Preparation and reactivity of mono- and dinuclear derivatives of niobium and tantalum pentahalides with alkyl aryl ethers

Article abstract of DOI:10.1002/ejic.200900896

The niobium and tantalum pentahalides MX₅ (X = F, Cl) react with a series of bifunctional alkyl aryl ethers in a 2:1 ratio, resulting in formation of the dinuclear species (MX₅)₂[μ- κ²-(O-O)] [2a-h, 3a-d; O-O = 1,4-(OMe)₂C ₆H₄, 1,4-(OMe)₂-2,5C₆H ₂F₂, 1,3-(OMe)₂C₆H₄, PhO(CH₂)₂OPh]. The mononuclear complexes MX₅(L) [L = κ¹-1,4-(OMe)₂C₆H₄, X = F, M = Nb, 4a; L = κ²-1,3-(OMe)₂C₆H ₄, X = Cl, M = Ta, 4c; L = MeOC₆H₅, X = F, M = Nb, 4d; L = MeOC₆H₅, X = Cl, M = Nb, 4e] have been prepared, by 1:1 molar reactions of MX₅ with the appropriate reactant. Alternatively, NbCl₅[κ¹-1,4-(OMe) ₂C₆H₄] (4b) has been obtained upon addition of acetone to (NbCl₅)₂-[μ-κ²-1,4-(OMe) ₂C₆H₄] (2b). The aryloxide complexes TaBr ₄[κ¹-OC₆H₄(4-OMe)] (5a), NbCl₄[κ¹-OC₆H₃(Me)(4-OEt)] (5b) and TaX₄[K²-OC₆H₄(2-OMe)] (X = Cl, 7a; X = Br, 7b) form an admixture with equimolar amounts of alkyl halide by addition of dialkoxyarenes to MX₅ (X = Cl, Br), as result of room-temperature C-O bond cleavage. Differently, the ionic species [MF ₄(κ²-O-O)₂][M₂F₁₁] [O-O = 1,2-(OMe)₂C₆H₄, M = Nb, 6a; O-O = 1,2-(OMe)₂C₆H₄, M = Ta, 6b; O-O = 1,2,4(OMe)₃C₆H₃, M = Nb, 6c] are produced cleanly by treating oriho-dimethoxyarenes with MF₅ in the opportune stoichiometry. All the products described herein were obtained selectively in good to excellent yields and were characterized by spectroscopic and analytical techniques. Moreover, the molecular structure of 2b was elucidated by an X-ray diffraction study.

Full text of DOI:10.1002/ejic.200900896

FULL PAPER
DOI: 10.1002/ejic.200900896
Preparation and Reactivity of Mono- and Dinuclear Derivatives of Niobium
and Tantalum Pentahalides with Alkyl Aryl Ethers
Fabio Marchetti,[a][‡] Guido Pampaloni,*[a] and Stefano Zacchini[b]
Keywords: Niobium / Tantalum / Bridging ligands / Cleavage reactions / Halides
The niobium and tantalum pentahalides MX5 (X = F, Cl) re- (5b) and TaX4[κ2-OC6H4(2-OMe)] (X = Cl, 7a; X = Br, 7b)
act with a series of bifunctional alkyl aryl ethers in a 2:1 ratio,
resulting in formation of the dinuclear species (MX5)2[µ-κ2-
(O–O)] [2a–h, 3a–d; O–O = 1,4-(OMe)2C6H4, 1,4-(OMe)2-2,5-
C6H2F2, 1,3-(OMe)2C6H4, PhO(CH2)2OPh]. The mononuclear
complexes MX5(L) [L = κ1-1,4-(OMe)2C6H4, X = F, M = Nb,
4a; L = κ2-1,3-(OMe)2C6H4, X = Cl, M = Ta, 4c; L = MeOC6H5,
X = F, M = Nb, 4d; L = MeOC6H5, X = Cl, M = Nb, 4e] have
been prepared by 1:1 molar reactions of MX5 with the appro-
priate reactant. Alternatively, NbCl5[κ1-1,4-(OMe)2C6H4]
(4b) has been obtained upon addition of acetone to (NbCl5)2-
[µ-κ2-1,4-(OMe)2C6H4] (2b). The aryloxide complexes
TaBr4[κ1-OC6H4(4-OMe)] (5a), NbCl4[κ1-OC6H3(Me)(4-OEt)]
form an admixture with equimolar amounts of alkyl halide
by addition of dialkoxyarenes to MX5 (X = Cl, Br), as result of
room-temperature C–O bond cleavage. Differently, the ionic
species [MF4(κ2-O–O)2][M2F11] [O–O = 1,2-(OMe)2C6H4, M =
Nb, 6a; O–O = 1,2-(OMe)2C6H4, M = Ta, 6b; O–O = 1,2,4-
(OMe)3C6H3, M = Nb, 6c] are produced cleanly by treating
ortho-dimethoxyarenes with MF5 in the opportune stoichi-
ometry. All the products described herein were obtained se-
lectively in good to excellent yields and were characterized
by spectroscopic and analytical techniques. Moreover, the
molecular structure of 2b was elucidated by an X-ray diffrac-
tion study.
Most intriguing results have been obtained by studying
the reactions of 1 with 1,2-dialkoxyalkanes. Indeed, these
Introduction
The use in organic synthesis of niobium and tantalum latter compounds undergo unusual multiple C–O bond acti-
pentahalides MX5 (1)[1] has seen significant progress in the vation when contacted with MX5 at room temperature: se-
last years due to the unique behaviour shown by these com- lective organic transformations may then occur, depending
plexes compared to other early transition-metal halides.[2] on the nature of the halide.[5e,5f] The importance of these
In particular, the strong oxophilicity of 1 has been exploited findings is double: firstly, it has to be noted that other early
to perform a variety of reactions requiring a C–O bond transition-metal halides are less effective in promoting the
cleavage step.[3]
cleavage of C–O bonds. For example, by operating under
In spite of the recent development of MX5-catalyzed re- analogous experimental conditions, the tetrachlorides of ti-
actions, the coordination chemistry of 1, especially with tanium, zirconium and hafnium form stable adducts with
oxygen-containing molecules, has been scarcely investi- thf or 1,2-dimethoxyethane (dme),[6] while C–O breaking
gated, and the little information available pertains mainly takes place in the presence of niobium or tantalum penta-
to chlorides.[4]
chlorides. Furthermore, the identification of the products
In order to expand the knowledge about the products of the reaction of MCl5 (M = Nb, Ta) with dme has con-
that form from the direct interaction of O-donor species tributed to clarify the pathway followed in several organic
with the pentahalides of the heavier group 5 metals, we re- or inorganic syntheses,[7] promoted by MCl5 and carried
cently started a research project on the stoichiometric reac- out in dme solution.[8]
tions of 1 with a variety of potential oxygen donor ligands.
