Synthesis of rare-earth-metal iminopyrrolyl complexes from alkyl precursors: Ln→Al N-ancillary ligand transfer

Article abstract of DOI:10.1021/om301002n

Protonolysis of [YMe₃]_n with 2-{(N-2,6-dialkylphenyl) iminomethyl)}pyrroles (alkyl = iPr (L¹), Me (L²)) gave homoleptic iminopyrrolyl complexes YL¹₃ and YL ²₃ as well as the complex [L²YL ^2,Me]₂ containing a dianionic pyrrolaldiminato ligand, formed via methylation of the imino backbone. Treatment of the half-sandwich complex [(C₅Me₅)YMe₂]₃ and yttrocene (C₅Me₅)₂YMe(THF) with either 2 or 1 equiv of HL afforded the monomeric complexes (C₅Me₅)YL₂ and (C₅Me₅)₂YL,respectively. The complex (C₅Me₅)YL²₂ readily underwent Ln→Al iminopyrrolyl ligand transfer in the presence of trimethylaluminum, producing the known (C₅Me₅)Y(AlMe₄) ₂. Salt metatheses of homoleptic Ln(AlMe₄)₃ (Ln = Y, La) with KL gave complicated reaction mixtures from which the η⁵/η¹:κ¹ pyrrolaldiminato-bridged complex [L^1,MeLa(AlMe₄)]₂ and bis(tetramethylaluminate) complex L²Y(AlMe₄)₂ could be isolated and crystallographically characterized. Moreover, the solid-state structures of YL²₃, [L²YL ^2,Me]₂, (C₅Me₅)YL¹ ₂, (C₅Me₅)₂YL¹, and L²AlMe₂ are presented.

Full text of DOI:10.1021/om301002n

Article
pubs.acs.org/Organometallics
Synthesis of Rare-Earth-Metal Iminopyrrolyl Complexes from Alkyl
Precursors: Ln→Al N‑Ancillary Ligand Transfer
Hiroshi Kaneko,† H. Martin Dietrich,‡,§ Christoph Schadle,§ Cacilia Maichle-Mossmer,§ Hayato Tsurugi,†
̈
̈
̈
Karl W. Tornroos,‡ Kazushi Mashima,*,† and Reiner Anwander*,§
̈
†Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8551, Japan
‡Department of Chemistry, University of Bergen, Alleg
aten 41, N-5007 Bergen, Norway
§Institut fur Anorganische Chemie, Universitat Tubingen, Auf der Morgenstelle 18, D-72076 Tubingen, Germany
́
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Protonolysis of [YMe3]n with 2-{(N-2,6-dialkylphenyl)iminomethyl)}pyrroles (alkyl = iPr (L1), Me (L2)) gave
homoleptic iminopyrrolyl complexes YL1 and YL2 as well as the complex [L2YL2,Me]2 containing a dianionic pyrrolaldiminato
3
3
ligand, formed via methylation of the imino backbone. Treatment of the half-sandwich complex [(C5Me5)YMe2]3 and yttrocene
(C5Me5)2YMe(THF) with either 2 or 1 equiv of HL afforded the monomeric complexes (C5Me5)YL2 and (C5Me5)2YL,
respectively. The complex (C5Me5)YL2 readily underwent Ln→Al iminopyrrolyl ligand transfer in the presence of
2
trimethylaluminum, producing the known (C5Me5)Y(AlMe4)2. Salt metatheses of homoleptic Ln(AlMe4)3 (Ln = Y, La) with KL
gave complicated reaction mixtures from which the η5/η1:κ1 pyrrolaldiminato-bridged complex [L1,MeLa(AlMe4)]2 and
bis(tetramethylaluminate) complex L2Y(AlMe4)2 could be isolated and crystallographically characterized. Moreover, the solid-
state structures of YL2 , [L2YL2,Me]2, (C5Me5)YL1 , (C5Me5)2YL1, and L2AlMe2 are presented.
3
2
alkane elimination,11,12 as well as a AlEt3-redox addition
involving Ln(CH2SiMe3)3(thf)2 and a divalent Sm(II)
iminopyrrolyl complex,14 respectively, have so far been applied
as the main synthesis protocols.
INTRODUCTION
■
The pyrrolyl unit features a popular monovalent functional
group for designing nitrogen-based (ancillary) ligands.1,2
Particularly, multidentate variants provide high complex
stability, which led to their reputation as versatile spectator
ligands in catalytic reactions, especially in so-called post-
metallocene catalysts for homogeneous polymerization.1,3,4
Complexes bearing mono(iminopyrrolyl) ligands were synthe-
sized and structurally characterized for a large variety of
metals.1 Crucially, pyrrolyl ligands can exhibit distinct
coordination behavior, as evidenced for η1 and η5/κ1 modes,
the latter featuring properties akin to those of Cp ligands.1 Also
in rare-earth-metal chemistry the pyrrolyl motif is found in
various multidentate ligand systems,5,6 including dipyrrolides7
or porphyrinogenates.8 A series of yttrium complexes with
monovalent iminopyrrolyl and bis(iminopyrrolyl) ligands was
initially synthesized by Mashima et al. according to silylamine
elimination reactions, utilizing Y[N(SiMe3)2]3 as a precursor.9
The resulting complexes were successfully used as initiators for
ε-caprolactone polymerization.9 Later on, Ln(III) hydrocarbyl
derivatives with N,N-bidentate iminopyrrolyl have been
exploited for the polymerization of methyl methacrylate
(samarium),10 lactide (yttrium),11 and isoprene (scandium,
yttrium, lanthanum).12 Salt metathesis10 and amine9,13 and
We have recently shown that alkylaluminate moieties readily
engage in protonolytic15,16 and salt metathetical ligand
exchange reactions.17 This aluminate route emerged in a
LLnIIIbis(tetramethylaluminate)-based post-metallocene library
(L = ancillary ligand),18 which until now was mainly exploited
for 1,3-diene polymerization, requiring additional activation by
fluorinated boranes/borates.18−20 Importantly, difficulties of
this aluminate route were encountered when nitrogen-based
ancillary ligands LN were employed. The two major drawbacks
are ancillary ligand transfer to aluminum, that is formation of
complexes LNAlMe2,20b,21,22 as well as ligand backbone (e.g.,
imine) alkylation, which as a rule leads to divalent ancillary
23
ligands LN,alkyl
.
Since known mono(iminopyrrolyl)-supported
post-metallocene catalysts were reported to also require further
activation by organoaluminum reagents such as MAO
(containing a considerable amount of AlMe3) or AlEt3,3,4 we
Special Issue: Recent Advances in Organo-f-Element Chemistry
Received: October 24, 2012
Published: February 20, 2013
© 2013 American Chemical Society
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envisaged monoiminopyrrolyl lanthanide tetramethylaluminate
complexes as relevant targets for assessing these prominent side
reactions.24
RESULTS AND DISCUSSION
■
Yttrium Methyl Complexes as Precursors. Sterically
readily accessible Ln−alkyl bonds featuring a donor- and ate-
free environment are rare in lanthanide chemistry, especially in
homoleptic or half-sandwich complexes.15b,25 Thus far,
tetramethylaluminate derivatives26 and methyl complexes
derived therefrom27,28 seem to provide the only alternative to
the sterically encumbered silylalkyls Ln[CH(SiMe3)2]3.29 To
avoid donor contamination and assess the ease of methylation
of the imino functionality, we reacted 2-{(N-2,6-dialkylphenyl)-
iminomethyl)}pyrrole (alkyl = iPr (HL1), Me (HL2)) with
[YMe3]n (Scheme 1).
