Rhodium acetylacetonate and iron tricarbonyl complexes of tetracyclone and 3-ferroceny1-2,4,5-triphenylcyclopentadienone: An X-ray crystallographic and NMR study

Article abstract of DOI:10.1021/om990559b

Tetracyclone reacts with Fe₂(CO)₉ and with (acac)Rh(C₂H₄)₂ to give (C₄Ph₄C=O)Fe(CO)₃ (3) and (C₄Ph₄C=O)Rh(acac) (11), respectively. Likewise, 3-f

Full text of DOI:10.1021/om990559b

184
Organometallics 2000, 19, 184-191
Rh od iu m Acetyla ceton a te a n d Ir on Tr ica r bon yl
Com p lexes of Tetr a cyclon e a n d
3-F er r ocen yl-2,4,5-tr ip h en ylcyclop en ta d ien on e: An X-r a y
Cr ysta llogr a p h ic a n d NMR Stu d y
Hari K. Gupta, Nicole Rampersad, Mark Stradiotto, and Michael J . McGlinchey*
Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada
Received J uly 19, 1999
Tetracyclone reacts with Fe2(CO)9 and with (acac)Rh(C2H4)2 to give (C4Ph4CdO)Fe(CO)3
(3) and (C4Ph4CdO)Rh(acac) (11), respectively. Likewise, 3-ferrocenyl-2,3,4-triphenylcyclo-
pentadienone (2) yields (C4Ph3FcCdO)Fe(CO)3 (7) and (C4Ph3FcCdO)Rh(acac) (14). In 3,
the peripheral phenyl substituents adopt a propeller conformation in the solid state, and
the barrier to fluxionality of the Fe(CO)3 fragment is so low as to preclude the observation
of slowed tripodal rotation at low temperature. In contrast, the ferrocenyl analogue 7 shows
restricted tripodal rotation, but this may be the result of steric interference by the bulky
ferrocenyl substituent. In the crystal, (tetracyclone)Rh(acac) (11) exists as a head-to-tail
dimer in which the rhodium center is bonded to the γ-carbon of the acetylacetonate ligand
in the other half of the molecule. The ferrocenyl analogue 14 is monomeric both in the solid
state and in solution, and the rotation barrier of the Rh(acac) fragment has been evaluated
as 12 kcal mol-1. The mass spectra of the rhodium complexes are discussed in terms of doubly
charged ions containing Rh(III). The potential use of these metal-complexed cyclopentadi-
enones as precursors to pentaarylcyclopentadienyl systems is discussed.
Sch em e 1. Syn th etic Rou te to
Cyclop en ta d ien on es
In tr od u ction
While metal complexes of cyclopentadienones are very
numerous, the majority of these species arose as minor
products from the reactions of alkynes with metal
carbonyls.1 However, cyclopentadienones are also avail-
able by direct synthesis from appropriately designed
benzils and 1,3-disubstituted propanones,2 as shown in
Scheme 1.
A crucial factor controlling the chemistry of cyclopen-
tadienones is the relatively small HOMO-LUMO gap,3
as evidenced by their intense visible absorption and
strong tendency to undergo Diels-Alder dimerization
unless hindered by the presence of bulky substituents.2
In these systems, the carbonyl group is considered to
be relatively nonpolarized, since the zwitterionic reso-
nance structure depicted in Scheme 1 would invoke a
four-π-electron manifold with antiaromatic character.4
The ready availability of monomeric tetracyclone
(2,3,4,5-tetraphenylcyclopentadienone, 1) has prompted
the preparation of a number of organometallic deriva-
tives,5-12 as exemplified in Scheme 2, which also shows
some complexes derived from diphenylacetylene.
Our current focus on metal complexes of cyclopenta-
dienones bearing bulky substituents derives from our
long-standing interest in (CxArx)MLn systems, where x
) 5,13 6,14 or 7,15 and their relevance to correlated
rotations.16 We here describe the syntheses, structures,
(6) (a) Bruce, M. I.; Knight, J . R. J . Organomet. Chem. 1968, 12,
411. (b) Blum, Y.; Shvo, Y.; Chodosh, D. F. Inorg. Chim. Acta 1985,
97, L25. (c) Bailey, N. A.; J assal, V. S.; Vefghi, R.; White, C. J . Chem.
Soc., Dalton Trans. 1987, 2815.
(7) Baker, P. K.; Broadley, K.; Connelly, N. G.; Kelly, B. A.; Kitchen,
M. D.; Woodward, P. J . Chem. Soc., Dalton Trans. 1980, 1710.
(8) (a) Markby, R.; Sternberg, H. W.; Wender, I. Chem. Ind. 1959,
1387. (b) Sheats, J . E.; Rausch, M. D. J . Org. Chem. 1970, 35, 3245.
(9) McVey, S. P.; Maitlis, P. M. Can. J . Chem. 1966, 44, 2429.
(10) Dickson, R. S.; Tailby, G. R. Aust. J . Chem. 1970, 23, 1531.
(11) Pasynskii, A. A.; Anisimov, K. N.; Kolobova, N. E.; Nesmeyanov,
A. N. Dokl. Akad. Nauk SSSR 1969, 185, 610.
(12) Burke, M. R.; Funk, T.; Takats, J . Organometallics 1994, 13,
2109.
(13) 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.
* To whom correspondence should be addressed. Phone: (905) 525-
9140 ext. 24504. Fax: (905) 522-2509. E-mail: mcglinc@mcmaster.ca.
(1) Adams, H.; Bailey, N. A.; Hempstead, P. D.; Morris, M. J .; Riley,
S.; Beddoes, R. L.; Cook, E. S. J . Chem. Soc., Dalton Trans. 1993, 91.
(2) (a) Allen, C. F. H. Chem. Rev. 1962, 62, 653. (b) Ogliaruso, M.
A.; Romanelli, M. G.; Becker, E. I. Chem. Rev. 1965, 65, 261.
