Reactivity of Yttrium Methyl Complexes: Hydrido Transfer Capability of Selected Alkylalanes

Article abstract of DOI:10.1021/acs.organomet.5b00013

The reactivity of alkylaluminum hydrides HAlMe₂, HAl(CH₂SiMe₃)₂, and H₂AlMes? (Mes? = C₆H₂tBu₃-2,4,6) toward yttrium methyl complexes was assessed. From the reaction with [Cp₂YMe]₂ the corresponding methylated alkylaluminum compounds could be isolated and characterized along with [Cp₂Y(thf)(μ-H)]₂, obtained upon workup in thf (Cp = C₅H₅ = cyclopentadienyl). Structurally characterized complexes Cp₁₄Y₆H₃Cl and Cp₁₅Y₆H₃ represent side-products of the transformation. The reactions of [YMe₃]_n and [(C₅Me₅)YMe₂]₃ indicated occurrence of hydrido transfer for H₂AlMes? and led to product mixtures for HAl(CH₂SiMe₃)₂. Following the reaction of HAlMe₂ with these compounds as well as the half-sandwich derivatives (C₅Me₄R)Y(AlMe₄)₂ (R = Me, SiMe₃) indicated reversible hydrido binding, leading ultimately to the formation of insoluble hydride clusters. The organoaluminum compounds [HAl(CH₂SiMe₃)₂]₃, [(μ-H)(Me)AlMes?]₂, and Me₂AlMes? were analyzed by X-ray crystallography.

Full text of DOI:10.1021/acs.organomet.5b00013

Article
pubs.acs.org/Organometallics
Reactivity of Yttrium Methyl Complexes: Hydrido Transfer Capability
of Selected Alkylalanes
Christoph Schadle,† Cacilia Maichle-Mossmer,† Karl W. Tornroos,‡ and Reiner Anwander*,†
̈
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†Institute of Inorganic Chemistry, University of Tubingen, Auf der Morgenstelle 18, 72076 Tubingen, Germany
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‡Department of Chemistry, University of Bergen, Alleg
́
aten 41, 5007 Bergen, Norway
S
* Supporting Information
ABSTRACT: The reactivity of alkylaluminum hydrides HAlMe2,
HAl(CH2SiMe3)2, and H2AlMes* (Mes* = C6H2tBu3-2,4,6)
toward yttrium methyl complexes was assessed. From the reaction
with [Cp2YMe]2 the corresponding methylated alkylaluminum
compounds could be isolated and characterized along with
[Cp2Y(thf)(μ-H)]2, obtained upon workup in thf (Cp = C5H5 =
cyclopentadienyl). Structurally characterized complexes Cp14Y6H3Cl and Cp15Y6H3 represent side-products of the
transformation. The reactions of [YMe3]n and [(C5Me5)YMe2]3 indicated occurrence of hydrido transfer for H2AlMes* and
led to product mixtures for HAl(CH2SiMe3)2. Following the reaction of HAlMe2 with these compounds as well as the half-
sandwich derivatives (C5Me4R)Y(AlMe4)2 (R = Me, SiMe3) indicated reversible hydrido binding, leading ultimately to the
formation of insoluble hydride clusters. The organoaluminum compounds [HAl(CH2SiMe3)2]3, [(μ-H)(Me)AlMes*]2, and
Me2AlMes* were analyzed by X-ray crystallography.
reactions of HAlMe2 with organolanthanide complexes afforded
unprecedented alkyl-hydrido heteroaluminates TptBu,MeLn[(μ-
H)AlMe3]2 (A; Ln = Y, Lu; TptBu,Me = hydrotris(3-tert-butyl-5-
methylpyrazolyl)borate; Chart 1)13 and [Cp*2Y(μ-H)AlMe2(μ-
INTRODUCTION
■
Alkylalanes, especially diisobutylaluminum hydride (DIBAH),
are routinely employed as cocatalysts in rare-earth-metal-
catalyzed transformations, such as the polymerization of
butadiene and isoprene,1 ethylene,2 and thf3 and in the
copolymerization of butadiene/styrene,4 isoprene/styrene,4 or
isoprene/ε-caprolactone.5 However, the structure and compo-
sition of complexes forming in these reaction systems as well as
the role of the aluminum hydride are still not well understood.
Empirical studies on polymerization have shown that DIBAH is
an efficient chain transfer agent and involved in the formation
of the catalytically active species,6,7 while Bercaw and
Brintzinger were able to identify cationic, bimetallic hydride
complexes [(rac-Me2Si(1-Ind)2)Zr(μ-H)3(AlR2)2]+ (Ind =
indenyl; R = iBu, Me) as key components in zirconium-based
catalyst mixtures.8 We have previously shown that lanthanide
hydride complexes are accessible from the reaction of DIBAH
with lanthanide silylamides rac-[Me2Si(2-Me-C9H5)2]Ln[N-
(SiHMe2)2] (Ln = Y, Ho) by two possible pathways: one
involving direct hydrido transfer from aluminum and one
involving a β-hydride elimination route.9 Different from our
findings Kempe et al. observed transfer of the ancillary ligand
from the lanthanide to the aluminum metal center when
aminopyridinato-stabilized lanthanide amide complexes were
reacted with DIBAH.10
Chart 1. Structurally Characterized Rare-Earth-Metal Alkyl-
Hydrido Heteroaluminate Complexes
H)AlMe2(μ-CH3)]2 (B; Cp* = C5Me5).14 While monomeric A
could be obtained from alkyl complexes TptBu,MeLuMe2 and
TptBu,MeY(Me)(AlMe4), dimeric B, featuring a 12-membered
ring structure, resulted from benzoate Cp*Y(OOCC6H2Me3-
2,4,6). Herein, we present a full account on the reactivity of
alkylaluminum hydrides HAlMe2, HAl(CH2SiMe3)2, and
H2AlMes* toward yttrium methyl complexes.15 The yttrium
alkyl complexes [Cp2YMe]2,16 [YMe3]n,17 [Cp*YMe2]3,18 and
(C5Me4R)Y(AlMe4)2 (Cp = C5H5, R = Me,19 SiMe320) were
chosen due to well-established, high-yield synthesis routes21
Due to various possible reaction pathways, we decided to
further investigate the reactivity of alkylaluminum hydrides
toward organolanthanide complexes. Looking for aluminum
hydrides not prone to side reactions such as β-hydride
elimination and carrying alkyl moieties of different steric bulk,
we envisaged HAlMe2,8b HAl(CH2SiMe3)2,11 and H2AlMes*
(Mes* = 2,4,6-tBu3C6H2) as suitable reagents.12 Previous
Special Issue: Mike Lappert Memorial Issue
Received: January 13, 2015
© XXXX American Chemical Society
A
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1
and the intrinsic properties of the 89Y nucleus for NMR
spectroscopy (100% abundance, spin 1/2) facilitating the
identification of possible reaction products via distinct coupling
patterns.
as hydrido transfer product AlMe3 by H NMR spectroscopy.
