Simple Syntheses, Structural Diversity, and Tishchenko Reaction Catalysis of Neutral Homoleptic Rare Earth(II or III) 3,5-Di-tert-butylpyrazolates - The Structures of [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln = La, Nd, Yb, Lu), and [Eu4(tB2pz)8]

Article abstract of DOI:10.1002/1521-3765(20010105)7:1<127::AID-CHEM127>3.0.CO;2-1

The homoleptic rare-earth pyrazolate complexes [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln = La, Nd, Sm, Lu), [Eu4(tBu2pz)8] and the mixed oxidation state species [Yb2(tBu2pz)5] (tBu2pz = 3,5-di-tert-butylpyrazolate) have been prepared by a simple reaction between the corresponding rare-earth metal and 3,5-di-tert-butylpyrazole, in the presence of mercury, at elevated temperatures. In addition, [Yb2(tBu2pz)6] was prepared by redox transmetallation/ligand exchange between ytterbium, diphenylmercury(II) and tBu2pzH in toluene, whilst the same reactants in toluene under different conditions or in diethyl ether gave [Yb2(tBu2pz)5]. The complexes of the trivalent lanthanoids display dimeric structures [Ln2(tBu2pz)6] (Ln = La, Nd, Yb, Lu) with chelating η-terminal and η²:η²-bridging pyrazolate coordination. The considerably smaller Sc(3+) ion forms monomeric [Sc(tBu2pz)3] of putative D_3h molecular symmetry, with pyrazolate ligands solely η²-bonded. [Eu4(tBu2pz)8] is a structurally remarkable tetranuclear Eu(II) complex with two types of europium centres in a linear array. The outer two are bonded to one terminal and two bridging pyrazolates, and the inner two are coordinated by four bridging ligands. Unprecedented μ-η⁵:η² pyrazolate ligation is observed, with each outer Eu(2+) sandwiched between two η⁵-bonded pyrazolate groups, which are also η²-linked to an inner Eu(2+). The two inner Eu(2+) ions are linked together by two equally occupied components of each of two symmetry related, disordered pyrazolate groups with one component η⁴:η² bridging and one η³:η² bridging. [La2(tBu2pz)6] has also been shown to be a Tishchenko reaction catalyst with several organic substrates.

Full text of DOI:10.1002/1521-3765(20010105)7:1<127::AID-CHEM127>3.0.CO;2-1

FULL PAPER
Simple Syntheses, Structural Diversity, and Tishchenko Reaction Catalysis of
Neutral Homoleptic Rare Earth(ii or iii) 3,5-Di-tert-butylpyrazolatesÐ
The Structures of [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln ˆ La, Nd, Yb, Lu), and
[Eu4(tBu2pz)8]
Glen B. Deacon,*[a] Alex Gitlits,[a] Peter W. Roesky,[b] Markus R. Bürgstein,[b]
Kevin C. Lim,[c] Brian W. Skelton,[c] and Allan H. White[c]
Abstract: The homoleptic rare-earth
pyrazolate complexes [Sc(tBu2pz)3],
[Ln2(tBu2pz)6] (Ln ˆ La, Nd, Sm, Lu),
[Eu4(tBu2pz)8] and the mixed oxidation
state species [Yb2(tBu2pz)5] (tBu2pz ˆ
3,5-di-tert-butylpyrazolate) have been
prepared by a simple reaction between
the corresponding rare-earth metal and
3,5-di-tert-butylpyrazole, in the presence
of mercury, at elevated temperatures. In
addition, [Yb2(tBu2pz)6] was prepared
by redox transmetallation/ligand ex-
change between ytterbium, diphenyl-
mercury(ii) and tBu2pzH in toluene,
whilst the same reactants in toluene
under different conditions or in diethyl
ether gave [Yb2(tBu2pz)5]. The com-
plexes of the trivalent lanthanoids dis-
play dimeric structures [Ln2(tBu2pz)6]
(Ln ˆ La, Nd, Yb, Lu) with chelating h2-
terminal and h2:h2-bridging pyrazolate
coordination. The considerably smaller
Sc3‡ ion forms monomeric [Sc(tBu2pz)3]
of putative D3h molecular symmetry,
with pyrazolate ligands solely h2-bond-
ed. [Eu4(tBu2pz)8] is a structurally re-
markable tetranuclear EuII complex
with two types of europium centres in
a linear array. The outer two are bonded
to one terminal and two bridging pyr-
azolates, and the inner two are coordi-
nated by four bridging ligands. Unpre-
cedented m-h5:h2 pyrazolate ligation is
observed, with each outer Eu2‡ sand-
wiched between two h5-bonded pyrazo-
late groups, which are also h2-linked to
an inner Eu2‡. The two inner Eu2‡ ions
are linked together by two equally
occupied components of each of two
symmetry related, disordered pyrazolate
groups with one component h4:h2 bridg-
ing and one h3:h2 bridging. [La2-
(tBu2pz)6] has also been shown to be a
Tishchenko reaction catalyst with sev-
eral organic substrates.
Keywords: catalysts ´ lanthanides ´
N ligands ´ pyrazolates ´ rare-earth
metals ´ structure elucidation
h1:h1, ii) h2 and iii) h1 (N-bonded) pyrazolate ligation.[1] In
addition h2 coordination has been extended from f-block
elements[1, 8] to early d-block elements[1e, 9±13] and some main
group metals.[14, 15] Recent studies have provided several
routes to lanthanoid pyrazolate complexes with the metals
being in ‡III[6, 16] or ‡II[4, 17] oxidation states. The majority of
structurally characterised rare-earth pyrazolates are hetero-
leptic complexes,[4, 16, 17] consistent with the large size of Lnn‡
which permits coordination of neutral co-ligands, most
commonly derived from the synthesis solvent, giving com-
plexes of general composition [Ln(Rmpz)n(L)x] (R are possi-
ble substituents and L are auxiliary neutral molecules; m ˆ
Introduction
Pyrazolate coordination chemistry[1] has recently received a
major injection of structurally unprecedented and exciting
compounds. Thus several new coordination modes, for
example, i) m3-h1:h2:h1,[2, 3] ii) m-h2:h2,[4] iii) p-h1 (C-bonded),[5, 6]
iv) p-h3 (N2C),[6] v) h5[7] and vi) m3-h1:h1:h1[3] have been
reported since 1997, and greatly enrich the established i) m-
[a] Prof. G. B. Deacon, A. Gitlits
School of Chemistry, Monash University
Victoria, 3800, (Australia)
0 ± 3, n ˆ 2 or 3; e.g., L ˆ DME (1,2-dimethoxyethane)[16e,h, 17]
,
,
Fax : (‡ 61)3-9905-4597
THF (tetrahydrofuran)[4, 16a,b,f,g]
, ,
Ph3PO[16b,f] pyridine[16c]
E-mail: glen.deacon@sci.monash.edu.au
4-tert-butylpyridine[16c,d], n-butylimidazole[6c) ]; ˆ 1 ± 3). Neu-
tral homoleptic complexes [Ln(Rmpz)n] (n ˆ 2 or 3) are of
considerable structural interest, since the metal has to achieve
coordination saturation in the absence of co-ligands, for
example by intra- or inter-molecular interactions with hydro-
carbon ligand fragments, but the sole known examples are in
the preliminary report of the present study.[18]
[b] Dr. P. W. Roesky, Dr. M. R. Bürgstein
Institut für Anorganische Chemie der Universität
Engesserstrasse, Geb. 30.45, 76128 Karlsruhe (Germany)
Fax : (‡ 49) 721-661921
E-mail: roesky@achibm6.chemie.uni-karlsruhe.de
[c] K. C. Lim, Dr. B. W. Skelton, Prof. A. H. White
Department of Chemistry, University of Western Australia
Nedlands WA, 6907 (Australia)
Chem. Eur. J. 2001, 7, No. 1
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127

G. B. Deacon et al.
FULL PAPER
Recently, we have successfully employed the direct reaction
between rare-earth elements and 2,6-diphenylphenol
(HOdpp) at elevated temperatures to yield homoleptic
[Ln(Odpp)n] (n ˆ 2, 3) complexes and the mixed oxidation
state [Ln2(Odpp)3][Ln(Odpp)4].[19, 20] It has now been found
that this simple method can be used to prepare homoleptic
pyrazolate complexes, and a preliminary account of the
synthesis of trivalent, divalent and mixed oxidation 3,5-di-
tert-butylpyrazolatolanthanoid complexes has been given.[18]
We now provide a detailed account of the synthesis of
homoleptic rare-earth (including scandium) 3,5-di-tert-butyl-
pyrazolates [Ln(tBu2pz)n], a structural survey establishing the
effect of metal-ion size and including the remarkable [Eu4-
(tBu2pz)8], which introduces a new mode of pyrazolate
coordination, and the application of the lanthanum complex
as a Tishchenko reaction catalyst.
1808C under vacuum, resulted in incomplete reaction and
some YbIII formation. Attempted metathesis by the reaction
given in Equation (5)
tBu2pzK
C6H14
ꢀ!
Yb‡I2
YbI2
[Yb(tBu2pz)2]
(5)
ꢀ!
C6H14 then PhMe
gave both YbII and YbIII species. The system presented
considerable difficulties owing to the insolubility of most of
the reagents in the non-polar solvents. Further reduction of
the mixed oxidation state 7 was attempted with ytterbium
metal plus mercury in molten 1,2,4,5-tetramethylbenzene at
3008C for a prolonged period, but surprisingly there was no
appreciable reaction. An attempt to oxidise the europium(ii)
complex 6 to [Eu(tBu2pz)3] with tBu2pzH also failed.
Microanalytical data established the composition
[Ln(tBu2pz)3] for the dried complexes 1 ± 5 and 8, and
[Eu(tBu2pz)2] for 6. This is in contrast with the isolation of
complexes 2, 3, 5, and 8 as solvated single crystals of
composition [Ln2(tBu2pz)6] ´ 2PhMe before drying. The struc-
tures of 1 ± 3, 5, 6 and 8 were established by single-crystal
X-ray studies (below). The mass spectra of 1 ± 5 displayed
Results and Discussion
Synthesis: Reaction of 3,5-di-tert-butylpyrazole with an excess
of rare-earth metal, in the presence of mercury, under vacuum
at elevated temperatures without any added solvent, followed
by extraction with hot toluene, crystallisation and drying,
affords the complexes [Sc(tBu2pz)3] (1), [Ln2(tBu2pz)6] (Ln ˆ
La 2, Nd 3, Sm 4, Lu 5), [Eu4(tBu2pz)8] (6) and [Yb2(tBu2pz)5]
(7) in good yields [Eq. (1)].
‡
[Ln(tBu2pz)3] ions with progressive loss of tBu2pz ligands,
and MeH (or Me) fragments (cf. failure to obtain a spectrum
for 3 in the preliminary communication[18]). In some cases,
species of higher molecular weight with tBu2pzH coordinated
were also observed. Both 2 and 3 gave Ln2 containing ions
consistent with their dimeric structures (below), whilst
tetranuclear 6 failed to give metal-containing ions. For 3, 4,
and 8, UV/visible ± near-IR absorptions characteristic[21] of
the appropriate Ln3‡ ions were observed, whilst features
indicative[21] of Eu3‡ species in the UV/visible ± near-IR
spectrum of 6 were absent in THF or xylene. 1H NMR studies
of the trivalent rare-earth complexes 2, 3, 5 and 8 suggested
that the dimeric moieties dissociate in [D8]THF, as a result of
solvent coordination [Eq. (6)], or that rapid exchange occurs
between terminal and bridging pyrazolate ligands, since only
single tBu and H4(pz) resonances were observed.
