Fluoride adducts of niobium(V): Activation reactions and alkene polymerizations

Article abstract of DOI:10.1016/j.ica.2013.01.027

Fluoride coordination derivatives of niobium(V) were tested for their activation capabilities with respect to acetone and to olefins. Activation of acetone (formation of mesityloxide) was observed with NbF₄(OMe). Several fluoride coordination derivatives of niobium(V) of different nature (neutral or ionic) and nuclearity, i.e. NbF₅L [L = Et₂O, 4, thf, 5 (thf is tetrahydrofuran), MeOH, 6, EtOH, 7], (NbF₄L ₂)(NbF₆) [L = dmf, 8 (dmf is dimethylformamide), dme, 9 (dme is dimethoxyethane)], (NbF₄L₄)(NbF₆) [L = thf, 10, Et₂O, 11, MeCN, 12], [S(NMe)₃][NbF₆], 13, NbF₄OMe, 1, NbF₄OPh, 3), NbF₃(OPh) ₂, 14, NbF₂(OPh)₃, 15 and NbF ₂(OEt)₃, 16, promoted the polymerization of ethylene using AlMe₃-depleted methylaluminoxane as cocatalyst. Highly linear polyethylene was obtained. Compound 3, upon activation with methylaluminoxane, promoted ring-opening metathesis polymerization (ROMP) of norbornene, affording polymers with a slight excess of trans content.

Full text of DOI:10.1016/j.ica.2013.01.027

Inorganica Chimica Acta 399 (2013) 214–218
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Fluoride adducts of niobium(V): Activation reactions and alkene polymerizations
1
⇑
Mohammad Hayatifar, Fabio Marchetti, Guido Pampaloni , Yogesh Patil , Anna Maria Raspolli Galletti
Università di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126 Pisa, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Fluoride coordination derivatives of niobium(V) were tested for their activation capabilities with respect
to acetone and to olefins. Activation of acetone (formation of mesityloxide) was observed with NbF4
(OMe). Several fluoride coordination derivatives of niobium(V) of different nature (neutral or ionic)
and nuclearity, i.e. NbF5L [L = Et2O, 4, thf, 5 (thf is tetrahydrofuran), MeOH, 6, EtOH, 7], (NbF4L2)(NbF6)
[L = dmf, 8 (dmf is dimethylformamide), dme, 9 (dme is dimethoxyethane)], (NbF4L4)(NbF6) [L = thf, 10,
Et2O, 11, MeCN, 12], [S(NMe)3][NbF6], 13, NbF4OMe, 1, NbF4OPh, 3), NbF3(OPh)2, 14, NbF2(OPh)3, 15
and NbF2(OEt)3, 16, promoted the polymerization of ethylene using AlMe3-depleted methylaluminoxane
as cocatalyst. Highly linear polyethylene was obtained. Compound 3, upon activation with methylalumi-
noxane, promoted ring-opening metathesis polymerization (ROMP) of norbornene, affording polymers
with a slight excess of trans content.
Received 26 November 2012
Received in revised form 28 January 2013
Accepted 29 January 2013
Available online 8 February 2013
Keywords:
Niobium
Fluoride
Activation
Olefin polymerization
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
The chemistry of MX5 with limited amounts of oxygen com-
pounds has been elucidated in the very last years [8,14]. Different
As a consequence of the exceptionally strong M–F bonds [1],
transition metal fluorides were considered for long time as syn-
thetically and catalytically inert [2]. Nevertheless, the study of
the chemistry of group 4 fluorides has provided several excellent
examples clearly demonstrating that the strong M–F bond does
not preclude their use in catalysis. For example, TiCp0F3
(Cp0 = substituted cyclopentadienyl ring) [3] or TiCpCl2(OR)/BF3
[4] derivatives are more active as ethylene polymerization catalyst
than the corresponding chloride. Similarly, the difluoride Zr[rac-
1,2-ethylene-1,10-bis(tetrahydroindenyl)F2 is more active than
the analogous chloride in the presence of AliBu3 (or AlHiBu2) [5].
