Transformations of β-hydroxo-substituted η3-allyl Pd complexes in neutral and weakly acidic solutions

Article abstract of DOI:10.1007/s11173-005-0156-5

The oxidation of some β-hydroxo-substituted η³-allyl Pd complexes based on the simplest 1,3-dienes is studied by the ¹H and ¹³C NMR methods in neutral and weakly acidic methods. The composition of the reaction products is

Full text of DOI:10.1007/s11173-005-0156-5

Russian Journal of Coordination Chemistry, Vol. 31, No. 10, 2005, pp. 685–694. Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 10, 2005, pp. 723–732.
Original Russian Text Copyright © 2005 by Finashina, Kramareva, Evstigneeva, Flid, Belov.
Transformations of b-Hydroxo-Substituted h3-Allyl Pd
Complexes in Neutral and Weakly Acidic Solutions
E. D. Finashina*, N. V. Kramareva*, E. M. Evstigneeva**,
V. R. Flid**, and A. P. Belov**†
*Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia
**Lomonosov Academy of Fine Chemical Technology, pr. Vernadskogo 86, 117571
Received December 8, 2004
Abstract—The oxidation of some β-hydroxo-substituted η3-allyl Pd complexes based on the simplest 1,3-
dienes is studied by the 1H and 13C NMR methods in neutral and weakly acidic methods. The composition of
the reaction products is determined by the nature of the oxidizing agent and the structure of allyl fragment. The
method of selective oxidation of the β-carbon atom of the allyl ligand with the allyl–metal bond remaining
unchanged is suggested.
†
The study of the structure and reactivity of the tran- η3-pentenyl)palladium chloride (II) is formed in addi-
tion to the main isomer 4-hydroxo-1,2,3-η3-penten-
sition metal allyl complexes is an important direction in
the coordination chemistry and controlled catalytic
ylpalladium chloride (I). The ratio (%) of regio-isomers
synthesis. The substituted η3-allyl Pd complexes play
I and II is determined by the synthesis temperature:
key role in the catalytic processes of oxidation of ole-
from 70 : 30 at 25°ë to 60 : 40 at 0°ë [2]
fine and diene hydrocarbons to the oxygen-containing
compounds and determine regio- and stereoselectivity
of these processes. These reactions can be controlled
OH
CH3
OH
mainly through the target action on the allyl intermedi-
ates. Today two methods are widely used by which this
action can be realized in the catalytic synthesis: the
introduction to the metal coordination sphere of a con-
trolling ligand, which activates the allyl–metal bond
and determines the direction of the complex decompo-
sition and the selection of a reagent, which determines
the nature of the products formed after the complex
destruction. However, there is also one more method
based on the selective action on the η3-allyl ligand
without affecting its bond with Pd. This action can be
realized through the reversible stabilization of the
allyl–metal bond or by the choice of the respective
reaction conditions.
The β-hydroxy-substituted η3-allyl complexes can
be formed easily from the simplest 1,3-dienes in aque-
ous solutions of Pd(II) salts. Their structure is deter-
mined by the initial diene structure, since the nucleo-
philic attack at the primary cationic η4-dienepalladium
intermediate is sufficiently regioselective (at its most
substituted periphery) [1]. Nevertheless, in the case of
1,3-pentadiene, the position isomer (1-hydroxo-1,2,3-
PdCl24–
H2O
CH3
+
–HCl
Pd
Pd
(I)
(II)
Note that complex I occurs in the reaction solution as
equimolar mixture of two diastereomers (I-R and I-S).
CH3
H
CH3
OH
H
OH
Pd
Pd
(I-S)
(I-R)
We reported previously [3, 4] that the pH value is the
main factor determining the course of transformation of
complex I in aqueous solutions:
†
Diseased.
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686
FINASHINA et al.