(3) Garbisch, E. W., J r.; Sprecher, R. F. J . Am. Chem. Soc. 1969,
91, 6785 and references therein.
(4) Bergmann, E. D.; Berthier, G.; Ginsburg, D.; Hirschberg, Y.;
Lavie, D.; Pinchas, S.; Pullman, B.; Pullmann, A. Bull. Soc. Chim. Fr.
1951, 18, 661.
(5) (a) Schrauzer, G. N. J . Am. Chem. Soc. 1959, 81, 5307. (b) Weiss,
E.; Hu¨bel, W. J . Inorg. Nucl. Chem. 1959, 11, 42.
(14) Mailvaganam, B.; Sayer, B. G.; McGlinchey, M. J . J . Organomet.
Chem. 1990, 395, 177.
(15) (a) 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. (b) Brydges, S.; Gupta, H. K.; Chao, L. C. F.; Pole, D. L.; Britten,
J . F.; McGlinchey, M. J . Chem. Eur. J . 1998, 4, 1201.
10.1021/om990559b CCC: $19.00 © 2000 American Chemical Society
Publication on Web 12/22/1999

Rh and Ir Complexes of Cyclopentadienones
Organometallics, Vol. 19, No. 2, 2000 185
Sch em e 2. Meta l Com p lexes of Tetr a cyclon e
Sch em e 3. Rea ction s of 1 a n d 2 w ith F e2(CO)9 a n d
(a ca c)Rh (C2H4)2
and molecular dynamics of Fe(CO)3 and Rh(acac) de-
rivatives of tetracyclone (1) and of 3-ferrocenyl-2,4,5-
triphenylcyclopentadienone (2).
F igu r e 1. Molecular structure of (C4Ph4CdO)Fe(CO)3 (3;
25% thermal ellipsoids), with hydrogen atoms omitted for
clarity.
Resu lts a n d Discu ssion
F e(CO)3 Com p lexes. As previously described,5 tet-
racyclone and Fe2(CO)9 yield the complex (C4Ph4CdO)-
Fe(CO)3 (3; Scheme 3), whose infrared and 13C NMR
spectra have already been reported.12 The X-ray crystal
structure of 3 is shown as Figure 1 and clearly il-
lustrates the η4 character of the bonding of the tripodal
group to the cyclic ligand; crystallographic refinement
parameters and selected metrical data are collected in
Tables 1 and 2, respectively. The average bonding
distance from the iron to the tetracyclone ring carbons
C(2)-C(5) is 2.14 Å and is markedly shorter than the
distance to the ketonic carbon (Fe-C(1) ) 2.40(1) Å).
There is no evidence of carbon-carbon bond alternation
within the diene system, and overall the pattern is
typical of those reported for a variety of (η4-diene)Fe-
(CO)3 structures.17 Moreover, the carbonyl moiety within
the five-membered ring does not lie in the plane defined
by C(2), C(3), C(4), and C(5), but, rather, is displaced
through 16° away from the metal. As in other sterically
crowded systems,18 the peripheral aryl rings in 3 adopt
(17) 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 449-450.
(18) (a) Adams, H.; Bailey, N. A.; Browning, A. F.; Ramsden, J . A.;
White, C. J . Organomet. Chem. 1990, 387, 305. (b) Harrison, W. M.;
Saadeh, C.; Colbran, S. B.; Craig, D. C. J . Chem. Soc., Dalton Trans.
1997, 3785 and references therein.
(16) Iwamura, H.; Mislow, K. Acc. Chem. Res. 1988, 21, 175.

186 Organometallics, Vol. 19, No. 2, 2000
Gupta et al.
Ta ble 1. Cr ysta llogr a p h ic Collection a n d Refin em en t P a r a m eter s for 3‚THF , 7, 11‚H2O a n d 14
3‚THF
7
11‚H2O
14
empirical formula
mol wt
C
36H28O5Fe
C36H24O4Fe2
632.25
C34H29O4Rh
604.48
C38H31O3FeRh
694.39
596.43
descripn
size, mm3
temp, K
red prism
0.30 × 0.21 × 0.13
299(2)
dark red prism
0.38 × 0.34 × 0.25
299(2)
red prism
0.12 × 0.09 × 0.06
299(2)
red prism
0.24 × 0.20 × 0.17
299(2)
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/ c
10.623(9)
11.739(9)
24.89(2)
90
102.28(1)
90
3032(4)
monoclinic
P21/ n
10.618(3)
21.506(6)
12.990(3)
90
102.33(1)
90
2898(1)
triclinic
P1h
8.823(9)
12.404(4)
15.694(5)
66.929(7)
81.291(8)
73.873(6)
1516.2(8)
2
monoclinic
I2/ a
20.834(9)
12.455(7)
25.75(2)
90
97.09(2)
90
6631(7)
R, deg
â, deg
γ, deg
V, Å3
Z
4
4
8
calcd density, g/cm3
scan mode
F(000)
1.306
ω-scans
1240
1.449
ω-scans
1296
1.324
ω-scans
620
1.391
ω-scans
2832
abs coeff, mm-1
θ range, deg
index ranges
0.539
1.041
0.597
0.969
1.67-22.50
-12 e h e 13
-14 e k e 14
-29 e l e 30
18 186
1.86-23.50
-12 e h e 13
-27 e k e 25
-16 e l e 16
19 222
1.41-23.50
-11 e h e 6
-14 e k e 16
-19 e l e 20
6445
1.59-23.50
-26 e h e 24
-16 e k e 14
-33 e l e 33
19 560
no. of rflns collected
no. of indep rflns
3972
4282
4396
4897
no. of data/restraints/params
3955/3/356
0.909
4280/0/380
0.909
4391/0/361
1.520
4889/0/388
0.913
GOF on F2 (all)
final R (I > 2σ(I))
R1 ) 0.0944;
wR2 ) 0.2008
R1 ) 0.2075;
wR2 ) 0.2594
0.9630, 0.5106
0.565
R1 ) 0.0283;
wR2 ) 0.0663
R1 ) 0.0506;
wR2 ) 0.0721
0.7340, 0.6331
0.188
