Organometallic derivatives of natural products: Dicobalt hexacarbonyl complexes of geranyl-alkynes

Article abstract of DOI:10.1039/c6nj00622a

Treatment of methyl geranyl ether with diiron nonacarbonyl leads to hydrogen migration to form previously unknown E and Z 1-methoxy-3,7-dimethyl-1,6-octadiene in low yield. Sodium propargyl alkoxide and geranyl bromide yield propargyl geranyl ether, 13; subsequent reaction with dicobalt octacarbonyl and then bis(diphenylphosphino)methane furnishes the corresponding alkyne-Co₂(CO)₄(dppm) tetrahedral cluster, 16. Reaction of geranylacetone with phenylethynyl-lithium, and then with Co₂(CO)₈, forms (1-phenyl-3,7,11-trimethyldodeca-6,10-dien-1-yn-3-ol)Co₂(CO)₆, 19. The carbynyltricobaltnonacarbonyl clusters RC(O)CCo₃(CO)₉, where R = geranyl, 23, or farnesyl, 25, are preparable in very good yield either by reaction of the appropriate alcohol with trichloroacetyl chloride and then Co₂(CO)₈, or by reaction with the metal-stabilized acylium ion [Co₃(CO)₉CCO]⁺, 24. Potential use of these (η²-alkyne)dicobalt complexes in Pauson-Khand or Nicholas cyclizations is discussed.

Full text of DOI:10.1039/c6nj00622a

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Page 1 of 21
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Organometallic derivatives of natural products:
dicobalt hexacarbonyl complexes of geranyl-alkynes
Angela Moore, Johannes Ostermann, Yannick Ortin
and Michael J. McGlinchey*
School of Chemistry, University College Dublin
Belfield, Dublin 4, Ireland
e-mail: michael.mcglinchey@ucd.ie
fax: +353 1 716 1178
Abstract: Treatment of methyl geranyl ether with diiron nonacarbonyl leads to hydrogen
migration to form previously unknown E and Z 1-methoxy-3,7-dimethyl-1,6-octadiene in low
yield. Sodium propargyl alkoxide and geranyl bromide yield propargyl geranyl ether, 13;
subsequent reaction with dicobalt octacarbonyl and then bis(diphenylphosphino)methane
furnishes the corresponding alkyne-Co
geranylacetone with phenylethynyl-lithium, and then with Co
trimethyldodeca-6,10-dien-1-yn-3-ol)Co (CO) 19. The carbynyltricobaltnonacarbonyl
clusters RC(=O)CCo (CO) , where R = geranyl, 22, or farnesyl, 25, are preparable in very
2
(CO)
4
(dppm) tetrahedral cluster, 16. Reaction of
2
(CO) , forms (1-phenyl-3,7,11-
8
2
6
,
3
9
good yield either by reaction of the appropriate alcohol with trichloroacetyl chloride and then
+
Co
2
(CO)
8
, or by reaction with the metal-stabilized acylium ion [Co
3
(CO)
9
C=C=O] , 24.
2
Potential use of these (ꢀ -alkyne)dicobalt complexes in Pauson-Khand or Nicholas
cyclizations is discussed.

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r î r
Introduction
In continuation of our studies on organometallic derivatives of natural products, such
1
2
3
4
5
as steroids (both estrogenic and androgenic ), terpenes (menthol, camphor, fenchone,
6
7
verbenone ) or chalcones, we here report syntheses of cobalt carbonyl complexes containing
the geranyl group. The use of organometallic reagents in the syntheses of natural products has
a long and distinguished pedigree. Particularly fine examples include Billups‘ nickel-
catalyzed dimerization of isoprene and subsequent conversion to grandisol, 1, a boll weevil
8
pheromone (Scheme 1), Baker‘s preparation of muscone, 2, from (1,5,9-cyclododeca-
9
10
triene)nickel (Scheme 2), and Vollhard‘s elegant cobalt-mediated route to estrone.
2
x
Ni(COD)2
Sia BH
2
OH
1
(grandisol)
Scheme 1. Nickel-mediated synthesis of (±)-grandisol, 1.
CH =C=CH
2
2
Ni
o
-
20 C
Ni
o
RNC -20 C
1
. HOAC / H SO
2 4
2
. H / Pd-C
2
O
2 (muscone)
RN
Scheme 2. Organometallic route to (±)-muscone, 2.

