Preparation and crystal structures of benzoylhydrazido- And -diazenidorhenium complexes with N,O-ligands and their catalytic activity towards peroxidative oxidation of cycloalkanes

Article abstract of DOI:10.1002/ejic.200400991

The η²-(benzoylhydrazido)rhenium(v) complex [Re{(OCH ₂-CH₂)₂N(CH₂CH ₂OH)}{N=NC(O)Ph}(PPh₃)] (2) and the η ¹-(benzoyldiazenido)rhenium(III) compounds [ReCl{N(CH ₂-COO)(CH₂CH₂OH)(CH₂CH ₂OH)}{N=NC(O)Ph}(PPh₃)] (3) and [ReCl(O,N-L){N=NC(O)Ph}(PPh₃)₂] [O,N-L = N(=O)-CH ₂COO (4), HN=C(Me)COO (5), C₅H₄N(COO) (6)], with chelating N,O-ligands (amino alkoxides, amino-, oxyamino-, imino- and pyridinocarboxylates) have been prepared by treatment of [ReCl ₂{N=NC(O)Ph}(PPh₃)₂] (1) with triethanolamine [N(CH₂CH₂OH)₃], N,N-bis(2-hydroxyethyl)glycine [N(CH₂CH₂OH)₂(CH₂COOH)], N-hydroxyiminodiacetic acid [HON(CH₂COOH)₂], N-hydroxy-2,2′-iminodipropionic acid [HON{CH(Me)COOH}₂] and picolinic acid (NC₅H₄COOH-2), respectively. The N,O-ligands in 4 and 5 result from fragmentation of the N-hydroxyiminodicarboxylic acids. All the com plexes have been characterized by IR, ¹H and ¹³C NMR spectroscopy, FAB⁺-MS, elemental analysis and X-ray diffraction structural analysis, which indicate a π-delocalized chelated benzoylhydrazidorhenium ring in 1 and 2, and, in the other complexes, an essentially linear η¹-diazenido ligand that is always trans to the O-coordinated carboxylate moiety of the N,O-ligand. The complexes act as catalysts (TON values up to about 45) for peroxidative oxidation, by radical mechanisms, of cyclohexane and cyclopentane to the corresponding alcohols and ketones, under mild conditions (room temperature, use of aqueous H₂O₂ and without added acid). This is an unprecedented use of inorganic Re coordination compounds as catalysts in alkane functionalization. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejic.200400991

FULL PAPER
Preparation and Crystal Structures of Benzoylhydrazido- and
-diazenidorhenium Complexes with N,O-Ligands and Their Catalytic Activity
Towards Peroxidative Oxidation of Cycloalkanes
Alexander M. Kirillov,[a] Matti Haukka,[b] M. Fátima C. Guedes da Silva,[a,c] and
Armando J. L. Pombeiro*[a]
Keywords: Alkanes / Homogeneous catalysis / N,O ligands / Oxidation / Rhenium
The η2-(benzoylhydrazido)rhenium(
CH2)2N(CH2CH2OH)}{N=NC(O)Ph}(PPh3)] (2) and the η1-
(benzoyldiazenido)rhenium(III compounds [ReCl{N(CH2-
COO)(CH2CH2OH)(CH2CH2OH)}{N=NC(O)Ph}(PPh3)] (3)
and [ReCl(O,N-L){N=NC(O)Ph}(PPh3)2] [O,N-L N(=O)-
CH2COO (4), HN=C(Me)COO (5), C5H4N(COO) (6)], with
chelating N,O-ligands (amino alkoxides, amino-, oxyamino-,
imino- and pyridinocarboxylates) have been prepared by
treatment of [ReCl2{N=NC(O)Ph}(PPh3)2] (1) with triethanol-
amine [N(CH2CH2OH)3], N,N-bis(2-hydroxyethyl)glycine
[N(CH2CH2OH)2(CH2COOH)], N-hydroxyiminodiacetic acid
[HON(CH2COOH)2], N-hydroxy-2,2Ј-iminodipropionic acid
[HON{CH(Me)COOH}2] and picolinic acid (NC5H4COOH-2),
V
) complex [Re{(OCH2-
plexes have been characterized by IR, 1H and 13C NMR spec-
troscopy, FAB+-MS, elemental analysis and X-ray diffraction
structural analysis, which indicate a π-delocalized chelated
benzoylhydrazidorhenium ring in 1 and 2, and, in the other
complexes, an essentially linear η1-diazenido ligand that is
always trans to the O-coordinated carboxylate moiety of the
N,O-ligand. The complexes act as catalysts (TON values up
to about 45) for peroxidative oxidation, by radical mecha-
nisms, of cyclohexane and cyclopentane to the correspond-
ing alcohols and ketones, under mild conditions (room tem-
perature, use of aqueous H2O2 and without added acid). This
is an unprecedented use of inorganic Re coordination com-
pounds as catalysts in alkane functionalization.
)
=
respectively. The N,O-ligands in 4 and 5 result from fragmen- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
tation of the N-hydroxyiminodicarboxylic acids. All the com- Germany, 2005)
ally limited to amines.[29–31] Hence, one of the aims of this
work is to extend the application of complex 1 to the syn-
thesis of benzoyldiazenido complexes with coligands of the
Introduction
The coordination chemistry of rhenium[1] is a field of
current growing interest from various viewpoints, especially
latter type.
for improving fundamental knowledge (e.g. on structural
Another objective of this study is to find catalytic appli-
and physicochemical properties and on reactivity) and in
cations of such complexes, thus providing a contribution
topics with an applied character such as the development
towards widening the field of catalysis with inorganic coor-
of diagnostic/radiotherapeutic cancer agents,[2,3] nitrogen
dination compounds of rhenium, which still remains little
fixation (a good number of Re dinitrogen and formally de-
explored.[32–41] This contrasts with the recently discovered
rived organodiazo-type complexes are known)[4–13] and ca-
catalytic behaviour of high-valent organorhenium ox-
talysis.[14–24]
ides,[14–24] in particular the methyltrioxide [(Me)ReO3],
For the synthesis of diazenido and dinitrogen complexes
whose catalytic behaviour has been extensively studied for
with phosphorus-containing coligands, the benzoylhydra-
a variety of processes, such as epoxidation and hydroxyla-
zide complex [ReCl2{N=NC(O)Ph}(PPh3)2] (1) is a key
tion of olefins, oxidation of alkynes, aromatic hydro-
starting material,[25–28] but its use as a precursor for com-
carbons, sulfides, amines, silanes, alcohols and ketones, and
plexes with N-based coligands is still very rare and is usu-
cyclization reactions.
