Preparation and structures of coordination complexes of the very hard Lewis acids ZrF4 and HfF4

Article abstract of DOI:10.1039/c2dt31501g

[MF₄(dmso)₂] (M = Zr or Hf) and [MF ₄(dmf)₂], prepared by dissolving MF₄· nH₂O in the appropriate solvent, have been used as synthons for a range of complexes of these otherwise intractable tetrafluorides. These reagents react with OPR₃ (R = Me or Ph) or OAsPh₃ (L) in anhydrous CH₂Cl₂ to form six-coordinate [MF₄L ₂] which exist as a mixture of cis (predominant form) and trans isomers in CH₂Cl₂ solution but which crystallise as trans (OPPh₃, OAsPh₃) or cis (OPMe₃) forms. Cis-[ZrF₄(OAsPh₃)₂] crystals were obtained from MeCN. Cis-[MF₄(pyNO)₂] and eight-coordinate (distorted dodecahedral) [MF₄(L-L)₂] (L-L = 2,2′-bipy, or 1,10-phen), and [MF₄(Me₄-cyclam)] were also obtained. Attempts to prepare complexes with the N-heterocyclic carbene, 1,3-(2,6-di-isopropylphenyl)imidazol-2-ylidene (IDiPP) or alkyl diphosphines were unsuccessful. Crystal structures are reported for trans-[ZrF ₄(OPPh₃)₂], cis- and trans-[ZrF ₄(OAsPh₃)₂], cis-[HfF₄(OPMe ₃)₂], [ZrF₄(2,2′-bipy)₂], cis-[HfF₄(dmf)₂], and geometric isomers (both pentagonal bipyramidal) of [(dmso)₂F₃M(μ-F)₂MF ₃(dmso)₂]. The failed attempts to make IDiPP adducts led to crystals of [IDiPPH]₃[M₃F₁₅] containing discrete anions based upon a triangle of M atoms with single F bridges. The results are compared with previous work on TiF₄ adducts and with complexes of MCl₄, and demonstrate that the MF₄ are very hard Lewis acids, with a marked preference for O- over N-donors.

Full text of DOI:10.1039/c2dt31501g

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PAPER
Preparation and structures of coordination complexes of the very hard Lewis
acids ZrF4 and HfF4†
Sophie L. Benjamin, William Levason,* David Pugh, Gillian Reid and Wenjian Zhang
Received 9th July 2012, Accepted 24th August 2012
DOI: 10.1039/c2dt31501g
[MF4(dmso)2] (M = Zr or Hf) and [MF4(dmf)2], prepared by dissolving MF4·nH2O in the appropriate
solvent, have been used as synthons for a range of complexes of these otherwise intractable tetrafluorides.
These reagents react with OPR3 (R = Me or Ph) or OAsPh3 (L) in anhydrous CH2Cl2 to form six-
coordinate [MF4L2] which exist as a mixture of cis (predominant form) and trans isomers in CH2Cl2
solution but which crystallise as trans (OPPh3, OAsPh3) or cis (OPMe3) forms. Cis-[ZrF4(OAsPh3)2]
crystals were obtained from MeCN. Cis-[MF4(pyNO)2] and eight-coordinate (distorted dodecahedral)
[MF4(L–L)2] (L–L = 2,2′-bipy, or 1,10-phen), and [MF4(Me4-cyclam)] were also obtained. Attempts to
prepare complexes with the N-heterocyclic carbene, 1,3-(2,6-di-isopropylphenyl)imidazol-2-ylidene
(IDiPP) or alkyl diphosphines were unsuccessful. Crystal structures are reported for trans-[ZrF4(OPPh3)2],
cis- and trans-[ZrF4(OAsPh3)2], cis-[HfF4(OPMe3)2], [ZrF4(2,2′-bipy)2], cis-[HfF4(dmf)2], and geometric
isomers (both pentagonal bipyramidal) of [(dmso)2F3M(μ-F)2MF3(dmso)2]. The failed attempts to make
IDiPP adducts led to crystals of [IDiPPH]3[M3F15] containing discrete anions based upon a triangle of
M atoms with single F bridges. The results are compared with previous work on TiF4 adducts and with
complexes of MCl4, and demonstrate that the MF4 are very hard Lewis acids, with a marked preference
for O- over N-donors.
hexafluorometallates(IV) [MF6]2− with six- (octahedral), seven-
(both pentagonal bipyramidal and capped octahedral), and eight-
Introduction
The coordination chemistry of high valent metal fluorides has
been relatively little explored and examples with neutral donor
ligands are particularly rare. This is despite the very different
electronic properties of fluoride ligands compared to the heavier
halides, which can radically modify the Lewis acidity and hard-
ness of the metal centre, and hence produce significantly differ-
ent coordination chemistry compared to that with heavier halide
co-ligands. Recent work addressing this area has included
coordinate (square antiprismatic) M are established, the structure
depending upon the cation present.12 Very few complexes with
neutral ligands have been isolated.13–20 Structurally authenticated
examples
include
the
hydrates
[(H2O)3F3Zr(μ-F)2Zr-
(H2O)3F3],14,15 and [HfF4(H2O)2], which is a chain polymer
with HfO2F2F4/2 coordination,16 several dmso complexes,17,18
including [(dmso)2F3Zr(μ-F)2ZrF3(dmso)2], and the N,N-
dimethylformamide complex [(dmf)2F3Zr(μ-F)2ZrF3(dmf)2].19
Complexes with nitrogen donor ligands are even rarer, but
include [M(NH3)4F4]·NH3 (M = Zr or Hf)21 and [HfF4(2,2′-
bipy)2].22
3,5
studies of complexes of GeF4,1 SnF4,1c,2 NbF5,3 TiF4,4 TaF5
VOF3,6 VO2F,7 MO2F2 (M = Mo or W)8 and WF6.9 Following
recent studies of TiF4 adducts, which included the first examples
of phosphines4a and N-heterocyclic carbene complexes,4b we
report here an investigation of complexes of ZrF4 and HfF4 with a
variety of neutral O- and N-donor ligands, together with attempts
to prepare N-heterocyclic carbene and phosphine complexes.
Zirconium and hafnium tetrafluorides are unreactive, poly-
meric solids which contain eight-coordinate metal centres.
Single crystal X-ray studies have confirmed monoclinic (β)
forms for both;10,11 and there is also a tetragonal high temp-
erature (α) form of ZrF4.11 A wide range of fluorometallate anions
are known, the stoichiometry giving no guide to the structures,
Results and discussion
Synthons
Given the very intractable nature of MF4 (M = Zr, Hf), develop-
ment of their coordination chemistry critically depends upon
obtaining suitable soluble synthons which can be reacted with
the relevant neutral ligands. The anhydrous MF4 are insoluble in
organic solvents,23 but the hydrates, MF4·nH2O dissolved‡ on
School of Chemistry, University of Southampton, Southampton SO17
1BJ, UK. E-mail: wxl@soton.ac.uk; Tel: +44 (0)2380 593792
†Electronic supplementary information (ESI) available. CCDC
890601–890611. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2dt31501g
‡Several commercial samples of “anhydrous” MF4 showed significant
water in the IR spectra and dissolved fairly easily in hot dmso or dmf, as
did commercial samples of the hydrates. Genuinely anhydrous MF4
samples were insoluble in the same solvents even after prolonged
heating,23 consistent with literature reports.
