Facile, near-quantitative, aqueous routes to nearly any [Cp*Ru(η6-arene)]Cl compound

Article abstract of DOI:10.1021/om0701773

Facile syntheses of water-soluble [Cp*Ru(arene)]Cl compounds exploiting the extraordinary properties of [Cp*Ru(μ₃-Cl)] ₄ in aqueous media are described. These methods produce no byproducts, involve little to no workup, and are applic

Full text of DOI:10.1021/om0701773

Organometallics 2007, 26, 3049-3053
3049
Notes
Facile, Near-Quantitative, Aqueous Routes to Nearly Any
[Cp*Ru(η6-arene)]Cl Compound
Robert M. Fairchild and K. Travis Holman*
Department of Chemistry, Georgetown UniVersity, Washington, DC, 20057
ReceiVed February 24, 2007
Scheme 1. Reaction Routes to [Cp*Ru(η6-arenes)]X
Summary: Facile syntheses of water-soluble [Cp*Ru(arene)]Cl
compounds exploiting the extraordinary properties of [Cp*Ru-
(µ3-Cl)]4 in aqueous media are described. These methods
produce no byproducts, inVolVe little to no workup, and are
applicable to almost any simple arene.
Introduction
[CpRM(η6-arene)]n+ (M ) FeII, RuII, IrIII, RhIII) compounds
are generally air-, water-, and heat-stable organometallic
sandwich compounds that have been extensively studied by
chemists of all disciplines.1-3 The positive charge and electron-
withdrawing nature of the [CpRM]n+ moieties enhances the
electrophilicity of arenes and activates them toward a variety
of synthetically useful organic transformations, most notably
nucleophilic additions and substitutions, benzylic deprotonation,
and Pd-catalyzed cross-coupling reactions.2-4 Recently, much
attention has focused on [CpRuII(arene)]+ and [Cp*RuII(arene)]+
compounds due to their (i) broad accessibility relative to their
Fe analogues, (ii) low cost relative to their IrIII/RhIII analogues,
and (iii) ease of arene recovery (typically via UV irradiation).5
Indeed, [CpRRu(arene)]+ compounds have shown promise in
natural product synthesis,6 in radioisotopic labeling of biomol-
ecules,7 in crystal engineering,8 as charge-transfer materials,9
and as supramolecular anion receptors.10Moreover, [CpRRu-
(arene)]+ compounds can serve as precursors to [CpRRu]+
species that are known to catalyze a variety of organic
transformations, many of which are C-C bond forming reac-
tions.11 It is therefore important to optimize protocols for the
synthesis of [CpRRu(arenes)]+.12
The arenophilic nature of the [Cp*Ru]+ fragment is well
documented, and thus several procedures exist for the synthesis
of simple [Cp*Ru(arene)]+ compounds. The most popular
procedures (Scheme 1) employ putative or well-defined [Cp*Ru-
(solvent)3]+ species, available via UV irradiation of [Cp*Ru-
(benzene)]+ (route A),5,13 halide abstraction from [Cp*RuII(µ3-
Cl)]4 (1) (route B),8 or zinc reduction of [Cp*RuIIICl2]2 (route
C)14,15 in the appropriate solvents. An alternative route involves
the two-step synthesis of the alkoxy-coordinated [Cp*Ru(OR)]2
(route D),16,17 which, in the presence of a proton donor, metalates
arenes. Also reported is a one-pot synthesis of [Cp*Ru(arene)]+
compounds via direct reaction of RuCl3 with Cp*H and Zn in
ethanol (Scheme 1, route E).18,19 Though these methods are
generally quite useful, each has its relative shortcomings and
there remains room for improvement. Some of these shortcom-
ings include the use of toxic or expensive Sn or Ag reagents
(routes A and B, respectively), subquantitative (routes A-D)
* To whom correspondence should be addressed. E-mail: kth7@
georgetown.edu. Tel: +1-202-687-4027. Fax: +1-202-687-6209.
(1) (a) Holman, K. T.; Halihan, M. M.; Jurisson, S. S.; Atwood, J. L.;
Burkhalter, R. S.; Mitchell, A. R.; Steed, J. W. J. Am. Chem. Soc. 1996,
118, 9567-9576. (b) Atwood, J. L.; Holman, K. T.; Steed, J. W. Chem.
Commun. 2006, 12, 1401-1407.
