Isomer distribution and structure of (2,2′-biphenyldiolato)bis(β-diketonato)titanium(IV) complexes: A single crystal X-ray, solution NMR and computational study

Article abstract of DOI:10.1016/j.ica.2009.02.006

Novel dichlorobis(β-diketonato)titanium(IV) Ti(C₆H₅COCHCOR)₂Cl₂ and (2,2′-biphenyldiolato)bis(β-diketonato)titanium(IV) Ti(C₆H₅COCHCOR)₂biphen complexes with R = CH₃,

Full text of DOI:10.1016/j.ica.2009.02.006

Inorganica Chimica Acta 362 (2009) 3088–3096
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Isomer distribution and structure of (2,20-biphenyldiolato)bis(b-diketonato)-
titanium(IV) complexes: A single crystal X-ray, solution NMR
and computational study
*
Annemarie Kuhn, Tsietsi A. Tsotetsi, Alfred Muller, Jeanet Conradie
Department of Chemistry, University of the Free State, Nelson Mandela Drive, Bloemfontein 9301, South Africa
a r t i c l e i n f o
a b s t r a c t
Novel dichlorobis(b-diketonato)titanium(IV) Ti(C6H5COCHCOR)2Cl2 and (2,20-biphenyldiolato)bis(b-dike-
tonato)titanium(IV) Ti(C6H5COCHCOR)2biphen complexes with R = CH3, C6H5 and CF3, are synthesized
and characterized by X-ray crystallography and further physical methods. There is a good agreement
between DFT calculated and experimental structural data. A configurational analysis gives a calculated
isomer distribution that is in agreement with the experimental data derived from low temperature 1H
NMR spectroscopy. The Ti(C6H5COCHCOR)2biphen complexes exhibit high hydrolytic stability.
Ó 2009 Elsevier B.V. All rights reserved.
Article history:
Received 15 September 2008
Received in revised form 2 February 2009
Accepted 6 February 2009
Available online 20 February 2009
Keywords:
b-Diketonato
Titanium
DFT
Isomer distribution
Structure
1. Introduction
predict reactivity of molecules with MM. With the improvement
of computational methods and computer power, methods such
Complexes of titanium(IV) are widely studied for a variety of
purposes, mainly serving as catalyst in different organic reactions
[1] as well as for antitumor activity [2]. Two monomeric Ti(IV)
complexes have qualified for clinical trials on antitumor activity:
Ti(ba)2(OEt)2 (budotitane, Hba = benzoylacetone) [3] and TiCp2Cl2
(titanocene dichloride) [4], but clinical phase II and phase III have
been stopped mainly as a consequence of problems with the gale-
nic formulation of the compound [5]. Since no information on the
isomer distribution of budotitane in the galenic formulation used
for the tests of the anticancer activity is available, it is of impor-
tance to understand the spatial arrangement of the monomeric Ti
complex and which of the five possible isomers of six-coordinate
octahedrally configurated Ti(ba)2X2 (X = OEt or Cl) complexes exhi-
bit anticancer activity. The decomposition of titanocene dichloride
and budotitane in aqueous solutions impeded mechanistic investi-
gations, lowered their efficiency and ultimately resulted in failure
of clinical trails. Thus producing titanium(IV) complexes exhibiting
enhanced water stability, is extremely valuable.
as density functional theory (DFT) is computationally less demand-
ing and can thus conveniently be used for the calculation of molec-
ular geometry, isomer distribution as well as electronic properties
of the molecule.
Utilizing a Single Crystal X-ray, variable temperature 1H and 19
F
NMR and DFT computational chemistry techniques, this paper
describes the isomeric abundance of series of octahedral
Ti(b-diketonato)2Cl2 and Ti(b-diketonato)2biphen-complexes,
a
biphen = biphenolato, b-diketonato = C6H5COCHCOR with R = CH3,
C6H5 and CF3. The novel Ti(b-diketonato)2biphen complexes, not
previously reported, exhibit high resistance towards hydrolysis.
2. Experimental
2.1. Materials and apparatus
Solid reagents used in preparations (Merck, Aldrich and Fluka)
were used without further purification. Liquid reactants and sol-
vents were distilled prior to use; water was doubly distilled. Or-
ganic solvents were dried according to published methods [7].
Molecular mechanics (MM) has successfully been used to calcu-
late the isomer distribution of budotitane [6]. The main disadvan-
tage of molecular mechanics is the lack of available parameters for
many compound types. Also, since electrons and orbitals are not
used in the MM method, we cannot study chemical reactions or
2.2. Synthesis of Ti(b-diketonato)2Cl2 complexes 1–3
The Ti(b-diketonato)2Cl2 complexes were synthesized according
to published methods for Ti(CH3COCHCOC6H5)2Cl2
Ti(C6H5COCHCOC6H5)2Cl2 2 [8,9].
