Mono- and dinuclear complexes of sulfones with the tetrachlorides of group 4

Article abstract of DOI:10.1039/b405871b

The reactions of dialkyl sulfones [R₂SO₂: R = Me (a), Et (b), Ph (c), R₂ = -(CH₂)4- (d)J with the metal tetrachlorides of Group 4 [MCl₄,: M = Ti (1), Zr(2), Hf (3)] give different products mainly depending on the sulfone/M molar ratio. Compounds of formula [M₂Cl₈(R₂SO₂)₂] [M = Ti, R₂ = -(CH₂)₄- (1d); M = Zr, R = Et (2b), R = Ph (2c)] and [MCl₄(R₂SO₂)₂ (sulfone/M = 2) [M = Ti, R = Me (1aa); M = Zr, R = Me (2aa), R = Ph (2cc), R₂ = -(CH₂)₄- (2dd); M = Hf, R = Me (3aa), R₂ = -(CH₂)₄- (3dd)] have been obtained. By X-ray diffraction methods the dinuclear titanium and zirconium adducts, [Ti ₂Cl₈(μ-sulfolane-O,O′)₂] (Id) and [Zr₂Cl₈(μ-Ph₂SO₂-O,O') ₂] (2c) have been established to contain bridging sulfone and hexacoordinated metal centres, while the mononuclear zirconium complex [ZrCl₄(Me₂SO₂)₂] (2aa) has cis-monodentate sulfones in a slightly distorted octahedral geometry. The reaction between TiCl₄ and sulfolane (tetrahydrothiophene 1,1-dioxide) in SOCl₂ affords the 1:1 adduct independent of the sulfone/Ti molar ratio. Ligand-exchange and inter-conversion between mononuclear and dinuclear species have been observed by NMR, while the spectral features of the SO₂ moiety have been assigned by IR- and Raman spectroscopies.