R1 ) 0.1161;
wR2 ) 0.3339
R1 ) 0.1330;
wR2 ) 0.3462
0.9821, 0.6422
2.842
R1 ) 0.0478;
wR2 ) 0.0997
R1 ) 0.0940;
wR2 ) 0.1123
0.9131, 0.5904
0.500
R indices (all data)
transmissn, (max, min)
largest diff peak, e/Å3
largest diff hole, e/Å3
-0.602
-0.204
-0.733
-0.414
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for 3‚THF , 7, 11‚H2O, 14, a n d Rela ted Str u ctu r es
3
4b
5c
7
11
14
M-C(5)a
M-C(4)
2.167(9)
2.126(8)
2.117(9)
2.147(9)
2.402(13)
1.216(11)
1.42(1)
1.52(1)
1.46(1)
1.47(1)
1.47(1)
2.240(3)
2.209(3)
2.216(3)
2.216(3)
2.530(3)
1.224(4)
1.438(4)
1.491(4)
1.437(4)
1.455(4)
1.485(4)
2.230(11)
2.231(12)
2.199(12)
2.265(11)
2.563(10)
1.207(15)
1.480(18)
1.509(16)
1.428(15)
1.456(17)
1.546(15)
2.136(3)
2.061(2)
2.112(2)
2.108(2)
2.422(3)
1.226(3)
1.449(3)
1.479(3)
1.444(3)
1.435(3)
1.478(3)
2.165(12)
2.123(11)
2.135(12)
2.166(12)
2.420(13)
1.21(2)
1.46(2)
1.46(2)
1.44(2)
1.45(2)
2.165(6)
2.098(5)
2.139(5)
2.149(5)
2.380(6)
1.227(7)
1.423(7)
1.495(8)
1.468(7)
1.425(7)
1.482(8)
M-C(3)
M-C(2)
M-C(1)
C(1)-O(1)
C(5)-C(4)
C(1)-C(5)
C(3)-C(4)
C(2)-C(3)
C(1)-C(2)
1.51(2)
C(5)-C(4)-C(3)
C(4)-C(3)-C(2)
C(3)-C(2)-C(1)
C(2)-C(1)-C(5)
C(5)-C(1)-O(1)
C(2)-C(1)-O(1)
fold angled
110.2(7)
105.9(7)
109.2(7)
104.2(9)
127.4(8)
128.0(9)
16
108.9
107.2
108.0
103.2
129.6
126.9
19
107.1(10)
111.6(10)
105.1(9)
103.5(9)
127.8(10)
128.5(10)
20
108.2(2)
107.3(2)
108.1(2)
103.8(2)
129.5(2)
126.5(2)
21
107.3(11)
108.7(11)
107.4(10)
104.2(10)
128.7(13)
126.4(13)
17
109.3(5)
106.5(5)
109.9(5)
103.9(5)
128.1(6)
127.3(5)
13
a
b
d
M ) Fe (3), Ru (4), Os (5), Fe (7), Rh (11), and Rh (14). Reference 6b. c Reference 12. The angle subtended by the planes defined
by C(2)-C(3)-C(4)-C(5) and C(2)-C(1)-C(5).
a propeller conformation such that the average dihedral
angle made by these phenyls and the central ring is
∼49°.
tripod in 3 is rotated by 28° away from the completely
eclipsed position, probably for steric reasons.
The closest analogue of 3 to have been structurally
characterized is the oxygen-bridged dication {[Fe(CO)3-
(η5-C5Ph4C-O-Ag)]2}2+ (6), obtained by silver hexafluoro-
phosphate oxidation of 3 and shown in Scheme 2.7 In
the silver complex, the propeller-like orientation of the
peripheral phenyls is maintained and the tripodal
Fe(CO)3 unit is rotated by 18° away from the eclipsed
position, somewhat less than is found in 3. However,
the dimerization is not mediated simply via bridging of
the ketonic oxygens to both silver atoms. While the
These structural data should be compared to those
of the analogous ruthenium6b and osmium12 complexes
4 and 5, as listed in Table 2, which illustrate the close
similarity in their propeller conformations; the exo fold
angle of the ketonic unit ranges from 16° in the Fe
system to ∼20° in the Ru and Os complexes. Moreover,
in the latter two systems, the alignment of the ring
carbonyl with one of the M-CO linkages is almost
perfect (dihedral angle ∼8°); in contrast, the Fe(CO)3

Rh and Ir Complexes of Cyclopentadienones
Organometallics, Vol. 19, No. 2, 2000 187
Ch a r t 1
F igu r e 2. Structure of {[Fe(CO)3(η5-C5Ph4C-O-Ag)]2}2+
(6). Data were taken from ref 7.
over the staggered isomer 8b (Chart 1) by 5.7 kcal mol-1
but also that the ring ketonic unit should fold away from
the metal through ∼10°. This latter phenomenon was
briefly discussed by Hoffmann some years ago.21
Likewise, the calculational22 and X-ray crystallo-
graphic23 evidence on the closely analogous (fulvene)-
Fe(CO)3 system 9 reveals that the exocyclic CdCR2
group eclipses a carbonyl ligand and is folded in a distal
fashion relative to the metal.
It is interesting to compare these data with a very
recent report describing high-level calculations on tri-
carbonylchromium complexes of benzyl cations, anions,
and radicals.24 In that study it was concluded that the
favored structure for the cation places the tripod in the
+
staggered orientation 10a , with the exocyclic -CH2
substituent folded 37° toward the chromium atom. In
contrast, the benzyl anion complex is predicted to adopt
the eclipsed conformation 10b, with the methylene
substituent folded 18° away from the chromium atom,
analogous to 8a . Moreover, the barriers to tripodal
rotation in the (benzyl)Cr(CO)3 cation and anion were
calculated to be 11.2 and 5.9 kcal mol-1, respectively.
