Diels-Alder Reactions of 3-Ferrocenyl-2,4,5-triphenylcyclopentadienone: Syntheses and Structures of the Sterically Crowded Systems C6Ph5Fc, C7Ph6FcH, and [C7Ph6FcH][SbCl6]

Article abstract of DOI:10.1021/om980645w

Diels-Alder addition of diphenylacetylene or of 1,2,3-triphenylcyclopropene to 3-ferrocenyl-2,4,5-triphenylcyclopentadienone yields, upon thermolysis, C₆Ph₅Fc (5) or C₇Ph₆FcH (8), respectively. Subsequent treatment of 8 with triethyloxonium hexachloroantimonate results in the formation of the ferricinium complex [C₇Ph₆FcH]⁺[SbCl₆]^- (13), rather than the anticipated tropylium cation [C₇Ph₆Fc]⁺. The substituted ferrocene derivatives 5, 8, and 13 have been characterized by X-ray crystallography. From the solid-state structure of 5 it is evident that the peripheral aryl substituents do not adopt a regular propeller type conformation, but instead exhibit an incremental progression of twist angles relative to the central ring. The dynamics of peripheral ring rotations in 5 and 8 have been studied by variable-temperature NMR.

Full text of DOI:10.1021/om980645w

Organometallics 1999, 18, 115-122
115
Articles
Diels-Ald er Rea ction s of
3-F er r ocen yl-2,4,5-tr ip h en ylcyclop en ta d ien on e:
Syn th eses a n d Str u ctu r es of th e Ster ica lly Cr ow d ed
System s C6P h 5F c, C7P h 6F cH, a n d [C7P h 6F cH][SbCl6]
Hari K. Gupta, Stacey Brydges, and Michael J . McGlinchey*
Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1
Received J uly 29, 1998
Diels-Alder addition of diphenylacetylene or of 1,2,3-triphenylcyclopropene to 3-ferrocenyl-
2,4,5-triphenylcyclopentadienone yields, upon thermolysis, C6Ph5Fc (5) or C7Ph6FcH (8),
respectively. Subsequent treatment of 8 with triethyloxonium hexachloroantimonate results
in the formation of the ferricinium complex [C7Ph6FcH]+[SbCl6]- (13), rather than the
anticipated tropylium cation [C7Ph6Fc]+. The substituted ferrocene derivatives 5, 8, and 13
have been characterized by X-ray crystallography. From the solid-state structure of 5 it is
evident that the peripheral aryl substituents do not adopt a regular propeller type
conformation, but instead exhibit an incremental progression of twist angles relative to the
central ring. The dynamics of peripheral ring rotations in 5 and 8 have been studied by
variable-temperature NMR.
In tr od u ction
is intricately tied to the time scale of observation and
is rendered more likely when the internal rotors (such
as aryl groups) of the propeller framework are tightly
intermeshed.1
Sterically crowded molecules, with their attendant
opportunities for correlated molecular motions,1 their
suggested roles as micromachines,2 and their conse-
quent relevance to nanotechnology,3 continue to attract
much interest. Typical examples include Kelly’s recent
reports of “molecular brakes and ratchets”4 and Moore’s
“molecular turnstile”.5
Whereas propellers of 2- or 3-fold symmetry (C2, C3
or D2, D3) have been studied in considerable detail,7 less
attention has been given to higher order systems. Not
(
only do molecular paddle-wheels of the type CnArn
present a synthetic and structural challenge8 but a
comprehensive probe of the stereochemistry of such
species, under static and dynamic conditions, may ulti-
mately allow one to extend the scope of the topological
analysis of isomerism and isomerization developed by
Gust and Mislow for triaryl and diaryl systems.7 To
date, our own contributions to the diverse collection of
molecular paddle-wheels and their organometallic de-
rivatives have included such species as (C5Ph5)Fe(CO)-
(HCdO)PR3, 1,9 (C6Ph6)Cr(CO)3, 2,10 and the novel
seven-bladed propeller [C7Ph7]+, 3.11 Relevant to our
long-term goal of preparing molecular machines pos-
sessing bulky organometallic fragments, we now de-
scribe the syntheses, structures, and molecular dynam-
ics of a series of polyphenylated systems incorporating
the ferrocenyl moiety.
Germane to the aforementioned theme are molecular
propellers, a broad class of compounds comprising two
or more substituents arranged in a helical (chiral)
conformation about a central core.6 Such a molecular
model combines structure with dynamic function, in-
troducing the possibility of correlated rotation and
complex stereoisomerization phenomena. This concept
* E-mail: mcglinc@mcmaster.ca. Phone: (905)-525-9140 ext 24504.
Fax: (905)-522-2509.
(1) Iwamura, H.; Mislow, K. Acc. Chem. Res. 1988, 21, 175.
(2) Mislow, K. Chemtracts: Org. Chem. 1989, 2, 151.
(3) Rouhi, A. M. Chem. Eng. News 1998, 76, 6(16), 57-62 (April
20).
(4) (a) Kelly, T. R.; Bowyer, M. C.; Bhaskar, K. V.; Bebbington, D.;
Garcia, A.; Lang, F.; Kim, M. H.; J ette, M. P. J . Am. Chem. Soc. 1994,
116, 3657. (b) Kelly, T. R.; Tellitu, I.; Sestelo, J . P. Angew. Chem., Int.
Ed. Engl. 1997, 36, 1866. (c) Kelly, T. R.; Sestelo, J . P.; Tellitu, I., J .
