Steric control at the wingtip of a bis-N-heterocyclic carbene ligand: Coordination behavior and catalytic responses of its ruthenium compounds

Article abstract of DOI:10.1021/om300469n

Changing the N-substituents of a methylene-linked bis-NHC ligand from n-butyl to bulky mesityl shifts ligand coordination from normal/normal to normal/abnormal mode. The mesityl wingtip groups afford [Ru^II( ^MesNHC(CH₂)NHC<

Full text of DOI:10.1021/om300469n

Article
pubs.acs.org/Organometallics
Steric Control at the Wingtip of a Bis-N-Heterocyclic Carbene Ligand:
Coordination Behavior and Catalytic Responses of Its Ruthenium
Compounds
Sayantani Saha,† Tapas Ghatak,† Biswajit Saha,† Henri Doucet,‡ and Jitendra K. Bera*,†
†Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
‡“Catalyse et Organometalliques”, Institut Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite
́
de Rennes, Campus de
Beaulieu, 35042 Rennes, France
S
* Supporting Information
ABSTRACT: Changing the N-substituents of a methylene-linked bis-NHC
ligand from n-butyl to bulky mesityl shifts ligand coordination from normal/
normal to normal/abnormal mode. The mesityl wingtip groups afford
[RuII(MesNHC(CH2)NHCMes)(MesNHC(CH2)aNHCMes)(CH3CN)2][PF6]2
(1), in which one of the ligands exhibits mixed C2/C4 binding to the same
metal, while the second ligand utilizes C2/C2 carbons for metal coordination.
On the contrary, the n-butyl analogue leads to metal oxidation, affording a
RuIII complex [Ru(nBuNHC(CH2)NHCnBu)2Cl2][PF6] (2) upon crystalliza-
tion in air, where both ligands show normal C2/C2 coordination. Thus, the
resulting complexes exhibit different structural and electronic characteristics,
which are further reflected in their catalytic responses. The catalytic utilities
of both compounds toward carboxylic acid addition onto terminal alkyne are
evaluated in this work. The abnormally bound 1 shows higher activity and
better selectivity compared to all-normal counterpart 2.
C4-coordination taken place.8b We have examined the effects of
the size and the electronic character of N-substituents of a
NHC−CH2−NHC ligand on the resulting metal complexes. A
methylene-bridged bis-NHC ligand L1 (Scheme 1) with mesityl
INTRODUCTION
■
Metal-NHC compounds have emerged as effective catalysts for
a wide range of reactions.1 Typically, a metal binds NHC
through the C2 atom of the heterocycle. A ligand that utilizes
the backbone C4 (or C5) carbon atom for metal binding is
characterized as abnormal NHC (aNHC).2 Although the
relative abundance of metal-aNHC compounds is less than
their NHC counterparts, various synthetic protocols are being
developed for their targeted synthesis, which include the
blocking of the C2 carbon,3 varying the bulk of wingtip groups,4
the choice of synthetic methods,5 and the identity of the
anions.6 Experimental and computational studies have shown
that C4-bound NHCs are stronger donors than their C2-bound
analogues.7 Metal-aNHC compounds are reported to exhibit
superior catalytic activity compared to their normal counterpart
and promote certain reactions that are not accessible by C2-
bound metal-NHC compounds.8
Bis-NHC ligands form a special class of compounds that
exhibit topological variation and diverse reactivity.9 Steric
congestion imposed by bulky groups at the wingtip imidazole
nitrogens favors the abnormal binding even when C2 is free.10
Bis-NHC units with rigid phenyl or pyridyl spacers have
afforded metal complexes featuring mixed normal (C2) and
abnormal (C4) coordination of the ligand to the same metal,11
whereas tetracarbene metal complexes made of two methylene-
spaced bis-NHC ligands show all-normal (C2) ligand
coordination.12 Only when C2 is blocked has the abnormal
Scheme 1. Schematic Diagram of the Ligands Used
wings exhibits mixed normal/abnormal coordination to a RuII
center. Sterically less imposing n-butyl wingtip groups for
ligand L2 provide a RuIII complex that shows all-normal metal
coordination. The catalytic responses of normal/abnormal and
all-normal RuII/III-NHC complexes toward carboxylic acid
addition to terminal alkynes are discussed in this work.
