Synthesis and catalytic applications of ruthenium(ii)-phosphino-oxime complexes

Article abstract of DOI:10.1039/c6ra07015a

In this work, the preparation of the first ruthenium complexes containing a phosphino-oxime ligand is presented. Thus, the reaction of cis-[RuCl₂(DMSO)₄] (3) with 2.4 equivalents of 2-Ph₂PC₆H₄CH=NOH (1) in refluxing THF led to the clean formation of the octahedral ruthenium(ii) derivative cis,cis,trans-[RuCl₂{κ²-(P,N)-2-Ph₂PC₆H₄CH=NOH}₂] (5), whose structure was unambiguously confirmed by means of a single-crystal X-ray diffraction study. Complex 5 could also be synthesized from the reaction of the dimer [{RuCl(μ-Cl)(η⁶-p-cymene)}₂] (4) with an excess of 1 in refluxing toluene. Treatment of 4 with 2 equivalents of 1, in CH₂Cl₂ at r.t., allowed also the preparation of the half-sandwich Ru(ii) derivative [RuCl{κ²-(P,N)-2-Ph₂PC₆H₄CH=NOH}(η⁶-p-cymene)][PF₆] (6). In addition, complexes 5 and 6 proved to be active catalysts for the rearrangement of aldoximes to primary amides, as well as for the α-alkylation/reduction of acetophenones with primary alcohols, with the former showing the best performances in both processes.

Full text of DOI:10.1039/c6ra07015a

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DOI: 10.1039/C6RA07015A
Journal Name
ARTICLE
Synthesis and catalytic applications of ruthenium(II)-phosphino-
oxime complexes
Received 00th January 20xx,
Accepted 00th January 20xx
Javier Francos,*a Lucía Menéndez-Rodríguez,a Eder Tomás-Mendivil,a Pascale Crochet*a and
Victorio Cadierno*a
DOI: 10.1039/x0xx00000x
In this work, the preparation of the first ruthenium complexes containing a phosphino-oxime ligand is presented. Thus, the
reaction of cis-[RuCl2(DMSO)4] (3) with 2.4 equivalents of 2-Ph2PC6H4CH=NOH (1) in refluxing THF led to the clean
formation of the octahedral ruthenium(II) derivative cis,cis,trans-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2] (5), whose
structure was unambiguously confirmed by means of a single-crystal X-ray diffraction study. Complex 5 could also be
synthesized from the reaction of dimer [{RuCl(µ-Cl)(η6-p-cymene)}2] (4) with an excess of 1 in refluxing toluene. Treatment
of 4 with 2 equivalents of 1, in CH2Cl2 at r.t., allowed also the preparation of the half-sandwich Ru(II) derivative [RuCl{κ2-
(P,N)-2-Ph2PC6H4CH=NOH}(η6-p-cymene)][PF6] (6). In addition, complexes 5 and 6 proved to be active catalysts for the
rearrangement of aldoximes to primary amides, as well as for the α-alkylation/reduction of acetophenones with primary
alcohols, with the former showing the best performances in both processes.
www.rsc.org/
activity in the hydrogenation of cyclooctene.4 Wan and co-
workers also described a series of copper-catalyzed arylation
Introduction
reactions of amines5 and thiols,6 as well as palladium-catalyzed
Suzuki-Miyaura cross-coupling processes,7 employing 2-
R2PC6H4CH=NOH (R = Ph, Cy) and their respective oxides as
auxiliary ligands (albeit without isolation of the corresponding
metal complexes). As already indicated in our previous work,
the low interest aroused by this type of ligands is quite
surprising since oximes (both ketoximes and aldoximes)
present a rich coordination chemistry.8 It is also striking that,
despite being commercially available from different chemical
suppliers at a relatively low price,9 there are no additional
works to those of Wan and ours with the phosphino-aldoxime
Hybrid ligands with hard nitrogen and soft phosphorus donor
sites are highly valuable in coordination chemistry and
homogeneous catalysis.1 In this context, we recently described
the preparation and X-ray crystal structures of the
palladium(II) complexes [PdCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}]
and [Pd{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2][Cl]2 (
A and B in Fig. 1),
which proved to be efficient catalyst precursors for the
rearrangement of aldoximes to primary amides in water.2,3
ligand 2-Ph2PC6H4CH=NOH (1). This fact contrasts with the rich
chemistry shown by its phosphino-aldehyde precursor 2-
Ph2PC6H4CHO,10,11 and structurally related phosphino-imine
ligands 2-Ph2PC6H4CH=NR (R = aryl or alkyl group), which have
been coordinated to a broad range of transition metals and
have found application in multitude of catalytic
transformations.12
Fig. 1 Structure of the palladium(II) complexes
A
and B.
Remarkably, compounds
A
and
B
represent rare examples
of transition metal complexes containing a phosphino-oxime
as ancillary ligand. Indeed, prior to our work, only two
representatives had been reported in the literature by Morris
group, namely [M(COD){κ2-(P,N)-Cy2PCH2CH=NOH}][PF6] (M =
Rh, Ir; COD = 1,5-cyclooctadiene), both showing catalytic
Herein, we give new evidences of the enormous synthetic
potential of the phosphino-oxime 2-Ph2PC6H4CH=NOH (1). In
particular, we describe the preparation of the first ruthenium
complexes containing this ligand, and their successful
application in the catalytic rearrangement of aldoximes to
amides,3 as well as in the α-alkylation/reduction of
acetophenones with primary alcohols.13
a.Laboratorio de Compuestos Organometálicos y Catálisis (Unidad Asociada al
CSIC), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Departamento
de Química Orgánica e Inorgánica, IUQOEM, Universidad de Oviedo, Julián
Clavería 8, E-33006 Oviedo, Spain. E-mail: francosjavier@uniovi.es (J.F.),
crochetpascale@uniovi.es (P.C.), vcm@uniovi.es (V.C.); Fax: +(34) 985103446;
Tel.: +(34) 985103453.
† Electronic Supplementary Information (ESI) available: Copies of the NMR spectra
of the amides and alcohols synthesized in this work. CCDC 1468182 (
DOI: 10.1039/x0xx00000x
Results and discussion
Some years ago, our group described the preparation of
5). See
different five- (
C) and six-coordinate (D-E) ruthenium(II)
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complexes containing chelated phosphino-imine 2- spectroscopy) and elemental analysis (details are given in the
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Ph2PC6H4CH=NR (R = aryl or alkyl group) ligands from their Experimental section). The spectroscopDicOId: 1a0t.a103s9h/oCw6ReAd070th15aAt
reactions with compounds [RuCl2(PPh3)3]
(2) and cis- only one of the five possible stereoisomers is formed (Fig. 2).
[RuCl2(DMSO)4] (
3
), respectively (Scheme 1).14
Fig. 2 Possible isomers for complex [RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2] (
5).
The presence of a single singlet signal in the 31P{1H} NMR
Scheme 1 Synthesis of the ruthenium(II) complexes C-E
.
spectrum of
stereoisomer
5
at δP 51.9 ppm allowed to discard the all cis
. On the other hand, the Far-IR spectrum
Based on these previous studies, we decided to explore the
reactivity of [RuCl2(PPh3)3] ( ) and cis-[RuCl2(DMSO)4] (
towards the phosphino-aldoxime 2-Ph2PC6H4CH=NOH ( ). In
the case of complex , it readily reacted with in THF at r.t. to
generate, regardless of the stoichiometry employed (from 1:1
to 1:4), a complex mixture of unidentified products.
