Spectroscopic characterization, reactivity, and reactions of (arene)Cr(CO)3-stabilized γ-propargyl-allenyl cations

Article abstract of DOI:10.1021/om9900824

(Arene)Cr(CO)₃-stabilized γ-propargyl-allenyl cations Cr(CO)₃(η⁶-R¹C₆H ₄)C≡CC⁺R²R³ (2) are reactive intermediates in the synthesis of arene-complex-substituted allenes or propargyl derivatives using mild in situ ionizations of the corresponding propargyl derivatives Cr-(CO)₃(η⁶-R¹C₆H ₄)C≡CCXR²R³ (X = OH, OAc). The regioselectivity of the nucleophilic attack is strongly dependent on the substitution pattern on the propargyl side chain, i.e., steric and electronic factors. In a representative case of a stable cation (2a; R¹ = H, R² = R³ = Ph) the structure investigation of this ambident electrophile by NMR spectroscopy and UV/vis spectroscopy reveals that a considerable contribution of the allenylium resonance structure accounts for a strong participation of the chromium carbonyl fragment in the efficient stabilization. The reactivity of 2a was studied by measuring the UV/vis kinetics for the nucleophilic trapping reactions revealing that the complexed cation 2a is by 2 orders of magnitude less reactive than the corresponding free ligand.

Full text of DOI:10.1021/om9900824

3690
Organometallics 1999, 18, 3690-3701
Sp ectr oscop ic Ch a r a cter iza tion , Rea ctivity, a n d
Rea ction s of (Ar en e)Cr (CO)3-Sta bilized
γ-P r op a r gyl-Allen yl Ca tion s
Thomas J . J . Mu¨ller,* Markus Ansorge, and Kurt Polborn
Institut fu¨r Organische Chemie, Ludwig-Maximilians-Universita¨t Mu¨nchen,
Butenandtstrasse 5-13 (Haus F), D-81377 Mu¨nchen, Germany
Received February 9, 1999
(Arene)Cr(CO)3-stabilized γ-propargyl-allenyl cations Cr(CO)3(η6-R1C6H4)CtCC+R2R3 (2)
are reactive intermediates in the synthesis of arene-complex-substituted allenes or propargyl
derivatives using mild in situ ionizations of the corresponding propargyl derivatives Cr-
(CO)3(η6-R1C6H4)CtCCXR2R3 (X ) OH, OAc). The regioselectivity of the nucleophilic attack
is strongly dependent on the substitution pattern on the propargyl side chain, i.e., steric
and electronic factors. In a representative case of a stable cation (2a ; R1 ) H, R2 ) R3 ) Ph)
the structure investigation of this ambident electrophile by NMR spectroscopy and UV/vis
spectroscopy reveals that a considerable contribution of the allenylium resonance structure
accounts for a strong participation of the chromium carbonyl fragment in the efficient
stabilization. The reactivity of 2a was studied by measuring the UV/vis kinetics for the
nucleophilic trapping reactions revealing that the complexed cation 2a is by 2 orders of
magnitude less reactive than the corresponding free ligand.
In tr od u ction
chromium carbonyl-complexed benzyl cations are ac-
cessible, both thermodynamically and kinetically. From
these general considerations the intriguing question
arises whether Cr(CO)3-complexed arenes would also
stabilize sp-hybridized positive charges such as R-allenyl
cations, i.e., if the generation of the cation occurs at the
remote γ-propargyl position. In particular, upon ioniza-
tion propargylic derivatives form ambident propargy-
lium-allenylium ions4 that can be very interesting
intermediates for more sophisticated arene side chain
functionalizations5 via aryl propargylic or allenyl de-
rivatives. So far, there are only ferrocenyl-substituted
γ-propargyl-R-allenyl cations among organometallic
π-complex representatives of stabilized propargylium-
allenylium ions.6 Recently, we have investigated the
electronic structure and ambident reactivity of a (ben-
zene)Cr(CO)3-stabilized R-propargylium ion.7 Here we
report on the NMR and UV/vis spectroscopic charac-
terization and the reactivity of a (phenyl)Cr(CO)3-
substituted γ-propargyl cation and nucleophilic trapping
reactions of several (arene)Cr(CO)3-stabilized γ-pro-
Benzylic carbenium ions stabilized by Cr(CO)3 com-
plexation have successfully been applied to a couple of
syntheses in the sense of nucleophilic substitutions.1
Thermodynamically, the Cr(CO)3-complexed benzyl cat-
ion is stabilized2 by at least 8 orders of magnitude
compared to the free ligand, the benzyl cation, and some
time ago the structure of (arene)Cr(CO)3-stabilized
benzyl cations had been elucidated unambiguously by
1H and 13C NMR spectroscopy.2d,3 Concerning the
reactivity in numerous nucleophilic substitutions on Cr-
(CO)3-complexed benzyl derivatives, the benzyl stabili-
zation has also been found responsible for a rate-
increasing anchimeric assistance.1 Although, the Cr(CO)3
complexation is generally used to exercise a strong net
electron-withdrawing effect, this peculiar feature can
be readily explained by taking into account an ideal
overlap of filled d-orbitals of the chromium carbonyl
fragment and the vacant pz-orbital of the sp2-hybridized
benzylic carbenium ion.1a,2a,d Last but not least this
remarkable effect plays its key role in the conservation
of the stereochemical integrity of an asymmetric ben-
zylic center in stereoselective transformations.1a,d Thus,
(4) (a) Murray, M. In Methoden zur Herstellung und Umwandlung
von Allenen bzw. Kumulenen; Houben-Weyl, Ed.; 1977; Vol. 5/2a, p
991. (b) Lukyanov, S. M.; Koblik, A. V.; Muradyan, L. A. Russ. Chem.
Rev. 1998, 67, 817. (c) Mayr, H.; Ba¨uml, E. Tetrahedron Lett. 1983,
24, 357. (d) Ba¨uml, E.; Mayr, H. Chem. Ber. 1985, 118, 694. (e) Dau-
Schmidt, J .-P.; Mayr, H. Chem. Ber. 1994, 127, 205.
(5) For side chain activation on arene complexes see, for example:
Davies, S. G.; McCarthy, T. D. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, U.K., 1995; Vol. 12, p 1039.
(6) (a) Abram, T. S.; Watts, W. E. J . Chem. Soc., Perkin Trans. 1
1977, 1532. (b) Boev, V. I.; Dombrovskii, A. V. Russ. J . Org. Chem.
1985, 21, 636. (c) Koch, E.-W.; Siehl, H.-U.; Hanack, M. Tetrahedron
Lett. 1985, 26, 1493. (d) Buchmeister, H.; Schottenberger, H. Orga-
nometallics 1993, 12, 2472. (e) Lukasser, J .; Angleitner, H.; Schotten-
berger, H.; Kopacka, H.; Schweiger, M.; Bildstein, B.; Ongania, K. H.;
Wurst, K. Organometallics 1995, 14, 5566.
(1) (a) For stabilization of positive charge in the benzyl chromium
carbonyl derivatives see, for example: Davies, S. G.; Donohoe, T. J .
Synlett 1993, 323-332. (b) For stereoselective C-C-bond forming
reactions via η6-arene chromium tricarbonyl cations see, for example:
Uemura, M.; Kobayashi, T.; Hayashi, Y. Synthesis 1986, 386. (c) Reetz,
M. T.; Sauerwald, M. Tetrahedron Lett. 1983, 24, 2837. (d) Corey, E.
J .; Helal, C. J . Tetrahedron Lett. 1996, 37, 4837.
(2) (a) Clack, D. W.; Kane-Maguire, L. A. P. J . Organomet. Chem.
1978, 145, 201. (b) Solladie´-Cavallo, A. Polyhedron 1985, 4, 910. (c)
J aouen, G. Pure Appl. Chem. 1986, 58, 597. (d) Downton, P. A.; Sayer,
B. G.; McGlinchey, M. J . Organometallics 1992, 11, 3281.
(3) (a) Olah, G. A.; Yu, S. H. J . Org. Chem. 1976, 41, 1694. (b)
Acampora, M.; Ceccon, A.; Dal Farra, M.; Giacometti, G.; Rigatti, G.
J . Chem. Soc., Perkin Trans. 2 1977, 483.
(7) Mu¨ller, T. J . J .; Netz, A. Organometallics 1998, 17, 3609.
10.1021/om9900824 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/12/1999

γ-Propargyl-Allenyl Cations
Organometallics, Vol. 18, No. 18, 1999 3691
Ch a r t 2
pargylium ions, some generated as stable species, others
by in situ ionization techniques.
Resu lts a n d Discu ssion
Gen er a tion of th e P r op a r gylic Ca tion . Propar-
gylic cations are most conveniently generated from a
suitable propargylic precursor upon ionization with a
Brønstedt or Lewis acid. Recently, we have found a
fairly general access to areneCr(CO)3-substituted pro-
pargylic derivatives 1 using the Sonogashira coupling
of terminal prop-2-yn-1-ols with Cr(CO)3-complexed
chloroarenes.8 Thus, the complexed 1,1,3-triphenyl al-
Ch a r t 1
13C NMR Sp ectr a of 1a a n d 2a . Most significantly
no splitting of the carbonyl resonance can be found in
the 13C NMR spectrum (proton-decoupled and DEPT)
of 2a (231.0 ppm; Table 1), although the carbonyl signal
of the propargyl alcohol 1a (232.5 ppm) experiences a
modest shift to high field upon ionization, indicating the
generation of an electron-withdrawing substituent.10
Surprisingly, the low-field shift of the para-carbon
resonances of the uncomplexed phenyl rings with ∆I )
9 (1a , 127.6, and 2a , 136.4) is considerably smaller in
comparison to the corresponding ionization shift of ∆I
) 16.6 for the free ligand pair 3/4, indicating a signifi-
cant resonance participation of the complexed arene
substituent at the remote allenyl position.
Applying a simple model,7,9 the relative contributions
of mesomeric forms to the stabilization of a resonance-
stabilized cation can be estimated. The benzhydryl
cation (5)11 was considered as a model for the Cγ-
lenyl cation (2a ) (R1 ) H, R2 ) R3 ) Ph) is formed in a
dichloromethane solution from the complex-substituted
propargyl alcohol (1a ) in the presence of a 1.3-fold excess
of HBF4 diethyl etherate at -78 °C (Scheme 1) as a
Ch a r t 3
Sch em e 1
localized carbenium ion as depicted in structure 2a A,
whereas 1,1-diphenyl ethene (6)12 serves as a model for
an allenylium structure (2a B) assuming the γ-carbon
atom does not bear positive charge. The substitution of
the corresponding carbon resonances (2a , δ ) 161.5; 5,11
δ ) 191.1; 6,12 δ ) 141.0) in eq 1 reveals a 59%
contribution of the resonance structure 2a B to the
stabilization of the cation 2a .
rel contrib of 2a B )
δ(Cγ - 5) - δ(Cγ - 2a )
× 100% )
stable, deep green intermediate (<20 °C) that can be
identified and characterized by NMR and UV/vis spec-
troscopy. Some time ago, the free ligand systems, i.e.,
the propargyl alcohol 3 and the cation 4, were thor-
oughly studied by 13C NMR spectroscopy in superacidic
media9 and can now be used for direct comparison with
chromium carbonyl-complexed systems, in particular,
to evaluate the electronical influence of the chromium
carbonyl fragment on the stabilization and, ultimately,
on the reactivity of the propargyl cation.
δ(Cγ - 5) - δ(Cγ - 6)
191.1 - 161.5
× 100% ) 59% (1)
191.1 - 141.0
Interestingly, the contribution of the corresponding
allenyl resonance form 4B of the free ligand9 using the
same procedure is estimated to be only 9%. Thus,
although the chromium carbonyl arene fragment is
placed at a remote position with respect to the leaving

