Highly selective silylformylation of internal and functionalised alkynes with a cationic dirhodium(II) complex catalyst

Article abstract of DOI:10.1016/j.jorganchem.2009.12.018

The tetracationic complex [Rh₂(MeCN)₂(Naft)₄](BF₄)₄ (Naft = μ-1,8-naphthyridine) was found to be an efficient catalyst for the silylformylation of internal and functionalised alkynes to yield useful synthetic intermediates. The complex exhibits an unprecedented chemoselectivity towards alkyne silylformylation instead of simple hydrosilylation, as well as a good stereoselectivity. The catalytic efficiency of the complex is markedly superior compared to that of previously reported catalysts such as [Rh⁺ C₇ H₈ BPh₄^-] or Rh₄(CO)₁₂; incidentally, the performance of the latter catalyst was found to vary dramatically with its shelf-life, which indicates that the catalyst evolves with ageing towards other species, most notably higher nuclearity rhodium carbonyl clusters, which are more chemoselective towards silylformylation. Preliminary results on the determination of the catalytically active species in the case of complex [Rh₂(MeCN)₂(Naft)₄](BF₄)₄ indicate that the complex is reduced in situ to a dirhodium(I) species which maintains the dimeric, lantern-shaped structure.

Full text of DOI:10.1016/j.jorganchem.2009.12.018

Journal of Organometallic Chemistry 695 (2010) 792–798
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Highly selective silylformylation of internal and functionalised alkynes
with a cationic dirhodium(II) complex catalyst
a
a
Andrea Biffis a, , Luca Conte , Cristina Tubaro , Marino Basato a,b, Laura Antonella Aronica c,
*
Angela Cuzzola c, Anna Maria Caporusso c
a Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, I-35131 Padova, Italy
b ISTM-CNR, via Marzolo 1, I-35131 Padova, Italy
c Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, I-56126 Pisa, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 October 2009
Received in revised form 14 December 2009
Accepted 15 December 2009
Available online 29 December 2009
The tetracationic complex [Rh2(MeCN)2(Naft)4](BF4)4 (Naft = l-1,8-naphthyridine) was found to be an
efficient catalyst for the silylformylation of internal and functionalised alkynes to yield useful synthetic
intermediates. The complex exhibits an unprecedented chemoselectivity towards alkyne silylformylation
instead of simple hydrosilylation, as well as a good stereoselectivity. The catalytic efficiency of the com-
plex is markedly superior compared to that of previously reported catalysts such as [RhþC7H8BPhꢀ] or
4
Rh4(CO)12; incidentally, the performance of the latter catalyst was found to vary dramatically with its
shelf-life, which indicates that the catalyst evolves with ageing towards other species, most notably
higher nuclearity rhodium carbonyl clusters, which are more chemoselective towards silylformylation.
Preliminary results on the determination of the catalytically active species in the case of complex
[Rh2(MeCN)2(Naft)4](BF4)4 indicate that the complex is reduced in situ to a dirhodium(I) species which
maintains the dimeric, lantern-shaped structure.
Keywords:
Rhodium
1,8-Naphthyridine
Silylformylation
Alkynes
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
atoms to the +III oxidation state [5e], introduction of an additional,
substitutionally inert ligand into one of the apical positions of the
Neutral dinuclear complexes of rhodium(II) are known to be
catalytically active in a number of synthetically useful transforma-
tions [1]. The most thoroughly investigated reactions are metal-
mediated carbene transfer reactions [2], but in the course of the
last ten years the successful application of this kind of catalysts
has been considerably extended to include nitrene transfer reac-
tions [3], allylic oxidations [4], cycloadditions [5], C–C coupling
reactions [6], and reactions involving silanes, such as silane alco-
holysis, hydrosilylations or silylformylations [7,8].
It has been recognised that in most of these reactions the elec-
trophilicity of the dirhodium(II) complex catalyst is a key factor in
determining its activity and selectivity [2c,d,3f,5e]. This parameter
has been generally modulated by varying the electron-donating
character of the anionic bridging ligands in the metal complex. Re-
cently, though, alternative approaches have been reported that al-
low to prepare novel dirhodium catalysts with tailored
electrophilicity, namely upon oxidation of one of the rhodium
complex [4d,6], or replacement of the bridging anionic ligands
with neutral ones yielding a cationic complex [9].
We have an ongoing research program aimed at the prepara-
tion of different kinds of electrophilic dirhodium(II) complexes
using the latter approach and at the evaluation of their catalytic
performance in technologically relevant reactions [9]. Although
cationic dirhodium(II) complexes in which the acetate ligands
have been substituted by coordinated solvent molecules, most
commonly acetonitrile, are quite well known [10], much less
common are examples in which the acetate ligands are substi-
tuted by neutral bidentate ligands [9b,11,12]. The most com-
monly employed ligands for this purpose belong to the class of
1,8-naphthyridines [9b,11,12a,b]. In particular, we have recently
prepared complex
1 (Scheme 1), a homoleptic, tetracationic
dirhodium(II) complex bearing four bridging 1,8-naphthyridines
as equatorial ligands and two loosely bound acetonitrile mole-
cules as axial ligands, and we have reported preliminary results
demonstrating the catalytic potency of this complex in the silyl-
formylation of a model terminal alkyne [9b]. We now present an
alternative, more efficient synthetic pathway leading to the same
complex as well as the results of an evaluation of its notable cat-
alytic activity and selectivity in the silylformylation of internal
as well as functionalised alkynes.
* Corresponding author.Tel.: +39 049 8275216; fax: +39 049 8275223.
E-mail address: andrea.biffis@unipd.it (A. Biffis).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.12.018

A. Biffis et al. / Journal of Organometallic Chemistry 695 (2010) 792–798
793
ready developed for terminal acetylenes, i.e. 30 atm of CO, equimo-
lar amounts of substrates, 0.5–1 mol% of catalysts, 100 °C, 24 h
(Table 1). The catalytic performance of the naphthyridine complex
1 was compared with that of three other literature-known rho-
dium species with different electronic and structural features:
dirhodium(II) precursor [Rh2(OAc)2(MeCN)6](BF4)2 (2), a neutral
cluster species such as Rh4(CO)12 (3) and the zwitterionic rho-
dium(I) catalyst [RhþC7H8BPhꢀ] (4). The last two catalysts had
4
been already used in the silylformylation reactions of several sub-
strates containing C@O and C–C terminal multiple bonds [17].
First of all the reactivity of phenylpropyne 5a with Me2PhSiH
was considered, since it is well known that the presence of an aro-
matic ring conjugated to the triple bond has an activating effect to-
wards the silylformylation reaction [17].
