 4b, and 4d−f
P(NsIDipp)iPr2 (4a)
P(NIDipp)iPr2 (4b)
P(NIMes)tBu2 (4d)
P(NIMes)iPr2 (4e)
P(NIMes)2iPr (4f)
%Vbur
58.6
53.1
58.6
49.1
64.5
Au−Cl
Au−P
P−N
Au···Caryl
PNC
2.3153(3)
2.2367(3)
1.6386(12)
3.2562(14)
134.79(10)
104.11(7)
119.98(12)
132.57(12)
129.98(12)
2.3097(9)
2.2316(9)
1.627(3)
2.3180(7)
2.2505(7)
1.627(2)
3.155(3)
137.6(2)
112.7(2)
123.0(2)
132.5(2)
125.4(2)
2.3118(9)
2.2461(7)
1.620(2)
2.3586(6)
2.2430(6)
1.638(2)/1.622(2)
3.233(3)/3.250(3)
140.3(2)/138.7(2)
130.2(3)
103.9(2)
125.9(3)
129.2(3)
124.5(3)
134.2(2)
103.57(14)
126.6(2)
128.3(2)
125.8(2)
CPC
N1CN3
N1CN2
CN2CAryl
122.1(2)
133.7(2)
125.0(2)
AgSbF6 in a mixture of CH2Cl2 and pyridine, subsequent
phosphine ligands adopt orientation A in both complexes 5
and 6 (Figures 4 and 5). The Au−P bonds in 5 (2.256 Å) and
6 (2.261 Å) are slightly longer than those in 4d (2.251 Å). The
Au−Cl bonds in 5 (2.362/2.372 Å) are significantly longer
(4d: 2.318 Å), owing to the bridging nature of the chloride
ligand in 5. The Au−N4 bond in 6 (2.104 Å) is slightly longer
than in comparable phosphine-gold(I)-pyridine complexes
filtration and addition of n-pentane gave complex 6 as a white
1
solid in 97% yield. The H NMR spectrum confirms the
complete chloride abstraction, and the 31P resonance of 6
appears as a sharp signal at 73.5 ppm (4d: 78.9 ppm).
Colorless crystals were obtained via diffusion of n-hexane into
a CHCl3 solution of 6. X-ray diffraction studies reveal that the
D
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Scheme 2. Two Conformers of Dialkyl-IAP Complexes
a
Conformer A allows stabilizing metal−arene interactions.
Table 4. DFT Results: %Vbur, and Energy Difference (kJ/
mol) between the Optimized Structures of Conformers A
and B of Complexes [Au(IAP)Cl] and [Au(IAP)]+
a
a
b
Figure 4. Molecular structure of 5. Counterion OTf− omitted for
clarity. Selected bond lengths [Å] and angles [deg]: 5: Au1−Cl
2.362(1), Au2−Cl 2.3723(13), Au1−P1 2.256(2), Au2−P2
2.2579(13), P1−N1 1.603(4), P2−N4 1.626(4), Au1···Caryl
3.325(4), Au2···Caryl 3.408(4), CN1P1 146.3(4), CN4P2 142.3(4),
N1CN3 132.9(5), N1CN3 122.7(5), N4CN5 133.0(5), N4CN6
122.1(4).
complex
4a
4b
4c
4d
%Vbur (A)
%Vbur (B)
ΔE298
54.6
54.0
57.6
56.6
50.7
64.4
62.4
67.6
65.4
57.1
56.3
55.8
55.5
50.5
48.0
58.0
62.0
59.1
51.0
7.4
10.1
−6.7
−21.1
−11.3
−24.3
−20.5
−68.8
−57.1
−13.0
4e
[Au(3a)]+
[Au(3b)]+
[Au(3c)]+
[Au(3d)]+
[Au(3e)]+
50.2
a
b
r = 3.5 Å, d = 2.2 Å, bondi radii scaled by 1.17. ΔE = E(A) − E(B).
Scheme 3. Synthesis of Cationic Gold(I) Complexes 5 and 6
Figure 5. Molecular structure of 6. Selected bond lengths [Å] and
angles [deg]: Au−P 2.2613(7), P−N1 1.611(2), Au1···Caryl 3.288(2),
Au−N4 2.104(2), CN1P 144.6(2), N1CN2 121.8(2), N1CN3
133.1(2).
(e.g., [Au(PPh3)(pyr)BF4] 2.073 Å).27 The Au···Caryl distances
in 5 (3.325/3.408 Å) are similar to those in 6 (3.288 Å) and in
4d (3.155 Å).
The best catalytic performance was observed with bulky
electron-rich phosphines such as JohnPhos, which the authors
explained by the fact that these ligands accelerate the
protodeauration and prevent the formation of [AuL2]+
complexes. Thus, we decided to test the new Buchwald-type
phosphines 4a−e in the hydroamination of phenylacetylene
with aniline, 4-methylaniline, and 2,4,6-trimethylaniline (Table
5). For comparison, phosphine 3g containing iPr groups at the
imidazole-N atoms and the very basic phosphines 3f and 3h
were included in our study. JohnPhos and PPh3 serve as
benchmark ligands. The catalyst was generated in situ by
mixing the [Au(L)Cl] complex with AgBF4 and filtering off the
AgCl precipitate. The results show that the most electron-rich
Gold(I)-Catalyzed Hydroamination Reactions. The
ancillary ligands play a crucial role in Au-catalyzed reactions
where very different reactivities and selectivities were often
observed depending on ligands.4b,d,28 A detailed study on how
the steric and electronic properties of phosphines influence
each stage in the gold catalytic cycle was reported by Xu and
co-workers.29 Their analysis on the ligand effects in the
hydroamination of phenylacetylene with aniline suggested that
protodeauration is the rate-determining step and the catalyst
deactivation via formation of [AuL2]+ complexes is significant.