Scheme 1. Protonolysis of [YMe3]n with Iminopyrroles
Affected by the Backbone Phenyl Substituents
Figure 1. Perspective ORTEP view of the molecular structure of Y[2-
(2,6-Me2C6H3NCH)C4H3N]3 (1b). Thermal ellipsoids are drawn
at the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected distances (Å) and angles (deg): Y−N1 = 2.331(3), Y−N2 =
2.457(3), Y−N3 = 2.323(4), Y−N4 = 2.448(4), Y−N5 = 2.327(4), Y−
N6 = 2.470(3); N1−Y−N2 = 71.1(2), N3−Y−N4 = 71.4(2), N5−Y−
N6 = 71.3(2), N1−Y−N5 = 91.6(2), N1−Y−N3 = 88.2(2), N1−Y−
N4 = 90.1(2), N1−Y−N6 = 162.8(2), N6−Y−N2 = 108.9(2), N6−
Y−N3 = 92.4(2), N6−Y−N4 = 106.4(2).
For one reaction run applying the same conditions, dimethyl-
substituted HL2 afforded small amounts of the complex
[L2YL2,Me]2 (2), involving imino backbone methylation and
formation of the dianionic ligand L2,Me. Despite several tries,
also using [YMe3]/HL2 ratios of 1/1 and 1/2, we were not able
to isolate larger amounts of this complex. According to NMR
spectroscopy and elemental analyses, only pure 1b could be
harvested from crystallizations. Such imino alkylations have
been observed previously in metal alkyl promoted protonolysis
reactions23,30,31 and were also shown for the equimolar reaction
of Y(CH2SiMe3)3(THF)2 with HL1.11 Generally, the steric bulk
of the aryl substituents seems to direct the pathway of the
competing protonolysis and intramolecular alkyl migration.30,31
It is noteworthy that ancillary ligand transformation involving a
switch from mono- to dianionic coordination often leads to a
loss of catalytic activity (when additional activation such as
cationization is required), as exemplified for the application of
corresponding group 4 salen complexes in ethylene polymer-
ization.32
The protonolysis reactions with a methyl group/HL ratio of
1/1 proceeded relatively fast in toluene, as indicated by
complete dissolution of the yttrium precursors within 45 min.
According to NMR spectroscopy, both the dimethyl- and
diisopropyl-substituted pyrrolines HL gave homoleptic com-
plexes Y(L1)3 (1a) and Y(L2)3 (1b) in high yields and high
purity. Complexes 1 can be efficiently crystallized from n-
hexane/toluene solutions at −35 °C. The complex Y[2-(2,6-
iPr2C6H3NCH)C4H3N]3 (1a) was synthesized recently in a
similar protonolysis reaction employing the silylalkyl complex
Y(CH2SiMe3)3(THF)2 and its solid-state structure determined
by X-ray crystallography.11 In comparison to 1a, the obtained
single crystals of Y[2-(2,6-Me2C6H3NCH)C4H3N]3 (1b)
were generally very small, but solvent-free (monoclinic space
group P21/c, Figure 1). Like 1a, homoleptic complex 1b
features three η1:κ1-N,N bidentate iminopyrrolyl ligands L2,
resulting in a slightly distorted octahedral coordination
geometry. The Y−N distances in 1b range from 2.323(4) to
2.331(3) Å for the anionic pyrrolyl nitrogen and from 2.448(4)
to 2.470(3) Å for the longer imino nitrogen donor bonds (1a:
2.315(2)−2.334(2), 2.471(2)−2.493(2) Å).
Compound 2 crystallized from a n-hexane/toluene/benzene
mixture at −35 °C in the monoclinic space group P21/c as a
dimeric complex (Figure 2). The pyrrolyl ring of the dianionic
ligand L2,Me bridges the yttrium centers in a η5/η1:κ1 fashion.
While this coordination mode is a common structural motif of
pyrrolyl ligands,11,12,33−36 for dianionic pyrrolaldiminato ligands
it was observed only recently in yttrium and calcium
complexes.11,31b In complex 2, the yttrium centers are each
surrounded by the monoanionic pyrrolylimine L2 and the
dianionic pyrrolaldiminato L2,Me. Since the bridging pyrrolyl
moiety of the latter dianionic species coordinates one yttrium
center in an η5 fashion, this amounts to a formal coordination
number of 7 for each yttrium center. The pyrrolyl ring is
slightly tilted with an Y−N1 distance of 2.647(2) Å and Y−C
distances ranging from 2.621(2) to 2.798(3) Å (Y−Ctr(Pyr) =
2.439 Å). For comparison, the Y−C distances in the complex
[YL1,CH SiMe (CH2SiMe3)(THF)]2 range from 2.631(6) to
2
3
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formation. Evaporation of the yellow solutions gave residues of
composition [(C5Me5)Y(L1)2] (3) and [(C5Me5)Y(L2)2] (4),
while NMR spectroscopy revealed already a high purity of the
crude reaction products. Complexes 3 and 4 can be further
purified by recrystallization from toluene/n-hexane mixtures at
−35 °C.
The solid-state structure of 3 revealed the monomeric
complex (C5Me5)Y[2-(2,6-iPr2C6H3NCH)C4H3N]2 (3)
with a seven-coordinate yttrium center. The four pyrrolyl
nitrogen atoms and the cyclopentadienyl centroid adopt a
tetragonal-pyramidal geometry (Figure 3). Very recently,
Figure 2. Perspective ORTEP view of the molecular structure of {[2-
(2,6-Me2C6H3NCH)C4H3N]Y[2-(2,6-Me2C6H3NC(H)(Me))-
C4H3N]}2 (2, [L2YL2,Me]2). Displacement ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): Y−N1 = 2.411(2), Y′−N1 = 2.647(2),
Y−N2 = 2.194(2), Y−N3 = 2.341(2), Y−N4 = 2.432(2), N2−C5 =
1.463(4), N4−C19 = 1.304(4), Y−Ctr = 2.439; N3−Y−N4 =
100.53(8), N1−Y−N2 = 72.55(8), N2−Y−N3 = 98.02(9), N1−Y−
N4 = 89.98(8), N1−Y−Ctr = 103.31, N2−Y−Ctr = 116.31, N3−Y−
Ctr = 105.27, N4−Y−Ctr = 121.53.
2.851(6) Å.11 The Y−N1 bond length of 2.411(2) Å of the
bridging pyrrolyl moiety is considerably longer than the Y1−
N2 amido bond (2.194(2) Å) of this chelating ligand but equals
the Y−N4 imino bond of the second ligand L2. The Ln−N3
distance of 2.341(2) Å of the latter ligand L2 is, on the other
hand, considerably longer than the Y1−N2 amide bond.