Received: May 29, 2012
Published: July 20, 2012
© 2012 American Chemical Society
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RESULTS AND DISCUSSION
■
Treatment of bis(1,1′-mesitylimidazolium)-3,3′-methylene diio-
dide with tBuOK in THF and subsequent addition of
[Ru(PPh3)3Cl2], followed by the addition of KPF6 in
CH3CN, afforded [Ru(MesNHC(CH2)NHCMes)(MesNHC-
(CH2)aNHCMes)(CH3CN)2][PF6]2 (1) in high yield (82%).
1
The H NMR spectrum of 1 in acetonitrile-d3 confirms the
composition of the complex, consisting of two bis-NHC ligands
(Figure S2). Four doublets observed at δ 6.05, 5.77, 5.21, and
4.85 ppm with the same coupling constants (JHH = 13.2 Hz) are
assigned for four diastereotopic protons belonging to two
methylene groups linking two imidazolylidene rings. A
downfield singlet at δ 8.48 ppm is indicative of a C2 proton
of the NHC ring bifurcated between two electronegative
nitrogen atoms. Eight signals are expected for backbone
imidazole protons (four each for C4 and C5); however, only
seven are observed. Among those, six appear as doublets at δ
7.41, 7.40, 7.38, 6.84, 6.72, and 6.65 ppm with coupling
3
Figure 2. ORTEP diagram (30% probability thermal ellipsoids) of the
dicationic unit in 1 with important atoms labeled. Hydrogen atoms are
omitted for the sake of clarity. Selected bond distances (Å) and angles
(deg): Ru1−C1 2.090(5), Ru1−C2 2.030(5), Ru1−C3 2.089(5),
Ru1−C11 2.044(4), Ru1−N9 2.077(4), Ru1−N10 2.077(4), C2−
Ru1−C1 84.5(2), C2−Ru1−C11 92.6 (1), C2−Ru1−C3 92.4(2),
C11−Ru1−C3 83.9(2), C11−Ru1−C1 89.83(19), C2−Ru1−C11
92.60(19), C2−Ru1−C1 84.5(2), N9−Ru1−N10 85.3(1), N9−
Ru1−C1 93.11(18), N10−Ru1−C1 91.59(18), N9−Ru1−C3
93.57(18), N10−Ru1−C3 91.49(18).
constant J (HH) = 2 Hz, and the remaining one appears as a
singlet at δ 5.98 ppm. A shift difference of δ 2.50 ppm between
two singlet ring protons (C2 and C4) suggests an abnormal
binding of one of the L1 ligands. The observed shift differences
between C4 and C5 protons for a normal NHC heterocycle are
less than 1 ppm. The eight aromatic mesityl protons appear in
the range δ 6.69−7.04 ppm. The different NHC coordination
motifs are also reflected in the 13C NMR spectrum (Figure S1).
Three distinct signals at δ 190.8, 189.8, and 188.6 ppm are
assigned for the normal C2 carbene carbons, whereas the
abnormal C4 carbene carbon appears upfield at δ 162.4 ppm
(Figure 1). The ESI-MS exhibits signals at m/z 1097 (25%) and
steric congestion on the resulting complex. The C−C distances
in normal- and abnormal-bound imidazole rings are similar
(1.351(8), 1.336 (8), 1.339(8) Å for C2- and 1.363(7) Å for C4-
bound NHC units). The chelate angles imposed by two NHC
ligands at Ru are 84.5(2)° and 83.9(2)°. The N9−Ru1−N10
angle is 85.4(1)°, formed by two acetonitriles.
− +
1056 (35%), attributed to [{M}2+ + PF6 ] and [{M −
CH3CN}2+ + PF6−]+, respectively, where {M} =
[RuL1 (CH3CN)2] (Figure S3).
