Bis(alkyne)cycloheptadienyl and Bis(alkyne)σ,η3- cycloheptenediyl complexes of tungsten

Article abstract of DOI:10.1021/om060111s

The syntheses of several new bis(alkyne)(carbonyl)(η⁵- cycloheptadienyl)tungsten(II) and bis(alkyne)-(carbonyl)(σ, η³-cycloheptenediyl)tungsten(II) complexes are described. Addition of HBF₄·Et₂O to [(η⁶

Full text of DOI:10.1021/om060111s

2574
Organometallics 2006, 25, 2574-2577
Bis(alkyne)cycloheptadienyl and Bis(alkyne)σ,η3-cycloheptenediyl
Complexes of Tungsten
Hojae Choi,† Weichun Chen,† Arnis Aistars,† Alan J. Lough,‡ and John B. Sheridan*,†
Department of Chemistry, Rutgers, The State UniVersity of New Jersey, UniVersity Heights,
Newark, New Jersey 07102, and Department of Chemistry, UniVersity of Toronto, 80 St. George Street,
Toronto, Ontario, M5S 3H6, Canada
ReceiVed February 3, 2006
The syntheses of several new bis(alkyne)(carbonyl)(η5-cycloheptadienyl)tungsten(II) and bis(alkyne)-
(carbonyl)(σ,η3-cycloheptenediyl)tungsten(II) complexes are described. Addition of HBF4‚Et2O to [(η6-
C7H8)W(CO)3] (1) followed by treatment with diarylalkynes gave the cationic complexes [(η5-
C7H9)W(CO)(ArCtCAr)2][BF4] (3a,b; Ar ) C6H5, 4-MeC6H4). These complexes react with nucleophiles
LiHBEt3, MeLi, and PhLi to form the neutral σ,η3-cycloheptenediyl complexes [(σ,η3-C7H9R)W(CO)-
(ArCtCAr)2] (4a-e; R ) H, Me, Ph), which contain η1, η2, and η3 ligands. In all complexes, the two
alkyne ligands act as net three-electron donors, although in the neutral complexes the two alkynes are
inequivalent. The X-ray structure of [(σ,η3-C7H9Ph)W(CO)(PhCtCPh)2] (4e) is reported. Complexes
4a,b (Ar ) C6H5, 4-MeC6H4, R ) H) can be converted back to the cations 3a,b using the
triphenylcarbenium ion.
a
Scheme 1
Introduction
We have previously described the [6 + 2] and [5 + 2]
cycloaddition reactions of alkynes to η6-cycloheptatriene and
η5-cyclohexadienyl manifolds respectively coordinated to chro-
mium and manganese.1-6 These reactions result in the formation
of a number of different organic ring products depending upon
the transition-metal manifold and the reaction stoichiometry,
and Rigby and co-workers have utilized the [6 + 2] process in
some elegant syntheses.7,8 In each case the products are proposed
to arise via a series of stepwise insertions of the alkyne into the
polyene manifolds. The proposed mechanism for the triene-
alkyne [6 + 2] cycloaddition (Scheme 1) involves the photo-
ejection of CO followed by coordination of the alkyne to the
metal prior to insertion. A key intermediate is the triene-alkyne
species A or, in the case of the [5 + 2] additions, a dienyl-
alkyne species.
a
X ) CHR, N-CO2Et; R ) Ar, SiMe3.
attempted to isolate such complexes via the reaction of various
alkynes with tricarbonyl metal triene or dienyl complexes either
thermally or by using UV irradiation at low temperature. In all
cases, either cycloaddition products or decomposition was
observed. The rationale for using UV light is to displace a
carbonyl ligand and generate a 16-electron species that might
capture the alkyne substrate. An alternative route to coordina-
tively unsaturated polyene or polyenyl complexes is protonation
of the polyene ring, leading to oxidation at the metal center.