On the other hand, examples do not lack of metal fluoride species
behaving as less active catalysts with respect to the corresponding
chlorides [6].
types of coordination adducts (neutral or ionic) have been isolated
upon reaction of controlled amounts of oxygen donors with NbX5
and a significant difference of behavior has been noticed when
moving from fluoride to the heavier halides. In general, organic ha-
lides are generated in the course of the activation processes involv-
ing NbX5 (X = Cl, Br, I), while NbF5 is able to activate several
oxygen-containing molecules without the formation of organic flu-
orides [15]. Such a behavior is generally related to the increase of
the bond energy with decreasing the atomic weight of the halide
[8].
It has been demonstrated that simple coordination adducts of
NbCl5 with oxygen ligands are active catalysts in a series of poly-
merization reactions, providing generally greater performances
with respect to NbCl5 [16].
In spite of the belief that niobium and tantalum live in the shadow
of metal complexes of Group 4 [7], niobium and tantalum pentaha-
lides, MX5, have found increasing application in effective metal-di-
rected organic synthesis [8,9].
In this context, also the pentafluorides of niobium and tantalum
have found application in a variety of processes [10], including
fluorination [11], alkylation [12] and ring opening polymerizations
[13], sometimes showing reactivities markedly different from the
corresponding heavier halides [10,13].
On account of this state of art, we decided to investigate the
possible activation reactions of some of the recently prepared
NbF5 derivatives [17,19], including some fluoride-alkoxide(arylox-
ide) compounds of general formula MF5ꢀn(OR)n, obtained straight-
forwardly from MF5 [18]2 via reactions with trimethylsilyl ethers
[19].
The results, including the polymerization of ethylene and the
ROMP of norbornene, are reported in this paper.
⇑
Corresponding author. Tel.: +39 050 2219 219; fax: +39 050 2219 246.
E-mail addresses: fabmar@dcci.unipi.it (F. Marchetti), pampa@dcci.unipi.it (G.
2
Pampaloni).
The pentafluoride of niobium(V) has tetranuclear structure in the solid state
1
Present address: Ingénierie & Architectures Macromoléculaires, Institut Charles
Gerhardt, UMR 5253, ENSCM 34296 Montpellier Cedex, France.
(ref19). For sake of simplicity, the empirical formula NbF5 has been used throughout
the present paper.
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.027

M. Hayatifar et al. / Inorganica Chimica Acta 399 (2013) 214–218
215
1) acetone
MeOSiMe
1 eq.
2) H O
3
2
NbF (OMe)
4
CH C(=O)CH=C(CH )
3
3 2
1
1) acetone
MeOSiMe
2 eq.
3
2) H O
2
NbF (OMe)
acetone
3
2
2
1) acetone
PhOSiMe
1 eq.
3
2) H O
2
NbF (OPh)
4
acetone + phenol (traces)
NbF
5
3
1) acetone (1 eq)
2) H O
2
acetone
1) acetone (2-5 eq)
2) H O
2
acetone
Scheme 1. Comparative view of the reactivity of NbF5, NbF4(OMe) and NbF3(OMe)2 with acetone.
R = Ph
[NbF4L2][NbF6]
L = dmf, 8, dme, 9
NbF4OPh
L/Nb = 1
3
R = Ph
NbF3(OPh)2
L/Nb = 2
L; L/Nb=1
14
Me SiOR
L, L/Nb = 2
L, L/Nb = 1
3
R = Ph
[NbF4L4][NbF6]
NbF5
NbF2(OPh)3
L/Nb = 3
15
L = thf, 10, Et O, 11, MeCN, 12
2
[S(NMe) ]
3
R = Et
[SiF Me ]
2
3
NbF2(OEt)3
L/Nb = 3
16
R = Me
NbF5L
L = Et O, 4, thf, 5,
NbF4OMe
[S(NMe)3][NbF6] L/Nb = 1
1
2
MeOH, 6, EtOH, 7
13
Scheme 2. Synthesis of niobium fluoride adducts.
idea that mesityl oxide forms directly as result of the interaction be-
tween acetone and the fluoride alcoholate complex.
