Chiral diphosphine derivatives of alkylidyne tricobalt carbonyl clusters - A comparative study of different cobalt carbonyl (pre)catalysts for (asymmetric) intermolecular Pauson-Khand reactions

Article abstract of DOI:10.1016/j.poly.2015.04.021

Reaction of the tricobalt carbyne cluster [Co₃(μ₃-CH)(CO)₉] with chiral diphosphines of the Josiphos and Walphos families affords the new clusters [Co₃(μ₃-CH)(CO)₇(P-P^μ)] in good yield (P-P^μ = J004 (1), J005 (2), J007 (3), W001 (4), W003 (5)). The new alkylidyne tricobalt clusters, and the previously known [Co₃(μ₃-CH)(CO)₇(μ-J003)], have been tested as catalysts/catalyst precursors for intermolecular Pauson-Khand cyclization, using norbornene and phenylacetylene as substrate. The diphosphine-substituted tricobalt carbonyl clusters proved to be viable catalysts/catalyst precursors that gave products in moderate to good yields, but the enantiomeric excesses were low. When the chiral diphosphine ligands were used as promoters/auxiliary ligands for the same Pauson-Khand reaction, using either [Co₂(CO)₈] or [Co₄(CO)₁₂] as catalyst precursors, both the overall yields and the selectivities with respect to cyclopentenone formation were significantly improved. The best results were obtained for ligands J007 and W001, with [Co₄(CO)₁₂] as pre-catalyst, where yields of 96%, and virtually 100% selectivity were obtained. However, the enantioselectivity of product formation was low or non-existent. The crystal structure of [Co₃(μ₃-CH)(CO)₇(μ-J004)] is described. [J003 = [(R)-1-{(S)-2-(dicyclohexylphosphino)-ferrocenyl} ethyldicyclohexylphosphine], J004 = [(R)-1-{(S)-2-(dicyclohexylphosphino)-ferrocenyl} ethyldiphenylphosphine], J005 = [(R)-1-{(S)-2-(diphenylphosphino)ferrocenyl}ethyl-di-3,5-xylylphosphine], J007 = [(R)-1-{(S)-2-di-(4-methoxy-3,5-dimethylphenyl)phosphino)ferrocenyl} ethyldicyclohexylphosphine], W001 = [(R)-1-{(R)-2-(2′-diphenyl phosphinophenyl)ferrocenyl} ethyldi(bis-3,5-trifluoromethylphenyl)phosphine], W003 [(R)-1-{(R)-2-(2′-diphenylphosphino-phenyl)ferrocenyl}ethyldi(3,5-xylyl)phosphine].

Full text of DOI:10.1016/j.poly.2015.04.021

Accepted Manuscript
Chiral diphosphine derivatives of alkylidyne tricobalt carbonyl clusters – a
comparative study of different cobalt carbonyl (pre)catalysts for (asymmetric)
intermolecular Pauson-Khand reactions
M. Abdul Mottalib, Matti Haukka, Ebbe Nordlander
PII:
S0277-5387(15)00218-1
DOI:
http://dx.doi.org/10.1016/j.poly.2015.04.021
POLY 11285
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
27 January 2015
20 April 2015
Please cite this article as: M. Abdul Mottalib, M. Haukka, E. Nordlander, Chiral diphosphine derivatives of
alkylidyne tricobalt carbonyl clusters – a comparative study of different cobalt carbonyl (pre)catalysts for
(
asymmetric) intermolecular Pauson-Khand reactions, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.
2
015.04.021
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Chiral diphosphine derivatives of alkylidyne tricobalt carbonyl clusters – a
comparative study of different cobalt carbonyl (pre)catalysts for (asymmetric)
intermolecular Pauson-Khand reactions
a
b
a
M. Abdul Mottalib, Matti Haukka and Ebbe Nordlander *
a. Inorganic Chemistry Research Group, Chemical Physics, Department of Chemistry, Lund
University, Box 124, SE-221 00 Lund, Sweden. E-mail: Ebbe.Nordlander@chemphys.lu.se
b. Department of Chemistry, University of Jyväskylä, Box 35, FI-40014 Jyväskylä, Finland
th
Dedicated to Prof. Catherine E. Housecroft on the occasion of her 60 birthday, in recognition of
her outstanding contributions to inorganic and organometallic chemistry
Abstract: Reaction of the tricobalt carbyne cluster [Co
of the Josiphos and Walphos families affords the new clusters [Co
yield (P-P* = J004 (1), J005 (2), J007 (3), W001 (4), W003 (5)). The new alkylidyne tricobalt
clusters, and the previously known [Co (µ -CH)(CO) (µ-J003)], have been tested as
3
(µ
3
-CH)(CO)
9
] with chiral diphosphines
3
(µ
3
-CH)(CO) (P-P*)] in good
7
3
3
7
catalysts/catalyst precursors for intermolecular Pauson-Khand cyclization, using norbornene and
phenylacetylene as substrate. The diphosphine-substituted tricobalt carbonyl clusters proved to be
viable catalyst/catalyst precursors that gave products in moderate to good yields, but the
enantiomeric excesses were low. When the chiral diphosphine ligands were used as
promoters/auxiliary ligands for the same Pauson-Khand reaction, using either [Co
Co (CO)12] as catalyst precursors, both the overall yields and the selectivities with respect to
cyclopentenone formation were significantly improved. The best results were obtained for
ligands J007 and W001, with [Co (CO)12] as pre-catalyst, where yields of 96%, and virtually
00% selectivity were obtained. However, the enantioselectivity of product formation was low or
non-existent. The crystal structure of [Co (µ -CH)(CO) (µ-J004)] is described. [J003 = [(R)-1-
(S)-2-(dicyclohexylphosphino)-ferrocenyl} ethyldicyclohexylphosphine], J004 = [(R)-1-{(S)-2-
dicyclohexylphosphino)- ferrocenyl} ethyldiphenylphosphine], J005 [(R)-1-{(S)-2-
diphenylphosphino) ferrocenyl}ethyl-di-3,5-xylylphosphine], J007 = [(R)-1-{(S)-2-di-(4-
2
(CO)
8
] or
[
4
4
1
3
3
7
{
(
=
(
methoxy-3,5-dimethylphenyl)phosphino)ferrocenyl} ethyldicyclohexylphosphine], W001 = [(R)-
-{(R)-2-(2’-diphenyl phosphinophenyl) ferrocenyl} ethyldi(bis-3,5-
trifluoromethylphenyl)phosphine], W003 [(R)-1-{(R)-2-(2’-diphenylphosphino-
phenyl)ferrocenyl}ethyldi(3,5-xylyl)phosphine]
1
Keywords: cluster, chirality, enantioselectivity, Pauson-Khand reaction, catalysis

