Hetero-bis(σ-aryl)dirhodium(III) caprolactamates. Electronic communication between aryl groups through dirhodium(III)

Article abstract of DOI:10.1039/b821592h

Fourteen hetero-bis(σ-aryl)dirhodium(III) caprolactamates that differ by the two aryl groups at the axial positions of dirhodium have been synthesized in good yield and characterized. Copper(II) catalyzed oxidation of dirhodium(II) caprolactamate at room

Full text of DOI:10.1039/b821592h

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Hetero-bis(r-aryl)dirhodium(III) caprolactamates. Electronic communication
between aryl groups through dirhodium(III)†
Jian-Hua Xie, Lei Zhou, Conrad Lubek and Michael P. Doyle*
Received 5th December 2008, Accepted 2nd February 2009
First published as an Advance Article on the web 26th February 2009
DOI: 10.1039/b821592h
Fourteen hetero-bis(s-aryl)dirhodium(III) caprolactamates that differ by the two aryl groups at the
axial positions of dirhodium have been synthesized in good yield and characterized. Copper(II)
catalyzed oxidation of dirhodium(II) caprolactamate at room temperature in the presence of two
arylboronic acids results in a mixture of a hetero-bis(s-aryl)dirhodium(III) caprolactamate and two
homo-bis(s-aryl)dirhodium(III) caprolactamates for each arylboronic acid combination. The UV-vis
lmax values for hetero-bisaryldirhodium(III) caprolactamates fall in between those for the
corresponding homo-bisaryldirhodium(III) caprolactamates; electronic interaction between the two
aryl groups occurs through dirhodium, but this transmission is probably indirect through the
caprolactamate ligands rather than directly between rhodiums. The chemical shift for the carbon bound
to Rh shows very limited dependence on the substituent from the aryl group on the adjacent Rh.
Bisaryldirhodium(III) caprolactamates with electron-withdrawing substitutions have higher oxidation
potentials than those with electron-donating substitutions. A plot of oxidation potentials versus the
corresponding UV-visible absorption maxima for the bisaryldirhodium(III) caprolactamates shows a
relationship between oxidation potentials and lmax values. The electronic/electrochemical information
obtained for hetero-bis(s-aryl)dirhodium(III) caprolactamates suggests that communication between
aryl substituents occurs.
When we began these studies, and before our realization that
bisphenyldirhodium(III) carboxamidates do not have a Rh–Rh
bond, we considered that they may have potential as molecu-
lar wires. The elegant studies of Ren et al. with paddlewheel
Introduction
We have reported the first example of a bis-aryl dimetallic com-
pound in a paddlewheel structure.1 Formed from dirhodium(II)
caprolactamate by oxidative coupling with sodium tetraphenylb-
diruthenium s-alkynyl compounds established them as conjugated
orate or arylboronic acids,2 bisphenyldirhodium(III) carboxami-
dates are now well characterized.3 They exhibit severe structural
distortions of the phenyl groups from expected C–Rh–Rh–C
linearity that is attributed to long range interactions between
the electron-deficient rhodium and distal oxygen atoms,3 and the
Rh–Rh–O bond angles that are much less than the idealized
perpendicular are inagreementwiththis interpretation. Consistent
with experimental and computational results, these compounds do
not have a Rh–Rh bond.3 Fig. 1 gives structural representations
for one of these bisphenyldirhodium(III) carboxamidates.
organometallics suitably constructed to be molecular wires.4 In
these structures the acetylide moieties are collinear with the
Ru–Ru vector and have characteristics of a molecular diode.5
However, bisphenyldirhodium(III) carboxamidates have neither a
Rh–Rh bond nor are the phenyl moieties collinear with the Rh–Rh
vector. Given the potential synthetic ease for structural variations
in aryl substituents in bisaryldirhodium(III) carboxamidates, we
initiated the construction of these derivatives having two different
aryl groups (Scheme 1). The challenges for this investigation
were (1) delineating the potential electronic bias in coupling of
the first and second aryl groups, (2) isolation of the individual
Fig. 1 Structural representations for bisphenyldirhodium(III) carprolac-
tamate: (a) line drawing; (b) Ortep representation from CCDC# 615577.
Department of Chemistry and Biochemistry, University of Maryland,
College Park, Maryland, 20742, USA. E-mail: mdoyle3@umd.edu;
Fax: +13013142779; Tel: +13014051788
† Electronic supplementary information (ESI) available: NMR spectra.
See DOI: 10.1039/b821592h
Scheme 1
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isomers, and (3) characterization of the bisphenyldirhodium(III)
carboxamidates with mixed aryl groups.
caprolactamate 2a (Fig. 2, Ar1 = C6H5 and Ar2 = p-MeOOCC6H4).
Similarly, increasing the number of equivalents of (4-methoxy-
carbonyl)phenylboronic acid led to higher yields of bis(s-4-
methoxycarbonylphenyl)dirhodium(III) caprolactamate 3a. In
both cases, the yield of hetero bis(s-aryl)dirhodium(III) capro-
lactamate 1a decreased.
