New preparative methods for the halides of titanium(II) and vanadium(II): Reduction of titanium(IV) halides with sodium and oxidation of Bis(mesitylene)vanadium(0)

Article abstract of DOI:10.1515/znb-1996-0413

TiCl₄(THF)₂ reacts with two equivalents of sodium in THF to afford the soluble TiCl₂(THF)n (1), which has been characterized analytically and by spectroscopic and magnetic measurements. By redox reactions, TiCl₂(THF)_n gives TiCl₂(9, 10-C₁₀H₈O₂) (2), or TiCl₂(benzoate)₂ (3), with 9,10-phenanthrenequinone or dibenzoylperoxide in toluene, respectively. By operating in 1,2-dimethoxyethane (DME), Na(DME)_1.5[TiCl₄(DME)] (4), or NaTiCl₃(DME)₂ have been isolated from the reaction of TiCl₄(DME) with one or two equivalents of sodium, respectively. From 4, by cation exchange, PPN[TiCl₄(DME)] [PPN = bis(triphenylphosphine)iminium] (5), has been obtained and characterized analytically, spectroscopically and by X-ray diffraction methods. Crystal data: C₄₀H₄₀Cl₄NO₂P₂Ti, MW = 818.4, space group: Pna2₁ (No 33), a = 14.445(2), b = 15.690(2), c = 17.544(2) ?, V = 3976(2) ?³, Z = 4, F(000) = 1692, R = 0.041, Rw = 0.0420. The titanium(III) atom in the anion has the expected cis-octahedral, slightly distorted, geometry. By reaction of TiBr₄(DME)_0.5 with sodium in DME, TiBr₃(DME)_1.5, 1.5 DME (7), is the product. Bis(mesitylene)vanadium(0), Vmes₂, reacts with two equivalents of CPh₃Cl in DME, to give VCl₂(DME)_n.

Full text of DOI:10.1515/znb-1996-0413

New Preparative Methods for the Halides of Titanium(II) and Vanadium(II):
Reduction of Titanium(IV) Halides with Sodium and Oxidation of
Bis(mesitylene)vanadium(0)
Fausto Calderazzoa, Giuseppe E. De Benedettoa+, Ulli Englertb, Isabella Ferri3,
Guido Pampalonr1-*, Trixie Wagnerb
a Universitä di Pisa. Dipartimento di Chimica e Chimica Industriale,
Sezione di Chimica Inorganica, Via Risorgimento 35. I-56126-Pisa. Italy
b Institut für Anorganische Chemie der Rheinisch-Westfälischen Technischen Hochschule.
Professor-Pirlet-Straße 1, D-52074 Aachen. Germany
Z. Naturforsch. 51b, 506-516 (1996); received September 12. 1995
Titanium(II) Chloride. Vanadium(II) Chloride, Sodium Reduction
TiCl4(THF)2 reacts with two equivalents of sodium in THF to afford the soluble
TiCl2(THF)„ (1), which has been characterized analytically and by spectroscopic and mag-
netic measurements. By redox reactions. TiCl2(THF)„ gives TiCl2(9,10-C1()H802) (2), or
TiCl2(benzoate)2 (3), with 9,10-phenanthrenequinone or dibenzoylperoxide in toluene,
respectively. By operating in 1,2-dimethoxyethane (DME), Na(DME)! ?[TiCl4(DME)] (4),
or NaTiCl3(DM E)2 have been isolated from the reaction of TiCl4(DME) with one or two
equivalents of sodium, respectively. From 4, by cation exchange, PPN[TiCl4(DME)] [PPN =
bis(triphenylphosphine)iminium] (5), has been obtained and characterized analytically,
spectroscopically and by X-ray diffraction methods. Crystal data: C4,)H4()Cl4NOTP2Ti. MW =
818.4, space group: Pna2[ (N° 33). a = 14.445(2), b = 15.690(2), c = 17.544(2) Ä. V = 3976(2) A 3,
Z = 4, F(000) = 1692, R = 0.041, Rw = 0.0420. The titanium(III) atom in the anion has the
expected c/s-octahedral, slightly distorted, geometry. By reaction of TiBr4(DM E)0.5 with so-
dium in DME, TiBr3(DM E)! 5.I.5 DME (7), is the product. Bis(mesitylene)vanadium(0),
Vmes2, reacts with two equivalents of CPh3Cl in DME, to give VC12(DME)„.
coordinated tetrahydrofuran (THF) are known for
zinc(II) [3], copper(II) [3], nickel(II) [3], cobalt(II)
[3], iron(II) [3], manganese(II) [3, 4], chromi-
um(II) [4]. X-ray crystallography of the tetra-
nuclear iron(II) THF-adduct, Fe4Cl8(THF)6, has
shown [5] the compound to contain chloride-
bridged pentacoordinate and hexacoordinate iron
atoms.
Also in view of the apparently substitutional in-
ertness of titanium(II) (a d2 system) and of vana-
dium(II) (a d3 system), the preparation of the
ether-substituted dihalides of titanium(II) requires
the preliminary addition of acetonitrile to the an-
hydrous dihalide, followed by displacement by the
ether [6]. As an additional example, anhydrous
VC12 was observed [7] to be completely unreactive
towards pyridine after heating for several months
in the neat amine.
Introduction
The anhydrous dihalides of 3d transition metals
are known from titanium to zinc. They are polynu-
clear compounds with bridging halides; for exam-
ple, TiCl2 [1] and VC12 [1] have layered structures
with hexacoordinate metals . The dichlorides of
groups 4 to 6 are highly reducing, their prepara-
tion therefore involving the syn-proportionation of
higher chlorides with the metal itself, the dispro-
portionation in the solid state (e.g., TiCl2 from
TiCl3), or the reduction with dihydrogen at ele-
vated temperatures [2]. Coordination of the dihal-
ides of the 3d transition elements with ethers usu-
ally decreases the molecular complexity and leads
to low-nuclearity molecular complexes of general
formula MX2(ether)„: compounds of this type with
Conventional syntheses of Lewis base adducts
of TiCl2 [8] and VC12 [9] by reduction in organic
solvents of higher titanium halides or by chlorina-
tion of vanadium complexes in low oxidation
states are still relatively unexplored. This paper re-
* Reprint requests to Prof. G. Pampaloni.
+ Present address: Universitä’ di Bari. Dipartimento di
Chimica. Laboratorio di Chimica Analitica. Via Ora-
bona 4. 1-70126 Bari. Italy.
