Dimethyltin(IV) bis(3,5-diphenylpyrazolate) as a synthetic reagent in the preparation of rare-earth pyrazolate complexes

Article abstract of DOI:10.1002/ejic.200800642

Reaction of SnMe₂Cl₂ with [Li(Ph₂pz)] (Ph₂pz = 3,5-diphenylpyrazolate) in diethyl ether in a 1:2 ratio afforded the new transmetallation reagent [SnMe₂(Ph ₂pz)₂]. Treatment of [S

Full text of DOI:10.1002/ejic.200800642

FULL PAPER
DOI: 10.1002/ejic.200800642
Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as a Synthetic Reagent in the
Preparation of Rare-Earth Pyrazolate Complexes
Samar Beaini,[a] Glen B. Deacon,*[a] Ewan E. Delbridge,[a] Peter C. Junk,*[a]
Brian W. Skelton,[b] and Allan H. White[b]
Keywords: Redox transmetallation / Lanthanoids / Dimethyltin reagents / Organotin(IV) / Pyrazolate / Rare-earth elements
Reaction of SnMe2Cl2 with [Li(Ph2pz)] (Ph2pz = 3,5-diphenyl-
pyrazolate) in diethyl ether in a 1:2 ratio afforded the new
transmetallation reagent [SnMe2(Ph2pz)2]. Treatment of
were performed on the reaction mixture and/or residue to
identify the tin-containing products and suggest formation of
SnMe4, Sn2Me6, tin metal and two other SnMe3 species,
[SnMe2(Ph2pz)2] with Ln metals in either 1,2-dimethoxye- which plausibly result from decomposition of unstable
thane (dme) or tetrahydrofuran (thf) provided a new route to
the divalent [Ln(Ph2pz)2(dme)2] (Ln = Sm, Eu, Yb) and the
trivalent [La(Ph2pz)3(dme)2] and [Yb(Ph2pz)3(thf)2] com-
plexes in comparable yields to those from alternative meth-
ods. These reactions enabled isolation of the highly reactive
[Sm(Ph2pz)2(dme)2] complex in good yield, in addition to the
new cis isomer of [Eu(Ph2pz)2(dme)2], thereby establishing a
rare case of geometric isomerism in lanthanoid chemistry. 1H
and 119Sn NMR spectral studies and EDAX measurements
“SnMe2”.
Treatment
of
[Yb(Ph2pz)2(dme)2]
with
[SnMe2(Ph2pz)2] or [Tl(Ph2pz)] resulted in the isolation of
[Yb(Ph2pz)3(thf)2]·2C6D6 and [Yb(Ph2pz)3(dme)]·0.5dme com-
plexes, the structures of which have eight-coordinate Yb
atoms and contrast nine-coordination observed for previous
[Ln(Ph2pz)3(thf or dme)n] complexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
As an alternative approach, trimethyltin(IV) compounds
have recently been shown to be effective reagents in redox
transmetallation reactions with Ln metals in the synthesis
of both trivalent [Equation (4)] and divalent [Equation (5)]
metal–organic lanthanoid complexes,[7] by utilisation of the
SnIV ǞSnIII reduction.
Introduction
Redox transmetallation reactions provide simple halide-free
reaction routes to both divalent and trivalent rare-earth
complexes.[1] The use of organomercurial[1–4] and thal-
lium[4–6] reagents is now well established for the synthesis
of various metal–organic lanthanoid derivatives [Equa-
tions (1)–(3)].
Earlier, Lappert had provided a single example of the use
of the SnII ǞSn0 reduction in redox transmetallation.[8] The
new use of organotin reagents in redox transmetallation
with lanthanoid elements contrasts their common use as
non-redox metathesis reagents.[9]
[a] School of Chemistry, Monash University,
P. O. Box 23, Clayton, Victoria 3800, Australia
Fax: 61-3-99054597
In a recent study by Westerhausen,[10] treatment of the
dimethyltin(IV) reagent [SnMe2(N{SiMe3})2]2 with Ca
metal in a redox transmetallation reaction resulted in the
preparation of [Ca(N{SiMe3}2)2(thf)2] [Equation (6)].
E-mail: glen.deacon@sci.monash.edu.au
peter.junk@sci.monash.edu.au
[b] Chemistry M313, School of Biomedical, Biomolecular and
Chemical Sciences, The University of Western Australia,
Crawley, Western Australia, 6009, Australia
4586
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Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as Reagent for Rare-Earth Complexes
This raises the possibility of use of dimethyltin(IV) com- non-bonding and their proximity is solely due to the N–N
pounds in the redox transmetallation synthesis of lan- connectivity of the pyrazolate ligand. This is supported by
thanoid
complexes,
though
Ln
elements
[E0 the N(2)–N(1)–Sn(1) [114.28(18)°] and N(4)–N(3)–Sn(1)
(Ln3+ +3eǞLn) = –2.38Ǟ–2.30 V] are less electropositive [112.59(17)°] bond angles, both of which are close to the
than Ca [E0 (Ca2+ ǞCa+2e) = –2.87 V].[11] We now report N(2)–N(1)–Sn(1)
bond
angle
in
[SnMe3(Ph2pz)]
the successful preparation of both divalent and trivalent [115.7(4)°],[12] in which Ph2pz is also considered unidentate.
lanthanoid 3,5-diphenylpyrazolate complexes [Ln(Ph2pz)n- Further, both pseudo bite angles N(1)–Sn(1)···N(2)
(solv)m] (n = 2, 3; solv = dme, thf; m = 2, 3) by treating the
newly synthesised [SnMe2(Ph2pz)2] reagent with an excess
of Ln metal. With two Ph2pz groups per tin atom,
[SnMe2(Ph2pz)2] is potentially a more effective pyrazolate
transfer reagent than [SnMe3(Ph2pz)]. The study provides
proof of concept for a new general synthetic method in lan-
thanoid metal–organic chemistry.
Results and Discussion
Synthesis and Structure of the [SnMe2(Ph2pz)2] Reagent
The air- and moisture-sensitive [SnMe2(Ph2pz)2] complex
was obtained by a metathesis reaction between [Li(Ph2pz)]
and SnMe2Cl2 in Et2O [Equation (7)].
The 1H NMR spectrum in C6D6 shows the expected 6:22
ratio for Me/Ph2pz protons. A single resonance at δ =
0.48 ppm is observed for the SnMe2 moiety and shows two
sets of tin satellites corresponding to the two tin isotopes,
with the smaller coupling constant (J = 69 Hz) assigned to
Figure 1. Molecular structure of [SnMe2(Ph2pz)2(thf)]; ellipsoids
117Sn and the larger (J = 72 Hz) to 119Sn. The 119Sn{1H} are shown with 35% probability; hydrogen atoms are removed for
1
clarity. Selected bond lengths [Å] and angles [°] for this structure
are given in Table 1.
NMR spectrum is consistent with the H NMR spectrum,
shows a single tin resonance at –8.1 ppm attributable to
[SnMe2(Ph2pz)2] and suggests a monomeric four-coordinate
SnIV species.[12–16] The IR spectrum is void of an NH
Table 1. Selected bond lengths [Å] and angles [°] for [SnMe2(Ph2pz)2-
(thf)].
stretching absorption attributable to Ph2pzH at 3150–
3300 cm–1.
