Triarylphosphine ligands with hemilabile alkoxy groups: Ligands for nickel(II)-catalyzed olefin dimerization reactions. hydrovinylation of vinylarenes, 1,3-dienes, and cycloisomerization of 1,6-dienes

Article abstract of DOI:10.1002/adsc.201400237

Substitution of one of the phenyl groups of triphenylphosphine with a 2-benzyloxy-, 2-benzyloxymethyl- or 2-benzyloxyethyl-phenyl moiety results in a set of simple ligands, which exhibit strikingly different behaviour in various nickel(II)-catalyzed olefin dimerization reactions. Complexes of ligands with 2-benzyloxyphenyl- and 2-benzyloxymethylphenyldiphenylphosphine (L5 and L6, respectively) are most active for hydrovinylation (HV) of vinylarenes, with the former leading to extensive isomerization of the primary 3-aryl-1-butenes into the conjugated 2-aryl-2-butenes even at -55 °C. However, 2-benzyloxymethyl-substituted ligand L6 is slightly less active, affording up to quantitative yields of the primary products of HV at ambient temperature with no trace of isomerization, thus providing the best option for a practical synthesis of these compounds. In sharp contrast, hydrovinylation of a variety of 1,3-dienes is best catalyzed by nickel(II) complexes of 2- benzyloxyphenyldiphenylphosphine, L5. The other two ligands, 2-benzyloxymethyl- (L6) and 2-benzyloxyethyldiphenylphosphine (L7) are much less effective in the HV of 1,3-dienes. Nickel(II)-catalyzed cycloisomerization of 1,6-dienes into methylenecyclopentanes, a reaction mechanistically related to the other hydrovinylation reactions, is also uniquely effected by nickel(II) complexes of L5, but not of L6 or L7. In an attempt to prepare authentic samples of the methylencyclohexane products, nickel(II) complexes of N-heterocyclic carbene ligands were examined. In sharp contrast to the phosphines, which give the methylenecyclopentanes, methylenecyclohexanes are the major products in the (N-heterocyclic carbene)nickel(II)-mediated reactions.

Full text of DOI:10.1002/adsc.201400237

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DOI: 10.1002/adsc.201400237
Triarylphosphine Ligands with Hemilabile Alkoxy Groups:
Ligands for Nickel(II)-Catalyzed Olefin Dimerization
Reactions. Hydrovinylation of Vinylarenes, 1,3-Dienes, and
Cycloisomerization of 1,6-Dienes
Souvagya Biswas,a Aibin Zhang,a Balaram Raya,a and T. V. RajanBabua,*
a
Department of Chemistry and Biochemistry, The Ohio State University, 100 West 18thAvenue, Columbus, Ohio 43210,
USA
Fax : (+1)-614-292-1685; phone: (001)-614-688-3543; e-mail: rajanbabu.1@osu.edu
Received: March 9, 2014; Revised: April 29, 2014; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400237.
Abstract: Substitution of one of the phenyl groups of yphenyldiphenylphosphine, L5. The other two li-
triphenylphosphine with a 2-benzyloxy-, 2-benzyloxy- gands, 2-benzyloxymethyl- (L6) and 2-benzyloxye-
methyl- or 2-benzyloxyethyl-phenyl moiety results in thyldiphenylphosphine (L7) are much less effective
a set of simple ligands, which exhibit strikingly differ- in the HV of 1,3-dienes. Nickel(II)-catalyzed cycloi-
ent behaviour in various nickel(II)-catalyzed olefin somerization of 1,6-dienes into methylenecyclopen-
dimerization reactions. Complexes of ligands with 2- tanes, a reaction mechanistically related to the other
benzyloxyphenyl- and 2-benzyloxymethylphenyldi- hydrovinylation reactions, is also uniquely effected
phenylphosphine (L5 and L6, respectively) are most by nickel(II) complexes of L5, but not of L6 or L7.
active for hydrovinylation (HV) of vinylarenes, with In an attempt to prepare authentic samples of the
the former leading to extensive isomerization of the methylencyclohexane products, nickel(II) complexes
primary 3-aryl-1-butenes into the conjugated 2-aryl- of N-heterocyclic carbene ligands were examined. In
2-butenes even at À558C. However, 2-benzyloxy- sharp contrast to the phosphines, which give the
methyl-substituted ligand L6 is slightly less active, af- methylenecyclopentanes, methylenecyclohexanes are
fording up to quantitative yields of the primary prod- the major products in the (N-heterocyclic car-
ucts of HV at ambient temperature with no trace of
isomerization, thus providing the best option for
a practical synthesis of these compounds. In sharp
ACHTUNGTRENNbUNG ene)nickel(II)-mediated reactions.
contrast, hydrovinylation of a variety of 1,3-dienes is Keywords: cycloisomerization; dienes; hemilabile li-
best catalyzed by nickel(II) complexes of 2-benzylox- gands; hydrovinylation; ligand effects; nickel
Introduction
During these investigations we concentrated most
of our efforts on the development of asymmetric var-
Our attempts to find new protocols for the Ni(II)-cat- iants of these reactions, and, thus on enantio-pure li-
alyzed asymmetric hydrovinylation (HV)[1] of activat- gands. For the synthesis of racemic mixtures of the
ed alkenes such as vinylarenes,[2] 1,3-dienes,[3] and products, we often resorted to the original protocol
bicycloACHTUNGTRENNUNG
[2.2.1]heptenes[4] have resulted in the identifi- that was developed for the HV of vinylarenes, which
cation of several different types of ligands that are ca- involved the use of a combination of [(allyl)NiBr]2,
pable of effecting this remarkable transformation Ph3P and AgOTf [Eq. (1)][2a] or, in some cases, the
with very high efficiency and selectivity (Scheme 1). use of the more expensive 1:1 mixture of the enantio-
These include 2’-alkoxy-1-diarylphosphino-1,1’-bi- pure ligands with a Ni(II) precursor. While these have
naphthyl derivatives (L1),[2a] 1-aryl-2,5-dialkylphos- been reliable procedures and served our purpose well,
pholanes (L2),[2b,c] phosphoramidites derived from occasionally we faced difficulties with the former pro-
1,1’-biaryl-2,2’-dihydroxy compounds (L3),[2e,f,5] and di- tocol [Eq. (1)] due to the extreme sensitivity of the
arylphosphinites derived from readily available mono- reaction to temperature, especially in the case of reac-
saccharides (L4) (Figure 1).[6]
tions of vinylarenes. Unless the temperature is rigor-
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Scheme 1. Selected examples of asymmetric hydrovinylation of alkenes.
Figure 1. Assorted ligands for asymmetric hydrovinylation reactions.
