Synthesis, structural characterization and catalytic properties of a novel monomeric rhenium(V)methyl(oxo)bis(η2-picolinato) complex: [CH3Re(O)(pic)2]

Article abstract of DOI:10.1039/a904952e

A methyl mono-oxo rhenium(V) complex with two picolinato chelating ligands has been synthesized and structurally characterized. When reacted with excess 10 or 30% H₂O₂ it forms peroxo species responsible for the catalytic activity of a highly selective two-phase medium.

Full text of DOI:10.1039/a904952e

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Synthesis, structural characterization and catalytic properties of a
novel monomeric rhenium(V)methyl(oxo)bis(ꢀ2-picolinato) complex:
[CH3Re(O)(pic)2]†
Alexis Deloffre,a Sabine Halut,b Laurent Salles,a Jean-Marie Brégeault,*a José Ribeiro Gregorio,c
Bernard Denisec and Henri Rudlerc
a Systèmes Interfaciaux à l’Echelle Nanométrique, Université Paris 6 and CNRS-ESA 7069,
case 196; 4, place Jussieu, 75252 Paris cedex 05 - France. E-mail: bregeaul@ccr.jussieu.fr
b Chimie des Métaux de Transition, Université Paris 6 and CNRS-ESA 7071;
4, place Jussieu, 75252 Paris cedex 05 - France
c Laboratoire de Synthèse Organique et Organométallique, Université Paris 6 and
CNRS-UMR 7611; 4, place Jussieu, 75252 Paris cedex 05 - France
Received 22nd June 1999, Accepted 15th July 1999
A
methyl mono-oxo rhenium(V) complex with two
picolinato chelating ligands has been synthesized and
structurally characterized. When reacted with excess 10 or
30% H2O2 it forms peroxo species responsible for the
catalytic activity of a highly selective two-phase medium.
Rhenium heptaoxide, Re2O7, has been considered as a precur-
sor for oxidations of alkenes with hydrogen peroxide; epoxides
and/or ketones are formed and cyclododecene is oxidatively
cleaved. Improvements in dihydroxy addition to C᎐C bonds
᎐
(with diol yields up to 80%) and in oxidative olefin cleavage
by “Re2O7/H2O2” (with carboxylic acid yields of 50–80%)
have been reported.1 An important improvement in this field
arose with the discovery of a novel catalytic system: “methyl-
trioxorhenium (CH3ReO3)/H2O2–t-BuOH” which can be used
for olefin epoxidation and hydroxylation.2 The precursor
CH3ReO3 3 (MTO) is expensive but can be recycled. Therefore,
rhenium compounds should be studied as oxidation catalysts
for synthetic purposes and compared to d0 transition metal pre-
cursors, particularly to the molybdenum() and tungsten()
analogues.4 While studying oxidation reactions with hydrogen
Fig. 1 CAMERON representation12 of [CH3Re(O)(pic)2] showing the
atom labelling scheme. Ellipsoids represent 20% probability. Selected
bond lengths (Å) and bond angles (Њ): Re(l)–O(1) 2.094(4), Re(l)–O(3)
2.003(4), Re(l)–O(5) 1.658(5), Re(l)–N(1) 2.097(5), Re(l)–N(2) 2.149(5),
Re(l)–C(13) 2.128(7), O(l)–C(6) 1.283(8), O(2)–C(6) 1.204(8), O(3)–
C(12) 1.329(8), O(4)–C(12) 1.198(8); O(l)–Re(l)–O(3) 85.3(2), O(l)–
Re(l)–O(5) 164.6(2), O(3)–Re(l)–O(5) 109.9(2), O(l)–Re(l)–N(l) 74.4(2),
O(3)–Re(1)–N(1) 159.7(2), O(5)–Re(l)–N(l) 90.4(2), O(l)–Re(l)–N(2)
76.2(2), O(3)–Re(l)–N(2) 78.3(2), O(5)–Re(l)–N(2) 103.8(2), N(l)–
Re(l)–N(2) 97.8(2), O(l)–Re(l)–C(13) 83.5(3), O(3)–Re(l)–C(13) 87.9(2),
