Gold-nanoparticle-catalyzed mild diboration and indirect silaboration of alkynes without the use of silylboranes

Article abstract of DOI:10.1002/ejoc.201700754

Commercially available Au nanoparticles supported on TiO₂ were used to catalyze the cis diboration of terminal and internal alkynes with bis(pinacolato)diboron. The products were obtained in excellent yields by using milder conditions, shorter reaction times, and lower catalyst loadings than those required for a heterogeneous Au nanopore catalyst. The catalytic system could be recovered and reused for five consecutive runs without any loss of activity. The combination of bis(pinacolato)- diboron with the 1,2-disilane in the presence of Au/TiO₂ allowed for the σ-bond metathesis to take place and the in situ formation of the Au nanoparticle-tethered silylborane. Given that the Au-catalyzed silaboration of alkynes is faster than the rates of the corresponding disilylation and diboration pathways, we were able to achieve the indirect silaboration of alkynes with good chemoselectivities (65–85 %) without the direct use of silylboranes, which are expensive and difficult to synthesize.

Full text of DOI:10.1002/ejoc.201700754

A Journal of
Accepted Article
Title: Gold Nanoparticles-Catalysed Mild Diboration and the Indirect
Silaboration of Alkynes Without Using Silylboranes
Authors: Manolis Stratakis and Marios Kidonakis
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700754
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Supported by

10.1002/ejoc.201700754
European Journal of Organic Chemistry
FULL PAPER
DOI: 10.1002/ejoc.200((will be filled in by the editorial staff))
Gold Nanoparticles-Catalysed Mild Diboration and the Indirect Silaboration of
Alkynes Without Using Silylboranes
Marios Kidonakis and Manolis Stratakis*[a]
Keywords: Heterogeneous catalysis / Au nanoparticles / diboration / silaboration / alkynes / -bond metathesis
Commercially available Au nanoparticles supported on TiO2 is taking place forming in situ Au nanoparticle-tethered
catalyze the cis-1,2-diboration of terminal and internal alkynes with silylboranes. Given that the Au-catalyzed silaboration of alkynes
bis(pinacolato)diboron in excellent yields and at much milder is faster than the corresponding disilylation or diboration
conditions, lower reaction times and catalyst loading compared to a pathways, the indirect silaboration of alkynes can be achieved in
heterogeneous Au nanopore catalyst. The catalytic system is good selectivities (65-85%), essentially without directly using
recyclable and reusable for 5 consecutive runs without loss of the high cost and difficult to synthesize, corresponding
activity. Upon mixing bis(pinacolato)diboron with a  1,2-disilane silylboranes.
in the presence of Au/TiO2, an equilibrium sigma bond metathesis
Apart from the Au nanopore-catalytic protocol,12 alkyne diboration
Introduction
with pinB-Bpin16 can be achieved primarily by Pt(0)-catalysis,
either under homogeneous,17 or heterogeneous conditions with
supported platinum nanoparticles,13,18 while some scattered
examples also appeared under homogeneous conditions catalyzed
by Fe(II),19 Cu(II),20 Ir(I)21 and more recently for the first time by a
homogeneous palladium catalyst.22
Activation of inter-heteroelement sigma bonds by nano Au
catalysts and subsequent addition to  systems has recently
received a substantial attention.1 The surprising ability of metal
oxide-supported Au nanoparticles (Au NPs) to catalyse reaction
motifs that other metals are able to do through two electron redox
catalytic cycles, such as Pd(0), Pt(0), Rh(I), etc.,2 is amazing and
unexpected. Formally Au(I) species should be able to participate in
such catalytic cycles through the Au(I/III) redox couple,3 but only
one synthetic example, namely the distannation of a specific class
of alkynes (propiolates) has been reported so far.4 Nanogold-
catalyzed addition to  systems include: hydrosilylation of alkynes
and carbonyl compounds catalysed by Au nanoparticles5 and Au
nanopore,6 hydrosilylation of allenes by Au/TiO2,7 disilylation8 and
oxidative disilylation9 of alkynes catalysed by Au/TiO2,
silaboration of alkynes10 by Au/TiO2, diboration of alkenes11 by Au
NPs and diboration of alkynes in the presence of a nanoporous Au
catalyst.12
Results and Discussion
a) Diboration of alkynes
As noted, homemade supported Au nanoparticles were inefficient
in catalysing the diboration of phenylacetylene,13 and the only so
far example using a Au-based catalyst was provided by Jin and co-
workers in the presence of a nanoporous Au catalyst.12 Typically,
this diboration protocol requires extensive reaction times, elevated
temperatures and often high catalyst loading, however, the reported
yields are high. Seeking for milder reaction conditions, we were
delighted to find that commercial Au nanoparticles supported on
titania (Au/TiO2) is a far more efficient diboration catalyst. For
example, diboration of phenylacetylene (substrate 1, Table 1) with
1.2 molar equivalents of pinB-Bpin takes place quantitatively (no
side-products are formed) in just 1.5 h at lower temperature (65 oC),
using lower catalyst loading (1 mol%). The solvent of choice is dry
benzene (toluene is also an alternative) and the isolated yield of
addition product after column chromatography was 85%. The
stereoselectivity of the addition is also excellent, as only the cis-
adduct 1a was seen. Surprisingly, in chlorinated solvents such as
DCE the reaction does not take place. In general, dry solvent is
required, otherwise bis(pinacolato)diboron gradually undergoes a
Au-catalyzed hydrolytic destruction yielding pinB-O-Bpin and H2,
a pathway also known under Pd-catalysis conditions.23
Regarding alkyne diboration from their reaction with
bis(pinacolato)diboron (pinB-Bpin), no catalytic protocol using
supported Au NPs has been reported so far. A nanoporous Au
material (2-10 mol%) obtained via dealloying of a Au-Ag alloy
was reported as an effective catalyst, giving high yields of cis-
diboration products,12 typically operating at temperatures 100-140
oC. On the other hand, homemade supported Au nanoparticles on
MgO, CeO2 and TiO2 are inefficient catalysts in the diboration of
phenylacetylene with pinB-Bpin.13 Our previous smooth
achievement of disilylation8 and silaboration10 of terminal alkynes
14
in the presence of the commercially available catalyst Au/TiO2
was an initiative to study alkyne diboration. This recyclable
catalyst has also been recently shown by other group15 to be highly
effective in several oxidative or reductive processes on alkynes.