Scheme 1. Structure of complex 1.
As described in Table 1, while a negligible conversion was ob-
served running the process at room temperature (entry 1), high
conversion and chemoselectivity towards the aldehydic products
(93%) could be reached at 100 °C in reactions performed with a cat-
alytic amount (0.4 mol%) of complex 1 (entry 2), the less hindered
aldehydic isomer (Z)-7a being formed in more than 80% yield. On
the contrary, all the other rhodium complexes afforded mainly
the hydrosilylation by-products (Z)-8(80), even if a higher amount
of catalyst was used (Table 1, entries 3–5 and 8 vs. 2). In particular,
the dirhodium complex [Rh2(OAc)2(MeCN)6](BF4)2 (2) (Table 1, en-
try 1) turned out to be the most active towards the hydrosilylation
reaction, which result highlights the importance of the naphthyri-
dine ligand in steering the reaction chemoselectivity.
We were surprised by the low chemoselectivity towards the
silylformylation reaction recorded with Rh4(CO)12. Indeed, Matsu-
da et al. used Rh4(CO)12 in the silylformylation of phenylpropyne
and reported a very different result (82% total selectivity for the
b-silylalkenals) [17a], in spite of the fact that the reactions were
performed under almost the same experimental conditions. We
set out to investigate on this discrepancy in more detail and found
that a sample of freshly prepared and recrystallised Rh4(CO)12 be-
haved as a poor silylformylation catalyst regardless of the amount
of complex employed (Table 1, entries 4–6, catalyst indicated as
3N), which was also unexpected since we had previously pointed
out [17b] the importance of using a low quantity of Rh4(CO)12 in
the silylformylation of sterically hindered acetylenes to improve
the chemoselectivity of the process. On the other hand, when a
sample of ‘‘old” Rh4(CO)12, i.e. kept under argon and at low temper-
ature (3 °C) for at least 6 months (Table 1, entry 7, catalyst indi-
cated as 3O), was reacted with phenylpropyne and Me2PhSiH
under CO, a dramatic increase in the chemoselectivity for the silyl-
formylation reaction was observed. An analogous trend was ob-
served in the reactions carried out with 5-decyne (Table 1,
entries 10 and 11). The obtained results indicate that freshly pre-
pared Rh4(CO)12 indeed displays poor chemoselectivity towards
silylformylation; on the other hand, the catalyst evolves with age-
ing even if properly stored towards catalytic species which are
much more chemoselective. Preliminary investigations based on
electrospray mass spectrometry (ESI-MS) of the two Rh4(CO)12
(3N and 3O) samples showed a correlation between the ageing time
of the rhodium complexes and the presence of increasing amounts
of Rh6(CO)16. We employed the method of Handerson et al. [18],
who described the structural characterisation of metal carbonyl
2. Results and discussion
The first problem that we intended to address was the develop-
ment of a more practical synthesis for complex 1. The previously
reported procedure [9b] for the synthesis of the complex involved
namely at first reaction of Rh2(OAc)4 with 4 equiv. of 1,8-naph-
thyridine in acetic acid at reflux, with formation of a tetrakis-
dirhodium(II) tetranaphthyridino complex with two acetate li-
gands occupying the axial coordination sites and two acetate coun-
terions. Treatment with NaBPh4 caused the substitution of the
acetate counterions with two BPhꢀ4 anions, and subsequent reac-
tion with Meerwein’s salt triethyloxonium tetrafluoborate re-
moved the apical acetates yielding the tetracationic complex 1.
The overall yield of this process was moderate (38%), it required
extensive purification of the final product and generated a lot of
waste. We have devised a cleaner and more straightforward proce-
dure for the same synthesis which moves from the literature-
known cationic complex [Rh2(OAc)2(MeCN)6](BF4)2, readily obtain-
able in one step and high yield from commercial Rh2(OAc)4 [10a].
Reaction of this complex with 4 equiv. of 1,8-naphthyridine in ace-
tonitrile yielded the intermediate dicationic complex [Rh2(OAc)2(-
Naft)4](BF4)2,
which
was
subsequently
treated
with
triethyloxonium tetrafluoborate without further purification to re-
move the two apical acetates yielding complex 1.
The catalytic performance of complex 1 had already been pre-
liminarily evaluated [9b] in the silylformylation reaction of 1-hex-
yne with dimethylphenylsilane as model reagents. The complex
showed both high efficiency and selectivity towards the formation
of (Z)-2-[(dimethyl-phenyl-silyl)-methylene]-hexanal (‘‘b-silylalk-
enal”). Moreover, it resulted completely unable to promote the
hydrosilylation process, a common side reaction often observed
under the experimental conditions of the silylformylation reaction.
It seemed therefore reasonable to evaluate 1 as a general catalyst
for the synthesis of b-silylalkenals, polyfunctionalised molecules
that can be converted into dienes [13], dienones [14], a,b-unsatu-
rated alcohols [15], esters and ketones [16] and can undergo fluo-
ride promoted aryl migration [17b] thus generating 2-
(arylmethyl)-aldehydes, important industrial precursors of per-
fumes. Consequently, we extended our investigation to internal al-
kynes, which are notoriously difficult to silylformylate selectively
[17]. The silylformylation reactions of disubstituted alkynes
(Scheme 2) were carried out under the experimental conditions al-
Scheme 2. Silylformylation of 1,2-disubstituted alkynes.

794
A. Biffis et al. / Journal of Organometallic Chemistry 695 (2010) 792–798
Table 1
Silylformylation of internal acetylenes with dimethylphenylsilane.a
Entry
R1
R2
5
[Rh]b (mol%)
Conv. (%)c
Selectivity (%)d
(Z)-7(70)
(E)-8(80)
(8/80)
(7/70)e
1f
2
3
Me
Me
Me
Me
Me
Me
Me
Me
nBu
nBu
nBu
nBu
Me
Me
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
nBu
nBu
nBu
nBu
nPr
nPr
a
a
a
a
a
a
a
a
b
b
b
b
c
1 (0.4)
1 (0.4)
2 (0.8)
3N (0.5)
3N (0.2)
3N (0.05)
3O (0.5)
4 (1)
1 (0.4)
3N (0.5)
3O (0.5)
4 (1)
7
94
6
100
100
100
100
100
86
100
98
87
93(83/17) [71]
8(86/24)
14(100/0)
16(100/0)
13(100/0)
60(82/18)
24(100/0)
96 [56]
7(50/50)
92(68/32)
86(75/25)
84(72/28)
87(70/30)
40(75/25)
76(60/40)
4
73
50
47
18(52/48)
45(62/38)
4
5g
6
7
8h
9
10
11
12
13
14
27
50
82
100
97
53 [41]
82(65/35) [43]
55(73/27) [30]
1 (0.4)
4 (1)
c
100
a
b
c
Reaction conditions: 3 mmol Me2PhSiH, 3 mmol alkyne, 3 ml CH2Cl2, 24 h, 30 atm PCO, 100 °C.
