Ring opening of a cobalt-stabilized bornyl cation: Mechanistic study of the alkyne-dicobalt/carbynyl-tricobalt cluster transformation

Article abstract of DOI:10.1021/om020727r

Upon protonation with HBF₄, [2-endo-((allyldimethylsilyl)ethynyl)borneol]Co₂(CO)₆ (2) suffers elimination of water or propene, to yield [2-((allyldimethylsilyl)ethynyl)born-2-ene]-Co₂(CO)₆ (11) and [2-endo-((dimethylfluorosilyl)ethynyl)borneol]Co₂(CO)₆) (12), respectively, and, surprisingly, the tricobalt complex (2-norbornylidene)CHCCo₃(CO)₉ (13). In contrast, protonation of the terminal alkyne (2-endo-ethynylborneol)Co₂(CO)₆ (19), an anticipated precursor to 13, led instead to (2-ethynyl-2-bornene)Co₂(CO)₆ (21) and the ring-opened species (2-ethynyl-4-isopropyl-1-methylcyclohexa-1,3-diene)Co₂ (CO)₆ (22). However, conversion of 19 to 13 was achievable upon prolonged heating at reflux in acetone, thereby also affording the corresponding alcohol [2-(2-hydroxybornyl)]CH₂CCo₃(CO)₉ (20). A mechanistic rationale is offered for the formation of RCH₂CCo₃(CO)₉ clusters upon protonation of alkyne complexes of the type (RC≡CH)Co₂(CO)₆.

Full text of DOI:10.1021/om020727r

Organometallics 2003, 22, 1293-1301
1293
Rin g Op en in g of a Coba lt-Sta bilized Bor n yl Ca tion :
Mech a n istic Stu d y of th e Alk yn e-Dicoba lt/
Ca r byn yl-Tr icoba lt Clu ster Tr a n sfor m a tion
J ohn H. Kaldis,† Peter Morawietz,† and Michael J . McGlinchey*,†,‡
Departments of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1, and
University College Dublin, Belfield, Dublin 4, Ireland
Received September 4, 2002
Upon protonation with HBF4, [2-endo-((allyldimethylsilyl)ethynyl)borneol]Co2(CO)6 (2)
suffers elimination of water or propene, to yield [2-((allyldimethylsilyl)ethynyl)born-2-ene]-
Co2(CO)6 (11) and [2-endo-((dimethylfluorosilyl)ethynyl)borneol]Co2(CO)6 (12), respectively,
and, surprisingly, the tricobalt complex (2-norbornylidene)CHCCo3(CO)9 (13). In contrast,
protonation of the terminal alkyne (2-endo-ethynylborneol)Co2(CO)6 (19), an anticipated
precursor to 13, led instead to (2-ethynyl-2-bornene)Co2(CO)6 (21) and the ring-opened species
(2-ethynyl-4-isopropyl-1-methylcyclohexa-1,3-diene)Co2(CO)6 (22). However, conversion of
19 to 13 was achievable upon prolonged heating at reflux in acetone, thereby also affording
the corresponding alcohol [2-(2-hydroxybornyl)]CH2CCo3(CO)9 (20). A mechanistic rationale
is offered for the formation of RCH2CCo3(CO)9 clusters upon protonation of alkyne complexes
of the type (RCtCH)Co2(CO)6.
Sch em e 1. Allyl Tr a n sfer via a
In tr od u ction
Seven -Mem ber ed -Rin g In ter m ed ia te
We have recently shown that an allyl transfer from
silicon to a metal-stabilized carbocation occurs readily
with concomitant formation of a thermodynamically
favored Si-F bond.1 This migration is thought to
proceed via a â-silyl cation, 1, in a seven-membered ring,
as shown in Scheme 1. Related studies by Green2 and
by Schreiber3 are in accord with this proposal.
Our original goal was to investigate the stereochem-
ical requirements for this general reaction by incorpo-
rating the allylalkynylsilane within a rigid terpenoid
skeleton. In particular, we were intrigued by the
potential migration of an allyl group from an endo site
to the exo face of a bornyl system (i.e., 2 f 3), and vice
versa (i.e., 4 f 5) for the fenchyl analogue, as depicted
in Scheme 2.
We here describe the syntheses of these terpene
derivatives and the complex nature of their behavior
upon treatment with tetrafluoroboric acid.
a cobalt-stabilized 2-bornyl cation, 7a , which has been
identified by NMR spectroscopy.4 More compellingly,
replacement of a tricarbonylcobalt moiety by an isolobal
(cyclopentadienyl)dicarbonylmolybdenum vertex, as in
6b , affords the corresponding molybdenum-stabilized
cation 7b, which has been characterized by X-ray
crystallography.5 Conversely, the analogous fenchyl-
dicobalt cluster cation 9a immediately undergoes a
Wagner-Meerwein rearrangement to 10, while the
corresponding fenchyl-molybdenum cation 9b is con-
siderably more stable and has been structurally char-
acterized (Scheme 3).6
Resu lts a n d Discu ssion
We have previously reported the syntheses of the
2-endo-propynylborneol and 2-exo-propynylfenchol hexa-
carbonyldicobalt derivatives 6a and 8a , respectively.
Protonation of the bornyl cluster 6a , at -78 °C, yields
* To whom correspondence should be addressed at University
College Dublin. E-mail:
michael.mcglinchey@ucd.ie. Phone:
+353.1.716.2880. Fax: +353.1.716.2127.
† McMaster University.
‡ University College Dublin.
(1) Ruffolo, R.; Brook, M. A.; McGlinchey, M. J . Organometallics
1998, 17, 4992.
(2) (a) Green, J . R. J . Chem. Soc., Chem. Commun. 1998, 1751. (b)
Patel, M. M.; Green, J . R. J . Chem. Soc., Chem. Commun. 1999, 509.
(c) Lu, Y.; Green, J . R. Synlett 2001, 243. (d) Green, J . R. Synlett 2001,
353. (e) Green, J . R. Curr. Org. Chem. 2001, 5, 809.
(3) Schreiber, S. L.; Sammakia, T.; Crowe, W. E. J . Am. Chem. Soc.
1986, 108, 3128.
(4) D’Agostino, M. F.; Frampton, C. S.; McGlinchey, M. J . J .
Organomet. Chem. 1990, 394, 145.
(5) Gruselle, M.; El Hafa, H.; Nikolski, M.; J aouen, G.; Vaissermann,
J .; Li, L.; McGlinchey, M. J . Organometallics 1993, 12, 4917.
(6) Kondratenko, M.; El Hafa, H.; Gruselle, M.; Vaissermann, J .;
J aouen, G.; McGlinchey, M. J . J . Am. Chem. Soc. 1995, 117, 6907.
10.1021/om020727r CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/15/2003

1294 Organometallics, Vol. 22, No. 6, 2003
Kaldis et al.
Sch em e 4. Syn th etic Rou te to
Sch em e 2. P r op osed Allyl Migr a tion s in th e
Bor n yl a n d F en ch yl System s
2-en d o-((Allyld im eth ylsilyl)eth yn yl)bor n eol
Sch em e 3. Ca tion ic Clu ster s Der ived fr om
Bor n eol a n d F en ch ol
Sch em e 5. P r od u cts Der ived fr om th e
P r oton a tion of 2
the anticipated allyl transfer product was, at best, a
minor constituent among many others. We therefore
chose to focus our efforts on the more tractable bornyl
system.