12548 | Dalton Trans., 2012, 41, 12548–12557
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heating in dmso or dmf, and crystalline 1 : 2 adducts separated
on allowing the solutions to stand. The synthesis of complexes
analogous to those used to obtain TiF4 adducts, [TiF4(thf)2]4a or
[TiF4(MeCN)2]24 was explored, but the MF4·nH2O do not dis-
solve in MeCN or thf even under reflux, and the [MF4(dmso)2]
were recovered from attempted recrystallisation from thf or
MeCN.
singlet in the 19F{1H} NMR spectra, δ ∼ +43 (M = Zr) and ∼−1
(M = Hf) (Table 1), which indicates fluxionality or reversible
dissociation. Singlets at similar frequencies are seen in freshly
prepared d6-dmso or d7-dmf solutions as appropriate (Experi-
mental section). The spectra in d7-dmf solution are little different
at 220 K, but low temperature studies in CD2Cl2 were prevented
by very poor solubility. There are reports of the low temperature
NMR spectra of [MF4(dmso)2] in mixed donor solvents,20,25
which observed several species, but the identities are speculative
due to the limited data.
The [MF4(dmso)2] and [MF4(dmf)2] dissolve easily in the
parent solvent on warming, are very poorly soluble in CH2Cl2 or
methanol and essentially insoluble in MeCN or acetone. The
structure of [ZrF4(dmso)2] has been determined independently
twice17,18 and shown to have a monoclinic cell, containing
[(dmso)2F3Zr(μ-F)2ZrF3(dmso)2] molecules composed of two
pentagonal bipyramidal zirconium centres with axial fluorides.
In the present study a few small colourless crystals were obtained
serendipitously from a failed attempt to obtain crystals of
[ZrF4(2,2′-bipy)2] from a 1 : 2 mol. ratio of [ZrF4(dmso)2] and
2,2′-bipy in 1 : 1 dmso–CH2Cl2 solution. The structure of these
revealed them to have a tetragonal cell containing a geometric
isomer of the known form (Fig. 1). The key difference is the
arrangement of ligands in the pentagonal plane which in the
monoclinic form is O–F–O–F–F with an <O–Zr–O of 152.8°,
but in the tetragonal form is O–O–F–F–F with <O–Zr–O =
72.6°. The Zr–F, Zr–O and S–O distances are not significantly
different in the two isomers.
Oxygen donor ligand complexes. The reaction of
[MF4(dmso)2] and [ZrF4(dmf)2] or [HfF4(dmf)2] with 2 mol.
Colourless crystals of [{HfF4(dmso)2}2] (Fig. 2) were found
to be isomorphous with the monoclinic form of
[{ZrF4(dmso)2}2]; the Hf–F and Hf–O bond lengths are very
slighter shorter (∼0.01 Å) than the corresponding bonds in the
zirconium complex.
The structure of [(dmf)2F3Zr(μ-F)2ZrF3(dmf)2] also has penta-
gonal bipyramidal zirconium centres, axial fluorines, and an
O–O–F–F–F sequence of donors in the equatorial plane.19 In
contrast, crystals of [HfF4(dmf)2], which separated on standing
over several days from a solution of HfF4·nH2O in dmf, contain
cis-octahedral monomers (Fig. 3).
Fig. 2 Crystal structure of [{HfF4(dmso)2}2] showing the atom num-
bering scheme. The dimeric molecule has a centre of symmetry. Ellip-
soids are drawn at the 50% probability level and H atoms are omitted for
clarity. Symmetry operation: a = −x, −y, 1 − z. Selected bond lengths
(Å) and angles (°): Hf1–F2 = 1.963(4), Hf1–F1 = 1.979(5), Hf1–F4 =
1.985(4), Hf1–F3a = 2.141(4), Hf1–F3 = 2.144(4), Hf1–O1 = 2.178(5),
Hf1–O2 = 2.181(5), F2–Hf1–F1 175.36(18), O1–Hf1–O2 152.53(18).
The key IR spectroscopic data is given in the Experimental
section. In CD2Cl2 at 295 K all four complexes show a broad
Fig. 1 Crystal structure of [{ZrF4(dmso)2}2] (tetragonal form) showing
the atom numbering scheme. The dimeric molecule has a centre of sym-
metry. Ellipsoids are drawn at the 50% probability level and H atoms are
omitted for clarity. Symmetry operation: a = −x, −y, 1 − z. Selected
bond lengths (Å) and angles (°): Zr1–F1 = 1.977(1), Zr1–F2 = 1.977(1),
Zr1–F4 = 1.988(1), Zr1–F3 = 2.148(1), Zr1–F3a = 2.155(1), Zr1–O2 =
2.196(2), Zr1–O1 = 2.212(2), F1–Zr1–F2 = 177.23(5), O2–Zr1–O1 =
72.64(5).
Fig. 3 Crystal structure of cis-[HfF4(dmf)2] showing the atom number-
ing scheme. The molecule has a two-fold symmetry axis. Ellipsoids are
drawn at the 50% probability level and H atoms are omitted for clarity.
Symmetry operation: a = 1 − x, y, 1/2 − z. Selected bond lengths (Å)
and angles (°): Hf1–F2 = 1.954(4), Hf1–F1 = 1.975(4), Hf1–O1 = 2.159(4).
F2–Hf1–F2a
= 91.4(2), F2–Hf1–F1 = 94.93(17), F2–Hf1–F1a
92.94(16), F2–Hf1–O1 = 90.38(18), F1–Hf1–O1 = 85.80(17), F1–Hf1–
O1a 86.08(17), O1–Hf1–O1a = 87.8(2).
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Table 1 19F{1H} NMR dataa
Complex
δ
19F{1H} (295 K)b
Complex
δ
19F{1H} (295 K)b
[ZrF4(dmso)2]
[ZrF4(dmf)2]
43.5 (s)
[HfF4(dmso)2]
[HfF4(dmf)2]
−1.5 (s)
−1.7 (s)
43.5 (s)
[ZrF4(OPPh3)2]
[ZrF4(OAsPh3)2]
[ZrF4(OPMe3)2]
[ZrF4(pyNO)2]
[ZrF4(phen)2]
[ZrF4(bipy)2]
48.1 (s) [2F], 24.2 (s) [2F], 23.8 (sh)c (253 K)
[HfF4(OPPh3)2]
[HfF4(OAsPh3)2]
[HfF4(OPMe3)2]
[HfF4(pyNO)2]
[HfF4(phen)2]
[HfF4(bipy)2]
−2.35 (s) [2F], −17.6 (s) [2F], −18.3 (s)c (223 K)
29.5 (s) [2F], 17.0 (s) [2F], 16.3 (s)c (223 K)
−10.7 (s) [2F], −20.7 (s) [2F], −21.9 (s)c (243 K)
41.2 (s) [2F], 19.1 (s) [2F], 18.9 (sh)c (243 K)
−4.1 (s) [2F], −20.2 (s) [2F], −20.7 (s)c (243K)
37.7 (s)
21.3 (s)
24.5 (s)
−6.5 (s)
−17.8 (s)
−11.2 (s)
[ZrF4(Me4-cyclam)]
14.2 (s)
[HfF4(Me4-cyclam)]
−12.0 (s)
[ZrF6]2− d
−16 (H2O),d −10 (CD2Cl2)e
[HfF6]2− d
−47 (H2O),d −44 (CD2Cl2)e
a In CH2Cl2 solution. b Temperature unless indicated otherwise. c Resonance of trans isomer. d M. A. Fedotov and A. V. Belyaev, J. Struct. Chem.,
2011, 52, 69 and references therein. e [NMe4]+ salt this work.
Fig. 4 Crystal structure of trans-[ZrF4(OPPh3)2]·2CH2Cl2 showing the
Fig. 5 Crystal structure of trans-[ZrF4(OAsPh3)2]·2CH2Cl2 showing
the atom numbering scheme. The molecule has a centre of symmetry.