The remaining white solid turned out to be soluble in hot thf.
Upon cooling of the clear solution, a crystalline material could
1
be obtained and identified as [Cp2Y(thf)(μ-H)]2 by H NMR
spectroscopy (SI Figure S1). The 1H NMR spectrum displays a
triplet at 1.98 ppm with a coupling constant of 27 Hz, a feature
that is characteristic for a hydrido ligand bridging between two
yttrium metal centers, as reported in the seminal paper by
Evans et al.23
RESULTS AND DISCUSSION
■
All aluminum hydride precursors employed in this study are
literature-known compounds with established synthesis proto-
cols; however, the solid-state structure for [HAl(CH2SiMe3)2]3
(1) has not been reported to date. In the original paper by
Beachley and Tessier-Youngs11 describing the synthesis of 1, a
trimeric structure was proposed based on cryoscopic molecular
weight data and infrared spectroscopy. Repeating the synthesis,
we were able to obtain crystals of 1 suitable for crystallographic
analysis from an n-hexane solution at −35 °C (Figure 1).
Neosilylaluminum hydride HAl(CH2SiMe3)2 showed similar
reactivity to HAlMe2 (Scheme 1, a), also forming a white
precipitate in the course of the reaction. After separation of the
white solid and drying of the supernatant solution under
vacuum a colorless oil was obtained and identified as
24
1
MeAl(CH2SiMe3)2 by H NMR spectroscopy. Again, the
white solid was soluble in hot thf and identified as the yttrium
hydride complex [Cp2Y(thf)(μ-H)]2. On one occasion we were
able to collect a few crystals from the toluene solution for
crystallographic analysis. The obtained crystal structure
revealed two overlapping molecules of general formulas
[Cp14Y6H3Cl] (2a) and [Cp15Y6H3] (2b)25 (Figure 2), with
2b exhibiting a metallacycle consisting of six yttrium atoms
bridged by three hydrido and three cyclopentadienyl ligands.
Complex 2a differs only in a chlorido ligand instead of a Cp
ligand bridging between yttrium metal centers; the chlorido
ligand stems from the precursor for [Cp2YMe]2, namely,
[Cp2YCl]2.
Figure 1. Solid-state structure of 1 with thermal ellipsoids set at the
50% level. Methyl groups of the SiMe3 moieties and hydrogen atoms
except for those bridging aluminum metal centers are omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Al1−H1 1.67(7),
Al1−H3 1.73(7), Al2−H2 1.71(7), Al2−H1 1.70(6), Al3−H3 1.63(7),
Al3−H2 1.72(7), H1−Al1−H3 94(3), H1−Al2−H2 94(3), H2−Al3−
H3 92(3), Al1−H1−Al2 144(4), Al2−H2−Al3 137(4), Al3−H3−Al1
143(4).
There are only a few reports on yttrium hydride clusters
containing as much as six yttrium nuclei, one example being a
complex synthesized by Hou et al. consisting of six
[(C5Me4SiMe3)YH2] units.26 In the same paper the corre-
sponding penta- and tetranuclear complexes are also described.
Such half-sandwich complexes adopt more tightly packed
geometries of distorted octahedral, square pyramidal, and
tetrahedral metal core structures.27 A cyclic yttrium hydride
complex was reported by Evans et al. consisting of three
[(C5H3Me2)YH] units.28 In complexes 2 yttrium−hydrido
bond lengths vary between 2.03(7) and 2.20(6) Å, covering
about the same range as in dimeric complexes [(C5H4Me)2Y-
(thf)(μ-H)]2 (2.17(8)/2.19(8) Å)23 and [(C5H3Me2)2Y(thf)-
(μ-H)]2 (2.03(7)/2.27(6) Å).28 The yttrium Cp(terminal,
centroid) distances found in 2 range from 2.275 to 2.431 Å and
are markedly shorter than those found in [(C5H3Me2)YH]3,
[(C5H3Me2)2Y(thf)(μ-H)]2, and [(C5H4Me)2Y(thf)(μ-H)]2
(2.62/2.69/2.69 Å) but compare better to those found in the
homoleptic yttrocene YCp3 (2.393−2.503 Å).29 Different from
the terminal Cp ligands the distances of the yttrium metal
centers to the bridging Cp ligands (centroids) fall among the
longer bond lengths (2.547−2.576 Å) in comparison with the
above-mentioned complexes. It is also noteworthy that the
The originally proposed connectivity displaying “a six-
membered ring composed of alternating dialkylaluminum
groups and hydrogen atoms”11 could be confirmed, revealing
a close similarity to isostructural di(tert-butyl)alane, which is
also trimeric, forming a six-membered Al−H ring.22 Both
structures reveal similar Al−H distances (1.72 Å vs average 1.70
Å in 1), while the H−Al−H (89° vs average 93° in 1) and Al−
H−Al (151° vs average 141° in 1) angles are markedly
different.
We began our study using the least sterically demanding
alkylaluminum hydride HAlMe2, which was reacted with
[Cp2YMe]2 in toluene (Scheme 1, a). After separating a
white solid from the toluene solution we were able to obtain a
colorless oil upon vacuum concentrating, which was identified
Scheme 1. Reactivity of Alkylaluminum Hydrides toward [Cp2YMe]2
B
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exchange.34 While a possible intermediate Cp2(H)Zr(μ-H)2Al-
(Me)Mes* could be isolated from the reaction mixture and
structurally characterized, further analytical data of Me2AlMes*
remained elusive.34
The 1H NMR spectrum of [(μ-H)(Me)AlMes*]2 (3)
compares well to the starting material H2AlMes*. It shows
sharp singlets for the aryl protons at 7.47 ppm and for the tert-
butyl groups in ortho- and para-position (1.49 and 1.37 ppm) as
well as broad signals for the hydrido ligand (4.72 ppm) and the
Al-Me group (−0.34 ppm). A very similar NMR spectrum was
also obtained for Me2AlMes* (4) with resonances for the aryl
protons and tert-butyl groups at 7.44, 1.42, and 1.36 ppm,
respectively, as well as a sharp singlet for the two methyl groups
at −0.08 ppm.
