Zinc(II)/ketoxime system as a simple and efficient catalyst for hydrolysis of organonitriles

Article abstract of DOI:10.1021/ic0256720

The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R = Me, CH₂Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC₆H₄CH₂, Ph), to carboxamides is catalyzed by a novel system of superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds, that is, a ZnX₂/ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken alone. The nature of the anion X- in the zinc salt (X = NO₃, Cl, CF₃SO₃) or of the ketoxime (Me₂C=NOH, C₄H₈C=NOH, C₅H₁₀C=NOH) does not affect strongly the catalytic properties of the system, but the best results were obtained so far with a Zn(NO₃)₂·6H₂O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically above ca. 100 but reach as high as 1000 for p-MeOC₆H₄CH₂C(=O)NH₂. The previously unknown structures of the two carboxamide products n-BuC(=O)NH₂ and p-MeOC₆H₄CH₂C(=O)NH₂ were determined by X-ray diffraction studies. The complexes [ZnX₂(R₂C=NOH)₂] (X = Cl, R₂ = 2Me, C₄H₈, C₅H₁₀; X = NO₃, R = C₄H₈), prepared by heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses, FAB-MS, ¹H and ¹³C{¹H} NMR spectroscopies, and also X-ray crystallography (for X = Cl, R₂ = 2Me; X = NO₃, R = C₄H₈), proved to be catalyst precursors in the conversions because the activity of these species is high only in the presence of 2 equiv of the ketoxime.

Full text of DOI:10.1021/ic0256720

Inorg. Chem. 2002, 41, 4798−4804
Zinc(II)/Ketoxime System as a Simple and Efficient Catalyst for
Hydrolysis of Organonitriles
,‡
Maximilian N. Kopylovich,† Vadim Yu. Kukushkin,* Matti Haukka,§ Joa˜o J. R. Frau´sto da Silva,† and
,†
Armando J. L. Pombeiro*
Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, AV. RoVisco Pais,
1049-001 Lisbon, Portugal, Department of Chemistry, St. Petersburg State UniVersity,
198904 Stary Petergof, Russian Federation, and Department of Chemistry, UniVersity of Joensuu,
P.O. Box 111, FIN-80101, Joensuu, Finland
Received April 25, 2002
The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R
) Me, CH Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC H CH , Ph), to carboxamides is catalyzed by a novel system of
2
6
4
2
superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds,
that is, a ZnX /ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken
2
alone. The nature of the anion X- in the zinc salt (X ) NO , Cl, CF SO ) or of the ketoxime (Me2CdNOH,
3
3
3
C H CdNOH, C H CdNOH) does not affect strongly the catalytic properties of the system, but the best results
4
8
5 10
were obtained so far with a Zn(NO ) ‚6H O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically
3 2
2
above ca. 100 but reach as high as 1000 for p-MeOC H CH C(dO)NH . The previously unknown structures of the
6
4
2
2
two carboxamide products n-BuC(dO)NH and p-MeOC H CH C(dO)NH were determined by X-ray diffraction
2
6
4
2
2
studies. The complexes [ZnX (R CdNOH)2] (X ) Cl, R ) 2Me, C H , C H ; X ) NO , R ) C H ), prepared by
2
2
2
4
8
5
10
3
4 8
heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses,
FAB-MS, 1H and 13C{1H} NMR spectroscopies, and also X-ray crystallography (for X ) Cl, R ) 2Me; X ) NO ,
2
3
R ) C H ), proved to be catalyst precursors in the conversions because the activity of these species is high only
4
8
in the presence of 2 equiv of the ketoxime.
Introduction
involves hydrolysis of organonitriles. However, in the vast
majority of cases, a base-catalyzed reaction leads to a
carboxylate salt, because the second step of the hydrolysis
(conversion of amides to carboxylic acids) is faster than the
first one (conversion of nitriles to amides), and the reaction
thus proceeds to the final hydration product rather than
stopping at the amide stage.1,3 Although in strong acidic
solutions it can be possible to obtain amides, it is then
necessary to have careful control of the temperature and of
the ratio of reagents in order to avoid the formation of
polymers which is promoted by the exothermic character of
the hydrolysis.4 Moreover, the final neutralization leads to
an extensive salt formation with inconvenient product
contamination and pollution effects.4,5
The development of efficient methods for the formation
of the C-N amide linkage is of great importance because
of the high synthetic utility of amides, their industrial
applications, and pharmacological interest.1,2 Most of the
known synthetic transformations leading to amides are based
on the reaction between an activated carboxylic acid and an
amine or ammonia.1 An alternative preparative pathway
* To whom correspondence should be addressed. E-mail: kukushkin@
VK2100.spb.edu (V.Yu.K.); pombeiro@ist.utl.pt (A.J.L.P.).
† Instituto Superior Te´cnico.
‡ St. Petersburg State University.
§ University of Joensuu.
