Ligand-interchange reactions between M(iv) (M = Ti, V) oxide bis-acetylacetonates and halides of high-valent group 4 and 5 metals. A synthetic and electrochemical study

Article abstract of DOI:10.1039/c3dt51378e

The reactions of M′O(acac)₂ [M′ = Ti, V; acac = acetylacetonato anion] with equimolar amounts of MF₅ (M = Nb, Ta) in CH₂Cl₂ afforded Ti(acac)₂F₂, 1a, and [V(acac)₃][MF₆] (M = Nb, 4a; M = Ta, 4b), respectively. MOF₃ (M = Nb, 2a; M = Ta, 2b) were co-produced from MF ₅/TiO(acac)₂. The intermediate species [TaF ₄{OTi(acac)₂}₂][TaF₆], 3, was intercepted in the course of the formation of 1a from TiO(acac) ₂/TaF₅. NbCl₅ reacted with TiO(acac) ₂ yielding selectively the previously reported [NbO(acac)Cl ₂]_x, 5, and Ti₂(acac)₂(μ-Cl) ₂Cl₄, 6. Complex 6 was alternatively obtained from the addition of a two-fold excess of TiCl₄ to VO(acac)₂. The 1 : 1 reactions of TiX₄ (X = F, Cl) with TiO(acac)₂ in dichloromethane gave Ti(acac)₂X₂ (X = F, 1a; X = Cl, 1b) and TiOX₂ (X = F, 7a; X = Cl, 7b). The 1 : 1 combination of TiX ₄ (X = F, Cl) with VO(acac)₂ led to 1a,b and VOX ₂ (X = F, 8a; X = Cl, 8b). The μ-oxido compounds (C ₆F₅)₃B-O-M′(acac)₂ (M′ = Ti, V) underwent fragmentation by [PF₆]^- in chlorinated solvent, yielding POF₃, 9, and [B(C₆F₅) ₃F]^-, 10, according to NMR studies; 1a and V(acac) ₃⁺, respectively, were detected as the metal-containing species. Electrochemical studies were carried out aiming at the full characterization of the products and the observation of possible degradation pathways.

Full text of DOI:10.1039/c3dt51378e

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Ligand-interchange reactions between M(IV) (M = Ti, V)
oxide bis-acetylacetonates and halides of high-valent
group 4 and 5 metals. A synthetic and electrochemical
study†
Cite this: Dalton Trans., 2013, 42, 14168
Tiziana Funaioli,a Fabio Marchetti,*a Guido Pampalonia and Stefano Zacchinib
The reactions of M’O(acac)2 [M’ = Ti, V; acac = acetylacetonato anion] with equimolar amounts of MF5
(M = Nb, Ta) in CH2Cl2 afforded Ti(acac)2F2, 1a, and [V(acac)3][MF6] (M = Nb, 4a; M = Ta, 4b), respectively.
MOF3 (M = Nb, 2a; M = Ta, 2b) were co-produced from MF5/TiO(acac)2. The intermediate species
[TaF4{OTi(acac)2}2][TaF6], 3, was intercepted in the course of the formation of 1a from TiO(acac)2/TaF5.
NbCl5 reacted with TiO(acac)2 yielding selectively the previously reported [NbO(acac)Cl2]x, 5, and
Ti2(acac)2(μ-Cl)2Cl4, 6. Complex 6 was alternatively obtained from the addition of a two-fold excess of TiCl4
to VO(acac)2. The 1 : 1 reactions of TiX4 (X = F, Cl) with TiO(acac)2 in dichloromethane gave Ti(acac)2X2 (X =
F, 1a; X = Cl, 1b) and TiOX2 (X = F, 7a; X = Cl, 7b). The 1 : 1 combination of TiX4 (X = F, Cl) with VO(acac)2
led to 1a,b and VOX2 (X = F, 8a; X = Cl, 8b). The μ-oxido compounds (C6F5)3B–O–M’(acac)2 (M’ = Ti, V)
underwent fragmentation by [PF6]− in chlorinated solvent, yielding POF3, 9, and [B(C6F5)3F]−, 10, accord-
ing to NMR studies; 1a and V(acac)3+, respectively, were detected as the metal-containing species. Electro-
chemical studies were carried out aiming at the full characterization of the products and the observation
of possible degradation pathways.
Received 27th May 2013,
Accepted 26th July 2013
DOI: 10.1039/c3dt51378e
www.rsc.org/dalton
to our findings, the high reactivity of MX5 towards O-contain-
ing species frequently renders the O-to-metal coordination just
Introduction
In principle, the direct combination of a metal-containing the preliminary step of subsequent fragmentation of the
Lewis-base fragment of the type [M–O] with an oxophilic metal oxygen substrate. Thus, oxygen abstraction by the metal centre
species (Lewis acid, M′) affords a [M–O–M′] adduct. This strat- has been observed in a number of cases, resulting in the for-
egy has been employed for the preparation of O-bridged mation of the oxido-halide unit [MOX3] (X = Cl, Br).10 Interest-
[M–O–M′] derivatives,1 composed of either two transition metal ingly, when the O-abstraction reaction is carried out with an
centres2 or a transition metal adjacent to a main group opportune stoichiometry, stable oxido-bridged dinuclear
element such as boron3 and phosphorus.4 [M–O–M′] com- adducts of the formula X5M–Ο–MX3(O−O) [M = Nb, Ta; X = Cl,
pounds are potential intermediates in oxygen atom transfer Br; O–O = MeO(CH2)2OMe, MeOCH2CO2Me, (MeCO2)CHvCH-
reactions,5 including the synthesis of diverse metal derivatives (CO2Me), CH2(CO2Me)2] are obtained. Spectroscopic and X-ray
employed in homogeneous catalysis.6
evidence suggests that the latter dinuclear compounds could
Recently, we have been involved in the study of the reactivity be viewed as coordination adducts of the inorganic oxygen
of niobium and tantalum pentahalides, MX5 (M = Nb, Ta; X = ligand OvMX3(O−O) with MX5.
F, Cl, Br, I),7,8 with potential oxygen donor ligands.9 According
In the light of this preface, we became interested in the
reactivity of MX5 with coordination complexes containing a
metal–oxygen moiety. Our choice fell on M′O(acac)2 (M′ =
Ti,11,12 V; acac = acetylacetonato), on account of their easy
availability and their proved capability to bind Lewis acidic
species.13 As a natural extension, the group 4 tetrahalides TiX4
(X = F, Cl) were included in the investigation.14
We show herein that the reactions of M′O(acac)2 with high-
valent metal halides occur with highly selective interchange of
ligands between the different metal centres. Evidence will be
aUniversity of Pisa, Dipartimento di Chimica e Chimica Industriale,
Via Risorgimento 35, I-56126 Pisa, Italy. E-mail: fabmar@dcci.unipi.it;
http://www.dcci.unipi.it/~fabmar/; Tel: +39 050 2219245
bUniversity of Bologna, Dipartimento di Chimica Industriale “Toso Montanari”,
Viale Risorgimento 4, I-40136 Bologna, Italy
†Electronic supplementary information (ESI) available: Infrared spectra
(solid state) of TiO(acac)2, VO(acac)2, [TaF4{OTi(acac)2}2][TaF6], 3, [V(acac)3][MF6]
(M = Nb, 4a; M = Ta, 4b). CCDC 782632. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c3dt51378e
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provided for the establishment of metal–O–M′ interaction in
the course of those reactions proceeding with oxygen transfer.