(2) Astruc, D. Top. Curr. Chem. 1992, 160, 47-95.
(3) Pigge, F. C.; Coniglio, J. J. Curr. Org. Chem. 2001, 5, 757-784.
(4) Harre, K.; Enkelmann, V.; Schulze, M.; Bunz, U. H. F. Chem. Ber.
1996, 129, 1323-1325.
(11) Trost, B. M.; Frederiksen, M. U.; Rudd, M. T. Angew. Chem., Int.
Ed. 2005, 44, 6630-6666.
(12) Trost, B. M.; Older, C. M. Organometallics 2002, 21, 2544-2546.
(13) Zelonka, R. A.; Baird, M. C. J. Organomet. Chem. 1972, 44, 383.
(14) Chaudret, B.; Jalon, F. A. J. Chem. Soc., Chem. Commun. 1988,
711-713.
(5) Schrenk, J. L.; McNair, A. M.; McCormick, F. B.; Mann, K. R. Inorg.
Chem. 1986, 25, 3501-3504.
(6) Pearson, A. J.; Heo, J.-N. Org. Lett. 2000, 2, 2987-2990 and
(15) Chaudret, B.; Jalon, F.; Perez-Manrique, M. New J. Chem. 1990,
14, 331-338.
references therein.
(7) Leone-Stumpf, D.; Lindel, T. Eur. J. Org. Chem. 2003, 1853-1858.
(8) Fagan, P. J.; Ward, M. D.; Calabrese, J. C. J. Am. Chem. Soc. 1989,
111, 1698-1719.
(16) He, X. D.; Chaudret, B.; Dahan, F.; Huang, Y. S. Organometallics
1991, 10, 970-979.
(17) Koelle, U.; Kossakowski, J.; Boese, R. J. Organomet. Chem. 1989,
378, 449.
(9) Ward, M. D.; Fagan, P. J.; Calabrese, J. C.; Johnson, D. C. J. Am.
Chem. Soc. 1989, 111, 1719-1732.
(18) Evju, J. K.; Mann, K. R. Organometallics 2002, 21, 993-996.
(19) Schmid, A.; Piotrowski, H.; Lindel, T. Eur. J. Inorg. Chem. 2003,
2255-2263.
(10) Fairchild, R. M.; Holman, K. T. J. Am. Chem. Soc. 2005, 127,
16364-16365.
10.1021/om0701773 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/03/2007

3050 Organometallics, Vol. 26, No. 12, 2007
Notes
Scheme 2. Three Methods to [Cp*Ru(η6-arenes)]Cl
Table 1. Microwave-Assisted Metalation of Arenes with 1
in H2Oa
or even low (route E) yields, and the need for organic solvents
(routes A-D), revealing an incompatibility with many biomol-
ecules (e.g., proteins). As with any reaction, the ideal protocol
would employ simple or mild reaction conditions, proceed in
aqueous solution, give quantitative yields, produce no byprod-
ucts, involve little to no workup, and be widely applicable. We
report herein three general methods for [Cp*Ru(arene)]+
synthesis that embody, as much as possible, the aforementioned
principles (Scheme 2). These methods are not grossly different
from the approaches described above (routes B-D) but, rather,
exploit the extraordinary properties of 1, or the chloride salt of
[Cp*Ru(solvent)3]+, in aqueous (or mostly aqueous) media,
affording water-soluble [Cp*Ru(η6-arene)]Cl compounds in
near-quantitative yields. To our knowledge, the only other report
of aqueous [CpRRu(arene)]+ synthesis exploits a water solubi-
lizing, amino-derivatized Cp ligand that necessitates an extensive
synthesis.20
Results and Discussion
Method I. With the goal of optimizing protocols for the
synthesis of [Cp*Ru(arenes)]+, we discovered that the readily
available21 1 reacts directly with arenes in pure, anaerobic water
at elevated temperatures, without the need for chloride abstrac-
tion. The procedure is fast, extremely convenient, and essentially
quantitative, giving water-soluble [Cp*Ru(η6-arene)]Cl com
poundsseven for arenes that are insoluble in water. The typical
reaction (method I) involves combination of 1 and the chosen
