The (η6-benzene)Cr(CO)3-substituted propargyl cation: Spectroscopic characterization and reactions of an ambident electrophile

Article abstract of DOI:10.1021/om980257u

An (arene)Cr(CO)₃-stabilized propargyl cation can be easily generated upon ionization of the propargyl acetate Cr(CO)₃(η⁶-C₆H₅)CH(OC(O)CH ₃)C≡CPh with boron trifluoride. The structure inves

Full text of DOI:10.1021/om980257u

Organometallics 1998, 17, 3609-3614
3609
Th e (η6-ben zen e)Cr (CO)3-Su bstitu ted P r op a r gyl Ca tion :
Sp ectr oscop ic Ch a r a cter iza tion a n d Rea ction s of a n
Am bid en t Electr op h ile†
Thomas J . J . Mu¨ller* and Astrid Netz
Institut fu¨r Organische Chemie, Ludwig-Maximilians-Universita¨t Mu¨nchen, Karlstrasse 23,
D-80333 Mu¨nchen, Germany
Received April 3, 1998
An (arene)Cr(CO)3-stabilized propargyl cation can be easily generated upon ionization of
the propargyl acetate Cr(CO)3(η6-C6H5)CH(OC(O)CH3)CtCPh with boron trifluoride. The
structure investigation of this π-complex stabilized ambident electrophile by NMR spec-
troscopy and extended Hu¨ckel calculations reveals that the charge density in the propargylic
position is higher than in the allenylic position. The rapid formation of the cation can be
followed by measuring the UV/vis kinetics for the ionization of the acetate. The cationic
species reacts with alcohols to give exclusively propargyl ethers Cr(CO)3(η6-C6H5)CH(OR)Ct
CPh and with thiols to give regioselectively allenyl thioethers Cr(CO)3(η6-C6H5)CHdCdC(SR)-
Ph.
In tr od u ction
protection of the alkyne can be reacted with a number
of nucleophiles giving rise to functionalized propargylic
derivatives, interesting building blocks in complex
natural product syntheses.5 Surprisingly, no methodol-
ogy taking advantage of the delocalization of benzylic
charges by a conjugated chain has been investigated so
far. In particular, upon ionization, propargylic systems
form ambident propargylium-allenylium ions6 that can
be interesting intermediates for more sophisticated
arene side chain functionalizations via aryl propargyl
or aryl allenyl derivatives. As part of our program
initiated to synthesize and to study (arene)Cr(CO)3
complexes bearing π-substituents7 and to probe their
synthetic potential8 we are particularly interested in
conjugated cationic intermediates and their synthetic
utility. Here we report on the spectroscopic character-
ization of a (benzene)Cr(CO)3-stabilized propargylium
ion and first nucleophilic trapping reactions.
The stabilization of carbenium ions by the aid of
transition metal π-complexes1 has not only aroused
considerable theoretical interest but has also had an
increasing impact on the application in organic synthe-
ses. Taking into account an ideal overlap of filled
d-orbitals of the metal fragment, like (arene)Cr(CO)3,
(alkyne)Co2(CO)6, or ferrocene, and the vacant p-orbital
of the carbenium ion in the R-position with the proper
symmetry of the interacting wave functions, a rate-
increasing anchimeric assistance of nucleophilic sub-
stitutions can be easily explained.2 Thus, taking ad-
vantage of the R-activation, Cr(CO)3-complexed benzyl
derivatives can be ionized, spectroscopically studied,2a,b,g,h
and even isolated.2c Therefore, a couple of syntheses
have been based upon the stabilization of benzylic
cations.2c,3 In the extensive work of Nicholas the
activation of the propargylic position was achieved by
attaching a dicobalt hexacarbonyl cluster to a triple
bond.4 The generated propargylic cation stabilized by
the adjacent cobalt(0) fragment under simultanous
Resu lts a n d Discu ssion
Syn th eses. The most efficient way to generate a
propargylic cation starts from a propargylic derivative
with an appropriate leaving group. Thus, nucleophilic
addition of phenyl acetylide (2) to (η6-benzaldehyde)Cr-
† This contribution is dedicated to Prof. Dr. Heinrich No¨th on the
occasion of his 70th birthday.
(1) (a) Haynes, L.; Pettit, R. In Carbonium Ions; Olah, G. A.,
Schleyer, P. R., Eds.; Wiley: New York, 1975; Vol. 5. (b) Watts, W. E.
In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F.
G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 8, Chapter
59, p 1051.
