Synthesis, properties and structures of NbOF3 complexes and comparisons with NbOCl3 analogues

Article abstract of DOI:10.1039/c3dt53322k

The first series of complexes of niobium(v) oxide trifluoride, [NbOF ₃(OPR₃)₂] (R = Me or Ph), [NbOF ₃(dppmO₂)] (dppmO₂ = Ph₂P(O)CH ₂P(O)Ph₂), [NbOF₃

Full text of DOI:10.1039/c3dt53322k

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Synthesis, properties and structures of NbOF3
complexes and comparisons with NbOCl3
analogues†
Cite this: Dalton Trans., 2014, 43,
3649
William Levason,* Gillian Reid, Jonathan Trayer and Wenjian Zhang
The first series of complexes of niobium(V) oxide trifluoride, [NbOF3(OPR3)2] (R
= Me or Ph),
[NbOF3(dppmO2)] (dppmO2 = Ph2P(O)CH2P(O)Ph2), [NbOF3(dmso)2], [NbOF3(tmeda)] (tmeda = Me2N-
(CH2)2NMe2) and [NbOF3(diimine)] (diimine = 2,2’-bipy, 1,10-phen) have been prepared, either by reaction
of the corresponding complexes of NbF5 and hexamethyldisiloxane (HMDSO) in CH2Cl2–MeCN solution,
or directly from NbF5, ligand and HMDSO. They were characterised by IR, 1H, 31P{1H} and 19F{1H} NMR
spectroscopy, and X-ray crystal structures are reported for [NbOF3(OPR3)2] (R = Me or Ph) and
[NbOF3(dppmO2)]. Complexes of NbOCl3, [NbOCl3(OPPh3)2], [NbOCl3(dppmO2)], [NbOCl3(dppeO2)]
(dppeO2 = Ph2P(O)(CH2)2P(O)Ph2), [NbOCl3(tmeda)] and [NbOCl3(diimine)] were made from NbCl5 and
HMDSO in MeCN (which forms [NbOCl3(MeCN)2] in situ), followed by addition of the neutral ligand.
Their properties are compared with the oxide fluoride analogues. X-ray structures are reported for
[NbOCl3(dppmO2)], [NbOCl3(dppeO2)], [NbOCl3(tmeda)] and [NbOCl3(2,2’-bipy)]. The synthesis and spec-
troscopic characterisation of [MF5L] (M = Nb or Ta; L = OPR3, OAsPh3) and [MF4(diimine)2][MF6] are also
described, and the key properties of the four series of complexes compared.
Received 25th November 2013,
Accepted 23rd December 2013
DOI: 10.1039/c3dt53322k
www.rsc.org/dalton
are known, but the oxide-fluorides, MOF3, are intractable and
very little studied.6,7 Here we report the synthesis, spectro-
Introduction
The fluorides and oxide fluorides of early transition metals in scopic and structural characterisation of a series of adducts of
high oxidation states are strong Lewis acids and form a sub- NbOF3. Complexes of NbOCl3 have long been known, orig-
stantial range of complexes with F− and with hard N- or inally obtained by adventitious hydrolysis, or O-abstraction
O-donor ligands, whilst their more limited chemistry with soft from the solvent or ligand in reactions of NbCl5.8 More sys-
donor ligands (P, S etc.) sometimes includes redox chemistry tematic syntheses used the reaction of NbCl5 with siloxanes or
at the metal centre and oxidation/fluorination of the hetero- occasionally direct reaction with the polymeric NbOCl3,9 and
atom donor, in addition to adduct formation.1 The properties selected examples have been re-examined in the present work
of the metal centre are significantly altered by the small to provide comparisons with the NbOF3 complexes. NbOF3 is
very electronegative fluoride ligands, and the chemistry of obtained by heating NbF5 with NbO2F in argon, and has a
these fluorides/oxide fluorides is often very different to that of structure based upon six-coordinate niobium (SnF4 type), but
the chloride analogues.1
the O/F disorder is only partially understood.6 It decomposes
Within Group V, the coordination chemistry of the oxide on heating above 180 °C, hydrolyses in air in a few hours, and
fluorides VOF3,2 and VO2F2,3 has been studied in some detail is insoluble in organic solvents, making it completely unsuita-
recently, whilst that of VF5 is completely unexplored. In con- ble as a synthon to explore the coordination chemistry. TaOF3,
trast, an extensive series of complexes of MF5 (M = Nb or Ta) which is formed similarly from TaO2F and TaF5, is also dis-
with both hard N- and O-donor1,4 and soft S-donor5 ligands ordered and unreactive.6
We describe here a convenient alternative route to NbOF3
complexes involving F/O exchange from the corresponding
School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
E-mail: wxl@soton.ac.uk; Tel: +44 (0)23 80593792
†Electronic supplementary information (ESI) available: The crystallographic data
NbF5 adducts, using hexamethyldisiloxane (HMDSO). Similar
halogen/oxygen exchange has proved to be a useful route for
the preparation of complexes of polymeric oxide halides,
including, for example, MO2X2 (M = Mo or W; X = Cl or Br),10
although it has rarely been used for oxide fluoride complexes.1
and selected bond lengths and angles for [Me3TACNH]2[NbOCl5] are also avail-
able in the ESI. CCDC 973570–973577. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/C3DT53322K
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Table 1 Comparison of spectroscopic data
Complex
19F{1H}a
31P{1H}a
ν(P/AsO)b
ν(Nb/TaX)b/cm−1
ν(NbO)b/cm−1
[NbF5(OPPh3)]
[NbF5(OPMe3)]
[NbF5(OAsPh3)]
[NbF4(2,2′-bipy)2][NbF6]
161.8(s, [F]), 128.6(s, [4F])
157.6(s, [F]), 134.5(s, [4F])
145.0(s, [F]), 110.5(s, [4F)]
139.7(s, [4F]), 103.2 (10 lines,
J = 335 Hz)
53.9c
75.6d
—
1061(vs)c
1092(vs)d
845(s)
—
624(sh), 608(vs, br)
615(vs, br), 582(m)
620(sh), 600(vs, br)
—
—
—
—
615(vs), 603(s), 585(vs)
—
[NbF4(1,10-phen)2][NbF6] 138.0(s, [4F]), 103.4 (10 lines,
—
—
608(vs), 586(vs), 565(sh)
—
J = 335 Hz)
49.5(s, [F]), 37.8(s, [2F])
41.5(s, [F]), 30.6(s, [2F])
55.7(s, [F]), 36.4(s, [2F])
50.4(s, [F]), 38.0(s, [2F])
49.0(s, [F]), 42.8(s, [2F])
Insol
Insol
84.2(s, [F]), 54.7(s, [4F])
82.5(s, [F]), 55.9(s, [4F])
62.5(s, [F]), 48.6(s, [4F])
68.1(s, [4F]), 38.0(s, [6F])
[NbOF3(OPPh3)2]
[NbOF3(OPMe3)2]
[NbOF3(dppmO2)]
[NbOF3(dmso)2]
[NbOF3(2,2′-bipy)]
[NbOF3(1,10-phen)]
[NbOF3(tmeda)]
[TaF5(OPPh3)]
[TaF5(OPMe3)]
[TaF5(OAsPh3)]
[TaF4(2,2′-bipy)2][TaF6]
[TaF4(1,10-phen)2][TaF6]
[NbOCl3(OPPh3)2]
[NbOCl3(dppmO2)]
[NbOCl3(dppeO2)]
[NbOCl3(2,2′-bipy)]
[NbOCl3(1,10-phen)]
[NbOCl3(tmeda)]
45.0(s, [P]), 36.0(s, [P])
67.1(s, [P]), 53.3(s, [P])
1155(m), 1067(s) 602(m), 579(s)
941(s)
958(s)
944(s)
920(s)
959(s)
970(s)
920(s)
—
—
—
—
—
936(s)
928(s)
943(s)
943(s)
944(s)
945(s)
1140(m), 1087(s) 614(s), 582(m), 555(s)
46.6(d, [P])e, 36.8(d, [P])f 1156(s), 1088(s) f 608(vs), 582(s)
—
—
—
—
53.2(s)
76.9(s)
—
—
—
590(s), 564(s)
—
—
—
612(vs), 579(s)
610(sh), 594(s), 583(s)
587(s), 557(s)
1078(s)
1092(vs)
845(s)
617(sh), 592(vs, br)
601(sh), 583(vs, br)
617(sh), 592(vs, br)
605(sh), 581(vs)
605(sh), 576(s)
325(s), 294(m)
327(s), 296(m)
320(s), 293(w)
349(s), 338(s)
66.1(s, [4F]), 37.9(s, [6F])
—
—
—
—
—
—
—
—
50.0(s, [P]), 38.8(s, [P])
48.5(d, [P]), 36.8(d, [P])
56.7(s, [P]), 44.9(s, [P])
—
—
—
1159(s), 1074(s)
1157(s), 1095(s)
1172(s), 1066(s)
—
—
—
338(br)
341(s), 320(sh)
a CH2Cl2–CD2Cl2 solution 298 K. b Nujol mull. c Ligand δ(P) = +28.0, ν(PO) = 1195. d Ligand δ(P) = +35.0, ν(PO) = 1160. e Ligand δ(P) = +25.0, ν(PO)
= 1187. f Ligand δ(P) = +35.0, ν(PO) = 1174 cm−1 data from ref. 24.