Unfortunately, all purification attempts by crystallization or
column chromatography did not allow the separation of the
products formed (extensive decomposition was observed by
column chromatography). The use of other solvents (CH2Cl2,
MeOH or toluene) or higher temperatures (refluxing
conditions) did not lead to better results. In marked contrast,
I
showed two νRu-Cl absorptions at 322 and 263 cm-1, consistent
2
3)
with a cis dichloride complex.15 Consequently, isomers IV, i.e.
the analogue of complexes
1
2
1
D previously obtained in the
reaction of
3
with phosphino-imines 2-Ph2PC6H4CH=NR (iPr,
(S)-CHMeCy), and
V were ruled out (a single νRu-Cl absorption
would be expected for these stereoisomers).14b,15 Concerning
1
the H and 13C{1H} NMR spectra, the former showed broad
signals at 8.52 and 11.27 ppm for the CH=N and OH protons of
the phosphino-aldoxime ligand, and the latter the
inequivalence of the phenyl rings of the PPh2 units, along with
a characteristic singlet signal for the iminic CH=N carbon at δC
154.5 ppm. Since these spectroscopic data did not allow to
distinguish between stereoisomer II and III, to determine
the treatment of cis-[RuCl2(DMSO)4] (
refluxing THF resulted in the clean formation of the
octahedral-ruthenium(II) derivative
[RuCl2{κ2-(P,N)-2-
Ph2PC6H4CH=NOH}2] ( ), which could be isolated in 87% yield
(Scheme 2). It is worthy of noting that the same reaction
performed with only 1 equiv. of did not allow the
preparation of a monophosphine complex analogous to
(Scheme 1). Instead, the reaction led to the formation of a
mixture of and the unreacted precursor
3) with 2.4 equiv. of 1 in
unambiguously the stereochemistry of 5, an X-ray diffraction
5
study was carried out. X-ray quality crystals were obtained by
slow diffusion of diethyl ether into a saturated solution of the
complex in THF. An ORTEP diagram of the molecule, along with
selected structural parameters, is shown in Fig. 3. The
1
E
ruthenium atom is in
a slightly distorted octahedral
5
3.
environment with the two chloride ligands and PPh2 units each
mutually cis oriented (Cl(1)-Ru-Cl(2) = 84.28(3)° and P(1)-Ru-
P(2) 98.21(3)°), and the oxime groups mutually trans disposed
(N(1)-Ru-N(2) 171.9(1)°), i.e. the cis,cis,trans stereoisomer II
was formed in the reaction. The observed bond distances for
the aldoxime units (C(7)-N(1) 1.279(4) Å, C(27)-N(2) 1.273(4) Å,
N(1)-O(1) 1.404(3) Å and N(2)-O(2) 1.395(4) Å) were almost
identical to those previously found in the solid-state crystal
structures of the palladium(II) complexes [PdCl2{κ2-(P,N)-2-
Ph2PC6H4CH=NOH}] (
A
in Fig. 1; C-N = 1.27(1) Å and N-O =
in Fig.
1.39(1) Å) and [Pd{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2][Cl]2 (
B
1; C-N = 1.275(4) Å and N-O = 1.389(5) Å).2 On the other hand,
the close proximity of the hydroxyl-oxime functions to the
chloride ligands enabled the establishment of intramolecular
hydrogen bonds between both groups.16 The distances and
angles of the O(1)-H(1o)···Cl(1) and O(2)-H(2o)···Cl(2) contacts
(O(1)-H(1o) = 1.030 Å, H(1o)-Cl(1) = 1.979 Å, O(1)-Cl(1) = 2.974
Å and O(1)-H(1o)-Cl(1) = 161.37°; O(2)-H(2o) = 0.849 Å, H(2o)-
Scheme 2 Synthesis of the ruthenium(II) complexes
5 and 6.
Complex
5 was characterized by means of spectroscopic
methods (IR, Far-IR, and 31P{1H}, 1H and 13C{1H} NMR
2 | J. Name., 2012, 00, 1-3
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Cl(2) = 2.122 Å, O(2)-Cl(2) = 2.940 Å and O(2)-H(2o)-Cl(2) = experimental conditions to those used previously with
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2
161.62°) indicate, according with the Jeffrey´s terminology,17 palladium (pure water, 100 °C and a metal loading of 5 mol%),
DOI: 10.1039/C6RA07015A
that the intensity of these H-bond interactions is moderate both complexes were able to promote the rearrangement of
(mostly electrostatic).
commercially available (E)-benzaldoxime, providing benzamide
in ≥ 85% yield (entries 1 and 2 in Table 1). The best results
were obtained with the octahedral derivative 5, which was
able to generate benzamide in 94% GC-yield after only 5 h
(entry 1). In the reaction, the substrate was totally consumed
and only a small amount of the intermediate benzonitrile (ca.
5%) was present in the crude.20 The catalytic activity found for
complex
complexes
5
compares favorably with that of the palladium
and , which required 24 h to generate the amide
A
B
in similar yields.2 Reduction of the catalyst loading to 3 mol%
still produced benzamide in 93% GC-yield, although in this case
the reaction rate decreased considerably (entry 3). The same
happened when the reaction was carried out at 80 °C (entry 4).
Compared with the arene-ruthenium(II) complexes F-H (Fig. 4),
which are the only ruthenium catalysts active in pure water
Fig. 3 ORTEP diagram of the structure of complex
5 showing the crystallographic
labelling scheme. Phenyl groups of the PPh2 fragments and hydrogen atoms,
except those on O(1), O(2), C(7) and C(27), have been omitted for clarity.
Thermal ellipsoids are drawn at 30% probability level. Selected bond lengths (Å):
Ru-Cl(1) 2.4782(8), Ru-Cl(2) 2.4914(8), Ru-P(1) 2.2724(7), Ru-P(2) 2.2881(8), Ru-
N(1) 2.056(3), Ru-N(2) 2.050(3), C(7)-N(1) 1.279(4), C(27)-N(2) 1.273(4), N(1)-
O(1) 1.404(3), N(2)-O(2) 1.395(4). Selected bond angles (˚): Cl(1)-Ru-Cl(2)
84.28(3), P(1)-Ru-P(2) 98.21(3), N(1)-Ru-N(2) 171.9(1), P(1)-Ru-N(1) 87.76(7),
P(2)-Ru-N(2) 92.01(8), C(2)-C(7)-N(1) 126.5(3), C(7)-N(1)-Ru 135.0(2), C(7)-N(1)-
O(1) 110.6(3), O(1)-N(1)-Ru 114.3(2), C(21)-C(27)-N(2) 127.8(3), C(27)-N(2)-Ru
133.4(2), C(27)-N(2)-O(2) 109.9(3), O(2)-N(2)-Ru 115.9(2).
previously reported in the literature, the effectiveness of 5 was
very similar to that of F-G (98% GC-yield of benzamide after 5-
6 h of heating at 100 °C with 5 mol% of Ru)19b,e and slightly
lower to that of
heating at 100 °C with 3 mol% of Ru).19c As expected, a blank
experiment in the absence of showed no benzamide
formation after 5 h of heating. On the other hand, as shown in
entry 6, the precursor complex was also active in the
H (93% GC-yield of benzamide after 7 h of
5
As shown in Scheme 2, complex cis,cis,trans-[RuCl2{κ2-
3
(P,N)-2-Ph2PC6H4CH=NOH}2]
synthesized by reacting the arene-ruthenium(II) dimer
[{RuCl(µ-Cl)(η6-p-cymene)}2] (
) with an excess (6 equiv.) of the
phosphino-aldoxime ligand 2-Ph2PC6H4CH=NOH ( ) in refluxing
toluene (75% isolated yield).18 Dimer
also readily reacted
(5
)
could be alternatively
reaction under the same experimental conditions, but it
showed a poorer selectivity.
