Syntheses and characterization of iridium and rhodium ethylene complexes containing a doubly linked cyclopentadienyl ligand

Article abstract of DOI:10.1016/j.ica.2008.04.025

The dimerization of 6,6-dimethylfulvene with Ni(cod)₂ yields the 4,4,8,8-tetramethyl-3a,4,7a,8-tetrahydro-s-indacene isomer (1a). Heating a solution of 1a converts it to the 1,4,5,8 (1b) and 1,4,7,8 (1c) tetrahydro-s-indacene isomers. The activ

Full text of DOI:10.1016/j.ica.2008.04.025

Inorganica Chimica Acta 362 (2009) 389–394
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Syntheses and characterization of iridium and rhodium ethylene complexes
containing a doubly linked cyclopentadienyl ligand
a
a
a
a
a
Robert M. Chin a, , Devin Maurer , Mitchell Parr , Neysa Allworth , Robbie Schwenker , Daniel Sullivan ,
*
Samantha Enabnit a, William Brennessel b
a Department of Chemistry and Biochemistry, University of Northern Iowa, Cedar Falls, IA 50614-0423, United States
b Department of Chemistry, University of Rochester, Rochester, NY 14627, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 April 2008
Received in revised form 15 April 2008
Accepted 15 April 2008
Available online 22 April 2008
The dimerization of 6,6-dimethylfulvene with Ni(cod)2 yields the 4,4,8,8-tetramethyl-3a,4,7a,8-tetrahy-
dro-s-indacene isomer (1a). Heating a solution of 1a converts it to the 1,4,5,8 (1b) and 1,4,7,8 (1c)
tetrahydro-s-indacene isomers. The activation energy for the isomerization is 23(1) kcal/mol. 1b and
1c can be deprotonated with n-BuLi and the reaction of the dianion with [ClIr(C2H4)2]2 gives two isomers,
cis-[(g5-C5H3)(CMe2)Ir(C2H4)2]2 (cis-2) and trans-[(g5-C5H3)(CMe2)Ir(C2H4)2]2 (trans-2). Reaction of 1b
and 1c with RhCl3 ꢀ xH2O in refluxing methanol yields a red-orange solid, which was consistent with
the empirical formula, [(C5H3)(CMe2)RhCl2]n (3). Reaction of 3 with C2H4 in a Na2CO3/ethanol mixture
afforded cis-[(g5-C5H3)(CMe2)Rh(C2H4)2]2 in 5% yield.
Keywords:
Iridium
Rhodium
Cyclopentadienyl
Dinuclear
Fulvene
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Herein we report the solution syntheses and characterization of
1a, 1b, and 1c from commercially available reagents, and the sub-
Linked cyclopentadienyl ligands have been previously synthe-
sized to study the interaction of two metal centers next to each
other. The dicyclopentadienyl ligands typically have one or two
linking units. For the singly linked ligands, the bridging groups
can vary from methylene [1], dimethylsilylene [2], dimethylmeth-
ylene [3] to no intermediate group as in fulvalene (Scheme 1) [4].
One of the problems with the singly linked ligands is that the
two metal centers are not always next to each other due to the free
rotation about the linking unit. Use of two linkers would stop the
free rotation of the cyclopentadienyl rings and ensure that the
two metal centers stay close to one another (Scheme 2).
While there have been a number of complexes reported con-
taining different linking groups [3], one combination that is con-
spicuously absent is the one containing two CMe2 groups as the
linkers. In 1979, McGlinchey and coworkers reported the synthesis
of two isomers of 4,4,8,8-tetramethyl-tetrahydro-s-indacene, the
1,4,5,8 (1b) and 1,4,7,8 (1c) isomers. The products were formed
via the dimerization of 6,6-dimethylfulvene using nickel atoms in
a metal atom reactor [5]. The expected 3a,4,7a,8 isomer, 1a, was
never isolated but was presumed to be the common intermediate
in the formation of 1b and 1c (Scheme 3).
sequent syntheses and characterization of three iridium and rho-
dium ethylene complexes containing this robust and versatile
ligand with two CMe2 linkers.
2. Experimental
2.1. General procedures
Reactions that required inert conditions were performed using
modified Schlenk techniques or in an MBraun Unilab glovebox
under a nitrogen atmosphere. 1H and 13C NMR spectra were
recorded on Varian Unity Inova 400 MHz or GE-QE 300 MHz spec-
trometers. 1H and 13C NMR chemical shifts are given relative to the
residual proton or 13C solvent resonances. Mass spectra were
recorded on a Hewlett–Packard 6890-5973 GC–MS. X-ray data
were collected on a Bruker SMART Apex II CCD Platform diffracto-
meter.
