Alkynylaluminum Synthesis Catalyzed by a Zwitterionic Neodymium(III) Heterobimetallic Compound

Article abstract of DOI:10.1021/acs.organomet.8b00374

The reaction of H{PhB(Ox^Me2)₂C₅H₅} (Ox^Me2 = 4,4-dimethyl-2-oxazoline) with Nd(AlMe₄)₃ (1) provides Me₂Al{(Ox^Me2)₂PhBCp}Nd(AlMe₄)₂

Full text of DOI:10.1021/acs.organomet.8b00374

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Alkynylaluminum Synthesis Catalyzed by a Zwitterionic
Neodymium(III) Heterobimetallic Compound
Uddhav Kanbur, Arkady Ellern, and Aaron D. Sadow*
Department of Chemistry, Iowa State University, 1605 Gilman Hall, 2415 Osborn Drive, Ames, Iowa 50011, United States
S
* Supporting Information
ABSTRACT: The reaction of H{PhB(OxMe2)2C5H5} (OxMe2 = 4,4-dimethyl-2-
oxazoline) with Nd(AlMe4)3 (1) provides Me2Al{(OxMe2)2PhBCp}Nd(AlMe4)2
(2) as a heterobimetallic complex containing inequivalent organoaluminum sites.
The piano-stool coordination geometry around Nd includes a rare O-bonded
oxazoline, while both oxazolines coordinate to AlMe2 as part of a 6-membered,
nonplanar BC2N2Al ring. The zwitterionic κ2-Ph(C5H5)B(OxMe2)2AlMe2 (3),
formed by the protolytic reaction of H{PhB(OxMe2)2C5H5} and (AlMe3)2, also
provides 2 upon reaction with Nd(AlMe4)3. Compounds 1−3 are precatalysts for
the selective metalation of terminal alkynes by trialkylaluminums to yield (alkynyl)dialkylalanes of the type R′CC−AlR2,
which are valuable as alkynyl transfer reagents. This catalytic reaction provides metalation products exclusively, as compared to
the mixture of products from uncatalyzed processes. In addition, heteroleptic heterobimetallic 2 is a superior catalyst to 1 and 3.
isobutylene and diisobutyl(1-hepten-1-yl)aluminum.14 Tertiary
INTRODUCTION
■
Organoaluminum alkynyl transfer agents1 are useful in
amine Lewis bases catalyze selective metalations of terminal
conjugate additions to α,β-unsaturated ketones,2,3 alkynylation
alkynes by trimethylaluminum, whereas alkynyl diisobutylalu-
of carbonyls,4,5 and ring opening of epoxides,6 lactones,7 and
minum is formed by H2 elimination from DIBAL-H and
alkynes.15−17 In contrast, Lewis base-catalyzed alumination of
alkynes using higher trialkylaluminums, such as AlEt3 or
AliBu3, is not reported. A catalytic, organometallic mediated
process could bypass the salt metathesis route and more
broadly access alkyl/alkynyl mixed alanes. Instead, transition
metals typically mediate insertion reactions, leading to
carboaluminations or polymerizations. For example, zircono-
cene dichloride catalyzes carboalumination of alkynes
selectively (Scheme 1d),18−22 and cationic group 4 compounds
mediate carboalumination of olefins.23−26 Internal alkyne and
alkene methylalumination is catalyzed by cationic piano-stool
scandium compounds,27 while (C5Me5)2Y{H2AlMeN-
(SiMe3)2} or [YMe3]n catalyze the hydroalumination of 1-
octene.28 These processes likely involve insertion of the
unsaturated hydrocarbon for C−C or C−H bond formation.
In contrast, a number of experiments suggest that insertion-
based mechanisms are disfavored in another addition process,
namely hydroamination reactions, catalyzed by group 4 and
yttrium compounds coordinated by the zwitterionic
cyclopentadienylbis(2-oxazolinyl)borate family of ligands.29−31
We were curious to test these ligands in other reactions where
selectivity might result from slow insertion processes and thus
extend this effect to alumination versus carboalumination for
the synthesis of alkynylaluminum compounds. Toward this
goal, we have prepared a Nd/Al heterobimetallic compound
aziridines.8 These reagents are typically synthesized by the salt
elimination of corresponding lithium acetylides and dialkyla-
luminum chlorides and used in situ (Scheme 1a).9,10 Routes
a
Scheme 1. Syntheses of Alkynylaluminum Reagents
a
(a) Salt metathesis, (b) unselective thermal addition, and (c) tertiary
amine- or neodymium aluminate-catalyzed alkane elimination. In
contrast, (d) zirconium catalyzed carboalumination.
avoiding salt formation and separation are potentially advanta-
geous; however, the uncatalyzed reactions of terminal alkynes
and trialkylaluminums provide mixtures of alkynyl- and
vinylaluminums from protonolytic alkane elimination and
carboalumination, respectively (Scheme 1b).11−14 The ratio
of products varies with the substituents on both aluminum and
terminal alkyne starting materials. In addition, hydroalumina-
tion occurs in the combination of AliBu3 and 1-heptyne to give
Special Issue: Organometallic Complexes of Electropositive Ele-
ments for Selective Synthesis
Received: June 1, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00374
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
that catalyzes the selective metalation of terminal alkynes by
trialkylaluminums, thereby establishing a dichotomy in metal
mediated alumination reactions.
