Synthesis of Silver(I) and Gold(I) Complexes Containing Enantiopure Pybox Ligands. First Assays on the Silver(I)-Catalyzed Asymmetric Addition of Alkynes to Imines

Article abstract of DOI:10.1021/acs.inorgchem.6b01323

Dinuclear complexes [Ag₂(CF₃SO₃){(S,S)-ⁱPr-pybox}₂][CF₃SO₃] (1), [Ag₂(R-pybox)₂][X]₂ [R-pybox = 2,6-bis[4-(S)-isopropyloxazolin-2-yl]pyridine (S,

Full text of DOI:10.1021/acs.inorgchem.6b01323

Article
pubs.acs.org/IC
Synthesis of Silver(I) and Gold(I) Complexes Containing Enantiopure
Pybox Ligands. First Assays on the Silver(I)-Catalyzed Asymmetric
Addition of Alkynes to Imines
Gustavo M. Borrajo-Calleja,† Eire de Julian,† Esther Bayon,† Josefina Díez,† Elena Lastra,† Isabel Merino,‡
́
́
and M. Pilar Gamasa*,†
†Departamento de Química Organ
Avanzada (ORFEO−CINQA), Universidad de Oviedo, E-33006 Oviedo, Principado de Asturias, Spain
‡Unidad de Resonancia Magnet
ica Nuclear, Servicios Científico-Tecnicos de la Universidad de Oviedo, E-33006 Oviedo, Principado
́ ́ ́
ica e Inorganica, IUQOEM (Unidad Asociada al CSIC), Centro de Innovacion en Química
́
́
de Asturias, Spain
S
* Supporting Information
ABSTRACT: Dinuclear complexes [Ag2(CF3SO3){(S,S)-iPr-pybox}2][CF3SO3] (1), [Ag2(R-pybox)2][X]2 [R-pybox = 2,6-
bis[4-(S)-isopropyloxazolin-2-yl]pyridine (S,S)-iPr-pybox and X = PF6 (2) and BF4 (3); R-pybox = 2,6-bis[(3aS,8aR)-8,8a-
dihydro-3aH-indeno[1,2-d]oxazol-2-yl]pyridine (3aS,3a′S,8aR,8a′R)-indane-pybox and X = CF3SO3 (4)], [Ag2{(S,S)-iPr-
pybox}{(3aS,3a′S,8aR,8a′R)-indane-pybox}][CF3SO3]2 (5), and [Ag2(R-pybox)3][X]2 [R-pybox = (3aS,3a′S,8aR,8a′R)-indane-
pybox and X = CF3SO3 (10), SF6 (11), and PF6 (12)] as well as mononuclear complexes [Ag(R-pybox)2][X] [R-pybox =
(S,S)-iPr-pybox and X = SbF6 (6), PF6 (7), and BF4 (8); R-pybox = (3aS,3a′S,8aR,8a′R)-indane-pybox) and X = BF4 (9)] have
been prepared by the reaction of the corresponding silver salts and pybox ligands using the appropriate molar ratio conditions.
The first gold(I)/pybox complex [Au6Cl4{(S,S)-iPr-pybox}4][AuCl2]2 (13) has been synthesized by the reaction of
[AuCl{S(CH3)2}] and (S,S)-iPr-pybox (1:1 molar ratio) in acetonitrile. The structures of the dinuclear (1, 4, 5, 10, and 11)
and mononuclear (6 and 9) silver complexes and the hexanuclear gold complex 13 have been determined by single-crystal X-ray
diffraction analysis. These studies have been complemented with a solution-state study by NMR spectroscopy, which included
structure elucidation, variable-temperature measurements, and diffusion studies using diffusion-ordered spectroscopy (DOSY; for
complexes 1, 4, 10, and 12). Complexes 1, 2, 4, and 10 have been assayed as catalysts in the asymmetric addition of
phenylacetylene to N-benzylideneaniline.
azomethine imines,10 and addition of terminal alkynes to both
INTRODUCTION
■
α-iminophosphonates11 and imines.2,12 In addition, copper(II)/
pybox complexes are able to catalyze the three-component
coupling of aldehydes, amines, and alkynes13 as well as the
enantioselective Friedel−Crafts reaction of indoles.14 On the
contrary, examples of catalytic reactions involving other group
11 metal complexes containing enantiopure pybox ligands are
very rare, and negligible enantiomeric excess (e.e.) has been
reported.15 A reason that might account for this gap deals with
The last years have witnessed a major advance in the use of
enantiopure pybox-containing transition metals in the
fundamental scenario of asymmetric synthesis.1 In particular,
pybox-containing copper(I) complexes have proven to be
highly effective for asymmetric reactions. Thus, isolated2,3 or in
situ generated4−12 copper(I) complexes have been shown to
catalyze several asymmetric reactions, e.g., cyclopropanation of
alkenes,5 cycloaddition of azides with alkynes,6 allylic oxidation
of alkenes,7 propargylic etherification of propargylic esters,3
intramolecular propargylic amination of propargylic acetates,8
propargylation of benzofuranones,9 alkynylation of C,N-cyclic
Received: June 4, 2016
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of the Dinuclear Complexes 1−4
the lack of synthetic methods of these complexes. In this sense,
it is relevant that, unlike the particular case of copper(I),2,3,16
studies on the coordination chemistry of pybox with silver and
gold metals are almost unknown because only the structures of
the dinuclear and trinuclear silver(I) complexes [Ag2{(S,S)-Bz-
pybox}2][BF4]2 and [Ag3{(R,R)-Ph-pybox}3][BF4]3 have been
reported.17,18
In this paper, a simple and direct preparation of various
enantiopure complexes of silver(I)- and gold(I)-containing
pybox ligands is presented. Different mono- and dinuclear
complexes of silver(I) have been selectively synthesized by
using appropriate molar ratios of reactants. Furthermore, the
first gold(I)/pybox complex that crystallizes as a hexanuclear
species is described. Preliminary attempts toward the use of
silver(I)/pybox complexes in asymmetric catalysis are per-
formed, although only moderate results are reached.
a silver cation was confirmed in solution and the solid state (see
NMR studies and the crystal structure of complex 1). The H
1
and 13C NMR resonance signals of complexes 1−4 in solution
(293 K) were fully consistent with the presence of a C2-
symmetry axis. Thus, the 13C{1H} NMR spectra for complexes
1−3 show single resonance signals for the OCH2, OCN, and
CHiPr carbon atoms of both oxazoline rings and for the C3/C5
and C2/C6 carbon atoms of the pyridine ring. Similarly, single
resonances for the OCN, OCH, and NCH carbon atoms of
both oxazoline rings and for the C3/C5 and C2/C6 carbon
atoms of the pyridine ring are observed in the case of complex
4 [see the variable-temperature (VT)-NMR experiments and
diffusion studies undertaken for 1 and 4]. Attempts at the
synthesis of the analogous dicationic complex starting from
AgSbF6 were unsuccessful because an unidentified solid was
formed whose 1H NMR spectrum showed very broad peaks. All
attempts to crystallize this solid from mixtures of different
solvents resulted in the formation of the mononuclear complex
6 (see below).
RESULTS AND DISCUSSION
■
Synthesis of the Dinuclear Complexes [Ag2(CF3SO3)-
{(S,S)-iPr-pybox}2][CF3SO3] (1), [Ag2{(S,S)-iPr-pybox}2][X]2
[X = PF6 (2) and BF4 (3)], and [Ag2{(3aS,3a′S,8aR,8a′R)-
indane-pybox}2][CF3SO3]2 (4). The reaction of equimolar
amounts of the corresponding silver salt AgX (X = CF3SO3,
PF6, and BF4) with (S,S)-iPr-pybox and (3aS,3a′S,8aR,8a′R)-
indane-pybox in dichloromethane at room temperature led to
the dinuclear complexes 1, 2, and 4 in 50−84% yield. Complex
3 was alternatively synthesized by stirring a mixture of AgF,
The structures of complexes 1 and 4 were confirmed by
single-crystal X-ray analyses. Complexes 1 and 4 crystallize in
chiral space group P212121 with Flack parameters of −0.011(5)
and −0.020(4), respectively. In the same manner, all of the
complexes described in this paper crystallize in chiral space
groups because of the presence of an enantiopure ligand. In all
cases, the Flack parameter was found to be nearly zero after
refinement20 (see Tables 2−4). The asymmetric unit of
complex 1 consists of two molecules that have similar relevant
structural parameters, and therefore only the data correspond-
ing to one of them are discussed. ORTEP-type views of the
cation of one of the molecules of 1 and the cation of 4 are
shown in Figures 1 and 2, respectively. Selected bonding data
are listed in Table 1. The structure of complex 1 shows a
dimeric cation [Ag2(CF3SO3){(S,S)-iPr-pybox}2]+ and one
i
BF3·OEt2, and Pr-pybox (2:2:2 molar ratio) in dichloro-
methane at room temperature (66% yield; Scheme 1). All of
the complexes reported in this paper were characterized by
elemental analysis, molar conductivity, fast-atom-bombardment
(FAB) mass spectrometry (MS; 1, 4, 6, 9, and 13), and NMR
spectroscopy (see the Experimental Section and Supporting
Information for details). The molar conductivity value for
complex 1 in nitromethane (86 S cm2 mol−1) or acetone (210 S
cm2 mol−1) was in the expected range for 1:1 or 1:2 electrolytes
in these solvents, respectively.19 The ΛM nitromethane value
can be explained by assuming that the interaction of one triflate
anion with a silver cation is maintained in a nitromethane
solution. In fact, the interaction between one triflate anion and
−
uncoordinated CF3SO3 anion, whereas the structure of
c o m p l e x
4
s h o w s
a
d i m e r i c d i c a t i o n
[Ag2{(3aS,3a′S,8aR,8a′R)-indane-pybox}2]2+ and two uncoor-
−
dinated CF3SO3 anions. The lack of interaction between the
silver atoms and triflate anions in the case of complex 4 might
be attributed to the higher steric demand of the (3aS,3a′-
S,8aR,8a′R)-indane-pybox ligand versus the (S,S)-iPr-pybox
B
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different indane-pybox ligands with angle values of 172.78(19)°
for N1−Ag1−N4 and 140.54(18)° for N3−Ag1−N6. The
coordination of the Ag1 atom is near linearity while that of the
Ag2 atom is not strictly linear because of weak interactions with
pyridine nitrogen groups [Ag2−N5 2.794(3) Å; Ag2−N2
2.683(3) Å]. These distances are larger than those found in
complex 1 (Ag2−Npyridine av. 2.579 Å) but shorter than the sum
of the van der Waals radii of silver and nitrogen atoms (3.27
Å).26 The distances Ag−Noxazoline are sligthly shorter for the
dicoordinate Ag1 atom [Ag1−N1 2.090(4) Å; Ag1−N4
2.087(4) Å] than for the Ag2 atom [Ag2−N3 2.152(4) Å;
Ag2−N6 2.146(4) Å], whereas the silver(1) triflate coordina-
tion in complex 1 makes the four distances Ag−Noxazoline be
very close to each other (see above). All of the Noxazoline−AgI
distances in complexes 1 and 4 are typical of covalent bonds.23
Moreover, complexes 1 and 4 show also very weak interactions
between the pyridine nitrogen atoms and the Ag1 atom [av.