Full text of DOI:10.1039/b405871b

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F U L L P A P E R
Mono- and dinuclear complexes of sulfones with the tetrachlorides
of group 4
Paolo Biagini,*a Fausto Calderazzo,b Fabio Marchetti,b Guido Pampaloni,*b
Stefano Ramello,a Mario Salvalaggio,a Roberto Santi†a and Silvia Speraa
a
Polimeri Europa S.p.A-Centro Ricerche “Guido Donegani”, via G. Fauser 4, I-28100, Novara,
Italy. E-mail: paolo.biagini@polimerieuropa.com
Università di Pisa, Dipartimento di Chimica e Chimica Industriale, via Risorgimento 35,
b
I-56126, Pisa, Italy. E-mail: pampa@dcci.unipi.it
Received 19th April 2004, Accepted 1st June 2004
First published as an Advance Article on the web 24th June 2004
The reactions of dialkyl sulfones [R2SO2: R = Me (a), Et (b), Ph (c), R2 = –(CH2)4– (d)] with the metal tetrachlorides
of Group 4 [MCl4: M = Ti (1), Zr(2), Hf (3)] give different products mainly depending on the sulfone/M molar
ratio. Compounds of formula [M2Cl8(R2SO2)2] [M = Ti, R2 = –(CH2)4– (1d); M = Zr, R = Et (2b), R = Ph (2c)] and
[MCl4(R2SO2)2] (sulfone/M = 2) [M = Ti, R = Me (1aa); M = Zr, R = Me (2aa), R = Ph (2cc), R2 = –(CH2)4– (2dd);
M = Hf, R = Me (3aa), R2 = –(CH2)4– (3dd)] have been obtained. By X-ray diffraction methods the dinuclear titanium
and zirconium adducts, [Ti2Cl8(-sulfolane-O,O′)2] (1d) and [Zr2Cl8(-Ph2SO2-O,O′)2] (2c) have been established to
contain bridging sulfone and hexacoordinated metal centres, while the mononuclear zirconium complex [ZrCl4(Me2SO2)2]
(2aa) has cis-monodentate sulfones in a slightly distorted octahedral geometry. The reaction between TiCl4 and sulfolane
(tetrahydrothiophene 1,1-dioxide) in SOCl2 affords the 1:1 adduct independent of the sulfone/Ti molar ratio. Ligand-
exchange and inter-conversion between mononuclear and dinuclear species have been observed by NMR, while the
spectral features of the SO2 moiety have been assigned by IR- and Raman spectroscopies.
Introduction
Some of us recently reported1 that thionyl chloride forms
unstable, oxygen-bonded 1:1 complexes with TiCl4 of formula
[Ti2Cl8(SOCl2)2], three crystal modifications being isolated in the
temperature range between 220 and 234 K. In the same paper ZrCl4
and HfCl4 were reported to form adducts of the same stoichiometry
stable at room temperature. On increasing the donor number of the
Lewis base, i.e., on going from SOCl2 to SeOCl2 (DNSOCl = 0.4;
2
DNSeOCl = 12.2),2 zirconium tetrachloride was found to give1:1 or
Scheme 1 Preparation of Ti, Zr and Hf sulfone complexes.
2
2:1 adducts of formula [ZrCl4(SeOCl2)n], n = 1 or 2, depending on
the stoichiometry of the reagents.3
release of the sulfone. In the case of titanium(IV), the dinuclear
[Ti2Cl8(-sulfolane-O,O′)2] (1d) has been obtained in SOCl2
as solvent even in the presence of a large excess of sulfolane,
suggesting that the bis-adduct of titanium is not stable under our
experimental conditions.
Some coordination compounds of alkyl sulfones have been
prepared, in agreement with their weak donor properties, the
DN value of tetrahydrothiophene 1,1-dioxide (sulfolane) being
14.8,4 according to Gutmann. Known examples are the adducts
of LiCl,5 SnCl4,5b,6 MgCl2,5c HgX2,5c TlCl3,5c BF3 with sulfolane
7
or of transition metal compounds with dimethyl sulfone, [Rh2-
(CF3COO)4(Me2SO2)2],8 diethyl sulfone, [Co2Cl4(-Et2SO2-
O,O′)2],9 or sulfolane such as [MCl2(C4H8SO2)], M = Mn,5c Co,5c,
X-Ray crystallography
The sulfolane adduct [Ti2Cl8(-sulfolane-O,O′)2] (1d) is a
centrosymmetric dimer containing bridging sulfolano ligands,
see Fig. 1 and Table 1. The two titanium atoms in the dinuclear
unit (TiTi distance 5.33 Å) form a Ti2O4S2 eight-membered
ring. The titanium atom has a distorted octahedral geometry
as generally found in cis-adducts of formula TiCl4(oxygenated
ligand)2.12 The Cl(3)–Ti–Cl(4) angle is 165.81°, and compares
well with the range 161.08(4)–172.1° observed in cis-octahedral
derivatives of titanium(IV) containing oxygen donors such as
[TiCl4(MeCO)2O]12a and [TiCl4L2], L = Et2O,12f THF12g]. The mean
Ti–Cleq (eq = equatorial) bond distance of 2.219 Å (av.) is slightly
shorter than the Ti–Clax (ax = axial) bond distance of 2.289 Å (av.).
The O–Ti–Clax bond angle is 84.87° (av.).
The sulfolane ligand is characterized by S–O distances (1.463 Å,
av.) slightly longer than those observed in the plastic phase of
sulfolane13 (1.45 Å), and by an O–S–O angle of 116.1° similar
to that observed in [LiCl(sulfolane)]5a [S–O, 1.447(2) Å; O–S–O,
114.8(1)°], whose structure consists of a three-dimensional infinite
network containing four-coordinate lithium atoms, with Cl and
O,O′-sulfolano bridges.
10
Cu,5c,11 Zn,5c Cd,5c and [Co(C4H8SO2)3](ClO4)2.10 A few of these
compounds have been structurally characterized.5,8,9
These observations prompted us to investigate the reactions of
Group 4 metal tetrachlorides MCl4 (M = Ti, Zr, Hf) with sulfones
and here we report the spectroscopic and structural characterisation
of both mononuclear and dinuclear derivatives.
Results and discussion
The tetrachlorides of Group 4, MCl4, M = Ti, Zr, Hf, react
exothermally with sulfones R2SO2 [R = Me, Et, Ph; R2 = –CH2)4–]
forming different products, predominantly, but not exclusively (vide
infra), depending on the sulfone/MCl4 molar ratio, see Scheme 1.
All compounds with a sulfone/MCl4 molar ratio of 2 have a
solubility in chlorinated solvents which depends on the nature of
both the metal (Hf < Zr  Ti) and the sulfone [Me < Ph < Et ≈
–(CH2)4–]. The different solubility of the complexes allowed the
isolation of the solid products (see Experimental section) to be
carried out. The products are readily hydrolized by moisture with
The structure of [Zr2Cl8(-Ph2SO2-O,O′)2] (2c) has also been
solved: to the best of our knowledge, it represents the first
† Deceased on December 26th, 2003.
2 3 6 4
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Table 1 Selected bond distances (Å) and angles (°) for [Ti2Cl8(-sulfolane-
O,O′)2] (1d)
Table 2 Selected bond distances (Å) and angles (°) for [Zr2Cl8(-Ph2SO2-
O,O′)2]·C2H2Cl4 (2c·C2H2Cl4) (primed atoms related to unprimed equiva-
lents by the symmetry operation −x, −y, −z + 1)
Ti–O(1′)
Ti–Cl(1)
Ti–Cl(3)
S–O(1)
2.146(2)
2.2125(8)
2.2471(8)
1.462(2)
Ti–O(2)
Ti–Cl(2)
Ti–Cl(4)
S–O(2)
2.180(2)
2.2261(8)
2.3304(8)
1.465(2)
Zr–O(1)
Zr–Cl(1)
Zr–Cl(2)
S–O(1)
2.257(3)
2.422(1)
2.356(1)
1.456(3)
Zr–O(2)
Zr–Cl(3)
Zr–Cl(4)
S–O(2′)
2.264(3)
2.407(1)
2.359(1)
1.463(3)
O(1′)–Ti–O(2)
O(1′)–Ti–Cl(1)
O(2)–Ti–Cl(1)
O(1′)–Ti–Cl(2)
O(2)–Ti–Cl(2)
Cl(1)–Ti–Cl(2)
O(1′)–Ti–Cl(3)
O(2)–Ti–Cl(3)
Cl(1)–Ti–Cl(3)
80.00(6)
91.44(5)
171.37(5)
169.46(5)
89.48(5)
99.09(4)
83.29(5)
83.90(5)
96.28(3)
Cl(2)–Ti–Cl(3)
O(1′)–Ti–Cl(4)
O(2)–Ti–Cl(4)
Cl(1)–Ti–Cl(4)
Cl(2)–Ti–Cl(4)
Cl(3)–Ti–Cl(4)
O(1)–S–O(2)
S–O(1)–Ti′
95.06(3)
85.85(5)
85.24(5)
93.08(3)
93.96(3)
165.81(3)
116.1(1)
143.0(1)
140.7(1)
O(1)–Zr–O(2)
O(1)–Zr–Cl(2)
O(2)–Zr–Cl(2)
O(1)–Zr–Cl(4)
O(2)–Zr–Cl(4)
Cl(2)–Zr–Cl(4)
O(1)–Zr–Cl(3)
O(2)–Zr–Cl(3)
Cl(2)–Zr–Cl(3)
82.8(1)
171.84(9)
89.18(9)
90.34(9)
173.11(9)
97.71(6)
82.53(9)
83.09(9)
97.86(6)
Cl(4)–Zr–Cl(3)
O(1)–Zr–Cl(1)
O(2)–Zr–Cl(1)
Cl(2)–Zr–Cl(1)
Cl(4)–Zr–Cl(1)
Cl(3)–Zr–Cl(1)
O(1)–S–O(2′)
S–O(1)–Zr
96.00(6)
82.28(9)
83.26(8)
95.51(6)
95.91(6)
160.71(5)
115.8(2)
147.6(2)
144.5(2)
S–O(2)–Ti
S′–O(2)–Zr
2c. Bond distances are similar to those observed in the O-ligated
adducts of ZrCl4:14 the diphenyl sulfone ligand has S–O distances
(1.459 Å, av.) and an O–S–O bond angle of 115.76°, comparable to
those observed in uncoordinated diphenyl sulfone15 (1.436 Å and
119.21°).
The structures of [Ti2Cl8(-sulfolane-O,O′)2] (1d) and [Zr2Cl8(-
Ph2SO2-O,O′)2] (2c) are reminiscent of those of the zirconium(IV)
and cobalt(II) derivatives [Zr2Cl8[-Ph3AsN)(Tolyl)SO2-O,O′)2]16
[Co2Cl4(-Et2SO2-O,O′)2], respectively, the latter being a by-
product of the reaction of [CoCl(PEt3)3] with disodium ethane-1,2-
thiolato.9 The two metal atoms are linked by the oxygen atoms of
two substituted sulfone ligands forming a M2O4S2 eight-membered
ring. The S–O distances, 1.448 and 1.51 Å, av., and the O–S–O
angle, 109.9 and 117.1°, for the zirconium and cobalt derivatives,
respectively, are comparable to those observed in our compounds.
It is interesting to observe that at variance with the structurally
characterized dinuclear adducts of Group 4 tetrachlorides which
generally have bridging chlorides,1,17,18 the dinuclear compounds
reported in this paper contain sulfone bridges. Probably the bite
of the terminal sulfolane or diphenyl sulfone ligand would be too
small, making the monodentate arrangement on a single metal
centre highly unfavourable.
The bis-adduct [ZrCl4(Me2SO2)2] (2aa) crystallizes in the space
group P212121 with four molecules in the unit cell. The coordination
at zirconium is slightly distorted octahedral, see Fig. 3 and Table 3,
with the dimethyl sulfone ligands in cis-position [(O(1)–Zr–O(2)
84.5(3)°]. The Zr–Cl distances (2.393 Å, av.), as well as the
Zr–O distances (2.174 Å, av.) are similar to those observed in
2c and comparable to other O-adducts of ZrCl4.14 The structural
parameters of the dimethyl sulfone ligand [S–O 1.430 Å, av.;
O–S–O 115.0(4) °] are similar to those found in the rhodium(II)
complex [Rh2(CF3COO)4(Me2SO2)2] [S–O 1.453 Å, av.; O–S–O
115.48(6) °],8 and comparable to those reported for uncoordinated
Me2SO2 [S–O 1.448 Å, av.; O–S–O 117.2(6) °].19
Fig. 1 View of the molecular structure of [Ti2Cl8(-sulfolane-O,O′)2]
(1d). Thermal ellipsoids are at 30% probability (primed atoms related to
unprimed equivalents by the symmetry operation −x + 1, −y, −z).
structurally characterized compound containing coordinated
diphenyl sulfone. It is centrosymmetric with a ZrZr distance
of 5.498 Å and bridging diphenylsulfone groups, see Fig. 2 and
Table 2. The two hexacoordinated zirconium atoms in the dimer
form a Zr2O4S2 eight-membered ring.
The mean Zr–Cleq bond distance of 2.357 Å (av.) is slightly
shorter than the mean Zr–Clax bond distance of 2.415 Å. Deviations
the O–Zr–Cl angles from the ideal octahedral geometry of the same
type as those found in the titanium derivative 1d are observed in
Fig. 3 The molecular structure of [ZrCl4(Me2SO2)2] (2aa). Thermal
ellipsoids are at 30% probability.
It is noteworthy that the compounds described in the present
paper, either the cyclic dinuclear compounds or the mononuclear
one, show a comparable deformation of the coordination sphere of
the metal, so that the chlorine atoms are leaning towards the oxygen
ligands. As a matter of fact, the Clax–M–Clax angles are smaller than
Fig. 2 View of the molecular structure of [Zr2Cl8(-Ph2SO2-O,O′)2] in
[Zr2Cl8(-Ph2SO2-O,O′)2]·C2H2Cl4 (2c·C2H2Cl4). Thermal ellipsoids of
Zr, Cl, S and O atoms are at 30% probability, those of C atoms have been
omitted for clarity.
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1
2 3 6 5