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934. (c) Challis, B. C.; Challis, A. J. In ComprehensiVe Organic
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4798 Inorganic Chemistry, Vol. 41, No. 18, 2002
10.1021/ic0256720 CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/02/2002

Zn(II)/Ketoxime Catalyst for Hydrolysis
These difficulties can be overcome with the use of metal
ions which can behave as extremely strong activators of RCN
toward nucleophilic attack by OH-/H2O. This activation can
result in an enhancement of the rate of hydrolysis commonly
in the range 106-108 (ref 6) or even higher when involving
an intramolecular attack by an hydroxide ligand,7 and many
metal-mediated processes (reviewed recently by two of us8a),
that bring about hydration of nitriles and selective formation
of metal-bound carboxamides, are known from the litera-
ture.5,8,9 Despite that, most of the systems are not catalytic,
and only a few methods are known so far to hydrate RCN
under homogeneous catalytic conditions,10-16 usually exhibit-
ing a rather low activity. The most advantageous of them
are based on some platinum(II) phosphinito complexes10 and
on other, less active, phosphino complexes of platinum(II)
(and Pd and Ni analogues),11,12 nonphosphinic dipalladium(II)
complexes with N,S-coordinated ligands,13a various mono-
nuclear Pd(II) complexes with aqua, amine, and so forth
ligands,13b as well as some hydride phosphine complexes of
low valent Ru or Ir.5,9f Other systems are based on Fe- or
Co-containing enzymes, nitrile hydratases, which catalyze
the hydration of nitriles in vivo17,18 and, for some complexes,
mimic these enzymes (although so far exhibiting a much
lesser efficiency).19 Those catalysts are rather expensive, and
in addition, their preparation requires some particular skills.
These drawbacks certainly restrict the application of the listed
catalysts, not only in the laboratory, but also in industry,
although some of them have found application therein. We
now report on a system of superior simplicity for hydrolysis
of aryl, benzyl, and both sterically hindered and unhindered
alkyl nitriles which consists of cheap and widely com-
mercially available compounds such as a zinc salt and a
ketoxime, for example, zinc nitrate and 2-propanone oxime,
and operates in air and under neutral conditions (the use of
bases or acids is not required and the resulting formation of
contaminating salts is thus eliminated) and without needing
an excess of water thus facilitating the isolation of the
product.
Results and Discussion
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Inorganic Chemistry, Vol. 41, No. 18, 2002 4799

Kopylovich et al.
Figure 2. ORTEP view of the molecular structure of p-MeOC6H4CH2C-
(dO)NH2 with atomic numbering. The thermal ellipsoids are drawn at the
50% probability level. Selected bond lengths (Å) and angles (deg): C(1)-
O(1) 1.237(2), N(1)-C(1) 1.319(3), C(1)-C(2) 1.514(3), C(6)-O(2)
1.373(2), O(2)-C(9) 1.429(3), N(1)-C(1)-O(1) 122.3(2), N(1)-C(1)-
C(2) 117.0(2), C(6)-O(2)-C(9) 117.1(2).
Figure 1. ORTEP view of the molecular structure of n-BuC(dO)NH2
with atomic numbering. The thermal ellipsoids are drawn at the 50%
probability level. Selected bond lengths (Å) and angles (deg): O(1)-C(1)
1.239(2), N(1)-C(1) 1.329(2), C(2)-C(1) 1.512(2), O(1)-C(1)-N(1)
121.83(12), N(1)-C(1)-C(2) 116.31(10).
Table 1. Quantitative Parameters for the Zinc(II)/Ketoxime Catalyzed
Synthesisa of Carboxamides RC(dO)NH2
we have recently found25 that a Co(II)/ketoxime system
promotes a facile conversion of an alkyl nitrile, RCN, to the
appropriate amidine, RC(dNH)NH2, and carboxylic acid,
RC(dO)OH. Moreover, when the nitrile was diluted with
water, giving a molar ratio of 5:1, the reaction went in
another direction giving carboxamides, although in a non-
catalytic way.26 Inspired with this observed metal-promoted
reaction, we attempted to extend it to some other metals in
order to find an environmentally acceptable catalyst, derived
from simple components, for generation of amides. We now
report a catalytic system for the hydrolysis, under mild
conditions, of organonitriles to carboxamides, based on a
Zn(II)/ketoxime combination.
TOF,b
mol/(mol‚h)
yield,
%
TON,c
mol/mol
R
Me
CH2Cl
Et
n-Pr
i-Pr
n-Bu
t-Bu
7.7
13.1
11.3
11.0
8.6
14.3
4.5
45.0
10.8
46
77
68
66
52
86
27
90
65
77
131
113
110
86
143
45
p-MeOC6H4CH2
450d
108
Ph
a See Experimental Section for the conditions. b Turnover frequency
[mol(carboxamide)/{mol(Zn2+)‚hour}]. c Turnover number [mol(carbox-
amide)/mol(Zn2+)]. d Can increase to ca. 1000 by further addition of RCN/
H2O to the mother liquor separated from the carboxamide (concomitant
decrease of the TOF to ca. 20).