2.2. Solvents and reagents
Unless otherwise indicated, all chemicals were used as received
(reagents from Aldrich, Acros, or Strem Chemical Company).
Deuterated solvents were obtained from Cambridge Isotope Labo-
ratories. Tetrahydrofuran (THF), benzene, dichloromethane, and
pentane were passed through an MBraun Solvent Purification
* Corresponding author. Tel.: +1 319 273 7898; fax: +1 319 273 7127.
E-mail address: martin.chin@uni.edu (R.M. Chin).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.04.025

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R.M. Chin et al. / Inorganica Chimica Acta 362 (2009) 389–394
mixture was then filtered through a SiO2 padded frit and the fil-
X
trate collected. The hexane was removed by rotary evaporation
resulting in an oil to which was added ꢁ25 mL of methanol. The
methanol/oil mixture was placed into an ice bath forming a white
crystalline precipitate. The mixture was filtered and washed with
cold methanol to give 1a as a white solid (0.520 g, 8% yield). Safety
note: The black nickel residue on the SiO2 padded frit would sometimes
smoke upon standing in the hood. We now pour dilute aqueous (ꢁ1 M)
HCl onto the black Ni residue and then cover the mixture to deactivate
any reactive Ni metal. 1H NMR (400 MHz, CDCl3, 21 °C), d 6.39 (m,
2H), 6.25 (m, 2H), 6.12 (m, 2H), 2.96 (m, 2H), 1.49 (s, 6H), 0.75
(s, 6H) 13C{1H} NMR (75 MHz, CDCl3 20 °C) d 159.92 (quat C),
132.65, 132.26, 121.67 (CH), 61.76 (CH), 38.39 (C(CH3)2), 27.07
(CH3), 25.00 (CH3). Anal. Calc. for C16H20: C, 90.60; H, 9.40. Found:
C, 90.62; H, 9.46%. MS (EI, 70 eV, m/z) 212 (17), 197 (100), 183 (82),
167 (25), 165 (27), 152 (15).
Alternatively, 1b and 1c can be prepared by heating 1a in situ.
The synthesis was carried out as described above except instead
of adding MeOH to precipitate 1a, the resulting oil was heated at
80 °C for 30 min, at which point the oil became a semi-solid. The
resulting solid was sublimed at 80 °C, 20 mtorr, to give a white
solid mixture of 1a and 1b (20% yield). The 1H NMR spectral data
matched the reported data in CD2Cl2. 1H NMR (400 MHz, CDCl3,
21 °C), d 6.55 (m, 2H), 6.36 (dt, J = 5.3, 1.4 Hz, 2H), 3.03 (m, 4H),
1.34 (s, 3H), 1.32 (s, 6H), 1.31 (s, 3H).
fulvalene
X = CH2, SiMe2, CMe2
Scheme 1. Examples of singly linked Cp ligands.
X
Y
X = CH2 or CMe2 or SiMe2,
Y= CH2 or SiMe2 or GeMe2,
Scheme 2. Examples of doubly linked Cp ligands.
System prior to use. C6D6 was distilled from a dark purple solution
of sodium benzophenone ketyl. CDCl3 and CD2Cl2 were distilled
under vacuum from CaH2. Elemental analyses were either per-
formed by Atlantic Microlab, Norcross GA, or on a Thermo Flash
EA1112 Series analyzer at the National Ag-Based Industrial
Lubricant laboratory in Waverly, IA. 6,6-dimethylfulvene was
obtained from Aldrich or prepared as described [6]. Ni(cod)2 was
purchased from Strem Chemical or prepared as described [7].
[IrCl(C2H4)2]2 was prepared according to the literature method
[8]. 4,4,8,8-Tetramethyl-1,4,5,8-tetrahydro-s-indacene, 1b, and
4,4,8,8-tetramethyl-1,4,7,8-s-indacene, 1c were prepared as
described [5] or by using Ni(cod)2 as a reactive source of nickel.
Cl2 gas was prepared by the reaction of 6 M HCl with household
bleach (5% NaOCl) as described by Mattson and coworkers [9].
The kinetic data for the isomerization of 1a to 1b and 1c were
collected as follows:
One mL (0.026–0.071 M) CDCl3 solutions of 1a were charged
into a J. Young NMR tube and 5 lL of toluene added via microsy-
ringe. The tube was kept in an ice bath upon mixing and trans-
ferred quickly into the NMR spectrometer. The temperature of
the NMR probe was maintained using a Varian variable tempera-
ture controller and the temperature was calibrated using ethylene
glycol and standard operating procedures. Approximately 10–20
spectra were obtained at regular time intervals over the period of
2–3 half lives for each sample of a given temperature. The NMR
spectroscopic data was integrated using ACDLABS version 10.0.2
1D NMR Processor software. The resulting data was then analyzed
by Microsoft Excel.
