The catalytic hydration of 1,2-, 1,3- and 1,4-dicyanobenzenes using nickel(0) catalysts

Article abstract of DOI:10.1016/j.molcata.2006.10.054

The homogeneous catalytic hydration of 1,2-, 1,3- and 1,4-dicyanobenzenes using organometallic nickel(0) catalysts of general formula [(dippe)Ni(η²-N,C-1,n-(CN)₂-benzene)] (n = 2-4; complexes 2-4, respectively) was achieved under hea

Full text of DOI:10.1016/j.molcata.2006.10.054

Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
The catalytic hydration of 1,2-, 1,3- and 1,4-dicyanobenzenes
using nickel(0) catalysts
∗
´
´
Carmela Crisostomo, Marco G. Crestani, Juventino J. Garcıa
Facultad de Qu´ımica, Universidad Nacional Auto´noma de Me´xico, Me´xico, D.F. 04510, Me´xico
Received 4 October 2006; received in revised form 25 October 2006; accepted 25 October 2006
Available online 6 December 2006
Abstract
The homogeneous catalytic hydration of 1,2-, 1,3- and 1,4-dicyanobenzenes using organometallic nickel(0) catalysts of general formula
[(dippe)Ni(␩2-N,C-1,n-(CN)2-benzene)] (n = 2–4; complexes 2–4, respectively) was achieved under heating, the products of hydration, at least in
the case of 1,3- and 1,4-dicyanobenzene being strongly dependent on the temperature used for the process; the production of the respective 1,3-
and 1,4-cyanobenzamides been observed at 120 ◦C, while catalysis at 180 ◦C resulted in the quantitative formation of the 1,3- and 1,4-dicarboxylic
acids. In the case of 1,2-dicyanobenzene, catalysis at either temperature yielded the hemihydration product 1,2-phthalamide, implying an important
difference in overall reactivity for this system. All the hydration products were obtained in excellent selectivity and yield, using 0.5 mol% loadings
of the corresponding nickel(0) catalyst and thus, the current work provides important evidences that could be of use for both synthetic organic
chemistry and in the eventual production of polyamides.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Homogeneous; Catalysis; Dinitriles; Hydration; Nickel
1. Introduction
production), in high yield and selectivity, through environmen-
tally friendly routes, have become major issues in modern
production techniques and in this instance, the use of inorganic
[6] or enzymatic [7] catalysts to assist the direct hydration of the
starting dinitriles are particularly attractive strategies [8].
Thecatalytichydrationorhydrolysisofnitrilesisaveryactive
fieldincontemporarychemistry, giventhattheproductsobtained
from this process (either amides or their parent carboxylic acids)
present a large practical use in synthesis, pharmacology and
in industry in general [1]. In the case of polyamides (nylons),
their large-scale production for the manufacture of high perfor-
mance synthetic fibers, films, insulators, etc., is of considerable
technical [2] and economical [3,2b,2c] importance. Fabrics and
materials made of nylon are widely known for fire-retardancy
application. Also, most polyamides are biologically inert and
offer no toxicological problems to the point of being used as
suture materials; these are also non-leaching polymers and as
such, compacted sanitary landfills pose no danger to subsur-
face water [2d,2e]. Thus, the straightforward preparation of
these products either through one-pot reactions or from their
precursor monomers (e.g. cyanobenzamides [4], aromatic di-
carboxamides [5], etc.) in separate hydration processes (batch
For a number of years, our group has been interested in
the activation of aryl-, heteroaryl- and alkyl-substituted nitriles,
using nickel(I) precatalysts of the formula [(P–P)NiH]2; (P–P),
a chelating bisphosphine ligand such as dippe (dippe = 1,2-
bis(di-isopropylphosphino)ethane) [9]. In all cases, the reactions
that occur with nitriles yield nickel(0) complexes of the type
[(P–P)Ni(␩2-N,C-R)] (R = aryl-, heteroaryl- or alkyl-), in which
the corresponding nitrile is ␲-bonded to the [(P–P)Ni] moiety
through a side-on, ␩2-N,C coordination [10], and may undergo
thermal or photochemically induced oxidative addition of the
C–CN bond to produce the respective nickel(II) complexes
[(P–P)Ni(CN)(R)]. In the case of aryl- and heteroaryl-nitriles,
the oxidative cleavage of the C–CN bond is thermally driven
and occurs upon gentle heating (50 ◦C) [9b,9c]. In the case of
alkyl-nitriles, the oxidative addition is inhibited with longer
chain lengths even when subjecting the corresponding com-
plex to irradiation with a UV source as was the case of
the adamantyl cyanide system [9a]. A similar stabilization
∗
Corresponding author. Tel.: +52 55 56223514; fax: +52 55 56162010.
E-mail address: juvent@servidor.unam.mx (J.J. Garc´ıa).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.10.054

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C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
effect was also observed with the smaller ethyl-, n-propyl-, i-
propyl-, t-butyl-, c-propyl- and c-butyl-analogs, which did not
undergo oxidative addition under heating, but could only be
converted into their respective nickel(II) derivatives upon pho-
tolysis (λ = 300 nm). The results are in contrast to the acetonitrile
complex [(dippe)Ni(␩2-N,C-CH3)], in which the C–CN oxida-
tive addition reaction was observed to take place even at room
temperature after 2 h in solution.
of [(dippe)NiH]2 (1) as catalyst precursor. The respective
hydrations were performed using water suspensions of the cor-
responding dinitrile and the nickel(I) precatalyst at the 50:1
mole proportion of water to the corresponding dinitrile; the
effect of THF solvent was also investigated. Table 1 summa-
rizes the results obtained for the three substrates at 120 and
180 ◦C.