The solid-state structures of both aluminum compounds
could be determined by X-ray crystallography. Similar to the
dihydride starting material H2AlMes*,12 the isolated [(μ-
H)(Me)AlMes*]2 (3) also forms a dimer with bridging hydrido
ligands in the solid state (Figure 3) resembling the aluminum
Figure 2. Solid-state structure of 2 with ellipsoids of Y, Cl, and
bridging Ct’s set at the 50% level. Terminal Ct’s were drawn as ball-
and-stick models, and nonbridging hydrogen atoms were omitted for
clarity. Shown in (a) is the structural model with a chlorido bridging
Y1 and Y6 (2a) and in (b) the structural model with a Ct ring on the
same position (2b). Selected bond lengths [Å] and angles [deg] for
2a: Y1−H1 2.08(7), Y1−Cl 2.679(3), Y2−H1 2.09(7), Y2−Ct1 2.547,
Y3−Ct1 2.555, Y3−H2 2.20, Y4−H2 2.06, Y4−Ct2 2.576, Y5−Ct2
2.564, Y5−H3 2.14(7), Y6−H3 2.03(7), Y6−Cl 2.666(3), Y1−H1−Y2
171(4), Y2−Ct1−Y3 174, Y3−H2−Y4 173(3), Y4−Ct2−Y5 178, Y5−
H3−Y6 176(4), Y1−Cl−Y6 130.6(2); for 2b Y1−Ct3 2.33, Y6−Ct3
2.55, Y1−Ct3−Y6 168; all other values are the same as for 2a. (Ct =
cyclopentadienyl centroid.)
Figure 3. Solid-state structure of 3 with ellipsoids set at the 50% level.
Hydrogen atoms except for the bridging hydrido ligands were omitted
for clarity. Selected bond lengths [Å] and angles [deg]: Al−C1
1.968(3), Al−C19 1.946(4), Al−H1 1.69(5), Al−H1′ 1.73(5), Al···Al′
2.647(2), C1−Al−C19 138.5(2), C1−Al−H1 105(2), C1−Al−Al′
108.4(2), C2−C1−Al−C19 101.1(3).
hydride dialkyl moiety found coordinated to Cp2ZrH2 in the
previously mentioned Cp2(H)Zr(μ-H)2Al(Me)Mes*.34 Dime-
rization via bridging hydrido ligands is also observed in other
35
aluminum complexes such as [2,6-Trip2C6H3AlH2]2 (Trip =
35
C6H2iPr3-2,4,6), [2,6-Mes2C6H3AlH2]2 (Mes = C6H2Me3-
structural motif of η5-bridging Cp ligands is well known for
other lanthanide complexes of, for example, lanthanum,30
samarium,31 and ytterbium.32 The yttrium chlorido distances in
2a (2.666(3)/2.679(3) Å) are well within the range of those
found in [Cp2YCl]2 (2.674(4)/2.689(4) Å).33
2,4,6), AriPr4AlH2]2 (AriPr4 = C6H3-2,6-(C6H3iPr2-2,6),36 and
[AriPr8AlH2]2 (AriPr8 = C6H-2,6-(C6H2iPr3-2,4,6)-3,5-iPr2);36
however, 3 appears to be the first example of a defined aryl-
methyl-aluminum hydride. When comparing these structures it
needs to be mentioned that the crystal structures of [2,6-
Trip2C6H3AlH2]2 and [2,6-Mes2C6H3AlH2]2 are contaminated
by the presence of −OH impurities on hydrido positions (14%
and 28%, respectively).35 Overall these four complexes show
very similar structural features around the aluminum metal
centers. The Al−H distances in 3 (1.69(5)/1.73(5) Å)
compare well with those found for the bridging hydrido ligands
in H2AlMes* (1.69(4)/1.70(4) Å)12 and lie well within the
range of those found in [2,6-Trip2C6H3AlH2]2 (1.65(5) Å)35
and [2,6-Mes2C6H3AlH2]2 (1.74(5) Å)35. Also the Al−C1
distance observed in 3 (1.968(3) Å) and the other compared
complexes (H2AlMes* 1.966(3) Å, [2,6-Trip2C6H3AlH2]2
1.963(4) Å, [2,6-Mes2C6H3AlH2]2 1.956(3) Å) match very
closely. Only the Al···Al separations differ slightly with 3
(2.647(2) Å), being intermediate between H2AlMes*
(2.652(2) Å) and [2,6-Mes2C6H3AlH2]2 (2.630(2) Å).
Inspired by the work of Power and Wehmschulte on the
reaction system Cp2ZrMe2/H2AlMes*34 we examined the
reactivity of the bulky aluminum dihydride H2AlMes* toward
[Cp2YMe]2 (Scheme 1, b and c). As for the dialkylaluminum
hydrides an insoluble white solid could be isolated and
identified as [Cp2Y(thf)(μ-H)]2 upon addition of thf.
Furthermore, depending on the employed Y:Al ratio, two
different alkylaluminum species were identified and fully
characterized. Using a Y:Al ratio of 1:1 led to the formation
of mixed alkylaluminum hydride [(μ-H)(Me)AlMes*]2 (3)
(Scheme 1, b), while using a Y:Al ratio of 2:1 the
dimethylaluminum compound Me2AlMes* (4) was obtained
(Scheme 1, c). In accordance with these findings the reaction of
Cp2ZrMe2 with H2AlMes* resulted in the formation of
Cp2ZrH2 and Me2AlMes*, showing the same methyl−hydrido
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a
Different from dimeric [(μ-H)(Me)AlMes*]2 the second
hydrido transfer product, Me2AlMes* (4, Figure 4), is a
Scheme 2. Reactivity of Alkylalanes toward [YMe3]n
a
Nuclearity not accounted for.
Following the reaction in situ by 1H NMR spectroscopy did not
allow for the identification of a major reaction product either.
Finally, we treated [YMe3]n suspended in toluene with
HAlMe2 in a Y:Al ratio of 1:3 (Scheme 2, c). The occurrence of
a reaction was again visually indicated by the formation of a
clear solution after 2 min, which started to produce an
intractable white precipitate after 15 min. Analysis of the
soluble part via 1H NMR spectroscopy allowed for the
identification of trimethylaluminum as reaction product,
indicating the occurrence of hydrido transfer. For further
Figure 4. Solid-state structure of 4 with ellipsoids set at the 50% level.
Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and
angles [deg]: Al−C1 1.993(2), Al−C19 1.965(2), Al−C20 1.964(3),
C1−Al−C19 121.2(2), C1−Al−C20 123.2(2), C19−Al−C20
115.6(2), C2−C1−Al−C19 96.5(2).
monomer in the solid state similar to the halide analogues
X2AlMes* (X = Br,37 Cl38). It is also one of the few examples of
a mixed aryl-alkyl-aluminum compound featuring a three-
coordinate aluminum center as for example in Dipp*AlEt239 or
1
investigation, the reaction was monitored in situ via H NMR
spectroscopy, and the obtained spectrum revealed a doublet at
1
4.68 ppm with a coupling constant JY−H = 20.5 Hz, clearly
39
DcpAlEt2 (Dipp* = 2,6-(C6H3iPr2-2,6)2C6H3, Dcp = 2,6-
indicating yttrium−hydrido bonding (SI, Figure S9). In
addition to this tentative heteroaluminate species “Y-
(AlHMe3)3” we could unambiguously identify Y(AlMe4)3 and
Al2Me6 from the reaction mixture.41
(C6H3Cl2-2,6)2C6H3). The crystal structure of 4 features an
aluminum metal center in a trigonal planar coordination
environment with angles close to 120°, the largest deviation
being the C19−Al−C20 angle (115.6(2)°). It also shows the
typical rotation of the C19−Al−C20 plane relative to the Mes*
plane, both being almost orthogonal to each other (torsion
angle C6−C1−Al−C20 = 96.3(2)°). The Al−C1 distance in 4
(1.993(2) Å) is longer compared to related complexes (3
1.946(4), Dipp*AlEt2 1.968(2), DcpAlEt2 1.985(6) Å), while
the Al−C19 and Al−C20 bond lengths (1.965(2)/1.964(3) Å)
lie between those found for 3 (1.946(4) Å) and Dipp*AlEt2
(1.969(2)/1.978(2) Å). For both Mes*AlCl2 and Mes*AlBr2
short contacts between two hydrogen atoms of the ortho-tert-
butyl groups and the aluminum (2.1 Å) were reported,
implying an agostic interaction between the two. This effect
does not seem to be as pronounced in 4 since only one close
contact of 2.15 Å is found, while the others range from 2.21 to
2.56 Å.
