Highly active, chemo- and enantioselective Pt-SPO catalytic systems for the synthesis of aromatic carboxamides

Article abstract of DOI:10.1039/c5cy00627a

Platinum complexes modified with a chiral non-racemizing SPO preligand 1 have been applied in the hydration of aromatic nitriles. [Pt(1)₃Cl]Cl formed readily from Pt(COD)Cl₂. The chiral secondary phosphine oxide complex showed moderate activity in the hydration of para- and meta-substituted benzonitriles, but failed in converting the ortho-substituted derivatives. The hydride complex PtH(PR₂OH)(PR₂O-H?OR₂P) (PR₂OH = 1) formed from Pt(PPh₃)₄ and 1, and the cationic complex derived from [Pt(1)₃Cl]Cl via direct chloride abstraction with AgNO₃ were proven to be considerably more active, allowing us to extend the scope to the hydration of ortho-substituted aromatic nitriles, including axially chiral [1,1′-binaphthalene]-2,2′-dicarbonitrile. In the hydration of the racemic dinitrile, successful kinetic resolution has been achieved. The catalysts derived from non-racemizing 1 are the first chiral transition metal-SPO complexes that provide kinetic resolution in the hydration of a racemic chiral nitrile.

Full text of DOI:10.1039/c5cy00627a

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Highly active, chemo- and enantioselective Pt-SPO catalytic systems for the
synthesis of aromatic carboxamides
Henrik Gulyás,a Ivan Rivilla,b Simona Curreli,c Zoraida Freixa,d,e Piet W.N.M. van Leeuwenc*
a XiMo Hungary Ltd., Budapest, Hungary
b Department of Organic Chemistry I, University of the Basque Country (UPV/EHU), and Donostia
International Physics Center (DIPC), San Sebastián - Donostia, Spain
c Institute of Chemical Research of Catalonia (ICIQ), Avda Països Catalans 16, 43007, Tarragona, Spain.
pvanleeuwen@iciq.es
d Department of Applied Chemistry, Faculty of Chemistry, University of the Basque Country (UPV-EHU),
San Sebastián, Spain.
e IKERBASQUE, Basque Foundation for Science, Bilbao, Spain.
Graphical Abstract
Abstract
Platinum complexes modified with a chiral non-racemizing SPO preligand 1 have been applied in the
hydration of aromatic nitriles. [Pt(1)3Cl]Cl formed readily from Pt(COD)Cl2. The chiral secondary
phosphine oxide complex showed moderate activity in the hydration of para- and meta-substituted
benzonitriles, but failed in converting the ortho-substituted derivatives. The hydride complex
PtH(PR2OH)(PR2O--H--OR2P) (PR2OH = 1) formed from Pt(PPh3)4 and 1, and the cationic complex derived
1

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from [Pt(1)3Cl]Cl via direct chloride abstraction with AgNO3 proved considerably more active, allowing us
to extend the scope to the hydration of ortho-substituted aromatic nitriles, including axially chiral [1,1’-
binaphthalene]-2,2’-dicarbonitrile. In the hydration of the racemic dinitrile successful kinetic resolution
has been achieved. The catalysts derived from non-racemizing 1 are the first chiral transition metal-SPO
complexes that provide kinetic resolution in the hydration of a racemic chiral nitrile.