Rhodium catalysts: 1: [Rh2(MeCN)2(Naft)4](BF4)4 2: [Rh2(OAc)2(MeCN)6](BF4)2, 3: Rh4(CO)12; 4: [RhþC7H8BPh4ꢀ].
Determined by GC analysis.
d
e
f
Determined by GC and 1H NMR analysis; the diastereomers ratio is reported in round brackets.
Isolated yields (%) are reported in square brackets.
Reaction performed at room temperature.
Reaction performed in toluene.
Reaction performed under 40 atm of CO.
G
h
compounds using ESI-MS in negative ion-mode, provided that the
complexes are dissolved in methanol and treated with a drop of
NaOMe in MeOH immediately before sample injection. When this
alkoxide-ionization method was applied to 3N and 3O, together
with the expected peak at m/z 779 for [Rh4(CO)12 + MeOꢀ] another
peak was observed at m/z 1097 which considerably grew on going
from 3N to 3O and corresponded to the adduct Rh6(CO)16, a known
decomposition product of the tetramer [19]. As a matter of fact, a
preliminary test of silylformylation of phenylpropyne performed
with a pure sample of Rh6(CO)16 (0.5 mol%) showed indeed at
100% conversion a good (57%) chemoselectivity towards the for-
mation of the aldehydic products, fully comparable to the value ob-
tained with 3O. Consequently, our results indicate that the
difference in the catalytic performance of the two rhodium sam-
ples is related to the formation of Rh4(CO)12 decomposition prod-
ucts whose exact nature and catalytic role is currently under study.
Gratifyingly, the naphthyridine complex 1 showed a reproduc-
ible behavior if stored under argon atmosphere. Most notably, it
delivered a good catalytic performance also in the silylformylation
reactions of internal alkynes with aliphatic substituents. Complex
1 clearly stood out as the best catalytic precursor in terms of che-
moselectivity towards the b-silylalkenals (Z)-7b and (Z)-7(70)c (Ta-
ble 1, entries 9 and 13), thus allowing the extension of the
silyformylation reaction to internal alkynes, regardless of the elec-
tronic and steric requirements of the groups connected to the triple
bond.
Scheme
3. Rhodium
catalysed
synthesis
of
2-
(methylaryl)cyclopropanecarbaldehydes.
Therefore, a few homopropargyl tosylates 9 were prepared
starting from the corresponding alcohols [21] and reacted with
an equimolar amount of Me2PhSiH under CO pressure, in the pres-
ence of a rhodium catalyst. The obtained results are reported in
Scheme 4 and Table 2 and clearly indicate that both the conversion
and the chemoselectivity of the process are strongly dependent on
the structure of the acetylenic substrate and of the rhodium cata-
lyst. Indeed, in the reactions performed with catalyst 3, a dramatic
reduction of the selectivity towards the aldehydic products was
The following step was to apply the naphthyridine complex 1 to
the preparation of functionalised b-silylalkenals. Indeed, some of
us have been studying the silyformylation reaction of
x-function-
alised acetylenes for ten years [17b] and have demonstrated that
the corresponding aldehydes can be obtained in high yields with-
out involving double or triple bonds, nitrile, halogens, epoxide, hy-
droxyl or ester moieties present in the substrates. We were
particularly interested in the silylformylation reaction of homo-
propargyl substituted acetylenes containing a good leaving group
(Scheme 3, LG = OTs, OMs, etc.) since the corresponding b-sily-
lalkenals can be subsequently treated with a fluoride source
[17b] yielding cyclopropanecarbaldehydes (Scheme 3), important
key fragments in many natural products and useful synthetic inter-
mediates due to the ease of their ring opening [20].
Scheme 4. Silylformylation of functionalised alkynes.

A. Biffis et al. / Journal of Organometallic Chemistry 695 (2010) 792–798
795
Table 2
Silylformylation of homopropargyl tosylates.a
Entry
R
9
[Rh]b (mol%)
PCO (atm)
t (h)
Conv. (%)c
Selectivity (%)c
(E),(Z)-10
11d
1
2
3
4
5
6
H
a
b
b
b
b
c
3N (0.1)
3N (0.1)
3N (0.5)
4 (0.5)
1 (0.5)
1 (0.5)
30
30
50
50
50
50
24
24
24
24
48
48
95
100(62/38)
45(89/11)
42(71/29)
71(88/12)
100(79/21)
–
–
Et
Et
Et
Et
Ph
100
100
100
72
55
58
29
–
0
–
a
b
c
Reactions conditions: 3 mmol Me2PhSiH, 3 mmol alkyne 9, 3 ml CH2Cl2, 100 °C.
Rhodium catalysts: 1: [Rh2(MeCN)2(Naft)4](BF4)4, 3: Rh4(CO)12; 4: [RhþC7H8BPh4ꢀ].
Determined by GC and 1H NMR analysis; the diastereomeric ratio is reported in brackets.
A mixture of the three possible isomers was detected by 1H NMR analysis.
d
observed on going from linear to
tries 1–3), even if both the CO pressure and the amount of the cat-
alyst were enhanced.
a
-branched tosylates (Table 2, en-
the products dissolved in CH3CN by ESI-MS (Fig. 1). Quite interest-
ingly, the carbon monoxide atmosphere determined the complete
reduction of the rhodium(II) centers to rhodium(I). Moreover,
when the CO pressure was increased, all CH3CN molecules were re-
placed by CO as clearly showed by the mass spectrum reported in
the figure. In this case, the base peak was due to the ion
[Rh2(Naft)3ꢁ2COꢁ8H2O]2+ (398 m/z) containing exclusively naph-
thyridines and CO ligands. The second most intense peak at 333
m/z was also demonstratedly originating from the first one and
was found to be attributable to [Rh2(Naft)2ꢁ2COꢁ8H2O]2+. The pres-
ence of several molecules of water, associated to the rhodium spe-
cies and presumably originally present in the employed mobile
phase (i.e. acetonitrile), was confirmed by the loss of fragments
of 18 Da from the precursor ion (data not shown). We are currently
trying to ascertain whether the rather peculiar structure of such
species may help explaining the particular reactivity exhibited by
this catalytic system in the silylformylation reaction.