3692 Organometallics, Vol. 18, No. 18, 1999
Mu¨ller et al.
Ta ble 1. Assign m en ts a n d Ion iza tion Sh ifts ∆I of th e Alcoh ols (1a ,a 3b) - Ca tion s (2a ,c 4d )
1a
2a
∆
39
49
∆
I
I
para (compl.)
meta (compl.)
ortho (compl.)
ipso (compl.)
91.5
92.6
95.1
89.3
82.4
97.5
95.9
103.4
82.4
150.4
120.8
161.5
138.3
133.9
130.2
136.5
231.0
6.0
3.3
7.9
-6.9
68.0
30.0
87.7
-5.6
5.7
para (allenyl terminus)
meta (allenyl terminus)
ortho (allenyl terminus)
ipso (allenyl terminus)
128.0
131.4
128.0
121.9
86.6
91.5
74.5
144.6
125.7
128.0
127.4
137.6
130.7
138.7
119.9
159.1
105.9
186.8
138.7
139.4
131.4
144.0
9.6
-0.7
10.7
-2.0
72.5
14.4
112.3
-5.9
13.7
3.4
R
R
â
90.8
73.8
â
γ
γ
ipso
ortho
meta
para
CO
143.9
128.2
125.1
127.6
232.5
ipso
ortho
meta
para
5.1
8.9
-1.5
16.6
a
b
Recorded at -70 °C in CD2Cl2 (100 MHz). Recorded at 35 °C in CDCl3 (25 MHz).9 c Recorded at -70 °C in CD2Cl2/HBF4 (100 MHz).
Recorded at -60 °C in FSO3H/SbF5/SO2 (25 MHz).9
d
Ta ble 2. Com p lexa tion Sh ifts ∆C for th e Alcoh ols
1a a n d 3 a n d th e Ca tion s 2a a n d 4 (for Recor d in g
Con d ition s See Ta ble 1)
UV/Vis Sp ectr a of th e Ca tion 2a . The successful
NMR studies prompted us to investigate the electronic
spectrum of the cationic intermediate 2a . Upon ioniza-
tion with tetrafluoroboric acid etherate solution of a
dichloromethane solution of 1a at -70 °C, a color change
from light yellow to deep green can be monitored by
following the characteristic appearance of a long-
wavelength absorption bands with maxima at 440, 515,
and 880 nm. According to calculations on a MM2
optimized structure13 of 2a using the ZINDO/CI formal-
ism with INDO/1 parameters,13 the absorptions at 880
39
1a
∆
49
2a
∆
C
C
para (allenyl 128.0
terminus)
meta (allenyl 131.4
terminus)
ortho (allenyl 128.0
terminus)
91.5
-36.5 137.6
-38.8 130.7
97.5
-40.1
-34.8
-35.3
-37.5
92.6
95.1
89.3
95.9
-32.9 138.7 103.4
-32.6 119.9 82.4
ipso (allenyl
121.9
terminus)
R
86.6
91.5
74.5
144.6 143.9
125.7 128.2
128.0 125.1
127.4 127.6
232.5
82.4
90.8
73.8
-4.2 159.1 150.4
-0.7 105.9 120.8
-0.7 186.8 161.5
-0.7 138.7 138.3
2.5 139.4 133.9
-2.9 131.4 130.2
0.2 144.0 136.5
231.0
-8.7
14.9
2
nm (calcd 674 nm; chromium-centered dz -orbital HOMO
â
to the propargyl moiety localized LUMO), at 515 nm
γ
-25.3
-0.4
-5.5
-1.2
-7.5
2
2
(calcd 541 nm; dx -y -orbital HOMO-1 to the LUMO),
and at 440 nm (calcd 401 nm, π-π* transitions within
the propargyl fragment (HOMO-5 to LUMO) and from
the uncomplexed phenyl rings to the propargyl fragment
(HOMO-6 to LUMO)) are readily reproduced.
ipso
ortho
meta
para
∑∆C
-219.4
-258.2
Nu cleop h ilic Tr a p p in g Rea ction s a n d Electr o-
p h ilicity of 2a . At -78 °C the trapping reactions of
the complex-substituted propargyl cation 2a with a
slight excess of various π- and n-nucleophiles give a
facile access to allenyl- and propargyl-substituted arene
complexes 7 in good yields and with excellent regiose-
lectivity as yellow-orange crystalline solids (Scheme 2).
In any case only the depicted isomer can be isolated.
The spectroscopic data support the suggested structural
assignments showing for the allenyl derivatives in the
13C NMR spectra most significantly by the appearance
of the characteristic resonance of the â-allenyl carbon
atoms between δ ) 205 and 219 depending on the
electronic nature of the substituent at the R-position.14
Additionally, the structure of the allylated complex 7d
was confirmed by an X-ray crystal structure analysis15
(Figure 1, Table 3).
Especially remarkable is the straightforward alterna-
tive synthesis of an allenylamine derivative 7f from the
propargyl alcohol 1a via the stable cation 2a . Starting
from the uncomplexed propargyl alcohol 3, this syn-
thetic pathway to allenylamines is not feasible even
under in-situ-ionization conditions in acidic media,16 and
classically, allenylamines are prepared by a base-
group, it still participates to a considerable extent in
the stabilization of the positive charge. The inspection
of the complexation shifts (Table 2) of 1a and 2a reveals
that the positive charge is as well delocalized onto the
chromium atom3a to a certain extent (∆Σ(∆C) ) 38.8 ≈
15% ∆C(cation)). The allenyl cation resonance form is
stabilized by the anchimeric assistance of the chromium
carbonyl tripod, causing a decrease of the strong deshield-
ing of the carbon resonance at CR and Cγ.
According to molecular orbital calculations on a η6-
phenylCr(CO)3-substituted γ-propargyl cation 2d as a
model at the extended Hu¨ckel level of theory,7,13 the
bending of the propargyl fragment by an angle of 4°
toward the chromium carbonyl tripod results only in a
small gain of ∼0.33 kcal/mol. The overlap of the pz-
orbital at the sp-hybridized carbon atom with the
2
2
chromium-centered dx -y -orbital is significantly lower
compared to the sp2-hybridized η6-phenylCr(CO)3-
substituted R-propargyl cation.
(8) (a) Mu¨ller, T. J . J .; Ansorge, M. Chem. Ber./ Recl. 1997, 130,
1135. (b) Mu¨ller, T. J . J .; Ansorge, M. Tetrahedron 1998, 54, 1457. (c)
Ansorge, M.; Polborn, K.; Mu¨ller, T. J . J . Eur. J . Inorg. Chem. 1999,
225.
(9) Olah, G. A.; Spear, R. J .; Westerman, P. W.; Denis, J .-M. J . Am.
Chem. Soc. 1974, 96, 5855.
(14) Kalinowski, H.-O.; Berger, S.; Braun, S. 13C NMR Spektroskopie;
Georg Thieme Verlag: Stuttgart, New York, 1984; p 273.
(15) Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publication
nos. CCDC-114222 (7d ) and CCDC-114223 (9). Copies of the data can
be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (Fax + 44-1223/336-033; E-mail deposit@
ccdc.cam.ac.uk).
(10) (a) Gansow, O. A.; Schexnayder, D. A.; Kimura, B. Y. J . Am.
Chem. Soc. 1972, 94, 3406. (b) Brown, D. A.; Chester, J . P.; Fitzpatrick,
N. J .; King, I. J . Inorg. Chem. 1977, 16, 2497.
(11) Kalinowski, H.-O.; Berger, S.; Braun, S. 13C NMR Spektroskopie;
Georg Thieme Verlag: Stuttgart, New York, 1984; p 371.
(12) Kalinowski, H.-O.; Berger, S.; Braun, S. 13C NMR Spektroskopie,
Georg Thieme Verlag: Stuttgart, New York, 1984, p 144.
(13) Quantum CAChe 3.0 Program; Oxford Molecular Group, 1997.

γ-Propargyl-Allenyl Cations
Organometallics, Vol. 18, No. 18, 1999 3693
Sch em e 2
catalyzed rearrangement of the corresponding propar-
gylamines.17 Furthermore, this arene complex-substi-
tuted allenylamine is fairly acid sensitive. Even on silica
gel (thin-layer chromatography) a complete conversion
via a violet, strongly polar intermediate, presumably the
allyl cation, proceeds readily to give 50% of the hydroly-
sis product, the enone 9, as red crystals (Scheme 3).
Independently, 9 can be synthesized by the acid-
catalyzed Meyer-Schuster rearrangement18 from the
propargyl alcohol 1a in 73% yield. The structure of 9
was unambiguously corroborated by X-ray crystal-
lography15 (Figure 2, Table 3). Due to the torsional
strain imposed on the enone by the two geminal phenyl
groups at the γ-terminus of the side chain, the enone
strongly deviates from coplanarity, as indicated by the
torsional angles.
In all trapping reactions with carbon π, phosphorus,
and nitrogen nucleophiles exclusively allenes were
formed. Ethanol and the hydride donor triethylsilane,
however, regioselectively gave rise to the formation of
(16) For reactions with propargyl alcohols under in-situ ionization
conditions see, for example: Mayr, H.; Ba¨uml, E. Tetrahedron Lett.
1984, 25, 1127.
(17) See, for example: (a) Normant, H.; Mantione, R.; C. R. Hebd.
Seances Acad. Sci. 1964, 259, 1635. (b) Pourcelot, G.; Cadiot, P.;
Georgoulis, C.; Tetrahedron 1982, 38, 2123.
F igu r e 1. ORTEP plot of 7d and selected bond lengths
[Å], bond angles [deg], and torsional angles [deg]: C(4)-
C(10) 1.482(5), C(10)-C(11) 1.306(4), C(11)-C(12) 1.317-
(4), C(10)-C(11)-C(12) 176.5(4), C(5)-C(4)-C(10)-C(11)
-14.1(5), C(9)-C(4)-C(10)-C(25) 165.8(3).
(18) Swaminathan, S.; Narayanan, K. V. Chem. Rev. 1971, 71, 429.