2.985 Å (1), 3.055 Å (4)], although these distances are shorter
than the sum of the van der Waals radii of silver and nitrogen
atoms (3.27 Å).26
The Ag1···Ag2 distance is slightly shorter for complex 1
[2.8885(9) Å] than for complexes 4 [3.0295(9) Å] and
[Ag2{(S,S)-Bz-pybox}2][BF4]2 [2.985(1) Å].17 These distances
are in the range expected for the sum of the covalent radii of
two Ag atoms and suggest a significant argentophilic interaction
between the silver atoms.27 The Ag−Ag distances observed in
complexes exhibiting argentophilic interactions are commonly
found in the range of the sum of the covalent radii of two Ag
atoms (2.90 Å)23 and the 2-fold van der Waals radius of silver
(3.44 Å).26
Figure 1. ORTEP drawing of the cationic complex 1 showing the
atom-labeling scheme. Thermal ellipsoids are shown at the 10%
probability level. Hydrogen atoms and the CF3SO3 anion are omitted
for clarity.
Remarkably, the pybox skeleton is not planar in complexes 1
and 4, with the two pybox ligands being twisted around the
Ag1−Ag2 axis, thus generating a double-helical structure with P
(1) and M (4) helicity.28 The torsion angle N−C−C−N values
of the pybox ligands for complexes 1 and 4 are in the ranges of
8.3(13)−35.7(12)° (1) and −35.0(8) to −11.7(8)° (4). The
cation units of complexes 1 and 4 were formed as single
diastereoisomers P(S,S)(S,S) (1) and M(3aS,3a′S,8aR,8a′R)-
(3aS,3a′S,8aR,8a′R) (4).
Figure 2. ORTEP drawing of the cationic complex 4 showing the
atom-labeling scheme. Thermal ellipsoids are shown at the 20%
probability level. Hydrogen atoms and the CF3SO3 anions are omitted
for clarity.
Synthesis of the Dinuclear Complex [Ag2{(S,S)-iPr-
pybox}{(3aS,3a′S,8aR,8a′R)-indane-pybox}][CF3SO3]2 (5).
When a mixture of AgOSO2CF3, (S,S)-iPr-pybox, and
(3aS,3a′S,8aR,8a′R)-indane-pybox (2:1:1 molar ratio) was
stirred in dichloromethane at room temperature, the dinuclear
mixed complex 5 was isolated in moderate yield (56%) as the
sole reaction product (Scheme 2). No traces of complexes 1 or
4 were detected.
ligand. In the case of complex 1, the Ag1 and Ag2 atoms are
coordinated to two oxazoline nitrogen atoms of two different
pybox ligands with angle values of 157.4(2)° for N1−Ag1−N4
and 155.1(2)° for N3−Ag2−N6. These angles are quite
different from the idealized linear value of 180° due to the
coordination of a triflate group and pyridine nitrogen atoms
(N2 and N5) to the Ag1 and Ag2 metal centers, respectively.21
The four Ag−Noxazoline bond lengths are in the range of
2.183(6)−2.203(6) Å (av. 2.1915 Å) and are similar to those
observed in other silver(I) oxazoline complexes (usually found
in the range of 1.97−2.18 Å).21,22 The Ag1−O5 bond distance
[2.562(10) Å] is longer than the sum of the covalent radii for
silver and oxygen atoms (2.11 Å)23 but in the range found for
other silver(I) triflate complexes (Ag−O, with a range of 2.67−
2.362 Å).24 The Ag2−Npyridine bond lengths [Ag2−N5 2.510(6)
Å; Ag2−N2 2.6476(6) Å] are longer than those reported for
other silver(I) pyridine complexes [av. 2.24 Å, range of
2.138(3)−2.391(1) Å].25
1
The room temperature H NMR spectrum of complex 5
i
shows the CHMe2 group of Pr-pybox appearing at much
higher field [0.50 (CHMe2), 0.48 (CHMe2), −0.01 (m,
CHMe2) ppm] than that in the case of complex 1 [1.48
(CHMe2), 0.91 (CHMe2), 0.83 (CHMe2) ppm] probably
because of the shielding ring current effect of the indane
group.29 The structure of complex 5 was determined by single-
crystal X-ray analysis, and selected bonding data are shown in
Table 1. The asymmetric unit of complex 5 consists of two
molecules that have similar relevant structural parameters. The
ORTEP-type view of the dication [Ag2{(S,S)-iPr-pybox}-
{(3aS,3a′S,8aR,8a′R)-indane-pybox}]2+ of one of them is
shown in Figure S1. As in the case of complex 4, no interaction
between the silver atoms and triflate anion was observed. On
the other hand, as in the cases of complexes 1 and 4, the two
pybox ligands were twisted around the Ag1−Ag2 axis,
On the other hand, the Ag1 and Ag2 atoms in complex 4 are
also coordinated to two oxazoline nitrogen atoms of two
C
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Table 1. Selected Bond Distances (Å) and Angles (deg) for Silver(I) Complexes 1, 4−6, and 9−11 and Gold(I) Complex 13
Complex 1
Ag2−N3
Complex 9·CH2Cl2
Ag1−N1
Ag1−N2
Ag1−N4
Ag1−N5
Ag2−N2
2.203(6)
2.855(6)
2.191(6)
3.116(6)
2.647(6)
2.183(6)
2.510(6)
2.189(6)
2.562(10)
2.8885(9)
N2−Ag1−N5
N1−Ag1−N4
N1−Ag1−N5
N4−Ag1−N5
N1−Ag1−N2
177.31(19)
N2−Ag1−N4
N1−Ag1−N6
N4−Ag1−N6
N5−Ag1−N6
N2−Ag1−N6
116.56(19)
89.12(18)
130.2(2)
Ag2−N5
Ag2−N6
Ag1−O5
Ag1−Ag2
114.1(2)
113.94(18)
65.6(2)
64.7(2)
67.01(18)
113.00(18)
Complex 10·CH2Cl2
2.270(11)
N1−Ag1−N4
N4−Ag1−O5
N1−Ag1−O5
157.4(2)
85.3(3)
N3−Ag2−N6
N3−Ag2−N5
N6−Ag2−N5
155.1(2)
130.3(2)
71.7(2)
Ag1−N1
Ag1−N4
Ag1−N7
Ag2−N3
Ag2−N6
Ag2−N9
Ag1−Ag2
2.316(10)
2.252(10)
3.1020(11)
2.263(9)
117.3(3)
2.285(11)
Complex 4
2.266(11)
Ag1−N1
Ag1−N2
Ag1−N4
Ag1−N5
Ag2−N2
2.090(4)
3.061(3)
2.087(4)
3.050(3)
2.683(3)
Ag2−N3
Ag2−N5
Ag2−N6
Ag1−Ag2
2.152(4)
2.794(3)
2.146(4)
3.0295(9)
N1−Ag1−N4
N1−Ag1−N7
N4−Ag1−N7
113.6(4)
121.5(4)
121.1(4)
N3−Ag2−N6
N3−Ag2−N9
N6−Ag2−N9
127.6(4)
117.2(4)
109.8(4)
Complex 11·CH2Cl2
Ag1−N1
Ag1−N4
Ag1−N7
Ag2−N3
2.258(13)
2.306(15)
2.272(14)
2.287(15)
Ag2−N6
Ag2−N9
Ag1−Ag2
2.334(15)
2.237(15)
3.1008(18)
N1−Ag1−N4
172.78(19)
N3−Ag2−N6
140.54(18)
Complex 5
Ag1−N1
Ag1−N2
Ag1−N4
Ag1−N5
Ag2−N2
2.148(8)
2.867(9)
2.166(7)
2.831(9)
2.968(9)
Ag2−N3
Ag2−N5
Ag2−N6
Ag1−Ag2
2.131(7)
3.013(9)
2.137(7)
3.0530(11)
N1−Ag1−N4
N1−Ag1−N7
N4−Ag1−N7
114.9(5)
125.1(5)
116.8(5)
N3−Ag2−N6
N3−Ag2−N9
N6−Ag2−N9
123.9(5)
121.8(6)
110.1(5)
Complex 13·Et2O·2Me2CO
N1−Ag1−N4
163.0(3)
N3−Ag2−N6
167.6(3)
Au1−N1
Au1−Cl1
Au2−N3
Au2−N4
Au5−N9
Au5−N10
Au6−N12
Au6−Cl4
Au1−Au2
Au2−Au3
Au3−Au4
2.031(12)
2.254(4)
2.019(12)
2.025(12)
2.024(12)
2.032(11)
2.008(14)
2.267(4)
3.474(1)
3.474(1)
3.139(1)
Au3−Cl2
Au3−N6
Au4−N7
Au4−Cl3
Au4−Au5
Au5−Au6
Au7−Cl5
Au7−Cl6
Au8−Cl7
Au8−Cl8
2.247(3)
2.039(12)
2.036(13)
2.251(4)
3.302(1)
3.518(1)
2.248(10)
2.230(14)
2.165(18)
2.240(16)
Complex 6·0.5CH2Cl2
Ag1−N1
Ag1−N2
Ag1−N3
2.541(7)
2.416(5)
2.652(6)
Ag1−N4
Ag1−N5
Ag1−N6
2.562(7)
2.417(6)
2.561(7)
N2−Ag1−N5
N1−Ag1−N2
N1−Ag1−N5
N2−Ag1−N6
N5−Ag1−N6
169.9(2)
67.6(2)
119.0(2)
103.5(2)
66.9(2)
N1−Ag1−N6
N2−Ag1−N4
N4−Ag1−N5
N1−Ag1−N4
N4−Ag1−N6
116.8(3)
122.6(2)
66.7(2)
88.4(2)
133.5(2)
Complex 9·CH2Cl2
Ag1−N1
Ag1−N2
Ag1−N3
2.479(6)
2.508(6)
2.836(5)
Ag1−N4
Ag1−N5
Ag1−N6
2.479(6)
2.496(6)
2.581(7)
N1−Au1−Cl1
N3−Au2−N4
N6−Au3−Cl2
N7−Au4−Cl3
174.5(4)
175.7(5)
175.1(4)
177.1(4)
N9−Au5−N10
N12−Au6−Cl4
Cl5−Au7−Cl6
Cl7−Au8−Cl8
175.7(5)
174.2(4)
178.8(3)
179.6(4)
of the ligand (1:2 molar ratio), in dichloromethane at room
Scheme 2. Synthesis of the Dinuclear Complex 5
̈
temperature, the mononuclear complexes [Ag{(S,S)-iPr-
pybox)2][X]2 (6−8, 80−83% yield) were obtained as the sole
reaction products. In turn, complex 9 was synthesized by the
reaction of AgF, BF3·OEt2, and the indane-pybox ligand in
dichloromethane at room temperature (1:1:2 molar ratio, 61%
yield; Scheme 3).