On the basis of the independent work of Okuda42 and
Hou26,43 on half-sandwich dihydride complexes we next
assessed the reactivity of the aluminum hydrides toward
yttrium dimethyl complex [Cp*YMe2]3. The reaction with
H2AlMes* in toluene proceeded in a manner similar to the
previous reactions; upon addition of the aluminum hydride to
the yttrium alkyl, a clear solution was obtained, from which an
insoluble white precipitate formed (Scheme 3, a). From the
a
Scheme 3. Reactivity of Alkylalanes toward [Cp*YMe2]3
Intrigued by the ability of the alkylalanes to generate yttrium
hydride complexes, we investigated their reactivity toward
17
polymeric [YMe3]n aiming at the hitherto elusive molecular
trihydride [LnH3](M)x (M = stabilizing, solubilizing mole-
cules).40 Reasoning that the bulky Mes* backbone would be
beneficial for stabilizing a possible adduct complex, we reacted
H2AlMes* with [YMe3]n in toluene (Scheme 2, a). Upon
addition of the reactants, a clear solution was obtained, from
which a white solid precipitated in the course of the reaction.
From the toluene solution another white solid was isolated and
identified as 4, while attempts to further characterize the white
precipitate gave inconclusive results, although stoichiometry
suggests the formation of “[YH3]n”.
a
Nuclearity not accounted for.
toluene solution hydrido transfer product 3 could be isolated as
expected. Interestingly, the same reaction performed in n-
hexane allowed the isolation of hydrido transfer product 4,
which can be rationalized by the lower solubility of the
dihydride, allowing a double methyl−hydrido exchange to
occur more easily (Scheme 3, b). Although one possible
yttrium hydride complex, (Cp*YH2)6, was isolated and
structurally characterized earlier by Hou et al.,26 the nature of
the yttrium species in this case remained elusive.
Visual inspection of the reaction between HAl(CH2SiMe3)2
and [YMe3]n (Scheme 2, b) suggested a similar methyl−hy-
drido exchange, as evidenced by formation of a clear solution,
from which a white solid precipitated upon workup. However,
the colorless oil isolated from the toluene solution was a
1
mixture of products, as evidenced by H NMR spectroscopy.
D
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Moving on to the neosilylaluminum hydride, progression of
the reaction was evidenced by formation of a clear solution,
from which a white intractable solid precipitated. From the
toluene solution a product mixture in the form of a colorless oil
was obtained, which did not allow further purification (Scheme
3, c).
Scheme 4. Reactivity of (CpMe4R)Y(AlMe4)2 toward
HAlMe2
In anticipation of a dihydride complex of low nuclearity we
next followed the reaction of [Cp*YMe2]3 with HAlMe2 (Y:Al
at 3.87 ppm (1JY−H = 25.5 Hz), and additionally one doublet
signal for homoleptic Y(AlMe4)3. The observed coupling
constant is much smaller than those reported for terminal
yttrium hydride complexes Ind*2YH(thf) (1JY−H = 82.0 Hz,
Ind* = heptamethylindenyl)44 and (C5H4SiMe3)2YH(thf)
(1JY−H = 74.8 Hz)45 and lies more in the range of half-
sandwich yttrium hydrides [(C5Me4R)YH2]n(thf)x (R = SiMe3,
n = 5, x = 0, 1JY−H = 35.8 Hz; R = Me, n = 5, x = 2, 1JY−H = 32.8
Hz; obtained from low-temperature NMR data)26 and the
earlier mentioned [Cp2YH(thf)]2 (27.0 Hz)23 and TptBu,MeY-
[(μ-H)AlMe3]2 (AY) (doublet at 5.05 ppm with a coupling
1
1:2) by H NMR spectroscopy (Scheme 3, d). Unfortunately,
the formation of a mixture of products was observed, as
evidenced by a vast number of signals in the CpMe region.
Reasoning that the reaction might be forced toward a hydride
complex using an excess of the aluminum hydride, reactions
with Y:Al ratios of 1:4 and 1:10 were performed. From the clear
solutions in the beginning a white precipitate started to form,
and the 1H NMR spectra of the remaining soluble parts showed
again a mixture of products along with the signals for the excess
aluminum hydride.
constant JY−H = 30.8 Hz).13 Attempts to crystallize an yttrium
1
1
A more conclusive H NMR spectrum was obtained when
HAlMe2 was used for the reaction in an Y:Al ratio of 1:1. Next
to a number of signals in the Cp region that could not be
assigned, signal sets from Cp*Y(AlMe4)2 and free AlMe3 were
observed as well as a further set of signals that would belong to
a species formally denoted as Cp*Y(H)(AlMe4) (Figure 5). A
hydride species from the reaction mixture were not successful
because at −35 °C only crystals of precursor Cp*Y(AlMe4)2
could be harvested in almost quantitative yield. Attempts to
grow crystals at ambient temperature led to the formation of a
completely insoluble white precipitate of unknown composi-
tion. Formation of hydride clusters, which are soluble at first,
causing the observed Cp signals in the 1H NMR spectrum, and
becoming insoluble upon agglomeration to complexes of higher
nuclearity, might be one explanation.