As shown in Scheme 5, when the exo alcohol 2 was
treated with an equimolar quantity of HBF4 in ether at
-78 °C, the 2-alkynyl-2-bornene 11 and the fluorosilane
12 were formed. However, when HBF4 was added in
excess and the reaction mixture warmed to room tem-
perature over a 12 h period, chromatographic separation
yielded a third isolable product, the tricobalt cluster 13,
involving an exocyclic elimination, as revealed by its 2-D
1H-1H COSY and 1H-13C shift-correlated NMR spectra.
There was no evidence for production of the allyl
migration product 3.
In the expectation that alkynyl anions would attack
camphor from the endo face and fenchone from the exo
face, these ketones were each treated with ((trimethyl-
silyl)ethynyl)lithium, at -78 °C. Removal of the TMS
functionality with tetra-n-butylammonium fluoride and
incorporation of the allyldimethylsilyl group proved
successful, as shown in Scheme 4 for the bornyl system.
Addition of octacarbonyldicobalt to the appropriate
alkynylallylsilanes afforded 2 and 4, respectively, which
were each treated with HBF4 in ether at -78 °C and
the products examined after chromatographic separa-
tion. It was immediately evident that the fenchyl system
had yielded a multitude of products, each in very low
yield. The mass spectra of these materials indicated that
One can readily envisage routes to 11 and 12; the
former simply arises from elimination of water from the
starting alcohol, while the latter results from protona-
tion of the allyl group in 11 to generate a â-silyl cation

Ring Opening of a Co-Stabilized Bornyl Cation
Organometallics, Vol. 22, No. 6, 2003 1295
Sch em e 6. P r od u cts Der ived fr om th e P r oton a tion of 14
with subsequent elimination of propene and concomi-
tant formation of a silicon-fluorine bond.
Formation of the tricobalt cluster 13 was unexpected
and implies the intermediacy of a terminal alkyne
complex via cleavage of the allyldimethylsilyl function-
ality. Interestingly, protonation of [2-endo-((trimethylsil-
yl)ethynyl)borneol]Co2(CO)6 yields only the elimination
product, [2-((trimethylsilyl)ethynyl)born-2-ene]Co2(CO)6,
with no evidence for cleavage of the trimethylsilyl
moiety. It has long been known that terminal alkyne-
dicobalt complexes of the type (RCtCH)Co2(CO)6 can
rearrange under acidic conditions to yield the alkylidyne
clusters RCH2CCo3(CO)9.7-9 However, the mechanism
of this transformation has never been elucidated, and
we advance some hypotheses later in this paper.
In light of the apparent facile cleavage of the al-
lyldimethylsilyl moiety from 2, the closely analogous
cluster [Me3SiCtCSiMe2(allyl)]Co2(CO)6 (14) was pro-
tonated with HBF4 in ether at -78 °C and yielded [Me3-
SiCtCSiMe2F]Co2(CO)6 (15) and [Me3SiCtCSiMe2OH]-
Co2(CO)6 (16) (Scheme 6); the latter compound is not
evident as an initial product and is apparently formed
during chromatography on the silica column. After
chromatographic purification, 15 was reprotonated in
ether at -78 °C and afforded exclusively the terminal
alkyne cluster 17, verifying cleavage of the fluorodi-
methylsilyl functionality. It is worth noting that Knox
and co-workers have demonstrated that protonation of
similar monosilyl- and disilyl-substituted molybdenum-
alkynyl clusters readily leads to desilylation.10 Further
protonation of 17 did not produce the expected tricobalt
species, Me3SiCH2CCo3(CO)9 (18); however, when 17
was heated at reflux in acetone over a 36 h period, 18
was produced.
F igu r e 1. X-ray crystal structure of 20 showing the atom
numbering system, with hydrogen atoms omitted for clar-
ity.
of which was definitively established by X-ray crystal-
lography. The endo positioning of the cluster in 20 is
evident in Figure 1. In contrast, duplication of this
reaction in diethyl ether resulted merely in reisolation
of the starting material, 19. It is perhaps somewhat
surprising that such rearrangements have been shown
to occur in acetone, and one cannot entirely eliminate
the possibility that traces of an acidic impurity remain,
even after purification of the solvent.
Treatment of the (2-endo-ethynylborneol)Co2(CO)6
complex 19 with HBF4 in ether at -78 °C, and chro-
matographic separation of the mixture after warming
to room temperature, furnished two major products: the
2-alkynyl-2-bornene complex 21 and a second complex,
22, isomeric with 21, as shown in Scheme 7. A third
product, obtained in minimal yield, appears to have
undergone ring opening and a carbonyl insertion but
remains currently unidentified.
Concluding that either 2 or 12 can suffer desilylation
under acidic conditions, we chose to study the behavior
of (2-endo-ethynylborneol)Co2(CO)6 (19) to investigate
the susceptibility of both the alkyne and hydroxyl sites
toward protonation, under various conditions. Initially
19 was heated in refluxing acetone for 36 h, thereby
generating two tricobalt clusters: the previously pre-
pared 13 and its corresponding alcohol 20, the structure
(7) Markby, R.; Wender, I., Friedel, R. A.; Cotton, F. A.; Sternberg,
H. W. J . Am. Chem. Soc. 1958, 80, 6529.
(8) Kru¨erke, U.; Hu¨bel, W. Chem. Ind. 1960, 1264.
(9) Sutton, P. W.; Dahl, L. F. J . Am. Chem. Soc. 1967, 89, 261.
(10) Beck, J . A.; Knox, S. A. R.; Stansfield, R. F. D.; Stone, F. G. A.;
Winter, M. J .; Woodward, P. J . Chem. Soc., Dalton Trans. 1982, 195.

1296 Organometallics, Vol. 22, No. 6, 2003
Kaldis et al.
Sch em e 9. Rea r r a n gem en ts of en d o a n d exo
Sch em e 7. P r od u cts Der ived fr om th e
P r oton a tion of 19
Bor n yl Dia zon iu m Ion s
A search for purely organic precedents led us to the
now classic work given in ref 12, in which it was shown
that 2-endo-bornylamine (25) furnishes, upon diazoti-
zation, the bridge-opened products 26 and 27. In
complete contrast, 2-exo-bornylamine (28) is perfectly
aligned for a Wagner-Meerwein rearrangement and
gives 29 and 30, as in Scheme 9.
Sch em e 8. Rin g Op en in g a n d Rea r r a n gem en t of a
Bor n yl Ca tion
One can now appreciate how the fenchyl cluster 4
might yield a plethora of products, not merely via
generation and rearrangement of a terminal alkyne
cluster, but also through Wagner-Meerwein skeletal
rearrangements of the terpene skeleton, which are
known to be very extensive in fenchol itself.13
These results, while rationalizing the observed prod-
ucts, do not explain the failure of the bornyl-allylsilane
dicobalt complex 2 to undergo an allyl migration, and
one should consider steric effects that might hinder
formation of the crucial seven-membered-ring cationic
intermediate 31. To this end, the structure of this
intermediate has been modeled14 (Figure 2), and one can
see that the presence of the spiro-C(2) center brings
about unfavorable interactions between the allyl unit
and one of the methyl groups attached to C(7). Presum-
ably, this effect hinders the allyl transfer process and
makes the terpene skeletal rearrangements and the
cluster transformations more competitive.
