New five-coordinate Ru(ii) phosphoramidite complexes and their catalytic activity in propargylic amination reactions

Article abstract of DOI:10.1039/c1nj20520j

The first five-coordinate, square-pyramidal ruthenium complexes of the general formula [RuCl₂(PPh₃)₂L] have been prepared, where L is a phosphoramidite ligand. The new complexes were employed as catalysts for the amination

Full text of DOI:10.1039/c1nj20520j

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PAPER
New five-coordinate Ru(II) phosphoramidite complexes and their catalytic
activity in propargylic amination reactionsw
Andria K. Widaman,a Nigam P. Rathab and Eike B. Bauer*a
Received (in Gainesville, FL, USA) 14th June 2011, Accepted 27th June 2011
DOI: 10.1039/c1nj20520j
The first five-coordinate, square-pyramidal ruthenium complexes of the general formula
[RuCl2(PPh3)2L] have been prepared, where L is a phosphoramidite ligand. The new complexes
were employed as catalysts for the amination reactions of propargylic esters (18 h, at room
temperature or 45 1C, Cs2CO3) to give propargylic amines in isolated yields up to 94%.
two equivalents of the amine.16 Since then, other copper-
Introduction
catalyzed propargylic amination reactions of the corresponding
esters have been published.17 Furthermore, catalysis by other
Propargylic alcohols (1a in Scheme 1) are important starting
materials in organic synthesis.1 They are readily available by
transition metals such as Rh18a and Ir,18b as well as that by
Brønsted19 and Lewis acids20 has been employed. However,
addition of acetylides to ketones and can easily be functionalized
further, e.g. by Sonogashira coupling2 or by 1,3-dipolar
cycloadditions to a triple bond.3 The related propargylic
only one ruthenium catalyzed achiral propargylic amination
reaction employing 1-arylprop-2-yn-1-ols has been reported.21
amines (2) are important structural motifs found in natural
products,4 and are building blocks for bioorganic chemistry,3
To the best of our knowledge, ruthenium catalyzed amination
reactions of propargylic acetates 1b are thus far unknown.
pharmaceutical production5 and material science.6 Due to the
Some of the current catalytic systems for amination reactions
availability of propargylic alcohols 1a, their conversion to
of propargylic esters are restricted to internal propargylic
acetates,22 and, with a few exceptions,8,18b,22 the catalytically
propargylic amines is an attractive synthetic goal. Allylic
substitution reactions are well established in organic synthesis;7
active complexes are formed in situ. Consequently, their exact
however, their sister reaction—propargylic substitution—is
nature is unknown, making mechanistic investigations and
far less investigated and understood.8 Potential rearrangements
rational ligand design more difficult.
of propargylic alcohols or their derivatives to allenes9 or
As part of our long-standing interest in the catalytic activation
aldehydes10 can lead to lower yields of the corresponding
of propargylic alcohols,23 we are currently investigating
substitution reactions. Consequently, access to propargylic
ruthenium phosphoramidite complexes to serve that purpose.
amines is mainly performed by other methods, such as the
As open coordination sites are crucial for catalytic activity, we
addition of alkynes to imines.11
were interested in determining whether five-coordinate, square
The direct substitution of the –OH functionality in 1a is
challenging,12 albeit some progress has been made in recent
years.13,14 Conversion of the poor –OH leaving group to a
pyramidal ruthenium phosphoramidite complexes would
exhibit activity in the title reaction. The commercial ruthenium
complex [RuCl2(PPh3)3] (5) was a promising candidate for
better one is a commonly employed strategy to facilitate such
substitution reactions. Propargylic esters (1b in Scheme 1) are
readily accessible and are therefore attractive for this purpose.15
Early reports of the achiral amination of propargylic esters
appeared in the literature in 1994, employing catalytic CuI and
a University of Missouri-St. Louis, Department of Chemistry and
Biochemistry, One University Boulevard, St. Louis, MO 63121,
USA. E-mail: bauere@umsl.edu; Fax: +1-314-516-5342;
Tel: +1-314-516- 5311
b Center for Nanoscience, University of Missouri-St. Louis,
St. Louis, MO 63121, USA
w Electronic supplementary information (ESI) available: Experimental
details, 1H and 31P NMR spectra of the ruthenium complexes,
analytical data and 1H and 13C spectra of the catalysis products in
Table 3. CCDC reference number 805144. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c1nj20520j
Scheme 1 Propargylic alcohols and their functionalization.
c
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Fig. 1 31P NMR spectra of commercial [RuCl2(PPh3)3] (5, top) and
[RuCl2(PPh3)2(7b)] (8b, bottom, partial spectrum), both in CDCl3.
investigation as it displays such a coordination geometry, as
shown by X-ray studies,24 and is known for its rich chemistry
with propargylic alcohols.25 Partially due to its coordinative
unsaturation, complex 5 exhibits dynamic behavior in solution;26
for example, it can form chloro-bridged dimers, such as 6 in
eqn (1), or oligomers. These bridge systems can be very
stable27 and have been described as exhibiting decreased
catalytic activity for some organic transformations.28
Scheme 2 Synthesis of ruthenium phosphoramidite complexes 8.