Org. Chem. 1998, 63, 3655.
(5) Bedard, T. C.; Moore, J . S. J . Am. Chem. Soc. 1995, 117, 10662.
(6) For a review of molecular propellers, refer to: Meurer, K. P.;
Vo¨gtle, F. Top. Curr. Chem. 1985, 127, 3-75.
(7) (a) Gust, D.; Mislow, K. J . Am. Chem. Soc. 1973, 95, 1535, and
references therein. (b) Finocchiaro, P.; Gust, D.; Mislow, K. J . Am.
Chem. Soc. 1974, 96, 3198. (c) Mislow, K.; Gust, D.; Finocchiaro, P.;
Boettcher, R. Top. Curr. Chem. 1974, 47, 1. (d) Finocchiaro, P. Gazz.
Chim. Ital. 1975, 105, 149. (e) Mislow, K. Acc. Chem. Res. 1976, 9, 26.
(f) Glaser, R.; Blount, J . F.; Mislow, K. J . Am. Chem. Soc. 1980, 102,
2777. (g) Willem, R.; Gielen, M.; Hoogzand, C.; Pepermans, H. Adv.
Dyn. Stereochem. 1985, 1, 207.
(8) For examples of CnArn( systems, see: Olah, G. A.; Mateescu, G.
D. J . Am. Chem. Soc. 1970, 92, 1430.
(9) Li, L.; Decken, A.; Sayer, B. G.; McGlinchey, M. J .; Bre´gaint, P.;
The´pot, J .-Y.; Toupet, L.; Hamon, J .-R.; Lapinte, C. Organometallics
1994, 13, 682.
(10) Mailvaganam, B.; Sayer, B. G.; McGlinchey, M. J . J . Organomet.
Chem. 1990, 395, 177.
(11) Brydges, S.; Gupta, H. K.; Chao, L. C. F.; Pole, D. L.; Britten,
J . F.; McGlinchey, M. J . Chem. Eur. J . 1998, 7, 1199.
10.1021/om980645w CCC: $18.00 © 1999 American Chemical Society
Publication on Web 12/24/1998

116 Organometallics, Vol. 18, No. 2, 1999
Gupta et al.
dienones as Diels-Alder reagents has recently been
exploited in the preparation of spherical polyphenylene
dendrimers16 and polyphenyl polycyclic aromatic hy-
drocarbons.17,18
The X-ray crystal structure of C6Ph5Fc, 5, appears as
Figure 1, and crystallographic refinement parameters
and selected structural data are provided in Tables 1
and 2, respectively. In the solid state 5 exhibits several
intriguing features and may be contrasted with the
structure of C6Ph6, which adopts a propeller configura-
tion with interplanar angles of approximately 67(75)°
between the phenyl groups and the central ring.19a,b,20
Steric requirements undoubtedly influence the geometry
of C6Ph5Fc, as evinced by the severe twisting of the
peripheral phenyls out of the central plane. However,
the dihedral angles made by the ferrocenyl and phenyl
substituents relative to the central ring follow a curious
progression, as illustrated in Figure 2. The ferrocenyl
ring bonded to C(1) is oriented at 51° to the central
plane, and the phenyls attached to C(2) through C(6)
exhibit dihedral angles of 64°, 70°, 81°, 89°, and 120°,
respectively. The net effect is to provide a series of
peripheral rings each displaced slightly more than its
immediately preceding neighbor. One is tempted to
postulate that rotation of the ferrocenyl moiety would
induce a domino effect such that all the phenyls turn
in a synchronous fashion. Verification of such an asser-
tion would require extensive labeling studies, and we
make no definitive claims at this time.
Resu lts a n d Discu ssion
(C6Ar 5)MLx Com p lexes, MLx ) (C5H 4)F e(C5H 5).
The pioneering papers by Gust et al. on the mechanisms
of aryl rotations in C6Ar6 systems, and their associated
barriers, established (i) that peripheral aryl ring rota-
tions are uncorrelated and (ii) that the incorporation of
ortho-methoxy or meta-methyl or methoxy substituents
give rise to rotational barriers of 33 and 17 kcal mol-1
,
respectively.12 These experiments have subsequently
been extended to complexes of the type (CnPhn)MLx
whereby the π-bonded organometallic fragment(s) ren-
der inequivalent the faces rather than the edges of the
aryl rings.13
Accordingly, a dynamic NMR spectroscopic analysis
of (C6Ph6)Cr(CO)3, in which the tricarbonylchromium
moiety is complexed to a peripheral ring, yielded a ∆Gq
value of 12.2 kcal mol-1 for the independent rotation of
the substituted ring relative to the central plane.10
Although not detectable under the experimental condi-
tions, a concomitant isomerization process involving a
low-energy oscillation which inverts the handedness of
the enantiomerically related chiral propellers was pro-
posed. Thus, (C6Ph6)Cr(CO)3 exists in two stereoisomeric
forms, a d,l pair having C1 symmetry, which may only
be observed as a NMR time-averaged Cs isomer at low
temperature (193 K) and as an effective C2v conforma-
tion at 300 K.
