Synthesis, structure, and reactivity of bis(N,N′-bis(2-hydroxybenzylidene)-2-hydroxyphenylmethanediaminato) zirconium(IV), a Schiff base complex with 6,4,6-membered chelate rings

Article abstract of DOI:10.1016/S0277-5387(01)00979-2

The title complex Zr(dshpm)₂ has been successfully prepared by heating a 1:2 mole ratio of Zr(OBuⁿ)₄ and the free ligand in absolute ethanol. It is mononuclear and eight-coordinate in the solid state with a dodecahedral coordination sphere. The two O,N,N,O donor atom quadridentate Schiff base ligands each form 6,4,6-membered chelate rings. As expected, the change in a chelate ring sizes from 6,5,6- to 6,4,6- resulted in significantly more labile complex, as indicated by TLC and NMR of heated solutions and its subsequent chemical reactions. The 0.010 ?, shorter average Zr-N bond distance was not anticipated, and appears to result from the zirconium atom's preference that the oxygen atoms occupy certain locations. Preparations of two heteroleptic complexes from the title complex were undertaken to evaluate potential of the title compound as a synthon. A new fluorine-substituted homoleptic Schiff base Zr complex was also prepared, for comparison purposes. Despite the reasonable stability of Zr(dshpm)₂ in air, the decomposition of labilized Hdshpm(2-) ligand on silica gel and in heated solution interfered with the purifications of the desired heteroleptic products.

Full text of DOI:10.1016/S0277-5387(01)00979-2

Polyhedron 21 (2002) 211–218
www.elsevier.com/locate/poly
Synthesis, structure, and reactivity of bis(N,N%-bis(2-hydroxy-
benzylidene)-2-hydroxyphenylmethanediaminato)zirconium(IV), a
Schiff base complex with 6,4,6-membered chelate rings
Marvin L. Illingsworth a,*, Leslie J. Schwartz a,1, Andrew J. Jensen a, Tong Zhu a,
Eric J. Knappenberger a, Julie E. Sweet a, Patricia S. Wilkinson b, Beth E. Waltermire c,
Arnold L. Rheingold c
a Department of Chemistry, Rochester Institute of Technology, Rochester, NY 14623, USA
b Bruker Instruments, Inc., 19 Fortune Dri6e, Manning Park, Billerica, MA 01821, USA
c Department of Chemistry and Biochemistry, Uni6ersity of Delaware, Newark, DE 19716, USA
Received 6 April 2001; accepted 22 October 2001
Abstract
The title complex Zr(dshpm)2 has been successfully prepared by heating a 1:2 mole ratio of Zr(OBun)4 and the free ligand in
absolute ethanol. It is mononuclear and eight-coordinate in the solid state with a dodecahedral coordination sphere. The two
O,N,N,O donor atom quadridentate Schiff base ligands each form 6,4,6-membered chelate rings. As expected, the change in a
chelate ring sizes from 6,5,6- to 6,4,6- resulted in significantly more labile complex, as indicated by TLC and NMR of heated
,
solutions and its subsequent chemical reactions. The 0.010 A shorter average ZrꢀN bond distance was not anticipated, and
appears to result from the zirconium atom’s preference that the oxygen atoms occupy certain locations. Preparations of two
heteroleptic complexes from the title complex were undertaken to evaluate potential of the title compound as a synthon. A new
fluorine-substituted homoleptic Schiff base Zr complex was also prepared, for comparison purposes. Despite the reasonable
stability of Zr(dshpm)2 in air, the decomposition of labilized Hdshpm(2-) ligand on silica gel and in heated solution interfered with
the purifications of the desired heteroleptic products. © 2002 Published by Elsevier Science Ltd.
Keywords: Eight-coordinate; Schiff base; Zirconium complexes; X-ray crystal structure; Synthon; Heteroleptic
Commercially available entry points for the preparation
of zirconium(IV) complexes include zirconium te-
traalkoxides and zirconium tetrachloride, which are
polymeric to some degree and/or susceptible to atmo-
spheric hydrolysis, and tetrakis(acetylacetonato)zirco-
nium(IV), which can exhibit varying degrees of ligand
substitution.
Bis(quadridentate) Schiff base complexes of zirconiu-
m(IV), which have fused 6,5,6-membered chelate rings
and two O,N,N,O donor atom sets, are sufficiently inert
that chromatographic separation on silica gel can be
accomplished [15]. However, we have observed that the
temperatures needed to overcome this inertness cause
decomposition of the freed ligands in dimethyl sulfox-
ide. By choosing a quadridentate Schiff base ligand
capable of forming fused 6,4,6-membered chelate rings
1. Introduction
The recent publication of articles dealing with early
transition metal eight-coordinate complexes reflects a
continuing interest in this subject, especially with regard
to their structural aspects [1–6] intramolecular dynam-
ics [7–10] and ligand exchange properties [11–14]. Our
current interest is in the development of a more facile
route to heteroleptic (mixed ligand) bis(quadridentate)
complexes for use as polymer pendent groups [15].
