Dinuclear zinc(II) complexes with hydrogen bond donors as structural and functional phosphatase models

Article abstract of DOI:10.1021/ic5009945

It is becoming increasingly apparent that the secondary coordination sphere can have a crucial role in determining the functional properties of biomimetic metal complexes. We have therefore designed and prepared a variety of ligands as metallo-hydrolase mimics, where hydrogen bonding in the second coordination sphere is able to influence the structure of the primary coordination sphere and the substrate binding. The assessment of a structure-function relationship is based on derivates of 2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4- methylphenol (HBPMP = HL¹) and 2-{[bis(pyridin-2-ylmethyl)amino] methyl}-6-{[(2-hydroxybenzyl)(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol (H₂BPBPMP = H₂L⁵), well-known phenolate-based ligands for metallo-hydrolase mimics. The model systems provide similar primary coordination spheres but site-specific modifications in the secondary coordination sphere. Pivaloylamide and amine moieties were chosen to mimic the secondary coordination sphere of the phosphatase models, and the four new ligands H₃L², H₃L³, HL⁴, and H₄L⁶ vary in the type and geometric position of the H-bond donors and acceptors, responsible for the positioning of the substrate and release of the product molecules. Five dinuclear Zn^II complexes were prepared and structurally characterized in the solid, and four also in solution. The investigation of the phosphatase activity of four model complexes illustrates the impact of the H-bonding network: the Michaelis-Menten constants (catalyst-substrate binding) for all complexes that support hydrogen bonding are smaller than for the reference complex, and this generally leads to higher catalytic efficiency and higher turnover numbers.

Full text of DOI:10.1021/ic5009945

Article
pubs.acs.org/IC
Dinuclear Zinc(II) Complexes with Hydrogen Bond Donors as
Structural and Functional Phosphatase Models
†
,‡
,†
‡
‡
Simone Bosch, Peter Comba,* Lawrence R. Gahan, and Gerhard Schenk
†
Anorganisch-Chemisches Institut, Universitat
̈
Heidelberg, INF 270, D-69120, Heidelberg, Germany
School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
S Supporting Information
‡
*
ABSTRACT: It is becoming increasingly apparent that the secondary coordination sphere can
have a crucial role in determining the functional properties of biomimetic metal complexes. We
have therefore designed and prepared a variety of ligands as metallo-hydrolase mimics, where
hydrogen bonding in the second coordination sphere is able to influence the structure of the
primary coordination sphere and the substrate binding. The assessment of a structure−function
relationship is based on derivates of 2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4-
1
methylphenol (HBPMP = HL ) and 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-6-{[(2-
5
hydroxybenzyl)(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol (H BPBPMP = H L ),
2
2
well-known phenolate-based ligands for metallo-hydrolase mimics. The model systems provide
similar primary coordination spheres but site-specific modifications in the secondary
coordination sphere. Pivaloylamide and amine moieties were chosen to mimic the secondary
2
3
4
coordination sphere of the phosphatase models, and the four new ligands H L , H L , HL , and
3
3
6
H L vary in the type and geometric position of the H-bond donors and acceptors, responsible
for the positioning of the substrate and release of the product molecules. Five dinuclear Zn
4
II
complexes were prepared and structurally characterized in the solid, and four also in solution. The investigation of the
phosphatase activity of four model complexes illustrates the impact of the H-bonding network: the Michaelis−Menten constants
(
catalyst−substrate binding) for all complexes that support hydrogen bonding are smaller than for the reference complex, and
this generally leads to higher catalytic efficiency and higher turnover numbers.
INTRODUCTION
■
The facile catalyzed cleavage of phosphoesters is a crucial
reaction for living organisms, for example in processing RNA
replication and bone metabolism, and it is of ecological
importance in the detoxification of pesticides. Natural
phosphatases, which accomplish this hydrolysis, commonly
II
II
contain Zn ions in their active sites. Zn is frequently chosen
by nature due to its high Lewis acidity, fast ligand exchange, and
flexibility of the coordination geometry. Therefore, dizinc(II)
complexes have been widely used as artificial models to expand
our understanding of the hydrolysis mechanism in the native
enzymes. Two structural forms for the binding of the substrate
have been proposed, and three mechanisms of the nucleophilic
attack at the phosphorus atom during the hydrolysis of
phosphoesters by dinuclear metalloenzymes and their model
compounds have been discussed; these structures and
Figure 1. Proposals for the substrate binding and the three possibilities
for the nucleophilic attack on the phosphorus atom during
phosphoester hydrolysis by dinuclear metalloenzymes and model
compounds.
guanidine groups near the dimetal site of model complexes
have demonstrated a significant impact of hydrogen bonding on
9
−14
the efficiency of phosphoester cleavage.
In order to study
the precise role of hydrogen bonding and the magnitude of the
resulting increase in reactivity, attempts have now been made to
combine the two strategies, i.e., hydrogen bonding in the
second coordination sphere and asymmetrization of the
dinuclear coordination site, by introducing symmetric and
asymmetric hydrogen bonding in model systems and
investigating the emerging structural properties and phospha-
tase reactivities. The model systems adopted for this
comparative study are the symmetric phenolate-based ligand
1
−5
mechanistic proposals are depicted in Figure 1.
Studies with model systems revealed that complexes with the
II
two Zn ions in two different coordination geometries catalyze
the hydrolysis of the highly stable P−O bond more efficiently
4
−8
than symmetric analogues.
These complexes also reflect
structural properties of the natural enzyme more precisely. The
influence of the metal ions and of the first coordination sphere
has been studied in much detail previously, but the influence of
the secondary coordination sphere has not been fully
appreciated so far. Recent studies with ammonium, amido, or
Received: April 30, 2014
©
XXXX American Chemical Society
A
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Inorganic Chemistry
Article
HBPMP (2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4-
obtained by reaction of 3-(chloromethyl)-2-hydroxy-5-methyl-
benzaldehyde (2) with bis(pyridin-2-ylmethyl)amine (1)
(Scheme 1), followed by reaction with N,N-bis((2-pivaloyla-
methylphenol) and its asymmetric counterpart H BPBPMP
2
(
2-{[bis(pyridin-2-ylmethyl)amino]methyl}-6-{[(2-
3
4
hydroxybenzyl)(pyridin-2-ylmethyl)amino]methyl}-4-methyl-
phenol), labeled HL and H L here (see Chart 1). HL and
midopyridin-6-yl)methyl)amine (4), yielding ligand H L ; HL
3
1
5
1
3
2
was generated by deprotection of the amine moieties in H L .
H L was prepared following the same procedure but using 2-
3
6
4
a
Chart 1. Series of Ligands Discussed in This Work
(((pyridin-2-ylmethyl)amino)methyl)phenol (1a) as secondary
amine in the first step.
II
1
2
3
4
The dinuclear Zn complexes of HL , H L , H L , HL , and
3
3
6
H L were obtained from the metal-free ligands and
Zn (OAc) in methanol. Addition of sodium hexafluorido-
4
II
2
phosphate resulted, upon standing, in X-ray quality crystals of
1
2
the five complexes [Zn (L )(OAc) ]PF , [Zn (H L )(OAc) ]-
2
2
6
2
2
2
3
4
PF , [Zn (H L )(OAc)(OH)]PF , [Zn (L )(OAc) ]PF , and
Zn (H L )(OAc)(OH)], and the corresponding structures
6
2
2
6
2
2
6
6
[
2 2
facilite the visualization of the H-bonding interactions,
promoted by different ligands in the solid state and the analysis
of the influence of the hydrogen bond donors on the
II
coordination geometry of the two Zn centers. The structural
studies in the solid were then extended to the solution state,
1
using H NMR spectroscopy, and correlated with the solution
hydrolytic reactivity.
Structural Characterization of the Complexes. Solid-
1
State Structures. The structures of [Zn (L )(OAc) ]PF ,
2
2
6
2
3
[
[
Zn (H L )(OAc) ]PF , [Zn (H L )(OAc)(OH)]PF ,
2 2 2 6 2 2 6
4
6
Zn (L )(OAc) ]PF , and [Zn (H L )(OAc)(OH)] are com-
2
2
6
2
2
posed of the respective ligand anions, resulting from the
deprotonation of the phenol backbone and the additional
a
Atom numbers refer to the assignments in Figures 3−6.
6
II
phenol moiety in H L , two Zn ions, bridging acetate anions,
4
and a noncoordinated hexafluoridophosphate anion (except for
5
6
H L were derivatized with amino and pivaloylamido residues
the neutral complex [Zn
(H
2
L )(OAc)(OH)]). Selected bond
2
2
at symmetric and asymmetric positions, in order to mimic the
secondary coordination sphere and analyze its influence on the
symmetry of the complexes and their reactivity (Chart 1). Here
we report the Zn chemistry of these ligands in terms of their
reactivity as biomimetic phosphate hydrolysis catalysts.
lengths and valence angles of the complexes are displayed in
3
Table 1. When [Zn (H L )(OAc)(OH)]PF was reacted in
2 2 6
acetonitrile with an excess of the unreactive phosphomonoester
II
4-nitrophenyl phosphate (PNPP), the substrate−catalyst
3
adduct [Zn (H L )(O POC H NO )]PF crystallized (this
2
2
3
6
4
2
6
structure is discussed in more detail below; the structural
data are included in Table 1).
RESULTS AND DISCUSSION
■
II
II
1
2
Synthesis of the Ligands and Their Zn Complexes.
While the dinuclear Zn complexes of the ligands HL , H
3
L ,
1
2
4
The previously reported ligands HL and H L were prepared
and HL show the common structure for this type of phenolate-
3
3
6
II
with minor modifications according to literature proce-
based complex, reaction of H L or H L with Zn (OAc)
3 4 2
1
3,15,16
3
4
1
dures.
The asymmetric ligands H L and HL were
resulted in a different coordination geometry. In [Zn (L )-
3
2
3
4
6
Scheme 1. Synthesis of the Asymmetric Ligands H L , HL , and H L
3
4
B
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Inorganic Chemistry
Table 1. Selected Bond Lengths (Å) and Angles (deg) for [Zn (L )(OAc) ]PF , [Zn (H L )(OAc) ]PF ,
Article
1
2
2
2
6
2
2
2
6
3
3
4
6
[
Zn (H L )(OAc)(OH)]PF , [Zn (H L )(O POC H NO )]PF , [Zn (L )(OAc) ]PF , and [Zn (H L )(OAc)(OH)]
2 2 6 2 2 3 6 4 2 6 2 2 6 2 2
1
2
3
3
4
6
[
(
Zn (L )
[Zn (H L )
[Zn (H L )(OAc)
[Zn (H L )
[Zn (L )
[Zn (H L )(OAc)
2
2
2
2
2
2
2
2
2
2
+
+
+
+
+
OAc)2]
(OAc)2]
(OH)]
(O POC H NO )]
(OAc)2]
(OH)]
3
6
4
2
Zn(1)···Zn(2)
Zn(1)−O(1)
Zn(1)−O(2A)
Zn(1)−O(2B)
Zn(1)−N(1)
Zn(1)−N(2)
3.3714(4)
2.0135(14)
2.1825(16)
2.0088(15)
2.2346(19)
2.2306(19)
2.1443(19)
2.0342(14)
2.0198(17)
2.0849(16)
2.223(2)
3.3992(6)
2.025(3)
2.092(3)
2.056(3)
2.169(3)
2.214(3)
2.284(3)
2.000(3)
2.039(3)
2.077(3)
2.155(3)
2.199(3)
2.289(3)
3.5422(7)
1.954(3)
2.003(3)
3.6971(8)
1.987(3)
2.011(3)
3.3948(10)
1.994(4)
2.112(4)
2.008(4)
2.216(5)
2.206(5)
2.132(5)
1.995(4)
2.008(4)
2.114(4)
2.239(5)
2.165(5)
2.123(5)
3.5892(6)
1.9904(19)
2.065(2)
2.057(3)
2.233(2)
2.102(3)
2.120(2)
2.133(3)
2.074(4)
2.269(4)
2.062(4)
2.140(3)
1.941(3)
2.096(2)
2.213(2)
1.934(2)
2.1380(19)
2.102(2)
a
Zn(1)−N(3)
Zn(2)−O(1)
Zn(2)−O(3A)
Zn(2)−O(3B)
Zn(2)−N(4)
Zn(2)−N(5)
Zn(2)−N(6)
Zn(2)−O(6)
Zn(2)−O(5)
b
2.322(3)
2.136(3)
2.336(3)
1.945(2)
2.443(4)
2.133(4)
2.107(4)
2.295(2)
2.148(2)
2.473(2)
1.9571(19)
2.247(2)
2.1764(19)
2.122(3)
Zn(1)−O(1)−Zn(2)
O(1)−Zn(1)−N(1)
O(1)−Zn(1)−N(2)
112.80(7)
87.65(6)
88.88(7)
163.19(7)
87.91(6)
100.20(6)
86.73(7)
87.53(6)
163.04(7)
100.51(6)
92.43(6)
115.23(13)
89.95(12)
87.20(11)
160.92(12)
89.64(11)
100.55(11)
93.20(12)
88.29(12)
159.77(12)
101.25(11)
90.00(11)
120.75(12)
118.71(12)
91.48(11)
124.82(11)
99.48(12)
127.16(17)
136.52(16)
89.85(14)
100.53(16)
98.94(13)
116.65(18)
88.63(18)
88.12(17)
161.07(18)
89.65(16)
101.16(17)
91.46(16)
89.20(17)
162.28(16)
98.04(17)
88.12(15)
120.73(9)
130.04(9)
91.80(8)
109.92(9)
90.21(8)
a
O(1)−Zn(1)−N(3)
b
O(1)−Zn(1)−O(2A)
O(1)−Zn(1)−O(2B)
O(1)−Zn(2)−N(4)
O(1)−Zn(2)−N(5)
O(1)−Zn(2)−N(6)
O(1)−Zn(2)−O(3A)
O(1)−Zn(2)−O(3B)
O(1)−Zn(2)−O(6)
O(5)−Zn(2)−O(1)
88.66(10)
90.65(11)
161.27(10)
87.91(11)
162.62(14)
91.55(14)
87.68(14)
93.42(13)
86.80(8)
91.44(9)
161.12(8)
91.27(8)
b
102.84(10)
107.30(8)
100.35(13)
3
a
6
b
+
3
+
In the case of [Zn (H L )(OAc)(OH)] N(3) is O(1a). In the case of [Zn (H L )(OAc)(OH)] , [Zn (H L )(O POC H NO )] , and
2
2
2
2
2
2
3
6
4
2
6
[
Zn (H L )(OAc)(OH)] O(2A) is O(2) and O(3A) is O(3).