This subtle variation in the ligand has a dramatic
effect on the efficiency and selectivity of several HV
reactions. Such ligand effects extend to a mechanisti-
cally related cycloisomerization of 1,6-dienes. Here
we report the results of these studies.
Before we document these results, it should be em-
phasized that thanks to investigations by several
groups during the past decade, asymmetric hydroviny-
lations of a number of alkenes (Scheme 1) have been
satisfactorily accomplished.[1–5] What then, the reader
might wonder, is the point of this paper which deals
ously maintained (À508C to À568C) in this moderate- with synthesis of racemic products. We submit that
ly exothermic reaction, in addition to the expected there is great value in the unequivocal demonstration
product 2, varying amounts of an isomerization prod- of significant ligand effects brought on by operation-
uct, 3 and a dimer, 4[7] are formed as impurities. We ally simple changes in widely used ligands such as tri-
wondered whether we could design a simple, yet phenylphosphine. We expect this to have value
more robust phosphine ligand based on our recogni- beyond the reactions described here. Besides, hemila-
tion[2b] of the role of an appropriately placed hemila- bile ligands have attracted considerable attention in
bile ligating atom in this reaction. Accordingly, we homogeneous catalysis, and the results described in
prepared a series of 2-alkoxyaryl- and 2-(alkoxyalky- this paper add to a growing list of highly selective re-
l)aryl-diphenylphosphines [Eq. (2), L5, L6, L7] in actions catalyzed by this class of ligands.[8]
which the hemilabile oxygen atom is placed on a b-,
g- or d-carbon in relation to the chelating phosphine.
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Triarylphosphine Ligands with Hemilabile Alkoxy Groups
Table 1. Effect of ligands on Ni(II)-catalyzed hydrovinylation of 4-methylstyrene (6b).[a]
Entry
Ligand
Temp. [oC]
Time [h]
Conv. [%]
Products (Yield [%])
Selectivity (% 7)
1a
1b
1c
1d
À55
23
2
20
2
>99
67
0
<4
70
33
>99
0
67
0
–
>99
À55
<4[b,c]
>99[d]
À55
2
29
70
2a
2b
À55
16
11
<0.5
>99
<0.5
>99
–
0
–
>99
23
3a
3b
À55
16
11
0
80
0
72
0
2
–
23
97[e]
[a]
see Eq. (3) for procedure. See Supporting Information for GC traces.
Using AgOTf.
Rest starting material.
Using AgSbF6.
~4% dimer and ~2% isomerization.
[b]
[c]
[d]
[e]
Results and Discussion
Ligand Effects on Hydrovinylation of Vinylarenes
Our initial investigations of styrene and 4-methylstyr-
ene as prototypical substrates using the previously dis-
closed catalyst system [(allyl)NiBr]2/Ph3P/AgOTf
showed the extreme sensitivity of the reaction to tem-
perature changes [Eq. (1)]. While at À788C (6 h)
there is very low conversion of styrene, at room tem- from the entries 1–3, the activities of the putative
perature, extensive isomerization of the initially [(allyl)NiL]ACTHNUTRGNE[UNG BARF] complexes as catalysts for the hy-
formed product 2 to a mixture of 2-aryl-2-butenes (3) drovinylation reaction are dramatically different de-
and formation of a styrene dimer (4) are observed. pending on L. The ortho-benzyloxyphenyldiphenyl-
The same result is observed when AgSbF6 or phosphine (L5) complex is the most active ligand,
NaBARF replaces AgOTf. Varying amounts of these even more active than the [(allyl)NiACTHNUTRGENN(UG Ph3P)]ACHTUNGTRENNUNG[OTf],
side products are observed at intermediate tempera- used in the original protocol [Eq. (1)]. This catalyst
tures, and the reaction was eventually optimized for with L5 not only effects the hydrovinylation of 4-
a series of vinylarenes where these products were methylstyrene at À558C, but it also promotes further
found to be virtually absent around À558C.[2a]
isomerization of the primary product 7b at this low
We turned our attention to the ligands L5, L6 and temperature (entry 1a) giving up to 33% of a conjugat-
L7, each carrying a hemilabile oxygen with the hope ed product 8b as a mixture of E- and Z-isomers in
of finding a HV protocol under ambient conditions, a ratio of 2.0:1.2.[9] At room temperature (entry 1b)
without the complications of isomerization of the an exceptionally clean reaction ensues giving a mix-
double bond or the dimerization reaction. These aryl- ture of the isomerized products Z-8 and E-8 with
diphenylphosphino ligands were readily synthesized none of the primary product 7b. We also noticed
from the corresponding bromoaryl derivatives by lith- a very significant salt effect in these reactions. While
ium-bromine exchange followed by treatment with AgOTf, with a coordinating counter ion, is ineffective
Ph2PCl at low temperature [Eq. (2)].
in conjunction with a hemilabile ligand (entry 1c),
Ligands L5, L6 and L7 were examined in the hy- AgSbF6 with a more dissociating anion is a suitable
drovinylation of a number of vinylarenes including 4- replacement for NaBARF (entry 1d).
methylstyrene, using the procedure shown in Eq. (3).
In sharp contrast to L5, the (ortho-benzyloxyme-
The illustrative results are shown in Table 1. As seen thyl)phenyldiphenylphosphine (L6) promotes only
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Table 2. Use of 2-benzyloxymethylphenyldiphenylphosphine (L6) for room temperature HV of vinylarenes.[a]
Entry
Vinylarenes (6)
Cat. (equiv.)
Time [h]
Yield [%]
Regiosel. (% 7)
1
2
3
4
5
6
7
8
9
styrene (6a)
4-Me-styrene (6b)
3-F-4-Ph-styrene (6c)
3-PhC(O)-styrene (6d)
2-vinyl-6-MeO-naphthalene (6e)
2-vinylfuran (6f)
3-vinylfuran (6g)
4-Br-styrene (6h)
4-MeO-styrene (6i)
2,3-(MeO)2-4-Me-styrene (6j)
0.007
0.007
0.014
0.014
0.014
0.007
0.007
0.014
0.007
0.007
15
11
20
20
64
2
>98
>99
89[c]
>98[b]
>98
>99
>99
>99
>99
>99
87[b]
83[c]
>99
>90[d]
>90[d]
98
2
48
72
44
>99
87[b]
[c]
10
>99
[a]
See Eq. (3) for procedure. Ratios of products determined by GC and NMR. See the Supporting Information for GC
traces.
[b]
[c]
[d]
Rest isomerized product.
Rest starting material.