Supplementary Informationw). The FAB mass spectra showed
a molecular ion peak for both complexes. In addition, a
diagnostic fragmentation pattern was present due to loss of
1
Cl, PPh3 and (R)-7 ligands. The H NMR spectra exhibited a
complex aromatic region, but the NCH3 and NCH2 units
gave resonances in the aliphatic region at 1.9 and 4.2 ppm,
respectively. Due to the numerous aromatic carbon atoms, a
complex aromatic region in the 13C NMR spectra resulted, but
again, the NCH3 and NCH2 groups gave distinct signals at
37.8 and 48.9 ppm.
ð1Þ
The most striking feature of the new complexes were their
sharp 31P NMR peaks, as exemplified by complex 8b, whose
partial 31P NMR spectrum is shown in Fig. 1 (bottom). The
two PPh3 ligands exhibited a well-resolved AB pattern at 34.6
and 29.9 ppm, coupled to the phosphoramidite ligand (R)-7b
(38.8 Hz). Due to coupling to the two PPh3 ligands, the
phosphoramidite ligand appeared as a triplet at 171.3 ppm
(the full spectrum is provided in the Supplementary Information).
As opposed to the starting material 5, the spectra of complexes
8 are well resolved and show no sign of dynamic behavior in
solution. Thus, replacement of one PPh3 ligand in 5 by the
ligands 7 resulted in a configurationally more stable structure.
To unequivocally establish the structure of the new complexes,
an X-ray diffraction analysis was performed for complex 8b
(Fig. 2), confirming its slightly distorted, five-coordinate,
square-pyramidal geometry, similar to that of 5.24 Key bond
lengths and angles are compiled in Table 1 and, for comparison,
the corresponding values for the structurally related complex
[RuCl2(PPh3)3] (5) are also listed.24
The dynamic behavior of complex 5 can be best observed in
the 31P NMR spectrum, which exhibits only a broad peak
around 42 ppm, as confirmed by measurements in our laboratory
(Fig. 1, top).
We speculated that complex 5 could be modified to give a
more stable, monomeric, five-coordinate architecture in solution.
Such a stabilized complex could exhibit more predictable
catalytic activity compared to multiple species resulting from
the dynamic solution behavior of [RuCl2(PPh3)3]. Herein, we
report the synthesis of complexes of the general formulation
[RuCl2(PPh3)2L] (L = phosphoramidite ligand) and their
catalytic application in propargylic amination reactions.
Results and discussion
Synthesis and characterization of the ruthenium complexes
Accordingly, we first sought access to appropriate ruthenium
phosphoramidite29 complexes. When the known29c phosphor-
amidite ligand (R)-7a was added to a solution of complex 5, an
immediate color change to blue took place (Scheme 2). After
20 min, removing the solvent and washing the residue with
several portions of cold Et2O afforded the complex
[RuCl2(PPh3)2((R)-7a)] (8a) as a grey solid in 41% isolated
yield. Similarly, the known29c phosphoramidite ligand (R)-7b
could be converted to the green complex [RuCl2(PPh3)2((R)-7b)]
(8b) in 80% isolated yield.
In the complex 8b, specifically the apical PPh3 ligand in the
position trans to the open coordination site is exchanged by
the phosphoramidite (R)-7b. The two PPh3 ligands occupy
approximately trans positions, with an angle of 164.08(3)1.
The two chloro ligands are also located approximately trans to
each other, as seen by their Cl(1)–Ru–Cl(2) angle of
155.20(3)1. The phosphoramidite ligand and the two PPh3
ligands form angles of 95.73(3) and 99.67(3)1, respectively.
The Ru–P bond lengths are significantly shorter for the
phosphoramidite ligand 7b (2.1561(9) A) than for the PPh3
ligands (2.3793(9) and 2.4072(9) A). We have previously
The new complexes were fully characterized by multinuclear
NMR, MS and elemental analysis, which confirmed the general
formulation [RuCl2(PPh3)2((R)-7)] (spectra are provided in the
c
2428 New J. Chem., 2011, 35, 2427–2434
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phosphoramidite ligand. The combination of both the s- and
p-influence results in a shorter Ru–P bond length for the
phosphoramidite ligand in complex 8b (2.1561(9) A), which
is even shorter than the corresponding apical Ru–PPh3 bond
in the ‘‘parent’’ complex [RuCl2(PPh3)3] (2.230(8) A).