Following are the selected spectroscopic data: (i) The mass
spectra (FAB) of complexes 6 and 9 show the base peak
corresponding to the ion molecular [Ag(R-pybox)2]+ at m/z
709 (6) and 893 (9). (ii) The molar conductivity values found
for complexes 6−9 (110−134 S cm2 mol−1) are in the range as
those expected for 1:1 electrolytes.19 (iii) The presence of a C2-
generating a double-heterostranded helicate structure and
giving rise to complex 5 as the single diastereoisomer M
(S,S)(3aS,3a′S,8aR,8a′R).
1
symmetry axis is evidenced by the room temperature H and
13C{1H} NMR studies carried out on complexes 6−9. For
instance, complexes 6−8 display single 13C{1H} NMR signals
for the OCN, OCH2, and CHiPr carbon atoms of oxazoline
rings and for the C3/C5 and C2/C6 carbon atoms of the
pyridine rings of both pybox ligands. The 13C{1H} NMR
Synthesis of the Mononuclear Complexes [Ag-
{(S,S)-iPr-pybox}2][X] [X = SbF6 (6), PF6 (7), and BF4 (8)]
and [Ag{(3aS,3a′S,8aR,8a′R)-indane-pybox}2][BF4] (9).
When the reaction of the silver salts AgX (X = SbF6, PF6,
i
and BF4) and Pr-pybox was carried out using a larger amount
D
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Noxazoline distances are larger than the sum of the covalent
radii of silver and nitrogen atoms (2.16 Å),23 indicating a weak
interaction of both pybox ligands with the silver atom. The
oxazoline nitrogen N3 atom lies further away [Ag1−N3
2.652(6) Å for 6 and 2.836(5) Å for 9], whereas the rest of
the Ag−N distances are in the ranges of 2.416(5)−2.562(7) Å
for 6 and 2.479(6)−2.581(7) Å for 9. Both pybox skeletons are
near the planarity for 6 and get away somewhat from the
planarity for 9, with the N−C−C−N torsion angles being in
the ranges of −3.4(13) to +10.8(13)° (for 6) and −26.6(9) to
−7.2(9)° (for 9).
Scheme 3. Synthesis of the Mononuclear Complexes 6−9
i
On the other hand, the reaction of Pr-pybox and the silver
salt of a more coordinating anion, AgOSO2CF3 (2:1 molar
ratio), takes place to give a solid that could not be characterized
by NMR analysis. Moreover, suitable crystals for X-ray analysis
could not be obtained because all attempts of crystallizing this
solid resulted in formation of the dinuclear complex 1.
Synthesis of the Dinuclear Complexes
[Ag2{(3aS,3a′S,8aR,8a′R)-indane-pybox}3][X]2 [X =
CF3SO3 (10), SbF6 (11), and PF6 (12)]. The reaction of the
corresponding silver salt AgX (X = CF3SO3, SbF6, and PF6) and
indane-pybox (2:3 molar ratio) in dichloromethane at room
temperature led to the dinuclear complexes
[Ag2{(3aS,3a′S,8aR,8a′R)-indane-pybox}3][X]2 (10−12) in
42−63% yield (Scheme 4).
spectrum of complex 9 shows also single resonances for OCN,
OCH, and NCH, C3/C5 and C2/C6 carbon atoms of the
oxazoline and pyridine rings of both pybox ligands (see the
1
Experimental Section for details). (iv) VT H NMR measure-
ments (298−183 K) for complex 6 did not show any splitting
of the signals nor did they lead to the observation of other
species in solution. The structures of complexes 6 and 9 were
confirmed by single-crystal X-ray analysis. An ORTEP-type
view of the cation of 6 is shown in Figure 3, and selected
Scheme 4. Synthesis of the Dinuclear Complexes 10−12
1
The H NMR spectra of complexes 10−12 (acetone-d6,
room temperature) show broad peaks, suggesting the presence
of a dynamic process in solution (see the NMR Elucidation and
Diffusion Studies section for these complexes). The structures
of complexes 10 and 11 were confirmed by single-crystal X-ray
a n a l y s i s a n d c o n s i s t o f
a
d i m e r i c c a t i o n
[Ag2{(3aS,3a′S,8aR,8a′R)-indane-pybox}3]2+ and two uncoor-
dinated anions.30 Both structures are very similar, and therefore
only the data corresponding to 10 will be discussed. Selected
bonding data of complexes 10 and 11 and an ORTEP-type
view of the cation of 10 are shown in Table 1 and Figure 4. An
ORTEP-type view of the cation of 11 is shown in Figure S3.
Both silver atoms of 10 have similar coordination environ-
ments, being coordinated to three oxazoline nitrogen atoms of
different pybox ligands showing a distorted trigonal-planar array
[bond angles Nox−Ag1−Nox and Nox−Ag2−Nox in the range of
109.8(4)−127.6(4)°]. Each silver atom is almost located in the
plane defined by the three oxazoline nitrogen atoms [+0.256(1)
and −0.305(1) Å deviations for Ag1 and Ag2, respectively].
The Ag−Noxazoline bond lengths in complex 10 [range of
2.252(10)−2.316(10) Å] are longer than those found in
complex 4. Among the pyridine nitrogen atoms, it should be
noted that the N5 atom is closer to silver atoms [Ag1−N(5)
Figure 3. ORTEP drawing of the cationic complex 6 showing the
atom-labeling scheme. Thermal ellipsoids are shown at the 20%
probability level. Hydrogen atoms and the SbF6 anion are omitted for
clarity.
bonding data of complexes 6 and 9 are shown in Table 1. An
ORTEP-type view of the cation of 9 is shown in Figure S2.
Both structures show a monomer cation, [Ag{(S,S)-iPr-
pybox}2]+ or [Ag{(3aS,3a′S,8aR,8a′R)-indane-pybox}2]+, and
−
−
an uncoordinated anion, SbF6 (6) or BF4 (9). In both
structures, the silver atom is surrounded by a strongly distorted
octahedral coordination environment that results from the
tridentate coordination of two pybox ligands through the
pyridine and oxazoline nitrogen atoms, giving rise to a formal
22-electron complex. However, all Ag−Npyridine and Ag−
E
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Inorganic Chemistry
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and the pybox ligands are twisted around the Ag1−Ag2 axis,
generating a triple-stranded helicate structure.28b The N−C−
C−N torsion angle values of the pybox ligands are in the range
of 20(2)−34(2)°.
Synthesis of the Hexanuclear Gold Complex
[Au6Cl4{(S,S)-iPr-pybox}4][AuCl2]2 (13). The reaction of
equimolar amounts of complexes [AuCl{S(CH3)2}] and
(S,S)-iPr-pybox in acetonitrile at room temperature led
diasteroselectively to the hexanuclear complex 13, which was
isolated in moderate yield (43%; Figure 5). The room
1
temperature H and 13C{1H} NMR spectra of complex 13
are fully consistent with the presence of a C2-symmetry axis.
Thus, the 13C{1H} NMR spectrum shows single resonance
signals for the OCH2, OCN, and CHiPr carbon atoms of both
oxazoline rings and for the C3/C5 and C2/C6 carbon atoms of
the pyridine ring. The mass spectrum (FAB) of 13 shows the
base peak at m/z 730 ([Au2Cl(iPr-pybox)]+). The NMR (1H,
13C, and HSQC experiments) and mass spectrum (FAB) data
do not allow one to unambiguously determine the structure of
complex 13. Therefore, single-crystal X-ray analysis was carried
out, showing that 13 consists of a hexanuclear dication
[Au6Cl4{(S,S)-iPr-pybox}4]2+ and two mononuclear [AuCl2]−
anions. The ORTEP-type view of the cation of complex 13 is
depicted in Figure 5, and selected bonding data are collected in
Table 1. The cation unit is comprised by six gold atoms, four
iPr-pybox ligands, and four chlorine atoms. The iPr-pybox/gold
coordination occurs only through the oxazoline nitrogen atoms,
and gold atoms do not present the same coordination
environment: Au1, Au3, Au4, and Au6 are coordinated to
one of the oxazoline nitrogen atoms of the four pybox ligands
[Au1−N1, Au3−N6, Au4−N7, and Au6−N12] and to a
chlorine atom, whereas Au2 and Au5 are coordinated to the
other oxazoline nitrogen atom of the pybox bonded to Au1 and
Au3 and to A4 and Au6, respectively. The bonds distances Au−
Noxazoline [2.008(14)−2.039(12) Å] and Au−Cl [2.247(3)−
Figure 4. ORTEP drawing of the cationic complex 10 showing the
atom-labeling scheme. Thermal ellipsoids are shown at the 20%
probability level. Hydrogen atoms and the CF3SO3 anions are omitted
for clarity.
2.877(9) Å; Ag2−N5 2.753(9)] than the N2 and N8 atoms (av.
3.046(12) Å; range of 2.922(12)−3.127(12) Å), with the Ag−
N
pyridine distances in all cases being shorter than the sum of the
van der Waals radii (3.27 Å).26
The Ag1···Ag2 distance [3.1020(11) Å], consistent with an
argentophilic interaction between the silver atoms, is slightly
larger for complex 10 that for complex 4 [3.029(6) Å]. As in
the case of complexes 1 and 4, the pybox skeleton is not planar,
Figure 5. ORTEP drawing of the cationic complex 13 showing the atom-labeling scheme. Thermal ellipsoids are shown at the 20% probability level.
Hydrogen atoms and the [AuCl2]− anions are omitted for clarity.
