Stoichiometric cyclotrimerisation of chiral alkynes at a ruthenium centre: Preparation of optically active (η6-arene)(η4-cycloocta-1,5-diene)ruthenium(0) complexes

Article abstract of DOI:10.1016/S0022-328X(00)00881-0

The chiral alkynes (S)-MeCH(R)-C≡CH, 2 (R = Et, 3-methyl-1-pentyne, a; ⁱPr, 3,4-dimethyl-1-pentyne, b; ^tBu, 3,4,4-trimethyl-1-pentyne, c), containing a stereogenic centre in α position to the triple bond, react at room temperature with the complex Ru(η₆-naphthalene)(η⁴-COD), 1, to give the corresponding optically active complexes Ru{η⁶-(S)-1,3,5-C₆H₃[CH(Me)R] ₃}(η⁴-COD), 6, and Ru{η⁶-(S)-1,2,4-C₆H₃[CH(Me)R] ₃}(η⁴-COD), 7, the η⁶-1,3,5-arene regioisomer being the prevalent product. With (S)-2a, a mixture of 6a and 7a (6a/7a = 90:10) is obtained and, with the more sterically demanding alkynes (S)-2b and (S)-2c, the regioselectivity to the corresponding complexes 6b and 6c is almost complete. This synthetic procedure does not involve the stereogenic centres on the alkynes and it proceeds with complete stereoselectivity.

Full text of DOI:10.1016/S0022-328X(00)00881-0

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 621 (2001) 246–253
Stoichiometric cyclotrimerisation of chiral alkynes at a ruthenium
centre: preparation of optically active
(h6-arene)(h4-cycloocta-1,5-diene)ruthenium(0) complexes
Paolo Pertici, Alessandra Verrazzani, Emanuela Pitzalis, Anna Maria Caporusso,
Giovanni Vitulli *
Centro di Studio del CNR per le Macromolecole Stereordinate ed Otticamente Atti6e, Dipartimento di Chimica e Chimica Industriale,
Uni6ersita` di Pisa, 6ia Risorgimento 35, 56126 Pisa, Italy
Received 2 October 2000; accepted 13 November 2000
Abstract
i
t
The chiral alkynes (S)-MeCH(R)ꢀCꢁCH, 2 (R=Et, 3-methyl-1-pentyne, a; Pr, 3,4-dimethyl-1-pentyne, b; Bu, 3,4,4-trimethyl-
1-pentyne, c), containing a stereogenic centre in a position to the triple bond, react at room temperature with the complex
Ru(h6-naphthalene)(h4-COD), 1, to give the corresponding optically active complexes Ru{h6-(S)-1,3,5-C6H3[CH(Me)R]3}(h4-
COD), 6, and Ru{h6-(S)-1,2,4-C6H3[CH(Me)R]3}(h4-COD), 7, the h6-1,3,5-arene regioisomer being the prevalent product. With
(S)-2a, a mixture of 6a and 7a (6a/7a=90:10) is obtained and, with the more sterically demanding alkynes (S)-2b and (S)-2c, the
regioselectivity to the corresponding complexes 6b and 6c is almost complete. This synthetic procedure does not involve the
stereogenic centres on the alkynes and it proceeds with complete stereoselectivity. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Optically active complexes; Ruthenium; Alkyne cyclotrimerisation; Arene complexes; 1,5-Cyclooctadiene complexes
1. Introduction
We recently found that the stoichiometric cy-
clotrimerisation of alkynes promoted by Ru(h6-naph-
thalene)(h4-COD), 1, allows the preparation of a wide
range of Ru(h6-arene)(h4-COD) complexes, some of
which cannot be obtained by alternative way [13]. We
report here that using chiral alkynes such as
(S)ꢀMeCH(R)ꢀCꢁCH, 2 (R=Et, 3-methyl-1-pentyne,
Arene ruthenium complexes are of great interest in
preparative chemistry and catalysis [1,2]. In the pres-
ence of additional chiral phosphine ligands, (h6-
arene)Ru(II) species have been found to be excellent
enantioselective hydrogen transfer catalysts [3]. In these
compounds the arene–metal bond is very stable [4–6]
and this makes them attractive for asymmetric synthesis
due to the availability of chiral complexes in which the
chirality depends on the arene ligand. Chiral (h6-
arene)(h4-COD)ruthenium(0) complexes (COD=1,5-
cyclooctadiene) have been previously prepared by
replacing the h6-ligand in the complexes Ru(h6-cy-
cloocta-1,3,5-triene)(h4-COD) [7–9] or Ru(h6-naphthal-
ene)(h4-COD) [10–12] by the suitable arene. The subse-
quent reaction with hydrochloric acid affords the corre-
sponding [RuCl2(h6-arene)]2 complex [7,10].