Main text
Benzamide derivatives are widely used in chemical industries. They are applied as synthetic fibers,
pharmaceutical agents, building blocks in supramolecular chemistry, ligands in transition metal
complexes.1 Among the various possible synthetic routes towards amides, the selective hydration of
nitriles stands out as the most “atom economic” and “greenest” procedure, if carried out under
appropriate conditions. The addition of water as sole stoichiometric reagent to nitriles seems to be the
ideal reaction to produce N-unsubstituted amides. Although the C≡N triple bond is remarkably inert, the
functional group can be activated with appropriate catalysts. For instance, the hydration of organic
nitriles can be catalyzed with strong acids and bases. On the downside it should be noted that these
simple catalysts require the application of rather harsh conditions, which may lead to the formation of
the corresponding carboxylic acids, thus compromising the chemoselectivity of the reaction. Enzyme
catalysis is a much more efficient alternative, requiring significantly milder conditions and providing
higher selectivities.2 Another advantage of enzyme catalysis is that racemic chiral nitriles can be
kinetically resolved.3 Several transition metal complexes (with much simpler structures than those of
enzymes) have also been reported as catalysts for the selective hydration of nitriles under mild
conditions. The most active transition metal catalysts include Co(III), Pt(II), Ru(II), Ru(IV), Pd(II), Rh(I), and
Au(I) complexes.4 Parkins and Ghaffar showed that the platinum-hydride complex of dimethylphosphine
oxide, PtH(PMe2OH)(PMe2O--H--OMe2P), as well as the corresponding chloride complex,
PtCl(PMe2OH)(PMe2O--H--OMe2P), are active catalysts for the hydration of nitriles.5 Thereafter, de Vries
and co-workers applied platinum complexes of the chiral secondary phosphine oxide (SPO), PhtBuP(O)H,
in the hydration of various nitriles.6 Although the complexes of the chiral ligand were active and
chemoselective, they did not induce any enantioselectivity in the case of racemic chiral substrates. The
authors found that the P-chiral SPO racemized under the reaction conditions, which may explain the lack
of kinetic resolution.7
Although, to the best of our knowledge no chiral transition metal complex exists up to date capable of
kinetic resolution of racemic chiral nitriles, an example of enantioselective desymmetrization of a Cs
2

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symmetric dinitrile, MeBnC(CN)2, has recently been published. The best enantiomeric excess of the
monoamide product MeBnC(CN)(CONH2), 62% at 9% yield, was achieved with a ruthenium complex
modified with a chiral sulfonyldiamine ligand.8
In our laboratories we have developed a facile synthetic route towards a secondary phosphine oxide that
appears to have structural features ideal for platinum catalyzed hydration of nitriles. SPO 1 is a chiral
derivative of dimethylphosphine oxide, the preligand that provides the most active platinum based
catalysts for the hydration of aromatic nitriles (Figure 1). Being equipped with the chiral binaphthyl
substituent, DMPO evolves into the chiral, non-racemizing SPO 1, gaining the potential for kinetic
resolution in the case of racemic chiral nitriles.
Figure 1. Design of the preligand for platinum catalyzed hydration of aromatic nitriles
SPO 1 is synthesized via the hydrolysis of the corresponding binaphthophosphepin-1-amine. Recently we
have improved the synthesis by avoiding the isolation of the binaphthophosphepinamine, and modifying
the conditions of the hydrolysis (Scheme 1).9
Scheme 1. Improved synthesis of 1
3

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SPO 1 readily reacts with commercially available Pt(II) and Pt(0) precursors forming well-defined
complexes (Scheme 2), some of which we have found to be efficient precatalysts for nitrile hydration.
The square planar cis-Pt(1)2Cl2 generated from Pt(COD)Cl2 with two equivalents of 1 proved entirely
inactive, but the chloride and hydride precursors with three coordinating SPO-s, [Pt(1)3Cl]Cl and
PtH(PR2OH)(PR2O--H--OR2P) (PR2OH = 1), both provided the active, supposedly cationic complex under
catalytic conditions.5b (routes A and C in Scheme 2) The formation of the putative active species could
also be facilitated with the combination of the Pt(COD)Cl2 precursor, SPO 1, and AgNO3 as halogen
sponge. (route B in Scheme 2)
Scheme 2. Formation of precatalysts and the putative catalytically active species for nitrile hydration via the
combination of SPO 1 and common Pt(II) and Pt(0) precursors
After optimization of the catalytic conditions,10 the performance of the three active systems was
compared in the hydration of a carefully chosen set of benzonitrile derivatives. The substrates were
selected so that clear conclusions could be drawn how electronic and steric effects of the substituents
influenced reactivity.