F
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1
Table 2. H and 19F DOSY NMR Experiments for
2.267(4) Å] are within the range found for other gold(I)
complexes with oxazoline31 or chlorine ligands.32,33
Complexes 1 and 4
The gold atoms of complex 13 feature aurophilic interactions
and adopt a linear coordination mode with small deviations
from the 180° axis [N−Au−Cl or N−Au−N angles between
174.2(4) and 177.1(4)°]. The shortest Au−Au distance
[3.139(1) Å] corresponds to Au3···Au4, whereas the other
distances are in the range 3.302(1) to 3.518(1) Å. The last one
is at the upper end of the generally accepted range of aurophilic
interactions.33,34 On the other hand, the pybox skeletons are
not planar, and the four pybox ligands show N−C−C−N
torsion angle values between −28(3) and −12(2)°.
a
́
́
rX‑ray (Å)
complex
nucleus
log D (m2 s−1
)
rH (Å)
b
c
d
1
1
4
4
1H
19F
1H
19F
−9.07
−8.90
−9.08
−8.95
6.2
4.2
6.3
4.7
6.08 /6.27 /6.44
e
2.75
f
g
6.27 /6.61
e
2.75
a
Reported values for a diffusion time parameter Δ = 300 ms.
b
c
d
[Ag2(iPr-pybox)2]2+. [Ag2(CF3SO3)(iPr-pybox)2]+. [Ag2(CF3SO3)-
e
(iPr-pybox)2][CF3SO3]. [CF3SO3]. The radius of the triflate anion
f
was calculated from its van der Waals volume. [Ag2(indane-
g
pybox)2]2+. [Ag2(indane-pybox)2][CF3SO3]2.
All attempts to synthesize other gold/pybox complexes using
the same precursor [AuCl{S(CH3)2}] and other pybox ligands
[(R,R)-Ph-pybox and (S,S)-iPr-Pybox-diPh] under different
reaction conditions were unsuccessful.
in 1 and with the indane protons (H9, H10, H15, and H16) in
4 in 1H/19F HOESY NMR (see Figure 6) proved that the two
Compound 13 represents, to the best of our knowledge, the
sole gold/pybox complex as yet reported.18
NMR Elucidation and Diffusion Studies for Complexes
1, 4, 10, and 12. The solid-state characterization of the new
silver(I)/pybox complexes 1, 4, 10, and 12 was complemented
with a solution-state study by NMR spectroscopy because the
catalytic activity of these complexes is always studied in
solution. We performed several experiments including structure
elucidation, VT measurements, and diffusion studies using
diffusion-ordered spectroscopy.
The NMR study of complexes 1 and 4 showed that their
crystalline structures (see Figures 1 and 2) are not maintained
in solution. Thus, 1H NMR spectra of both complexes 1 and 4
in CD2Cl2 at 298 K showed one set of signals for the oxazoline
(1), indenoxazole (4), and pyridine rings of both ligands. This
observation is consistent with a fast pyridine ligand exchange
between the two silver nuclei that would result in the observed
time-averaged C2-symmetry structure.35 The unique signal at
the 19F NMR spectrum (δ = −78.9 ppm for 1 and −78.8 ppm
for 4) also suggests the same chemical environment for the two
triflate anions. Low-temperature measurements in CD2Cl2
revealed that the 19F NMR signal does not exhibit any splitting
in the ranges of 298−183 K (for 1) and 298−213 K (for 4),
1
whereas the splitting of the H NMR signals start at 223 K,
leading to two sets of peaks at 183 K (80:20 ratio for 1) and
213 K (85:15 ratio for 4), which would be in accordance with
the presence of two conformer structures in solution.
The possible existence of a dynamic fast coordination process
of the two triflate anions was studied through DOSY
experiments for complexes 1 and 4.36−39 The diffusion
coefficients of the cationic complexes and triflate anion were
obtained from the 1H and 19F DOSY NMR spectra,
respectively. The measured diffusion coefficients of both
complexes 1 and 4 at 298 K, the hydrodynamic radii afforded
via the Stokes−Einstein equation, and the radii calculated from
the X-ray structure are presented in Table 2.
Significantly, the large value of the hydrodynamic radius of
the triflate anion in both complexes (1, 4.2 Å; 4, 4.7 Å) versus
its X-ray radius (2.75 Å) clearly indicates the existence of an
intimate ion pair between the CF3SO3 anion with the cation
complex. Because the sizes of the cations are much bigger than
that of the anion, the values obtained for them are less
significant, although they also point in the same direction.
The cation−anion interaction for both complexes 1 and 4
was also corroborated through HOESY NMR experiments.40
Strong cross peaks between the fluorine atom with the CHiPr
(H10) and CHMe2 (H13 and H14) proton atoms of the pybox
Figure 6. 1H/19F HOESY NMR spectra of complexes (a) 1 and (b) 4.
ionic fragments behave in a CD2Cl2 solution as tight ion pairs.
The existence of a unique chemical shift in the 19F NMR
spectrum supports the presence of a dynamic process in the
dinuclear compounds 1 and 4, involving a fast triflate anion
exchange between the two silver nuclei, causing the two anions
to be equivalent and producing a balanced 19F chemical shift
and 19F diffusion coefficient values.
A NMR study was also carried out for complexes
[Ag2(indane-pybox)3][CF3SO3]2 (10) and [Ag2(indane-
pybox)3][PF6]2 (12). The 19F NMR spectra in CD2Cl2 at
298 K showed unique signals at δ = −78.9 ppm (10) and −73.2
ppm (12), whereas the signal for the PF6 anion was observed at
δ = −144.7 ppm in the 31P NMR spectrum of 12. However, the
1H NMR spectra at 298 K show a number of broad peaks that
suggest the presence of several species in solution (see Figure
1
S4a for 10 and Figure S5a for 12). When H DOSY NMR
experiments were accomplished for compounds 10 and 12 at
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1
298 K, the same diffusion coefficient was measured for all of the
proton signals in each compound (log D = −9.10 and −9.08 m2
s−1 for 10 and 12, respectively), supporting also the existence of
these equilibria at room temperature. As observed for
complexes 1 and 4, heteronuclear NOE contacts between the
protons of the cationic fragments and the fluorine atoms of the
anions were detected for both the triflate complex 10 and the
Table 3. H DOSY NMR Experiments for Complex 12
1/3
species in solution
D (×10−10 m2 s−1
)
DL2/D12
(MW12/MWL2)
a
b
L2 and L2′
2.98
2.74
1.1
1.12 /1.09
12
a
b
Ratio for [Ag2(indane-pybox)2]2+/[Ag2(indane-pybox)3]2+. Ratio for
[Ag2(indane-pybox)2][PF6]2/[Ag2(indane-pybox)3][PF6]2. Interac-
tions between the PF6 anions and the cation fragments in L2, L2′,
and 12 may be assumed to occur in solution, as was previously
1
PF6 complex 12 through H/19F HOESY experiments (see the
Supporting Information), which again indicates the existence of
tight ion pairs. When the temperature was decreased from 298
to 193 K (Figure S4), the 1H NMR broad peaks of complex 10
sharpened and two species were observed in an approximate
90:10 ratio, while no splitting for the 19F NMR signal was
observed in the same range of temperatures. The major
compound was identified, after analysis of the COSY, TOCSY,
HSQC, HMBC, and 13C NMR spectra at 213 K, as the three-
detected from the H19F HOESY NMR spectrum of these species at
1
298 K.
showed exchange cross peaks between the parent signals of the
two-ligand conformers (L2 and L2′), but no exchange peaks
were detected between the resonances of the [Ag2(indane-
pybox)3]2+ 12 and the [Ag2(indane-pybox)2]2+ L2/L2′ species.
These observations show that at 213 K the two-ligand complex
exists in solution as two exchangeable conformers, but the two
different sized complexes do not experience any observable
interconversion process.
In conclusion, the three-ligand complexes [Ag2(indane-
pybox)3][X]2 10 and 12 exist in CD2Cl2 solution together
with variable amounts of their corresponding two-ligand
complexes [Ag2(indane-pybox)2][X]2. On the other hand, the
anions PF6 and CF3SO3 have different abilities to stabilize the
two- or three-ligand complexes. At 213 K, the triflate
counteranion favors the three-ligand complex, while for PF6,
it is the two-ligand structure that is the one preferred. Also, the
anion significantly affects the ratio of the conformers of the
two-ligand complexes. Thus, in the case of complex 10 (X =
CF3SO3), a highly preferred conformation is observed at low
temperature. However, for complex 12 (X = PF6), the two-
ligand complex conformers L2 and L2′ are present in a nearly
equimolar ratio.
Silver(I)-Catalyzed Addition of Alkynes to Imines.
Probably, the addition of terminal alkynes to either
imines12a−e,42 or aldehydes/amines12h,i,43 catalyzed by tran-
sition metals can be considered as the most useful direct access
to enantiopure propargylamines. The synthetic potential of
these species is well recognized because they have been
extensively employed for the construction of privileged
nitrogen-containing structures, particularly biologically active
compounds and natural products. Recently, we reported the
efficient alkynylation reaction of imines catalyzed by the
dinuclear complexes [Cu2{(R,R)-Ph-pybox}2][X]2 (X =
CF3SO3 and PF6; up to 89% e.e.).2,44 In this paper, we report
the results on the addition of phenylacetylene to N-
benzylideneaniline catalyzed by the new silver(I)/pybox
complexes 1, 2, 4, and 10. In a typical experiment, dried and
deoxygenated CH2Cl2 (0.5 mL) was placed in a three-neck
Schlenk flask, under an argon atmosphere, followed by the
addition of the precatalyst (0.02 mmol). After the addition of
N-benzylideneaniline (0.4 mmol) and phenylacetylene (0.6
mmol), the resulting mixture was stirred in the absence of light
(48 h, room temperature) to provide N-(1,3-diphenyl-2-
propynyl)aniline. As summarized in Table 4, the results of
this screening reveal that the catalytic activity of these
complexes is only moderate.
ligand cationic complex [Ag2(indane-pybox)3]2+ 10.41 The H
1
NMR spectrum at 213 K of complex 10 shows one set of
signals for the six oxazoline and three pyridine rings of the three
pybox moieties, denoting a high degree of symmetry in the
cationic complex. The minor species was identified as the major
conformer of the two-ligand complex [Ag2(indane-pybox)2]-
[CF3SO3]2 (4). The ratio between complexes 10 and 4 varies
with the temperature and was measured at 213 K (82:18) and
193 K (90:10).
Also the temperature dependence of complex 12 was studied
1
through several H NMR experiments recorded in CD2Cl2
(Figure S5). The broad signals observed at room temperature
were resolved at 213 K (Figure S5d) in three sets of peaks. A
careful comparison between this spectrum and the spectra of 4
(Figure S5e) and 10 (Figure S4c) at the same temperature
revealed that two of the three sets of peaks observed for 12 also
appeared in the 1H NMR spectrum of complex 4, and therefore
they were tentatively assigned to two conformers of the cationic
PF6 complex [Ag2(indane-pybox)2]2+ (L2 and L2′). The third
set of peaks, which remains unchanged through over the entire
range of temperatures evaluated, resembles the 1H NMR
signals of the CF3SO3 cationic three-ligand cationic complex
10, and analysis of the COSY, TOCSY, HSQC, and HMBC
NMR spectra confirmed its assignment as the PF6 cationic
three-ligand complex [Ag2(indane-pybox)3]2+ 12. The two
conformers (L2 and L2′) are present in nearly equal
proportion (51:49) at 213 K. Thus, at 213 K the solution
contains a mixture of the three- and two-ligand complexes in a
ratio of 12:L2:L2′ = 25:38:37.