i
t
a; Pr, 3,4-dimethyl-1-pentyne, b; Bu, 3,4,4-trimethyl-1-
pentyne, c), characterised by different steric require-
ments, the above reaction provides
a
valuable
preparative route to the corresponding new optically
active Ru(h6-arene)(h4-COD) complexes.
2. Results and discussion
2.1. Preparation of the optically acti6e 1-alkynes (S)-
3-methyl-1-pentyne, 2a, (S)-3,4-dimethyl-1-pentyne, 2b
and (S)-3,4,4-trimethyl-1-pentyne, 2c
* Corresponding author. Tel.: +39-050-918224; fax: +39-050-
918260.
The enantiomerically enriched 1-alkynes 2a–c have
E-mail address: pervit@dcci.unipi.it (G. Vitulli).
been prepared according to Scheme 1. The optically
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00881-0

P. Pertici et al. / Journal of Organometallic Chemistry 621 (2001) 246–253
247
Wittig-type reactions starting from chiral aldehydes are
affected by significant racemization phenomena [23].
active propargylic carbinols (S)-4a–c, used as starting
materials, have been easily obtained by resolution of
their hydrogen phthalates with (−)-brucine in acetone
as solvent and subsequent hydrolysis [14–17]. They
were converted into the methanesulfonates (S)-5a–c by
reaction, at −70°C, with one equivalent of butyl-
lithium followed by treatment with methanesulfonyl
chloride. Compounds (S)-5a–c react nicely in situ with
a suspension of LiCu2Br3 in THF at −70°C, to give,
after 5 min at room temperature (r.t.), the bromoallenes
(R)-3a–c in excellent yields [14,18]. The reaction of
compounds (R)-3a–c with two equivalents of lithium
aluminium hydride in diethyl carbitol at r.t. [19] gives,
after hydrolysis, the 1-alkynes (S)-2a–c with good over-
all yields and high purity.
The stereochemical results obtained, reported in
Table 1, indicate that the sequence alcohol“alkyne
occurs with complete stereoselectivity [14,20]. These
reactions can be considered as a suitable pathway to
easily obtain optically active a-branched 1-alkynes,
most of the other procedures reported in the literature
[21–25] lacking in one or more of the fundamental
requirements of low racemization, good chemical yields
and availability of the chiral reaction intermediates.
For instance, the high number of steps in the sequence
based on the bromination–dehydrobromination of the
corresponding a-olefins dramatically affects the 1-
alkyne overall yield [21,22], while methods based on
2.2. Reaction of complex Ru(p6-naphthalene)(p4-COD),
1, with the alkynes (S)-2a–c: synthesis of the optically
acti6e Ru(p6-arene)(p4-COD) complexes, 6 and 7
Complex 1 reacts with the chiral alkynes (S)-2a–c at
r.t. to give the new optically active Ru(h6-arene)(h4-
COD) complexes, 6 and 7, in which the arene is formed
by cyclotrimerisation of the acetylenic compound
(Scheme 2).
The reactions have been performed in THF as sol-
vent, other solvents (i.e., aliphatic hydrocarbons, ace-
tone, dichloromethane, chloroform) giving rise to
partial decomposition. The best yields have been ob-
tained using an excess of alkyne with respect to com-
plex 1 (molar ratio alkyne/complex$6). The progress
1
of the reaction was examined analysing by H-NMR
samples withdrawn at different times; the reactions
were stopped when the starting complex 1 had com-
pletely reacted.
The regiomeric mixture of complexes 6 and 7 was
recovered after chromatography on alumina in good to
moderate yield [65, 40 and 25% using the alkynes 2a, 2b
and 2c, respectively] as a yellow oily material and they
have been characterised by elemental analysis, 1H-
NMR spectroscopy and EI-MS spectrometry as re-
ported in Tables 2 and 3. In all the reactions small
Scheme 1.
