Intramolecular cyclizations of Co2(CO)6-complexed propargyl radicals: Synthesis of d,l- And meso-1,5-cyclodecadiynes

Article abstract of DOI:10.1021/om7010497

Intramolecular radical cyclizations of Co₂(CO) ₆-complexed bis-propargyl alcohols 1-5 provide an easy, two-step access to the otherwise hardly accessible d,l- and meso-3,4-diaryl-1,5- cyclodecadiynes 21-25. The acid-induced generation of bis-cations 6-10 is followed by reduction with a 100-fold excess of zinc, generating key reactive intermediates, i.e. the cobalt-complexed bis-propargyl radicals 11-15. The substitution pattern (0-, 4-, 3,4-, 3,4,5-) and the nature of aromatic substituents (H, i-Pr, OMe) are found essential both to the diastereoselectivity of the process - with d.l:meso ratios varying from 54:46 to 80:20 - and the isolability of individual stereoisomers. In particular, an accumulation of methoxy groups on the periphery of the aromatic rings facilitates separation in both intra- and intermolecular reactions. The observed disparity in the level of diastereoselection in intra- and intermolecular reactions is accounted for on the basis of conformational analysis, calculation data for cobalt-complexed propargyl radicals, and the concept of a CH/π coordination. The new knowledge thus acquired has a predicting power, allowing future substrates to be designed, both topologically and stereoelectronically, in a manner favoring either d,l or meso diastereomers.

Full text of DOI:10.1021/om7010497

Organometallics 2008, 27, 1569–1581
1569
Intramolecular Cyclizations of Co2(CO)6-Complexed Propargyl
Radicals: Synthesis of d,l- and meso-1,5-Cyclodecadiynes
Gagik G. Melikyan,* Christopher Wild, and Pogban Toure
Department of Chemistry and Biochemistry, California State UniVersity Northridge, Northridge,
California 91330-8262
ReceiVed October 18, 2007
Intramolecular radical cyclizations of Co2(CO)6-complexed bis-propargyl alcohols 1-5 provide an
easy, two-step access to the otherwise hardly accessible d,l- and meso-3,4-diaryl-1,5-cyclodecadiynes
21-25. The acid-induced generation of bis-cations 6-10 is followed by reduction with a 100-fold excess
of zinc, generating key reactive intermediates, i.e. the cobalt-complexed bis-propargyl radicals 11-15.
The substitution pattern (0-, 4-, 3,4-, 3,4,5-) and the nature of aromatic substituents (H, i-Pr, OMe) are
found essential both to the diastereoselectivity of the processswith d,l:meso ratios varying from 54:46
to 80:20sand the isolability of individual stereoisomers. In particular, an accumulation of methoxy groups
on the periphery of the aromatic rings facilitates separation in both intra- and intermolecular reactions.
The observed disparity in the level of diastereoselection in intra- and intermolecular reactions is accounted
for on the basis of conformational analysis, calculation data for cobalt-complexed propargyl radicals,
and the concept of a CH/π coordination. The new knowledge thus acquired has a predicting power,
allowing future substrates to be designed, both topologically and stereoelectronically, in a manner favoring
either d,l or meso diastereomers.
diverse polyfunctional environment have been developed, in a
highly selective manner.1,2,4 Among radical coupling reactions,
intermolecular dimerizations constutite the bulk of the experi-
mental material available so far.1,2,4,5 Our contribution to this
field6 is best represented by novel methods for generation and
coupling of Co2(CO)6-coordinated propargyl radicals, including
the spontaneous conversion6g,i of diamagnetic cobalt-complexed
propargyl cations to respective radical species, and mediation
Introduction
Over the last two decades, the area of ligand-based organo-
metallic radical chemistry has risen from relative obscurity to
be a recognized research field, ripe for major contributions to
the arsenal of organic and organometallic chemistry.1 Com-
plexation of organic molecules allows the moderation of radical
species due to the relative bulkiness of the metal core and also
the alteration of their electronic nature by interaction, through
space or via bonds, with an orbital system of the transition
metal.1,2 Most importantly, the presence of the clusters allows
for generation of radicals which cannot be accessed under
conventional “organic” settings3 and also for control of the
chemo-, regio-, and stereoselectivity of radical transformations.
To date, the synthetic potential uncovered so far is truly
remarkable: a variety of novel methods for inter- and intramo-
lecular radical C-C bond formation readily occurring in a
(4) (pentadienyl radical)Fe(CO)3: (a) Mahler, J. E.; Gibson, D. H.; Pettit,
R. J. Am. Chem. Soc. 1963, 85, 3959. (b) Sapienza, R. S.; Riley, P. E.;
Davis, R. E.; Pettit, R. J. Organomet. Chem. 1976, 121, C35. (c) Pearson,
A. J.; Chen, Y.-S.; Daroux, M. L.; Tanaka, A. A.; Zettler, M. J. Chem.
Soc., Chem. Commun. 1987, 155. (d) Hwang, W. S.; Liao, R. L.; Horng,
Y. L.; Ong, C. W. Polyhedron 1989, 8, 479. (propargyl radical)-
Cp2Mo2(CO)4: (e) Le Berre-Cosquer, N.; Kergoat, R.; L’Haridon, P.
Organometallics 1992, 11, 721. (benzyl radical)Cr(CO)3: (f) Top, S.; Jaouen,
G. J. Organomet. Chem. 1987, 336, 143. Ferrocenyl radical:(g) Cais, M.;
Eisenstadt, A. J. Chem. Soc. 1965, 30, 1148. (h) Cais, M.; Askhenazi, P.;
Dani, S.; Gottlieb, J. J. Organomet. Chem. 1977, 540, 127. CpCo(η5-C7H9)
radical: (i) Geiger, W. E.; Genneth, T.; Lane, G. A. Organometallics 1986,
5, 1352. (propargyl radical)Co2(CO)6: (j) Padmanabhan, S.; Nicholas, K. M.
J. Organomet. Chem. 1981, 212, 115. (k) Salazar, K. L.; Khan, M. A.;
Nicholas, K. M. J. Am. Chem. Soc. 1997, 119, 9053. (l) Salazar, K. L.;
Nicholas, K. M. Tetrahedron 2000, 56, 2211.
* To whom correspondence should be addressed. E-mail:
gagik.melikyan@csun.edu.
(1) Melikyan, G. G. In Frontiers in Organometallic Chemistry; Cato,
M. A.; Ed.; Nova Science: New York, 2006; p 155.
(2) (a) Organometallic Radical Processes; Trogler, W. C., Ed.; Elsevier:
Amsterdam, 1990; Chapters 3, 4, 9, 10. (b) Astruc, D. Acc. Chem. Res.
1991, 24, 36. (c) Astruc, D. Electron Transfer and Radical Processes in
Transition-Metal Chemistry; VCH: New York, 1995; Chapters 3, 5, 6. (d)
Torraca, K. E.; McElwee-White, L. Coord. Chem. ReV. 2000, 206–207, 469.
(5) Melikyan, G. G.; Nicholas, K. M. In Modern Acetylene Chemistry;
Stang, P. J., Diederich, F., Eds.; VCH: Weinheim, Germany, 1995;
Chapter 4.
(6) (a) Melikyan, G. G.; Vostrowsky, O.; Bauer, W.; Bestmann, H. J.
J. Organomet. Chem. 1992, 423, C24. (b) Melikyan, G. G.; Combs, R. C.;
Lamirand, J.; Khan, M.; Nicholas, K. M. Tetrahedron Lett. 1994, 363. (c)
Melikyan, G. G.; Deravakian, A. J. Organomet. Chem. 1997, 544, 143. (d)
Melikyan, G. G.; Bright, S.; Monroe, T.; Hardcastle, K. M.; Ciurash, J.
Angew. Chem., Int. Ed. 1998, 37, 161. (e) Melikyan, G. G.; Deravakian,
A.; Myer, S.; Yadegar, S.; Hardcastle, K. I.; Ciurash, J.; Toure, P. J.
Organomet. Chem. 1999, 578, 68. (f) Melikyan, G. G.; Sepanian, S.; Riahi,
B.; Villena, F.; Jerome, J.; Ahrens, B.; McClain, R.; Matchett, J.; Scanlon,
S.; Abrenica, E.; Paulsen, K.; Hardcastle, K. I. J. Organomet. Chem. 2003,
683, 324. (g) Melikyan, G. G.; Villena, F.; Sepanian, S.; Pulido, M.;
Sarkissian, H.; Florut, A. Org. Lett. 2003, 5, 3395. (h) Melikyan, G. G.;
Villena, F.; Florut, A.; Sepanian, S.; Sarkissian, H.; Rowe, A.; Toure, P.;
Mehta, D.; Christian, N.; Myer, S.; Miller, D.; Scanlon, S.; Porazik, M.
Organometallics 2006, 25, 4680. (i) Melikyan, G. G.; Floruti, A.; Devletyan,
L.; Toure, P.; Dean, N.; Carlson, L. Organometallics 2007, 26, 3173.
(3) (a) Curran, D. P. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Ed.; Pergamon Press: London, 1992; Vol. 5, pp 716–780. (b) Malacria, M.
Chem. ReV. 1996, 96, 289. (c) Giese, B.; Kopping, B.; Gobel, T.; Dickhaut,
J.; Thoma, G.; Kulicke, K. J.; Trach, F. In Organic Reactions; Paquette,
L., Ed.; Wiley: New York, 1996; Vol. 48, p 301. (d) Curran, D. P.; Porter,
N. A.; Giese, B. Stereochemistry of Radical Reactions; VCH: Weinheim,
Germany, 1997. (e) Sibi, M. P.; Porter, N. A. Acc. Chem. Res. 1999, 32,
163. (f) Sibi, M. P.; Ternes, T. R. Stereoselective Radical Reaction. In
Modern Carbonyl Chemistry; Otera, J., Ed.;Wiley-VCH:New York, 2000.
(g) Radicals in Organic Synthesis; Sibi, M., Ed.; Wiley: New York, 2001;
Vol. 1. (h) Zard, S. Z. Radical Reactions in Organic Synthesis; Oxford
University Press: New York, 2003. (i) Togo, H. AdVanced Free Radical
Reactions for Organic Synthesis; Elsevier: Amsterdam, 2004.
10.1021/om7010497 CCC: $40.75
2008 American Chemical Society
Publication on Web 03/13/2008

1570 Organometallics, Vol. 27, No. 7, 2008
Melikyan et al.
Scheme 1
with THF which has a remarkable accelerating effect.6c,e,f,h,i In
homo-coupling and cross-coupling reactions, the level of
stereocontrol achieved (up to 97% d,l) remains unprecedented
for intermolecular organometallic radical dimerizations.1,2,4 In
contrast, intramolecular radical coupling reactions mediated
by the transition metals remain an uncharted territory.1,2
Sporadic reports on bis(1,3-pentadienyl)irontricarbonyl com-
plexes4a,b describe the exclusive formation of trans-cyclized
products, although given the description of the experimental
protocol and the nature of analytical methods employed, these
claims need to be further validated. In the cobalt-alkyne series,
formation of the parent 3,4-diphenyl-1,5-cyclodecadiyne, via
respective bis-cationic species, was reported in a 51% yield, as
a mixture of d,l and meso diastereomers (90:10).6b Smaller rings,
such as 1,5-cyclononadiyne6e and 1,5-cyclooctadiynes,7 can also
be assembled with high d,l diastereoselectivity (>98%), although
isolation of organic products, given their instability, proved to
be problematic.7 Herewith we present the first systematic
account on the diastereoselectiVity of the intramolecular
coupling of cobalt-complexed bis-propargyl radicals leading to
the formation of 10-membered cycloalkadiynes with 1,5-disposed
acetylenic bonds. The current study was undertaken to identify
the steric, electronic, and conformational parameters governing
the cyclization process and to better understand the impact of
aromatic substituents and their topology and electronic nature.
acid5,10 generates the bis-propargyl cations 6-10, which can
be precipitated from ethereal solutions at low temperatures.
Given the very nature of intramolecular cyclizations, the radical
centers in 11-15 have to be generated at a high rate to avoid
intermolecular interactions, thermal decomposition, and side
reactions, such as H-atom abstraction from the solvent. The bent
geometry of cobalt-alkyne units (140–145°), proven by X-ray
crystallography studies of the respective alcohols5,10,11 and
doubly stabilized cation,6d may also be retained in the requisite
radicals, thus bringing propargyl radical centers in closer
proximity to each other and facilitating a cyclization step.
Empirically, the optimal molar ratio of substrates 1-5 and Zn,
acting as a reducing agent, was found to be 1:100, a 50-fold
excess per propargyl unit. Utilization of lesser quantities of Zn
resulted in trace amounts of cyclized products 16-20. Careful
experimentation also revealed that the mode of addition of a
large (100-fold) excess of zinc can itself affect the diastereo-
selectivity of the process. An optimized proceduresadding zinc
at -50 °C, in one portion, and raising the reaction temperature
to 20 °Csallows us to avoid local overheating and provides
for reproducible results.
The stereoselectivity data on the cyclization reactions, both
in crude mixtures and upon isolation, are summarized in Table
1. By NMR, the highest level of diastereoselection (d,l-17:meso-
17 ) 80:20) is observed for the bis-cluster 2, containing an
isopropyl group in the para position of the aromatic ring (R1 )
i-Pr; R2 ) R3 ) H). Removal of the aromatic substituent results
in a substantial decrease in stereoselectivity: derived from parent
substrate 1, the bis-cluster 16 (R1 ) R2 ) R3 ) H), consists of
d,l and meso diastereomers in the ratio of 67:33. Not only the
topology but also the electronic nature of the substituents appears
to be a contributing factor in the cyclization reaction. In substrate
3 (R1 ) OMe, R2 ) R3 ) H), an incorporation of a 4-OMe
Results and Discussion
The requisite bis-propargyl alcohols 1-5 were synthesized
by the metalation of 1,7-octadiyne with BuLi and subsequent
in situ condensation of the bis-lithium derivative with respective
benzaldehydes,8 followed by the complexation of triple bonds9
with Co2(CO)8 (Scheme 1). Treatment with tetrafluoroboric
(10) (a) McGlinchey, M. J.; Girard, L.; Ruffolo, R. Coord. Chem. ReV.
1995, 143, 331. (b) Amouri, H. E.; Gruselle, M. Chem. ReV. 1996, 96,
1077. (c) Went, M. AdV. Organomet. Chem. 1997, 41, 69. (d) Green, J. R.
Curr. Org. Chem. 2001, 5, 809. (e) Muller, T. J. J. Eur. J. Org. Chem.
2001, 2021. (f) Teobald, B. J. Tetrahedron 2002, 58, 4133.
(7) Melikyan, G. G.; Khan, M. A.; Nicholas, K. M. Organometallics
1995, 14, 2170.
(8) Brandsma, L.; Verkruijsse, H. D. Synthesis of Acetylenes, Allenes
and Cumulenes; Elsevier: New York, 1981; p 80.
(9) Greenfield, H.; Sternberg, H. W.; Friedel, R. A.; Wotiz, J. H.;
Markby, R.; Wender, I. J. Am. Chem. Soc. 1956, 78, 120.
(11) Dickson, R. S.; Fraser, P. J. AdVances in Organometallic Chemistry
12; Academic Press: New York, 1974; p 323.