One complex that can be protonated in this way is tricarbonyl-
(η6-cycloheptatriene)tungsten(0) (1)10 to give the unsaturated
cation 2. This method has been used to generate many
cycloheptadienyl tungsten and molybdenum species with various
ancillary ligands.11,12
Whereas there are many known transition-metal alkyne
complexes,9 examples containing noncyclically conjugated triene
or dienyl ligands such as intermediate A are rare; indeed we
are unaware of any such species prior to this study. We have
* Corresponding author. E-mail: jsheridn@newark.rutgers.edu.
† Rutgers, The State University of New Jersey.
‡ University of Toronto.
(1) Chen, W.; Chaffee, K.; Chung, H.-J.; Sheridan, J. B. J. Am. Chem.
Soc. 1996, 118, 9980-9981.
(2) Chaffee, K.; Huo, P.; Sheridan, J. B.; Barbieri, A.; Aistars, A.;
Lalancette, R. A.; Ostrander, R. L.; Rheingold, A. L. J. Am. Chem. Soc.
1995, 117, 1900-1907.
(3) Chaffee, K.; Sheridan, J. B.; Aistars, A. Organometallics 1992, 11,
18-19.
(4) Chen, W.; Chung, H.-J.; Wang, C.; Sheridan, J. B.; Cote, M. L.;
Lalancette, R. A. Organometallics 1996, 15, 3337-3344.
(5) Chung, H.-J.; Sheridan, J. B.; Cote, M. L.; Lalancette, R. A.
Organometallics 1996, 15, 4575-4585.
Herein, we report the isolation of cationic cycloheptadienyl
alkyne complexes through reaction of 2, generated in situ from
(6) Wang, C.; Sheridan, J. B.; Chung, H.-J.; Cote, M. L.; Lalancette, R.
A.; Rheingold, A. L. J. Am. Chem. Soc. 1994, 116, 8966-8972.
(7) Rigby, J. H.; Laxmisha, M. S.; Hudson, A. R.; Heap, C. H.; Heeg,
M. J. J. Org. Chem. 2004, 69, 6751-6760.
(10) Salzer, A.; Werner, H. Z. Anorg. Allg. Chem. 1975, 41B, 88.
(11) Carruthers, K. P.; Helliwell, M.; Hinchliffe, J. R.; de Souza, A.-L.
A. B.; Spencer, D. M.; Whiteley, M. W. J. Organomet. Chem. 2004, 689,
848-859.
(12) Beddoes, R. L.; Hinchliffe, J. R.; Whiteley, M. W. J. Chem. Soc.,
Dalton Trans. 1993, 501-508.
(8) Rigby, J. H.; Heap, C. R.; Warshakoon, N. C. Tetrahedron 2000,
56, 2305-2311.
(9) Templeton, J. L. AdV. Organomet. Chem. 1989, 29, 1.
10.1021/om060111s CCC: $33.50 © 2006 American Chemical Society
Publication on Web 03/24/2006

Bis(alkyne)cycloheptadienyl Complexes of Tungsten
Organometallics, Vol. 25, No. 10, 2006 2575
1, with diphenyl- and ditolylacetylene. Each complex contains
two alkyne ligands acting as net 3e- donors. These cations react
with nucleophiles at C2 of the dienyl ring to form neutral σ,η3-
enediyl bis(alkyne) species that have two inequivalent alkyne
ligands that again donate a total of 6e- to the tungsten center.
Results and Discussion
Addition of HBF4‚Et2O to tricarbonyl(η6-cycloheptatriene)-
tungsten(0) (1) at -78 °C gave the known intermediate 2.
Subsequent addition of excess diphenyl- or ditolylacetylene gave
the moderately air stable yellow solids bis(diphenylacetylene)-
(carbonyl)(η5-cycloheptadienyl)tungsten(II) tetrafluoroborate (3a)
and bis(ditolylacetylene)(carbonyl)(η5-cycloheptadienyl)tung-
sten(II) tetrafluoroborate (3b), respectively (eq 1). The new
complexes are similar to the known cyclopentadienyl species13
[CpW(MeCtCMe)2CO]+ but have the noncyclically conjugated
cycloheptadienyl ligand. To our knowledge, cations 3a and 3b
are the only examples of noncyclically conjugated diene or
dienyl species with alkyne ligands, although such species have
been postulated as intermediates in metal-promoted cycloaddi-
tion reactions by us and others. In general, the paucity of
dienyl-alkyne complexes is due to the facile insertion of
alkynes into dienyl or diene ligands; however in this case the
third-row metal appears to disfavor insertion and provides a
stable alkyne-dienyl species.
