Selective Isomerization of Terminal Alkenes to (Z)-2-Alkenes Catalyzed by an Air-Stable Molybdenum(0) Complex

Article abstract of DOI:10.1021/acs.organomet.7b00914

Positional and stereochemical selectivity in the isomerization of terminal alkenes to internal alkenes is observed using the cis-Mo(CO)₄(PPh₃)₂ precatalyst. A p-toluenesulfonic acid (TsOH) cocatalyst is essential for catalyst activity. Various functionalized terminal alkenes have been converted to the corresponding 2-alkenes, generally favoring the Z isomer with selectivity as high as 8:1 Z:E at high conversion. Interrogation of the catalyst initiation mechanism by ³¹P NMR reveals that cis-Mo(CO)₄(PPh₃)₂ reacts with TsOH at elevated temperatures to yield a phosphine-ligated Mo hydride (MoH) species. Catalysis may proceed via 2,1-insertion of a terminal alkene into a MoH group and stereoselective β-hydride elimination to yield the (Z)-2-alkene.

Full text of DOI:10.1021/acs.organomet.7b00914

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Selective Isomerization of Terminal Alkenes to (Z)‑2-Alkenes
Catalyzed by an Air-Stable Molybdenum(0) Complex
Joseph Becica, Owen D. Glaze, Derek I. Wozniak, and Graham E. Dobereiner*
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, United States
S
* Supporting Information
ABSTRACT: Positional and stereochemical selectivity in the
isomerization of terminal alkenes to internal alkenes is observed
using the cis-Mo(CO)4(PPh3)2 precatalyst. A p-toluenesulfonic
acid (TsOH) cocatalyst is essential for catalyst activity. Various
functionalized terminal alkenes have been converted to the
corresponding 2-alkenes, generally favoring the Z isomer with
selectivity as high as 8:1 Z:E at high conversion. Interrogation of
the catalyst initiation mechanism by 31P NMR reveals that cis-
Mo(CO)4(PPh3)2 reacts with TsOH at elevated temperatures to yield a phosphine-ligated Mo hydride (MoH) species. Catalysis
may proceed via 2,1-insertion of a terminal alkene into a MoH group and stereoselective β-hydride elimination to yield the (Z)-2-
alkene.
INTRODUCTION
■
Alkene-containing compounds are an important class of organic
building blocks largely due to the diversity of alkene
functionalization methods available.1,2 Alkene isomers of
different substitution and stereochemistry can have different
physical and chemical properties, and therefore, synthetic
methods that access specific alkene isomers are desirable.3
Advances in transition-metal-catalyzed alkene isomerization
have recently emerged,4−11 finding applications in complex
molecule synthesis12,13 and tandem catalysis.14 However, due to
the often negligible differences in heats of formation of alkene
isomers,15,16 isomerization under thermodynamic control tends
to give mixtures of products, generally favoring (E)-alkenes.
Isomerization that proceeds via transition-metal hydride
catalysts can enable kinetic preference for (Z)-2-alkenes on
the basis of the reduced steric hindrance of an η2-bound (Z)-
alkene.9
Notable catalysts for selective alkene isomerization are
represented in Figure 1. Skrydstrup and co-workers5 have
reported that Pd(PtBu3)2(H)(Cl), generated in situ from
Pd(PtBu3)2 and isobutyryl chloride, is highly active for E:Z
alkene interconversion and will selectively isomerize terminal
allylbenzenes and other allylic substrates to the respective (E)-
2-alkenes. Isomerizing terminal alkenes with longer alkyl chains
to the 2-alkene without forming higher internal isomers is more
challenging. Grotjahn’s catalyst,6,7 [(Cp)Ru(PR3)(NCCH3)]-
[PF6] (where PR3 is an imidazol-2-yl-substituted phosphine),
promotes the selective one-carbon migration of terminal
alkenes, favoring selectivity for the (E)-2-alkene. Recently,
Huang and co-workers8 reported a NCP pincer-ligated Ir
catalyst that generates 2-alkenes from a broad scope of terminal
alkenes with high selectivity for the E isomer (∼1:30 Z:E).
Catalysts that favor the less thermodynamically stable (Z)-
alkene isomers are less common. A breakthrough in this area
Figure 1. Selected recent examples of organometallic catalysts for
selective alkene isomerization.4−10
was realized by Weix, Holland, and co-workers,9 who showed
that a (nacnac)Co complex forms (Z)-2-alkenes from a variety
of terminal olefins. However, this catalyst suffers from
overisomerization to higher alkene isomers, and stereo-
selectivity degrades with longer reaction duration. Hilt and
co-workers10 reported a procedure for Z-selective isomerization
of terminal alkenes with bisphosphine-ligated Co catalysts,
HPPh2, ZnI2, and Zn powder cocatalysts. The Hilt group
followed up with a similar procedure using bisphosphine-ligated
Ni catalysts for alkene isomerizations.11 The state of the art in
Z-selective isomerization of unactivated terminal alkenes is
represented by the work of Weix, Holland, and Hilt: typical
stereoselectivity reported by either Co catalyst is ∼(5−7):1 Z:E
of the 2-alkene. Hilt’s Ni catalyst is reported to invoke higher
Received: December 29, 2017
© XXXX American Chemical Society
A
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selectivity for the (Z)-2-alkene (∼9:1 Z:E); however, these
reactions were performed at −60 to −10 °C, where the
equilibrium lies closer to (Z)-alkene.
Table 1. Initial Screening of Mo Catalysts in the
Isomerization of 1-Hexene to Internal Alkenes
a
Beyond positional and stereochemical selectivity, a practical
isomerization precatalyst would be simple to prepare, air stable,
active enough for low catalyst loadings (<1 mol %), and general
for a wide variety of substrates.7 In considering these attributes,
low-valent Mo complexes have great promise as alkene
isomerization precatalysts.17−21 A patent17 suggests that
Mo(CO)6 (1) is active for isomerization under thermal
conditions (>150 °C), and qualitative positional selectivity is
reported. We reasoned that, if alkene isomerization occurred
under milder conditions with preformed Mo complexes,
selectivity and activity could be improved. Indeed, phosphine-
ligated Mo0 complexes selectively promote the one-carbon
migration of functionalized terminal alkenes to (Z)-2-alkenes
when an acid cocatalyst is employed. Preliminary mechanistic
experiments demonstrate the competency of the acid cocatalyst
to generate a Mo hydride species (MoH), with isomerization
plausibly occurring via 2,1-insertion of a terminal alkene into
the MoH, followed by selective β-hydride elimination to furnish
(Z)-2-alkene.
conversn
yield of 6a
b
b
b
entry
[Mo]
acid
N/A
(%)
(%)
Z:E (6a)
1
2
3
4
5
6
1
2
3
nd
nd
nd
37
73
85
91
79
44
nd
nd
65
nd
91
nd
2
N/A
nd
3-cis
1
N/A
1
nd
TsOH
TsOH
TsOH
TsOH
TsOH·H2O
61
96
94
94
96
46
4
1.6:1
0.4:1
2.2:1
4.0:1
1.1:1
8.1:1
nd
2
3-cis
3-cis
3-cis
c
7
8
9
3-trans TsOH
10
11
12
13
4a
4b
4c
4d
4d
TsOH
TsOH
4
nd
TsOH·H2O
TsOH·H2O
TsOH·H2O
67
23
92
5.6:1
nd
d
14
4.2:1
a
Reaction conditions unless specified otherwise: 1 mmol of 5a, 0.5
mol % of Mo catalyst, 5 mol % of TsOH or TsOH·H2O, 1 mL of
RESULTS AND DISCUSSION
■
b
1
THF, 66 °C, 24 h. Determined by H NMR. The remaining mass
Simple, air-stable, phosphine-ligated Mo0 complexes were
targeted and prepared by literature procedures (Figure
2).22−25 1 is refluxed in PhMe with piperidine to generate cis-
c
balance corresponds to other internal isomers. Reaction time 30 min.
1 mol % of Mo catalyst and 10 mol % of acid were used.
d
species necessary to observe alkene isomerization. p-Toluene-
sulfonic acid (TsOH) was chosen, as it is an easily dispensed
solid acid and is readily prepared in anhydrous form. In the
absence of acid, complexes 1−3 are not active for 1-hexene
isomerization in refluxing THF. With added TsOH, 1 and 2
were active but poorly selective for alkene isomerization, while
3-cis showed superior activity and selectivity. 5a with 0.5 mol %
of 3-cis and 5 mol % of TsOH in refluxing THF generated (Z)-
2-hexene (6a, 85% yield, 4.0:1 Z:E) after 24 h of reaction, with
only trace 3-hexene generated. The use of TsOH·H2O resulted
in a more active, but less selective, catalyst. Surprisingly, 3-trans
was a significantly less active catalyst than 3-cis, proceeding to
only 46% conversion of 5a under identical conditions. Although
a cis phosphine orientation gave higher catalytic activity, cis-
bidentate phosphine complexes 4a−d were generally less active
than 3-cis under identical conditions. Performance comparable
to that of catalyst 3-cis could be achieved under modified
conditions: complex 4d (1 mol %) and TsOH·H2O (10 mol %)
in refluxing THF catalyzed the isomerization of 5a to 6a (91%
yield, 4.2:1 Z:E). When isomerization was attempted with 5
mol % TsOH and no Mo catalyst, no conversion of 5a is
observed. We determined 3-cis to be the optimal catalyst of
those screened due to the ease and low cost of preparation, air
stability, and a combination of catalytic activity and selectivity at
low catalyst loadings.