Table 1
Synthesis of 1-alkynes (S)-2 via LiAlH4 reduction of the corresponding bromoallenes (R)-5
Propargyl Carbinol
Bromoallene (R)-5
1-alkyne (S)-2
Stereoselectivity
a
a
a
(S)-4
R
[a]D
ee% b [a]D
Yield%
[a]D
ee% b overall yield%
(S)-4a
(S)-4b
(S)-4c
Et
+2.84 c
+5.20 d
+1.02 c
94
86
89
−74.7 d
−87.9 d
−86.1 c
70
68
83
+43.40 c
+25.5 d
+11.2 d
93 e
84 f
89 f
63
59
66
\99
99
100
iPr
tBu
a Rotations were measured on neat liquids.
b By complexation GLC analyses on a [Ni-(S)-CAM] column.
c At 20°C.
d At 25°C.
e See Ref. [21].
f See Ref. [22].

248
P. Pertici et al. / Journal of Organometallic Chemistry 621 (2001) 246–253
Scheme 2.
Table 2
Ru(h6-arene)(h4-COD) complexes, 6 and 7, obtained according to Scheme 2 a
Alkyne
Time (h)
Yield (%)
Products b (%)
(S)-3-Methyl-1-pentyne, 2a c
(S)-3,4-Dimethyl-1-pentyne, 2b d
24
31
65
40
Ru{h6-1,3,5-tri-[(S)-1-methylpropyl]benzene}(h4-COD), 6a (90)
Ru{h6-1,2,4-tri-[(S)-1-methylpropyl]benzene}(h4-COD), 7a (10)
Ru{h6-1,3,5-tri-[(S)-1,2-dimethylpropyl]benzene}(h4-COD),
6b (\95)
Ru{h6-1,2,4-tri-[(S)-1,2-dimethylpropyl]benzene}(h4-COD),
7b (just detectable)
(S)-3,4,4-Trimethyl-1-pentyne, 2c e
36
25
Ru{h6-1,3,5-tri-[(S)-1,2,2-trimethylpropyl]benzene}(h4-COD),
6c (\95)
Ru{h6-1,2,4-tri-[(S)-1,2,2-trimethylpropyl]benzene}(h4-COD),
7c (just detectable)
a Reaction conditions: 1 (0.5 g, 1.48 mmol), alkyne (8.9 mmol), THF (5 ml), r.t.
b The regioisomeric composition (6 and 7%) was determined by 1H-NMR spectroscopy.
c 93% ee.
d 84% ee.
e 89% ee.
amounts of free arenes and linear oligomers have been
detected by H-NMR and EI-MS analysis.
considerable influence to determine the regioselectivity
1
of the cyclotrimerisation. Accordingly to the generally
accepted mechanism of cyclotrimerisation of alkynes
[26], the ruthenacyclopentadienes 8 and 9 are possible
intermediates of the reaction (Scheme 3) and the bulky
alkynes 2a–c will react preferentially with the interme-
diate 8 with formation of the less sterically hindered
1,3,5-substituted arene. As indicated by spectroscopic
analyses, the stoichiometric cyclotrimerisation of the
alkynes 2a–c to the aromatic derivatives with forma-
tion of the complexes 6 and 7 does not involve the
stereogenic centres on the alkynes and it occurs with
almost complete stereoselectivity. Diastereomeric mix-
tures have not been observed by 1H- and 13C-NMR
measurements. The 1H-NMR spectra of the 1,3,5-re-
gioisomers 6 exhibit only one singlet around l 4.9 ppm,
due to the equivalent aromatic protons, hence deriving
from only one diastereoisomer present in solution. Sim-
ilarly, the 13C-NMR spectra of complexes 6 show one
The regiomeric composition (6 vs 7) of the resulting
mixture of arene-ruthenium complexes can be valued
by the intensity of the aromatic proton resonances
1
between l 4 and 6 ppm in their H-NMR spectra. The
equivalent protons of the 1,3,5-substituted arene deriva-
tive 6 give a singlet while the non-equivalent protons of
the 1,2,4-substituted arene derivative 7 furnish three
different signals [13]. It was found that the alkyne 2a
gives a mixture of 6a and 7a, in which the first regioiso-
mer containing the more stable symmetric 1,3,5-substi-
tuted arene is the main product (6a/7a=90/10).