* Corresponding author. Tel.: +1-585-475-2497; fax: +1-585-475-
7800.
E-mail address: mlish@rit.edu (M.L. Illingsworth).
1 On leave from the Department of Chemistry, St. John Fisher
College, Rochester, NY 14618, USA.
0277-5387/02/$ - see front matter © 2002 Published by Elsevier Science Ltd.
PII: S0277-5387(01)00979-2

212
M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
upon coordination, we hoped to isolate a mononuclear
complex with a convenient balance of ligand lability
and air stability to serve as a new reaction intermediate
(synthon). The increased lability would be a conse-
quence of the greater ring strain, i.e. poorer overlaps, in
the 4-membered chelate ring portion of the complex.
The quadridentate Schiff base that we chose to use is
N,N% - bis(2 - hydroxybenzylidene) - 2 - hydroxyphenyl-
methanediamine, also called N,N%-bis(salicylidene)-2-
hydroxy-a,a benzyldiamine, or more commonly N,N%-
di(salicylidene) - 2 - hydroxyphenylmethanediamine,
H3dshpm. It can be made by mixing reagents found in
most synthetic chemistry labs, ammonium hydroxide
and salicylaldehyde, at room temperature [16,17]. This
reaction is an example of one of the earliest known
‘spontaneous assembly’ reactions [18]. This compound
allows facile modification of its structure [19–23] and is
known to form complexes with other transition metals
[24].
chloride and deuterated dimethyl sulfoxide were ob-
tained from Aldrich and used as received. The ammo-
nium hydroxide and all solvents used were of reagent
grade. Silica Gel (Merck), grade 60, 230–400 mesh, 60
,
A pore size was obtained from Aldrich, and silica TLC
plates were obtained from Kodak.
Prior to all TLC separations, silica plates were acti-
vated by heating at 110 °C for approximately 10 min,
cooled in a desiccator for at least 5 min, and then
stored for approximately 1 h or less in a glove bag filled
with dry dinitrogen. Ligands and complexes were spot-
ted while in the glove bag, and the plates returned to
the oven for at least 2 min to drive away the spotting
solvent.
Infrared spectra were obtained on a Perkin–Elmer
FT-IR X spectrophotometer as KBr pellets using
1
polystyrene for external calibration. H NMR spectra
for preliminary identification purposes were obtained
on either a Nicolet NT-200 or a Bruker WP200 SY
NMR instrument using tetramethylsilane as internal
The synthesis, structural characterization and further
reactions of the title complex, Zr(dshpm)2, are reported
here (Fig. 1).
1
standard. H, 19F (using a,a,a-trifluorotoluene or inter-
nal referencing based on sample solvent), and all 2-D
NMR spectra for detailed analyses were obtained on a
Bruker Avance 400 NMR instrument.
X-ray crystallographic data for the title compound
were obtained as follows: Large yellow block crystals
were mounted on fine glass fibers and found to be
monoclinic with systematic absences for C centering
and a c glide along b indicating either Cc or C2/c as
2. Experimental
Zirconium n-butoxide (80% in n-butanol), salicylalde-
hyde, 3-fluorosalicylaldehyde, deuterated methylene
Fig. 1. Proposed structures for all new complexes in this report. Top left, Zr(dshpm)2; top right, Zr(3-Fdsp)2; bottom left, Zr(dshpm)(3-Fdsp);
bottom right, Zr(ndsp)(3-Fdsp).

M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
213
possible space groups. The latter was confirmed by the
presence of a crystallographic twofold rotation axis in
the Zr complex and the stability of the refinement in the
centrosymmetric setting. The structure was solved by
direct methods. All nonhydrogen atoms were refined
anisotropically and hydrogen atoms were included as
idealized isotropic contributions. All computations used
the programs contained in the SHELXTL library (version
4, G. Sheldrick, Siemens XRD, Madison, WI).
2.3. N,N%-Di(3-fluorosalicylidene)-1,2-phenylenediamine,
H23-Fdsp
A 1:2 mole ratio of 1,2-phenylenediamine and 3-
fluorosalicylaldehyde, respectively, were heated at reflux
in absolute ethanol for 6 h, concentrated, and chilled to
give an orange precipitate; m.p. 148–150 °C.
Anal. Calc. for C20H14F2N2O2: C, 68.2; H, 3.98; N,
1
7.95. Found: C, 67.95; H, 3.86; N, 7.87%. H NMR
(CD2Cl2): l 13.2 (br) [2], 8.9 [2], 7.5–6.9 [10]. 19F NMR
(CD2Cl2): −140.6. IR (cm−1): 1620s, 1275m, 1250s,
1230s.