Description of the Catalytic System and Products
Formed. The hydrolysis of sterically hindered and unhin-
dered alkyl nitriles, and also of benzyl and phenyl nitriles
RCN (R ) Me, CH2Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC6H4-
CH2, Ph), is catalyzed by the Zn(NO3)2‚6H2O (0.7 mol %
relative to the nitrile)/2-propanone oxime (2.8 mol %) system
but does not proceed at all with either the zinc compound
or the ketoxime taken alone. The obtained carboxamides
were identified by comparison of their melting points, IR,
and 1H and 13C{1H} NMR spectra with those of the
commercially available carboxamides. Moreover, the previ-
ously unknown structures of the two carboxamides n-
BuC(dO)NH2 and p-MeOC6H4CH2C(dO)NH2 were deter-
mined by X-ray diffraction studies (Figures 1 and 2). In the
carboxamides, the CH2C(dO)NH2 fragments are almost
planar, and the CdO and CsN bond lengths and OsCsN
bond angle within these moieties are in good agreement with
those for other reported carboxamide structures.27 The
molecules in the crystal are held by hydrogen bonding
between the complementary carbonyl and amido groups.
In the catalysis, the best results were obtained so far with
a Zn(NO3)2‚6H2O/2-propanone oxime molar ratio of 1:4
(turnover numbers (TONs) typically above ca. 100, Table
1); with less oxime, for example, 1:2, the rate of reaction,
TON, and yield decrease significantly. Other ketoximes, for
example, C4H8CdNOH or C5H10CdNOH, can also be used
with a similar efficiency. The reaction with all nitriles (with
the exception of MeCN when a homogeneous system is
formed) is biphasic and requires vigorous stirring and reflux.
At those conditions, however, 5-9% (R ) Et, n-Pr, i-Pr,
n-Bu, t-Bu, p-MeOC6H4CH2, Ph) of the corresponding
carboxylic acids are formed, but those byproducts are easily
removed by recrystallization. In the cases of R ) Me and
CH2Cl, the amount of the acids is larger (ca. 20%).
The hydrolysis of p-MeOC6H4CH2CN is different from
that of the other nitriles because the appropriate carboxamide,
that is, p-MeOC6H4CH2C(dO)NH2, is insoluble in the
reaction mixture. Most likely, its precipitation and removal
from the reaction medium facilitate the process, and this is
reflected in the highest turnover number reached (Table 1).
Moreover, if p-MeOC6H4CH2C(dO)NH2 is filtered off after
10 h when the reaction is completed and a new portion of
the nitrile/H2O is added to the filtrate, the process goes
further, and the turnover number can be increased to ca. 1000.
(24) (a) Wagner, G.; Pombeiro, A. J. L.; Kukushkin, V. Yu. J. Am. Chem.
Soc. 2000, 122, 3106. (b) Wagner, G.; Haukka, M.; Frau´sto da Silva,
J. J. R.; Pombeiro, A. J. L.; Kukushkin, V. Yu. Inorg. Chem. 2001,
40, 264. (c) Wagner, G.; Pakhomova, T. B.; Bokach, N. A.; Frau´sto
da Silva, J. J. R.; Vicente, J.; Pombeiro, A. J. L.; Kukushkin, V. Y.
Inorg. Chem. 2001, 40, 1683.
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Haukka, M.; Frau´sto da Silva, J. J. R.; Pombeiro, A. J. L. J. Chem.
Soc., Perkin Trans. 1 2001, 1569.
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lished results.
4800 Inorganic Chemistry, Vol. 41, No. 18, 2002

Zn(II)/Ketoxime Catalyst for Hydrolysis
Figure 3. ORTEP view of the molecular structure of [Zn(NO3)2(C4H8Cd
NOH)2] with the atomic numbering. The thermal ellipsoids are drown at
the 50% probability level. Selected bond lengths (Å) and angles (deg):
Zn(1)-N(1) 2.044(2), Zn(1)-O(2) 2.0387(14), Zn(1)-O(3) 2.483(2), N(1)-
O(1) 1.415(2), N(1)-C(1) 1.274(2), N(2)-O(4) 1.216(2), N(2)-O(3)
1.240(2), N(2)-O(2) 1.294(2), N(1)-Zn(1)-O(3) 160.67(6), O(2)-Zn(1)-
N(1) 106.41(6), C(1)-N(1)-Zn(1) 129.57(13), O(1)-N(1)-Zn(1) 118.38(11),
O(4)-N(2)-O(3) 124.8(2), O(4)-N(2)-O(2) 118.8(2), O(3)-N(2)-O(2)
116.5(2).
Figure 4. ORTEP view of the molecular structure of [ZnCl2(Me2Cd
NOH)2] with the atomic numbering. The thermal ellipsoids are drown at
the 50% probability level. Selected bond lengths (Å) and angles (deg):
Zn(1)-Cl(1), 2.2177(12), Zn(1)-Cl(2) 2.2291(12), Zn(1)-N(1) 2.049(4),
Zn(1)-N(2) 2.054(3), N(1)-O(1) 1.407(4), C(1)-N(1) 1.282(5), N(2)-
O(2) 1.408(4), C(4)-N(2) 1.279(5), N(1)-Zn(1)-Cl(1) 114.71(10), N(2)-
Zn(1)-Cl(1) 101.38(10), Cl(1)-Zn(1)-Cl(2) 119.33(6), N(1)-Zn(1)-N(2)
104.64(14), O(1)-N(1)-Zn(1) 116.5(2), C(1)-N(1)-Zn(1) 130.0(3),
O(2)-N(2)-Zn(1) 115.8(2), C(4)-N(2)-Zn(1) 129.3(3).