As indicated in the table, the selectivity of the overall cat-
alytic hydration may be affected by the substrate that is used,
the temperature of the process and the characteristics of the
reaction media (illustrated in the table by the use of THF or
water; entries 6 and 7). In the cases of the 1,3- and 1,4-DCB, the
hydrations are strongly temperature-dependent and thus, catal-
ysis at 120 ◦C led only to the partial hemihydration products
1,3- and 1,4-cyanobenzamide (entries 4, 6, 7), while catalysis
at 180 ◦C yielded the total hydrolysis products 1,3-isophthalic
and 1,4-terephthalic acids along with the corresponding amounts
of ammonia (entries 3 and 5). In the case of 1,2-DCB (entries 1
and2), the hemihydrationproduct1,2-phthalamidewasobtained
at both 120 and 180 ◦C, without any influence over product
selectivity, yield, turnover number (TON) or frequency (TOF),
therefore, suggesting a dramatic difference with respect to the
other two systems, probably due to steric constraint afforded by
the adjacent amido substituents in the 1,2-phthalamide prod-
uct, that prevents further hydrolysis of this compound (vide
infra).
In the above-described nickel(0) complexes (aryl-, hetero-
aryl- and alkyl-substituted), the coordinated carbon atoms
undergo a significant increase in their electrophilic character
due to the ␴-donation into the nickel(0) center. This is con-
1
firmedfrom13C{ H}NMRspectraofthecomplexesthatexhibit
chemical shifts of the coordinated carbon atoms around 160 ppm
as doublets of doublets (dd), which are significantly downfield
from those of the free nitrile ligands, typically singlets (s) around
120 ppm [9]. These facts have prompted us to explore the chem-
istry of these nickel(0) complexes in a number of nucleophilic
substitution reactions, which in the case of water as nucleophile
gives the nitrile hydration reaction. Our previous findings using
benzo- and acetonitrile have been published [11]. The catalytic
hydration of these substrates are proposed to occur over the
[(P–P)Ni(␩2-N,C-R)] (R = phenyl-, methyl-) complexes by a
concerted N,N-dihydro-C-oxo-biaddition of water to the side-
on coordinated nitrile moieties. In the current work, we have
extended the scope of the hydration reaction to some industri-
ally important substrates such as the aromatic dinitriles 1,2-,
1,3- and 1,4-dicyanobenzene (1,2-DCB, 1,3-DCB, 1,4-DCB).
To the best of our knowledge, few examples of the catalytic
hydration of these three substrates, incorporating at least one-
water molecule into the corresponding dinitrile (production of
cyanobenzamides) have been reported [4,5,7c,12]. On the sto-
ichiometric level, the situation is similar and few examples
of the activation of dicyanobenzenes – all of them depicting
end-on ␩1-coordinated nitrile moieties – have been reported
[13].
2.2. Mechanisms for dinitrile hydration
As in the cases of benzo- and acetonitrile [11], the catalytic
hydrations of dicyanobenzenes are expected to be effected by
nickel(0) complexes that exhibit a ␩2-coordination of a –CN
bond to a [(dippe)Ni] moiety [9]; the immediate formation of
monocoordinated nickel(0) complexes with the general formula
[(dippe)Ni(␩2-N,C-1,n-(CN)2-benzene)] (n = 2–4; complexes
2–4, respectively) been confirmed to take place in THF-d8 and
toluene-d8, on using a 2:1 ratio of the respective dinitrile ver-
sus 1. The results are in agreement to what is expected to occur
at the larger mole proportion of organic substrate that is used
in catalysis and thus, they strongly support the premise of a
nickel(0)-assisted catalytic reaction. Eq. (1) illustrates the reac-
tions that occur in the presence of stoichiometric amounts of the
dinitrile substrate, over the nickel(I) dihydride dimer.
2. Results and discussion
2.1. Catalysis of dinitrile hydration
The catalytic hydration of 1,2-DCB, 1,3-DCB and 1,4-
DCB was successfully achieved with heating using 0.25 mol%
Table 1
Catalytic hydration of dicyanobenzenes using nickel(0)
Entry
Substrate
T (◦C)
THF
Product
TON
TOF (TON/h)
Yielda (%)
1
2
3
4
5
6
7
1,2-DCB
1,2-DCB
1,3-DCB
1,3-DCB
1,4-DCB
1,4-DCB
1,4-DCB
120
180
180
120
180
120
120
No
No
No
No
No
No
Yes
1,2-Phthalamide
1,2-Phthalamide
135
135
259
82
325
64
2
2
4
1
5
1
1
71
71
68
86
86
68
87
1,3-Isophthalic acid + ammonia
1,3-Cyanobenzamide
1,4-Terephthalic acid + ammonia
1,4-Cyanobenzamide
1,4-Cyanobenzamide
83
a
All yields indicated in this table have been obtained on the basis of isolated product after work-up.

C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
141
Complexes 2–4 depict archetypical features that are charac-
teristic of complexes in which nitriles are ␩2-coordinated to a
Complexes 2–4 are reasonably stable under argon at room
temperature in THF or toluene solutions and in this instance,
no evolution of these complexes into their respective nickel(II)
derivatives [(dippe)Ni(CN)(1,n-(CN)-benzene)] (n = 2–4), was
observed to occur on standing in these media, prior to 24 h
(see Section 4). Addition of water prevents this reaction and
in this instance, the suppression of the oxidative addition by
water is consistent with the fact that no inhibition of cataly-
sis was observed at the temperatures used for the processes.