Gratifyingly, variable-temperature NMR measurements
have yielded values of 11-12 kcal mol-1 for a series of
Cr(CO)3-complexed benzyl cations;25 although the cor-
responding (benzyl)Cr(CO)3 anions have also been ex-
amined at low temperature,26 the barriers are presum-
ably so small as to prevent the observation of slowed
tripodal rotation on the time scale of NMR line-shape
measurements.
F igu r e 3. Molecular structure of (C4Ph3FcCdO)Fe(CO)3
(7; 25% thermal ellipsoids), with hydrogen atoms omitted
for clarity.
Ag(1)-O(4) and Ag(1)-O(4A) distances are 2.27(2) and
2.65(8) Å, respectively, each silver is also only 2.46(5)
Å from a phenyl carbon, as depicted in Figure 2.
Treatment of a THF solution of 3-ferrocenyl-2,4,5-
triphenylcyclopentadienone (2) with Fe2(CO)9 yields 7,
the complex analogous to 3 whereby a peripheral phenyl
substituent has been replaced by a ferrocenyl unit.
While the major structural features of 7 (see Figure 3)
resemble those of the (C4Ph4CdO)M(CO)3 systems
discussed above, the orientations of the peripheral
phenyls are markedly different. The C5H4 ring of the
ferrocenyl substituent is almost coplanar (dihedral angle
∼9.8°) with the central ring, thus causing considerable
twisting of its phenyl neighbors away from the conven-
tional propeller arrangement; we have previously noted
a similar effect in ferrocenyl-pentaphenylbenzene, in
which the peripheral phenyls adopt sequentially greater
dihedral angles,19 perhaps implying some degree of
correlated rotation. However, in the absence of extensive
labeling experiments, such an assertion must remain
speculative.
Previous attempts by Kruczynski and Takats to detect
slowed tripodal rotation in (C4Ph4CdO)M(CO)3, where
M ) Fe (3), Ru (4), were unsuccessful;27 in that study,
(20) High-level ab initio calculations have been carried out for
(C4H4CdO)Fe(CO)3 and for (C4H4CdO)Co(C5H5), but the main focus
of the study was a comparison of the two isolobal MLn fragments:
Chinn, J . W., J r.; Hall, M. B. Organometallics 1984, 3, 284.
(21) Hoffmann, R.; Hofmann, P. J . Am. Chem. Soc. 1976, 98, 598.
(22) Albright, T. A.; Hoffmann, R.; Hofmann, P. Chem. Ber. 1978,
111, 1591.
(23) In (6,6-diphenylfulvene)Fe(CO)3 the exo fold angle is 18.5°:
Edelmann, F.; Lubke, B.; Behrens, U. Chem. Ber. 1982, 115, 1325.
(24) Pfletschinger, A.; Dargel, T. K.; Bats, J . W.; Schmalz, H.-G.;
Koch, W. Chem. Eur. J . 1999, 5, 537.
(25) (a) Acampora, M.; Ceccon, A.; Dal Farra, M.; Giacometti, G.;
Rigatti, G. J . Chem. Soc., Perkin Trans. 2 1977, 483. (b) Downton, P.
A.; Sayer, B. G.; McGlinchey, M. J . Organometallics 1992, 11, 3281.
(26) (a) J aouen, G.; Top, S.; Sayer, B. G.; McGlinchey, M. J . J . Am.
Chem. Soc. 1983, 105, 6426. (b) Ceccon, A.; Gambaro, A.; Venzo, A. J .
Organomet. Chem. 1984, 275, 209.
The observed orientation of the M(CO)3 tripod in these
complexes can be rationalized by means of molecular
orbital calculations20 at the extended Hu¨ckel level which
show not only that the eclipsed rotamer 8a is favored
(19) Gupta, H. K.; Brydges, S.; McGlinchey, M. J . Organometallics
1999, 18, 115.
(27) Kruczynski, L.; Takats, J . Inorg. Chem. 1976, 15, 3140.

188 Organometallics, Vol. 19, No. 2, 2000
Gupta et al.
13C NMR spectra were obtained at 22.6 MHz on a 90
MHz instrument at 183 K. Moreover, these workers
pointed out that the range of 13CO chemical shifts in
(cyclopentadienone)M(CO)3 systems is rather narrow;27
nevertheless, we attempted to detect slowed rotation of
the Fe(CO)3 moiety in 3. However, even at 167 K on a
500 MHz instrument (13C spectra acquired at 125 MHz)
the Fe(CO)3 resonance in (C4Ph4CdO)Fe(CO)3 remained
as a sharp singlet. This observation suggests either that
the barrier is rather low (as indicated by the EHMO
calculations) or that the chemical shift difference be-
tween the carbonyl environments is very small. Solid-
state 13C NMR measurements on this and related
systems will be described in a future report.
In contrast, when the ferrocenyl complex 7 was cooled
to 177 K in CD2Cl2, it gave rise to three equally intense
resonances at 209.1, 207.2, and 207.0 ppm; the barrier
was evaluated as 12.5 ( 0.5 kcal mol-1. Interestingly,
1
over the temperature range 173-300 K, the H and 13C
NMR spectra of 7 indicated the presence of two isomers
in an approximate 80/20 ratio, as shown by the observa-
tion of two different ferrocenyl environments. Whether
these represent two rotamers in which the ferrocenyl
substituents occupy exo and endo positions remains an
open question. The X-ray crystal structure clearly shows
that, at least in the solid state, the exo rotamer is
favored, but the situation in solution is less clear. It was
not possible to detect the 13CO resonances of the minor
component.