As the catalytic reaction to be tested, we chose the oxi-
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
dation of cyclohexane and of cyclopentane to the corre-
Técnico,
sponding alcohols and ketones, as examples with industrial
significance within the challenging field of functionalization
of alkanes.[42–47] In fact, the cyclohexanol/cyclohexanone
mixture is used[42,48–50] for the synthesis of adipic acid,
Nylon-6,6Ј, polyamide-6 and urethane foams and as an aci-
dulant in baking powder and lubricating additives, whereas
cyclopentanol and cyclopentanone are used[51–57] in the
Av. Rovisco Pais, 1049-001 Lisbon, Portugal
Fax: +351-21-8464455
E-mail: pombeiro@ist.utl.pt
[b] University of Joensuu, Department of Chemistry,
P. O. Box 111, 80101, Joensuu, Finland
[c] Universidade Lusófona de Humanidades e Tecnologias,
Campo Grande 376, 1749-024 Lisbon, Portugal
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2005, 2071–2080
DOI: 10.1002/ejic.200400991
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FULL PAPER
preparation of perfumes, dibasic carboxylic acids, dyes and anol led to the formation of neutral benzoylhydrazido (2)
liquid herbicide compositions. We have previously found and diazenido (3–6) complexes, in 30–55% yields, as shown
that the peroxidative oxidation of cyclohexane and cyclo- in Scheme 1. All complexes were characterized by IR,
1
pentane to those products is catalyzed by some vanadi- FAB+-MS, H and 13C{1H} NMR spectroscopy, elemental
um(iv) or (v) complexes with N,O-ligands,[58] as well as by analysis and single-crystal X-ray diffraction analysis.
heteronuclear iron(iii)–chromium(iii) hydroxo complexes
In the reaction of 1 with triethanolamine (reaction 1,
Scheme 1) the latter, upon deprotonation of two alcohol
and hydroxides.[59]
For the current study, as sources of N-ligands we have
moieties, provides a dianionic tridentate N,O,O-ligand that
addressed N,O-types (or related compounds) that we have
replaces one triphenylphosphane and two chloride ligands,
used for the preparation of vanadium catalysts for alkane
with preservation of the chelated benzoylhydrazido frag-
functionalization reactions, namely peroxidative hydroxyla-
ment in the green product [Re{(OCH2CH2)2N-
tion, oxygenation and halogenation,[58] and carboxyla-
(CH2CH2OH)}{N=NC(O)Ph}(PPh3)]
(2).
N,N-Bis(2-
tion.[60] They are the amino alcohol N(CH2CH2OH)3, the
glycine derivative N(CH2CH2OH)2(CH2COOH), picolinic
acid (NC5H4COOH-2), N-hydroxyiminodiacetic acid
[HON(CH2COOH)2, HIDA] and N-hydroxy-2,2Ј-imino-
dipropionic acid [HON{CH(Me)COOH}2, HIDPA].
Hence, we report herein the synthesis and characteriza-
tion, including the crystal structures, of a series of new ben-
zoylhydrazido- and -diazenidorhenium complexes with
these, or derived, chelating N,O-ligands, as well as their
catalytic activity for the peroxidative oxidation under mild
conditions (room temperature, aqueous H2O2 and without
added acid) of cyclohexane and cyclopentane to the corre-
sponding alcohols and ketones, which, to the best of our
knowledge, is the first example of such a type of alkane
functionalization with Re coordination compounds as cata-
lysts.
hydroxyethyl)glycine [bicine, N(CH2CH2OH)2(CH2-
COOH)] also generates an N,O,O-ligand by deprotonation
of the carboxylic acid group. Reduction of the metal to the
+3 oxidation state also occurs, the chelated benzoylhy-
drazido ring opens to form the η1-NNCOPh diazenido li-
gand and only one ligated chloride is replaced (besides one
of the phosphanes) to afford the greenish-blue complex
[ReCl{N(CH2COO)(CH2CH2OH)(CH2COOH)}{N=NC-
(O)Ph}(PPh3)] (3) (reaction 2, Scheme 1). In complexes 2
and 3 the N,O,O-ligands contain hydroxyethyl arms, in
agreement with the detection, in the IR spectra, of strong
and broad bands in the 3500–3200 cm–1 range assigned to
ν(OH). The IR spectra of 3 and all the other benzoyldiazen-
ido compounds show a strong band in the 1700–1630 cm–1
range assigned to ν(C=O), whereas for all the complexes
ν(N=N), associated to either η2- or η1-NNC(O)Ph, is ob-
served in the 1513–1436 cm–1 range.
In their reactions with complex 1, the N-hydroxyiminod-
icarboxylic acids (HIDA and HIDPA) undergo fragmenta-
tion, leading to the formation of the OǟNCH2COO– (N-
oxyaminoacetate) and HN=C(Me)COO– (2-iminopropi-
Results and Discussion
Synthesis and Spectroscopic Characterization
The reaction of the benzoylhydrazido chelate 1 with vari- onate) ligands in the η1-benzoyldiazenidorhenium(iii) prod-
ous potential N,O-polydentate ligands in refluxing meth- ucts [ReCl{N(=O)CH2COO}{N=NC(O)Ph}(PPh3)2] (4)
Scheme 1. (1) N(CH2CH2OH)3; (2) N(CH2CH2OH)2(CH2COOH) (bicine); (3) HON(CH2COOH)2 (HIDA); (4) HON{CH(CH3)COOH}2
(HIDPA); (5) NC5H4COOH-2.
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Benzoylhydrazido and -diazenidorhenium Complexes with N,O-Ligands
FULL PAPER
[ν(N=O)
=
1626 cm–1] and [ReCl{HN=C(Me)COO}-
{N=NC(O)Ph}(PPh3)2] (5), respectively (reactions 3 and 4,
Scheme 1). HIDPA fragmentations have been rarely charac-
terized, although some examples[61] are provided by the re-
action with [PPh4][ReOBr4], [ReOCl3(PPh3)2], [ReOCl2(O-
Et)(PPh3)2] or [PPh4][MoOCl4(H2O)], leading to the forma-
tion
of
2-[(1-carboxyethoxy)imino]propionic
acid
[HOOCC(Me)=N{OCH(Me)COO–}], 2-iminopropionate
[HN=C(Me)COO–], 2,2Ј-iminodipropionate [HN{CH(Me)-
COO–}2] and 2-oxidoiminopropionic acid [HOOCC-
(Me)=NǞO] ligands, respectively. The 2-iminopropionate
ligand in 5 has a precedent in [PPh4][ReOBr3{HN=C-
(Me)COO}],[61] whereas the N-oxyaminoacetate in 4 ap-
pears to result from a different type of HIDA fragmenta-
tion.