The Electrochemistry section will describe the electrochemical
behaviour of the previously reported compounds M′O(acac)2
(M′ = Ti, V), (C6F5)3B–O–M′(acac)2 and 1a,b, and of the new
ones 3 and 4a,b. Our outcomes supply novel, possible pro-
cedures for the synthesis of mixed-ligand early transition
metal derivatives.
Table 1 Selected bond lengths (Å) and angles (°) for Ti(acac)2F2·0.5C2H4Cl2
(1a·0.5C2H4Cl2)
F(1)–Ti(1)
O(1)–Ti(1)
O(3)–Ti(1)
C(1)–C(2)
C(2)–C(3)
C(4)–O(2)
C(6)–C(7)
C(7)–C(8)
C(9)–O(4)
1.799(4)
1.954(5)
2.004(5)
1.503(10)
1.389(11)
1.260(9)
1.501(10)
1.405(11)
1.271(8)
F(2)–Ti(1)
O(2)–Ti(1)
O(4)–Ti(1)
C(2)–O(1)
C(3)–C(4)
C(4)–C(5)
C(7)–O(3)
C(8)–C(9)
C(9)–C(10)
1.806(4)
2.006(5)
1.938(5)
1.295(8)
1.387(11)
1.498(10)
1.272(8)
1.390(10)
1.487(10)
C(2)–O(1)–Ti(1)
C(7)–O(3)–Ti(1)
F(1)–Ti(1)–F(2)
F(2)–Ti(1)–O(4)
F(2)–Ti(1)–O(1)
F(1)–Ti(1)–O(3)
O(4)–Ti(1)–O(3)
F(1)–Ti(1)–O(2)
O(4)–Ti(1)–O(2)
O(3)–Ti(1)–O(2)
134.2(5)
132.7(4)
96.3(2)
97.9(2)
88.0(2)
171.7(2)
83.4(2)
89.9(2)
89.6(2)
84.2(2)
C(4)–O(2)–Ti(1)
C(9)–O(4)–Ti(1)
F(1)–Ti(1)–O(4)
F(1)–Ti(1)–O(1)
O(4)–Ti(1)–O(1)
F(2)–Ti(1)–O(3)
O(1)–Ti(1)–O(3)
F(2)–Ti(1)–O(2)
O(1)–Ti(1)–O(2)
133.2(5)
135.9(5)
90.64(19)
97.1(2)
169.7(2)
90.2(2)
88.2(2)
170.1(2)
83.6(2)
Results and discussion
Synthesis and characterization
The group 5 metal pentafluorides MF5 (M = Nb, Ta) reacted
with TiO(acac)2 in chlorinated solvent affording Ti(acac)2F2,
1a, and MOF3 (M = Nb, 2a; M = Ta, 2b) in good yields, see eqn
(1). The previously reported compound 1a15 has been identi-
fied by elemental analysis and NMR spectroscopy (see the
Experimental section for details), and characterized by X-ray
diffractometry (Fig. 1 and Table 1).16 Evidence for the for-
mation of 2a,b has been collected by IR spectroscopy (band
around 1000 cm−1, ref. 17) and analysis of the metal content
(see the Experimental section).
from Ti (668 kJ mol−1) to Nb (726.5 kJ mol−1) and Ta (839 kJ
mol−1).21
It is reasonable that the interaction between MF5 and TiO-
(acac)2 begins with the formation of a [M–O–Ti] adduct (see
the Introduction section). Such an adduct could be isolated in
good yield in the reaction involving TaF5, and is thus identi-
fied as [TaF4{OTi(acac)2}2][TaF6], 3 (Scheme 1). It is noteworthy
that a good number of [TaF4(L)x][TaF6] complexes (x = 2–4)
have been described as obtained by the addition of O-9,22 or
S-donors23 to TaF5. The molar conductivity value of 3 (in CH2Cl2
solution) manifests the ionic nature.9,22b In addition, the 19F
NMR spectrum clearly shows the resonance due to the [TaF6]−
anion at a typical chemical shift (δ = 38.4 ppm);9,22,23 instead
no 19F signal has been found for the [TaF4]+ moiety, in analogy
with previous findings for similar salts.24 The 1H and 13C NMR
spectra of 3 (in CD2Cl2) contain the resonances of the biden-
tate acac moieties shifted to a high frequency with respect to
those seen in TiO(acac)2,25 as a result of the TiO−Ta bond for-
mation. The solid state IR spectrum displays a single carbonyl
absorption at 1530 cm−1 (Fig. S3 within ESI†). Based on a com-
parison of the IR spectra of TiO(acac)2 and 3 (see Fig. S3 and
S1;† the Ti–O–Ti stretching frequency in TiO(acac)2 falls at
817 cm−1 26), it may be concluded that the titanyl moiety has
comparable bond order in such compounds.11 Further evi-
dence for the formation of 3 will be discussed in the Electro-
chemistry section. Compound 3 belongs to the rare family
of titanyl-Lewis acid addition compounds, which includes
(C6F5)3B–O–Ti(acac)2.13
MF5 þ TiOðacacÞ2 ! TiðacacÞ2F2 þ
MOF3
ð1Þ
1a
ðM¼Nb; 2a; Ta; 2bÞ
It should be noted that the procedures available in the lit-
erature for the preparation of 2a,b usually require severe
conditions.17,18
Complex 1a displays a distorted octahedral geometry with
the F-ligands in mutual cis-position, as previously found in
15b,19
Ti(acac)2Cl2
and in the closely related complexes cis-Ti-
[κ2-RC(O)CHC(O)R′]2Cl2 (R = Me, R′ = Ph; R = R′ = tBu, Ph).20
The reaction described in eqn (1) is the result of selective
interchange of ligands between different metal centres: the
oxygen transfer from TiO(acac)2 to MF5 is counterbalanced by
two fluorines following the opposite direction. This fact
reflects the increase of the metal–oxygen bond energy on going
Fig. 1 Molecular structure of Ti(acac)2F2·0.5C2H4Cl2, 1a·0.5C2H4Cl2 (dichloro-
ethane solvate not shown). Displacement ellipsoids are at the 50% probability
level.
Scheme 1 Titanium to tantalum oxygen transfer.