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Since geranyl pyrophosphate is the precursor to a wide variety of monoterpenes
whose syntheses proceed via cyclizations on enzyme templates leading to very specific, often
1
1
chiral, products, one might envisage the folding of a geranyl (or even a farnesyl)
unsaturated chain on a transition metal template, thus leading to a single product in a
controlled fashion. A recent closely related example of such a process (Scheme 3) is Tyrrell‘s
cyclization of an alkynyl dicobalt-hexacarbonyl derivative of citronellol to form 2-
1
2
phenylethynyl-1-isopropenyl-4-methylcyclohexane, 3, a near relative of menthene.
1
3
Likewise, in earlier work, Marshall used this approach to prepare a cyclododecadienynol, as
shown in Scheme 4.
CH3
CH3
OH
1
. Co (CO)
2
8
CH Cl
2
2
Ph
2
3
. BF OEt
3
2
o
. CAN 0 C
Ph
3
CH3
Co(CO)3
Ph
+
Co
CO)3
(
Scheme 3. Cobalt-mediated cyclization of an alkynyl-citronellol to form 3.
1
. Co (CO)8
2
CH Cl2
2
2
. BF OEt2
3
o
3
. CAN 0 C
R
O
R
SnBu3
H
OH
R = OCH OCH Ph
2
2
Scheme 4. Cobalt-mediated cyclization to form a cyclododecadienynol.

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1
4
Pioneering work by Schwartz and Dunn involved the reaction of geranyl (and
farnesyl) methyl ether with K PtCl to form complexes tentatively assigned as 4 and 5
Scheme 5). In a subsequent study by Åkermark and Vitagliano, it was reported that cationic
2
4
(
(
3
3
ꢀ -geranyl)- and (ꢀ -neryl)-palladium complexes, 6 and 7, respectively, undergo
nucleophilic attack to yield initially linalyl-amines that subsequently isomerize to a mixture
1
5
of geranyl- and neryl-amines.
PtCl2
PtCl2
Pt
Cl
2
4
5
H
H
H
H
L
Pd
+
Pd
+
L
L
L
6
7
Scheme 5. Selected geranyl and neryl platinum and palladium complexes.
We here report syntheses of cobalt carbonyl complexes of prop-2-ynyl geranyl ether,
of geranyl acetate, and of the phenylethynyl adduct to geranyl-acetone.
Results and discussion
Reaction of geranyl methyl ether with diiron nonacarbonyl
Initially, it was decided to study the reaction of geranyl methyl ether, 8, with iron
4
carbonyl to see whether the diene would yield an ꢀ -Fe(CO)
3
complex that could be further
(CO) in THF
then at reflux for a further 3 d, and the products separated by chromatography on silica, two
elaborated. When the ether 8 was stirred for 48 h. at room temperature with Fe
2
9

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organic products, 9 and 10, were isolated in very low (5%) yield. There was also a trace of an
-1
iron complex exhibiting carbonyl infrared absorptions at 2036 and 1963 cm ; however, its
existence was fleeting and isolation was not possible. The products 9 and 10 were shown to
be the cis and trans isomers, respectively, of previously unknown 1-methoxy-3,7-dimethyl-
1,6-octadiene whereby the C(2)=C(3) double bond has migrated so as to form the
1
6
corresponding pair of vinyl ethers (Scheme 6). The closest analogues of 9 and 10 of which
we are aware are the E and Z isomers of methyl 2,6-dimethyl-1-hepten-6-yl ether, 11, made
1
7
3
by the Wittig reaction of 6-methyl-5-hepten-2-one with Ph P=C(H)OMe (Scheme 7).
One can readily envisage the intermediacy of an allyl iron hydride, 12, a well-
1
8
established mechanistic scenario. These isomers were unambiguously identified from their
1
13
1
H and C NMR spectra. In particular, the doublet character of the H resonance for the 10-
methyl group revealed the presence of a hydrogen now attached to C(3); the identities of the
3
Z and E isomers, 9 and 10, were evident from the J(H
1
-H
2
) coupling constants of 6 Hz and
1
9
1
3 Hz, respectively, entirely typical values for vinyl methyl ethers. Although the overall
isomerization yield is very low, it is interesting since this molecular rearrangement in some
ways parallels the migration of pyrophosphate from C(1) to C(3) in the conversion of
geranyl- to linalyl-pyrophosphate that is a key feature of the enzyme-mediated pathway to
1
1
monoterpenes such as menthol, camphor and many others. However, in this case, it is a
hydrogen atom rather than the methoxy (or pyrophosphate) substituent that undergoes
migration from C(1) to C(3).