Figure 1. Molecular structure of 4e‚0.5CH2Cl2 with hydrogen
atoms and solvate omitted for clarity. Thermal ellipsoids are shown
at the 30% probability level.
yield (eq 2). In each case, addition of the nucleophile occurs at
C2 of the dienyl manifold to yield the novel σ,η3-cyclohep-
tenediyl bis(alkyne) complexes that contain η1, η2, and η3
carbon-bound ligands. Complexes 4a-e were fully characterized
by IR and 1H, 13C, and 1H-1H (2D COSY) NMR spectroscopy
as well as by elemental analysis (4a,b). The neutral complexes
contain a carbonyl ligand (νmax 2039 cm-1) and two nonequiva-
lent alkyne ligands. The 1H NMR spectrum of 4a has peaks at
δ 1.19, 4.04, 4.98, and 6.11 for protons on the σ,η3-enediyl-
coordinated carbons. The 13C NMR spectrum is consistent with
the assigned structure and shows a single carbonyl signal (δ
218.7), coordinated alkyne carbons (δ 152.9, 168.1, 177.8, and
183.6), and the σ,η3-enediyl carbons at 30.2, 73.8, 83.7, and
117.7. The four resonances for the alkyne carbons indicate
nonequivalent alkynes, and although the chemical shifts again
suggest net three-electron donors, the wide range (153-184
ppm) indicates the different environments of the two ligands.
Complexes 3a,b were fully characterized by IR and 1H, 13C,
and 2D NMR spectroscopy as well as by elemental analysis.
The IR spectrum shows a single carbonyl peak at νmax 2076
cm-1, close to the published value of 2040 cm-1 for [CpW-
(MeCtCMe)2(CO)][PF6]13 but shifted to higher wavenumber
1
due to the weaker donor diarylalkyne ligands. The H NMR
spectrum shows resonances characteristic of symmetric cationic
η5-dienyl groups, suggesting either that the carbonyl lies beneath
the methylene carbons or C3 of cycloheptadienyl ligand or that
the dienyl group rotates rapidly. The 13C NMR spectrum is also
consistent with the assigned structure and shows a single
carbonyl at 211.5 ppm and alkyne carbons at 159 and 181.8
ppm. The chemical shift of these latter carbons is consistent
with each alkyne being a net three-electron donor to tungsten,9
giving a formal 18-electron configuration at the metal. Attempts
to use other alkynes, phenylacetylene, 2-butyne, and bis-
(trimethylsilyl)acetylene, failed to yield tractable products.
Likewise, attempts to prepare the analogous molybdenum
derivatives from the protonation of tricarbonyl(η6-cyclo-
heptatriene)molybdenum(0) in the presence of diphenylacetylene
also failed to give isolable products.
The structure of the phenyl adduct 4e was solved using X-ray
crystallography (Figure 1) and shows one alkyne is virtually
trans to the sigma-bonded C1, whereas the other is trans to the
allyl group. A closer analysis of the structural data clearly shows
the difference between the alkyne ligands, with that trans to
C1 (C15tC16) having a slightly shorter bond (1.299(3) Å) and
longer W-C distances (av W-C15, W-C16 ) 2.125(3) Å)
and greater Ph-CtC bond angles (144°). The second alkyne
trans to the allyl group has a longer bond (1.315(4) Å), shorter
W-C distances (av W-C17, W-C18 ) 2.075(3) Å), and
smaller Ph-CtC bond angles (av 139°). Whereas these data
do not conclusively show that one alkyne is a 2e donor and the
Reactions with Nucleophiles. The addition of lithium
triethylborohydride, methyllithium, or phenyllithium to both
3a,b gave the neutral complexes 4a-e as orange oils in good
(13) Watson, P. L.; Bergman, R. G. J. Am. Chem. Soc. 1980, 102, 2698.

