Ln(II)/Pb(II)-Ln(III)/Pb(0) Redox Approach toward Rare-Earth-Metal Half-Sandwich Complexes

Article abstract of DOI:10.1021/acs.organomet.5b00837

The divalent bis(trimethylsilyl)amide complexes Ln[N(SiMe₃)₂]₂(THF)₂ (Ln = Sm, Yb) react with 0.5 equiv of lead(II) pentamethylcyclopentadienide, Cp?₂Pb (Cp? = C₅Me₅), in n-hexane to form the half-sandwich complexes Cp?Ln[N(SiMe₃)₂]₂ (Ln = Sm, Yb) in almost quantitative yield. The same reaction performed with Eu[N(SiMe₃)₂]₂(THF)₂ resulted in the cocrystallization of the sandwich complex Cp?₂Eu[N(SiMe₃)₂] and homoleptic Eu[N(SiMe₃)₂]₃. The divalent bis(dimethylsilyl)amide complexes Ln{[μ-N(SiHMe₂)₂]₂Ln[N(SiHMe₂)₂](THF)}₂ (Ln = Sm, Yb) react with 1.5 equiv of Cp?₂Pb in n-hexane/THF to form the half-sandwich complexes Cp?Ln[N(SiHMe₂)₂]₂(THF) (Ln = Sm, Yb). The corresponding europium reaction did not provide any crystalline material. Treatment of divalent Eu[N(SiMe₃)₂]₂(THF)₂ with 2 equiv of 3-tert-butyl-5-methylpyrazole (Hpz^tBu,Me) in THF generates [(pz^tBu,Me)Eu(μ-pz^tBu,Me)(THF)₂]₂. Oxidation of the europium(II) pyrazolate complex with 1 equiv of Cp?₂Pb in THF afforded Cp?Eu(μ-pz^tBu,Me)₂(THF)₂. The tetramethylaluminate compounds {Ln(AlMe₄)₂}_n (Ln = Sm, Yb) react with 0.5 equiv of PbCp?₂ in n-hexane to produce mixtures of half-sandwich and metallocene complexes Cp?Ln(AlMe₄)₂ and [Cp?₂Ln(μ-AlMe₄)]₂, respectively. The attempted oxidation of {Eu(AlMe₄)₂}_n led to the formation of {Cp?Eu(AlMe₄)}, which could be crystallized from THF to give polymeric {Cp?Eu(μ-AlMe₄)(THF)₃}_n. The reaction of chloro-contaminated {Sm(AlMe₄)₂}_n with 2 equiv of HCp? performed in THF led to the isolation of the unexpected mixed chloride methylidene complex [Cp?₃Sm₃(μ₂-Cl)₃(μ₃-Cl)(μ₃-CH₂)(THF)₃]. Reacting {Yb(AlEt₄)₂}_n with 0.5 equiv of Cp?₂Pb in n-hexane gave a mixture of products, from which Cp?₂Yb(AlEt₄) was identified. Performing the same reaction in toluene in the presence of diethyl ether resulted in the formation of the divalent metathesis product Cp?Yb(AlEt₄)(Et₂O)₂.

Full text of DOI:10.1021/acs.organomet.5b00837

Article
pubs.acs.org/Organometallics
Ln(II)/Pb(II)−Ln(III)/Pb(0) Redox Approach toward Rare-Earth-Metal
Half-Sandwich Complexes
†
‡
†
,‡
Andre
́
̈
M. Bienfait, Benjamin M. Wolf, Karl W. Tornroos, and Reiner Anwander*
†
Department of Chemistry, University of Bergen, Alleg
́
aten 41, N-5007 Bergen, Norway
‡
Institut fu
̈
r Anorganische Chemie, Universitat
̈
Tu
̈
bingen, Auf der Morgenstelle 18, D-72076 Tu
̈
bingen, Germany
*
S Supporting Information
ABSTRACT: The divalent bis(trimethylsilyl)amide com-
plexes Ln[N(SiMe ) ] (THF) (Ln = Sm, Yb) react with 0.5
3
2 2
2
equiv of lead(II) pentamethylcyclopentadienide, Cp* Pb (Cp*
2
=
C Me ), in n-hexane to form the half-sandwich complexes
5 5
Cp*Ln[N(SiMe ) ] (Ln = Sm, Yb) in almost quantitative
3
2 2
yield. The same reaction performed with Eu[N-
SiMe ) ] (THF) resulted in the cocrystallization of the sandwich complex Cp* Eu[N(SiMe ) ] and homoleptic
(
3
2 2
2
2
3 2
Eu[N(SiMe ) ] . The divalent bis(dimethylsilyl)amide complexes Ln{[μ-N(SiHMe ) ] Ln[N(SiHMe ) ](THF)} (Ln = Sm,
3
2 3
2 2 2
2 2
2
Yb) react with 1.5 equiv of Cp* Pb in n-hexane/THF to form the half-sandwich complexes Cp*Ln[N(SiHMe ) ] (THF) (Ln =
2
2 2 2
Sm, Yb). The corresponding europium reaction did not provide any crystalline material. Treatment of divalent
tBu,Me
tBu,Me
Eu[N(SiMe ) ] (THF) with 2 equiv of 3-tert-butyl-5-methylpyrazole (Hpz
) in THF generates [(pz
)Eu(μ-
3
2 2
2
tBu,Me
tBu,Me
pz
pz
)(THF) ] . Oxidation of the europium(II) pyrazolate complex with 1 equiv of Cp* Pb in THF afforded Cp*Eu(μ-
2
2
2
) (THF) . The tetramethylaluminate compounds {Ln(AlMe ) } (Ln = Sm, Yb) react with 0.5 equiv of PbCp* in n-
2
2
4 2
n
2
hexane to produce mixtures of half-sandwich and metallocene complexes Cp*Ln(AlMe4)2 and [Cp* Ln(μ-AlMe )] ,
2
4
2
respectively. The attempted oxidation of {Eu(AlMe ) } led to the formation of {Cp*Eu(AlMe )}, which could be crystallized
4
2
n
4
from THF to give polymeric {Cp*Eu(μ-AlMe )(THF) } . The reaction of “chloro-contaminated” {Sm(AlMe ) } with 2 equiv
4
3
n
4 2 n
of HCp* performed in THF led to the isolation of the unexpected mixed chloride methylidene complex [Cp* Sm (μ -Cl) (μ -
3
3
2
3
3
Cl)(μ -CH )(THF) ]. Reacting {Yb(AlEt ) } with 0.5 equiv of Cp* Pb in n-hexane gave a mixture of products, from which
3
2
3
4 2
n
2
Cp* Yb(AlEt ) was identified. Performing the same reaction in toluene in the presence of diethyl ether resulted in the formation
2
4
of the divalent metathesis product Cp*Yb(AlEt )(Et O) .
4
2
2
9
INTRODUCTION
−1.15 V. The bis(trimethylsilyl)amide complexes Ln[N-
■
10
(
SiMe ) ] (THF) (Ln = Sm, Eu, Yb) are attractive
3 2 2 2
Trivalent rare-earth-metal half-sandwich complexes have gained
considerable attention as catalysts or precatalysts for polymer-
candidates for redox reactions due to their straightforward
(ate complex free!) and high-yield synthesis. Alternatively, the
complexes Ln{[μ-N(SiHMe ) ] Ln[N(SiHMe ) ](THF)}
2
(Ln = Sm, Eu, Yb), which can easily be prepared by a
transsilylamination using Ln[N(SiMe ) ] (THF) and 2 equiv
of HN(SiHMe ) , bear the sterically less demanding and
more flexible ligand N(SiHMe ) , which proved to be superior
in various exchange reactions. Moreover, such divalent
silylamide complexes are easily converted into tetraalkylalumi-
nates of the type {Ln(AlMe ) } and {Ln(AlEt ) } by
1
ization reactions. Especially, half-sandwich dialkyl complexes
2
2
2
2
2
have emerged as highly efficient and selective initiators for
2
,3
diene and styrene homo- and copolymerization reactions.
X
III
3
2 2
2
Such derivatives Cp Ln R (R = amido, hydrido, alkyl) are
2
11
2
2
usually generated via protonolysis or salt metathesis reac-
−
2
,3
2 2
tions.
For example, dineosilyl and dibenzyl complexes
1
2
X
III
X
III
Cp Ln (CH SiMe ) (THF) and Cp Ln (CH Ar) (THF)
2
3
2
2
2
are readily obtained from Ln(CH SiMe ) (THF)/Ln-
2
3 3
X
4,5
4
2
n
4 2 n
(
CH Ar) (THF) and cyclopentadiene HCp .
Similarly,
2
3
8
treatment with an excess of trialkylaluminum reagents. While
tetramethylaluminate half-sandwich complexes Cp Ln(AlMe )
have been studied in detail, all attempts to isolate the
tetraethylaluminum analogues Cp Ln(AlEt ) have failed,
homoleptic tetramethylaluminate complexes Ln(AlMe ) give
4
3
X
X
X
4
2
access to Cp Ln(AlMe ) by reaction with either HCp or
4
2
13
X
6,7
M(I)Cp (M = alkali metal).
Such Ln(AlMe ) -based
4 3
X
protonolysis and salt metathesis protocols, however, are either
inconvenient or nonapplicable for Yb(III) and Eu(III),
4 2
presumably due to the thermal instability of homoleptic
1
4
Ln(AlEt4)3 undergoing β-H abstraction and/or the increased
steric demand of the ethyl groups.
respectively, which readily form the divalent derivatives
8
{
Ln(AlMe ) } . In the present study, we assessed the
4
2 n
X
III
When they are combined with potentially reducing agents,
organometallic lead(II) compounds can act similarly to Tl(I)
feasibility of half-sandwich complexes Cp Ln R (R = amido,
alkyl) by oxidizing well-defined divalent complexes
2
II
Ln R (donor) . The redox potentials of the most common
2
x
Ln(II) derivatives had been determined as follows: Sm(III)/
Received: October 4, 2015
Sm(II), −1.55 V; Eu(III)/Eu(II), −0.35 V; Yb(III)/Yb(II),
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 1. Redox Reactions Performed on Complexes with Nitrogen-Based Ligands
15
compounds as oxidation/ligand transfer reagents, as indicated
by their redox potentials: Tl(I)/Ti(0) at −0.34 V vs Pb(II)/
0
2−
16
Pb(0) at −0.13 V (PbSO /Pb , SO at −0.36 V). In organo
4
4
rare-earth-metal chemistry, this method was first studied by
Evans et al., who accessed homoleptic Cp* Sm from Cp* Sm-
Et O) and Cp* Pb (Cp* = C Me ). Recently, the Lappert
3
2
17
(
2 2 5 5
group used a similar approach to generate the likewise sterically
encumbered [C H (SiMe ) -1,3] Yb from divalent
5
3
3
2
3
18
[
C H (SiMe ) -1,3] Yb and [C H (SiMe ) -1,3] Pb. Both
5 3 3 2 2 5 3 3 2 2
studies examined the preparation of homoleptic, sterically
crowded Ln(III) compounds. Surprisingly, the organolead(II)-
based redox route was not employed for the synthesis of
trivalent heteroleptic organolanthanide compounds. Herein, we
present the synthesis and X-ray crystallographic study of a
series of rare-earth-metal half-sandwich complexes via oxida-
tion/ligand transfer (redox transmetalation) accomplished by
Figure 1. Solid-state structure of Cp*Sm[N(SiMe ) ] (1a). Hydro-
3
2 2
gen atoms are omitted for clarity. Atoms are represented by atomic
displacement ellipsoids at the 50% probability level. Selected
interatomic distances (Å) and angles (deg): 1a, Sm−N1 2.315(1),
Sm−N2 2.303(1), N1−Si1 1.709(2), N1−Si2 1.716(2), N2−Si3
Cp* Pb.