4

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Scheme 3. Selective hydration of aromatic nitriles into carboxamides using the Pt(COD)Cl2/1 catalytic system
H2O
O
CN
C
Pt(COD)Cl2/1
t-amyl alcohol, 80 o
FG
FG
NH2
C
O
O
O
NH2
NH2
NH2
a
b
c
Br
t = 2h, yield: 16%
t = 24h, yield: 95%
t = 2h, yield: 15%
t = 24h, yield: 97%
t = 2h, yield: 51%, para-Br = +0.232
t = 24h, yield: 99% (99%)
O
Br
O
O
Br
NH2
NH2
NH2
d
e
F
f
t = 2h, yield: 60%, meta-Br = +0.393
t = 24h, yield: >99% (97%)
t = 2h, yield: 1.7%
t = 24h, yield: 11%
t = 2h, yield: 19%, para-F = +0.062
t = 24h, yield: >99%
O
NH2 O
O
NH2
NH2
NH2
g
h
i
H2N
HO
t = 2h, yield: 0%,
-NH2 = -0.66
t = 2h, yield: 0%, para-OH = -0.37
t = 24h, yield: 64%
t = 2h, yield: 0%
para
t = 24h, yield: 51%
t = 24h, yield: 20%
O
NH2
j
O
NH2
k
t = 2h, yield: 1.3%
t = 24h, yield: 45%
t = 2h, yield: 1.4%
t = 24h, yield: 19%
General conditions: substituted benzonitrile (0.5 mmol), Pt(COD)Cl2 (0.01 mmol), 1 (0.035 mmol, 1:Pt ratio: 3.5), t-amyl alcohol (3
mL), H2O (0.6 mL), 80 oC, 2 or 24 hours, reactions performed in air. The given yields are GC yields. Complete chemoselectivity
was observed in all cases. Isolated yields are shown in brackets. Hammett constant s is shown for each meta and para substituent.
First the substrate scope of precatalyst [Pt(1)3Cl]Cl was surveyed. The complex was generated in situ
from Pt(COD)Cl2 and 3.5 equivalents of 1. The results are shown in Scheme 3. In situ generated
[Pt(1)3Cl]Cl catalyzed the hydration of aromatic nitriles, but the reactivity of the substrates strongly
depended on their electronic and steric nature. Importantly, in all instances complete chemoselectivity
was observed, no hydrolysis of the amide functionality could be detected by TLC, GC, GC-MS or NMR. In
the course of the hydration of benzonitrile, at 2 mol% catalyst loading, [Pt(1)3Cl]Cl provided 16%
conversion in two hours. Increasing the reaction time to 24 hours the GC yield of benzamide reached
95% (a in Scheme 3). In the case of substituted benzonitriles we have found that the conversions
observed at an early stage of the reaction nicely correlated with the Hammett substituent constants.11
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Electron withdrawing groups clearly facilitated the hydration of the C≡N triple bond, while electron
donating groups strongly impeded the catalytic activation of the substrate. The highest initial rate, 60%
conversion after two hours, was observed for 3-bromobenzonitrile (d in Scheme 3). This observation is
in perfect accordance with the fact that the Hammett constant of the meta-bromo substituent has the
highest positive value, +0.393, in the pool of the chosen functional groups. 4-Bromobenzonitrile (σpara-Br
=
+0.23) gave a lower initial rate, 51% conversion (c in Scheme 3). Nevertheless, within 24 hours the
catalytic system fully converted both meta- and the para-bromobenzonitrile. The products were isolated
as pure crystalline materials in excellent yields (c and d, Scheme 3).12 The conversion of 4-
fluorobenzonitrile into the corresponding amide after two hours of reaction time, 19%, hardly differs
from the conversion of benzonitrile, 16%, in accordance with the fact that the fluorine atom in the para
position of a phenyl ring is only slightly electron withdrawing (σpara-F = +0.0629, f and a in Scheme 3).