Volatile product prone to polymerization.
a sluggish reaction at À558C, requiring a prolonged ence in the reactivities of the three ligands is shown
period (~11 h) at room temperature for complete in Eq. (4). The less reactive complexes of ligands L6
conversion of the starting material (entry 2).[9] Most and L7 gave very low conversions. Under otherwise
gratifyingly, unlike many other ligand systems we have
examined, there is no sign of isomerization of the pri-
mary product, 7, to 8 even at room temperature.[5c] Di-
merization of the vinylarenes[7] was also not observed.
Ligand L7, with an ethano-bridge between the
oxygen and the aryl moiety, behaves like L6, except
that the corresponding Ni(II) complex is much less re-
active (Table 1, entries 3a and 3b). At room tempera-
ture under conditions that gave ~100% conversion
using L6, this ligand showed only ~80% conversion
(entry 2b vs. 3b),[9] with up to 4% dimerization, in ad-
dition to ~2% isomerization of the primary product.
The modified procedure [Eq. (3)] for hydrovinyla-
tion using ligand L6 was applied to several vinylar-
enes and the results are shown in Table 2.[9] As ex-
pected, most vinylarenes react with ethylene (1 atm)
at room temperature to give nearly quantitative yields identical conditions, the electron-deficient vinylarenes
of the HV products (3-aryl-1-butenes, 7). Electroni- 10c gave a lower yield. For comparison, Ph3P/AgOTf
cally deactivated vinylarenes (entries 3, 4, 8, Table 2) under identical conditions returned no product,
and those with Lewis basic substituents (entries 5, 9 whereas Ph3P/NaBARF gave a low yielding reaction
and 10) react slower compared to electron-rich ones. with significant isomerization of the starting material
Activated substrates such as 2- and 3-vinylfurans un- to a trisubstituted alkene. The ligand L5 facilitates
dergo very fast reactions (<2 h at room temperature) the conversion of 1-methylenetetraline (11) to the
to give >99% yield of the expected products (en- corresponding adduct 12 [Eq. (5)]. A minor side
tries 6 and 7). Substrates that need prolonged reaction product in the reaction has been identified as the iso-
times (e.g., 4-bromostyrene and 4-methoxystyrene) do
undergo competitive isomerization of the primary
product to give varying amounts of the 2-aryl-2-bu-
tenes (8). Most notably, even in these cases the yields
of the primary products are quite acceptable.
Finally, the enhanced reactivity of the ligand L5 has
one other significant application where the isomeriza-
tion is not a competitive process. This is in the room
temperature-HV of 1-alkylstyrenes, which generate an
all-carbon quaternary center.[10] The dramatic differ-
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merized product 13. Here also a catalyst prepared
from [(allyl)NiBr]2, Ph3P and AgOTf gave no prod-
ucts.
Ligand Effects on Hydrovinylation of 1,3-Dienes
Nickel(II)-catalyzed HV of 1,3-cyclooctadiene is one
of the first metal-catalyzed asymmetric reactions ever
reported[11] even though the useful levels of selectivi-
ties were achieved only recently.[1a] Alternate proce-
dures using Ru[12] and Co[13] as catalysts have recently
appeared. In connection with our own work in the
Ni(II)-catalyzed asymmetric HV of selected 1,3-
dienes using phospholane (L2) and phosphoramidite
These ligand effects are further confirmed by the
(L3) complexes of Ni(II), we have briefly reported on hydrovinylation of two other prototypical 1,3-dienes,
the use of ligand L5 for the synthesis of authentic rac- 1,3-cyclohexadiene (16) and the benzopyran deriva-
emic products.[3a] A comparison of the efficacy of this tive (18) [Eq. (7) and Eq. (8)].[9] Other results
ligand with that of L6 and L7 in the Ni(II)-catalyzed (Table 3, entries 1–6) are included here for the sake
HV of a prototypical 1,3-diene, 4-tert-butyl-1-vinylcy- of completion.[3a,b] Entries in column 5 of Table 3 con-
clohexene (14), is shown in Eq. (6).
firm the utility of L5 as an excellent ligand for the
1,2-hydrovinylation of a broad class of 1,3-dienes.
Only 1-vinylcyclohexene 20 and estrone-derived diene
30 gave a mixture of 1,2- and 1,4-hydrovinylation
products.
Ligand Effects on Cycloisomerization of 1,6-Dienes
Soon after the discovery of the original HV protocol
[Eq. (1)], we reported[15a] that these conditions can be
modified to effect cycloisomerization of 1,6-dienes to
methylenecyclopentanes, examples of which are
shown in Eq. (9) and Eq. (10).[15,16] Both [(allyl)NiBr]2
and a related palladium source, [(allyl)PdCl]2, were
used as precursors in otherwise identical conditions.
As compared to the vinylarenes, 1,3-dienes are
much less reactive, yet the regioselectivity in the for-
mation of the 1,2-HV product (15) from racemic 14 is
excellent. The most useful ligand for this transforma-
tion is L5, which gives a quantitative yield of the
product(s) as a 2:1 mixture of diastereomers.[9] In
sharp contrast, the catalysts from ligands L6 and L7,
even after prolonged periods at room temperature,
left significant amounts of unreacted starting material.
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Table 3. Hydrovinylation of 1,3-dienes using L5.[a]
Entry
Substrate
Product
Cat (equiv.)/Temp. [oC]/Time [h] Yield/Select. (% 1,2-HV)
1
20
21
0.014/À40/23
>99/68[b]
2a
2b
0.014/À43/21
0.014/À43/21
>99/99
>98/98
22a, b
23a, b
3
4
24
26
25
27
0.014/À23/21
>99/94
>99/96
0.028/25/43
5
28
30
29
31
0.025/0/4
>95/95[c]
6
0.020/r.t./14
63[d]/66[e]
[a]
See Eq. (6) for procedure, major product: 1,2-HV. See the Supporting Information for GC traces. Data from ref.[3a] (en-
tries 1–4), ref.[14] (entry 5) and ref.[3b] (entry 6).
Rest 1,4-addition product (1,2:1,4=2.9:1.0).
Diastereoselectivity C3(S:R=59:41).
Diastereoselectivity C20(S:R=54:46).
[b]
[c]
[d]
[e]
Rest 1,4-HV with C16-vinyl.
The Pd(II)-catalyzed reaction appears to be more
compatible with a broader set of substrates, even
though isomerization of the primary product [e.g., 33a
to 35a, Eq. (9)] can be a serious problem in these re-
actions. Occasionally regioselectivity (e.g., formation
of a 6-membered isomer, 34e, in [Eq. (10b)] can also
be different from the Ni(II)-catalyzed reactions.
Since formally this cyclization reaction can be de-
scribed as an intramolecular version of the hydroviny-
lation (strictly, a hydroalkenylation)[16] reaction, we
decided to examine the modified hemilabile ligands
L5–L7 for this reaction. The results are shown in Eq.
(11).