OH
O
pH < 1
pH > 7
Pd
(I)
H2O2, pH 1–4
H2O2, pH 5–7
OH
O
OH
+
OH
OH
(IV)
Pd
(IV)
(III)
H2O2, H+
p-benzoquinone
PdCl42–
O
OH
O
OH
OH
PdCl42–
+
OH
O
OH
OH
O
OH
O
H+
H+
+
CH3
O
OH
OH
In strongly acidic solutions (pH < 1), protodemetalla- bility of these reaction for the complexes obtained from
tion of the complex occurs that results in the formation another simplest 1,3-dienes are unavailable. Such reac-
of 1,3-pentadiene [5]. In alkaline solutions (pH > 7), the tions can be of interest for the researchers of organome-
reductive destruction is observed with the formation of tallic compounds, since they allow one to modify the
trans-3-pentene-2-one [6]. At pH 1–4, complex I reacts allyl ligand directly in the complex
with hydrogen peroxide with a high selectivity and
The aim of this work was to establish the direction
gives trans-pentene-1,4-diol (IV), whose further oxida-
of transformations of complexes I and II and of some
tion gives a mixture of ketodiol isomers, one of which
β-hydroxo-substituted complexes based on the sim-
plest 1,3-dienes when treated with hydrogen peroxide
is closed into a cycle of 2-methylfurane [7].
The reaction follows unusual route in a narrow inter-
val of pH 5–7. Under these conditions, the hydroxyl
group of the allyl ligand of complex I is oxidized to the
carbonyl group without destruction of η3-allyl structure
of the complex (allyl–metal bond).
and another oxidants in neutral and weakly acidic
aqueous solutions and to choose the conditions for the
selective formation of the corresponding carbonyl
complexes.
The formation of carbonyl compounds after treat-
ment of the Pd allyl complexes with typical oxidants
was reported in [8, 9]. The data on the oxidation of the
allyl complexes, in which the functional group of the
allyl ligand can be oxidized without the destruction of
the complex structure (i.e., with the allyl–metal bond
remaining unchanged) are few in the literature and refer
to substantially bulky allyl ligands [10, 11].
EXPERIMENTAL
The synthesis of hydroxo-containing η3-allyl Pd
complexes was performed by reacting an aqueous solu-
tion of sodium tetrachloropalladate with the corre-
sponding 1,3-diene at room temperature and vigorous
stirring. The molar ratio of Na2[PdCl4] : 1,3-diene was
1 : 1.2. The reaction course was visually observed by
The possibility of such an oxidation for hydroxyl- the change of the color from red-brown (due to
containing complexes based on 1,3-pentadiene was Na2[PdCl4]) to lemon yellow (typical of the η3-allyl
reported in [2]. However, the data on stoichiometry and complex). The diene excess was distilled off in vacuum.
mechanisms of such reactions, as well as on the possi- The solutions of the complexes were filtered off and
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TRANSFORMATIONS OF β-HYDROXO-SUBSTITUTED η3-ALLYL PD COMPLEXES
687
identified by the 1H and 13C NMR methods. The spec- enechloride–chloroform, or acetone–methylenechlo-
tral characteristics of the complexes coincide with the
literature data [1]. The complexes remained stable for
5 days when stored at ~0°ë.
ride–chloroform mixtures used as eluents. The fraction
containing carbonyl complexes was stored at –18°ë for
48–60 h until yellow crystals precipitated. The separated
1
complexes were identified by the H and 13C NMR
The synthesis of the Pd allyl complexes containing
the carbonyl group in the composition of the allyl frag-
ment (further on “carbonyl complexes”) was performed
as follows. An excess of the acid formed after the syn-
thesis of hydroxyl complexes in aqueous solutions was
neutralized with sodium bicarbonate until termination
of the gas liberation. The pH values of the reaction solu-
tions were monitored using a pH-340 instrument.
NaHCO3 and Na2[PdCl4] taken in threefold excess were
added to the solutions obtained. The reaction mixtures
were stored for 1–3 days. The metallic palladium was
filtered off, the reaction solution was extracted with
CHCl3 or CH2Cl2. The carbonyl-containing η3-alyl and
nonconverted hydroxyl-containing complexes were
separated in 1–2 h.
method. The degree of separation was monitored by a
thin-film chromatography on silica gel (Silufol uv 254)
with the same organic mixtures used as eluents. The
plates were developed in iodine chamber.