O(5)–Re(l)–C(13) 99.1(3), N(l)–Re(l)–C(13) 88.5(3), N(2)–Re(l)–C(13)
156.1(3).
peroxide, d0 species and assembling ([PO4]3Ϫ; [HPO4]2Ϫ; [SO4]2Ϫ
;
etc.) or chelating ligands (with phase transfer catalysis4,5 or in a
two-phase medium4,6), we became interested in establishing
relationships between anionic or neutral peroxo complexes and
the precursor or species formed without H2O2. Addition of
pyridine derivatives to two-phase MTO systems gave epoxides
selectively.4,6–8 The bipyridine system was also used for the
preparation of previously unknown epoxides.6 Novel species
isolated from the reaction media include the molecular complex
[CH3Re(O)(pic)2], (picH = 2-pyridinecarboxylic acid) which is
a stoichiometric 1:1 or 1:2 reaction may occur to yield the
picolinic acid N-oxide. No evidence was found for formation of
the acid or picolinato N-oxide complexes. At the same time,
competitive oxidation of the methyl group of MTO occurs,
leading to HReO4 characterized by precipitation of [n-Bu4Nϩ-
ReO4Ϫ] (addition of an aqueous solution of [n-Bu4NϩHSO4Ϫ]),
and also by isolation of protonated picH in the form of single
crystals of [{(picH2)ϩ(picH)}ReO4Ϫ]. It is known9 that MTO
can be decomposed by nucleophilic attack in aqueous solutions
as acidic as pH 2–3 by transient amine N-oxide or even by
OHϪ or a free radical process.
A representation of the molecular complex 1 is shown in Fig.
1. The monomeric, neutral and pseudo-octahedral dipicolin-
ato complex 1 is formally a rhenium() species. The rhenium
centre has a distorted octahedral environment consisting of
four coordinated atoms of the two chelating ligands with
cis-nitrogen and cis-oxygen configurations; one pic ligand is
bridging an equatorial and an apical position and the other is
bridging two equatorial sites. A carbon atom of the methyl
group completes the equatorial plane.
the first Re() complex with a H C–Re᎐O moiety and is a new
᎐
3
precursor for hydrogen peroxide oxidations.
MTO (0.06 g, 0.24 mmol) was added to an aqueous solution
of picH (0.0885 g, 0.72 mmol). The solution was stirred for two
or three days at room temperature, during which it gradually
became yellow, then olive-green; a green microcrystalline
powder was formed (yield ≈ 30%). This was washed with Et2O
and recrystallized from dichloromethane–n-hexane mixtures
to give dark-green crystals of [CH3Re(O)(pic)2] 1 suitable for
X-ray analysis.‡
Irrespective of the exact nature of the intermediates, two of
the three oxo ligands of MTO are labilized by the picolinato
chelate. Metal–oxo complexes frequently undergo reduction by
organophosphines, but less readily by amines. With CH3ReO3,
A “twisted mode” is reflected in the N(1)–Re(1)–O(3)
[159.7(2)], N(2)–Re(1)–C(13) [156.1(3)] and O(1)–Re(1)–O(5)
[164.6(2)Њ] angles which deviate from 180Њ and in the position of
the Re atom located 0.38 Å outside the mean equatorial plane
defined by the N(1), N(2), O(3) and C(13) atoms. Comparison
† Non-IUPAC nomenclature employed. Picolinato and the abbrevi-
ation (pic) are being used to represent the anion of 2-pyridinecarb-
oxylic acid.
J. Chem. Soc., Dalton Trans., 1999, 2897–2898
2897