Preparation of cis-2 and trans-2. A mixture of 1b and 1c
(470.5 mg, 2.22 mmol) was placed in a 100 mL flask and 12 mL of
THF added. n-BuLi (1.8 mL, 2.5 M solution in hexanes) was added
dropwise to the stirred solution at 21 °C. A white participate
formed towards the end of the n-BuLi addition. The mixture was
stirred for 20 min and the THF was then removed in vacuo. The
resulting dianion was re-suspended in 10 mL of pentane.
2.2.1. Preparation of 1a using Ni(cod)2 as a reactive source of nickel
6,6-Dimethylfulvene (6.6383 g, 62.6 mmol) was placed in a
100 mL cylindrical drying chamber and stirred vigorously in a
nitrogen filled glove box. Ni(cod)2 (6.5823 g, 23.93 mmol) was
added all at once to the stirred 6,6-dimethylfulvene. The mixture
darkened immediately and became highly viscous. Approximately
8 mL of C6H6 was then added to the reaction and stirred manually
with a spatula for 10 min. Unreacted 6,6-dimethylfulvene and ben-
zene were removed under vacuum inside the glove box. The result-
ing black residue was suspended in 20 mL of CH2Cl2 and added to
ꢁ100 mL of stirred hexane inside a 250 mL Erlenmyer flask. The
1,5 hydrogen shift
Ni atoms
1b
1a
1c
3a,4,4a,8 isomer
Scheme 3. Proposed mechanism for the formation of 1b and 1c by McGlinchey and coworkers.

R.M. Chin et al. / Inorganica Chimica Acta 362 (2009) 389–394
391
[ClIr(C2H4)2]2 (1.203 g, 2.13mmol) was added to the mixture and
the reaction stirred for 18 h at 21 °C. The resulting dark brown
mixture was filtered through a Celite padded frit to remove the LiCl
and washed with CH2Cl2 (ꢁ50 mL). The solvent was removed in
vacuo to yield a red/brown residue. A 1H NMR spectrum of the
crude reaction mixture showed a 4:1 ratio of trans-2:cis-2. The res-
idue was chromatographed on an Analogix SF40-150 g SiO2 col-
umn using a 6:1 hexane:CH2Cl2 mixture as the eluent to separate
the cis and trans isomers. cis-2 (80 mg, 5%) came off the column
first followed by trans-2 (133 mg, 9%). The reaction was performed
in a nitrogen atmosphere but the chromatographic separation was
performed in air. Solutions of cis-2 and trans-2 were determined to
be air stable for short time periods.
(d, JRh–C = 13.4 Hz CH2), 37.83 (s, CH3), 33.95 (quat C, C(CH3)2),
28.40 (s, CH3). Anal. Calc. for C24H34Rh2: C, 54.54; H, 6.59. Found: C,
54.76; H, 6.69%.
Structure determination of trans-2.
A
crystal (0.16 ꢃ 0.16 ꢃ
0.12 mm3) was placed onto the tip of a 0.1 mm diameter glass cap-
illary tube or fiber and mounted on a Bruker SMART APEX II CCD
Platform diffractometer for a data collection at 100.0(1) K [10]. A
preliminary set of cell constants and an orientation matrix were
calculated from 910 reflections harvested from three sets of 20
frames. These initial sets of frames were oriented such that orthog-
onal wedges of reciprocal space were surveyed. The data collection
was carried out using Mo Ka radiation (graphite monochromator)
with a frame time of 10 s and a detector distance of 5.03 cm. A ran-
domly oriented region of reciprocal space was surveyed: four
major sections of frames were collected with 0.50° steps in x at
four different / settings and a detector position of ꢂ33° in 2h.
The intensity data were corrected for absorption [11]. Final cell
constants were calculated from the xyz centroids of 3903 strong
reflections from the actual data collection after integration [3,12]
(see Table 1 for additional crystal and refinement information).
cis-[(g5-C5H3)(CMe2)Ir(C2H4)2]2 (cis-2). 1H NMR (400 MHz, C6D6,
20 °C) d 5.14 (t, J = 2.5 Hz, 2H), 4.31 (d, J = 2.5 Hz, 4H), 3.00 (m, 8H),
1.22 (s, 6H), 1.16 (s, 6H), 0.94 (m, 8H) 13C{1H} NMR (75 MHz, C6D6
20 °C) d 107.91 (quat C, Cp), 80.61 (CH), 77.70 (CH), 38.23 (CH3),
33.92 (quat C, C(CH3)2), 27.86 (CH3), 21.16 (CH2). Anal. Calc. for
C24H34Ir2: C, 40.77; H, 4.85. Found: C, 41.12; H, 4.88%.