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Scheme 2 The reactions of MF5 with VO(acac)2.
Scheme 4 Reactions of TiX4 with VO(acac)2.
Compound 3 is not stable in CH2Cl2 solution at room temp-
erature, slowly converting into 1a and TaOF3 (Scheme 1). This
fact prevented X-ray quality crystals from being obtained.
Our study went on with the reactions of MF5 with VO(acac)2
in dichloromethane, leading to the clean isolation of the com-
plexes [V(acac)3][MF6] (M = Nb, 4a; M = Ta, 4b) in good yields
(Scheme 2). A nonsoluble material was obtained as a co-
product, whose identity could not be ascertained (see the
Experimental section).
The study of the reactivity of M′O(acac)2 (M′ = Ti, V) with
metal halides was extended to titanium tetrahalides. Thus the
1 : 1 molar reactions of TiO(acac)2 with TiX4 (X = F, Cl) gave Ti-
(acac)2X2 (X = F, 1a; X = Cl, 1b15,31) and TiOX2 (X = F, 7a,32 X =
Cl, 7b33) in high yields, see eqn (2). 1 and 7 could be efficiently
separated from each other, in the respective cases, by exploit-
ing their different solubilities in the reaction medium. Com-
pound 1b was crystallized from pentane/CH2Cl2 at low
Although the hexacoordinated [V(acac)3]+ cation27 and the
[MF6]− anions9,22b are known species, the ionic derivatives 4a,
b are new compounds that have been characterized by various
techniques (see the Experimental section). A salient feature of
the solid state IR spectra (Fig. S4 and S5†) is the disappearance
of the absorption due to the [VvO] moiety as found in the
parent compound VO(acac)2 (ν = 992 cm−1, see Fig. S2†). The
absorption related to the carbonyl moieties has been recog-
1
temperature and characterized by elemental analysis, H-NMR
spectroscopy (CDCl3 solution; resonances at 6.01, 2.17 ppm)
and by comparison of the obtained X-ray data with those de-
posited with the Cambridge Crystallographic Data Centre
(Refcodes QIHXEX, ZZZEBO).30
TiX4 þ TiOðacacÞ2 ! TiðacacÞ2X2 þ TiOX2 ðX ¼ F; ClÞ ð2Þ
7a;b
1a;b
1
nized around 1520 cm−1. The H and 13C NMR spectra of 4a,b
We moved to examine the 1 : 1 reaction of VO(acac)2 with
TiX4 (X = F, Cl). The formation of the hypothetical vanadium
derivatives V(acac)2X2 (X = F, Cl34) was not observed (Scheme 4,
pathway a). Instead 1a,b were selectively obtained and identi-
fied (Scheme 4, pathway b); in addition, the oxido-halides
VOX2 (X = F, 8a;35 X = Cl, 8b36) were recognized as co-products
in the respective cases. These outcomes indicate that selective
interchange of X and acac ligands (Scheme 4, pathway b)
rather than oxygen transfer (Scheme 4, pathway a) takes place
between the metal centres. The same mechanism might be
operative in the reactions indicated in eqn (2).
When the reaction of TiCl4 with VO(acac)2 was performed
by using a Ti/V > 2 molar ratio, the crystalline, dinuclear
compound 650 was recovered in good yield in the place of
Ti(acac)2Cl2 [eqn (3)]. VOCl2 was found to be the reaction
co-product.
(in CDCl3) exhibit a single set of resonances due to the equi-
valent acac ligands; otherwise the 19F NMR spectra clearly
show the typical resonances related to the MF6 anions. 4a,b
are well-soluble in chlorinated solvents, conferring an intense
violet colour on their solutions, and can be easily isolated in
the solid state as microcrystalline materials. X-ray analysis was
carried out on 4b, confirming the identity of the compound;28
however, severe twinning prevented accurate determination of
geometric parameters.
−
The 1 : 1 molar reaction of NbCl5 with TiO(acac)2 occurs
with selective transfer of oxygen ligands from Ti to Nb,
accompanied by reverse Cl migration. Hence the compounds
[NbO(acac)Cl2]x, 5,29 and Ti2(acac)2(μ-Cl)2Cl4, 6, which were
prepared in the past by different procedures, have been recog-
nized as the major products of the reaction (Scheme 3). The
niobium(V) compound 5 was clearly identified by elemental
analysis and by the IR (solid state) absorptions at 1545 and
815 cm−1, due respectively to the CvO and the Nb–O stretch-
ing vibrations.29 The titanium(IV) derivative 6 was crystallized
2TiCl4 þ VOðacacÞ2 ! Ti2ðacacÞ2ðμ-ClÞ2Cl4 þ VOCl2
ð3Þ
8b
6
1
from pentane/CH2Cl2 at low temperature and identified by H
Electrochemistry
NMR (resonances at 6.00 and 2.19 ppm), IR (intense band at
1554 cm−1) and by comparison of the collected X-ray data with
those deposited with the Cambridge Crystallographic Data
Centre (Refcode CLACIT).30
To the best of our knowledge, no cyclic voltammetric study has
been performed on TiO(acac)2 to date, while the literature data
related to VO(acac)2 are rather sparse.37 Therefore we decided
to start our investigation with the study of the CV behaviour of
M′O(acac)2 (M′ = Ti, V).
We found that TiO(acac)2 underwent a reduction process at
−1.79 V in CH2Cl2 solution in the presence of [NnBu4][PF6] as a
supporting electrolyte (Table 2).38 Instead the vanadium(IV)
analogue underwent a reversible one-electron oxidation at
+0.66 V, and one irreversible reduction at −2.32 V (vs. FeCp2)39
(Table 2). Analysis of the cyclic voltammetric response with
Scheme 3 Titanium to niobium oxygen ligand transfer.
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Table 2 Formal electrode potentials (V, vs. FeCp2a) and peak-to-peak separ-
ations (mV) in 0.2 M [NnBu4][PF6]–CH2Cl2 solution for the cited redox changes
b
b
b
E°′
ΔEp
E°′
ΔEp
E°′
ΔEp
Oxidation
Reduction
TiO(acac)2
VO(acac)2
(C6F5)3B–O–V(acac)2
−1.79c 66
−2.32d
+0.66 70
−0.90c 90
−0.56c 70
−2.36d
−2.40d
−2.02
e
(C6F5)3B–O–Ti(acac)2
[V(acac)3]+
+0.24
65
90
[TaF4{OTi(acac)2}2]+
−0.57c 62
−1.29c 92
−0.69c 70
−2.37d
1a
1bf
a Under the cited experimental conditions, the redox process relative to
the ferrocene/ferrocenium couple was observed at +0.39 V vs. SCE.