E
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 5. Au-Catalyzed Hydroamination of Phenylacetylene
EXPERIMETAL SECTION
■
with Anilines Using Phosphines 3a−h, PPh3, and JohnPhos
General Remarks. Unless otherwise specified, all manipulations
were performed under an inert atmosphere of dry argon, using
standard Schlenk and drybox techniques. Aniline and 2,4,6-
trimethylaniline were dried and distilled over n-butyllithium, 4-
methylaniline was sublimated, and phenylacetylene was dried passing
a
as Supporting Ligands (Yield in %)
1
through alumina. Dry and oxygen-free solvents were employed. H
and 13C and 31P NMR spectra were recorded at 300 K on Bruker
AVANCE I 400 or Bruker AVANCE III 400 spectrometers. All
spectra were obtained in the solvent indicated. Chemical shifts are
given in parts per million (ppm) relative to SiMe4 (1H, 13C) and 85%
H3PO4 (31P) and were referenced internally to the residual solvent
signals. NMR multiplicities are abbreviated as follows: s = singlet, d =
doublet, t = triplet, sept = septet, m = multiplet, br = broad signal.
Mass spectra were obtained with an Orbitrap LTQ XL (Thermo
Scientific) spectrometer; IR spectra were obtained on a Bruker Vector
22 FT Spectrometer. TMS(NsIDipp) 2a,21 TMS(NIDipp) 2b,22
TMS(NIMes) 2c,21 P(NIMes)iPr2 3e,16 P(NIMes)2iPr 3f,16 P-
(NIiPr)iPr2 3g,17b P(NIiPr)2iPr 3h,17b and [Au(tht)Cl]30 were
prepared following literature procedures. [Au{P(NIiPr)2iPr}Cl] 4h
was previously published with a different synthesis.17b All other
compounds were purchased from commercial sources.
ligand L
Ph-NH2
Mes-NH2
p-Tol-NH2
b
P(NIMes)tBu2 (3d)
JohnPhos
P(NIMes)tBu2 (3d)
99
85
85
75
72
71
67
45
12
13
7
99
98
97
95
99
73
81
66
17
21
30
95
89
86
84
82
87
65
51
21
12
3
P(NsIDipp)iPr2 (3a)
P(NIDipp)tBu2 (3c)
P(NIDipp)iPr2 (3b)
P(NIMes)iPr2 (3e)
P(NIiPr)iPr2 (3g)
P(NIMes)2iPr (3f)
P(NIiPr)2iPr (3h)
PPh3
a
Yields were determined using NMR spectroscopy and refer to the
average of two runs. Complex 6 was used as catalyst.
b
Preparation of P(NsIDipp)iPr2 (3a). Diisopropylchlorophos-
phine (96%, 0.1 mL, 0.60 mmol) was added to a solution of
TMS(NsIDipp) (2a) (284 mg, 0.59 mmol) in THF (3 mL). The
reaction mixture was stirred for 3 h at 70 °C. After removing the
volatiles under reduced pressure, the resulting solid was dried in vacuo
phosphines 3f and 3h are not very efficient in triggering the
reaction. Considering the very different steric bulk of the
ligands, this observation indicates that the alkyne activation
might become rate-determining with these strongly donating
ligands. In contrast, the Buchwald-type phosphines 3a−e are
significantly more efficient than PPh3 or 3g, whereas 3d and
JohnPhos are equally efficient. The highest yields were
obtained by using the isolated cationic complex 6, which
could be due to the absence of silver salts in the isolated
complex. Interestingly, phosphines 3g, 3e, and 3c have the
same TEP values and the reaction yields seem to increase with
the steric bulk of the ligands. Collectively, these findings
indicate that the catalytic efficiency of IAPs in the hydro-
amination of phenylacetylene with anilines is governed by the
structural features rather than electronic parameters of the
phosphines. In this respect, it is interesting to note that the
highest yields were obtained for those IAPs with conformer A,
which allows for stabilizing Au···arene interactions, being
energetically strongly favored for the cationic [Au(IAP)]+
complexes.
1
to afford a white powder of P(NsIDipp)iPr2 in quantitative yield. H
NMR (C6D6, 400.1 MHz) δ (ppm) = 7.24−7.09 (m, 6H, Mes-H);
3
3.52 (s, 4H, 2xCH2); 3.44 (sept, 4H, Dipp-CH); 1.45 (d, JHH = 6.8
3
Hz, 12H, Dipp-CH3); 1.27 (m, 2H, P-CH); 1.23 (d, JHH = 6.8 Hz,
3
3
12H, Dipp-CH3); 0.95 (dd, JPH = 11.4 Hz, JHH = 7.1 Hz, 6H,
3
3
Isopropyl-CH3); 0.85 (dd, JPH = 13.1 Hz, JHH = 7.2 Hz, 6H,
isopropyl-CH3). 31P{1H} NMR (C6D6, 162.0 MHz): δ (ppm) = 58.3.
31P NMR (C6D6, 162.0 MHz): δ (ppm) = 58.3 (m). HRMS (ESI-
TOFMS): m/z [M + H]+ 522.39636 (calculated 522.39771).
