Redox reactions with bis(η6-arene) derivatives of early transition metals

Article abstract of DOI:10.1016/j.jorganchem.2005.03.064

The reactivity of M(η⁶-arene)₂ derivatives of early transition metals (M = Ti, Cr, Mo, arene = MeC₆H₅; M = V, Nb, arene = 1,3,5-Me₃C₆H₃) has been investigated and the syntheses of new and known compounds are described. The derivatives M(CH₃COO)₃, M = Ti, V, Nb, Cr; M(CF ₃COO)₃, M = Ti, Nb, Cr; M(acac)₃, M = Ti, V, Mo, acac = acetylacetonato, and M(F₆acac)₃, F ₆acac = hexafluoroacetylacetonato, M = V, Nb have been prepared by reaction of the metal bis(arene) derivatives with the appropriate Lewis acid. The crystal and molecular structure of V(F₆acac)₃ has been determined. Hydrogen halides or halogens react with M(η⁶-arene) ₂ with formation of metal halides, a highly reactive form of VCl ₃ being obtained from V(η⁶-1,3,5-Me₃C ₆H₃)₂ and hydrogen chloride in heptane. TiCl₄ oxidizes Ti(η⁶-arene)₂ with complete loss of the arene ligands. An electron transfer process affording ionic derivatives of formula [M(η⁶-MeC₆H₅) ₂][TiCl₄(THF)₂], M = Cr (structurally characterized), Mo, has been observed between the THF-adduct of TiCl₄ and the appropriate metal-arene derivative of Group 6.

Full text of DOI:10.1016/j.jorganchem.2005.03.064

Journal of Organometallic Chemistry 690 (2005) 3321–3332
www.elsevier.com/locate/jorganchem
Redox reactions with bis(g6-arene) derivatives of early
transition metals
a
b
a,
a
Fausto Calderazzo , Ulli Englert , Guido Pampaloni *, Manuel Volpe
a
`
Universita di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126 Pisa, Italy
b
Institut fu¨r Anorganische Chemie der RWTH Aachen, Professor-Pirlet-Strasse 1, D-52074 Aachen, Germany
Received 21 February 2005; accepted 29 March 2005
Available online 31 May 2005
Abstract
The reactivity of M(g6-arene)2 derivatives of early transition metals (M = Ti, Cr, Mo, arene = MeC6H5; M = V, Nb,
arene = 1,3,5-Me3C6H3) has been investigated and the syntheses of new and known compounds are described. The derivatives
M(CH3COO)3, M = Ti, V, Nb, Cr; M(CF3COO)3, M = Ti, Nb, Cr; M(acac)3, M = Ti, V, Mo, acac = acetylacetonato, and
M(F6acac)3, F6acac = hexafluoroacetylacetonato, M = V, Nb have been prepared by reaction of the metal bis(arene) derivatives
with the appropriate Lewis acid. The crystal and molecular structure of V(F6acac)3 has been determined. Hydrogen halides or hal-
ogens react with M(g6-arene)2 with formation of metal halides, a highly reactive form of VCl3 being obtained from V(g6-1,3,5-
Me3C6H3)2 and hydrogen chloride in heptane. TiCl4 oxidizes Ti(g6-arene)2 with complete loss of the arene ligands. An electron
transfer process affording ionic derivatives of formula [M(g6-MeC6H5)2][TiCl4(THF)2], M = Cr (structurally characterized), Mo,
has been observed between the THF-adduct of TiCl4 and the appropriate metal-arene derivative of Group 6.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Early transition elements; Arene; Oxidation; Reactivity; Structure
Vðg6-1;3;5-Me3C6H3Þ2 þ CHnF3ꢁnCOOH
1. Introduction
! ½Vðg6-1;3;5-Me3C6H3Þ2ꢀ½CHnF3ꢁnCOOꢀ þ 1=2H2
Recent contributions from us and from these labora-
n ¼ 1;2
ð2Þ
ð3Þ
tories have described the use of transition metal com-
plexes in low oxidation states as precursors to
organometallic, inorganic or coordination compounds
[1]. As far as bis(g6-arene) derivatives are concerned,
we have shown that the treatment of V(g6-1,3,5-
Me3C6H3)2 with CF3COOH in THF of triphenylmethyl
halides in DME [1k–1n] proceeds with loss of the arene
ligands affording vanadium(I) and vanadium(II) deriva-
tives according to the following equations:
Vðg6-1; 3; 5-Me3C6H3Þ2 þ 2CPh3X þ nDME
! VX2ðDMEÞn þ 2 1; 3; 5-Me3C6H3 þ \C2Ph6"
X ¼ Cl; n ¼ 1–1.5;
X ¼ Br; I; n ¼ 2
Monoelectronic oxidizing agents such as [FeCp2]+ [2]
or Ag+ [3] react with Ti(g6-1,3,5-iPr3C6H3)2 or V(g6-
arene)2 (arene = 1,3,5-Me3C6H3, 1,3,5-tBu3C6H3) giving
the [M(g6-arene)2]+ cations. Similarly, bis(g6-arene)
compounds of niobium(0) afford [Nb(g6-arene)2]+,
L = CO, alkynes, PMe3 [4].
Vðg6-1; 3; 5-Me3C6H3Þ2 þ 3CF3COOH þ nTHF
! HðTHFÞn½VðCF3COOÞ3ꢀ þ 2 1; 3; 5-Me3C6H3 þ H2 ð1Þ
As it is now possible to prepare gram quantities of
M(g6-arene)2 (M = V, Nb, arene = 1,3,5-trimethylben-
zene; M = Cr, Mo, arene = toluene) via the Fischer –
Hafner synthesis, i.e., by using conventional laboratory
*
Corresponding author. Tel.: +39 50 2219 219; fax: +39 50 2219 246.
E-mail address: pampa@dcci.unipi.it (G. Pampaloni).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.03.064

3322
F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
techniques, see Section 4, we became interested in
further developing the use of low-valent bis(arene) me-
tal complexes as precursors to classical inorganic or
coordination compounds. This study appeared of
interest especially when considering that some of our
recent results show that VCl2 [1n], as obtained from
V(g6-1,3,5-Me3C6H3)2 at room temperature or below,
has a higher reactivity with respect to commercial
compounds due to the stabilization of metastable crys-
talline phases. Being interested in looking for periodic
trends in the behaviour of the arene derivatives, we
have also examined the reactivity of Ti(g6-MeC6H5)2,
as prepared via the metal vapour synthesis (MVS)
technique [5].
In this paper, we report the reactions of bis(g6-arene)
derivatives of Groups 4, 5 and 6 elements with sub-
stances containing active protons such as carboxylic
acids or b-diketones and a variety of oxidizing species,
namely halogens, triphenylmethyl halides, and transi-
tion metal-based reagents, e.g., TiCl4.
Ti(O2CCF3)3 and Ti(O2CCF3)2 have been mentioned
but not characterized [11].
Addition of a slight excess of CH3COOH to a solu-
tion of Ti(g6-MeC6H5)2 in toluene resulted in the imme-
diate precipitation of the light green Ti(O2CCH3)3 (see
Eq. (4)).
Tiðg6-MeC6H5Þ2 þ 3CH3COOH
! TiðO2CCH3Þ3 þ 2MeC6H5 þ 3=2H2
ð4Þ
The solid-state IR spectrum shows three strong absorp-
tions in the typical range (1800–1300 cmꢁ1) of the car-
boxylate stretching vibrations, at 1618, 1544 and 1455
cmꢁ1. Based on the data reported in the literature and
on the separation (D) between the asymmetric and the
symmetric stretching vibrations [13], the absorptions
are assigned to the asymmetric stretching of a bridging
acetato group, the asymmetric stretching of a chelating
acetato group and to the symmetric stretching of both
groups, respectively. The presence of bridging acetato
groups suggests a polynuclear structure for this com-
pound, even though its solubility in toluene excludes
the possibility of a high nuclearity. The magnetic mo-
ment (0.99 BM at 296 K), much lower than the expected
value (1.73 BM) for a compound containing a metal cat-
ion of d1 configuration, can be explained on the basis of
interactions between neighbouring titanium atoms
through the p system of the carboxylato bridges.