3694 Organometallics, Vol. 18, No. 18, 1999
Mu¨ller et al.
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e Refin em en ts for 7d a n d 9
7d
9
empirical formula
color, form
C
27H20CrO3
C24H16CrO4
red plates
420.37
yellow plates
444.43
fw
temperature (K)
wavelength (Å), radiation
crystal system
space group
295(2)
294(2)
0.71073 (Mo KR)
0.71073 (Mo KR)
monoclinic
C2/c
triclinic
P1h
unit cell dimens (Å, deg),
a ) 9.9946(15); R ) 82.246 (14)
a ) 18.5944(21); R ) 90.00(13)
b ) 10.277(2); â ) 84.525(15)
b ) 7.3122(17); â ) 96.487(9)
c ) 11.3709(15); γ ) 84.94(2)
c ) 29.2020(34); γ ) 90.000(14)
volume (Å3)
1148.6(3)
3945.0(1)
Z
2
8
density (calcd) (g/cm3)
1.285
1.416
absorption coeff (mm-1
F(000)
)
0.522
0.608
460
1728
crystal size (mm)
0.17 × 0.27 × 0.43
0.10 × 0.33 × 0.66
θ range for data collection (deg)
2.53-23.97
2.20-23.98
index ranges
-11 e h e 11
-11 e k e 11
0 e l e 12
-20 e h e 21
0 e k e 8
-33 e l e 0
3178
3103 [R(int) ) 0.0117]
2617
no. of reflns collected
no. of indep reflns
no. obsd (I > 2σ(I))
absorption corr
3798
3592 [R(int) ) 0.0200]
2465
semiempirical from ψ-scans
0.8917 and 0.9998
full-matrix least-squares on F2
3592/24/368
1.099
semiempirical from ψ-scans
0.9298 and 0.9997
full-matrix least-squares on F2
3103/0/262
max. and min. transmission
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1
1.096
0.0532
0.1140
0.0322
0.0781
wR2
R indices (all data)
R1
0.0827
0.0435
wR2
0.1298
0.0858
largest diff. peak and hole (e/Å3)
0.249 and -0.164
0.218 and -0.277
Sch em e 3
propargyl derivatives. This prompted us to look in more
detail into the nucleophile-dependent ambident reactiv-
ity of the cation 2a .
According to the UV/vis studies, the ambident cation
2a is stable from -70 °C (for several hours) to room
temperature (rapid decomposition over 20 °C). There-
fore, a semiquantitative treatment of the reactivity of
2a according to Mayr’s electrophilicity-nucleophilicity
equation,19
log k(20 °C) ) s(E + N)
(2)
where s is the nucleophile-dependent slope parameter,
E is the electrophilicity parameter, and N is the nu-
cleophilicity parameter, was pursued by determining the
kinetics of the nucleophilic trapping reactions of 2a with
an excess of four well-characterized nucleophiles (allyl-
trimethylsilane, 1,3-dimethoxybenzene, allyltriphenyl-
stannane, and triphenylsilane).19 Thus, the time-
dependent decrease of the long-wavelength absorption
band of 2a at 460 nm was measured at various tem-
peratures and found to follow a pseudo-first-order rate
F igu r e 2. ORTEP plot of 9 and selected bond lengths [Å],
bond angles [deg], and torsional angles [deg]: C(4)-C(10)
1.498(3), C(10)-C(11) 1.474(3), C(11)-C(12) 1.344 (3),
O(4)-C(10) 1.218(3), C(10)-C(11)-C(12) 127.2(2), C(9)-
C(4)-C(10)-C(11) -19.5(3), C(9)-C(4)-C(10)-O(4) 163.4-
(2), O(4)-C(10)-C(11)-C(12) -26.9(4), C(4)-C(10)-C(11)-
C(12) 156.1(2).
(19) Mayr, H.; Patz, M. Angew. Chem. 1994, 106, 990.

γ-Propargyl-Allenyl Cations
Organometallics, Vol. 18, No. 18, 1999 3695
Ta ble 4. Kin etics of th e Nu cleop h ilic Tr a p p in g Rea ction of 2a w ith Selected Nu cleop h iles
a
b
1.08 × 10-3 M solution of 1a in dry and degassed dichloromethane; neat allyl trimethylsilane (6.26 M). 1.02 × 10-3 M solution of 1a
in dry and degassed dichloromethane; neat 1,3-dimethoxybenzene (1.045 M). c 9.51 × 10-4 M solution of 1a in dry and degassed
dichloromethane; 1.126 M solution of allyltriphenylstannane in dichloromethane. 1.01 × 10-3 M solution of 1a in dry and degassed
d
dichloromethane; 1.61 M solution of triphenylsilane in dichloromethane.
law. The results of the kinetic measurements are
summarized in Table 4.
centers. However, since a nucleophilic attack to the
cation 2a very likely occurs in an anti-fashion with
respect to the chromium carbonyl tripod, a strong
participation of steric rather than electronic effects
cannot be fully excluded. Regarding the Eyring activa-
tion entropy terms, the transition states for the attack
at the R-position (π-nucleophiles) are significantly higher
ordered than for those for the attack at the γ-position
(triphenyl silane). This also suggests for an incoming
π-nucleophile a coplanar orientation of its π-orbitals
with those of the propargyl-allenyl cation in order to
maximize the stabilizing interactions. Thus, the π-nu-
cleophiles tend to react rather by orbital control and by
minimization of steric strain, whereas the hydride donor
triphenylsilane reacts by charge control, i.e., at the
γ-position. In comparison to the free ligand 4 (Eh )
1.64)20 the reactivity of the chromium carbonyl-stabi-
lized γ-propargyl-allenyl cation 2a is lowered by 2
orders of magnitude.
Along with the rate constants at various temperatures
an Eyringplot (ln(k/T) ) -(∆Hq/R)(1/T) + (∆Sq/R) + ln-
(kB/h)) gives the activation parameters (Arrhenius and
Eyring parameters) of the nucleophilic trapping reac-
tions and allows the extrapolation to a rate constant at
20 °C. The results of the Eyring plots and the calculated
electrophilicity parameters E are summarized in Table
5.
From the kinetics of the trapping reactions with allyl
trimethylsilane, 1,3-dimethoxybenzene, and allyltriph-
enylstannane an average electrophilicity parameter Eh
) -0.36 ( 0.18 can be calculated. The electrophilicity
as determined from the trapping reaction with the
hydride donor triphenyl silane deviates by 1 order of
magnitude from the average parameter for the π-nu-
cleophiles. Since all types of π-nucleophiles attack the
ambident cation 2a at the R-position giving rise to
allenyl derivatives (vide supra) and triphenylsilane
reacts with 2a at the γ-position to give a propargyl
derivative, the assumption lies at hand that there exists
a nucleophile-dependent reactivity of the two reaction
In -Situ Ion iza tion s w ith Ar en e Com p lex-Su bsti-
tu ted P r op a r gyl Alcoh ols. Unfortunately, all at-
(20) Siegmund, T.; Mayr, H. Unpublished results.

3696 Organometallics, Vol. 18, No. 18, 1999
Mu¨ller et al.
Ta ble 5. Activa tion a n d Electr op h ilicity P a r a m eter s fr om th e Eva lu a tion of th e Eyr in g P lot a n d Ma yr ’s
Equ a tion
tempts to generate stable cationic intermediates from
the propargyl alcohols 1b and 1c where the two stabi-
lizing phenyl goups have been replaced by methyl
groups were unsuccessful. Although, a short-lived deep
blue species was observed when adding the propargyl
alcohol 1b to a solution of tetrafluoroboric acid in
dichloromethane at -78 °C, it was not possible to trap
this intermediate prior to decomposition with a nucleo-
phile. However, if the nucleophilic trapping reactions
are conducted under in-situ ionization conditions (the
propargyl alcohol and the nucleophile are added to HBF4
etherate in dichloromethane at -78 °C) with acid-stable
nucleophiles such as allyltrimethylsilane, triethylsilane,
1,3-dimethoxybenzene, or triphenylphosphane, the pro-
pargyl derivatives 8c-g are formed regioselectively as
yellow crystals with moderate to good yields (Scheme
2) and it seems to be very likely that the product
formation proceeds through a nucleophilic addition to
an intermediate propargyl cation.
substituent was present at the γ-position. A model
system such as 1e also would rule out steric biases.
Under the conditions of the in-situ ionization for either
the alcohol 1e with tetrafluoroboric acid and acid-stable
nucleophiles or the acetate 1f with boron trifluoride and
acid-labile nucleophiles exclusively the propargylic de-
rivatives 8h -k were found and isolated in good to
excellent yields (Scheme 2).
Finally, omitting any stabilizing substituents at the
γ-position should lead to a very reactive cationic inter-
mediate that forms upon the protonation of complexed
3-phenylprop-2-yn-1-ol (1d ) under the conditions of in-
situ ionization in the presence of 1,3-dimethoxybenzene.
A 2:1 product 10 can be isolated in 44% yield as a yellow
solid (Scheme 4), and its structure was unambiguously
confirmed by 2D-NMR spectroscopy (NOESY, HET-
COR). Presumably, the reaction path here does not
proceed via a propargyl cation, but, in analogy with
ferrocenyl-substituted propargyl alcohols6a the forma-
tion of a (benzene)Cr(CO)3-stabilized vinyl cation (in
analogy with ref 6c) seems to be reasonable. Therefore,
Therefore, we were intrigued to investigate the regi-
oselectivity of the nucleophilic attack if only one phenyl
Sch em e 4

