"Piano-stool" complexes of ruthenium(II) designed with arenes and N-[2-(arylchalcogeno)ethyl]morpholines: Highly active catalysts for the oxidation of alcohols with N-methylmorpholine N-oxide, tert-butyl hydroperoxide and sodium periodate and oxychloride

Article abstract of DOI:10.1002/ejic.201000319

The reactions of [{(η⁶C₆H₆)RuCl(μ- Cl)}₂] and [{(η⁶-p-cymene)RuCl(μ,-Cl)}₂] with N-[2-(arylchalcogeno)ethyl]morpholines (L) (aryl = Ph/2-pyridyl for S, Ph for Se, 4-MeOC₆H_4<

Full text of DOI:10.1002/ejic.201000319

FULL PAPER
DOI: 10.1002/ejic.201000319
“Piano-Stool” Complexes of Ruthenium(II) Designed with Arenes and
N-[2-(Arylchalcogeno)ethyl]morpholines: Highly Active Catalysts for the
Oxidation of Alcohols with N-Methylmorpholine N-Oxide, tert-Butyl
Hydroperoxide and Sodium Periodate and Oxychloride
Pradhumn Singh[a] and Ajai K. Singh*[a]
Keywords: Alcohols / Chalcogens / Homogeneous catalysis / Oxidation / Ruthenium
The reactions of [{(η6-C6H6)RuCl(µ-Cl)}2] and [{(η6-p-cymene)-
RuCl(µ-Cl)}2] with N-[2-(arylchalcogeno)ethyl]morpholines
(L) (aryl = Ph/2-pyridyl for S, Ph for Se, 4-MeOC6H4 for Te)
and NH4PF6 result in “piano-stool” complexes of RuII of com-
that all the complexes undergo irreversible oxidation (E
=
½
0.290–0.586 V). All the ruthenium complexes have been ex-
plored for their catalytic activity in the oxidation of primary
and secondary alcohols with N-methylmorpholine N-oxide
(NMO), tBuOOH, NaOCl, and NaIO4 (TON values upto
9.8ϫ104). The efficiency of the catalytic oxidation reaction
decreases in the order TeϾSeϾS. The intermediate species
involved in the oxidation reactions appear to incorporate the
RuIV=O group.
position
[RuCl(η6-C6H6)(L)][PF6]/[RuCl(η6-p-cymene)(L)]-
[PF6], which give characteristic 1H, 13C{1H}, 77Se{1H}, and
125Te{1H} NMR spectra. Some of them have also been charac-
terized by X-ray crystallography [Ru–S, Ru–Se, and Ru–Te
bond lengths: 2.3815(12)/2.3742(14), 2.4837(14), and
2.6143(7) Å, respectively]. The cyclic voltammograms show
[RuCl2(carbene)(arene)], have been used in the catalytic syn-
thesis of furans.[7] Kharasch additions are catalyzed by
[RuCl2(η6-p-cymene)(PAr3)].[8] Demonceau and co-workers
recently reported the exceptional efficacy of [RuCl2(η6-p-
cymene)(PR3)] complexes as a catalyst precursor for the
ring-opening metathesis polymerization of low-strain cyclic
olefins.[9] Chiral cationic (η6-arene)(pyridylamino)rutheni-
um(II) complexes act as enantioselective catalysts in Diels–
Alder reactions with good exo/endo selectivity.[10] The half-
sandwich compounds of RuII show promising anticancer
activity.[11–15] Thiolate ligand oxygenation is believed to ac-
tivate cytotoxic half-sandwich [Ru(η6-arene)(en)(SR)]+
complexes towards DNA-binding.[16] (arene)RuII complexes
with pyrone-derived ligands are rendered active against can-
cer cells by the replacement of the coordinated (O,O) donor
with the (S,O) donor.[17] Hartinger and co-workers[18] have
reported that promising cytotoxic effects of water-soluble
dinuclear (arene)Ru complexes in human cancer cells can
be increased by increasing the spacer length between metal
centers. The interaction of [RuCl2(η6-p-cymene)(pta)], re-
ported to be an effective anticancer and antimetastatic
agent, with biological nucleophiles, important with respect
to the mechanism of action, has been studied.[19] Organo-
metallic (arene)ruthenium(II) complexes coordinated to
maltol-derived ligands have been prepared and their anti-
cancer activity against human tumor cell lines studied.[20]
Therrien and co-workers found that water-soluble (arene)-
ruthenium complexes containing pyridinethiolato ligands
show cytotoxicity towards ovarian cancer cells.[21] In vitro
Introduction
The current interest in “piano-stool” complexes of RuII
having an η6-benzene or η6-p-cymene unit stems from the
fact that some of them are known for their diverse catalytic
activities. Süss-Fink et al. carried out the hydrogenation of
benzene using a cluster with Ru(η6-arene) units.[1] (Arene)-
ruthenium complexes with salicyloxazolines are suitable as
asymmetric catalysts for Diels–Alder reactions.[2] The com-
pounds [Ru=C=C=CR2(L)(Cl)(arene)][PF6] (L = PCy3,
PiPr3) have been reported by Dixneuf and co-workers to be
excellent catalyst precursors for ring-closing olefin metathe-
sis.[3] The atom-transfer radical polymerization of methyl
methacrylate has been catalyzed by [RuCl2(η6-p-cy-
mene)(PCy3)].[4] Dixneuf and co-workers have reported that
the in situ generated catalyst from [RuCl2(η6-p-cymene)]2
and a pyrimidinium or benzimidazolium salt in the pres-
ence of Cs2CO3 selectively promotes the diarylation of 2-
pyridylbenzene with aryl bromides.[5] The acetate-assisted
C–H activation of 2-substituted pyridines with [RuCl2(η6-
p-cymene)]2 has been reported by Davies and co-workers.[6]
A
variety of neutral (carbene)ruthenium complexes,
[a] Department of Chemistry, Indian Institute of Technology
Delhi,
New Delhi 110016, India
Fax: +91-11-26581102
E-mail: aksingh@chemistry.iitd.ac.in
ajai57@hotmail.com
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000319.
View this journal online at
wileyonlinelibrary.com
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P. Singh, A. K. Singh
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studies by Dyson and co-workers have revealed that the
(3,5,6-bicyclophosphite-α--glucofuranoside)(η6-p-cymene)-
dihalogenidoruthenium(II) complex is the most cytotoxic
compound for human cancer cell lines.[22] Because morph-
oline derivatives are biologically active,[23–25] it is worth-
while gaining an understanding of the chemistry of half-
sandwich compounds that have such ligands. Therefore, the
ligands L1–L4 have been designed and their RuII complexes
with the (η6-benzene/η6-p-cymene) unit synthesized. Their
catalytic activity in the oxidation of alcohols with N-meth-
ylmorpholine N-oxide (NMO), tert-butyl hydroperoxide
(tBuOOH), sodium oxychloride (NaOCl), and sodium per-
iodate (NaIO4) have also been explored. The results of all
these investigations are presented in this paper.