Finally, it is worth noting that the strongly electron donating para-hydroxy and para-amino substituents
(σpara-OH = -0.37, σpara-NH2 = -0.66, g and h in Scheme 3) completely suppressed the initial rates of the
reactions. Considering steric effects, the catalytic results clearly show that ortho-substituents strongly
impede the reaction, regardless of their electronic nature. No activity was detected after two hours of
reaction when the strongly electron donating amino group and the electron withdrawing bromo atom
were introduced as ortho-substituents (e and i in Scheme 3). Nevertheless, some conversion was
observed at 24 hours, 20% and 11% respectively. The comparison of these values suggests that the size
of the ortho-substituent is more important than their electronic nature, since the larger bromo atom
suppressed the reaction more effectively than the electron donating amino group (e and i in Scheme 3).
We should mention that in order to gain preliminary information on the full catalytic potential of the
new platinum complex, [Pt(1)3Cl]Cl, we also tested two aliphatic nitriles, phenylacetonitrile and 2-
phenylpropanenitrile, as substrates, and we found that their reactivity falls well behind that of the
benzonitrile derivatives (j and k in Scheme 3).
Having presumed that the putative catalytically active species had been generated from [Pt(1)3Cl]Cl via
the hydrolysis of the Pt–Cl bond, formation of the corresponding hydroxide complex, and dissociation of
the hydroxide ion from the coordination sphere,5b we expected increased catalytic activity from the
hydride precursor, and particularly from the Pt(COD)Cl2/1/AgNO3 system. The hydride complex
PtH(PR2OH)(PR2O--H--OR2P) (PR2OH = 1) was generated in situ from Pt(PPh3)4 and 3.5 equivalents of 1.13
Direct chloride extraction from the chloride precursor was achieved via in situ mixing Pt(COD)Cl2, 1 and
AgNO3 in a 1:3.5:2 ratio. The two catalytic systems were tested in the same set of test reactions as
[Pt(1)3Cl]Cl. The results are summarized in Scheme 4.
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Scheme 4. Selective hydration of aromatic nitriles into carboxamides using the Pt(PPh3)4/1 and Pt(COD)Cl2/AgNO3/1
catalytic systems
H2O
O
CN
C
Pt(PPh3)4/1 or Pt(COD)Cl2/AgNO3/1
t-amyl alcohol, 80 oC, 1 hour
FG
FG
NH2
O
O
O
NH2
NH2
NH2
a
b
c
Br
Pt(PPh3)4/1, yield: >99%
Pt(PPh3)4/1, yield: >99%
Pt(PPh3)4/1, yield: >99%
Pt(COD)Cl2/AgNO3/1, yield: >99% (>99%)
Pt(COD)Cl2/AgNO3/1, yield: >99%
Pt(COD)Cl2/AgNO3/1, yield: 99% (99%)
O
Br
O
O
Br
NH2
NH2
NH2
d
e
F
f
Pt(PPh3)4/1, yield: >99%
Pt(PPh3)4/1, yield: 96%
Pt(PPh3)4/1, yield: >99%
Pt(COD)Cl2/AgNO3/1, yield: >99% (97%)
Pt(COD)Cl2/AgNO3/1, yield: 88% (87%)
Pt(COD)Cl2/AgNO3/1, yield: >99% (>99%)
O
NH2 O
O
NH2
NH2
NH2
g
i
h
H2N
HO
Pt(PPh3)4/1, yield: >99%
Pt(PPh3)4/1, yield: 91%
Pt(PPh3)4/1, yield: 74%
Pt(COD)Cl2/AgNO3/1, yield: 99% (92%)
Pt(COD)Cl2/AgNO3/1, yield: >99% (92%)
Pt(COD)Cl2/AgNO3/1, yield: 93% (93%)
O
O
NH2
NH2
k
j
Pt(PPh3)4/1, yield: >99%
Pt(PPh3)4/1, yield: 99%
Pt(COD)Cl2/AgNO3/1, yield (i.y.): >99% (92%)
Pt(COD)Cl2/AgNO3/1, yield: 99% (99%)
General conditions: substrate (0.5 mmol); Pt(PPh3)4 (0.01 mmol), 1 (0.035 mmol) or Pt(COD)Cl2 (0.01 mmol), 1 (0.035 mmol), AgNO3 (0.02 mmol); t-
amyl alcohol (3 mL), water (0.6 mL), 80 °C, 1 hour. The experiments involving Pt(PPh3)4 were carried out under argon. Reactions involving Pt(COD)Cl2
were performed in air. The given yields are GC yields. Complete chemoselectivity was observed in all cases. Isolated yields are shown in brackets.