Preparation of P(NIDipp)iPr2 (3b). Diisopropylchlorophosphine
(0.34 M in toluene, 1.0 mL, 0.34 mmol) was added to a solution of
TMS(NIDipp) (2b) (161 mg, 0.34 mmol) in THF (2 mL). The
reaction mixture was stirred for 18 h at 70 °C. After removing the
volatiles under reduced pressure, the resulting solid was dried in vacuo
1
to afford a white powder of P(NIDipp)iPr2 in quantitative yield. H
NMR (C6D6, 400.0 MHz): δ (ppm) = 7.24 (t, JHH = 7.7 Hz, 2H, p-
H); 7.14 (d, JHH = 7.7 Hz, 4H, m-H); 5.97 (s, 2H, Imidazole-H); 3.25
(sep, JHH = 6.9 Hz 4H, Dipp-iPr-H); 1.42 (d, JHH = 6.9 Hz, 12H,
Dipp-iPr-CH3); 1.26 (m, 2H, P-iPr-H); 1.18 (d, JHH = 6.9 Hz, 12H,
DippiPr-CH3); 0.96 (dd, JPH = 11.8 Hz, JHH = 7.1 Hz, 12H, P-iPr-
CH3); (dd, JPH = 11.8 Hz, JHH = 7.1 Hz, 12H, P-iPr-CH3); 0.87 (dd,
J
PH = 12.7 Hz, JHH = 7.2 Hz, 12H, P-iPr-CH3). 13C{1H} NMR (C6D6,
CONCLUSION
100.6 MHz): δ (ppm) = 147.98 ((N)2-CN); 129.4; 123.6; 115.1;
16.3 Hz, P-iPr-CH3); 18.1 (d, JPC = 15.2 Hz, P-iPr-CH3). 31P NMR
(C6D6, 161.9 MHz): δ (ppm) = 59.4 (m). 31P{1H} NMR (C6D6,
161.9 MHz): δ (ppm) = 59.4. HRMS (ESI-TOFMS): m/z [MO +
H]+ 536.37660 (calculated 536.37752).
■
29.1; 28.4 (d, JPC = 15.4 Hz, P-iPr-CH); 25.3; 22.8; 19.4 (d, JPC
=
In summary, a series of strongly electron-donating dialkyl(1,3-
diarylimidazolin-2-ylidenamino)phosphines (IAP) have been
prepared. Their structural features and %Vbur resemble those of
Buchwald-type ligands, whereas their donor abilities exceed
those of alkylphosphines and classical NHC ligands. Depend-
ing on the substitution pattern at the phosphorus atom and the
imidazolin-N atoms, two distinct conformers A and B were
observed in Au complexes with these IAP ligands. Conformer
A allows for stabilizing interactions of the metal center with the
π-system of the aryl groups at the imidazolin-N atoms. DFT
calculations reveal that A is energetically most favored for
phosphine 3d, containing the combination of bulky tBu and
flat mesityl substituents. Phosphine 3d has also been identified
as the most efficient ligand in Au-catalyzed hydroamination
reactions, which illustrates the potential of these phosphines in
homogeneous catalysis, especially if electron-rich metal centers
are important.
Preparation of P(NIDipp)tBu2 (3c). TMS(NIDipp) (2b) (474
mg, 1.0 mmol) and PCltBu2 (0.2 mL, 1.0 mmol) were dissolved in 5
mL of THF and heated under reflux for 24 h (prolonged heating for
140 h did not lead to a higher yield). The volatiles were removed and
the residue was dried in vacuo for 2 h at room temperature to afford a
white solid. NMR analysis revealed 56% conversion, which
1
corresponds to 59% 3c by mass. H NMR (C6D6, 400.1 MHz) δ
(ppm) = 7.25−7.12 (m, Dipp-H); 6.01 (s, 2H, N(CH)2N); 3.31
3
3
(sept, JHH = 6.9 Hz, 4H, Dipp-CH); 1.42 (d, JHH = 6.9 Hz, 12H,
Dipp-CH3); 1.42 (d, 3JHH = 6.9 Hz, 12H, Dipp-CH3); 0.96 (d, 3JHP
=
10.8 Hz, 18H, C(CH3)3); 31P NMR (CDCl3, 161.9 MHz): δ (ppm) =
74.5 (m); 31P{1H} NMR (CDCl3, 161.9 MHz): δ (ppm) = 74.5.
Preparation of P(NIMes)tBu2 (3d). Di-tert-butylchlorophos-
phine (0.1 mL, 0.50 mmol) was added to a solution of TMS(NIMes)
F
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2
3
(2c) (210 mg, 0.50 mmol) in THF (2 mL). The reaction mixture was
stirred for 2 h at 80 °C. After removing the volatiles under reduced
pressure, the resulting solid was dried in vacuo to afford a white
powder of P(NIMes)tBu2 in quantitative yield. 1H NMR (C6D6,
400.1 MHz) δ (ppm) = 6.84 (s, 4H, Mes-H); 2.30 (s, 12H, Mes-
CH3); 2.12 (s, 6H); 1.14 (s, 6H, CH3); 1.03 (d, 3JPH = 10.5 Hz, 18H,
tert-butyl-CH). 13C{1H} NMR (C6D6, 100.6 MHz) δ (ppm) = 148.3
(d, JPC = 24 Hz, N2CN); 137.9−137.7 (m); 133.9; 129.1; 115.4; 33.7
(d, JPC = 23 Hz); 28.8 (d, JPC = 16 Hz); 21.2; 18.8 (d, JPC = 2 Hz);
9.1..31P{1H} NMR (C6D6, 162.0 MHz): δ (ppm) = 74.0. 31P NMR
(C6D6, 162.0 MHz): δ (ppm) = 74.0 (m). HRMS (ESI-TOFMS): m/
z [M + H]+ 392.34952 (calculated 392.35021).
General Procedure for [Au(IAP)Cl]. The respective phosphines
(0.50 mmol) and [Au(tht)Cl] (0.50 mmol) were dissolved in THF (2
mL) and stirred for 1 h at room temperature. The volatiles were
removed in vacuo and the resulting white solid was dried for 1 h at
room temperature to afford the gold(I) complexes [Au(IAP)Cl] in
quantitative yield.
