Preparation of an lsocyano-β-di ketone via its metal complexes, by use of metal ions as protecting groups

Article abstract of DOI:10.1021/ic900202e

A ligand containing isocyanlde and β-diketone functional groups, 3-(4-isocyanophenyl)-2,4-pentanedione (HacphNC), and several of its metal complexes have been prepared. The free isocyano-β-diketone could not be prepared by dehydration of the analogous formamide, HacphNHCHO, because of the reactivity of its β-diketone moiety. Instead, the metal complexes Al(acphNC)₃, Fe(acphNC)₃, Cu(acphNC)₂, and Zn(acphNC)₂ were synthesized by dehydration of the formamldo-β-diketonate complexes Al(acphNHCHO)₃, Fe(acphNHCHO)₃, Cu(acphNHCHO)₂, and Zn(acphNHCHO) ₂. The free isocyano-β-diketone, HacphNC, can be liberated from its Al and Fe complexes by treatment with oxalate (C₂O ₄^2-) and HC₂O₄^-. In addition to these O-bound complexes, C(N)-bound complexes can be prepared by the reaction of either Al(acphNC)₃ or HacphNC with Au(I). X-ray analyses of HacphNC, Al(acphNC)₃, (HacphNC)AuCl, Cu(acphNHCHO)₂, trans-Zn(acphNHCHO)₂(H₂O)₂, and two other intermediates are also reported.

Full text of DOI:10.1021/ic900202e

10512 Inorg. Chem. 2009, 48, 10512–10518
DOI: 10.1021/ic900202e
Preparation of an Isocyano-β-diketone via its Metal Complexes, by Use of Metal
Ions as Protecting Groups
Yixun Zhang† and Andrew W. Maverick*
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803. †Present address:
Department of Physical Sciences, University of Texas of the Permian Basin, Odessa, Texas 79762.
Received February 1, 2009
A ligand containing isocyanide and β-diketone functional groups, 3-(4-isocyanophenyl)-2,4-pentanedione
(HacphNC), and several of its metal complexes have been prepared. The free isocyano-β-diketone could not be
prepared by dehydration of the analogous formamide, HacphNHCHO, because of the reactivity of its β-diketone
moiety. Instead, the metal complexes Al(acphNC)3, Fe(acphNC)3, Cu(acphNC)2, and Zn(acphNC)2 were synthe-
sized by dehydration of the formamido-β-diketonate complexes Al(acphNHCHO)3, Fe(acphNHCHO)3, Cu-
(acphNHCHO)2, and Zn(acphNHCHO)2. The free isocyano-β-diketone, HacphNC, can be liberated from its Al and
Fe complexes by treatment with oxalate (C2O42-) and HC2O4-. In addition to these O-bound complexes, C(N)-bound
complexes can be prepared by the reaction of either Al(acphNC)3 or HacphNC with Au(I). X-ray analyses of HacphNC,
Al(acphNC)3, (HacphNC)AuCl, Cu(acphNHCHO)2, trans-Zn(acphNHCHO)2(H2O)2, and two other intermediates are
also reported.
Introduction
porous 1D ladder structure prepared from Fe(pyac)3 and
AgNO3 is of interest because the solvent guests in its pores
can be exchanged in single-crystal-to-single-crystal transfor-
mations.9
Heterofunctional ligands are of interest because of their
ability to bind to different types of metal ions. This is impor-
tant in the construction of metal-organic frameworks
(MOFs). MOFs have attracted scientists because the various
coordination geometries and abilities of metal ions together
with different types of ligands provide many possible open
framework structures. Rational design of ligands can lead to
predictable extended solid frameworks with potential appli-
cations in separation, gas storage, molecular recognition, and
catalysis.1-5
Although the above 1D Fe(pyac)3-AgNO3 porous frame-
work is stable under solvent exchange, the others are not, and
all are unstable ina vacuum. This limited stability is likelydue
to the weakness of the interactions between layers in these
networks. Our goal is to develop ligands that are suitable for
the construction of porous 3D frameworks, because they are
expected to show greatly enhanced stability. The most
promising route to 3D structures is to use conditions that
favor the assembly of six ligands coordinated octahedrally
around one metal. Although a few M(py)6nþ complexes are
known, they generally form only in the presence of excess
pyridine.10-12 Thus, pyridine-based ligands, such as pyac-,
are unlikely to be useful in preparing 3D supramolecular
materials. One common method for stabilizing metal com-
plexes is choosing chelating ligands. However, in our case, a
chelating ligand (e.g., a 2,2-bipyridine derivative) is difficult
to functionalize so that it will also bind to two other metal
atoms. Therefore, in order to improve the prospects for 3D
materials, we need to use building blocks based on stron-
gly coordinating monodentate ligands. Nitriles, such as
3-(4-cyanophenyl)acetylacetone, have been studied as
Several porous frameworks have been prepared from the
heterofunctional ligand pyridylacetylacetone (pyacH) by
Domasevitch et al.6,7 and by our group.8,9 For example, a
*To whom correspondence should be addressed. E-mail: maverick@
lsu.edu.