4
1
4
with 2 equiv. of 1, in dichloromethane at r.t., to generate the
cationic species [RuCl{κ2-(P,N)-2-Ph2PC6H4CH=NOH}(η6-p-
cymene)][Cl]. This complex was isolated as the corresponding
-
hexafluorophosphate salt
6
in 80% yield after Cl-/PF6 counter-
anion exchange with a methanolic solution of NaPF6.
Characterization of was straightforward by following its
Fig. 4 Structure of the arene-ruthenium(II) complexes F-H
.
6
analytical and spectroscopic data (details are given in the
Experimental section). Key spectroscopic features are: (i)
(31P{1H} NMR) a singlet resonance at δP 38.9 ppm, consistent
with the coordination of the PPh2 unit to the metal (Δδ = 53
ppm with respect to the free ligand), and (ii) (1H and 13C{1H}
Table 1 Catalytic rearrangement of (E)-benzaldoxime using the ruthenium(II)
complexes 5 and 6.a
NMR) the presence of characteristic resonances for the
4
aldoxime CH=NOH protons and carbon at δH 8.90 (dd, JPH
=
4
4
13.5 Hz, JHH = 2.1 Hz, CH=N) and 12.54 (d, JHH = 2.1 Hz, OH)
ppm, and δC 172.0 (d, 3JPC = 8.2 Hz) ppm, respectively.
The catalytic potential of the new ruthenium complexes
Entry Catalyst
mol % of Ru t (h)
Conv. (%)b
Yield (%)b
cis,cis,trans-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2]
(
5
)
and
1
2
5
6
5
5
6
3
5
5
3
5
5
5
5
> 99
96
> 99
> 99
98
94
85
93
90
91
76
24
20
16
8
[RuCl{κ2-(P,N)-2-Ph2PC6H4CH=NOH}(η6-p-cymene)][PF6] (
6
) was
3
4c
5d
6
subsequently explored. In particular, given the good results
obtained with the palladium(II) derivatives and (Fig. 1) in
A
B
the rearrangement of aldoximes to primary amides in water,2
we initially focused on this catalytic transformation. It should
be mentioned at this point that, despite several late-transition
metal catalysts able to promote rearrangement of aldoximes
to amides are already known,3 examples active in aqueous
media still remain scarce.19 To our delight, employing the same
5
> 99
a
Reactions were performed under Ar atmosphere starting from 1 mmol of
b
the (E)-benzaldoxime (0.33 M in water). Determined by GC (uncorrected
GC areas). Differences between GC conversions and yields correspond to the
c
intermediate benzonitrile present in the reaction mixture.
Reaction
performed at 80 °C. d Reaction performed in presence of 5 mol% of AgSbF6.
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On the other hand, the lower reactivity of the half-
To further expand the catalytic utility of compVleiexw A5rtwicleeOanllsinoe
sandwich complex vs
6
5
can be rationalized in terms of its explored its behaviour in one C-C bond DfoOrIm: 1i0n.1g03r9e/aCc6tRioA0n7;0t1h5eA
cationic nature, which disfavors the generation of a vacant site α-alkylation/reduction of acetophenones with primary
on the metal by dissociation of the chloride ligand.21 In alcohols. The α-alkylation of methyl-ketones employing
complete accord with this, a marked increase in activity was alcohols as alkylating agents has been extensively studied in
observed when the rearrangement of (E)-benzaldoxime was the last years with both homo- and heterogeneous catalysts,
performed with
The versatility of the most active catalyst cis,cis,trans- methodology (also known as hydrogen autotransfer
[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2] ( ) was subsequently methodology).23 The process involves the initial catalytic
6
in the presence of a Ag(I) salt (entry 5 vs 2).
and represents a nice example of the borrowing hydrogen
5
explored using an array of other aromatic, heteroaromatic, oxidation of the primary alcohol into the corresponding
aliphatic and α,β-unsaturated aldoximes.22 As shown in Table aldehyde, which subsequently undergoes aldol condensation
2, the corresponding amide products were obtained in all the with the methyl-ketone substrate to generate an enone. Final
cases in good yields (≥ 91% by GC; ≥ 77% isolated yield after catalytic reduction of the enone furnishes the saturated α-
chromatographic purification). For the family of substituted alkylated ketone product (Scheme 3).
benzaldoximes, influence of the electronic properties of the
aryl rings on the activity of
5 was observed, those containing
electron-withdrawing groups reacting faster (entries 2-8 vs 9-
13). On the other hand, as expected on the basis of steric
grounds, ortho-substituted substrates showed
a lower
reactivity compared to their meta- and para-substituted
counterparts (entry 3 vs 4-5 and entry 9 vs 10-11).
Table 2 Catalytic rearrangement of aldoximes using the octahedral Ru(II)
complex cis,cis,trans-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2] (5).a
Scheme 3 The α-alkylation and the α-alkylation/reduction of methyl-ketones
with primary alcohols.
Despite its great synthetic potential for the preparation of
secondary alcohols, a similar process in which the α-alkylated
ketone product is reduced in an additional step has been
comparatively much less studied (Scheme 3).13 With regard to
the use of ruthenium catalysts, Cho and co-workers reported
the selective α-alkylation/reduction of both aryl and alkyl
methyl-ketones with different primary alcohols employing 5
Entry Aldoxime
t (h)
Conv. (%)b
Yield (%)b
1
R = Ph
5
4
5
3
3
4
2
2
12
6
7
9
7
24
6
5
5
8
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
94 (83)
98 (89)
96 (83)
96 (83)
97 (88)
95 (86)
98 (90)
96 (86)
94 (82)
98 (89)
93 (84)
91 (75)
94 (85)
91 (77)
96 (86)
95 (84)
92 (79)
93 (80)
2
3
4
5
6
7
R = 4-C6H4F
R = 2-C6H4Cl
R = 3-C6H4Cl
R = 4-C6H4Cl
R = 4-C6H4Br
R = C6F5
mol% of [RuCl2(PPh3)3] (2), 3 equiv. of the alcohol, and KOH as
the base (3 equiv.). The reactions, which were performed in
1,4-dioxane at 80 °C for 40 h, delivered the desired saturated
alcohols in 43-85% yield.24 Yus and co-workers also
demonstrated that, depending of the stoichiometry employed,
either alkylated ketones or the corresponding saturated
alcohols can be obtained using 2 mol% of the complex cis-
8
9
R = 4-C6H4NO2
R = 2-C6H4Me
R = 3-C6H4Me
R = 4-C6H4Me
R = 4-C6H4OMe
R = 4-C6H4SMe
R = 2-Pyridyl
R = 3-Pyridyl
R = n-C6H13
10
11
12
13
14
15
16
17
18
[RuCl2(DMSO)4] (3) in combination with PPh3 (2 mol%) and 1
equiv. of KOH in 1,4-dioxane at 80 °C. The saturated alcohols
were isolated in 25-82% yield after 24 h when the primary
alcohol was used in a two-fold excess relative to the methyl-
ketone.25,26
R = Cy
R = (E)-CH=CHPh
With these precedents in mind, we initially checked the
catalytic behaviour of complex cis,cis,trans-[RuCl2{κ2-(P,N)-2-
a
Reactions were performed under Ar atmosphere starting from 1 mmol of
b
Ph2PC6H4CH=NOH}2] (5) in the α-alkylation/reduction of
the corresponding aldoxime (0.33 M in water).