Hg
ꢀ!
Ln‡ntBu2pzH
[Ln(tBu2pz)n]‡n/2H2
(n ˆ 2, 2.5 or 3)
(1)
Mercury assists by way of metal surface amalgamation/
cleaning, while the molten ligand possibly acts initially as a
solvent until the reaction mixture solidifies. Mercury metal
has been shown previously to be an important component in
these direct syntheses.[19, 20]
This simple synthetic method is generally very versatile in
giving homoleptic complexes of the rare earths in various
oxidation states. However, since the reaction in Equation (1)
yields only the mixed oxidation state complex 7 for Ln ˆ Yb,
alternative routes to homoleptic YbIII and YbII complexes
were sought. Thus, a prolonged redox transmetallation/ligand
exchange reaction in toluene between Yb metal, diphenyl-
mercury and 3,5-di-tert-butylpyrazole was found to give
[Yb2(tBu2pz)6] (8), [Eq. (2)]. With a shorter reaction time,
the mixed oxidation state species 7 was obtained [Eq. (3)].
Oxidation of 7 to 8, on extended reaction [Eq. (4)] may
involve formation and protolysis of [Yb2(tBu2pz)5Ph].
[Ln2(tBu2pz)6]‡4C4D8O
>
2[Ln(tBu2pz)3(C4D8O)2]
(6)
However, in the NMR spectrum of complex 2 in [D6]ben-
zene two H4 resonances and a broadened tBu resonance were
observed, consistent with the preservation of the dimeric
structure in this solvent.
Structural investigations: X-ray structure determinations have
been carried out for the trivalent complexes 1 ± 3, 5, and 8, as
well as divalent 6, augmenting that of the structure of the
mixed valent 7, reported in the preliminary communication.[18]
For the homoleptic trivalent complexes, the full range of rare-
earth ion sizes (from Sc3‡ to La3‡) has been encompassed. In
addition, the structure of the parent 3,5-di-tert-butylpyrazole
has been obtained at low temperature and redetermined (cf.
ref. [22]) at room temperature.
Hg
ꢀ!
Hg
ꢀ!
2Yb‡6tBu2pzH‡3HgPh2
4Yb‡10tBu2pzH‡5HgPh2
[Yb2(tBu2pz)6] (8)‡3Hg‡6PhH
(2)
2[Yb2(tBu2pz)5] (7)‡5Hg‡10PhH (3)
27‡2tBu2pzH‡HgPh2 ꢀ! 28‡Hg‡2PhH
(4)
By contrast with the success in obtaining 8, attempts to
prepare [Yb(tBu2pz)2] were unsuccessful. Thus redox trans-
metallation/ligand exchange between Yb metal, HgPh2 and
tBu2pzH in diethyl ether (sometimes non-coordinating in
crowded systems) gave mainly 7 with some 8, and attempted
desolvation of [Yb2(tBu2pz)4(thf)2][4] in hot toluene, then at
The structure of [Sc(tBu2pz)3] (1): The low-temperature
single-crystal structure of 1 establishes the compound to be
monomeric with one molecule comprising the asymmetric
unit (Figure 1). Three symmetrically chelating h2-pyrazolate
128
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Chem. Eur. J. 2001, 7, No. 1

Rare-Earth Pyrazolates
127±138
[K([18]crown-6)(dme)(h1-PhMe)][Er(h2-tBu2pz)4],[6] the sole
reported homoleptic lanthanoid h2-pyrazolate. Compound 1 is
the first neutral homoleptic, solely h2-bonded, rare-earth
pyrazolate. Values for the N-Sc-N bite angles (Table 1)
correlate well with the ion size, being smaller than that
(43.18(9)8) of the much smaller [Al(tBu2pz)3],[15] comparable
with those (38 ± 418) of [Ti(h2-tBu2pz)4][9] (ionic radius of eight
coordinate Ti4‡ is 0.74 Š)[23] and larger than those (31 ± 358) of
[Ln(R2pz)3L2] complexes[16] and [Er(h2-tBu2pz)4]ꢀ.[6]
The structures of [Ln2(tBu2pz)6] (Ln ˆ La 2, Nd 3, Lu 5, Yb
8): The low-temperature structure determinations of the
complexes 2, 3, 5 and 8 show them to be isolated from toluene
as solvated dimers [Ln2(tBu2pz)6] ´ 2PhMe, all isomorphous.
In Figure 2 (top and middle) the structures for the largest (2)
and the smallest (5) lanthanoid are shown, respectively. Each
dimer is disposed about a crystallographic inversion centre in
Å
space group P1, with Z being one dimeric formula unit with
Figure 1. A single molecule of [Sc(tBu2pz)3] (1) projected quasi-normal to
the putative C3 axis of the quasi D3h coordination environment.
associated solvent per unit cell and Ln(tBu2pz)3 ´ PhMe being
the asymmetric unit. Each lanthanoid ion is eight coordinate
with two terminal h2-pyrazolate ligands and two bridging m-
h2:h2 ligands. The latter binding has only been observed once
previously, namely in [Yb2(tBu2pz)4(thf)2],[4] but the current
four structures suggest that it is of more general significance.
The Ln,N(n1,n2) (n ˆ 2 or 3) planes are quasi-coplanar with
the terminal tBu2pz ligands, as each plane intersects the
corresponding C3N2 plane at 2.5 ± 5.7(1)8. The bridging ligands
lie with the pyrazolate planes quasi-normal to the Ln ´´´ Ln*
axis (* denotes the inversion relation). This is clearly
manifested by the angle between the Ln ´´´ Ln* line and the
C3N2 plane of the bridging ligand (ligand 1; 2 79.2(1); 3
88.03(8); 8 89.14(9); 5 89.24(6)8). Thus ligand 1 is significantly
more tilted in the La complex 2 than in 3, 5 and 8 as is evident
from a comparison of the top and middle structures in
Figure 2. Metal atom deviations d Ln, Ln* (ˆ Ln (1ꢀx, 2 ꢀ y,
2 ꢀ z)) from the bridging ligand C3N2 plane are: 2 1.650(6),
ꢀ2.307(4); 3 1.888(4), ꢀ2.006(4); 8 1.825(5), ꢀ1.859(5); 5
1.819(3), ꢀ1.847(3) Š, and are much more unsymmetrical for
La, though the change is foreshadowed with Nd. Accordingly,
a structural variation appears to be developing for La with
slightly unsymmetrical ligation by the bridging ligands. When
the structure of 2 (Figure 2, bottom) is viewed down the La ´´´
La* axis, it can be seen that there is incomplete overlap
between ligands 3* and 2 and between 2* and 3, whereas the
corresponding pyrazolates are eclipsed in 5. In each case, the
bridging ligands (1, 1*) are twisted to either side. This
presumably results from accommodation of the bulk of the
tert-butyl groups, and is consistent with dodecahedral stereo-
chemistry about the metals.
ligands (Table 1) are coordinated to scandium, with the six
coordinate ScN6 geometry closely trigonal prismatic and the
pyrazolate planes parallel to the putative C3 axis, which in turn
is closely aligned to the crystallographic c axis. Although 1 has
a similar molecular array to those of the recently determined
Table 1. Selected bond geometries of the Sc environment in [Sc(tBu2pz)3]
ꢀ
(1); r is the Sc N bond length [Š], other entries being the angles [8]
subtended at Sc by the relevant atoms at the head of the row and
column.[a]
Atom
r
N(12)
N(21)
N(22)
N(31)
N(32)
N(11) 2.109(1) 38.71(6) 109.03(6) 122.41(6) 106.82(5) 124.50(5)
N(12) 2.107(2)
N(21) 2.115(1)
N(22) 2.105(1)
N(31) 2.100(1)
N(32) 2.126(1)
121.48(6) 107.05(6) 123.27(6) 112.84(6)
38.71(6) 111.35(6) 122.88(6)
127.54(6) 110.57(5)
38.72(6)
[a] Sc-N(n1)-N(n2) are 70.57(8), 70.26(8), 71.64(8)8; Sc-N(n2)-N(n1)
70.73(9), 71.03(8), 69.65(8)8; Sc-N(n1)-C(n5) 178.4(1), 178.0(1), 179.2(1)8;
Sc-N(n2)-C(n3) 178.8(1), 178.7(1), 177.2(1)8 (n ˆ 1, 2, 3). The scandium
deviates from the C3N2 ligand planes by 0.026(3), 0.037(3), 0.027(3) Š.
[M(h2-tBu2pz)3] complexes (M ˆ Al[15] or Ti[13]), it is not
isomorphous with them. In the latter pair, the three ligands
Å
are related by a three-fold axis in space group P3 (cf. P21/c for
ꢀ
1). Nevertheless, the angles between the centres of the N N
bonds [N(n0); e.g., N(10) is the centre of the bond between
N(11) and N(12); (N(10)-Sc-N(20) 118.2; N(10)-Sc-N(30)
120.3; N(20)-Sc-N(30) 121.58; S 360.08] are only slightly
For all complexes, the terminal ligands are symmetrically h2
ꢀ
ꢀ
divergent from 1208, and the Sc N(n0) lengths show little
coordinated with the maximum variation in Ln N(n1) and
ꢀ
variation (average 1.987(4) Š). It is interesting that similar
six-coordination should be maintained over metals varying in
ionic radii by approximately 0.2 Š (Sc3‡, 0.75; Ti3‡, 0.67; Al3‡,
Ln N(n2) (n ˆ 2 or 3) bond lengths of 0.035 Š (Table 2). Each
ꢀ
terminal Ln N bond length decreases by 0.17 ± 0.19 Š from 2
to 5 (Table 2) consistent with a reduction of 0.18 Š in the
radius for eight-coordinate Ln3‡ from La3‡ to Lu3‡.[23] The
average value (1.29 Š) from subtraction of the eight-coordi-
nate ionic radii from the Ln N bond length is at the low end of
the range[16a,b,e,f, 17] 1.27 ± 1.38 Š for heteroleptic pyrazolato-
0.54 Š).[23] Subtraction of appropriate ionic radii from hM Ni
ꢀ
(M ˆ Sc (Table 1), Ti and Al) gives 1.37, 1.37 and 1.38 Š,
respectively, consistent with similar bonding. The value for 1
lies at the upper end of the range 1.27 ± 1.38 for lanthanoid
pyrazolates,[16a,b,e,f, 17] but is close to that (1.35 Š) found in
ꢀ
lanthanoid complexes, by contrast with the Sc complex 1.