2. Results and discussion
When acetone was allowed to react with NbF4(OPh) and NbF3
(OMe)2 in dichloromethane, acetone/phenol and acetone, respec-
tively, were the species which could be clearly recognized after
hydrolysis of the reaction mixtures.
These findings reveal that the nature of the R group (i.e. Me or
Ph) and the nuclearity of the metal influence the reactivity with
acetone. More specifically, NbF4(OMe) has revealed to be a highly
acidic species, able to promote CꢀH activation of acetone in mild
conditions, to give the CꢀC coupling product mesityl oxide (see
Scheme 1). It is noteworthy that the analogous CꢀH activation is
not verified by using NbF5 [17].
Reactivity of NbFn(OR)5ꢀn (n = 4, R = Me, 1; Ph, 3; n = 3; R = Me,
2) with acetone.
According to our recent results [19], fluoride–alkoxides of
Nb(V), NbFn(OR)5ꢀn, have different nuclearities depending on the
fluorine content. Thus NbF4(OPh), 3, is probably tetranuclear both
in the solid state and in chlorinated solvent, while NbF4(OMe), 1,
exists as mixture of tetra- and trinuclear forms. NbF3(OPh)2 has
got a trinuclear structure, and NbF2(OR)3 (R = Et, 15; R = Ph, 16)
are presumably dinuclear.
In view of the availability of the newly prepared fluoride-alkox-
ide complexes [19], we decided to investigate the reactivity of
some of them with an oxygen donor such as acetone. Hence slow
darkening of the mixtures was noticed after addition of acetone
to NbF4(OMe) (acetone/Nb molar ratio = 1), in CD2Cl2. The 1H and
13C NMR spectra of the reaction solutions consisted of complicated
patterns. Otherwise the corresponding 19F NMR spectra revealed
the presence of significant amounts of the [NbF6]ꢀ ions (see Section
4, NMR studies), suggesting that the addition of the ketone deter-
mines the disruption of the polynuclear units of the alkoxides [19].
Upon hydrolysis of the mixture, Me2C@CHC(@O)Me (mesityl
oxide) was recognized as prevalent species from NbF4(OMe)/ace-
tone/H2O3. The presence of some singlets around 6.5 ppm, in the
1H NMR spectra of the mixtures NbF4(OMe)/acetone, supports the
Olefin polymerization reactions
A variety of well-soluble niobium compounds obtained by high-
yield reaction of NbF5 with controlled amount of Lewis bases was
tested in the ethylene polymerization. The employed compounds
are reported in Scheme 2 and include neutral mononuclear (4–7),
ionic (8–13), and polynuclear species (1, 3, 14–16).
The polymerization reactions have been carried out under the
same experimental conditions successfully employed for analogous
niobium(V) chloride derivatives [20], i.e. using DMAO as cocatalyst
(see Table 1). Although NbF5 is inactive in ethylene polymerization,
the mononuclear complexes 4–7 are able to produce polyethylene
with low to moderate activity, thus suggesting that the breaking of
the tetranuclear structure of NbF5 [18], by addition of a neutral mol-
ecule(L) to formsolubleNbF5L adducts, representsa straightforward
approachto enhancethecatalyticperformances ofthemetalspecies.
Nevertheless, NbF5(OEt2), 4, resulted ineffective in contrast with
what observedwith the chlorinatedadduct NbCl5(OEt2) [21], the lat-
3
Hydrolysis of CDCl3 solutions of [NbF4(acetone)4][NbF6] and NbF5(acetone) gave
acetone in nearly quantitative yield.

216
M. Hayatifar et al. / Inorganica Chimica Acta 399 (2013) 214–218
Table 1
Table 2
Results of ethylene polymerization runs with precatalysts 1–16.a
ROMP of norbornene with compounds 3 and with NbF5.a
Run
Precursor
Activityb
Mw (Da)
PDIc
Tm (°C)
Run
Precursor (
lmol)
t (min)
Activityb
Trans (mol.-%)
1
2
3
4
5
6
7
8
NbF5(OEt2), 4
–
–
–
–
1
2
3
4
5
3 (22)
3 (2.2)
3 (2.2)
5
5
1
5
5
56
n.d.
