Cleavage of acetylenic substituents from camphor-derivatives by copper(I) chloride

Article abstract of DOI:10.1016/j.jorganchem.2008.06.004

Copper(I) chloride was found to be a highly efficient reagent to promote the cleavage of acetylenic substituents from the camphor skeleton of compounds 1 containing two C-C triple bonds as well as from the compounds 6 and 7 containing one. This is a formal reversal of the formation of these compounds by the reaction of acetylides with keto and imino groups in compound 18. The substituent R at the triple bond modifies the reactivity and regioselectivity. As intermediates in the process we identified complexes of the types [Cu(L)_depr] (where (L)_depr denotes a deprotonated camphor-derived ligand (L)) and [CuCl(L)]. Quantum mechanical calculations support and rationalize the experimental results.

Full text of DOI:10.1016/j.jorganchem.2008.06.004

Journal of Organometallic Chemistry 693 (2008) 2847–2855
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Journal of Organometallic Chemistry
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Cleavage of acetylenic substituents from camphor-derivatives by copper(I) chloride
a
a
a
b,
M.F.N.N. Carvalho a, , T.A. Fernandes , A.S.D. Ferreira , L.G. Alves , R. Herrmann
*
*
a C.Q.E., Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
b Institut für Physik, Universität Augsburg, Universitätsstr. 1, D-86133 Augsburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 April 2008
Received in revised form 31 May 2008
Accepted 2 June 2008
Available online 7 June 2008
Copper(I) chloride was found to be a highly efficient reagent to promote the cleavage of acetylenic sub-
stituents from the camphor skeleton of compounds 1 containing two C–C triple bonds as well as from the
compounds 6 and 7 containing one. This is a formal reversal of the formation of these compounds by the
reaction of acetylides with keto and imino groups in compound 18. The substituent R at the triple bond
modifies the reactivity and regioselectivity. As intermediates in the process we identified complexes of
the types [Cu(L)depr] (where (L)depr denotes a deprotonated camphor-derived ligand (L)) and [CuCl(L)].
Quantum mechanical calculations support and rationalize the experimental results.
Keywords:
Copper(I)
Camphor alkynes
Complexes
Ó 2008 Elsevier B.V. All rights reserved.
CC bond rupture
Dealkynylation
DFT calculations
1. Introduction
2. Results and discussion
The triple bonds of the camphor-derived compounds (1, see
Fig. 1) can react with a variety of electrophiles including many me-
tal salts with unique reaction patterns such as cyclisations, ring-
opening/ring-closure cascades and C–H activations [1–6], leading
to peculiar products such as taxol analogues by expansion of a
six-membered to an eight-membered ring under platinum(II)
catalysis [3,4]. We found that CuCl2 reacts with compound 1c
(R = Ph) under annulation of a five-membered ring to the camphor
skeleton accompanied by sulfur reduction [3]. In order to gain in-
sight in the activation of triple bonds by coordination to closed-
shell transition metal ions, we studied the reaction of copper(I)
chloride with the camphor-derived mono- (compounds 6 and 7)
and di-alkyne species (compounds 1). Surprisingly, the reaction
followed a totally different pathway and led to the cleavage of
acetylenic substituents from the camphor skeleton, a formal rever-
sal of the formation of these compounds by the reaction between
(3aS)-8,8-dimethyl-5,6-dihydro-3H-3a,6-methano-2,1-benzisothia-
zol-7(4H)-one 2,2-di-oxide (18) and lithium acetylides. We there-
fore employed quantum mechanical calculations on model
compounds in order to rationalize this behaviour.
2.1. Experimental results
The camphor-derived alkynes 1, 6 and 7 do not react directly
with copper(I) chloride, in contrast to CuCl2. To promote their reac-
tivity, it is necessary to deprotonate them. Both sodium amide and
triethylamine can serve for this purpose. In the di-alkynes (1), po-
tential deprotonation sites are the hydroxy and the sulfonamide
groups. A remarkable selectivity is observed in the deprotonation
reaction: depending on the substituent R of the triple bonds, either
OH (for R = Ph, compound 1c) or NH (for R = CH2-Ph, compound 1d)
is deprotonated exclusively. This can easily be followed by 1H NMR
spectroscopy. When the corresponding signals of the OH or NH
groups have disappeared, a stoichiometric amount of CuCl is
added, and the formation of the compounds 4 or 5 starts. However,
isolation in pure form was possible only for the ligand 1d (with the
benzyl group at the triple bonds). Although generally precipitation
of these complexes from the dichloromethane solution in which
they are prepared readily occurs, any attempts of re-dissolution
(or prolonged stirring in the mother liquor as well as increasing
the amount of solvent) led to the formation of reprotonated com-
plexes which we formulate on the basis of elemental analysis (C,
H, N, S) as [CuCl(1)] ꢀ xH2O. The presence of water in the analytical
data is mainly due to the hygroscopic nature of the compounds
since the elemental analyses could not be performed under inert
atmosphere. Small amounts of copper(II) chloride readily form in
solution that are responsible for in ill-resolved paramagnetic
NMR spectra.
* Corresponding authors.
E-mail addresses: fcarvalho@ist.utl.pt (M.F.N.N. Carvalho), rudolf.herrmann@
physik.uni-augsburg.de (R. Herrmann).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.06.004

2848
M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
OH
10
7
N-
R
9
Base
OH
3
4
R
S
5
O
2
O
R
NH
6
1
(2)
8
R
S
O-
O
O
Base
R
NH
(1)
R
S
O
O
(3)
OH
OH
+
H
R
R
N
N
+
PRODUCTS
Cu
R
S
S
O
O
O
O
(4)
(6)
Cu
O
O
+
R
H
NH
NH
+
PRODUCTS
R
S
R
S
O
O
O
O
(5)
(7)
Fig. 1. Site-selective deprotonation and complexation of camphor-derived diynes with copper(I) and dealkynylation by protonation.