Results and discussion
Synthesis
Using the optimized reaction conditions for the synthesis of
homo-bis(s-aryl)dirhodium(III) caprolactamates,2 hetero-bis(s-
aryl)dirhodium(III) caprolactamates were prepared by treatment
of two different arylboronic acids with dirhodium(II) caprolac-
tamate under oxidizing conditions. Rh2(cap)4 reacted smoothly
under an atmosphere of air with a mixture of phenylboronic
acid (2 equiv) and (4-methoxycarbonyl)phenylboronic acid
(5 equiv) in the presence of 10 mol% CuSO4.5H2O and 10 equiv.
of NaOMe in methanol at room temperature for 24 h yielding
a mixture of bis(s-aryl)dirhodium(III) caprolactamates from
which hetero-bis(s-aryl)dirhodium(III) caprolactamate 1a was
isolated in 39% yield (Scheme 2). Homo-bis(s-aryl)dirhodium(III)
caprolactamates 2a and 3a were generated in 24% and 27% yields,
respectively. Increasing the number of equivalents of phenyl-
boronic acid led to higher yields of bis(s-phenyl)dirhodium(III)
Fig. 2 Rh2(cap)4(CH3CN)2 with variable amounts of phenylboronic acid
and (4-methoxycarbonyl)-phenylboronic acid in air, catalyzed by 10 mol%
CuSO4. Total molar equivalents of both arylboronic acids is 7.0 equiv.
Other combinations of arylboronic acids were treated under
similar reaction conditions, and the results are reported in Table 1.
As can be seen from these results, product ratios are not very
sensitive to aryl substituents, although arylboronic acids having
electron-withdrawing substituents are more reactive than those
Scheme 2
Table 1 Synthesis of hetero-bis(s-aryl)dirhodium(III) caprolactamatesa
ꢀ
ꢀ
ꢀ
Comp.
Ar1 (equiv)
Ar2 (equiv), XC6H4 X =
1/ 1–3 (%)b
2/ 1–3 (%)b
3/ 1–3 (%)b
Total yield (%)c
a
b
c
d
e
f
C6H5 (2)
4-MeOOC (5)
4-MeOOC (5)
4-MeOOC (5)
4-MeOOC (5)
4-MeOOC (5)
4-MeOOC (5)
4-MeOOC (5)
4-MeOOC (5)
4-Me2N (2.5)
4-MeO (2.5)
4-HCO (5)
43
42
51
56
51
40
55
48
40
46
48
45
57
50
40
27
25
23
21
19
30
20
29
22
14
20
8
30
33
26
23
30
30
25
23
38
40
32
47
17
40
25
90
87
81
86
75
77
85
65
78
65
91
91
84
79
60
4-MeC6H4 (2)
4-Ph-C6H4 (2)
6-MeO-2-naphthyl (2)
4-BrC6H4 (2)
3-Thiopheneyl (2)
4-CF3C6H4 (5)
3-NO2C6H4 (5)
C6H5 (2.5)
C6H5 (2.5)
C6H5 (2)
C6H5 (2)
4-MeOC6H4 (2)
4-Me2NC6H4 (2)
4-CF3C6H4 (5)
g
h
i
j
k
k
l
4-HCO (8)
4-HCO (5)
3-HCO (5)
4-NO2 (5)
26
10
35
m
n
a Reactions were performed at room temperature in 4:1 CH2Cl2/MeOH with 10 mol% CuSO4·5H2O and 10 equiv NaOMe with a reaction time of 12–24 h.
b Relative yield of isolated products. c Isolated yield after column chromatography on silica gel.
2872 | Dalton Trans., 2009, 2871–2877
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with electron-donating substituents. Overall product yields were
high for all arylboronic acid combinations.
UV-visible spectroscopy
The UV-visible spectra of the hetero-bis(s-aryl)dirhodium(III)
caprolactamates were obtained, and those for 1i, 2i, and 3i
are shown in Fig. 3. Focus was placed on the HOMO–LUMO
transition that in all compounds occurs between 400 and 500 nm.
This transition was determined by DFT methods to be from
the d* HOMO to an unoccupied mixed RhRhCAr orbital in a
compound whose Rh–Rh interaction is formally described as
p d p*4d*2 so that the formal bond order for Rh–Rh is zero,
suggesting that there should be no direct substituent influence
on lmax. Compared with the corresponding UV-vis spectra of
homo-bis(s-aryl)dirhodium (III) caprolactamates,2 hetero-bis(s-
aryl)dirhodium(III) caprolactamates display their lmax between
those of the two homo-bis(s-aryl)dirhodium(III) caprolactamates
(Table 2). For example, the lmax of compound 2i and 3i are at
430 nm and 485 nm, respectively, and lmax for the corresponding
hetero bis(s-aryl)dirhodium (III) caprolactamate 1i is at 440 nm.
This result suggests electronic interaction between the two aryl
groups through dirhodium, but this transmission is probably
occurring indirectly through the caprolactamate ligands rather
than directly through rhodium (Scheme 3, solid line or via
dashed line). Similar indirect transmission of substituent effects
in electronic spectra has been reported by Kadish, Bear et al. for
tetrakis(2-anilinopyridinate) complexes of dirhodium in the +4,
+5, and +6 oxidation states.6
Scheme 3
13C chemical shift
The 13C chemical shift of the carbon directly attached to rhodium
is dependent on the substituent on the phenyl group. With
electron-withdrawing substitutions higher chemical shifts are
observed; lower chemical shifts are found when substituents are
electron donating (Table 3). As can be seen from the series 1a
through 1h the chemical shift for the carbon bound to Rh in
4-MeO2CC6H4 shows very limited dependence on the substituent
from the distant aryl group. The JRh-C coupling constants from
mononuclear phenylrhodium(III) compounds are much lower
than those reported here for bis(s-aryl)dirhodium(III).7
4
2
Electrochemistry
Finally, cyclic voltammetry data was obtained for this set
of hetero-bis(s-aryl)dirhodium(III) caprolactamates (Table 4).