Rh (a ca c) Com p lexes. In 1966, Maitlis described the
synthesis of (C4Ph4CdO)Rh(acac) 11, which was ob-
tained by treatment of the chlorine-bridged dimer
[(C4Ph4CdO)RhCl]2 with thallium acetylacetonate.9 The
current, more direct approach simply involved gentle
reflux in THF of the appropriate ligand 1 or 2 with
(acac)Rh(C2H4)2, in which the ethylene ligands are
known to be readily replaceable.
Since the Rh-acetylacetonate moiety is presumed to
straddle the molecular mirror plane, there would appear
to be no probe with which to measure its rotational
barrier in (tetracyclone)Rh(acac). The X-ray crystal
structure of 11 is shown in Figure 4a and shows that
the molecule adopts a head-to-tail dimeric arrangement
in which the rhodium in one monomer lies only 2.39(1)
Å from the γ-carbon of the other acac ligand. The
interplanar angle between the cyclopentadienone and
Rh-acac rings in 11 is ∼65°, and the peripheral phenyls
do not adopt a propeller conformation but rather a “cup-
shaped” geometry (Figure 4b), as previously found1 for
the [(C4Ph4CdO)Mo(CO)3] dimeric complex 12, depicted
in Scheme 2.
F igu r e 4. (a, top) Molecular structure of the dimer [(C4-
Ph4CdO)Rh(acac)]2 (11; 25% thermal ellipsoids), showing
only the ipso carbons of the peripheral phenyl rings.
Hydrogen atoms are omitted for clarity. (b, bottom) Bird’s
eye view of a tetraphenylcyclopentadienone ring in 11,
showing the “cup-shaped” arrangement of the phenyl rings.
discussed the monomer-dimer equilibrium in Cp*Ru-
(benzyl-acac), 13, and has noted that the 13C NMR shifts
of the acac γ-carbon change very little compared to those
in monomeric Ru(II)-acac complexes.31
The reaction of (acac)Rh(C2H4)2 with 2 furnished the
ferrocenyl complex 14, whose structure appears in
Figure 5. As with the Fe(CO)3 analogue 7, the presence
of the bulky ferrocenyl substituent (which lies almost
coplanar with the central ring) distorts the phenyl
orientations away from the normal propeller conforma-
tion. The (acac)Rh ring lies almost orthogonal to the
plane defined by C(2)-C(5)sthe interplanar angle is
88°sand also to the line containing the ketonic linkage.
The rhodium is essentially in a conventional square-
planar environment with rhodium-diene carbon dis-
tances ranging from 2.098(5) to 2.165(6) Å; as with 3,
7, and 11, the M‚‚‚CdO distance is markedly longer
Dimeric metal-acetylacetonate structures of this type
28
were first reported for [Me3Pt(acac)]2 and have since
29
been found for [(C5Me5)Ru(acac)]2 and for {[(C5Me5)-
Rh(acac)]2}2+ 30
In the latter case, the Rh-γ-carbon
.
distance of 2.287(6) Å is significantly shorter than the
2.39(1) Å value found in 11, presumably attributable
to the cationic nature of the rhodium center. Ko¨lle has
(28) (a) Hargreaves, R. N.; Truter, M. R. J . Chem. Soc. A 1969, 2282.
(b) Kite, K.; Psaila, A. F. J . Organomet. Chem. 1992, 441, 159.
(29) (a) Ko¨lle, U.; Kossakowsi, J .; Raabe, G. Angew. Chem., Int. Ed.
Engl. 1990, 29, 773. (b) Smith, M. E.; Hollander, F. J .; Andersen, R.
A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1294.
(30) Rigby, W.; Lee, H.-B.; Bailey, P. M.; McCleverty, J . A.; Maitlis,
P. M. J . Chem. Soc., Dalton Trans. 1979, 387.
(31) Ko¨lle, U.; Rietmann, C.; Raabe, G. Organometallics 1997, 16,
3273. In this paper it is reported that interconversion of four isomers
of Cp*Ru(benzyl-acac) (13) occurs through monomerization; we are
entirely in accord with this mechanistic proposal but note that the
dimers can exist in only d,l (C2) and meso (Ci) forms.

Rh and Ir Complexes of Cyclopentadienones
Organometallics, Vol. 19, No. 2, 2000 189
Ch a r t 2
however, there was also a much more intense peak at
m/z 279 for the corresponding doubly charged species
[(C4Ph4)Rh(acac)]2+. In this latter ion, one could assign
a formal charge of +3 to the rhodium atom, in keeping
with its normal chemical behavior. Similarly, there are
peaks at m/z values of 459 and 229.5 for [(C4Ph4)Rh]+
and [(C4Ph4)Rh]2+, respectively. This phenomenon is
even more evident in the ferrocenyl analogue 14, for
which the [M - CO]+ fragment at m/z 666 is barely
detectable, yet the doubly charged ion at m/z 333,
assignable to [(C4Ph3Fc)Rh(acac)]2+, is a major peak.
One can speculate whether the second ionization occurs
at rhodium or at iron, and electrochemical measure-
ments on these complexes are in progress. Interestingly,
the mass spectra of 11 and 14 do not give rise to
fragment ions of the type [C4Ph3R]+, where R is phenyl
or ferrocenyl.
F igu r e 5. Molecular structure of (C4Ph3FcCdO)Rh(acac)
(14; 25% thermal ellipsoids), with hydrogen atoms omitted
for clarity.
(Rh-C(1) ) 2.380(6) Å), and the ketonic moiety is bent
exo through 13°. In contrast to the dimeric structure of
(C4Ph4CdO)Rh(acac) (11), the ferrocenyl analogue 14
is clearly monomeric; the closest distance of approach
between Rh and a γ-carbon of another acetylacetonate
ligand is 3.73 Å, clearly too long to represent a viable
bonding interaction.
Interestingly, EHMO calculations reveal that the
HOMO of (C4H4CdO)Rh(acac) is very heavily localized
on the metal, and the question arises as to the preferred
site of electrophilic attack on such a system. It is
known8b that protonation of (tetracyclone)Co(C5H5) oc-
curs at the ketonic oxygen to yield the cobaltocenium
salt [(C5Ph4OH)Co(C5H5)]+ (15), shown in Scheme 2.