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Table 3 Selected bond distances (Å) and angles (°) for [ZrCl4(Me2SO2)2]
(2aa)
Zr–O(1)
2.173(6)
2.367(3)
2.405(3)
1.425(6)
1.431(6)
Zr–O(3)
2.175(6)
2.378(2)
2.422(3)
1.464(5)
1.399(7)
Zr–Cl(1)
Zr–Cl(4)
S(1)–O(1)
S(1)–O(2)
Zr–Cl(2)
Zr–Cl(3)
S(2)–O(3)
S(2)–O(4)
O(1)–Zr–O(3)
O(1)–Zr–Cl(1)
O(3)–Zr–Cl(1)
O(1)–Zr–Cl(2)
O(3)–Zr–Cl(2)
Cl(1)–Zr–Cl(2)
O(1)–Zr–Cl(4)
O(3)–Zr–Cl(4)
Cl(1)–Zr–Cl(4)
Cl(2)–Zr–Cl(4)
84.5(3)
172.8(2)
88.6(2)
90.3(2)
174.7(2)
96.7(1)
85.8(2)
86.6(2)
95.8(2)
92.3(1)
O(1)–Zr–Cl(3)
O(3)–Zr–Cl(3)
Cl(1)–Zr–Cl(3)
Cl(2)–Zr–Cl(3)
Cl(4)–Zr–Cl(3)
S(1)–O(1)–Zr
S(2)–O(3)–Zr
O(1)–S(1)–O(2)
O(3)–S(2)–O(4)
85.2(2)
86.2(2)
92.4(1)
94.1(1)
169.0(1)
174.8(6)
151.9(5)
115.0(4)
115.8(4)
180° [165.81(3), 160.71(5), and 169.0(1)° for 1d, 2c·C2H2Cl4 and
2aa, respectively] and, correspondingly, the Cleq–M–Cleq angles are
larger than 90° [99.09(4), 97.71(6) and 96.7(1)° for 1d, 2c·C2H2Cl4
and 2aa, respectively]. This trend is present also in the sulfur and
selenium adducts of ZrCl4 and it has been attributed to the repulsion
between the lone pairs of the chlorine atoms.20
1H NMR spectroscopy
The 1H NMR spectra of the [MCl4(Me2SO2)2] complexes [M = Zr
(2aa), Hf (3aa)] in CD2Cl2 at room temperature show a single
broad peak at 3.39 ppm (Zr) and two equally broad peaks at 3.43
and 2.95 ppm (Hf). On the other hand, the titanium complex 1aa
shows only one single narrow peak at 3.25 ppm. By lowering the
temperature down to −80 °C (−90 °C for the titanium derivative),
two sharp singlets are observed for all three complexes, namely the
signal at higher fields (2.95 ppm), due to the uncomplexed ligand,
and the signal at lower field attributed to the metal-coordinated
dimethyl sulfone (3.38 ppm for titanium, 3.41 ppm for zirconium
and 3.43 ppm for hafnium). This has been confirmed by addition of
an excess of the ligand to the solution, see Fig. 4, the intensity of the
peaks at −90 °C being consistent with the expected concentrations
of [MCl4(Me2SO2)2] and Me2SO2. The broad spectra reported in
Fig. 4 are clearly due to a ligand-exchange process.
Fig. 4 1H NMR spectra in CD2Cl2: (A) TiCl4(Me2SO2)2 (1aa) + Me2SO2,
(B)
ZrCl4(Me2SO2)2
(2aa) + Me2SO2,
(C)
HfCl4(Me2SO2)2
(3aa) + Me2SO2.
The coalescence temperature depends on the nature of the metal:
it is below −70 °C for titanium, around 0 °C for zirconium and just
above 25 °C in the case of hafnium, so that the relative rates of
exchange are in the following order: kTi  kZr > kHf. This behaviour
is consistent with the trend observed in the water exchange process
within transition d elements belonging to the same Group.21
A more complicated situation has been found for the dinuclear
complexes [M2Cl8(-R2SO2-O,O′)2], particularly in the case of
1
R = Et. The H NMR spectrum in CD2Cl2 of [Zr2Cl8(-Et2SO2-
O,O′)2] (2b) shows two broad signals at 3.63 (CH2) and 1.60 ppm
(CH3) at room temperature. By lowering the temperature down
to −80 °C, two different ethyl resonances are observed at 3.90 (CH2)
and 1.62 (CH3) and at 3.45 (CH2) and 1.45 (CH3) ppm.
In order to study the behaviour of 2b in solution, two samples
were prepared, one containing a large excess of additional Et2SO2
(sulfone/2b molar ratio = 4), the other one with a sulfone/2b molar
ratio of about 0.5. The variable-temperature spectra are reported in
Fig. 5. In the former case (Fig. 5(A)), two sets of well-separated
resonances were observed at −80 °C, attributed to uncomplexed
[2.93 ppm (CH2), 1.24 ppm (CH3)] and to coordinated Et2SO2
[3.45 ppm (CH2), 1.43 ppm (CH3)] of the mononuclear derivative
[ZrCl4(Et2SO2)2] (2bb), probably formed in solution in the presence
of the large excess of Et2SO2.
Fig. 5 1H NMR spectra in CD2Cl2: (A) Et2SO2 + Zr2Cl8(-Et2SO2-
O,O′)2 (2b) (Et2SO2/2b molar ratio = 4), (B) Zr2Cl8(-Et2SO2-O,O′)2 (2b)
(Et2SO2/2b molar ratio = 0.5).
In the second experiment (Fig. 5(B)) the two broad peaks at 3.53
and 1.56 ppm at room temperature give two couples of well resolved
resonances at −80 °C, which match the situation observed for 2b, in
the same solvent at the same temperature without addition of diethyl
sulfone. This suggests that the solutions of [Zr2Cl8(-Et2SO2-O,O′)2]
(2b) in dichloromethane contain both the dinuclear 1:1 derivative
2b [resonances (−80 °C) at 3.90 ppm (CH2) and 1.62 ppm (CH3)]
and the 2:1 complex [ZrCl4(Et2SO2)2] (2bb) [resonances (−80 °C)
at 3.45 ppm (CH2) and 1.43 ppm (CH3)], the relative amounts of the
two components depending on the Et2SO2/Zr molar ratio. In fact,
2 3 6 6
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1

