Hydrogen transfer hydrozirconation of alkenes with iBuZrCp2Cl catalyzed by Lewis-acidic metal compounds containing Al, Zn, Si, Ag, and Pd

Article abstract of DOI:10.1002/(SICI)1099-0690(199905)1999:5<969::AID-EJOC969>3.0.CO;2-G

The hydrozirconation reaction of monosubstituted alkenes with iBuZrCp₂Cl can be significantly accelerated by catalytic amounts of various Lewis acidic metal compounds, most notably AlCl₃, Me₃SiI, and Pd complexes, such as Li₂PdCl₄ and Cl₂Pd(PPh₃)₂.

Full text of DOI:10.1002/(SICI)1099-0690(199905)1999:5<969::AID-EJOC969>3.0.CO;2-G

SHORT COMMUNICATION
Hydrogen Transfer Hydrozirconation of Alkenes with iBuZrCp2Cl
Catalyzed by Lewis-Acidic Metal Compounds Containing
Al, Zn, Si, Ag, and Pd
Hidefumi Makabe[a] and Ei-ichi Negishi*[a]
Keywords: Hydrogen transfer / Zirconium / Alkenes / Isobutylzirconocene chloride / Lewis acid catalysis / Lewis acid
catalysis
The hydrozirconation reaction of monosubstituted alkenes
with iBuZrCp2Cl can be significantly accelerated by catalytic
amounts of various Lewis acidic metal compounds, most
notably AlCl3, Me3SiI, and Pd complexes, such as Li2PdCl4
and Cl2Pd(PPh3)2.
Hydrozirconation is commonly carried out with pre- (Entry 1). In the AlCl3-catalyzed reaction, it is essential to
formed HZrCp2Cl.[1] Although commercially available, its evaporate ether used to generate iBuZrCp2Cl before ad-
preparation requiring sluggish filtration under inert atmos- dition of AlCl3, and the amount of AlCl3 must be kept at
phere is somewhat cumbersome. Various procedures for in a minimum, as alkylzirconocene chlorides and AlCl3 are
situ generation of HZrCp2Cl using metal hydrides, such as known to undergo transmetalation to produce Cp2ZrCl2
LiAlH4, NaAlH2(OCH2CH2OCH3)2, and LiBH(sBu)3, and alkylaluminum derivatives.[9]
have been devised.[2][3] However, these procedures can be
The results presented above clearly established the feasi-
complicated by the formation of by-products and their sub-
bility of catalyzing hydrogen transfer hydrozirconation of
sequent reactions, although solutions to some such prob-
alkenes with alkylzirconocene chlorides, e.g., iBuZrCp2Cl.
lems have been devised.[4] Hydrogen transfer hydrozir-
To further explore the scope of this novel catalytic protocol,
conation with iBuZrCp2Cl[2][5] has also provided a con-
various other metal compounds were tested. As the results
venient and potentially more economical alternative. In-
shown in Table 1 indicate, an unexpectedly wide range of
deed, the reaction of both terminal and internal alkynes
metal compounds display catalytic activities, and the fol-
with iBuZrCp2Cl[5] is a clean and high-yielding process, al-
lowing findings are particularly noteworthy. Firstly, in ad-
beit slower than hydrozirconation with HZrCp2Cl. On the
dition to AlCl3, several other metal compounds including
other hand, the corresponding reaction of terminal alkenes
ZnCl2 (Entries 6 and 7), AgBF4 (Entry 11), Me3SiI (Entry
is generally sluggish, producing the desired products in vari-
15), Li2PdCl4, and Cl2Pd(PPh3)2 (Entries 18 and 19) exhibit
able yields, despite our earlier more favorable claim.[2] An-
significant and potentially useful catalytic activities. Unlike
other earlier report of Zr-catalyzed hydroalumination with
AlCl3, none of these other catalysts requires evaporation of
iBu3Al and a catalytic amount of Cl2ZrCp2,[6,7] which was
ether. Secondly, metal chlorides containing Zn and Hg are
thought to involve hydrogen transfer hydrozirconation, sug-
more effective than the corresponding bromides and io-
gested an intriguing possibility of catalyzing hydrozir-
dides. On the other hand, Me3SiI (Entry 15) is decidedly
conation with iBuZrCp2Cl by Al and other Lewis acidic
more effective than Me3SiCl (Entry 14), suggesting that
metal compounds.[8]
more than one mechanism may be operative in the catalysis
We now report that the hydrozirconation reaction of
reported herein. Thirdly, selection of solvents is critically
monosubstituted alkenes with iBuZrCp2Cl can be signifi-
important. Somewhat unexpectedly, benzene and toluene
cantly accelerated by catalytic amounts of a variety of
are far superior to CH2Cl2 and ethereal solvents, e.g., THF,
Lewis acidic metal compounds, most notably AlCl3 (2
in most cases. Additionally, various other compounds in-
mol%), Me3SiI (5 mol%), and Pd complexes, such as
cluding LiI, EtAlCl2, Et2AlCl, SnCl4, Bu3SnBr, Bu3SnI,
Li2PdCl4 and Cl2Pd(PPh3)2, as indicated by the results sum-
and SbCl5 were tested, but none yielded satisfactory results.
marized in Table 1. Under otherwise the same conditions,
With EtAlCl2 and tributyltin halides, extensive isomeri-
the uncatalyzed reaction of 1-decene with iBuZrCp2Cl pro-
zation of 1-decene to a mixture of internal decenes similar
duced even after 15 h the desired hydrozirconation product
to that observed in the reaction of 1-alkenes with nBuMgCl
only in 20% yield with about 70% of 1-decene remaining
[10]
and Cl2ZrCp2
took place, although its mechanistic de-
[a]
tails are unclear.
Department of Chemistry, Purdue University
West Lafayette, Indiana 47907-1393, USA
Fax: (internat.) ϩ1-765/494-0239
The synthetic utility of two procedures with AlCl3 (2
mol%) and Me3SiI (5 mol%) has been examined with sev-
eral representative functionally substituted terminal al-
kenes. Either catalyst was satisfactory in converting 11-
E-mail: negishi@chem.purdue.edu
Supporting information for this article is available on the
WWW under http://www.wiley-vch.de/home/eurjoc or from
the author.
Eur. J. Org. Chem. 1999, 969Ϫ971
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ193X/99/0505Ϫ0969 $ 17.50ϩ.50/0
969