1
and
* Corresponding author. Tel.: +27 51 401 2194; fax: +27 51 444 6384.
E-mail address: conradj.sci@ufs.ac.za (J. Conradie).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.02.006

A. Kuhn et al. / Inorganica Chimica Acta 362 (2009) 3088–3096
3089
Ti(C6H5COCHCOCF3)2Cl2 3: Yield: 16.0%. M.p. > 250 °C. 1H NMR
(d/ppm, CDCl3): 7.05 (2H, s, tfbaH), 7.58 (4H, t, PhH), 7.77 (2H, t,
PhH), 8.11 (4H, br, PhH). 19F NMR (d/ppm, CDCl3): ꢀ74.50 (6F, br,
CF3). Elemental Anal. Calc.: for TiC20H12O4Cl2F6 C, 43.8; H, 2.2.
Found: C, 43.8; H, 2.1%.
densities and the deepest holes were all within 1 Å from non-
hydrogen atoms which presented no physical meaning in the final
refinements. Aromatic protons were placed in geometrically ideal-
ized positions (C–H = 0.95 Å) and constrained to ride on their par-
ent atoms with Uiso(H) = 1.2Ueq(C). Initial positions of the methyl
protons were obtained from a Fourier difference map and refined
as fixed rotors with Uiso(H) = 1.5Ueq(C) and C–H = 0.98 Å.
2.3. Synthesis of Ti(b-diketonato)2biphen complexes 4–6
Atomic scattering factors were taken from the International Ta-
bles for Crystallography Volume C [17]. The molecular plot was
drawn using the DIAMOND program [18] with a 30% thermal envelope
probability for non-hydrogen atoms. Hydrogen atoms were drawn
as arbitrary sized spheres with a radius of 0.135 Å.
To stirred solution of 2,20-biphenyldiol (0.186 g, 1 mmol in
15 ml CH3CN) at RT, a solution of Ti(C6H5COCHCOR)2Cl2 (1 mmol
in 15 ml CH3CN) was added dropwise at room temperature with
an immediate colour change. After refluxing for 4.6 h, the reaction
mixture was cooled and solvent evaporated until it was dry. The
residue was washed in MeOH to dissolve unreacted biphenol in 4
and 5. Pure product was obtained recrystallization from dichloro-
methane/n-hexane and stored under N2 atmosphere.
Ti(C6H5COCHCOCH3)2biphen 4: Yield: 0.113 g (20.4%).
M.p. > 250 °C. 1H NMR (d/ppm, CDCl3): 2.20 (6H, s, CH3), 6.48
(2H, s, baH), 7.02 (2H, d, biphenH), 7.08 (2H, t, biphenH), 7.32
(2H, t, biphenH), 7.38 (4H, t, PhH), 7.45 (2H, d, biphenH), 7.50
(2H, t, PhH), 7.81 (4H, d, PhH). Elemental Anal. Calc. for TiC32H26O6:
C, 69.3; H, 4.7. Found: C, 69.3; H, 4.6%.
Ti(C6H5COCHCOC6H5)2biphen 5: Yield: 0.154 g (22.3%). M.p.
244.93 °C. 1H NMR (d/ppm, CDCl3): 7.11 (2H, d, biphenH), 7.14
(2H, t, biphenH), 7.18 (2H, s, dbmH), 7.35–7.57 (16H, m, aroma-
ticH), 7.95 (8H, d, PhH). Elemental Anal. Calc. for TiC38H26O6S2: C,
66.1; H, 3.8. Found: C, 66.0; H, 3.7%.
Ti(C6H5COCHCOCF3)2biphen 6: Yield: 0.106 g (24.6%).
M.p. > 250 °C. 1H NMR (d/ppm, CDCl3): 6.89 (2H, s, tfbaH), 7.02
(2H, d, biphenH), 7.16 (2H, t, biphenH), 7.36 (2H, t, biphenH),
7.47 (4H, t, PhH), 7.52 (2H, d, biphenH), 7.64 (2H, t, PhH), 7.91
(4H, d, PhH). 19F NMR (d/ppm, CDCl3): –75.03 (6F, br, CF3). Elemen-
tal Anal. Calc. for TiC32H20O6F7: C, 58.0; H, 3.0. Found: C, 57.8; H,
3.0%.
2.6. Theoretical approach
Density Functional Theory (DFT) calculations were carried out
using the Amsterdam Density Functional 2007 (ADF) program sys-
tem [19] with the PW91 (Perdew-Wang, 1991) exchange and cor-
relation functional [20]. The TZP (Triple f polarized) basis set, a fine
mesh for numerical integration (5.2 for geometry optimizations
and 6.0 for frequency calculations), a spin-restricted (gas-phase)
formalism and full geometry optimization with tight convergence
criteria as implemented in the ADF 2007 program, were used.