Hence, a family of coordination adducts of 1 with mono-
functional O ligands has been reported.[5]
The aptitude of early transition-metal halides, with the
metal in high oxidation state, to mediate organic reactions
involving O-containing arene substrates is well documen-
ted, and significant examples regard the use of NbCl5 in
Friedel–Crafts acylation of dimethoxybenzenes[3a] and the
MoCl5-directed trimerization of ortho-dialkoxybenzenes.[9]
Quite recently, the excellent capability of NbCl5 to promote
the high-temperature, regioselective, C–O bond cleavage of
alkyl aryl ethers to give phenols has been described.[10]
In light of these considerations, we have decided to inves-
tigate the room-temperature reactions of 1 with limited
[a] Dipartimento di Chimica e Chimica Industriale, Università di
Pisa,
Via Risorgimento 35, 56126 Pisa, Italy
Fax: +39-050-221-246
E-mail: pampa@dcci.unipi.it
[b] Dipartimento di Chimica Fisica e Inorganica, Università di Bo-
logna,
Viale Risorgimento 4, 40136 Bologna, Italy
[‡] Born in Bologna (Italy) in 1974
Eur. J. Inorg. Chem. 2010, 767–774
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
767

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
amounts of mono-, di- and tri(alkoxy)arenes: the present Table 1. Preparation of dinuclear complexes bridged by alkyl aryl
ethers.
work goes into the direction to rationalize the coordination
chemistry of 1 with alkyl aryl ethers, in the perspective to
extend further the use of pentahalides 1 to related metal-
promoted organic syntheses. We will describe herein the re-
sults, putting in evidence the role of the halide, the influence
of the stoichiometry employed and the effects of ring substi-
tution.
Results and Discussion
A series of dimethoxybenzenes and 1,2-diphenoxyethane
act as bidentate bridging ligands when allowed to react in
a 1:2 molar ratio with MX5 (M = Nb, Ta; X = F, Cl) in
dichloromethane suspensions. Thus, the novel dinuclear
compounds (MX5)2[µ-κ2-(O–O)2] (2a–h) and (MX5)2[µ-κ2-
{PhO(CH2)2OPh}] (X = F, M = Nb, 3a; X = F, M = Ta,
3b; X = Cl, M = Nb, 3c; X = Cl, M = Ta, 3d) were obtained
in very good yields (Table 1).
Complexes 2a–h and 3a–d were characterized by spectro-
scopic and analytical techniques. Moreover, the molecular
structure of 2b was determined by X-ray diffraction (Fig-
ure 1). The crystals of 2b appear to be non-merohedrally
twinned, thus producing a structure of low quality. There-
fore, even if the connectivity indisputably confirms the pro-
posed structure, the bonding parameters cannot be com-
mented on any further. Concerning the connectivity of the
molecule, this latter is composed by two square pyramidal
NbCl5 moieties coordinated to a 1,4-dimethoxybenzene
unit acting as a bridging ligand. The two NbCl5 units are
placed on a relative trans position respect to the aromatic
ring plane, and the Nb centres are octahedrally coordi-
nated.
The possibility for a bifunctional O donor to act as a
bridging ligand between metal complexes is not unusual:
for instance, it has been reported that titanium tetrachloride
adds diesters to afford polymeric species in which each
TiCl4 unit is linked to the next one through a diester mole-
cule.[11]
The NMR features of 2a–h and 3a–d are in agreement
with the structure exhibited by 2b in the solid state: the
diether ligand is symmetrically coordinated to the metal
1
centres; therefore, only two resonances are found in the H
NMR spectra [e.g., at 7.31 (arom. CH) and 4.54 (OMe)
ppm in the case of 2b (CDCl3 solution), to be compared
with 6.83 and 3.75 ppm observed for uncoordinated 1,4-
dimethoxybenzene]. In principle, the possibility exists that
the apparent symmetry shown by the O ligand in the NMR
spectra of 2 and 3 is the consequence of some exchange
process, as it has been observed for the complex NbCl5(1,4-
dioxane).[5b] Such a possibility has been ruled out by re-
1
cording the H NMR spectra of 2 and 3 at –60 °C, which
Figure 1. View of the molecular structure of 2b. Displacement ellip-
soids are at the 50% probability level. Only one of the two indepen-
dent molecules is represented. An inversion centre is located in the
centre of the aromatic ring, generating the whole molecule (the
underscore x_2 refers to symmetry-generated atoms by operation
appear almost identical to the corresponding ones collected
at 25 °C. This observation confirms that 2 and 3 exist in
solution as dinuclear species bridged by a bidentate oxygen
donor, rather than as mononuclear complexes with a mono-
dentate diether exhibiting fluxional behaviour at room tem- #1).
768
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 767–774

Reactivity of Niobium and Tantalum Pentahalides with Alkyl Aryl Ethers
perature. In addition, the room-temperature 19F NMR
Compounds 4 were fully characterized by NMR spec-
spectra of 2a,d,e and 3a,b show one broad resonance ascrib- troscopy and elemental analyses. The methoxy unit of 4d,e
ing to two equivalent [MF5] frames.[5h,12]
resonates at higher frequencies with respect to uncoordi-
1
Confirmation of the structures of 2 and 3 was supplied nated anisole in both the H and 13C NMR spectra [e.g.,
by electrical conductivity measurements carried out on in the case of 4e: δ = 4.45 ppm (1H), 71.2 ppm (13C); the
dichloromethane solutions of 2e,g,h and 3c. The molar con- corresponding resonances of free anisole are at 3.75 and
ductivities obtained (see the Experimental Section) fall in 55.1 ppm]. Coherently, the nonequivalent methoxy groups
1
the range typical for neutral MX5 (M = Nb, Ta) deriva- in 4a–c appear as two distinct singlets, in both the H and
tives.[5e,5f,5h]
13C NMR spectra [e.g., for the H NMR spectrum of 4a: δ
1
Compounds 2a,h add further arene to give the mononu- = 4.86 (NbOMe), 3.87 (OMe) ppm]. The 19F NMR spec-
clear complexes MX5(L) (4a,c; Scheme 1a). Analogously, 4d trum of both 4a and 4d at room temperature exhibits a
and 4e are formed from NbX5 (X = F, Cl) upon treatment unique broad resonance, accounting for five exchanging
with one equivalent of anisole (Scheme 1b).
fluorines, at ca. 150 ppm, in agreement with the neutral,
monomeric structure of these adducts.[5h,12]
The thermal stability of compounds 3c and 4d,e in
CDCl3 solution was tested in order to see the possibility
to activate C–O bonds: under the experimental conditions
employed, 4d comes unchanged, while 3c and 4e undergo
C–O bond cleavage. Thus, phenol and methyl chloride have
been detected from 4e after hydrolysis of the sample,
whereas phenol, 1-phenoxy-2-Cl-ethane and 1,2-dichloro-
ethane (recognized after hydrolysis) come from 3c
(Scheme 3).
Scheme 1. Preparation of 1:1 adducts.
It is noteworthy that MCl5 (M = Nb, Ta) react with 1,4-
dimethoxybenzene to afford selectively 2b,c even if the ar-
ene is used in molar excess (up to 3 equiv.). In fact, the
room-temperature 1H NMR spectra (in CDCl3) of the mix-
tures display only two resonances due to aromatic CH and
methoxy moieties. The chemical shift values depend on the
relative amount of the arene employed and fall, respectively,
between those of uncoordinated 1,4-dimethoxybenzene and
1
those related to 2b,c. Conversely, the H NMR spectra at
Scheme 3. Thermal stability of niobium complexes.
–60 °C show distinct resonances for 2b,c and uncoordinated
1,4-dimethoxybenzene, thus revealing that an exchange be-
tween κ2-coordinated and free 1,4-dimethoxybenzene takes
place at room temperature. Coherently, the treatment of 2b
with an additional amount of 1,4-dimethoxybenzene is inef-
fective in producing a mononuclear derivative. These
features are presumably a consequence of some inertness of
the bridged systems 2b,c.[13] Nevertheless, the adduct
NbCl5[κ1-1,4-C6H4(OMe)2] (4b) could be obtained as an
admixture with NbCl5[O=CMe2][5a] upon treatment of 2b
with acetone (Scheme 2).