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Table 4 Asymmetric and symmetric OSO stretching absorptions of complexed and uncomplexed sulfones (FT-Raman values are reported in parenthesis)
−1
−1
−1



Compound
νas(OSO)/cm
νs(OSO)/cm
ν/cm
Bonding mode
Sulfolanea
1301s (1302vw)
1148s (1142s)
1090s (1096ms)
1073–1056s (1079–1060m)
1137s (1121s)
1114–1093s (1110–1090s)
1112–1082s (1100–1082m)
1111–1085s (1106–1082s)
1138–1125s (1122s)
1100s (1110s)
153 (160)
130 (−)
—
[Ti2Cl8(-sulfolane-O,O′)2]b
1220vs (−)c
Bidentated
Monodentate
—
[ZrCl4(sulfolane)2]b
1297–1280vs (1297w)
1301s (1269w)
224 (227)
164 (148)
177 (171)
182 (185)
180 (183)
156 (158)
107 (−)
155 (155)
104 (−)
181 (182)
b
Me2SO2
[TiCl4(Me2SO2)2]b
[ZrCl4(Me2SO2)2]b
[HfCl4(Me2SO2)2]b
[Et2SO2]b
1295–1266s (1278–1263m)
1290–1267s (1284–1269w)
1284–1271vs (1283–1271m)
1287s (1280w)
Monodentate
Monodentated
Monodentate
—
[Zr2Cl8(-Et2SO2-O,O′)2]b
1207s (−)c
Bidentate
—
b
Ph2SO2
1309s (1308vw)
1154s (1153s)
1123s (1133s)
1133–1111s (1131–1111s)
[Zr2Cl8(-Ph2SO2-O,O′)2]b
1227s (−)c
Bidentated
Monodentate
[ZrCl4(Ph2SO2)2]b
1309–1297s (1310–1295m)
a Neat liquid, FT-IR and FT-Raman. b Nujol mull for FT-IR and neat substance by FT-Raman. c Too weak to be detected. d X-Ray structure is available.
1
ones are too weak to be detected (Fig. 6(a) and (b)). On the other
when the H NMR spectrum of [Zr2Cl8(-Et2SO2-O,O′)2] (2b) is
recorded in the presence of an excess of ZrCl4, i.e. under conditions
preventing the presence in solution of free sulfone through fortu-
itous hydrolysis, well resolved signals at 3.81 (CH2) and 1.73 ppm
(CH3) are observed even at room temperature, the situation not
changing on lowering the temperature down to −80 °C (3.82 and
1.67 ppm). The small difference observed in the chemical shifts
[3.90 and 1.62 vs. 3.81 and 1.73 ppm is probably due to the presence
of solid ZrCl4.

hand, an intensification of the [νas(OSO)] mode is observed for the
monodentate ligation in 2aa (Fig. 6(c)), as a consequence of the SO2
asymmetric configuration. These Raman features turned out to be
particularly useful to locate the OSO stretching bands in these com-
plexes. The wavenumber values of the asymmetric and symmetric
stretchings and the related separations are summarised in Table 4:


when solid-state splitting of the νas(OSO) and/or νs(OSO) vibra-
tions was observed, the respective barycentre was used to determine

the separation ν.
In conclusion, the NMR spectra of Fig. 5(B) suggest the existence
in solution of an equilibrium between mononuclear and dinuclear
species.
Finally the different spectral patterns at −80 °C, see Fig. 5, of the
methylene signals of the bonded diethyl sulfone (quartet for 2b and
overlapped quartets for 2bb) deserve some additional comments.
Only in the mononuclear derivative 2bb the rotation around the
Zr–O– and/or the S–C bond could be hindered so to generate
some inequivalence in the chemical shifts of the four CH2’s. This
behaviour also depends on the nature of the sulfone ligand: in fact,
no splitting is observed for the methyl signals of the bonded Me2SO2
in 2aa even at −90 °C (see Fig. 4(B)).
Infrared and Raman spectroscopy
Sulfone coordination to a metal centre results in spectroscopic
modifications of the SO2 vibrations with respect to the uncomplexed

molecule, especially for the asymmetric [νas(OSO)] and symmetric

[νs(OSO)] stretching modes, see Table 4. In agreement with the
expected reduction of the sulfur–oxygen bond order on coordination,
the OSO stretching modes are shifted to lower wavenumbers.
Furthermore, similarly to carboxylato complexes,22 the separation