The formation of the complexes [CuCl(1)] is surprising since one
The yield of the organic species can be greatly increased by add-
ing a few drops of aqueous HCl to the reaction mixture or to a sus-
pension of the isolated complexes [CuCl(1)] in dichloromethane,
and an excess of CuCl over the stoichiometric amount also helps.
When the same technique is applied to the complexes [CuClL] (L:
6e, 7d or 7e) the cleavage of the acetylenic substituent occurs in
exactly the same manner leading to 3-oxo-camphorsulfonimine
18, and is thus a complete reversal of the reaction in which the
compounds 1, 6 and 7 are formed by its reaction with lithium acet-
ylides [1,3,7]. This very different behaviour of copper(I) when com-
pared with other metal salts is not easy to understand. We
therefore undertook a series of quantum mechanical calculations
in order to obtain further insight in the reaction path.
might expect that they can also be formed directly from CuCl and
the camphor-dialkynes 1 which is, however, not the case. The pres-
ence of at least one triple bond is confirmed by IR spectroscopy and
excludes the known modifications of the compounds 1 which oc-
cur with other metals and even with CuCl2 [3].
Similar complexes can be obtained from the camphor-derived
mono-alkynes (6 and 7) by deprotonation and reaction with CuCl.
Species 7c (R = Ph) behaves similar to 1 in the sense that both the
primary product [Cu(7c)depr
] and the reprotonated complex
[CuCl(7c)] can be obtained, while from 6e only [CuCl(6e)] can be
isolated.
A detailed analysis of the organic products which accompany
the formation of the [CuCl(1)] complexes gave the very surprising
result that a reaction with high selectivity had occurred with the
formation of the compounds 7c from 1c on one hand and 6d and
6e from 1d and 1e on the other.
2.2. Quantum mechanical calculations
2.2.1. Copper coordination site in camphor-derived diynes
The cleavage of an acetylenic substituent is an unprecedented
type of reaction in the series of camphor derivatives studied. The
regioselectivity of the bond cleavage reflects the selectivity in the
deprotonation reaction and suggests that copper coordination
preferably occurs at the deprotonated heteroatom.
Experimentally, there is a surprisingly clear preference for
deprotonation of the diyne 1c at the hydroxy group, in contrast
to 1d and 1e where the proton at the sulfonamide nitrogen is re-
moved by base. The deprotonation site is important since copper
coordination can be expected to occur initially in this position

M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
2849
and trigger the regioselectivity of the final cleavage of the acety-
lenic substituent. In an attempt to understand better this behav-
iour, we studied the influence of the substituent R in compounds
1 on the initial deprotonation by theoretical means.
We calculated the compound 1c (R = Ph) where experimental
results exist, 1a (R = H) as the simplest compound of this type for
comparison, and 1b (R = Me) as a reasonable model for 1d
(R = CH2Ph), in order to limit the size of the calculation. The calcu-
lations were done at the HF level using 6-31G* as basis set which
seems to be a reasonable compromise between accuracy and com-
putation time.
There are two main reasons that can drive preferential N or O
deprotonation: (i) different acidities of the protons (reflected in
the calculated partial charges in the neutral molecules 1), these
acidities may have an effect on the deprotonation rate – kinetic
argument or (ii) the stability of the monoanions 2 and 3 (Fig. 1)
may be different, thus the more stable anion forms – thermody-
namic argument.
ble steric hindrance but rather electronic effects of the R substitu-
ents (Fig. 2).
For calculations of copper-containing compounds an ECP basis
set appeared appropriate, and we decided to include electron cor-
relation by a DFT method (PBE0) (see Section 4). Only closed-shell
copper(I) complexes of propargylic alcohols were studied since it is
well known that terminal alkynes undergo Glaser coupling in the
presence of copper(II) [8–10]. We also decided to calculate mono-
mers only since in the real systems the camphor moiety introduces
a considerable steric bulkiness that should make oligomerisation
difficult although copper–organic compounds are known to form
polymers or oligomers [11–13].
The results of these calculations are presented in more detail in
the Supplementary material (available online).
In the linear model no interaction between copper and the tri-
ple bond is possible whereas in the bent (cyclic) isomers the inter-
action of copper with the triple bond is possible as well as the
interaction with the R substituent (Table 2).
The relevant results from the calculation made on the neutral
compounds 1a–c are displayed in Table 1. Both Mulliken and Löw-
din charges are quoted for the chain of atoms connecting directly
the protons under consideration. According to the electronegativ-
ity of the participating atoms and groups, the tendency appears
reasonable. All charges for a specific atom are very similar for
any of the substituents (H: a; CH3: b; C6H5: c) except for the Mul-
liken charges at the carbon C-1 (neighbour to the oxygen atom)
which show a moderate increase in charge with increasing bulki-
ness of the substituent. There is no obvious connection of those dif-
ferences with deprotonation at oxygen in 1c or nitrogen in 1d.
The thermodynamic stability of the anions 2b vs. 3b and 2c vs.
3c was compared by calculation of the total energies, neglecting
zero-point corrections which are similar for 2 and 3. For anions
2b and 3b (R = Me), it was still possible to include diffuse basis
functions at the heteroatoms which is expected to give more reli-
able results for anions, but this did not change the energy differ-
ence significantly (12.6 kcal/mol with diffuse functions vs.
12.4 kcal/mol without).
The N-deprotonated isomer turned out to be more stable by
12.4 kcal/mol (R = CH3) and 11.7 kcal/mol (R = C6H5) pointing to
deprotonation at the nitrogen atom being thermodynamically fa-
voured. The influence of the solvent (dichloromethane) in both
cases is unlikely to be very different, so no obvious reason for pref-
erential deprotonation at the oxygen atom in 1c to form 3c is
found. However, the experimental results show that it occurs and
former studies [3–5] indicate that coordination of type 1 camphor
ligands to platinum(II) involves the oxygen atom of the OH group.