The accuracy of the computational method was evaluated by com-
paring the root-mean-square deviations (RMSD’s) between the
optimized molecular structure and the crystal structure, using
the non-hydrogen atoms in the molecule. RMSD values were calcu-
lated using the ‘‘RMS Compare Structures” utility in ChemCraft
Version 1.5 [21]. Whether artificially generated atomic coordinates
or coordinates obtained from X-ray crystal data were used in the
input files, optimizations for each compound resulted in the same
minimum energy optimized geometry. Optimized structures were
verified as a minimum through frequency calculations.
3. Results and discussion
2.4. Spectroscopy and spectrophotometry
3.1. Synthesis and identification of complexes
NMR measurements at 25 °C were recorded on a Bruker Ad-
vance II 600 NMR spectrometer [1H (600.130 MHz), 19F
(564.686 MHz)]. The chemical shifts were reported relative to
SiMe4 (0.00 ppm) for 1H and relative to CFCl3 (0.00 ppm) for 19F.
Positive values indicate downfield shift.
The
dichlorobis(b-diketonato)titanium(IV),
Ti(C6H5COCH-
COR)2Cl2 with R = CH3 (ba, 1), C6H5 (dbm, 2) and CF3 (tfba, 3) com-
plexes were prepared by treating TiCl4 with 2 equiv. of the
appropriate b-diketone and isolated and purified by recrystallisa-
tion before use [7,8], see Scheme 1. The low yield obtained for the
more acidic complex 3 (16% versus 80% for 1 and 2) may be attrib-
uted to the electron withdrawing capability of the CF3 groups mak-
ing the b-diketone a poorer electrophile, thus making complex
formation more difficult. Another contributing factor may be the
titanium–fluorine single bond energy of 581 kJ molꢀ1 that is higher
than that of the titanium–oxygen single bond, (478 kJ molꢀ1) [22]
favouring Ti–F bond formation, leading to side products and a lower
yield of 3. Products 1–3 were stored under an argon atmosphere
since the Ti(b-diketonato)2Cl2 complexes are highly susceptible to
hydrolysis. Complex 3 with a CF3 containing b-diketonato is consid-
erably less stable with respect to hydrolysis than the analogous
complexes 1 and 2, both in the solid state and in solution. The hydro-
lytic stability increases in the order Ti(tfba)2Cl2 ꢁ Ti(dbm)2
Cl2 < Ti(ba)2Cl2 [8]. Keppler and Heim evaluated the rate of hydroly-
sis (determined by the development of turbidity of the solution as a
result of the precipitation on TiO2), showing that complex 1 precip-
itates within 10 s when dissolved in dry CH3CN treated with 0.01%
water [23].
2.5. X-ray crystal structure determination
Crystals of Ti(C6H5COCHCOCH3)2biphen (4) were obtained from
recrystallization in chloroform. X-ray intensity data for 2 was mea-
sured on a Bruker X8 Apex II 4 K CCD area detector, equipped with
a graphite monochromator and Mo K
a fine-focus sealed tube
(k = 0.71073 Å) operated at 1.5 kW power (50 kV, 30 mA). The
detector was placed at a distance of 3.75 cm from the crystal. Sam-
ple temperature was kept constant at 100(2) K using an Oxford 700
series cryostream cooler.
The initial unit cell and data collection of 2 were achieved by
the APEX2 software [10] utilizing COSMO [11] for optimum collection
of more than a hemisphere of reciprocal space. A total of 1149
frames were collected with a scan width of 0.5° in u and
x with
an exposure time of 60 s per frame. The frames were integrated
using a narrow frame integration algorithm and reduced with the
Bruker SAINTPLUS and XPREP software [12] packages, respectively.
Analysis of the data collections showed no significant decay during
the data collection. Data were corrected for absorption effects
using the multi-scan technique SADABS [13].
The structure was solved by the direct methods package SIR97
[14] and refined using the WINGX software package [15] incorporat-
ing SHELXL [16]. The largest peaks on the final difference electron
The (biphenyldiolato)bis(b-diketonato)titanium(IV), Ti(C6H5CO
CHCOR)2(biphen) with R = CH3 (ba, 4), C6H5 (dbm, 5) and CF3 (tfba,
6) complexes were obtained by the substitution of the bidentate
biphenol ligand for the two monodentate Clꢀ ligands in Ti(b-dike-
tonato)2Cl2, following a synthetic route similar to the one pub-

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Ph
Ph
HO
O
O
Ti
O
R
R
R
R
O
O
Cl
Cl
O
O
O
O
O
OH
CHCl3
HO
+
2 HCl
+
2 HCl
Ti
O
Ti Cl4
+
2
Ph
N2 / Heat
R
CH3CN
2
Ph
Ph
R = CH3 (1), Ph (2), CF3 (3)
R = CH3 (4), Ph (5), CF3 (6)
Scheme 1. Synthetic route for the synthesis of Ti(b-diketonato)2Cl2 and Ti(b-diketonato)2(biphen).