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10 CH3
OCH3
CH3
OCH3
1
3
4
5
2
Fe (CO) / THF
2
9
H-Fe(CO)3
6
7
H C
CH
9
3
3
8
H
3
C
CH3
1
2
8
CH3
CH3
OCH3
H
H
OCH3
+
H
H
J = 6 Hz
J = 13 Hz
H C
CH3
H C
CH3
3
3
1
0
9
Scheme 6. Iron carbonyl mediated isomerization of geranyl methyl ether.
CH3
CH3
CH3
OCH3
H
O
Ph P=C(H)OMe
3
H
OCH3
+
H C
CH3
H C
CH3
H C
CH3
3
3
3
1
1(E)
11(Z)
Scheme 7. Schlosser‘s route to methyl 2,6-dimethyl-1-hepten-6-yl ether, 11.
Syntheses of dicobalt-hexacarbonyl and tricobalt-nonacarbonyl geranyl derivatives
The reaction of sodium propargyl alkoxide with geranyl bromide furnished propargyl
geranyl ether, 13, in 75% yield. Subsequent treatment with dicobalt octacarbonyl in THF
gave the cobalt complex, 14, as a maroon oil in 78% yield. This system may be appropriate
2
0
for a Pauson-Khand cyclization to form the corresponding cyclopentenone, 15, and work in
this area is continuing.

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1
3
major isomer and it was found to be the geranyl complex, 19, as revealed by its C NMR
spectrum. Although the geranyl and neryl frameworks exhibit similar NMR spectra, there is a
1
3
characteristic difference in the C chemical shift of C(4); in the geranyl system this is found
at 39-40 ppm, whereas in the corresponding neryl analogues this peak is in the range 32-35
22
ppm. In 17 and 18, the signals for C(8) (which correspond to C(4) in geraniol or nerol)
appear at 39.8 and 32.1, respectively, and in the cobalt complex, 19, the corresponding
resonance is also found at 39.8 ppm. Future work will involve protonation of the 19/20
mixture in the expectation that the (Z) C(2)=C(3) linkage in the minor (neryl) isomer should
favour cyclization to form 21, and so facilitate separation of the products.
1
5
O
HO
CH3
14
CH3
2
CH3
CH3
4
5
3
1
Ph
7
8
9
6
10
1
2
13
CH3
H C
CH3
11
3
H C
3
1
. H
Ph
1
7
CH3
2. BuLi 3. H O
2
CH3
HO
CH3
CH3
Ph
O
CH3
H C
CH3
3
H C
3
18
Scheme 9. Reaction of geranyl- and neryl-acetone with phenylethynyl-lithium.

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Interestingly, such products are also preparable in better yields by treatment of the
+
23,24
metal-stabilized acylium ion, [Co
3
(CO)
9
C-C=O] , 24,
with geraniol (or farnesol) as
depicted in Scheme 12. Indeed, this alternative route furnishes the geranyl ester, 23, and also
the corresponding farnesyl complex, 25, in 92% and 74% yields, respectively.
O
O
EtO
C+
C
Cl C-CO -Et
3
2
HPF6
geraniol
C
2
3
+
Ac O
2
Co(CO)3
(OC) Co
Co(CO)3
Co (CO) / THF
(OC)
3
Co
3
2
8
Co(CO)3
Co(CO)3
2
4
farnesol
2
4
6
10
(
OC) Co
Co(CO)3
3
12
3
8
1
7
11
5
9
(
OC) Co
C
3
O
15
14
13
25
O
Scheme 12. Synthesis of geranyl- (23) and farnesyl- (25) carbynyltricobalt nonacarbonyl
clusters via the cluster-stabilized acylium ion (24).
Conclusions
Attachment of an alkynyl functionality to the geranyl (or neryl) chain, and subsequent
2 2
addition of a dicobalt hexacarbonyl unit to form a tetrahedral Co C cluster, yields molecular
frameworks appropriate for further elaboration via Pauson-Khand cyclizations or metal-
stabilized carbocationic intermediates (Nicholas reactions). In addition, geranyl and farnesyl
derivatives of nonacarbonyltricobaltcarbynyl clusters are readily preparable either via
reaction of dicobalt octacarbonyl with an appropriately substituted trichloroacetate, or by
reaction of geraniol or farnesol with a cobalt-stabilized acylium ion. The chemistry of the
geranyl-containing cobalt clusters will be the focus of a future report.