2
In order to assess the influence of wingtip groups on the
ligand coordination, we employed the n-butyl analogue L2. A
synthetic procedure similar to 1, followed by crystallization in
air, afforded the RuIII complex [Ru(nBuNHC(CH2)-
NHCnBu)2Cl2][PF6] (2). Our repeated attempts to identify a
product under strict anaerobic conditions remain thus far
unsuccessful. Analytically pure product 2 could be obtained
only upon crystallization in air. Presumably, the greater electron
Figure 1. 13C NMR signals for three normal and one abnormal
carbene carbon for compound 1.
n
The molecular structure of 1 is determined by single-crystal
X-ray analysis. The geometry around the Ru center can be
rationalized as distorted octahedral, comprising of two L1
ligands coordinating four positions. The remaining two sites
are occupied by two mutually cis acetonitrile molecules. The X-
ray structure unambiguously confirms that one of the ligands
binds Ru through the usual imidazole C2 carbon atoms,
whereas the second ligand adopts a mixed normal and
abnormal coordination to the same metal center (Figure 2).
The two mutually trans NHC units display slightly longer Ru−
C distances (Ru1−C1/Ru1−C3 = 2.090(5)/2.089(5) Å)
compared to the cis pairs (Ru1−C2/Ru1−C11 = 2.030(5)/
2.044(4) Å). Two wingtip mesityl groups attached to two trans
imidazolylidene rings are oriented parallel to each other with a
centroid distance of 6.173 Å (Figure S4). Both of these
imidazole rings exhibit normal C2 coordination to the metal.
The other two mesityl groups are disposed away from each
other (Cipso···Cipso = 8.656 Å) (Figure S4). This is the direct
consequence of the abnormal C4 coordination of one of the
NHC units. An all-normal situation would have imposed severe
density imparted by Bu substituents makes the metal center
vulnerable toward oxidation. The NMR spectra exhibit very
broad signals, indicating the paramagnetic nature of the
compound. The X-ray structure, as shown in Figure 3, reveals
two chelate-bound ligands occupying four equatorial sites, and
two axial chlorides completing the distorted octahedral
geometry around the Ru. Both ligands exhibit normal
coordination modes involving C1, C2, C3, and C4 carbene
carbons. The Ru−C distances are in the range 2.077(7)−
2.116(8) Å. Two Ru−Cl distances are comparable. The bite
angles for the two L2 ligands are 83.2(3)° and 82.8(3)°. The
methylene carbons are disposed in the opposite direction for
double RuC3N2 boats (Figure S5). This essentially places the
wingtip n-butyl groups to either side of the equatorial plane
comprising Ru and carbene carbons.
Enol esters are mild acylating agents, important intermedi-
ates for carbon−carbon and carbon−heteroatom bond
formation, and are useful industrial monomers for the
preparation of several polymers and copolymers. Several Ru-
based compounds with varied nuclearity and metal-oxidation
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catalyze the addition reactions of carboxylic acid to alkyne. It
appears that the metal valency is impervious to the catalyst
activity.13 While most of the Ru catalysts provided predom-
inantly Markovnikov (M) addition products,14 Dixneuf et al.
pioneered the [Ru(η3-allyl)2(diphosphine)] systems to reverse
the regioselectivity, affording exclusively the anti-Markovnikov
(AM) products with Z-selectivity.13b,15 It is now widely
recognized that the origin of the regioselectivity of a catalyst
lies in its ability to stabilize different metal-alkyne adducts. A π-
alkyne coordination gives M products, whereas the rearranged
vinylidene intermediate affords AM products on addition of a
carboxylate anion.13d Tertiary phosphines have been the most
favored ligands for promoting the addition reaction. We have
examined the catalytic utility of RuII/III-NHC compounds for
carboxylic acid addition to terminal alkynes.
Initial exploratory experiments using equimolar (1 mmol)
amounts of phenylacetylene (1a) and benzoic acid (2a) with
catalyst 1 (0.05 mmol) inside a closed Schlenk tube at 60 °C in
THF afforded very low conversion (<5%) after 6 h. Switching
the solvent system to CH2Cl2 or dichloroethane at respective
boiling points improved the yields only marginally (10−15%).