ν between the asymmetric [νas(OSO)] and symmetric [νs(OSO)]
stretching vibrations is expected to be influenced by the type of
coordination. In particular, bridging bidentate coordination should
result in a less pronounced separation than in the free molecule, due
to the S–O bond order decrease and to the consequent reduction
of OSO vibrational coupling.23 Moreover, in the case of chelation
vibrational coupling is expected to be lower, thus producing a

further decrease of ν, because of the decreased O–S–O angle.
Vice versa, a greater separation is expected for a monodentate
sulfone, essentially reflecting the larger red-shift of the symmetric

stretching mode [νs(OSO)] (pseudo single-bond order of the
coordinated S–O bond).
In order to further strengthen the SO2 vibrational assignments,
Raman spectroscopy has been used. For uncoordinated sulfones,
both IR asymmetric and symmetric stretching vibrations are of
high intensity while the Raman spectra show intense symmetric
stretching vibrations, whereas the corresponding asymmetric mode
is often not easily detected24 (see Table 4). Due to the essentially
localised character of the sulfone ligand vibrations, a similar differ-
Fig. 6 Vibrational spectra in the OSO stretching region of: (a) [TiCl4(-
sulfolane-O,O′)]2 (1d), (b) [ZrCl4(-Ph2SO2-O,O′)]2 (2c), (c) ZrCl4(Me2SO2)2
(2aa).
As established by X-ray diffractometry, vide infra, the
dinuclear complexes [Ti2Cl8(-sulfolane-O,O′)2] (1d) and [Zr2Cl8
(-Ph2SO2-O,O′)2] (2c) contain bridging bidentate sulfones: the

ence in the intensity of the [ν(OSO)] Raman vibrations is expected
for symmetric bidentate coordination. In fact, the structurally char-
acterised complexes containing bridging bidentate sulfones (1d and

measured ν separations are significantly smaller than those

2c) exhibit strong [νs(OSO)] Raman bands, while the asymmetric
observed in the uncomplexed species (see Table 4); on the other
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1
2 3 6 7

View Article Online
hand, the mononuclear compound [ZrCl4(Me2SO2)2] (2aa)
containing the monodentate sulfone displays a greater separation
−1

215m. FT-Raman ν/cm : 3005w, 2999w, 2987wm, 2945w (sh),
2936m, 2871w, 1443w, 1399w, 1182m, 1133w, 1096ms, 1085wm,
1025w, 961w, 873m, 786w, 729w, 662ms, 564w, 516w, 445w,
404vs, 392m (sh), 372m, 356m, 301s, 269w, 195m, 176s, 154m.

ν with respect to that found in the uncomplexed dimethyl
sulfone. Accordingly, the bonding mode of sulfones in the other
complexes was inferred from the measured separations on the

basis of the ν, as previously discussed. Thus, contrary to some
[MCl4(sulfolane)2], M = Zr (2dd), Hf (3dd). Only the
preparation of the zirconium adduct is described in detail, the
hafnium compound being obtained in a similar way.
earlier considerations,25 the sulfone coordination mode can be

inferred from vibrational spectroscopy. In conclusion, when ν
is significantly greater than in the corresponding uncomplexed
molecule, monodentate coordination is to expected; the opposite
being the case for bidentate coordination.
(a) In dichloromethane. The chloride ZrCl4 (3.59 g,
15.39 mmol) was suspended in 100 ml of CH2Cl2 and a solution
of 3 ml of sulfolane (31.48 mmol) in CH2Cl2 (20 ml) was then
added dropwise at room temperature. At the end of the addition,
a slightly turbid pale yellow solution was obtained, which was
filtered to remove the insoluble material. The volume of the
clear solution was reduced in vacuo to about 50 ml and 30 ml
of hexane were then added. The colourless crystalline solid thus
formed was filtered off, washed with two 10-ml portions of hexane
and dried in vacuo at room temperature, obtaining 4.88 g (67%
Conclusions
This paper describes preparations and structural characterisations
of sulfone derivatives of the tetrachlorides of Group 4 metals. It has
been shown that TiCl4 reacts with sulfolane, in SOCl2 as solvent, to
give a 1:1 dinuclear compound containing sulfone bridges rather
than chloride bridges, similar to the situation already established
for the TiCl4/SOCl2 adduct of formula [Ti2Cl8(SOCl2)2]. This is
due to the low stability of the 2:1 adducts in these experimental
conditions, contrary to what is observed with more basic ligands
containing oxygen or nitrogen as donor atoms.26 On the other
hand, in chlorinated hydrocarbons as solvents, both 1:1 and 2:1
adducts have been obtained, depending on the stoichiometry of the
reagents for all three Group 4 metals. Combination of IR and Raman
spectroscopies turned out to be a valid method for determining the
coordination mode of the sulfone ligand confirming that the 1:1
adducts are dinuclear with bridging bidentate sulfones, while
the 2:1 complexes are mononuclear with monodentate sulfone
coordination.
yield) of [ZrCl4(sulfolane)2] (2dd) Found: Cl, 28.6; Zr, 18.3%.
−1

C8H16Cl4O4S2Zr requires Cl, 29.9; Zr, 19.3%. IR (Nujol) ν/cm :
3001w, 1449w (sh), 1408m, 1297vs, 1288s, 1271s, 1251s, 1205w,
1138s, 1104ms (sh), 1073s, 1056s, 1030w (sh), 999w, 909s, 777m,
−1