arene (8:1 arene-Ru) in degassed H2O, followed by microwave
irradiation in a sealed vessel (0-50 W to maintain ca. 130 °C)
for ca. 10 min. The dark, brick red color of 1 serves as a con-
venient indicator of reaction progress, affording near-colorless
solutions by completion. For most arenes, 1 reacts cleanly and
completely, resulting in solutions that contain only the desired
product, excess unreacted arene, and water. Typically, the excess
arene can be removed under reduced pressure or by trituration
of the crude salt in organic solvent, yielding pure product in
near-quantitative yields. It is important to point out that this
protocol is an aqueous relative of the method used by Chaudret
and co-workers (route C),14,15 wherein “Zn-reduced solutions”
of [Cp*RuIIICl2]2 in ethanol, acetone, THF, or tolueneswhich
are, in effect, solutions of residual ZnCl2 and 1 (or [Cp*Ru-
(solvent)3]Cl)swere used to metalate arenes, with the resulting
[Cp*Ru(arenes)]+ compounds typically being isolated as their
[PF6]- salts. Notably, these researchers have expressed concern
about the scalability of their reaction due to “deposition of the
a Reaction mixtures were heated at 130 °C (0-50 W) for 10-30 min
with 8:1 arene-Ru in degassed H2O. b The product also contained 5%
[Cp*OHRu(benzene)]Cl. c The product also contained 19% [Cp*OHRu
(bromobenzene)]Cl and 17% 2. d The product also contained 14%
[Cp*OHRu(iodobenzene)]Cl. e Isolated as a zwitterion. f Reactions resulted
in >99% spectroscopic yield, remaining product lost in workup. g The
product also contained 40% [Cp*Ru(phenylmethanediol)]Cl and 8%
[Cp*Ru((4-(hydroxymethyl)phenyl)methanol)]Cl. h The product also con-
tained 4% [Cp*OHRu(naphthalene)]Cl. i Coordination occurs at the car-
bocyclic ring. j The product also contained 66% 12b.
ruthenium complex on zinc”22 and have abandoned the proce-
dure for the synthesis of some [Cp*Ru(arenes)]+. Additionally,
direct reaction of 1 with neat arene solvents (e.g., toluene15 and
hexamethylbenzene23) has also been reported previously, but
the reaction rates are known to be extremely slow, give low
yields, and are not amenable to a wide variety of arenes.
To explore the breadth of method I, a variety of arenes were
subjected to this protocol and the outcomes are highlighted in
Table 1. All compounds in this paper were isolated as their
chloride salts, with the exception of the zwitterionic 13, and
were characterized by 1H and 13C NMR, IR, ESI-MS, and, for
(20) Grotjahn, D. B.; Joubran, C.; Combs, D.; Brune, D. C. J. Am. Chem.
Soc. 1998, 120, 11814-11815.
(21) The synthesis of 1 is straightforward and high yielding (ca. 80%
overall from RuCl3‚xH2O, Scheme 1). Moreover, unlike its precursor,
[Cp*RuIIICl2]2, 1 can be made in bulk and stored under nitrogen for
prolonged periods of time.8
(22) Chaudret, B.; He, X. D.; Huang, Y. S. J. Chem. Soc., Chem.
Commun. 1989, 1844-1846.
(23) Koelle, U.; Kossakowski, J. J. Chem. Soc., Chem. Commun. 1988,
549-551.

Notes
Organometallics, Vol. 26, No. 12, 2007 3051
8 and 12b, single-crystal X-ray diffraction24 (see the Supporting
Information). The cations of 8, 12b, 20, and (()-24 have not
been previously reported.