Chem. Eur. J. 2001, 7, No. 1
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129

G. B. Deacon et al.
FULL PAPER
Table 2. Selected bond lengths [Š] and angles [8] for complexes
[Ln2(tBu2pz)6] ´ 2PhMe (Ln ˆ La 2, Nd 3, Yb 8 and Lu 5).[a]
2
3
8
5
ꢀ
Ln N(11)
2.593(3)
2.738(4)
2.571
2.638(3)
2.787(3)
2.621
2.462(3)
2.439(3)
2.345
2.454(3)
2.460(2)
2.360
2.555(2)
2.719(3)
2.548
2.556(2)
2.729(2)
2.554
2.403(3)
2.383(2)
2.291
2.395(2)
2.401(2)
2.293
2.422(2)
2.617(4)
2.421
2.415(3)
2.624(3)
2.425
2.301(4)
2.268(3)
2.172
2.269(4)
2.297(3)
2.171
2.411(2)
2.609(2)
2.407
2.404(2)
2.614(2)
2.404
2.286(2)
2.251(2)
2.159
2.262(2)
2.285(2)
2.162
ꢀ
Ln N(12)
ꢀ
Ln N(10)
ꢀ
Ln N(11*)
ꢀ
Ln N(12*)
ꢀ
La N(10*)
ꢀ
Ln N(21)
ꢀ
Ln N(22)
ꢀ
Ln N(20)
ꢀ
Ln N(31)
ꢀ
Ln N(32)
ꢀ
Ln N(30)
Ln ´´´ Ln*
4.0290(5)
3.9011(3)
3.6862(4)
3.6663(2)
N(10)-Ln-N(20)
N(10*)-Ln-N(30)
N(10)-Ln-N(30)
N(10*)-Ln-N(20)
N(20)-Ln-N(30)
N(10)-Ln-N(10*)
N(11)-Ln-N(12)
N(21)-Ln-N(22)
N(31)-Ln-N(32)
N(11*)-Ln-N(12*)
97.0
106.0
142.6
141.6
100.6
78.2
30.5(1)
33.1(1)
32.9(1)
30.0(1)
99.7
101.8
142.5
141.4
100.9
80.2
30.94(8)
34.0(1)
34.0(1)
30.85(8)
100.9
102.0
141.8
140.4
100.1
81.0
32.5(1)
35.9(2)
36.2(2)
32.4(1)
100.8
101.8
142.2
140.8
100.1
80.7
32.67(7)
36.1(1)
35.9(1)
32.65(7)
[a] Asterisked atoms are inversion related. N(n0) is the midpoint of the
ꢀ
bond N(n1) N(n2).
(Figure 2 top). However, chelation is unsymmetrical with
ꢀ
ꢀ
differences between Ln N(11) and Ln N(12) and between
ꢀ
ꢀ
Ln* N(11) and Ln* N(12) of 0.145, 0.15 (2), 0.16, 0.17 (3),
0.20, 0.21 (8), 0.20, 0.21 Š (5), respectively (Table 2), the
increased asymmetry in chelation with reduction in Ln3‡ size
ꢀ
consistent with increased steric strain. Whilst Ln N(11) and
ꢀ
Ln* N(12) show the expected decrease (0.18, 0.17 Š) from 2
ꢀ
to 5, the decrease for Ln N(12) is unusually small (0.13 Š)
and for Ln* N(11) unusually large (0.23 Š). Subtraction of
ꢀ
ꢀ
ionic radii from Ln(Ln*) N(1n) (n ˆ 1 or 2) bond lengths
(Table 2) gives approximately constant values (1.42 ± 1.45 Š)
ꢀ
ꢀ
for Ln(Ln*) N(11), except for La* N(11) (1.48 Š), and near
ꢀ
constant values (1.61 ± 1.63 Š) for Ln(Ln*) N(12), except for
ꢀ
La N(12) (1.58 Š). These data also suggest a developing
structural deviation for 2 (Ln ˆ La). The structural gradation
from Ln ˆ Lu (5) to Ln ˆ La (2), but within the context of the
same overall structure, is particularly evident from nonbond-
ing Ln ´´´ C separations for the bridging pyrazolate ring. Thus,
Ln* ´´´ C(13) (5 3.662(3); 2 3.655(4) Š) and Ln* ´´´ C(15) (5
3.430(2); 2 3.471(2) Š) separations do not show the expected
increase (ca. 0.18 Š) from Ln ˆ Lu to Ln ˆ La, appropriate
for tilting of the ligand towards La* in 2. By contrast, Ln ´´´
C(13) (5 3.672(3); 2 3.888(4) Š) and Ln ´´´ C(15) (5 3.455(2); 2
3.731(4) Š) increase by more than 0.18 Š from Lu to La,
consistent with inclination of the ligand away from La. Tilting
reflects a trend towards increased coordination favoured by
reduced steric crowding with the largest lanthanoid, even
though it does not lead to actual La ´´´ C interactions.
Figure 2. Top: A view of [La2(tBu2pz)6] (2), normal to the La ´´´ La* line.
Middle: Aview of [Lu2(tBu2pz)6] (5), normal to the Lu ´´´ Lu* line. Bottom:
A view of 2 projected down the La ´´´ La* axis; tert-butyl groups removed
for clarity.
For the m-h2:h2 ligands, bridging is highly symmetrical with
Evidence of distinctive features for 2 is also observed
sporadically in the bond angles and interplanar angles,
(Table 2 and (mainly) supplementary data deposited at the
Cambridge Crystallographic Data Centre; see Experimental
ꢀ
differences between Ln ꢀ N(1n) and Ln* N(1n) (n ˆ 1 or 2)
ꢁ0.01 Š for 3, 5, and 8, but slightly larger (ca. 0.05 Š) for 2,
the slight lengthening being on the side of the ligand tilt
130
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Chem. Eur. J. 2001, 7, No. 1

Rare-Earth Pyrazolates
127±138
Section). For example, there is a significant variation in the
intracentroid angles N(10)-Ln-N(20) and N(10*)-Ln-N(30)
between Ln ˆ La and Ln ˆ Nd (Table 2), but not for the
related N(10)-Ln-N(30) and N(10*)-Ln-N(20) angles. Values
for the N(n1)-Ln-N(n2) bite angles (Table 2) show the
expected (see discussion of 1) increase with decrease in
lanthanoid ion size for both bridging and terminal pyrazolate
ligands.
atoms have four apparent m-h2:h2 ligands. Although the
precision of the determination is inferior to that of the
dimers, as a consequence of the considerable substituent
disorder, the structure is of major interest because of its
novelty in pyrazolate coordination. The molecule is centro-
symmetric, one half of the [Eu4(tBu2pz)8] unit comprising the
asymmetric unit. Effectively it is a dimer of dinuclear units
[{Eu2(tBu2pz)4}2]. Bridging ligand 1 and the symmetry related
1* are disordered (Figure 3 top and middle) over two possible
positions with equal occupancy. Figure 3 (bottom) shows both
disordered components of 1 and 1* situated between Eu(1)
and Eu(1*); considerable crowding is observed.
The bridging ligands 2 and 3 are almost coplanar with the
plane defined by Eu(1),N(n1,n2) (n ˆ 2 or 3), respectively,
(deviations 0.26(2), 0.15(2) Š, respectively) in the same way
that terminal ligands 2 and 3 of [Ln2(tBu2pz)6] are near
coplanar with Ln,N(n1,n2) (n ˆ 2 or 3) planes (Figure 2 top
and middle). Furthermore, none of the bridging pyrazolate
ligands of 6 is perpendicular to the Eu4 axis; ligands 1, 1', 2 and
3 are substantially inclined at angles of 62.4(5), 60.9(6), 47.2(4)
and 46.1(3)8, respectively.
The structure of [Eu4(tBu2pz)8] (6): The low-temperature
structure determination of complex 6 establishes it to be a
linear tetranuclear species (Figure 3 top and middle) with the
outer Eu atoms coordinated by one terminal (h2) and two (at
first sight) m-h2:h2-pyrazolate ligands, whilst the inner Eu
Bridging ligands 2 or 3 are inclined towards Eu(2) and away
from Eu(1), whilst the disordered components, ligands 1 and
1' (Figure 3 top and middle) are tilted towards Eu(1*) and
away from Eu(1). Ligands 1*, 1*' have inverse behavior. The
ꢀ
Eu Nbr bond lengths cover a wide range (2.38(1) ± 2.95(1) Š;
ꢀ
Tables 3 ± 5), the shortest surprisingly being less than Eu Nter
(2.429(6), 2.493(6) Š). Bridging is unsymmetrical with longer
bond lengths to the Eu atom towards which the ligand tilts
(Tables 3 ± 5), and greater asymmetry is associated with
ligands 1, 1' than with 2 or 3. As a consequence of the
inclination of the pyrazolate ligands, there are close contacts
between pyrazolate ring carbons and the Eu atoms towards
which the ligands tilt (Table 3). Many of these can be argued to
be bonding interactions (below), and their formation in
response to coordination unsaturation and the relatively large
size of Eu2‡ (the radius for six-coordination corresponds to
Table 3. Selected molecular geometries for the europium environment of
[Eu4(tBu2pz)8] (6).
Eu(1)
r [Š]
Eu(1*)
r [Š]
Eu(2)
r [Š]
N(11)
N(12)
N(11')
N(12')
N(21)
N(22)
N(31)
N(32)
N(10)
N(10')
N(20)
N(30)
Eu(1*)
Eu(2)
2.38(1)
2.46(2)
2.47(2)
2.41(2)
2.65(1)
2.59(1)
2.603(8)
2.59(1)
2.32
2.34
2.52
2.50
3.9327(8)
3.9035(7)
N(11)
N(12)
C(13)
C(14)
C(15)
N(11')
N(12')
C(13')
C(14')
C(15')
N(10)
N(10')
2.95(1)
2.74(1)
3.14(1)
3.54(1)
3.44(2)
2.82(1)
2.92(1)
3.36(1)
3.47(2)
3.21(2)
2.76
N(21)
N(22)
C(23)
C(24)
C(25)
N(31)
N(32)
C(33)
C(34)
C(35)
N(41)
N(42)
N(20)
N(30)
N(40)
2.749(9)
2.737(9)
3.12(1)
3.32(2)
3.16(1)
2.734(9)
2.74(1)
3.03(2)
3.24(1)
3.08(1)
2.429(6)
2.493(6)
2.64
2.78
2.64
2.36
[a] Primed and unprimed atoms with the same number are equally
occupied disordered components, as shown in Figure 3. Asterisked atoms
are related by inversion. [b] r is the distance from the europium atom at the
head of the column to the following atoms. Non-bonding distances are
Figure 3. Top and middle: [Eu4(tBu2pz)8] (6); the two deconvoluted
components devoid of their tBu substituents. Bottom: The ligand environ-
ment between Eu(1) and Eu(1*) viewed down the Eu(1) ´´´ Eu(1*) line,
both disordered components of ligand 1 and 1* being shown.
ꢀ
ꢀ
given in italics. Eu N(n0) is the distance to the N(1) N(2) centre of
pyrazolate n.
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131

G. B. Deacon et al.
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Table 4. Selected bond angles for the europium environment of [Eu4-
(tBu2pz)8] (6).
(Cen ˆ centroid of the pyrazolate ring) vectors intersect the
ligand 2 and 3 ring planes at angles of 87.8(4) and 84.6(3)8,
respectively, close to the 908 optimum for p bonding. The
same ligands are nearly coplanar with the Eu(1),N(n1,n2)
(n ˆ 2 or 3) plane (above), indicative of a s-h2-tBu2pz-Eu(1)
interaction. Thus ligands 2 and 3 bind m-h5:h2 to Eu(2) and
Eu(1), illustrating a new type of pyrazolate coordination.