Scheme 5 Reactivity of (C6F5)3B–O–M’(acac)2 (M’ = Ti, V) with [NEt4][PF6].
b Measured at 0.1 V s−1 c Partially chemically-reversible process. d Peak
.
potential value for irreversible processes. e In [NnBu4][BPh4]–CH2Cl2
solution. f In [NnBu4][ClO4]–CH2Cl2 solution.
formed [(C6F5)3B−O−M′(acac)2] frames are susceptible to reac-
tion with [PF6]− (Scheme 5). Thus NMR experiments were
carried out in order to shed light on this point. According to
the NMR outcomes, O/F interchange takes place between
[(C6F5)3B−O−M′(acac)2] and [PF6]−, cleanly affording
[B(C6F5)3F]−, 9,41 and POF3, 10.42 In addition, the reaction of
(C6F5)3B–O–Ti(acac)2 with [PF6]− selectively produces 1a
(detected by NMR analysis) in high yield, while the cation
[V(acac)3]+ has been recognized (NMR, UV-Vis) from (C6F5)3B–O–
V(acac)2/[PF6]−. Accordingly, the voltammetric profile of the
mixture (C6F5)3B–O–V(acac)2/[NnBu4][PF6] displayed two dis-
tinct one-electron reductions at +0.24 V and at −2.02 V, with
features of chemical reversibility in the CV time scale. Such
reductions have been attributed to V(IV)/V(III) and V(III)/V(II)
couples.43 Coherently, the same pattern, due to the [V(acac)3]+
cation, has been found for [V(acac)3][MF6], 4a,b, in CH2Cl2–
[NnBu4][PF6].
scan rates varying between 0.02 and 1.00 V s−1 has confirmed
the electrochemically-reversible nature of the reduction of TiO-
(acac)2 (the peak-to-peak separation ΔEp approaches the
theoretical value of 59 mV40). This reduction is complicated by
a subsequent chemical reaction (ipa/ipc = 0.8 at 0.10 V s−1).
In view of the hypothetical bonding similarities between
the stable [B−O−M′] compounds (C6F5)3B–O–M′(acac)2 (M′ =
Ti, V)13 and the possible intermediates formed in the reactions
between M′O(acac)2 and metal halides, we decided to examine
the electrochemical behaviour of (C6F5)3B–O–M′(acac)2.
Green crystals of (C6F5)3B–O–V(acac)2 dissolved in a CH2Cl2
solution of [NnBu4][PF6] (supporting electrolyte) giving a deep-
violet solution. The latter exhibited a voltammetric profile with
two reversible monoelectronic reductions at +0.24 and −2.02 V.
Otherwise the yellow titanium species (C6F5)3B–O–Ti(acac)2
dissolved in CH2Cl2–[NnBu4][PF6] to give a yellow solution. The
voltammetric profile of the latter solution did change in some
When freshly prepared 3 was dissolved in CH2Cl2–[NnBu4]-
[PF6], the voltammetric profile of the solution changed with
time (Fig. 2a), in accordance with the results reported in the
previous section (Scheme 1). More precisely, the CV recorded
minutes: the initial reversible reduction at −0.56 V (ipa/ipc
=
0.94 at 0.10 V s−1) and the irreversible one at −2.40 V pro-
gressively disappeared, while a new reduction wave at −1.29 V
became evident.
These outcomes indicate that the electrolyte [NnBu4][PF6] is
not inert towards (C6F5)3B–O–M′(acac)2; therefore, we con-
sidered [NnBu4][BPh4] as an alternative electrolyte. Hence
green (C6F5)3B–O–V(acac)2 dissolved in CH2Cl2–[NnBu4][BPh4]
to give a light-green solution. Subsequent cyclic voltammetry
showed one reversible reduction process at −0.90 V (compli-
cated by a subsequent chemical reaction, ipa/ipc = 0.8 at 0.10 V
s−1), followed by an irreversible reduction at −2.36 V. These
reductions were no longer appreciable after some minutes.
The light-yellow solution of (C6F5)3B–O–Ti(acac)2 in [NnBu4]-
[BPh4]–CH2Cl2 showed only irreversible reduction processes at
potentials lower than −1.5 V. Based on this evidence, we have
assigned the reductions at −0.90 V and at −0.56 V to (C6F5)3B–
O–V(acac)2 and (C6F5)3B–O–Ti(acac)2, respectively (Table 2).
We are able to conclude that the coordination to the
strongly electron-deficient B(C6F5)3 enhances the tendency of
Fig. 2 Cyclic voltammograms recorded at the Pt electrode in CH2Cl2 solution
of: (a) 3 immediately after dissolution (black), after 10’ (red), after 20’ (blue); (b)
M′O(acac)2 (M = Ti, V) to be reduced. Furthermore, the so 1a. Supporting electrolyte: [NnBu4][PF6] (0.2 mol dm−3); scan rates = 0.1 V s−1
.
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immediately after the dissolution showed
a
reversible formed by F− abstraction from the supporting electrolyte. A
reduction at −0.57 V (ipa/ipc = 0.88 for scan rate ν = 0.1 V s−1), previous investigation on the chemistry of 1b demonstrated
accompanied by an irreversible reduction at a more negative the possibility of easy, partial or complete replacement of
potential (−2.37 V). Such electrochemical behaviour represents chloride ligands in the presence of a potential fluoride
a significant proof for the existence of the [Ta−O−Ti] skeleton source.46 It has to be noted that the voltammetric response of
in 3; in fact, a very similar CV is exhibited by the [B−O−Ti] 1b in CH2Cl2–[NnBu4][ClO4] solution remained unchanged for
adduct (C6F5)3B–O–Ti(acac)2 (Table 2). The absence of pro- several hours and exhibited only the reduction at −0.69 V.
cesses involving the [TaF6]− anion in 3 is consistent with the
We attempted to detect short-lived M–O–V adducts in the
observation that a solution of [S(NMe2)3][TaF6]22b in CH2Cl2– course of the reactions of MF5 with VO(acac)2 (Scheme 2).
[NnBu4][PF6] showed no reduction peaks until the solvent dis- Cyclic voltammograms were collected immediately after the
charge occurring at ca. −2.6 V.44
mixing of the reagents in the electrochemical cell. A quick
The signals due to [TaF4{OTi(acac)2}2]+ decreased in inten- colour change of the solution from light-blue to deep-violet
sity within 20 minutes, while a new wave became evident at accompanied the dissolution of MF5, and the voltammetric
−1.29 V (Fig. 2a). This wave remained the only observable profile typical of [V(acac)3]+ was observed. This fact points out
redox process after some hours, and was attributed to 1a. In that oxygen transfer from vanadium to metal centre takes
fact the CV trace of 1a in the range +1.4 to −2.6 V is character- place readily, thus preventing the recognition of the redox
ized by one monoelectronic reduction process at −1.29 V, com- changes due to short-lived M–O–V adducts.
plicated by a subsequent chemical reaction (ipa/ipc = 0.84 for
scan rate ν = 0.1 V s−1), see Fig. 2b.