53
54
48
47
NbF5(thf), 5
55
22
20
32
trace
10
45
–
–
0.3
60
41
20
trace
trace
11
102000
255000
110000
463000
–
101000
220000
–
13.5
12.1
15.5
13.7
–
14.6
13.2
–
–
–
10.3
11.5
11.7
–
133
133
132
134
174
272
93
NbF5(MeOH), 6
NbF5(EtOH), 7
NbF5 (2.2)
[NbF4(dmf)2 [NbF6], 8
[NbF4(dme)2][NbF6], 9
[NbF4(thf)4][NbF6], 10
[NbF4(OEt2)4][NbF6], 11
[NbF4(NCMe)4][NbF6] , 12
[S(NMe2)3][NbF6], 13
NbF4(OMe), 1
NbF4(OPh), 3
NbF3(OPh)2, 14
NbF2(OPh)3, 15
NbF2(OEt)3, 16
NbCl5 (2.2)c
1250
a
Reaction conditions: 20.7 mL of 20 wt.% norbornene solution in chlorobenzene;
133
133
MAO/Nb molar ratio = 500; T = 50 °C; cocatalyst: MAO.
b
c
ꢀ1
Activity expressed as kgPNB ꢁ molNb ꢁ hꢀ1
.
9
From Ref. [25].
10
11
12
13
14
15
16
17
–
–
133
133
133
134
–
tion conditions were selected on the basis of our previously re-
ported experiments [25]. When the precursor 3 was treated with
MAO at 50 °C for 5 min of reaction time, (run 1, Table 2), the result-
147000
186000
210000
–
ꢀ1
ing catalytic system gave a moderate activity (56 kgPNB molNb
NbF5
NbCl5
–
–
–
–
ꢁ hꢀ1). Polymer characterization revealed that the polymerization
mechanism took place only by ring-opening metathesis polymeri-
zation (ROMP).
d
136000
132.3
a
Reaction conditions: precursor = 40 lmol; DMAO/Nb molar ratio = 600;
T = 50 °C; PC2H4 = 0.1 MPa; t = 15 min; solvent: chlorobenzene (50 mL); re-activator:
The decrease of precatalyst concentration up to 2.2 lmol in-
1,2-dichloroethane (2 mmol).
Activity expressed as kgpolymer ꢁ molNb ꢁ hꢀ1 ꢁ barꢀ1
.
b
c
ꢀ1
creased the catalytic activity almost three-times. A further remark-
able improvement of the productivity was ascertained when
reaction time was reduced to 1ꢀm1in (run3, Table 2): the value
was reached to 272 kgPNB molNb ꢁ hꢀ1. The enhanced perfor-
mance at shorter reaction time can be attributed to the much lower
viscosity of the reaction medium, which allows a more efficient
mixing, reducing diffusion limitations.
In order to confirm the importance of the phenoxide moiety on
the polymerization behavior, NbF5 was employed as precursor for
ROMP carried out under the same polymerization conditions (run
4, Table 2). As it can be seen from the data of Table 2, the produc-
tivity of NbF4OPh is well higher than that obtained with NbF5 un-
der the same experimental conditions.
Polydispersity index.
From Ref. [28].
d
ter showing an activity of 95 kgpolymer molNbꢀ1 hꢀ1 barꢀ1 [20]. This
observation may be attributed to the fact that ethyl ether is a Lewis
base not strong enough to fragment the tetranuclear structure of
NbF5 as instead happens in the case of the dinuclear NbCl5 [18]. On
the other hand, the ionic diethylether adduct 11 shows one of the
highest activities reported in Table 1. An opposite trend is observed
whengoing from 5 to 10(neutral and ionicthfadducts, respectively),
probably due to the stronger coordinating power of thf with respect
to Et2O [22]. The easier accessibility of the monomer to the hexaco-
ordinatedcentralmetalatomin5 mayexplainthehigheractivityob-
served with 5 respect to 10, that contains octacoordinated niobium
atom. Moreover, the activity exhibited by 10 is reasonably due to
the cation only, in consideration of the fact that the [NbF6]ꢀ salt 13
does not produce polymer.