The presence of the ferrocenyl group in 14 lowers the
molecular symmetry such that the methyl groups of the
acetylacetonate ring are no longer NMR-equivalent
under conditions of slowed rotation. This results in the
Con clu d in g Rem a r k s. One of our longer term goals
involves using the presence of the organometallic moiety
to control the site of nucleophilic attack on the cyclo-
pentadienone ring system, and the reactions with al-
kynyl Grignard reagents or C6F5Li will be the subject
of a future report.
Finally, we note that reactions involving 3-ferrocenyl-
2,3,4-triphenylcyclopentadienone (2) frequently yield,
after chromatographic separation of the products, small
quantities of a compound of formula (C4H2Ph3FcCdO).
This dihydro complex, resulting from incomplete oxida-
tion of the mixed benzoin derived from benzaldehyde
and formylferrocene, has now been characterized as
3-ferrocenyl-2,4,5-triphenylcyclopent-2-en-1-one (16). Its
identification as the isomer with two hydrogens at-
tached to adjacent phenyl-bearing carbons is evident
1
observation of two methyl signals in both the H and
13C regimes at low temperature; peak coalescence data
yield a barrier of 12.5 ( 0.5 kcal mol-1, somewhat higher
than the 8-9 kcal mol-1 value estimated from our
EHMO calculations. We are unaware of any previously
measured rotational barriers in (cyclopentadienone)Rh-
(acac) systems, but values of 11-12 kcal mol-1 have
been reported for [tetrakis(trifluoromethyl)cyclopenta-
dienone]M(CO)3, where M ) Fe, Ru.32
1
from the H NMR spectrum, which exhibits two sets of
Ma ss Sp ectr a . Tetrasubstituted cyclopentadienones
have been the subject of detailed mass spectral studies.
The facile loss of CO to yield radical cations of the type
[C4Ar4]•+ led to much speculation as to the structure of
this species: i.e., whether it adopted a square-planar
(cyclobutadiene) or a tetrahedral geometry. This ion
dissociates to yield the appropriately substituted [ArCt
CAr′]+ fragments, but careful labeling experiments
demonstrated the formation of alkynes that would have
been “diagonally related” in the square-planar precur-
sor; it was therefore concluded that [C4Ar4]•+ radical
cations are tetrahedral.33
doublets (J ) 1.9 Hz) at δ 4.46 and 3.67. The magnitude
of the coupling between these protons suggests a
dihedral angle between them of ∼90°, i.e. a diequatorial
arrangement, as shown for 16 (Chart 2). Moreover, in
1
the H-1H COSY spectrum, each of these hydrogens is
clearly coupled to the ortho protons of its neighboring
phenyl ring. These data match closely the NMR param-
eters for 2,3,4,5-tetraphenylcyclopent-2-en-1-one,34 pre-
pared by reduction of tetracyclone.35
Exp er im en ta l Section
The electron impact mass spectrum of (C4Ph4CdO)-
Rh(acac) (11) shows a parent peak (m/z 586) and a
fragment at m/z 558 assignable to [(C4Ph4)Rh(acac)]+;
Gen er a l Meth od s. All reactions were carried out under an
atmosphere of dry nitrogen employing conventional benchtop
and glovebag techniques. All solvents were dried according to
(32) Kruczynski, L.; Martin, J . L.; Takats, J . J . Organomet. Chem.
1974, 80, C9.
(33) Bursey, M. M.; Harvan, D. J .; Hass, J . R. Org. Mass Spectrom.
1985, 20, 197 and references therein.
(34) The 1H NMR spectrum of 2,3,4,5-tetraphenylcyclopent-2-en-1-
one exhibits doublets (J ) 2.6 Hz) at δ 4.65 and 3.75.
(35) Brown, D. A.; Hargaden, J . P.; McMullin, C. M.; Gogan, N.;
Sloan, H. J . Chem. Soc. 1963, 4914.

190 Organometallics, Vol. 19, No. 2, 2000
Gupta et al.
standard procedures before use.36 Silica gel (particle size 20-
45 µm) was employed for flash column chromatography. 1H
and 13C solution NMR spectra were acquired on a Bruker DRX
500 spectrometer and were referenced to the residual proton
signal or the 13C solvent signal. Mass spectra were determined
using a Finnigan 4500 spectrometer by direct electron impact
(DEI) or direct chemical ionization (DCI) with NH3. Infrared
spectra were recorded on a Bio-Rad FTS-40 spectrometer.
Melting points (uncorrected) were determined on a Thomas-
Hoover melting point apparatus. Elemental analyses were
performed by Guelph Chemical Laboratories, Guelph, Ontario,
Canada.
[C3Ph2C5H5]+ (37), 118 [Hacac + NH4]+ (30), 101 [Hacac + H]+
(50). Anal. Calcd for C38H31FeRhO3: C, 65.70; H, 4.50. Found:
C, 61.30, 61.36; H, 4.52, 4.31. (Repeated analyses on crystalline
samples gave a consistently low carbon percentage.)