The identification of 22 relies on its mass and NMR
spectra. The presence of the (HCtC)Co2(CO)6 moiety
is evident from the characteristic loss of six carbonyls
in the mass spectrum, while the isopropyl group is
1
readily observable in the H and 13C NMR spectra and
(RCtCH)Co2(CO)6 to RCH2CCo3(CO)9 Tr a n sfor -
m a tion . Currently, the most widely used route to
alkylidyne-tricobalt nonacarbonyl clusters involves the
reaction of the appropriate trichloromethyl precursor,
RCCl3, with Co2(CO)8.15 However, the very first (and
entirely serendipitous) synthesis of such a cluster arose
from the reaction of the parent compound, (HCtCH)-
Co2(CO)6, with aqueous sulfuric acid in methanol;7 the
resulting product, CH3CCo3(CO)9, was characterized
was confirmed by 1H-1H COSY and 1H-13C shift-
correlated experiments. These latter data also estab-
lished that the methylene groups were adjacent; more-
over, one pair of methylene protons exhibited a long-
range correlation to the ring carbon bearing the isopropyl
substituent. The final assignment as the 2-ethynyl-4-
isopropyl-1-methylcyclohexa-1,3-diene complex 22 is
unambiguous,11 and a mechanistic rationale appears in
Scheme 8.
Ring opening of the dimethyl bridge in cation 23 to
yield the tertiary cation 24 is favored by the anti-
periplanar alignment of the C(1)-C(7) linkage with the
endo-C(2)-Co bond. A 1,2-hydride shift, to generate the
isopropyl group, and subsequent elimination leads
directly to the conjugated diene-yne complex 22.
(12) (a) Hu¨ckel, W.; Kern, H. J . J ustus Liebigs Ann. Chem. 1969,
728, 49. (b) Banthorpe, D. V.; Morris, D. G.; Bunton, C. A. J . Chem.
Soc. B 1971, 687.
(13) (a) Lutz, R. P.; Roberts, J . D. J . Am. Chem. Soc. 1962, 84, 3715.
(b) Sorensen, T. S. Acc. Chem. Res. 1976, 9, 257.
(14) (a) HyperChem Pro Version 5.1; Hypercube Inc., 1115 NW 4th
Street, Gainesville, FL 32601, 1997. (b) Stewart, J . J . P. J . Comput.
Chem. 1989, 10, 209. (c) Stewart, J . J . P. J . Comput. Chem. 1989, 10,
221.
(15) (a) Seyferth, D. Adv. Organomet. Chem. 1976, 14, 97. (b) Bor,
G.; Marko´, L.; Marko´, B. Chem. Ber. 1962, 95, 333. (c) Dent, W. T.;
Duncanson, L. A.; Guy, R. G.; Reed, H. W. B.; Shaw, B. L. Proc. Chem.
Soc. 1961, 169.
(11) The 13C NMR spectra of 22 match closely with the data for
1-isopropyl-4-methylcyclohexa-1,3-diene (R-terpinene): Bohlmann, F.;
Zeisberg, R.; Klein, E. Org. Magn. Reson. 1975, 7, 426.

Ring Opening of a Co-Stabilized Bornyl Cation
Organometallics, Vol. 22, No. 6, 2003 1297
Sch em e 10. Con ver sion of P h en yla cetylen e to
Meth yl P h en yla ceta te
Sch em e 11. P r op osed Mech a n ism for
Acid -P r om oted Rea r r a n gem en t of Ter m in a l
Alk yn e Dicoba lt Com p lexes
F igu r e 2. Semiempirically derived model of 31 (PM3
Hamiltonian), showing only pertinent hydrogen interac-
tions.14
protonation of the terminal dimolybdenum-alkyne
clusters Cp2Mo2(CO)4(RCtCH) generates the µ-η1:η3-
vinyl complex 33. Curtis also noted that, in all cases
studied, the vinyl units have the E configuration, thus
implying that the initial site of attack by the proton was
at the metal-metal bond, with subsequent migration
to the coordinated alkyne.17 This assertion is greatly
strengthened by Stone’s isolation of [Cp2W2(CO)4(µ-H)-
(RCtCR)]+ (34), in which the hydrogen bridges the
tungsten vertexes.19 Moreover, Stone has also charac-
terized Cp2W2(CO)4[Et(µ-H)BtCMe] (35), whereby the
hydrogen bridges the tungsten-boron bond.20
One can now venture a hypothesis based upon these
observations which, when taken together with the
isolobal analogy,21 lend themselves to a viable mecha-
nistic proposal. Scheme 11 presents a series of steps
involving (a) initial protonation across a cobalt-cobalt
bond, as in 36, (b) bridging and then transfer of this
hydrogen to the internal carbon of the alkyne linkage,
F igu r e 3. 13C NMR spectrum of 32 in CDCl3.
spectroscopically by Hu¨bel8 and X-ray crystallographi-
cally by Dahl.9 Subsequently, Pauson used this reaction
(Scheme 10) to convert terminal alkynes into the cor-
responding esters.16
Any mechanistic description must first determine the
source of the methylene hydrogens in the final product.
This was readily accomplished by reaction of (PhCtCD)-
Co2(CO)6 with acetic acid (CH3CO2H), which furnished
PhCHDCCo3(CO)9 (32); likewise, treatment of (PhCt
CH)Co2(CO)6 with CH3CO2D also led to 32. Figure 3
shows the 13C NMR resonance of the -CHD- linkage
in 32, which appears as a deuterium-coupled triplet at
62.9 ppm. These experiments established unequivocally
that one of the methylene hydrogens was originally
bonded to the terminal alkyne carbon, while the acid
provides its partner.
(17) Gerlach, R. F.; Duffy, D. N.; Curtis, M. D. Organometallics 1983,
2, 1172.
(18) Beck, J . A.; Knox, S. A. R.; Riding, G. H.; Taylor, G. E.; Winter,
M. J . J . Organomet. Chem. 1980, 202, C49.
(19) J effery, J . C.; Laurie, J . C. V.; Moore, I.; Stone, F. G. A. J .
Organomet. Chem. 1983, 258, C37.
We now remind ourselves of an important observation
made independently by Curtis17 and by Knox:18 that
(20) Carriedo, G. A.; Elliot, G. P.; Howard, J . A. K.; Lewis, D. B.;
Stone, F. G. A. J . Chem. Soc., Chem. Commun. 1984, 1585.
(21) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711.
(16) Khand, I. U.; Knox, G. R.; Pauson, P. L.; Watts, W. E. J .
Organomet. Chem. 1974, 73, 383.

1298 Organometallics, Vol. 22, No. 6, 2003
Kaldis et al.
eters; spectra were recorded at ambient temperatures and
referenced to the residual proton or 13C solvent signal. One-
dimensional 1H, 13C, and 13C DEPT and two-dimensional 1H-
1H COSY, 1H--3C shift-correlated, and long-range 1H-13C shift-
correlated experiments recorded on the Bruker DRX-500
spectrometer were measured on nonspinning samples that
were prepared by filtering the dissolved compound through a
small glass pipet containing glass wool and silica gel. Mass
spectra were acquired with a Finnigan EI/CI mass spectrom-
eter system, using direct electron impact and chemical ioniza-
tion methods. Chemical ionization was induced using NH3 as
the collision gas. High-resolution mass spectra (HRMS) were
obtained using a Micromass GCT, GC time-of-flight mass
spectrometer.