Results and Discussion
Scheme 1 summarizes the syntheses of L1–L4 and their
“piano-stool”-type ruthenium(II) complexes. L1 was pre-
pared by a synthetic procedure different to that previously
reported; our synthetic procedure is easier and also gives a
better yield.[26] Furthermore, L1 is also commercially avail-
able. Similarly, the procedure described herein for the syn-
thesis of L4 by using a different workup procedure (diethyl
ether/water) resulted in a better yield than that reported
previously.[27,28] The molar conductance values in acetoni-
trile (see Exp. Sect.) indicates a 1:1 electrolyte nature of the
complexes 1–6, which are soluble in CH3OH, CH3CN,
CH2Cl2, and CHCl3. Their solutions in DMSO show signs
of decomposition within a few hours. The complexes 1, 3, 4,
and 6 were characterized by X-ray crystallography; crystals
suitable for X-ray diffraction could not be grown for 2 or
5. The ORTEP diagrams of 1, 3, 4, and 6 are given in Fig-
ures 1, 2, 3, and 4, respectively. There are inter- and intra-
molecular Cl···H and F···H interactions [2.630(8)–2.856(2)
and 2.308(9)–2.863(9) Å, respectively] in all crystals except
for 6 in which intermolecular Cl···H interactions are not
observed (see Figures S1–S7 and Table S3 in the Supporting
Information). The crystal packing appears to be one of the
reasons for these interactions, which are strongest in 1, in
which the chalcogen is sulfur, and weakest in 6, which has
tellurated morpholine as the ligand. The F···H interactions
in the case of 4 are shown in Figure 5.
Scheme 1. Synthesis of L1–L4 and their “piano-stool”-type RuII
complexes. (a) [{(η6-C6H6)RuCl(µ-Cl)}2], NH4PF6, MeOH, r.t.,
12 h; (b) [{(η6-p-cymene)RuCl(µ-Cl)}2], NH4PF6, MeOH, r.t., 15 h.
Figure 1. ORTEP diagram of the cation of 1 with ellipsoids at the
–
50% probability level. Hydrogen atoms and the PF6 anion have
been omitted for clarity. Bond lengths [Å]: Ru(1)–S(1) 2.3815(12),
Ru(1)–N(1) 2.208(3), Ru(1)–Cl(1) 2.394(12), Ru(1)–C 2.181(4)–
2.224(4); bond angles [°]: Cl(1)–Ru(1)–S(1) 81.94(4), N(1)–Ru(1)–
S(1) 83.06(9), N(1)–Ru(1)–Cl(1) 85.28(9).
There is a pseudo-octahedral half-sandwich “piano-
stool” disposition of ligands around the ruthenium atom in
the cations of 1, 3, 4, and 6. The arene ring occupies one
face of the octahedron and Cl and L (L1–L4) the opposite
one. The Ru–S bond length in the cation of 1 is
Figure 2. ORTEP diagram of the cation of 3 with ellipsoids at the
–
30% probability level. Hydrogen atoms and the PF6 anion have
2.3815(12) Å, somewhat longer than that in
3
been omitted for clarity. Bond lengths [Å]: Ru(1)–S(1) 2.3742(14),
Ru(1)–N(1) 2.205(4), Ru(1)–Cl(1) 2.3996(15), Ru(1)–C 2.172(6)–
2.196(6); bond angles [°]: Cl(1)–Ru(1)–S(1) 82.26(5), N(1)–Ru(1)–
S(1) 82.62(11), N(1)–Ru(1)–Cl(1) 82.32(11).
[2.3742(14) Å]. Both are within the range 2.3548(15)–
2.4156(9) Å in which the Ru–S bond lengths of [(η6-C6H6)
ruthenium(II)Cl(S,N)ligand]+,
[(η6-C6H6)ruthenium(II)-
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“Piano-Stool” Complexes of Ruthenium(II)
(S,N,Se)ligand]+, [Cp*Ru(PMe3)2(SC6F4H)], and [Cp*Ru-
(NO)(SC6F4H)2] are reported[29–31] to fall. Complex 4 is a
new example of the little known (η6-arene)(seleno ether)ru-
thenium(II) complex (arene
=
η6-C6H6 or η6-p-cy-
mene).[29,30,32] The Ru–Se bond length of the cation of 4
[2.4837(14) Å] is consistent with the value reported for the
half-sandwich complex of RuII with N-[2-(phenylseleno)-
ethyl]pyrrolidine[29] [2.4770(5)–2.480(11) Å] and falls within
the range 2.4756(10)–2.5240(9) Å reported for the Ru–Se
bond lengths in the clusters [Ru3(µ3-Se)(CO)7(µ3-CO)(µ-
dppm)] and [Ru3(µ3-Se)(µ3-S)(CO)7(µ-dppm)].[33] For the
RuIV complex [Cp*Ru{η2-Se2P(iPr)2}{η2-SeP(iPr)2}][PF6],
the Ru–Se bond lengths[31] are reported to be in the range
2.538(2)–2.590(2) Å, longer than that in the cation of 4 as
a result of steric crowding. The Ru–Se bond length found
in the dimetallic species [CpRu(CO)(CϵCPh)(µ-Se)ZrCp2]
[2.494(1) Å][34] is closer to that in the cation of 4. In [Ru(η5-
C5Me5)(µ2-SeR)3Ru(η5-C5Me5)]Cl (R = tolyl), the Ru–Se
bond lengths are in the range 2.446(4)–2.466(4) Å[35] and
shorter than that in the cation of 4, because RSe– is ex-
pected to be bonded more strongly than the seleno ether.
In the diselenide-bridged complex [Ru(η5-C5Me5)(PPh3)]2-
(µ-Se2)2(Otf)2, the Ru–Se bond lengths are 2.518(1) and
2.556(1) Å,[36] respectively, somewhat longer than that in
the cation of 4.
Figure 3. ORTEP diagram of the cation of 4 with ellipsoids at the
–
30% probability level. Hydrogen atoms and the PF6 anion have
been omitted for clarity. Bond lengths [Å]: Ru(1)–Se(1) 2.4837(14),
Ru(1)–N(1) 2.234(8), Ru(1)–Cl(1) 2.413(3), Ru(1)–C 2.172(13)–
2.220(12); bond angles [°]: Cl(1)–Ru(1)–Se(1) 80.57(9), N(1)–
Ru(1)–Se(1) 83.50(2), N(1)–Ru(1)–Cl(1) 85.90(2).