The nature of the anion in the zinc salt does not affect
strongly the catalytic properties of the Zn(II)/ketoxime
systems. Thus, experiments with the hydrolysis of p-MeOC6-
H4CH2CN mediated by 2-propanone oxime and Zn(NO3)2‚
6H2O, ZnCl2, and Zn(CF3SO3)2 gave the following turnover
frequency (TOF), yield, and TON values: 45, 90, 450 for
the nitrate; 37, 81, 370 for the chloride; and 33, 77, 330 for
the triflate.
Trapping and Characterization of Intermediates. Upon
investigation of the hydrolysis mediated by the Zn(NO3)2‚
6H2O/C4H8CdNOH system, we observed the release of some
crystals formed if the reaction mixture was cooled after 10
min. An X-ray crystallographic study allowed their identi-
fication as the complex [Zn(NO3)2(C4H8CdNOH)2] (see
later). This compound and other similar ones, that is,
[ZnX2(R2CdNOH)2] (X ) Cl, R2 ) 2Me, C4H8, C5H10; X
) NO3, R ) C4H8), were prepared by independent syntheses
via heating the appropriate zinc salts with 2 equiv of the
oxime in acetone (see Experimental Section). All these
complexes gave satisfactory C, H, and N elemental analyses
and expected fragmentation/isotopic patterns in the FAB
mass spectra; they were also characterized by IR and 1H and
13C{1H} NMR spectroscopies, while [Zn(NO3)2(C4H8Cd
NOH)2] and [ZnCl2(Me2CdNOH)2] were also characterized
by X-ray diffraction studies (Figures 3 and 4).
structures, it is worthwhile to mention the following points:
(i) Despite the wealth of X-ray structures for zinc compounds
containing Vic-dioximes, the complexes characterized here
are the first Zn complexes with “simple” oximes, that is,
containing merely one oxime group as the only coordination
site. (ii) In [ZnCl2(Me2CdNOH)2], weak intramolecular
hydrogen bond interactions O(1)sH(11)‚‚‚Cl(2) and O(2)s
H(21)‚‚‚Cl(1) (with O‚‚‚Cl distances 3.193(4) and 3.234(3)
Å, respectively) are stabilizing the structure. A weak interac-
tion between O(2) and Cl(1) [O(2)‚‚‚Cl(1) 3.294(3) Å] from
the neighboring molecule (at equivalent position -x, 1 - y,
2 - z) can also be found (see Supporting Information for
the hydrogen bonding). It is also noteworthy that the potential
interest of oxime/oximato complexes for the construction of
extended arrays, as has been shown previously for Pt(II)31
and Ag(I)32 systems, is now extended to the oxime Zn(II)
compound.
We have demonstrated in separate experiments that all of
the complexes [ZnX2(R2CdNOH)2] catalyze the described
conversion of nitriles into carboxamides but a significant
catalytic activity requires the presence of 2 equiv of the
appropriate oxime; experiments with [ZnX2(R2CdNOH)2]
and without added oxime showed a dramatic decrease of the
(29) (a) Withersby, M. A.; Blake, A. J.; Champness, N. R.; Cooke, P. A.;
Hubberstey, P.; Li, W.-S.; Schroder, M. Inorg. Chem. 1999, 38, 2259.
(b) Tandon, S. S.; Chander, S.; Thompson, L. K.; Bridson, J. N.;
McKee, V. Inorg. Chim. Acta 1994, 219, 55. (c) Chen, H.; Olmstead,
M. M.; Albright, R. L.; Devenyi, J.; Fish, R. H. Angew. Chem., Int.
Ed. Engl. 1997, 36, 642. (d) Kaminskaia, N. V.; Spingler, B.; Lippard,
S. J. J. Am. Chem. Soc. 2000, 122, 6411.
(30) For recent examples see: (a) Rosa, D. T.; Krause-Bauer, J. A.;
Baldwin, M. J. Inorg. Chem. 2001, 40, 1606. (b) Cibulka, R.; Cisarova,
I.; Ondracek, J.; Liska, F.; Ludvik, J. Collect. Czech. Chem. Commun.
2001, 66, 170. (c) Angeloff, A.; Daran, J.-C.; Bernadou, J.; Meunier,
B. Eur. J. Inorg. Chem. 2000, 1985. (d) Potocnak, I.; Heinemann, F.
W.; Rausch, M.; Steinborn, D. Acta Crystallogr., Sect. C 1997, 53,
54.
In both complexes, the main bond lengths are well-
coherent with the observed values for other ZnsCl28 and
ZnsONO229 compounds; geometric parameters of the oxime
ligands agree with other oxime complexes where the ligands
are bound via the oxime N atom.30 In connection to the
(28) (a) Adams, H.; Bradshaw, D.; Fenton, D. E. Eur. J. Inorg. Chem.
2001, 859. (b) Pfistner, H.; Fenske, D. Z. Anorg. Allg. Chem. 2001,
627, 575. (c) Charmant, J. P. H.; Fallis, I. A.; Hunt, N. J.; Lloyd-
Jones, G. C.; Murray, M.; Nowak, T. J. Chem. Soc., Dalton Trans.