(2) (a) Wells, D. K.; Trahanovsky, W. S. J . Am. Chem. Soc. 1969,
91, 5870. (b) Olah, G. A.; Yu, S. H. J . Org. Chem. 1976, 41, 1694. (e)
Seyferth, D.; Merola, S.; Eschbach, C. S. J . Am. Chem. Soc. 1978, 100,
4124. (d) Clack, D. W.; Kane-Maguire, L. A. P. J . Organomet. Chem.
1978, 145, 201. (e) Solladie´-Cavallo, A. Polyhedron 1985, 4, 910. (f)
J aouen, G. Pure Appl. Chem. 1986, 58, 597. (g) Rausch, M. D.;
Kowalski, D. J .; Mintz, E. A. J . Organomet. Chem. 1988, 342, 201. (h)
Downton, P. A.; Sayer, B. G.; McGlinchey, M. J . Organometallics 1992,
11, 3281.
(3) (a) For stabilization of positive charge in the benzylic positions,
see e.g.: Davies, S. G.; Donohoe, T. J . Synlett 1993, 323. (b) For side
chain activation, see e.g.: Davies, S. G.; McCarthy, T. D. In Compre-
hensive Organometallic Chemistry II; Abel, E. W., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon: London, 1995; Vol. 12, p 1039. (c)
Corey, E. J .; Helal, C. J . Tetrahedron Lett. 1996, 37, 4837.
(4) For excellent reviews, see e.g.: (a) Nicholas, K. M. Acc. Chem.
Res. 1987, 20, 207. (b) Melikyan, G. G.; Nicholas, K. M. In Modern
Acetylene Chemistry; Stang, P. J ., Diederich, F., Eds.; VCH: Weinheim,
Germany, 1995; p 118. (c) Caffyn, A. J . M.; Nicholas, K. M. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, p
685.
(5) (a) Nicolaou, K. C.; Dai, W. M. Angew. Chem., Int. Ed. Engl. 1991,
30, 1387. (b) Magnus, P.; Pitterna, T. J . Chem. Soc., Chem. Commun.
1991, 541. (c) Magnus, P. Tetrahedron 1994, 50, 1397.
(6) (a) Murray, M. In Methoden zur Herstellung und Umwandlung
von Allenen bzw. Kumulenen; Houben-Weyl, Eds.; 1977; Vol. 5/2a, p
991. (b) Mayr, H.; Ba¨uml, E.; Tetrahedron Lett. 1983, 24, 357. (c)
Ba¨uml, E.; Mayr, H. Chem. Ber. 1985, 118, 694. (d) Dau-Schmidt, J .-
P.; Mayr, H. Chem. Ber. 1994, 127, 205.
(7) (a) Mu¨ller, T. J . J .; Lindner, H. J . Chem. Ber. 1996, 129, 607. (b)
Mu¨ller, T. J . J . Tetrahedron Lett. 1997, 38, 1025. (c) Mu¨ller, T. J . J .;
Ansorge, M. Chem. Ber./ Recl. 1997, 130, 1135.
(8) Mu¨ller, T. J . J .; Ansorge, M. Tetrahedron 1998, 54, 1457.
S0276-7333(98)00257-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/17/1998

3610 Organometallics, Vol. 17, No. 16, 1998
Mu¨ller and Netz
Sch em e 1
Sch em e 3
Sch em e 2
(Figure 1). An unambiguous assignment of the quater-
nary resonances of the alkyne carbon atoms of the
acetate 3 was based upon a thorough inspection of a
selective proton-decoupled spectrum. The major differ-
ences in the spectra (Table 1) can be detected in the
region of the CO-ligand resonance (Figure 2) and in the
region of the complexed arene signals.
As expected, upon ionization, the rotation around the
Cipso-CR bond is restricted due to the back-bonding of
the chromium carbonyl tripod to the benzylic carbenium
ion (Chart 1). According to molecular orbital calcula-
tions on a (η6-phenyl)Cr(CO)3-substituted propargyl
cation at the extended Hu¨ckel level11 the bending of the
propargyl fragment by an angle of 10° (22° in the case
of the Cr(CO)3-complexed benzyl cation)2h toward the
chromium carbonyl tripod results in a gain of ≈1.1 kcal/
mol (Figure 3). In particular, the principal stabilizing
interaction allowing the delocalization of the positive
charge onto the Cr(CO)3 fragment mainly stems from
the in-phase combination of the vacant pz orbital of the
(CO)3 (1)9 at -78 °C in THF followed by the addition of
acetic anhydride gives rise to the formation of a (ben-
zene)Cr(CO)3-substituted acetate 3 in excellent yields
(Scheme 1).
