Action of Organoaluminum Reagents on Esters: Alkene Production and the Degradation of Synthetic Lubricants

Article abstract of DOI:10.1021/acs.organomet.8b00763

Reactions of methylaluminum reagents with ester-based lubricating oils are mimicked through the reaction of trimethylaluminum (TMA) with tetraesters C(CH₂OC(O)R)₄ (R = C₅H₁₁ 4^Pent, Bn 4^Bn). Using a 2:1 stoichiometry gave adduct 4^Pent(TMA)₄. NMR spectroscopy on 1:1-12:1 TMA/4^Pent systems suggested 4^Pent gave dimethylated adduct C₅H₁₁CMe₂OAlMe₂(TMA), 2^Pent(TMA). Similar combination of TMA with 4^Bn at raised temperatures transformed 4^Bn into C(CH₂OAlMe₂)₄(2^Bn)₄ 5(2^Bn)₄ by sequential reaction of each ester group. Doubly reacted {BnC(O)OCH₂}₂C(CH₂OAlMe₂)₂(2^Bn)₂ 7^Bn(2^Bn)₂ was isolated and characterized. A Mitsubishi molecule could also be isolated, its formation rationalized by the elimination of 2^Bn and TMA from 5(2^Bn)₄. The action of Me_nAlCl_3-n (n = 1, 1.5, 2) was studied initially on monoester BnC(O)OMe 1^Bn. Combining excess Me₂AlCl with 1^Bn gave adduct 1^Bn(Me₂AlCl) and small amounts of dimethylated BnCMe₂OAlMe₂(Me₂AlCl), 2^Bn(Me₂AlCl), and MeOAlCl₂ 10. 2^Bn(Me₂AlCl) was fully characterized and, in the presence of 10, acted as a source of 2^Bn(MeAlCl₂). From this species, a mixture of alkenes could be generated by formal elimination of Me₃Al₂(OH)Cl₂ 13, the decomposition of which was presumed to also explain MeH observation. Replacing Me₂AlCl with aluminum sesquichloride or MeAlCl₂ led to progressively more sluggish but similar reactions. Using Me_nAlCl_3-n (n = 1, 1.5, 2) with tetraesters suggested similar reactivity to monoesters.

Full text of DOI:10.1021/acs.organomet.8b00763

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Action of Organoaluminum Reagents on Esters: Alkene Production
and the Degradation of Synthetic Lubricants
Jonathan Slaughter, Samuel A. Molyneux, Andrew J. Peel, and Andrew E. H. Wheatley*
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
S
* Supporting Information
ABSTRACT: Reactions of methylaluminum reagents with
ester-based lubricating oils are mimicked through the reaction
of trimethylaluminum (TMA) with tetraesters C(CH2OC-
(O)R)4 (R = C5H11 4Pent, Bn 4Bn). Using a 2:1 stoichiometry
gave adduct 4Pent(TMA)4. NMR spectroscopy on 1:1−12:1
TMA/4Pent systems suggested 4Pent gave dimethylated adduct
C5H11CMe2OAlMe2(TMA), 2Pent(TMA). Similar combina-
tion of TMA with 4Bn at raised temperatures transformed 4Bn
into C(CH2OAlMe2)4(2Bn)4 5(2Bn)4 by sequential reaction of
each ester group. Doubly reacted {BnC(O)OCH2}2C-
(CH2OAlMe2)2(2Bn)2 7Bn(2Bn)2 was isolated and character-
ized. A Mitsubishi molecule could also be isolated, its
formation rationalized by the elimination of 2Bn and TMA from 5(2Bn)4. The action of MenAlCl3−n (n = 1, 1.5, 2) was
studied initially on monoester BnC(O)OMe 1Bn. Combining excess Me2AlCl with 1Bn gave adduct 1Bn(Me2AlCl) and small
amounts of dimethylated BnCMe2OAlMe2(Me2AlCl), 2Bn(Me2AlCl), and MeOAlCl2 10. 2Bn(Me2AlCl) was fully characterized
and, in the presence of 10, acted as a source of 2Bn(MeAlCl2). From this species, a mixture of alkenes could be generated by
formal elimination of Me3Al2(OH)Cl2 13, the decomposition of which was presumed to also explain MeH observation.
Replacing Me2AlCl with aluminum sesquichloride or MeAlCl2 led to progressively more sluggish but similar reactions. Using
MenAlCl3−n (n = 1, 1.5, 2) with tetraesters suggested similar reactivity to monoesters.
One such compound is RL 32H, a commonly used polyolester
(POE) compound oil designed to be compatible with HFC
refrigerants. While this has led to interest in the reactions of
aluminum-based organometallics with esters,11 the field has
hitherto been dominated by the study of trialkylaluminums.
Trimethylaluminum (TMA) has been used to generate reactive
complexes,12 hemialkoxides,13 alkylated acetates,14 and keton-
ized heteroaromatic esters,15,16 to induce the reduction of
cyclic ketones,17 and to modify poly(methyl methacrylate).18
Meanwhile, both TMA and triethylaluminum have been used
to produce ketones,16,19 aldehydes,19 and amides20 from esters.
Surprisingly, given the interest in alkylaluminum sesqui-
chloride cocatalysts to the polymer industry,21 reactions of
MenAlCl3−n (n = 1, 1.5, 2) with esters are difficult to find in the
literature. Only limited work has been done on derivatizing
methyl benzoate with methylaluminum chlorides. Adduct
formation between the ester and Me2AlCl has been recorded.22
Thereafter, Me2AlCl (but not TMA) was suggested to
promote PhCMe2OAlMeCl formation, presumably alongside
that of MeOAlMeCl, the subsequent reaction of which gave
either alkene PhC(CH2)Me, presumably alongside HOAl-
MeCl, or Ph(t-Bu), presumably alongside O(AlMeCl)2.23 The
expected byproduct of methyl ester reaction with TMA itself,
INTRODUCTION
■
The enormous interest that recent years have seen in
hydrofluorocarbons (HFCs) has stemmed from the global
move away from the use of ozone-depleting chlorofluor-
ocarbons1 as refrigerants. However, while the fact that these
so-called F-gases had only indirect effects on the ozone layer
led to their increased use,2 so studies have revealed a more
detailed picture of the real extent of their greenhouse effects.3
This has led to successive regulations, the latest of which4
outlawed products containing F-gases with a global warming
potential (GWP)5 > 150 as part of a worldwide strategy aimed
at reducing HFC dependence.6 Subsequently, the remit of
regulations has been expanded to impact on most refrigeration
and vapor compression systems for air conditioning,7 leading
to efforts to replace commonly used high-GWP refrigerants
like R-134a (1,1,1,2-tetrafluoroethane).8 Concurrent with the
introduction of new regulatory frameworks, the illicit use of R-
40 (chloromethane) in refrigeration systems has emerged as a
major problem.9 While R-40 has a GWP of just 13, the
reaction of alkyl chlorides with aluminum (viz. components in
industrial refrigeration units) promoted by aluminum halide
catalyst is established.10 Moreover, reports exist that reaction
can proceed in the absence of a catalyst and that using heat
only11 alkyl chlorides can react with aluminum to give
RnAlCl3−n. For R-40, this would yield methylaluminum
chlorides, which can in turn react with ancillary organics.
Received: October 22, 2018
© XXXX American Chemical Society
A
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Figure 1. Adducts 1(TMA), 2(TMA), 2(3), and pentaerythritol-based tetraester 4.
Figure 2. 1H NMR spectra of aliquots from the introduction of TMA to 4Pent in a 2:1 ratio at room temperature in toluene (visible at δ 2.11 ppm)
after reagent combination (bottom) and 12 h (top). The solvent is benzene-d6.
Me2AlOMe, has been extensively studied.24 However, whereas
the byproducts of methylaluminum chloride reaction with
esters proposed in ref 23 were reasonable, direct evidence for
their formation was not presented. Indeed, while some
aluminum hydroxides have been reviewed,24,25 only a very
few literature reports of AlCl-incorporating hydroxides26 and
oxides (aluminoxanes) exist.27 More broadly, aluminoxanes
have been extensively studied,25 particularly as alkene
polymerization cocatalysts.28 Whereas most work has focused
on the hydrolysis of alkylaluminum compounds,29 anhydrous
aluminoxane formation has been reported. Thus, TMA has
been reacted with carboxylic acids30 and alcohols,31 and with
Mg or Mn alkoxides.32 DMSO has been used to oxidize
[{(Me3Si)2CH}2Al]2,33 and reaction of (Mes*AlH2)2 with
(Me2SiO)3 has given (Mes*AlO)4 (Mes* = 2,4,6-(t-Bu)3-
C6H2).34 Lastly, dual aluminum oxide−hydroxides have been
investigated.35
Recently, reaction of TMA with POEs was modeled using
methyl propionate and methyl phenylacetate.11 Data pointed
to the formation of adducts MeORCO(TMA) (R = Et, Bn)
1(TMA) that reacted, particularly in the presence of excess
TMA, to give Me2RCOAlMe2 2 and Me2AlOMe 3. The
preference for reaction in the presence of excess TMA led to
capture of this by 2, with 2(TMA) thereafter reacting with 3 at
raised temperatures to give Me4Al2(μ2-OMe)(μ2-OCRMe2)
2(3) while regenerating TMA (Figure 1).
We now extend the recent ester derivatization by TMA,
using pentaerythritol-based tetraesters 4 (Figure 1) that closely
mimic RL 32H.36,37 The reaction of monoesters and tetraesters
with methylaluminum chlorides, MenAlCl3−n (n = 1, 2), and
the sesquichloride Me1.5AlCl1.5 is explored. NMR spectroscopy
suggests that the enhanced Lewis acidity of MenAlCl3−n
promotes the thermal elimination of alkenes, and even
methane, presenting significant safety implications.
RESULTS AND DISCUSSION
■
Tetraester Reaction with TMA. To extend our recent
analysis of ester derivatization by TMA using improved POE
mimics, tetraesters C(CH2OC(O)R)4 4R (R = Bn 4Bn, C5H11
4Pent) were prepared (Figures S1−S5).38 TMA was introduced
to 4Pent in 1:1, 2:1, 4:1, 8:1, and 12:1 ratios (Figures S6 and
S7). While the first of these systems only yielded evidence for
1:1 adduct formation (13C NMR δ 174.1 ppm, cf. δ 172.3 ppm
for 4Pent), the 2:1 system proved more variable. Immediately
after combination at room temperature, NMR spectroscopy
suggested empirically 2:1 adduct formation (i.e., formally half
of the ester functions in all the 4Pent were complexed), with
exchange averaging the resulting ester signal to δ 177.0 ppm in
B
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the 13C NMR spectrum. However, after 12 h, 1H NMR
spectroscopy revealed the evolution of a singlet at δ 1.11 ppm
characteristic of dimethylation (Figures 2 and S6). On the
basis of this, attempts were made to isolate the initial species
that resulted when TMA and 4Pent were combined. While
spectroscopy suggested that the 2:1 combination of TMA with
4Pent gave a 2:1 adduct, chilling the mixture to −27 °C
immediately after combination of the reagents led to
crystallization of a material that suggested averaging of the
ester 13C NMR signal could be attributed not only to intra- but
also to intermolecular exchange. This material proved highly
reactive at room temperature and largely resisted thorough
characterization. However, crystallographic determination
suggested (tetra)adduct 4Pent(TMA)4 (Scheme 1 and Figure
S10).