2
1
.707(2), N2−Si4 1.716(2), Sm−C(Cp*) 2.702(2)−2.731(2), Sm···
RESULTS AND DISCUSSION
■
Si1 3.2078(5), Sm···Si2 3.7055(7), Sm···Si3 3.1810(5), Sm···Si4
3.6971(7), Sm−N1−Si1 104.71(7), Sm−N1−Si2 133.05(8), Sm−
N2−Si3 103.99(7), Sm−N2−Si4 133.28(8), Si1−N1−Si2 121.74(8),
Si3−N2−Si4 122.53(8), N1−Sm−N2 115.29(5); 1b, Yb−N1
Reactions Involving Ln[N(SiMe ) ] (THF) . Cp* Pb
3
2 2
2
2
performed excellently in the oxidation of the divalent samarium
and ytterbium silylamide complexes, giving virtually quantita-
tive conversions into the desired products Cp*Ln[N(SiMe ) ]
2
.206(5), Yb−N2 2.215(8), N1−Si1 1.712(5), N1−Si2 1.732(4),
N2−Si3 1.719(8), N2−Si4 1.702(6), Yb−C(Cp*) 2.594(17)−
.623(6), Yb···Si1 3.121(1), Yb···Si2 3.640(1), Yb···Si3 3.639(1),
3
2 2
(Ln = Sm (1a), Yb (1b); Scheme 1). The reactions were
2
performed in the absence of (UV) light to protect Cp* Pb from
2
Yb···Si4 3.093(1), Yb−N1−Si1 104.9(2), Yb−N1−Si2 134.8(2), Yb−
N2−Si3 135.0(3), Yb−N2−Si4 103.5(4), Si1−N1−Si2 119.6(3), Si3−
N2−Si4 121.3(5), N1− Yb−N2 115.0(2).
decomposition. Even though both reactions proceeded fairly
quickly, surprisingly the Sm reaction seemed to require a
certain induction period. The Yb reaction, on the other hand,
started immediately, forming a black suspension upon addition
of the first drop of Cp* Pb solution. Given the larger size and
In THF, on the other hand, such disproportionation reactions
did not occur, allowing the isolation of 1 in moderate to high
yields.
2
higher reducing potential of Sm(II), this is very surprising, since
the reaction conditions were the same. In our hands, the crude
products of complexes 1, which were obtained as orange (1a)
or purple (1b) crystalline solids, were of high purity, meaning
that purification before further derivatization was unnecessary.
Upon recrystallization from saturated n-hexane or toluene
solutions single-crystal X-ray diffraction studies revealed the
formation of the target compound Cp*Ln[N(SiMe ) ] (1;
The Nd analogue, Cp*Nd[N(SiMe ) ] , not accessible via
3
2 2
redox transmetalation, has been obtained in high yields via a
19
salt-metathesis protocol. The isolation of the crystallo-
graphically authenticated cerium complex Cp*Ce[N(SiMe ) ]
3
2 2
20
was achieved by a metathesis route in low yield. Recently, the
Sc analogue was synthesized in good yield by a protonolytic
3
2 2
21
Figure 1 and Figure S1 in the Supporting Information) along
reaction at high temperatures (100 °C) over 48 h. Complexes
1 exhibit a distorted-trigonal coordination geometry with
asymmetrically arranged amido ligands, as observed for the
with metallocene complexes Cp* Ln[N(SiMe ) ] (2) and
2
3 2
homoleptic Ln[N(SiMe ) ] as a result of ligand redistribution.
3
2 3
B
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2
4
cerium and scandium derivatives. The Ln−N distances
Å, respectively). This distinct amido coordination might be
due to opposing trends of Lewis acidity and steric unsaturation.
Reactions Involving Ln{[μ-N(SiHMe ) ] Ln[N-
(
2.3154(14) and 2.3029(14) Å in 1a; 2.206(5), 2.215(8) Å
in 1b) are consistent with the changes in the ion radii of the
lanthanide atoms (Sc, 2.086(5) Å; Ce, 2.357(7) and 2.349(7)
Å).
2
2 2
(SiHMe ) ](THF)} . The bis(dimethylsilyl)amide complexes
Ln{[μ-N(SiHMe ) ] Ln[N(SiHMe ) ](THF)} (Ln = Sm,
2
2
2
2
2 2
2 2
2
The europium(II) complex Eu[N(SiMe ) ] (THF) revealed
a reactivity distinct from that of the ytterbium and samarium
Yb) reacted with Cp* Pb to afford the half-sandwich complexes
3
2 2
2
2
Cp*Ln[N(SiHMe ) ] (THF) (Ln = Sm (3a), Yb (3b)) in high
2
2 2
congeners. Instead of the putative Cp*Eu[N(SiMe ) ] , we
yields (Scheme 1). In contrast to the derivatization reactions of
Ln[N(SiMe ) ] (THF) , the addition of THF during the
3
2 2
could only isolate the sandwich complex Cp* Eu[N(SiMe ) ]
2
3 2
3 2 2
2
2
2
(
2; Figure 2) along with homoleptic Eu[N(SiMe ) ] .
synthesis was crucial for complete conversion. Several
crystallization steps were necessary to obtain pure, crystalline
compounds 3. However, ligand redistribution of 3 was by far
not as pronounced as in the case of complexes 1 and occurred
only to a negligible extent upon long-term storage of n-hexane
solutions. Single crystals of 3 formed from concentrated n-
hexane solutions. The respective europium reaction only
produced a green oily residue, which did not form any
crystalline material even after several months at −40 °C. Due to
the paramagnetic nature of europium, the NMR spectroscopic
characterization of the reaction outcome was inconclusive.
Such half-sandwich complexes of composition Cp*Ln[N-
3
2 3
(
SiHMe ) ] (THF) seem to be rather scarce and have only
2 2 2 x
been reported for diamagnetic rare-earth-metals (Ln = Sc, Lu, x
21,26,27
=
0; Ln = Y, x = 1).
In all cases protonolytic amine
elimination was used as the synthesis strategy, employing
Ln[N(SiHMe ) ] (THF) and pentamethylcyclopentadiene.
The crystal structures of 3a,b show the same distorted-
Figure 2. Solid-state structure of Cp* Eu[N(SiMe ) ] (2). Hydrogen
2
3 2
2
2 3
x
atoms are omitted for clarity. Atoms are represented by atomic
displacement ellipsoids at the 50% probability level. Selected
interatomic distances (Å) and angles (deg): Eu−N 2.293(2), N−Si1
tetrahedral coordination geometry as the Y analogue (Figure
3
). The Ln−N (2.3368(9) and 2.3368(9) Å in 3a; 2.244(1)
1
.700(3), N−Si2 1.699(3), Eu−C(Cp*) 2.724(3)-2.769(3), Eu···Si1
3.410(1), Eu···Si2 3.3777(9), Eu···C1 3.278(4), Eu···C4 3.204(4);
and 2.224(1) Å in 3b) and Ln−O bonds (2.4649(8) Å in 3a,
2.331(1) Å in 3b) are in the expected ranges. The solid-state
structures of 3a,b feature distinct secondary interactions. In
compound 3b only one amido ligand is strongly tilted toward
the central atom, comparable to the case for the yttrium
derivative, with a close Yb···Si3 contact of 3.0640(4) Å and a
relatively acute Yb−N2−Si3 angle of 102.03(5)°. In compound
Eu−N−Si1 116.55(13), Eu−N−Si2 114.76(13), Si1−N−Si2
28.62(15).
1
Although the exact mechanism for the formation of 2 is
unclear, we assume that either the target compound Cp*Eu-
[
N(SiMe ) ] was initially formed as an intermediate, which
3 2 2
III
then disproportionates, or the initial reaction might simply
involve ligand exchange between two molecules of Eu[N-
3a, both amido ligands are tilted toward the larger Sm center,
III
III
as opposed to the Y and Yb complexes, with Sm···Si1 and
Sm···Si3 distances of only 3.2732(4) and 3.1404(3) Å,
respectively. The corresponding Sm−N1(2)−Si1(3) angles
are as acute as 107.45(4) and 101.89(4)°. These additional
agostic interactions are also indicated in the DRIFT spectrum
(
SiMe ) ] (THF) and one molecule of Cp* Pb, giving the
3 2 2 2 2
putative “Cp*Eu[N(SiMe ) ](THF) ” and Pb[N(SiMe ) ] ,
3
2
x
3 2 2
followed by a disproportionation into Cp* Eu(THF) and
2
2
precursor Eu[N(SiMe ) ] (THF) and in a final step the
3
2 2
2
−1
oxidation/ligand transfer reaction. The second hypothesis is
substantiated by the fact that compound 1a (Sm and Eu being
of similar size) does not undergo such a ligand redistribution
under the same reaction conditions with THF as a solvent. The
most striking difference between Sm(II) and Eu(II) is the
significantly lower redox potential of Eu, which will cause a
slower reduction of Pb(II) to Pb(0), thus allowing enough time
to perform a ligand transfer beforehand. A structural motif
similar to that for 2 was observed previously for the Y(III)
of 3a, which revealed a Si−H stretching vibration at 2065 cm ,
−1
featured by two lower energy shoulders at 2046 and 1948 cm .
tBu,Me
tBu,Me
Reaction Involving [(pz
)Eu(μ-pz
) (THF) ] (4).
2 2
To probe a more general applicability of this redox protocol for
Ln(II) complexes bearing non silylamido nitrogen based
28
ligands, we envisaged pyrazolates. For the rare-earth-metals,
this ligand class has been intensively explored by the Deacon
29
group and found to engage in Ln(II) → Ln(III) redox
1
5,29,30
chemistry.
The synthesis of the divalent europium
2
3
24
tBu,Me
tBu,Me
(
P2 /c, measured at 98 K), Sm(III) (R3
̅
pyrazolate precursor [(pz
)Eu(μ-pz
) (THF) ] (4) is
2 2
1
25
La(III) congeners (P3
̅
accomplished via a straightforward protonolysis reaction
involving Eu[N(SiMe ) ] (THF) and 2 equiv of proligand 3-
prepared by applying salt metathesis protocols. Evans and co-
workers pointed out that even though both the smaller-sized
Y(III) and the large La(III) centers showed secondary “agostic”
3
2 2
2
tBu,Me
tert-butyl-5-methylpyrazole (Hpz
) in THF (Scheme 1 and
Figure S2 in the Supporting Information). Oxidation of 4 with
III
interactions of the type Ln ···CH (Ln−N(SiMe ) ), the
1 equiv of Cp* Pb in THF yielded the trivalent target
3
3 2
2
2
5
tBu,Me
midsized Sm(III) would not. This finding is confirmed by the
compound Cp*Eu(μ-pz
) (THF) (5) in 66% crystallized
2 2
X-ray structure analysis of compound 2 (R3
̅
yield.
being only marginally smaller than Sm. The Eu−N bond length
The successful redox protocol provided evidence that (a)
(2.293(2) Å), as well as the Eu···C1 (3.278(4) Å) and Eu···C4
(3.204(4) Å) distances are comparable to the metric para-
Cp* Pb is capable of oxidizing Eu(II) to Eu(III), also meaning
2
that the formation of compound 2 is not an exception, and (b)
maters of Cp* Sm[N(SiMe ) ] (2.301(3) Å, 3.286 and 3.216
the synthesis strategy is not limited to silylamide complexes.
2
3 2
C
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 4. Solid-state structure of Cp*Eu(pztBu,Me)2(THF)2 (5).