Backbone alkylation of L2,Me is also reflected in the N2−C5
single bond showing the expected elongation to 1.463(4) Å in
comparison to the N4−C19 double bond (1.304(4) Å) in the
monoanionic ligand L2.
Figure 3. Perspective ORTEP view of the molecular structure of
(C5Me5)Y[2-(2,6-iPr2C6H3NCH)C4H3N]2 (3, (C5Me5)YL1 ). Dis-
2
placement ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected distances (Å) and angles (deg):
Y−N1 = 2.377(2), Y−N2 = 2.487(3), Y−N3 = 2.364(2), Y−N4 =
2.457(2), Y−Ctr = 2.344, N4−C22 = 1.303(4), N4−C23 = 1.444(4),
N1−Y−N2 = 71.16(8), N3−Y−N4 = 70.89(8), N2−Y−N3 =
98.07(8), N1−Y−N4 = 87.28(8), N1−Y−Ctr = 106.92, N2−Y−Ctr
= 114.86, N3−Y−Ctr = 108.01, N4−Y−Ctr = 120.73.
Trifonov et al. reported on the synthesis and characterization
of the structurally comparable bis(iminopyrridyl) half-sandwich
complex (C5Me5)Yb{(2,6-iPr2C6H3NCH(C5H5N)•−}2.37 Its
formation takes place in a rather unusual oxidation reaction
of the divalent ytterbocene (C5Me5)2Yb(THF)2 with 2-{[(2,6-
diisopropylphenyl)imino]methyl}pyridine. While complex 3
reveals distinct amido (Y−N1 = 2.377(2) Å) and imino
donor bonding (Y−N2 = 2.487(3) Å), the aforementioned
ytterbium complex displays two almost equidistant Yb−N
bonds (Yb1−N1A = 2.356(2) Å, Yb1−N2A = 2.345(2) Å)
resulting from charge distribution along the backbone of the
radical ligand. The N−Y−Ctr angles in 3 range from 106.92 to
120.73° and the N1−Y−N2 angles at 71.6(8)° lie in the
expected range from other yttrium iminopyrrolyl complexes.
In order to complete this series, we examined the reaction of
the iminopyrroles HL1 and HL2 with yttrocene methyl
complexes. Treatment of (C5Me5)2YMe(THF) with equimolar
amounts of proligand in toluene led to the desired products
(C5Me5)2YL (5, L = L1; 6, L = L2; Scheme 3). The reaction of
(C5Me5)2Y(AlMe4) with 2 equiv of HL1 or HL2 also gave
complexes 5 and 6, but isolation of the pure products was
hampered by the formation of coproducts Me2AlL. The
yttrocene complexes 5 and 6 exhibit low solubility in aromatic
solvents, facilitating recrystallization from benzene at ambient
temperature.
Next, we examined the effects of pentamethylcyclopenta-
dienyl as a monovalent ancillary ligand on this methyl/
iminopyrrole ligand exchange reaction. Half-sandwich com-
plexes have gathered great interest in lanthanide chemistry,
especially during the past decade.25 The bulky and rigid
properties of this archetypal ligand should be ideal for studying
these exchange reactions by providing stability, minimizing
agglomeration, and yielding traceable products upon subse-
quent alkylation (vide infra). The trimeric yttrium dimethyl
complex [(C5Me5)YMe2]3 is readily obtained according to the
aluminate route,15 and its moderate solubility in aromatic
solvents seemed to qualify for the envisaged methane
elimination reactions (Scheme 2). As for [YMe3]n, the half-
sandwich complex [(C5Me5)YMe2]3 dissolved quickly upon
addition of 2 equiv of pyrrole HL1 or HL2 with slight gas
Scheme 2. Generation of Bis(iminopyrrolyl) Yttrium
Complexes via Protonolysis from [(C5Me5)YMe2]3
The solid-state structure of (C5Me5)2Y[2-(2,6-iPr2C6H3N
CH)C4H3N] (5) revealed a formally eight-coordinate mono-
meric complex (Figure 4) and a more distinct amido and imino
donor bonding (Y−N1 = 2.330(1) Å and Y−N2 = 2.531(1) Å;
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performed with increasing amounts of trimethylaluminum, an
Scheme 3. Preparation of Iminopyrrolyl Yttrocene
Complexes from (C5Me5)2YMe(THF) via Protonolysis
enhanced instability of the Y−L1 moiety was observed (Scheme
4).
Scheme 4. Half-Sandwich Pyrrolyl Complex 4 Displaying
Rapid N-Ligand Exchange with Trimethylaluminum
Iminopyrrolyl ligand L2 was displaced immediately by a
tetramethylaluminato moiety. Using 1 equiv of AlMe3 led to a
mixture of unreacted 4, (C5Me5)YL2(AlMe4), the known
bisaluminate (C5Me5)Y(AlMe4)2,18a and the byproduct
Me2AlL2. When 4 equiv of AlMe3 were applied, complete
exchange was indicated by the exclusive formation of
(C5Me5)Y(AlMe4)2 and Me2AlL2. No intermediate trimethyl-
aluminum adducts of the type [Y(L2)(AlMe3)] were observed,
which could be previously isolated and structurally charac-
terized for several monoanionic amido moieties.41 This implies
that addition of AlMe3 and subsequent displacement of L2 with
a second molecule of trimethylaluminum takes place rather
quickly. This can be rationalized on the basis of the dinuclear
nature of (AlMe3)2 approaching the Y−iminopyrrolyl moiety in
a way that one AlMe3 unit interacts with the pyrrolyl amido
nitrogen, while the second AlMe3 group resides at the reaction
site via donor bonding to the imino nitrogen. Thus, the
pyrrolyl/aluminato exchange can proceed without the delay of a
kinetically controlled subsequent coordination of AlMe3. A
similar (AlMe3)2-based reaction pathway was proposed
previously along with a ligand exchange reaction at an
organoaluminum-modified thulium 2,3,4,5-tetramethylpyrrolyl
complex.42 We did not observe any methylation of the L2 imino
function. Treatment of both HL2 and [KL2] with AlMe3 (even
excess) led to L2AlMe2 as the only observable product (Scheme
5), which is in accordance with known aluminum chemistry
involving similar ligands.43
Single crystals of Me2Al[2-(2,6-Me2C6H3NCH)C4H3N]
(L2AlMe2) were gained from concentrated n-hexane solutions
at −40 °C. Several dimethylaluminum pyrrolylaldiminate
complexes were previously structurally characterized, including
5-tert-butyl-2-[(2,6-diisopropylphenyl)aldimino]pyrrolyl44 and
2,5-bis(N-aryliminomethyl)pyrrolyl derivatives.45 Unsurpris-
ingly, the complex L2AlMe2 shows a distorted-tetrahedral
geometry (Figure 5), originating from a relatively acute N1−
Al−N2 angle of 84.68(5)° of the pyrrolaldiminato ligand, which
is comparable to those in complex 5-tert-butyl-2-[(2,6-
diisopropylphenyl)aldimino]pyrrole aluminum dimethyl
Figure 4. Perspective ORTEP view of the molecular structure of
(C5Me5)2Y[2-(2,6-iPr2C6H3NCH)C4H3N] (5, (C5Me5)2YL1). Dis-
placement ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected distances (Å) and angles (deg):
Y1−N1 = 2.330(2), Y1−N2 = 2.531(2), Y1−Ctr1 = 2.405, N2−C5 =
1.318(2), N2−C6 = 1.443(2); N1−Y1−N2 = 73.09(4), N1−Y1−Ctr1
= 101.06, N2−Y1−Ctr2 = 114.82.