The optimized conditions using 3-cis were used to establish
the substrate scope for the catalytic reaction (Chart 1). In
general, high levels of both positional selectivity and stereo-
selectivity are observed in alkene isomerization (20 examples,
33−93% of the 2-alkene, up to 8.2:1 Z:E selectivity). 5a and 1-
octene (5b) are converted to the 2-alkenes under the standard
conditions (0.5 mol % 3-cis, 5 mol % TsOH, 1.0 M refluxing
THF) to high conversion in 30 min. 2-Octene (6b) is formed
in 87% yield (5.1:1 Z:E). Longer-chain alkenes (1-decene (5c)
and 1-dodecene (5d)) require longer reaction times or higher
Figure 2. Synthesis of relevant Mo complexes. Reaction conditions:
(a) 1, 5−7 equiv of piperidine, refluxing PhMe; (b) 2, 2 equiv of PPh3,
refluxing CH2Cl2; (c) 2 with 2 equiv of PPh3 or 3-cis, refluxing PhMe;
(d) 2 and 1 equiv of L, refluxing CH2Cl2. Bottom left: X-ray structure
of 4d.
Mo(CO)4(pip)2 (2). 2 can be converted to cis-Mo-
(CO)4(PPh3)2 (3-cis) by the addition of 2 equiv of PPh3 in
refluxing CH2Cl2, while the thermodynamic product, trans-
Mo(CO)4(PPh3)2 (3-trans), is generated on refluxing in PhMe.
By analogy, bidentate ligands (dppf,26,27 dppbz,28,29 DPE-phos,
xantphos) were used to prepare complexes 4a−d.
The competency of the synthesized Mo complexes to
isomerize terminal alkenes to internal alkenes was evaluated
using 1-hexene (5a) (Table 1). On the basis of the ability of
Brønsted acids to protonate Mo0 to generate MoH
species,21,30,31 we reasoned that incorporation of acid
cocatalysts to the reaction mixture could generate the MoH
B
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a
1:4.9 Z:E). The oxygen functionalities of 5j−l may chelate and
favor formation of six-membered metallacycles where the
substrate is prearranged to eliminate the (E)-alkene.32 Absent a
directing effect, other kinetic influences may allow product
ratios to approach equilibrium mixtures of 2-isomers.33
In addition to aromatic groups, the reaction slowed when
substrates with δ and ε substituents are used. The reaction of
but-3-en-1-ylbenzene (5m) proceeded to only 11% conversion
under standard conditions; however, at higher catalyst (2 mol
% 3-cis) and acid (20 mol % TsOH) loadings, prop-2-en-1-
ylbenzene (6m) was formed in 81% yield and 4.8:1 Z:E
selectivity. Similarly, the reaction of allylbenzene (5n)
proceeded to only 9% conversion under standard conditions,
but 6n was formed in 83% yield (1.6:1 Z:E) using 1 mol % of 3-
cis and 20 mol % of TsOH. Higher catalyst loadings were also
necessary to isomerize allyltrimethylsilane (5o), which is
isomerized to the (E)-alkene (6o), likely due to the steric
bulk of the SiMe3 group.
Chart 1. Substrate Scope
Other substrates with potentially reactive functional groups
were then evaluated: 1-(pent-4-en-1-yl)piperidine (5p) con-
tains a Brønsted basic amine group which could potentially
neutralize the acid necessary to generate an active catalyst.
Although no conversion was observed using 5p, the reaction of
5p·HCl proceeded using 0.5 mol % of 3-cis and 5 mol % of
TsOH to generate 6p·HCl (79% yield, 1.3:1 Z:E). 2-(But-3-en-
1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (5q) is a potential
nucleophile yet still undergoes facile isomerization to yield the
synthetically valuable allyl boronate ester34 6q (74% yield, 7.7:1
Z:E). The 1,5-diene 5r, featuring both internal and terminal
alkene groups, is isomerized selectively to the (Z,Z)-2,5-diene
6r (60%, 2:1 Z:E) with no evident isomerization of the internal
alkene.
With the scope of alkene isomerization in hand, we sought a
mechanistic rationale for the observed Z selectivity. Weix,
Holland, and co-workers9 propose that Z-selective Co isomer-
ization proceeds through an inner-sphere alkyl35 (Figure 3A)
a
Reaction conditions unless specified otherwise: 1 mmol of 5, 0.5 mol
% of Mo catalyst, 5 mol % of TsOH, 1 mL of THF, 66 °C. The yields
of 2-alkene are indicated; yields of higher internal alkene isomers are
1
indicated in parentheses. Yield and selectivity are determined by H
b
c
NMR. 1 mol % of 3-cis, 10 mol % of TsOH. Selectivity determined
d
by inverse-gated decoupled 13C NMR. 2 mol % of 3-cis, 20 mol % of
e
TsOH. Starting material and product were the HCl salt.
catalyst loadings. The reaction of 5c under standard conditions
forms 2-decene (6c, 83% yield, 5.4:1 Z:E) after 20 h of reaction.
The reaction of 5d using 1 mol % of 3-cis gave 6d in 87% yield
(5.0:1 Z:E). Despite prolonged reaction times, only a small
quantity of higher internal olefins was observed (8% for 5c, 3%
for 5d).
Figure 3. Commonly proposed mechanisms for metal mediated alkene
isomerization: (A) alkyl mechanism; (B) allyl mechanism.
Next, functionalized alkenes were evaluated in catalysis. The
long-chain alcohol undec-10-en-1-ol (5e) is converted to the 2-
alkene with high selectivity for the Z isomer under standard
conditions to give undec-9-en-1-ol (6e, 74% yield, 8.2:1 Z:E).
The ester undec-10-en-1-yl propionate (5f) is converted to 62%
(6.5:1 Z:E) of the 2-alkene after 20 h of reaction using
increased catalyst loadings. In addition, substrates with aryl
substituents are slower, as indicated by substrates 5g−i, and
required higher catalyst and acid loadings. Using 1 mol % of 3-
cis and 10 mol % of TsOH, 1-phenylhex-4-en-1-ol (6g) was
prepared in 68% yield (2.6:1 Z:E), and (pent-3-en-1-yloxy)-
benzene was prepared in 76% yield (5.9:1 Z:E).
pathway. Here, a Z-selective alkyl mechanism requires alkene
insertion into MoH to generate a Mo(alkyl) species followed
by selective β-hydride elimination to furnish the respective (Z)-
2-alkene. Other mechanisms proceeding through η3-allyl36
(Figure 3B), β-carbocation,37 or radical intermediates are also
possible.9,13,38 Another mode of reactivity would involve the
direct protonation of alkenes by acidic M−H species.39
In a thermodynamic mixture of linear alkenes generated by
unselective isomerization catalysts, many internal isomers (Z-2,
E-2, Z-3, E-3, etc.) are present. Our catalyst system apparently
promotes a rapid conversion of 1-alkene to (Z)-2-alkenes, with
comparatively slow Z to E isomerization of internal alkenes, as
well as low rates of 2-alkene to 3-alkene isomerization. Indeed,
catalyst 3-cis is poorly reactive toward internal alkenes. (Z)-2-
Hexene or (E)-2-hexene subjected to standard reaction
With some substrates, selectivity for the (E)-2-isomer is
observed. Pent-4-enoic acid (5j), hex-5-en-2-ol (5k), and ethyl
2-methylpent-4-enoate (5l) form (E)-2-isomers preferentially
(6j, 85% yield, 1:2.7 Z:E; 6k, 93% yield, 1:2 Z:E; 6l, 81% yield,
C
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conditions (0.5 mol % 3-cis, 5 mol % TsOH, THF, reflux, 24 h)
yields minimal conversion (<2%) to 3-hexenes. This observa-
tion is consistent with facile migratory insertion of a terminal
alkene relative to internal alkenes. Trace 3-alkenes observed in
catalysis could be generated directly from the terminal alkene
through a “chain-walking” mechanism, rather than reinsertion
of the 2-alkene products by a MoH species.9 We also observed
that catalysis was inhibited (<2% conversion) when the
standard reaction conditions were modified with (a) 1 atm of
CO, (b) additional PPh3 (2−5 mol %), (c) TEMPO (2 mol %).
Given the capacity of TEMPO to act as a M−H trap,40
inhibition of catalysis by TEMPO may indicate M−H
intermediates.