The zwitterionic complex 4 showed a better selectivity with
branched tosylates, but 30% of hydrosilylation by-products were
still present (Table 2, entry 4). On the contrary, complex 1 yielded
the desired aldehydes quantitatively (Table 2, entry 5) albeit at a
lower reaction rate. Unfortunately, the steric requirements of the
tosylates turned out to be still the limiting factor of the reaction,
which proved unsuccessful when 4-phenyl-4-tosyl-1-butyne 9c
was reacted.
The functionalised aldehydes (E),(Z)-10a and (E),(Z)-10b were
then submitted to the fluoride promoted rearrangement affording
the corresponding cyclopropanecarbaldehydes 12 quantitatively
and with a good stereoselectivity (Scheme 5). Indeed, according
to the mechanism depicted in Scheme 3, each of the two different
stereoisomers (E),(Z)-10a and (E),(Z)-10b was expected to be con-
verted into the corresponding cyclic aldehydes 12a and 12b exclu-
sively and maintaining the original diastereomeric ratio: this is
precisely what was experimentally observed.
3. Conclusion
Finally we started an investigation aimed at understanding the
nature of the rhodium species that gives rise to the catalytic cycle
of the silylformylation process. This may well be different from
complex 1, given the relatively harsh reaction conditions employed
in the silylformylation protocol, and in particular the reducing nat-
ure of the reaction mixture. Indeed, complex 1 was found to
decompose in the course of the reaction ultimately yielding cata-
lytically inactive rhodium black as the final product. On the other
hand, Doyle et al. already demonstrated that the dirhodium(II) per-
fluorobutyrate complex that they employed as efficient silylformy-
lation catalyst was actually reduced in situ to form monometallic
rhodium(I) species [7e].
In conclusion, we have demonstrated that the tetracationic
complex catalyst 1 exhibits a unique and synthetically useful che-
moselectivity towards the silylformylation reaction of internal and
functionalised alkynes. The stereoselectivity of the reaction is also
good. On the contrary, preliminary investigations on Rh4(CO)12
indicate that this complex, often referred to as a typical catalyst
for silylformylation reactions, is poorly chemoselective, although
the catalyst was found to evolve with ageing generating other cat-
alytically active species with enhanced chemoselectivity. We are
currently further investigating on the reaction mechanism of com-
plex 1 and on the extension of its application to the silylformyla-
tion of other functionalised alkynes yielding valuable synthetic
intermediates.
We made some preliminary attempts to evaluate the stability of
complex 1 under the reaction conditions by subjecting a solution of
1 in CH2Cl2 to CO pressure (40 atm) and subsequently analysing
4. Experimental
4.1. General procedures
The reagents (Aldrich-Chemie) were high purity products and
generally used as received. 1,8-Naphthyridine (Naft) was prepared
following the method of Skraup [22]. The cationic complex
[Rh2(OAc)2(MeCN)6](BF4)2 was prepared in almost quantitative
yield from Rh2(OAc)4 according to the literature [10a]. Rh4(CO)12
[23] (3) and [RhþC7H8BPhꢀ] [24] (4) were prepared and purified
4
as previously reported. All rhodium species were stored refriger-
ated under argon. 5-Hexyn-3-ol, 1-phenyl-3-butyn-1-ol were ob-
tained according to the procedure described by Dimitriadis and
co-workers [21]. 3-Butynyl-p-toluenesulfonate (9a) was used as
received. Me2PhSiH (6), 1-phenylpropyne (5a), 5-octadiyne (5b)
and 2-hexyne (5c) were distilled and kept under argon.
Scheme
cyclopropanecarbaldehydes.
5. TBAF
promoted
synthesis
of
functionalised
(cis/trans)

796
A. Biffis et al. / Journal of Organometallic Chemistry 695 (2010) 792–798
398
1.3e6
1.1e6
9.0e5
7.0e5
5.0e5
3.0e5
1.0e5
333
243
345
341
270
327
292
300
427
420
490
500
246
260
380
355
229
220
340
m/z, amu
380
460
Fig. 1. ESI-MS (positive ion-mode) of complex 1 under 40 atm CO pressure.
Unless otherwise noted, solvents were dried before use and the
37.41; H, 2.61; N, 12.11. Found: C, 37.43; H, 2.86; N, 12.01%. The
characterisation data exactly matched the previously reported
ones [9b].
reaction apparatus carefully deoxygenated; reactions were per-
formed under argon and all operations were carried out under an
inert atmosphere. The solution 1H and 13C{1H} NMR spectra were
recorded on a Bruker Avance 300 MHz at room temperature. The
chemical shifts were determined by reference to the residual sol-
vent peaks, using tetramethylsilane as internal standard. The FT
IR spectra were recorded on a Bruker Tensor27 spectrophotometer
(KBr disks). GLC analyses were performed on a Perkin–Elmer 8600
4.3. Catalytic tests
Catalytic reactions were performed in a 25 mL stainless steel
autoclave fitted with a Teflon inner crucible and a stirring bar. In
a typical run, 3 mmol Me2PhSiH, 3 mmol alkyne, 3 mL CH2Cl2 and
a chosen amount of rhodium catalyst were put, under CO atmo-
sphere, in a Pyrex Schlenk tube. This solution was introduced in
the autoclave, previously placed under vacuum (0.1 Torr), by a
steel siphon. The reactor was pressurized with carbon monoxide
and the mixture was stirred for a chosen time. After removal of ex-
cess CO (fume hood), the reaction mixture was diluted with CH2Cl2,
filtered on celite and concentrated under vacuum. The reagent con-
version and the product composition were determined by GC and
GC–MS analysis. Yields were confirmed by purification of the crude
oil by column chromatography on silica gel 60 (230–400 mesh)
using CH2Cl2 as eluent affording the pure aldehydes.
Model instrument, equipped with
a DB1 capillary column
(30 m ꢂ 0.52 mm, 5 m) and a flame ionization detector, with He
l
as carrier gas. Mass spectra were obtained with an Applied Biosys-
tems-MDS Sciex API 4000 triple quadrupole mass spectrometer
(Concord, Ont., Canada), equipped with a Turbo-V ion-spray (TIS)
source. The operative parameters were as follows: ion-spray volt-
age (IS), 5.0 kV; gas source 1(GS1), 25; gas source 2(GS2), 25; turbo
temperature (TEM), 0 °C; entrance potential (EP), 10 V; decluster-
ing potential (DP), 20 V; scan range, 300–1500 m/z. MS–MS spectra
were produced by collision-induced dissociation (CID) of selected
precursor ions in a LINAC collision cell (Q2) and mass-analyzed
in the second mass filter (Q3). Additional experimental conditions
for MS–MS spectra included: collision (CAD) gas, nitrogen; CAD gas
pressure, 4 mPa; collision energy (CE), ramp from 5 to 130 eV
(step = 2); collision cell exit potential (CXP), 15 V. Each sample
for MS (ESI) was infused by a syringe pump Harvard Mod.22 (Har-
vard Apparatus, Holliston, MA, USA).