RESULTS AND DISCUSSION
■
Nd(AlMe4)3 (1) and H{PhB(OxMe2)2C5H5} react in toluene
under ambient conditions with a vigorous evolution of
methane and an instantaneous color change from blue to
green affording Me2Al{(OxMe2)2PhBCp}Nd(AlMe4)2 (2) as a
light green, highly air- and moisture-sensitive powder in a high
yield (eq 1; 91%).
The reaction also proceeds to completion within 10 min in
1
benzene-d6. A H NMR spectrum of the reaction mixture
revealed new signals for 2 and methane at 0.13 ppm, while the
broad singlet of 1 at 10.5 ppm was not detected.
The H NMR spectrum of isolated 2 was characteristic and
1
Figure 1. Molecular structure of Me2Al{(OxMe2)2PhBCp}Nd-
(AlMe4)2 (2). H atoms are omitted for clarity. Atomic displacement
parameters are rendered at 50% probability.
contained distinct resonances at −1.85 and −2.09 ppm (6 H
each) and 3.32 and 4.28 ppm (2 H each), assigned to the
diastereotopic methyl and methylene protons, respectively, of
the oxazoline groups. The C5H4 moiety appeared downfield as
a broad singlet at 12.86 ppm. A broad downfield singlet at 6.41
ppm (24 H) was assigned to the two Nd-bound AlMe4 groups,
whereas upfield resonances at −2.39 and −3.91 ppm (3 H
each) were assigned to inequivalent methyls of the AlMe2 unit.
The unusually upfield resonance at −40 ppm in the 11B NMR
spectrum was further indicative of the coordination of the
borate ligand to the paramagnetic neodymium center. The
CN stretching frequency at 1596 cm−1 in the IR spectrum of
2 suggests that both oxazoline-nitrogen atoms are coordinated.
For comparison, crystalline {PhB(OxMe2)2Cp}Zr(NMe2)2
contained two bands at 1505 and 1603 cm−1 assigned to
coordinated and noncoordinated oxazolines.31
distances are 2.645(2) and 2.731(2) Å33 in structurally related
CpSiNd(AlMe4)2 and are 2.704(2) Å, 2.672(2), 2.606(2), and
2.608(2) Å in FluSiNd(AlMe4)2.34 The Al1−N1 and Al1−N2
distances in the 6-membered BC2N2Al chelate ring are
1.933(2) and 1.955(2) Å. The corresponding distances are
shorter in {κ2-PhMeB(OxMe2)2}AlMe2 (1.918(5) and 1.931(5)
Å),40 which adopts a planar conformation of its six-membered
ring. In contrast, the Al1, B1, N1, N2, C5, and C10 centers in 2
assume a boat structure.
The reaction of the proligand H{PhB(OxMe2)2C5H5} and
(AlMe3)2 yields a deep yellow powder of κ2-Ph(C5H5)B-
(OxMe2)2AlMe2 (3) as a mixture of two major and one minor
isomers of the cyclopentadiene:
Single crystal X-ray diffraction analysis of 2 elucidates the
unexpected yet spectroscopically consistent structure shown in
Figure 1. Compound 2 crystallizes with Nd1 coordinated in a
distorted octahedral geometry with Cp, O1 from an oxazoline,
and four bridging methyl groups from AlMe4 moieties as the
six ligands (Cpcent−Nd1−C24, 169.5°; O1−Nd1−C29,
162.81(6)°; C25−Nd1−C28, 154.13(8)°). N1 and N2
coordinate to Al1 of the AlMe2 group, which balances one of
two negative charges of the dianionic ligand. The compound
resembles known half-sandwich lanthanide bis-
(tetramethylaluminate) compounds of the type CpSiLn-
(AlMe4)2 (CpSi = η5-1,3-C5H3(SiMe3)2)32,33 and FluSiLn-
(AlMe4)2 (FluSi = η5-C13H8SiMe3).34 One of the two
oxazolines is coordinated to neodymium via the Nd1−O1
bond, making this the first example of a pendent oxazoline-
oxygen coordinated trivalent lanthanoid complex. In fact, a
search of the Cambridge Structural database reveals only three
examples of an oxazoline coordinating to a metal center via its
oxygen.35−37 The Nd1−O1 distance of 2.588(2) Å is
comparable to known Nd−OC4H8 distances, for example
Vigorous effervescence occurs immediately upon mixing, and
reactions in benzene-d6 are complete at room temperature
within 10 min as determined by H NMR spectroscopy.
The methyls of the AlMe2 group are inequivalent and appear
upfield in the 1H NMR spectrum of 3 as three sets of
overlapping peaks in the region of −0.3 to −0.4 ppm. The
significant upfield shift in the resonances of the oxazoline
methylene (3.37−3.26 ppm) and methyl protons (1.03−0.95
ppm) in 3 compared to the free ligand (methylene: 4.09−4.00
ppm; methyl: 1.35−1.28 ppm) is evidence for a bidentate
1
38
2.508(3) Å in [(COT)Nd(OEt)THF]2 or 2.534(4) Å in
[C5Me4CH2SiMe2NPh]Nd(BH4)THF2.39 The Nd−C distan-
ces of the Nd(μ-Me)2Al groups are 2.639(3), 2.707(3),
2.711(3), and 2.759(3) Å. For comparison, the corresponding
B
DOI: 10.1021/acs.organomet.8b00374
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
coordination of the bis-oxazoline ligand to aluminum.