CONCLUSION
■
A method for selective alkene isomerization via Mo has been
discovered. The methodology is complementary to the few
available catalysts that form (Z)-2-alkenes from terminal
alkenes, showing comparable or improved selectivity. The air-
stable precatalyst 3-cis is easily prepared with inexpensive
ligands and with TON ranges as high as 200 and initial TOF
ranges as high as 400 h−1. A variety of functionalized alkenes
are tolerated under the reaction conditions, though some
substrates require higher catalyst and acid loadings. Efforts in
our laboratory are underway to understand the origins of
selectivity observed for this catalyst and develop additional
synthetic protocols for selective transformations of alkenes.
Catalyst initiation of 3-cis was investigated by 31P NMR in
hopes of establishing the catalyst resting state. Substrate 5b (1
mmol), 3-cis (0.01 mmol), TsOH (0.1 mmol), and C6D6 (0.6
mL) were combined in an NMR tube and heated to 80 °C for
10 min. The reaction proceeded to 70% conversion of 5b to 6b,
and the 31P NMR spectrum (C6D6, 292 K) revealed conversion
of 3-cis to 3-trans, trans-Mo(CO)4(PPh3)3 (7-trans),41 two
EXPERIMENTAL SECTION
■
General Information. Air-free manipulations were performed
under a dry N2 atmosphere using a Vacuum Atmospheres inert-
atmosphere glovebox or using standard Schlenk techniques. NMR
spectra were collected on Bruker Avance III 500 MHz and DRX 500
MHz instruments. 1H NMR chemical shifts (δ, ppm) are referenced to
residual protio-solvent resonances, and 13C NMR chemical shifts are
referenced to the deuterated solvent peak. 31P NMR and 19F NMR
chemical shifts are referenced to external standards. Microanalysis data
were obtained from the CENTC Elemental Analysis Facility at the
University of Rochester, funded by NSF CHE-0650456. Toluene
(PhMe), methylene chloride (CH2Cl2), tetrahydrofuran (THF),
diethyl ether (Et2O), and pentane were purified using a commercial
solvent purification system. Unless otherwise noted, commercial
chemicals were used as received without further purification.
1,4,7,10,13,16-Hexaoxacyclooctadecane (18-crown-6), molybdenum
hexacarbonyl (Mo(CO)6), and sodium hexamethyldisilazide
(NaHMDS) were supplied by Strem. Allylbenzene, allyltrimethylsi-
lane, 1,2-bis(diphenylphosphino)benzene (dppbz), dec-1-ene, hex-1-
ene, oct-1-ene, and piperidine were supplied by Sigma-Aldrich. 5-
Bromobut-1-ene, 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene
(xantphos), 1,1′-ferrocenediylbis(diphenylphosphine) (dppf), hex-5-
en-2-one, 4-fluorobenzaldehyde, (oxidi-2,1-phenylene)bis-
(diphenylphosphine) (DPE-phos), 4-pentenoic acid, 4-phenylbut-1-
ene, triphenylphosphine (PPh3), and undec-10-en-1-ol were supplied
by Oakwood. Ethyl 2-methylpent-4-enoate and propionyl chloride
were supplied by Alfa Aesar. 2-(But-3-en-1-yl)-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane and dodec-1-ene were supplied by Combi Blocks.
p-Toluenesulfonic acid was supplied by Fisher. Deuterated solvents
were supplied by Cambridge Isotopes.
+
unidentified Mo(PPh3) species, and the liberation of HPPh3 .
The same 31P NMR resonances are visible in the absence of
alkene. Presumably, catalyst initiation begins by the dissociation
of PPh3 from 3-cis,22 consistent with inhibition by additional
PPh3 and with reduced catalytic activity when bidentate
phosphines are employed. Solvent-dependent coordination
behavior of 3-cis is also observed. When 3-cis is dissolved in
CD3CN, CO for CD3CN ligand exchange is indicated by the
formation of multiple CD3CN-bound Mo species observed in
the 31P NMR spectrum. In contrast, no evidence for CO
dissociation from 3-cis is found in THF solvent, consistent with
the reluctance of Mo0 to liberate CO ligands.
In search of catalyst intermediates, we sought a MoH species
capable of promoting alkene isomerization via an alkyl
mechanism (Figure 3A). No MoH is observed when 3-cis
and TsOH are combined in THF (the solvent used under
optimized catalytic conditions), but a MoH species can be
generated from 3-cis and TsOH in MeCN.42 Although the
complex could not be isolated and fully characterized, a
1
resonance in the H NMR spectrum (CD3CN, 292 K) is
observed at −4.3 ppm (8-cis, d, 2JPH = 66 Hz), consistent with
an octahedral Mo complex with mutually cis H and PPh3
ligands.30,43 The resulting mixture of Mo species containing 8-
cis isomerizes 5b to 6b at room temperature. Without isolation
of 8-cis, catalytic activity cannot be unambiguously attributed
to this hydride complex. Nonetheless, the observation of 8-cis
confirms TsOH can promote MoH formation under certain
conditions.
p-Toluenesulfonic acid (Anhydrous). TsOH·H2O was placed in
an oven-dried 250 mL round-bottom flask along with a stir bar, and
the flask was sealed using a Schlenk adapter with a PTFE stopcock.
The flask was placed under vacuum, submerged into an oil bath, and
heated to 50 °C. As anhydrous TsOH was formed, the solids began to
melt to form a viscous gray liquid. The liquid was stirred under
vacuum at this temperature for 2 h. The mixture was then cooled to
room temperature, at which point the liquid solidified. The flask was
opened to air, and the solid was ground into a powder with a spatula.
Then, the solids were placed under vacuum at room temperature
Myriad six-coordinate catalyst intermediates can be envisaged
for our system, as can seven-coordinate species, such as the
isomerization-active seven-coordinate Mo hydride generated by
Jones and co-workers21 via addition of HBF4·Et2O to a Mo
tricarbonyl pincer complex. Here, phosphine is unnecessary for
isomerization activity but is necessary for (Z)-2-alkene
selectivity (Table 1). However, on the basis of 31P NMR
studies of the 3-cis reaction mixture, partial PPh3 dissociation
occurs readily during catalysis, and additional PPh3 inhibits the
reaction. PPh3 could preserve selectivity for (Z)-2-alkenes as a
sterically demanding ligand on the active catalyst species.
Alternatively it can compete with 2-alkene for binding to the
active catalyst (thereby slowing Z to E isomerization) or inhibit
other isomerization catalysts that lack selectivity for the (Z)-2-
alkene.
1
overnight. H NMR of the resulting solid indicated the absence of
H2O.
Synthesis and Characterization of Mo Complexes. Mo-
(CO)4(piperidine)2 (2). The complex was prepared by a modified
literature procedure.22 Caution! The following reaction evolves carbon
monoxide and is performed in a sealed vessel. This procedure should
be carried out behind a blast shield. An oven-dried thick-walled
Schlenk tube was charged with Mo(CO)6 (2 g, 7.58 mmol) under an
N2 atmosphere. The solids were suspended in 30 mL of PhMe, and
piperidine (7 equiv, 5.3 mL, 53.0 mmol) was added. The tube was
sealed with a PTFE stopper under inert conditions. The tube was
submerged in an oil bath and heated to 120 °C. The reaction mixture
was stirred at this temperature for 2 h. Periodically, the PTFE stopper
was carefully opened to the reaction to vent CO pressure evolved
D
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during the reaction and quickly resealed. After completion of the
reaction, a yellow crystalline solid precipitated. The solid was collected
by filtration under N2 (2.87 g, 78% yield). Anal. Calcd for
C14H22MoN2O4: C, 44.45; H, 5.86; N, 7.41. Found: C, 44.395; H,
5.941; N, 7.145.
washed with brine, dried over MgSO4, filtered, and evaporated in
vacuo to yield a yellow oil (2.00 g, 56%). 1H NMR (500 MHz, CDCl3,
292 K, ppm): δ 7.32−7.17 (5H, m), 5.72 (1H, m), 4.97−4.87 (2H,
m), 4.57−4.52 (1H, m), 2.47 (1H, s), 2.00 (2H, m), 1.76−1.68 (1H,
m), 1.67−1.59 (1H, m), 1.45 (1H, m), 1.30 (1H, m).
cis-Mo(CO)4(PPh3)2 (3-cis). The complex was prepared by a
modified literature procedure.25 Under an N2 atmosphere, an oven-
dried Schlenk tube was charged with Mo(CO)4(piperidine)2 (1.0 g,
2.64 mmol) and the solid was dissolved in 15 mL of CH2Cl2. A
solution of triphenylphosphine (2 equiv, 1.4 g, 5.3 mmol) in 10 mL of
CH2Cl2 was added to the mixture. The tube was sealed with a PTFE
stopper under inert conditions and then submerged in an oil bath
preheated to 40 °C. The reaction mixture stirred at this temperature
for 2 h. After it was cooled to room temperature, the mixture was
opened to air and filtered through Celite. The solvent volume of the
filtrate was reduced in vacuo, and the product was precipitated with
MeOH to yield a pale yellow solid (1.94 g, 93%). Crystalline material
was obtained by cooling a solution of 3-cis in 4/1 Et2O/CH2Cl2 to
−30 °C. 1H NMR (500 MHz, CDCl3, 292 K, ppm): δ 7.3−7.1 (30H).