2 2
2
4
6
(
OAc) ]PF , [Zn (H L )(OAc) ]PF , and [Zn (L )(OAc) ]-
PF and [Zn (H L )(OAc)(OH)] are doubly bridged by the
6 2 2
2
6
2
2
2
6
2
2
II
PF6 both Zn ions are coordinated in a six-coordinate
arrangement and are bridged by the ligand backbone phenoxo
group and two acetate coligands. The remaining coordination
sites are occupied by the nitrogen donors of two pyridine
phenoxo group of the supporting ligand and an acetate
coligand; the coordination environment of the octahedral
Zn(2) site is completed by a hydroxido group; this is unusual
and confirmed by comparison with the structures of previously
2
II
ligands and the tertiary amines. The structure of [Zn (H L )-
published Zn complexes with aqua, μ-hydroxido, and terminal
2
2
(
OAc) ]PF is shown in Figure 2a.
hydroxido donor groups. For example, for the dizinc(II)
2
6
3
1
1
In contrast to the other ligands, the reaction of H L with
complex of HL , [Zn (L )(OH ) ](ClO ) , Zn−OH distances
3
2
2 2
4 3
2
II
Zn (OAc) resulted in the asymmetric dizinc(II) complex
are on the order of 2.04 Å, and the corresponding distances to
bridging hydroxido ligands are reduced to 1.99 Å, as in
2
3
II
[
Zn (H L )(OAc)(OH)]PF (Figure 2b). Zn(1), the Zn ion
2 2 6
1
18
in the amide-free binding site, adopts here a pentacoordinate
trigonal bipyramidal geometry (τ = 0.94; τ = 1 and τ = 0 for
regular trigonal bipyramidal and square pyramidal geometries,
respectively). The trigonal plane is formed by the donors of
two pyridines and the bridging phenoxo group, and the Zn
center is out of the trigonal plane by 0.257 Å toward O(2). The
axial positions are occupied by the tertiary amine and an acetate
oxygen donor. The asymmetric ligand H L forms a similar
complex, [Zn (H L )(OAc)(OH)], when treated with Zn
[Zn (L )(μ-OH)](ClO ) . Similar Zn−(μ-OH) distances
2
4 2
have been found for a variety of dizinc(II) complexes:
7
7
[{(L )Zn} (μ-OH) ](ClO ) ] (1.983(3) Å; L = N-methyl-N-
2
2
4 2
1
7
((6-neopentylamino-2-pyridyl)methyl)-N-((2-pyridyl)methyl)-
II
8
amine), [{(L )Zn} (μ-OH) ](ClO ) ·0.5CH CN] (2.070(3)
2
2
4 2
3
Å; L8 = N-methyl-N-((6-neopentylamino-2-pyridyl)methyl)-
9
N-((2-pyridyl)ethyl)amine), [Zn (L )(μ-OH)(py) ](ClO ) ]
2
2
4 2
6
(1.946(3) Å; HL9 = 2,6-bis(N-((2-dimethylamino)ethyl)-
4
6
II
10
iminomethyl)-4-methylphenol), [Zn (L )(μ-OH)(py) ]-
(ClO ) (1.951(4) Å; HL = 2,6-bis(N-((2-pyridyl)ethyl)-
iminomethyl)-4-methylphenol), [Zn (L )(μ-OH)](ClO ) ]
2 4 2
(1.943(3)) Å.
2
2
2
3
10
acetate (Figure 2c). The five donors around the Zn(1) ion in
4 2
6
1
[
Zn (H L )(OAc)(OH)] arrange in a coordination geometry
2
2
1
8−20
1
with a τ-value of 0.58, in between a trigonal bipyramidal and a
square pyramidal geometry. In both complexes [Zn (H L )-
Interestingly, with HL , there is an
3
asymmetric acetate-bridged dizinc(III) structure with a
2
2
6
II
(OAc)(OH)]PF and [Zn (H L )(OAc)(OH)], the second
pentacoordinate Zn site and a hexacoordinate site, similar to
6
2
2
II
II
Zn ion, Zn(2), is six-coordinate, similar to the Zn sites in
our structures in Figure 2b,c; however, in the published
1
2
4
1
[
Zn (L )(OAc) ]PF , [Zn (H L )(OAc) ]PF , and [Zn (L )-
structure with HL , the coordination sphere of the
2
2
6
2
2
2
6
2
II
3
(OAc) ]PF . The two Zn ions in [Zn (H L )(OAc)(OH)]-
hexacoordinate site is completed by a methanol molecule
2
6
2
2
C
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Inorganic Chemistry
Article
3
3
[
.936 Å in [Zn (H L )(OAc)(OH)]PF and 4.199 Å in−
2
2
6
6
Zn (H L )(OAc)(OH)] support the assignment of the OH
2 2
group in question as a terminal hydroxido coligand.
We are not aware of any other example with a terminal
II
hydroxido coligand in dinuclear Zn complexes with similar
phenolate-based ligand scaffolds. The observation of the two
hydroxido complexes is consistent with the proposition that the
hydrogen bond donors, i.e., the two adjacent amide residues at
II
3
the binding site of one Zn center of [Zn (H L )(OAc)-
2
2
6
(
OH)]PF and [Zn (H L )(OAc)(OH)], stabilize this unusual
6 2 2
hydroxido coligand. Moreover, the hydrogen bond donor
3
formation within the structures of [Zn (H L )(OAc)(OH)]PF
2
2
6
6
and [Zn (H L )(OAc)(OH)] is confirmed by the observed
2
2
geometry of the amide hydrogen atoms with respect to the free
electron pairs of the hydroxido oxygen atom. This is in
agreement with the previous finding that the incorporation of
two H-bond donors (neopentylamino groups) in tripodal N
4
II
ligands leads to the generation of the stable Zn −OH complex
11
11
[
Zn(L )(OH)](ClO ) due to H-bonding (L = N,N-bis(6-
4
neopentylamino-2-pyridylmethyl)-N-(2-pyridylmethyl)amine);
3
6
[
[
∼
Zn (H L )(OAc)(OH)]PF , [Zn (H L )(OAc)(OH)], and
2 2 6 2 2
1
1
Zn(L )(OH)](ClO ) have a similar Zn−O distance of
4
21
1.94 Å. Hydrogen bond formation in the mononuclear
II
11
Zn complex [Zn(L )(OH)](ClO ) was proposed from the
4
short distances between the amino nitrogen and hydroxido
21
oxygen atoms (2.741 and 2.727 Å); the corresponding
3
6
distances for [Zn (H L )(OAc)(OH)]PF and [Zn (H L )-
2
2
6
2
2
(
OAc)(OH)] are listed in Table 2. This table also contains the
2
corresponding distances for [Zn (H L )(OAc) ]PF and
2
2
2
6
4
[Zn (L )(OAc) ]PF , and those between the amine or amide
2 2 6
nitrogen atoms and the nearby acetate oxygen atoms are in the
range of 2.750 and 2.982 Å. These short distances demonstrate
that the desired hydrogen bond formation is also present in
these complexes. Importantly, the protons of the amine or
amide moieties in question point toward the oxygen atoms of
the bridging acetate groups.
2
Figure 2. POV-Ray plots of (a) [Zn (H L )(OAc) ]PF , (b)
2
2
2
6
In all five complexes discussed here as well as in the catalyst−
3
6
[
Zn (H L )(OAc)(OH)]PF , and (c) [Zn (H L )(OAc)(OH)],
II
2
2
6
2
2
substrate complex discussed below, the Zn ions are
showing hydrogen bonding (green dotted lines; counterions, non-
coordinated solvent molecules, and hydrogen atoms not involved in
hydrogen bonding are omitted for clarity; labels are included only for
atoms discussed in the text or tables; ORTEP plots with 50%
probability level thermal ellipsoids of all complexes appear as
Supporting Information).
coordinated in the anti-configuration with respect to the
II
II
phenoxide ring. The resulting Zn ···Zn distances (see Table
1
) are at the short end of the range reported for similar
II
dinuclear Zn complexes. The variation of ligand symmetry and
substituents in the range of the five ligands discussed here leads
II
II
to only a relatively small variation of the Zn ···Zn distance
4
5
with a Zn−OHMe distance of 2.0849(8) Å. Therefore, the
(3.37 to 3.59 Å, phosphate-bridged complex excluded).
3
II
II
Zn−O distances in [Zn (H L )(OAc)(OH)]PF (1.945(2) Å)
Importantly, the Zn ···Zn distances are slightly elongated in
3
2
2
6
6
and [Zn (H L )(OAc)(OH)] (1.9571(19) Å) are significantly
the asymmetric complexes [Zn
2
(H
[Zn (H L )(OAc)(OH)] to 3.54 and 3.59 Å. Consequently,
2 2
2
L )(OAc)(OH)]PF and
6
2
2
6
shorter than in reported complexes with terminal aqua ligands
and compare with the range of complexes containing bridging
hydroxides. This supports the interpretation of our data as rare
examples with a terminal hydroxido group coordinated to one
II
II
the Zn −O−Zn angle is increased there to ∼120°, close to a
highly symmetric trigonal angle with respect to the phenoxide
II
II
bridge, and this compares with Zn −O−Zn angles in the
range 112.8° to 116.1° in the more symmetric derivatives
II
of the two Zn centers. Moreover, the Zn(1)···OH distances of
2
3
Table 2. Selected Distances (Å) Corresponding to H-Bond Formation in [Zn (H L )(OAc) ]PF , [Zn (H L )(OAc)(OH)]PF ,
2
2
2
6
2
2
6
4
6
[
Zn (L )(OAc) ]PF , and [Zn (H L )(OAc)(OH)]
2
2
6
2
2
2
+
3
+
4
+
6
[
Zn (H L )(OAc) ]
[Zn (H L )(OAc)(OH)]
[Zn (L )(OAc) ]
[Zn (H L )(OAc)(OH)]
2 2
2
2
2
2
2
2
2
N(7)−O(2B)
N(7)−O(3A)
N(7)−O(6)
N(8)−O(3A)
N(8)−O(6)
2.982(4)
2.803(9)
2.750(8)
2.810(4)
2.875(4)
D
2.764(3)
2.870(3)
2.977(5)
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
2
4
[
(
Zn (L )(OAc) ]PF , [Zn (H L )(OAc) ]PF , and [Zn (L )-
2
2
6
2
2
2
6
2
3
OAc) ]PF . This suggests that the asymmetric ligands H L
2
6
3
6
and H L enforce a cavity that leads to the complexation of two
Zn ions in different coordination geometries: one Zn site is
trigonal bipyramidal, the geometry found for both Zn ions in
the active site of phospholipase C, and the other Zn site in
the asymmetric model system with H L is square bipyramidal,
as in the Ser/Thr phosphatase-1. Interestingly and as
expected, the biomimetic systems [Zn (H L )(OAc)(OH)]PF
and [Zn (H L )(OAc)(OH)] demonstrate the formation of a
4
II
II
II
22
II
3
3
2
3
3
2
2
6
6
2
2
hydrogen-bond network similar to that found in the active site
3
of the native enzymes. The environment engendered by H L
3
and H4L6 upon complexation with Zn ions mimics the
structural characteristics of the backbone built by the nucleic
acids within the active site of phosphatases more accurately
than other model systems published to date.
II
1
L2 (bottom)
3
Figure 3. Aromatic region of the H NMR spectra of H
2
+
and [Zn (H L )(OAc) ] (top) in CD CN.
2
2
2
3
2
Infrared Spectroscopy. Solid-state FT-IR measurements of
the metal-free ligands and the complexes were studied and
compared in order to investigate the strength of hydrogen
group of H L as well as for the acetate coligands was visible in
2
1
2
+
the H NMR spectrum of [Zn (H L )(OAc) ] (see
Supporting Information). H NMR measurements were also
conducted in mixtures of CD CN/D O, which resulted in
similar resonances, leading to identical interpretations, but with
lower resolution of the spectra. Importantly, the stepwise
addition of sodium deuteroxide (up to a pH value of 10.5 for
the deuterium oxide phase) did not show a significant shift of
the resonances (see Supporting Information).
2
2
2
1
24
bonds (see Supporting Information for the IR spectra). The
3
2
2
3
6
very similar IR spectra of H L , H L , and H L show the N−H
3
3
4
−1
vibrational band at around 3440 cm . Due to the weakening of
the N−H bond emerging from hydrogen bond formation, this
−1
N−H vibrational band is shifted to 3295 cm in the spectrum
2
3
of [Zn (H L )(OAc) ]PF . In the spectra of [Zn (H L )-
2
2
2
6
2
2
6
3
+
(
OAc)(OH)]PF and [Zn (H L )(OAc)(OH)] there are only
The asymmetry of [Zn (H L )(OAc)(OH)] in solution
6
2
2
2 2
very broad N−H vibrational bands, and this suggests that the
(similar to the observations in the solid, see above) emerges
from its H NMR spectrum, where the aromatic region exhibits
24−26
1
hydrogen bonds are even stronger in these complexes.