CH3); 1.18 (dsept, JPH = 14.0 Hz, JHH = 7.2 Hz, 2H, Isopropyl-
CH); 0.77 (dd, 3JPH = 17.9 Hz, 3JHH = Hz, 6H, Isopropyl-CH3); 0.64
(dd, JPH = 17.0 Hz, JHH = 7.0 Hz, 6H, isopropyl-CH3). 13C{1H}
NMR (C6D6, 100.6 MHz) δ (ppm) = 145.0 (d, JPC = 4.3 Hz, N2CN);
139.3; 136.9; 131.1; 129.4; 117.3; 30.7 (d, JPC = 50.0 Hz); 21.2; 18.6;
17.9 (d, JPC = 3.0 Hz); 17.4; 9.1. 31P{1H} NMR (C6D6, 162.0 MHz):
δ (ppm) = 66.5. 31P NMR (C6D6, 162.0 MHz): δ (ppm) = 66.5 (m).
HRMS (ESI-TOFMS): m/z [M + H]+ 696.25521 (calculated
696.25432).
[Au{P(NIMes)2iPr}Cl] (4f). Prepared according to general
procedure. H NMR (C6D6, 400.1 MHz): δ (ppm) = 6.97 (s, 8H,
Mes-H); 2.29 (s, 12H, CH3); 2.19 (s, 12H, CH3); 2.01 (s, 12H,
CH3); 1.37 (s, 12H, CH3); 0.70 (dd, JPH = 17.5 Hz, JHH = 6.8 Hz,
3H, isopropyl-CH3). 13C{1H} NMR (C6D6, 100.6 MHz) δ (ppm) =
142.0 (d, JPC = 7.6 Hz, N2CN); 138.4; 137.6; 137.5; 132.2; 130.2;
129.7; 116.1; 35.7 (d, JPC = 65.5 Hz); 21.4; 18.8 (d, JPC = 31.8 Hz);
16.9; 9.0. 31P{1H} NMR (C6D6, 162.0 MHz): δ (ppm) = 44.1. 31P
3
3
1
3
3
3
NMR (C6D6, 162.0 MHz): δ (ppm) = 44.1 (sept, JPH = 17.5 Hz).
HRMS (ESI-TOFMS): m/z [M + H]+ 999.43418 (calculated
999.42786).
[Au{P(NsIDipp)iPr2}Cl] (4a). Prepared according to general
1
procedure B. H NMR (CDCl3, 400.1 MHz) δ (ppm) = 7.40 (t,
3JHH = 7.7 Hz, 2H, p-Mes-H); 7.23 (d, 3JHH = 7.7 Hz, 4H, m-Mes-H);
3.95 (s, 4H, CH2); 3.29 (sept, 3JHH = 6.8 Hz, 4H, Mes-CH); 1.35 (dd,
3JHH = 6.8 Hz, J = 57.3 Hz, 24H, CH3); 1.30−1.25 (m, 2H, CH); 0.76
[Au{P(NIiPr)iPr2}Cl] (4g). Prepared according to the general
procedure. 1H NMR (C6D6, 400.1 MHz) δ (ppm) = 5.09 (sept, JHH
=
7.2 Hz, 2H, NCHMe2), 1,77 (m, 2H, PCHMe2), 1.57 (s, 6H, CH3),
1.13 (d, JHH = 7.2 Hz, 12H, NCH(CH3)2), 1.13−1.03 (m, 12 H,
PCH(CH3)2). 13C{1H} NMR (C6D6, 100.6 MHz) δ (ppm) = 147.7
(d, JPC = 3.2 Hz, N2CN); 117.5; 47.2; 31.3; 30.8; 21.6; 18.6; 18.7;
17.2; 17.2; 9.9. 31P{1H} NMR (C6D6, 162.0 MHz): δ (ppm) = 73.5.
31P NMR (C6D6, 162.0 MHz): δ (ppm) = 73.5 (m). HRMS (ESI-
TOFMS): m/z [M + H]+ 754.33239 (calculated 754.33257).
[Au2{P(NIMes)tBu2}2Cl]OTf (5). 4d (44 mg, 0.06 mmol) and
AgOTf (16 mg, 0.06 mmol) were stirred in CH2Cl2 (2 mL) at room
temperature for 5 min. The solid components were filtered off and the
volatiles were removed in vacuo. Colorless crystals were obtained by
diffusion of n-pentane into a concentrated solution of 5 in
3
(ddd, J = 46.7 H J = 7.0 Hz, JPH = 17.7 Hz, 12H). 13C{1H} NMR
(CDCl3, 100.6 MHz) δ (ppm) = 155.8 (d, JPC = 2.0 Hz, N2CN);
147.6; 134.6; 129.4; 128.3; 124.6; 49.2; 30.4 (d, J = 48 Hz) 28.7;
26.1; 23.8; 17.8 (d, J = 2 Hz), 17.5 (d, J = 3 Hz). 31P{1H} NMR
(CDCl3, 162.0 MHz): δ (ppm) = 69.6. 31P NMR (CDCl3, 162.0
MHz): δ (ppm) = 69.6 (m). HRMS (ESI-TOFMS): m/z [M + H]+
754.33239 (calculated 754.33257).
