Rapid Access to Derivatized, Dimeric, Ring-Substituted Dichloro(cyclopentadienyl)rhodium(III) and Iridium(III) Complexes

Article abstract of DOI:10.1021/acs.organomet.6b00580

The present work describes the design and synthesis of a series of rhodium and iridium dimers [(η⁵-ring)MCl]₂(μ²-Cl)₂ (where (η⁵-ring)MCl = (η⁵-Me₄C₅R)Rh(III)Cl or (η<

Full text of DOI:10.1021/acs.organomet.6b00580

Article
pubs.acs.org/Organometallics
Rapid Access to Derivatized, Dimeric, Ring-Substituted
Dichloro(cyclopentadienyl)rhodium(III) and Iridium(III) Complexes
Loren C. Brown, Emily Ressegue, and Joseph S. Merola*
Department of Chemistry, 306B Hahn Hall North, 900 West Campus Drive, Virginia Tech, Blacksburg, Virginia 24061, United States
S
* Supporting Information
ABSTRACT: The present work describes the design and
synthesis of a series of rhodium and iridium dimers [(η5-
ring)MCl]2(μ2-Cl)2 (where (η5-ring)MCl = (η5-Me4C5R)Rh-
(III)Cl or (η5-Me4C5R)Ir(III)Cl) using a new and efficient 1 h
procedure. Rhodium and iridium dimeric complexes were
synthesized via a microwave reaction. The modified HMe4C5R
(R = isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-
heptyl, n-octyl, phenyl, benzyl, phenethyl, cyclohexyl, and
cyclopentyl) type ligands were synthesized by reaction of 2,3,4,5-tetramethylcyclopent-2-en-1-one with the respective Grignard
reagent (RMgX), followed by elimination of water under acidic conditions to produce the tetramethyl(alkyl or
aryl)cyclopentadienes in moderate to excellent yields (40−98%). Reaction of the HMe4C5R ligands with [M(COD)](μ2-Cl)2
(M = Rh, Ir; COD = 1,5-cyclooctadiene) gave the dimeric complexes [(η5-Me4C5R)MCl]2(μ2-Cl)2 in yields ranging from 47% to
96%. The derivatized dimers were tested for antimicrobial activity, showing activity against Mycobacterium smegmatis and
improved activity with derivatized R groups against Staphylococcus aureus and MRSA 43300. The characterization of these
complexes was completed by NMR spectroscopy, single-crystal X-ray diffraction, high-resolution mass spectrometry, and
elemental analysis.
substrates into best alignment with the metal center. As a
result, this may lead to unique complexes with catalytic
properties yet to be explored. In addition to catalysis, chain
length of η5-Me4C5R rhodium and iridium dimeric complexes
has been shown to affect biological activity.12,41,42 Therefore,
expanding the library of varying chain lengths is of particular
interest. However, syntheses of most derivatized η5-Me4C5R
rhodium and iridium dimeric complexes proceed with low
yields.11,38,43−45 As a result, we have investigated a more
efficient procedure than the conventional method, which aims
to exploit the benefits of a microwave reactor.
Microwave reactors have been shown to expedite the
synthesis of organic and organometallic reactions, providing
an alternative to time-consuming conventional techniques.46−50
Traditionally, the synthesis of rhodium and iridium dimers
requires alcoholic solvents, and these solvents are excellent
hydrogen-bonding solvents for microwave irradiation. In
addition, the increased temperature and pressure provided by
a closed system used in the microwave reactors are advanta-
geous synthetic conditions that are absent in benchtop reflux.
Modified η5-Me4C5R rhodium and iridium dimers have been
explored, but not to the depth that would be required to
understand how “R” affects sandwich and half-sandwich
compound chemistry. Moreover, most of the dimers previously
reported were synthesized in low yield. The work reported
herein describes the successful use of a microwave reactor to
INTRODUCTION
■
The importance of cyclopentadienyl ligands to the develop-
ment of organometallic chemistry cannot be overstated.1−7
Metal complex chemistry of cyclopentadienyl systems was
further elaborated with the use of pentamethylcyclopentadienyl
ligands that blocked unwanted reactions of the metal center
with cyclopentadiene C−H bonds.8−10 Our group has focused
on the synthesis of η5-Me4C5R-type complexes of rhodium and
iridium with an eye toward developing both catalytic and
biological chemistry of these metals.11−13 Rhodium and iridium
dimers of the type [(η5-Me5C5)MCl]2(μ2-Cl)2 (M = Rh, Ir) are
employed in various catalytic systems14−27 and are useful
synthetic precursors in half-sandwich chemistry.28
Rhodium and iridium dimers have many uses in catalytic
applications, as do the subsequent half-sandwich complexes
synthesized from their respective dimers.11,29−31 The literature
features an abundance of half-sandwich (piano-stool) com-
plexes with various chelating agents including acacs,32 amino
alcohols,30,33,34 amino acids,12 ethylenediamines,13 C,N chelat-
ing ligands,35 hydroxyquinolines,36,37 and bipyridyls.38 The
facile synthesis of these compounds allows half-sandwich
complexes to be easily tailored for catalytic or biological
applications. Recently, η4-Me5C5H complexes have been shown
to be effective catalysts for H2 evolution and an essential
intermediate in the catalytic reduction of NAD.39,40 This
development opens the door for modified complexes, as they
can help influence H migration onto the η5-ring via select R
groups that can direct that migration. Various substituents on
substituted cyclopentadienes may facilitate and/or direct
Received: July 22, 2016
© XXXX American Chemical Society
A
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synthesize iridium and rhodium dimeric cyclopentadienyl
complexes with yields ranging from 47% to 96%. This alternate
approach was developed based on modifications to previously
reported methodology in order to provide an efficient and cost-
effective pathway to further rhodium and iridium dimers. This
article describes the highly efficient, microwave reactor assisted
synthesis of a series of η5-ring (η5-Me4C5R) complexes in only
1 h.
HMe4C5R ligands are quite complex since the reaction does not
form a single isomer. Multiple double-bond positions around
the asymmetrically substituted ring are produced including
having a double bond exo to the ring (Figures S1−S6).
Fortunately, all isomers can react under the synthesis
conditions to form the desired cyclopentadienyl metal
complexes.
Microwave Synthesis vs Conventional Synthesis.
Rhodium(III) and iridium(III) dimers [(η5-Me4C5R)-
MCl]2(μ2-Cl)2 (M = Rh, Ir) are conventionally obtained
from refluxing MCl3·xH2O and pentamethylcyclopentadiene in
aqueous alcohol for 36−48 h.55 In addition to long reaction
times, conventional syntheses of [(η5-Me4C5R)MCl]2(μ2-Cl)2
(M = Rh, Ir) pentasubstituted cyclopentadiene derivatives yield
less than 50% in some cases.11,38,43−45 An alternative to the
conventional synthesis of [(η5-Me4C5R)MCl]2(μ2-Cl)2 involves
oxidation of the rhodium(I) and iridium(I) cyclooctadiene,
COD, dimers with concentrated HCl.56 As COD is displaced
with stronger coordinating ligands, dimeric cyclooctadiene
compounds are excellent precursors to cyclopentadienyl dimers
that are more challenging to synthesize. Therefore, the
synthesis of modified pentasubstituted cyclopentadienyl iridium
and rhodium dimeric species was carried out using an
adaptation of a previously reported literature procedure
(Scheme 2) in combination with a microwave reactor.56
RESULTS AND DISCUSSION
■
General Comments and Naming Scheme. The
numbering scheme used throughout this paper to discuss the
various ligands and corresponding complexes may be found in
Chart 1.