ΔY−N = 0.201 Å) in comparison to half-sandwich complex 3
(ΔY−N = 0.110 Å). This might originate from enhanced steric
repulsion between the diisopropyl substituents of the
iminopyrrolyl ligand and the pentamethylcyclopentadienyl
ligands. The Ln−N distance is also comparable to those in
diazabutadiene lanthanidocene complexes.38,39
Reactions with Trimethylaluminum. d-transition-metal-
based and f-element-based polymerization catalysis often
involves methylalumoxane (MAO) as the most prominent
organoaluminum activator.40 Other routinely employed orga-
noaluminum reagents comprise homoleptic AlR3 (R = Me, Et,
iBu) as well as heteroleptic HAliBu2 or R2AlCl (R = Me, Et,
iBu). It is also noteworthy that commercially available MAO
contains a considerable amount of Al2Me6. Much effort has
been put into the synthesis of new ancillary proligands as
alternatives to cyclopentadienyl derivatives (keywords non-
cyclopentadienyl or post-metallocene).3,4 In contrast to the
ubiquitous η5-C5R5 ligands, N- and O-donor-based ancillaries L
are much more prone to Ln → Al L transfer in the presence of
activating organoaluminum reagents, as revealed by studies of
the LLnIIIbis(tetramethylaluminate)-based post-metallocene
library (L = ancillary ligand),18,20−22 Since derivatives
L1LnIII(AlMe4)2 and L2LnIII(AlMe4)2 display potential candi-
dates for this library, we initially studied the proneness of these
η5-coordinating iminopyrrolyl ligands to Ln → Al L transfer.
The half-sandwich complex (C5Me5)YL1 (4) seemed to be a
2
good target due to its mononuclearity, the comparatively
unsaturated metal environment, and immediate comparability
with the cyclopentadienyl ligand. When the reaction of 4 was
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Scheme 5. Synthesis of Iminopyrrolyl Dimethyl Aluminum
Complexes via Protonolysis or Salt Metathesis Reactions
Utilizing Trimethylaluminum
Scheme 6. Synthesis of Iminopyrrolyl Tetramethylaluminate
Complexes via Salt Metathesis Utilizing Homoleptic
Ln(AlMe4)3 Featuring Backbone Methylation as a Main
Reaction Pathway
a
a
Backbone methylation was not observed in the absence of rare-earth
metals.
In contrast to the case for cyclopentadienyl ligands, this
makes the reaction rather unpredictable. Due to complicated
NMR spectra not all byproducts could be unambiguously
identified. However, we were able to isolate and fully
characterize some main products in reasonable yields via
fractionate crystallization. From the reaction with KL1 the
dimeric complex [L1,MeLa(AlMe4)]2 (7) could be crystallized,
revealing methylation of the imino group in the presence of
tetraalkylaluminato ligands. Bearing in mind that neither HL
nor KL is methylated by free AlMe3 (Scheme 5), it can be
speculated about scenarios involving either the migration of
transient terminal La−CH3 groups or imino group methylation
via highly mobile La−η1-AlMe4 moieties.
Complex 7 features a formally seven-cooordinate lanthanum
center and a η5/η1:κ1 bridging coordination mode of the pyrrole
moieties, as detected for complex 2 (Figure 6).11,12 Complex 7
shows an amido and imino donor bonding (La−N1 = 2.560(3)
Å and La−N2 = 2.278(3) Å; ΔLa−N = 0.282 Å) even more
pronounced than in yttrocene 5 (ΔY−N = 0.201 Å). The
tetramethylaluminato ligand is coordinated in an η2 fashion
with an La−C distance of 2.743(4) Å, which is significantly
longer than the La−C(η2-AlMe4) contacts in seven-coordinate
homoleptic La(AlMe4)3 (2.696(3) and 2.701(3) Å).26 The
tetramethylaluminato moiety in 7 shows a torsion angle C19−
Al1−C20−La1 of 26.42°, which features a conformation less
“bent” than that found in the half-sandwich complex (C5Me5)-
La(AlMe4)2 (62.0(2)°)16a and homoleptic La(AlMe4)3
(49.0(1)°).26b
Figure 5. Perspective ORTEP view of the molecular structure of
Me2Al[2-(2,6-Me2C6H3NCH)C4H3N] (L2AlMe2). Thermal ellip-
soids are drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity. Selected distances (Å) and angles (deg): Al−N1 =
1.981(2), Al−N2 = 1.911(2), Al−C12 = 1.966(2), Al−C13 =
1.951(2), C4−N1 = 1.440(2), C5−N1 = 1.305(2), C6−N2 =
1.388(2), C11−N2 = 1.352(2); N1−Al−N2 = 84.68(5), N1−Al−
C13 = 109.21(6), N1−Al−C12 = 113.81(6), N2−Al−C12 =
110.17(6), N2−Al−C13 = 116.48(7), C12−Al−C13 = 117.90(7).
(85.5(2)°) and its chloride precursor (88.2(2)°).44 Also, the
Al−C12(13) (1.966(2) and 1.951(2) Å) and Al−N1(2) bond
lengths (1.981(2) and 1.911(2) Å) lie in the expected range.
Finally, we examined the feasibility of conducting a reverse
ligand exchange, meaning the displacement of a tetramethyl-
aluminate moiety by such iminopyrrolyl ligands. We chose
homoleptic complexes Ln(AlMe4)3 (Ln = Y, La) as metal
precursors,26 since that might result in complexes LLn(AlMe4)2
of relevance for the bis(aluminate) library. Moreover, the large
diamagnetic La(III) center might reveal another metal-size
effect implied by this multifunctional ligand environment. In
order to avoid soluble side products, such as LAlMe2, a salt
metathesis route applying KL was chosen over a protonolysis
with HL (Scheme 6). The stirring of equimolar reaction
mixtures overnight in toluene led to yellow solutions with white
precipitates (KAlMe4). The NMR spectra of the obtained
yellowish oily solids indicated product mixtures, which is not
surprising since complexes Ln(AlMe4)3 exhibit three equally
reactive sites and the iminopyrrolyls under study are not
superbulky ancillaries, as evidenced for the formation of even
homoleptic complexes (cf. complex 1).