(Acetylaceton ato)(tetr aph en ylcyclopen tadien on e)r h o-
d iu m (I) (11). As for 14, tetracyclone (0.384 g, 1.0 mmol) and
(acac)Rh(C2H4)2 (0.258 g, 1.0 mmol) in THF (40 mL) yielded
11 (0.41 g, 0.70 mmol; 70%) as dark red crystals, mp 260 °C
dec (lit.9 mp 255-270 °C). 1H NMR (500 MHz, CD2Cl2): δ 7.8-
7.1 (m, 20H, phenyl rings), 5.45 (s, 1H, γ-CH of acac), 2.09 (s,
6H, 2 CH3’s). 13C NMR (125 MHz, CD2Cl2): δ 187.72 (CdO),
163.24 (2 CO’s in acac), 131.5, 131.4, 131.2, 131.0, 128.7, 128.3,
128.1 (phenyl C’s), 99.46 (γ-CH of acac), 27.38 (2 CH3’s). IR
(CH2Cl2): νCO at 1635 cm-1. MS (DEI; m/z (%)): 586 [M]+ (11),
558 [M - CO; (C4Ph4)Rh(acac)]+ (8), 486 [M - Hacac]+ (17),
459 [(C4Ph4)Rh]+ (15), 380 [(C2Ph2)Rh(acac)]+ (10), 279 [(C4-
Ph4)Rh(acac)]2+ (50), 229.5 [(C4Ph4)Rh]2+ (3), 178 [PhCtCPh]+
(55), 103 [Rh]+ (50), 43 [CH3CO]+ (100). MS (DCI; m/z (%)):
587 [M + H]+ (100), 178 [C6H5CtCC6H5]+ (7), 118 [Hacac +
NH4]+ (25), 101 [Hacac + H]+ (50).
3-F er r ocen yl-2,4,5-tr ip h en ylcyclop en t-2-en -1-on e (16).
During the chromatographic separation of pure 2, miniscule
quantities of 16 were consistently obtained as a red solid, mp
141 °C. 1H NMR (500 MHz, CD2Cl2): δ 7.7-7.2 (m, 15H phenyl
rings), 4.46 (d, 1H, J ) 1.9 Hz), 4.31 (m, 2H, C5H4), 4.13 (m,
2H, C5H4), 4.02 (s, 5H, C5H5), 3.67 (d, 1H, J ) 1.9 Hz). 13C
NMR (125 MHz, CD2Cl2): δ 171.16 (CO), 143.88, 140.54,
138.36, 133.62, 129.54, 129.22, 129.03, 128.62, 128.08, 127.49,
127.21, 127.11, 126.97 (phenyl C’s), 71.33, 71.13, 71.00 (C5H4),
69.97 (C5H5), 62.86 (CH), 57.92 (CH). IR (CH2Cl2): νCO at 1687
cm-1. MS (DEI; m/z (%)): 494 [M]+ (100); 429 [M - C5H5]+
(5); 178 [C6H5CtCC6H5]+ (7), 165 [C6H5CtCC5H4]+ (10), 121
[C5H5Fe]+ (20); 56 [Fe]+ (32). MS (DCI; m/z (%)): 495 [M +
H]+ (100). Anal. Calcd for C33H26FeO: C, 80.14; H, 5.30.
Found: C, 80.26; H, 5.42.
3-Ferrocenyl-2,4,5-triphenylcyclopentadienone (2)19,37 and
(tetraphenylcyclopentadienone)tricarbonyliron (3)27 were pre-
pared by literature methods.
(3-F er r ocen yl-2,4,5-t r ip h en ylcyclop en t a d ien on e)t r i-
ca r bon ylir on (7). 3-Ferrocenyl-2,4,5-triphenylcyclopentadi-
enone (0.246 g, 0.5 mmol) and Fe2(CO)9 (0.182 g, 0.5 mmol)
were stirred under reflux in THF (20 mL) for 4 h. The reaction
mixture was cooled to room temperature, reduced to half its
volume under reduced pressure, and then treated with hexane
(15 mL). The dark brown precipitate was filtered, dried under
vacuum, and recrystallized from CH2Cl2/hexane (1:1) to give
7 (0.183 g, 0.29 mmol; 58%) as dark red crystals, mp 210 °C.
1H NMR (500 MHz, CD2Cl2): δ 7.7-7.1 (m, 15H phenyl rings),
4.1* (m, 2H, C5H4), 4.08 (s, 5H, C5H5), 4.06 (m, 2H, C5H4), 3.92*
(s, 5H, C5H5), 3.84 (m, 1H, C5H4), 3.76 (m, 1H, C5H4), 3.57*
(m, 1H, C5H4), 3.50* (m, 1H, C5H4). Ferrocenyl peaks for the
major isomer (∼80%) are marked by asterisks. 13C NMR (125
MHz, CD2Cl2): δ 208.77 (Fe-CO), 171.79 (CO), 133.2-127.3
(phenyl C’s), 99.88, 91.30, 86.49, 81.90 (central ring C’s), 73.90
(1 CH), 70.74* (2 CH’s), 70.65 (C5H5), 70.34* (C5H5), 69.25* (2
CH’s), 69.00 (1 CH), 64.34 (1 CH), 63.58 (1 CH). Ferrocenyl
peaks for the major isomer (∼80%) are marked by asterisks;
at 177 K, Fe-13CO resonances are observed at δ 209.1, 207.2,
and 207.0. IR (CH2Cl2): νCO at 2067, 2012, and 1636 cm-1. MS
(DEI; m/z (%)): 632 [M]+ (8), 548 [M - 3CO]+ (15), 520 [M -
Cr ysta llogr a p h ic Da ta for 3, 7, 11, a n d 14. X-ray
crystallographic data for 3‚THF, 7, 11‚H2O, and 14 were each
collected from a suitable sample mounted with epoxy on the
end of a thin glass fiber. Data were collected on a P4 Siemens
diffractometer equipped with a Siemens SMART 1K CCD area
detector (employing the program SMART38) and a rotating
anode utilizing graphite-monochromated Mo KR radiation (λ
) 0.710 73 Å). Data processing was carried out by use of the
program SAINT,39 while the program SADABS40 was utilized
for the scaling of diffraction data, the application of a decay
correction, and an empirical absorption correction based on
redundant reflections. Structures were solved by using the
direct-methods procedure in the Siemens SHELXTL41 program
library and refined by full-matrix least-squares methods on
F2. All non-hydrogen atoms (with the exception of the carbon
atoms of the tetrahydrofuran solvate in 3‚THF) were refined
using anisotropic thermal parameters. Hydrogen atoms were
added as fixed contributors at calculated positions, with
isotropic thermal parameters based on the carbon atom to
which they are bonded. In the course of the refinement process,
a solvated molecule of tetrahydrofuran was located in the
asymmetric unit of 3; similarly, a single water molecule was
located in the asymmetric unit of 11. Although in both cases
the diffraction data readily allowed for a complete anisotropic
refinement of the target molecule, a satisfactory refinement
of the solvate atomic positions proved more difficult to obtain,
leading to rather high values for the residual electron density
4CO]+ (12), 492 [M - Fe(CO)3]+ (17), 427 [M -Fe(CO)3
-
C5H5]+ (17), 399 [M - Fe(CO)4 -C5H5]+ (11), 342 [M - Fe(CO)4
- Fe(C5H6)]+ (60), 286 [(C6H5CtCC5H4)Fe(C5H5)]+ (70), 165
[C6H5CtCC5H4]+ (15), 121 [C5H5Fe]+ (100), 56 [Fe]+ (15). Anal.