Similarly, with the bulkier alkynes 2b and 2c, the
complexes 6b and 6c are largely prevalent in the reac-
tion mixture (\95%), the complexes 7b and 7c being
only just detectable.
This result indicates that the steric hindrance at the
stereogenic centre in a position to the triple bond has a

P. Pertici et al. / Journal of Organometallic Chemistry 621 (2001) 246–253
249
Table 3
Analytical and spectroscopic complexes 6 and 7
Scheme 3.

250
P. Pertici et al. / Journal of Organometallic Chemistry 621 (2001) 246–253
Dm= +0.7 and negative one at 250 nm with Dm=
−0.75. Similar results have also been obtained with the
mixture 6a+7a, resulting from the reaction of 1 with
the alkyne (S)-2a, indicating that the relative position
of the stereogenic centres does not affect the chiroopti-
cal properties of the complexes.
It is worthy to note that the title synthetic route
appears as the only method to prepare the complexes 6
and 7, different procedures to get such kind of com-
plexes, which employ preformed arenes [7,29,30], being
unsuccessful. The reactions of the (R)(S)-1,3,5-tri-(1-
methylpropyl)benzene with the complex 1, in the pres-
ence of acetonitrile [29,30], and with the complex
Ru(h6-cycloocta-1,3,5-triene)(h4-COD), under hydro-
gen atmosphere [7], were examined but in no case the
formation of the complex 6a was observed.
Fig. 1. UV and CD spectra of the complex Ru{h6-1,3,5-tri-[(S)-1,2-
dimethylpropyl]-benzene}(h4-COD), 6b (purity\95%) (c=1.35×
10−3 mol dm−3, hexane).
3. Concluding remarks
singlet in the range l 110–108 ppm and another singlet
in the range l 86–84 ppm, due to the substituted and
unsubstituted aromatic carbon atoms, respectively. This
result is in agreement with the mechanism of cy-
clotrimerisation of alkynes [26], which does not involve
the carbon atom in a position to the triple bond, as
observed, for example, in the catalytic cyclotrimerisa-
tion of optically active 1-alkynes to benzene derivatives
with nickel- and titanium-based catalysts which pro-
ceeds with complete stereoselectivity [27].
The results reported here show that the complex
Ru(h6-naphthalene)(h4-COD), 1, containing the naph-
thalene weakly bonded to the metal, is a very useful
starting material to get with a simple procedure opti-
cally active arene ruthenium complexes, Ru(h6-
arene)(h4-COD), by cyclotrimerisation of chiral
1-alkynes with a stereogenic centre in a position to the
triple bond. This method appears as the only synthetic
procedure to prepare complexes 6 and 7 and, probably,
other similar complexes in which the arene contains
bulky substituents. The starting alkynes 2a–c have been
conveniently obtained from the corresponding propar-
gylic alcohols utilising a simple pathway which occurs
with complete stereoselectivity and which represents a
suitable and general synthetic procedure. It has been
observed that the steric hindrance of the substituent at
the stereogenic centre determines the regiochemistry of
the cyclotrimerisation with formation of the thermodi-
namically more stable 1,3,5-trisubstituted isomer.
The chirooptical properties of complexes 6 and 7,
examined measuring the absorption and circular
dichroism (CD) spectra, agree also with the stereoselec-
tivity in their formation. In Fig. 1 the UV and CD
spectra of the complex 6b, obtained with very high
chemoselectivity (\95%) in the reaction of complex 1
with the alkyne 2b, are reported. The UV-Vis spectrum,
measured between 450 and 200 nm, shows a maximum
at u=260 nm (m=12.000–13.000). At u\260 nm a
long tail is observed till to 450 nm while at uB260 nm
the absorption increases rapidly (i.e. at u=200 nm,
m=25.000). As far as the maximum at 260 nm is
concerned, its high intensity strongly indicates that this
absorption is due to an electrically allowed transition
Finally, it is worth noting that the arene-ruthe-
nium(0) complexes 6 can be converted in good yield to
the corresponding arene-ruthenium(II) dichloride com-
pounds by reaction with hydrocloric acid [7,10] and,
hence, they are the starting material to get a wide range
of other optically active h6-arene ruthenium complexes.