2576 Organometallics, Vol. 25, No. 10, 2006
Choi et al.
other a 4e donor, they do indicate that alkyne C17tC18 is more
tightly bonded to tungsten, most likely a consequence of the
weaker trans effect of the allyl group compared to the sigma-
bonded C1. The allyl group itself shows nonsymmetrical
bonding to tungsten with W-C(4) 2.371(3) Å, W-C(5) 2.342-
(3) Å, and W-C(3) 2.507(3) Å. The sigma-bonded carbon C1
is 2.253(3) Å from the metal center.
In addition to the major isomers described above, minor
isomers were observed for each of the reactions and tentatively
identified as rotamers in which the carbonyl ligand lies beneath
the methylene carbons C6 and C7 rather than beneath C2.
Although not fully characterized, for the reaction of 3a with
phenyllithium, the minor species represented ca. 25% of the
isolated product and all the ring proton NMR signals were
observable. The general pattern and multiplicity of these signals
were similar to those of the major species, suggesting a similar
structure. The alternative, in which the nucleophile adds to C1
of the dienyl ring, producing an η4-cycloheptadiene complex,
would be expected to give a significantly different pattern of
proton NMR signals and was therefore ruled out. The 1H NMR
spectrum of the crystals used in the X-ray study was also
measured and showed only one species (the major isomer) was
present.
contrast to the reactions of alkynes with other dienyl transition-
metal manifolds, no coupling or insertion of the alkynes into
the metal-dienyl, metal-sigma, or metal-allyl bonds was
observed, due perhaps to the stronger metal-alkyne bonds.
Experimental Section
The preparation, purification, and reactions of all complexes
described were performed under an inert atmosphere of dry nitrogen
using standard Schlenk techniques unless otherwise stated. Solvents
were dried over Na/benzophenone (THF, Et2O) and CaH2 (n-
hexane, CH2Cl2) and were freshly distilled prior to use. NMR
spectra were recorded on a Varian Unity Inova (500 MHz) NMR
Fourier transform spectrometer. The solvents used for NMR studies
were CDCl3 and C6D6 as purchased from Cambridge Isotope
Laboratories, Inc. (Andover, MA). Chromatography was performed
on silica gel (100-200 mesh, purchased from Sorbent Technologies,
Atlanta, GA) or alumina (basic). Filtrations used Celite purchased
from Fisher Scientific that was preheated and dried before use.
Tricarbonyl(cycloheptatriene)tungsten(0)19 and ditolylacetylene20
were prepared via the published procedures.
Bis(diphenylacetylene)(carbonyl)(η5-cycloheptadienyl)tung-
sten(II) Tetrafluoroborate (3a). Tetrafluoroboric acid diethyl ether
complex (HBF4‚Et2O) (0.14 mL) was added dropwise to a stirred
solution of (η6-C7H8)W(CO)3 (0.20 g, 0.556 mmol) in dichlo-
romethane (10 mL) at -78 °C. After 5 min, the solution was
warmed to room temperature and stirred for 30 min. Diphenyl-
acetylene (0.24 g, 1.35 mmol) was added in one portion and the
mixture stirred for an additional 30 min under nitrogen. Removal
of the solvent under reduced pressure gave an oily residue, which
was washed with cold dry ether and recrystallized from CH2Cl2/
Et2O (1:5). The product 3a‚BF4 (0.333 g, 80%) was obtained as a
solid yellow powder after filtration. 3a‚BF4: νmax (CO)/cm-1, CH2-
Nucleophilic attack at C2 of dienyl systems is rare, with attack
at C1 to give η4-diene derivatives being the norm. However,
isolated examples of C2 attack to generate σ,η3-enediyl species
have been reported14-16 and with third-row metals17 and
electron-donating ancillary ligands18 appearing to favor attack
at C2. Therefore, the presence of the third-row metal and the
electron-rich alkyne ligands in cations 3a,b appears to direct
addition to C2 of the cycloheptadienyl ligand and form the σ,η3-
enediyl complexes.