2. Results and discussion
2.1. Ti(g6-MeC6H5)2
The available data concerning the reactivity of bis-
arene derivatives of titanium(0) are limited. Reduction
to the [Ti(g6-arene)2]ꢁ anion (arene = C6H6 and
MeC6H5) can be achieved by using a potassium film
[6]. Oxidation to the [Ti(g6-arene)2]+ cation was re-
ported only in the case of Ti(g6-1,3,5-iPr3C6H3)2 by
the reaction with ferricinium derivatives [2]. All other
reactions involving the oxidation of the metal centre
resulted in the loss of the aromatic ligand. For exam-
ple, the reaction of Ti(g6-MeC6H5)2 with CO2 was
reported to afford an oxalato derivative of low-valent
titanium [7], whereas the reactions with acetylacetone
and hydrogen sulfide or sulfur gave the corresponding
complexes of titanium(III), Ti(acac)3 and Ti2S3,
respectively [8]. The bis-cyclopentadienyl derivative of
titanium(III) [TiCp2Cl]2 was obtained by reacting
Ti(g6-MeC6H5)2 with TiCp2Cl2 [8], and both Ti(g6-
MeC6H5)2 and Ti(g6-1,3,5-tBu3C6H3)2 gave TiI4 with
I2 [9].
The reaction of the titanium(0) arene complexes with
carboxylic acids was anticipated to produce carboxylato
derivatives of titanium, whose chemistry is well estab-
lished, although only TiCp2(O2CCF3)2, TiO(O2CCF3)2
[10,11], the titanium(III) species Ti(O2CCH3)3 ꢁ nCln
[12] and the corresponding trifluoro-substituted ones
[11] have been thoroughly characterized. As far as the
homoleptic trifluoroacetato derivatives Ti(O2CCF3)n
are concerned, Ti(O2CCF3)4 does not appear to have
been prepared as yet, although the corresponding zirco-
nium and hafnium derivatives are known [11], and both
When a solution of Ti(g6-MeC6H5)2 in toluene was
treated with CF3COOH, a green-brown solid precipi-
tated out. Although the presence of trifluoroacetato
groups was confirmed by IR, elemental analyses were
not reproducible. In a coordinating solvents, such as
THF, addition of CF3COOH to a freshly prepared solu-
tion of Ti(g6-MeC6H5)2 resulted in an immediate reac-
tion with formation of a brick red solution, from
which solid Ti(O2CCF3)3 could be isolated (Eq. (5)).
Tiðg6-MeC6H5Þ2 þ 3CF3COOH
! TiðO2CCF3Þ3 þ 2MeC6H5 þ 3=2H2
ð5Þ
The IR spectrum of the solid shows two strong
absorptions at 1698 and 1485 cmꢁ1, assigned to the
asymmetric and symmetric C–O stretching vibrations,
and two strong absorptions at 1208 and 1165 cmꢁ1, as-
signed to the C–F stretching vibrations of the trifluoro-
methyl group. The separation of the C–O stretching
vibrations (Dm ꢂ 215 cmꢁ1) indicates the presence of
either chelating or bridging trifluoroacetato groups.
The polynuclear nature of the compound is also evi-
denced by the strongly reduced magnetic moment of
the compound (0.86 BM at 292 K), as compared to
the value of 1.73 BM expected for a Ti(III) centre of
d1 electronic configuration.
The tendency of titanium(0) in Ti(g6-MeC6H5)2 to at-
tain the +III oxidation state was further confirmed by
the reaction of Ti(g6-MeC6H5)2 with TiCl4, which

F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
3323
affords substantially amorphous [14] TiCl3 as a brown
solid (Eq. (6)).
cis-VX2(DME)2, X = Br, I [1l], were obtained. It has
to be noticed that intractable oily substances were ob-
tained when a HX/V molar ratio higher than 2 was used.
The reaction of V(g6-1,3,5-Me3C6H3)2 with neat
CH3COOH [22] is fast and exothermic giving a green so-
lid almost insoluble in the common organic solvents
which has been identified as V(O2CCH3)3. A compound
of similar properties, formulated as V2(O2CCH3)6, was
reported to be formed by the reaction of VB2 with acetic
acid at 110 ꢁC for 2 weeks [23]. The magnetic moment of
our compound is 2.64 BM at 296 K, slightly reduced
with respect to the spin-only value (2.84 BM) calculated
for a vanadium(III) ion of d2 configuration, probably
due to spin coupling through bridging acetates.
b-Diketones react with V(g6-1,3,5-Me3C6H3)2 giving
b-diketonato derivatives [24] of vanadium(III), see Eq.
(11), the reaction rates being related to the acid strength
of the diketone itself. Acetylacetone (pKa = 8.80) [25] re-
acts at appreciable rate only as a neat liquid at the boil-
ing point of the mixture, while hexafluoroacetylacetone
(pKa = 4.35 [25]) quickly evolves dihydrogen when trea-
ted with an heptane solution of V(g6-1,3,5-Me3C6H3)2
at room temperature.
Tiðg6-MeC6H5Þ2 þ 3TiCl4 ! 4TiCl3 þ 2MeC6H5
ð6Þ
Ti(g6-MeC6H5)2 reacts with AlCl3 as well, the reac-
tion products being the well-established derivative of
titanium(II) Ti(g6-MeC6H5)[(l-Cl)2(AlCl2)]2 [15] and
aluminum (Eq. (7)).
Tiðg6-MeC6H5Þ2 þ 8=3AlCl3
! Tiðg6-MeC6H5Þ½ðl-ClÞ2ðAlCl2Þꢀ þ 2=3Al
ð7Þ
2
This reactivity parallels the reactions of bis-arene
derivatives of vanadium(0) [16] and chromium(0) [17]
with aluminum trichloride, see Eqs. (8) and (9). The dif-
ferent reactivity of the chromium, vanadium and tita-
nium systems
Crðg6-areneÞ2 þ 4=3AlX3 ! ½Crðg6-areneÞ2ꢀAlX4 þ 1=3Al
arene ¼ C6H6; C6H5–C6H5; X ¼ Cl; Br; I
ð8Þ
Vðg6-1; 3; 5-Me3C6H3Þ2 þ 4=3AlCl3
! ½Vðg6-1; 3; 5-Me3C6H3Þ2ꢀAlCl4 þ 1=3Al
ð9Þ
can be explained by considering that the primary prod-
ucts of the Fischer–Hafner reductions are the [M(g6-
arene)2]+ cations in the case of vanadium and chromium
[16], while the reaction of TiX4 with Al/AlX3 in arene
gives the titanium(II) derivatives Ti(g6-arene)[(l-
X)2(AlX2)]2, X = Cl, Br, I [15,18].
Vðg6-1; 3; 5-Me3C6H3Þ2 þ 3b-dikH
! Vðb-dikÞ3 þ 2 1; 3; 5-Me3C6H3 þ 3=2H2
b-dikH ¼ acetylacetone; hexafluoroacetylacetone ð11Þ
The molecular structure of V(F6acac)3 has been
solved by X-ray diffraction methods. It consists of dis-
crete molecules separated by normal intermolecular con-
tacts. Within each molecule (Fig. 1), the central metal
atom is surrounded by the six oxygen atoms of the three
b-diketonato ligands. The V–O bond distances (mean
2.2. V(g6-1,3,5-Me3C6H3)2
The g6-arene derivatives of vanadium(0) were re-
ported to react with alcohols such as ethylene glycol
and glycerine, or with dithioacetic acid to afford vana-
dium(III) compounds of formula V(OR)3 [19] or
(CH3CS2)2V(l-g2-S2)2V(S2CCH3)2 [20], respectively.