To better understand the increased stability of complexes 8
in solution, the structural parameters of complex 8b are
compared to those of complex [RuCl2(PPh3)3] (Table 1). The
P(2)–Ru(1)–P(3) angle for complex 8b (164.08(3)1) is larger
than the corresponding angle in the complex [RuCl2(PPh3)3]
(156.4(2)1). In turn, the P(1)–Ru(1)–P(2) and P(1)–Ru(1)–P(3)
angles in 8b (95.73(3)1 and 99.67(3)1) are smaller than the
corresponding angles in [RuCl2(PPh3)3] (101.1(2)1 and 101.4
(2)1). These values suggest diminished steric bulk of the
phosphoramidite ligand in 8b compared to PPh3 in the
complex [RuCl2(PPh3)3]. Albeit the phosphoramidite ligand
7b contains more atoms, it may have a smaller cone angle than
PPh3.33 Consequently, the two remaining PPh3 ligands in 8b
are not as strongly repelled by the phosphoramidite ligand as
they are by the apical PPh3 ligand in [RuCl2(PPh3)3].
Due to the decreased steric demand of the phosphoramidite
ligands in complexes 8, it is possible that their tendency
to undergo a dissociative dimerization process according to
eqn (1) is diminished, resulting in an increased stability of the
monomeric structures.
Fig. 2 Molecular structure of 8b (depicted with 50% probability
ellipsoids; H atoms are omitted for clarity). Key bond lengths and
bond angles are listed in Table 1.
Table 1 Key bond lenght (A) and angles (1)
8b
[RuCl2(PPh3)3]24
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–P(3)
P(1)–N(1)
P(1)–Ru(1)–Cl(1)
P(1)–Ru(1)–Cl(2)
Cl(1)–Ru(1)–Cl(2)
P(1)–Ru(1)–P(2)
Cl(2)–Ru(1)–P(2)
Cl(1)–Ru(1)–P(2)
P(1)–Ru(1)–P(3)
Cl(2)–Ru(1)–P(3)
Cl(1)–Ru(1)–P(3)
P(2)–Ru(1)–P(3)
2.3779(8)
2.3700(8)
2.1561(9)
2.3793(9)
2.4072(9)
1.657(3)
95.50(3)
109.28(3)
155.20(3)
95.73(3)
85.66(3)
91.19(3)
99.67(3)
85.49(3)
91.31(3)
164.08(3)
2.387(7)
2.388(7)
2.230(8)
2.374(6)
2.412(6)
—
92.9 (2)
109.9 (2)
157.2 (2)
101.1(2)
82.1(2)
93.4(2)
101.4 (2)
83.7(2)
92.4 (2)
156.4(2)
Catalysis
We subsequently employed the new complexes as catalysts in
propargylic amination reactions. The higher yielding complex
8b was employed for screening reactions and for all isolated
yields, and complex 8a showed comparable activity as shown
by GC measurements. Initial screening reactions revealed that
employment of propargylic alcohols gave at most moderate
conversions to the corresponding propargylic amines.
However, when the corresponding propargylic acetates 9
were employed in the presence of a base, the conversions were
higher (Table 2). The bases NEt3 and NaOH gave only trace
quantities of the expected products. Using the sterically
hindered base diazabicycloundecene (DBU) resulted in higher
conversions (entries 1 and 2), but a 90 1C temperature was
required. In addition, as determined by GC-MS, DBU
derivatives formed, complicating purification. This issue was
resolved by using Cs2CO3 (Table 2, entries 3–9), which was
superior in our screening experiments; however, we observed
solvent-dependencies for that base. In THF or C6H5Cl, only
low conversions were observed at 90 1C (entry 3), but 53%
conversion and fewer side products were observed in THF at
22 1C (entry 4). In i-PrOH, up to 72% conversion was
observed at 22 1C (entry 5) and was increased only slightly
by employing heat (entries 6–8), but the isolated yields never
exceeded 37% (entries 6 and 7). We speculate that the acetate
starting material decomposes under the conditions in entries 6
to 8. However, employment of CH2Cl2 resulted not only in
complete consumption of the acetate starting material at room
temperature, but also in high yields of the corresponding
propargyl amine (entry 9). The ‘‘parent’’ propargylic acetate
HCRCCH2OAc gave only minimal formation of the corres-
ponding propargylic amine (entry 10). No product formation
observed this difference in bond length30 and tentatively
attributed the shortened bond to the increased p-acidity of
the phosphoramidite ligands 7 compared to PPh3. It has been
previously described in the literature, that phosphine ligands
PX3 with electronegative X substituents, such as F, promote
p-backbonding, resulting in shortened M–P bond lengths.31
Accordingly, increased p-acidity has been ascribed to phosphor-
amidites.29a In addition, the coordination site trans to the
phosphoramidite ligand is unoccupied, thus no competition
between ligands for the d-electrons of the metal takes place.
Both effects result in a higher degree of metal-to-ligand back-
bonding, which would shorten the Ru–P bond.