Introduction
The asymmetric catalytic Pauson-Khand reaction has attracted considerable attention in organic
chemistry, especially bio-organic chemistry including natural products synthesis [1] and the
synthesis of various biomolecules [2]. The reaction is widely used to prepare cyclopentenone
ring systems through the formal [2+2+1] cycloaddition of an alkene, alkyne and carbon
monoxide (Scheme 1), usually promoted by [Co
2
(CO) ]. The usefulness and potential impact of
8
this reaction has been the subject of numerous reviews [3].
Scheme 1. A schematic general reaction scheme for the intermolecular catalytic Pauson-Khand
reaction.
In addition to [Co
2
(CO)
(indenyl)Co(cod)] [4], [Co(acac)
Co (µ -CH)(CO) ] [7], [Co (CO)11{P(OPh)
8
], alternative sources of zero or low-valent cobalt, such as
]/NaBH and the cobalt carbonyl clusters [Co (CO)12] [5,6],
}] [5], [Co (µ ] (x = 1,2: L= mono-
[
[
2
4
4
3
3
9
4
3
3
3
-CH)(CO)9-x
L
x
or diphosphines, vide infra) [8] have also been developed as promoters/precatalysts for the
Pauson-Khand reaction, but are less frequently employed. In the original Pauson-Khand reaction
[
9], the alkyne was coordinated to [Co
2
(CO)
8
] to form [Co
2
(CO) (µ-alkyne)], which was heated
6
in the presence of a suitable alkene. It has been found that the cyclization reaction can be
accelerated by the addition of promoters like tertiary amine oxides [10], silica gel [11], and
DMSO [12].
While intermolecular cyclization giving cyclopentenones that are substituted in positions 4 and 5
of the cyclopentenone usually leads to the exo compound, it has been shown that endo
isomers/diastereomers may also be formed [13] (vide infra). Cyclizations to form
cyclopentenones that are substituted only in position 4 give rise to enantiomers. Stereoselective
cyclopentenone formation has been addressed in several ways. The most common approach is to
use chiral auxiliaries that are attached to either the alkene or alkyne moiety [14]. Another

interesting approach is the coordination of a chiral phosphine to introduce asymmetry into the
dicobalt carbonyl complex by replacing a carbonyl ligand [15]. High enantioselectivies have been
reported for intramolecular Pauson-Khand reactions catalyzed by Co
chiral auxiliary ligand. The intramolecular cyclization of a prochiral substrate containing an
alkyne and alkene moiety catalyzed by Co (CO) /MeO-BIPHEP resulted in 91.5 % ee [16] and in
a similar reaction using Co (CO) /BINAP 91 % e.e. was obtained [17]. A very efficient catalytic
2
(CO)
8
with addition of a
2
8
2
8
and highly enantioselective method for intramolecular cocyclization to form cycolpentenones in
the presence of titanocene complexes has been introduced by Buchwald and coworkers [18].
1
6
Jeong et al. [19] have reported intramolecular Pauson-Khand cyclization with excellent
enantioselectivity, using the rhodium carbonyl chloride dimer [RhCl(CO) with (S)-BINAP as
]
2 2
an (auxiliary) chiral ligand. Pauson-Khand reactions with high enantio- and diastereoselectivities
have also been reported using chiral BINAP-based Ir- complexes as catalysts [20,21].
Sugihara and coworkers [7,22] have shown that alkylidyne tricobalt carbonyl clusters are
efficient catalysts/catalyst precursors for the Pauson-Khand reaction. In earlier work, we have
prepared chiral cobalt carbyne clusters via coordination of the chiral mono- and didentate
phosphines (S)-NMDPP, (R,R)-DIPAMP, (S,S)-CHIRAPHOS, (R)-BINAP, (R)-(S)-J003, (R,R)-
1
Me-DUPHOS, (R)-PROPHOS, (R,R)-NORPHOS) to the tricobalt carbyne framework, and have
investigated the abilities of the resultant chiral clusters to effect enantioselective Pauson-Khand
cyclizations [8]. Here, we wish to present the synthesis and characterization of five new cobalt
carbyne clusters of the general formula [Co
3
(µ
3
-CH)(CO) (P-P*)] (P-P* = chiral diphosphine of
7
the Josiphos or Walphos families, viz. J004, J005, J007, W001, Fig. 1), and an investigation of
their abilities to effect enantioselective intermolecular Pauson-Khand cyclizations. The catalytic
efficiences of the new cobalt carbyne clusters, and the previously known [Co
3
(µ
3
-CH)(CO)
7
(µ-
J003)] [8] were compared to those of the homoleptic carbonyl clusters [Co
2
(CO) ] and
8
[
Co (CO)12], when Josiphos and Walphos ligands are added as auxiliary ligands.
4
1
(
R)-(R)-NORPHOS = [(2R,3R)-(-)-2,3-bis(diphenylphosphino)-bicyclo-[2.2.1]hept-5-ene], (R)-PROPHOS = [(R)-
(
+)-1,2-bis(diphenylphosphino)propane], (R,R)-Me-DUPHOS = [(-)-1,2-bis((2R,5R)-2,5-dimethylphospholano)
benzene], (R)-(S)-J003 = [=(R)-(-)-1-[(S)-2-(dicyclohexylphosphino)ferrocenyl]ethyldicyclohexyl-phosphine].
Throughout this paper, chiral diphosphines will be referred to by their acronyms only, without stereodescriptors; the
specific chiralities are specified in this footnote, in Fig. 1 and in the Experimental Section.