To confirm the presence of these different size species in
solution, DOSY NMR experiments were carried out on the
CD2Cl2 sample of compound 12. The 1H DOSY NMR
spectrum of complex 12 measured at 213 K (Figure S6)
showed, as expected, two well-defined traces corresponding to
two diffusion coefficients, one of which can be assigned to the
two-ligand complexes L2 and L2′ with a larger diffusion
coefficient (DL2 = 2.98 × 10−10 m2 s−1) and the other to the
three-ligand complex 12 (D12 = 2.74 × 10−10 m2 s−1). The
calculated ratio from the measured diffusion coefficients (DL2/
D12 = 1.1) agrees with the expected ratio for the two molecules
having two- and three-coordinated indane-pybox ligands
[(MW12/MWL2)1/3; see Table 3].
The results of the DOSY NMR experiments at 298 and 213
K suggest that complex 12 maintains a dynamic equilibrium
with its corresponding two-ligand complexes L2 and L2′ at
room temperature, which is resolved at 213 K. In addition, the
2D ROESY NMR spectra of complex 12 recorded at 213 K
H
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The resulting N-(1,3-diphenyl-2-propynyl)aniline was ob-
tained in high chemical yield when triflate complexes were
utilized as catalysts (entries 1 and 3 vs 2). Also, we observed
that silver (3aS,3a′S,8aR,8a′R)-indane-pybox complexes provide
higher enantioselectivity than (S,S)-iPr-pybox derivatives (entry
3 vs 1 and 2). The best results were reached using the dinuclear
triflate complexes 4 and 10 (entries 3 and 4).
Moreover, it has been reported that both the yield and e.e. of
the catalytic addition of phenylacetylene to imines are strongly
affected by the solvent.12c,45 Thus, Kesavan and co-workers
observed that the best results for the copper(I)-catalyzed
addition of phenylacetylene to benzylidene(p-methoxyaniline)
were obtained using chlorinated solvents (CH2Cl2 and,
particularly, CHCl3). In this context, we have checked the
solvent effect for catalyst 4 using CH2Cl2 and CHCl3 and
different concentrations. The use of CHCl3 significantly
decreases the e.e. compared with CH2Cl2 (entries 6 and 7 vs
3 and 5). In addition, increasing the reagent concentration
(CH2Cl2, 0.25 mL; CHCl3, 0.25 or 0.1 mL) leads to poorer
results in terms of conversion and/or asymmetric induction
(entries 5−7 vs 3), although the reaction time is substantially
reduced.
Table 4. Catalytic Activity of Dinuclear Silver(I) Complexes
for the Enantioselective Synthesis of (1,3-Diphenyl-2-
propynyl)aniline
a
b
c
catalyst
conv (%)
yield (%)
e.e. (%) (R)
1
2
3
4
5
6
7
1
99
59
97
86
89
50
86
75
69
76
78
24
26
44
40
34
8
2
4
10
d
4
e
4
f
4
14
a
The reactions were carried out using benzylideneaniline (0.4 mmol).
The ratio of benzylideneaniline:phenylacetylene:silver complex =
1:1.5:0.05. The reactions were carried out in anhydrous CH2Cl2 (0.5
mL), under an argon atmosphere, in the absence of light, at room
b
temperature for 48 h. Isolated yield after chromatographic
c
purification. Enantiomeric excess determined by HPLC with a
Chiralcel OD-H column. The absolute configuration was assigned
d
on the basis of the literature data. Similar reaction conditions in
e
CH2Cl2 (0.25 mL) for 24 h. Similar reaction conditions in CHCl3
f
(0.25 mL) for 24 h. Similar reaction conditions in CHCl3 (0.10 mL)
for 6 h.
Table 5. Crystal Data and Structure Refinement for Complexes 1, 4, and 5
1
4
5
empirical formula
fw
C36H46N6F6O10S2Ag2
1116.64
C52H38N6F6O10S2Ag2
1300.74
C44H42N6F6O10S2Ag2
1208.69
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
173(2)
100(2)
123(2)
1.5418
1.5418
1.5418
orthorhombic
P212121
orthorhombic
P212121
monoclinic
P21
13.5986(1)
21.2402(2)
31.0125(3)
90
12.8183(2)
16.1215(2)
23.4147(4)
90
18.8039(3)
12.5654(1)
21.0568(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
90
90
111.442(2)
90
γ (deg)
volume (Å3)
90
90
8957.56(14)
8
4838.65(13)
4
4630.92(12)
4
Z
ρcalcd (Mg m−3
)
1.656
1.786
1.734
μ (mm−1
)
8.634
8.110
8.412
F(000)
4512
2608
2432
cryst size (mm3)
θ range (deg)
index ranges
0.072 × 0.120 × 0.255
2.850−74.126
−16 ≤ h ≤ 15
−22 ≤ k ≤ 25
−37 ≤ l ≤ 26
28254
0.121 × 0.095 × 0.046
3.931−69.463
−15 ≤ h ≤ 5
−16 ≤ k ≤ 19
−28 ≤ l ≤ 26
20406
0.144 × 0.105 × 0.04
3.954−74.626
−23 ≤ h ≤ 23
−15 ≤ k ≤ 15
−26 ≤ l ≤ 25
37484
no. of reflns collected
no. of indep reflns
completeness (%) (θ)
refinement method
no. of param/restraints
GOF on F2
14770 [R(int) = 0.0399]
99.6 (67.000)
full-matrix least squares on F2
1121/15
8865 [R(int) = 0.0378]
99.5 (67.680)
full-matrix least squares on F2
703/0
18384 [R(int) = 0.0490]
99.9 (67.684)
full-matrix least squares on F2
1269/48
1.025
1.046
1.017
weight function (a, b)
0.0728, 6.9205
R1 = 0.0442, wR2 = 0.1175
R1 = 0.0472, wR2 = 0.1218
−0.011(5)
0.0359, 3.0954
R1 = 0.0348, wR2 = 0.0790
R1 = 0.0404, wR2 = 0.0829
−0.020(4)
0.0777, 3.8685
R1 = 0.0520, wR2 = 0.1304
R1 = 0.0635, wR2 = 0.1416
−0.030(8)
a
R [I > 2σ(I)]
R (all data)
absolute structure param
largest diff peak and hole (e Å−3
)
1.239 and −1.264
0.635 and −1.174
1.163 and −1.177
a
2
2
R1 = ∑(|Fo| − |Fc|)/∑|Fo|; wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2
.
I
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CONCLUSIONS
Table 6. Crystal Data and Structure Refinement for
Complexes 6 and 9
■
The synthesis of enantiopure mono- and dinuclear silver(I)/
pybox complexes, [AgL2]2+ (L = Pr-pybox and indane-pybox),
i
6·0.5CH2Cl2
9·CH2Cl2
[Ag2L2]2+ (L = iPr-pybox and indane-pybox), and [Ag2L3]2+ (L
= indane-pybox), has been carried out from silver salts and
pybox ligands in the appropriate molar ratio. The structures of
the dinuclear (1, 4, 5, 10, and 11) and mononuclear (6 and 9)
silver complexes have been determined by single-crystal X-ray
diffraction analysis. From the VT-NMR study of complexes, it
can be derived that for complexes 1 and 4 two conformers are
present in the solution and that the three-ligand complexes
[Ag2(indane-pybox)3][X]2 10 (X = CF3SO3) and 12 (X = PF6)
exist in CD2Cl2 solution together with variable amounts of their
corresponding two-ligand complexes [Ag2(indane-pybox)2]-
[X]2. The dinuclear complexes 1, 2, 4, and 10 were tested as
catalysts in the addition of phenylacetylene to benzylideneani-
line, and complexes 4 and 10 were found to be the most active
catalysts, providing high chemical yields but unsatisfactory
chiral induction (e.e. 40−44%). Interestingly, the studies herein
reported represent, to the best of our knowledge, the first
examples of an asymmetric catalytic reaction using silver(I)/
pybox complexes. The synthesis of the first gold(I)/pybox
complex 13 is also reported.
empirical formula
fw
C34.5H47N6SbClF6O4Ag
988.85
C51H40N6BCl2F4O4Ag
1066.47
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
123(2)
100(2)
1.5418
1.5418
monoclinic
C2
monoclinic
P21
23.8574(6)
15.1992(3)
11.4192(2)
90
12.818(5)
11.676(5)
14.992(5)
90
b (Å)
c (Å)
α (deg)
β (deg)
103.804(2)
90
95.998(5)
90
γ (deg)
volume (Å3)
4021.16(15)
4
2231.5(15)
2
Z
ρcalcd (Mg m−3
)
1.633
1.587
μ (mm−1
)
10.476
5.340
F(000)
1988
1084
cryst size (mm3)
θ range (deg)
index ranges
0.113 × 0.069 × 0.062
3.478−74.639
−29 ≤ h ≤ 23
−18 ≤ k ≤ 12
−11 ≤ l ≤ 14
7914
0.177 × 0.163 × 0.151
2.964−68.302
−15 ≤ h ≤ 15
−14 ≤ k ≤ 14
−17 ≤ l ≤ 17
30650
EXPERIMENTAL SECTION
■
no. of reflns collected
no. of indep reflns
General Procedures. The reactions were performed under an
atmosphere of dry argon using vacuum-line and standard Schlenk
techniques. Solvents were dried by standard methods and distilled
under argon before use. The (S,S)-iPr-pybox46 and indane-pybox47
ligands and the complex [AuCl{S(CH3)2}]48 were prepared by
reported methods. IR spectra were recorded on a PerkinElmer 1720-
XFT spectrometer. The conductivities were measured at room
temperature, in ca. 5 × 10−4 mol L−1 acetone solution, with a with
a Crison EC-Meter Basic 30+ conductimeter. Carbon, hydrogen, and
nitrogen analyses were carried out with PerkinElmer 240-B and LECO
CHNS-TruSpec microanalyzers. Mass spectra (FAB) were determined
with a VG-AUTOSPEC mass spectrometer, operating in the positive
mode; 3-nitrobenzyl alcohol was used as the matrix. Experimental
conditions for NMR experiments are available in the Supporting
Information. Coupling constants J are given in hertz. Abbreviations
used: s, singlet; br s, broad singlet; d, doublet; t, triplet; q, quartet;
sept, septuplet; m, multiplet. The following atom labels were used for
5387 [R(int) = 0.0299]
7824 [R(int) = 0.0272]
99.4 (67.000)
completeness (%) (θ) 99.3 (67.000)
refinement method full-matrix least squares
on F2
no. of param/restraints 493/8
GOF on F2
1.086
weight function (a, b) 0.0537, 0.2962
full-matrix least squares
on F2
622/1
1.057
0.0983, 2.4337
a
R [I > 2σ(I)]
R1 = 0.0386, wR2 =
0.1042
R1 = 0.0525, wR2 =
0.1411
R (all data)
R1 = 0.0428, wR2 =
0.1087
R1 = 0.0527, wR2 =
0.1414
absolute structure
param
0.029(8)
0.006(4)
largest diff peak and
0.546 and −1.356
2.067 and −0.688
hole (e Å−3
)
a
2
2
R1 = ∑(|Fo| − |Fc|)/∑|Fo|. wR2 = {∑[w(Fo − Fc )2]/
1
the H and 13C{1H} NMR spectroscopic data of the pybox ligands:
2
∑[w(Fo )2]}1/2
.