(Alternatively the bridging of ligands 2 and 3 to Eu(2) could
be described as p-h2-N2‡p-h3-C3). The {Eu(1)(tBu2pz)2} unit
forms an h5-sandwich with Eu(2), which also has a terminal h2-
pyrazolate.
N(11)-Eu(1)-N(12)
N(11')-Eu(1)-N(12')
N(21)-Eu(1)-N(22)
N(31)-Eu(1)-N(32)
N(10)-Eu(1)-N(10*)
N(10)-Eu(1)-N(20)
N(10)-Eu(1)-N(30)
N(10')-Eu(1)-N(20)
N(10')-Eu(1)-N(30)
N(20)-Eu(1)-N(30)
N(10')-Eu(1)-N(10'*)
33.7(6)
33.1(4)
31.2(3)
31.9(3)
55.9
100.6
134.0
142.1
93.2
N(10'*)-Eu(1)-N(20)
N(10'*)-Eu(1)-N(30)
N(11)-Eu(1*)-N(12)
N(11')-Eu(1*)-N(12')
N(21)-Eu(2)-N(22)
N(31)-Eu(2)-N(32)
N(41)-Eu(2)-N(42)
N(20)-Eu(2)-N(30)
N(30)-Eu(2)-N(40)
113.3
159.6
28.3(5)
28.0(4)
29.8(3)
30.3(3)
32.6(3)
78.9
137.6
83.9
80.0
Similar evaluation of the Eu(1*) ´´´ C interactions in con-
[a] Primed and unprimed atoms with the same number are equally
occupied disordered components, as shown in Figure 3. Asterisked atoms
are related by inversion.
ꢀ
junction with the Eu(1,1*) N bond lengths suggests that
Eu(1*) is (minimally) p-h3-(N,N,C)-bonded by ligand 1 and p-
h4-(N2C2)-bonded by ligand 1'. (Both could be viewed as p-h5-
bonded with a more generous view of Eu ´´´ C interactionsÐ
Table 5. Interplanar dihedral angles (q [8]) for [Eu4(tBu2pz)8] (6).[a]
ꢀ
see also below). Consistent with this, Eu(1*) Cen(1,1') makes
Plane
n ˆ 1
n ˆ 1'
n ˆ 2
n ˆ 3
n ˆ 4
angles of 81.0(5) and 84.9(5)8 with the ligand 1 and 1' planes.
Accordingly ligands 1 and 1' bind m-h2:h3 and m-h2:h4
respectively to Eu(1*). The latter form is new, but the former
has been recently observed in [KEr(tBu2pz)4]n.[6] Given the
D
1
1'
2
72.8(5)
(72.8(5))
34.3(8)
49.3(4)
58.3(7)
24.9(7)
46.1(3)
34.5(6)
66.0(7)
86.1(5)
7.3(3)
70.9(6)
74.9(7)
52.7(5)
41.4(4)
ꢀ
ꢀ
very short Eu(1) N(11,12) and Eu(1) N(11',12') binding and
the not overlarge displacement of Eu(1) from the 1 and 1'
ligand planes (0.50(3), 0.39(3) Š), the h2-bonding can be
viewed as essentially s-h2-(N2).
3
[a] N(41,42), C(43,44,45), Eu(2), Eu(1) with inverses are taken as the
reference plane D (c2 ˆ 4277); other planes n are the C3N2 pyrazolates.
Subtraction of ionic radii for six- and eight-coordinate Eu2‡
from Eu(2) ´´´ C and Eu(1*) ´´´ C distances, respectively, gives
the residual values listed in Table 6. The bulk of the values fall
within the upper limit ꢁ2.16 Š suggested for p-arene ´´´ Ln
bonding from consideration of a wide range of structures.[30]
Moreover it can be suggested that the values (Table 6) are
overestimated as the coordination numbers of six and eight
for Eu(2) and Eu(1*) are actually higher owing to Eu ´´´ C
interactions. Under these circumstances, some consideration
that for eight- coordinate La3‡)[23] is considered to account for
the tilting of the pyrazolate ligands.
All the proposed Eu ´´´ C bonding interactions (Eu(2):
3.03(2) ± 3.32(2); Eu(1): 3.14(1) ± 3.36(1) Š; Table 3) lie well
within the sum (3.8 Š) of the metallic radius (pseudo
van der Waals radius) of Eu (2.06 Š)[24] and the van der Waals
radius of an aromatic ring (1.73 Š).[25] Additional contacts to
Eu(1) in the range 3.44(1) ± 3.54(1) also meet this criterion,
but are viewed as more marginal in their interaction (see
ꢀ
could also be given to viewing the Eu(1*) C(14,15,14')
ꢀ
contacts as weakly bonding.
below). All are somewhat longer than hEu Ci (2.83 and
3.00 Š, respectively) of the naphthalenide dianion bridged
[(Eu(dme)2I)2(m-h4:h4-C10H8)][26] and the indisputably p-arene
bonded [Eu(h6-C6Me6)(AlCl4)2]4,[27] but this is not unreason-
able for intramolecular hp-tBu2pz-Ln interactions. In [Eu2-
(Odpp)4] (Odpp ˆ 2,6-diphenylphenolate), intramolecular p-
Ph ´´´ EuII coordination with Eu ´´´ C interactions 2.987(4) ±
3.240(4) Š has been established for formally three and four
coordinate Eu2‡.[19] A higher limit, consistent with the current
proposals, would be expected for formally six and eight
coordinate Eu2‡. In [{Eu{1,3-(SiMe3)2C5H3}2}1], a formally six
coordinate Eu2‡ ion forms intermolecular (agostic) Eu ´´´
C(Me) interactions of about 3.09 ± 3.30 Š[28], similar to those
currently observed. Also relevant to 6, dimeric [{La(OAr)2(m-
[O:h6-Ar]-OAr)}2] (Arˆ 2,6-iPr2C6H3) is held together by h6-
Ar´´´ La p interactions of 2.979(10) ± 3.164(9) Š[29], and six-
coordinate La3‡ is 0.14 and 0.22 Š smaller than six- and eight-
coordinate Eu2‡, respectively.[23] Thus the proposed Eu ´´´ C
interactions (Table 3 ± 5) are in accord with reported intra-
and intermolecular p-arene ± Ln interactions. With the
Table 6. Residual values [Š] obtained by subtraction of the ionic radius[23]
for six-coordinate Eu2‡ (for Eu(2)) and eight-coordinate Eu2‡ (for Eu(1*))
from Eu ´´´ C distances of 6. Non-bonding distances are given in italics.
Contact
Residual value
Contact
Residual value
Eu(2) ´´´ C(23)
Eu(2) ´´´ C(24)
Eu(2) ´´´ C(25)
Eu(2) ´´´ C(33)
Eu(2) ´´´ C(34)
Eu(2) ´´´ C(35)
1.95
2.15
1.99
1.86
2.07
1.91
Eu(1*) ´´´ C(13)
Eu(1*) ´´´ C(14)
Eu(1*) ´´´ C(15)
Eu(1*) ´´´ C(13')
Eu(1*) ´´´ C(14')
Eu(1*) ´´´ C(15')
1.89
2.29
2.19
2.11
2.22
1.96
The terminal ligand 4 is almost parallel (4.7(3)8) to Eu4, and
the bonding to Eu(2) is more unsymmetrical (Table 3)
ꢀ
(Eu(2) N(41), N(42) differ by 0.064 Š) than for the terminal
ligands in 2, 3, 5 and 8. Subtraction of the ionic radius for
six-coordinate Eu2‡ from hEu(2) N(4n)i gives 1.29 Š, which
ꢀ
ꢀ
Eu(2) ´´´ C interactions added to the long Eu(2) N(n1) and
is at the low end of the range (1.27 ± 1.38 Š) for hetero-
leptic lanthanoid complexes,[16a,b,e,f, 17] but in keeping with the
ꢀ
Eu(2) N(n2) (n ˆ 2 or 3) bonds, it is proposed that ligands 2
and 3 are p-h5-bonded to Eu(2), in addition to their stronger
value derived from hLn Nteri of [Ln2(tBu2pz)6] complexes
ꢀ
2
ꢀ
h -bonding to Eu(1). Consistent with this, the Eu(2) Cen
(above).
132
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Chem. Eur. J. 2001, 7, No. 1

Rare-Earth Pyrazolates
127±138
Comparison of the structures of complexes 6, 7, and 8:
Relationships are evident between the structures of 6, 8, and
that of the mixed oxidation state complex 7 (shown without
the tBu groups for simplicity), reported in the preliminary
communication.[18]
about 153 K, the NH hydrogen can be resolved and refined
over two sites corresponding to association with either
nitrogen, occupancies 0.74(3)/0.75(3) (two different crystals)
and complements, but with rotational disorder only resolvable
in tert-butyl 5 (see Figure 4 for numbering scheme), occupan-
cies of the two sets of sites being 0.614(5)/0.609(6) and their
In complex 8, each Yb has two terminal (h2) and two
bridging (m-h2:h2) pyrazolate ligands, and YbIII of 7 has a
similar environment. Likewise, there are one terminal and
two bridging pyrazolates attached to the outer Eu atoms of 6
and YbII of 7. Accordingly, replacement of a terminal
{YbIII(h2-tBu2pz)2} moiety of 8 by {YbII(h2-tBu2pz)}, analogous
to an {Eu(h2-tBu2pz)} unit of 6, gives the structure 7. However,
the mode of attachment of the terminal {LnII(h2-tBu2pz)}
group differs in 6 and 7. In the latter, {YbII(h2-tBu2pz)} is h2-
bonded to two m-h2:h2 pyrazolates, each inclined at 59.0(3)8 to
the YbII ´´´ YbIII line, and there is the possibility of very weak
interactions of C(3) and C(5) of the pyrazolates with YbII. By
contrast, the terminal {Eu(h2-tBu2pz)} units of 6 are each h5-
sandwiched by two m-h5:h2-pyrazolate ligands, which are
inclined at 47.2(4) and 46.1(3)8 to the Eu4 line. The terminal
Figure 4. The tBu2pzH dimer, determined at room temperature, showing
the disorder of 3- and 5-tBu groups and the NH hydrogens.
complements. Any disorder of tert-butyl 3 is on a scale not
permitting resolution, presumably no more than a few
percent. At about 300 K, our unit cell dimensions agree
closely with those reported,[22] presumptively at Tˆ 295 K. In
the present work, the tert-butyl 5 component and hydrogen
site occupancies (major components, in correspondence for all
experiments in assignment) were 0.566(9) and 0.57(5). Only
the former value is not significantly different from previous
data (0.60(4)/0.9-error unspecified).[22] Furthermore, it is also
found that tert-butyl 3 dispositions are now resolvable over two
sets of sites, occupancies 0.879(5) and its complement (Fig-
ure 4).
Thus from 153 K to room temperature, disorder in tert-
butyl 5 increases so that occupancy of the major component
falls from 0.614(5) to 0.566(9), a significant difference in the
present experiments. Similarly, the occupancy of the major
component of disorder in tert-butyl 3 falls from about 1 to
0.879(5), seemingly a greater change and, at the least, likely to
be a contributing component to the NMR behaviour, which
was interpreted[22] solely in terms of a change in tert-butyl 5
disorder.