In addition, s-effects may contribute to a shortening of this
bond. Compounds PX3 with electronegative substituents X
increase the s-character of the lone pair on the phosphorus.32
Furthermore, s-bonds in position trans to a ligand weaken the
ligand bond to the metal center, but the phosphoramidite
ligand in complex 8b lacks a ligand in that position. These two
s-effects might also contribute to a shorter Ru–P bond of the
c
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Table 2 Screening reactions
Table 3 Propargylic amination reactions
Entrya R,R0,R0 0
Base/solvent
Temperature
Conversionb
(isolated yield)
Entrya
Substrates
Temperature
Product
Isolated
yield
1
Ph, Bn, Me
DBU/C6H5Cl
17%c
90 1C
C5H11, Bn, Me DBU/C6H5Cl
90 1C
2
50%c (30%)
1
45 1C
71%
72%
75%
76%
64%
3
C5H11, Bn, Me CsCO3/THF or C6H5Cl 8–14%
90 1C
CsCO3/THF
22 1C
CsCO3/i-PrOH
22 1C
CsCO3/i-PrOH
4
Ph, Bn, Me
Ph, Bn, Me
Ph, Bn, Me
53%
2
3
4
5
22 1C
45 1C
22 1C
45 1C
5
72%
6
100%d (37%)
75% (36%)
75%
90 1C
C5H11, Bn, Me CsCO3/i-PrOH
90 1C
C5H11, Bn, Bn CsCO3/i-PrOH
90 1C
7
8
9e
10e
Ph, Bn, Me
CsCO3/CH2Cl2
100% (76%)
2%
22 1C
CsCO3/CH2Cl2
22 1C
H, Bn, Me
a
Acetate (0.23 mmol), amine (0.46 mmol), base (0.8 mmol), catalyst
8b (0.01 mmol) in the solvent (1 mL) in a screw-capped vial for one
b
day. Determined by GC relative to the acetate starting material.
c
Isolated yields after column chromatography. DBU produced a
complex reaction mixture, in which DBU derivatives were identified.
d
No acetate starting material was detected but the isolated yields
never exceeded 37%, presumably due to substrate decomposition
e
during the reaction. Acetate (0.2 mmol), amine (0.8 mmol), base
(0.4 mmol), catalyst 8b (0.01 mmol) in the solvent (1 mL) in a screw-
capped vial for one day.
6
7
8
45 1C
22 1C
22 1C
84%
71%
55%
was observed with primary amines or anilines, and no reaction
took place without ruthenium catalysts 8.
Under optimized conditions, we employed the title reaction for
a variety of propargylic acetates 11 and amines 12 and the results
are compiled in Table 3. Employing a molar ratio of 1 (propargyl
acetate 11): 3.5 to 4 (amine 12) and shaking for 18 h at room
temperature or 45 1C in CH2Cl2 afforded the propargylic amines
13 that were isolated by column chromatography or flash
filtration in 55–94% yield. Two equivalents of Cs2CO3 were
added to the reaction mixture to help drive the reaction to
completion. As Table 3 demonstrates, the reaction shows a
broad substrate scope. Both secondary (11b) and tertiary
(11a,c,d) propargylic acetates were aminated with secondary
amines, and both phenyl and alkyl substituents can be tolerated
on the propargylic ester. The tertiary acetates required slightly
elevated temperatures for the reaction to go to completion. The
substituents on the amine exhibited different levels of steric
congestion; benzyl, methyl, isopropyl and cyclohexyl amines all
were successfully employed in the reaction with only slight
differences in the isolated yields. The chiral amine (R)-(14) also
was converted to the corresponding propargylamine 15 (entry
10); during the reaction, a stereocenter at the triple bond is
formed, and the amine 15 was isolated as a 1:1 mixture of
diastereomers, as assessed by 1H NMR spectroscopy.
9
22 1C
22 1C
94%
10
82%b
a
Typical conditions: Substrate (0.32 mmol), amine (1.10 mmol),
Cs2CO3 (0.64 mmol) and 8b (5 mol%), 18 h in CH2Cl2 (0.5 mL) in
a screw-capped vial at the temperature indicated in the table. The
products were isolated by column chromatography or filtration utiliz-
b
ing silica or alumina. The product was isolated as a 1 : 1 mixture of
1
diastereomers (as assessed by H NMR).
c
2430 New J. Chem., 2011, 35, 2427–2434
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The substrate scope presented in Table 3 complements that
of other catalytic systems employed for the title reaction.
Copper-pyridine-2,6-bisoxazoline complexes were reported to
be catalytically active in the amination of secondary propargylic
acetates with primary amines,17b while copper-diphosphine
complexes were reported to show catalytic activity for secondary
propargylic acetates and secondary amines.17c The unsaturated
complexes 8a and 8b are able to aminate secondary and
tertiary propargylic acetates.
our knowledge, ruthenium-stabilized carbocations have not
been reported in the literature and have not been suggested as
intermediates in propargylic substitution reactions,34 which
suggests that the title reaction proceeds through an allenylidene
intermediate.