Mass Spectrometry. In order to investigate the complex
structure of the dizinc(II) complexes in solution, mass
spectrometric data were obtained in acetonitrile (see
Supporting Information). All highest mass peaks show the
16 resonances (Figure 4, top). In this complex, every hydrogen
atom has a different electronic environment, leading to the
difference in the spectrum, when compared to the metal-free
ligand (Figure 4, bottom). The resonances from the protons
II
II
distinctive isotopic pattern of dinuclear Zn complexes; the m/
proximal to the Zn centers show a downfield shift, while
z separation of 0.5 between the peaks within the isotopic
pattern suggests the presence of doubly charged species. In the
protons that are distant from the metal centers, especially those
pointing to the opposite side of the phenolate backbone, show
an upfield shift. Similarly, the proton signals of each methylene
group are separated, which gives rise to a set of 12 doublets in
the region between 3.3 and 4.5 ppm (Figure 5, top). This
implies that the electronic environment of protons bound to
the same methylene carbon are not identical, in contrast to the
spectrum of the free ligand (Figure 5, bottom), and this again is
consistent with the observed X-ray structure (see above). The
coupling to the other hydrogen atom of the same carbon center
leads to the appearance of doublets. As a result of the
asymmetry within this structure, the two tert-butyl groups in
1
case of [Zn (L )(OAc) ]PF , the highest mass peak was found
2
2
6
1
at m/z 360.0704 (calcd 360.0689), corresponding to [Zn (L )-
OAc)] . The corresponding singly charged species [Zn (L )-
OAc)] was found at m/z 779.1507 (calcd 779.1517). The
highest mass peak for [Zn (H L )(OAc) ]PF at m/z 429.1283
2
2
+
1
(
(
2
+
2
2
2
2
6
2
2+
(
[
calcd 429.1268) was likewise assigned to [Zn (H L )] . For
2 2
3
Zn (H L )(OAc)(OH)]PF the highest mass peaks at m/z
2 2 6
4
29.1298 (calcd 429.1268) and m/z 917.2757 (calcd 917.2674)
3
2+
3
+
were assigned to [Zn (H L )] and [Zn (H L )(OAc)] . In
the case of [Zn (L )(OAc) ]PF , a [Zn (L )] species was
2
2
2
2
4
4
2+
2
2
6
2
3
+
detected with m/z 344.0730 (calcd 344.0701). The highest
[Zn (H L )(OAc)(OH)] give rise to two resonances in the
2 2
6
1
mass peak in the spectra of [Zn (H L )(OAc)(OH)] was
H NMR spectrum. Unfortunately, the poor solubility of
2
2
6
2+
6
found at 435.6226 and assigned to [Zn (H L )] .
[Zn (H L )(OAc)(OH)] made it impossible to conduct a
2
2
2
2
1
NMR Studies. In order to study the symmetry of the
comparable set of H NMR measurements for this complex.
Although the crystal structure of [Zn (L )(OAc) ]PF
1
13
4
complexes in solution H and C NMR spectra were measured
in deuterated acetonitrile. The equivalence of the two binding
2
2
6
suggests that, in the solid state, the complex is symmetric, the
2
1
sites of [Zn (H L )(OAc) ]PF on the NMR time scale was
H NMR spectrum exhibits 16 resonances in the aromatic
2
2
2
6
2
+
confirmed with the 16 aromatic protons resulting in eight
region (Figure 6, top). In contrast to [Zn (H L )(OAc) ] , the
two bridging acetate coligands in [Zn (L )(OAc) ] produce
2 2
two resonances in the H NMR spectrum. Therefore, the
substitution of two pyridine groups in one of the binding sites
of HL creates two different coordination environments in HL ,
2 2 2
1
4
+
resonances in the aromatic region of the H NMR spectrum,
1
with each of the multiplet resonances integrating for two
1
protons. Comparison with the H NMR spectrum of the metal-
2
1
4
free ligand H L shows a downfield shift of protons of the
3
II
amidated pyridine residues and an upfield shift of protons of
which induce the formation of an asymmetric dinuclear Zn
II
the unsubstituted pyridine groups upon binding to Zn (Figure
complex in solution, in contrast to the symmetric structure
observed in the solid state by X-ray crystallography (see above).
This suggests that the asymmetry of the amide-based complex
1
3
). As expected, complex [Zn (L )(OAc) ]PF shows an
2
2
6
1
analogous behavior, leading to a H NMR spectrum
corresponding to a pair of two identical picolyl groups within
the complex. Moreover, only one resonance for the tert-butyl
3
[Zn (H L )(OAc)(OH)]PF not only is the result of the two
2
2
6
II
different coordination geometries of the two Zn centers but is
E
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Inorganic Chemistry
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1
3
3
+
Figure 4. Aromatic region of the H NMR spectra of H L (bottom) and [Zn (H L )(OAc)(OH)] (top) in CD CN.
3
2
2
3
1
3
3
+
Figure 5. Methylene proton signals in the H NMR spectra of H L (bottom) and [Zn (H L )(OAc)(OH)] (top) in CD CN.
3
2
2
3
1
4
4
+
Figure 6. Aromatic region of the H NMR spectra of HL (bottom) and [Zn (L )(OAc) ] (top) in CD CN.
2
2
3
2
also due to the H-bond donating groups in proximity to one of
the coordination sites.
In order to study the behavior of the complexes [Zn (H L )-
2
2
+
3
+
4
+
(OAc) ] , [Zn (H L )(OAc)(OH)] , and [Zn (L )(OAc) ]
2 2 2 2 2
Electronic Properties. Electronic spectrum of the complexes
under basic conditions, UV−vis spectroscopic measurements
were also conducted in acetonitrile/aqueous buffer mixtures
(1:1). The aqueous buffer consisted of 2-(N-morpholino)-
ethanesulfonic acid (MES), 4-(2-hydroxyethyl)piperazine-1-
ethanesulfonic acid (HEPES), 2-(cyclohexylamino)-
ethanesulfonic acid (CHES), 3-(cyclohexylamino)-1-propane-
sulfonic acid (CAPS), and lithium perchlorate for ionic strength
control and was adjusted to a specific pH value by addition of
aqueous sodium hydroxide solution (see also Kinetic Studies,
below). The same buffer solutions were also used for the
hydrolytic activity assays discussed in the next section.
1
2
3
[
(
Zn (L )(OAc) ]PF , [Zn (H L )(OAc) ]PF , [Zn (H L )-
2 2 6 2 2 2 6 2 2
4
OAc)(OH)]PF , and [Zn (L )(OAc) ]PF were recorded in
6
2
2
6
II
acetonitrile (Figure 7). All four dinuclear Zn complexes show
two bands in the regions of 230−260 and 280−320 nm,
respectively, attributed to pπ → pπ* ligand internal transitions.
The substitution with a pivaloyl amido group in position six of
two pyridine residues in [Zn (H L )(OAc) ]PF and
Zn (H L )(OAc)(OH)]PF leads to a hypsochromic effect
2 2 6
2
2
2
2
6
3
[
in the UV−vis spectroscopic measurements, compared with the
1
spectrum of the unsubstituted compound [Zn (L )(OAc) ]-
2
2
With increasing basicity, the band in the absorbance
2
+
PF . The substitution by amino moieties instead, as in
spectrum of [Zn (H L )(OAc) ] at 287 nm experiences a
6
2 2 2
4
[
Zn (L )(OAc) ]PF , has a similar but less pronounced effect.
shift to 294 nm. Also, the band at 233 nm decreases in
2
2
6
F
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Inorganic Chemistry
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the pH range of 5 to 11 indicates that dizinc(II) complexes are
stable (and the only species of relevance) in these solutions,
and this emerges also from the NMR studies, specifically in
mixed CD CN/D O solutions at varying pH values (see above
3
2
and Supporting Information).
Kinetic Studies. pH and Concentration Dependence. The
influence of hydrogen bonding on the phosphoester hydrolysis
reactivity was probed with a spectrophotometric assay using
BDNPP (bis(2,4-dinitrophenyl)phosphate) as substrate. Cleav-
age of the phosphorus−oxygen bond was followed at 25 °C by
monitoring the generated product, 4-nitrophenolate, by its
strong absorption at 400 nm (ε = 12 100 M− cm ). All
measurements were carried out in an 1:1 acetonitrile/buffer
mixture. The aqueous buffer consisted of MES, HEPES, CHES,
CAPS, and lithium perchlorate for ionic strength control. By
varying the pH of the multicomponent buffer, the pH
dependence of the activity was studied in the pH range of 5
to 11 (Figure 9a). The pH values refer to the aqueous
component, and it should be noted that the pH of an aqueous
1
−1
1
+
Figure 7. UV−vis absorption spectra in CH CN of [Zn (L )(OAc) ]
3
2
2
2
+
3
(
(
dashed line), [Zn (H L )(OAc) ] (dotted line), [Zn (H L )(OAc)-
2 2 2 2 2
solution of the buffer is the same within error as in a 1:1
+
4
+
OH)] (solid line), and [Zn (L )(OAc) ] (dash dotted line).
8,27
2
2
mixture of buffer and acetonitrile.
The resulting data were
fitted to eq 2, which is based on a model for a diprotic system
with two active species.
1
+
Table 3. UV−Vis Spectral Properties of [Zn (L )(OAc) ] ,
28
2
2
2
+
3
+
[
[
Zn (H L )(OAc) ] , [Zn (H L )(OAc)(OH)] , and
2 2 2 2 2
4
+
Zn (L )(OAc) ] in CH CN
γK
2
2
3
a2
vmax 1 +
(
+
)
[H ]
UV−vis
ε [L mol− cm−1
1
]
transition
v0 =
complex
[nm]
⎛
⎜
+
K
⎞
[
H ]
a2
1 +
+
⎟
1
+
+
[
Zn (L )(OAc) ]
260
113 168
37 161
pπ → pπ*
pπ → pπ*
pπ → pπ*
pπ → pπ*
pπ → pπ*
pπ → pπ*
pπ → pπ*
pπ → pπ*
⎝
Ka1
[H ] ⎠
(2)
2
2
3
11
238
89
239
90
237
05
2
+
[
[
[
Zn (H L )(OAc) ]
249 438
177 075
198 843
151 351
213 347
120 667
Here, v is the initial reaction rate and v is the maximum
0 max
reaction rate that is reached under given conditions. The factor
2
2
2
2
3
+
Zn (H L )(OAc)(OH)]
γ is related to the relative activity of the two active species in
2
2
n
n−1
2
equilibrium (E S and E S); a value of γ less than unity
4
+
n
Zn (L )(OAc) ]
corresponds to a more active E S adduct, and a value higher
than 1 considers the deprotonated adduct E S as more
2
2
n−1
3
2
8,29
active.
The Ka values obtained are the protonation
intensity, while new bands at 259 and 326 nm arise (Figure 8a).
Figure 8b shows the change of absorbance at different
wavelengths as a function of rising pH value. The overlay of
the spectra at different pH values indicates the presence of
three isosbestic points at 246, 270, and 297 nm. Fitting of the
equilibrium constants between the two relevant active species.
The resulting pK and γ values are listed in Table 4. The rate vs
a
pH profiles for three of the dizinc(II) complexes show a nearly
sigmoidal shape, whereas the corresponding profile for
3
+
[Zn (H L )(OAc)(OH)] appears to be bell-shaped. This
2
2
pH-dependent spectroscopic data to eq 1 leads to the pK value
bell-shaped profile indicates that the catalyst−substrate
a
2
+
n
of [Zn (H L )(OAc) ] : pK = 8.14 ± 0.25 (ε : extinction
coefficient of protonated complex cation, ε : extinction
complex (E S) is most active in its mixed protonation state,
2
2
2
a
1
2
whereas both protonation and deprotonation lead to a decrease
of activity. Based on a fit adopting the equation for a
monoprotic system, the assumed two active species in the
coefficient of deprotonated complex cation, c : initial complex
0
concentration, d: path length).
1
+
4
+
case of [Zn (L )(OAc) ] and [Zn (HL )(OAc) ] have the
c d
2
2
2
2
0
Abs = (ε − ε )
+ ε c d
same activity. In contrast, the deprotonated active species of
1
2
pH−pKa
2 0
10
+ 1
(1)
2
+
[
Zn (H L )(OAc) ] appears to play an important role in the
2 2 2
pH-dependent UV−vis spectroscopic measurements of
catalytic cycle, as the rate vs pH profile rises steadily as the pH
increases, leading to a γ value of 4.19. Comparison of the
profiles leads to the conclusion that the presence of two amine
3
+
[
Zn (H L )(OAc)(OH)] show similar effects (Figure 8c,d),
2 2
and from fitting of these data to eq 1, the pK value of
a
3
+
II
4
+
[
Zn (H L )(OAc)(OH)] was obtained: pK = 7.27 ± 0.65.
Unfortunately, the variation of the pH value from 5 to 11 did
not result in any change of the UV−vis spectra of [Zn (L )-
groups near one Zn center in [Zn (L )(OAc) ] lowers the
2
2
a
2 2
kinetically relevant pK value by 1.3 pK units, in agreement
a a
30
1
with previously published results. The influence of two amide
2
4
II
3
+
(
OAc) ]PF and [Zn (L )(OAc) ]PF .
groups at one Zn center in [Zn (H L )(OAc)(OH)] is
2
6
2
2
6
2 2
The spectrophotometrically determined pK values of
comparatively small; in contrast the symmetric incorporation of
a
2
+
3
+
2
+
[
Zn (H L )(OAc) ] and [Zn (H L )(OAc)(OH)] can be
two amide moieties in [Zn (H L )(OAc) ] causes a significant
2
2
2
2
2
2 2 2
compared to corresponding data obtained from the analysis of
the kinetic data of the phosphoester hydrolysis, and this
supports the mechanistic interpretation (see below). Impor-
tantly, the data described here also support the solution
structural analysis; that is, the observation of isosbestic points in
effect, both in the profile shape (highest reactivity at high pH;
Figure 7a) and in the pK values.
a
The measurements of the dependence of the BDNPP
hydrolysis rate on the complex concentration were determined
at three pH values (i.e., pH = 7.0, 9.5, and 11) to assess the
G
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Figure 8. UV−vis spectroscopic titration spectra (5 μM in acetonitrile/buffer between pH 5 and 11) and absorbance vs pH plots for
2
+
3
+
[
Zn (H L )(OAc) ] (a, b) and [Zn (H L )(OAc)(OH)] (c, d).