Thus, we decided to check first the possibility of forming copper(I)
complexes with propargylic alcohols deprotonated at oxygen both
in a linear (10) or bent (cyclic) fashion (11). In these models, the
sterically demanding camphor-derived residue is replaced by a
CH2 group. The results are therefore expected not to reflect possi-
Energetically, the bent structures 11 are favoured by 6–7 kcal/
mol over the linear ones for R = H, CH3 and C6H5 and considerably
more favoured for benzyl and aminomethyl substituents due to
additional interactions of copper with the phenyl group or the
nitrogen atom, respectively.
the copper atom is accompanied by longer Cu–O distances and
lower
(C„C) frequencies (by 50–200 cmꢁ1, Table 2). For the ben-
p-Coordination of the triple bond to
m
zyl-substituted compound 11d, the Cu–C2, Cu–C3 and Cu–C1 bond
distances are all in the same range. Since C-1 coordination does not
occur, there can hardly be any interaction between copper and the
triple bond. The high stability of 11d (bent) compared with10d
(linear) is therefore mainly due to the g
2-coordination of copper
to the phenyl group (Cu–CPh: 2.098 and 2.167 Å, respectively).
We also find that in the aminomethyl-substituted compound 11e
copper coordinates directly to the nitrogen atom (Cu–N: 1.975 Å
and angle N–Cu–O 154.4°) and the interaction with the triple bond
is weak.
Besides the linear and cyclic structures 10 and 11, no other min-
ima on the potential hypersurface were detected. We therefore
conclude that bonding in complexes of camphor-derived diynes
should resemble model 11, with copper coordinating to the triple
bond in a degree which depends strongly on the nature of the sub-
stituent R.
In fact, by reaction of CuCl with 1d a reasonably stable com-
pound formulated as [Cu(1d)depr] was obtained while no analogous
products could be isolated from 1c or 1e under the same reaction
conditions; in contrast, protonated species [CuCl(1)] are formed.
2.2.2. Protonation of copper(I) model complexes of propargylic
alcohols
Following by 1H NMR the reaction of 1c with CuCl, there is some
evidence for formation of a complex of type 5, although it is not
stable enough to be isolated and further reacts to the dealkynylat-
ed camphor derivatives 7. The process is highly sensitive to proton
concentration (even moisture fastens the process).
To get some insight into the protonation process that prompts
dealkynylation we used the model systems 8 (Fig. 2) where the ex-
pected final products are formaldehyde, a terminal alkyne, and Cu+
(9, Fig. 2) or their isomeric ensembles where copper remains coor-
dinated to the two organic products. The possible sites for proton
attack (at model molecules 10 or 11) are oxygen, the carbon atoms
of the triple bond and amino nitrogen for 11e.
In the simplest case (R = H, 10a and 11a) we found seven min-
ima on the potential hypersurface together with a transition state
(12TS, Fig. 3). Protonation at oxygen is straightforward and leads to
12A from 10a or 12E from 11a where the structure of the starting
complexes is almost maintained. As for the neutral compounds, the
Table 1
Calculated charges (Mulliken and Löwdin method) in the H1–O–C1–C2–N2–H chain of
the camphor-derived diynes
Ra
1a
1b
1c
Mulliken
Löwdin
Mulliken
Löwdin
Mulliken
Löwdin
H1
O
0.466
ꢁ0.781
0.358
0.379
ꢁ0.483
0.169
0.462
ꢁ0.785
0.376
0.377
ꢁ0.487
0.172
0.465
ꢁ0.785
0.396
0.378
ꢁ0.486
0.172
C1
C2
N
0.012
0.072
0.017
0.075
0.026
0.075
ꢁ0.843
ꢁ0.539
ꢁ0.842
ꢁ0.540
ꢁ0.840
ꢁ0.539
H2
0.434
0.315
0.432
0.314
0.434
0.315
a
1a (R = H), 1b (R = CH3), 1c (R = C6H5).
cyclic isomer is more stable than the linear (DE = 15.5 kcal/mol).

2850
M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
Cu
O
H
H
+
intermediate
H
O
..........
+
C
C
Cu
H
C
C
H
H
C
C
R
R
C
(8)
(9)
R
1
C
2
C
H
C
2
3C
O
C
H
2
O
R
Cu
Cu
(10)
(11a-c)
Fig. 2. Modelling the cleavage of acetylenic substituents from camphor derivatives with neutral copper(I) complexes (8) of propargylic alcohols. Open (10) and ring-closed
(11a–c) structures used in the calculations. R = H: a; R = CH3: b; R = C6H5: c; R = CH2C6H5: d; R = CH2NH2: e.
Table 2
Calculated bond distances (Å), angles (°) and frequencies (m
C„C; cmꢁ1) for cyclic neutral Cu(I) complexes (11)
Cu–O
Cu–C1
Cu–C2
Cu–C3
C„C
C1–C2–C3
C2–C3–R
m(C„C)
11a
11b
11c
11d
11e
1.930
1.925
1.911
1.832
1.859
2.486
2.475
2.498
2.812
2.708
2.054
2.066
2.125
2.816
2.539
2.167
2.235
2.371
3.066
2.614
1.276
1.273
1.265
1.251
1.253
164.0
166.1
169.7
163.6
158.8
157.8
162.5
173.1
162.6
154.7
1951
2110
2158
2253
2218
See Fig. 2 for numbering.
H
3 C
H
H
C
H
C
2
H
H
C
C
C
H
1
H
C
O
CH2
H
C
O
Cu
O
H
Cu
Cu
A, 19.6 Kcal/mol
B, 19.7 Kcal/mol
C, 43.5 Kcal/mol
H
C
CH2
CH
Cu
C
H
O
Cu
C
O
H
H
H
C
C
O
H
H
C
C
H
H
Cu
H
H
E, 4,1 Kcal/mol
F, 0 Kcal/mol
D, 42.6 Kcal/mol
H
H2C
C
C
C
CH2
Cu
O
C
Cu
O
H
H
TS, 58.6 Kcal/mol
G, 8.0 Kcal/mol
Fig. 3. Calculated structures (and energies) of protonated Cu(I) complexes (12, R = H). The (often delocalized) positive charge is not shown.