The results are similar to those of benzo- and acetonitrile [11]
using nickel(0) catalysts of the type [(dippe)Ni(␩2-N,C-R)]
(R = -Me, -Ph), and in this instance, the catalytic hydration of
dicyanobenzenes is also expected to occur by concerted N,N-
dihydro-C-oxo-biadditions of water to the side-on coordinated
nitriles in complexes 2–4, respectively. The degree of hydra-
tion is temperature- and substrate-dependent and as such, the
1
metal center [9] and in this instance, examination of the 31P{ H}
NMR spectra of complexes 2–4 (see Table 2), has confirmed
the presence of two slightly broadened asymmetric doublets
2
with JP–P coupling constants of 63 Hz, characteristic of two
types of phosphorus environments; the magnitude of the cou-
pling constant being consistent with a monocoordination of the
1
dicyanobenzenes as is illustrated in Eq. (1) [9b]. The 13C{ H}
NMR spectra of the pure compounds is also consistent with this
description, and thus the apparition of two doublets of doublets
(dd) in the surroundings of δ 165 in all spectra has confirmed
the presence of a ␩2-coordinated –CN bond to a [(dippe)Ni]
moiety; the uncoordinated nitrile substituents in complexes 2–4
appearing as singlets usually around δ 117 [14]. Table 2 summa-
rizes the key spectroscopic information, for the three nickel(0)
complexes.
Scheme 1. Progressive hydration of dinitriles using nickel(0) catalysts [11]: 1,4-terephthalonitrile.

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C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
Table 2
Distinctive 31P{ H} and 13C{ H} NMR chemical shifts of complexes 2–4
1
1
1
1
Complex
31P{ H}
13C{ H}
Coordinated CN
Uncoordinated CN
2
3
4
80.2 (d, 2JP–P = 63 Hz)
77.6 (d, 2JP–P = 63 Hz)
77.5 (d, 2JP–P = 63 Hz)
69.4 (d, 2JP–P = 63 Hz)
65.9 (d, 2JP–P = 63 Hz)
65.7 (d, 2JP–P = 63 Hz)
169.9 (dd, J1 = 72.4 Hz, J2 = 28.2 Hz)
162.9 (dd, J1 = 73 Hz, J2 = 28.5 Hz)
169.9 (dd, J1 = 30 Hz, J2 = 9 Hz)
118.6
117
119.4
distribution of products may range from the one-water-addition
process yielding cyanobenzamides, to the total hydration of the
dicyanobenzene substrate, producing dicarboxylic acids. The
conclusion that can be brought from these instances is that the
catalytic hydration of each nitrile in a dicyanobenzene substrate
can be rationalized as if occurring independently of the even-
tual hydration of the other and as such, a series of intermediates
involving the progressive hydration of the substrate can be estab-
lished [15]. A general scheme that describes this conclusion is
depicted in Scheme 1.
nickel catalyst going on and off for catalysis) being expected
to yield mixtures of partially and fully hydrolysed products,
which was not the case [18]. Interestingly, the migration
process (or alternatively, the first –CN hydration, assuming a
completely intermolecular reactivity by which free [(dippe)Ni]
fragments were to coordinate randomly to these substrates)
should be temperature-dependent provided that only one water
molecule is transferred into the organic substrate at 120 ◦C,
as only cyanobenzamides are produced at this temperature
(see Table 1) and as such, a high energy barrier limiting the
migration of the [(dippe)Ni] moiety undergone through an
intramolecular pathway at such temperature, could be presumed
to exist in order to prevent any further hydrolysis of the two
dicyanobenzenes (1,3- and 1,4-DCB). At 180 ◦C however, the
Implicit in Scheme 1, the incorporation of water molecules
into the organic functionalities—nitriles or carbonyls [16],
is always assumed to take place over the ␩2-coordinated
functions and thus a number of related nickel(0) intermediates
besides of complexes 2–4 can be envisioned, depending on
the stage of hydration catalysis they assist. The additional
complexes are proposed to form within the catalytic cycles
according to the temperature and the substrate used and in
this instance, a number of catalytic proposals that describe
these intermediates have been included in Schemes 2–4 (vide
infra). The proposed intermediates could be described as
having amido/cyano moieties, only amides or amido/carboxyl,
depending of the particular stage of catalysis occurring and thus,
their complexes could be formulated following these leads as
[(dippe)Ni(␩2-N,C-1,n-(CN)(C(O)NH2)-benzene)] (A) for the
amido/cyano [(dippe)Ni(␩2-C,O-1,n-(C(O)NH2)2-benzene)]
(B) for the double amido complex and [(dippe)Ni(␩2-C,O-1,n-
(C(O)NH2)(C(O)OH)-benzene)] (C) for the amido/carboxyl
derivative; presumably the last intermediate before the total
hydration is achieved (see Scheme 3). In the cases of the
1,3- and 1,4-dicyanobenzenes, the catalytic cycle at 120 ◦C
(Scheme 2) would require only one additional intermediate,
namely
[(dippe)Ni(␩2-N,C-1,n-(C(OH)NH)(CN)-benzene)]
(for n = 3, 4) to produce the corresponding cyanobenzamides,
while catalysis at 180 ◦C would require all the other nickel(0)
intermediates to be formed as well. At this temperature, the
migration of the [(dippe)Ni] moiety over the arene ring through
a series of stepwise ␩2-bonded [(dippe)Ni(␩2-C,C-2-(X)(Y)-
benzene)] (X, Y = –CN, –C(O)NH2, –C(O)OH) intermediates
– alternatively to intermolecular catalysis, involving decoor-
dination and re-coordination of the nickel(0) catalyst – could
be proposed to take place, shifting the position of the nickel(0)
catalyst from one organic function to the other (amido to cyano,
amido to amido and amido to carboxyl), therefore, linking
the series of intermediates mentioned above within the same
catalytic cycle [17]. The selectivities to 1,3-isophthalic and
1,4-terephthalic acids at 180 ◦C are indicative of such premise:
a non-sequential hydration process (such as that involving the
Scheme 2. Mechanistic proposal for the partial hemihydration of 1,3- and 1,4-
DCB at 120 ◦C, using nickel(0) catalysts.