(Pent-4-en-1-yloxy)benzene (5h).46 5-Bromo-1-pentene (2.38 g,
15.9 mmol) was placed in a 250 mL round-bottom flask containing a
suspension of phenol (1.50 g, 15.9 mmol) and K2CO3 (4.41 g, 31.88
mmol, 691.1 mg) in acetone (100 mL). The reaction mixture was
heated to 66 °C for 20 h, cooled, and filtered. The solvent volume was
reduced in vacuo, diluted with water, and extracted with Et2O. The
combined extracts were washed with brine, dried over MgSO4, filtered,
1
and evaporated in vacuo to yield a yellow oil (1.59 g, 57%). H NMR
(500 MHz, CDCl3, 292 K, ppm): δ 7.22−7.15 (2H, m), 6.87−6.82
(2H, m), 5.78 (1H, m), 4.99 (1H, m), 4.92 (1H, m), 3.90 (2H, t, 3JH−H
= 6.6 Hz), 2.16 (2H, m), 2.81 (2H, m).
((Pent-4-en-1-yloxy)methyl)benzene (5i).9 In a N2 atmosphere
glovebox, NaH (0.400 g, 16.65) was slowly added to a solution of
benzyl alcohol (1.50 g, 13.9 mmol) in DMF (20 mL) and stirred for 1
h. A solution of 5-bromo-1-pentene (2.07 g, 13.9 mmol) in 10 mL of
DMF was slowly added to the reaction mixture, which was stirred at
room temperature for 20 h. The reaction mixture was removed from
the glovebox, diluted with water, and extracted with Et2O. The
combined extracts were washed with brine, dried over MgSO4, filtered,
and evaporated in vacuo to yield a yellow oil (0.894 g, 37%). 1H NMR
(500 MHz, CDCl3, 292 K, ppm): δ 7.39−7.31 (Ar, 4H, m), 7.30−7.27
(Ar, 1H, m), 5.87−5.77 (alkene CH, 1H, m), 5.05−5.00 (alkene CH,
1H, dq), 4.98−4.94 (alkene CH, 1H, m), 4.51 (CH2, 2H, s), 3.49
(CH2, 2H, t), 2.15 (CH2, 2H, m), 1.72 (CH3, 3H, m).
2
13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 215.3 (t, JC−P = 9.2
2
2
Hz), 210.5 (t, JC−P = 9.2 Hz), 136.5 (m), 133.7 (t, JC−P = 6.5 Hz),
129.7, 128.4 (t, 2JC−P = 4.6 Hz). 31P NMR (202 MHz, CDCl3, 292 K,
ppm): δ 37.0. Anal. Calcd for C40H30MoO4P2·H2O: C, 64.01; H 4.30.
Found: C, 64.333; H 4.109. trans-Mo(CO)4(PPh3)2 (3-trans)25 can
be prepared by heating a toluene solution of 3-cis to reflux.
Mo(CO)4(dppf) (4a), Mo(CO)4(dppbz) (4b), Mo(CO)4(DPE-phos)
(4c), and Mo(CO)4(xantphos) (4d). These complexes can be prepared
by literature methods.25−29 4d can be prepared in higher purity via 3-
cis. Under an N2 atmosphere, 3-cis (0.9 g, 1.23 mmol) was placed in a
vial and dissolved in 5 mL of PhMe. A separate solution of xantphos
(0.71 g, 1.23 mmol) in 5 mL of PhMe was prepared, and the solutions
were combined. The vial was sealed and heated to 110 °C for 2 h.
Then, the reaction mixture was cooled to room temperature and the
vial was opened to air. The solution was filtered through Celite and
then evaporated. The resulting beige solids were rinsed with Et2O to
remove triphenylphosphine, and the product was then dried in vacuo
(890 mg, 92% yield). X-ray-quality crystals were grown from a solution
Hex-5-en-2-ol (5k).47 In an oven-dried 80 mL vial, NaBH4 (1.55 g,
41.0 mmol) was added to a stirred solution of 5-hexen-2-one (2.01 g,
20.5 mmol) in EtOH (40 mL) at 0 °C. The resulting solution was
warmed to room temperature and stirred for 18 h. The solution was
poured into a saturated solution of NH4Cl(aq). When effervescence
had ceased, the mixture was extracted with ether. The combined
extracts were washed with brine, dried over MgSO4, and filtered, and
the solvent was carefully removed in vacuo to yield a volatile, colorless
1
1
of 4d in 4/1 Et2O/CH2Cl2. H NMR (500 MHz, CDCl3, 292 K,
oil (1.21 g, 59%). H NMR (500 MHz, CDCl3, 292 K, ppm): δ 5.84
ppm): δ 7.45 (2H, d), 7.22−7.07 (20H), 6.98 (2H, t), 1.55 (6H, t).
(1H, m), 5.07−4.95 (2H, m), 3.83 (1H, m), 2.22−2.07 (2H, m),
3
13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 215.9 (m), 210.0 (t),
1.61−1.50 (3H, m), 1.20 (3H, d, JH−H = 6.2 Hz).
1-(Pent-4-en-1-yl)piperidine (5p).9 The compound was prepared in
a fashion analogous to that for 1-(but-3-en-1-yl)piperidine. A 250 mL
round-bottom flask was charged with a solution of 5-bromo-1-butene
(5.00 g, 33.6 mmol), piperidine (2.39 mL, 28.1 mmol), 18-crown-6
(0.360 g, 1.36 mmol), K2CO3 (4.83 g, 35.0 mmol), and CH3CN (40
mL). The reaction mixture was heated at reflux for 18 h. The crude
reaction mixture was filtered through alumina, rinsed with water, and
extracted with Et2O. The organics were washed with brine, dried over
MgSO4, filtered, and concentrated under vacuum. The desired product
134.7 (m), 133.2 (t), 132.3, 130.9, 120.5, 128.3 (t), 127.5, 124.1,
124.0, 123.3 (m), 35.39, 29.97. 31P NMR (202 MHz, CDCl3, 292 K,
ppm): δ 20.8. Anal. Calcd for C43H32MoO5P2·C7H8: C, 67.96; H, 4.56.
Found: C, 67.402; H, 4.469.
Synthesis and Characterization of Alkene Substrates. Undec-
10-en-1-yl Propanoate (5f).44 A 500 mL round-bottom flask was
charged with undec-10-en-1-ol (1.067 g, 6.27 mmol), 20 mL of
CH2Cl2, and 2 mL of pyridine. The reaction mixture was cooled to 0
°C. A solution containing a slight excess of propionyl chloride (0.600
g, 6.5 mmol) in 10 mL of CH2Cl2 was added dropwise into the
reaction mixture. The reaction mixture was then stirred vigorously at 0
°C for 30 min, after which the mixture was stirred at room
temperature for 1 h. Dilute HCl in H2O was then added to the
solution. The organic layer was separated and rinsed with saturated
Na2CO3(aq), H2O, brine, and H2O, dried over MgSO4, filtered, and
1
was isolated as an orange oil (1.91 g, 43%). H NMR (500 MHz,
CDCl3, 292 K): δ 5.81 (1H, m), 5.03−4.92 (2H, m), 2.35 (4H, br s),
2.28 (2H, m), 2.39−2.36 (2H, m), 1.62−1.54 (6H, m), 1.42 (2H, m).
1-(pent-4-en-1-yl)piperidine·HCl (5p·HCl). A 1 M solution of HCl in
Et2O (4 mL) was placed in a 16 mL vial containing a solution of 1-
(pent-4-en-1-yl)piperidine (0.500 g, 3.26 mmol) in THF (3 mL). The
mixture was stirred at room temperature for 15 min, and then the solid
was filtered, rinsed with ether, and dried in vacuo to yield a beige solid
1
evaporated to yield a colorless liquid (0.874 g, 62%). H NMR (500
MHz, CDCl3, 292 K, ppm): δ 5.79 (1H, m), 5.00−4.89 (2H, m), 4.04
3
3
1
(2H, t, JH−H = 6.8 Hz), 2.30 (2H, q, JH−H = 7.5 Hz), 2.02 (2H, m),
1.60 (2H, m), 1.39−1.21 (12H, m), 1.12 (3H, t, J = 7.6 Hz).
(0.548 g, 89%). H NMR (500 MHz, CDCl3, 292 K, ppm): δ 12.19
(1H, br s), 5.77 (1H, m), 5.07 (2H, m), 3.54 (2H, d), 2.91 (2H, m),
2.61 (2H, m), 2.34 (2H, m), 2.15 (2H, m), 2.05 (2H, m), 1.92 (1H,
m), 1.85 (2H, m), 1.41 (1H, m). 13C NMR (126 MHz, 292 K, CDCl3,
ppm): δ 136.0, 116.7, 57.0, 53.2, 30.8, 22.5, 22.4, 22.2.
1-Phenylhex-5-en-1-ol (5g).45 In a N2 atmosphere glovebox, an
oven-dried 250 round-bottom flask was charged with Mg turnings
(0.736 g, 30.2 mmol), a crystal of I2, and anhydrous THF (15 mL).