trans-[(g5-C5H3)(CMe2)Ir(C2H4)2]2 (trans-2). 1H NMR (400 MHz,
C6D6, 20 °C) d 4.81 (t, J = 2.5 Hz, 2H), 4.62 (d, J = 2.5 Hz, 4H), 2.63
(m, 8H), 1.46 (s, 12H), 0.73 (m, 8H) 13C{1H} NMR (75 MHz, C6D6
20 °C) d 111.83 (quat C, Cp), 80.94 (CH), 78.99 (CH), 34.92 (CH3),
33.61 (quat C, C(CH3)2), 19.60 (CH2). Anal. Calc. for C24H34Ir2: C,
40.77; H, 4.85. Found: C, 41.02; H, 4.86%.
Synthesis of cis-[(g5-C5H3)(CMe2)IrCl2]n. cis-2 (39.35 mg,
0.056 mmol) was dissolved in 2 mL of CH2Cl2 and the round bot-
tom flask capped with a rubber septum. 30 mL of Cl2 gas (22 °C,
1 atm) was injected into the flask whereupon the colorless solution
immediately turned bright orange. The mixture was stirred for 1 h,
then filtered and washed with 5 mL CH2Cl2. The orange solid was
dried in vacuo to give 34.9 mg (85%) of product. The solid was
insoluble in common organic solvents and therefore no NMR spec-
troscopic data was obtained. Anal. Calc. for C16H18Ir2Cl4: C, 26.09; H,
2.46. Found: C, 25.37; H, 2.67%.
2.2.2. Structure solution and refinement
The structure was solved using SHELXS-97 and refined using SHEL-
XL-97 [13]. The space group P21/n was determined based on sys-
tematic absences and intensity statistics. A Patterson solution
was calculated which located the two iridium atoms in the
E-map. Full-matrix least squares/difference Fourier cycles were
performed which located the remaining non-hydrogen atoms. All
non-hydrogen atoms were refined with anisotropic displacement
parameters. An attempt was made to refine the ethylene ligand
hydrogen atoms independently from their carbon atoms; however,
the refined C—H distances were unreasonable. Therefore, all hydro-
gen atoms were placed in ideal positions and refined as riding
atoms with relative isotropic displacement parameters. The final
full matrix least squares refinement converged to R1 = 0.0176 (F2,
I > 2r(I)) and wR2 = 0.0385 (F2, all data).
Synthesis of trans-[(g5-C5H3)(CMe2)IrCl2]n. The procedure was
the same as described for cis-[(g5-C5H3)(CMe2)IrCl2]n. trans-2
(43.2 mg, 0.061 mmol) gave 37.1 mg (82%) of product. The orange
solid had the same insoluble properties as cis-[(g5- C5H3)-
(CMe2)IrCl2]n. Anal. Calc. for C16H18Ir2Cl4: C, 26.09; H, 2.46. Found:
C, 26.19; H, 2.51%.
Structure determination for cis-2.
A
crystal (0.20 ꢃ 0.18 ꢃ
0.14 mm3) was placed onto the tip of a 0.1 mm diameter glass cap-
illary tube or fiber and mounted on a Bruker SMART APEX II CCD
Platform diffractometer for a data collection at 100.0(1) K [10]. A
preliminary set of cell constants and an orientation matrix were
calculated from 683 reflections harvested from three sets of 20
frames. These initial sets of frames were oriented such that orthog-
onal wedges of reciprocal space were surveyed. The data collection
was carried out using Mo Ka radiation (graphite monochromator)
with a frame time of 10 s and a detector distance of 5.03 cm. A ran-
domly oriented region of reciprocal space was surveyed: four
major sections of frames were collected with 0.50° steps in x at
four different / settings and a detector position of ꢂ33° in 2h.
The intensity data were corrected for absorption [11]. Final cell
constants were calculated from the xyz centroids of 3872 strong
reflections from the actual data collection after integration [12]
(see Table 1 for additional crystal and refinement information).
Synthesis of [(g5-C5H3)(CMe2)RhCl2]n (3). RhCl3 ꢀ 3H2O (500.5 mg,
1.90 mmol), a mixture of 1b and 1c (253.6 mg, 0.971 mmol) and
10 mL of MeOH were added to a 50 mL round bottom flask and
the mixture refluxed for 48 h. The resulting orange-brown suspen-
sion was cooled to 0 °C and filtered. The red-orange solid was
washed with ꢁ15 mL MeOH and dried in vacuo yielding
459.5 mg (87%) of product. The solid was insoluble in common
organic solvents, therefore no NMR spectroscopic data was ob-
tained. Anal. Calc. for C16H18Rh2Cl4: C, 34.44; H, 3.25. Found: C,
34.37; H, 3.72%.