M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
2851
Protonation at C3 produces the compounds 12A and 12B and
protonation at C2 leads to the compounds 12C and 12G from the
bent isomer. A slightly different starting geometry leads to C–C
bond rupture and the formation of a cationic copper complex
12F where both acetylene and formaldehyde coordinate. This is
the most stable point detected on the potential hypersurface. Pro-
tonation at C-2 in 10a (linear isomer) also leads to C–C bond rup-
ture but to a situation where only formaldehyde coordinates to
copper (12D, Fig. 3). This is of course a computational artifact since
in a real system the acetylene is mobile and can easily adopt a po-
sition where it can coordinate to copper. Albeit at high energy, the
transition state 12TS connects the oxeten 12G with 12D (Fig. 3) as
shown by an IRC (intrinsic reaction path) calculation on this reac-
tion. Although the oxeten is considerably more stable than the
ensemble 12D, it is less stable by 8.0 kcal/mol than the isomeric
ensemble 12F which can easily form from 12D by acetylene diffu-
sion. This reaction path shows therefore a potential reaction mech-
anism for the cleavage of the camphor-derived diynes 5 (or even 4,
if the properties of the ketone and imine groups were similar) to
the ketone 7 (Fig. 1), although we cannot exclude other transition
states (possibly with lower energy) which may lead to the same
cleaved products. The proposed reaction mechanism seems to be
almost an inversion of that suggested for the formation of propar-
gylic amines from terminal alkynes and imines under catalysis by
copper(I) [13].
that not only the substituent R at the triple bonds but also the sul-
fonamide group has an influence on the course of the reaction.
Thus, we decided to go a step forward and use mono-deprotonated
derivatives of N-[(3S, 4R)-3-hydroxy-1,5-hexadiyn-4-yl]methane-
sulfonamide (R = H (17), CH3 (19), Ph (20), CH2Ph (21), CH2–NH2
(22), Fig. 4) instead of propargylic alcohols as models for coordina-
tion to Cu(I).
Both deprotonation at N and O were considered, and copper(I)
complexes were calculated from different starting geometries in
order to find most of the minima on the potential hypersurface.
Since rotation around the C3–C4 bond (Fig. 4, for numbering) is
inhibited in the camphor-derived diynes we mimicked this behav-
iour by fixing the dihedral angle (H–C3–C4–H) to zero. The disad-
vantage of this procedure is that the resulting constrained minima
are not true minima on the unconstrained potential hypersurface,
and therefore the Hessian calculation always gives imaginary fre-
quencies. The calculated stretching frequencies for the C„C bonds
should thus be considered as estimates.
The introduction of the sulfonamide group in the models for
coordination of 1 to copper(I) considerably changes the bonding
situation compared to propargylic alcohols. Now, the copper ion
can coordinate to almost any nucleophilic atom or group (exclud-
ing the nitrogen atom of the sulfonamide when it is not deproto-
nated) allowing a variety of coordination modes with different
stabilities. The principal aim of the calculations was therefore to
Information about bond distances of the isomeric molecules 12
can be found in Table 3, and a more detailed description including
the protonated copper(I) complexes of substituted propargylic
alcohols (with R = Me (13), Ph (14), CH2Ph (15) and CH2NH2 (16))
is given in the Supplementary material. As shown in Table 3, bond-
ing and stability of the protonated copper(I) complexes of these
derivatives generally follows the patterns observed with the neu-
tral complexes 10 and 11, i.e., additional stabilization is achieved
R
R
C
C
C
C
1(2)
2(3)
6(7)
5(6)
H
H
3(4)
by coordination of the phenyl (
to copper.
g
2-coordination) or amino group
C
H
C
O
N
HO
CH3
S
2.2.3. Copper(I) compounds using mono-deprotonated derivatives of
N-[(3S,4R)-3-hydroxy-1,5-hexadiyn-4-yl]methanesulfonamide as
model ligands
O
Fig. 4. Scheme for N-[(3S, 4R)-3-hydroxy-1,5-hexadiyn-4-yl]methanesulfonamide
(17); N-[(4S, 5R)-4-hydroxy-2,6-octadiyn-5-yl]methanesulfonamide (19); N-[(3S,
4R)-3-hydroxy-1,6-diphenyl-1,5-hexadiyn-4-l]methanesulfonamide, (20); and N-
[(4S,5R)-4-hydroxy-1,8-diphenyl-2,6-octadiyn-5-yl]methanesulfonamide (21) used
as models.
Propargylic alcohols were used as models in a first attempt to
rationalize the reaction of di-alkyne species (1) with CuCl. The pro-
cess is not straightforward and the reactivity most probably is not
only controlled by the site of deprotonation. It appeared possible
Table 3
Structures of protonated Cu(I) complexesa of substituted propargylic alcohols HO–C1H2–C2„C3–R
D
E
Cu–O
Cu–C1
Cu–C2
Cu–C3
C2–C3
m
(C„C)
Other
12A
12B
12C
12E
12G
12TS
13A
13B
13C
14A
14B
14C
15A
15B
15C
15X
16A
16B
0
1.891
1.881
1.764
2.096
1.876
1.821
1.816
1.879
1.753
1.806
2.039
1.787
1.814
1.944
1.750
1.831
1.815
1.753
3.072
3.296
2.758
2.703
3.197
2.912
2.981
3.262
2.787
2.874
3.600
2.763
2.965
3.430
2.773
2.681
2.971
2.787
4.271
3.203
2.767
2.108
3.979
4.207
3.903
3.180
2.759
4.167
2.941
2.742
3.921
3.095
2.758
1.898
3.879
2.759
5.390
4.041
1.917
2.211
3.114
4.346
4.935
4.018
1.909
4.460
3.259
1.919
4.958
3.810
1.940
3.048
4.933
1.909
1.248
1.342
1.369
1.259
1.359
1.300
1.290
1.344
1.357
1.320
1.350
1.352
1.294
1.349
1.360
1.446
1.298
1.357
2175
1856
1563
2071
1608
1679
1953
1876
1707
1919
1828
1776
1921
1859
1689
–
Cu–H(O): 2.556
+0.1
+23.9
ꢁ15.5
ꢁ11.6
+39.0
0
ꢁ16.4
ꢁ0.9
0
ꢁ19.2
ꢁ6.2
0
ꢁ52.6
ꢁ34.8
+10.7
0
Cu–CH3: 2.589
Cu–CPh: 2.070, 2.484
Cu–CPh: 2.305
Cu–CPh: 2.727 (subst), 2.518, 2.228, 2.150, 2.413, 2.689
Cu–CPh: 2.287 (subst), 2.131,
C3–CH2: 1.391, Cu–CPh: 1.846
1892
1707
ꢁ47.1
Cu–CH2: 2.589 Cu–N: 2.382
Energies relative to acyclic structure 12A (kcal/mol), bond distances (Å), C„C stretching frequency (cmꢁ1).
a
12: R = H; 13: R = CH3; 14: R = C6H5; 15: R = CH2–C6H5; 16: R = CH2NH2.