These outcomes are in accordance with the niobium–
halogen bond energies scale, for which the activation of M–
F linkages is predicted to be much more inhibited than that
of M–Cl bonds.[14]
On considering that the reactivity of niobium and tanta-
lum pentahalides with O donors has shown to be strongly
dependent on the nature of the halide,[5] we decided to ex-
amine the reaction of the pentabromide TaBr5 with 1,4-di-
methoxybenzene. Hence, this reaction has yielded the aryl-
oxide species TaBr4[κ1-OC6H4(4-OMe)] (5a), which is sup-
posed to exist as a dimer with two terminal aryloxy li-
gands.[5g] Compound 5a is the result of room-temperature
C–O bond cleavage of one methoxy unit within the aryl
diether, methyl bromide (identified by NMR) being the co-
product of the reaction (Scheme 4a). The different reactivity
exhibited by TaBr5 when contacted with 1,4-dimethoxyben-
zene compared to that of MX5 (M = Nb, Ta; X = F, Cl)
Scheme 2. Formation of dinuclear and mononuclear derivatives.
Eur. J. Inorg. Chem. 2010, 767–774
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
769

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
should be attributed to the relatively low Ta–Br bond en-
ergy, which favours release of methyl bromide under mild
conditions and, thus, the formation of 5a.[14]
Scheme 5. Reactivity of MF5 with ortho-methoxy-substituted ben-
zenes.
Scheme 4. Formation of aryloxide complexes from MX5 and dialk-
oxyarenes.
tra [e.g., for 6b: δ = 4.14 ppm (1H), 57.8 ppm (13C)]. Coher-
ently, three 13C NMR resonances are seen for the aryl car-
bon atoms [e.g., for 6b: δ = 147.9 (CO), 123.4, 113.6 (CH)
ppm].
According to previous reports, the presence of alkyl sub-
stituents on the aryl ring seems to enhance the C–O bond
activation process:[10a] in fact, we have found that NbCl5
reacts with 2,5-diethoxytoluene at room temperature with
release of EtCl (1H NMR) and formation of the (presum-
ably dimeric) aryloxide NbCl4[κ1-OC6H3(Me)(4-OEt)] (5b)
in good yield (Scheme 4b).
As a consequence of the fact that the methyl substituent
on the metal-bonded aryloxide can occupy two different
sites in principle, that is, ortho or meta positions with re-
spect to the metal-bound oxygen (see Scheme 4b), com-
pound 5b exists in solution in two isomeric forms (1H NMR
spectroscopy).
Furthermore, the reaction of NbCl5 with 1,2,4-trimeth-
oxybenzene has been studied by NMR spectroscopy. For-
mation of a complicated mixture of products takes place
with concomitant release of methyl chloride. The main sets
of resonances have been tentatively attributed to the
alcoholato compound NbCl4[κ1-3,4-OC6H3(OMe)2] (5c).
The formation of 5c resembles that of α-5b (see Scheme 4)
and corroborates the hypothesis that the presence of elec-
tron-donor substituents (-OMe in the case of 1,2,4-trime-
thoxybenzene) on the arene ring favours the cleavage of
Similarly, the 1H NMR spectrum of 6c displays two sing-
lets accounting for two coordinated methoxy groups (δ =
4.10, 4.05 ppm), and one more resonance attributed to the
non-coordinated methoxy, at δ = 3.81 ppm (the OMe reso-
nances of uncoordinated 1,2,4-trimethoxybenzene fall in
the range 3.83–3.74 ppm). Coherent features are traced by
13C NMR spectroscopy. Similar results were obtained in the
case of the reaction of TiCl4 with trimethyl 1,3,5-benzene-
tricarboxylate.[11b]
In accord with the ionic structure [the values of molar
conductivity obtained for 6a,c fall in the range typical of
ionic M(V) (M = Nb, Ta) derivatives[5f,5h]], the 19F NMR
spectra of 6a–c consist of two resonances, assigned to the
[MF4]+ and [M2F11]– frames, respectively (the chemical shift
values for [M2F11]– are comparable to those found for the
salts [S(NMe2)3][M2F11], M = Nb, Ta[12]). It must be noted
that the stoichiometry stated above for the reactions of MF5
(M = Nb, Ta) with 1,2-dimethoxybenzene or 1,2,4-trime-
thoxybenzene (i.e., 1:0.7) leads selectively to the synthesis
of 6a–c. The use of major amounts of organic reactant
(one–two equivalents per metal) does result in formation of
–
mixtures containing 6 and, presumably, the MF6 contain-
C
sp3–O bonds at room temperature.
ing analogues of 6.[15]
In order to complete the screening on the reactivity of 1
In agreement with the observations that MF5 (M = Nb,
Ta) often show chemistry rather different from that of the
heavier halides, the reactions of TaX5 (X = Cl, Br) with 1,2-
dimethoxybenzene afford TaX4[κ2-OC6H4(2-OMe)] (X =
Cl, 7a; X = Br, 7b) in high yields [see Equation (1)]. The
release of MeX (X = Cl, Br, respectively) occurs, as indi-
with alkoxybenzenes, we took in consideration the reactions
of MF5 with ortho-substituted species, that is, 1,2-dimeth-
oxybenzene, and 1,2,4-trimethoxybenzene (see Scheme 5).
The pentafluorides MF5, suspended in dichloromethane,
quickly dissolve upon the addition of ca. 0.7 equiv. of these
reactants to give coloured solutions of the ionic complexes
[MF4(κ2-O–O)2][M2F11] [O–O = 1,2-(OMe)2C6H4, M = Nb,
6a; O–O = 1,2-(OMe)2C6H4, M = Ta, 6b; O–O = 1,2,4-
(OMe)3C6H3, M = Nb, 6c].
1
cated by H NMR experiments (see Experimental Section).
The high-frequency NMR resonances found for the meth-
oxy unit in 7a,b [e.g., for 7a at 4.58 (1H) and 64.1 (13C)
ppm] suggest that the arene ligand adopts a κ2-coordination
mode to the metal centre.
Compounds 6 were isolated in high yields and fully char-
acterized by spectroscopic and analytical techniques. Ac-
cording to the NMR spectra of 6a,b, recorded at both room
temperature and at –60 °C, 1,2-dimethoxybenzene is sym-
metrically coordinated: a unique resonance is exhibited for
1
the two methoxy units, in both the H and in the 13C spec-
(1)
770
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 767–774

Reactivity of Niobium and Tantalum Pentahalides with Alkyl Aryl Ethers
NMR signals due to eventual second isomeric form are italicized.
The fact that NbCl5 reacts with 1,2-dimethoxybenzene
to give the aryloxyether NbCl4[κ2-OC6H4(2-OMe)], analo-
gous to 7a, and MeCl[16] is a further confirmation that the
metal (i.e., Nb or Ta) does not play a determinant role in
the chemistry of 1 with O donors.
Molar conductivities (ΛM) were calculated on the basis of resis-
tance measurements performed at 293 K by a Metrohm AG Kon-
duktometer E382 Instrument (cell constant = 0.815 cm–1) on
dichloromethane solutions ca. 0.010  of the distinct com-
pounds.[18] Carbon and hydrogen analyses were performed at the
Dipartimento di Chimica Farmaceutica of the University of Pisa
on a Carlo Erba mod. 1106 instrument, paying particular attention
to the more sensitive compounds, which were weighed and directly
introduced into the analyzer. The halide content (Cl or Br) was
determined by the Volhard method[19] after exhaustive hydrolysis
of the sample. Metal (Nb or Ta) was analyzed as M2O5 obtained
by hydrolysis of the sample followed by calcination in a platinum
crucible. The halide and the metal analyses were repeated twice in
order to check for reproducibility.