In general, both the hydride complex and the precursor generated by direct chloride extraction showed
markedly higher catalytic activities than [Pt(1)3Cl]Cl. Para- and meta-substituted benzonitriles gave in
most cases complete conversions within one hour, irrespective of the electronic properties of the
substituents. The application of the Pt(PPh3)4/1 and Pt(COD)Cl2/1/AgNO3 systems also significantly
improved the rates of the hydration of the sterically hindered benzonitrile derivatives. Interestingly, in
the case of the 2-bromobenzonitrile the Pt(PPh3)4/1 proved more active, providing carboxamide e in 96%
yield,14 while in the hydration of 2-aminobenzonitrile the Pt(COD)Cl2/1/AgNO3 system was found more
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efficient, converting 93% of the substrate into carboxamide i in one hour. Pt(PPh3)4/1 and
Pt(COD)Cl2/1/AgNO3 effectively converted aliphatic substrates, as well (j and k, Scheme 4).
The enhanced activity of the in situ formed hydride and cationic precursors, that is, their capacity to
hydrate ortho-substituted nitriles, enabled us to set more challenging goals. Thus, we turned our
attention to the chiral racemic [1,1’-binaphthalene]-2,2’-dicarbonitrile, formally a bulky ortho-
substituted biscarbonitrile. The reactions were carried out at 5% catalyst loading, using either Pt(PPh3)4/1
or Pt(COD)Cl2/AgNO3/1, and 70 °C. The product distributions and enantiomeric ratios for both the
substrate and the products were determined at increasing reaction times (Table 1, Figure 2). Conversions
of the substrate at 0.5h, 1h, 1.5h and 2h were comparable for the two catalytic systems, with the
Pt(COD)Cl2/AgNO3/1 system starting slightly faster but becoming more sluggish at longer reaction times.
Both catalytic systems provided complete chemoselectivities again. Only three products could be
observed in the reaction mixtures: the unreacted, enantioenriched dinitrile (2), the mononitrile-
monoamide intermediate (3), and the diamide (4). The racemic dinitrile (substrate), the enantioenriched
dinitrile (2), as well as the diamide (4), have been characterized by X-ray crystallography.15 Considering
the similar activities of the two catalytic systems, we were surprised to see that there were significant
differences in their enantioselectivities. While Pt(PPh3)4/1 at 15% HPLC yield of the dihydrated product 4
provided virtually complete enantioselectivity, Pt(COD)Cl2/AgNO3/1 at 17% yield induced only 85:15
enantiomeric ratio (Entries 1, 5 in Table 1). The same phenomenon was observed for the kinetic
resolution of the substrate, although in that case it could be detected only at higher conversions. After
half an hour both the yields and the enantioselectivities were still very similar (Entries 1 and 5, Table 1).
After one hour the yields for the enantioenriched substrate were still comparable, 33% and 37%, but the
enantioselectivities were rather different. The enantiomeric ratio reached 90:10 using the Pt(PPh3)4/1
system, but only 81:19 when the Pt(COD)Cl2/AgNO3/1 catalytic system was applied (Entries 2 and 6,
Table 1). The difference becomes even more pronounced at longer reaction times. The enantiomeric
ratio of the remaining dinitrile reaches 98:2 after two hours in the presence of Pt(PPh3)4/1, while it is
only 86:14 when the hydration is catalyzed with the Pt(COD)Cl2/AgNO3/1 system (Entry 4 and 8, Table 1).