4.3.1. Catalytic silylformylation of internal alkynes
(Z)-2-Phenyl-3-(dimethylphenylsilyl)-2-butenal, (Z)-7a [17a]: col-
orless oil. 1H NMR (CDCl3): d = 0.62 (s, 6H), 2.02 (s, 3H), 7.22 (m,
10H), 9.96 (s, 1H). EI-MS: m/z (relative intensity) = (265, M+ꢀ15,
100), 203(20), 159 (10), 135(12), 115(5).
(Z)-2-Methyl-3-phenyl-3-(dimethylphenylsilyl)-propenal, (Z)-70a
[17a]: colorless oil. 1H NMR (CDCl3): d = 0.37 (s, 6H), 1.68 (s, 3H),
7.20 (m, 10H), 10.03 (s, 1H). EI-MS: m/z (relative intensity) = (265,
M+ꢀ15, 100), 203(57), 174(6), 159(10), 135(20), 115(8), 91(5).
(E)-1-Phenyl-2-(dimethylphenylsilyl)-propylene, (E)-8a [25]: col-
orless oil. 1H NMR (CDCl3): d = 0.43 (s, 6H), 2.04 (d, J = 1.8 Hz,
3H), 6.86 (q, J = 1.8 Hz, 1H), 7.35 (10H); EI-MS: m/z (relative inten-
sity) = 252 (M+, 38), 237 (100), 197 (10), 159 (30), 135 (21), 115 (7).
(E)-1-Phenyl-1-(dimethylphenylsilyl)-propylene, (E)-80a [26]: col-
orless oil. 1H NMR: 0.40 (s, 6H), 1.68 (d, J = 6.6 Hz, 3H), 6.22 (q,
J = 6.6 Hz, 1H), 7.28 (m, 10H). EI-MS: m/z (relative intensity) = 252
(M+, 47), 237 (100), 197 (16), 159 (8), 135 (35), 115 (8).
(Z)-2-Butyl-3-(dimethylphenylsilyl)-2-heptenal, (Z)-7b: colorless
oil. 1H NMR (CDCl3): d = 0.52 (s, 6H), 0.92 (m, 6H), 1.36 (m, 8H),
2.35 (t, J = 6.9 Hz, 2H), 2.46 (t, J = 7.2 Hz, 2H), 7.36 (m, 3H), 7.47
(m. 2H), 9.77 (s, 1H); 13C NMR (CDCl3): d = 0.6 (2C), 13.7, 13.9,
23.1, 23.2, 25.6, 31.8 (2C), 33.7, 128.1, 129.2, 133.4, 139.0, 152.1,
4.2. Synthesis of complex 1
150 mg (0.20 mmol) [Rh2(OAc)2(MeCN)6](BF4)2 were dissolved
into 30 mL acetonitrile under an inert atmosphere. 150 mg
(0.80 mmol 4 equiv.) 1,8-naphthyridine (Naft) were then added,
and the resulting solution was heated at reflux for 4 h. The solution
was cooled to room temperature and the complex product
[Rh2(OAc)2(Naft)4](BF4)2 was subsequently precipitated by addi-
tion of diethylether and filtered off. The complex (115 mg,
0.113 mmol) was redissolved without further purification into
10 mL acetonitrile. 0.34 mL of a 1 M solution of (Et3O)(BF4) in
dichloromethane (0.34 mmol, 3 equiv.) were added. The reaction
mixture was stirred for 24 h, then treated with diethyl ether to pre-
cipitate the product as a light brown solid, which was filtered and
dried under vacuum (95 mg, 0.082 mmol, 41% overall yield from
Rh2(OAc)4). Anal. Calc. for C36H30N10B4F16Rh2 (M = 1155.67): C,

A. Biffis et al. / Journal of Organometallic Chemistry 695 (2010) 792–798
797
164.2, 193.8; EI-MS: m/z (relative intensity) = 287 (M+ꢀ15, 47),
245 (100), 195 (3), 167 (5), 135 (9), 107 (4).
(d, J = 8.1 Hz, 2H), 7.41 (m, 3H), 7.54 (m, 2H), 7.70 (d, J = 8.1 Hz,
2H), 9.31 (s, 1H); 13C NMR (CDCl3): d = ꢀ1.6 (2C), 21.8, 28.4, 68.1,
128.2, 128.5, 130.0 (2C), 133.1, 134.0, 136.6, 145.0, 151.3, 156.1,
195.1.
(Z)-2-[(dimethylphenylsilyl)-methylene]-4-p-toluensulfonyl-but-
anal, (Z)-10a: colorless oil. 1H NMR (CDCl3): d = 0.52 (s, 6H), 2.45 (s,
3H), 2.67 (t, J = 6.3 Hz, 2H), 4.14 (t, J = 6.3 Hz, 2H), 7.07 (s, 1H), 7.47
(m, 9H), 9.67 (s, 1H).
(E)-2-[(dimethylphenylsilyl)-methylene]-4-p-toluensulfonyl-hex-
anal, (E)-10b: colorless oil. 1H NMR (CDCl3): d = 0.52 (s, 3H), 0.53 (s,
3H), 0.75 (t, J = 7.5 Hz, 3H), 1.52 (dq, J = 7.5, 5.7 Hz, 2H), 2.42 (s,
3H), 2.45 (m, 2H), 4.62 (m, 1H), 6.74 (s, 1H), 7.25 (d, J = 7.8 Hz,
2H), 7.40 (m, 3H), 7.54 (m, 2H), 7.63 (d, J = 7.8 Hz, 2H), 9.09 (s,
1H); 13C NMR (CDCl3): d = ꢀ1.8, ꢀ1.6, 8.7, 21.6, 28.1, 32.9, 82.2,
128.3, 128.7, 129.9(2C), 134.1, 134.4, 136.9, 144.6, 155.2, 154.9,
195.2.
(Z)-2-[(dimethylphenylsilyl)-methylene]-4-p-toluensulfonyl-hex-
anal, (Z)-10b: colorless oil. 1H NMR (CDCl3): d = 0.56 (s, 3H), 0.58 (s,
3H), 0.84 (t, J = 7.8 Hz, 3H), 1.50 (m, 2H), 2.48 (s, 3H), 2.53 (m, 2H),
4.51 (m, 1H), 7.08 (s, 1H), 7.34 (m, 5H), 7.52 (m, 2H), 7.70 (d,
J = 7.5 Hz, 2H), 9.68 (s, 1H).