[Au{P(NIDipp)iPr2}Cl] (4b). Prepared according to general
1
procedure. H NMR (CDCl3, 400.0 MHz) δ (ppm) = 7.45 (t, JHH
= 7.7 Hz, 4H, p-H); 7.26 (d, JHH = 7.7 Hz, 4H, m-H); 6.54 (s, 2H,
Imidazole-H); 2.97 (sep, JHH = 6.9 Hz, 4H, DippiPr-H); 1.38 (d, JHH
1
fluorobenzene. H NMR (CD2Cl2, 400.0 MHz) δ (ppm) = 7.00 (s,
= 6.9 Hz, 12H, Dipp-iPr-CH3); 1.23 (m, 2H, P-iPr-H); 1.16 (d, JHH
=
8H, Mes-H); 2.37 (s, 12H, CH3); 2.13 (s, 24H, CH3); 1.71 (s, 12H,
6.9 Hz, 12H, Dipp-iPr-CH3); 0.74 (dd, JPH = 18.0 Hz, JHH = 7.1 Hz,
6H, P-iPrCH3); 0.74 (dd, JPH = 17.4 Hz, JHH = 7.1 Hz, 6H, P-iPr-
CH3). 13C{1H} NMR (CDCl3, 100.6 MHz) δ (ppm) = 147.8 ((N)2-
CN); 132.8; 130.2; 124.2; 116.6; 31.0; 30.5; 28.7; 25.4; 23.0; 17.4
(m). 31P NMR (CDCl3, 161.9 MHz): δ (ppm) = 69.4 (m). 31P{1H}
NMR (CDCl3, 161.9 MHz): δ (ppm) = 69.4. HRMS (ESI-TOFMS):
m/z [M + Na]+ 774.29898 (calculated 774.29941).
CH3); 0.91 (d, JPH = 15.9 Hz, 36H, tert-buty-CH3). 13C{1H} NMR
3
(CDCl3, 100.6 MHz) δ (ppm) = 144.2; 140.0; 136.9; 131.7; 130.3;
118.1; 38.7 (d, JPC = 49.1 Hz); 28.1 (d, JPC = 6.6 Hz); 21.7; 18.5; 9.1.
19F NMR (CD2Cl2, 376.4 MHz): δ (ppm) = −78.9. 19F{1H} NMR
(CD2Cl2, 376.4 MHz): δ (ppm) = −78.9. 31P NMR (CD2Cl2, 161.9
MHz): δ (ppm) = 75.7 (br). 31P{1H} NMR (CD2Cl2, 161.9 MHz): δ
(ppm) = 75.7 (br). HRMS (ESI-TOFMS): m/z [M-OTf]+
1411.58863 (calculated 1411.58728).
[Au{P(NIDipp)tBu2}Cl] (4c). The reaction mixture of 3c (59%,
534 mg, 0.50 mmol) and [Au(tht)Cl] (160 mg, 0.50 mmol) were
dissolved in THF (2 mL) and stirred for 1 h at room temperature.
Then the volatiles were removed in vacuo for 1 h at room
temperature. The impurities from the synthesis of 3c were separated
from 4c by washing the isolated solid with n-hexane (3 × 10 mL). 1H
[Au{P(NIMes)tBu2}(py)](SbF6) (6). 4d (72 mg, 0.1 mmol) and
pyridine (78 μL, 1.0 mmol) were dissolved in CH2Cl2 (2 mL).
AgSbF6 (34 mg, 0.1 mmol) was added and the reaction mixture was
stirred at room temperature overnight. The solid components were
filtered off and n-pentane (20 mL) was added to the solution,
resulting in a white precipitate, which was isolated by filtration,
washed with n-pentane (3 × 10 mL), and dried in vacuo for 1 min.
3
NMR (CDCl3, 400.1 MHz) δ (ppm) = 7.51 (t, JHH = 7.8 Hz, 2H,
3
Dipp-H); 7.28 (d, JH3H = 7.8 Hz, 4H,Dipp-H); 6.44 (s, 2H,
3
N(CH)2N); 2.96 (sept, JHH = 6.8 Hz, 4H, Dipp-CH); 1.39 (d, JHH
1
3
Colorless crystals of 6 were obtained from CH2Cl2/n-pentane. H
= 6.8 Hz, 12H, CH(CH3)2); 1.15 (d, JHH = 6.8 Hz, 12H,
3
CH(CH3)2); 0.95 (d, JPH = 15.7 Hz, 18H). 13C{1H} NMR
NMR (CD2Cl2, 400.0 MHz) δ (ppm) = 8.21 (s, br, 2H, pyridine);
8.10 (s, br, 1H, pyridine); 7.73 (s, br, 2H, pyridine); 6.91 (s, 4H, Mes-
H); 2.18 (s, 12H, CH3); 1.99 (s, 6H, CH3); 1.70 (s, 6H, CH3); 1.01
(CDCl3, 100.6 MHz) δ (ppm) = 146.1, 133.5, 130.5, 124.6, 116.8,
77.0, 38.1, 37.6, 28.9, 28.0, 27.9, 26.0, 22.3. 31P{1H} NMR (CDCl3,
162.0 MHz): δ (ppm) = 80.2. 31P NMR (CDCl3, 162.0 MHz): δ
(ppm) = 80.2 (m).
(d, JPH = 16.0 Hz, tert-buty-CH3). 13C{1H} NMR (CDCl3, 100.6
3
MHz) δ (ppm) = 150.5 (br, pyridine) 144.5 c (d, JPC = 2.0 Hz,
N2CN); 141.4 (br, pyridine); 139.6; 137.3; 131.9; 129.9; 127.0 (br,
pyridine); 118.3; 38.3 (d, JPC = 47.0 Hz); 28.9 (d, JPC = 6.1 Hz), 20.9;
18.5; 9.1. 19F NMR (CD2Cl2, 376.4 MHz): δ (ppm) = −123.97 (m).
19F{1H} NMR (CD2Cl2, 376.4 MHz): δ (ppm) = −123.97 (m); 31P
NMR (CDCl3, 161.9 MHz): δ S67(ppm) = 73.5 (m). 31P{1H} NMR
(CDCl3, 161.9 MHz): δ (ppm) = 73.5.