The reaction of NbF5 with 2,2′-bipyridyl or 1,10-phenanthro-
Results and discussion
MF5 complexes
line in CH2Cl2 solution gave very poorly soluble complexes
with a 1 : 1 NbF5 : diimine composition, originally assumed12
The reaction of NbF5 with OPR3 (R = Me or Ph) in rigorously to be seven-coordinate monomers. We found them to be
anhydrous CH2Cl2 solution gave [NbF5(OPR3)] as white sufficiently soluble in CD2Cl2 solution to obtain 1H and 19F
powders, easily soluble in halocarbon solvents. The complexes {1H} NMR spectra after long accumulations, which show equi-
have been mentioned before, but with limited characterisation valent pyridyl rings and two 19F resonances with intensity ratio
data.4d,11 The 19F{1H} NMR spectra show two singlets with rela- of 2 : 3. The more intense resonance is the characteristic 10
tive intensities 1 : 4 and the 31P{1H} NMR spectra are singlets line multiplet of [NbF6]−,5a leading to the revised formulation,
with large, high frequency coordination shifts (Table 1), con- [NbF4(diimine)2][NbF6], with an eight-coordinate cation, as
sistent with their formulation as octahedral monomers. They found in other adducts with chelating bidentate ligands.1 The
also show broad singlet 93Nb NMR resonances‡ δ ∼ −1530. [TaF4(diimine)2][TaF6] were made similarly and were even less
The IR spectra show strong terminal Nb–F vibrations in the soluble. Eight-coordination is also found in the diimine com-
range 630–570 cm−1, and ν(PO) are markedly lower than the plexes of Zr and Hf (M′), [M′F4(diimine)2].13 The very poor solu-
“free” ligand values (Table 1). The [NbF5(OAsPh3)] was made bility of the isolated [MF4(diimine)2][MF6] complexes made
similarly from cold (0 °C) CH2Cl2 solution, but must be iso- them unsuitable as synthons for the O/F exchange reactions,
lated rapidly, otherwise significant decomposition occurs, and hence studies were switched to using in situ syntheses,
forming Ph3AsF2 (δ(19F) = −89.4),3a [NbF6]− (identified by although the data on the isolated MF5 adducts are useful for
in situ 19F NMR spectroscopy)5a and other unidentified comparison purposes (Table 1).
products. The tantalum complexes [TaF5(OPR3)] and
[TaF5(OAsPh3)] were prepared similarly, and show corres-
NbOF3 complexes
ponding trends in their spectroscopic properties (Table 1).
However, the large quadrupole moment of 181Ta (I = 7/2, Q = 3
× 10−28 m2) results in fast quadrupolar relaxation and hence
181Ta NMR resonances are not observable.
Treatment of an anhydrous CH2Cl2 solution of [NbF5(OPPh3)]
with one mol. equivalent of OPPh3, followed by one mol. equi-
valent of HMDSO, resulted in slow formation of a white pre-
cipitate, identified as [NbOF3(OPPh3)2]. We subsequently
found that “one-pot” syntheses were possible and more con-
venient, although the sequence of addition of the reactants
and the time-scales are key to obtaining pure complexes
(Scheme 1). The addition of NbF5 and two mol. equivalents of
OPPh3 to anhydrous CH2Cl2 yields a colourless solution,
‡
93Nb 100% abundance, I = 9/2, Ξ = 24.44 MHz, Q = −0.2 × 10−28 m2, Dc = 2740
is one of the more sensitive nuclei and, despite the medium size quadrupole
moment, is readily observed in many systems. The zero reference is [NbCl6]− in
MeCN.
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Scheme 1 Synthesis of NbOF3 adducts.
which was stirred for 20 min. and then one mol. equivalent of and HMDSO also failed. Ether, nitrile and thioether adducts of
HMDSO and a small amount of MeCN were added. After 24 h NbF5 are well characterised,1,4,5 but it seems that these ligands
the mixture, now containing much white precipitate, was con- are too weakly bound to the “NbOF3” to prevent polymeris-
centrated in vacuo, and the [NbOF3(OPPh3)2] isolated. If the ation and precipitation of ligand-free NbOF3. Similar behav-
HMDSO was added before, or simultaneously with, the OPPh3, iour was observed with VO2F,3 and the niobium system seems
very impure products resulted, and several hours seem necess- to be a further example of the metal centre preferring to form
ary to complete the O/F exchange. The role of the MeCN is not oxide/fluoride bridges rather than coordinate to weak, neutral
entirely clear, but its presence seems necessary to obtain pure donor groups.1 Thus far, attempts to isolate TaOF3 complexes
samples from the in situ preparations. In the syntheses of from TaF5, ligand (ligand = OPR3, dmso or 2,2′-bipy) and
[WO2Cl2{RS(CH2)2SR}] from WCl6 or WOCl4, RS(CH2)2SR and HMDSO under similar reaction conditions, have been
HMDSO, use of MeCN–CH2Cl2 as solvent prevents the precipi- unsuccessful.
tation of polymeric WO2Cl2, by forming the nitrile adduct
The
solid
[NbOF3(OPR3)2],
[NbOF3(dmso)2]
and
in situ.10c While a similar role may be present in the niobium [NbOF3(dppmO2)] complexes are white powders, relatively air-
systems, we note that attempts to isolate nitrile complexes stable in the solid state (some appear hygroscopic on pro-
failed (see below). The complexes [NbOF3(OPMe3)2] and longed exposure), although hydrolysed by wet solvents. They
[NbOF3(dppmO2)] were prepared similarly to [NbOF3(OPPh3)2], are easily soluble in CH2Cl2, whereas the [NbOF3(diimine)] are
but all attempts to obtain [NbOF3(OAsPh3)2] gave mixtures con- very poorly soluble, and [NbOF3(tmeda)] is insoluble. The 1H
taining [NbF5(OAsPh3)], [NbF6]− and Ph3AsF2 (identified based and 31P{1H} NMR spectra (Table 1) of [NbOF3(OPMe3)2] show
upon in situ 19F and 93Nb NMR spectra). [NbOF3(OAsPh3)] was two phosphine oxide environments, and the 19F{1H} NMR
originally reported to be formed from adding OAsPh3 to a solu- spectrum contains two singlets with integrals in the ratio 1 : 2,
tion of Nb2O5 in conc. aqueous HF, although identified only which is consistent with mer-fluorines and one OPMe3 trans to
by an IR spectrum.7b Using a 4 : 2 : 1 molar ratio of OPPh3 : O and one trans to F. Attempts to record a 93Nb NMR spectrum
HMDSO : NbF5 in CH2Cl2–MeCN resulted only in isolation of were unsuccessful (an effect observed for all the NbOF3
[NbOF3(OPPh3)2], further O/F exchange did not occur. The adducts), contrasting with the ready observation of resonances
complex [NbOF3(dmso)2] was also isolated in high yield from from the NbF5 adducts described above. The low symmetry at
reaction of NbF5, dmso and HMDSO. As noted above, the very the niobium centre will result in a large electric field gradient,
poor solubility of [NbF4(diimine)2][NbF6] made it impossible and unobservably broad lines due to fast quadrupolar relax-
to redissolve them in CH2Cl2 for conversion to oxide-fluoride ation. The different trans-influences of Nb–F and NbvO
complexes. However, combination of the diimine and NbF5 in groups in these complexes are also shown by the difference in
a large volume of CH2Cl2 (which gave a opalescent solution), 31P chemical shifts for the trans disposed OPMe3 ligands
followed by addition of HMDSO, did give [NbOF3(diimine)]. (∼14 ppm), and similar differences are seen in the ν(PO) fre-
The [NbOF3(tmeda)] was made in high yield as an air-stable quencies in the IR spectra which differ by >50 cm−1. A strong
white powder by sequential reaction of NbF5, tmeda and band in the range 970–920 cm−1 is assignable to the terminal
HMDSO.