C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
143
Scheme 3. Mechanistic proposal of the total hydration of 1,3- and 1,4-DCB at 180 ◦C, using nickel(0) catalysts.
temperature would be enough to overcome such energy barrier
and as a result, the two nitriles in each dicyanobenzene substrate
become fully hydrolysed.
end-on coordinated nitrile complex [(NH3)5Ru(␩1-N,C-1,4-
(CN)(C(O)NH2)-benzene)]. The reaction was proposed to
occur through a series of stepwise ␩2-bonded (NH3)5Ru(II)
1,4-cyanobenzamide complexes, consistent with previous ref-
erences using isonicotinamide [19].
In the case of 1,2-DCB – and in contrast with the 1,3- and
1,4-DCB mechanistic proposals illustrated above – the cat-
alytic hydration of this substrate resulted in the formation of
1,2-phthalamide at both 120 and 180 ◦C, selectively: cataly-
sis was thus found to be independent of the temperature and
in this instance, the product was also unique (the expected
1,2-dicarboxylic acid not formed at 180 ◦C). A number of pos-
sibilities to explain this issue have been thought and in this
The mechanistic proposals that illustrate the premise of
an intramolecular migration of [(dippe)Ni] moieties to yield
the hemi- and complete hydration of the 1,3- and 1,4-DCB
are included in Schemes 2 and 3, as follows. To note,
the mechanistic proposal of sequential dinitrile hydrations
afforded by the stepwise migration of the nickel(0) catalyst
[(dippe)Ni] over each arene ring, have also been reported by
Tfouni et al. using penta-ammineruthenium complexes [13a]:
an N-amide to N-nitrile linkage isomerization reaction been
predicted to take place (∼55%), producing the corresponding

144
C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
instance, one possible conclusion that was raised, regardless of
the mechanistic pathway by which hydration is accomplished,
is to presume the steric hindrance of the adjacent amides in 1,2-
phthalamidetoberesponsibleofstoppinganyfurtherhydrolysis,
limiting the effective re-coordination of the [(dippe)Ni] moi-
ety to the carbonyl functions in it. The mechanistic pathway by
which hemi-hydrolysis of 1,2-DCB takes place is clearly also
open for discussion, but given the experimental results obtained
thus far, we are inclined to trust this process not be driven by
a stepwise migration of the [(dippe)Ni] catalyst over the arene
ring, but rather by an intermolecular nitrile-to-nitrile shift over
this substrate, provided that the two organic functions are so
closetoeachother:thecorresponding1,2-diamidebeenobtained
even at 120 ◦C, where the high energy barrier predicted by anal-
ogy with the other two systems might have been expected to
limit the intramolecular migration of the [(dippe)Ni] moiety pro-
ducing 2-cyanobenzamide, instead. A mechanistic proposal that
summarizes these conclusions for the catalytic hydration of 1,2-
DCB at 120 and 180 ◦C using nickel(0) catalysts, is presented
in Scheme 4.
previous studies using 2-cyanobenzamide in the presence of sto-
ichiometric amounts of ruthenium and cobalt complexes been
found to result in the intramolecular cyclization of coordinated
2-cyanobenzamide, therefore yielding 3-imino-1-oxo-isoindole
complexes [13].
3. Conclusions
The catalytic hydration of 1,2-, 1,3- and 1,4-dicyanobenzenes
was achieved under thermal conditions, using monocoordinated
nickel(0) complexes with general formula [(dippe)Ni(␩2-
N,C-1,n-(CN)2-benzene)] (n = 2–4). For these systems, the
experimental distributions of products show that there is an
important dependence on the isomer that is chosen and on the
temperature that is used for catalysis. The hydration products
are obtained in excellent selectivity and thus, the potential use of
these catalysts in organic synthesis could be envisioned. Current
studies are in progress to extend this reaction to dicyano-alkyl
substrates.
To note, the fact that 1,2-phthalamide could be obtained
selectively from 1,2-DCB in this work is also important: the
4. Experimental
4.1. General considerations
Unless otherwise noted, all manipulations were performed
using standard Schlenk techniques in an inert-gas/vacuum dou-
ble manifold or under argon atmosphere in an MBraun glovebox
(<1 ppm H2O and O2). Catalysis experiments were conducted
in a 300 mL stainless steel Parr Series 4560 Bench Top Mini
Reactor or alternatively in a 100 mL stainless steel Parr Series
4590 Micro Bench Top Reactor; the catalytic mixtures were
loaded in the reactor inside the glovebox. All argon used in this
work was supplied by Praxair in high purity grade (99.998%).
Solvents were purchased from J.T. Baker in reagent grade and
in the case of THF and hexane, that were used in the prepara-
tion of [(dippe)NiH]2 (1) (vide infra), these were additionally
dried and distilled from sodium/benzophenone ketyl; THF used
in catalysis experiments distilled likewise. Ethyl acetate and
acetone were used for the chromatographic separation of the
hydration products, and were used as received. Deuterated sol-
vents for NMR experiments were purchased from Cambridge
˚
Isotope Laboratories and were stored over 3 A molecular sieves
in the glovebox for at least 24 h before their use. NMR spectra
of complexes and products were recorded at ambient temper-
ature on a 300 MHz Varian Unity spectrometer. H, 31P{ H}
NMR spectra of all nickel complexes were obtained using
concentrated solutions of the pure nickel complex (30 mg) in
an inert solvent such as toluene-d8 or THF-d8, unless other-
wise stated. All the samples were handled under argon, using
thin wall – 0.38 mm – WILMAD NMR tubes with J Youngs
1
1
1
1
valves. H and 13C{ H} chemical shifts (δ, ppm) are reported
relative to either the residual protiated solvent or deuterated-
carbon resonances of the solvent, respectively. 31P{ H} NMR
1
spectra were recorded in units of parts-per-million (ppm) rel-
ative to external 85% H3PO4. H and 13C{ H} NMR spectra
of the hydration products were obtained in DMSO-d6. Com-
plex 1 was prepared from Super-Hydride and [(dippe)NiCl2]
1
1
Scheme 4. Mechanistic proposal for the hemihydration of 1,2-DCB at 120 and
180 ◦C, using nickel(0) catalysts.