First experiments showed that the ionization of 3
was smoothly carried out with boron trifluoride etherate
in dichloromethane at -78 °C. Remarkably, the color
of a solution of 3 changes immediately from light yellow
to deep purple red upon the addition of the Lewis acid
indicating the formation of a new species, a (benzene)-
Cr(CO)3-stabilized propargylium ion 4 (see Scheme 2).
After a reaction time of 50 min the trapping alcohol or
thiol was added, pure or dissolved in dichloromethane,
to the solution of 4 resulting in a rapid color change from
deep purple red to yellow. After workup the isolated
products (Scheme 3) of the trapping alcohols were
exclusively propargyl ethers 5 and those of the thiols
were solely allenyl thioethers 6 as indicated by the
characteristic appearance of the central allenyl carbon
resonances in the 13C NMR spectra between δ ) 202
and 208.10 Although allenes are the expected thermo-
dynamic products,6 no contamination of either allenes
(in the case of 5) or propargyl derivatives (in the case
of 6) can be detected. Thus, the nucleophilic attack of
alcohols or thiols at low temperatures can be regarded
as kinetically controlled trapping reactions. Interest-
ingly, in the mass spectra of all propargylic and allenylic
derivatives 3, 5, and 6 an intense fragment at m/z )
191 can be detected. This stable intermediate can be
assigned to the 1,3-diphenylpropargyl cation, i.e., the
hydrocarbon ligand of 4.
2
2
propargylic carbon atom with the filled dx -y orbital on
the chromium atom (Figure 4). This orbital (HOMO-2)
is gradually stabilized as the propargyl moiety bends
down toward the tripod (Figure 5). The corresponding
out-of-phase combination of the nonbonding propargylic
2
2
πz and the chromium dx -y orbitals is the LUMO (Figure
4), and expectedly, its energy gradually increases as
shown in the Walsh diagram (Figure 5). The highest
occupied molecular orbitals (HOMO and HOMO-1)
2
display predominantly chromium 3d (dz and dxy) and
carbonyl π* character and are only affected to a minor
extent by the bending of the propargyl fragment. In
turn, this back-bonding lowers the pseudo-C3v symmetry
of the carbonyl ligands now giving rise to a splitting to
3 CO resonances (Figure 2).
In comparison to the CO signal at δ ) 229.4 the
resonances at δ ) 227.7 and 227.6 experience a consid-
erably larger ionization shift. Therefore, they can be
assigned to the CO ligands directly aligned with the
ortho-carbon atoms in agreement with the charge
distribution in arene complexes with electron-withdraw-
ing substituents,2h,12 i.e., the propargylium substituent.
13C NMR Sp ectr a of 3 a n d 4. The spectra (proton-
decoupled and DEPT) of the propargylic acetate 3 and
the propargylium ion 4 were both recorded at -70 °C
(11) Quantum CAChe 3.0 Program, Oxford Molecular Group, 1997.
(12) (a) Carter, O. L.; McPhail, A. T.; Sim, G. A. J . Chem. Soc. A
1967, 228. (b) Albright, T. A.; Hofmann, P.; Hoffmann, R. J . Am. Chem.
Soc. 1977, 99, 7546. (c) McGlinchey, M. J . Adv. Organomet. Chem.
1992, 34, 285.
(9) Davies, S. G.; Donohoe, T. J .; Williams, J . M. J . Pure Appl. Chem.
1992, 64, 379.
(10) Kalinowski, H.-O.; Berger, S.; Braun, S. 13C NMR Spectroskopie;
Georg Thieme Verlag: Stuttgart, New York, 1984; p 273.

(η6-benzene)Cr(CO)3-Substituted Propargyl Cation
Organometallics, Vol. 17, No. 16, 1998 3611
F igu r e 1. 13C NMR spectra (-70 °C) of 3 (top) and of 4 (bottom).
Ta ble 1. Assign m en t a n d Ion iza tion Sh ifts of
Selected 13C NMR Sign a ls (CD2Cl2, 100 MHz)
acetate 3
cation 4
ionization shift
carbonyl
231.92
229.4
227.7
227.6
183.5
132.9
132.2
128.9
119.8
89.7
112.4
103.7
105.8
100.5
98.3
-2.5
-4.2
-4.3
14.2
1.7
ester carbonyl
ortho-phenyl
para-phenyl
meta-phenyl
ipso-phenyl
ipso-η6-phenyl
ortho-η6-phenyl
para-η6-phenyl
ortho-η6-phenyl
meta-η6-phenyl
meta-η6-phenyl
Cγ
169.27
131.23
128.79
127.96
120.38
103.98
94.93
94.14
93.23
90.66
90.47
86.55
82.27
63.69
20.54
3.4
1.0
-0.6
-14.3
17.5
9.56
12.6
9.84
7.8
32.1
27.8
64.3
0.4
118.7
110.1
128.0
20.9
Câ
CR
CH3
All complexed arene carbon signals experience a
larger ionization shift than the uncomplexed phenyl
carbon resonances at the γ-terminus (Table 1) indicating
that the complexed aromatic ring system participates
to a larger extent in the charge delocalization. The
charge distribution as reflected by the ionization shifts
also supports the view that in benzyl cations the ipso-
carbon atom bears negative charge whereas the ortho-,
meta-, and para-positions display less electron density.