Chart 1. List of Various HMe4C5R Dienes Synthesized
Scheme 2. General Scheme for the Synthesis of [(η5-
Me4C5R)MCl]2(μ2-Cl)2 from [M(COD)]2(μ2-Cl)2 (M = Rh,
Ir)
Cyclopentadienyl Ligand Synthesis. One approach to
synthesizing HMe4C5R dienes is via lithiation of 2-bromo-2-
butene followed by reaction with the appropriate ester or
lactone.10,51 This synthesis requires multiple steps and is an
unfavorable method for producing a series of HMe4C5R
ligands. Therefore, we decided a more rational approach to
synthesizing a series of HMe4C5R ligands is via Grignard
reactions with 2,3,4,5-tetramethylcyclopent-2-enone. While this
has been used previously to make pentamethylcyclopenta-
diene52 and a few other unsymmetrically substituted
pentaalkylcyclopentadienyl compounds,53,54 we extend this
method to utilize a wide variety of Grignard reagents that are
commercially available to develop an extensive library of
unsymmetrical Cp*-type ligands and Rh and Ir dimers as
precursors to half-sandwich compounds.
The modified HMe4C5R variants were synthesized via
reaction of 1.25 molar equiv of a Grignard reagent and
2,3,4,5-tetramethylcyclopent-2-enone in anhydrous THF. The
resulting reaction produced an alcohol intermediate; sub-
sequently, elimination of water under acidic conditions gave the
corresponding diene (Scheme 1).
The reaction of [M(COD)]2(μ2-Cl)2 with 3.5−5 equiv of the
HMe4C5R in the presence of HCl led to formation of the
corresponding [(η5-Me4C5R)MCl]2(μ2-Cl)2. For rhodium, the
yellow suspension of [Rh(COD)]2(μ2-Cl)2 and diene was
microwaved for 1 h to yield a red precipitate or a red solution.
Similarly, for iridium, the orange suspension formed an orange
precipitate or an orange solution after being microwaved for 1
h. In both syntheses, the solvent was removed under reduced
pressure and the crude product was recrystallized from
dichloromethane (DCM) and hexanes to yield the desired
product as a red powder (Rh) or an orange powder (Ir). Upon
removal of the sample from the microwave, we noticed a small
amount of byproduct, which was decanted from the methanolic
solution of the dimer prior to the workup. Further investigation
of this byproduct led us to identify excess diene, as expected, as
well as cyclooctene by NMR spectroscopy (Figure S67). This
finding contrasts that of an earlier publication suggesting
cyclooctane is the fate of the reduced diene.56
Purification of the final HMe4C5R dienes was carried out via
column chromatography on silica gel using hexanes as the
eluent. The solvent was removed under reduced pressure to
1
obtain the ligand as a yellow oil. The H NMR spectra of the
The iridium dimers were obtained in yields ranging from
47% to 96% (Table 1), whereas the rhodium dimers were
obtained in yields ranging from 50% to 89% (Table 2). A few
reactions of rhodium complexes did not go to completion,
giving instead a mixture of desired product and starting
material. This phenomenon was not observed for reactions of
iridium complexes, which suggests that [Rh(COD)]2(μ2-Cl)2
does not oxidize as readily as [Ir(COD)]2(μ2-Cl)2. This leads
us to the conclusion that the rate of oxidation of [Rh-
Scheme 1. General Scheme for the Modifications of
HMe4C5R Dienes
B
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seen due to the presence of a chiral center on the ligand. All
complexes synthesized exhibited a typical piano-stool arrange-
ment with chloro bridges between the metal centers and a
terminal chloride bound to the metal, similarly to other
reported iridium and rhodium dimers.11,38,44,57−60
Table 1. Comparison of Iridium Dimers Synthesized
Conventionally and with a Microwave Reactor
a
bc
,
e
iridium dimer
conventional yield
microwave yield
overall yield
2a
2b
2c
2d
2e
2f
45%, (16%)44
50%
61%
70%
55%
76%
96%
86%
57%
47%
83%
69%
87%
84%
48%
60%
46%
57%
64%
51%
70%
88%
79%
52%
43%
77%
64%
80%
78%
45%
55%
17%
The conventional syntheses for rhodium dimers with long
chains and saturated rings yielded numerous undesired and
unidentifiable side products. Consequently, these reactions gave
low yields, as the product could not be isolated from impurities,
despite great efforts. As a result, only rhodium dimers with
short chains or conjugated rings were successfully synthesized
and purified via the conventional method. Modified cyclo-
pentadienyl dimers synthesized via the alternative route
between [Rh(COD)]2(μ2-Cl)2 and the appropriate HMe4C5R
proceeded without any complications or difficulties in purifying
the final product. The difficulties encountered when following
the conventional synthesis emphasize not only the importance
of the alternative method in synthesizing difficult dimers but
also the efficiency and cost effectiveness of this synthetic
pathway.
56%
20%
d
NR
d
NR
2g
2h
2i
16%
9%
4%
2j
(58%)61
(39%)62
42%
2k
2l
2m
2n
2o
23%
49%
d
NR
a
The reaction was carried out using IrCl3·xH2O and the
b
Characterization. The [(η5-ring)MCl]2(μ2-Cl)2 complexes
described in this paper have been structurally characterized
corresponding ligand refluxed in MeOH for 48 h under N2. The
c
reaction was carried out in a microwave pressure tube for 1 h. Isolated
d
e
yield. No reaction. Based on a 92% yield for [Ir(COD)]2(μ2-Cl)2.
1
using high-resolution mass spectrometry (HRMS), H NMR,
f
Yields in parentheses are reported literature values.
13C NMR, X-ray diffraction (XRD), and elemental analysis. A
notable trend was observed with the methylene adjacent to the
η5-ring among Me4C5R chains ranging from n-propyl to n-octyl.
The 1H NMR spectrum of each methylene did not show a well-
resolved triplet as expected, which implies slightly hindered
rotation of the alkyl chain. A variable-temperature NMR study
was conducted to investigate this hypothesis using complex 2b
on a 500 MHz NMR (Figure S68). At 70 °C (a), there was
little difference between the spectrum at room temperature (b).
When the temperature was lowered to −10 °C (c), the
methylene began to resolve into a more triplet-like shape than
observed at higher temperatures. This result corroborates our
hypothesis that the methylene adjacent to the η5-ring of longer
chain complexes experiences hindered rotation.
Molecular Structures. The crystal structures of complexes
2a, 2d, 2e, 2f, 2g, 2m, 2o, 3a, 3b, 3d, 3e, 3g, 3h, 3l, 3m, 3n, and
3o were determined by single-crystal X-ray diffraction. X-ray
crystallographic data are listed in the Supporting Information
(Tables S1−S4), and the cif files for all structures are also
available. The [(η5-ring)MCl]2(μ2-Cl)2 complexes exhibit a
pseudotetrahedral, piano-stool geometry around the metal
center with the η5-ring occupying the “seat” position and three
chloride ligands (two bridging and one terminal) making up the
“legs” of the stool. Examination of the various metal complexes
reveals little to no difference between the M−C(centroid), M−
Cl, and M−Cl(bridging) bond distances. Greater variability is
observed with bond angles for both iridium and rhodium
complexes. Rhodium complexes had larger X1−M−X2, X1−M−
Cl, and X2−M−Cl bond angles, whereas iridium complexes had
a larger M−Cl−M bond angle.
Table 2. Comparison of Various Rhodium Dimers
Synthesized Conventionally and with a Microwave Reactor
a
bc
,
e
rhodium dimer conventional yield
microwave yield
overall yield
3a
3b
3c
3d
3e
3f
(95%)44
79%
80%
50%
63%
89%
74%
75%
47%
59%
83%
51%
72%
68%
49%
49%
70%
83%
72%
60%
51%
47%
(72%),63 (77%)64
3%
d
54%
3g
3h
3i
77%
73%
52%
52%
75%
89%
77%
3j
3k
3l
(71%),65 (78%)60
35%
66%, (45%)45
3m
3n
3o
d
64%
d
54%
a
The reaction was carried out using RhCl3·xH2O and the
b
corresponding ligand refluxed in MeOH for 48 h under N2. The
c
reaction was carried out in a microwave pressure tube for 1 h. Isolated
d
e
yield. Reacted yield. Based on a 94% yield for [Rh(COD)]2(μ2-Cl)2.
f
Yields in parentheses are reported literature values.
(COD)]2(μ2-Cl)2 is slower than the rate of complex formation.
The yields reported are for the conditions listed in the
Experimental Section. In general, reaction performed on larger
scales led to higher yields.