Co2(CO)6-Complexed Propargyl Radicals
Organometallics, Vol. 27, No. 7, 2008 1571
Table 1. Diastereoselectivity of Radical Reactions
substitution
pattern
rel chromatographic
decomplexed
product
substrate
product
d,l:mesoa
mobility
d,l:mesob
d,l:meso
1
2
3
4
5
26
0
4
4
3,4
3,4,5
3,4,5
16
17
18
19
20
29
67:33
80:20
67:33
67:33
54:46
80:20
inseparable
inseparable
inseparable
separable
separable
separable
68:32
80:20
66:34
c
c
c
21
22
23
24
25
30
84:16e
80:20
73:27
100:0d
100:0d
100:0d
a Diastereomeric ratios of the crude products. b Diastereomeric ratios of the isolated cobalt complexes. c Pure d,l and meso diastereomers were
isolated by chromatographic means. d Only individual d,l diastereomers were decomplexed with ceric ammonium nitrate. e d,l-16:meso-16 was equal to
80:20.
group at the aromatic nuclei “failed” to restore the level of d,l
diastereoselectivity (d,l-18:meso-18 ) 67:33) observed for
4-isopropyl derivative 17. The stereoselectivity seems to be
indifferent toward the presence of an additional methoxy group
(R1 ) R2 ) OMe, R3 ) H; d,l-19:meso-19 ) 67:33) but drops
sharply with incorporation of the third group (R1 ) R2 ) R3 )
OMe; d,l-20:meso-20 ) 54:46). The separability of diastereo-
meric pairs 16-20 is dependent upon the substitution pattern
around aromatic nuclei (Table 1). The parent bis-cluster 16, as
well as its 4-substituted derivatives 17 and 18, exhibited a
comparable mobility on inorganic sorbents and could not be
fully separated by means of either column or thin-layer
chromatography. As Table 1 testifies (columns 4 and 6), the
isolation procedures developed were such that the selective
decomposition of diastereomers was completely avoided and
isomeric compositions in the isolated material were fully
representative of the genuine diastereoselectivity determined in
crude mixtures. The 3,4-dimethoxy and 3,4,5-trimethoxy deriva-
tives 19 and 20 can be readily separated on Florisil, affording
respective d,l and meso diastereomers in homogeneous forms.
The overview of cyclization data (Table 1) allows us to
conclude that a level of diastereoselection is dependent upon
substituents located on the periphery of the molecule, at the
aromatic nuclei. A priori, such an effect was difficult to predict
Figure 1. ORTEP diagram of the molecular structure of d,l-20 with
30% probability ellipsoids.
on the basis of either chemical logic or existing literature
precedence.1–5,10 In bis-radicals 11-15, aromatic substituents
cyclononadiyne,6e the value of the same dihedral angle is much
seem to be quite remote from the reaction site where two
higher (28.5°), indicating that, unexpectedly, a largers10-
propargyl radicals couple and form a new carbon-carbon bond.
It is worth mentioning that the common feature for all
cyclization reactions studied is the preponderant formation of
memberedsring is sterically more distorted. For comparison,
in acyclic 1,5-alkadiynes bearing phenyl6b,f or methyl6e groups,
the observed deviation from an ideal gauche orientation is less
significant (44–46°). Analogously, both propargyl bonds are
nearlyeclipsedwithrespectiveC-Hbonds(C13-C22-C21-H21
d,l diastereomers 16-20. The relative configuration of d,l-20
was determined by X-ray crystallography12 (Figure 1, Tables 2
and 3). The disposition of substituents around the central
) 12.6°, C20-C21-C22-H22 ) 12.6°) further contributing
C21-C22 bond confirms the stereochemical assignment and
to the torsional strain of the molecule. Perhaps the latter is best
allows us to assess the amount of strain in the ring system
manifested by the severely stretched internal bond C21-C22
bearing the bulky Co2(CO)6 cores. The dihedral angle between
reaching a high value of 1.597 Å! Metal coressCo2C2s
propargyl H atoms is equal to 127.0° (H21-C21-C22-H22),
represent the tetrahedrons with a skew geometry where the
representing a significant deviation from the typical anti-
angles between Co-Co and C-C triple bonds noticeably deviate
from the perpendicular arrangement (73.1, 73.4°).5,10 Other
noteworthy structural features of d,l-20 include (a) a distorted
planarity of alkyne moieties (C22-C13-C14-C15 ) 10.4°,
C18-C19-C20-C21 ) 12.4°) which is less emphasized in
acyclic d,l-1,5-alkadiynes (0.6–7.7°)6e,f,i and even in a smallers9-
memberedsring (3.6, 6.3°),6e (b) a lengthened coordinated C-C
triple bond (1.33–1.34 Å vs 1.21 Å for the free ligand) reflective
of the nature of the bonding between the unsaturated ligand
and the transition metal,5,10 (c) a bent geometry for coordinated
alkyne units (140–149°) attendant with coordination to the
transition metal and consequent decrease in bond order, (d)
inequivalency of alkyne units, with one of them being signifi-
cantly flatter than the other (C14-C13-C22 ) 140.4°,
C13-C14-C15)141.0°;C19-C20-C21)145.1°,C20-C19-C18
disposed H atoms in acyclic d,l isomers (171–180°).6b,e,f In
contrast to expectations, a smallersnine-memberedsring of
analogous structure6e exhibited a lesser degree of distortion
(150.8°). All three pairs of substituents around the internal
C21-C22 bond are, in fact, nearly eclipsed. The dihedral angle
between aromatic ringssC23-C21-C22-C32sis only 0.2°,
instead of the anticipated staggered gauche arrangement. In 1,5-
(12) (a) APEX II; Bruker AXS, Inc., Analytical X-ray Systems; 5465
East Cheryl Parkway, Madison, WI 53711-5373, 2005. (b) SAINT Version
6.45A; Bruker AXS, Inc., Analytical X-ray Systems, 5465 East Cheryl
Parkway, Madison, WI 53711-5373, 2003. (c) SHELXTL V6.12, Bruker
AXS, Inc., Analytical X-ray Systems, 5465 East Cheryl Parkway, Madison
WI 53711-5373, 2003. (d) Wilson, A. J. C., Ed. International Tables for
X-ray Crystallography; Kynoch Academic: Dordrecht, The Netherlands,
1992; Vol. C, Tables 6.1.1.4 and 4.2.6.8, pp 500-502, 219-222.

1572 Organometallics, Vol. 27, No. 7, 2008
Melikyan et al.
Table 2. Summary of the Crystal Structure Data for d,l-20
formula
fw
C41H34Cl2Co4O18
1121.30
temp, K
173(2)
cryst color
cryst size
wavelength
dark red
0.27 × 0.26 × 0.08 mm3
0.71073 Å
cryst syst
monoclinic
unit cell dimens
a
22.2291(5) Å
b
19.5356(5) Å
c
21.5056(5) Å
R
90°
92.0230(10)°
ꢀ
γ
V
90°
9333.2(4) Å3
space group
Z
D(calcd)
P21/c
8
1.596 Mg/m3
abs coeff
1.583 mm-1
F(000)
4528
θ range for data collecn
1.66-26.37°
index ranges
-27 e h e 27, -23 e k e 24,
-26 e l e 26
75 555
no. of rflns collected
no. of indep rflns
completeness to θ ) 26.37°
abs cor
max, min transmission
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak, hole
19 061 (R(int) ) 0.0674)
99.9%
semiempirical from equivalents
0.8838, 0.6744
full-matrix least squares on F2
19 061/0/1183
1.031
R1 ) 0.0699, wR2 ) 0.1725
R1 ) 0.1201, wR2 ) 0.2011
3.215, -1.761 e Å-3
Figure 2. ORTEP diagram of the molecular structure of d,l-25 with
30% probability ellipsoids.
Decomplexation reactions were carried out under oxidative
conditions with ceric ammonium nitrate.5,11 1,5-Cyclodecadiynes
21-25 were isolated and characterized either as an inseparable
mixture of d,l and meso diastereomers (21-23), or as individual
stereoisomers (24, 25). Given the structural delicacy of the
requisite bis-clusters 16-20 and the sensitivity of organic
products 21-25, the experimental protocols were developed
under which decomplexation was effected at low temperatures
(-78 °C) with an excess of an oxidizing agent (9–12 equiv),
followed by workup and isolation under anaerobic conditions
(degassed water, NaCl; Florisil, organic solvents). No stereo-
chemical mutations were observed in the course of oxidative
removal of the metal cores. Stereochemical assignments were
based on the configurations of requisite bis-clusters and also
on the NMR signatures of the methyne protons. For diastere-
omeric mixtures (21-23), the stereochemical makeup of organic
products was either the same as that of the requisite bis-clusters
(22) or contained lesser concentrations of meso diastereomers,
by 4–7%, because of the relative instability of the latter
compared to that of the d,l counterparts (Table 1). To obtain
independent proof for the configuration of individual d,l
diastereomers, the relative configuration of d,l-25 was deter-
mined by X-ray crystallography12 (Figure 2, Tables 4 and 5).
The lesser ring strainsdue to the removal of bulky Co2(CO)6
coresstranspires in the staggered arrangement of substituents
around the central C1-C10 bond, as opposed to a nearly
eclipsed conformation in d,l-20 (Figure 1). The dihedral angle
between propargyl H atoms is equal to 79.9° (H1-C1-
C10-H10), while endocyclic C-C bonds are disposed at 43.9°
(C2-C1-C10-C9). The striking difference between X-ray
structures of the bis-cluster d,l-20 and its organic counterpart,
d,l-25, is the disposition of aromatic rings. In the former, the
presence of bulky metal cores forces aromatic rings into a nearly
eclipsed spatial arrangement (Figure 1; C23-C21-C22-C32
) 0.2°), while in the latter, partially relieved from a steric burden
due to the removal of metal cores, the aromatic rings move into
an anti arrangement toward each other (Figure 2; C11-C1-
Table 3. Selected Bond Lengths (Å) and Bond and Torsion Angles
(deg) for d,l-20
Bond Lengths
Co1-Co2
Co1-C13
Co1-C14
C13-C14
Co2-C13
Co2-C14
C13-C22
C14-C15
C21-C22
2.464(10)
1.967(5)
1.961(5)
1.341(7)
1.991(5)
1.964(5)
1.498(7)
1.492(7)
1.597(7)
Co3-Co4
Co3-C19
Co3-C20
C19-C20
Co4-C19
Co4-C20
C20-C21
C18-C19
2.464(12)
1.967(6)
1.973(5)
1.332(8)
1.972(6)
1.988(6)
1.504(7)
1.495(8)
Bond Angles
C14-C13-C22
C13-C14-C15
140.4(5)
141.0(5)
C19-C20-C21
C20-C19-C18
145.1(5)
148.6(6)
Dihedral Angles
C22-C13-C14-C15
C23-C21-C22-C32
C13-C22-C21-H21
C21-C22-C32-C37
C22-C21-C23-C28
Co1-Co2-C13-C14
C20-C21-C22-C13
C20-C21-C22-C32
C18-C19-C20-C21
H21-C21-C22-H22
C20-C21-C22-H22
C21-C22-C32-C33
C22-C21-C23-C24
Co3-Co4-C19-C20
C23-C21-C22-C13
10.4
0.2
12.6
57.9
61.8
73.1
101.8
130.1
12.4
127.0
12.6
125.7
118.8
73.4
128.4
) 148.6°). Overall, d,l-20, containing a 10-membered ring with
1,5-disposed metal-alkyne units, appears to be severely dis-
torted, revealing substantial deviations from standard bond
lengths and bond and torsional angles.