734s, 673w, 569m, 518w, 442s. FT-Raman ν/cm : 3002w, 2983m,
2943s, 2882w, 1450m, 1408m, 1297w, 1253m, 1204w, 1138w,
1105m, 1079m, 1060m, 1032m, 966m, 874m, 787w, 735w, 674s,
569w, 519w, 440m, 395w, 383w, 347vs, 302w, 143s.
[HfCl4(sulfolane)2] (3dd). Colourless solid, 71% yield. Found:
Cl, 23.9; Hf, 32.1%. C8H16Cl4HfO4S2 requires Cl, 25.3; Hf, 31.8%.
(b) In neat sulfolane. The chloride ZrCl4 (8.9 g, 38.19 mmol)
was treated with sulfolane (30 ml) (exothermic reaction). The
colourless suspension was filtered off and CH2Cl2 (30 ml),
toluene (30 ml) and hexane (30 ml) were added to the filtrate.27
After 15 days, the colourless microcrystalline solid was collected
by filtration, washed three times with hexane and dried in vacuo
affording 2.7 g (15% yield) of [ZrCl4(sulfolane)2] (2dd). Found: Cl,
28.9; Zr, 19.8%. C8H16Cl4O4S2Zr requires Cl, 29.9; Zr, 19.3%.
Experimental
All operations were carried out using standard Schlenk-tube
techniques, under an atmosphere of prepurified nitrogen. The
reaction vessels were oven-dried prior to use. Solvents were dried
by conventional methods. IR spectra were recorded at 2 cm−1
resolution on a Nicolet Nexus FT-IR spectrophotometer; the analysis
being carried out in the transmission mode, on Nujol mulls prepared
under rigorous exclusion of moisture and oxygen. Raman spectra
were recorded at 4 cm−1 resolution on a Bruker FRA 106 FT-Raman
module attached to a Bruker IFS88 FT-IR spectrophotometer,
equipped with a Nd:YAG excitation laser (1064 nm) and a highly
sensitive Ge detector. The solid samples were analysed in quartz
tubes filled and sealed under a dry and oxygen-free atmosphere.
1H NMR spectra were recorded with a Varian VXR 300 NMR
spectrometer in CD2Cl2 (reference peak at 5.30 ppm) with a pulse
width of 7 s (40°) and a relaxation delay of 1.5 s.
TiCl4 (Merck) was distilled at atmospheric pressure. ZrCl4
(Fluka) and HfCl4 (Cezus Chemie) were treated with boiling SOCl2;
the solutions were partially evaporated under reduced pressure, and
heptane was added to precipitate the metal chloride. The suspension
was filtered off and the solid was dried in vacuo at ca. 200 °C over
several hours. Sulfolanes were distilled over CaH2 prior to use,
Me2SO2 (Aldrich), Et2SO2 (Aldrich) and Ph2SO2 (Aldrich) were
used as received.
[HfCl4(sulfolane)2] (3dd). Colourless solid, 21% yield. Found:
Cl, 24.8; Hf, 31.6%. C8H16Cl4HfO4S2 requires Cl, 25.3; Hf, 31.8%.
Synthesis of [MCl4(Me2SO2)2], M = Ti (1aa), Zr (2aa), Hf
(3aa)]. Only the preparation of the zirconium complex is described
in detail, the corresponding titanium and hafnium compounds being
obtained similarly. To a suspension of ZrCl4 (3.69 g, 15.8 mmol) in
120mlofdichloromethane, Me2SO2 (2.99g, 31.8mmol)dissolvedin
40 ml of dichloromethane was added dropwise at room temperature.
At the end of the addition, the mixture was stirred for additional
2 h, which led to the formation of the colourless microcrystalline
product. This was recovered by filtration, washed with hexane and
dried in vacuo at room temperature. An additional crop of product
was recovered, in a similar way, by adding 30 ml of hexane to the
mother-liquor, for a total yield of 5.98 g (89%) of [ZrCl4(Me2SO2)2]
(2aa). Found: Cl, 33.4; Zr, 21.4%. C4H12Cl4O4S2Zr requires Cl, 33.7;
1
−1

Zr, 21.6%. H NMR (CD2Cl2): 3.39 (s, 12H). IR (Nujol) ν/cm :
Synthesis
3030w, 3006m, 1422vw, 1397w, 1336m, 1317m, 1290s, 1267s,
1112m, 1082s, 1015w, 953s, 775ms, 702w, 490ms, 459ms, 397w,
[Ti2Cl8(-sulfolane-O,O′)2] (1d). A solution of TiCl4 (3 ml,
27.4 mmol) in SOCl2 (50 ml) was treated with sulfolane (13 ml,
136.5 mmol) at room temperature to give a yellow solution. After
addition of hexane (50 ml), a light yellow microcrystalline product
separated out. The solid was recovered by filtration, washed three
times with hexane and dried in vacuo at room temperature affording
1.5 g (28% yield) of [Ti2Cl8(-sulfolane-O,O′)2] (1d). Found: Cl,
−1

353s, 335s, 318s, 301m (sh), 291m (sh). FT-Raman ν/cm : 3030w,
3010mw, 2939w (sh), 2925ms, 1425w, 1390wm (sh), 1337vw,
1319vw, 1284w, 1269wm, 1100ms, 1082m, 1017w, 777ms, 705vs,
498m, 464m, 406w, 344vs, 323m (sh), 294ms, 145vs.
[TiCl4(Me2SO2)2] (1aa). Yellow crystals, 78% yield. Found: Cl,
1
1
45.8; Ti, 15.3%. C4H8Cl4O2STi requires: Cl, 45.8; Ti, 15.4%. H
37.3; Ti, 12.1%. C4H12Cl4O4S2Ti requires Cl, 37.5; Ti, 12.7%. H
−1

NMR (CDCl3–SOCl2): 3.41 (m, 4H), 2.31 (m, 4H). IR (Nujol)
NMR (CD2Cl2): 3,25 (s, 12H). IR (Nujol) ν/cm : 3030w, 3006m,
−1

ν/cm : 3004wm, 1444m, 1401m, 1325w, 1303m, 1271s, 1265m
1424vw, 1398w, 1336m, 1317m, 1285ms (sh), 1266s, 1114s–1093s,
(sh), 1220vs, 1193ms, 1130s, 1090s, 1082s, 1022m, 911m, 785wm,
1014w, 950s, 773ms, 700w, 490ms, 473s, 409s, 393wm (sh), 364s,
−1

730s, 660w, 552wm, 514w, 458s, 411vs, 379vs, 355m (sh), 302s,
333s, 294m. FT-Raman ν/cm : 3021m, 3005m, 2924s, 1430w,
2 3 6 8
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1