The ligands L5, L6 and L7 were tested in the
Ni(II)-catalyzed cyclization reactions using essentially
the same procedure used for the intermolecular reac-
tions [Eq. (11)]. Most strikingly, the ligands L6 and
L7 were found to be totally ineffective in the cycliza-
tion, whereas L5 gave excellent yields for the cycliza-
tion of the prototypical substrates 32a–e. These sub-
strates shown under Eq. (11), gave the methylenecy- GC. The reaction works equally well for the forma-
clopentane (33a–e), along with traces of a methylene- tion of nitrogen-containing heterocyclic compounds
cyclohexane (34a–e), resulting from a different regio- from the corresponding 1,6-dienes. Judicious choice of
selectivity [33 vs. 34 in Eq. (11)] in the insertion. the protecting group on nitrogen is crucial for the suc-
Under these conditions, only small amounts (<5%) cess of the reaction. While an arylsulfonyl protecting
of isomerized products (e.g., 35) were detected by group (e.g., 32d, 32e) is perfectly compatible with the
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Scheme 2. A mechanistic proposal to explain the absence of isomerization with hemilabile ligand-nickel complexes.
reaction, leading to excellent yields of the cyclization Table 4. Cyclization of 1,6-dienes using (allyl)Ni
ACHTUNGTRENNUNG(NHC)
BARF.[a]
product, Lewis basic centers present in the benzyla-
mine 32f or the benzamide 32g totally inhibit the cyc-
lization reaction.
Entry
Substrate
Ligand L8
33 [%] 34 [%]
Ligand L9
33 [%]
34 [%]
1
2
3
4
5
6
32a
3
6
92
82
29
29
35
0
<1
trace
9[c]
35
32
0
>97
>92
71
59
67
32b
Identification of the Minor Methylenecyclohexane
Products (34) via Use of N-Heterocyclic Carbene
(NHC) Complexes
32c[b]
32d
71[c]
65
65
0
32e
32f, 32g
0
Various anecdotal observations on the effect of phos-
phine ligands of differing steric demands in the
Ni(II)- and Pd(II)-catalyzed cyclization reactions of
1,6-dienes suggested that it might be possible to con-
trol the regioselectivity of the addition of the pre-
sumed catalytic species (a metal hydride or equiva-
lent, see Scheme 2), and, hence the product distribu-
tion [in Eq. (11): methylenecyclopentane (33) vs.
methylenecyclohexane (34)] by ligand tuning. Such
a possibility was further bolstered by the uncommon
regioselectivity observed by Ho et al. in the tail-to-
[a]
See Eq. (12) for procedure. See Supporting Information
for GC traces.
[b]
The reaction mixture contains other products, the pro-
portions shown are normalized with respect to the cy-
clized products to highlight the effect of NHC ligands on
the cyclization (see Supporting Information, p. S69).
Phosphine ligand L5 gives only 33c [see Eq. (11)].
dr=2.2:1.0.
[c]
tail heterodimerization of styrene with 1-alkenes.[17] In NHC ligand[19,20] followed by addition of NaBARF
this reaction, which involves the addition of a metal [Eq. (12)]. As documented in Eq. (12) and entries 1–
hydride as a key step in mechanism (as in the initial 5, Table 4, smaller NHC ligands L8 and L9 are com-
step of the diene cyclization), the larger size of an petent to effect the cyclization, whereas larger ligands
NHC carbene ligand has been invoked to rationalize L10 and L11 gave no products. Substrates 32a and
the selectivity. Thus to prepare an authentic sample of 32b, where the Thorpe–Ingold effect is operative,
34 we decided to examine a series of NHC carbenes gave excellent yields of the methylenecyclohexane de-
with varying steric demands[18] as ligands for the cycli- rivative 34, with the cyclopentane derivative 33 as
zation under our new protocol [Eq. (12)] and results a side-product (entries 1 and 2, columns 4 and 6). The
are shown in Table 4.
The reactive carbene complexes were prepared in the cyclohexane derivative 34 (entries 1 and 2,
situ starting from Ni(COD)2, allyl bromide and the column 6). Other substrates 32c--32e gave varying
larger of the two ligands, L9 gave almost exclusively
AHCTUNGTRENNUNG
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ever, for the inherently less reactive 1,3-dienes, these
highly active ligands are the most suitable.
Conclusions
A set of readily accessible ligands, 2-benzyloxy-, 2-
benzyloxymethyl- or 2-benzyloxyethylphenyl-diphe-
nylphosphines (L5, L6 and L7), exhibit strikingly dif-
ferent behaviour in various Ni(II)-catalyzed olefin di-
merization reactions. Complexes of ligands L5 and L6
are most active for hydrovinylation (HV) of vinylar-
enes, with the former leading to extensive isomeriza-
tion of the primary 3-aryl-1-butenes into the conjugat-
ed 2-aryl-2-butenes even at low temperature. Ligand
L6 is the most optimal for the HV of vinylarenes, lead-
ing to up to quantitative yields of products at ambient
temperature with no trace of isomerization. In sharp
contrast, hydrovinylation of a variety of 1,3-dienes is
best catalyzed by Ni(II) complexes of L5. Ligands L6
proportions of the two cyclic products, in each case and L7 are much less effective in the HV of dienes.
giving more of the six-membered (34) product with Nickel(II)-catalyzed cycloisomerization of 1,6-dienes
the larger NHC ligand L9.
into methylenecyclopentanes, a reaction mechanistical-
ly related to the other hydrovinylation reactions, is also
uniquely effected by Ni(II) complexes of L5. Attempts
to prepare authentic samples of the methylenecyclo-
hexane products led to Ni(II) complexes of NHC li-
A Mechanistic Proposal
The absence of isomerization of the primary products gands which, in sharp contrast to the phosphines, gave
in reactions catalyzed by {(allyl)Ni(L6) [BARF]} [Eq. methylenecyclohexanes as the major products.