2 2 2 2 2
catalytic behavior of different protonation states (Figure
phosphodiester substrate and therefore reveal higher catalytic
4
+
1
+
2
9
b,c,d). [Zn (L )(OAc) ] was not tested at pH = 11, as no
efficiencies than [Zn (L )(OAc) ] (except for [Zn (H L )-
2
2
2 2 2 2
+
difference in the hydrolysis rate, compared to pH = 9.5, was
detected during the previous pH dependence experiments. The
results show that for each complex the hydrolysis rates are
linearly dependent on the complex concentration. The
dependence of the rate of hydrolysis on the BDNPP
concentration shows Michaelis−Menten saturation behavior
for all complexes. Due to the poor solubility of BDNPP in
acetonitrile, assays with a starting concentration of the substrate
higher than 11.5 mM could not be investigated. The
experimental data were fitted to eq 3, and the parameter
(OAc) ] at pH = 7).
2
Furthermore, the measurements at pH = 11 resulted in
significantly higher kcat values for the complexes that support
hydrogen bond formation, compared to the reference complex
1
+
[
Zn (L )(OAc) ] . The Michaelis−Menten constants obtained
2
2
under these more basic conditions are comparable for all three
3
complexes. Therefore, the complexes [Zn (H L )(OAc)-
2
2
+
2
+
(
OH)] and [Zn (H L )(OAc) ] have two and five times
2 2 2
1
+
higher catalytic efficiencies than [Zn (L )(OAc) ] .
2
2
Product Inhibition at the Active Site. Similar to the
values K , vmax, and kcat are listed in Table 4.
31,32
m
phosphate inhibition of phosphatases,
the formation of an
adduct with a bridging phosphomonoester between the two
vmax[BDNPP]0
v0 =
Zn sites is known to lead to inhibition of phosphoester
II
K + [BDNPP]
(3)
(4)
m
0
33
hydrolysis in model complexes. Therefore, the influence of
addition of DNPP to the reaction mixtures was explored (see
Supporting Information). The presence of DNPP (1 mM) in
the kinetic assays was shown to decrease the hydrolytic rate,
independently of whether the phosphomonoester was added
before or simultaneously with the substrate BDNPP (see
Supporting Information). The inhibited hydrolysis rates
obtained in the presence of catalyst are, within the relatively
large errors of these measurements, indistinguishable from the
autohydrolysis rates under the same conditions (autohydrolysis
experiments contain only phosphomono- and phosphodiester).
These results demonstrate not only product inhibition but also
vmax
kcat = [
complex]0
1
+
While at pH = 7 [Zn (L )(OAc) ] , without hydrogen bond
2
2
4
donors, exhibits the highest rate of hydrolysis, [Zn (L )-
2
+
(
OAc) ] is the most efficient catalyst due to its smaller K
2
m
value. Moreover, the Michaelis−Menten constants Km are
lower for all complexes providing a hydrogen bond network,
1
+
compared to [Zn (L )(OAc) ] , both at pH = 7 and pH = 9.5.
2
2
The net interpretation of this observation is that complexes that
facilitate hydrogen bonding exhibit higher affinities toward the
H
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Inorganic Chemistry
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1
+
2
+
Figure 9. pH dependence of BDNPP hydrolysis activity for [Zn (L )(OAc) ] (black triangles), [Zn (H L )(OAc) ] (blue diamonds),
2
2
2
2
2
3
+
4
+
[
Zn (H L )(OAc)(OH)] (red squares), and [Zn (L )(OAc) ] (green circles) (a) and substrate concentration dependence at pH = 7 (b), pH =
2
2
2
2
9
.5 (c), and pH = 11 (d).
−
3
−1
−3 −1
−1
Table 4. Kinetic Data (k in [10 s ], K in [mM], and k /K in [10 s mM ]) of BDNPP Hydrolysis for
cat
m
cat
m
1
+
2
+
3
+
4
+
[
Zn (L )(OAc) ] , [Zn (H L )(OAc) ] , [Zn (H L )(OAc)(OH)] , and [Zn (L )(OAc) ]
2
2
2
2
2
2
2
2
2
1
+
2
+
3
+
4
+
pH
[Zn (L )(OAc) ]
[Zn (H L )(OAc) ]
[Zn (H L )(OAc)(OH)]
[Zn (L )(OAc) ]
2
2
2
2
2
2
2
2
2
pKa1
pKa2
γ
6.5
7.7
9.5
7.0
5.2
10.3
10.7
10.0
1.26 ± 0.08
7.18 ± 4.39
123 ± 79
0.06
4.19 ± 0.67
0.09 ± 0.01
2 ± 1
0.45 ± 0.14
0.57 ± 0.04
4 ± 1
1.05 ± 0.03
3.49 ± 0.25
18 ± 2
0.20
kcat
Km
7
7
k /K
cat
7
0.04
0.14
m
m
m
kcat
Km
9.5
9.5
9.5
11
11
11
9.5
5.08 ± 0.85
80 ± 14
0.06
3.20 ± 0.21
9 ± 1
0.34
2.70 ± 0.21
18 ± 2
0.15
9.58 ± 0.70
52 ± 4
0.18
k /K
cat
kcat
Km
2.07 ± 0.29
27 ± 5
0.08
10.83 ± 0.62
26 ± 2
0.42
3.68 ± 0.25
28 ± 2
0.13
k /K
cat
TON (after 8 d)
109 ± 5
158 ± 8
101 ± 4
121 ± 6
that the hydrolysis product DNPP is more strongly bound to
the complex than the phosphodiester substrate BDNPP.
Turnover Numbers. Studies of the turnover number (TON)
were conducted at pH = 9.5 and 25 °C with [complex] = 15
nM and [BDNPP] = 5.25 μM. Samples were taken at various
intervals during the experiment and diluted with solvent, and
their UV−vis spectra were recorded to determine the amount
of phosphoester hydrolysis. The increase in the absorbance at
were calculated using the Beer−Lambert law. The resulting data
are given in Figure 10 and Table 4.
Complexes generated from ligands that engender asymmetry
2
exhibit a lower TON than the symmetric complex [Zn (H L )-
2
2
+
(
OAc) ] . This implies that the presence of an amide moiety
2
on each coordination site has a beneficial impact on the
hydrolytic activity. The comparison of the time-dependent
3
traces for the two asymmetric catalysts [Zn (H L )(OAc)-
2
2
+
4
+
(
OH)] and [Zn (L )(OAc) ] indicates that there is also a
2 2
400 nm, assigned to the hydrolysis product 2,4-dinitropheno-
decrease of the TON as a result of the bulky nature of the
pivaloyl group in the former complex. Therefore, the hydrolysis
late, was monitored over time, and TON values after 8 days
I
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2
+
Figure 10. UV−vis spectra of the BDNPP hydrolysis assay with [Zn (H L )(OAc) ] , taken at different time points after substrate addition (left)
2
2
2
1
+
2
+
and time dependence of the absorbance band of 2,4-nitrophenolate (400 nm) with [Zn (L )(OAc) ] (black triangles), [Zn (H L )(OAc) ] (blue
diamonds), [Zn (H L )(OAc)(OH)] (red squares), and [Zn (L )(OAc) ] (green circles) (right).
2
2
2
2
2
3
+
4
+
2
2
2
2
4
+
rate of [Zn (L )(OAc) ] is, in the first 70 h, significantly
structure reveals that the inhibited complex contains one μ-
PNPP molecule, which forms a bridge between the two Zn
centers of the dizinc(II) complex (Figure 11; selected structural
2
2
3
II
higher. Furthermore, the data obtained with [Zn (H L )-
2
2
+
(
OAc)(OH)] are similar compared to those of the reference
1
+
system [Zn (L )(OAc) ] during the first 150 h after BDNPP
2
2
addition, but the difference in the traces after 150 h reveals
earlier inhibition in the presence of two amide moieties at one
of the two zinc(II) centers. It is proposed that an increased
affinity for the hydrolysis product DNPP is the reason for this,
resulting in the inhibition of the complex at an earlier point in
time. The experiments demonstrate that the phosphoester
hydrolysis rate of dizinc(II) complexes is influenced by (i) the
availability of the catalytic center and (ii) the possibility to
interact with amine or amido hydrogen bond donors, whereas
the opportunity for the formation of hydrogen bonds on both
metal centers appears to have a beneficial effect. Studies with a
variety of complexes of bis[bis(2-substituted-pyridinyl-6-
methyl)]amine type ligands have illustrated the impact of (i)
enhanced H-bonding effects in the second coordination sphere,
3
Figure 11. POV-Ray plot of [Zn (H L )(O POC H NO )]PF
2
2
3
6
4
2
6
(ii) the steric hindrance in the active site and beyond, and (iii)
(counterions, noncoordinated solvent molecules, and H atoms not
involved in H-bonding are omitted for clarity; labels not mentioned in
text or Table 1 are omitted; an ORTEP plot with 50% probability level
of thermal ellipsoids appears as Supporting Information).
the polarity of the substituents on the intramolecular hydrolysis
of the substrate, for example, the RNA model HpNPP (2-
1
4
hydroxypropyl p-nitrophenyl phosphate). Moreover, an
impaired BDNPP affinity was found for the dizinc(II) complex
of a bulky phenolate-based ligand (2-(((2-methoxyethyl)-
parameters are included in Table 1), in contrast to a previously
published complex, [Zn (L ) (O POC H NO )(H O) ]-
PF ) (L = 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)-
amino)methyl)-4-methylphenol), in which the PNPP molecule
forms not only an intramolecular bridge between the two Zn
ions but also an intermolecular bridge between two Zn centers
of adjacent dizinc(II) complexes.
(O POC H NO )]PF , both Zn ions are bound to the
bridging phenoxo residue, to the nitrogen atoms of two
pyridine ligands, to a tertiary amine, and additionally to an
oxygen atom of the bridging PNPP molecule.
Comparison with the structure of the corresponding acetate-
bridged complex [Zn (H L )(OAc)(OH)]PF (Figure 2b),
used as the starting material for the synthesis of [Zn (H L )-
(O POC H NO )]PF , illustrates important similarities: the
Zn ions in both structures are on different sides of the
1
2
(
pyridine-2-ylmethyl)amino)methyl)-4-methyl-6-(((pyridin-2-
4
2
3
6
4
2
2
2
12
ylmethyl)(4-vinylbenzyl)amino)methyl)phenol) compared to
its unconcealed counterpart (2-(((2-methoxyethyl)(pyridine-2-
ylmethyl)amino)methyl)-4-methyl-6-(((pyridin-2-ylmethyl)-
amino)methyl)phenol), which was proposed to be a steric
(
6 2
II
II
8
3
4
3
effect attributed to the bulky vinylbenzyl group. Therefore, the
In [Zn (H L )-
2 2
II
exact origin of the acceleration of the BDNPP hydrolysis with
the dizinc(II) complexes studied in this work may be attributed
in part to the enhanced H-bonding effects, but the effects of
other parameters in combination with H-bonding need also to
be considered.
3 6 4 2 6
3
Crystal Structure of an Asymmetric Dizinc(II) Complex
with the Phosphomonoester PNPP. In order to explore the
nature of product inhibition, the asymmetric complex
2
2
6
3
2
2
3
6
4
2
6
3
+
II
[
Zn (H L )(OAc)(OH)] was treated with an excess of the
2
2
phosphomonoester 4-nitrophenyl phosphate in acetonitrile.
PNPP was chosen as phosphomonoester substrate mimic due
to its higher stability toward autohydrolysis compared to
DNPP. After the solvent was removed and the remaining oil
dissolved in methanol, colorless crystals suitable for X-ray
crystallography were obtained by slow evaporation. The
phenoxo plane and exhibit different coordination geometries. In
3
the catalyst-inhibitor adduct [Zn (H L )(O POC H NO )]-
2
2
3
6
4
2
PF , Zn(1) is also coordinated in a trigonal bipyramidal
6
geometry (τ-value of 0.88), while Zn(2) is at the center of a six-
coordinate site. In contrast to the catalyst complex, the
remaining coordination site of Zn(2) is no longer completed
J
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 12. (a) Chemical shifts of 31P NMR resonances for phosphoester substrates (OP(OH)3−x(OR) ) in water containing CD CN vs extent of
x
3
31
substitution (x) of phosphoric acid with 2,4-dinitrophenyl, 4-nitrophenyl, and phenyl residues. Comparison of P NMR spectra in CD CN after
addition of DNPP to (b) [Zn (H L )(OAc)(OH)] , (c) [Zn (H L )(OAc) ] , and (d) [Zn (L )(OAc) ] directly after addition (e) after 48 h.