The reaction of Y(AlMe4)3 with 1 equiv of KL2 led to the
isolation of the envisaged mono(iminopyrrolyl) bis-
(tetramethylaluminate) complex L2Y(AlMe4)2 (8) (Scheme
6). NMR spectroscopy revealed only one sharp signal for the
aluminate methyl group, in accordance with a highly fluxional
behavior as reported previously for bis(tetramethylaluminate)
complexes such as (C5Me5)Ln(AlMe4)2.18a Complex 8 is stable
in benzene solution for at least 2 days, showing no sign of a
methylation reaction at the imino backbone. However, due to
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Organometallics
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Figure 7. Perspective ORTEP view of the molecular structure of [2-
(2,6-Me2C6H3NCH)C4H3N]Y(AlMe4)2 (8, L2Y(AlMe4)2). Dis-
placement ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. Selected distances (Å) and angles (deg):
Y1−N1 = 2.3024(9), Y1−N2 = 2.4131(9), Y1−C14 = 2.526(1), Y1−
C15 = 2.528(1), Y1−C18 = 2.535(1), Y1−C19 = 2.521(1), Y- - -Al1 =
3.0772(4), Y- - -Al2 = 3.1009(3), Al1−C14 = 2.078(1), Al1−C15 =
2.080(1), Al1−C16 = 1.968(1), Al1−C17 = 1.970(1), Al2−C18 =
2.083(1), Al2−C19 = 2.072(1), Al2−C20 = 1.976(1), Al2−C21 =
1.962(1); N1−Y1−N2 = 72.21(3), C14−Y1−C15 = 84.27(4), C18−
Y1−C19 = 83.38(4), C15−Y1−C18 = 89.03(4), C14−Y1−C18 =
171.06(4), C15−Y1−N1 = 90.92(4), C19−Y1−N1 = 169.14(4),
C19−Y1−N2 = 97.11(9).
Figure 6. Perspective ORTEP view of the molecular structure of the
complex {(AlMe4)La[2-(2,6-iPr2C6H3NC(H)(Me))C4H3N]}2 (7,
L
1,MeLa(AlMe4)). Displacement ellipsoids are drawn at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
distances (Å) and angles (deg): La−N1 = 2.560(3), La−N2 =
2.278(3), La−N1′ = 2.822(3), La−C19 = 2.743(4), La−C20 =
2.743(4), La- - -Al = 3.261(2), Al−C19 = 2.074(5), Al−C20 =
2.065(4), Al−C21 = 1.959(4), Al−C22 = 1.994(5), La−Ctr = 2.637;
N1−La−N2 = 67.61(10), N1−La−Ctr = 97.40, N2−La−Ctr =
110.72, C19−La−C20 = 76.4(1), C19−La−Ctr = 112.07, C20−La−
Ctr = 126.18, C19−A1−C20 = 110.1(2).
rather complicated NMR spectra of the crude product mixture,
an initial independent formation of such a methylated species
analogue to complex 7 cannot be undoubtedly ruled out. The
solid-state structure of complex 8 shows a six-coordinate
yttrium center involving two η2-coordinating alkylaluminato
ligands and one bidentate iminopyrrolyl ligand (ΔY−N = 0.110
Å) (Figure 7). While the iminopyrrolyl bonding is comparable
to that in half-sandwich complex 3 showing the same ΔY−N
value of 0.110 Å, the almost planar coordination mode of both
tetramethylaluminate ligands (maximum torsion angle 7.40°)
was also found in benzamidinate complex [PhC(NC6H4iPr2-
2,6)2]Y(AlMe4)2.20a Also, the Y−C distances (2.521(1)−
2.535(1) Å) and C−Y−C angles (average 84.27(4)°) of 8
match those in the latter benzamidinate complex (2.523(2)−
2.542(2) Å, 81.94(8)°). It is noteworthy that complexes of type
[PhC(NC6H4iPr2-2,6)2]Y(AlMe4)2 have shown remarkable
performance in 1,3-diene polymerization.20a
of polymerization catalysts composed of nitrogen (oxygen)-
based ancillary ligands and organoaluminum activators, with
ancillary ligand transfer to aluminum and ligand backbone (e.g.,
imine) alkylation being prominent reaction pathways. The
stability of the bis(tetramethylaluminate) complex [2-(2,6-
Me2C6H3NCH)C4H3N]Y(AlMe4)2 might be further as-
sessed in polymerization reactions.
EXPERIMENTAL SECTION
■
All operations were performed with rigorous exclusion of air and
water, using standard Schlenk, high-vacuum, and glovebox techniques
(MBraun MBLab; <1 ppm O2, <1 ppm H2O). n-Hexane, THF, and
toluene were purified by using Grubbs columns (MBraun SPS, solvent
purification system) and stored in a glovebox. C6H6 and C6D6 were
obtained from Aldrich, degassed, dried over Na for 96 h, and filtered.
AlMe3 was purchased from Aldrich and used as received. Homoleptic
Ln(AlMe4)3 (Ln = Y (7a), La (7b)),26 [YMe3]n,27 [(C5Me5)YMe2]3,28
and (C5Me5)2YMe(THF)28 were synthesized according to literature
procedures. Iminopyrroles HL1 and HL2 were prepared according to
literature procedures2a and deprotonated with KN(SiMe3)2 in n-
CONCLUSION
■
Iminopyrrolyl ligands can be easily introduced into organo-
lanthanide complexes via alkane elimination (Ln methyl
precursors) or salt metathesis (tetramethylaluminate elimina-
tion). Alkylation of the imino backbone, resulting in the
formation of a dianionic pyrrolaldiminato ligand, is a major
reaction pathway in the presence of reactive Ln−CH3 or Ln−
AlMe4 moieties. Furthermore, the steric bulk of the aryl
substituents and the Ln(III) size seem to codirect such
intramolecular alkyl migration. Free trimethylaluminum does
not alkylate the imino backbone of such iminopyrrolyl ligands
but is capable of abstracting these N-ancillary ligands from the
rare-earth-metal center. This Ln → Al N-ligand transfer
involves the formation of Ln−AlMe4 moieties. Generally,
these findings have important implications for the deactivation
1
hexane. H and 13C{1H} NMR spectra were recorded at 25 °C on a
Bruker-BIOSPIN-AV500 (5 mm BBO; H, 500.13 MHz; 13C, 125.77
1
1
MHz) and a Bruker-BIOSPIN-AV600 (5 mm cryo probe; H, 600.13
1
MHz; 13C, 150.91 MHz). H and 13C shifts are referenced to internal
solvent resonances and reported in parts per million relative to TMS.
IR spectra were recorded on a Nicolet Impact 410 FTIR spectrometer
as Nujol mulls sandwiched between CsI plates or on a Nicolet 6700
FTIR spectrometer as DRIFT measurements of KBr triturations.
Elemental analyses were performed on an Elementar Vario EL III
instrument. Since the reactions routinely produce hard to separate
mixtures, some of the combustion analyses are unsatisfactory (4, C
value; 5, N; 8, H). Caution! aluminate compounds and volatiles
containing trimethylaluminum react violently when exposed to air.