(E)-5-(Dimethylphenylsilyl)-5-decene, (E)-8b: colorless oil. 1H
NMR (CDCl3): d = 0.35 (s, 6H), 0.83 (t, J = 6.9 Hz, 3H), 0.92 (t,
J = 6.9 Hz, 3H), 1.28 (m, 8H), 2.12 (m, 4H), 5.80 (t, J = 7.2 Hz, 1H),
7.43 (m, 5H); EI-MS: m/z (relative intensity) = 259 (M+ꢀ15, 20),
217 (8), 197 (26), 135 (100).
(Z)-2-Propyl-3-(dimethylphenylsilyl)-2-butenal, (Z)-7c [17a]: col-
orless oil. 1H NMR (CDCl3): d = 0.53 (s, 6H), 0.93 (t, J = 7.4 Hz, 3H),
1.38 (m, 2H), 2.10 (s, 3H), 2.39 (m, 2H), 7.37 (m, 3H), 7.48 (m, 2H),
9.78 (s, 1H); 13C NMR (CDCl3): d = 0.3(2C), 14.4, 22.1, 27.9, 36.7,
128.4, 129.6, 133.6, 138.7, 152.8, 162.8, 193.5.
(Z)-2-Methyl-3-(dimethylphenylsilyl)-2-hexenal, (Z)-70c [17a]:
colorless oil. 1H NMR (CDCl3): d = 0.53 (s, 6 H), 0.97 (t, J = 7.2 Hz,
3H), 1.38 (m, 2H), 1.89 (s, 3H), 2.46 (m, 2H), 7.37 (m, 3H), 7.48
(m, 2H), 9.82 (s, 1H); 13C NMR (CDCl3): d = 0.6(2C), 14.7, 22.4,
27.9, 36.7, 128.3, 129.5, 133.7, 139.0, 147.8, 164.8, 194.0.
(E)-2-(Dimethylphenylsilyl)-2-hexene, (E)-8c: colorless oil. 1H
NMR (CDCl3): d = 0.40 (s, 6H), 0.98 (t, J = 7.4 Hz, 3H), 1.49 (m,
2H), 1.72 (d, J = 1.8 Hz, 3H), 2.22 (m, 2H), 5.88 (tq, J = 1.8, 7.0 Hz,
1H), 7.29 (m, 3H), 7.65 (m, 2H). EI-MS: m/z (relative inten-
sity) = 218 (M+, 46), 203 (100), 175 (52), 161 (14), 135 (66), 121
(27), 105 (12).
4.3.5. Synthesis of 1-benzyl-cyclopropanecarbaldehyde (12a) [15]
0.376 g (1 mmol) (E),(Z)-2-[(dimethylphenylsilyl)-methylene]-
4-p-toluensulfonyl-butanal, dissolved in 5 mL of THF, were added
to 3 mL of tetrabutylammonium fluoride (1 M in THF) diluted with
5 mL of THF, at room temperature. The obtained solution was
immediately hydrolysed with water, extracted with CH2Cl2
(3 ꢂ 20 mL) and the organic layers were dried over Na2SO4. After
concentration under vacuum, the crude product was purified by
column chromatography on silica gel using CH2Cl2 as eluent, yield-
ing 0.108 g (0.73 mmol, 73%) of pure product as a colorless oil. 1H
NMR (CDCl3): d = 1.09 (m, 2H), 1.28 (m, 2H), 3.12 (s, 2H), 7.34 (m,
5H), 8.87 (m, 1H).
(E)-3-(Dimethylphenylsilyl)-2-hexene, (E)-80c: colorless oil. 1H
NMR (CDCl3): d = 0.42 (s, 6H), 0.90 (t, J = 7.2 Hz, 3H), 1.33 (m,
2H), 1.67 (d, J = 6.6 Hz, 3H), 2.17 (m, 2H), 6.00 (qt, J = 6.6, 0.9 Hz,
1H), 7.42 (m, 3H), 7.61 (m, 2H). EI-MS: m/z (relative inten-
sity) = 218 (M+, 30), 203 (100), 189 (10), 141 (14), 135 (24), 121
(11), 105 (5).
4.3.2. Synthesis of toluene-4-sulfonic acid 1-ethyl-but-3-ynyl ester
(9b)
2.09 g (21.3 mmol) of 5-hexyn-3-ol [21] were added to a solu-
tion of 6.16 g (31.5 mmol) of p-toluensulfonyl chloride in 60 mL
diethyl ether at ꢀ15 °C. 10.50 g (187 mmol) of finely powdered
KOH were then added and the obtained solution was stirred for
2 h at 0 °C, quenched with ice and extracted with Et2O
(3 ꢂ 50 mL). The combined organic layers were dried over Na2SO4,
the solvent was removed under reduced pressure yielding 4.30 g
(17.0 mmol, 80%) of crude 9b as a colorless oil that was used with-
out any further purification. 1H NMR (CDCl3): d = 0.81 (t, J = 7.2 Hz,
3H), 1.75 (m, 2H), 1.94 (t, J = 2.5 Hz, 1H), 2.43 (s, 3H), 2.50 (m, 2H),
4.50 (m, 1H), 7.32 (d, J = 8.2 Hz, 2H), 7.79 (d, J = 8.2 Hz, 2H); 13C
NMR (CDCl3): d = 8.9, 21.6, 24.1, 26.3, 71.1, 78.4, 81.4, 127.7,
129.7, 133.9, 144.7.
4.3.6. Synthesis of 1-benzyl-2-ethyl-cyclopropanecarbaldehyde (12b)
0.500 g (1.2 mmol) (E),(Z)-2-[(dimethylphenylsilyl)-methy-
lene]-4-p-toluensulfonyl-hexanal, dissolved in 5 mL of THF, were
added to 3 mL of tetrabutylammonium fluoride (1 M in THF) di-
luted with 5 mL of THF, at room temperature. The obtained solu-
tion was immediately hydrolysed with water, extracted with
CH2Cl2 (3 ꢂ 20 mL) and the organic layers were dried over Na2SO4.