3
3
+
2
+
4
+
2
2
2
2
2
2
2
3
1
2
+
Table 5. Phosphoester P NMR Resonances Obtained before and after Addition of Dizinc(II) Complexes [Zn (H L )(OAc) ] ,
2
2
2
3
+
4
+
[
Zn (H L )(OAc)(OH)] , and [Zn (L )(OAc) ]
2
2
2
2
resonances arising from phosphoesters [ppm]
Zn(II) complex
phospho-ester
metal-free
treated with the Zn(II) complexes
2
2
3
3+
[
[
Zn (H L )]
PNPP
DNPP
DNPP
DNPP
DNPP
DNPP
DNPP
BDNPP
−5.05
−5.76
0.62
2
2
3
3+
Zn (H L )]
−6.85
−6.85
−6.80
−6.80
−3.90
−5.01
−2.89
2
2
after 14 weeks
−5.01
−4.25
−4.25
−3.37
2
3+
[
Zn (H L )]
−5.76
−5.76
2
2
after 14 weeks
−2.93
−2.81
4
3+
[
Zn (L )]
−2.50
−0.64
−0.63
−0.40
−0.16
−0.09
−0.08
2
after 48 h
2
3+
[
Zn (H L )]
−14.10
2
2
0
0
0
.25eq
−10.25
−10.20
−10.22
−10.21
−10.20
.5eq
.75eq
(−11.46)
−11.40
(−6.88)
−6.95
−7.01
−7.26
(−4.58)
−4.54
−4.48
−4.45
after 24 h
after 3 weeks
0.75eq
.0eq
1.0eq
−1.40
−1.41
−1.42
1
3
6
by a terminal hydroxido group but by the neighboring amide
oxygen atom of the supporting dinucleating ligand. The
[Zn (H L )(O POC H NO )]PF , and [Zn (H L )(OAc)-
2 2 3 6 4 2 6 2 2
2
(OH)] indicates that, while the symmetric ligand H L forms
3
3
coordination of the bulky PNPP inhibitor in [Zn (H L )-
two hydrogen bonds to the two bridging acetate coligands (one
hydrogen bond to each acetate), the symmetric complexes,
2
2
(
O POC H NO )]PF , compared to the acetate coligand in
3 6 4 2 6
3
II
3
6
[
Zn (H L )(OAc)(OH)]PF , leads to an increase of the Zn ···
[Zn (H L )(OAc)(OH)]PF and [Zn (H L )(OAc)(OH)],
2
2
6
2 2 6 2 2
II
Zn distance by 0.16 Å, accompanied by the widening of the
form two hydrogen bonds to the hydroxido ligand, stabilizing
this unusual structure. However, the introduction of the
monophosphate PNPP, replacing the bridging acetate, leads
to the coordination of one of the amide groups, stabilized by
hydrogen bonding to the second amide function. The distance
between these nitrogen and oxygen atoms of 3.210(6) Å is long
Zn−O−Zn angle by 6.4°. The structural differences in the
3
3
dizinc(II) complexes of H L , [Zn (H L )(O POC H NO )]-
3
2
2
3
6
4
2
3
PF , and [Zn (H L )(OAc)(OH)]PF are mainly in the angles
6
2
2
6
within the triangular plane of the trigonal bipyramidal site. Due
to the bulkier 4-nitrophenolate residue of PNPP in
3
2
[
Zn (H L )(O POC H NO )]PF , compared to the acetate
compared to the corresponding distances in [Zn (H L )-
2
2
3
6
4
2
6
2
2
3
3
6
coligand in [Zn (H L )(OAc)(OH)]PF , the O(1)−Zn(1)−
(OAc) ]PF , [Zn (H L )(OAc)(OH)]PF , and [Zn (H L )-
2
2
6
2 6 2 2 6 2 2
N(1) angle is widened (136.53(16)° vs 118.77(16)°) and the
O(1)−Zn(1)−N(3) angle is contracted (100.50(16)° vs
(OAc)(OH)] (see Table 2). We assume that steric hindrance
by the tert-butyl groups causes this elongation. Interestingly, no
hydrogen bonding to the bridging phosphate, as previously
1
24.76(15)°). However, the primary coordination sphere of
1
3
the two complexes is similar. Further investigation of the
second coordination sphere in the amide-based complexes
observed with the amino group-containing complex [Zn L (μ-
2
PNPP)]+ (L = N,N-bis(2-pyridylmethyl)-N-(6-amino-2-
13
2
3
10
[
Zn (H L )(OAc) ]PF , [Zn (H L )(OAc)(OH)]PF ,
pyridylmethyl)amine), occurs.
2
2
2
6
2
2
6
K
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
31P NMR Studies of Phosphoester Binding. Phosphomo-
NMR spectra (−6.85, −5.01 ppm and −6.80, −4.25 ppm)
noester Binding. In order to gain further insight into the
(Figure 12b,c). Therefore, we assume similar coordination
3
1
2
n+
3
catalytic mechanism, substrate binding was studied by
P
modes of DNPP to [Zn (H L )(solv) ] and [Zn (H L )-
2 2 x 2 2
3
1
n+
NMR spectroscopy. P NMR spectra of the hexafluoridophos-
phate salts of the dizinc(II) complexes were measured with 85%
H PO as an external standard, and the resonance of PF was
(solv) ] . Moreover, the resonances detected were downfield
x
and upfield shifted, respectively, compared to the free
phosphomonoester. The extent of the shifts (0.75 to 1.51
ppm) is small compared to the cases discussed above. This
suggests a rather different coordination mode of DNPP to
3
4
6
then used as internal standard for the phosphoester binding
experiments. First the phosphoester substrates were measured
3
1
2
n+
3
n+
to study the influence of the ester groups on the P chemical
[Zn (H L )(solv) ] and [Zn (H L )(solv) ] than observed
2 2 x 2 2 x
3
+
shifts (Figure 12a; NaPF referenced to −144.30 ppm).
in the X-ray structure of [Zn (H L )(O POC H NO )] .
2 2 3 6 4 2
6
3
1
Comparison of the P shifts in phosphoric acid, PNPP,
bis(4-nitrophenyl)phosphate (BPNPP), DNPP, BDNPP, di-
phenyl phosphate, and triphenyl phosphate shows a linear
correlation with the number of protons substituted by phenyl
groups in H PO . Importantly, a comparison of the resonances
Studies with cyclic phosphoesters have shown that the O−
31
P−O angle has a significant impact on the P NMR chemical
35
shift. For example, an increase in the bond angle of
phosphotriesters results in the better shielding of the
3
1
phosphorus atom and therefore in an upfield shift of the
P
3
4
of the phosphodiesters BDNPP and BPNPP as well as of the
phosphomonoesters DNPP and PNPP indicates that the
impact of an additional nitro substituent at the phenyl groups
is rather small.
NMR resonance. Assuming the same binding mode for DNPP
and PNPP, an upfield shift due to a larger O−P−O angle in the
case of DNPP competes with a downfield shift due to
II
coordination to two Zn ions, and this could explain the
3
1
The P NMR spectrum of the crystallographically
smaller extent of the downfield shifts in the cases of DNPP with
3
+
2
+
3
+
investigated complex [Zn (H L )(O POC H NO )] in aceto-
[Zn (H L )(OAc) ] and [Zn (H L )(OAc)(OH)] . The
2
2
3
6
4
2
2 2 2 2 2
nitrile has a single resonance at 0.62 ppm, compared to −5.05
ppm for the uncoordinated phosphoester. This effect was also
studied using the phosphomonoester DNPP for the four
dizinc(II) complexes, in order to gain a deeper understanding
of the product-inhibited structure during the BDNPP
hydrolysis; the detected resonances are summarized in Table 5.
The spectra recorded after the addition of DNPP to the
major resonances at around −6.8 and −4 to −5 ppm can be
attributed either to a complex structure with two DNPP ligands
in two different electronic environments or to two different
complex structures, each of them containing only one bound
DNPP. Although the two major resonances upon binding
2
n+
DNPP by the amide-based complexes [Zn (H L )(solv) ]
2
2
x
3
n+
31
and [Zn (H L )(solv) ] are similar, their P NMR spectra
2
2
x
4
+
amine-based complex [Zn (L )(OAc) ] in deuterated acetoni-
are different: while the third resonance at −2.89 ppm was
2
2
3
trile (∼20 vol % water content) show eight resonances shortly
detected immediately after addition of DNPP to [Zn (H L )-
2
2
+
after addition (−3.90, −3.37, −2.81, −2.50, −0.64, −0.40,
(OAc)(OH)] and disappears after 14 weeks, a species with a
similar signal was not observed with [Zn (H L )(OAc) ] but
2
+
−
0.16, and −0.09 ppm) (Figure 12d). Over 48 h further
2 2 2
reaction results in the observation of only two resonances, at
when a spectrum was measured after 14 weeks (−2.93 ppm).
This implies that both complexes form different species with
DNPP in different coordination modes, but the equilibrium
constants are dependent on the symmetry of the complex
backbone. This could explain the different catalytic activity of
−
0.61 and −0.08 ppm (Figure 12e). A more detailed analysis of
the spectrum obtained immediately after addition revealed a
pattern of two sets of four resonances, in which always two
resonances of the four are separated by about 0.3 ppm (50 Hz)
3
1
2
+
3
or 0.5 ppm (78 and 85 Hz). P NMR studies performed with a
series of cyclic phosphates disclosed that, besides the
electronegativity effect, the chemical shifts of P NMR
resonances are also significantly influenced by (i) the O−P−
O angle and (ii) the torsional angle R−O−P−O(R) of the
the complexes [Zn (H L )(OAc) ] and [Zn (H L )(OAc)-
2 2 2 2 2
+
(OH)] .
Phosphodiester Binding. The binding of BDNPP was
investigated for the most active complex [Zn (H L )(OAc) ]
3
1
2
+
2
2
2
by stepwise addition of 0.25 equiv of the phosphodiester and
3
5
31
phosphate. Therefore, we attribute the eight resonances to
four different species (−3.64, −2.66, −0.41, and −0.25 ppm),
each of them present in two conformers with varied positions
of the dinitrophenyl residue of the phosphoester. After 48 h
only the “doublet” at −0.25 ppm remains. The chemical shift
difference of 5.51 ppm between the resonances of DNPP in its
recording the P NMR spectra at each step (∼1.0 vol % water
content) (Figure 13). Addition up to 0.5 equiv of BDNPP to a
solution of the complex in CD CN resulted in the formation of
3
3
1
only one phosphorus-containing species with a P NMR
resonance at −10.22 ppm (Figure 13b,c), in addition to free
BDNPP with a resonance at −14.43 ppm (Figure 13a). After
further addition of BDNPP two additional signals at −6.86 and
4
n+
free form and bound to complex [Zn (L )(solv) ] is in the
2
x
31
same range as found by comparison of free PNPP and
−4.58 ppm occurred in the P NMR spectrum, and the signal
integration increases upon increase of BDNPP concentration.
Further reaction led to the disappearance of the initially
detected species and formation of a new species with a
resonance at −1.41 ppm.
3
+
[
Zn (H L )(O POC H NO )] . Therefore, we propose a
2 2 3 6 4 2
similar bridging coordination mode of DNPP to complex
4
n +
3
[
(
Zn (L )(solv) ]
as found in [Zn (H L )-
2
x
2 2
+
O POC H NO )] . Once more, it should be emphasized
3
6
4
2
that until this most stable phosphoester-bridged dizinc(II)
complex was formed, three different intermediate stages were
detectable.
Comparison with the spectra monitored after addition of the
2
+
phosphomonoester DNPP to [Zn (H L )(OAc) ] (Figure
2
2
2
12c) allows to assign the resonances at −6.86 and −4.58 ppm
to species containing DNPP. The increase of the integrals of
these two species is accompanied by the decrease of the initially
detected resonance at −10.22 ppm. Therefore, we suggest that
the resonance at −10.22 ppm originates from a BDNPP−
complex adduct. It follows that the binding of the
2
In contrast, when the amido-based complexes [Zn (H L )-
2
2
+
3
+
(
OAc) ] and [Zn (H L )(OAc)(OH)] dissolved in deuter-
2 2 2
2
ated acetonitrile (∼3.0 vol % water content for [Zn (H L )-
2
2
+
3
(
(
OAc) ] and ∼1.2 vol % water content for [Zn (H L )-
2
2
2
+
OAc)(OH)] ) were treated with 1 equiv of DNPP, two major
31
II
resonances with similar chemical shifts appeared in the
P
phosphodiester to the Zn ion leads to a downfield shift by
L
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
appears that at pH = 7 the asymmetrical amine-based system
4
+
[
Zn (L )(OAc) ] is the most efficient due to an increased
2 2
substrate affinity imposed by hydrogen bonding, while at pH =
.5 and pH = 11, the symmetric, sterically hindered, amide-
9
2
+
based system [Zn (H L )(OAc) ] is more efficient, and this is
2
2
2
primarily due to less stable catalyst−inhibitor complexes.
EXPERIMENTAL SECTION
■
Materials and Methods. Nuclear magnetic resonance (NMR)
spectra were carried out with Bruker AV400 and AV500 instruments.
The spectra were conducted in CD OD or CD CN. Chemical shifts of
3
3
1
13
H and C NMR spectra are reported in ppm, relative to known
31
solvent peak references. For P NMR spectra 85% phosphoric acid
was used as the external reference. Two-dimensional correlation
spectroscopy (COSY), nuclear Overhauser-effect spectroscopy
(
NOESY), heterodinuclear single quantum correlation (HSQC), and
hetereodinuclear multiple-bond connectivity (HMBC) experiments
were used to assign each signal in the spectra. The following
abbreviations were used: s (singlet), bs (broad singlet), d (doublet), dd
(
(
doublet of doublets), ddd (doublet of doublets of doublets), t
triplet), dt (doublet of triplets), sep (septet), and m (multiplet).
Coupling constants are given in Hz. High-resolution mass spectra were
collected with a Bruker microTOFQ ESI-MS spectrometer by Mr.
Graham Macfarlane at the University of Queensland and processed
with Bruker Compass Data Analysis 4.0 software. FT-infrared
spectroscopy was carried out with a PerkinElmer SPECTRUM 2000
FT-IR spectrometer with a Smiths DuraSamplIR II ATR diamond
window. Elemental microanalyses were performed in the analytic
laboratories of the Institute of Chemistry at the University of
Heidelberg with an Elementar Vario EL machine. X-ray crystallo-
graphic data were collected with an Oxford Diffraction Gemini Ultra
dual source CCD diffractometer. The structures were solved by direct
methods using the SHELXS computer program and refined by the full-
matrix least-squares method, with the SHELXL97 computer
Figure 13. 31P NMR measurements upon addition of BDNPP to
2
+
[
Zn (H L )(OAc) ] in CD CN: (a) BDNPP reference, (b) 0.25
2 2 2 3
equiv of BDNPP, (c) 0.5 equiv of BDNPP, (d) 0.75 equiv of BDNPP,
(
e) 0.75 equiv of BDNPP after 24 h, (f) 1.0 equiv of BDNPP, (g) 1.0
equiv of BDNPP after 16 days, and (h) DNPP reference (* unreacted
BDNPP).
4.2 ppm compared to free BDNPP, accompanied by the
activation of the phosphodiester BDNPP. The following
hydrolysis of BDNPP provides the phosphomonoester
DNPP, which binds in the same way as by direct addition of
DNPP to the complex. The decrease of the signal assigned to
the BDNPP−complex adduct is accompanied by an increase of
a signal at −1.41 ppm. Although the structure of the
corresponding species remains unclear, we speculate that this
complex adduct is able to release the DNPP product and
therefore continues to catalyze the BDNPP hydrolysis.
3
6,37
program.