Fig. 1. Chiral diphosphine ligands of the Josiphos (J) and Walphos (W) ligand families that have
been used in the present study.
Experimental
All reactions were performed under a nitrogen atmosphere using standard Schlenk techniques.
Solvents were dried and distilled by standard methods, and were deoxygenated by bubbling with
nitrogen gas prior to use. All chiral phosphines were purchased from STREM Chemicals and
used as received. The parent cluster [Co
3
(µ
3
-CH)(CO)
9
] [23] and [Co
3
(µ-CH)(CO) (µ-J003)] [8]
7
were prepared according to literature methods. Infrared spectra were recorded on a Nicolet
1
31
Avatar 360 FT-IR spectrometer, H and P NMR spectra were recorded on a Varian Unity Plus
1
31
5
00 spectrometer. All H NMR spectra were referenced to solvent signals while the P NMR
+
spectra were referenced to 85% H
3
PO
4
. Fast Atom Bombardment (FAB ) mass spectra were
obtained on a JEOL SX spectrometer with 2-nitrobenzyl alcohol (NBA) as matrix. Thin-layer
chromatography was performed on commercially available 20 x 20 cm glass plates, covered with
Merck Kieselgel 60 to 0.25 mm thickness. Catalysis experiments were carried out in a Parr
autoclave fitted with a PTFE liner (30 mL).
1
.1 Synthesis of [Co
3
(µ
3
-CH)(CO)
7
(J004)] 1
of
A
CH
ferrocenyl}ethyldiphenylphosphine] (18 mg, 0.030 mmol) was added dropwise to a refluxing
dichloromethane solution (6 ml) of [Co (µ -CH)(CO) ] (10 mg, 0.023 mmol). After few minutes
2
Cl
2
solution
(5 ml)
J004
[(R)-1-{(S)-2-(dicyclohexylphosphino)-
3
3
9

of stirring, the solution turned deep red. The reaction was monitored by spot TLC until no trace
of starting material could be found, which occurred after 2 h of reflux. The solvent was removed
under reduced pressure and the residue was purified by thin layer chromatography. Elution with
CH
2
Cl
2
/hexane (1:1, v/v) gave one deep red band that afforded [Co
Cl
3
(µ
3
-CH)(CO) (J004)] 1 (18
7
o
mg, 82 %) as red crystals after recrystallization from CH
2
2
/hexane at -20 C. IR [νC-O, n-
Hexane]; 2053(s), 2021(s), 2010(sh), 1999(sh), 1993(vs), 1957(w), 1881(w), 1863(m), 1822(w),
-
1
1
o
1
4
805(m) cm ; H NMR (CDCl
3
, 25 C): δ 10.33 (s, 1H), 7.56-7.30 (m,10H), 4.41(s, 1H, Cp),
.26(s), 2H, Cp), 4.08(s, 5H, Cp), 2.88(br, 1H), 2.44-1.25(m, 22H), 0.89(t, J= 7.0 Hz, 3H);
3
1
1
o
P{ H} NMR (CDCl , 25 C): δ 63.50(br, 1P), 51.29(br. 1P), 49.88(s, 1P), 36.61(s, 1P). MS: m/z
3
+
9
80 (M ).
1
3 3 7
.2 Synthesis of [Co (µ -CH)(CO) (J005)] 2
A total of 10 mg (0.023 mmol) of [Co
solution heated to reflux. A dropping funnel was charged with J005 [(R)-1-{(S)-2-
diphenylphosphino) ferrocenyl}ethyl-di-3,5-xylylphosphine] (19 mg, 0.029 mmol) dissolved in
CH Cl (5 ml) and the solution was added dropwise to the refluxing solution. After a couple of
3
(µ
3
-CH)(CO)
9
] was dissolved in 6 ml of CH
2
Cl
2
and the
(
2
2
minutes, the solution turned red. The reaction was monitored by spot TLC, and no trace of the
starting material could be found after 2 h of reflux. The solvent was removed under reduced
pressure and the residue was purified by thin layer chromatography. Elution with CH
1:1, v/v) gave one deep red band which afforded [Co (µ -CH)(CO) (J005)] 2 (18 mg, 78 %) as a
red microcrystalline solid. IR [νC-O, hexane]; 2054(s), 2024(s), 2002(sh), 1994(vs), 1968(w),
2
Cl
2
/hexane
(
3
3
7
-1
1
o
1
872(m), 1806(m), 1750(w) cm ; H NMR (CDCl
3
, 25 C): δ 9.98 (s, 1H), 8.76(t, J =8.5 & 18.0
Hz, 1H), 8.04(t, J =8.5 & 17.5 Hz, 1H), 7.61(m, 2H), 7.45(m, 3H), 7.18(m, 5H), 6.9(br, 1H),
6
1
6
1
.73(d, J= 9.0 Hz, 1H), 6.68(d, J=10.0 Hz, 1H), 6.43(d, J= 9.0 Hz, 1H), 4.53(s, 1H, Cp), 4.47(s,
H, Cp), 4.43(s, 1H, Cp), 3.71(s, 5H, Cp), 2.92(q, J= 7.0, 13.0 Hz, 1H), 2.35(s, 6H), 2.17 (s,
3
1
1
o
H), 0.88(t, J = 7.0 Hz, 3H) ; P{ H} NMR (CDCl
3
, 25 C): δ 66.73 (br, 1P, 50%), 50.06 (br, 1P,
+
00%), 46.53 (br, 1P, 50%), 40.89 (br, 1P, 100%). MS: m/z 1028 (M ).

