Novel catalyst system for hydrostannation of alkynes

Article abstract of DOI:10.1002/chem.201303057

A catalyst system was developed for the highly regio-and stereoselective hydrostannation of a range of alkynes with tributylstannane under mild conditions. The active catalytic species was generated from a stable diruthenium complex by illuminating household fluorescent light (30 W) at room temperature.

Full text of DOI:10.1002/chem.201303057

DOI: 10.1002/chem.201303057
Communication
&
Synthetic Methods
Novel Catalyst System for Hydrostannation of Alkynes
Sreya Gupta,[a] Youngshil Do,[a] Jin Hee Lee,[a] Miryeong Lee,[b] Junghoon Han,[a]
Young Ho Rhee,*[b] and Jaiwook Park*[a]
metal-catalyzed carbon–carbon cross-coupling reactions due
to the difficulty of discriminating the vinyl group from the
phenyl ones.[8] Recently, Organ and co-workers found that
regio- and Z-selective hydrostannation of propargylic alcohol
derivatives with tributyltin hydride (Bu3SnH) is possible by ex-
tending the reaction time at room temperature or heating at
808C with BEt3 plus air system.[6e] In the consecutive paper,
they reported that borinates, boronates, and even boric acid in
air can also promote the hydrostannation with a mechanism
involving ionic species.[6f] Diethylzinc has been used as a radical
initiator for tin-mediated radical reactions at low reaction tem-
perature,[7 g] but its strong nucleophilicity is a potential draw-
back.[6b] Herein we describe an efficient ruthenium catalyst
system for the regio- and stereoselective hydrostannation of al-
kynes with Bu3SnH (Scheme 1). The essential feature of our cat-
alytic hydrostannation is the involvement of a ruthenium hy-
dride species, which presumably acts as the hydrogen-atom
donor for the hydrostannation of alkynes.
Abstract: A catalyst system was developed for the highly
regio- and stereoselective hydrostannation of a range of
alkynes with tributylstannane under mild conditions. The
active catalytic species was generated from a stable diru-
thenium complex by illuminating household fluorescent
light (30 W) at room temperature.
Organostannanes are valuable intermediates in organic synthe-
sis due to their versatility in organic reactions.[1] Vinylstannanes
are particularly useful substrates of metal-catalyzed carbon–
carbon cross-coupling reactions.[2] Moreover, vinylstannanes
have been used frequently as vinyl anion synthons in various
organic synthesis.[1] Although there are many methods for pre-
paring vinylstannanes,[3–7] the direct addition of tin hydride to
alkynes (hydrostannation) is the most attractive one in the
view of efficiency and atom-economy. Transition
metal-catalyzed hydrostannations, particularly with
Pd-based systems, have been developed with the ad-
vantage of syn-addition stereoselectivity.[3b] However,
the regioselectivity for a- and b-product is often low
with terminal alkynes.[3a,e] Notably, high a-selectivity
has been observed in the hydrostannation of termi-
nal alkynes with molybdenum and tungsten cata-
lysts.[3d] The use of Lewis acid catalysts for the hydro-
stannation of alkynes leads to selective formation of
trans-addition products.[4] Radical-induced hydrostan-
Scheme 1. Hydrostannation of terminal alkynes.
nation has also been widely employed, but generally
gives regio- and stereoisomeric mixture of vinylstan-
nanes, particularly in the reactions performed at high tempera-
ture.[5] The use of triethylborane (BEt3) at room temperature
may improve the selectivity,[6] but the scope of this method is
generally limited to the synthesis of vinyltriphenylstan-
nanes.[6b–d] Vinyltriphenylstannanes have a critical drawback to
The advantage of our catalyst system is clearly revealed by
the comparison experiments shown in Scheme 2. The com-
plete hydrostannation of 1-phenyl-1-butyne (1a) with Bu3SnH
was achieved within 10 min with 1.0 mol% of a diruthenium
complex (I) under illumination of household fluorescent light
(30 W) at room temperature with excellent regio- and stereose-
lectivity. Meanwhile, the use of azobisisobutyronitrile (AIBN) re-
quired a high reaction temperature and gave a 40:60 mixture
of E- and Z-isomer of 2a in moderate yield, and that of BEt3
provided the product in a poor yield even after 24 h at room
temperature.