Synthesis of Ligands and Complexes. Ligand HL ,
1
15,16
ligand
2
13
38
H L , bis(pyridin-2-ylmethyl)amine (1), 2-(((pyridin-2-ylmethyl)-
3
39
amino)methyl)phenol (1a), 3-(chloromethyl)-2-hydroxy-5-methyl-
4
0,41
benzaldehyde (2),
hydroxy-5-methylbenzaldehyde (3),
hydroxybenzyl)(pyridin-2-ylmethyl)amino)methyl)-5-methylbenzalde-
hyde (3a), and N,N-bis((2-pivaloylamidopyridin-6-yl)methyl)amine
4) were prepared as described previously with minor modifications.
3-((bis(pyridin-2-ylmethyl)amino)methyl)-2-
42
2-hydroxy-3-(((2-
4
3
4
4
(
1
2
For comparison reasons the analysis data of the ligands HL and H L
CONCLUSION
3
■
(
are given additionally.
1
+
2
The four phosphatase models [Zn (L )(OAc) ] , [Zn (H L )-
1 1
2
2
2
2
HL . H NMR (CD CN, 500.13 MHz): 2.18 (s, 3H, H17), 3.68 (s,
3
+
3
+
4
+
OAc) ] , [Zn (H L )(OAc)(OH)] , and [Zn (L )(OAc) ]
2
2
2
2
2
4H, H13, H21), 3.76 (s, 8H, H6, H12, H27, H33), 6.96 (s, 2H, H15,
3
3
4
with no substituents, two symmetrically disposed and two
asymmetrically disposed amides or two asymmetrically
disposed amine anchor groups for hydrogen bonding,
respectively, lead to strikingly different structures of the
dizinc(II) complexes and their adducts with the phosphoester
substrates and their hydrolysis products. NMR spectroscopy
indicates that the solution structures of the two complexes built
H18), 7.15 (ddd, 4H, J = 7.52 Hz, J = 4.95 Hz, J = 1.10 Hz, H2, H8,
3
H23, H29), 7.44 (d, 4H, J = 7.70 Hz, H4, H10, H25, H31), 7.62 (td,
4H, J = 7.70 Hz, J =1.83 Hz, H3, H9, H24, H30), 8.45 (ddd, 4H, J =
.77 Hz, J = 4.77 Hz, J = 1.00 Hz, H1, H7, H22, H28) ppm.
3
4
3
3
4
13
4
C
NMR (CD CN, 100.62 MHz): 20.58 (C17), 55.34 (C13, C21), 60.26
3
(
C6, C12, C27, C33), 123.01 (C2, C8, C23, C29), 123.88 (C4, C10,
C25, C31), 124.85 (C14, C19), 128.08 (C16), 130.84 (C15, C18),
1
1
37.43 (C3, C9, C24, C30), 149.73(C1, C7, C22, C28), 150.66 (C20),
60.16 (C5, C11, C26, C32) ppm. FT-IR spectroscopy (ν, cm ):
II
up by an asymmetric ligand backbone contain two unequal Zn
−1
3
+
centers. Interestingly, in [Zn (H L )(OAc)(OH)] , the
2
2
3063 (ν(Ar−H)), 3011 (ν(Ar−H)), 2924 (ν(C−H)), 2828 (ν(C−
asymmetry of the ligand with respect to the amide groups
H)), 1590 (ν(CC)), 1569 (ν(CC)), 1475 (ν(CC)), 1433
II
+
leads to two strikingly different Zn sites, one being six- and
(ν(CC)), 754 (δ(py-H)). HRMS (ESI , CH CN): m/z 729.424
3
+
+
one five-coordinate, and the former site exhibiting a rare
([C43
H
53
N
8
6
O
3
] , 729.424). HRMS (ESI , CH
3
CN): m/z 531.287
+
II
([C H N O] , 531.287).
example with a Zn −OH bond. The main impact of the
33 35
2
1
H L . H NMR (CD CN, 500.13 MHz): 1.24 (s, 18H, H36, H39),
3
3
secondary interactions is shown to be reduced stability of the
catalyst−substrate and catalyst−inhibitor (hydrolysis product)
adducts, and this obviously depends on the hydrogen-bonding
sites (symmetric vs asymmetric arrangement) and the type of
hydrogen donor group. Moreover, the impact of the hydrogen
bond donors of the catalyst on their hydrolytic activity is clearly
pH dependent. For the zinc(II)-based phosphatase mimics, it
2
3
.21 (s, 3H, H17), 3.72 (s, 4H, H13, H21), 3.75 (s, 4H, H27, H33),
.78 (s, 4H, H6, H12), 7.04 (s, 2H, H15, H18), 7.15 (m,4H, H2, H8,
3
3
H25, H31), 7.46 (d, 2H, J = 8.07 Hz, H4, H10), 7.62 (td, 2H, J =
4
3
7
.70 Hz, J = 1.83 Hz, H3, H9), 7.64 (t, 2H, J = 7.89 Hz, H24, H30),
3
7
.97 (d, 2H, J = 8.44 Hz, H23, H29), 8.28 (bs, 2H, NH), 8.44 (ddd,
3
3
4
13
2H, J = 5.14 Hz, J = 4.04 Hz, J = 0.90 Hz, H1, H7) ppm. C NMR
(CDCl , 100.55 MHz): 20.60 (C17), 27.45 (C36, C39), 39.75 (C35,
3
M
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
C38), 54.72 (C13, C21), 58.97 (C27, C33), 59.88 (C6, C12), 111.69
(C2, C8), 124.26 (C4, C10), 124.72 (C14), 124.99 (C19), 131.20
(C15), 131.39 (C18), 137.74 (C3, C9), 139.16 (C24, C30), 149.87
(C1, C7), 157.85 (C26, C32), 160.01 (C5/C11/C22/C28), 160.28
(
C23, C29), 117.97 (C25, C31), 121.91 (C2, C8), 122.71 (C4, C10),
23.84 (C14, C19), 127.63 (C16), 129.65 (C15, C18), 136.51 (C3,
C9), 138.86 (C24, C30), 148.73 (C1, C7), 150.97 (C22, C28), 153.08
C20), 157.28 (C26, C32), 159.37 (C5, C11), 177.13 (C34, C37) ppm.
1
−1
(C5/C11/C22/C28) ppm. FT-IR spectroscopy (ν, cm ): 3322 (ν
(N−H)), 3199 (ν (N−H)), 3059 (ν(Ar−H)), 3011 (ν(Ar−H)), 2917
(ν(C−H)), 2816 (ν(C−H)), 1594 (ν(CC)), 1574 (ν(CC)),
(
−1
FT-IR spectroscopy (ν, cm ): 3438 (ν(N−H)), 3389 (ν(O−H)),
964 (ν(C−H)), 2869 (ν(C−H)), 2817 (ν(C−H)), 1686 (ν(C
O)), 1523 (ν(C−N), δ(CNH)), 1405 (ν(C−(CH ) ), 797 (δ(py−
2
1466 (ν(CC)), 1435 (ν(CC)), 1299 (ν(C−N)), 1221 (ν(C−
+
N)), 758 (δ(py-H)). HRMS (ESI , CH CN): m/z 561.308
3
3
3
+
+
+
H)). HRMS (ESI , CH CN): m/z 729.424 ([C H N O ] ,
([C H N O] , 561.309).
3
43 53
8
3
33 37
8
6
7
7
29.424). Anal. (%) Calcd for C H N O ·CH OH: C 69.45, H
H L . A solution of 3a (3.56 g, 9.8 mmol) in anhydrous CH Cl (25
4 2 2
4
3
52
8
3
3
.42, N 14.73;. Found: C 69.47, H 7.10, N 14.98.
mL) was treated with molecular sieves (4 Å) before a solution of 4
3
H L . Molecular sieves (4 Å) were added to a solution of 3 (3.13 g,
(4.10 g, 10.3 mmol) in anhydrous CH Cl2 (11 mL) was added
3
2
9
.0 mmol) in anhydrous CH Cl (23 mL), followed by the dropwise
dropwise. After the mixture was stirred for 3 h at room temperature
sodium triacetoxyborohydride (4.59 g, 21.7 mmol) was added in small
portions, and the reaction mixture left to react at room temperature
while stirring. The reaction was quenched by addition of saturated
sodium bicarbonate solution (30 mL) and stirring for 45 min before
the pH was adjusted to 8 by addition of solid sodium carbonate. The
phases were separated, and the aqueous phase was extracted three
times with CH Cl (30 mL). The combined organic phases were
2
2
addition of a solution of 4 (3.58 g, 9.0 mmol) in anhydrous CH Cl
2
2
(
10 mL). The mixture was stirred for 3 h at room temperature.
Afterward the solution was treated with sodium triacetoxyborohydride
4.20 g, 19.8 mmol) by addition in portions, and the mixture stirred at
(
room temperature overnight. The reaction was quenched by addition
of saturated sodium bicarbonate solution (30 mL) and stirring for 45
min. The pH was subsequently adjusted to 8 by addition of solid
sodium carbonate. The phases were separated, and the aqueous phase
was extracted three times with CH Cl2 (30 mL). The combined
organic phases were washed with saturated sodium carbonate solution
2
2
washed with saturated sodium carbonate solution (20 mL) and brine
(20 mL) and dried over sodium sulfate. Removal of solvent under
reduced pressure gave an orange foam. Purification by column
chromatography (SiO , DEE/n-hexane/NH in MeOH (7 N), 90:8:2,
2
(
20 mL) and brine (20 mL) and dried over sodium sulfate. Removal of
2
3
6
1
solvent under reduced pressure gave a brownish foam. Purification by
column chromatography (SiO , DEE/NH in MeOH (7 N), 98:2, R =
R
f
= 0.57) yielded H
L as a white solid (4.50 g, 62%). H NMR
4
(CD CN, 500.13 MHz): 1.26 (s, 18H, H36, H39), 2.16 (s, 3H, H17),
2
3
f
3
3
1
0
5
2
.48) yielded H L as a white solid (1.94 g, 30%). H NMR (CD CN,
00.13 MHz): 1.25 (s, 18H, H36, H39), 2.21 (s, 3H, H17), 3.69 (s,
H, H21), 3.73 (s, 4H, H27, H33), 3.74 (s, 2H, H13), 3.79 (s, 4H, H6,
3.69 (s, 2H, H21), 3.74 (s, 4H, H27, H33), 3.75 (s, 2H, H13), 3.76 (s,
3
3
4
2H, H6), 3.78 (s, 2H, H12), 6.74 (m, 2H, H7, H9), 6.85 (sd, 1H, J =
4
3
1.83 Hz, H18), 6.99 (sd, 1H, J = 1.47 Hz, H15), 7.05 (d, 3H, J = 7.34
4
3
3
4
H12), 6.88 (ds, 1H, J = 1.74 Hz, H18), 7.10 (d, 2H, J = 8.06 Hz,
H25, H31), 7.15 (ds, 1H, J = 0.92 Hz, H15), 7.15 (ddd, 2H, J = 7.28
Hz, J = 6.22 Hz, J = 1.06 Hz, H2, H8), 7.50 (d, 2H, J = 8.07 Hz, H4,
Hz, H10, H25, H31), 7.11 (td, 1H, J = 7.70 Hz, J = 1.83 Hz, H8),
7.14 (d, 1H, J = 7.70 Hz, H4), 7.19 (ddd, 1H, J = 7.70 Hz, J = 6.60
Hz, J = 1.10 Hz, H2), 7.58 (td, 1H, J = 7.70 Hz, J = 1.83 Hz, H3),
7.61 (t, 2H, J = 7.70 Hz, H24, H30), 7.97 (d, 2H, J = 7.70 Hz, H23,
H29), 8.33 (bs, 2H, NH), 8.52 (ddd, 1H, J = 5.14 Hz, J = 4.03 Hz, J
= 0.73 Hz, H1) ppm. C NMR (CD CN, 100.61 MHz): 20.62 (C17),
4
3
3
3
3
3
4
3
4
3
4
3
3
3
3
H10), 7.62 (t, 2H, J = 8.44 Hz, H24, H30), 7.64 (dt, 2H, J = 7.70 Hz,
4
3
3
3
4
J = 1.83 Hz, H3, H9), 7.96 (d, 2H, J = 8.44 Hz, H23, H29), 8.28 (bs,
3
3
4
13
2
H, NH), 8.46 (ddd, 2H, J = 6.60 Hz, J = 4.77 Hz, J = 1.10 Hz, H1,
3
13
H7) ppm. C NMR (CD CN, 100.61 MHz): 20.77 (C17), 27.68
27.70 (C36, C39), 40.53 (C35, C38), 53.17 (C13), 57.22 (C21), 57.85
(C12), 59.28 (C27, C33), 59.36 (C6), 112.58 (C23, C29), 116.92
(C9), 119.12 (C25, C31), 119.85 (C7), 123.33 (C2), 124.14 (C11),
124.44 (C4), 124.53 (C14/C19), 124.85 (C14/C19), 128.71 (C16),
129.72 (C8), 130.84 (C10), 131.28 (C18), 131.55 (C15), 137.67 (C3),
139.99 (C24, C30), 149.86 (C1), 152.37 (C22, C28), 154.51 (C20),
158.22 (C26, C32), 158.84 (C5/C11), 158.93 (C5/C11), 177.96 (C34,
3
(C36, C39), 40.51 (C35, C38), 54.35 (C13), 56.33 (C21), 59.59 (C27,
C33), 60.75 (C6, C12), 112.49 (C23, C29), 119.19 (C25, C31), 123.06
(
(
C2, C8), 123.76 (C4, C10), 124.72 (C19), 125.64 (C14), 128.49
C16), 130.71 (C15), 130.95 (C18), 137.44 (C3, C9), 139.86 (C24,
C30), 149.88 (C1, C7), 152.29 (C22, C28), 154.37 (C20), 158.66
(C26, C32), 160.60 (C5, C11), 177.93 (C34, C37) ppm. FT-IR
−1
−1
spectroscopy (ν, cm ): 3438 (ν(N−H)), 3389 (ν(O−H)), 2964
ν(C−H)), 2869 (ν(C−H)), 2817 (ν(C−H)), 1687 (ν(CO)),
517 (ν(C−N), δ(CNH)), 1403 (ν(C−(CH ) ), 798 (δ(py−H)).