1
3 3 7
.3 Synthesis of [Co (µ -CH)(CO) (J007)] 3
A total of 10 mg (0.023 mmol) [Co
3
(µ
3
-CH)(CO)
9
] was dissolved in 6 ml of CH
2
Cl and the
2
solution was heated to reflux. A dropping funnel was charged with J007 [(R)-1-{(S)-2-di-(4-
methoxy-3,5-dimethylphenyl)phosphino)ferrocenyl}ethyldicyclohexylphosphine] (20 mg, 0.030
mmol) dissolved in CH
2
Cl (5 ml) and the solution was added dropwise to the refluxing solution.
2
After a few minutes, the reaction mixture turned red. The reaction was monitored by spot TLC,
and no trace of the starting material could be found after 2 h of reflux. The solvent was removed
under reduced pressure and the residue was purified by thin layer chromatography. Elution with
CH
2
Cl
2
/hexane (1:1, v/v) gave one deep red band which afforded [Co
3
(µ
3
-CH)(CO) (J007)] 3 (20
7
mg, 81 %) as a red microcrystalline solid. IR [νC-O, hexane]; 2050(s), 2018(s), 1990(vs), 1880w,
-1
1
o
1
861(s), 1813(m), 1773(m) cm ; H NMR (CDCl
3
, 25 C): δ 10.01 (s, 1H), 7.15 (br, 1H), 6.68(d,
J =10.5 Hz, 2H), 5.77 (t, J= 8.0 Hz, 1H), 4.70 (s, 1H, Cp), 4.41 (s, 1H, Cp), 4.34 (s, 1H, Cp),
4
6
.10 (m, 1H), 3.72 (s, 5H, Cp), 3.68 (s, 3H, OMe), 3.64 (s, 3H, OMe), 2.29 (s, 6H, CH
3
), 2.15 (s,
3
1
1
o
H, CH
3
), 1.85-1.01 (m, 22H), 0.88 (t, J= 10.0 Hz, 3H); P{ H} NMR (CDCl
3
, 25 C): δ 38.58
+
(
s, 1P), 37.22 (s, 1P). MS: m/z 1096 (M ).
1
3 3 7
.4 Synthesis of [Co (µ -CH)(CO) (W001)] 4
In a 25 ml two-necked round bottom flask fitted with a condenser and a dropping funnel, [Co
3
(µ-
o
CH)(CO)
9
] (10 mg, 0.023 mmol) was dissolved in 6 ml of toluene and heated to 90 C. The
dropping funnel was charged with W001 [(R)-1-{(R)-2-(2’-diphenyl phosphinophenyl)
ferrocenyl}ethyldi(bis-3,5-trifluoromethylphenyl)phosphine] (28 mg, 0.030 mmol, 1.3 eq.)
dissolved in toluene (5 ml) and the solution was added dropwise to the round bottom flask. The
reaction was monitored by spot TLC, and no trace of the starting material could be found after 2
h of heating. The solvent was removed under reduced pressure and the residue was purified by
thin layer chromatography. Elution with CH
2
Cl
2
/hexane (1:1, v/v) gave [Co
3
(µ
3
-
CH)(CO) (W001)] 4 (9 mg, 30 %). IR [νC-O, Hexane]; 2050(s), 2024(vs), 2002(s), 1996(s),
7
-
1
1
o
1
8
6
986(sh), 1969(w), 1874(w) cm ; H NMR (CDCl , 25 C): δ 10.14 (s, 1H), 8.33 (d, J =9.5, 2H),
3
.12 (d, J =10.0 Hz, 2H), 7.97 (br, 2H), 7.53 (br, 3H), 7.17 (m, 5H), 7.02 (m, 4H), 6.69 (br, 1H),
.46 (br, 1H), 4.78 (s, 1H, Cp), 4.59 (s, 1H, Cp), 4.39 (s, 1H, Cp), 4.03 (s, 5H, Cp), 3.62 (q, J=

3
1
1
o
5
2
.5, 10.0 Hz), 0.88 (t, J= 5.0, 10.0 Hz, 3H) ; P{ H} NMR (CDCl , 25 C): δ 51.06 (br, 1P),
3
+
7.90 (br, 1P). MS: m/z 1316 (M )
1
3 3 7
.5 Synthesis of [Co (µ -CH)(CO) (W003)] 5
In a 25 ml two-necked round bottom flask fitted with a condenser and a dropping funnel,
o
[
Co
3
(µ-CH)(CO)
9
] (10 mg, 0.023 mmol) was dissolved in 7 ml of toluene and heated to 90 C.
The dropping funnel was charged with W003 [(R)-1-{(R)-2-(2’-diphenylphosphinophenyl)
ferrocenyl}ethyldi(3,5-xylyl)phosphine] (23 mg, 0.033 mmol, 1.5 eq) dissolved in toluene (4 ml)
and the solution was added dropwise to the round bottom flask. The reaction was monitored by
spot TLC, and no trace of the starting material could be found after 2 h of heating. The solvent
was removed under reduced pressure and the residue was purified by thin layer chromatography.
Elution with CH
2
Cl
2
/hexane (1:1, v/v) afforded [Co
3
(µ
3
-CH)(CO)
7
(1,2-W003)] 6 (16 mg, 70 %)
as a black/deep reddish microcrystalline solid. IR [νC-O, hexane]; 2048(s), 2014(vs), 1995(s),
-1
1
o
1
972(s), 1883(w) cm ; H NMR (CDCl
3
, 25 C): δ 10.03 (s, 1H), 7.83 (d, J =8.0, 1H), 7.78 (d, J
=
9.0 Hz, 1H), 7.43 (t, J= 7.5 Hz, 1H), 7.35 (t, J =7.5, 1H), 7.11 (t, J = 7.5 Hz, 1H), 6.98 (dd, J=
1
7
7
5
8, 8.5 Hz, 2H), 6.95 (d, J = 7.0 Hz, 1H), 6.88 (t, J= 7.5 Hz, 2H), 6.82 (t, J =7.5, 2H), 6.70 (t, J =
.5 Hz, 2H), 4.27 (s, 1H, Cp), 4.24 (s, 5H, Cp), 3.98 (s, 1H, Cp), 3.05 (s, 1H, Cp), 2.65 (q, J=
3
1
1
o
.0, 14.0 Hz, 1H), 1.67-1.11 (m, 22H), 0.88 (t, J= 8.0 Hz, 3H) ; P{ H} NMR (CDCl , 25 C): δ
3
+
5.53 (br, 2P). MS: m/z 1056 (M )
1
.6. Catalysis experiments - intermolecular Pauson-Khand reaction
In a typical experiment, the autoclave was loaded with 10 mg of the relevant catalyst ([Co
3
(µ-
CH)(CO) (J003)], 1-5) and the substrates norbornene and phenyl acetylene, each in a 50 molar
7
excess relative to the catalyst. Toluene (5 ml) was added and the autoclave was purged several
o
times before being pressurized with 10 bar of CO. The reaction mixture was stirred at 120 C for
1
2h, after which the reaction was allowed to cool down to room temperature. The autoclave was
depressurized carefully before it was opened at room temperature. The reaction mixture was
transferred into a round bottom flask and the solvent was removed in vacuo. The resultant oily