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pubs.acs.org/IC
Published on Web 10/12/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 22, 2009 10513
Figure 1. The bifunctional isocyano-β-diketone HacphNC.
heterofunctional ligands,13 but nitriles tend to bind weakly to
metals, making it difficult to generate six-coordinate com-
plexes M(NCR)6nþ. On the other hand, isocyanide ligands
Figure 2. Synthetic strategy for the isocyano-β-diketone HacphNC (1).
nþ
(CNR) are known to make stable complexes M(CNR)6
with metals such as Cr,14-20 Mn,21-26 Fe,27-29 and Re.30-34
Early on, Sacco and Naldini synthesized highly stable
manganese(I) isocyanide complexes [(RNC)6Mn]þ.21-23
More recently, Barybin et al. have prepared a number of
homoleptic isocyanide complexes (e.g., Cr(CNFc)6 (Fc =
ferrocenyl)19) in high yield, using only a slight excess of the
isocyanide ligand.
We were interested in HacphNC (1, Figure 1), with one
isocyanide and one β-diketone moiety, for possible conver-
sion to 3D porous materials. This ligand’s isocyanide moiety
should be able to bind to “soft” metals such as Cr(0), Mn(I),
or Fe(II) and its β-diketone moiety to “hard” metals such as
Cu(II) or Zn(II). We report here the preparation of the
HacphNC ligand and the properties of several of its metal
complexes.
Figure 3. Two possible routes for preparing HacphNHCHO (2).
Results and Discussion
Synthetic Strategy. Figure 2 illustrates the overall
route we chose for synthesizing the target compound,
HacphNC (1), via 3-(4-formamidophenyl)acetylacetone
(HacphNHCHO, 2), from 4-nitrobenzaldehyde (3). Re-
duction of the nitro group of 3 and formylation of the
resulting amine, and conversion of its aldehyde to a
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Figure 4. Protection of the β-diketone group by coordination to metal
ions prior to isocyanide synthesis.
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β-diketone, was expected to yield 2. Isocyanides are
normally prepared by dehydration of formamides; thus,
dehydration of 2 was expected to produce 1.
::
(24) Ericsson, M. S.; Jagner, S.; Ljungstrom, E. Acta Chem. Scand. A
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::
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We tested two possible routes starting from 4-nitro-
benzaldehyde (3) to make 2 (Figure 3). In route A, the
aldehyde group is converted into a β-diketone first
(making 5), and then the nitro group is reduced to an
amino group and formylated. In route B, the nitro
group is reduced to an amino group and formylated
first (6), and then the aldehyde is converted into a
β-diketone.
After the aldehyde group is converted into a β-dike-
tone, it is coordinated to metal ions, which serve as a
“protecting group” (Figure 4). The metal formamido-
β-diketonate complex 7 can then be dehydrated to an iso-
cyanide complex (8). Free HacphNC (1) can be liberated
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10514 Inorganic Chemistry, Vol. 48, No. 22, 2009
Zhang and Maverick
Figure 5. Synthesis and ellipsoid plot of (4-nitrophenyl)phospholane
intermediate 9.
by treatment of the metal isocyano-β-diketonate complex
with a suitable metal-complexing agent or with dilute
acid.
Synthesis of HacphNHCHO (2). We attempted to
prepare 3-(4-nitrophenyl)acetylacetone (5) by route A.
4-Nitrobenzaldehyde (3) was mixed with 2,2,2-tri-
methoxy-4,5-dimethyl-1,3,2-dioxaphospholene (4) in di-
chloromethane for one day, and then the mixture was
refluxed in anhydrous methanol for three days. (The
conversion of aromatic aldehydes to 3-arylacetylacetones
by reaction with 4 was first explored by Ramirez et al.35)
The first stage of this reaction proceeds cleanly, produ-
cing 9 (4-acetyl-4-methyl-5-(4-nitrophenyl)-2,2,2-trime-
thoxy1,3,2-dioxaphospholane; Figure 5). We identified
9 by NMR spectroscopy and by X-ray analysis (see the
Supporting Information). However, our attempts to con-
vert 9 to the desired (4-nitrophenyl)acetylacetone 5, under
several different conditions, were unsuccessful. (This may
be due to the electron-withdrawing effect of the nitro
group in 9.)
Because route A was not successful (see Figure 3), we
turned to route B for the synthesis of 2. Conversion of 3 to
6 proceeds by initial reduction to produce 4-aminoben-
zaldehyde, followed by rapid formylation to make 6. The
intermediate 4-aminobenzaldehyde self-condenses to
yield insoluble polymeric products; thus, it should be
formylated as quickly as possible to give a good yield of
4-formamidobenzaldehyde (6). Hrvatin and Sykes36 re-
ported the conversion of 3 to 6 using tin metal and formic
acid in toluene. We modified their procedure by replacing
toluene (as solvent) with a mixture of ethyl formate and
ethyl acetate, increasing the amount of formic acid, and
adding the tin metal in smaller portions. Our modifica-
tions in the procedure were designed to keep all of the
liquid components of the reaction mixture miscible, gen-
erate 4-aminobenzaldehyde more slowly, and formylate it
faster to make 6; the resulting yield was higher (66%, vs
lit.36 47%).