RESULTS AND DISCUSSION
The Effect of the Oxidant Nature on the Direction
of Transformations of η3-Allyl Pd Complexes Based
on 1,3-Pentadiene
According to the data in [6, 7], the oxidation of the
hydroxyl group of complex I to the carbonyl group with
hydrogen peroxide occurs in solution at pH 5–7. The
main task at the first stage of a study was to establish the
reaction stoichiometry.
The η3-allyl complex based on 4-methyl-3-pentene-
2-one (mesityl oxide) was prepared following the
known procedure [12]. The complex was purified by
recrystallization from THF heated to 50°ë. The com-
plex decomposed above the indicated temperature.
The study of the products of reaction of com-
plexes I and II with hydrogen peroxide (pH 5–7).
While comparing the reaction paths of oxidation of
complexes I and II with hydrogen peroxide under dif-
ferent conditions (pH 1–4 and 5–7), one should note that
the reaction carried out at pH 5–7 has low selectivity. The
process involves the induction period (4–20 min), which
depends on the pH value. The optical density of the
reaction solution changes slowly due to accumulation
1
The H and 13C NMR spectra were recorded on a
Bruker DPX instrument (300.13 and 75.033 MHz,
respectively). The identification of the products and the
control of the reaction course were performed directly
in the tube of NMR spectrometer. The reactions were
carried out in the D2O medium at 25°ë. The organic
products were analyzed by GC method (the column:9%
IRTS-17 + 1%PEG 40 on polychrome; Chrom-4 (DIP)
chromatograph).
of the PdCl24– ions. Then, the metallic Pd is precipi-
tated, which is accompanied by a vigorous decomposi-
1
The conditions of the oxidation of complexes I and
tion of hydrogen peroxide. As follows from the H
II with hydrogen peroxide are as follows: [η3] = 0.1 NMR data, the only one reaction product formed in the
(η3-complex), [ç2é2] = 0.4, [NaHCO3] = 0.15, [NaCl] =
induction period is diol IV. The spectral parameters of
complexes I (I-R, I-S) and pentadiol IV agree well with
the literature data [1, 2, 7].
0.5 mol/l. Hydrochloric acid formed in the reaction
solution in the synthesis of the initial hydroxyl-contain-
ing complexes was neutralized with NaHCO3. The pH
values were monitored before and in the course of a
reaction. The oxidation of complexes I and II with Pd
chloride was performed at [η3] = 0.1, [PdCl42– ] = 0.3,
[NaHCO3] = 0.3, [NaCl] = 0.5 mol/l. In the case of
MnO2, [η3] = 0.1 mol/l, the quantity of MnO2 in 100 ml
of the reaction solution was 0.5 mol; the concentrations
[NaHCO3] and [NaCl] were 0.3 and 0.5 mol/l, respec-
tively. Since MnO2 complicates the NMR study of the
reaction mixtures, the CDCl3 extracts of the reaction
solutions were analyzed.
The spectra of the reaction solutions recorded after
the induction period contain, in addition to the signals
of the starting isomeric complexes and diol IV, the sig-
nals of 1-acetyl-η3-allylpalladium chloride (III), whose
spectral characteristics also coincide with the reported
data [1, 7]. The color of the reaction solution gradually
changed from dark brown to yellow, while its pH value
decreased to 1–3. In 16 h, the content of III in the reac-
tion mixture reached 40%.