Co2(CO)6-Complexed Propargyl Radicals
Organometallics, Vol. 27, No. 7, 2008 1573
Table 4. Summary of the Crystal Structure Data for d,l-25
Scheme 2
formula
C28H32O6
fw
464.54
temp
173(2) K
cryst color
cryst size
wavelength
cryst syst
pale yellow
0.14 × 0.12 × 0.07 mm3
0.710 73 Å
monoclinic
unit cell dimens
a
6.9725(13) Å
b
9.5826(17) Å
c
36.815(7) Å
R
90°
91.424(8)°
ꢀ
γ
V
90°
2459.0(8) Å3
space group
Z
D (calcd)
abs coeff
F(000)
P21/n
4
1.255 Mg/m3
0.087 mm-1
what extent could the conformational rigiditysattendant with
the tethering of reacting propargyl terminisinfluence the level
of stereocontrol in radical cyclizations. Propargyl alcohol 26
was treated with HBF4 (6-fold excess, -20 °C), and upon
isolation, the bis-cation 27 was reduced, at -50 °C, with a 50-
fold excess of zinc, thus mimicking conditions of the intramo-
lecular cyclization reaction (Scheme 2). From NMR data,
radicals 28 dimerized with an enhanced stereoselectivity,
affording d,l- and meso-29 in the ratio of 80:20 (Table 1). Both
stereoisomers were readily isolated in a homogeneous form with
the major one being decomplexed, under oxidative conditions,
to yield d,l-30.
The very fact that an intermolecular radical reaction could
exhibit better stereoselectivity than its intramolecular variant is
counterintuitive and is not consistent with literature precedents.3,13
The incorporation of a carbon tether between two reactive sites
restricts conformational freedom and brings reacting termini into
a closer proximity to each other, thus positively impacting the
stereochemical outcome of the reaction. Among representative
examples are pinacol coupling, affording acyclic threo- and
erythro-diols with low diastereoselectivity in intermolecular
reactions (de 0–40%), and cyclic threo-diols with an excellent
stereoselectivity (de 82–100%) in intramolecular cyclizations.13a
The trend is further corroborated with [4 + 2] cycloadditions
of nitroalkenes to olefins13b and electrooxidative alkylation of
ethers.13c Shortening the tether is also proven to be a valuable
tool in affecting the diastereoselectivity of cyclization reactions
(de 90% vs 40%).13d
Conformational analysis of the bis-propargyl radicals 11-15
identifies three alternative orientations for the converging
propargyl moieties (Figures 3 and 4). The d,l diastereomers
16-20 can be best formed from structure A (Figure 3), having
eclipsed cobalt-alkyne units and a pair of H atom/Ar ring
overlaps. Given the length of a four-carbon tether and bent
geometry of propargyl moieties complexed to the metal core,
the conformational flexibilities in structure A are severely
limited. Consequently, the alternative orientations B and C, also
leading to d,l diastereomers 16-20, cannot materialize, a notion
corroborated by molecular modeling studies. The conformational
profile is analogous for meso diastereomers 16-20 (Figure 4):
three alternative conformations can be envisionedsD, E, and
Fswith the former being the least constrained. Having identified
992
θ range for data collecn
2.20-26.47°
index ranges
-8 e h e 8, -11 e k e 11, -46 e l
e 25
19 450
5017 (R(int) ) 0.1737)
98.9%
no. of rflns collected
no. of indep rflns
completeness to θ ) 26.47°
abs cor
max, min transmissn
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak, hole
semiempirical from equivalents
0.9939, 0.9879
full-matrix least squares on F2
5017/0/313
1.017
R1 ) 0.0870, wR2 ) 0.1380
R1 ) 0.2470, wR2 ) 0.1817
0.238, -0.244 e Å-3
Table 5. Selected Bond Lengths (Å) and Bond and Torsion Angles
(deg) for d,l-25
Bond Lengths
C1-C10
C2-C3
1.576(6)
1.173(6)
C5-C6
C8-C9
1.538(6)
1.189(6)
Bond Angles
C3-C2-C1
C8-C9-C10
167.5(5)
167.3(5)
C2-C3-C4
C9-C8-C7
170.9(5)
172.7(6)
Dihedral Angles
C1-C2-C3-C4
23.0
C2-C1-C10-C9
C11-C1-C10-C9
C11-C1-C10-C20
C7-C8-C9-C10
H1-C1-C10-H10
C2-C1-C10-C20
C11-C1-C10-H10
43.9
77.5
158.3
22.0
79.9
80.2
39.6
C10-C20 ) 158.3°). Other noteworthy structural features of
d,l-25 include (a) a significant deviation from planarity in alkyne
moieties (C1-C2-C3-C4 ) 23.0°, C7-C8-C9-C10 )
22.0°), even more enhanced than in the bis-cluster d,l-20 (10.4,
12.4°), and (b) inequivalency of bond angles in alkyne units,
with those closer to the four-carbon tether having a higher value
(C3-C2-C1 ) 167.5°, C8-C9-C10 ) 167.3°; C2-C3-C4
) 170.9°, C9-C8-C7 ) 172.7°).
To gain more insight into the stereoelectronic and confor-
mational parameters governing the stereoselectivity of intramo-
lecular cyclizations, an intermolecular radical coupling was
studied with the Co-complexed propargyl alcohol 26, an acyclic
and isocarbon analogue of the 3,4,5-trimethoxy derivative 5.
The specific aim was to determine the impact of the tether by
comparing the diastereoselectivity of the intermolecular reaction
with that of the intramolecular cyclization. In other words, to
(13) (a) Yamamoto, Y.; Hattori, R.; Miwa, T.; Nakagai, Y.; Kubota,
T.; Yamamoto, C.; Okamoto, Y.; Itoh, K. J. Org. Chem. 2001, 66, 3865.
(b) Denmark, S. E.; Kesler, B. S.; Moon, Y. C. J. Org. Chem. 1992, 57,
4912. (c) Yoshida, J.; Sugawara, M.; Tatsumi, M.; Kise, N. J. Org. Chem.
1998, 63, 5950. (d) Spino, C.; Rezaei, H.; Dupont-Gaudet, K.; Belanger,
F. J. Am. Chem. Soc. 2004, 126, 9926. See also: (e) Jung, M. E.; Rayle,
H. L. J. Org. Chem. 1997, 62, 4601.

1574 Organometallics, Vol. 27, No. 7, 2008
Melikyan et al.
Figure 3. Eclipsed conformations forming d,l diastereomers 16–20.
Figure 5. Charge distribution and total charges (TC) of the aromatic
rings derived from PM3 calculations.
on the aromatic nuclei. For example, the stereoisomeric ratio
remains the same for 4-methoxy and 3,4-dimethoxy derivatives
18 and 19 (d,l:meso ) 67:33; Table 1), while the negative charge
of the ring decreases significantly, from -0.503 761 (I) to
-0.279 558 (J) (Figure 5). An increased amount of meso
diastereomer in the 3,4,5-derivative 20sd,l:meso ) 54:46scan
hardly be explained by an incremental decrease in the negative
charge, from -0.279 558 (J) to -0.238 713 (K). Analogously,
an improved diastereoselectivity in the 4-i-Pr derivative 17 (d,l:
meso ) 80:20) is hard to interpret by using the total charge as
a main stereodirecting factor, since an aromatic ring in
conformation H is less negative than that in parent species G
(-0.526 483 vs -0.563 425).
The totality of these data indicate that while a negative charge
of aromatic nuclei, and, attendant with it, the destabilizing
repulsion between them (conformation D; Figure 4), can still
be a contributing factor, the stereochemical outcome of in-
tramolecular cyclizations is determined by other structural and
electronic parameters. It is conceivable that a purely steric factor
is the reason for an increased diastereoselectivity observed for
4-i-Pr derivative 17 (d,l:meso ) 80:20; Table 1). When R1 )
i-Pr (Figure 4), an increased bulkiness of the substituents in
the para positions of eclipsed aromatic rings by 71.5 Å3 per
isopropyl group (PCModel) could destabilize conformation D,
leading to meso diastereomer 17, and trigger a rotation around
a propargyl bond, thus converting conformation D into A,
leading to d,l diastereomer 17.
Diastereoselectivity data for the 3,4,5-trimethoxy derivative
20 could be accounted for on the basis of CH/π-stacking
coordination.14a–d It is a well established fact that a C–δ-H+δ
bond can coordinate to the face of the aromatic ring, which
represents a negative end of the electric quadrupole moment.14a–c
Although, in energetic terms, it is a weak inter or intramolecular
interaction, it has a profound effect on molecular recognition,
selectivity of organic reactions, stability of inclusion complexes,
three-dimensional structure of proteins, and topology of pro-
tein–ligand complexes.14b,c The nature of the C-H bond, a soft
acid, capable of coordinating with the centroid of the aromatic
ring, a soft base, can be as diverse as that in methane,14b
ethane,14c acetylene,14b,c benzene,14a,b methyl,14b methylene,14b
or isopropyl14c groups. Most relevant to the current context are
the reports in which OMe groups, acting as electrophiles,
coordinate weakly polar C-H bonds with the aromatic
moieties.14d–f By X-ray data, a more efficient interaction is
observed in case of the aromatic ring bearing three MeO-groups
of various topology (2,4,6-,14d,e 1,3,5-14f). Depicted in Figure 6
Figure 4. Eclipsed conformations forming meso diastereomers
16–20.
two most favorable conformations for tethered propargyl
radicalssA and Dsit can be postulated that the diastereose-
lectivity observed for the unsubstituted 1,5-cyclodecadiyne 16
(d,l:meso ) 67:33; Table 1) is reflective of the relative stabilities
of converging radical species, with conformation A being
energetically more preferred. The most noticeable feature of
conformation D is the presence of eclipsing aromatic rings that
can be a factor in determining its conformational stability. Its
destabilizing effect may be caused by through-space repulsion
between bulky aromatic substituents (R1, R2, R3) or the same
polarity, negative electronic clouds (“face-to-face” stacking).14a–c
To the contrary, the stabilization may occur due to the CH/π
coordination (“slipped parallel” stacking)14b–d between partially
positive H atoms and the electron density over the aromatic
nuclei. To establish if the repulsion between aromatic rings can
affect the diastereoselectivity of the processsby decreasing the
concentration of the respective meso diastereomersssemiempirical
studies15 were carried out for cobalt-complexed propargyl
radicals G-K (Figure 5). The charges over the carbon atoms
and radical centers allow us to assess the impact of the
substituents upon electronic distribution and also provide the
total charges over the aromatic nuclei. As numerical data
suggest, an incorporation of an isopropyl group into the para
position somewhat decreases the negative charge of the aromatic
ring (G, -0.563 425; H, -0.526 483). Analogously, consecu-
tive replacement of H atoms with methoxy groups in 4-, 3,4-,
and 3,4,5-positions further lowers the negative charge, from
-0.503 761 (I), via -0.279 558 (J), to -0.238 713 (K). Careful
comparison of the cyclization and calculation data (Table 1,
Figure 5) allows us to conclude that there is no concurrent
change in the leVel of diastereocontrol and negatiVe charges
(14) (a) Williams, J. H. Acc. Chem. Res. 1993, 26, 593. (b) Nishio, M.;
Umezawa, Y.; Hirota, M.; Takeuchi, Y. Tetrahedron 1995, 51, 8665 and
references cited therein. (c) Meyer, E. A.; Castellano, R. K.; Diederich, F.
Angew. Chem. 2003, 42, 1210 and references cited therein. (d) van de Velde,
C. M. L.; Chen, L. J.; Baeke, J. K.; Moens, M.; Dieltiens, P.; Geise, H. J.;
Zeller, M.; Hunter, A. D.; Blockhuys, F. Cryst. Growth Des. 2004, 4, 823.
(e) Wallet, J. C.; Molins, E.; Miravitlles, C. Acta Crystallogr. 2001, E57,
o1073. (f) Wolska, I.; Poplawski, J.; Lozowicka, B. Pol. J. Chem. 1998,
72, 2331. See also: (g) Gallivan, J. P.; Dougherty, D. A. Org. Lett. 1999,
1, 103.
(15) Titan; Wavefunction, Inc. All geometries were optimized at the
PM3 level.