1
making unlikely the assignment to the Lb transition,
typical of the substituted arenes, which generally ex-
hibits an m$500 [28]. The 260 nm band is probably due
to a charge transfer transition involving the orbital of
the metal and the p-electrons of the ligand. This is
supported with the comparable values of both the
position and the intensity of this band observed also for
the other complexes (mixture 6a+7a and 6c) which
present a very similar structure of the transition metal–
arene ‘core’. The CD spectrum of 6b shows the follow-
ing sequence of the signals: negative Cotton effect at
400 nm with Dm= −0.03, positive one at 300 nm with
4. Experimental
All the operations regarding the manipulation of the
ruthenium complexes were performed under argon at-
mosphere using conventional Schlenk-tube techniques.
Solvents were purified by conventional methods. The
complexes Ru(h6-naphthalene)(h4-COD), 1, [30] and
Ru(h6-cycloocta-1,3,5-triene)(h4-COD) [31–33] were
obtained as previously reported. The (R)(S)-1,3,5-tri-

P. Pertici et al. / Journal of Organometallic Chemistry 621 (2001) 246–253
251
1
(1-methylpropyl)benzene [27] and the racemic propar-
gylic alcohols (R)(S)-4a–c [34] were prepared and
purified according to literature methods.
(86% ee); H-NMR (20%, CDCl3), l 0.95 (d, 3H, J=7
Hz, CH3); 0.99 (d, 3H, J=7 Hz, CH3); 1.39 (s, 3H,
CH3); 1.76 (m, 1H, CH); 2.22 (s, 1H, ꢁCH); 2.37 (s, 1H,
OH).
1H- and 13C-NMR spectra were recorded on a Varian
Gemini 200 instrument at 200 and 50.3 MHz, respec-
tively. Chemical shifts were determined relative to inter-
nal Si(CH3)4 (l=0 ppm); coupling constants J are in
Hz. Mass spectra (EI) were recorded on a VG 7070E
spectrometer. GC-MS analyses were performed on a
Perkin–Elmer Q-Mass 910 spectrometer connected
with a Perkin–Elmer gas chromatograph, equipped
with a ‘split-splitless’ injector, using a SiO2 capillary
column and helium as carrier gas. GLC analyses were
4.1.3. (S)-3,4,4-trimethyl-1-pentyn-3-ol, (S)-4c
From five recrystallizations of the hydrogen phtha-
late brucine salt: b.p. 50°C/17 torr; d240 0.8664; [a]D20
+1.02 (89% ee); 1H-NMR (20%, CDCl3), l 1.03 (s, 9H,
CH3); 1.40 (s, 3H, CH3); 2.43 (s, 1H, ꢁCH); 3.23 (s, 1H,
OH).
4.2. Preparation of (R)-1-bromo-1,2-dienes, (R)-5a–c.
General procedure
performed on
a
Perkin–Elmer 8600 gas chro-
matograph, equipped with an ‘in column’ injector and a
flame ionisation detector (FID), using an SiO2 ‘Wide
Bore’ column (DB1, 30m×0.53mm, 5 mm) and helium
as carrier gas. Complexation GLC analyses were per-
formed using a glass capillary column (25 m×0.25
mm) with 0.1% nickel bis [3-(heptafluorobutyryl)-1-(S)-
camphorate] in OV-1 [Ni-(S)-CAM column] [35]. Opti-
cal rotations were measured with a Perkin–Elmer 142
automatic polarimeter using standard cuvettes (l=0.1
and 1 dm). Microanalyses were carried out by the
Laboratorio di Microanalisi, Facolta` di Farmacia, Uni-
versita` di Pisa, Italy.