Sch em e 12. P r op osed Rou te to a
Dim eta lla cyclop r op en iu m In ter m ed ia te
37 f 38, and (c) migration of the terminal hydrogen so
as to generate the required methylene group, thus
placing the cationic charge either on a metal vertex, as
in 39, or on the bridging carbon atom. However, a more
attractive resonance structure would regard this species
as a Hu¨ckel-type 2π aromatic cyclopropenium cation,
40, in which two of the CH units have been replaced by
isolobal Co(CO)3 vertexes.21
It is particularly noteworthy that the previously
mentioned [(µ-η1:η3-CHdCH2)Mo2(CO)4Cp2]+ complex,
33, is fluxional, whereby the cyclopentadienyl environ-
ments, and also the geminal vinylic protons, undergo
site exchange. Knox has suggested a mirror-symmetric
transition state, 41, such that the vinyl fragment
bridges the molybdenum-molybdenum bond.18 We note
that an intermediate of this type would facilitate migra-
tion of the unique hydrogen and lead directly to the
dimetallacyclopropenium structure 42, as depicted in
Scheme 12.
We freely admit that this is merely a proposed
mechanistic pathway for the dicobalt system, but we
also note that several of the intermediates invoked, in
particular 36-38, have been unequivocally character-
ized where the Co(CO)3 vertexes have been replaced by
other isolobal metal vertexes such as (C5H5)Mo(CO)2 or
(C5H5)W(CO)2, in 34, 35, and 33, respectively. The final
step, whereby the third metal is incorporated to gener-
ate the tetrahedral cluster, remains unclear at present
and may involve reduction of the dimetallacycloprope-
nium cation to the corresponding radical that subse-
quently couples with (CO)4Co• or a related species.
To conclude, we report that (propargyl alcohol)Co2-
(CO)6 systems derived from terminal alkynes can exhibit
a wide variety of reactivity patterns. Moreover, we trust
that our mechanistic speculations concerning the acid-
promoted conversion of (RCtCH)Co2(CO)6 complexes
into alkylidyne-nonacarbonyltricobalt clusters, RCH2-
CCo3(CO)9, will prompt others to attempt to provide a
more precise explanation of this fascinating transforma-
tion.
Gen er a l Syn th etic P r oced u r es. Each reaction was con-
ducted at -78 °C in a dry ice/2-propanol bath and monitored
to completion using thin-layer chromatography, before it was
warmed to room temperature and quenched with H2O. In a
typical reaction, addition of (1R)-(+)-camphor (1.63 g, 10.70
mmol) to a mixture of (trimethylsilyl)acetylene (1.51 mL, 10.70
mmol) and n-butyllithium (10.70 mmol) in ether (30 mL) gave,
after hydrolysis and flash chromatography with a 2:1 mixture
of CH2Cl2/hexanes as eluent, (2-endo-trimethylsilyl)ethynyl-
borneol22 (2.17 g, 8.67 mmol; 81%), as a white solid. Treatment
with tetra-n-butylammonium fluoride (5.42 mL, 8.67 mmol)
in ether (30 mL) yielded, after flash chromatography with a
2:1 mixture of CH2Cl2/hexanes as eluent, 2-endo-ethynyl-
borneol (93%),23 as a white solid. Subsequent treatment of the
alkynol with an equimolar quantity of Co2(CO)8 in THF at
room temperature for 12 h yielded (2-endo-ethynylborneol)-
Co2(CO)6 (19) as a dark red solid (90%), after chromatographic
separation with hexanes. When an equimolar amount of HBF4
in ether was added to 19 in ether (30 mL) at -78 °C, and the
mixture was warmed gradually to room temperature, removal
of solvent and chromatographic separation with hexanes
yielded 21 (53%) and 22 (32%).
2-en d o-((Allyld im eth ylsilyl)eth yn yl)bor n eol was pre-
pared analogously by using 2 equiv of n-butyllithium for the
initial reaction with 2-ethynylborneol, followed by the addition
of allyldimethylchlorosilane to yield the product as a yellow
oil (76%). 1H NMR (200.13 MHz, CDCl3): δ 5.77 (ddt, 1H,
3
SiCH2CHdCH2, J H-H ) 16.4, 10.5, and 8.1 Hz), 4.91 (m, 1H)
and 4.87 (m, 1H) (SiCH2CHdCH2), 2.17 (ddd, 1H, H3, 2J H-H
)
3
13.4 Hz, J H-H ) 3.7 and 3.7 Hz), 2.03 (s, 1H, OH), 1.53-1.88
(m, 6H), 1.42 (m, 1H), 1.09 (m, 1H), 1.01 (s, 3H) and 0.83 (s,
3H) (Me8, Me9), 0.90 (s, 3H, Me10), 0.12 (s, 6H, SiMe2). 13C NMR
(50.13 MHz): δ 133.9 (SiCH2CHdCH2), 113.7 (SiCH2CHd
CH2), 111.1 (CtCSi), 85.5 (C2), 77.9 (CtSi), 53.3 (C1), 48.2 (C3),
47.7 (C7), 45.3 (C4), 32.3 (C6), 26.7 (C5), 24.0 (SiCH2CHdCH2),
21.2 and 20.9 (Me8/9), 10.2 (Me10), -2.3 (SiMe2). MS (DEI, m/z
(%)): 276 (3) [(M)]+, 259 (25) [(M - OH)]+, 235 (7) [(M -
C3H5)]+, 217 (6) [(M - H2O - C3H5)]+, 159 (7) [(M - H2O -
(CH3)2SiCH2CHdCH2)]+. MS (DCI, NH3, m/z (%)): 277 (4) [(M
+ H)]+, 276 (14) [(M)]+, 259 (60) [(M - OH)]+, 235 (5) [(M -
C3H5)]+, 217 (3) [(M - H2O - C3H5)]+. HRMS: m/z calcd for
Exp er im en ta l Section
C
17H28OSi 276.1909 [(M)]+, found 276.1899.
Ma ter ia ls. All syntheses were carried out under a dry
nitrogen atmosphere in an enclosed round-bottom flask, with
constant stirring. All reactants and products were weighed in
a glovebag. Solvents were dried and distilled according to
standard procedures. All chemicals were purchased and used
as supplied by the Aldrich Chemical Co., with the exception
of dicobalt octacarbonyl and allyldimethylchlorosilane obtained
from Strem Chemicals Inc. and Gelest Inc., respectively. Silica
gel, 230-400 mesh, was used for flash column chromatogra-
phy. Melting points (uncorrected) were determined with a
Thomas-Hoover Unimelt capillary melting point apparatus.
Elemental analyses are from Guelph Chemical Laboratories,
Guelph, Ontario, Canada.
[2-en d o-((a lly ld im e t h y ls ily l)e t h y n y l)b o r n e o l]C o 2-
(CO)6 (2): dark red solid (88%); mp 96-97 °C. 1H NMR (500.13
MHz, CDCl3): δ 5.81 (m, 1H, SiCH2CHdCH2), 4.97 (m, 1H)
2
and 4.93 (m, 1H) (SiCH2CHdCH2), 2.41 (m, 1H, H3, J H-H
)
12.2 Hz), 1.98 (s, 1H, OH), 1.84 (m, 2H, SiCH2CHdCH2), 1.83
(m, 1H, H4), 1.82 (m, 1H, H5), 1.60 (m, 1H, H3), 1.57 (m, 1H,
H6), 1.43 (m, 1H, H6), 1.28 (m, 1H, H5), 1.17 (s, 3H) and 0.91
(s, 3H) (Me8/9), 0.94 (s, 3H, Me10), 0.35 (s, 6H, SiMe2). 13C NMR
(125.77 MHz): δ 195.0 (6CO), 133.8 (SiCH2CHdCH2), 122.0
(CCSi), 114.7 (SiCH2CHdCH2), 83.3 (C2), 78.6 (CCSi), 54.0 (C1),
(22) van der Linden, J . B.; van Asten, P. F. T. M.; Braverman, S.;
Zwanenburg, B. Recl. Trav. Chim. Pays-Bas 1995, 114, 51.