Cyclic voltammetry analyses were carried out by dissolving
the respective hetero-bis(s-aryl)dirhodium(III) caprolactamates
in CH2Cl2 solution under nitrogen with 0.10 M NBu4PF6 as
the supporting electrolyte. Electrochemical oxidation/reduction
was obtained on Pt (working/auxiliary) and Ag/AgCl reference
electrodes and referenced to ferrocene(0,+). All complexes exhibited
reversible oxidation (Rh6+/Rh7+) waves with the reduction peak
separated from the oxidation peak by 100–140 mV except for
the two complexes having the dimethylamino group (2i and 2m),
which exhibited multiple redox peaks, presumably associated with
that easily oxidized functional group. As had been previously
reported for bisphenyldirhodium(III) carboxamidates,3 an addi-
tional irreversible redox couple, attributed to Rh5+/Rh6+, could
be observed near the reduction limit of the solvent. Complexes
with electron-withdrawing substitutions have higher oxidation
potentials than those with electron-donating substitutions. The
Fig. 3 Uv-vis spectra of compound 1i, 2i and 3i (red line for compound 1i,
green line for compound 2i and gray line for compound 3i, 1.0 ¥ 10-4 mmol
mL-1).
Table 2 UV-vis data of hetero bis(s-aryl)dirhodium(III) caprolactamates
Compound
Ar1
Ar2, XC6H4 X =
l
max/nm (e ¥ 10-3 M-1 cm-1)
1 (Ar1Ar2)
430 (6.2)
430 (7.7)
430 (7.2)
435 (6.1)
430 (6.7)
430 (5.3)
425 (5.4)
425 (6.6)
440 (4.0)
440 (4.8)
425 (5.4)
435 (5.2)
430 (4.1)
420 (8.9)
2 (Ar1Ar1)
430(4.5)
440(8.1)
440(1.3)
455(6.2)
432(8.0)
457(5.9)
420(4.2)
423(6.4)
430(4.5)
430(4.5)
430(4.5)
452(6.2)
485(3.1)
420(4.2)
3 (Ar2Ar2)
425(8.2)
425(8.2)
425(8.2)
425(8.2)
425(8.2)
425(8.2)
425(8.2)
425(8.2)
485(3.1)
452(6.2)
422(7.9)
422(7.9)
425(4.1)
415(8.9)
a
b
c
d
e
f
g
h
i
j
k
l
m
n
C6H5
4-MeOOCC6H4
4-MeOOCC6H4
4-MeOOCC6H4
4-MeOOCC6H4
4-MeOOCC6H4
4-MeOOCC6H4
4-MeOOCC6H4
4-MeOOCC6H4
4-Me2NC6H4
4-MeOC6H4
4-HCOC6H4
4-HCOC6H4
3-HCOC6H4
4-NO2C6H4
4-MeC6H4
4-Ph-C6H4
6-MeO-2-naphthyl
4-BrC6H4
3-Thiopheneyl
4-CF3C6H4
3-NO2C6H4
C6H5
C6H5
C6H5
4-MeOC6H4
4-Me2NC6H4
4-CF3C6H4
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Table 3 13C Chemical shift of Rh–C of hetero bis(s-aryl)dirhodium(III) caprolactamates
1: (Ar1Ar2), d, ppm
3: Ar2, XC6H4, X =, d, ppm
(multiplicity, J, Hz)
Compound
(multiplicity, J, Hz)
2: Ar1, d, ppm (multiplicity, J, Hz)
a
b
c
d
e
f
g
h
j
146.9 (d, 36.1); 157.9 (d, 39.0)
142.3 (d, 36.9); 158.2 (d, 37.2)
146.5 (d, 36.7); 157.9 (d, 38.0)
140.4 (d, 36.8); 157.9 (d, 36.2)
144.8 (d, 38.2); 157.3 (d, 37.1)
128.0 (d, 42.8); 156.7 (d, 36.7)
153.7 (d, 29.2); 157.6 (d, 37.8)
146.4 (d, 39.1); 156.6 (d, 36.7)
147.3 (d, 37.0); 131.2 (d, 37.0)
147.8 (d, 37.1); 163.4 (d, 33.8)
134.0 (d, 37.5); 162.5 (d, 33.9)
130.7 (d, 37.8); 147.9 (d, 39.3)
C6H5, 147.8 (d, 37.1)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-MeO2C, 157.6 (d, 37.0)
4-Me2N, 131.4 (d, 37.6)
4-HCO, 162.3 (d, 37.0)
4-HCO, 161.5 (d, 37.0)
3-HCO, 148.3 (d, J = 37.0)
4-MeC6H4, 142.8 (d, 37.0)
4-PhC6H4, 146.6 (d, 37.0)
6-MeO-2-naphthyl, 140.4 (d, 36.8)
4-BrC6H4, 144.8 (d, 38.2)
3-Thiophenyl, 128.0 (d, 42.8)
4-CF3C6H4,NA
3-NO2C6H4, 146.4 (d, 39.1)
C6H4, 147.8 (d, 37.1)
C6H4, 146.8 (d, 36.3)
k
l
n
4-MeOC6H4, 134.2 (d, 38.7)
4-Me2NC6H4, 130.7 (d, 37.8)
Table 4 CV data for Ar1Ar2Rh2cap4
Compound
Ar1
Ar2 XC6H4, X =
E
pa/Va
Epc/V
E1/2/V
a
b
c
d
e
f
g
h
i
j
k
l
m
n
C6H5
4-MeOOC
4-MeOOC
4-MeOOC
4-MeOOC
4-MeOOC
4-MeOOC
4-MeOOC
4-MeOOC
4-Me2N
4-MeO
4-HCO
4-HCO
3-HCO
0.980
0.973
1.002
1.009
1.031
1.031
1.069
0.841
0.838
0.864
0.852
0.898
0.897
0.937
0.9105
0.9055
0.933
0.9305
0.9645
0.964
4-MeC6H4
4-Ph-C6H4
6-MeO-2-naphthyl
4-BrC6H4
3-Thiopheneyl
4-CF3C6H4
3-NO2C6H4
C6H5
C6H5
C6H5
4-MeOC6H4
4-Me2NC6H4
4-CF3C6H4
1.003
1.102
0.979
1.0405
b
b
b
0.893
1.005
0.776
0.896
0.8345
0.9505
0.982
0.877
0.9295
b
b
b
4-NO2
1.124
1.016
1.07
a Pt (working and auxiliary) and Ag/AgCl reference electrodes, CH2Cl2, Bu4NPF6. b Multiple irreversible redox peaks were found.
