Complexes of niobium(V) and tantalum(V) halides with ligands that contain N-C=O and P=O functionalities: A synthetic and structural study

Article abstract of DOI:10.1002/ejic.200700911

The reactions of niobium and tantalum pentahalides, MX₅, with dialkylureas (tetramethyl- and tetraethylurea, TMU and TEU, respectively), amides (N,N,dimethylformamide, DMF, N,N-diethylformamide, DEF, N-phenylacetamide, PhA), and P=O-containing compounds (triphenylphosphane oxide, TPPO, and trimethyl phosphate, TMP) are not dependent on the reactant to metal molar ratio, and afford hexacoordinate complexes of the general formula MX ₅(L). The only exception is given by the reaction of TaBr₅ with TMU, which proceeds by bromide migration from one metal center to another, and provides the ionic adduct [TaBr₄(TMU)₂][TaBr ₆]. Hydrolysis of TaCl₅(TMP), due to adventitious water, has yielded the dinuclear species Ta₂(μ-O)Cl₈(TMP) ₂. All compounds have been fully characterized in solution, and X-ray crystal structures have been determined for NbCl₅(TEU), NbCl ₅(DMF), TaCl₅(DMF), TaCl₅(PhA), TaBr ₅(PhA), TaCl₅(TPPO), [TaBr₄(TMU) ₂][TaBr₆], and Ta₂(μ-O)Cl ₈(TMP)₂. No evidence for formation of M=O bonds due to oxygen atom transfer from the ligand to the metal has been observed in any case. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200700911

FULL PAPER
DOI: 10.1002/ejic.200700911
Complexes of Niobium(V) and Tantalum(V) Halides with Ligands that Contain
N–C=O and P=O Functionalities: A Synthetic and Structural Study
Fabio Marchetti,[a][‡] Guido Pampaloni,*[a] and Stefano Zacchini[b]
Keywords: Niobium / Tantalum / Halides / Amide / P=O ligands / X-ray structure
The reactions of niobium and tantalum pentahalides, MX5,
with dialkylureas (tetramethyl- and tetraethylurea, TMU and
TEU, respectively), amides (N,N,dimethylformamide, DMF,
N,N-diethylformamide, DEF, N-phenylacetamide, PhA), and
P=O-containing compounds (triphenylphosphane oxide,
TPPO, and trimethyl phosphate, TMP) are not dependent on
the reactant to metal molar ratio, and afford hexacoordinate
complexes of the general formula MX5(L). The only excep-
tion is given by the reaction of TaBr5 with TMU, which pro-
ceeds by bromide migration from one metal center to an-
other, and provides the ionic adduct [TaBr4(TMU)2][TaBr6].
Hydrolysis of TaCl5(TMP), due to adventitious water, has
yielded the dinuclear species Ta2(µ-O)Cl8(TMP)2. All com-
pounds have been fully characterized in solution, and X-ray
crystal structures have been determined for NbCl5(TEU),
NbCl5(DMF),
TaCl5(DMF),
TaCl5(PhA),
TaBr5(PhA),
TaCl5(TPPO), [TaBr4(TMU)2][TaBr6], and Ta2(µ-O)Cl8(TMP)2.
No evidence for formation of M=O bonds due to oxygen atom
transfer from the ligand to the metal has been observed in
any case.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
equiv. of THF to MX5 can lead to formation of the ionic
species
[MX6].
Introduction
[MX4(THF){O(CH2)4O2(CH2)3C8H2}(O2–C8)]-
The halides of early transition elements are often used as
starting materials for the synthesis of inorganic or organo-
metallic compounds, although they can induce parasitic re-
actions when contacted with species that contain Lewis ba-
sic functionalities. This is particularly true in the case of the
metal halides of the group 5 metals in the highest oxidation
state, MX5 (M = Nb, Ta).[1] For instance, deoxygenation
reactions[2] have been reported with these powerful Lewis
acids, and examples include sulfoxides,[3] phosphane ox-
ides,[4] and crown ethers.[5] Therefore, the coordination
chemistry of MX5 (M = Nb, Ta) with oxygen donor ligands
is scarcely developed, if we except alcohols or diols.[6]
We recently showed[7] that, when niobium and tantalum
pentahalides react with ketones (aldehydes) or aliphatic cy-
clic ethers, different reactions can take place, beyond the
formation of the expected acid-base adducts MX5(L). These
alternative pathways depend on the nature of the halide and
are favored by specific O-ligand to metal molar ratios. At
variance to previous reports, we did not collect evidence for
M=O double-bond formation in the reactions of MX5 with
carbonyl compounds, in any stoichiometric ratio.[7]
Furthermore, we have observed[8] that the addition of 1.5
This latter compound, which contains information on
the mechanism of THF polymerization promoted by MX5,
is formed together with the simple octahedral complex
MCl5(THF) when X = Cl, whereas it has not been detected
at all for X = F and represents the only product for X =
Br, I.[8]
In the framework of our studies in the field, we decided
to investigate the chemistry of the pentahalides MX5 (M =
Nb, X = Cl, 1a; M = Ta, X = F, 1b; Cl, 1c; Br, 1d) with
amides, ureas, and P=O-containing species. In this paper,
we report on the preparation and characterization of ad-
ducts between MX5 and these types of molecules, showing
that, working under the rigorous absence of water, the main
reaction is the O-coordination of the Lewis base. The X-ray
characterization of the products has become necessary for
their unambiguous identification, and to contribute to ex-
tend the restricted family of structurally characterized ad-
ducts of MX5 with O-donor ligands.
Results and Discussion
[a] Dipartimento di Chimica e Chimica Industriale, Università di
Pisa,
The compounds MX5 (M = Nb, Ta, X = F, Cl, 1a–c), in
CH2Cl2 suspensions, have ureas added (TMU = tetrameth-
ylurea, TEU = tetraethylurea) to afford the octahedral ad-
ducts MX5(L) [M = Nb, X = Cl, L = TMU, 2a; M = Ta,
X = F, L = TMU, 2b; M = Ta, X = Cl, L = TMU, 2c; M
= Nb, X = Cl, L = TEU, 3a; M = Ta, X = F, L = TEU,
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
Bologna,
Viale Risorgimento 4, 40136 Bologna, Italy
[‡] Born in Bologna (Italy) in 1974.
Eur. J. Inorg. Chem. 2008, 453–462
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
453

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
3b; M = Ta, X = Cl, L = TEU, 3c], in high yields (see (niobium) complex containing a urea ligand. More gen-
Scheme 1).
erally, the O-coordination fashion is the most common
adopted by ureas and TMU in particular, a rare example
of N-coordination mode being observed in [Pt(dien)-
(NH2CONMe2)](CF3SO3)2 (dien = diethylenetriamine).[9]
The salient IR feature found for complexes 2–3 (IR spec-
tra recorded in the solid state) regards the absorption due
to the carbonylic stretching, which falls in the ranges 1625–
1630 cm–1, for TMU complexes, and at about 1580 cm–1 for
TEU derivatives. These values are lower than those known
for the free ureas (1647 and 1645 cm–1 for TMU and TEU,
Scheme 1. Preparation of urea derivatives of niobium and tanta-
lum.
1
respectively[10]) as a consequence of coordination. The H
NMR spectra of 2 show one resonance attributed to four
equivalent methyl groups, at 3.29–2.75 ppm (to be com-
pared to δ = 2.81 ppm for uncoordinated TMU[11]), whereas
in the 13C NMR spectra, the resonances accounting for the
carbonylic carbon and the methyl groups appear at about
164 ppm and 40 ppm, respectively [for uncoordinated
The reactions occur rapidly by using a slight excess of
the corresponding urea, and proceed without formation of
byproducts: when the same reactions were followed by H
1
NMR spectroscopy in CDCl3 solutions, only compounds
2–3 were detected. Compounds 2–3 have been fully charac-
terized by means of IR and NMR spectroscopy, and ele-
mental analysis. Moreover, the molecular structure of 3a
has been ascertained by X-ray diffraction (Figure 1 and
Table 1). The molecule displays a distorted octahedral ge-
ometry with an O-coordinated tetramethylurea. As a conse-
quence, the O(1)–C(1) interaction [1.328(2) Å] is signifi-
cantly longer than a pure double bond, whereas C(1)–N(1)
and C(1)–N(2) [1.336(2) and 1.334(2) Å] possess a signifi-
cant π character, in order to maintain electron density on
the sp2 carbon.