The mixture was stirred for 15 min at room temperature. A solution of
5-bromo-1-pentene (3.00 g, 20.1 mmol) in THF (20 mL) was added
to the Mg dropwise via addition funnel, and the resultant solution was
stirred for 1 h. The flask was then sealed with a rubber septum and
removed from the glovebox. Under N2, benzaldehyde (2.35 g, 22.1
mmol) was added dropwise via syringe, and the solution was stirred at
room temperature for 1 h. The crude reaction mixture was quenched
with water and extracted with CH2Cl2. The combined extracts were
(Z)-1-Fluoro-4-(hexa-1,5-dien-1-yl)benzene (5r).48 The compound
was prepared in a fashion analogous to that for (Z)-hexa-1,5-dien-1-
ylbenzene. A solution of 5-bromo-1-pentene (1.50 g, 10.1 mmol) and
triphenylphosphine (2.64 g, 10.1 mmol) in CH3CN (40 mL) was
refluxed for 3 days, after which the solvent was removed in vacuo to
yield a white solid. The solid was rinsed with Et2O to yield pent-4-en-
1-yltriphenylphosphonium bromide (4.04 g, 97%). The solid was
further oven-dried (120 °C) to remove residual H2O. In an N2
E
DOI: 10.1021/acs.organomet.7b00914
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Organometallics
Article
atmosphere glovebox, pent-4-en-1-yltriphenylphosphonium bromide
(3.62 g, 14.3 mmol) was placed in a 250 mL round-bottom flask and
suspended in 25 mL of THF. A solution of NaHMDS (1.61 g, 8.80
mmol) in THF (10 mL) was added to the mixture, which was then
stirred at room temperature for 30 min, yielding an orange solution.
Then, a solution of 4-fluorobenzaldehyde (1.09 g, 8.80 mmol) in THF
(5 mL) was added. The reaction mixture slowly turned beige,
indicating consumption of the Wittig reagent. The mixture was stirred
for 20 h at room temperature, after which the solvent was removed in
vacuo. The resulting residual solid was stirred in hexane for 4 h,
filtered, and concentrated under vacuum to yield a yellow oil. The oil
was purified by column chromatography on silica (hexane) to give the
mg, 1 mmol), TEMPO (2 mol %), 500 μL of a 10 mM stock solution
of 3-cis in THF (5 μmol, 0.5 mol %), and 500 μL of a 100 mM stock
solution of TsOH in THF (50 μmol, 5 mol %). The vial was immersed
in an aluminum heating block preheated to 80 °C. The reaction
mixture was stirred at this temperature for 30 min, at which point the
vial was cooled to room temperature and was opened to air. An aliquot
of the reaction mixture was removed from the crude reaction mixture
1
for H NMR analysis. No conversion of the hex-1-ene substrate was
observed.
Synthesis and Characterization of Alkene Products. Com-
pounds were prepared using the General Procedure for Catalytic
Reactions. Unless otherwise noted, 0.5 mol % of 3-cis and 5 mol % of
TsOH were used as catalysts.
1
product as a colorless liquid (1.00 g, 64%). H NMR (500 MHz,
Hex-2-ene (6a).9 The compound was not isolated due to high
volatility. The spectroscopic data agree with the literature.
Oct-2-ene (6b).9 The compound was purified on a short pad of
silica gel (pentane), and the product was carefully evaporated to obtain
a mixture of isomers (25 mg, 22% yield). Oct-2-ene (6b) was present
as approximately 84% of the mixture (5.3:1 Z:E) ,and oct-1-ene (5b)
remained as 7% of the mixture. The total percentage of higher internal
CDCl3, 292 K, ppm): δ 7.16−7.11 (Ar, 2H, m), 6.95−6.85 (Ar, 2H,
m), 6.35−6.24 (alkene CH, 1H, m), 5.78−5.69 (alkene CH, 1H, m),
3
3
5.55 (alkene CH, 1H, dt, JH−H = 11.7, JH−H = 7.2 Hz), 4.97−4.88
(alkene CH, 1H, m), 2.33−2.27 (CH2, 2H, m), 2.15−2.08 (CH2, 2H,
m).
General Procedure for Catalytic Reactions. In a nitrogen
atmosphere glovebox, an 8 mL vial was charged with hex-1-ene (84
mg, 1 mmol), 500 μL of a 10 mM stock solution of 3-cis in THF (5
μmol, 0.5 mol %), and 500 μL of a 100 mM stock solution of TsOH in
THF (50 μmol, 5 mol %). The vial was capped and immersed in an
aluminum heating block preheated to 80 °C. The reaction mixture was
stirred at this temperature for 30 min, at which point the vial was
cooled to room temperature and was opened to air. An aliquot of the
reaction mixture was removed from the crude reaction mixture for 1H
NMR analysis. Unless otherwise noted, reactions were performed in
triplicate. The conversion, yield, and selectivity represent an average of
three trials. NMR yield and selectivity were determined using 1H
NMR by published methods.6,8
1
alkenes was 7%. Data for the Z isomer are as follows. H NMR (500
MHz, CDCl3, 292 K, ppm): δ 5.49−5.32 (alkene CH, 2H, m), 2.09−
1.90 (CH2, 2H, m), 1.60 (CH3, 3H, m), 1.39−1.23 (CH2, 8H, m),
0.92−0.96 (CH3, 3H, m). 13C NMR (126 MHz, CDCl3, 292 K, ppm):
δ 131.0 (alkene CH), 123.7 (alkene CH), 31.7 (CH2), 29.4 (CH2),
26.9 (CH2), 22.7 (CH2), 14.2 (CH3), 12.9 (CH3).
Dec-2-ene (6c).49,50 The compound was purified on a short pad of
silica gel (pentane), and the product was carefully evaporated to obtain
as a mixture of isomers (37 mg, 26% yield). Dec-2-ene (6c) was
present as approximately 77% of the mixture (5.5:1 Z:E), and dec-1-
ene remained as 9% of the mixture. The total percentage of higher
1
internal alkenes was <1%. Data for the Z isomer are as follows. H
Attempted Catalysis with Internal Alkene Substrates. In a
nitrogen atmosphere glovebox, an 8 mL vial was charged with (Z)-hex-
2-ene or (E)-hex-2-ene (84 mg, 1 mmol), 500 μL of a 10 mM stock
solution of 3-cis in THF (5 μmol, 0.5 mol %), and 500 μL of a 100
mM stock solution of TsOH in THF (50 μmol, 5 mol %). The vial was
immersed in an aluminum heating block preheated to 80 °C. The
reaction mixture was stirred at this temperature for 24 h, at which
point the vial was cooled to room temperature and was opened to air.
An aliquot of the reaction mixture was removed from the crude
NMR (500 MHz, CDCl3, 292 K, ppm): δ 5.47−5.31 (alkene CH, 2H,
m), 2.07−2.00 (CH2, 2H, m), 1.60−1.57 (CH3, 3H, m), 1.42−1.22
(CH2, 10H, m), 0.92−0.85 (CH3, 3H, m). 13C NMR (126 MHz,
CDCl3, 292 K, ppm): δ 130.9 (alkene CH), 123.6 (alkene CH), 31.9
(CH2), 29.6 (CH2), 29.30 (CH2), 29.27 (CH2), 26.9 (CH2), 22.7
(CH2), 14.1 (CH3), 12.7 (CH3). Data for the E isomer are as follows.
1H NMR (500 MHz, CDCl3, 292 K, ppm): δ 5.47−5.31 (alkene CH,
2H, m), 1.99−1.93 (CH2, 2H, m), 1.65−1.57 (CH3, 3H, m), 1.42−
1.22 (CH2, 10H, m), 0.92−0.85 (CH3, 3H, m).
1
reaction mixture for H NMR analysis. Approximately 2% conversion
Dodec-2-ene (6d).9,51 A 1 mol % amount of 3-cis and 10 mol % of
TsOH were used. The compound was purified on a short pad of silica
gel (hexane), and the product was obtained as a mixture of isomers
(161 mg, 96%). Dodec-2-ene (6d) was present as approximately 89%
of the mixture (5.0:1 Z:E), and dodec-1-ene remained as 10% of the
mixture. The total percentage of higher internal alkenes was <1%. Data
was observed when (Z)-2-hexene was used as substrate. No conversion
was observed for (E)-2-hexene.
Attempted Catalysis under Pressure of Carbon Monoxide.