Similar to complexes 4 and 5, the η1-benzoyldiazeni-
dorhenium(iii) product [ReCl{C5H4N(COO)}{N=NC(O)-
Ph}(PPh3)2] (6) obtained from the reaction of picolinic acid
with 1 (reaction 5, Scheme 1) also has an anionic bidentate
N,O-ligand, in this case simply corresponding to the basic
form of the acid reagent.
The molecular ions were clearly observed with the ex-
pected isotopic patterns in the FAB+-mass spectra of all
compounds, except 3. Other typical peaks correspond to
the stepwise fragmentations by loss of Cl, N2COPh, PPh3
and N,O-ligand fragments. The 1H and 13C{1H} NMR
spectra show resonances at the usual chemical shifts for the
coordinated PPh3, N2COPh and N,O-ligands.[29–31,62–69] El-
emental analyses are also consistent with the proposed for-
mulations, which were authenticated by single-crystal X-ray
diffraction studies, as indicated below.
Figure 1. An ORTEP-3 representation of 1. Hydrogen atoms and
solvent molecule have been omitted for clarity.
bond lengths indicate significant multiple bonding charac-
ter, and therefore a delocalized π-system, which is also in
agreement with the Re–N1–N2 angles of 133.4(4)° in 1 and
131.7(3)° in 2.[70,71] According to a classification of organ-
ohydrazido ligands[71] (assuming the convention that all
electrons involved in the Re–N bond are donated by the
hydrazine precursor), the benzoylhydrazido ligand in the
chelates 1 and 2 exhibits features of both a hydrazido(3–)
(a) and a diazenido(1–) (b) species.
X-ray Crystal Structures
Green single crystals of the starting material 1·C6H6 were
grown by slow evaporation at 5 °C of an EtOH/C6H6 solu-
tion and the crystal structure was solved in order to com-
pare its crystal data with those of the newly obtained com-
plexes. The molecular structure of 1 (Figure 1) consists of
discrete mononuclear species of distorted octahedral geom-
etry with trans phosphane ligands and the other ligands in
equatorial sites. Hence, the chloride ligands are trans to the
nitrogen and carbonyl oxygen donors of the chelating ben-
zoylhydrazido ligand. The bonding parameters (Table 1) are
similar to those of the analogous complex [ReCl2{N=NC-
(O)C6H4Cl-4}(PPh3)2].[70]
Figure 2. An ORTEP-3 representation of 2. Ph hydrogen atoms
have been omitted for clarity.
All the other complexes also exhibit distorted octahedral
coordinations and, for those with two phosphanes (4–6),
these bulky ligands are trans to each other, as in complex
1, in agreement with steric requirements.
In complex 2 (Figure 2), one triethanolamine is depro-
tonated at two oxygen atoms (O2, O3) and binds the metal
through the amino-N and these atoms. The Re–N1, Re–O1,
Re–P1 and N1–N2 distances (Table 1) are similar to those
of 1. Within the chelating benzoylhydrazide ligand, the
In 2 the Re–O2 and Re–O3 lengths of 1.94–1.97 Å are
short Re–N1 [1.776(5) and 1.798(3) Å in 1 and 2, respec- unexceptional for deprotonated oxygen atoms bonded to a
tively] and N1–N2 [1.309(6) and 1.336(4) Å, respectively] metal centre, and are shorter than Re–O1 [2.170(3) Å]. The
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A. M. Kirillov, M. Haukka, M. F. C Guedes da Silva, A. J. L Pombeiro
Table 1. Selected bond lengths [Å] and angles [°] for compounds 1–6.
FULL PAPER
1
2
3
4
5
6
Re–N(1)
N(1)–N(2)
C(1)–N(2)
C(1)–O(1)
C(1)–C(2)
Re–O(1)
Re–N(3)
Re–O(2)
Re–O(3)
Re–Cl(1)
Re–Cl(2)
Re–P(1)
Re–P(2)
C(3)–N(3)
C(3)–C(4)
C(4)–O(3)
C(4)–O(2)
N(3)–O(4)
Re–N(1)–N(2)
N(1)–N(2)–C(1)
O(1)–C(1)–N(2)
N(1)–Re–O(1)
N(1)–Re–O(2)
N(1)–Re–N(3)
N(3)–Re–O(2)
Re–N(3)–C(3)
Re–O(2)–C(4)
P(1)–Re–P(2)
N(3)–Re–P(1)
N(3)–Re–Cl(1)
1.776(5)
1.309(6)
1.376(7)
1.272(7)
1.470(8)
2.122(4)
1.798(3)
1.336(4)
1.358(5)
1.279(5)
1.469(6)
2.170(3)
2.217(3)
1.944(3)
1.974(3)
1.740(3)
1.280(5)
1.381(6)
1.234(5)
1.496(6)
1.734(7)
1.264(9)
1.408(11)
1.234(11)
1.476(12)
1.735(3)
1.271(5)
1.398(6)
1.228(5)
1.489(6)
1.745(6)
1.259(9)
1.396(11)
1.211(11)
1.482(13)
2.243(4)
2.119(3)
2.095(3)
2.3948(10)
2.078(8)
2.090(6)
2.175(3)
2.089(3)
2.109(7)
2.067(5)
2.3723(14)
2.3672(14)
2.4528(15)
2.4654(15)
2.420(2)
2.4017(10)
2.409(2)
2.3798(12)
2.3758(11)
2.475(2)
2.487(2)
1.470(12)
1.465(15)
1.241(11)
1.295(11)
1.246(14)
169.3(6)
120.8(7)
124.0(8)
2.4438(8)
2.4583(8)
1.417(15)
1.577(16)
1.223(5)
1.305(5)
2.4660(16)
2.4588(16)
1.497(5)
1.502(6)
1.434(5)
1.503(6)
1.489(7)
1.391(15)
1.456(5)
133.4(4)
104.3(5)
117.7(5)
71.48(18)
131.7(3)
105.6(3)
119.0(4)
71.72(13)
152.65(14)
98.67(13)
79.51(12)
103.9(2)
176.0(3)
115.7(3)
124.3(4)
177.4(3)
115.2(3)
123.8(4)
168.3(6)
119.3(7)
124.1(8)
96.40(14)
97.55(15)
80.27(13)
102.9(3)
113.1(3)
176.4(3)
99.6(3)
77.6(3)
113.8(6)
118.1(6)
178.11(7)
90.1(2)
170.42(13)
94.55(14)
75.91(12)
114.1(7)
168.0(2)
92.7(3)
75.4(2)
121.4(2)
174.77(5)
174.79(8)
91.98(10)
164.87(9)
175.9(7)
89.5(3)
164.68(19)
171.06(9)
174.87(10)
89.25(10)
164.5(2)
binding of the triethanolamine ligand involves the chelate
rings Re–N3–C3–C4–O3 and Re–N3–C5–C6–O2 with O3–
Re–N3 and O2–Re–N3 bite angles of 82.14(12)° and
79.51(12)°, respectively. The Re–N3 bond [2.217(3) Å] is
significantly longer than Re–O2 [1.944(3) Å] and Re–O3
[1.974(3) Å], as commonly observed for O,N,O- or N,O-do-
nor ligands,[61,72] and is also longer than the Re–N1 bond
[1.798(3) Å], as anticipated for sp3 hybridization at the N3
site and sp2 hybridization at N1, and in agreement with the
appreciable double-bond character of the latter bond.