Hydrogen atoms are omitted for clarity. Atoms are represented by
atomic displacement ellipsoids at the 50% probability level. Selected
interatomic distances (Å) and angles (deg): Eu−N1 2.420(2), Eu−N2
2
.366(2), Eu−N3 2.372(2), Eu−N4 2.494(2), Eu−O1 2.470(2), Eu−
O2 2.5758(18), Eu−C(Cp*) 2.702(2)−2.741(2); O1−Eu−O2
7
3
3.26(7), N1−Eu−O1 88.78(7), O1−Eu−N4 94.18(7), N1−Eu−N2
3.52(7), N3−Eu−N2 96.86(7).
This finding is consistent with the N1−Eu−O1 and N4−Eu−
O1 angles of 88.78(7) and 94.18(7)°, respectively.
Reactions Involving {Ln(AlR ) }. Aiming at half-sandwich
4
2
complexes Cp*Ln(AlR ) (Ln = Sm, Yb; R = Me, Et), one
4
2
might choose the oxidation protocols leading to bis(amide)
complexes 1 and 3 and then proceed with the well-established
alkylation employing an excess of AlR , concomitantly forming
3
aluminum amide. The drawback of this approach is the need for
multiple crystallizations of the target compounds, since the
byproducts, {R Al[μ-N(SiMe ) ]} and {R Al[μ-N-
Figure 3. Solid-state structures of Cp*Sm[N(SiHMe ) ] (THF) (3a,
2
2 2
top) and Cp*Yb[N(SiHMe ) ] (THF) (3b, bottom). Hydrogen
2
2
2
2
3
2
2
2
atoms, except those attached to silicon atoms, are omitted for clarity.
Atoms are represented by atomic displacement ellipsoids at the 50%
probability level. Selected interatomic distances (Å) and angles (deg):
(SiHMe )]} , are highly soluble, nonvolatile solids. Alter-
2 2
natively, the Ln(II)/Pb(II)−Ln(III)/Pb(0) redox approach
might be a viable strategy. Synthesis protocols for polymeric, n-
hexane-insoluble {Ln(AlMe ) } , from which {Me Al[μ-N-
3
a, Sm−N1 2.3368(9), Sm−N2 2.3206(9), Sm−O 2.4649(8), N1−Si1
4
2
n
2
1
.696(1), N1−Si2 1.708(1), N2−Si3 1.6911(9), N2−Si4 1.7045(9),
(
SiMe ) ]} can easily be extracted with n-hexane, and
3 2 2
Sm−C(Cp*) 2.710(1)−2.727(1), Sm···Si1 3.2732(4), Sm···Si2
polymeric, soluble {Ln(AlEt ) } , which could be separated
4
2 n
3
1
.6654(4), Sm···Si3 3.1404(3), Sm···Si4 3.6863(5), Sm−N1−Si1
07.45(4), Sm−N1−Si2 129.33(5), Sm−N2−Si3 101.89(4), Sm−
from {Et Al[μ-N(SiMe ) ]} and other byproducts by several
2
3 2
2
12
recrystallization steps, are well established. Unfortunately, the
oxidation of divalent tetramethylaluminate complexes of
samarium and ytterbium, {Ln(AlMe ) } , with Cp* Pb gave
N2−Si4 132.05(5), Si1−N1−Si2 123.21(5), Si3−N2−Si4 126.05(5),
N1−Sm−N2 119.31(3), N1−Sm−O 102.43(3), N2−Sm−O
8
3.81(3); 3b, Yb−N1 2.244(1), Yb−N2 2.224(1), Yb−O 2.331(1),
4
2
n
2
N1−Si1 1.710(1), N1−Si2 1.716(1), N2−Si3 1.695(1), N2−Si4
.705(1), Yb−C(Cp*) 2.609(1)−2.621(1), Yb···Si1 3.3671(4), Yb···
Si2 3.5150(4), Yb···Si3 3.0640(4), Yb···Si4 3.6087(4), Yb−N1−Si1
product mixtures consisting of the desired half-sandwich
1
complexes Cp*Ln(AlMe ) (Ln = Sm (6a), Yb (6b)) and
4
2
the metallocene species [Cp* Ln(μ-AlMe )] (Ln = Sm (7a),
2
4
2
1
16.16(6), Yb−N1−Si2 124.64(6), Yb−N2−Si3 102.03(5), Yb−N2−
Yb (7b); Scheme 2). Complexes 6 and 7 could be cleanly
separated by crystallization using n-hexane (6) and extraction
with toluene (7), since the dimeric complexes 7 are insoluble in
n-hexane. The isolated yields for Cp*Ln(AlMe ) are 32% (6a)
Si4 132.99(6), Si1−N1−Si2 119.16(7), Si3−N2−Si4 124.96(7), N1−
Yb−N2 121.01(4), N1−Yb−O 95.05(4), N2−Yb−O 84.94(4).
4
2
Interestingly, compound 5 is the first example of a structurally
and 46% (6b) and for [Cp* Ln(μ-AlMe )] are 35% (7a) and
2 4 2
characterized half-sandwich rare-earth-metal bis(pyrazolate)
21% (7b). Thus, both reactions gave yields of 67% (based on
Ln atoms); the overall yield with respect to Cp*, on the other
hand, is quantitative for the Sm reaction and 88% for Yb. It is
Ph
complex. For comparison, the isolation of Cp* Yb(pz 2) has
2
been accomplished by the redox reaction of Cp* Yb(THF) and
Tl(pz 2). The Eu(III) metal center in complex 5 adopts a
2
Ph 15
noteworthy that homoleptic Yb(AlMe ) , which is another
4 3
pseudo-trigonal-bipyramidal geometry (Figure 4). The Cp*
centroid and O2(THF) represent the vertices, while the σ-η2
binding pyrazolate ligands together with O1(THF) span the
triangular plane. The central atom is positioned about 0.6 Å
above that plane toward the Cp* ligand. The Ct(Cp*)−Eu−
O2 angle is 175.27° and is slightly bent in the direction of O1.
The pyrazolato ligands are coordinated asymmetrically in the
sense that one is pointing its methyl group toward the in-plane
THF molecule, while the other is pointing its tert-butyl group.
potential precursor for half-sandwich complex 6b, is obtainable
in low yield only and engages in extensive Yb(AlMe ) −
4
3
8
c
{Yb(AlMe ) } “self-reductions” at ambient temperature.
4
2 n
Complexes 6 are isomorphous with diamagnetic Cp*Ln-
26
6
31
(AlMe ) (Lu, La, and Y; space group Pbca; Figure 5 and
4
2
Figure S3 in the Supporting Information). The interatomic
distances of 6 are in the expected range. In particular, the close
distance between the lanthanide center and one terminal
methyl group of the bent AlMe moiety appears to increase
4
D
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 2. Derivatization of Tetraalkylaluminate Complexes with Cp* Pb and HCp*
2
̅
from toluene in the space group P1, incorporating two solvent
molecules into the lattice (Figure 6 and Figure S4 in the
Supporting Information), being isostructural with the latter
lanthanum derivative.
Figure 5. Solid-state structure of Cp*Yb(AlMe ) (6b). Hydrogen
4
2
atoms are omitted for clarity. Atoms are represented by atomic
displacement ellipsoids at the 50% probability level. Selected
interatomic distances (Å) and angles (deg): 6b, Yb−C1 2.6179(15),
Yb−C2 2.599(2), Yb−C5 2.519(2), Yb−C6 2.516(2), Yb−C(Cp*)
Figure 6. Solid-state structure of [Cp* Yb(μ-AlMe )] (7b). Hydro-
2
3
8
.577(1)−2.610(1), Yb···Al1 2.9007(5), Yb···Al2 3.0683(5), Yb···C4
.354(2), Yb−C1−Al1 75.54(5), Yb−C2−Al1 76.02(5), Yb−C5−Al2
3.16(5), Yb−C6−Al2 83.13(5), torsion angles Yb−C1−Al1−C4
2
4
2
gen atoms and lattice solvent (two molecules of toluene) are omitted
for clarity. Atoms are represented by atomic displacement ellipsoids at
the 50% probability level. Selected interatomic distances (Å) and
angles (deg): 7b, Yb−C1 2.625(2), Yb−C4′ 2.643(2), Yb−C5−
−
73.90(7), Yb−C2−Al1−C4 74.52(7), Yb−C5−Al2−C8 123.02(7),
Yb−C6−Al2−C8−122.81(6); 6a, Sm−C1 2.725(2), Sm−C2
9
(Cp*) 2.598(2)−2.622(2), Yb−C15−19(Cp*) 2.598(2)− 2.640(2),
2.729(2), Sm−C5 2.614(2), Sm−C6 2.603(2), Sm−C(Cp*)
.670(2)−2.714(2), Sm···Al1 2.9275(5), Sm···Al2 3.1695(6), Sm···
Yb···Al 4.6646(8), Yb···Al′ 4.6893(7), Yb−C1−Al 175.46(11), Yb′−
C4−Al 173.15(10), C1−Yb−C4′ 87.12(6); 7a, Sm−C1 2.743(4),
Sm−C4′ 2.755(4), Sm−C5−9(Cp*) 2.686(4)−2.708(5), Sm−C15−
2
C4 3.113(2), Sm−C1−Al1 74.02(6), Sm−C2−Al1 73.96(6), Sm−
C5−Al2 84.13(6), Sm−C6−Al2 84.42(6), torsion angles Sm−C1−
Al1−C4 −65.44(7), Sm−C2−Al1−C4 66.33(7), Sm−C5−Al2−C8
1
9(Cp*) 2.686(5)−2.728(5), Sm···Al 4.770(1), Sm···Al′ 4.791(1),
Sm−C1−Al 175.3(2), Sm′−C4−Al 174.0(2), C1−Sm−C4′
119.59(7), Sm−C6−Al2−C8 −119.81(8).
8
7.69(13).
with decreasing size of the metal center (La···C4 3.140(3) Å,
The exact mechanism for the formation of dimeric
6
,26,31
Y···C4 3.304(3)Å, Lu···C4(17) 3.447 (3) Å),
which is in
metallocenes [Cp* Ln(μ-AlMe )] (7) is not entirely clear. It
2 4 2
accord with the Yb···C(CH ) distance of 3.354(2) Å in
is very unlikely that the monomeric half-sandwich complexes
3
complex 6b. The Sm analogue 6a, however, revealed a distance
slightly shorter (Sm1···C4 3.113(2) Å) than that of the
significantly larger lanthanum center. The crystal structure of
Cp*Ln(AlMe ) disproportionate into [Cp* Ln(μ-AlMe )]
4
2
2
4
2
and Ln(AlMe ) , since formation of the latter homoleptic
4
3
tetramethylaluminates has not been observed for the half-
32
samarocene complex 7a was determined earlier (space group
sandwich complexes Cp*Ln(AlMe ) . The reaction proceeds
4
2
P2 /n) and found to be isostructural with the yttrocene
presumably via a ligand exchange reaction between the divalent
1
3
3
[
Cp* Y(AlMe )] . The respective lanthanum complex
produced crystals in two different space groups: P2 /n
precursor {Ln(AlMe ) } and Cp* Pb to afford an intermediate
2
4
2
4 2
n
2
species such as “Cp*Ln(AlMe )”. This divalent intermediate
1
4
(
isomorphous with Y and Sm) and P1
̅
(containing one
could get oxidized by another Cp* Pb molecule to form
2
31
molecule of lattice toluene). Compounds 7a,b crystallized
[Cp* Ln(μ-AlMe )] (7). Preliminary experiments, in which
2
4
2
E
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
4
Pb[N(SiMe ) ] was treated with 4 equiv of AlR in n-hexane,
3
2 2
3
established that putative “Pb(AlR ) ” rapidly decomposed with
4
2
formation of Pb(0). The degradation is presumably following a
35
radical mechanism similar to that for Tl(I) organyls. Since
36
Pb(II) alkyl species are known to be unstable, any transient
Pb(AlMe ) ” would decompose into Pb(0), Al Me , and
“
4
2
2
6
methyl-radical coupling products, predominantly ethane; to
some degree it might act again as an oxidation/ligand transfer
agent. Three facts support this hypothesis: (i) there has been
no evidence for the formation of homoleptic Ln(AlMe ) , (ii)
4
3
the yield based on Cp* is almost quantitative, whereas the yield
of trivalent lanthanide complexes is 66%, meaning that all the
Cp* Pb was consumed without oxidizing all available Ln(II)
2
metal centers, and (iii) the results from the attempted oxidation
of the europium complex {Eu(AlMe ) } . In the case of
europium, we could not detect any Ln-containing product, in
either the n-hexane mother liquor or the toluene extract.