General Procedure for the Catalysis. The [Au(IAP)Cl] (0.09
mmol, 1 equiv) and AgBF4 (0.09 mmol, 1 equiv) were dissolved in
MeCN (3 mL) and stirred for 10 min at room temperature. The
solution was then filtered over a glass microfiber filter, and a standard
solution (0.018 M) in MeCN was prepared. [Au(PPh3)Cl] was used
exactly the same way but with twice the amount of solvents due to
solubility, resulting in a 0.009 M standard solution. Phenylacetylene
[Au{P(NIMes)tBu2}Cl] (4d). Prepared according to general
1
procedure. H NMR (CDCl3, 400.1 MHz): δ (ppm) = 6.99 (s, 4H,
Mes-H); 2.37 (s, 6H, CH3); 2.13 (s, 12H, CH3); 1.69 (s, 6H, CH3);
1.37 (s, 12H, CH3); 0.90 (d, 3JPH = 15.6 Hz, tert-buty-CH3). 13C{1H}
NMR (CDCl3, 100.6 MHz) δ (ppm) = 144.1 (d, JPC = 2.5 Hz,
N2CN); 139.5; 136.2; 131.3; 129.9; 117.0; 37.9 (d, JPC = 44.6 Hz),
27.9 (d, JPC = 6.9 Hz), 21.4; 18.3; 9.0. 31P{1H} NMR (CDCl3, 162.0
MHz): δ (ppm) = 78.9. 31P NMR (CDCl3, 162.0 MHz): δ (ppm) =
78.9 (m). HRMS (ESI-TOFMS): m/z [M + H]+ 724.28662
(calculated 724.28562).
[Au{P(NIMes)iPr2}Cl] (4e). Prepared according to general
1
procedure. H NMR (C6D6, 400.1 MHz) δ (ppm) = 6.98 (s, 4H,
Mes-H); 2.34 (s, 6H, 2xCH3); 2.18 (s, 12H, Mes-CH3); 1.76 (s, 6H,
G
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(0.455 M), aniline, 2,4,6-trimethylaniline, and 4-methylaniline (1.06
M each) were used as standard solutions in MeCN as well. The
respective standard solutions of (IAP)Au−NCMe (0.5 or 1.0 mL;
0.02 equiv), phenylacetylene (1.0 mL, 1 equiv), and the respective
aryl amines (0.5 mL, 1.2 equiv) were mixed and stirred for 16 h at 60
°C. The yields were determined by 1H NMR spectroscopy as an
average of two runs using pyrazine as an internal standard. The
characteristic singlet of the CH3 group of the reaction product that
appears around 2.3 ppm was used for the integration.
K. Homogeneous gold catalysis beyond assumptions and proposals–
characterized intermediates. Angew. Chem., Int. Ed. 2010, 49, 5232−
5241. (e) Dorel, R.; Echavarren, A. M. Gold(I)-Catalyzed Activation
of Alkynes for the Construction of Molecular Complexity. Chem. Rev.
2015, 115, 9028−9072.
(5) Reid, S. M.; Boyle, R. C.; Mague, J. T.; Fink, M. J. A dicoordinate
palladium(0) complex with an unusual intramolecular eta(1)-arene
coordination. J. Am. Chem. Soc. 2003, 125, 7816−7817.
(6) (a) Watson, D. A.; Su, M.; Teverovskiy, G.; Zhang, Y.; García-
Fortanet, J.; Kinzel, T.; Buchwald, S. L. Formation of ArF from
LPdAr(F): catalytic conversion of aryl triflates to aryl fluorides. Science
2009, 325, 1661−1664. (b) Yandulov, D. V.; Tran, N. T. Aryl-
Fluoride Reductive Elimination from Pd(II): Feasibility Assessment
from Theory and Experiment. J. Am. Chem. Soc. 2007, 129, 1342−
1358.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00439.
■
S
(7) (a) Wang, Y.; Wang, Z.; Li, Y.; Wu, G.; Cao, Z.; Zhang, L. A
general ligand design for gold catalysis allowing ligand-directed anti-
nucleophilic attack of alkynes. Nat. Commun. 2014, 5, 3470. (b) Liao,
S.; Porta, A.; Cheng, X.; Ma, X.; Zanoni, G.; Zhang, L. Bifunctional
Ligand Enables Efficient Gold-Catalyzed Hydroalkenylation of
Propargylic Alcohol. Angew. Chem., Int. Ed. 2018, 57, 8250−8254.
(8) Qiu, X.; Wang, M.; Zhao, Y.; Shi, Z. Rhodium(I)-Catalyzed
Tertiary Phosphine Directed C-H Arylation: Rapid Construction of
Ligand Libraries. Angew. Chem., Int. Ed. 2017, 56, 7233−7237.
All NMR spectra, X-ray diffraction data, figures of all
calculated compounds (PDF)
Cartesian coordinates of all calculated compounds
(XYZ)
Accession Codes
CCDC 1848785−1848793 contain the supplementary crys-
tallographic 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.
̈
(9) (a) Noel-Duchesneau, L.; Lugan, N.; Lavigne, G.; Labande, A.;
́
Cesar, V. Tailoring Buchwald-Type Phosphines with Pyrimidinium
Betaines as Versatile Aryl Group Surrogates. Organometallics 2014, 33,
̈
5085−5088. (b) Noel-Duchesneau, L.; Lugan, N.; Lavigne, G.;
́
Labande, A.; Cesar, V. Customized Buchwald-Type Phosphines
Bearing an “Inverted” Pyrimidinium Betaine as an Aryl Group
Surrogate - Synthesis and Coordination Chemistry with Gold(I). Eur.
J. Inorg. Chem. 2015, 2015, 1752−1758.
AUTHOR INFORMATION
Corresponding Author
*E-mail: dielmann@uni-muenster.de.
ORCID
Fabian Dielmann: 0000-0002-7025-5450
Notes
The authors declare no competing financial interest.
■
(10) (a) Tinnermann, H.; Wille, C.; Alcarazo, M. Synthesis,
structure, and applications of pyridiniophosphines. Angew. Chem.,
́
́
Int. Ed. 2014, 53, 8732−8736. (b) Gonzalez-Fernandez, E.; Nicholls,
̀
L. D. M.; Schaaf, L. D.; Fares, C.; Lehmann, C. W.; Alcarazo, M.
Enantioselective Synthesis of 6Carbohelicenes. J. Am. Chem. Soc.