C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
145
[20] suspended in hexane as previously reported [21]; the
4.2. Reaction of [(dippe)NiH]2 (1) with 1,2-DCB:
neutral alumina used for the preparation of the nickel(I) di-
␮-hydride dimer was heated to 200 ◦C under vacuum for 2
days and stored in the glovebox, prior to its use. The chelat-
ing bisphosphine ligand, 1,2-bis(di-isopropylphosphino)ethane
(dippe) was synthesized from 1,2-bis(dichlorophosphino)ethane
(Strem) and isopropylmagnesium chloride (2.0 M solution in
THF, Aldrich), following the reported procedure [22]. The dini-
trile reactants 1,2-DCB (98%), 1,3-DCB (98%), and 1,4-DCB
(98%) were purchased from Aldrich and were used without
further purification. The water used for all hydrations was dis-
tilled and was purged with argon for at least 30 min prior to
use. All other chemicals used, filter aids and chromatographic
materials were reagent grade and were used as received. The cat-
alytic experiments were performed by the in situ preparation of
the respective nickel(0) complex [(dippe)Ni(␩2-N,C-1,n-(CN)2-
benzene)] (n = 2–4), unless otherwise stated. The total amount
of nitrile used, was calculated on the basis of 0.5 mol% of the
corresponding nickel(0) catalyst, as calculated on the basis of
the total mole amount of nickel(0) versus the total mole amount
of nitrile functionalities available, such that every mole of dini-
trile substrate affords two moles of nitrile functionalities that
may be subject to hydration. All the hydration products were
purified by column chromatography, unless otherwise stated
and the quoted yields are isolated yields. Characterization of
preparation of [(dippe)Ni(η2-N,C-1,2-(CN)2-benzene)] (2)
The reaction of [(dippe)NiH]2 (0.020 g, 0.031 mmol) and
a 2:1 excess of 1,2-DCB (0.008 g, 0.062 mmol), yielded
the formation of the monocoordinated nickel(0) complex
[(dippe)Ni(␩2-N,C-1,2-(CN)2-benzene)] (2). The reagents were
mixed at room temperature, adding the 1,2-dicyanobenzene to
a dark red THF-d8 solution (1 mL) of the nickel(I) dimer. After
mixing, a strong effervescence was observed to occur; all the
released gas was vented to the glovebox. The mixture was left
under stirring for 1 h, after which time it was examined by
NMR. On standing in solution for 24 h at room temperature,
in the absence of additional water, the oxidative addition com-
plex [(dippe)Ni(CN)(2-CN-phenyl)] (5) gradually forms. NMR
spectra of 2 in THF-d8 solution: 1H, δ 7.64 (m, 1H, CH), 7.45 (m,
1H, CH), 7.29 (m, 1H, CH), 7.07 (m, 1H, CH), 2.2–1.9 (m, 4H,
1
CH), 1.85–1.6 (m, 4H, CH2), 1.2–0.92 (m, 24H, CH3). 13C{ H},
δ 169.9 (dd, J1 = 72.4 Hz, J2 = 28.2 Hz, coordinated CN), 137.8
(s, C), 134.5 (s, CH), 132.6 (s, CH), 129.5 (s, CH), 128.1 (s,
CH), 118.6 (s, CN), 110.6 (s, C), 25.9 (d, JC–P = 22.6 Hz, CH),
24.5 (d, JC–P = 24 Hz, CH), 23.0–22.5 (m, CH2), 20.4 (s, CH3),
1
20.2 (s, CH3), 19.6 (s, CH3), 19.2 (s, CH3). 31P{ H}, δ 80.2
2
2
(d, JP–P = 63 Hz), 69.4 (d, JP–P = 63 Hz). NMR spectra of 5
in THF-d8 solution: 31P{ H}, δ 86.2 (d, J = 25 Hz), 74.3 (d,
1
2
1
1
these was made by direct comparison of the H and 13C{ H}
NMR spectra and melting points of the products, with those
of expressly prepared standards and available literature [23].
Elemental analyses and mass spectra (MS-EI+) of the purified
organics were carried out by USAI-UNAM using an EA 1108
FISONS Instruments analyser and a Jeol SX-102A mass spec-
trometer, respectively. Infrared spectra were obtained using a
Perkin-Elmer 1600 FT spectrophotometer. All the ammonia pro-
duced from catalysis experiments at 180 ◦C was bubbled from
the reactor into concentrated hydrochloric acid before opening
the reactor vessel; the resulting acid solution been neutral-
ized after, using NaHCO3. The mixture of ammonium chloride
(NH4Cl) and sodium chloride (NaCl) produced from this pro-
cedures, was then filtered in buchner, dried and analysed by
X-raypowderdiffraction(PowderXRD);theresultsofwhichare
included in the Supporting Information of this work. All Powder
XRD analyses were performed using graphite monochromatized
2J = 25 Hz).