Ellipsoids are drawn at the 50% probability level and H atoms and the
solvate molecules are omitted for clarity. Symmetry operation: a = 1 − x,
1 − y, −z. Selected bond lengths (Å) and angles (°): Zr1–F1 = 1.993(3),
Zr1–F2 = 1.994(3), Zr1–O1 = 2.093(3), As1–O1 = 1.668(3). F1–Zr1–F2a
= 89.08(13), F1–Zr1–F2 = 90.92(14), F1–Zr1–O1a = 88.88(13), F1–Zr1–
O1 = 91.12(13), F2–Zr1–O1 = 88.97(14), F2–Zr1–O1a = 91.03(14),
O1–Zr1–O1a = 180.00(18).
atom numbering scheme. The molecule has a centre of symmetry. The
carbon atoms are numbered cyclically starting at the ipso C. Ellipsoids
are drawn at the 50% probability level and H atoms and the solvate mole-
cule are omitted for clarity. Symmetry operation: a = 1 − x, 1 − y, −z.
Selected bond lengths (Å) and angles (°): Zr1–F2 = 1.9742(19), Zr1–F1
= 1.987(2), Zr1–O1 = 2.116(2), P1–O1 = 1.516(2). F2–Zr1–F1a = 88.96(8),
F2–Zr1–F1 = 91.04(8), F2–Zr1–O1a = 91.03(8), F2–Zr1–O1 = 88.97(8),
F1–Zr1–O1
= 91.24(9), F1–Zr1–O1a = 88.76(9), O1–Zr1–O1a =
180.00(11).
equivalents of OEPh3 (E = P or As) in CH2Cl2 led to high yields
of [ZrF4(OEPh3)2] or [HfF4(OAsPh3)2]. The [MF4(OEPh3)2]
were also obtained using a two-fold excess of OEPh3, and in situ
31P and 19F NMR studies showed no evidence of species with a
higher OEPh3 : M ratio. Unusually for the fluoride complexes of
these two metals, the pnictogen oxide complexes are easily
soluble in chlorocarbon solvents. They also dissolve in dmso or
dmf, but NMR studies suggest partial displacement of the OER3
occurs. The filtrates from the bulk preparations deposited colour-
less crystals [ZrF4(OEPh3)2]·2CH2Cl2, which are isomorphous
and contain trans-octahedral molecules (Fig. 4 and 5). The Zr–F
and Zr–O distances are very similar in the two complexes, with
the Zr–O(As) very slightly shorter than Zr–O(P); the correspond-
ing effect is much more pronounced in the cis-[TiF4(OEPh3)2]
complexes.4a
Fig. 6 Crystal structure of cis-[ZrF4(OAsPh3)2]·2CH2Cl2 showing the
atom numbering scheme. Symmetry operation: a = 1 − x, y, 1/2 − z.
Ellipsoids are drawn at the 50% probability level. The solvate molecules
and the H atoms are omitted for clarity. Selected bond lengths (Å) and
angles (°): Zr1–F1 = 1.973(3), Zr1–F2 = 1.995(3), Zr1–O1 = 2.125(4),
As1–O1 = 1.680(4), F1–Zr1–F1a = 93.1(2), F1–Zr1–F2 = 95.21(14),
F1–Zr1–F2a = 88.99(15), F1–Zr1–O1a = 89.54(15), F2–Zr1–O1a =
86.28(15), F2–Zr1–O1 = 89.34(15), O1–Zr1–O1a = 88.2(2).
Unexpectedly, a few crystals of cis-[ZrF4(OAsPh3)2]·2CH2Cl2
were deposited from a solution of [ZrF4(2,2′-bipy)2] and
OAsPh3 in MeCN–CH2Cl2 (Fig. 6). Comparison of the bond
lengths in the two structures reveal that whilst Zr–FtransF are
effectively identical, Zr–FtransO in the cis-isomer is shorter by
12550 | Dalton Trans., 2012, 41, 12548–12557
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∼0.02 Å and Zr–OtransF longer than Zr–OtransO by ∼0.03 Å,
showing the dominant Zr–F bonding.4
but the complexes were too poorly soluble for low temperature
NMR studies. The complexes dissolve easily in d7-dmf, but the
1H and 19F NMR spectra show the pyNO is largely displaced by
dmf.
The IR spectra of the bulk solid [MF4(OPPh3)2] show single
sharp strong bands at ∼1080 and ∼514 (Zr) or ∼493 (Hf) cm−1
assigned as ν(PO) and ν(MF) respectively, as expected for trans
isomers (D4h). In the [MF4(OAsPh3)2] the ν(AsO) at ∼875 cm−1
are only slightly shifted from the value in OAsPh3 (881 cm−1) as
is often the case in arsine oxide complexes,26 but are relatively
more intense and much broader. In solution in CD2Cl2 at 295 K
very broad resonances are present in the 19F{1H} NMR spectra
of all four complexes, consistent with exchanging systems, but
on cooling the solutions two broad singlets of approximately
equal intensity appear which sharpen on further cooling, but no
FF couplings were resolved. This indicates that the predominant
forms in solution are cis isomers. Careful integration of the res-
onances measured at 243 K show typically 1 : ≤1.2, with the
lower frequency resonance the more intense, and under high res-
olution, a small peak or a shoulder is evident on the lower fre-
quency resonance which are attributable to a small amount of the
trans isomer. The 31P{1H} NMR spectra of the phosphine oxide
complexes show a singlet with a modest high frequency coordi-
nation shift assigned to the cis isomers; again under high resolu-
tion at low temperatures a second weak feature with a very
similar chemical shift is observed in each, due to the trans
isomer. The fact that [MF4(OEPh3)2] are trans in the solid state
presumably reflects crystallisation of the least soluble isomer
from the solution containing reversibly dissociating ligands. In
contrast, the IR spectra of the [MF4(OPMe3)2] indicate they are
cis isomers in the solid state and this was confirmed by the
X-ray structure of the Hf complex (Fig. 7); the data were col-
lected from a twinned crystal of modest quality and detailed
comparison of bond lengths are not appropriate.
Nitrogen donor ligands. The reaction of 2,2′-bipyridyl or
1,10-phenanthroline with [MF4(dmso)2] or [MF4(dmf)2] in a
>2 : 1 mol. ratio in CH2Cl2 results in precipitation of the
[MF4(L–L)2] (L–L = 2,2′-bipy, 1,10-phen) as white powders.
The [ZrF4(2,2′-bipy)2] has been obtained previously by melting
together ZrF4 and 2,2′-bipy.27 [HfF4(2,2′-bipy)2] has an eight-
coordinate geometry in crystals which separated from a HfF4/
dmso/2,2′-bipy solution in which the complex was a minor con-
stituent (NMR evidence).14 Crystals of [ZrF4(2,2′-bipy)2]
obtained in this study by slow evaporation of a dilute solution of
the complex in MeCN, were isomorphous with the Hf analogue
and show a flattened dodecahedron with very similar geometry
(Fig. 8).
The complexes are very slightly soluble in CD2Cl2 and 19F-
{1H} NMR spectra show a single sharp resonance in each, with
chemical shifts to low frequency of those in O-donor ligand
complexes (Table 1). The diimine complexes dissolve more
1
easily in dmso or dmf, but the H and 19F{1H} NMR spectra
show partial displacement of the diimine occurs. Repeated
attempts to isolate pyridine adducts from reaction of
[MF4(dmf)2] with excess pyridine in anhydrous CH2Cl2 or from
neat pyridine failed, the products always retained significant
amounts of the dmf complex, whilst if the reactions were
exposed to moisture, the IR and 19F{1H} showed pyridinium
fluorometallates formed.
The addition of a solution of [MF4(dmf)2] in the minimum
amount of warm dmf to a solution of Me4-cyclam in CH2Cl2
under strictly anhydrous conditions, gave clear solutions, which
over ∼2 d deposited white precipitates of [MF4(Me4-cyclam)].