C37) ppm. FT-IR spectroscopy (ν, cm ): 3392 (ν(N−H)), 2968
(
1
(ν(C−H)), 2870 (ν(C−H)), 2824 (ν(C−H)), 1689 (ν(CO)),
1522 (ν(C−N), δ(CNH)), 1450 (ν(C−(CH ) ), 751 (δ(py−H)).
3 3
+
3
3
+
+
+
HRMS (ESI , CH CN): m/z 729.424 ([C H N O ] , 729.424).
HRMS (ESI , CH
CN): m/z 744.421 ([C44H N O ] , 744.423).
3 54 7 4
3
43 53
8
3
Anal. (%) Calcd for C H N O : C 71.04, H 7.18, N 13.18. Found: C
Anal. (%) Calcd for C H N O : C 70.85, H 7.19, N 15.37. Found: C
7
43 52
8
3
4
3
52
8
3
7
1.11, H 7.26, N 12.93.
Synthesis of Dinuclear Zn Complexes. The ligand (0.137
mmol) was dissolved in methanol (5 mL), and sodium hydroxide
0.63, H 7.06, N 15.29.
HL . A solution of H L (300.0 mg, 0.41 mmol) in ethanol (10.0
II
4
3
3
mL) was treated with aqueous sodium hydroxide solution (6 M, 2
mL), after which the mixture was heated at 70 °C for 3 days while
stirring. Subsequently the solvent was removed under reduced
pressure, and the remaining solid taken up in water (10 mL).
Concentrated hydrochloric acid was added until the pH reached 1, and
the pH was subsequently adjusted to 7 using saturated sodium
bicarbonate solution. After the product was extracted into CH Cl (3
II
solution (2 M, 69 μL) was added. After addition of Zn (OAc) acetate
2
(57.8 mg, 0.274 mmol) the mixture was heated to 50 °C for 20 min.
Sodium hexafluoridophosphate (46.0 mg, 0.274 mmol) was added to
the hot solution. The compounds were obtained as colorless crystals
upon standing, and these were collected by filtration.
1
1
[
Zn (L )(OAc) ]PF (102.5 mg, 81%). H NMR (CD CN, 500.13
2
2
6
3
2
2
2
MHz): 1.95 (s, 3H, H17), 1.99 (s, 6H, H2a, H4a), 3.17 (d, 2H, J =
1.37 Hz, H13), 3.35 (d, 2H, J = 16.51 Hz, H12, H33), 3.48 (d, 2H,
J = 16.14 Hz, H12, H33), 3.88 (d, 2H, J = 11.37 Hz, H13), 3.97 (d,
2H, J = 14.31 Hz, H6, H27), 4.50 (d, 2H, J = 14.31 Hz, H6, H27),
×
10 mL) the combined organic phases were washed with saturated
2
1
sodium bicarbonate solution (10 mL) and dried over sodium sulfate.
2
2
Removal of the solvent yielded a crude product, which was purified by
column chromatography (Alox
product HL as a white solid (108.8 mg, 47%). H NMR (CD CN,
2
2
, MeOH), yielding the desired
neutral
4
1
3
6.40 (s, 2H, H15, H18), 6.44 (d, 2H, J = 7.70 Hz, H10, H31), 7.01
3
3
3
3
5
00.13 MHz): 2.18 (s, 3H, H17), 3.51 (s, 4H, H27, H33), 3.57 (s, 2H,
(dd, 2H, J = 7.34 Hz, J = 5.14, H8, H29), 7.29 (td, 2H, J = 7.70 Hz,,
3
4
3
3
H21), 3.70 (s, 2H, H13), 3.77 (s, 4H, H6, H12), 6.35 (d, 2H, J = 8.07
J = 1.47 Hz, H9, H30), 7.43 (dd, 2H, J = 7.34 Hz, J = 5.14 Hz, H2,
H23), 7.48 (d, 2H, J = 8.07 Hz, H4, H25), 7.92 (td, 1H, J = 7.79 Hz,
J = 1.65 Hz, H3, H24), 8.24 (d, 2H, J = 4.774 Hz, H7, H28), 8.76 (d,
2H, J = 4.40 Hz, H1, H22) ppm. C NMR (CD CN, 100.61 MHz):
3
3
3
Hz, H23, H29), 6.61 (d, 2H, J = 6.97 Hz, H25, H31), 6.88 (s, 1H,
H18), 6.95 (s, 1H, H15), 7.17 (ddd, 2H, J = 6.24 Hz, J = 5.14 Hz, J
3
3
4
4
3
3
3
13
=
1.10 Hz, H2, H8), 7.33 (t, 2H, J = 7.70 Hz, H24, H30), 7.46 (d, 2H,
3
3
3
4
J = 7.70 Hz, H4, H10), 7.66 (td, 2H, J = 7.70 Hz, J = 1.83 Hz, H3,
20.15 (C17), 24.91 (C35), 58.50 (C12, C33), 60.67 (C13, C21), 60.76
(C6, C27), 121.94 (C10, C31), 123.63 (C8, C29), 124.32 (C14, C19),
124.95 (C2, C23), 125.08 (C16), 125.18 (C4, C25), 131.90 (C15,
C18), 138.60 (C9, C30), 140.30 (C3, C24), 147.18 (C7, C28), 148.58
3
13
H9), 8.48 (d, 2H, J = 5.14 Hz, H1, H7) ppm. C NMR (CD CN,
3
1
00.61 MHz): 20.47 (C17), 52.51 (C13), 54.96 (C21), 60.20 (C27,
C33), 60.54 (C6, C12), 107.83 (C23, C29), 113.09 (C25, C31), 123.24
N
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4
1
(
C1, C22), 155.83 (C11, C32), 156.30 (C5, C26), 160.22 (C20),
[Zn (L )(OAc) ]PF (47.5 mg, 50%):. H NMR (CD CN, 500.13
2 2 6 3
−1
1
2
8
79.27 (C34) ppm. FT-IR spectroscopy (ν, cm ): 2996 (ν(C−H)),
MHz): 1.85 (s, 3H, H2a/H4a), 1.94 (s, 3H, H17), 2.05 (s, 3H, H2a/
H4a), 3.02 (d, 1H, J = 11.37 Hz, H13/H21), 3.17 (d, 1H, J = 15.77
Hz, H33), 3.24 (d, 1H, J = 15.77 Hz, H33), 3.28 (d, 1H, J = 10.64
Hz, H13/H21), 3.35 (d, 1H, J = 16.51 Hz, H12), 3.50 (d, 1H, J =
16.51 Hz, H12), 3.57 (d, 1H, J = 13.94 Hz, H27), 3.80 (d, 1H, J =
11.37 Hz, H13/H21), 4.03 (d, 1H, J = 14.67 Hz, H6), 4.33 (d, 1H, J
= 10.64 Hz, H13/H21), 4.40 (dd, 2H, J = 14.12 Hz, J = 10.09 Hz,
H6, H27), 5.58 (d, 1H, J = 7.34 Hz, H31), 5.78 (bs, 2H, NH ), 6.05
2
2
931 (ν(C−H)), 2844 (ν(C−H)), 1600 (ν (OAc)), 1406 (ν (OAc)),
a
s
+
2
2
31 (ν(P−F)), 650 (δ(py-H)), 556 (δ(F−P−F)). HRMS (ESI ,
2+
2
2
CH CN): m/z 360.070 ([C H N O Zn ] , 360.069); 765.138
(
7
C H N O PF Zn : C 48.10, H 4.26, N 9.11. Found: C 48.10, H
4
3
35 36
6
3
2
+
+
2
2
[C H N O Zn ] , 765.136). HRMS (ESI , CH OH): m/z
79.154 ([C H N O Zn ] , 779.153). Anal. (%) Calcd for
3
6
37
6
5
2
3
+
2
2
3
7
39
6
5
2
2
2
3
7
39
6
5
6
2
3
.50, N 9.11.
2
Zn (H L )(OAc) ]PF (116.6 mg, 76%). 1H NMR (CD CN,
2
3
4
[
(d, 1H, J = 8.10 Hz, H29), 6.29 (d, 1H, J = 1.83 Hz, H15/H18),
6.45−6.53 (m, 3H, H10, H15/H18, H23), 6.55 (d, 1H, J = 7.34 Hz,
H25), 6.67 (bs, 2H, NH ), 6.88 (dd, 1H, J = 8.44 Hz, J = 7.34 Hz,
2
2
2
6
3
3
5
6
4
00.13 MHz): 1.27 (s, 18H, H36, H39), 1.91 (s, 3H, H17), 2.12 (s,
2
3
3
H, H2a, H4a), 3.19 (d, 2H, J = 11.37 Hz, H13, H21),3.42−3.56 (m,
2
2
2
3
4
H, H6, H12), 3.82 (d, 2H, J = 11.74 Hz, H13, H21), 3.97 (d, 2H, J
H30), 6.98−7.03 (m, 1H, H8), 7.33 (td, 1H, J = 7.61 Hz, J = 1.65
2
3
=
15.04 Hz, H27, H33), 4.59 (d, 2H, J = 15.04 Hz, H27, H33), 6.40
Hz, H9), 7.41−7.50 (m, 3H, H2, H4, H24), 7.93 (td, 1H, J = 7.79 Hz,
3
4
13
(
s, 2H, H15, H18), 6.59 (d, 2H, J = 7.70 Hz, H4, H10), 7.05 (dd, 2H,
J = 1.65 Hz, H3), 8.28 (m, 1H, H7), 8.72 (m, 1H, H1) ppm.
C
3
3
3
J = 6.79 Hz, J = 6.05 Hz, H2, H8), 7.16 (d, 2H, J = 7.70 Hz, H25,
NMR (CD
(C2a/C4a), 58.67 (C12), 58.72 (C33), 60.35 (C13/C21), 60.68 (C6),
0.82 (C27), 60.95 (C13/C21), 108.66 (C29), 110.53 (C31), 110.77
C23/C25), 112.71 (C23/C25), 122.02 (C10), 123.63 (C8), 124.36
C19/C14), 124.93 (C2/C19/C14), 125.00 (C2/C19/C14), 125.21
C4/C16), 125.29 (C4/C16), 131.63 (C15/C18), 131.70 (C15/C18),
38.88 (C9), 139.20 (C30), 140.32 (C3), 140.56 (C24), 147.05 (C7),
48.50 (C1), 153.88 (C26/C32), 153.94 (C26/C32), 156.09 (C5/
C11), 156.14 (C5/C11), 159.96 (C28), 160.42 (C22), 160.51 (C20),
3
CN, 100.62 MHz): 20.19 (C17), 25.03 (C2a/C4a) 25.87
3
4
3
H31), 7.38 (td, 2H, J = 7.70 Hz, J = 1.47 Hz, H3, H9), 7.85 (t, 2H, J
=
2
MHz) 19.16 (C17), 25.25 (C2a, C4a) 26.65 (C36, C39), 39.82 (C35,
C38), 57.10 (C6, C12), 60.16 (C13, C21), 61.12 (C27, C33), 115.87
3
6
7.70 Hz, H24, H30), 8.14 (d, 2H, J = 8.44 Hz, H23, H29), 8.39 (m,
H, H1, H7), 9.89 (s, 2H, NH) ppm. 13C NMR (CD CN, 100.61
(
(
(
1
1
3
(C23, C29), 119.07 (C25, C31), 121.74 (C4, C10), 122.87 (C2/C8/
C14/C19), 122.94 (C2/C8/C14/C19), 124.74 (C16), 130.42 (C15,
C18), 138.89 (C3, C9), 141.03 (C24, C30), 146.22 (C1, C7), 151.98
31
1
79.13 (C1a/C3a), 179.31 (C1a/C3a) ppm. P NMR (CD CN,
(C22, C28), 154.39 (C26, C32), 155.14 (C5, C11), 158.96 (C20),
3
−
3
1
100.61 MHz) −144.31 (sep, PF ) ppm. FT-IR spectroscopy (ν,
1
1
77.81 (C34, C37), 178.89 (C1a, C3a) ppm. P NMR (CD CN,
6
3
−1
−
cm ): 3484 (ν(N−H)), 3332 (ν(N−H)), 3218 (ν(N−H)), 2984
(ν(C−H)), 2935 (ν(C−H)), 2906 (ν(C−H)), 1643 (δ(CNH)), 1606
00.61 MHz): −144.29 (sep, PF ) ppm. FT-IR spectroscopy (ν,
6
−1
cm ): 3293 (ν(N−H)), 2976 (ν(C−H)), 2924 (ν(C−H)), 2877
(
(
ν (OAc)), 1476 (ν (OAc)), 1275 (ν(C−N)), 827 (ν(P−F)), 658
(
ν(C−H)), 1700 (ν(CO)), 1600 (ν (OAc)), 1536 (ν(C−N),
a
s
a
+
δ(py−H)), 557 (δ(F−P−F)). HRMS (ESI , CH CN): m/z 344.073
δ(CNH)), 1458 (ν(C−(CH ) ), 1406 (ν (OAc)), 1277 (ν(C−N)),
8
3
3
3
s
2 +
+
( [ C
H
N
O Z n 2
8
]
,
3 4 4 . 0 7 0 ) ; 7 4 9 . 1 5 2
41 (ν(P−F)), 650 (δ(py−H)), 557 (δ(F−P−F)). HRMS (ESI ,
3 3
3 4
+
+
2
+
+
([C H N OZn CH COO] , 749.152). HRMS (ESI , CH OH): m/
CH CN): m/z 429.128 ([C H N O Zn ] , 429.127). HRMS (ESI ,
CH OH): m/z 977.295 ([C H N O Zn ] , 977.293). Anal. (%)
Calcd for C H N O PF Zn : C 50.32, H 5.12, N 9.99. Found: C
5
33 34 8 2 3 3
3
43 50
8
3
2
+
+
z 809.177 ([C H N O Zn ] , 809.175). Anal. (%) Calcd for
37 41 8 5 2
C H N O PF Zn : C 46.61, H 4.33, N 11.75. Found: C 46.42, H
.34, N 11.74.
3
47 57
8
7
2
37 41
8
5
6
2
47
57
8
7
6
2
4
0.09, H 5.26, N 9.96.