(23) Capmau, M. L.; Chodkiewicz, W.; Cadiot, P. Bull. Soc. Chim.
Fr. 1968, 8, 3233.
1
In str u m en ta tion . H and 13C solution NMR spectra were
acquired on Bruker DRX-500, WM 250, and AC-200 spectrom-

Ring Opening of a Co-Stabilized Bornyl Cation
Organometallics, Vol. 22, No. 6, 2003 1299
53.8 (C3), 51.0 (C7), 45.4 (C4), 30.6 (C6), 27.7 (C5), 25.3 (SiCH2-
CHdCH2), 21.7 and 21.5 (Me8/9), 10.7 (Me10), -0.8 (SiMe2). MS
(DEI, m/z (%)): 506 (2) [(M - 2CO)]+, 478 (3) [(M - 3CO)]+,
450 (11) [(M - 4CO)]+, 422 (5) [(M - 5CO)]+, 394 (14) [(M -
6CO)]+, 352 (15) [(M - 6CO - C3H6)]+. MS (DCI, NH3, m/z
(%)): 545 (100) [(M - OH)]+, 517 (52) [(M - OH - CO)]+, 489
(41) [(M - OH - 2CO)]+, 461 (33) [(M - OH - 3CO)]+, 450
(94) [(M - 4CO)]+, 433 (52) [(M - OH - 4CO)]+, 394 (43) [(M
- 6CO)]+, 352 (46) [(M - 6CO - C3H6)]+, 335 (27) [(M - Co -
6CO)]+, 276 (58) [(M - Co2(CO)6)]+, 259 (85) [(M - OH - Co2-
(CO)6)]+, 217 (3) [(M - Co2(CO)6 - H2O - C3H5)]+. Anal. Calcd
for C23H28O7Co2Si: C, 49.12; H, 5.02. Found: C, 49.70; H, 5.61.
P r oton a tion of [2-en d o-((a llyld im eth ylsilyl)eth yn yl)-
bor n eol]Co2(CO)6 (2) and subsequent chromatographic sepa-
ration yielded [2-((allyldimethylsilyl)ethynyl)born-2-ene]Co2-
(CO)6 (11; 45%) and [2-endo-((dimethylfluorosilyl)ethynyl)born-
2-ene]Co2(CO)6 (12; 36%) as dark red oily solids.
[2-en do-((tr im eth ylsilyl)eth yn yl)bor n eol]Co2(CO)6: dark
red solid (89%), mp 77-78 °C. 1H NMR (500.13 MHz, CDCl3):
δ 2.40 (m, 1H, H3), 1.98 (s, 1H, OH), 1.82 (m, 2H), 1.67 (m,
1H), 1.62 (m, 1H), 1.45 (m, 1H), 1.26 (m, 1H), 1.18 (s, 3H, Me),
0.94 (s, 3H, Me), 0.91 (s, 3H, Me), 0.37 (s, 9H, SiMe3). 13C NMR
(125.77 MHz): δ 200.6 (6CO), 121.9 (CCSi), 83.2 (C2), 80.3
(CCSi), 54.0 (C1), 53.7 (C3), 51.0 (C7), 45.4 (C4), 30.6 (C6), 27.7
(C5), 21.7 and 21.5 (Me8/9), 10.7 (Me10), 1.5 (Me3Si). MS (DEI,
m/z (%)): 368 (3) [(M - 6CO)]+, 233 (2) [(M - OH
-
Co2(CO)6)]+. MS (DCI, NH3, m/z (%)): 519 (2) [(M - OH)]+,
424 (8) [(M - 4CO)]+, 250 (4) [(M - Co2(CO)6)]+, 233 (100) [(M
- OH - Co2(CO)6)]+, 153 (17) [(M - C2Co2(CO)6 - SiMe3)]+.
HRMS: m/z calcd for C21H26O7SiCo2 536.0112 [(M)]+, found
536.0106.
[2-((Tr im eth ylsilyl)eth yn yl)bor n -2-en e]Co2(CO)6. Pro-
tonation of the precursor alcohol yielded the elimination
product [2-((trimethylsilyl)ethynyl)born-2-ene]Co2(CO)6 exclu-
sively, as a dark red solid (81%), mp 46-47 °C. Reflux in
acetone resulted primarily in decomposition, with 37% yield.
1H NMR (200.13 MHz, CDCl3): δ 6.29 (broad s, 1H, H3), 2.40
(broad s, 1H), 1.92 (m, 1H), 1.61 (m, 1H), 1.42 (m, 1H), 1.24
(m, 1H), 1.09 (s, 3H, Me), 0.82 (s, 6H, 2Me), 0.34 (s, 9H, SMe3).
13C NMR (50.13 MHz): δ 200.6 (6CO), 146.0 (CCSi), 139.8 (C3),
99.2 (C2), 81.3 (CCSi), 57.3 (C1), 56.6 (C7), 52.3 (C4), 31.8 (C6),
25.4 (C5), 19.6 and 19.4 (Me8/9), 12.7 (Me10), 1.4 (Me3Si). MS
(DEI, m/z (%)): 490 (1) [(M - CO)]+, 462 (4) [(M - 2CO)]+,
434 (4) [(M - 3CO)]+, 406 (9) [(M - 4CO)]+, 378 (17) [(M -
5CO)]+, 350 (7) [(M - 6CO)]+, 291 (3) [(M - Co - 6CO)]+, 232
(20) [(M - Co2(CO)6)]+, 217 (33) [(M - Co2(CO)6 - CH3)]+, 73
(79) [(SiMe3)]+. MS (DCI, NH3, m/z (%)): 519 (8) [(M + H)]+,
491 (6) [(M + H - CO)]+, 480 (4) [(M + NH4 - 2CO)]+, 452 (3)
[(M + NH4 - 3CO)]+, 424 (11) [(M + NH4 - 4CO)]+, 233 (54)
1
Data for 11 are as follows. H NMR (200.13 MHz, CDCl3):
δ 6.25 (broad, 1H, H3), 5.82 (m, 1H, SiCH2CHdCH2) and 4.98
(m, 2H, SiCH2CHdCH2), 1.21-2.48 (broad, 7H), 1.10 (s, 3H,
Me), 0.86 (s, 6H, 2Me), 0.35 (s, 6H, SiMe2). 13C NMR (50.13
MHz): δ 200.7 (6CO), 145.8 (C2), 139.9 (C3), 134.0 (SiCH2CHd
CH2), 114.4 (SiCH2CHdCH2), 79.7 (CCSi), 78.2 (CCSi), 57.4
(C1), 56.6 (C7), 52.4 (C4), 31.9 (C6), 29.7 (C5), 25.4 (SiCH2CHd
CH2), 19.6 (Me8/9), 2.9 (Me10), -0.8 and -0.9 (SiMe2). MS (DEI,
m/z (%)): 488 (1) [(M - 2CO)]+, 432 (3) [(M - 4CO)]+, 404 (6)
[(M - 5CO)]+, 376 (21) [(M - 6CO)]+, 317 (4) [(M - Co -
6CO)]+, 217 (4) [(M - Co2(CO)6 - C3H5)]+. MS (DCI, NH3, m/z
(%)): 545 (2) [(M + H)]+, 517 (2) [(M + H-CO)]+, 489 (2) [(M
+ H - 2CO)]+, 461 (4) [(M + H - 3CO)]+, 450 (20) [(M + NH4
- 4CO)]+, 433 (11) [(M + H - 4CO)]+, 376 (7) [(M - 6CO)]+,
317 (5) [(M - Co - 6CO)]+, 276 (12) [(M + NH4 - Co2(CO)6)]+,
259 (27) [(M + H - Co2(CO)6)]+, 99 (52) [(Me2SiCH2CHd
CH2)]+.