After concentration under vacuum, the crude product was purified
by column chromatography on silica gel using CH2Cl2 as eluent,
yielding 0.210 g (1.11 mmol, 93%) of pure product (diastereomeric
mixture: Z/E = 79/21). Cis isomer: 1H NMR (CDCl3): d = 0.83 (t,
J = 7.3 Hz, 3H), 1.35 (m, 5H), 2.85 (d, J = 15.0 Hz, 1H), 2.96 (d,
J = 15.0 Hz, 1H), 7.14 (m, 5H), 9.18 (s, 1H); 13C NMR (CDCl3):
d = 14.1, 21.1, 21.7, 32.6, 36.8, 37.4, 126.2, 128.2, 129.2, 139.1,
202.2. Trans isomer: 1H NMR (CDCl3): d = 0.96 (t, J = 7.2 Hz, 3H),
1.28 (m, 5H), 2.57 (d, J = 15.5 Hz, 1H), 3.36 (d, J = 15.5 Hz, 1H),
7.14 (m, 5H), 8.75 (s, 1H); 13C NMR (CDCl3): d = 13.7, 19.5, 22.2,
28.7, 30.8, 37.0, 126.0, 128.3, 128.8, 139.9, 202.0.
4.3.3. Toluene-4-sulfonic acid 1-phenyl-but-3-ynyl ester (9c)
2.60 g (18.1 mmol) of 1-phenyl-3-butyn-1-ol [21] were added
to a solution of 5.07 g (26.6 mmol) of p-toluensulfonyl chloride in
60 mL diethyl ether at ꢀ15 °C. 8.86 g (158 mmol) of finely powered
KOH were then added and the obtained solution was stirred for 2 h
at 0 °C, quenched with ice and extracted with Et2O (3 ꢂ 50 mL).
The combined organic layers were dried over Na2SO4, the solvent
was removed under reduced pressure yielding 5.4 g (18 mmol,
99%) of crude 9c as a white solid that was used without any further
purification. 1H NMR (CDCl3): d = 1.91 (t, J = 2.7 Hz, 1H), 2.37 (s,
3H), 2.78 (ddd, J = 16.8, 6.8, 2.7 Hz, 1H), 2.87 (ddd, J = 16,8, 6.8,
2.7 Hz, 1H), 5.50 (t, J = 6.8 Hz, 1H), 7.18 (d, J = 8.3 Hz, 2H), 7.20
(m, 5H), 7.63 (d, J = 8.3 Hz, 2H); 13C NMR: (CDCl3): d = 21.5, 27.3,
71.4, 78.1, 81.3, 126.7, 127.8, 128.3, 128.8, 129.4, 133.9, 136.7,
144.5.
Acknowledgement
We are grateful to Prof. Giuseppe Fachinetti, University of Pisa,
for providing us a sample of freshly prepared Rh6(CO)16
.
References
[1] (a) P.A. Evans (Ed.), Modern Rhodium-Catalyzed Organic Reactions, Wiley-
VCH, Weinheim, 2005;
4.3.4. Catalytic silylformylation of homopropargyl tosylates
(E)-2-[(Dimethylphenylsilyl)-methylene]-4-p-toluensulfonyl-but-
anal, (E)-10a: colorless oil. 1H NMR (CDCl3): d = 0.53 (s, 6H), 2.45 (s,
3H), 2.67 (t, J = 6.3 Hz, 2H), 3.97 (t, J = 6.8 Hz, 2H), 6.95 (s, 1H), 7.32
(b) M.P. Doyle, J. Org. Chem. 71 (2006) 9253;
(c) R.D. Adams, F.A. Cotton, Catalysis by Di- and Polynuclear Metal Cluster
Complexes, Wiley, New York, 1998.

798
A. Biffis et al. / Journal of Organometallic Chemistry 695 (2010) 792–798
[2] (a) H.M.L. Davies, Ø. Loe, Synthesis (2004) 2595;
[10] (a) G. Pimblett, C.D. Garner, J. Chem. Soc., Dalton Trans. (1985) 1977;
(b) G. Pimblett, C.D. Garner, W. Clegg, J. Chem. Soc., Dalton Trans. (1986) 1257.
[11] (a) W.R. Tikkanen, E. Binamira-Soriaga, W.C. Kaska, P.C. Ford, Inorg. Chem. 22
(1983) 1147;
(b) W.R. Tikkanen, E. Binamira-Soriaga, W.C. Kaska, P.C. Ford, Inorg. Chem. 23
(1984) 141.
[12] (a) C.S. Campos-Fernandez, X. Ouyang, K.R. Dunbar, Inorg. Chem. 39 (2000)
2432;
(b) H.M.L. Davies, R.E.J. Beckwith, Chem. Rev. 103 (2003) 2861;
(c) C.A. Merlic, A.L. Zechman, Synthesis (2003) 1137;
(d) M.P. Doyle, T. Ren, Prog. Inorg. Chem. 49 (2001) 113;
(e) H.M.L. Davies, E.G. Antoulinakis, Org. React. 57 (2001) 1;
(f) D.C. Forbes, M.C. McMills, Curr. Org. Chem. 5 (2001) 1091;
(g) M.P. Doyle, M.A. McKervey, T. Ye, Modern Catalytic Methods for Organic
Synthesis with Diazo Compounds, Wiley, New York, 1998;
(h) M.P. Doyle, D.C. Forbes, Chem. Rev. 98 (1998) 911.
[3] (a) P. Müller, C. Fruit, Chem. Rev. 103 (2003) 2905;
(b) P. Dauban, R.H. Dodd, Synlett (2003) 1586;
(b) C.S. Campos-Fernandez, L.M. Thomson, J.R. Galan-Mascaros, X. Ouyang,
K.R. Dunbar, Inorg. Chem. 41 (2002) 1523;
(c) A.M. Angeles-Boza, P.M. Bradley, P.K.-L. Fu, S.E. Wicke, J. Bacsa, K.R.
Dunbar, C. Turro, Inorg. Chem. 43 (2004) 8510;
(d) A.M. Angeles-Boza, H.T. Chifotides, J.D. Aguirre, A. Chouai, P. K.-L. Fu, K.R.
Dunbar, C. Turro, J. Med. Chem. 49 (2006) 6841.
(c) H.M.L. Davies, M.S. Long, Angew. Chem., Int. Ed. 44 (2005) 3518;
(d) C. Liang, F. Robert-Peillard, C. Fruit, P. Müller, R.H. Dodd, P. Dauban, Angew.
Chem., Int. Ed. 45 (2006) 4641;
(e) K.W. Fiori, J. Du Bois, J. Am. Chem. Soc. 129 (2007) 562. and references cited
therein;
(f) H.M.L. Davies, J.R. Manning, Nature 451 (2008) 417.
[4] (a) C.J. Moody, F.N. Palmer, Tetrahedron Lett. 43 (2002) 139. and earlier
references cited therein;
[13] (a) M.J. Carter, I. Fleming, J. Chem. Soc., Chem. Commun. 17 (1976) 679;
(b) M.E. Jung, B. Gaede, Tetrahedron 35 (1979) 621.
[14] J.P. Pillot, J. Dunogues, R. Calas, J. Chem. Res.-S 1 (1977) 268.