Figure 4. ORTEP diagram of the cation of 6 with ellipsoids at the
In the cation of complex 6, ligand L4 is coordinated to
Ru in a bidentate (Te,N) mode, forming a five-membered
chelate ring. The Ru–Te bond length [2.6143(7) Å] of the
cation of 6 is consistent with earlier reports of 2.619(8) Å
for [RuCl2(η6-p-cymene)L] [L = 2-(4-ethoxyphenyltelluro-
–
30% probability level. Hydrogen atoms and the PF6 anion have
been omitted for clarity. Bond lengths [Å]: Ru(1)–Te(1) 2.6143(7),
Ru(1)–N(1) 2.238(4), Ru(1)–Cl(1) 2.4078(14), Ru(1)–C 2.159(7)–
2.217(8); bond angles [°]: Cl(1)–Ru(1)–Te(1) 80.25(4), N(1)–Ru(1)–
Te(1) 84.61(10), N(1)–Ru(1)–Cl(1) 86.21(10).
Figure 5. ORTEP diagram showing the P–F···H interactions in 4. Distances [Å]: P(1)–F(1)···H(2) 2.594(10), P(1)–F(2)···H(7B) 2.810(15),
P(1)–F(4)···H(12A) 2.394(10), P(1)–F(5)···H(10A) 2.638(16), P(1)–F(6)···H(15A) 2.463(14).
Eur. J. Inorg. Chem. 2010, 4187–4195
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P. Singh, A. K. Singh
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methyl)tetrahydro-2H-pyran][37]
and
shorter
than to higher frequency is much larger for C5 to C7 (by up to
2.6371(4) Å reported for [RuCl(η6-p-cymene)(H2NCH2CH2- 45 ppm) in the 13C{1H} NMR spectra and for the protons
TeC6H4OMe)]Cl·H2O.[38] It is also shorter than the reported (up to 1 ppm) attached to them. Furthermore, in the H
1
value 2.6528(9) Å for dichloro(η6-p-cymene){bis[2-(2-thienyl)- and 13C{1H} NMR spectra of 6, the signals experience a
ethyl] telluride}ruthenium(II),[39] 2.651(5) Å for [RuCl2(η6- much larger shift to higher frequency (by ca. 45 and
p-cymene){bis[(1,3-dioxan-2-yl)ethyl] telluride}],[40] and 1.07 ppm, respectively) than those of the other complexes.
2.6559(9) Å for [RuCl2(η6-p-cymene)(N-{2-(4-methoxy-
The complexes 1–6 were tested in the catalytic oxidation
phenyltelluro)ethyl}phthalimide)].[41] The hybrid organotel- of primary and secondary alcohols (Scheme 2). The
lurium ligands in all these complexes of RuII(η6-p-cymene) alcohols were oxidized with NaOCl and NaIO4 at pH = 9–
bind in a monodentate mode through Te, and this may be 10 because of earlier reports[53,54] that suggested that this
responsible to some extent for their longer Ru–Te bonds. pH range is optimum. A series of blank experiments were
The bond angles at the coordinating S, Se, and Te atoms carried out under identical conditions (see the Exp. Sect.),
are as expected for near trigonal-pyramidal geometry.
which suggests that neither the ruthenium(II) complexes
The Ru–C bond lengths of the cations of 1, 3, 4, and nor the oxidants (NMO, tBuOOH, NaOCl, or NaIO4)
6 [2.159(7)–2.224(4) Å] are consistent with those in earlier alone cause the catalytic oxidation to any significant extent.
reports[29,30,33,37,39–46] [2.168(5)–2.228(5) Å]. The C–Ru–C The cyclic voltammetric experiments performed at 298 K in
bond angles are normal. The Ru–Cl bond lengths (sum of CH3CN (0.01  nBu4NClO4 as supporting electrolyte) for
the covalent radii ca. 2.24 Å) of 1 and 3 are 2.394(12) and 1–6 at a scan rate of 100 mVs–1 (anodic sweep) reveal a
2.3996(15) Å, respectively, similar and consistent with the one-electron irreversible oxidation with E1/2 values of
value 2.3914(12) Å reported[29] for [(η6-C6H6)ruthenium(II)- 0.290–0.586 V (vs. Ag/AgCl; see Table S4 and Figures S8–
Cl(S,N)ligand]+. For the cation of 4, the Ru–Cl bond length S13 in the Supporting Information), which is not extreme,
[2.413(3) Å] is consistent with those of 1 and 3. The Ru–Cl implying that both RuII and RuIII are equally stabilized by
bond length of the cation of 6 [2.4078(14) Å] is consistent the same set of ligands. The narrow range of E1/2 has pre-
with those in earlier reports of 2.415(2)/2.422(2) Å for viously been reported to be favorable for the catalytic oxi-
dichloro(η6-p-cymene){bis[2-(2-thienyl)ethyl]
ruthenium(II)[39] and 2.417(2)–2.436(2) Å for [RuCl2(η6-p- quivocally been established.
cymene)L] (L
monodentate Te ligand)[44–46] and
telluride}- dation process;[55,56] however, no 1:1 relationship has une-
=
[RuCl{η2-C,N-C6H3(CH2NMe2)2-2,6}{η6-C10H14}].[47] It is
somewhat longer than the value 2.308(2) Å reported for
[(η6-p-cymene)RuCl(H2NCH2CH2TeC6H4OMe)]Cl·H2O,[38]
but the difference with the values for 1, 3, and 4 are not
very significant.
The Ru–N bond lengths (sum of the covalent radii ca.
1.95 Å) of the cations of 1, 3, 4, and 6 are 2.208(3), 2.205(4),
2.234(8), and 2.238(4) Å, respectively. The first two are con-
sistent with each other and with those of the half-sandwich
Scheme 2. Oxidation of alcohols catalyzed by 1–6.