To a stirred solution of the appropriate optically
active carbinol (S)-4 (100 mmol) in THF (200 ml) were
successively added, at −70°C, 100 mmol of buthyl-
lithium in hexane and 110 mmol of methanesulfonyl
cloride. After 5 min at −70°C, a suspension of
LiCu2Br3 (from 120 mmol of LiBr and 240 mmol of
CuBr in 200 ml of anhydrous THF) was added and the
mixture was allowed to warm to r.t. within 30 min. The
reaction mixture was quenched with saturated ammo-
nium chloride and the organic materials were extracted
with ether. The combined extracts were washed with
additional ammonium chloride and water, dried
(Na2SO4) and concentrated in vacuo (15–20 torr). The
pure bromoallene was obtained by fractional distilla-
tion as a colorless liquid.
4.1. Optical resolution of propargylic alcohols
(R)(S)-4a–c. General procedure
The hydrogen phthalate of racemic carbinols (R)(S)-
4a–c (0.7–0.8 mol), obtained by a published procedure
[15,16] in 80–90% yield, was dissolved with stoichio-
metric amount of anhydrous (−)-brucine in ca. 4 l of
boiling acetone. After the mixture was cooled to r.t. the
brucine salt was filtered off, recrystallised from acetone
several times, and decomposed with dilute HCl solution
(6 N). The obtained (+)-hydrogen phthalate was
treated with 10 M KOH solution and the (+)(S)-carbi-
nol [20] was recovered by steam distillation. The enan-
tiomeric excesses (ee%) of the recovered samples were
evaluated by complexation GLC analysis on
[Niꢀ(S)ꢀCAM] column; samples from the racemic alco-
hols gave baseline-separated chromatographic peaks to
allow the accurate estimation of the ee.
4.2.1. (R)-1-Bromo-3-methyl-1,2-pentadiene, (R)-5a
70% yield; b.p. 42°C/17 torr; d245 1.2546; [a]D25 −74.7;
1H-NMR (CDCl3), l 1.05 (t, 3H, J=7 Hz, CH3); 1.83
(d, 3H, J=2 Hz, CH3Cꢂ); 2.10 (m, 2H, CH2Cꢂ); 5.85
(m, 1H, ꢂCꢂCHBr).
4.2.2. (R)-1-Bromo-3,4-dimethyl-1,2-pentadiene, (R)-5b
68% yield; b.p. 58°C/17 torr; d245 1.1949; [a]D25 −87.9;
1H-NMR (CDCl3), l 1.08 (d, 6H, J=7 Hz, CH3); 1.85
(d, 3H, J=2.3 Hz, CH3Cꢂ); 2.27 (m, 1H, CHCꢂ); 5.87
(m, 1H, ꢂCꢂCHBr).
4.2.3. (R)-1-Bromo-3,4,4-trimethyl-1,2-pentadiene,
(R)-5c
83% yield; b.p. 66°C/17 torr; d240 1.1612; [a]D20 −86.1;
1H-NMR (CDCl3), l 1.08 (s, 9H, CH3); 1.79 (d, 3H,
J=2.2 Hz, CH3C=); 5.88 (q, 1H, J=2.2 Hz,
ꢂCꢂCHBr).
4.1.1. (S)-3-Methyl-1-pentyn-3-ol, (S)-4a
From two recrystallizations of the hydrogen phtha-
late brucine salt: b.p. 66°C/760 torr; d240 0.8688; [a]D20+
1
2.84 (94% ee); H-NMR (20%, CDCl3), l 1.02 (t, 3H,
4.3. LiAlH4 reduction of (R)-1-Bromo-1,2-dienes,
(R)-5, to (S)-1-alkynes, (S)-2. General procedure
J=7 Hz, CH3); 1.46 (s, 3H, CH3); 1.70 (q, 2H, J=7
Hz, CH2); 2.43 (s, 1H, ꢁCH); 3.18 (s, 1H, OH).
A solution of the appropriate (R)-1-bromo-1,2-diene,
(R)-5 (60–70 mmol), in anhydrous diethylcarbitol (5–
10 ml) was added dropwise, at 0°C, to a suspension of
two equivalents of LiAlH4 (30–40 mmol) in the same
4.1.2. (S)-3,4-Dimethyl-1-pentyn-3-ol, (S)-4b
From one recrystallization of the hydrogen phthalate
brucine salt: b.p. 68°C/60 torr; d245 0.8658; [a]D25 +5.20

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P. Pertici et al. / Journal of Organometallic Chemistry 621 (2001) 246–253
solvent (30–50 ml). The reaction mixture was stirred
for 20–24 h at r.t. and then hydrolysed with water. The
crude product was recovered at 17 torr in a liquid
nitrogen trap. Subsequent careful distillation yielded
pure products.