Figure 6. Preparation of formamido-β-diketonate complexes 10-13
and their conversion to isocyano-β-diketonate complexes 14-17.
Figure 7. Crystal structure of Cu(Z-acphNHCHO)2 (12).
tautomerism (in CDCl3, 94% enol: 6% keto by 1H
NMR).
Syntheses of M(acphNHCHO)n. The β-diketone moi-
ety of 2 required protection before dehydration of the
formamido group to an isocyanide. (Attempts to prepare
1 directly by the dehydration of 2 were unsuccessful;
see below.) We chose metal ions as “protecting groups”
for the β-diketone because there are numerous proce-
dures available for preparing metal β-diketonates.
Also, dehydration of the resulting metal formamido-
β-diketonates (M(acphNHCHO)n) should yield metal
isocyano-β-diketonates (M(acphNC)n), which may be
useful in building supramolecular structures even with-
out isolation of free HacphNC (1). We chose the metal
ions Al3þ, Fe3þ, Cu2þ, and Zn2þ, to react with 2
(Figure 6).
We prepared Al(acphNHCHO)3 (10) and Fe(acphNH-
CHO)3 (11) by the reaction of Al(NO3)3 and Fe(NO3)3, res-
pectively, with HacphNHCHO (2) in the presence of NaH-
CO3. This is similar to previously published procedures for
Al(pyac)3 and Fe(pyac)3.7,9,37 The products are soluble in
DMSO and acetone, and slightly soluble in chloroform and
dichloromethane.
Compound 6 reacts with phospholene 4 in dichloro-
methane to generate β-diketone 2 (HacphNHCHO,
Figure 3), which was purified by column chromatography
and isolated as yellow crystals. Both E and Z forms of 2
and 6 were characterized (see the Supporting In-
formation). The new β-diketone 2 also exhibits keto-enol
Bluish-green Cu(acphNHCHO)2 (12) precipitates im-
mediately when 2 and copper(II) acetate are mixed to-
gether in water/methanol solution. Compound 12 (see
Figure 7) is slightly soluble in DMSO and soluble in
pyridine, but insoluble in almost all other common
(35) Ramirez, F.; Bhatia, S. B.; Patwardhan, A. V.; Smith, C. P. J. Org.
Chem. 1967, 32, 3547–3553.
(36) Hrvatin, P.; Sykes, A. G. Synlett 1997, 1069–1070.
(37) Mackay, L. G.; Anderson, H. L.; Sanders, J. K. M. J. Chem. Soc.,
Perkin Trans. 1 1995, 2269–2273.

Article
Inorganic Chemistry, Vol. 48, No. 22, 2009 10515
Figure 8. Ellipsoid plot of trans-Zn(Z-acphNHCHO)2(H2O)2 (13),
from the crystal structure of its dihydrate.
solvents. The structure of 12 also contains intermolecular
˚
contacts (Cu1 O3, 2.838(2) A), which make the struc-
3 3 3
ture polymeric and give the Cu atoms an approximately
octahedral coordination geometry overall.
trans-Zn(acphNHCHO)2(H2O)2 (13) is made from zinc
acetate and 2, with added NaHCO3. Crystals grown
during the synthesis were suitable for single-crystal
X-ray analysis. In the structure of 13 (see Figure 8), the
two β-diketonate groups form a stepped arrangement
about Zn2þ. This contrasts with the structure of 12, in
which the two acac moieties are coplanar. Compound 13
is readily soluble in DMSO and pyridine, and slightly
soluble in chloroform and dichloromethane.
Figure 9. Ellipsoid plot of Al(acphNC)3 (14), from the crystal structure
of its hexane solvate.
M(acphNC)n Complexes. All four metal formamido-
β-diketonate complexes (10-13) can be dehydrated by
POCl3 in the presence of diisopropylamine (Figure 6), in a
dichloromethane solution. The starting materials are not
very soluble in CH2Cl2, whereas the products dissolve
readily. The Al, Fe, and Zn starting materials (10, 11, and
13) all react within 2 h. In contrast, most of the copper
starting material (12) still remains as unreacted solid even
after five days. This slow reaction may be due to the fact
that 12 is polymeric in the solid state (see Figure 7). Such
polymerization would explain the low solubility of 12 and
also interfere sterically with the dehydration reaction. A
similar phenomenon is observed with Cu(pyac)2: its
crystals are also polymeric, which leads to low solubility
in a variety of solvents.38
Figure 10. Illustration of the crystal structure of Al(acphNC)3, viewed
parallel to the a axis. One orientation of the Al(acphNC)3 molecules is
shown in purple, and the inversion-related orientation is in gold. The blue
˚
˚
surfaces, calculated with a 0.9 A probe radius and a 0.7 A grid, enclose
3
voids of ca. 400 A , or 21% of the unit cell volume.