Oxidation to vanadium(II) occurs when V(g6-1,3,5-
Me3C6H3)2 is reacted with CF3COOH in heptane or
THF [1m] or with triphenylmethyl halides in DME [1l]
(see Eqs. (1)–(3)).
The vanadium(0) complex V(g6-1,3,5-Me3C6H3)2
rapidly reacts with hydrogen chloride at room tempera-
ture in heptane affording quantitative yields of an al-
most amorphous form of VCl3 [14] (Eq. (10)), which
reacts vigorously with THF affording VCl3(THF)3 [21]
within the time of mixing the reagents at ca. ꢁ30 ꢁC.
Vðg6-1; 3; 5-Me3C6H3Þ2 þ HCl
! VCl3 þ 3=2H2 þ 2 1; 3; 5-Me3C6H3
ð10Þ
However, the heavier hydrogen halides HX (X = Br, I)
in heptane afford mixtures of [V(g6-1,3,5-Me3C6H3)2]X,
VX2 and VX3. On changing the medium with a coordi-
nating one (DME), the reaction does not proceed be-
yond the oxidation to vanadium(II) and high yields of
Fig. 1. ORTEP [26] view of tris(1,1,1,5,5,5-hexafluoroacetylaceto-
nate)vanadium(III), V(F6acac)3. Displacement ellipsoids are drawn at
30% probability. Hydrogen atoms have been omitted.

3324
F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
ing Nb(g6-1,3,5-Me3C6H3)2 with dry hydrogen halides
in a hydrocarbon or in coordinating solvents. Moreover,
attempts to perform a monoelectronic oxidation to the
[Nb(g6-1,3,5-Me3C6H3)2]+ cation failed: niobium(0)
was still present in the reaction mixture after prolonged
reaction times.
Table 1
˚
Bond distances (A) and angles (ꢁ) in tris(1,1,1,5,5,5-hexafluoroacetyl-
acetonate)vanadium(III), V(F6acac)3
V–O(11)
V–O(33)
1.962(2)
1.963(2)
1.980(2)
1.987(2)
1.991(2)
1.995(2)
1.265(4)
1.250(4)
1.255(4)
1.246(4)
1.259(4)
1.266(4)
O(33)–V–O(31)
O(11)–V–O(23)
O(33)–V–O(23)
O(31)–V–O(23)
O(11)–V–O(13)
O(33)–V–O(13)
O(31)–V–O(13)
O(23)–V–O(13)
O(11)–V–O(21)
O(33)–V–O(21)
O(31)–V–O(21)
O(23)–V–O(21)
O(13)–V–O(21)
O(11)–V–O(33)
O(11)–V–O(31)
87.92(9)
178.19(10)
92.77(10)
89.76(10)
87.90(9)
V–O(31)
V–O(23)
V–O(13)
V–O(21)
Nbðg6-1; 3; 5-Me3C6H3Þ2 þ 3CPh3Cl þ 0.8DME
! NbCl3ðDMEÞ0.8 þ 2 1; 3; 5-Me3C6H3
90.06(9)
O(11)–C(11)
O(13)–C(13)
O(21)–C(21)
O(23)–C(23)
O(31)–C(31)
O(33)–C(33)
177.74(9)
91.34(10)
91.70(10)
179.33(9)
91.72(9)
þ 3=2\C2Ph6"
ð12Þ
The same oxidation state of the metal (+III) is at-
tained in the reaction of Nb(g6-1,3,5-Me3C6H3)2 with
CF3COOH, the product being identified as
Nb(CF3COO)3 (see Eq. (13)).
86.67(9)
90.32(10)
88.87(10)
91.06(10)
Nbðg6-1; 3; 5Me3C6H3Þ2 þ 3CF3COOH
! NbðCF3COOÞ3 þ 2 1; 3; 5-Me3C6H3 þ 3=2H2
ð13Þ
The relative positions of the symmetric and asymmetric
C@O stretching modes (IR absorptions are observed at
1635 and 1460 cmꢁ1) suggest a bidentate coordination
of the trifluoroacetato ligand, thus suggesting this deriv-
ative to be a hexacoordinated compound of nio-
bium(III). No pure product was isolated from the
reaction with acetic acid under the same experimental
conditions (hydrocarbons or THF or DME).
Numbers in parenthesis refer to the least significant digits.
˚
value: 1.979 A) and the O–V–O angles (mean value
88.6ꢁ) indicate a quasi-regular octahedral coordination
of the vanadium atom (see Table 1).
Structurally characterized vanadium(III) b-diketo-
nato complexes are not common in the literature,
examples being V(acac)3 [27] and V(CF3COCHC-
OCH3)3 [28]. Moreover, the V(b-diketonato)3 unit has
been found in the vanadium(IV) complexes
[V(acac)3]SbCl6 and [V(Bzacac)3]SbCl6 (BzacacH = 1-
phenylbutane-1,3-dione) [29]. The VO6 units in
V(acac)3, [V(acac)3]+ and [V(Bzacac)3]+ show a tetrago-
nal distortion (two of the six V–O bond distances are
significantly shorter than the other) which is not present
in V(F6acac)3, where the average values of the equato-
rial and axial V–O distances are identical within experi-
The reaction of Nb(g6-1,3,5-Me3C6H3)2 with acety-
lacetone was conducted at the reflux temperature of
the mixture: instead of the expected Nb(acac)3, the
oxo-acetylacetonato of niobium(IV) Nb(acac)2(O)
was obtained. The isolation of this compound suggests
that deoxygenation of the organic ligand takes place.
As a matter of fact, detectable amounts of 2-penta-
none (C5H10O, GCMS) were present in the reaction
mixture, thus suggesting the overall stoicheiometry of
Eq. (14). Furthermore, the analysis of the IR spec-
trum of the solid inorganic product allowed us to
identify a broad band of medium intensity centred
at 930 cmꢁ1, typical of complexes containing the
Nb@O moiety [34].
˚
mental error (1.979 and 1.975 A, respectively). The
bidentate ligands are substantially planar, with maxi-
˚
mum deviation of 0.129 A for O(11).
2.3. Nb(g6-1,3,5-Me3C6H3)2
Bis-arene derivatives of niobium(0) have been studied
in recent years, mainly concerning the monoelectronic
Nb(0) ! Nb(I) oxidation, a reaction which proceeds
without loss of coordinated arene [4]. On the other
hand, little is known about the exhaustive oxidation of
niobium(0). To the best of our knowledge, only the reac-
tion of Nb(g6-1,3,5-Me3C6H3)2 with di-iodine has been
reported, giving the dinuclear neutral compound of
Nb(II), Nb2(g6-1,3,5-Me3C6H3)2(l-I)4 [30], or NbI5 [9],
depending on the I2/Nb molar ratio.
The reaction of Nb(g6-1,3,5-Me3C6H3)2 with three
equivalents of CPh3Cl in DME forms NbCl3(DME)0.8
[31], and ‘‘C2Ph6’’ [32,33], see Eq. (12). It is important
to note that neither the reaction with CPh3Cl in heptane
or toluene nor the use of CPh3Br afforded pure com-
pounds. Mixture of halides were obtained also by react-
Nbðg6-1; 3; 5-Me3C6H3Þ2 þ 3C5H8O2
! NbðOÞðC5H7O2Þ2 þ 2 1; 3; 5-Me3C6H3 þ C5H10O ð14Þ
The reaction of Nb(g6-1,3,5Me3C6H3)2 with F6acacH
proceeds smoothly at room temperature with dihydro-
gen evolution and formation of the niobium(III) deriva-
tive Nb(F6acac)3, see Eq. (15). This new compound has
also been prepared, albeit in low yields, from
NbCl3(DME)1.3 and Tl(F6acac) (Eq. (16)).