In a nitrogen atmosphere glovebox, an 8 mL vial was charged with hex-
1-ene (84 mg, 1 mmol), 500 μL of a 10 mM stock solution of 3-cis in
THF (5 μmol, 0.5 mol %), and 500 μL of a 100 mM stock solution of
TsOH in THF (50 μmol, 5 mol %). The vial was sealed with a rubber
septum, and a carbon monoxide pressure was bubbled through the
solution for 5 min. Then, the vial was immersed in an aluminum
heating block preheated to 80 °C. The reaction mixture was stirred at
this temperature for 30 min, at which point the vial was cooled to
room temperature and was opened to air. An aliquot of the reaction
1
for the Z isomer are as follows. H NMR (500 MHz, CDCl3, 292 K,
ppm): δ 5.47−5.31 (alkene CH, 2H, m), 2.06−2.02 (CH2, 2H, m),
1.61 (CH3, 2H, m), 1.39−1.21 (CH2, 12H, m), 0.90 (CH3, 3H, t,
3JH−H = 7.1 Hz). 13C NMR (126 MHz, CDCl3, 292 K, ppm): 130.9
(alkene CH), 123.6 (alkene CH), 29.7−29.4 (CH2, multiple peaks
overlap in this region), 26.9 (CH2), 22.8 (CH2), 14.1 (CH3), 12.7
(CH3).
1
mixture was removed from the crude reaction mixture for H NMR
Undec-9-en-1-ol (6e).8,50 The compound was purified on a short
pad of silica gel (hexane), and the product was obtained as a mixture of
isomers (111 mg, 65%). Undec-9-en-1-ol (6e) was present as 83%
(8.4:1 Z:E) of the mixture, and undec-10-en-1-ol (5e) remained as
11% of the mixture. The total percentage of higher internal alkenes
analysis. Approximatley 2% conversion of the hex-1-ene substrate was
observed.
Attempted Catalysis in the Presence of Added PPh3. In a
nitrogen atmosphere glovebox, an 8 mL vial was charged with hex-1-
ene (84 mg, 1 mmol), PPh3 (2−5 mol %), 500 μL of a 10 mM stock
solution of 3-cis in THF (5 μmol, 0.5 mol %), and 500 μL of a 100
mM stock solution of TsOH in THF (50 μmol, 5 mol %). The vial was
immersed in an aluminum heating block preheated to 80 °C. The
reaction mixture was stirred at this temperature for 30 min, at which
point the vial was cooled to room temperature and was opened to air.
An aliquot of the reaction mixture was removed from the crude
1
was 5%. Data for the Z isomer are as follows. H NMR (500 MHz,
CDCl3, 292 K, ppm): δ 5.43−5.30 (alkene CH, 2H, m), 3.56 (CH2,
3
2H, t, JH−H = 6.8 Hz), 2.57 (OH, 1H, s), 2.07−1.97 (2H, m), 1.91
(3H, m), 1.54−1.49 (2H, m), 1.38−1.19 (10H, m). 13C NMR (126
MHz, CDCl3, 292 K, ppm, selected peaks): δ 130.8 (alkene CH),
123.8 (alkene CH), 62.7 (CH2), 12.7 (CH3). Data for the E isomer are
1
1
reaction mixture for H NMR analysis. Approximately 2% conversion
as follows. H NMR (500 MHz, CDCl3, 292 K, ppm): δ 5.43−5.30
3
of the hex-1-ene substrate was observed when 2 or 5 mol % added
PPh3 was present.
Attempted Catalysis with Added TEMPO. In a nitrogen
(alkene CH, 2H, m), 3.56 (CH2, 2H, t, JH−H = 6.8 Hz), 2.57 (OH,
1H, s), 2.07−1.97 (2H, m), 1.91 (3H, m), 1.68−1.55 (2H, m), 1.38−
1.19 (10H, m). 13C NMR (126 MHz, CDCl3, 292 K, ppm, selected
peaks): δ 131.6 (alkene CH), 124.5 (alkene CH), 62.7 (CH2), 17.9
atmosphere glovebox, an 8 mL vial was charged with hex-1-ene (84
F
DOI: 10.1021/acs.organomet.7b00914
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Organometallics
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1
(CH3). Data for undec-8-en-1-ol (E and Z) are as follows. H NMR
(500 MHz, CDCl3, 292 K, ppm, selected peaks): δ 0.94−0.90 (CH3,
3H, m), 0.87−0.79 (CH3, 3H, m). 13C NMR (126 MHz, CDCl3, 292
K, ppm, selected peaks): δ 131.9 (alkene CH), 131.5 (alkene CH),
129.22 (alkene CH), 129.17 (alkene CH), 62.7 (CH2), 20.7 (CH2),
20.5 (CH2), 14.4 (CH3), 14.1 (CH3). Data for other resonances from
all present isomers are as follows. 13C NMR (126 MHz, CDCl3, 292 K,
selected peaks): δ 34.6, 34.5, 33.8, 32.7, 32.6, 31.6, 26.6, 29.6, 29.53,
29.52, 29.5, 29.4, 29.2, 29.1, 28.9, 26.8, 25.8, 25.2.
Pent-3-en-1-yloxymethylbenzene (6i).9,56 A 2 mol % portion of 3-
cis and 20 mol % of TsOH were used. The compound was purified on
a short pad of silica gel (hexane), and the product was obtained as a
mixture of isomers (146 mg, 90% yield). Pent-3-en-1-yloxymethyl-
benzene (6i) was present as approximately 83% of the mixture (3.1:1
Z:E), and pent-4-en-1-yloxymethylbenzene (5i) remained as 14% of
the mixture. The total percentage of higher internal alkenes was 2%.
Data for the Z isomer are as follows. 1H NMR (500 MHz, CDCl3, 292
K, ppm): δ 7.28−7.13 (Ar, 5H, m), 5.65−5.46 (alkene CH, 2H, m),
4.41 (CH2, 2H, s), 3.38 (CH2, 2H, m), 2.29 (CH2, 2H, m), 1.53 (CH3,
3H, m). 13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 138.5 (Ar),
128.4 (Ar), 127.9 (Ar), 127.7 (Ar), 126.5 (alkene CH), 125.9 (alkene
CH), 72.9 (CH2), 69.9 (CH2), 27.8 (CH2), 13.0 (CH3).
Undec-9-en-1-yl Propionate (6f).52 A 1 mol % portion of 3-cis and
10 mol % of TsOH were used. The compound was purified on a short
pad of silica gel (hexane), and the product was obtained as a mixture of
isomers (139 mg, 62%). Undec-9-en-1-yl propionate (6f) was present
as 57% of the mixture, and undec-10-en-1-yl propionate (5f) remained
as 34% of the mixture. The total percentage of higher internal alkenes
Pent-3-enoic Acid (6j).57−59 The compound was purified on a short
pad of silica gel (pentane), and the product was carefully evaporated to
obtain as a mixture of isomers (34 mg, 34% yield). 6j was present as
76% of the mixture (2.8:1 E:Z). Pent-4-enoic acid (5j) remained as
20% of the mixture. Pent-2-enoic acid was present as 20% of the
1
was 9%. Data for the Z isomer are as follows. H NMR (500 MHz,
3
CDCl3, 292 K, ppm): δ 5.46−5.31 (m, 2H), 4.04 (t, JH−H = 6.8 Hz,
2H), 2.30 (q, 3JH−H = 7.5 Hz, 2H), 2.02 (m, 2H), 1.60 (m, 2H), 1.39−
1.21 (m, 12H), 1.12 (t, J = 7.6 Hz, 3H). 13C NMR (126 MHz, CDCl3,
292 K, ppm): δ 174.3 (CO), 130.6 (alkene CH), 123.5 (alkene CH),
64.3 (CH2), 33.7 (CH2), 29.5 (CH2), 29.4 (CH2), 29.4 (CH2), 29.2
(CH2), 29.1 (CH2), 29.0 (CH2), 28.9 (CH2), 28.6 (CH2), 27.5 (CH2),
26.7 (CH2), 25.9 (CH2),12.6 (CH3), 9.0 (CH3).
1
mixture. Data for the E isomer are as follows. H NMR (500 MHz,
CDCl3, 292 K, ppm): δ 10.4 (COOH, 1H, br s), 5.65−5.49 (alkene
CH, 2H, m), 3.06 (CH2, 2H, m), 1.70 (CH3, 3H, dq, 3JH−H = 6.2, 1.3
Hz). 13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 178.9 (CO), 130.1
(alkene CH), 121.9 (alkene CH), 37.8 (CH2), 17.9 (CH3). Data for
1
1-Phenylhex-4-en-1-ol (6g).53−55 A 1 mol % portion of 3-cis and
10 mol % of TsOH were used. The compound was purified on a short
pad of silica gel (hexane), and the product was obtained as a mixture of
isomers (148 mg, 84% yield). 1-Phenylhex-4-en-1-ol (6g) was present
as approximately 63% of the mixture (2.3:1 Z:E). 1-phenylhex-5-en-1-
ol (5g) remained as 21% of the mixture. 1-Phenylhex-5-en-1-ol (2.3:1
Z:E) constituted the majority of the remaining 16% of the mixture.
Data for the Z isomer are as follows. 1H NMR (500 MHz, CDCl3, 292
K, ppm): δ 7.29−7.04 (Ar, 5H, m), 5.44−5.24 (alkene CH, 2H, m),
4.59−4.49 (CH, 1H, m), 2.07−1.88 (CH2, 2H, m), 1.7−1.5 (CH2, 2H,
m), 1.48 (CH3, 3H, m). 13C NMR (126 MHz, CDCl3, 292 K, ppm): δ
144.7 (Ar), 129.7 (Ar), 128.3 (alkene CH), 127.4 (Ar), 125.8 (Ar),
124.5 (alkene CH), 74.0 (CH), 38.6 (CH2), 23.2 (CH2), 12.7 (CH3).