Turning to toluene as reaction solvent significantly enhanced
the conversion, reaching 60% at 100 °C after 24 h. Addition of
a small quantity of CH2Cl2 (toluene/CH2Cl2 = 4:1) improved
the catalyst solubility and thus afforded the best results. Gradual
increase in the reaction time resulted in higher conversion (t: 6,
12, 16, 24 h; conversion: 40, 57, 78, 100%). No significant
increase in the activity of the catalyst 1 was observed using
Figure 3. ORTEP diagram (30% probability thermal ellipsoids) of the
cationic unit in 2 with important atoms labeled. Hydrogen atoms are
omitted for the sake of clarity. Selected bond distances (Å) and angles
(deg): Ru1−C1 2.104(7), Ru1−C2 2.107(7), Ru1−C3 2.116(8),
Ru1−C4 2.078(7), Ru1−Cl1 2.350(2), Ru1−Cl2 2.361(2), C4−Ru1−
C3 82.8(3), C1−Ru1−C2 83.2(3), C2−Ru1−C3 98.1(3), C4−Ru1−
C1 95.8(3), C1−Ru1−Cl1 87.6(2), C2−Ru1−Cl1 87.0(2), C3−Ru1−
Cl1 91.7(2), C4−Ru1−Cl1 92.2(3), C1−Ru1−Cl2 91.9(2), C2−
Ru1−Cl2 92.2(2), C3−Ru1−Cl2 88.9(2), C4−Ru1−Cl2 88.7(3),
Cl1−Ru1−Cl2 178.99(10), C1−Ru1−C3 178.4(3), C4−Ru1−C2
178.7(3).
states, for example, zerovalent Ru3(CO)12,13a metal−metal
singly bonded [RuI2(O2CH)(CO)2(PR3)2]2,13b [(p-cymene)-
RuIICl2]2/PR3,13c and [(bis-allyl)RuIVCl2]2,13d are reported to
a
Table 1. [Ru]-Catalyzed Addition of Carboxylic Acid to Terminal Alkyne
b
conversion
AM-Z/AM-E/M
entry
R1
R2
catalyst 1
catalyst 2
catalyst 1
catalyst 2
c
1
1a
1b
1c
1d
1e
1a
1g
1h
1i
2a
2a
2a
2a
2a
2e
2a
2a
2a
2a
2b
2c
2d
2f
100
95
100
89
28
40
52
40
45
66
85
90
94
82
82
80
97
91
84/6/10
84/12/4
79/21/−
94/6/−
50/50/−
70/30/−
61/39/−
79/21/−
63/37/−
50/50/−
100/−/−
100/−/−
100/−/−
100/−/−
76/24/−
68/32/−
75/25/−
60/40/−
60/40/−
100/−/−
75/25/−
2
74
58
60
30
3
4
5
88/12/−
100/−/−
100/−/−
100/−/−
100/−/−
100/−/−
79/21/−
84/16/−
81/14/5
80/20/−
84/16/−
85/7/8
c
6
77
7
77
68
75
42
8
9
10
11
12
13
14
15
16
17
18
1f
c
1a
1a
1a
1a
1a
1a
1k
1j
64
68
73
c
84
2g
2h
66
60
65
d
2a
96/4/−
2a
a
b
Acid/alkyne/catalyst: 1 mmol/1 mmol/0.02 mmol; 100 °C; 24 h; solvent: toluene/CH2Cl2 = 4/1 mL. Determined by GC analysis using n-
c
d
dodecane as an internal standard. 2−5% of alkyne dimerized products. Two equivalents.
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different types of base including NaOH, Na2CO3, and Et3N.
Reduction of the catalyst loading from 5 to 2 mol % did not
amend the product amount in the model reaction. Hence, we
explored the substrate scope for both catalysts under the
following optimized reaction conditions: alkyne/acid/catalyst =
1 mmol/1 mmol/0.02 mmol; solvent: toluene/CH2Cl2 = 4/1
mL; 100 °C, 24 h.
observed for trifluoroacetic acid. Catalyst 2 gave 100% Z-
selectivity compared to 85% for catalyst 1. 1,3-Diethynylben-
zene (1K) showed some interesting behavior. Addition of two
equivalents of benzoic acid afforded a double-addition product
with high conversion (97%) and excellent selectivity (96/4/0).