In any event, further experiments are necessary to firmly
establish a mechanism for the reaction.
Conclusion
During synthesis of the propargylic amines, a new stereo-
genic center is formed. For most of the propargylic amines in
Table 3, no literature precedent for the determination of
enantiomeric excesses exists, and our attempts to chromato-
graphically separate enantiomers by chiral GC or HPLC have
failed thus far. However, the optical rotation of compound
13b in Table 3 was measured to be zero. Furthermore, no
diastereomeric excess for compound 15 was obtained, so the
reactions in Table 3 presumably do not provide an enantio-
meric excess. Ligand modifications to promote enantio-
differentiation for the title reaction are currently underway.
Mechanistically, the reaction might proceed either through
a transition-metal-stabilized propargyl cation (16)34 or an
allenylidene intermediate (17, Scheme 3).17b,c
In conclusion, we have synthesized for the first time five-
coordinate, square pyramidal ruthenium complexes of the
general formula [RuCl2(PPh3)2L], where L is a phosphoramidite
ligand, one example of which has been characterized structurally.
As seen by sharp resonances in the NMR spectra, the new
complexes exhibited no dynamic behavior in solution as
opposed to their precursor, [RuCl2(PPh3)3]. The new complexes
were employed successfully in propargylic amination reactions
of propargylic acetates (room temperature or 45 1C, 18 h,
Cs2CO3 as auxiliary base) to give the corresponding
propargylic amines in 55 to 94% isolated yields. It is the first
ruthenium—based catalytic system for the amination of
propargylic acetates, and thus, we introduce the complexes
[RuCl2(PPh3)2L] as a new, tunable platform to promote the
title reaction under mild conditions. Mechanistic investigations
and further experiments to widen the substrate scope are
currently underway.
To determine the involvement of a potential allenylidene
intermediate, we performed a stoichiometric reaction between
complex 8b and propargylic acetate 11b, but no evidence for
allenylidene formation was obtained. On the contrary, the
internal propargylic acetate 18 cannot be aminated under the
conditions in Table 3 to give the corresponding propargylamine
19 [eqn (2)], despite the structural diversity among propargylic
acetates employed in Table 3. Internal propargylic alcohols or
their derivatives cannot be easily converted to allenylidene
complexes,35 which suggests, indirectly, that an allenylidene
intermediate 17 may be involved.
Experimental section
General
Chemicals were treated as follows: diethyl ether, distilled from
Na/benzophenone; CH2Cl2, distilled from CaCl2; petroleum
ether and ethyl acetate used as received. [RuCl2(PPh3)3]
(5, Strem), amine substrates for catalytic experiments,
Cs2CO3, silica (all Aldrich), and other materials used
as received. ‘‘(R)-BINOL-N,N-dimethyl-phosphoramidite’’
(R)-7a,29c ‘‘(R)-BINOL-N,N-dibenzyl-phosphoramidite’’ (R)-7b,29c
and the propargylic acetates 11a,37a 11b,17b 11c,37b and 11d37c
were synthesized with slight modification to literature procedures.
All reactions were carried out under nitrogen employing
standard Schlenk techniques; workups and catalytic experiments
were carried out in open air.
ð2Þ
A potential allenylidene intermediate also could explain why
the acetate of the parent propargylic alcohol showed only
minimal product formation (Table 2, entry 10, with R = H for 9).
For this substrate, an intermediate allenylidene complex 17
would result, where R and R0 are H (Scheme 3). Such
allenylidene complexes are unknown,35 and could not undergo
the catalytic cycle as depicted in Scheme 3.
NMR spectra were obtained at room temperature on a
Bruker Avance 300 MHz or a Varian Unity Plus 300 MHz
instrument and referenced to a residual solvent signal; all
assignments are tentative. GC/MS spectra were recorded on
a Hewlett Packard GC/MS System Model 5988A. Exact
masses were obtained on a JEOL MStation [JMS-700] Mass
Spectrometer. IR spectra were recorded on a Thermo Nicolet
360 FT-IR spectrometer. Elemental analyses were performed
by Atlantic Microlab Inc., Norcross, GA, USA.
Furthermore, metal-stabilized carbocations are known
for transition metals such as Mo36a or Co.36b To the best of
[(RuCl2(PPh3)2((R)-BINOL-N,N-dimethyl-phosphoramidite)]
(8a). To a Schlenk flask containing phosphoramidite (R)-7a
(83 mg, 0.23 mmol) and [RuCl2(PPh3)3] (5, 215 mg,
0.22 mmol), CH2Cl2 (4 mL) was added and the solids dissolved.