γ-Propargyl-Allenyl Cations
Organometallics, Vol. 18, No. 18, 1999 3697
of the Institut fu¨r Organische Chemie, Ludwig-Maximilians-
Universita¨t Mu¨nchen.
a sequence based upon the different reactivity of vinyl
and allyl cations that commences with a triple-bond
protonation, followed by an electrophilic aromatic sub-
stitution with a vinyl cation, followed by an acidic allyl
alcohol ionization to give a allyl cation, and concludes
with another electrophilic aromatic substitution ratio-
nalizes the formation of 10.
Based upon this methodology, regioselective function-
alizations at the γ-position of arene complex-substituted
γ-propargyl derivatives easily can be envisioned. How-
ever, a control of the stereochemistry at this remote
position still remains a challenge in the field of side
chain functionalizations. Presumably, a stronger stabi-
lization of the propargyl-allenyl cation by an electron-
richer chromium fragment would allow fine-tuning of
the regioselectivity, i.e., propargyl vs allenyl substitu-
tion.
Cr (CO)3(η6-C6H5)CtCCHOH(C6H5) (1e). Over 2 min 2.6
mL (4.20 mmol) of a 1.6 M BuLi solution was added dropwise
to a solution of 1.0 g (4.20 mmol) of the Cr(CO)3-complexed
phenylacetylene in 25 mL of THF at -78 °C. The reaction
mixture was stirred for 1 h, and then over 2 min a solution of
447 mg (4.20 mmol) of benzaldehyde in 5 mL of THF was
added dropwise. Then the mixture was allowed to come to room
temperature and was stirred for 1 h. After the addition of 10
mL of a saturated ammonium chloride solution to the reaction
mixture the aqueous phase was extracted several times with
diethyl ether. The combined organic phases were washed with
distilled water and dried over magnesium sulfate. After
evaporation of the solvents on the rotovap the residue was
chromatographed on silica gel (gradient diethyl ether/pentane,
1:3, to diethyl ether) 1.11 g (77%) of the analytically pure
propargyl alcohol 1e is isolated as a yellow oil.1H NMR ([D6]-
DMSO, 300 MHz): δ ) 5.57 (d, J ) 4.9 Hz, 1 H), 5.66 (t, J )
6.0 Hz, 1 H), 5.72 (t, J ) 6.4 Hz, 2 H), 5.84 (d, J ) 6.2 Hz, 2
H), 6.23 (d, J ) 4.8 Hz, 1 H), 7.29 (m, 1 H), 7.36 (t, J ) 6.8 Hz,
2 H), 7.51 (d, J ) 7.1 Hz, 2 H). 13C NMR ([D6]DMSO, 75
MHz): δ ) 62.15 (CH), 80.11 (Cquat.), 90.72 (Cquat.), 90.74 (Cquat.),
93.23 (CH), 93.64 (CH, double intensity), 96.38 (CH), 96.42
(CH), 126.03 (CH), 127.26 (CH), 127.76 (CH), 140.86 (Cquat.),
232.68 (Cquat., CO). MS (EI, 70 eV), m/z (%): 344 (M+, 2), 260
(M+ - 3 CO, 8), 52 (Cr+, 100). IR (KBr): ν˜ ) 3560 cm-1, 3369,
3089, 3033, 2924, 1966, 1889, 1524, 1493, 1455, 1408, 1285,
1247, 1189, 1151, 1079, 1025, 993, 957, 918, 815, 763, 722,
699, 672, 653, 627, 580, 532, 471. UV/vis (DMSO): λmax (ꢀ) )
321 nm (9400). Anal. Calcd for C18H12CrO4 (344.28): C, 62.79;
H, 3.51. Found: C, 62.79; H, 3.59.
Con clu sion
The chromium carbonyl complexation has a signifi-
cant effect on the electronic nature of the triphenyl pro-
pargylium ion 4. This stable species 2a can be studied
by NMR and UV/vis spectroscopy, and its reactivity was
investigated by kinetic measurements. Compared with
its free ligand 4, the cation 2a is by 2 orders of magni-
tude less reactive in nucleophilic addition reactions. The
nucleophilic trapping reactions occurred with a pre-
dominant regioselectivity at the allenyl position due to
steric biases imposed by the γ-terminal phenyl substit-
uents. However, the corresponding dialkyl- or monophe-
nyl-substituted systems were found to react under the
conditions of the in-situ ionization to give regioselec-
tively the propargyl derivatives. Nevertheless, these
findings represent an extension of the well-established
benzyl cation stabilization by chromium arene complex-
ation to conjugated side chains. Further studies directed
to control and reverse the regioselectivity of the nucleo-
philic additions by ligand substitutions on the chromium
carbonyl tripod for fine-tuning the side chain function-
alizations are currently under way.
Cr (CO)3(η6-C6H5)CtCCH[OC(O)CH3](C6H5) (1f). The pro-
cedure followed the preceding to give the propargyl alcoholate.
The reaction mixture was then allowed to come to 0 °C over
30 min before being recooled to -78 °C. To the mixture was
added 0.85 mL (9.0 mmol) of acetic anhydride. After stirring
the solution for 2 h at - 78 °C water was added and the
aqueous phase was extracted several times with diethyl ether
and then dried over magnesium sulfate. After evaporation of
the solvents on the rotovap the residue was chromatographed
on silica gel (gradient of diethyl ether/pentane, 1:4 to 1:2) 1.06
g (65%) of the acetate 1f was isolated as yellow crystals. Mp:
1
118-120 °C. H NMR ([D6]DMSO, 300 MHz): δ ) 2.09 (s, 3
H), 5.68 (t, J ) 6.4 Hz, 1 H), 5.74 (t, J ) 6.1 Hz, 2 H), 5.88-
5.91 (m, 2 H), 6.61 (s, 1 H), 7.40-7.45 (m, 3 H), 7.55-7.58 (m,
2 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 20.79 (CH3), 65.09
(CH), 82.95 (Cquat.), 86.17 (Cquat.), 89.82 (Cquat.), 94.00 (CH),
94.29 (CH), 94.30 (CH), 97.05 (CH), 97.12 (CH), 127.82 (CH),
128.87 (CH), 129.26 (CH), 136.42 (Cquat.), 169.30 (Cquat.), 233.16
(Cquat.). MS (EI, 70 eV), m/z (%): 386 (M+, 20), 330 (M+ - 2
CO, 1), 302 (M+ - 3 CO, 100), 244 (M+ - 3 CO - OAc, 37),
191 (M+ - Cr(CO)3 - OAc, 52), 52 (Cr+, 31). IR (KBr): ν˜ )
3094 cm-1, 1968, 1915, 1895, 1740, 1637, 1527, 1495, 1457,
1430, 1409, 1368, 1348, 1307, 1291, 1280, 1224, 1190, 1149,
1017, 983, 952, 931, 891, 819, 756, 696, 673, 653, 631, 565,
544, 529, 470, 413. UV/vis (DMSO): λmax (ꢀ) ) 322 nm (9700).
Exp er im en ta l Section
All reactions involving tricarbonyl chromium 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.21 Column
chromatography: silica gel 60 (0.063-0.2 mm/70-230 mesh,
Firma Merck). TLC: silica gel plates (60 F254 Merck, Darm-
stadt). Melting points (uncorrected values): Reichert-J ung
Thermovar. The chromium carbonyl-complexed aryl propar-
gylic alcohols 1 were prepared according to our previously
published protocols.8 The trapping nucleophiles were pur-
chased from Merck, Aldrich, or Fluka and used 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
diodes array spectrometer) with a Hellma low-temperature
quartz probe and J &M Spektralys program 1.5.5 for evalua-
tion, Scho¨lly UV-spectrometer KGS III Intraphotometer (UV/
vis kinetics). MS: Finnigan MAT 90 and MAT 95 Q. Elemental
analyses were carried out in the Microanalytical Laboratory
Anal. Calcd for
C20H14CrO5 (386.32): C, 62.18; H, 3.65.
Found: C, 62.32; H, 3.73.
Gen er a tion of th e Ca tion 2a a n d Nu cleop h ilic Tr a p -
p in g Rea ction s (Gen er a l P r oced u r e). To a degassed solu-
tion of 100 µL (0.62 mmol) of HBF4 diethyl etherate in 10 mL
of dichloromethane was added a solution of 0.20 g (0.48 mmol)
of complex 1a in 5 mL of dichloromethane dropwise and under
nitrogen at -78 °C. Instantaneously, a dark green solution of
the propargyl cation was formed, which was stirred for 60 min
at -78 °C before a solution of 1.0-7.0 mmol of the nucleophile
in 5 mL of dichloromethane was added to the reaction mixture.
After stirring for 40 min at -78 °C the reaction mixture was
allowed to come to room temperature, and after 2 h at room
temperature 10 mL of water was added. The aqueous layer
(21) Various editors, Organikum, 14th ed.; VEB Deutscher Verlag
der Wissenschaften: Berlin, 1993.