Extraction of the solid reaction residue with THF, on the other
Figure 8. Solid-state structure of [Cp* Sm (μ -Cl) (μ -Cl)(μ -CH )-
3
3
2
3
3
3
2
4
2 n
(
THF) ] (9). Hydrogen atoms, except those attached to the
3
methylidene group, are omitted for clarity. Atoms are represented
by atomic displacement ellipsoids at the 50% probability level. Selected
interatomic distances (Å) and angles (deg): Sm1−Cl1 2.7990(6),
Sm1−Cl2 2.9056(5), Sm1−Cl4 2.8038(6), Sm1−C25 2.464(2),
Sm1−O3 2.533(2), Sm2−Cl2 2.9407(5), Sm2−Cl3 2.8079(6),
Sm2−Cl4 2.8038(6), Sm2−C25 2.486(2), Sm2−O2 2.485(2),
Sm3−Cl1 2.7834(6), Sm3−Cl2 2.9069(5), Sm3−Cl3 2.7824(6),
Sm3−C25 2.534(2), Sm3−O1 2.530(2), Sm1−C(Cp*) 2.697(2)−
hand, led to the isolation of polymeric {Cp*Eu(μ-AlMe )-
4
(
THF) } (8, Figure 7) and elemental lead.
3 n
2
2
.750(2), Sm2−C(Cp*) 2.699(2)−2.738(2), Sm3−C(Cp*)
.696(2)−2.720(2), Sm1···Sm2 3.6869(2), Sm1···Sm3 3.7359(2),
Sm2···Sm3 3.7711(2); Sm1−Cl1−Sm3 84.01(2), Sm3−Cl3−Sm2
8
Sm1−Cl2−Sm3 79.99(1), Sm2−Cl2−Sm3 80.31(1), Sm1−C25−
Sm2 96.28(7), Sm1−C25−Sm3 96.74(8), Sm2−C25−Sm3
9
4.84(2), Sm2−Cl4−Sm1 82.22(2), Sm1−Cl2−Sm2 78.19(1),
7.40(8), Cl2−Sm1−O3 71.22(4), Cl2−Sm2−O2 73.15(4), Cl2−
Sm3−O1 72.87(4).
Figure 7. Connectivity of {Cp*Eu(μ-AlMe )(THF) } (8) in the solid
the precursor {Sm(AlMe ) } . This impurity might form a
4
3
n
4 2 n
state. Hydrogen atoms are omitted, and all atoms are represented by
spheres of arbitrary radii (green, Eu; orange, Al; red, O; gray, C).
Crystal data: monoclinic unit cell, a = 18.387(4) Å, b = 8.989(2) Å, c =
mixed, divalent AlMe /chloride species {Sm(Cl) (AlMe ) } (x
4 x 4 y
+
y = 2), which is only soluble in donating solvents, such as
THF, and therefore inseparable from the main product
Sm(AlMe ) } .
19.826(4) Å, β = 101.445(3)° at 103 K, solved and refined in space
{
4
2 n
group Cm. Due to the poor quality of the data, a ball and stick
representation visualizes the connectivity. A detailed discussion of
interatomic distances and angles has to be ruled out.
While heteroleptic tetramethylaluminates have been inves-
tigated in detail, the respective tetraethylaluminates have
attracted much less attention. The substitution of the alkyl
groups seem to be a marginal variation, but for example half-
sandwich derivatives Cp*Ln(AlEt4)2 have not yet been
Compound 8 is the THF adduct of the aforementioned
putative intermediate “Cp*Ln(AlMe )”. The polymeric nature
reported. The increased steric demand of the AlEt ligand
4
4
of 8, with tetramethylaluminate ligands bridging between the
and its enhanced sensitivity to alkyl degradation via β-H
abstraction presumably cause this dearth of data. When
{Yb(AlEt ) } was reacted with 0.5 equiv of Cp* Pb in n-
37
rare-earth-metal centers, seems to be unique and rather
unexpected, especially since a related Yb compound was
obtained as the separated ion pair [Cp*Yb-
4
2
n
2
hexane, instant precipitation of Pb(0) was observed. Upon
workup of the reaction mixture, two products could be isolated.
Attempts to obtain crystals from the yellow, toluene-soluble
+
−
8b
(
THF) ] [AlMe ] . In order to investigate whether the
4 4
formation of polymeric 8 is size-related or an intrinsic
europium effect, the analogous reaction that led to [Cp*Yb-
39
component produced only glasslike solids. From the n-
hexane-soluble component, however, blue single crystals
suitable for X-ray crystallography were obtained, revealing the
formation of the metallocene complex Cp* Yb(AlEt ) (10;
+
−
8b
(
THF) ] [AlMe ]
was performed with {Sm(AlMe ) } .
4
4
4 2 n
Accordingly, {Sm(AlMe ) } was reacted with 2 equiv of
4
2 n
HCp*. Crystallization of the crude product from THF afforded
few orange single crystals, which to our surprise were
determined as the methylidene complex Cp* Sm (μ -Cl) (μ -
2
4
Figure 9).
This finding is consistent with the corresponding reaction of
3
3
2
3
3
Cl)(μ -CH )(THF) (9; Figure 8).
{Yb(AlMe ) } and plumbocene, resulting in the isolation of
3
2
3
4 2 n
Complex 9 is isostructural with Cp* Ln (μ -Cl) (μ -Cl)(μ -
[Cp* Yb(μ-AlMe )] (7b). For structural comparison, the
3
3
2
3
3
3
2 4 2
CH )(THF) (Ln = Y, La; P2 /n), which were synthesized by
samarocene complex Cp* Sm(AlEt ) features a motif similar to
2 4
40
2
3
1
adding Me AlCl to the half-sandwich complexes Cp*Ln-
that of 10, while the larger size of lanthanum led to a
2
(
AlMe ) and subsequently treating the isolable multinuclear
dimerization and therewith to the formation of [Cp* La(μ-
4
2
2
3
8
16
complexes [Cp*Ln(AlMe ) Cl ] with THF. Since the
Sm(II) amide precursor Sm[N(SiMe ) ] (THF) was obtained
AlEt )] . In order to investigate the influence of donor
4
x
y z
4
2
molecules on the {Yb(AlEt ) } /Cp* Pb reaction, diethyl ether
4 2 n 2
3
2 2
2
from SmI (THF) , we assume that the chlorido ligands stem
(Et O), as a softer donor than THF, was admitted. Addition of
2
x
2
from an Me AlCl impurity in AlMe used for the synthesis of
Et O to a bright orange solution of {Yb(AlEt ) } in toluene
2
3
2
4 2 n
F
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Apparently, the softer donor Et O did not cleave the AlEt
2
4
ligand or lead to the formation of an ion pair as observed for
+
−
8b
[
Cp*Yb(THF) ] [AlMe ] .
4
4
CONCLUSIONS
■
The Cp* Pb-based oxidative route toward Ln(III) half-
2
sandwich complexes, employing 0.5 equiv of oxidant per
divalent rare-earth-metal atom, proved to be highly effective for
samarium and ytterbium (dimethylsilyl)amide and
(
trimethylsilyl)amide complexes. Cp*Ln[N(SiMe ) ] and
3 2 2
Cp*Ln[N(SiHMe ) ] (THF) (Ln = Sm, Yb) could be isolated
2
2 2
in moderate to excellent yields. When the reactions were
performed with Eu[N(SiMe ) ] (THF) , an inevitable dis-
3
2 2
2
Figure 9. Solid-state structure of molecule A of Cp* Yb(AlEt ) (10).
2
4
proportionation into the sandwich complex Cp* Eu[N-
2
Hydrogen atoms and lattice solvent (two molecules of toluene) are
omitted for clarity. Atoms are represented by atomic displacement
ellipsoids at the 50% probability level. Selected interatomic distances
(
SiMe ) ] and homoleptic Eu[N(SiMe ) ] was observed.
3 2 3 2 3
The complementary reaction employing the (dimethylsilyl)-
amido ligand did not deliver crystalline material. Using the
(
Å) and angles (deg): molecule A, Yb1−C1 2.64(2), Yb1−C3 2.60(2),
Yb1−C9−13(Cp*) 2.60(2)-2.63(2), Yb1−C19−23(Cp*) 2.62(2)-
.65(2), Yb1···Al1 3.094(6), Al1···C2 2.88(2), Al1···C4 2.78(3),
tBu,Me
plumbocene-based oxidation routine on divalent [(pz
)Eu-
tBu,Me
(
(
μ-pz
pz
)(THF) ] resulted in the formation of Cp*Eu-
2 2
tBu,Me
2
) (THF) , proving that Pb(II) compounds are able to
2 2
Yb1−C1−Al1 80.5(5), Yb1−C3−Al1 82.2(6), C1−Yb1−C3 83.7(5),
C1−Al1−C3 113.2(7), Al1−C1−C2 103.3(13), Al1−C3−C4
oxidize Eu(II) in complexes with nitrogen-based ligands. The
reactions performed on the divalent tetramethylaluminates
{Ln(AlMe ) } (Ln = Sm, Yb) gave a product mixture, from
99.3(13); molecule B, Yb2−C29 2.65(2), Yb2−C31 2.58(2), Yb2−
C37−41(Cp*) 2.58(8)-2.64(2), Yb2−C47−51(Cp*) 2.62(2)-2.64(2),
Yb2···Al2 3.084(6), Al2···C30 2.90(3), Al2···C32 2.80(3), Yb2−C29−
Al2 79.9(6), Yb2−C31−Al2 82.4(6), C29−Yb2−C31 83.8(5), C29−
Al2−C31 113.4(8), Al2−C29−C30 104.0(14), Al2−C31−C32
4
2 n
which half-sandwich complexes Cp*Ln(AlMe ) and sandwich
4
2
complexes [Cp* Ln(μ-AlMe )] (Ln = Sm, Yb) were isolated,
2
4
2
indicating two competing reaction mechanisms: (i) the
envisaged oxidation/ligand transfer (redox transmetalation)
and (ii) the undesired, redox-inactive ligand exchange (meta-
thesis) followed by decomposition via radicals originating from
Pb(II) alkyl species. In the case of europium, polymeric
100.3(13).
caused a color change, clearly indicating Yb(II)···donor
interactions, presumably forming the diethyl ether analogue
41
of Ln(AlEt ) (THF) (Ln = Sm, Yb). A black suspension
4
2
2
{
Cp*Eu(μ-AlMe )(THF) } could be isolated, clearly showing
4 3 n
formed upon addition of 0.5 equiv of Cp* Pb indicated a redox
2
that for Eu(II) the second redox-inactive mechanism prevails.
reaction with Pb(0) as the byproduct. Single-crystal X-ray
diffraction studies, however, revealed the formation of divalent
Cp*Yb(AlEt )(Et O) (11; Figure 10) in 69% crystallized
The reaction of {Sm(AlMe ) } with 2 equiv of HCp* led to
4
2 n
the formation of the mixed methylidene/chloride complex
4
2
2
Cp* Sm (μ -Cl) (μ -Cl)(μ -CH )(THF) in minor yields,
3
3
2
3
3
3
2
3
suggesting dimethylaluminum chloride as a contaminant in
commercially available trimethylaluminum. In a switch from
tetramethyl- to tetraethylaluminates, the reaction of {Yb-
(
AlEt ) } with plumbocene afforded only the sandwich
4 2 n
complex Cp* Yb(AlEt ) as crystalline material, suggesting
that the intermediate Cp*Yb(AlEt ) is destabilized by either
2
4
4
2
intra- or intermolecular decomposition pathways of the
tetraethylaluminato ligands. A solvent switch from n-hexane
to toluene−diethyl ether led to the isolation of divalent
Cp*Yb(AlEt )(Et O) via redox-inactive ligand transfer of
4
2
2
Cp* Pb. Overall, the feasibility of such redox protocols is
2
crucially affected by the redox potentials of the rare-earth-metal
centers (Sm versus Eu versus Yb), the counter ligands (alkyl
versus amido), and the reaction conditions (reaction time and
solvent).