Nbðg6-1; 3; 5-Me3C6H3Þ2 þ 3F6acacH
! NbðF6acacÞ3 þ 2 1; 3; 5-Me3C6H3 þ 3=2H2
ð15Þ
ð16Þ
NbCl3ðDMEÞ1.3 þ 3TlðF6acacÞ
! NbðF6acacÞ3 þ 3TlCl

F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
3325
Nb(F6acac)3 is not as volatile as the corresponding
vanadium compound, suggesting a higher nuclearity
for the niobium derivative. Strictly connected is the
observation that both compounds are paramagnetic,
but the magnetic moment of the vanadium species
(2.62 BM at 296 K) is close to the value expected for a
3d3 system (2.84 BM), while the corresponding niobium
derivative shows a reduced magnetic moment of 0.89
BM (295 K) which is well reduced with respect to the
expected value. These data strongly suggest that
Nb(F6acac)3 has a polynuclear structure, probably con-
taining bridging hexafluoroacetylacetonato ligands as
observed in some silver(I) compounds such as [Ag(1,5-
COD)(F6acac)]2, 1,5-COD = 1,5-cyclooctadiene [35],
[Ag(Me2COD)(F6acac)]2, Me2COD = 1,5-dimethylcy-
cloocta-1,5-diene [36], [Ag2(l2-F6acac)2(diglyme)2 [37],
and Ag2(l2-F6acac)(l2-CF3COO)(diglyme)2] [37].
depending on the V(g6-1,3,5-Me3C6H3)2/TiCl4 molar
ratio [41]. Mixed niobium/titanium halides of general
formula NbTinClm were obtained with Nb(g6-1,3,5-
Me3C6H3)2, the composition depending on the Nb/Ti
molar ratio [42]. As far as arene derivatives of Group
6 are concerned, the interaction between Cr(g6-C6H6)2
and TiCl4 gives a product able to promote the polymer-
ization of iso-butylvinyl ether [43], the real nature of the
Cr/Ti species not being established. It appeared there-
fore of interest to examine the reactivity of Group 6 me-
tal arenes with TiCl4.
When a heptane solution of TiCl4 was added to an
equimolar amount of Cr(g6-MeC6H5)2 in the same sol-
vent a quick reaction took place with formation of a
bulky grey solid: neither chloride ions nor toluene were
found in solution, thus suggesting that both chromium
and titanium had been incorporated in the precipitate.
The grey solid is almost insoluble in hydrocarbons and
it is extremely moisture sensitive, turning yellow and
partially dissolving in THF. Work up of the reaction
mixture afforded [Cr(g6-MeC6H5)2][TiCl4(THF)2], see
Eq. (20), whose IR spectrum shows arene CH stretching
at 3059 and 2982 cmꢁ1 and two strong bands (1020–860
cmꢁ1) due to coordinated THF. The compound was pre-
pared also by reacting [Cr(g6-MeC6H5)2]Cl with
TiCl3(THF)3 (see Eq. (21)).
2.4. M(g6-MeC6H5)2, M = Cr, Mo
At variance to niobium and vanadium [1l], the reac-
tion between Cr(g6-MeC6H3)2 and CPh3X results in a
monoelectronic oxidation of the chromium(0) derivative
[32]. By adding one equivalent of CPh3X to the solution
of Cr(g6-MeC6H5)2, the deep yellow [Cr(g6-
MeC6H5)2]X (X = Br, Cl) [38], Eq. (17), was identified.
Crðg6-MeC6H5Þ2 þ TiCl4 þ 2THF
Crðg6-MeC6H5Þ2 þ CPh3X
! ½Crðg6-MeC6H5Þ2ꢀ½TiCl4ðTHFÞ2ꢀ
ð20Þ
ð21Þ
! ½Crðg6-MeC6H5Þ2ꢀX þ 1=2\C2Ph6"
ð17Þ
½Crðg6-MeC6H5Þ2ꢀCl þ TiCl3ðTHFÞ3
Total loss of the arene rings was brought about by
bromine: the reaction affords intractable mixtures when
performed in hydrocarbons. However, in dimethoxye-
thane, products were obtained which were identified as
the chromium(III) and the molybdenum(II) bromides,
CrBr3(DME)1.5 and MoBr2(DME)1.5, respectively (Eq.
(18)).
! ½Crðg6-MeC6H5Þ2ꢀ½TiCl4ðTHFÞ2ꢀ þ THF
The product was characterized by X-ray single-crys-
tal diffraction and its structure is shown in Fig. 2; a
selection of bond distances and angles is in Table 2.
Mðg6-MeC6H5Þ2 þ n=2Br2
! MBrnðDMEÞ1.5 þ 2MeC6H5
M ¼ Cr; n ¼ 3; M ¼ Mo; n ¼ 2
ð18Þ
With trifluoroacetic acid, Cr(g6-MeC6H3)2 gave
Cr(CF3COO)3 which was isolated and characterized,
see Eq. (19).
Crðg6-MeC6H5Þ2 þ 3CF3COOH
! CrðCF3COOÞ3 þ 2MeC6H5 þ 3=2H2
ð19Þ
Molybdenum acetylacetonate Mo(acac)3 [39] resulted
from the reaction of Mo(g6-MeC6H5)2 with acacH.
Some years ago, it was reported that metal carbonyls
such as V(CO)6, Cr(CO)6 and Mo(CO)6 react with TiCl4
to give binary chlorides of general formula MCln Æ n-
TiCl3 [40]. Some of us, have extended this reaction to
V(g6-1,3,5-Me3C6H3)2 showing the formation of solid
compounds of general formula VTinClm, with n and m
Fig. 2. ORTEP [26] view of [Cr(g6-MeC6H5)2][TiCl4(THF)2]. Dis-
placement ellipsoids are drawn at 30% probability. Hydrogen atoms
have been omitted.

3326
F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
VCl2(DME)x
Table 2
TiCl3
H(THF)2[V(CF3COO)3]
Ti(CF3COO)3
6
˚
Bond distances (A) and angles (ꢁ) in [Cr(g -MeC6H5)2][TiCl4(THF)2]
Ti–O(1)
Ti–Cl(2)
Ti–Cl(1)
2.082(2)
2.4018(9)
2.4083(10)
1.457(4)
1.473(4)
2.124(4)
2.132(3)
2.139(3)
2.144(3)
2.153(3)
2.169(3)
O(1)#1–Ti–Cl(2)#1
O(1)–Ti–Cl(2)#1
O(1)#1–Ti–Cl(1)
O(1)–Ti–Cl(1)
88.75(7)
91.25(7)
89.11(7)
90.89(7)
90.34(3)
89.66(3)
109.3(2)
123.36(19)
127.05(19)
104.6(3)
CPh3Cl
CF3COOH
O(1)–C(11)
O(1)–C(8)
Cr(1)–C(3)
Cr(1)–C(2)
Cr(1)–C(4)
Cr(1)–C(5)
Cr(1)–C(6)
Cr(1)–C(1)
[Cr(η6-MeC6H5)2]Cl
Cl(2)#1–Ti–Cl(1)
Cl(2)–Ti–Cl(1)
C(11)–O(1)–C(8)
C(11)–O(1)–Ti
C(8)–O(1)–Ti
NbCl3(DME)x
Nb(CF3COO)3
Cr(CF3COO)3
Scheme 1. Reactivity of metal bis(arene) complexes with CPh3Cl and
CF3COOH.