A thermal ellipsoid plot of 3m, the [bis(phenethyl-
cyclopentadienyl)dirhodium tetrachloride) compound, is pro-
vided in Figure 1 as an exemplar. For 3m, the asymmetric unit
is half of the dinuclear complex with the full complex generated
by the inversion operation. In Figure 1, the generated atoms are
labeled with (i) to show they are produced by the inversion
operation. Thermal ellipsoid plots and full listings of angles and
bonds for 18 structures can be found in the Supporting
Information. In addition, cif files are provided in the Supporting
Information.
Microwave-facilitated reaction of modified dienes with
[M(COD)]2(μ2-Cl)2 showed a significantly improved yield
for most complexes in comparison to that obtained by
1
conventional heating methods. The H NMR pattern of the
Me4C5R complexes is very straightforward since there is no
longer an isomer issue. Modified dimers exhibit two singlets
from the chemically nonequivalent methyl groups of the η5-
Me4C5R ring upon introduction of the R group, dissimilar to
the typical [(η5-Me5C5)MCl]2(μ2-Cl)2, which exhibits a singlet
for all methyl groups. In the case of sec-butyl, more peaks are
C
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Table 3. Antimicrobial Activity of Derivatized Iridium
Complexes
a
MIC (μM)
b
bacteria line
IrCp*
2g
90 40
2i
2o
S. aureus
E. coli
600
630
10
0
44 19
184 80
0
0
0
550
0
0
0
173 75
550
18
0
0
M. smegmatis
18
70
17
0
MRSA 43300
630
44 19
180 80
a
b
Minimal inhibitory concentration. [(Cp*)IrCl]2(μ2-Cl)2. All results
are the averages of triplicates and are expressed as means standard
deviation.
Table 4. Antimicrobial Activity of Derivatized Rhodium
Complexes
Figure 1. Thermal ellipsoid plot of the phenethylcylopentadienyl
rhodium dimer, 3m. Ellipsoids are shown at 50% probability.
a
MIC (μM)
b
bacteria line
RhCp*
3g
3i
3o
340
It is worth noting that complexes 3a, 3h, and 3n exhibited
disorder within their respective structures, and those disorders
were easily handled with two-site models. While most
compounds crystallized without lattice solvent, complexes 3b,
2g, 3g, and 3n had solvent present within the crystal lattice.
Complex 3b crystallizes both without solvent and as a structure
with dichloromethane in the lattice. Comparison of the two
shows the structures have varied chain behavior, with the
propyl chain projecting out from the ring in the case of the
dichloromethane solvate, while the solventless structure finds
those chains folding back over the Cp ring (Figures S71 and
S72). In addition, the structure with dichloromethane exhibited
a shorter Rh−Rh distance between metal centers (Table S3).
There are short C−H−Cl interactions between the H on
dichloromethane and Cl on Rh as well that could account for
the differing bond distances.
S. aureus
400
400
4
0
0
0
0
228 100
133
320
0
0
0
0
0
0
E. coli
680
5
0
688
6
M. smegmatis
MRSA 43300
1.6
4.2 1.5
107 45
400
143 48
344
a
b
Minimal inhibitory concentration. [(Cp*)RhCl]2(μ2-Cl)2. All results
are the averages of triplicates and are expressed as means standard
deviation.
CONCLUSIONS
■
An extensive library of iridium and rhodium dimeric complexes
of the form [(η5-ring)MCl]2(μ2-Cl)2 was synthesized and
characterized. The use of a microwave reactor reduced the
conventional reaction time of 48 h to 1 h.
Until now, nine of the modified dimers have been described
using the conventional method. In this paper, we report
comparable, if not improved, yields via a microwave route. The
other 21 modified dimers reported here allow for a complete
comparison of the substituent effect on modified cyclo-
pentadienes with various R groups between iridium and
rhodium.
In summary, this work has shown that modular design is
greatly facilitated by the use of a microwave reactor. This new
route lessens the number and amounts of reagents used,
involves less chromatography, and reduces the amount of
rhodium and iridium metal lost during reactions. The range of
new substituted Cp*R dimers allows for examining the potential
structure/activity relationships not only in the biological arena
but in the catalytic arena as well.43,64 Rhodium and iridium
derivatized dimeric species are being explored further in
catalysis, with preliminary results showing both iridium and
rhodium dimers catalyze diols into their corresponding lactones
without a need for additional ligand substitution.34 More details
on the effect of substitution of the Cp ring will be forthcoming.
At this time, this is the first complete study of modified η5-
ring dimers with group 9 metals. Each of these modified
complexes showed that rhodium and iridium behave similarly in
the solid state. These results suggest that various substituents
on the η5-ring do not show a significant change in structure.
Antimicrobial Results. We, and others, have been
exploring the biological activity of rhodium and iridium
sandwich compounds. The bulk of work examining the activity
of metal complexes for medicinal purposes has been directed
toward anticancer activity.35,41,62,66 We, on the other hand, have
become more interested in the activity against resistant
bacterial strains such as tuberculosis and MRSA.12,13 While
our previous work was with piano-stool complexes of amino
acids and ethylenediamines, we find that the dimers reported
here also show high antimicrobial activity. The complexes
reported herein were tested against various strains of microbes,
showing that long chains impart improved activity against S.
aureus, E. coli, M. smegmatis, and MRSA (Tables 3 and 4).
Rhodium appears to have greater antimicrobial activity than its
iridium counterpart. Complexes 2i and 3i exhibited improved
activity across all microbes, with the exception of M. smegmatis.
These results of improved potency with increasing chain length
are consistent with similar findings by Lucas et al.41 for
anticancer activity. An in-depth structure−activity relationship
study is under way with [(η5-ring)MCl]2(μ2-Cl)2 complexes as
well as their corresponding half-sandwich compounds with a
variety of ligands. Overall, as we found for amino acid
complexes, the dimers are most effective against mycobac-
teria.12,13 Further work on additional mycobacteria including
tuberculosis is planned.
EXPERIMENTAL SECTION
■
All materials for synthesis, purification, and characterization were used
as received unless otherwise stated. Snap ring tops and 10 mL pressure
tubes were purchased from CEM Corporation. RhCl3·xH2O and IrCl3·
xH2O were purchased from Pressure Chemical (Pittsburgh, PA, USA).
Heptylmagnesium chloride and 2,3,4,5-tetramethylcyclopent-2-en-1-
one were purchased from Alfa Aesar (Ward Hill, MA, USA). Reagent-
grade solvents, ethyl-tetramethylcyclopentadiene (1a), tetramethyl(n-
propyl)cyclopentadiene (1b), benzylmagnesium chloride, cyclohex-
ylmagnesium chloride, cyclopentylmagnesium bromide, phenylmagne-
sium bromide, phenethylmagnesium chloride, isopropylmagnesium
D
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bromide, butylmagnesium chloride, isobutylmagnesium chloride, sec-
butylmagnesium chloride, pentylmagnesium bromide, hexylmagnesi-
um bromide, and octylmagnesium bromide were purchased from
Sigma-Aldrich (St. Louis, MO, USA). Deuterated solvents for NMR
spectroscopy were obtained from Cambridge Isotope Laboratories.
Elemental analyses were performed by Atlantic Microlabs (Norcross,
GA, USA). 1H NMR and 13C NMR spectra were collected on a Varian
MR-400 NMR spectrometer. 13C NMR spectra were correspondingly
recorded at 101 MHz. HRMS were collected on an Agilent 6220
Accurate Mass TOF LC-MS.
Synthesis of [Cp*ethylIrCl]2(μ2-Cl)2 (2a). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.100 g, 0.149 mmol), 1a (0.045 g,
0.298 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 2a (0.061 g, 50% yield). H NMR (400 MHz, CDCl3): δ 2.16−
2.10 (q, 4H, 2JHH = 7.7 Hz, 2 CH2), 1.58 (s, 12H, 4 CpCH3), 1.56 (s,
2
12H, 4 CpCH3), 1.07−1.03 (t, 6H, JHH = 7.7 Hz, 2 CH3). 13C{1H}
NMR (101 MHz, CDCl3): δ 89.06 (CpC), 86.49 (CpC), 86.18
(CpC), 17.56 (CH2), 11.63 (CH3), 9.30 (CpCH3), 9.13 (CpCH3).