In order to verify the number of electrons involved in the
reduction process occurring at −1.29 V, a solution of 1a was
Conclusions
subjected to controlled potential Coulometry (Ew = −1.4 V). By In this paper, we have described the chemistry of titanium(IV)
monitoring the electrolysis progress with cyclic voltammetry, and vanadium(IV) oxide bis-acetylacetonates, M′O(acac)2, with
we noticed that the height of the cathodic peak at −1.29 V TiX4 (X = F, Cl), MF5 (M = Nb, Ta), and NbCl5, respectively. All
decreased in proportion to the advancement of Coulometry. the reactions, driven by thermodynamic factors, take place
Moreover a new anodic reversible peak at −0.58 V and a catho- with selective interchange of ligands between the different
dic irreversible peak at −2.4 V appeared. The wave corres- metal centres, and represent novel routes for the preparation
ponding to the reduction of 1a completely disappeared after of halo-acetylacetonato or oxido-halide complexes of group 4
consumption of 0.5 mol of electrons per mole of complex.
and 5 metals. The interchange of ligands is presumably
The blue colour of the solution and the appearance of the initiated by the formation of an oxido-bridged adduct, which
reversible oxidation at −0.58 V have suggested the formation of could be detected (Ta−O−Ti adduct) in the case of the reaction
a Ti(III) species; otherwise the irreversible reduction at −2.4 V between TaF5 and TiO(acac)2. This feature has found support
has been tentatively assigned to [Ti(acac)2F3]−. As a matter of in the fact that compounds M′O(acac)2 do not undergo oxygen
fact, a superimposable voltammetric profile in the negative loss in the presence of [PF6]−, unless they are preliminarily
scan (0/−2.6 V) was obtained when the mixture 1a/TASF (TASF, activated by coordination to a Lewis acid such as B(C6F5)3.
[(Me2N)3S][Me3SiF2], is a well-established F− transferer22b,45
was examined by CV under the same experimental conditions.
)
Electrochemical analyses have assisted in the charact-
erization of new compounds and have allowed the study of degra-
In other words, the reduction of 1a seems to occur accord- dation pathways. The electrochemical outcomes demonstrate
ing to Scheme 6: fluoride abstraction by 1a from the complex that the coordination of a Lewis acid to MO(acac)2 (M = Ti, V)
1a− presumably generates the Ti(III) complex Ti(acac)2F and enhances the tendency of the latter to be reduced. By a parallel
the hard to reduce Ti(IV) anion [Ti(acac)2F3]−. Attempts to study of the electrochemical behaviours of (C6F5)3B–O–Ti-
isolate these species for further characterization were (acac)2 and [TaF4{OTi(acac)2}2][TaF6], dissolved in CH2Cl2–
unsuccessful.
[NnBu4][PF6], the quick formation of Ti(acac)2F2 from the tan-
The voltammetric response of Ti(acac)2Cl2, 1b, in CH2Cl2– talum adduct has been ascertained. V-containing intermediate
[NnBu4][PF6] solution showed one reversible reduction at −0.69 products, analogous to [TaF4{OTi(acac)2}2][TaF6], could not be
V (ipa/ipc = 0.9 at a scan rate of 0.1 V s−1). The intensity of this recognized due to fast O-transfer. A detailed description of the
wave promptly decreased, while new reduction processes electrochemical behaviours of TiO(acac)2 and Ti(acac)2X2 (X =
became evident at −0.93 and −1.29 V. We have assigned the F, Cl) has been reported for the first time.
reduction at −1.29 V to the difluoride complex 1a and the
reduction at −0.93 V to the mixed halide Ti(acac)2ClF, both
Experimental section
General features
All of the manipulations of air and/or moisture sensitive com-
pounds were performed under an atmosphere of pre-purified
Scheme 6 Reduction of Ti(acac)2F2, 1a.
argon using standard Schlenk techniques. The reaction vessels
14172 | Dalton Trans., 2013, 42, 14168–14177
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Paper
were oven dried at 150 °C prior to use, evacuated (10−2 mmHg) cathodic limits of interest until no change in the charging
and then filled with argon. MX5 (M = Nb, Ta, X = F; M = Nb, current. The substrate was introduced to obtain a 1 mM solu-
X = Cl), TiX4 (X = F, Cl), M′O(acac)2 (M = Ti, V) and [(Me2N)3S]- tion, and voltammograms were recorded at a sweep rate of =
[Me3SiF2] (TASF) were commercial products (Sigma-Aldrich), 100 mV s−1. After several voltammograms were obtained on
stored under an argon atmosphere as received and used the substrate solution, a small amount of ferrocene was added,
without further purification. [NnBu4][PF6] (Fluka, puriss. elec- and the voltammogram was repeated. The E° values of the ana-
trochemical grade), [NnBu4][BPh4] (Sigma-Aldrich, 99%) and lyzed compounds were determined placing the E1/2 of the
[NnBu4][ClO4] (Fluka, puriss. electrochemical grade) were used ferrocene couple at 0.0 V.
as purchased. Ferrocene (FeCp2, Fc),47 (C6F5)3B–O–V(acac)2,13
and (C6F5)3B–O–Ti(acac)2 were prepared according to a lit- shaped cell with anodic and cathodic compartments separated
Controlled potential Coulometry was performed in an H-
13
erature method. Solvents were distilled before use under an by
a
sintered-glass disk. The working macroelectrode
argon atmosphere from appropriate drying agents. Infrared was a platinum gauze; a platinum spiral was used as the
spectra were recorded at 298 K either using an FT IR-Perkin- counterelectrode.
Elmer Spectrum One Spectrometer equipped with UATR
sampling accessories or using an FT IR-Perkin-Elmer Spectrum
Reactivity of MF5 (M = Nb, M = Ta) with TiO(acac)2
100 Spectrometer equipped with a CsI beam splitter. UV-Vis
(1) Synthesis of Ti(acac)2F2, 1a, and MOF3 (M = Nb, 2a;
spectra were recorded using a Perkin-Elmer Lambda EZ201 M = Ta, 2b). A solution of TiO(acac)2 (0.131 g, 0.500 mmol) in
spectrophotometer at 293 K. 1H, 13C and 19F NMR spectra were 1,2-dichloroethane (15 mL) was treated with MF5 (M = Nb, Ta;
recorded using a Varian Gemini 200BB instrument at 293 K, 0.500 mmol). The mixture was stirred at room temperature for
unless otherwise stated. Chemical shifts for 1H and 13C were 12 hours. An analogous outcome was obtained by performing
referenced to the non-deuterated aliquot of the solvent; chemi- the reaction at reflux temperature for 4 hours. The resulting
cal shifts for 19F were referenced to external CFCl3; chemical precipitate was filtered; thus the light-orange solution was
shifts for 31P were referenced to external H3PO4. Conductivity layered with heptane and stored at −30 °C. A yellow-orange
measurements were carried out on ca. 0.010 M CH2Cl2 solu- crystalline precipitate of Ti(acac)2F2, 1a15 (0.106 g, 75% yield),
tions using a Eutech Con 700 Instrument (cell constant = was obtained after 3 days. Compound 1a was identified by
1.0 cm−1), at 298 K.48 Carbon and hydrogen analyses were per- elemental analysis, NMR spectroscopy and X-ray diffracto-
formed using a Carlo Erba mod. 1106 instrument. The content metry. Anal. Calcd for C10H14F2O4Ti: C, 42.28; H, 4.97; Ti, 16.85.