1
Cl2, 2076 (vs). H NMR (500 MHz, CDCl3): δ 9.11 (t, 1H, H3),
Complexes 4a,b react with triphenylcarbenium hexafluoro-
phosphate or tetrafluoroborate to form the parent cations 3a,b
as their PF6 or BF4 salts, respectively. Interstingly, the IR and
1H NMR spectral data of 3a‚PF6 and 3b‚PF6 are slightly
different from their tetrafluoroborate analogues; for example,
in 3b‚PF6 H3 resonates at 9.03 ppm, whereas in 3b‚BF4 H3 is
observed at 8.90 ppm. Clearly the counterion has some
interaction with the cation; however, crystals could not be
obtained for an X-ray study. Complexes 4c-e were also reacted
with triphenylcarbenium hexafluorophosphate or triphenylcar-
benium tetrafluoroborate but failed to give tractable products
presumably due to the fact that a methyl or phenyl group at C2
prevents formation of a conjugated η5-dienyl group following
hydride abstraction.
7.23-7.82 (m, 20H, 4Ph), 5.98(t, 2H, H2,4), 4.79 (m, 2H, H1,5),
2.80 (m, 2H, H6′,7′), 2.61 (d, 2H, H6,7). 13C NMR (125 MHz,
CDCl3): δ 211.5 (CO), 181.8 (CtC), 159.0 (CtC), 142.5, 140.2
(ipso-Ph), 125-133 (4Ph), 121.9 (C2,4), 102.1 (C3), 100.1 (C1,5),
34.9 (C6,7). Anal. Calcd for C36H29BF4OW; C, 57.75; H, 3.88 (%).
Found: C, 58.04; H, 3.84 (%).
Bis(ditolylacetylene)(carbonyl)(η5-cycloheptadienyl)tungsten-
(II) Tetrafluoroborate (3b). Complex 3b was prepared similarly
to 3a using ditolylacetylene. 3b‚BF4 (0.473 g, yield 85%): νmax
1
(CO)/cm-1, CH2Cl2, 2072 (vs). H NMR (500 MHz, CDCl3): δ
9.03 (t, 1H, H3), 7.77 (d, 4H, Ph), 7.37 (d, 8H, 2Ph), 7.19 (d, 4H,
Ph), 5.93 (t, 2H, H2,4), 4.69 (m, 2H, H1,5), 2.79 (m, 2H, H6′,7′), 2.58
(d, 2H, H6,7), 2.48 (s, 6H, 2Me), 2.40 (s, 6H, 2Me). 13C NMR (125
MHz, CDCl3): δ 211.8 (CO), 179.1 (CtC), 157.0 (CtC), 142.9,
140.3 (ipso-Ph), 133.0, 130.9, 130.7, 130.0, 129.9, 127.6 (4Ph),
121.6 (C2,4), 101.6 (C3), 97.0 (C1,5), 34.5 (C6,7), 21.39 (2Me), 21.37
(2Me).
Conclusions
New bis(alkyne)(carbonyl)(η5-cycloheptadienyl)tungsten(II)
tetrafluoroborate complexes (3a,b) were formed from tri-
carbonyl(η6-cycloheptatriene)tungsten(0) (1) and diphenyl- or
ditolylacetylene in the presence of HBF4‚Et2O. These cations
contain two three-electron donor alkynes and react with nu-
cleophiles (e.g., hydride, MeLi, or PhLi) at C2 of the dienyl
ligand to form neutral σ,η3-cycloheptenediyl complexes. In
Preparation of 4a. Lithium triethylborohydride (0.5 mL of a
1.0 M solution in THF, 0.5 mmol) was added dropwise to a stirred
solution of 3a‚BF4 (0.333 g, 0.445 mmol) in ether (10 mL) at -78
°C. The solution was slowly warmed to room temperature over 30
min and filtered through Celite, and the filtrate dried under reduced
pressure. Chromatography of the residue (silica gel, 30 cm × 2.5
cm), loading (0.5 mL), and eluting with n-hexane gave analytically
pure 4a (0.265 g, 90%) as an orange oil after removal of solvent
in vacuo. 4a: νmax (CO)/cm-1 (hex), 2044 (vs), (CH2Cl2) 2039 (vs).