ꢀ
Yb N bond lengths of 8 (Table 2) are comparable with
YbIII Nter (2.287(7), 2.270(7) Š) of 7,[18] whilst subtraction of
ꢀ
0.15 Š, the difference in the six coordinate ionic radius
2‡
between Eu2‡ and Yb , from terminal Eu(2) N(41,42) bond
ꢀ
lengths (Table 3) of 6 gives 2.28 and 2.34 Š, similar to
Yb Nter (2.334(7) Š) of 7.[18] In 7, the two bridging YbIII
bond lengths (2.402(8), 2.425(8) Š) are close to the shorter of
II
ꢀ
ꢀ
N
ꢀ
the bridging Yb N bond lengths of 8, but about 0.2 Š less
than the longer ones (Table 2). Further, subtraction of 0.15 Š
ꢀ
from hEu(2) N(21,22,31,32)i gives 2.47 Š, a value that is
II
ꢀ
significantly smaller than that for Yb Nbr (2.534(8),
2.587(8) Š) of 7, indicating weaker attachment to Yb than
Eu, probably as a consequence of sharing the bridging tBu2pz
with the more Lewis acidic YbIII.
Ligand tBu2pzH: The structural studies of the complexes were
complemented by determination of the structure of 3,5-di-
tert-butylpyrazole at 153 K, and a reinvestigation of the
structure at room temperature with higher precision than
recently reported[22] (recorded as at 295 K in the Cambridge
Data Base). The results of an accompanying variable-temper-
ature solid-state NMR study were rationalised in terms of the
population of conformers differing in NH hydrogen disposi-
tions between pairs of centrosymmetrically related pairs of
molecules, and of occupancy of two sets of rotationally related
tert-butyl 5 sites, by thermal excitation.[22] In our structure at
Comparison with the ligand dimensions of complex 1
ꢀ
(Table 7) shows N N bond lengthening in the complex with
consistent changes in the N-based angles. A significant
asymmetry, of consistent magnitude through the more precise
determinations, and seemingly unaffected by disorder, is
found in the exocyclic angles to the either side of the bonds to
the pendants at C(3,5).
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133

G. B. Deacon et al.
FULL PAPER
Table 7. Comparison of ligand geometries [bond lengths in Š and angles in 8] of tBu2pzH and 1.
tBu2pzH
1
153 K
1.365(1)
1.344(1)
1.338(1)
1.404(1)
1.385(1)
300 K[a]
1.364(2)
ligand 1
1.397(2)
ligand 2
1.399(2)
ligand 3
1.402(2)
1.338(2)
1.347(2)
1.393(3)
hSci
1.399(2)
N(1)-N(2)
N(1)-C(5)
N(2)-C(3)
C(3)-C(4)
C(4)-C(5)
ꢀ
ꢀ
1.339(2)
1.336(2)
1.391(3)
1.380(3)
1.343(2)
1.342(2)
1.391(3)
1.396(3)
1.343(2)
1.342(2)
1.393(3)
1.399(2)
1.343(2)
1.395(3)
1.395(3)
ꢀ
C(5)-N(1)-N(2)
N(1)-N(2)-C(3)
N(2)-C(3)-C(4)
N(1)-C(5)-C(4)
C(3)-C(4)-C(5)
N(1)-C(5)-C(51)
C(4)-C(5)-C(51)
N(2)-C(3)-C(31)
C(4)-C(3)-C(31)
112.71(8)
104.89(8)
110.43(9)
109.95(9)
106.02(9)
122.36(9)
131.7(1)
111.4(3)
108.0(1)
108.1(1)
108.4(1)
108.1(1)
106.0(1)
109.6(2)
106.4(2)
106.6(2)
122.3(2)
131.35(2)
120.5(2)
129.9(2)
108.2(1)
108.9(2)
108.6(2)
106.3(3)
120.9(2)
130.3(2)
120.9(2)
130.2(2)
108.2(1)
108.7(1)
108.6(2)
106.4(2)
121.7(1)
129.7(2)
120.7(2)
130.5(1)
107.7(1)
108.8(2)
108.7(2)
106.4(2)
121.1(2)
130.2(2)
121.9(2)
129.2(2)
ꢀ
108.7(1)
106.4(1)
121.2(3)
130.1(3)
121.2(5)
130.0(6)
120.22(9)
129.34(9)
[a] Same crystal as for the measurement at 153 K.
Table 8. Tishchenko reaction with 2 as catalyst.[a]
reactant product tof/
La atom
[hꢀ1
Catalytic studies: Compound 2 was also examined as catalyst
in the Tishchenko reaction (or Claisen ± Tishchenko reac-
tion),[31] the dimerization of aldehydes to form the corre-
sponding carboxylic ester [Eq. (7)], normally carried out with
aluminium alkoxides as homogeneous catalysts.[32±34]
conversion in
NMR scale
[%][a]
]
R
R
(7)
1
2
3
4
5
phenyl
4.2
< 1
±
±
±
quant.
87
22
16
±
4-fluorophenyl
4-chlorophenyl
4-bromophenyl
4-methylthiophenyl
4-methoxy
The reaction has been known for about a century[31] and its
industrial importance is mirrored in numerous patents.[32, 33]
Thus the Tishchenko ester of 3-cyclohexenecarbaldehyde is
the precursor for the formation of environmentally durable
epoxy resin,[32] and benyzl benzoate is used as chewing gum
flavor and in the perfume industry for the production of
mochus.[35] Recently, it was shown the lanthanoid complexes
[(C5Me5)2LaCH(SiMe3)2][36] and [Ln{N(SiMe3)2}3][37] are high-
ly active Tishchenko reaction catalysts. With high Lewis
acidity and easy interchangeability of the ligand sphere, the
compounds [Ln{N(SiMe3)2}3] have a number of further
advantages such as ready accessibility (the yttrium compound
is available commercially), environmentally benign metals,
the highest reported activities, and high durability of the
catalysts.
The catalytic properties of 2 (Ln ˆ La) in the Tishchenko
reaction were compared with those of [La{N(SiMe3)2}3], the
most active of the silylamide catalysts. Various benzaldehydes
as well as some aliphatic aldehydes were used to assay the
efficacy of 2 as a precatalyst. The reaction rates for some
selected substrates and the yields for all substrates were
determined by NMR spectroscopy in [D6]benzene with
approximately 5 mol% catalyst at 218C (Table 8). Turnover
frequencies (tof) were determined from a turnover of 50%
and the large range of applications of 2 is also given in Table 8.
It can be seen from entry 1, that benzaldehyde is converted to
benzyl benzoate in quantitative yield, but, in comparison with
[La{N(SiMe3)2)}3],[37] at moderate rates. On the other hand the
yields are significantly higher than those reported recently for
ªhigh-speedº aluminum-based catalysts.[38] In contrast the
aliphatic aldehydes (entry 7 ± 10) and o-phthalaldehyde (en-
try 11) are converted in quantitative yields with extremely
6
±
±
7
8
9
10
i-propyl
t-butyl
3-cyclohexenyl
cyclohexyl
> 1500
±
> 1500
> 1500
quant.
96
quant.
quant.
11
±
quant.
[a] 218C; 5 mol% 2 in [D6]benzene.
high tofs. These data are comparable with those for [La-
{N(SiMe3)2}3].[37]
Since lanthanoid catalysts are sometimes inhibited by
heteroatoms, substituted benzaldehydes were used as sub-
strates to determine the tolerance of 2 to functional groups. To
exclude the steric influence of the substituents, para-substi-
tuted benzaldehydes were chosen as substrates (Table 8,
entries 2 ± 6). It can be seen from Table 8 that halogen
substituents on the substrate decrease the yield and the
turnover compared with the unsubstituted reactants. When
the heteroatoms O and S are present, no Tishchenko reaction
takes place. Presumably these atoms coordinate to the
catalyst and hamper the catalytic activity. As observed for
benzaldehyde, the tofs for 2 as a catalyst for substituted
benzaldehydes (Table 8) are lower than those observed for
[La{N(SiMe3)2}3].[39]
Structural and steric factors appear to contribute to the
lower reactivity of 2 than [La{N(SiMe3)2}3]. Thus, 2 retains a
134
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0947-6539/01/0701-0134 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 1

Rare-Earth Pyrazolates
127±138
Preparation of [Sc(tBu2pz)3] (1):
A
mixture of Sc chunks (0.36 g,
dimeric structure in [D6]benzene (above), the reaction
solvent, and substrate-induced dissociation of 2 into a
monomer is probably a necessary prelude to catalytic activity.
By contrast [La{N(SiMe3)2}3] is monomeric and is less
hindered, despite the size of the N(SiMe3)2 groups, than
dimeric 2, which has four bulky tBu2pz around each La
(Figure 2, top). Moreover, catalysis by [La{N(SiMe3)2}3]
involves complete loss of the ligand sphere, a less likely
occurrence with the bidentate tBu2pz donors. Of the two
compounds, HN(SiMe3)2 and tBu2pzH, produced by ligand
loss, the latter will compete for coordination sites on La,
unlike the former.
8.0 mmol), tBu2pzH (0.72 g, 4.0 mmol) and mercury metal (2 drops) was
heated in a sealed tube at 2208C and then at 2508C for a total of 39 h. The
product partly sublimed in the tube as colourless single crystals suitable for
X-ray crystal structure determination. The bulk product was extracted with
hot toluene (80 mL). Evaporation to 10 mL and cooling to ambient
temperature for several hours gave colourless microcrystalline 1, which was
dried under vacuum at 1008C for 2 h. Yield: 0.49 g (63%); m.p. 165 ±
1688C; IR: nÄ ˆ 1527 (s), 1503 (s), 1416 (s), 1361 (s), 1313 (m), 1252 (s),
1230 (s), 1206 (m), 1114 (w), 1057 (s), 1020 (s), 972 (s), 823 (w), 802 cmꢀ1
‡
(s); MS (70 eV, EI): m/z (%): 582 (27) [Sc(tBu2pz)3] , 567 (45)
‡
‡
[Sc(tBu2pz)3 ꢀ Me] , 403 (12) [Sc(tBu2pz)2] , 387 (27) [Sc(tBu2pz)2 ꢀ
‡
‡
MeH] , 371 (8) [Sc(tBu2pz)2 ꢀ 2MeH] , 276 (6) [Sc(tBu2pz)2 ꢀ 2C4H8 ꢀ
‡
‡
‡
Me] , 180 (25) [tBu2pzH] , 165 (100) [tBu2pzH ꢀ Me] ; 1H NMR
([D8]THF): d ˆ 1.20 (s, 54H; tBu), 6.07 (s, 3H; H4);
1H NMR([D6]benzene): d ˆ 1.39 (s, 54H; tBu), 6.35 (s, 3H; H4); 13C
{1H}NMR ([D8]THF): d ˆ 159.16 (C3,5), 103.19 (C4), 32.62 (C(CH3)), 31.65
(C(CH3)); elemental analysis calcd (%) for C33H57N6Sc (582.81): C 68.00, H
9.86, N 14.42, Sc 7.71; found C 67.74, H 9.66, N 14.58, Sc 7.62.