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Experimental
All reactions were carried under a nitrogen atmosphere, and solvents were dried by
1
13
31
standard procedures. H, C and P NMR spectra were recorded on Varian VNMRS 400 or
500 MHz spectrometers. Assignments were based on standard 2-dimensional NMR
1
1
1
13
techniques ( H- H COSY, H- C HSQC and HMBC, NOESY). Electrospray mass
spectrometry was performed on a Micromass Quattro micro instrument. Infrared spectra were
recorded on a Perkin-Elmer Paragon 1000 FT-IR spectrometer and were calibrated with
polystyrene. Merck silica gel 60 (230-400 mesh) was used for flash chromatography.
Geraniol and geranylacetone were obtained from Aldrich, and dicarbonyl octacarbonyl was
purchased from Strem Chemicals.
Reaction of geranyl methyl ether with diiron nonacarbonyl. (E)-1-Methoxy-3,7-dimethyl-
2
,6-octadiene (geranyl methyl ether), 8, (5.00 g, 29.7 mmol), prepared from geraniol, sodium
hydride and methyl iodide, was added to dry THF (250 mL) containing diiron nonacarbonyl
10.8 g, 29.7 mmol) and the mixture stirred at room temperature for 2 d, and then at reflux for
(
a further 3 d. After removal of solvent and chromatography on silica using pentane/
dichloromethane as eluent, and recovery of unchanged starting material, two new isomers
were isolated in very low yield: (Z)-1-methoxy-3,7-dimethyl-1,6-octadiene, 9, (86 mg, 0.51
mmol; 1.7 %), and (E)-1-methoxy-3,7-dimethyl-1,6-octadiene, 10, (154 mg, 0.92 mmol; 3.1
1
%
). Data for 9: H NMR (400 MHz, CDCl
3
): / 5.83 (d, J = 6.0 Hz, 1H, H
), 3.55 (s, 3H, OMe), 2.59 (m, 1H, H
), 1.59 (s, 3H, Me ), 1.26 (m, 2H, H4,4'), 0.95 (d, J = 6.9
Hz, 3H, Me10). C NMR (100 MHz, CDCl ): / 145.1 (C ), 130.9 (C ), 125.7 (C ), 113.5 (C ),
), 25.7 (Me ), 21.3 (Me10), 17.6 (Me ). Data for 10:
): / 6.25 (d, J = 13.0 Hz, 1H, H ), 5.11 (t, J = 5.5 Hz, 1H, H ),
1
), 5.11 (t, J = 5.5
Hz, 1H, H
.95 (m, 2H, H5,5'), 1.68 (s, 3H, Me
6
), 4.15 (dd, J = 6.0 Hz, J = 7.1 Hz, 1H, H
2
3
),
1
9
8
1
3
3
1
7
6
2
5
9.4 (OMe), 37.8 (C
4
), 28.7 (C
3
), 26.0 (C
5
9
8
1
H NMR (400 MHz, CDCl
3
1
6

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4
.58 (dd, J = 13.0 Hz, J = 8.9 Hz, 1H, H
2
), 3.50 (s, 3H, OMe), 2.01 (m, 1H, H
3
), 1.95 (m, 2H,
H
5,5'), 1.68 (s, 3H, Me
9
), 1.59 (s, 3H, Me
): / 146.1 (C
), 25.7 (Me ), 21.1 (Me10), 17.6 (Me
20O 168.1514, found 168.1511.
8
), 1.26 (m, 2H, H4,4'), 0.98 (d, J = 6.9 Hz, 3H, Me10).
1
3
C NMR (100 MHz, CDCl
3
1
), 131.1 (C
7
), 124.7 (C
6
), 109.0 (C
2
), 55.8 (OMe),
+
38.1 (C ), 32.4 (C ), 25.8 (C
4
3
5
9
8
). (MS ESI): [M] calcd for
C
11
H
(E)-3,7-Dimethyl-1-(prop-2-ynyloxy)octa-2,6-diene (13). Analogously to the literature
2
5
procedure, sodium hydride (0.16 g, 6.67 mmol) was added to a solution of propargyl
alcohol (0.35 mL, 6.01 mmol) in THF (60 mL) at -78 ºC and the mixture was stirred for 1.5
h, and then allowed to warm to room temperature. Upon addition of geranyl bromide (1.10
mL, 5.51 mmol), the solution was allowed to stir for 12 h, then quenched with water (30 mL)
and extracted with diethyl ether (3 x 30 mL). The combined organic layers were washed with
brine (100 mL), dried over MgSO
4
, and evaporated to yield a residue that was subjected to
1
flash chromatography to yield 13 (800 mg, 4.16 mmol; 75%) as a colourless oil. H NMR
(400 MHz, CDCl
3 2 6
): / 5.31 (t, J = 7.0 Hz, 1H, H ), 5.07 (t, J = 6.5 Hz, 1H, H ), 4.10 (t, J = 2.5
Hz, 2H, H11,11'), 4.07 (d, J = 7.0 Hz, 2H, H1,1'), 2.40 (t, J = 2.5 Hz, 1H, CACH), 2.08 (dt, J =
6.5 Hz, J = 7.0 Hz, 2H, H5,5'), 2.02 (t, J = 7.0 Hz, 2H, H4,4'), 1.67 (s, 3H, Me10), 1.66 (s, 3H,
1
3
Me
9
), 1.59 (s, 3H, Me
), 80.2 (CACH), 74.2 (CACH), 66.0 (C
), 17.7 (Me ), 16.5 (Me10).
8
). C NMR (100 MHz, CDCl
3
): / 141.6 (C
3
), 131.7 (C
7
), 124.0 (C
6
),
120.0 (C
2
1
), 56.7 (C11), 39.7 (C
4
), 26.4 (C
5
), 25.7
(Me
9
8
[
(E)-3,7-Dimethyl-1-(prop-2-ynyloxy)octa-2,6-diene]hexacarbonyldicobalt (14). To a
solution of dicobalt octacarbonyl (860 mg, 2.52 mmol) in THF (40 mL) was added a solution
of 13 (484 mg, 2.52 mmol) in THF (20 mL) via cannula. The solution was stirred for 24 h at
room temperature, becoming a deep red; after removal of the solvent under vacuum, the
resulting product was chromatographed on silica using chloroform/cyclohexane as eluent to
1
give 14 as a maroon oil (935 mg, 1.96 mmol; 78%). H NMR (400 MHz, CDCl
3
): / 6.06 (s,