It was shown that the excess of hydrogen peroxide,
which was not used fully in the formation of IV, is
decomposed by the metallic Pd being one of the reac-
tion products. It was also discovered that on addition of
PdCl2 to the reaction solution, the induction period dis-
The carbonyl-containing complexes were purified
in pure form using liquid-adsorption column chroma-
tagraphy (silica gel, glass column with l = 50 cm, d =
1.5 cm) with acetone–chloroform, acetone–methyl- appears. Taking into account the above data, we per-
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688
FINASHINA et al.
formed a series of experiments where the initial com-
The results we obtained made it possible to suggest
plexes were treated with PdCl2 without the addition of that the formation of complex III in the reactions of
hydrogen peroxide as an oxidant. The main product of complexes I and II with hydrogen peroxide (pH 5–7)
the reaction carried out under these conditions was can be described by the following simultaneous and
complex III.
subsequent processes:
OH
H
OH
CH3
H
+ PdCl42–
H2O2
OH
Pd
(II)
(IV)
OH
O
PdCl42–
+ Pd0 + HCl
Pd
Pd
(III)
(I)
Complex III can form as a result of: 1) direct inter-
action of complex I with the [PdCl4]2– ion, which accu-
mulates in the reaction solution in the course of the
induction period of diol IV formation; 2) interaction of
One of the reasons for different reactivity of ketones
can be the structure of their carbon framework. The
steric and electronic effects of the methyl group at the
second carbon atom of mesityl oxide hamper the dou-
ble bond oxidation, and the process of complex forma-
tion becomes preferable. When trans-3-pentene-2-one
is used as a substrate, the oxidation reaction prevails.
PdCl24– with trans-3-pentene-2-one, formed due to the
reductive destruction of complex I. Although the sig-
1
nals of this ketone were not recorded in the H NMR
spectra of the reaction solutions, the pH value (5–7) and
the formation of metallic Pd do not allow one to
exclude its formation as a result of the reductive
destruction of complex I.
When a model reaction of trans-3-pentene-2-one
with PdCl24– was performed under analogous condi-
The yield of III in the reaction of the initial
hydroxyl-containing complexes with PdCl2 noticeably
depends on the concentration of the Cl– ions in the solu-
tion. Since an increase in the sodium chloride concen-
tration increases the stability of the PdCl24– ion, the
content of III in the solution decreases (Fig. 1). At
[NaCl] ≥ 2 mol/l, no carbonyl complex is formed.
tions, the precipitation of the metallic Pd and the forma-
tion of acetylacetone were observed:
Oxidation of regio-isomers I and II. One of the
most interesting aspects of the reaction under consider-
ation is different reactivity of regio-isomers I and II.
O
O
O
PdCl2, H2O
+ Pd0 + 2HCl.
1
The analysis of the H NMR spectra recorded in a
The formation of the carbonyl complex III in this
reaction was not established. On the other hand, the
reaction of mesityl oxide with PdCl2 performed even in
an aqueous solution results in the corresponding carbo-
nyl-containing allyl complex [12]:
dynamic mode during the induction period shows that
diol IV is formed directly from position isomer II.
Shown in Fig. 2a is a fragment of the spectrum of a start-
ing reaction solution (containing three complexes I-R, I-
S, and II), which exhibits the signals from protons of
the methyl groups of the complexes (three doublets with
close upfield intensities (δ ≈ 1.4 ppm) and the signals
from the allyl protons (H1) in a region of ~5.5 ppm. One
should note that in an aqueous solution, the signals
from the allyl protons in enantiomer complexes I-R and
I-S are indistinguishable.
CH3
O
O
CH3
PdCl42–
Pd
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TRANSFORMATIONS OF β-HYDROXO-SUBSTITUTED η3-ALLYL PD COMPLEXES
689
The same fragments of the spectrum recorded 20 min 1 : 0.75, while after the induction period is was 1 : 0.18.
1
after the addition of ç2é2 to the reaction solution are The H NMR kinetic data revealed that the content of
shown in Fig. 2b. The comparative analysis of the spec- diol IV and complex I in the reaction solution does not
tra in Fig. 2a and Fig. 2b indicates that in the upfield almost change after termination of the induction period
region, the signal from the methyl group protons of (Fig. 3).
complex II almost disappears, while the doublet signal
The results obtained convincingly prove that diol IV
of the ëç3 group of diol IV appears instead. In the
is formed from the position isomer II during the induc-
downfield region, the intensity of the signal from the
tion period, i.e., the initial complexes have different
allyl protons of complex II significantly decreases, and
reactivity under the indicated conditions.