(3)] as compared to (allyl)Ni
G
G
After submission of the proof of this article,
striking, and may be rationalized by a mechanism a paper describing the effect of N-heterocyclic car-
(Scheme 2) which derives considerable support from benes on the regioselectivity of cycloisomerization of
our recent computational study of this reaction.[21] In 1,n-dienes (Eq. 12) appeared in the literature. See: J.
this mechanism, the pre-catalyst 36 reacts with ethyl- Org. Chem. 2014 (ASAP) DOI: org/10.1021/jo5008477.
ene to give the insertion product 38 (formed through
the ethylene complex 37), which undergoes a b-hy-
dride transfer to the vinylarene via 40 to give 41, pre-
Experimental Section
sumed to be the catalyst resting state. An alternate
route that involves b-hydride elimination from 38 to
General Methods
+
Reactions requiring air-sensitive manipulations were con-
ducted under an inert atmosphere of nitrogen by using
À
give a discrete [LNi H] intermediate 39 is energeti-
cally unlikely. In the computational study of a very
Schlenk techniques or a Vacuum Atmospheres glovebox.
closely related system,[21a] we found that a discrete
Dichloromethane was distilled from calcium hydride under
nickel hydride such as 39, most likely responsible for
nitrogen and stored over molecular sieves. Tetrahydrofuran
the isomerization reactions, is very high in energy on
was distilled under nitrogen from sodium/benzophenone
the reaction coordinate diagram. Going forward, once
ketyl. Catalyst precursors [(allyl)NiBr]2 and NaBARF were
prepared according to the literature.[22] The [(allyl)NiBr]2
was stored in a freezer in the drybox. Ethylene (99.5%) was
41 is generated, it undergoes further coupling with
ethylene to give 43, which transfers a b-hydride to a vi-
nylarene to give the product 45, in that process regen- purchased from Matheson Inc., and passed through
a column of Drieriteꢁ before use. Analytical TLC was per-
formed on E. Merck precoated (0.25 mm) silica gel 60 F254
plates. Flash column chromatography was carried out on
silica gel 40 (Scientific Adsorbents Incorporated, Microns
Flash). Conversion of the products was determined by gas
chromatographic analysis, which was performed on an Agi-
lent HP-5 column (30 m lengthꢂ0.325 mm diameter) using
helium or hydrogen as a carrier gas (25 psi). Absence of
polymeric impurities was ascertained by NMR, and, except
for the volatile materials, the isolated yields of the products
erating the species 41. As before, a b-hydride elimina-
tion from 43 to 39 (and the product 45) has a prohibi-
tively high energy of activation. The stability and re-
activity of the putative intermediates 36 and 41 for
different ligands L5–L7 may explain the considerable
differences in reactivities between these ligands. It is
likely that the hemilabile oxygen, when directly at-
tached to the aryl group, as in L5, may not sufficiently
moderate the reactivity of the catalyst to prevent the
isomerization reaction of the 3-aryl-1-butenes. How- were not significantly different from the conversions.
8
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Triarylphosphine Ligands with Hemilabile Alkoxy Groups
Ligands L5, L6 and L7 were prepared according to litera-
ture procedures.[3a] Precursors for the NHC ligands, L8, L9,
L10 and L11 were purchased as the corresponding imidazo-
lium salts from Strem Chemicals.
ported are of isolated materials and ratio of products were
calculated from the chromatograms included.
Hydrovinylation of Vinylfurans
The 2- and 3-vinylfurans were prepared by known meth-
ods.[23] All other precursors are described in the publications
that deal with the synthesis of the HV products (see the
Supporting Information for details). Spectroscopic and gas
chromatographic data for the HV products (including sepa-
rations on chiral stationary phase gas or liquid chromatogra-
phy of chiral materials) are described the publications cited
in the Supporting Information under each compound.
The procedure was the same as that for typical vinylarenes.
3-(2’-Furanyl)but-1-ene (7f): H NMR (500 MHz, CDCl3):
d=7.41 (s, 1H), 6.29 (s, 1H), 6.01 (s, 1H), 5.94 (ddd, J=
17.2, 10.2, 7.0 Hz, 1H), 5.15–5.05 (m, 2H), 3.60–3.50 (M,
1H), 1.34 (d, J=7.0 Hz, 3H). Purity ascertained by GC (see
later for chromatogram).
1
3-(3’-Furanyl)but-1-ene (7j): The procedure was the same
1
as that for typical vinylarenes. H NMR (500 MHz, CDCl3):
d=7.35 (s, 1H), 7.20 (s, 1H), 6.28 (s, 1H), 5.91 (ddd, J=
17.0, 12.8, 7.0 Hz, 1H), 5.10–4.95 (m, 2H), 3.40–3.25 (m,
1H), 1.30 (d, J=7.0 Hz, 3H). Purity ascertained by GC (see
later for chromatogram).
Typical Procedure for Hydrovinylation of Vinylarenes
[Table 1 and Table 2, Eqs. (3)–(5)]
To a solution of [(allyl)NiBr]2 (2.5 mg, 0.007 mol) in CH2Cl2
(1 mL) at room temperature was added a solution of ligand
Typical Procedure for the Hydrovinylation of 1,3-
Dienes [Eqs. (6)–(8) and Table 3][3a]
2-benzoxymethylphenyldiphenylphosphine
(L5,
5.3 mg,
0.014 mmol) in CH2Cl2 (1 mL) in drybox. The resulting solu-
tion was added to a suspension of NaBARF (12.9 mg,
0.0146 mmol) in CH2Cl2 (1 mL). CH2Cl2 (1 mL) was used to
rinse the vial and combined with the above mixture and the
resulting mixture was stirred for 1.5 h at room temperature.
The resulting catalyst was filtered through a small pad of
celite into a dry Schlenk flask and taken out of the drybox.
CH2Cl2 (1 mL) was used to facilitate complete transfer. For
room temperature reactions, the catalyst solution was
cooled to 08C, and was exposed to an ethylene atmosphere
from a Schlenk line, and to the solution was added dropwise
the solution of vinylarenes (2 mmol) in CH2Cl2 (3 mL)
under 1 atm of ethylene. After the addition was over, the
mixture was allowed to warm to room temperature and
stirred for the time designated in the tables. For low temper-
ature reactions (Table 1) the catalyst solution was main-
tained at the prescribed temperature and the substrate was
added under ethylene at this temperature, and the reaction
was maintained for the suggested period. The reaction was
followed by GC for completion of reaction. The mixture
was quenched with half-saturated aqueous NH4Cl solution
and extracted three times with 10 mL portions of CH2Cl2.
The combined organic layers were dried over anhydrous
MgSO4 and concentrated and the residue was passed
through a small plug of silica gel eluting with hexanes/ethyl
acetate system (for styrene and 2- and 3-vinylfurans, pen-
tane was used). The filtrate was concentrated to afford the
crude products, which were analyzed by GC (for 2- and 3-vi-
nylfuran, the solvent was removed by distillation during
work-up). The product was analyzed by GC (attached) and
NMR, the later to ascertain the absence of polymeric mate-
rials. For mixtures of products the yields are calculated by
isolated mass and proportion of individual compounds de-
termined by uncalibrated GC.