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1
4
2
H, CACH), 5.36 (t, J = 6.5 Hz, 1H, H
2 6
), 5.09 (t, J = 6.0 Hz, 1H, H ), 4.63 (bs, 2H, H11,11'),
.16 (d, J = 6.5 Hz, 2H, H1,1'), 2.09 (dt, J = 6.0 Hz, J = 6.5 Hz, 2H, H5,5'), 2.04 (t, J = 6.5 Hz,
1
3
H, H4,4'), 1.69 (s, 3H, Me10), 1.68 (s, 3H, Me
): / 199.8 (CO‘s), 140.8 (C ), 131.8 (C ), 124.1 (C
CACH), 70.0 (C11), 67.2 (C ), 39.7 (C ), 26.5 (C
CH Cl
49.9924, found 449.9926.
9
), 1.60 (s, 3H, Me
8
). C NMR (100 MHz,
CDCl
3
3
7
6
), 120.6 (C ), 91.7 (CACH), 72.2
2
(
(
1
4
5
), 25.8 (Me
9
), 17.8 (Me
8
), 16.6 (Me10). IR
Co
2
-1
+
2
2
) ꢁ(CO) 2094, 2054, 2027 cm . (MS ESI): [M œ CO] calcd for C18
H
20
O
6
4
[
(E)-3,7-Dimethyl-1-(prop-2-ynyloxy)octa-2,6-diene][bis(diphenylphosphino)methane]-
tetracarbonyldicobalt (16). To a solution of 14 (214 mg, 0.45 mmol) in THF (20 mL) was
added dppm (173 mg, 0.45 mmol), and the mixture was heated at reflux for 16 h, after which
time the solution appeared brown-black in colour. Removal of solvent under vacuum and
chromatography on silica using chloroform/cyclohexane as eluent gave 16 as a maroon oil
1
3
(
109 mg, 0.14 mmol; 30%). H NMR (400 MHz, CDCl
3
): / 7.41 (d, JH-P = 4.8 Hz, 4H,
3
phenyl o-H), 7.33 (d, JH-P = 5.6 Hz, 4H, phenyl o-H), 7.26 (m, 8H, phenyl m/p-H), 7.15 (m,
3
4
H, phenyl m-H), 5.64 (t, JH-P = 4.8 Hz, 1H, CACH), 5.40 (t, J = 6.5 Hz, 1H, H
2
), 5.11 (t, J =
6
5.2 Hz, 1H, H ), 4.80 (m, 2H, H11,11'), 4.22 (d, J = 6.5 Hz, 2H, H1,1'), 3.52 (m, 1H, H14), 3.37
(
m, 1H, H14'), 2.11-2.05 (m, 4H, H4,4',5,5'), 1.70 (s, 3H, Me10), 1.67 (s, 3H, Me
9
), 1.60 (s, 3H,
1
3
1
Me
8
). C NMR (100 MHz, CDCl
3
): / 206.2, 204.2 (CO‘s), 139.8 (C
3
), 137.5 (d, JC-P = 20
1
2
Hz, phenyl ipso-C), 136.5 (d, JC-P = 20 Hz, phenyl ipso-C), 132.1 (d, JC-P = 6.3 Hz, phenyl
2
o-C), 131.8 (C
7
), 131.7 (d, JC-P = 6.3 Hz, phenyl o-C), 129.6 (phenyl p-C), 129.5 (phenyl p-
3
3
C), 128.3 (d, JC-P = 4.5 Hz, phenyl m-C), 128.2 (d, JC-P = 4.5 Hz, phenyl m-C), 124.2 (C
6
),
),
1
21.4 (C
5.8 (Me
(CO) 2021, 1992, 1965 cm .
2
), 95.6 (CACH), 75.0 (CACH), 72.9 (C11), 67.0 (C
1
), 41.3 (C14), 39.7 (C
4
), 26.6 (C
5
3
1
2
9
), 17.8 (Me
8
), 16.7 (Me10). P NMR (162 MHz, CDCl
3
2 2
): / 43.0. IR (CH Cl )
-1
ꢁ