Swelling of polymer samples in CDCl3 allowed to clarify the
microstructureof thepolymers. Inall casesthe 13CNMRspectraindi-
catethat thepolymerhas an almostrandomsequenceof cis and trans
double bonds [25] with a slight higher content of the latter.
We also tested the catalytic activity of the known dme-octaco-
ordinated cation 9 [15a], and the acetonitrile adduct 12 reported
here for the first time. Both compounds are not effective in ethyl-
ene polymerization, possibly for steric reasons due to the presence
of two bidentate dme ligands (compound 9) or for some detrimen-
tal effects caused by the unsaturated nitrogen ligand (compound
12).
Finally, in view of the good outcomes previously obtained with
mixed chloride-alkoxide niobium compounds [16], some fluoride-
alkoxides [19] have been tested for ethylene polymerization. Thus,
the phenoxides 3, 14, 15 have provided some polymer, the activity
increasing on increasing the relative fluoridecontent. This is in
agreement with the observation that when the electrophilicity of
the metal center increases, a relatively positive niobium center will
exhibit high activities for ethylene polymerization [23]. Otherwise,
the presence of ethyl group in the place of phenyl (compare 15
with 16) is sufficient to cause a drop in the activity.
Molecular weight distribution (Mw/Mn) data revealed in every
case broad polydispersity and multimodal distribution, thus indi-
cating the non-single-site nature of the catalyst.
The melting points (Tm) of poly(ethylene)s were determined by
DSC analysis. The melting point ranges between 132 and 134 °C,
typical of high density polyethylene. The FT-IR spectrum of poly-
meric samples displays the typical bands corresponding to the high
density polyethylene [24].
3. Conclusion
Fluoride coordination derivatives of niobium(V) have been
tested for their activation capabilities with respect to acetone
and to olefins. Activation of acetone (formation of mesityloxide)
has been observed with NbF4(OMe), thus suggesting that this fluo-
ride-alcoholato complex probably has an acidic character stronger
with respect to that exhibited by the parent pentafluoride and
pentachloride.
Fluoride derivatives of different nature (neutral or ionic) and
nuclearity have been tested as catalytic precursors in the polymeri-
zation of ethylene. The best results reported herein in terms of activ-
ity (compounds 3, 5) toward ethylene polymerization are less
valuable with respect to those obtained with analogous chloride-
containing species. However, they are interesting in the context of
olefin polymerizationcatalyzed by niobium precursors, on consider-
ation of the fact that no studies have been reported hitherto in this
field concerning niobium fluoride derivatives. Moreover, compound
3catalyzedtheROMPof norbornenewithmoderatetohighactivities
and gave polymer samples with slightly higher trans content.
4. Experimental
4.1. General
The catalytic behavior of compound 3, which presented the
highest activity in ethylene polymerization, was also studied in a
limited number of norbornene polymerization reactions. The reac-
All manipulations of air and/or moisture sensitive compounds
were performed under atmosphere of pre-purified argon using

M. Hayatifar et al. / Inorganica Chimica Acta 399 (2013) 214–218
217
standard Schlenk techniques. The reaction vessels were oven dried
at 150 °C prior to use, evacuated (10ꢀ2 mmHg) and then filled with
argon. NbF5 was the commercial product (Aldrich) of the highest
purity available, stored under Argon atmosphere as received. Sol-
vents and compounds used as ligands were commercial products
(Aldrich) of the highest purity available. Ethylene (>99%; Rivoira)
was used as received. Norbornene (Aldrich) was distilled from
CaH2 and then dissolved in chlorobenzene in appropriate concen-
trations. Compounds 4 [21], 5–7, 10, 11, 13 [17], 8 [26], 9 [15], 1,
3, 14–16 [19] were prepared according to the literature. Infrared
spectra were recorded at 293 K on a FT IR Spectrum One Perkin El-
mer Spectrometer, equipped with a UATR sampling accessory.