As in earlier cases, catalyst 2 showed lower activity (65%) and
poorer selectivity (75/25/0) (entry 17). Use of one equivalent
of benzoic acid gave exclusively the monoadduct product, and
no trace of bis-adduct was observed for both catalysts. Aliphatic
alkyne did not afford any product (entry 18).
Taking into account that internal alkynes do not show any
activity, together with the AM selectivity of the products, lead
us to conclude that the reaction proceeds through the
intermediacy of a Ru-vinylidene species. In general, catalyst 1
was found to be more reactive than 2 except for bulky
substrates. The apparent lack of reactivity toward bulky
substrates is attributed to the higher steric congestion around
the metal in 1. Intriguingly, fluorinated precursors provided
lower yields of 1. Addition of external bases such as NaOH,
NaOAc, or Na2CO3 in catalytic amounts did not alter the
conversion for either of the catalysts. This suggests that the
chlorides in catalyst 2 are probably not responsible for its lower
activity. Increased acidity of the carboxylic acid does not alter
the conversion by any significant amount. Catalyst 1, by
contrast to 2, favors anti-Markovnikov addition of carboxylic
acid to terminal alkynes except for trifluoroacetic acid.
Both catalysts were unresponsive toward internal alkynes but
showed excellent reactivity for terminal alkynes. Small amounts
(2−5%) of alkyne dimers were observed in a few cases only for
catalyst 2 (Table 1). Under the optimized reaction conditions,
catalyst 1 afforded 100% conversion with high selectivity (AM-
Z/AM-E/M = 84/6/10) for the model alkyne and acid
precursors 1a and 2a. For catalyst 2, lower conversion was
observed (91%) with no selectivity (50/50/0) (entry 1). The
presence of a p-methyl group on phenylacetylene (1b) leads to
slightly lower conversion (95%) for catalyst 1 with good Z-
selectivity (84%). Catalyst 2, on the other hand, gave lower
conversion (74%) and inferior selectivity (70:30) (entry 2).
Introduction of a p-methoxy group on phenylacetylene (1c)
afforded quantitative conversion (100%) for catalyst 1 but gave
considerably lower conversion (58%) for catalyst 2. Catalyst 1
showed better Z-selectivity (79/21/0) compared to catalyst 2
(61/39/0) (entry 3). The inclusion of −CF3 groups at the 3, 5
positions of the aryl ring of phenylacetylene (1d) diminished
the product conversion (89%) for catalyst 1 but gave excellent
selectivity (94/6/0). Again, catalyst 2 afforded lower
conversion (60%) and comparatively poor selectivity (79/21/
0) (entry 4). Introduction of a fluoro group on either substrate
shows some anomalous behavior. In the case of p-
fluorophenylacetylene and benzoic acid (entry 5), poor yields
were obtained for both catalysts (28% and 30% for 1 and 2,
respectively), together with better Z-selectivity (88/12/0) for
catalyst 1 than catalyst 2 (63/37/0). For the reaction between
phenylacetylene and p-fluorobenzoic acid (entry 6), catalyst 1
showed poor activity and afforded only 40% conversion with
100% Z-selectivity. For catalyst 2, a higher conversion (77%)
but poor selectivity (Z:E = 50:50) were observed. Bulky alkynes
(R1 = 6-methoxynaphthyl, mesityl, and anthracenyl) resulted in
lower yields for catalyst 1 compared to catalyst 2 by 25−30%
(entries 7−9). This is understandable since the metal ion in
catalyst 1 is sterically encumbered, whereas 2 is relatively more
accessible for bulky substrates, affording higher yields.
Interestingly, both catalysts afforded 100% Z-selectivity.
Lower yields were observed for 3-ethynylthiophene (entry
10) (66% and 42% for 1 and 2), which is attributed to the
catalyst poisoning by thiophene coordination to the metal.