O(1)–C(8)–C(9)
reactions are reported of bis(g6-toluene)titanium(0),
whose preparation still requires the use of MVS
techniques.
Numbers in parenthesis refer to the least significant digits. Symmetry
transformations used to generate equivalent atoms: #1: ꢁx, ꢁy + 1,
ꢁz + 1; #2: ꢁx + 1, ꢁy + 1, ꢁz.
Generally speaking, metal arenes can be converted to
metal halides (or to their adducts with Lewis bases such
as DME) by hydrogen halides, halogens and triphe-
nylmethyl halides or to carboxylato or b-diketonato
derivatives by carboxylic acids or substituted b-dike-
tones, respectively. It has been found, for instance, that
Nb(g6-1,3,5-Me3C6H3)2 can be used as a starting mate-
rial for the synthesis of NbCl3(DME)x, as an alternative
to the literature method [31]. Moreover, different ace-
tato- and trifluoroacetato complexes can be obtained
via redox reactions, which are high-yielding reactions
and produce arenes and hydrogen only as by-products,
thus favouring the recovery of the metal-containing
product.
Zerovalent metal arene derivatives of early transition
elements (Ti, V, Nb) easily lose coordinated arene li-
gands, a behaviour linked to their high tendency to un-
dergo further oxidation (see Scheme 1).
In the reaction of M(g6 arene)2 with TiCl4, Ti(g6-
MeC6H5)2, V(g6-1,3,5-Me3C6H3)2 and Nb(g6-1,3,5-
Me3C6H3)2 undergo oxidation with loss of the arene
ligands and formation of metal halides. The arene
derivatives of Group 6, M(g6-MeC6H5)2, give the
bis(g6-toluene) cations (see Scheme 2).
The structure consists of discrete [Cr(g6-MeC6H5)2]+
cations and [TiCl4(THF)2]ꢁ anions. The chromium
atom is sandwiched between two staggered toluene
rings which represents the conformation generally
adopted by alkyl-substituted arene complexes of
˚
Cr(I) [44]. The Cr–centroid distance (1.615 A) and
˚
the Cr–C distances (2.144 A, mean value) are similar
to those observed in other chromium(I) bis(toluene)
derivatives [44].
As far as the [TiCl4(THF)2]ꢁ anion is concerned,
˚
˚
the average Ti–Cl (2.405 A) and Ti–O (2.083 A) bond
distances are comparable to those reported for the
same anion in the [Bu4N]+ derivative (2.394 and
˚
2.099 A, respectively) [45]. Some relevant differences
are noted on comparing the Ti(III) derivative with
the parent neutral molecule of titanium(IV) trans-
TiCl4(THF)2, whose Ti–Cl distances are notably shorter
˚
(2.293 A) [46].
The reaction of Mo(g6-MeC6H5)2 with TiCl4 pro-
ceeds similarly, i.e., with immediate precipitation of a
bulky grey solid, which turned green on changing the
solvent from heptane to THF. The compound was iden-
tified as [Mo(g6-MeC6H5)2][TiCl4(THF)2] on the basis
of elemental analysis and on the similarity of its IR spec-
trum with that of the chromium analogue. Several at-
tempts to crystallize this product always produced
twinned crystals.
NbTi3Cl12
[Cr(η6-MeC6H5)2]
[TiCl4(THF)2]
VTi3Cl12
3. Conclusions
TiCl4
The use of metal bis(arene) complexes as precursors
to classical coordination compounds has been further
developed. The recent publication of conventional,
high-yielding syntheses of vanadium(0) and niobium(0)
bis(g6-mesitylene) derivatives, together with the long-
standing preparative method of the bis(g6-toluene) spe-
cies of chromium and molybdenum, has allowed this
chemistry to be explored in some detail. Moreover, some
[Mo(η6-MeC6H5)2]
[TiCl4(THF)2]
TiCl3
Scheme 2. Summary of the reactivity of TiCl4 towards metal bis(g6-
arene) complexes.

F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
3327
4. Experimental
4.2.2. CF3COOH
A freshly prepared solution of Ti(g6-MeC6H5)2 (0.14
g, 0.60 mmol) in THF (20 mL) was added of CF3COOH
(0.43 mL, 5.50 mmol). An immediate reaction took
place with formation of a red-brown solution. After 18
h stirring at room temperature, the solvent was evapo-
rated in vacuo affording a brown oil. Addition of hep-
tane (25 mL) caused the formation of a brick red
solid, which was filtered off and dried in vacuo. It was
analytically and spectroscopically identified as Ti(CF3-
COO)3 (0.10 g, 42% yield). Anal. Calc. for C6F9O6Ti:
C, 18.6; H, 0.0; Ti, 12.4. Found: C, 19.4; H, 0.1; Ti,
4.1. General procedures
Unless otherwise stated, all the operations were car-
ried out under an atmosphere of prepurified argon.
Solvents were dried by conventional methods prior
to use. IR spectra were measured with the FT1725X
instrument on or Nujol and/or polychlorotrifluoroeth-
ylene (PCTFE) mulls prepared under rigorous
exclusion of moisture and air. Magnetic susceptibility
measurements were performed with a Faraday balance
using CuSO4 Æ 5H2O as standard. Pascal contributions
were used to calculate the diamagnetic correction
[47].
Hydrogen halides (Matheson), bromine (Carlo
Erba, Milan), CH3COOH (Carlo Erba, Milan),
CF3COOH (Carlo Erba, Milan), CPh3Cl (Aldrich)
and CPh3Br (Aldrich) were used as received. TiCl4
(Aldrich) was distilled prior to use. AlCl3 was sub-
limed prior to use and stored in ampoules sealed un-
der a dinitrogen atmosphere. Acetylacetone, acacH,
and hexafluoroacetylacetone, F6acacH, were distilled
prior to use. The following compounds were prepared
as reported in the literature: Ti(g6-MeC6H5)2 [5],
V(g6-1,3,5-Me3C6H3)2 [16], Nb(g6-1,3,5-Me3C6H3)2
[48], M(g6-MeC6H5)2, M = Cr [16], Mo [16],
TiCl3(THF)3 [49], TiCl4(THF)2 [49], NbCl3(DME)1.3
[31]. The experimental procedure [50] for preparing
Tl(F6acac) was modified as follows. A solution of
TlOEt (2.8 mL, 9.9 g, 39.5 mmol) in toluene (50
mL) was added within 30 min to a solution of
F6acacH (5.7 mL, 8.4 g, 40.3 mmol) in toluene (40
mL). The yellow solution was evaporated to dryness
and heptane (30 mL) was added to the residue. The
solid was recovered by filtration and dried in vacuo
affording 6.9 g (60% yield) of Tl(F6acac).
11.7%. IR (PCTFE and Nujol mull) m=cmꢁ1: 1793 w,
~
1699 s, 1485 m, 1434 w, 1208 vs, 1165 vs, 862 m, 788
m, 728 s, 528 w, 508 w. vMcorr ¼ 314 ꢃ 10ꢁ6 cgsu; diamag-
netic correction = ꢁ122 · 10ꢁ6 cgsu; leff = 0.86 BM (292
K). When the reaction was performed in toluene or
heptane, green-brown solids were isolated with composi-
tion Ti(CF3COO)n, n = 2.5–2.8 depending on drying
conditions.
4.2.3. TiCl4
A 0.1 M solution of TiCl4 in heptane (26 mL, 2.60
mmol) was added to a solution of Ti(g6-MeC6H5)2
(0.20 g, 0.86 mmol) in heptane (20 mL). An immediate
reaction took place with formation of a brown solid.