1
NMR (282.40 MHz, CD2Cl2, 298 K): δ −78.9. H NMR (400.13
MHz, CDCl3, 298 K): δ 8.32 (s, 6H, H3,4,5 C5H3N), 4.98 (dd, JHH
=
9.8 Hz, JHH = 9.1 Hz, 4H, OCH2), 4.53 (t, JHH = 9.1 Hz, 4H, OCH2),
4.33 (m, 4H, CHiPr), 1.86 (sept, JHH = 6.7 Hz, 4H,CHMe2), 0.92 (d,
JHH = 6.7 Hz, 12H, CHMe2), 0.86 (d, JHH = 6.7 Hz, 12H, CHMe2).
13C{1H} NMR (100.61 MHz, CD2Cl2, 298 K): δ 165.5 (s, OCN),
144.2 (s, C2,6 C5H3N), 140.5 (s, C4 C5H3N), 128.3 (s, C3,5 C5H3N),
Synthesis of the Dinuclear Complexes [Ag2(CF3SO3){(S,S)-iPr-
pybox}2][CF3SO3] (1), [Ag2{(S,S)-iPr-pybox}2][PF6]2 (2), and
[Ag2{(3aS,3a′S,8aR,8a′R)-indane-pybox}2][CF3SO3]2 (4). The corre-
sponding pybox ligand (0.20 mmol) was added to a suspension of the
different silver salts (0.20 mmol) in CH2Cl2 (20 mL), and the mixture
was stirred, in the absence of light, for 1 h (for 1 and 2) or 1.5 h (for
4) at room temperature. Then, the suspension was exposed to light for
1 h, filtered through a cannula transfer, and concentrated under
reduced pressure to a volume of ca. 2 mL. The addition of diethyl
ether (20 mL; for 1 and 2) or a mixture of 1:4 diethyl ether/hexane
(25 mL; for 4) afforded a precipitate. The solvents were decanted, and
the solid was washed with diethyl ether (3 × 10 mL; for 1 and 2) or
hexane (3 × 10 mL; for 4) and vacuum-dried.
−
120.4 (q, JCF = 321.0 Hz, CF3SO3 ), 73.8 (s, OCH2), 71.7 (s, CHiPr),
32.6 (s, CHMe2), 18.7, 18.1 (2s, CHMe2). 19F{1H} NMR (282.4 MHz,
−
1
CD2Cl2, 298 K): δ −78.3 (s, 3F, CF3SO3 ). H NMR (400.13 MHz,
CD2Cl2, 193 K): δ 8.29 (br s, 6H, H3,4,5 C5H3N), 4.92, 4.55, 4.53, 4.21
(4m, 12H, CHiPr, OCH2), 1.93 (m, 1H, CHMe2), 1.56 (m, 3H,
CHMe2), 0.79 (m, 24H, CHMe2). 13C{1H} NMR (100.61 MHz,
CD2Cl2, 193 K): δ 165.9, 165.7 (2s, OCN), 143.7, 143.5 (2s, C2,6
C5H3N), 141.4 (s, C4 C5H3N), 129.1, 128.6 (2s, C3,5 C5H3N), 120.4
−
(q, JCF = 321.0 Hz, CF3SO3 ), 74.9, 72.5, 72.2, 70.2 (4s, CHiPr,
OCH2), 33.7, 31.4 (2s, CHMe2), 19.1, 18.9, 18.2, 16.0 (4s, CHMe2).
Anal. Calcd for C36H46N6F6O10Ag2S2 (1116.64): C, 38.72; H, 4.15; N,
7.53; S, 5.74. Found: C, 38.78; H, 4.12; N, 7.70; S, 6.04.
Complex 1. Color: colorless. Yield: 84% (0.094 g). ΛM = 86 S cm2
mol−1 (nitromethane, 293 K). ΛM = 210 S cm2 mol−1 (acetone, 293
Complex 4. Color: gray. Yield: 67% (0.087 g). ΛM = 284 S cm2
−
−
K). IR (KBr): ν(CF3SO3 ) 1265 (vs), 1156 (s), 1026 (vs) cm−1. MS-
mol−1 (acetone, 293 K). IR (KBr): ν(CF3SO3 ) 1260 (vs), 1162 (s),
FAB: m/z 709 ([Ag(iPr-pybox)2]+), 408 ([Ag(iPr-pybox)]+). 19F{1H}
1033 (vs) cm−1. MS-FAB: m/z 500 ([Ag(indane-pybox)]+). 19F{1H}
J
DOI: 10.1021/acs.inorgchem.6b01323
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 7. Crystal Data and Structure Refinement for Complexes 10, 11, and 13
10·CH2Cl2
11·CH2Cl2
13·Et2O·2Me2CO
empirical formula
fw
C78H59N9Cl2F6O12S2Ag2
1779.10
C76H59N9Sb2Cl2F12O6Ag2
1952.46
C78H114N12Cl8Au8O11
3249.10
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
150(2)
150(2)
123(2)
1.5418
1.5418
1.5418
monoclinic
monoclinic
monoclinic
P21
P21
P21
13.6217(5)
21.2392(8)
13.9381(6)
90
13.7551(9)
21.2733(9)
13.9694(8)
90
9.9624(2)
27.3747(6)
18.1167(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
117.097(5)
90
116.471(8)
90
95.148(2)
90
γ (deg)
volume (Å3)
3589.9(3)
3659.1(4)
4920.81(17)
2
Z
2
2
ρcalcd (Mg m−3
)
1.646
1.772
2.193
μ (mm−1
)
6.355
11.484
24.290
F(000)
1800
1928
3032
cryst size (mm3)
θ range (deg)
index ranges
0.216 × 0.087 × 0.048
3.562−74.414
−16 ≤ h ≤ 12
−26 ≤ k ≤ 26
−16 ≤ l ≤ 17
27045
0.053 × 0.024 × 0.014
3.59−74.79
−15 ≤ h ≤ 14
−25 ≤ k ≤ 18
−17 ≤ l ≤ 16
13619
0.057 × 0.043 × 0.018
2.93−72.08
−12 ≤ h ≤ 10
−31 ≤ k ≤ 32
−21 ≤ l ≤ 19
19105
no. of reflns collected
no. of indep reflns
completeness (%) (θ)
refinement method
no. of param/restraints
GOF on F2
13840 [R(int) = 0.0409]
100 (67.000)
full-matrix least squares on F2
989/30
9391 [R(int) = 0.0432]
94.8 (67.00)
full-matrix least squares on F2
970/22
14038 [R(int) = 0.0353]
96.4 (72.08)
full-matrix least squares on F2
1066/37
1.026
1.088
1.043
weight function (a, b)
0.1279, 2.0533
R1 = 0.0685, wR2 = 0.1857
R1 = 0.0864, wR2 = 0.2076
0.013(6)
0.1278, 15.6655
R1 = 0.0774, wR2 = 0.2223
R1 = 0.0851, wR2 = 0.2307
0.047(14)
0.0858, 5.8772
a
R [I > 2σ(I)]
R1 = 0.0476, wR2 = 0.1238
R1 = 0.0506, wR2 = 0.1268
−0.028(15)
R (all data)
absolute structure param
largest diff peak and hole (e Å−3
R1 = ∑(|Fo| − |Fc|)/∑|Fo|; wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2
)
1.169 and −1.227
2.203 and −1.261
2.202 and −2.151
a
2
2
.
1
NMR (282.40 MHz, CD2Cl2, 298 K): δ −78.8. H NMR (400.13
method B: 70% (0.052 g). ΛM = 261 S cm2 mol−1 (acetone, 298 K). IR
−
MHz, CD2Cl2, 298 K): δ 8.42 (s, 6H, H3,4,5 C5H3N), 7.24 (t, JHH = 7.5
Hz, 4H, CHarom), 7.12 (d, JHH = 7.5 Hz, 4H, CHarom), 6.88 (t, JHH
(KBr): ν(BF4 ) 1064 (vs) cm−1. 1H NMR (400.13 MHz, CD2Cl2, 298
=
K): δ 8.56 (t, JHH = 6.9 Hz, 2H, H4 C5H3N), 8.38 (m, 4H, H3,5
C5H3N), 5.06 (t, JHH = 9.6 Hz, 4H, OCH2), 4.68 (t, JHH = 9.6 Hz, 4H,
7.3 Hz, 4H, CHarom), 6.80 (d, JHH = 7.3 Hz, 4H, CHarom), 5.91 (dd, JHH
= 8.7 Hz, JHH= 7.3 Hz, 4H, OCH), 5.83 (d, JHH = 8.7 Hz, 4H, NCH),
3.47 (dd, JHH = 18.4 Hz, JHH = 7.3 Hz, 4H, CH2), 3.19 (d, JHH = 18.4
Hz, 4H, CH2). 13C{1H} NMR (100.61 MHz, CD2Cl2, 298 K): δ 165.4
(s, OCN), 144.6 (s, C2,6 C5H3N), 141.0 (s, C4 C5H3N), 139.3, 138.5
(2s, Carom), 129.0 (s, CHarom), 128.3 (s, C3,5 C5H3N), 127.2, 126.4,
OCH2), 4.42 (m, 4H, CHiPr), 1.97 (m, 4H, CHMe2), 1.02 (d, JHH
=
6.6 Hz, 12H, CHMe2), 0.97 (d, JHH = 6.6 Hz, 12H, CHMe2). 13C{1H}
NMR (100.61 MHz, CD2Cl2, 298 K): δ 166.3 (s, OCN), 144.0 (s, C2,6
C5H3N), 141.7 (s, C4 C5H3N), 126.4 (s, C3,5 C5H3N), 73.3 (s, OCH2),
70.9 (s, CHiPr), 31.4 (s, CHMe2), 17.7, 16.5 (2s, CHMe2). 19F{1H}
−
−
124.1 (3s, CHarom), 120.6 (q, JCF = 319.9 Hz, CF3SO3 ), 88.1 (s,
NMR (282.4 MHz, CD2Cl2, 298 K): δ −151.3 (s, BF4 ). Anal. Calcd
OCH), 75.6 (s, NCH), 38.8 (s, CH2). Anal. Calcd for
C52H38N6F6O10Ag2S2 (1300.75): C, 48.02; H, 2.94; N, 6.46; S, 4.93.