Figure 10. Solid-state structure of Cp*Yb(AlEt ) (Et O) (11).
4
2
2
Hydrogen atoms are omitted for the sake of clarity. Atoms are
represented by atomic displacement ellipsoids at the 50% probability
level. Selected interatomic distances (Å) and angles (deg): Yb−C9
2
.687(2), Yb−C16 2.923(2) Yb−O1 2.396(1), Yb−O2 2.411(1), Yb−
EXPERIMENTAL SECTION
General Considerations. All manipulations were performed
under rigorous exclusion of air and moisture, using glovebox
techniques (MB Braun MB200B; <1 ppm of O , <1 ppm of H O,
■
C(Cp*) 2.645(2)−2.694(2), Al−C9 2.053(2), Al···C16 3.004(2);
Yb−C9−Al 163.66(9), Al−C9−C16 112.8(1), C9−Yb−O1 93.00(5),
C9−Yb−O2 105.25(6), O1−Yb−O2 100.94(5).
2
2
argon atmosphere). The solvents n-hexane, toluene, diethyl ether
(
Et O), and tetrahydrofuran (THF) were purified using Grubbs
2
yield, suggesting the absence of any pronounced Yb(II) →
columns (MBraun SPS, solvent purification system). C D (99.6%,
6
6
Yb(III) redox chemistry. Interestingly, the coordination mode
4
2
Sigma-Aldrich) was dried over Na/K alloy. All solvents were stored
inside a glovebox. 1,1,1,3,3,3-Hexamethyldisilazane (95%, Sigma-
Aldrich) was used as received, 1,2-Diiodoethane (99%, Sigma-Aldrich)
was recrystallized from diethyl ether prior to use, ytterbium metal
(99.9%, Sigma-Aldrich), samarium metal (99.9%, ABCR), and
europium metal (99.9%, ABCR) were used as received, n-butyllithium
of the AlEt moiety resembles that of Cp* Yb(AlEt ·THF),
4
2
3
which was generated by the addition of 1 equiv of AlEt to
3
Cp* Yb(THF) in toluene. The Yb−C distances involving the
2
side-on coordinated ethyl group are 2.687(2) and 2.923(2) Å in
1
1 and 2.85(2) and 2.94(2) Å in Cp* Yb(AlEt ·THF).
2 3
G
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
1.6 M in hexanes, Sigma-Aldrich) was used as received, and sodium
bis(trimethylsilyl)amide was synthesized by reacting sodium amide
95%, Sigma-Aldrich) with 1.1 equiv of 1,1,1,3,3,3-hexamethyldisila-
zane in n-hexane. LnI (THF) (Ln = Sm, Eu, Yb) were synthesized
dark suspension had formed; after another 20 min the solution had
turned dark green and a gray-black metallic precipitate had formed.
The reaction mixture was stirred for another 18 h at ambient
temperature and centrifuged, the resulting dark green solution was
filtered, and the gray-black solid residue was extracted with n-hexane
(2 mL). The solution was dried under vacuum, leaving a mixture of
green and orange solids (0.142 g). The solid was recrystallized from n-
hexane at −40 °C, yielding Cp* Eu[N(SiMe ) ] as dark green
(
2
2
4
3
according to the original procedure described by Kagan et al.
Accordingly, excess metal was reacted with 1,2-diiodoethane in THF
for 18 h followed by centrifugation, filtration, and crystallization from
saturated THF solutions at −40 °C. Ln[N(SiMe ) ] (THF) (Ln =
3
2
2
2
2
3 2
1
0
Sm, Eu, Yb), Ln{[μ-N(SiHMe ) ] Ln[N(SiHMe ) ](THF)} (Ln =
hexagonal plates and Eu[N(SiMe ) ] as bright orange needles.
2
2
2
2
2
2
3 2 3
11
8
Sm, Eu, Yb), and {Ln(AlR ) } (Ln = Sm, Eu, Yb; R = Me, Et) were
synthesized according to slightly modified literature procedures.
Determination of the yield was not possible, due to cocrystallization of
Eu[N(SiMe ) ] . Anal. Calcd for C H EuNSi (582.81 g/mol): C,
4
2
3
2
3
26 48
2
Cp* Pb was obtained from the reaction of PbCl with 1.9 equiv of
53.58; H, 8.30; N, 2.40. Found: C, 51.39; H, 6.93; N, 2.77. Although
these results are outside the range viewed as establishing analytical
purity (C, −1.79%; H, −0.97%), they are provided to illustrate the best
values obtained to date. Since the crystals needed to be manually
separated under a light microscope, the sufficiently pure material
received was just enough for an elemental analysis but not for DRIFT.
Deviation from the calculated values for carbon and nitrogen might be
explained by contamination of minimal amounts of cocrystallized
needles of Eu[N(SiMe ) ] , which were mechanically inseparable from
2
2
Cp*Li in THF and its solid-state structure reinvestigated (Figure S5 in
44
1
13
the Supporting Information).
H NMR and C spectra were
recorded on a Bruker Biospin DPX 400 or on a Bruker Biospin AV500.
Due to the paramagnetic nature of Eu(II), Eu(III), Sm(III), and
Yb(III), some of the NMR spectroscopic characterizations were
1
inconclusive, but H chemical shifts (without integrals) were included
in cases of the correct number of signals. IR spectra were recorded on
a Nicolet protege 460 instrument using DRIFT (diffuse reflectance
́ ́
infrared Fourier transform) or on a Thermo Scientific Nicolet 6700
FT-IR spectrometer using CsI plates and Nujol. For all the DRIFT
measurements, the ratio of potassium bromide to metal complex was
kept constant at 20:1. Elemental analyses were performed on an
Elementar Vario EL III instrument.
3
2 3
the plates of Cp* Eu[N(SiMe ) ].
2 3 2
Cp*Sm[N(SiHMe ) ] (THF) (3a). Cp* Pb (0.098 g, 0.21 mmol)
2
2 2
2
was dissolved in n-hexane (4 mL) and added dropwise to Sm{[μ-
N(SiHMe ) ] Sm[N(SiHMe ) ](THF)} (0.194 g, 0.14 mmol)
2
2
2
2
2
2
dissolved in n-hexane (4 mL). After addition was complete, a dark
suspension had formed. The reaction mixture was stirred for another 3
h at ambient temperature and centrifuged, the resulting dark yellow to
orange solution was filtered, and the gray-black solid residue was
extracted with n-hexane (2 mL). The solution was dried under reduced
pressure, leaving a slightly oily orange-red solid (0.247 g). The solid
was recrystallized from n-hexane at −40 °C. Crystallized yield: 0.088 g
(0.14 mmol, 33%). After X-ray structure determination, the entire
sample was dried under vacuum, dissolved in THF to provide each
metal center with coordinating THF molecules, dried again (0.246 g,
0.40 mmol, 97%), and recrystallized from n-hexane. Two crops with a
combined yield of 0.133 g (0.21 mmol, 50%) were collected. DRIFT
Cp*Sm[N(SiMe ) ] (1a). Cp* Pb (0.098 g, 0.20 mmol) was
3
2 2
2
dissolved in n-hexane (5 mL) and added dropwise to Sm[N-
(
SiMe ) ] (THF) (0.251 g, 0.41 mmol) dissolved in n-hexane (5
3 2 2 2
mL). The reaction mixture was stirred for another 18 h at ambient
temperature, during which a black suspension had formed; this was
centrifuged to remove elemental lead, which appeared as a gray-black
solid residue, and the resulting orange solution was filtered. The
solution was dried under reduced pressure, leaving an orange
crystalline solid (0.243 g, 0.40 mmol, 98%). The solid was
recrystallized from THF at −40 °C to give the product as orange
plates. Crystallized yield: 0.150 g, 0.25 mmol, 61%. Single crystals for
X-ray structure determination were grown from a saturated toluene
̃
(ν): 2962 (m), 2904 (m), 2862 (w), 2729 (vw), 2119 (w, sh), 2065
1
solution. H NMR (400 MHz, THF-D , 26 °C): δ 1.45 (s, 15H,
(m), 2046 (w, shoulder), 1948 (w, br sh), 1865 (vw), 1446 (w), 1379
(vw), 1348 (vw), 1244 (s), 1178 (vw), 1153 (vw), 1026 (s), 953 (s,
sh), 893 (vs), 837 (vs), 787 (s), 764 (s), 694 (w), 690 (w), 633 (vw),
8
13
C Me CH ), −4.28 (s, 36H, SiMe ) ppm. C NMR (400 MHz,
5
5
3
3
THF-D , 26 °C): δ 121.6 (C Me ), 20.8 (C Me CH ), −0.5 (br,
8
5
5
5
5
3
−1
SiMe ) ppm. DRIFT (ν
̃
): 2951 (s), 2912 (m), 2879 (m), 2735 (vw),
652 (vw), 2480 (vw), 1919 (vw), 1858 (vw), 1495 (vw), 1443 (w),
389 (w), 1350 (vw), 1246 (s), 989 (vs), 879 (s), 835 (vs), 769 (s),
602 (w) cm . Anal. Calcd for C H N OSi Sm (622.36 g/mol): C,
3
22 51 2 4
2
1
7
42.46; H, 8.26; N, 4.50. Found: C, 43.04; H, 8.24; N, 4.35. Although
these results are outside the range viewed as establishing analytical
purity (C, +0.18%), they are provided to illustrate the best values
obtained to date.