D
0932-0776/96/0400-0506 $06.00 © 1996 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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F. Calderazzo et al. ■Halides of Titanium(II) and Vanadium(II)
507
th f^ ^ t h f
ports the preparation of ether adducts of titani-
um(II) and vanadium(II), MCl2(ether)„, obtained,
respectively, by sodium reduction of TiCl4 in THF
as medium or by oxidation of bis(mesitylene) va-
nadium ^) with CPh3Cl in DME. Also, the effect
of the halide and of the reaction medium on these
reactions has been studied. The crystal and molec-
ular structure of an intermediate reduction pro-
duct, PPN[TiCl4(DME)] is also reported. Part of
this work was communicated in a preliminary form
[10]. Between our preliminary communication and
the submission of this paper, the preparation of
TiCl2(THF)2 [11], obtained by a different method,
has appeared, the compound being used essen-
tially for the reductive coupling of organic halides,
ketones and aldehydes. Thus, our results should be
regarded as complementary to those by Eisch and
coworkers which recently appeared in print in
this Journal.
Fig. 1. A sketch of the suggested molecular structure of
M4C18(THF)6, based on the results of the diffractometric
study [6] of the iron(II) compound. Dashed lines indi-
cate the positions possibly occupied by additional THF
groups in M4C1K(THF)8.
By taking into consideration the molecular
structure of TiCl2 (Cdl2-type, i. e., while hexacoor-
dinate titanium centres and triply bridging chlo-
rides) [1], the possibility exists for TiCl2(THF)„ of
a molecular arrangement similar to that reported
for the iron(II) derivative, Fe2Cl8(THF)6 [5],
which contains hexacoordinate and pentacoordi-
nate atoms bonded to terminal, doubly- and triply-
bridging chlorides. Such a structure, see Fig. 1,
could explain both the variable content of THF
(addition of one THF to each of the pentacoordi-
nate metal atoms would lead to a formula with a
THF/Ti molar ratio of 2) and the solubility of our
titanium complex. Presumably, Fowles’ compound
corresponds to another structural polynuclear
modification of the type suggested [4] for the THF
adduct of manganese(II), MnCl2(THF)2.
Results and Discussion
By reaction of TiCl4(THF)2 with two equiva-
lents of sodium in THF at room temperature the
black-brown TiCl2(THF)„, (1), was obtained
through the probable intermediacy of the light
blue TiCl3(THF)3 as evidenced by the blue-green
colour of the solution in the initial stages of the
reaction (sequence 1 ).
Na
Na
TiCl3(THF)3
TiCl2(THF)„
TiCl4(THF)2
THF
THF
(1)
The magnetic behaviour of 1 in the solid state
has been examined in the temperature range 70-
2 Na
THF
290 K, the 1/x m tt
T plot being in Fig. 2. The
magnetic moment of 1.33 BM at 290 K, well below
the value of 2.88 BM expected for magnetically di-
luted octahedral titanium(II) with d2 configura-
The IR spectrum of 1 is characterized by two
strong absorptions at 1009 and 855 cm' 1 typical
of coordinated THF [12]. A similar spectrum
(vc _0 -c = 1015 and 860 cm-1) was reported by
Fowles and coworkers [6] for the compound of
formula TiCl2(THF)2 obtained by reacting
TiCl2(CH3CN)2 with THF, the parent compound
being prepared by reacting TiCl2 [13] with acetoni-
trile. Even though the infrared spectra and the
magnetic behaviour (vide infra) of our compound
and that reported in the literature [6] are similar,
compound 1 is soluble in THF with a deep brown
colour and slightly soluble in aromatic hydrocar-
bons, while the product isolated by Fowles is de-
scribed as substantially insoluble in THF and in
non-polar solvents [6].
T
(K )
Fig. 2. Plot of l / ^ rr vs. T for TiCl2(THF)„ (1).
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508
F. Calderazzo et al. • H alides of Titanium(II) and Vanadium(II)
tion, confirms the oligonuclear structure of the
compound. Halide-bridging is known in low-valent
titanium halides [1] giving rise to low magnetic
The diamagnetic, blue-green quinone derivative
2, which is not further oxidized by excess quinone,
is a microcrystalline solid, soluble in aromatic hy-
moments [14]. It has to be noted that TiCl2 shows drocarbons and stable in air for short periods of
time. The IR spectrum is characterized by a strong
a xm tv °f 570xl6-6 cgsu at 288 K [15] correspond-
ing to a magnetic moment of 1.15 BM. The higher absorption at 1454 cm-1 attributed [16] to the
value of magnetic moment found for compound 1, C -O stretching vibration of the semiquinone li-
with respect to TiCl2, is in agreement with a lower
degree of spin pairing due to the cleavage of the
polynuclear structure of TiCl2 allegedly operated
by THF.
gand, [C]4H80 2]~. The compound, which is dia-
magnetic as observed in other semiquinone com-
plexes [16], can be best described as a derivative
of d 1 titanium(III) with strong coupling with the
unpaired electron on the partially reduced qui-
none ligand.
The oxidation of 1 by dibenzoylperoxide pro-
ceeds in toluene at room temperature affording
the diamagnetic, microcrystalline dibenzoato de-
rivative of titanium(IV) (3), which shows strong
absorptions at 1525 and 1397 cm-1 attributed to
the asymmetric and symmetric stretching
vibrations of the carboxylato ligand, respectively.
The titanium(II) chloro complex, TiCl2(THF)„,
is not soluble in water and does not react with
it: addition of diluted sulfuric acid causes slow H2
evolution up to a H2/Ti molar ratio of 0.42, titani-
um(II) being therefore oxidized to titanium(III).
When the reduction of titanium(IV) chloride
As shown by the l/^Mrr vs- T plot (Fig. 2) for 1,
the Curie-Weiss law is obeyed with a Weiss con-
stant 6 = 9.8 K, which is in the range of values
obtained by Fowles and coworkers [6] for TiCl2-
(o-phenanthroline) (0 = 24 K), TiCl2(CH3CN)2
(i9 = 44 K) and TiBr2(CH3CN)2 (0 = ca. 100 K).
As a consequence of the paramagnetism of the
molecule, the ’H NMR spectrum of 1 shows broad
signals downfield with respect to uncomplexed
THF. However, once the paramagnetic centre is
oxidized by treatment with D20 and air, sharp sig-
nals due to free THF at 3.57 and 1.42 ppm were
observed.