residue was purified using preparative TLC, eluting with a hexane/ethyl acetate mixture (4:1 v/v).
Besides the starting materials, two products were collected. The UV-active colorless band with
the highest Rf gave 1,3,5-triphenyl benzene (6) and the slower moving band afforded gave 4-
1
phenyltricyclo[5.2.1.0]dec-en-3-one (7), both of which were unambiguously identified by H
2
NMR and mass spectrometry.
1
.7. Catalytic Pauson-Khand reactions effected by [Co
2 8 4
(CO) ] or [Co (CO)12] in conjunction
with chiral auxiliary diphosphine ligands
In a typical experiment, the autoclave was loaded with either 6 mol % [Co
2
(CO)
8
], or 3.5 mol %
[
Co (CO)12], 8 mol % of the relevant chiral diphosphine (Josiphos or Walphos) as auxiliary chiral
4
ligand/promoter, and the substrates norbornene and phenyl acetylene. Toluene (5 ml) was added
and the autoclave was purged several times before being pressurized with 10 bar of CO. The
o
reaction mixture was stirred at 120 C for 12 h, after which the reaction was allowed to cool down
to room temperature. The autoclave was depressurized carefully before it was opened at room
temperature. The reaction mixture was transferred into a round bottom flask and the solvent was
removed in vacuo. Ensuing work-up as described above gave 1,3,5-triphenyl benzene (6) and 4-
phenyltricyclo[5.2.1.0]dec-en-3-one (7) in varying yields.
1
.8. HPLC analysis: The diastereomeric excess of the product, 4-phenyltricyclo[5.2.1.0]dec-en-
-one 7 obtained in the catalytic experiments was assessed by HPLC analysis using a Varian
3
Prostar chromatograph (PDA detector) with a Chiralpak AD-H analytical column. The eluent was
-1
n-hexane-isopropanol (8:2; v/v) and the flow rate was 0.4 ml min . The retention times for the
first and second enantiomers (not identified) were 15 and 17 min, respectively.
2
o
1
,3,5-triphenyl benzene 6 (CDCl
3
, 25 C): δ 7.68(m, 4H), 7.52(d, J =8.0 Hz, 1H), 7.47(t, J =7.5 Hz, 2H), 7.37(t, J
1
=
2
7.5 Hz, 1H), 7.22(m, 10H); mass spectrum, m/z: 306; 4-phenyltricyclo[5.2.1.0]dec-en-3-one 7, H NMR (CDCl
5 C): δ 7.70 (d, J=7.0 Hz, 2H), 7.64(d, J =3.0, 2H), 7.37(t, J =7.5 Hz, 2H), 7.30(d, J =7.5 Hz, 2H,), 2.50(d, J =4.0
3
,
o
Hz, 1H), 2.36(d, J=5.0 Hz,1H), 2.28(d, J=4.50 Hz,1H), 1.71(m, 1H), 1.61(m,1H), 1.35(m, 1H), 1.12(d, J=10.5
Hz,1H), 0.99(d, J=10.5 Hz, 1H); mass spectrum, m/z: 224.

1
.9. X-ray crystallography
The diffraction data for 1 were collected at 100 K using a Nonius Kappa CCD diffractometer.
The Denzo/Scalepack program package [24] was used for cell refinement and data reduction. The
structure solution was carried out by direct methods, using SIR2004 [25], and SHELXL-97 [26]
was used for structure refinement. The absolute structure was determined on the basis of the
Flack index [27] during the refinement process. The non-substituted cyclopentadienyl ring of the
ligand ferrocenyl moiety was disordered over two sites with occupancies 0.61/0.38. The Fe1-C
and C-C distances in the disordered groups were restrained to be similar. Also, the anisotropic
displacement parameters within the disordered hydrogen atoms were positioned geometrically
and constrained to ride on their parent atoms, with C-H = 0.95-1.00 Å, and Uiso = 1.2-1.5 Ueq
(
parent atom). Relevant crystal, data collection and refinement data are summarised in Table 1.
Results and discussion
2
.1. Synthesis and characterization of Josiphos derivatives of [Co
of [Co (µ -CH)(CO) ] with the chiral Josiphos diphosphines J004, J005 or J007 (cf. Fig 1) in
refluxing CH Cl gave [Co (µ -CH)(CO) (P-P*)] in good yield (P-P* = J004 (1), 82%; J005 (2),
8%; J007 (3), 81%). As mentioned in the introduction, we have earlier reported the preparation,
3 3 9
(µ -CH)(CO) ]. Treatment
3
3
9
2
2
3
3
7
7
characterization and potential of [Co
CH)(CO)
3
(µ
3
-CH)(CO)
7
(P-P*)] clusters, including [Co
3
(µ -
3
7
(J003)], to act as (pre)catalysts for an (asymmetric) intramolecular Pauson-Khand
1
31
reaction [8]. Clusters 1-3 were characterized by IR, H and P NMR spectroscopy as well as
mass spectrometry, all of which afforded data that were consistent with the proposed structures
(
Fig 1). In addition, the structure of 1 could be confirmed by single crystal X-ray diffraction (vide
-
1
infra). The νCO frequencies in the IR spectra of 1-3 include resonances in the 1750-1900 cm
region, which clearly indicate the presence of bridging carbonyl ligands. The mass spectra exhibit
a molecular ion peak at m/z 980 for 1 and 1028 for 2, corresponding to the molecular formula
[
Co
3
(µ
3
-CH)(CO) (P-P*)], and also show fragment ions due to the sequential loss of all seven
7
1
31
CO ligands for each cluster. The H and P NMR spectra of 1 and 2 indicate the presence of two
1
isomers in solution for each cluster. The H NMR spectra show double sets of protons and in the
3
1
1
P{ H} NMR spectra, four singlets are observed at δ 63.50, 51.29, 49.88, 36.61 for cluster 1 as

well as at δ 66.73(s), 50.06(s), 46.53(s), 40.89(s) for 2, consistent with the presence of two
isomers. This is in agreement with our earlier observation of a similar phenomenon for [Co (µ
CH)(CO) (J003)] [8]. Interconversion between bridging (µ-1eq,2eq-diphosphine) and chelating
eq,1ax-diphosphine [28,29] or 1eq,1eq-diphosphine [28], Fig. 2) coordination modes have been
3
3
-
7
(
1
established previously in diphosphine-substituted alkylidene tricobalt carbonyl clusters.
Furthermore, related interconversions between bridging and chelating coordination modes of
diphosphines have been found in H
chelating coordination modes for J003 at a tetrahedral cluster core have been detected for two
isomers of [H Ru (CO) 10(J003)] [32] but in the case of this ruthenium cluster, no interconversion
between the two isomers could be detected. We postulate that it is interconversion between µ-
eq,2eq-diphosphine and 1eq,1ax-diphosphine coordination modes that are observed in the case of
clusters 1 and 2; the IR spectra of the clusters constitute indirect evidence for the presence of
eq,1ax chelating coordination modes (presence of bridging carbonyl ligands), while the µ-1eq,2eq
4
Ru
4
[30] and Os
3
[31] carbonyl clusters. Bridging and
4
4
1
1
-
diphosphine bridging coordination mode is expected to involve terminal carbonyls only (Fig. 2).
An alternative explanation is that both isomers contain the diphosphine in a bridging mode, but
the two different coordination modes are µ-1eq,2eq and µ-1eq,2ax, i.e. that one phosphine moiety
switches between equatorial and axial coordination modes (Fig. 1). The bridging axial-equatorial
bonding mode has been detected in other cluster frameworks for diphosphines with relatively
long backbones, e.g. in [Os
3
(CO)10(PSSP)] (PSSP = Ph
2
P(CH
2
)
2
S(CH
2
)
2
S(CH
2
)
2
PPh
2
,
coordinating via the phosphine moieties only) [33] and in [H
4
Ru
4
(CO)10(µ-W001)] [32];
however, it is unclear whether a µ-1eq,2ax coordination mode would be compatible with the
presence of bridging carbonyls in a tricobalt carbyne cluster (vide infra). Finally, the possibility
of the presence of diastereomers must be considered. For each of the four coordination modes
depicted in Fig. 2, chiral cluster frameworks will be generated when heterodidentate ligands are
used [34]. Thus, for each coordination mode, a different chiral cluster framework will be
generated when the two different ligand donor moieties exchange positions. In combination with
the chiralities of the ligands, diastereomers may thus be generated. For the chiral clusters
[
H
2
Ru
3
(CO)
7
(µ -S)(P-P*)] (P-P* = Walphos diphosphine ligand), we have previously shown that
3
such diastereomers may be generated, separated and isolated [35]. However, no such separation
could be detected in the case of the clusters studied here. We favour the presence of different