NMR measurements were recorded on Varian Gemini 200BB
instrument at 293 K, unless otherwise specified. The thermal
behavior of polyethylene was examined with a Perkin Elmer Pyris
1520 m, 1445m, 1406m, 1382m, 1109s, 986s, 880br-vs 716br-
vs cmꢀ1
Mesityl oxide was detected by NMR as largely prevalent species
after hydrolysis of the reaction mixtures NbF4(OMe)/acetone; ace-
tone was the only species which could be clearly recognized after
hydrolysis of the reaction mixtures NbF3(OMe)2/acetone.
.
4.4. Reactivity of NbF4(OPh), 3, with acetone
The reaction of 3 (0.43 mmol) with dry acetone (0.43 mmol)
was conducted in CD2Cl2 (0.60 mL) in an NMR tube. The tube
was sealed, shaken in order to homogenize the content, and stored
at room temperature for 18 h. The solution was analyzed by NMR.
NbF4(OPh)/acetone: d(1H, 198 K) = 7.26, 7.08, 6.88 (Ph); 2.21 (CH3)
ppm; d(13C, 198 K) = 210.1 (CO); 155.9, 129.5, 128.1, 120.4, 115.3
(Ph); 30.6 (CH3) ppm. NbF4(OPh)/acetone (after hydrolysis): d(1H,
198 K) = 7.26, 6.93, 6.86 (Ph); 6.14(OH); 2.19 (CH3) ppm; d(13C,
198 K) = 208.1 (CO); 156.0, 127.8, 120.3, 115.2 (Ph); 30.7 (CH3)
ppm.
Diamond DSC at a standard heating/cooling rate of 10 °C minꢀ1
,
under nitrogen flow. The reported melting temperature values re-
fer to the second heating scan. SEC measurements were carried out
with a high temperature Waters GPCV2000 system equipped with
a differential refractometer as concentration detector. The experi-
mental conditions consisted of three PL Gel Olexis columns,
o-dichlorobenzene as the mobile phase, 0.8 mL minꢀ1 as the flow
rate and a column temperature of 145 °C. The calibration of
the SEC system was constructed using 18 narrow MWD
polystyrene standards with molar weights ranging from 162 to
Acknowledgments
The authors wish to thank the Ministero dell’Istruzione,
dell’Università e della Ricerca (MIUR, Roma), Programma di Ricerca
Scientifica di Notevole Interesse Nazionale 2009.
5.6 ꢁ 106 g molꢀ1
.
The ethylene polymerization reactions were carried out by
adopting the optimized experimental conditions used in the ethyl-
References
ene polymerization by NbCl4[j
2-O(CH2)2OMe] and analogous
Nb(V) chloro-alkoxide complexes [22]. Dry methylaluminoxane
(DMAO) was prepared by removing trimethylaluminium and tolu-
ene from commercial MAO (Sigma Aldrich, toluene solution 10% w/
w) in vacuo at 30 °C for 6 h, followed by repeated slurring in hep-
tane. The colorless solid was recovered by filtration and dried in
vacuo at room temperature [27]. Norbornene polymerization reac-
tions were carried out as previously reported [25].
[1] (a) N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, second ed.,
Elsevier, Amsterdam, 1997;
(b) Y.R. Luo, J.A. Kerr, in: David R. Lide (Ed.), Bond Dissociation Energies in CRC
Handbook of Chemistry and Physics, 87th ed., Taylor and Francis, Boca Raton,
FL, 2006.
[2] E.F. Murphy, R. Murugavel, H.W. Roesky, Chem. Rev. 97 (1997) 3425.
[3] (a) S.K. Mandal, H.W. Roesky, Adv. Catal. 54 (2011) 1;
(b) C. Schwecke, W. Kaminsky, Macromol. Rapid Commun. 22 (2001) 508;
(c) W. Kaminsky, S. Lenk, V. Scholz, H.W. Roesky, H. Herzog, Macromolecules
30 (1997) 7647;
(d) W. Kaminsky, Macromol. Chem. Phys. 197 (1996) 3907.
[4] Y. Qian, H. Zhang, X. Qian, J. Huang, C. Shen, J. Mol. Catal. A: Chem. 192 (2003)
25–33.