2000, 1723. (d) Yang, W.; Schmider, H.; Wu, Q.; Zhang, Y.-S.; Wang,
S. Inorg. Chem. 2000, 39, 2397. (e) Muller, B.; Vahrenkamp, H. Eur.
J. Inorg. Chem. 1999, 129. (f) Alexakis, A.; Tomassini, A.; Chouillet,
C.; Roland, S.; Mangeney, P.; Bernardinelli, G. Angew. Chem., Int.
Ed. 2000, 39, 4093.
(31) Kukushkin, V. Yu.; Nishioka, T.; Tudela, D.; Isobe, K.; Kinoshita, I.
Inorg. Chem. 1997, 36, 6157.
(32) Aakeroey, C. B.; Beatty, A. M.; Leinen, D. S. J. Am. Chem. Soc.
1998, 120, 7383.
Inorganic Chemistry, Vol. 41, No. 18, 2002 4801

Kopylovich et al.
Table 2. Quantitative Parametersa for the Hydrolysis of
p-MeOC6H4CH2CN Catalyzed by [ZnCl2(R2C)NOH)2]/R2CdNOH and
ZnCl2/R2CdNOH Systems
systems, to give a [Zn]sNHdC(R′)sONdCR2 imino in-
termediate. Hydrolysis of the latter furnishes the carboxamide
with concomitant regeneration of the Zn(II)/ketoxime catalyst
upon solvolysis. In fact, the need for an additional 2 equiv
of oxime to achieve the catalytic system and the previously
reported results36-38 on substitution of the OR′ moiety, by
other groups, in [M]sNHdC(R)OR′ complexes support the
latter pathway.
The facile catalytic one-pot hydrolysis of nitriles represents
a viable route to carboxamides because of the simplicity and
availability of the catalytic system discovered. In addition,
the use of rather environmentally friendly39 zinc systems
suggests further benefits. Investigations of other metal/oxime
systems in conversions of nitriles are on the way in our
group.
TOF,
mol/
(mol‚h)
yield,
%
TON,
mol/mol
catalytic system (molar ratio)
ZnCl2/2-propanone oxime
37.0
36.5
25.6
27.0
23.0
24.0
81
76
65
70
65
67
370
365
256
270
230
240
(1:4)
[ZnCl2(Me2CdNOH)2]/2-propanone oxime
(1:2)
ZnCl2/C4H8CdNOH
(1:4)
[ZnCl2(C4H8CdNOH)2]/C4H8CdNOH
(1:2)
ZnCl2/C5H10CdNOH
(1:4)
[ZnCl2(C5H10CdNOH)2]/C5H10CdNOH
(1:2)
a See footnotes a and b of Table 1.
Experimental Section
1
activity (typically TON drops to about /10). Representative
results for [ZnCl2(R2CdNOH)2] complexes along with data
for the corresponding mixtures of ZnCl2/R2CdNOH are
given in Table 2. Identical results, within the experimental
error, were obtained for both types of systems.
Materials and Instruments. Nitriles RCN (R ) Et, n-Pr, i-Pr,
n-Bu, t-Bu, ClCH2, p-MeOC6H4CH2, Ph) (Aldrich), MeCN (Lab-
Scan), Me2CdNOH (Lancaster), C4H8CdNOH, C5H10CdNOH
(Aldrich), Zn(NO3)2‚6H2O (Merck), ZnCl2 (Aldrich), and Zn-
(CF3SO3)2 (Fluka) were obtained from commercial sources and used
as received. All instruments used were described in refs 20-24.
Synthetic Work and Characterization. Hydrolysis of Organo-
nitriles. (a) From a Zn(II) Salt. 2-Propanone oxime (1.37 mmol)
is added to a mixture of RCN (50 mmol) and undissolved Zn(NO3)2‚
6H2O (0.33 mmol), and the system becomes homogeneous within
10 min (in the case of MeCN where the zinc salt is soluble, the
homogeneous solution is immediately formed). Water (0.10 mol)
is added dropwise for 1 h to the vigorously stirred reaction mixture
giving a biphase system which is refluxed on continuous stirring
for 10 h whereupon the reaction mixture is cooled to room
temperature, the solvent is removed in vacuo at 20-25 °C to
dryness, and the residue is purified by a conventional recrystalli-
zation. In the case of MeCN, in which Zn(NO3)2‚6H2O is soluble,
addition of water gives a single solution. Quantitative parameters
The complexes of the type [ZnX2(oxime)2] are so far the
only isolable intermediates (or catalyst precursors) for the
conversion, and our attempts to detect other species involved
in the process were not yet successful. Thus, in preparative
experiments, treatment of [ZnX2(oxime)2] with an additional
amount of the oxime (the complex/oxime molar ratio has
ranged from 1:2 to 1:10) in acetone followed by removal of
the solvent in vacuo and of the excess of the oxime by
washing with diethyl ether led to recovery of the metal
complexes intact. In NMR experiments, a fast exchange
between [ZnX2(oxime)2] and excess of oxime, leading to only
one set of signals in the temperature range from -50 to 60
°C, has been detected, and that precluded observation of other
Zn-containing species by this method. In addition, attempted
reaction between [ZnX2(oxime)2] and MeCN (the complex/
nitrile molar ratio has ranged from 1:2 to 1:12) in CDCl3
showed no interaction.