1
TMU: δ(CO) = 165.7; δ(CH3) = 38.6 ppm]. The H NMR
spectra of 3 exhibit two multiplets, one at about 3.6 ppm
ascribable to the CH2 units (δ = 2.97 ppm in uncoordinated
TEU) and the other one at about 1.3 ppm due to the CH3
groups (δ = 0.92 ppm in uncoordinated TEU). The 13C
NMR spectra of 3 show the resonance for the CO in the
range 162.7–168.7, and two resonances attributed to the
equivalent ethyl chains, at about 45 ppm and 14 ppm
respectively [for uncoordinated TEU: δ(CO) = 165.0,
δ(CH2) = 42.4, δ(CH3) = 13.3 ppm]. The equivalence of the
alkyl units, within each ligand, suggests that the ureas are
O-coordinated to the metal centers, in line with what was
found in solid for 3a. Moreover, the 19F NMR spectra avail-
able for 2b and 3b are as expected for octahedral TaF5L
adducts, that is, they exhibit two distinct resonances for cis-
and trans-fluorines, respectively [e.g., for 2b: δ(trans-F) =
56.8, δ(cis-F) = 38.3 ppm].[12]
Interestingly, the reaction of TaBr5 with TMU, per-
formed in conditions analogous to those used for the prepa-
ration of 2 and 3, gave the ionic compound [TaBr4(TMU)2]-
[TaBr6] (4) exclusively, which was identified by X-ray dif-
fraction (Figure 2 and Table 2) and fully characterized by
IR and NMR spectroscopy. It has to be noted that when
the reaction of TaBr5 with TMU was followed by 1H NMR
spectroscopy in CDCl3 solution, compound 4 was the only
species present in solution.
Figure 1. Molecular structure of NbCl5(TEU), 3a. Thermal ellip-
soids are drawn at 30% probability level.
Table 1. Selected bond lengths [Å] and angles [°] of NbCl5(TEU),
3a.
Nb(1)–Cl(1)
Nb(1)–Cl(2)
Nb(1)–Cl(3)
Nb(1)–Cl(4)
Nb(1)–Cl(5)
Nb(1)–O(1)
O(1)–C(1)
O(1)–Nb(1)–Cl(2) 174.98(4)
Cl(3)–Nb(1)–Cl(1) 176.63(2)
Cl(4)–Nb(1)–Cl(5) 178.042(19)
2.3531(4)
2.3375(5)
2.3407(4)
2.3488(5)
2.3597(5)
1.9596(12)
1.328(2)
C(1)–N(1)
C(1)–N(2)
N(1)–C(4)
N(1)–C(2)
N(2)–C(6)
N(2)–C(8)
1.336(2)
1.334(2)
1.477(2)
1.486(2)
1.477(2)
1.483(2)
C(1)–N(1)–C(4)
C(1)–N(1)–C(2)
C(4)–N(1)–C(2)
C(1)–N(2)–C(6)
C(1)–N(2)–C(8)
C(6)–N(2)–C(8)
124.99(14)
120.35(14)
114.46(13)
124.94(14)
120.15(14)
113.25(13)
O(1)–C(1)–N(2)
O(1)–C(1)–N(1)
N(2)–C(1)–N(1)
116.49(14)
117.43(14)
126.07(15)
Figure 2. View of the [TaBr4(TMU)2]+ cation in [TaBr4(TMU)2]-
[TaBr6], 4. Thermal ellipsoids are drawn at 30% probability level.
best of our knowledge, the first one reported for a tantalum Only independent atoms are labeled.
It is noteworthy that the X-ray structure of 3a is, to the
454 Eur. J. Inorg. Chem. 2008, 453–462
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Complexes of Niobium(V) and Tantalum(V) Halides
Table 2. Selected bond lengths [Å] and angles [°] of [TaBr4(TMU)2]- series of amides (DMF = N,N,dimethylformamide, DEF =
[TaBr6], 4.
N,N-diethylformamide, PhA = N-phenylacetamide), afford-
ing the complexes MX5(L) [M = Nb, X = Cl, L = DMF,
5a; M = Ta, X = F, L = DMF, 5b; M = Ta, X = Cl, L =
DMF, 5c; M = Ta, X = Cl, L = DEF, 6; M = Ta, X = Cl,
L = PhA, 7a; M = Ta, X = Br, L = PhA, 7b] (see Scheme 2).
Ta(1)–O(1)
Ta(1)–Br(1)
Ta(1)–Br(2)
C(1)–O(1)
C(1)–N(2)
O(1)–Ta(1)–Br(1) 89.6(3)
O(1)–Ta(1)–Br(2) 89.8(3)
Br(1)–Ta(1)–Br(2) 90.73(5)
1.932(8)
C(1)–N(1)
C(2)–N(1)
C(3)–N(1)
C(4)–N(2)
1.340(15)
1.450(16)
1.465(16)
1.480(17)
1.453(16)
121.5(10)
124.1(10)
114.3(10)
122.7(11)
122.6(11)
114.1(10)
2.4447(16)
2.5050(13)
1.314(15)
1.324(16)
C(5)–N(2)
C(1)–N(1)–C(2)
C(1)–N(1)–C(3)
C(2)–N(1)–C(3)
C(1)–N(2)–C(5)
C(1)–N(2)–C(4)
C(5)–N(2)–C(4)
O(1)–C(1)–N(2)
O(1)–C(1)–N(1)
N(1)–C(1)–N(2)
118.2(11)
117.9(10)
123.9(11)
The cationic part of 4 displays an octahedral geometry,
with the two TMU ligands in trans position. The Ta–Br
bonds within the cation (mean value: 2.475 Å) and the
anion (2.464 Å) are similar to those observed (2.583 and
2.487 Å, respectively) in the arsine derivative {TaBr4[1,2-
(Me2As)2C6H4]}[TaBr6].[13] As in 3a, the coordinated TMU
ligands show an elongation of the C(1)–O(1) interaction
[1.314(15) Å] and shortening of C(1)–N(1) [1.340(15) Å]
and C(1)–N(2) [1.324(16) Å], compared to free ureas.
The IR spectrum of 4 shows the band due to the CO
stretching vibration at 1632 cm–1. A major NMR feature is
represented by the CO resonance, which is downfield
shifted (δ = 170.8 ppm) with respect to that found for com-
plexes 2.
The different outcomes of the reactions giving 2–3 and 4
can be explained on the basis of the different nature of the
halides. As the formation of the ionic adduct 4 requires ha-
lide migration from one metal center to another, this step
should be favored by a relatively low metal–halide bond
energy, as is the case of bromide. This result is not surpris-
ing: our recent findings concerning the chemistry of MX5
with cyclic ethers[8] have pointed out that MX5 can react
with limited amounts of THF, affording, besides the ex-
pected MX5(THF) adduct, an ionic species, the formation
of which proceeds by halide migration from one metal to
another, to generate the [MX6]– anion (see Introduction).
Indeed, this reaction has been observed to be favored on
decreasing the metal–halide bond energy. Halide migration
promoted by addition of neutral molecules to MX5 has also
been observed when NbCl5 reacts with dialkyl disulfides,
S2R2, to give the ionic species [NbCl4(S2R2)2][NbCl6], in
which the cationic unit contains an octacoordinated ni-
obium center.[14]
Scheme 2. Preparation of derivatives of niobium and tantalum con-
taining amides as ligands.