a multiplet signal from the protons at the double bond
of complex IV appears. The intensity of the signals of
It was shown [7] that during oxidation with hydro-
enantiomers of I remains almost unchanged. The ratio gen peroxide in an acid medium, diol IV is formed from
of I : II in the reaction solution before the reaction was two regio-isomers that are spent at almost equal rate:
OH
OH
OH
H
CH3
H2O2
H2O2
H
CH3
H
OH
Pd
Pd
(II)
(IV)
(I)
This fact seems unusual and is explained by the author
by symmetric structure of σ-allylpalladium intermedi-
ates obtained from complexes I and II at the stage of
oxopallaladization of a double bond.
In addition to complex III, the spectrum of reaction
solution also exhibits the signals due to the aldehyde
complex V:
OH
H
O
The observed difference in the reactivity of com-
plexes I and II in a neutral medium is likely to be due
to their interaction with different oxidants. Taking into
account that the oxidation potential of hydrogen perox-
ide decreases substantially when going from an acid
medium to a neutral medium [13] and that the primary
alcohols (complex II) are oxidized more readily than
the secondary alcohols (complex I), one can suggest
that under the reaction conditions, H2O2 oxidizes only
regio-isomer II to diol IV, while complex I is oxidized
with PdCl2 to the carbonyl complex III.
CH3
CH3
H
H
Pd
(II)
Pd
(V)
PdCl42–
OH
O
CH3
CH3
Pd
Pd
(I)
(III)
The above data indicate that the oxidation of the
hydroxyl group of complex I to the carbonyl group
takes place without H2O2 participation. Complex III is
formed as a result of interaction of complex I with
PdCl2. Therefore, it was necessary to study in detail the
reactions of complexes I and II with Pd chloride.
Its quantity is about 5%, which is insufficient for
reliable identification. In order to accumulate the alde-
hyde complex in the reaction solution, we used a mix-
ture of hydroxo-substituted complexes synthesized
from 1,3-pentadiene at 0°ë as the initial complexes. In
the indicated conditions, the content of regio-isomer II
reaches 40%. The analysis of the spectra of reaction
solutions for contact time τ = 36 h showed that the con-
tent of the aldehyde complex V did not almost change,
although conversion of complexes I and II was close to
90%. The low content of complex V is explained by
isomerization of complex II under the action of
NaHCO3, which was used to maintain pH value of the
reaction solution at a level of 5–7.
The study of the product of reactions of com-
plexes I and II with PdCl2 and MnO2 (pH 5–7). The
1
analysis of the H NMR spectra of reactions of com-
plexes I and II with PdCl2 in solutions showed that with
a threefold excess of NaHCO3 used to neutralize acids
formed in the reaction, the carbonyl complex III is
obtained at a high selectivity with conversion of I and
II equal to 88%.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 10 2005

690
FINASHINA et al.
Content of III in the reaction mixture, %
40
Thus, it was established that the position isomer II
shows selectivity with respect to the oxidants used,
because its reaction with H2O2 and PdCl2 results in dif-
ferent products (pentadiol IV and aldehyde complex V,
respectively).
30
20
Although Pd chloride is a standard reagent of oxida-
tion of the hydroxyl groups to the carbonyl groups, it
seems unreasonable to use it in the case, when the Pd
allyl complex serves as “substrate”. Therefore, we per-
formed a series of experiments to find an oxidant that
can selectively oxidize the hydroxyl-containing com-
plexes I and II to the corresponding carbonyl com-
plexes under mild conditions.
10
0
0.5
1.0
1.5
2.0
The hydroxyl groups in the allyl alcohold are usu-
[Cl–], mol/l
1
ally oxidized by Mn dioxide. The H NMR data indi-
cate that the reactions of complexes I and II with MnO2
lead to the formation of the carbonyl complex III.
–
Fig. 1. The curve of the complex III yield vs. the Cl con-
centration in the reaction mixture (τ = 24 h).