2.1. N,N%-di(salicylidene)-2-hydroxyphenyl-
methanediamine, H3dshpm
In a 125 ml Erlenmeyer flask was placed 20.5 g (0.168
mole) salicylaldehyde. Concentrated ammonium hy-
droxide was added almost to the top (ca. 115 ml), the
flask stoppered and vigorously shaken. Bright yellow
precipitate formed almost immediately. The flask was
allowed to sit unopened for 3 days. At this point, the
flask contained tamped-down, fused-looking yellow or-
ange precipitate with a clear yellow supernate. The
solution was gravity filtered, and the precipitate washed
with ethyl ether. A powdery yellow solid containing
some shiny orange spheres was obtained. Trituration of
this product in 40 ml of absolute ethanol failed to
completely remove the orange spheres. Yield, 13.0 g
(66.9%).
2.4. Bis(N,N%-di(3-fluorosalicylidene)-1,2-
phenylenediaminato)zirconium(IV), Zr(3 Fdsp)2
Under a dinitrogen atmosphere, 0.49 ml (0.52 g, 1.1
mmole) Zr(OBun)4 were added to 0.80 g (2.3 mmole)
H23-Fdsp in 50 ml absolute ethanol and heated at
reflux for 1 h, suction filtered, washed with absolute
ethanol, and allowed to dry to give a bright yellow
powder; m.p. approximately 416 °C (422 °C dec.).
Yield, 0.73 g (81%).
The sample submitted for elemental analysis was
dried in vacuo at 100 °C for 3 days. Anal. Calc. for
C40H24F4N4O4Zr: C, 60.7; H, 3.06; N, 7.08. Found: C,
1
60.86; H, 3.03; N, 7.00%. H NMR (CD2Cl2): l 8.7 [4],
A portion of this product was dissolved in acetone,
petroleum ether added, and the volume of solvents
reduced using rotary evaporation to induce recrystal-
lization. After filtering, and washing with pertroleum
ether, the fluffy yellow solid obtained lacked any visible
orange component, and was only slightly soluble in
methylene chloride; m.p. 159–160 °C. Anal. Calc. for
C21H18N2O3: C, 72.8; H, 5.20; N, 8.09. Found: C,
7.5–6.4 [20]. 19F NMR (CD2Cl2): −137.4. IR (cm−1):
1615s, 1320m, 1255m, 1240m.
2.5. (N,N%-di(salicylidene)-2-hydroxyphenyl-
methanediaminato)(N,N%-di(3-fluorosalicylidene)-
1,2-phenylenediaminato)zirconium(IV),
Zr(dshpm)(3-Fdsp)
1
72.58; H, 5.31; N, 8.09%. H NMR (acetone-d6): l 13.1
2.5.1. Method 1
(br) [1], 8.7 [2], 7.5–6.8 [12], 6.35 [1]. IR (cm−1): 1628s,
In 200 and 100 ml portions of methylene chloride,
1.97 g (2.5 mmole) Zr(dshpm)2 and 0.30 g (0.85 mmole)
H23-Fdsp, respectively, were separately dissolved. The
former solution was heated to reflux, and the latter
added in five increments with 2 h intervals between
additions, and reflux maintained overnight. TLC
separation of the resulting solution (using methylene
chloride eluent on silica) indicated that some unreacted
Schiff base remained, whereupon 100 ml absolute
ethanol was added. Reflux was maintained, periodically
monitoring the reaction with TLC. A pale spot having
a value of RF clearly lower than those for the reactants
or Zr(3-Fdsp)2 or H3dshpm appeared. After 22.5 h at
reflux, TLC of the reaction solution revealed a spot due
to Zr(3-Fdsp)2, at which time the reaction was stopped.
The volume was reduced by rotary evaporation to one
half of its original volume, 80 ml absolute ethanol
added, and concentrated again to induce precipitation.
The impure product was redissolved in minimal methyl-
ene chloride and subjected to column chromatography
1276m.
2.2. Bis(N,N%-di(salicylidene)-2-hydroxyphenyl-
methanediaminato)zirconium(IV), Zr(dshpm)2
A 1.69 g (4.86 mmol) portion of the yellow and
orange H3dshpm product was covered with 80 ml abso-
lute ethanol in a 500 ml round bottom flask. Under a
dinitrogen tmosphere, 0.50 ml (1.2 mmol) of Zr(OBun)4
was then precipitated to the flask, causing the immedi-
ate formation of a cloudy, white precipitate. The flask
was heated at reflux for 24 h, and filtered, to give a fine
yellow powder; m.p. ca. 250 °C (slow dec.). Yield, 0.62
g (67%).