Analogously to the discussed reactions with ureas, the
reactions yielding 5–7 occur rapidly by using a slight excess
of the amide, and proceed without formation of byproducts,
1
as ascertained by H NMR spectroscopy. Compounds 5–7
have been fully characterized by means of IR and NMR
spectroscopy and elemental analyses. Moreover, in view of
the fact that a search on the Cambridge Crystallographic
Database[16] has shown that the only structurally charac-
terized amide complexes of the heavier group 5 elements
are the DMF adducts of heterodimetallic niobium–copper
chalcogenide clusters,[17] we became particularly interested
in determining the solid-state structures of the new com-
pounds. The X-ray analyses were carried out on 5a, 5c, 7a,
and 7b (Figures 3 and 4 report a view of compounds 5a
and 7b, Tables 3 and 4 list a selection of bond lengths and
angles for compounds of 5a, 5c, 7a, and 7b). All these com-
plexes are monomers, and the amide behaves as an O-donor
ligand.
Figure 3. Molecular structure of NbCl5(DMF), 5a. Thermal ellip-
soids are drawn at 30% probability level.
According to earlier reports, the reaction of MX5 with
excess of ureas may lead to C=O bond activation, and con-
sequent formation of species of the general formula
The mean values of the angles (Cl–M–Cl)trans [174.7(1)°]
MOX3L2.[15] In order to investigate the point, we tested the and Cl–M–O [175.8(3)°] for compounds 5a and 5c and of
reactivity of TaCl5 with excess TMU (from two- to five- the angles (X–Ta–X)trans [174.5°] and X–Ta–O [177.8°] for
fold), in strictly anhydrous conditions. No traces of products compounds 7a and 7b indicate an only slightly distorted
1
different from 2c were detected in solution by H NMR octahedral geometry of the MX5(L) systems.
spectroscopy. Thus, the study of the chemistry of MX5 with
The Nb–O bond length in 5a [2.018(10) Å] is comparable
ureas has not evidenced the occurrence of O-abstraction with those observed in Cu3NbS3Cl2(PPh3)3(DMF)2·
processes.
1.5DMF [2.270(4) and 2.280(3) Å][17] and NEt4-
To clarify these topics, we decided to move our study to [Cu3NbS3Cl3(DMF)3] [2.260(5) Å].[17] The average M–Cl
the reactivity of 1 with amides. Hence, MX5 reacts with a [M = Nb, 2.336 Å; M = Ta, 2.334(6) Å in 5c and 2.336(8) Å
Eur. J. Inorg. Chem. 2008, 453–462
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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455

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
in 7a] and Ta–Br distances [2.479(1) Å] compare well with
those of the terminal M–X bonds in MX5 (Nb–Cl, 2.29 Å;
Ta–Cl, 2.30 Å; Ta–Br, 2.45 Å).[18]
Major IR features of 5–7 are given by the absorption due
to the CO group, which falls in the range 1655–1643 cm–1
for 5–6 and at about 1610 cm–1 for 7, and by the NH
stretching vibration of 7, observed as a medium sharp peak
1
at about 3300 cm–1. The OCH H NMR resonance for 5–6
is seen at δ = 8.02–8.57 ppm, while the carbonylic carbon
resonates at about 160 ppm. In accordance with what was
reported for the urea complexes 2–4, the resonances related
to the alkyl chains in 5–6 appear downfield shifted with
respect to the corresponding free amide [e.g., for 5a: δ(CH3)
= 3.43, 3.33 ppm; δ(CH3) = 41.3, 33.5 ppm. For uncoordi-
nated DMF: δ(CH3) = 2.97, 2.88 ppm; δ(CH3) = 36.4,
31.3 ppm]. This feature is likely to be a consequence of O-
coordination, which would enhance the electronic donation
from the nitrogen atom to the CO carbon. Finally, the 19F
NMR spectrum of 5b is analogous to those of 2b–3b, show-
ing two resonances for cis- and trans-fluorines, respectively
[δ(trans-F) = 65.9, δ(cis-F) = 38.8 ppm]. This point repre-
sents a significant confirmation for the MX5L-type struc-
ture of 5b.
Figure 4. Molecular structure of TaBr5(PhA), 7b. Thermal ellip-
soids are drawn at 30% probability level.
Table 3. Selected bond lengths [Å] and angles [°] of NbCl5(DMF),
5a, and TaCl5(DMF), 5c.
5a
5c
M(1)–Cl(1)
M(1)–Cl(2)
M(1)–Cl(3)
M(1)–Cl(4)
M(1)–Cl(5)
M(1)–O(1)
O(1)–C(1)
C(1)–N(1)
2.331(4)
2.337(3)
2.350(4)
2.366(3)
2.329(6)
2.362(4)
2.336(6)
2.338(4)
2.302(5)
2.000(12)
1.29(2)
1.26(2)
1.47(2)
1.48(2)
176.26(17)
173.49(16)
175.9(4)
123.0(18)
123.0(16)
122.1(16)
114.8(14)
Interestingly, the reaction of TaCl5 with DMF, studied in
CDCl3 solution by 1H NMR spectroscopy, is almost imme-
diate and initially yields a mixture of two products, 5c and
5d, in about a 1:14 ratio. Then, compound 5d converts into
2.297(4)
2.018(10)
1.290(18)
1.278(19)
1.470(17)
1.456(19)
176.08(16)
172.96(14)
175.7(3)
122.4(13)
121.9(13)
121.3(13)
116.8(12)
1
5c in 3 days, in CDCl3 solution. Compound 5d shows H
N(1)–C(2)
N(1)–C(3)
NMR peaks at 7.80 (CH), 2.75 and 2.63 (NMe) ppm, 13C
NMR resonances at 162.0 (CO), 36.0 and 30.9 (NMe) ppm,
and an IR absorption accounting for the CO group at
1660 cm–1. As far as 5c is concerned, the NMR resonances
are shifted toward higher frequencies [1H NMR: 8.57 (CH);
3.48, 3.36 (NMe) ppm. 13C NMR 167.0 (CO); 40.4, 36.5
(NMe) ppm] and the IR stretching vibration of the C=O
group appears at lower wavenumbers (1648 cm–1) than
those observed for 5d.
Cl(1)–M(1)–Cl(3)
Cl(2)–M(1)–Cl(4)
Cl(5)–M(1)–O(1)
O(1)–C(1)–N(1)
C(1)–N(1)–C(2)
C(1)–N(1)–C(3)
C(2)–N(1)–C(3)
The O-coordination of DMF to tantalum in 5c (see
above), the shift towards higher frequencies of the methyl
resonances passing from 5d to 5c, and the increase of the
discrepancy between the wavenumbers of the CO stretching
vibration of the uncoordinated[19] and the coordinated
DMF on going from 5d (∆ = 19 cm–1) to 5c (∆ = 31 cm–1)
suggest that we are dealing with isomeric compounds, with
DMF probably acting as an O-donor ligand in 5c and as a
N-donor in 5d. Studies on the stability and structure (in
solution) of N- or O-bonded amide groups to metal ions
have appeared.[20]
Evidence of possible initial coordination of potentially
bivalent N- or O-ligands to MX5 through the nitrogen
atom, followed by rearrangement giving the final, stable, O-
coordinated isomer, have been collected exclusively in the
case of the reaction between TaCl5 and DMF. Indeed the
spectroscopical features regarding 5a,b–6 resemble those of
5c, thus suggesting that these complexes contain O-coordi-
nated amides.
Table 4. Selected bond lengths [Å] and angles [°] of TaCl5(PhA),
7a,[a] and TaBr5(PhA), 7b.