˚
The IR absorptions (νCtN) for the isocyano-β-diketo-
nate complexes Al(acphNC)3 (14), Fe(acphNC)3 (15),
Cu(acphNC)2 (16), and Zn(acphNC)2 (17) appear at
2121, 2126, 2147, and 2124 cm-1, respectively. The values
for 14, 15, and 17 are very close to those for free aryl
isocyanide ligands39-42 and for the free ligand HacphNC
(2122 cm-1; see below). The higher frequency for the Cu
complex (16) may again indicate coordination of the
isocyanide groups to adjacent Cu atoms, but it could be
obtained only in impure form. The yield for 17 was low
(13%); this may be due to the fact that the Zn complex
reactant, 13, was hydrated, and its water of hydration
could react readily with POCl3. However, an attempt
using an excess of POCl3 still gave a low yield of 17.
Preparation of Al(acphNC)3 and Fe(acphNC)3 (14 and
15), on the other hand, proceeded in 75% and 90% yield,
respectively, relatively high values for the transformation
of three identical functional groups in the same molecule.
The crystal structure of Al(acphNC)3 (14) is shown in
Figure 9. Molecules of Al(acphNC)3 in the crystal are
crudely trigonal in shape, but their CN Al NC
3 3 3 3 3 3
angles (137.7°, 81.9°, and 140.3°) show large deviations
from the ideal 120°. Similarly large distortions have been
observed in the structures of Al(pyac)343 and Fe(pyac)3.7,9
Initial solution of the crystal structure of Al(acphNC)3
revealed molecules of 14, but also a region with poorly
defined electron density attributable to solvent molecules.
Several approximately evenly spaced difference electron
density peaks of similar intensity were observed in the
solvent region, which suggested a hydrocarbon. Because
hexane had been used in the crystallization process, our
first model included disordered partially occupied hexane
molecules in this region, with an overall formula of
Al(acphNC)3 0.5C6H14. For the final refinement, how-
3
ever, the solvent contribution to the data was removed
using SQUEEZE44 (in PLATON45): approximately 58
electrons were removed per unit cell (corresponding to ca.
0.58 molecule of hexane per formula unit), and a void of
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10516 Inorganic Chemistry, Vol. 48, No. 22, 2009
Zhang and Maverick
Figure 11. Displacement of metal ions from Al(acphNC)3 (14) and
Fe(acphNC)3 (15) to produce the free isocyano-β-diketone ligand
HacphNC (1).
Figure 13. Crystal structure of HacphNCAuCl (18). Adjacent mole-
cules in the crystal are arranged to form zigzag chains of weak Au Au
3 3 3
˚
interactions (3.466 A), similar to those previously reported for (2,6-
Me2C6H3NC)AuX (X = Br, I).39
complex (14) with (Me2S)AuCl, giving HacphNCAuCl
(18) and Al(acphNCAuCl)3 (19), respectively. These pro-
ducts were characterized by NMR and IR, and crystals of
18 suitable for X-ray analysis were also obtained
(Figure 13). The νCtN values are higher in the products
compared to HacphNC (2122 cm-1), as expected: 2223
and 2222 cm-1 for 18 and 19, respectively. These values
are very close to that observed by Uson et al. for
PhNCAuCl (2230 cm-1).41 The Al-Au complex 19 is
an example in which both the soft (isocyanide) and hard
(β-diketonate) moieties of HacphNC are coordinated to
metal ions.
Figure 12. Crystal structure of HacphNC (1).
3
ca. 400 A per unit cell was left behind, see Figure 10. This
˚
void has approximately the right volume for two hexane
molecules (on the basis of the density of liquid hexane at
25 °C, 0.655 g cm-3, the volume of one molecule of hexane
Conclusion
The first ligand combining isocyanide and β-diketone
groups, 3-(4-isocyanophenyl)-2,4-pentanedione (HacphNC),
has been synthesized. The ligand was first prepared in the form
of its Al, Fe(III), Cu(II), and Zn complexes. Treatment of the
Al and Zn complexes with dilute acid, or of the Al and Fe
complexes with C2O42-/HC2O4-, liberates the target ligand
HacphNC. The isocyanide moieties in both the free ligand
HacphNC and its Al complex Al(acphNC)3 can also bind to
Au(I). We are now extending the chemistry of HacphNC to
metals that will yield higher coordination numbers, for the
construction of 3D supramolecular structures.
3
˚
is approximately 219 A ). Thus, it is possible that the
crystals formed as Al(acphNC)3 C6H14 (Z=2), but some
3
hexane was lost during selection and mounting. This
propensity for solvent loss is consistent with the micro-
analysis for 14 (see the Experimental Section), which fits
well with the ansolvous compound.