−1
54 (m), 727 (w), 673 (m), 600 (m) cm . Anal. Calcd for
C H N Si Sm (606.36 g/mol): C, 43.58; H, 8.48; N, 4.62. Found: C,
22
51
2
4
4
3.71; H, 9.09; N, 4.62. Although these results are outside the range
Cp*Yb[N(SiHMe ) ] (THF) (3b). Cp* Pb (0.114 g, 0.24 mmol)
2
2 2
2
viewed as establishing analytical purity (H, +0.21%), they are provided
to illustrate the best values obtained to date.
was dissolved in THF (5 mL) and added dropwise to Yb{[μ-
N(SiHMe ) ] Yb[N(SiHMe ) ](THF)} (0.235 g, 0.16 mmol)
2
2
2
2
2
2
Cp*Yb[N(SiMe ) ] (1b). Cp* Pb (0.104 g, 0.22 mmol) was
dissolved in THF (3 mL). After addition was complete, a cloudy
red solution and a metal (Pb) ball had formed. The reaction mixture
was stirred for another 18 h at ambient temperature before the
solution was filtered and dried under reduced pressure, leaving an oily
red-purple solid (0.316 g). The solid was recrystallized from n-hexane
at −40 °C. Crystallized yield: purple crystals, 0.228 g (0.35 mmol,
3
2 2
2
dissolved in n-hexane (5 mL) and added dropwise to Yb[N-
(
SiMe ) ] (THF) (0.277 g, 0.43 mmol) dissolved in n-hexane (5
3 2 2 2
mL). After addition was complete, a dark suspension had formed. The
reaction mixture was stirred for another 18 h at ambient temperature
and centrifuged to remove elemental lead, which appeared as a gray-
black solid residue, and the resulting purple solution was filtered. The
solution was dried under reduced pressure, leaving a purple crystalline
solid (0.269 g, 0.43 mmol, 99%). The solid was recrystallized from
̃
73%). DRIFT (ν): 2964 (m), 2910 (m), 2868 (w), 2742 (vw), 2129
(w, shoulder), 2075 (m), 1849 (w), 1450 (w), 1379 (vw), 1350 (vw),
1250 (s), 1180 (vw), 1157 (vw), 1066 (m, shoulder), 1036 (m,
broad), 895 (vs), 839 (s), 793 (m), 764 (s), 704 (w), 683 (w), 631
THF at −40 °C to give the product as purple plates. Crystallized yield:
1
−1
0
8
(
(
(
.213 g, 0.34 mmol, 79%. H NMR (400 MHz, THF-D , 26 °C): δ
(w) cm . Anal. Calcd for C H N OSi Yb (645.04 g/mol): C, 40.96;
8
22 51
2
4
2.90 (vbr), 0.68 (br) ppm. DRIFT (ν
m), 2730 (vw), 2480 (vw), 1910 (vw), 1856 (vw), 1487 (vw), 1437
̃
): 2951 (s), 2897 (m), 2862
H, 7.97; N, 4.34. Found: C, 40.61; H, 8.11; N, 4.29.
tBu,Me
tBu,Me
[(pz
Hpz
)Eu(μ-pz
(0.112 g, 0.81 mmol) in THF (8 mL) was added dropwise
to Eu[N(SiMe ) ] (THF) (0.250 g, 0.40 mmol) dissolved in THF (2
)(THF)2]2 (4). A colorless solution of
tBu,Me
w), 1383 (w), 1332 (vw), 1250 (s), 1025 (w), 975 (vs), 882 (s), 843
−1
vs), 769 (m), 750 (m), 726 (w), 672 (m), 610 (m) cm . Anal. Calcd
3
2
2
2
for C H N Si Yb (629.04 g/mol): C, 42.01; H, 8.17; N, 4.45. Found:
C, 42.40; H, 8.12; N, 4.53.
mL). After addition was complete, the solution had changed from dark
to light yellow. The reaction mixture was stirred for another 18 h at
ambient temperature before the solution was dried under vacuum,
leaving a yellow solid residue (0.208 g). The residue was redissolved in
THF, filtered, and concentrated under reduced pressure. At −40 °C
the concentrated solution afforded bright yellow single crystals of
22
51
2
4
Cp* Eu[N(SiMe ) ] (2). Cp* Pb (0.057 g, 0.12 mmol) was
2
3 2
2
dissolved in n-hexane (4 mL) and added dropwise to Eu[N-
(
SiMe ) ] (THF) (0.147 g, 0.24 mmol) dissolved in n-hexane (5
3 2 2 2
mL). After addition was complete, formation of gray and yellow
precipitates in an orange solution was observed. Ten minutes later, a
̃
compound 4 (0.164 g, 0.14 mmol, 72% on Eu). DRIFT (ν): 3343
H
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
2
1
vw), 3103 (vw), 3083 (vw), 2957 (vs), 2923 (s), 2902 (s), 2875 (s),
714 (vw), 2691 (vw), 1564 (vw), 1508 (m), 1461 (m), 1413 (m),
359 (m), 1307 (w), 1233 (m), 1207 (w), 1044 (m), 1028 (m), 999
801 (m), 777 (m), 742 (s), 677 (m), 622 (s), 566 (s), 546 (s), 525
−1
(vw) cm . Anal. Calcd for C H Al Sm (1015.86 g/mol): C, 56.75;
48 84 2 2
H, 8.33. Found: C, 56.71; H, 8.20.
Cp*Yb(AlMe4)2 (6b) and [Cp* Yb(μ-AlMe )] (7b). Cp* Pb
(w), 965 (w), 919 (w), 886 (w), 785 (m), 766 (w), 725 (vw), 689 (w),
2
4
2
2
−1
6
68 (vw), 566 (vw), 497 (w) cm . Anal. Calcd for C H Eu N O
(0.118 g, 0.25 mmol) was dissolved in n-hexane (5 mL) and added
dropwise to {Yb(AlMe ) } (0.171 g, 0.49 mmol) suspended in n-
48
84
2
8
4
(1141.15 g/mol): C, 50.52; H, 7.42; N, 9.82. Found: C, 48.94; H,
4
2
7
.19; N, 10.47. Although these results are outside the range viewed as
hexane (3 mL). After addition was complete, a dark blue suspension
had formed. The reaction mixture was stirred for another 18 h at
ambient temperature and centrifuged, the resulting blue solution was
filtered, and the black solid residue was extracted with n-hexane (4
mL). The solid residue was collected and dried under vacuum. The
weight (0.092 g) indicated that Yb-containing species were still
undissolved. Repeated extraction with n-hexane only dissolved another
2 mg, whereas use of toluene allowed the isolation of 0.043 g of a dark
blue substance. The solutions were dried under reduced pressure,
leaving both blue crystalline solids with a combined weight of 0.175 g
(0.132 g n-hexane fraction, 0.043 g toluene fraction). The combined
solids were dissolved in toluene and crystallized at −40 °C to give dark
blue crystals of [Cp* Yb(μ-AlMe )] ·2C H Me (7b). Yield: 0.055 g
establishing analytical purity (C, −1.16%), they are provided to
illustrate the best values obtained to date. We assume that about half of
the coordinated THF molecules are removed by vacuum drying,
tBu,Me
tBu,Me
leaving [(pz
)Eu(μ-pz
)(thf)] ; corrected yield of 0.16 mmol,
2
8
2% on Eu. Anal. Calcd for C H Eu N O (996.97 g/mol): C, 48.19;
40
68
2
8
2
H, 6.88; N, 11.24. Found: C, 48.94; H, 7.19; N, 10.47.
tBu,Me
Cp*Eu(pz
) (THF) (5). Compound 4 (0.169 g 0.18 mmol)
2 2
was obtained from the reaction of Eu[N(SiMe ) ] (THF) (0.214 g,
3
2
2
2
tBu,Me
0
.35 mmol) with 2 equiv of Hpz
(0.096 g, 0.69 mmol) in THF (8
mL) as described above. The yellow solid was dissolved in THF (4
mL), and a solution of Cp* Pb (0.084 g, 0.18 mmol) in THF (4 mL)
2
was added dropwise. During the addition, a dark red suspension
formed. The reaction mixture was stirred for another 18 h at ambient
temperature, during which a suspension of a dark blue solution and
gray Pb powder had formed. The suspension was centrifuged, the blue
THF solution was filtered, and the gray residue was extracted with
THF. The solution was dried under vacuum, leaving a blue oily solid
2
4
2
6
5
(0.05 mmol, 21% Yb). The mother liquor was dried under reduced
pressure, dissolved in n-hexane, filtered, and crystallized at −40 °C to
give blue platelike crystals of Cp*Yb(AlMe ) (6b) (0.052 g, 0.11
4
2
mmol, 22%).
Complex 6b. DRIFT (ν
(vw), 1494 (vw), 1443 (w), 1434 (w), 1411 (vw), 1382 (w), 1238
̃
): 2923 (m), 2890 (m), 2839 (w), 2743
(
0.257 g). The weight of the Pb powder (0.038 g, 0.18 mmol, >99%)
indicated full conversion. The reaction product was dissolved in THF,
(w), 1214 (m), 1194 (m), 1187 (m), 1066 (vw), 1027 (w), 695 (vs),
−1
filtered, and crystallized at −40 °C, forming blue rhombohedra. Yield
638 (w), 582 (m), 508 (w), 471 (w), 469 (w), 413 (vw) cm . Anal.
Calcd for C H Al Yb (482.53 g/mol): C, 44.81; H, 8.15. Found: C,
1
(
two crops combined): 0.162 g, 0.23 mmol, 66% (Eu). H NMR (400
18
39
2
MHz, C D , 21 °C): δ 8.80 (vbr), 1.76 (s), − 2.15 (s), − 10.58 (s)
45.18; H, 7.95.
̃
Complex 7b. DRIFT (ν): 2958 (m, sh), 2913 (vs), 2891 (m), 2866
6
6
ppm. DRIFT (ν
717 (vw), 1558 (vw), 1516 (s), 1502 (m), 1458 (s), 1444 (m), 1419
s), 1385 (w), 1358 (m), 1315 (w), 1232 (m), 1205 (w), 1034 (vs),
001 (m), 962 (w), 922 (w), 883 (s), 777 (s), 723 (w), 687 (w), 665
̃
): 3107 (vw), 2958 (vs), 2920 (s), 2897 (vs), 2856 (s),
2
(
(m), 2827 (w), 2734 (vw), 1490 (w), 1439 (m), 1428 (w), 1382 (w),
1179 (m), 1065 (vw), 1023 (w), 878 (s), 805 (m), 782 (m), 744 (m),
−1
1
675 (m), 622 (s), 593 (w), 568 (m), 544 (m), 521 (w) cm . Anal.
Calcd for C H Al Yb (1061.27 g/mol): C, 54.32; H, 7.98. Found:
−
1
(
(
vw), 567 (vw), 505 (w) cm . Anal. Calcd for C H EuN O
705.82 g/mol): C, 57.86; H, 8.14; N, 7.94. Found: C, 57.71; H,
34 57 4 2
48 84
2
2
C, 54.33; H, 7.79.
8
.17; N, 7.99.