We then decided to use additional NMR spectroscopic
methods to shed further light on the reaction. First, we wanted
to verify that the observed doublet at 3.87 ppm really stems
from an yttrium coupling and did so by taking an 89Y decoupled
1H NMR spectrum. In this spectrum the doublet collapsed to a
broad singlet, as did the other doublet signals observed for the
methyl groups of Cp*Y(AlMe4)2 and Y(AlMe4)3. We then
went on and performed an 89Y DEPT45 NMR experiment,
which yielded a spectrum containing three sharp signals for
Cp*Y(AlMe4)2 (223 ppm), Y(AlMe4) (394 ppm), and one at
175 ppm, which we assigned to the previously proposed species
Cp*Y(HAlMe3)(AlMe4). Finally, we also conducted a variable-
1
temperature H NMR experiment in the temperature range
1
from −90 to 25 °C (Figure 6), which gave us some insight into
the dynamics. The most interesting information from this
experiment was that the hydride formation seems to be
Figure 5. H NMR spectrum (benzene-d6, 400 MHz, 25 °C) of the
reaction Cp*YMe2 + HAlMe2 (nuclearity not accounted for). Signal
assignment: Cp*Y(AlMe4)H δ = 3.88 (Y−H), 1.82 (C5(CH3)5),
−0.29 (Al(CH3)4) ppm. Cp*Y(AlMe4)2 δ = 1.74 (C5(CH3)5), −0.33
(Al(CH3)4) ppm. AlMe3 δ = −0.41 (Al(CH3)3) ppm.
striking feature of the spectrum is the observed doublet at 3.88
ppm, which implies that the hydrido ligand is bonded to only
one yttrium metal center. Otherwise a triplet or quartet would
be observed when two or three yttrium centers, respectively, are
involved in bonding. Taking this and the availability of
trimethylaluminum into account a better proposal for the
observed species would be Cp*Y(HAlMe3)(AlMe4).
Since Cp*Y(AlMe4)2 readily formed in the reaction mixture,
1
as evidenced by H NMR spectroscopy, and due to its better
solubility in organic solvents compared to [Cp*YMe2]3, we
reacted this complex with one equivalent of HAlMe2, also
trying to reduce the number of species present in solution
(Scheme 4). The 1H NMR spectrum obtained from the
reaction mixture looked very similar to the one found before
showing sets of signals for precursor Cp*Y(AlMe4)2, free
AlMe3, a species Cp*Y(HAlMe3)(AlMe4) with a doublet signal
Figure 6. 1H VT-NMR spectrum of the reaction mixture Cp*Y-
(AlMe4)2 + HAlMe2. The small inset shows the region of the
anticipated yttrium-hydride signal.
E
DOI: 10.1021/acs.organomet.5b00013
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
reversible.46 At lower temperature the main component in the
solution is starting material Cp*Y(AlMe4)2, and at increasing
temperatures the concentration of Cp*Y(HAlMe3)(AlMe4)
increases until it seems to be the main, but not the only,
component in solution at ambient temperature. This finding is
also in accordance with the previous observation that we could
only crystallize Cp*Y(AlMe4)2 from chilled solutions (−35
°C). In the aluminate region of the 1H NMR spectrum we also
observed the characteristic splitting of the peak for free
trimethylaluminum into two singlets, with a 3:6 ratio of the
integrals, belonging to the bridging and terminal methyl groups
of the Al2Me6 dimer.
not have an influence on the reaction pathway in that no adduct
formation occurred, which might have been expected for the
less sterically demanding aluminum hydrides. The structurally
characterized cyclic yttrium complexes Cp14Y6H3Cl and
Cp15Y6H3 allowed some insight into the possible structure of
a donor-free CpYH species. Furthermore, the hydrido transfer
products [(μ-H)(Me)AlMes*]2 and Me2AlMes* were isolated
and completely characterized, one forming a dimer in the solid
state similar to the starting material H2AlMes*, while the other
is monomeric, similar to the corresponding halide compounds,
adding to the library of fully characterized three-coordinated
aryl-alkyl aluminum compounds.
Our final approach trying to eventually isolate a half-
sandwich yttrium hydride species was to switch to the ligand
CpSiMe3 (= C5H4SiMe3).26 As before, we started from the
readily available CpSiMe3Y(AlMe4)2,20 reacted it with one
equivalent of HAlMe2 (Scheme 4), and monitored the reaction
Probing the reactivity of the selected alkylalanes toward
[YMe3]n and [Cp*YMe2]3, only mixtures of products were
obtained for bis-neosilylaluminum hydride, while for super-
mesityl- and dimethylaluminum hydride isolation of the
corresponding methylated aluminum compounds suggests
occurrence of hydrido transfer. However, isolation of an
yttrium hydride species was not successful. The similar reaction
of half-sandwich yttrium tetramethylaluminate complexes
Cp*Y(AlMe4)2 and (C5Me4SiMe3)Y(AlMe4)2 with dimethyla-
luminum hydride also did not produce any isolable yttrium
hydride complex, but NMR spectroscopic methods propose the
following scenario: Upon mixing together the two reagents,
trimethylaluminum is released and a transient species, CpRY-
(HAlMe3)(AlMe4), forms. This transient species then reacts
further to ultimately form yttrium hydride clusters while
releasing more trimethylaluminum, which then drives the
formation of homoleptic yttrium aluminates. Overall this shows
that the reaction yields a variety of products by forming adducts
and higher nuclearity complexes and by ligand scrambling.
These findings may also have implications for polymerization
catalyst mixtures where a defined precursor or a preformed
alkyl complex is treated with an alkylaluminum hydride as a
cocatalyst.
1
by H NMR spectroscopy. Similar to the previous reaction we
found sets of signals in the NMR spectrum belonging to
starting material CpSiMe3Y(AlMe4)2, homoleptic Y(AlMe4)3,
and one set that could be accounted for by a formal species
CpSiMe3Y(HAlMe3)(AlMe4) with a characteristic doublet at
3.93 ppm (1JY−H = 24.5 Hz). Additionally, two minor peaks
observed in the 1H NMR spectrum at 2.16 and 2.07 ppm match
closely to those reported for the Cp-methyl groups in
[CpSiMe3YH2]4(thf)43b (2.16 and 2.06 ppm), although no thf
is present in the reaction mixture. The corresponding peaks for
the thf-free [CpSiMe3YH2]n complexes (n = 4, 2.37/2.20 ppm;47
n = 5 2.53/2.28 ppm26), however, are shifted a bit further
downfield, but nonetheless formation of a polynuclear yttrium
hydride cluster can be anticipated, taking also the formation of
free trimethylaluminum into account.
Unfortunately, we were again not able to crystallize an
yttrium hydride complex and turned to NMR spectroscopic
investigations. As for the Cp* derivative, we collected a 89Y
decoupled 1H NMR spectrum in which the prominent doublet
at 3.93 ppm collapsed into a broad singlet together with the
signals for the aluminates in CpSiMe3Y(AlMe4)2 and Y(AlMe4)3,
confirming the 89Y coupling. An 89Y DEPT45 NMR experiment
yielded a spectrum with three sharp signals, which we assigned
to Y(AlMe4)3 (395 ppm), CpSiMe3Y(AlMe4)2 (216 ppm), and
the formal species CpSiMe3Y(HAlMe3)(AlMe4) (173 ppm).
Interestingly, the chemical shifts for the CpSiMe3 species match
closely to those found for the Cp* species, suggesting the
presence of structurally similar complexes. A variable low-
EXPERIMENTAL SECTION
■
General Considerations. All operations were performed with
rigorous exclusion of air and water, using standard Schlenk and
glovebox techniques (MBraun 200B; <1 ppm of O2, <1 ppm of H2O).