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r íð r
(E)- and (Z)-1-Phenyl-3,7,11-trimethyldodeca-6,10-dien-1-yn-3-ol, (17) and (18). In a
typical procedure, nBuLi (17.7 mL of a 1.6 M hexane solution, 28.3 mmol) was added
dropwise to a solution of phenylacetylene (3.1 mL, 28.3 mmol) in THF (250 mL) at -78 ºC
and the mixture was stirred for 30 min. The solution was allowed to warm to room
temperature and, after 15 min, a 65/35 mixture of geranyl- and neryl-acetone (5.7 mL, 25.7
mmol) was added dropwise over 5 min. The solution was stirred at room temperature for 12
h, quenched with water (150 mL) and extracted with diethyl ether (3 x 100 mL). The organic
4
layers were combined, washed with brine, dried over MgSO , and the solvent removed under
vacuum. Chromatography on silica using pentane/dichloromethane as eluent gave a mixture
1
of E and Z isomers, 17 and 18, respectively, (6.58 g, 22.2 mmol; 86%) as a yellow oil. H
NMR (400 MHz, CDCl
3
): / 7.43 (d, J = 8 Hz, 2H, phenyl o-H), 7.29 (m, 3H, phenyl m/p-H),
), 5.11 (m, 1H, H10), 2.40 (m, 1H, H ), 2.27 (m, 1H, H4'), 2.10 (m, 2H, H9,9'),
.02 (t, J = 7.5 Hz, 2H, H8,8'), 1.81 (m, 2H, H5,5'), 1.71 (m, 3H, Me), 1.68 (m, 3H, Me), 1.62
5
.23 (m, 1H, H
6
4
2
1
3
(
s, 3H, Me), 1.60 (s, 3H, Me). C data for 17: (100 MHz, CDCl
3
) / 136.0 (C
), 92.9 (C ), 83.6 (C
), 25.7 (Me13), 23.8 (C ), 17.8 (Me12), 16.1 (Me14).
) / 136.1 (C ), 131.7 (C11), 131.6, 128.3, 128.2 (phenyl-
), 92.9 (C ), 83.6 (C ), 68.8 (C ), 43.9 (C ), 32.1 (C ), 30.0
5
), 23.4 (Me13), 17.7 (Me12), 16.1 (Me14).
7
), 131.7 (C11),
1
31.5, 128.3, 128.2 (phenyl-o,m,p), 124.3 (C10), 123.9 (C
3.6 (C ), 39.8 (C ), 30.0 (Me15), 26.7 (C
C data for 18: (100 MHz, CDCl
o,m,p), 124.4 (C10), 122.9 (C
Me15), 26.7 (C ), 23.7 (C
6
2
1
), 68.9 (C ),
3
4
4
8
9
5
1
3
3
7
6
2
1
3
4
8
(
9
[
(E)-
dicobalt, (19) and (20). To a solution of dicobalt octacarbonyl (380 mg, 1.11 mmol) in THF
20 mL) was added a solution of the dienynes 17 and 18 (328 mg, 1.11 mmol) via cannula.
and
(Z)-1-Phenyl-3,7,11-trimethyldodeca-6,10-dien-1-yn-3-ol]hexacarbonyl-
(
Upon stirring for 12 h at room temperature, the deep red solution was concentrated under
vacuum and chromatographed on silica using pentane/dichloromethane as eluent to give a
mixture of the isomers 19 and 20 as a maroon solid (444 mg, 0,76 mmol; 69%). Further

