Synthesis and reactivity of
7,9-diphenyl-nido-carbaundecaboranes: rearrangement
processes in carbaplatinaboranes revisited
Abstract
A number of synthetic routes towards diphenyl
nido-carbaborane
[7,9-Ph
2
-7,9-nido-C
2
B
9
H
10
]
-
have been elucidated. Base-induced
degradation of
1,7-Ph
2
-1,7-closo-C
2
B
10
H
10
afforded two isolable products
[NEt
3
H][7,9-Ph
2
-x-OEt-7,9-nido
-C
2
B
9
H
9
] (x = 3
1a or 2 1b), both of which contain an
ethoxide-substituted cage. The structural identity of 1a was
established by a single-crystal X-ray diffraction study.
Fluoride-induced degradation gave a product assigned as
[NBu
4
][7,9-Ph
2
-10-OH-7,9-nido-C
2
B
9
H
9
] 2, also studied
crystallographically. Heating a solid sample of
Cs[7,8-Ph
2
-7,8-nido-C
2
B
9
H
10
] in a sealed tube under vacuum for 4 h at
300 °C afforded the target species
[NEt
3
H][7,9-Ph
2
-7,9-nido-C
2
B
9
H
10
] 3, after cation metathesis.
Deprotonation of 3 and reaction with
[PtCl
2
(PMe
2
Ph)
2
] afforded the new
compound
1,1-(PMe
2
Ph)
2
-2,4-Ph
2
-1,2,4-closo
-PtC
2
B
9
H
9
4. Compound
4 has been characterised by multinuclear (
1
H,
11
B and
31
P-{
1
H}) NMR
spectroscopy as well as a single-crystal X-ray diffraction study. The
isolation of this stable (in refluxing toluene) compound having a
1,2,4-MC
2
B
9
cage architecture indicates that a
hextuple-concerted diamond–square–diamond mechanism cannot
be operating in the spontaneous isomerisation of
1,2-Ph
2
-3,3-(PMe
2
Ph)
2
-3,1,2-closo
-PtC
2
B
9
H
9
below ambient
temperature to afford
1,1-(PMe
2
Ph)
2
-2,8-Ph
2
-1,2,8-closo
-PtC
2
B
9
H
9
. The new compounds
1,1-(PR
3
)
2
-2,4-Ph
2
-7-OEt-closo
-1,2,4-PtC
2
B
9
H
8
(R
3
= Me
2
Ph 5a or
Et
3
5b), both fully characterised by multinuclear
NMR spectroscopy, have also been synthesized.
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