Table 5 CV and UV-vis data for Ar2Rh2cap4
opposite trend is found in the UV-visible data of the hetero-
bis(s-aryl)dirhodium(III) caprolactamates in that complexes with
electron-withdrawing substituents have lower absorption maxima
than those with electron-donating substituents. A plot of half-wave
potentials versus the corresponding UV-visible absorption maxima
for the hetero-bis(s-aryl)dirhodium(III) caprolactamates (Fig. 4)
Ar =
E
pa/Va
Epc/V
E
1/2/V
l
max/nm
3-HCOC6H4
4-BrC6H4
4-HCOC6H4
4-MeOC6H4
4-(BocNH)C6H4
4-MeOOCC6H4
4-CF3C6H4
1.017
0.992
1.057
0.855
0.877
1.038
1.064
0.864
0.921
0.946
0.919
0.986
0.781
0.797
0.926
0.962
0.760
0.817
0.9815
0.9555
1.0215
0.818
0.837
0.982
1.013
0.812
0.869
425.1
430
425.1
449.9
449.9
425.1
420
4-MeC6H4
4-PhC6H4
440
440
a Pt (working and auxiliary) and Ag/AgCl reference electrodes, CH2Cl2,
Bu4NPF6.
defines the relationship between oxidation potentials and lmax
values. The trend shows that the higher the half-wave potential, the
lower UV-visible absorption maximum. Similar data was obtained
for homo-bis(s-aryl)dirhodium(III) caprolactamates (Table 5 and
Fig. 5).
Noteworthy in Tables 4 and 5 is the distinctive influence of
lmax for aryl substituents on the half-wave potential. The results
in Table 4 from Ar1Ar2Rh2cap4 for Ar2 = 4-MeOOCC6H4 (a-h)
show correlation of E1 with those in Table 5 for homo-
bis(s-aryl)dirhodium(III) caprolactamates. The oxidized bis-
aryldirhodium(III,IV) caprolactamates are obviously stable, but
2
Fig. 4 Plot of E1/2/V vs. lmax/nm for Ar1Ar2Rh2cap4. (R2 = 0.7508;
slope = -0.0101).
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Conclusions
Electrochemical and spectroscopic information have been abun-
dantly provided for selected dirhodium12 and diruthenium13
complexes. Substituent effects from anilinopyridinate (4)5,14 and
diarylformamidinate (5)15 complexes have been reported, and
linear free energy relationships have been provided. However,
the alignment of aryl rings in these complexes is inherently
different from that of bisaryldirhodium(III) carboxamidates, and
direct comparisons cannot be made. Indeed, we know of no
comparable dimetallic system from which similar data could be
extracted. Bisaryldirhodium(III) carboxamidates provide a unique
opportunity to probe substituent effects that are transmitted
from remote positions directly to rhodium. That the values for
l
max and E1/2 in hetero-bis(s-aryl)dirhodium(III) caprolactamates
fall between those for homo-bis(s-aryl)dirhodium(III) caprolac-
tamates suggests that communication between aryl substituents
does occur. Without a Rh–Rh bond the effects are localized on
an individual rhodium and passed onto the adjacent rhodium
through carboxamidate ligands (Scheme 3).
Fig. 5 Plot of E1/2/V vs. lmax/nm for Ar2Rh2cap4. (R2 = 0.8835; slope =
-0.0071).
the corresponding bisaryldirhodium(II,III) caprolactamates are
not. However, we have not yet been able to chemically oxidize
bis(s-aryl)dirhodium(III) caprolactamates (ferricinium salts, ni-
trosonium salts).
The influence of aryl substituents on half-wave potentials has
allowed the establishment of a linear free energy relationship
between E1/2 for homo-bis(s-aryl)dirhodium(III) caprolactamates
and s (Fig. 6) through the Hammett equation.8 Linear corre-
lation with published s-values (sp and sm)9 is observed with
R2 = 0.9866 and a slope (reaction constant) of +0.306 (r).