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Organometallics
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Y[2-(2,6-iPr2C6H3NCH)C4H3N]3 (1a). A toluene solution of 3
equiv of HL1 (399 mg, 1.567 mmol) and a suspension of freshly
prepared [YMe3]n (70 mg, 0.522 mmol) in toluene were cooled to
−35 °C and combined. The mixture cleared up after 1 h to give a
yellow solution. After the mixture was stirred for 16 h, the solvent was
removed in vacuo to yield the raw product as a pale yellow solid (441
mg, 99%). Two subsequent crystallizations from an n-hexane/toluene
mixture at −35 °C gave 119 mg (27%) of 1 as colorless crystals. NMR
data matched the literature values.11 IR (Nujol, cm−1): 1593 vs, 1424
vs, 1386 vs, 1342s, 1319 s, 1290 vs, 1259 vs, 1168 vs, 1035 vs, 979 vs,
894 vs, 878 s, 802 s, 786 m.
with [(C5Me5)YMe2]3 (40 mg, 0.157 mmol). Crystallization from an
n-hexane/toluene/benzene mixture at −35 °C gave 76 mg (78%) of
compound 4 as colorless crystals. IR (Nujol, cm−1): 1596 vs, 1301 vs,
1258 s, 1172 vs, 1095 m 1087 m, 1038 vs, 977 vs, 892 m, 882 s, 774 s
1
681 m, 607 m. H NMR (600 MHz, C6D6, 25 °C): δ 6.95 (t, 2H, p-
C6H3), 6.95 (br s, 2H, m-C6H3), 6.82 (br s, 2H, m-C6H3), 6.72 (d, 2H,
3-pyr), 6.57 (s, 2H, 5-pyr), 6.30 (dd, 2H, 4-pyr), 2.25 (br s, 6H, C6H3-
CH3), 1.90 (s, 15H, Cp-CH3), 1.49 (br s, 6H, C6H3-CH3) ppm.
13C{1H} NMR (151 MHz, C6D6, 25 °C): δ 163.5 (NCH) 148.7
(ipso-C6H3), 136.3 (p-C6H3), 132.8 (m-C6H3), 129.7 (m-C6H3), 125.1
(2-pyr), 123.0 (3-pyr), 119.5 (5-pyr), 113.3 (4-pyr), 19.3 (C6H3-CH3),
17.7 (C6H3-CH3), 11.4 (Cp-CH3) ppm. Anal. Calcd for C38H42N4Y
(643.683): C, 70.91; H, 6.58; N, 8.70. Found: C, 69.70; H, 6.32; N,
8.85.
Y[2-(2,6-Me2C6H3NCH)C4H3N]3 (1b). Proligand HL2 (446 mg,
2.25 mmol) was dissolved in 5 mL of toluene and added to a stirred
suspension of 100 mg of [YMe3]n (0.75 mmol) in 5 mL of toluene.
After it was stirred at ambient temperature for approximately 45 min,
the mixture cleared up but was stirred further overnight (16 h). The
solution was filtered, its volume reduced to about 3 mL, 1 mL of
hexane added, and the solution cooled to −35 °C. Crystallization of 1b
as small slightly yellow needles was initiated when the vial was taken
briefly out of the freezer. Within 2 h at −35 °C, 388 mg (76%) of 1b
crystallized and was isolated by decantation and washing with 1 mL of
toluene. DRIFT-IR (KBr, cm−1): 2968 w, 1595 m, 1566 vs, 1486 w,
1465 w, 1436 m, 1388 s, 1299 vs, 1260 m, 1172 s, 1033 vs, 978 m, 893
(C5Me5)2Y[2-(2,6-iPr2C6H3NCH)C4H3N] (5). A pentane solu-
tion of 1 equiv of HL1 (17.1 mg, 0.0672 mmol) was cooled to −35 °C
and added to a solution of (C5Me5)2YMe(THF) (30.0 mg, 0.0672
mmol) that was likewise precooled to −35 °C. The mixture cleared up
after 1 h to give a yellow solution. After the mixture was stirred for 16
h, the solvent was removed in vacuo to yield the raw product as a pale
yellow solid (39.5 mg, 96%). IR (KBr, cm−1): 2962 m, 2920 m, 2859
m, 1594 m, 1569 s, 1430 m, 1308 m, 1285 w, 1037 m, 873 w, 749 m,
1
699 w. H NMR (400 MHz, C6D6, 25 °C): δ 7.84 (s, 1H, NCH),
1
7.04 (dd, 1H, 3JHH = 3.4 Hz, 4JHH = 1.6 Hz, 3-pyr), 7.26−7.29 (m, 4H,
w, 883 m, 772 m, 750 s, 735 w, 679 w, 535 w. H NMR (400 MHz,
m-C6H3, p-C6H3, 5-pyr), 6.69 (dd, 1H, 3JHH = 3.4 Hz, 4JHH = 1.6 Hz, 4-
C6D6, 26 °C): δ 7.16 (m, 1H, 3-pyr), 6.85 (m, 1H, p-C6H3), 6.81 (m,
2H, m-C6H3), 6.80 (m, 1H, NCH), 6.58 (br s, 1H, 5-pyr), 6.24 (m,
1H, 4-pyr), 1.78 (s, 6H, C6H3-CH3) ppm. 13C {1H} NMR (100 MHz,
C6D6, 26 °C): δ 163.9 (NCH), 149.1 (i-C6H3), 139.8 (m, 3-pyr),
137.2 (2-pyr), 131.4 (o-C6H3), 128.7 (m-C6H3), 125.4 (p-C6H3),
123.2 (5-pyr), 113.7 (4-pyr), 18.5 (C6H3-CH3) ppm. Anal. Calcd for
C39H39N6Y (680.684): C, 68.82; H, 5.78; N, 12.35. Found: C, 68.59;
H, 5.50; N, 12.01.
3
pyr), 3.04 (sept, 2H, JHH = 6.7 Hz, CH(CH3)2), 1.97 (s, 30H,
3
Cp(CH3)), 1.35 (dd, 12H, JHH = 6.6 Hz, 4JHH = 3.1 Hz, CH(CH3)2)
ppm. 13C{1H} NMR (151 MHz, C6D6, 25 °C): δ 163.8 (NCH),
149.8 (ipso-C6H3), 140.1 (5-pyr), 129.3 (o-C6H3), 128.5 (m-C6H3),
125.6 (p-C6H3), 125.4 (2-pyr), 125.0 (3-pyr), 118.8 (Cp), 115.1 (4-
pyr), 28.8 (CH(CH3)2), 26.9 (CH(CH3)2), 25.7 (CH(CH3)2), 11.3
(Cp-CH3) ppm. Anal. Calcd for C37H51N2Y (612.720): C, 72.53; H,
8.39; N, 4.57. Found: C, 71.76; H, 8.17; N, 5.58.
{[2-(2,6-Me2C6H3NCH)C4H3N]Y[2-(2,6-Me2C6H3NC(H)(Me))-
C4H3N]}2 (2). In an experiment similar to the procedure described for
the synthesis of 1b, a toluene solution of 3 equiv of HL2 (311 mg,
1.567 mmol) and a suspension of freshly prepared [YMe3]n (70 mg,
0.522 mmol) in toluene were cooled to −35 °C and combined. After
45 min a clear yellow solution was observed. Stirring for another 16 h
and subsequent removal of the solvent in vacuo gave a mixture
(C5Me5)2Y[2-(2,6-Me2C6H3NCH)C4H3N] (6). Applying a pro-
cedure similar to the synthesis of 5, HL2 (13.3 mg, 0.0672 mmol) was
reacted with (C5Me5)2YMe(THF) (30.0 mg, 0.0672 mmol) in
toluene. Yield: 35.5 mg (94% yield). IR (KBr, cm−1): 2903 m, 2855
m, 1595 m, 1562 s, 1566 vs, 1468 m, 1388 m, 1306 m, 765 w, 749 w.