The dark blue solution was stirred at room temperature for
20 min. The solvent was then removed under vacuum, giving
Scheme 3 Simplified mechanistic picture.
c
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dark blue solids. The solids were washed with diethyl ether
(3 ꢀ 2 mL) to obtain 8a as a light blue solid (0.097 g,
0.09 mmol, 41%). Found: C, 66.0; H, 4.7. C58H48Cl2NO2P3Ru
requires C, 66.0; H, 4.6%.38 1H-NMR dH (300.13 MHz;
CDCl3; Me4Si) 7.56–7.91 (m, 12H, arom), 7.10–7.45 (m,
23H, arom), 6.98–7.06 (m, 5H, arom), 6.77–6.82 (m, 2H,
arom), 1.91 (s, 3H, CH3), 1.88 (s, 3H, CH3); 13C-NMR
dC (75.5 MHz; CDCl3; Me4Si; partial)39 37.8 (2CH3);
n
max/cmꢂ1 3294m (CRC–H), 3061m, 3027m, 2924m, 2846m,
1493m, 1447m, 697s.
2-Methyl-N-(1-phenyl-2-propynyl)pyrrolidine (15). To a vial
containing [RuCl2(PPh3)2((R)-7b)] (8b, 0.014 g, 0.012 mmol)
and Cs2CO3 (0.151 g, 0.46 mmol), CH2Cl2 (0.5 mL) was added
to dissolve the metal complex, followed by 1-phenyl-2-propynyl
acetate (11b, 0.040 g, 0.23 mmol) and 2-methylpyrrolidine (14,
0.077 g, 0.90 mmol) under open atmosphere. The mixture was
shaken for 18 h at room temperature. The residue was purified
by vacuum filtration through Al2O3 in a fritted funnel with
petroleum ether and ethyl acetate (10 : 1), then concentrated
under reduced pressure to give yellow oil 15 as a mixture of
diastereomers (1 : 1, 1H NMR) (0.037 g, 0.19 mmol; 82%).
1H-NMR dH (300.13 MHz; CDCl3; Me4Si; the starred signals*
2
31P{1H}-NMR dP (CDCl3; H3PO4) 173.5 (t, JPP = 40.7 Hz,
phosphoramidite), 41.0, 34.7 (ABq, 2JAB = 332.6 Hz, 2JPP
=
38.8 Hz, 2PPh3). HRMS calcd for C58H4835Cl2NO2P3102Ru:
1055.1317. Found 1055.1345. MS (FAB, 4-NBA) m/z: 1055
(8a+, 20%), 1020 ([8a–Cl]+, 15), 793 ([8a–PPh3]+, 65), 696
([RuCl2(PPh3)]+, 30).
3
[(RuCl2(PPh3)2((R)-BINOL-N,N-dibenzyl-phosphoramidite)-
(Et2O)] (8b). To a Schlenk flask containing phosphoramidite
(R)-7b (0.1248 g, 0.244 mmol) and [RuCl2(PPh3)3] (5, 0.233 g,
0.243 mmol), CH2Cl2 (4 mL) was added and the solids
dissolved. The green solution was stirred at room temperature
for 20 min. The solvent was then removed under vacuum, giving
dark green solids. The solids were washed with diethyl ether
(3 ꢀ 2 mL) to obtain 8b as a green solid (0.234 g, 0.194 mmol,
80%). Found: C, 69.2; H, 5.1. C70H56Cl2NO2P3Ruꢁ(Et2O)
requires C, 69.3; H, 5.2%.38 1H-NMR dH (300.13 MHz;
denote the second diastereomer) 7.51 (d, JHH = 7.3 Hz, 2H,
3
Ph), 7.46 (d, JHH = 6.7 Hz, 2H, Ph*), 7.17–7.30 (m, 6H,
4
Ph/Ph*), 4.87 (d, JHH = 2.1 Hz, 1H, Ph-CH), 4.80 (d,
4JHH = 2.2 Hz, 1H, PhCH*), 3.04–3.10 (m, 1H, H3CCH),
2.65–2.83 (m, 2H, NCH2), 2.52–2.61 (m, 1H, H3CCH*), 2.41
(d, 4JHH = 2.1 Hz, 1H, CRCH), 2.40 (d, 4JHH = 2.2 Hz, 1H,
CRCH*), 2.37–2.51 (m, 2H, NCH2*), 1.26–1.94 (m, 8H,
3
2CH2 and 2CH2*), 1.13 (d, JHH = 6.0 Hz, 3H, CH3), 0.74
(d, 3JHH = 6.0 Hz, 3H, CH3*); 13C{1H}-NMR dC (75.5 MHz;
CDCl3; Me4Si) 139.1 (Ph), 137.5 (Ph), 133.8 (Ph), 133.6 (Ph),
128.6 (Ph), 128.1 (Ph), 128.0 (Ph), 127.9 (Ph), 127.5 (Ph), 127.3
(Ph), 81.9 (CRCH), 79.3 (CRCH*), 75.1 (CRCH), 73.8
(CRCH*), 56.3, 56.2, 54.7, 54.2, 51.8, 46.9, 33.2, 32.7, 22.2,
21.4, 20.8, 18.9. HRMS calcd for C14H17N: 199.1361. Found:
199.1358. MS (EI) m/z: 199 (2%), 184 (30), 115 (100), 89 (11).
IR (neat oil) nmax/cmꢂ1 3300m (CRC–H), 3060w, 3030w,
2960s, 2871m, 2819m, 1492m, 1450m, 1376m, 1265m, 1136m,
1073w, 1030w, 947w, 741m, 698s, 642s.