3698 Organometallics, Vol. 18, No. 18, 1999
Mu¨ller et al.
129.0 (CH), 134.7 (CH), 135.4 (Cquat.), 205.6 (Cquat.), 234.1 (Cquat.
was extracted several times with dichloromethane. The com-
bined organic phases were dried over magnesium sulfate, and
the solvents were removed in vacuo (water bath 25 °C). The
residue (with exception of 7a and 7f) was chromatographed
on silica gel (diethyl ether/pentane, 1:1), and the yellow to
orange band was isolated to give the allenyl (7) or propargyl
derivatives (8a ,b) as crystalline products. Further purification
was achieved by recrystallization from suitable solvents.
Cr (CO)3(η6-C6H5)C[P +(C6H5)3]dCdC(C6H5)2BF4- (7a). Ac-
cording to the GP, the reaction with 0.262 g (1.0 mmol) of
triphenylphosphane gave rise to 200 mg (55%) of pure 7a after
recrystallization of the crude residue from dichloromethane/
,
CO). MS (EI, 70 eV), m/z (%): 444 (M+, 8), 360 (M+ - 3 CO,
100), 308 (M+ - Cr(CO)3, 8), 52 (Cr+, 3). IR (KBr): ν˜ ) 3078
cm-1, 1967, 1903, 1884, 1644, 1597, 1522, 1492, 1454, 1415,
1268, 1072, 1029, 991, 912, 819, 772, 754, 700, 681, 657, 629,
580, 531, 474. UV/vis (DMSO): λmax (ꢀ) ) 325 nm (10500).
Anal. Calcd for
C27H20CrO3 (444.44): C, 72.96; H, 4.54.
Found: C, 73.37; H, 4.72.
Cr (CO)3(η6-C6H5)C[o,p-C6H3(OCH3)2]dCdC(C6H5)2 (7e).
According to the GP, the reaction with 0.26 mL (2.0 mmol) of
1,3-dimethoxybenzene gave rise to 190 mg (73%) of pure 7e.
1
Mp: 174-178 °C. H NMR ([D6]DMSO, 300 MHz): δ ) 3.73
1
(s, 3 H), 3.78 (s, 3 H), 5.55 (d, J ) 6.0 Hz, 2 H), 5.66-5.73 (m,
3 H), 6.64 (d, J ) 8.2 Hz, 1 H), 6.69 (s, 1 H), 7.19 (d, J ) 8.0
Hz, 1 H), 7.38 (m, 10 H). 13C NMR ([D6]DMSO, 75 MHz): δ )
55.50 (CH3), 55.65 (CH3), 93.19 (CH), 94.25 (CH), 94.73 (CH),
99.21 (CH), 105.09 (Cquat.), 105.61 (CH), 107.03 (Cquat.), 112.86
(Cquat.), 114.08 (Cquat.), 128.18 (CH), 128.33 (CH), 128.86 (CH),
131.14 (CH), 134.95 (Cquat.), 157.98 (Cquat.), 161.26 (Cquat.),
206.37 (Cquat.), 233.97 (Cquat., CO). MS (EI, 70 eV), m/z (%): 540
(M+, 10), 456 (M+ - 3 CO, 100), 404 (M+ - Cr(CO)3, 64), 52
(Cr+, 9). IR (KBr): ν˜ ) 3059 cm-1, 2937, 2837, 1959, 1889,
1606, 1578, 1505, 1492, 1455, 1441, 1414, 1306, 1282, 1246,
1209, 1170, 1157, 1095, 1073, 1032, 927, 900, 836, 769, 745,
696, 659, 631, 581, 534, 475. UV/vis (DMSO): λmax (ꢀ) ) 315
nm (11600). Anal. Calcd for C32H24CrO5 (540.53): C, 71.10;
H, 4.47. Found: C, 71.47; H, 4.57.
diethyl ether. Mp: 197-200 °C. H NMR (CD2Cl2, 300 MHz):
δ ) 5.09-5.19 (m, 5 H), 6.85-7.46 (m, 25 H). 13C NMR (CD2-
Cl2, 75 MHz): δ ) 90.90 (CH), 90.90 (Cquat., 2 signals), 92.84
(Cquat., J P,C ) 87.5 Hz), 94.09 (CH), 94.40 (CH, J P,C ) 3.3 Hz),
98.79 (Cquat.), 117.08 (Cquat., J P,C ) 88.2 Hz), 128.73 (CH, J P,C
) 2.6 Hz), 129.53 (CH), 130.92 (CH), 131.08 (Cquat.), 131.09
(CH), 134.54 (CH, J P,C ) 10.6 Hz), 136.41 (CH, J P,C ) 3.3 Hz),
218.61 (Cquat., J P,C ) 3.9 Hz), 231.41 (Cquat., CO). 31P NMR (CD2-
Cl2, 121 MHz): δ ) 22.9 ppm. MS (FAB), m/z (%): 665 (M+
-
BF4-, 17), 581 (M+ - BF4 - 3 CO, 10), (M+ - BF4 - Cr-
(CO)3, 12). IR (KBr): ν˜ ) 3058 cm-1, 2924, 1967, 1890, 1629,
1586, 1483, 1453, 1439, 1407, 1309, 1187, 1123, 1108, 1062,
997, 901, 817, 770, 753, 725, 695, 656, 629, 576, 531, 519, 503.
UV/vis (DMSO): λmax (ꢀ) ) 340 nm (6300), 430 (1600).
Anal.Calcd for [C42H30CrO3P]+[BF4]- (752.46): C, 67.04; H,
4.01. Found: C, 66.93; H, 3.90.
-
-
Cr (CO)3(η6-C6H5)C{N[CH(CH3)2]2}dCdC(C6H5)2 (7f). De-
viating from the GP, the reaction with 1.0 mL (7.0 mmol) of
diisopropylamine was subjected to an aqueous workup with
saturated sodium bicarbonate solution. After extraction of the
aqueous phase with ether the combined organic extracts were
dried over magnesium sulfate and the solvents were removed
on the rotovap. The residue was recrystallized from pentane
to give 220 mg (91%) of pure 7f. Mp: 134-136 °C. 1H NMR
([D6]DMSO, 300 MHz): δ ) 1.01 (d, J ) 6.4 Hz, 12 H), 3.41
(sept, J ) 6.4 Hz, 2 H), 5.66 (t, J ) 6.3 Hz, 2 H), 5.77 (t, J )
6.1 Hz, 1 H), 6.07 (d, J ) 6.4 Hz, 2 H), 7.31-7.42 (m, 10 H).
13C NMR ([D6]DMSO, 75 MHz): δ ) 21.31 (CH3), 49.72 (CH),
92.71 (CH), 95.03 (CH), 96.36 (CH), 109.26 (Cquat.), 115.65
(Cquat.), 116.33 (Cquat.), 128.11 (CH), 128.24 (CH), 128.78 (CH),
135.96 (Cquat.), 206.05 (Cquat.), 233.92 (Cquat., CO). MS (EI, 70
eV), m/z (%): 503 (M+, 7), 447 (M+ - 2 CO, 7), 419 (M+ - 3
CO, 100), 367 (M+ - Cr(CO)3, 5), 52 (Cr+, 15). IR (KBr): ν˜ )
3081 cm-1, 2971, 2929, 1958, 1892, 1869, 1653, 1596, 1520,
1491, 1452, 1413, 1381, 1364, 1247, 1183, 1145, 1119, 1073,
1030, 897, 920, 827, 768, 737, 696, 661, 631, 605, 533, 476.
UV/vis (DMSO): λmax (ꢀ) ) 322 nm (11800). Anal. Calcd for
Cr (CO)3(η6-C6H5)C[C(CH3)2CO2CH3]dCdC(C6H5)2 (7b).
According to the GP, the reaction with 0.30 mL (1.50 mmol)
of 1-methoxy-2,2-dimethyl-1-(trimethylsiloxy)ethene gave rise
1
to 210 mg (87%) of pure 7b. Mp: 141-143 °C. H NMR ([D6]-
DMSO, 300 MHz): δ ) 1.41 (s, 6 H), 3.65 (s, 3 H), 5.69-5.78
(m, 5 H), 7.23-7.43 (m, 10 H). 13C NMR ([D6]DMSO, 75
MHz): δ ) 26.05 (CH3), 48.79 (Cquat.), 52.78 (CH3), 93.58 (CH),
95.07 (CH, broad, 2 signals), 106.15 (Cquat.), 111.24 (Cquat.),
114.18 (Cquat.), 128.19 (CH), 128.20 (CH), 128.91 (CH), 135.08
(Cquat.), 175.70 (Cquat.), 205.18 (Cquat.), 233.52 (Cquat., CO). MS
(EI, 70 eV), m/z (%): 504 (M+, 1), 448 (M+ - 2 CO, 1), 420 (M+
- 3 CO, 100), 368 (M+ - Cr(CO)3, 3), 52 (Cr+, 16). IR (KBr):
ν˜ ) 1956 cm-1, 1893, 1872, 1727, 1629, 1524, 1492, 1454, 1413,
1388, 1355, 1258, 1184, 1145, 1079, 821, 770, 747, 696, 659,
631, 585, 536, 475. UV/vis (DMSO): λmax (ꢀ) ) 324 nm (9100).
Anal. Calcd for C29H24CrO5 (504.49): C, 69.04; H, 4.79.
Found: C, 69.11; H, 4.79.
Cr (CO)3(η6-C6H5)C(2-cycloh exa n -1-on yl)dCdC(C6H5)2
(7c). According to the GP, the reaction with 0.19 mL (1.00
mmol) of 1-(trimethylsiloxy)cyclohexene gave rise to 110 mg
1
C
30H29CrNO3 (503.55): C, 71.55; H, 5.80, N: 2.78. Found: C,
(46%) of pure 7c. Mp: 122-125 °C. H NMR ([D6]DMSO, 300
71.57; H, 5.76, N: 2.63.
MHz): δ ) 1.60-3.65 (m, 9 H), 5.62-5.80 (m, 5 H), 7.37-
7.32 (m, 10 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 24.58
(CH2), 27.50 (CH2), 33.13 (CH2), 41.65 (CH2), 50.63 (CH), 92.38
(CH), 92.53 (CH), 93.51 (CH), 95.34 (CH), 95.84 (CH), 106.73
(Cquat.), 107.68 (Cquat.), 115.42 (Cquat.), 128.03 (CH), 128.11 (CH),
128.18 (CH), 128.85 (CH), 134.96 (Cquat.), 135.00 (Cquat.), 205.75
(Cquat.), 209.01 (Cquat.), 234.02 (Cquat., CO). MS (EI, 70 eV), m/z
(%): 500 (M+, 4), 472 (M+ - CO, 1), 444 (M+ - 2 CO, 1), 416
(M+ - 3 CO, 76), 364 (M+ - Cr(CO)3, 40), 52 (Cr+, 3). IR
(KBr): ν˜ ) 2939 cm-1, 2862, 1962, 1883, 1707, 1629, 1523,
1492, 1449, 1312, 1127, 1073, 771, 697, 659, 630, 532, 473.
UV/vis (DMSO): λmax (ꢀ) ) 324 nm (9200). Anal. Calcd for
Cr (CO)3(η6-C6H5)C(dO)CdC(C6H5)2 (9). (a ) Hyd r olysis
of th e Allen yla m in e 7f on Silica Gel. The crude alleny-
lamine (from a 0.48 mmol scale reaction, vide supra) was
chromatographed on wet silica gel (gradient ether to dichlo-
romethane) to give 100 mg (50%) of pure 9 as dark red needles
(from dichloromethane/pentane).
(b) Meyer -Sch u ster Rea r r a n gem en t of 1a . To a de-
gassed solution of 0.3 g (0.7 mmol) of 1a in 20 mL of THF was
added 6 mL of degassed 25% aqueous sulfuric acid. The
reaction mixture was heated to reflux temperature for 3 h.
After cooling the mixture was neutralized with a 2 N aqueous
sodium hydroxide solution, and the aqueous phase was
extracted several times with diethyl ether. The combined
organic extracts were washed with a saturated sodium bicar-
bonate solution and dried over magnesium sulfate. The
solvents were removed on the rotovap, and the residue was
chromatographed on silica gel (gradient diethyl ether/pentane,
1:4, to ether) to 220 mg (73%) of pure 9 as dark red needles
(from dichloromethane/pentane).
C
30H24CrO4 (500.51): C, 71.99; H, 4.83. Found: C, 72.06; H,
5.00.
Cr (CO)3(η6-C6H5)C[CH2CHdCH2]dCdC(C6H5)2 (7d ). Ac-
cording to the GP, the reaction with 0.24 mL (1.50 mmol) of
allyltrimethylsilane gave rise to 190 mg (89%) of pure 7d .
1
Mp: 136-138 °C. H NMR ([D6]DMSO, 300 MHz): δ ) 3.21
(d, J ) 5.1 Hz, 2 H), 5.11-5.26 (m, 2 H), 5.68 (m, 1 H), 5.80-
5.84 (m, 5 H), 7.35 (m, 10 H). 13C NMR ([D6]DMSO, 75 MHz):
δ ) 33.7 (CH2), 92.6 (CH), 94.1 (CH), 95.4 (CH), 105.3 (Cquat.),
107.0 (Cquat.), 114.7 (Cquat.), 117.7 (CH2), 128.2 (CH), 128.2 (CH),
Mp: 143-145 °C. 1H NMR ([D6]DMSO, 300 MHz): δ ) 5.64
(t, J ) 6.5 Hz, 2 H), 6.07 (t, J ) 6.3 Hz, 1 H), 6.44 (d, J ) 6.5