Furthermore, crosspeaks in a 15N−1H HMBC experiment
showed correlations between the oxazoline nitrogen to the
aluminum methyl groups, as well to methyl and methylene
protons of the oxazoline. Compound 3 is comparable to κ2-
PhMeB(OxMe2)2AlMe2 and κ2-ToMAlMe2 (ToM = tris(4,4-
dimethyl-2-oxazolinyl)phenylborate),40 which are obtained
from the methyl abstraction reaction of (AlMe3)2 by
1.78 (t, 2 H), and 0.65 ppm (t, 3 H) assigned to aluminum
methyl, propargylic methylene, and terminal methyl groups,
respectively. For comparison, the 1H NMR spectrum of
(AlMe3)2 in benzene-d6 contained a singlet at −0.36 ppm,
while the propargylic methylene and terminal methyl groups in
the starting material 1-hexyne appeared at 1.94 and 0.75 ppm.
In addition, 1H NMR signals for methane, ethane, or isobutane
were observed in spectra of reactions involving (AlMe3)2,
(AlEt3)2, and AliBu3, respectively. The organoaluminum
products were quenched with acetophenone, and subsequent
workup provided alkynyl alcohols used to measure isolated
yields.
Neodymium compound 2, which is supported by the
PhB(OxMe2)2Cp ligand and also contains an oxazolinylborate-
coordinated dimethyl aluminum, gives 46% conversion after 8
h at 60 °C, whereas aluminum-only oxazolinylborate 3 affords
only ∼20% conversion under equivalent conditions. Com-
pound 2 is also more active than homoleptic 1 (see Table 1).
The catalytic performance, and product yields, are equivalent
in syntheses ranging from micromolar to millimolar scale.
Compound 2 catalyzes the alkane elimination from
combinations of AlR3 and terminal alkynes containing alkyl,
alicyclic, and olefinic substituents. For example, the enyne 1-
ethynylcyclohexene reacts to give the alkynylaluminum
product, and 1,2- or 1,4-addition products were not detected
in the crude reaction mixture or isolated, quenched product.
That is, the double bond in the enyne is inert under these
conditions, while the terminal alkyne is metalated. The trend in
apparent reaction rates is (Me3Al)2 < (Et3Al)2 < iBu3Al. Much
of trialkylaluminum chemistry is governed by the monomer−
dimer equilibrium,41−44 and these equilibria may provide a
rationalization for the observed trend in the catalytic
chemistry.
PhB(OxMe2
) and the protonolysis between (AlMe3)2 and
2
H{ToM}, respectively. Like the aforementioned compounds, 3
is also thermally stable (in toluene-d8) at 120 °C for 4 days
without showing any signs of decomposition. 2 was also
synthesized by the reaction of 1 and 3 in benzene or toluene,
demonstrating the general synthetic utility of 3 toward the
formation of heterobimetallic compounds:
Compounds 1−3 are precatalysts for selective protolytic
metalation of terminal alkynes with trialkylaluminums to yield
alkynyldialkylaluminum compounds quantitatively (Table 1).
1
The reactions were monitored using H NMR spectroscopy
through the disappearance of signals associated with starting
materials and appearance of those for the products. For
example, the hex-1-ynyldimethyl aluminum product was
1
characterized by new H NMR signals at −0.09 (s, 6 H),
Table 1. Alumination of Terminal Alkynes by
Trialkylaluminum
In contrast, there is no apparent trend in the rates of
uncatalyzed additions, perhaps due to complications from
additional pathways. The variation in uncatalyzed reaction rate
only seems to affect the catalyzed combination of 1-hexyne and
triethylaluminum, which gives vinyl products from the
background carboalumination (Scheme 1b) process in this
reaction mixture even in the presence of 2. Reactions of
alkynes with trimethylaluminum in the absence of 1, 2, or 3
provides carboalumination (vinylaluminum) products in larger
proportions than in the absence of a catalyst.
Triisobutylaluminum reacts (in the uncatalyzed process) to
give hydroalumination, via a β-H transfer mechanism and loss
of isobutene as the major pathway,14 as well as carboalumi-
nation and metalation products. In contrast, only alumination
is observed in the presence of 2, without any detectable
quantities of hydroalumination products. The similarities
between reactivity of 2 with (AlMe3)2, (AlEt3)2, and AliBu3
suggest that a related mechanism operates in all three cases,
likely involving a common intermediate structure. One such
possibility is a bridging acetylide/aluminate moiety related to
those formed from homoleptic rare earth tetramethylalumi-
nates and alkynes,45 although we note that these are only
known for methylaluminates. Olefins and internal alkynes are
unreactive toward trialkylaluminum species under the catalytic
reaction conditions and carboalumination products were not
observed. Thus, selectivity for metalation versus carboalumi-
nation in the 2-catalyzed reactions of terminal alkynes can be
rationalized by a high barrier toward insertion.
a
The remaining products (22%) are vinylaluminum species from
carboalumination.
C
DOI: 10.1021/acs.organomet.8b00374
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
C31H55BN2O2Al3Nd: C, 51.45; H, 7.61; N, 3.87. Found: C, 51.48; H,
7.76; N, 3.86. Mp: 105−110 °C, dec.