The reaction of [MF4(dmso)2] with pyridine-N-oxide in
CH2Cl2 solution formed [MF4(pyNO)2], the IR spectra
suggesting cis isomers in the solid state (Experimental section),
Fig. 7 Crystal structure of cis-[HfF4(OPMe3)2] showing the atom num-
bering scheme. Ellipsoids are drawn at the 50% probability level and H
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (°): Hf1–F4 = 1.973(9), Hf1–F1 = 1.983(7), Hf1–F2 = 1.983(8),
Hf1–F3 = 1.990(7), Hf1–O2 = 2.116(9), Hf1–O1 = 2.121(9), P1–O1 =
1.518(8), P2–O2 = 1.532(8), F4–Hf1–F1 = 92.4(3), F4–Hf1–F2 = 89.8(4),
F1–Hf1–F2 = 92.9(3), F4–Hf1–F3 = 93.7(4), F2–Hf1–F3 = 92.5(3),
F4–Hf1–O2 = 91.0(4), F1–Hf1–O2 = 87.6(3), F3–Hf1–O2 = 86.9(3),
F1–Hf1–O1 = 87.3(3), F2–Hf1–O1 = 91.5(4), F3–Hf1–O1 = 86.4(3),
O2–Hf1–O1 = 87.8(4).
Fig. 8 Crystal structure of [ZrF4(2,2′-bipy)2] showing the atom num-
bering scheme. Ellipsoids are drawn at the 50% probability level and H
atoms are omitted for clarity. Selected bond lengths (Å) and angles (°):
Zr1–F1 = 1.980(3), Zr1–F4 = 1.987(4), Zr1–F2 = 1.989(3), Zr1–F3 =
1.991(4), Zr1–N3 = 2.465(5), Zr1–N2 = 2.467(5), Zr1–N1 = 2.473(5),
Zr1–N4 = 2.482(5), F1–Zr1–F4 = 93.72(17), F1–Zr1–F2 = 96.96(16),
F4–Zr1–F3 = 96.62(19), F2–Zr1–F3 = 94.04(16), N2–Zr1–N1 = 65.1(2),
N3–Zr1–N4 = 66.05(19).
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The complexes are poorly soluble in CD2Cl2, but show simple
1H NMR spectra with a single δ(Me) resonance and three rather
broad δ(CH2) resonances with ill-defined couplings, indicating a
symmetrical coordination of the ligand with all four Me groups
on the same side of the N4 plane.28 Together with a singlet 19F
NMR resonance, this suggests an eight-coordinate environment,
possibly a square antiprism. Low temperature NMR studies were
not possible due to the very poor solubility. The solutions are
readily hydrolysed to form [MF6]2− salts and these are a major
impurity in the products if the Me4-cyclam is not thoroughly
dried before use.
Attempted
synthesis
of
soft
donor
complexes.
Me2PCH2CH2PMe2 did not displace dmso from [ZrF4(dmso)2]
in CH2Cl2, which is not particularly surprising given the difficul-
ties experienced with the harder N-donor ligands. Stirring a
Fig. 9 Crystal
structure
of
the
anion
in
[IDiPPH]3[Zr3F15]·4thf·nCH2Cl2 showing the atom numbering scheme.
Ellipsoids are drawn at the 50% probability level. Selected bond lengths
(Å) and angles (°): Zr–Fterminal = 1.942(4)–1.988(4), Zr–Fbridging = 2.124(4)–
2.139(4), Zr–F–Zr 155.6(2)–159.6(2).
CH2Cl2 solution of [ZrI4(diphosphine)2] (diphosphine
=
Me2PCH2CH2PMe2 or o-C6H4(PMe2)2)29,30 with 4.5 mol.
equivalents of powdered Me3SnF caused the initially orange-
yellow solutions to become colourless after ∼12 h and after 48 h
fine white precipitates had formed. These were identified as ZrF4
(and some residual Me3SnF) by IR spectroscopy. The filtrates
examined by 1H, 19F{1H} and 31P{1H} NMR spectroscopy
showed Me3SnI,31 free diphosphine, and traces of phosphine
oxides, presumably from some air oxidation. Thus, I/F exchange
is accompanied by dissociation of the phosphine from the
“ZrF4” which then polymerises and precipitates. Similar loss of
phosphine and precipitation of TiF4 was observed in dilute
CH2Cl2 solutions of [TiF4(diphosphine)],4a and with the
Conclusions
A series of O- and N-donor complexes of the tetrafluorides with
a range of coordination numbers (6, 7 or 8) and geometries have
been characterised both structurally and spectroscopically. Most
complexes show systematic changes on replacing Zr by Hf, for
example in the 19F NMR chemical shifts (Table 1), which are
good indicators of the speciation, although some unexpected
differences remain such as the dimer vs. monomer structures of the
dmf adducts [(dmf)2F3Zr(μ-F)2ZrF3(dmf)2] and [HfF4(dmf)2].
The large metal centres clearly accommodate eight-coordination
without any steric problems, and hence the failure of the OPR3
and OAsPh3 ligands to achieve a coordination number higher
than six must be electronic in origin. In contrast, TiF4 adducts
are six-coordinate, apart from some seven coordinate cations
with crown ethers.34,36 The chemistry of the MF4 acceptor units
are dominated by two factors, the ability to form very strong F-
bridges, which means that reformation of the polymeric parent
tetrafluoride can compete with coordination to a neutral ligand in
many cases, and also their extreme oxophilicity. The difficulty of
displacing O-donor dmso or dmf from the synthons, and the (at
least partial) displacement of usually strong chelating ligands
such as 2,2′-bipyridyl or 1,10-phenanthroline by O-donor sol-
vents, clearly demonstrates the latter point. The failure to obtain
complexes with the soft, but usually very strong, σ-donor alkyl
diphosphines, could simply be a mismatch of orbital size and
energy, but given that the Cl/F exchange route resulted in pre-
cipitation of ZrF4 and liberation of the diphosphine, it seems to
be a clear example of the zirconium centre preferring fluorine
bridges to the soft donor. This is a more extreme case of the
chemistry observed previously with TiF4.4a The failure to form
adducts with SMe2 is less surprising and ascribed to the same
cause, although it should be noted that NbF5 and TaF5 both form
[MF5(SMe2)] and [MF4(SMe2)4][MF6] adducts by direct reaction
with the [MF5]4.3a,5 Similarly, thio- and seleno-ethers and dipho-
sphines and diarsines form stable (although very readily hydro-
lysed) complexes with the heavier ZrX4 and HfX4 salts.29,30,32
We note that [MX4(L–L)2] (M = Zr of Hf; X = Cl or Br; L–L =
even harder
zirconium(IV)
centre, the diphosphine
coordination cannot compete with the formation of fluorine
bridges and precipitation of ZrF4. Attempts to react [ZrF4(dmf)2]
or ZrF4·3H2O with neat SMe2 failed, no reaction being apparent
after 48 h. This contrasts with the Group V pentafluorides, MF5
(M = Nb or Ta), and with ZrX4 (X = Cl or Br) which react easily
with SMe2 to form [MF5(SMe2)]3a,5 and [ZrX4(SMe2)2]32
respectively.
The reaction of the NHC, 1,3-(2,6-di-isopropylphenyl)imid-
azol-2-ylidene (IDiPP) with [ZrF4(dmf)2] in CH2Cl2 produced
[IDiPPH]Cl, indicating protonation of the carbene rather than
adduct formation. From anhydrous thf solutions isomorphous
brown crystals were obtained which proved to be
[IDiPPH]3[M3F15]·4thf (M = Zr or Hf) from crystal structure
determinations. The hafnium system formed poor quality crys-
tals, but the zirconium data set was satisfactorily refined. Dis-
crete trinuclear anions were clear in both structures (Fig. 9), and
have not been identified previously. There are literature examples
of LnM3F15 (Ln = lanthanide),12 but these contain infinite poly-
mers rather than discrete anions. The latter, which are composed
of octahedral MF6 units sharing two cis-vertices, are reminiscent
of units present in TiF4 or [Ti4F18]2− 4a,33,34
.