γ-Propargyl-Allenyl Cations
Organometallics, Vol. 18, No. 18, 1999 3699
Hz, 2 H), 7.17-7.37 (m, 11 H). 13C NMR ([D6]DMSO, 75
MHz): δ ) 91.98 (CH), 96.98 (CH), 98.54 (CH), 99.18 (Cquat.),
121.05 (CH, olefin.), 128.28 (CH), 128.40 (CH), 128.61 (CH),
128.77 (CH), 129.36 (CH), 129.96 (CH), 139.01 (Cquat.), 140.61
(Cquat.), 155.36 (Cquat.), 187.89 (Cquat.), 232.33 (Cquat., CO). MS
(EI, 70 eV), m/z (%): 420 (M+, 3), 392 (M+ - CO, 3), 364 (M+
- 2 CO, 8), 336 (M+ - 3 CO, 100), 284 (M+ - Cr(CO)3, 10), 52
(Cr+, 94). IR (KBr): ν˜ ) 1970 cm-1, 1888, 1651, 1587, 1569,
1445, 1367, 1266, 1205, 1147, 1021, 955, 865, 750, 698, 657,
619. UV/vis (DMSO): λmax (ꢀ) ) 317 nm (15500), 438 (3800).
(9100). Anal. Calcd for C14H12CrO3 (280.24): C, 60.00; H, 4.31.
Found: C, 60.04; H, 4.40.
Cr (CO)3(η6-C6H5)CtCC[o,p-C6H3(OCH3)2](CH3)2 (8d). Ac-
cording to the GP the reaction with 0.20 g (0.64 mmol) of
complex 1c and 0.42 mL (3.2 mmol) of 1,3-dimethoxybenzene
gave rise to 230 mg (86%) of pure 8d . Mp: 79-81 °C. 1H NMR
([D6]DMSO, 300 MHz): δ ) 1.61 (s, 6 H), 3.73 (s, 3 H), 3.82
(s, 3 H), 5.60-5.76 (m, 5 H), 6.45 (d, J ) 8.5 Hz, 1 H), 6.58 (s,
1 H), 7.39 (d, J ) 8.4 Hz, 1 H). 13C NMR ([D6]DMSO, 75
MHz): δ ) 29.16 (CH3), 34.57 (Cquat.), 55.30 (CH3), 55.64 (CH3),
77.07 (Cquat.), 93.03 (CH), 93.76 (Cquat.), 95.07 (CH), 96.64 (CH),
98.37 (Cquat.), 99.99 (CH), 104.32 (CH), 124.71 (Cquat.), 127.39
(CH), 158.52 (Cquat.), 159.77 (Cquat.), 233.69 (Cquat., CO). MS (EI,
Anal. Calcd for
C24H16CrO4 (420.38): C, 68.57; H, 3.84.
Found: C, 68.33; H, 3.74.
Cr (CO)3(η6-C6H 5)CtCCH (C6H 5)2 (8a ). According to the
GP, the reaction with 0.24 mL (1.50 mmol) of triethylsilane
gave rise to 180 mg (93%) of pure 8a . Mp: 94-97 °C. 1H NMR
([D6]DMSO, 300 MHz): δ ) 5.44 (s, 1 H), 5.65 (m, 1 H), 5.74-
5.76 (m, 2 H), 5.90-5.92 (m, 2 H), 7.22-7.55 (m, 10 H). 13C
NMR ([D6]DMSO, 75 MHz): δ ) 42.19 (CH), 80.59 (Cquat.),
91.14 (Cquat.), 92.19 (Cquat.), 93.62 (CH), 94.69 (CH), 97.07 (CH),
127.15 (CH), 127.66 (CH), 128.84 (CH), 141.42 (Cquat.), 233.54
70 eV), m/z (%): 416 (M+, 19), 360 (M+ - 2 CO, 3), 332 (M+
-
3 CO, 100), 280 (M+ - Cr(CO)3, 5), 52 (Cr+, 12). IR (KBr): ν˜ )
3076 cm-1, 2970, 2934, 2838, 2238, 1968, 1886, 1610, 1582,
1524, 1503, 1455, 1415, 1378, 1357, 1311, 1290, 1262, 1209,
1159, 1085, 1039, 995, 938, 842, 808, 724, 674, 655, 630, 573,
532, 472. UV/vis (DMSO): λmax (ꢀ) ) 323 nm (9100). Anal.
Calcd for C22H20CrO5 (416.39): C, 63.46; H, 4.84. Found: C,
63.27; H, 4.71.
(Cquat., CO). MS (EI, 70 eV), m/z (%): 404 (M+, 12), 348 (M+
-
-
Cr (CO)3(η6-C6H5)CtCC[P +(C6H5)3](CH3)2BF 4 (8e). Ac-
2 CO, 3), 320 (M+ - 3 CO, 100), 268 (M+ - Cr(CO)3, 13), 52
(Cr+, 3). IR (KBr): ν˜ ) 2981 cm-1, 1968, 1895, 1720, 1627,
1492, 1455, 1437, 1369, 1326, 1241, 1153, 1049, 1022, 866, 772,
745, 701, 673, 655, 628, 535, 470. UV/vis (DMSO): λmax (ꢀ) )
322 nm (9100). Anal. Calcd for C24H16CrO3 (404.38): C, 71.28;
H, 3.98. Found: C, 71.53; H, 4.38.
cording to the previous protocol, the reaction with 335 mg (1.28
mmol) of triphenylphosphane gave rise to 270 mg (67%) of 8e
after aqueous workup and recrystallization of the crude
product from dichloromethane/diethyl ether. Mp: 145-148 °C.
1H NMR (CD2Cl2, 300 MHz): δ ) 1.73 (d, 3J P,H ) 6.2 Hz, 6 H),
5.11-5.33 (m, 5 H), 7.56-7.85 (m, 15 H). 13C NMR (CD2Cl2,
75 MHz): δ ) 26.83 (CH3), 34.23 (Cquat., J P,C ) 50.4 Hz), 86.08
(Cquat., J P,C ) 3.7 Hz), 87.43 (Cquat., J P,C ) 7.5 Hz), 91.37 (Cquat.),
Cr (CO)3(η6-C6H5)CtCCOC2H5(C6H5)2 (8b). According to
the GP, the reaction with 117 µL (2.0 mmol) of ethanol gave
rise to 180 mg (84%) of pure 8b. Mp: 98-100 °C. 1H NMR
([D6]DMSO, 300 MHz): δ ) 1.22 (t, J ) 6.7 Hz, 3 H), 3.52 (q,
J ) 6.8 Hz, 2 H), 5.70 (t, J ) 6.1 Hz, 1 H), 5.78 (t, J ) 6.3 Hz,
2 H), 6.02 (d, J ) 6.2 Hz, 2 H), 7.26 (t, J ) 7.1 Hz, 2 H), 7.34
(t, J ) 7.2 Hz, 4 H), 7.55 (d, J ) 7.4 Hz, 4 H). 13C NMR ([D6]-
DMSO, 75 MHz): δ ) 15.35 (CH3), 60.23 (CH2), 79.99 (Cquat.),
85.24 (Cquat.), 88.91 (Cquat.), 90.21 (Cquat.), 94.11 (CH), 94.39
(CH), 97.34 (CH), 126.09 (CH), 127.91 (CH), 128.50 (CH),
143.25 (Cquat), 233.33 (Cquat., CO). MS (EI, 70 eV), m/z (%): 448
(M+, 9), 392 (M+ - 2 CO, 1), 364 (M+ - 3 CO, 18), 52 (Cr+,
14). IR (KBr): ν˜ ) 3082 cm-1, 2976, 2927, 2881, 1968, 1897,
1628, 1524, 1489, 1451, 1407, 1392, 1318, 1259, 1180, 1157,
1114, 1091, 1067, 1030, 1003, 940, 924, 815, 795, 760, 702,
672, 655, 630, 562, 532, 471. UV/vis (DMSO): λmax (ꢀ) ) 323
nm (9600). Anal. Calcd for C26H20CrO4 (448.43): C, 69.63; H,
4.49. Found: C, 70.25; H, 4.52.
91.37 (CH), 93.42 (CH), 96.27 (CH, J P,C ) 2.2 Hz), 116.61 (Cquat.
,
J P,C ) 82.2 Hz), 131.01 (CH, J P,C ) 11.9 Hz), 134.25 (CH, J P,C
) 12.6 Hz), 134.79 (CH, J P,C ) 8.6 Hz), 232.10 (Cquat., CO).
MS (EI, 70 eV), m/z (%): 541 (M+ - BF4-, 100), 513 (M+
-
BF4- - CO, 3), 457 (M+ - BF4- - 3 CO, 34), 405 (M+ - BF4
- Cr(CO)3, 89). IR (KBr): ν˜ ) 3068 cm-1, 2925, 1964, 1883,
1635, 1586, 1525, 1483, 1454, 1439, 1407, 1393, 1371, 1309,
1283, 1191, 1123, 1107, 1083, 1061, 996, 948, 913, 885, 840,
821, 755, 725, 693, 672, 654, 630, 618, 543, 532, 522, 510, 490.
UV/vis (DMSO): λmax (ꢀ) ) 324 nm (6900). Anal. Calcd for
[C32H26CrO3P]+[BF4]- (628.32): C, 61.17; H, 4.17. Found: C,
61.87; H, 4.44.
-
Cr (CO)3(η6-p -H 3CC6H 4)CtCC[o,p -C6H 3(OCH 3)2](CH 3)2
(8f). According to the GP, the reaction with 0.42 mL (3.2 mmol)
of 1,3-dimethoxybenzene gave rise to 190 mg (69%) of pure
8f. Mp: 122-124 °C. 1H NMR ([D6]DMSO, 300 MHz): δ )
1.59 (s, 6 H), 2.10 (s, 3 H), 3.73 (s, 3 H), 3.81 (s, 3 H), 5.62 (d,
Gen er a l P r oced u r e for th e in -Situ Ion iza tion of 1b
a n d 1c. To a cooled solution (-78 °C) of 150 µL (0.93 mmol)
of HBF4 diethyl etherate and 3.2 mmol of the acid-stable
nucleophile in 10 mL of dichloromethane was added dropwise
a solution of 0.64 mmol of the complex 1b or 1c in 5 mL of
dichloromethane over a period of 5 min. After 30 min of stirring
at -78 °C 10 mL of water was added to the reaction mixture.
The mixture was extracted several times with diethyl ether,
and the combined organic phases were dried over magnesium
sulfate. The residue was chromatographed on silica gel (1:3
diethyl ether/pentane) to give the pure propargylic products
(8c-g).
3
J ) 6.7 Hz, 2 H), 5.87 (d, J ) 6.6 Hz, 2 H), 6.43 (dd, J ) 8.7
4
4
3
Hz, J ) 2.4 Hz, 1 H), 6.57 (d, J ) 2.4 Hz, 1 H), 7.38 (d, J )
8.5 Hz, 1 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 20.02 (CH3),
29.15 (CH3), 34.54 (Cquat.), 55.30 (CH3), 55.66 (CH3), 76.81
(Cquat.), 90.43 (Cquat.), 94.71 (CH), 97.55 (Cquat.), 98.10 (CH),
100.02 (CH), 104.29 (CH), 109.81 (Cquat.), 124.83 (Cquat.), 127.38
(CH), 158.53 (Cquat.), 159.75 (Cquat.), 233.87 (Cquat., CO). MS (EI,
70 eV), m/z (%): 430 (M+, 18), 374 (M+ - 2 CO, 2), 346 (M+
-
3 CO, 100), 294 (M+ - Cr(CO)3, 4), 52 (Cr+, 12). IR (KBr): ν˜ )
3071 cm-1, 3013, 2974, 2936, 2241, 1965, 1906, 1891, 1610,
1581, 1504, 1457, 1439, 1387, 1357, 1310, 1291, 1271, 1258,
1209, 1160, 1139, 1085, 1044, 1028, 923, 887, 848, 798, 700,
676, 660, 644, 630, 574, 528, 471. UV/vis (DMSO): λmax (ꢀ) )
324 nm (9400). Anal. Calcd for C23H22CrO5 (430.41): C, 64.18;
H, 5.15. Found: C, 64.25; H, 5.27.
Cr (CO)3(η6-C6H5)CtCCH(CH3)2 (8c). According to the GP,
the reaction with 0.50 mL (3.2 mmol) of triethylsilane gave
rise to 160 mg (89%) of pure 8c. Mp: 57-60 °C. 1H NMR ([D6]-
DMSO, 300 MHz): δ ) 1.16 (d, J ) 6.7 Hz, 6 H), 2.76 (sept, J
) 6.8 Hz, 1 H), 5.52-5.76 (m, 5 H). 13C NMR ([D6]DMSO, 75
MHz): δ ) 22.65 (CH3), 31.23 (CH), 65.16 (Cquat.), 76.01 (Cquat.),
Cr (CO)3(η6-p-H3CC6H4)CtCC(CH2CHdCH2)(CH3)2 (8g).
To a cooled solution (-78 °C) of 150 µL (0.93 mmol) of HBF4
diethyl etherate in 10 mL of dichloromethane was added
dropwise a solution of 200 mg (0.64 mmol) of 1c and 0.51 mL
(3.2 mmol) of allyltrimethylsilane in 5 mL of dichloromethane
over a period of 5 min. After stirring at -78 °C for 15 min the
reaction mixture was allowed to come to room temperature
and was stirred for a further 15 min. The mixture was
extracted several times with diethyl ether, and the combined
92.94 (CH), 93.53 (Cquat.), 95.09 (CH), 96.53 (CH), 233.64 (Cquat.
,
CO). MS (EI, 70 eV), m/z (%): 280 (M+, 24), 252 (M+ - CO, 2),
224 (M+ - 2 CO, 17), 196 (M+ - 3 CO, 87), 144 (M+ - Cr-
(CO)3, 9), 52 (Cr+, 100). IR (KBr): ν˜ ) 3089 cm-1, 2976, 2931,
1872, 2235, 1968, 1900, 1869, 1635, 1527, 1454, 1408, 1383,
1365, 1322, 1254, 1151, 1098, 1047, 1011, 996, 936, 813, 673,
656, 628, 528, 512, 470. UV/vis (DMSO): λmax (ꢀ) ) 322 nm