In the quest to obtain a system that could be locked
as a chiral propeller, perhaps even at ambient temper-
ature, it was thus of considerable appeal to construct
another C6Ph5MLn molecule possessing a different
sterically demanding organometallic fragment. The
ferrocenyl analogue of 2, i.e., C6Ph5Fc, 5, was prepared
by Rausch and Siegel in 1978, but no structural or
dynamic data were reported.14 The original synthesis
involved the Diels-Alder addition of ferrocenylpheny-
lacetylene to tetraphenylcyclopentadienone (commonly
referred to as tetracyclone), followed by decarbonylation
of the intermediate bicyclic ketone to yield 5. Our
somewhat complementary approach required the prior
preparation of 3-ferrocenyl-2,4,5-triphenylcyclopenta-
dienone, 4,15 as depicted in Scheme 1. This latter
methodology has the advantage of also providing a route
to the seven-membered ring system C7Ph6FcH, 8, a
consideration that is discussed below. It is important
to recognize that the versatility of tetraarylcyclopenta-
1
Perhaps surprisingly, the 500 MHz H and 125 MHz
13C data on 5 indicate that both fluxional processes
previously detailed for (C6Ph6)Cr(CO)3 are fast on the
NMR time scale. Even at 188 K, the 13C spectrum of
the phenyl rings remains essentially unchanged from
its appearance at room temperature; apparently, the
overall effect of replacing a (C6H5)Cr(CO)3 substituent
by a ferrocenyl fragment is to lower substantially the
barriers to fluxionality, thus rendering more difficult
the generation of a chiral propeller. In retrospect, the
typical cone volume of a Cr(CO)3 moiety (∼21 Å3) is
somewhat greater than that of its ferrocenyl counterpart
(∼17 Å3), on account of the spatial extension engendered
by the carbonyl ligands.21 To achieve hindered rotation
(16) (a) Morgenroth, F.; Reuther, E.; Mu¨llen, K. Angew. Chem. 1997,
109, 1067. (b) Morgenroth, F.; Reuther, E.; Mu¨llen, K. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 361. (c) Morgenroth, F.; Ku¨bel, C.; Mu¨llen, K.
J . Mater. Chem. 1997, 7, 1207. (d) Morgenroth, F.; Berresheim, A. J .;
Wagner, M.; Mu¨llen, K. Chem. Commun. 1998, 1139.
(17) (a) Qiao, X.; Padula, M. A.; Ho, D. M.; Vogelaar, N. J .; Schutt,
C. E.; Pascal, R. A., J r. J . Am. Chem. Soc. 1996, 118, 741. (b) Qiao, X.;
Ho, D. M.; Pascal, R. A., J r. Angew. Chem., Int. Ed. Engl. 1997, 36,
1531. (c) Tong, L.; Ho, D. M.; Vogelaar, N. J .; Schutt, C. E.; Pascal, R.
A., J r. Tetrahedron Lett. 1997, 38, 7. (d) Tong, L.; Ho, D. M.; Vogelaar,
N. J .; Schutt, C. E.; Pascal, R. A., J r. J . Am. Chem. Soc. 1997, 119,
7291. (e) Tong, L.; Lau, H.; Ho, D. M.; Pascal, R. A., J r. J . Am. Chem.
Soc. 1998, 120, 6000.
(18) (a) Iyer, V. S.; Wehmeier, M.; Brand, J . D.; Keegstra, M. A.;
Mu¨llen, K. Angew. Chem., Int. Ed. Engl. 1997, 36, 1604. (b) Mu¨ller,
M.; Iyer, V. S.; Ku¨bel, C.; Enkelmann, V.; Mu¨llen, K. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 1607.
(12) (a) Gust, D. J . Am. Chem. Soc. 1977, 99, 6980. (b) Gust, D.;
Patton, J . J . Am. Chem. Soc. 1978, 100, 8175.
(13) (a) Mailvaganam, B.; McCarry, B. E.; Sayer, B. G.; Perrier, R.
E.; Faggiani, R.; McGlinchey, M. J . J . Organomet. Chem. 1987, 335,
213. (b) Malisza, K. L.; Chao, L. C. F.; Britten, J . F.; Sayer, B. G.;
J aouen, G.; Top, S.; Decken, A.; McGlinchey, M. J . Organometallics
1993, 12, 2462.
(14) Siegel, A.; Rausch, M. D. Synth. React. Inorg. Met.-Org. Chem.
1978, 8 (3), 209.
(15) For details of the synthesis, refer to: Rausch, M. D.; Siegel, A.
J . Org. Chem. 1968, 33, 4545.
(19) (a) Bart, J . C. J . Acta Crystallogr. 1968, B24, 1277. (b) Larson,
E. M.; Von Dreele, R. B.; Hanson, P.; Gust, J . D. Acta Crystallogr. 1990,
C46, 784.
(20) Early electron diffraction studies of hexaphenylbenzene vapor
found that the peripheral phenyl rings oscillate at (10° from the
orthogonal form. Almenningen, A.; Bastiansen, O.; Skancke, P. N. Acta
Chem. Scand. 1958, 12, 1215.
(21) Ligand cone volumes (πr2h/3) were estimated from the struc-
tural data of several organometallic complexes, utilizing the dimensions
defined by the ligand base (r) and the centroid of the CnHn ring to the
centroid of the ligand base (h).

