www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 597 (2000) 3 – 9
Syntheses of some bulky alkylalanes and alkyltrihydroaluminates:
crystal structures of [Li(THF)
2
AlH
3
C(SiMe
3
)
2
(SiMe
2
NMe
2
)]
2
,
Li(THF)
2
Al
2
H
5
{C(SiMe
3
)
3
}
2
, (Me
3
Si)
3
CAlH
2
·THF and the
pyrazolato derivative [LiAlH(C
3
H
3
N
2
)
2
C(SiMe
3
)
3
]
2
(THF = tetrahydrofuran)
Colin Eaborn, Salima M. El-Hamruni, Michael S. Hill, Peter B. Hitchcock,
Martijn Hopman, Armelle Le Gouic, J. David Smith *
School of Chemistry, Physics and Enironmental Science, Uniersity of Sussex, Brighton, BN19QJ, UK
Received 20 July 1999; received in revised form 27 August 1999
Dedicated to Professor S. Pasynkiewicz in recognition of his notable contributions to organometallic chemistry, especially the chemistry of
organoaluminium compounds, and of his work for the Federation of European Chemical Societies.
Abstract
The alkylaluminate [Li(THF)
2
AlH
3
C(SiMe
3
)
2
(SiMe
2
NMe
2
)]
2
(3), obtained by the reaction between [LiC(SiMe
3
)
2
-
(SiMe
2
NMe
2
)·2THF] and LiAlH
4
, has a cyclic structure like those of the compounds [Li(THF)
2
AlH
3
R]
2
(R =C(SiMe
3
)
3
(1), or
C(SiMe
2
Ph)
3
(2)). The Al and Li atoms are linked by hydride bridges and the NMe
2
groups are not coordinated to metal centres.
The compound 1 reacts (i) with one equivalent of SiMe
3
Cl to give the cyclic dialuminate Li(THF)2(-H)AlHR(-H)AlHRH
(4)
(characterised by an X-ray study); (ii) with two equivalents of SiMe
3
Cl to give the alaneTHF complex (Me
3
Si)
3
CAlH
2
·THF (5);
and (iii) with an excess of pyrazole to give [LiAlH(C
3
H
3
N
2
)
2
C(SiMe
3
)
3
]
2
(7), in which Al and Li atoms are linked by both hydride
and pyrazolato bridges. The compound (Me
2
PhSi)
3
CAlH
2
·THF (6) has been obtained by the reaction of 2 with two equivalents
of SiMe
3
Cl. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Alkylalanes; Aluminium; Lithium; Pyrazolato
1. Introduction
The selectivity of lithium tetrahydroaluminate,
LiAlH
4
, as a reducing agent in organic chemistry can be
modified by the introduction of bulky substituents in
place of hydrogen [1]. Alkyltrihydroaluminates are nor-
mally difficult to isolate because the species [AlRH
3
]
-
readily rearrange in solution to give [AlR
2
H
2
]
-
and
[AlH
4
]
-
[2]. However, when the organic groups are
large, stable alkyl- [3] and aryltrihydroaluminates [4]
can be obtained, and these prove to be excellent
reagents for the syntheses of further organoaluminium
compounds [5,6]. In this paper we describe the synthesis
and structure of the alkyltrihydroaluminate [Li(THF)
2
AlH
3
C(SiMe
3
)
2
(SiMe
2
NMe
2
)]
2
(3). We also describe the
conversion of the alkyltrihydroaluminates [Li(THF)
2
-
AlH
3
R]
2
,R =C(SiMe
3
)
3
(1) or C(SiMe
2
Ph)
3
(2), into
the alkylalaneTHF adducts 5 and 6 (THF =tetrahy-
drofuran). The few monoorganoalanes RAlH
2
that
were described previously were all aryl derivatives, with
R =2,4,6-Bu
t
3
C
6
H
2
[6], 2,6-Mes
2
C
6
H
3
(Mes =2,4,6-
Me
3
C
6
H
2
), 2,6-Trip
2
C
6
H
3
(Trip =2,4,6-Pr
i
3
C
6
H
2
) [4], 2-
Me
2
NC
6
H
5
[7], or 2,6-(Me
2
N)
2
C
6
H
3
[8], and the first in
particular has been the source of much interesting
chemistry [9]. The compounds 5 and 6 are the first
monoalkylalanes to be characterised. The conversion of
the compound 1 into 5 proceeds via the novel diorgan-
odialuminate 4, which has been structurally character-
ised. The pyrazolato compound 7, in which the THF
* Corresponding author. Fax: +44-1273-677196.
E-mail address: j.d.smith@sussex.ac.uk (J.D. Smith)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
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