Determined by GC
(uncorrected GC areas), isolated yields after work-up are given in brackets.
Differences between GC conversions and yields correspond to the
intermediate nitrile present in the crude reaction mixture.
acetophenone with benzyl alcohol in 1,4-dioxane at 80 °C.
Thus, as shown in Table 3, when the reaction was carried out
with equimolar amounts of the reactants and KOH (1 equiv.) as
the base, 24 h of heating were required to achieve a 96%
conversion, the reaction affording a mixture of the desired 1,3-
Remarkably,
complex
cis,cis,trans-[RuCl2{κ2-(P,N)-2-
Ph2PC6H4CH=NOH}2] (
5
) was able to rearrange pyridine-2-
diphenylpropan-1-ol
ketone 1,3-diphenylpropan-1-one
8
and the intermediate α-alkylated
in almost 1:1 ratio (entry
carbaldoxime, a challenging substrate given its tendency to
form catalytically inert metal-chelates (entry 14).19b,g However,
compared to its 3-substituted isomer (entry 15), a longer
reaction time was in this case required to obtain the desired
picolinamide in high yield.
7
1). In addition, ca. 7% of 1-phenylethanol resulting from the
conventional transfer hydrogenation (TH) of the acetophenone
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Table 3 Catalytic α-alkylation/reduction of acetophenone with benzyl alcohol using cis,cis,trans-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH} ] (5): VOiepwtiAmrtiizcaletiOonnlinoef
DOI:210.1039/C6RA07015A
the reaction conditions.a
Entry
Equiv. of KOH
Equiv. of BnOH
T (°C)
Solvent
t (h)
Conv. (%)b
7/8 yield (%)b
7/8 ratio (%)b
1
2
3
4
1
1
1
1
1
1
1
1
1
2
3
1
2
3
3
3
3
80
80
80
120
120
120
120
120
120
1,4-dioxane 24
1,4-dioxane 3 (24)
1,4-dioxane 3 (24)
96
89c
47:42
94 (> 99)
92 (> 99)
> 99
> 99
> 99
> 99
> 99
98
88 (94)d
86 (94)d
> 99
65:23 (14:80)
63:23 (11:83)
50:50
22:78
13:87
21:79
32:68
36:62
toluene
toluene
toluene
toluene
toluene
toluene
24
3
3
3
3
5
> 99
> 99
> 99
> 99
6
7e
8f
9
0.5
3
98
a Reactions were performed under Ar atmosphere starting from 1 mmol of acetophenone (1 M solution in the appropriate solvent) and 1-3 mmol of benzyl
b
c
d
alcohol. Determined by GC (uncorrected GC areas). 7% of 1-phenylethanol was detected by GC in the reaction mixture. 6% of 1-phenylethanol was
detected by GC in the reaction mixture. e Reaction performed with 2 mol% of complex 6. f Reaction performed with 2 mol% of complex 3.
substrate was detected by GC in the crude reaction mixture.24 secondary aryl-carbinols in 77-91% GC-yield (63-83% isolated
An increase in the benzyl alcohol/acetophenone ratio to 2:1 yield after chromatographic work-up). As in the case of
and 3:1 led to a faster consumption of the ketone substrate, acetophenone (entry 1), minor amounts of the intermediate α-
but 24 h were still required to generate the saturated aryl- alkylated ketone were detected in all these reactions by GC.
carbinol
entries 2 and 3). At shorter times (3 h), the α-alkylated ketone
was in both cases the predominant species in solution. As in
8 as the major reaction product (up to 83% GC-yield;
Table 4 Catalytic α-alkylation/reduction of acetophenones with primary
alcohols using cis,cis,trans-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2] (5).a
7
the previous case, small amounts of 1-phenylethanol were also
formed. To our delight, better results in terms of both activity
and selectivity were obtained when the same C-C coupling
process was performed in toluene at 120 °C (entries 4-6).
Under these conditions, the formation of 1-phenylethanol
could be completely suppressed. In particular, employing a
benzyl alcohol/acetophenone ratio of 3:1, the total
consumption of acetophenone was reached in only 3 h, with
Entry
R1
R2
Conv. (%)b
Yield (%)b
1c
H
Ph
Ph
Ph
Ph
Ph
Ph
> 99
> 99
> 99
> 99
> 99
> 99
> 99
> 99
98
87 (75)
86 (72)
89 (73)
88 (74)
91 (83)
77 (63)
76 (64)
73 (60)
72 (60)
70 (56)
79 (68)
2c
2-Me
2-OMe
3-Cl
2-Br
4-Br
H
H
H
H
H
3c
4c
5c
the desired alcohol
8 being formed in a remarkable 87% GC-
6c
yield (entry 6).27 At this point, it is pertinent to note that,
7d
8e
9f
CH2Bn
CH2CH2Bn
nPr
under identical conditions, the use of complexes [RuCl{κ2-
(P,N)-2-Ph2PC6H4CH=NOH}(η6-p-cymene)][PF6]
(6
)
and cis-
10g
11c
iBu
98
> 99
[RuCl2(DMSO)4] (3) also resulted in the complete conversion of
n-C5H11
the starting acetophenone substrate after 3 h of heating.
However, the selectivity of the process was in all the cases
slightly lower (entries 7-8 vs 6). An additional experiment
a
Reactions were performed under Ar atmosphere starting from 1 mmol of
the corresponding acetophenone (1 M in toluene) and 3 mmol of the
b
corresponding primary alcohol. Determined by GC (uncorrected GC areas),
performed with complex
5 pointed out the need to use a
isolated yields after work-up are given in brackets. c Differences between GC
stoichiometric amount of base to achieve an optimal
selectivity towards the desired alcohol (entry 9 vs 6). A blank
conversions and yields correspond to the α-alkylated ketone present in the
crude reaction mixture.
diphenylpentan-1-one were detected by GC in the crude reaction mixture.
19% of 1-phenylethanol and 8% of 1,6-diphenylhexan-1-one were detected
by GC in the crude reaction mixture. 20% of 1-phenylethanol and 6% of 1-
phenylhexan-1-one were detected by GC in the crude reaction mixture.
10% of 1-phenylethanol and 18% of 5-methyl-1-phenylhexan-1-one were
detected by GC in the crude reaction mixture.
d
16% of 1-phenylethanol and 7% of 1,5-
e
experiment in the absence of
reaction leading to a mixture of
Having established suitable reaction conditions to generate
the desired 1,3-diphenylpropan-1-ol in high yield (entry 6 in
5
was also performed, the
7
and in ca. 1:1 ratio.