[a] S. Gupta, Y. Do, J. H. Lee, J. Han, Prof. Dr. J. Park
Department of Chemistry
POSTECH (Pohang University of Science and Technology)
Pohang, 790-784 (Korea)
Fax: (+82)54-279-3399
E-mail: pjw@postech.ac.kr
Recently we have reported the synthesis of I and its applica-
tions for the racemization of secondary alcohols in chemoenzy-
matic dynamic kinetic resolution,[9] the selective hydrosilylation
of aldehydes,[10] and the generation of N-unsubstituted imines
from alkyl azides.[11] The ruthenium complex I is a solid com-
pound stable in air, but transforms into catalytic species simply
[b] M. Lee, Prof. Dr. Y. H. Rhee
Department of Chemistry
POSTECH (Pohang University of Science and Technology)
Pohang, 790-784 (Korea)
E-mail: yhrhee@postech.ac.kr
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303057.
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Table 1. Hydrostannation of 1-phenyl-1-butyne under various condi-
tions.[a]
Catalyst
T [oC]
t [min]
Yield [%][b]
E/Z[b]
Scheme 2. Hydrostannation of 1-phenyl-1-butyne.
1
I
I
30
30
30
30
30
30
30
30
80
10
720
720
10
10
10
10
1440
720
99
<5
<5
98
3:97
n.d.[d]
n.d.
9:91
10:90
n.d
n.d.
5:95
40:60
2[c]
3
none
II
III
IV
V[e]
by the illumination of household fluorescent light in solution
state for the activation of CÀH[9] and SiÀH[10] bonds in the race-
mization of secondary alcohols and the selective hydrosilyl-
ation of aldehydes, respectively. The activation of azides in-
volves the liberation of N2 molecule and the 1,2-hydrogen shift
from the a-carbon to the nitrogen.[11]
4
5
6
7
8
9
97
<5
<5
53
[f]
BEt3
AIBN[g]
85
[a] A solution of 1a (0.50 mmol), Bu3SnH (0.60 mmol), and I–IV
(1.0 mol%) in THF (0.5 mL) was illuminated under fluorescent light (30 W)
at ambient temperature (308C). [b] Determined by 1H NMR analysis using
1,2-dichloroethane as an internal standard. [c] In the dark. [d] n.d. =not
determined. [e] 2 mol% of V was used. [f] 10 mol% of BEt3 (1.0m solution
in THF) was used. [g] 10 mol% of AIBN was used.
It is well known that Ru radical species can be generated
from the related diruthenium [CpRu(CO)2]2 complex under
photolytic reactions.[12] Therefore, we envisioned that the com-
bination of diruthenium complexes I–IV with trialkyltin hy-
drides might be useful in radical-mediated hydrostannation re-
action. First, we tested the hydrostannation of 1a
Table 2. Hydrostannation of internal alkynes.[a]
with Bu3SnH in the presence of a diruthenium com-
plex (Table 1); 2a was formed with almost perfect
regio- and stereoselectivity within 10 min in the reac-
tion with I (entry 1). Fluorescent light and the ruthe-
nium catalyst were found essential; in the absence
of either I or light the conversion was significantly
lower (entries 2 and 3). A N-phenyl analogue (II)[13]
and [CpRu(CO)2]2 (III) showed activity comparable to
I, but the stereoselectivity was lower (entries 4 and
5). [Cp*Ru(CO)2]2 (IV) and a mononuclear ruthenium
chloride (V)[14] were inactive for the hydrostannation
(entries 6 and 7). The use of BEt3 (10 mol%) provided
2a with high stereoselectivity at room temperature,
but the yield of the vinylstannane was poor even
with an extended reaction time (24 h; entry 8). The
yield of 2a in the reaction with AIBN was low even
at 808C, and a 40:60 mixture of stereoisomers was
produced (entry 9).
In general, Z-b-phenylvinylstannanes were ob-
tained selectively as the major products in good
yields in the hydrostannation of various internal al-
kynes (Table 2). As in the case of 1a, aryl groups ap-
peared to strongly control the regioselectivity of the
hydrostannation of 1b–k. The stereoselectivity, how-
ever, was affected by functional groups. Satisfactory
stereoselectivity in the reaction of the esters (1c–e)
was achieved by lowering reaction temperature to
08C, while the stereoselectivity in that of primary al-
cohols and their corresponding silyl ethers (1 f–i) was
[a] A solution of an alkyne (0.50 mmol), Bu3SnH (0.60 mmol), and I (1.0 mol%) in THF
(0.5 mL) was illuminated under fluorescent light (30 W) at ambient temperature under
an argon atmosphere. [b] Isolation yield. [c] The ratio of E/Z was determined by
1H NMR analysis. [d] Combined yield of (Z)-a and (Z)-b regioisomers (a/b=90:10).