In the structures of 3–6 (Figures 3, 4, 5 and 6, respec-
tively), the opening of the chelated benzoylhydrazido ring
has occurred and the Re–N1–N2 angle of the resulting η1-
diazenido ligand is essentially linear [176.0(3)° in 3,
169.3(6)° in 4, 177.4(3)° in 5 and 168.3(6)° in 6]. The Re–
N1, N1–N2 and C1–O1 distances (Table 1) are slightly
shorter than those in the η2-NNC(O)Ph ligand in 1 and 2,
which is indicative of a slight increase of the double-bond
character. According to the above classification,[71] the η1-
NNC(O)Ph ligand in compounds 3–6 exhibits features of
a linear, four-electron donor diazenido(1–) (c). In all these
complexes, this ligand adopts the position trans to the O-
coordinated carboxylato group of the chelating N,O-ligand,
in preference to being trans to any N, Cl or P atoms.
Figure 3. An ORTEP-3 representation of 3. Ph hydrogen atoms and
solvent molecules have been omitted for clarity.
The bicine ligand in 3 involves the chelate rings Re–N3–
C3–C4–O2 and Re–N3–C5–C6–O3, with O2–Re–N3 and
O3–Re–N3 bite angles of 80.27(13)° 78.84(12)°, respectively.
The Re–N3(amine) distance of 2.243(4) Å (Table 1) is com-
parable with the corresponding one observed for complex
2, although the Re–O2 and Re–O3 bond lengths of 2.119(3)
and 2.095(3) Å are slightly longer than those in 2.
In the structures of 4–6 (Figures 4, 5 and 6, respectively)
most of the corresponding bond lengths and angles are sim-
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Benzoylhydrazido and -diazenidorhenium Complexes with N,O-Ligands
FULL PAPER
Figure 5. An ORTEP-3 representation of 5. Ph hydrogen atoms and
solvent molecules have been omitted for clarity.
Figure 4. An ORTEP-3 representation of 4. Ph hydrogen atoms
have been omitted for clarity.
to those of related complexes with picolinate or 3-hydroxy-
picolinate ligands such as [ReO(Me)(NC5H4COO)2],
ilar (Table 1). Each N,O-ligand forms a chelate ring with a [ReH(NC5H4COO)2(PPh3)2], [ReOI2{NC5H3(OH-3)COO}-
restricted O–Re–N bite angle, the N3 atom being always (PPh3)] and [ReOCl3{NC5H3(OH-3)COO}].[74–77] However,
trans to the chloride and the O2 atom trans to the diazenido the Re–N3 bond length [2.175(3) Å] in 5 is longer than the
ligand. The Re–O2 and Re–N3 bond lengths are usually Re–O2 distance [2.089(3) Å].
similar to those of other Re complexes.[61,73] Hence, for ex-
In the HN=C(CH3)COO– ligand in 5, the C3–N3 dis-
ample, for complex 6 most of the bond lengths are similar tance of 1.417(15) Å is much longer than the corresponding
Figure 6. An ORTEP-3 representation of 6. Hydrogen atoms and solvent molecule have been omitted for clarity.
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FULL PAPER
C=N bond length in [PPh4][ReOBr3{HN=C(Me)COO}],[61]
even though the X-ray diffraction analysis shows that there
is no hydrogen at the C3 atom.
Peroxidative Oxidation of Cyclohexane and Cyclopentane
Acetonitrile solutions of all our complexes 1–6 exhibit
catalytic activity for the peroxidative oxidation of cyclohex-
ane to the corresponding cyclohexanone and cyclohexanol
at room temperature (see Scheme 2 and Table 2 for selected
data and Table S1 in the Supporting Information). The
amount of hydrogen peroxide has a strong effect, and in-
creasing the peroxide-to-catalyst molar ratio within the
2000–32000 range leads to an enhancement of the turnover
numbers (TONs); for example, the total TON when using
complex 3 as a catalyst increases from 5 to 43 on increasing Figure 7. Effect of the oxidant-to-catalyst molar ratio on the total
TON values in the oxidation of cyclohexane catalyzed by com-
plexes 2 and 3.
this ratio from 4000 to 32000 (Figure 7). The highest ac-
tivity is displayed by complexes 3 and 6, followed by the
chelate 1, with total TONs of 43, 42 and 39 and turnover
frequency (TOF) values of 7.2, 7.0 and 6.5 h–1, respectively,
play a higher selectivity towards the formation of cyclo-
for the latter peroxide-to-catalyst ratio. These values are
hexanol, in comparison with cyclohexanone, and the
comparable to those we have achieved (maximum TON of
average alcohol/ketone molar ratio is within the 1.5–1.8
range.