[15] L.A. Aronica, P. Raffa, A.M. Caporusso, P. Salvadori, J. Org. Chem. 68 (2003)
9292.
(b) A.J. Catino, R.E. Forslund, M.P. Doyle, J. Am. Chem. Soc. 126 (2004) 13622;
(c) A.J. Catino, J.M. Nichols, M.P. Doyle, J. Am. Chem. Soc. 128 (2006) 5648;
(d) S.J. Na, B.Y. Lee, N.-N. Bui, S.-I. Mho, H.-Y. Jang, J. Organomet. Chem. 692
(2007) 5523.
[16] (a) I. Fleming, D.A. Perry, Tetrahedron 37 (1981) 4027;
(b) M.J. Carter, I. Fleming, A. Percival, J. Chem. Soc., Perkin I (1981) 2415;
(c) R. Takeuchi, M. Sugiura, J. Chem. Soc., Perkin I (1993) 1031.
[17] (a) I. Matsuda, Y. Fukuta, T. Tsuchinashi, H. Nagashima, K. Itoh,
Organometallics 16 (1997) 4327;
[5] (a) M.P. Doyle, I.M. Phillips, W. Hu, J. Am. Chem. Soc. 123 (2001) 5366;
(b) M.P. Doyle, M. Valenzuela, P. Huang, Proc. Natl. Acad. Sci. USA 101 (2004)
5391;
(b) L.A. Aronica, A.M. Caporusso, P. Salvadori, Eur. J. Org. Chem. (2008) 3039.
and references therein.
(c) M. Anada, T. Washio, N. Shimada, S. Kitagaki, M. Nakajima, M. Shiro, S.
Hashimoto, Angew. Chem., Int. Ed. 43 (2004) 2665;
[18] W. Handerson, J.S. McIndoe, B.K. Nicholson, P.J. Dyson, J. Chem. Soc., Dalton
Trans. (1998) 519.
(d) R.E. Forslund, J. Cain, J. Colyer, M.P. Doyle, Adv. Synth. Catal. 347 (2005) 87;
(e) Y. Wang, J. Wolf, P. Zavalij, M.P. Doyle, Angew. Chem., Int. Ed. 47 (2008)
1439.
[19] (a) P. Chini, S. Martinengo, Inorg. Chim. Acta 3 (1969) 315;
(b) A. Theolier, A.K. Smith, M. Leconte, J.N. Vasset, G.M. Zanderighi, R. Psaro, R.
Ugo, J. Organomet. Chem. 191 (1980) 415;
[6] (a) P.M.P. Gois, A.F. Trindade, L.F. Veiros, V. Andrè, M.T. Duarte, C.A.M. Afonso,
S. Caddick, F.G.N. Cloke, Angew. Chem., Int. Ed. 46 (2007) 5750;
(b) P.M.P. Gois, A.F. Trindade, L.F. Veiros, V. Andrè, M.T. Duarte, C.A.M. Afonso,
S. Caddick, F.G.N. Cloke, J. Org. Chem. 73 (2008) 1076.
[7] (a) M.P. Doyle, K.G. High, V. Bagheri, R.J. Pieters, P.J. Lewis, M.W. Pearson, J.
Org. Chem. 55 (1990) 6082;
(c) R. Pince, R. Queau, D. Labroque, J. Organomet. Chem. 306 (1986) 251.
[20] (a) H.N.C. Wong, M.Y. Hon, Y.C. Yip, J. Tanko, T. Hudlicky, Chem. Rev. 89 (1989)
165;
(b) S. Ono, S. Shuto, A. Matsuda, Tetrahedron Lett. 37 (1996) 221;
(c) D.M. Pawar, E.A. Noe, J. Org. Chem. 63 (1998) 2850;
(d) Y. Kazuta, A. Matsuda, S. Shuto, J. Org. Chem. 67 (2002) 1669;
(e) K. Yamaguchi, Y. Kazuta, H. Abe, A. Matsuda, S. Shuto, J. Org. Chem. 68
(2003) 9255;
(b) M.P. Doyle, K.G. High, C.L. Nesloney, T.W. Clayton Jr., J. Lin, Organometallics
10 (1991) 1225;
(c) M.P. Doyle, G.A. Devora, A.O. Nefedov, K.G. High, Organometallics 11
(1992) 549;
(f) Y. Kazuta, K. Hirano, K. Natsume, S. Yamada, R. Kimura, S. Matsumoto, K.
Furuichi, A. Matsuda, S. Shuto, J. Med. Chem. 46 (2003) 1980;
(g) Y. Kazuta, H. Abe, T. Yamamoto, A. Matsuda, S. Shuto, Tetrahedron 60
(2004) 6689.
(d) M.P. Doyle, M.S. Shanklin, Organometallics 12 (1993) 11;
(e) M.P. Doyle, M.S. Shanklin, Organometallics 13 (1994) 1081.
[8] (a) A. Biffis, E. Castello, M. Zecca, M. Basato, Tetrahedron 57 (2001) 10391;
(b) A. Biffis, M. Zecca, M. Basato, Green Chem. 5 (2003) 170;
(c) A. Biffis, M. Braga, M. Basato, Adv. Synth. Catal. 346 (2004) 451.
[9] (a) M. Basato, A. Biffis, G. Martinati, M. Zecca, P. Ganis, F. Benetollo, L.A.
Aronica, A.M. Caporusso, Organometallics 23 (2004) 1947;
(b) M. Basato, A. Biffis, G. Martinati, C. Tubaro, C. Graiff, A. Tiripicchio, L.A.
Aronica, A.M. Caporusso, J. Organomet. Chem. 691 (2006) 3464;
(c) A. Biffis, M. Basato, M. Brichese, L. Ronconi, C. Tubaro, A. Zanella, C. Graiff,
A. Tiripicchio, Adv. Synth. Catal. 349 (2007) 2485.
[21] (a) L. Brandsma, Preparative Acetylenic Chemistry, Elsevier, Amsterdam,
1988;
(b) C. Dimitriadis, Tetrahedron Asymmetr. 8 (1997) 215.
[22] T.J. Kress, W.W. Paudler, J. Org. Chem. 31 (1966) 3055.
[23] S. Martinengo, G. Giordano, P. Chini, Inorg. Synth. 28 (1990) 242.
[24] R.R. Schrock, J.A. Osborn, Inorg. Chem. 9 (1970) 2339.
[25] I. Fleming, M. Rowley, Tetrahedron 45 (1989) 413.
[26] A. Chenedé, I. Fleming, R. Salmon, M.C. West, J. Organomet. Chem. 686 (2003)
84.