[(M + H - Co2(CO)6)]+, 177 (13) [(M + NH4 - Co2(CO)6
-
SiMe3)]+. HRMS: m/z calcd for C21H24O6SiCo2 536.0006 [(M)]+,
found 536.0016.
1
Data for 12 are as follows. H NMR (200.13 MHz, CDCl3):
P r oton a tion of [(tr im eth ylsilyl)(a llyld im eth ylsilyl)-
eth yn e]Co2(CO)6 (14). 14 was prepared according to the
method of Ruffolo et al.24 and protonated, thereby affording
[Me3SiCtCSiMe2F]Co2(CO)6 (15)24 and [Me3CtCSiMe2OH]-
Co2(CO)6 (16). The latter was apparently produced during
purification of 15 by column chromatography.
δ 6.36 (broad, 1H, H3), 1.22-2.49 (broad, 5H), 1.11 (s, 3H),
and 0.87 (s, 6H) (Me8,9,10), 0.55 (s, 6H, SiMe2). 13C NMR (50.13
MHz): δ 200.1 (6CO), 145.9 (C2), 140.9 (C3), 97.0 (CCSi), 78.3
(CCSi), 57.4 (C1), 56.7 (C7), 52.5 (C4), 31.8 (C6), 25.3 (C5), 19.6
and 19.4 (Me8/9), 12.3 (Me10), 0.8 and 0.4 (SiMe2). MS (DEI,
m/z (%)): 438 (1) [(M - 3CO)]+, 410 (3) [(M - 4CO)]+, 382 (4)
[(M - 5CO)]+, 354 (3) [(M - 6CO)]+, 236 (6) [(M - Co2(CO)6)]+,
221 (12) [(M - Co2(CO)6 - Me)]+. MS (DCI, NH3, m/z (%)):
523 (2) [(M + H)]+, 495 (1) [(M + H - CO)]+, 456 (2) [(M +
NH4 - 3CO)]+, 428 (8) [(M + NH4 - 4CO)]+, 237 (25) [(M + H
- Co2(CO)6)]+.
(2-n or bor n ylid en e)CHCCo3(CO)9 (13). Meth od 1. A
5-fold excess of HBF4 in ether was added dropwise to [2-endo-
((allyldimethylsilyl)ethynyl)borneol]Co2(CO)6 (2; 0.11 g, 0.20
mmol) in an NMR tube at -78 °C, and the mixture was
warmed gradually to room temperature over 12 h. Chromato-
graphic separation yielded a dark red solid (19%), mp 47-48
°C.
Meth od 2. [2-endo-ethynylborneol]Co2(CO)6 (19; 1.95 g, 4.37
mmol) was heated at reflux in acetone (30 mL) for 36 h and,
after flash chromatography, yielded 13 (38%). 1H NMR (500.13
MHz, CDCl3): δ 7.37 (s, 1H, CdCH), 2.39 (m, 1H, H3), 2.36
(m, 1H, H3), 1.88 (m, 1H, H4), 1.80 (m, 1H, H5), 1.70 (m, 1H,
H6, 2J H-H ) 11.5 Hz), 1.28 (m, 1H, H6), 1.18 (m, 1H, H5, 3J H-H
) 8.9 Hz), 0.99 (s, 3H, Me10), 0.92 (s, 3H) and 0.75 (s, 3H)
(Me8/9). 13C NMR (125.77 MHz): δ 200.5 (9CO), 152.4 (CdCH),
139.5 (CdCH), 53.1 (C1), 48.2 (C7), 45.2 (C4), 38.0 (C3), 29.7
(C6), 27.6 (C5), 19.6 and 19.0 (Me8/9), 12.9 (Me10). MS (DEI, m/z
(%)): 562 (3) [(M - CO)]+, 534 (1) [(M - 2CO)]+, 506 (1) [(M -
3CO)]+, 478 (4) [(M - 4CO)]+, 450 (4) [(M - 5CO)]+, 422 (4)
[(M - 6CO)]+, 394 (2) [(M - 7CO)]+, 366 (3) [(M - 8CO)]+,
338 (3) [(M - 9CO)]+. MS (DCI, NH3, m/z (%)): 591 (6) [(M +
H)]+, 563 (4) [(M + H - CO)]+, 535 (3) [(M + H - 2CO)]+.
Anal. Calcd for C21H17O9Co3‚(C2H5)2O: C, 45.20; H, 4.10.
Found: C, 45.42; H, 3.63. HRMS: m/z calcd for C21H17O9Co3
589.8869 [(M)]+, found 589.8884.
15: dark red oily solid (72%). 1H NMR (200.13 MHz,
3
CDCl3): δ 0.48 (d, 6H, SiMe2F, J H-F ) 6.8 Hz), 0.30 (s, 9H,
SiMe3). 13C NMR (50.13 MHz): δ 200.1 (6CO), 0.9 (SiMe3), 0.4
(SiMe2F, 2J C-F ) 16.3 Hz). MS (DEI, m/z (%)): 432 (53) [(M -
CO)]+, 404 (22) [(M - 2CO)]+, 376 (24) [(M - 3CO)]+, 348 (26)
[(M - 4CO)]+, 320 (46) [(M - 5CO)]+, 292 (48) [(M - 6CO)]+,
233 (50) [(M - Co - 6CO)]+. MS (DCI, NH3, m/z (%)): 478 (2)
[(M + NH4)]+, 441 (1) [(M - F)]+, 433 (3) [(M + H - CO)]+,
410 (11) [(M - HF - 2CH3)]+, 383 (15) [(M - SiMe2F)]+, 354
(27) [(M - H - SiMe2F - CO)]+, 326 (43) [(M - H - SiMe2F
- 2CO)]+, 250 (58) [(M + NH4 - Co - 6CO)]+. HRMS: m/z
calcd for C13H15O6FSi2Co2 459.9055 [(M)]+, found 459.9046.
16: dark red oily solid (10%). 1H NMR (200.13 MHz,
CDCl3): δ 2.46 (broad s, 1H, OH), 0.39 (s, 6H, SiMe2OH), 0.29
(s, 9H, SiMe3). 13C NMR (50.13 MHz): δ 200.7 (6CO), 91.7 and
90.2 (CtC), 1.6 (SiMe2OH), 0.9 (SiMe3). MS (DCI, NH3, m/z
(%)): 476 (10) [(M + NH4)]+, 459 (26) [(M + H)]+, 431 (15) [(M
+ H - CO)]+, 410 (20) [(M - H2O - 2CH3)]+, 392 (51) [(M +
NH4 - 3CO)]+, 382 (16) [(M - H - SiMe2OH)]+, 364 (47) [(M
+ NH4 - 4CO)]+, 354 (55) [(M - H - SiMe2OH - CO)]+, 326
(100) [(M - H - SiMe2OH - 2CO)]+, 248 (94) [(M + NH4
Co - 6CO)]+, 190 (31) [(M + NH4 - Co2(CO)6)]+.