2852
M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
Table 4
a crucial step in the cleavage of the acetylide residue from the cam-
phor skeleton. We therefore attempted protonation of the con-
strained complexes 17. Since in these multi-functional molecules
there are many potential sites for protonation, the final position
of the proton after geometry optimisation may be different from
the initial situation and even rearrangements with migration of
the acetylenic groups may occur which, however, were not found
experimentally. For details, see the Supplementary material.
Proceeding from R = H (17) to R = Me (19), R = Ph (20) or
R = CH2Ph (21) and CH2NH2 (22), the influence of the functional
groups on the structure of the copper complexes was studied.
The general behaviour of the compounds with terminal hydrogen
(17) is maintained throughout, particularly the stabilization of
structures by coordination of an oxygen atom of the SO2 group to
copper. Thus, we observe for both the methyl and phenyl substit-
uents that the three structures containing this bonding element
are clearly more stable (11–13 kcal/mol) than the one which does
not. In both the methyl and the phenyl series, it is the simulta-
neous coordination of a triple bond and the oxygen atom of the
SO2 group which leads to the most stable isomers. The close anal-
ogy in the stability ranking of the compounds 17, 19 and 20 shows
that simple alkyl and aryl substituents do not have a significant
influence on the structures of the species and probably also not
on their reactivity.
Calculated data for copper(I) complexes of deprotonated N-[(3S,4R)-3-hydroxy-1,5-
hexadiyn-4-yl]methanesulfonamide
Compound
D
E (kcal/mol)
Site
m )
(C„C) (cmꢁ1
Deprotonated
Cu Coordination
17a
17b
17c
17d
0
9.4
10.4
20.7
N
O
N
O
O(S), C„C
Oꢁ, O(S)
2140, 2008
2168, 2146
2166, 2158
2162, 1963
Nꢁ, OH, O(S)
Oꢁ, CꢂC
identify the most stable species which might give hints to the
structures of the copper complexes obtained experimentally with
the camphor-derived ligands 1, 6 or 7 (Fig. 1).
In these models, the coordination of copper to one of the oxygen
atoms of the SO2 group becomes highly relevant for the stability
(Table 4). Simultaneous coordination of copper to the triple bond
at C4 and to other nucleophilic centres is unflavored by the con-
straint and does not occur. A detailed discussion of bonding and
stability in the substituted derivatives is given in the Supplemen-
tary material.
A typical coordination pattern involves copper bonding to Nꢁ,
OH and one of the oxygen atoms of the SO2 group (17c, see the
Supplementary material for figures). Energetically it occupies a
medium position in the isomeric series. Another common arrange-
ment is the simultaneous coordination to copper of the oxygen an-
ion and the triple bond (at C3, 17d). Lacking the stabilizing effect of
the oxygen atom of the SO2 group this isomer has always the high-
est energy.
A very different situation was found for benzyl-substituted
ligands where the phenyl group can interact with the metal ion.
The two most stable isomers correspond to a situation where
g
2-coordination of copper to the phenyl ring (ortho/meta position)
occurs (see Supplementary material). This stabilizing effect corre-
sponds to ca. 14 kcal/mol. Once more the model accounts for the
relevance of the R group in the process as experimentally observed.
Another special case is the aminomethyl (–CH2NH2) group
which is much more nucleophilic than any of the other R groups
discussed till now, and it is therefore not surprising that coordina-
2.2.4. Protonation of copper(I) complexes of deprotonated N-[(3S,4R)-
3-hydroxy-1,5-hexadiyn-4-yl]methanesulfonamide
From the experiment and the results of the calculations on the
copper complexes of propargylic alcohols, protonation seems to be
OH
NH
R
S
R
O
O
CuCl
(i)
(1)
CuCl
(ii)
H+
H+
OH
O
R
NH
Li
R
N
(iii)
S
S
R
O
O
O
O
CuCl
(
Li
R
(7
6)
H+
CuCl
H+
Li
R
O
N
S
O
(18)
O
Fig. 5. Formation of camphor-derived diynes (1) or camphor-derived monoynes (6) or (7) from 3-oxo-camphorsulfonylimine (18), and its reversal by reaction with copper(I)
chloride.

M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
2853
tion to copper occurs readily leading to the most stable isomers of
4.2. Synthesis
the series (see Supplementary material). However, simultaneous
coordination of one triple bond and the oxygen atom of the SO2
group leads to an isomer of similar energy (the corresponding
structure is also lowest in energy with the methyl and phenyl sub-
stituents). Thus, there is no safe way to predict if the presence of
the aminomethyl group will have an influence on the course of
reactions between copper(I) and the species 1.
The experiments involving CuCl or LiBun were carried out under
inert atmosphere by using vacuum and the Schlenk techniques.
Camphor di-alkyne (R = Ph, 1c; CH2Ph, 1d) species were prepared
by published methods [3,7]. CuCl was synthesised from CuCl2 by
reduction with sodium sulphite [22]. Solvents were purchased
from Fluka or Panreac purified by conventional techniques and dis-
tilled before use.
