ca01 only detailed ToC 1..24

120 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands
ing dichloro dimers with lithium or Grignard reagents and they are not isolated in view of
their extreme thermolability. A large variety of alkyl groups, (trimethylsilyl)methyl, and
phenyl have been used as R 3 , including ones where the â-hydrogen elimination process is
possible. [60] The procedure consists of the addition of the carbonyl substrate to 75 in tetrahydrofuran
at –788C, followed by warming to reflux and room-temperature base hydrolysis.
Various substituents (e.g., methoxy, dimethylamino, fluoro, chloro, and hydroxy)
on phenyl groups are tolerated (e.g., see synthesis of 76), but the nitro and ethoxycarbonyl
groups are not. [135] For R 3 = Me, the carbonyl group must be conjugated with an unsaturated
group, otherwise the monomeric carbinol is obtained. With R 3 = Ph, however,
even saturated ketones yield the additive–reductive carbonyl dimerization product. Rearrangement
products can also be obtained, depending on the substituents linked to the
carbonyl group; see, for example, the reaction of 2-furaldehyde (77). [60]
Scheme 31 Additive–Reductive Carbonyl Dimerization [60,135]
2
Me 2N
O
R 1 R 2
O
77
73
CHO
2 [R3 + M]
O
H
R1 2(PrO) 2W W(OPr) 2R
O
1 Pr
O
2
Pr 75
R 1 = Me 82%
Pr
O
Me2(PrO) 2W W(OPr) 2Me2 O
Pr
75 R 1 = Me
R 1
R 1
R
74
2
R3 R2 R3 O
Me2N
43%
O
+
76
O O
1,2-Bis[4-(dimethylamino)phenyl]-1,2-dimethylethane (76); Typical Procedure: [135]
[W 2Cl 4(ì-OPr) 4(OPr) 4] (2.2 g, 2.50 mmol) was dissolved in THF (100 mL) at –788C, followed
by treatment with 1.5 M MeLi in Et 2O (4 equiv), resulting in a color change to dark green.
After 30 min, the Gilman test indicated the absence of MeLi. To this soln was added a THF
soln (25 mL) of 4-(dimethylamino)benzaldehyde (2.50 mmol). After stirring for 15 min at
–78 8C, the mixture was slowly warmed and refluxed for 3 h. The mixture was then hydrolyzed
with 2 M NaOH (100 mL) at 20 8C. Et 2O (50 mL) and petroleum ether were added and
the mixture was stirred until dissolution of the amorphous hydrolysis product occurred.
The organic phase was removed and the aqueous phase was extracted with Et 2O
(2 ” 100 mL). The combined organic phases were washed with H 2O and dried (Na 2SO 4).
The solvents were removed by rotary evaporation, leaving a crude material which was
identified (by GC in comparison with authentic samples) as a mixture of the title compound
76; yield: 82% and 1-[4-(dimethylamino)phenyl]ethanol; yield: 4%.
2.6.5 Product Subclass 5:
Metallacyclic Complexes
In many respects, the synthetic methods and reactivity of metallacyclic complexes parallel
those of analogous dialkyl complexes. Metallacyclobutanes and metallacyclopentanes,
on the other hand, display unique features. They may easily transform into, or be pre-
30%
NMe2
Et