Repeated attempts to isolate products of reaction between
TMA and 4Pent failed. This led us to investigate the use of the
benzyl tetraester 4Bn, in the hope that inclusion of the benzyl
group would aid recrystallization. TMA was introduced to 4Bn
in 2:1, 4:1, 8:1, and 12:1 ratios. NMR spectroscopic analysis of
aliquots of the resulting mixtures suggested analogous behavior
to that seen for 4Pent (Figures S11 and S12). This was
evidenced by the observation of 2Bn(TMA) (δ 136.7, 130.3,
128.1, 126.7, 79.5, 50.8, 28.0, −4.5 and −7.0 ppm (13C); δ
2.86, 1.11, 0.13, and −0.42 ppm (1H)) and retention of a
broad signal at ca. 4.0 ppm (Scheme 2).
To further investigate this broad central tetrolate core
region, the TMA−4Bn reactions were repeated but were heated
to reflux for 2 h, as it had previously been shown that heating a
TMA−monoester mixture resulted in the formation of an
OMe-bridged species, 2(3). The reaction was undertaken at
2:1, 4:1, 6:1, and 8:1 TMA/4Bn ratios. This resulted in the
appearance of a number of sharp signals in the δ 4.6−2.9 ppm
Scheme 1. Conversion of 4R to the Corresponding TMA
a
(Tetra)adduct
1
region of the H NMR spectrum that were attributable to
CH2O protons (Figure S13). The 13C NMR spectrum (Figure
S14) also revealed a number of new signals from the CH2O
carbons. Two types of dimethylaluminum alkoxide product of
reaction were identified. The first was dimethylated 2Bn, and
the second was the tetrolate-based product of ester cleavage
retaining 3, 2, 1, or 0 unreacted ester groups (6Bn, 7Bn, 8Bn, or
5). These two types of alkoxide formed adducts based on 4-
membered Al2O2 rings, all of which were identified
spectroscopically (Scheme 3).
a
R = C5H11.
In fact, Figure S13 reveals that the 8:1 reaction of TMA with
4Bn yielded aliquots that comprised two tetrolate-containing
species. In both of these, the ester groups had completely
reacted. Data suggested the explanation for this to be the
coexistence of 5(2Bn)4 alongside a species in which 5 had then
undergone the elimination of 3 equiv of dimethylated 2Bn
complexant and 1 equiv of TMA to form tetrolate product
9(2Bn)2 (δ 3.94, 2.96, 2.79, 1.07, −0.35, and −0.46 ppm (1H)),
4 equiv of 2Bn (presumed to exist as two dimers; δ 3.00, 1.23,
and −0.28 ppm (1H)) and 2 equiv of 2Bn(TMA) (δ 2.86, 1.12,
0.13, and −0.42 ppm (1H)) (Figure 4 and Scheme 4). Five
further observations are relevant to extracting a structure for
9(2Bn)2: First, the tetrolate/free 2Bn ratio. Second, the nature of
the tetrolate ligand, whereby the retention of 1 equiv of 2Bn per
tetrolate suggests the availability of three alkoxide O-centers
for further bonding. Third, consistent with this, replacement of
Aliquots from 8:1 and 12:1 reactions between TMA and
4Pent revealed that immediately after combining reagents there
w a s a n a b s e n c e o f e s t e r g r o u p s , a n d
C5H11CMe2OAlMe2(TMA), 2Pent(TMA), itself could clearly
be observed (δ 79.2, 44.3, 32.0, 28.4, 24.3, 22.6, 13.8, −4.5,
and −7.0 ppm (13C); δ 1.44, 1.22, 1.12, 1.11, 1.10, 0.87, 0.10,
and −0.45 ppm (1H), Figures 3, S6, and S7). In the analogous
monoester work, dimethylation gave 2(TMA) and eliminated
Me2AlOMe 3. However, in the current case, spectroscopy
revealed less clear evidence for the presence of the tetrolate-
based elimination byproduct. A very broad signal centered at
1
ca. 3.8 ppm in the H NMR spectra could be tentatively
attributed to the CH2O region of the tetrolate-based
elimination byproduct C(CH2OAlMe2)4 5 (Scheme 2). This
broad feature showed the correct integration (2H per
dimethylated 2Pent(TMA), Figure 3).
1
Figure 3. H NMR spectrum of an aliquot from the 12:1 reaction of TMA with 4Pent at room temperature in toluene (δ 2.11 ppm) showing
complete ester cleavage. The solvent is benzene-d6.
C
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a
Scheme 2. Generation of Tetrolate-Based C(CH2OAlMe2)4 5 from the Reaction of 4R with TMA
a
R = C5H11, Bn.
a
Scheme 3. Sequential De-Esterification of 4R to Finally Give 5R with the Concomitant Trapping of 1−4 equiv of 2R
a
R = Bn.
1
1
the CH2 signal in the H NMR spectrum of 5(2Bn)2 (δ 4.47
extracted from the H NMR spectroscopic data and are given
in Table 1. Data reveal that for every 2 equiv of TMA added
approximately one ester group reacts. This observation
replicates the reactivity of monoesters (see above). The
binomial distribution of products seen indicates a lack of
cooperativity.
ppm) with signals at δ 3.93 and 2.94 ppm (6H and 2H,
respectively). Fourth, the observation of two types of Al-
bonded Me group in 9(2Bn)2 in the ratio of 4:3. Fifth, the 27Al
NMR spectrum reveals a sharp signal at δ 8.7 ppm (W1/2 = 300
Hz) which is characteristic of 6-coordinate aluminum, along
with a broad signal at δ 156.8 ppm (W1/2 = 3500 Hz) due to 4-
coordinate aluminum. Taken together, these data are
consistent with the creation of a so-called Mitsubishi
molecule,39 which is based on an Al4O6 core in which a
central Al3+ is coordinated by six O-centers, in this case
provided by two tridentate alkoxide ligands that also capture
three AlMe2 moieties (Scheme 4).
Attempts to crystallize the products of reaction between
TMA and 4Bn have met with mixed results. The addition of
hexane to the reaction mixture of 4:1 TMA/4Bn in toluene has
allowed the isolation of crystalline material. X-ray diffraction
confirmed this to be 7Bn(2Bn)2 (Figure 5 and Scheme 3), the
structure of which is consistent with the NMR spectroscopic
formulation of the major component of the reaction mixture.
The isolation of this material establishes two important points.
First, two out of the four ester groups in 4Bn have undergone
The proportions of 4Bn and 5(2Bn)4−9(2Bn)2 formed as a
function of 1 equiv of TMA per molecule of 4Bn have been
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Figure 4. 1H NMR spectrum of an aliquot from the reaction of TMA with 4Bn in an 8:1 ratio after heating to reflux for 2 h in toluene (δ 2.11 ppm),
showing the formation and subsequent reaction of 5(2Bn)4 to give 9(2Bn)2. The solvent is benzene-d6.
Scheme 4. Formation of 9(2Bn)2, 2Bn, and TMA from 5(2Bn)4
Table 1. Proportions of Substrate 4Bn and Ester Cleavage Products 5(2Bn)4−9(2Bn)2 as a Function of Equivalents of TMA
a
1
Relative to 4Bn from H NMR Spectroscopic Integrals
No. ester groups reacted
TMA (equiv) wrt 4Bn
0 (4Bn
)
1 (6Bn(2Bn))
2 (7Bn(2Bn)2)
3 (8Bn(2Bn)3)
4 (5(2Bn)4 + 9(2Bn)2)
total % ester groups reacted
0
2
4
6
8
100
35
0
0
0
0
50
25
0
0
15
54
16
0
0
0
21
50
0
0
0
0
34
100
0
20
49
80
100
0
a
Analysis based on aliquots withdrawn after reflux in toluene for 2 h. Solvent: benzene-d6.
dimethylation. Second, as for 2(3), the 4-membered Al2O2
metallacycles incurred by ester cleavage/alkoxide capture are
symmetrical, based on (AlMe2)2(μ2-OR)2 metallacycles. The
isolation of 7Bn(2Bn)2 plainly verifies the cleavage of two esters
en route to the production of two molecules of dimethylated
BnMe2COAlMe2 2Bn, that could then be captured by
eliminated {BnC(O)OCH2}2C(CH2OAlMe2)2 7Bn (Scheme
3).
white solid, which could be redissolved in hexane. This
solution yielded crystals that X-ray diffraction confirmed to be
9(2Bn)2 (Figure 6), establishing reaction of all four ester groups
in 4Bn. Rather than demonstrating the formation of 5(2Bn)4,
diffraction supports the spectroscopic analysis of this reaction
mixture, corroborating the exclusion of 2Bn and TMA from
5(2Bn)4 to give 9(2Bn)2 (Scheme 4).
Monoester Reaction with MenAlCl3−n (n = 1, 1.5, 2).
Our interest in the role of alkyl chloride−aluminum
combinations in the autocatalytic generation of alkylalumi-
In a similar vein to the 4:1 TMA/4Bn reaction, removal of
solvent from the reaction mixture of 6:1 TMA/4Bn produced a
E
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NMR spectroscopy reinforces this message, pointing to 96%
adduct formation through characteristic signals at δ 3.54 and
2.78 ppm (CH2 and OMe, respectively). Meanwhile, 4%
dimethylation is evidenced by minor signals for CH2 and CMe
in a 1:3 ratio at δ 2.85 and 1.08 ppm. These shifts are similar to
those seen for 2Bn(TMA) (δ 2.86 and 1.11 ppm)11 and suggest
3:1 reaction of Me2AlCl with ester, initially yielding BnMeC
O and MeClAlOMe 11, before forming a dimethylated species.
A signal at δ −0.27 ppm reveals an integral twice that of the
resonance at δ 1.08 ppm. This suggests that although it might
be expected that the dimethylation of 1Bn(Me2AlCl) should
yield 2Bn(MeAlCl2) in the event (and akin to previous work
with 2Bn(TMA)), 2Bn traps unreacted Me2AlCl to give
2Bn(Me2AlCl). In this species, the chloride ligand bridges the
two metals, leaving four identical Al-bonded methyl groups
(Figures 7 and 8 and Scheme 5).
Figure 5. Molecular structure of 7Bn(2Bn)2. Thermal ellipsoids at 30%
probability and hydrogen atoms omitted. Selected bond lengths (Å)
and angles (deg): O1−Al1 1.851(2), O1−Al2 1.853(2), O2−Al1
1.848(2), O2−Al2 1.854(2), O1−Al2−O2 80.86(10), O1−Al1−O2
81.07(10), Al1−O1−Al2 99.00(10), Al1−O2−Al2 99.07(10).