View Article Online
Table 5 Crystal data and details of the structure refinement for [Ti2Cl8(-sulfolane-O,O′)2] (1d), [Zr2Cl8(-Ph2SO2-O,O′)2] in [Zr2Cl8(-Ph2SO2-
O,O′)2]·C2H2Cl4 (2c·C2H2Cl4) and [ZrCl4(Me2SO2)2] (2aa)
Compound
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
b/Å
c/Å
/°
/°
1d
2c·C2H2Cl4
C26H22Cl12O4S2Zr2
1070.40
293(2)
2aa
C8H16Cl8O4S2Ti2
619.73
293(2)
Monoclinic
P21/n (no. 14)
10.987(2)
8.828(1)
11.659(1)
—
100.00(1)
—
1113.7(3)
2
1.848
1.875
C4H12Cl4O4S2Zr
421.28
293(2)
Orthorhombic
P212121 (no. 19)
7.074(1)
13.239(2)
16.400(4)
—
—
—
1535.9(5)
4
1.822
Triclinic
P1 (no. 2)
9.466(1)
10.357(1)
11.654(2)
71.80(1)
69.52(1)
82.48(1)
1016.5(2)
1
/°
V/Å3
Z
Dc/Mg m−3
/mm−1
1.745
1.434
1.674
Data/restr./param.
3254/0/109
0.0335
0.0808
3541/6/207
0.0386
0.1014
1583/0/137
0.0346
0.0828
R(Fo) [I > 2(I)]a
2
Rw (Fo ) [I > 2(I)]a
Goodness-of-fit on F2a
1.032
0.997
1.006
2
2
2
2
a R(Fo) = ∑||Fo − |Fc||/∑|Fo|; Rw(Fo ) = [∑[w(Fo2 − Fc2)2]/∑[w(Fo )2]]ꢀ; w = 1/[2(Fo ) + (AQ)2 + BQ] where Q = [max(Fo ,0) + 2Fc2]/3; Goodness-of-
fit = [∑[w(Fo2 − Fc2)2]/(N − P)]ꢀ, where N, P are the numbers of observations and parameters, respectively.
1421w, 1405w (sh), 1395m, 1335vw, 1317w, 1278w, 1263m, 1110s,
1091ms, 1017w, 1101w, 948w, 775m, 704vs, 491ms, 480m, 412ms,
386s, 364vs, 329w, 297s, 174vs, 150m.
with two portions (20 ml each) of hexane and dried in vacuo at
room temperature, obtaining 7.91 g (74% yield) of [Zr2Cl8(-
Ph2SO2-O,O′)2] (2c). Found: Cl, 29.8; Zr, 18.8%. C12H10Cl4O2SZr
requires Cl, 31.4; Zr, 20.2%. 1H NMR (C2D2Cl4): 8.25–7.45
−1

(unresolved multiplets). IR (Nujol) ν/cm : 3084w, 3060w, 1575m,
[HfCl4(Me2SO2)2] (3aa). Colourless crystals, 82% yield. Found:
1449s, 1395w, 1337m, 1293m, 1227s, 1166w, 1130w (sh), 1123s,
Cl, 26.9; Hf, 34.0%. C4H12Cl4HfO4S2 requires Cl, 27.89; Hf, 35.11%.
1
−1
1093s, 1059s, 1019m, 995s, 934w, 790w, 753s, 740s, 700w, 677s,

H NMR (CD2Cl2): 3.43 (s, 12H). IR (Nujol) ν/cm : 3030w, 3004m,
611w, 586s, 554ms, 417w, 389m, 360vs, 344vs, 310w. FT-Raman
1424w, 1400wm, 1338m, 1321m, 1284m (sh), 1271vs, 1111s,
−1

ν/cm :3156vw, 3084m, 3066s, 1579s, 1450w, 1318vw, 1186ms,
1085s, 1013w, 952s, 777ms, 703w, 491ms, 471s, 401m, 343m,
−1
1169w, 1133s, 1098w, 1064w, 1023m, 996vs, 935vw, 757vw, 703m,

326ms (sh), 312vs, 293s. FT-Raman ν/cm : 3030m, 3008m, 2926s,
611m, 364vs, 341m, 317ms, 280m, 220m, 147s.
1425w, 1414w, 1400w (sh), 1393m, 1338vw, 1320vw, 1283w (sh),
1271m, 1106s, 1082m, 1015w, 1101w, 947w, 778m, 707vs, 492s,
475m, 402m, 345vs, 328s, 306m (sh), 295s, 157s.
[Zr2Cl8(-Et2SO2-O,O′)2] (2b). A suspension of ZrCl4 (3.57 g,
15.3 mmol) in 100 ml of dichloromethane was added of 1.81 g
(14.8 mmol) of Et2SO2 dissolved in 30 ml of dichloromethane.
Following a procedure similar to that described for the preparation
of (2c), were obtained 4.51 g (83% yield) of [Zr2Cl8(-Et2SO2-
O,O′)2] (2b) as a colourless crystalline solid. Found: Cl, 38.9;
[ZrCl4(Ph2SO2)2] (2cc). To a suspension of ZrCl4 (3.70 g,
15.9 mmol) in 100 ml of dichloromethane was added dropwise,
at room temperature, a solution of 7.03 g of Ph2SO2 (32.2 mmol)
in 50 ml of dichloromethane. At the end of the addition, a slightly
turbid pale yellow solution was obtained, which was filtered to
remove the insoluble material and 80 ml of hexane were then
added to the filtrate. The colourless crystalline solid thus formed
was filtered off, washed with two portions (20 ml each) of hexane
and dried in vacuo at room temperature, thus obtaining 8.48 g
(80% yield) of [ZrCl4(Ph2SO2)2] (2cc). Found: Cl, 20.8; Zr, 13.0%.
1
Zr, 25.3%. C4H10Cl4O2SZr requires Cl, 39.9; Zr, 25.7%. H NMR
−1

(CD2Cl2): 3.63 (s br, 4H), 1.60 (s br, 6H). IR (Nujol) ν/cm : 2994w,
1454m, 1405w, 1382w, 1297m, 1279m, 1226w (sh), 1207s, 1100s,
1066w, 1048wm, 1036wm, 968w, 798m, 784w (sh), 735w, 502m,
−1

477w, 419m, 371m (sh), 336m (sh), 340s, 302m. FT-Raman ν/cm :
3004w, 2964m, 2946w, 2925ms, 2880w, 2672w, 1455m, 1404w,
1386w, 1236w, 1174s, 1110s, 1078w, 1051m, 979w, 639s, 510w,
475w, 418m, 373vs, 348s, 294m, 177w, 148s.
C24H20Cl4O4S2Zr requires Cl, 21.2; Zr, 13.6%. 1H NMR (C2D2Cl4):
−1

8.01 (d, 8H), 7.66 (t, 4H), 7.54 (t, 8H). IR (Nujol) ν/cm :3087wm,
3061wm, 1581m, 1449vs, 1309s, 1297m, 1162wm, 1133s, 1111s,
1100m (sh), 1062s, 1050s, 1021m, 995m, 975w, 932w, 848w, 760m
(sh), 755m, 729s, 699w, 685m, 678w (sh), 589m (sh), 581s, 563mw
X-Ray diffraction studies
Single crystals suitable for the X-ray diffractometric studies were
obtained by slowly cooling a SOCl2 solution of [Ti2Cl8(-sulfolane-
O,O′)2] (1d), a boiling C2H2Cl4 solution of [Zr2Cl8(-Ph2SO2-
O,O′)2] (2c), and by slow diffusion of hexane into a CH2Cl2 solution
of [ZrCl4(Me2SO2)2] (2aa). The X-ray diffraction experiments were
carried out at room temperature (T = 293 K) by means of a Bruker
P4 diffractometer equipped with a graphite-monochromated Mo-
K radiation. The samples were sealed in glass capillaries under an
atmosphere of dinitrogen. The intensity data collection was carried
out with the /2 scan mode, collecting a redundant set of data.
Three standard reflections were measured every 97 measurements
to check sample decay. The intensities were corrected for Lorentz
and polarisation effects and for absorption by means of the -
scan method.28 The structure solutions were obtained by means
of the automatic direct methods contained in SHELXS97.29 The
refinements, based on full-matrix least squares on F2, were done
by means of the SHELXL9729 programme. Some other utilities
contained in the WINGX suite30 were also used. The more relevant
crystal parameters are listed in Table 5.
(sh), 557m, 495m, 462w, 428w, 348s, 337s, 325s, 293m, 206vw. FT-
−1