[Cp*Eu(μ-AlMe )(THF) ] (8). Cp* Pb (0.119 g, 0.25 mmol) was
4 3 n 2
dissolved in n-hexane (5 mL) and added dropwise to {Eu(AlMe ) }
4 2
Cp*Sm(AlMe4)2 (6a) and [Cp* Sm(μ-AlMe )] (7a). Cp* Pb
2
4
2
2
(
0.131 g, 0.28 mmol) was dissolved in n-hexane (5 mL) and added
(0.165 g, 0.50 mmol) suspended in n-hexane (7 mL). After addition
was complete, a red-orange suspension had formed. The reaction
mixture was stirred for 18 h at ambient temperature in the dark and
centrifuged, and the resulting colorless solution was filtered and dried
under vacuum and found to contain only an insignificant amount of
solid product (0.014 g). In addition, extraction of the dark colored
solid residue with 4 mL of toluene led to minor isolated yields (0.002
g). Therefore, the solid residue was extracted with THF (2 × 4 mL)
and the resulting yellow solution was filtered and concentrated under
reduced pressure. Storage of that solution at −40 °C led to the
formation of yellow-green crystals (0.272 g, 0.46 mmol, 92%). DRIFT
dropwise to {Sm(AlMe ) } (0.179 g, 0.55 mmol) suspended in n-
4
2
hexane (7 mL). After addition was complete, the suspension had
changed from light violet to black. The reaction mixture was stirred for
another 18 h at ambient temperature and centrifuged, the resulting red
solution was filtered, and the black solid residue was extracted with n-
hexane (2 × 6 mL). The solid residue was collected and dried under
vacuum. The weight (0.196 g) indicated that the Sm-containing
compound remained undissolved. Extracting with toluene (3 × 4 mL)
gave an orange solution. The n-hexane solution was dried under
reduced pressure, leaving red crystalline Cp*Sm(AlMe ) (6a; 0.080 g,
4
2
0
.17 mmol, 32% Sm). Recrystallization from n-hexane (two crops)
̃
(ν): 3080 (vw), 3017 (w), 2981 (s), 2958 (s), 2903 (vs), 2854 (vs),
gave 0.032 g (0.07 mmol, 13%) of the product. The toluene extract
contained 0.097 g of [Cp* Sm(μ-AlMe )] (7a) (0.10 mmol, 35%
Sm) of which 0.090 g (0.09 mmol, 32% Sm) could be crystallized from
2809 (m), 2724 (vw), 2120 (vw), 1602 (vw), 1492 (w), 1461 (m),
1448 (m), 1374 (w), 1341 (w), 1293 (vw), 1244 (vw), 1160 (m),
1081 (s), 1037 (vs), 920 (m), 876 (s), 852 (w), 741−673 multiple
2
4
2
−1
a very concentrated toluene solution at −40 °C, in the form of
signals (s), 565 (s), 467 (w) cm . Anal. Calcd for C H AlEuO
26 51 3
[
Cp* Sm(μ-AlMe )] ·2C H Me.
(590.63 g/mol): C, 52.87; H, 8.70. Found: C, 54.07; H, 8.21. Although
these results are outside the range viewed as establishing analytical
purity (C, +0.80%; H, −0.09%), they are provided to illustrate the best
values obtained to date.
2
4
2
6
5
1
Complex 6a. H NMR (400 MHz, C D , 21 °C): δ 0.84 (s,
6
6
C Me ), −3.24 (s, AlMe4) ppm. DRIFT (ν
̃
): 3016 (w), 2970 (m, sh),
5
5
2914 (s), 2902 (s), 2875 (s, sh), 2796 (m), 2737 (w), 2449 (vw), 2278
(
(
(
vw), 1795 (vw), 1768 (vw), 1489 (w), 1441 (m), 1381 (m), 1228
m), 1201 (s), 1192 (s), 1163 (vw), 1024 (w), 935 (w), 800 (w), 694
vs), 650 (m), 584 (s), 555 (s), 513 (m), 478 (m), 451 (w), 417 (w)
[Cp* Sm (μ -Cl) (μ -Cl)(μ -CH )(THF) ] (9). {Sm(AlMe ) }
3
3
2
3
3
3
2
3
4 2 n
(0.112 g, 0.34 mmol) was dissolved in THF (5 mL), and HCp*
(0.094 g, 0.69 mmol) diluted with THF (5 mL) was added slowly. The
reaction mixture was stirred for 18 h before all volatiles were removed
under vacuum, leaving an almost black oily solid (0.266 g). The
residue was dissolved in a few drops of THF and crystallized at −40
°C, yielding a few orange single crystals which were identified as 9 by
−1
cm . Anal. Calcd for C H Al Sm (459.83 g/mol): C, 47.02; H, 8.55.
Found: C, 47.37; H, 8.47.
18
39
2
Complex 7a. 1H NMR (400 MHz, C D , 21 °C): δ 1.73 (s,
6
6
monomer), 0.85 (s, dimer), 0.68 (s, monomer), −2.14 (s, dimer),
14.30 (s, dimer), −17.51 (s, monomer) ppm. The two sets of signals
are attributed to the monomer−dimer equilibrium 2 Cp* Sm(AlMe )
1
−
X-ray diffraction. H NMR (400 MHz, C D , 21 °C): δ 3.09 (s), 1.77
6
6
(d, 22 Hz), 0.21 (s), −0.38 (s) ppm.
2
4
=
[Cp* Sm(μ-AlMe )] ; for a detailed discussion, see ref 32. DRIFT
Cp* Yb(AlEt ) (10). Cp* Pb (0.073 g, 0.15 mmol) was dissolved
2
4
2
2 4 2
(ν
̃
): 3017 (w), 2958 (m, sh), 2914 (vs), 2880 (s), 2863 (s), 2824 (w),
in n-hexane (6 mL) and added dropwise to {Yb(AlEt ) } (0.140 g,
4 2
2
1
732 (vw), 2309 (vw), 1490 (w), 1438 (m), 1420 (w), 1381 (m),
177 (m), 1094 (vw, sh), 1065 (vw), 1021 (w), 936 (vs), 817 (m),
0.31 mmol) dissolved in n-hexane (8 mL). The dark yellow solution
turned instantly greenish before a gray suspension formed. The
I
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
reaction mixture was stirred for 18 h at ambient temperature in the
dark and centrifuged, and the resulting blue-purple solution was
filtered and dried under vacuum, leaving 0.084 g of a blue solid. The
gray-green solid residue was extracted with toluene, and the resulting
gold-yellow solution was dried under vacuum, leaving 0.101 g of a
greenish yellow solid. The blue compound was dissolved in a small
amount of n-hexane and filtered, where 0.007 g of a yellow toluene-
soluble solid residue was recovered. The blue n-hexane solution was
dried under vacuum to yield 0.069 g of blue solid. Recrystallization of
the blue solid from an n-hexane solution at −40 °C led to the
formation of a small amount of sticky blue rhombohedra, which were
identified as compound 10 by X-ray crystallography (0.069 g, 0.12
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00837.
■
*
S
NMR spectroscopic and crystallographic data (PDF)
Crystallographic data (CIF)
AUTHOR INFORMATION
■
*
mmol, 39% Yb). DRIFT (ν
̃
): 2933 (vs), 2902 (vs), 2860 (vs), 2792
Corresponding Author
R.A.: fax, (+49) 07071/29 2436; e-mail, reiner.anwander@
uni-tuebingen.de.
(
m), 2729 (w), 1649 (vw), 1452 (m), 1409 (m), 1381 (m), 1240 (w),
1186 (w), 1147 (w), 1101 (vw), 1059 (m), 1018 (m), 985 (m), 955
(
(
(
m), 920 (w), 897 (w), 864 (w), 841 (vw), 804 (vw), 712 (vw), 650
−1
Author Contributions
All authors have given approval to the final version of the
s), 594 (m, sh), 544 (m), 455 (m) cm . Anal. Calcd for C H AlYb
28
50
586.74 g/mol): C, 57.32; H, 8.59. Found: C, 54.94; H, 8.51. Although
these results are outside the range viewed as establishing analytical
purity (C, −1.98%), they are provided to illustrate the best values
obtained to date.
manuscript.
Notes
The authors declare no competing financial interest.
Cp*Yb(AlEt )(Et O) (11). {Yb(AlEt ) } (0.201 g, 0.44 mmol) was
4
2
2
4 2
dissolved in toluene (4 mL) and diethyl ether (Et O, 1 mL) was added
2
with stirring. During the addition the solution changed from orange to
ACKNOWLEDGMENTS
■
1
brown-green. Cp* Pb (0.105 g, 0.22 mmol) was dissolved in toluene
2
We thank the Norwegian Research Council (Project No.
82547/I30) and Meltzer foundation at the University of
Bergen.
(
4 mL) and added dropwise. Instantly, a black suspension formed. The
reaction mixture was stirred for 18 h at ambient temperature in the
dark and centrifuged, and the solid residue was extracted with toluene
(
3 mL). The resulting red-brown solution was filtered and dried under
vacuum, leaving 0.311 g of a green oil. Metallic lead was collected, and
its weight was determined as 0.035 g (0.17 mmol, 77%). Since the
green oil was only sparingly soluble in n-hexane, 0.5 mL of Et O was
added to dissolve the oil completely. The solution was concentrated
under reduced pressure and left to crystallize at −40 °C. Compound
1
which seemed to lose one of the coordinated Et O molecules and
thereby turn oily. H NMR (500 MHz, C D , 26 °C): δ 3.05 (q, J
6
REFERENCES
■
(
1) (a) For reviews, see: Arndt, S.; Okuda, J. Chem. Rev. 2002, 102,
1953−1976. (b) Hou, Z. Bull. Chem. Soc. Jpn. 2003, 76, 2253−2266.
c) Okuda, J. Dalton Trans. 2003, 2367−2378. (d) Fischbach, A.;
2
(
Anwander, R. Adv. Polym. Sci. 2006, 204, 155−281. (e) Zeimentz, P.
M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. Rev. 2006, 106, 2404−
2433. (f) Zimmermann, M.; Anwander, R. Chem. Rev. 2010, 110,
6194−6259. (g) Nishiura, M.; Hou, Z. Nat. Chem. 2010, 2, 257−268.
(h) Zhang, Z.; Cui, D.; Wang, B.; Liu, B.; Yang, Y. In Molecular
Catalysis of Rare-Earth Elements; Roesky, P. W., Ed.; Springer: Berlin,
Heidelberg, 2010; Vol. 137, pp 49−108. (i) Valente, A.; Mortreux, A.;
Visseaux, M.; Zinck, P. Chem. Rev. 2013, 113, 3836−3857.
(2) Nishiura, M.; Guo, F.; Hou, Z. Acc. Chem. Res. 2015, 48, 2209−
2220.
1 crystallized as shapeless orange chunks (0.182 g, 0.30 mmol, 69%),
2
1
3
7
8
HH
3
.9 Hz, 3H, Et O CH ), 2.02 (s, 15H, C Me CH ), 1.37 (t, J 7.8
2 2 5 5 3 HH
3
Hz, 12H, AlCH CH ), 0.82 (t, J 7.1 Hz, 5H, Et O CH ), −0.04 (q,
2
3
HH
2
3
3
13
JHH 7.9 Hz, 8H, AlCH CH ) ppm. C NMR (500 MHz, C D , 26
2
3
7
8
°
(
(
C): δ 115.1 (C Me ), 66.6 (Et O CH ), 14.5 (Et O CH ), 12.0
5 5 2 2 2 3
AlCH CH ), 11.6 (C Me CH ), 5.7 (br, AlCH CH ) ppm. IR
2
3
5
5
3
2
3
̃
Nujol; ν): 2924 (vs), 2725 (m), 2670 (m), 1460 (s, Nujol), 1377 (s,
Nujol), 1304 (m), 1169 (w), 1153 (w), 1123 (vw), 1089 (vw), 1077
(3) For examples, see: (a) Luo, Y.; Baldamus, J.; Hou, Z. J. Am. Chem.
Soc. 2004, 126, 13910−13911. (b) Zhang, L.; Luo, Y.; Hou, Z. J. Am.
Chem. Soc. 2005, 127, 14562−14563. (c) Li, X.; Baldamus, J.; Hou, Z.
Angew. Chem., Int. Ed. 2005, 44, 962−965. (d) Zimmermann, M.;
(
vw), 1059 (vw), 1042 (vw), 966 (w), 919 (vw), 892 (w), 846 (w),
−
1
7
71 (w), 722 (m, Nujol), 646 (w) cm . Anal. Calcd for
C H AlO Yb (599.72 g/mol): C, 52.07; H, 9.24. Found: C, 50.25;
26
55
2
H, 9.52. Although these results are outside the range viewed as
establishing analytical purity (C, −1.42%), they are provided to
illustrate the best values obtained to date. Loss of one molecule of
Et O would result in Cp*Yb(AlEt ) (Et O). Anal. Calcd for
C H AlOYb (525.64 g/mol): C, 50.27; H, 8.63. Found: C, 50.25;
H, 9.52.