Additionally, the positive charge is also delocalized by
the conjugating π-bridge. All three carbon resonances
of the propargyl system are shifted to downfield: CR
appears at δ ) 128.0 (∆δ ) 64.3), Câ at δ ) 110.1 (∆δ )
27.8), and Cγ at δ ) 118.7 (∆δ ) 32.1). Taking into
account the resonance stabilization of a cation by several
canonical structures, a major contribution of one reso-
F igu r e 2. CO resonances of 3 (bottom) and 4 (top).
nance hybride can be estimated by applying a simple
lever rule model.13 The complexed benzylic cation 7 was
considered as an equivalent for the CR-localized carbe-
nium ion 4A, and the complexed styrene 8 serves as a
model for an allenylium structure 4B where the R-car-
bon does not bear the positive charge (Chart 2). The
R-carbon resonances (4, δ ) 128.0; 7,14 δ ) 126.6; 8,15
) 133.6) are substituted in eq 1 to give an 80%
δ
(13) Olah, G. A.; Spear, R. J .; Westerman, P. W.; Denis, J .-M. J .
Am. Chem. Soc. 1974, 96, 5855.
(14) Acampora, M.; Ceccon, A.; Dal Farra, M.; Giacometti, G.;
Rigatti, G. J . Chem. Soc., Perkin Trans. 2 1977, 483.
(15) Bitterwolf, T. E.; Dai, X. J . Organomet. Chem. 1992, 440, 103.

3612 Organometallics, Vol. 17, No. 16, 1998
Mu¨ller and Netz
Ch a r t 1
romethane solution of 3 at -65 °C a color change from
light yellow to deep purple red can be monitored by
following the characteristic appearance of a long wave-
length absorption band with a maximum at 485 nm
(Figure 6). The ionization kinetics were determined by
measuring the time-dependent increase of the long
wavelength absorption at a wavelength of 485 nm (Table
2). After an induction period the formation of 4 can be
described between 3.4 and 7.4 min (after addition of the
Lewis acid) by a pseudo-first-order rate law. The
evaluation gives for a conversion of 36% and an initial
BF3OEt2 concentration of 3.2 × 10-3 mol L-1 a rate
constant kh ) 2.95 ( 0.33 L mol-1 s-1 and half-life time
τ1/2 ) 73.5 s. In the initial nonlinear phase rapid
preequilibria forming Lewis acid adducts from BF3 and
3 can be assumed which, in turn, decompose to give the
title compound 4. In an ionization interval between 9.4
and 12.3 min ([3]0 ) 1.6 × 10-5 mol L-1) the reaction
converges toward complete formation of 4.17
According to the UV/vis kinetical measurements the
cationic species 4 is stable at -70 °C for several hours
but readily decomposes on an increase of the tempera-
ture over -30 °C. The ambident cation 4 gains its
stability to the largest extent by an intense back-
bonding of the chromium carbonyl tripod. In compari-
son, the free ligand 918 (Chart 3) does not ionize under
comparable circumstances, i.e., in particular, in the
presence of the mild Lewis acid boron trifluoride.
Con clu sion
F igu r e 3.
NMR and UV/vis studies have shown that chromium
carbonyl complexation can be applied to stabilize pro-
pargyl cations, an interesting class of ambident elec-
trophiles. This represents an extension of a well-
established feature of chromium arene complexes to
conjugated side chains. (Arene)Cr(CO)3-substituted
propargyl cations such as 4 are stable intermediates
that allow a facile access to (arene)Cr(CO)3-substituted
propargyl or allenyl derivatives such as 5 or 6. This
possibility implies the application to diastereoselective
transformations with planar-chiral arene complexes
with propargyl acetate substituents. Further studies
directed to screen the scope, the regio- and the diaste-
reoselectivity of the nucleophilic trapping reactions as
a novel access to side chain functionalizations are
currently underway.
contribution of the resonance structure 4A to the
stabilization of the cation 4.
relative contribution of 4A )
δ(8,CR) - δ(4,CR)
δ(8,CR) - δ(7,CR)
‚100% )
133.6 - 128.0
‚100% ) 80% (1)
133.6 - 126.6
The high positive charge density in the propargylic
position is also reflected by the fact that the LUMO
coefficient at the propargyl position (according to ex-
tended Hu¨ckel calculations11) is higher than in the
allenyl position (Figure 3). Thus, considering the
principle of hard and soft acids and bases16 (HSAB),
hard nucleophiles such as alcohols should react in a
charge and orbital controlled fashion at the propargylic
position whereas softer nucleophiles such as thiols tend
to attack the less charged γ- or allenylic position. The
product analyses of the nucleophilic trapping experi-
ments with the ambident electrophile 4 just support this
qualitative rationale.