Data for the E isomer are as follows. 1H NMR (500 MHz, CDCl3, 292
K, ppm): δ 7.29−7.04 (Ar, 5H, m), 5.44−5.24 (alkene CH, 2H, m),
4.59−4.49 (CH, 1H, m), 2.00−1.89 (CH2, 2H, m), 1.7−1.5 (CH2, 2H,
m), 1.48 (CH3, 3H, m).13C NMR (126 MHz, CDCl3, 292 K, ppm): δ
144.0 (Ar), 130.6 (alkene CH), 128.3 (Ar), 127.3 (Ar), 125.81 (Ar),
125.76 (alkene CH), 73.9 (CH), 38.4 (CH2), 28.8 (CH2), 17.9 (CH3).
Data for (Z)-1-phenylhex-3-en-1-ol are as follows. 1H NMR (500
MHz, CDCl3, 292 K, ppm, selected peaks): δ 2.32−2.26(CH2, 2H, m),
0.79 (CH3, 3H, t, 3JH−H = 7.5 Hz). 13C NMR (126 MHz, CDCl3, 292
K, ppm, selected peaks): δ 125.0 (alkene CH), 73.8 (CH), 42.5
(CH2), 25.6 (CH2), 14.0 (CH3). Data for (E)-1-phenylhex-3-en-1-ol
the Z isomer are as follows. H NMR (500 MHz, CDCl3, 292 K,
ppm): δ 10.4 (COOH, 1H, br s), 5.65−5.49 (alkene CH, 2H, m), 3.14
(CH2, 2H, m), 1.64 (CH3, 3H, m). 13C NMR (126 MHz, CDCl3, 292
K, ppm): δ 178.7 (CO), 128.2 (alkene CH), 119.6 (alkene CH), 32.4
1
(CH2), 25.4 (CH2). Data for (E)-pent-2-enoic acid are as follows. H
NMR (500 MHz, CDCl3, 292 K, ppm): δ 10.4 (COOH, 1H, br s),
3
3
7.14 (alkene CH, 1H, dt, JH−H = 15.5, JH−H = 6.3 Hz), 5.87−5.78
(alkene CH, 1H, m), 2.29−2.20 (CH2, 2H, m), 1.08 (CH3, 3H, t,
3JH−H = 7.5 Hz). 13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 172.4
(CO), 153.9 (alkene CH), 120.9 (alkene CH), 25.4 (CH2), 12.0
(CH3).
Hex-4-en-2-ol (6k).60−63 The compound was purified on a short
pad of silica gel (pentane), and the product was carefully evaporated to
obtain as a mixture of isomers (79 mg, 79% yield). Hex-4-en-2-ol (6k)
was present as approximately 73% of the mixture (2.1:1 E:Z). Hex-5-
en-1-ol (5k) remained as 3% of the mixture. Higher internal isomers
(hex-3-en-2-ol) that were observed constituted 23% of the mixture.
The greater percentage of hex-3-en-2-ol observed in the purified
mixture is likely due to the greater volatility of 6k in comparison to
1
hex-3-en-2-ol. Data for the E isomer are as follows. H NMR (500
MHz, CDCl3, 292 K, ppm): δ 5.58−5.51 (alkene CH, 1H, m), 5.45−
5.37 (alkene CH, 1H, m), 3.75−3.70 (CH, 1H, m), 2.20−2.13 (CH2,
1H, m), 2.10−1.99 (CH2, 1H, m), 1.74 (OH, 1H, br s), 1.70−1.65
3
(CH3, 3H, m), 1.16 (CH3, 3H, d, JH−H = 6.2 Hz). 13C NMR (126
1
MHz, CDCl3, 292 K, ppm): δ 128.9 (alkene CH), 127.1 (alkene CH),
67.2 (CH), 42.5 (CH2), 22.6 (CH3), 18.0 (CH3). Data for the Z
are as follows. H NMR (500 MHz, CDCl3, 292 K, ppm, selected
peaks): δ 2.39−2.32 (CH2, 2H, m), 0.87 (CH3, 3H, t, 3JH−H = 7.5 Hz).
13C NMR (126 MHz, CDCl3, 292 K, ppm, selected peaks): δ 125.4
(alkene CH), 73.5 (CH), 42.7 (CH2), 25.5 (CH2), 13.7 (CH3).
Pent-3-en-1-yloxybenzene (6h). A 1 mol % portion of 3-cis and 10
mol % of TsOH were used. The compound was purified on a short
pad of silica gel (hexane), and the product was obtained as a mixture of
isomers (146 mg, 90% yield). Pent-3-en-1-yloxybenzene (6h) was
present as 66% of the mixture (6.3:1 Z:E). Pent-4-en-1-yloxybenzene
(5h) remained as 33% of the mixture. Higher internal isomers that
were observed constituted <1% of the mixture. Data for the Z isomer
are as follows. 1H NMR (500 MHz, CDCl3, 292 K, ppm): δ 7.34−7.30
(Ar, 2H, m), 6.99−6.93 (Ar, 3H, m), 5.69−5.60 (alkene CH, 1H, m),
5.59−5.50 (alkene CH, 1H, m), 4.02−3.99 (CH2, 2H, m), 2.59 (CH2,
2H, m), 1.71 (CH3, 3H, m). 13C NMR (126 MHz, CDCl3, 292 K,
ppm): δ 158.9 (Ar), 129.4 (Ar), 126.6 (CH), 125.7 (CH), 120.6 (Ar),
114.5 (Ar), 67.2 (CH2), 27.2 (CH2), 12.9 (CH3). Data for the E
1
isomer are as follows. H NMR (500 MHz, CDCl3, 292 K, ppm): δ
5.67−5.59 (alkene CH, m, 1H), 3.82 (CH, 1H, m), 2.28−2.20 (CH2,
3
1H, m), 1.63 (CH3, 3H, m), 1.19 (CH3, 3H, d, JH−H = 6.2 Hz). 13C
NMR (126 MHz, CDCl3, 292 K, ppm): δ 127.1 (alkene CH), 126.1
(alkene CH), 67.7 (CH), 36.7 (CH2), 22.7 (CH3), 13.0 (CH3).
Ethyl 2-Methylpent-3-enoate (6l).33,64 A 1 mol % portion of 3-cis
and 10 mol % of TsOH were used. The compound was purified on a
short pad of silica gel (hexane), and the product was obtained as a
mixture of isomers (40 mg, 28% yield). Ethyl 2-methylpent-3-enoate
(6l) was present as 65% of the mixture (13:1 E:Z). Ethyl 2-
methylpent-4-enoate (5l) remained as 5% of the mixture. Higher
internal isomers (ethyl 2-methylpent-2-enoate) constituted 16% of the
mixture. The greater percentage of ethyl 2-methylpent-2-enoate
observed in the purified mixture is likely due to the greater volatility
of 6l in comparison to ethyl 2-methylpent-2-enoate. Data for the E
1
1
isomer are as follows. H NMR (500 MHz, CDCl3, 292 K, ppm): δ
isomer are as follows. H NMR (500 MHz, CDCl3, 292 K, ppm): δ
3
5.58−5.47 (alkene CH, 2H, m), 4.11 (CH2, 2H, q, JH−H = 10.7 Hz,
7.34−7.30 (Ar, 2H, m), 6.99−6.93 (Ar, 3H, m), 5.69−5.60 (alkene
CH, 1H, m), 5.59−5.50 (alkene CH, 1H, m), 4.02−3.99 (CH2, 2H,
m), 2.51 (CH2, 2H, m), 1.73 (CH3, 3H, m). 13C NMR (126 MHz,
CDCl3, 292 K, ppm): δ 159.0 (Ar), 126.8 (CH), 127.7 (CH), 67.0
(CH2), 32.6 (CH2), 18.1 (CH3).
3JH−H = 7.1 Hz), 1.69−1.64 (CH3, m, 3H), 1.26−1.19 (CH3, m, 6H).
13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 175.1 (CO), 130.0
(alkene CH), 126.7 (alkene CH), 62.9 (CH), 60.4 (CH2), 17.9 (CH3),
17.4 (CH3), 14.2 (CH3). Data for ethyl 2-methylpent-2-enoate (E and
G
DOI: 10.1021/acs.organomet.7b00914
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Z) are as follows. 1H NMR (500 MHz, CDCl3, 292 K, ppm): δ 6.75−
6.71 (alkene CH, 1H, m), 4.20−4.15 (CH2), 3.10−3.02 (Z, CH2, 2H,
m), 2.20−2.12 (E, CH2, 2H, m), 1.81 (CH3, 3H, s), 1.28 (CH3, 3H, t,
2.35 (CH2, 2H, m), 0.98 (CH3, 3H, t, 3JH−H = 7.5 Hz). Data for (E)-2-
(but-1-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane are as follows.
