Palladium-catalyzed hydrometalation and bismetalation of biphenylene

Article abstract of DOI:10.1021/om200436d

2-Silyl- and 2-borylbiphenyls have been synthesized by the palladium-catalyzed reaction of biphenylene with hydrosilanes and a hydroborane, respectively, via the cleavage of the four-membered ring of biphenylene. Under similar conditions, the C-C bond of

Full text of DOI:10.1021/om200436d

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pubs.acs.org/Organometallics
Palladium-Catalyzed Hydrometalation and Bismetalation of
Biphenylene
Takanori Matsuda* and Haruki Kirikae
Department of Applied Chemistry, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
S Supporting Information
b
ABSTRACT: 2-Silyl- and 2-borylbiphenyls have been synthe-
sized by the palladium-catalyzed reaction of biphenylene with
hydrosilanes and a hydroborane, respectively, via the cleavage of
the four-membered ring of biphenylene. Under similar condi-
tions, the CꢀC bond of biphenylene undergoes formal σ-bond
metathesis with various intermetallic linkages to afford 2,20-
bis(metallo)biphenyls.
ignificant developments have been made in the area of
catalytic cleavage of CꢀC bonds by transition metals, which
S
allow the utilization of the CꢀC bonds as a functional group in
organic synthesis.1 The known catalytic functionalization of
biphenylene involving the cleavage of CꢀC bonds2 includes
dimerization,3 hydrogenolysis,4 carbonylation,5 alkyne insertion,5b,6
and coupling with alkenes, arylboronic acids, and ketones;6a,7 in
such catalytic functionalization, CꢀC or CꢀH bonds are formed
concomitantly with the cleavage of the CꢀC bond of bipheny-
lene.8 Thus far, the catalytic introduction of atoms other than
carbon and hydrogen into biphenylene via CꢀC bond cleavage
has been limited to only one example, where biphenylene reacts
with bis(trimethylsilyl)acetylene in the presence of a nickel
catalyst to give alkynylsilylation products arising from a formal
CꢀC/CꢀSi σ-bond metathesis.9
Figure 1. Buchwald-type biaryl phosphine ligands used in this study.
hydrosilylating agents, forming the corresponding 2-silylbiphe-
nyls 3b,c in 92% and 43% yields, respectively (entries 4 and 5).
Analogously, 1 underwent hydroboration with pinacolborane
(2d) but with lower efficiency under the conditions that were
optimal for hydrosilylation. The reaction at 140 °C using L3 as
the ligand gave the hydroboration product 3d in 56% yield (entry 8).
Next, we examined the reaction of 1 with organometallic
compounds possessing intermetallic linkages; the results are
summarized in Table 2.14 The bis-silylation reaction of 1 with
hexamethyldisilane (4a) carried out in the presence of Pd(dba)2
(5 mol %) and L1 or L2 (10 mol %) in toluene at 110 °C gave
2,20-bis(trimethylsilyl)biphenyl (5a) in good yields (entries 1
and 2).15 The reaction of 1 with 1,1,2,2-tetramethyl-1,2-diphe-
nyldisilane (4b) afforded bis(silyl)biphenyl 5b in 75% yield
(entry 4). Digermane 4c also reacted in the presence of the
Pd(dba)2ꢀL3 catalyst, affording bis(germyl)biphenyl 5c in
excellent yield (entry 5). In contrast, the reaction with distannane
4d was sluggish and the corresponding product 5d was formed in
fairly low yield, even with a higher catalyst loading and a longer
reaction time (entry 6). In addition to the homointermetallic
linkages, heterointermetallic linkages of group 13 and 14 ele-
ments could also be employed in the bismetalative CꢀC bond
cleavage of 1. The addition of silylstannane 4e across 1 similarly
occurred to form 2-silyl-20-stannylbiphenyl 5e in 57%
yield (entry 7). 2-Boryl-20-silylbiphenyls 5f,g were obtained in
While hydrometalation10 and bismetalation reactions11 re-
present an attractive transformation enabling the introduction of
metallic elements such as silicon and boron into unsaturated
organic molecules, biphenylene has never been exploited for
these addition reactions. In this paper, we describe reactions of
biphenylene with hydrosilanes and a hydroborane in the pre-
sence of palladium catalysts to give the corresponding hydro-
metalation products via cleavage of the CꢀC bond of bipheny-
lene. Moreover, the formal σ-bond metathesis reaction of biphe-
nylene is applicable to homo- and heterointermetallic linkages
such as SiꢀSi and SiꢀB bonds, affording 2,20-bis(metallo)biphenyls.
Our initial attempt explored the reaction of biphenylene (1)
with hydrosilanes. In the presence of palladium catalysts pre-
pared in situ from 5 mol % of Pd(dba)2 (dba = dibenzylid-
eneacetone) and 10 mol % of Buchwald-type biaryl phosphine
ligands (Figure 1), 1 was reacted with triethylsilane (2a, 1.5
equiv) in toluene at 110 °C to afford 2-(triethylsilyl)biphenyl
(3a) via hydrosilylative CꢀC bond cleavage (Table 1).12 Among
the ligands studied, DavePhos (L1) and MePhos (L3) exhibited