Hence, the lack of additional experimental data on
intermediates involved in the catalytic system makes the
interpretation of the catalysis mechanism somehow ambigu-
ous. However, we anticipate that two principal routes for
the hydrolysis are possible. In one of them, the complexes
[ZnX2(R2CdNOH)2], formed in the initial stage of the
reaction, might provide two neighboring coordination sites
for ligation of a nitrile and water followed by the intra-
molecular hydration of RCN and release of the carboxamide
formed. This route is coherent with one suggested in a recent
theoretical study on Zn-mediated hydration of nitriles on
heterogeneous catalysts.33 However, the need for an ad-
ditional 2 equiv of oxime would not be easily accounted for
by this route. In the other route, a nitrile ligates to a Zn site
(nitrile Zn complexes are known34), whereupon the ligated
RCN species is attacked by the oxime, as was observed by
us20-23 and others35 for kinetically substitutionally inert metal
(34) (a) Mu¨ller, B.; Vahrenkamp, H. Eur. J. Inorg. Chem. 1999, 117. (b)
Batten, S. R.; Hoskins, B. F.; Robson R. Chem. Commun. 1991, 445.
(c) Castro, J. A.; Romero, J.; Garcia-Vazquez, J. A.; Macias, A.; Sousa,
A.; Englert, U. Polyhedron 1993, 12, 1391. (d) Ohtsu, H.; Shimazaki,
Y.; Odani, A.; Yamauchi, O. Chem. Commun. 1999, 2393. (e)
Matthews, C. J.; Clegg, W.; Heath, S. L.; Martin, N. C.; Hill, M. N.
S.; Lockhart, J. C. Inorg. Chem. 1998, 37, 199. (f) Bhyrappa, P.;
Krishnan, V.; Nethaji, M. J. Chem. Soc., Dalton Trans. 1993, 1901.
(g) Gunter, M. J.; Jeynes, T. P.; Johnston, M. R.; Turner, P.; Chen, Z.
J. Chem. Soc., Perkin Trans. 1 1998, 1945. (h) Eichhofer, A.; Fenske,
D.; Fuhr, O. Z. Anorg. Allg. Chem. 1997, 623, 762. (i) Becker, B.;
Radacki, K.; Wojnowski, W. J. Organomet. Chem. 1996, 521, 39. (j)
Woller, E. K.; DiMagno, S. G. J. Org. Chem. 1997, 62, 1588. (k)
Raubacher, F.; Weller, F. Z. Kristallogr. 1996, 211, 576. (l) Bel’sky,
V. K.; Streltsova, N. R.; Bulychev, B. M.; Storozhenko, P. A.;
Ivankina, L. V.; Gorbunov, A. I. Inorg. Chim. Acta 1989, 164, 211.
(m) Isakov, I. V.; Zvonkova, Z. V. Dokl. Akad. Nauk SSSR 1962,
145, 801.
(35) (a) Pavlishchuk, V. V.; Kolotilov, S. V.; Addison, A. W.; Prushan,
M. J.; Butcher, R. J.; Thompson, L. K. Inorg. Chem. 1999, 38, 1759.
(b) Pavlishchuk, V. V.; Kolotilov, S. V.; Addison, A. W.; Prushan,
M. J.; Butcher, R. J.; Thompson, L. K. Chem. Commun. 2002, 468.
(36) (a) Fanizzi, F. P.; Intini, F. P.; Natile, G. J. Chem. Soc., Dalton Trans.
1989, 947. (b) Cini, R.; Caputo, P. A.; Intini, F. P.; Natile, G. Inorg.
Chem. 1995, 34, 1130.
(37) Raubenheimer, H. G.; Kruger, G. J.; Scott, F.; Otte, R. Organometallics
1987, 6, 1789.
(38) Pakhomova, T. B.; Kukushkin, V. Yu.; Pombeiro, A. J. L. Unpublished
material.
(33) Barbosa, L. A. M. M.; van Santen, R. A. J. Mol. Catal. A: Chem.
2001, 166, 101.
(39) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice;
Oxford University Press: Oxford, 1998.
4802 Inorganic Chemistry, Vol. 41, No. 18, 2002

Zn(II)/Ketoxime Catalyst for Hydrolysis
Table 3. Crystal Data for n-BuC(dO)NH2 (1),
p-MeOC6H4CH2C()O)NH2 (2), [Zn(NO3)2(C4H8C)NOH)2] (3), and
[ZnCl2(Me2C)NOH)2] (4)
of the reaction are given in Table 1. Identical procedures were
followed in the case of ZnCl2 or Zn(CF3SO3)2 as the zinc salt.
(b) From a (Ketoxime)Zn(II) Complex. The procedure is
similar to that described for the zinc salts, but only 2 equiv of the
oxime is needed.