8
f
g
8
Table 3), the scope of the process was next explored. The
results are summarized in Table 4. As shown in entries 2-6, the
reaction could be successfully expanded to a series of
substituted acetophenone derivatives, which, regardless of
their substitution pattern and electronic nature, readily
reacted with benzyl alcohol to generate the corresponding
On the other hand, in addition to benzyl alcohol, other
primary alcohols could also be employed for the α-
alkylation/reduction of acetophenone (entries 7-11). However,
in these cases the yields were slightly lower and, in addition to the
corresponding α-alkylated ketones, formation of 1-phenylethanol
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was also observed. Regardless of this, the desired secondary
alcohols were the major reaction products and could be isolated in
pure form in 56-68% yield.
A suspension of cis-[RuCl2(DMSO)4] (
3) (0.100 g, V0ie.w21A0rticmle Omnolinle)
and 2-Ph2PC6H4CH=NOH (
1
) (0.152 g, 0.5D0O0I:m10m.1o0l3)9i/nC63R0A0m70L15oAf
THF was heated under reflux for 6 h. The resulting brown
solution was then evaporated to dryness, and the solid residue
thus generated dissolved in CH2Cl2 (ca. 10 mL). Addition of
diethyl ether (ca. 50 mL) precipitated a yellow solid, which was
washed with diethyl ether (2 x 20 mL) and vacuum-dried. Yield:
0.143 g (87%). IR (KBr): ν = 3290 (br, O-H), 1623 (m, C=N) cm-1.
Conclusions
In summary, in this work we have described the preparation
and spectroscopic characterization of the first examples of
ruthenium complexes containing a phosphino-oxime ligand,
31P{1H} NMR (CD2Cl2): δ = 51.9 (s) ppm. H NMR (CD2Cl2): δ =
1
namely cis,cis,trans-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2] (
5)
6.57 (br, 4H, CHarom), 6.92-7.59 (m, 24H, CHarom), 8.52 (br, 2H,
CH=N), 11.27 (br, 2H, OH) ppm. 13C{1H} NMR (CD2Cl2): δ =
126.6 (m, part AA´of an AA´XX´ spin system, Carom), 127.3 (m, 3
CHarom), 129.8 (d, JPC = 11.2 Hz, CHarom), 130.0 (s, CHarom), 131.1
(s, part AA´of an AA´XX´ spin system, CHarom), 132.1 (s, part
AA´of an AA´XX´ spin system, Carom), 132.5 (s, CHarom), 132.7 (s,
part AA´of an AA´XX´ spin system, Carom), 133.3 (m, part AA´of
an AA´XX´ spin system, CHarom), 134.1 (m, part AA´of an AA´XX´
spin system, CHarom), 134.5 (m, part AA´of an AA´XX´ spin
system, CHarom), 135.6 (m, part AA´of an AA´XX´ spin system,
Carom), 154.5 (s, C=N) ppm. Elemental analysis calcd. (%) for
RuC38H32Cl2N2O2P2: C 58.32, H 4.12, N 3.58; found: C 58.45, H
4.07, N 3.67.
and
). In addition, the stereochemistry of the former has been
[RuCl{κ2-(P,N)-2-Ph2PC6H4CH=NOH}(η6-p-cymene)][PF6]
(6
unequivocally established by means of single-crystal X-ray
diffraction techniques. On the other hand, the utility of these
species in homogeneous catalysis has also been demonstrated.
In particular, the octahedral complex
5 proved to be an
efficient and broad scope catalyst for the rearrangement of
aldoximes to primary amides, and for the synthesis of
secondary aryl-carbinols by α-alkylation/reduction of
acetophenone derivatives with primary alcohols. The results
reported herein, along with our previous work with related
palladium(II) systems,2 support further studies on the
coordination chemistry and catalytic applications of
phosphino-oxime ligands, a field almost unexplored to date.
Synthesis
of
cis,cis,trans-[RuCl2{κ2-(P,N)-2-
Ph2PC6H4CH=NOH}2] (5) from [{RuCl(µ-Cl)(η6-p-cymene)}2] (4)
A solution of [{RuCl(µ-Cl)(η6-p-cymene)}2] (
) (0.122 g, 0.200
mmol) and 2-Ph2PC6H4CH=NOH ( ) (0.366 g, 1.200 mmol) in 30
4
Experimental
1
mL of toluene was heated under reflux overnight. The resulting
brown solution was then concentrated under vacuum to ca. 10
mL and stored in a freezer at -10 °C for 24 h. The cooling led to
the precipitation of cis-[RuCl2{κ2-(P,N)-2-Ph2PC6H4CH=NOH}2]
General methods
All the manipulations were performed under argon
atmosphere using vacuum-line and standard Schlenk or
sealed-tube techniques. Organic solvents were dried by
standard methods and distilled under argon before use.28 All
reagents were obtained from commercial suppliers and used
as received, with the exception of compounds [RuCl2(PPh3)3]
(5
) as a yellow solid, which was separated, washed with diethyl
ether (2 x 20 mL) and vacuum-dried. Yield: 0.234 g (75%).
[RuCl{κ2-(P,N)-2-Ph2PC6H4CH=NOH}(η6-p-
(
(
2
4
),29 cis-[RuCl2(DMSO)4] (
3
),30 [{RuCl(µ-Cl)(η6-p-cymene)}2]
Synthesis
of
cymene)][PF6] (6)
31
)
and most of the aldoximes employed in the catalytic
A solution of [{RuCl(µ-Cl)(η6-p-cymene)}2] (
mmol) and 2-Ph2PC6H4CH=NOH ( ) (0.125 g, 0.410 mmol) in 30
4) (0.122 g, 0.200
experiments,19 which were prepared by following the method
reported in the literature. GC measurements were performed
with a Hewlett-Packard HP6890 equipment using a Supelco
Beta-DexTM 120 column (30 m length; 250 µm diameter).
Elemental analyses and Far-IR measurements were provided
by the Analytical Service of the Instituto de Investigaciones
Químicas (IIQ-CSIC) of Seville. Infrared spectra were recorded
on a Perkin-Elmer 1720-XFT spectrometer. NMR spectra were
recorded on Bruker DPX-300 or AV400 instruments. The
chemical shift values (δ) are given in parts per million and are
referred to the residual peak of the deuterated solvent
employed (1H and 13C), or to an external 85% aqueous H3PO4
solution (31P). DEPT experiments have been carried out for all
the compounds reported in this paper.
1
mL of CH2Cl2 was stirred at room temperature for 1 h. The
resulting orange solution was then evaporated to dryness, and
the solid residue thus formed dissolved in MeOH (20 mL) and
treated overnight with NaPF6 (0.084 g, 0.500 mmol). The
solvent was then removed under vacuum, the crude product
extracted with CH2Cl2 (ca. 50 mL), and the extract filtered.