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Table 1. Kinetic resolution in the hydration of [1,1’-binaphthalene]-2,2’-dicarbonitrile using the Pt(PPh3)4/1 and
Pt(COD)Cl2/AgNO3/1 catalytic systems
2
3
4
Entry
Catalyst
Time Conv.
Yield; E.r.
Yield; E.r.
Yield; E.r.
1
2
3
4
Pt(PPh3)4/1 0.5h
Pt(PPh3)4/1 1h
Pt(PPh3)4/1 1.5h
45%
67%
77%
83%
55%; 29/71
33%; 10/90
23%; 4/96
17%; 2/98
30%; 32/68 15%; >99/1
32%; 50/50 35%; 86/14
27%; 72/28 50%; 83/17
23%; 86/14 60%; 76/24
Pt(PPh3)4/1
2h
Pt(COD)Cl2/
5
6
7
8
0.5h
48%
63%
72%
74%
52%; 28/72
37%; 19/81
28%; 14/86
26%; 14/86
31%; 33/67 17%; 85/15
30%; 45/55 33%; 84/16
27%; 56/44 45%; 80/20
25%; 61/39 49%; 78/22
AgNO3/1
Pt(COD)Cl2/
1h
1.5h
2h
AgNO3/1
Pt(COD)Cl2/
AgNO3/1
Pt(COD)Cl2/
AgNO3/1
General conditions: substrate (0.1 mmol); Pt(COD)Cl2 (0.005 mmol), 1 (0.0175 mmol), AgNO3 (0.01 mmol) or
Pt(PPh3)4 (0.005 mmol), 1 (0.0175 mmol); t-amyl alcohol (3 mL), water (0.6 mL), 80 °C. The experiments involving
Pt(PPh3)4 were carried out under argon.
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Figure 2. Product distribution as a function of time in the hydration of [1,1’-binaphthalene]-2,2’-dicarbonitrile,
using the Pt(PPh3)4/1 (top) and Pt(COD)Cl2/AgNO3/1 (bottom) catalytic systems; the enantiomers are arbitrarily
labelled with the Greek letters ρ and σ
We do not have sufficient data to derive the relative rate constants, but one can see from Figure 2 (top)
that 2σ reacts approximately 4 times faster than 2ρ, while the enantiomeric ratios in Table 1 for 2
indicate values up to 5 in the plot derived from Kagan´s equation.16
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Conclusions
In summary, we have shown that Pt(II) complexes of chiral, non-racemizing SPO 1 are efficient catalysts
for the selective hydration of aromatic nitriles. A broad range of electronically and sterically different
substrates could be converted into the desired aromatic carboxamide products. The novel catalysts also
provided significant kinetic resolution in the hydration of the chiral racemic 2,2’-dicarbonitrile-1,1’-
binaphthyl. These are the first examples of transition metal-SPO complexes that are capable of kinetic
resolution of a chiral nitrile. We believe that the successful kinetic resolution may partly originate from
the fact that the catalyst was based on a non-racemizing (i.e. not P-chiral) SPO preligand. This aspect of
the ligand design could be generally important in a broad range of SPO based enantioselective transition
metal catalyzed reactions.
Acknowledgements
Financial support by Spanish MICINN (CTQ2011-23333) is kindly acknowledged. We are grateful to Mr.
Eduardo Carmelo Escudero and Dr. Eddy Martin for determining the X-ray structures of SPO 1, and
various carboxamides isolated in the course of this study.
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6 X. Jiang, A. J. Minnaard, B. L. Feringa, J. G. de Vries, J. Org. Chem., 2004, 69, 2327.
7 For examples of successful asymmetric catalysis using SPO-transition metal complexes see: (a) N. V. Dubrovina, A.
Börner, Angew. Chem. Int. Ed., 2004, 43(44), 5883; (b) X. Jiang, ; A. J. Minnaard, B. Hessen; B. L. Feringa, A. L. L.