Synthesis of cis-[(g5-C5H3)(CMe2)Rh(C2H4)2]2 (4).
3 (405 mg,
0.726 mmol), anhydrous Na2CO3 (200.0 mg, 1.89 mmol) and
25 mL of EtOH were placed in a 100 mL Schlenk flask. A 1 L round
bottom flask was placed on top of the Schlenk flask and 1 atm of
C2H4 placed over the solution. The mixture was heated at 60 °C
for 18 h. The solvent was removed from the resulting black solu-
tion and the crude reaction mixture extracted with pentane
(50 mL). The pentane extract was filtered through a Celite padded
frit and the pentane removed until ꢁ1–2 mL of solution remained.
The solution was placed in a ꢂ40 °C freezer for 18 h which afforded
pure cis-4 (18.0 mg, 5%). 1H NMR (400 MHz, C6D6, 20 °C) d 5.31
(dt, J = 2.7 Hz, JRh–H = 1.2 Hz, 2H), 4.38 (d, J = 2.7 Hz, 4H), 3.26 (br
m, 8H), 1.25 (br m, 8H), 1.23 (s, 6H), 1.15 (s, 6H). 13C{1H} NMR
(75 MHz, C6D6 20 °C) d 114.10 (d, JRh–C = 3.7 Hz, quat C, Cp), 85.6
(d, JRh–C = 4.9 Hz, CH), 81.63 (d,, JRh–C = 3.7 Hz CH), 39.42
2.2.3. Structure solution and refinement
The structure was solved using SHELXS-97 and refined using SHELXL
-
ꢀ
97 [13]. The space group P1 was determined based on the lack of
systematic absences and intensity statistics. A direct-methods
solution was calculated which provided most non-hydrogen atoms
from the E-map. Full-matrix least squares/difference Fourier cycles
were performed which located the remaining non-hydrogen
atoms. All non-hydrogen atoms were refined with anisotropic dis-
placement parameters. Although the ethylene hydrogen atoms
could be refined independently from their respective carbon
atoms, the refined C—H distances varied more than was deemed
appropriate. Therefore, all hydrogen atoms were placed in ideal

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R.M. Chin et al. / Inorganica Chimica Acta 362 (2009) 389–394
Table 1
Crystal data for cis-2 and trans-2
cis-[(C5H3)(CMe2)Ir(C2H4)2]2 (cis-2)
trans-[(C5H3)(CMe2)Ir(C2H4)2]2 (trans-2)
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C24H34Ir2
706.91
C24H34Ir2
706.91
100.0(1)
0.71073
monoclinic
P21/n
100.0(1)
0.71073
triclinic
ꢀ
P1
12.505(2)
8.8818(18)
b (Å)
13.464(2)
17.655(4)
a (°)
67.411(2)
90
b (°)
67.696(2)
103.357(2)
c (Å)
14.558(3)
13.497(3)
c (°)
82.425(2)
2093.5(6)
4
2.243
12.706
1328
90
2059.2(8)
4
2.280
12.917
1328
Volume (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢂ1
F(000)
)
Crystal color, morphology
Crystal size (mm)
h Range (°)
colorless, block
0.20 ꢃ 0.18 ꢃ 0.14
1.64–31.50
colorless, block
0.16 ꢃ 0.16 ꢃ 0.12
1.93–32.57
Index ranges
Reflections collected
ꢂ18 6 h 6 18, ꢂ19 6 k 6 19, ꢂ21 6 l 6 21
ꢂ13 6 h 6 13, ꢂ26 6 k 6 26, ꢂ20 6 l 6 20
36294
36342
Independent reflections [Rint
Observed reflections
]
13838 [0.0277]
12547
7427 [0.0282]
6958
Absorption correction
multi-scan
multi-scan
Maximum and minimum transmission
Refinement method
0.1693 and 0.0955
full-matrix least-squares on F2
13838/0/477
0.2163 and 0.1517
full-matrix least-squares on F2
7427/0/239
Data/restraints/parameters
Goodness-of-fit on F2
1.059
1.085
Final R indices [I > 2r(I)]
R1 = 0.0210, wR2 = 0.0508
R1 = 0.0243, wR2 = 0.0521
1.668 and ꢂ3.228
R1 = 0.0176, wR2 = 0.0379
R1 = 0.0199, wR2 = 0.0385
1.831 and ꢂ1.350
R indices (all data)
Largest difference in peak and hole (e Åꢂ3
)
P
P
P
P
P
P
2
2
1=2
2
Definitions: Rint
¼
jF2o ꢂ hF2oij= jFo2j; R1
=
||Fo| ꢂ |Fc||/ |Fo|; wR2 ¼ ½ ½wðF2o ꢂ Fc2Þ ꢄ= ½wðFo2Þ ꢄꢄ , where w ¼ 1=½r2ðF2oÞ þ ðaPÞ þ bPꢄ and P ¼ 1=3 maxð0; Fo2Þ þ 2=3F2c ;
P
Goodness-of-fit ¼ S ¼ ½ ½wðF2o ꢂ Fc2Þ ꢄ=ðm ꢂ nÞꢄ1=2, where m = number of reflections and n = number of parameters.