Compound 1 shows a rather surprising low reac-
tivity in substitution reactions: it does not react
with nitrogen bases such as pyridine or N,N-tetra- with sodium was performed in DME, a different
reaction pathway was observed: the reduction of
TiCl4(DME) with one equivalent of sodium in
DME affords the sodium salt Na(DME)„[TiCl4-
(DME)] (4), which was further reduced by treat-
ment with another equivalent of sodium to give a
methylethylenediamine at room temperature; it
reacts slowly with DME to give TiCl2(DME)„
(eq. (2)) and with the cyclopentadienyl anion in
the presence of CO (eq. (3)). The latter reaction
produces TiCp2(CO)2 in good yields, thus defi-
nitely showing the oxidation state II of titanium in
the THF adduct.
microcrystalline
solid
identified
as
NaT-
iCl3(DME)2 (6). The same titanium(II) derivative
can be prepared directly from TiCl4(DME) by
treatment with two equivalents of sodium; see re-
action sequence 6.
DME
TiCl2(THF)„ --------- > TiCl2(DME)„
(2)
TiCl2(THF)„ + 2 NaCp + 2 CO t0lUene >
TiCp2(CO)2 + 2 NaCl + «THF
(3)
In CH2C12 as medium, compound 4 reacts with
[PPN]C1 to give the paramagnetic ((j,eff = 1.51 BM
at 295 K) PPN[TiCl4(DME)] (5), which was
characterized analytically and spectroscopically
(vc _0 _c = 857, 1030 and 1078 cm "1). The same
product was obtained by the reaction of the DME
adduct of TiCl3 with [PPN]C1 in dichloromethane.
In order to establish conclusively that 4 con-
tained the still unknown [TiCl4(DME)]~ anion, a
diffractometric study was planned on the easily
recrystallized PPN derivative 5. The diffractomet-
ric experiment on a single crystal of 5 has shown
that the titanium atom is six-coordinate with four
The THF adduct 1, on the contrary, reacts
smoothly with oxygen containing oxidizing rea-
gents: with 9,10-phenanthrenequinone and diben-
zoylperoxide it gives the compounds 2 and 3,
respectively, see eqs. (4) and (5).
TiCl2(THF)„ + 9.10-C14Hk0 2 — - — -»
TiCl2(9,10-C14H80 2) + n THF
(4)
2
TiCl2(THF)„ + C6H5C (0 )0 0 C (0 )C 6H5 t0lUene>
TiCU(OOCC6Hs)'> + n THF
(5)
3
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F. Calderazzo et al. • Halides of Titanium(II) and Vanadium(II)
509
a
a
TiCl4(DM E) -------» Na(DME)„[TiCl4(DME)] -------*
NaTiCl3(DM E)2
6
DME
.
DME
(6)
4
______________________ 2_Na________________
DME
chlorine atoms and a bidentate DME molecule.
those observed in other DME complexes such as
The cis geometry of the [TiCl4(DME)]~ anion is c/s-VI2(DME)2 [9m] , [Li(DME)2]I [19] and cis-
shown in Fig. 3. Selected bond distances and an- MgCl2(DME)2 [20].
gles are summarized in Table I. The TiCl40 2 moi-
Compound 6 , which dissolves in DME with a
ety forms a distorted octahedron, the Cll-Ti-C13,
deep brown colour, is paramagnetic ([xeff =
Clax-Ti-0 and Clax-Ti-Cleq angles being 170.19(4)°, 1.86 BM at 290 K) and promptly decomposes in
86.2(1)° (mean value) and 93.28(4)° (mean value), the presence of moisture or dioxygen. The DME
respectively. In agreement with the larger covalent ligand shows absorptions at 855, 1033 and 1077
radii of chlorine with respect to oxygen, the O l- cm"1 to be compared with the absorptions at 853,
Ti-02 angle [75.7(1)°] is smaller than C12-Ti-C14 1119 and 1195 cm' 1 observed in the free ligand.
[95.08(3)°] . The average Ti-Cl and Ti-O bond The magnetic properties of 6 were measured in
lengths are 2.374(1) and 2.172(2) A and are similar
to the values found [17] in NBu^rans-
the range 70-290 K. From a l/^Mrr vs- T plot, it
has been found that 6 obeys the Curie-Weiss law
TiCl4(THF)2] [2.395(9) and 2.10(1) Ä] and in with a Weiss constant 6 = -16 K.
TiCl3(THF)3 [2.352(3) and 2.118(7) A] [18]. It is Compound is not stable in halogenated
6
perhaps worth noting that the Ti-Cl(l) bond dis- solvents such as dichloromethane. In attempts to
tance is significantly shorter than the other tita- exchange the sodium cation with PPN+ in dichlo-
nium-chloride bond distances: this might suggest romethane, well formed crystals of 5 were ob-
that a Jahn-Teller distortion operates in this tained in good yields. Although not investigated in
TiCl40 2 chromophore of idealized C2v symmetry, detail, the reaction probably proceeds with reduc-
similar to what has been predicted for d 1 com- tion of dichloromethane.
plexes of O h symmetry. The parameters of the co-
ordinated 1 ,2-dimethoxyethane ligand are close to
We have also examined the interaction of the
DME adduct of TiBr4, TiBr4(DM E)05 [21], with
Cll
Table I. Selected bond distances (A) and angles (deg) in
PPN[TiCl4(DME)] (5). Estimated standard deviations in
parentheses refer to the least significant digit.
T i-C l 1
Ti-C13
T i-O 1
O l - C l
0 2 - C 2
C 1 -C 2
2.360(1)
2.374(1)
2.174(2)
1.446(5)
1.442(4)
1.511(6)
Ti-C12
Ti-C14
T i- 0 2
0 1 - C 3
0 2 - C 4
2.381(1)
2.383(1)
2.171(2)
1.445(4)
1.427(5)
Cl 1-T i- C12
Cl 1-T i - C14
T i-O 1 - C l
C11-T i- 0 2
Cl 2 -T i--C14
C 12-T i--O l
C 12-T i--0 2
C 13-T i--Cl 4
C 13-T i- O l
C 13-T i- 0 2
C 14-T i- O l
C 14-T i- 0 2
91.63(4)
93.41(3)
113.4(3)
85.0(1)
95.08(3)
94.6(1)
169.8(1)
92.22(4)
85.7(1)
Cl 1 -T i-C l 3
Cl 1 -T i-O 1
T i-O 1-C 3
C 12-Ti-C 13
T i- 0 2 - C 2
T i- 0 2 - C 4
C 2 - 0 2 - C 4
P 1 -N -P 2
170.19(4)
87.4(1)
124.4(2)
95.87(4)
112.4(2)
125.5(2)
110.7(3)
138.1(3)
106.7(3)
107.0(2)
75.7(1)
Cl 3
0 1 - C 1 - C 2
0 2 - C 2 - C 1
O 1-T i-O 2
Fig. 3. ORTEP plot of the [TiCl4(DME)]~ anion in
PPN[TiCl4(DME)] (5). Thermal ellipsoids are drawn at
30% probability level.