3700 Organometallics, Vol. 18, No. 18, 1999
Mu¨ller et al.
organic phases were dried over magnesium sulfate. The
residue was chromatographed on silica gel (1:3 diethyl ether/
pentane) to give 200 mg (93%) of pure 8g as yellow crystals.
nucleophile in 5 mL of dichloromethane dropwise over 2 min.
After stirring for 30 min at -78 °C 10 mL of distilled water
was added, and the reaction mixture was allowed to come to
room temperature. The aqueous phase was extracted several
times with diethyl ether, and the combined organic phases
were dried over magnesium sulfate; the solvents were removed
on the rotovap. Chromatography of the residue on silica gel
(diethyl ether/pentane) afforded the pure substitution products
(8j,k ).
Cr (CO)3(η6-C6H 5)CtCCH [C(CH 3)2CO2CH 3](C6H 5) (8j).
According to the GP, 100 mg (0.26 mmol) of 1f, 0.20 mL (1.0
mmol) of 1-methoxy-2,2-dimethyl-1-(trimethylsiloxy)ethene,
and 63 µL (0.50 mmol) of boron trifluoride etherate gave rise
to 110 mg (98%) of 8j as a yellow oil. 1H NMR ([D6]DMSO,
300 MHz): δ ) 1.09 (s, 3 H), 1.27 (s, 3 H), 3.59 (s, 3 H), 4.27
(s, 1 H), 5.65-5.83 (m, 5 H), 7.31 (m, 5 H). 13C NMR
([D6]DMSO, 75 MHz): δ ) 21.58 (CH3), 23.27 (CH3), 45.68
(CH), 47.20 (Cquat.), 51.99 (CH3, OMe), 80.53 (Cquat.), 89.69
(Cquat.), 91.87 (Cquat.), 93.76 (CH), 94.52 (CH, double intensity),
97.14 (CH), 97.19 (CH), 127.75 (CH), 128.21 (CH), 129.36 (CH),
136.60 (Cquat.), 175.50 (Cquat.), 233.50 (Cquat.), CO). MS (EI, 70
eV), m/z (%): 428 (M+, 13), 372 (M+ - 2 CO, 2), 344 (M+ - 3
CO, 66), 292 (M+ - Cr(CO)3, 1), 52 (Cr+, 21). IR (KBr): ν˜ )
3087 cm-1, 3031, 2981, 2950, 2234, 1965, 1887, 1731, 1601,
1524, 1493, 1455, 1434, 1408, 1388, 1367, 1343, 1303, 1243,
1191, 1150, 1126, 1079, 1047, 1017, 985, 917, 867, 815, 770,
752, 737, 703, 672, 654, 628, 532, 472. UV/vis (DMSO): λmax
(ꢀ) ) 323 nm (8000). Anal. Calcd for C23H20CrO5 (428.40): C,
64.48; H, 4.71. Found: C, 65.02; H, 5.26.
Cr (CO)3(η6-C6H5)CtCCH(CH2COC6H5](C6H5) (8k ). Ac-
cording to the GP, 200 mg (0.52 mmol) of 1f, 0.42 mL (2.05
mmol) of 1-phenyl-1-(trimethylsiloxy)ethene silylenol ether,
and 126 µL (1.0 mmol) of boron trifluoride etherate gave rise
to 192 mg (86%) of 8k as a yellow oil. 1H NMR ([D6]DMSO,
300 MHz): δ ) 3.53 (dd, J ) 5.9 Hz, J ) 17.2 Hz, 1 H), 3.68
(dd, J ) 8.3 Hz, J ) 17.2 Hz, 1 H), 4.50 (dd, J ) 5.9 Hz, J )
8.1 Hz, 1 H), 5.60-5.72 (m, 5 H), 7.23-8.05 (m, 10 H). 13C
NMR ([D6]DMSO, 75 MHz): δ ) 32.87 (CH), 46.20 (CH2), 78.90
(Cquat), 92.32 (Cquat.), 92.56 (Cquat.), 93.25 (CH), 94.73 (CH), 96.69
(CH), 127.24 (CH), 127.77 (CH), 128.26 (CH), 128.71 (CH),
128.86 (CH), 133.52 (CH), 136.54 (Cquat.), 140.38 (Cquat.), 196.87
(Cquat.), 233.46 (Cquat.). MS (70 eV, EI), m/z (%): 446 (M+, 8),
362 (M+ - 3 CO, 100), 319 (M+ - Cr(CO)3, 16), 52 (Cr+, 17).
IR (KBr): ν˜ ) 2239 cm-1, 1965, 1887, 1687, 1597, 1580, 1525,
1493, 1449, 1407, 1351, 1308, 1258, 1240, 1206, 1181, 1151,
1077, 1047, 1002, 988, 970, 912, 814, 750, 699, 672, 653, 627,
589, 532, 471. UV/vis (DMSO): λmax (ꢀ) ) 321 nm (7300). Anal.
Calcd for C26H18CrO4 (446.42): C: 69.95, H: 4.06. Found: C:
69.47, H: 4.78.
1
Mp: 41-45 °C. H NMR ([D6]DMSO, 300 MHz): δ ) 1.18 (s,
6 H), 2.09 (s, 3 H), 2.18 (d, J ) 7.3 Hz, 2 H), 5.10 (d, J ) 12.8
Hz, 2 H), 5.62 (d, J ) 6.6 Hz, 2 H), 5.81 (d, J ) 6.7 Hz, 2 H),
5.86-5.97 (m, 1 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 19.99
(CH3), 28.43 (CH3), 31.24 (Cquat.), 46.88 (CH2), 76.68 (Cquat.),
90.17 (Cquat.), 94.80 (CH), 96.91 (Cquat.), 97.87 (CH), 109.56
(Cquat.), 118.19 (CH2), 134.80 (CH), 233.79 (Cquat., CO). MS (EI,
70 eV), m/z (%): 334 (M+, 26), 278 (M+ - 2 CO, 2), 250 (M+
-
3 CO, 86), 198 (M+ - Cr(CO)3, 1), 52 (Cr+, 34). IR (KBr): ν˜ )
3079 cm-1, 2973, 2926, 2235, 1966, 1891, 1641, 1540, 1466,
1443, 1384, 1363, 1314, 1298, 1156, 1096, 1035, 997, 919, 843,
815, 661, 626, 532, 472. UV/vis (DMSO): λmax (ꢀ) ) 324 nm
(9400). Anal. Calcd for C18H18CrO3 (334.33): C, 64.66; H, 5.42.
Found: C, 64.59; H, 5.45.
In -Situ Ion iza tion of th e P r op a r gyl Alcoh ol 1e (Gen -
er a l P r oced u r e). To a cooled solution (-78 °C) of 1.4 equiv
of 54% HBF4 etherate in 10 mL of dichloromethane was added
dropwise a solution of 1 equiv of 1e and 4 equiv of the acid-
stable nucleophile in 5 mL of dichloromethane over 2 min.
After stirring for 30 min at -78 °C 10 mL of distilled water
was added and the reaction mixture was allowed to come to
room temperature. The aqueous phase was extracted several
times with diethyl ether, the combined organic phases were
dried over magnesium sulfate, and the solvents were removed
on the rotovap. Chromatography of the residue on silica gel
(diethyl ether/pentane) afforded the pure substitution products
(8h ,i).
Cr (CO)3(η6-C6H5)CtCCH(CH2CHdCH2)(C6H5) (8h ). Ac-
cording to the GP, 90 mg (0.26 mmol) of 1e, 0.16 mL (1.0 mmol)
of allyltrimethylsilane, and 60 µL (0.37 mmol) of tetrafluo-
1
roboric acid gave rise to 80 mg (84%) of 8h as a yellow oil. H
NMR ([D6]DMSO, 300 MHz): δ ) 2.46-2.53 (m, 2 H), 4.04 (t,
J ) 7.5 Hz, 1 H), 5.03-5.10 (m, 3 H), 5.63 (t, J ) 6.2 Hz, 1 H),
5.75 (t, J ) 6.3 Hz, 2 H), 5.82 (d, J ) 6.2 Hz, 2 H), 7.24 (t, J
) 7.0 Hz, 1 H), 7.33 (t, J ) 7.1 Hz, 2 H), 7.40 (d, J ) 7.1 Hz,
2 H). 13C NMR ([D6]DMSO, 75 MHz): δ ) 37.07 (CH), 42.04
(CH2), 79.77 (Cquat.), 92.00 (Cquat.), 92.59 (Cquat.), 93.44 (CH),
94.72 (CH, double intensity), 96.94 (CH), 96.98 (CH), 117.74
(CH2), 127.09 (CH), 127.59 (CH), 128.34 (CH), 135.08 (CH),
140.46 (Cquat.), 233.55 (Cquat., CO). MS (EI, 70 eV), m/z (%): 368
(M+, 13), 312 (M+ - 2 CO, 1), 284 (M+ - 3 CO, 100), 232 (M+
- Cr(CO)3, 1), 52 (Cr+, 16). IR (KBr): ν˜ ) 3083 cm-1, 2917,
2238, 1969, 1892, 1641, 1600, 1524, 1493, 1455, 1408, 1343,
1306, 1261, 1181, 1150, 1075, 1046, 1030, 994, 920, 813, 759,
699, 672, 653, 627, 531, 471. UV/vis (DMSO): λmax (ꢀ) ) 322
nm (9000). Anal. Calcd for C21H16CrO3 (368.35): C, 68.47; H,
4.37. Found: C, 69.55; H, 4.85.
E-Cr (CO)3(η6-C6H5)C[o,p-C6H3(OCH3)2]dCHCH2[o,p-C6H3-
(OCH3)2] (10). To a cooled solution (-78 °C) of 173 µL (1.07
mmol) of HBF4 diethyl etherate and 0.48 mL (3.70 mmol) of
1,3-dimethoxybenzene in 10 mL of dichloromethane was added
dropwise a solution of 200 mg (0.74 mmol) of 1d in 5 mL of
dichloromethane over a period of 5 min. After stirring at -78
°C for 15 min the reaction mixture was allowed to come to
room temperature and was stirred for a further 90 min. The
mixture was extracted several times with diethyl ether, the
combined organic phases were dried over magnesium sulfate,
and the solvents were removed in vacuo (water bath 25 °C).
The residue was chromatographed on silica gel (1:2 diethyl
ether/pentane) to give 170 mg (44%) of pure 10 as a yellow oil
Cr (CO)3(η6-C6H5)CtCCH2(C6H5) (8i). According to the
GP, 140 mg (0.40 mmol) of 1e, 0.19 mL (1.20 mmol) of
triethylsilane, and 93 µL (0.58 mmol) of tetrafluoroboric acid
gave rise to 80 mg (61%) of 8i as a yellow crystals. Mp: 60-
62 °C. 1H NMR ([D6]DMSO, 300 MHz): δ ) 3.88 (s, 2 H), 5.64
(t, J ) 6.2 Hz, 1 H), 5.74 (t, J ) 6.4 Hz, 2 H), 5.86 (d, J ) 5.9
Hz, 2 H), 7.22-7.26 (m, 5 H). 13C NMR ([D6]DMSO, 75 MHz):
δ ) 24.57 (CH2), 78.51 (Cquat.), 89.08 (Cquat.), 92.67 (Cquat.), 93.64
(CH), 94.67 (CH), 97.13 (CH), 126.88 (CH), 128.03 (CH), 128.70
(CH), 136.05 (Cquat.), 233.59 (Cquat., CO). MS (EI, 70 eV), m/z
(%): 328 (M+, 16), 272 (M+ - 2 CO, 7), 244 (M+ - 3 CO, 100),
192 (M+ - Cr(CO)3, 16), 52 (Cr+, 35). IR (KBr): ν˜ ) 3086 cm-1
,
1
3031, 1969, 1887, 1629, 1525, 1495, 1455, 1408, 1338, 1289,
1183, 1151, 1075, 1047, 1029, 1012, 999, 939, 813, 737, 716,
696, 673, 654, 628, 532, 474. UV/vis (DMSO): λmax (ꢀ) ) 322
nm (9600). Anal. Calcd for C18H12CrO3 (328.28): C, 65.85; H,
3.68. Found: C, 65.76; H, 3.25.
In -Situ Ion iza tion of th e P r op a r gyl Aceta te 1f (Gen -
er a l P r oced u r e). To a cooled solution (-78 °C) of 2 equiv of
boron trifluoride etherate in 10 mL of dichloromethane was
added a solution of 1 equiv of 1f and 4 equiv of the acid-labile
that solidifies as a foam under vacuum. H NMR ([D6]DMSO,
400 MHz): δ ) 3.03 (d, J ) 7.1 Hz, 2 H), 3.69 (s, 3 H), 3.71
(br, 6 H), 3.79 (s, 3 H), 5.49-5.71 (m, 5 H), 6.41 (d, J ) 8.3
Hz, 1 H), 6.47-6.48 (m, 2 H), 6.61-6.65 (m, 2 H), 6.95 (d, J )
8.3 Hz, 1 H), 7.0 (d, J ) 8.1 Hz, 1 H). 13C NMR ([D6]DMSO,
75 MHz): δ ) 29.18 (CH2), 55.02 (CH3), 55.12 (CH3), 55.16
(CH3), 55.26 (CH3), 94.27 (CH, br, 2 signals), 94.58 (CH), 98.40
(CH), 98.80 (CH), 104.47 (CH), 105.16 (CH), 111.32 (Cquat.),
117.46 (Cquat.), 119.64 (Cquat.), 129.54 (CH), 130.83 (CH), 131.27