Co2(CO)6-Complexed Propargyl Radicals
Organometallics, Vol. 27, No. 7, 2008 1575
Figure 6. Incorporation of three methoxy groups stabilizing
conformations D due to CH/π-coordination.
Figure 8. Eclipsed conformations forming meso and d,l diastere-
omers 29.
54:46). Conformational analysis and the concept of CH/π
coordination also allow us to interpret the diastereoselectivity
observed in intermolecular radical coupling, leading to the
acyclic 1,5-alkadiyne 29 (Scheme 2, Table 1: d,l:meso ) 80:
20). A pair of converging propargyl radicals (L, Figure 8), in
comparison to its tethered analogue A (Figure 3), will be inferior
in its stability due to the repulsion between terminal methyl
groups. Rotation around a benzylic bond will allow the radicals
to facilitate reapproachment by distancing methyl groups, and
metal cores, from each other. Upon rotation, the converging
radical pair M will preserve a slipped parallel stacking
between aromatic rings and give rise to the d,l diastereomer
29 (Figure 8).
Medium-sized ring closures of diacetylenes are synthetically
challenging; therefore, only a few examples of symmetrical 1,5-
cyclodecadiynes have been reported.16 The parent 1,5-cyclo-
decadiyne was prepared via thermolysis of selenadiazoles16a and
lithium-initiated ring closure of R,ω-dichlorides16b in low yields
(1.9%, eight steps;16a ∼4.6%, three steps16b). The 3,4-dihydroxy
derivative of 1,5-cyclodecadiyne was synthesized by different
methods,16c–g varying in their efficiency and stereochemical
outcome (two to seven steps; 0.9–40%). Most importantly, the
methodologies developed for 3,4-dihydroxy-1,5-cyclodecadiyne
are inherently limited in scope by utilizing unstable propargyl
dialdehydes as substrates.16e,f To the best of our knowledge,
there are no alternative methods for the preparation of the
reported 3,4-diaryl-1,5-cyclodecadiynes 21-25, or their struc-
tural analogues. This class of compounds is synthetically and
medicinally relevant because the aromatic nuclei allow for the
introduction of a multitude of substituents with a variety of
Figure 7. The CH/π-coordination stabilizing conformation D and
leading to meso diastereomer 20.
is the conformation D (Figure 4), leading to meso diastereomer
20, wherein the atom charges over the aromatic ring, as well as
the total charge are shown. In the presence of three methoxy
groups, the 3′-, 4′-, and 5′-carbon atoms appear to be nearly
neutral (C3′, 0.058 208; C4′, -0.014 830; C5′, 0.056 510), while
C2′ and C6′ atoms gather significant electron density (-0.164 396,
-0.158 986) (Figures 5 and 6). Thus, the coordination with H
atoms of the methoxy groups, in a CH/π mode, could occur
either with C2′/C6′ carbon atoms (L-shaped coordination14b
)
or with the centroid of the benzene ring (T-shaped
coordination14b), the negative end of the electric quadrupole
moment (TC, -0.238 713; Figure 5). An alternative way to
depict a CH/π coordination that stabilizes conformation D is
shown in Figure 7. The 3′-methoxy group of ring A, an
electrophile, can coordinate in a T-shaped mode14b,d with the
center of ring B, a nucleophile, with both aromatic rings being
shifted away from each other in order to avoid a destabilizing
face-to-face repulsion. It is conceivable that the stabilizing CH/
π-coordination leading to meso diastereomers is the most
effective in the 3,4,5-trimethoxy bis-radical 15 (Scheme 1)
because of its substitution pattern. The presence of a C2V
symmetry axis allows for coordination to occur in any of two
conformations around the benzylic bond (Figure 7). In contrast,
in the 3′,4′-dimethoxy derivative 14 (Scheme 1) the rotation
around the benzylic bond can disrupt the coordination in
question, thus lowering the concentration of the respective meso
diastereomer (Table 1: 19, d,l:meso ) 67:33; 20, d,l:meso )
(16) (a) Gleiter, R.; Kratz, D.; Schafer, W.; Schehlmann, V. J. Am. Chem.
Soc. 1991, 113, 9258. (b) Haberhauer, G.; Roers, R.; Gleiter, R. Tetrahedron
Lett. 1997, 38, 8679. (c) Semmelhack, M. F.; Gallagher, J. Tetrahedron
Lett. 1993, 4121. (d) Boss, C.; Keese, R. Tetrahedron 1997, 53, 3111. (e)
Myers, A. G.; Dragovich, P. S. J. Am. Chem. Soc. 1992, 114, 5859. (f)
Klein, M.; Zabel, M.; Bernhardt, G.; König, B. J. Org. Chem. 2003, 68,
9379. (g) Pitsch, W.; Klein, M.; Zabel, M.; König, B. J. Org. Chem. 2002,
67, 6805.

1576 Organometallics, Vol. 27, No. 7, 2008
Melikyan et al.
increased to 0 °C (15 min), and the reaction mixture was stirred
for an additional 45 min. A solution of LiBr (1.91 g, 22 mmol;
dried at 180 °C for 2 h) in dry THF (50 mL) was added dropwise
(15 min) at -40 °C, and the reaction mixture was stirred for 1 h.
A solution of benzaldehyde (2.31 g, 22 mmol) in dry THF (10
mL) was added dropwise (15 min) at -40 °C; the reaction mixture
was stirred overnight at room temperature, cooled to 0 °C, and then
quenched with H2O (100 mL) and saturated NH4Cl (100 mL). Ether
(100 mL) was added to the reaction mixture, and the organic product
was salted out. The aqueous layer was extracted with ether (2 ×
50 mL), and the combined ethereal fractions were dried (Na2SO4).
Upon concentration under reduced pressure (1/2 of the initial
volume), under an atmosphere of nitrogen, the crude diol (3.18 g,
10 mmol; assuming 100% yield) was added to a solution of dicobalt
octacarbonyl (7.18 g, 21 mmol) in dry ether (150 mL). The reaction
mixture was stirred at room temperature overnight, concentrated
under reduced pressure, and fractionated on silica gel (400 g, 5:1
PE:E) to give complex 1 (5.72 g, 64.3%) as dark red crystals. Tdec
) 110–130 °C (without melting; sealed capillary; dried by
coevaporation with benzene, 3 × 1 mL). TLC (3:1 P:E): Rf ) 0.48.
1H NMR (400 MHz, CDCl3): δ 1.74 (4H, m, 2CH2), d,l-1/meso-1
2.346, 2.348 (2H, d, 2OH, J ) 3.6, J ) 3.6), 2.75 (4H, m, 2CH2),
substitution patterns, thus generating 1,5-cyclodecadiynes which
may serve as precursors to their respective enediynes, potential
anticancer agents.17
Conclusion
The intramolecular cyclization of cobalt-complexed propargyl
radicals represents a viable synthetic approach to otherwise
hardly accessible d,l- and meso-3,4-diaryl-1,5-cyclodecadiynes.
Diastereoselectivitysd,l:meso ratiosvaries in the range of 54:
46 to 80:20, with the separability of individial stereoisomers
being dependent upon the nature of substituents and their
substitution pattern. In particular, an accumulation of methoxy
groups on the periphery of the aromatic rings facilitates the
separation in both intra- and intermolecular reactions. Calcula-
tion data indicate that a negative charge over the aromatic ring
and, attendant with it, an electrostatic repulsion between nuclei
are not the main determinants of stereochemical outcome of
the cyclization reactions. The concept of CH/π coordination is
invoked to interpret diastereoselectivity data for 3,4,5-trimethoxy
derivatives, which favors the meso stereoisomer in intramo-
lecular cyclizations and, in contrast, facilitates the formation
of the d,l counterpart in intermolecular coupling reactions. The
knowledge thus acquired has a predicting power, allowing future
substrates to be designed, both topologically and stereoelec-
tronically, in a manner favoring either d,l or meso diastereomers.
5.93 (2H, d, 2CH, J ) 3.2), 7.29-7.50 (10H, m, aromatic H). 13
C
NMR (100 MHz, CDCl3): δ 32.1, 33.8 (C4, C5), 74.8 (C1), 98.6,
102.1 (C2, C3), 125.8, 128.6, 129.0, 144.2 (aromatic C), 199.8,
200.1 (CO). MS FAB+: m/z 873 (M+ - OH), 806 (M+ - 3CO),
761 (M+ - 4CO - OH), 722 (M+ - 6CO), 666 (M+ - 8CO),
638 (M+ - 9CO), 610 (M+ - 10CO), 564 (M+ - 11CO - H2O),
554 (M+ - 12CO), 536 (M+ - 12CO - H2O), 477 (M+ - 12CO
- H2O - Co), 419 (M+ - 12CO - OH - 2Co). Anal. Found: C,
45.86; H, 2.40. Calcd for C34H22O14Co4: C, 45.84; H, 2.47.
Experimental Section
All manipulations of air-sensitive materials were carried out in
flame-dried Schlenk-type glassware on a dual-manifold Schlenk line
interfaced to a vacuum line. Argon and nitrogen (Airgas, ultrahigh
purity) were dried by passing through a Drierite tube (Hammond).
All solvents were distilled before use under dry nitrogen over
appropriate drying agents (ether, THF, from sodium benzophenone
ketyl; CH2Cl2, from CaH2; benzene, from sodium). All reagents
were purchased from Sigma-Aldrich and Acros and used as
received. Co2(CO)8 and Ce(NH4)2(NO3)4 were purchased from
Strem. NMR solvents were supplied by Cambridge Isotope
Laboratories. 1H and 13C NMR spectra were recorded on a Bruker
DRX-400 (1H, 400 MHz) spectrometer. Chemical shifts were
referenced to internal solvent resonances and are reported relative
to tetramethylsilane. Spin–spin coupling constants (J) are given in
hertz. Elemental analyses were performed by Desert Analytics
(Tucson, AZ). Melting temperatures (uncorrected) were measured
on a Mel-Temp II (Laboratory Devices) apparatus and Optimelt
Automated Meltemp. Silica Gel S735-1 (60–100 mesh; Fisher) was
used for flash column chromatography. Analytical and preparative
TLC analysis (PTLC) were conducted on silica gel 60 F254 (EM
Science; aluminum sheets) and silica gel 60 PF254 (EM Science;
w/gypsum; 20 × 20 cm), respectively. Eluents used were ether (E),
petroleum ether (PE), pentane (P), and benzene (B). Mass spectra
were run at the Regional Center on Mass-Spectroscopy, UC
Riverside, Riverside, CA (FAB, ZAB-SE; CI-NH3, 7070EHF;
Micromass; TOF Agilent 6210 LCTOF instrument with a Multi-
mode source).
d,l- and meso-(µ-η2-3,4-Diphenyl-1,5-cyclodecadiyne)bis(di-
cobalt hexacarbonyl) (16). Under an atmosphere of nitrogen, a
solution of the bis-alcohol 1 (89 mg, 0.10 mmol) in dry ether (10
mL) was added dropwise (10 min) to a solution of HBF4 · Me2O
(161 mg, 1.20 mmol) in dry ether (20 mL) at +5 °C. The reaction
mixture was stirred at +5 °C for 10 min, the temperature was
decreased to 0 °C, an ethereal layer was removed, and the bis-
cation 6 was washed with dry ether (2 × 15 mL). The residual
amount of ether was removed under reduced pressure at -30 °C,
and the cation 6 was partially dissolved in dry CH2Cl2 (20 mL) at
-10 °C and treated with Zn (650 mg, 10.00 mmol) at +5 °C. The
reaction mixture was stirred for 90 min at 20 °C (TLC control),
filtered through a short bed of Florisil (1 cm), concentrated under
reduced pressure, and fractionated on a PTLC plate (7:1 pentane:
CH2Cl2; 2 plates) to give 16 (35 mg, 41.2%; by NMR, 80:20 d,l-
16:meso-16) as a dark red solid. Tdec ) 90–146 °C (with partial
melting; sealed capillary; dried by coevaporation with benzene, 3
1
× 1 mL). TLC (7:1 pentane:CH2Cl2): Rf ) 0.45. H NMR (400
MHz, CDCl3): d,l-16 + meso-16 δ meso 1.66 (1H, m, CH), d,l
1.85 (2H, m, 2CH), meso 1.89 (1H, m, CH), d,l + meso 2.14 (2H
+ 1H, m, CH), meso 2.35 (1H, m, CH), d,l 3.18 (2H, m, 2CH),
meso 3.25 (2H, m, 2CH), meso 3.38 (1H, m, CH), d,l 3.47 (2H, m,
2CH), meso 3.79 (1H, 7 lines, CH), d,l 4.60 (2H, s, H3, H4), meso
4.66 (1H, s, H3), meso 4.86 (1H, s, H4), d,l 6.57 (2H, d, aromatic
H, J ) 7.6), d,l 6.86 (2H, t, aromatic H, J ) 7.6), d,l 7.07 (4H, m,
aromatic H), d,l (2H) + meso 7.18–7.41 (m, aromatic H). MS
FAB+: m/z 828 (M+ - CO), 800 (M+ - 2CO), 772 (M+ - 3CO),
744 (M+ - 4CO), 716 (M+ - 5CO), 688 (M+ - 6CO), 660 (M+
- 7CO), 632 (M+ - 8CO), 604 (M+ - 9CO), 601 (M+ - Co -
7CO), 576 (M+ - 10CO), 548 (M+ - 11CO), 520 (M+ - 12CO),
517 (M+ - Co - 10CO). HR MS-FAB: calcd for C31H20O9Co4
(M+ - 3CO), 771.843 524; found, 771.842 200.
(µ-η2-1,10-Diphenyl-2,8-decadiyne-1,10-diol)bis(dicobalthexa-
carbonyl) (1). Under an atmosphere of nitrogen, a solution of
n-BuLi in hexane (21 mmol, 13 mL/1.6 M) was added dropwise
(20 min) to a solution of 1,7-octadiyne (1.06 g, 10 mmol) in dry
THF (100 mL) at -20 °C. Upon addition, the reaction mixture
was stirred at -20 °C for 1 h. The temperature was gradually
At -50 °C, under analogous conditions, the ratio of d,l-16 and
meso-16 in the crude mixture was equal to 67:33 (Table 1). Upon
isolation on a PTLC plate, the ratio of inseparable diastereomers
remains practically the same (68:32 d,l-16:meso-16).
(17) (a) Grissom, J. W.; Gunawardena, G. U.; Klingberg, D.; Huang,
D. Tetrahedron 1996, 52, 6453. (b) Smith, A. L.; Nicolaou, K. C. J. Med.
Chem. 1996, 39, 2103. (c) Basak, A.; Mandal, S.; Bag, S. S. Chem. ReV.
2003, 103, 4077.