General Procedure for the Synthesis of (MX5)2[µ-κ2-(O–O)] [O–O
= 1,4-(OMe)2C6H4, X = F, M = Nb, 2a; O–O = 1,4-(OMe)2C6H4,
X = Cl, M = Nb, 2b; O–O = 1,4-(OMe)2C6H4, X = Cl, M = Ta,
2c; O–O = 1,4-(OMe)2-2,5-C6H2F2, X = F, M = Nb, 2d; O–O =
1,4-(OMe)2-2,5-C6H2F2, X = F, M = Ta, 2e; O–O = 1,4-(OMe)2-
2,5-C6H2F2, X = Cl, M = Nb, 2f; O–O = 1,4-(OMe)2-2,5-C6H2F2,
X = Cl, M = Ta, 2g; O–O = 1,3-(OMe)2C6H4, X = Cl, M = Ta,
2h]: Compound MX5 (0.50 mmol) was added to a stirred solution
of the appropriate arene (0.25 mmol) in CH2Cl2 (12 mL). The re-
sulting mixture was stirred for 4 h. The final product was obtained
as a crystalline powder upon crystallization from CH2Cl2/pentane
at –20 °C.
Conclusions
In this paper, we have described the room-temperature,
high-yielding and selective reactions of niobium and tanta-
lum pentahalides, MX5, with stoichiometric, limited,
amounts of a variety of alkoxyarenes. Isolable species con-
taining an alkyl aryl ether unit bridging between two metal
centres were obtained by using suitable dialkoxybenzene re-
actants.
Fragmentation of the O ligand may occur, with conse-
quent production of alcoholato species and alkyl halides.
The fragmentation, when observed, always regards Csp3–O
bonds, whereas Csp2–O linkages are preserved even under
drastic temperature conditions. The fragmentation is fav-
oured (i) on increasing the degree of substitution on the
arene and (ii) on decreasing the metal–halide bond energy.
One significant example can be traced for each of these two
factors. Thus, among dialkoxyarenes, 2,5-diethoxytoluene
undergoes C–O activation in the presence of NbCl5 in chlo-
rinated solvents, while 1,4-dimethoxybenzene is not broken
under the same conditions (i). Moreover, 1,2-dimethoxy-
benzene is activated by MX5 (X = Cl, Br), whereas it just
behaves as a bidentate ligand towards MF5 (ii). The results
presented herein represent a further contribution to the
knowledge of the coordination chemistry of niobium and
tantalum pentahalides with oxygen donor ligands, and to
the development of their usage in metal-directed syntheses
involving oxygen-containing species.
2a: Blue (137 mg, 80% yield). C8H10F10Nb2O2 (513.96): calcd. C
18.70, H 1.96, Nb 36.15; found C 18.66, H 2.03, Nb 36.02. 1H
NMR (CDCl3): δ = 7.20 (s, 4 H, arom. CH), 4.20 (s, 6 H, OMe)
ppm. 13C{1H} NMR (CDCl3): δ = 156.1 (arom. CO), 119.9 (arom.
CH), 68.7 (OMe) ppm. 19F NMR (CDCl3): δ = 159.4 (br. s, 10 F,
NbF5) ppm.
2b: Dark red (202 mg, 81% yield). C8H10Cl10Nb2O2 (678.51): calcd.
C 14.16, H 1.49, Cl 52.25, Nb 27.39; found C 14.22, H 1.36, Cl
1
51.35, Nb 27.26. H NMR (CDCl3): δ = 7.31 (s, 4 H, arom. CH),
4.54 (s, 6 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 158.0 (arom.
CO), 123.5 (arom. CH), 75.7 (OMe) ppm. IR (solid state): ν = 2950
˜
(w), 2845 (w), 1505 (m), 1489 (s), 1198 (m), 1132 (s), 1093 (m),
Experimental Section
1011 (m), 939 (vs), 871 (m), 847 (s), 725 (vs) cm–1.
2c: Yellow (239 mg, 85% yield). C8H10Cl10O2Ta2 (854.59): calcd. C
General Considerations: All manipulations of air- and/or moisture-
sensitive compounds were performed under an atmosphere of pre-
purified argon by using standard Schlenk techniques. The reaction
vessels were oven dried at 150 °C prior to use, evacuated (10–2 Torr)
and then filled with argon. MX5 (1; M = Nb, X = F; M = Ta, X
= F; M = Nb, X = Cl; M = Ta, X = Cl) were commercial products
(Aldrich), stored under an argon atmosphere as received, whereas
MBr5 (M = Nb, Ta) were prepared according to published pro-
cedures.[17] Methoxybenzene, 1,2-dimethoxybenzene, 1,3-dimethox-
ybenzene, 1,4-dimethoxybenzene, 1,2,4-trimethoxybenzene and
1,4-dimethoxy-2,5-difluorobenzene were commercial products of
the highest purity available. Solvents were distilled before use under
an argon atmosphere from appropriate drying agents: CH2Cl2 and
CDCl3 from P4O10, pentane and heptane from LiAlH4. Infrared
spectra were recorded at 298 K with an FTIR-Perkin–Elmer Spec-
trometer equipped with a UATR sampling accessory (solid sam-
ples). NMR measurements were performed at 298 K with a Mer-
cury Plus 400 Instrument (1H 400 MHz, 13C 100.6 MHz, 19F
376.3 MHz) and NMR assignments were confirmed by recording
the NMR spectra at 213 K. The chemical shifts for 1H and 13C
were referenced to the nondeuterated aliquot of the solvent, while
the chemical shifts for 19F NMR spectra were referenced to CFCl3.
11.24, H 1.18, Cl 41.49, Ta 42.35; found C 11.33, H 1.23, Cl 41.15,
1
Ta 41.20. H NMR (CDCl3): δ = 7.36 (s, 4 H, arom. CH), 4.68 (s,
6 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 158.3 (arom. CO),
123.6 (arom. CH), 77.4 (OMe) ppm. IR (solid state): ν = 2954 (w),
˜
1593 (m), 1505 (s), 1489 (vs), 1441 (m), 1287 (w), 1223 (m), 1179
(m), 1127 (s), 1095 (m), 1012 (m), 928 (vs), 847 (s), 726 (vs) cm–1.
2d: Yellow (142 mg, 78% yield). C8H8F12Nb2O2 (549.94): calcd. C
17.47, H 1.47, Nb 33.79; found C 17.51, H 1.40, Nb 33.87. 1H
NMR (CDCl3): δ = 7.05 (br. s, 2 H, arom. CH), 3.92 (br. s, 6 H,
OMe) ppm. 19F NMR (CDCl3): δ = 159.8 (br. s, 10 F, NbF5),
–131.5 (br. s, 2 F, arom. CF) ppm.
2e: Yellow (169 mg, 82% yield). C8H8F12O2Ta2 (726.02): calcd. C
13.23, H 1.11, Ta 49.85; found C 13.32, H 1.04, Nb 49.26. 1H NMR
(CDCl3): δ = 7.03 (br., 2 H, arom. CH), 3.90 (br. s, 6 H, OMe)
ppm. 19F NMR (CDCl3): δ = 88.9 (br. s, 10 F, TaF5), –131.8 (br.,
2 F, arom. CF) ppm. ΛM = 0.24 Scm2 mol–1.
2f: Red (181 mg, 77% yield). C8H8Cl10F2Nb2O2 (714.49): calcd. C
13.45, H 1.13, Cl 49.62, Nb 26.01; found C 13.58, H 1.02, Cl 49.37,
1
Nb 25.96. H NMR (CDCl3): δ = 7.01 (br., 2 H, arom. CH), 4.11
(br. s, 6 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 148.3 (1JC,F
Eur. J. Inorg. Chem. 2010, 767–774
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
771

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
= 244 Hz, arom. CF), 142.0 (2JC,F = 11 Hz, arom. CO), 103.6 (2JC,F
and GC–MS, which revealed the presence of 1,2-dichloroethane,
= 17 Hz, arom. CH), 58.9 (OMe) ppm. 19F NMR (CDCl3): δ = phenol and 1-phenoxy-2-Cl-ethane, in ca. 2:7:3 ratio.