The TON values are given in Table 1 for the oxidation
complex of RuII with N-{2-(phenylseleno)ethyl}pyrrolidine (catalyzed by 1–6) of various alcohols by four oxidants,
[2.190(3)–2.201(5) Å].[29] The final two values are also con- namely N-methylmorpholine N-oxide (NMO), tert-butyl
sistent with each other, but larger than the first two and hydroperoxide (tBuOOH), sodium oxychloride (NaOCl),
those of complexes in several recent literature reports and sodium periodate (NaIO4). For all four oxidants 6 ap-
[2.0511(17)–2.163(10) Å].[33,43] In the half-sandwich com- pears to be the most efficient of all six Ru species. The ben-
plexes of [RuCl(η6-p-cymene)][48–52] with several nitrogen li- zene derivatives show somewhat better catalytic efficiency
gands, the Ru–N bond lengths have been reported generally than their p-cymene counterparts (Table 1). The catalytic
to be between 2.060(5) and 2.156(2) Å, less than those of 1, efficiency varies with chalcogen ligands in the order
3, 4, and 6. The bond angles at the coordinating N atoms Te ϾSeϾS, which is also the order of “softness” of these
are as expected for near-tetrahedral geometries.
donor sites. The softer ligand makes easier the formation
The NMR spectroscopic data for complexes 1–6 are con- of RuIV=O species, which are believed to be the intermedi-
sistent with the structures revealed by single-crystal X-ray ates in the oxidation process on the basis of several observa-
diffraction. The signals in the 77Se{1H} NMR spectra of 4 tions mentioned below. Undoubtedly, unambiguous deter-
and 5 appear shifted to a higher frequency (by ca. 100 ppm) mination of the mechanism of these oxidative transforma-
in comparison with that of free L3 as Se is coordinated tions is not straightforward as the intermediate species are
to the ruthenium center. Similarly, in the 125Te{1H} NMR of low stability. On the basis of earlier work[53,54,57–59] and
spectrum of 6 the signal appears at a frequency much some of the observations made by us, the mechanism of the
higher (by ca. 260 ppm) than that of free L4. In the 1H and catalytic oxidation appears to involve RuIV=O species that
13C{1H} NMR spectra of 1–6, the signals of all the protons seem to be formed by free radicals (generated by heterolytic
and carbon atoms appear at a higher frequency than those cleavage of the oxidants). The addition of AIBN [a free-
of the free ligands, which coordinate to the ruthenium atom radical initiator, azobis(isobutyronitrile)] to the oxidation of
in a bidentate mode. However, the magnitude of the shift benzyl alcohol in the presence of 6 (most efficient catalyst)
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“Piano-Stool” Complexes of Ruthenium(II)
Table 1. Catalytic oxidation of primary and secondary alcohols by using complexes 1–6 as catalyst.[a]
[a] Oxidant: a = NMO; b = tBuOOH; c = NaIO4; d = NaOCl; Blank = control experiment in the absence of catalyst.
with any one of the four oxidants under the same reaction alcohols. Moreover, the catalytic activities of the RuIV=O
conditions resulted in enhanced conversion (86–95%). Fur- species towards oxidation reported earlier[58–60] further
ther addition of AIBN in the same oxidation reaction in strengthens our proposition. The short life-times of the
the absence of 6 did not result in any oxidation. In the pres- RuIV=O transient species restricted us from acquiring MS
ence of benzoquinone (a free-radical inhibitor) the conver- evidence. The 1H NMR spectra of the ruthenium complexes
sion was minimal. These observations are consistent with recorded after the addition of an oxidant are broadened,
those made by Goldstein and Drago with H2O2 and OCl– which indicates the formation of paramagnetic intermediate
in the oxidation of alkanes.[59d] On addition of an oxidant species.
to the solutions of complexes 4 and 5, the signals in the
77Se{1H} NMR spectra are shifted to a higher frequency
(by Ն473 ppm). Similarly, in the case of 6 the signal in the
125Te{1H} NMR spectrum shifts to a higher frequency (by
Conclusions
ca. 288 ppm) in the presence of an oxidant. The signals in
the 77Se{1H} NMR spectrum of L3 and the 125Te{1H}
“Piano-stool” complexes of RuII of composition
NMR spectrum of L4 remain unshifted on addition of any [RuCl(η6-C6H6)(L)][PF6]/[RuCl(η6-p-cymene)(L)][PF6] (1–
of the four oxidants. Therefore, the ruthenium center is 6) have been prepared and characterized. Their catalytic ac-
most probably oxidized to RuIV=O. The UV/Vis spectra on tivity in the oxidation of primary and secondary alcohols
addition of any one of these oxidants to dichloromethane with N-methylmorpholine N-oxide (NMO), tBuOOH, Na-
solutions of 1–6 show a new shoulder at 390–394 nm, which OCl, and NaIO4 has been investigated. The advantages of
is believed[59,61,64a] to be due to RuIV=O, the species re- 1–6 over recently reported good ruthenium-based catalytic
ported to be responsible for the transfer of the oxygen atom species[57c,59b,64–68] in the oxidation of alcohols are (i) high
to the alcohol substrates resulting in their catalytic oxi- efficiency and yield so that smaller quantities are needed,
dation. The IR spectra of the residues left after evaporating (ii) short reaction times, and (iii) flexibility regarding oxi-
the solvent from the mixtures of any of the oxidants with dants. The efficiencies of the catalysts 1–6 in the oxidation
complexes 1–6 exhibit very strong bands at 845–848 cm–1 of alcohols with any of the oxidants (TON upto 9.8ϫ104)
(νP–F band at 840–850 cm–1 is of medium intensity only), are comparable to those of the half-sandwich RuII com-
which further supports the formation of the RuIV=O spe- plexes containing chalcogenated pyrrolidine, benzotriazole,
cies[59a,59b,60–63,64a] responsible for the catalytic oxidation of and Schiff bases with NMO.[29,30,32]
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H + 2-H), 7.67–7.87 (m, 2 H, 3-H) ppm. 13C{1H} NMR (CD3CN,
25 °C): δ = 30.7 (C-8), 58.4 (C-7), 62.4 (C-5), 67.2 (C-6), 87.1 (Ru-
Ar-C), 129.8 (C-1), 131.5 (C-2), 132.6 (C-3), 134.2 (C-4) ppm. IR
Experimental Section
General Procedure: Perkin–Elmer 2400 Series II C,H,N analyzer
was used for elemental analysis. The H, 13C{1H}, 77Se{1H}, and
1
(KBr): ν
= 3083 (m, νC–H,aromatic), 2984, 2877 (s, νC–H,aliphatic),
˜
max
125Te{1H} NMR spectra were recorded with a Bruker Spectrospin
DPX-300 NMR spectrometer at 300.13, 75.47, 57.24, and
94.69 MHz, respectively. IR spectra in the range 4000–400 cm–1
were recorded with a Nicolet Protége 460 FT-IR spectrometer as
KBr pellets. The UV/Vis spectra were recorded with a Perkin–El-
mer Lambda BIO-20 model 330 spectrometer. The conductivity
measurements were carried out in CH3CN (conc. ca. 1 m) by
using an ORION conductivity meter, model 162. The catalytic oxi-
dation yields were determined with a NUCON Engineers (New
Delhi, India) gas chromatograph (with FID detector), model 5765,
equipped with an Alltech (EcTM-1) column of 30 m length,
0.25 mm diameter and having a liquid film thickness of 0.25 µm.