1H NMR (500 MHz, assignments refer to Figure 1, CDCl3): δ
7.17-7.87 (m, 20H, 4Ph), 6.11 (t, 1H, H5), 4.98 (t, 1H, H3), 4.04
(t, 1H, H4), 2.92 (d, 1H, H2), 2.31-2.44 (m,4H, H6,6′,7,2′), 1.19 (m,
1H, H1), 0.99 (d, 1H, H7′). 13C NMR (125 MHz, CDCl3): δ 218.7
(CO), 183.6 (CtC), 177.8 (C′tC), 168.1 (CtC), 152.9 (CtC′),
(14) Roell, B. C., Jr.; McDaniel, K. F.; Vaughan, W. S.; Macy, T. S.
Organometallics 1993, 12, 224-228.
(15) Roell, B. C., Jr.; McDaniel, K. F. J. Am. Chem. Soc. 1990, 112,
9004-9006.
(16) McDaniel, K. F.; Kracker, L. R., II; Thamburaj, P. K. Tetrahedron
Lett. 1990, 31, 2373-2376.
(17) Burrows, A. L.; Johnson, B. F. G.; Lewis, J.; Parker, D. G. J.
Organomet. Chem. 1980, 194, C11-C13.
(18) Pearson, A. J.; L., K. S.; Ray, T. J. Am. Chem. Soc. 1984, 106,
6060-6074.
(19) King, R. B.; A., F. Inorg. Chem. 1966, 5, 1837.
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Bis(alkyne)cycloheptadienyl Complexes of Tungsten
Organometallics, Vol. 25, No. 10, 2006 2577
140.6, 140.4, 138.9, 137.4 (ipso-Ph), 127-131 (Ph), 117.5 (C4),
83.7 (C3), 73.8 (C5), 44.1 (C1), 30.2 (C2), 28.69 (C6), 28.65 (C7).
Anal. Calcd for C36H30OW: C, 65.26; H, 4.53 (%). Found: C,
65.30; H, 4.70 (%).
in vacuo. The product is a mixture of two isomers in a 3:1 ratio.
Yellow crystals of 4e‚0.5CH2Cl2 used in the X-ray study were
grown from a hexane/dichloromethane solution at -10 °C over a
1
few days. 4e-major: νmax (CO)/cm-1 (hex), 2041 (vs). H NMR
Preparation of 4b. Complex 4b was prepared similarly to 4a
from 3b‚BF4 (0.38 g, 0.473 mmol) as an analytically pure orange
oil (0.178 g, 38%). 4b: νmax (CO)/cm-1 (hex), 2044 (vs), (CH2-
Cl2) 2036 (vs). 1H NMR (500 MHz, assignments refer to Figure 1,
CDCl3): δ 7.2-7.8 (m, 16H, 4Ar), 6.09 (t, 1H, H5), 4.94 (t, 1H,
H3), 3.97 (t, 1H, H4), 2.89 (d, 1H, H2), 2.2-2.5 (m, 16H, 4Me,
(500 MHz, assignments refer to Figure 1, CDCl3): δ 7.85-6.94
(m, 25H, 5Ph), 6.20 (t, 1H, H5), 4.87 (t, 1H, H3), 4.70 (t, 1H, H4),
3.90 (m, 1H, H2), 2.06 (m, 1H, H6), 1.85 (m, 1H, H7), 1.63 (m,
1H, H6′), 1.45 (d, 1H, H1), 0.85 (m, 1H, H7′). 13C NMR (125 MHz,
C6D6): δ 218.4 (CO), 181.2 (CtC), 175.6 (C′tC), 166.2 (CtC),
153.0 (CtC′), 148.1 (ipso-Ph attached to C5), 140.7, 140.4, 138.8,
137.6 (ipso-Ph), 125.6-130.1 (Ph), 119.6 (C4), 81.3 (C3), 77.1 (C5),
45.7 (C2), 38.4 (C1), 36.2 (C6), 29.4 (C7). 4e-minor: 1H NMR (500
MHz, CDCl3): δ 7.85-6.94 (m, Ph), 6.50 (t, 1H), 5.58 (dd, 1H),
3.80 (dd, 1H), 3.29 (dd, 1H), 1.95 (m, 1H), 1.77 (m, 3H), 0.60 (d,
1H).