–132.5 (br., 2 F, arom. CF) ppm.
General Procedure for the Synthesis of MX5(L) [L = κ1-1,4-(OMe)2-
C6H4, X = F, M = Nb, 4a; L = κ1-1,4-(OMe)2C6H4, X = Cl, M =
2g: Orange (208 mg, 75% yield). C8H8Cl10F2O2Ta2 (890.57): calcd.
Nb, 4b; L = κ2-1,3-(OMe)2C6H4, X = Cl, M = Ta, 4c; L =
C 10.78, H 0.91, Cl 39.81, Ta 40.64; found C 10.83, H 0.83, Cl
39.66, Ta 40.71. 1H NMR (CDCl3): δ = 7.03 (br., 2 H, arom. CH),
4.13 (br. s, 6 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 148.3
(1JC,F = 244 Hz, arom. CF), 142.0 (2JC,F = 11 Hz, arom. CO), 104.6
MeOC6H5, X = F, M = Nb, 4d; L = MeOC6H5, X = Cl, M = Nb,
4e]: A slight excess amount of the appropriate arene (0.55 mmol)
was added to a suspension of MX5 (0.50 mmol) in CH2Cl2 (10 mL),
and the resulting mixture was stirred for 2 h. The volatile materials
were removed in vacuo, and hence, the final product was obtained
as a solid upon crystallization from CH2Cl2/pentane at –20 °C.
(2JC,F = 17 Hz, arom. CH), 59.5 (OMe) ppm. IR (solid state): ν =
˜
2964 (w), 1500 (vs), 1445 (m), 1406 (m), 1215 (w-m), 1182 (s), 1131
(m-s), 938 (vs), 879 (vs), 821 (vs), 775 (s), 734 (s), 677 (s) cm–1. ΛM
= 0.45 Scm2 mol–1.
4a: Orange (187 mg, 91% yield). C8H10F5NbO2 (326.06): calcd. C
29.47, H 3.09, Nb 28.49; found C 29.55, H 3.03, Nb 28.20. 1H
2h: Pink (184 mg, 79% yield). C8H10Cl10O2Ta2 (854.59): calcd. C
3
NMR (CDCl3): δ = 7.50, 7.05 (d, JH,H = 9.52 Hz, 4 H, arom.
11.24, H 1.18, Cl 41.49, Ta 42.35; found C 11.12, H 1.23, Cl 41.22,
CH), 4.86 (s, 3 H, NbOMe), 3.87 (s, 3 H, OMe) ppm. 19F NMR
(CDCl3): δ = 150.0 (br. s, 5 F, NbF5) ppm.
1
Ta 42.64. H NMR (CDCl3): δ = 7.67–7.32 (m, 3 H, arom. CH),
4.70 (s, 6 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 162.4 (arom.
CO); 131.1, 114.4, 108.3 (C6H4); 76.8 (OMe) ppm. IR (solid state):
4c: Red (225 mg, 86% yield). C8H10Cl5O2Ta (496.38): calcd. C
19.36, H 2.03, Cl 35.71, Ta 36.45; found C 19.27, H 1.97, Cl 35.44,
Ta 36.36. 1H NMR (CDCl3): δ = 7.44 (m, 1 H, arom. CH), 6.98
(m, 3 H, arom. CH), 4.72 (s, 3 H, NbOMe), 3.89 (s, 3 H, OMe)
ppm. 13C{1H} NMR (CDCl3): δ = 162.4, 160.3 (arom. CO), 131.0,
114.5, 114.0, 108.3 (arom. CH), 76.0, 56.4 (OMe) ppm.
ν = 2982 (w), 1638 (m), 1597 (w-m), 1504 (vs), 1471 (s), 1411 (m-
˜
s), 1324 (m-s), 1240 (vs), 1149 (s), 1091 (s), 1009 (vs), 830 (vs) cm–1.
ΛM = 0.50 Scm2 mol–1.
General Procedure for the Synthesis of (MX5)2[µ-κ2-{PhO(CH2)2-
OPh}] (X = F, M = Nb, 3a; X = F, M = Ta, 3b; X = Cl, M = Nb,
3c; X = Cl, M = Ta, 3d): A suspension of MX5 (0.45 mmol) in
CH2Cl2 (10 mL) was allowed to react with 1,2-diphenoxyethane
(0.20 mmol), and the resulting mixture was stirred for 5 h. Then,
the mixture was filtered, and the filtered solution was dried in
vacuo. The final product was obtained as a microcrystalline powder
upon crystallization of the residue from CH2Cl2/pentane at –20 °C.
4d: Orange (161 mg, 87% yield). C7H8F5NbO (296.04): calcd. C
28.40, H 2.72, Nb 31.38; found C 28.55, H 2.66, Nb 31.24. 1H
NMR (CDCl3): δ = 7.45–7.26 (5 H, arom. CH), 4.25 (s, 3 H, OMe)
ppm. 13C{1H} NMR (CDCl3): δ = 158.9 (arom. CO), 130.9, 125.0,
118.3 (arom. CH), 64.9 (OMe) ppm. 19F NMR (CDCl3): δ = 157.9
(br. s, 5 F, NbF5) ppm.
4e: Red (174 mg, 86% yield). C7H8Cl5NbO (378.31): calcd. C
3a: Orange (159 mg, 91% yield). C14H14F10Nb2O2 (590.06): calcd.
C 28.50, H 2.39, Nb 31.49; found C 28.36, H 2.06, Nb 30.67. H
NMR (CDCl3): δ = 7.45, 7.17 (br. m, 10 H, Ph), 4.64 (s, 4 H, CH2)
ppm. 13C{1H} NMR (CDCl3): δ = 158.7 (arom. CO), 131.0, 126.7,
119.0 (Ph), 73.1 (CH2) ppm. 19F NMR (CDCl3): δ = 157.8 (br. s,
10 F, NbF5) ppm.
1
22.22, H 2.13, Cl 46.86, Nb 24.56; found C 22.13, H 2.06, Cl 46.59,
1
Nb 24.71. H NMR (CDCl3): δ = 7.49–7.30 (5 H, arom. CH), 4.45
(s, 3 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 162.2 (arom.
CO), 130.2, 126.8, 121.1 (arom. CH), 71.2 (OMe) ppm. IR (solid
state): ν = 2952 (w), 2946 (w), 1584 (m), 1482 (s), 1454 (m), 1199
˜
(w-m), 1136 (s), 1070 (m), 1020 (m), 941 (vs), 868 (m), 837 (m),
3b: Red (184 mg, 88% yield). C14H14F10O2Ta2 (766.14): calcd. C
21.95, H 1.84, Ta 47.24; found C 22.07, H 1.93, Ta 47.02. 1H NMR
(CDCl3): δ = 7.42, 7.13 (br. m, 10 H, Ph), 4.72 (s, 4 H, CH2) ppm.
13C{1H} NMR (CDCl3): δ = 161.3 (arom. CO), 128.6, 124.1, 117.0,
(Ph), 72.0 (CH2) ppm. 19F NMR (CDCl3): δ = 76.5 (br. s, 10 F,
TaF5) ppm.