7a (molecule 1) 7a (molecule 2) 7b
Ta(1)–X(1)
Ta(1)–X(2)
Ta(1)–X(3)
Ta(1)–X(4)
Ta(1)–X(5)
Ta(1)–O(1)
O(1)–C(1)
C(1)–C(2)
2.3597(8)
2.3843(9)
2.3186(9)
2.3184(9)
2.2872(8)
2.007(2)
1.293(4)
1.480(5)
1.317(4)
1.430(4)
172.72(3)
175.97(3)
178.95(7)
120.6(3)
119.0(3)
120.4(3)
128.8(3)
2.3848(8)
2.3314(9)
2.3145(8)
2.3548(9)
2.3041(8)
1.991(2)
1.289(4)
1.485(4)
1.308(4)
1.440(4)
175.17(3)
175.70(3)
177.20(7)
120.3(3)
119.2(3)
120.5(3)
127.9(3)
2.5380(16)
2.4736(17)
2.4635(17)
2.4756(17)
2.4451(15)
1.999(8)
1.235(13)
1.491(15)
1.310(15)
1.425(15)
171.67(6)
175.64(6)
177.2(3)
C(1)–N(1)
N(1)–C(3)
X(1)–Ta(1)–X(3)
X(2)–Ta(1)–X(4)
X(5)–Ta(1)–O(1)
O(1)–C(1)–C(2)
O(1)–C(1)–N(1)
C(2)–C(1)–N(1)
C(1)–N(1)–C(3)
119.1(10)
120.5(10)
120.4(10)
124.2(10)
[a] Compound 7a crystallizes with two independent molecules in
the unit cell. See CIF file for the numbering of molecule 2. X = Cl,
7a; Br, 7b.
Further attempts to verify the possibility of O-abstrac-
tion processes were carried out by treating TaCl5 with a
456
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 453–462

Complexes of Niobium(V) and Tantalum(V) Halides
fivefold excess of DEF and PhA, respectively. Notwith-
standing, only products 6 and 7 could be detected by means
of 1H NMR spectroscopy. In general, the nature of the
products derived from the reactions of MX5 (X = F, Cl)
with amides is as expected on the basis of the results col-
lected for the chemistry of MX5 with ureas.
The parallelism with the reactions with ureas suggested
that TaBr5 could add DMF or DEF in a different fashion,
so affording ionic products analogous to 4. We tried the
reaction of TaBr5 with DMF, however attempts to get good
quality crystals were unsuccessful. As X-ray analysis would
be crucial for unambiguous determination of the structure
of the product, TaBr5 was treated with PhA and single crys-
tals were obtained for 7b. The structure of 7b (see above)
belongs to the general type MX5L, therefore in this case
bromide migration does not occur, in contrast with reports
on the synthesis of 4. The reasons for the different out-
comes of the reactions of TaBr5 with TMU and PhA should
be searched in the characteristics of the ligands, with both
steric and electronic factors probably playing a role in de-
termining the outcome of the reaction.
Figure 5. Molecular structure of TaCl5(TPPO), 8b. Thermal ellip-
soids are drawn at 30% probability level. Only one of the two inde-
pendent molecules present in the unit cell is represented.
Table 5. Selected bond lengths [Å] and angles [°] of TaCl5(TPPO),
8b.
Molecule 1
Molecule 2[a]
As far as species containing the P=O functionality are
concerned, examples of niobium(V) adducts with O=PR3
ligands (R = NMe2,[21] Ph,[22]) have been reported. More
interestingly, examples of transition-metal adducts of
O=P(OR)3 species (R = alkyl chain) are significantly few,
while more cases include lanthanide and actinide com-
plexes.[23]
Thus MCl5 (M = Nb, Ta) reacts with triphenylphos-
phane oxide (TPPO) and trimethylphosphate (TMP) to give Cl(4)–Ta(1)–O(1)
the octahedral species MCl5(L) [M = Nb, L = TPPO, 8a; M
Ta(1)–Cl(1)
Ta(1)–Cl(2)
Ta(1)–Cl(3)
Ta(1)–Cl(4)
Ta(1)–Cl(5)
Ta(1)–O(1)
O(1)–P(1)
Cl(1)–Ta(1)–Cl(3)
Cl(2)–Ta(1)–Cl(5)
2.319(5)
2.341(5)
2.365(5)
2.325(5)
2.326(5)
2.016(12)
1.515(12)
177.0(2)
175.59(18)
177.5(4)
153.7(8)
2.333(5)
2.328(5)
2.335(5)
2.339(5)
2.342(5)
2.017(13)
1.517(14)
176.34(19)
176.3(2)
178.2(4)
151.7(9)
Ta(1)–O(1)–P(1)
= Ta, L = TPPO, 8b; M = Ta, L = TMP, 9] [Equation (1)].
[a] For the numbering scheme of molecule 2, see CIF file deposited
in the Cambridge Crystallographic Data Centre (ref. number
(1) CCDC-653907).
plex, which falls at δ = 58.1 ppm. The NMR spectroscopic
Complexes 8–9 were characterized by spectroscopic tech- features for compound 9 consist of one 1H NMR resonance
niques and elemental analyses; moreover, the identity of 8b at δ = 4.16 ppm, which appears as a doublet due to coup-
was corroborated by an X-ray diffraction study (Figure 5 ling with the phosphane nucleus (3JPH = 13.2 Hz), attrib-
and Table 5). Two independent molecules are present in the uted to three equivalent methyl groups, a corresponding res-
unit cell of 8b, displaying the same connectivity and only onance at δ = 58.0 ppm in the 13C NMR spectrum, and a
minor differences in the bonding parameters. The bonding signal at –2.60 ppm in the 31P NMR spectrum. According
parameters of 8b are similar to those observed in other to these data, the identity of 9 could not be established
structurally characterized TPPO derivatives, such as without ambiguity. Unfortunately, the procedure used for
MoCl2(O)2(TPPO)2,[24]
MoCl4(TPPO)2,[25]
WCl2(O)2- isolating the products under strictly anhydrous conditions
(TPPO)2,[26] and WOCl3(TPPO)2,[27] once the differences in was not successful in this case, as the crystals that could be
the ionic radii of the different metals are taken into con- obtained corresponded to a compound different from 9,
sideration. Geometrical parameters similar to those ob- that is, Ta2(µ-O)Cl8(TMP)2 (10). The identification of this
served in 8b have been reported for the niobium pentachlo- compound was made possible by an X-ray diffraction
ride adduct NbCl5(S=PPh3).[28]
analysis (Figure 6 and Table 6). The structure of compound
The IR spectra of 8a–b (recorded in the solid state) show 10 somehow confirms the identity proposed for the precur-
a strong band accounting for the P–O stretching, at 1005 sor 9. Thus, 10 is composed of two TaCl4(TMP) units
and 1007 cm–1, respectively. Reasonably, these values ap- joined by a bridging oxo-ligand, trans to the coordinated
pear at lower frequencies with regards to those observed for TMP molecules. The two TaCl4 units are exactly eclipsed
free TPPO [ν(P=O) = 1182 cm–1, in the solid state].
(actually, the second one is generated by an inversion center
The 31P NMR spectrum of 8b exhibits the signal ex- on the bridging oxygen atom) and, therefore, the molecule
pected for the unique phosphane present within the com- possesses an idealized D4h symmetry.
Eur. J. Inorg. Chem. 2008, 453–462
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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457

F. Marchetti, G. Pampaloni, S. Zacchini
(2)
FULL PAPER
It is noteworthy that further hydrolysis of 10 should pro-
duce the species TaOCl3(TMP) [see Equation (3)]. This was
not actually observed, however this consideration suggests
the possibility that the reported aptitude of MX5 species
(M = Nb, Ta) to activate C=O and P=O bonds, generating
M=O moieties, is in reality one aspect of the great tendency
of MX5 to undergo quick hydrolysis.
Figure 6. Molecular structure of Ta2(µ-O)Cl8(TMP)2, 10. Thermal
ellipsoids are drawn at 30% probability level. Only independent
atoms are labeled.
Ta2(µ-O)Cl8(TMP)2 + H2O Ǟ 2 TaOCl3(TMP) + 2 HCl
(3)
Table 6. Selected bond lengths [Å] and angles [°] of Ta2(µ-O)-
Cl8(TMP)2, 10.