2017, 139, 1428−1431.
(11) (a) Ruiz-Castillo, P.; Blackmond, D. G.; Buchwald, S. L.
Rational ligand design for the arylation of hindered primary amines
guided by reaction progress kinetic analysis. J. Am. Chem. Soc. 2015,
137, 3085−3092. (b) Kendall, A. J.; Zakharov, L. N.; Tyler, D. R.
Steric and Electronic Influences of Buchwald-Type Alkyl-JohnPhos
Ligands. Inorg. Chem. 2016, 55, 3079−3090.
ACKNOWLEDGMENTS
■
We gratefully acknowledge financial support from the DFG
(Emmy Noether program: DI 2054/1-1, SFB 858, IRTG
2027). We thank Prof. F. E. Hahn for his generous support.
(12) Diebolt, O.; Fortman, G. C.; Clavier, H.; Slawin, A. M. Z.;
REFERENCES
́
Escudero-Adan, E. C.; Benet-Buchholz, J.; Nolan, S. P. Steric and
■
Electronic Parameters Characterizing Bulky and Electron-Rich
Dialkylbiarylphosphines. Organometallics 2011, 30, 1668−1676.
(13) Tolman, C. A. Electron donor-acceptor properties of
phosphorus ligands. Substituent additivity. J. Am. Chem. Soc. 1970,
92, 2953−2956.
(1) Kamer, P. C. J.; van Leeuwen, P. W. N. M. Phosphorus(III)
Ligands in Homogeneous Catalysis: Design and Synthesis; John Wiley &
Sons: Hoboken, NJ, 2012.
(2) Old, D. W.; Wolfe, J. P.; Buchwald, S. L. A Highly Active
Catalyst for Palladium-Catalyzed Cross-Coupling Reactions: Room-
Temperature Suzuki Couplings and Amination of Unactivated Aryl
Chlorides. J. Am. Chem. Soc. 1998, 120, 9722−9723.
(3) (a) Ruiz-Castillo, P.; Buchwald, S. L. Applications of Palladium-
Catalyzed C-N Cross-Coupling Reactions. Chem. Rev. 2016, 116,
12564−12649. (b) Sather, A. C.; Buchwald, S. L. The Evolution of
Pd0/PdII-Catalyzed Aromatic Fluorination. Acc. Chem. Res. 2016, 49,
2146−2157. (c) Surry, D. S.; Buchwald, S. L. Dialkylbiaryl
Phosphines in Pd-Catalyzed Amination: A User’s Guide. Chem. sci.
2011, 2, 27−50. (d) Surry, D. S.; Buchwald, S. L. Biaryl phosphane
ligands in palladium-catalyzed amination. Angew. Chem., Int. Ed. 2008,
47, 6338−6361. (e) Martin, R.; Buchwald, S. L. Palladium-catalyzed
Suzuki-Miyaura cross-coupling reactions employing dialkylbiaryl
phosphine ligands. Acc. Chem. Res. 2008, 41, 1461−1473.
(4) (a) Hashmi, A. S. K. Gold-Catalyzed Organic Reactions. Chem.
Rev. 2007, 107, 3180−3211. (b) Gorin, D. J.; Sherry, B. D.; Toste, F.
D. Ligand effects in homogeneous Au catalysis. Chem. Rev. 2008, 108,
3351−3378. (c) Li, Z.; Brouwer, C.; He, C. Gold-catalyzed organic
transformations. Chem. Rev. 2008, 108, 3239−3265. (d) Hashmi, A. S.
(14) (a) Nelson, D. J.; Nolan, S. P. Quantifying and understanding
the electronic properties of N-heterocyclic carbenes. Chem. Soc. Rev.
2013, 42, 6723−6753. (b) Huynh, H. V.; Han, Y.; Jothibasu, R.;
Yang, J. A. 13 C NMR Spectroscopic Determination of Ligand Donor
Strengths Using N-Heterocyclic Carbene Complexes of Palladium-
(II). Organometallics 2009, 28, 5395−5404.
(15) (a) Wu, X.; Tamm, M. Transition metal complexes supported
by highly basic imidazolin-2-iminato and imidazolin-2-imine N-donor
ligands. Coord. Chem. Rev. 2014, 260, 116−138. (b) Ochiai, T.; Franz,
D.; Inoue, S. Applications of N-heterocyclic imines in main group
chemistry. Chem. Soc. Rev. 2016, 45, 6327−6344.
(16) Wunsche, M. A.; Mehlmann, P.; Witteler, T.; Buß, F.;
̈
Rathmann, P.; Dielmann, F. Imidazolin-2-ylidenaminophosphines as
Highly Electron-Rich Ligands for Transition-Metal Catalysts. Angew.
Chem., Int. Ed. 2015, 54, 11857−11860.
(17) (a) Mehlmann, P.; Muck-Lichtenfeld, C.; Tan, T. T. Y.;
̈
Dielmann, F. Tris(imidazolin-2-ylidenamino)phosphine: A Crystalline
Phosphorus(III) Superbase That Splits Carbon Dioxide. Chem. - Eur.
H
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
J. 2017, 23, 5929−5933. (b) Buß, F.; Mehlmann, P.; Mu
̈
ck-
(30) Uson, R.; Laguna, A.; Laguna, M.; Briggs, D. A.; Murray, H. H.;
Fackler, J. P. In Inorganic Syntheses; Kaesz, H. D., Ed.; Inorganic
Syntheses; Wiley: New York, 1989; pp 85−91.