3
CDCl3; Me4Si) 7.95 (d, JHH = 8.0 Hz, 2H, arom), 7.85
3
(d, JHH = 9.0 Hz, 2H, arom), 7.63–7.72 (m, 9H, arom),
7.42–7.56 (m, 9H, arom), 7.03–7.36 (m, 26H, arom), 6.91–6.94
(d, 3JHH = 8.0 Hz, 4H, arom), 6.50 (br, 1H, CHH0Ph), 6.44 (d,
3JHH = 8.9 Hz, 1H, CHH0Ph), 4.21 (br, 2H, CH2Ph);
13C-NMR dC (75.5 MHz; CDCl3; Me4Si; partial)39 48.97
(NCH2), 48.91 (NCH2 ); 31P{1H}-NMR dP (CDCl3; H3PO4)
0
2
171.3 (t, JPP = 38.8 Hz, phosphoramidite), 34.6, 29.9 (ABq,
2
2JAB = 326.9 Hz, JPP = 38.8 Hz, 2PPh3). HRMS calcd for
The other compounds in Table 3 have been reported in the
literature.17c,40 The experimental details for these compounds
can be found in the Supplementary Information, as well as
1H and 13C NMR spectra of all catalysis products in Table 3.
C70H5635Cl2NO2P3102Ru: 1207.1943. Found: 1207.1909. MS
(FAB, 4-NBA) m/z: 1207 (8b+, 4%), 1172 ([8b–Cl]+, 2),
945 ([8b–PPh3]+, 24), 910 ([RuCl(PPh3)((R)-7b)]+, 15), 648
([RuCl((R)-7b)]+, 24).
X-Ray crystallography
Representative catalytic procedures (Table 3)
Crystals of appropriate dimension were obtained by slow
diffusion of Et2O into a solution of complex 8b in CH2Cl2 at
ꢂ18 1C. A crystal with approximate dimensions 0.21 ꢀ 0.19 ꢀ
0.17 mm3 was mounted on a Mitgen cryoloop in a random
orientation. Preliminary examination and data collection were
performed using a Bruker Kappa Apex II Charge Coupled
Device (CCD) Detector system single crystal X-Ray diffracto-
meter equipped with an Oxford Cryostream LT device. All
data were collected using graphite monochromated Mo Ka
radiation (l = 0.71073 A) from a fine focus sealed tube X-Ray
source. Preliminary unit cell constants were determined with a
set of 36 narrow frame scans. Intensity data were collected
using a combinations of $ and f scan frames with typical scan
width of 0.51 at a crystal to detector distance of 3.5 cm. The
collected frames were integrated using an orientation matrix
determined from the narrow frame scans. Apex II and SAINT
software packages were used for data collection and data
integration.41 Analysis of the integrated data did not show any
decay. Final cell constants were determined by global refinement
of xyz centroids of 9055 reflections from the complete data set.
1-Methyl-1-phenyl-N,N-dibenzyl-2-propyn-1-amine (13e). To
a screw-capped vial containing [RuCl2(PPh3)2((R)-7b)] (8b,
0.013 g, 0.011 mmol) and Cs2CO3 (0.133 g, 0.41 mmol),
CH2Cl2 (0.5 mL) was added to dissolve the metal complex,
followed by 1-methyl-1-phenyl-2-propynyl acetate (11c, 0.039 g,
0.21 mmol) and dibenzylamine (0.167 g, 0.85 mmol) under
open atmosphere. The mixture was heated in a heating block
at 45 1C for 18 h. The residue was purified by flash chromato-
graphy (1 ꢀ 10 cm SiO2, petroleum ether/EtOAc 10 : 1 v/v),
then concentrated under reduced pressure to obtain 13e as a
yellow oil (0.043 g, 0.13 mmol; 64%). 1H-NMR dH
(300.13 MHz; CDCl3; Me4Si) 7.83–7.86 (m, 2H, Ph),
7.02–7.33 (m, 13H, Ph), 3.63 (s, 4H, 2CH2), 2.66 (s, 1H,
CRCH), 1.30 (s, 3H, CH3); 13C{1H}-NMR dC (75.5 MHz;
CDCl3; Me4Si) 145.7 (Ph), 141.7 (Ph), 128.3 (Ph), 128.0 (Ph),
127.4 (Ph), 126.53 (Ph), 126.50 (Ph), 83.5 (CRCH), 75.2
(CRCH), 65.6 (PhC), 55.7 (2CH2), 33.4 (CH3). HRMS calcd
for C24H23N: 325.1830. Found: 325.1819. MS (EI) m/z: 325
(3%), 310 (22), 248 (8), 181 (7), 129 (56), 91 (100). IR (neat oil)
c
2432 New J. Chem., 2011, 35, 2427–2434
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View Article Online
Collected data were corrected for systematic errors using
SADABS based on the Laue symmetry using equivalent
reflections.41
7 (a) N. Nomura, K. Tsurugi, N. Yoshida and M. Okada, Curr. Org.
