DOI: 10.1002/ejic.201501221 Full Paper
Half-Sandwich Guanidinates
Half-Sandwich Guanidinate–Osmium(II) Complexes: Synthesis
and Application in the Selective Dehydration of Aldoximes
Javier Francos,
[a]
Pedro J. González-Liste,
[a]
Lucía Menéndez-Rodríguez,
[a]
Pascale Crochet,
[a]
Victorio Cadierno,*
[a]
Javier Borge,
[b]
Antonio Antiñolo,*
[c]
Rafael Fernández-Galán,
[c]
and
Fernando Carrillo-Hermosilla
[c]
Abstract: The novel guanidinate–osmium(II) complexes
[OsCl{κ
2
-(N,N′)-C(NR)(NiPr)NHiPr}(η
6
-p-cymene)] [R = Ph (3a), 4-
C
6
H
4
F(3b), 4-C
6
H
4
Cl (3c), 4-C
6
H
4
CF
3
(3d), 3-C
6
H
4
CF
3
(3e), 3,5-
C
6
H
3
(CF
3
)
2
(3f ), 4-C
6
H
4
CN (3g), 4-C
6
H
4
Me (3h), 3-C
6
H
4
Me (3i),
2-C
6
H
4
Me (3j), 4-C
6
H
4
tBu (3k), 2,6-C
6
H
3
iPr
2
(3l), 2,4,6-C
6
H
2
Me
3
(3m)] have been synthesized in high yields (70–88 %) by treat-
ment of THF solutions of the dimeric precursor [{OsCl(μ-Cl)(η
6
-
p-cymene)}
2
](1) with 4 equivalents of the corresponding guan-
idine (iPrHN)
2
C=NR (2a–m) at room temperature. The easily
separable guanidinium chloride salts [(iPrHN)
2
C(NHR)]Cl (4a–m)
Introduction
Since the seminal work by Lappert and co-workers in 1970,
[1]
a
large number of metal complexes containing guanidinate li-
gands have been described in the literature.
[2]
Notably, some of
them have found utility in catalysis (e.g., polymerization of ole-
fins, hydroamination of alkynes), as well as in materials science
as precursors for chemical vapor deposition (CVD) and atom
layer deposition (ALD) applications.
[2]
The easy generation of
guanidinate mono- and dianions from readily available guan-
idines,
[3]
along with their high steric and electronic modulabil-
ity, have allowed the coordination of these ligands to virtually
all transition metals.
[2]
In this context, we recently reported the
preparation of a series of ruthenium(II)– and ruthenium(IV)–
guanidinate derivatives (see A and B in Figure 1), which proved
[a] Laboratorio de Compuestos Organometálicos y Catálisis (Unidad Asociada
al CSIC), Centro de Innovación en Química Avanzada (ORFEO-CINQA),
Departamento de Química Orgánica e Inorgánica, Instituto Universitario
de Química Organometálica “Enrique Moles“, Universidad de Oviedo,
Julián Clavería 8, 33006 Oviedo, Spain
E-mail: vcm@uniovi.es
http://www.unioviedo.es/comorca
[b] Departamento de Química Física y Analítica, Centro de Innovación en
Química Avanzada (ORFEO-CINQA), Universidad de Oviedo,
Julián Clavería 8, 33006 Oviedo, Spain
[c] Centro de Innovación en Química Avanzada (ORFEO-CINQA), Depar-
tamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de
Ciencias y Tecnologías Químicas - Campus de Ciudad Real, Universidad de
Castilla La Mancha,
Campus Universitario, 13071 Ciudad Real, Spain
E-mail: Antonio.Antinolo@uclm.es
https://www.uclm.es/profesorado/afantinolo/
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejic.201501221.
Eur. J. Inorg. Chem. 2016, 393–402 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 393
were also formed in these reactions. The structures of 3a, 3d,
and 3h were unequivocally confirmed by X-ray diffraction
methods. Complexes 3a–m proved to be active in the catalytic
dehydration of aldoximes. The best results were obtained with
[OsCl{κ
2
-(N,N′)-C(N-4-C
6
H
4
CF
3
)(NiPr)NHiPr}(η
6
-p-cymene)] (3d;
5 mol-%), which, in acetonitrile at 80 °C, was able to convert
selectively a large variety of aromatic, heteroaromatic, α,-un-
saturated, and aliphatic aldoximes into the corresponding
nitriles in high yields and short reaction times.
to be very efficient catalysts for the base-free redox isomeriza-
tion of allylic alcohols [turnover frequency (TOF) up to
1200 h
–1
].
[4]
These complexes were easily obtained from the
reactions of the dimeric precursors [{RuCl(μ-Cl)(η
6
-p-cymene)}
2
]
and [{RuCl(μ-Cl)(η
3
:η
3
-C
10
H
16
)}
2
] (C
10
H
16
= 2,7-dimethylocta-2,6-
diene-1,8-diyl), respectively, with an excess of the correspond-
ing guanidine (iPrHN)
2
C=NR.
[4]
Figure 1. Structures of the ruthenium–guanidinate complexes A and B.
In addition to A and B, the synthesis of a significant number
of other mono- and dinuclear ruthenium–guanidinate com-
plexes have been reported,
[5]
and several iron representatives
are known.
[6]
In marked contrast, within this group of the peri-
odic table, little attention has been devoted to the chemistry
of osmium compounds with this class of ligands. In fact, to the
best of our knowledge, only four examples have been de-
scribed so far in the literature (see Figure 2): 1) The mononu-
clear complexes C and D, containing a mono- and dianionic
guanidinate ligand, respectively,
[5c,5f ]
and 2) the dinuclear pad-
dlewheel-type species E and F , in which anions of the bicyclic
guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine
act as bridges in Os
2
n+
cores (n = 6, 7).
[7]
Worthy of note, none
of them has found applications in homogeneous catalysis.