The temperature dependence of Me2AlCl−1Bn reaction was
probed by heating the reaction mixture to reflux. Spectroscopic
analysis of an aliquot then revealed significant growth of δ 50.4
and 28.0 ppm 13C NMR peaks, pointing to increased formation
of the dimethylated derivative (Figure S25). 1H NMR
spectroscopy corroborates this view and points to a mixture
containing multiple components. A new set of peaks
attributable to a dimethylated species were observed (1H
NMR δ 2.92 and 1.12 ppm), suggesting another adduct of 2Bn.
Using NOESY (Figure S27), this species was identified as the
expected product of the dimethylation of 1Bn(Me2AlCl) and
2Bn(MeAlCl2). We propose this to be formed from
2Bn(Me2AlCl) (see above and Scheme 5). The dominant
species are adduct 1Bn(Me2AlCl) (44%) and dimethylated 2Bn
(54%). However, two minor components present are alkenes
12 in a 2% combined yield of 12a (PhCHCMe2, singlet, δ
6.28 ppm) and 12b (BnC(CH2)Me, singlets, δ 4.80 and
4.75 ppm) that arise from the formal elimination from
2Bn(MeAlCl2) of Me3Al2(OH)Cl2 13 (Scheme 5). The same
reaction was attempted at 100 °C for 24 h in toluene-d8 in a
sealed J. Young NMR tube. The resulting mixture now
revealed signals consistent with MeH (1H NMR δ 0.17 ppm,
13C NMR −4.3 ppm, Figures S28 and S29),40 leading us to
propose that 13 converts to oxide Me2Al2OCl2 14. Further
attempts to study the effects of temperature on reaction in
toluene proved not to be straightforward. While heating to
reflux for 2 h yielded 1Bn(Me2AlCl) (40%) and alkenes 12
(60% combined, 1:4 12a/12b), extended heating (24 h) gave
also Friedel−Crafts reaction of the solvent41 (Scheme S1).
Notwithstanding, variable-temperature studies in toluene
successfully revealed alkene formation from 60 °C and
exhaustive methylation29e,42 to give Bn(t-Bu) 15 from 80 °C
with adducts of 2Bn eliminated at temperatures in excess of 70
°C (Figure S31 and Scheme S1). Lastly, investigation of
reaction stoichiometry revealed data consistent with the
mechanism in Scheme 5. 1Bn(Me2AlCl) (42%) and alkenes
12 (58% combined) formed when using 2:1 Me2AlCl/ester in
toluene while a 1:1 ratio led to the dominance of
1Bn(Me2AlCl).
Figure 6. Molecular structure of 9(2Bn)2. Thermal ellipsoids at 30%
probability and hydrogen atoms omitted. Selected bond lengths (Å)
and angles (deg): O1/2/3−Al2/3 1.822(2)−1.828(2), O1/2/3−Al1
1.874(2)−1.888(2), O4−Al 1.851(3)−1.858(3), O5−Al 1.838(3)−
1.848(3), O−Al1−O 77.96(10)−104.13(11), Al−O1/2/3−Al
99.21(12)−100.72(11), O−Al2/3−O 80.96(11)−81.15(15), O4−
Al4−O5 81.07(11), O4−Al5−O5 81.00(11), Al4−O4−Al5
98.42(11), Al4−O5−Al5 99.21(12).
nums led us to recently test reactions of TMA with
monoesters.11 However, since this work aims to mimic the
reactivity of organoaluminums generated through the attack of
chloromethane on aluminum, it followed that reactions of
MenAlCl3−n warranted study. A hexane solution of Me2AlCl
was therefore added to methyl phenylacetate at −78 °C, after
which the mixture was left to reach room temperature. A 3-fold
excess of Me2AlCl was used based on the observed preference
for reaction of TMA with esters when the former was in
excess.11 However, in contrast to work in which 3:1 TMA/
ester reacted to quantitatively give 2Bn(TMA), work with
Me2AlCl was dominated by adduct formation, with 13C NMR
spectroscopy revealing a CO signal at δ 182.3 ppm (cf. δ
170.9 ppm for 1Bn)11 for 1Bn(Me2AlCl) (Figures 7 and S22).
The same spectrum points to limited formation of a second
species, with signals at δ 50.4 and 28.0 ppm tentatively
1
attributed to CH2 and CMe from a dimethylated product. H
Moving from Me2AlCl to MeAlCl2, the increased Lewis
acidity of the Al-reagent led adduct formation to dominate,
with 13C NMR spectroscopy revealing a CO signal at δ
184.2 ppm for 1Bn(MeAlCl2) (cf. Scheme 5). Meanwhile,
treatment of 1Bn with aluminum sesquichloride, (Me1.5AlCl1.5
from 1:1 AlCl3/TMA), yielded activity intermediate between
Me2AlCl and MeAlCl2. Data point to the enhanced Lewis
acidity of the resulting systems, with 1:3 ester/aluminum
Figure 7. Methylaluminum chloride adducts of 1Bn and 2Bn.
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Figure 8. 1H NMR spectrum from the room-temperature reaction between Me2AlCl and methyl phenylacetate 1Bn employing a 3:1 ratio in hexane.
The solvent is benzene-d6.
Scheme 5. Generation of 2Bn(MeAlCl2) and 11 En Route to
the Production of Volatiles 12 and MeH
Figure 9. Molecular structure of 2Bn(Me2AlCl). Thermal ellipsoids at
30% probability and hydrogen atoms omitted. Selected bond lengths
(Å) and angles (deg): O1−Al1 1.837(3), C1−Al1 1.954(5), C2−Al1
1.982(5), Cl1−Al1 2.308(2), C3−O1 1.474(8), Al1−Cl1−Al1A
80.06(9), Al1−O1−Al1A 107.8(2), Cl1−Al1−O1 85.08(13), C1−
Al1−C2 120.5(2).
becoming prominent at higher temperatures. It transpires that
the structural motif demonstrated by 2Bn(Me2AlCl) is highly
unusual, with fully characterized Al2(μ2-O)(μ2-Cl) metalla-
cycles being rare. To the best of our knowledge, only two other
examples have been crystallographically characterized, both the
result of AlCl3 adduct formation.43 The coexistence of
2Bn(MeAlCl2) and 2Bn(Me2AlCl) made it impossible to obtain
accurate elemental analysis for the latter in spite of repeated
attempts.
To further investigate MeH production from the products of
1Bn−Me2AlCl reactions, attempts were made to separately
isolate 2Bn(Me2AlCl) and 2Bn(MeAlCl2) via an alternative
method. The reaction of phenylacetyl chloride 16 with 2 equiv
of TMA resulted in complete conversion to 2Bn(Me2AlCl)
(Figure S32). This is believed to proceed by TMA first
undergoing a chloride exchange with 16 to produce phenyl-
acetone 17 (and Me2AlCl), which then reacts with TMA to
produce 2Bn(Me2AlCl) (Scheme 6). Heating the toluene
solution of 2Bn(Me2AlCl) to reflux for 2 h formed a small
amount (10%) of (2Bn)2 but failed to yield either alkenes or
methane (Figure S35). Concentration of the room temper-
ature reaction mixture resulted in the formation of crystalline
material at −27 °C. These crystals were shown by X-ray
crystallography to exhibit a unit cell the same as that of the
product from the 1Bn−Me2AlCl reaction (Figure 9). Indeed,
further analysis confirmed the crystals as 2Bn(Me2AlCl).
mixtures giving predominantly adduct 1Bn(Me1.5AlCl1.5), which
reveals a 13C NMR CO signal at δ 183.6 ppm (cf. δ 182.3
ppm for 1Bn(Me2AlCl), δ 184.2 ppm for 1Bn(MeAlCl2)). At
<60 °C, adduct formation is quantitative, and dimethylation is
not observed. Evidence that dimethylation can proceed at
high-temperature comes from the observation of alkenes 12
(5% combined) alongside 1Bn(Me1.5AlCl1.5) (91%) after
heating to 80 °C for 24 h. However, once again, present
alongside these components is the product of reaction with
toluene solvent (Scheme S2).
Attempts to isolate 2Bn(Me2AlCl) and 2Bn(MeAlCl2) were
undertaken. The 1Bn−Me2AlCl reaction that was heated to 60
°C for 24 h was shown spectroscopically to yield the most
dimethylation, and this system was therefore reduced in vacuo
to remove toluene and alkenes. The remaining liquid yielded a
solid, which could be melted and then left to cool slowly to
give crystals. These were analyzed by X-ray crystallography
(Figure 9). Diffraction revealed metallacyclic Me4Al2(μ2-
Cl)(μ2-OCBnMe2), 2Bn(Me2AlCl). This motif is similar to
that seen recently for 2Bn(TMA)11 and is consistent with
solution studies (see above) that pointed to a mixture of
expected dimethylation product 2Bn(MeAlCl2) and spectro-
scopically dominant 2Bn(Me2AlCl), with the former complex
G
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Article
Scheme 6. Generation of Adduct 2Bn(Me2AlCl) from 16
to give alkenes 12a and 12b, while a small amount of
exhaustive methylation gave Bn(t-Bu) 15 and Friedel−Crafts
products were also noted (Figure S45). 1H NMR spectroscopy
revealed a broad signal, centered at ca. δ 3.9 ppm, which we
tentatively attribute to the CH2O region of the tetrolate-based
byproduct of complete reaction, C(CH2OAlMemCln)4 18 (m +
n = 2, viz. 5 in Scheme 2). On the basis of observed monoester
reactivity (see above), the reaction of Me2AlCl with 4Bn was
investigated by heating an identical 12:1 reaction mixture to 70
Attempts to produce 2Bn(MeAlCl2) involved reacting 16
with TMA and Me2AlCl (1 equiv of each). This initially
formed 17 and 2 equiv of Me2AlCl in a reaction which proved
to be much slower (viz. the reduced nucleophilicity of Me2AlCl
compared to that of TMA). Stirring at room temperature for 2
h resulted in 49% 17, 33% 2Bn(Me2AlCl), and 18%
2Bn(MeAlCl2) (Figure S41). Raising the reaction temperature
to 60 °C led to an increase in the amount of 2Bn(MeAlCl2)
(8% 17, 31% 2Bn(Me2AlCl), and 61% 2Bn(MeAlCl2)).
However, above 70 °C, the formation of alkenes 12a/b was
observed (Scheme 7), with reaction of toluene to form
1
°C for 2 h (Figure S48). H NMR spectroscopy of an aliquot
of the reaction now revealed the conversion of 35% of the ester
groups to give 2Bn(Me2AlCl) and 16% to give 2Bn(MeAlCl2). A
very broad signal centered at ca. δ 3.8 ppm resulted from the
remaining esters and various CH2OAl groups present. In
contrast to the monoester system, carefully raising the reaction
temperature now resulted in an increase in the amount of
2Bn(Me2AlCl) and 2Bn(MeAlCl2) produced, with
2Bn(MeAlCl2) becoming most abundant at 100 °C. Formation
of alkenes 12a and 12b was now seen from 90 °C, which again
contrasts with Me2AlCl−monoester reactions, where alkene
formation was seen from 60 °C (viz. Figure S31).