In contrast, reaction of NbF5 with ethers, including thf and
NbvO vibrations.
Confirmation of the geometry of [NbOF3(OPMe3)2] comes
MeO(CH2)2OMe or with MeCN in CH2Cl2 followed by addition from the X-ray crystal structure (Fig. 1).
of HMDSO, gave white insoluble powders, which showed only
There is no evidence in this molecule for O/F disorder in
traces of organic ligand in the IR spectra, and had very broad, plane, which is a common problem in this area of chemistry
ill-defined bands in the IR spectra, similar to those reported (cf. [VOF3(OPPh3)2]2b). The niobium is in a distorted octahedral
for NbOF3.6,7a The attempted reaction of NbF5, MeS(CH2)2SMe environment with the axial F–Nb–F unit bent away from the
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Fig. 1 The structure of the Nb1 centred molecule in [NbO-
F3(OPMe3)2]·1/3CH2Cl2 showing the atom labelling scheme. Displace-
ment ellipsoids are drawn at the 50% probability level and H-atoms and
the solvate molecule are omitted for clarity. The second Nb2 centred
molecule is similar with the third (Nb3) being disordered. Selected bond
lengths (Å) and angles (°): Nb1–O1 = 1.773(2), Nb1–F2 = 1.868(2), Nb1–
F3 = 1.9184(19), Nb1–F1 = 1.935(2), Nb1–O2 = 2.104(2), Nb1–O3 =
2.205(2), P1–O2 = 1.526(2), P2–O3 = 1.521(2), O1–Nb1–F2 = 98.58(10),
O1–Nb1–F3 = 97.00(11), F2–Nb1–F3 = 92.20(10), O1–Nb1–F1 = 95.09
(11), F2–Nb1–F1 = 92.72(10), F3–Nb1–F1 = 166.12(9), O1–Nb1–O2 =
91.75(9), F3–Nb1–O2 = 86.21(9), F1–Nb1–O2 = 86.63(9), F2–Nb1–O3 =
87.90(8), F3–Nb1–O3 = 84.76(9), F1–Nb1–O3 = 82.46(9), O2–Nb1–O3
= 81.80(8).
Fig. 2 The structure of [NbOF3(OPPh3)2] showing the atom numbering
scheme. The phenyl rings are numbered cyclically starting at the ipso C
atom. Ellipsoids are drawn at the 50% probability level and H atoms are
omitted for clarity. The molecule has two-fold symmetry. Notice the dis-
order at the atom site O1/F2. Symmetry operation: a = 1 − x, −y, z.
Selected bond lengths (Å) and angles (°): Nb1–O1 = 1.850(4), Nb1–F2 =
1.850(4), Nb1–F1 = 1.932(4), Nb1–O2 = 2.189(4), P1–O2 = 1.532(4), O1–
Nb1–F2 = 108.2(4), O1–Nb1–F1 = 92.06(19), F2–Nb1–F1 = 95.36(18),
F1–Nb1–F1a = 167.3(2), O1–Nb1–O2 = 86.8(2), F1–Nb1–O2 = 84.23(16),
O2–Nb1–O2 = 78.3(2).
oxido-ligand. The Nb–Ftrans are longer than Nb–Ftrans
by
O
F
∼0.06 Å and the NbvO of 1.773(2) Å is consistent with the
expected multiple bond character. The Nb–O(P)trans F distances
of 2.104(2) Å and Nb–O(P)trans O = 2.205(2) Å show the disparate
effects of the trans donor and parallel the spectroscopic evi-
dence. Curiously, d(P–O) in the two phosphine oxide ligands
are only slightly different. The spectroscopic data on [NbO-
F3(OPPh3)2] (Table 1) are very similar to those of the OPMe3
complex discussed, but in this case the X-ray structure (Fig. 2)
shows F/O disorder trans to OPPh3, and the bond length and
angle data are correspondingly unreliable, although the iden-
tity of the complex is confirmed.
The structural parameters of [NbOF3(dppmO2)] are gener-
ally similar to those already discussed above, and this complex
seems free of O/F disorder (Fig. 3).
The [NbOF3(tmeda)] is insoluble in non-coordinating sol-
vents and MeCN, and is partially decomposed by dmf or dmso
Fig. 3 The structure of [NbOF3(dppmO2)] showing the atom labelling
scheme. Displacement ellipsoids are drawn at the 50% probability level
and H-atoms are omitted for clarity. Selected bond lengths (Å) and
angles (°): Nb1–O3 = 1.782(4), Nb1–F1 = 1.850(3), Nb1–F2 = 1.912(3),
Nb1–F3 = 1.970(3), Nb1–O2 = 2.171(3), Nb1–O1 = 2.257(4), P1–O1 =
which prevented solution measurements. However, the 1.508(4), P2–O2 = 1.509(3), O3–Nb1–F1 = 100.96(17), O3–Nb1–F2 =
98.04(16), F1–Nb1–F2 = 95.28(15), O3–Nb1–F3 = 95.34(16), F1–Nb1–F3
= 94.41(15), O3–Nb1–O2 = 91.31(15), F2–Nb1–O2 = 83.99(13), F3–
Nb1–O2 = 83.24(13), F1–Nb1–O1 = 87.03(15), F2–Nb1–O1 = 84.16(14),
F3–Nb1–O1 = 80.84(13), O2–Nb1–O1 = 80.66(13), F2–Nb1–F3 = 161.67
[NbOF3(diimine)], although very poorly soluble in chloro-
carbons or MeCN (a property shared with the NbF5 analogues
above, and also the ZrF4, HfF4, VOF3 and VO2F diimine com-
plexes),2,3,13 gave 1H NMR spectra showing inequivalent
(13).
pyridyl rings, and hence that the diimine was trans to O/F. The
19F{1H} NMR spectrum of [NbOF3(2,2′-bipy)] (Table 1) shows
two resonances in the ratio 1 : 2 consistent with a mer arrange-
solution in CH2Cl2 or MeCN forming [NbF6]− ions, based
ment of the fluorines, and the chemical shifts are ∼100 ppm
to low frequency of those observed for the [NbF4(diimine)2]+.
The [NbOF3(1,10-phen)] was very poorly soluble in weakly coor-
dinating solvents and a convincing 19F{1H} NMR spectrum was
not obtained. The diimine complexes are readily hydrolysed in
upon 19F NMR evidence and also shown by attempts to obtain
crystals of [NbOF3(2,2′-bipy)] for an X-ray study which pro-
duced a few poor quality crystals of [2,2′-bipyH][NbF6]. The
solids also hydrolyse slowly on exposure to the atmosphere.
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Scheme 2 Synthesis of NbOCl3 adducts.
NbOCl3 complexes
Solid NbOCl3 contains dimeric [Cl2Nb(O)(µ-Cl)2Nb(O)Cl2]
units linked into chains via unsymmetrical oxide bridges,
giving six-coordinate niobium.14 The syntheses of the
[NbOCl3(L–L)] (L–L = 2,2′-bipy, 1,10-phen, dppmO2, dppeO2,
tmeda and 2 × OPPh3) were carried out in anhydrous MeCN
solution, with the reversed order of reagent addition to that
used for the oxide-fluoride syntheses, i.e. reacting NbCl5 with
HMDSO to form ‘NbOCl3’ in situ, followed by addition of the
neutral ligand (Scheme 2). The initially yellow solution of
NbCl5 in MeCN rapidly pales on addition of HMDSO, indicat-
ing formation of [NbOCl3(MeCN)2] in situ,9b,15 which was con-
verted into near colourless [NbOCl3(L–L)] upon addition of the
neutral ligand. Once isolated, the [NbOCl3(tmeda)] is essen-
tially insoluble in non-coordinating solvents, although crystals
were grown adventitiously from the reaction filtrate. The other
complexes are soluble in CH2Cl2 or MeCN. The IR spectra of
the complexes (Table 1) show strong ν(NbvO) in the region
920–950 cm−1 and ν(NbCl) 290–350 cm−1 with disparate
ν(PvO) vibrations for the phosphine oxide groups trans to Cl
and trans to O. In solution, the 1H and 31P{1H} NMR spectra of
[NbOCl3(L–L)] (L–L = dppmO2, dppeO2, 2 × OPPh3) show the
expected inequivalence of the neutral donor groups, but
attempts to record 93Nb spectra were unsuccessful; as with the
oxide-fluorides this is attributed to fast quadrupolar relaxation
in the low symmetry electric fields.