Conclusion
Preparation of [La2(tBu2pz)6] (2): A mixture of La powder (1.12 g,
8.1 mmol), tBu2pzH (0.72 g, 4.0 mmol) and mercury metal (2 drops) was
heated in a sealed tube at 2208C for 24 h. The reaction mixture was
extracted twice with hot toluene (70 and 50 mL) to give a colourless
solution, which was reduced in volume under vacuum. Colourless single
crystals of [La2(tBu2pz)6] ´ 2PhMe appeared in a few hours and were
collected for structure determination. Further evaporation gave the bulk
product which was dried at 808C under vacuum affording the unsolvated
complex. Yield: 0.51 g (57%); IR: nÄ ˆ 1521 (s), 1503 (s), 1412 (s), 1361 (s),
1305 (m), 1252 (s), 1220 (s), 1204 (m), 1018 (s), 1007 (m), 982 (s), 813 (m),
793 cmꢀ1 (s); MS (70 eV, EI): m/z (%): 791 (10) [La(tBu2pz)3(tBu2pzH) ꢀ
The direct reaction between lanthanoid metals and 3,5-di-tert-
butylpyrazole is an effective and simple route to homoleptic
rare-earth pyrazolates. For the trivalent complexes, the small-
est metal (Sc) gives a monomer with solely h2-pyrazolates,
whereas the lanthanoids give dimers, [{Ln(h2- tBu2pz)2(m-
h2:h2-tBu2pz)}2], regardless of metal ion size. Nevertheless,
some structural deviations are evident with the largest
lanthanoid. The novel tetranuclear structure observed for
[Eu4(tBu2pz)8] introduces the new pyrazolate coordination
modes m-h5:h2 and m-h4:h2 and also includes the rarely
observed m-h3:h2 ligation. Tishchenko reaction catalysis is
effected by the La complex 2.
‡
‡
4MeH ꢀ H] , 775 (4) [La(tBu2pz)3(tBu2pzH) ꢀ 5MeH ꢀ H] , 739 (14)
‡
‡
[La2(tBu2pz)3 ꢀ 4Me ꢀ MeH] , 723 (4) [La2(tBu2pz)3 ꢀ 4Me ꢀ 2MeH] ,
‡
‡
676 (14) [La(tBu2pz)3] , 661 (12) [La(tBu2pz)3 ꢀ Me] , 497 (24)
‡
‡
[La(tBu2pz)2] , 481 (27) [La(tBu2pz)2 ꢀ MeH] , 465 (8) [La(tBu2pz)2 ꢀ
2MeH] , 180 (20) [tBu2pzH] , 165 (100) [tBu2pzH ꢀ Me] ; 1H NMR
‡
‡
‡
1
([D8]THF): d ˆ 1.23 (s, 108H; tBu), 6.11 (s, 6H; H4); H NMR ([D6]ben-
zene): d 1.31 (brm, 108H; tBu), 6.24 (s, 4H; H4 pzter), 6.47 (s, 2H; H4 pzbr);
elemental analysis calcd (%) for C66H114La2N12 (1353.49): C 58.56, H 8.49,
La 20.53, N 12.42; found C 58.67, H 8.45, La 20.59, N, 12.69.
Experimental Section
Preparation of [Nd2(tBu2pz)6] (3): Details of the preparation and
characterisation, apart from X-ray crystallography, melting point, and the
mass spectrum which could not previously be obtained, are given in the
preliminary communication.[18] M.p.: 263 ± 2648C; MS (70 eV, EI): m/z (%):
General: Homoleptic lanthanoid pyrazolates are extremely air and water
sensitive, hence all operations were carried out in an inert atmosphere
1
(purified Ar or N2). H and 13C chemical shifts are referenced to internal
‡
‡
681 (12) [Nd(tBu2pz)3] , 666 (22) [Nd(tBu2pz)3 ꢀ Me] , 500 (27)
solvent resonances and reported relative to SiMe4.
‡
‡
[Nd(tBu2pz)2 ꢀ 2H] , 486 (30) [Nd(tBu2pz)2 ꢀ MeH] , 470 (12)
Preparative studies: Handling methods, analytical procedures, and solvent
purifications were generally as described previously.[20, 40] Diethyl ether was
purified as described previously for THF,[40] and [D8]THF was purified,
transferred, and stored as described previously for [D6]benzene.[20] Low
solubility precluded 13C NMR examination of 2 in [D6]benzene, in which
the dimeric nature is maintained. IR data (4000 ± 650 cmꢀ1) are for
compounds as Nujol mulls. Each listed m/z value for metal-containing
ions (where the metal has more than one isotope) is the most intense peak
of a cluster with an isotope pattern in good agreement with the calculated
pattern. Lanthanoid metals were obtained as powders or chunks from
‡
‡
[Nd(tBu2pz)2 ꢀ 2MeH] ,
354
(55)
[Nd2pz ꢀ H] ,
326
(28)
‡
‡
‡
[Nd(tBu2pzH)H2] , 180 (20) [tBu2pzH] , 165 (100) [tBu2pzH ꢀ Me] ;
owing to the 13C contribution to a multicarbon molecule, ions containing
144Nd (and 142Nd13C2) are the most intense peaks of some neodymium-
containing clusters.
Preparation of [Sm2(tBu2pz)6] (4): A mixture of Sm powder (1.50 g,
10.0 mmol), tBu2pzH (0.54 g, 3.0 mmol) and mercury metal (2 drops) was
heated in a sealed tube under vacuum at 200, 220 and then 2508C for a total
of 90.5 h. Work up as for 2 and crystallisation for several days gave
colourless crystals, which were dried as for 2, to give 4. Yield: 0.39 g (57%);
IR: nÄ ˆ 1523 (m), 1506 (s), 1414 (m), 1362 (s), 1303 (w), 1253 (s), 1224 (s),
1204 (w), 1018 (m), 1006 (w), 979 (s), 809 (s), 796 cmꢀ1 (s); MS (70 eV, EI):
Ã
either Rhone-Poulenc, Phoenix (USA) or Johnson-Mattey Rare Earth
Products (REACTON Grade). 3,5-Di-tert-butylpyrazole was synthesised[41]
by treating 2,2,6,6-tetramethyl-3,5-heptanedione with an equimolar
amount of hydrazine hydrate in refluxing ethanol. The pyrazole was then
recrystallised from acetone/light petroleum. The dimeric complexes 2 ± 5,
tetranuclear 6 and the mixed oxidation state complex 7 melt above 2208C,
as the reaction mixtures giving these compounds solidified at 2208C or
higher. Specific values are given for 1, 3 (representative dimer) and 6.
‡
‡
m/z (%): 689 (17) [Sm(tBu2pz)3] , 674 (29) [Sm(tBu2pz)3 ꢀ Me] , 510 (20)
‡
‡
‡
[Sm(tBu2pz)2] , 494 (19) [Sm(tBu2pz)2 ꢀ MeH] , 331 (9) [Sm(tBu2pz) ] ,
‡
‡
315 (18) [Sm(tBu2pz) ꢀ MeH] , 181 (21) [tBu2pzH2] , 165 (100)
‡
[tBu2pzH ꢀ Me] ; UV/Vis/near IR (THF): lmax (e) ˆ 362 (16), 374 (19),
404 (14), 944 (8), 1063 (14), 1072 (16), 1085 (16), 1107 (10), 1227 (33), 1256
(sh, 12), 1361 nm (21); elemental analysis calcd (%) for C66H114N12Sm2
(1376.49): C 57.59, H 8.35, N 12.21, Sm 21.85; found C 57.45, H 8.18, N 12.28,
Sm 21.97.
Catalytic studies: Flamed Schlenk-type glassware either on a dual manifold
Schlenk line or interfaced to a high vacuum line (10ꢀ4 torr), or a Braun dry
box was used. Diethyl ether and THF were purified over sodium and
distilled under N2 from Na/K/benzophenone, whilst toluene and pentane
were distilled from LiAlH4. All solvents for vacuum line manipulations
were stored in vacuo over LiAlH4 in resealable flasks. Deuterated solvents
(Aldrich 99 atom% D) were degassed, dried, and stored in vacuo over Na/
K alloy in resealable flasks. NMR spectra were recorded on a Bruker
AC250 instrument. All organic substrates were from Aldrich.
Preparation of [Lu2(tBu2pz)6] (5):
A mixture of Lu grains (1.05 g,
6.0 mmol), tBu2pzH (0.54 g, 3.0 mmol) and mercury metal (2 drops) was
heated in a sealed tube at 2508C and then 2708C for a total of 48 h.
Extraction as for 2 and evaporation to 5 mL gave colourless single crystals
of [Lu2(tBu2pz)6] ´ 2PhMe on standing overnight, and a few were removed
for X-ray crystallography. Further standing gave the bulk product, which
Chem. Eur. J. 2001, 7, No. 1
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0947-6539/01/0701-0135 $ 17.50+.50/0
135

G. B. Deacon et al.
FULL PAPER
was dried as for 2, to give 5. Yield: 0.35 g (49%); IR: nÄ ˆ 1525 (s), 1507 (s),
for 21 h followed by stirring at room temperature for 37 h and ultrusoni-
cation for 1.5 h. The reaction mixture was filtered giving a clear yellow
solution, which was concentrated to 5 mL. Yellow-orange crystals formed
in a few hours. These were dried under vacuum. 1H NMR ([D8]THF)
revealed that the product was 7 with impurities of 8 and tBu2pzH.
1416 (s), 1361 (s), 1316 (m), 1251 (s), 1228 (s), 1206 (m), 1112 (w), 1019 (s),
‡
973 (s), 798 cmꢀ1 (s); MS (70 eV, EI): m/z (%): 712 (42) [Lu(tBu2pz)3] , 697
‡
‡
(67) [Lu(tBu2pz)3 ꢀ Me] , 533 (11) [Lu(tBu2pz)2] , 517 (15) [Lu(tBu2pz)2 ꢀ
‡
‡
‡
MeH] , 501 (9) [Lu(tBu2pz)2 ꢀ 2MeH] , 341 (36) [Lu(tBu2pzH) ꢀ CH2] ,
180 (17) [tBu2pzH] , 165 (100) [tBu2pzH ꢀ Me] ; 1H NMR ([D8]THF): d ˆ
1.22 (s, 108H; tBu), 6.12 (s, 6H; H4); elemental analysis calcd (%) for
C66H114Lu2N12 (1425.69): C 55.60, H 8.06, Lu 24.55, N 11.79; found C 55.87,
H 8.13, Lu 24.20, N 12.01.
‡
‡
Method D: A mixture of 7 (0.25 g, 0.21 mmol), amalgamated ytterbium
chips (14.6 g, excess) and 1,2,4,5-tetramethylbenzene (1.34 g, 10.0 mmol)
was heated in an evacuated sealed tube for 48 h at 3008C. The reaction
mixture was extracted with hot toluene (70 mL) and filtered giving an
orange solution, shown to contain 7 by UV/Vis/near IR spectroscopy.