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Table 1 A two-phase system: [CH3Re(O)(pic)2]/H2O2–H2O/CH2Cl2 for
Notes and references
epoxidation of acid-sensitive epoxidesa
‡ Complex 1 gave satisfactory elemental analyses. Calc.: C, 33.84; H,
2.40; N, 6.07. Found for C13H11N2O5Re: C, 33.70; H, 2.20; N, 5.85%.
§ Crystal data and collection parameters:13 C13H11N2O5Re 1, M =
461.44, monoclinic, space group C2/c (no. 15), a = 28.339(7),
b = 7.070(3), c = 15.124(3) Å, β = 111.75(2)Њ, U = 2814(2) Å3, T = 293 K,
graphite-monochromated Mo-Kα radiation, λ = 0.71069 Å, Z = 8,
µ(Mo-Kα) = 87.7 cmϪ1, 2 ≤ 2θ ≤ 50Њ, 2607 unique data collected of
which 2072 with (Fo)2 > 3σ(Fo)2 were used in all calculations. Correc-
tions were made for Lorentz and polarization effects, an extinction cor-
rection was also applied and empirical absorption correction on the
basis of ψ-scan data was introduced before anisotropic refinement
(min. 0.77, max. 1.69). Secondary extinction correction was necessary.
Hydrogen atoms were found on difference maps; their positions were
not refined and they were given an overall isotropic thermal parameter
Uiso = 0.09(1). The final R factors as defined in ref. 12 were R = 0.033
and Rw = 0.041 for 190 parameters and weighting scheme, GOF = 1.11,
maximum ∆ρ = 1.03 e ÅϪ3, minimum ∆ρ = Ϫ1.07 e ÅϪ3 . CCDC refer-
ence number 186/1578. See http://www.rsc.org/suppdata/dt/1999/2897/
for crystallographic files in .cif format.
Conversion
(%)
Selectivity
(%)
Substrate
Time/h
Temperature
1-Octene
Limonene
2-Methyl-3- 24
buten-2-ol
24
2
RT e
4 ЊC
RT e
96
94
92
99b
93c
99d
a Reaction conditions: olefin (6–10 mmol) in dichloromethane 5 ml, 1
(1 mol%/olefin), 10% H2O2 (aq.) (150 equivalents of H2O2 added with
vigorous stirring). The progress of the reaction was monitored by GC
and the products were analysed after quenching with MnO2. b With
“MTO/H2O2–t-BuOH/oct-1-ene” (homogeneous system): diol yield
≥70%,2 depending on the acidity. c A nearly 1:1 mixture of the two
isomeric monoepoxides (cis and trans).5,6 d With the homogeneous
system: epoxide yield 10%. e RT = room temperature.
of 1 and [CH3Re(O)(O2)2(HMPA)]10 shows that the Re᎐O and
1 S. Warwel, M. Rüsch gen. Klaas and M. Sojka, J. Chem. Soc., Chem.
Commun., 1991, 1578.
᎐
Re–C distances are unaffected by the oxidation number and the
geometry about Re. The latter bond length (Re–C) compares
well with the mean ReIII–C (2.086 0.008 Å) in K4[Re(CN)7]ؒ
2H2O in which the cyanide is a π-acceptor.11 It is inferred that
2 W. A. Herrmann, D. Marz, W. Wagner, J. G. Kuchler, G. Weichsel-
baumer and R. Fischer (Hoechst), Eur. Pat. 0.380.085A1, 1990.
3 I. R. Beattie and P. J. Jones, Inorg. Chem., 1979, 18, 2318.
4 J.-M. Brégeault, C. Lepetit, F. Ziani-Derdar, O. Mohammedi,
L. Salles and A. Deloffre, Studies in Surface Science and Catalysis,
eds. R. K. Grasselli, S. T. Oyama, A. M. Gaffney and J. E. Lyons,
Elsevier, Amsterdam, 1997, 110, 545.
5 L. Salles, J.-Y. Piquemal, R. Thouvenot, C. Minot and J.-M.
Brégeault, J. Mol. Catal. A, 1997, 117, 375.
6 H. Rudler, J. Ribeiro Gregorio, B. Denise, J.-M. Brégeault and
A. Deloffre, J. Mol. Catal. A, 1998, 133, 255.
7 C. Copéret, A. Adolfsson and K. B. Sharpless, Chem. Commun.,
1997, 1565; J. Rudolph, K. L. Reddy, J. P. Chiang and K. B. Sharp-
less, J. Am. Chem. Soc., 1997, 119, 6189.
8 W. A. Herrmann, H. Ding, R. M. Kratzer, F. E. Kühn, J. J. Haider
and R. W. Fischer, J. Organomet. Chem., 1997, 549, 319.
9 J. H. Espenson, H. Tan, S. Mollah, R. S. Houk and M. D. Eager,
Inorg. Chem., 1998, 37, 4621.
10 W. A. Herrmann, J. D. G. Correia, G. R. J. Artus, R. W. Fischer and
C. C. Romão, J. Organomet. Chem., 1996, 520, 139.
11 J.-M. Manoli, C. Potvin, J.-M. Brégeault and W. P. Griffith, J. Chem.
Soc., Dalton Trans., 1980, 192.
the structure of the O᎐Re–CH moiety does not change during
᎐
3
the redox process, and the stabilization of a rhenium–carbon
bond by one oxo ligand can be achieved not only with Re(),
but also with Re().
The IR spectra of complex 1 show features comparable to
those of mononuclear picolinato species; in addition to two
strong bands at 1700 and 1679 cmϪ1, assigned to ν(C᎐O)
,
᎐
there is a very sharp band at 1006 cmϪ1 [ν(Re᎐O)]; Raes–ymC
᎐
stretch appears at ca. 552–538 cmϪ1 (sh). Comparison of IR and
Raman spectra and 13C NMR in the solid state and CH2Cl2
solution suggests that the overall structure of the molecular
species is conserved in solution.
The Re() complex is also an active precursor in olefin oxid-
ation and forms epoxides in the range 4–20 ЊC (Table 1) in a
two-phase “H2O2–H2O/CH2Cl2” system. Several unidentified
—
peroxo species are formed with characteristic Raman ν(O–O)
bands near 850 cmϪ1; they transfer active oxygen to olefinic
substrates, even to 2-methyl-3-buten-2-ol, a tertiary allylic
alcohol which rearranges easily in the presence of alkoxides
with Re() or Re() precursors. Conversions and yields com-
pare well with recent data in which MTO is used in place of 1.
The activity of this rhenium-based two-phase system under
mild conditions encourages further work to prepare analogues
in the hope of finding novel precursors for oxidations by H2O2
and particularly of alkenes.
12 L. J. Pearce and D. J. Watkin, CAMERON, Chemical Crystallo-
graphic Laboratory, University of Oxford, 1996.
13 D. J. Watkin, J. R. Carruthers and P. W. Betteridge, CRYSTALS, An
Advanced Crystallographic Program System, Chemical Crystallo-
graphic Laboratory, University of Oxford, 1989.
Communication 9/04952E
2898
J. Chem. Soc., Dalton Trans., 1999, 2897–2898