1H NMR (400 MHz, C6D6, 25 °C): δ 7.81 (s, 1H, NCH), 7.50 (m,
containing the free ligand HL2, homoleptic complex YL2 , and 2, as
3
3
1H, 5-pyr), 7.44 (m, 3H, m-C6H3, p-C6H3), 7.17 (dd, 1H, JHH = 3.6
Hz, 4JHH = 1 Hz, 3-pyr), 6.93 (dd, 1H, 3JHH = 3.6 Hz, 4JHH = 1 Hz, 4-
pyr), 2.16 (s, 6H, C6H3-CH3), 2.15 (s, 30H, Cp(CH3)) ppm. 13C{1H}
NMR (151 MHz, C6D6, 25 °C): δ 160.8 (NCH), 150.3 (ipso-
C6H3), 141.0 (5-pyr), 135.0 (o-C6H3), 130.0 (m-C6H3), 128.8 (p-
C6H3), 124.5 (2-pyr), 124.4 (3-pyr), 115.0 (4-pyr), 118.2 (Cp), 21.2
(C6H3-CH3), 11.2 (Cp-CH3) ppm. Anal. Calcd for C33H43N2Y·C4H8O
(628.719): C, 70.68; H, 8.18; N, 4.46. Found: C, 70.31; H, 8.64; N,
4.63.
{(AlMe4)La[2-(2,6-iPr2C6H3NC(H)(Me))C4H3N]}2 (7). An n-hex-
ane solution of La(AlMe4)3 (100 mg, 0.250 mmol) was combined with
a suspension of an equimolar amount of KL1 (73.07 mg, 0.250 mmol)
in n-hexane. The suspension turned yellow after 45 min, and the solid
part was evenly distributed. After the mixture was stirred for 16 h, the
white solid part was separated by centrifugation. The yellow solution
was filtered and the solvent removed in vacuo to yield a slightly yellow
oily solid. Crystallization from an n-hexane/toluene/benzene mixture
at −35 °C gave 20.9 mg (17%) of compound 7 as colorless crystals. IR
(KBr, cm−1): 2957 s, 2924 s, 2880 s, 1458 m, 1437 m, 1246 s, 1187 s,
912 w, 861 m, 798 m, 695 vs, 667 s. Anal. Calcd for C44H72Al2N4La2
(988.866): C, 53.44; H, 7.34; N, 5.67. Found: C, 53.04; H, 7.48; N,
4.89.
(AlMe4)2Y[2-(2,6-Me2C6H3NCH)C4H3N] (8). In a procedure
similar to the synthesis of 7, KL2 (67.5 mg, 0.286 mmol) was reacted
with Y(AlMe4)3 (100 mg, 0.286 mmol). Crystallization from an n-
hexane/toluene/benzene mixture at −35 °C gave 53.5 mg (41%) of 8
as colorless crystals. IR (KBr, cm−1): 2915 s, 2880 m, 1587 w, 1454 m,
1302 w, 1250 m, 1189 m, 793 m, 768 m, 693 s, 573 m. 1H NMR (600
MHz, C6D6, 25 °C): δ 7.16 (s, 1H, 5-pyr), 6.86 (s, 2H, m-C6H3), 6.83
(m, 1H, p-C6H3), 6.69 (d, 1H, 3-pyr), 6.33 (dd, 1H, 4-pyr), 1.93 (s,
6H, C6H3-CH3), −0.17 (d, 24H, Al-CH3) ppm. 13C{1H} NMR (151
indicated by NMR spectroscopy. Fractionate crystallization from a
toluene/hexane mixture at −35 °C gave complex 2 in form of several
small colorless blocks. Collecting these crystals for X-ray structure
analysis with a pipet initiated the crystallization of the main product 1b
in large amounts.
(C5Me5)Y[2-(2,6-iPr2C6H3NCH)C4H3N]2 (3). A toluene solution
of 2 equiv of HL1 (80.1 mg, 0.315 mmol) was cooled to −35 °C and
added to a suspension of freshly prepared [(C5Me5)YMe2]3 (40 mg,
0.157 mmol) in toluene likewise precooled to −35 °C. The mixture
cleared up totally after 45 min to give a yellow solution. After the
mixture was stirred for 5 h, the solvent was removed in vacuo to yield
the raw product as a pale yellow solid. Crystallization from an n-
hexane/toluene/benzene mixture at −35 °C gave 71 mg (62%) of
compound 3 as colorless crystals. IR (KBr, cm−1): 2962 s, 2925 s, 2864
s, 1592 s, 1566 vs, 1496 m, 1454 s, 1283 s, 1039 s, 749 s, 690 s, 681 s.
1H NMR (600 MHz, C6D6, 25 °C): δ 7.82 (s, 2H, NCH), 7.03 (t,
2H, p-C6H3), 7.02 (br s, 2H, m-C6H3), 6.95 (br s, 2H, m-C6H3), 6.70
(d, 2H, 3-pyr), 6.59 (s, 2H, 5-pyr), 6.40 (m, 2H, 4-pyr), 3.44 (h, 2H,
CH(CH3)2), 2.75 (h, 2H, CH(CH3)2), 1.90 (s, 15H, Cp-CH3), 1.44
(d, 6H, CH(CH3)2), 1.14 (d, 6H, CH(CH3)2), 0.92 (d, 6H,
CH(CH3)2), 0.69 (d, 6H, CH(CH3)2) ppm. 13C{1H} NMR (151
MHz, C6D6, 25 °C): δ 163.5 (NCH), 149.4 (ipso-C6H3), 139.5 (5-
pyr), 129.1 (o-C6H3), 128.1 (o-C6H3), 126.2 (m-C6H3), 125.6 (m-
C6H3), 123.2 (3-pyr), 123.4 (2-pyr), 119.8 (Cp), 113.2 (4-pyr), 30.2
(CH(CH3)2), 28.0 (CH(CH3)2), 27.2 (CH(CH3)2), 26.9 (CH-
(CH3)2), 23.2 (CH(CH3)2), 20.3 (CH(CH3)2), 11.5 (Cp-CH3)