H. Makabe, E. Negishi
SHORT COMMUNICATION
Table 1. Hydrogen transfer hydrozirconation of 1-decene with iBuZrCp2Cl catalyzed by metal compounds[a]
[a] The reaction was carried out with iBuZrCp2Cl generated in situ in 90Ϫ95% yield by treatment of 1.1 equiv. each (relative to an alkene)
[b]
[c]
1
of Cp2ZrCl2 with tBuMgCl at 50°C for 1 h. Ϫ In cases where Et2O is not shown, it was evaporated. Ϫ By H-NMR spectroscopy.
[d]
[e]
[f]
Ϫ
By GLC. Ϫ Yield of isolated product. Ϫ Not determined.
chloro-1-undecene into 1-iodo-11-chlorodecane in 70Ϫ80%
The catalytic activity of AlCl3 may be interpreted within
yields. However, 11-benzyloxy-1-undecene, 11-(tert-butyldi- the context of activation of iBuZrCp2Cl by AlCl3 through
Ϫ
phenylsilyloxy)-1-undecene, and allyl phenyl ether all de- Zr-Cl-Al interaction to generate either iBuZrϩCp2AlCl4
composed in the presence of AlCl3. On the other hand, or iBuZrCp2 δϩϪClϪδϪAlCl3, which may be further con-
their reaction in the presence of 5 mol% of Me3SiI gave, verted to the corresponding zirconium hydrides as transient
after iodinolysis, the corresponding iodoalkanes in 74, 75, reactive species.[8] Interestingly, however, the reaction of 3-
and 50% yields, respectively. 4-Vinylcyclohexene was simi- hexyne with iBuZrCp2Cl in the presence of 2 mol% of
larly converted into 4-(2-iodoethyl)cyclohexene in 74% yield AlCl3 produced, after iodinolysis, (E)-3-iodo-3-hexene (4)
with 5 mol% Me3SiI, whereas its yield observed with 2 in 76% yield with no indication of the formation of (E)-
mol% of AlCl3 was 55%. With Cl2Pd(PPh3)2 as a catalyst, 3-iodo-2-hexene (5) (< 2%). As reported previously,[6] the
even ester-containing alkenes can be chemoselectively corresponding reaction with iBu3Al (3 equiv) in the pres-
hydrozirconated. Thus, for example, 9-decenyl benzoate re- ence of 10 mol% of Cp2ZrCl2 gave, after iodinolysis, 4 and
acted with iBuZrCp2Cl and 5 mol% of Cl2Pd(PPh3)2 to 5 in 38 and 35% yields, respectively (Scheme 1). Further
give, after protonolysis, decyl benzoate in 74% yield. No mechanistic studies are necessary to clarify mechanistic de-
starting compound remained unchanged, and the extent of tails.
competitive ester reduction was about 5%. As the corre-
sponding reaction with preformed HZrCp2Cl in the absence
Experimental Section
All reactions were run under Ar atmosphere with exclusion of light
(Al foil).
of any catalyst gave 9-decenol in 40% yield along with the
desired decyl benzoate only in 20% yield and the unchanged
starting compounds (20%), the Pd-catalyzed hydrogen
transfer hydrozirconation herein reported is expected to
show a significantly different and more favorable chemose-
lectivity profile than the conventional hydrozirconation.
Hydrozirconation of 1-Decene with iBuZrCp2Cl in the Presence of 2
mol% of AlCl3: Ether was removed from an ethereal solution of
tBuMgCl (2 , 1.1 mL, 2.2 mmol) at room temperature under re-
970
Eur. J. Org. Chem. 1999, 969Ϫ971