Solvents were purified using Grubbs columns (MBraun SPS, solvent
purification system) and stored in a glovebox. Benzene-d6 and thf-d8
were purchased from Eurisotop, degassed, dried over sodium for a
minimum of 48 h, and purified by vacuum transfer. [Cp2YMe]2,16
[YMe3]n,17 [Cp*YMe2]3,18 Cp*Y(AlMe4)2,19 CpSiMe3Y(AlMe4)220 (Cp
= C5H5, Cp* = C5Me5, CpSiMe3 = C5Me4SiMe3), HAl(CH2SiMe3)2,11
HAlMe2,8b and H2AlMes*12 (Mes* = C6H2tBu3-2,4,6) were
synthesized according to literature procedures. NMR spectra of air-
and moisture-sensitive compounds were recorded using J.-Young valve
NMR tubes on a Bruker AVII+400 spectrometer (1H, 400.13 MHz;
13C, 100.61 MHz) and a Bruker AVII+500 spectrometer (1H, 500.13
MHz; 13C, 125.76 MHz; 89Y, 24.50 MHz). 1H and 13C shifts are
referenced to internal solvent resonances and reported in parts per
million relative to TMS. DRIFT spectra were obtained on a Nicolet
6700 FT-IR spectrometer using dried KBr powder and KBr windows.
Elemental analyses were performed on an EL Vario MICRO Cube.
Reaction of [Cp2YMe]2 with HAlMe2. A solution of HAlMe2 (9
mg, 0.15 mmol) in 2 mL of toluene was added to a suspension of
[Cp2YMe]2 (37 mg, 0.15 mmol) in 3 mL of toluene and stirred at
ambient temperature for 18 h. After removal of the white residue the
remaining solution was dried under vacuum to obtain a colorless oil
containing AlMe3. The white residue was dried under vacuum,
redissolved in 2 mL of hot thf (55 °C), and stored at −35 °C to obtain
two batches of crystalline material, which was identified as Cp2YH-
1
temperature H NMR experiment in the range from −90 to
−50 °C finally showed a behavior different from that observed
using Cp* as ancillary ligand. The signals for the CpSiMe3 ligand
did not change over the measured temperature range and
stayed also the same in a final spectrum taken at room
temperature, indicating the presence of CpSiMe3Y(HAlMe3)-
(AlMe4) even at low temperatures. This was also evidenced by
the observation of the corresponding doublet signal at 3.93
ppm. Distinct splitting patterns were, however, observed for the
aluminate signals.
CONCLUSION
■
Reacting [Cp2YMe]2 with alkylaluminum hydrides of different
steric demand led to a direct methyl−hydrido exchange, as
evidenced by the isolation of well-known yttrium hydride
complex [Cp2Y(thf)(μ-H)]2 after workup with thf as well as the
corresponding methyl aluminum complexes. Interestingly,
varying the steric demand of the alkylaluminum hydrides did
(thf)23 (39 mg, 0.13 mmol, 88%) by H NMR spectroscopy.
1
F
DOI: 10.1021/acs.organomet.5b00013
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Reaction of [Cp2YMe]2 with HAl(CH2SiMe3)2. A solution of
HAl(CH2SiMe3)2 (61 mg, 0.3 mmol) in 5 mL of toluene was slowly
added to a suspension of [Cp2YMe]2 (73 mg, 0.3 mmol) in 5 mL of
toluene and stirred at ambient temperature for 18 h. Then the white
residue was filtered off, and from the remaining toluene solution a
colorless oil was obtained by removing the volatiles in vacuo and
identified as MeAl(CH2SiMe3)2 (49 mg, 0.23 mmol, 77%) by H
NMR spectroscopy. The toluene solution afforded a few single
crystals, which were identified as complex 2. Parts of the white residue
were dissolved in thf-d8 and could be identified as Cp2YH(thf)23 by 1H
NMR spectroscopy.
showed a mixture of compounds including also starting material
HAl(CH2SiMe3)2.
Reaction of [YMe3]n with HAlMe2. To a suspension of [YMe3]n
(42 mg, 0.31 mmol) in toluene (3 mL) was slowly added a solution of
HAlMe2 (54.6 mg, 0.94 mmol) in toluene (3 mL). Upon addition, a
clear solution was obtained within 2 min, and after another 15 min
formation of a white precipitate was observed. Further analysis of the
precipitate via NMR spectroscopy was hampered because of a lack of
solubility, and the results from IR spectroscopy and elemental analysis
were inconclusive. 1H NMR spectroscopic analysis of the solubles
however showed formation of AlMe3 (36 mg, 0.5 mmol, 53%).
[YMe3]n/HAlMe2 (NMR-Scale). In a 1 mL vial [YMe3]n (20 mg,
0.14 mmol) was suspended in 0.3 mL of benzene-d6, and a solution of
HAlMe2 (26 mg, 0.44 mmol) in 0.3 mL of benzene-d6 added. The
forming clear solution was transferred into a J.-Young valve NMR
24
1
Reaction of [Cp2YMe]2 with H2AlMes*. (a) A solution of
H2AlMes* (0.3 mmol, 82 mg) in 5 mL of toluene was added to a
suspension of [Cp2YMe]2 (73 mg, 0.3 mmol) in 5 mL of toluene and
stirred for 18 h at ambient temperature. Subsequently the white
precipitate was separated, and the remaining toluene solution was
stored at −35 °C to obtain clear, colorless crystals of [(μ-
1
1
tube, and the reaction was monitored by H NMR spectroscopy. H
NMR (benzene-d6, 400 MHz, 25 °C): “Y(HAlMe3)3” δ = 4.68 (d,
1JY−H = 20.5 Hz, 3 H, Y-H-Al), −0.17 (s, 27 H, Al(CH3)3) ppm.
1
H)(Me)AlMes*]2 (3, 63 mg, 0.22 mmol, 73%). H NMR (benzene-
2
d6, 500 MHz, 25 °C): δ = 7.47 (s, 2 H, Phen-H), 4.72 (br s, 1 H, AlH),
1.49 (s, 18 H, o-C(CH3)3), 1.37 (s, 9 H, p-C(CH3)3), −0.34 (br s, 3 H,
AlCH3) ppm. 13C{1H} NMR (benzene-d6, 126 MHz, 25 °C): δ =
158.7 (o-C(2)), 150.2 (p-C(4)), 136.4 (i-C(1), taken from HMBC
measurement), 120.6 (m-C(3)), 38.3 (o-C(CH3)3), 34.7 (p-C(CH3)3),
32.8 (o-C(CH3)3), 31.3 (p-C(CH3)3), −3.9 (AlCH3) ppm. IR (KBr,
cm−1): 3065 vw, 3049 vw, 2962 vs, 2950 vs, 2903 s, 2859 s, 2730 vw,
2705 vw, 1866 w, 1592 m, 1524 m, 1507 s, 1454 s, 1391 s, 1362 s,
1245 m, 1210 m, 1194 m, 1126 w, 1037 w, 936 m, 880 m, 831 s, 662
m, 570 w, 477 w. Anal. Calcd for C19H33Al (288.45 g·mol−1): C, 79.11;
H, 11.53. Found: C, 79.10; H, 10.62. The white residue was dissolved
in thf and could be identified as Cp2YH(thf)23 by 1H NMR
spectroscopy.