NMR spectra (1H, 13C, DEPT, HSQC HMBC) were obtained in
CDCl3 or DMSO-d6 using Bruker 300 or 400 MHz Avance II+ Spec-
trometers; TMS (d = 0 ppm) was used as internal reference. The
numbering of the carbon and attached hydrogen atoms in the
NMR spectra of compounds 1, 6, and 7 is shown in Fig. 1. IR spectra
were obtained in a JASCO FTIR 430 spectrometer. FAB mass spectra,
was obtained in a Trio 2000 mass spectrometer using nitrobenzylic
alcohol as matrix.
3. Conclusions
Deprotonated camphor-derived mono- and di-alkynes (L = 6, 7
and1), react with CuCl to form complexes of the type [Cu(L)depr
]
where (L)depr denotes deprotonated (L). Under slightly basic condi-
tions (before removal of unreacted base) it is possible to isolate
these complexes for L = 1d and 7c. In contrast, under slightly acidic
conditions only the protonated species [CuCl(L)] were detected. An
unprecedented cleavage of one alkyne substituent from the ligands
was observed on addition of excess HCl to the complexes to form
the mono-alkynes (6d, 6e, and 7c, respectively) from the di-al-
kynes (1) in high yields. This process can already be started by
adventitious water, e.g., from the solvents used for workup, making
the purification of the complexes difficult. The formation of a small
amount of a copper(II) compound accompanies this bond cleavage.
The oxidation of copper(I) to copper(II) cannot occur in an initial
stage of the reaction since it is well known that CuCl2 reacts with
alkynes 1 to form products of ring annulation and sulfur reduction
[3]. The final product of repeated CC bond rupture is the compound
18 from which ligands 1 were originally obtained (Fig. 5). The mod-
el calculations on copper complexes of propargylic alcohols repre-
sent some features of the activation of the triple bonds towards
cleavage. A transition state was found which connects the cleaved
products with a cyclic precursor. There is a clear relation between
this model and the experimental behaviour of compound 1c. On
the other hand, the calculations on the complexes of the model li-
4.3. Organic species
The species were prepared from 3-oxo-camphorsulfonimide 18
by reaction with the appropriate lithiated alkyne, typically follow-
ing the procedure below:
4.3.1. (1aS3aS,7R)-7-Hydroxy-1a,7-bis[3-(N,N-diethylamino)propyn-
1-yl]-8,8-dimethyl-1,1a,4,5,6,7-hexahydro-3H-3a,6-methano-2,1-
benzisothiazole 2,2-dioxide (1e)
LiBun (2.4 mL, 4.8 mmol of a solution 2 M in hexane) was fur-
ther diluted in 10 mL of Et2O and slowly added (under nitrogen)
to a solution of N,N-diethylpropargylamine (0.65 mL; 4.5 mmol)
in Et2O (30 mL) and the mixture stirred for 3 h upon which solid
3-oxo-camphorsulfonimine (18, Fig. 5) (0.35 g; 1.5 mmol) was
added and the stirring kept for ca. 24 h. Addition of H2O (10 mL)
stopped the reaction. The two phases were separated and the or-
ganic layer dried over MgSO4. The aqueous solution was further ex-
tracted with four portions of CH2Cl2 (4 ꢃ 50 mL) and the organic
phase dried over MgSO4. After filtration the combined organic lay-
ers afforded pale yellow micro crystals of 1e, 1.25 g; 68%. Anal.
Calc. for C24H39N3O3S 1/8CH2Cl2: C, 62.7; H, 8.5; N 9.1; S, 6.9.
gand
N-[(3S,4R)-3-hydroxy-1,5-hexadiyne-4-yl]methanesulfon-
amide represent better the behaviour of the other camphor-
derived ligands (1d, 1e, 6e, 7c). They clearly show the importance
of the coordination of copper to one oxygen atom of the sulfon-
amide group. A successful search for transition states of this model
would certainly help to elucidate the reaction mechanism in more
detail.
Found: C, 62.9; H, 8.8; N, 9.0; S, 7.1.
m
OH = 3444,
m
NH = 3196 cmꢁ1
,
mC„C not observable, mSO = 1298; 1123 cmꢁ1
.
1H NMR (CDCl3):
2
d = 3.51 (2d, 2H, J = 3.0 Hz, CH2NEt2), 3.46 (s, 2H, CH2NEt2), 3.25
(s, 2H, H-8), 2.56 (quintet, J = 6.9 Hz, 8H, NCH2CH3), 2.25–1.60
(m, 4H, CH2, H-5,6), 2.03 (d, 1H, J = 4.5 Hz, H-4), 1.43, 0.98 (s, 6H,
CH3, H-9,10), 1.05, 1.06 (2t, 12H, J = 7.0 Hz, NCH2CH3) ppm; 13C
NMR (CDCl3): d = 85.5, 85.0, 83.4, 83.0 (C„C), 81.5 (C-3), 72.3 (C-
2), 62.3 (C-1), 56.6 (C-4), 51.3 (C-8), 48.8 (C-7), 47.3, 47.2 (CH2CH3),
41.2, 41.1 (CH2N), 28.3, 23.8 (C5,6), 24.1, 23.6 (C9,10), 12.7, 12.4
(CH2CH3) ppm.
4. Experimental
4.1. Computational methods
All calculation were performed with Pc Gamess, version 7.1
[14], which is based on Gamess (US) [15,16]. For the camphor-de-
rived diynes, 6-31G* was used as basis set at the HF level. The
inclusion of diffuse basis function for the anions did not change
the relative energies significantly. We employed the ECP basis set
SBKJC [17–19] for all atoms in the calculations of the copper-con-
taining model systems, in combination with the DFT functional
PBE0 [20]. For all copper complexes of the model compounds con-
taining the sulfonamide group, we constrained the dihedral angle
H–C(O)–C(N)–H to 0° in accord with the situation in the camphor
derivatives 1. Since in these cases the optimized geometries do
not correspond to minima on the unconstrained potential hyper-
surface, imaginary frequencies were observed in the Hessian calcu-
lations. The IR frequencies quoted were calculated from the
Hessian matrix with a scaling factor of 0.975 which was derived
from a calculation of 1,2-dicyanobenzene by comparison with
the experimental value of the C„N stretching frequency in a KBr
pellet. For visualization and analysis of the results, the program
MOLDEN [21] was used.