Synthesis of HacphNC. We attempted to prepare the
free HacphNC ligand (1) directly from 2 by treatment
with POCl3. Spectra of this reaction mixture indicated
that the formamide moieties were consumed (NMR) and
isocyanide was formed (IR). However, the NMR spectra
indicated that the β-diketone group was destroyed under
the reaction conditions. Instead, we isolated HacphNC
from its Al, Fe, and Zn complexes (14, 15, and 17).
We explored two strategies for obtaining HacphNC (1)
from its complexes. First, we treated 14, 15, and 17 with
dilute acetic acid; this produced the desired HacphNC,
but only in low yields (ca. 10%). Second, we treated
CH2Cl2 solutions of Al(acphNC)3 (14) and Fe(acphNC)3
(15) with aqueous solutions prepared from oxalic
acid and oxalate salts as extractants. In this scheme
(Figure 11), the Hþ from the acid is designed to protonate
the coordinated β-diketonate ligand, and the oxalate is
designed to complex the liberated Fe3þ. The procedure
with Fe(III) has the advantage that the colors of
Fe(acphNC)3 and Fe(C2O4)33- make it easy to determine
visually when the extraction of the metal ion into the
aqueous layer is complete. With an excess of oxalate, we
obtained HacphNC in 37% yield from Fe(acphNC)3;
yields from Al(acphNC)3 were lower. The crystal struc-
ture of 1 (IR νCtN 2122 cm-1) is shown in Figure 12.
To explore the reactivity of the isocyanide moiety of
HacphNC, we treated both the free ligand (1) and its Al
Experimental Section
A Bruker DPX-250 instrument (250 MHz) was used for
NMR spectroscopy. All IR spectra were performed on thin
films with the use of a Bruker Tensor 27 spectrometer. Single-
crystal X-ray diffraction data were collected with use of a
Nonius KappaCCD instrument; the results are summarized
in Tables 1 and 2. All experimental procedures were carried
out in the air unless otherwise noted. Crystal-structure illus-
trations were prepared using CSD Mercury, version 2.2
(Figure 10) and Ortep-3 for Windows.
4-Formamidobenzaldehyde (OHC-4-C6H4NHCHO, 6). 4-
Formamidobenzaldehyde was first synthesized by Hrvatin and
Sykes36 in formic acid/toluene. We obtained a higher yield of the
product by using a mixture of ethyl formate and ethyl acetate as
the reactant/solvent, and by adding the tin metal in two por-
tions. 4-Nitrobenzaldehyde (6.04 g, 40 mmol) was dissolved in a
mixture of formic acid (90%, 60 mL), ethyl formate (50 mL),
and ethyl acetate (150 mL). The solution was refluxed under
nitrogen with stirring. Tin metal (9.0 g, 76 mmol) was added in
two equal portions: one immediately and the other after 24 h.
The reaction was complete after three days, as judged by TLC.
The solution was filtered hot and evaporated nearly to dryness.
Toluene (300 mL) was added to the residue and the mixture
refluxed with a Dean-Stark trap for about 2 h to remove the

Article
Inorganic Chemistry, Vol. 48, No. 22, 2009 10517
Table 1. Crystal Data and Refinement Parameters for the Isocyano-β-diketone 1 and Related Compounds
compd
formula
fw
1
(E)-2
(Z)-2
(E)-6
9
C
12H11NO2
201.22
P21/c
7.0820(15)
11.606(3)
12.427(3)
90
93.666(13)
90
1019.3(4)
4
110
1.311
0.090
C12H13NO3
219.23
C2/c
14.379(3)
10.339(2)
14.974(4)
90
91.296(15)
90
2225.5(9)
8
110
C12H13NO3
219.23
P21/c
13.289(2)
7.5180(15)
11.561(2)
90
111.153(8)
90
1077.2(3)
4
110
C8H7NO2
149.15
P21
4.3910(15)
6.917(2)
11.793(3)
90
97.81(2)
90
354.86(18)
2
110
C14H20NO8P
361.28
Pca21
13.383(2)
17.884(2)
13.509(3)
90
space group
˚
a, A
˚
b, A
˚
c, A
R
β
γ
V, A
Z
90
90
3
˚
3233.3(9)
8
110
T, K
Dcalcd, g cm-3
μ, mm-1
R (I > 2σ(I))
Rw (all data)
1.309
0.095
0.0473
0.1194
1.352
0.098
0.0424
0.1109
1.396
0.102
0.0396
0.0995
1.484
0.214
0.0539
0.1572
0.0233
0.0629
Table 2. Crystal Data and Refinement Parameters for Metal Complexes
a
12
Cu(acphNH- CHO)2
13 2H2O
3
14 0.58C6H14
3
compd
formula
fw
[trans-Zn(acphNHCHO)2(H2O)2] 2H2O
Al(acphNC)3 0.58C6H14
18 HacphNCAuCl
3
3
C24H24CuN2O6
500.00
P21/n
8.136(2)
7.480(2)
17.771(4)
90
103.166(7)
90
1053.1(5)
2
110
C24H28N2O8Zn 2H2O
3
C36H30AlN3O6 0.58C6H14
3
C12H11AuClNO2
433.63
P21/n
14.638(3)
6.4219(12)
14.919(2)
90
117.761(6)
90
1241.0(4)
4
90
573.89
P21/c
677.59
P1
space group
˚
a, A
12.442(5)
9.637(4)
11.947(5)
90
114.60(2)
90
1302.5(10)
2
110
1.463
1.001
7.433(5)
13.510(10)
20.66(2)
107.65(3)
97.53(3)
94.57(3)
1944(3)
2
110
1.158
0.099
0.069
0.185
˚
b, A
˚
c, A
R
β
γ
V, A
Z
3
˚
T, K
Dcalcd, g cm-3
μ, mm-1
R (I > 2σ(I))
Rw (all data)
1.577
1.084
0.0543
0.1385
2.321
12.057
0.043
0.128
0.0537
0.1385
a 0.58C6H14 was included in fw, D, and μ; it represents the approximate amount of electron density removed by SQUEEZE44 before final refinement.