Preparation of 3b‚PF6 from 4b. Triphenylcarbenium hexafluo-
rophosphate ([Ph3C]PF6) (32 mg, 0.083 mmol) was added in one
portion to a solution of 4b (60 mg, 0.084 mmol) in CH2Cl2 (10
mL) at 0 °C. The reaction was stirred for 10 min at 0 °C and
warmed to room temperature over 30 min. Removal of the solvent
in vacuo until 0.5 mL of solution remained and precipitation with
ether (10 mL) gave the solid yellow product 3b‚PF6 (60 mg, 76%),
which was washed with cold dry ether (2 × 3 mL) and dried under
vacuum. Analytically pure product was obtained by precipitation
from CH2Cl2 solution using ether. 3b‚PF6: νmax (CO)/cm-1, (CH2-
Cl2) 2069 (vs). 3b‚PF6.CH2Cl2: Anal. Calcd for C41H39Cl2PF6-
OW: C, 51.96; H, 4.12. Found: C, 51.89; H, 4.23. 1H NMR (500
MHz, CDCl3): δ 8.90 (t, 1H, H3), 7.71 (d, 4H, Ph), 7.35 (d, 8H,
2Ph), 7.17 (d, 4H, Ph), 5.88 (dd, 2H, H2,4), 4.67 (d, 2H, H1,5), 2.77
(d, 2H, H6′,7′), 2.57 (m, 2H, H6,7), 2.45 (s, 6H, 2Me), 2.38 (s, 6H,
2Me).
H
6,6′,7,2′), 1.16 (m, 1H, H1), 0.89 (d, 1H, H7′). 13C NMR (125 MHz,
CDCl3): δ 219.7 (CO), 182.3 (CtC), 176.8 (C′tC), 167.3 (Ct
C), 152.2 (CtC′), 133-138 (ipso-Ar), 125-131 (Ar), 117.5 (C4),
83.2 (C3), 73.2 (C5), 44.0 (C1), 30.1 (C2), 28.7 (C6), 28.2 (C7), 21.44
(Me), 21.34 (Me), 21.25 (Me), 21.19 (Me). Anal. Calcd for C40H38-
OW: C, 66.87; H, 5.29 (%). Found: C, 66.99; H, 5.40 (%).
Preparation of 4c. Methyllithium (0.56 mL of a 1.0 M solution
in THF, 0.56 mmol) was added dropwise to a stirred solution of
3a‚BF4 (0.400 g, 0.535 mmol) in ether (20 mL) at -78 °C. The
solution was slowly warmed to room temperature over 30 min and
filtered through Celite, and the filtrate dried under reduced pressure.