4.3.2. (1aS,3aS)-8,8-Dimethyl-1a-(2-phenylethyn-1-yl)-1,1a,4,5,6,7-
hexahydro-3H-3a,6-methano-7-oxo-2,1-benzisothiazole 2,2-dioxide
(7c)
LiBun (5.2 mL of a 2 M solution in hexane, 10.4 mmol) was di-
luted in Et2O (70 mL) and slowly added (under nitrogen) to a solu-
tion of ethynylbenzene (1 mL, 10.0 mmol). The mixture was stirred
overnight affording a deep red solution that was slowly added to a
solution of 3-oxo-camphorsulfonimide (18, Fig. 5) (2.16 g;
9.5 mmol) in Et2O (60 mL) and stirred for 1 day. The reaction was
stopped by addition of H2O. Separation of the organic and aqueous
phases followed by extraction of the aqueous layer with CH2Cl2
(3 ꢃ 50 mL) and drying over MgSO4 afforded 7c, 1.6 g, 51%. Anal.
Calc. for C18H19NO3S ꢀ H2O: C, 62.2; H, 6.0; N, 4.0; S, 9.2. Found:
C, 62.4; H, 5.6; N, 4.3; S, 9.5.
CO = 1762 cmꢁ1 mSO = 1314; 1159 cmꢁ1
d = 7.4–7.2 (m, 5H, C6H5), 4.88 (s, 1H, NH), 3.44 (d, 2H, J = 4.4 Hz,
m
NH = 3237;
.
mC„C = 2222,
m
,
1H NMR (CDCl3):
2

2854
M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
H-8), 2.5-1.9 (m, 5H, H-4, H-5,6), 1.29; 1.10 (s, 6H, CH3, H-
9,10) ppm; 13C NMR (CDCl3): d = 205.2 (C-3), 132.0, 129.2, 128.3
(Ph), 121.3 (Cipso-Ph), 89.8, 84.0 (C„C), 65.3 (C-2), 57.2 (C-1),
58.4 (C-4), 49.6 (C-8), 45.1 (C-7), 29.1, 21.7 (C5,6), 22.6, 19.7
(C9,10).
4.4.2. [CuCl(1c)]ꢀ2H2O
NaNH2 (0.023 g, 0.59 mmol) was added to a solution of 1c
(0.25 g, 0.58 mmol) in CH2Cl2 (60 mL) and the mixture stirred for
1/2 h. Addition of CuCl (0.057 g, 0.58 mmol) and stirring overnight
afforded a greenish suspension that was filtered to separate traces
of a non-identified bright yellow precipitate. By partial evaporation
of the solvent and addition of Et2O a green precipitate forms that
upon filtration afforded the complex (M/z + 23 = 588): 0.10 g,
0.18 mmol. Yield, 31%. Anal. Calc. for CuCl(C26H25NO3S)ꢀ2H2O: C,
55.1; H, 5.1; N, 2.5; S, 5.7. Found: C, 55.0; H, 4.2; N, 2.4; S, 5.7.
4.3.3. (1aS,3aS)-1a-[3-(N,N-Diethylamino)propyn-1-yl]-8,8-dimethyl-
1,1a,4,5,6,7-hexahydro-3H-3a,6-methano-7-oxo-2,1-benzisothiazole
2,2-dioxide (7e)
A procedure similar to that for 7c led to pale yellow micro crys-
tals of 7e, yield: ca. <10%. Anal. Calc. for C17H26N2O3S: C, 60.3; H,
7.7; N, 8.3; S, 9.5. Found: C, 60.4; H, 8.0; N, 8.1; S, 9.3.
m
CꢂC = 2215 cmꢁ1
,
mSO = 1102 cmꢁ1
.
2
CO = 1762 cmꢁ1
,
mSO = 1308; 1141 cmꢁ1
.
1H NMR (CDCl3):
4.4.3. [CuCl(1e)]ꢀH2O
m
2
NaNH2 (0.011 g, 0.28 mmol) was added to a solution of 1e
(0.12 g, 0.27 mmol) in CH2Cl2 (35 mL) and the mixture stirred for
1/2 h. Then CuCl (0.026 g, 0.26 mmol) was added and the mixture
stirred overnight. Upon filtration the title compound was obtained:
d = 3.50 (s, 2H, CH2NEt2), 3.33 (s, 2H, H-8), 2.50 (q, 4H, J = 7.2 Hz,
NCH2CH3), 2.40 (d, 1H, J = 5.1 Hz, H-4), 1.7–2.4 (m, 4H, CH2, H-
5,6), 1.23; 1.05 (s, 6H, CH3, H-9,10), 0.99–1.3 (m, 6H, NCH2CH3)
ppm; 13C NMR (CDCl3): d = 205.4 (C-3), 85.6, 80.4 (C„C), 65.0 (C-
2), 56.8 (C-1), 58.4 (C-4), 49.6 (C-8), 47.4 (CH2NEt2), 45.0 (C-7),
40.8 (CH2NEt2), 29.1, 21.7 (C5,6), 22.6, 19.7 (C9,10), 12.6
(NCH2CH3) ppm.
0.046 g,
0.077 mmol,
30%
yield.
Anal.
Calc.
for
CuCl(C24H36N3O3S) ꢀ H2O ꢀ 1/10CH2Cl2: C, 50.7; H, 6.7; N, 7.3; S,
5.6. Found: C, 50.7; H, 6.7; N, 6.9; S, 5.5. mSO = 1145; 1104 cmꢁ1
.
2
4.4.4. [Cu(7c)]
4.3.4. (3aS,7R)-7-[3-(N,N-Diethylamino)propyn-1-yl]-7-hydroxy-8,8-
dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,1-benzisothiazole
2,2-dioxide (6e)
NaNH2 (0.027 g, 0.68 mmol) was added to a solution of 7c
(0.20 g, 0.61 mmol) in CH2Cl2 (60 mL) and CuCl (0.065 g,
0.66 mmol) added. The mixture was stirred for 3 days. Upon filtra-
tion to separate unreacted CuCl, evaporation of the solvent and
washing of the solid residue with Et2O (ca. 50 mL) the title com-
pound was obtained: 0.085 g, 0.18 mmol, 30% yield. Anal. Calc.
for Cu(C18H18NO3S)n1/4CH2Cl2: C, 52.8; H, 4.5; N, 3.4; S, 7.7.