Scheme 7. Generation of 2Bn(MeAlCl2) from 16 Yielding
Volatiles 12 and MeH
The use of MeAlCl2 in place of Me2AlCl resulted in the
formation of a white precipitate when it was introduced to 4Bn
in a 12:1 ratio. This material proved intractable. In contrast,
use of an equimolar mixture of Me2AlCl and MeAlCl2 (i.e.,
aluminum sesquichloride) with 4Bn (6 equiv of each of
Me2AlCl and MeAlCl2 per 4Bn) resulted in similar reactivity to
that seen using MeAlCl2, with a white precipitate formed at
lower temperatures but with heating of the reaction to reflux in
toluene achieving a yellow solution. NMR spectroscopy of an
aliquot revealed the presence of alkenes 12a and 12b, Friedel−
Crafts products, trimethylated 15, and a broad set of peaks at
4.5−3.5 ppm suggesting a mixture of unreacted ester groups
and CH2OAl units (Figure S49).
The observation that 4Pent(TMA)4 crystallized (Figure S10)
but did so as a highly sensitive material that proved difficult to
analyze led to attempts to produce the analogous Me2AlCl and
MeAlCl2 structures. Pleasingly, the addition of 2 equiv of
Me2AlCl to 4Pent allowed the isolation of crystalline
4Pent(Me2AlCl)4 (Figure 10). Relative to similarly structured
4Pent(TMA)4, the O−Al distances are shorter (mean 1.845 Å vs
mean 1.920 Å in the TMA adduct). This is consistent with
Me2AlCl being a stronger Lewis acid, and appeared to impart
additional stability that enabled more thorough character-
ization of the adduct.
Friedel−Crafts products also seen. Heating the reaction
mixture to 100 °C in toluene-d8 in a sealed J. Young NMR
tube for 2 h also resulted in the observation of MeH (1H NMR
δ 0.17 ppm, 13C NMR −4.3 ppm, Figures S42 and S43),
indicating that it is 2Bn(MeAlCl2) and not 2Bn(Me2AlCl) that
represents a source of MeH. We attribute this to the greater
number of chloride ligands increasing the Lewis acidity of
MeAlCl2 relative to that of Me2AlCl.
Tetraester Reaction with MenAlCl3−n (n = 1, 1.5, 2).
The study of methylaluminum chlorides with monoesters was
next extended to pentaerythritol-based tetraester mimics of
POEs. In the first instance, the use of 4Bn with 12 equiv of
Me2AlCl (3 equiv per ester group) in toluene resulted in
limited reactivity that was, nonetheless, similar to that of the
monoester. 1H NMR spectroscopy revealed that only 2% of the
ester groups had reacted to form 2Bn(Me2AlCl) after 2 h at
room temperature (viz. Scheme 5). Heating to reflux in
toluene for 2 h resulted in complete reaction of the tetraester
CONCLUSIONS
■
The reaction of TMA has been extended from mono- to
tetraester systems that are close relatives of industrial
lubricants. Results revealed the ability of pentaerythritol-
based C(CH2OC(O)R)4 to form adducts that could be
isolated (4Pent(TMA)4). Subsequent sequential reaction of
each of the four ester functions was monitored, with
spectroscopic observation of the stepwise conversion of each
group corroborated by the isolation of twice-reacted {BnC-
(O)OCH2}2C(CH2OAlMe2)2(2Bn)2 7Bn(2Bn)2, where 2Bn is
BnCMe2OAlMe2. These data demonstrated that reactivity
reported recently for monoesters can be extended to more
complex, multifunctional polyolesters highly relevant to the
refrigeration and transport industries. The reactions of
methylaluminums with monoesters have also been extended
beyond our recent report of the activity of TMA through the
use of methylaluminum chlorides, MenAlCl3−n. New results
H
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Article
attached to the goniometer head via a MicroLoop, which was then
centered on the diffractometer. Data were collected on a Bruker D8
Quest (Cu Kα, λ = 1.54184 Å), equipped with an Oxford
Cryosystems low-temperature device. Structures were solved using
SHELXT,45 with refinement, based on F2, by full-matrix least-
squares.46 Non-hydrogen atoms were refined anisotropically (for
disorder, standard restraints and constraints were employed as
appropriate) and a riding model with idealized geometry was
employed for the refinement of hydrogen atoms. Compound
9(2Bn)2 crystallized as a two-component nonmerohedral twin.
Orientation matrices for the two components were found using the
program Cell Now, and the two components were integrated with
SAINT. The exact twin law determined by the integration program
was (0.99997, −0.00021, 1.27249), (−0.00012, −1.00000, 0.00008),
(0.00004, −0.00010, −0.99997). The data were corrected for
absorption using Twinabs. 21800 reflections (3354 unique) involved
domain 1 only (mean I/σ = 22.5), 21604 reflections (3344 unique)
involved domain 2 only (mean I/σ = 20.1) and 15765 reflections
(3230 unique) involved two domains (mean I/σ = 24.8). The
structure was solved with SHELXT using data from domain 1 only
(HKLF 4). For refinement, all observations involving domain 1 were
included (HKLF 5); single reflections that also occurred in
composites were omitted. Rint is based on agreement between
observed single and composite intensities and those calculated from
refined unique intensities and twin fractions. All crystallographic data
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publications CCDC 1867820−1867825.
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk).
Figure 10. Molecular structure of 4Pent(Me2AlCl)4. Thermal ellipsoids
at 30% probability, with hydrogen atoms and minor disorder omitted.
Selected bond lengths (Å) and angles (deg): O2−Al1 1.8729(18),
C16−Al1 1.944(3), C17−Al1 1.960(3), Cl1−Al1 2.1839(10), O4−
Al2 1.817(9), C18−Al2 1.958(14), C19−Al2 1.974(12), Cl2−Al2
2.172(8), C3−O2−Al1 149.15(16), C10−O4−Al2 163.6(3).
point to similar but suppressed reactivity as n is decreased. The
use of Me2AlCl with BnC(O)OMe 1Bn initially yielded a
simple adduct but also provided evidence for dimethylation
and the formation of a mixture of 2Bn(Me2AlCl) and
2Bn(MeAlCl2). In stark contrast to results obtained with
TMA, this system proved capable of thermally eliminating
alkenes (directly) and methane (indirectly). Replacing the
monoesters with tetraesters showed similar reactivity, again
seen with the production of alkenes and methane. These data,
and the production of volatiles particularly, have significant
health and safety implications for industry given the recently
reported complications caused by the use of counterfit
additives in refrigeration technologies.
Synthesis and Characterization of 7Bn(2Bn)2. TMA (1.0 mL,
2.0 mmol, 2.0 M in toluene) was added dropwise to 4Bn (304 mg, 0.5
mmol) in toluene (4 mL) under a N2 atmosphere at −78 °C and
allowed to reach room temperature. The solution was heated to reflux
for 2 h. Addition of hexane (6 mL) and storage at −27 °C resulted in
the formation of colorless needle crystals. Yield 100 mg (22% wrt
1
4Bn). Mp 140−142 °C. H NMR spectroscopy (400 MHz, benzene-
d6): δ 7.28−6.85 (m, 20H, Ph), 4.25 (s, 4H, CH2O), 3.84 (s, 4H,
CH2O), 3.51 (s, 4H, CH2), 2.87 (s, 4H, CH2), 1.12 (s, 12H, Me),
−0.37 (s, 24H, AlMe). 13C NMR (100 MHz, benzene-d6): δ 170.0
(CO), 136.7, 133.5 (i-Ph), 130.3, 129.4 (o-Ph), 128.6, 128.0 (m-
Ph), 127.2, 126.7 (p-Ph), 77.7 (CO), 62.1, 62.0(CH2O), 51.1 (CH2),
44.2 (Cquat), 40.9 (CH2), 28.4 (Me), −8.4 (AlMe). 27Al NMR (104
MHz, benzene-d6): Only see background signal; elemental analysis
calculated (%) for C49H72Al4O8: C 65.61, H 8.09. Found: C 65.46, H
8.01. X-ray crystal data: C49H72Al4O8, M = 896.98, triclinic, space
EXPERIMENTAL SECTION
■
General Synthetic and Analytical Details. Reactions and
manipulations were carried out under dry nitrogen, using double
manifold and glovebox methods. Solvents were distilled off sodium−
potassium amalgam (hexane) or sodium (toluene) immediately prior
to use. Methyl phenylacetate (Sigma-Aldrich) was stored over
molecular sieve (4 Å). TMA (2.0 M in toluene) and Me2AlCl (1.0
M in hexane) were purchased from Sigma-Aldrich and used as
received. Caution: TMA is pyrophoric and should only be handled under
anaerobic conditions. AlCl3 was purchased from Sigma-Aldrich and
stored in a glovebox. Pentaerythritol was purchased from Alfa Aesar
and stored in a glovebox. Phenylacetyl chloride and hexanoyl chloride
were purchased from Fisher Scientific and used as received. For all
new compounds and adducts we report elemental analysis, 1H,
{1H}13C, and (where appropriate) 27Al NMR spectroscopy, and single
crystal X-ray diffraction. Exceptions to this are 4Pent (which lacks X-ray
diffraction) and 4Pent(TMA)4 (characterized only by X-ray diffrac-
tion). Elemental analysis was carried out on a PerkinElmer 240
Elemental Analyzer. NMR data were collected on a Bruker Avance III
HD 400 MHz Smart Probe FT NMR spectrometer (400.130 MHz for
1H, 100.613 MHz for 13C, 104.261 for 27Al). Spectra were obtained at
25 °C. 1H and 13C chemical shifts are internally referenced to
deuterated solvent and calculated relative to TMS. 27Al used an
external reference (1 M AlCl3(H2O)6 in D2O). Chemical shifts are
given in δ ppm. Abbreviations used are br = broad, d = doublet, m =
multiplet, quin = quintet, s = singlet, t = triplet, F/C = Friedel−Crafts.
Crystallographic Details. Crystals were transferred from the
mother liquor to a drop of perfluoropolyether oil mounted upon a
microscope slide under cold nitrogen gas.44 Suitable crystals were
̅
group P1, a = 12.3772(4), b = 13.6608(5) c = 17.5106(6) Å, α =
68.249(2), β = 70.040(2), γ = 79.421(2), V = 2579.22(16) Å3, Z = 2,
ρcalcd = 1.155 g cm−3, μ = 1.222 mm−1, T = 180(2) K. 74 742 data
(9120 unique, Rint = 0.1304, θ < 66.810°) were collected. wR2 =
2
{Σ[w(Fo2 − Fc2)2]/Σ[w(Fo )2]}1/2 = 0.1473, conventional R = 0.0609
on F values of 5198 reflections with F2 > 2σ(F2), GoF = 1.017, 562
parameters. Max. peak/hole 0.440 eÅ−3.
Co-Synthesis and Characterization of 9(2Bn)2 and (2Bn)2.