Fig. 4 The structure of [NbOCl3(dppmO2)]·nMeCN showing the atom
labelling scheme. Displacement ellipsoids are drawn at the 50% prob-
ability level and H-atoms are omitted for clarity. The solvate acetonitrile
is also omitted. The phenyl rings are numbered cyclically starting at the
ipso-C atom. Selected bond lengths (Å) and angles (°): Nb1–O3 = 1.706(3),
Nb1–O2 = 2.095(3), Nb1–O1 = 2.266(3), Nb1–Cl3 = 2.3463(13), Nb1–
Cl1 = 2.3815(13), Nb1–Cl2 = 2.4203(12), O3–Nb1–O2 = 94.47(12), O2–
Nb1–O1 = 80.48(10), O3–Nb1–Cl3 = 98.84(10), O1–Nb1–Cl3 = 86.17(7),
O3–Nb1–Cl1
= 97.53(10), O2–Nb1–Cl = 86.85(8), O1–Nb1–Cl1 =
84.56(7), Cl3–Nb1–Cl1 = 92.45(6), O3–Nb1–Cl2 = 93.91(10), O2–Nb1–
Cl2 = 85.00(8), O1–Nb1–Cl2 = 83.41(7), Cl3–Nb1–Cl2 92.98(5), Cl1–
Nb1–Cl2 = 166.43(4).
X-Ray crystal structures were obtained for five of the com-
plexes. The structure of [NbOCl3(OPPh3)2] has been reported
The structure of [NbOCl3(tmeda)] (Fig. 6) shows the same
previously and shows16 mer-chlorines, and cis OPPh3 groups, features as those of the oxygen donor complexes, although the
with O/Cl disorder trans to OPPh3. The crystal structures of the carbon atoms about N2 show some disorder; there is no evi-
two diphosphine dioxide complexes (Fig. 4 and 5) show dence for O/Cl disorder. The dimensions in the structure of
d(NbvO) slightly shorter by ∼0.1 Å compared to the oxide [NbOCl3(2,2′-bipy)] (Fig. 7) are also unexceptional, although
fluoride complexes, but with similarly disparate d(Nb–O(P)) the octahedron about the niobium is more distorted due to
suggesting the trans influence of F and Cl are similar in these the small chelate bite of the 2,2′-bipyridyl (<N1–Nb1–N2 =
complexes. The d(NbvO) and d(Nb–Cl) distances in a range of 69.52(21)°).
NbOCl3 adducts cover quite a narrow range,8,9,15,16 suggesting
Attempts to obtain a complex of NbOCl3 with 1,4,7-tri-
that these are the dominant bonding interactions, with the methyl-1,4,7-triazacyclononane (Me3-tacn) gave a mixture of
neutral ligands completing the coordination sphere, but products. Recrystallisation of the mixture from MeCN gave a
having little influence on the NbvO and Nb–Cl bonds.
few crystals identified as [(Me3-tacn)H]2[NbOCl5]. The anion
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Fig. 7 The structure of the Nb1 centred molecule in [NbOCl3(2,2’-bipy)]
showing the atom labelling scheme. This molecule has no crystallo-
graphic symmetry whereas the Nb2 centred molecule has 2-fold sym-
metry. Displacement ellipsoids are drawn at the 50% probability level
and H-atoms are omitted for clarity. Selected bond lengths (Å) and
angles (°): Nb1–O1 = 1.694(6), Nb1–Cl1 = 2.363(2), Nb1–Cl2 = 2.356(2),
Nb1–Cl3 = 2.372(2), Nb–N1 = 2.262(6), Nb1–N2 = 2.385(6), O1–Nb1–N1
= 89.3(3), O1–Nb1–Cl2 = 104.8(2), O1–Nb1–Cl1 = 98.0(2), O1–Nb1–Cl3
= 97.7(2), Cl2–Nb1–N2 = 96.41(15), N1–Nb1–N2 = 69.5(2), Cl1–Nb1–N1
= 84.50(16), Cl2–Nb1–Cl1 = 94.18(7), Cl3–Nb1–Cl2 = 92.76(7), Cl3–
Nb1–N1 = 84.37(16), N2–Nb1–Cl1 = 81.08(15), Cl3–Nb1–N2 = 80.13
(15).
Fig. 5 The structure of [NbOCl3(dppeO2)]·nMeCN showing the atom
labelling scheme. Displacement ellipsoids are drawn at the 50% prob-
ability level and H-atoms are omitted for clarity. The phenyl rings are
numbered cyclically starting at the ipso-C atom. The solvate acetonitrile
is also omitted. Selected bond lengths (Å) and angles (°): Nb1–O1 =
1.702(3), Nb1–O2 = 2.077(3), Nb1–O3 = 2.219(3), Nb1–Cl1 = 2.3602(12),
Nb1–Cl3 = 2.4136(12), Nb1–Cl2 = 2.4210(13), O1–Nb1–O2 = 93.09(12),
O2–Nb1–O3 = 82.31(10), O1–Nb1–Cl1 = 97.74(10), O3–Nb1–Cl1 =
86.86(8), O1–Nb1–Cl3 = 97.02(10), O2–Nb1–Cl3 = 86.17(8), O3–Nb1–
Cl3 = 84.91(8), Cl1–Nb1–Cl3 = 92.43(4), O1–Nb1–Cl2 = 94.82(10), O2–
Nb1–Cl2 = 86.11(8), O3–Nb1–Cl2 = 82.73(8), Cl1–Nb1–Cl2 93.00(4),
Cl3–Nb1–Cl2 = 166.19(4).
Comparisons of NbF5, NbOF3 and NbOCl3 complexes
Comparison of the spectroscopic data in Table
1 for
[NbF5(OPR3)] and [NbOF3(OPR3)2] shows very significant differ-
ences due to replacement of two fluoride ligands by the oxo-
group. The 19F and 31P chemical shifts are very different, with
those of [NbF5(OPR3)] at much higher frequency for each
nucleus. Similar differences are apparent in the 19F chemical
shifts for the two series of N-donor complexes. The data
demonstrate that the presence of the strong π-donating oxo-
group significantly changes the electron density at the Nb(V)
centre, making it much less electron poor, and hence a weaker
Lewis acid. Within the NbOF3 complexes there is also a large
trans influence of the oxo-group which results in significantly
longer bonds to the trans ligand than for those groups trans to
fluorine. The d(PvO) show very small differences, although
the relative trans influence is clear in the ν(PvO) vibrations in
the IR spectra. Comparing the structural and spectroscopic
data on corresponding NbOF3 and NbOCl3 complexes reveals
rather small differences. The d(NbvO) in these and in litera-
ture examples of the oxide chloride complexes8,9,15,16 show
they occur in a narrow range, ∼1.7–1.8 Å, irrespective of the
halide or neutral co-ligands present. Similarly, d(Nb–Cl)trans L
are relatively insensitive to the nature of L (the ligand types are
too restricted to make a similar comparison for the fluoride).
The bond angles about the niobium centres also show sig-
nificant deviations from those expected for a regular octa-
hedral geometry. The factors determining the geometry
adopted by ML6 complexes of transition metals as a function
of ligand types (σ-donor only, or σ and π donor), dn count and
ligand architecture have been discussed in several articles,18
and the fact that [MF6]n− species are Oh and [M(CH3)6]n− (n =
Fig. 6 The structure of [NbOCl3(tmeda)] showing the atom labelling
scheme. The carbon atoms associated with N2 show some disorder.