CONCLUSION
■
κ2-Ph(C5H5)B(OxMe2)2AlMe2 (3). Neat (AlMe3)2 (41.3 μL, 0.22
mmol) was added slowly to a vigorously stirring benzene solution of
H{PhB(OxMe2)2C5H5} (0.150 g, 0.43 mmol) with a syringe. Bubbling,
from evolving methane, was observed immediately. The solution was
stirred for 12 h once the methane evolution had ceased, and the
solvent was removed under reduced pressure. Washing with pentane
(2 × 5 mL) and subsequent drying provided a yellow powder of 3
Compound 2 shows remarkable catalytic activity and
selectivity for the metalation of terminal alkynes by
trialkylaluminums, making it the first organometallic-catalyzed
route to alkynyl aluminum compounds. The catalytic
conversion is faster under the reaction conditions than the
background carboalumination chemistry, and the exclusive
formation of alkynylaluminum species indicate that alkyne
insertion is disfavored. Notably, compound 2 is a faster catalyst
than 1 or 3. There is no evidence for an interaction between
the neodymium center and bis(oxazolinyl)aluminum moieties
that might increase the reaction rate; however, we are currently
studying the kinetics of these metalation processes to test for
this possibility. In addition, we are working to isolate and
characterize diamagnetic congeners of 2. Although yttrium and
lanthanum-based analogues are not yet established through
diffraction studies, in situ studies suggest promising perform-
ance in catalytic alkynyl aluminum synthesis.
1
quantitatively as a mixture of three isomers. H NMR (benzene-d6,
600 MHz): δ 7.80−7.17 (m, 5 H, C6H5), 6.91−6.49 (m, 3 H, C5H5-
sp2), 3.34 (m, 1 H, C5H5-sp3), 3.29−3.20 (m, 4 H, CNCMe2CH2O),
3.10 (m, 1 H, C5H5-sp3), 0.95−0.84 (m, 12 H, CNCMe2CH2O),
−0.31 to −0.41 (m, 6 H, AlMe2). 13C{1H} NMR (benzene-d6, 225
MHz): δ 199.18 (br, CNCMe2CH2O), 141.22 (C5H5-sp2), 140.43
(C5H5-sp2), 135.37 (o-C6H5), 135.21 (C5H5-sp2), 134.47 (C5H5-sp2),
134.34 (C5H5-sp2), 134.06 (C5H5-sp2), 133.50 (C5H5-sp2), 131.40
(m-C6H5), 126.50, 126.26, 126.20 (p-C6H5), 125.97, 80.16, 80.14,
79.82, 79.80 (CNCMe2CH2O), 79.63, 65.82 (CNCMe2CH2O), 65.67
(CNCMe2CH2O), 63.25, 47.21 (C5H5-sp3), 43.37 (C5H5-sp3), 27.99,
27.54, 27.45, 27.42 (CNCMe2CH2O), 27.01, −5.25 (AlMe2), −5.78
(AlMe2). 11B NMR (benzene-d6, 192 MHz): δ −15.38, −15.70,
−16.19. 15N{1H} NMR (benzene-d6, 106.5 MHz): δ −186.27
(CNCMe2CH2O). IR (KBr, cm−1): 3064 w, 2969 m, 2931 m, 2892
w, 1678 w, 1594 w, 1554 s (CN), 1463 m, 1371 m, 1293 s, 1260 w,
1198 s, 1163 w, 973 s, 711 s, 674 s. Anal. Calcd for C26H35BN2O2Al2:
C, 66.12; H, 7.42; N, 5.93. Found: C, 66.17; H, 7.67; N, 5.84. Mp:
146−152 °C, dec.
Interestingly, the synthesis of neodymium compound 2 from
alumino bis(oxazolinyl)borate 3 via a protonolysis reaction
suggests a potentially valuable strategy to access other
heterobimetallic compounds. Such compounds could also
show synergistic activity in multisite catalysis and efforts to
deduce and probing such mechanisms are currently underway.
General Procedure for Metalation Reactions. Caution!
Trialkylaluminum and alkynyldialkylaluminum reagents are highly
pyrophoric and must be handled under inert atmosphere. Trialkylalumi-
num (0.21 mmol) and terminal alkyne were added to a 3 mol %
solution of the catalyst in benzene-d6. The reaction mixture was
heated at 60 °C. Conversion of starting materials was monitored at
regular intervals by 1H NMR spectroscopy. Following full conversion,
24.5 μL (0.21 mmol) of acetophenone was added to the reaction
mixture. The reaction mixture was heated at 60 °C for 6 h to ensure
complete quenching. The solution was transferred to a vial, 0.5 mL of
saturated NH4Cl solution added, and then the mixture vigorously
stirred for 10 min. Anhydrous MgSO4 was added to the biphasic
mixture to absorb water, and the alkynyl alcohol was extracted with
CH2Cl2 (10 mL). The solution was filtered and evaporated under
reduced pressure giving crude products, which were purified by flash
chromatography over SiO2 gel (10% ethyl acetate/hexanes) to obtain
EXPERIMENTAL SECTION
■
General. All manipulations were carried out under inert
conditions, either using Schlenk techniques or in gloveboxes under
nitrogen atmospheres, unless stated otherwise. Benzene and toluene
were degassed by sparging with nitrogen, passed through activated
alumina columns to remove water, and stored under a nitrogen
atmosphere. Deuterated benzene and toluene were degassed via three
consecutive freeze−pump−thaw cycles, stirred over Na/K alloy,
vacuum transferred, and stored over molecular sieves under nitrogen.