4.2. Preparation of [NbF4(MeCN)4][NbF6] (12)
[5] (a) S. Becke, U. Rosenthal, German Patent DE 19932409 A1, to Bayer AG, 2001.;
(b) S. Becke, U. Rosenthal, US Patent 6,303,718 B1, to Bayer AG, 2001.;
(c) S. Becke, U. Rosenthal, W. Baumann, P. Arndt, A. Spannenberg, German
Patent DE 10110227A1, to Bayer AG, 2002.
[6] (a) D.A. Straus, M. Kamigaito, A.P. Cole, R.M. Waymouth, Inorg. Chim. Acta 349
(2003) 65;
(b) S.A.A. Shah, H. Dorn, A. Voigt, H.W. Roesky, E. Parisini, H.-G. Schmidt, M.
Noltemeyer, Organometallics 15 (1996) 3176;
(c) F. Garbassi, L. Gila, A. Proto, J. Mol. Catal. A: Chem. 101 (1995) 199–209;
(d) G. Natta, P. Pino, G. Mazzanti, P. Longi, Gazz. Chim. Ital. 87 (1957) 570.
[7] A. Spannenberg, H. Fuhrmann, P. Arndt, W. Baumann, R. Kempe, Angew. Chem.,
Int. Ed. 37 (1998) 3363.
A suspension of NbF5 (0.150 g, 0.798 mmol) in dichloromethane
(12 ml) was treated with MeCN (1.70 mmol). The mixture was stir-
red for 3 h, then the resulting pale-yellow solution was dried under
vacuo. The residue was washed with hexane (2 ꢁ 10 mL), thus
compound 12 was obtained as a colorless sticky solid. Yield
0.179 g, 83%. 1H NMR (CDCl3, 298 K): d = 2.57 (s, Me) ppm. 13C
NMR (CDCl3, 298 K): d = 101.2 (NCMe), 2.3 (Me) ppm. 19F NMR
(CDCl3, 298 K): d = 164.3 (s-br, [NbF4]+), 112.3 (br, [NbF6]ꢀ) ppm.
[8] F. Marchetti, G. Pampaloni, Chem. Commun. 48 (2012) 635 (and references
therein).
[9] V. Lacerda Jr., D. Araujo dos Santos, L.C. Da Silva-Filho, S.J. Greco, R. Bezerra dos
Santos, Aldrichim. Acta 45 (2012) 19.
4.3. Reactivity of NbF4(OMe), 1, and NbF3(OMe)2, 2, with acetone
In an NMR tube, a colorless solution of the metal compound (1
or 2, 0.50 mmol) in CD2Cl2 (0.60 mL) was added of dry acetone
(0.50 mmol). The tube was sealed, shaken in order to homogenize
the content, and stored at room temperature for 18 h. Turning of
the color of the mixture to dark red was observed. The solution
was analyzed by NMR. NbF4(OMe)/acetone: d(1H, 198 K) = 9.05
(br), 6.93, 6.82, 6.58 (major), 4.59, 4.52 (major), 3.78 (major),
3.69, 2.78, 2.69, 2.64, 2.50, 2.42, 2.36 (major) ppm; d(19F,
198 K) = 103 (decet, major, [NbF6]ꢀ), 92.0 (s), 72.7 (s) ppm. NbF3
(OMe)2/acetone: d(1H, 298 K) = 8.39 (br), 4.08 (s, 3 H), 2.29 (s, 3
H) ppm; d(19F, 198 K) = 103 (decet, [NbF6]ꢀ), 92.0 (s, major), 70.6
(s, br) ppm.
[10] (a) S.S. Kim, G. Rajagopal, Synthesis (2007) 215;
(b) S.S. Kim, G. Rajagopal, S.C. George, Appl. Organomet. Chem. 21 (2007) 368;
(c) T. Masuda, T. Mouri, T. Higashimura, Bull. Chem. Soc. Jpn. 53 (1980) 1152;
(d) T. Masuda, T. Takahashi, A. Niki, T. Higashimura, J. Polym. Sci., Part A:
Polym. Chem. 24 (1986) 809;
(e) Y. Koyama, K. Harima, K. Matsuzaki, T. Uryu, J. Polym. Sci., Part A: Polym.