788 (vs), 761 (vs), 695 (vs) cm–1.
Complex 4b was detected as follows: compound 2b (0.30 mmol), in
a solution of CDCl3 (0.75 mL) in an NMR tube, was treated with
acetone (0.35 mmol). Then the tube was sealed, and the resulting
mixture was analyzed by 1H NMR after 3 h: complexes NbCl5[1,4-
C6H4(OMe)2] (4b) and NbCl5(OCMe2)[5a] were found in about 1:1
3
ratio. 4b (orange). 1H NMR (CDCl3): δ = 7.65, 7.10 (d, 4 H, JH,H
3c: Orange (221 mg, 91% yield). C14H14Cl10Nb2O2 (754.61): calcd.
C 22.28, H 1.87, Cl 46.98, Nb 24.62; found C 21.79, H 1.92, Cl
= 9.5 Hz, arom. CH), 4.96 (s, 3 H, NbOMe), 3.89 (s, 3 H, OMe)
ppm.
1
46.66, Nb 24.31. H NMR (CDCl3): δ = 7.50, 7.36 (br. m, 10 H,
Ph), 4.79 (s, 4 H, CH2) ppm. 13C{1H} NMR (CDCl3): δ = 159.0
(arom. CO), 130.1, 124.0, 117.5 (Ph), 75.6 (CH2) ppm. IR (solid
Solutions of complexes 4d,e (0.40 mmol), in CDCl3 (0.80 mL) in-
side sealed NMR tubes, were heated at 90 °C (temperature of the
external oil bath) for 60 min. The resulting mixtures were treated
with water (ca. 3 mmol), causing precipitation of a colourless solid
from a solution. Hence, the solutions were analyzed by NMR and
GC–MS, which revealed the presence of PhOMe (from 4d), MeCl
and PhOH (from 4e), ratio 1:1.
Preparation of TaBr4[κ1-OC6H4(4-OMe)] (5a) and NbCl4[κ1-
OC6H3(Me)(4-OEt)] (5b) and the Reaction of NbCl5 with 1,2,4-Tri-
methoxybenzene: Compound MX5 (0.50 mmol) was suspended in
CH2Cl2 (10 mL) and treated with the appropriate arene
(0.52 mmol). The mixture was stirred overnight, then the final
product was obtained as a powder upon removal of the volatile
materials. The same reaction, performed in CDCl3 (0.75 mL), was
monitored via 1H NMR: clean formation of 5a,b, in nearly equi-
molar admixture with RX (R = Me, Et; X = Cl, Br), was completed
after 3 h.
state): ν = 3052 (w), 2948 (w), 1599 (s), 1585 (s), 1497 (m-s), 1483
˜
(s), 1453 (s), 1382 (w-m), 1293 (m), 1243 (vs), 1229 (vs), 1176 (s),
1155 (m-s), 1143 (m-s), 1087 (m), 1065 (m-s), 1042 (m), 940 (m),
923 (m), 903 (vs), 885 (vs), 871 (vs), 806 (s), 748 (vs), 730 (s), 690
(vs) cm–1. ΛM = 0.18 Scm2 mol–1.
3d: Orange (212, 84% yield). C14H14Cl10O2Ta2 (930.69): calcd. C
18.07, H 1.52, Cl 38.09, Ta 38.88; found C 17.99, H 1.63, Cl 37.50,
1
Ta 38.46. H NMR (CDCl3): δ = 7.66–7.08 (10 H, Ph), 4.85 (s, 4
H, CH2) ppm. 13C{1H} NMR (CDCl3): δ = 158.7 (ipso-Ph), 129.9,
125.0, 119.2 (Ph), 74.0 (CH2) ppm.
In a different experiment, a CDCl3 solution of 3c (0.25 mmol in
0.75 mL), inside a sealed NMR tube, was heated at 90 °C (tempera-
ture of the external oil bath) for 1 h. Then, the tube was opened,
and the mixture was treated with an excess amount water (ca.
5 mmol). The resulting light red solution was analyzed by NMR
772
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 767–774

Reactivity of Niobium and Tantalum Pentahalides with Alkyl Aryl Ethers
1
5a: Orange (322 mg, 81% yield). C7H7Br4O2Ta (623.70): calcd. C
Ta 40.66. H NMR (CDCl3): δ = 7.30–6.88 (4 H, arom. CH), 4.58
(s, 3 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 151.3, 146.7
13.48, H 1.13, Br 51.25, Ta 29.01; found C 13.36, H 1.08, Br 50.55,
1
Ta 29.36. H NMR (CDCl3): δ = 7.35–7.06 (m, 4 H, arom. CH), (arom. CO), 127.2, 125.7, 117.1, 112.2 (arom. CH), 64.1 (OMe)
4.08 (s, 3 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 150.3, 144.8 ppm. IR (solid state): ν = 2983 (w), 2835 (w), 1592 (w-m), 1503 (s),
˜
(arom. CO), 120.6, 116.0 (arom. CH), 60.0 (OMe) ppm. IR (solid
1485 (s), 1440 (s), 1249 (vs), 1223 (s), 1174 (m-s), 1122 (m-s), 1107
state): ν = 2962 (w), 2901 (vw), 2836 (w), 1601 (w), 1496 (s), 1465 (m), 1024 (m), 980 (m), 945 (m), 865 (m-s), 831 (s), 769 (s), 739
˜
(w), 1441 (w), 1388 (vw), 1259 (s), 1224 (s), 1173 (m), 1032 (m), (vs), 658 (s) cm–1.
942 (s), 896 (vs), 796 (vs), 709 (s) cm–1. ΛM = 0.10 Scm2 mol–1.
7b: Orange (314 mg, 84% yield). C7H7Br4O2Ta (623.70): calcd. C
5b: Dark red (237 mg, 77% yield). C9H11Cl4NbO2 (385.90): calcd.
C 28.01, H 2.87, Cl 36.75, Nb 24.08; found C 28.06, H 2.96, Cl
36.23, Nb 23.92. 1H NMR (CDCl3): δ = 7.63–7.16 (3 H, arom.
13.48, H 1.13, Br 51.25, Ta 29.01; found C 13.31, H 1.16, Br 50.69,
Ta 28.96. 1H NMR (CDCl3): δ = 7.26Ϭ6.78 (4 H, arom. CH), 4.57
(s, 3 H, OMe) ppm. 13C{1H} NMR (CDCl3): δ = 152.1, 149.9
(arom. CO), 125.0, 122.5, 116.9, 111.5 (arom. CH), 63.3 (OMe)
3
CH), 4.14 (q, JH,H = 7.1 Hz, 2 H, CH2CH3), 2.58, 2.20 (s, 3 H,
3
Me), 1.51 (t, JH,H = 7.1 Hz, 3 H, CH2CH3) ppm. α-Isomer/β-iso-
ppm. IR (solid state): ν = 2981 (w), 2881 (w), 1481 (s), 1461 (m),
˜
mer, 3:2. 13C{1H} NMR (CDCl3): δ = 152.9 (arom. CO), 141.7,
139.9 (arom. C-CH3), 128.8, 123.7, 122.7, 120.0, 117.0, 113.9
(arom. CH), 65.5 (CH2CH3), 19.2, 17.2 (Me), 16.7 (CH2CH3) ppm.
1320 (w-m), 1276 (w), 1246 (s), 1149 (w), 1105 (m-s), 978 (s), 865
(s), 810 (s), 766 (s), 737 (vs), 658 (vs) cm–1.