Bond lengths
Crystals of [SnMe2(Ph2pz)2(thf)] were obtained by
recrystallisation from tetrahydrofuran. An X-ray crystal-
structure determination shows a monomeric complex (Fig-
ure 1). The five-coordinate SnIV atom adopts a distorted
trigonal-bipyramidal geometry, binding η1 to two pyrazol-
ate ligands [N(1) and N(3)], two carbon atoms of the methyl
groups [C(37) and C(38)] and O(1) of the thf solvent mole-
cule. Although the apical N(1)–Sn(1)–O(1) angle is near
180° (Table 1), the equatorial angles (Σ = 352.28°) deviate
considerably from 120°. The Sn(1)–N(1)/N(3) bond lengths
of 2.142(3) and 2.092(2) Å, respectively, are close to the Sn–
Sn(1)–N(1)
Sn(1)–N(2)[a]
Sn(1)–N(3)
Sn(1)–N(4)[a]
Sn(1)–C(37)
Sn(1)–C(38)
Sn(1)–O(1)
2.142(3)
2.986(2)
2.092(2)
2.913(2)
2.104(3)
2.111(3)
2.524(3)
Bond angles
N(3)–Sn(1)–N(1)
N(3)–Sn(1)–C(37)
N(3)–Sn(1)–C(38)
C(37)–Sn(1)–N(1)
C(38)–Sn(1)–N(1)
N(1)–Sn(1)–O(1)
C(37)–Sn(1)–C(38)
N(2)–N(1)–Sn(1)
N(3)–Sn(1)–O(1)
C(37)–Sn(1)–O(1)
C(38)–Sn(1)–O(1)
98.59(10)
109.19(12)
115.28(11)
101.69(14)
97.41(12)
175.18(10)
127.81(13)
114.28(18)
78.90(11)
83.06(14)
80.12(12)
N
bond length of four-coordinate SnMe3(Ph2pz)
[2.102(5) Å][12] and to the Sn–N bond lengths reported for
Sn compounds containing various N-heterocycles (for ex-
ample some pyrazoles,[17] tetrazolates,[13] triazolates[16] and
thiodiazolates[18]). Although Sn(1)···N(2) [2.986(2) Å] and
Sn(1)···N(4) [2.913(2) Å] are within the sum of van der
Waals radii of tin and nitrogen (3.6 Å), they are considered [a] Considered nonbonding.
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G. B. Deacon, P. C. Junk et al.
FULL PAPER
[24.88(7)°] and N(3)–Sn(1)···N(4) [25.90(6)°] are much this approach. In general, syntheses from [SnMe2(Ph2pz)2]
smaller than the bite angles for η2-pyrazolate bonding, and Ln metals [Equation (8) and (9)] gave good yields (60–
which are in the range 31–35°.[4,6,7,12,19–21] The differences 80%), comparable with those from redox transmetallation
between the Sn(1)–N(1)/N(2) distance and the Sn(1)–N(3)/ reactions between Ln metals and [SnMe3(Ph2pz)] or
N(4) distance, 0.84 and 0.82 Å respectively, are higher than [Tl(Ph2pz)] and from other methods (Table 2). Transfer of
the upper limit proposed for unsymmetrical η2 coordina- two Ph2pz groups per heavy metal is an advantage over
tion.[22] The Sn(1)–O(1) bond length of 2.524(3) Å is rather [SnMe3(Ph2pz)] or [Tl(Ph2pz)], as is the faster reaction of
long for a typical Sn–O bond, but is not unusual.[23] The Yb metal with [SnMe2(Ph2pz)2] than with the other two
119Sn NMR spectrum of the thf complex in C6D6 indicates reagents.[4,7]
dissociation of thf in solution.
There were some differences in outcomes between the
present reactions [Equation (8) and (9)] and redox transme-
tallation reactions of [SnMe3(Ph2pz)] or [Tl(Ph2pz)].[6,7]
Most notably, only crystals of cis-[Eu(Ph2pz)2(dme)2] were
obtained from the reaction of Eu metal with [SnMe2-
(Ph2pz)2] (Table 2), whereas reactions with [Tl(Ph2pz)] or
[SnMe3(Ph2pz)] gave only or predominantly (14 out of 15
crystals) transoid-[Eu(Ph2pz)2(dme)2], respectively,[4,6,7]
{termed transoid rather than trans as cen[N(1)/N(2)]–
Eu–cen[N(3)/N(4)] and cen[O(1)/O(2)]–Eu–cen[O(3)/O(4)]
angles (cen[N/NЈ] and cen[O/OЈ] are centres of Ph2pz N–NЈ
bonds and dme O···OЈ vectors, respectively} are ca. 140°
rather than 180°). Thus, this provides a rare example of
geometric isomerism in lanthanoid chemistry (the first ex-
ample of lanthanoid geometric isomers is cis- and trans-
[SmI2(diglyme)2] [diglyme = bis(2-methoxyethyl) ether[25]),
where the lability of lanthanoid complexes militates against
their formation. Reactions of Sm metal with [Tl(Ph2pz)][6]
and [SnMe3(Ph2pz)][7] in thf yield [Sm(Ph2pz)3(thf)3],
whereas the present synthesis in dme yields [Sm(Ph2pz)2-
(dme)2] (Table 2), previously obtained only by metathesis or
protolysis from divalent precursors.[6]
Redox Transmetallation Reactions
Syntheses
[SnMe2(Ph2pz)2] was treated with the rare-earth metals
La, Sm, Eu and Yb in either dme [Equation (8)] or thf
[Equation (9)] at room temperature to yield both divalent
[Ln(Ph2pz)2(dme)2] (Ln = Sm, Eu, Yb) and trivalent
[Ln(Ph2pz)3(solv)2] (Ln = La; solv = dme, Ln = Yb; solv =
thf) complexes [Equation (8) and (9)].
Reactions of Sm and Eu metals required 3 d of stirring
and/or sonication, respectively, and activation by mercury
metal. An analogous reaction of Eu without activation by
mercury gave a low yield. Reactions of Yb metal with
[SnMe2(Ph2pz)2] in thf or dme with Hg activation were
complete in 1 and 2 h, respectively, at room temperature.
Without Hg activation, it was necessary to stir for 24 h fol-
lowed by sonication for 3 and 1 h, respectively, for complete
reaction. As an alternative to the use of mercury, activation
with iodine[2,24] was examined in the reaction between
[SnMe2(Ph2pz)2] and La metal in dme, and complete reac-
tion giving [La(Ph2pz)3(dme)2] was achieved in 4 d at room
temperature without stirring and indicates the viability of
The formation of a YbII complex in dme and YbIII in
thf suggested that [Yb(Ph2pz)2(dme)2] could be oxidised by
[SnMe2(Ph2pz)2] in thf [Equation (10)], and this reaction
was carried out at room temperature.
Table 2. Comparison of yields of [Ln(Ph2pz)n(solv)m] (n, m = 2, 3; solv = thf, dme) obtained from [SnMe2(Ph2pz)2] with yields from
literature methods.[a]
[Ln(Ph2pz)n(solv)m]
Activation
Yield [%] from Yield [%] from Ln +
this work
Yield [%] from other Reported method
SnMe3(Ph2pz) (Hg activated)[7] reported methods
[20]
[La(Ph2pz)3(dme)2]
[Sm(Ph2pz)2(dme)2]
[Eu(Ph2pz)2(dme)2]
I2
Hg
none
Hg
none
Hg
79
77
82[7]
–
77[20]
62[6]
La/Ph2pzH/Hg(C6F5)2
[6]
[K(Ph2pz)]/SmI2(thf)2
Eu/Tl(Ph2pz)[6]
Eu/Tl(Ph2pz)[6]
several[6]
33[b][c]
77[c]
71
88[7][d]
88[7][d]
80[7]
90[6][d]
90[6][d]
66[4]
[Yb(Ph2pz)2(dme)2]
[Yb(Ph2pz)3(thf)2]
73
58
none
51[7]
64[26b]
Yb/Tl(Ph2pz)+oxid. with
Tl(Ph2pz)[26b]
Hg
74
[a] Syntheses in dme, except for the last two reactions, which were performed in thf. [b] Incomplete reaction. [c] cis isomer. [d] transoid
isomer.