Y(AlMe3)4 δ = −0.24 (d, JY−H = 2.3 Hz, 36 H, Al(CH3)4) ppm.
AlMe3 δ = −0.35 (s, 9 H, Al(CH3)3) ppm.
Reaction of [Cp*YMe2]3 with H2AlMes*. (a) A solution of
H2AlMes* (55 mg, 0.2 mmol) in 5 mL of n-hexane was added to a
suspension of [Cp*YMe2]3 (25 mg, 0.1 mmol) in 5 mL of n-hexane
and stirred at ambient temperature for 18 h. The suspension cleared
up within a few minutes before a white precipitate started to form
again. After separation of the precipitate a white solid could be
obtained upon removal of the volatiles under vacuum and indentified
as [(μ-H)(Me)AlMes*]2 (3, 46 mg, 0.16 mmol, 79%) by NMR
spectroscopy.
(b) A solution of H2AlMes* (143 mg, 0.52 mmol) in 5 mL of
toluene was slowly added to a suspension of [Cp*YMe2]3 (66 mg, 0.26
mmol) in toluene (5 mL), and the resulting clear solution stirred at
ambient temperature for 18 h. After ca. 20 min a white precipitate
started to form, which was separated from the toluene solution upon
completion of the reaction. From the remaining solution a white solid
was obtained and identified as Me2AlMes* (4, 67 mg, 0.22 mmol,
43%) by NMR spectroscopy.
(b) A solution of H2AlMes* (0.2 mmol, 55 mg) in 5 mL of toluene
was added to a suspension of [Cp2YMe]2 (97 mg, 0.4 mmol) in 5 mL
of toluene and stirred for 18 h at ambient temperature. Subsequently,
the white precipitate was separated, and the remaining toluene
solution was stored at −35 °C to obtain clear, colorless crystals of
1
Me2AlMes* (4, 46 mg, 0.15 mmol, 76%). H NMR (benzene-d6, 400
MHz, 25 °C): δ = 7.44 (s, 2 H, Phen-H), 1.42 (s, 18 H, o-C(CH3)3),
1.36 (s, 9 H, p-C(CH3)3), −0.08 (s, 6 H, Al(CH3)2) ppm. 13C{1H}
NMR (benzene-d6, 100 MHz, 25 °C): δ = 157.9 (o-C(2)), 149.7 (p-
C(4)), 136.1 (i-C(1)), 120.5 (m-C(3)), 38.2 (o-C(CH3)3), 34.5 (p-
C(CH3)3), 32.9 (o-C(CH3)3), 31.6 (p-C(CH3)3), −4.0 (AlCH3) ppm.
IR (KBr, cm−1): 3063 vw, 2953 vs, 2859 s, 2838 m, 1597 m, 1527 m,
1475 m, 1456 m, 1388 m, 1663 m, 1344 m, 1255 m, 1246 m, 1196 s,
1187 s, 1170 m, 1128 w, 1041 w, 1007 vw, 934 w, 904 m, 875 m, 777
m, 716 s, 672 vs, 606 m, 573 w, 552 w. Anal. Calcd for C20H35Al
(302.48 g·mol−1): C, 79.42; H, 11.66. Found: C, 79.36; H, 10.72. The
white residue was dissolved in thf and could be identified as
In both cases the insolubility of the remaining solid hampered
further analysis.
Reaction of [Cp*YMe2]3 with HAl(CH2SiMe3)2. To a suspension
of [Cp*YMe2]3 (102 mg, 0.4 mmol) in 5 mL of toluene was added a
solution of HAl(CH2SiMe3)2 (162 mg, 0.8 mmol) in 5 mL of toluene,
and the reaction mixture stirred at ambient temperature for 18 h. After
a few minutes a clear solution was obtained, from which a white solid
started to precipitate within 30 min. Upon removal of the precipitate,
the remaining solution was dried under vacuum to obtain a white solid,
which was identified as a mixture of compounds by NMR
spectroscopy. Unfortunately attempts to separate the components by
crystallization were not successful.
1
Cp2YH(thf)23 by H NMR spectroscopy.
Reaction of [YMe3]n with H2AlMes*. To a suspension of
[YMe3]n (20 mg, 0.15 mmol) in toluene (3 mL) was slowly added a
solution of H2AlMes* (61 mg, 0.23 mmol) in toluene (3 mL). Upon
addition, a clear solution was obtained, from which a white solid
precipitated after several minutes and the reaction was further stirred
for 18 h at ambient temperature. After separation from the white
precipitate the remaining solution was dried under vacuum to obtain a
white powder, which was identified as Me2AlMes* (4, 48 mg, 0.16
mmol, 69%) by NMR spectroscopy. Further analysis of the precipitate
via NMR spectroscopy was hampered because of a lack of solubility,
and the results from IR spectroscopy and elemental analysis were
inconclusive.
Reaction of [YMe3]n with HAl(CH2SiMe3)2. To a suspension of
[YMe3]n (42 mg, 0.31 mmol) in 4 mL of toluene was added a solution
of HAl(CH2SiMe3)2 (189 mg, 0.93 mmol) in toluene (4 mL), and the
reaction mixture stirred at ambient temperature for 18 h. A clear
solution was obtained upon addition of the aluminum hydride, and a
white precipitate started to form several minutes later. After separation
from the white solid the remaining solution was dried under vacuum
to obtain a colorless, oily product. NMR spectroscopic investigations
General Procedure of NMR-Scale Reactions. Each yttrium
complex was weighed in a glovebox into a 1 mL vial and dissolved/
suspended in 0.3 mL of benzene-d6 or toluene-d8. Aluminum hydride
HAlMe2 was weighed into a second 1 mL vial and also dissolved in
benzene-d6 or toluene-d8, respectively. The aluminum hydride solution
was transferred to the yttrium complex solution, and the resulting
reaction mixture was stirred for a given amount of time. Then the
solution was transferred into a J.-Young valve NMR tube for analysis.
[Cp*YMe2]3/HAlMe2 (Y:Al = 1:1). [Cp*YMe2]3 (10 mg, 0.039
mmol), HAlMe2 (2.3 mg, 0.039 mmol), benzene-d6, 20 min. After
about 2 min a clear solution was obtained. 1H NMR (benzene-d6, 400
MHz, 25 °C): Cp*Y(AlMe4)H δ = 3.88 (d, 1JY−H = 25.3 Hz, 1 H, Y−
2
H), 1.82 (s, 15 H, C5(CH3)5), −0.29 (d, JY−H = 2.5 Hz, 12 H,
Al(CH3)4) ppm. Cp*Y(AlMe4)2 δ = 1.74 (s, 15 H, C5(CH3)5), −0.33
2
(d, JY−H = 2.2 Hz, 24 H, Al(CH3)4) ppm. AlMe3 δ = −0.41 (s, 9 H,
Al(CH3)3) ppm.