See text for details.
remaining water and formic acid. The mixture was filtered when
it was still hot, and the filtrate was evaporated to dryness. The
residue was chromatographed on silica gel with 2:1 ethyl acet-
ate/hexane. Colorless crystals of the E conformer of 6 grew
easily from the eluate by evaporation. Yield: 3.91 g (66%). MP:
134-136 °C (lit. 139 °C36). 1H NMR spectra of 6 show a mixture
of E and Z conformers immediately on mixing. In CDCl3, E:
7.24, 7.91 (E3-4, 4H, AB), 8.30 (E1, 1H, d), 8.91 (NH, 1H, d),
9.95 (E5, 1H, s). Z: 7.60 (Z1, 1H, s), 7.75, 7.88 (Z3-4, 4H, AB),
8.47 (NH, 1H, s), 9.94 (Z5, 1H, s). In DMSO-d6, E: 7.40, 7.86
(E3-4, 4H, AB), 9.03 (NH, 1H, d), 9.89 (E5, 1H, s), 10.56 (E1,
1H, d). Z: 7.79, 7.89 (Z3-4, 4H, AB), 8.37 (NH, 1H, s), 9.89 (Z5,
1H, s), 10.64 (Z1, 1H, s).
In CDCl3, E: 7.12, 7.18 (E3-4, 4H, AB), 8.19 (E1, 1H, d),
8.74 (E2, 1H, d). Z: 7.15, 7.58 (Z3-4, 4H, AB), 7.45 (Z1, 1H, s),
8.41 (Z2, 1H, s). Enol: 1.88 (CH3, 6H, s), 16.66 (OH, 1H, s).
Keto: 2.20 (CH3, 6H, s), 4.83 (CH, 1H, s). In DMSO-d6, E: 7.16,
7.23 (E3-4, 4H, AB), 8.84 (E2, 1H, d), 10.20 (E1, 1H, d). Z: 7.20,
7.62 (Z3-4, 4H, AB), 8.29 (Z2, 1H, s), 10.26 (Z1, 1H, s). Enol:
1.85 (CH3, 6H, s), 16.79 (OH, 1H, s). Keto: 2.13 (CH3, 6H, s),
5.30 (CH, 1H, s).
Al(acphNHCHO)3 (10). A solution of Al(NO3)3 9H2O
3
(1.125 g, 3.00 mmol) in 15 mL of H2O was added to a solution
of HacphNHCHO (2.19 g, 10.0 mmol) in 15 mL of CH3OH with
stirring. Then, NaHCO3 (0.756 g, 9.0 mmol) in 5 mL of H2O was
added. A light yellow precipitate formed, which was collected,
triturated with H2O (2 ꢀ 15 mL) and methanol (10 mL), and air-
dried. Yield: 1.89 g (92%). Anal. Calcd for C36H36AlN3O9: C,
3-(4-Formamidophenyl)pentane-2,4-dione (HacphNHCHO, 2).
Compound 6 (2.56 g, 17.2 mmol) and phospholene 4 (2,2,2-
trimethoxy-4,5-dimethyl-1,3,2-dioxaphospholene; 4.02 g, 19.2
mmol) were dissolved in 15 mL of dichloromethane under
argon. The reaction was complete after 3 days, as judged by
the disappearance of the aldehyde resonance in 1H NMR. The
solvent was removed, and the residue was chromatographed on
silica gel with 2:1 ethyl acetate/hexane. Yield: 1.95 g (52%). MP
(Z): 124 °C. Anal. Calcd for C12H13NO3: C, 65.74; H, 5.98; N,
6.39. Found: C, 65.59; H, 6.14; N, 6.48. Slow evaporation of
solutions of 2 yields crystals. In most of our experiments, the
crystals were of the Z conformer; in one case, we also obtained a
small amount of the E conformer in crystalline form. However,
solutions of either conformer quickly develop a second set of
1H NMR resonances attributable to the other conformer.