Anal. Calcd for C22H34Cl4Ir2: C, 32.04; H, 4.16. Found: C, 31.88; H,
3.96.
Synthesis of [Cp*n‑propylIrCl]2(μ2-Cl)2 (2b). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.100 g, 0.149 mmol), 1b (0.0851 g,
0.521 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
Synthesis of HMe4C5R Dienes. Unless otherwise stated, all
reactions were conducted under a N2 atmosphere.
General Procedure of HMe4C5R Dienes. A solution of the
respective Grignard reagent (18.1 mmol) in THF was added to a
stirred solution of 2,3,4,5-tetramethyl-2-cyclopentenone (2.00 g, 15.2
mmol) in anhydrous THF (20 mL). The mixture was refluxed for 24
h, then cooled to 0 °C and quenched with HCl. This solution was
warmed to room temperature and agitated for 2 h. The mixture was
diluted with diethyl ether (30 mL) and washed with water (3 × 30
mL), and the organic layer was dried over MgSO4. The products were
concentrated under reduced pressure and purified by column
chromatography (silica gel, hexanes) to afford the product and
isomers as a yellow oil. The 1H NMR spectra of the dienes are
1
give 2b (0.078 g, 61% yield). H NMR (400 MHz, CDCl3): δ 2.13−
2.09 (m, 4H, 2 CH2CH2CH3), 1.59 (s, 12H, 4 CpCH3), 1.57 (s, 12H,
4 CpCH3), 1.49−1.40 (m, 4H, 2 CH2CH2CH3), 0.94−0.90 (app t, 6H,
2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 87.96 (CpC), 86.52
(CpC), 86.52 (CpC), 26.16 (CH2CH2CH3), 21.00 (CH2CH2CH3),
14.36 (CH3), 9.55 (CpCH3), 9.47 (CpCH3). HRMS/ESI+ (m/z):
C24H38[193Ir]2Cl3 817.1298; found 817.1331.
Synthesis of [Cp*isopropylIrCl]2(μ2-Cl)2 (2c). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.100 g, 0.149 mmol), 1c (0.0851 g,
0.521 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
complex due to the signal overlap of the isomers. Both H and 13C
1
give 2c (0.089 g, 70% yield). H NMR (400 MHz, CDCl3): δ 2.54−
NMR spectra of dienes 1i, 1m, and 1n are reproduced in the
Supporting Information (Figures S1−S6) to illustrate that complexity.
We relied on HRMS and success in further reactions as proof of
synthesis. Dienes 1c−1h and 1j−1o have previously been
reported.11,38,67−73
2.43 (m, 2H, 2 CH), 1.68 (s, 12H, 4 CpCH3), 1.60 (s, 12H, 4
2
CpCH3), 1.29−1.27 (d, 12H, JHH = 7.1 Hz, 4 CH3). 13C{1H} NMR
(101 MHz, CDCl3): δ 90.38 (CpC), 86.47 (CpC), 86.21 (CpC), 25.39
(CH(CH3)2), 20.78 (CH(CH3)2), 10.40 (CpCH3), 9.68 CpCH3).
HRMS/ESI+ (m/z): C24 H38[193Ir]2Cl3 817.1298; found 817.1326.
Anal. Calcd for C24H38Cl4Ir2: C, 33.80; H, 4.49. Found: C, 34.01; H,
4.48.
Synthesis of 5-isopropyl-2,3,4,5-tetramethylcyclopenta-1,3-diene
(1c). Yield: 1.04 g (44%).
Synthesis of 5-butyl-1,2,3,4-tetramethylcyclopenta-1,3-diene
(1d). Yield: 2.53 g (98%).
Synthesis of 5-isobutyl-1,2,3,4-tetramethylcyclopenta-1,3-diene
(1e). Yield: 2.49 g (96%). HRMS/APCI+ (m/z): calcd for C13H23
179.1800; found 179.1798.
Synthesis of [Cp*n‑butylIrCl]2(μ2-Cl)2 (2d). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.300 g, 0.447 mmol), 1d (0.159 g,
0.893 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 2d (0.109 g, 55% yield). H NMR (400 MHz, CDCl3): δ 2.15−
2.11 (m, 4H, 2 CH2(CH2)2CH3), 1.60 (s, 12H, 4 CpCH3), 1.58 (s,
12H, 4 CpCH3), 1.41−1.28 (m, 8H, 2 CH2(CH2)2CH3), 0.91−0.88
(app t, 6H, 2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 88.26
(CpC), 86.57 (CpC), 86.55 (CpC), 29.97 (CH2CH2CH2CH3), 24.05
(CH2CH2CH2CH3), 23.00 (CH2CH2CH2CH3), 14.04 (CH3), 9.55
(CpCH3), 9.51 (CpCH3). HRMS/ESI+ (m/z): C26H42[193Ir]2Cl3
845.1611; found 845.1617. Anal. Calcd for C26H42Cl4Ir2: C, 35.45;
H, 4.81. Found: C, 35.61; H, 4.80.
Synthesis of 5-(sec-butyl)-1,2,3,4-tetramethylcyclopenta-1,3-
diene (1f). Yield: 1.02 g (40%). HRMS/APCI+ (m/z): calcd for
C13H23 179.1800; found 179.1794.
Synthesis of 1,2,3,4-tetramethyl-5-pentylcyclopenta-1,3-diene
(1g). Yield: 1.76 g (63%). HRMS/ESI+ (m/z): calcd for C14H23
191.1800; found 191.1792.
Synthesis of 5-hexyl-1,2,3,4-tetramethylcyclopenta-1,3-diene
(1h). Yield: 0.651 g (52%).
Synthesis of 5-heptyl-1,2,3,4-tetramethylcyclopenta-1,3-diene
(1i). Yield: 2.53 g (79%). HRMS/APCI+ (m/z): calcd for C16H29
221.2269; found 221.2264.
Synthesis of 1,2,3,4-tetramethyl-5-octylcyclopenta-1,3-diene (1j).
Yield: 2.61g (77%).
Synthesis of (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)-
benzene (1k). Yield: 2.78 g (97%).
Synthesis of ((2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)-
methyl)benzene (1l). Yield: 2.58 g (84%).
Synthesis of (2-(2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)-
ethyl)benzene (1m). Yield: 2.51 g (77%). HRMS/APCI+ (m/z):
calcd for C17H23 227.1800; found 227.1799.
Synthesis of [Cp*isobutylIrCl]2(μ2-Cl)2 (2e). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.200 g, 0.298 mmol), 1e (0.186 g,
1.04 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 2e (0.199 g, 76% yield). H NMR (400 MHz, CDCl3): δ 2.06−
2.04 (d, 4H, 2JHH = 7.5 Hz, 2 CH2), 1.77−1.66 (m, 2H, 2 CH), 1.61 (s,
2
12H, 4 CpCH3), 1.60 (s, 12H, 4 CpCH3), 0.90−0.89 (d, 12H, JHH
=
6.7 Hz, 4 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 87.48 (CpC),
87.00 (CpC), 86.59 (CpC), 33.13 (CH2CH(CH3)2), 27.91 (CH2CH-
(CH3)2), 22.83 (CH2CH(CH3)2), 10.08 (CpCH3), 9.55 (CpCH3).
HRMS/ESI+ (m/z): C26H42[193Ir]2Cl3 845.1611, found 845.1602.
Anal. Calcd for C26H42Cl4Ir2: C, 35.45; H, 4.81. Found: C, 35.66; H,
4.70.
Synthesis of (2,3,4,5-tetramethylcyclopenta-2,4-dien-1-yl)-
cyclohexane (1n). Yield: 2.18 g (74%).
Synthesis of 2,3,4,5-tetramethyl[1,1′-bi(cyclopentane)]-2,4-diene
(1o). Yield: 1.57 g (57%). HRMS/APCI+ (m/z): calcd for C14H21
191.1800; found 191.1794.