86.6(1)
170.3(1)
94.8(1)
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510
F. Calderazzo et al. • Halides of Titanium(II) and Vanadium(II)
sodium in DME [22] and we have found that, in
agreement with the decreased M-X bond strength
on going from X=C1 to X=Br [23], the titani-
um(IV) derivative is reduced at room temperature
with formation of the dark green, crystalline
TiBr3(DM E)1 5 -1.5 DME (7) (reaction 7). The
magnetic moment of the crystalline material at
296 K is 1.71 BM, suggesting the presence of mag-
netically diluted titanium(III) ions of d 1 electronic
configuration. In this connection it is worth men-
tioning that an X-ray crystallographic experiment
on TiBr3(DME)! 5 has shown an ionic structure
consisting of [TiBr2(DM E)2]+ cations and
[TiBr4(DME)]' anions [24],
DME
Vmes2 ------------* VCb(DME)„ + 2 mes
(9)
CPh3Cl
The DME-adduct of vanadium(II) chloride was
isolated in high yields directly from the reaction
mixture due to its low solubility in DME. It is in-
teresting to note that the compound is pale-green
in the presence of DME, gives bright green THF
solutions (Amax= 655 nm; 8 - 8.3 M -1 cm-1) and
turns gray during the drying procedure in vacuo at
room temperature, thus suggesting progressive
loss of DME; accordingly, the DME content varies
depending on the drying conditions.
It is noteworth that the analogous compounds
of vanadium(II) with the heavier halides give
mononuclear 1:2 DME adducts of formula
VX2(DME)2, X = Br, I [9m], the different behavi-
our being clearly related to the size of the halide.
Presumably the smaller chloride bridge favours
the formation of an ionic or a polynuclear struc-
ture, the latter with all-bridging chlorides.
Na
TiBr4(DME)05 --------* TiBr3(DME), 5 •1.5 DME
DME
(7)
With two equivalents of sodium, the titani-
um(II) derivative, Na[TiBr3(DME)i 2], 8, was ob-
tained in ca. 50 % yield, reaction (8), characterized
analytically and spectroscopically (vc _0 _c - 859,
1029 and 1082 cm-1). The magnetic properties of
8 were measured in the temperature range 70-
290 K. As observed for the other compounds re-
ported in this paper, 8 shows a magnetic moment
(2.11 BM at 290 K) which is reduced with respect
to the value expected for magnetically diluted tita-
n iu m ^ ) of d2 electronic configuration, the Curie-
Weiss law being obeyed with a Weiss constant
0 - -28 K. This and the low number of DME
ligands per titanium suggest an oligonuclear bro-
mide-bridged structure for the anion in this com-
Conclusions
This work has shown that the course of the reduc-
tion of titanium(IV) halides with sodium depends
both on the solvent and the halide. While the reduc-
tion of TiCl4 in THF with one or two equivalents of
sodium affords the neutral species TiCl3(THF)3
and TiCl2(THF)2 respectively, the reaction in
DME affords products containing a Cl/Ti molar ra-
tio higher than 2, namely, the titanium(III) deriva-
tive Na[TiCl4(DME)] and the titanium(II) complex
NaTiCl3(DME)2 This is presumably due to the
chelate effect of DME on titanium, which disfa-
vours sodium solvation by the same ether. In
DME the products of the sodium reduction de-
pend on the halide, and TiBr4(DME)05 affords
both neutral TiBr3(DME)! 5 •1,5 DME or ionic
NaTiBr3(DME), 2.
TiBr4(DME)<>5
NaTiBr3(D M E)12
(8)
DME
pound, with part of the analytically detected DME
coordinated around the sodium cation.
Some of us have recently used [9m, 25] bis(mesi-
Moreover, this work reports new simple pro-
tylene)vanadium(O), Vmes2, obtained in high cedures for the synthesis of the THF-soluble tita-
nium(II) and vanadium(II) chlorides, namely
TiCl2(THF)„ and VC12(DME)„. The titanium(II)
compound is characterized by a rather low reactiv-
ity toward substitution; on the other hand, it
promptly reacts with oxygen-containing oxidizing
agents (9,10-phenanthrenequinone or dibenzoyl-
peroxide) to the corresponding complexes of oxi-
dized titanium.
yields from VC13/A1/A1C13 in mesitylene, as a
starting material for the preparation of inorganic
and coordination compounds of vanadium(II) and
vanadium(III) in non-aqueous media by reaction
with protic acids or oxidizing agents.
We have now found that Vmes2 is promptly oxi-
dized to VCl2(DM E)n by CPh3Cl in DME solu-
tion, according to eq. (9).
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F. Calderazzo et al. ■H alides of Titanium(II) and Vanadium(II)
511
Experimental Section
drocarbons. The 'H-NMR spectra in C6D6 show
broad signals at 5.40, 3.75, 3.33, and 1.66 ppm; by
treatment with D20 in the presence of air, decom-
position of the compound was observed and the
'H-NMR spectrum of the resulting yellow-orange
solution showed two sharp signals at 3.57 and 1.42
ppm attributed to THF.
The magnetic moment at 290 K was found to be
1.33 B.M. (^Mrr = 696xl0-6 cgsu, diam. corr. =
-171xl0-6 cgsu). The values of ^Mrr and of the
magnetic moment as a function of temperature are
listed in Table II.
All operations were carried out in a conven-
tional vacuum line using standard Schlenk-tube
techniques, under an atmosphere of prepurified
argon. The reaction vessels were oven dried prior
to use.