Chromatography of the residue (silica gel, 30 cm × 2.5 cm), loading
(0.5 mL), and eluting with n-hexane gave 4c (0.27 g, 75%) as a
yellow oil after removal of solvent in vacuo. The product is a
mixture of two isomers in a 4:1 ratio; only the major isomer was
fully characterized. 4c-major: νmax (CO)/cm-1 (hex), 2045 (vs),
(CH2Cl2) 2039 (vs). 1H NMR (500 MHz, assignments refer to
Figure 1, CDCl3): δ 7.21-7.85 (m, 20H, 4Ph), 6.08 (t, 1H, H5),
4.97 (dd, 1H, J(HH) ) 6.5 Hz, H3), 4.26 (dd, 1H, J(HH) ) 6.5
Hz, H4), 2.62 (d, 1H, H2), 2.45 (m, 2H, H6,7), 2.23 (m, 1H, H6′),
0.97 (m, 2H, H7′,1), 0.51 (d, 3H, Me). 13C NMR (125 MHz,
CDCl3): δ 218.3 (CO), 181.2 (CtC), 175.8 (C′tC), 166.2
(CtC), 152.2 (CtC′), 126.9-140.3 (Ph), 117.5 (C4), 90.3 (C3),
74.7 (C5), 36.4 (C1), 36.2 (C2), 35.5 (C6), 31.7 (C7), 25.6 (Me).
Preparation of 4d. Complex 4d was prepared similarly to 4c
from 3b‚BF4 (0.400 g, 0.498 mmol) as a yellow oil (0.30 g, 82%).
The product is a mixture of two isomers in a 7:1 ratio; only the
major isomer was fully characterized. 4d-major: νmax (CO)/cm-1
(Et2O), 2038 (vs). 1H NMR (500 MHz, assignments refer to Figure
1, CDCl3): δ 7.0-7.9 (m, 16H, 4Ar), 6.03 (t, 1H, H5), 4.92 (dd,
1H, J(HH) ) 6.0 Hz, H3), 4.19 (dd, 1H, J(HH) ) 6.0 Hz, H4),
2.62 (m, 1H, H2), 2.3-2.5 (m, 14H, 4Me, H6′7), 2.20 (m, 1H, H6′),
0.91 (m, 2H, H6′,1), 0.49 (d, 3H, J(HH) ) 5.3 Hz, Me). 13C NMR
(125 MHz, CDCl3): δ 218.0 (CO), 180.0 (CtC), 174.7 (C′tC),
165.4 (CtC), 151.5 (CtC′), 134-139 (ipso-Ar), 126-130 (Ar),
117.4 (C4), 89.9 (C3), 74.3 (C5), 36.4 (C1), 36.0 (C2), 35.5 (C6),
31.6 (C7), 25.6 (Me), 21.1-21.4 (4Me).
3a‚PF6 was prepared similarly from 4a in 82% yield.
X-ray crystallographic Study. Data were collected on a Nonius
Kappa-CCD diffractometer using monochromated Mo KR radiation
and were measured using a combination of φ scans and ω scans
with κ offsets, to fill the Ewald sphere. The data were processed
using the Denzo-SMN package.21 The structure was solved and
refined using SHELXTL V6.122 for full-matrix least-squares
refinement that was based on F2. All H atoms were included in
calculated positions and allowed to refine in riding-motion ap-
proximation with Uiso tied to the carrier atom.
Acknowledgment. We thank the Rutgers Research Council
for financial support.
Supporting Information Available: Crystallographic data for
4e in cif format are available free of charge via the Internet at
http://pubs.acs.org.
Preparation of 4e. Phenyllithium (0.11 mL of a 2.0 M solution
in THF, 0.22 mmol) was added dropwise to a stirred solution of
3a‚BF4 (0.146 g, 0.195 mmol) in ether (20 mL) at -78 °C. The
solution was slowly warmed to room temperature over 30 min and
filtered through Celite, and the filtrate dried under reduced pressure.
Chromatography of the residue (alumina, 30 cm × 2.5 cm), loading
with hexane (0.5 mL), and eluting with n-hexane/THF (94:4) gave
4e (0.27 g, yield 75%) as a yellow powder after removal of solvent
OM060111S
(21) Otwinowski, Z.; Minor, W. In Methods in Enzymology, Macro-
molecular Crystallography, Part A; Carter, C. W., Sweet, R. M., Eds.;
Academic Press: London, 1997; Vol. 276, pp 307-326.
(22) Sheldrick, G. M. SHELXTL/PC, Version 6.1 Windows NT Version;
Bruker AXS Inc.: Madison, WI, 2001.