Co2(CO)6-Complexed Propargyl Radicals
Organometallics, Vol. 27, No. 7, 2008 1577
d,l- and meso-3,4-Diphenyl-1,5-cyclodecadiyne (21). Under an
atmosphere of nitrogen, Ce(NH4)2(NO3)6 (406 mg, 0.74 mmol) was
degassed and dissolved in acetone (11 mL, degassed). The solution
was cooled to -78 °C and added dropwise (10 min) at -78 °C to
a degassed solution of 16 (57 mg, 0.067 mmol, 80:20 d,l:meso)
dissolved in acetone (10 mL, degassed). The reaction mixture was
stirred for 2 h at -78 °C (TLC control), treated (-78 °C, N2) with
a degassed saturated aqueous solution of NaCl (10 mL), and
extracted with pentane (3 × 15 mL). The combined organic layers
were dried (4 Å); the solvent, upon filtration of the solution through
a short bed of Florisil (5 cm), was stripped away under reduced
pressure. Diyne 21 was obtained (18 mg, 95.1%; by NMR, 84:16
d,l-21:meso-21) as a yellowish wax. The compound crystallized,
as a yellowish solid, in 90 days at -20 °C. Mp: 67.9–83.2 °C
(sealed capillary; dried by coevaporation with benzene, 3 × 1 mL).
temperature was decreased to -30 °C, an ethereal layer was
removed, and the bis-cation 7 was washed with dry ether (2 × 15
mL). The residual amount of ether was removed under reduced
pressure, and the cation 7 was dissolved in dry CH2Cl2 (20 mL),
cooled to -50 °C, and stirred for 15 min. The solution was treated
with Zn (650 mg, 10.00 mmol) at -50 °C and stirred for 5 min.
The cooling bath was replaced with a water bath, and the reaction
mixture was stirred for 16 h at 20 °C (TLC control). The crude
mixture was filtered through a short bed of Florisil (1 cm),
concentrated under reduced pressure (by NMR, 80:20 d,l-17:meso-
17), and fractionated on a PTLC plate (20:1 pentane:benzene; 2
plates activated at 150 °C for 2 h) to give 17 (40 mg, 42.8%; by
NMR, 80:20 d,l-17:meso-17) as a dark red solid. Tdec ) 130–150
°C (sealed capillary; dried by coevaporation with benzene, 3 × 1
1
mL, monitored by TLC). TLC (20:1 PE:E): Rf ) 0.49. H NMR
1
TLC (5:1 PE:E): Rf ) 0.53. H NMR (400 MHz, CDCl3): d,l-21
(400 MHz, CDCl3): d,l-17 + meso-17 δ d,l 1.09 (6H, d, 2CH3, J
) 6.8), 1.10 (6H, d, 2CH3, J ) 6.8), meso 1.175 (3H, d, CH3, J )
7.2), 1.178 (3H, d, CH3, J ) 6.8), 1.229 (3H, d, CH3, J ) 6.8),
1.233 (3H, d, CH3, J ) 7.2), 1.64 (1H, m, CH), d,l 1.83 (2H, m,
CH2), meso 1.88 (1H, m, CH), d,l 2.11 (2H, m, CH2), meso 2.11
(1H, m, CH), 2.31 (1H, m, CH), d,l 2.75 (2H, sept, 2CH), meso
2.84 (1H, sept, CH, J ) 6.8), 2.91 (1H, sept, CH, J ) 6.8), d,l
3.16 (2H, m, CH2), meso 3.22 (2H, m, CH2), 3.35 (1H, m, CH), d,l
3.45 (2H, m, CH2), meso 3.77 (1H, m 7 lines, CH), d,l 4.54 (2H,
s, H3, H4), meso 4.67 (1H, s, H3(4)), 4.79 (1H, s, H4(3)-), d,l 6.45
(2H, d, aromatic H, J ) 7.2), 6.68 (2H, d, aromatic H), 7.00 (4H,
AB spectrum, aromatic H, Jav ) 7.4), meso 7.16–7.24 (8H, m,
aromatic H). MS FAB+: m/z M+ 940, 856 (M+ - 3CO), 828 (M+
- 4CO), 800 (M+ - 5CO), 772 (M+ - 6CO), 744 (M+ - 7CO),
716 (M+ - 8CO), 688 (M+ - 9CO), 660 (M+ - 10CO), 632
(M+ - 11CO), 514 (M+ - 11CO - 2Co), 486 (M+ - 12CO -
2Co), 427 (M+ - 12CO - 3Co), 369 (M+ - 12CO - 4Co +
H+). HR MS FAB: calcd for C37H32O9Co4 (M+ - 3CO),
855.937 424; found, 855.933 500.
+ meso-21 δ 1.93 (4H, m, 2CH2), 2.32 (4H, m, 2CH2), d,l 3.78
(2H, s, 2CH), meso 4.21 (2H, s, 2CH), 6.94–6.99, 7.05–7.10,
7.20–7.30 (10H, m, aromatic H). 13C NMR (100 MHz, CDCl3): δ
d,l-21 20.9, 28.0 (C7-C10), 48.9 (C3, C4), 82.1, 89.7 (C1, C2,
C5, C6), 127.2, 127.9, 128.3, 141.0 (aromatic C); meso-21 20.9,
27.9 (C7-C10), 46.0 (C3, C4), 82.8, 89.1 (C1, C2, C5, C6), 126.7,
127.5, 128.8, 137.9 (aromatic C). MS FAB+: m/z 284 (M+), 254,
241, 228, 205, 193, 178, 165, 128, 91. HR MS-FAB: calcd for
C22H21 (M+ + H), 285.1643; found, 285.1641.
[µ-η2-1,10-Bis(4′-isopropylphenyl)-2,8-decadiyne-1,10-diol]-
bis(dicobalt hexacarbonyl) (2). Under an atmosphere of nitrogen,
a solution of n-BuLi in hexane (42 mmol, 26.25 mL/1.6 M) was
added dropwise to a solution of 1,7-octadiyne (2.12 g, 20 mmol)
in dry THF (65 mL) at -20 °C (20 min). Upon addition, the reaction
mixture was stirred at -20 °C for 1 h. The temperature was
gradually increased to 0 °C (15 min), and the reaction mixture was
stirred for an additional 45 min. A solution of LiBr (3.92 g, 45
mmol) in dry THF (35 mL) was added dropwise (15 min) to the
reaction mixture at -40 °C and the mixture stirred for 1 h. A
solution of 4-isopropylbenzaldehyde (6.51 g, 44 mmol) in dry THF
(20 mL) was added dropwise (15 min) to the reaction mixture at
-40 °C. The reaction mixture was stirred overnight at room
temperature, cooled to 0 °C, and then quenched with H2O (50 mL)
and saturated NH4Cl (50 mL). An aqueous layer was extracted with
ether (2 × 25 mL), and combined ethereal fractions were dried
over Na2SO4. Upon concentration under reduced pressure (half of
the initial volume), under an atmosphere of nitrogen, the crude diol
(8.04 g, 20 mmol; assuming 100% yield) was added to a solution
of dicobalt octacarbonyl (15.05 g, 44 mmol) in dry ether (150 mL).
The reaction mixture was stirred at room temperature overnight,
concentrated under reduced pressure, and fractionated on a silica
gel column (420 g; 7:1, 3:1, 1:1 PE:E) to give 2 (6.93 g, 35.6%) as
dark red crystals. Mp: 120–124 °C (sealed capillary; dried by
coevaporation with benzene, 3 × 1 mL). TLC (5:1 E:A): Rf ) 0.38.
1H NMR (200 MHz, CDCl3): δ 1.22 (12H, d, 4CH3, J ) 6.9),
1.56 (4H, s, 2CH2), 2.32 (2H, d, 2OH, J ) 3.2), 2.79 (4H, br s,
2CH2), 2.90 (2H, sep, 2CH), 5.90 (2H, d, 2CH), 7.29 (8H, AB
spectrum, aromatic H, J ) 8.0). MS FAB+: m/z M+ 974, 956 (M+
- H2O), 890 (M+ - 3CO), 845 (M+ - H2O - 4CO + H+), 806
d,l- and meso-3,4-Bis(4′-isopropylphenyl)-1,5-cyclodecadiyne
(22). Under an atmosphere of nitrogen, Ce(NH4)2(NO3)6 (114 mg,
0.208 mmol) was degassed and dissolved in acetone (8 mL,
degassed). The solution was cooled to -78 °C and added dropwise
(10 min) to a degassed solution of 17 (24 mg, 0.026 mmol, 80:20
d,l:meso) dissolved in acetone (10 mL, degassed) at -78 °C. The
reaction mixture was stirred for 1 h at -78 °C, and an additional
amount of CAN (14 mg, 0.026 mmol), dissolved in acetone (1 mL,
degassed), was cooled to -78 °C and added dropwise (1 min) to
the reaction mixture. The temperature was increased to -50 °C
(15 min), and the reaction mixture was stirred for an additional 45
min (TLC control). The reaction mixture was treated (-78 °C, N2)
with a degassed saturated aqueous solution of NaCl (20 mL). The
mixture was then transferred to a separatory funnel charged with a
saturated aqueous solution of NaCl (20 mL) and extracted with
dry ether (2 × 15 mL). The combined organic layers were dried
(Na2SO4), and the solvent, upon filtration, was stripped away under
reduced pressure. By PTLC (pentane), 22, a yellow wax, was
obtained (6.2 mg, 64.6%) as an inseparable mixture of diastereomers
(by NMR, 80:20 d,l-22:meso-22). TLC (10:1 PE:E): Rf ) 0.58. 1H
NMR (400 MHz, CDCl3): d,l-22 + meso-22 δ meso 1.15 (12H, d,
4CH3, J ) 6.8), d,l 1.24 (6H, d, 2CH3, J ) 7.0), 1.25 (6H, d, 2CH3,
J ) 6.8), d,l + meso 1.95 (4H, m, 2CH2), 2.31 (4H, m, 2CH2),
meso 2.78 (2H, sept, 2CH), d,l 2.89 (2H, sept, 2CH), 3.74 (2H, s,
2CH), meso 4.13 (2H, s, 2CH), 6.86 (8H, AB spectrum, aromatic
(M+ - 6CO), 750 (M+ - 8CO), 722 (M+ - 9CO), 705 (M+
-
H2O - 9CO + H+), 694 (M+ - 10CO), 677 (M+ - H2O - 10CO
+ H+), 648 (M+ - H2O - 11CO), 620 (M+ - H2O - 12CO),
561 (M+ - H2O - 12CO - Co), 503 (M+ - H2O - 12CO -
2Co + H+). Anal. Found: C, 49.61; H, 3.66. Calcd for
C40H33O14Co4: C, 49.28; H, 3.42.
H, J ) 8.4), d,l 7.21 (8H, AB spectrum, aromatic H, J ) 8.0). 13
C
NMR (100 MHz, CDCl3): d,l-22 + meso-22 δ d,l + meso 21.0
(C7, C10), 24.0 (4C, i-Pr), meso 27.9 (C8, C9), d,l 28.0 (C8, C9),
meso 33.6 (C3, C4), d,l 33.7 (C3, C4), meso 45.8 (2C, i-Pr), dl
48.3 (2C, i-Pr), d,l 82.6, 89.2 (C1, C2, C5, C6), meso 83.1, 88.5
(C1, C2, C5, C6), d,l 126.4, 127.6, 138.5, 147.6 (aromatic C), meso
125.4, 128.5, 135.0, 147.6 (aromatic C). MS TOF: m/z calcd for
MH+, 369.2582; found, 369.2578.
d,l- and meso-[µ-η2-3,4-Bis(4-isopropylphenyl)-1,5-cyclodeca-
diyne]bis(dicobalt hexacarbonyl) (17). Under an atmosphere of
nitrogen, a solution of bis-alcohol 2 (97 mg, 0.10 mmol) in dry
ether (10 mL) was added dropwise (10 min) to a solution of
HBF4 · Me2O (161 mg, 1.20 mmol) in dry ether (20 mL) at +5 °C.
The reaction mixture was stirred at +5 °C for 10 min, the