Infrared spectra were recorded with a Perkin
Elmer mod. FT 1725X instrument on solutions or
nujol or polychlorotrifluoroethylene (PCTFE)
mulls of the compounds prepared under rigorous
exclusion of moisture and oxygen. NMR spectra
{!H: 200 MHz, reference TMS} were recorded with
a Varian Gemini 200 BB spectrometer.
Magnetic susceptibility measurements were per-
formed in the temperature range 290-70 K with a
Faraday balance using C uS04.5 H20 as standard.
For the diamagnetic correction, Pascal contribu-
tions [26] were used.
b) By reduction
with sodium
amalgam:
TiCl4(THF)2 (4.62 g, 13.84 mmol) was treated at
room temperature with 2% sodium amalgam ob-
tained from mercury (31.5 g) and sodium metal
(0.63 g, 27.40 mmol) in THF (100 ml). After 24 h
stirring, the reaction mixture was filtered on glass
wool, the volume of the solution reduced in vacuo
to about 40 ml and heptane (100 ml) added. The
solid which formed was filtered off and dried in
vacuo (0.68 g, 22% yield of TiCl2(THF)15).
Titanium analyses were performed by ICP-AES
using a Perkin Elmer Elan 4000 instrument. The
same technique was used for sodium analyses.
The THF or DME adducts of TiCl4, TiCl3, and
TiBr4 were prepared according to literature with
variable amounts of ether solvents according to
the drying procedure [27], [PPN]C1 [28] and
NaCp-0.5 THF [29] were prepared according to
literature. Commercial (Fluka) 9,10-phenan-
threnequinone was sublimed at 160 °C/0.05
mmHg. Benzoyl peroxide (C. Erba) was recrystal-
lized from ethyl alcohol, dried in vacuo at room
temperature and stored at ca. 4 °C.
Analysis for C6H n C h O , 5Ti
Calcd
Cl 31.2" Ti 21.1 %,
Found Cl 32.6 Ti20.9%.
Reactions o f TiCl2(TH F)2
A ) Substitution reactions
a) DM E: TiCl2(THF)2 (0.273 g, 1.04 mmol) was
treated with DME (12 ml) to form a dark brown
suspension. After 48 h stirring at room temper-
ature the light brown solid was filtered off and
dried in vacuo (0.14 g, 52% yield). The solid was
By reduction with sodium: A solution of
analytically identified as TiCl2(DME)! 4.
Synthesis o f TiCl2(TH F)n (1)
a)
TiCl4(THF)2 (6.27 g, 18.78 mmol) in THF (120 ml)
was treated with finely divided sodium (0.87 g,
38.0 mmol). The colour of the solution changed
gradually from yellow to green and finally to
black. After 48 h stirring at room temperature, the
solution was filtered, the volume reduced to 40 ml
in vacuo and heptane (100 ml) was added. The
black solid which formed was filtered off and dried
in vacuo. It was analytically and spectroscopically
identified as TiCl2(THF)2.0.25 THF (2.41 g, 46%
yield).
Analysis for C56H !4Cl2()2s Ti
Calcd
Cl 28.9 “ Ti l 9.5%,
Found Cl 30.5 Ti 18.9%.
IR spectrum (nujol mull): 1277vw, 1241vw,
1194w, 1153w, 1088m, 1039s, 973vw, 900s, 851vs,
641w, 599w, 448m and 403s cm-1. By treatment
with D20 in the presence of air, decomposition
of the compound was observed and the 'H NMR
spectrum of the resulting yellow-orange solution
showed two sharp resonances at 1.88 and 1.64 ppm
due to DME.
Analysis fo r CgH I8Cl20 22sTi
The preparation was repeated several times, the
DME content of the isolated product depending
on the time of the drying procedure in vacuo at
Calcd
Cl 25.2 Ti 17.0%,
Found Cl 24.8 Ti 17.1%.
IR spectrum (nujol mull): 1347vw, 1040w, room temperature.
1009m-s, 855s, 728w, 682w, 639w, 589w, 464w and
451m cm"1. The compound is extremely sensitive
to oxygen and moisture and is soluble in inert or-
ganic solvents, such as THF and aromatic hy-
b) Sodium cyclopentadienide/CO: A suspension
of NaCp-0.5 THF (0.42 g, 3.4 mmol) and
TiCl2(TITF)2 (0.44 g, 1.7 mmol) in toluene (50 ml),
was stirred for 24 h at room temperature under an
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512
F. Calderazzo et al. • Halides of Titanium(II) and Vanadium(II)
Table II. Magnetic data for TiCl2(THF)„ (1), NaTiCl3(DM E)2 (6). and NaTiBr^DME)] 2 (8). in the range 290-70 K.
TiCl2(THF)2 (1)
*Mcorr (106 cgsu) //eff (B. M.)
NaTiCl3(DM E)2 (6)
/ Mcorr (106 cgsu) ue{{ (B.M.)
NaTiBr3(DM E)j 2
*Mcorr (106 cgsu)
(8)
/leff (B.M.)
T (K)
2909.7
1.26
68
70
4557.7
1.60
5331.0
1.73
2851.6
2840.1
2706.4
2331.2
2142.7
1.31
1.35
1.40
1.37
1.38
75
80
90
5216.9
5324.2
4700.2
4537.0
4227.4
4362.7
4400.5
3837.9
3689.6
3404.7
1.68
1.79
1.76
1.81
1.81
1.83
1.96
1.95
2.01
2.02
100
110
120
125
130
140
150
160
180
200
210
220
230
240
250
260
270
280
290
1936.9
1.40
3192.6
3031.3
1.83
1.85
3928.2
3754.2
2.03
2.03
1585.9
1298.6
1077.6
1.39
1.37
1.35
1.86
1.86
1.85
3367.5
3006.6
2674.5
2680.5
2381.1
2115.4
2.08
2.09
2.08
2455.4
2261.7
2043.7
1.85
1.86
1.83
2.09
2.09
2.07
1931.3
1779.9
1602.3
948.7
860.8
877.1
827.5
793.3
804.8
695.9
1.33
1.29
1.33
1.32
1.31
1.35
1.34
1951.4
1904.7
1490.2
1481.5
1.83
1.86
2.10
2.11
thylene mull): 2958m-w, 2929m, 2856vw, 1595s,
1559m, 1514m-s, 1494s, 1454vs, 1391s, 1347m-s,
1292m-s, 1259s, 1224m, 1165w, 942w, 787w, 759m-s,
1126w, 718m, 688m, 587m-w, 544m and 443w cm-1.