Table 2. Microwave-Assisted Metalation of Arenes by 1 at
1:1 Arene-Ru Ratiosa
arene
benzene
Cp*Ru(arene)Cl
yield (%)
Generally, method I tolerates most functional groups, includ-
ing alkyl, fluoro, chloro, hydroxyl, amino, methoxy, vinyl,
acetyl, carboxyl, and sulfonate. The three aryl amino acids (()-
phenylalanine, (()-tyrosine, and (()-tryptophan reacted quan-
2
3
>95b
>99
>99
>99
>99
>99
97
ethylbenzene
chlorobenzene
phenol
benzoic acid
(()-tryptophan
(()-cryptophane-Ec
5
7
11
(()-16a,b
[(()-23⊂THF]Cl6
1
titatively according to H NMR spectroscopy, though removal
of the excess unreacted arenes required a Sephadex column and
lowered the isolated yields slightly. Notably, reaction with (()-
tryptophan gave a roughly equal mixture of the possible
diastereomeric products, (()-16a and (()-16b. Products 2-16,
19, and 20 are air, water, and heat stable, though 12a hydrolyzes
to 12b at elevated temperatures in water. Unsurprisingly,25 the
[Cp*Ru(arene)]+ compounds of the fused aromatics 17 and (()-
18 decompose slowly in warm solutions exposed to air, the
former being qualitatively more stable. Indeed, even as a solid,
(()-18 decomposes slowly in air, marked by a gradual darkening
of the material. As expected, quinoline is metalated exclusively
at the carbocylic ring, and we were unable to synthesize [Cp*Ru-
(η6-pyridine)]Cl (22) by method I (an alternative methodology
proved successful; Vide infra). The more sensitive bromo- and
iodo-substituted arenes gave moderate yields of 19 (64%) and
20 (86%) along with significant amounts of their respective
Cp*OH-substituted impurity.26 Reaction with bromobenzene
additionally resulted in 2 (17%), an apparent product of dispro-
portionation. Reaction with benzonitrile gave primarily the
hydrolysis product 12b (66%) and only 33% of 12a. Metalation
of benzaldehyde gave 21 (52%) along with two additional com-
plexes that we tentatively assign as [Cp*Ru(phenylmethanediol)]-
Cl (40%) and [Cp*Ru((4-(hydroxymethyl)phenyl)methanol)]Cl
(8%) by ESI-MS and 1H NMR (see the Supporting Information).
We note that method I can also be performed thermally,
without the need for microwave irradiation. Indeed, similar
results were obtained when identical reactions were carried out
in a sealed flask that was heated in an oil bath at 115 °C.
Reactions times, however, ranged from 1 to 3 days and the yields
tended to be slightly lower due to slow degradation of 1 under
these conditions (see the Supporting Information).
Method II. Although method I is efficient at high arene:Ru
ratios, 1:1 stoichiometric reactions proceed very slowly or do
not proceed at all. The reaction of 1 with (()-phenylalanine at
a 1:1 ratio of arene to Ru went to less than 20% completion
after microwave irradiation at 130 °C for 1 h. To facilitate
reactions at stoichiometric arene to Ru ratios, method II employs
2:1 water-THF as the reaction solvent, thus increasing the
solubility of both 1 and the arenes in the reaction solvent. The
ability to conduct stoichiometric metalations is advantageous
for arenes that (i) are valuable (e.g., the products of multistep
syntheses), (ii) are to be multiply metalated (e.g., polyaromatic
hydrocarbons), or (iii) are difficult to separate from their
resulting [Cp*Ru(arene)]Cl products (e.g., amino acids).
Method II reactionssidentical to method I, but employing
1:1 ratios of arene to Ru and 2:1 H2O-THF as the solvents
a Reaction mixtures were heated at 130 °C (0-50 W) for 15 min with
28 µmol of 1 and 0.11 mmol of arene (1:1 arene-Ru) in 3 mL of H2O and
1.5 mL of THF. b With an additional 5% [Cp*OHRu(benzene)]Cl impurity.
c Heated at 135 °C (0-100 W) for 30 min with 10.7 µmol of (()-
cryptophane E and 18.7 µmol of 1 (6:7 arene-Ru) in 2 mL of H2O and 1
mL of THF, giving exclusively hexametalated [(Cp*Ru)6((()-cryptophane-
E)⊂THF]Cl6.
Table 3. Room-Temperature Metalation of Arenesa
arene
Cp*Ru(arene)Cl
yield (%)
phenol
7
13b
(()-16a,b
(()-18
12a
>99
>99
98
>99
>99
97
toluenesulfonic acid
(()-tryptophan
(()-quinoline
benzonitrile
pyridine
22
(1R,2S)-(-)-N-methylephedrine
(()-24
>99
a Reactions were performed by dissolving 28 µmol of 1 in 500 µL of
CH3CN (heated and then cooled to ca. 25 °C), followed by the addition of
a solution of 0.11 mmol of arene in 8 mL of H2O (ca. 25 °C); this mixture
was sealed under nitrogen and reacted overnight. b Isolated as a zwitterion.
generally proceed quantitatively in 15-30 min (Table 2).