Conclusions
This paper represents an extension of our recent studies
on the chemistry of group 5 metal pentahalides, MX5, with
oxygen donor ligands to ureas, amides, and P=O-contain-
ing species. By contrast with the variety of products re-
ported for the reactions of MX5 with ketones, ureas and
amides usually add to MX5, acting as O-donors and giving
octahedral species of the type MX5L, in whatever stoichi-
ometry used. The formation of the cationic species
[MX4L2][MX6] has been observed in one case only, and
seems to be the consequence of concomitant factors, that
is, low metal–halide bond energy and steric and electronic
properties of the ligand L. The NMR study of the reaction
of TaCl5 with DMF has outlined the possibility for these
reactions to proceed through the formation of a kinetic
product, in which the ligand is N-coordinated to the metal
center, and which evolves affording the final stable O-donor
ligand containing complex. No evidence for any type of
bond activation process has been found. In particular, the
possibility of O-abstraction reactions by MX5 should be
discounted on the basis of our results, in contrast to pre-
vious reports. The presence of the Ta–O–Ta unit in the
complex Ta2(µ-O)Cl8(TMP)2, isolated from reaction of
TaCl5 with trimethylphosphate, is believed to be the conse-
quence of the partial hydrolysis of TaCl5(TMP) due to ad-
ventitious water.
Ta(1)–Cl(1)
Ta(1)–Cl(2)
Ta(1)–Cl(3)
Ta(1)–Cl(4)
Ta(1)–O(1)
Cl(1)–Ta(1)–Cl(2) 175.6(2)
Cl(3)–Ta(1)–Cl(4) 175.6(2)
2.356(6)
2.356(6)
2.343(6)
2.333(6)
1.881(1)
Ta(1)–O(2)
O(2)–P(1)
P(1)–O(3)
P(1)–O(4)
P(1)–O(5)
O(1)–Ta(1)–O(2) 178.4(5)
Ta(1)–O(2)–P(1) 160.2(12)
2.046(16)
1.466(16)
1.46(2)
1.64(2)
1.56(2)
The geometrical parameters (Ta–Cl and Ta–Ophosphate) of
10 are directly comparable with those of 8b. As far as the
Ta–O–Ta bridge is concerned, the bond length [1.881(1) Å]
and the bond angle (180°) are similar to those observed in
similar oxo-bridged compounds of tantalum(V), examples
being the [Ta2Cl10O]2– anion [1.880(1) Å, 180°],[29]
[TaCl2(NMe2)2(NHMe2)]2(µ–O) [1.917(6) Å, 174.3(3)°],[30]
and [TaCl3py(NMe2)]2(µ–O) [1.877(9) Å, 176.0(5)°].[31] The
linearity of the Ta–O–Ta bridge can be readily accounted
for by the presence of a oxygen-p to metal-d π-bonding to
both tantalum centers in agreement with the M–O–M
bonding scheme first proposed by Dunitz and Orgel.[32]
The characterization of compound 10 was completed by
elemental analyses for C, H, Ta, and Cl, and by NMR spec-
troscopy. The equivalent methyl groups give rise to reso-
nances at 3.82 (1H NMR) and 60.0 ppm (13C NMR),
respectively. In addition, the 31P NMR spectrum exhibits a
unique resonance at δ = 3.88 ppm, ascribable to the two
phosphorus nuclei, confirming the symmetry of the com-
plex.
Experimental Section
General: All manipulations of air- and/or moisture-sensitive com-
pounds were performed under prepurified argon using standard
The presence of the Ta–O–Ta unit within complex 10
deserves some additional comment. It may be discounted Schlenk techniques. The reaction vessels were oven-dried at 150 °C
prior to use, evacuated (10–2 Torr), and then filled with argon. All
that this unit is originated by oxygen abstraction from a
the reagents, including MX5 (M = Nb, Ta, X = Cl; M = Ta, X = F),
TMP molecule because when the reaction of TaCl5 with 3
were commercial products (Aldrich) of the highest purity available.
equiv. of TMP was performed in an NMR tube, in CD2Cl2,
TaBr5 was prepared according to published procedures.[33] Solvents
1
only free TMP and complex 9 were observed by H NMR
and liquid reagents were carefully distilled before use under argon
spectroscopy. Furthermore, no traces of trimethylphosphite
from appropriate drying agents. IR spectra were recorded on solid
(which would be the expected organic product of a hypo-
thetical O-abstraction reaction from TMP) were detected
samples with an FTIR Spectrometer equipped with a Perkin–Elmer
UATR sampling accessory. NMR measurements were performed
after 1 d. Therefore, it is reasonable that the µ-oxo moiety
of 10 is the result of a partial hydrolysis of 9, due to adven-
titious water [see Equation (2)].
on a Varian Gemini 200BB spectrometer, at 298 K. The chemical
shifts for 1H and 13C were referenced to internal TMS. The chemi-
cal shifts for 19F were referenced to CFCl3.
458
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 453–462

Complexes of Niobium(V) and Tantalum(V) Halides
Preparation of MX5(TMU) [M = Nb, X = Cl, 2a; M = Ta, X = F,
2b; M = Ta, X = Cl, 2c]
TaBr5 (1.20 mmol) with tetramethylurea (1.22 mmol). Crystals suit-
able for X-ray analysis were collected by a CH2Cl2 solution layered
with pentane, at room temperature.
General Procedure: Tetramethylurea (0.150 mL, 1.25 mmol) was
added to a suspension of MX5 (1.20 mmol) in CH2Cl2 (10 mL) in
a Schlenk tube. The mixture was stirred for 30 min, during which
progressive dissolution of the solid occurred. The final solution was
layered with pentane (30 mL) and a microcrystalline solid was
formed after 8 h at room temperature.
4: Yellow, C10H24Br10N4O2Ta2 (1393.26): calcd. C 8.6, H 1.7, Cl
57.4, N 4.0, Ta 26.0; found C 8.4, H 1.7, Cl 56.9, N 3.9, Ta 24.5.
Yield: 0.635 g, 76%. 1H NMR (CDCl3): δ = 2.96 (s, 24 H, Me)
ppm. 13C NMR (CDCl3): δ = 170.8 (CO), 39.4 (Me) ppm. IR (solid
state): ν = 2965 (w), 2943 (w), 2799 (vw), 1632 [s (CO)], 1607 (m-
˜
sh), 1515 (s), 1456 (s), 1399 (vs), 1284 (vs), 1210 (vs), 1170 (s), 1146
2a: Orange, C5H12Cl5N2NbO (386.33): calcd. C 15.5, H 3.1, Cl
45.9, N 7.3, Nb 24.1; found C 15.2, H 3.2, Cl 45.4, N 7.6, Nb 23.6.
Yield: 0.389 g, 84%. 1H NMR (CDCl3): δ = 3.29 (s, 12 H, Me)
ppm. 13C NMR (CDCl3): δ = 163.2 (CO), 41.1 (NMe) ppm. IR
(m), 1058 (s), 895 (m), 807 (wm), 783 (vs), 714 (vs) cm–1.
Preparation of MX5(DMF) [M = Nb, X = Cl, 5a; M = Ta, X = F,
5b; M = Ta, X = Cl, 5c (O isomer); M = Ta, X = Cl, 5d (N isomer)]
(solid state): ν = 2946 (wm), 1625 [s (CO)], 1606 (m), 1514 (s), 1461
˜
General
Procedure:
N,N-Dimethylformamide
(0.200 mL,
(ms), 1401 (vs), 1290 (vs), 1222 (ms), 1170 (m), 1058 (s), 894 (m),
2.60 mmol) was added to a Schlenk tube containing a suspension
of MX5 (2.50 mmol) in CH2Cl2 (10 mL). The mixture was stirred
for 20 min, during which progressive dissolution of the solid oc-
curred. The resulting solution was layered with pentane (20 mL),
thus a microcrystalline material was formed after 24–48 h at ambi-
ent temperature. Crystals suitable for X-ray analysis were collected
in the case of 5a and 5c.