Introduction of p-methoxy and p-methyl groups on the aryl ring
of benzoic acid lowered the conversions by 15% and 10% for
catalyst 1, respectively. For catalyst 2, the corresponding values
were 27% and 23% (entries 11 and 12). An electron-
withdrawing group (−CN) at the p-position of benzoic acid
did not alter the conversion or the selectivity significantly (94%
and 73% with AM-Z/AM-E/M ratios 81/14/5 and 75/25/0 for
catalysts 1 and 2, respectively) in comparison to electron-
donating groups (p-OMe and p-CH3) (entry 13). In the case of
trans-cinnamic acid (entry 14), both catalysts gave comparable
yields, but better Z-selectivity was observed for catalyst 1.
When aliphatic carboxylic acids (CH3COOH and CF3COOH)
are employed as substrates, catalyst 1 gave higher yields for
both cases compared to catalyst 2 (entries 15 and 16). In the
case of acetic acid, higher Z-selectivity (84%) was observed for
catalyst 1 than catalyst 2 (60%), but a reverse trend was
CONCLUSION
■
We have demonstrated steric control of the wingtip groups of a
NHC−CH2−NHC ligand over its metal-coordination modes.
Increasing the size of N-substituents from n-butyl to mesityl
shifts coordination from an all-normal to a mixed normal/
abnormal mode to the same metal. The mesityl wingtip groups
afford RuII complex 1, in which two bis-NHC ligands are cis-
oriented, and one of the ligands exhibits mixed C2/C4 binding,
while the second ligand utilizes C2/C2 carbons for metal
coordination. The n-butyl analogue leads to metal oxidation,
affording RuIII complex 2 upon crystallization in air. In this
complex, the NHC ligands are trans to each other, and both
show normal C2/C2 coordination. The different structural and
electronic characteristics are reflected in their catalytic
responses toward addition of carboxylic acids onto terminal
alkynes. In general, the C2/C4-bound RuII complex 1 performs
better than the C2/C2-bound RuIII complex 2 in terms of
activity and selectivity.
EXPERIMENTAL SECTION
■
General Procedures. All reactions with metal complexes were
carried out under an atmosphere of purified nitrogen using standard
Schlenk-vessel and vacuum-line techniques. NMR spectra were
obtained on a JEOL JNM-LA 500 MHz spectrometer. 1H NMR
chemical shifts were referenced to the residual hydrogen signal of the
deuterated solvents. The chemical shift is given as dimensionless δ
values and is frequency referenced relative to TMS for H and 13C
1
NMR spectroscopy. Elemental analyses were performed on a
Thermoquest EA1110 CHNS/O analyzer. The crystallized com-
pounds were powdered, washed several times with dry diethyl ether,
and dried under vacuum for at least 48 h prior to elemental analyses.
ESI-MS were recorded on a Waters Micromass Quattro Micro triple-
quadrupole mass spectrometer.
Materials. Solvents were dried by conventional methods, distilled
under nitrogen, and deoxygenated prior to use. RuCl3·xH2O was
purchased from Arora Matthey, India. KOtBu and KPF6 were
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purchased from Sigma-Aldrich. [Ru(PPh3)3Cl2]16 and ligands L1 and
L2 were synthesized according to the published procedures.17
Synthesis of 1. To a stirring suspension of bis(1,1′-mesitylimida-
zolium)-3,3′-methylenediiodide (0.051 g, 0.079 mmol) in 10 mL of
ASSOCIATED CONTENT
* Supporting Information
X-ray details, NMR spectra, and ESI-MS for compounds 1 and
2 are provided. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
t
THF was added 0.019 g (0.175 mmol) of BuOK at low temperature
(−78 °C). A THF solution (10 mL) of [Ru(PPh3)3Cl2] (0.038 g,
0.049 mmol) was added slowly over a period of 30 min. The reaction
mixture was then allowed to attain room temperature. Two equivalents
of KPF6 (0.019 g, 0.108 mmol) was added, and the solution was
refluxed for 4 h. The brown reaction mixture was filtered through a
small pad of Celite. The solvent was removed under vacuum, and the
resultant solid mass was redissolved in 1 mL of acetonitrile. Diethyl
ether was added to induce precipitation, and the solid precipitate was
filtered, washed with diethyl ether (5 mL, 3 times), and dried under
vacuum. X-ray quality crystals were grown by layering petroleum ether
onto a saturated dichloromethane solution of 1 inside an 8 mm o.d.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jbera@iitk.ac.in.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is financially supported by the Department of
Science and Technology (DST), India, and Indo-French
Centre for the Promotion of Advanced Research (IFCPAR).