Raman ν/cm : 3163w, 3091w (sh), 3069s, 1582s, 1480w, 1446w,
1310m, 1295w (sh), 1186m, 1164m, 1131s, 1111m, 1099w, 1052m,
1024m, 997vs, 931vw, 702ms, 613m, 586w, 498w, 358m (sh),
341m, 327ms, 294m, 253ms, 213w, 171w, 147s, 116s.
[Zr2Cl8(-Ph2SO2-O,O′)2] (2c). Anhydrous ZrCl4 (5.52 g,
23.7 mmol) was suspended in 120 ml of dichloromethane and
Ph2SO2 (5.01 g, 22.9 mmol), dissolved in 40 ml of dichloromethane,
was added dropwise to the suspension.At the end of the addition, the
reaction mixture was further stirred at room temperature for 2 h and
the solvent was then completely removed under reduced pressure.
The resulting solid was transferred to an extractor equipped with
a porous septum and a reflux condenser and extracted for 12 h
using tetrachloroethane as solvent. At the end of the extraction, a
small amount of insoluble material remained on the septum. The
extract was treated with 50 ml of hexane and cooled at 0 °C. The
colourless crystalline solid thus formed was filtered off, washed
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1
2 3 6 9

View Article Online
The systematic absences in the diffraction intensity data of
1d univocally indicated the monoclinic P21/n space group. The
structure solution showed that the asymmetric unit was a [TiCl4(-
sulfolane-O,O′)] group, forming dinuclear molecules through the
inversion centre. The final refinement cycle was done by using
anisotropic thermal parameters for all the heavy atoms and allowing
the hydrogen atoms to ‘ride’ on the connected carbon atoms. The
resulting reliability factors are listed in Table 5. The solution of the
structure of 2c·C2H2Cl4 was found in the triclinic centrosymmetric
P1 space group. The structure was found to consist of dinuclear
molecules, obtained by the action of the inversion operator placed
at 0 0 ꢀ on the {ZrCl4(-Ph2SO2-O,O′)} asymmetric unit. The unit
cell contains one molecule of C2H2Cl4, placed on the inversion
centre at ꢀ 0 0. The initial refinement cycles showed slightly
excessive values for some anisotropic thermal parameters of the
phenyl carbon atoms and definitely large values for the isotropic
thermal parameters of the Cl and C atoms of C2H2Cl4, the latter
being characterised by a slightly unreliable geometry, probably
due to disorder in the phenyl groups and especially in the position
of C2H2Cl4. Some geometric constraints were then introduced to
force C2H2Cl4 to keep a reasonable geometry. The final refinement
cycle was carried on with anisotropic thermal parameters for all the
heavy atoms and isotropic for the hydrogen and the carbon atoms of
C2H2Cl4, giving the reliability factors listed in Table 5.
References
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The solution of the structure of 2aa was found in the orthorhombic
space group P212121. The asymmetric unit corresponds to the
molecule. The final refinement cycle was done by using anisotropic
thermal parameters for all the heavy atoms and allowing the
hydrogen atoms ‘ride’on the connected carbon atoms. The resulting
reliability factors are listed in Table 5.
CCDC reference numbers 236507–236509.
See http://www.rsc.org/suppdata/dt/b4/b405871b/ for crystallo-
graphic data in CIF or other electronic format.
1H NMR experiments
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[MCl4(Me2SO2)2] in the presence of Me2SO2, M = Ti, Zr, Hf.
Only the preparation of solutions of the zirconium complex 2aa
is described in detail, the corresponding titanium and hafnium
derivatives, 1aa and 3aa being handled similarly. To a suspension of
15.1 mg (0.036 mmol) of 2aa in 1 ml of CD2Cl2, Me2SO2 (2.3 mg,
0.025 mmol) was added. The reaction mixture was stirred for 10
min at room temperature and then decanted. The clear colourless
solution was transferred into a NMR tube and analysed at variable
temperature (Fig. 4). Samples of 1aa [11.1 mg, 0.029 mmol, 1 ml
of CD2Cl2, 5.9 mg (0.063 mmol) of Me2SO2] and 3aa (7.7 mg,
0.015 mmol, 1 ml of CD2Cl2; 4.5 mg, 0.048 mmol of Me2SO2),
were examined under similar conditions.
The 2b–Et2SO2 system. Compound [Zr2Cl8(-Et2SO2-O,O′)2]
(0.055 g, 0.16 mmol was suspended in 1.2 ml of CD2Cl2 and 0.078 g
(0.64 mmol) of Et2SO2 were added. After stirring for 5 min at room
temperature, a clear colourless solution was obtained, which was
transferred into a NMR tube and analysed at different temperatures
(Fig. 5(A)).
Compound 2b (0.087 g, 0.25 mmol) was suspended in 1.2 ml
of CD2Cl2 and treated with 0.029 g (0.024 mmol) of Et2SO2. After
stirring for 10 min at room temperature and then decanting, the clear
colourless solution thus obtained was transferred into a NMR tube
and analysed at variable temperature (Fig. 5(B)).
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1, and references therein. Broadening of the peaks at room temperature
and weak resonances at low temperatures due to uncoordinated sulfone
have been observed in the 1H NMR spectra of almost all the MCl4(R2SO2)2
derivatives reported in this paper, due to a small amount of hydrolysis.
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Gol’dshtein, Zh. Obshch. Khim., 1976, 46, 892; V. V. Puchkova,
The 2b–ZrCl4 system. A suspension of ZrCl4 (0.046 g,
0.20 mmol) in CD2Cl2 (1 ml) was treated with 0.029 g (0.08 mmol)
of [Zr2Cl8(-Et2SO2-O,O′)2], (2b). After 15 min stirring at room
temperature, the colourless solution was transferred into a NMR
tube and analysed: 1H NMR: 3.81 (q, 2H), 1.73 (t, 3H).
Acknowledgements
This work was partly supported by the Ministero dell’ Università e
della Ricerca Scientifica (MIUR), Programmi di Rilevante Interesse
Nazionale 2002–3.
2 3 7 0
D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1

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D a l t o n T r a n s . , 2 0 0 4 , 2 3 6 4 – 2 3 7 1
2 3 7 1