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r íñ r
separation of the isomers using ethyl acetate/ pentane furnished a pure sample of 19. Data for
1
1
9: H NMR (500 MHz, CDCl
3
): / 7.62 (d, J = 7 Hz, 2H, phenyl o-H), 7.36 (t, J = 7 Hz, 2H,
), 5.08 (t, J = 7 Hz,
), 1.92 (s, 3H, Me15), 1.86 (m, 2H, H ), 1.79 (m,
), 1.59 (s, 3H, Me13), 1.41 (s, 3H, Me14), 1.40 (s, 3H, Me12). C NMR (125 MHz,
): / 199.8 (CO‘s), 136.4 (C ), 131.7 (C11), 130.0 (phenyl o-C), 128.9 (phenyl m-C),
27.8 (phenyl p-C), 124.3 (C10), 123.7 (C ), 107.9 (CACH), 92.4 (CACH), 75.5 (C-OH), 44.6
), 39.8 (C ), 29.7 (Me15), 26.7 (C ), 25.7 (Me13), 23.4 (C
CH Cl
54.0550, found 554.0547.
phenyl m-H), 7.31 (t, J = 7 Hz, 1H, phenyl p-H), 5.16 (t, J = 7 Hz, 1H, H
6
1
H, H10), 2.24 (m, 2H, H
4
), 2.16 (m, 2H, H
5
9
13
2
H, H
8
CDCl
3
7
1
6
(C
4
8
9
5
), 17.8 (Me12), 16.6 (Me14). IR
-1
+
(
2
2
) ꢁ(CO) 2087 2050, 2020 cm . (MS ESI): [M œ CO] calcd for C26
H
28
O Co
6 2
5
(E)-3,7-Dimethyl-2,6-octadienyl 2,2,2-trichloroacetate (22). To a solution of geraniol
(0.95 mL, 4.50 mmol) in THF (50 mL) at 0 ºC was added sodium hydride (130 mg, 5.4
mmol) and the reaction mixture was stirred for 30 min. It was allowed to warm to room
temperature, 2,2,2-trichloroacetyl chloride (0.65 mL, 5.82 mmol) was added and the mixture
was stirred overnight at room temperature. After quenching with water (20 mL) and
extraction with diethyl ether (2 x 30 mL), the combined organic layers were washed with
4
brine (100 mL), dried over MgSO , and evaporated to give a residue that was subjected to
flash chromatography on silica to furnish the trichloromethyl ester, 22, 876 mg, 2.91 mmol;
1
6
4%) as a colourless oil. H NMR (400 MHz, CDCl
3
): / 5.41 (t, J = 8 Hz, 1H, H
2
), 5.05 (t, J
=
7 Hz, 1H, H
s, 3H, Me ), 1.58 (s, 3H, Me
), 123.4 (C ), 116.2 (C
), 16.6 (Me10).
6
), 4.84 (d, J = 8 Hz, 2H, H1,1'), 2.08 (m, 4H, H4,4',5,5'), 1.75 (s, 3H, Me10), 1.65
1
3
(
8
9
). C NMR (100 MHz, CDCl
3
): / 161.8 (C=O), 145.4 (C
3
9
),
),
131.5 (C
7
2
6
), 90.1 (CCl ), 66.0 (C ), 39.5 (C
3
1
4
), 26.1 (C ), 25.6 (Me
5
17.6 (Me
8
(E)-3,7-Dimethyl-2,6-octadienyl nonacarbonyltricobaltcarbynylcarboxylate (23).(Method
A) To a solution of dicobalt octacarbonyl 960 mg, 2.80 mmol) in THF (20 mL) was added a