In solution the 19F{1H} NMR spectra (at 295 and 243 K)
show only singlets at δ = −11.5 (Zr) or −44.5 (Hf), indicating
breakdown to [MF6]2− anions or possibly dynamic exchange.
Cl/F exchange using [ZrCl4(IDiPP)2]35 and Me3SnF gave crys-
tals of [IDiPPH][SnMe3Cl2] (ESI†), showing halide exchange
had occurred, but there was no spectroscopic evidence for for-
mation of a carbene adduct.
12552 | Dalton Trans., 2012, 41, 12548–12557
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o-C6H4(PMe2)2 or o-C6H4(AsMe2)2) can be made by reaction of
the diphosphine or diarsine ligand with MX4 in thf solution,29
i.e. in the presence of a large excess of the O-donor solvent,
which contrasts with their inability to displace O-donor ligands
from ZrF4 adducts in a non-coordinating solvent in the present
work. The case of the NHC’s is slightly more complicated in
that whilst metal tetrafluoride adducts were not obtained, proto-
nation of the carbene to the imidazolium salt was observed.
Extrapolation from the properties of the known TiF4/NHC
adducts4b would suggest that Zr(Hf)F4 adducts may well be less
stable, but does not allow us to conclude that they do not exist.
The isolation of examples of the new trimeric anions [M3F15]3−
(M = Zr or Hf) can be added to our previous structural
authentication of protonated thioethers (in NbF5 chemistry)3b or
diprotonated o-phenylene-diphosphines (from TiF4 systems)4a as
unexpected spin-offs arising from the very different reaction
conditions in high valent metal fluoride coordination chemistry.
The isolation of the geometric isomers of [(dmso)2F3Zr-
(μ-F)2ZrF3(dmso)2], albeit from different solvents, was unex-
pected in that the complex appears to be exchanging ligands in
solution and the isomers identified structurally both contain pen-
tagonal bipyramidal geometry, but differ in the sequence of
donors in the pentagonal plane, so one would expect their inter-
conversion to be facile.37
when the solid dissolved. The colourless solution was cooled
and allowed to stand at ambient temperatures for 2 d. A mixture
of white powder and colourless crystals separated, which were
filtered off, rinsed with diethyl ether (5 mL) and dried in vacuo.
Yield: 0.85 g, 87%. Anal. Calc. for C4H12F4O2S2Zr (323.5): C,
14.8; H, 3.7. Found: C, 14.3; H, 3.9%. 1H NMR (CD2Cl2,
295 K): δ = 2.56 (s); (d7-dmf, 295 K): 2.68 (s). 19F{1H} NMR
(CD2Cl2, 295 K): 43.5 (s); (d6-dmso, 295 K): 43.5 (s); (d7-dmf,
295 K): 43.1 (s); (220 K): 41.7 (s). IR (Nujol/cm−1): ν =
1012vbr (SvO), 537s, 489s, 449s (Zr–F), 353 (Zr–F–Zr).
[HfF4(dmso)2]
Was made similarly to the zirconium complex, although crystalli-
sation took ∼1 week, to produce colourless crystals. Yield: 90%.
Anal. Calc. for C4H12F4HfO2S2 (410.7): C, 11.7; H, 2.9. Found:
C, 11.5; H, 2.6%. 1H NMR (CD2Cl2, 295 K): δ = 2.55 (s);
(d7-dmf, 295 K): 2.82 (s). 19F{1H} NMR (CD2Cl2, 295 K):
−1.5 (s); (d6-dmso, 295 K): −1.5 (s); (d7-dmf, 295 K): −1.2 (s);
(220 K): −1.0 (s). IR (Nujol/cm−1): ν = 1003vbr (SvO), 508s,
492s, 453s (Hf–F), 347vbr (Hf–F–Hf).
[ZrF4(dmf)2]
Was made similarly to [ZrF4(dmso)2] as colourless crystals.
Yield: 76%. Anal. Calc. for C6H14F4N2O2Zr (313.4): C, 23.0;
H, 4.5; N, 8.9. Found: C, 22.8; H, 5.2; N, 8.8%. 1H NMR
(CD2Cl2, 295 K): δ = 2.89 (s) [3H], 2.91 (s) [3H], 8.00 (s) [H].
19F{1H} NMR (CD2Cl2, 295 K): 43.5 (s); (d7-dmf, 295 K): 43.9
(s); (220 K): 44.2 (s). IR (Nujol/cm−1): ν = 1651s,br (CvO),
554s, 524s (Zr–F), 375m (Zr–F–Zr).
Experimental
Anhydrous and hydrated ZrF4 and HfF4 was obtained from
Apollo or Aldrich and used as received. Solvents were dried by
distillation from CaH2 (CH2Cl2, MeCN, dmf), Na-benzo-
phenone-ketyl (thf, Et2O) or over molecular sieves (dmso).
Ligands (Aldrich or Strem) were dried by heating in vacuo (0.1
torr) (2,2′-bipyridyl, 1,10-phenanthroline, OPPh3, OAsPh3,
OPMe3, pyNO, Me4-cyclam) or distilled from BaO (py) and
stored in a glove box. The ligand o-C6H4(PMe2)2 was made by
the literature method,38 Me2P(CH2)2PMe2 was obtained from
Strem and used as received. 1,3-(2,6-Di-isopropylphenyl)-imid-
azolium chloride was made as described,39 deprotonated using
potassium hexamethyldisilazide in toluene, and the free NHC
ligand (IDiPP) was stored in a glove box.
[HfF4(dmf)2]
Was made similarly to the Zr complex, as colourless crystals
which separated from the synthesis solution over ∼3 d. Yield:
74%. Anal. Calc. for C6H14F4HfN2O2 (400.7): C, 18.0; H, 3.5;
1
N, 7.0. Found: C, 17.8; H, 2.9; N, 6.5%. H NMR (CD2Cl2,
295 K): δ = 2.82 (s) [3H], 2.92 (s) [3H], 7.99 (s) [H]. 19F{1H}
NMR (CD2Cl2, 295 K): −1.7 (br s); (d7-dmf, 295 K): −1.26 (s);
(220 K): −1.44 (s). IR (Nujol/cm−1): ν = 1671s, 1656s (CvO),
584s, 531br, 520sh (Hf–F).
Infrared spectra were recorded as Nujol mulls between CsI
plates using a Perkin-Elmer Spectrum 100 spectrometer over the
range 4000–200 cm−1 1H NMR spectra were recorded from
.
d7-dmf, d6-dmso or CD2Cl2 solutions using a Bruker DPX400
spectrometer and are referenced to the residual protiosolvent
resonance. 19F{1H} and 31P{1H} NMR spectra were recorded
using a Bruker DPX400 spectrometer and are referenced to
external CFCl3 and external 85% H3PO4 respectively. Microana-
lyses on new complexes were undertaken by Medac Ltd. All
preparations were carried out under a dry dinitrogen atmosphere
using Schlenk and glove-box techniques. Generally pure and dry
samples of the O- and N-donor complexes can be handled in air,
although most take up water on prolonged exposure.
[ZrF4(OPPh3)2]
[ZrF4(dmso)2] (0.32 g, 21.0 mmol) was dissolved in hot dmso
(5 mL), the solution cooled, and a solution of OPPh3 (0.56 g,
2.0 mmol) in CH2Cl2 (25 mL) added. The colourless solution
was stirred for 5 h, and then concentrated to ∼10 mL in vacuo.