____________
[a]
Department of Chemistry, University of Crete, Voutes 71003,
Iraklion, Greece.
E-mail: stratakis@chemistry.uoc.gr
Following this highly promising result we undertook an
examination of the scope and limitations of alkyne diboration. The
results are presented in Table 1, and reveal that not only terminal
Supporting information for this article is available on the WWW
under http://www.eurjoc.org
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10.1002/ejoc.201700754
European Journal of Organic Chemistry
Table 1. Diboration of alkynes by pinB-Bpin catalyzed by Au/TiO2.a
loading (0.5 mol% in Au). Only in the case of
trimethylsilylacetylene (16) and ester 21, mixtures of geometrical
isomers were formed, with the cis-adducts prevailing in both cases.
The explanation for the lack of stereoselectivity in these two
specific substrates is analysed in the mechanistic discussion. In
addition, deuterium-labelled alkyne 14-D (95% D),8a provided 14a-
D in which the deuterium content was 88%, indicative that
intermediate acetylides are not formed. The partial (<10%)
depletion of deuterium observed in product 14a-D occurs in the
starting alkyne under the reaction conditions; in general the extend
of depletion of deuterated terminal alkynes depends on reaction
time and temperature.8,24 As occurs with previous addition
reactions to alkynes catalysed by Au/TiO2, which have been
studied in our group, the catalyst is recyclable by simple filtration
and was reused for 5 consecutive runs. All runs went to completion
(100% conversion) without a substantial loss of its activity. For
instance, the reaction of the fifth run required 2.5-3 h, rather
attributable to the partial loss of catalyst during the process of
recycling. This protocol, as occurs with other analogous addition
reactions from our lab in the past, is purely heterogeneous. ICP-MS
analysis revealed that Au leaking into the solution was below ppm
level (8 ppb). Moreover, XPS analysis, prior and after catalysis
revealed that the profile of catalyst is essentially unchanged (see
Supporting Information).
Scheme 1. Mechanistic considerations regarding the Au nanoparticle-
catalyzed alkyne diboration and the explanation for the lack of
stereoselectivity in the case of two specific substrates.
Regarding the mechanistic considerations, we invoke as in the
previous additions of disilanes8 and silylborane10 to alkynes, the
insertion of Au nanoparticle (denoted as Aun) on the  B-B bond of
diborane (intermediate I), followed by delivery of the boron
moieties on the alkyne  bond in a cis-fashion via intermediate II
(Scheme 1). The nature of intermediates of Au nanoparticle (Aun)
insertion on sigma bonds, such as I, is currently under theoretical
investigation. The possibility that Au(I) species that typically occur
at the interface of Au nanoparticle and the support25 are the true
catalytic sites cannot be excluded. As noted in the introduction,
gold(I) species could in principle catalyze this addition, following
the typical oxidative insertion/reductive elimination sequence,3
although this type of reactivity has been limited so far to one
specific case.4 The clean cis-addition to the vast majority of
alkynes, but internal as well are equally reactive. Thus,
diphenylacetylene (17), as a typical example, forms under the same
conditions the cis-diboration product 17a in 86% isolated yield
after 2 h of reaction. The reactivity of internal alkynes is in sharp
contrast to the Au/TiO2-catalyzed disilylation8 or silaboration,10
where internal alkynes are in principle unreactive. All alkynes
(Table 1) reacted to completion using 1.2 equivalents of pinB-Bpin
within 2 h, and no side-products were observed. An exception is
enyne 4, which requires additional time to react completely and an
excess of pinB-Bpin is needed. Among the characteristics of this
diboration protocol is the tolerance of several functional groups
such as ester, cyano, halide, alkene, silane, THP- or silyl-protected
alcohols, etc. In two examples (substrates 1 and 19) the diboration
was run under solvent-free conditions, and both reactions went to
completion in relatively shorter reaction times (1 h) and catalyst
substrates rather excludes
a carbocationic intermediate as
suggested in the Au nanopore-catalyzed diboration.12 The lack of
Submitted to the European Journal of Organic Chemistry
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10.1002/ejoc.201700754
European Journal of Organic Chemistry
stereoselectivity in two specific substrates, TMS-acetylene (16)
and ,-unsaturated ester 21, could be rationalized, as previously
postulated in the disilylation and silaboration of these compounds,
due to a resonance-delocalization of electron density in the
plausible intermediates II from the bonded metal cluster to the
olefinic carbon that bears the electron-withdrawing silyl or ester
group and Bpin (rotamers III, Scheme 1).8a,10
separated from the desired silaboration products via column
chromatography. The regioselectivity in terms of formation of the
Table 2. Indirect silaboration of terminal alkynes by an equimolar mixture
pinB-Bpin/R3Si-SiR3 catalyzed by Au/TiO2.
b) Indirect silaboration of alkynes using mixtures of
disilane/diborane
In our previous studies of alkyne silaboration catalyzed by
Au/TiO2,10 a partial sigma bond metathesis of reacting silylborane
into disilane and diborane had been partially observed, leading
unnexpectedly to minor amounts of disilylation side-products in
certain cases. Since the reaction conditions and rates to achieve the
Au nanoparticle-catalyzed alkyne 1,2-disilylation8a and the current
o
1,2-diboration are more or less similar (heating to 60-70 C for a
few hours), and the 1,2-silaboration occurs readily at ambient
conditions, we envisioned that mixing the diborane pinB-Bpin and
a  1,2-disilane, should form in situ a Au-tethered silylborane via
sigma bond metathesis, and as a silylborane is more reactive
compared to disilane or diborane, indirect silaboration might be
anticipated. This silaboration concept requires that the sigma bond
metathesis[26] is reversible, and occurs, either by initial activation
of the diborane or disilane, as analyzed in Scheme 2.