ppm. Anal. Calcd for C44H57N4Y (730.868): C, 72.31; H, 7.86; N,
7.67. Found: C, 72.77; H, 7.86; N, 7.32.
(C5Me5)Y[2-(2,6-Me2C6H3NCH)C4H3N]2 (4). By a procedure
similar to the synthesis of 3, HL2 (62.5 mg, 0.315 mmol) was reacted
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Organometallics
Article
Table 1. Crystallographic Data for Complexes 1b, 2, 3, 5, 7, 8, and L2AlMe2
1b
2
3
5
7
8
L2AlMe2
formula
Mr
C39H39N6Y
680.67
C78H82N8Y2
1309.34
C47H64N4Y
773.93
C43H57N2Y
690.82
C44H72N4Al2La2
988.84
C21H37N2AlY2
460.40
C15H19N2Al
254.30
space group
a/Å
P21/c
P21/c
P21/c
P21/c
P21/c
P1
P21/c
̅
9.7346(5)
17.5172(11)
20.4851(13)
11.9605(4)
23.4161(8)
12.3163(4)
15.4304(7)
13.3008(6)
20.858(1)
9.9779(4)
16.8309(6)
21.9970(8)
11.0471(5)
18.7061(9)
13.7101(6)
9.2848(3)
11.5466(4)
12.5982(5)
105.821(1)
106.197(1)
93.899(1)
1232.62(8)
2
8.5714(16)
8.6724(16)
19.893(4)
b/Å
c/Å
α/deg
β/deg
γ/deg
V/Å3
95.894(4)
107.273(1)
93.685(1)
92.770(1)
109.152(1)
96.567(5)
3474.7(4)
4
3293.8(2)
2
4272.0(3)
4
3689.8(2)
4
2676.4(2)
2
1469.0(5)
4
Z
F(000)
1416
1368
1652
1472
1008
484
544
T/K
100(2)
1.301
2.633
0.0459
0.1170
1.305
100(2)
1.320
1.804
0.0395
0.0943
100(2)
1.203
1.401
0.0481
0.1118
120(2)
1.244
1.612
0.0318
0.0492
120(2)
1.227
1.636
0.0503
0.1294
120(2)
100(2)
1.150
0.123
0.0397
0.0931
1.077
ρcalcd/g cm−3
μ/mm−1
1.240
2.444
a
R1(obsd)
0.0198
b
wR2(all)
0.0520
c
S
1.082
1.094
1.045
1.244
1.081
a
b
c
2
2
2
R1 = ∑(|Fo| − |Fc|)/∑|Fo|, Fo > 4σ(Fo). wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2. S = [∑w(Fo − Fc2)2/(no − np)]1/2
.
MHz, C6D6, 25 °C): δ 164.3 (NCH), 147.3 (ipso-C6H3), 140.3 (5-
pyr), 136.0 (p-C6H3), 130.5 (m-C6H3), 126.3 (2-pyr), 125.2 (3-pyr),
114.6 (4-pyr), 19.3 (C6H3-CH3), 2.1 (Al-CH3) ppm. Anal. Calcd for
C21H37Al2N2Y (460.406): C, 54.78; H, 8.10; N, 6.08. Found: C, 55.47;
H, 7.18; N, 6.57.
Further details of the refinement and crystallographic data are given in
Table 1 and in the Supporting Information.
ASSOCIATED CONTENT
■
S
* Supporting Information
Me2Al[2-(2,6-Me2C6H3NCH)C4H3N]. In addition to its occur-
rence as a byproduct in alkylation reactions of e.g. (C5Me5)Y[2-(2,6-
Me2C6H3NCH)C4H3N]2 (4) with AlMe3, this dimethylaluminum
pyrrolylaldiminate complex can be synthesized in high yield and purity
as follows: HL2 (200 mg, 1.01 mmol) was dissolved in 3 mL of
toluene, and 146 mg (2.02 equiv) of AlMe3 in 2 mL of toluene was
added with rigorous stirring. The mixture was stirred for 3 h at
ambient temperature and subsequently its volume reduced under
vacuum. The resulting oil was dissolved in 2 mL of n-hexane and
evaporated to dryness to give a crystalline solid. Recrystallization from
small amounts (1−2 mL) of n-hexane at −40 °C yielded 235 mg
(91%) of colorless crystals. IR (KBr, cm−1): 2932 m, 2890 w, 1593 s,
1567 vs, 1503 m, 1452 m, 1393 vs, 1288 vs, 1183, vs, 1096 w, 1040 vs,
993 m, 904 m, 793 m, 771 m, 755 m, 739 w, 689 s, 679 vs, 603 w, 574
w. 1H NMR (400 MHz, C6D6, 26 °C): δ 7.20 (m, 1H, 3-pyr), 6.99 (m,
1H, p-C6H3), 6.96 (m, 2H, m-C6H3), 6.86 (m, 1H, NCH), 6.86 (m,
1H, 5-pyr), 6.50 (m, 1H, 4-pyr), 1.99 (s, 6H, C6H3-CH3), −0.35 (s,
6H, Al-CH3) ppm. 13C {1H} NMR (100 MHz, C6D6, 26 °C): δ 161.9
(NCH), 143.9 (i-C6H3), 136.9 (m, 3-pyr), 136.1 (2-pyr), 132.4 (o-
C6H3), 128.8 (m-C6H3), 126.8 (p-C6H3), 121.2 (5-pyr), 115.9 (4-pyr),
18.5 (C6H3-CH3), −9.0 (br, Al-CH3) ppm. Anal. Calcd for
C15H19AlN2 (254.311): C, 70.84; H, 7.53; N, 11.02. Found: C,
70.79; H, 7.96; N, 11.12.
Crystallographic Data Collection and Refinement. Crystals
were grown by standard techniques from saturated solutions using
toluene at −35 °C (1b, 2, 3, 5, 7, and 8) or n-hexane at −35 °C
(L2AlMe2). Suitable single crystals were selected in a glovebox and
coated with Paratone-N (Hampton Research) and fixed in a nylon
loop. Data collection was done on a Bruker SMART 2K CCD
diffractometer using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å) performing 182° ω scans in four orthogonal ϕ positions
(2, 3, 5, 7, and 8) and on a Bruker APEX DUO diffractometer using
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å)
(L2AlMe2) or Cu Kα radiation (λ = 1.54178 Å) (1b) performing ω
and ϕ scans. Raw data were collected using the program SMART,46
integrated, and reduced with the program SAINT.47 Numerical
corrections for absorption effects were applied using SHELXTL.48 The
structures were solved by direct or Patterson methods using SHELXS
and SHELXL for structure solution and refinement, respectively.49
CIF files giving full crystallographic data for complexes 1b, 2, 3,
5, 7, 8, and L2AlMe2. This material is available free of charge via
the Internet at http://pubs.acs.org. Crystallographic data have
also been deposited at the Cambridge Crystallographic Data
Centre under CCDC reference numbers 907091 (2), 907092
(3), 907093 (5), 907094 (7), 907095 (8), 920027 (L2AlMe2),
and 922387 (1b) and can be obtained free of charge via www.
ccdc.cam.ac.uk/data_request/cif.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: mashima@chem.es.osaka-u.ac.jp (K.M.); reiner.
anwander@uni-tuebingen.de (R.A.).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Norwegian Research Council (Project No.
182547/I30) and the German Science Foundation for financial
support. H.K. is grateful to the Japan Society for the Promotion
of Science (Support Program for Improving Graduate School
Education, Integrated Education System Based on the
Promotion of International Student Mobility) for generously
supporting his research stays in Bergen and Tubingen.
̈
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