784 (vs), 719 (ms) cm–1.
2b: Colorless, C5H12F5N2OTa (392.10): calcd. C 15.3, H 3.1, N 7.1,
Ta 46.2; found C 14.9, H 2.9, N 6.9, Ta 45.7. Yield: 0.362 g, 77%.
1H NMR (CDCl3): δ = 3.01 (s, 12 H, Me) ppm. 13C NMR (CDCl3):
δ = 163.9 (CO), 39.2 (NMe) ppm. 19F NMR (CDCl3): δ = 56.8 (s,
1 F, trans-F), 38.3 (s, 4 F, cis-F) ppm. IR (solid state): ν = 2956
˜
(w), 1626 [s (CO)], 1537 (s), 1474 (ms), 1408 (s), 1321 (m), 1176
5a: Yellow, C3H7Cl5NNbO (343.26): calcd. C 10.5, H 2.1, Cl 51.6,
N 4.1, Nb 27.1; found C 10.2, H 2.3, Cl 50.6, N 3.9, Nb 26.4.
Yield: 0.644 g, 75%. 1H NMR (CDCl3): δ = 8.48 (s, 1 H, CH),
3.43, 3.33 (s, 6 H, NMe) ppm. 13C NMR (CDCl3): δ = 156.7 (CO),
(m), 1062 (m), 900 (m), 808 (m), 734 (wm), 666 (m) cm–1.
2c: Colorless, C5H12Cl5N2OTa (474.37): calcd. C 12.7, H 2.6, Cl
37.4, N 5.9, Ta 38.1; found C 12.4, H 2.4, Cl 38.1, N 6.1, Ta 37.9.
Yield: 0.427 g, 75%. 1H NMR (CDCl3): δ = 2.75 (s, 12 H, Me)
ppm. 13C NMR (CDCl3): δ = 165.3 (CO), 38.4 (NMe) ppm. IR
41.3, 33.5 (NMe) ppm. IR (solid state): ν = 3063 (w), 2968 (w),
˜
2653 (w), 1946 (w), 1651 [vs (CO)], 1472 (m), 1443 (m), 1421 (ms),
1408 (s), 1333 (vs), 1234 (m), 1130 (m), 1052 (m), 976 (wm), 700
(vs) cm–1.
(solid state): ν = 2972 (vw), 2947 (w), 2805 (vw), 1630 [s (CO)],
˜
1516 (s), 1462 (ms), 1402 (vs), 1287 (vs), 1213 (s), 1170 (m), 1142
(m), 1060 (m), 940 (w), 893 (w), 838 (m), 784 (vs), 714 (m) cm–1.
5b: Colorless, C3H7F5NOTa (349.03): calcd. C 10.3, H 2.0, N 4.0,
Ta 51.8; found C 10.0, H 1.6, N 4.3, Ta 51.0. Yield: 0.593 g, 68%.
1H NMR (CDCl3): δ = 8.02 (s, 1 H, CH), 3.01, 2.86 (s, 6 H, NMe)
ppm. 13C NMR (CDCl3): δ = 164.8 (CO), 38.6, 33.5 (NMe) ppm.
19F NMR (CDCl3): δ = 65.9 (br., 1 F, trans-F), 38.8 (br., 4 F, cis-
Preparation of MX5(TEU) [M = Nb, X = Cl, 3a; M = Ta, X = F,
3b; M = Ta, X = Cl, 3c]: These compounds were synthesized by
the same procedure described for 2a–c, by treating MX5
(1.30 mmol) with tetraethylurea (1.35 mmol). Crystals suitable for
X-ray analysis were collected in the case of 3a.
F) ppm. IR (solid state): ν = 2951 (w), 1655 [vs (CO)], 1490 (wm),
˜
1428 (m), 1352 (s), 1246 (m), 1123 (m), 1058 (m), 880 (w), 812 (m),
3a: Red, C9H20Cl5N2NbO (442.44): calcd. C 24.4, H 4.6, Cl 40.1,
789 (m), 690 (s) cm–1.
N 6.3, Nb 21.0; found C 24.2, H 4.9, Cl 38.9, N 6.5, Nb 20.5.
1
Yield: 0.472 g, 82%. H NMR (CDCl3): δ = 3.67 (m, 8 H, CH2),
5c: O-coordinated isomer. Colorless, C3H7Cl5NOTa (431.31):
1.32 (m, 12 H, CH3) ppm. 13C NMR (CDCl3): δ = 168.7 (CO),
calcd. C 8.4, H 1.6, Cl 41.1, N 3.2, Ta 42.0; found C 8.1, H 1.3, Cl
44.6 (CH ), 13.5 (CH ) ppm. IR (solid state): ν = 2979 (m), 2938
˜
1
2
3
39.9, N 3.0, Ta 41.3. Yield: 0.852 g, 79%. H NMR (CDCl3): δ =
(w), 1579 [vs (CO)], 1495 (m), 1483 (m), 1428 (vs), 1383 (s), 1349
(m), 1307 (s), 1276 (vs), 1220 (ms), 1210 (m), 1176 (s), 1148 (m),
1100 (w), 1069 (m), 997 (wm), 971 (s), 841 (w), 788 (w), 729 (vs)
cm–1.
8.57 (s, 1 H, CH), 3.48, 3.36 (s, 6 H, NMe) ppm. 13C NMR
(CDCl3): δ = 167.0 (CO), 40.4, 36.5 (NMe) ppm. IR (solid state):
ν = 1648 [s (CO)] cm–1.
˜
The reaction of TaCl5, suspended in CDCl3 inside a NMR tube
with DMF gave a solution containing 5c and 5d. The 5c/5d ratio
value measured after 5 min was 1:14. Conversion of 5d into 5c was
completed in 72 h.
3b: Colorless, C9H20F5N2OTa (448.21): calcd. C 24.1, H 4.5, N 6.3,
Ta 40.4; found C 23.8, H 4.2, N 6.4, Ta 39.6. Yield: 0.431 g, 74%.
1H NMR (CDCl3): δ = 3.49 (m, 8 H, CH2), 1.28 (m, 12 H, CH3)
ppm. 13C NMR (CDCl3): δ = 162.7 (CO), 43.8 (CH2), 12.7 (CH3)
ppm. 19F NMR (CDCl3): δ = 56.4 (s, 1 F, trans-F), 39.5 (s, 4 F, cis-
F) ppm.
5d: N-coordinated isomer. 1H NMR (CDCl3): δ = 7.80 (s, 1 H,
CH), 2.75, 2.63 (s, 6 H, NMe) ppm. 13C NMR (CDCl3): δ = 162.0
(CO), 36.0, 30.9 (NMe) ppm. IR (solid state): ν = 1660 [s (CO)]
˜
3c: Yellow, C9H20Cl5N2OTa (530.48): calcd. C 20.4, H 3.8, Cl 33.4,
cm–1.
N 5.3, Ta 34.1; found C 19.8, H 3.8, Cl 32.6, N 4.9, Ta 33.5. Yield:
1
3
Preparation of TaCl5(DEF) (6): This compound was synthesized by
the same procedure described for 5a–c, by treating TaCl5
(2.00 mmol) with N,N-diethylformamide (2.20 mmol).
0.552 g, 80%. H NMR (CDCl3): δ = 3.66 (q, JHH = 7.33 Hz, 8
H, CH2), 1.33 (t, JHH = 7.33 Hz, 12 H, CH3) ppm. 13C NMR
3
(CDCl3): δ = 164.8 (CO), 44.6 (CH2), 13.5 (CH3) ppm. IR (solid
state): ν = 2979 (m), 2936 (w), 2873 (vw), 1578 [vs (CO)], 1485 (s),
˜
6: Colorless, C5H11Cl5NOTa (459.36): calcd. C 13.0, H 2.4, Cl 38.6,
1468 (s), 1433 (vs), 1383 (m), 1360 (m), 1308 (vs), 1285 (vs), 1218
(s), 1183 (s), 1148 (m), 1115 (w), 1076 (m), 1055 (wm), 1002 (m),
976 (s), 945 (m), 844 (w), 792 (m), 736 (vs), 717 (s) cm–1.