lished by Rao et al. [24] for the reaction between Ti(CH3COCHC-
OCH3)Cl2 and 1,10-methylenedi-2-naphtol, see Scheme 1. The
biphenolato complexes 4–6 exhibit a high hydrolytic stability
and are ‘‘air stable” for more than 3 years. The solution stability
was tested under the same conditions as Keppler and Heim, i.e.,
0.01% water/CH3CN, and it was found that the biphenolato com-
plexes 4–6 do not precipitate within 6 weeks.
gands, i.e., the two six-membered benzoylacetonato and seven-
membered biphenolato rings. The O–Ti–O bond angles vary from
83° to 97° compared to 90° in a perfect octahedron. The ligand
O–Ti–O angle is 82.9° for the six-membered ba chelated ligand
and 91.3° for the seven-membered biphenolato ring. The Ti–O
bonds lengths in 4 are in the order Ti–Obiphen (1.851 Å) < Ti–Oba axial
(1.977 Å) < Ti–O
(2.018 Å) as illustrated in Fig. 1b. The for-
ba equatorial
mal Ti–O single bond is 1.94–1.99 Å (Ti–O distances found in rutile,
TiO2 [25]) and Ti@O double bond is 1.61–1.68 Å [26]. Therefore, the
shortest Ti–O distance is clearly shorter than one expected for a
single bond, suggesting that this Ti–O bond possesses partial dou-
ble bond character arising from donation of the electrons from the
py and pz filled oxygen orbitals to the empty titanium d orbitals
[27]. The Ti–Oba bonds trans to another ba oxygen, are shorter
(1.977 Å) than those trans to the oxygen of the chelated dianion
biphenalato ligand (2.018 Å).
3.2. X-ray structure of (4)
A molecular diagram showing the numbering scheme of the ti-
tle compound Ti(ba)2biphen (4) is presented in Fig. 1a. Crystal data
and details for data collections and refinements are summarized in
Table 1. Selected bond lengths and angles for the molecule are
listed in Table 2.
The compound Ti(ba)2biphen, 4, crystallizes in the non-centro-
symmetric trigonal space group, P3221 with Z = 3, resulting in only
half the molecule necessary for the asymmetric unit as it is situ-
ated on a twofold rotational axis. The Ti(ba)2biphen, 4, structure
consists of an octahedrally coordinated titanium atom with all
three ligands acting as bidentate. The octahedral coordination
around titanium is distorted to accommodate the three chelated li-
Fig. 2 illustrates that the intermolecular molecular packing of 4
is mainly governed by edge-to-face CꢀHꢂ ꢂ ꢂ
p interactions [28],
giving rise to the well-known herringbone packing motif illus-
trated in Fig. 3. Simple aromatic residues prefer to associate via
enthalpically favourable edge-to-face CꢀHꢂ ꢂ ꢂ
p interactions [29].
interactions are (a) between biphen CꢀH and the
The CꢀHꢂ ꢂ ꢂ
p
a
b
Ph
O
H3C
dax=1.9767(16)
O
O
dL=1.8512(18)
91.3°
deq=2.0183(19)
Ti
82.9°
O
O
O
H3C
Ph
Fig. 1. (a) The molecular structure (30% probability displacement ellipsoids) of Ti(ba)2biphen (4) showing the numbering scheme (primed labels indicate atoms generated by
symmetry operations). (b) Diagram indicating coordination, distances (Å) and angles (°) around the titanium centre.

A. Kuhn et al. / Inorganica Chimica Acta 362 (2009) 3088–3096
3091
Table 1
figurations are more strained but preferred by electronic effects
(p -d (t2g) bonding of the b-diketonato ligands) [30]. According
Crystal and structure refinement data for Ti(ba)2biphen (4).