Concentration of the filtrate to ca. 5 mL, followed by the
addition of diethyl ether (ca. 50 mL), precipitated a yellow
solid, which was washed with diethyl ether (2 x 20 mL) and
vacuum-dried. Yield: 0.230 g (80%). IR (KBr): ν = 3206 (br, O-H),
1616 (m, C=N) cm-1. 31P{1H} NMR (acetone-d6): δ = -144.1
1
-
1
(sept, JPF = 701.7 Hz, PF6 ), 38.9 (s, PPh2) ppm. H NMR
(acetone-d6): δ = 0.70 (d, 3H, 3JHH = 6.6 Hz, CHMe2), 0.97 (d, 3H,
3JHH = 7.5 Hz, CHMe2), 2.15 (s, Me), 2.55 (m, 1H, CHMe2), 5.70
3
3
Synthesis
of
cis,cis,trans-[RuCl2{κ2-(P,N)-2-
(d, 1H, JHH = 5.4 Hz, CH of cymene), 6.00 (d, 1H, JHH = 6.6 Hz,
Ph2PC6H4CH=NOH}2] (5) from cis-[RuCl2(DMSO)4] (3)
3
CH of cymene), 6.05 (d, 1H, JHH = 5.4 Hz, CH of cymene), 6.20
(d, 1H, 3JHH = 6.6 Hz, CH of cymene), 7.29 (m, 1H, CHarom), 7.54-
6 | J. Name., 2012, 00, 1-3
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4
7.88 (m, 11H, CHarom), 8.12 (m, 2H, CHarom), 8.90 (dd, 1H, JPH
=
saturated solution of the complex in THF. The most relevant
View Article Online
DOI: 10.1039/C6RA07015A
4
4
13.5 Hz, JHH = 2.1 Hz, CH=N), 12.54 (d, 1H, JHH = 2.1 Hz, OH) crystal and refinement data are collected in Table 5. Data
ppm. 13C{1H} NMR (acetone-d6): δ = 17.3 (s, Me), 20.0 (s, collection was performed with an Oxford Diffraction Xcalibur
CHMe2), 21.9 (s, CHMe2), 30.1 (s, CHMe2), 89.5 (d, 2JPC = 2.8 Hz, Nova single crystal diffractometer using Cu-Kα radiation (λ =
2
CH of cymene), 91.3 (d, JPC = 2.5 Hz, CH of cymene), 93.7 (d, 1.5418 Å). Images were collected at a fixed crystal-to-detector
2JPC = 7.2 Hz, CH of cymene), 96.5 (d, JPC = 6.1 Hz, CH of distance of 63 mm, using the oscillation method with 1.3°
2
cymene), 102.8 (s, C of cymene), 110.9 (s, C of cymene), 125.5 oscillation and 23.77-38.88 s variable exposure time per image.
1
(d, JPC = 47.3 Hz, Carom), 128.8 (d, JPC = 12.1 Hz, CHarom), 129.3 Data collection strategy was calculated with the program
(d, JPC = 10.2 Hz, CHarom), 129.4 (s, Carom), 131.3 (d, JPC = 2.8 Hz, CrysAlis Pro CCD.32 Data reduction and cell refinement was
CHarom), 131.8 (d, JPC = 2.8 Hz, CHarom), 132.9 (d, JPC = 10.5 Hz, performed with the program CrysAlis Pro RED.32 An empirical
CHarom), 132.4 (s, CHarom), 133.8 (d, JPC = 7.1 Hz, CHarom), 134.2 absorption correction was applied using the SCALE3 ABSPACK
(d, 1JPC = 48.5 Hz, Carom), 135.4 (d, JPC = 9.7 Hz, CHarom), 136.3 (d, algorithm as implemented in the program CrysAlis Pro RED.32
JPC = 8.8 Hz, CHarom), 136.4 (d, JPC = 9.7 Hz, CHarom), 172.0 (d, 3JPC
Table 5 Crystal data and structure refinement for compound 5
= 8.2 Hz, C=N) ppm. Elemental analysis calcd. (%) for
Empirical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
Crystal size/mm
a/Å
b/Å
c/Å
α (ᵒ)
β (ᵒ)
C38H32Cl2N2O2P2Ru∙C4H8O
854.67
293(2)
1.54184
Triclinic
RuC29H30F6P2ClNO: C 48.31, H 4.19, N 1.94; found: C 48.44, H
4.10, N 2.07.
General procedure for the catalytic rearrangement of
aldoximes using complex 5
P-1
0.10 x 0.03 x 0.03
10.6726(5)
11.5721(8)
17.6589(9)
83.597(5)
78.172(4)
63.038(6)
2
The corresponding aldoxime (1 mmol), water (3 mL) and
complex
5 (0.039 g, 0.05 mmol) were introduced into a Teflon-
capped sealed tube, and the reaction mixture stirred at 100 °C
for the indicated time (see Table 2). The course of the reaction
was monitored regularly taking samples of ca. 20 µL, which,
after extraction with CH2Cl2 (3 mL), were analyzed by GC. To
isolate the amide products, whose identity was assessed by
comparison of their NMR spectroscopic data with those
reported in the literature, the solvent was eliminated under
reduced pressure and the crude reaction mixture purified by
column chromatography over silica gel using CH2Cl2 as eluent.
γ (ᵒ)
Z
Volume/Å3
Calculated density/g cm-3
µ/mm-1
1905.6(2)
1.489
5.751
F(000)
θ range/°
Index ranges
876
4.29-69.34
-6 ≤ h ≤ 12
-13 ≤ k ≤ 14
-21 ≤ l ≤ 21
97.9%
Completeness to θmax
No. of reflns. collected
No. of unique reflns.
No. of parameters/restraints
Refinement method
Goodness-of-fit on F2
R1 [I > 2σ(I)]a
General procedure for the catalytic α-alkylation/reduction of
acetophenones with primary alcohols using complex 5
15022
6968 (Rint = 0.049)
485/18
The corresponding acetophenone (1 mmol), the appropriate
Full-matrix least-squares on F2
1.027
alcohol (3 mmol), KOH (0.056 g, 1 mmol) and complex
5 (0.016
g, 0.02 mmol) were introduced into a Teflon-capped sealed
tube under an argon atmosphere. Toluene (1 mL) was then
added at room temperature, and the resulting suspension
heated at 120 °C for the indicated time (see Table 4). After this
time, a sample of ca. 20 μL was taken and, after dilution with
CH2Cl2 (3 mL), analyzed by GC to determine the composition of
the reaction mixture. To isolate the alcohol products, whose
identity was assessed by comparison of their NMR
spectroscopic data with those reported in the literature, the
reaction mixture was diluted with Et2O (5 mL) and extracted
with water (5 mL). The aqueous phase was extracted twice
with Et2O (2 x 5 mL) and the combined organic phases washed
with brine (5 mL). After removal of the volatiles under vacuum,
the oily residue was purified by column chromatography (silica
gel) using Et2O/hexane (1:20) as eluent.
0.0373
0.0923
0.0445
0.0980
wR2 [I > 2σ(I)]a
R1 (all data)
R2 (all data)
Largest diff. peak and hole/e Å-3
0.443, -0.674
a R1 = ∑(|Fo|-|Fc|)/∑|Fo|; wR2 = {∑[w(Fo2-Fc2)2]/∑[w(Fo2)2]}1/2
The software package WINGX was used for space group
determination, structure solution, and refinement.33 The
structure was solved by direct methods using SIR92,34 and
refined by full-matrix least-squares on F2 using SHELXL2014.35
During the final stages of the refinements, all the positional
parameters and the anisotropic temperature factors of all non-
H atoms were refined. H atoms were geometrically located
and their coordinates were refined riding on their parent
atoms, with the exception of H1o, H2o, H7 and H27 which
were found from the difference Fourier maps and included in a
refinement with isotropic temperature parameters. One THF
molecule of solvation per molecule of the complex was found
in the asymmetric unit. The maximum residual electron
density is located near to heavy atoms. The function minimized
X-Ray crystal structure determination of complex 5
Crystals of complex
5 suitable for X-ray diffraction analysis
were obtained by slow diffusion of diethyl ether into a
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2
2 2
2 2
2
(Fo ) ]}1/2 where


= 1/[2(Fo ) +
12 For recent works with this type of ligands, seeVfieowrAertxicalemOpnllinee:
(a) E. Badetti, G. Franc, J.-P. Majoral, A.-M. Caminade, R. M.