-
P r oton a tion of (Me3SiCtCSiMe2F )Co2(CO)6 (15) with
HBF4 in ether at -78 °C gave [Me3SiCtCH]Co2(CO)6 (17)25
in 32% yield.
Me3SiCH2CCo3(CO)9 (18).26 When 15 was heated at reflux
in acetone for 36 h, it afforded 18 in 12% yield: dark red solid,
(24) Ruffolo, R.; Kainz, S.; Gupta, H. K.; Brook, M. A.; McGlinchey,
M. J . J . Organomet. Chem. 1997, 547, 217.
(25) Kru¨erke, U.; Hu¨bel, W. Chem. Ber. 1961, 94, 2829.

1300 Organometallics, Vol. 22, No. 6, 2003
Kaldis et al.
1
mp 37 °C (lit.26 mp 36-37 °C). 1H NMR (200.13 MHz, CDCl3):
δ 3.81 (s, 2H, CH2CCo3), 0.20 (s, 9H, SiMe3). 13C NMR (50.13
MHz): δ 200.6 (6CO), 56.9 (CH2CCo3), -1.0 (SiMe3). MS (DEI,
m/z (%)): 528 (11) [(M)]+, 500 (84) [(M - CO)]+, 472 (41) [(M
- 2CO)]+, 444 (39) [(M - 3CO)]+, 416 (55) [(M - 4CO)]+, 388
(98) [(M - 5CO)]+, 360 (100) [(M - 6CO)]+, 332 (60) [(M -
7CO)]+, 304 (38) [(M - 8CO)]+, 276 (71) [(M - 9CO)]+, 217
(22) [(M - Co - 9CO)]+.
Data for 22 are as follows. H NMR (500.13 MHz, CDCl3):
δ 6.34 (s, 1H, CCH), 5.40 (s, 1H, H3), 2.87 (m, 2H, H5), 2.74
(m, 2H, H6), 2.30 (m, H7), 1.87 (broad, 3H, Me10), 1.06 and 1.05
(broad, 6H, 2Me). 13C NMR (125.77 MHz): δ 200.1 (6CO), 141.4
(C4), 133.4 (C1), 123.0 (C2), 114.7 (C3), 89.6 (CCH), 74.7 (CCH),
35.2 (C6), 34.3 (C7), 33.9 (C5), 21.1 (2Me), 21.0 (Me). MS (DEI,
m/z (%)): 446 (4) [(M)]+, 418 (9) [(M - CO)]+, 390 (6) [(M -
2CO)]+, 362 (5) [(M - 3CO)]+, 334 (8) [(M - 4CO)]+, 306 (18)
[(M - 5CO)]+, 278 (21) [(M - 6CO)]+. MS (DCI, NH3, m/z
(%)): 447 (100) [(M + H)]+, 419 (7) [(M + H - CO)]+, 391 (4)
[(M - H - 2CO)]+, 380 (5) [(M + NH4 - 3CO)]+, 352 (5) [(M +
NH4 - 4CO)]+, 161 (13) [(M + H - Co2(CO)6)]+.
(2-en d o-eth yn ylbor n eol)Co2(CO)6 (19): dark red solid
(90%), mp 53-54 °C. 1H NMR (200.13 MHz, CDCl3): δ 6.09
(s, 1H, CCH), 2.46 (m, 1H, H3), 2.40 (m, 1H, H3), 1.90 (s, 1H,
OH), 1.79 (m, 2H), 1.55 (m, 1H), 1.52 (m, 1H), 1.45 (m, 1H),
1.17 (s, 3H, Me), 0.92 (s, 3H, Me), 0.89 (s, 3H, Me). 13C NMR
(50.13 MHz): δ 199.8 (6CO), 105.6 (CCH), 82.8 (CCH), 74.5
(C2), 54.7 (C3), 53.7 (C1), 51.0 (C7), 45.4 (C4), 30.4 (C6), 27.7
(C5), 21.5 and 21.3 (Me8/9), 10.6 (Me10). MS (DEI, m/z (%)): 408
(1) [(M - 2CO)]+, 380 (3) [(M - 3CO)]+, 324 (4) [(M - 5CO)]+,
296 (11) [(M - 6CO)]+. MS (DCI, NH3, m/z (%)): 447 (13) [(M
- OH)]+, 419 (3) [(M - OH - CO)]+, 408 (3) [(M - 2CO)]+,
352 (9) [(M - 4CO)]+, 296 (1) [(M - 6CO)]+, 237 (2) [(M - Co
- 6CO)]+, 161 (40) [(M - OH - Co2(CO)6)]+. Anal. Calcd for
P h CHDCCo3(CO)9 (32). Following Pauson’s method,16
addition of glacial acetic acid to D(PhCtCD)Co2(CO)6 or of
CH3CO2D to (PhCtCH)Co2(CO)6 gave 32 in 17% and 24%
yields, respectively. 1H NMR (250.13 MHz, CDCl3): δ 7.3-
7.4 (m, 5H, Ph), 4.8 (s, 1H). 13C NMR (62.86 MHz): δ 199.8
1
(6CO), 143.1, 129.3, 128.8, 127.7 (Ph C’s), 62.9 (t, CHD, J C-D
) 19.5 Hz). MS (EI+, m/z): 533 [(M)]+, 505 [(M - CO)]+, 477
[(M - 2CO)]+, 449 [(M - 3CO)]+, 421 [(M - 4CO)]+, 393 [(M
- 5CO)]+, 365 [(M - 6CO)]+, 337 [(M - 7CO)]+, 309 [(M -
8CO)]+, 281 [(M - 9CO)]+.
C
18H18O7Co2‚1/2(C2H5)2O: C, 47.92; H, 4.62. Found: C, 48.35;
H, 4.81. HRMS: m/z calcd for C17H18O6Co2 435.9767 [(M -
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s. X-ray crystal-
lographic data were collected from a single crystal of 20
mounted on a glass fiber. Data were collected using a P4
Bruker diffractometer, equipped with a Bruker SMART 1K
charge coupled device (CCD) area detector, using the program
SMART,27 and a rotating anode, using graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å). The crystal-to-
detector distance was 4.987 cm, and the data collection was
carried out in 512 × 512 pixel mode, utilizing 2 × 2 pixel
binning. The initial unit cell parameters were determined by
a least-squares fit of the angular settings of the strong
reflections, collected by a 12° scan in 40 frames over three
different sections of reciprocal space (120 frames in total). A
hemisphere of data was collected with high redundancy, to
better than 0.8 Å resolution at 298 K. Upon completion of the
data collection, the first 40 frames were re-collected in order
to improve the decay correction analyses. Processing was
carried out using the program SAINT,28 which applied Lorentz
and polarization corrections to the three-dimensionally inte-
grated diffraction spots. The program SADABS29 was utilized
for the scaling of the diffraction data, the application of a decay
correction, and an empirical absorption correction based on
redundant reflections for each data set. The structures were
solved by using the direct-methods procedure in the Bruker
SHELXTL program library30 and refined by full-matrix least-
squares methods on F2 with anisotropic thermal parameters
for the bridging methylene carbon, cluster carbon, carbonyl,
and cobalt atoms. A slight rotational disorder of the borneol
ligand prevented anisotropic refinement of this functionality.