Workup involves merely the removal of the solvent. Thus, the
diastereomeric mixture (()-16a,b is isolated in quantitative
yield, without the need to remove excess nonmetalated (()-
tryptophan. To assess the utility of method II for metalating
polyaromatics, the supramolecular host (()-cryptophane-E was
subjected to a similar protocol with only a slight excess (6:7
arene-Ru) of 1. (()-Cryptophane-E is a molecular “container”
with six alkoxy-substituted aryl moieties per molecule, and its
hexametalation has previously been reported by us via route B
(78% yield).10 Under conditions of method II, (()-cryptophane-
E is hexametalated cleanly, giving [(Cp*Ru)6((()-cryptophane-
E⊂THF)]Cl6 ([(()-23⊂THF]Cl6) in 97% yield. Conveniently,
excess unreacted/decomposed 1 precipitates from the solution
after exposure to air and is easily removed by filtration.
Method III. Though microwave reactions provide a conve-
nient method to rapidly metalate most simple arenes, the meta-
lation of water-soluble, heat-sensitive arenes (biomolecules etc.)
necessitates stoichiometric reaction at or near room temperature.
This can be achieved by first dissolving 1 in minimal amounts
of CH3CN, presumably forming the water-soluble [Cp*Ru(CH3-
CN)3]Cl, followed by addition of an aqueous solution of the
arene such that the ratio of H2O to CH3CN is roughly 16:1
(method III). As with methods I and II, the formation of
[Cp*Ru(η6-arene)]Cl products is near-quantitative, though reac-
tion times are considerably longer (ca. 8-20 h) under stoichio-
metric conditions (Table 3). Again, reaction progress can be
conveniently followed by a gradual change of the solution color
from yellow to near-colorless. Again also, the workup involves
only the removal of solvent. Notably, under the mild conditions
of method III, reaction with benzonitrile affords pure 12a with
no trace of hydrolysis product 12b (appears in 66% yield by
method I). This result clearly demonstrates the effectiveness of
this procedure for the mild, near-quantitative [Cp*Ru]+ func-
tionalization of water-soluble arenes of questionable thermal
stability. Remarkably, method III also proved highly useful for
the η6 metalation of heterocyclics such as quinoline and pyridine,
(24) CCDC 634128 and 634129 contain supplementary crystallographic
data for 8 and 12b. These data can be obtained online free of charge (or
from the Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, U.K., fax (+44) 1223-336-033, or deposit@ccdc.cam.ac.uk).
(25) McNair, A. M.; Mann, K. R. Inorg. Chem. 1986, 25, 2519-2527.
(26) The impurities, [Cp*OHRu(η6-arene)]Cl (Cp*OH ) η5-1-(hydroxym-
ethyl)-2,3,4,5-tetramethylcyclopentadienyl anion), found in the synthesis
of 2, 17, 19, and 20 are analogous to the “Cp*OMe” impurity described by
Lindel and coworkers7 in their one-step methanolic synthesis of [Cp*Ru-
(arene)]+ compounds (Scheme 1, route D). Lindel’s proposed explanation
for the occurrence of “Cp*OMe” can similarly explain the observation of
Cp*OH species here.

3052 Organometallics, Vol. 26, No. 12, 2007
Notes
Spectrum One FT-IR spectrometer fitted with a Pike Technologies
MIRacle Single Reflection ATR adapter for solid sample analysis.
ESI-MS data was obtained on a JEOL AccuTOF instrument at the
University of Maryland. Elemental analyses were carried out on a
Perkin-Elmer PE2400 microanalyzer at Georgetown University.
Synthetic Methods. Complete synthetic and spectroscopic details
for all compounds can be found in the Supporting Information.
Reported herein are the general protocols for methods I-III, along
with one specific example for each method.
Method I: Microwave Reaction of 1 with Arenes (8:1 Arene-
Ru). Arene (0.88 mmol, 8 equiv), 1 (30 mg, 28 µmol, 1 equiv of
Ru), and 8 mL of H2O were combined in a 10 mL glass microwave
reaction vessel fitted with a stir bar. The vessel was sealed and
reacted at 50 W until the desired temperature was reached and was
thereafter maintained automatically via wattage regulation (usually
ca. 130 °C and 10 min). The resulting solution was evaporated under
reduced pressure, extracted/triturated with toluene or appropriate
solvent, and subsequently dried to give the desired [Cp*Ru(η6-
arene)]Cl product.