Preparation of [Eu4(tBu2pz)8] (6): A mixture of Eu chunks (0.76 g,
5.0 mmol), tBu2pzH (0.27 g, 1.5 mmol) and mercury metal (2 drops) was
heated in a sealed tube under vacuum at 2208C for 15.5 h. Extraction as for
2 and evaporation to 50 mL gave bright yellow crystals of [Eu4(tBu2pz)8] in
a few days; some were removed for X-ray crystallography. The bulk
product was dried as for 2. Yield: 0.37 g (95%); m.p. 355 ± 3598C; IR: nÄ ˆ
1499 (s), 1300 (m), 1249 (s), 1217 (s), 1206 (s), 1164 (w), 1006 (s), 993 (s),
Method E: A Schlenk flask was charged with ytterbium metal powder
(3.00 g, 17.3 mmol), iodine (0.88 g, 3.5 mmol) and light petroleum (50 mL).
The purple reaction mixture was stirred at ambient temperature for 30 h,
during which time it changed colour from initial purple to orange and
finally green. tBu2pzK (0.76 g, 3.5 mmol), which was prepared from KH
and tBu2pzH in toluene by a reported method,[6] was added to the reaction
mixture and the stirring continued overnight, followed by ultrasonication
for 24 h. Solvent was taken off and replaced by toluene followed by further
ultrasonication for 4 days until all green colour disappeared. The reaction
mixture was then refluxed for further 2 h. Attempts to filter the reaction
mixture were unsuccessful as fine metal passed through a Celite pad. This
partly settled on standing, enabling separation of some supernatant orange-
yellow solution. The visible/near IR spectrum showed lmax ˆ 976 (YbIII),
420, 336 nm (YbII).
‡
798 (s), 778 cmꢀ1 (s); MS (70 eV, EI): m/z (%): 180 (22) [tBu2pzH] , 165
‡
(100) [tBu2pzH ꢀ Me] ; UV/Vis/near IR (THF) and (xylene): no peaks
attributable to EuIII were observed; elemental analysis calcd (%) for
C88H152Eu4N16 (2042.26): C 51.75, H 7.50, Eu 29.77, N 10.98; found C 51.53,
H 7.68, Eu 29.33, N 11.20.
Preparation of [Yb2(tBu2pz)5] (7): Details of the preparation and
characterisation are given in the preliminary communication.[18]
Preparation of [Yb2(tBu2pz)6] (8): A mixture of ytterbium chips (3.46 g,
20.0 mmol), mercury (2 drops), tBu2pzH (1.80 g, 10.0 mmol) and diphenyl-
mercury(ii) (1.77 g, 5.0 mmol) was refluxed in toluene (80 mL) under
nitrogen for 9 h to give a dark red reaction mixture. The reaction mixture
was then stirred at ambient temperature for 10 h and turned yellow. After
filtration, storage for several days at room temperature gave yellow single
crystals of [Yb2(tBu2pz)6] ´ 2PhMe. Some were used for X-ray crystal
structure determination. The bulk product was dried as for 2, giving 8.
Yield: 0.55 g (23%); IR: nÄ ˆ 3288 (w) (an impurity of tBu2pzH), 1526 (m),
1509 (s), 1406 (m), 1362 (s), 1306 (w), 1278 (w), 1253 (s), 1225 (m), 1206
(m), 1019 (m), 1006 (m), 992 (w), 978 (m), 966 (m), 814 (m), 796 cmꢀ1 (m);
Method F: Crude [{Yb(tBu2pz)(m-tBu2pz)(thf)}2], prepared by the reported
method,[4] was dissolved in hot toluene (80 mL). Evaporation of the solvent
under vacuum and heating the resulting red solid under vacuum at 1808C
for 2 h gave a residue shown to contain residual THF and [Yb2(tBu2pz)6] by
1
the H NMR spectrum ([D6]benzene).
Attempted preparation of [Eu(tBu2pz)3]: A thick walled Carius tube was
charged with [Eu4(tBu2pz)8] (0.26 g, 0.13 mmol), tBu2pzH (0.092 g,
0.51 mmol) and xylene (2 mL). Heating the reaction mixture at 2208C
(12 h) then progressively at 2708C and at 3008C failed to achieve any
reaction.
‡
MS (70 eV, EI): m/z (%): 892 (14) [Yb(tBu2pz)2(tBu2pzH)2] , 711 (68)
Structure determinations: Full spheres of low-temperature CCD area-
detector diffractometer data were measured (Bruker AXS instrument; T
ca. 153 K; w-scans; 2qmax ˆ 588; monochromatic MoKa radiation, l ˆ
0.71073 Š) yielding a total of Nt reflections, merging after ªempiricalº/
multiscan absorption correction to N unique reflections (Rint quoted), with
No reflections [F > 4s(F)] being considered ªobservedº and used in the full-
matrix least-square refinements [anisotropic displacement parameter
‡
‡
[Yb(tBu2pz)3] , 695 (66) [Yb(tBu2pz)3 ꢀ MeH] , 624 (6) [Yb(tBu2pz)3 ꢀ
‡
‡
tBu ꢀ 2Me] , 531 (39) [Yb(tBu2pz)2 ꢀ H] , 516 (19) [Yb(tBu2pz)2 ꢀ
‡
‡
‡
MeH] , 500 (4) [Yb(tBu2pz)2 ꢀ 2MeH] , 353 (45) [Yb(tBu2pz)] , 337
‡
‡
(62) [Yb(tBu2pz) ꢀ MeH] , 321 (20) [Yb(tBu2pz) ꢀ 2MeH] , 276 (22)
‡
‡
[Yb(tBu2pz) ꢀ 2MeH ꢀ 3Me] , 180 (23) [tBu2pzH] , 165 (100) [tBu2pzH ꢀ
Me] ; 1H NMR ([D8]THF): d ˆ ꢀ39.38 (s, 6H; H4), ꢀ14.83 (brs, 108H;
‡
tBu), 1.07 (s; tBu, tBu2pzH impurity), 5.84 (s; H4, tBu2pzH impurity), 11.18
(s; NH, tBu2pzH impurity); UV/Vis/near IR (THF): lmax (e) ˆ 933 (10),
975 nm (156); elemental analysis calcd (%) for C66H114N12Yb2 (1421.77): C
55.75, H 8.08, N 11.82, Yb 24.34; found C 55.56, H 8.27, N 11.64, Yb 24.29.
refinement for non-hydrogen atoms; (x, y, z, Uiso
) were refined for the
H
free ligand, and for complex 5 only, being constrained at estimated values
for the remainder]. Conventional R, Rw (weights: (s2(F)‡0.0004(F 2)ꢀ1) are
quoted on jF j at convergence. Neutral atom complex scattering factors
were employed within the Xtal 3.4 program system.[42] Pertinent data/
results are given below and in the figures and tables; full atomic parameters
and non-hydrogen geometries have been deposited at the Cambridge
Crystallographic Data Centre (see below). In the figures, displacement
ellipsoid amplitudes are shown at the 50 (153 K), or 20% (293 K) level.
Hydrogen atoms where shown have arbitrary radii of 0.1 Š. Carbon atoms
are denoted by number only. Individual features, variations, difficulties,
etc., are shown as ªvariataº.
Attempted preparation of [Yb(tBu2pz)2]
Method A: A mixture of Yb powder (2.00 g, 11.6 mmol), tBu2pzH (0.52 g,
2.9 mmol) and mercury metal (2 drops) was heated in a sealed tube under
vacuum at 2408C for 116 h (cf. 5 h at 2208C for 7).[18] The colour of the
reaction product suggested it to be 7 despite the prolonged reaction time.
The reaction product was then extracted with hot toluene (80 mL) and
filtered giving a dark orange-red solution to which a large excess of
ytterbium metal powder (0.49 g, 2.9 mmol) and mercury (2 drops) were
added. After vigorous stirring for 6 days in hot toluene, the reaction
Crystal/refinement data
mixture was filtered giving
a dark orange-red solution, which was
Ligand tBu2pzH: C11H20N2, M ˆ 180.3, orthorhombic, space group Pbca
evaporated to 3 mL. The solution was kept at ꢀ208C for a few days
resulting in formation of dark orange-red crystals which were isolated and
dried under vacuum; The 1H NMR spectrum of the product [D8]THF
showed it to be complex 7.[18]
(no. 61), Z ˆ 8. Cell and coordinate settings follow those of ref. [22].
3
(T ca. 300 K): a ˆ 11.482(1), b ˆ 21.112(2), c ˆ 9.984(1) Š, Vˆ 2420 Š
1calcd ˆ 0.989 gcmꢀ3. mMo ˆ 0.59 cmꢀ1; crystal size: 0.45  0.45  0.20 mm;
ꢁtransmissionꢂ (min/max) ˆ 0.63/0.91. Nt ˆ 23562, N ˆ 3114 (Rint ˆ 0.030),
No ˆ 1949. R ˆ 0.057, Rw ˆ 0.066. jD1max jˆ 0.16(1) eŠꢀ3. Crystals were
grown from a saturated acetone/hexane solution.
Method B: A mixture of ytterbium chips (3.46 g, 20.0 mmol), tBu2pzH
(1.80 g, 10.0 mmol), diphenylmercury(ii) (1.77 g, 5.0 mmol) and mercury
(2 drops) was stirred in refluxing toluene (80 mL) under nitrogen for 4.5 h.
The dark red-orange reaction mixture was filtered and reduced in volume
to about 5 mL resulting in deposition of orange-red crystalline 7, which was
dried under vacuum. Yield: 1.35 g (54%); IR, UV/Vis/near IR (toluene)
and 1H NMR ([D8]THF) spectra were identical with those previously
reported.[18]
Variata: The present cell dimensions are essentially consistent with those of
ref. [22] (a ˆ 11.4779(3), b ˆ 21.1004(1), c ˆ 9.9801(2) Š, Vˆ 2417 Š3) for
which the only record of the temperature of the determination (295 K) is in
the Cambridge Crystallographic Data Base deposition. In ref. [22] tert-
butyl ªIIº (C(5n) in the present report) is described as rotationally
disordered over two sets of sites, occupancies 0.60(4) and its complement.
In the present refinement, site occupancies were refined to 0.566(9) and its
complement; in addition, a disordered component has been resolved for
the other tert-butyl group C(3n), occupancies refining to 0.879(5) and
Method C: A mixture of amalgamated ytterbium chips and mercury
(19.5 g, excess), tBu2pzH (0.72 g, 4.0 mmol) and diphenylmercury(ii)
(0.71 g, 2.0 mmol) was refluxed in diethyl ether (80 mL) under nitrogen
136
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Chem. Eur. J. 2001, 7, No. 1

Rare-Earth Pyrazolates
127±138
complement. Generally, hydrogen atom parameters would not refine
meaningfully, excepting those associated with the nitrogen atoms, occu-
pancies 0.57(5) (H(1) and complement (H(2)).
CCDC-148052. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
(‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
tBu2pzH (T ca. 153 K; same crystal): a ˆ 11.357(1), b ˆ 20.688(2), c ˆ
9.871(1) Š, Vˆ 2319 Š3. 1calcd ˆ 1.033 gcmꢀ3. mMo ˆ 0.61 cmꢀ1; ꢁtransmis-
General catalytic testing procedure: NMR-scale reaction: [La2(tBu2pz)6]
(0.05 mmol) was weighed under protective gas into an NMR tube.