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not so satisfactory even at lower temperature. However, nota-
bly, the substrate having secondary a-hydroxyl (1j) or a-silyl-
oxy group (1k) transformed selectively to the corresponding
Z-vinylstannanes at room temperature. In the cases of aliphatic
internal alkynes (1l–o) a-hydroxyl or a-silyloxy group appears
to control the regio- and stereoselectivity of the hydrostan-
nation. The regioselectivity in the reaction of a propargylic pri-
mary alcohol (1l) was high, while a stereoisomeric mixture (E/
Z=9:91) was obtained. In contrast, the stereoselectivity in the
reaction of a propargylic secondary alcohol (1m) was high,
while a regioisomeric mixture (a/b=90:10) was formed. Inter-
estingly, both of the regio- and stereoselectivity were excellent
in the reaction of the silyl-protected derivative 1n. The hydro-
stannation of a simple aliphatic internal alkyne (1o) also gave
the corresponding Z-vinylstannane selectively in high yield, al-
though a much longer reaction time was required.
reduction reaction was suppressed by lowering the reaction
temperature; at 08C the reduction product 4a was formed
only in trace amount. Our catalyst system was also effective for
the hydrostannation of aliphatic terminal alkynes (3g–k). Hy-
droxy- (3h) and chloro- (3i) groups were compatible with the
reaction conditions. Regioselectivity was very high (only b-iso-
1
mers were detected in crude mixtures by H NMR spectrosco-
py), while stereoselectivity was lower than that in the reaction
of aromatic terminal alkynes. Although a small amount (5%) of
a-isomer was formed from the substrate (3j) having a silyloxy
group, the stereoselectivity for the b-isomer was excellent (E/
Z=98:2). Another interesting example is a propargylglycine
derivative (3k), which was reported as a substrate difficult to
control regioselectivity.[16] With our catalyst system at 808C, the
b-addition products (4k; E/Z=88:12) were formed in good
yield.
Then, the scope of the catalytic hydrostannation was investi-
gated for terminal alkynes (Table 3).[15] Aromatic terminal al-
kynes (3a–f) were reacted with almost perfect regio- and ste-
reoselectivity to give the corresponding E-b-vinylstannanes
(4a–f) in high yields under the conditions similar to those for
internal alkynes. The substituent effect of the aromatic rings
was not significant on the reaction efficiency. The CÀBr bond
of bromophenylacetylene (3c) was reduced partially during
the hydrostannation to give a 75:25 mixture of 4c and a. The
A noticeable example showing another merit of our catalyst
system is the tandem cyclization reaction of a 1,6-enyne (5; Ta-
ble 4).[6c,d,20] The hydrostannation of 5 with I produced the cor-
responding cyclic vinylstannane 6 in>95% yield in 10 min at
room temperature (entry 1). In contrast, the use of BEt3 gave 6
in 30% yield after 3 h (entry 2). The hydrostannation with AIBN
did not proceed at room temperature (entry 3), but the cycliza-
tion reaction was completed in 10 min at 808C (entry 4).
Table 4. Cyclization of (E)-ethyloct-2-en-7-ynoate.[a]
Table 3. Hydrostannation of terminal alkynes.[a]
Entry
Catalyst
T [8C]
t [min]
Yield [%][b]
1
2
3
4
I (1 mol%)[c]
BEt3 (10 mol%)
AIBN (10 mol%)
AIBN (10 mol%)
30
30
30
80
10
180
720
10
>95
30[d]
<5
91[e]
[a] A solution of 5 (0.25 mmol), Bu3SnH (0.30 mmol), and catalyst in THF
(0.5 mL) was reacted. [b] Determined by 1H NMR analysis using 1,2-di-
chloroethane as an internal standard. [c] Illuminated with a 30 W fluores-
cent light. [d] Unreacted 5 (67%) was found in the reaction mixture by
1H NMR analysis. [e] 75% of unreacted 5 was found in crude 1H NMR
sprecta. [e] Linear vinylstannane (7%) was observed in the reaction mix-
1
ture by H NMR analysis.