H{PhB(OxMe2)2C5H5}46 and Nd(AlMe4)347 were synthesized accord-
ing to corresponding literature procedures. Trimethylaluminum,
triethylaluminum, and triisobutylaluminum were purchased from
Aldrich and were used as received. Terminal alkynes were obtained
from Aldrich, dried over anhydrous MgSO4, distilled, and stored over
activated molecular sieves in the glovebox. 1H, 13C{1H}, and 11B
NMR spectra were obtained on a Bruker Avance III 600 MHz
spectrometer. 15N chemical shifts obtained via 15N−1H HMBC
experiments, originally referenced to liquid NH3, were rereferenced to
CH3NO2 by subtracting 381.9 ppm.
1
corresponding alkynyl alcohols. H NMR spectra of crude reaction
mixtures as well as isolated alcohols are provided in the Supporting
Information.
Me2Al{(OxMe2)2PhBCp}Nd(AlMe4)2 (2). H{PhB(OxMe2)2C5H5}
(0.100 g, 0.29 mmol) and Nd(AlMe4)3 (1) (0.118 g, 0.29 mmol)
were mixed in toluene (10 mL) at room temperature. Methane
rapidly evolved from the green solution. The reaction mixture was
stirred vigorously for 45 min, and all volatiles were removed in vacuo,
washed with pentane (2 × 5 mL), and dried to obtain 2 as a light
green powder (0.190 mg, 0.26 mmol, 91%). Recrystallization from a
concentrated toluene solution cooled at −30 °C for a week yielded
light green crystals that were suitable for single crystal X-ray analysis.
1H NMR (benzene-d6): δ 12.83 (br s, 4 H, C5H4), 6.41 (br s, 24 H,
AlMe4), 4.28 (m, 2 H, CNCMe2CH2O), 3.32 (m, 2 H,
CNCMe2CH2O), −1.85 (br s, 6 H, CNCMe2CH2O), −2.09 (br s,
6 H, CNCMe2CH2O), −2.39 (br s, 3 H, AlMe2), −2.25 (br s, 1 H, p-
C6H5), −2.84 (br s, 2 H, C6H5), −3.91 (br s, 3 H, AlMe2), −4.00 (br
s, 2 H, C6H5). 13C{1H} NMR (benzene-d6, 225 MHz): δ 288.94
(C5H4), 281.53 (C5H4), 264.48 (AlMe4), 200.89 (CNCMe2CH2O),
126.24 (C6H5), 124.63 (C6H5), 123.65 (C6H5), 70.58
(CNCMe2CH2O), 63.54 (CNCMe2CH2O), 24.29 (CNCMe2CH2O),
22.92 (CNCMe2CH2O), −10.69 (AlMe2). 11B NMR (benzene-d6, 192
MHz): δ −39.98. IR (KBr, cm−1): 3070 w, 3049 w, 2969 m, 2927 s,
2819 w, 1596 s (CN), 1552 m, 1464 m, 1374 m, 1292 m, 1261 m,
1197 s, 1053 m, 970 s, 798 m, 697 s, 579 m. Anal. Calcd for
1-Hexyn-1-yl-dimethylaluminum. Trimethylaluminum (20 μL,
0.21 mmol), 1-hexyne (24 μL, 0.21 mmol), and 2 (0.0046 g, 6.3
μmol) were reacted for 18 h at 60 °C, followed by quenching with
acetophenone (24.5 μL, 0.21 mmol) to afford 2-phenyl-3-octyn-2-ol
(0.0298 g, 0.148 mmol, 70%).
Dimethyl(2-phenylethynyl)aluminum. Trimethylaluminum (20
μL, 0.21 mmol), phenylacetylene (23 μL, 0.21 mmol), and 2
(0.0046 g, 6.3 μmol) were reacted for 18 h at 60 °C followed by
quenching with acetophenone (24.5 μL, 0.21 mmol) to yield 2,4-
diphenyl-3-butyn-2-ol (0.0342 g, 0.154 mmol, 73%).
Dimethyl(2-cyclohexylmethylethynyl)aluminum. Trimethylalu-
minum (20 μL, 0.21 mmol), 3-cyclohexyl-1-propyne (30.2 μL, 0.21
mmol), and 2 (0.0046 g, 6.3 μmol) were reacted for 18 h at 60 °C
followed by quenching with acetophenone (24.5 μL, 0.21 mmol) to
yield 5-cyclohexyl-2-phenyl-3-pentyn-2-ol (0.0326 g, 0.135 mmol,
64%).
2-(1-Cyclohexen-1-yl)ethynyl)dimethylaluminum. Trimethylalu-
minum (20 μL, 0.21 mmol), 1-ethynyl-1-cyclohexene (24.5 μL,
0.21 mmol), and 2 (0.0046 g, 6.3 μmol) were reacted for 18 h at 60
°C followed by quenching with acetophenone (24.5 μL, 0.21 mmol)
to yield 4-cyclohexenyl-2-phenyl-3-butyn-2-ol (0.0431 g, 0.191 mmol,
91%).