TMA (1.5 mL, 3.0 mmol, 2.0 M in toluene) was added dropwise to
4Bn (304 mg, 0.5 mmol) in toluene (4 mL) under a N2 atmosphere at
−78 °C and allowed to reach room temperature. The solution was
heated to reflux for 2 h, and then the solvent was removed under
vacuum. The solid was redissolved in hexane (8 mL), and storage at
room temperature for 1 day resulted in the formation of colorless
1
crystals. Yield 40 mg. Mp 221−224 °C. H NMR spectroscopy (400
MHz, benzene-d6): δ 7.08−6.83 (m, 12.5H, 9(2Bn)2 + (2Bn)2 Ph),
3.93 (s, 12H, 9(2Bn)2 CH2O), 3.00 (s, 1H, (2Bn)2 CH2), 2.94 (s, 4H,
9(2Bn)2 CH2O), 2.79 (s, 4H, 9(2Bn)2 CH2), 1.22 (s, 3H, (2Bn)2 Me),
1.06 (s, 12H, 9(2Bn)2 Me), −0.27 (s, 3H, (2Bn)2 AlMe), −0.34 (s,
18H, 9(2Bn)2 AlMe), −0.46 (s, 24H, 9(2Bn)2 AlMe). 13C NMR (100
MHz, benzene-d6): δ 136.5 (9(2Bn)2 i-Ph), 130.3 (9(2Bn)2 o-Ph),
128.1 (9(2Bn)2 m-Ph), 126.8 (9(2Bn)2 p-Ph), 77.9 (9(2Bn)2 CO), 69.8
(9(2Bn)2 CH2O), 62.2 (9(2Bn)2 CH2O), 51.2 ((2Bn)2 CH2), 51.0
(9(2Bn)2 CH2), 40.6 (9(2Bn)2 Cquat), 28.5 ((2Bn)2 Me), 28.3 (9(2Bn)2
I
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Me), −8.5 (9(2Bn)2 AlMe), −12.1 (9(2Bn)2 AlMe). 27Al NMR (104
MHz, benzene-d6): δ 8.7 (W1/2 = 340 Hz); elemental analysis
calculated (%) for C50H93.5Al8.5O10.5 (representing NMR spectrosco-
py): C 54.97, H 8.63. Found: C 52.33, H 8.48. X-ray crystal data:
C44H84Al8O10, M = 988.95, monoclinic, space group C2/c, a =
26.8564(8), b = 16.9050(5) c = 13.6338(4) Å, β = 108.8420(10), V =
5858.1(3) Å3, Z = 4, ρcalcd = 1.121 g cm−3, μ = 1.694 mm−1, T =
180(2) K. 5149 data (5149 unique, Rint = 0.0614, θ < 66.623°) were
27Al NMR (104 MHz, benzene-d6): δ 174.1 (W1/2 = 3500 Hz), 126.7
(W1/2 = 1300 Hz).
50 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
1
7.09−6.76 (m, 5H, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2)
Ph), 3.57 (m, br, 2H, 1Bn(Me2AlCl) CH2), 3.30−2.96 (m, 0.64H,
unassigned), 2.93 (s, 0.26H, 2Bn(MeAlCl2) CH2), 2.86 (s, 0.48H,
2Bn(Me2AlCl) CH2), 2.85−2.62 (m, br, 3H, 1Bn(Me2AlCl) OMe),
1.13 (s, 0.49H, 2Bn(MeAlCl2) Me), 1.08 (s, 1.4H, 2Bn(Me2AlCl) Me),
0.01 to −0.20 (m, 2.2H, unassigned AlMe), −0.22 (s, 0.4H,
2Bn(MeAlCl2) AlMe), −0.27 (s, 9.5H, 2Bn(Me2AlCl) + 2Bn(MeAlCl2)
AlMe), −0.36 (s, 0.4H, 2Bn(MeAlCl2) AlMe), −0.45 (s, 2.2H,
unassigned AlMe). 13C NMR (100 MHz, benzene-d6): δ 182.5
(1Bn(Me2AlCl) CO), 135.9, 130.2, 129.5, 128.8, 128.1
(1Bn(Me2AlCl) + 2Bn(Me2AlCl) Ph + 2Bn(MeAlCl2) Ph), 83.7
(2Bn(MeAlCl2) CO), 81.1 (2Bn(Me2AlCl) CO), 56.7, 56.5
(1Bn(Me2AlCl) OMe), 50.4 (2Bn(Me2AlCl) CH2), 50.1
(2Bn(MeAlCl2) CH2), 41.1 (1Bn(Me2AlCl) CH2), 27.9
(2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me), −6.7 (1Bn(Me2AlCl) +
2Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe). 27Al NMR (104 MHz,
benzene-d6): δ 176.6 (W1/2 = 3400 Hz), 127.2 (W1/2 = 1300 Hz).
2
2
collected. wR2 = {Σ[w(Fo − Fc2)2]/Σ[w(Fo )2]}1/2 = 0.1622,
conventional R = 0.0583 on F values of 4542 reflections with F2 >
2σ(F2), GoF = 1.154, 291 parameters. Max. peak/hole 0.487 eÅ−3.
Spectroscopic Characterization of BnC(O)OMe 1Bn
+
Me2AlCl Reaction Mixtures. Method 1. Me2AlCl (6 mL, 6
mmol, 1.0 M in hexane) was added dropwise at −78 °C to methyl
phenylacetate 1Bn (0.28 mL, 2 mmol) and the mixture allowed to
warm to room temperature. After stirring for 2 h, the solvent was
removed in vacuo to give a clear residue which was analyzed by NMR
spectroscopy. 1H NMR spectroscopy (400 MHz, benzene-d6) δ 7.09−
6.76 (m, 4.5H, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) Ph), 3.54 (s, 2H,
1Bn(Me2AlCl) CH2), 2.85 (s, 0.08H, 2Bn(Me2AlCl) CH2), 2.78 (s, br,
3H, 1Bn(Me2AlCl) OMe), 1.08 (s, 0.22H, 2Bn(Me2AlCl) Me), −0.21
(s, 7.9H, 1Bn(Me2AlCl) AlMe), −0.27 (s, 0.45H, 2Bn(Me2AlCl)
AlMe). 13C NMR (100 MHz, benzene-d6): δ 182.3 (1Bn(Me2AlCl)
CO), 130.2, 129.4, 128.8, 128.1 (1Bn(Me2AlCl) + 2Bn(Me2AlCl)
Ph), 56.1 (1Bn(Me2AlCl) OMe), 50.4 (2Bn(Me2AlCl) CH2), 41.1
(1Bn(Me2AlCl) CH2), 28.0 (2Bn(Me2AlCl) Me), −7.2 (1Bn(Me2AlCl)
+ 2Bn(Me2AlCl) AlMe). 27Al NMR (104 MHz, benzene-d6): δ 170.5
(W1/2 = 3800 Hz), 127.7 (W1/2 = 1400 Hz).
1
60 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.34−6.76 (m, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) + 12a
+ 12b Ph), 6.28 (s, 0.01H, 12a CHC), 4.80 (m, 0.02H, 12b C
CH2), 4.75 (m, 0.02H, 12b CCH2), 3.59 (m, br, 2H, 1Bn(Me2AlCl)
CH2), 3.32−2.97 (m, 1.67H, unassigned), 2.93 (s, 0.57H,
2Bn(MeAlCl2) CH2), 2.86 (s, 0.73H, 2Bn(Me2AlCl) CH2), 2.83−
2.58 (m, br, 2.6H, 1Bn(Me2AlCl) OMe), 1.72 (s, 0.02H, 12a Me),
1.70 (s, 0.02H, 12a Me), 1.55 (s, 0.06H, 12b Me), 1.38−1.17 (m,
0.75H, unassigned), 1.13 (s, 1.2H, 2Bn(MeAlCl2) Me), 1.08 (s, 1.9H,
2Bn(Me2AlCl) Me), 0.01 to −0.20 (m, 2.9H, unassigned AlMe),
−0.22 (s, 0.55H, 2Bn(MeAlCl2) AlMe), −0.27 (s, 4.1H, 2Bn(Me2AlCl)
AlMe), −0.30 (s, 9.1H, 1Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe), −0.37
(s, 0.68H, 2Bn(MeAlCl2) AlMe), −0.45 (s, 2.8H, unassigned AlMe).
13C NMR (100 MHz, benzene-d6): δ 183.5 (1Bn(Me2AlCl) CO),
135.9, 135.4, 130.2, 129.5, 128.8, (1Bn(Me2AlCl) + 2Bn(Me2AlCl) Ph
+ 2Bn(MeAlCl2) Ph), 83.7 (2Bn(MeAlCl2) CO), 81.1 (2Bn(Me2AlCl)
CO), 56.7 (1Bn(Me2AlCl) OMe), 50.4 (2Bn(Me2AlCl) CH2), 50.1
(2Bn(MeAlCl2) CH2), 41.1 (1Bn(Me2AlCl) CH2), 27.9
(2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me), −6.1, −6.7 (1Bn(Me2AlCl) +
2Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe). 27Al NMR (104 MHz,
benzene-d6): δ 171.7 (W1/2 = 3000 Hz), 124.2 (W1/2 = 1700 Hz).
Method 2. The above method was repeated, but after warming to
room temperature, the reaction was heated to reflux for 24 h and then
solvent removed in vacuo to give a clear residue which was analyzed
1
by NMR spectroscopy. H NMR spectroscopy (400 MHz, benzene-
d6) δ 7.09−6.76 (m, 9.7H, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) +
2Bn(MeAlCl2) Ph), 6.28 (s, 0.01H, 12a CHC), 4.80 (s, 0.03H,
12b CCH2), 4.75 (s, 0.03H, 12b CCH2), 3.90−3.48 (m, 2.3H,
1Bn(Me2AlCl) CH2), 3.30−2.96 (m, 4.7H, unassigned), 2.92 (s, 0.8H,
2Bn(MeAlCl2) CH2), 2.85 (s, 0.8H, 2Bn(Me2AlCl) CH2), 2.66 (s, br,
2.5H, 1Bn(Me2AlCl) OMe), 1.71 (s, 0.04H, 12a Me), 1.68 (s, 0.03H,
12a Me), 1.40−1.16 (m, 1.7H, unassigned), 1.12 (s, 2.1H,
2Bn(MeAlCl2) Me), 1.08 (s, 2H, 2Bn(Me2AlCl) Me), 0.22 to −0.20
(m, 3.5H, unassigned AlMe), −0.22 (s, 1.4H, 2Bn(MeAlCl2) AlMe),
−0.27 (s, 5.4H, 2Bn(Me2AlCl) AlMe), −0.29 (s, 1H, 2Bn(MeAlCl2)
AlMe), −0.30 to −0.70 (m, 8.9H, unassigned AlMe). 13C NMR (100
MHz, benzene-d6): δ 183.4 (1Bn(Me2AlCl) CO), 135.9, 135.4,
130.3, 130.2, 129.5, 128.8, 128.2 (1Bn(Me2AlCl) + 2Bn(Me2AlCl) +
2Bn(MeAlCl2) Ph), 83.7 (2Bn(MeAlCl2) CO), 81.1 (2Bn(Me2AlCl)
CO), 56.7 (1Bn(Me2AlCl) OMe), 53.0−51.8 (unassigned OMe), 50.4
(2Bn(Me2AlCl) CH2), 50.1 (2Bn(MeAlCl2) CH2), 41.1
(1Bn(Me2AlCl) CH2), 28.0 (2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me),
−6.1, −6.4, −8.5 (1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2)
AlMe). 27Al NMR (104 MHz, benzene-d6): δ 164.8 (W1/2 = 3800
Hz), 124.4 (W1/2 = 1700 Hz).
