ca01 only detailed ToC 1..24

108 Science of Synthesis 2.6 Complexes of Cr, Mo, and W without CO Ligands
Benzylidynetribromo(1,2-dimethoxyethane-O,O¢)tungsten(VI) (45,M=W): [81,82]
Me 4N[W(COPh)(CO) 5] (10.00 g, 19.87 mmol) was completely dissolved in CH 2Cl 2 (300 mL)
then the soln was cooled to –788C. Oxalyl bromide (1.87 mL, 20.0 mmol) was dissolved in
CH 2Cl 2 (40 mL) and cooled to –78 8C, then quickly added against a N 2 stream to the acyl
soln. This soln was left to stir at –788C for 15 min, then warmed in an ice bath just until
a bright yellow color developed. It was immediately recooled to –788C; then this soln was
filtered through a dry-ice jacketed frit, having a 2-cm layer of dry cellulose on it, into a
cooled (–78 8C) receiving flask (500-mLSchlenk). To the soln of [WBr(”CPh)(CO) 4] at
–78 8C was added DME (10 mL). A freshly prepared 1.0 M soln of Br 2 in CH 2Cl 2 (20 mL)
with an additional quantity of CH 2Cl 2 (20 mL) was cooled to –788C and added (poured)
against a strong N 2 stream as quickly as possible. The color became red briefly then dark
orange. The stirred soln was allowed to warm to rt under vacuum; much gas was evolved
during the warming step. The solvent was removed in vacuo and the dark brown oily solid
was washed with pentane (50 mL). The solid was then dissolved in CH 2Cl 2 (30 mL) and filtered.
The volume was reduced to 15 mLand pentane (100 mL) was added gradually to precipitate
the product as a green-brown solid. This precipitation process was repeated until
the product in CH 2Cl 2 was emerald green. The final product was a dark green microcrystalline
powder; yield: 10.49 g (88%); 13 C{ 1 H} NMR (benzene-d 6, ä): 331.7 (W”CPh).
2.6.2.5 Method 5:
By Rearrangement of Vinyl Complexes
Vinyl complexes can, under favorable circumstances, rearrange by a [1,2]-H shift to carbyne
complexes (Scheme 18). [83] The reaction appears to proceed via a ç 2 -vinyl complex
46, which has been isolated in some cases, [84] and thus requires an open coordination
site on the metal center. The vinyl precursors are often prepared in situ by hydride addition
to alkyne complexes, e.g. for the synthesis of 47 and indenyl analogues, [84] by deprotonation
of alkene complexes, [13] or by transmetalation, as for the synthesis of 48. [73] The
vinyl complex intermediate may not be observed in some cases. ç 3 -Allyl complexes are
possible byproducts of this reaction when the substituents R 2 and R 3 bear Æ-hydrogen atoms
(e.g., 47), [85] in which case the rearrangement to the carbyne product is favored by the
presence of free ligands and higher temperatures.
Scheme 18 [1,2]-H Shift from Vinyl Complexes [73,84]
[M]
R 3
R 1
R 2
Mo
(MeO)3P
(MeO)3P
WCl 2(PMe 3) 4
H
Pr i
+
[M]
R 3
R 2
R1 46
NaBH4 P(OMe) 3 (excess)
THF, rt, 2 h
58%
(5 equiv)
Si(OMe) 3
THF, reflux, 8 h
93%
[1,2]-R 1 shift
Mo
(MeO) 3P
(MeO)3P
47
CMe
PMe3 Me3P W PMe3 Me3P Cl
48
[M]
CH 2Pr i
R1 R3 R2