D
DOI: 10.1021/acs.organomet.8b00374
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1-Hexyn-1-yl-diisobutylaluminum. Triisobutylaluminum (53.4
μL, 0.21 mmol), 1-hexyne (24 μL, 0.21 mmol), and 2 (0.0046 g,
6.3 μmol) were reacted for 6 h at 60 °C followed by quenching with
acetophenone (24.5 μL, 0.21 mmol) to yield 2-phenyl-3-octyn-2-ol
(0.0342 g, 0.169 mmol, 81%).
Diethyl(2-phenylethynyl)aluminum. Triethylaluminum (30 μL,
0.21 mmol), phenylacetylene (23 μL, 0.21 mmol), and 2 (0.0046 g,
6.3 μmol) were reacted for 10 h at 60 °C followed by quenching with
acetophenone (24.5 μL, 0.21 mmol) to yield 2,4-diphenyl-3-butyn-2-
ol (0.0333 g, 0.150 mmol, 71%).
(2) Hansen, R. T.; Carr, D. B.; Schwartz, J. Nickel-catalyzed
conjugate addition of organoaluminum acetylides to α,β-enones. J.
Am. Chem. Soc. 1978, 100, 2244−2245.
(3) Schwartz, J.; Carr, D. B.; Hansen, R. T.; Dayrit, F. M. Nickel-
catalyzed conjugate addition of alkynyl groups to α,β-unsaturated
ketones. J. Org. Chem. 1980, 45, 3053−3061.
(4) Ley, S. V.; Meek, G. Diastereoselective additions to aldehyde
groups in the side-chain of π-allyltricarbonyliron lactone complexes.
Chem. Commun. 1996, 317−318.
(5) Ley, S. V.; Cox, L. R.; Meek, G.; Metten, K.-H.; Pique, C.;
Worrall, J. M. 1,5-Asymmetric induction of chirality: highly
diastereoselective addition reactions of organoaluminium reagents
into ketone groups in the side-chain of π-allyltricarbonyliron lactone
complexes. J. Chem. Soc., Perkin Trans. 1 1997, 1, 3299−3314.
(6) Matthews, R. S.; Eickhoff, D. J. The regioselectivity of epoxide-
opening reactions using alkynylaluminum reagents. J. Org. Chem.
1985, 50, 3923−3925.
1-Hexyn-1-yl-diethylaluminum. Triethylaluminum (30 μL, 0.11
mmol), 1-hexyne (24 μL, 0.21 mmol), and 2 (0.0046 g, 6.3 μmol)
were reacted for 10 h at 60 °C. Vinylaluminum compounds were
1
observed by H NMR, and 2-phenyl-3-octyn-2-ol was not isolated.
Representative Scaled-up Synthesis. Compound 2 (0.0450 g,
62.2 μmol) was dissolved in benzene (6 mL) and transferred to a
storage tube equipped with a magnetic stirrer in the glovebox.
Trimethylaluminum (200 μL, 2.1 mmol) and 1-hexyne (240 μL, 2.1
mmol) were added dropwise via syringe. The tube was sealed and
heated at 60 °C, and the reaction was monitored by taking regular
aliquots that were analyzed by 1H NMR spectroscopy. Following
complete conversion of starting materials, acetophenone (240 μL, 2.1
mmol) was added to the reaction mixture, which was heated at 60 °C
for 6 h. Saturated NH4Cl solution (5 mL) was added, and the
resulting biphasic mixture was vigorously stirred for 30 min. The
mixture was dried over anhydrous MgSO4, and the product alcohol
was extracted into CH2Cl2 (15 mL). Removal of volatiles under
reduced pressure afforded the crude product, which was purified over
SiO2 gel (10% ethyl acetate/hexanes) to obtain 2-phenyl-3-octyn-2-ol
(0.2940 g, 1.45 mmol, 69%).
(7) Shinoda, M.; Iseki, K.; Oguri, T.; Hayasi, Y.; Yamada, S.-i.;
Shibasaki, M. A. convenient synthesis of β-alkynylpropionic acids
from β-propiolactones. Synthesis of 4,4,5,5-tetradehydro-9(O)-meth-
ano-Δ6(9α)-PGI1. Tetrahedron Lett. 1986, 27, 87−90.
(8) Bertolini, F.; Woodward, S.; Crotti, S.; Pineschi, M. A practical
regioselective ring-opening of activated aziridines with organoalanes.
Tetrahedron Lett. 2009, 50, 4515−4518.
(9) Talalaeva, T. V.; Timofeyuk, G. V.; Rodionov, A. N.;
Kocheshkov, K. A. Lithium acetylides. Bull. Acad. Sci. USSR, Div.
Chem. Sci. 1965, 14, 1570−1574.
(10) Brandsma, L.; Zwikker, J. W. Science of Synthesis; Thieme
Chemistry, 2006; Vol. 8.
(11) Wilke, G.; Muller, H. Metallorganische Verbindungen, XXXIX
̈
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00374.
■
Reaktionen von Organoaluminium-Verbindungen mit Acetylenen.
Liebigs Ann. Chem. 1960, 629, 222−240.
S
(12) Binger, P. Alkinyl-Verbindungen des Aluminiums. Angew.
Chem. 1963, 75, 918−918.