superior activity for the reaction as compared to other biaryl
phosphines such as t-BuDavePhos (L2) (entries 1ꢀ3).13 Dime-
thyl(phenyl)silane (2b) and triethoxysilane (2c) can be used as
Received: May 24, 2011
Published: July 12, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/om200436d Organometallics 2011, 30, 3923–3925
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Table 1. Palladium-Catalyzed Hydrosilylation and
Hydroboration of Biphenylene (1)a
Table 3. Reaction of 1 with Diboron 4h
entry
2 (HꢀE)
ligand
3 (yield, %b)
yield, %a
1
2
3
4
5
6
7
8
2a (HꢀSiEt3)
L1
L2
L3
L1
L1
L1
L2
L3
3a (95)
3a (77)
3a (92)
3b (92)
3c (43)
3d (35)
3d (19)
3d (56d)
2a
entry
cat. (amt, mol %)
conditions
5h
3d
2a
1
2
3
Pd(dba)2/L1 (5/10)
toluene, 110 °C, 4 h
8
34
2b (HꢀSiMe2Ph)
2c (HꢀSi(OEt)3)
2d (HꢀB(pin)c)
2d
Pd(dba)2/P(n-Bu)3 (10/20) xylene, 140 °C, 5 h
Pd(PPh3)4 (10) toluene, 110 °C, 9 h
57
57
a Isolated yield.
2d
a Reaction conditions for hydrosilylation: 1, 2aꢀc (1.5 equiv), Pd(dba)2
(5 mol %), ligand (10 mol %), toluene, 110 °C, 2ꢀ3 h. Reaction
conditions for hydroboration: 1, 2d (2.0 equiv), Pd(dba)2 (5 mol %),
ligand (10 mol %), xylene, 140 °C, 8 h. b Isolated yield. c pin = pinacolato
(ꢀOCMe2CMe2Oꢀ). d 3d was obtained in 20% yield when the reaction
was carried out in toluene at 110 °C for 13 h.
Scheme 1. Catalytic Cycle for the Hydrometalative and Bis-
metalative CꢀC Bond Cleavage of 1a
Table 2. Bismetalative CꢀC Bond Cleavage of 1a
amt of Pd,
time,
h
entry
4 (EꢀE0)
mol % ligand
5 (yield, %b)
1
2
3
4
5
6
7
8
9
4a (Me3SiꢀSiMe3)
4a
5
5
L1
L2
L3
L1
L3
L1
L3
L2
L2
6
3.5
3
5a (75)
5a (77c)
5a (66)
5b (75)
5c (90)
5d (22)
5e (57)
5f (61)
5g (41)
a E stands for H, B, Si, etc.
4a
5
monoboration with 4h occurred with Pd(PPh3)4 as the
catalyst (entry 3).
4b (PhMe2SiꢀSiMe2Ph)d
4c (Me3GeꢀGeMe3)
4d (Me3SnꢀSnMe3)
4e (Bu3SnꢀSiMe3)
4f (PhMe2SiꢀB(pin))e
4g (Et3SiꢀB(pin))e
5
3
5
4
Scheme 1 depicts a plausible catalytic cycle for the hydro-
metalative and bismetalative CꢀC bond cleavage of biphenylene,
although we have no experimental evidence for the inter-
mediate species.17,18 First, the oxidative addition of the EꢀE
bond of A to Pd(0) species B occurs to form palladium(II)
intermediate C. The CꢀC bond of biphenylene (1) then
oxidatively adds to C to form the palladium(IV) intermediate
D. Finally, a double reductive elimination process (D f E f B)
yields product F and regenerates the catalyst.19
10
10
5
24
7
5
10
4
a Reaction conditions: 1, 4 (1.5 equiv), Pd(dba)2 (5 or 10 mol %), ligand
(10 or 20 mol %), toluene, 110 °C, 3ꢀ9 h. b Isolated yield. c 80% yield
with 10 mol % of Pd(dba)2 and 20 mol % of L2. d 1.2 equiv. e 2.0 equiv.
In summary, we have developed a method for synthesizing
2-metallo- and 2,20-bis(metallo)biphenyls by hydrometalation and
bismetalation of biphenylene. Palladium(0)ꢀbiaryl phosphine com-
plexes work efficiently as catalysts for the introduction of main-group
metallic elements into biphenylene via the cleavage of the CꢀC bond.
moderate yields by the silaborative CꢀC bond cleavage of 1
using silylboranes 4f,g, respectively (entries 8 and 9).
Diboration of 1 with bis(pinacolato)diboron (4h) using
biaryl phosphines as the ligands resulted in the formation of a
mixture of the desired diboration product 5h and monobora-
tion product 3d, with the latter predominating (Table 3,
entry 1).16 After several ligands were screened, tri-n-butyl-
phosphine was found to be an optimal ligand for the selec-
tive diboration of 1 in xylene at 140 °C, affording the 2,20-
bis(boryl)biphenyl 4h in 57% yield. Interestingly, selective
’ ASSOCIATED CONTENT
S
Supporting Information. Figures, text, and tables giving
b
experimental procedures and characterization data for new
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dx.doi.org/10.1021/om200436d |Organometallics 2011, 30, 3923–3925

Organometallics
COMMUNICATION
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
Soc. 2000, 122, 11015. (d) Suginome, M.; Matsuda, T.; Yoshimoto, T.;
Ito, Y. Organometallics 2002, 21, 1537. (e) Ohmura, T.; Taniguchi, H.;
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(15) The following results were obtained with other ligands (isolated
yield): t-BuMePhos (75%); JohnPhos (64%); TrixiePhos (51%); XPhos
(45%); RuPhos (39%); CyJohnPhos (26%); SPhos (26%); PhDave-
Phos (trace); t-BuXPhos (no reaction).
(16) Protodeboronation of 5h under the reaction conditions was
negligible. The formation of 3d is presumably due to traces of adven-
titious water that might protonate the putative organopalladium inter-
mediate of E.
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’ AUTHOR INFORMATION
Corresponding Author
*Fax: +81 3 5261 4631. E-mail: matta@rs.kagu.tus.ac.jp.
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