Found: C, 48.13; H, 3.24; N, 6.25; S, 5.13.
for C34H46N6B2F8O4Ag2 (992.12): C, 41.16; H, 4.67; N, 8.47. Found:
C, 41.11; H, 4.87; N, 8.13.
Synthesis of the Dinuclear Complex [Ag2{(S,S)-iPr-pybox}-
i
Synthesis of the Dinuclear Complex [Ag2{(S,S)-iPr-pybox}2][BF4]2
(3). Method A: To a suspension of AgF (0.019 g, 0.15 mmol) in
{(3aS,3a′S,8aR,8a′R)-indane-pybox}][CF3SO3]2 (5). Pr-pybox (0.10
mmol) and indane-pybox (0.10 mmol) were added to a suspension of
AgOSO2CF3 (0.052 g, 0.20 mmol) in CH2Cl2 (10 mL), and the
mixture was stirred, in the absence of light, for 1.5 h at room
temperature. Then, the suspension was exposed to light for 1 h,
filtered through a cannula transfer, and concentrated under reduced
pressure to a volume of ca. 2 mL. The addition of a mixture of 1:4
diethyl ether/hexane (25 mL) afforded a pale-brown precipitate. The
solvents were decanted, and the solid was washed with hexane (3 × 10
mL) and vacuum-dried. Color: pale brown. Yield: 56% (0.068 g). ΛM
i
dichloromethane (5 mL) were added the Pr-pybox ligand (0.045 g,
0.15 mmol) and BF3·OEt2 (18 μL, 0.15 mmol). The mixture was
stirred at room temperature in the absence of light, for 3 h. Then, the
suspension was exposed to light for 1 h, filtered through a cannula
transfer, and concentrated under reduced pressure to a volume of ca. 2
mL. The addition of diethyl ether (20 mL) afforded a pale-yellow
solid. The solvents were decanted, and the solid was washed with
diethyl ether (3 × 5 mL) and vacuum-dried. Method B: The (S,S)-iPr-
pybox ligand (0.045 g, 0.15 mmol) was added to a suspension of
AgBF4 (0.029 g, 0.15 mmol) in dichloromethane (5 mL), and the
mixture was stirred at room temperature, in the absence of light, for 3
h. The reaction mixture was worked up as described in Method A.
Color: Pale yellow. Yield for method A: 66% (0.049 g). Yield for
−
= 219 S cm2 mol−1 (acetone, 293 K). IR (KBr): ν(CF3SO3 ) 1260
1
(vs), 1159 (vs), 1029 (s) cm−1. H NMR (400.13 MHz, CD2Cl2, 298
K): δ 8.44, 8.31 (2m, 6H, H3,4,5 C5H3N), 7.39 (m, 4H, CHarom), 7.10
(m, 4H, CHarom), 6.07 (d, JHH = 8.4 Hz, 1H, NCH), 6.00 (t, JHH = 7.6
Hz, 1H, OCH), 4.75 (m, 2H, OCH2), 3.99 (m, 4H, OCH2, CHiPr),
K
DOI: 10.1021/acs.inorgchem.6b01323
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3.72 (dd, JHH = 18.4 Hz, JHH = 7.6 Hz, 2H, CH2), 3.40 (d, JHH = 18.4
Hz, 2H, CH2), 0.50 (d, JHH = 6.4 Hz, 6H, CHMe2), 0.48 (d, JHH = 6.4
Hz, 6H, CHMe2), −0.01 (m, 2H, CHMe2). 13C{1H } NMR (100.61
MHz, CD2Cl2, 298 K): δ 165.3, 165.1 (2s, OCN), 144.7, 144.1 (2s,
C2,6 C5H3N), 140.9, 140.6 (2s, C4 C5H3N), 140.1, 139.4 (2s, Carom),
129.6 (s, CHarom), 128.3 (s, C3,5 C5H3N), 127.7, 125.7, 125.3 (3s,
(s), 1030 (vs) cm−1. 19F{1H} NMR (282.40 MHz, CD2Cl2, 298 K): δ
−
−78.9 (s, 6F, CF3SO3 ). 1H NMR (600.15 MHz, Me2CO-d6, 298 K):
δ 8.51 (m, 9H, H3,4,5 C5H3N), 7.35 (br s, 12H, CHarom), 6.77 (br s, 6H,
CHarom), 6.41 (br s, 6H, CHarom), 5.76 (br s, 6H, OCH), 4.39 (br s,
6H, NCH), 3.58 (br m, 12H, CH2). 13C{1H} NMR (100.61 MHz,
Me2CO-d6, 298 K): δ 164.2 (s, OCN), 144.9 (s, C2,6 C5H3N), 140.9
(s, C4 C5H3N), 140.0, 139.5 (2s, Carom), 129.1 (s, CHarom), 128.8 (s,
C3,5 C5H3N), 125.7, 125.1 (2s, CHarom), 121.0 (q, JCF = 322.0 Hz,
−
CHarom), 120.6 (q, JCF = 320.8 Hz, CF3SO3 ), 87.4 (s, OCH), 75.8 (s,
NCH), 73.9 (s, OCH2), 72.0 (s, CHiPr), 39.5 (s, CH2), 32.0 (s,
CHMe2 ), 19.4, 18.2 (2s, CHMe2 ). Anal. Calcd for
C44H42N6F6O10Ag2S2 (1208.70): C, 43.72; H, 3.50; N, 6.95; S, 5.30.
Found: C, 43.90; H, 3.65; N, 6.81; S, 5.15.
−
1
CF3SO3 ), 86.3 (s, OCH), 76.1 (s, NCH), 39.4 (s, CH2). H NMR
(600.15 MHz, CD2Cl2, 298 K): δ 8.36 (br s, C5H3N), 7.34, 7.21, 7.09,
6.95 (br s, CHarom), 6.68, 6.34 (br s, CHarom), 5.6 (br m, OCH), 4.2
(br m, NCH), 3.7−2.7 (br m, CH2). Anal. Calcd for
C77H57N9F6O12Ag2S2 (1694.20): C, 54.59; H, 3.39; N, 7.44; S, 3.78.
Found: C, 54.28; H, 3.59; N, 7.38; S, 3.98.
Synthesis of the Mononuclear Complexes [Ag{(S,S)-iPr-pybox}2]-
i
[X] [X = SbF6 (6), PF6 (7), and BF4 (8)]. Pr-pybox (0.3 mmol) was
added to a suspension of the corresponding silver salt (0.15 mmol) in
CH2Cl2 (20 mL), and the mixture was stirred, in the absence of light,
for 1 h at room temperature. Then, the suspension was exposed to
light for 1 h, filtered through a cannula transfer, and concentrated
under reduced pressure to a volume of ca. 2 mL. The addition of
hexane (20 mL) afforded a precipitate. The solvents were decanted,
and the solid was washed with hexane (3 × 10 mL) and vacuum-dried.
Complex 6. Color: pale yellow. Yield: 80% (0.114 g). ΛM = 134 S
Complex 12. Color: pale yellow. Yield: 63% (0.053 g). ΛM = 229 S
−
cm2 mol−1 (acetone, 293 K). IR (KBr): ν(PF6 ) 843 (vs). 19F{1H}
NMR (282.40 MHz, CD2Cl2, 298 K): δ −73.2 (d, JPF = 712.0 Hz,
−
PF6 ). 31P NMR (121.5 MHz, CD2Cl2, 298 K): δ −144.0 (sp, JPF
=
−
1
712.0 Hz, PF6 ). H NMR (400.13 MHz, Me2CO-d6, 298 K): δ 8.47
(br s, 9H, H3,4,5 C5H3N), 7.33 (br s, 12H, CHarom), 6.77 (br s, 6H,
CHarom), 6.41 (br s, 6H, CHarom), 5.73 (m, 6H, OCH), 4.39 (br s, 6H,
NCH), 3.55 (br s, 12H, CH2). 13C{1H} NMR (100.61 MHz, Me2CO-
d6, 298 K): δ 164.2 (s, OCN), 144.9 (s, C2,6 C5H3N), 140.8 (s, C4
C5H3N), 140.0, 139.4 (2s, Carom), 129.1 (s, CHarom), 128.8 (s, C3,5
C5H3N), 127.9, 125.7, 125.2 (3s, CHarom), 86.3 (s, OCH), 76.2 (s,
−
cm2 mol−1 (acetone, 293 K). IR (KBr): ν(SbF6 ) 656 (vs) cm−1. MS-
FAB: m/z 709 ([Ag(iPr-pybox)2]+), 408 ([Ag(iPr-pybox)]+). 19F{1H}
1
NMR (282.40 MHz, CD2Cl2, 298 K): δ −124.0. H NMR (600.15
MHz, CD2Cl2, 298 K): δ 8.17 (s, 6H, H3,4,5 C5H3N), 4.63 (dd, 4H, JHH
= 9.8 Hz, JHH = 8.7 Hz, OCH2), 4.53 (t, 4H, JHH= 8.7 Hz, OCH2),
3.91 (m, 4H, CHiPr), 1.67 (sept, 4H, JHH = 6.7 Hz, CHMe2), 0.82 (d,
JHH = 6.7 Hz, 12H, CHMe2), 0.79 (d, JHH = 6.7 Hz, 12H,
CHMe2).13C{1H} NMR (100.61 MHz, CD2Cl2, 298 K): δ 162.2 (s,
OCN), 144.2 (s, C2,6 C5H3N), 139.7 (s, C3,5 C5H3N), 125.9 (s, C4
C5H3N), 72.6 (s, OCH2), 72.1 (s, CHiPr), 32.6 (s, CHMe2), 18.5, 17.2
(2s, CHMe2). Anal. Calcd for C34H46N6SbF6O4Ag (946.40): C, 43.15;
H, 4.90; N, 8.88. Found: C, 42.94; H, 4.80; N, 8.90.
1
NCH), 39.4 (s, CH2). H NMR (600.15 MHz, CD2Cl2, 293 K): δ
8.44, 8.34 (br s, H3,4,5 C5H3N, 12, L2, and L2′), 7.35, 7.28, 7.19 (br s,
CHarom, 12, L2, and L2′), 6.88, 6.75, 6.68 (br s, CHarom, 12, L2, and
L2′), 6.34 (br s, CHarom, 12), 5.98, 5.76, 5.58 (br s, OCH, 12, L2, and
L2′, NCH, L2 and L2′), 4.12 (br d, J = 5.3 Hz, NCH, 12), 3.49, 3.26
(br m, CH2, 12, L2, and L2′). Anal. Calcd for C75H57N9F12O6P2Ag2
(1686.00): C, 53.43; H, 3.41; N, 7.48. Found: C, 53.42; H, 3.66; N,
7.08.