MeC(dO)NH2, ClCH2C(dO)NH2, EtC(dO)NH2, n-PrC(dO)-
NH2, i-PrC(dO)NH2, n-BuC(dO)NH2, t-BuC(dO)NH2, PhC-
(dO)NH2, p-MeOC6H4CH2C(dO)NH2. Mp/(Mp lit.), 81°/(81°,
p 3840), 119°/(119°, p 210840), 80°/(80°, p 783840), 116°/(115-
116°, p 321840), 129°/(127-129° p 128140), 122°/(120-122° 41),
156°/(154-157° p 23340), 130°/(130°, p 17740), 184°/(182-184°).41
IR and 1H and 13C{1H} NMR spectra of the samples correspond to
those of the commercially available carboxamides.
Preparation of (Ketoxime)Zn(II) Complexes. The ketoxime
R2CdNOH (X ) Cl, R2 ) 2Me, C4H8, C5H10; X ) NO3, R )
C4H8; 4 mmol) is added to ZnCl2 or Zn(NO3)2‚6H2O (2 mmol),
whereupon acetone (10 mL) is added. The obtained slurry within
ca. 1 min of stirring turns into a colorless solution which is refluxed
for 8 h, the solvent is removed under vacuum to dryness at room
temperature, and the residue formed is washed with three 5-mL
portions of diethyl ether. Yields are 90-97%, based on Zn.
[ZnCl2(Me2CdNOH)2]. Anal. Calcd for C6H14N2Cl2O2Zn: C,
25.51; H, 5.00; N, 9.92. Found: C, 25.51; H, 5.33; N, 9.70. FAB+-
MS, m/z: 137 [ZnMe2CNOH + H]+, 172 [ZnClMe2CNOH]+, 247
[ZnCl(Me2CNOH)2]+, 285 [M + 4H]+. Mp ) 105 °C (dec). IR
spectrum in KBr, selected bands, cm-1: 3580 mw, br ν(OsH),
1616 s ν(CdN), 1397 s + 1377 s νs(NO3) + δs(CH3). 1H NMR in
CDCl3, δ: 2.08 (s, 6H, 2CH3), 2.10 (s, 6H, 2CH3), 9.03 (s, br, 2H,
2OH). 13C{1H} NMR in CDCl3, δ: 17.6 (CH3), 22.3 (CH3), 164.8
(CdN).
1
2
3
4
empirical
formula
fw
temp, K
λ, Å
cryst syst
space group
a, Å
b, Å
c, Å
C5H11NO
C9H11NO2
C10H18N4O8Zn C6H14Cl2N2O2Zn
101.15
150(2)
0.71073
165.19
150(2)
0.71073
387.65
150(2)
0.71073
282.46
150(2)
0.71073
triclinic
P1h
monoclinic monoclinic monoclinic
P21/c P21/c C2/c
11.0625(6) 15.9368(8) 13.8283(4)
5.8294(3)
9.7921(4)
90
103.513(2) 96.096(2)
90
613.99(5)
4
1.094
0.076
7.10960(10)
8.8985(2)
10.9267(3)
88.086(1)
71.811(1)
67.061(1)
601.71
5.5722(2)
9.6511(4)
90
11.8788(4)
9.8884(3)
90
110.142(2)
90
R, deg
â, deg
γ, deg
V, Å3
90
852.20(6)
4
1.287
0.092
1524.96(8)
4
Z
F
2
calcd, g/cm3
1.688
1.559
µ(Mo KR),
1.659
2.459
mm-1
R1a (I g 2σ)
0.0400
0.0493
0.1199
0.0255
0.0612
0.0393
0.1070
wR2b (I g 2σ) 0.1056
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]]1/2
.
from acetone and methanol, respectively, while crystals of
[Zn(NO3)2(C4H8CdNOH)2] and [ZnCl2(Me2CdNOH)2] were grown
by slow evaporation of the reaction mixtures. The X-ray diffraction
data were collected on a Nonius KappaCCD diffractometer using
Mo KR radiation (λ ) 0.71073 Å) and the Collect42 data collection
program. The Denzo-Scalepack43 program package was used for
cell refinements and data reduction. The structures [Zn(NO3)2-
(C4H8CdNOH)2] and [ZnCl2(Me2CdNOH)2] were solved by the
Patterson method, and the others, by direct methods using the
SHELXS-97 program.44 An empirical absorption correction based
on equivalent reflections45 was applied to [Zn(NO3)2(C4H8Cd
NOH)2] and [ZnCl2(Me2CdNOH)2] (Tmax/Tmin) 0.32258/0.26475
and 0.38090/0.34442, respectively). Structures were refined with
the SHELXL-9746 program and the WinGX graphical user inter-
face.47 In [Zn(NO3)2(C4H8CdNOH)2], the Zn atom was positioned
on a 2-fold axis. All hydrogens, except the ones in NH2 and OH
groups, were placed in idealized positions and constrained to ride
on their parent atom. NH2 and OH hydrogens were located from
the difference Fourier map and were fixed or constrained to ride
on their parent atom. Crystallographic data are summarized in Table
3, and selected bond lengths and angles, in the figure legends.