Sebastián and M. Moreno-Mañas, EurD. OJ.I:O10r.g10. 3C9h/Ce6mR.A,027001151A,
1256; (b) T. Inami, S. Sako, T. Kurahashi and S. Matsubara,
Org. Lett., 2011, 13, 3837; (c) S. Sako, T. Kurahashi and S.
Matsubara, Chem. Commun., 2011, 47, 6150; (d) T. F.
Vaughan, D. J. Koedyk and J. L. Spencer, Organometallics,
2011, 30, 5170; (e) H. Lei, A. M. Royer, T. B. Rauchfuss and D.
Gray, Organometallics, 2012, 716, 55; (f) D. A. Rooke and E.
M. Ferreira, Org. Lett., 2012, 14, 338; (g) B. C. E. Makhubela,
A. Jardine and G. S. Smith, Green Chem., 2012, 14, 338; (h) Y.
Li, F. Liang, R. Wu, Q. Li, Q.-R. Wang, Y.-C. Xu and L. Jiang,
Synlett, 2012, 23, 1805; (i) H. Chiririwa, J. R. Moss, D.
Hendricks, G. S. Smith and R. Meijboom, Polyhedron, 2013,
49, 29; (j) W. M. Motswainyana, M. O. Onani, O. M.
Madiehe, M. Saibu, N. Thovhogi and R. A. Lalancette, J.
Inorg. Biochem., 2013, 129, 112; (k) M. K. Yilmaz and B.
Güzel, Appl. Organomet. Chem., 2014, 28, 529; (l) M.
Tristany, R. Laurent, H. Dib, L. Gonsalvi, M. Peruzzini, J.-P.
was {
[

(Fo - Fc ) ]/
[

(0.0465P)2 + 0.9823P] with
(Fo ) from counting statistics and
2
2
2
P = [Max (Fo ,0) + 2Fc ]/3. Atomic scattering factors were taken
from the International Tables for X-Ray Crystallography.36
Geometrical calculations were made with PARST.37 The
crystallographic plots were made with ORTEP-3.33
Acknowledgements
This work was supported by the Spanish MINECO (project
CTQ2013-40591-P) and the Gobierno del Principado de
Asturias (project GRUPIN14-006). J.F., L.M.-R. and E. T.-M.
thank MINECO, MECD and ESF for the award of a Juan de la
Cierva contract (IJCI-2014-19174), and FPI and FPU fellowships,
respectively.
Majoral and A.-M. Caminade, Inorg. Chim. Acta, 2014, 409
,
121; (m) L. Maqeda, B. C. E. Makhubela and G. S. Smith,
Polyhedron, 2015, 91, 128; (n) T. Traut-Johnstone, S.
Kanyanda, F. H. Kriel, T. Viljoen, P. D. R. Kotze, W. E. van Xyl,
J. Coates, D. J. G. Rees, M. Meyer, R. Hewer and D. B. G.
Williams, J. Inorg. Biochem., 2015, 145, 108.
Notes and references
1
For reviews related to this topic, see: (a) G. R. Newkome,
Chem. Rev., 1993, 93, 2067; (b) P. Espinet and K. Soulantica,
Coord. Chem. Rev., 1999, 193-195, 499; (c) C. S. Slone, D. A.
13 For a review on this catalytic transformation, see: H.
Lundberg and H. Adolfsson, Synthesis, 2016, 48, 644.
14 (a) P. Crochet, J. Gimeno, S. García-Granda and J. Borge,
Organometallics, 2001, 20, 4369; (b) P. Crochet, J. Gimeno, J.
Borge and S. García-Granda, New J. Chem., 2003, 27, 414.
15 (a) M. S. Lupin and B. L. Shaw, J. Chem. Soc. A, 1968, 741; (b)
Weinberger and C. A. Mirkin, Prog. Inorg. Chem., 1999, 48
,
233; (d) P. Braunstein and F. Naud, Angew. Chem. Int. Ed.,
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Tetrahedron, 2003, 59, 9471; (f) P. J. Guiry and C. P.
Saunders, Adv. Synth. Catal., 2004, 346, 497; (g) P.
Braunstein, J. Organomet. Chem., 2004, 689, 3953; (h) I. D.
J. T. Mague and J. P. Mitchener, Inorg. Chem., 1972, 11
2714.
,
Kostas, Curr. Org. Synth., 2008, 5, 227; (i) W.-H. Zhang, S. W.
Chien and T. S. A. Hor, Coord. Chem. Rev., 2011, 255, 1991;
(j) T. Noël and J. Van der Eycken, Green Process Synth., 2013,
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43, 819; (l) J. García-Álvarez, S. E. García-Garrido and V.
Cadierno, J. Organomet. Chem., 2014, 751, 792.
16 Metal-bound chlorine atoms are well-known H-bond
acceptors: G. Aullón, D. Bellamy, L. Brammer, E. A. Bruton
and A. G. Orpen, Chem. Commun., 1998, 653.
17 (a) G. A. Jeffrey, An Introduction to Hydrogen Bonding,
Oxford University Press, Oxford, 1997; (b) T. Steiner, Angew.
Chem. Int. Ed., 2002, 41, 48.
2
L. Menéndez-Rodríguez, E. Tomás-Mendivil, J. Francos, C.
Nájera, P. Crochet and V. Cadierno, Catal. Sci. Technol., 2015,
18 Formation of complexes trans,cis,cis-[RuCl2{κ2-(P,N)-2-
5
, 3754.
Ph2PC6H4CH=NR}2], related to
D
(Scheme 1), from the
) with an
3
4
5
6
7
8
For a review on this catalytic transformation, see: P. Crochet
and V. Cadierno, Chem. Commun., 2015, 51, 2495.
K. Park, P. O. Lagaditis, A. J. Lough and R. H. Morris, Inorg.
Chem., 2013, 52, 5448.
L. Xu, D. Zhu, F. Wu, R. Wang and B. Wan, Tetrahedron, 2005,
61, 6553.
D. Zhu, L. Xu, F. Wu and B. Wan, Tetrahedron Lett., 2006, 47
5781.
L. Xu, D. Zhu, F. Wu, R. Wang and B. Wan, J. Mol. Catal. A:
Chem., 2005, 237, 210.
reaction of dimer [{RuCl(µ-Cl)(η6-p-cymene)}2] (
4
excess of the phosphino-imines 2-Ph2PC6H4CH=NR (R =
CH2CH2-4-C6H4OH, 2-Me-4-C6H3OH, 2-Me-2-Py) in refluxing
toluene has been recently described: M. Keleş, C. Şahinoğlu,
D. M. Emir and M. Mart, Appl. Organomet. Chem., 2014, 28
,
768.
,
19 (a) H. Fujiwara, Y. Ogasawara, M. Kotani, K. Yamaguchi and
N. Mizuno, Chem. Asian J., 2008,
3, 1715; (b) R. García-
Álvarez, A. E. Díaz-Álvarez, J. Borge, P. Crochet and V.