Chem. 23 (1985) 2989;
(f) V.A. Petrov, Synthesis (2002) 2225.
[11] (a) A.E. Feiring, J. Fluorine Chem. 13 (1979) 7;
(b) D.E. Bradley, D. Nalewajek, R.L. Bell, US Patent 2007/0118003 A1, to
Honeywell International Inc., 2007.
[12] (a) J. Sommer, M. Müller, K. Laali Nouv, J. Chim. 6 (1982) 3;
(b) M. Siskin, G.R. Chludzinski, R. Hulme, J.J. Porcelli, W.E. Tyler III, Ind. Eng.
Chem., Prod. Res. Dev. 19 (1980) 379;
(c) A.P. Lien, D.A. McCaulay, US Patent 2,683,763, to Standard Oil, Company,
1954.
[13] F. Marchetti, G. Pampaloni, T. Repo, Eur. J. Inorg. Chem. (2008) 2107.
[14] (a) F. Marchetti, G. Pampaloni, C. Pinzino, S. Zacchini, Angew. Chem., Int. Ed. 49
(2010) 5268;
An aliquot of the solution obtained by NbF4(OMe)/acetone was
dried under vacuo, thus the resulting red residue was analyzed by
IR spectroscopy. The spectrum showed bands at 2965w, 1608m,

218
M. Hayatifar et al. / Inorganica Chimica Acta 399 (2013) 214–218
(b) F. Marchetti, G. Pampaloni, C. Pinzino, J. Organomet. Chem. 696 (2011)
1294.
[15] (a) R. Bini, C. Chiappe, F. Marchetti, G. Pampaloni, S. Zacchini, Inorg. Chem. 49
(2010) 339;
[21] F. Marchetti, G. Pampaloni, S. Zacchini, Dalton Trans. (2009) 6759.
[22] (a) V. Gutmann, Coord. Chem. Rev. 18 (1976) 225;
(b) V. Gutmann, The Donor–Acceptor Approach to Molecular Interactions,
Plenum Press, New York, 1978.
(b) R. Bini, F. Marchetti, G. Pampaloni, S. Zacchini, Polyhedron 30 (2011) 1412.
[16] F. Marchetti, G. Pampaloni, Y. Patil, A.M. Raspolli Galletti, S. Zacchini, J. Polym.
Sci., Part A: Polym. Chem. 49 (2011) 1664.
[23] G. Pampaloni, A.M. Raspolli Galletti, Coord. Chem. Rev. 254 (2010) 525.
[24] A.M. Domínguez, A. Zárate, R. Quijada, T. Lopez, J. Mol. Catal. A: Chem. 207
(2004) 155.
[17] F. Marchetti, G. Pampaloni, S. Zacchini, J. Fluorine Chem. 131 (2010) 21.
[18] (a) A.F. Wells, Structural Inorganic Chemistry, fifth ed., Clarendon Press,
Oxford, 1993;
(b) A.J. Edwards, J. Chem. Soc. (1964) 3714.
[19] M. Bortoluzzi, N. Guazzelli, F. Marchetti, G. Pampaloni, S. Zacchini, Dalton
Trans. 41 (2012) 12898.
[25] A.M. Raspolli Galletti, G. Pampaloni, A. D’Alessio, Y. Patil, F. Renili, S. Giaiacopi,
Macromol. Rapid Commun. 30 (2009) 1762.
[26] K.J. Packer, E.L. Muetterties, J. Am. Chem. Soc. 85 (1963) 3035.
[27] J.-N. Pedeutour, K. Radhakrishnan, H. Cramail, A. Deffieux, J. Mol. Catal. A:
Chem. 185 (2002) 119.
[28] F. Marchetti, G. Pampaloni, Y. Patil, A.M. Raspolli Galletti, F. Renili, S. Zacchini,
Organometallics 30 (2011) 1682.
[20] F. Marchetti, G. Pampaloni, Y. Patil, A.M. Raspolli Galletti, M. Hayatifar, Polym.
Int. 60 (2011) 1722.