The cyclic voltammetry studies were performed with a BAS CV
50W instrument at the University of Delhi (Department of Chemis-
try). A three-electrode configuration composed of a Pt disk work-
ing electrode (3.1 mm2 area), a Pt wire counter electrode, and an
Ag/AgCl reference electrode was used for the measurements. Ferro-
cene was used as an internal standard (E1/2 = 0.500 V vs. Ag/AgCl),
and all the potentials are expressed with reference to Ag/AgCl. The
melting points were measured in an open capillary tube. The ruthe-
nium(II) precursor complexes [{(η6-C6H6)RuCl(µ-Cl)}2] and [{(η6-
p-cymene)RuCl(µ-Cl)}2] were prepared according to literature
methods.[69,70]
1631 (m, νC–C,aromatic), 1185, 1114 (w, νC–N), 850 (s, νP–F), 749 (m,
νC–H,aromatic) cm–1. C18H23ClNORuS·PF6 (437.97): calcd. C 37.09,
H 3.98, N 2.40; found C 37.00, H 4.05, N 2.49.
2: Yield: 0.10 g, 80%. M.p. 182 °C. Mol. cond. (ΛM)
=
144.2 Scm2 mol–1. 1H NMR (CD3CN): δ = 1.28 (d, 3JHH = 6.6 Hz,
6 H, CH3 in iPr), 2.82 (s, 3 H, CH3 p to iPr), 2.86–2.92 (m, 4 H,
8-H), 3.01 (sept, 1 H, CH in iPr), 3.17–3.26 (m, 4 H, 7-H), 3.34–
3.37 (m, 2 H, 5-H), 3.89 (m, 2 H, 6-H), 5.28–5.83 (m, 4 H, Ar-H
in p-cymene), 7.27–7.39 (m, 3 H, 1-H + 2-H), 7.48–7.58 (m, 2 H,
3-H) ppm. 13C{1H} NMR (CD3CN, 25 °C): δ = 18.9 (CH3 p to
iPr), 22.1, 22.3 (CH3 in iPr), 31.6 (CH in iPr), 31.8 (C-8), 52.9 (C-
7), 56.8 (C-5), 64.4 (C-6), 82.3–106.5 (Ar-C in p-cymene), 128.1 (C-
1), 130.4 (C-2), 130.6 (C-3), 134.7 (C-4) ppm. IR (KBr): ν
=
˜
max
3032 (m, νC–H,aromatic), 2973, 2861 (s, νC–H,aliphatic), 1630 (m,
νC–C,aromatic), 1196, 1112 (w, νC–N), 840 (s, νP–F), 750 (m,
νC–H,aromatic) cm–1. C22H31ClNORuS·PF6 (494.08): calcd. C 41.35,
H 4.89, N 2.19; found C 41.86, H 4.81, N 2.07.
Synthesis of L2: A solution of 2,2Ј-dipyridyl disulfide (0.44 g,
2.0 mmol) in ethanol (30 mL) under N2 was added dropwise to
NaBH4 (0.14 g, 4.0 mmol) dissolved in NaOH (5%, ca. 15 mL) un-
der N2 until it became colorless due to the formation of PySNa. 4-
(2-Chloroethyl)morpholine hydrochloride (0.74 g, 4.0 mmol) dis-
solved in ethanol (5 mL) was added to this colorless solution with
constant stirring. The reaction mixture was further stirred for 3–
4 h and poured into ice-cold water (20 mL containing 0.2 g of
NaOH). The aqueous phase was extracted with CHCl3
(5ϫ40 mL). The extract was washed with water (3ϫ50 mL) and
dried with anhydrous sodium sulfate. On evaporation of the chloro-
form under reduced pressure in a rotary evaporator, L2 was ob-
tained as a yellow oil. Yield: 0.80 g, 80%. 1H NMR (CDCl3,
Synthesis of L1: Thiophenol (0.5 mL, 5.0 mmol) was heated at re-
flux in dry ethanol (50 mL) under N2 for 0.5 h. Aqueous NaOH
(0.44 g, 11.0 mmol in 5 mL) and 4-(2-chloroethyl)morpholine hy-
drochloride [0.92 g, 5.0 mmol dissolved in ethanol (20 mL)] were
added dropwise successively. After continued heating at reflux for
a further 3 h, the reaction mixture was cooled to room temperature
and poured into distilled water (100 mL). It was then neutralized
with dilute sodium hydroxide and extracted with chloroform
(100 mL). The chloroform extract was washed with distilled water
(2ϫ50 mL) and dried with anhydrous sodium sulfate. On evapora-
tion of the chloroform in a rotary evaporator, L1 was obtained as
3
25 °C): δ = 2.52–2.55 (m, 4 H, 8-H), 2.69 (t, JHH = 7.5 Hz, 2 H,
3
6-H), 3.34 (t, JHH = 7.5 Hz, 2 H, 7-H), 3.69–3.74 (m, 4 H, 9-H),
3
6.95–6.99 (m, 1 H, 3-H), 7.18 (d, JHH = 8.1 Hz, 1 H, 4-H), 7.43–
1
7.49 (m, 1 H, 2-H), 8.42 (d, 3JHH = 7.5 Hz, 1 H, 1-H) ppm. 13C{1H}
NMR (CDCl3, 25 °C): δ = 26.8 (C-8), 53.5 (C-6), 58.2 (C-7), 66.9
(C9), 119.3 (C-3), 122.3 (C-4), 135.8 (C-2), 149.4 (C-1), 158.7 (C-
a pale-yellow oil. Yield: 0.87 g, 78%. H NMR (CDCl3, 25 °C): δ
3
= 2.48–2.51 (m, 4 H, 7-H), 2.65 (t, JHH = 7.5 Hz, 2 H, 5-H), 3.06
3
(t, JHH = 7.5 Hz, 2 H, 6-H), 3.71–3.76 (m, 4 H, 8-H), 7.17–7.22
(m, 1 H, 1-H), 7.28–7.33 (m, 2 H, 2-H) 7.35–7.38 (m, 2 H, 3-H)
ppm. 13C{1H} NMR (CDCl3, 25 °C): δ = 30.6 (C-7), 53.5 (C-5),
58.0 (C-6), 66.8 (C-8), 126.0 (C-1), 128.9 (C-2), 129.1 (C-4), 136.3
5) ppm. IR (KBr): ν
= 3065 (m, νC–H,aromatic), 2924 (s,
˜
max
νC–H,aliphatic), 1575 (m, νC–N,aromatic), 1568 (m, νC–C,aromatic), 1209,
1114 (w, νC–N), 735 (m, νC–H,aromatic) cm–1.