Scheme 2. Rational protocol for the Au nanoparticle-catalyzed silaboration
for alkynes using a mixture of 1,2-disilane and pinB-Bpin.
To our delight, this rational proposal operates nicely,
obtaining silaboration products in good chemoselectivities ranging
from 65-85% depending on the substrate and the disilane. Thus,
treatment of an equimolar mixture of PhMe2SiSiMe2Ph with pinB-
Bpin in the presence of an alkyne (0.7 equiv), in benzene or
toluene as solvent, mainly results to the formation of silaboration
adducts in selectivities 65-85% for the alkyl-substituted alkynes
and 68-78% for aryl-substituted ones. The rest of the products are
mixtures of diboration and disilylation adducts which can be easily
C-B and C-Si bonds is exactly the same as in the direct Au/TiO2-
catalyzed silaboration with PhMe2SiBpin.10 Thus, Bpin moiety is
bonded on the more substituted sp-C of the terminal alkyne in 83-
95% relative ratio depending on the substrate. When using the
bulkier Ph2MeSiSiMePh2 and the less activated Me3SiSiMe3, very
similar results were obtained in terms of relative yields and
regioselectivity of silaboration. Ph3SiSiPh3 mixed with pinB-Bpin
Submitted to the European Journal of Organic Chemistry
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10.1002/ejoc.201700754
European Journal of Organic Chemistry
2H), 7.00-6.96 (m, 2H), 6.24 (s, 1H), 1.37 (s, 12H), 1.30 (s, 12H); 13C
NMR (125 MHz, CDCl3): 162.5 (d, JC-F = 245.0 Hz), 139.1 (d, JC-F = 3.0
Hz), 128.2 (d, JC-F = 8.0 Hz), 115.1 (d, JC-F = 21.0 Hz), 84.2, 83.6, 25.0,
24.8.
did not yield silaboration adduct, other than diboration. This
extremely bulky disilane is sluggishly activated by Au
nanoparticles.27 As in the diboration process, Au/TiO2 was
recycled and reused for 3 consecutive runs, again without any
obvious loss of its activity, while ICP-MS analysis revealed that
Au leaking into the solution was also below ppm level. PhMe2Si-
Bpin from the treatment of PhMe2SiSiMe2Ph with pinB-Bpin was
not detected by GC-MS, because according to our mechanism in
Scheme 2 it is formed in a steady state concentration due to the fact
that silylborane is far more reactive than pinB-Bpin or disilane. Yet,
PhMe2Si-O-Bpin was clearly seen, from the dehydrogenative
reaction among PhMe2Si-Aun-Bpin and moisture.10 The overall
results in terms of isolated yield, relative yields of the silaboration
pathway and regioselectivity of Si-C versus B-C bond formation,
are presented in Table 2.
(E)-2,2'-(1-(Cyclohex-1-en-1-yl)ethene-1,2-diyl)bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolane) (4a)22: 1H NMR (500 MHz, CDCl3): 5.95 (br s, 1H),
5.85 (s, 1H), 2.18-2.14 (m, 4H), 1.67-1.53 (m, 4H), 1.38 (s, 12H), 1.26 (s,
12H); 13C NMR (125 MHz, CDCl3): 140.1, 131.8, 83.9, 83.2, 26.4, 25.4,
25.0, 24.8, 22.7, 22.2.
(E)-2,2'-(Hept-1-ene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (5a)32: 1H NMR (500 MHz, CDCl3): 5.83 (s, 1H), 2.20 (td,
J1 = 7.5 Hz, J2 = 1.5 Hz, 2H), 1.44-1.38 (m, 2H), 1.30 (s, 12H), 1.28-1.24
(m, 4H), 1.25 (s, 12H), 0.84 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz,
CDCl3): 83.6, 83.2, 39.8, 31.5, 28.3, 24.9, 24.8, 22.5, 13.9.
(E)-2,2'-(1-Cyclopropylethene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (6a): 1H NMR (500 MHz, CDCl3): 5.79 (s, 1H), 1.59-1.54
(m, 1H), 1.31 (s, 12H), 1.23 (s, 12H), 0.74-0.70 (m, 2H), 0.66-0.63 (m,
2H); 13C NMR (125 MHz, CDCl3): 83.8, 83.1, 25.0, 24.8, 20.2, 7.7; 11B
NMR (160 MHz, CDCl3): 30.1; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd
for C17H30B2O4+H, 321.2408; found 321.2405.
Alkyne silaboration has been so far achieved using directly a
silylborane and a suitable catalyst.28 Typically, under Pd or Pt-
catalysis conditions, Bpin moiety is attached on the terminal sp-C
of a terminal alkyne and the addition is cis,29a,d while trans-addition
may also be observed under certain conditions.29b Opposite
regioselectivity with the Bpin moiety attached on the more
substituted sp-C has been also reported.29c,10 Our indirect protocol
allows silaboration without the requirement of synthesizing the
corresponding silylboranes pinB-SiPhMe2, pinB-SiPh2Me and
pinB-SiMe3,30 simply by using commercially available diborane
(pinB-Bpin) and 1,2-disilane substances.