A similar procedure to that used for 7c led to 6e in 49% yield.
Anal. Calc. for C17H26N2O3S: C, 60.4; H, 7.7; N, 8.3; S, 9.5. Found:
C, 60.9; H, 8.4; N, 8.2; S, 9.1.
mOH = 3410, m ,
CN = 1654 cmꢁ1
mSO = 1342; 1156 cmꢁ1. 1H NMR (CDCl3): d = 3.51 (s, 2H, CH2NEt2),
2
3.21, 3.09 (2d, 2H, J = 13.5 Hz, H-8), 2.52 (quartet, 4H, J = 7.0 Hz,
NCH2CH3), 2.22 (d, 1H, J = 3.6 Hz, H-4), 1.7–2.2 (m, CH2, H-5,6),
1.07; 1.04 (s, 6H, CH3, H-9,10), 1.08–1.02 (m, 6H, NCH2CH3) ppm;
13C NMR (CDCl3): d = 194.4 (C-2), 84.5, 82.5 (C„C), 72.8 (C-3),
64.1 (C-1), 55.8 (C-4), 50.1 (C-8), 47.1, 47.2 (NCH2CH3), 47.4 (C-
7), 41.1 (CH2NEt2), 28.0, 23.9 (C5,6), 21.1, 21.0 (C9,10), 12.2
(NCH2CH3) ppm.
Camphor-derivatives 7c, 6d, 6e were obtained, respectively,
from [CuCl(1c)], [CuCl(1d)], [CuCl(1e)] by addition of concentrated
HCl (2 mL) to the suspension of the complex (0.10 g) in of CH2Cl2
(10 mL). The aqueous and organic layers were separated and the
last one dried over MgSO4 and filtered. The organic species 7c,
6d, 6e were obtained by solvent evaporation. Compound (23)
was obtained in a similar way from [CuCl(7c)] or [CuCl(6e)].
Found: C, 52.8; H, 4.4; N, 3.7; S, 7.7. mC„C = 2217, m ,
CO = 1756 cmꢁ1
mSO = multiple signals in the range 1315–1102 cmꢁ1
.
2
4.4.5. [CuCl(7c)]n2H2O
NaNH2 (0.024 g, 0.61 mmol) was added to a solution of 7c
(0.20 g, 0.61 mmol) in CH2Cl2 (55 mL) then CuCl (0.133 g,
1.34 mmol) was added and the mixture stirred for 2 weeks. Upon
filtration of a yellow impurity the title compound was obtained:
0.100 g,
0.23 mmol,
18%
yield.
Anal.
Calc.
for
CuCl(C18H19NO3S)ꢀ2H2O ꢀ 1/2CH2Cl2: C, 43.8; H, 4.7; N, 2.7; S, 6.3.
Found: C, 43.4; H, 3.5; N, 2.8; S, 6.5.
m
C„C = 2212,
m
CO = 1755 cmꢁ1
,
mSO = 1103 cmꢁ1
.
2
4.4.6. [CuCl(6e)]ꢀ2H2O
NaNH2 (0.008 g, 0.21 mmol) was added to a solution of 6e
(0.073 g, 0.22 mmol) in CH2Cl2 (25 mL), CuCl (0.022 g, 0.22 mmol)
and the mixture stirred overnight. The precipitate was filtered
affording the title compound (0.032 g, 0.068 mmol, 31% yield).
Anal. Calc. for CuCl(C17H26N2O3S) ꢀ 2H2O: C, 43.1; H, 6.3; N, 5.9;
4.4. Complexes
[Cu(L)depr] (L = 1d; 7c) or [CuClL]nxH2O (L = 1c; 1d; 1e; 7c; 6e)
were prepared from the corresponding camphor-derived deproto-
nated ligand by reaction with CuCl. A typical procedure is as
follows:
S, 5.9. Found: C, 43.5; H, 5.5; N, 5.9; S, 5.6.
mC„C = 2077,
m
CN = 1634 cmꢁ1
,
mSO = 1162 cmꢁ1
.
2
4.4.1. [Cu(1d)depr
]
Acknowledgement
NaNH2 (0.020 g, 0.51 mmol) was added to a solution of 1d
(0.23 g, 0.50 mmol) in CH2Cl2 (20 mL) and the solution was stirred
for 1/2 h. Then, CuCl (0.050 g, 0.51 mmol) was added and the mix-
ture stirred overnight. The suspension was filtered and n-hexane
added to the yellow solution. The yellowish precipitate was filtered
affording the title complex, ca. 15% yield. Anal. Calc. for Cu(C28H28-
NO3S) ꢀ H2O: C, 62.3; H, 5.6; N, 2.6; S, 5.9. Found: C, 62.7; H, 6.5; N,
Financial support by FCT-Fundação para a Ciência e Tecnologia
(Project PPCDT 58119/QUI/2004).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2008.06.004.
2.7; S, 6.8.
nals in the range 1334–1118 cmꢁ1
m , m , mSO = multiple sig-
OH = 3425 cmꢁ1 C„C = 2231 cmꢁ1
2
.
By using a larger excess of solvent (3ꢃ) under prolonged stirring
(3 days) a different compound is isolated [CuCl(1d)]. Yield, 31%.
Anal. Calc. for CuCl(C28H29NO3S) ꢀ 2H2Oꢀ1/2CH2Cl2: C, 53.7; H,
5.3; N, 2.2; S, 5.0. Found: C, 53.7; H, 4.6; N, 2.4; S, 5.0.
References
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m
C„C = 2231 cmꢁ1
,
mSO = 1109 cmꢁ1
.
2

M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 693 (2008) 2847–2855
2855
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