of niobium and tantalum was analyzed as M2O5, obtained by Found (from the reaction with NbF5): C, 42.49; H, 4.63; Ti,
1
high temperature treatment of the solid sample with a HNO3 17.02. H NMR (CD2Cl2) δ 5.93 (s, 1 H, CH); 2.13 (s, 6 H, CH3)
solution, followed by calcination in a platinum crucible. The ppm. 13C{1H} NMR (CD2Cl2) δ 194.0 (CO); 107.0 (CH); 25.8
titanium content was determined spectrophotometrically by (CH3) ppm. 19F NMR (CD2Cl2) δ 231.6 ppm. The reaction pre-
measuring the 410 nm absorbance of an aqueous solution cipitate was washed with 1,2-dichloroethane (3 × 10 mL), dried
after treatment with a few drops of 30% aqueous H2O2. The in vacuo and identified as MOF3 (M = Nb, 2a; M = Ta, 2b) by
chloride content was determined by the Mohr method49 on metal analysis and IR spectroscopy.17 2a (yield 65%). Anal.
solutions prepared by dissolution of the solid in aqueous KOH Calcd for F3NbO: Nb, 56.00. Found: Nb, 55.20. IR (solid state):
at boiling temperature, followed by cooling down to room ν = 994s (νNbvO) cm−1. 2b (yield 61%). Anal. Calcd for F3OTa:
temperature and addition of HNO3 up to neutralization. The Ta, 71.26. Found: Ta, 69.92. IR (solid state): ν = 1020s (νTavO
)
ESI MS spectrum was recorded using a Waters Micromass ZQ cm−1
4000 with the sample dissolved in CH3CN.
.
(2) Isolation and characterization of [TaF4{OTi(acac)2}2]-
Unless otherwise indicated, electrochemical measurements [TaF6], 3. An NMR tube was charged with TaF5 (0.055 g,
were performed on 0.2 M dichloromethane solutions of 0.200 mmol), TiO(acac)2 (0.052 g, 0.200 mmol) and CD2Cl2
[NnBu4][PF6] as a supporting electrolyte. Cyclic voltammo- (0.70 mL), in the order given. The tube was sealed and shaken
grams were performed using a Princeton Applied Research in order to homogenize the content. After 30 minutes, NMR
(PAR) 273A Potentiostat/Galvanostat, interfaced to a personal analysis of the resulting yellow solution pointed the formation
1
computer, employing PAR M270 Electrochemical Software. All of 3. H NMR (CD2Cl2) δ 6.22 (s, 1 H, CH); 2.27 (s, 6 H, CH3)
the measurements were carried out using a three-electrode ppm. 13C{1H} NMR (CD2Cl2) δ 194.4 (CO); 109.7 (CH); 25.7
home-built cell at room temperature (20 5 °C). The working (CH3) ppm. 19F NMR (CD2Cl2) δ 38.4 (s, TaF6) ppm. Conversion
electrode and the counterelectrode consisted of a platinum of 3 into 1a was completed after heating the tube at 50 °C for
disk electrode and a platinum wire spiral, respectively, both 4 hours.
sealed in a glass tube. A quasi-reference electrode of platinum
A CH2Cl2 solution (28 mL) of 3 was obtained from equi-
was employed as the reference. The Schlenk-type construction molar amounts of TaF5 and TiO(acac)2 (0.800 mmol). Conduc-
of the cell maintained anhydrous and anaerobic conditions. tivity analysis was as follows: ΛM = 6.0 S cm2 mol−1. An aliquot
The cell was pre-dried by prolonged heating under vacuum (0.3 mL) of the solution, mixed with CD2Cl2 (0.4 mL), was ana-
1
and filled with argon. A 0.2 M CH2Cl2 solution of [NnBu4][PF6] lyzed by H NMR, confirming the formation of 3. The remain-
under argon was then introduced into the cell and the working ing portion of the solution was dried under vacuum thus
electrode was repeatedly cycled between the anodic and the giving a pale-orange powder. Yield: 0.353 g, 82%. Anal. Calcd
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for C20H28F10O10Ta2Ti2: C, 22.32; H, 2.62; Ti, 8.90. Found: C, 2 hours. The final mixture was filtered in order to separate the
22.05; H, 2.41; Ti, 9.06. IR (solid state): ν = 1530vs (νCvO), solution from the solid. The solid was washed with 1,2-dichloro-
1422m, 1293s, 1033m, 933m, 811m-s, 782s, 670vs cm−1
.
ethane (3 × 10 mL) and then dried under vacuum. IR spectro-
scopy52,53 and Ti analysis (anal. calcd for F2OTi 46.99,
found 46.60; anal. calcd for Cl2OTi 35.52, found 35.33) on the
solid pointed out the formation of 7a,b in high yield (ca. 80%).
Reactivity of MF5 (M = Nb, Ta) with VO(acac)2. Synthesis of
[V(acac)3][MF6] (M = Nb, 4a; M = Ta, 4b)
A solution of VO(acac)2 (0.215 g, 0.811 mmol) in 1,2-dichloro- The light-orange solution was dried under vacuum, thus giving
ethane (15 mL) was added to NbF5 (0.154 g, 0.820 mmol). After a residue of Ti(acac)2X2. Yield: 0.155 g, 78% (1a); 0.184 g, 83%
6 h stirring at room temperature, the resulting dark-violet solu- (1b). Compounds 1a,b were identified by elemental analysis,
tion was separated from a dark precipitate by filtration. IR ana- 1H NMR spectroscopy15 and X-ray diffractometry (the crystals
lysis on the precipitate suggested the presence of a mixture of were obtained from dichloromethane solutions layered with
non identifiable products. The solution was concentrated pentane and stored at −30 °C).54 Anal. Calcd for C10H14F2O4Ti
(2 mL), layered with pentane and stored at −30 °C. The (1a): C, 42.28; H, 4.97; Ti, 16.85. Found: C, 42.14; H, 4.83; Ti,
product 4a was obtained as a microcrystalline dark-violet 16.39. Anal. Calcd for C10H14Cl2O4Ti (1b): C, 37.89; H, 4.45; Cl,
material after 4 days. Yield: 0.212 g, 71%. Anal. Calcd for 22.37; Ti, 15.10. Found: C, 37.63; H, 4.67; Cl, 22.19; Ti, 15.21.