γ-Propargyl-Allenyl Cations
Organometallics, Vol. 18, No. 18, 1999 3701
(CH), 133.39 (Cquat.), 157.76 (Cquat.), 157.95 (Cquat.), 159.28
(Cquat.), 160.66 (Cquat.), 234.36 (Cquat., CO). MS (EI, 70 eV), m/z
(%): 526 (M+, 9), 442 (M+ - 3 CO, 100), 390 (M+ - Cr(CO)3,
13), 52 (Cr+, 6). IR (KBr): ν˜ ) 3084 cm-1, 3001, 2936, 2836,
1959, 1878, 1505, 1458, 1414, 1333, 1303, 1291, 1261, 1208,
1177, 1156, 1118, 1035, 935, 828, 697, 661, 631, 581, 534, 477.
UV/vis (DMSO): λmax (ꢀ) ) 276 nm (11000), 323 (9400). Anal.
Calcd for C28H26CrO7 (526.50): C, 63.87; H, 4.97. Found: C,
63.75; H, 5.08.
and for allowing us to use his J &M and Scho¨lly UV/
vis spectrometers for the kinetic investigations. We
heartily thank Dr. David S. Stephenson for recording
the low-temperature NMR spectra.
Su p p or tin g In for m a tion Ava ila ble: Figures of the 13C
NMR and UV/vis spectra of the propargyl alcohol 1a and the
cation 2a , the Walsh plots on the extended Hu¨ckel calculations
on the cation 2d , the MO plots of the ZINDO/CI calculations
on the cation 2a , and tables of data collection parameters, bond
lengths and angles, positional and thermal parameters, and
least-squares planes for 7d and 9. This material is available
free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. The financial support of the
Fonds der Chemischen Industrie, Deutsche Forschungs-
gemeinschaft, and the Dr.-Otto-Ro¨hm Geda¨chtnisstif-
tung is gratefully acknowledged. We wish to express our
appreciation to Prof. H. Mayr for his generous support
OM9900824