CH3(I-R, I-S; II)
CH3(I-R, I-S; II)
CH3(IV)
(a)
(b)
H1,3(IV)
H1(I-R, I- S; II)
H1(II)
H1(I-R, I-S)
H1(II)
1.4 1.2 1.0
δ, ppm
5.8 5.6 5.4 5.2
5.5
1.5
δ, ppm
1
Fig. 2. Fragments of the H NMR spectra (D O, 25°ë): (a) the initial complexes I-S, I-R, and II; (b) the reaction solution in 20 min
2
after introduction of hydrogen peroxide.
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TRANSFORMATIONS OF β-HYDROXO-SUBSTITUTED η3-ALLYL PD COMPLEXES
691
Content of I–IV in the reaction mixture, %
However, the reaction solution spectra also contain sig-
nals from the product of a reductive destruction of com-
plex I, i.e., trans-3-pentene-2-one, whose concentra-
tion in the reaction mixture reaches 20%. In this case,
Mn dioxide acts not only as an oxidant, but also as
nucleophilic agent, which causes the destruction of the
initial complexes and thus reduces the reaction selectiv-
ity with respect to the carbonyl complexes.
70
60
50
40
1
3
Thus, one can conclude that the composition of the
products of oxidation of hydroxyl-containing com-
plexes based on 1,3-pentadiene in neutral solutions is
determined by the nature of the oxidant used. The for-
mation of the carbonyl complex III is the most selec-
tive, when the initial complexes react with Pd chloride.
30
20
10
4
2
The Effect of Alkyl Substituents in the Allyl Ligand
on the Direction of Transformations of η3-Allyl Pd
Complexes Based on the Simplest 1,3-Dienes
0
2
4
6
8
10 12 14 16
τ, h
Taking into account the data obtained for the com-
plexes based on 1,3-pentadiene, we studied the reac-
tions of some hydroxyl-containing complexes based on
the simplest 1,3-dienes (1,3-butadiene (VI), isoprene
(VII), 2-methyl-1,3-pentadiene (VIII)) with different
reagents (ç2é2, MnO2, PdCl2) in aqueous solutions at
pH 5–7. Our task was to select an oxidant that can give
the corresponding carbonyl-containing complexes with
a high selectivity and conversion and to establish the
influence of the allyl fragment structure on the reactiv-
ity of the initial hydroxyl-containing complexes.
Fig. 3. The plot of the composition of the reaction mixture (I,
II + H O ) vs. reaction time: (1) I, (2) II, (3) III, and (4) IV.
2
2
The carbonyl complexes are formed in the reaction
with hydrogen peroxide as a result of simultaneous and
subsequent reactions only in the case of complexes I
and VIII. The 1H NMR spectra of the reaction solutions
show that the interaction of complexes VI and VII with
hydrogen peroxide in neutral aqueous solutions results
in their destruction and formation of unsaturated alde-
hydes and diols. Thus, for complexes based on isoprene
(VII), the reductive destruction proceeds with a high
selectivity and yields methylcrotonaldehyde. The
spectrum of reaction solution of complex VI contains
the signals due to crotonaldehyde and trans-2-butene-
1,4-diol (Table 1).
In the case of MnO2, complexes VI and VII were
found to undergo the reductive destruction with the for-
mation of unsaturated aldehydes. The signals of the
respective aldehyde complexes in the reaction solutions
were not recorded.
The reaction of complex VIII with MnO2 proceeds at
very low rate. Complex VIII is stable to oxidation and
though the signals of the carbonyl complex based on
VIII were recorded in the reaction solution, its content
did not exceed 2% at the reaction time equal to 72 h.
The study of the oxidation of complexes VI–VIII
with Pd chloride showed that the corresponding
carbonyl-containing complexes (1-acetyl-η3-bute-
nyl)palladium chloride (IX), (1-acetyl-2-methyl-η3-
butenyl)palladium chloride (X), (1-acetyl-2-methyl-η3-
pentenyl)palladium chloride (XI) are formed with a
high selectivity and conversion of the initial complexes
equal to 85% independent of the structure of the allyl
fragment.
