Polyhedron 20 (2001) 2405 – 2414
Synthesis and characterization of niobium(V) and tantalum(V)
derivatives with diamido ligands. Molecular structure of
{4,5-Me
2
-o -C
6
H
2
(NSiMe
3
)
2
}
2
NbCl and of a tantalum imide
Jean Manuel Decams
a
, Ste ´phane Daniele
a
, Liliane G. Hubert-Pfalzgraf
a,
*,
Jacqueline Vaissermann
b
, Sylvain Lecocq
c
a
Uniersite ´ de Lyon 1, IRC-CNRS, 2 Aenue A Einstein, 69626 Villeurbanne Cedex, France
b
Laboratoire de Chimie des Me ´taux de Transition, UMR-CNRS, 4 Place Jussieu, 75230 Paris Cedex, France
c
UMR-CNRS, 43 Bouleard du 11 Noembre 1918, 69622 Villeurbanne, Cedex, France
Received 8 February 2001; accepted 10 May 2001
Abstract
The reactions between lithium bis(trimethyl)phenylenediamide and niobium or tantalum pentachlorides at low temperature
afforded [{4,5-Me
2
-C
6
H
2
(NSiMe
3
)
2
}
2
MCl] (M=Nb (1), Ta (2)) independently of the stoichiometry used, 1:1 or 2:1. The reaction
between tantalum pentachloride and N,N-bis(trimethylsilyl)-o -dimethylphenylene diamide o -C
6
H
2
Me
2
(NSiMe
3
)
2
in Et
2
O–DME
at -78 °C leads to a tantalum(V) imide 3. Monosubstitution with diamides was achieved on tantalum with the more rigid
1,8-diamido-naphtalene. The various compounds were characterized by elemental analysis, FT-IR and NMR. Compounds 1 and
3 were characterized also by single crystal X-ray diffraction. The metal is pentacoordinated for 1 bearing two bidentate
o -phenylenediamide ligands and a chlorine in the apical position of a distorted square-tetragonal pyramid. The salient features are
a disymmetrical coordination mode of the diamide ligand with two quite different Nb – N distances namely 1.981(2) and 2.053(3)
A , as well as short Nb–C distances with the phenyl ring [2.495(3) and 2.471(3) A ]. The diamide ligand is thus coordinated in a
4
-fashion in the solid state. The salient feature of the structure of 3 is the presence in the metal coordination sphere of the
functional imido ligand [Me
2
C
6
H
2
N(SiMe
2
Cl)(NSiMe
3 -x
Cl
x
)]
2 -
(x =1 or 0) which was generated by N–Si bond cleavage and
Si–Me/Si–Cl scrambling. Tantalum is six-coordinate, linked to the bulky imido ligand, three chlorine and a bidentate
dimethoxyethane. The surrounding of the metal is distorted with a TaN bond distance of 1.706(5) A and a large Ta–N(2)–C(2)
angle [170.7(5)°]. The thermal behavior as well as the reactivity as soluble -olefin polymerization catalyst were evaluated for 1.
© 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Niobium; Tantalum; Amides; Imides; X-ray structures; Catalysts
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1. Introduction
The recent years have shown the growing interest in
the use of anionic N-donor ligands of various denticity,
especially for early transition metals [1]. Work in this
area is motivated by the use of ancillary ligands differ-
ent from the much used cyclopentadienyl anion for
catalysis and new metal-mediated transformations [2]
or by the development of potential precursors for ni-
tride materials [3]. In order to explore structure – activ-
ity relationships, considerable attention has been
focused on novel ancillary ligands [1], such as for
instance cyclopentadienyl with pendant amides [4],
macrocycles [5], tetradentate Schiff-bases [6], amidi-
nates [7], diazabutadienes [8] and bis- or multidentate
amides [9], often bearing silylamide substituents. These
ligands have advantages, over cyclopentadienyl sys-
tems, as they offer a large number of possibilities
(number and type of donor atoms, possible C or N
alkylation, ring size,…) for tailoring properties to suit
specific requirements for applications. Complexes based
on anionic chelating amide ligands appeared to be the
most promising in polymerising ethylene and higher
* Corresponding author. Tel.: +33-4-7244-5322; fax: +33-4-7244-
5399.
E-mail address: hubert@catalyse.univ-lyon1.fr (L.G. Hubert-Pfalz-
graf).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII:S0277-5387(01)00834-8