Displacement ellipsoids are drawn at the 50% probability level and
H-atoms are omitted for clarity. Selected bond lengths (Å) and
angles (°): Nb1–O1 = 1.798(5), Nb1–N2 = 2.331(8), Nb1–N1 = 2.518(5),
Nb1–Cl3 = 2.328(3), Nb1–Cl2 = 2.348(3), Nb1–Cl1 = 2.358(2), O1–Nb1–
N2 = 92.5(3), O1–Nb1–Cl3 = 103.5(2), O1–Nb1–Cl2 = 94.3(3), N2–Nb1–
Cl2 = 86.1(3), Cl3–Nb1–Cl2 = 91.21(16), O1–Nb1–Cl1 = 96.5(3), N2–
Nb1–Cl1 = 87.6(3), Cl3–Nb1–Cl1 = 91.87(10), N2–Nb1–N1 = 74.1(2),
Cl3–Nb1–N1 = 89.86(16), Cl2–Nb1–N1 = 84.00(15), Cl1–Nb1–N1 =
84.09(15), Cl2–Nb1–Cl1 = 167.70(10).
has been structurally characterised with a variety of cations,
but often the niobium is on a high symmetry site which
results in O/Cl disorder.17 In the present case the structure
appears to free of such disorder and the data are presented
as ESI.†
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0, 1, 2 etc.) are trigonal prisms has been rationalised in terms
The HMDSO/MFn route may well offer a synthetic
of electronic factors by MO calculations.19 The niobium oxide pathway to oxide fluoride complexes of other high valent
halide structures discussed in the present work (12e, d0 com- early metal complexes, e.g. those of Mo, W, Ti or Zr. TaOF3
plexes) are based upon distorted octahedral geometries, as complexes are not formed under analogous reaction con-
would be expected, given the presence of dominant σ and π ditions; further studies are required to develop a suitable route
donor ligands. As observed in many early transition metal to these.
complexes containing MvO bonds, the angles involving the
latter, OvM–L and OvM–X are larger than X–M–X, X–M–L, or
L–M–L, in effect the electron rich multiply bonded MvO unit
occupies more space about the metal centre. Superimposed
upon this are smaller effects arising from the steric demands
Experimental
of the X and L groups and constraints of neutral ligand geome- Infrared spectra were recorded as Nujol mulls between CsI
tries, such as chelate bites in the bidentates. In the cis-MOX3L2 plates using a Perkin-Elmer Spectrum 100 spectrometer over
1
unit the axial X–M–X group bends away from the MvO and the range 4000–200 cm−1. H, 19F{1H}, 31P{1H} and 93Nb NMR
towards the neutral co-ligands.2,3,5,8–10
spectra were recorded using a Bruker DPX400 spectrometer
Comparing the IR data within the two series of NbOX3 com- and are referenced to the protio resonance of the solvent, exter-
plexes shows ν(NbvO) lying in a range ∼920–970 cm−1, and nal CFCl3, 85% H3PO4, and [NEt4][NbCl6] in CD3CN, respect-
the ν(PvO) in corresponding phosphine oxide adducts also ively. Microanalyses were undertaken by Medac Ltd or London
show little difference. Hence we conclude that the NbOX3 core Metropolitan University. Solvents were dried prior to use: THF,
has the dominant structural and spectroscopic effects in these Et2O and MeOCH2CH2OMe by distillation from sodium benzo-
complexes.
phenone ketyl, MeCN and CH2Cl2 from CaH2. OPMe3 was sub-
The differences between NbOF3 and NbOCl3 as acceptors limed in vacuo, OPPh3, OAsPh3, 2,2′-bipy, 1,10-phen were
towards weaker donor ligands such as ethers or nitriles, where heated in vacuo, and tmeda distilled from BaO. All prep-
the latter forms complexes with thf, MeO(CH2)2OMe, MeCN, arations were undertaken using standard Schlenk techniques
etc.,4,9,15 but attempts to isolate analogues with NbOF3 result under a N2 atmosphere.
in intractable, ligand-free products (NbOF3 polymer). This can
[NbF5(OPPh3)]: A solution of OPPh3 (0.262 g, 1.0 mmol) in
be ascribed to the preference of the niobium centre to form CH2Cl2 (20 mL) was added to finely powdered NbF5 (0.188 g,
fluoride bridges over weak Nb–L bonds, and is seen in other 1.0 mmol), and vigorously stirred to give a clear solution. This
fluoride and oxide fluoride systems.1
was filtered to remove any residual solid and concentrated
Finally, these niobium complexes can be compared with in vacuo to ∼5 mL. On standing a white powdered separated,
those of the 3d analogue, vanadium. VOF3 forms similar phos- which was filtered off and dried in vacuo. Yield 0.40 g, 85%.
phine oxide, diimine and diamine complexes to NbOF3, but Anal: required for C18H15F5NbOP (466.2): C, 46.4; H, 3.2.
also complexes with ethers, thioethers and nitriles.2 The differ- Found: C, 46.9; H, 3.6%. 1H NMR (CD2Cl2, 293 K): 7.1–7.6 (m).
ences are again readily rationalised by the niobium’s prefer- 19F{1H} NMR (CD2Cl2, 293 K): +161.8 (s, [F]), +128.6 (s, [4F]);
ence for fluorine bridges; NbOF3 is an inert, very strongly (210 K): +157.0 (s, [F]), +125.7 (s, [4F]). 31P{1H} NMR (CD2Cl2,
bridged polymer (above), whereas VOF3 although (weakly) 293 K): 53.9 (s). 93Nb NMR (CD2Cl2, 293 K): −1530 (br s). IR
F-bridged in the solid,20 easily vapourises as a monomer on (Nujol/cm−1): 1061 (vs) PO, 624 (sh), 608 (vs, br) NbF.
heating and dissolves in most organic solvents. The complexes
[NbF5(OPMe3)]: Made similarly to the OPPh3 adduct. Yield
of VOCl3 with neutral ligands are thermally and often photo- 75%. Anal: required for C3H9F5NbOP (280.0): C, 12.9; H, 3.2.
1
2
chemically unstable, and extremely readily hydrolysed and Found: C, 13.2; H, 3.5%. H NMR (CD2Cl2, 293 K): 1.9 (d, JPH
reduced (often spontaneously) to V(IV) or V(III) compounds,21 = 15 Hz). 19F{1H} NMR (CD2Cl2, 293 K): 157.6 (s, [F]), 134.5 (s,
whereas the NbOCl3 adducts remain pentavalent, unless [4F]). 31P{1H} NMR (CD2Cl2, 293 K): +75.6 93Nb NMR (CD2Cl2,
specifically treated with reducing agents.
293 K): −1530 (br, s). IR (Nujol/cm−1): 1092 (vs) PO, 615 (vs,
br), 582 (m) NbF.
[NbF5(OAsPh3)]: Prepared as for the OPPh3 analogue except
that the complex was prepared in ice-bath and solution stirred
for 5 min. It was then concentrated in vacuo and the precipi-
Conclusions
The O/F exchange reaction between complexes of the binary tated solid isolated immediately. If the solid is left in solution
fluoride NbF5 and a siloxane have been shown to produce a yellow and then brown colour develops and in situ NMR data
complexes of the otherwise intractable oxide-fluoride, NbOF3, shows formation of Ph3AsF2, [NbF6]− and other unidentified
in good yield. However, further O/F exchange to form deriva- impurities. The pure solid seems stable for some weeks in a
tives of NbO2F did not occur under similar conditions. Com- freezer. Yield 55%. Anal: required for C18H15AsF5NbO (510.1):
parison of the spectroscopic properties of the NbF5 and NbOF3 C, 42.4; H, 3.0. Found: C, 42.4; H, 3.0%. 1H NMR (CD2Cl2,
complexes demonstrates the substantial effect on the metal 293 K): 7.2–7.6 (m). 19F{1H} NMR (CD2Cl2, 293 K): +145.0 (s,
centre of replacing two fluoride by the stronger π-donor oxido- [F]), +110.5 (s, [4F)]. 93Nb NMR (CD2Cl2, 293 K): −1511 (br, s).
group.
IR (Nujol/cm−1): 845 (m) AsO, 620 (sh), 600 (vs, br) NbF.