1
63.43; H, 5.32; N, 6.16. Found: C, 63.47; H, 5.33; N, 6.24. H
NMR (DMSO-d6): 1.77 (s, Me, 18H). E: 7.18, 7.22 (E3-4, 12H,
AB), 8.81 (E2, 3H, d), 10.18 (E1, 3H, d). Z: 7.14, 7.61 (Z3-4,
12H, AB), 8.28 (Z2, 3H, s), 10.23 (Z1, 3H, s).
Fe(acphNHCHO)3 (11). A solution of Fe(NO3)3 9H2O (3.43
3
g, 8.5 mmol) in 15 mL of H2O was added to a solution of
HacphNHCHO (6.65 g, 30.4 mmol) in 40 mL of CH3OH with
stirring. Then, NaHCO3 (2.14 g, 25.5 mmol) in 25 mL of H2O
was added. A deep red precipitate formed, which was collected;
washed with H2O (2 ꢀ 15 mL), methanol (2 ꢀ 15 mL), and
acetone (2 ꢀ 15 mL); and dried at 100 °C. Yield: 3.77 g (62%).
Cu(acphNHCHO)2 (12). Cu(OAc)2 H2O (0.363 g, 1.82
3
mmol) in 7 mL of H2O was added to a solution of HacphNHCHO

10518 Inorganic Chemistry, Vol. 48, No. 22, 2009
Zhang and Maverick
(0.92 g, 4.2 mmol) in 8 mL of methanol, with stirring. A blue-
green precipitate formed, which was collected, washed with H2O
and methanol, and air-dried. Yield: 0.90 g (99%). Anal. Calcd
for C24H24CuN2O6: C, 57.64; H, 4.84; N, 5.60. Found: C, 57.49;
H, 4.63; N, 5.58. Crystals suitable for X-ray analysis were grown
from DMSO/water.
form, even after trituration with several solvents, but its IR
.
spectrum showed νCtN=2147 cm-1
Zn(acphNC)2 (17). Zn(acphNHCHO)2 2H2O (0.163 g, 0.30
3
i
mmol) and Pr2NH (0.217 g, 2.15 mmol) were dissolved in
dichloromethane (10 mL). POCl3 (0.110 g, 0.72 mmol) was
added slowly to the solution, with stirring. The whole solution
became clear in 30 min. The solution was washed with 10 mL of
10% NaHCO3(aq). The CH2Cl2 layer was separated, dried
(Na2SO4), and evaporated to 10-15 mL, and hexane was added
to precipitate the product as a yellow powder. Yield: 0.018 g
(13%). IR: 2124 cm-1. 1H NMR (250 MHz, CDCl3): 1.87 (12H,
s), 7.23, 7.42 (8H, AB).
trans-Zn(acphNHCHO)2(H2O)2 (13). Solutions of Zn(OAc)2
3
2H2O (0.11 g, 0.50 mmol, in 5 mL of H2O) and HacphNHCHO
(0.22 g, 1.00 mmol, in 3 mL of CH3OH) were mixed. NaHCO3
(0.08 g, 1.0 mmol) in 2 mL of H2O was added to this mixture, and
a yellow precipitate formed immediately. The precipitate was
collected; washed with dichloromethane, H2O, and diethyl
ether; and dried at 70 °C overnight. Yield: 0.11 g (40%). This
material contained both E and Z conformers of its formamide
moieties, as judged by its 1H NMR spectrum immediately after
dissolving in DMSO-d6: 1.65 (s, Me, 12H). E: 7.16, 7.19 (E3-4,
8H, AB), 8.81 (E2, 2H, d), 10.13 (E1, 2H, d). Z: 7.14, 7.58 (Z3-4,
8H, AB), 8.28 (Z2, 2H, s), 10.18 (Z1, 2H, s). Meanwhile, light
3-(4-Isocyanophenyl)pentane-2,4-dione (HacphNC, 1). The
iron(III) isocyano-β-diketonate complex Fe(acphNC)3 (17;
1.36 g, 2.07 mmol) was dissolved in 100 mL of dichloromethane.
Oxalic acid (H2C2O4 2H2O, 2.52 g, 20.0 mmol) and potassium
3
oxalate (K2C2O4 H2O, 33.12 g, 180.0 mmol) were dissolved in
3
200 mL of distilled water. These two solutions were stirred
together for 20 min, and the red color in the organic layer
disappeared, indicating that the reaction was complete. The
organic phase was then separated, and the aqueous layer was
extracted with 50 mL of dichloromethane. The organic phases
were combined, dried over Na2SO4, and evaporated to ca. 3 mL.