1H NMR (500 MHz, CDCl3, 292 K, ppm, selected peaks): δ 6.69
(alkene CH, 1H, dt, 17.8, 5.8 Hz).
3
3JH−H = 7.2 Hz), 1.04 (CH3, 3H, t, JH−H = 7.6 Hz).13C NMR (126
MHz, CDCl3, 292 K, ppm): δ 168.3 (CO), 143.7 (alkene CH), 127.2
(alkene C), 60.4 (CH2), 42.7 (Z, CH2), 32.0 (E, CH2), 21.9 (CH2),
13.04 (CH3), 12.96 (CH3), 12.2(CH3).
1-Fluoro-4-(penta-1,4-dien-1-yl)benzene (6r). The compound is
analogous to (penta-1,4-dien-1-yl)benzene.69,70 The compound was
purified on a short pad of silica gel (hexane), and the product was
obtained as a mixture of isomers (102 mg, 58%). 1-Fluoro-4-(penta-
1,4-dien-1-yl)benzene (6r) was present as approximately 64% of the
mixture (5.3:1 Z:E), and 1-fluoro-4-(penta-1,5-dien-1-yl)benzene (5r)
remained as 28% of the mixture. The total percentage of higher
internal alkenes was approximately 8%. Data for the Z isomer are as
But-2-en-1-ylbenzene (6m).10 A 2 mol % portion of 3-cis and 20
mol % of TsOH were used. The compound was purified on a short
pad of silica gel (hexane), and the product was obtained as a mixture of
isomers (130 mg, 98% yield). 6m was present as 76% of the mixture
(5.4:1 Z:E). 5m remained as 16% of the mixture. But-1-en-1-ylbenzene
was present as 8% of the mixture (5.8:1 Z:E). Data for the Z isomer
are as follows. 1H NMR (500 MHz, CDCl3, 292 K, ppm): δ 7.22−7.19
(Ar, 2H, m), 7.13−7.09 (Ar, 3H, m), 5.52 (alkene CH, 2H, m), 3.34
1
follows. H NMR (500 MHz, CDCl3, 292 K, ppm): δ 7.18−7.08 (Ar,
2H, m), 6.96−6.90 (Ar, 2H, m), 6.90−6.88 (alkene CH, 1H, m),
5.61−5.52 (alkene CH, 1H, m), 5.42−5.39 (alkene CH, 1H, m),
5.39−5.32 (alkene C H, 1H, m), 2.93 (CH2, 2H, m), 1.53−1.50 (CH3,
3H, m). 13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 131.0 (alkene
CH), 128.1 (alkene CH), 125.0 (alkene CH), 26.8 (CH2), 13.1
3
(CH2, 2H, d, JH−H = 5.5 Hz), 1.65 (CH3, 3H, m). 13C NMR (126
MHz, CDCl3, 292 K, ppm): δ 141.2 (i-Ar), 129.0, 128.4, 128.33,
128.28, 125.8, 124.8, 33.1, 12.8. Data for the E isomer are as follows.
1H NMR (500 MHz, CDCl3, 292 K, ppm): δ 7.22−7.19 (Ar, 2H, m),
7.13−7.09 (Ar, 3H, m), 5.52 (alkene CH, 2H, m), 3.24 (CH2, 2H, d,
3JH−H = 6.5 Hz), 1.61 (CH3, 3H, m).
1
(CH3). Data for the E isomer are as follows. H NMR (500 MHz,
CDCl3, 292 K, ppm): δ 2.89−2.83 (CH2, 2H, m), 1.61−1.56 (CH3,
3H, m).
Prop-1-en-1-ylbenzene (6n).65 A 1 mol % portion of 3-cis and 10
mol % of TsOH were used. The compound was purified on a short
pad of silica gel (hexane), and the product was obtained as a mixture of
isomers (64 mg, 54%). 6n was present as 71% of the mixture (1.6:1
Z:E), and allylbenzene remained as 15% of the mixture. Data for the Z
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.7b00914.
1
isomer are as follows. H NMR (500 MHz, CDCl3, 292 K, ppm): δ
7.38−7.28 (Ar, 3H, m), 7.25−7.17 (Ar, 2H, m), 6.49−6.44 (alkene
CH, 1H, m), 5.81 (alkene CH, 1H, dq, 3JH−H = 11.8, 3JH−H = 7.2 Hz),
1.93 (CH3, 3H, dd, J = 7.3, 1.9 Hz). 13C NMR (126 MHz, CDCl3, 292
K, ppm): δ 137.6, 129.8, 128.8, 128.1, 126.8, 126.4, 14.6. Data for the
E isomer are as follows. 1H NMR (500 MHz, CDCl3, 292 K, ppm): δ
7.38−7.28 (Ar, 3H, m), 7.25−7.17 (Ar, 2H, m), 6.44−6.40 (alkene
CH, 1H, m), 6.25 (alkene CH, 1H, dq, 3JH−H = 15.8, 3JH−H = 6.5 Hz),
Characterization of potential catalyst intermediates,
NMR spectral data for products, and crystal structure
report for 4d (PDF)
Accession Codes
CCDC 1577757 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 Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336033.
3
3
1.89 (CH3, 3H, dd, JH−H = 6.6, JH−H = 1.6 Hz).
Trimethyl(prop-1-en-1-yl)silane (6o).9 A 1 mol % portion of 3-cis
and 10 mol % TsOH were used. The compound was not isolated due
to high volatility. The spectroscopic data agree with the literature.
1-(pent-3-en-1-yl)piperidine (6p). The crude reaction mixture was
filtered, and a beige solid was collected and rinsed with ∼1 mL of THF
and then Et2O. Residual free amine was removed in vacuo to yield a
mixture of isomers (177 mg, 93%). The mixture of alkenes contained
1-(pent-3-en-1-yl)piperidine (80%), 1-(pent-4-en-1-yl)piperidine
AUTHOR INFORMATION
Corresponding Author
*E-mail for G.E.D.: dob@temple.edu.
■
1
(12%), and 1-(pent-2-en-1-yl)piperidine (8%). H NMR (500 MHz,
CDCl3, 292 K, ppm): δ 11.9−11.6 (NH, 1H, br s), 5.59−5.47 (alkene
CH, 1H, m), 5.29−5.19 (alkene CH, 1H, m), 3.51−3.35 (CH2, 2H,
m), 2.85−2.56 (CH2, 2H, m), 2.71−2.47 (CH2, 4H, m), 2.25−2.11
(CH2, 2H, m), 1.86−1.71 (CH2, 3H, m), 1.56 (CH3, 3H, t, 3JH−H = 6.9
Hz), 1.44−1.29 (CH2, 1H, m). 13C NMR (126 MHz, CDCl3, 292 K,
ppm): δ 129.3 (E, alkene CH), 128.2 (Z, alkene CH), 124.6 (E, alkene
CH), 123.5 (Z, alkene CH), 56.4, 53.0, 52.9, 26.7, 22.43, 22.40, 22.3.
17.9 (E, CH3), 12.9 (Z, CH3).
ORCID
Graham E. Dobereiner: 0000-0001-6885-2021
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Science Foundation
(CHE-1565721). Acknowledgment is made to the Donors of
the American Chemical Society Petroleum Research Fund for
partial support of this research. Support for the NMR facility at
Temple University by a CURE grant from the Pennsylvania
Department of Health is gratefully acknowledged. We acknowl-
edge the support of the Temple University Diamond Research
Scholars Program (O.D.G.).
2-(But-2-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(6q).10,66−69 The compound was purified on a short pad of silica gel
(Et2O), and the product was obtained as a mixture of isomers (171
mg, 94%). The mixture of alkenes contained the title compound (6r,
78%), unreacted starting material (5r, 21%), and the respective 3-
alkene (9%, 1.7:1 Z:E). Data for the Z isomer are as follows. 1H NMR
(500 MHz, CDCl3, 292 K, ppm): δ 5.52−5.42 (alkene CH, 2H, m),
3
1.66 (CH2, 2H, d, JH−H = 7.3 Hz), 1.59 (CH3, 3H, m), 1.24 (CH3,
12H, s). 13C NMR (126 MHz, CDCl3, 292 K, ppm): δ 124.9 (alkene
CH), 123.6 (alkene CH), 83.0 (C(CH3)2), 24.6 (CH31), 12.4 (CH3).
11.3 (CH2, br s). Data for the E isomer are as follows. H NMR (500
MHz, CDCl3, 292 K, ppm, selected peaks): δ 5.52−5.33 (alkene CH,
2H, m), 1.64−1.61 (CH2, CH3, 5H). 13C NMR (126 MHz, CDCl3,
292 K, ppm): δ 125.7 (alkene CH), 125.1 (alkene CH), 83.0
(C(CH3)2), 24.6 (CH3), 12.4 (CH3). Data for 3(Z)-2-(but-1-en-1-yl)-
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DOI: 10.1021/acs.organomet.7b00914
Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.7b00914
Organometallics XXXX, XXX, XXX−XXX