Cadierno, Organometallics, 2012, 31, 6482; (c) R. García-
Álvarez, M. Zablocka, P. Crochet, C. Duhayon, J.-P. Majoral
and V. Cadierno, Green Chem., 2013, 15, 2447; (d) K.
See, for example: (a) A. Chakravorty, Coord. Chem. Rev.,
1974, 13, 1; (b) V. Y. Kukushkin, D. Tudela, A. J. L. Pombeiro,
Coord. Chem. Rev., 1996, 156, 333; (c) V. Y. Kukushkin, A. J. L.
Pombeiro, Coord. Chem. Rev., 1999, 181, 147; (d) A. G.
Smith, P. A. Tasker, D. J. White, Coord. Chem. Rev., 2003,
241, 61; (e) P. Chaudhuri, Coord. Chem. Rev., 2003, 243, 143;
(f) D. A. Alonso, L. Botella, C. Nájera and M. C. Pacheco,
Synthesis, 2004, 1713; (g) C. J. Milios, T. C. Stamatatos, S. P.
Perlepes, Polyhedron, 2006, 25, 134; (h) D. A. Alonso and C.
Nájera, Chem. Soc. Rev., 2010, 39, 2891.
Tambara and G. D. Pantoş, Org. Biomol. Chem., 2013, 11
,
2466; (e) E. Tomás-Mendivil, L. Menéndez-Rodríguez, J.
Francos, P. Crochet and V. Cadierno, RSC Adv., 2014,
63466; (f) C. Sun, P. Qu and F. Li, Catal. Sci. Technol., 2014,
4
4
,
,
988; (g) P. J. Gonzalez-Liste, V. Cadierno and S. E. García-
Garrido, ACS Sustainable Chem. Eng., 2015, , 3004.
20 From mechanistic point of view, the catalytic
3
a
rearrangement of aldoximes involves the initial dehydration
of the substrate to generate a nitrile intermediate, which is
subsequently rehydrated (by water or the own aldoxime)
into the final amide. For a detailed mechanistic study, see: C.
L. Allen, R. Lawrence, L. Emmett and J. M. J. Williams, Adv.
Synth. Catal., 2011, 353, 3262.
9
The current average price of this ligand is about 50 €/gr.
10 For a review on the chemistry of 2-Ph2PC6H4CHO, see: M. A.
Garralda, C. R. Chimie, 2005,
8
, 1413.
is synthesized by simple
11 The phosphino-aldoxime ligand
1
condensation of the aldehyde unit of 2-Ph2PC6H4CHO with
hydroxylamine. See ref. 5 and: A. Nikitidis and C. Andersson,
Phosphorus, Sulfur Silicon Relat. Elem., 1993, 78, 141.
21 (a) H. Le Bozec, D. Touchard and P. H. Dixneuf, Adv.
Organomet. Chem., 1989, 29, 163; (b) M. A. Bennett, Coord.
8 | J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
Chem. Rev., 1997, 166, 225; (c) L. Delaude and A.
Demonceau, Dalton Trans., 2012, 41, 9257; (d) P. Kumar, R.
K. Gupta and D. S. Pandey, Chem. Soc. Rev., 2014, 43, 707;
View Article Online
DOI: 10.1039/C6RA07015A
(e) P. Crochet and V. Cadierno, Dalton Trans., 2014, 43
,
12447.
22 Most of the aldoximes included in Table 2 were synthesized
by condensation of the corresponding aldehyde with
hydroxylamine, and obtained as mixtures of E and Z isomers
in ratios ranging from 95:5 to 30:70. Differences in reactivity
between both stereoisomers were not observed. The
monitoring of the reactions by GC showed that E and Z
isomers are consumed at similar rates.
23 For selected reviews, see: (a) G. Guillena, D. J. Ramón and M.
Yus, Angew. Chem. Int. Ed., 2007, 46, 2358; (b) M. H. S. A.
Hamid, P. A. Slatford and J. M. J. Williams, Adv. Synth. Catal.,
2007, 349, 1555; (c) T. D. Nixon, M. K. Whittlesey and J. M. J.
Williams, Dalton Trans., 2009, 753; (d) Y. Obora and Y. Ishii,
Synlett, 2011, 30; (e) J. Muzart, Eur. J. Org. Chem., 2015,
5693; (f) Y. Obora, Top. Curr. Chem., 2016, 374, 11.
24 (a) C. S. Cho, B. T. Kim, T.-J. Kim and S. C. Shim, J. Org. Chem.,
2001, 66, 9020; (b) When the same reactions were
performed in the presence of ethylenediamine, the use of
only 1.2 equiv. of the primary alcohol was required to
generate the saturated alcohols in 47-81% yield: C. S. Cho, J.
Mol. Catal. A: Chem., 2007, 267, 49.
25 (a) R. Martínez, G. J. Brand, D. J. Ramón and M. Yus,
Tetrahedron Lett., 2005, 46, 3683; (b) R. Martínez, D. J.
Ramón and M. Yus, Tetrahedron, 2006, 62, 8988.
26 Adolfsson and co-workers also described the asymmetric
version of this α-alkylation/reduction process employing 0.5
mol% of dimer [{RuCl(µ-Cl)(η6-p-cymene)}2]
(4
)
in
combination with a chiral alanine-derived ligand (1.1 mol%),
LiCl (10 mol%) and KOtBu (50 mol%). The reactions,
performed with 3 equiv. of the primary alcohol in DMSO at
40-65 °C for 5 h, afforded the saturated alcohols in low yield
(15-40%) and moderate to good enantioselectivities (57-89%
ee): O. O. Kovalenko, H. Lundberg, D. Hübner and H.
Adolfsson, Eur. J. Org. Chem., 2014, 6639.
27 Unfortunately, no changes in the 7/8 ratio were observed
when the reaction time was extended to 6 or 24 h.
28 W. L. F. Armarego and C. L. L. Chai, in Purification of
Laboratory Chemicals (5th ed.), Butterworth-Heinemann,
Oxford, 2003.
29 P. S. Hallman, T. A. Stephenson and G. Wilkinson, Inorg.
Synth., 1970, 12, 237.
30 I. P. Evans, A. Spencer and G. Wilkinson, J. Chem. Soc., Dalton
Trans., 1973, 204.
31 M. A. Bennett, T.-N. Huang, T. W. Matheson and A. K. Smith,
Inorg. Synth., 1982, 21, 74.
32 CrysAlisPro CCD & CrysAlisPro RED, Oxford Diffraction Ltd.,
Oxford, UK, 2008.
33 L. J. Farrugia, J. Appl. Crystallogr., 2012, 45, 849.
34 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.
C. Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr.,
1994, 27, 435.
35 G. M. Sheldrick, Acta Crystallogr. 2015, C71, 3.
36 International Tables for X-Ray Crystallography, Volume C, ed.
A. J. C. Wilson, Kluwer Academic Publishers, Dordrecht, The
Netherlands, 1992.
37 M. Nardelli, Comput. Chem., 1983, 7, 95.
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DOI: 10.1039/C6RA07015A
For Graphical Abstract use only
The first ruthenium complexes containing a phosphino-oxime ligand have been
synthesized, and their catalytic utility for the rearrangement of aldoximes to primary
amides, as well as for the α-alkylation/reduction of acetophenones with primary
alcohols, demonstrated.