C-Centred chiral metal alkyls,
[MR*(Cl)(η-C5H5)2],
rac- and
meso-[ZrR*2(η-C5H5
)2]
[R* = CH(SiMe3)C6H4
Me-o], and their one-electron reductions; reaction of
Li[CH(SiMe3)2](Me2NCH2CH
2NMe2) with
[MCl2(η-C5H5)2]
(M = Zr or Hf
)
Abstract
The chloro(alkyl)metallocenes
[MR*(Cl)(η-C
5
H
5
)
2
]
[R* =
-
CH(SiMe
3
)C
6
H
4
Me-o; M = Zr 1 or Hf 2] have been
prepared from
[MCl
2
(η-C
5
H
5
)
2
] and
LiR*(tmen)
(tmen = N,N,N′,N
′-tetramethylethane-1,2-diamine); further alkylation
occurred only for M = Zr, affording rac-3a and
meso-3b,
[ZrR*
2
(η-C
5
H
5
)
2
]. In
contrast, reaction of 2 equivalents of
Li[CH(SiMe
3
)
2
](tmen) with
[ZrCl
2
(η-C
5
H
5
)
2
] yielded
an alkyl elimination product possessing
µ-η
1
∶η
5
-C
5
H
4
2-
ligands. Compound 1 was reversibly
reduced
(E
1/2
red
= -1.72 V
vs. saturated calomel electrode, SCE) whereas 2, 3a or 3b were
irreversibly reduced
(E
red
= -2.12,
-2.08, -2.00 V respectively vs. SCE). Thermolysis
of 3b in toluene gave 3a (80 °C) or
‘Zr(C
10
H
8
)’ (120 °C).
Photolysis of 3a or 3b at 20 °C in tetrahydrofuran
(thf) yielded a 1∶1 mixture of 3a and 3b; a d
1
intermediate has been unambiguously identified as
[ZrR*(η-C
5
H
5
)
2
]. Reduction of 1
(Na–Hg), or 3a and 3b (Na[C
10
H
8
]), in thf
also gave [ZrR*(η-C
5
H
5
)
2
] but this
slowly transformed into
[ZrR*(η-C
5
H
5
)
2
(thf)], and 1
with Na[C
10
H
8
] and PPh
3
gave
[ZrR*(η-C
5
H
5
)
2
(PPh
3
)].
Reduction of 1, 3a or 3b, or photolysis of 3a or 3b, in the presence of
PMe
3
gave
[ZrR*(η-C
5
H
5
)
2
(PMe
3
)].
Crystal structure determinations showed a slightly more crowded metal
environment in 2 than in 1, consistent with the view that dialkylation
in 2 is limited on steric grounds; M–σ-C 2.359(4) (1),
2.322(8) (2), metal–centroid 2.22 (1), 2.21 (2), M–Cl
2.444(1) (1), 2.418(3) (2) Å. The structure of 3a confirms the
rac assignment, M–σ-C 2.37
4
Å,
metal–centroid 2.23, 2.24 Å.
′-tetramethylethane-1,2-diamine); further alkylation
occurred only for M = Zr, affording rac-3a and
meso-3b,
[ZrR*
2
(η-C
5
H
5
)
2
]. In
contrast, reaction of 2 equivalents of
Li[CH(SiMe
3
)
2
](tmen) with
[ZrCl
2
(η-C
5
H
5
)
2
] yielded
an alkyl elimination product possessing
µ-η
1
∶η
5
-C
5
H
4
2-
ligands. Compound 1 was reversibly
reduced
(E
1/2
red
= -1.72 V
vs. saturated calomel electrode, SCE) whereas 2, 3a or 3b were
irreversibly reduced
(E
red
= -2.12,
-2.08, -2.00 V respectively vs. SCE). Thermolysis
of 3b in toluene gave 3a (80 °C) or
‘Zr(C
10
H
8
)’ (120 °C).
Photolysis of 3a or 3b at 20 °C in tetrahydrofuran
(thf) yielded a 1∶1 mixture of 3a and 3b; a d
1
intermediate has been unambiguously identified as
[ZrR*(η-C
5
H
5
)
2
]. Reduction of 1
(Na–Hg), or 3a and 3b (Na[C
10
H
8
]), in thf
also gave [ZrR*(η-C
5
H
5
)
2
] but this
slowly transformed into
[ZrR*(η-C
5
H
5
)
2
(thf)], and 1
with Na[C
10
H
8
] and PPh
3
gave
[ZrR*(η-C
5
H
5
)
2
(PPh
3
)].
Reduction of 1, 3a or 3b, or photolysis of 3a or 3b, in the presence of
PMe
3
gave
[ZrR*(η-C
5
H
5
)
2
(PMe
3
)].
Crystal structure determinations showed a slightly more crowded metal
environment in 2 than in 1, consistent with the view that dialkylation
in 2 is limited on steric grounds; M–σ-C 2.359(4) (1),
2.322(8) (2), metal–centroid 2.22 (1), 2.21 (2), M–Cl
2.444(1) (1), 2.418(3) (2) Å. The structure of 3a confirms the
rac assignment, M–σ-C 2.37
4
Å,
metal–centroid 2.23, 2.24 Å.
Please wait while we load your content...
)