(E)-2,2'-(3-Cyclohexylprop-1-ene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (7a)12: 1H NMR (500 MHz, CDCl3): 5.79 (s, 1H), 2.12 (d,
J = 7.0 Hz, 2H), 1.72-1.62 (m, 6H), 1.42-1.11 (m, 3H), 1.30 (s, 12H), 1.25
(s, 12H), 0.85-0.80 (m, 2H); 13C NMR (125 MHz, CDCl3): 83.5, 83.2, 48.4,
37.1, 33.3, 26.5, 26.4, 24.9.
(E)-2,2'-(1-Cyclohexylethene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
1
dioxaborolane) (8a)32: H NMR (500 MHz, CDCl3): 5.78 (d, J = 0.5 Hz,
1H), 2.09 (dt, J1 = 7.0 Hz, J2 = 0.5 Hz, 1H), 1.74-1.70 (m, 4H), 1.65-1.61
(m, 1H), 1.32 (s, 12H), 1.24 (s, 12H), 1.27-1.07 (m, 5H); 13C NMR (125
MHz, CDCl3): 83.6, 83.2, 47.6, 32.2, 26.6, 26.2, 25.0, 24.8.
Conclusions
In conclusion, we provide herein a highly efficient commercially
available Au nanoparticle catalytic system for the cis-diboration of
alkynes with bis(pinacolato)diboron, applicable to terminal and
internal functionalized alkynes. Taking advantage of the fast and
reversible Au/TiO2-catalyzed -bond metathesis among diboranes
and disilanes forming silylboranes, the indirect silaboration of
terminal alkynes can be achieved in good selectivities without
(E)-2,2'-(3-Phenylprop-1-ene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
1
dioxaborolane) (9a)33: H NMR (500 MHz, CDCl3): 7.24 (t, J = 7.0 Hz,
2H), 7.18-7.15 (m, 3H), 5.79 (br s, 1H), 3.55 (d, J = 1.0 Hz, 2H), 1.26 (s,
12H), 1.19 (s, 12H); 13C NMR (125 MHz, CDCl3): 139.2, 129.6, 128.1,
125.9, 83.6, 83.3, 45.6, 24.9, 24.7.
(E)-2,2'-(6-Chlorohex-1-ene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
1
dioxaborolane) (10a)18a,33: H NMR (500 MHz, CDCl3): 5.86 (br s, 1H),
using silylboranes,31 but an equimolar mixture
bis(pinacolato)diboron and a 1,2-disilane, instead.
of
3.51 (t, J = 7.0 Hz, 2H), 2.24 (td, J1 = 7.5 Hz, J2 = 1.0 Hz, 2H), 1.79-1.73
(m, 2H), 1.60-1.54 (m, 2H), 1.30 (s, 12H), 1.26 (s, 12H); 13C NMR (125
MHz, CDCl3): 83.7, 83.3, 45.0, 38.8, 32.1, 25.8, 24.9, 24.8.
Experimental Section
(E)-2,2'-(4-Bromobut-1-ene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (11a): 1H NMR (500 MHz, CDCl3): 6.00 (br s, 1H), 3.43 (t,
J = 7.0 Hz, 2H), 2.75 (td, J = 8.0 Hz, 2H), 1.29 (s, 12H), 1.28 (s, 12H); 13C
NMR (125 MHz, CDCl3): 83.9, 83.6, 42.9, 31.3, 24.9, 24.8; 11B NMR (160
MHz, CDCl3): 29.9; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for
C16H29BrB2O4+H, 387.1514; found 387.1508.
General procedure for the Au/TiO2-catalyzed diboration of alkynes: To
a vial containing the alkyne (0.2 mmol), bis(pinacolato)diboron (0.24
mmol) and 0.6 mL dry benzene are added 40 mg of Au/TiO2 (1.0 mol% in
Au). Typically, after 2 h at 65 oC (Table 1), the reaction is complete (TLC,
GC-MS). The slurry is filtered with the aid of DCM under a low pressure
through a short pad of silica gel or celite, and the filtrate is evaporated to
afford the diboration products which are purified by flash column
chromatography.
(E)-5,6-bis(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)hex-5-
enenitrile (12a)17: 1H NMR (500 MHz, CDCl3): 5.92 (s, 1H), 2.36-2.29 (m,
4H), 1.83-1.78 (m, 2H), 1.29 (s, 12H), 1.27 (s, 12H); 13C NMR (125 MHz,
CDCl3): 119.7, 83.9, 83.5, 38.2, 24.9, 24.8, 24.4, 16.4.
Spectroscopic data of diboration products
(E)-2,3-bis(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)allyl
acetate
(E)-2,2'-(1-Phenylethene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (1a)12: H NMR (500 MHz, CDCl3): 7.43 (d, J = 7.5 Hz,
1
(13a): H NMR (500 MHz, CDCl3): 6.10 (br s, 1H), 4.70 (d, J = 1.5 Hz,
2H), 2.04 (s, 3H), 1.29 (s, 12H), 1.27 (s, 12H); 11B NMR (160 MHz,
CDCl3): 30.2; 13C NMR (125 MHz, CDCl3): 170.5, 84.0, 83.6, 68.7, 24.8,
20.8; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for C17H30B2O6+H,
353.2307; found 353.2306.