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Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as Reagent for Rare-Earth Complexes
In unpublished work by Delbridge,[26a] a similar result structurally characterised thf and dme complexes of
was obtained when [Yb(Ph2pz)2(dme)2] was treated with Ln(Ph2pz)3, which have the composition [Ln(Ph2pz)3-
[SnMe3(Ph2pz)]. Repeating the reported oxidation of (dme)2] (Ln = La, Nd, Eu, Er)[7,20] and [Ln (Ph2pz)3(thf)3]
[Yb(Ph2pz)2(dme)2] with [Tl(Ph2pz)][26b] in thf [Equa- (Ln = La, Nd, Sm),[7,21] respectively, in which the Ln metals
tion (11)], followed by recrystallisation of [Yb(Ph2pz)3- are nine coordinate. Complexes with the composition [Ln
(thf)2] from dme, afforded [Yb(Ph2pz)3(dme)]·0.5dme in (Ph2pz)3(thf)2] have been obtained with the rare-earth met-
good yield. The same product was also obtained after als (Ln = Sc, Gd, Er, Y, Yb, Lu),[26b,27] but no structures
[Yb(Ph2pz)2(dme)2] was treated with stoichiometric have been determined.
amounts of [Hg(C6F5)2] and Ph2pzH in thf followed by
recrystallisation from dme [Equation (12)].
The Sn Coproduct(s)
Characterisation of the Lanthanoid Pyrazolate Complexes
1
The H NMR spectra of the crude products from reac-
Infrared data for all compounds confirm the absence of tions with La, Sm, Eu and Yb metals display multiple reso-
the NH functional group, with no absorption bands be- nances corresponding to methyltin derivatives at around
tween 3150 and 3300 cm–1, consistent with previously re- 0.66, 0.81–0.90 and 1.23–1.83 ppm, though the integrations
ported examples.[4,6,7] For complexes for which NMR spec- are low when compared with those of the lanthanoid com-
tra were feasible, the NH resonance at ca. 10 ppm was ab- plexes. Comparison of the chemical shifts with those re-
sent. For the diamagnetic La3+ and Yb2+ species, the chemi- ported for plausible methyltin products (Table 3) suggests
1
cal shifts are in agreement with those reported.[4,7] The H that species with SnMe3 and SnMe2 groups may be pres-
NMR spectrum of the [Sm(Ph2pz)2(dme)2] complex in ent.[28,29] No resonances attributable to [SnMe2(Ph2pz)2]
C6D6 shows the presence of both divalent and trivalent Sm– were present, hence the reactant is fully consumed. After a
pyrazolate species, although the divalent complex is pre- separate reaction between Yb metal and [SnMe2(Ph2pz)2],
dominant and it is likely that the extremely air-sensitive a sample of the reaction mixture diluted with C6D6 was
[Sm(Ph2pz)2(dme)2] oxidised slightly during preparation examined by 119Sn{1H} NMR spectroscopy. Four distinct
and handling of the solution. The identity of the divalent resonances are observed, namely 1.8, –95.5, –97.4 and
compound is supported by a unit cell determination and a –108 ppm, which supports the presence of several products
1
UV/Vis spectrum, both consistent with reported values,[6] as indicated by the H NMR spectra. The resonances at
1
and a Sm metal analysis. The H NMR spectrum of cis- 1.8 and –108 ppm can be attributed to SnMe4 and Sn2Me6
[Eu(Ph2pz)2(dme)2] is similar to that recorded for the (confirmed by GC/MS), respectively,[14,30] (Table 3). The
transoid isomer[7] and suggests a single species in solution resonances at –95.5 and –97.4 ppm are near the value
or fast exchange between the isomers. The IR spectrum of (–95 ppm) reported for
a Sn–Yb bonded complex,
[Yb(Ph2pz)3(thf)2] is in agreement with those reported for [Yb{Sn(Nep)3}2(thf)2] (Nep = 2,2-dimethylpropyl).[31]
A
structurally uncharacterised [Ln(Ph2pz)3(thf)2] (Ln = Gd, corresponding resonance in the 171Yb NMR spectrum near
1
Er, Y, Yb, Lu) complexes.[27] A satisfactory H NMR spec- ca. 725 ppm was not observed, the sole signal being at δ =
trum of the paramagnetic compound could not be obtained 488 ppm, which corresponds to [Yb(Ph2pz)2(dme)2].[4]
(grossly broadened), but single crystals of [Yb(Ph2pz)3- However, there may be a problem with detection, as the
(thf)2]·2C6D6 deposited and the structure was determined. more sensitive 119Sn{1H} resonances are of weak intensity.
The IR spectrum of the new complex [Yb(Ph2pz)3(dme)]· The chemical shifts at –95 and –97 ppm are also close to
0.5dme is similar to those of the [Ln(Ph2pz)3(dme)2] (Ln = resonances for SnMe3 reported for [SnMe3]2SnMe2 or
La, Nd, Eu, Er)[7,20] complexes, while the visible/near IR (SnMe3)3SnMe (–99.5 and –89.5 ppm, respectively)[32,33]
spectrum shows a weak absorption at 975 nm (ε = 15), (Table 3). However, despite a prolonged scan time (17 h),
which is consistent with YbIII. No absorption band is seen the corresponding SnMe2 or SnMe resonances were not ob-
[34]
near 350 nm, in contrast to the intense absorption band at served, nor were resonances attributable to (SnMe2)6
410 nm (ε = 744) for [Yb(Ph2pz)2(dme)2].[4] Satisfactory (–231 and/or –241 ppm). An energy dispersive analysis by
analyses were obtained, and the structure was established X-rays (EDAX) on the metallic residue detected the pres-
by X-ray crystallography. The structures of the two Yb ence of elemental Sn, in addition to excess Yb metal. The
complexes, [Yb(Ph2pz)3(thf)2]·2C6D6 and [Yb(Ph2pz)3(dme)]· products are consistent with the transitory existence and
0.5dme, are of importance, since they contrast previous decomposition of molecular SnMe2 [Equation (13)],[9a,9b]
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G. B. Deacon, P. C. Junk et al.
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the putative initial product of reactions (8) and (9), and nearly symmetrically chelating in the cis isomer with only a
they resemble those from reaction of Ca metal with small divergence in Ln–N distances (0.01 and 0.05 Å). The
[SnMe2(N(SiMe3)2)2] [Equation (6)].
η2-dme ligands have a slightly larger difference in Eu–O
distances (0.05 and 0.07 Å), possibly because of steric hin-
drance imposed by the phenyl rings and the cis arrange-
ment. Table 4 provides a comparison of selected key bond
lengths and angles of the structures of the four divalent
[Ln(Ph2pz)2(dme)2] complexes. Crystallisation of cis-
[Eu(Ph2pz)2(dme)2] means that this isomer is established for
all three normal divalent elements. However, Eu now pro-
vides a rare example of geometric isomerism for labile lan-
thanoid complexes. The Ln–N bond lengths in [Sm(Ph2pz)2-
(dme)2][6] and the two [Eu(Ph2pz)2(dme)2] isomers are com-
parable, whilst that of [Yb(Ph2pz)2(dme)2] is smaller owing
to the smaller ionic radius of Yb.[36] Generally, the differ-
Table 3. 1H NMR and 119Sn{1H} NMR chemical shifts [ppm] of
some organotin(IV) compounds [119Sn(1H) chemical shifts relative
to external SnMe4].