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[NbF4(2,2′-bipy)2][NbF6]: NbF5 (0.188 g, 1.0 mmol) was 7.72 (s, [H]). 19F{1H} NMR (CD2Cl2, 293 K): 49.0 (s, [F]), 42.8 (s,
added to CH2Cl2 (20 mL) and vigorously stirred, whilst a solu- [2F]). IR (Nujol/cm−1): 959 (s) NbO, 612 (vs), 579 (s) NbF.
tion of 2,2′-bipy (0.16 g, 1.0 mmol) in CH2Cl2 (10 mL) was
[NbOF3(1,10-phen)]: NbF5 (0.19 g, 1 mmol) was dissolved in
added, resulting in rapid precipitation of a fine white powder. CH2Cl2 (200 mL) and dry 1,10-phen (0.18 g, 1 mmol) in
After 2 h the solid was isolated by filtration, rinsed with CH2Cl2 (10 mL) added with stirring, producing some fine
diethyl ether (5 mL) and dried in vacuo. Yield 0.30 g, 86%. white precipitate. After 5 min hexamethyldisiloxane (0.16 g,
Anal: required for C20H16F10N4Nb2 (688.2): C, 34.9; H, 2.3; N, 1 mmol) and MeCN (0.5 mL) were added and the mixture
1
8.1. Found: C, 34.7; H, 2.2, N, 8.1%. H NMR (CD2Cl2, 293 K): stirred for 48 h. at room temperature, producing a dense white
9.34 (d, [2H], J = 9 Hz), 8.63 (d, [2H], J = 9 Hz), 8.40 (m, [2H]), precipitate. The precipitate was filtered off, rinsed with diethyl
7.78 (m, [2H]). 19F{1H} NMR (CD2Cl2, 293 K): +139.7 (s, [4F]), ether (10 mL) and dried in vacuo. Yield 0.30 g, 86%. Anal:
+103.2 (10 lines, J = 335 Hz). IR (Nujol/cm−1): 615 (vs), 603 (s), required for C12H8F3N2NbO (346.1): C, 41.6; H, 2.3; N, 8.1.
1
585 (vs) NbF.
Found: C, 41.4; H, 2.3; N, 7.9%. H NMR (CD2Cl2, 293 K): 9.36
[NbF4(1,10-phen)2][NbF6]: was made similarly in 89% yield. (s, [H]), 9.28 (s, [H]), 8.77 (m, [H]), 8.56 (m, [H]), 8.19 (s, [H]),
Anal: required for C24H16F10N4Nb2 (736.2): C, 39.2; H, 2.2; N, 8.13 (s, [H]), 8.02 (s, [H]), 7.90 (s, [H]). 19F{1H} NMR (CD2Cl2,
1
7.6. Found: C, 39.2; H, 2.3, N, 7.4%. H NMR (CD3CN, 293 K): 293 K): insufficiently soluble. IR (Nujol/cm−1): 970 (s) NbO,
9.20 (d, [2H], J = 9 Hz), 8.96 (d, [2H], J = 9 Hz), 8.27 (m, [2H]), 610 (sh), 594 (s), 583 (s) NbF.
8.17 (m, [2H]). 19F{1H} NMR (CD3CN, 293 K): +138.0 (s, [4F]),
[NbOF3(dppmO2)]: NbF5 (0.19 g, 1 mmol) and dppmO2
+103.4 (10 lines, J = 335 Hz). IR (Nujol/cm−1): 608 (vs), 586 (vs), (0.41 g, 1 mmol) were added to dry CH2Cl2 (25 mL) and the
565 (sh) NbF. mixture stirred for 20 min. Hexamethyldisiloxane (0.16 g,
[NbOF3(OPPh3)2]: NbF5 (0.19 g, 1 mmol) and OPPh3 (0.56 g, 1 mmol) and MeCN (0.5 mL) were added and the mixture
2 mmol) were added to dry CH2Cl2 (25 mL) and the mixture stirred overnight at room temperature. The solvents were
stirred for 20 min. Hexamethyldisiloxane (0.16 g, 1 mmol) and removed in vacuo leaving a slightly sticky cream powder which
MeCN (0.5 mL) were added and the mixture stirred overnight was extracted with CH2Cl2 (20 mL), filtered to remove some
at room temperature. The solvents were removed in vacuo undissolved solid, and concentrated to ∼5 mL. Dry diethyl
leaving a slightly sticky white powder which was stirred with ether (20 mL) was added slowly and the cream precipitate
dry diethyl ether (40 mL) when it became a fine white powder. filtered off and dried in vacuo. Yield 0.34 g, 45%. Refrigeration
This was filtered off, rinsed with diethyl ether (10 mL) and of the filtrate for 5 d. gave crystals suitable for the X-ray data
dried in vacuo. Yield 0.41 g, 57%. Refrigeration of the filtrate collection. Anal: required for C25H22F3NbO3P2 (582.3): C, 51.6;
gave small crystals used for the X-ray data collection. Anal: H, 3.8. Found: C, 51.5; H, 3.9%. 1H NMR (CD2Cl2, 293 K):
required for C36H30F3NbO3P2 (722.5): C, 59.9; H, 4.2. Found: C, 7.82–7.15 (m, [10H]), 3.70 (m, [H], J = 13 Hz). 19F{1H} NMR
59.6; H, 4.3%. 1H NMR (CD2Cl2, 293 K): 7.1–7.7 (m). 19F{1H} (CD2Cl2, 293 K): 55.7 (s, [F]), 36.4 (s, [2F]). 31P{1H} NMR
2
2
NMR (CD2Cl2, 293 K): 49.5 (s, [F]), 37.8 (s, [2F]). 31P{1H} NMR (CD2Cl2, 293 K): 46.4(d, [P], Jpp = 17 Hz), 36.8 (s, [P], Jpp
=
(CD2Cl2, 293 K): 45.0 (s, [P]), 36.0 (s, [P]). 93Nb NMR (CD2Cl2, 17 Hz). IR (Nujol/cm−1): 1156 (s), 1088 (s) PO, 944 (s) NbO,
293 K): not observed. IR (Nujol/cm−1): 1155 (m), 1067 (s) PO, 608 (vs), 582 (s) NbF.
941 (s) NbO, 602 (m), 579 (s) NbF.
[NbOF3(dmso)2]: NbF5 (0.19 g, 1 mmol) was added to dry
[NbOF3(OPMe3)2]: was made similarly Yield 50.5%. Crystals CH2Cl2 (25 mL), followed by dry dmso (0.5 mL) and the
were obtained by refrigeration overnight of the filtrate mixture stirred for 20 min. producing a clear colourless solu-
from the synthesis solution. Anal: required for tion. Hexamethyldisiloxane (0.16 g, 1 mmol) and MeCN
C6H18F3NbO3P2·CH2Cl2 (435.0): C, 19.3; H, 4.6. Found: C, 18.7; (0.5 mL) were added and the mixture stirred for 6 h at room
1
2
H, 4.3%. H NMR (CD2Cl2, 293 K): 1.60 (d, [H] JPH = 13 Hz), temperature, during which a fine microcrystalline solid was de-
1.86 (d, [H] JPH = 13 Hz). 19F{1H} NMR (CD2Cl2, 293 K): 41.5 posited. The solid was filtered off, rinsed by diethyl ether
2
(s, [F]), 30.6 (s, [2F]). 31P{1H} NMR (CD2Cl2, 293 K): 67.1 (s, [P]), (5 mL) and dried in vacuo. Yield 0.25 g, 78%. Anal: required for
53.3 (s, [P]). 93Nb NMR (CD2Cl2, 293 K): not observed. IR C4H12F3NbO3S2 (322.2): C, 14.9; H, 3.8. Found: C, 15.1; H,
(Nujol/cm−1): 1140 (m), 1087 (s) (PO), 958 (s), NbO, 614 (s), 555 3.9%. H NMR (CD2Cl2, 293 K): 2.65 (br); (253 K): 2.59 ([6H]),
1
(s) NbF.
2.55 ([6H]). 19F{1H} NMR (CD2Cl2, 293 K): 50.4 (s, [F]), 38.0 (s,
[NbOF3(2,2′bipy)]: NbF5 (0.19 g, 1 mmol) was dissolved in [2F]). IR (Nujol/cm−1): 1039 (s), 1005 (s) Me2SO, 920 (s) NbO,
CH2Cl2 (200 mL) and dry 2,2′-bipy (0.16 g, 1 mmol) in CH2Cl2 590 (s), 564 (s) NbF.