giving both (()-18 and 22 in near-quantitative yield. The im-
provement afforded by this protocol in the synthesis of 22 is a
striking example of the power of this aqueous methodology that
merits additional comment. Chaudret et al. have previously syn-
thesized 22 by route C, but it was impure and was obtained in
only ∼46% yield.15 The metalation of pyridine is dependent
on the interconversion between η1 and η6 coordination to the
1
[Cp*Ru]+ moiety. Notably, H NMR of the aqueous reaction
mixture (16:1 H2O-CH3CN, method III) of [Cp*Ru(CH3CN)3]-
Cl and a stoichiometric amount of pyridine after ca. 8 h revealed
no trace of 22 but significant formation of the η1 complex,
presumably [Cp*Ru(η1-pyridine)(CH3CN)2]Cl. Interestingly, the
formation of 22 requires removal of CH3CN from the reaction
mixture, resulting in quantitative formation in the complete ab-
sence of CH3CN. The failure of method I (8:1 arene-Ru) to
produce 22 is likely due to the excess of pyridine, which
presumably drives the equilibrium exclusively to the η1-
coordinated species.
Finally, it should be noted that a logical extension of the
methods presented herein requires a protocol for the mild,
stoichiometric metalation of water-insoluble arenes (e.g., bro-
mobenzene, which was not quantitatively metalated by method
I). It seems clear that direct reaction of 1 with arenes in weakly
coordinating organic solvents (e.g., THF) would work well for
the mild preparation of many such [Cp*Ru(arene)]Cl com-
pounds. Indeed, Chaudret and co-workers have successfully
employed their “Zn-reduced solutions” for the high-yield
synthesis of [Cp*Ru(benzene)]Cl and [Cp*Ru(benzene)][PF6].
Direct reaction of arenes with 1, however, should greatly
facilitate workup by providing clean solutions with no possibility
for ZnII-containing byproducts.
[Cp*Ru(η6-ethylbenzene)]Cl (3). Ethylbenzene (110.0 µL, 0.896
mmol, 8 equiv) and 1 (30.4 mg, 28.0 µmol, 1 equiv of Ru) were
reacted according to method I. The colorless, clear solution was
evaporated under reduced pressure. The oily solid was then triturated
with hexane, yielding 3 as a white powder (42.1 mg, 99% yield).
IR (ATR, cm-1): 3422, 2952, 1615, 1523, 1450, 1038, 821, 503.
1H NMR (D2O, 300 MHz): δ 1.21 (3H, triplet, J 7.6, η6-CarCCH3),
1.93 (15H, singlet, η5-CCH3), 2.40 (2H, quartet, J 7.6, η6-CarCH2),
5.74 (5H, multiplet, η6-CHar). 13C NMR (D2O, CH3OH, 75.5
MHz): δ 107.12, 97.32, 88.48, 88.25, 87.55, 27.21, 15.68, 10.54.
ESI-MS (102Ru, m/z): 343.101 (C18H25Ru requires 343.100).
Thermal Reaction of 1 with Arenes (8:1 Arene-Ru). Arene
(0.88 mmol, 8 equiv), 1 (30 mg, 28 µmol, 1 equiv of Ru), and 10
mL of H2O and were combined in a Schlenk tube fitted with a stir
bar under nitrogen. The heterogeneous solution was subsequently
heated in an oil bath (ca. 115 °C) with intermittent sonication for
1-3 days (reaction completion determined by change from red to
colorless, correlating with the consumption of 1). Warning! Contents
under pressure. The reaction vessel was cooled (ca. 25 °C), and
the resulting [Cp*Ru(η6-arene)]Cl compounds were isolated using
the procedures outlined in method I.
Conclusion
In conclusion, we have described three facile, near-quantita-
tive, aqueous (or near-aqueous) routes to nearly any [Cp*Ru-
(arene)]Cl. Though several reasonable methods are currently
available for the synthesis of [Cp*Ru(arene)]+ compounds, the
clear facility, universality, and near-quantitative nature of the
aqueous methods reported here significantly expands the scope
of [Cp*Ru(arene)]+ chemistry. In particular, this chemistry
opens the door to aqueous applications of the water-soluble
chloride salts, compounds which have not been widely available
previously.
Method II: General Microwave Reaction of 1 with Arenes
(1:1 Arene-Ru). Arene (0.11 mmol, 1 equiv), 1 (30 mg, 28 µmol,
1 equiv of Ru), 3 mL of H2O, and 1.5 mL THF were combined,
reacted (ca. 15 min), and isolated using the procedures outlined in
method I.