The sample submitted for elemental analysis was
dried in vacuo at 100 °C for 3 days. Anal. Calc. for
C42H32N4O6Zr: C, 64.7; H, 4.11; N, 7.19. Found: C,
1
64.56; H, 4.14; N, 6.97%. H NMR (CD2Cl2): l 9.5 (br)
[2], 8.2 [2], 8.0 [2], 7.6–6.5 [28]. IR (cm−1): 1638s,
1604s, 1310m, 1288m.

214
M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
using methylene chloride eluent on silica gel. Fractions
containing only the trailing spot (as shown by TLC)
were combined, and the solvent evaporated to give a
yellow product. Subsequent recrystallizations and
column separations failed to produce a product having
experimental elemental analyses within established lim-
3. Results and discussion
The physical and spectroscopic data collected in this
study are consistent with the following reaction
schemes:
Reaction Scheme I.
1
its from their theoretical values. H NMR (CD2Cl2): l
3NH3 (aq)+2 salicylaldehyde (aq)
9.0 br [less than 1], 8.5 [1], 8.4 [1], 8.0 [2], 7.5–5.8 [ca.
29] 19F NMR (CD2Cl2): −138.5, −133.5. IR (cm−1):
1641s, 1616s, 1317m, 1300m, 1238m.
(−3 H O)
2
ꢀꢀꢀꢀꢀꢀꢀꢁH3dshpm (s)
2 H3dshpm+Zr(OBun)4
(−4 HOBu)
ꢀꢀꢀꢀꢀꢀꢀꢀꢁZr(dshpm)2ꢀꢀꢀꢀꢀꢀꢀꢁZr(dshpm)(3-Fdsp)
(H 3-Fdsp)
2
2.5.1.1. Deri6ati6e preparation. An impure sample of
Zr(dshpm)(3-Fdsp) was mixed with N,N%-di(salicyli-
dene)-4-nitro-1,2-phenylenediamine, H2ndsp, in 30:70
methylene chloride and absolute ethanol, respectively,
and heated at reflux. The reaction was monitored by
TLC using the TLC system noted above. When the
spots attributed to the starting materials were no longer
apparent, the reaction solution was concentrated by
rotary evaporation to give a red solid. A 0.1 g portion
of this product was separated on a silica gel column
using methylene chloride as eluent. Fractions having
single spot TLCs which appeared to correspond with
the desired product were consolidated and evaporated
to give a red product. The sample submitted for ele-
mental analysis was dried in vacuo at 100 °C for 3
days. Anal. Calc. for C40H25F2N5O6Zr [Zr(ndsp)(3-
Fdsp)]: C, 60.0; H, 3.15; N, 8.74. Found: C, 61.24; H,
3.50; N, 8.60%. 1H NMR (CD2Cl2): l 8.6–8.2 [6],
7.5–5.9 [19]. These NMR signals matched those for a
sample of Zr(ndsp)(3-Fdsp) prepared directly from
Zr(OBun)4 and the corresponding free Schiff base lig-
ands, to be reported elsewhere (Found: C, 60.66; H,
3.44; N, 8.52%).
(H ndsp)
2
ꢀꢀꢀꢀꢀꢀꢁZr(ndsp)(3-Fdsp)
Reaction Scheme II.
1,2-phenylenediamine+2 3-fluorosalicylaldehyde
(−2 H O)
2
ꢀꢀꢀꢀꢀꢀꢀꢁH23-Fdsp (s)
2 H23-Fdsp+Zr(OBun)4
(−4 HOBu)
ꢀꢀꢀꢀꢀꢀꢀꢀꢁZr(3-Fdsp)2
The 1628 and 1276 cm−1 infrared bands for
H3dshpm are comparable to those observed for the
dsp-type ligands used in our previous studies [25,26]
and are assigned to imine stretching and ring-to-oxygen
1
stretching, respectively. The broad H NMR signal at
13.1 ppm is assigned to exchangeable salicylidene OꢀH,
the 8.7 ppm singlet to the two imine protons, 7.5–6.8
ppm multiplets to the 12 aromatic protons, and a
singlet at 6.35 to a methine proton. The appearance of
an orange component in the initial product, the variety
of melting points reported [16,17,27] and the differences
between the NMR spectra in deuterated acetone versus
methylene chloride (of poor quality due to low solubil-
ity) indicate the presence of tautomeric forms of this
material. Very similar observations were made for the
ethyl ester substituted H2dsp ligand, for which either
tautomer gave the same product upon complexation
[28].
2.5.2. Attempted method 2
Under a dinitrogen atmosphere, 1:1:1 mole ratio
amounts of H3dshpm, H23-Fdsp, and Zr(OBun)4 were
heated at reflux in absolute ethanol for 7 h, until the
TLC spot from H3dshpm was no longer apparent (us-
ing a 16:1 petroleum ether to ethanol eluent). After
being allowed to cool, the mixture was filtered to give a
bright yellow powder.