2
positions and refined as riding atoms with relative isotropic dis-
placement parameters. The final full matrix least squares refine-
ment converged to R1 = 0.0210 (F2, I > 2r(I)) and wR2 = 0.0521
(F2, all data). Table 1 contains the crystallographic data for cis-2
and trans-2.
which is consistent with the proposed isomeric structure. How-
ever, we have not been able to determine the stereochemistry of
the hydrogens at the 3a and 7a positions. Therefore it is unclear
whether we have a mixture of the R,R and S,S isomers or the
meso-isomer of 1a.
1a can be converted cleanly to the 1,4,5,8 (1b) and 1,4,7,8 (1c)
isomers by heating a solution of 1a to 80 °C for 1 h as shown in
Scheme 1. The interconversion of 1a into isomers 1b and 1bc obeys
first order kinetics with a rate constant of 1.10(7) ꢃ 10ꢂ5 sꢂ1 at
296 K in CDCl3. Measuring the rate constants between 296 and
329 K gave the activation energy for the 1,5-hydrogen shift to be
23(1) kcal/mol (Table 2).
3. Results and discussion
Our work began with repeating the work of McGlinchey and co-
workers using a metal atom reactor. We were able to reproduce
their results with similar yields. However, while it was tremendous
fun vaporizing nickel metal, we began to investigate an alternative
solution phase synthesis of 1b and 1c since the metal atom reactor
yielded only ꢁ150 mg of product with each run. We found that
Ni(cod)2 (cod = 1,5-cyclooctadiene) could be used as a source of
reactive nickel metal which negated the need for the metal reactor.
Another advantage to the solution phase synthesis was that the
reaction could be carried out on the multigram scale. Our initial
reactions of Ni(cod)2 with 6,6-dimethylfulvene involved extracting
the crude reaction mixture with hexanes, removing the solvent and
then immediately subliming the crude oil/semi-solid mixture at
80 °C to obtain pure 1b and 1c (20% yield). It was not until we elim-
inated the sublimation/heating step that we discovered that the 1a
isomer could be cleanly isolated from the crude oil mixture
obtained from the hexane extraction step. Addition of CH3OH to
the resulting oil from the hexane extraction step results in 1a pre-
cipitating from the mixture as a white solid (8% yield). The 13C
NMR spectrum of 1a has eight resonances which is consistent with
it being the 3a,4,7a,8 isomer and not the 3a,4,4a,8 isomer which
would be expected to have at least nine resonances.
An Arrhenius plot of ln k versus 1/T is shown in Fig. 1.
This activation energy of 23 kcal/mol is slightly higher than the
measured value of 19.9 kcal/mol for the 1,5-sigmatropic shift of
5-methylcyclopentadiene [14]. Therefore the isomerization of 1a,
k = 1.10 ꢃ 10ꢂ5 sꢂ1, is slower than the isomerization of 5-methyl-
cyclopentadiene, k = 36.8 ꢃ 10ꢂ5 sꢂ1, at ꢁ25 °C. Alternatively, the
isolation step of 1a can be bypassed and isomers 1b and 1c col-
lected by heating and subliming crude 1a when it exists as an
oil/semi-solid. It should be noted that the isomerization of 1a to
Table 2
Rate constants for the 1,5-hydrogen shift of 1a as a function of temperature
kobs (ꢃ105 sꢂ1
)
Temperature (K)
1.10(7)
1.98(5)
3.7(1)
296
303
307
312
316
322
329
6.5(9)
10.4(5)
19.7(7)
59(6)
The 1H NMR spectrum of 1a displays three olefinic resonances
in the 6.0–6.4 ppm range and two different sets of CH3 groups

R.M. Chin et al. / Inorganica Chimica Acta 362 (2009) 389–394
393
-6
-7
R2 = 0.9921
-8
-9
-10
-11
-12
3
3.05
3.1
3.15
3.2
3.25
3.3
3.35
3.4
T-1 x 103 K-1
Fig. 1. Arrhenius plot for the 1,5-hydrogen shift of 1a.