δ(1H)
δ(119Sn{1H})
This work
0.63
–1.8
–95.5
–97.4
Ln +[SnMe2(Ph2pz)2] 0.81–0.90
1.23–1.83
–108.0
Sn2Me6
(SnMe2)n
(SnMe2)6
0.20[46]
–108.0[32]
1.15–1.36[29]
0.63 (conc.)[34]
0.53 + 0.63 (dil.)[34]
–231.04 and/or –241[34]
[SnMe3]4Sn
[SnMe3]3SnMe
[SnMe3]2SnMe2
–80 and –739[32]
–89.5 and –489[32]
–99.5 and –261[32]
The well documented pyrolysis of polymeric diethyltin
gives similar products, viz. SnEt4, Sn2Et6, Sn and other spe-
cies with SnEtn [(n = 1–3) groups].[35]
Single-Crystal X-ray Studies – The Structures of cis-
[Eu(Ph2pz)2(dme)2], [Yb(Ph2pz)3(dme)]·0.5dme and
[Yb(Ph2pz)3(thf)2]·2C6D6
Single crystals of [Sm(Ph2pz)2(dme)2] and [Yb(Ph2pz)2-
(dme)2] were grown, and their unit cells (as determined by
single-crystal X-ray diffraction) are in agreement with re-
ported data[4,6] (see Experimental Section). Although a
crystalline product was obtained for [La(Ph2pz)3(dme)2]·
dme, the material was not satisfactory for an X-ray crystal-
lographic structure determination. However, the structures
of the new EuII isomer cis-[Eu(Ph2pz)2(dme)2], [Yb(Ph2pz)3-
(dme)]·0.5dme and [Yb(Ph2pz)3(thf)2]·2C6D6 were deter-
mined.
The structure of cis-[Eu(Ph2pz)2(dme)2] has an eight-co-
ordinate Eu atom with two chelating dme ligands and two
chelating (η2) pyrazolate ligands (Figure 2) and is isotypic
with the reported [Yb(Ph2pz)2(dme)2] analogue.[4] The
cen[N(1)/N(2)]–Eu–cen[N(3)/N(4)] (cen = centre of the N–
N bond of the pyrazolate ligand) angle of 102.09° corre-
sponds to a cis disposition of the pyrazolate ligands and is
consistent with values (103–108°) observed for the cis LnII
complexes [Yb(Ph2pz)2(dme)2],[4] [Sm(Ph2pz)2(dme)2],[6]
[Eu(tBu2pz)2(dme)2][6] and [Yb(bind)2(dme)2] (tBu2pz =
3,5-di-tert-butylpyrazolate; bind = 4,5-dihydro-2H-benz[g]-
indazolate).[6] In comparison, transoid LnII cen–Ln–cen
angles are in the range 141–143°.[6] Similarly, the present
cen[O(1)/O(2)]–Eu–cen[O(3)/O(4)] angle is 95° and con-
Figure 2. (top) X-ray crystal structure of cis-[Eu(Ph2pz)2(dme)2];
ellipsoids shown at 40% probability; hydrogen atoms removed for
clarity. Selected bond lengths [Å] and angles [°] for this structure
are given in Table 4; (bottom) X-ray crystal structure of transoid-
[Eu(Ph2pz)2(dme)2];[6] hydrogen atoms and Me groups of dme
trasts 140° for the transoid isomer. Both Ph2pz ligands are molecules are removed for clarity.
4590 Eur. J. Inorg. Chem. 2008, 4586–4596
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Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as Reagent for Rare-Earth Complexes
Table 4. Selected bond lengths [Å] and angles [°] for cis-[Ln(Ph2pz)2(dme)2] and transoid-[Eu(Ph2pz)2(dme)2].[a]
cis-[Sm(Ph2pz)2(dme)2][6]
transoid-[Eu(Ph2pz)2(dme)2][6]
cis-[Eu(Ph2pz)2(dme)2]
cis-[Yb(Ph2pz)2(dme)2][4]
Ln–N
N1
N2
N3
N4
2.556(3)
2.556(3)
2.538(3)
2.538(3)
2.552(5)
2.582(4)
2.554(6)
2.536(6)
2.520(7)
2.532(6)
2.512(7)
2.559(7)
2.426(7)
2.414(7)
2.424(7)
2.430(7)
Ln-O
O1
O2
O3
O4
2.720(7)
2.708(5)
2.551(4)
2.627(7)
2.637(6)
2.660(5)
2.614(5)
2.684(5)
2.606(5)
2.671(5)
2.575(4)
2.623(6)
2.502(6)
2.558(7)
2.484(6)
2.576(7)
N–Ln-N
N1–Ln–N2
N3–Ln–N4
31.07(8)
30.99(10)
31.0(2)
31.0(2)
31.55(15)
31.34(16)
32.7(2)
32.5(2)
O–Ln-O
O1–Ln–O2
O3–Ln–O4
60.2(2)
69.5(2)
63.5(2)
62.9(2)
62.71(16)
64.41(17)
65.2(2)
65.6(2)
[a] N1–N4 and O1–O4 are generalised atom labels for literature compounds – Sm: N(11), N(11Ј), N(21), N(21Ј), O(102), O(105), O(202),
O(205); transoid-Eu: N(111), N(112), N(211), N(212), O(102), O(105), O(202), O(205); Yb: N(11), N(12), N(21), N(22), O(31), O(31Ј),
O(41), O(41Ј).
ence is close to that expected,[36] but in the case of Ln–O(4),
the difference is only 0.05 Å. Although the two [Eu(Ph2pz)2-
(dme)2] isomers have similar Eu–N and Eu–O bond lengths
(Table 4), the average Eu–N and Eu–O bond lengths for
the cis isomer (2.53(2) and 2.62(4) Å, respectively) may be
marginally shorter than those for the transoid [2.56(2) and
2.65(3) Å]. The overall position with the two isomers is that
the cis isomer is somewhat distorted towards trans and the
transoid isomer is considerably distorted towards the cis iso-
mer. Thus, the geometric isomerism contrasts [SmI2-
(diglyme)2], which forms normal cis- and trans isomers.
The Yb3+ ions in both [Yb(Ph2pz)3(thf)2]·2C6D6 (Fig-
ure 3) and [Yb(Ph2pz)3(dme)]·0.5dme (Figure 4) are eight
coordinate and are bonded in an η2-fashion by three pyra-
zolate ligands and two transoid thf molecules or a chelating
dme molecule, respectively. The eight-coordinate Yb com-
plexes contrast the previously reported nine-coordinate
[Ln(Ph2pz)3(dme)2] (Ln
=
Nd, Eu, Er)[7,20,37] and
([Ln(Ph2pz)3(thf)3] Ln = Nd[21] or Sm[7]) complexes and re-
flect the lanthanoid contraction. It is thus likely that
[Ln(Ph2pz)3(thf)2] (Ln = Y, Er and Lu)[27] complexes have
a similar structure to [Yb(Ph2pz)3(thf)2]. In contrast to the
nine-coordinate [Ln(Ph2pz)3(dme)2] complexes of the light
lanthanoids, eight coordination is observed in the polymeric
[Nd(tBu2pz)3(µ-dme)]n complex,[20] owing to the bulkier pyr-
azolate ligand.
Figure 3. X-ray crystal structure of [Yb(Ph2pz)3(thf)2]·2C6D6; ellip-
soids shown at 50% probability; hydrogen atoms removed for clar-
ity. Selected bond lengths [Å] and angles [°] for this structure are
given in Table 5.