3-Ferrocenyl-2,4,5-triphenylcyclopentadienone
Organometallics, Vol. 18, No. 2, 1999 117
Sch em e 1. Syn th etic Rou tes to C6P h 5F c, 5
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 5, 8, a n d 13
5
8
13
empirical formula
molecular weight
description
C
46H34Fe
C53H40Fe
732.70
red-orange
prism
C53H40Cl6FeSb
1067.15
dark blue
prism
642.58
red plate
dimens, mm
0.05 × 0.15 × 0.20 × 0.18 × 0.09 × 0.10 ×
0.30
213(2)
0.10
267(2)
0.12
210(2)
temp, K
wavelength, Å
(Mo KR)
0.710 73
(Mo KR)
0.710 73
(Mo KR)
0.710 73
cryst syst
space group
a, Å
b, Å
c, Å
orthorhombic triclinic
monoclinic
P21/n
Pccn
P(1h)
45.1814(1)
11.6417(2)
12.2057(2)
90.000(0)
90.000(0)
90.000(0)
6420.1(2)
8
9.7962(1)
11.0580(0)
18.8717(2)
87.795(1)
89.927(1)
69.973(1)
1919.18(3)
2
10.8063(0)
11.9269(1)
39.0821(3)
90.000(0)
96.256(1)
90.000(0)
5007.13(6)
4
R, deg
â, deg
γ, deg
volume, Å3
Z
calcd density, g/cm3
abs coeff, mm-1
F(000)
1.330
1.268
1.416
1.183
2148
0.503
0.430
2688
768
θ-range for
collection, deg
transmission (min)
transmission (max)
index ranges
0.90-23.00
1.08-22.50
1.05-22.50
0.629
0.941
0.850
0.977
0.592
0.914
F igu r e 1. Top view of the molecular structure of C6Ph5-
Fc, 5 (30% thermal ellipsoids), with hydrogen atoms
omitted for clarity.
-56 e h e 56 -8 e h e 12 -12 e h e 13
-14 e k e 11 -13 e k e 13 -14 e k e 14
-15 e l e 15 -23 e l e 23 -48 e l e 48
no. reflns collected
no. ind reflns
R(int)
36 391
4472
0.1962
11 499
4906
0.0273
20 633
6520
0.1034
about the single bond joining the central and peripheral
aryl groups, the steric influence imparted by an orga-
nometallic fragment must be reflected in both of its
dimensions.
refinement method
no. data/restraints/
params
full-matrix least-squares on F2
4448/0/424
4887/0/488
6520/0/551
Syn th esis a n d Str u ctu r e of C7P h 6F cH. As noted
above, 3-ferrocenyl-2,4,5-triphenylcyclopentadienone, 4,
is an effective diene in the Diels-Alder reaction and,
when treated with diphenylacetylene, gives 5 after
extrusion of carbon monoxide. We have previously
reported the synthesis, structure, and molecular dy-
namics of C7Ph7H, 7, which is readily prepared by
decarbonylation of the Diels-Alder adduct of tetracy-
clone with 1,2,3-triphenylcyclopropene (Scheme 2).22,23
It was also emphasized that the initial decarbonyla-
tion product, 6, in which the unique hydrogen is endo,
goodness-of-fit on F2
final R indices
(I > 2σ(I))*
1.101
R1 ) 0.0734
1.054
0.0354
0.784
0.0365
wR2 ) 0.1110 0.0793
R1 ) 0.1340 0.0492
wR2 ) 0.1316 0.0865
0.0759
0.0620
0.0807
0.565
R indices (all data)a
largest diff peak, e/Å3 0.288
0.289
-0.245
largest diff hole, e/Å3 -0.337
-0.516
R1 ) ∑(||Fo|- |Fc||)/∑|Fo|; wR2 ) [∑[ω(Fo2 - Fc2)2]/∑[ω(Fo2)2]]0.5
.
a
undergoes facile [1,5]-suprafacial sigmatropic hydrogen
shifts to generate a mixture of isomeric products from
suitably labeled precursors.23 This product distribution
is frozen after an irreversible ring inversion which
places the unique hydrogen in the favored exo-site, as
in compound 7.
(22) (a) Battiste, M. A. J . Am. Chem. Soc. 1961, 83, 4101. (b)
Battiste, M. A. Chem. Ind. 1961, 550.
(23) Chao, L. C. F.; Gupta, H. K.; Hughes, D. W.; Britten, J . F.;
Rigby, S. S.; Bain, A. D.; McGlinchey, M. J . Organometallics 1995, 14,
1139.

118 Organometallics, Vol. 18, No. 2, 1999
Gupta et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 5, 8, a n d 13
substituents: in C7Ph7H (C7Cl8) the corresponding
angles for ([plane 1])/[plane 2]) and for ([plane 2]/[plane
3]) are 55° (52°) and 35° (32°), respectively.23,25
5
8
13
As a complement to these crystallographic studies, the
conformational flexibility of C7Ph6FcH, 8, in solution
was probed by variable-temperature NMR spectroscopy.
The room-temperature 500 MHz 1H and 13C NMR
spectra of 8 were completely assigned (with the excep-
tion of phenyl rings 3 and 4, which cannot be differenti-
ated) by means of 1H-1H COSY and 1H-13C shift-
correlated experiments. In its perphenylated analogue,
C7Ph7H, 7, the rotation of phenyl 7 could not be
monitored because the mirror plane renders its ortho
and meta protons equivalent at any temperature. This
symmetry is disrupted in C7Ph6FcH, and on warming
the sample, the pair of doublets (at 7.71 and 8.08 ppm)
attributable to the ortho protons of phenyl 7 (H72/H76)
broaden and converge to give a doublet at 7.97 ppm.
These coalescence data, obtained at 202 K, yield a
rotational barrier of 9.3 ((0.5) kcal/mol. Likewise, the
ortho protons of phenyl 4 (H42/H46), which at 193 K
resonate at 5.59 and 6.16 ppm, exhibited coalescence
at 223 K, corresponding to a free energy of activation
of 10.1 ((0.5) kcal/mol for the analogous process. Rota-
tion of the other phenyls in 8 is also clearly slowed on
the NMR time scale (refer to Figure 4), but overlapping
resonances leave the assignments less certain.
