ca01 only detailed ToC 1..24

Scheme 16 Stoichiometric Alkyne Metathesis [67,74]
M( CR 2 )(OR 1 ) 3(L) + R 3 C CR 4 (excess) (R 1 O) 3(L)M
44
R 2
R 3
M( CR 3 )(OR 1 ) 3(L)
R 4
+ R 2 C CR 4
M L R 1 R 2 R 3 R 4 Conditions Yield (%) of
[M(”CR 3 )
(=OR 1 ) 3(L)]
Mo DMECMe(CF 3) 2 t-Bu a a Et 2O, rt,
15 min
Mo – t-Bu t-Bu b H E t 2O, rt,
30 min
W quinoline t-Bu Me C”CEt Et pentane, rt,
2d
a R 3 =R 4 = Me, Et, Pr, Ph.
b R 3 = Pr, iPr, Ph.
2.6.2 Metal–Carbyne Complexes 107
80–90
quant.
Addition of one equivalent of an internal alkyne, trichloro(1,2-dimethoxyethane-O,O¢)-
(2,2-dimethylpropylidyne)tungsten(VI) affords a stable tungstacyclobutadiene product,
but reaction with additional alkyne yields ç 5 -cyclopentadienyl products of further alkyne
insertion rather than products of alkyne metathesis. [69,80]
Butylidynetris(1,1,1-trifluoro-2-methylpropan-2-olato)molybdenum(VI);
Typical Procedure: [67]
Excess PrC”CPr (125 ìL, 0.85 mmol) was added to [Mo(”Ct-Bu){OCMe 2(CF 3)} 3] (0.09 g,
0.16 mmol) dissolved in Et 2O (3 mL). After 30 min, the solvent was removed in vacuo, leaving
white needles that were pure by NMR; 13 C{ 1 H} NMR (benzene-d 6, ä): 299.3 (Mo”CPr).
2.6.2.4 Method 4:
By Oxidation of Fischer-Type Carbyne Complexes
The dibromine oxidation of (alkylidyne)bromotetracarbonyl complexes of molybdenum
and tungsten in the presence of 1,2-dimethoxyethane (DME) provides a direct access to
DME-stabilized (alkylidyne)tribromo complexes, while the corresponding chromium systems
lead to complete degradation. [81] The advantage of this procedure is the direct access
to complexes with a wide variety of carbyne substituents starting from the corresponding,
easily accessible Fischer-type carbyne precursor. The phenyl derivative 45, in particular,
is easily synthesized in a one-pot procedure from the precursor as shown in Scheme
17.
Scheme 17 Oxidation of Fischer-Type Carbyne Complexes [81,82]
Me 4N[M(COPh)(CO) 5]
oxalyl bromide
CH2Cl2, −78 oC MBr( CPh)(CO) 4
Br2, DME
CH2Cl2 −78 oC M = Mo 80%
M = W 88%
64
Ref
[67]
[67]
[74]
MBr3( CPh)(DME)
45
for references see p 135