Synthesis of [Cp*sec‑butylIrCl]2(μ2-Cl)2 (2f). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.500 g, 0.744 mmol), 1f (0.465 g,
2.61 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 2f (0.6276 g, 96% yield). H NMR (400 MHz, CDCl3): δ 2.23−
General Procedure for Synthesis of [(η5-Me4C5R)IrCl]2(μ2-Cl)2.
A microwave pressure tube was fitted with the appropriate amounts of
the respective [Ir(COD)]2(μ2-Cl)2, HMe4C5R, in 4 mL of methanol
with 0.5 mL of concentrated HCl. The reaction mixture was heated to
115 °C at 50 W and 150 psi and held for 1 h, yielding an orange
solution. The solvent was evaporated under reduced pressure, and the
resulting powder recrystallized from DCM and cold hexanes, collected
via filtration, and washed with cold hexanes. Complexes 2a, 2b, 2c, 2k,
2l, 2m, and 2n have previously been reported and were identified via
spectral comparison.11,38,44,74,75
2.18 (m, 2H, CH), 1.68 (s, 6H, 2 CpCH3), 1.66−1.67 (m, 2H, CHH),
1.66 (s, 6H, 2 CpCH3), 1.62 (s, 6H, 2 CpCH3), 1.58 (s, 6H, 2
CpCH3), 1.53−1.43 (m, 2H, CHH), 1.33−1.31 (d, 6H, 2JHH = 7.2 Hz,
CH3CH), 0.90−0.86 (t, 6H, 2JHH = 7.4 Hz, CH2CH3). 13C{1H} NMR
(101 MHz, CDCl3): δ 91.03 (CpC), 90.44 (CpC), 87.08 (CpC), 86.29
(CpC), 85.01 (CpC), 32.04 (CH), 27.71 (CH2), 18.47 (CH3CH),
12.84 (CH3CH2), 10.77 (CpCH3), 10.40 (CpCH3), 9.82 (CpCH3),
9.61 (CpCH3). HRMS/ESI+ (m/z): C26H42[193Ir]2Cl3 845.1611;
found 845.1695. Anal. Calcd for C26H42Cl4Ir2: C, 35.45; H, 4.81.
Found: C, 35.19; H, 4.71.
E
DOI: 10.1021/acs.organomet.6b00580
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Synthesis of [Cp*n‑pentylIrCl]2(μ2-Cl)2 (2g). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.100 g, 0.149 mmol), 1g (0.100 g,
0.521 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
(CpCH3), 9.53 (CpCH3). HRMS/ESI+ (m/z): calcd for
C32H38[193Ir]2Cl3 913.1298; found 913.1347. Anal. Calcd for
C32H38Ir2Cl4: C, 40.51; H, 4.04. Found: C, 40.40; H, 3.98.
1
give 2g (0.116 g, 86% yield). H NMR (400 MHz, CDCl3): δ 2.14−
Synthesis of [Cp*phenethylIrCl]2(μ2-Cl)2 (2m). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.200 g, 0.298 mmol), 1m (0.336 g,
1.49 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
2.11 (m, 4H, 2 CH2(CH2)3CH3), 1.61 (s, 12H, 4 CpCH3), 1.59 (s,
12H, 4 CpCH3), 1.43−1.34 (m, 4H, 2 CH2CH2(CH2)2CH3), 1.34−
1.24 (m, 8H, 2 CH2CH2(CH2)2CH3), 0.88−0.85 (app t, 6H, 2 CH3).
13C{1H} NMR (101 MHz, CDCl3): δ 88.23 (CpC), 86.49 (CpC),
86.46 (CpC), 31.90 (CH2), 27.43 (CH2), 24.16 (CH2), 22.48 (CH2),
13.95 (CH3), 9.51 (CpCH3), 9.48 (CpCH3). HRMS/ESI+ (m/z):
C28H46[193Ir]2Cl3 873.1924; found 873.1965. Anal. Calcd for
C28H46Cl4Ir2: C, 37.00; H, 5.10. Found: C, 37.60; H, 5.08.
1
give 2m (0.245 g, 84% yield). H NMR (400 MHz, CDCl3): δ 7.25−
7.16 (m, 6H, ArH), 7.04−7.02 (m, 4H, ArH), 2.77−2.73 (t, 4H, 2JHH
=
2
7.3 Hz, 2 PhCH2CH2), 2.48−2.45 (t, 4H, JHH = 7.3 Hz, 2
PhCH2CH2), 1.55 (s, 12H, 4 CpCH3), 1.36 (s, 12H, 4 CpCH3).
13C{1H} NMR (101 MHz, CDCl3): δ 140.14 (ArC), 128.64 (ArC),
128.46 (ArC), 126.35 (ArC), 87.22 (CpC), 86.30 (CpC), 86.29
(CpC), 33.60 (PhCH2CH2), 26.60 (PhCH2CH2), 9.27 (CpCH3), 9.09
(CpCH3). HRMS/ESI+ (m/z): calcd for C34H42[193Ir]2Cl3 941.1611;
found 941.1616. Anal. Calcd for C34H42Ir2Cl4: C, 41.80; H, 4.33.
Found: C, 41.92; H, 4.22.
Synthesis of [Cp*n‑hexylIrCl]2(μ2-Cl)2 (2h). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.300 g, 0.447 mmol), 1h (0.230 g,
1.12 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 2h (1.56 g, 52% yield). H NMR (400 MHz, CDCl3): δ 2.14−
Synthesis of [Cp*cyclohexylIrCl]2(μ2-Cl)2 (2n). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.200 g, 0.298 mmol), 1n (0.152 g,
0.744 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
2.10 (m, 4H, 2 CH2(CH2)4CH3), 1.61 (s, 12H, 4 CpCH3), 1.59 (s,
12H, 4 CpCH3), 1.42−1.23 (m, 16H, 2 CH2(CH2)4CH3), 0.88−0.84
(app t, 6H, 2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 88.34
(CpC), 86.60 (CpC), 86.56 (CpC), 31.65 (CH2), 29.53 (CH2), 27.76
(CH2), 24.26 (CH2), 22.62 (CH2), 14.16 (CH3), 9.54 (CpCH3), 9.51
(CpCH3). HRMS/ESI+ (m/z): C30H50[193Ir]2Cl3 901.2237; found
901.2145. Anal. Calcd for C30H50Cl4Ir2: C, 38.46; H, 5.38. Found: C,
38.46; H, 5.38.
1
give 2n (0.079 g, 48% yield). H NMR (400 MHz, CDCl3): δ 2.08−
2.01 (m, 2H, 2 CH), 1.93−1.89 (m, 4H, 2 CH2), 1.78−1.74 (m, 4H, 2
CH2), 1.67 (s, 12H, 4 CpCH3), 1.59 (s, 12H, 4 CpCH3), 1.43−1.22
(m, 10H, CH2), 1.18−1.09 (m, 2H, CH2). 13C{1H} NMR (101 MHz,
CDCl3): δ 90.77 (CpC), 85.99 (CpC), 84.81 (CpC), 35.75 (CH),
30.88 (CH2), 27.10 (CH2), 26.20 (CH2), 10.70 (CpCH3), 9.74
(CpCH3). HRMS/ESI+ (m/z): calcd for C30H46[193Ir]2Cl3 897.1924;
found 897.1946. Anal. Calcd for C30H46Ir2Cl4: C, 38.62; H, 4.97.
Found: C, 38.77; H, 4.92.
Synthesis of [Cp*n‑heptylIrCl]2(μ2-Cl)2 (2i). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.250 g, 0.372 mmol), 1i (0.287 g,
1.30 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
give 2i (0.168, 47% yield). 1H NMR (400 MHz, CDCl3): δ 2.14−2.10
(m, 4H, 2 CH2(CH2)5CH3), 1.60 (s, 12H, 4 CpCH3), 1.59 (s, 12H, 4
CpCH3), 1.41−1.34 (m, 4H, 2 CH2CH2(CH2)4CH3), 1.31−1.21 (m,
16H, CH2CH2(CH2)4CH3), 0.88−0.84 (app t, 6H, 2 CH3). 13C{1H}
NMR (101 MHz, CDCl3): δ 88.32 (CpC), 86.59 (CpC), 86.53
(CpC), 31.82 (CH2), 29.84 (CH2), 29.18 (CH2), 27.81 (CH2), 24.27
(CH2), 22.75 (CH2), 14.23 (CH3), 9.57 (CpCH3), 9.52 (CpCH3).