3.1. Zr(dshpm)2
The shift in salicylidene ring-to-oxygen vibration fre-
quency from 1276 to 1310 cm−1 upon Zr complexation
is analogous to those seen for all H2dsp-type ligands
studied previously by us [25,26]. The essentially non-
shifted band at 1288 cm−1 is assigned to the phenyoxy
ring-to-oxygen vibration since coordination does not
take place at this site (vide infra). Either of the bands at
1638 or 1604 cm−1 could be assigned to an imine
vibration. However, the former is more the likely, given
the increase in frequency upon complexation noted
2.5.3. Attempted method 3
Under a dinitrogen atmosphere, 1:1 mole ratio
amounts of Zr(dshpm)2 and Zr(3-Fdsp)2 were sepa-
rately dissolved in d6-DMSO. The solutions were
mixed, and heated for 20 h intervals at 40, 43, and
50 °C. Changes in the reaction solution were moni-
tored by TLC (using a 16:1 petroleum ether–ethanol
eluent), and compared with those for the separate
complexes.
1
above. The absence of a peak near 13.1 ppm in the H
NMR spectrum of Zr(dshpm)2 is expected, as the Zr
displaces the salicylidene OꢀH protons of each ligand.

M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
215
become nonequivalent upon complexation, giving sin-
glets at 8.2 and 8.0 which each integrate for 2. The
methine proton signal from each ligand occurs among
the aromatic proton multiplets which extend from 7.6
to 6.5 ppm, the region integrating for 28 protons. The
upfield shift upon Zr complexation, especially for the
salicylidene protons meta to the oxygen, is comparable
to those observed for all H2dsp-type ligands studied by
us [25,26]. The doublets at 7.0 and 6.8 ppm which have
no apparent fine structure and integrate for one proton
each, are most likely from the methine protons. If these
assignments are accurate, as indicated by the 2-D
COSY spectrum, then the salicylidene and/or phenyoxy
rings must have different average positions in solution,
e.g. an equilibrium could exist between coordinated
phenoxy and salicylidene moieties, or, less likely, the
short bite NꢀCꢀN moieties could span different edges
in the coordination sphere in solution to create different
methine proton environments.
Fig. 2. Labeled thermal ellipsoid drawing for Zr(dshpm)2.
The broad signal at 9.5 ppm, which integrates for a
little less than two protons, is assigned to an exchange-
able phenoxy proton on each ligand. The imine protons
Table 1
Selected bond lengths, bond angles, and coordination sphere parameters for Zr(dshpm)2; see Fig. 2
,
Bond lengths (A)
ZrꢀO(1)
ZrꢀO(3)
ZrꢀN(1)
ZrꢀN(2)
2.090(2)
2.151(3)
2.318(3)
2.334(3)
O(1)ꢀC(1)
O(3)ꢀC(21)
1.323(5)
1.324(4)
N(1)ꢀC(7), imine
N(2)ꢀC(15), imine
N(1)ꢀC(8), methine
N(2)ꢀC(8), methine
1.270(5)
1.263(5)
1.468(4)
1.476(5)
O(2)ꢀC(10)
1.364(4)
Bond angles (°)
O(1)ꢀZrꢀO(3)
O(1)ꢀZrꢀN(1)
O(1)ꢀZrꢀN(2)
O(3)ꢀZrꢀN(2)
O(3)ꢀZrꢀN(1)
N(1)ꢀZrꢀN(2)
154.0(1)
74.2(1)
131.2(1)
74.4(1)
131.3(1)
57.0(1)
ZrꢀO(1)ꢀC(1)
ZrꢀO(3)ꢀC(21)
142.1(2)
139.4(3)
ZrꢀN(1)ꢀC(7)
ZrꢀN(1)ꢀC(8)
ZrꢀN(2)ꢀC(15)
ZrꢀN(2)ꢀC(8)
135.5(2)
102.0(2)
135.6(3)
101.0(2)
C(7)ꢀN(1)ꢀC(8)
C(15)ꢀN(2)ꢀC(8)
122.4(3)
123.4(3)
N(1)ꢀC(8)ꢀN(2)
97.9(3)
,
De6iations from planarity (A)
O(1)ꢀN(1)ꢀN(2)ꢀO(3)
ZrꢀN(1)ꢀN(2)ꢀC(8)
0.0047(5)
0.2360(3) a
O(1)ꢀN(1)ꢀN(2)ꢀO(3)ꢀZr
0.0211(3)
b
,
‘a’ Edges (A)
N(1)ꢀN(2)
2.220(4)
b
,
‘b’ Edges (A)
O(1)ꢀO(1a)
O(1)ꢀO(3a)
3.126(5)
3.096(5)
b
,
‘m’ Edges (A)
O(1)ꢀN(1)
2.666(4)
2.714(5)
2.803(5)
2.714(5)
O(3)ꢀN(2)
O(1a)ꢀN(1a)
O(3a)ꢀN(2a)
b
,
‘g’ Edges (A)
O(1)ꢀN(1a)
O(1)ꢀN(2a)
O(3)ꢀN(1a)
O(3)ꢀN(2a)
2.803(5)
2.757(5)
2.917(5)
2.835(5)
Mean edge length ratios
b/a
b/m
b/g
1.38
1.14
1.085
a The deviation of C(8) from the N(1)ꢀZrꢀN(2) plane is away from the phenoxy group.