b) Benzoyl peroxide: The THF adduct
TiCl2(THF)2 (0.56 g, 2.13 mmol) was added to a
solution of benzoyl peroxide (0.52 g, 2.15 mmol)
atmosphere of argon without any apparent
change. After this period, the suspension was
placed in a glass autoclave (Büchi, Uster, CH) and
stirred at room temperature for 48 h under CO at
a pressure of 7 atm. An IR spectrum of the solu-
tion in the carbonyl stretching region showed the
absorptions typical of Cp2Ti(CO)2 [30] (1968 and
1885 cm"1); a conversion of about 64% was calcu- in toluene (50 ml). An immediate colour change
took place. After 48 h stirring at room temper-
ature, the pale yellow solid was filtered off, washed
with toluene (5 ml) and dried in vacuo. The solid
was identified as TiCl2(OOCC6H5)2, 3, (0.43 g, 56
% yield).
lated from the intensity of the 1885 cm-1 band (e =
2200 M '1cm-1). After heating at 70 °C for 7 h, the
IR spectrum was found to be unchanged.
B) Redox reactions
Analysis for C i4H l0Cl2O 4Ti
a)
9,10-Phenanthrenequinone:
TiCl2(THF)2
Calcd
Cl 19.6" Ti 13.3%,
(0.15 g, 0.57 mmol) was added to a solution of
9,10-phenanthrenequinone (0.12 g, 0.57 mmol) in
toluene (30 ml). An immediate reaction took place
with formation of a blue-green solid in a blue solu-
tion. The solid was filtered off and dried in vacuo
and analyzed as TiCl2(C14H80 2) (2), (0.17 g, 91%
yield).
Found Cl 20.5 Ti 13.8%.
IR spectrum (polychlorotrifluoroethylene mull):
3392bw. 2955w, 2928w, 2857vw, 1597m, 1525s,
1493m, 1447m, 1397vs cm“1.
The same reaction performed in heptane af-
forded the same product (IR) but contaminated
by some starting material.
c) Diluted sulfuric acid: In a gas-volumetric ap-
paratus, TiCl2(THF)2 (0.285 g, 1.1 mmol) was
treated with water at 24.3 °C. No gas evolution
was observed. After treatment with 10 mmol of
Analysis for C j4H 8Cl?0->Ti
' Calcd
C 50.9 H 2.9%,
Found C 51.4 H 2.5%.
IR spectrum (nujol and polychlorotri-fluoroe-
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513
F. Calderazzo et al. • H alides of Titanium(II) and Vanadium(II)
Table III. Lattice constants and parameters of the struc-
ture determination of PPN[TiCl4(DM E)] (5).
diluted H2S 0 4 (10% v/v), dihydrogen (0.46 mmol)
was slowly evolved up to a H2/Ti molar ratio of
0.42 (after 24 h).
PPN[TiCl4(DME)]
C4()H4()C14N O^P^Ti
818.4
Compound
Formula
Molecular weight
Reduction o f TiCl4(D M E ) with sodium in D M E
0.65x0.65x0.65
253
Crystal dimensions (mm)
Temperature (K)
A ) With one equivalent: Synthesis o f N a(D M E )n
Pna2j (No. 33)
Space group
Cell constants (A)
[TiC l4(DM E)J (4)
A solution of TiCl4(DME) (4.48 g, 16.0 mmol)
in DME (100 ml) was stirred with finely divided
sodium (0.33 g, 14.3 mmol) for 24 h at room tem-
perature. The green reaction mixture was heated
at 50 °C and filtered while still hot. Slow cooling
of the solution afforded a bright green crystalline
solid. A second crop of crystals was obtained by
adding heptane (3.87 g, 55% yield).
14.445(4)
15.690(4)
17.544(6)
3976(2)
4
1.366
5.96
1692
a
b
c
Volume (A 3)
Z
D c a ic (gem -3)
fx (cm -1)
F(000)
Data collection range (0, deg)
Scan type
3 -2 7
O J
Analysis fo r N a(D M E )/ 5[TiC l4(DM E)],
C K)H25Cl4NaOsTi
Measured reflections
Absorption correction
Indep. refls. in refinement
Refined parameters
Resd. electron dens. (e/A 3)
Ra
9301
none
7403 [I
450
>
cr(I)]
Calcd
Cl 31.7 Ti 10,9%,
Found Cl 31.2 Ti 10.9%.
0.56
0.041
0.042
1.153
IR spectrum (nujol mull): 2096w, 2027w, 1932w,
1279m-s, 1243m-s, 1191s, 1156m, 1125vs, 1078vs,
1030vs, 857vs, 825m, 773w, 650vw, 600vw, 572vw
and 418vs cm-1. The magnetic moment at 295 K
was found to be 1.55 B.M. (x\?rr= 1006 xlO-6 cgsu,
diam. corr. = -274.5 xlO "6 cgsu).
Rwb
GOF
IF0 I2]1/2; w = l/a 2IF0 l.
FI/ZIF0I; b [2w(Zl F)2/Zw
When the preparation was repeated several
times, the DME content of the isolated product
clearly depended on the drying procedure in vacuo
at room temperature.
The same compound was obtained by addition
of PPNC1 to preformed TiC ^D M E)! 5•1.5 DME.
X -ray structure determination o f
PPN [TiC l4(D M E )] (5): The structure was deter-
mined at 253 K with an ENRAF Nonius CAD4
Synthesis o f P P N f TiCl4(D M E )] (5)
diffractometer using Mo-Ka radiation (A
=
To a suspension of Na(DME), 5 [TiCl4(DME)]
(0.58 g, 1.32 mmol) in CH2C12 (15 ml) was added 0.71073 A, graphite-monochromator). Crystal
PPNC1 (0.77 g, 1.35 mmol). After 10 min stirring, data, data collection parameters and refinement
a green solution with a colourless precipitate was results are collected in Table III. The structure
obtained. After filtration, Et20 (15 ml) was added was refined with the local version of the SDP pro-
to the resulting solution, and a bright green crys- gram system [31].
talline solid was thus obtained (0.70 g, 62% yield).
The compound crystallizes in the orthorhombic
space group Pna2i with four cations and four ani-
ons in the unit cell. The positional parameters of
the central titanium and the four chlorine ligands
in the anion as well as those of the P -N -P moiety
and parts of the phenyl rings were obtained from
direct methods [32], The structure model was com-
pleted by subsequent difference Fourier maps. Hy-
Analysis fo r P P N [T iC l4(D M E )],
C40H 40Cl4N O 2P2 pi
Calcd
C 58.7 H 4.9 N 1.7 Ti5.9%,
Found C 57.3 H 4.6 N 1.7 Ti5.5%.