Lichtenfeld, C.; Bergander, K.; Dielmann, F. Reversible Carbon
Dioxide Binding by Simple Lewis Base Adducts with Electron-Rich
Phosphines. J. Am. Chem. Soc. 2016, 138, 1840−1843.
(18) Buß, F.; Rotering, P.; Muck-Lichtenfeld, C.; Dielmann, F.
̈
Crystalline, Room-Temperature Stable Phophine−SO 2 Adducts:
Generation of Sulfur Monoxide from Sulfur Dioxide. Dalton Trans
2018, 47, 10420.
(19) Buß, F.; Muck-Lichtenfeld, C.; Mehlmann, P.; Dielmann, F.
̈
Nucleophilic Activation of Sulfur Hexafluoride: Metal-Free, Selective
Degradation by Phosphines. Angew. Chem. 2018, 130, 5045−5049.
(20) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi, J.
P.; Buchwald, S. L. Novel Electron-Rich Bulky Phosphine Ligands
Facilitate the Palladium-Catalyzed Preparation of Diaryl Ethers. J. Am.
Chem. Soc. 1999, 121, 4369−4378.
(21) Tamm, M.; Petrovic, D.; Randoll, S.; Beer, S.; Bannenberg, T.;
Jones, P. G.; Grunenberg, J. Structural and theoretical investigation of
2-iminoimidazolines–carbene analogues of iminophosphoranes. Org.
Biomol. Chem. 2007, 5, 523−530.
(22) Tamm, M.; Randoll, S.; Herdtweck, E.; Kleigrewe, N.; Kehr, G.;
Erker, G.; Rieger, B. Imidazolin-2-iminato titanium complexes:
synthesis, structure and use in ethylenepolymerization catalysis.
Dalton Trans 2006, 38, 459−467.
(23) Scott, N. M.; Nolan, S. P. Stabilization of Organometallic
Species Achieved by the Use of N-Heterocyclic Carbene (NHC)
Ligands. Eur. J. Inorg. Chem. 2005, 2005, 1815−1828.
(24) Gusev, D. G. Electronic and Steric Parameters of 76 N-
Heterocyclic Carbenes in Ni(CO) 3 (NHC). Organometallics 2009,
28, 6458−6461.
(25) Falivene, L.; Credendino, R.; Poater, A.; Petta, A.; Serra, L.;
Oliva, R.; Scarano, V.; Cavallo, L. SambVca 2. A Web Tool for
Analyzing Catalytic Pockets with Topographic Steric Maps. Organo-
metallics 2016, 35, 2286−2293.
(26) Zhu, Y.; Day, C. S.; Zhang, L.; Hauser, K. J.; Jones, A. C. A
unique Au-Ag-Au triangular motif in a trimetallic halonium dication:
silver incorporation in a gold(I) catalyst. Chem. - Eur. J. 2013, 19,
12264−12271.
(27) Thwaite, S. E.; Schier, A.; Schmidbaur, H. The auration of 2-
hydroxy-pyridine (2-pyridone): preparative and structural studies and
a comparison with reactions of related aliphatic O,N-donors. Inorg.
Chim. Acta 2004, 357, 1549−1557.
(28) (a) Marion, N.; Nolan, S. P. N-Heterocyclic carbenes in gold
catalysis. Chem. Soc. Rev. 2008, 37, 1776−1782. (b) Gaggioli, C. A.;
Ciancaleoni, G.; Biasiolo, L.; Bistoni, G.; Zuccaccia, D.; Belpassi, L.;
Belanzoni, P.; Tarantelli, F. Anomalous ligand effect in gold(I)-
catalyzed intramolecular hydroamination of alkynes. Chem. Commun.
2015, 51, 5990−5993. (c) Gaggioli, C. A.; Ciancaleoni, G.; Zuccaccia,
D.; Bistoni, G.; Belpassi, L.; Tarantelli, F.; Belanzoni, P. Strong
Electron-Donating Ligands Accelerate the Protodeauration Step in
Gold(I)-Catalyzed Reactions: A Quantitative Understanding of the
Ligand Effect. Organometallics 2016, 35, 2275−2285. (d) Christian, A.
H.; Niemeyer, Z. L.; Sigman, M. S.; Toste, F. D. Uncovering Subtle
Ligand Effects of Phosphines Using Gold(I) Catalysis. ACS Catal.
2017, 7, 3973−3978. (e) Benitez, D.; Tkatchouk, E.; Gonzalez, A. Z.;
Goddard, W. A.; Toste, F. D. On the Impact of Steric and Electronic
Properties of Ligands on Gold(I)-Catalyzed Cycloaddition Reactions.
́
́
̃
ez, E.; Echavarren,
Org. Lett. 2009, 11, 4798−4801. (f) Jimenez-Nun
A. M. Gold-Catalyzed Cycloisomerizations of Enynes: A Mechanistic
Perspective. Chem. Rev. 2008, 108, 3326−3350. (g) Alcarazo, M.;
̈
Stork, T.; Anoop, A.; Thiel, W.; Furstner, A. Steering the surprisingly
modular pi-acceptor properties of N-heterocyclic carbenes: implica-
tions for gold catalysis. Angew. Chem., Int. Ed. 2010, 49, 2542−2546.
(h) Xi, Y.; Su, Y.; Yu, Z.; Dong, B.; McClain, E. J.; Lan, Y.; Shi, X.
Chemoselective Carbophilic Addition of α-Diazoesters through
Ligand-Controlled Gold Catalysis. Angew. Chem., Int. Ed. 2014, 53,
9817−9821.
(29) Wang, W.; Hammond, G. B.; Xu, B. Ligand effects and ligand
design in homogeneous gold(I) catalysis. J. Am. Chem. Soc. 2012, 134,
5697−5705.
I
DOI: 10.1021/acs.organomet.8b00439
Organometallics XXXX, XXX, XXX−XXX