(C-3) ppm. IR (KBr): ν
= 3056 (m, νC–H,aromatic), 2957 (s,
˜
max
Synthesis of [RuCl(η6-C6H6)(L2)][PF6] (3): Solid [{(η6-C6H6)-
RuCl(µ-Cl)}2] (0.05 g, 0.1 mmol) and L2 (0.046 g, 0.2 mmol) were
allowed to react as described for the synthesis of 1 and 2 to give
the yellow microcrystalline solid 3, which was filtered, washed with
cold CH3OH (10 mL), and dried in vacuo. Single crystals of 3 suit-
able for X-ray diffraction were obtained similarly to those of 1.
νC–H,aliphatic), 1582 (m, νC–C,aromatic), 1207, 1118 (w, νC–N), 741 (m,
νC–H,aromatic) cm–1.
Synthesis of [RuCl(η6-C6H6)(L1)][PF6] (1) and [RuCl(η6-p-cymene)-
(L1)][PF6] (2): Solid [{(η6-C6H6)RuCl(µ-Cl)}2] (0.05 g, 0.1 mmol)
or [{(η6-p-cymene)RuCl(µ-Cl)}2] (0.06 g, 0.1 mmol) was added to
a solution of L1 (0.045 g, 0.2 mmol) in CH3OH (15 mL). The mix-
ture was stirred at room temperature for 12 or 15 h. The resulting
yellow solution was filtered, and the volume of the filtrate was re-
duced (to ca. 7 mL) in a rotary evaporator. It was mixed with solid
NH4PF6 (0.032 g, 0.2 mmol), and the resulting yellow microcrystal-
line solid 1 or 2 was filtered, washed with cold CH3OH (10 mL)
and dried in vacuo. Single crystals of 1 suitable for X-ray diffrac-
tion were obtained by the diffusion of diethyl ether into its solution
(1 mL) in CH3OH/CH3CN (v/v, 1:4).
Yield: 0.10 g, 85%. M.p. 176.0 °C. Mol. cond. (ΛM)
=
1
143.6 Scm2 mol–1. H NMR (CD3CN, 25 °C): δ = 2.72 (m, 4 H, 8-
H), 2.88–3.32 (m, 2 H, 6-H), 3.52–3.70 (m, 2 H, 7-H), 3.86–4.32
(m, 4 H, 9-H), 5.55 (s, 6 H, Ru-Ar-H), 7.47–7.61 (m, 1 H, 3-H),
3
7.99 (m, 1 H, 2-H), 8.44 (d, JHH = 8.1 Hz, 1 H, 4-H), 8.78 (d,
3JHH = 7.5 Hz, 1 H, 1-H) ppm. 13C{H} NMR (CD3CN, 25 °C): δ
= 27.4 (C-8), 54.1 (C-6), 59.4 (C-7), 66.9 (C-9), 87.1 (Ru-Ar-C),
123.3 (C-3), 123.4 (C-4), 137.9 (C-2), 150.2 (C-1), 160.6 (C-5) ppm.
IR (KBr): νmax = 3053 (m, νC–H,aromatic), 2968 (s, νC–H,aliphatic), 1576
˜
1: Yield: 0.10 g, 85%. M.p. 173 °C. Mol. cond. (ΛM)
=
(m, νC–N,aromatic), 1571 (m, νC–C,aromatic), 1203, 1104 (w, νC–N), 842
1
148.8 Scm2 mol–1. H NMR (CD3CN, 25 °C): δ = 2.26–2.65 (m, 4
(s, νP–F), 743 (m, νC–H,aromatic
H, 8-H), 3.11–3.21 (m, 4 H, 7-H), 3.54–3.74 (m, 2 H, 5-H), 3.97– (438.96): calcd. C 34.97, H 3.80, N 4.80; found C 34.44, H 3.72, N
4.34 (m, 2 H, 6-H), 5.63 (s, 6 H, Ru-Ar-H), 7.22–7.44 (m, 1 H, 1- 4.48.
)
cm–1. C17H22ClN2ORuS·PF6
4192
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 4187–4195

“Piano-Stool” Complexes of Ruthenium(II)
Synthesis of L3: Diphenyl diselenide (0.62 g, 2.0 mmol) was treated
with NaBH4 (0.14 g, 4.0 mmol) as described for the synthesis of
L2. The resulting PhSeNa was treated with 4-(2-chloroethyl)-
morpholine hydrochloride (0.74 g, 4.0 mmol) in a manner similar
to that described above for L2 to give L3 as a pale-yellow oil. Yield:
νC–H,aromatic), 2918 (s, νC–H,aliphatic), 1578 (m, νC–C,aromatic), 1211,
1118 (w, νC–N) cm–1.
Synthesis of [RuCl(η6-C6H6)(L4)][PF6] (6): Solid [{(η6-C6H6)-
RuCl(µ-Cl)}2] (0.05 g, 0.1 mmol) and L4 [0.070 g, 0.2 mmol dis-
solved in CH3OH (15 mL)] were allowed to react and treated there-
after with solid NH4PF6 (0.032 g, 0.2 mmol) as described above for
the synthesis of 1 and 2. Complex 6 was isolated, and single crystals
suitable for X-ray diffraction were grown by the procedure used for
those of 1 and 2. Yield: 0.12 g, 85%. M.p. 186.0 °C. Mol cond.