46)[58] with vanadium catalysts like Amavadine [V(O,N-
L)]2– (O,N-L
=
tribasic form of HIDPA) and
The Re complexes also catalyze the peroxidative oxi-
dation of cyclopentane to the corresponding cyclopentanol
and cyclopentanone, but the catalytic activity (Table S2 in
the Supporting Information) is lower than for the oxidation
of cyclohexane. The TONs also increase with the amount
of hydrogen peroxide. For a peroxide-to-catalyst molar ratio
of 32000, the total TON is 13 when using complex 6 as a
catalyst, whereas the other complexes exhibit lower TON
values (from 3 to 8).
[VO{N(CH2CH2O)3}]. The other complexes (2, 4 and 5) are
less active for sufficiently high H2O2/catalyst ratios, with to-
tal TONs (ca. 21–22) that are half of those of the other
complexes, for the above peroxide-to-catalyst ratio.
In contrast with the lower activity for cyclopentane than
for cyclohexane oxidation, a higher selectivity is observed
for the formation of the alcohol, i.e. cyclopentanol, for
moderately high peroxide-to-catalyst molar ratios. In fact,
cyclopentanol is the only oxidation product detected for all
the complexes at n(H2O2)/n(catalyst) = 16000. However, the
formation of cyclopentanone, a more oxidized product, also
occurs for complexes 3 and 6 at the higher value of 32000
for the peroxide-to-catalyst molar ratio.
The peroxidative oxidation of cycloalkanes is believed to
proceed by a radical mechanism since no traces of cyclo-
hexanol or cyclohexanone are detected when the above re-
actions that normally lead to the highest TON values are
performed in the presence of a radical trap like 2,6-di-tert-
butyl-4-methylphenol (BHT; 0.5 molar ratio with respect
to the alkane). Although we have not yet succeeded in the
isolation and full characterization of intermediates, the pro-
cess conceivably involves[46,47,50,58,78–80] the formation of in-
termediate peroxo and oxo complexes. It is noteworthy that
the oxo-peroxomethylrhenium(vii) complex [(Me)ReO-
(O2)2] is the active species of the known [(Me)ReO3]/H2O2
system in olefin and aromatic oxidations.[16] Peroxo-derived
Scheme 2.
Table 2. Peroxidative oxidation of cyclohexane catalyzed by the Re
complexes.[a]
Catalyst
Turnover number (TON)[b]
Turnover frequency
(TOF)[d]
Cyclohexanol Cyclohexanone Total[c]
1
24
13
27
14
13
25
15
8
16
8
9
17
39
21
43
22
22
42
6.5
3.5
7.2
3.7
3.7
7.0
2
3[e]
4
5
6[f]
[a] Selected data from Table S1. n(H2O2)/n(C6H12) = 2:1, n(H2O2)/
n(Re catalyst) = 32000, molar yield (% relative to substrate) =
6.3×TON×10–3, unless stated otherwise. [b] Mol product/mol Re
catalyst precursor. [c] Cyclohexanol + cyclohexanone. [d] Mol
products/mol Re catalyst precursor per hour. [e] For n(H2O2)/n-
(C6H12) = 16:1 the molar yield is 1.9%. [f] For n(H2O2)/n(C6H12)
= 16:1 the molar yield is 2.4%.
Higher catalytic activities would be expected upon fur- radical complexes could abstract an H atom from the al-
ther increase of the peroxide-to-catalyst ratio (see Figure 7), kane (RH) to generate an R· radical, which, on reaction
but this was not tested for safety reasons. All catalysts dis- with a hydroperoxo or hydroxo complex, could lead to the
2076
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 2071–2080

Benzoylhydrazido and -diazenidorhenium Complexes with N,O-Ligands
FULL PAPER
alcohol ROH; further oxidation of the latter would yield contribution towards the development of the still under-
the corresponding ketone. developed field of catalysis with rhenium inorganic coordi-
The role of the chelating N,O and diazenido ligands in nation compounds. However, more-effective systems are
our systems is still unclear but one can postulate their in- needed, as well as the extension to other types of alkane-
volvement (e.g. upon decoordination, in the former, of a functionalization reactions, points that are currently being
single N or O atom) in proton-transfer steps among oxo-, addressed in our laboratory.
peroxo- and hydroxo-Re complexes. Such a role in the pro-
motion of proton transfer from coordinated H2O2 to oxo
ligands has been proposed[78,79] for some vanadium systems Experimental Section
with N,O additives as cocatalysts.
General Materials and Procedures: All synthetic work was per-
Re-catalyzed alkane oxidations are essentially unex-
formed under nitrogen using standard Schlenk techniques. The sol-
plored. In the only previously published case, the or-
vents were dried over appropriate drying agents and degassed by
ganometallic [(Me)ReO3]/pyrazine-2-carboxylic acid system
was found to be active for the peroxidative oxidation of
cyclohexane by anhydrous H2O2 in refluxing acetonitrile
solution at 80 °C (TON of 126);[80] however, if aqueous
30% H2O2 was used almost no oxidation of cyclohexane
occurred.[80] Our systems have the advantage of operating
under milder conditions, i.e. at room temperature, with
aqueous H2O2 and without added acid. Nevertheless, in all
the cases the yields (based on the alkane), under the experi-
mental conditions used, are still modest (not above 3% for
our complexes and even lower (1.5%) for [(Me)ReO3]), al-
though these are still significant in the field of alkane func-
tionalization under mild or moderate conditions. A maxi-
mum yield of 9% was achieved[58] for the same alkane reac-
tion with the above vanadium catalysts.
standard methods. Potassium perrhenate (Merck), triphenylphos-
phane (Aldrich), benzoylhydrazine (Aldrich), triethanolamine
(Fluka), N,N-bis(2-hydroxyethyl)glycine (bicine; Aldrich), picolinic
acid (Aldrich), 2,6-di-tert-butyl-4-methylphenol (BHT; Aldrich),
bromoacetic acid (Merck), hydroxylammonium chloride (Aldrich)
and zinc acetate (Aldrich) were obtained from commercial sources
and used as received. [N-Benzoylhydrazido(3–)-NЈ,O]dichlorobis-
(triphenylphosphane)rhenium(v)
[ReCl2{NNC(O)Ph}(PPh3)2]
(1),[25,26] N-hydroxyiminodiacetic acid[81] and N-hydroxy-2,2Ј-
iminodipropionic acid[81] were prepared by published methods.