[D6]benzene (ca. 0.7 mL) was condensed into the NMR tube, and the
mixture was frozen at ꢀ1968C. The reactant (1.0 mmol) was injected onto
the solid mixture, and the whole sample was frozen at ꢀ1968C. To
determine the reaction kinetics the sample was melted and mixed just
before the insertion into the core of the NMR machine (to). The ratio
between the reactant (product) and the catalyst was exactly calculated by
comparison of the integration of all CHO (CH2O) signals with the C(CH3)3
signals, which were used as an internal standard for the kinetic measure-
ments.
sionꢂ (min/max) ˆ 0.71/0.96. Nt ˆ 22444, N ˆ 2974 (Rint ˆ 0.023), No ˆ 2483.
ꢀ3
R ˆ 0.042, Rw ˆ 0.050. jD1max jˆ 0.25(1) eŠ
.
Variata: At low temperature, ªthermalº parameters of C(3n), now
modelled as ordered, were consistent with the remainder of the structure.
tert-Butyl C(5n) remain disordered at this temperature, occupancies now
refining to 0.614(5) and complement, all hydrogens refining in (x, y, z, Uiso),
occupancies 0.74(3) (H(1)) and its complement.
tBu2pzH (T ca. 153 K; crystal obtained by sublimation): a ˆ 11.363(2), b ˆ
20.708(3), c ˆ 9.880(1) Š, Vˆ 2325 Š3. 1calcd ˆ 1.030 gcmꢀ3. mMo ˆ 0.61 cmꢀ1
;
specimen: 0.35  0.20  0.06 mm; ꢁtransmissionꢂ (min/max) ˆ 0.69/0.86.
Nt ˆ 22815, N ˆ 3009 (Rint ˆ 0.036), No ˆ 2060. R ˆ 0.045, Rw ˆ 0.049.
jD1max jˆ 0.17(2) eŠꢀ3. Refinement as for the other specimen, occupancies
C(5n) 0.609(6), H(1) 0.75(3).
Acknowledgements
We are grateful to the Australian Research Council and the Deutsche
Forschungsgemeinschaft for support, and for an Australian Postgraduate
Award to A.G.
[Sc(tBu2pz)3] (1): C33H57N6Sc, M ˆ 582.8, monoclinic, space group P21/c
(no. 14), a ˆ 10.696(1), b ˆ 19.743(2), c ˆ 17.474(2) Š, b ˆ 102.163(2)8, Vˆ
3607 Š3. 1calcd ˆ 1.073 gcmꢀ3, Z ˆ 4. mMo ˆ 4.2 cmꢀ1; crystal size: 0.45 Â
0.30  0.25 mm; ꢁtransmissionꢂ (min/max) ˆ 0.79/0.89. Nt ˆ 41797, N ˆ
9120 (Rint ˆ 0.022), No ˆ 7510. R ˆ 0.047, Rw ˆ 0.058. jD1max jˆ
ꢀ3
0.96(4) eŠ
.
[1] a) S. Trofimenko, Chem. Rev. 1972, 72, 497 ± 509; b) S. Trofimenko,
Prog. Inorg. Chem. 1986, 34, 115 ± 210; c) G. LaMonica, G. A.
Ardizzoia, Prog. Inorg. Chem. 1997, 46, 151 ± 238; d) A. P. Sadimenko,
S. S. Basson, Coord. Chem. Rev. 1996, 147, 247 ± 297; e) J. E. Cosgriff,
G. B. Deacon, Angew. Chem. 1998, 110, 298 ± 299; Angew. Chem. Int.
Ed. 1998, 37, 286 ± 287.
Variata: tert-Butyl group 25 was modelled as rotationally disordered about
the pendant bond, over two sets of sites, occupancies refining to 0.601(9)
and complement. (x, y, z, Uiso
) were refined for all the hydrogen atoms
H
except those associated with this disorder and on methyl 132 where
ªthermal motionº was high.
Â
[2] C. Yelamos, M. J. Heeg, C. H. Winter, Inorg. Chem. 1998, 37, 3892 ±
[La2(tBu2pz)6] ´ 2PhMe (2) ´ 2PhMe: C80H130La2N12, M ˆ 1537.8, triclinic,
3894.
Å
space group P1 (no. 2). a ˆ 12.478(1), b ˆ 13.858(2), c ˆ 13.912(2) Š, a ˆ
[3] G. B. Deacon, E. E. Delbridge, C. M. Forsyth, B. W. Skelton, A. H.
White, J. Chem. Soc. Dalton Trans. 2000, 745 ± 751.
[4] G. B. Deacon, E. E. Delbridge, B. W. Skelton, A. H. White, Angew.
Chem. 1998, 110, 2372 ± 2373; Angew. Chem. Int. Ed. 1998, 37, 2251 ±
2252.
119.045(2), b ˆ 96.435(2), g ˆ 94.904(2)8, Vˆ 2062.6 Š3. 1calcd ˆ 1.238 gcmꢀ3
,
Z ˆ 1. mMo ˆ 10.7 cmꢀ1; crystal size: 0.28  0.15  0.10 mm; ꢁtransmissionꢂ
(min/max) ˆ 0.73/0.83. Nt ˆ 20650, N ˆ 10151 (Rint ˆ 0.034), No ˆ 7335. R ˆ
ꢀ3
0.039, Rw ˆ 0.043. jD1max jˆ 1.21(8) eŠ
.
[Nd2(tBu2pz)6] ´ 2PhMe (3) ´ 2PhMe: C80H130Nd2N12, M ˆ 1558.5, triclinic,
Â
[5] L. R. Falvello, J. Fornies, A. Martin, R. Navarro, V. Sicilia, P.
Å
space group P1 (no. 2), a ˆ 12.4301(9), b ˆ 13.807(1), c ˆ 14.0146(10) Š,
Villarroya, Chem. Commun. 1998, 2429 ± 2430.
[6] G. B. Deacon, E. E. Delbridge, C. M. Forsyth, Angew. Chem. 1999,
111, 1880 ± 1882; Angew. Chem. Int. Ed. 1999, 38, 1766 ± 1767.
[7] J. R. Perera, M. J. Heeg, H. B. Schlegel, C. H. Winter, J. Am. Chem.
Soc. 1999, 121, 4536 ± 4537.
[8] a) C. W. Eigenbrot, Jr., K. N. Raymond, Inorg. Chem. 1981, 20, 1553 ±
1556; b) C. W. Eigenbrot, Jr., K. N. Raymond, Inorg. Chem. 1982, 21,
2653 ± 2660.
[9] L. A. Guzei, A. G. Baboul, G. P. A. Yap, A. L. Rheingold, H. B.
Schlegel, C. H. Winter, J. Am. Chem. Soc. 1997, 119, 3387 ± 3388.
[10] L. A. Guzei, G. P. A. Yap, C. H. Winter, Inorg. Chem. 1997, 36, 1738 ±
1739.
a ˆ 119.480(1), b ˆ 96.436(1), g ˆ 95.262(1)8, Vˆ 2050.4 Š3. 1calcd
ˆ
1.254 gcmꢀ3, Z ˆ 1. mMo ˆ 13.0 cmꢀ1; crystal size: 0.40  0.38  0.13 mm;
ꢁtransmissionꢂ (min/max) ˆ 0.77/0.90. Nt ˆ 24095, N ˆ 10069 (Rint ˆ 0.026),
ꢀ3
No ˆ 8766. R ˆ 0.033, Rw ˆ 0.041. jD1max jˆ 2.0(1) eŠ
.
[Yb2(tBu2pz)6] ´ 2PhMe (8) ´ 2PhMe: C80H130Yb2N12, M ˆ 1606.1, triclinic,
Å
space group P1 (no. 2). a ˆ 12.352(2), b ˆ 13.757(2), c ˆ 14.071(2) Š, a ˆ
120.260(2), b ˆ 96.136(2), g ˆ 95.340(2)8, Vˆ 2023.1 Š3. 1calcd ˆ 1.318 gcmꢀ3
,
Z ˆ 1. mMo ˆ 23.5 cmꢀ1; crystal size: 0.40  0.40  0.25 mm; ꢁtransmissionꢂ
(min/max) ˆ 0.64/0.80. Nt ˆ 20098, N ˆ 9814 (Rint ˆ 0.024), No ˆ 8530. R ˆ
ꢀ3
0.033, Rw ˆ 0.042. jD1max jˆ 1.66(8) eŠ
.
[Lu2(tBu2pz)6] ´ 2PhMe (5) ´ 2PhMe: C80H130Lu2N12, M ˆ 1609.9, triclinic,
Å
Â
[11] C. Yelamos, M. J. Heeg, C. H. Winter, Inorg. Chem. 1999, 38, 1871 ±
space group P1 (no. 2). a ˆ 12.3650(8), b ˆ 13.7324(9), c ˆ 14.0544(9) Š,
a ˆ 120.340(1), b ˆ 96.024(1), g ˆ 95.485(1)8, Vˆ 2017.3 Š3. 1calcd
ˆ
1878.
1.325 gcmꢀ3, Z ˆ 1. mMo ˆ 24.8 cmꢀ1; crystal size: 0.30  0.25  0.15 mm;
Â
[12] C. Yelamos, M. J. Heeg, C. H. Winter, Organometallics 1999, 18,
1168 ± 1176.
ꢁtransmissionꢂ (min/max) ˆ 0.67/0.91. Nt ˆ 23601, N ˆ 9863 (Rint ˆ 0.018),
ꢀ3
[13] N. C. Mösch-Zanetti, R. Krätzner, C. Lehmann, T. R. Schneider, I.
No ˆ 9098. R ˆ 0.023, Rw ˆ 0.029. jD1max jˆ 1.49(3) eŠ
.
Â
Uson, Eur. J. Inorg. Chem. 2000, 13 ± 16.
Variata: Difference map residues refined convincingly throughout as
toluene of crystallisation, site occupancies set at unity after trial refine-
ment, albeit with high ªthermal motionº, but without disorder.
[14] D. Pfeiffer, M. J. Heeg, C. H. Winter, Angew. Chem. 1998, 110, 2674 ±
2676; Angew. Chem., Int. Ed. 1998, 37, 2517 ± 2519.
[15] G. B. Deacon, E. E. Delbridge, C. M. Forsyth, P. C. Junk, B. W.
Skelton, A. H. White, Aust. J. Chem. 1999, 52, 733 ± 739.
[Eu4(tBu2pz)8] (6): C88H152Eu4N16, M ˆ 2042.1. a ˆ 13.134(2), b ˆ 13.577(2),
c ˆ 15.743(2) Š, a ˆ 76.975(3), b ˆ 73.277(2), g ˆ 65.419(2)8, Vˆ 2426.8 Š3.
1calcd ˆ 1.397 gcmꢀ3, Z ˆ 1 centrosymmetric tetramer. mMo ˆ 26.0 cmꢀ1; crys-
tal size: cuboid, ca. 0.1 mm; ꢁtransmissionꢂ (min/max) ˆ 0.60/0.84. Nt ˆ
[16] LnIII: see, for example: a) J. E. Cosgriff, G. B. Deacon, B. M. Gate-
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j
ꢀ3
ˆ 3.36(6) eŠ
.
Å
Variata: As modelled in space group P1, ligand 1 was distributed over two
sets of sites, occupancies set at 0.5 after trial refinement; tert-butyl group
(45n) was modelled as disordered over two sets of sites, occupancies
refining to 0.650(9) and its complement.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication no. CCDC-148044 ±
Chem. Eur. J. 2001, 7, No. 1
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Received: August 28, 2000 [F2694]
138
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