[Cp*YMe2]3/HAlMe2 (Y:Al = 1:2). [Cp*YMe2]3 (10 mg, 0.039
mmol), HAlMe2 (4.5 mg, 0.078 mmol), benzene-d6, 20 min and 18 h.
After about 1 min a clear solution was obtained. Both 1H NMR spectra
indicate the formation of a mixture of products.
G
DOI: 10.1021/acs.organomet.5b00013
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
[Cp*YMe2]3/HAlMe2 (Y:Al = 1:4). [Cp*YMe2]3 (4 mg, 0.016
mmol), HAlMe2 (4.5 mg, 0.063 mmol), benzene-d6, 20 min and 18 h.
Upon addition of HAlMe2 a clear solution formed, and after several
hours precipitation of a white solid was observed. The 1H NMR
spectrum showed signals for HAlMe2 and a mixture of other products.
[Cp*YMe2]3/HAlMe2 (Y:Al = 1:10). [Cp*YMe2]3 (18 mg, 0.07
mmol), HAlMe2 (40 mg, 0.7 mmol), benzene-d6, 20 min and 18 h.
Upon addition of HAlMe2 a clear solution formed, and after several
hours precipitation of a white solid was observed. The 1H NMR
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: reiner.anwander@uni-tuebingen.de.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
1
spectrum after 20 min showed a mixture of products, while the H
NMR spectrum after 18 h showed only signals for HAlMe2.
We thank the German Science Foundation DFG for financial
support (Grant: AN 238/14-2).
Cp*Y(AlMe4)2/HAlMe2 (Y:Al = 1:1). Cp*Y(AlMe4)2 (14 mg, 0.04
1
mmol), HAlMe2 (2.4 mg, 0.04 mmol), benzene-d6, 20 min. H NMR
DEDICATION
1
■
(benzene-d6, 400 MHz, 25 °C): Cp*Y(AlMe4)H δ = 3.87 (d, JY−H
=
25.5 Hz, 1 H, Y−H), 1.82 (s, 15 H, C5(CH3)5), −0.30 (d, 2JY−H = 2.5
Hz, 12 H, Al(CH3)4) ppm. Cp*Y(AlMe4)2 δ = 1.74 (s, 15 H,
C5(CH3)5), −0.33 (d, JY−2H = 2.2 Hz, 24 H, Al(CH3)4) ppm.
This article is dedicated to the memory of Professor Michael F.
Lappert.
2
Y(AlMe4)3 δ = −0.25 (d, JY−H = 2.4 Hz, 36 H, Al(CH3)4) ppm.
AlMe3 δ = −0.36 (s, 9 H, Al(CH3)3) ppm. 89Y DEPT45 NMR
(benzene-d6, 25 MHz, 25 °C): δ = 394 (s, Y(AlMe4)3), 223 (s,
Cp*Y(AlMe4)2), 175 (s, Cp*Y(AlMe4)H) ppm. VT-NMR: Cp*Y-
(AlMe4)2 (20 mg, 0.05 mmol), HAlMe2 (2.9 mg, 0.05 mmol), toluene-
d8. 1H NMR spectra were recorded on the Bruker AVII+500
spectrometer in the temperature range from −90 to 25 °C.
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■
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CpSiMe3Y(AlMe4)2/HAlMe2 (Y:Al = 1:1). CpSiMe3Y(AlMe4)2 (20 mg,
0.044 mmol), HAlMe2 (2.5 mg, 0.044 mmol), benzene-d6, 20 min. 1H
NMR (benzene-d6, 400 MHz, 25 °C): CpSiMe3Y(AlMe4)H δ = 3.93 (d,
1JY−H = 24.5 Hz, 1 H, Y−H), 2.08 (s, 6 H, C5(CH3)4), 1.78 (s, 6 H,
2
C5(CH3)4), 0.26 (s, 9 H, C5Me4Si(CH3)3), −0.27 (d, JY−H = 2.5 Hz,
12 H, Al(CH3)4) ppm. CpSiMe3Y(AlMe4)2 δ = 1.99 (s, 6 H, C5(CH3)4),
1.74 (s, 6 H, C5(CH3)4), 0.23 (s, 9 H, C5Me4Si(CH3)3), −0.29 (d,
2JY−H = 2.2 Hz, 24 H, Al(CH3)4) ppm. Y(AlMe4)3 δ = −0.25 (d, 2JY−H
= 2.4 Hz, 36 H, Al(CH3)4) ppm. AlMe3 δ = −0.37 (s, 9 H, Al(CH3)3)
ppm. 89Y DEPT45 NMR (benzene-d6, 25 MHz, 25 °C): δ = 395 (s,
Y(AlMe4)3), 216 (s, CpSiMe3Y(AlMe4)2), 173 (s, CpSiMe3Y(AlMe4)H)
ppm. VT-NMR: CpSiMe3Y(AlMe4)2 (20 mg, 0.044 mmol), HAlMe2
(2.5 mg, 0.044 mmol), toluene-d8. 1H NMR spectra were recorded on
the Bruker AVII+500 spectrometer in the temperature range from −90
to 25 °C.
Crystallography. Crystals suitable for X-ray crystallography were
grown by standard techniques from toluene solutions at −35 °C.
Suitable single crystals were selected in a glovebox, coated with
Parabar 10312 (Hampton Research, formerly known as Paratone-N)
and fixed on a glass fiber (1, 3) or a nylon loop (2, 4). Data of 1 and 3
were collected on a Stoe IPDS 2T instrument using Mo Kα radiation
(λ = 0.710 73 Å). Raw data were processed using Stoe’s X-Area
software suite;48 structure solution and final model refinement was
done using the WinGX49 suite of programs including SHELXS,50
SHELXL,50 and PLATON.51 Corrections for absorption effects were
applied using MulAbs as implemented in PLATON. Data of 2 were
collected on a Bruker AXS II instrument, and data of 4 were collected
on a Bruker APEX DUO instrument using Mo Kα radiation (λ =
0.710 73 Å). The raw data were processed using APEX252 and
SAINT;53 structure solution and final model refinement were done
with SHELXTL.54 Corrections for absorption effects were applied
using SADABS.55 All graphics were produced employing ORTEP-356
and POV-Ray.57 Further details of the crystallographic analysis can be
found in the Supporting Information. CCDC-968685 (1), 968686 (2),
968687 (3), and 968688 (4) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
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ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectroscopic data and crystallographic details. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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DOI: 10.1021/acs.organomet.5b00013
Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.5b00013
Organometallics XXXX, XXX, XXX−XXX