This residue was chromatographed with ethyl acetate-hexane
(1:1 v/v). Yield: 0.46 g (37%). Anal. Calcd for C12H11NO2: C,
yellow single crystals of [trans-Zn(acphNHCHO)2(H2O)2]
2H2O (i.e., 13 2H2O, with Z-formamides) were obtained from
3
3
the H2O/methanol filtrate the next day; this material was
suitable for X-ray analysis.
Al(acphNC)3 (14). To a solution of Al(acphNHCHO)3 (1.023
g, 1.50 mmol) and diisopropylamine (1.50 g, 14.8 mmol) in
CH2Cl2 (50 mL) was added POCl3 (0.690 g, 4.50 mmol) at room
temperature under argon. After stirring for 1 h, the whole
solution became clear. It was washed with 10% NaHCO3 (20
mL), and the CH2Cl2 layer was separated and evaporated to
10-15 mL. Hexane was added to this solution to precipitate the
powdery yellow product, which was dried at 70 °C. Yield: 0.710
g (75%). Anal. Calcd. for C36H30AlN3O6: C, 68.89; H, 4.82; N,
1
71.63; H, 5.51; N, 6.96. Found: C, 71.44; H, 5.36; N, 7.03. H
NMR (250 MHz, CDCl3): 1.89 (6H, s), 7.23, 7.42 (4H, AB),
16.71 (1H, s). IR: 2122 cm-1. Compound 1 decomposed at ca.
140 °C without melting. Crystals suitable for X-ray crystal-
lography were grown by slow evaporation of a solution in ethyl
acetate-hexane (1:2 v/v).
6.70. Found: C, 68.69; H, 4.81; N, 6.78. IR: 2121 cm-1 1H
.
HacphNCAuCl (18). (Me2S)AuCl (0.059 g, 0.20 mmol) and
HacphNC (0.044 g, 0.22 mmol) were dissolved in CHCl3 (3 mL)
and refluxed for 1 h. The solution was evaporated at 45 °C to
remove the solvent and Me2S. The residue was dissolved in 0.6
mL of CHCl3 and precipitated with 3 mL of hexanes. The
NMR(250 MHz, CDCl3): 1.87 (18H, s), 7.25, 7.41 (12H, AB).
Single crystals of the hexane solvate of 14 suitable for X-ray
diffraction were grown by vapor diffusion of hexane into a
dichloromethane solution of the compound.
1
Fe(acphNC)3 (15). To a mixture of Fe(acphNHCHO)3 (2.65
g, 3.73 mmol) and diisopropylamine (5.56 g, 55.0 mmol) in
CH2Cl2 (15 mL) was added POCl3 (2.61 g, 17.0 mmol) at room
temperature under argon and stirred for 2 h. The above solution
was then washed with 10% NaHCO3 (2 ꢀ 40 mL), and the
CH2Cl2 layer was separated and evaporated to 5 mL. The
addition of hexanes (100 mL) to this solution precipitated the
powdery red product, which was collected, washed with 50 mL
of hexanes, and dried at 70 °C. Yield: 2.20 g (90%). IR: 2126
precipitate was air-dried. Yield: 0.028 g (32%). H NMR (250
MHz, CDCl3): 1.88 (6H, s), 7.37, 7.60 (4H, AB), 16.75 (1H, s).
IR: 2223 cm-1. Crystals suitable for X-ray crystallography were
grown from CHCl3 by layering with hexanes.
Al(acphNCAuCl)3 (19). Al(acphNC)3 (14; 0.0314 g, 0.050
mmol) and (Me2S)AuCl (0.0441 g, 0.150 mmol) were dissolved
in 10 mL of CH2Cl2 and refluxed under nitrogen for 2 h. The
solution was then evaporated to dryness. 1H NMR (250 MHz,
CDCl3): 1.86 (18H, s), 7.34, 7.60 (12H, AB). IR: 2222 cm-1
.
cm-1
.
Cu(acphNC)2 (16). To a mixture of Cu(acphNHCHO)2 (12;
0.350 g, 0.70 mmol) and diisopropylamine (0.446 g, 4.4 mmol) in
CH2Cl2 (20 mL) was added POCl3 (0.220 g, 1.44 mmol) at room
temperature under argon. The color slowly changed from blue
to green. After stirring for 5 days, not all of the Cu-
(acphNHCHO)2 had dissolved. The mixture was filtered and
the filtrate washed with water (2 ꢀ 15 mL) and with 10%
NaHCO3(aq). When hexane was added to the dichloromethane
phase, a brown gum separated. It could not be isolated in pure
Acknowledgment. We thank Drs. Frank R. Fronczek and
Emily F. Maverick for assistance with the X-ray analyses. This
work was supported by the Department of Energy (DE-FG02-
01ER15267).
Supporting Information Available: X-ray data for compounds
1, (E)- and (Z)-2, (E)-6, 9, 12, 13 2H2O, 14 0.58C6H14, and 18,
3
3
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.