%0 Journal Article 
%A Arteaga Müller, Rocío Alejandra
%A Sánchez-Nieves Fernández, Javier
%A Royo Gracia, Pascual
%A González Mosquera, Marta Elena
%T Synthesis and reactivity of oxametallacyclic niobium compounds by using α,ß-unsaturated carbonyl ligands
%D 2008
%@ 1434-1948
%U http://hdl.handle.net/10017/4974
%X Reduction of mono(cyclopentadienyl)niobium complexes
[NbCpRCl4] [CpR = C5Me4H (1), C5H4SiMe2Cl (2),
C5H4SiMe3 (3)] with Na/Hg in the presence of methyl methacrylate
[MMA, CH2=C(Me)C(O)OMe (a)], methyl acrylate
[MA, CH2=CHC(O)OMe (b)] and mesityl oxide [MO,
CMe2=CHC(O)Me (c)] afforded the corresponding derivatives
[NbCpRCl2(LL)] [CpR = C5Me4H, LL = MMA (1a); CpR
= C5H4SiMe2Cl, LL = MMA (2a), MA (2b), MO (2c); CpR =
C5H4SiMe3, LL = MMA (3a), MA (3b)] in variable yields depending
on both the cyclopentadienyl and the ¿,ß-unsaturated
carbonyl compounds. The reactivity of these complexes
was studied toward protic and Lewis acids. Addition of triflic
acid TfOH (Tf = CF3SO2) to 3b gave the triflate complex
[NbCpRCl2{(CH2)2C(O)OMe}(OTf)] [CpR = C5H4SiMe3 (4)].
The Lewis acids E(C6F5)3 (E = B, Al) reacted with complexes
Introduction
The bonding interaction of a butadiene ligand with a
metal center is clearly dependent on the metal atom and
may be formulated as a system containing a dianionic ligand
for early high-valent transition metals or as a neutral
ligand for low-valent late transition metals. However, the
stability of the formal oxidation state of the metal atom and
the nature of the ancillary substituents of both the complex
and the diene ligand could play an important role in defining
this interaction. Hence, complexes with this type of ligand
are better represented with contributions from two
main canonical forms, ¿2,¿-metallacyclic or ¿2-butadiene
(Figure 1).[1¿5]
[a] Departamento de Química Inorgánica, Universidad de Alcalá,
Campus Universitario,
28871 Alcalá de Henares (Madrid), Spain
Fax: 34-91-885-4683
E-mail: pascual.royo@uah.es
[¿] X-ray diffraction studies
Supporting information for this article is available on the
WWW under http://www.eurjic.org/ or from the author.
Eur. J. Inorg. Chem. 2008, 2313¿2320 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2313
2b and 3b to give the three-membered metallacyclic (or ¿2-
enone) compounds [NbCpRCl2{¿2-CH2=CHC(OMe){O·
E(C6F5)3}}] [CpR = C5H4SiMe2Cl, E = B (5), Al (6); CpR =
C5H4SiMe3, E = B (7), Al (8)], which decomposed to the corresponding
adducts MA·E(C6F5)3. The same reaction with the
2a and 3a derivatives only allowed the observation of the
corresponding adducts MMA·E(C6F5)3. Complexes 2a,b and
3a,b reacted with CO with elimination of the acrylate compounds,
MA and MMA, respectively, to give the carbonylniobium(
III) compounds [NbCpRCl2(CO)2]2 [CpR = C5H4Si-
Me2Cl (9), C5H4SiMe3 (10)]. Analogous reactions with CNAr
showed the elimination of the free MA and MMA compounds.
%K Niobium
%K Cyclopentadienyl ligands
%K Diene ligands
%K Metallacycles
%K Acrylate ligands
%K Ciencia
%K Química inorgánica
%K Science
%K Chemistry, inorganic
%~ Biblioteca Universidad de Alcala