The results of the hydrostannation with our catalyst system
implicate a radical pathway.[17,18] In fact, we could obtain the
ruthenium hydride complex VI and hexabutyldistannane in the
stoichiometric reaction of the diruthenium complex I with
Bu3SnH in the absence of alkyne (Scheme 3).[19] In addition, I
was regenerated by heating VI in the presence of a radical
source (AIBN).[20,21] Meanwhile, we could recover VI formed in
the hydrostannation reaction by treating the reaction mixture
with chloroform to give the air-stable ruthenium chloride V,
which can be reconverted to VI by the reaction with 2-propa-
nol under basic conditions.[20,22]
[a] A solution of an alkyne (0.50 mmol), Bu3SnH (0.60 mmol), and
I
(1.0 mol%) in THF (0.5 mL) was illuminated with fluorescent light (30 W)
at ambient temperature under an argon atmosphere. [b] Determined by
1H NMR analysis using 1,2-dichloroethane as an internal standard. [c] The
values in parentheses are isolation yields. [d] Stereoisomeric ratios (E/Z)
were determined by 1H NMR analysis. [e] The reaction was carried out
using 2.0 mol% of I at 08C. [f] The debrominated product was formed in
trace amount. [g] 5% of a-isomer was detected in crude mixture by
1H NMR analysis. [h] The reaction was carried out at 808C.
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Son, Org. Lett. 2003, 5, 3443; f) A. Barbero, F. J. Pulido, J. A. Rincꢁn, P.
Cuadrado, D. Galisteo, H. Martꢂnez-Garcꢂa, Angew. Chem. 2001, 113,
2159; Angew. Chem. Int. Ed. 2001, 40, 2101.
[2] a) M. Cai, G. Zheng, G. Ding, Green Chem. 2009, 11, 1687; b) D. G.
Brooke, J. C. Morris, Tetrahedron Lett. 2008, 49, 2414; c) T. Hosoya, K.
Sumi, H. Doi, M. Wakao, M. Suzuki, Org. Biomol. Chem. 2006, 4, 410;
d) B. Stulgies, P. Prinz, J. Magull, K. Rauch, K. Meindl, S. Rꢃhl, A. de Mei-
jere, Chem. Eur. J. 2005, 11, 308; e) D. A. Powell, T. Maki, G. C. Fu, J. Am.
Chem. Soc. 2005, 127, 510; f) F. Liron, M. Gervais, J.-F. Peyrat, M. Alami,
J.-D. Brion, Tetrahedron Lett. 2003, 44, 2789; g) S. R. Dubbaka, P. Vogel, J.
Am. Chem. Soc. 2003, 125, 15292; h) R. E. Maleczka, Jr., J M. Lavis, D. H.
Clark, W. P. Gallagher, Org. Lett. 2000, 2, 3655; i) X. Han, B. M. Stoltz, E. J.
Corey, J. Am. Chem. Soc. 1999, 121, 7600; j) J. K. Stille, B. L. Groh, J. Am.
Chem. Soc. 1987, 109, 813; k) J. W. Labadie, J. K. Stille, J. Am. Chem. Soc.
1983, 105, 6129.
Scheme 3. Interconversion between the diruthenium complex I and the
ruthenium hydride VI.
[3] a) A. Hamze, D. Veau, O. Provot, J.-D. Brion, M. Alami, J. Org. Chem.
2009, 74, 1337; b) N. D. Smith, J. Mancuso, M. Lautens, Chem. Rev. 2000,
100, 3257; c) C. D. J. Boden, G. Pattenden, T. Ye, J. Chem. Soc. Perkin
Trans. 1 1996, 2417; d) A. O. Wesquet, U. Kazmaier, Adv. Synth. Catal.
2009, 351, 1395 and references therein; e) Bulky and electron-donating
phosphines enhance the regioselectivity for (E)-1-stannyl-1-alkenes in
the Pd-catalyzed hydrostannation of terminal alkynes, see: A. Darwish,
A. Lang, T. Kim, J. M. Chong, Org. Lett. 2008, 10, 861.
[4] a) N. Asao, J.-X. Liu, T. Sudoh, Y. Yamamoto, J. Chem. Soc. Chem.