HRMS/ESI+ (m/z): C32H54[193Ir]2Cl3 929.2550; found 929.2531.
Anal. Calcd for C32H54Cl4Ir2: C, 39.83; H, 5.64. Found: C, 39.89; H,
5.60.
Synthesis of [Cp*cyclopentylIrCl]2(μ2-Cl)2 (2o). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.250 g, 0.372 mmol), 1o (0.248 g,
1.30 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 2o (0.213 g, 59% yield). H NMR (400 MHz, CDCl3): δ 2.63−
2.54 (m, 2H, 2 CH), 2.09−2.02 (m, 4H, 2 CH2), 1.74−1.71 (m, 2H,
CH2), 1. 68 (s, 12H, 4 CpCH3), 1.67−1.60 (m, 10H, CH2), 1.59 (s,
12H, 4 CpCH3). 13C{1H} NMR (101 MHz, CDCl3): δ 89.60 (CpC),
86.07 (CpC), 85.92 (CpC), 36.05 (CH), 31.34 (CH2), 26.67 (CH2),
10.46 (CpCH3), 9.72 (CpCH3). HRMS/ESI+ (m/z): calcd for
C28H42[193Ir]2Cl3 869.1611; found 869.1567.
Synthesis of [Cp*n‑octylIrCl]2(μ2-Cl)2 (2j). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.200 g, 0.298 mmol), 1j (0.349 g,
1.49 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
General Procetdure for Synthesis of [(η5-Me4C5R)RhCl]2(μ2-
Cl)2. A microwave pressure tube was fitted with the appropriate
amounts of the respective [Rh(COD)]2(μ2-Cl)2, HMe4C5R, in 4 mL
of methanol with 0.5 mL of concentrated HCl. The reaction mixture
was heated to 115 °C at 50 W and 150 psi and held for 1 h, yielding a
red solution. The solvent was evaporated under reduced pressure, and
the resulting powder recrystallized from DCM and cold hexanes,
collected via filtration, and washed with cold hexanes. Complexes 3a,
3c, 3k, 3m, and 3n have previously been reported and were identified
by HRMS as well as by comparison of NMR spectra with those
reported in the literature.43−45,63,65
1
give 2j (0.246 g, 83% yield). H NMR (400 MHz, CDCl3): δ 2.14−
2.10 (app t, 4H, 2 CH2(CH2)6CH3), 1.61 (s, 12H, 4 CpCH3), 1.59 (s,
12H, 4 CpCH3), 1.44−1.34 (m, 4H, 2 CH2CH2(CH2)5CH3), 1.33−
1.19 (m, 20H, 2 CH2CH2(CH2)5CH3), 0.88−0.85 (app t, 6H, 2 CH3).
13C{1H} NMR (101 MHz, CDCl3): δ 88.33 (CpC), 86.60 (CpC),
86.54 (CpC), 31.95 (CH2), 29.88 (CH2), 29.47 (CH2), 29.27 (CH2),
27.81 (CH2), 24.28 (CH2), 22.78 (CH2), 14.23 (CH3), 9.58 (CpCH3),
9.54 (CpCH3). HRMS/ESI+ (m/z): C34H58[193Ir]2Cl3 957.2863;
found 957.2828. Anal. Calcd for C34H58Cl4Ir2: C, 41.12; H, 5.89.
Found: C, 41.28; H, 5.74.
Synthesis of [Cp*ethylRhCl]2(μ2-Cl)2 (3a). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.250 g, 0.507 mmol), 1a (0.244 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
Synthesis of [Cp*phenylIrCl]2(μ2-Cl)2 (2k). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.250 g, 0.372 mmol), 1k (0.295 g,
1.49 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 3a (0.259 g, 79% yield). H NMR (400 MHz, CDCl3): δ 2.27−
2.23 (q, 4H, 2JHH = 7.7 Hz, 2 CH2), 1.61 (s, 12H, 4 CpCH3), 1.60 (s,
1
give 2k (0.237 g, 69% yield). H NMR (400 MHz, CDCl3): δ 7.58−
2
12H, 4 CpCH3), 1.01−0.97 (t, 6H, JHH = 7.7 Hz, 2 CH3). 13C{1H}
7.55 (m, 4H, ArH), 7.37−7.34 (m, 6H, ArH), 1.72 (s, 12H, 4 CpCH3),
1.63 (s, 12H, 4 CpCH3). 13C{1H} NMR (101 MHz, CDCl3): δ 130.34
(ArC), 129.94 (ArC), 128.79 (ArC), 128.58 (ArC), 93.64 (CpC),
85.61 (CpC), 82.10 (CpC), 10.50 (CpCH3), 9.77 (CpCH3). HRMS/
ESI+ (m/z): calcd for C30H34[193Ir]2Cl3 885.0985; found 885.1018.
Anal. Calcd for C30H34Ir2Cl4: C, 39.13; H, 3.72. Found: C, 38.89; H,
3.51.
NMR (101 MHz, CDCl3): δ 97.41−97.31 (d, JCRh = 9.3 Hz, CpC),
94.76−94.66 (d, JCRh = 9.2 Hz, CpC), 94.00−93.91 (d, JCRh = 9.1 Hz,
CpC), 17.61 (CH2), 11.55 (CH3), 9.51 (CpCH3), 9.30 (CpCH3).
HRMS/ESI+ (m/z): calcd for C22H34Cl3Rh2 608.9836; found
608.9761.
Synthesis of [Cp*n‑propylRhCl]2(μ2-Cl)2 (3b). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.150 g, 0.304 mmol), 1b (0.200 g,
1.22 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
Synthesis of [Cp*benzylIrCl]2(μ2-Cl)2 (2l). Following the general
procedure, [Ir(COD)]2(μ2-Cl)2 (0.100 g, 0.149 mmol), 1l (0.111 g,
0.521 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 3b (0.164 g, 80% yield). H NMR (400 MHz, CDCl3): δ 2.27−
1
2.23 (m, 4H, 2 CH2CH2CH3), 1.64 (s, 12H, 4 CpCH3), 1.62 (s, 12H,
4 CpCH3), 1.45−1.36 (m, 4H, 2 CH2CH2CH3), 0.94−0.91 (app t, 6H,
give 2l (0.123 g, 87% yield). H NMR (400 MHz, CDCl3): δ 7.30−
7.27 (m, 2H, ArH), 7.26−7.25 (m, 2H, ArH), 7.23−7.18 (m, 2H,
ArH), 7.11−7.09 (m, 4H, ArH), 3.57 (s, 4H, 2 CH2), 1.65 (s, 12H, 4
CpCH3), 1.63 (s, 12H, 4 CpCH3). 13C{1H} NMR (101 MHz,
CDCl3): δ 136.97 (ArC), 128.88 (ArC), 128.38 (ArC), 126.90 (ArC),
87.68 (CpC), 86.90 (CpC), 85.93 (CpC), 30.58 (CH2), 9.97
2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 96.19−96.10 (d, JCRh
=
9.4 Hz, CpC), 94.73−94.64 (d, JCRh = 9.2 Hz, CpC), 94.36−94.27 (d,
JCRh = 9.3 Hz, CpC), 26.06 (CH2CH2CH3), 20.91 (CH2CH2CH3),
14.33 (CH3), 9.61 (CpCH3), 9.55 (CpCH3). HRMS/ESI+ (m/z):
F
DOI: 10.1021/acs.organomet.6b00580
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
calcd for C24H38Cl3Rh2 637.0149; found 637.0173. Anal. Calcd for
C24H38Cl4Rh2: C, 42.76; H, 5.68. Found: C, 42.47; H, 5.68.
693.0788. Anal. Calcd for C28H46Cl4Rh2: C, 46.05; H, 6.35. Found:
C, 45.77; H, 6.16.