C15H21F6NbO6V: C, 32.45; H, 3.81. Found: C, 32.13; H, 3.90. IR
Reactivity of TiX4 (X = F, Cl) with VO(acac)2. Synthesis of
Ti(acac)2X2 (X = F, 1a; X = Cl, 1b), Ti2(acac)2(μ-Cl)2Cl4, 6, and
VOX2 (X = F, 8a; X = Cl, 8b)
(solid state): ν = 1520vs (νCvO), 1421m-s, 1359m, 1280s, 1168w,
1030m, 934m, 780m, 664s cm−1 1H NMR (CDCl3) δ 6.38 (s,
.
1 H, CH); 2.35 (s, 6 H, CH3) ppm. 19F NMR (CDCl3, 183 K) δ
1
103.2 ppm (decet, JNbF = 350 Hz, NbF6−) ppm. UV-vis TiX4 (0.700 mmol) was added to a solution of VO(acac)2
(CH2Cl2): λmax = 560 nm. ΛM = 8.7 S cm2 mol−1. ESI-MS (ES+): (0.185 g, 0.698 mmol) in 1,2-dichloroethane (15 mL). The
348 [M+, 25%], 249 [M+ − acac, 100%] m/z.
mixture from TiF4 was stirred overnight at room temperature,
Compound 4b was obtained by a procedure analogous to while the one from TiCl4 was heated at reflux temperature for
that described for the synthesis of 4a, from VO(acac)2 (0.250 g, 2 hours. The final mixture was filtered in order to separate the
0.943 mmol) and TaF5 (0.260 g, 0.942 mmol). Yield: 0.273 g, solution from the solid. The latter was identified as VOX2, 8a,
68%. Anal. Calcd for C15H21F6O6TaV: C, 28.01; H, 3.29. Found: b, by IR spectroscopy35,55 and, in the case of 8b, by Cl analysis
C, 27.75; H, 3.24. IR (solid state): ν = 1521vs (νCvO), 1419s, (anal. calcd for Cl2OV: Cl, 51.44; found: Cl, 50.70). The solu-
1359m, 1281vs, 1168w, 1031s, 934s, 780m-s, 663vs cm−1 1H tion was layered with heptane in a Schlenk tube and main-
.
NMR (CDCl3) δ 6.33 (s, 1 H, CH); 2.33 (s, 6 H, CH3) ppm. tained at −30 °C for one week. Thus compounds 1a,b were
19F NMR (CDCl3) δ 42.6 ppm (s, TaF6−) ppm. UV-vis (CH2Cl2): recovered as crystalline yellow solids. Yield: 0.161 g, 81% (1a);
λmax = 560 nm. ΛM = 6.3 S cm2 mol−1
.
0.157 g, 79% (1b). Compound 1a was identified by elemental
1
analysis and H and 19F NMR spectroscopy, while compound
Reactivity of NbCl5 with TiO(acac)2. Synthesis of [NbO(acac)-
Cl2]x, 5, and Ti2(acac)2(μ-Cl)2Cl4, 6
1b was identified by elemental analysis. 1H NMR and single-
crystal X-ray diffractometry. Anal. Calcd for C10H14F2O4Ti (1a):
A suspension of NbCl5 (0.115 g, 0.426 mmol) in CH2Cl2 C, 42.28; H, 4.97; Ti, 16.85. Found: C, 42.83; H, 5.06; Ti, 16.69.
(12 mL) was treated with TiO(acac)2 (0.112 g, 0.427 mmol). The Anal. Calcd for C10H14Cl2O4Ti (1b): C, 37.89; H, 4.45; Cl, 22.37;
mixture was stirred at room temperature for 3 hours, during Ti, 15.10. Found: C, 38.01; H, 4.49; Cl, 22.03; Ti, 14.90.
which a progressive change in colour to orange was observed.
In a different experiment, TiCl4 (1.200 mmol) was added to
Then the mixture was filtered in order to separate a yellow a solution of VO(acac)2 (0.600 mmol) in dichloromethane
solid from an orange solution. The solid was washed with (10 mL). The mixture was stirred for 4 hours at room temp-
heptane (2 × 10 mL); thus it was identified as 5 (yield 69%) on erature. The final mixture was filtered in order to separate the
the basis of IR spectroscopy29 and elemental analysis. Anal. solution from the solid. The solid was identified as 8b by IR55
Calcd for C5H7Cl2NbO3: C, 21.53; H, 2.53; Cl, 25.42; Nb, 33.31. and Cl analyses (anal. calcd for Cl2OV: Cl, 51.44; found: Cl,
Found: C, 21.78; H, 2.39; Cl, 25.29; Nb, 33.13. The solution 50.53). The filtrated solution was layered with heptane in a
was layered with pentane in a Schlenk tube. Orange crystals of Schlenk tube. Thus the compound Ti2(acac)2(μ-Cl)2Cl4, 6, was
6 were obtained after storing the Schlenk tube for 3 days at obtained as a crystalline solid after storing the Schlenk tube at
−30 °C. Yield: 0.072 g, 67%. The identity of 6 was established −30 °C for one week. Yield: 0.094 g, 62%. The identity of the
by X-ray analysis (on a single crystal)50,51 and IR and NMR product 6 was ascertained by means of elemental analysis, IR,
spectroscopy.51
NMR51 and X-ray. Anal. Calcd for C10H14Cl6O4Ti2: C, 23.71; H,
2.79; Cl, 41.98; Ti, 18.89. Found: C, 23.64; H, 2.92; Cl, 41.73;
Ti, 18.96.
Reactivity of TiX4 (X = F, Cl) with TiO(acac)2. Synthesis of
Ti(acac)2X2 (X = F, 1a; X = Cl, 1b) and TiOX2 (X = F, 7a; X = Cl, 7b)
Reactivity of (C6F5)3B–O–M′(acac)2 (M′ = Ti, V) with [NEt4][PF6]
(1) M′ = V. Formation of [V(acac)3]+, [B(C6F5)3F]−, 9, and
TiX4 (0.700 mmol) was added to a solution of TiO(acac)2
(0.183 g, 0.698 mmol) in 1,2-dichloroethane (15 mL). The
mixture from TiF4 was stirred overnight at room temperature, POF3, 10. A green solution of the complex (C6F5)3B–O–V(acac)2
while the one from TiCl4 was heated at reflux temperature for (0.350 g, 0.450 mmol) in toluene (8 mL) was treated with
14174 | Dalton Trans., 2013, 42, 14168–14177
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[NEt4][PF6] (0.125 g, 0.454 mmol). The mixture was stirred at squares based on all data using F2.57 All non-hydrogen atoms
room temperature for 30 minutes, and a progressive change in were refined with anisotropic displacement parameters.
color to dark-violet was noticed. The final mixture was filtered H-atoms were placed in calculated positions and treated iso-
in order to remove insoluble material; thus a dark-violet solu- tropically using the 1.2 fold Uiso value of the parent atom except
tion was obtained. The cation [V(acac)3]+ was clearly identified methyl protons, which were assigned the 1.5 fold Uiso value of
by electrochemistry (Table 2) and UV-vis spectroscopy (intense the parent C-atom. The C2H4Cl2 unit is located on an inversion
band at 560 nm).27
centre and only half of a molecule is independent.