b Standard Hoard and Silverton symbolism [29]. The remaining dodecahedral edge lengths for Zr(dshpm)2 are dictated by symmetry.

216
M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
Results of X-ray crystallography on Zr(dshpm)2 es-
lished [15,25,28]. The IR bands at 1615 and 1320 cm−1
are assigned to the imine and coordinated-oxygen-to-
ring stretching vibrations, respectively [25,26], while the
band at 1255 or 1240 cm−1 arises from a fluorine-to-
ring stretching vibration. The absence of the proton
NMR signal at 13.2 ppm, observed for the free ligand,
is consistent with ligand coordination. The imine pro-
ton signals are virtually equivalent, and shifted upfield
by approximately 0.15 ppm from that of the free ligand.
Similar upfield shifts are observed in the Zr(dsp)2 and
Zr(trans-dsd)2 systems [25,26]. Symmetrical multiplets
at 7.5–7.4 ppm arise from the 1,2-phenylenediamine
protons, as observed for Zr(dsp)2 [26]. Nearly identical
doublets at 7.1–7.0 arise from the salicylidene ring
protons para to F and meta to O; less similar doublets
at 6.9–6.7 arise from the salicylidene ring protons ortho
to F and meta to O; and two distinct triplets at 6.5–6.4
arise from the salicylidene ring protons meta to F and
para to O. Off diagonal features in the ROESY (with
400 ms mixing) and DQF COSY NMR experiments
confirm these assignments and indicate interactions be-
tween the imine protons and aromatic protons of the
phenylenediamine (a and b) and salicylidene (para to F)
moieties.
tablish its solid state structure as eight-coordinate with
a dodecahedral coordination sphere, point group 2/m,
and space group C2/c. A labeled thermal ellipsoid
drawing is shown in Fig. 2. Important bond lengths,
bond angles, and coordination sphere parameters are
summarized in the Table 1. Comparisons with
bis(N,N% - disalicylidene - 1,2 - phenylenediaminato)zirco-
nium(IV), Zr(dsp)2 [26] and bis(N,N%-disalicylidene-1,2-
trans-diaminocyclohexanato)zirconium(IV), Zr(trans-
dsd)2 [25] which have fused 6,5,6-membered Schiff base
ligands, reveal the following: While the mean ZrꢀO
distances are approximately equal for each complex,
the mean ZrꢀN distance for Zr(dshpm)2 is approxi-
,
mately 0.010 A shorter. Considering the ring strain
normally associated with four-membered rings, poor
bonding overlaps would justify longer bonds. In this
case, the shorter bonds probably arise due to zirconi-
um’s preference for the oxygen atoms to be located in
certain positions, the ‘B’ positions of a dodecahedron
[29], which is consistent with theory for d0 dodecahe-
dral systems [30]. The imine bond is highly localized in
Zr(dshpm)2, as for the other complexes, and the me-
thine-to-nitrogen bond lengths are ordinary. The
OꢀZrꢀO bond angles are larger for Zr(dshpm)2 than for
the other complexes, which indicates that the 6,4,6
ligands do not engulf the Zr as extensively. The
NꢀZrꢀN bond angle is the smallest for Zr(dshpm)2, due
to the limited reach of the methine diamine moiety
versus those of the phenylenediamine and diaminocy-
clohexane moieties [25,26]. The above mentioned bond
length and angle constraints produce a dodecahedron
having the shortest NꢀN distance (‘a edges’), and a
ZrꢀN (ave.) to ZrꢀO (ave.) bond length ratio of 1.09.
The latter is closer to the Hard Sphere Model (1.00)
and Most Favorable Model (1.03) [29] than the other
members of this series. The angle made between the
trapezoidal O,N,N,O donor atom planes is 89.0° for
Zr(dshpm)2, which is comparable to those for Zr(dsp)2
and Zr(trans-dsd)2 [25,26]. The angle made between the
phenoxy ring and the donor atom plane of the same
ligand is 85.2°. The corresponding value for the other
ligand is equivalent by symmetry.