p
p
to NMR data as well as to force field calculation results [30], no
configurations with the X ligands in the trans position are to be
expected. Only those Ti(b-diketonato)2X2 complexes with the ex-
tremely bulky substituents such as iodide or p-dimethylamino-
phenoxy as hydrolyzable group X have the trans form. The
stereochemistry of the complexes can be inferred from NMR spec-
tra. The cis–cis–cis isomer with no symmetry (point group C1) may
give rise to two methyl (only for 1), two phenyl, and two ring pro-
Formula
TiO6C32H26
554.43
Orange, cuboid
Trigonal
Formula weight
Crystal colour/habit
Crystal system
Space group
Unit cell dimensions
a (Å)
P3221
8.91750(10)
8.91750(10)
29.2648(7)
90
90
120
2015.40(6)
3
b (Å)
c (Å)
a
(°)
b (°)
(°)
ton resonances. Fluorine NMR spectra of cis–cis–cis-Ti(tfba)2Cl2
3
should show two nonequivalent fluorine groups. The other four
isomers, cis–trans–cis (point group C2), cis–cis–trans (C2), trans–
cis–cis (C2v) and trans–trans–trans (C2h) all possess at least a two-
fold axis and should give a single resonance for each type of group,
see Scheme 2. Ti(b-diketonato)2(biphen) complexes can adopt only
a cis orientation, one possible cis isomer if the bound b-diketone in
the 1 and 5-position has the same (symmetrically substituted) sub-
stituents, or three possible cis isomers if the bound b-diketone in
the 1 and 5-position has different substituents (asymmetrically
substituted), see Scheme 2. If a statistical distribution of three cis
Ti(b-diketonato)2(biphen) diastereomers exists, the relative equi-
librium concentrations will be 50% cis–cis–cis, 25% cis–cis–trans
and 25% cis–trans–cis and four equally intense terminal group
resonances are expected.
c
Volume (Å3)
Z
Dcalc (Mg mꢀ3
)
1.370
Temperature (°C)
Wavelength (Å)
ꢀ173
0.71073
Absorption coefficient (mmꢀ1
F(000)
)
0.363
864
Crystal size (mm)
h Range for data collection (°)
Index ranges
0.40 ꢃ 0.22 ꢃ 0.20
2.09–28.30
–11 6 h 6 10, ꢀ11 6 k 6 11,
ꢀ39 6 l 6 39
Reflections collected
25594
Independent reflections
Completeness to h = 28.35 (%)
Absorption correction
Max. and min. transmission
Refinement method
3326 [Rint = 0.0468]
99.9
Semi-empirical from equivalents
0.9309 and 0.8684
Full-matrix least-squares on F2
3326/0/178
At room temperature (294 K) only one single set of 1H NMR sig-
nals was observed for compounds 1–3. The resonance signal of the
methine H is sharp, but the resonance signals of the methyl and Ph
groups on the b-diketonato ligand are relatively broad due to rapid
isomerization process (relative to the NMR time scale) which ex-
changes groups between non equivalent environments. For com-
pounds 4–6 one single set of sharp signals was observed. The
signals broaden and split up into three to four signals upon lower-
ing in temperature. With further temperature lowering the split
resonance signals sharpen up again.
Data/restraints/parameters
Goodness-of-fit on F2
1.242
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0370, wR2 = 0.1001
R1 = 0.0552, wR2 = 0.1410
0.500 and ꢀ1.054
Largest difference in peak and hole
(e Åꢀ3
)
Table 2
Selected bond lengths [Å] and angles [°] for Ti(ba)2biphen (4).
Fig. 4 (left) illustrates the temperature dependence of selected
proton resonances of Ti(ba)2Cl2 1 and Ti(ba)2(biphen) 4 in CDCl3
solution. Below ꢀ40 °C, three proton–CH3 resonances are observed
at ca 2.2 ppm, which, on raising the temperature, collapse into a
singlet as a result of the rapid isomerization process at RT which
exchanges methyl groups between the four non equivalent envi-
ronments of the three cis diasterioisomers. The two proton phenyl
resonance of 4 at 7.81 ppm followed the same trend consistent
with a rapidly interconverting changing of the phenyl groups of
the three cis diasterioisomers. The ring methine proton (–CH@)
resonance of 4 at 6.48 ppm also shows on temperature lowering
at least three resonance peaks.
Ti–O(3)
Ti–O(2)
Ti–O(1)
1.8512(18)
1.9767(16)
2.0183(19)
1.279(3)
1.286(3)
1.356(3)
1.494(4)
1.397(4)
1.392(4)
1.399(4)
1.493(5)
O(2)–Ti–O(1)
O(3)#1–Ti–O(3)
O(3)–Ti–O(2)
O(2)#1–Ti–O(2)
O(3)–Ti–O(1)
C(2)–O(1)–Ti
82.90(7)
91.34(11)
88.90(7)
171.52(11)
171.80(7)
133.06(17)
133.87(17)
123.0(2)
O(1)–C(2)
O(2)–C(4)
O(3)–C(11)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(11)–C(16)
C(16)–C(16)#1
C(4)–O(2)–Ti
O(1)–C(2)–C(3)
O(1)–C(2)–C(1)
C(4)–C(3)–C(2)
O(2)–C(4)–C(3)
116.9(2)
122.8(2)
122.9(2)
Symmetry transformations used to generate equivalent atoms: #1 x ꢀ y, ꢀy, ꢀz + 1/3.