Hydrogen atoms were added as fixed contributors at calculated
positions with isotropic thermal parameters, on the basis of
the carbon atom to which they were bonded. The unit cell
consisted of two crystallographically unrelated molecules (Z
) Z′ ) 2).
CO)]+, found 435.9754.
[2-(2-Hyd r oxybor n yl)]CH2CCo3(CO)9 (20). The synthesis
and purification of this product were identical with method 2
for 13: dark red solid (24%), mp 88 °C dec. Crystals suitable
for X-ray diffraction were grown for 20 by slow evaporation
from a 50/50 solution of CH2Cl2 and hexanes. 1H NMR (500.13
MHz, CDCl3): δ 4.00 (d, 1H, CH2CCo3, 2J H-H ) 16.6 Hz), 3.81
2
2
(d, 1H, H11, J H-H ) 16.5 Hz), 2.12 (m, 1H, H3, J H-H ) 13.1
3
Hz), 1.83 (m, 1H, H4, J H-H ) 6.3 Hz), 1.80 (m, 1H, H3), 1.75
(m, 1H, H5), 1.59 (s, 1H, OH), 1.51 (m, 1H, H6), 1.47 (m, 1H,
H6), 1.13 (s, 3H) and 0.90 (s, 3H) (Me8/9), 1.07 (m, 1H, H5), 0.92
(s, 3H, Me10). 13C NMR (125.77 MHz): δ 200.4 (9CO), 81.1 (C2),
64.7 (CH2CCo3), 53.8 (C1), 48.6 (C7), 46.0 (C3), 45.4 (C4), 30.1
(C6), 27.0 (C5), 21.6 and 21.0 (Me8/9), 10.1 (Me10). MS (DEI, m/z
(%)): 478 (3) [(M - H2O - 4CO)]+, 450 (4) [(M - H2O - 5CO)]+,
422 (4) [(M - H2O - 6CO)]+, 304 (13) [(M - H2O - Co2(CO)6)]+,
276 (22) [(M - H2O - CO - Co2(CO)6)]+. MS (DCI, NH3, m/z
(%)): 591 (9) [(M - OH)]+, 563 (5) [(M - OH - CO)]+, 535 (3)
[(M - OH - 2CO)]+, 395 (100) [(M - OH - 7CO)]+. Anal. Calcd
for (C21H18O9Co3)2O: C, 42.10; H, 3.03. Found: C, 42.10; H,
3.20 (loss of water from the alcohol to form the ether). HRMS:
m/z calcd for C20H19O9Co3 579.9025 [(M - CO)]+, found
579.9095.
P r oton a tion of (2-en d o-eth yn ylbor n eol)Co2(CO)6 (19)
at -78 °C yielded (2-ethynyl-2-bornene)Co2(CO)6 (21; 53%), mp
41-43 °C, and (2-ethynyl-4-isopropyl-1-methylcyclohexa-1,3-
diene)Co2(CO)6 (22) as a dark red oily solid (32%). Repetition
at room temperature afforded 21 (74%) and 22 (13%).
1
Data for 21 are as follows. H NMR (200.13 MHz, CDCl3):
δ 6.38 (broad, 1H, H3), 6.21 (s, 1H, CCH), 2.41 (m, 1H), 1.47-
1.93 (m, 4H), 1.05 (s, 3H, Me), 0.80 (s, 6H, 2Me). 13C NMR
(50.13 MHz): δ 200.1 (6CO), 145.7 (C2), 141.1 (C3), 83.4 (CCH),
73.4 (CCH), 57.3 (C1), 56.4 (C7), 52.6 (C4), 31.6 (C6), 25.1 (C5),
19.6 and 19.4 (Me8/9), 12.0 (Me10). MS (DEI, m/z (%)): 446 (3)
[(M)]+, 418 (15) [(M - CO)]+, 390 (35) [(M - 2CO)]+, 362 (25)
[(M - 3CO)]+, 334 (46) [(M - 4CO)]+, 306 (41) [(M - 5CO)]+,
278 (18) [(M - 6CO)]+. MS (DCI, NH3, m/z (%)): 447 (100)
X-ray crystal data for 20: C21H19Co3O10, red plate (0.03 ×
0.10 × 0.17 mm), triclinic, P1, a ) 7.761(4) Å, b ) 12.739(7)
Å, c ) 13.332(8) Å, R ) 90.486(14)°, â ) 106.479(12)°, γ )
91.064(18)°, V ) 1263.6(13) Å3, Z ) 2, Fcalcd ) 1.598 g cm-3, T
) 299(2) K, µ ) 1.996 mm-1; R1 ) 0.0567, wR2 ) 0.0872 (based
on F2) for 425 variables and 9539 reflections (6746 indepen-
dent); R(int) ) 0.0656 with I < 2σ(I), and 1.59 < θ < 25.00°.
[(M + H)]+, 419 (40) [(M + H - CO)]+, 380 (10) [(M + NH4
3CO)]+, 352 (27) [(M + NH4 - 4CO)]+, 178 (11) [(M + NH4
-
-
Co2(CO)6)]+, 161 (19) [(M + H - Co2(CO)6)]+. Anal. Calcd for
C
18H16O6Co2‚(C2H5)2O: C, 50.79; H, 5.04. Found: C, 50.84; H,
(27) SMART, Release 5.611; Bruker AXS Inc., Madison, WI 53711,
4.91.
2000.
(28) SAINT, Release 6.02a; Bruker AXS Inc., Madison, WI 53711,
2000.
(29) Sheldrick, G. M. SADABS; Bruker AXS Inc., Madison, WI
53711, 2000.
(30) Sheldrick, G. M. SHELXTL, Version 5.1; Bruker AXS Inc.,
Madison, WI 53711, 1998.
(26) Previously synthesized from heating Hg(CHBrSiMe3)2 and
HCCo3(CO)9 in benzene at reflux and characterized by 1H NMR,
melting point, and elemental analysis: Seyferth, D.; Hallgren, J . E.;
Spohn, R. J .; Williams, G. H.; Nestle, M. O.; Hung, P. L. K. J .
Organomet. Chem. 1974, 65, 99.

Ring Opening of a Co-Stabilized Bornyl Cation
Organometallics, Vol. 22, No. 6, 2003 1301
Crystallographic data (excluding structure factors) for the
molecule reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as Supplementary
Publication No. CCDC 190592 (20). Copies of the data can be
obtained free of charge on application to the CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. (fax, (+44) 1223-336-033;
e-mail, deposit@ccdc.cam.ac.uk).
of Duisberg. Mass spectra were acquired courtesy of Dr.
Kirk Green of the McMaster Regional Mass Spectrom-
etry Center. We thank Dr. D. G. Morris (University of
Glasgow) for valuable discussions concerning the rear-
rangement behavior of bornyl cations.
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for 20 and figures giving NMR spectra
for some of the compounds prepared in this paper. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Ackn owledgm en t. Financial support from the Natu-
ral Sciences and Engineering Research Council of
Canada (NSERC) is gratefully acknowledged. J .H.K.
thanks the NSERC and the Province of Ontario for
graduate scholarships, and P.M. was the recipient of a
DAAD student exchange fellowship from the University
OM020727R