IR (nujol mull): 1587w, 1300m, 1281m, 1249s,
1183m, 1162m, 1113s, 1086s, 1053s, 998m, 973m,
902w, 861s, 826w, 791w, 766m, 754m, 746s, 616m, drogen atoms in calculated standard geometry
(C -H = 0.98 A) were included in structure factor
calculations with isotropic temperature factors
BH = 1.3 Bc. The fractional coordinates of the
non-hydrogen atoms are listed in Table IV.
Further details of the crystal structure investiga-
tion are available on request from the Fachinfor-
548s, 536s, 503s, 470m, 448m and 404w cm"1.
The magnetic moment at 295 K was found to be
1.51 B.M. (^Mrr = 955.7xl0-6 cgsu, diam. corr. =
-508.3 xl0~6 cgsu). Crystals suitable for the sub-
sequent X-ray diffractometric study were obtained
from a CH2C12 solution layered with Et20.
Unauthenticated
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514
F. Calderazzo et al. ■Flalides of Titanium(II) and Vanadium(II)
mationszentrum Karlsruhe, D-76344 Eggenstein-
Leopoldhafen, on quoting the depository number
CSD 59177.
B) With two equivalents: Synthesis o f
Na TiCl3(D M E )2 (6)
a)
From
TiCl4(DM E):
A
solution
of
TiCl4(DME) (6.69 g, 23.9 mmol) in DME (150 ml)
was treated with finely divided sodium (1.09 g,
47.4 mmol). After 24 h stirring, the reaction mix-
ture was filtered: the resulting solid was extracted
with boiling DME for 7 h. The volume of the ex-
tract was reduced in vacuo and the resulting black
solid was filtered off, washed with heptane and
dried in vacuo (4.50 g, 55% yield).
Table IV.
Table
of
positional
parameters
of
PPN[TiCl4(DM E)] (5). Estimated standard deviations in
parentheses refer to the least significant digit.
Atom
X
Beq (Ä 2)
z
y
Ti
0.79491(4) 0.18314(3) 0.6837
1.876(9)
0.85608(6)
C ll
0.04369(5) 0.68612(5) 2.97(1)
Cl 2
Cl 3
Cl 4
PI
0.70641(6) 0.15732(6)
0.75932(7) 0.33051(5)
0.67389(5) 0.14602(5)
0.79582(5) 3.19(2)
0.67506(6) 4.02(2)
0.59755(5) 2.60(1)
Analysis for NaTiCI^(DM E)2, C8H 20C l3NaC)4Ti
"Calcd
Cl 29J Ti 13.4%,
0.71695(5) 0.20741(4) 1.08348(4)
1.47(1)
1.56(1)
3.04(5)
2.82(4)
1.75(4)
4.23(8)
4.30(9)
5.2(1)
Found Cl 30.3 Ti 13.9%.
P2
0.69330(5) 0.18925(5) 1.25072(4)
0.9181(2)
0.8967(2)
0.7087(2)
0.9879(3)
0.9900(3)
0.9171(3)
0.8949(3)
0.7128(2)
0.7034(2)
0.7102(3)
0.7263(2)
0.7360(2)
0.7291(2)
0.6886(2)
0.6768(2)
0.6811(3)
0.6957(3)
0.7044(3)
0.7014(2)
0.6282(2)
0.5462(2)
0.4763(2)
0.4859(3)
O l
0 2
N
C l
C2
C3
C4
0.2236(2)
0.2060(2)
0.2342(1)
0.2609(3)
0.2082(3)
0.2655(3)
0.1701(3)
0.3031(2)
0.2974(2)
0.3704(2)
0.4486(2)
0.4545(2)
0.3819(2)
0.2714(2)
0.2484(2)
0.3100(2)
0.3938(2)
0.4179(2)
0.3560(2)
0.1356(2)
0.1655(2)
0.1092(2)
0.0233(3)
0.7451(1)
0.5950(1)
1.1705(1)
0.6964(2)
0.6243(2)
0.8184(2)
0.5203(2)
1.0273(2)
0.9481(2)
0.9041(2)
0.9382(2)
1.0169(2)
1.0613(2)
1.3222(2)
1.3984(2)
1.4546(2)
1.4352(2)
1.3597(2)
1.3027(2)
1.0505(2)
1.0190(2)
1.0020(2)
1.0166(2)
1.0476(2)
1.0641(2)
1.2772(2)
1.2471(2)
1.2562(2)
1.2946(2)
1.3248(2)
1.3165(2)
1.0607(2)
1.1123(2)
1.0934(2)
1.0227(3)
0.9701(2)
0.9889(2)
1.2546(2)
1.2962(2)
1.2943(3)
1.2520(3)
1.2123(2)
1.2131(2)
IR spectrum (nujol mull): 1278w, 1240m, 1186m,
1155w, 1077vs, 1033vs, 1000s, 855vs, 829s and 416s
cm "1.
The same product was obtained by treating a
solution of Na(DME) x5[TiCl4(DME)] (0.89 g, 2.03
mmol) in DME (60 ml) with finely divided sodium
(0.05 g, 2.17 mmol). After 12 h stirring the reaction
mixture was filtered off and the solvent evapo-
4.10(9)
1.68(5)
2.37(6)
2.98(7)
2.36(6)
2.22(6)
1.69(5)
1.75(5)
2.45(6)
3.17(7)
3.26(7)
3.03(7)
2.35(6)
1.92(5)
2.31(6)
3.24(7)
4.01(9)
3.61(8)
2.50(6)
1.75(5)
2.04(5)
2.61(6)
2.87(7)
2.67(7)
2.23(6)
1.80(5)
2.28(6)
3.22(7)
3.71(8)
4.09(8)
3.05(7)
1.83(5)
3.13(7)
3.85(8)
3.78(8)
3.72(8)
2.68(7)
C ll
C 12
C13
C14
C 15
C 16
C21
C22
C23
C24
C25
C26
C31
C32
C33
C34
C35
C36
C41
C42
C43
C44
C45
C46
C51
C52
C53
C54
C55
C56
C61
C62
C63
C64
C65
C66
rated to dryness affording
a 92% yield of
NaTiCl3(DME)2 (IR and Ti, Cl analysis). The
magnetic moment at 290 K was found to be 1.86
B.M. (^Mrr = 1481 xlO-6 cgsu, diam. corr. =
-2 1 7 xlO-6 cgsu). The values of ^Mrr and of the
magnetic moment as a function of temperature are
reported in Table II.