coordination modes (eq:eq vs eq:ax) for the different isomers, as such an observation is in
accordance with earlier studies for tricobalt carbyne clusters (vide supra).
3
1
1
In contrast to clusters 1 and 2, the P{ H} NMR spectrum of 3 reveals only two singlets at δ
8.58 and 37.22, indicating only one isomer in solution, and its mass spectrum shows a molecular
ion peak at m/z = 1096, which is fully consistent with the proposed molecular formula. The
3
3
1
similar P chemical shifts and the presence of νCO IR resonances consistent with bridging
carbonyl ligands suggest that a chelating coordination mode of the diphosphine ligand may be
preferred for this cluster.
Fig. 2. Potential coordination modes of the diphosphines used in the present study. Note that
because the diphosphines used in this study are heterodidentate (two different phosphine
moieties, cf. Fig. 1) diastereomers may exist for each coordination mode (see text). The labelling
“1” and “2” in this figure is a general reference to donor moieties in didentate ligands and is not
directly related to the numbering of the phosphine moieties in Fig. 1.
2
3 3 7
.2. X-ray crystal structure of [Co (µ -CH)(CO) (J004)] 1. It was possible to grow X-ray
quality crystals of 1, and in order to establish the coordination mode (in the solid state) of the
Josiphos ligand that is found in this cluster, its crystal structure was determined. The molecular
structure of [Co
3
(µ
3
-CH)(CO) (J004)] 1 is shown in Fig. 3 and selected bond lengths are listed in
7
the figure caption; relevant crystallographic data are presented in Table 1. Although the IR
spectrum of 1 is consistent with the presence of bridging carbonyl ligands in solution (vide
supra), the solid state structure contains only terminally coordinated carbonyl ligands. As has
been previously found in the structures of several [Co
Co (µ -CCH )(CO) (µ-1,2-dppm)] [36], [Co (µ -CPh)(CO)
CH)(CO) (µ-1,2-DIPAMP)] [8], the diphosphine bridges a Co-Co edge with the phosphine
3
(µ
3
-CR)(CO)
7
(diphosphine)] clusters, e.g.
[
3
3
3
7
3
3
7
(µ-1,2-dmpe)] [37] and [Co
3
(µ -
3
7

moieties coordinated cis to each other in equatorial positions on the cluster, i.e. the µ-1eq,2eq
coordination mode discussed above. The alternative diastereomer where the P1 and P2 phosphine
moieties would change places, and the ferrocenyl moiety would point away from (be in trans
position to) the carbyne cap is not encountered. The Co-Co bond lengths in 1 are different -
2
.4765(4) Å for the bridged metal-metal bond (Co(1)-Co(2)) and 2.4846(4) Å and 2.5115(4) Å
for the unbridged metal-metal bonds (Co(1)-Co(3) and Co(2)-Co(3), respectively). Despite the
longer backbone of J004, the metal-metal distance is shorter than that observed for both [Co (µ
CH)(CO) (µ-1,2-DIPAMP)] (2.500(2) Å) and [Co (µ -CCH )(CO) (µ-1,2-dppm)] (2.490(3) Å);
3
3
-
7
3
3
3
7
in the latter cluster, the bridged Co-Co edge is the longest, despite the narrow bite angle of the
dppm ligand. The Co-P bond distances are 2.2017(6) Å [Co(1)-P(1)] and 2.2265(6) Å, and the
average Co-P bond length of 2.2141 Å is comparable to those observed for the dppm, dmpe and
DIPAMP-substituted cobalt carbyne clusters mentioned above. The cobalt to alkylidyne carbon
bond distances are significantly different - the bond lengths of 1.876(2) Å [Co(1)-CH], 1.892(2)
Å [Co(2)-CH] and 1.936(2) Å for the three Co-Capical bonds displace the carbyne carbon atom
towards the diphosphine-substituted cobalt atoms in such way that the carbyne ligand adopts as a
“
semicapping” orientation with respect to the cobalt triangle. This is a known phenomenon that
has been previously observed in related cobalt carbyne clusters [8,36]. It is suggested that the
probable cause of the observed distortion is the buildup of electron density on the Co C core as a
3
result of the substitution of two carbonyl ligands with diphosphine. The equatorial diphosphine
ligand prevents the carbonyl ligands from adopting bridged coordination modes that would assist
in the dissipation of electron density from metals. An alternative mechanism for delocalization of
this additional electron density is then the involvement of the appropriate carbyne p
localized interaction with the t2g orbitals of the Co(1) and Co(2) atoms [38].
π
orbital in a

Fig. 3. A Mercury drawing of the molecular structure of [Co
3
(µ
3
-CCH
3
)(CO) (µ-1,2-J004)] 1.
7
Thermal ellipsoids are drawn at the 30% probability level. For the sake of clarity, all hydrogen
o
atoms have been omitted. Selected bond lengths [Å] and angles [ ] for 1: Co(1)-Co(2) 2.4765(4),
Co(1)-Co(3) 2.4846(4), Co(2)-Co(3) 2.5115(4), Co(1)-P(1) 2.2017(6) Co(2)-P(2) 2.2265(6)
Co(1)-C(8) 1.876(2) Co(2)-C(8) 1.892(2) Co(3)-C(8) 1.936(2) P(1)-Co(1)-Co(2) 118.566(19)
P(2)-Co(2)-Co(1) 102.811(18) Co(2)-Co(1)-Co(3) 60.827(11) Co(1)-Co(2)-Co(3) 59.746(11)
Co(1)-Co(3)-Co(2) 59.746(11).