To investigate if significant conjugation occurs between the
Experimental
General
All reagents and solvents were used without further purifica-
tion. Yields reported are those obtained after chromatogra-
phy on silica gel (SiliCycle, 60A, 40–63 mesh), unless other-
wise noted. The preparation of dirhodium(II) caprolactamate
[Rh2(cap)4(CH3CN)2] has been previously described.16 1H NMR
and 13C NMR spectra were obtained on a Bruker DRX-400
NMR as solutions in CDCl3 unless otherwise noted. Chemical
shifts are reported in parts per million (ppm, d) downfield
from Me4Si (TMS); coupling constants are reported in Hertz
(Hz). UV-visible spectra were obtained on a Varian Cary 50
spectrophotometer using a xenon lash lamp. IR spectra were
recorded on a JASCO FT/IR 4100 spectrometer. Mass spectra
were recorded at high resolution with either a VG Micromass
70/70H or VG ZAB-E spectrometer. Electrochemical measure-
ments were performed in freshly distilled CH2Cl2 (N2 degassed)
with a CHI 610c instrument. A three-electrode cell was used (Pt
working and auxiliary electrodes, Ag/AgCl reference electrode).
The ferrocenium/ferrocene couple was observed at 0.487 V (vs.
Ag/AgCl) under the experimental conditions. Scans were run at
100 mV s-1 under a nitrogen atmosphere. Solutions were 0.5–
1.0 mM of analyte in 10 mL of CH2Cl2 of 0.1 M Bu4NPF6 as
the supporting electrolyte. Nitrogen gas was bubbled through the
solution for 10 min before each set of measurements and was
passed continuously over the surface of the solution during the
measurements.
+
phenyl substituent and the dirhodium core, plots with s and
s- were also attempted, but each had low correlation coeffi-
cients. The correlation exhibited in Fig. 6 is in good agreement
with the electron-donating-withdrawing properties of phenyl
substituents. Substituent effects with E1/2 values in dimetallic
systems have been previously reported and discussed,10 and similar
correlations in iron-phenylacetylide compounds have also been
examined.11
General procedure
CuSO4·5H2O (3.0 mg, 12 mmol) was dissolved in 4 mL MeOH,
Fig. 6 Plot of E1/2/V vs. s for Ar2Rh2cap4.
and this solution was added to the mixture of Rh2(cap)4(MeCN)2
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(88.4 mg, 0.12 mmol), NaOMe (64.8 mg, 1.2 mmol) and aryl-
boronic acids (0.24–0.96 mmol) in 16 mL CH2Cl2. The generated
purple reaction solution was stirred at room temperature for 12–
24 hrs to complete the reaction (determined by TLC, CH2Cl2 or
CH2Cl2/acetone = 98:2). The solvents were then removed under
reduced pressure, and the green or yellow solid residue was purified
by chromatography on silica gel using CH2Cl2 or CH2Cl2/acetone
as the eluent. The products were identified spectroscopically.
NMR (400 MHz, CDCl3): d 7.75 (d, J = 8.8 Hz, 2H), 7.65 (d, J =
8.8 Hz, 2H), 7.38 (d, J = 8.8 Hz, 2H), 7.25 (d, J = 8.8 Hz, 2H), 3.91
(s, 3H), 2.98–2.89 (comp, 8H), 2.48–2.34 (comp, 8H), 1.82 (comp,
4H), 1.62–1.37 (comp, 20H); 13C NMR (100 MHz, CDCl3): d
184.2, 168.1, 157.3 (d, J = 37.1 Hz), 144.8 (d, J = 38.2 Hz), 138.3,
137.0, 132.3, 129.6, 126.4, 119.0, 117.2, 51.8, 51.6, 51.5, 38.9,
30.7, 29.8, 24.3; UV-visible (CH2Cl2): lmax (e M-1 cm-1) = 425
(6670); HRMS (ESI): Calcd for C38H51N4O6Rh2 (M+): 944.1102;
Found: 944.1069.
trans-{r-Phenyl-r-(4-methoxycarbonylphenyl)}-tetrakis-l-(cap-
rolactamato)dirhodium(III) (1a). Green solid; 1H NMR
(400 MHz, CDCl3): d 7.76 (d, J = 8.4 Hz, 2H), 7.68 (d, J =
8.4 Hz, 2H), 7.50 (comp, 2H), 7.11 (comp, 3H), 3.91 (s, 3H),
3.02–2.929 (comp, 8H), 2.51–2.32 (comp, 8H), 1.81 (comp, 4H),
1.68–1.38 (comp, 20H); 13C NMR (100 MHz, CDCl3): d 184.3,
184.0, 168.2, 157.9 (d, J = 39.0 Hz), 146.9 (d, J = 36.1 Hz), 137.1,
136.8, 126.8, 126.5, 126.2, 124.4, 51.6, 51.5, 39.0, 38.9, 30.7, 29.9,
29.8, 24.4; UV-visible (CH2Cl2): lmax (e M-1 cm-1) = 425 (6200);
HRMS (ESI): Calcd for C38H53N4O6Rh2 ([M + H]+): 867.2075;
Found: 867.2078.