The Yb–N bond lengths of [Yb(Ph2pz)3(thf)2]·2C6D6 2.305 Å {[Yb(Ph2pz)3(dme)]·0.5dme}, are 0.12 and 0.13 Å,
and [Yb(Ph2pz)3(dme)]·0.5dme are remarkably similar respectively, shorter than the average Nd–N bond length of
(Table 5), given the contrasting nature of the two coordinat- the eight-coordinate [Nd(tBu2pz)3(µ-dme)]n complex[20] and
ing neutral ligands. η2-Pyrazolate binding is reasonably are very close to ionic radii differences.[36] The O(1)–Yb–
symmetric, with Yb–N bond length differences ranging O(2) angle of 153.45(7)° in [Yb(Ph2pz)3(thf)2]·2C6D6 is
from 0.014–0.087 {[Yb(Ph2pz)3(thf)2]·2C6D6} and 0.09– close to that of O(1)–Nd–O(3)[21] in [Nd(tBu2pz)3(µ-dme)]n
0.093 Å {[Yb(Ph2pz)3(dme)]·0.5dme}. The average Yb–N [153.5(2)°],[20] but is much larger than that of O(1)–Er–O(2)
bond lengths, 2.310 {[Yb(Ph2pz)3(thf)2]·2C6D6} and [140.1(4)°] in [Er(tBu2pz)3(thf)2].[38]
Eur. J. Inorg. Chem. 2008, 4586–4596
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4591

G. B. Deacon, P. C. Junk et al.
FULL PAPER
diate is formed and then reacts further. In the redox trans-
metallation reaction between Ca and [SnMe2(N{Si-
Me3}2)2], a Ca/Sn complex [Ca{Sn(SnMe3)3}2(thf)2] was
obtained in addition to the target [Ca(N{SiMe3}2)2(thf)2]
compound[10,39] [Equation (6)]. The very low solubility of
this intermediate in any solvent suggests that it is polymeric
in nature. An attempt to prepare a Sn/Ln pyrazolate dimet-
allic without redox, by reaction of [SnMe2(Ph2pz)2] with
[Nd(Ph2pz)3(thf)3]·thf, was not successful.
Conclusions
This study further highlights the efficacy of organo-
tin(IV) reagents in redox transmetallation reactions for the
synthesis of rare-earth complexes. Treatment of the new rea-
gent [SnMe2(Ph2pz)2] with Ln metals (Ln = La, Sm, Eu and
Yb) enables the preparation of both divalent and trivalent
Ln-pyrazolate complexes. A second geometric isomer (cis)
of [Eu(Ph2pz)2(dme)2] was characterised. This work com-
plements the success of [SnMe3(Ph2pz)] in the synthesis of
Ln(Ph2pz)n (n = 2, 3) complexes.[7] The yields of products
obtained were comparable to those obtained from
[SnMe3(Ph2pz)] and from other literature methods. How-
ever, reactions involving [SnMe2(Ph2pz)2] occur faster than
those of [SnMe3(Ph2pz)] and even [Tl(Ph2pz)], especially
with Yb metal, and have the advantages of transferring two
Ph2pz groups per Sn atom. The organotin product un-
dergoes decomposition to form tin metal, Sn2Me6, SnMe4,
in addition to two other species. From oxidation reactions
of [Yb(Ph2pz)2(dme)2], the new crystallographically charac-
terised [Yb(Ph2pz)3(thf)2] and [Yb(Ph2pz)3(dme)] com-
plexes were obtained.
Figure 4. X-ray crystal structure of [Yb(Ph2pz)3(dme)]·0.5dme; el-
lipsoids shown at 20% probability. Selected bond lengths [Å] and
angles [°] for this structure are given in Table 5.
Table 5. Selected bond lengths [Å] and angles [°] for [Yb(Ph2pz)3-
(thf)2]·2C6D6 and [Yb(Ph2pz)3(dme)]·0.5dme.
[Yb(Ph2pz)3(thf)2]·2C6D6 [Yb(Ph2pz)3(dme)]·0.5dme
Bond lengths
Yb–N(1)
Yb–N(2)
Yb–N(3)
Yb–N(4)
Yb–N(5)
Yb–N(6)
Yb–O(1)
Yb–O(2)
2.291(2)
2.305(2)
2.274(2)
2.361(2)
2.352(2)
2.280(2)
2.3260(19)
2.357(2)
2.251(4)
2.347(4)
2.337(4)
2.282(4)
2.356(4)
2.266(4)
2.404(3)
2.342(3)
Bond angles
N(1)–Yb–N(2) 34.90(8)
N(3)–Yb–N(4) 34.50(8)
N(6)–Yb–N(5) 34.38(8)
O(1)–Yb–O(2) 153.45(7)
34.44(12)
34.80(13)
34.28(12)
68.33(11)
Experimental Section
General Remarks: All reactions were carried out under dry nitrogen
by using standard Schlenk and dry box equipment. Tetra-
hydrofuran and diethyl ether were freshly distilled from sodium/
benzophenone, while 1,2-dimethoxyethane was distilled from so-
dium. Infrared spectra (4000–650 cm–1) were recorded as Nujol
mulls with a Perkin–Elmer 1600 FTIR spectrophotometer. 1H
NMR spectra were recorded with a Bruker DPX 300 MHz spec-
trometer by using dry degassed deuterated benzene, and resonances
were referenced to residual hydrogen from the solvent. 119Sn NMR
spectra were obtained by using a Bruker DRX 400 spectrometer,
and resonances were referenced to tetramethyltin. Metal analyses
Observation of a Reaction Intermediate
A feature of reactions (8) and (9) is that they appear to
proceed via an “intermediate” stage, where a white precipi-
tate is formed 5–30 min after solvent addition. This “inter-
mediate” then redissolved within 1 h [Yb/dme; Hg acti-
vation], 1 d [Yb/thf or Yb/dme; no Hg activation] or 3 d
{La [I2 activation, Eu and Sm (Hg activation)]}, which sig-
nifies reaction completion. Attempts were made to identify
the “intermediate” species formed during the preparation
of [Eu(Ph2pz)2(dme)2] and during the preparation of of the lanthanoid complexes were performed by EDTA titration
with Xylenol Orange indicator following digestion in concentrated
nitric and sulfuric acids unless indicated otherwise and buffering
with hexamine.[6] Microanalysis samples were sealed in glass am-
poules under purified N2 and were determined by the Campbell
Microanalytical service, University of Otago, New Zealand. EDAX
(Energy Dispersive Analysis by X-rays) was used to qualitatively
determine the presence of lanthanoid and tin metals in specific
samples. Measurements were carried out by using a Joel JSM 840A
scanning microscope in EDS mode. GC Mass spectra were ob-
tained by using the Agilent 5973 spectrometer. Dimethyltin dichlo-
[La(Ph2pz)3(dme)2]·dme. Lack of crystallinity and near in-
solubility in suitable NMR solvents hindered structural
1
evaluation. The H NMR spectra suggest the presence of
SnMe and Ph2pz moieties, but adsorption of soluble species
in the precipitate is possible. The IR spectrum of the pre-
cipitate from the reaction with Eu differs from those of
[SnMe2(Ph2pz)2] and [Eu(Ph2pz)2(dme)2], but shows fea-
tures indicative of Ph2pz and SnMe groups. An EDAX
measurement on this product indicates the presence of Sn
and Eu (2:1). It is possible that a dimetallic Sn/Ln interme- ride was purchased from Aldrich and used as is. 3,5-Diphenylpyr-
4592 Eur. J. Inorg. Chem. 2008, 4586–4596
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Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as Reagent for Rare-Earth Complexes
azole[40] and bis(pentafluorophenyl)mercury[41] were prepared by
literature methods.
solution was stirred for 1 h, whereby after 15 min reaction time a
precipitate had formed. The mixture was then placed in a sonic-
ation bath for a further 1 h and 30 min, but the precipitate was still
present. The mixture was then stirred at room temperature for 2 d,
resulting in a deep-yellow solution. After standing for 3 d, the solu-
tion had darkened to a deep colour. The filtrate was collected by a
filter cannula, and the dme solution was concentrated to ca. 3 mL,
yielding a dark sludgy precipitate, amongst which were a few single
crystals. The IR spectrum was in agreement with that reported for
[Sm(Ph2pz)2(dme)2].[6] Visible/near IR (thf): λmax (ε) = 545 (841, br.)