After 18 h stirring at room temperature, the solid was
recovered by filtration, washed with heptane (10 mL)
and dried in vacuo. It was analytically identified as TiCl3
(0.39 g, 62% yield). Anal. Calc. for Cl3Ti: Cl, 68.9; Ti,
31.1. Found: Cl, 69.2; Ti, 30.4%.
4.2.4. AlCl3
AlCl3 (2.1 g, 15.7 mmol) was added to a solution of
Ti(g6-MeC6H5)2 (1.4 g, 6.2 mmol) in toluene (100
mL). A slow reaction took place with formation of a
black sticky solid, while colour fading of the solution
was noticed. After 18 h stirring at room temperature,
the solid was separated by filtration from the dark pur-
ple solution, washed with toluene (5 · 5 mL), dried in
vacuo and identified as aluminum metal (0.095 g, 85%
yield). The solution was evaporated to dryness, the pur-
ple solid washed with heptane (25 mL) and dried in
vacuo. It was identified (Cl and Ti) as Ti(g6-MeC6H5)-
[(l-Cl)2(AlCl2)]2 (2.36 g, 80% yield) [15b].
4.2. Reactivity of Ti(g6-MeC6H5)2
4.2.1. CH3COOH
A solution of Ti(g6-MeC6H5)2 (0.20 g, 0.86 mmol)
in toluene (20 mL) was added of CH3COOH (2 mL,
34.69 mmol). An immediate reaction took place with
formation of a light green solid. After 2 h stirring at
room temperature the solid was filtered off, washed
with light petroleum and dried in vacuo. It was ana-
lytically and spectroscopically identified as Ti(CH3-
COO)3 (0.10 g, 53% yield). Anal. Calc. for
C6H9O6Ti: C, 32.0; H, 4.0; Ti, 21.3. Found: C, 32.5;
H, 3.8; Ti, 21.0%. IR (PCTFE and Nujol mull)
4.3. Reactivity of V(g6-1,3,5-Me3C6H3)2
4.3.1. Hydrogen chloride in heptane
A red brown solution of V(g6-1,3,5-Me3C6H3)2 (2.2
g, 7.6 mmol) in heptane (100 mL) was treated with dry
hydrogen chloride, with immediate decolouration of
the solution and formation of the dark violet VCl3.
After 2 h, the suspension was filtered and the solid
was dried in vacuo at room temperature affording 1.17
m=cmꢁ1: 2930 m, 2861 w, 1618 s, 1544 vs, 1455 vs,
~
1347 ms, 1028 m, 803 w, 723w, 656 ms. vcMorr
¼
410 ꢃ 10ꢁ6 cgsu; diamagnetic correction = ꢁ92 · 10ꢁ6
cgsu; leff (296 K) = 0.99 BM.

3328
F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
g (98%) of VCl3. Anal. Calc. for Cl3V: Cl, 67.6; Ti, 32.4.
Found: Cl, 67.7; V, 32.3%.
the solid was dried in vacuo at room temperature and
identified as V(F6acac)3 [24b–24d] (0.381 g, 45% yield)
from elemental analysis (C, H) and spectroscopic data
(IR spectroscopy). vMcorr ¼ 2878 ꢃ 10ꢁ6 cgsu; diamag-
netic correction = ꢁ241 · 10ꢁ6 cgsu; leff (296 K) = 2.62
BM.
4.3.2. Hydrogen halides (HBr, HI) in
1,2-dimethoxyethane
A solution of V(g6-1,3,5-Me3C6H3)2 (0.507 g, 1.74
mmol) in DME (25 mL) was treated with 3.43 mmol
of dry hydrogen bromide introduced in the reaction
flask through a silicon cap. An immediate reaction with
formation of a green solid in a pale green solution was
obtained. The solid was filtered and dried in vacuo at
room temperature affording 0.523 g (77% yield) of cis-
VBr2 (dme)2 [1l] (IR and elemental analysis) as a green
microcrystalline solid.
4.3.6. Crystal structure of V(F6acac)3: solution and
refinement
Deep red crystals of V(F6acac)3 were grown by
slow sublimation at 25 ꢁC/10ꢁ2 mmHg. Diffraction
data were collected at ꢁ70 ꢁC with an automatic dif-
fractometer ENRAF-NONIUS CAD4 by the x-scan
method in the range 3.0 6 h 6 28ꢁ using graphite-
˚
cis-VI2(dme)2 [1l] was obtained as a green solid (80%
yield, IR and elemental analysis) by a similar procedure.
monochromatized Mo Ka (k = 0.71073 A) radiation.
Crystal data are reported in Table 3. The structure
model was obtained by conventional heavy atom
methods [51], completed by Fourier difference synthe-
ses, and refined with full-matrix least-squares on F2
[52]. Hydrogen atoms were calculated in idealized
positions and allowed to ride on their carbon atoms
with freely refined isotropic displacement parameters.
Convergence was reached for 5282 reflections and
391 variables at wR2 = 0.1398 (all data), R1 = 0.0540
[observations with I > 2r(I)]. Maxima and minima
from a final Fourier map were 0.394 and ꢁ0.449
4.3.3. CH3COOH
V(g6-1,3,5-Me3C6H3)2 (2.23 g, 7.6 mmol) was
added to glacial acetic acid (44.7 g, 7.4 mol). An exo-
thermic reaction took place with formation of a pale
green solid. After 30 min stirring at room tempera-
ture, the suspension was filtered and the solid was
washed with heptane (3 · 5 mL) and dried in vacuo
at room temperature affording 1.616 g (93% yield)
of V(O2CCH3)3 in the form of a pale green, mois-
ture-sensitive solid almost insoluble both in polar
and non-polar organic solvents. Anal. Calc. for
C6H9O6V: C, 31.6; H, 4.0; V, 22.3. Found: C, 31.0;
H, 4.0; V, 23.1%. IR (PCTFE and Nujol mull)
~m=cmꢁ1: 2988 w, 2934 w, 1753 ms, 1548 vs, 1452 vs,
1422 s, 1170 s, 1029 s, 869 s, 663 vs, 428 s, 493 ms.
vMcorr ¼ 2928 ꢃ 10ꢁ6 cgsu; diamagnetic correction =
ꢁ101 · 10ꢁ6 cgsu; leff (296 K) = 2.64 BM.
e Aꢁ3
.
Table 3
Crystal data and parameters of the structure solution of V(F6acac)3
and [Cr(g6-MeC6H5)2][TiCl4(THF)2]
Empirical formula
Formula weight
Crystal system
C15H3F18O6V
672.11
C22H32Cl4CrO2Ti
570.18
Triclinic
Monoclinic
P21/n
4.3.4. acacH
ꢀ
Space group
Unit cell dimensions
P1
V(g6-1,3,5-Me3C6H3)2 (1.95 g, 6.7 mmol) was dis-
solved in neat acetylacetone (29.25 g, 0.29 mmol). No
reaction was observed after 2 h stirring at room temper-
ature. After refluxing for 5 h, a brown solution was ob-
tained. The excess acetylacetone was removed in vacuo
at room temperature and the residue was suspended in
heptane (25 mL). The resulting suspension was filtered
and the solid was dried in vacuo at room temperature
and identified as V(acac)3 [24a,24c] (1.67 g, 73% yield)
from analytical (C, H, and V analysis) and spectroscopic
data (IR spectroscopy). vMcorr ¼ 3534 ꢃ 10ꢁ6 cgsu; dia-
magnetic correction = ꢁ 101 · 10ꢁ6 cgsu; leff (296
K) = 2.90 BM.