trans-{r-(3-Thienyl)-r-(4-methoxycarbonylphenyl)}-tetrakis-l-
(caprolactamato)dirhodium(III) (1f). Green solid; 1H NMR
(400 MHz, CDCl3): d 7.74 (d, J = 8.4 Hz, 2H), 7.65 (d, J =
8.4 Hz, 2H), 7.37 (d, J = 4.8 Hz, 1H), 7.32 (dd, J = 4.8, 2.8 Hz,
1H), 7.08 (d, J = 2.8 Hz, 1H), 3.90 (s, 3H), 3.10–2.89 (comp, 8H),
2.50–2.32 (comp, 8H), 1.82 (comp, 4H), 1.65–1.38 (comp, 20H);
13C NMR (100 MHz, CDCl3): d 184.1, 184.0, 168.1, 156.7 (d, J =
36.7 Hz), 137.0, 132.9, 128.0 (d, J = 42.8 Hz), 126.8, 126.4, 120.1,
119.3, 51.8, 51.7, 51.6, 39.0, 38.8, 30.7, 29.9, 29.7, 24.4; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) = 435 (5304); HRMS (ESI): Calcd for
C36H50N4O6Rh2S (M+): 872.1561; Found: 872.1512.
trans-{r-(4-Methylphenyl)-r-(4-methoxycarbonylphenyl)}-
tetrakis-l-(caprolactamato)-dirhodium(III) (1b). Green solid; 1H
NMR (400 MHz, CDCl3): d 7.75 (d, J = 8.8 Hz, 2H), 7.68 (d, J =
8.8 Hz, 2H), 7.35 (d, J = 8.4 Hz, 2H), 6.95 (d, J = 8.4 Hz, 2H), 3.91
(s, 3H), 3.06–2.90 (comp, 8H), 2.40 (comp, 8H), 1.80 (comp, 4H),
1.65–1.38 (comp, 20H); 13C NMR (100 MHz, CDCl3): d 184.2,
183.9, 168.2, 158.2 (d, J = 37.2 Hz), 142.3 (d, J = 36.9 Hz),
137.1, 136.4, 133.7, 127.5, 126.7, 126.1, 51.8, 51.7, 51.6, 38.9,
38.8, 30.7, 29.9, 29.7, 29.7, 24.4, 20.7; UV-visible (CH2Cl2): lmax
(e M-1 cm-1) = 430 (7660); HRMS (ESI): Calcd for C39H54N4O6Rh2
(M+): 880.2153; Found: 880.2168.
trans-{r-(4-Trifluoromethylphenyl)-r-(4-methoxycarbonyl-
phenyl)}-tetrakis-l-(caprolactamato)-dirhodium(III) (1g). Green
1
solid; H NMR (400 MHz, CDCl3): d 7.75 (d, J = 8.8 Hz, 2H),
7.68 (d, J = 8.8 Hz, 2H), 7.35 (d, J = 8.4 Hz, 2H), 6.95 (d, J =
8.4 Hz, 2H), 3.91 (s, 3H), 3.06–2.90 (comp, 8H), 2.40 (comp, 8H),
1.80 (comp, 4H), 1.65–1.38 (comp, 20H); 13C NMR (100 MHz,
CD2Cl2): d 184.2, 184.1, 167.7, 157.6 (d, J = 37.8 Hz), 153.7
(d, J = 29.2 Hz), 137.2, 137.0, 126.9, 126.6, 126.5, 122.2 (q,
J = 3.2 Hz), 115.5, 51.7, 51.6, 38.7, 30.6, 29.7, 24.3; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) = 420 (5361); HRMS (ESI): Calcd for
C39H52F3N4O6Rh2 ([M + H]+): 935.1949; Found: 935.1964.
trans-{r-(4-Phenylphenyl)-r-(4-methoxycarbonylphenyl)}-tet-
rakis-l-(caprolactamato)-dirhodium(III) (1c). Green solid; 1H
NMR (400 MHz, CDCl3): d 7.16 (d, J = 8.4 Hz, 2H), 7.68 (d,
J = 8.8 Hz, 2H), 7.65 (d, J = 8.4 Hz, 2H), 7.57 (d, J = 8.4 Hz,
2H), 7.44 (t, J = 7.6 Hz, 2H), 7.36 (d, J = 8.4 Hz, 2H), 7.30 (t, J =
7.6 Hz, 1H), 3.91 (s, 3H), 3.12–2.4 (comp, 8H), 2.44 (comp, 8H),
1.82 (comp, 4H), 1.68–1.38 (comp, 20H); 13C NMR (100 MHz,
CDCl3): d 184.3, 184.1, 168.2, 157.9 (d, J = 38.0 Hz), 146.5 (d,
J = 36.7 Hz), 141.6, 137.5, 137.1, 137.0, 128.6, 127.1, 126.8, 126.5,
126.2, 125.2, 51.8, 51.7, 39.0, 38.9, 30.8, 29.9, 29.8, 24.4; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) = 435 (7200); HRMS (ESI): Calcd for
C44H57N4O6Rh2 ([M + H]+): 943.2388; Found: 943.2392.