Preparation of [SnMe2(Ph2pz)2]: [SnMe2Cl2] (1.50 g; 6.86 mmol)
was added to a solution of [Li(Ph2pz)] (3.09 g; 13.7 mmol) in Et2O
(50 mL), causing formation of a milky white suspension, which was
stirred at room temperature overnight. After filtration through a
filter cannula, the Et2O was removed under vacuum. The white
product was washed with hexane (40 mL). Yield: 2.91 g (72%). IR:
ν = 1602 (m), 1538 (w), 1268 (m), 1158 (m), 1111 (m), 1071 (m),
˜
1026 (m), 955 (m), 798 (m), 758 (vs), 698 (s) cm–1. 1H NMR
1
nm. The H NMR spectrum showed the presence of both trivalent
2
2
(300 MHz, C6D6, 25 °C): δ = 0.48 (s, JH,117Sn = 69, JH,119Sn
=
[Sm(Ph2pz)3(dme)2][4] and divalent [Sm(Ph2pz)2(dme)2][6] species,
with the latter dominant (300 MHz, C6D6, 25 °C): δ = for
[Sm(Ph2pz)2(dme)2]: –9.67 (v br. s, H4), –4.43 (v br. s, o-H) (reso-
nances too broad owing to paramagnetism for meaningful integra-
tion), 3.73 (br. s, 20 H, CH2 and CH3-dme), 5.22 (br. s, 4 H, p-H),
5.91 (br. s, 8 H, m-H) ppm; for Sm(Ph2pz)3 the pyrazolate reso-
nances are: 7.46–7.96 (br. m, p- and m-H), 8.30 (br. s, H4), 9.12
(br. s, o-H). A unit cell for the purple crystals [orthorhombic, a =
8.02(2), b = 24.39(14), c = 19.22(5) Å; V = 3762(10) Å3] was consis-
tent with formation of [Sm(Ph2pz)2(dme)2][6] [orthorhombic, Pnma,
a = 7.9941(6), b = 24.263(3), c = 19.080(3) Å; V = 3701 Å3]. The
metal analysis of the samarium complex was performed by EDTA
titration with Xylenol Orange indicator following degradation with
4  HCl and buffering with hexamine. C38H42N4O4Sm (769.12):
calcd. Sm 19.54; found Sm 18.70 [For trivalent C53H53N6O4Sm
(988.38): calcd. Sm 15.22; found Sm 18.70].
72 Hz, 6 H, Me2Sn), 6.79 [s, 2 H, H4 (pz)], 7.12 (t, 4 H, p-H), 7.34
(br. t, 8 H, m-H), 7.79 (br. s, 8 H, o-H). 119Sn{1H} NMR
(149 MHz, C6D6, 25 °C): δ = –8.1 ppm. Crystals of [SnMe2(Ph2pz)2-
(thf)] were obtained after recrystallisation from thf. 1H NMR
2
2
(300 MHz, C6D6, 25 °C): δ = 0.49 (s, JH,117Sn = 69, JH,119Sn
=
72 Hz, 6 H, Me2Sn), 1.25–1.30 (m, 4 H, CH2-thf), 3.34–3.47 (m,
4 H, OCH2-thf), 6.74 [s, 2 H, H4(pz)], 7.12 (t, 4 H, p-H), 7.34 (br.
t, 8 H, m-H), 7.77 (br. s, 8 H, o-H) ppm. 119Sn{1H} NMR
(149 MHz, C6D6, 25 °C): δ = –9.3 ppm. For [SnMe2(Ph2pz)2(thf)]:
C36H36N4OSn (659.38): calcd. C 65.57, H 5.50, N 8.49; found C
63.13,
H 5.12, N 8.85. For unsolvated [SnMe2(Ph2pz)2]:
C32H28N4Sn (587.30): calcd. C 65.44, H 4.81, N 9.54; found C
63.13, H 5.12, N 8.85.
Redox Transmetallation Reactions with La, Sm and Eu
[La(Ph2pz)3(dme)2]·dme
cis-[Eu(Ph2pz)2(dme)2]
(a) Activation by I2: dme (50 mL) was added by a cannula to a
mixture of La metal filings (1.11 g; 8.03 mmol), [SnMe2(Ph2pz)2]
(1.14 g; 1.94 mmol) and I2 (≈ 0.1 g). The resulting deep-orange
solution was allowed to stand at room temperature. Within 1 h of
standing, the solution lightened to a light yellow, and after 6 h this
colour was pale orange-yellow with crystalline white material form-
ing. This product then redissolved after 4 d of standing when the
solution was again deep orange. The filtrate was collected by a filter
cannula, and the dme was concentrated to 15 mL, resulting in deep
orange-yellow (microcrystalline) material. Yield 1.09 g (79%). The
IR spectrum was identical with that reported for [La(Ph2pz)3-
(dme)2],[7] and the 1H NMR spectrum was also in agreement
with that reported for [La(Ph2pz)3(dme)2]·dme in C6D6.[7]
C57H63LaN6O6 (1067.05): calcd. La 13.02; found La 12.74.
(a) Without Activation by Mercury: dme (40 mL) was added by a
cannula to a mixture of Eu metal pieces (0.77 g; 5.09 mmol) and
[SnMe2(Ph2pz)2] (0.33 g; 0.56 mmol). After 30 min of sonication, a
murky peach-coloured solution was observed and a precipitate be-
gan to deposit. After 2 d of sonication, a yellow colour was ob-
served with the precipitate still visible. The yellow solution was fil-
tered by a filter cannula, and the precipitate was collected. The
yellow filtrate was concentrated under reduced pressure, yielding
yellow crystalline material (0.14 g, 33%). X-ray analysis on five
crystals showed formation of the cis-[Eu(Ph2pz)2(dme)2] species.
The IR spectrum agreed with that reported for transoid-[Eu(Ph2pz)2-
(dme)2].[6] 1H NMR (300 MHz, C6D6, 25 °C): δ = 0.28 (br. m, 12
H, CH3-dme), 0.63 (br. s, 8 H, CH2-dme), 0.92 (br. s, 4 H, p-H),
1.34 (br. s, 18 H, H4, o-H,m-H) ppm. The precipitate was only
barely soluble in available deuterated solvents (C6D6, CD3C6D5,
C2D6OS, C4D8O), with the resulting NMR spectra inconclusive.
However, no starting material [SnMe2(Ph2pz)2] was present. The
IR was different from those of both starting material and the target
(b) Activation by Hg: dme (40 mL) was added by a cannula to a
mixture of La metal filings (0.55 g; 3.97 mmol), [SnMe2(Ph2pz)2]
(0.51 g; 0.87 mmol) and 1–2 drops of Hg. The resulting colourless
solution was stirred at room temperature. A white precipitate ap-
peared after 20 min and was still visible after 5 h. Approximately
5 mL of “intermediate suspension” was collected by a cannula, and
dme was concentrated to 1 mL. 1H NMR (300 MHz, diluted by
C6D6, 25 °C): δ = 0.31–1.81 (multiple resonances) 7.15–7.19 (t, p-
H), 7.24–7.30 (tr, m-H), 8.00–8.02 (br. d, o-H) ppm. 1H NMR spec-
trum of sample exposed to air (300 MHz, 3:1 CD3CN/C6D6,
25 °C): δ = 2.26 (br. s, H2O), 3.27–3.38 (br. s, CH3-dme), 3.52–3.53
(br. s, CH2-dme), 7.09 (s, H4), 7.44–7.71 (m, p-H, m-H), 7.82–8.01
(br. d, o-H), 11.62 (br. s, NH) ppm. The bulk reaction mixture was
stirred for 2 d, after which time the precipitate had redissolved.
The dme filtrate was collected by a filter cannula, and dme was
concentrated to 5 mL, resulting in a white precipitate. The IR and
1H NMR (in C6D6) spectra were consistent with that reported for
[La(Ph2pz)3(dme)2]·dme.[7].