1
70 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.34−6.76 (m, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) + 12a
+ 12b Ph), 6.28 (s, 0.02H, 12a CHC), 4.80 (m, 0.15H, 12b C
CH2), 4.75 (m, 0.15H, 12b CCH2), 3.59 (m, br, 2H, 1Bn(Me2AlCl)
CH2), 3.32−2.97 (m, 4H, unassigned), 2.93 (s, 0.81H, 2Bn(MeAlCl2)
CH2), 2.86 (s, 0.91H, 2Bn(Me2AlCl) CH2), 2.83−2.58 (m, br, 2.4H,
1Bn(Me2AlCl) OMe), 1.72 (s, 0.12H, 12a Me), 1.69 (s, 0.11H, 12a
Me), 1.55 (s, 0.51H, 12b Me), 1.38−1.17 (m, 1.9H, unassigned), 1.13
(s, 1.9H, 2Bn(MeAlCl2) Me), 1.08 (s, 2H, 2Bn(Me2AlCl) Me), 0.01 to
−0.20 (m, 5H, unassigned AlMe), −0.22 (s, 1.3H, 2Bn(MeAlCl2)
AlMe), −0.28 (s, 4.1H, 2Bn(Me2AlCl) AlMe), −0.32 (s, 10.8H,
1Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe), −0.37 (s, 1.4H, 2Bn(MeAlCl2)
AlMe), −0.45 (s, 3.1H, unassigned AlMe). 13C NMR (100 MHz,
benzene-d6): δ 135.9, 135.4, 130.2, 129.5, 128.8, (1Bn(Me2AlCl) +
2Bn(Me2AlCl) Ph + 2Bn(MeAlCl2) Ph), 83.7 (2Bn(MeAlCl2) CO),
81.1 (2Bn(Me2AlCl) CO), 56.7 (1Bn(Me2AlCl) OMe), 50.4
(2Bn(Me2AlCl) CH2), 50.1 (2Bn(MeAlCl2) CH2), 44.6 (12b CH2),
41.1 (1Bn(Me2AlCl) CH2), 27.9 (2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me),
−6.6 (1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe). 27Al
NMR (104 MHz, benzene-d6): δ 174.2 (W1/2 = 3000 Hz), 124.5
(W1/2 = 1600 Hz).
Method 3. AlCl3 (267 mg, 2 mmol), toluene (1 mL), and TMA (2
mL, 4 mmol, 2.0 M in toluene) were reacted to form Me2AlCl (6
mmol, 2.0 M in toluene). Methyl phenylacetate 1Bn (0.28 mL, 2
mmol) was added dropwise at −78 °C and the mixture allowed to
warm to room temperature to give a colorless solution. After stirring
for 24 h at the desired temperature an aliquot of the solution was
analyzed by NMR spectroscopy.
1
Room-Temperature Reaction. H NMR spectroscopy (400 MHz,
benzene-d6) δ 7.09−6.76 (m, 5H, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) Ph),
3.53 (s, br, 2H, 1Bn(Me2AlCl) CH2), 2.86 (s, 0.24H, 2Bn(Me2AlCl)
CH2), 2.82 (s, br, 3H, 1Bn(Me2AlCl) OMe), 1.08 (s, 0.6H,
2Bn(Me2AlCl) Me), 0.01 to −0.25 (m, 1.2H, unassigned AlMe),
−0.27 (s, 13.5H, 1Bn(Me2AlCl) + 2Bn(Me2AlCl) AlMe), −0.34 to
−0.49 (m, 2.5H, unassigned AlMe). 13C NMR (100 MHz, benzene-
d6): δ 181.5 (1Bn(Me2AlCl) CO), 130.2, 129.4, 128.8, 128.1
(1Bn(Me2AlCl) + 2Bn(Me2AlCl) Ph), 56.2 (1Bn(Me2AlCl) OMe), 50.4
(2Bn(Me2AlCl) CH2), 41.1 (1Bn(Me2AlCl) CH2), 27.9
(2Bn(Me2AlCl) Me), −7.0 (1Bn(Me2AlCl) + 2Bn(Me2AlCl) AlMe).
1
80 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.34−6.76 (m, 1Bn(Me2AlCl) + 12a + 12b Ph), 6.28 (s, 0.21H, 12a
CHC), 4.80 (m, 0.93H, 12b CCH2), 4.75 (m, 0.93H, 12b C
CH2), 3.59, 3.54 (m, br, 2H, 1Bn(Me2AlCl) CH2), 3.32−2.97 (m,
4.7H, unassigned OMe), 3.15 (s, 2.3H, 12b CH2), 2.83−2.62 (m, br,
1.8H, 1Bn(Me2AlCl) OMe), 2.37 (s, 0.04H, 15 CH2), 1.72 (s, 0.78H,
12a Me), 1.69 (s, 0.78H, 12a Me), 1.55 (s, 0.51H, 12b Me), 0.84 (s,
0.26H, 15 Me), 0.01 to −0.60 (m, 20H, unassigned AlMe), −0.34 (s,
J
DOI: 10.1021/acs.organomet.8b00763
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
12.7H, 1Bn(Me2AlCl) AlMe). 13C NMR (100 MHz, benzene-d6): δ
144.8, 139.6 (12b C), 129.5, 129.4 (1Bn(Me2AlCl) Ph), 128.9 (12b
Ph), 125.6 (12aCH), 111.8 (12bCH2), 57.9 (1Bn(Me2AlCl)
OMe), 44.6 (12b CH2), 41.5, 41.1 (1Bn(Me2AlCl) CH2), 26.4 (12a
Me), 21.6 (12b Me), 18.9 (12a Me), −6.8 (1Bn(Me2AlCl) AlMe).
27Al NMR (104 MHz, benzene-d6): δ 177.1 (W1/2 = 2500 Hz), 124.3
(W1/2 = 1800 Hz).
dropwise under a N2 atmosphere at −78 °C and allowed to reach
room temperature. After stirring for 2 h, at the desired temperature an
aliquot of the solution was analyzed by NMR spectroscopy.
1
Room-Temperature Reaction. H NMR spectroscopy (400 MHz,
benzene-d6) δ 7.15−6.61 (m, 17(MeAlCl2) + 2Bn(Me2AlCl) +
2Bn(MeAlCl2) Ph), 3.09 (s, 2H, 17(MeAlCl2) CH2), 2.93 (s, 0.8H,
2Bn(MeAlCl2) CH2), 2.86 (s, 1.4H, 2Bn(Me2AlCl) CH2), 1.64 (s, 3H,
17(MeAlCl2) Me), 1.13 (s, 2.3H, 2Bn(MeAlCl2) Me), 1.08 (s, 4.2H,
2Bn(Me2AlCl) Me), −0.05 (s, 2H, 17(MeAlCl2) AlMe), −0.22 (s,
1.3H, 2Bn(MeAlCl2) AlMe), −0.28 (s, 16.5H, 2Bn(Me2AlCl) +
2Bn(MeAlCl2) AlMe), −0.38 (s, 1.1H, 2Bn(MeAlCl2) AlMe). 13C
NMR (100 MHz, benzene-d6): δ 233.2 (17(MeAlCl2) CO), 135.9,
135.4, 130.2, 129.2, 129.1, 128.2, 127.1, 127.0 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) + 17(MeAlCl2) Ph), 83.7 (2Bn(MeAlCl2) CO), 81.1
(2Bn(Me2AlCl) Cquat), 51.0 (17(MeAlCl2) CH2), 50.4 (2Bn(Me2AlCl)
CH2), 50.1 (2Bn(MeAlCl2) CH2), 29.6 (17(MeAlCl2) Me), 28.0
(2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me), −6.1 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) AlMe). 27Al NMR (104 MHz, benzene-d6): δ 173.7
(W1/2 = 4000 Hz), 127.6 (W1/2 = 2000 Hz).
1
Reaction Heated to Reflux. H NMR spectroscopy (400 MHz,
benzene-d6) δ 7.34−6.76 (m, 1Bn(Me2AlCl) + 12a + 12b Ph), 6.28 (s,
0.39H, 12a CHC), 4.80 (m, 1H, 12b CCH2), 4.75 (m, 1H, 12b
CCH2), 3.58 (s, 0.39H, 1Bn(Me2AlCl) CH2), 3.32−2.97 (m, 3H,
unassigned OMe), 3.15 (s, 3.2H, 12b CH2), 2.99 (s, 1.1H, unassigned
OMe), 2.81−2.72 (m, br, 1.2H, unassigned OMe), 2.37 (s, 0.16H, 15
CH2), 1.72 (s, 1.5H, 12a Me), 1.69 (s, 1.5H, 12a Me), 1.55 (s, 3.2H,
12b Me), 1.33 (s, 0.44H, F/C Me), 1.22 (s, 0.56, F/C Me), 0.91−
0.78 (m, 2.2H, F/C Me), 0.84 (s, 0.82H, 15 Me), 0.11 to −0.60 (m,
21H, unassigned AlMe), −0.36 (s, 12.7H, 1Bn(Me2AlCl) AlMe). 13C
NMR (100 MHz, benzene-d6): δ 144.8, 139.6 (12b C), 134.7, 130.8,
129.4 (1Bn(Me2AlCl) Ph), 128.9 (12b Ph), 125.3 (12a = CH), 111.9
(12b = CH2), 44.6 (12b CH2), 29.1 (15 Me), 26.4 (12a Me), 21.6
(12b Me), 18.9 (12a Me). 27Al NMR (104 MHz, benzene-d6): δ
190.6 (W1/2 = 3100 Hz), 136.1 (W1/2 = 3000 Hz), 94.9 (W1/2 = 300
Hz), 93.5 (W1/2 = 300 Hz).
1
50 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.15−6.61 (m, 17(MeAlCl2) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) Ph),
3.06 (s, 2H, 17(MeAlCl2) CH2), 2.93 (s, 5.4H, 2Bn(MeAlCl2) CH2),
2.86 (s, 3.1H, 2Bn(Me2AlCl) CH2), 1.63 (s, 3H, 17(MeAlCl2) Me),
1.13 (s, 16H, 2Bn(MeAlCl2) Me), 1.08 (s, 10H, 2Bn(Me2AlCl) Me),
−0.05 (s, 2.8H, 17(MeAlCl2) AlMe), −0.22 (s, 8H, 2Bn(MeAlCl2)
AlMe), −0.28 (s, 20H, 2Bn(Me2AlCl) AlMe) − 0.29 (s, 7H,
2Bn(MeAlCl2) AlMe), −0.38 (s, 7H, 2Bn(MeAlCl2) AlMe). 13C
NMR (100 MHz, benzene-d6): δ 233.2 (17(MeAlCl2) CO), 135.9,
135.4, 130.2, 129.2, 129.1, 128.2, 127.1, 127.0 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) + 17(MeAlCl2) Ph), 83.7 (2Bn(MeAlCl2) CO), 81.1
(2Bn(Me2AlCl) Cquat), 51.0 (17(MeAlCl2) CH2), 50.4 (2Bn(Me2AlCl)
CH2), 50.1 (2Bn(MeAlCl2) CH2), 29.6 (17(MeAlCl2) Me), 27.9
(2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me), −6.3 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) AlMe). 27Al NMR (104 MHz, benzene-d6): δ 174.7
(W1/2 = 4100 Hz), 128.2 (W1/2 = 2700 Hz).