trans-{r-(3-Nitrophenyl)-r-(4-methoxycarbonylphenyl)}-tet-
rakis-l-(caprolactamato)dirhodium(III) (1h). Green solid; 1H
NMR (400 MHz, CDCl3): d 8.38 (s, 1H), 8.00 (dd, J = 8.0,
1.6 Hz, 1H), 7.91 (d, J = 8.0 Hz, 1H), 7.76 (d, J = 8.4 Hz, 2H),
7.64 (d, J = 8.4 Hz, 2H), 7.25 (t, J = 8.0 Hz, 1H), 3.92 (s, 3H),
3.02–2.87 (comp, 8H), 2.51–2.37 (comp, 8H), 1.81 (comp, 4H),
1.71–1.38 (comp, 20H); 13C NMR (100 MHz, CDCl3): d 184.6,
184.4, 168.2, 156.6 (d, J = 36.7 Hz), 146.4 (d, J = 39.1 Hz), 145.6,
143.6, 136.8, 131.3, 130.0, 127.0, 126.6, 126.0, 122.0, 119.7, 15.2,
110.6, 51.9, 51.8, 51.7, 39.0, 38.9, 30.7, 29.7, 29.6, 24.3; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) = 425 (6642); HRMS (ESI): Calcd for
C38H52N5O8Rh2 ([M + H]+): 912.1926; Found: 912.1898.
trans-{r-(6-Methoxynaphthalen-2-yl)-r-(4-methoxycarbonyl-
phenyl)}-tetrakis-l-(caprolactamato)-dirhodium(III) (1d). Green
trans-{r-(4-N,N-Dimethylaminophenyl)-r-phenyl}-tetrakis-l-
(caprolactamato)dirhodium(III) (1i). Green solid; 1H NMR
(400 MHz, CDCl3): d 7.54 (comp, 2H), 7.33 (d, J = 8.8 Hz,
2H), 7.11 (comp, 3H), 6.70 (d, J = 8.8 Hz, 2H), 3.13–2.89 (comp,
8H), 2.95 (s, 6H), 2.54–2.32 (comp, 8H), 1.81 (comp, 4H), 1.68–
1.38 (comp, 20H); 13C NMR (CDCl3): d 183.8, 183.7, 149.0, 147.3
(d, J = 37.0 Hz), 137.1, 136.3, 131.2 (d, J = 37.0 Hz), 127.8,
126.3, 124, 114.0, 112.8, 51.6, 41.5, 39.0, 30.9, 30.8, 30.0, 24.5,
24.4; UV-visible (CH2Cl2): lmax (e M-1 cm-1) = 440 (4960); HRMS
(ESI): Calcd for C38H56N5O4Rh2 ([M + H]+): 852.2442; Found:
852.2422.
1
solid; H NMR (400 MHz, CDCl3): d 7.82 (s, 1H), 7.77 (d, J =
8.8 Hz, 2H), 7.74–7.62 (m, 4H), 7.51 (d, J = 8.8 Hz, 1H), 7.18
(d, J = 2.4 Hz, 1H), 7.08 (dd, J = 8.8, 2.4 Hz, 1H), 3.93 (s, 3H),
3.92 (s, 3H), 3.06–2.90 (comp, 8H), 2.45 (comp, 8H), 1.83 (comp,
4H), 1.70–1.42 (comp, 20H); 13C NMR (CDCl3): d 184.3, 184.1,
168.2, 157.9 (J = 36.2 Hz), 156.6, 140.4 (J = 36.8 Hz), 137.1,
135.6, 134.3, 132.9, 128.8, 128.5, 126.8, 126.6, 123.9, 117.4, 105.6,
55.3, 51.8, 51.7, 51.6, 39.0, 38.9, 30.8, 29.9, 29.8, 24.4; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) = 435 (6068); HRMS (ESI): Calcd for
C43H57N4O6Rh2 ([M + H]+): 947.2337; Found: 947.2323.
trans-{r-(4-Bromophenyl)-r-(4-methoxycarbonylphenyl)}-tet-
rakis-l-(caprolactamato)-dirhodium(III) (1e). Green solid; 1H
trans-{r-(4-Methoxyphenyl)-r-phenyl}-tetrakis-l-(caprolac-
1
tamato)dirhodium(III) (1j). Green solid; H NMR (400 MHz,
2876 | Dalton Trans., 2009, 2871–2877
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CDCl3): d 7.51 (comp, 2H), 7.39 (d, J = 8.8 Hz, 2H), 7.10 (comp,
3H), 6.80(d, J = 8.8 Hz, 2H), 3.84 (s, 3H), 3.08–2.91 (comp, 8H),
2.48–2.35 (comp, 8H), 1.80 (comp, 4H), 1.67–1.36 (comp, 20H);
13C NMR (100 MHz, CDCl3): d 184.0, 183.9, 157.8, 147.0 (d, J =
36.6 Hz), 137.0, 136.6, 134.9 (d, J = 39.1 Hz), 126.4, 124.1, 116.0,
114.8, 112.5, 55.8, 55.5, 51.6, 51.5, 38.9, 30.8, 29.9, 24.4; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) = 440 (4750); HRMS (ESI): Calcd for
C37H52N4O5Rh2 (M+): 838.2048; Found: 838.2057.
trans-(r-4-Trifluoromethylphenyl-r-4-nitrophenyl)-tetrakis-l-
(caprolactamato)dirhodium(III) (1m). Green solid; 1H NMR
(400 MHz, CD2Cl2): d 7.95 (d, J = 8.8 Hz, 2H), 7.77 (d, J =
8.8 Hz, 2H), 7.65 (d, J = 8.4 Hz, 2H), 7.37 (d, J = 8.4 Hz,
2H), 2.97 (comp, 8H), 2.52–2.34 (comp, 8H), 1.80 (comp, 4H),
1.65–1.40 (comp, 20H); This compound was insoluble in all
NMR solvents to the extent that its 13C NMR spectrum was not
obtained. UV-visible (CH2Cl2): lmax (e M-1 cm-1) = 430 (8860);
HRMS (ESI): Calcd for C37H48N5O6Rh2 (M+): 921.1667; Found:
921.1696.