Fig. 2. ORTEP plot of cis-2 (50% probability). Hydrogens are omitted for clarity.
Selected bond distances (Å) and angles (°): Ir(1)–Cp(centroid), 1.893; Ir(1)–C(1),
2.119(3); Ir(1)–C(2), 2.124(3); C(1)–C(2), 1.428(4); Ir(1)–C(10), 2.274(2); Ir(1)ꢀ ꢀ ꢀIr(2),
4.6915(6); \C(2)–Ir(1)–C(4), 85.71(12); \C(1)–Ir(1)–(C2), 39.34(11); \Cp(cen-
troid)–Ir(1)–Ir(2)–Cp(centroid) torsional angle, 2.77; \Cp–Cp fold angle 175.9(2).
1b and 1c does not occur in the solid phase and that 1a has to be in
solution in order for the isomerization to occur.
A mixture of 1b and 1c can be doubly deprotonated with
2 equiv. of n-BuLi and the subsequent reaction of the dianion with
[ClIr(C2H4)2]2 yields two new iridium ethylene complexes, cis-[(g5-
C5H3)(CMe2)Ir(C2H4)2]2 (cis-2) and trans-[(g5-C5H3)(CMe2)Ir(C2H4)2]2
(trans-2) (Scheme 4).
The reaction gave a cis:trans ratio of 1:4 by 1H NMR spectros-
copy. cis-2 was distinguishable from trans-2 due to the two differ-
ent resonances of the gem-CMe2 groups on the two linking bridges
for the cis isomer. The trans isomer is expected to display just one
resonance for the gem-CMe2 groups since the methyl groups are
equivalent. The ethylene ligands for both cis-2 and trans-2 show
hindered rotation about the Ir-C2H4 bond since two different reso-
nances are observed for the ethylene hydrogens. The resonances
have the characteristic AA‘XX’ pattern for both sets of ethylene
hydrogens as seen in other cyclopentadienyl iridium ethylene
complexes [15]. The cis and trans isomers can be separated by col-
umn chromatography and cooling an Et2O solution of either isomer
to ꢂ35 °C afforded colorless X-ray quality crystals (Table 1, Section
2).
Since there are two independent molecules in the structure of
cis-2 that are structurally equivalent, only one will be discussed
below. The structure of cis-2 (Fig. 2) shows the C-C bond of the eth-
ylene ligands to be roughly ‘‘parallel” with the Cp plane which is
consistent with the number of observed resonances in the 13C
NMR spectrum. The Ir(1)–C(Cp) bond distances range from
2.192–2.309 Å while the Ir(1)–C(ethylene) bond distances vary
from 2.094–2.124 Å. Also, the Ir(1)–Cp(centroid) distance is
1.893 Å. These bond distances are similar to those observed by
Enders and co-workers for a quinolyl-CpIr(C2H4)2 complex [16].
The Ir(1)ꢀ ꢀ ꢀIr(2) distance is 4.6915(6) Å and the Cp–Cp fold angle
175.9(2)°. The metal-metal distance and fold angles are similar to
those observed by Angelici and co-workers for the analogous (g5-
C5H3)2(SiMe2)2Ru2(CO)4(I)2, a ruthenium carbonyl complex with
doubly linked Cps using SiMe2 linkers [17]. They report a Ruꢀ ꢀ ꢀRu
distance of 4.9762 Å and a Cp–Cp fold angle of 175.9°.
Fig. 3. ORTEP plot of trans-2 (50% probability). Hydrogens are omitted for clarity.
Selected bond distances (Å) and angles (°): Ir(1)–Cp(centroid), 1.905; Ir(1)–C(1),
2.126(2); Ir(1)–C(2), 2.115(2); C(1)–C(2), 1.434(4); Ir(1)–C(10), 2.283(2);
\C(2)–Ir(1)–C(4), 85.13(11); \C(1)–Ir(1)–(C2), 39.54(10); \Cp(centroid)–Ir(1)–
Ir(2)–Cp(centroid) torsional angle, 7.53; \Cp–Cp fold angle 147.85(8).
The structure of trans-2 is shown in Fig. 3 along with selected
bond lengths and angles. The Ir–Cp and Ir–ethylene bond lengths
of trans-2 are similar to those of cis-2. The biggest structural differ-
ence between the two complexes is the Cp–Cp fold angle. In
trans-2, the Cp–Cp fold angle is 147.85(8)°, and the Cp(centroid)–
Ir(1)–Ir(2)–Cp(centroid) torsional angle is 7.53°. This means that
Li+
Li+
Ir
21 oC
Cl
Cl
Ir
Ir
+
+
Ir
Ir
pentane, 18 h
Ir
cis-2
trans-2
Scheme 4.