The ring methine proton (–CH@) resonance of both Ti(tfba)2Cl2
3 and Ti(tfba)2(biphen) 6 at 7.05 and 6.89 ppm, respectively
(Fig. 4 right) shows four distinguishable signals of three different
intensities at ꢀ60 °C, consistent with the existence of three cis iso-
mers for both 3 and 6, in CDCl3 solution. The two lines of equal
intensity are assigned to the cis–cis–cis isomer. More than one–
CH@ ring methine resonance in this slow exchange methine region
was not previously observed for The Ti(b-diketonato)2X2 com-
plexes. Ti(ba)2X2 complexes with X = F, Cl, Br, revealed a single
although considerably broadened resonance signal even at
ꢀ65 °C [8]. This may be due to poor NMR resolution or due to
the fact that the exchange between the isomers was fast, even at
low temperatures. Ti(ba)2(OiC3H7)2 showed four resonances at
ꢀ36.8 °C for the methyl resonance [31]. Low temperature 19F
NMR of the CF3 containing complexes 3 and 6 showed four sharp
signals at ꢀ60 °C at ca ꢀ74 ppm due to the slow exchange (on
NMR timescale) of the CF3 groups between the four non equivalent
environments. Unambiguous assignment of the two resonance
signals of equal intensity at low temperature to the cis–cis–cis
phenyl substituents of the ba ligand of a neighbouring molecule
creating infinite chains (3.257 Å), (b) between phenyl CꢀH and
the phenyl substituent of the ba ligands of neighbouring molecule
(3.309 Å) and (c) between the biphen CꢀH to both of the ba b-dike-
tonato chelated ring systems of a neighbouring molecule (2.747 Å).
Each of the four phenyl residues on one molecule of 4 is thus in-
volved in at least two CꢀHꢂ ꢂ ꢂ
p interactions each, resulting in a sta-
bilized interlocking 3D network.
3.3. isomer distribution
Unsymmetrically substituted Ti(b-diketonato)2Cl2 complexes
can adopt three different cis and two trans orientations, see Scheme
2. The isomeric configuration has been defined by three cis or trans
prefixes which specify first the relative position of the Cl-ligands,
then the relative orientation of the phenyl groups, and finally the
relative orientation of the R group on the b-diketonato ligand
C6H5COCHCOR. It was argued on qualitative basis that the cis con-

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Fig. 2. Part of the packing diagram of Ti(ba)2biphen 4 showing intermolecular edge-to-face CꢀHꢂ ꢂ ꢂp interactions creating infinite chains. The CꢀHꢂ ꢂ ꢂp interactions are (a)
between biphen CꢀH and ba phenyl of adjacent molecules, between ba CꢀH and ba phenyl of a adjacent molecule and (b) biphen CꢀH and the aromatic b-diketonato chelated
ring systems in a neighbouring molecule.
Fig. 3. Packing diagram showing the herringbone packing motif of Ti(ba)2biphen 4.

A. Kuhn et al. / Inorganica Chimica Acta 362 (2009) 3088–3096
3093
Cl
R
R
O
O
a
a
a
Ti
H
H
a
a
Ph
a
R
Ph
H
H
H
O
O
Ph
Ph
R
R
Ph
Cl
O
O
O
Ti
O
O
O
Cl
O
Cl
Cl
trans-cis-cis (C2v
)
Ti
O
Ti
O
Cl
O
Cl
O
Cl
O
Cl
R
Ph
R
Ph
Ph
O
O
a
a
b
a
Ti
H
H
H
H
H
Ph
R
R
O
O
cis-cis-trans (C2)
cis-cis-cis (C1)
cis-trans-cis (C2)
Ph
R
Cl
trans-trans-trans (C2h
)
a
Ph
a
Ph
a
R
H
H
H
R
R
Ph
O
O
O
Ti
O
O
O
O
O
O
O
Ti
O
Ti
O
O
O
O
O
O
O
Ph
R
Ph
b
a
a
H
H
H
R
Ph
R
cis-cis-cis (C1)
cis-trans-cis (C2)
cis-cis-trans (C2)
Scheme 2. The stereochemistry the isomers of asymmetrically substituted bis(b-diketonato) complexes of the type Ti(PhCOCHCOR)2Cl2 and Ti(PhCOCHCOR)2(biphen): cis–
cis–cis isomer (point group C1, give rise to two proton 1H NMR resonances for each type of group), cis–trans–cis (point group C2, give a single resonance for each type of group),
cis–cis–trans (C2, give a single resonance for each type of group), trans–cis–cis (C2v, give a single resonance for each type of group) and trans–trans–trans (C2h, give a single
resonance for each type of group).