Synthesis of [Cp*n‑hexylRhCl]2(μ2-Cl)2 (3h). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.304 mmol), 1h (0.344 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
Synthesis of [Cp*isopropylRhCl]2(μ2-Cl)2 (3c). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.100 g, 0.203 mmol), 1c (0.112 g,
0.710 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
1
give 3h (0.224 g, 73% yield). H NMR (400 MHz, CDCl3): δ 2.26−
give 3c (0.067 g, 50% yield). H NMR (400 MHz, CDCl3): δ 2.66−
2.23 (m, 4H, 2 CH2(CH2)4CH3), 1.63 (s, 12H, 4 CpCH3), 1.61 (s,
12H, 4 CpCH3), 1.37−1.24 (m, 16H, 2 CH2(CH2)4CH3), 0.87−0.84
(app t, 6H, 2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 96.41−
96.31 (d, JCRh = 9.4 Hz, CpC), 94.68−94.59 (d, JCRh = 9.1 Hz, CpC),
94.26−94.17 (d, JCRh = 9.3 Hz, CpC), 31.61 (CH2), 29.46 (CH2),
27.62 (CH2), 24.14 (CH2), 22.58 (CH2), 14.13 (CH3), 9.57 (CpCH3),
9.55 (CpCH3). HRMS/ESI+ (m/z): calcd for C30H50Cl3Rh2 721.1088;
found 721.1106.
2.55 (m, 2H, 2 CH), 1.72 (s, 12H, 4 CpCH3), 1.60 (s, 12H, 4
2
CpCH3), 1.31−1.29 (d, 12H, JHH = 7.1 Hz, 4 CH3). 13C{1H} NMR
(101 MHz, CDCl3): δ 97.71−97.62 (d, JCRh = 9.1 Hz, CpC), 95.44−
95.34 (d, JCRh = 10.0 Hz, CpC), 94.22−94.13 (d, JCRh = 9.2 Hz, CpC),
25.09 (CH(CH3)2), 20.79 (CH(CH3)2), 10.51 (CpCH3), 9.62
(CpCH3). HRMS/ESI+ (m/z): calcd for C24H38Cl3Rh2 637.0149;
found 637.014.
Synthesis of [Cp*n‑butylRhCl]2(μ2-Cl)2 (3d). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.406 mmol), 1d (0.289 g,
1.62 mmol), and 0.5 mL of concentrated HCl were reacted in
Synthesis of [Cp*n‑heptylRhCl]2(μ2-Cl)2 (3i). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.150 g, 0.304 mmol), 1i (0.344 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
methanol (4 mL) to give 3d (0.180 g, 63%). H NMR (400 MHz,
1
give 3i (0.125g, 52% yield). H NMR (400 MHz, CDCl3): δ 2.26−
CDCl3): δ 2.27−2.24 (m, 4H, 2 CH2(CH2)2CH3), 1.63 (s, 12H, 4
CpCH3), 1.61 (s, 12H, 4 CpCH3), 1.38−1.27 (m, 8H, 2
CH2(CH2)2CH3), 0.90−0.87 (app t, 6H, 2 CH3). 13C{1H} NMR
(101 MHz, CDCl3): δ 96.33−96.24 (d, JCRh = 9.6 Hz, CpC), 94.64−
94.55 (d, JCRh = 9.2 Hz, CpC), 94.26−94.17 (d, JCRh = 9.2 Hz, CpC),
29.76, 23.85, 22.90, 13.96 (CH3), 9.54 (CpCH3), 9.54 (CpCH3).
HRMS/ESI+ (m/z): calcd for C26H42Cl3Rh2 665.0462; found
665.0447. Anal. Calcd for C26H42Cl4Rh2, C, 44.47; H, 6.03. Found:
C, 44.55; H, 5.96.
2.22 (m, 4H, 2 CH2(CH2)5CH3), 1.63 (s, 12H, 4 CpCH3), 1.61 (s,
12H, 4 CpCH3), 1.33−1.22 (m, 20H, CH2(CH2)5CH3), 0.87−0.83
(app t, 6H, 2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 96.41−
96.32 (d, JCRh = 9.5 Hz, CpC), 94.69−94.60 (d, JCRh = 9.2 Hz, CpC),
94.26−94.17 (d, JCRh = 9.2 Hz, CpC), 31.77 (CH2), 29.76 (CH2),
29.13 (CH2), 27.66 (CH2), 24.13 (CH2), 22.17 (CH2), 14.20 (CH3),
9.57 (CpCH3), 9.55 (CpCH3). HRMS/ESI+ (m/z): calcd for
C32H54Cl3Rh2 749.1401; found 749.1413. Anal. Calcd for
C32H54Cl4Rh2: C, 48.88; H, 6.92. Found: C, 49.11; H, 6.87.
Synthesis of [Cp*isobutylRhCl]2(μ2-Cl)2 (3e). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.406 mmol), 1e (0.362 g,
2.03 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
Synthesis of [Cp*n‑octylRhCl]2(μ2-Cl)2 (3j). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.304 mmol), 1j (0.344 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 3e (0.252 g, 89% yield). H NMR (400 MHz, CDCl3): δ 2.19−
1
give 3j (0.173 g, 52% yield). H NMR (400 MHz, CDCl3): δ 2.26−
2.17 (d, 4H, 2JHH = 7.5 Hz, 2 CH2), 1.73−1.64 (m, 2H, 2 CH), 1.63 (s,
2.22 (app t, 4H, 2 CH2(CH2)6CH3), 1.63 (s, 12H, 4 CpCH3), 1.61 (s,
12H, 4 CpCH3), 1.29−1.23 (m, 24H, CH2(CH2)6CH3), 0.87−0.84
(app t, 6H, 2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 96.41−
96.32 (d, JCRh = 9.5 Hz), 94.69−94.60 (d, JCRh = 9.2 Hz, CpC), 94.26−
94.17 (d, JCRh = 9.2 Hz, CpC), 32.23 (CH2), 30.12 (CH2), 29.74
(CH2), 29.53 (CH2), 27.98 (CH2), 24.46 (CH2), 23.07 (CH2), 14.53
(CH3), 9.89 (CpCH3), 9.87 (CpCH3). HRMS/ESI+ (m/z): calcd for
C34H58Cl3Rh2 777.1717; found 777.1701. Anal. Calcd for
C34H58Cl4Rh2: C, 50.14; H, 7.18. Found: C, 50.43; H, 7.09.
2
12H, 4 CpCH3), 1.62 (s, 12H, 4 CpCH3), 0.88−0.87 (d, 12H, JHH
=
6.7 Hz, 4 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 95.58−95.49
(d, JCRh = 9.4 Hz, CpC), 94.74−94.66 (d, JCRh = 9.2 Hz, CpC), 94.70−
94.61 (d, JCRh = 9.2 Hz, CpC), 32.93 (CH2CH(CH3)2), 27.98
(CH2CH(CH3)2), 23.84 (CH2CH(CH3)2), 10.09 (CpCH3), 9.58
(CpCH3). HRMS/ESI+ (m/z): C26H42Cl3Rh2 665.0462; found
665.0459. Anal. Calcd for C26H42Cl4Rh2: C, 44.47; H, 6.03. Found:
C, 44.18; H, 5.96.
Synthesis of [Cp*sec‑butylRhCl]2(μ2-Cl)2 (3f). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2, 1f (0.289 g, 1.62 mmol), and 0.5 mL
of HCl were reacted in methanol (4 mL). Upon cooling, an orange-
yellow powder (0.123 g) formed in a red solution. The powder was
isolated and the red solution evaporated under reduced pressure. The
resulting red powder was recrystallized from DCM and cold hexanes
and collected by filtration. The red powder was washed with cold
hexanes to give 3f in a reacted yield of 0.0589 g (54%). 1H NMR (400
MHz, CDCl3): δ 2.37−2.28 (m, 2H, 2 CH), 1.72 (s, 6H, 2 CpCH3),
1.69 (s, 6H, 2 CpCH3), 1.67−1.64 (m, 2H, CHH), 1.61 (s, 6H, 2
CpCH3), 1.60 (s, 6H, 2 CpCH3), 1.51−1.42 (m, 2H, CHH), 1.39−
1.37 (d, 6H, 2JHH = 7.1 Hz, CH3CH), 0.90−0.86 (t, 6H, 2JHH = 7.4 Hz,
CH2CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 98.37−98.29 (d, JCRh
= 8.8 Hz, CpC), 97.61−97.53 (d, JCRh = 8.9 Hz, CpC), 95.35−95.25
(d, JCRh = 10.1 Hz, CpC), 95.29−95.20 (d, JCRh = 9.0 Hz, CpC),
92.83−92.73 (d, JCRh = 9.4 Hz, CpC), 31.65 (CH), 27.79 (CH2), 18.41
(CH3CH), 12.65 (CH3CH2), 10.89 (CpCH3), 10.45 (CpCH3), 9.83
(CpCH3), 9.44 (CpCH3). HRMS/ESI+ (m/z): C26H42Cl3Rh2
665.0462; found 665.0472.