1
2H), 7.30 (t, J = 7.5 Hz, 2H), 7.23 (t, J = 7.5 Hz, 1H), 6.29 (s, 1H), 1.38 (s,
12H), 1.31 (s, 12H); 13C NMR (125 MHz, CDCl3): 143.0, 128.3, 127.6,
126.6, 84.1, 83.6, 25.1, 24.9.
(E)-2,2'-(1-(p-Tolyl)ethene-1,2-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (2a)12: H NMR (500 MHz, CDCl3): 7.33 (d, J = 8.0 Hz,
(E)-((2,3-bis(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
1
yl)allyl)oxy)(tert-butyl)diphenylsilane (14a): 1H NMR (500 MHz,
CDCl3): 7.68 (dd, J1 = 7.5 Hz, J2 = 1.0 Hz, 4H), 7.42-7.34 (m, 6H), 6.43 (br
s, 1H), 4.34 (d, J = 2.0 Hz, 2H), 1.31 (s, 12H), 1.26 (s, 12H), 1.04 (s, 9H);
11B NMR (160 MHz, CDCl3): 30.8; 13C NMR (125 MHz, CDCl3): 135.5,
133.7, 129.4, 127.6, 83.7, 83.4, 67.4, 26.8, 24.9, 19.3; HRMS (ESI-Orbit
trap) m/z: [M+H]+ calcd for C31H46B2O5Si+H, 549.3379; found 549.3374.
2H), 7.11 (t, J = 8.0 Hz, 2H), 6.26 (s, 1H), 2.32 (s, 3H), 1.38 (s, 12H), 1.30
(s, 12H); 13C NMR (125 MHz, CDCl3): 140.2, 137.4, 129.0, 126.5, 84.1,
83.5, 25.1, 24.9, 21.1.
(E)-2,2'-(1-(4-Fluorophenyl)ethene-1,2-diyl)bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolane) (3a)12: H NMR (500 MHz, CDCl3): 7.42-7.38 (m,
1
Submitted to the European Journal of Organic Chemistry
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10.1002/ejoc.201700754
European Journal of Organic Chemistry
(E)-2,2'-(3-((Tetrahydro-2H-pyran-2-yl)oxy)prop-1-ene-1,2-
diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (15a)12: H NMR (500
83.8, 24.6, -2.1; 11B NMR (160 MHz, CDCl3): 30.5; HRMS (ESI-Orbit
trap) m/z: [M+H]+ calcd for C27H31BO2Si+H, 427.2265; found 427.2260.
(E)-Trimethyl(2-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)vinyl)silane (1d): 1H NMR (500 MHz, CDCl3): 7.40-7.37 (m, 2H), 7.30-
7.19 (m, 3H), 6.72 (br s, 1H), 1.33 (s, 12H), 0.21 (s, 9H); 13C NMR (125
MHz, CDCl3): 150.6, 145.6, 128.0, 126.9, 126.7, 83.8, 25.1, 0.3; 11B NMR
(160 MHz, CDCl3): 30.2; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for
C17H27BO2Si+H, 303.1952; found 303.1950.
1
MHz, CDCl3): 6.14 (br s, 1H), 4.65 (m, 1H), 4.38 (dd, J1 = 14.5 Hz, J2 =
2.0 Hz, 1H), 4.10 (dd, J1 = 14.5 Hz, J2 = 1.5 Hz, 1H), 3.87-3.82 (m, 1H),
3.49-3.45 (m, 1H), 1.89-1.81 (m, 1H), 1.72-1.50 (m, 5H), 1.30 (s, 12H),
1.27 (s, 12H); 13C NMR (125 MHz, CDCl3): 97.5, 83.8, 83.4, 71.6, 61.5,
30.4, 25.5, 24.9, 24.9, 24.8, 19.0.
(1,2-bis(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-
1
yl)vinyl)trimethylsilane (16a): E-isomer18a. H NMR (500 MHz, CDCl3):
(E)-Trimethyl(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-(p-
6.59 (s, 1H), 1.33 (s, 12H), 1.26 (s, 12H), 0.09 (s, 9H); 13C NMR (125 MHz,
tolyl)vinyl)silane (2d): H NMR (500 MHz, CDCl3): 7.30 (d, J = 8.0 Hz,
1
CDCl3): 83.5, 83.5, 25.2, 24.9, -1.5; 11B NMR (160 MHz, CDCl3): 32.0. Ζ-
2H), 7.10 (d, J = 8.0 Hz, 2H), 6.70 (s, 1H), 2.33 (s, 3H), 1.33 (s, 12H), 0.21
(s, 9H); 13C NMR (125 MHz, CDCl3): 149.4, 142.7, 136.4, 128.7, 126.8,
83.8, 25.1, 21.1, 0.3; 11B NMR (160 MHz, CDCl3): 30.4; HRMS (ESI-Orbit
trap) m/z: [M+H]+ calcd for C18H29BO2Si+H, 317.2108; found 317.2102.
(E)-(2-(4-Fluorophenyl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
isomer: H NMR (500 MHz, CDCl3): 7.03 (s, 1H), 1.25 (s, 12H), 1.24 (s,
12H), 0.17 (s, 9H); 13C NMR (125 MHz, CDCl3): 83.4, 83.3, 24.9, 24.7,
0.3; 11B NMR (160 MHz, CDCl3): 28.9.