Table 1. Crystal data and structure refinement parameters for [Co
3
(µ
3
-CCH
3
)(CO) (µ-1,2-J004)]
7
1
Empirical formula
Formula weight
Wave length, Å
Crystal system
Space group
Unit cell dimensions
a(Å)
44 3 7 2
C H45Co FeO P
980.38
0.71073
Monoclinic
P2
1
11.2822(2)
15.3913(2)
12.7737(2)
90
111.7281(9)
90
2060.53(6)
2
1.580
1.660
1004
0.23 x 0.22 x 0.16
1.94 to 30.01
b(Å)
c(Å)
o
α( )
o
β( )
o
γ( )
V(Å )
3
Z
-3
Density/Mg m
-
1
Abs. coefficient mm
F(000)
3
Crystal size/mm
o
Theta range
Index ranges
-15<=h<=15, -19<=k<=21,
-
17<=1<=17
Refection collected
Final R indices
Goodness-of-fit on F
54299
R1= 0.0308, wR2=0.0604
1.037
2
Ab. Struct. (Flack) Parameter
Largest diff. peak, hole e.Å
-0.014(7)
0.480 and -0.593
-3
2
.3. Synthesis and characterization of Walphos derivatives of [Co
3 3 9
(µ -CH)(CO) ]. Thermal
substitution on [Co (µ -CH)(CO) ] to generate Walphos derivatives was found to require
3
3
9
considerably higher temperatures than the corresponding reactions with Josiphos diphosphines.
Attempts to achieve substitution with the W001 ligand in toluene solution at temperatures of 40-
o
o
7
0 C led to no reaction, but when the temperature was raised to 90 C the W001 ligand was
found to react with the parent cluster to form the expected product, albeit with a significant
amount of decomposition products. Thus, the compounds [Co (µ -CH)(CO) (W001)] 4 and
(W003)] 5 could be prepared in 30% and 70% yields, respectively, by
3
3
7
[
Co
3
(µ
3
-CH)(CO)
7
o
reactions at 90 C. It is possible that the relatively wide bite angles of the Walphos ligands, which
have a longer backbone than the Josiphos ligands, mean that a higher energy barrier must be
overcome in order to achieve multiple coordination to the Co
3
(µ -CH) framework.
3

1
31
1
Compounds 4 and 5 were characterized by IR, H and P{ H} NMR spectroscopy, as well as
mass spectrometry. The mass spectra of each compound are consistent with the proposed
molecular formulae shown above. For each cluster, the IR νCO resonances indicate the exclusive
3
1
1
presence of terminal carbonyl ligands. In the case of cluster 4, the P{ H} NMR spectrum
shows four singlets at δ 51.06, 49.02, 27.98 and 27.01, consistent with the presence of two
isomers, while the analogous spectrum of 5 shows only one broad signal at δ 55.5, indicating a
dynamic nature of the two phosphine moieties at room temperature. Considering that the IR
spectra indicate the absence of bridging carbonyl ligands, we propose that in both 4 and 5, the
diphosphine ligands coordinate in bridging coordination modes exclusively, and that there is a
dynamic equilibrium between µ-1eq,2eq (as observed for the Josiphos ligands, vide supra) and µ-
1
eq,2ax coordination modes (cf. Fig. 1). As already mentioned, the µ-1eq,2ax coordination mode has
been demonstrated for the W001 ligand on the tetrahedral cluster framework of [H
4
Ru (CO)10(µ-
4
W001)] [32].
2
.4. Catalytic Pauson-Khand reactions
The abilities of clusters 1-5, and [Co (µ
3
3
-CH)(CO) (J003)], to act as catalysts/catalyst precursors
7
for intermolecular Pauson-Khand reactions were investigated. The co-cyclization of norbornene
and phenyl acetylene in the presence of CO (Scheme 2) was used as the test reaction. The
o
reactions were carried out in toluene at 120 C under a CO pressure of 10 bar with tricobalt
carbyne clusters and substrates. No additives were used. The two products 6 and 7 (Scheme 2)
were isolated by preparative thin layer chromatography. In order to compare and gauge the effect
of the chiral diphosphine on catalytic outcome and stereoselectivity, analogous catalytic Pauson-
Khand reactions, employing [Co
2
(CO)
8
] or [Co (CO)12] as (pre-)catalysts in the presence of the
4
relevant chiral diphosphines as promoters, were also studied.

Scheme 2. The cyclization reaction of norbornene, phenyl acetylene and carbon monoxide in
presence of catalysts/catalyst precursors to form 1,3,5-triphenylbenzene 6 and 4-
2
,6
phenyltricyclo[5.2.1.0 ]dec-4-en-3-one 7.
Use of the Josiphos-containing clusters [Co
3
(µ
3
-CH)(CO) (J003)] and 1-3 as catalysts/catalyst
7
2
,6
precursors gave the desired cyclopentenone 4-phenyltricyclo[5.2.1.0 ]dec-4-en-3-one 7 in
moderate isolated yields (approximately 45 %, cf. Table 3) with no significant variation. In these
(
and subsequent) reactions, only the exo-form(s) of 7 were detected. Relatively significant
amounts (ca 10 % yield) of the side product triphenyl benzene, formed by trimerization of phenyl
acetylene, were also obtained - the cyclotrimerization of alkynes by cobalt complexes and on
cobalt carbonyl clusters is a well-established phenomenon [39,40]. No clusters could be
recovered from the reaction mixtures after catalysis, suggesting that the Josiphos cobalt carbyne
clusters act as catalyst precursors only. Unfortunately, the Walphos-containing clusters 4 and 5
gave only very low yields of 7 along with significant amounts of decomposed material. It may be
that the significant steric bulk of the Walphos ligands prevent effective coordination/coupling of
the starting materials at the active catalyst.
Table 3
Entry
Catalyst
% of yield, 7 % of yield, 6
ee %
racemate
4
racemate
racemate
-
-
[
3 3 7
Co (µ -CH)(CO) (J003)]
1
2
3
4
5
6
48
46
46
44
4
10
8
10
9
trace
trace
1
2
3
4
5
6
o
Reaction conditions: n(substrate)/n(catalyst)=50, p(CO)=10 bar, T=120 C, solvent = toluene,
duration = 12 h

