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Scheme 6.17
ROMP of 7-oxanorbornene derivative in water.
6.5.2
First-Generation Grubbs Catalysts: RuCl
2
(PR
3
)
2
CHR
1
6.5.2.1
Synthesis and Activity
Although there were a number of ruthenium carbene complexes described in the
literature by 1992, none of these were reported as being active for olefin metath-
esis. In 1992, the synthesis of complex
3
was described. The method is analogous
to that used to make tungsten and titanium alkylidenes, namely reaction of
RuCl
2
(PPh
3
)
3
or RuCl
2
(PPh
3
)
4
with the strained olefin 3,3-diphenylcyclopropene
[77] (Scheme 6.18).
Phosphine exchange reactions give the analogous bis-trialkylphosphine com-
plexes such as
4
[78]. Calorimetric studies indicated that the exothermicity of the
phosphine exchange scales well with various measurements of the electronic char-
acter of the phosphine, such as the basicity of the phosphine, and was not depen-
dent on the steric bulk (Tolman cone angle) of the phosphine. Phosphine ex-
change of PPh
3
with PCy
3
(
3
to
4
) is exothermic by 6.5 kcal mol
-1
[79].
Another noteworthy synthesis of complexes of this type involves the insertion of
a propargyl halide into the Ru-H bond of Ru(H)(H
2
)Cl(PR
3
)
2
(Scheme 6.19),
Scheme 6.18
Synthesis of complexes
3
and
4
.
Scheme 6.19
Alternative synthesis of vinyl carbene complexes.
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