(Z)-1,2-Diphenyl-1,2-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
1
yl)ethene (17a)12: H NMR (500 MHz, CDCl3): 7.07-7.01 (m, 6H), 6.96-
yl)vinyl)dimethyl(phenyl)silane (3b): H NMR (500 MHz, CDCl3): 7.60-
6.93 (m, 4H), 1.32 (s, 24H); 13C NMR (125 MHz, CDCl3): 141.2, 129.3,
7.57 (m, 2H), 7.42-7.39 (m, 2H), 7.35-7.32 (m, 3H), 6.93-6.89 (m, 2H),
6.83 (s, 1H), 1.16 (s, 12H), 0.48 (s, 6H); 13C NMR (125 MHz, CDCl3):
162.2 (d, JC-F = 244.0 Hz), 147.8, 141.2, 140.9 (d, JC-F = 3.0 Hz), 133.8,
128.6, 128.6 (d, JC-F = 8.0 Hz), 127.6, 114.7 (d, JC-F = 21.0 Hz), 83.9, 24.8,
-0.6; 11B NMR (160 MHz, CDCl3): 29.7; HRMS (ESI-Orbit trap) m/z:
[M+H]+ calcd for C22H29BFO2Si+H, 383.2014; found 383.2009.
127.4, 125.8, 84.0, 24.9.
(Z)-2,2'-(Hex-3-ene-3,4-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (18a)18a: 1H NMR (500 MHz, CDCl3): 2.21 (q, J = 7.5 Hz,
4H), 1.29 (s, 24H), 0.97 (t, J = 7.5 Hz, 6H); 13C NMR (125 MHz, CDCl3):
83.3, 24.9, 23.6, 14.3.
(Z)-2,2'-(Dec-5-ene-5,6-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (19a)20: H NMR (500 MHz, CDCl3): 2.19-2.16 (m, 4H),
(E)-(2-(4-Fluorophenyl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
1
yl)vinyl)(methyl)diphenylsilane (3c): H NMR (300 MHz, CDCl3): 7.62-
1.38-1.30 (m, 8H), 1.28 (s, 24H), 0.88 (t, J = 7.5 Hz, 6H); 13C NMR (125
7.34 (m, 12H), 7.06-6.99 (m, 3H), 1.02 (s, 12H), 0.87 (s, 3H); 13C NMR (75
MHz, CDCl3): 162.3 (d, JC-F = 244.5 Hz), 145.6, 140.9 (d, JC-F = 3.0 Hz),
138.7, 134.6, 128.9, 128.7 (d, JC-F = 8.0 Hz), 127.4, 114.9 (d, JC-F = 21.0
Hz), 84.0, 24.6, -2.1; 11B NMR (160 MHz, CDCl3): 30.3; HRMS (ESI-Orbit
trap) m/z: [M+H]+ calcd for C27H30BFO2Si+H, 445.2170; found 445.2166.
(E)-Methyldiphenyl(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
MHz, CDCl3): 83.2, 32.0, 30.5, 24.9, 23.0, 14.0.
(Z)-2,2'-(Hept-2-ene-2,3-diyl)bis(4,4,5,5-tetramethyl-1,3,2-
1
dioxaborolane) (20a): H NMR (500 MHz, CDCl3): 2.18 (t, J = 7.5 Hz,
2H), 1.74 (s, 3H), 1.36-1.30 (m, 4H), 1.28 (s, 12H), 1.27 (s, 12H), 0.88 (t, J
= 7.5 Hz, 6H); 13C NMR (125 MHz, CDCl3): 83.3, 83.2, 31.1, 30.8, 24.9,
24.8, 23.0, 15.9, 14.0; 11B NMR (160 MHz, CDCl3): 30.8; HRMS (ESI-
Orbit trap) m/z: [M+H]+ calcd for C19H36B2O4+H, 351.2878; found
351.2874.
1
yl)hept-1-en-1-yl)silane (5c): H NMR (500 MHz, CDCl3): 7.55-7.52 (m,
4H), 7.33-7.28 (m, 6H), 6.57 (s, 1H), 2.32 (t, J = 7.5 Hz, 2H), 1.49-1.26 (m,
6H), 0.95 (s, 12H), 0.90 (t, J = 7.5 Hz, 3H), 0.74 (s, 3H); 13C NMR (125
MHz, CDCl3): 141.6, 139.3, 134.6, 128.5, 127.5, 83.3, 41.3, 31.5, 29.1,
24.5, 22.6, 14.1, -2.1; 11B NMR (160 MHz, CDCl3): 30.1; HRMS (ESI-
Orbit trap) m/z: [M+H]+ calcd for C26H37BO2Si+H, 421.2734; found
421.2727.
Ethyl 2,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)but-2-enoate
1
(20a): Ζ-isomer: H NMR (500 MHz, CDCl3): 4.18 (q, J = 7.0 Hz, 2H),
2.04 (s, 3H), 1.30 (s, 12H), 1.28 (s, 12H), 1.26 (t, J = 7.0 Hz, 6H); 13C
NMR (125 MHz, CDCl3): 168.8, 84.2, 84.0, 60.0, 24.8, 24.7, 19.3, 14.3. E-
1
isomer34: H NMR (500 MHz, CDCl3): 4.24 (q, J = 7.0 Hz, 2H), 2.06 (s,
(E)-(2-Cyclopropyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
3H), 1.29 (s, 12H), 1.27 (s, 12H), 1.27 (t, J = 7.0 Hz, 6H); 13C NMR (125
MHz, CDCl3): 173.0, 83.4, 82.9, 61.8, 24.8, 24.6, 19.9, 14.0; 11B NMR
(160 MHz, CDCl3): 30.0.
yl)vinyl)(methyl)diphenylsilane (6c): H NMR (500 MHz, CDCl3): 7.55-
1
7.51 (m, 4H), 7.323-7.28 (m, 6H), 6.39 (s, 1H), 0.95 (s, 12H), 0.73 (s, 3H);
13C NMR (125 MHz, CDCl3): 139.3, 135.9, 134.6, 128.5, 127.5, 83.4, 24.6,
19.9, 8.6, -2.1; 11B NMR (160 MHz, CDCl3): 30.0; HRMS (ESI-Orbit trap)
m/z: [M+H]+ calcd for C24H31BO2Si+H, 391.2265; found 391.2261.