(ΛM) = 143.7 Scm2 mol–1. 1H NMR (CD3CN, 25 °C): δ = 2.98–
3.28 (m, 4 H, 8-H), 3.35–3.68 (m, 4 H, 7-H), 3.85 (s, 3 H, OCH3),
3.97–4.03 (m, 2 H, 5-H), 4.12–4.49 (m, 2 H, 6-H), 5.67 (s, 6 H, Ru-
1
0.86 g, 80%. H NMR (CDCl3, 25 °C): δ = 2.44–2.46 (m, 4 H, 7-
3
3
H), 2.68 (t, JHH = 7.5 Hz, 2 H, 5-H), 3.02 (t, JHH = 7.5 Hz, 2 H,
6-H), 3.66–3.69 (m, 4 H, 8-H), 7.19–7.24 (m, 3 H, 1-H + 2-H), 7.48
(d, 3JHH = 6.6 Hz, 2 H, 3-H) ppm. 13C{1H} NMR (CDCl3, 25 °C):
δ = 24.4 (C-7), 53.1 (C-5), 58.5 (C-6), 66.6 (C-8), 126.6 (C-1), 128.8
(C-2), 130.1 (C-4), 132.2 (C-3) ppm. 77Se{1H} NMR (CDCl3,
25 °C): δ = 279.5 ppm. IR (KBr): ν
= 3061 (m, νC–H,aromatic),
˜
max
2920 (s, νC–H,aliphatic), 1578 (m, νC–C,aromatic), 1212, 1117 (w, νC–N),
3
3
Ar-H), 7.03 (d, JHH = 6.9 Hz, 2 H, 2-H), 7.88 (d, JHH = 6.9 Hz,
2 H, 3-H) ppm. 13C{1H} NMR (CD3CN, 25 °C): δ = 30.1 (C-8),
53.3 (C-7), 56.7 (OCH3), 61.6 (C-5), 65.4 (C-6), 87.2 (Ru-Ar-C),
118.3 (C-1), 130.2 (C-2), 142.2 (C-3), 161.7 (C-4) ppm. 125Te{1H}
738 (m, νC–H,aromatic) cm–1.
Synthesis of [RuCl(η6-C6H6)(L3)][PF6] (4) and [RuCl(η6-p-cymene)-
(L3)][PF6] (5): L3 (0.054 g, 0.2 mmol) was treated with solid [{(η6-
C6H6)RuCl(µ-Cl)}2] (0.05 g, 0.1 mmol) or [{(η6-p-cymene)RuCl(µ-
Cl)}2] (0.06 g, 0.1 mmol) as described for the synthesis of 1 and 2.
Solid NH4PF6 (0.032 g, 0.2 mmol) was added to the concentrated
(to ca. 7 mL) reaction mixture as described above for 1 and 2 to
give 4 and 5. Single crystals of 4 were obtained similarly to those
of 1.
NMR (CDCl , 25 °C): δ = 691.9 ppm. IR (KBr): ν
= 3088 (m,
˜
3
max
νC–H,aromatic), 2982, 2878 (s, νC–H,aliphatic), 1627 (m, νC–C,aromatic),
1195, 1117 (w, νC–N), 845 (s, νP–F), 748 (m, νC–H,aromatic) cm–1.
C19H25ClNO2RuTe·PF6 (563.54): calcd. C 32.21, H 3.56, N 1.98;
found C 32.11, H 3.50, N 2.06.
X-ray Crystallographic Analysis: The data for the single-crystal
structures were collected (at IIT Delhi and IIT Kanpur, India) with
a Bruker AXS SMART Apex CCD diffractometer by using Mo-Kα
(0.71073 Å) radiation. SADABS software was used for absorption
correction (if needed) and SHELXTL for space group, structure
determination, and refinements.[71–73] Selected crystal data are
given below. Further details of crystal data and structural refine-
ments, bond lengths and angles are available in Tables S1–S3 in the
Supporting Information. CCDC-768670 (1), -768671 (3), -768672
(4), and -768673 (6) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
the Cambridge crystallographic data centre via www.ccdc.cam.a-
c.uk/data_request.cif.
4: Yield: 0.10 g, 80%. M.p. 181.0 °C. Mol. cond. (ΛM)
=
144.2 Scm2 mol–1. H NMR (CD3CN, 25 °C): δ = 2.62–2.88 (m, 4
H, 8-H), 3.46–3.58 (m, 4 H, 7-H), 3.88–3.96 (m, 2 H, 5-H), 4.25–
4.31 (m, 2 H, 6-H), 5.69 (s, 6 H, Ru-Ar-H), 7.61–7.63 (m, 3 H, 1-
H + 2-H), 7.82–7.85 (m, 2 H, 3-H) ppm. 13C{1H} NMR (CD3CN,
25 °C): δ = 32.3 (C-8), 56.2 (C-7), 61.8 (C-5), 64.6 (C-6), 87.4 (Ru-
Ar-C), 129.1 (C-1), 130.2 (C-2), 132.1 (C-3), 133.0 (C-4) ppm.
1
77Se{1H} NMR (CDCl , 25 °C): δ = 379.6 ppm. IR (KBr): ν
=
˜
3
max
3083 (m, νC–H,aromatic), 2994, 2877 (s, νC–H,aliphatic), 1578 (m,
νC–C,aromatic), 1194, 1113 (w, νC–N), 845 (s, νP–F), 742 (m,
νC–H,aromatic) cm–1. C18H23ClNORuSe·PF6 (484.87): calcd. C 34.33,
H 3.68, N 2.22; found C 34.03, H 3.60, N 2.28.
¯
1: C18H23ClF6NOPRuS, Mr = 582.93, triclinic space group, P1, a
5: Yield: 0.11 g, 80%. M.p. 178.0 °C. Mol. cond. (ΛM)
=
=
= 9.825(3), b = 10.348(2), c = 10.569(3) Å, α = 93.753(5), β =
1
3
140.4 Scm2 mol–1. H NMR (CD3CN, 25 °C): δ = 1.31 (d, JHH
96.363(4), γ = 101.484(5)°, V = 1042.3(5) Å3, Z = 2, ρcalcd.
=
6.6 Hz, 6 H, CH3 in iPr), 2.25 (s, 3 H, CH3 p to iPr), 2.62–2.67 (m,
4 H, 8-H), 2.90 (sept, 1 H, CH in iPr), 3.02 (m, 4 H, 7-H), 3.28
(m, 2 H, 5-H), 3.91 (m, 2 H, 6-H), 5.31–5.86 (m, 4 H, Ar-H in p-
cymene), 7.41 (m, 3 H, 1-H + 2-H), 7.66 (m, 2 H, 3-H) ppm.
13C{1H} NMR (CD3CN, 25 °C): δ = 18.8 (CH3 p to iPr), 22.4, 22.3
(CH3 in iPr), 31.7 (CH in iPr), 31.9 (C-8), 52.8 (C-7), 57.9 (C-5),
64.5 (C-6), 82.8–106.6 (Ar-C in p-cymene), 129.0 (C-1), 130.6 (C-
2), 131.9 (C-3), 133.5 (C-4) ppm. 77Se{1H} NMR (CDCl3, 25 °C):
1.857 gcm–3,
µ
=
1.121 mm–1, –11ՅhՅ11, –12ՅkՅ12,
–12ՅlՅ12, T = 100(2) K, GOF = 1.098, R1 = 0.0453, wR2
=
0.1268 [IϾ2σ(I)], R1 = 0.0492, wR2 = 0.1356 (all data). Out of
5284 total reflections collected, 3599 (Rint = 0.0298) were unique.