[Eu(Ph pz) (dme) ] complex: ν = 1600 (s), 1536 (m), 1512 (m), 1427
˜
2
2
2
(s), 1400 (s), 1319 (w), 1295 (w), 1276 (w), 1224 (w), 1189 (m), 1152
(w), 1121 (w), 1078 (s), 1062 (vs), 1026 (s), 1000 (w), 980 (vs), 961
(s), 912 (s), 869 (m), 846 (w), 807 (m), 758 (vs), 707 (s), 682 (vs),
658 (w) cm–1. EDAX showed 2:1 Sn/Eu ratio.
(b) With Activation by Mercury: dme (50 mL) was added by a can-
nula to
a mixture of Eu metal pieces (0.87 g; 5.76 mmol),
[SnMe2(Phpz)2] (0.40 g; 0.68 mmol) and two Hg drops. An instant
golden-yellow solution was obtained, with all [SnMe2(Ph2pz)2] dis-
solved. After 5 min of stirring at room temperature, a precipitate
was seen, and the solution was a lemon-yellow colour. The mixture
was stirred at room temperature for 2 d, after which time all the
precipitate had redissolved giving a golden-yellow solution. Con-
centrating the filtrate resulted in crystalline material of [Eu(Ph2pz)2-
(dme)2]. Yield: 0.40 g (77%). The IR and 1H NMR spectra were as
above for the [Eu(Ph2pz)2(dme)2] complex.[6] C38H42EuN4O4
[Sm(Ph2pz)2(dme)2]: dme (40 mL) was added by a cannula to a stir-
ring mixture of [SnMe2(Ph2pz)2] (0.24 g; 0.42 mmol), Sm metal
powder (0.49 g; 3.25 mmol) and 1–2 drops of Hg. The pale-yellow
Eur. J. Inorg. Chem. 2008, 4586–4596
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4593

G. B. Deacon, P. C. Junk et al.
FULL PAPER
(770.73): calcd. Eu 19.72; found Eu 20.05. Single-crystal X-ray de-
termination on three representative crystals of the bulk yellow crys-
tals showed formation of the cis-[Eu(Ph2pz)2(dme)2] isomer.
Yb 17.74; found Yb 18.59. For loss of one thf molecule
C49H41N6OYb (902.92): calcd. 19.16; found 18.59.
(b) Without Activation by Hg: thf (40 mL) was added by a cannula
[Yb(Ph2pz)2(dme)2]
to a mixture of Yb metal filings (0.76 g; 4.40 mmol) and
[SnMe2(Ph2pz)2] (0.42 g; 0.72 mmol). No colour change was ob-
served after 5 min. The solution was stirred overnight, after which
time a white precipitate was observed. The mixture was placed in
the sonication bath for 3 h. After 2 h of sonication, a deep-yellow
colour was obtained, which deepened to deep orange-red after 3 h.
The deep-coloured solution was allowed to settle and was then fil-
tered by a filter cannula. As the solution was concentrated, the
colour lightened to an orange colour. No crystals formed, and thf
was removed under vacuum, yielding pale orange-yellow precipi-
tate (0.27 g; 58%). The IR spectrum was in agreement with that of
[Yb(Ph2pz)3(thf)2].[27] For C53H49N6O2Yb (975.03): calcd. Yb
17.74; found Yb 17.76.
(a) Activation by Hg: dme (40 mL) was added by a cannula to a
mixture of [SnMe2(Ph2pz)2] (0.62 g; 1.06 mmol), Yb metal filings
(0.91 g; 5.26 mmol) and 2 drops of Hg. An orange colour was ob-
served immediately. After 10 min of stirring, the initial orange col-
our lightened to a light-orange hue as a white precipitate began to
form. This precipitate redissolved into solution after 2 h of stirring,
causing the solution to deepen into a deep orange/red colour. The
deep-coloured filtrate was collected by a filter cannula, and the dme
solution was concentrated under vacuum to ca. 10 mL, resulting in
deep-red crystalline material. Yield: 0.61 g (73%). A unit cell of
these crystals [monoclinic, P21/c, a = 24.12(8), b = 18.53(6), c =
7.63(3) Å; β = 95.6(2)°, V = 3394(5) Å3] was in agreement with that
reported for [Yb(Ph2pz)2(dme)2][4] [monoclinic, P21/a, a = 7.882(4),
b = 18.959(3), c = 24.080(14) Å; β = 91.03(2)°, V = 3598(3) Å3].
This was also confirmed by the 1H NMR and IR spectra, which
were identical with those reported.[4] C38H42N4O4Yb (791.80):
calcd. Yb 21.85; found Yb 21.51.
[Yb(Ph2pz)3(thf)2]·2C6D6: thf (10 mL) was added to [Yb(Ph2pz)2-
(dme)2] (0.14 g; 0.18 mmol) and [SnMe2(Ph2pz)2] (0.08 g;
0.13 mmol), and an instant orange-red solution was observed. The
solution was stirred at room temperature for 2 d, after which time
an orange solution was obtained. Concentration of the thf solution
resulted in an orange precipitate. The IR spectrum of the orange
precipitate was different to both starting materials and was similar
(b) Without Activation by Hg: dme (40 mL) was added by a cannula
to
a mixture of Yb metal filings (0.67 g; 3.89 mmol) and
to other reported [Ln(Ph2pz)3(thf)2][27,41] complexes: ν = 1601 (m),
˜
[SnMe2(Ph2pz)2] (0.48 g; 0.82 mmol). A golden-yellow solution was
observed after 5 min. As with mercury activation, a white precipi-
tate appeared with progression of the reaction. The mixture was
stirred overnight, after which time the colour had deepened to an
orange colour with some precipitate still observed. The mixture
was sonicated for 1 h, causing the remaining precipitate to dissolve,
and the solution was orange-red. The filtrate was collected by a
filter cannula and dme was concentrated to 10 mL, resulting in
deep-red crystalline material. Yield 0.65 g (71%). The IR and 1H
NMR spectra of these crystals were identical with those reported
for [Yb(Ph2pz)2(dme)2].[4] A unit cell on these crystals [monoclinic,
P21/a, a = 7.827(3), b = 18.835(6), c = 24.005(7) Å; β = 91.17(3)°,
1574 (w), 1537 (w), 1511 (w), 1401 (m), 1294 (w), 1099 (br. s), 1059
(br. s), 1020 (br. s), 976 (m s), 915 (m), 866 (m), 792 (br. s), 754 (s),
706 (m), 688 (s), 668 (m) cm–1. The 1H NMR spectrum was at-
tempted in C6D6. However, due to the paramagnetic nature of
Yb3+, a spectrum could not be obtained due to excessive broaden-
ing and shifting of the resonances. The NMR solution was returned
to the dry box, and crystalline product [Yb(Ph2pz)3(thf)2]·2C6D6
was obtained after allowing the C6D6 solution to slowly evaporate
over time.
[Yb(Ph2pz)3(dme)]·0.5dme
(a) Oxidation with [Tl(Ph2pz)]: [Tl(Ph2pz)] (0.42 g; 1.00 mmol) was
added to a thf solution (30 mL) of [Yb(Ph2pz)2(dme)2] (0.79 g;
1.00 mmol), causing an immediate colour change from deep red to
pale yellow and suspension of a grey solid. The solid was isolated
and thf was removed under reduced pressure to give an off-white
solid. The precipitate was recrystallised from dme to give yellow
V
=
3538(1) Å3] was in agreement with that reported for
[Yb(Ph2pz)2(dme)2].[4] C38H42N4O4Yb (791.80): calcd. Yb 21.85;
found Yb 22.44.