The reactions of TaX5 (0.45 mmol) with 1,2-dimethoxybenzene
(0.45 mmol), in CDCl3 (0.75 mL), were monitored via 1H NMR:
clean formation of equimolar amounts of 7a,b and MeX (X = Cl,
Br) occurred in 3 h.
The reaction of NbCl5 (0.250 mmol) with 1,2,4-trimethoxybenzene
(0.240 mmol) was carried out in CDCl3 (0.80 mL) in an NMR tube.
Complete dissolution of the solid occurred in 2 h and gave a dark-
red solution. The main sets of resonances were attributed to com-
plex NbCl4[κ1-3,4-OC6H3(OMe)2] (5c). 1H NMR (CDCl3): δ =
7.30–6.51 (3 H, arom. CH), 3.90, 3.88 (s, 3 H, OMe) ppm. 13C{1H}
NMR (CDCl3): δ = 156.1, 154.2, 146.7 (arom. CO), 115.2, 108.6,
104.3 (arom. CH), 57.2, 57.0 (OMe) ppm.
General Procedure for the Synthesis of [MF4(κ2-O–O)2][M2F11] [O–
O = 1,2-(OMe)2C6H4, M = Nb, 6a; O–O = 1,2-(OMe)2C6H4, M =
Ta, 6b; O–O = 1,2,4-(OMe)3C6H3, M = Nb, 6c]: A suspension of
MF5 (0.60 mmol) in CH2Cl2 (15 mL) was treated with the appro-
priate arene (0.40 mmol), and the mixture was stirred for 2 h. The,
the final mixture was filtered. The filtered solution was dried in
vacuo, and thus the product was obtained as a powder upon re-
moval of the solvent.
X-ray Crystallographic Study. Crystal data and collection details
for 2b are reported in Table 2. The diffraction experiments were
carried out with a Bruker APEX II diffractometer equipped with
a CCD detector using Mo-Kα radiation. Data were corrected for
Lorentz polarization and absorption effects (empirical absorption
correction SADABS).[20] Structures were solved by direct methods
and refined by full-matrix least-squares based on all data using
F2.[21] Hydrogen atoms were fixed at calculated positions and re-
fined by a riding model. Two independent halves of two different
molecules are present within the asymmetric unit; the whole mole-
cules are obtained by applying an inversion centre. The crystals
appear to be non-merohedrally twinned. The TwinRotMat routine
of PLATON[22] was used to determine the twinning matrix (1.001
–0.009 0 0.250 –1.001 0 0 0 –1; 2-axis (8 1 0) [1 0 0]) and to write
the reflection data file (hkl) containing the two twin components.
Refinement was performed using the instruction HKLF 5 in
SHELX and one BASF parameter, which refined as 0.24041. Sim-
6a: Purple (275 mg, 88% yield). C16H20F15Nb3O4 (840.02): calcd.
C 22.87, H 2.39; found C 22.45, H 2.12. 1H NMR (CDCl3): δ =
7.4 (m, 8 H, arom. CH), 4.49 (s, 12 H, OMe) ppm. 13C{1H} NMR
(CDCl3): δ = 146.7 (arom. CO), 127.1 (ortho CH), 116.5 (meta CH),
65.9 (OMe) ppm. 19F NMR (CDCl3): δ = 197.3 (br. s, 4 F, NbF4),
160.2 (br. s, 11 F, Nb2F11) ppm. ΛM = 3.1 Scm2 mol–1.
Table 2. Crystal data and experimental details for 2b.
6b: Pink (336 mg, 79% yield). C16H20F15O4Ta3 (1104.15): calcd. C
17.40, H 1.82; found C 17.10, H 1.65. 1H NMR (CDCl3): δ = 7.27–
6.96 (8 H, arom. CH), 4.14 (s, 12 H, OMe) ppm. 13C{1H} NMR
(CDCl3): δ = 147.9 (arom. CO), 123.4, 113.6 (arom. CH), 57.8
(OMe) ppm. 19F NMR (CDCl3): δ = 103.1 (br. s, 4 F, TaF4), 58.3
Formula
Fw
T [K]
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C8H10Cl10Nb2O2
678.48
100(2)
0.71073
triclinic
¯
P1
(br. s, 11 F, Ta F ) ppm. IR (solid state): ν = 2101 (w), 2024 (w-
˜
2
11
6.2801(19)
12.094(4)
13.255(4)
86.390(4)
89.954(4)
85.792(4)
1002.0(5)
2
m), 1627 (s), 1505 (s), 1467 (m), 1252 (m), 1223 (m), 1175 (w-m),
1124 (m), 1016 (m-s), 877 (s) cm–1.
α [°]
β [°]
γ [°]
6c: Green (291 mg, 88% yield). C18H24F15Nb3O6 (900.07): calcd. C
24.01, H 2.69; found C 23.70, H 2.12. 1H NMR (CDCl3): δ = 7.03,
6.64 (m, 6 H, CH), 4.10, 4.05 (s, 12 H, NbOMe), 3.81 (s, 6 H,
OMe) ppm. 13C{1H} NMR (CDCl3): δ = 156.6, 150.0, 142.8 (arom.
CO), 115.6, 106.5, 101.7 (arom. CH), 61.8, 61.0 (NbOMe), 56.7
(OMe) ppm. 19F NMR (CDCl3): δ = 197.0 (br. s, 4 F, NbF4), 152.7
(br. s, 11 F, Nb2F11) ppm. ΛM = 3.9 Scm2 mol–1.
Cell Volume [Å3]
Z
Dcalcd. [gcm–3]
2.249
2.476
652
µ [mm–1]
F(000)
Crystal size [mm]
θ limits [°]
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness on fit on F2
R1 [IϾ2σ(I)]
wR2 (all data)
0.26ϫ0.21ϫ0.15
1.54–25.50
6926
3629 [Rint = 0.037]
3622/48/202
1.055
Synthesis of TaX4[κ2-OC6H4(2-OMe)] (X = Cl, 7a; X = Br, 7b): 1,2-
Dimethoxybenzene (0.65 mmol) was added dropwise to a stirred
suspension of TaX5 (0.60 mmol) in CH2Cl2 (15 mL). The mixture
was stirred for 2 h, during which progressive dissolution of the solid
was noticed. Hence, pentane (20 mL) was added, causing the pre-
cipitation of powdery 7.
0.0888
0.2456
7a: Orange (212 mg, 80% yield). C7H7Cl4O2Ta (445.89): calcd. C
18.86, H 1.58, Cl 31.80, Ta 40.58; found C 18.92, H 1.44, Cl 31.59,
Largest diff. peak and hole [eÅ–3] 7.507/–1.633
Eur. J. Inorg. Chem. 2010, 767–774
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
773

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
yama, Y. Kataoka, K. Mashima, K. Tani, K. Takai, Organome-
tallics 2003, 22, 464–472; J. A. Varela, C. Saá, Chem. Rev. 2003,
103, 3787–3801, and the references cited therein; E. J. Ros-
kamp, P. S. Dragovich, J. B. Hartung Jr., S. F. Pedersen, J. Org.
Chem. 1989, 54, 4736–4737; E. J. Roskamp, S. F. Pedersen, J.
Am. Chem. Soc. 1987, 109, 3152–3154.
ilar U restraints were applied, on all C atoms (s.u. 0.005). Because
of this heavy twinning, high residual electron density remains in
the final model; nonetheless, the resulting connectivity and main
bonding parameters are non disputable.