J.K.B. thanks DST for the Swarnajayanti fellowship. S.S. and
B.S. thank CSIR, India and T.G. thanks UGC, India for
fellowships.
1
vacuum-sealed glass tube. Yield: 55 mg (82%). H NMR (500 MHz,
CD3CN, 292 K): δ 8.48 (s, 1H, Im), 7.43 (d, J = 2 Hz, 1H Im), 7.41
(d, J = 2 Hz, 1H, Im), 7.38 (d, J = 2 Hz, 1H, Im), 7.04 (s, 1H, mes-
CH), 6.99 (s, 1H, mes-CH), 6.91 (s, 1H, mes-CH), 6.87 (s, 1H, mes-
CH), 6.85 (d, J = 2 Hz, 1H, Im), 6.83 (s, 1H, mes-CH), 6.75 (s, 1H,
mes-CH), 6.73 (d, J = 2 Hz, 1H, Im), 6.69 (s, 1H, mes-CH), 6.66 (d, J
= 2 Hz, 1H, Im), 6.05 (d, J = 13 Hz, 1H, methylene-CH2), 5.98 (s, 1H,
Im), 5.78 (d, J = 13 Hz, 1H, methylene-CH2), 5.21 (d, J = 13 Hz, 1H,
methylene-CH2), 4.85 (d, J = 13 Hz, 1H, methylene-CH2), 2.29 (s,
3H, mes-CH3), 2.26 (s, 3H, mes-CH3), 2.22 (s, 3H, mes-CH3), 2.15
(s, 3H, mes-CH3), 2.08 (s, 3H, mes-CH3), 2.04 (s, 3H, mes-CH3),
1.85 (s, 3H, mes-CH3), 1.84 (s, 3H, mes-CH3), 1.72 (s, 3H, mes-
CH3), 1.52 (s, 3H, mes-CH3), 1.28 (s, 3H, mes-CH3), 1.21 (s, 3H,
mes-CH3) 13C NMR (125 MHz, CD3CN, 294 K): 190.8 (Ru-CN2),
189.8 (Ru-CN2), 188.6 (Ru-CN2), 162.4 (Ru-C(C)N), 141.1 (mes-
CR4), 140.1 (mes-CR4), 139.6 (mes-CR4), 139.4 (mes-CR4), 138.7
(mes-CR4), 137.6 (mes-CR4), 137.5 (mes-CR4), 137.4 (mes-CR4),
137.1 (mes-CR4), 136.7 (mes-CR4), 136.5 (mes-CR4), 136.4 (mes-
CR4), 135.8 (mes-CR4), 135.6 (mes-CR4), 135.4 (mes-CR4), 135.3
(mes-CR4), 132.9 (NCHN), 130.4 (mes-CH), 130.0 (2 mes-CH),
129.3 (mes-CH), 129.0 (mes-CH), 128.9 (mes-CH), 128.7 (2 mes-
CH) 126.3, 125.2 (CHIm), 125.1 (CHIm), 124.5 (CHIm), 124.2 (CHIm),
123.7 (CHIm), 123.6 (CHIm), 122.8 (CHIm), 64.1 (NCH2N), 63.1
(NCH2N), 21.0 (mes-CH3), 20.9 (mes-CH3), 20.8 (mes-CH3), 20.7
(mes-CH3), 18.8 (mes-CH3), 18.7 (mes-CH3), 18.2 (mes-CH3), 17.9
(mes-CH3), 17.6 (mes-CH3), 17.4 (mes-CH3), 17.0 (mes-CH3), 16.7
(mes-CH3). Anal. Calcd for C54H62N10RuP2F12: C, 52.21; H, 5.03; N,
11.28. Found: C, 52.41; H, 5.13; N, 11.48. UV−vis [CH3CN; λmax, nm
(ε, dm3·mol−1 cm−1)]: 284 (sh), 325 (4.37 × 104).
DEDICATION
■
Dedicated to Professor Sabyasachi Sarkar on the occasion of his
65th birthday.
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