4.3. Reaction of [(dippe)NiH]2 (1) with 1,3-DCB:
preparation of [(dippe)Ni(η2-N,C-1,3-(CN)2-benzene)] (3)
The reaction of [(dippe)NiH]2 (0.020 g, 0.031 mmol) and
a 2:1 excess of 1,3-DCB (0.008 g, 0.062 mmol), yielded
the formation of the monocoordinated nickel(0) complex
[(dippe)Ni(␩2-N,C-1,3-(CN)2-benzene)] (3). The reagents were
mixed at room temperature, similarly to the procedures
described for 1,2-dicyanobenzene, adding the amount of 1,3-
dicyanobenzene to a dark red toluene-d8 solution (1 mL) of the
nickel(I) dimer. On standing in solution for 24 h at room temper-
ature, in the absence of additional water, the oxidative addition
complex [(dippe)Ni(CN)(3-CN-phenyl)] (6) gradually evolves.
1
NMR spectra of 3 in toluene-d8 solution: H, δ 7.82–7.97 (m,
1H, CH), 7.09 (m, 2H, CH), 7.2–6.88 (m, br, 1H, CH), 2.12–1.7
(m, 4H, CH), 1.6–1.4 (m, 4H, CH2), 1.2–0.9 (m, 24H, CH3).
˚
Cu K␣ radiation (λ = 1.5406 A) in a Siemens D5000 diffrac-
1
tometer;byUSAI-UNAM. Allexperimentalmeltingpointswere
obtained by closed capillary methods, using an Electrother-
mal Digital Melting Point Apparatus. All the turnover numbers
(TON) for the catalytic hydrations in this work were calculated
as moles of isolated product over moles of nickel(0) catalyst,
multiplied by a factor of 1 in the case of cyanobenzamides, 2 for
diamides, and 4 for dicarboxylic acids, according to the degree
of hydration achieved in each product. Turnover frequencies
(TOF) are calculated as TON over reaction time. All the calcu-
13C{ H}, δ 162.9 (dd, J1 = 73 Hz, J2 = 28.5 Hz, coordinated
CN), 142.3 (s, CH), 140.4 (s, CH), 135.5 (s, CH), 135.3 (s, CH),
126.5 (s, C), 117 (s, CN), 114 (s, C), 25.9 (d, JC–P = 22.1 Hz,
CH), 24.5 (d, JC–P = 24 Hz, CH), 22.9–22.3 (m, CH2), 20.41 (s,
1
CH3), 20.38 (s, CH3), 19.2 (s, CH3), 18.05 (s, CH3). 31P{ H},
δ 77.6 (d, 2JP–P = 63 Hz), 65.9 (d, 2JP–P = 63 Hz). NMR spectra
of 6 in THF-d8 solution: 31P{ H}, δ 81.9 (d, 2JP–P = 24.5 Hz),
1
70.9 (d, 2JP–P = 24.5 Hz).
1
lated 1H and 13C{ H} NMR spectra in this work were obtained
4.4. Reaction of [(dippe)NiH]2 (1) with 1,4-DCB:
using ACD/HNMR Predictor [24] and ACD/CNMR Predictor
[25], respectively; the chemical formulas for all the calculated
structures in these spectra, obtained using ACD/ChemSketch
[26].
preparation of [(dippe)Ni(η2-N,C-1,4-(CN)2-benzene)] (4)
The reaction of [(dippe)NiH]2 (0.020 g, 0.031 mmol) and
a 2:1 excess of 1,4-DCB (0.008 g, 0.062 mmol), yielded

146
C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
1
NH2). 13C{ H}, δ 166.3 (carbonyl), 134.4 (s, C), 131.4 (s, CH),
the formation of the monocoordinated nickel(0) complex
[(dippe)Ni(␩2-C,N-1,4-(CN)2-benzene)] (4). The reagents were
mixed at room temperature, similarly to the procedure
described for 1,2-dicyanobenzene, adding the amount of 1,4-
dicyanobenzene to a dark red toluene-d8 solution (1 mL) of
the nickel(I) dimer. No oxidative addition of the C–CN bond
to the nickel(0) center in 4 was obtained at room temper-
ature, after 24 h in solution; however, as reported before in
Ref. [9b], on warming a solution of this complex to 50 ◦C for
12 h in the absence of additional water, the oxidative addi-
tion complex [(dippe)Ni(CN)(4-CN-phenyl)] (7) was indeed
obtained. Also, as reported in that same reference, the use of an
equimolecular mixture of [(dippe)NiH]2 (0.040 g, 0.062 mmol)
and 1,4-terephthalonitrile (0.008 g, 0.062 mmol) in solution,
allowed the production of the doubly coordinated dinitrile
complex[(dippe)Ni2(␩2-,␩2-C,N-1,4-(CN)2-benzene)](8)[9b].
Recrystallisation of 8 from hexanes precipitates this product in
pure crystalline form. NMR spectra of 4 in toluene-d8 solution:
1H, δ 7.6 (d, J = 8 Hz, 2H, CH), 6.98 (d, J = 8.0 Hz, 2H, CH),
2.01–1.88 (m, 4H, CH), 1.85–1.71 (m, 4H, CH2), 1.28–1.09
130.5 (s, CH).
5.2. Total hydration of 1,3-DCB at 180 ◦C: production of
1,3-isophthalic acid
The reactor vessel was loaded in the glovebox with
[(dippe)NiH]2 (0.0801 g, 0.124 mmol), 1,3-DCB (3 g,
0.023 mol) and water (21 mL, 1.17 mol). The mixture was
heated at 180 ◦C, under vigorous stirring for 72 h, after which
time the reactor vessel was left to cool down and opened in a
hood prior to work-up; all the ammonia produced in the reactor
during the hydration process was bubbled into a concentrated
hydrochloric acid before opening the reactor vessel. A brown
crude solid residue was removed from the reactor vessel and
subjected to acid/base purification, dissolving it in a concen-
trated solution of NaOH, which was then filtered through a
frit. Dropwise addition of concentrated HCl until a neutral pH,
precipitated a white powder, that was recovered as a pure mate-
rial after repeated washings using distilled water. The washed
product was vacuum dried overnight (P < 10−4 mmHg). Yield
of 1,3-isophthalic acid after work-up: 68% (2.61 g, 0.016 mol),
with a TON of 259 and a TOF of 4 cycles per hour. Mp of
1,3-isophthalic acid: >250 ◦C (sublimes). MS (EI+): m/z = 166.7
(molecular ion). Losses: m/z = 149 (–OH), 121 (–COOH). Anal.