CCDC-751545 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[8] S. F. Pedersen, J. B. Hartung Jr., E. J. Roskamp, P. S. Dragov-
ich, Inorg. Synth. 1992, 29, 119–123; C. G. Dewey, J. E. Ellis,
K. L. Fjare, K. M. Pfahl, G. F. P. Warnock, Organometallics
1983, 2, 388–391; J. E. Ellis, G. F. P. Warnock, M. V. Barybin,
M. K. Pomije, Chem. Eur. J. 1995, 1, 521–527; K. S. Heinsel-
man, V. M. Miskowski, S. J. Geib, L. C. Wang, M. D. Hopkins,
Inorg. Chem. 1997, 36, 5530–5538; M. V. Barybin, J. E. Ellis,
M. K. Pomije, M. L. Tinkham, G. F. P. Warnock, Inorg. Chem.
1998, 37, 6518–6527; W. W. Brennessel, J. E. Ellis, M. K. Pom-
ije, V. J. Sussman, E. Urnezius, V. G. Young Jr., J. Am. Chem.
Soc. 2002, 124, 10258–10259.
[9] D. Pérez, E. Guitian, Chem. Soc. Rev. 2004, 33, 274–283, and
references cited therein.
[10] a) Y. Sudo, S. Arai, A. Nishida, Eur. J. Inorg. Chem. 2006, 752–
758; b) S. Arai, Y. Sudo, A. Nishida, Synlett 2004, 1104–1106.
[11] a) P. Sobota, J. Utko, T. Lis, J. Organomet. Chem. 1990, 393,
349–358; b) P. Sobota, J. Utko, T. Lis, J. Organomet. Chem.
1993, 447, 213–220.
Acknowledgments
The authors wish to thank the Ministero dell’Istruzione, dell’Univ-
ersità e della Ricerca (MIUR, Roma), Programma di Ricerca Sci-
entifica di Notevole Interesse Nazionale 2007-8, for financial sup-
port. Dr. Calogero Pinzino (Istituto per i Processi Chimico-Fisici,
CNR, Pisa) is gratefully acknowledged for performing the DFT
calculations.
[1] The fluorides of niobium(V) and tantalum(V) have tetranuclear
structures in the solid state, while the corresponding heavier
halides are dinuclear in the solid state and mononuclear in the
vapour phase [A. F. Wells, Structural Inorganic Chemistry, 5th
ed., Clarendon Press, Oxford, 1993]. For the sake of simplicity,
in this paper the general formula MX5, when dealing with the
niobium(V) and tantalum(V) halides, will be used.
[12] F. Marchetti, G. Pampaloni, S. Zacchini, J. Fluorine Chem.
2010, 131, 21–28.
[13] DFT calculations indicate that the formation of mononuclear
derivative 4c from TaCl5 and 1,4-dimethoxybenzene is favoured
by only 0.5 kcalmol–1 with respect to the formation of dinu-
clear 2c. This implies that, in the gas phase, both products 2c
and 4c may form from TaCl5 and 1,4-dimethoxybenzene; on
the other hand, slight variations in the properties of the metal
compounds in solution may address the reaction towards the
formation of mononuclear adducts rather than dinuclear ones
or vice versa.
[2] Q. Guo, T. Miyaji, R. Hara, B. Shen, T. Takahashi, Tetrahedron
2002, 58, 7327–7334, and references cited therein.
[3] a) S. Arai, Y. Sudo, A. Nishida, Tetrahedron 2005, 61, 4639–
4642; b) S. Kobayashi, K. Arai, H. Shimizu, Y. Ihori, H. Ishit-
ani, Y. Yamashita, Angew. Chem. Int. Ed. 2005, 44, 761–764;
c) A. Ortiz, L. Quintero, H. Hernández, S. Maldonado, G.
Mendoza, S. Bernès, Tetrahedron Lett. 2003, 44, 1129–1132; d)
C. Kleber, Z. Andrade, R. A. F. Matos, Synlett 2003, 1189–
1191; e) C. Kleber, Z. Andrade, N. R. Azevedo, Tetrahedron
Lett. 2001, 42, 6473–6476; f) J. Horwath, K. Gillespie, Tetrahe-
dron Lett. 1996, 37, 6011–6012; g) M. Yamamoto, M. Nakaz-
awa, K. Kishikawa, S. Kohmoto, Chem. Commun. 1996, 2353–
2354; h) H. Maeta, T. Nagasawa, Y. Handa, T. Takei, Y. Osa-
mura, K. Suzuki, Tetrahedron Lett. 1995, 36, 899–902; i) K.
Suzuki, T. Hashimoto, H. Maeta, M. Hideki, T. Matsumoto,
Synlett 1992, 125–128.
[14] CRC Handbook of Chemistry and Physics, 82nd ed. (Ed.: D. R.
Linde), CRC Press, Boca Raton, FL, USA, 2001, 9-51–9-63.
[15] 19F NMR spectra recorded on the mixture produced by the
addition of 1,2-dimethoxybenzene (0.50 mmol) to NbF5
(0.30 mmol) exhibit resonances accounting for both the
[Nb2F11]– and the [NbF6]– anions (δ = 155 and 110 ppm,
respectively).
[16] The formation of NbCl4[κ2-OC6H4(2-OMe)] and MeCl has
been proposed on the basis of a NMR study of the reaction
between 1,2-dimethoxybenzene and NbCl5 at 55 °C; however,
the product has not been isolated.[10a]
.
[4] A. Merbach, J. C. Bünzli, Helv. Chim. Acta 1972, 55, 580.
[5] a) F. Marchetti, G. Pampaloni, S. Zacchini, Dalton Trans. 2007,
4343–4351; b) F. Marchetti, G. Pampaloni, S. Zacchini, Inorg.
Chem. 2008, 47, 365–372; c) F. Marchetti, G. Pampaloni, S.
Zacchini, Polyhedron 2008, 27, 1969–1976; d) F. Marchetti, G.
Pampaloni, S. Zacchini, Eur. J. Inorg. Chem. 2008, 453–462; e)
F. Marchetti, G. Pampaloni, S. Zacchini, Chem. Commun.
2008, 3651–3653; f) F. Marchetti, G. Pampaloni, S. Zacchini,
Dalton Trans. 2008, 7026–7035; g) F. Marchetti, G. Pampaloni,
S. Zacchini, Polyhedron 2009, 28, 1235–1240; h) F. Marchetti,
G. Pampaloni, S. Zacchini, Dalton Trans. 2009, 6759–6772.
[6] L. E. Manzer, Inorg. Synth. 1982, 21, 135–140; E. Turin, R. M.
Nielson, A. E. Merbach, Inorg. Chim. Acta 1987, 134, 67–78.
[7] F. Marchetti, G. Pampaloni, S. Zacchini, Eur. J. Inorg. Chem.
2008, 2107–2112; T. Oshiki, K. Tanaka, J. Jamada, T. Ishi-
[17] F. Calderazzo, P. Pallavicini, G. Pampaloni, P. F. Zanazzi, J.
Chem. Soc., Dalton Trans. 1990, 2743–2746.
[18] a) A. Jutand, Eur. J. Inorg. Chem. 2003, 2017–2040; b) W. J.
Geary, Coord. Chem. Rev. 1971, 7, 81–122.
[19] D. A. Skoog, D. M. West, Fundamentals of Analytical Chemis-
try, 2nd ed., Holt, Rinehart and Winston, Chatham, UK, 1974,
p. 233.
[20] G. M. Sheldrick, SADABS, University of Göttingen,
Göttingen, Germany.
[21] G. M. Sheldrick, SHELX97, University of Gottingen,
Göttingen, Germany.
[22] A. L. Spek, PLATON, A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 2005.
Received: September 9, 2009
Published Online: December 17, 2009
774
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 767–774