Fig. 4. Variable temperature 1H NMR spectra of the indicated complexes showing selected phenyl (ca 7.8 ppm), methine (ca 6.5–7 ppm) and methyl (ca 2.2 ppm, only for 1
and 4) resonances.
isomer of 3 and 6, leads to an experimental isomer distribution of
ca 35:25:40 and 20:60:20 for 3 and 6, respectively, the first
value belongs to the cis–cis–cis isomer. The isomer distribution
of 3 and 6 thus deviates largely from the statistical value of
50:25:25.
ment of the accuracy of the ground state geometry of the calcu-
lated structures. Excellent agreement between experimental and
theoretical structures is obtained as reflected by the RMSD values
of 0.061 and 0.041 Å for 1 and 4, respectively. In Fig. 5, the super-
imposed calculated and solid state structures of 1 and 4 are pre-
sented. The bonds in
1 and 4 were reproduced by DFT
3.4. Theoretical studies
calculations within 0.01–0.07 Å for Ti–O bonds, within 0.00–0.01
for O–C bonds and within 0.01–0.02 Å for C–C bonds from the
experimental values. Since comparisons of experimental metal–li-
gand bond lengths with calculated bond lengths below a threshold
of 0.02 Å are considered as meaningless [32], the computational
method used thus gives a good account of experimental bond
lengths. The O1–Ti–O2 angles were calculated accurately within
1.2°. Structural data computed with this computational method
for related compounds may therefore, be presented with an
extrapolative equally high degree of accuracy.
Density functional theory (DFT) calculations were carried out
on the different isomers of Ti(b-diketonato)2Cl2 1–3 and Ti(b-dike-
tonato)2(biphen) 4–6. The validity of the density functional meth-
od was obtained by comparing the calculated data with known
single crystal X-ray diffraction structural data of 1 and 4. The
root-mean-square distances (RMSD) calculated for non-hydrogen
atoms for the best three-dimensional superposition of calculated
structures on experimental structures give a qualitative measure-

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A. Kuhn et al. / Inorganica Chimica Acta 362 (2009) 3088–3096
Selected calculated geometrical parameters of the main isomers
of complexes 1–6 are represented in Figs. 6–8. Three different Ti–O
bond lengths as defined in Fig. 1b and summarized in Table 4 are
found in complexes 1–6. The longest Ti–O bonds, deq
, are
Ti–Ob-diketonato bonds trans to dL, a Ti–Cl or a Ti–Obiphen bond. The
shortest Ti–O bonds for 1–3 are axial Ti–Ob-diketonato bonds trans
to another dax Ti–Ob-diketonato bond. The calculated Ti–O bonds
lengths in complexes 1–6 are in the order Ti–Obiphen (1.82–
1.87 Å) < Ti–Ob
(1.97–2.04 Å) < Ti–Ob
(2.05–2.12 Å).
axial
equatorial
The different type of bond lengths did not change significantly
when going from the one cis isomer to another.
The relative energies of the three cis isomers of each complex
clearly highlight the geometry preferences and also enable a pop-
ulation analysis of the isomers by application of the Boltzmann
equation. Especially pleasing is that the geometry of the lowest en-
ergy isomer of both 1 and 4 was the same as the isomer that crys-
tallized from solution. The calculated isomer distribution is given
in Table 3. The experimentally observed cis–trans–cis and cis–cis–
trans populations are assigned according to the calculated isomer
distribution. A generally good agreement is obtained between the
experimentally observed isomer distribution and the calculated
values.
Fig. 5. An overlay view of the calculated (solid black) and the experimental (dashed
blue) X-ray determined structure of Ti(ba)2Cl2 (1) and Ti(ba)2biphen (4). All
unmarked molecules are C. H omitted for clarity.
cis-cis-cis
cis-trans-cis
cis-cis-trans
Ph
Ph
CH3
O
O
O
H3C
H3C
O
Ph
Ph
1.984
83.3°
Cl
1.982
O
Cl
1.989 Cl
O
2.060
O
2.274
2.051
2.061
O
99.7°
99.5°
Ti
Ti
82.8°
98.4°
2.054
Ti
82.9°
2.278
Cl
2.279
Cl
2.276
Cl
82.9°
1.985
O
O
O
O
Ph
H3C
CH3
Ph
CH3
Ti(ba)2Cl2 (1)
Ph
O
Ph
CH3
O
O
H3C
H3C
H3C
Ph
Ph
2.002
2.008
O
O
O
2.086
2.077
O
O
2.013
O
O
2.088
O
83.3°
1.845
90.6°
89.6°
Ti
Ti
82.6°
O
2.045
90.4°
Ti
83.0°
1.868
O
1.840
O
1.840
83.2°
O
2.023
O
O
Ph
O
CH3
Ph
CH3
Ti(ba)2biphen (4)
Fig. 6. Selected calculated bond lengths [Å] and angles [°] for Ti(ba)2Cl2 and Ti(ba)2biphen.
cis-cis-cis
trans-trans-trans
cis-cis-cis
Ph
Ph
H
Ph
Ph
O
Ph
Ph
O
2.007
O
O
2.085
O
O
1.966
Ph
90.3°
Ti
Cl
O
O
1.843
O
2.317
82.9°
Cl
Ti
Cl
97.8°
Ti
82.6°
2.065
O
O
2.278
Cl
1.994
O
85.4°
Ph
O
O
Ph
Ph
Ph
Ph
Ti(dbm)2Cl2 (2)
H
Ti(dbm)2biphen (5)
Fig. 7. Selected calculated bond lengths [Å] and angles [°] for Ti(dbm)2Cl2 and Ti(dbm)2biphen.