Synth., 2005, 2, 21; (b) T. Graening and H. G. Schmalz, Angew.
Chem., Int. Ed., 2003, 42, 2580; (c) G. Helmchen, J. Organomet.
Chem., 1999, 576, 203.
Crystal data and intensity data collection parameters are
listed in Table S1.w
8 (a) R. J. Detz, H. Hiemstra and J. H. van Maarseveen, Eur. J. Org.
Chem., 2009, 6263; (b) N. Ljungdahl and N. Kann, Angew. Chem.,
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Dalton Trans., 2010, 39, 4015.
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15 G. Hattori, Y. Miyake and Y. Nishibayashi, ChemCatChem, 2010,
2, 155.
Structure solution and refinement were carried out using the
SHELXTL-PLUS software package.42 The structure was
solved by direct methods and refined successfully in the space
group P-1. Full matrix least-squares refinement was carried
2
2
out by minimizing Sw(Fo ꢂ Fc )2. The non-hydrogen atoms
were refined anisotropically to convergence. All hydrogen
atoms were treated using appropriate riding model (AFIX m3).
A disordered molecule of Et2O was located in the lattice as
solvent of crystallization. The disorder was resolved with two
orientations for all atoms with 50% occupancies and were
refined with geometrical and displacement parameter restraints.
Crystal data for 8b: C70H56Cl2NO2P3Ruꢁ(C4H10O),
M = 1282.16, T = 100(2) K, wavelength 0.71073 A, triclinic,
space group P-1, a = 13.6805(3) A, b = 14.5594(3) A,
c = 17.2394(4) A, a = 77.1170(10)1, b = 71.5080(10)1,
g = 71.6980(10)1, V = 3062.57(12) A3, Z = 2, density
16 Y. Imada, M. Yuasa, I. Nakamura and S.-I. Murahashi, J. Org.
Chem., 1994, 59, 2282.
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Int. Ed., 2008, 47, 3777; (c) G. Hattori, K. Sakata, H. Matsuzawa,
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2010, 132, 10592; (d) A. Yoshida, G. Hattori, Y. Miyake and
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2011, 17, 5921.
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45, 4970; (b) K. Kondo, Y. Kanda, A. Baba, K. Fukuda,
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(calculated)
= =
1.390 Mg/m3, absorption coefficient
0.472 mmꢂ1, F(000) = 1328, theta range for data collection
1.49 to 26.391, index ranges ꢂ17 r h r 17, ꢂ18 r k r 18,
ꢂ21 r l r 21, reflections collected = 88 454, independent
reflections, 12 305 [R(int) = 0.0428], completeness to theta =
25.001 (98.6%), absorption correction semi-empirical from
equivalents, max. and min. transmission 0.9257 and 0.9077,
refinement method full-matrix least-squares on F2, data/
restraints/parameters 12 305/176/806, goodness-of-fit on
F2 = 1.142, final R indices [I 4 2sigma(I)] R1 = 0.0459,
wR2 = 0.1271, R indices (all data) R1 = 0.0632, wR2
0.1489, largest diff. peak and hole 1.068 and ꢂ0.695 e.Aꢂ3
=
.
23 (a) S. Costin, N. P. Rath and E. B. Bauer, Tetrahedron Lett., 2009,
50, 5485; (b) S. Costin, N. P. Rath and E. B. Bauer, Adv. Synth.
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Acknowledgements
24 S. J. La Placa and J. A. Ibers, Inorg. Chem., 1965, 4, 778.
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27 S. Gauthier, R. Scopelliti and K. Severin, Organometallics, 2005,
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We would like to thank the University of Missouri—Research
Board for financial support. Funding from the National
Science Foundation for the purchase of the NMR spectro-
meter (CHE-9974801), the purchase of the ApexII diffracto-
meter (MRI, CHE-0420497) and the purchase of the mass
spectrometer (CHE-9708640) are acknowledged.
28 D. Amoroso, G. P. A. Yap and D. E. Fogg, Organometallics, 2002,
21, 3335.
29 Reviews, recent applications and syntheses: (a) J. F. Teichert and
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structure of 8b also contains an ether molecule in the crystal lattice.
1
Ruthenium-coordinated ether can also be observed in the H NMR
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c
2434 New J. Chem., 2011, 35, 2427–2434
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011