Preparation of new zirconium benzamidinates: alkyl derivatives and
low-valent chemistry yielding metallacycles via coupling of
alkynes and ethylene
Abstract
A wide range of new zirconium(IV) derivatives utilizing
the
N,N′-bis(trimethylsilyl)benzamidinato
ligand are reported. The previously reported dichloride,
L
2
ZrCl
2
[L = PhC(NSiMe
3
)
2
], reacted cleanly
with 1 equivalent of Me
2
Mg in Et
2
O to give
L
2
ZrMe
2
which was isolated as colorless crystals
from CH
2
Cl
2
or Et
2
O. Attempting to
prepare the methyl chloride derivative using 0.5 equivalent of
Me
2
Mg yielded mixtures of dichloride, dimethyl and methyl
chloride derivatives. The compound L
2
ZrCl
2
reacted
cleanly with 1 equivalent of the bulkier alkyl
LiCH
2
SiMe
3
giving
L
2
Zr(CH
2
SiMe
3
)Cl. Reactivity of methyl
derivatives with a variety of small molecules (CO, CO
2
or
acetone) is reported. The dimethyl compound,
L
2
ZrMe
2
, reacted cleanly with
B(C
6
F
5
)
3
to form the
methyltriarylborate complex
L
2
Zr[MeB(C
6
F
5
)
3
]Me which is
moderately active towards ethylene polymerization. Additionally, several
other derivatives are conveniently prepared by salt-metathesis reactions
with the dichloride including:
L
2
Zr(CH
2
Ph)
2
,
L
2
Zr(OSO
2
CF
3
)
2
,
L
2
Zr[NH(C
6
H
3
Pr
i
2
-2,6)]Cl, L
2
Zr(BH
4
)
2
,
L
2
Zr[ESi(SiMe
3
)
3
]Cl
(E = Se or Te). The 1% Na–Hg amalgam reduction of
L
2
ZrCl
2
in the presence of diphenylacetylene or
trimethylsilylacetylene yielded orange zirconacyclopentadienes
L
2
Zr(C
4
Ph
4
) and
L
2
Zr[C
4
H
2
(SiMe
3
)
2
-2,4] in moderate yields. The compound
L
2
Zr(C
4
Ph
4
) reacted readily with CO to
give the dark red η
2
-cyclopentadienone
L
2
Zr[η
2
-C(O)C
4
Ph
4
].
Analogous to the formation of the zirconacyclopentadienes, reduction in
the presence of ethylene gave the zirconacyclopentane,
L
2
Zr(C
4
H
8
), in good yield. When the
reduction is carried out in the absence of any trapping ligands,
however, a benzamidinate ligand is oxidatively cleaved and the dimeric
imido-iminoacyl compound,
[LZr(η
2
-PhCNSiMe
3
)(µ-NSiMe
3
)]
2
, is isolated as orange crystals in moderate yield.
Single-crystal X-ray diffraction data are reported for
L
2
ZrCl
2
, L
2
ZrMe
2
and
L
2
Zr(C
4
H
8
).
′-bis(trimethylsilyl)benzamidinato
ligand are reported. The previously reported dichloride,
L
2
ZrCl
2
[L = PhC(NSiMe
3
)
2
], reacted cleanly
with 1 equivalent of Me
2
Mg in Et
2
O to give
L
2
ZrMe
2
which was isolated as colorless crystals
from CH
2
Cl
2
or Et
2
O. Attempting to
prepare the methyl chloride derivative using 0.5 equivalent of
Me
2
Mg yielded mixtures of dichloride, dimethyl and methyl
chloride derivatives. The compound L
2
ZrCl
2
reacted
cleanly with 1 equivalent of the bulkier alkyl
LiCH
2
SiMe
3
giving
L
2
Zr(CH
2
SiMe
3
)Cl. Reactivity of methyl
derivatives with a variety of small molecules (CO, CO
2
or
acetone) is reported. The dimethyl compound,
L
2
ZrMe
2
, reacted cleanly with
B(C
6
F
5
)
3
to form the
methyltriarylborate complex
L
2
Zr[MeB(C
6
F
5
)
3
]Me which is
moderately active towards ethylene polymerization. Additionally, several
other derivatives are conveniently prepared by salt-metathesis reactions
with the dichloride including:
L
2
Zr(CH
2
Ph)
2
,
L
2
Zr(OSO
2
CF
3
)
2
,
L
2
Zr[NH(C
6
H
3
Pr
i
2
-2,6)]Cl, L
2
Zr(BH
4
)
2
,
L
2
Zr[ESi(SiMe
3
)
3
]Cl
(E = Se or Te). The 1% Na–Hg amalgam reduction of
L
2
ZrCl
2
in the presence of diphenylacetylene or
trimethylsilylacetylene yielded orange zirconacyclopentadienes
L
2
Zr(C
4
Ph
4
) and
L
2
Zr[C
4
H
2
(SiMe
3
)
2
-2,4] in moderate yields. The compound
L
2
Zr(C
4
Ph
4
) reacted readily with CO to
give the dark red η
2
-cyclopentadienone
L
2
Zr[η
2
-C(O)C
4
Ph
4
].
Analogous to the formation of the zirconacyclopentadienes, reduction in
the presence of ethylene gave the zirconacyclopentane,
L
2
Zr(C
4
H
8
), in good yield. When the
reduction is carried out in the absence of any trapping ligands,
however, a benzamidinate ligand is oxidatively cleaved and the dimeric
imido-iminoacyl compound,
[LZr(η
2
-PhCNSiMe
3
)(µ-NSiMe
3
)]
2
, is isolated as orange crystals in moderate yield.
Single-crystal X-ray diffraction data are reported for
L
2
ZrCl
2
, L
2
ZrMe
2
and
L
2
Zr(C
4
H
8
).
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