Analysis of [Yb(Ph2pz)2(dme)2] Reaction Mixture (for Identification
of Sn Coproducts): dme (15 mL) was added by a cannula to a mix-
ture of Yb metal filings (0.98 g; 5.68 mmol), [SnMe2(Ph2pz)2]
(0.59 g; 1.01 mmol) and 1–2 drops of Hg. The resulting solution
was stirred for 2 h, resulting in a deep-red solution. Samples of the
reaction mixture were collected in the drybox for 119Sn and 171Yb
NMR spectroscopy. 119Sn{1H} NMR (149 MHz, C6D6, 25 °C): δ
= 1.8, –95.5, –97.4, –108.0 ppm. 171Yb NMR: δ = 488.6 ppm. GC/
MS of the reaction mixture indicated formation of hexamethylditin
(m/z 326, most intense peak of cluster with the correct isotope
pattern).
crystals of [Yb(Ph pz) (dme)]·0.5dme (0.74 g; 77%). IR: ν = 3060
˜
2
3
(m), 3036 (m), 1605 (m), 1512 (m), 1422 (w), 1408 (w), 1250 (w),
1191 (w), 1124 (m), 1108 (m), 1092 (m), 1072 (w), 1047 (s), 1021
(m), 974 (s), 909 (w), 861 (s), 803 (m), 761 (vs), 694 (vs), 683 (vs)
cm–1. Visible/near IR (thf): λmax (ε) = 975 (15) nm. C51H48N6O3Yb
(966.0): calcd. C 63.41, H 5.01, N 8.70, Yb 17.91; found C 62.74,
H 5.28, N 8.56, Yb 17.50.
(b) Treatment with Ph2pzH and [Hg(C6F5)2]: Ph2pzH (0.33 g;
1.50 mmol) and [Hg(C6F5)2] (0.41 g; 0.75 mmol) were successively
added to a thf solution (30 mL) of [Yb(Ph2pz)2(dme)2] (1.19 g;
1.5 mmol) causing an immediate colour change (on addition of
[Hg(C6F5)2]) from deep red to pale yellow and suspension of a grey
solid. After filtration thf was removed under reduced pressure to
give an off-white solid, which was recrystallised from dme to give
large yellow crystals of [Yb(Ph2pz)3(dme)]·0.5dme (1.16 g; 80%).
The IR spectrum was the same as that obtained in method a.
C51H48N6O3Yb (966.0): calcd. Yb 17.91; found Yb 17.50. Single
crystals suitable for X-ray were grown at –20 °C from a saturated
solution in dme.
[Yb(Ph2pz)3(thf)2]
(a) Activation by Hg: thf (40 mL) was added by a cannula to a
mixture of Yb metal filings (0.66 g; 3.81 mmol), [SnMe2(Ph2pz)2]
(0.54 g; 0.93 mmol) and Hg (2 drops). An instant deep-orange col-
our was observed. The mixture was stirred for 1 h, after which time
the resulting deep orange-red solution was filtered by a filter can-
nula. Upon concentration of the filtrate, the deep-coloured solution
lightened gradually to a yellow solution, and very fine yellow crys-
talline material formed. These crystals were unsuitable for X-ray
determination. The solvent thf was removed under vacuum, yield-
ing a pale-yellow precipitate (0.43 g; 74%). The IR spectrum agreed
Reaction of [Nd(Ph2pz)3(thf)3]·thf with [SnMe2(Ph2pz)2] in thf: thf
with that of [Yb(Ph2pz)3(thf)2].[27] C53H49N6O2Yb (975.03): calcd. (10 mL) was added by a cannula to a mixture of [SnMe2(Ph2pz)2]
4594
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 4586–4596

Dimethyltin(IV) Bis(3,5-diphenylpyrazolate) as Reagent for Rare-Earth Complexes
(0.13 g; 0.22 mmol) and [Nd(Ph2pz)3(thf)3]·thf (0.44 g; 0.40 mmol),
Acknowledgments
and the resulting mixture was stirred at room temperature for 1 h.
Concentration of the thf solution resulted in pale-blue crystalline
material. A unit cell of these crystals [orthorhombic, P212121, a =
14.13(2), b = 16.11(1), c = 22.61(2) Å; V = 5147(8) Å3] was in agree-
ment with that of [Nd(Ph2pz)3(thf)3]·thf[21] [orthorhombic, P212121,
a = 14.009(9), b = 16.280(8), c = 22.640(16) Å; V = 5163(5) Å],
The authors gratefully acknowledge the financial support of the
Australian Research Council and for support received from the
Monash University Postgraduate Publications Award.
1
indicating no reaction. The IR and H NMR spectra both agreed
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with data for [Nd(Ph2pz)3(thf)3]·thf.[21]
X-ray Crystallography: Crystalline samples of [SnMe2(Ph2pz)2-
(thf)], [Eu(Ph2pz)2(dme)2], [Yb(Ph2pz)2(dme)].0.5dme and [Yb-
(Ph2pz)3(thf)2]·2C6D6 were mounted on glass fibres in viscous hy-
drocarbon oil. Crystal data were collected by using the Bruker Ap-
exII diffractometer, equipped with monochromated Mo-Kα radia-
tion, λ = 0.71073 Å. All data were collected at 123 K, maintained
by using an open flow of nitrogen from an Oxford Cryostreams
cryostat. X-ray data were processed by using the SAINT[42] pack-
age (Bruker). Structural solution and refinement was carried out
by using SHELXS-97[43] and SHELXL-97[44] utilising the graphical
interface X-Seed.[45] For [SnMe2(Ph2pz)2(thf)], the thf molecule
showed signs of disorder and was successfully modelled over two
positions. Crystal data and refinement parameters for all complexes
are compiled below. CCDC-676346, -676347, -676348 and -676463
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_requ-
est/cif.
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[SnMe2(Ph2pz)2(thf)]: C36H36N4OSn, M = 659.38, colourless block,
0.25ϫ0.18ϫ0.16 mm, monoclinic, space group P21/n (No. 14), a
= 11.3424(3), b = 17.1623(4), c = 16.4613(3) Å, β = 102.7590(10)°,
V = 3125.26(12) Å3, Z = 4, Dc = 1.401 g/cm3, 2θmax = 55.0°, 80348
reflections collected, 7176 unique (Rint = 0.0353). Final GooF =
1.12, R1 = 0.042, wR2 = 0.083, R indices based on 6810 reflections
with IϾ2σ(I) (refinement on F2), 382 parameters, 0 restraints. Lp
and absorption corrections applied, µ = 0.85 mm–1.
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cis-[Eu(Ph2pz)2(dme)2]: C38H42EuN4O4, M = 770.72, yellow block,
0.20ϫ0.15ϫ0.12 mm, monoclinic, space group P21/c (No. 14), a
= 23.894(4), b = 18.840(3), c = 7.8584(13) Å, β = 90.163(5)°, V =
3537.7(10) Å3, Z = 4, Dc = 1.447 g/cm3, 2θmax = 55.0°, 62824 reflec-
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R1 = 0.048, wR2 = 0.105, R indices based on 7686 reflections with
IϾ2σ(I) (refinement on F2), 425 parameters, 24 restraints. Lp and
absorption corrections applied, µ = 1.82 mm–1.
[Yb(Ph2pz)3(thf)2]·2C6D6: C65H61N6O2Yb, M = 1131.24, colourless
block, 0.10ϫ0.08ϫ0.07 mm, monoclinic, space group P21/c (No.
14), a = 15.5107(3), b = 10.1644(2), c = 34.8291(6) Å, β =
100.9280(10)°, V = 5391.48(18) Å3, Z = 4, Dc = 1.394 g/cm3, 2θmax
= 55.0°, 64783 reflections collected, 12379 unique (Rint = 0.0414).
Final GooF = 1.085, R1 = 0.034, wR2 = 0.063, R indices based on
10378 reflections with IϾ2σ(I) (refinement on F2), 667 parameters,
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Received: June 26, 2008
Published Online: September 4, 2008
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Eur. J. Inorg. Chem. 2008, 4586–4596