Method 4. First, 0.1 mL of the 3:1 solution from Method 3 was
placed in a sealed J. Young NMR tube with 0.6 mL of toluene-d8 and
heated to 100 °C for 24 h. 1H NMR spectroscopy (400 MHz,
toluene-d8) δ 7.34−6.76 (m, 1Bn(Me2AlCl) + 12a + 12b Ph), 6.22
(m, 1H, 12a CHC), 4.77 (m, 4.2H, 12b CCH2), 4.72 (m, 4.2H,
12b CCH2), 3.60, 3.56 (s, 4.5H, 1Bn(Me2AlCl) CH2), 3.27, 3.16,
2.79 (s, 5.9H, 1Bn(Me2AlCl) OMe) 3.20, 2.86 (m, 6.6H, unassigned
OMe), 3.13 (s, 9H, 12b CH2), 2.99 (s, 1.1H, unassigned OMe),
2.81−2.72 (m, br, 1.2H, unassigned OMe), 1.72 (d, 3.7H, 12a Me),
1.68 (s, 3.7H, 12a Me), 1.54 (s, 13.4H, 12b Me), 0.17 (s, 4.1H,
MeH), 0.11 to −0.64 (m, 52H, unassigned AlMe), −0.35 (s, 37H,
Me2AlCl AlMe). 13C NMR (100 MHz, toluene-d8): δ 184.5
(1Bn(Me2AlCl) CO), 145.1, 139.9 (12b C), 134.9 (12b C),
129.8 (1Bn(Me2AlCl) Ph), 128.9 (12b Ph), 125.6 (12a = CH), 112.2
(12b = CH2), 58.9, 57.2 (1Bn(Me2AlCl) OMe), 44.9 (12b CH2),
41.8, 41.5 (1Bn(Me2AlCl) CH2), 26.8 (12a Me), 22.0 (12b Me), 19.3
(12a Me), −4.3 (MeH), −6.3 (1Bn(Me2AlCl) AlMe). 27Al NMR (104
MHz, toluene-d8): δ 183.0 (W1/2 = 2300 Hz), 129.9 (W1/2 = 2000
Hz), 99.8 (W1/2 = 300 Hz), 97.8 (W1/2 = 400 Hz).
1
60 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.15−6.61 (m, 17(MeAlCl2) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) Ph),
3.04 (s, 0.3H, 17(MeAlCl2) CH2), 2.92 (s, 2H, 2Bn(MeAlCl2) CH2),
2.85 (s, 1H, 2Bn(Me2AlCl) CH2), 1.61 (s, 0.4H, 17(MeAlCl2) Me),
1.13 (s, 6H, 2Bn(MeAlCl2) Me), 1.08 (s, 3H, 2Bn(Me2AlCl) Me),
−0.04 (s, 0.4H, 17(MeAlCl2) AlMe), −0.22 (s, 3H, 2Bn(MeAlCl2)
AlMe), −0.28 (s, 6H, 2Bn(Me2AlCl) AlMe), −0.29 (s, 3H,
2Bn(MeAlCl2) AlMe), −0.38 (s, 3H, 2Bn(MeAlCl2) AlMe). 13C
NMR (100 MHz, benzene-d6): δ 233.2 (17(MeAlCl2) CO), 135.9,
135.4, 130.2, 129.2, 129.1, 128.2, 127.1, 127.0 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) + 17(MeAlCl2) Ph), 83.7 (2Bn(MeAlCl2) CO), 81.1
(2Bn(Me2AlCl) Cquat), 51.0 (17(MeAlCl2) CH2), 50.4 (2Bn(Me2AlCl)
CH2), 50.1 (2Bn(MeAlCl2) CH2), 29.6 (17(MeAlCl2) Me), 27.9
(2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me), −6.4 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) AlMe). 27Al NMR (104 MHz, benzene-d6): δ 175.5
(W1/2 = 4000 Hz), 129.4 (W1/2 = 2700 Hz).
Spectroscopic Characterization of BnC(O)Cl 16 + TMA
Reaction Mixtures. TMA (2 mL, 4 mmol, 2.0 M in toluene) was
added dropwise to phenylacetyl chloride 16 (0.26 mL, 2 mmol) under
a N2 atmosphere at −78 °C and allowed to reach room temperature.
After stirring for 2 h at the desired temperature an aliquot of the
solution was analyzed by NMR spectroscopy.
1
Room-Temperature Reaction. H NMR spectroscopy (400 MHz,
benzene-d6) δ 7.14−6.77 (m, 5H, 2Bn(Me2AlCl) Ph), 2.85 (s, 2H,
2Bn(Me2AlCl) CH2), 1.08 (s, 6H, 2Bn(Me2AlCl) Me), −0.28 (s, 12H,
2Bn(Me2AlCl) AlMe). 13C NMR (100 MHz, benzene-d6): δ 135.9,
130.2, 128.2, 126.9 (2Bn(Me2AlCl) Ph), 81.1 (2Bn(Me2AlCl) Cquat),
50.4 (2Bn(Me2AlCl) CH2), 27.9 (2Bn(Me2AlCl) Me), −6.1
(2Bn(Me2AlCl) AlMe). 27Al NMR (104 MHz, benzene-d6): δ 169.4
(W1/2 = 5200 Hz).
1
70 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.15−6.61 (m, 2Bn(Me2AlCl) + 2Bn(MeAlCl2) + 12b Ph), 4.80 (s,
0.03H, 12b CCH2), 4.75 (s, 0.03H, 12b CCH2), 2.92 (s, 2H,
2Bn(MeAlCl2) CH2), 2.85 (s, 0.7H, 2Bn(Me2AlCl) CH2), 1.55 (s,
0.1H, 12b Me), 1.13 (s, 6H, 2Bn(MeAlCl2) Me), 1.08 (s, 2.1H,
2Bn(Me2AlCl) Me), −0.23 (s, 3H, 2Bn(MeAlCl2) AlMe), −0.28 (s,
5H, 2Bn(Me2AlCl) AlMe) −0.29 (s, 3H, 2Bn(MeAlCl2) AlMe), −0.38
(s, 3H, 2Bn(MeAlCl2) AlMe). 13C NMR (100 MHz, benzene-d6): δ
135.9, 135.4, 135.0, 130.2, 128.2, 127.1, 127.0, 111.8 (2Bn(Me2AlCl)
+ 2Bn(MeAlCl2) + 12b Ph), 111.8 (12b = CH2), 83.7 (2Bn(MeAlCl2)
CO), 81.1 (2Bn(Me2AlCl) Cquat), 50.4 (2Bn(Me2AlCl) CH2), 50.1
(2Bn(MeAlCl2) CH2), 44.6 (12b CH2), 27.9 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) Me), −6.4 (2Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe).
27Al NMR (104 MHz, benzene-d6): δ 174.1 (W1/2 = 4100 Hz), 131.0
(W1/2 = 3000 Hz).
1
Reaction Heated to Reflux. H NMR spectroscopy (400 MHz,
benzene-d6) δ 7.15−6.77 (m, 5H, 2Bn(Me2AlCl) Ph), 2.99 (s, 0.2H,
(2Bn)2 CH2), 2.85 (s, 2H, 2Bn(Me2AlCl) CH2), 1.22 (s, 0.6H, (2Bn)2
Me), 1.08 (s, 6H, 2Bn(Me2AlCl) Me), −0.28 (s, 12.6H, 2Bn(Me2AlCl)
+ (2Bn)2 AlMe). 13C NMR (100 MHz, benzene-d6): δ 135.9, 130.2,
128.2, 126.9 (2Bn(Me2AlCl) Ph), 81.1 (2Bn(Me2AlCl) Cquat), 77.6
((2Bn)2 Cquat), 51.2 (((2Bn)2 CH2), 50.4 (2Bn(Me2AlCl) CH2), 28.5
(((2Bn)2 Me), 27.9 (2Bn(Me2AlCl) Me), −6.1 (2Bn(Me2AlCl) AlMe).
27Al NMR (104 MHz, benzene-d6): δ 173.6 (W1/2 = 5300 Hz).
Spectroscopic Characterization of BnC(O)Cl 16 + TMA +
Me2AlCl Reaction Mixtures. Method 1. AlCl3 (89 mg, 0.67 mmol),
toluene (0.33 mL), and TMA (1.67 mL, 3.33 mmol, 2.0 M in
toluene) were reacted to form Me2.5AlCl0.5 (4 mmol, 2.0 M in
toluene). Phenylacetyl chloride (0.26 mL, 2 mmol) was added
1
80 °C Reaction. H NMR spectroscopy (400 MHz, benzene-d6) δ
7.15−6.61 (m, 2Bn(MeAlCl2) + 12a + 12b Ph), 6.27 (s, 0.1H, 12a),
4.80 (s, 0.5H, 12b CCH2), 4.75 (s, 0.5H, 12b CCH2), 3.15 (s,
1.2H, 12b CH2), 2.92 (s, 2H, 2Bn(MeAlCl2) CH2), 1.71 (s, 0.4H, 12a
K
DOI: 10.1021/acs.organomet.8b00763
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Me), 1.69 (s, 0.4H, 12a Me), 1.55 (s, 1.5H, 12b Me), 1.13 (s, 6H,
2Bn(MeAlCl2) Me), −0.22 (s, 3H, 2Bn(MeAlCl2) AlMe), −0.27 (s,
3H, 2Bn(MeAlCl2) AlMe), −0.35 (s, 3H, 2Bn(MeAlCl2) AlMe). 13C
NMR (100 MHz, benzene-d6): δ 135.9, 135.4, 135.0, 130.2, 128.2,
127.1, 127.0 (2Bn(MeAlCl2) + 12a + 12b Ph), 111.8 (12b = CH2),
83.7 (2Bn(MeAlCl2) CO), 50.1 (2Bn(MeAlCl2) CH2), 44.6 (12b
CH2), 27.9 (2Bn(MeAlCl2) Me), −6.4 (2Bn(Me2AlCl) +
2Bn(MeAlCl2) AlMe). 27Al NMR (104 MHz, benzene-d6): δ 180.0
(W1/2 = 3700 Hz), 133.3 (W1/2 = 2700 Hz).
16.3610(11) Å, V = 1739.1(2) Å3, Z = 4, ρcalcd = 1.141 g cm−3, μ =
2.820 mm−1, T = 180(2) K. 9242 data (1590 unique, Rint = 0.0955, θ
2
< 66.789°) were collected. wR2 = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo )2]}1/2
=
0.2071, conventional R = 0.0725 on F values of 1025 reflections with
F2 > 2σ(F2), GoF = 1.042, 91 parameters. Max. peak/hole 0.497
eÅ−3.