˚
a (A)
8.824(2)
13.167(3)
19.245(5)
90
8.072(2)
8.182(2)
˚
b (A)
˚
c (A)
10.192(3)
69.916(5)
79.924(5)
88.993(5)
621.8(3)
a (ꢁ)
b (ꢁ)
c (ꢁ)
91.90(2)
90
3
˚
V (A )
2234.8(9)
4
1.998
Z
1
1.523
1.205
Dcalc (Mg mꢁ3
l (mmꢁ1
Index ranges
)
)
0.626
0 6 h 6 11,
0 6 k 6 16,
ꢁ25 6 l 6 25
5601
ꢁ10 6 h 6 10,
ꢁ10 6 k 6 10,
ꢁ13 6 l 6 13
7850
Reflections collected
Independent reflections (Rint
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
)
5282 (0.020)
None
2717 (0.059)
Empirical
2717/0/140
1.035
4.3.5. F6acacH
5282/0/391
1.003
V(g6-1,3,5-Me3C6H3)2 (0.369 g, 1.27 mmol) was dis-
solved in heptane (25 mL) and treated with F6acacH
(0.79 g, 3.80 mmol) at room temperature. An immediate
reaction took place with formation of a dark solid in a
pale green solution. The suspension was filtered and
Final R indices [I > 2r(I)]
R1 = 0.0540,
wR2 = 0.1262
R1 = 0.1231,
wR2 = 0.1398
R1 = 0.0422,
wR2 = 0.0865
R1 = 0.0644,
wR2 = 0.1057
R indices (all data)

F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
3329
4.4. Reactivity of Nb(g6-1,3,5-Me3C6H3)2
1607 s, 1567 m, 1542 m, 1362 m, 1201 br, 1043 w,
969 s, 901 m, 740 w, 661 w. vMcorr ¼ 331 ꢃ 10ꢁ6 cgsu;
diamagnetic correction = ꢁ246 · 10ꢁ6 cgsu; leff (295
K) = 0.89 BM.
4.4.1. CPh3Cl
After dissolving Nb(g6-1,3,5-Me3C6H3)2 (0.573 g, 1.7
mmol) in DME (25 mL), a solution of CPh3Cl (1.470 g,
5.2 mmol) in DME (25 mL) was added dropwise. The
colour of the solution changed from red to orange-
yellow to brown followed by the formation of a brown
precipitate. The brick-red solid was filtered, washed with
heptane (2 · 5 mL), dried in vacuo and identified as
NbCl3(DME)0.8. Anal. Calc. for C3.2H8Cl3NbO1.6: Cl,
39.2; Nb, 34.2. Found: Cl, 38.7; Nb, 34.8%.
4.4.5. Preparation of Nb(F6acac)3 from NbCl3(DME)1.3
and Tl(F6acac)
A suspension of NbCl3(DME)1.3 (0.415 g, 1.31
mmol) in heptane (100 mL) was added of Tl(F6acac)
(1.61 g, 3.83 mmol). A pale yellow solid in a blue-
green solution was obtained after 48 h stirring at
room temperature. The solid was eliminated by filtra-
tion, and the solution was dried in vacuo affording
Nb(F6acac)3 (0.17 g, 18% yield) whose IR spectrum
was superimposable to that of the compound obtained
as described in Section 4.4.4.
4.4.2. CF3COOH
A solution of CF3COOH (7 mL, 1.2 mM in heptane)
was diluted with toluene (50 mL), Nb(g6-1,3,5-
Me3C6H3)2 (0.678 g, 2.0 mmol) was added. Immediate
reaction was observed with colour change from red to
brown-green. After stirring overnight, an abundant
mustard solid was filtered, washed with toluene (2 · 5
mL) and dried in vacuo to afford the air-sensitive light
brown Nb(O2CCF3)3 (0.637 g, 72.6% yield). Anal. Calc.
for C6F9NbO6: C, 16.7; H, 0.0; Nb, 21.5. Found: C,
16.2; H, 0.1; Nb, 20.5%. IR (PCTFE and Nujol mull)
4.5. Reactivity of Cr(g6-MeC6H5)2
4.5.1. TiCl4
To a brown-yellow solution of Cr(g6-MeC6H5)2
(0.710 g, 3 mmol) in heptane, TiCl4 (0.35 mL, 3 mmol)
was slowly added. Immediately, the solution turned to
a bulky grey-green suspension; which was filtered. The
solid was washed with heptane (2 · 10 mL) and dried
in vacuo. After contacting with THF (60 mL), the solid
turned its colour to bright yellow in a blue-green solu-
tion. The solid was filtered, washed with THF (2 · 5
mL) and dried in vacuo, obtaining 1.11 g (65% yield)
of [Cr(g6-MeC6H5)2][TiCl4(THF)2]. Anal. Calc. for
C22H32Cl4CrO2Ti: C, 46.3; H, 5.7; Cl, 24.9. Found: C,
m=cmꢁ1: 1646 s, 1635 ms, 1460 mw, 1205 s, 967 m, 857
~
w, 726 m.
4.4.3. acacH
Nb(g6-1,3,5-Me3C6H3)2 (0.584, 1.72 mmol) was dis-
solved in toluene (50 mL) and the resulting blood-red
solution was added of acacH (0.54 mL, 5.3 mmol) and
the reaction mixture was stirred overnight. After this
time, the resulting golden solution was concentrated un-
der reduced pressure until an oily consistency was
reached and heptane (50 mL) was added: a grey solid
precipitated out, which was filtered, washed with hep-
tane (2 · 5 mL) and dried in vacuo. After workup, grey
Nb(O)(acac)2 (0.370 g, 70% yield) was isolated and char-
acterized by IR and elemental analysis. Anal. Calc. for
C10H14NbO5: C, 39.1; H, 4.6; Nb, 30.3. Found: C,
46.0; H, 5.3; Cl, 25.1%. IR (Nujol) m=cmꢁ1: 3059 m,
~
2982 w, 1495 w, 1441 m, 1383 w, 1339 w, 1055 w,
1039 m, 1018 vs, 993 w, 860 vs, 818 vs, 683 m.
vMcorr ¼ 2.44 ꢃ 10ꢁ3 cgsu,
diamagnetic
correction =
ꢁ344 · 10ꢁ6 cgsu, leff (299 K) = 2.45 BM.
The compound [Cr(g6-MeC6H5)2][TiCl4(THF)2] was
also obtained by the following method. The chloride
[Cr(g6-MeC6H5)2]Cl (0.148 g, 0.54 mmol) was sus-
pended in THF (25 mL) and TiCl3(THF)3 (0.211 g,
0.57 mmol) was added. An immediate reaction was ob-
served and the orange suspension quickly changed to a
blue-green one: after 30 min stirring, the reaction mix-
ture was filtered, obtaining a yellow solid that, after
washing with heptane and drying in vacuo, was identi-
fied as [Cr(g6-MeC6H5)2][TiCl4(THF)2] (0.226 g, 72.6%
yield) by comparison of its IR spectrum with that of
the compound reported above.
39.5; H, 5.4; Nb, 29.0%. IR (Nujol) m=cmꢁ1: 1689 m,
~
1592 s, 1530 s, 1278 m, 1146 m, 1018 w, 930 br,s, 837
s, 661 m. The liquid collected in a cold trap during the
evaporation of the original solution was shown (GC–
MS) to contain pentan-2-one.