On standing at room temperature for 3 d a mixture of white
powder and some colourless crystals separated. These were
filtered off and dried in vacuo. Yield: 0.75 g, 76%. Anal. Calc.
for C36H30F4O2P2Zr·3CH2Cl2 (978.6): C, 47.9; H, 3.7. Found:
1
C, 48.1; H, 3.3%. H NMR (CD2Cl2, 295 K): δ = 7.42 (s) [2H],
[ZrF4(dmso)2]
7.63 (m) [3H]. 19F{1H} NMR (CD2Cl2, 295 K): 49.0 (vbr) [2F],
26.0 (vbr) [2F]; (253K): 48.1 (s) [2F], 24.2 (s) [2F], 23.8 (sh).
31P{1H} NMR (CD2Cl2, 295 K): 40.6 (s); (243 K): 40.9, 40.7
Finely powdered ZrF4 hydrate (0.50 g, ∼3 mmol) was suspended
in dmso (10 mL) and the mixture stirred and heated to 80 °C
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(sh); (180 K): 41.2 (s). IR (Nujol/cm−1): ν = 1076 vs (PvO),
514 vs (Zr–F).
[HfF4(OPMe3)2]
Was made similarly from [HfF4(dmf)2]. Yield: 48%. Anal. Calc.
for C6H18F4HfO2P2 (438.6): C, 16.4; H, 4.1. Found: C, 16.9; H,
The following complexes were made by the same general
method as used for [ZrF4(OPPh3)2].
1
2
4.1%. H NMR (CD2Cl2, 295 K): δ = 1.73 (d) JPH = 13.5 Hz.
19F{1H} NMR (CD2Cl2, 295 K): −12 (br); (243 K): −4.1 (s)
[2F], −20.2 (s) [2F], −20.7 (s). 31P{1H} NMR (CD2Cl2, 295 K):
63.6 (br); (243 K): 64.8 (s). IR (Nujol/cm−1): ν = 1076vbr
(PvO), 559m, 515sh, 486 vs (Hf–F).
[ZrF4(OAsPh3)2]
White powder. Yield: 86%. Anal. Calc. for C36H30As2-
F4O2Zr·2CH2Cl2 (981.6): C, 46.5; H, 3.8. Found: C, 46.5; H,
1
4.3%. H NMR (CD2Cl2, 295 K): δ = 7.41 (s) [2H], 7.63 (m)
[ZrF4(pyNO)2]
[H], 7.74 (m) [2H]. 19F{1H} NMR (CD2Cl2, 295 K): ∼18 (vbr);
(223 K): 29.5 (s) [2F], 17.0 (s) [2F], 16.3 (s). IR (Nujol/cm−1):
ν = 875s (AsvO), 515 vs (Zr–F). Colourless crystals used for
the X-ray data collection were grown from a solution of the
complex in CH2Cl2 in a freezer (−18 °C) for several days.
Finely powdered [ZrF4(dmso)2] (0.32 g, 1.0 mmol) was sus-
pended in rapidly stirred CH2Cl2 (40 mL) and a solution of
pyNO (0.19 g, 2.0 mmol) in CH2Cl2 (10 mL) added. After some
hours, a colourless solution was formed, which was concentrated
to ∼15 mL and stirred for a further 48 h. A fine white powder
precipitated. This was filtered off and dried in vacuo. Yield:
0.25 g, 70%. Anal. Calc. for C10H10F4N2O2Zr (357.4): C, 33.6;
H, 2.6, N 7.8. Found: C, 33.4; H, 3.2; N, 7.9%. 1H NMR
(CD2Cl2, 295 K): δ = 7.36 (s) [3H], 8.17 (m) [2H]. 19F{1H}
NMR (CD2Cl2, 295 K): 37.7 (br); (253 K): insoluble. IR (Nujol/
cm−1): ν = 1232 vs, 1225s (NvO), 518s, 505s (Zr–F).
[HfF4(OAsPh3)2]
White powder. Yield: 83%. Anal. Calc. for C36H30As2F4HfO2·1/
1
2CH2Cl2 (941.4): C, 46.6; H, 3.3. Found: C, 47.2; H, 3.9%. H
NMR (CD2Cl2, 295 K): δ = 7.50 (m) [2H], 7.64 (m) [H], 7.73
(m) [2H]. 19F{1H} NMR (CD2Cl2, 295 K): −9.1 (br), −20.6
(br); (243 K): −10.7 (s) [2F], −20.7 (s) [2F], −21.9 (s). IR
(Nujol/cm−1): ν = 875s (AsvO), 490 vs (Hf–F).
[HfF4(pyNO)2]
Finely powdered [HfF4(dmf)2] (0.42 g, 1.0 mmol) was sus-
pended in rapidly stirred CH2Cl2 (40 mL) and a solution of
pyNO (0.19 g, 2.0 mmol) in CH2Cl2 (10 mL) added. After some
hours a colourless solution was formed, which was concentrated
to ∼15 mL and stirred for a further 48 h. A fine white powder
precipitated over this time. This was filtered off and dried
in vacuo. Yield: 0.29 g, 66%. Anal. Calc. for C10H10F4-
HfN2O2·2CH2Cl2 (614.6): C, 23.5; H, 2.3, N, 4.6. Found: C,
[HfF4(OPPh3)2]
White powder prepared similarly using [HfF4(dmf)2] in dmf/
CH2Cl2 in place of [HfF4(dmso)2], since use of the latter resulted
in isolation of a mixture containing substantial amounts of
[HfF4(dmso)2]. Yield: 55%. Anal. Calc. for C36H30F4HfO2P2
(811.1): C, 53.3; H, 3.7. Found: C, 52.8; H, 3.4%. 1H NMR
(CD2Cl2, 295 K): δ = 7.42 (m) [2H], 7.61 (m) [3H]. 19F{1H}
NMR (CD2Cl2, 295 K): 4.1 (s) [2F], −16.6 (s) [2F]; (243 K):
2.35 (s) [2F], −17.6 (s) [2F], −18.3 (sh). 31P{1H} NMR
(CD2Cl2, 295 K): 41.9 (s); (273 K): 42.2 (s); (243 K): 42.4, 42.3
(sh). IR (Nujol/cm−1): ν = 1090s (PvO), 493 vs br (Hf–F).
1
23.2; H, 2.0; N, 5.4%. H NMR (CD2Cl2, 295 K): δ = 7.27 (m)
(s) [3H], 8.16 (m) [2H]. 19F{1H} NMR (CD2Cl2, 295 K): −6.5
(s); (253 K): insoluble. IR (Nujol/cm−1): ν = 1231s, 1221s
(NvO), 504m, 490s, 480s (Hf–F).
[ZrF4(1,10-phen)2]
[ZrF4(OPMe3)2]
Finely powdered [ZrF4(dmso)2] (0.32 g, 1.0 mmol) was dis-
solved in warm dmso (5 mL) and vigorously stirred whilst
adding a solution of 1,10-phen (0.32 g, 2.05 mmol) in dry
CH2Cl2 (80 mL). After ca. 1 h a clear solution was formed
which was stirred at room temperature for 48 h, during which
time a large amount of fine white precipitate formed. This was
filtered off, rinsed with CH2Cl2 (5 mL) and dried in vacuo.