Calcd. for C8H6O4 (1,3-isophthalic acid): C 57.8, H 3.6.
Found: C 57.9, H 3.8. NMR spectra for 1,3-isophthalic acid in
DMSO-d6: 1H, δ 13 (s, br, 2H, OH), 8.4 (m, 1H, CH), 8.2 (m,
(m, 24H, CH3). 13C{ H}, δ 169.9 (dd, J1 = 30 Hz, J2 = 9 Hz,
1
coordinated CN), 134.2 (s, C), 132.6 (s, CH), 130.1 (s, CH),
119.4 (s, CN), 112.3 (s, C), 26.2–25.2 (m, CH), 23.6–22.4 (m,
CH2), 20.5 (s, CH3), 20.2 (s, CH3), 19.5 (s, CH3), 19.3 (s, CH3).
1
2
2
31P{ H}, δ 77.5 (d, JP–P = 63 Hz), 65.7 (d, JP–P = 63 Hz).
NMR spectra of 7 in toluene-d8 solution: 31P{ H}, δ 81.7
1
2
2
(d, JP–P = 23.5 Hz), 70.9 (d, JP–P = 23.5 Hz). NMR spectra
1
of 8 in THF-d8: H, δ 7.82–7.97 (m, 1H, CH), 7.09 (m, 2H,
CH), 7.2–6.88 (m, br, 1H, CH), 2.12–1.7 (m, 4H, CH), 1.6–1.4
2H, CH), 7.6 (m, 1H, CH). 13C{ H}, δ 166.7 (carbonyl), 133.5
1
1
(m, 4H, CH2), 1.2–0.9 (m, 24H, CH3). 13C{ H}, δ 169.2
(s, CH), 131.3 (s, CH), 130.1 (s, CH), 129.2 (s, C).
(dd, J1 = 30 Hz, J2 = 10 Hz, coordinated CN), 133 (s, C), 130.5
(s, CH), 26.7 (d, JC–P = 22.6 Hz, CH), 26.5 (d, JC–P = 24 Hz,
CH), 26–25.5 (m, CH2), 20.6 (s, CH3), 19.99 (s, CH3), 19.53
5.3. Partial hemihydration of 1,3-DCB at 120 ◦C:
production of 1,3-cyanobenzamide
1
2
(s, CH3), 19.2 (s, CH3). 31P{ H}, δ 79.9 (d, JP–P = 68 Hz),
67.9 (d, 2JP–P = 68 Hz).
The reactor vessel was loaded in the glovebox with
[(dippe)NiH]2 (0.0801 g, 0.124 mmol), 1,3-DCB (3 g,
0.023 mol) and water (21 mL, 1.17 mol). The mixture was
heated at 120 ◦C, under vigorous stirring for 72 h, after which
time the reactor vessel was left to cool down and opened in
a hood prior to work-up, which was performed following the
procedure described infra for 4-cyanobenzamide. Yield of
1,3-cyanobenzamide after work-up: 86% (2.92 g, 0.020 mol)
with a TON of 82 and a TOF of 1 cycle per hour. Mp of
1,3-cyanobenzamide: 225–228 ◦C. Anal. Calcd. for C8H6N2O1
(1,3-cyanobenzamide): C 65.1, H 4.1, N 19.1. Found: C
65.1, H 3.9, N 19.1. NMR spectra for 1,3-cyanobenzamide in
DMSO-d6: 1H, δ 8.22 (m, 1H, CH), 8.08 (m, 1H, CH), 8.0 (m,
5. Catalysis
5.1. Hemihydration of 1,2-DCB at 180 and 120 ◦C:
production of 1,2-phthalamide
The reactor vessel was loaded in separate runs with [(dippe)
NiH]2 (0.0801 g, 0.124 mmol), 1,2-DCB (3 g, 0.023 mol) and
water (21 mL, 1.17 mol). The resulting mixtures were heated at
180 and 120 ◦C for 72 h, similarly to the procedures already
described. In either case, a green crude solid residue was
removed from the reactor vessel with the aid of additional water.
The aqueous solutions were each filtered through a frit. Water
was removed from the residues by evaporation and these were
recrystallised from hot methanol, precipitating a white crys-
talline solid in each case, using hexane. Yield of 1,2-phthalamide
at 180 ◦C, after work-up: 71% (2.6 g, 0.016 mol) with a TON of
135 and a TOF of 2 cycles per hour. Yield of 1,2-phthalamide
at 120 ◦C, after work-up: 71% (2.6 g, 0.016 mol) with a TON
of 135 and a TOF of 2 cycles per hour. Mp of 1,2-phthalamide:
222–225 ◦C. NMR spectra for 1,2-phthalamide in DMSO-d6:
1H, δ 8.04 (m, 2H, CH), 7.54 (m, 2H, CH), 7.12 (s, br, 4H,
1
1H, CH), 7.64 (m, 1H, CH), 7.63 (br, s, 2H, NH2). 13C{ H},
δ 166.4 (carbonyl), 135.3 (s, C), 134.8 (s, CH), 132.3 (s, CH),
131.1 (s, CH), 129.8 (s, CH), 118.4 (s, CN), 111.5 (s, C).