Bond Lengths
1.412(7)
1.403(7)
1.406(7)
1.403(7)
C(1)-C(2)
1.353(3)
1.478(3)
1.360(3)
1.487(3)
1.355(3)
1.369(5)
1.479(6)
1.362(6)
1.475(5)
1.360(4)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.396(7)
1.434(7)
C(6)-C(1)
C(6)-C(7)
1.527(3)
1.526(3)
1.486(3)
2.044
1.523(5)
1.502(7)
1.487(6)
2.089
C(7)-C(1)
C(1)-C(11)
Fe-C5H4R (avg)
Fe-C5H5 (avg)
1.493(7)
2.052
2.053
2.037
2.072
Bond Angles
119.9(5)
121.1(5)
119.3(5)
120.3(5)
120.6(5)
118.3(5)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(5)-C(6)-C(1)
C(6)-C(1)-C(2)
C(5)-C(6)-C(7)
C(6)-C(7)-C(1)
C(7)-C(1)-C(2)
122.8(2)
124.9(2)
124.7(2)
122.7(2)
122.1(5)
124.5(3)
125.6(3)
124.1(3)
120.6(2)
107.5(2)
121.1(2)
119.6(3)
107.7(4)
121.8(4)
Treatment of 4 with triphenylcyclopropene, and sub-
sequent decarbonylation, resulted in the corresponding
polyphenylated species, C7Ph6FcH, in an acceptable
yield. Despite the complexity of the H and 13C NMR
1
spectra, only one of several possible isomers (as depicted
in Scheme 2) appeared to be present, and the identifica-
tion of this product was realized by X-ray crystal-
lography. From the two views of the molecular structure
of 8 that are provided in Figure 3, it is evident that the
ferrocenyl substituent is positioned at C(1), adjacent to
the sp3-hybridized carbon of the CHPh unit.
Clearly, such an isomer must have arisen as the result
of a [1,5]-hydrogen shift after decarbonylation but prior
to inversion of the cycloheptatriene ring. Comparison
of the structure of 8 with that of C7Ph7H reveals that
the ferrocenyl unit is located in the sterically least
demanding site. In C7Ph7H itself, variable-temperature
1H and 13C NMR data disclosed that the phenyls at C(2)/
C(5) have relatively high rotational barriers (11.0 ( 0.5
kcal mol-1) relative to the phenyls positioned at C(1)/
C(6) and C(3)/C(4) and presumably reside in the most
hindered locale.23
Consistent with the solid-state geometries of other Cn-
Arn systems,24 the peripheral aryl substitutents are
oriented in a twisted fashion relative to the central ring
in C7Ph6FcH, 8, affording dihedral angles of 56°, 82°,
81°, 68°, 55°, 132°, and 142° with the plane defined by
the attached central ring carbons C(1) to C(7), respec-
tively, and neighboring ring atoms. Moreover, the seven-
membered ring in 8 adopts a boat conformation that is
distinguished by the planes containing C(6)-C(7)-C(1)
[plane 1], C(1)-C(2)-C(5)-C(6), [plane 2], and C(2)-
C(3)-C(4)-C(5) [plane 3]. The interplanar angles of 54°
([plane 1]/[plane 2]) and 34° ([plane 2]/[plane 3]) are
consonant with the values that we have previously
reported for other cycloheptatrienes bearing very bulky
One of our aims in preparing C7Ph6FcH, 8, was to
attempt the isolation of the corresponding cation [C7-
Ph6Fc]+, 9, to compare its geometry with that of [C7-
Ph7]+, 3,11 and with other ferrocenyl cations.26 The
ability of the ferrocenyl moiety, in addition to other
cluster-based organometallic units, to alleviate electron
deficiency at a neighboring carbocationic center has
been well-established.27,28 This is generally accom-
plished by allowing the positively charged site to bend
toward the metal so as to optimize the orbital overlap
between the vacant p orbital on carbon and a filled d
orbital on iron.29 In the extreme, one may view the
resulting structure as a fulvene coordinated to a [(C5H5)-
Fe]+ unit, as in 10. On the contrary, if the carbocation
does not require anchimeric assistance from the electron-
rich metal center, it is reasonable to infer that the
organometallic fragment will effect minimal geometric
distortions in the adjacent cationic center. For instance,
it has been shown crystallographically that Hu¨ckel-type
aromatic cationic systems, which are stable in the
absence of a metal, retain their planarity even when
an organometallic moiety is present. Examples include
the tropylium and pyrylium complexes 11 and 12,
(25) Dunn, J . A.; Gupta, H. K.; Bain, A. D.; McGlinchey, M. J . Can.
J . Chem. 1996, 74, 2258.
(26) For examples, see: (a) Lupon, S.; Kapon, M.; Cais, M.; Herb-
stein, F. H. Angew. Chem., Int. Ed. Engl. 1972, 11, 1025. (b) Behrens,
U. J . Organomet. Chem. 1979, 182, 89.
(27) (a) Hill, E. A.; Wiesner, R. J . Am. Chem. Soc. 1969, 91, 510. (b)
Gleiter, R.; Seeger, R.; Binder, H.; Fluck, E.; Cais, M. Angew. Chem.,
Int. Ed. Engl. 1972, 11, 1028. (c) Dannenberg, J . J .; Levenberg, M. K.;
Richards, J . H. Tetrahedron 1973, 29, 1575.