Yield: 0.42 g, 80%. Anal. Calc. for C24H16F4N4Zr (527.6): C,
[ZrF4(dmf)2] (0.31 g, 1.0 mmol) was dissolved in warm dmf
(5 mL), the solution cooled to ambient, and a solution of OPMe3
(0.28 g, 3.0 mmol) in CH2Cl2 (25 mL) added. The colourless
solution was stirred for 5 h, and then all the solvents removed by
warming in vacuo, to leave a colourless oil. The oil was redis-
solved in CH2Cl2 (10 mL), filtered to remove a small amount of
insoluble material, and diethyl ether (5 mL) added. On standing
for ∼24 h, a mixture of colourless crystals and a white powder
separated. These were filtered off and dried in vacuo. Yield:
0.29 g, 65%. Anal. Calc. for C6H18F4O2P2·CH2Cl2 (436.3): C,
19.3; H, 4.6. Found: C, 19.5; H, 4.6%. 1H NMR (CD2Cl2,
1
54.6; H, 3.1; N, 10.6. Found: C, 54.5; H, 3.1; N, 10.4%. H
NMR (CD2Cl2, 295 K): very poorly soluble, 7.87 (m) [2H], 8.10
(s) [2H], 8.58 (m) [2H], 9.79 (m) [2H]. 19F{1H} NMR (CD2Cl2,
295 K): 21.3 (s). IR (Nujol/cm−1): ν = 505s, 478s, Zr–F.
295 K): δ = 1.74 (d) JPH = 13.5 Hz. 19F{1H} NMR (CD2Cl2,
2
295 K): 31.1 (br); (243 K): 41.2 (s) [2F], 19.1 (s) [2F], 18.9
(sh). 31P{1H} NMR (CD2Cl2, 295 K): 62 (s); (243 K): 61.9 (s).
IR (Nujol/cm−1): ν = 1092br (PvO), 527br, 480 vs br, 469sh
(Zr–F).
[HfF4(1,10-phen)2]
Was made similarly to the zirconium complex as a fine white
powder. Yield: 83%. Anal. Calc. for C24H16F4HfN4·1/2CH2Cl2
12554 | Dalton Trans., 2012, 41, 12548–12557
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Attempted preparation of [ZrF4(o-C6H4(PMe2)2}n] (n = 1 or 2)
(657.4): C, 44.8; H, 2.6; N, 8.5. Found: C, 44.7; H, 3.0; N,
1
8.2%. H NMR (CD2Cl2, 295 K): very poorly soluble, 7.89 (m)
[ZrI4{o-C6H4(PMe2)2}2]29 (0.2 g, 0.2 mmol) was added to dry
CH2Cl2 (80 mL) and finely powdered dry Me3SnF (0.165 g,
0.9 mmol) added. The mixture was vigorously stirred when the
orange-yellow colour discharged slowly and a fine white precipi-
tate formed. After stirring for 48 h, the precipitate was filtered
off, rinsed with CH2Cl2 (2 × 25 mL) and dried in vacuo. The
solid was identified as ZrF4 with some residual Me3SnF by its
[2H], 8.07 (s) [2H], 8.55 (m) [2H], 9.79 (m) [2H]. 19F{1H}
NMR (CD2Cl2, 295 K): −17.8 (s). IR (Nujol/cm−1): ν = 502s,
vbr, 480sh (Hf–F).
[ZrF4(2,2′-bipy)2]
1
IR spectrum. The filtrate and washings were examined by H
[ZrF4(dmf)2] (0.32 g, 1.0 mmol) was dissolved in warm dmf
(5 mL) and a solution of 2,2′-bipy (0.40 g, 2.5 mmol) in dry
CH2Cl2 (80 mL) added. Initially a clear colourless solution
formed, which over the course of ca. 1 h stirring at room temp-
erature precipitated a white powder. The mixture was allowed to
stand for 48 h and then the precipitate was filtered off, rinsed
with CH2Cl2 (5 mL) and dried in vacuo. Yield: 0.44 g, 68%.
Anal. Calc. for C20H16F4N4Zr·2CH2Cl2 (649.4): C, 40.1; H, 3.1;
and 31P{1H} NMR spectroscopy which showed o-C6H4(PMe2)2
δ(P) = −55.0 and Me3SnI δ(H) = +0.9, 2J(1H–119Sn) =
56 Hz,31,38 and did not exhibit any 19F resonances. The reaction
of [ZrI4(Me2PCH2CH2PMe2)2]30 with Me3SnF similarly gave
ZrF4 and Me3SnI and Me2PCH2CH2PMe2. The iodides were
used in preference to the chlorides due to much higher solubility
in CH2Cl2.
1
N, 8.6. Found: C, 39.1; H, 2.5; N, 9.2%. H NMR (CD2Cl2,
295 K): very poorly soluble, 7.34 (m) [2H], 7.87 (m) [2H], 8.43
(m) [2H], 8.66 (s) [2H]. 19F{1H} NMR (CD2Cl2, 295 K): 24.5
(s). IR (Nujol/cm−1): ν = 525 vs, br (Zr–F).
Attempted preparation of NHC complexes
Method 1. A CH2Cl2 solution of IDiPP (0.26 g, 0.67 mmol) was
added to a solution of [ZrF4(dmf)2] (0.104 g, 0.33 mmol). The
solution was stirred for 16 h, then concentrated to ca. 5 mL and
crystallised through the slow diffusion of Et2O into the CH2Cl2
solution. Large, pale brown crystals grew, which were identified
by their crystal structure as the imidazolium salt [IDiPPH]-
[HfF4(2,2′-bipy)2]
Was made similarly using either [HfF4(dmf)2] in dmf/CH2Cl2 or
[HfF4(dmso)2] in dmso/CH2Cl2, the product being obtained as a
very pale pink powder. Yield: 78%. Anal. Calc. for
C20H16F4HfN4 (566.9): C, 42.4; H, 2.9; N, 9.9. Found: C, 42.2;
H, 3.1; N, 9.9%. 1H NMR (CD2Cl2, 295 K): very poorly
soluble, 7.23 (m) [2H], 7.80 (m) [2H], 8.30 (m) [2H], 8.50 (s)
[2H]. 19F{1H} NMR (CD2Cl2, 295 K): −11.2 (s). IR (Nujol/
cm−1): ν = 505vbr, 490sh (Hf–F).
1
Cl·2CH2Cl2. H and 13C{1H} NMR spectroscopy supported this
result and no fluorine signal was observed in the 19F{1H} NMR
spectrum. Repeating the reaction using [HfF4(dmf)2] resulted in
the same product crystallising.
If thf is used as the solvent instead of CH2Cl2, then the sus-
pension of [ZrF4(dmf)2] mostly dissolves after addition of a thf
solution of IDiPP and stirring for one week. After this time the
reaction mixture was filtered, the supernatant concentrated to
ca. 5 mL and the product crystallised through the slow diffusion
of hexane into the thf solution. Pale brown crystals of
[IDiPPH]3[Zr3F15]·4thf·xCH2Cl2 formed, with disorder in some
of the thf moieties. 19F{1H} NMR (CD2Cl2, 295 K): −11.5.
Repeating the reaction using [HfF4(dmf)2] in thf afforded the
hafnium analogue with an [Hf3F15]3− anion. 19F{1H} NMR
(CD2Cl2, 295 K): −44.5. The crystals are isomorphous with the
zirconium compound, but the dataset was of poor quality and is
not presented.
Method 2. The compound [ZrCl4(IDiPP)2] made by the
method of Niehaus et al.35 (0.15 g, 0.27 mmol) was dissolved in
thf (10 mL), Me3SnF (0.23 g, 1.23 mmol) added, and the reac-
tion stirred for one week. After this time, the reaction mixture
was filtered and the supernatant concentrated to ca. 5 mL, then
crystallised through the slow diffusion of hexane into the thf solu-
tion. Crystals produced were identified by a structure determination
and 1H NMR spectroscopy as [IDiPPH][SnMe3Cl2] (ESI†).