To a solution of [(allyl)NiBr]2 (2.5 mg, 0.007 mmol) in
CH2Cl2 (1 mL) was added
a solution of ligand L5
(0.014 mmol) in CH2Cl2 (1 mL) at room temperature in the
drybox. The resulting solution was added to a suspension of
NaBARF (12.9 mg, 0.0146 mmol) in CH2Cl2 (1 mL) and the
mixture was stirred at room temperature for 1.5 h. Then the
catalyst solution was filtered through a short pad of Celite
into a flame-dried Schlenk flask and 1 mL of CH2Cl2 was
used to rinse the Celite. The flask was taken out of the
drybox and cooled to the designated temperature shown in
Table 3. After ethylene had been introduced to the flask,
a solution of 1,3-dienes (1 mmol) in CH2Cl2 (3 mL) was
added to the catalyst solution. The reactions were monitored
by GC. After the mixture had been stirred for the designat-
ed time shown in Table 3, the flask was disconnected from
ethylene and 0.5 mL of saturated aqueous ammonium chlo-
ride was added to quench the reaction. The flask was al-
lowed to warm to room temperature and the mixture was
diluted with hexanes (pentane for 1,3-cyclohexadiene). The
solution was filtered through a short pad of silica gel using
30 mL of hexanes/ethyl acetate (20/1) to elute the silica gel.
The filtrate was collected and concentrated on rotary evapo-
rator. For highly volatile compounds like 17 and 21 it was
concentrated by distillation to get the crude products, which
were analyzed by gas chromatography and NMR spectra.
Cycloisomerization of 1,6-Dienes
The following starting materials are prepared using litera-
ture methods: 32a,[24] 32b,[24] 32c,[25] 32d,[26] 32e,[26] 32f,[27]
32g.[28] Carbene precursor salts IMes.HCl, IPr.HCl, IA-
da.HCl, ItBu.HCl are commercially available from Strem
Chemicals.
The procedure was repeated with ligands L6 and L7
under conditions described in Table 1 and the exact ratio of
products obtained were determined by gas chromatography.
These chromatograms are included later in the Supporting
Information.
Hydrovinylations of substrates listed in Table 2 were con-
ducted using ligand L6 under conditions listed there using
the general procedure described above and the yields re-
Typical Procedure for 1,6-Diene Cyclization using
[(Allyl)NiBr] L5 Catalyst and NaBARF [Eq. (11),
32a to 33a and 34a]
In a glovebox, NaBARF (14.7 mg, 0.0167 mmol, 10 mol%),
ligand L5 (6.15 mg, 0.0167 mmol, 10 mol%), and [(allyl)-
NiBr]2 (3.0 mg, 0.008 mmol, 5.0 mol%) were weighed into
separate glass vials. The hemilabile ligand was dissolved in
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Souvagya Biswas et al.
anhydrous CH2Cl2 (1.0 mL) and transferred to the vial con-
Typical Procedure for the Preparation of Free
Carbene from the Corresponding Imidazolium Salt[20]
taining [(allyl)NiBr]2, followed by 1.0 mL rinsing of the
source vial. The resulting yellow solution of ligand L5 and
[(allyl)NiBr]2 was transferred to the vial containing
NaBARF, followed by 1.0 mL rinsing of the source vial. The
resulting orange-yellow solution was diluted with CH2Cl2
(1.0 mL) and allowed to stand for 1.5 h.
In
a glovebox, 1,3-bis(2,6-diisopropylphenyl)imidazolium
chloride (425 mg, 1.0 mmol, 1 equiv.) and KO-t-Bu
(168.4 mg, 1.5 mmol, 1.5 equiv.) were suspended in 5 mL
THF and stirred for 12 h. THF was then removed under re-
duced pressure to yield a yellow-orange solid. To the solid
was added 1 mL of toluene, which dissolved most of the ma-
terial. The resulting material was treated with 10 mL hex-
anes to precipitate excess KO-t-Bu and unreacted starting
material and the mixture was filtered through a glass fritted
funnel. The precipitate was washed with 2ꢂ1 mL portions
of hexanes. The filtrate was concentrated and dried under
vacuum to afford the carbene L9 as a solid; yield: 310 mg
(80%).
Cyclization procedure:
A 25-mL three-necked flask
equipped with a rubber septum, flow-controlled nitrogen
inlet, thermometer, and magnetic stirring bar was flame-
dried and purged with nitrogen. The catalyst solution pre-
pared above was transferred to the reaction vessel via can-
nula, followed by 1.0 mL rinsing of the source vial. The
system was cooled to 08C in an ice bath and diallyl malo-
nate (32a, 34 mg, 0.16 mmol) was added in to the reaction
mixture by microliter syringe. The reaction mixture was al-
lowed to stir at room temperature for 5 h. The reaction was
exposed to air and diluted with pentane to quench the reac-
tion. The crude cyclized product that was then eluted
through a plug of silica with pentane to remove any nickel
salts, concentrated and further analyzed by NMR and GC.
Typical Procedure for 1,6-Diene Cyclization using
NiACTHNUTRGEN(NUG COD)2 and Free Carbene
Synthesis of [(allyl)Ni(L9)Br]:[29] In a glovebox, Ni
ACHTUNGTRENNUNG(COD)2
(123 mg, 0.45 mmol) was dissolved in 1 mL 1,5-cycloocta-
diene. Allyl bromide (54.4 mg, 0.45 mmol) was then added
dropwise. The resulting slurry was then stirred for 5 min,
rapidly resulting in the formation of a blood-red allylnicke-
l(II) bromide dimer. Toluene (2 mL) was added to dissolve
all material. A solution of the free IPr carbene L9 (175 mg,
0.45 mmol) in 2 mL of toluene was then added and the mix-
ture was stirred for 5 min. The solution was filtered over
celite and concentrated under vacuum. The resulting orange
solid was washed with 3ꢂ1 mL portions of cold hexanes and
dried under reduced pressure to afford the complex; yield:
ca. 210 mg (82%).
Typical Procedure for 1,6-Diene Cyclization Starting
with Allyl Bromide NiACHTNUGRTENUNG(COD)2 and Ligand L5
In a glovebox, NiACHTUNGTRENNUNG(COD)2 (123 mg, 0.45 mmol) was dissolved
in 1 mL 1,5-cyclooctadiene. Allyl bromide (54.4 mg,
0.45 mmol) was then added dropwise. The resulting slurry
was then stirred for 5 min, rapidly resulting in the formation
of a blood-red allylnickel(II) bromide dimer. 2 mL of tolu-
ene were added to dissolve all material. A solution of hemi-
labile ligand L5 (165 mg, 0.45 mmol) in 2 mL of toluene was
then added and the mixture was stirred for 5 min. The solu-
tion was filtered over celite and concentrated under reduced
pressure. The resulting orange solid was washed with 3ꢂ
1 mL portions of cold hexanes and dried under vacuum to
afford the product; yield: ca. 200 mg (95%).