(10 mL) was added with stirring. After 15 min. hexamethyldisi-
[NbOF3(tmeda)]: NbF5 (0.19 g, 1 mmol) was added to dry
loxane (0.16 g, 1 mmol) and MeCN (0.5 mL) were added and CH2Cl2 (200 mL), followed by dry tmeda (0.12 g, 1 mmol) and
the mixture stirred overnight at room temperature, producing the mixture stirred for 20 min. producing a cloudy suspension.
a white precipitate. The mixture was concentrated to ∼5 mL Hexamethyldisiloxane (0.16 g, 1 mmol) and MeCN (0.5 mL)
in vacuo, the white solid filtered off, rinsed with diethyl ether were added and the mixture stirred overnight at room tempera-
and dried in vacuo. Yield 0.27 g, 83%. Anal: required for ture, during which a fine white powder was deposited.
C10H8F3N2NbO (322.1): C, 37.3; H, 2.5; N, 8.7. Found: C, 37.5; The solid was filtered off, rinsed by diethyl ether (5 mL) and
1
H, 2.4; N, 8.6%. H NMR (CD2Cl2, 293 K): 9.28 (s, [H]), 9.17 (s, dried in vacuo. Yield 0.24 g, 85%. Anal: required for
[H]), 8.54 (m, [H]), 8.36 (m, [H]), 8.32 (s, [2H]), 7.85 (s, [H]), C6H16F3N2NbO·CH2Cl2 (367.0): C, 21.9; H, 4.9; N, 7.6. Found:
3656 | Dalton Trans., 2014, 43, 3649–3659
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C, 21.4; H, 5.5; N, 7.9%. Insoluble in non-donor solvents. IR
(Nujol/cm−1): 920 (s) NbO, 587 (s) 557 (s) NbF.
[NbOCl3(dppmO2)]: was made similarly to [NbOCl3(dp-
peO2)]. Yield 67%. Crystals of [NbOCl3(dppmO2)] were grown
[NbOCl3(2,2′-bipy)]: NbCl5 (0.067 g, 0.25 mmol) was dis- from a saturated dichloromethane solution in the freezer.
solved into acetonitrile (4 mL) to give a bright yellow-green Anal: required for C25H22Cl3NbO3P2 (631.6): C, 46.7; H, 3.5.
solution. Hexamethyldisiloxane (0.040 g, 0.25 mmol) was Found: C, 46.8; H, 3.9%. 1H NMR (CD2Cl2, 295 K): 7.75–7.35
2
added and the mixture was stirred for 10 min. during which (m, [10H]), 3.80 (t, [H], JPH = 15 Hz). 31P{1H} NMR (CH2Cl2–
2
2
time the solution turned very pale. 2,2′-Bipy (0.039 g, CDCl3, 298 K): 48.5 (d, JPP = 19 Hz) 36.8 (d, JPP = 19 Hz). IR
0.25 mmol) in acetonitrile (4 mL) was added slowly with stir- (Nujol/cm−1): 1157 (s), 1095 (s) PO, 928 (s) NbO, 327 (s), 294
ring. After 30 min. the solution was concentrated in vacuo and (m) NbCl.
the white precipitate filtered off, and dried in vacuo. Yield
[TaF5(OPPh3)]: A solution of OPPh3 (0.26 g, 1.0 mmol) in
0.048 g, 52%. Crystals of [NbOCl3(2,2′-bipy)] were grown from CH2Cl2 (20 mL) was added to finely powdered TaF5 (0.28 g,
acetonitrile solution in the freezer. Anal: required for 1.0 mmol), and vigorously stirred to give a clear solution. This
C10H8Cl3N2NbO (371.4): C, 32.3; H, 2.2; N, 7.5. Found: C, 32.3; was filtered to remove any residual solid and concentrated
1
H, 2.1; N, 7.7%. H NMR (CD2Cl2, 295 K): 8.98 (s, [H]), 8.91 (s, in vacuo to ∼2 mL. On standing a white powder separated, which
[H]), 8.31 (br m, [4H]), 7.79 (s, [H]), 7.73 (s, [H]). IR (Nujol/ was filtered off and dried in vacuo. Yield 0.45 g, 81%. Anal:
cm−1): 943 (s) NbO, 349 (s), 338 (s) NbCl.
required for C18H15F5OPTa (554.2): C, 39.0; H, 2.7. Found:
[NbOCl3(1,10-phen)]: The white compound was made in an C, 38.5; H, 2.9%. 1H NMR (CD2Cl2, 293 K): 7.2–7.6 (m). 19F{1H}
analogous way to [NbOCl3(2,2′-bipy)]. Yield 61%. Anal: NMR (CD2Cl2, 293 K): 84.2 (s, [F)], 54.7 (s, [4F]; (210 K): 81.8 (s,
required for C12H8Cl3N2NbO (395.4): C, 36.4; H, 2.0; N, 7.1. [F]), 56.3 (s, [4F]). 31P{1H} NMR (CD2Cl2, 293 K): 53.2(s). IR
1
Found: C, 36.3; H, 2.0; N, 7.1%. H NMR (CD2Cl2, 295 K): 9.86 (Nujol/cm−1): 1078 (vs) PO, 617 (sh), 592 (vs, br) TaF.
(s, [H]), 9.75 (s, [H]), 8.88 (m, [H]), 8.74 (m, [H]), 8.17 (s, [2H]),
8.08 (s, [2H]). IR (Nujol/cm−1): 944 (s) NbO, 338 (vbr, s) NbCl.
[TaF5(OAsPh3)]: was made similarly, from OAsPh3 (0.32 g,
1.0 mmol) and TaF5 (0.28 g, 1.0 mmol), except that the reac-
[NbOCl3(tmeda)]: NbCl5 (0.270 g, 1.0 mmol) was dissolved tion was worked up and the solid isolated after 20 min. Yield
into acetonitrile (10 mL) and hexamethyldisiloxane (0.244 g, 0.50 g, 85%. Anal: required for C18H15AsF5OTa (598.2): C, 36.2;
1.5 mmol) was added. After 10 min. tmeda (0.14 g, 1.2 mmol) H, 2.5. Found: C, 37.3; H 2.6%. 1H NMR (CD2Cl2, 293 K):
in dichloromethane (4 mL) was added slowly to the reaction 7.2–7.6 (m). 19F{1H} NMR (CD2Cl2, 293 K): 62.5 (s, [F]), 48.6 (s,
mixture with stirring. After 2 h the mixture was concentrated [4F]), weak resonances at 38.6 ([TaF6]−) and −89.4 (Ph3AsF2).
in vacuo and the resulting precipitate was filtered off and dried IR (Nujol/cm−1): 845 (s) AsO, 620 (sh), 581 (vs, br) TaF.
in vacuo. Yield 0.055 g, 17%. Single crystals of [NbOCl3(tmeda)]
[TaF5(OPMe3)]: A solution of OPMe3 (0.092 g, 1.0 mmol) in
were grown from the filtrate in the freezer. Anal: required for CH2Cl2 (10 mL) was added to finely powdered TaF5 (0.276 g,
C6H16Cl3N2NbO (331.4): C, 21.7; H, 4.9; N, 8.5. Found: C, 21.6; 1.0 mmol), and vigorously stirred to give a clear solution. This
1
H, 4.8; N, 8.4%. H NMR (CD2Cl2, 295 K): insoluble. IR (Nujol/ was filtered to remove any residual solid and concentrated
cm−1): 945 (s) NbO, 341 (s) 320 (sh) NbCl.
in vacuo to ∼5 mL. A white powder separated, which was fil-
[NbOCl3(OPPh3)2]: NbCl5 (0.270 g, 1.0 mmol) was dissolved tered off and dried in vacuo. Yield 0.25 g, 65%. Anal: required
in acetonitrile (5 mL) whilst stirring and hexamethyldisiloxane for C3H9F5OPTa (368.0): C, 9.8; H, 2.5. Found: C, 10.2; H,
1
2
(0.162 g, 1.0 mmol) was added. After 10 min. OPPh3 (0.556 g, 2.3%. H NMR (CD2Cl2, 293 K): 1.9 (d, JPH = 15 Hz). 19F{1H}
2 mmol) was added producing a milky white mixture. The NMR (CD2Cl2, 293 K): 82.5 (s, [F]), 55.9 (s, [4F]). 31P{1H} NMR
reaction was left to stir for 2 h and the white solid filtered off (CD2Cl2, 293 K): 76.9 (s). IR (Nujol/cm−1): 1092 (vs) PO, 601
and dried in vacuo. Yield: 0.450 g, 58%. Anal: required for (sh), 583 (vs, br) TaF.