The above facts indicate that the reaction of the
hydroxyl-containing complexes, which differ in the
structure of allyl fragment, with MnO2 can be written as
follows:
R1
O
R1
The reaction of the hydroxyl complex VII with
PdCl2 yields the aldehyde complex X. The 1H and 13C
NMR data, in particular, the downfield shift of the H3
proton signal and the values of the chemical shifts in the
13C spectrum confirm that complex X occurs in the
solution as anti-configuration.
OH
R1 = H, CH3; R4 = H
R4
H
MnO2
Pd
R1
Pd
O
(I, VI, VII, VIII)
CH3
The prevalence in the reaction mixture of anti-iso-
mer is unusual for η3-allyl Pd complexes with nonbulky
substituents, which can be explained by either the steric
factor (the repulsion of the methyl and carbonyl
R1 = H, CH3; R4 = CH3
(III, XI)
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FINASHINA et al.
Table 1. The parameters of the 1H NMR spectra of the products of reactions of complexes VI and VII with MnO2 (the CDCl3
extracts) and H2O2 (D2O)
Compound
δ, ppm
ç1 = 6.85
Multiplicity
Multiplet
J, Hz
1
1–4J = 15.5, JCH = 6.8
H1
CH3
O
3
3
ç3 = 6.15
ç4 = 9.45
Multiplet
Doublet
3–4J = 7.9, JCH = 1.5, 1–3J = 15.5
H4
3
H3
3–4J = 7.9
3
1JCH = 6.8, JCH = 1.5
ëç3 = 2.01
Multiplet
3
3
ç1 = ç3 = 5.85
ëç2 = 4.28
Triplet*
Doublet
H1 OH
CH2
CH2
H3
OH
CH3
H3 = 4.88
H4 = 8.82
Doublet
3–4J = 8.7
O
3
4–3J = 8.7, JCH = 1.23
Multiplet
H4
3
CH3
3JCH = 1.14
H3
CH3 = 2.23
CH3 = 1.49
Doublet
Doublet
3
3JCH = 1.09
3
* Multiplet signals in the proton spectrum of trans-butene-1,4-diol are poorly resolved and therefore, the spin–spin coupling constants were
not determined for this compound.
groups) or electronic factor (coupling of unshared elec- syn- and anti-isomers (3 : 2), which was confirmed by
tron pairs of the O atom with unoccupied d orbitals of the the spectral method. Obviously, the formation of only
Pd atom). As follows from IR spectra of complex X, the one anti-isomer in the reaction of complex VII oxida-
frequency of the stretching vibrations of the C=O bond tion with Pd chloride can be explained by the reduced
almost coincides with the corresponding frequency in stability of syn-isomer due to the steric interaction of the
the spectrum of 2-methyl-butene-2-al. Thus, the steric methyl and acetyl groups, as in the case of complex X. It
factor becomes the key factor.
Complex VIII is oxidized with Pd chloride very
slowly. The signals from complex XI appear in the reac-
cannot be excluded also that syn-isomer cannot be
detected in the spectrum because of the low reaction rate.
With account of the above factors, the transforma-
tion solution only after 36 h. The carbonyl complex XI tions of the simplest 1,3-diene hydrocarbons in the
was identified as anti-isomer, although when synthe- reaction with Pd chloride in neutral aqueous solutions
sized from mesityl oxide, it occurred as a mixture of can be represented by the following scheme:
R1
R1
OH
R4
R1
Pd
O
PdCl42–
PdCl42–
R4
R4
,
Pd
R1 = H, CH3; R4 = H, CH3.