(28) (a) Caffyn, A. J . M.; Nicholas, K. M. In Comprehensive Orga-
nometallic Chemistry II; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, Chapter 7.1, pp 685-
702. (b) El Amouri, H.; Gruselle, M. Chem. Rev. 1996, 96, 1077. (c)
McGlinchey, M. J .; Girard, L.; Ruffolo, R. Coord. Chem. Rev. 1995,
143, 331.
(24) For examples, refer to: (a) C3Ph3: Cecconi, F.; Ghilardi, C. A.;
Midollini, S.; Moneti, S.; Orlandini, A. Angew. Chem. Int. Ed. Engl.
1986, 25, 833. (b) C4Ph4: Iyoda, M.; Sultana, F.; Sasaki, S.; Butenscho¨n,
H. Tetrahedron Lett. 1995, 36, 579. (c) C5Ph5: Schumann, H.; Lentz,
A.; Weimann, R.; Pickardt, J . Angew. Chem., Int. Ed. Engl. 1994, 33,
1731. (d) C6Ph6: Biagini, P.; Funaioli, T.; Fachinetti, G.; Laschi, F.;
Zanazzi, P. F. J . Chem. Soc., Chem. Commun. 1989, 405.
(29) Albright, T.; Hoffmann, R.; Hofmann, P. Chem. Ber. 1978, 111,
1591.

3-Ferrocenyl-2,4,5-triphenylcyclopentadienone
Organometallics, Vol. 18, No. 2, 1999 119
F igu r e 2. Views along successive peripheral ring-central ring axes in C6Ph5Fc, 5, showing the gradual change in phenyl
ring orientations.
Sch em e 2. P r ep a r a tion of a n d Isom er iza tion P r ocesses in C7Ar 6RH System s
respectively.30,31In our efforts to generate the cation [C7-
Ph6Fc]+ from C7Ph6FcH, several approaches were con-
sidered: attempted removal of the unique hydrogen by
use of the trityl cation or via successive replacement of
this hydrogen by bromine and methoxy substituents (as
was done with C7Ph7H) proved fruitless. Finally, treat-
ment of C7Ph6FcH with triethyloxonium hexachloroan-
timonate, [Et3O]+ [SbCl6]-, which is known to be an
excellent reagent for hydride abstractions,32 yielded
deep blue crystals, which were analyzed by use of X-ray
diffraction techniques; the resulting structure appears
as Figure 5. The product is not the anticipated ferro-
cenylhexaphenyltropylium cation but rather [C7Ph6-
FcH]+[SbCl6]-, 13, the ferricinium salt of the starting
material (Scheme 3). The characteristic boat conforma-
tion of the seven-membered ring is maintained, and the
unique hydrogen attached to the sp3-carbon was also
readily located. The major differences between 8 and
13, apart from the presence of the hexachloroanti-
monate counteranion, are found in the ferrocenyl unit,
where the average Fe-C distance has lengthened from
2.04 Å to 2.08 Å, a value that is typical for ferricinium
systems.33 Given the success of the aforementioned
reactions with C7Ph7H, it is plausible that the steric
bulk of the ferrocenyl unit in C7Ph6FcH, 8, hinders the
approach of any reagent that might abstract hydride,
such that an electron-transfer process intervenes.
(30) Brownstein, S. K.; Gabe, E. J .; Hynes, R. C. Can. J . Chem. 1992,
70, 1011.
(31) Malisza, K. L.; Top, S.; Vaissermann, J .; Caro, B.; Se´ne´chal-
Tocquer, M.-C.; Se´ne´chal, D.; Saillard, J .-Y.; Triki, S.; Kahlal, S.;
Britten, J . F.; McGlinchey, M. J .; J aouen, G. Organometallics 1995,
14, 5273.
(33) Deeming, A. J . In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford,
U.K., 1982; Vol. 4, Chapter 31.3, pp 479-481.
(32) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; Wiley: New York, 1993; p 131.

120 Organometallics, Vol. 18, No. 2, 1999
Gupta et al.
1
F igu r e 4. Variable-temperature 500 MHz H NMR spec-
tra of C7Ph6FcH, 8.
variety of fluxional processes and does not permit the
observation of chiral propellers on the NMR time scale
at room temperature. As conformationally flexible spe-
cies, CnArn molecular paddle-wheels are extremely
attractive, albeit challenging, synthetic and structural
targets. The studies described herein have afforded
insight into the steric demands of specific molecular
fragments and will serve as important calibration points
for the further construction of organometallic architec-
tures which may exhibit restricted rotations. Our ongo-
ing efforts to develop sterically encumbered CnArn
systems will be the subject of future reports.
F igu r e 3. (a) Side view of the molecular structure of C7-
Ph6FcH, 8 (30% thermal ellipsoids), depicting the atom-
numbering scheme. (b) “Bow” to “stern” view of the
molecular structure of C7Ph6FcH, 8 (30% thermal el-
lipsoids).