Elemental analyses were carried out by the Microanalytical Service
of the Instituto Superior Técnico. Melting points were determined
on a Kofler table. Positive-ion FAB mass spectra were obtained on
a Trio 2000 instrument by bombarding 3-nitrobenzyl alcohol
(NBA) matrices of the samples with 8 keV (ca. 1.18×1015 J) Xe
atoms. Mass calibration for data system acquisition was achieved
with CsI. IR spectra (4000–400 cm–1) were recorded on a Jasco FT/
1
IR-430 instrument as KBr pellets. H and 13C{1H} NMR spectra
were measured on a Varian UNITY 300 spectrometer at ambient
temperature.
Conclusions
This work has shown that the benzoylhydrazido chelate
[ReCl2{NNC(O)Ph}(PPh3)2] (1), which is a recognized key
starting material for a diversity of hydrazido, diazenido and
even dinitrogen Re complexes with P-based coligands (or-
ganophosphanes, -phosphites or -phosphonites), can also
provide a convenient entry point for the synthesis of benzo-
ylhydrazido and benzoyldiazenido complexes of Re (in the
+5 and the +3 oxidation states) with chelating N,O,O- and
N,O-coligands of various types, including amino alkoxides
and amino-, oxyamino-, imino- and pyridinocarboxylates.
π-Electron delocalization along the hydrazido- and diazeni-
dorhenium moiety has been observed, with the Re–N bond
exhibiting some double-bond character. The benzoyldiazen-
ido ligand occupies the trans position relative to the O-lig-
ated carboxylato group, preferably to the softer N atom of
the N,O- or N,O,O-ligand, an observation that may be of
synthetic significance and deserves further exploration.
This study also demonstrates, for the first time, that Re
coordination compounds can act as catalysts for alkane hy-
droxylation and oxygenation, by showing the unprece-
dented catalytic activity of such a type of complexes, under
mild conditions, in the peroxidative oxidation of cycloal-
kanes to the corresponding alcohols and ketones. The reac-
tions appear to follow a radical mechanism, although com-
plete details have yet to be established. The catalytic ac-
tivity, although appreciable in the field of mild alkane func-
[Re{(OCH2CH2)2N(CH2CH2OH)}{NNC(O)Ph}(PPh3)] (2): An ex-
cess of triethanolamine (43 μL, 0.327 mmol) was added to a sus-
pension of 1 (100 mg, 0.109 mmol) in 7.5 mL of MeOH and the
reaction mixture was refluxed for about 5 h. The resulting dark-
brown clear solution was concentrated under reduced pressure and
then treated with 20 mL of Et2O. The solid (triethanolamine hydro-
chloride) that separated out from the resulting solution was filtered
off and discarded. The filtrate was evaporated under reduced pres-
sure to give a green oil, which was dissolved in 1.5 mL of C6H6.
The addition of n-pentane (20 mL) caused the precipitation of a
solid, which was filtered off, washed with n-pentane (3×10 mL)
and dried in vacuo to yield complex 2 as a green solid. Yield: 43 mg
(54% based on 1). Product 2 is soluble in MeOH, Me2CO, Et2O
and C6H6. M.p. 153 °C (dec.). C31H33N3O4PRe (728.79): calcd. C
51.02, H 4.56, N 5.76; found C 50.50, H 4.53, N 5.56. FAB+-MS
(NBA): m/z = 730 [M+ + H], 612 [M+ – (N2COPh) + O], 596 [M+
–
(N2COPh)], 467 [M+ – PPh ]. FTIR (KBr): ν = 3416 and 3311 (s
˜
3
br.) ν(OH), 2960 (m) νas(CH), 2853 (m) νs(CH), 1436 (s) ν(NN),
1
1355 (s) ν(C–O) cm–1. H NMR (CDCl3): δ = 7.88–7.83 (m, 5 H,
Ph), 7.49–7.32 (m, 15 H, PPh3), 3.66 (t, J = 5.4 Hz, 4 H, CH2-O),
2.69 (t, J = 4.8 Hz, 4 H, CH2-N), 2.37–2.18 (m, 4 H, CH2CH2OH)
ppm. 13C{1H} NMR (CDCl3): δ = 134.2, 134.1, 130.0, 129.7, 128.1
and 128.0 (PPh3), 132.9, 131.6, 130.6 and 127.6 (Ph), 60.3, 58.1,
59.6 and 56.7 (CH2) ppm; PhCO was not observed. X-ray quality
crystals were grown at 5 °C by vapour diffusion of n-C5H12 into an
Et2O or an acetone solution of 2.
[ReCl{N(CH2COO)(CH2CH2OH)(CH2CH2OH)}{N=NC(O)Ph}-
(PPh3)] (3): A mixture of 1 (50 mg, 0.055 mmol) and bicine (27 mg,
tionalization, is still modest. Hence, this study provides a 0.165 mmol) was refluxed in MeOH (10 mL) for about 8 h. The
Eur. J. Inorg. Chem. 2005, 2071–2080
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A. M. Kirillov, M. Haukka, M. F. C Guedes da Silva, A. J. L Pombeiro
FULL PAPER
resulting dark-brown clear solution was concentrated to 5 mL un-
der reduced pressure and 30 mL of Et2O was added. The obtained
greenish-brown solution was left to stand for 2 d at room tempera-
ture. During this time greenish-blue microcrystals of 3 separated
out of the solution. They were collected, washed with MeOH
(3×10 mL) and dried in vacuo. Yield: 21 mg (48% based on 1).
Product 3 is slightly soluble in DMSO and insoluble in C6H6,
MeOH, Me2CO, CHCl3 and CH2Cl2. M.p. 201 °C (dec.).
C31H32ClN3O5PRe (779.24): calcd. C 47.78, H 4.14, N 5.39; found
C 47.57, H 3.96, N 5.21. FAB+-MS (NBA): m/z = 744 [M+ – Cl],
610 [M+ – Cl – (N2COPh)], 582 [M+ – Cl – {N(CH2CH2OH)2-
observed. X-ray quality crystals of 5·2EtOH were grown by slow
evaporation at 5 °C of EtOH/C6H6 or EtOH/CH2Cl2 solutions.
[ReCl{C5H4N(COO)}{N=NC(O)Ph}(PPh3)2] (6): A mixture of 1
(50 mg, 0.055 mmol) and picolinic acid (21 mg, 0.165 mmol) was
refluxed in MeOH (10 mL) for about 12 h. The resulting deep-red
cloudy solution was taken to dryness under reduced pressure to
give a red residue to which 30 mL of MeOH was added to obtain
a suspension of 6. This was filtered off, washed with MeOH
(3×15 mL) and dried in vacuo to furnish complex 6 as a red solid.