1578 Organometallics, Vol. 27, No. 7, 2008
Melikyan et al.
[µ-η2-1,10-Bis(4′-methoxyphenyl)-2,8-decadiyne-1,10-diol]bis-
(dicobalt hexacarbonyl) (3). Under an atmosphere of nitrogen, a
solution of n-BuLi in hexane (84 mmol, 52.5 mL/1.6 M) was added
dropwise (20 min) to a solution of 1,7-octadiyne (4.24 g, 40 mmol)
in dry THF (130 mL) at -20 °C. Upon addition, the reaction
mixture was stirred at -20 °C for 1 h. The temperature was
gradually increased to 0 °C (15 min), and the reaction mixture was
stirred for an additional 45 min. A solution of LiBr (7.83 g, 90
mmol; dried at 180 °C for 2 h) in dry THF (70 mL) was added
dropwise (15 min) to the reaction mixture at -40 °C and stirred
for 1 h. A solution of anisaldehyde (11.97 g, 88 mmol) in dry THF
(40 mL) was added to the reaction mixture dropwise (15 min) at
-40 °C. The reaction mixture was stirred overnight at room
temperature, cooled to 0 °C, and then quenched with H2O (50 mL)
and saturated NH4Cl (50 mL). An aqueous layer was extracted with
ether (2 × 25 mL), and combined ethereal fractions were dried
over Na2SO4. Upon concentration under reduced pressure (half of
the initial volume), under an atmosphere of nitrogen, the crude diol
(15.12 g, 40 mmol; assuming 100% yield) was added to a solution
of dicobalt octacarbonyl (30.10 g, 88 mmol) in dry ether (300 mL).
The reaction mixture was stirred at room temperature overnight,
concentrated under reduced pressure, and fractionated on a silica
gel column (500 g, 1:1 PE:E; 1:1 E:A) to give complex 3 (19.8 g,
52.1%) as dark red crystals. Mp: 86–109 °C (with decomposition;
sealed capillary; dried by coevaporation with benzene, 3 × 1 mL).
11CO - Co - H), 520 (M+ - 12CO - Co - H+), 461 (M+
-
12CO - 2Co - H+). HR MS FAB: calcd for C33H24O11Co4 (M+
- 3CO), 831.864 653; found, 831.863 500.
d,l- and meso-3,4-Bis(4′-methoxyphenyl)-1,5-cyclodecadiyne
(23). Under an atmosphere of nitrogen, Ce(NH4)2(NO3)6 (175 mg,
0.32 mmol) was degassed and dissolved in acetone (8 mL,
degassed). The solution was cooled to -78 °C and added dropwise
(10 min) to a degassed solution of 18 (38 mg, 0.04 mmol, 69:31
d,l:meso; repurified sample) dissolved in acetone (15 mL, degassed)
at -78 °C. The reaction mixture was stirred for 30 min at -78 °C,
an additional amount of Ce(NH4)2(NO3)6 (22 mg, 0.04 mmol) in
acetone (1 mL, degassed, precooled to -78 °C) was added dropwise
(1 min), and this mixture was stirred for an additional 30 min. To
bring the reaction to completion, 3 equiv more of Ce(NH4)2(NO3)6
(3 × 22 mg, 0.04 mmol) were added under analogous conditions
(1 equiv, -78 °C, 1.5 h; 1 equiv, -78 °C, 30 min; 1 equiv, -50
°C, 15 min). The temperature was then increased to -30 °C (5
min), and the mixture was stirred for 1 h (TLC control) and treated
(-78 °C, N2) with a degassed saturated aqueous solution of NaCl
(20 mL). The mixture was then transferred to a separatory funnel
charged with a saturated aqueous solution of NaCl (20 mL) and
extracted with dry ether (3 × 15 mL). The combined organic layers
were dried (Na2SO4), and the solvent, upon filtration, was stripped
away under reduced pressure. Diyne 23 was obtained (6 mg, 43.5%;
by NMR, 73:27 d,l-23:meso-23), as a pale yellow oil, by column
chromatography using Florisil (8 g, degassed, 5:1 P:E, degassed).
TLC (3:1 PE:E): Rf ) 0.35. 1H NMR (400 MHz, C6D6): d,l-23 +
meso-23 δ d,l + meso 1.68 – 1.89 (4H + 4H, m, 2CH2 + 2CH2),
2.08–2.35 (4H + 4H, m, 2CH2 + 2CH2), meso 3.24 (6H, s, 2OMe),
d,l 3.36 (6H, s, 2OMe), d,l 4.00 (2H, s, 2CH), meso 4.27 (2H, s,
2CH), meso 6.70 (4H, d, aromatic H, J ) 8.6), d,l 6.81 (4H, d,
aromatic H, J ) 8.6), meso 7.10 (4H, d, aromatic H), d,l 7.28 (4H,
d, aromatic H). 13C NMR (100 MHz, CDCl3): d,l-23 + meso-23 δ
d,l + meso 20.9 (C7, C10), meso 27.8 (C8, C9), d,l 27.9 (C8, C9),
meso 45.5 (C3, C4), d,l 48.2 (C3, C4), meso 55.15 (OMe), d,l 55.24
(OMe), d,l 82.9 (C1, C6), meso 83.3 (C1, C6), meso 88.6 (C2,
C5), d,l 88.8 (C2, C5), meso 113.0, 129.7, 129.9, 158.4 (aromatic
C); d,l 113.6, 128.9, 132.7, 158.6 (aromatic C). MS TOF: m/z calcd
for MH+, 345.1855; found, 345.1851.
1
TLC (1:1 PE:E): Rf ) 0.49. H NMR (200 MHz, CDCl3): δ 1.75
(4H, br s, 2CH2), 2.35 (2H, d, 2OH, J ) 3.0), 2.76 (4H, s, 2 CH2),
3.80 (6H, s, 2CH3), 5.88 (2H, d, 2CH), 6.91 (4H, d, aromatic H, J
) 6.0), 7.36 (4H, d, aromatic H). MS FAB+: m/z 933 (M+ - OH),
866 (M+ - 3CO), 849 (M+ - OH - 3CO), 782 (M+ - 6CO),
726 (M+ - 8CO), 698 (M+ - 9CO), 670 (M+ - 10CO), 624
(M+ - H2O - 11CO), 596 (M+ - H2O - 12CO), 537 (M+
-
H2O - 12CO - Co), 479 (M+ - H2O - 12CO - 2Co + H+).
Anal. Found: C, 45.70; H, 2.93. Calcd for C36H26O16Co4: C, 45.47;
H, 2.74.
d,l- and meso-[µ-η2-3,4-Bis(4′-methoxyphenyl)-1,5-cyclodeca-
diyne]bis(dicobalt hexacarbonyl) (18). Under an atmosphere of
nitrogen, a solution of the bis-alcohol 3 (95 mg, 0.10 mmol) in dry
ether (5 mL) was added dropwise (5 min) to a solution of
HBF4 · Me2O (161 mg, 1.2 mmol) in dry ether (20 mL) at +5 °C.
The reaction mixture was stirred at +5 °C for 10 min, the
temperature was decreased to 0 °C, an ethereal layer was removed,
and the bis-cation 8 was washed with dry ether (2 × 15 mL). The
temperature was decreased to -20 °C, the residual amount of ether
was removed under reduced pressure, and the bis-cation 8 was
dissolved in dry CH2Cl2 (20 mL). The solution was cooled to -50
°C, stirred for 15 min, and treated with Zn (650 mg, 10.00 mmol).
The reaction mixture was stirred for 5 min, the cold bath was
replaced with a water bath (20 °C), and the reaction mixture was
stirred for an additional 15 min (TLC control). The crude mixture
was filtered through a short bed of Florisil (1 cm), concentrated
under reduced pressure (NMR: 67:33 d,l-18:meso-18), and isolated
by PTLC (10:1 PE:E; 2 plates) to give 18 (38 mg, 41.5%; 66:34
d,l:meso) as a dark red solid. Tdec ) 59.7-69.5 °C (sealed capillary;
dried by coevaporation with benzene, 3 × 1 mL). TLC (2:1 PE:
[µ-η2-1,10-Bis(3′,4′-dimethoxyphenyl)-2,8-decadiyne-1,10-
diol]bis(dicobalt hexacarbonyl) (4). Under an atmosphere of
nitrogen, a solution of n-BuLi in hexane (42 mmol, 26.25 mL/1.6
M) was added dropwise (30 min) to a solution of 1,7-octadiyne
(2.12 g, 20 mmol) in dry ether (65 mL) at -20 °C. Upon addition,
the reaction mixture was stirred at 20 °C for 4.5 h. The temperature
was decreased to 0 °C, and ground solid 3,4-dimethoxybenzalde-
hyde (6.97 g, 42 mmol) was added along with dry ether (100 mL).
The reaction mixture was stirred for 18 h, cooled to 0 °C, and then
quenched with saturated NH4Cl (100 mL). An aqueous layer was
extracted with ether (5 × 35 mL). An additional amount of ether
(100 mL) and acetone (50 mL) was used to transfer the residual
amount of the product onto the organic layer. The combined organic
fractions were dried over Na2SO4. Upon concentration under
reduced pressure (half of the initial volume), under an atmosphere
of nitrogen, the crude diol (8.76 g, 20 mmol; assuming 100% yield)
was added to a solution of dicobalt octacarbonyl (15.05 g, 44 mmol)
in dry ether (150 mL). The reaction mixture was stirred at room
temperature for 5 h, brought to dryness under reduced pressure,
loaded with acetone (75 mL, flushed column for 30 min with N2
to remove acetone), and fractionated on a silica gel column (520
g, 20:1 CH2Cl2:E) to give complex 4 (4.22 g, 20.9%) as dark red
crystals. Tdec ) 138.6–156.8 °C (sealed capillary; dried by co-
evaporation with benzene, 3 × 1 mL). TLC (10:1 CH2Cl2:E): Rf )
1
E): Rf ) 0.57. H NMR (400 MHz, CDCl3): d,l-18 + meso-18 δ
meso 1.63 (1H, m, CH), d,l 1.83 (2H, m, 2CH), meso 1.88 (1H, m,
CH), d,l + meso 2.12 (2H + 1H, m, 2CH + CH), meso 2.32 (1H,
m, CH), d,l + meso 3.08-3.28 (2H + 2H, m, 2CH + 2CH), d,l +
meso 3.30–3.53 (2H + 2H, m, 2CH + 2CH), d,l 3.70 (6H, s,
2OMe), meso 3.77 (3H, s, OMe), 3.82 (3H, s, OMe), d,l 4.52 (2H,
s, 2CH), meso 4.59 (1H, s, CH), 4.79 (1H, s, CH), d,l 6.47 (4H, br
s, aromatic H), d,l + meso 6.63–7.22 (4H + 8H, m, aromatic H).
MS FAB+: m/z 832 (M+ - 3CO), 804 (M+ - 4CO), 776 (M+
5CO), 747 (M+ - 6CO - H), 719 (M+ - 7CO - H), 691 (M+
-
-
0.37. H NMR (400 MHz, CDCl3): δ 1.75 (4H, m, 2CH2), 2.32
1
(2H, d, 2OH, J ) 3.2), 2.78 (4H, m, 2CH2), 3.86 (6H, s, 2OMe),
3.89 (6H, s, 2OMe), 5.87 (2H, d, 2CH, J ) 2.8), 6.85 (2H, d,
aromatic H5, J ) 8.0), 6.95 (2H, dd, aromatic H6, J ) 1.6), 7.00
8CO - H), 663 (M+ - 9CO - H), 635 (M+ - 10CO - H), 607
(M+ - 11CO - H), 576 (M+ - 10CO - Co - H), 548 (M+
-