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were performed
under an atmosphere of dry nitrogen utilizing conventional
benchtop and glovebag techniques. Solvents were dried and
distilled according to standard procedures.34 Formylferrocene,
triethyloxonium hexachloroantimonate, dibenzyl ketone, and
diphenylacetylene were purchased from Aldrich Chemical Co.,
Inc., and used as received. NMR spectra were recorded on a
Bruker Avance DRX-500 spectrometer (1H, 500.13 MHz; 13C,
125.76 MHz) equipped with an 11.74 T superconducting
magnet, a Bruker B-VT 2000 temperature controller, and a 5
mm broad-band inverse probe with triple axis gradient capa-
bility. One-dimensional 1H and 13C NMR spectra, as well as
1
two-dimensional 1H-1H COSY, H-13C shift correlated, and
long range 1H-13C shift-correlated spectra were recorded on
spinning samples (except during the acquisition of 2-D spec-
tra), locked to a solvent signal. NMR resonances were refer-
enced to a residual proton signal of the solvent or to a 13C
solvent signal. Mass spectra were collected on a VG analytical
ZAB-E spectrometer by direct electron impact and direct
chemical ionization (NH3) methods. Melting points (uncor-
rected) were determined on a Thomas-Hoover melting point
apparatus.
Con clu d in g Rem a r k s
The incorporation of a ferrocenyl substituent, rather
than π-bonded addenda such as the Cr(CO)3 moiety, into
a perphenylated ring system lowers the barriers to a
(34) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: New York, 1980.

3-Ferrocenyl-2,4,5-triphenylcyclopentadienone
Organometallics, Vol. 18, No. 2, 1999 121
Sch em e 3. Gen er a tion of [C7P h 6F cH]+ [SbCl6]-, 13
NMR (CD2Cl2, 125 MHz, 25 °C) δ ) 132.6 (4C), 131.7 (4C),
131.5 (2C), 127.0 (4C), 126.7 (2C), 126.6 (4C), 126.1 (2C), 125.4
(1C), 125.3 (2C), 69.0 (2C, C5H4), 68.5 (5C, C5H5), 68.0 (2C,
C5H4); LRMS (DEI) m/z (%) ) 642 (64) [M+], 577 (74) [M -
C5H5]+, 120 (100) [M - C6Ph5(C5H5)]+, 55 (88); LRMS (DCI)
m/z (%) ) 643 (100) [M + H]+, 577 (25). A sample suitable for
structural determination by single-crystal X-ray diffraction
was obtained by recrystallization from hexane/CH2Cl2.
(η5-C5H5)F e(η5-C5H4C7P h 6H), 8. 3-Ferrocenyl-2,4,5-triph-
enylcyclopentadienone, 4, (0.049 g, 0.1 mmol) and 1,2,3-
triphenylcyclopropene (0.027 g, 0.1 mmol) were combined in
5 mL of dry xylene. The reaction mixture was refluxed at
approximately 170 °C in an atmosphere of N2 for 48 h and
then cooled to room temperature. Thereafter, the reaction flask
was stored at -20 °C for 72 h, yielding red-orange crystals of
8, which were isolated by filtration, washed with hexane (∼5
mL), and dried in vacuo, mp >265 °C (0.045 g, 0.062 mmol,
3
62%): 1H NMR (CD2Cl2, 500 MHz) δ ) 7.97 (d, 2H, J ) 8.2
Hz, H(72A) and H(76A) (ortho)), 7.54 (t, 2H, 3J ) 8.0 Hz,
3
H(73A) and H(75A) (meta)), 7.43 (t, 1H, J ) 7.1 Hz, H(74A)
3
(para)), 7.39 (d, 2H, J ) 6.4 Hz, H(62A) and H(66A) (ortho)),
7.20 (m, 3H, H(63A), H(65A) (meta) and H(64A) (para)), 7.15
(m, 3H, H(23A), H(25A) (meta) and H(24A) (para)), 6.90-7.10
(m, 5H, H(52A), H(56A) (ortho), H(53A), H(55A) (meta) and
H(54A) (para)), 6.88 (m, 2H, H(22A) and H(26A) (ortho)), 6.71
F igu r e 5. Side view of [C7Ph6FcH]+[SbCl6]-, 13 (30%
thermal ellipsoids), depicting the atom-numbering scheme.
(C6P h 5-C5H4)F e(C5H5), 5. 3-Ferrocenyl-2,4,5-triphenylcy-
clopentadienone, 4, was prepared according to the literature
procedure,15 from the reaction of ferrocenylphenylglyoxal35 and
dibenzyl ketone in refluxing ethanolic potassium hydroxide.
In a modification of the synthesis published by Siegel and
Rausch,14 4 (0.492 g, 1.0 mmol) and diphenylacetylene (0.018
g, 1.0 mmol) were sealed under vacuum in a glass tube and
heated at 200 °C for 48 h. The reaction mixture was subse-
quently cooled to room temperature, the tube broken carefully,
and the residue extracted from CH2Cl2 (∼50 mL) and filtered.