6
3
1
[Zn (H L )(OAc)(OH)] (85.7 mg, 67%). FT-IR spectroscopy (ν,
[
Zn (H L )(OAc)(OH)]PF (23.2 mg, 16%). H NMR (CD CN,
2 2
2
2
6
3
−1
cm ): 2978 (ν(C−H)), 2932 (ν(C−H)), 2867 (ν(C−H)), 1681
(ν(CO)), 1581 (ν (OAc)), 1453 (ν(C−(CH ) ), 1433 (ν (OAc)),
5
00.13 MHz): 0.85 (s, 9H, H36/H39), 1.35 (s, 9H, H36/H39), 1.99
2
a
3
3
s
(
s, 3H, H17), 2.03 (s, 3H, H2a), 3.36 (d, 1H, J = 11.74 Hz, H13),
+
2
2
1305 (ν(C−N)), 770 (δ(py−H)). HRMS (ESI , CH CN): m/z 435.6
3
3
3
3
4
.40 (d, 1H, J = 11.74 Hz, H21), 3.56 (d, 1H, J = 15.77 Hz, H27),
2+
2
2
([C H N O Zn ] , 435.627). Anal. (%) Calcd for C H N O Zn :
44 51 7 4 2 46 55 7 7 2
.67 (d, 1H, J = 15.41 Hz, H27), 3.78 (d, 1H, J = 16.87 Hz, H12),
2
2
C 58.24, H 5.84, N 10.33. Found: C 58.02, H 5.57, N 10.19.
.84 (d, 1H, J = 17.24 Hz, H12), 3.92 (d, 1H, J = 14.31 Hz, H33),
2
.03 (d, 1H, J = 11.37 Hz, H13), 4.12−4.21 (m, 2H, H6, H21), 4.28
2
2
(
d, 1H, J = 17.97 Hz, H6), 4.38 (d, 1H, J = 14.31 Hz, H33), 6.29 (d,
ASSOCIATED CONTENT
■
3
4
4
1
1
H, J = 7.34 Hz, H25), 6.61 (sd, J = 1.83 Hz, H15), 6.64 (sd, J =
3
3
*
S
Supporting Information
.83 Hz, H18), 7.10 (d, 1H, J = 7.70 Hz, H31), 7.14 (d, 1H, J = 7.70
3
3
Hz, H10), 7.25 (dd, 1H, J = 8.44 Hz, J = 7.70 Hz, H24), 7.36 (dd,
1
=
7
8
(
2
4
The Supporting Information includes details of the crystallo-
graphic experiments, ORTEP plots of all molecular structures,
the spectroscopic characterization of the compounds used, as
well as details on the inhibition studies. CCDC 998887−
98891 and CCDC 1009842 contain the supplementary
crystallographic data. This material is available free of charge
via the Internet at http://pubs.acs.org.
3
3
3
H, J = 6.20 Hz, H8), 7.53 (d, 1H, J = 8.07 Hz, H4), 7.60 (dd, 1H, J
3
4
6.20 Hz, H2), 7.80 (td, 1H, J = 7.79 Hz, J = 1.65 Hz, H9), 7.81−
.87 (m, 2H, H23, H30), 8.08 (td, 1H, J = 7.79 Hz, J = 1.65 Hz, H3),
.33 (d, 1H, J = 8.44 Hz, H29), 8.59 (d, 1H, J = 4.77 Hz, H7), 8.80
d, 1H, J = 5.14 Hz, H1) ppm. C NMR (CD CN, 125.76 MHz):
3 4
3
3
9
3
13
3
0.18 (C17), 27.80 (C16/C39), 27.87 (C16/C39), 40.54 (C35/C38),
1.24 (C35/C38), 57.74 (C12), 58.87 (C13), 59.86 (C27), 61.29
(
(
(
(
C33), 61.38 (C6), 61.69 (C21), 114.57 (C23), 115.74 (C29), 117.72
C25), 119.15 (C31), 124.67(C10/C14), 124.73 (C10/C14), 125.03
C4), 125.25 (C8/C19), 125.29 (C8/C19), 126.10 (C2), 127.42
C16), 133.16 (C18), 133.42 (C15), 139.92 (C24), 141.43 (C30),
AUTHOR INFORMATION
■
Corresponding Author
*Fax: +49-6221-546617. E-mail: peter.comba@aci.uni-
heidelberg.de.
1
41.65 (C9), 142.62 (C3), 149.07 (C7), 149.77 (C1), 153.42 (C22/
C28), 153.72 (C26), 154.29 (C32), 155.05 (C22/C28), 156.56 (C5),
1
1
57.12 (C11), 160.00 (C20), 179.60 (C34/C37), 179.64 (C34/C37),
Notes
31
80.66 (C1a) ppm. P NMR (CD CN, 100.61 MHz): −144.29 (sep,
6
3
−
−1
The authors declare no competing financial interest.
PF ) ppm. FT-IR spectroscopy (ν, cm ): 2982 (ν(C−H)), 2937
(
1
1
ν(C−H)), 2876 (ν(C−H)), 1687 (ν(CO)), 1581 (ν (OAc)),
a
545 (ν(C−N), δ(CNH)), 1461 (ν(C−(CH ) ), 1442 (ν (OAc)),
3
3
s
ACKNOWLEDGMENTS
■
306 (ν(C−N)), 834 (ν(P−F)), 650 (δ(py-H)), 556 (δ(F−P−F)).
+
2+
Financial support by the German Science Foundation (DFG)
and the University of Heidelberg is gratefully acknowledged.
We are grateful to Prof. Paul Bernhardt (UQ) for his help with
the crystal structure analyses.
HRMS (ESI , CH CN): m/z 429.130 ([C H N O Zn ] , 429.127);
8
C H N O PF Zn : C 50.06, H 5.13, N 10.38. Found: C 50.46, H
5
3
43 50
8
3
2
+
77.260 ([C H N O Zn F] , 877.253). Anal. (%) Calcd for
43 50 8 3 2
4
5
55
8
6
6
2
.38, N 10.57.
O
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
33) Kinoshita, E.; Takahashi, M.; Takeda, H.; Shiro, M.; Koike, T.
REFERENCES
■
Dalton Trans. 2004, 1189.
34) Daumann, L. J.; Dalle, K. E.; Schenk, G.; McGeary, R. P.;
Bernhardt, P. V.; Ollis, D. L.; Gahan, L. R. Dalton Trans. 2012, 41,
695−1708.
35) Gorenstein, D. G. Phosphorus-31 NMR: Principles and
Applications; Accademic Press: Orlando, FL, 1984.
36) Sheldrick, G. M.SHELXS; University of Gottingen: Go
Germany, 1997.
37) Sheldrick, G. M. SHELXL97; Release 97-2; Universitat
Gottingen: Gottingen, Germany, 1998.
38) Carvalho, N. M. F.; Horn, A., Jr.; Bortoluzzi, A. J.; Drago, V.;
Antunes, O. A. C. Inorg. Chim. Acta 2006, 359, 90−98.
39) Johannsson, A.; Abrahamsson, M.; Magnuson, A.; Huang, P.;
Martensson, J.; Styring, S.; Hammarstrom, L.; Sun, L.; Åkermark, B.
Inorg. Chem. 2003, 42, 7502−7511.
40) Carlsson, H.; Haukka, M.; Bousseksou, A.; Latour, J.-M.;
Nordlander, E. Inorg. Chem. 2004, 43, 8252−8262.
41) Sun, G.-C.; He, Z.-H.; Li, Z.-J.; Yuan, X.-D.; Yang, Z.-J.; Wang,
G.-X.; Wang, L.-F.; Liu, C.-R. Molecules 2001, 6, 1001−1005.
42) Lambert, E.; Chabut, B.; Chardon-Noblat, S.; Deronzier, A.;
(
(
(
1) Kimura, E. Curr. Opin. Chem. Biol. 2000, 4, 207−213.
(
2) Weston, J. Chem. Rev. 2005, 105, 2151−2174.
́
3) Mitic, N.; Smith, S. J.; Neves, A.; Guddat, L. W.; Gahan, L. R.;
1
(
Schenk, G. Chem. Rev. 2006, 106, 3338−3363.
4) Jarenmark, M.; Csapo, E.; Singh, J.; Wockel, S.; Farkas, E.; Meyer,
F.; Haukka, M.; Nordlander, E. Dalton Trans. 2010, 39, 8183−8194.
5) Schenk, G.; Mitic, N.; Hanson, G.; Comba, P. Coord. Chem. Rev.
Special Issue Ed Solomon) 2013, 257, 473−482.
6) Carlsson, H.; Nordlander, E.; Jarenmark, M. C. R. Chim. 2007,
0, 433−462.
7) Jarenmark, M.; Kappen, S.; Haukka, M.; Nordlander, E. Dalton
Trans. 2008, 993−996.
8) Daumann, L.; Marty, L.; Schenk, G.; Gahan, L. R. Dalton Trans.
013, 42, 9574−9584.
9) Desbouis, D.; Troitsky, I. P.; Belousoff, M. J.; Spiccia, L.; Graham,
B. Coord. Chem. Rev. 2012, 256, 897−937.
10) Feng, G.; Natale, D.; Prabaharan, R.; Mareque-Rivas, J. C.;
Williams, N. H. Angew. Chem., Int. Ed. 2006, 45, 7056−7059.
11) de Souza, B.; Kreft, G. L.; Bortolotto, T.; Terenzi, H.;
(
(
̈
̈
ttingen,
(
́
(
(
1
(
̈
̈
̈
(
(
(
(
2
(
̊
̈
(
(
(
(
(
Bertoluzzi, A. J.; Castellano, E. E.; Peralta, R. A.; Domingos, J. B.;
Neves, A. Inorg. Chem. 2013, 52, 3594−3596.
12) Comba, P.; Gahan, L. R.; Hanson, G. R.; Mereacre, V.; Noble,
Chottard, G.; Bousseksou, A.; Tuchagues, J.-P.; Laugier, J.; Bardet, M.;
Latou, J.-M. J. Am. Chem. Soc. 1997, 119, 9424−9437.
(43) Jovito, R.; Neves, A.; Bortoluzzi, A. J.; Lanznaster, M.; Drago,
V.; Haase, W. Inorg. Chem. Commun. 2005, 8, 323−327.
(44) Drewry, J. A.; Fletcher, S.; Hassan, H.; Gunning, P. T. Org.
Biomol. Chem. 2009, 7, 5074−5077.
(
C. J.; Powell, A. K.; Prisecaru, I.; Schenk, G.; Zajaczkowski-Fischer, M.
Chem.Eur. J. 2012, 18, 1700−1710.
(
13) Comba, P.; Gahan, L. R.; Mereacre, V.; Hanson, G. R.; Powell,
A. K.; Schenk, G.; Zajaczkowski-Fischer, M. Inorg. Chem. 2012, 51,
2195−12209.
14) Mohamed, M. F.; Brown, R. S. J. Org. Chem. 2010, 75, 8471−
477.
15) Suzuki, M.; Kanatomi, H.; Murase, I. Chem. Lett. 1981, 10,
745−1748.
16) Borovik, A. S.; Papaefthymiou, V.; Taylor, L. F.; Anderson, O.
P.; Que, L. J. Am. Chem. Soc. 1989, 111, 6183−6195.
17) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor,
G. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.
18) Selmeczi, K.; Michel, C.; Milet, A.; Gautier-Luneau, I.; Philouze,
C.; Pierre, J.-L.; Schnieders, D.; Rompel, A.; Belle, C. Chem.Eur. J.
007, 13, 9093−9106.
19) Berreau, L. M.; Saha, A.; Arif, A. M. Dalton Trans. 2006, 183−
92.
20) Matsufuji, K.; Shiraishi, H.; Miyasato, Y.; Shiga, T.; Ohba, M.;
Yokoyama, T.; Okawa, H. Bull. Chem. Soc. Jpn. 2005, 78, 851−858.
21) Mareque-Rivas, J. C.; Prabaharan, R.; Parsons, S. Dalton Trans.
004, 1648−1655.
22) Hough, E.; Hansen, L. K.; Birknes, B.; Jynge, K.; Hansen, S.;
Hordvik, A.; Little, C.; Dodson, E.; Derewenda, Z. Nature 1989, 338,
57−360.
23) Goldberg, J.; Huang, H. B.; Kwon, Y. G.; Greengard, P.; Nairn,
A. C.; Kuriyan, J. Nature 1995, 376, 745−753.
24) Hesse, M.; Meier, H.; Zeeh, B. Spectroscopic Methods in Organic
Chemistry, 2nd ed.; G. Thieme: New York, 1997.
25) Guenzler, H.; Gremlich, H.-U. IR Spectroscopy: An Introduction;
Wiley-VCH: Weinheim, 2002.
26) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, Part B; Wiley-VCH: New York, 1997.
27) Daumann, L. J.; Gahan, L. R.; Comba, P.; Schenk, G. Inorg.
Chem. 2012, 51, 7669−7681.
28) Segel, I. H. Enzyme Kinetics - Behavior and Analysis of Rapid
Equilibrium and Steady-State Enzyme Systems; Wiley-VCH: New York,
975.
29) Kantacha, A.; Buchholz, R.; Smith, S.; Schenk, G.; Gahan, L. J.
Biol. Inorg. Chem. 2011, 16, 25−32.
30) Mareque-Rivas, J. C.; Prabaharan, R.; de Rosales, R. T. M. Chem.
Commun. 2004, 76.
31) Coburn, S. P.; Mahuren, J. D.; Jain, M.; Zubovic, Y.; Wortsman,
J. J. Clin. Endocrinol. Metab. 1998, 83, 3951−3957.
32) Fernley, H. N.; Walker, P. G. Biochem. J. 1967, 104, 1011−1018.
(45) Das, B.; Haukka, M.; Nordlander, E. Acta Cryst. 2014, E70,
m120−m121.
1
(
8
(
1
(
(
(
2
(
1
(
(
2
(
3
(
(
(
(
(
(
1
(
(
(
(
P
dx.doi.org/10.1021/ic5009945 | Inorg. Chem. XXXX, XXX, XXX−XXX