Duchateau, J. G. O. Andrien, J. A. F. Boogers, J. G. de Vries, Org. Lett., 2003, 5(9), 1503; (c) H. Landert, F. Spindler,
A. Wyss, H.-U. Blaser, B. Pugin, Y. Ribourduoille, B. Gschwend, B. Ramalingam, A. Pfaltz, Angew. Chem. Int. Ed.,
2010, 49(38), 6873; (d) K. Dong, Y. Li, Z. Wang, K. Ding, Organic Chemistry Frontiers, 2014, 1(2), 155; (e) K. Dong, Y.
Li, Z. Wang, K. Ding, Angew. Chem. Int. Ed., 2013, 52(52), 14191.; (f) K. Dong, Y. Li, Z. Wang, K. Ding, J. Am. Chem.
Soc., 2012, 134(30), 12474; (g) X.-B. Wang, M. Goto, L.-B. Han, Chem. Eur. J., 2014, 20(13), 3631.
8 S. Kamezaki, S. Akiyama, Y. Kayaki, S. Kuwata, T. Ikariya Tetrahedron: Asymmetry, 2010, 21, 1169.
9 For the earlier, non-optimized procedure see: P. M. Castro, H. Gulyás, J. Benet-Buchholz, C. Bo, Z. Freixa, P. W. N.
M. van Leeuwen, Catal. Sci. Technol., 2011, 1, 401.
10 For details of the optimization of P:Pt ratio and solvent see the Supporting Information.
11 (a) L. P. Hammett J. Am. Chem. Soc., 1937, 59, 96; (b) C. Hansch, A. Leo, R. W. Taft, Chem. Rev., 1991, 91, 165.
12 For X-ray structures of the 3-bromobenzamide and 4-bromobenzamide formed using the Pt(COD)Cl2/1 catalytic
system see the supporting information.
13 Our approach was based on a method published by one of us: P. W. N. M. van Leeuwen, C. F. Roobeek, J. H. G.
Frijns, Organometallics, 1990, 9, 1211. For details see the supporting information.
14 For the X-ray structure of 2-bromobenzamide formed using the Pt(PPh3)4/1 catalytic system see the supporting
information.
15
It is worth noting that we were able to obtain single crystals both from the starting racemic dinitrile, and the
enantioenriched dinitrile. The former crystallizes in the achiral P21/c space group, while the latter crystallizes in the
chiral P21 space group. We could also obtain single crystals from the enantioenriched diamide. In relation to
structure of the diamide we should note that the space group of the crystals, the achiral P21/n, indicated that they
could not be completely enantiopure. Details can be found in the supporting information.
16 J. M. Goodman, A.-K. Köhler, S. C. M. Alderton, Tetrahedron Lett., 1999, 40, 8715.
12

Page 13 of 13
Catalysis Science & Technology
View Article Online
DOI: 10.1039/C5CY00627A
Highly active, chemo- and enantioselective Pt-SPO catalytic systems for the
synthesis of aromatic carboxamides
Henrik Gulyás,a Ivan Rivilla,b Simona Curreli,c Zoraida Freixa,d,e Piet W.N.M. van Leeuwenc*
a XiMo Hungary Ltd., Budapest, Hungary
b Department of Organic Chemistry I, University of the Basque Country (UPV/EHU), and Donostia
International Physics Center (DIPC), San Sebastián - Donostia, Spain
c Institute of Chemical Research of Catalonia (ICIQ), Avda Països Catalans 16, 43007, Tarragona, Spain.
pvanleeuwen@iciq.es
d Department of Applied Chemistry, Faculty of Chemistry, University of the Basque Country (UPV-EHU),
San Sebastián, Spain.
e IKERBASQUE, Basque Foundation for Science, Bilbao, Spain.
Table of contents
Platinum complexes of the chiral non-racemizing SPO ligand 1 have been discovered to be the first
artificial transition metal complexes providing kinetic resolution in the hydration of a racemic chiral
nitrile.
1