Yield: 30 mg (55% based on 1). Product 6 is soluble in Me2CO,
Et2O, C6H6, CH2Cl2 and CHCl3. M.p. 232 °C (dec.).
C49H39ClN3O3P2Re (1001.5): calcd. C 58.73, H 3.93, N 4.20; found
C 58.45, H 4.16, N 4.02. FAB+-MS (NBA): m/z = 1002 [M+ + H],
966 [M+ – Cl], 868 [M+ – (N2COPh)], 879 [M+ – (C5H4NCOO)],
833 [M+ – Cl – (N2COPh)], 746 [M+ – (C5H4NCOO) – (N2COPh)],
711 [Re(PPh3)2], 571 [M+ – Cl – (N2COPh) – PPh3], 448 [RePPh3].
(CH COO)}]. FTIR (KBr): ν = 3429 and 3265 (s br.) ν(OH), 2925
˜
2
(m) νas(CH), 2854 (m) νs(CH), 1631 (s) ν(C=O), 1458 (s) ν(N=N)
cm–1. 1H NMR (CDCl3): δ = 7.77–7.33 (m, 20 H, PPh3 + Ph), 4.25–
3.59 and 3.15–2.97 (m, 10 H, CH2) ppm. 13C{1H} NMR (CDCl3): δ
= 179.1 (PhC=O), 167.6 (CH2C=O), 134.1, 133.6, 132.9, 131.6,
130.7, 130.3, 129.3, 128.7 and 128.1 (PPh3 + Ph), 56.0, 55.6, 54.9,
53.6, and 16.2 (CH2) ppm. X-ray quality crystals of 3·H2O were
grown by slow evaporation at 5 °C of Et2O/MeOH or MeOH/
Me2CO solutions.
FTIR (KBr): ν = 1673 and 1638 (s) ν(C=O), 1456 (s) ν(N=N),
˜
1
1307 (m) ν(C–O) cm–1. H NMR (CDCl3): δ = 7.80–7.73 (m, 4 H,
PyH), 7.59–7.43 (m, 30 H, PPh3), 6.95–6.85 (m, 5 H, Ph) ppm.
13C{1H} NMR (CDCl3): δ = 134.6, 134.5, 134.2, 133.8, 130.2,
130.0, 128.4, 128.3, 128.0 and 127.8 (PyC, PPh3 and Ph) ppm; C=O
was not observed. X-ray quality crystals of 6·Me2CO were grown
by slow evaporation at 5 °C of an acetone solution.
[ReCl{N(=O)CH2COO}{N=NC(O)Ph}(PPh3)2] (4): An excess of
HIDA (28 mg, 0.18 mmol) was added to a suspension of 1 (50 mg,
0.055 mmol) in 10 mL of MeOH and the reaction mixture was re-
fluxed for about 7 h. The resulting reddish-yellow clear solution
was concentrated under reduced pressure and then treated with
30 mL of Et2O. The solid that separated out from the resulting
solution was filtered off and discarded. The filtrate was evaporated
under reduced pressure to give a light-brown oil, which was dis-
solved in 5 mL of C6H6 to form a yellow cloudy solution. Fil-
tration, followed by concentration under reduced pressure, yielded
a yellow oil to which 1 mL of benzene was added. The addition of
n-pentane (20 mL) led to the precipitation of a solid that was fil-
tered off, washed with n-pentane (3×10 mL) and dried in vacuo to
yield complex 4 as a yellow powder. Yield: 19 mg (35% based on
1). Product 4 is soluble in MeOH, EtOH, Me2CO, Et2O, C6H6 and
CHCl3. M.p. 220 °C (dec.). C45H37ClN3O4P2Re (967.40): calcd. C
55.84, H 3.83, N 4.34; found C 55.73, H 3.77, N 4.07. FAB+-MS
Catalytic Studies: The reaction mixtures were prepared as follows:
MeCN (3.00 mL), H2O2 (30% in H2O; 10.00 mmol) and cycloal-
kane (cyclohexane or cyclopentane; 5.00–0.625 mmol) were added,
in this order, to 0.313–5.00×10–3 mmol of the Re complex 1–6
(used either as a solid or as a 0.02 m MeCN solution) in the reac-
tion flask. The reaction mixture was stirred for 6 h at room tem-
perature and normal pressure, then 90 μL of cycloheptanone (as
internal standard) and 10.00 mL of diethyl ether (to extract the
substrate and the organic products from the reaction mixture) were
added. The obtained mixture was stirred for 10 min and then a
sample was taken from the organic phase and analyzed by gas
chromatography using a FISONS Instruments GC 8000 series gas
chromatograph with a DB WAX fused silica capillary column (P/N
123-7032) and the JASCO-BORWIN v.1.50 software. The obtained
results for cyclohexane and cyclopentane oxidation are given as
Supporting Information (Tables S1 and S2, respectively); selected
values are given in Table 2.
(NBA): m/z = 966 [M+ – H], 879 [M+ – (ONCH2COO)], 832 [M+
(N2COPh) – 2H], 746 [M+ – (ONCH2COO) – (N2COPh)]. FTIR
–
(KBr): ν = 2925 (w) ν (CH), 1700 (s) ν(C=O), 1626 (s) ν(N=O),
˜
as
1513 (s) ν(N=N) cm–1. 1H NMR (CDCl3): δ = 7.74–7.70 and 7.41–
Blank experiments were performed for both cycloalkanes with
H2O2 and confirmed that no product of alkane oxidation was ob-
tained in the absence of metal catalyst.
7.43 (m, 30 H, PPh3), 7.62–7.58 (m, 5 H, Ph), 2.32 (s, 2 H, CH2)
ppm. 13C{1H} NMR (CDCl3):
δ = 195.5 (PhC=O), 174.5
(CH2C=O), 134.4, 134.3, 130.4, 128.4 and 128.4 (PPh3), 133.7,
132.4, 128.8 and 127.9 (Ph), 29.0 (CH2) ppm. X-ray quality crystals
were grown by slow evaporation at 5 °C of an EtOH/Me2CO solu-
tion of 4.