N 3.0, Ta 39.4; found C 12.8, H 2.4, Cl 37.7, N 2.6, Ta 38.6. Yield:
1
0.735 g, 80%. H NMR (CDCl3): δ = 8.48 (s, 1 H, CH), 3.73 (m,
4 H, NCH2), 1.44 (m, 6 H, NCH2CH3) ppm. 13C NMR (CDCl3):
δ = 165.5 (CO), 47.1, 43.2 (NCH2CH3), 14.0, 12.9 (NCH2CH3)
Preparation of [TaBr4(TMU)2][TaBr6] (4): This compound was syn-
thesized by the same procedure described for 2a–c, by treating
ppm. IR (solid state): ν = 1643 [s (CO)], 1445 (ms), 1352 (m), 1195
˜
Eur. J. Inorg. Chem. 2008, 453–462
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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459

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
(wm), 1105 (m), 1087 (m), 996 (w), 950 (wm), 822 (ms), 675 (ms),
561 (w), 546 (w), 450 (m) cm–1.
Compound 9 was dissolved in CH2Cl2 (8 mL) and the mixture was
filtered, into a Schlenk tube, in order to obtain a clear solution.
Stratification with pentane (20 mL) gave a colorless microcrystal-
line material, corresponding to 10.
Preparation of TaX5(PhA) [X = Cl, 7a; X = Br, 7b]
General Procedure: TaX5 (2.30 mmol) was introduced into a
Schlenk tube containing a solution of N-phenylacetamide (0.320 g,
2.37 mmol) in CH2Cl2 (10 mL). The mixture was stirred for 15 min
and the resulting solution was layered with pentane (10 mL). X-ray
quality crystals were formed after 24 h, at room temperature (7a)
or at –20 °C (7b).
10: Colorless, C6H18Cl8O9P2Ta2 (941.67): calcd. C 7.7, H 1.9, Cl
30.1, Ta 38.4; found C 7.4, H 2.1, Cl 29.1, Ta 37.6. Yield: 0.299 g,
3
37%. 1H NMR (CDCl3): δ = 3.82 (d, JPH = 13 Hz, 18 H, Me)
ppm. 13C NMR {1H} (CDCl3): δ = 60.0 (Me) ppm. 31P NMR {1H}
(CDCl3): δ = 3.88 (s, 2 P) ppm.
X-ray Crystallographic Study: Crystal data and collection details
for NbCl5(TEU) (3a), [TaBr4(TMU)2][TaBr6] (4), NbCl5(DMF)
(5a), TaCl5(DMF) (5c), TaCl5(PhA) (7a), TaBr5(PhA) (7b),
[TaCl5(TPPO)]·0.5CH2Cl2 (8b·0.5CH2Cl2), and Ta2(µ-O)Cl8-
(TMP)2 (10) are reported in Tables 7 and 8. The diffraction experi-
ments were carried out on a Bruker APEX II diffractometer
equipped with a CCD detector using Mo-Kα radiation. Data were
corrected for Lorentz polarization and absorption effects (empiri-
cal absorption correction SADABS).[34] Structures were solved by
direct methods and refined by full-matrix least-squares based on
all data using F2.[35] Hydrogen atoms bonded to C atoms were fixed
at calculated positions and refined by a riding model. Nitrogen-
bonded hydrogen atoms in 7a and 7b were located in the Fourier
map and refined isotropically using the 1.2-fold Uiso value of the
parent N atom. Restraints were applied on the N–H bonds (DFIX
0.86 0.02 line in SHELX). All non-hydrogen atoms were refined
with anisotropic displacement parameters.
7a: Orange, C8H9Cl5NOTa (493.37): calcd. C 19.5, H 1.8, Cl 35.9,
N 2.8, Ta 36.7; found C 19.2, H 1.7, Cl 35.0, N 2.9, Ta 35.8. Yield:
0.930 g, 82%. 1H NMR (CDCl3): δ = 18.26 (s, 1 H, NH), 8.66–
7.19 (5 H, Ph), 2.75 (s, 3 H, Me) ppm. 13C NMR (CDCl3): δ =
175.6 (CO), 142.3 (ipso-Ph), 136.5, 132.6, 130.0, 129.3, 123.2 (Ph),
21.3 (Me) ppm. IR (solid state): ν = 3316 [m (NH)], 1615 [s (CO)],
˜
1578 (ms), 1521 (vs), 1491 (s), 1422 (s), 1367 (m), 1335 (m), 1304
(m), 1275 (ms), 1029 (s), 995 (vs), 911 (m), 753 (vs), 705 (s), 685
(vs) cm–1.
7b: Yellow, C8H9Br5NOTa (715.63): calcd. C 13.4, H 1.3, Br 55.8,
N 2.0, Ta 25.3; found C 13.1, H 1.5, Br 54.9, N 2.3, Ta 25.2. Yield:
1.234 g, 75%. 1H NMR (CDCl3): δ = 11.11 (s, 1 H, NH), 8.94–
7.29 (5 H, Ph), 2.43 (s, 3 H, Me) ppm. 13C NMR (CDCl3): δ =
176.5 (CO), 143.2 (ipso-Ph), 137.2, 130.6, 129.6, 129.3 (Ph), 19.0
(Me) ppm. IR (solid state): ν = 3268 [m (NH)], 1606 [s (CO)], 1582
˜
(s), 1515 (vs), 1424 (s), 1367 (m), 1302 (m), 1280 (ms), 1038 (s), 999
(vs), 916 (m), 810 (m), 751 (vs), 691 (vs) cm–1.
4: Ta(1) and Ta(2) were located on an inversion center and, there-
fore, only half of the two ions were independent. Similar U re-
straints were applied on the bromine atoms in order to obtain a
satisfactory model.
Preparation of MCl5(TPPO) [M = Nb, 8a; M = Ta, 8b]
General Procedure: MCl5 (1.20 mmol) was introduced into a
Schlenk tube containing a solution of Ph3PO (0.348 g, 1.25 mmol)
in CH2Cl2 (10 mL), hence the mixture was stirred for 20 min. The
final solution was layered with pentane (10 mL), thus a microcrys-
talline material was formed after 48 h. Crystals suitable for X-ray
analysis were collected in the case of 8b.
5a: These crystals appeared to be nonmerohedrally twinned. The
TwinRotMat routine of PLATON[36] was used to determine the
twinning matrix (–1 0 0 0 –1 0 0.606 0 1; 2-axis (0 0 1) [7 0 23])
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
0.23085.
8a: Yellow, C18H15Cl5NbOP (548.46): calcd. C 39.4, H 2.8, Cl 32.3,
Nb 16.9; found C 39.1, H 2.6, Cl 30.8, Nb 16.1. Yield: 0.559 g,
85%. 1H NMR (CDCl3): δ = 7.93–7.61 (15 H, Ph) ppm. 13C NMR
{1H} (CDCl3): δ = 140.6 (ipso-Ph), 134.8, 133.6, 129.4, 128.2 (Ph)
5b: These crystals appeared to be nonmerohedrally twinned. The
TwinRotMat routine of PLATON[36] was used to determine the
twinning matrix (–1 0 0 0 –1 0 0.610 0 1; 2-axis (0 0 1) [7 0 23])
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
0.15525.
ppm. IR (solid state): ν = 3057 (w), 1587 (w), 1485 (w), 1437 (m),
˜
1262 (w), 1118 (s), 1060 (m), 1023 (m), 1005 (ms), 975 (vs), 725
(vs), 685 (vs) cm–1.