[Cp*Ru(η6-benzoic acid)]Cl (11). Benzoic acid (12.9 mg, 0.106
mmol, 1 equiv) and 1 (28.7 mg, 26.5 µmol, 1 equiv of Ru) were
reacted according to method II. The clear solution was cooled to
room temperature, and the solvent was removed under reduced
pressure. The resulting solid was triturated with toluene to yield
11 as a pale green powder (41.3 mg, 99% yield). IR (ATR, cm-1):
Experimental Section
General Procedures. THF and CH3CN were obtained from
Fisher (Pittsburgh, PA), degassed with nitrogen, and used without
further purification. All arenes were obtained from Acros (Pitts-
burgh, PA) or Aldrich (Milwaukee, WI) and were used without
further purification. H2O was deionized, distilled, and degassed in
house. 18 and cryptophane-E27 were prepared according to previ-
ously reported literature procedures. All reactions were carried out
under a nitrogen atmosphere using standard Schlenk and/or glove-
box techniques. All microwave reactions were performed in a CEM
Discover microwave reactor using a 10 mL sealed glass microwave
reaction vessel fitted with a stir bar.
1
3377, 3074, 2571, 1718, 1632, 1381, 1220, 1039, 601. H NMR
(D2O, 300 MHz): δ 1.90 (15H, singlet, η5-CCH3), 6.00 (3H,
multiplet, η6-CHar), 6.32 (2H, multiplet, η6-CHar). 13C NMR (D2O,
CH3OH, 75.5 MHz): δ 126.14, 100.21, 98.18, 88.78, 88.35, 87.82,
9.85. ESI-MS (102Ru, m/z): 359.066 (C17H21O2Ru requires 359.059).
Method III: General Room-Temperature Reaction of 1 with
Arenes (1:1). A solution of 1 (30 mg, 0.11 mmol, 1 equiv) in 500
µL of CH3CN was heated until transparent and subsequently cooled
to ca. 25 °C. To this, a solution of arene (0.11 mmol, 1 equiv) in
8 mL of H2O was added and reacted overnight (ca. 25 °C). The
resulting [Cp*Ru(η6-arene)]Cl compounds were isolated using the
procedures outlined in method I.
1
Instrumentation. H (300.1 MHz) and 13C (75.5 MHz) NMR
were carried out on a Varian Unity Inova spectrometer. All NMR
spectra were collected at 25 °C unless otherwise noted and were
indirectly referenced using residual solvent signals as internal stan-
dards (references: 1H NMR, D2O, δ 4.79; 13C NMR, CH3OH in
D2O, δ 49.5). IR measurements were performed on a Perkin-Elmer
[Cp*Ru(η6-phenol)]Cl (7). Phenol (10.4 mg, 0.110 mmol, 1
equiv) and 1 (30.0 mg, 27.5 µmol, 1 equiv of Ru) were reacted
according to method III, above. The solvent was removed under
reduced pressure, giving 7 as an off-white powder (40.0 mg, 99%
(27) Canceill, J.; Collet, A. J. Chem. Soc., Chem. Commun. 1988, 582-
584.

Notes
Organometallics, Vol. 26, No. 12, 2007 3053
yield). IR (ATR, cm-1): 3387, 1651, 1437, 1260, 1240, 1040, 530.
1H NMR (D2O, 300 MHz): δ 1.93 (15H, singlet, η5-CCH3), 5.53
(1H, triplet, J ) 5.7 Hz, η6-CHar), 5.61 (2H, doublet, J ) 5.7 Hz,
η6-CHar), 5.70 (2H, triplet, J 5.7, η6-CHar). 13C NMR (D2O, CH3OH,
75.5 MHz): δ 129.62, 96.21, 86.33, 84.57, 77.39, 10.13. ESI-MS
Santacroce, Noel Whitaker, and the University of Maryland for
assistance and access to their ESI-mass spectrometer.
Supporting Information Available: Text, figures, and tables
giving complete experimental details, including individual synthe-
ses, spectroscopic data, and crystallographic data, and CIF files
giving crystallographic data for 12b‚H2O and 8‚H2O. This material
is available free of charge via the Internet at http://pubs.acs.org.
(
102Ru, m/z): 331.059 (C16H21ORu requires 331.064).
Acknowledgment. We are thankful for support by the
National Science Foundation (DMR-0349316) and the Ford
Foundation (predoctoral fellowship for R.M.F.). We thank Paul
OM0701773