(E)-(3-Cyclohexyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)prop-
General procedure for the Au/TiO2-catalyzed indirect silaboration of
alkynes: To a vial containing bis(pinacolato)diboron (0.3 mmol), and the
-disilane (0.3 mmol) in 1 mL dry benzene are added 40 mg of Au/TiO2
o
(1.0 mol% in Au) and the alkyne (0.21 mmol). After heating to 65 C for 2
1-en-1-yl)dimethyl(phenyl)silane (7b)29c 1H NMR (500 MHz, CDCl3):
:
h, the reaction is complete (TLC, GC-MS). The slurry is filtered with the
aid of DCM under a low pressure through a short pad of silica gel or celite,
and the filtrate is evaporated. The residue is purified by flash column
chromatography to afford the silaboration products.
7.56-7.53 (m, 2H), 7.33-7.30 (m, 3H), 6.37 (s, 1H), 2.17 (dd, J1 = 7.0 Hz, J2
= 1.0 Hz, 2H), 1.72-1.15 (m, 11H), 1.11 (s, 12H), 0.40 (s, 6H); 13C NMR
(125 MHz, CDCl3): 145.3, 141.3, 133.8, 128.3, 127.4, 83.2, 49.5, 37.9, 33.2,
26.7, 26.4, 24.7, -0.6.
Spectroscopic data of silaboration products
(E)-(3-Cyclohexyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)prop-
1-en-1-yl)(methyl)diphenylsilane (7c): 1H NMR (300 MHz, CDCl3): 7.56-
7.27 (m, 10H), 6.54 (s, 1H), 2.23 (d, J = 7.0 Hz, 2H), 1.73-1.16 (m, 11H),
0.95 (s, 12H), 0.76 (s, 3H); 13C NMR (75 MHz, CDCl3): 143.1, 139.4,
134.6, 128.5, 127.5, 83.2, 49.5, 37.9, 33.2, 26.6, 26.4, 24.5, -2.1; 11B NMR
(160 MHz, CDCl3): 30.1; HRMS (ESI-Orbit trap) m/z: [M+H]+
C28H39BO2Si+H, 447.2891; found 447.2885.
The spectroscopic data of silaboration adducts 1b, 2b, 4b, 5b, 6b and 8b,
have been reported earlier by our group (reference 10).
(E)-Dimethyl(phenyl)(2-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)vinyl)silane (1b)29c: 1H NMR (500 MHz, CDCl3): 7.62-
7.60 (m, 2H), 7.46 (br d, J = 7.5 Hz, 2H), 7.36-7.30 (m, 5H), 7.24 (t, J = 7.5
Hz, 1H), 6.89 (s, 1H), 1.18 (s, 12H), 0.51 (s, 6H); 13C NMR (125 MHz,
CDCl3): 147.6, 145.3, 140.5, 133.9, 128.5, 128.0, 127.6, 127.0, 127.0, 83.8,
24.8, -0.6.
(E)-(2-Cyclohexyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
1
yl)vinyl)trimethylsilane (8d): H NMR (500 MHz, CDCl3): 6.20 (s, 1H),
(E)-Methyldiphenyl(2-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-
2.14-2.09 (m, 1H), 1.75-1.12 (m, 10H), 1.28 (s, 12H), 0.11 (s, 9H); 13C
NMR (125 MHz, CDCl3): 141.8, 83.2, 47.7, 32.6, 26.8, 26.4, 25.1, 0.4; 11B
NMR (160 MHz, CDCl3): 30.4; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd
for C17H33BO2Si+H, 309.2421; found 309.2416.
1
dioxaborolan-2-yl)vinyl)silane (1c): H NMR (500 MHz, CDCl3): 7.64-
7.30 (m, 15H), 7.09 (br s, 1H), 1.03 (s, 12H), 0.88 (s, 3H); 13C NMR (125
MHz, CDCl3): 145.3, 144.9, 138.7, 134.6, 128.8, 128.1, 127.7, 127.2, 127.0,
Submitted to the European Journal of Organic Chemistry
5
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201700754
European Journal of Organic Chemistry
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(E)-Dimethyl(phenyl)(3-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)prop-1-en-1-yl)silane (9b): 1H NMR (500 MHz,
CDCl3): 7.57-7.54 (m, 2H), 7.33-7.17 (m, 8H), 6.44 (s, 1H), 3.62 (s, 2H),
1.01 (s, 12H), 0.41 (s, 6H); 13C NMR (125 MHz, CDCl3): 145.1, 140.9,
140.6, 133.8, 129.2, 128.4, 128.0, 127.5, 125.7, 83.4, 47.5, 24.6, -0.7; 11B
NMR (160 MHz, CDCl3): 30.1; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd
for C23H31BO2Si+H, 379.2265; found 379.2259.
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(E)-Methyldiphenyl(3-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)prop-1-en-1-yl)silane (9c): 1H NMR (300 MHz,
CDCl3): 7.59-7.56 (m, 4H), 7.36-7.21 (m, 11H), 6.67 (s, 1H), 3.72 (s, 2H),
0.87 (s, 12H), 0.79 (s, 3H); 13C NMR (75 MHz, CDCl3): 142.7, 140.4,
138.9, 134.6, 129.2, 128.6, 128.1, 127.6, 125.8, 83.4, 47.6, 24.4, -2.2; 11B
NMR (160 MHz, CDCl3): 29.9; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd
for C28H33BO2Si +H, 441.2421; found 441.2417.