trans-{r-(4-Formylphenyl)-r-phenyl}-tetrakis-l-(caprolact-
1
amato)dirhodium(III) (1k). Green solid. H NMR (400 MHz,
CDCl3): d 10.03 (s, 1H), 7.84 (d, J = 8.0 Hz, 2H), 7.61 (d, J =
8 Hz, 2H), 7.53–7.50 (comp, 2H), 7.15–7.13 (comp, 3H), 3.06–
2.96 (comp, 8H), 2.45–2.40 (comp, 8H), 1.83–1.79 (comp, 4H),
1.63–1.39 (comp, 20H); 13C NMR (100 MHz, CDCl3/MeOD,
4:1): d 192.7, 184.4, 184.0, 137.8, 136.8, 133.5, 126.7, 126.6,
124.5, 51.7, 51.5, 39.0, 38.9, 30.7, 29.9, 29.7, 24.4; UV-visible
(CH2Cl2): lmax (e M-1 cm-1) nm = 425 (5400); HRMS (ESI): Calcd
for C37H50N4O5Rh2 (M+): 836.1891; Found: 836.1915. HRMS
(ESI): Calcd for C37H50N4O5Rh2 (M+): 836.1891; Found: 836.1915.
C37H51N4O5Rh2 ([M + H]+): 837.1970; Found: 836.1979.
Notes and references
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trans-{r-(4-Methoxyphenyl)-r-(4-formylphenyl)}-tetrakis-l-
(caprolactamato)dirhodium(III) caprolactamate (1l). Green
1
solid. H NMR (400 MHz, CD2Cl2): d 10.00 (s, 1H), 7.79 (d,
J = 8.0 Hz, 2H), 7.57 (d, J = 8.0 Hz, 2H), 7.32 (d, J = 8.0 Hz,
2H), 6.79 (d, J = 8.0 Hz, 2H), 3.83 (s, 3H), 2.99 (comp, 8H),
2.47–2.36 (comp, 8H), 1.82 (comp, 4H), 1.63–1.39 (comp, 20H);
13C NMR (100 MHz, CD2Cl2): d 192.2, 184.1, 183.7, 162.5 (d,
J = 33.9 Hz), 158.0, 137.9, 136.5, 134.0 (d, J = 37.5 Hz), 133.5,
1130.1, 128.0, 126.3, 112.3, 55.4, 51.7, 51.4, 38.7, 38.6, 30.7, 29.9,
29.7, 24.3; UV-visible (CH2Cl2): lmax (e M-1 cm-1) nm = 435
(5190); HRMS (ESI): Calcd for C37H50N4O5Rh2 (M+): 836.1891;
Found: 836.1915. HRMS (ESI): Calcd for C38H52N4O6Rh2Na
([M + Na]+): 889.1895; Found: 889.1490. C38H52N4O6Rh2 (M+):
866.1997; Found: 866.1887.
5 J.-W. Ying and T. Ren, J. Organomet. Chem., 2008, 693, 1449; T. Ren,
Organometallics, 2005, 24, 4854.
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and H. Nishiyama, Chem. Commun., 1999, 131; Y. Motoyama, M.
Okano, H. Narusawa, N. Makihara, K. Aoki and H. Nishiyama,
Organometallics, 2001, 20, 1580.
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J. Chem. Soc., Dalton Trans., 2002, 1783.
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Atoms, 3rd Edition, ed. F. A. Cotton, C. A. Murillo, R. A. Walton,
Springer Science, New York, 2005, Chapter 12.
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C. A. Murillo and R. A. Walton, Springer Science, New York, 3rd edn,
2005, ch. 10.
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and J. L. Bear, Inorg. Chem., 2008, 47, 11423; G. Zou;, J. C. Alverez
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Boone, V. Bagheri and M. M. Pearson, J. Am. Chem. Soc., 1993, 115,
958.
trans-{r-(4-N,N-Dimethylaminophenyl)-r-(3-formylphenyl)}-
tetrakis-l-(caprolactamato)dirhodium(III) (1n). Orange solid;
1H NMR (400 MHz, CDCl3): d 9.99 (s, 1H), 8.09 (s, 1H), 7.87
(d, J = 7.6 Hz, 1H), 7.62 (d, J = 7.6 Hz, 1H), 7.31 (d, J =
8.4 Hz, 2H), 7.27 (t, J = 7.6 Hz, 1H), 6.69 (d, J = 8.4 Hz, 2H),
3.07 (comp, 2H), 3.00–2.93 (comp, 12H), 2.48–2.34 (comp, 8H),
1.82 (comp, 2H), 1.68–1.35 (comp, 20H); 13C NMR (100 MHz,
CDCl3): d 192.9, 184.1, 183.8, 149.0, 147.9 (d, J = 39.3 Hz),
143.9, 139.1, 136.2, 135.3, 130.7 (d, J = 37.8 Hz), 126.6, 125.8,
112.8, 51.7, 51.6, 41.5, 39.0, 38.9, 30.8, 29.9, 29.7, 24.5, 24.4;
UV-visible (CH2Cl2): lmax (e M-1 cm-1) = 430 (4090); IR (neat)
1689, 1585 cm-1; HRMS (ESI): Calcd for C39H55N5O5Rh2Na
([M + Na]+): 902.2211; Found: 902.1608.
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 2871–2877 | 2877
©