New Journal of Chemistry
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r íò r
solution of 22 (460 mg, 1.54 mmol) in THF (10 mL) via cannula. After stirring at room
temperature for 24 h, the deep red solution was concentrated under vacuum to give a maroon
oil that was chromatographed on silica using chloroform/cyclohexane as eluent. The tricobalt
ester, 23, (400 mg, 0.64 mmol; 42%) was isolated as a maroon oil.
(
2E)-3,7-Dimethyl-2,6-octadienyl
Method B) To a solution of ethyl nonacarbonyltricobaltcarbynylcarboxylate (0.18 g, 0.35
mmol) dissolved in acetic anhydride (4 mL) was added dropwise a 60% aqueous solution of
HPF (0.2 mL, 1.36 mmol). After 30 min, precipitation of a black solid was completed by
addition of ether (20 mL) and the solvent was then removed by filtration under a nitrogen
atmosphere. The residue was washed three times with ether and finally suspended in CH Cl
20 mL). To this was added quickly geraniol (0.5 mL, 2.64 mmol) in CH Cl (20 mL) and
nonacarbonyltricobaltcarbynylcarboxylate
(23).
2
6
(
6
2
2
(
2
2
resulted in formation of a homogeneous purple solution. After removal of solvent, the
product was chromatographed on silica using ether/pentane (1:9) as eluent to give the ester 23
1
3
(
0.20 g, 0.32 mmol; 92%) as a dark purple oil. H NMR (500 MHz, CDCl
3
): / 5.37 (t, J =
6
1
1
.5 Hz, 1H, H
.66 (s, 3H, Me
98.9 (CO‘s), 178.3 (C=O), 142.9 (C
), 26.3 (C ), 25.3 (Me ), 17.3 (Me
2
), 5.01 (m, 1H, H
6
), 4.71 (d, J = 6.5 Hz, 2H, H1,1'), 2.03-1.94 (m, 4H, H4,4',5,5'),
13
7
), 1.58 (s, 3H, Me
9
), 1.51 (s, 3H, Me10). C NMR (125 MHz, CDCl
3
): /
), 39.4
) ꢁ(CO) 2105 (m), 2063 (vs),
593.8818, found
3
), 131.6 (C
7
), 123.7 (C
2
), 118.2 (C
6
), 62.5 (C
1
(C
4
5
9
8
), 16.1 (Me10). IR (CH
2
Cl
2
-1
+
2
045 (s), 1681 (w) cm . (MS ESI): [M œ CO] calcd for C20
17 3
H O10Co
593.8822.
(
2E,6E)-3,7,11-Trimethyl-2,6,10-dodecatrienyl nonacarbonyltricobaltcarbynylcarboxylate
25). As for 23, ethyl nonacarbonyltricobaltcarbynylcarboxylate (0.28 g, 0.54 mmol)
dissolved in acetic anhydride (4 mL), treated with a 60% aqueous solution of HPF (0.3 mL,
.04 mmol), and subsequently with farnesol (0.3 mL, 1.20 mmol) in CH Cl (20 mL) gave,
after chromatography on silica using ether/pentane (1:9) as eluent gave the ester 25 as a dark
(
6
2
2
2

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r íó r
1
purple oil (0.28 g, 0.40 mmol; 74%). H NMR (400 MHz, CDCl
3
): / 5.48 (m, 1H, H
2
), 5.10
(
m, 2H, H
Me), 1.68 (s, 3H, Me), 1.60 (s, 3H, Me). C NMR (100 MHz, CDCl
C=O), 143.1, 135.4, 131.1 (C , C , C11), 124.4, 124.2, 123.6 (C , C
4.9 (C , C ), 31.2, 26.8 (Me), 25.7 (Me12), 17.6 (Me13), 16.0, 15.9 (Me14,Me15). IR (CH
(CO) 2109 (s), 2065 (s), 2046 (s), 1672 (m) cm . (MS ESI): [M œ CO] calcd for
661.9443, found 661.9446.
6
,H10), 4.82-4.69 (m, 2H, H1,1'), 2.06-1.97 (m, 8H, H4,4',H5,5',H8,8',H9,9'), 1.77 (s, 3H,
1
3
3
): / 198.6 (CO‘s), 178.6
, C10), 62.6 (C ), 45.0,
Cl
(
3
7
2
6
1
4
4
8
2
2
)
-1
+
ꢁ
25 25 3
C H O10Co
Acknowledgement: We thank Science Foundation Ireland, University College Dublin, and
the Centre for Synthesis and Chemical Biology funded by the Higher Education Authority‘s
Programme for Research in Third-Level Institutions (PRTLI) for generous financial support.

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r íô r
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r îì r
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r îí r
Çꢀꢁoꢂ }( ꢃ}všꢂvš• PŒꢀ‰Z]ꢃ
O
O
Co(CO)3
O
CH3
O
CH3
O
CCl3
Co(CO)3
CO)3
+
C
Co
(
(
OC) Co
Co(CO)3
Co(CO)3
3
Co (CO) / THF
geraniol
2
8
H C
CH3
H C
CH3
3
3
Di- and tri-cobalt carbonyl clusters bearing geranyl or neryl substituents offer
potential routes to novel terpenoid systems.