4.4.4. F6acacH
F6acacH (0.7 mL, 4.9 mmol) was added to a blood-
red solution of Nb(g6-1,3,5-Me3C6H3)2 (0.544 g, 1.63
mmol) in heptane (50 mL). As soon as the b-diketone
was added, a blue-green solid precipitated out. After
2 h stirring the suspension was filtered. The resulting
blue-green Nb(F6acac)3 was dried in vacuo (0.787 g,
67% yield), Anal. Calc. for C15H3F18NbO6: C, 25.2;
H, 0.4; Nb, 13.0. Found: C, 24.7; H, 1.2; Nb,
4.5.2. Crystal structure of [Cr(g6-MeC6H5)2]
[TiCl4(THF)2]: solution and refinement
Yellow tablets were obtained by slow cooling (243 K)
of a THF/acetonitrile (1:1) solution. Data were collected
˚
at 110 K with Mo Ka radiation (k = 0.71073 A, graphite
monochromator) on a Bruker D8 goniometer with a
SMART APEX CCD area detector on a crystal of
14.0%. IR (PCTFE and Nujol) m=cmꢁ1: 3152 mw,
~

3330
F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
approximate dimensions 0.18 · 0.18 · 0.03 mm. Crystal
data are reported in Table 3. 7850 reflections were col-
lected with the x-scan method in the range
2.16ꢁ 6 h 6 26.99ꢁ. An empirical absorption correction
(minimum transmission 0.8124, maximum transmission
0.9648) was applied with SADABS [53]. After merging,
2717 independent reflections remained for structure
solution by direct methods [51]. The structure model
was completed by Fourier difference syntheses and re-
fined by full-matrix least-squares on F2 [52]. Conver-
gence was reached for 2717 reflections and 140
variables at agreement factors of wR2 = 0.1057 (all
data), R1 = 0.0422 [observations with I > 2r(I)]. Maxi-
mum and minimum from a final Fourier map were
4.6. Reactivity of Mo(g6-MeC6H5)2
4.6.1. TiCl4
To a well-stirred solution of Mo(g6-MeC6H5)2
(0.463 g, 1.6 mmol) in heptane (50 mL), TiCl4 (0.2
mL, 1.6 mmol, in 5 mL heptane) was added dropwise.
Immediately, the solution became cloudy and changed
to a bulky suspension within 5 min. The solid was fil-
tered, washed with heptane, dried in vacuo and then
treated with THF (50 mL). The resulting suspension
was stirred overnight and the solid was recovered by
filtration. After drying in vacuo, [Mo(g6-MeC6H5)2]
[TiCl4(THF)2] (0.206 g, 20.6% yield) was isolated as
a green microcrystalline solid. Anal. Calc. for
C22H32Cl4MoO2Ti: C, 43.0; Br, 5.2; Cl, 23.1. Found:
C, 43.5; H, 4.7; Cl, 22.6%. IR (Nujol) m=cmꢁ1: 3060
w, 1020 m, 862 m, 721 m, 669 m.
0.464 and ꢁ0.396 eAꢁ3
.
~
4.5.3. CPh3X, X = Br, Cl
Only the reaction with CPh3Cl is described in detail,
that with CPh3Br being conducted in a similar manner.
A solution of CPh3Cl (0.751 g, 2.7 mmol) in 10 mL of
toluene was added into a toluene (25 mL) solution of
Cr(g6-MeC6H5)2 (0.635 g, 2.7 mmol). The yellow-
orange suspension immediately formed on addition of
the reagent was filtered and the orange product
[Cr(g6-MeC6H5)2]Cl was washed with toluene (2 · 10
mL) and dried in vacuo. (0.507 g, 69% yield) and iden-
tified by analytical and spectroscopic data.
4.6.2. Bromine
To a solution of Mo(g6-MeC6H5)2 (0.409 g, 1.5
mmol) in DME (125 mL), bromine (0.11 mL, 4.5 mmol)
in heptane (10 mL) was added dropwise. The resulting
cloudy solution changed from green to yellow to
brick-red in 2 h. The red-brown precipitate was recov-
ered by filtration, washed with heptane (2 · 5 mL) and
dried in vacuo (0.356 g, 60% yield). Anal. Calc. for
MoBr2(DME)1.5, C6H15Br2MoO3: Mo, 24.5; Br, 40.9.
Found: Mo, 24.1; Br, 39.6%. IR (Nujol) m=cmꢁ1: 1068 s,
~
1020 s, 970 m, 862 ms, 840 s.
4.5.4. CF3COOH
The compound Cr(g6-MeC6H5)2 (0.80 g, 3.4 mmol)
was dissolved in DME (100 mL) and an excess of tri-
fluoroacetic acid (1.3 mL, 17 mmol, in 25 mL DME)
was added to the resulting brown-yellow solution. The
mixture was refluxed for 12 h affording a dark green
solution. After concentration, an oily substance was
obtained which was added of heptane (50 mL). The
mixture was stirred for 5 days at room temperature
obtaining a green microcrystalline solid which gave
correct analytical data for Cr(CF3COO)3, with an IR
spectrum consistent with that of an authentic sample
[54].
4.6.3. acacH
Mo(g6-MeC6H5)2 (0.762 g, 2.7 mmol) was dissolved
in neat acacH (2 mL). The green colour of the starting
molybdenum complex quickly disappeared and a deep
brown-red solution was obtained. After 1 h stirring at
room temperature, excess pentan-2,4-dione was re-
moved in vacuo and heptane (15 mL) was added.
The mixture was cooled down to 243 K and filtered.
The product Mo(acac)3 (0.420 g, 38.9% yield) was
recovered and identified analytically and by compari-
son of its IR spectrum with that reported in the liter-
ature [39].
4.5.5. Bromine
The compound Cr(g6-MeC6H5)2 (0.702 g, 3 mmol)
was dissolved in DME (125 mL) and a solution of Br2
(0.24 mL, 4.5 mmol) in heptane (5 mL) was slowly
added. The reaction mixture turned immediately yellow
with formation of an abundant precipitate and then vio-
let after 2 h stirring. The suspension was filtered and the
solid washed with DME (2 · 5 mL). After drying in va-
cuo, CrBr3(DME)1.5 (1.164 g, 90% yield) was recovered
as a violet microcrystalline solid. Anal. Calc. for
C6H15Br3CrO3: Cr, 12.2; Br, 56.1. Found: Cr, 12.3; Br,
5. Supplementary material
Crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre, CCDC
263627 for V(F6acac)3 and CCDC 263628 for [Cr(g6-
MeC6H5)2][TiCl4(THF)2]. Copies can be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44 1223 336 033; email:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
56.0%. IR (Nujol) m=cmꢁ1: 1067 s, 1025 s, 981 s, 854 s,
~
838 s.

F. Calderazzo et al. / Journal of Organometallic Chemistry 690 (2005) 3321–3332
3331
[14] A powder diagram of this compound showed a low degree of
crystallinity with weak and broad diffraction lines.
[15] (a) G. Natta, G. Mazzanti, G. Pregaglia, Gazz. Chim. Ital. 89
(1959) 2065;
Acknowledgements
Thanks are due to the Ministero dellꢀIstruzione
`
dellꢀUniversita e della Ricerca (MIUR, Roma), Pro-
(b) H. Martin, F. Vohwinkel, Chem. Ber. 94 (1961) 2416;
(c) R. Giezynski, S. Dzierzgowski, S. Pasynkiewicz, J. Organomet.
Chem. 87 (1974) 295.
gramma di Ricerca Scientifica di Notevole Interesse
Nazionale 2004–2005 for financial support and Profes-
sor F.G.N. Cloke of the University of Sussex for
allowing M.V. to use the metal vapourization equip-
ment. M.V. thanks the European Community for a
Marie Curie fellowship at the School of Life Sciences,
University of Sussex at Brighton (UK).
[16] F. Calderazzo, R. Invernizzi, F. Marchetti, F. Masi, A.
Moalli, G. Pampaloni, L. Rocchi, Gazz. Chim. Ital. 123
(1993) 53.
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