8b: Colorless, C18H15Cl5OPTa (636.50): calcd. C 34.0, H 2.4, Cl
27.8, Ta 28.4; found C 33.7, H 2.5, Cl 27.2, Ta 28.1. Yield: 0.626 g,
82%. 1H NMR (CDCl3): δ = 7.94–7.67 (15 H, Ph) ppm. 13C NMR
{1H} (CDCl3): δ = 144.2 (ipso-Ph), 134.0, 133.7, 133.5, 129.6, 129.4
(Ph) ppm. 31P NMR {1H} (CDCl3): δ = 58.1 (s, 1 P) ppm. IR (solid
7a: Two independent molecules were present in the unit cell, which
had the same connectivity and differed only slightly in the bonding
parameters.
7b: Similar U restraints were applied, separately, on all C and Br
atoms in order to obtain a satisfactory model. Similarly, rigid bond
restraints were applied to Ta(1) Br(1) Br(2) Br(3) Br(4) Br(5).
state): ν = 1587 (w), 1485 (w), 1438 (m), 1262 (w), 1164 (w), 1109
˜
(m), 1030 (m), 1007 (s), 983 (vs), 747 (m), 727 (vs), 685 (vs) cm–1.
Preparation of TaCl5(TMP) (9) and of Ta2(µ-O)Cl8(TMP)2 (10):
TaCl5 (0.700 g, 1.95 mmol) was added to a solution of trimethyl
phosphate (2.10 mmol) in CH2Cl2 (10 mL), in a Schlenk tube. The
mixture was stirred for 30 min, then the resulting colorless solution
was dried under vacuum, affording a colorless solid corresponding
to 9.
8b·0.5CH2Cl2: These crystals appeared to be nonmerohedrally
twinned. The TwinRotMat routine of PLATON[36] was used to de-
termine the twinning matrix (–1 0 0 0 –1 0 0.285 0 1; 2-axis (0 0 1)
[1 0 7]) 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
0.08568. Two independent molecules and two halves of CH2Cl2
were present in the unit cell, which had the same connectivity and
differed only slightly in the bonding parameters. Similar U re-
straints were applied, separately, on all C, O, and Cl atoms in order
to obtain a satisfactory model.
9: Colorless, C3H9Cl5O4PTa (498.29): calcd. C 7.2, H 1.8, Cl 35.6,
Ta 36.3; found C 7.0, H 2.1, Cl 35.3, Ta 35.5. Yield: 0.855 g, 88%.
3
1H NMR (CDCl3): δ = 4.16 (d, JPH = 13.2 Hz, 9 H, Me) ppm.
13C NMR {1H} (CDCl3): δ = 58.0 (Me) ppm. 31P NMR {1H}
(CDCl3): δ = –2.60 (s, 1 P) ppm.
460
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 453–462

Complexes of Niobium(V) and Tantalum(V) Halides
Table 7. Crystal data and structure refinement for NbCl5(TEU) (3a), [TaBr4(TMU)2][TaBr6] (4), NbCl5(DMF) (5a), and TaCl5(DMF)
(5c).
3a
4
5a
5c
Empirical formula
Formula mass
T [K]
C9H20Cl5N2NbO
442.43
100(2)
0.71073
orthorhombic
Pna21
13.6337(7)
9.0589(5)
13.2912(7)
90
C10H24Br10N4O2Ta2
1393.33
100(2)
0.71073
monoclinic
P21/n
7.8796(6)
13.4170(10)
13.5487(10)
90
C3H7Cl5NNbO
343.26
100(2)
0.71073
monoclinic
P21/c
8.1622(19)
9.920(2)
13.734(3)
90
C3H7Cl5NOTa
431.30
100(2)
0.71073
monoclinic
P21/c
8.1633(18)
9.947(2)
13.759(3)
90
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
90
90
93.2410(10)
90
1430.09(19)
2
3.236
21.631
100.376(3)
90
1093.9(4)
4
2.084
2.271
100.422(3)
90
1098.8(4)
4
2.607
11.169
Cell volume [Å3]
Z
1641.55(15)
4
1.790
Dcalcd [g cm–3]
µ [mm–1]
1.537
F(000)
Crystal size [mm]
θ limits [°]
888
1248
664
792
0.20ϫ0.15ϫ0.12
2.70–28.00
8856
3503 (Rint = 0.0117)
3503/1/167
1.074
0.16ϫ0.13ϫ0.12
2.14–25.02
13225
2520 (Rint = 0.0323)
2520/3/134
1.071
0.0482
0.1522
4.023/–4.790
0.25ϫ0.14ϫ0.11
2.54–27.00
10369
2349 (Rint = 0.0391)
2349/0/103
1.138
0.0875
0.2812
3.479/–1.902
0.19ϫ0.15ϫ0.12
2.54–25.03
4563
1860 (Rint = 0.0401)
1860/6/103
1.165
0.0634
0.2206
3.777/–3.450
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
R1 [I Ͼ 2σ(I)]
wR2 (all data)
0.0144
0.0363
Largest diff. peak and hole [eÅ–3] 0.308/–0.341
Table 8. Crystal data and structure refinement for TaCl5(PhA) (7a), TaBr5(PhA) (7b), [TaCl5(TPPO)]·0.5CH2Cl2, (8b·0.5CH2Cl2), and
Ta2(µ-O)Cl8(TMP)2 (10).
7a
7b
8b·0.5CH2Cl2
10
Empirical formula
Formula mass
T [K]
C8H9Cl5NOTa
493.36
100(2)
0.71073
orthorhombic
Pna21
21.251(2)
20.6963(19)
6.2848(6)
90
C8H9Br5NOTa
715.66
100(2)
0.71073
orthorhombic
Pna21
13.641(3)
10.707(2)
10.244(2)
90
C18.5H16Cl6OPTa
678.93
100(2)
0.71073
monoclinic
C2
10.3036(18)
16.328(3)
27.110(15)
90
C6H18Cl8O9P2Ta2
941.64
100(2)
0.71073
monoclinic
C2/c
14.621(5)
9.738(3)
17.841(6)
90
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
90
90
2764.2(4)
8
2.371
90
90
1496.1(5)
4
3.177
93.104(3)
90
4554.3(15)
8
1.980
5.609
97.918(5)
90
2515.9(15)
4
2.486
9.701
Cell volume [Å3]
Z
Dcalcd [g cm–3]
µ [mm–1]
8.897
20.681
F(000)
Crystal size [mm]
θ limits [°]
1840
1280
2600
1752
0.17ϫ0.15ϫ0.13
1.37–27.00
29439
5997 (Rint = 0.0319)
5997/3/297
0.943
0.16ϫ0.14ϫ0.12
2.42–26.37
15169
3067 (Rint = 0.0368)
3067/59/149
1.108
0.0393
0.1128
2.358/–2.715
0.18ϫ0.13ϫ0.11
1.50–26.00
17354
8776 (Rint = 0.08661)
8776/235/498
1.026
0.0693
0.1656
4.064/–2.482
0.18ϫ0.16ϫ0.11
2.31–25.03
11485
2236 (Rint = 0.1271)
2236/38/127
1.034
0.0734
0.1274
4.461/–1.785
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
R1 [I Ͼ 2σ(I)]
wR2 (all data)
0.0147
0.0337
Largest diff. peak and hole [eÅ–3] 0.722/–0.566
10: The bridging oxygen atom [O(1)] was located on an inversion
center and, therefore, only half of the molecule was independent.
Rigid bond restraints were applied to all the independent atoms in
order to obtain a satisfactory model.
CCDC-653901 (for 3a), -653902 (for 4), -653903 (for 5a), -653904
(for 5c), -653905 (for 7a), -653906 (for 7b), -653907 (for
8b·0.5CH2Cl2), and -653908 (for 10) contain the supplementary
crystallographic data for this paper. These data can be obtained
Eur. J. Inorg. Chem. 2008, 453–462
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
461

F. Marchetti, G. Pampaloni, S. Zacchini
FULL PAPER
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Received: September 3, 2007
Published Online: November 23, 2007
462
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 453–462