3.3. Zr(dshpm)(3-Fdsp)
Method 2, the reaction of Zr butoxide and the free
ligands in 1:1:1 mole ratio, has successfully been used
to prepare heteroleptic complexes [15]. However, the
yellow product obtained in this research was deter-
mined to be mostly Zr(3-Fdsp)2, based on TLC and
proton NMR analyses. Since the solubilities of Zr(3-
Fdsp)2 and the desired Zr(dshpm)(3-Fdsp) are very
similar, recrystallization was precluded as an effective
method of purification. Furthermore, since Zr(dshpm)2
decomposes rapidly on a silica gel column (on the
elution time scale) and is the fastest moving of the three
Zr products, the Zr(dshpm)(3-Fdsp) band becomes con-
taminated. This precludes chromatography as a conve-
nient method of purification. With purification proving
to be difficult, Method 2 was deemed ineffective in this
case.
In vitro tests conducted by the National Cancer
Institute, Developmental Therapeutics Program (Sam-
ple and Test Identification NSC: 657558-U/0-1/38), in-
dicated that this compound was inactive against nine
cancers and HIV.
While Zr(3-Fdsp)2 withstood heating in d6-DMSO
up to 148 °C with no change in its TLC or proton
NMR, Zr(dshpm)2 was shown to undergo chemical
change upon heating to only 40 °C. Heating a 1:1 mole
ratio mixture of the two complexes, as per Method 3,
resulted in labilization and decomposition of the
H3dshpm ligand at low temperature without any evi-
dence of mixed ligand complex formation.
3.2. Zr(3-Fdsp)2
The preparation of Zr(3-Fdsp)2 was undertaken so
that its spectral data could be compared with those of
Zr(dshpm)(3-Fdsp) and Zr(ndsp)(3-Fdsp), see Reaction
Scheme II and the final two legs of Reaction Scheme I
(see Section 3). The method employed is well estab-
The relative success of Method 1 is, based upon
stopping the addition of H23-Fdsp to Zr(dshpm)2 as
soon as Zr(3-Fdsp)2 appears in the reaction solution’s
TLC. The approximately equal mixture of unreacted
Zr(dshpm)2 and Zr(dshpm)(3-Fdsp) which resulted

M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
217
could be substantially purified due to the limited solu-
bility of the former in absolute ethanol. However,
despite repeated recrystallizations followed by a column
separation, contamination of the desired product per-
sisted, as reflected by the elemental analyses. The impu-
rities, which are likely to arise from on-going
labilization of Hdshpm(2-), probably contributed to
our inability to grow a crystal suitable for X-ray crys-
tallography. Fortunately, the composition of the new
material could be established using IR and NMR spec-
troscopies, and by preparing chemical derivatives.
For the substantially purified product, infrared bands
at 1641 and 1616 cm−1 are assigned as imine stretching
vibrations arising from the Hdshpm(2-) and 3-Fdsp(2-)
ligands, respectively, by analogy to the corresponding
homoleptic complexes. The band at 1317 cm−1 and its
shoulder are assigned as ‘coordinated O-to-salicylidene
ring’ stretching vibrations for the two ligands. The
band at 1238 cm−1 and/or its higher frequency shoul-
der are assigned as an aromatic ring-to-F vibration,
analogous to that for Zr(3-Fdsp)2. Thus, all IR assign-
ments are consistent with the Zr(dshpm)(3-Fdsp)
formulation.
a poor H-bonding solvent, and appear strikingly differ-
ent in d6-DMSO, a good H-bonding solvent, while the
imine proton signal at 8.0 ppm appears the same in
each solvent. Furthermore, in the d6-DMSO spectrum,
the phenoxy OꢀH signal is a sharp singlet which inte-
grates for one proton; the aromatic range extends down
to 8.1 ppm; and, the integration of the aromatic region
corresponds to 22.8 protons, which is much closer to
the expected number of 23.
In addition to TLC evidence, rapid disproportiona-
tion of Zr(dshpm)(3-Fdsp) in solution to form a 1:1
mole ratio of homoleptic complexes was ruled out by
observing the CD2Cl2 1H NMR spectrum of a mixture
of separately prepared Zr(3-Fdsp)2 and Zr(dshpm)2.
The spectrum showed all of the signals apparent in the
spectra of the separate complexes with no perceptible
shifts, i.e. with no sign of interaction.