X-ray Crystallography and Crystal Structure Determination
of Complexes 1−11. Crystals of compounds 1−11 were grown by
standard techniques from saturated solutions at −40 °C. Suitable
crystals for diffraction experiments were selected in a glovebox and
mounted in Paratone-N (Hampton Research) on a nylon loop. Data
collection was done on a Bruker AXS TXS rotating anode APEXII
̈
Tornroos, K. W.; Anwander, R. Angew. Chem., Int. Ed. 2008, 47, 775−
778. (e) Ravasio, A.; Zampa, C.; Boggioni, L.; Tritto, I.; Hitzbleck, J.;
Okuda, J. Macromolecules 2008, 41, 9565−9569. (f) Li, X.; Nishiura,
M.; Hu, L.; Mori, K.; Hou, Z. J. Am. Chem. Soc. 2009, 131, 13870−
13882. (g) Pan, L.; Zhang, K.; Nishiura, M.; Hou, Z. Angew. Chem., Int.
Ed. 2011, 50, 12012−12015.
2
4
2
22
45
(4) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed.
1999, 38, 227−230.
(5) Li, X.; Nishiura, M.; Mori, K.; Mashiko, T.; Hou, Z. Chem.
Commun. 2007, 4137−4139.
(6) Dietrich, H. M.; Zapilko, C.; Herdtweck, E.; Anwander, R.
Organometallics 2005, 24, 5767−5771.
135
Pt CCD detector using graphite-monochromated Mo Kα radiation
λ = 0.71073 Å). Data collection and data processing were done using
48
̈
(7) Le Roux, E.; Nief, F.; Jaroschik, F.; Tornroos, K. W.; Anwander,
(
R. Dalton Trans. 2007, 4866−4870.
45
46
47
APEX2, SAINT, and SADABS version 2008/1 or TWINABS,
whereas structure solution and final model refinement were done using
(8) (a) Klimpel, M. G.; Anwander, R.; Tafipolsky, M.; Scherer, W.
Organometallics 2001, 20, 3983−3992. (b) Sommerfeldt, H.-M.;
4
9
50
SHELXS version 2013/1 or SHELXT version 2014/4 and
SHELXL version 2014/7. All molecular plots were generated using
the program ORTEP-3. Further details of the refinement and
crystallographic data are given in Table S1 and in the CIF files in the
Supporting Information. CCDC 1424143−1424157 also contain
supplementary crystallographic data for this paper.
̈
Meermann, C.; Schrems, M. G.; Tornroos, K. W.; Frøystein, N. A.;
51
Miller, R. J.; Scheidt, E.-W.; Scherer, W.; Anwander, R. Dalton Trans.
2008, 1899−1907. (c) Occhipinti, G.; Meermann, C.; Dietrich, H. M.;
52
̈ ̈
Litlabø, R.; Auras, F.; Tornroos, K. W.; Maichle-Mossmer, C.; Jensen,
V. R.; Anwander, R. J. Am. Chem. Soc. 2011, 133, 6323−6337.
(9) Morss, L. R. Chem. Rev. 1976, 76, 827−841.
J
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
10) (a) Tilley, T. D.; Zalkin, A.; Andersen, R. A.; Templeton, D. H.
(37) For distinct AlMe4− bridging modes, see: Dietrich, H. M.;
Inorg. Chem. 1981, 20, 551−554. (b) Evans, W. J.; Drummond, D. K.;
̈
Schuster, O.; Tornroos, K. W.; Anwander, R. Angew. Chem., Int. Ed.
Zhang, H. M.; Atwood, J. L. Inorg. Chem. 1988, 27, 575−579.
2006, 45, 4858−4863.
(
11) (a) Nagl, I.; Scherer, W.; Tafipolsky, M.; Anwander, R. Eur. J.
̈
(38) Dietrich, H. M.; Tornroos, K. W.; Anwander, R. J. Am. Chem.
Inorg. Chem. 1999, 1999, 1405−1407. (b) Rabe, G. W.; Rheingold, A.
L.; Incarvito, C. D. Z. Kristallogr. - New Cryst. Struct. 2000, 215, 560−
Soc. 2006, 128, 9298−9299.
(39) Due to the paramagnetism of trivalent ytterbium complexes, we
were not able to fully characterize the glassy yellow compound, which
presumably derives from the putative half-sandwich complex
5
̈ ̈ ̈
62. (c) Bienfait, A. M.; Schadle, C.; Maichle-Mossmer, C.; Tornroos,
K. W.; Anwander, R. Dalton Trans. 2014, 43, 17324−17332.
12) Runte, O.; Priermeier, T.; Anwander, R. Chem. Commun. 1996,
385−1386. (b) Herrmann, W. A.; Eppinger, J.; Spiegler, M.; Runte,
(
1
{Cp*Yb(AlEt ) }.
4 2
(40) Evans, W. J.; Chamberlain, L. R.; Ziller, J. W. J. Am. Chem. Soc.
1987, 109, 7209−7211.
O.; Anwander, R. Organometallics 1997, 16, 1813−1815. (c) Eppinger,
J.; Spiegler, M.; Hieringer, W.; Herrmann, W. A.; Anwander, R. J. Am.
Chem. Soc. 2000, 122, 3080−3096. (d) Gribkov, D. V.; Hultzsch, K.
C.; Hampel, F. Chem. - Eur. J. 2003, 9, 4796−4810.
(41) Schrems, M. G.; Dietrich, H. M.; To
R. Chem. Commun. 2005, 5922−5924.
42) Yamamoto, H.; Yasuda, H.; Yokota, K.; Nakamura, A.; Kai, Y.;
̈
rnroos, K. W.; Anwander,
(
Kasai, N. Chem. Lett. 1988, 17, 1963−1966.
(
̈
13) (a) Zimmermann, M.; Tornroos, K. W.; Sitzmann, H.;
(
(
43) Namy, J. L.; Girard, P.; Kagan, H. B. New J. Chem. 1977, 1, 5.
44) Atwood, J. L.; Hunter, W. E.; Cowley, A. H.; Jones, R. A.;
Anwander, R. Chem. - Eur. J. 2008, 14, 7266−7277. (b) Robert, D.;
Spaniol, T. P.; Okuda, J. Eur. J. Inorg. Chem. 2008, 2008, 2801−2809.
Stewart, C. A. J. Chem. Soc., Chem. Commun. 1981, 925−927.
45) Bruker APEX2, Version 2014. 11-0; Bruker AXS Inc., Madison,
WI, USA, 2014.
46) Bruker SAINT, Version 7.68A; Bruker AXS Inc., Madison, WI,
USA, 2010.
47) Krause, L.; Herbst-Irmer, R.; Sheldrick, G. M.; Stalke, D. J. Appl.
Crystallogr. 2015, 48, 3−10.
48) Sheldrick, G. M. TWINABS, Version 2012/1; Georg-August-
Universitat Gottingen, Gottingen, Germany, 2012.
49) Sheldrick, G. M. XS, Version 2013/1; Georg-August-Universitat
Gottingen, Gottingen, Germany, 2013.
(
c) Zimmermann, M.; Volbeda, J.; To
̈
rnroos, K. W.; Anwander, R. C.
ssmer, C.;
(
R. Chim. 2010, 13, 651−660. (d) Jende, L. N.; Maichle-Mo
Anwander, R. Chem. - Eur. J. 2013, 19, 16321−16333.
14) Dietrich, H. M.; Tornroos, K. W.; Anwander, R. Angew. Chem.,
Int. Ed. 2011, 50, 12089−12093.
15) Deacon, G. B.; Delbridge, E. E.; Fallon, G. D.; Jones, C.; Hibbs,
D. E.; Hursthouse, M. B.; Skelton, B. W.; White, A. H. Organometallics
000, 19, 1713−1721.
16) Atkins, P.; Paula, J. D. Atkins’ Physical Chemistry. 7th ed.; Oxford
University Press: Oxford, U.K., 2002.
17) Evans, W. J.; Forrestal, K. J.; Leman, J. T.; Ziller, J. W.
Organometallics 1996, 15, 527−531.
18) Coles, M. P.; Hitchcock, P. B.; Lappert, M. F.; Protchenko, A. V.
Organometallics 2012, 31, 2682−2690.
19) Tilley, T. D.; Andersen, R. A. Inorg. Chem. 1981, 20, 3267−
270.
20) Heeres, H. J.; Meetsma, A.; Teuben, J. H.; Rogers, R. D.
Organometallics 1989, 8, 2637−2646.
21) Luo, Y.; Feng, X.; Wang, Y.; Fan, S.; Chen, J.; Lei, Y.; Liang, H.
Organometallics 2011, 30, 3270−3274.
22) (a) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. J. Chem. Soc., Dalton
̈
(
(
̈
(
(
(
2
(
̈
̈
̈
(
̈
̈
̈
(
(
.
50) Sheldrick, G. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−
8
(
(51) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71,
3
(
−8.
(
3
(
52) Farrugia, L. J. J. Appl. Crystallogr. 2012, 45, 849−854.
(
(
Trans. 1973, 1021−1023. (b) Ghotra, J. S.; Hursthouse, M. B.; Welch,
A. J. J. Chem. Soc., Chem. Commun. 1973, 669−670.
(
23) Den Haan, K. H.; De Boer, J. L.; Teuben, J. H.; Spek, A. L.;
Kojic-Prodic, B.; Hays, G. R.; Huis, R. Organometallics 1986, 5, 1726−
733.
24) Evans, W. J.; Keyer, R. A.; Ziller, J. W. Organometallics 1993, 12,
618−2633.
25) Evans, W. J.; Mueller, T. J.; Ziller, J. W. J. Am. Chem. Soc. 2009,
31, 2678−2686.
26) Anwander, R.; Klimpel, M. G.; Martin Dietrich, H.; Shorokhov,
D. J.; Scherer, W. Chem. Commun. 2003, 1008−1009.
27) Lazarov, B. B.; Hampel, F.; Hultzsch, K. C. Z. Anorg. Allg. Chem.
1
(
2
(
1
(
(
2
(
(
007, 633, 2367−2373.
28) Halcrow, M. A. Dalton Trans. 2009, 2059−2073.
29) Deacon, G. B.; Harika, R.; Junk, P. C.; Skelton, B. W.; Werner,
D.; White, A. H. Eur. J. Inorg. Chem. 2014, 2014, 2412−2419.
30) Garcia, J.; Allen, M. J. Eur. J. Inorg. Chem. 2012, 2012, 4550−
563.
31) Dietrich, H. M.; To
Organometallics 2009, 28, 6739−6749.
32) Evans, W. J.; Chamberlain, L. R.; Ulibarri, T. A.; Ziller, J. W. J.
Am. Chem. Soc. 1988, 110, 6423−6432.
33) Busch, M. A.; Harlow, R.; Watson, P. L. Inorg. Chim. Acta 1987,
40, 15−20.
34) Harris, D. H.; Lappert, M. F. J. Chem. Soc., Chem. Commun.
974, 895−896.
35) Cheng, J.; Saliu, K.; Kiel, G. Y.; Ferguson, M. J.; McDonald, R.;
Takats, J. Angew. Chem., Int. Ed. 2008, 47, 4910−4913.
36) (a) Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc.,
Dalton Trans. 1976, 2268−2274. (b) Jousseaume, B. Microchim. Acta
992, 109, 5−12.
(
4
(
̈
rnroos, K. W.; Herdtweck, E.; Anwander, R.
(
(
1
(
1
(
(
1
K
DOI: 10.1021/acs.organomet.5b00837
Organometallics XXXX, XXX, XXX−XXX