In a different experiment, [NEt4][PF6] (0.150 mmol) was
CCDC 782632 contains the supplementary crystallographic
added to a solution of (C6F5)3B–O–V(acac)2 (0.150 mmol) and data for 1a.
benzene (C6H6, 0.150 mmol) in CDCl3 (0.70 mL) in an NMR
tube. The tube was sealed and shaken in order to homogenize
the content. After 3 hours, NMR analysis was carried out on
the dark-violet mixture. 1H NMR (CDCl3) δ 6.30 (s, 1 H, CH),
2.40 (s, 6 H, CH3) ppm ([V(acac)3]+; 40% yield relative to C6H6).
Acknowledgements
The authors thank the Ministero dell’Istruzione, dell’Università e
della Ricerca (PRIN 2009 project: ‘New strategies for the control
of reactions: interactions of molecular fragments with metallic
sites in unconventional species’) for financial support.
1
19F NMR (CDCl3) δ −88.6 (d, JPF = 1073 Hz, POF3); −136.5,
−161.4, −166.0 [s, B(C6F5)3F−]; −189.9 [br, B(C6F5)3F−] ppm.
31P NMR (CDCl3) δ −33.9 (q, 1JPF = 1072 Hz, POF3) ppm.
(2) M′ = Ti. Formation of Ti(acac)2F2, 1a, [B(C6F5)3F]−, 9,
and POF3, 10. The reaction of [NEt4][PF6] (0.150 mmol) with
(C6F5)3B–O–V(acac)2 (0.150 mmol) was performed in CDCl3
(0.70 mL) in the presence of benzene (C6H6, 0.150 mmol), by
the same procedure as that described for (C6F5)3B–O–V(acac)2/
Notes and references
1
[NEt4][PF6]. H, 19F and 31P NMR analyses on the light-orange
1 (a) Comprehensive Coordination Chemistry II, ed.
J. A. McCleverty and T. J. Meyer, Elsevier, Amsterdam, 2004;
(b) Comprehensive Organometallic Chemistry, ed. E. W. Abel,
F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995;
(c) F. Bottomley and L. Sutin, Adv. Organomet. Chem., 1988,
28, 339–396.
2 (a) A. Ishikawa, Y. Nakao, H. Sato and S. Sakaki, Inorg.
Chem., 2009, 48, 8154–8163; (b) K. C. Fortner, D. S. Laitar,
J. Muldoon, L. Pu, S. B. Braun-Sand, O. Wiest and
S. N. Brown, J. Am. Chem. Soc., 2007, 129, 588–600;
(c) P. Roussel, R. Boaretto, A. J. Kingsley, N. W. Alcock and
P. Scott, J. Chem. Soc., Dalton Trans., 2002, 1423–1428;
(d) M. Mazzanti, C. Floriani, A. Chiesi-Villa and
C. Guastini, Inorg. Chem., 1986, 25, 4158–4164.
solution pointed out the clean formation of 1a (88% yield rela-
tive to C6H6), 9 and 10.
X-ray crystallographic study
Crystal data and collection details for Ti(acac)2F2·0.5C2H4Cl2,
1a·0.5C2H4Cl2, are reported in Table 3. The diffraction experi-
ments were carried out on a Bruker APEX II diffractometer
equipped with a CCD detector and using Mo-Kα radiation.
Data were corrected for Lorentz polarization and absorption
effects (empirical absorption correction SADABS).56 Structures
were solved by direct methods and refined by full-matrix least-
Table 3 Crystal data and experimental details for 1a·0.5C2H4Cl2
3 G. Barrado, L. Doerrer, M. L. H. Green and M. A. Leech,
J. Chem. Soc., Dalton Trans., 1999, 1061–1066, and refer-
ences therein.
Formula
C11H16ClF2O4Ti
333.59
Fw
4 (a) V. N. Nemykin and P. Basu, Inorg. Chem., 2005, 44,
7494–7502; (b) S. Bhattacharyya, I. Chakraborty,
B. K. Dirghangi and A. Chakravorty, Inorg. Chem., 2001, 40,
286–293.
5 (a) R. H. Holm and J. P. Donahue, Polyhedron, 1993, 12,
571–589; (b) R. H. Holm, Chem. Rev., 1987, 87, 1401–1449.
6 S. K. Mandal and H. W. Roesky, Acc. Chem. Res., 2010, 43,
248–259.
7 The pentafluorides of niobium and tantalum have tetra-
nuclear structures in the solid state (ref. 8a) while the
corresponding chlorides are dinuclear in the solid state
and mononuclear in the vapour phase (ref. 8b). For the
sake of simplicity, these compounds will be mentioned
using the empirical formula MX5 throughout this paper.
8 (a) A. J. Edwards, J. Chem. Soc., 1964, 3714–3718;
(b) A. F. Wells, Structural Inorganic Chemistry, Clarendon
Press, Oxford, 5th edn, 1993.
T (K)
λ (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
100(2)
0.71073
Monoclinic
P21/n
7.348(2)
15.929(5)
12.843(4)
91.637(4)
1502.6(9)
4
1.475
0.774
684
0.23 × 0.21 × 0.15
2.04–26.00
7195
2926 [Rint = 0.0486]
2926/2/176
1.210
β (°)
Cell volume (Å3)
Z
Dc (g cm−3
)
μ (mm−1
F(000)
)
Crystal size (mm)
θ Limits (°)
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness of fit on F2
R1 (I > 2σ(I))
0.1051
0.2550
1.432/−1.209
wR2 (all data)
Largest diff. peak and hole (e Å−3
)
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9 F. Marchetti and G. Pampaloni, Chem. Commun., 2012, 48, 27 (a) R. B. von Dreele and R. C. Fay, J. Am. Chem. Soc., 1972,
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which prevented full solution and refinement. Nonetheless,
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The best information has been obtained by solving the
structure in the space group C2 a = 10.669(9) Å, b = 18.361
(9) Å, c = 10.509(9) Å, β = 90.065(10)° with both pseudo-
merohedral and racemic twinning. Alternatively, the same
structure has been solved in the space group P-31c a =
b = 10.618(4) Å, c = 10.509(6) Å with non-merohedral
twinning.
11 Titanium(IV) oxide bis-acetylacetonate is dinuclear in the
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44 Reduction of [TaF6]− at −2.17 V vs. SCE (−2.55 V vs. FeCp2)
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