Co2(CO)6-Complexed Propargyl Radicals
Organometallics, Vol. 27, No. 7, 2008 1579
(2H, s, aromatic H2). MS FAB+: m/z 992 (M+ - H2O), 926 (M+
mL). The mixture was then transferred to a separatory funnel
charged with a saturated aqueous solution of NaCl (20 mL) and
extracted with dry ether (2 × 15 mL). The combined organic layers
were dried (Na2SO4), and the solvents, upon filtration, were stripped
away under reduced pressure. PTLC isolation (20:1 CH2Cl2:E)
afforded d,l-24 (3.3 mg, 82.5%) as a pale yellow solid. Mp:
93.0-94.6 °C (sealed capillary; dried by coevaporation with
- 3CO), 881 (M+ - 4CO - OH), 842 (M+ - 6CO), 786 (M+
-
8CO), 758 (M+ - 9CO), 730 (M+ - 10CO), 684 (M+ - 11CO -
H2O), 656 (M+ - 12CO - H2O), 597 (M+ - 12CO - Co - H2O),
539 (M+ - 12CO - 2Co - OH). Anal. Found C, 45.32; H, 3.04.
Calcd for C38H30O18Co4: C, 45.15; H, 2.97.
d,l- and meso-[µ-η2-3,4-Bis(3′,4′-dimethoxyphenyl)-1,5-cyclo-
decadiyne]bis(dicobalt hexacarbonyl) (19). Under an atmosphere
of nitrogen, a solution of the bis-alcohol 4 (101 mg, 0.10 mmol) in
dry ether (15 mL) was added dropwise (15 min) to a solution of
HBF4 · Me2O (161 mg, 1.20 mmol) in dry ether (20 mL) at 5 °C.
The reaction mixture was stirred at 5 °C for 10 min, the temperature
was decreased to 0 °C, an ethereal layer was removed, and the
bis-cation 9 was washed with dry ether (2 × 15 mL). The residual
amount of ether was removed under reduced pressure, and the cation
9 was dissolved in dry CH2Cl2 (20 mL). The solution was cooled
to -50 °C, stirred for 15 min, and treated with Zn (650 mg, 10.00
mmol). The reaction mixture was stirred for 5 min, the cooling
bath was replaced with a water bath (20 °C), and the reaction
mixture was stirred for 18 h (unoptimized). The crude mixture was
filtered through a short bed of Florisil (1 cm) and concentrated under
reduced pressure (NMR: 67:33 d,l-19:meso-19). Fractionation on
a Florisil column (25 g, degassed, -5 °C, degassed 50:1 CH2Cl2:
E) gave meso-19 (10.9 mg, 11.2%) and d,l-19 that was further
purified by PTLC (2:1 PE:E; 17.1 mg, 17.5%).
1
benzene, 3 × 1 mL). TLC (20:1 CH2Cl2:E): Rf ) 0.47. H NMR
(400 MHz, CDCl3): δ 1.91 (4H, m, 2CH2), 2.31 (4H, m, 2CH2),
3.68 (2H, s, 2CH), 3.80 (6H, s, 2OMe), 3.85 (6H, s, 2OMe),
6.70–6.78 (6H, m, aromatic H). 13C NMR (100 MHz, CDCl3): δ
21.0 (C7, C10), 27.9 (C8, C9), 48.6 (C3, C4), 55.8, 55.9 (4OMe),
83.0, 88.9 (C1, C2, C5, C6), 110.8, 111.1, 120.1, 132.9, 148.1,
148.6 (aromatic C). MS TOF: m/z calcd for C26H29O4 (MH+),
405.2066; found, 405.2068.
[µ-η2-1,10-Bis(3′,4′,5′-trimethoxyphenyl)-2,8-decadiyne-1,10-
diol]bis(dicobalt hexacarbonyl) (5). Under an atmosphere of
nitrogen, a solution of n-BuLi in hexane (42 mmol, 26.25 mL/1.6
M) was added dropwise (15 min) to a solution of 1,7-octadiyne
(2.12 g, 20 mmol) in dry THF (65 mL) at -20 °C. Upon addition,
the reaction mixture was stirred at -20 °C for 30 min. The
temperature was gradually increased to 0 °C (15 min), and the
reaction mixture was stirred for an additional 45 min. A solution
of LiBr (3.65 g, 42 mmol; dried at 180 °C for 2 h) in dry THF (35
mL) was added dropwise (15 min) to the reaction mixture at -40
°C and stirred for 1 h. A solution of 3,4,5-trimethoxybenzaldehyde
(8.23 g, 42 mmol) in dry THF (30 mL) was added at -40 °C
dropwise (15 min) and stirred overnight at ambient temperature.
The reaction mixture was cooled to 0 °C and quenched with H2O
(50 mL) and saturated NH4Cl (50 mL). An aqueous layer was
extracted with ether (3 × 35 mL), and combined ethereal fractions
were dried over Na2SO4. Upon concentration under reduced pressure
(half of the initial volume), under an atmosphere of nitrogen, the
crude diol (9.96 g, 20 mmol; assuming 100% yield) was added to
a solution of dicobalt octacarbonyl (15.05 g, 44 mmol) in dry ether
(150 mL). The reaction mixture was stirred at room temperature
overnight, concentrated under reduced pressure, and fractionated
on a silica gel column (400 g, ether) to give complex 5 (2.95 g,
13.8%) as dark red crystals. Tdec ) 90–107 °C. TLC (ether): Rf )
meso-19: dark red crystals upon coevaporation with pentane (3
× 1 mL). Tdec ) 87.5 – 144.4 °C (without melting; sealed capillary;
dried by coevaporation with benzene, 3 × 1 mL). TLC (20:1
1
CH2Cl2:E): Rf ) 0.59. H NMR (400 MHz, CDCl3): δ 1.63 (1H,
m, CH), 1.90 (1H, m, CH), 2.15 (1H, m, CH), 2.33 (1H, m, CH),
3.17-3.42 (3H, m, CH2, CH), 3.79 (3H, s, OMe), 3.80 (1H, m,
CH), 3.83 (3H, s, OMe), 3.89 (6H, s, 2OMe), 4.57 (1H, br s, CH),
4.80 (1H, s, CH), 6.64–6.93 (6H, m, aromatic H). MS FAB+: m/z
892 (M+ - 3CO), 864 (M+ - 4CO), 752 (M+ - 8CO), 724 (M+
- 9CO), 696 (M+ - 10CO), 668 (M+ - 11CO), 640 (M+
-
12CO), 606 (M+ - 9CO - 2Co), 550 (M+ - 11CO - 2Co), 522
(M+ - 12CO - 2Co), 463 (M+ - 12CO - 3Co), 432 (M+
11CO - 4Co). HR MS/FAB: m/z calcd for C35H28O13Co4 (M+
3CO), 891.885 783; found, 891.8850.
-
-
1
d,l-19: dark red crystals upon coevaporation with pentane (3 ×
1 mL). Tdec ) 130.2-154.0 °C (with partial melting, sealed
capillary; dried by coevaporation with benzene, 3 × 1 mL). TLC
0.54. H NMR (400 MHz, CDCl3): δ 1.80 (4H, m, 2CH2), 2.45
(2H, d, 2OH, J ) 3.2), 2.85 (4H, m, 2CH2), 3.81 (6H, s, 2OMe),
3.87 (12H, s, 4OMe), 5.86 (2H, d, 2CH), 6.69 (4H, s, aromatic).
MS FAB+: m/z 986 (M+ - 3CO), 941 (M+ - 4CO - OH), 902
(M+ - 6CO), 846 (M+ - 8CO), 819 (M+ - 9CO + H), 791 (M+
- 10CO + H), 774 (M+ - 10CO + H - OH), 744 (M+ - 11CO
- H2O), 734 (M+ - 12CO), 731 (M+ - 10CO - Co), 716 (M+
- 12CO - H2O). Anal. Found: C, 44.14; H, 3.00. Calcd for
C40H34O20Co4: C, 44.36; H, 3.18.
d,l- and meso-[µ-η2-3,4-Bis(3′,4′,5′-trimethoxyphenyl)-1,5-
cyclodecadiyne]bis(dicobalt hexacarbonyl) (20). Under an atmo-
sphere of nitrogen, a solution of the bis-alcohol 5 (107 mg, 0.10
mmol) in dry ether (30 mL) was added dropwise (30 min) to a
solution of HBF4 · Me2O (161 mg, 1.20 mmol) in dry ether (20
mL) at +5 °C. The reaction mixture was stirred at +5 °C for 10
min, the temperature was decreased to -5 °C, the ethereal layer
was removed, and the bis-cation 10 was washed with dry ether (2
× 15 mL). The residual amount of ether was removed under
reduced pressure at -30 °C, and the cation 10 was suspended in
dry CH2Cl2 (20 mL) at -15 °C. The reaction mixture was treated
with Zn (650 mg, 10 mmol) at +5 °C and stirred for 1 h at 20 °C
(TLC control). The crude mixture was filtered through a short bed
of Florisil (1 cm), concentrated under reduced pressure (NMR: 54:
46 d,l-20:meso-20), and fractionated on a Florisil column (15 g,
degassed, -5 °C; degassed 1:1 PE:E; E). d,l-20 (19.7 mg, 19.0%;
after repurification on Florisil, 15 g, CH2Cl2:E, 10:1) and meso-20
(25.2 mg, 24.3%) were obtained.
1
(20:1 CH2Cl2:E): Rf ) 0.47. H NMR (400 MHz, CDCl3): δ 1.84
(2H, m, CH2), 2.14 (2H, m, CH2), 3.20 (2H, m, 2CH), 3.34 (3H, s,
OMe), 3.46 (2H, m, 2CH), 3.75 (3H, br s, OMe), 3.79 (3H, s, OMe),
3.83 (3H, br s, OMe), 4.54 (2H, s, 2CH), 5.90-6.25 (2H, m,
aromatic H), 6.38–6.85 (4H, m, aromatic H). MS FAB+: m/z 892
(M+ - 3CO), 864 (M+ - 4CO), 836 (M+ - 5CO), 808 (M+
-
6CO), 780 (M+ - 7 CO), 752 (M+ - 8CO), 724 (M+ - 9CO),
668 (M+ - 11CO). HR MS/FAB: m/z calcd for C35H28O13Co4 (M+
- 3CO), 891.885 783; found, 891.8880.
d,l-3,4-Bis(3′,4′-dimethoxyphenyl)-1,5-cyclodecadiyne (24). Un-
der an atmosphere of nitrogen, Ce(NH4)2(NO3)6 (49.32 mg, 0.09
mmol) was degassed and dissolved in acetone (8 mL, degassed).
The solution was cooled to -78 °C and added dropwise (15 min)
to a degassed solution of d,l-19 (11 mg, 0.01 mmol) dissolved in
acetone (5 mL, degassed) at -78 °C. The reaction mixture was
stirred for 1 h at -78 °C, and an additional amount of
Ce(NH4)2(NO3)6 (5.48 mg, 0.01 mmol) in acetone (1 mL, degassed;
precooled to -78 °C) was added dropwise (2 min). The temperature
was increased to -50 °C (10 min), and the reaction mixture was
stirred for 30 min. An additional amount of Ce(NH4)2(NO3)6 (5.48
mg, 0.01 mmol) in acetone (1 mL, degassed, precooled to -78
°C) was added dropwise (2 min) at -50 °C, and the reaction mixture
was stirred for another 15 min. The temperature was increased to
-30 °C (8 min), stirred for 30 min (TLC control), and treated (-78
°C, N2) with a degassed saturated aqueous solution of NaCl (20