X-ray Crystal Structure Determinations: Crystals of 1–5 were im-
mersed in perfluoropolyether, mounted in a cryo-loops and mea-
sured at 100 K. The X-ray diffraction data were collected with a
Nonius-Kappa CCD diffractometer (for 1–5) or an Enraf–Nonius
MACH3 diffractometer (for 6), equipped with graphite monochro-
mator and using Mo-Kα radiation. The Denzo-Scalepack program
[ReCl{HN=C(Me)COO}{N=NC(O)Ph}(PPh3)2] (5): Compound 5
was prepared by following the general procedure described for 4,
but using HIDPA instead of HIDA. Yield: 21 mg (40% based on
1). It is soluble in MeOH, EtOH, Me2CO, Et2O, C6H6 and CHCl3. package[82] was used for cell refinements and data reductions for
M.p. 114 °C (dec.). C46H39ClN3O3P2Re (965.43): calcd. C 57.20, H 1–5. All structures were solved by direct methods using the SIR97
4.07, N 4.35; found C 57.50, H 4.29, N 4.09. FAB+-MS (NBA):
or SIR2002 programs[83,84] with the WinGX graphical user inter-
face.[85] An empirical absorption correction was applied to all data
m/z = 967 [M+ + 2H], 932 [M+ – Cl + 2H], 879 [M+
–
{HN=C(CH3)COO}], 834 [M+ – (N2COPh) + 2H], 799 [M+ – Cl –
(N2COPh) + 2H], 746 [M+ – {HN=C(CH3)COO} – (N2COPh)],
(1–5) using XPREP in the SHELXTL v.6.12 program[86] (Tmin
/
Tmax: 0.21031/0.28346, 0.11746/0.15556, 0.21094/0.26735, 0.12878/
711 [Re(PPh ) ]. FTIR (KBr): ν = 3280 (w) ν(N–H), 1656 (s br.) 0.17642, 0.16825/0.21003 for 1–5, respectively). All structures were
˜
3 2
ν(C=O), 1630 (m) ν(C=N), 1436 (s) ν(N=N) cm–1. 1H NMR refined with the SHELXL-97 program.[87] In the structure of 5 C3
(CDCl3): δ = 7.88–7.84 and 7.17 (m, 5 H, Ph), 7.73–7.32 (m, 30 H,
PPh3), 1.46 (s) + 1.43 (s) (3 H, CH3) ppm; NH was not observed.
13C{1H} NMR (CDCl3): δ = 192.4 (PhC=O), 182.2 (N=C(Me)
C=O), 134.3, 134.0, 132.2, 132.0, 128.6 and 128.5 (PPh3), 130.5,
128.9, 128.1, 128.0 and 127.4 (Ph), 51.3 (CH3) ppm; C=N was not
and C5 were refined over two positions with occupancies of 0.57
and 0.43 and the position of the OH hydrogen (H98) was estimated
with the CALC-OH program.[88] Other OH, H2O and NH hydro-
gens were located from the difference Fourier map. All other hydro-
gens were placed in idealized positions and constrained to ride on
2078
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 2071–2080

Benzoylhydrazido and -diazenidorhenium Complexes with N,O-Ligands
FULL PAPER
Table 3. Crystal data for compounds 1–6.
1·C6H6
2
3·H2O
4
5·2EtOH
6·Me2CO
Empirical formula C49H41Cl2N2OP2Re C31H33N3O4PRe
C31H34ClN3O6PRe
797.23
100(2)
0.71073
triclinic
P1
8.9359(2)
11.2862(3)
16.0694(5)
73.7750(10)
80.903(2)
77.423(2)
1510.55(7)
2
C45H37ClN3O4P2Re C50H51ClN3O5P2Re C52H45ClN3O4P2Re
Molecular mass
Temp. (K)
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
992.88
100(2)
0.71073
triclinic
P1
11.2196(7)
11.9274(10)
17.6911(12)
108.027(4)
98.785(4)
106.011(4)
2089.2(3)
2
728.77
100(2)
0.71073
monoclinic
P21/n
9.783(2)
25.322(5)
11.297(2)
90
91.23(3)
90
2797.9(10)
4
967.37
100(2)
0.71073
monoclinic
P21/n
1057.53
100(2)
0.71073
monoclinic
P21
1059.50
293(2)
0.71069
orthorhombic
Pcab
13.8666(6)
13.9601(8)
20.4390(10)
90
96.954(3)
90
11.6355(2)
18.0462(5)
12.0749(3)
90
112.9970(10)
90
15.418(2)
19.021(2)
31.593(3)
90
90
90
γ [°]
V [Å3]
3927.5(3)
4
1.636
2333.94(10)
2
1.505
9265.1(18)
8
1.519
Z
ρcalcd. [Mgm–3
]
1.578
3.153
0.0379
1.730
4.443
0.0327
0.0590
1.753
4.213
0.0268
0.0648
μ(Mo-Kα) [mm–1
R1 [I Ն 2σ(I)]
]
3.292
0.0463
0.1010
2.779
0.0274
0.0594
2.799
0.0459
0.0652
[a]
[b]
wR2 [I Ն 2σ(I)]
0.0765
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = [Σ{w(Fo – Fc ) }/Σ{w(Fo2)2}]1/2
.
2
2 2
[12]
[13]
[14]
A. J. L. Pombeiro, R. L. Richards, Coord. Chem. Rev. 1990,
104, 13.
J. Chatt, J. R. Dilworth, R. L. Richards, Chem. Rev. 1978, 78,
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G. S. Owens, J. Arias, M. M. Abu-Omar, Catal. Today 2000,
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F. E. Kuhn, W. A. Herrmann, Struct. Bonding 2000, 97, 213.
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A. M. Santos, C. C. Romão, F. E. Kuhn, J. Am. Chem. Soc.
2003, 125, 2414.
R. Bernini, A. Coratti, G. Fabrizi, A. Goggiamani, Tetrahedron
their parent atom. The crystallographic data are summarized in
Table 3 and selected bond lengths and angles are given in Table 1.
CCDC-256902 to –256907 (for 1·C6H6, 2, 3·H2O, 4, 5·2EtOH and
6·Me2CO, respectively) 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.ac.uk/data_request/cif.
[15]
[16]
Supporting Information: Supplementary tables with the TON values
for the peroxidative oxidation of cyclohexane (Table S1) and cyclo-
pentane (Table S2) catalyzed by the Re complexes 1–6 (see also
footnote on first page of this article).
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This work was partially supported by the Fundação para a Ciência
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A.M.K. is grateful to the FCT and the POCTI program for a fel-
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for some NMR experiments, Dr. José Armando L. Silva for stimu-
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