UV/Vis Sp ectr a a n d Ion iza tion Kin etics. The
successful NMR studies prompted us to investigate the
electronic structure of the cationic intermediate 4.
Furthermore, the study of the ionization by UV/vis
spectroscopy could also facilitate the following synthetic
work. Upon addition of an excess (16-, 20-, or 40-fold)
of a boron trifluoride etherate solution to a dichlo-
Exp er im en ta l Section
All reactions involving tricarbonylchromium complexes were
carried out in flame-dried Schlenk flasks under nitrogen by
using septum and syringe techniques. Solvents were dried and
distilled according to standard procedures.19 Column chroma-
tography: silica gel 60 (0.063-0.2 mm/70-230 mesh, Firma
Merck). TLC: silica gel plates (60 F254 Merck, Darmstadt,
Germany). Melting points (uncorrected values): Reichert-
J ung Thermovar. The benzaldehyde complex 1 was prepared
from the benzaldehyde dimethyl acetal complex according to
the standard complexation procedure.20 The trapping nucleo-
philes were purchased from Merck, Aldrich, or Fluka and used
(17) Mayr, H.; Schneider, R.; Schade, C.; Bartl, J .; Bederke, R. J .
Am. Chem. Soc. 1990, 112, 4446.
(18) Brandsma, L. in Preparative Acetylenic Chemistry; Elsevier:
Amsterdam, 1992; p 422.
(16) (a) Fleming, I. In Grenzorbitale und Reaktionen organischer
Verbindungen, VCH: Weinheim, Germany, 1990; p 41. (b) Ho, T.
Tetrahedron 1985, 41, 1.
(19) Various Editors. Organikum, 13th ed.; VEB Deutscher Verlag
der Wissenschaften: Berlin, Germany, 1993.
(20) Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1990, 28, 136.

(η6-benzene)Cr(CO)3-Substituted Propargyl Cation
Organometallics, Vol. 17, No. 16, 1998 3613
2
2
F igu r e 4. In-phase (HOMO-2, left) and out-of-phase (LUMO, right) combination of the chromium dx -y and the propargylic
pz/πz orbitals.
F igu r e 6. UV/vis spectra of 3 (λ max at 325 nm) and 4 (λmax
at 485 nm).
Ta ble 2. Kin etics of th e Ion iza tion of Aceta te 3
w ith Bor on Tr iflu or id e Eth er a te in
F igu r e 5.
Dich lor om eth a n e a t -65 °Ca
104[3]0,
103[BF3OEt2]0,
k,
Ch a r t 2
no.
mol L-1
mol L-1
L mol-1 s-1
1
2
3
4
5
1.60
1.60
1.59
1.58
1.59
2.61
2.61
3.16
3.15
6.25
3.13
2.58
2.66
3.36
3.00
a
The kinetics of each measurement were evaluated according
to a pseudo-first-order rate law to give the average rate constant
kh ) 2.95 ( 0.33 L mol-1 s-1; thus with [BF3OEt2]0 ) 3.2 × 10-3
mol L-1 the half-lifetime can be calculated to τ1/2
ln 2/(kh[BF3OEt2]0) ) 73.5 s.
)
Ch a r t 3
without further purification. 1H and 13C spectra: Bruker ARX
300, Varian VXR 400S, [D6]DMSO. IR: Perkin-Elmer FT-IR
spectrometer 1000. The samples were pressed into KBr
pellets. UV/vis: Perkin-Elmer Models Lambda 16, J &M
TIDAS (transputer integrated diode array spectrometer) with
a Hellma low-temperature quarz probe. MS: Finnigan MAT
90 and MAT 95 Q. Elemental analyses were carried out in
the Microanalytical Laboratory of the Institut fu¨r Organische
Chemie, Ludwig-Maximilians-Universita¨t Mu¨nchen.