At pH 5–7, the corresponding carbonyl-substituted
Thus, Pd chloride is the sole reagent that can be used
complexes (III, IX–XI) are formed almost quantita- in order to carry out the selective oxidation of the
tively. They were detected and characterized by the 1H hydroxyl groups in the β-position of the allyl ligand for
and 13C NMR method in the reaction solutions and a series of η3-allyl Pd complexes without the destruc-
were isolated as yellow crystals. The spectral character- tion of the complex structure (allyl–metal bond), inde-
istics of the complexes are presented in Table 2.
pendent of the allyl fragment structure. The above data
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TRANSFORMATIONS OF β-HYDROXO-SUBSTITUTED η3-ALLYL PD COMPLEXES
693
Table 2. The parameters of the 1H and 13C NMR spectra of the carbonyl-containing η3-allyl complexes III, V, IX–XI*
R1
O
R1
C1
O
C4
R5
R5
R4
C2
C3
R4
H2
H3
Pd
Pd
(a)
Complex
(b)
1H NMR; δ, ppm
Multiplicity
J, Hz
13C NMR; δ, ppm
syn-IX
R1 = 5.95 (1H)
R4 = 9.61 (1H)
H5 = 4.34 (1H)
H2 = 3.43 (1H)
H3 = 3.83 (1H)
Multiplet
Doublet
Doublet
Doublet
Multiplet
1–5J = 6.0, 1–2J = 12.5, 1–3J = 10.8 C1 = 113.80
(R1 = R5 = R4 = H)
4–3J = 5.3
C2 = 67.28
C3 = 71.80
C4 = 200.32
5–8J = 6.0
5–9J = 12.5
1–3J = 10.8, 4–3J = 5.3
anti-X
R1 = 2.43 (3H)
R4 = 8.65 (1H)
H5 = 4.42 (1H)
H2 = 2.60 (1H)
H3 = 5.18 (1H)
Singlet
Doublet
Singlet
Singlet
Doublet
C1 = 128.82
R1 = 22.89
C2 = 63.61
C3 = 76.88
C4 = 188.83
(R1 = CH3, R5 = R4 = H)
4–3J = 7.7
4–3J= 7.7
syn-V
R1 = 6.12 (1H)
R4 = 9.55 (1H)
R5 = 1.62 (3H)
H2 = 3.85 (1H)
H3 = 5.58 (1H)
Multiplet
Doublet
Doublet
Doublet
Multiplet
1–5J = 6.3, 1–2J = 11.9, 1–3J = 10.8
4–3J = 7.3
(R5 = CH3, R1 = R4 = H)
**
1–5J = 6.3
1–2J = 11.9
1–3J = 10.8, 4–3J = 7.2
syn-III
R1 = 6.31 (1H)
R4 = 2.49 (3H)
H5 = 4.49 (1H)
H2 = 3.63 (1H)
H3 = 4.05 (1H)
Multiplet (d.d.d)
Singlet
1–5J = 7.2, 1–2J = 12.5, 1–3J = 10.8 C1 = 110.65
(R1 = R5 = H, R4 = CH3)
C2 = 65.84
Doublet
1–5J = 7.2
1–2J = 12.5
1–3J = 10.8
C3 = 71.52
C4 = 208.24
R4 = 29.14
Doublet
Doublet
anti-XI
R1 = 2.26 (3H)
R4 = 2.46 (3H)
H5 = 3.93 (1H)
H2 = 3.00 (1H)
H3 = 3.72 (1H)
Singlet
Singlet
Singlet
Singlet
Singlet
C1 = 124.96
C2 = 67.84
C3 = 73.24
R1 = 23.10
C4 = 202.78
R4 = 30.96
(R1 = R4 = CH3, R5 = H)
1
**a—The numbering of the protons and substituents in the H NMR spectra; b—the numbering of carbon atoms and substituents in the
13
NMR spectra.
13
**The C spectral parameters of complex V were not determined because of its low concentration in the reaction solutions.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 31 No. 10 2005

694
FINASHINA et al.
6. Andari, M.K., Cand. Sci. (Chem.) Dissertation, Mos-
cow: Lomonosov State Academy of Fine Chemical
Technology, 1983.
were obtained for the first time in the chemistry of
η3-allyl Pd complexes.
7. Evstigneeva, E.M., Cand. Sci. (Chem.) Dissertation,
Moscow: Lomonosov State Academy of Fine Chemical
Technology, 1993.
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