In summary, the Josiphos-containing clusters were found to be only moderately effective
catalysts for the specific Pauson-Khand reaction that was studied. They are inferior to the related
chiral clusters [Co
which gave > 65 % yield of 7 with no side products under the same conditions [8]; the catalytic
performances of the Josiphos clusters are similar to that of [Co (µ -CH)(CO) (PMe Ph) ], which
3
(µ
3
-CH)(CO)
7
(NORPHOS)] and [Co
3
(µ
3
-CH)(CO) (1,1-Me-DuPHOS)],
7
3
3
6
2
3
we found to be the poorest catalyst in a previous study [8]. Furthermore, the two Walphos
derivatives are clearly very poor catalysts that are unsuitable for this specific reaction. None of
the Josiphos or Walphos clusters gave any significant chiral induction for the Pauson-Khand
reaction in this study.
In contrast, we found that the use of catalytic amounts of the relevant Josiphos or Walphos
ligands in combination with either [Co
2
(CO)
8
] or [Co
4
(CO)12] gave good yields of 7 in the
benchmark Pauson-Khand reaction although, again, the enantioselectivities were negligible. In
the case of [Co
2
(CO)
8
], the use of 6 mol% of the dinuclear complex with 8 mol% of chiral
o
diphosphine under 8 bar of CO pressure, in toluene at 120 C, gave very good yields of
cyclopentenone (75-94%) and conversion rates approaching 100% in each reaction (Table 4).
Table 4
Entry
mol % of coligand,
% of yield
% of yield ee %
[
Co
2
(CO)
8
]
mol %
7
6
1
2
3
4
5
6
6
6
6
6
6
6
J003, 8
J004, 8
J005, 8
J007, 8
W001, 8
W003, 8
85
85
78
93
95
75
10
12
10
4
2
racemate
2
racemate
racemate
racemate
5
7
o
Reaction conditions: p(CO)=10 bar, T=120 C, solvent = toluene (5 ml), duration = 12 h
It has been reported that [Co
in hexane, heptanes or toluene [41] and, as mentioned in the introduction, [Co
a catalyst/catalyst precursor for Pauson-Khand reactions. Kim et al. [42] found [Co
4
(CO)12] can be formed from thermal decomposition of [Co
(CO)12] is in itself
(CO)12] to be
2
(CO)
8
]
4
4

catalytically inert in dichloromethane under one atm of CO pressure, while it shows optimal
catalytic behavior at high temperature and 10 atm pressure of CO. A similar result was found by
o
Krafft et al. who reported that the observed reactivity of [Co
suggests that the cluster decomposes/disproportionates to form [Co
catalytically active species [43]. Therefore, we also investigated catalytic systems based on the
tetracobalt cluster. In these reactions, 3.5 mol% of [Co (CO)12] and 8 mol% of phosphine were
reacted under the same conditions used for [Co (CO) ]. Interestingly, this catalytic system gave
as good or even better results than that based on [Co (CO) ], the conversions vary from 92 to
6% and the selectivity for the cyclopentenone 7 is very high, with yields 85 to 96% (Table 5).
Unfortunately, no enantioselectivity in product formation could be detected. However, it should
4
(CO)12] at 70 C and 1 atm of CO
2
(CO) ] or a similar
8
4
2
8
2
8
9
be noted that the loading/concentration of catalyst is approximately half that of the [Co
2
(CO)
8
]
system. Similar results in the relative activity relative to loading of [Co (CO) ] vs [Co (CO)12
2
8
4
]
have been observed by Lee and coworkers [44] (albeit in the absence of phosphine
promoters/auxiliary ligands), and these authors have proposed that the tetracobalt complex
dissociates to form a dicobalt-alkyne complex and [Co
2
(CO) ]. Considering the results obtained
8
in this study and the fact that [Co (CO)12] is less prone to air oxidation than the dicobalt complex,
4
the tetranuclear cluster appears to be an excellent alternative to [Co
Khand reactions.
2
(CO) ] for catalytic Pauson-
8
Table 5.
Entry
mol
Co
%
(CO)12
of coligand,
% yield of % of yield ee %
[
4
]
mol %
7
8
1
2
3
4
5
6
3.5
3.5
3.5
3.5
3.5
3.5
J003, 8
J004, 8
J005, 8
J007, 8
W001, 8
W003, 8
90
85
85
96
96
87
6
7
8
trace
trace
7
racemate
racemate
racemate
racemate
racemate
racemate
o
Reaction conditions: p(CO)=10 bar, T=120 C, solvent = toluene (5 ml), duration = 12 h

Conclusions
The chiral phosphine derivates [Co
3
(µ
3
-CH)(CO) (P-P*)] (P-P* = chiral diphosphines) that have
7
been described in this paper are capable of acting as catalysts/catalyst precursors for
intermolecular Pauson-Khand reactions, but conversions, selectivities and stereoselectivitires are
only moderate to poor. Considerably better results are reached when [Co
are used as precatalysts with a concomitant relatively high loading of a chiral diphosphine (8 mol
); in these cases conversions and product selectivities are good to excellent, but the
enantioselectivites are poor. The best results are obtained when [Co (CO)12] is used as catalyst
precursor. Considering the low stereoselectivity, but otherwise excellent catalytic performance, it
is likely that the use of catalytic systems based on [Co (CO) ] or [Co (CO)12] in the presence of
2
(CO)
8
] or [Co
4
(CO)12]
%
4
2
8
4
sterically bulky, but non-chiral mono- and/or diphosphines may give good results in both
intermolecular and intramolecular Pauson-Khand cyclization reactions.
Appendix A. Supplementary data
CCDC 1045716 contains the supplementary crystallographic data for [Co
3
(µ
3
-CCH
3
)(CO)
7
(µ-
1
,2-J004)] 1. These data can be obtained free of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
This research has been sponsored by the Crafoord Foundation. We thank Prof. Kenneth
Wärnmark and Dr. Josep Artacho Ruiz for the generous use of the HPLC instrument and
assistance with HPLC analyses.

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Graphical contents entry
Chiral diphosphine derivatives of alkylidyne tricobalt carbonyl clusters – a
comparative study of different cobalt carbonyl (pre)catalysts for (asymmetric)
intermolecular Pauson-Khand reactions
a
b
a
M. Abdul Mottalib, Matti Haukka and Ebbe Nordlander *
Catalytic systems based on either (i) [Co
Co (CO) ], with P-P* added as a promoter, or (iii) [Co
the ability to effect intermolecular Pauson-Khand reactions.
3
(µ
3
-CH)(CO)
7
(P-P*)] (P-P* = chiral diphosphine) or (ii)
[
2
8
4
(CO)12] + P-P*, have been assessed for