Syn th esis of th e Aceta te 3. To a degassed solution of 0.91
mL (8.29 mmol) of phenylacetylene in 15 mL of THF, cooled
to -78 °C, was added dropwise 5.68 mL (9.09 mmol) of a 1.6
M solution of n-butyllithium in hexanes. The turbid yellow
suspension was stirred at -78 °C for 5 min and was then
allowed to warm to room temperature. After being stirred for
80 min at room temperature, the clear yellow solution was
cooled again to -78 °C. To the suspension a solution of 2.00
g (8.26 mmol) of benzaldehyde complex in 15 mL of THF was
added dropwise. The reaction mixture turned to light orange
and was stirred at that temperature for 2 h. Then a solution
of 1.8 mL (19 mmol) of acetic anhydride in 3 mL of THF was
added dropwise to the solution and the mixture was stirred
for 100 min at -78 °C. The dry ice/acetone bath was removed,
and 50 mL of water was added. The reaction mixture was
allowed to come to room temperature. After several extrac-
tions with diethyl ether the combined organic phases were
washed with a 5% sodium hydrogen carbonate solution and
then dried over magnesium sulfate. After evaporation of the
solvents in vacuo the residue crystallized at -20 °C in the
refrigerator and recrystallized from diethyl ether/pentane to

3614 Organometallics, Vol. 17, No. 16, 1998
Mu¨ller and Netz
give 2.75 g (86%) of pure acetate complex as yellow crystals.
Mp: 95-97 °C. 1H NMR ([D6]DMSO, 300 MHz): δ ) 2.12 (s,
3 H), 5.66-5.73 (m, J ) 6.7 Hz, 2 H), 5.80 (m, 1 H), 6.02 (d, J
) 6.4 Hz, 1 H), 6.08 (d, J ) 6.4 Hz, 1 H), 6.40 (s, 1 H), 7.40-
7.51 (m, 5 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 20.70
(CH3), 63.97 (CH), 84.41 (Cquat.), 87.09 (Cquat.), 93.28 (CH), 94.91
(CH), 96.04 (CH), 107.31 (Cquat.), 121.05 (Cquat.), 128.95 (CH),
129.72 (CH), 131.91 (CH), 169.24 (Cquat.), 233.26 (Cquat., CO).
MS (EI, 70 eV), m/z (%): 386 (M+, 1), 330 (M+ - 2CO, 11),
302 (M+ - 3CO, 100), 243 (C15H11Cr+, 14), 191 (C6H5-
Cr (CO)3(η6-C6H5)CHdCdC[SCH(CH3)2]P h (6a ). Accord-
ing to the GP 150 mg (0.39 mmol) of 3 was ionized and allowed
to react for 30 min with 0.08 mL (0.85 mmol) of 2-propanethiol.
After workup the crude product was purified by flash chro-
matography on silica gel (1:2 diethyl ether/pentane) and
recrystallization from pentane gave 112 mg (72%) of pure 6a
as a yellow powder. Mp: 97-98 °C. 1H NMR ([D6]DMSO,
400 MHz): δ ) 1.27 (d, J ) 6.8 Hz, 3 H), 1.30 (d, J ) 6.6 Hz,
3 H), 3.15 (m, 1 H), 5.72-5.79 (m, 3 H), 5.86 (d, J ) 6.2 Hz, 1
H), 5.92 (d, J ) 6.3 Hz, 1 H), 7.09 (s, 1 H), 7.30 (t, J ) 6.9 Hz,
1 H), 7.36-7.43 (m, 4 H). 13C NMR ([D6]DMSO, 100 MHz): δ
) 22.90 (CH3), 23.12 (CH3), 37.92 (CH), 93.21 (CH), 94.34 (CH),
94.42 (CH), 94.65 (CH), 101.17 (CH), 103.65 (Cquat.), 105.44
(Cquat.), 127.56 (CH), 128.50 (CH), 129.16 (CH), 132.37 (Cquat.),
204.61 (Cquat.), 233.66 (Cquat., CO). MS (EI, 70 eV), m/z (%):
CHCCC6H5+, 48). IR (KBr): νj ) 2236, 1981, 1906, 1744 cm-1
UV/vis (DMSO): λmax (ꢀ) ) 317 nm (10 400). Anal. Calcd for
20H14CrO5 (386.3): C, 62.18; H 3.65. Found: C, 61.98; H,
3.68.
Gen er a tion of th e Ca tion a n d Nu cleop h ilic Tr a p p in g
.