(13) Mole, T.; Surtees, J. R. Organoaluminium compounds. VII. The
reactions of organoaluminium compounds with phenylacetylene. Aust.
J. Chem. 1964, 17, 1229−1235.
Spectra for compounds 2 and 3, alkynylaluminum
catalysis products, and quenched catalysis products
(PDF)
̈
(14) Reinacker, R.; Schwengers, D. Metallorganische Verbindungen,
LII1) Reaktionen von Aluminiumtrialkylen mit Alkinen-(1). Liebigs
Ann. Chem. 1970, 737, 182−184.
Accession Codes
(15) Feuvrie, C.; Blanchet, J.; Bonin, M.; Micouin, L. Synthesis and
Reactivity of Mixed Alkynylalanes by Direct Triethylamine-Catalyzed
Alumination of Terminal Alkynes. Org. Lett. 2004, 6, 2333−2336.
(16) Zhou, Y.; Lecourt, T.; Micouin, L. Room Temperature Lewis
Base-Catalyzed Alumination of Terminal Alkynes. Adv. Synth. Catal.
2009, 351, 2595−2598.
(17) Piccardi, R.; Coffinet, A.; Benedetti, E.; Turcaud, S.; Micouin,
L. Continuous Flow Synthesis of Dimethylalkynylaluminum Reagents.
Synthesis 2016, 48, 3272−3278.
(18) Negishi, E.; Okukado, N.; King, A. O.; Van Horn, D. E.;
Spiegel, B. I. Selective carbon-carbon bond formation via transition
metal catalysts. 9. Double metal catalysis in the cross-coupling
reaction and its application to the stereo- and regioselective synthesis
of trisubstituted olefins. J. Am. Chem. Soc. 1978, 100, 2254−2256.
(19) Van Horn, D. E.; Negishi, E. Selective carbon-carbon bond
formation via transition metal catalysts. 8. Controlled carbometala-
tion. Reaction of acetylenes with organoalane-zirconocene dichloride
complexes as a route to stereo- and regio-defined trisubstituted
olefins. J. Am. Chem. Soc. 1978, 100, 2252−2254.
(20) Yoshida, T.; Negishi, E. Mechanism of the zirconium-catalyzed
carboalumination of alkynes. Evidence for direct carboalumination. J.
Am. Chem. Soc. 1981, 103, 4985−4987.
(21) Negishi, E.-i.; Kondakov, D. Y.; Choueiry, D.; Kasai, K.;
Takahashi, T. Multiple Mechanistic Pathways for Zirconium-
Catalyzed Carboalumination of Alkynes. Requirements for Cyclic
Carbometalation Processes Involving C−H Activation. J. Am. Chem.
Soc. 1996, 118, 9577−9588.
CCDC 1846388 contains the supplementary crystallographic
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 Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: sadow@iastate.edu.
■
ORCID
Aaron D. Sadow: 0000-0002-9517-1704
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors gratefully thank the National Science Foundation
(CHE-1464774) for financial support
■
REFERENCES
■
(1) Piccardi, R.; Micouin, L.; Jackowski, O. The Chemistry of
Alkynylaluminum Species. In The Chemistry of Organoaluminum
Compounds; Micouin, L., Marek, I., Rappoport, Z., Eds.; Patai’s
Chemistry of Functional Groups Series; Rappoport, Z., Series Ed.;
Wiley, 2016.
E
DOI: 10.1021/acs.organomet.8b00374
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(22) Xu, S.; Negishi, E.-i. Zirconium-Catalyzed Asymmetric
Carboalumination of Unactivated Terminal Alkenes. Acc. Chem. Res.
2016, 49, 2158−2168.
(23) Shaughnessy, K. H.; Waymouth, R. M. Enantio- and
Diastereoselective Catalytic Carboalumination of 1-Alkenes and
α,ω-Dienes with Cationic Zirconocenes: Scope and Mechanism.
Organometallics 1998, 17, 5728−5745.
(24) Millward, D. B.; Cole, A. P.; Waymouth, R. M. Catalytic
Carboalumination of Olefins with Cyclopentadienylamidotitanium
Dichloride Complexes. Organometallics 2000, 19, 1870−1878.
(25) Petros, R. A.; Norton, J. R. Effectiveness in Catalyzing
Carboalumination Can Be Inferred from the Rate of Dissociation of
M/Al Dimers. Organometallics 2004, 23, 5105−5107.
(26) Camara, J. M.; Petros, R. A.; Norton, J. R. Zirconium-Catalyzed
Carboalumination of α-Olefins and Chain Growth of Aluminum
Alkyls: Kinetics and Mechanism. J. Am. Chem. Soc. 2011, 133, 5263−
5273.
(41) Smith, M. B. Monomer-dimer equilibria of liquid aluminum
alkyls. I. Triethylaluminum. J. Phys. Chem. 1967, 71, 364−370.
(42) Smith, M. B. The monomer-dimer equilibria of liquid
aluminum alkyls: II. Triisobutylaluminum. J. Organomet. Chem.
1970, 22, 273−281.
(43) Smith, M. B. The monomer−dimer equilibria of liquid
aliminum alkyls: III. Trimethylaluminum: the monomer−dimer
equilibria of liquid and gaseous trimethylaluminum and triethylalu-
minum. J. Organomet. Chem. 1972, 46, 31−49.