Hydrogen Transfer Hydrozirconation of Alkenes with iBuZrCp2Cl
SHORT COMMUNICATION
Hydrozirconation of 9-Decenyl Benzoate with iBuZrCp2Cl in the
Presence of Cl2Pd(PPh3)2: To iBuZrCp2Cl generated in situ as de-
scribed above from 2.2 mmol each of tBuMgCl and Cp2ZrCl2 were
added Cl2Pd(PPh3)2 (70 mg, 0.1 mmol) and 9-decenyl benzoate
(520 mg, 2 mmol). The resulting mixture was heated for 3 h at
50°C. Analysis by 1H-NMR spectroscopy indicated that 10-(ben-
zoyloxy)-1-decylzirconocene chloride (δ ϭ 5.81 for Cp) had been
formed in 71% along with 5% of Cp2ZrCl2. After protonation with
3  HCl and extractive workup, column chromatography (5%
EtOAc in hexane) provided 384 mg (74%) of decyl benzoate along
with a minor amount (ca. 5%) of decanol.
Scheme 1. Hydrogen transfer hydrometalation of 3-hexyne with
isobutyl-containing AlϪZr reagents
Acknowledgments
duced pressure. To this were added 5 mL of benzene and Cp2ZrCl2
(642 mg, 2.2 mmol), and the reaction mixture was heated for 1 h
at 50°C. The formation of iBuZrCp2Cl in 94% yield was observed
This research was supported by the US National Science Foun-
dation (CHE 9704994) and Purdue University. H. M. is a Postdoc-
toral Fellow on funds provided by Japan Society for Promotion of
Science for Research Abroad (1997Ϫ1999).
1
by H-NMR spectroscopy. To this were added AlCl3 (5.5 mg, 0.04
mmol) and 1-decene (0.38 mL, 2.0 mmol). The resulting mixture
was stirred at 50°C for 3 h. Analysis by 1H NMR spectroscopy
indicated the formation of nC10H21ZrCp2Cl (δ ϭ 5.80 for Cp) in
87% yield along with 5% of Cp2ZrCl2 (δ 5.91). Its treatment with
iodine (1.14 g, 4.5 mmol) in 10 mL of THF at 0 to 23°C followed
by the usual extractive workup and bulb-to-bulb distillation (0.5
mm Hg, 70Ϫ75°C) afforded 451 mg (84%) of 1-iododecane.
[1] [1a]
D. W. Hart, J. Schwartz, J. Am. Chem. Soc. 1974, 96, 8115.
[1b]
Ϫ
J. A. Labinger in Comprehensive Organic Synthesis, Vol.
8, B. M. Trost, I. Fleming, Eds., Pergamon Press, Oxford,
1991, 667.
[2]
[3]
[4]
[5]
[6]
E. Negishi, J. A. Miller, T. Yoshida, Tetrahedron Lett. 1984,
25, 3407.
B. H. Lipshutz, R. Keil, E. L. Ellsworth, Tetrahedron Lett. 1990,
31, 7257.
S. L. Buchwald, S. J. La Maire, R. B. Nielsen, B. T. Watson, S.
M. King, Tetrahedron Lett. 1987, 28, 3895.
D. R. Swanson, T. Nguyen, Y. Noda, E. Negishi, J. Org. Chem.
1991, 56, 2590.
Hydrozirconation of 11-(Benzyloxy)-1-decene with iBuZrCp2Cl in
the Presence of Me3SiI: To iBuZrCp2Cl, generated in situ by treat-
ment of tBuMgCl (2 , 1.1 mL, 2.2 mmol) in Et2O with Cp2ZrCl2
(642 mg, 2.2 mmol), and 5 mL of benzene at 50°C for 1 h were
added Me3SiI (15 µL, 0.1 mmol) and 11-(benzyloxy)-1-undecene
(521 mg, 2 mmol). The resulting mixture was heated for 3 h at
50°C. Analysis by 1H-NMR spectroscopy indicated that 11-
(benzyloxy)-1-undecylzirconocene chloride (δ ϭ 5.81 for Cp) had
been formed in 75% yield along with 6% yield of Cp2ZrCl2. After
iodination and workup as above, column chromatography (5%
EtOAc in hexane) provided 569 mg (76%) of 11-(benzyloxy)-1-
iodoundecane.
E. Negishi, D. Y. Kondakov, D. Choueiry, K. Kasai, T. Taka-
hashi, J. Am. Chem. Soc. 1996, 118, 9577.
E. Negishi, T. Yoshida, Tetrahedron Lett. 1980, 1501.
For a review discussing activation of Lewis acids by Lewis acids,
see E. Negishi, Chem. Eur. J. 1999, 5, 411.
D. B. Carr, J. Schwartz, J. Am. Chem. Soc., 1979, 101, 3521.
C. J. Rousset, E. Negishi, N. Suzuki, T. Takahashi, Tetrahedron
Lett., 1992, 33, 1965.
[7]
[8]
[9]
[10]
Received February 1, 1999
[99042]
Eur. J. Org. Chem. 1999, 969Ϫ971
971