C
402 (M+, 4), 346 (M+ - 2CO, 12), 318 (M+ - 3CO, 44), 244
Rea ction s (Gen er a l P r oced u r e, GP ). To a solution of the
acetate 3 in 18 mL of dichloromethane, cooled to -78 °C, was
added dropwise 1.4 equiv of boron trifluoride etherate. The
purple red solution was stirred at -78 °C for 50 min, and then
the desired nucleophile was added dropwise in substance or
dissolved in dichloromethane to the solution of the cation. The
color of the solution turns from purple red to yellow, and the
reaction mixture was stirred at the times indicated. Then 20
mL of diethyl ether and 20 mL of water were added succes-
sively to the reaction mixture which was subsequently allowed
to come to room temperature. After several extractions with
diethyl ether the combined organic phases were dried over
magnesium sulfate. The solvents were evaporated in vacuo,
and the residue was either recrystallized from diethyl ether/
pentane or purified by flash chromatography to give pure
allenyl or propargyl derivatives.
Cr (CO)3(η6-C6H5)CH(OC2H5)CtCP h (5a ). According to
the GP 100 mg (0.26 mmol) of 3 was ionized and allowed to
react for 15 min with 0.5 mL (8.6 mmol) of ethanol. After
workup the crude product was purified by flash chromatog-
raphy on silica gel (1:4 diethyl ether/pentane) to give 50 mg
(52%) of pure 5a as a yellow oil which crystallizes from pentane
as a light yellow solid. Mp: 67 °C. 1H NMR ([D6]DMSO, 400
MHz): δ ) 1.19 (t, J ) 6.8 Hz, 3 H), 3.62-3.66 (m, 1 H), 3.78-
3.82 (m, 1 H), 5.25 (s, 1 H), 5.70-5.73 (m, 3 H), 5.93 (d, J )
6.1 Hz, 1 H), 5.97 (d, J ) 5.8 Hz, 1 H), 7.41 (m, 3 H), 7.50 (m,
2 H). 13C NMR ([D6]DMSO, 100 MHz): δ ) 15.09 (CH3), 64.33
(CH2), 69.59 (CH), 85.87 (Cquat.), 87.26 (Cquat.), 93.77 (CH), 93.82
(CH), 94.23 (CH), 95.34 (CH), 95.54 (CH), 110.06 (Cquat.), 121.58
(C15H12Cr+, 100), 243 (C15H11Cr+, 6), 191 (C6H5CHCCC6H5
,
+
50), 52 (Cr+, 22). IR (KBr): νj ) 1964, 1901, 1875 cm-1. UV/
vis (DMSO): λmax (ꢀ) ) 319 nm (10 300). Anal. Calcd for
21H18CrO3S (402.4): C, 62.69; H, 4.51; S, 7.97. Found: C,
C
62.85; H, 4.76; S, 8.05.
Cr (CO)3(η6-C6H 5)CHdCdC(SCH2CH 2CO2CH 3)P h (6b ).
According to the GP 150 mg (0.39 mmol) of 3 was ionized and
allowed to react for 50 min with 0.11 mL (0.85 mmol) of methyl
3-mercaptopropionate. After workup the crude product was
purified by flash chromatography on silica gel (1:5-1:1 diethyl
ether/pentane) to give 129 mg (74%) of pure 6b as a yellow
oil. 1H NMR ([D6]DMSO, 300 MHz): δ ) 2.64 (m, 2 H), 2.92
(m, 2 H), 3.52 (s, 3 H), 5.74-5.78 (m, 2 H), 5.81 (m, 1 H), 5.87
(m, 2 H), 7.15 (s, 1 H), 7.33-7.40 (m, 5 H). 13C NMR ([D6]-
DMSO, 75 MHz): δ ) 28.0 (CH2), 33.6 (CH2), 51.8 (CH3), 93.1
(CH), 93.2 (CH), 94.5 (CH), 94.6 (CH), 94.7 (CH), 103.2 (CH),
104.7 (Cquat.), 105.0 (Cquat.), 127.6 (CH), 128.8 (CH), 129.3 (CH),
132.5 (Cquat.), 171.1 (Cquat.), 202.3 (Cquat.), 233.7 (Cquat., CO). MS
(EI, 70 eV), m/z (%): 446 (M+, 2), 362 (M+ - 3CO, 51), 310
(M+ - Cr(CO)3, 1), 244 (C15H12Cr+, 70), 243 (C15H11Cr+, 12),
191 (C6H5CHCCC6H5+, 100), 52 (Cr+, 25). IR (KBr): νj ) 1965,
1887, 1732 cm-1. UV/vis (DMSO): λmax (ꢀ) ) 318 nm (9400).
Anal. Calcd for C22H18CrO5S (446.4): C, 59.19; H, 4.06; S, 7.18.
Found: C, 59.45; H, 4.17; S, 7.01.