A. Kuhn et al. / Inorganica Chimica Acta 362 (2009) 3088–3096
3095
cis-cis-cis
cis-trans-cis
cis-cis-trans
CF3
Ph
Ph
O
O
O
2.000
F3C
F3C
O
Ph
Ph
1.979
Cl
1.975
Cl
O
Cl
O
2.080
O
82.4°
Ti
82.4°
1.991
O
2.247
2.090
2.074
O
99.8°
98.9°
Ti
82.7°
2.092
100.6°
Ti
82.8°
O
2.257
Cl
2.260
Cl
2.247
Cl
O
O
Ph
F3C
CF3
Ph
CF3
Ti(tfba)2Cl2 (3)
Ph
O
Ph
CF3
O
O
F3C
F3C
F3C
Ph
Ph
2.012
2.017
O
O
O
2.122
2.101
O
O
2.038
O
O
2.106
O
82.8°
1.825
90.3°
Ti
82.9°
90.6°
Ti
2.103
90.7°
Ti
1.833
O
1.825
O
1.823
O
82.9°
82.9°
O
O
2.035
O
O
Ph
CF3
Ph
CF3
Ti(tfba)2biphen (6)
Fig. 8. Selected calculated bond lengths [Å] and angles [°] for Ti(tfba)2Cl2 and Ti(tfba)2biphen.
Table 3
Observed and calculated isomer distribution of 1–6.
Compound
Isomer
% Observed 1H NMR
% Observed 19F NMR
% Calculated
Ti(ba)2Cl2 (1)
cis–cis–cis
27.9
54.7
17.4
0.0
31.0
61.7
6.7
0.5
0.1
cis–trans–cis
cis-cis–trans
trans–trans–trans
trans–cis–cis
0.0
Ti(dbm)2Cl2 (2)
Ti(tfba)2Cl2 (3)
cis–cis–cis
trans–trans–trans
100.0
0.0
97.1
2.9
cis–cis–cis
37.0
38.4
24.6
0.0
32.3
41.9
25.8
0.0
39.5
41.9
18.4
0.2
cis–trans–cis
cis–cis–trans
trans–trans–trans
trans–cis–cis
0.0
0.0
0.0
Ti(ba)2biphen (4)
cis–cis–cis
cis–trans–cis
cis–cis–trans
25.6
49.2
25.2
26.5
43.7
29.8
Ti(dbm)2biphen (5)
Ti(tfba)2biphen (6)
cis–cis–cis
100.0
100.0
cis–cis–cis
cis–trans–cis
cis–cis–trans
17.1
62.4
20.6
21.2
61.6
17.2
19.5
62.2
18.3
Table 4
Range of the calculated geometrical parameters (°, Å) for cis configurated octahedral monomeric complexes 1–6. Parameters are defined in Fig. 1b.
Compound
dax
deq
dL
O–Ti–O
Cl–Ti–Cl or OL–Ti–OL
Ti(b-diketonato)2Cl2
Ti(b-diketonato)2biphen
1.97–2.00
2.00–2.04
2.05–2.09
2.05–2.12
2.25–2.28
1.82–1.87
82–83
83
98–101
90–91
position. According to a DFT computational study of the relative
energies and abundance of the possible isomers of 4, this configu-
ration is in agreement with the most stable isomer. A RMSD value
of 0.041 Å for the overlay of the calculated and solid state structure
of 4 confirms the high degree of accuracy of the computational
4. Conclusions
Isomerically pure crystals of Ti(ba)2biphen (4) have been syn-
thesized. In the solid state 4 adopts the cis–trans–cis configuration
with the phenyl ends of the benzoylacetonato ligands in the trans

3096
A. Kuhn et al. / Inorganica Chimica Acta 362 (2009) 3088–3096
[11] COSMO (Version 1.48), Bruker AXS Inc., Madison, Wisconsin, USA, 2003.
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stable” and also exhibit high resistance towards hydrolysis.
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5. Supplementary material
CCDC No. 702014 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
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[19] The ADF program system was obtained from Scientific Computing and
Acknowledgements
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Financial assistance by the South African National Research
Foundation under Grant No. 2067416 and the Central Research
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