Synthesis of the Hexanuclear Gold Complex [Au6Cl4{(S,S)-iPr-
pybox}4][AuCl2]2 (13). iPr-pybox (0.061 g, 0.20 mmol) was added to a
solution of [AuCl{S(CH3)2}] (0.059 g, 0.20 mmol) in acetonitrile (20
mL). The solution was stirred, in the absence of light, for 2 h at room
temperature and subsequently concentrated under reduced pressure to
a volume of ca. 2 mL. The addition of diethyl ether (20 mL) afforded a
colorless precipitate. Solvents were decanted, and the solid was washed
with diethyl ether (3 × 10 mL) and vacuum-dried. Color: colorless.
Yield: 43.5% (0.033 g). ΛM = 174 S cm2 mol−1 (acetone, 293 K). MS-
FAB: m/z 730 ([Au2Cl(iPr-pybox)]+). 1H NMR (400.13 MHz,
CD2Cl2, 298 K): δ 8.34 (d, JHH = 7.6 Hz, 8H, H3,5 C5H3N), 8.17 (m,
4H, H4 C5H3N), 4.83 (m, 8H, OCH2), 4.65 (m, 16H, OCH2, CHiPr),
2.68 (m, 8H, CHMe2), 1.08 (d, JHH = 7.2 Hz, 24H, CHMe2), 1.05 (d,
JHH = 6.8 Hz, 24H, CHMe2). 13C{1H} NMR (100.61 MHz, Me2CO-
d6, 298 K): δ 165.7 (s, OCN), 143.3 (s, C2,6 C5H3N), 139.2 (s, C4
C5H3N), 127.9 (s, C3,5 C5H3N), 72.4 (s, CHiPr), 71.1 (s, OCH2), 31.3
(s, CHMe2), 18.2, 14.8 (2s, CHMe2). Anal. Calcd for
C68H92N12Cl8Au8O8 (3064.89): C, 26.65; H, 3.03; N, 5.48. Found:
C, 26.51; H, 3.22; N, 5.22.
General Procedure for the Enantioselective Addition of
Phenylacetylene to N-Benzylideneaniline. Under an argon
atmosphere, dried and deoxygenated CH2Cl2 (0.5 mL) was placed
in a three-neck Schlenk flask, followed by the addition of the dinuclear
precatalyst (0.02 mmol). After the addition of N-benzylideneaniline
(0.4 mmol) and phenylacetylene (0.6 mmol), the resulting mixture
was stirred in the absence of light (48 h, room temperature). The
volatiles were removed, and the residue was purified by chromatog-
raphy (silica gel, 5:1 hexane/ethyl acetate). The e.e. of the resulting
propargylamine was determined by high-performance liquid chroma-
tography (HPLC; Chiralcel OD-H column, 25 × 0.46 cm) using a
98:2 mixture of hexane/isopropyl alcohol as the eluent [flow rate = 0.5
mL min−1, tR = 23 min (R), and tR = 27 min (S)]. The absolute
configuration was assigned on the basis of the literature data.
X-ray Crystal Structure Determination of Complexes 1, 4−6,
9−11, and 13. Suitable crystals for X-ray diffraction analysis were
obtained by slow diffusion of a mixture of diethyl ether/hexane into a
dichloromethane solution of complexes 1, 5, 6, and 9−11. Mixtures of
Synthesis of the Mononuclear Complex [Ag{(3aS,3a′S,8aR,8a′R)-
indane-pybox}2][BF4] (9). To a suspension of AgF (0.019 g, 0.15
mmol) in dichloromethane (4 mL) were added indane-pybox (0.119 g,
0.30 mmol) and BF3·OEt2 (15 μL, 0.118 mmol). The mixture was
stirred at room temperature, in the absence of light, for 3 h. Then, the
suspension was exposed to light for 1 h, filtered through a cannula
transfer, and concentrated under reduced pressure to a volume of ca. 2
mL. The addition of diethyl ether (25 mL) afforded a solid. Then, the
solvents were decanted, and the solid was washed with diethyl ether (3
× 5 mL) and vacuum-dried. Color: pale yellow. Yield: 61% (0.090 g).
−
ΛM = 110 S cm2 mol−1 (acetone, 293 K). IR (KBr): ν(BF4 ) 1059
(mf) cm−1. MS-FAB: m/z 893 ([Ag(indane-pybox)2]+), 500 ([Ag-
1
(indane-pybox)]+). H NMR (400.13 MHz, CD2Cl2, 298 K): δ 8.32
(d, JHH = 7.6 Hz, 4H, H3,5 C5H3N), 8.22 (m, 2H, H4 C5H3N), 7.17 (m,
4H, Ph), 7.06−7.00 (m, 12H, Ph), 5.51 (d, JHH = 5.7 Hz, 4H, NCH),
5.12 (m, 4H, OCH), 3.20 (dd, JHH = 18.0, Hz, JHH = 6.0 Hz, 4H,
CH2), 2.88 (d, JHH = 18.0 Hz, 4H, CH2). 13C{1H} NMR (100.61
MHz, CD2Cl2, 298 K): δ 162.3 (s, OCN), 144.8 (s, C2,6 C5H3N),
140.2, 139.5 (2s, Carom), 139.7 (s, C4 C5H3N), 128.8, 127.1 (2s,
CHarom), 126.5 (s, C3,5 C5H3N), 125.4, 125.0 (2s, CHarom), 85.4 (s,
OCH), 76.3 (s, NCH), 39.1 (s, CH2). 19F{1H} NMR (282.4 MHz,
CD2Cl2, 298 K): δ −153.3 (s, BF4). Anal. Calcd for C50H38
N6BF4O4Ag (981.56): C, 61.18; H, 3.90; N, 8.56. Found: C, 60.94;
H, 4.15; N, 8.98.
Synthesis of the Dinuclear Complexes [Ag2{(3aS,3a′S,8aR,8a′R)-
indane-pybox}3][X]2 [X = CF3SO3 (10), SbF6 (11), and PF6 (12)].
Indane-pybox (0.15 mmol) was added to a suspension of the
corresponding silver salt (0.10 mmol) in CH2Cl2 (10 mL), and the
mixture was stirred, in the absence of light, for 1.5 h at room
temperature. Then, the suspension was exposed to light for 1 h,
filtered through a cannula transfer, and concentrated under reduced
pressure to a volume of ca. 1 mL. The addition of a mixture of 1:4
diethyl ether/hexane (25 mL) afforded a precipitate. Solvents were
decanted, and the solid was washed with hexane (3 × 10 mL) and
vacuum-dried.
Complex 10. Color: pale yellow. Yield: 63% (0.053 g). ΛM = 266 S
−
cm2 mol−1 (acetone, 293 K). IR (KBr): ν(CF3SO3 ) 1262 (vs), 1152
L
DOI: 10.1021/acs.inorgchem.6b01323
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
acetone/hexane (for 4) or acetone/diethyl ether (for 13) proved
effective for complexes 4 and 13. The most relevant crystal and
refinement data are collected in Tables 5−7.
Notes
The authors declare no competing financial interest.
For 1, 4−6, 10, 11, and 13, diffraction data were recorded on an
Oxford Diffraction Xcalibur Nova (Agilent) single-crystal diffractom-
eter, using Cu Kα radiation (λ = 1.5418 Å). Images were collected at a
65 mm fixed crystal−detector distance, using the oscillation method,
with 1° oscillation and variable exposure time per image. The data
collection strategy was calculated with the program CrysAlis Pro
CCD.49 Data reduction and cell refinement were performed with the
program CrysAlis Pro RED.49 An empirical absorption correction was
applied using the SCALE3 ABSPACK algorithm, as implemented in
the program CrysAlis Pro RED.49
Crystallographic data of 9 were collected using a Bruker Smart 6000
CCD detector and Cu Kα radiation (λ = 1.54178 Å) generated by an
Incoatec microfocus source equipped with Incoatec Quazar MX optics.
The software APEX250 was used for the collection of frames of data,
indexing of reflections, and determination of lattice parameters,
SAINT50 for integration of the intensity of reflections, and SADABS51
for scaling and empirical absorption correction.
ACKNOWLEDGMENTS
■
This work was supported by the MICINN of Spain (Grant
CTQ2011-26481). E.d.J. thanks the FICYT (Principado de
Asturias, Spain) for a predoctoral fellowship (BP12-158).
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2
The function minimized was [Σw(Fo2 − Fc2)/Σw(Fo )]1/2, where w
2
= 1/[σ2(Fo ) + (aP)2 + bP] (a and b values are collected in Tables
2
2
5−7) from counting statistics and P = [max(Fo ,0) + 2Fc ]/3.
Atomic scattering factors were taken from the International Tables
for X-ray Crystallography International.56 The crystallographic plots
were made with PLATON.57 Geometrical calculations were made with
PARST.58
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b01323.
X-ray crystallographic data in CIF format for 1, 4−6, 9−
11, and 13 (CIF)
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have been used for the asymmetric kinetic resolution of phenyl-2,3-
allen-1-ol with low efficiency (20% conversion, no e.e.): Wang, Y.;
Zheng, K.; Hong, R. J. Am. Chem. Soc. 2012, 134, 4096−4099. (b)
The asymmetric catalytic addition of 4-phenyl-1-butyne to the α-imino
ester PMP-NCH(CO2Et) (PMP = p-methoxyphenyl) was explored
using silver salts (AgOSO2CF3 and AgNO3) and several chiral ligands
(including pybox). Unfortunately, no chiral induction, as well as
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Experimental conditions for NMR experiments, ORTEP
drawing of cationic complexes 5, 9, and 11 (Figures S1−
S3) and full characterization of complexes 2, 7, 8, and 11,
low-temperature 1H and 13C{1H} NMR spectra for
complexes 1, 4, 6, 10, and 12, VT-NMR spectra (Figures
S4 and S5), 1H DOSY NMR spectrum of complex 12 at
213 K (Figure S6), NMR spectra for compounds 1, 4, 6,
1
1
10, and 12, including H, 13C, 31P, 19F, H DOSY, 19F
DOSY, COSY, 1H13C HSQC, 1H13C HMBC, 1H19F
HOESY, and ROESY at room or variable temperature
(PDF)
AUTHOR INFORMATION
■
(17) Provent, C.; Hewage, S.; Brand, G.; Bernardinelli, G.;
Corresponding Author
Charbonnier
1997, 36, 1287−1289.
̀
e, L. J.; Williams, A. F. Angew. Chem., Int. Ed. Engl.
*E-mail: pgb@uniovi.es. Fax: (+34) 985103446.
M
DOI: 10.1021/acs.inorgchem.6b01323
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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DOI: 10.1021/acs.inorgchem.6b01323
Inorg. Chem. XXXX, XXX, XXX−XXX