Cr (CO)3(η6-C6H5)CHdCdC(S-p-C6H4Cl)P h (6c). Accord-
ing to the GP 100 mg (0.26 mmol) of 3 was ionized and allowed
to react for 90 min with 85 mg (0.59 mmol) of p-chlorothiophe-
nol. After workup the crude product was purified by crystal-
lization from diethyl ether/pentane to give 98 mg (80%) of pure
6c as yellow crystalls. Mp: 85 °C. 1H NMR ([D6]DMSO, 300
MHz): δ ) 5.72-5.78 (m, 3 H), 5.92 (m, 2 H), 7.08 (s, 1 H),
7.34-7.39 (m, 7 H), 7.49 (d, J ) 8.4 Hz, 2 H). 13C NMR ([D6]-
DMSO, 75 MHz): δ ) 93.3 (CH), 94.5 (CH), 94.6 (CH), 100.5
(CH), 102.6 (Cquat.), 104.2 (Cquat.), 127.7 (CH), 128.8 (CH), 129.2
(CH), 129.5 (CH), 131.4 (Cquat.), 132.1 (CH), 132.5 (Cquat.), 132.6
(Cquat.), 208.1 (Cquat.), 233.6 (Cquat., CO). MS (EI, 70 eV), m/z
(%): 472, 470 (M+, 4, 10), 388, 386 (M+ - 3CO, 44, 100), 336,
(Cquat.), 128.83 (CH), 129.27 (CH), 131.72 (CH), 233.52 (Cquat.
,
CO). MS (EI, 70 eV), m/z (%): 372 (M+, 9), 316 (M+ - 2CO,
7), 288 (M+ - 3CO, 15), 244 (C15H12Cr+, 100), 191 (C6H5-
CHCCC6H5+, 18), 52 (Cr+, 20). IR (KBr): νj ) 1965, 1894, 1886
cm-1. UV/vis (DMSO): λmax (ꢀ) ) 313 nm (10 800). Anal. Calcd
for C20H16CrO4 (372.3): C, 64.52; H, 4.33. Found: C, 64.74;
H, 4.38.
Cr (CO)3(η6-C6H5)CH(OCH2CHdCH2)CtCP h (5b). Ac-
cording to the GP 200 mg (0.52 mmol) of 3 was ionized and
allowed to react for 60 min with 0.10 mL (1.46 mmol) of allyl
alcohol. After workup the crude product was purified by flash
chromatography on silica gel (1:3 diethyl ether/pentane) to give
122 mg (61%) of pure 5b as a yellow orange oil.
1H NMR ([D6]DMSO, 400 MHz): δ ) 4.19 (s, 1 H), 4.30 (s,
1 H), 5.20-5.37 (m, 4 H), 5.72 (m, 3 H), 5.94-5.99 (m, 2 H),
7.41-7.52 (m, 5 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 69.3
(CH), 69.6 (CH2), 85.4 (Cquat.), 87.6 (Cquat.), 93.6 (CH), 94.3 (CH),
95.4 (CH), 95.6 (CH), 109.5 (Cquat.), 117.5 (CH2), 121.5 (Cquat.),
334 (M+ - Cr(CO)3, 2, 5), 244 (C15H12Cr+, 28), 243 (C15H11
Cr+, 17), 191 (C6H5CHCCC6H5+, 93), 52 (Cr+, 43). IR (KBr):
νj ) 1966, 1883 cm-1
UV/vis (DMSO): λmax (ꢀ) ) 320 nm
-
.
(11200). Anal. Calcd for C24H15ClCrO3S (470.9): C, 61.22; H,
3.21; S, 6.81; Cl, 7.53. Found: C, 61.45; H, 3.24; S, 6.86; Cl,
7.22.
Ack n ow led gm en t. The financial support of the
Fonds der Chemischen Industrie and the Deutsche
Forschungsgemeinschaft is gratefully acknowledged. We
wish to express our appreciation to Prof. H. Mayr for
his generous support and the possibility of using his
J &M TIDAS UV/vis spectrometer. We heartily thank
Dr. David S. Stephenson for recording the low-temper-
ature NMR spectra.
128.8 (CH), 129.3 (CH), 131.8 (CH), 134.4 (CH), 233.5 (Cquat.
,
CO). MS (EI, 70 eV), m/z (%): 384 (M+, 4), 328 (M+ - 2CO,
5), 300 (M+ - 3CO, 11), 244 (C15H12Cr+, 100), 243 (C15H11Cr+,
7), 191 (C6H5CHCCC6H5+, 17), 52 (Cr+, 29). IR (KBr): νj )
1966, 1887, 1738 cm-1
. UV/vis (DMSO): λmax (ꢀ) ) 316 nm
(9980). Anal. Calcd for C21H16CrO4 (384.4): C, 65.62; H, 4.20.
Found: C, 66.18; H, 4.32.
OM980257U