394
R.M. Chin et al. / Inorganica Chimica Acta 362 (2009) 389–394
Cl
Rh
Cl
MeOH
+ RhCl3.xH2O
+
Rh
Rh
2 d reflux
Rh
Cl
Cl
Cl
Cl
Cl
n
Cl
n
Scheme 5.
the Cp ligands are bent more towards each other than in the cis iso-
mer and that there is a slight twist in the Cp planes relative to each
other.
Reaction of 1b and 1c with RhCl3 ꢀ xH2O in refluxing methanol
gave the cis and trans polymeric chlorobridged complexes, [(g5-
C5H3)(CMe2)RhCl2]n (3) as shown in Scheme 5.
port the cis isomeric formulation as opposed to the trans isomer.
The 13C NMR spectrum displays seven distinct resonances, with
the Cp carbons having JRh–C between 3.7 and 4.9 Hz. The ethylene
carbons have a JRh–C = 13.2 Hz, which is similar to (g5-C5H5)-
Rh(C2H4)2 which has a Rh–C coupling constant of 10 Hz [20].
We have reported a simple one step synthesis to a doubly linked
Cp ligand from commercially available reagents. Although the
yields of subsequent iridium and rhodium ethylene complexes
are low, the reaction of 1b and 1c with RhCl3 ꢀ xH2O to make the
polymeric chlorobridged complex, 3, proceeds in good yield. 3
should prove to be a valuable synthetic precursor to other Rh(III)
complexes as we continue to investigate the reactivity of new rho-
dium complexes with the doubly linked Cp ligand.
The reaction is similar to the reported reaction between C5H6
with RhCl3 ꢀ xH2O which yields the polymeric [(g5-C5H5)RhCl2]n
chlorobridged complex rather than the discrete dimeric complex
as seen in the C5Me5 chemistry [18]. The polymeric nature of our
product is based on the insolubility of the compound in a wide
variety of organic compounds. The elemental analysis of the red-
orange solid is consistent the empirical formula of [(C5H3)(CMe2)-
RhCl2]. Reaction of 1b and 1c with IrCl3 ꢀ xH2O in refluxing
methanol for 2 d failed to yield any chlorobridged complexes.
Rather, the reaction gave a deep purple solution which displayed
a complex mix of resonances in the 1H NMR spectrum with CD3OD
as the solvent. We had hoped that putting the Cp ligand on Ir(III)
and then performing the reduction to the Ir(I) ethylene complexes
would give a better yield of the cis isomer, but this has not proven
to be the case. At this time, we are unable to obtain either the cis or
trans isomers of [(g5-C5H3)(CMe2)IrCl2]n via this synthetic route.
However, reaction of either cis-2 or trans-2 with Cl2 in CH2Cl2
yielded bright orange insoluble powders [19]. The resulting pow-
ders have elemental analyses consistent with the [(C5H3)(CMe2)-
IrCl2]n formulation. Reaction of cis-[(g5-C5H3)(CMe2)IrCl2]n with
C2H4 in a Na2CO3/EtOH mixture at 70 °C, for 18 h gave a complex
mixture of products. However, in the forest of 1H peaks, we
observed cis-2 in ca. 5% yield, based on the intensity of the peaks
relative to the other peaks. So while converting cis-[(g5-C5H3)-
(CMe2)IrCl2]n to cis-2 is a viable synthetic process, it does not nec-
essarily give a better yield of cis-2.
Reaction of 3 with C2H4 in a Na2CO3/EtOH mixture gave both
the cis and trans isomers of the corresponding ethylene complexes,
[(g5-C5H3)(CMe2)Rh(C2H4)2]2 (4) (Scheme 6). A 1H NMR spectrum
of the crude reaction mixture showed a 4:1 ratio of cis:trans iso-
mers. No attempt was made to isolate and fully characterize the
trans isomer.
The cis isomer, cis-4, was isolated in a 5% yield by recrystalliza-
tion of the crude reaction mixture from pentane. The 1H NMR spec-
troscopic data is similar to that of cis-2 with the main differences
being the 103Rh coupling to the 1H nuclei and the ethylene proton
resonances being broad peaks instead of well resolved AA‘XX’ pat-
terns. The inequivalent methyl groups on the bridging linkers sup-
Acknowledgement
We thank the Research Corporation (CC-6330) for supporting
this work.
Appendix A. Supplementary material
CCDC-684715 and 684714 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2008.04.025.
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M
M
M
M
60-70oC, 18 h
Na2CO3, EtOH
Cl
Cl
Cl
Cl
n
M = Rh, Ir
[20] G.M. Bodner, B.N. Storhoff, D. Doddrell, L.J. Todd, Chem. Commun. (1970)
1530.
Scheme 6.