Cyclization procedure: In a glovebox, NaBARF (8.3 mg,
0.0094 mmol, 10 mol%) and [allyl)Ni(L5)Br] (4.5 mg,
0.0094 mmol, 10 mol%) were weighed into separate glass
vials. The complex was dissolved in anhydrous CH2Cl2
(1.0 mL). The resulting yellow solution of the complex was
transferred to the vial containing NaBARF, followed by
1.0 mL rinsing of the source vial. The resulting orange-
yellow solution was diluted with CH2Cl2 (1.0 mL) and al-
lowed to stand for 1.5 h. A 25-mL three-necked flask
equipped with a rubber septum, flow-controlled nitrogen
inlet, thermometer, and magnetic stirring bar was flame-
dried and purged with nitrogen. The catalyst solution pre-
pared above was transferred to the reaction vessel via can-
nula, followed by 1.0 mL rinsing of the source vial. The
system was cooled to 08C in an ice bath and diallyl malo-
nate (32a, 10 mg, 0.047 mmol) was added in to the reaction
mixture by microliter syringe. The reaction mixture was al-
lowed to stir at room temperature for 5 h. The reaction was
exposed to air and diluted with pentane to quench the reac-
tion. The crude cyclized product that was then eluted
through a plug of silica with pentane to remove any nickel
salts was concentrated and further analyzed by NMR and
GC.
Cyclization procedure using the NHC complex: In
a gloveACTHNUTRGENUGbN ox, NaBARF (8.3 mg, 0.0094 mmol, 10 mol%) and
[allyl)Ni(L9)Br] (5.3 mg, 0.0094 mmol, 10 mol%) were
weighed into separate glass vials. The complex was dissolved
in anhydrous CH2Cl2 (1.0 mL). The resulting yellow solution
of the complex was transferred to the vial containing
NaBARF, followed by 1.0 mL rinsing of the source vial. The
resulting orange-yellow solution was diluted with CH2Cl2
(1.0 mL) and allowed to stand for 1.5 h. A 25-mL three-
necked flask equipped with a rubber septum, flow-con-
trolled nitrogen inlet, thermometer, and magnetic stirring
bar was flame-dried and purged with nitrogen. The catalyst
solution prepared above was transferred to the reaction
vessel via cannula, followed by 1.0 mL rinsing of the source
vial. The system was cooled to 08C in an ice bath and diallyl
malonate (32a, 10 mg, 0.047 mmol) was added in to the reac-
tion mixture by microliter syringe. The reaction mixture was
allowed to stir at room temperature for 5 h. The reaction
was exposed to air and diluted with pentane to quench the
reaction. The crude cyclized product that was then eluted
through a plug of silica with pentane to remove any nickel
salts was concentrated and further analyzed by NMR and
GC.
33a:[30] 1H NMR (CDCl3, 400 MHz): d=4.91 (q, J=
2.1 Hz, 1H), 4.80 (q, J=2.1 Hz, 1H), 3.73 (s, 3H), 3.72 (s,
3H), 3.04–3.08 (m, 1H), 2.92–2.97 (m, 1H), 2.53–2.59 (m,
2H), 1.72–1.80 (m, 1H), 1.10 (d, J=6.3 Hz, 3H); 13C NMR
(CDCl3, 100 MHz): d=172.6, 172.5, 153.4, 105.8, 58.4, 53.0,
53.0, 42.5, 40.8, 37.5, 18.2; GC (methyl silicone 1208C): Rt =
6.76 min.
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Triarylphosphine Ligands with Hemilabile Alkoxy Groups
34a:[31] 1H NMR (CDCl3, 400 MHz): d=4.73 (s, 2H), 3.71
(s, 6H), 3.72 (s, 3H), 2.68 (s, 2H), 2.10–2.13 (m, 2H), 2.04–
2.07 (m, 2H), 1.63–1.69 (m, 2H); 13C NMR (CDCl3,
100 MHz): d=171.8, 144.3, 110.9, 57.0, 52.7, 39.9, 34.1, 31.8,
31.4, 24.4, 22.9; GC (methyl silicone 1208C): Rt =7.69 min.
33b:[32] 1H NMR (CDCl3, 400 MHz): d=4.89–4.90 (m,
1H), 4.78–4.79 (m, 1H), 4.14–4.21 (m, 4H), 3.01–3.06 (m,
1H), 2.90–2.96 (m, 1H), 2.51–2.57 (m, 2H), 1.74–1.78 (m,
1H), 1.21–1.25 (m, 6H), 1.10 (d, J=6.3 Hz, 3H); 13C NMR
(CDCl3, 100 MHz): d=172.2, 172.1, 153.7, 105.6, 61.6, 58.5,
42.3, 40.7, 37.5, 18.2, 14.2; GC (methyl silicone 1208C): Rt =
11.59 min.
133.2, 129.9, 128.0, 106.2, 55.3, 52.4, 37.7, 21.8, 16.3; GC
(methyl silicone 1808C): Rt =13.350 min.
AHCTUNGTRENNUNG
[33e+34e]:[27] 1H NMR (CDCl3, 400 MHz): d=7.68–7.72
(m, 2H, 5-membered ring), 7.65–7.68 (m, 2H, 6-membered
ring), 7.32–7.33 (m, 2H, 6- & 5-membered ring), 4.89–4.91
(m, 1H, 6- & 5-membered ring), 4.84–4.86 (m, 1H, 5-mem-
bered ring), 4.81–4.82 (m, 1H, 6-membered ring), 3.93–3.97
(m, 1H, 5-membered ring), 3.72–3.76 (m, 1H, 5-membered
ring), 3.56–3.60 (m, 1H, 5-membered ring), 3.51 (s, 2H, 6-
membered ring), 3.08 (t, J=5.5 Hz, 2H, 6-membered ring),
2.65–2.72 (m, 2H, 5-membered ring), 2.43 (s, 3H, 6- & 5-
membered ring), 2.09–2.12 (m, 2H, 6-membered ring), 1.66–
1.72 (m, 2H, 6-membered ring), 1.04 (d, J=6.5 Hz, 3H, 5-
membered ring). 13C NMR (CDCl3, 100 MHz, 6-membered
ring): d=143.7, 140.9, 133.5, 129.0, 128.0, 112.0, 52.6, 46.6,
32.2, 25.9, 21.7; GC (methyl silicone 1808C): Rt =13.35 min
(33e) and 14.667 min (34e).
34b:[33] 1H NMR (CDCl3, 400 MHz): d=4.74 (s, 2H),
4.13–4.21 (m, 4H), 2.67 (s, 2H), 2.10–2.14 (m, 2H), 2.04–
2.06 (m, 2H), 1.64–1.70 (m, 2H) 1.24 (t, J=8.7 Hz, 6H);
13C NMR (CDCl3, 100 MHz): d=171.4, 144.5, 110.7, 61.4,
56.8, 39.8, 34.2, 31.3, 24.4, 14.3; GC (methyl silicone 1208C):
Rt =13.76 min.