Commun. 1995, 2405; b) N. Asao, J.-X. Liu, T. Sudoh, Y. Yamamoto, J.
Org. Chem. 1996, 61, 4568; c) Y. Yamamoto, J. Org. Chem. 2007, 72,
7817; d) V. Gevorgyan, J.-X. Liu, Y. Yamamoto, Chem. Commun. 1998, 37;
e) M. S. Oderinde, M. G. Organ, Angew. Chem. 2012, 124, 9972; Angew.
Chem. Int. Ed. 2012, 51, 9834.
Based on the above results, the exceptional efficiency of the
current radical reaction can be reasonably explained by the
unique role of Ru catalyst that maintains high effective concen-
tration of Bu3Sn species in the radical chain reaction. Moreover,
the experiment shown in Scheme 4 indicates that the RuÀH
species rather than Bu3SnH donates a hydrogen atom to the
vinyl radical intermediate.[23,24] The resulting ruthenium radical
species would be dimerized to regenerate I in a reversible
manner,[25] minimizing any undesirable termination pathway,
which would be detrimental to the radical chain reaction.
[5] a) D. P. Curran, Synthesis 1988, 417; b) B. Giese, Angew. Chem. 1985, 97,
555; Angew. Chem. Int. Ed. Engl. 1985, 24, 553; c) D. H. R. Barton, D.
Crich, W. B. Motherwell, Tetrahedron 1985, 41, 3901; d) B. Giese in Radi-
cals in Organic Synthesis (Ed.: J. E. Baldwin), Pergamon Press, Oxford,
1986.
[6] a) P. Dimopoulos, A. Athlan, S. Manaviazar, J. George, M. Walters, L. Laz-
arides, A. E. Aliev, K. J. Hale, Org. Lett. 2005, 7, 5369; b) C. Ollivier, P.
Renaud, Chem. Rev. 2001, 101, 3415; c) K. Nozaki, K. Oshima, K. Utimoto,
Tetrahedron 1989, 45, 923; d) K. Nozaki, K. Oshima, K. Utimoto, J. Am.
Chem. Soc. 1987, 109, 2547; e) M. S. Oderinde, H. N. Hunter, M. G.
Organ, Chem. Eur. J. 2012, 18, 10817; f) M. S. Oderinde, H. N. Hunter,
R. D. J. Froese, M. G. Organ, Chem. Eur. J. 2012, 18, 10821.
Scheme 4. Reaction pathway for the Ru-catalyzed hydrostannation of al-
kynes.
[7] a) K. Miura, D. Wang, Y. Matsumoto, A. Hosomi, Org. Lett. 2005, 7, 503;
b) E. Shirakawa, R. Morita, T. Tsuchimoto, Y. Kawakami, J. Am. Chem. Soc.
2004, 126, 13614; c) Y. Obora, A. S. Baleta, M. Tokunaga, Y. Tsuji, J. Orga-
nomet. Chem. 2002, 660, 173; d) B. P. Warner, S. L. Buchwald, J. Org.
Chem. 1994, 59, 5822; e) C. H. Cummins, E. J. Gordon, Tetrahedron Lett.
1994, 35, 8133; f) B. L. Groh, Tetrahedron Lett. 1991, 32, 7647; g) I. Ryu,
F. Araki, S. Minakata, M. Komatsu, Tetrahedron Lett. 1998, 39, 6335.
[8] P. Dimopoulos, A. Athlan, S. Manaviazar, K. J. Hale, Org. Lett. 2005, 7,
5373.
[9] Y. Do, I.-C. Hwang, M.-J. Kim, J. Park, J. Org. Chem. 2010, 75, 5740.
[10] Y. Do, J. Han, Y. H. Rhee, J. Park, Adv. Synth. Catal. 2011, 353, 3363.
[11] J. H. Lee, S. Gupta, W. Jeong, Y. H. Rhee, J. Park, Angew. Chem. 2012,
124, 11009; Angew. Chem. Int. Ed. 2012, 51, 10851.
In summary, we have found a novel and efficient catalyst
system for the hydrostannation of a wide range of alkynes
with tributylstannane to give vinylstannanes under mild condi-
tions. The active catalytic species are generated from a stable
diruthenium complex by illuminating fluorescent light under
mild conditions. The regio- and stereoselectivity for the vinyl-
stannanes resemble to those in radical-mediated hydrostan-
nation, but has clear advantages in reaction efficiency over
conventional ones using AIBN and BEt3, including the recycla-
bility of the ruthenium catalyst.