C36H30O3Cl3NbP2 (771.8): C, 56.0; H, 3.9. Found: C, 55.7; H,
[TaF4(2,2′-bipy)2][TaF6]: TaF5 (0.28 g, 1.0 mmol) was added
3.6%. 1H NMR (CD2Cl2, 295 K): 7.7–7.2 (m). 31P{1H} NMR to CH2Cl2 (50 mL) and vigorously stirred, whilst a solution of
(CDCl3, 298 K): 50.0 (s, [P]), 38.8 (s, [P]). IR (Nujol/cm−1): 2,2′-bipy (0.16 g, 1.0 mmol) in CH2Cl2 (10 mL) was added,
1159 (s), 1074(s) PO, 936 (s) NbO, 325(s), 294(m) NbCl.
resulting in rapid precipitation of a fine white powder. After
[NbOCl3(dppeO2)]: NbCl5 (0.068 g, 0.25 mmol) was dis- 24 h the solid was isolated by filtration, rinsed with diethyl
solved in acetonitrile (5 mL) and hexamethyldisiloxane ether (5 mL) and dried in vacuo. Yield 0.35 g, 86%. Anal:
(0.062 g, 0.38 mmol) was added. The mixture was left to stir required for C20H16F10N4Ta2 (864.2): C, 27.8; H, 1.9; N, 6.5.
1
for 15 min. and then dppeO2 (0.108 g, 0.25 mmol) was added Found: C, 27.9; H,1.9; N, 6.4%. H NMR (CD2Cl2, 293 K): 9.34
and the reaction was left to stir overnight. The precipitate was (d, [2H], J = 9 Hz), 8.50 (d, [2H], J = 8 Hz), 8.37 (m, [2H]), 7.81
filtered off, rinsed with small amount of CH2Cl2 and dried (m, [2H]). 19F{1H} NMR (CD2Cl2, 293 K): 68.1 (s, [4F]), 38.0 (s,
in vacuo. Yield 0.102 g, 63%. Crystals of [NbOCl3(dppeO2)] were [6F]). IR (Nujol/cm−1): 605 (sh), 581 (vs) TaF.
grown from CH2Cl2 solution in the freezer. Anal: required for
[TaF4(1,10-phen)2][TaF6]: was made similarly. Yield 83%.
C26H24Cl3NbO3P2 (645.6): C, 48.4; H, 3.8. Found: C, 48.6; H, Anal: required for C24H16F10N4Ta2 (912.3): C, 31.6; H, 1.8; N,
1
1
4.0%. H NMR (CD2Cl2, 295 K): 7.89–7.48 (m [10H]), 2.84 (m, 6.1. Found: C, 31.5; H, 1.8; N, 6.0%. H NMR (CD2Cl2, 293 K):
[H]), 2.62 (m, [H]). 31P{1H} NMR (CDCl3, 298 K): 56.7 (s), 44.9 (s). 9.15 (s, [2H]), 8.63 (d, [2H], J = 10 Hz), 8.09 (s, [2H]), 7.92 (m,
IR (Nujol/cm−1): 1172 (s), 1066 (s) PO, 943 (s) NbO, 320 (s), [2H]). 19F{1H} NMR (CD2Cl2, 293 K): 66.1 (s, [4F]), 37.9 (s, [6F]).
293 (w) NbCl.
IR (Nujol/cm−1): 605 (sh), 576 (vs) TaF.
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Table 2 X-ray dataa
Compound
[NbOF3(OPPh3)2]
36H30F3NbO3P2
[NbOF3(OPMe3)2]·0.33CH2Cl2
[NbOF3(dppmO2)]
[NbOCl3(dppmO2)·0.3MeCN
Formula
M
C
C6H18F3NbO3P2·0.33CH2Cl2
378.36
C25H22F3NbO3P2
582.28
C25H22Cl3NbO3P2·0.3CH3CN
643.94
722.45
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/°
β/°
Orthorhombic
Fdd2 (no. 43)
18.762(9)
33.289(14)
10.152(5)
90
90
90
6340(5)
8
0.534
Triclinic
P1 (no 2)
Monoclinic
P21/n (no. 14)
13.154(8)
10.967(6)
17.248(10)
90
97.173(19)
90
2469(3)
Monoclinic
P21/n (no. 14)
10.694(2)
15.640(4)
17.181(4)
90
105.721(6)
90
2766.0(13)
4
ˉ
7.8890(15)
14.584(3)
20.046(4)
102.497(4)
99.803(4)
97.324(2)
2186.3(7)
6
γ/°
U/Å3
Z
4
μ(Mo-Kα)/mm−1
F(000)
1.191
1140
0.665
1176
0.867
1298
2944
Total number reflns
Rint
Unique reflns
No. of params, restraints
R1, wR2 [I > 2σ(I)]b
R1, wR2 (all data)
7136
0.0849
3000
204, 20
0.0719, 0.1062
0.0888, 0.1148
22 109
0.0250
9978
556, 15
0.0359, 0.0847
0.0430, 0.0880
15 969
0.0915
4794
307, 0
0.0770, 0.1725
0.0982, 0.1854
11 311
0.0386
5288
320, 2
0.0514, 0.0946
0.0742, 0.1045
Compound
[NbOCl3(dppeO2)]·0.5MeCN
[NbOCl3(2,2′-bipy)]
[NbOCl3(tmeda)]
Formula
M
C26H24Cl3NbO3P2·0.5CH3CN
666.18
C10H8Cl3N2NbO
371.44
C6H16Cl3N2NbO
331.47
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/°
Monoclinic
P21/n (no. 14)
10.752(2)
14.367(3)
18.048(4)
90
Orthorhombic
Fdd2 (no. 43)
12.4975(4)
21.6322(8)
29.090(2)
90
Orthorhombic
Pna21 (no. 33)
14.352(7)
7.368(4)
11.781(6)
90
β/°
92.519(10)
90
2785.1(10)
4
0.864
1348
90
90
7864.3(6)
24
1.512
90
90
γ/°
U/Å3
1245.8(11)
4
1.578
Z
μ(Mo-Kα)/mm−1
F(000)
4368
664
Total number reflns
Rint
14 141
0.0555
5418
0.0243
3500
0.0196
Unique reflns
No. of params, restraints
R1, wR2 [I > 2σ(I)]b
R1, wR2 (all data)
5451
338, 2
0.0591, 0.0921
0.0721, 0.0968
2991
240, 16
0.0469, 0.1169
0.0506, 0.1204
2135
119, 2
0.0449, 0.1102
0.0521, 0.1162
4 1/2
a Common items: T = 100 K; wavelength (Mo-Kα) = 0.71073 Å; θ(max) = 27.5°. b R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = [∑w(Fo2 − Fc2)2/∑wFo
]
.
X-Ray experimental
a very elongated ellipsoid with two large Q peaks close to Nb2.
A subsequent model displaced Nb2 by a few tenths of an Å
from the axis and this gave a better fit to the data, R1 reduced
from ∼0.08 to ∼0.05.
Details of the crystallographic data collection and refinement
parameters are given in Table 2. Crystals suitable for single
crystal X-ray analysis were obtained as described above. Data
collections used a Rigaku AFC12 goniometer equipped with an
enhanced sensitivity (HG) Saturn724+ detector mounted at the
window of an FR-E+ SuperBright molybdenum (λ = 0.71073 Å)
rotating anode generator with VHF Varimax optics (100 µm
focus) with the crystal held at 100 K (N2 cryostream). Structure
solution and refinement were straightforward,22,23 except as
detailed below, with H atoms bonded to C being placed in cal-
culated positions using the default C–H distance. Several cases
of O/X disorder have been discussed in the text. Three of the
carbon atoms in [NbOCl3(tmeda)], C4, C5 and C6 were
elongated, suggesting some disorder, but attempts to split
these over two positions were unsuccessful. For [NbOCl3(2,2′-
bipy)] Nb2 was initially placed on the two-fold axis but showed
Acknowledgements
We thank EPSRC for support (EP/1033394/1) and Drs
M. Webster and M. E. Light for assistance with the X-ray data
analyses.
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3658 | Dalton Trans., 2014, 43, 3649–3659
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