[ZrF4(Me4-cyclam)]
[ZrF4(dmf)2] (0.32 g, 1.0 mmol) was dissolved in warm dmf
(5 mL) and a solution of Me4-cyclam (0.25 g, 1.0 mmol) in dry
CH2Cl2 (30 mL) added. Initially a clear colourless solution
formed, which over the course of ca. 1 h stirring at room temp-
erature deposited a white precipitate. The mixture was stirred for
48 h, and then the precipitate was filtered off, rinsed with
CH2Cl2 (5 mL) and dried in vacuo. Yield: 0.22 g, 52%. Anal.
Calc. for C14H32F4N4Zr·CH2Cl2 (508.6): C, 35.4; H, 6.8; N,
11.0. Found: C, 35.7; H, 7.2; N, 11.0%. 1H NMR (CD2Cl2,
295 K): 1.88 (br,s) [4H], 2.45 (s) [12H], 2.78 (m) [8H], 2.92 (m)
[8H]. 19F{1H} (CD2Cl2, 295 K): 14.2 (s). IR (Nujol/cm−1): ν =
540s, 502s, 477m (Zr–F).
[HfF4(Me4-cyclam)]
Was made similarly from [HfF4(dmf)2] as a white powder in
68% yield. Anal. Calc. for C14H32F4HfN4·CH2Cl2 (595.9): C,
30.3; H, 5.8; N, 9.4. Found: C, 30.8; H, 6.6; N, 10.0%. 1H NMR
(CD2Cl2, 295 K): 1.90 (m) [4H], 2.42 (s) [12H], 2.72 (m) [8H],
2.82 (m) [8H]. 19F{1H} NMR (CD2Cl2, 295 K): −12.0 (s),
very poorly soluble. IR (Nujol/cm−1): ν = 552s, 493s, 460m
(Hf–F).
X-Ray crystallography
Crystals were obtained as described above. Details of the crystallo-
graphic data collection and refinement are in Table 2. Diffract-
ometer: Rigaku AFC12 goniometer equipped with an enhanced
sensitivity (HG) Saturn724 + detector mounted at the window of
an FR-E + SuperBright molybdenum rotating anode generator
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 12548–12557 | 12555

View Article Online
Table 2 Crystal data and structure refinement detailsa
Compound
[Zr2F8(Me2SO)4] [Hf2F8(Me2SO)4] [HfF4(Me2NCHO)2] [ZrF4(OPPh3)2]·2CH2Cl2 [ZrF4(OAsPh3)2]·2CH2Cl2
Formula
M
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/°
C8H24F8O4S4Zr2 C8H24F8Hf2O4S4 C6H14F4HfN2O2
C38H34Cl4F4O2P2Zr
893.61
Monoclinic
P21/n (no. 14)
8.900(3)
14.700(5)
14.547(5)
90
C38H34As2Cl4F4O2Zr
981.51
646.95
Tetragonal
P42/n (no. 86)
16.473(5)
16.473(5)
7.699(3)
90
821.49
Monoclinic
P21/n (no. 14)
8.675(4)
11.750(4)
10.667(4)
90
400.68
Monoclinic
C2/c (no. 15)
13.591(3)
7.2522(12)
11.6584(19)
90
Monoclinic
P21/n (no. 14)
8.898(3)
14.688(4)
14.688(4)
90
β/°
90
90
108.269(7)
90
1032.4(7)
2
10.534
768
100.919(7)
90
1128.3(4)
4
9.284
752
95.77(2)
90
1893.5(11)
2
0.711
711
94.348(7)
90
1933.8(10)
2
2.312
976
γ/°
U/Å3
2089.2(11)
4
1.478
Z
μ(Mo-Kα)/mm−1
F(000)
1280
Total no. reflections
Unique reflections
Rint
5120
2388
0.0161
0.892, 1.0
122, 0
1.045
5749
2359
0.1632
0.690, 1.0
118, 0
1.027
4.035
0.0489
0.0518
0.1159
0.1172
3801
1283
0.0601
0.613, 1.0
71, 0
1.061
2.539
0.0351
0.0367
0.0824
0.0838
9830
4270
0.1296
0.517, 1.0
230, 0
0.548
0.650
0.0432
0.1201
0.0548
0.0548
9807
4383
0.0391
0.608, 1.0
237, 0
1.107
0.748
0.0570
0.0746
Min., max. transmission
No. of parameters, restraints
Goodness-of-fit on F2
Resid. electron density/e Å−3 0.601
R1 b [Io > 2σ(Io)]
R1 (all data)
0.0224
0.0253
0.0526
0.0538
wR2 b [Io > 2σ(Io)]
wR2 (all data)
0.1172
0.1172
Compound
[ZrF4(OAsPh3)2]·2CH2Cl2
[HfF4(OPMe3)2]
[ZrF4(2,2′-bipy)2]
[C27H37N2 ]3[Zr3F15]·4thf ·0.55(CH2Cl2)
Formula
M
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
α/°
C38H34As2Cl4F4O2Zr
981.51
Orthorhombic
Pbcn (no. 60)
15.175(5)
16.254(6)
16.340(6)
90
90
90
4030(2)
4
2.218
C6H18F4HfO2P2
438.63
Monoclinic
C2/c (no. 15)
438.63
12.701(5)
14.612(5)
90
128.905(11)
90
2734.2(17)
8
C20H16F4N4Zr
479.59
Monoclinic
Cc (no 9)
12.991(4)
13.134(4)
11.714(4)
90
100.919(7)
90
1962.3(10)
4
C97.55H144.10Cl1.10F15 N6O4Zr3
2062.54
Triclinic
ˉ
P1 (no. 2)
15.935(4)
17.240(4)
21.679(7)
81.698(16)
85.337(17)
66.454(13)
5401(3)
2
β/°
γ/°
U/Å3
Z
μ(Mo-Kα)/mm−1
F(000)
7.892
1664
0.610
960
0.382
2154
1952
Total no. reflections
Unique reflections
Rint
15 254
3811
0.0739
0.628, 1.0
231, 0
1.304
1.471
0.0787
0.0887
0.1168
0.1203
4797
4797
0.0
0.70, 1.0
143, 3
1.108
2.211
0.0748
0.0758
0.1992
0.2000
4178
2920
0.0217
0.906, 1.0
262, 144
1.065
46 126
19 032
0.0707
0.9737, 0.9924
1062, 2
1.153
1.480
0.1010
Min., max. transmission
No. of parameters, restraints
Goodness-of-fit on F2
Resid. electron density/e Å−3
R1 b [Io > 2σ(Io)]
R1 (all data)
1.434
0.0384
0.0420
0.0951
0.0983
0.1229
0.2098
0.2231
wR2 b [Io > 2σ(Io)]
wR2 (all data)
2 2
4 1/2
a Common items temperature = 120 K; wavelength (Mo-Kα) = 0.71073 Å. b R1 = Σ||Fo| − |Fc||/Σ|Fo|. wR2 = [Σw(Fo2 − Fc ) /ΣwFo ]
.
with HF or VHF Varimax optics (100 μm or 70 μm focus). Cell
determination, data collection, data reduction, cell refinement
and absorption correction: CrystalClear-SM Expert 2.0 r7
(Rigaku, 2011). Structure solution and refinement were
routine40,41 except as noted below.
from one twin component. Further refinement was completed by
replacing the HKLF4 data with HKLF5 data combining the data
from both components.
[HfF4(OPMe3)2]
Acknowledgements
The data was indexed and integrated using the Twinsolve tool.42
The initial structure was solved by using HKLF 4 format data
We thank EPSRC for support and Dr M. Webster for assistance
with the crystallographic work.
12556 | Dalton Trans., 2012, 41, 12548–12557
This journal is © The Royal Society of Chemistry 2012

View Article Online
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Dalton Trans., 2012, 41, 12548–12557 | 12557