[12] W. Macyk, A. Herdegen, A. Karocki, G. Stochel, Z. Stasicka, S. Sostero, O.
Traverso, J. Photochem. Photobiol. A 1997, 103, 221.
[13] C. P. Casey, T. E. Vos, S. W. Singer, I. A. Guzei, Organometallics 2002, 21,
5038.
Acknowledgements
[14] J. H. Choi, Y. K. Choi, Y. H. Kim, E. S. Park, E. J. Kim, M.-J. Kim, J. Park, J.
Org. Chem. 2004, 69, 1972.
[15] The data in Table 3 were taken from the Ph.D. dissertation of Youngshil
Do, POSTECH, Pohang, 2011.
This work was supported by the National Research Foundation
of Korea (2012–007235) and by KOSEF through EPB center
(2012–0000534).
[16] G. T. Crisp, M. G. Gebauer, J. Organomet. Chem. 1997, 532, 83.
[17] The hydrostannation of hex-5-yn-1-ol was carried out in the presence
of a radical scavenger (2,6-di-tert-butyl-4-methylphenol). A mixture of b-
hydrostannation products (E/Z=20:80) was obtained only in 16% yield
after 12 h.
Keywords: alkynes · hydrostannation · photolysis · radicals ·
ruthenium
[1] a) A. Beauchard, V. A. Phillips, M. D. Lloyd, M. D. Threadgill, Tetrahedron
2009, 65, 8176; b) X. Huang, N. Shao, A. Palani, R. Aslanian, Tetrahedron
Lett. 2007, 48, 1967; c) B. M. Trost, Z. T. Ball, Synthesis 2005, 853; d) A.
Barbero, F. J. Pulido, Tetrahedron Lett. 2004, 45, 3765; e) C. Rim, D. Y.
[18] a) Recentely, Organ and coworkers reported that O2 SET oxidation of
vinyl radical to form an ionic intermediate in the hydrostannation of al-
kynes with radical initiators such as AIBN and BEt3: M. S. Oderinde,
R. D. J. Froese, M. G. Organ, Angew. Chem. 2013, 125, 11544–11548;
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Angew. Chem. Int. Ed. 2013, 52, 11334–11338; b) In a control experi-
ment using a nonpolar solvent to check the involvement of ionic inter-
mediates in our catalyst system, however, noticeable solvent effect was
not observed. The hydrostannation of phenylacetylene in benzene was
completed in 10 min to give the hydrostannation products (E/Z=96:4)
in 99% yield; c) In order to see the O2 effect the hydrostannation of an
internal alkyne (1b) was carried out under rigorous anaerobic condi-
tions using a glove box and Schlenk techniques. The results were
almost same as those decribed in Table 2; 2b was obtained in 95%
yield in 3 h. Meanwhile, in the hydrostannation in the air only 78% of
1b was consumed in 3 h to give 2b in 69% yield along with unidenti-
fied side products.
Ghosh, P. J. Fagan, W. J. Marshall, E. Hauptman, R. M. Bullock, Inorg.
Chem. 2009, 48, 6490.
[22] H. M. Jung, J. H. Choi, S. O. Lee, Y. H. Kim, J. H. Park, J. Park, Organome-
tallics 2002, 21, 5674.
[23] The bond strength of RuÀH in CpRu(CO)2H has been calculated to be~
65 kcalmolÀ1. For the references, see: M. Tilset, V. D. Parker, J. Am.
Chem. Soc. 1989, 111, 6711; M. Tilset, V. D. Parker, J. Am. Chem. Soc.
1990, 112, 2843.
[24] For the bond dissociation energy of SnÀH in Bu3SnH, see: T. J. Burkey,
M. Majewski, D. Griller, J. Am. Chem. Soc. 1986, 108, 2218.
[25] Continuous illumination was needed to complete the hydrostannation.
[19] The characteristic hydride peak for VI was observed at À9.6 ppm in the
1
reaction mixture (C6D6) by H NMR spectroscopy.
[20] See Supporting Information.
Received: August 2, 2013
[21] The conversion of a ruthenium hydride into the corresponding diruthe-
nium complex through the reaction with trityl radical is known: P.
Published online on January 8, 2014
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