Synthesis of [Cp*phenylRhCl]2(μ2-Cl)2 (3k). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.406 mmol), 1k (0.322 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 3k (0.225 g, 75%). H NMR (400 MHz, CDCl3): δ 7.66−7.64
(m, 4H, ArH), 7.39−7.36 (m, 6H, ArH), 1.71 (s, 12H, 4 CpCH3), 1.68
(s, 12H, 4 CpCH3). 13C{1H} NMR (101 MHz, CDCl3): δ 130.36
(ArC), 129.02 (ArC), 128.74 (ArC), 128.41 (ArC), 100.47−100.39 (d,
JCRh = 8.6 Hz, CpC), 93.67−93.58 (d, JCRh = 9.0 Hz, CpC), 90.70−
90.60 (d, JCRh = 10.2 Hz, CpC), 10.75 (CpCH3), 9.75 (CpCH3).
HRMS/ESI+ (m/z): calcd for C30H34Cl3Rh2 704.9836; found
704.9854.
Synthesis of [Cp*benzylRhCl]2(μ2-Cl)2 (3l). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.406 mmol), 1l (0.344 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 3l (0.276 g, 89% yield). H NMR (400 MHz, CDCl3): δ 7.28−
7.25 (m, 2H, ArH), 7.24−7.18 (m, 4H, ArH), 7.08−7.06 (m, 4H,
ArH), 3.71 (s, 4H, 2 CH2), 1.67 (s, 12H, 4 CpCH3), 1.65 (s, 12H, 4
CpCH3). 13C{1H} NMR (101 MHz, CDCl3): δ 136.17 (ArC), 128.81
(ArC), 128.26 (ArC), 126.86 (ArC), 95.09−95.00 (d, JCRh = 9.1 Hz,
Synthesis of [Cp*n‑pentylRhCl]2(μ2-Cl)2 (3g). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.406 mmol), 1g (0.312 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
CpC), 94.94−94.85 (d, JCRh = 9.0 Hz, CpC), 93.98−93.88 (d, JCRh
=
9.5 Hz, CpC), 30.14 (CH2), 9.87 (CpCH3), 9.44 (CpCH3). HRMS/
ESI+ (m/z): calcd for C32H38Cl3Rh2 733.0149; found 733.0158. Anal.
Calcd for C32H38Cl4Rh2: C, 49.90; H, 4.97. Found: C, 50.49; H, 5.19.
Synthesis of [Cp*phenethylRhCl]2(μ2-Cl)2 (3m). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.150 g, 0.304 mmol), 1m (0.274 g,
1.22 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL) to
1
give 3g (0.227 g, 77%). H NMR (400 MHz, CDCl3): δ 2.27−2.23
(m, 4H, 2 CH2(CH2)3CH3), 1.63 (s, 12H, 4 CpCH3), 1.62 (s, 12H, 4
CpCH3), 1.38−1.24 (m, 12H, CH2(CH2)3CH3), 0.87−0.84 (app t,
6H, 2 CH3). 13C{1H} NMR (101 MHz, CDCl3): δ 96.44−96.34 (d,
JCRh = 9.3 Hz, CpC), 94.69−94.60 (d, JCRh = 9.1 Hz, CpC), 94.29−
94.19 (d, JCRh = 9.2 Hz, CpC), 31.88 (CH2), 27.33 (CH2), 24.10
(CH2), 22.50 (CH2), 13.96 (CH3), 9.58 (CpCH3), 9.56 (CpCH3).
HRMS/ESI+ (m/z): calcd for C28H46Cl3Rh2 693.0775; found
1
give 3m (0.186 g, 77% yield). H NMR (400 MHz, CDCl3): δ 7.23−
7.14 (m, 6H, ArH), 6.99−6.97 (m, 4H, ArH), 2.72−2.69 (t, 4 H, 2JHH
2
= 7.3 Hz, 2 PhCH2CH2), 2.61−2.57 (t, 4 H, JHH = 7.3 Hz, 2
PhCH2CH2), 1.57 (s, 12H, 4 CpCH3), 1.36 (s, 12H, 4 CpCH3).
G
DOI: 10.1021/acs.organomet.6b00580
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
13C{1H} NMR (101 MHz, CDCl3): δ 139.75 (ArC), 128.60 (ArC),
128.50 (ArC), 126.47 (ArC), 94.82−94.73 (d, JCRh = 9.1 Hz, CpC),
94.61−94.52 (d, JCRh = 9.5 Hz, CpC), 94.44−94.35 (d, JCRh = 9.2 Hz,
CpC), 33.37 (PhCH2CH2), 26.45 (PhCH2CH2), 9.32 (CpCH3), 9.12
(CpCH3). HRMS/ESI+ (m/z): calcd for C34H38Cl3Rh2 761.0462;
found 761.0466. Anal. Calcd for C34H42Cl4Rh2: C, 51.15; H, 5.30.
Found: C, 50.89; H, 5.18.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jmerola@vt.edu.
ORCID
Joseph S. Merola: 0000-0002-1743-1777
Notes
The authors declare no competing financial interest.
■
Synthesis of [Cp*cyclohexylRhCl]2(μ2-Cl)2 (3n). Following the general
procedure, [Rh(COD)]2(μ2-Cl)2 (0.200 g, 0.406 mmol), 1n (0.332 g,
1.62 mmol), and 0.5 mL of HCl were reacted in methanol (4 mL).
Upon cooling, an orange-yellow powder (0.091 g) formed in a red
solution. The powder was isolated and the red solution evaporated
under reduced pressure. The resulting red powder was recrystallized
from DCM and cold hexanes and collected by filtration. The red
powder was washed with cold hexanes to give 3n in a reacted yield of
0.106 g (64%). 1H NMR (400 MHz, CDCl3): δ 2.20−2.12 (m, 2H, 2
CH), 2.01−1.98 (m, 4H, 2 CH2), 1.79−1.75 (m, 4H, 2 CH2), 1.71 (s,
12H, 4 CpCH3), 1.59 (s, 12H, 4 CpCH3), 1.44−1.25 (m, 10H, CH2),
1.19−1.08 (m, 2H, CH2). 13C{1H} NMR (101 MHz, CDCl3): δ
97.95−97.86 (d, JCRh = 8.9 Hz, CpC), 94.08−93.99 (d, JCRh = 9.1 Hz,
CpC), 93.83−93.74 (d, JCRh = 9.1 Hz, CpC), 35.39 (CH), 30.76
(CH2), 26.83 (CH2), 26.12 (CH2), 10.78 (CpCH3), 9.66 (CpCH3).
HRMS/ESI+ (m/z): calcd for C30H46Cl3Rh2 717.0775; found
717.0782. Anal. Calcd for C30H46Cl4Rh2: C, 47.77; H, 6.15. Found:
C, 47.27; H, 5.88.
ACKNOWLEDGMENTS
■
We thank the Virginia Tech Department of Chemistry for
funds and supplies as well as the Hamilton Company for a
generous grant of syringes and needles. We acknowledge Ms.
Christine DuChane for helpful discussions, Dr. Carla
Slebodnick for her assistance with several crystal structures,
and Dr. Joseph O. Falkinham for the preliminary data on the
antimicrobial activity of the various metal dimers.
REFERENCES
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DOI: 10.1021/acs.organomet.6b00580
Organometallics XXXX, XXX, XXX−XXX