Reduction o f TiBr4(D M E )05 with sodium
a) Sodium to titanium m olar ratio = 1; synthesis o f
TiB ri(D M E )} s-1.5 D M E (7):
A
solution of
TiBr4(DME)05 (1.16 g, 2.80 mmol) in DME (40
ml) was treated with finely divided sodium (0.065
g, 2.83 mmol). After 12 h stirring the dark green
reaction mixture was filtered. The volume of the
solution was reduced to 15 ml in vacuo. After 12
h at -30 °C, a green crystalline solid was obtained,
and identified analytically as TiBr3(DME)! 5•1.5
DME (0.47 g, 30% yield).
0.5679(3) -0.0075(2)
0.6391(2)
0.7895(2)
0.7985(2)
0.0481(2)
0.1225(2)
0.0405(2)
0.8806(2) -0.0036(2)
0.9537(2)
0.9460(2)
0.8634(2)
0.8260(2)
0.8978(2)
0.9818(2)
0.9933(2)
0.9222(3)
0.8378(2)
0.5879(2)
0.5779(2)
0.4936(3)
0.4212(2)
0.4305(2)
0.5133(2)
0.0322(2)
0.1134(2)
0.1586(2)
0.1572(2)
0.1577(2)
0.1193(2)
0.0835(3)
0.0857(3)
0.1215(2)
0.1284(2)
0.0531(2)
0.0104(2)
0.0404(2)
0.1166(3)
0.1595(2)
Analysis for C l2H^0Br^O6Ti
Calcd
Br 43,0 Ti 8.6%,
Found Br 43.2 Ti8.6%.
IR spectrum (nujol mull): 1279w, 1261vw, 1244w,
1192m, 1125s, 1082s, 1029s, 980w, 888w, 859s, 639w,
595w, 444m and 417m c m '1. The magnetic mo-
ment at 296 K was found to be 1.72 B.M. (%Mrr =
1242xlO-6 cgsu, diam. corr. = -2 1 1 x l0 -6 cgsu).
The preparation was repeated several times, and
it was observed that the DME content of the iso-
lated product depended on the drying procedure
in vacuo at room temperature.
Anisotropically refined atoms are given in the form of
the isotropic equivalent displacement parameter defined
as: (4/3)-[a2-b eta(l,l) + £>2-beta(2.2) + c2-beta(3.3).
Unauthenticated
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F. Calderazzo et al. • Halides of Titanium(II) and Vanadium(II)
515
b)
Sodium to titanium m olar ratio = 2: synthesis
oration of the solution and the formation of a pale
o f N aTiBr3(D M E )12 (8):
A
solution of green solid. After 15 h stirring at room temper-
TiBr4(DME)o.5 (1.26 g, 3.05 mmol) in DME (50
ml) was treated with two equivalents of finely di-
vided sodium (0.14 g, 6.08 mmol). After 72 h stir-
ature, the pale green solid was collected by filtra-
tion, washed with DME (2x10 ml) and dried in
vacuo at room temperature. The drying procedure
ring the brown reaction mixture was filtered and caused the colour of the solid to change from pale
the solid was washed with DME (10 ml); the vol- green to grey-green. The analytical data corre-
ume of the solution was then reduced to 15 ml in spond to the formula VC12(DM E)1i (0.335 g, 62%
vacuo. Treatment with heptane (25 ml) gave a dark
liquid phase, from which a light brown solid was
obtained after two successive washings with hep-
tane. The solid was analytically and spectroscopi-
cally identified as NaTiBr3(DME)! 2 (0.60 g, 47%
yield).
yield).
Analysis for C44H n C ljO i 7V
Calcd
Cl 32.1 V 23.1%,
Found Cl 31.7 V23.7%.
IR spectrum (nujol mull): 1282w, 1261w, 1243w,
1196w, 1096m-s, 1064vs, 975w, 867s, 802w, 723w,
604w and 594m cm-1.
Analysis for C48H I2Br^NaOo 4Ti
Calcd
Br 57.2 ' Ti 112%,
The compound dissolves in THF with a bright
green colour.
Found Br 57.4 Ti 10.5%.
IR spectrum (nujol mull): 1280vw, 1262vw,
1244vw, 1193w, 1126w-m, 1082m, 1029s, 975w,
859m-s, 800m and 423w cm-1. The magnetic mo-
ment at 290 K was found to be 2.11 B.M. (^Mrr =
1904.7xl0-6 cgsu, diam. corr. = -191.0xl0“6
cgsu). The values of ^Mrr and °f the magnetic mo-
ment as a function of temperature are reported
in Table II. The preparation was repeated several
times, the DME content of the product depending
on the drying procedure in vacuo at room temper-
ature.
N ote added in p ro o f
F. A. Cotton et al. have reported [M. A. Ataya,
F. A. Cotton, I. H. Matonic, C. A. Murillo, Inorg.
Chem. 34, 5424 (1995)] that THF solutions of tita-
nium(II) chloride are obtained by reduction of
TiCl3 with KC8.
Acknow ledgem ents
The authors wish to thank the Consiglio Nazi-
onale delle Ricerche (C.N.R., Roma) and the
Ministero dell’Universita’ e della Ricerca Scientif-
Reaction o f Vmes2 with CPh3Cl. Synthesis o f ica e Tecnologica (MURST) and the Deutsche
VCl2(D M E )n: A solution of Vmes2 (0.729 g, 2.50 Forschungsgemeinschaft for financial support. I.F.
mmol) in DME (50 ml) was treated dropwise with
a solution of CPh3Cl in DME. After addition of
20 ml of the solution of the chloride (2.5 mmol), a
mixture of a brown and a green solid in a deep red
solution was observed. The addition of the second
thanks ENI for financial support during her
studies at the Scuola Normale Superiore (Pisa) in
fulfilment of the requirements for the PhD pro-
gramme. The help of Dr. A. Vallieri (Polimeri Eu-
ropa, Ferrara) with the ICP-AES analyses of tita-
equivalent (20 ml of solution) caused the decol- nium is gratefully acknowledged.
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Unauthenticated
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