The 19F{1H} NMR of the proposed Zr(dshpm)(3-
Fdsp) product shows two proton decoupled signals,
neither of which matches the 19F signal from Zr(3-
Fdsp)2. The 19F signal from a mixture of Zr(3-Fdsp)2
and Zr(dshpm)2 was identical with the latter. The coor-
dinated Hdshpm(2-) ligand evidently imposes a differ-
ent chemical environment on the two fluorines of the
While strong parallels between Zr(dshpm)(3-Fdsp)
and the corresponding homoleptic complexes are read-
ily apparent from the IR spectra of solid state samples,
1
opposing 3-Fdsp(2-) ligand. H{19F} NMR (i.e. proton
observe with decoupled 19F using the above 19F NMR
frequencies) of the proposed Zr(dshpm)(3-Fdsp)
product in CD2Cl2 solution indicates that each F atom
couples with the nearest imine proton and nearest
salicylidene protons (ortho and meta).
1
fewer parallels are evident from their solution H NMR
spectra. The absence of a signal around 13.2 ppm is
consistent with the presence of coordinated ligands.
Small singlets at 11.0 and 9.9 ppm match signals ob-
served for salicylaldehyde, which is a likely decomposi-
tion by-product from the Hdshpm(2-) ligand. The
broad signal at 9.0 ppm, which integrates for less than
one proton, is assigned to an exchangeable phenoxy
OꢀH and is consistent with the presence of one Hd-
shpm(2-) ligand. This chemical shift is 0.5 ppm upfield
from the analogous signal for Zr(dshpm)2, which, from
examination of molecular models, could result from a
nearby fluorine on the opposing 3-Fdsp(2-) ligand. The
singlets at 8.5 and 8.4 ppm, which integrate for one
proton each, are assigned to the imine protons of the
3-Fdsp(2-) ligand, protons which had been equivalent
for Zr(3-Fdsp)2 at 8.7 ppm. The singlet at 8.0 ppm,
which integrates for two protons, is assigned to the
imine protons of the Hdshpm(2-) ligand, protons which
had been inequivalent for Zr(dshpm)2 at 8.2 and 8.0
ppm. Signals in the 7.5–5.8 ppm range are assigned to
the aromatic protons of the ligands. The upfield end of
this range appears higher than observed for either of
the homoleptic complexes, 6.4 ppm in both cases. The
integration over this range, corresponding to approxi-
mately 29 protons, is higher than expected for 22
aromatic protons and one methine proton, and is con-
sistent with the presence of some impurity, e.g. salicy-
laldehyde. We also note that the aromatic signals for
Zr(dshpm)(3-Fdsp) appear poorly resolved in CD2Cl2,
A plausible explanation for some of the observed
NMR differences between Zr(dshpm)(3-Fdsp) and the
corresponding homoleptic complexes is the presence of
H bonding between the phenoxy OꢀH of Hdshpm(2-)
and a fluorine atom on the opposing 3-Fdsp(2-). Such
an interaction would render the 19F NMR chemical
shifts of the 3 Fdsp(2-) inequivalent. Since the above
decoupling experiment established that each fluorine is
coupled to the nearest imine proton, the different Zr(d-
shpm)(3-Fdsp) fluorine environments could explain the
separate imine proton signals at 8.5 and 8.4 ppm. The
imine protons for Zr(3-Fdsp)2, where analogous H-
bonding is not possible, gave a singlet at 8.5 ppm.
However, alternate explanations for these observations,
such as coordination sphere structure in solution and
ligand puckering, cannot be ruled out.
3.4. Zr(ndsp)(3-Fdsp)
In light of the less-than-convincing elemental analysis
for Zr(dshpm)(3-Fdsp), the inability to obtain a suit-
able single crystal, and the complexity of its NMR
results, corroboration of its composition was sought
using chemical means. In this case, the 6,4,6-chelating
Hdshpm(2-)was replaced by the 6,5,6-chelating ndsp(2-).
As expected, the proposed Zr(ndsp)(3-Fdsp) derivative

218
M.L. Illingsworth et al. / Polyhedron 21 (2002) 211–218
was demonstrated by NMR to be identical to the
heteroleptic product from the 1:1:1 mole ratio reaction
of H2ndsp, H23-Fdsp, and Zr(OBun)4. The latter had a
satisfactory elemental analysis. Its NMR spectrum
shows four proton signals in the imine proton region
(8.6–8.3), attributed to the two imine protons and the
two protons adjacent to the nitro group; the multiplet
at 7.5–7.4 which integrates for five protons is attributed
to the remaining phenylenediamine protons [four from
3-Fdsp(2-) and one from ndsp(2-), meta to the nitro
group]; and the series of triplets and doublets over the
7.3–5.9 range, which each integrate for two protons
each, are assigned to salicylidene ring protons, and
correspond to the signals observed for the homoleptic
complexes [31].
Acknowledgements
Acknowledgment is made to the Donors of the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society, for partial support of this re-
search. Additional funding from the RIT College of
Science and Department of Chemistry, and technical
support from Astra Arcus USA, and Bruker are also
gratefully acknowledged.
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