¯
3: C17H22ClF6N2OPRuS, Mr = 583.93, triclinic space group, P1, a
= 9.7965(15), b = 10.3459(16), c = 10.8061(3) Å, α = 93.031(3), β
= 96.598(2), γ = 100.470(3)°, V = 1063.4(3) Å3, Z = 2, ρcalcd.
=
1.824 gcm–3,
µ
=
1.100 mm–1,–11ՅkՅ11, –12ՅkՅ12,
δ = 383.4 ppm. IR (KBr): νmax = 3028 (m, νC–H,aromatic), 2973, 2858
˜
–12ՅlՅ12, T = 273(2) K, GOF = 1.158, R1 = 0.0525, wR2
=
(s, νC–H,aliphatic), 1578 (m, νC–C,aromatic), 1189, 1113 (w, νC–N), 840 (s,
νP–F), 744 (m, νC–H,aromatic) cm–1. C22H31ClNORuSe·PF6 (540.98):
calcd. C 38.53, H 4.56, N 2.04; found C 38.33, H 4.50, N 2.07.
0.1207 [IϾ2σ(I)], R1 = 0.0558, wR2 = 0.1230 (all data). Out of
10082 total reflections collected, 3760 (Rint = 0.0307) were unique.
¯
4: C18H23ClF6NOPRuSe, Mr = 629.82, triclinic space group, P1, a
Synthesis of L4: Bis(4-methoxyphenyl) ditelluride (0.94 g, 2 mmol)
was treated first with NaBH4 (0.14 g, 4.0 mmol dissolved in 5%
NaOH) and thereafter with 4-(2-chloroethyl)morpholine hydro-
chloride [0.74 g, 4.0 mmol dissolved in ethanol (5 mL)] as described
for the synthesis of L2. After workup similar to that for L2, L4
was obtained as a white oil. Yield: 1.12 g, 80%. 1H NMR (CDCl3,
= 9.889(3), b = 10.508(3), c = 10.784(3) Å, α = 93.107(4), β =
96.293(5), γ = 101.934(4)°, V = 1086.4(5) Å3, Z = 2, ρcalcd.
=
1.925 gcm–3,
µ
=
2.655 mm–1,–11ՅhՅ11, –12ՅkՅ12,
–12ՅlՅ12, T = 273(2) K, GOF = 1.076, R1 = 0.0676, wR2
0.1414 [IϾσ(I)], R1 = 0.1134, wR2 = 0.1580 (all data). Out of 6767
total reflections collected, 3837 (Rint = 0.0963) were unique.
=
3
25 °C): δ = 2.46–2.49 (m, 4 H, 7-H), 2.78 (t, JHH = 7.5 Hz, 2 H,
3
5-H), 3.04 (t, JHH = 7.5 Hz, 2 H, 6-H), 3.68–3.71 (m, 4 H, 8-H),
6: C19H25ClF6NO2PRuTe, Mr = 708.49, monoclinic space group,
P21/n, a = 10.4151(17), b = 10.9106(17), c = 21.007(3) Å, α = 90.00,
3
3.79 (s, 3 H, OCH3), 6.76 (d, JHH = 6.9 Hz, 2 H, 2-H), 7.68 (d,
3JHH = 6.9 Hz, 2 H, 3-H) ppm. 13C{1H} NMR (CDCl3, 25 °C): δ
β = 96.636(3), γ = 90.00°, V = 2371.1(6) Å3, Z = 4, ρcalcd.
=
= 7.8 (C-7), 53.1 (C-5), 55.1 (C-6), 59.3 (C-8), 66.9 (OCH3), 101.3 1.985 gcm–3,
µ
=
2.111 mm–1, –12ՅhՅ12, –12ՅkՅ12,
(C-1), 115.0 (C-2), 140.7 (C-4), 159.5 (C-3) ppm. 125Te{1H} NMR –24ՅlՅ24, T = 273(2) K, GOF = 1.044, R1 = 0.0415, wR2
(CDCl , 25 °C): δ = 431.5 ppm. IR (KBr): ν = 3063 (m, 0.1092 [IϾ2σ(I)], R1 = 0.0487, wR2 = 0.1136 (all data). Out of
=
˜
3
max
Eur. J. Inorg. Chem. 2010, 4187–4195
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4193

P. Singh, A. K. Singh
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Catalytic Oxidation of Alcohols with tBuOOH: A mixture complex
1–6 (0.001 mol-%) dissolved in CH2Cl2 (20 mL) and neat alcohol
substrate (1 mmol) was prepared. tBuOOH (4 mmol) was added to
the mixture through a dropping funnel over 0.5 h, and the resulting
mixture was stirred at room temperature for 3 h. Most of the sol-
vent from the reaction mixture was evaporated in a rotary evapora-
tor to give a semi-solid containing the catalyst and the oxidized
alcohol. The mixture was extracted with petroleum ether (60–
80 °C; 20 mL). The extract containing the oxidized product was
analyzed by GC, and the residue containing the catalyst was pre-
served in a nearly quantitative amount for the next catalytic cycle.
[11]
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Catalytic Oxidation of Alcohols with NaOCl and NaIO4: A solution
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were added at 0 °C, and the mixture was stirred vigorously until
the organic phase became yellow or orange leaving the aqueous
phase colorless. The alcohol (1 mmol) in CH2Cl2 (5 mL) was added
in one portion to the reaction mixture with stirring. An aqueous
solution of 0.7  NaOCl (5.7 mL)/1.0  NaIO4 (4 mL) was added
to the reaction mixture dropwise through a dropping funnel over a
period of 1 h. The resulting reaction mixture was stirred at room
temperature maintaining its pH at ca. 9.5 for 3 h and shaken there-
after with CH2Cl2 (30 mL). The organic layer was separated, and
most of the solvent was evaporated in a rotary evaporator to give
a semi-solid, which was extracted with petroleum ether (60–80 °C;
20 mL). The catalyst left as a solid residue was recovered almost
quantitatively for another catalytic cycle. The resulting aldehydes/
ketones extracted into petroleum ether were analyzed by GC.
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Acknowledgments
The authors thank the Department of Science and Technology (In-
dia) for research project no. SR/S1/IC-23/06 and for partial finan-
cial assistance given to establishing the single-crystal X-ray diffrac-
tion facility at IIT Delhi, New Delhi (India) under the FIST pro-
gramme. P. S. thanks the University Grants Commission (India) for
the award of a Junior/Senior Research Fellowship.
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Received: March 20, 2010
Published Online: July 28, 2010
Eur. J. Inorg. Chem. 2010, 4187–4195
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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