33c: 1H NMR (CDCl3, 400 MHz): d=4.88–4.89 (m, 1H, Supporting Information
diastereomers), 4.79–4.80 (m, 1H, diastereomers), 4.10–4.17
Experimental procedures for the synthesis of ligands L5–L6
(m, 2H, diastereomers), 2.84–2.91 (m, 0.27H), 2.73–2.82 (m,
0.73H), 2.57–2.69 (m, 2H), 2.11–2.27 (m, 1H), 1.64–1.71 (m,
1H), 1.58–1.60 (m, 1H), 1.24–1.27 (m, 3H, diastereomers),
1.12 (d, J=6.6 Hz, 3H, one diastereomer), 1.065 (d, J=
6.8 Hz, 3H, one diastereomer); 13C NMR (CDCl3,
100 MHz): d=176.2, 175.7, 156.0, 155.3, 105.0, 105.0, 60.6,
42.6, 42.0, 41.6, 39.2, 39.1, 38.2, 37.5, 36.5, 36.4, 22.6, 19.6,
18.3, 14.5, 14.3, 13.7; GC (methyl silicone 908C): Rt =
7.099 min and 7.395 min.
and typical reaction conditions for hydrovinylation and cy-
cloisomerization reactions as well as gas chromatographic
data showing precise composition of products under various
reaction conditions are available in the Supporting Informa-
tion.
34c:[14] 1H NMR (CDCl3, 400 MHz): d=4.68 (s, 2H), 4.10–
4.16 (s, 2H), 2.47–2.51 (m, 1H), 2.33–2.40 (m, 1H), 2.17–
2.29 (m, 2H), 1.93–2.02 (m, 2H), 1.82–1.89 (m, 1H), 1.67–
1.69 (m, 1H), 1.54–1.60 (m, 1H), 1.24–1.28 (m, 3H);
13C NMR (CDCl3, 100 MHz): d=175.5, 147.2, 108.8, 60.5,
44.6, 43.6, 37.5, 34.6, 28.9, 26.8, 14.5; GC (methyl silicone
908C): Rt =8.44 min.
Acknowledgements
Financial assistance for this research provided by US Nation-
al Science Foundation (CHE-1057818) and National Insti-
tutes of Health (General Medical Sciences, R01 GM075107)
is gratefully acknowledged.
33d:[33] 1H NMR (CDCl3, 400 MHz):[13] d=7.82–7.85 (m,
2H), 7.59–7.63 (m, 1H), 7.52–7.56 (m, 2H), 4.90–4.92 (m,
1H), 4.84–4.87 (m, 1H), 3.94–3.99 (m, 1H), 3.74–3.79 (m,
1H), 3.58–3.62 (m, 1H), 2.70–2.74 (m, 1H), 2.64–2.68 (m,
1H), 1.04 (d, J=6.5 Hz, 3H); 13C NMR (CDCl3, 100 MHz):
d=149.4, 136.3, 133.0, 129.3, 127.9, 106.3, 55.3, 52.3, 37.7,
16.3; GC (methyl silicone 1808C): Rt =9.131 min.
References
[1] For reviews see: a) T. V. RajanBabu, C. R. Smith,
Enantioselective Hydrovinylation of Alkenes, in: Com-
prehensive Chirality, (Eds.: E. M. Carreira, H. Yama-
moto), Elsevier, London, 2012, Vol. 5, pp 355–398;
b) T. V. RajanBabu, Chem. Rev. 2003, 103, 2845;
c) P. W. Jolly, G. Wilke, Hydrovinylation, in: Applied
Homogeneous Catalysis with Organometallic Com-
pounds; (Eds.: B. Cornils, W. A. Herrmann), VCH,
New York, 1996, Vol. 2, pp 1024–1048.
[2] a) N. Nomura, J. Jin, H. Park, T. V. RajanBabu, J. Am.
Chem. Soc. 1998, 120, 459; b) M. Nandi, J. Jin, T. V. Ra-
janBabu, J. Am. Chem. Soc. 1999, 121, 9899; c) A.
Zhang, T. V. RajanBabu, Org. Lett. 2004, 6, 1515; d) A.
Zhang, T. V. RajanBabu, Org. Lett. 2004, 6, 3159; e) A.
Zhang, T. V. RajanBabu, J. Am. Chem. Soc. 2006, 128,
5620; f) C. R. Smith, T. V. RajanBabu, Org. Lett. 2008,
10, 1657.
ACHTUNGTRENNUNG
[33d+34d]:[35] 1H NMR (CDCl3, 400 MHz): d=7.78–7.84
(m, 2H, 6- & 5-membered ring), 7.49–7.62 (m, 2H, 6- & 5-
membered ring), 4.90–4.92 (m, 1H, 6- & 5-membered ring),
4.84–4.87 (m, 1H, 5-membered ring), 4.81–4.82 (m, 1H, 6-
membered ring), 3.94–3.99 (m, 1H, 5-membered ring), 3.74–
3.79 (m, 1H, 5-membered ring), 3.58–3.62 (m, 1H, 5-mem-
bered ring), 3.54 (s, 2H, 6-membered ring), 3.10 (t, J=
5.5 Hz, 2H, 6-membered ring), 2.70–2.74 (m, 1H), 2.64–2.68
(m, 1H), 2.09–2.12 (m, 2H, 6-membered ring), 1.66–1.72 (m,
2H, 6-membered ring), 1.04 (d, J=6.5 Hz, 3H, 5-membered
ring); 13C NMR (CDCl3, 100 MHz, 6-membered ring): d=
140.7, 136.6, 132.9, 129.2, 128.0, 112.0, 52.6, 46.6, 32.2, 25.9;
GC (methyl silicone 1808C): Rt =9.131 min (33d) and
9.978 min (34d).
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1H), 3.96–3.97 (m, 1H), 3.72–3.76 (m, 1H), 3.54–3.61 (m,
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Adv. Synth. Catal. 0000, 000, 0 – 0
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12
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 0000, 000, 0 – 0
ÝÝ
These are not the final page numbers!

FULL PAPERS
Triarylphosphine Ligands with Hemilabile Alkoxy Groups:
Ligands for Nickel(II)-Catalyzed Olefin Dimerization
Reactions. Hydrovinylation of Vinylarenes, 1,3-Dienes, and
Cycloisomerization of 1,6-Dienes
13
Adv. Synth. Catal. 2014, 356, 1 – 13
Souvagya Biswas, Aibin Zhang, Balaram Raya,
T. V. RajanBabu*
Adv. Synth. Catal. 0000, 000, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
13
ÞÞ
These are not the final page numbers!