Method 2. TMA (2 mL, 4 mmol, 2.0 M in toluene) was added
dropwise to phenylacetyl chloride 16 (0.26 mL, 2 mmol) under a N2
atmosphere at −78 °C and allowed to reach room temperature. After
stirring for 2 h, the solution was concentrated in vacuo and stored at
−27 °C to produce crystalline blocks. Yield 140 mg (23% wrt 16).
1
Reaction Heated to Reflux. H NMR spectroscopy (400 MHz,
benzene-d6) δ 7.15−6.61 (m, 12a + 12b + F/C Ph), 6.27 (s, 0.2H,
12a), 4.80 (s, 0.2H, 12b CCH2), 4.75 (s, 0.2H, 12b CCH2),
3.46 (d, 1H, F/C CH), 3.28 (d, 1.8H, F/C CH), 3.15 (s, 0.4H, 12b
CH2), 2.96−2.70 (m, 11H, F/C CH2), 1.71 (s, 0.8H, 12a Me), 1.69
(s, 0.8H, 12a Me), 1.55 (s, 1H, 12b Me), 1.33 (s, 5.5H, F/C Me),
1.22 (s, 12H, F/C Me), 0.95−0.60 (m, 38H, F/C Me), −0.10 to
−0.48 (m, 85H, unassigned AlMe). 13C NMR (100 MHz, benzene-
d6): δ 145.8, 143.0, 139.2, 138.9, 130.8, 130.5, 130.2, 128.2, 127.1,
127.0, 124.0, 122.7 (12a + 12b + F/C Ph), 60.5, 54.3 (F/C CH),
51.8, 51.0, 48.1, 47.8, 47.2, 46.7, 44.8 (F/C CH2), 31.6, 30.3, 29.1,
28.2, 27.3 (F/C Me), −7.0 (unassigned AlMe). 27Al NMR (104 MHz,
benzene-d6): δ 170.4 (W1/2 = 4100 Hz), 131.7 (W1/2 = 1500 Hz),
92.6 (W1/2 = 300 Hz), 79.9 (W1/2 = 300 Hz).
1
Mp 64−66 °C. H NMR spectroscopy (400 MHz, benzene-d6): δ
7.08−6.75 (m, 5H, Ph), 2.85 (s, 2H, CH2), 1.07 (s, 6H, Me), −0.27
(s, 12H, AlMe). 13C NMR (100 MHz, benzene-d6): δ 135.9 (i-Ph),
130.2 (o-Ph), 128.2 (m-Ph), 126.9 (p-Ph), 81.1 (CO), 50.5 (CH2),
27.9 (Me), −6.1 (br, AlMe). 27Al NMR (104 MHz, benzene-d6): δ
171.2 (W1/2 = 4900 Hz); elemental analysis calculated (%) for
C14H25Al2ClO: C 56.28, H 8.43, Cl 11.87. Found: C 56.21, H 8.41, Cl
11.82. X-ray crystal data: verified to be 2Bn(Me2AlCl) by crystallo-
graphic cell check.
Synthesis and Characterization of 4Pent (Me2AlCl)4. AlCl3 (44
mg, 0.33 mmol), toluene (2 mL), and TMA (0.33 mL, 0.66 mmol, 2.0
M in toluene) were reacted to form Me2AlCl (1 mmol). 4Pent (0.27
mL, 0.5 mmol) was added dropwise under a N2 atmosphere at −78
°C and allowed to reach room temperature. Once the solution
reached room temperature, it was stored at −27 °C for 1 day to
produce colorless needle crystals. Yield 75 mg (33% wrt AlCl3). Mp
Method 2. First, 0.1 mL of the 16 + TMA + Me2AlCl toluene
solution from Method 1 was placed in a sealed J. Young NMR tube
1
with 0.6 mL of toluene-d8 and heated to 100 °C for 2 h. H NMR
spectroscopy (400 MHz, toluene-d8) δ 7.15−6.95 (m, 12a + 12b + F/
C Ph), 6.23 (s, 1H, 12a), 4.77 (s, 3.3H, 12b CCH2), 4.72 (s, 3.3H,
12b CCH2), 3.40 (d, 0.3H, F/C CH), 3.23 (d, 0.8H, F/C CH),
3.13 (s, 7H, 12b CH2), 2.72 (s, 2.7H, F/C CH2), 1.72 (s, 3.6H, 12a
Me), 1.68 (s, 3.6H, 12a Me), 1.54 (s, 10.5H, 12b Me), 1.30 (s, 3.7H,
F/C Me), 1.19 (s, 7.7H, F/C Me), 0.89−0.77 (m, 15H, F/C Me),
0.17 (s, 8.3H, MeH), −0.10 to −0.45 (m, 100H, unassigned AlMe).
13C NMR (100 MHz, toluene-d8): δ 145.1, 139.9, 139.2, 131.1, 130.7,
1
120−123 °C. H NMR spectroscopy (400 MHz, chloroform-d): δ
4.54 (s, 8H, CH2O), 2.75 (t, 8H, CH2), 1.74 (quin, 8H, CH2), 1.40−
1.31 (m, 16H, CH2), 0.92 (t, 12H, Me), −0.63 (s, 24H, AlMe). 13C
NMR (100 MHz, chloroform-d): δ 182.6 (CO), 65.8 (CH2O),
42.1 (Cquat), 35.2, 31.1, 24.6, 22.1 (CH2), 13.8 (Me), −7.9 (br,
AlMe). 27Al NMR (104 MHz, chloroform-d): only background signal;
elemental analysis calculated (%) for C37H76Al4Cl4O8: C 49.45, H
8.52, Cl 15.78. Found: C 48.64, H 8.24, Cl 15.94. X-ray crystal data:
C37H76Al4Cl4O8, M = 898.69, monoclinic, space group C2/c, a =
31.4647(12), b = 8.2194(3) c = 20.7543(8) Å, β = 92.278(2), V =
5363.3(4) Å3, Z = 4, ρcalcd = 1.113 g cm−3, μ = 2.957 mm−1, T =
180(2) K. 53 023 data (4735 unique, Rint = 0.0420, θ < 66.699°) were
130.2, 128.2, 127.1, 127.0, 124.9, 123.0 (12a + 12b + F/C Ph), 112.2
(12b = CH2), 52.1, 51.4, 48.4, 47.6, 47.1, 45.1, 38.7, 38.5 (F/C CH2),
44.9 (12b CH2), 32.0, 31.8, 30.4, 29.4, 28.6, 27.8, 17.1 (F/C Me),
−4.3 (MeH), −6.6 (unassigned AlMe). 27Al NMR (104 MHz,
toluene-d8): δ 183.8 (W1/2 = 4100 Hz), 136.6 (W1/2 = 1400 Hz), 93.0
(W1/2 = 300 Hz), 80.0 (W1/2 = 300 Hz).
2
2
collected. wR2 = {Σ[w(Fo − Fc2)2]/Σ[w(Fo )2]}1/2 = 0.1731,
conventional R = 0.0580 on F values of 4271 reflections with F2 >
2σ(F2), GoF = 1.049, 262 parameters. Max. peak/hole 0.748 eÅ−3.
S y n t h e s i s a n d C h a r a c t e r i z a t i o n o f
BnMe2COAlMe2(Me2AlCl), 2Bn(Me2AlCl). Method 1. AlCl3 (267
mg, 2 mmol), toluene (1 mL), and TMA (2 mL, 4 mmol, 2.0 M in
toluene) were reacted to form Me2AlCl (6 mmol, 2.0 M in toluene).
Methyl phenylacetate 1Bn (0.28 mL, 2 mmol) was added dropwise at
−78 °C and the mixture allowed to warm to room temperature to give
a colorless solution. The solution was heated to 60 °C for 24 h and
then placed under vacuum to remove the solvent and stored at −27
°C to produce a white solid. The solid was melted by heating to 40 °C
and then left at room temperature to produce crystalline blocks. Yield
40 mg (7% wrt 1Bn). Mp decomposed to a yellow solid at 120 °C. 1H
NMR spectroscopy (400 MHz, benzene-d6): δ 7.10−6.74 (m,
1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) Ph), 6.28 (s,
0.01H, 12a CHC), 4.80 (m, 0.02H, 12b CCH2), 4.75 (m,
0.02H, 12b CCH2), 3.57 (s, br, 2.8H, 1Bn(Me2AlCl) CH2), 2.92 (s,
0.83H, 2Bn(MeAlCl2) CH2), 2.85 (s, 2H, 2Bn(Me2AlCl) CH2), 2.74−
2.60 (m, br, 3.5H, 1Bn(Me2AlCl) OMe), 1.38−1.17 (m, 2.2H,
unassigned), 1.12 (s, 2.6H, 2Bn(MeAlCl2) Me), 1.07 (s, 6H,
2Bn(Me2AlCl) Me), −0.22 (s, 1.4H, 2Bn(MeAlCl2) AlMe), −0.27 (s,
12H, 2Bn(Me2AlCl) AlMe), −0.28 (s, 1.4H, 2Bn(MeAlCl2) AlMe),
−0.38 (s, 1.4H, 2Bn(MeAlCl2) AlMe). 13C NMR (100 MHz, benzene-
d6): δ 135.9, 130.2, 129.5, 128.8, 128.2, 127.0(1Bn(Me2AlCl) +
2Bn(Me2AlCl) + 2Bn(MeAlCl2) Ph), 81.1 (2Bn(Me2AlCl) CO), 50.4
(2Bn(Me2AlCl) CH2), 50.1 (2Bn(MeAlCl2) CH2), 41.1
(1Bn(Me2AlCl) CH2), 27.9 (2Bn(Me2AlCl) + 2Bn(MeAlCl2) Me),
−6.1 (1Bn(Me2AlCl) + 2Bn(Me2AlCl) + 2Bn(MeAlCl2) AlMe). 27Al
NMR (104 MHz, benzene-d6): δ 163.6 (W1/2 = 3900 Hz), 126.0
(W1/2 = 1700 Hz); satisfactory elemental analysis could not be
obtained. X-ray crystal data: C14H25Al2ClO, M = 298.75, ortho-
rhombic, space group Pnma, a = 7.4160(5), b = 14.3329(10) c =
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00763.
Synthetic and analytical (NMR spectroscopic) details
(PDF)
Accession Codes
CCDC 1867820−1867825 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*Fax: (+) 44 1223 336362. E-mail: aehw2@cam.ac.uk.
■
ORCID
Andrew E. H. Wheatley: 0000-0002-2624-6063
Notes
The authors declare no competing financial interest.
L
DOI: 10.1021/acs.organomet.8b00763
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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ACKNOWLEDGMENTS
■
We thank Cambridge Refrigerant Technology for financial
support (J.S.) and Richard Lawton for informative discussions.
A.J.P. thanks the UK EPSRC (EP/N509620/1) for a Doctoral
Prize, and we also acknowledge grant EP/K039520/1. Detailed
supporting data for this paper are available at the University of
Cambridge data repository (see https://doi.org/10.17863/
CAM.33772).
(17) Clark, J. S.; Wong, Y.-S. Construction of the 11-
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between trimethylaluminum and poly(methyl methacrylate) during
sequential vapor infiltration: experimental and ab initio analysis. J.
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DOI: 10.1021/acs.organomet.8b00763
Organometallics XXXX, XXX, XXX−XXX