(E)-Trimethyl(3-phenyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)prop-1-en-1-yl)silane (9d): 1H NMR (500 MHz, CDCl3): 7.25 (t, J = 7.5
Hz, 2H), 7.18-7.10 (m, 3H), 6.29 (s, 1H), 3.55 (s, 2H), 1.16 (s, 12H), 0.12
(s, 9H); 13C NMR (125 MHz, CDCl3): 148.1, 140.8, 129.2, 128.0, 125.6,
83.4, 47.4, 24.8, 0.2; 11B NMR (160 MHz, CDCl3): 29.9; HRMS (ESI-Orbit
trap) m/z: [M+H]+ calcd for C18H29BO2Si+H, 317.2108; found 317.2103.
(E)-(6-Chloro-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)hex-1-en-
1-yl)(methyl)diphenylsilane (10c): 1H NMR (500 MHz, CDCl3): 7.54-7.52
(m, 4H), 7.33-7.29 (m, 6H), 6.60 (s, 1H), 3.56 (t, J = 7.0 Hz, 2H), 2.35 (td,
J1 = 7.5 Hz, J2 = 1.0 Hz, 2H), 1.83-1.77 (m, 2H), 1.65-1.59 (m, 2H), 0.95 (s,
12H), 0.74 (s, 3H); 13C NMR (125 MHz, CDCl3): 142.9, 139.1, 134.6,
128.6, 127.6, 83.4, 45.1, 40.4, 32.2, 26.7, 24.5, -2.2; 11B NMR (160 MHz,
CDCl3): 29.6; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for
C25H34BClO2Si+H, 441.2188; found 441.2183.
(E)-6-(Dimethyl(phenyl)silyl)-5-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)hex-5-enenitrile (12b)29c: 1H NMR (500 MHz, CDCl3):
7.54-7.52 (m, 2H), 7.34-7.30 (m, 3H), 6.51 (s, 1H), 2.38 (td, J1 = 7.5 Hz, J2
= 1.0 Hz, 2H), 2.30 (t, J = 7.5 Hz, 2H), 1.85-1.79 (m, 2H), 1.12 (s, 12H),
0.41 (s, 6H); 13C NMR (125 MHz, CDCl3): 147.7, 140.7, 133.7, 128.5,
127.5, 119.9, 83.6, 40.1, 25.2, 24.7, 16.5, -0.8.
(E)-5-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-6-
1
(trimethylsilyl)hex-5-enenitrile (12d): H NMR (500 MHz, CDCl3): 6.37
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(s, 1H), 2.32 (td, J1 = 7.5 Hz, J2 = 1.0 Hz, 2H), 2.28 (t, J = 7.5 Hz, 2H),
1.82-1.76 (m, 2H), 1.26 (s, 12H), 0.13 (s, 9H); 13C NMR (125 MHz,
CDCl3): 150.6, 120.0, 83.5, 40.0, 25.2, 24.9, 16.4, 0.2; 11B NMR (160 MHz,
CDCl3): 30.3; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd for
C15H28BNO2Si +H, 294.2061; found 294.2054.
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(E)-3-(Dimethyl(phenyl)silyl)-2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)allyl acetate (13b): 1H NMR (500 MHz, CDCl3): 7.55-
7.53 (m, 2H), 7.33-7.30 (m, 3H), 6.67 (br s, 1H), 4.75 (d, J = 2.0 Hz, 2H),
2.09 (s, 3H), 1.13 (s, 12H), 0.43 (s, 6H); 13C NMR (125 MHz, CDCl3):
170.6, 145.3, 140.2, 133.8, 128.5, 127.5, 83.7, 69.6, 24.7, 21.0, -1.0; 11B
NMR (160 MHz, CDCl3): 29.2; HRMS (ESI-Orbit trap) m/z: [M+H]+ calcd
for C19H29BO4Si +H, 361.2006; found 361.2002.
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Supporting Information (see also the footnote on the first page of this
article): Copies of 1H/13C NMR of all compounds, and XPS analysis of
Au/TiO2 before and after catalysis.
[30] a) T. Kurahashi, T. Hata, H. Masai, H. Kitagawa, M. Shimizu, T.
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[31] For a recent example of a Cu-catalyzed alkyne borylstannylation
without the direct use of a stannylborane, see: H. Yoshida, M.
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Acknowledgments
We thank ProFI (ITE, Heraklion, Greece) for obtaining the HRMS spectra,
and prof. D. Gournis and Dr. K. Spyrou (Department of Materials Science
& Engineering, University of Ioannina, Greece) for the XPS analysis.
____________
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Submitted to the European Journal of Organic Chemistry
6
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10.1002/ejoc.201700754
European Journal of Organic Chemistry
Submitted to the European Journal of Organic Chemistry
7
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10.1002/ejoc.201700754
European Journal of Organic Chemistry
((Key Topic))
Marios Kidonakis and Manolis
Stratakis,*….... Page No. – Page No.
Gold
nanoparticles-catalysed
mild
diboration and the indirect silaboration of
alkynes without using silylboranes
Catalysis by Au nanoparticles
Au nanoparticles supported on TiO2 is an
excellent catalytic system for cis-1,2-
among
1,2-disilanes
and
bis(pinacolato)diboron in the presence of
Au NPs, an indirect method for alkyne
silaboration was developed without the
direct use of silylboranes.
Keywords: Heterogeneous catalysis / Au
nanoparticles / diboration / silaboration /
alkynes / -bond metathesis
alkyne
diboration
with
Taking
bis(pinacolato)diboron.
advantage of a fast  bond metathesis
Submitted to the European Journal of Organic Chemistry
8
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201700754
European Journal of Organic Chemistry
Submitted to the European Journal of Organic Chemistry
9
This article is protected by copyright. All rights reserved.