Calcd for C36H24Fe2O4 C, 68.39, H, 3.83. Found, C, 67.85; H,
3.93.
(Acet yla cet on a t o)(3-fer r ocen yl-2,4,5-t r ip h en ylcyclo-
p en ta d ien on e)r h od iu m (I) (14). To a solution of 3-ferrocenyl-
2,4,5-triphenylcyclopentadienone (0.246 g, 0.5 mmol) in THF
(10 mL) was added dropwise a solution of (acac)Rh(C2H4)2
(0.128 g, 0.5 mmol) in THF (10 mL), and the mixture was
stirred under reflux for 4 h, after which time the color had
changed from deep blue to purple-red. The reaction mixture
was cooled to room temperature, reduced to half its volume
under reduced pressure, and then treated with hexane (10
mL). The dark red precipitate was filtered, dried under
vacuum, and recrystallized from CH2Cl2/hexane (1:1) to give
14 (0.17 g, 0.25 mmol; 49%) as burgundy red crystals, mp 169
°C. 1H NMR (500 MHz, CD2Cl2): δ 8.05-7.15 (m, 15H phenyl
rings), 5.48 (s, 1H, γ-CH of acac), 4.18 (m, 2H, C5H4) 4.03 (t,
1H, C5H4), 3.86 (s, 5H, C5H5), 3.77 (t, 1H, C5H4), 2.16 (s, 6H,
2 CH3’s); at 198 K, CH3’s at δ 2.09 and 2.05. 13C NMR (125
MHz, CD2Cl2): δ 187.49 (CdO), 163.14 (2 CO’s in acac), 133.5-
127.9 (phenyl C’s), 99.59 (γ-CH of acac), 72.60, 71.12, 70.66,
70.42 (CH’s of C5H4), 69.99 (C5H5), 27.46 (2 CH3’s); at 198 K,
CH3’s at δ 27.41 and 27.05. IR (CH2Cl2): νCO at 1635 cm-1
.
MS (DEI; m/z (%)): 694 [M]+ (5), 666 [M - CO; (C4Ph3Fc)Rh-
(acac)]+ (1), 333 [(C4Ph3Fc)Rh(acac)]2+ (16), 168 [(C5H5)Rh]+
(6), 165 [C6H5CtCC5H4]+ (20), 84 [(C5H5)Rh]2+ (63), 43
[CH3CO]+ (100). MS (DCI; m/z (%)): 695 [M + H]+ (5), 255
(38) Sheldrick, G. M. SMART, Release 4.05; Siemens Energy and
Automation Inc., Madison, WI 53719, 1996.
(39) Sheldrick, G. M. SAINT, Release 4.05; Siemens Energy and
Automation Inc., Madison, WI 53719, 1996.
(40) Sheldrick, G. M. SADABS (Siemens Area Detector Absorption
Corrections); Siemens Energy and Automation Inc., Madison, WI
53719, 1996.
(41) Sheldrick, G. M. SHELXTL, Version 5.03; Siemens Crystal-
lographic Research Systems, Madison, WI, 1994.
(36) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: New York, 1980.
(37) Rausch, M. D.; Siegel, A. J . Org. Chem. 1968, 33, 4545.

Rh and Ir Complexes of Cyclopentadienones
Organometallics, Vol. 19, No. 2, 2000 191
(concentrated primarily in the region of the solvent molecules)
and the refinement statistics associated with these crystal
structures.
Molecu la r Or bita l Ca lcu la tion s. These calculations were
performed within the extended Hu¨ckel formalism using
weighted Hij values,42 by using the program CACAO.43 The
molecular geometries were idealized versions taken from the
X-ray crystal structures of 3 and 11.
NMR Sim u la tion s. These simulations were carried out by
using the multisite EXCHANGE program generously provided
by Professor R. E. D. McClung (University of Alberta at
Edmonton).
Ackn owledgm en t. Financial support from the Natu-
ral Sciences and Engineering Council of Canada and
from the Petroleum Research Fund, administered by the
Americal Chemical Society, is gratefully acknowledged.
M.S. thanks the NSERC for a Graduate Fellowship and
McMaster University for a Centennial scholarship.
Mass spectra were acquired courtesy of Dr. Kirk Green
of the McMaster Regional Mass Spectrometry Centre.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic parameters, bond lengths and angles, anisotropic
displacement parameters, and hydrogen coordinates for 3, 7,
11, and 14. This material is available free of charge via the
Internet at http://pubs.acs.org.
(42) (a) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397. (b) Hoffmann,
R.; Lipscomb, W. N. J . Chem. Phys. 1962, 36, 2179, 3489. (c) Ammeter,
J . H.; Bu¨rgi, H.-B.; Thibeault, J . C.; Hoffmann, R. J . Am. Chem. Soc.
1978, 100, 3686.
(43) (a) CACAO, Version 5.0; 1998. (b) Mealli, C.; Proserpio, D. M.
J . Chem. Educ. 1990, 67, 399.
OM990559B