1580 Organometallics, Vol. 27, No. 7, 2008
Melikyan et al.
d,l-20: dark red solid. Tdec ) 121.1-159.8 °C. TLC (1:1 PE:E):
a small fiber loop, and placed in a cooled nitrogen gas stream at
173 K on a Bruker D8 APEX II CCD sealed-tube diffractometer
with graphite-monochromated Mo KR (0.710 73 Å) radiation. Data
were measured using a series of combinations of ψ and ω scans
with 10 s frame exposures and 0.5° frame widths. Data collection,
indexing, and initial cell refinements were all carried out using
APEX II12a software. Frame integration and final cell refinements
were done using SAINT12b software. The final cell parameters were
determined from least-squares refinement on 9860 and 556 reflec-
tions, respectively.
1
Rf ) 0.34. H NMR (400 MHz, CDCl3): δ 1.82 (2H, m, 2CH),
2.13 (2H, m, 2CH), 3.17 (2H, m, 2CH), 3.35 (6H, s, 2OMe), 3.45
(2H, m, 2CH), 3.71 (6H, s, 2OMe), 3.80 (6H, s, 2OMe), 4.47 (2H,
s, 2CH), 5.80 (2H, d, aromatic H, J ) 1.6), 6.41 (2H, d, aromatic
H). MS FAB+: m/z 952 (M+ - 3CO), 924 (M+ - 4CO), 896
(M+ - 5CO), 868 (M+ - 6CO), 840 (M+ - 7CO), 812 (M+
-
8CO), 784 (M+ - 9CO), 728 (M+ -11CO), 700 (M+ -12CO).
HR-MS/FAB: calcd for C40H33O18Co4 (MH+), 1036.899 481; found,
1036.9000. Single crystals suitable for X-ray structure analysis
(Figure 1) were obtained by methanol vapor diffusion into a solution
of d,l-20 in CH2Cl2 (+5 °C, 3 days).
The structures were solved using direct methods and difference
Fourier techniques (SHELXTL, V6.12).12c Hydrogen atoms were
placed in their expected chemical positions using the HFIX
command and were included in the final cycles of least-squares
with isotropic Uij’s related to the atom’s ridden upon. All non-
hydrogen atoms were refined anisotropically. Scattering factors
and anomalous dispersion corrections are taken from ref 12d.
Structure solution, refinement, graphics, and generation of
publication materials were performed by using SHELXTL V6.12
software. Additional details of data collection and structure
refinement are given in Table 1.
meso-20: dark red oil. TLC (1:1 PE:E): Rf ) 0.39. 1H NMR
(400 MHz, CDCl3): δ 1.62 (1H, m, CH), 1.91 (1H, m, CH), 2.17
(1H, m, CH), 2.35 (1H, m, CH), 3.19–3.39 (2H, m, 2CH), 3.74
(6H, s, 2OMe), 3.80 (6H, s, 2OMe), 3.82 (6H, s, 2OMe), 3.92 (2H,
m, 2CH), 4.59 (1H, s, CH), 4.76 (1H, s, CH), 6.44 (1H, br s,
aromatic H), 6.50 (2H, s, aromatic H), 6.51 (1H, br s, aromatic H).
MS-FAB+: m/z M+ 952 (M+ - 3CO), 924 (M+ - 4CO), 868
(M+ - 6CO), 812 (M+ - 8CO), 784 (M+ - 9CO), 756 (M+
10CO), 728 (M+ - 11CO), 697 (M+ - 10CO - Co), 666 (M+
-
-
9CO - 2Co), 582 (M+ - 12CO - 2Co). HR MS/FAB: calcd for
C37H32O15Co4 (M+ - 3CO), 951.906 912; found, 951.9088.
[µ-η2-1-(3′,4′,5′-Trimethoxyphenyl)-2-pentyn-1-ol]dicobalt Oc-
tacarbonyl (26). Under an atmosphere of nitrogen, 1-butyne (1.62
g, 30 mmol) was bubbled through a solution of n-BuLi/hexane (33
mmol, 21 mL/1.6 M) in dry THF (100 mL) at -10 °C and stirred
for 5 h. A solution of 3,4,5-trimethoxybenzaldehyde (5.88 g, 30
mmol) in dry THF (25 mL) was added dropwise (20 min) at -10
°C. The reaction mixture was stirred overnight at 20 °C, cooled to
0 °C, and quenched with H2O (50 mL) and a saturated aqueous
solution of NH4Cl (50 mL). The aqueous layer was extracted with
ether (3 × 35 mL), and combined ethereal fractions were dried
(Na2SO4). Upon concentration under reduced pressure (half of the
initial volume), under an atmosphere of nitrogen, the crude alcohol
(7.50 g, 30 mmol; assuming 100% yield) was added to a solution
of dicobalt octacarbonyl (11.29 g, 33 mmol) in dry ether (150 mL)
at 20 °C and stirred for 3 h. The crude mixture was concentrated
under reduced pressure and fractionated on silica gel (240 g, 3:1
PE:E) to give complex 26 (7.63 g, 47.4%) as a brick red solid.
Mp: 95.1–98.5 °C (sealed capillary, dried by coevaporation with
At -50 °C, under analogous conditions, the ratio of d,l-20 and
meso-20 in the crude mixture was equal to 54:46 (Table 1).
d,l-3,4-Bis(3′,4′,5′-trimethoxyphenyl)-1,5-cyclodecadiyne
(25). Under an atmosphere of nitrogen, Ce(NH4)2(NO3)6 (29.8 mg,
0.0544 mmol) was degassed and dissolved in acetone (8 mL,
degassed). The solution was cooled to -78 °C and added dropwise
(12 min) to a degassed solution of d,l-20 (7 mg, 0.0068 mmol) in
acetone (5 mL, degassed) at -78 °C. The reaction mixture was
stirred for 1 h at -78 °C. The temperature was increased to -50
°C (10 min), and the reaction mixture was stirred for an additional
1 h. The temperature was then decreased to -78 °C, and an
additional amount of Ce(NH4)2(NO3)6 (3.7 mg, 0.0068 mmol) in
acetone (1 mL, degassed, precooled to -78 °C) was added dropwise
(1 min). The temperature was increased to -50 °C (10 min), and
the reaction mixture was stirred for 30 min. Then an additional
amount of Ce(NH4)2(NO3)6 (3.7 mg, 0.0068 mmol) in acetone (1
mL, degassed, precooled to -78 °C) was added dropwise (1 min)
at -50 °C and stirred for 45 min. The final amount of
Ce(NH4)2(NO3)6 (3.7 mg, 0.0068 mmol) in acetone (1 mL,
degassed, precooled to -78 °C) was added dropwise (1 min) at
-50 °C and stirred for 2 h. The temperature was increased to -40
°C (2 min), stirred for 30 min, warmed to -30 °C (1 min), and
stirred for 15 min (TLC control). The reaction mixture was treated
(-78 °C, N2) with a degassed, saturated aqueous solution of NaCl
(10 mL), transferred to a separatory funnel charged with a saturated
aqueous solution of NaCl (10 mL), and extracted with dry ether (3
× 15 mL). The combined organic layers were dried (Na2SO4), and
the solvents, upon filtration, were stripped away under reduced
pressure. The crude product was chromatographed on Florisil (10
g, ether, acetone) to afford d,l-25 (2.7 mg, 85.6%) as a pale yellow
solid. An analytical sample was obtained by PTLC (20:1 CH2Cl2:
E; 2.0 mg, 63.4%). Mp: 111.5–112.9 °C (sealed capillary, dried
by coevaporation with benzene, 3 × 1 mL). TLC (ether): Rf )
1
benzene, 3 × 1 mL). TLC (1:2 PE:E): Rf ) 0.48. H NMR (400
MHz, CDCl3): δ 1.29 (3H, t, CH3, J ) 7.2), 2.32 (1H, m, OH),
2.79 (2H, ABX3, CH2, J ) 15.6), 3.79 (3H, s, OMe), 3.87 (6H, s,
OMe), 5.84 (1H, d, CH, J ) 3.2), 6.68 (2H, s, aromatic H). MS
TOF: m/z calcd for C20H18O10Co2Na (MNa+), 558.9462; found,
558.9447.
d,l- and meso-[µ-η2-5,6-Bis(3′,4′,5′-trimethoxyphenyl)-3,7-
decadiyne]bis(dicobalt hexacarbonyl) (29). Under an atmosphere
of nitrogen, a solution of the alcohol 26 (107 mg, 0.2 mmol) in
dry ether (5 mL) was added dropwise (8 min) to a solution of
HBF4 · Me2O (161 mg, 1.20 mmol) in dry ether (20 mL) at +5 °C.
The reaction mixture was stirred at +5 °C for 10 min, the
temperature was decreased to 0 °C, ether was removed, and the
cation 27 was washed with dry ether (2 × 15 mL). The residual
amount of ether was removed under reduced pressure at -30 °C.
The cation 27 was dissolved in dry CH2Cl2 (20 mL), cooled to
-50 °C, and stirred for 15 min. Zinc (650 mg, 10 mmol) was added
at -50 °C, and the reaction mixture was stirred for 5 min. The
cooling bath was replaced with a water bath (20 °C), and the
suspension was stirred for an additional 15 min (TLC/NMR control)
and filtered through a short bed of Florisil (1 cm). The crude mixture
was concentrated under reduced pressure (NMR: 80:20 d,l-29:meso-
29) and fractionated on a Florisil column (20 g, degassed, -5 °C,
CH2Cl2) to give d,l-29 (41.6 mg, 40.1%) and meso-29 (14.7 mg,
14.2%).
1
0.41. H NMR (400 MHz, CDCl3): δ 1.91 (4H, m, 2CH2), 2.31
(4H, m, 2CH2), 3.65 (2H, s, 2CH), 3.78 (12H, s, 4OMe), 3.80 (6H,
s, 2OMe), 6.41 (4H, s, aromatic H). 13C NMR (100 MHz, CDCl3):
δ 21.0 (C7, C10), 27.7 (C8, C9), 49.1 (C3, C4), 56.1, 60.9 (6OMe),
82.6, 89.2 (C1, C2, C5, C6), 105.1, 135.7, 137.1, 152.9 (aromatic
C). MS TOF: m/z calcd for C28H33O6 (MH+), 465.2277; found,
465.2261. Single crystals suitable for X-ray structure analysis
(Figure 2) were obtained by methanol vapor diffusion into a solution
of d,l-25 in CH2Cl2 (+5 °C, 1 day).
d,l-29: dark red solid. Tdec ) 149.5–156.6 °C (sealed capillary,
dried by coevaporation with benzene, 3 × 1 mL). TLC (1:2 PE:
X-ray Crystallography of d,l-20 and d,l-25.12 Suitable crystals
of d,l-20 and d,l-25 were coated with Paratone N oil, suspended in
1
E): Rf ) 0.46. H NMR (400 MHz, CDCl3): δ 1.25 (6H, t, 2CH3,

Co2(CO)6-Complexed Propargyl Radicals
Organometallics, Vol. 27, No. 7, 2008 1581
J ) 7.2), 2.71 (4H, ABX3, 2CH2, J ) 15.8), 3.65 (12H, br s, 4OMe),
3.77 (6H, s, 2OMe), 4.68 (2H, s, 2CH), 6.15 (4H, broad signal,
aromatic H). 13C NMR (100 MHz, CDCl3): δ 15.8, 27.0 (C2, C9,
C1, C10), 55.7 (C5, C6), 60.7 (2OMe), 60.9 (4OMe), 100.9, 101.1
(C3, C4, C7, C8), 108.3 (br signal, aromatic C), 136.9, 137.6, 152.2
(aromatic C), 199.4, 200.5 (CO). MS TOF: m/z calcd for
C40H34O18Co4Na (MNa+), 1060.8971; found, 1060.8953.
temperature was increased to -15 °C (5 min) and the mixture stirred
for 15 min (TLC control). The reaction mixture was treated (-78
°C, N2) with a degassed, saturated aqueous solution of NaCl (20
mL). The mixture was then transferred to a separatory funnel
charged with a saturated aqueous solution of NaCl (20 mL) and
extracted with dry ether (2 × 15 mL). The combined organic layers
were dried (Na2SO4), and the solvents, upon filtration, were stripped
away under reduced pressure. The crude product was filtered
through a short bed of Florisil (1 cm) to afford d,l-30 (10.9 mg,
97.3%) as a pale yellow solid. Mp: 100–101 °C (sealed capillary,
dried by coevaporation with benzene, 3 × 1 mL). TLC (1:3 PE:
meso-29 (an analytical sample was obtained by decomplexation-
recomplexation sequence, by using Ce(NH4)2(NO3)6 and Co2(CO)8,
respectively): dark red solid. Tdec ) 166.6–179.2 °C (sealed
capillary, dried by coevaporation with benzene, 3 × 1 mL). TLC
1
(CH2Cl2): Rf ) 0.43. H NMR (400 MHz, CDCl3): δ 0.98 (6H, t,
1
E): Rf ) 0.31. H NMR (400 MHz, CDCl3): δ 1.18 (6H, t, 2CH3,
CH3, J ) 7.2), 1.74 (4H, ABX3, 2CH2, J ) 16.0), 3.81 (6H, s,
2OMe), 3.85 (6H, s, 2OMe), 3.95 (6H, s, 2OMe), 4.44 (2H, s, 2CH),
6.50 (2H, d, aromatic H, J ) 1.6), 6.76 (2H, d, aromatic). MS TOF:
m/z calcd for C40H34O18Co4Na (MNa+), 1060.8971; found,
1060.8968.
J ) 7.2), 2.27 (4H, q, 2CH2), 3.75 (12H, s, 4OMe), 3.80 (6H, s,
2OMe), 3.83 (2H, s, 2CH), 6.41 (4H, s, aromatic H). 13C NMR
(100 MHz, CDCl3): δ 12.6 (C2, C9), 14.3 (C1, C10), 46.0 (C5,
C6), 56.0 (4OMe), 60.8 (2OMe), 79.2 (C4, C7), 86.8 (C3, C8),
106.0, 134.8, 137.0, 152.5 (aromatic C). MS TOF: m/z calcd for
C28H34O6Na (MNa+), 489.2253; found, 489.2259.
d,l-5,6-Bis(3′,4′,5′-trimethoxyphenyl)-3,7-decadiyne (30). Un-
der an atmosphere of nitrogen, Ce(NH4)2(NO3)6 (104 mg, 0.192
mmol) was degassed and dissolved in acetone (8 mL, degassed).
The solution, precooled to -78 °C, was added dropwise (8 min)
to a degassed solution of d,l-29 (24.9 mg, 0.024 mmol) dissolved
in acetone (10 mL, degassed) at -78 °C. The reaction mixture was
stirred for 30 min at -78 °C, and an additional amount of
Ce(NH4)2(NO3)6 (13 mg, 0.024 mmol) dissolved in acetone (1 mL,
degassed, precooled to -78 °C) was added dropwise (1 min). The
reaction mixture was stirred at -78 °C for 15 min, an additional
amount of Ce(NH4)2(NO3)6 (13 mg, 0.024 mmol) dissolved in
acetone (1 mL, degassed, precooled to -78 °C) was added dropwise
(1 min), and then stirring was continued for another 15 min. The
temperature was increased to -50 °C (15 min), the reaction mixture
was stirred for 15 min and then warmed to -30 °C (5 min) and
stirred for an additional 30 min. The final amount of
Ce(NH4)2(NO3)6 (13 mg, 0.024 mmol) was dissolved in acetone
(1 mL, degassed), precooled to -78 °C, and added dropwise (1
min) to the reaction mixture and stirred for 30 min at -30 °C. The
Acknowledgment. This material is based upon work
supported by the National Science Foundation under Grant
No. CHE-0707865. We are also greatly indebted to the Office
of Graduate Studies, Research and International Programs,
and University Corporation, California State University
Northridge, for their generous support. We are grateful to
Jennifer Blake and Anasheh Babakhanian for assistance with
experimental work.
Supporting Information Available: CIF files and tables giving
crystallographic details, bond distances and angles, atomic coor-
dinates and equivalent isotropic displacement parameters, and
torsion angles for d,l-20 and d,l-25. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM7010497