5.4. Total hydration of 1,4-DCB at 180 ◦C: production of
1,4-terephthalic acid
The reactor vessel was loaded in the glovebox with [(dippe)
NiH]2 (0.0801 g, 0.124 mmol), 1,4-DCB (3 g, 0.023 mol) and

C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
147
water (21 mL, 1.17 mol). The mixture was heated at 180 ◦C,
Appendix A. Supplementary data
under vigorous stirring for 72 h, after which time the reac-
tor vessel was left to cool down and opened in a hood prior
to work-up; all the ammonia produced in the reactor dur-
ing the hydration process was bubbled into a concentrated
hydrochloric acid before opening the reactor vessel. A white
crude solid residue was removed from the reactor vessel and
subjected to acid/base purification, following the procedure for
1,3-isophthalic acid, described above. Yield of 1,4-terephthalic
acid after work-up: 86% (3.36 g, 0.020 mol), with a TON of
325 and a TOF of 5 cycles per hour. Mp of 1,4-terephthalic
acid: >300 ◦C (sublimes). NMR spectra for 1,4-terephthalic acid
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.molcata.2006.10.054.
References
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The reactor vessel was loaded in two separate runs
with [(dippe)NiH]2 (0.0801 g, 0.124 mmol), 1,4-DCB (3 g,
0.023 mol) and water (21 mL, 1.17 mol); the second run been
additionally charged with 50 mL of THF. Each mixture was
then heated at 120 ◦C, under vigorous stirring for 72 h, after
which time the reactor vessel was left to cool down and opened
in a hood prior to work-up. A white crude solid residue was
removed from the reactor vessel in both occasions and puri-
fied by column chromatography eluting over neutral alumina.
Unreacted 1,4-DCB was recovered as the first fraction, elut-
ing with ethyl acetate only. 4-Cyanobenzamide was recovered
as the second fraction, eluting with a 1:1 (v/v) mixture of
ethyl acetate and acetone. Solvent evaporation yielded a white
crystalline powder from the two experiments, which was char-
acterized as 1,4-cyanobenzamide. Yield of 1,4-cyanobenzamide
produced in the absence of THF, after work-up: 68% (2.34 g,
0.016 mol) with a TON of 64 and a TOF of 1 cycle per
hour. Yield of 1,4-cyanobenzamide produced in the pres-
ence of THF, after work-up: 87% (3 g, 0.020 mol) with a
TON of 83 and a TOF of 1 cycle per hour. Mp of 1,4-
cyanobenzamide: 225–228 ◦C. MS (EI+): m/z = 146 (molecular
ion). Losses: m/z = 130 (–NH2), 102 (–CONH2), 44 (–C7H4N).
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4.1, N 19.1. Found: C 65.0, H 3.9, N 18.9. NMR spectra for
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8.02 (m, 2H, CH), 7.86 (m, 2H, CH), 7.64 (s, br, 1H, NH).
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1
13C{ H}, δ 166.5 (carbonyl), 138.3 (s, C), 132.4 (s, CH), 128.3
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Acknowledgements
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We thank DGAPA-UNAM (IN-205603) and CONACYT
(C02-42467) for their support to this work. MGC also thanks
CONACYT for a Ph.D. grant.

148
C. Criso´stomo et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 139–148
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[18] The alternative of nickel(0) going on and off for catalysis would imply
that all nickel(0) intermediates required to yield the complete hydration of
1,3- and 1,4-DCB would have been formed within 72 h, at 180 ◦C. In the
case of 1,2-DCB the same premise might imply additionally, that at the
same temperature the free nickel catalysts should coordinate to the 1,2-
phthalamide produced in situ in a fashion not conducive towards further
hydration, therefore, not producing the corresponding dicarboxylic acid.
Still, the selectivity and yield afforded at 120 ◦C for such product and not
to2-cyanobenzamidewhichwouldbeexpectedtoformotherwise, specially
if free [(dippe)Ni] catalysts were to react randomly, an explanation based
on an intramolecular migration of these species was found to be reasonable,
at least for the time being.
[14] The smaller magnitudes of the 2JC–P coupling constants for the coordinated
–CN group in complex 4 have been attributed to the electron withdrawing
effect that is imposed by the other cyano substituent that is present in 1,4-
DCB. In this instance, previous Hammett studies with a number of electron
donating and electron withdrawing substituents in the para-position of the
benzene ring (the case of 1,4-DCB been addressed in such studies) have
shown that the latter ones induce the localization of negative charge around
the ipso carbon of the coordinated –CN moiety (see Ref. [9b]). In the light of
such results, one possible outcome is that the magnitude of ␲-back bonding
to the nickel(0) center may be expected to diminish as a consequence of
this Ni␦+–C␦− polarization, therefore, affecting the magnitude of the 2JC–P
coupling constants; an effect that is seemingly most dramatic in the case
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dihydro-C-oxo-biaddition of water promoted by the second –CN is
expected to exist in all DCB substrates. The extent of such effect is expected
to be particularly dramatic in the case of complex 4 as it shows the smaller
2JC–P coupling constants from the series (indicated in Table 2) and in this
instance, it seems reasonable to conclude that from all DCB substrates, it
is this complex that would depict the more electron poor character at the
coordinated –CN moiety and thus probably, the faster hydration rate.
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derivative to the [(dippe)Ni] moiety is proposed on the basis of its sim-
ilarity with an imine; the hydroxy N-protonated imines that result from
the concerted N,N-dihydro-C-oxo-biaddition of water to ␩2-C,N coordi-
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(d) The National Institute of Advanced Industrial Science and Technology
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[25] Advanced Chemistry Development Inc., ACD/CNMR Predictor, Version
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[26] Advanced Chemistry Development Inc., ACD/ChemSketch, Version 5.08,
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