4.5. Reaction of Ru(p6-naphthalene)(p4-COD), 1, with
(R)(S)-1,3,5-tri-(1-methylpropyl)benzene in the presence
of acetonitrile
Complex 1 (0.1 g, 0.29 mmol) and (R)(S)-1,3,5-tri-(1-
methylpropyl)benzene (0.714 g, 2.9 mmol) were treated
with THF (5 ml) and acetonitrile (0.3 ml, 5.8 mmol).
The red–orange mixture was stirred for 48 h at r.t. The
resulting pale red–orange solution was separated from
the solid material by filtration and then evaporated to
4.3.1. (S)-3-Methyl-1-pentyne, (S)-2a
90% yield; b.p. 58°C/760 torr; [a]2D0 +43.40 (93% ee)
1
[21]; H-NMR, l 1.00 (t, 3H, J=7.3 Hz, CH3); 1.17 (d,
1
3H, J=6.9 Hz, CH3); 1.47 (m, 2H, CH2); 2.02 (d, 1H,
J=2.4 Hz, ꢁCH); 2.36 (m, 1H, CH); 13C-NMR, l 11.5,
20.5, 27.3, 29.7, 68.1, 88.9.
dryness (0.1 torr). The H-NMR (C6D6) of the residue
showed presence of complex 1, arene and free
naphthalene.
4.6. Reaction of Ru(p6-cycloocta-1,3,5-triene)(p4-COD)
with (R)(S)-1,3,5-tri-(1-methylpropyl)benzene under
hydrogen atmosphere
4.3.2. (S)-3,4-Dimethyl-1-pentyne, (S)-2b
87% yield; b.p. 81°C/760 torr; [a]2D5 +25.5 (84% ee)
[22]; 1H-NMR, l 0.97 (d, 6H, J=6.6 Hz, CH3); 1.15 (d,
3H, J=7 Hz, CH3); 1.55–1.74 (m, 1H, CH); 2.02 (d,
1H, J=2.4 Hz, ꢁCH); 2.25–2.42 (m, 1H, CHCꢁ);
13C-NMR, l 18.4, 18.5, 20.4, 32.6, 32.8, 68.9, 87.5.
(R)(S)-1,3,5-Tri-(1-methylpropyl)benzene (0.78 g, 3.2
mmol) was added to a solution of Ru(h6-cycloocta-
1,3,5-triene)(h4-COD) (0.1 g, 0.32 mmol) in THF (5 ml)
and the yellow solution was stirred under hydrogen (1
atm) at r.t. After ca. 3 h the solution became colourless
and metallic ruthenium precipitated. The solution was
separated from the solid by filtration and then evapo-
4.3.3. (S)-3,4,4-Trimethyl-1-pentyne, (S)-2c
80% yield; b.p. 100°C/760 torr; [a]2D5 +11.2 (89% ee)
1
[22]; H-NMR, l 0.97 (s, 9H, CH3); 1.15 (d, 3H, J=7
Hz, CH3); 2.05 (d, 1H, J=2.4 Hz, ꢁCH); 2.25 (dq, 1H,
J=2.4 and 7 Hz, CH); 13C-NMR, l 15.9, 27.0, 33.0,
37.1, 69.2, 88.0.
1
rated to dryness (0.1 torr). The H-NMR (C6D6) of the
residue showed presence of the unreacted arene.
4.4. Reaction of Ru(p6-naphthalene)(p4-COD), 1, with
the alkynes (S)-2a–c: synthesis of
Acknowledgements
Ru(p6-arene)(p4-COD) complexes 6 and 7. General
procedure
This work was in part supported by the Ministero
della Universita` e della Ricerca Scientifica e Tecnolog-
ica (MURST), Italy.
Complex 1 (0.5 g, 1.48 mmol) was dissolved in THF
(5 ml) and the alkyne (8.9 mmol) was added. The
solution was stirred at r.t. The progress of the reaction
was checked by removing liquid samples of the solution
and analysing the residue, obtained after evaporation of
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