(44) Smith, M. B. The MonomerDimer Equilibria of liquid
Aluminum Alkyls: V. Tri-n-Propylaluminum, Tri-n-Butylaluminum
and Tri-n-Octylaluminum: The effect of chain length on the
equilibria. J. Organomet. Chem. 1974, 70, 13−33.
(45) Nieland, A.; Mix, A.; Neumann, B.; Stammler, H. G.; Mitzel, N.
W. Rare-Earth-Metal Dialkynyl Dimethyl Aluminates. Chem. - Eur. J.
2013, 19, 8268−8275.
(46) Manna, K.; Ellern, A.; Sadow, A. D. A zwitterionic zirconium
complex that catalyzes hydroamination of aminoalkenes at room
temperature. Chem. Commun. 2010, 46, 339−341.
(47) Evans, W. J.; Anwander, R.; Doedens, R. J.; Ziller, J. W. The
Use of Heterometallic Bridging Moieties To Generate Tractable
Lanthanide Complexes of Small Ligands. Angew. Chem., Int. Ed. Engl.
1994, 33, 1641−1644.
(27) Takimoto, M.; Usami, S.; Hou, Z. Scandium-Catalyzed Regio-
and Stereospecific Methylalumination of Silyloxy/Alkoxy-Substituted
Alkynes and Alkenes. J. Am. Chem. Soc. 2009, 131, 18266−18268.
̈
(28) Schadle, C.; Anwander, R. Rare-Earth-Metal-Promoted Hydro-
alumination. Eur. J. Inorg. Chem. 2013, 2013, 3302−3306.
(29) Manna, K.; Kruse, M. L.; Sadow, A. D. Concerted C-N/C-H
Bond Formation in Highly Enantioselective Yttrium(III)-Catalyzed
Hydroamination. ACS Catal. 2011, 1, 1637−1642.
(30) Manna, K.; Xu, S.; Sadow, A. D. A Highly Enantioselective
Zirconium Catalyst for Intramolecular Alkene Hydroamination:
Significant Isotope Effects on Rate and Stereoselectivity. Angew.
Chem., Int. Ed. 2011, 50, 1865−1868.
(31) Manna, K.; Everett, W. C.; Schoendorff, G.; Ellern, A.; Windus,
T. L.; Sadow, A. D. Highly Enantioselective Zirconium-Catalyzed
Cyclization of Aminoalkenes. J. Am. Chem. Soc. 2013, 135, 7235−
7250.
̈
(32) Zimmermann, M.; Tornroos, K. W.; Sitzmann, H.; Anwander,
R. Half-Sandwich Bis(tetramethylaluminate) Complexes of the Rare-
Earth Metals: Synthesis, Structural Chemistry, and Performance in
Isoprene Polymerization. Chem. - Eur. J. 2008, 14, 7266−7277.
̈
(33) Zimmermann, M.; Tornroos, K. W.; Anwander, R. Cationic
Rare-Earth-Metal Half-Sandwich Complexes for the Living trans-1,4-
Isoprene Polymerization13. Angew. Chem., Int. Ed. 2008, 47, 775−
778.
̈
(34) Diether, D.; Tyulyunov, K.; Maichle-Mossmer, C.; Anwander,
R. Fluorenyl Half-Sandwich Bis(tetramethylaluminate) Complexes of
the Rare-Earth Metals: Synthesis, Structure, and Isoprene Polymer-
ization. Organometallics 2017, 36, 4649−4659.
(35) Lampland, N. L.; Pindwal, A.; Yan, K.; Ellern, A.; Sadow, A. D.
Rare Earth and Main Group Metal Poly(hydrosilyl) Compounds.
Organometallics 2017, 36, 4546−4557.
(36) Mukherjee, D.; Ellern, A.; Sadow, A. D. Conversion of a Zinc
Disilazide to a Zinc Hydride Mediated by LiCl. J. Am. Chem. Soc.
2010, 132, 7582−7583.
(37) Pawlikowski, A. V.; Gray, T. S.; Schoendorff, G.; Baird, B.;
Ellern, A.; Windus, T. L.; Sadow, A. D. Structure, bonding, and ligand-
based reactions of zwitterionic boratoiridium(I) complexes with
oxazolinyl scorpionate ligands. Inorg. Chim. Acta 2009, 362, 4517−
4525.
(38) Cendrowski-Guillaume, S. M.; Le Gland, G.; Nierlich, M.;
Ephritikhine, M. Lanthanide Borohydrides as Precursors to Organo-
metallic Compounds. Mono(cyclooctatetraenyl) Neodymium Com-
plexes. Organometallics 2000, 19, 5654−5660.
(39) Visseaux, M.; Terrier, M.; Mortreux, A.; Roussel, P. Facile
Synthesis of Lanthanidocenes by the “Borohydride/Alkyl Route” and
Their Application in Isoprene Polymerization. Eur. J. Inorg. Chem.
2010, 2010, 2867−2876.
(40) Dunne, J. F.; Manna, K.; Wiench, J. W.; Ellern, A.; Pruski, M.;
Sadow, A. D. Bis(oxazolinyl)phenylborane: A Lewis acid-containing
ligand for methide abstraction based coordination to aluminum(III).
Dalton Trans. 2010, 39, 641−653.
F
DOI: 10.1021/acs.organomet.8b00374
Organometallics XXXX, XXX, XXX−XXX