[ZnCl2(C4H8CdNOH)2]. Anal. Calcd for C10H18Cl2N2O2Zn: C,
35.90; H, 5.42; N, 8.37. Found: C, 35.98; H, 5.45; N, 8.30. FAB+-
MS, m/z: 299 [M - Cl], 337 [M + 3H]+, 397 [Zn2Cl2(Me2CNOH)2
- 2H]+, 436 [Zn2Cl3(Me2CNOH)2 + H]+. Mp ) 96 °C (dec). IR
spectrum in KBr, selected bands, cm-1: 3386 s ν(OsH), 2982 mw
1
νas(CsH), 2874 mw νs(CsH), 1677 mw ν(CdN). H NMR in
CDCl3, δ: 1.76 (m, 8H, 4CH2), 2.41 (t, 4H, 2CH2), 2.49 (t, 4H,
2CH2), 8.97 (s, br, 2H, 2OH). 13C{1H} NMR in CDCl3, δ: 24.4
(CH2), 25.2 (CH2), 28.0 (CH2), 31.1 (CH2), 170.5 (CdN).
[ZnCl2(C5H10CdNOH)2]. Anal. Calcd for C12H22Cl2N2O2Zn:
C, 39.75; H, 6.12; N, 7.73. Found: C, 39.88; H, 6.13; N, 7.68.
FAB+-MS, m/z: 212 [Zn(C5H10CNOH)Cl - 2H+], 325 [M - Cl
- 2H+], 365 [M + 3H+], 576 [Zn2(C5H10CNOH)3Cl3]. Mp ) 91
°C (dec). IR spectrum in KBr, selected bands, cm-1: 3365 s, br
1
ν(OsH), 2939 s νas(CsH), 2860 s νs(CsH), 1663 s ν(CdN). H
Acknowledgment. M.N.K. and V.Yu.K. express gratitude
to the PRAXIS XXI program (Portugal) for Grants BPD/
20169/99 and BCC16428/98, respectively. The work has
been partially supported by the FCT (Foundation for Science
and Technology) and the PRAXIS XXI and POCTI pro-
grams. The authors thank Dr. N. A. Bokach for variable
temperature NMR experiments.
NMR in CDCl3, δ: 1.64 (m, 12H, 4CH2 + 2CH2), 2.38 (t, 4H,
2CH2), 2.62 (t, 4H, 2CH2), 8.90 (s, br, 2H, 2OH). 13C{1H} NMR
in CDCl3, δ: 25.0 (CH2), 25.7 (CH2), 26.5 (CH2), 26.7 (CH2), 32.6
(CH2), 169.0 (CdN).
[Zn(NO3)2(C4H8CdNOH)2]. Anal. Calcd for C10H18N4O8Zn: C,
30.98; H, 4.68; N, 14.45. Found: C, 30.69; H, 4.85; N, 14.10.
FAB+-MS, m/z: 324 [M - NO3 - H+]+. Mp ) 147 °C (dec). IR
spectrum in KBr, selected bands, cm-1: 3391 s br ν(OsH), 2978
mw νas(CsH), 2874 mw νs(CsH), 1675 s ν(CdN) + νas(NO3),
1377 vs, br νs(NO3) + δ(CsH), 825 s δ (NO3). 1H NMR in D2O,
δ: 3.58 (m, 8H, 4CH2), 4.16 (t, 2H, 2CH2), 4.23 (t, 2H, 2CH2),
OH were not observed. 13C{1H} NMR in D2O, δ: 24.2 (CH2), 24.9
(CH2), 27.3 (CH2), 30.7 (CH2), 171.7 (CdN).
(42) Data collection software: Collect; Nonius B. V.: Delft, The Nether-
lands, 1997-2000.
(43) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. Methods in Enzymology, Vol. 276;
Macromolecular Crystallography, Part A; Carter, C. W., Jr., Sweet,
R. M., Eds.; Academic Press: New York, 1997, pp 307-326.
(44) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Deter-
mination; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(45) Sheldrick, G. M. SHELXTL, Version 5.1; Bruker Analytical X-ray
Systems, Bruker AXS, Inc.: Madison, WI, 1998.
X-ray Structure Determinations. Crystals of n-BuC(dO)NH2
and p-MeOC6H4CH2C(dO)NH2 were obtained by recrystallization
(46) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(47) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(40) The Merck Index, 11th ed.; Merck & Co.: Rahway, NJ, 1989.
(41) Katritzky, A. R.; Pilarski, B.; Urogdi, L. Synthesis 1989, 949.
Inorganic Chemistry, Vol. 41, No. 18, 2002 4803

Kopylovich et al.
Supporting Information Available: Tables listing crystal-
lographic data, atomic coordinates, bond lengths and bond angles,
anisotropic displacement parameters, hydrogen coordinates and
isotropic displacement parameters, torsion angles and hydrogen
bonds. X-ray crystallographic data for n-BuC(dO)NH2, p-MeOC6H4-
CH2C(dO)NH2, [Zn(NO3)2(C4H8CdNOH)2], and [ZnCl2(Me2Cd
NOH)2] in CIF format. Packing diagram of [Zn(NO3)2(C4H8Cd
NOH)2]. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC0256720
4804 Inorganic Chemistry, Vol. 41, No. 18, 2002