The addition of hexane (∼50 mL) to the filtrate facilitated the
precipitation of a dark solid. After removal of the solvent the
recovered material was subjected to flash chromatography on
silica gel. Elution with hexane/CH2Cl2 (50:50, 25:75, 0:100)
afforded a orange-yellow band, which was collected and
evaporated to give 5 as an orange-yellow solid, mp > 265 °C
(0.215 g, 0.335 mmol, 34%): 1H NMR (CD2Cl2, 500 MHz, 25
°C) δ ) 7.07 (m, 10H, H(aromatic)), 6.81 (m, 15H, H(aromatic)),
3
3
(t, 1H, J ) 7.3 Hz, H(44A) (para)), 6.64 (t, 2H, J ) 7.9 Hz,
H(43A) and H(45A) (meta), 6.55 (m, 3H, H(33A), H(35A) (meta)
and H(34A) (para)), 6.31 (m, 2H, H(32A) and H(36A) (ortho)),
3
6.05 (d, 2H, J ) 7.3 Hz, H(42A) and H(46A) (ortho)), 5.64 (s,
1H, sp3-H (H(7A))), 3.88 (s, 5H, η5-C5H5 (H(16A), H(17A),
H(18A), H(19A), H(20A))), 3.90 (s, 1H, η5-C5H4), 3.82 (s, 1H,
η5-C5H4), 3.78 (s, 1H, η5-C5H4), 3.22 (s, 1H, η5-C5H4); 13C NMR
(CD2Cl2, 125 MHz) δ ) 144.2, 143.7, 143.4, 141.4, 141.2, 140.8,
136.5 (C-ipso and C7-ring), 131.7, 131.1, 131.0, 130.8, 130.7,
128.1, 127.7, 127.3, 127.2, 127.0, 126.6, 126.1, 125.8, 124.9,
124.6 (C-ortho, C-meta, C-para), 68.5 (η5-C5H5, C(16-C(20)),
68.9, 68.5, 67.9, 67.8 (η5-C5H4, C(11)-C(15)), 56.3 (sp3-C, C(7));*
LRMS (DEI) m/z (%) ) 732 (75) [M+]; LRMS (DCI) m/z (%) )
733 (100) [M + H]+, 141 (86). Anal. Calcd for C53H40Fe
(732.70): C, 86.88; H, 5.50. Found: C, 87.00; H, 5.76. Single
crystals suitable for X-ray diffraction studies were selected
directly from the xylene solution. (*Note: Definitive NMR
assignment of phenyl rings 3 and 4 was not possible; it should
be recognized that the chemical shift assignments could be
interchanged.)
3.85 (m, 2H, C5H4), 3.75 (m, 2H, C5H4), 3.71 (s, 5H, C5H5); 13
C
(35) Prepared according to the procedure outlined in: Broadhead,
G. D.; Osgerby, J . M.; Pauson, P. L. J . Chem. Soc. 1958, 650.
[(η5-C5H5)F e(η5-C5H4-C7P h 6H]+[SbCl6]- 13. (η5-C5H5)Fe-

122 Organometallics, Vol. 18, No. 2, 1999
Gupta et al.
(η5-C5H4-C7Ph6H), 8 (0.073 g, 0.1 mmol), and triethyloxonium
hexachloroantimonate (0.044 g, 0.1 mmol) were dissolved in
freshly distilled CH2Cl2 (∼5 mL) and stirred under an atmo-
sphere of N2 at ambient temperature for 24 h. The reaction
mixture was filtered, and from the filtrate dark blue-green
crystals of 13 were isolated after several days of slow solvent
evaporation at reduced temperatures; 13 decomposes on
heating (0.026 g, 0.062 mmol, 24%). Crystals suitable for
structural determination by single-crystal X-ray diffraction
were carefully selected.
Cr yst a llogr a p h ic Da t a for (C6P h 5-C5H 4)F e(C5H 5),
(η5-C5H5)F e(η5-C5H4-C7P h 6H, a n d [(η5-C5H5)F e(η5-C5H4-
C7P h 6H]+[SbCl6]-. X-ray crystallographic data for 5, 8, and
13 were obtained from single-crystal samples, which were
mounted on glass fibers. Data were collected using a P4
Siemens diffractometer, equipped with a Siemens SMART 1K
charge-coupled device (CCD) area detector (employing the
program SMART36) and a rotating anode utilizing graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å). The crystal-
to-detector distance was 3.991 cm, and the data collection was
carried out in 512 × 512 pixel mode, employing 2 × 2 pixel
binning. The initial unit cell parameters were determined by
a least-squares fit of the angular settings of the strong
reflections, collected by 4.5° scans in 15 frames over three
different parts of reciprocal space (45 frames total). One
complete hemisphere of data was collected, to better than 0.8
Å resolution. Upon completion of the data collection, the first
50 frames were re-collected in order to improve the decay
analysis. Processing was carried out by use of the program
SAINT,37 which applied Lorentz and polarization corrections
to three dimensionally integrated diffraction spots. The pro-
gram SADABS38 was utilized for the scaling of diffraction data,
the application of a decay correction, and an empirical absorp-
tion correction based on redundant reflections. The structures
were solved by use of the direct method (procedure outlined
in the Siemens SHELXTL program library39) followed by full-
matrix least-squares refinement on F2 with anisotropic ther-
mal parameters for all non-hydrogen atoms. Hydrogen atoms
were added as fixed contributors at calculated positions, with
isotropic thermal parameters based on the atoms to which they
were bonded. (For cell parameters and intensity collection refer
to Table 1).
Ack n ow led gm en t. Financial support from NSERC
Canada and from the Petroleum Research Fund, ad-
ministered by the American Chemical Society, is grate-
fully acknowledged. S.B. thanks the Government of
Ontario and the NSERC for graduate fellowships.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, bond lengths and angles, anisotropic
displacement parameters, and hydrogen coordinates for 5, 8,
and 13 (25 pages). Ordering information is given on any
current masthead page.
OM980645W
(37) SAINT, Release 4.05; Siemens Energy and Automation Inc.,
Madison, WI 53719, 1996.
(38) Sheldrick, G. M. SADABS (Siemens Area Detector Absorption
Corrections); Siemens Energy and Automation, Madison, WI, 1996.
(39) Sheldrick, G. M. SHELXTL, Version 5.03; Siemens Analytical
X-ray Instruments Inc.: Madison, WI, 1994.
(36) SMART, Release 4.05; Siemens Energy and Automation Inc.,
Madison, WI 53719, 1996.