ca01 only detailed ToC 1..24

2.6.4 Metal–s-Alkyl and –s-Aryl Non-homoleptic Complexes 115
Scheme 25 Two-Electron Oxidative Addition of an Alkyl Halide [102]
W(Cp ∗ ) 2(
O)
MeI, toluene
rt, 12 h
77%
[WMe(Cp ∗ ) 2(
62
O)] + I −
Methyloxobis(ç 5 -pentamethylcyclopentadienyl)tungsten(VI) Iodide (62): [102]
A soln of [W(Cp*) 2(=O)] (150 mg, 0.32 mmol) in toluene (3 mL) was treated with MeI
(0.2 mL, 3.2 mmol) and the mixture was stirred. After ca. 5 min a yellow microcrystalline
deposit started to form. The stirring was continued for 12 h. The mixture was filtered and
the solid was washed with pentane (3 ” 2 mL) and dried in vacuo to give yellow crystals of
62; yield: 150 mg (77%); IR (Nujol) í~ max: [W(=O)] 868 (s) cm –1 ; 1 H NMR (CDCl 3, ä): 2.13 (s,
15H, C 5Me 5), 1.07 (s, 3H, WMe).
2.6.4.3 Method 3:
By Oxidative Addition of Alkanes and Arenes
Alkanes and arenes may be able to add oxidatively to a suitable metal complex, forming
an alkyl (or aryl) hydride product (Scheme 26). Arenes are more suitable than alkanes for
this methodology, for both kinetic and thermodynamic reasons. The metal complex must
be quite electron-rich to accomplish this process. Sufficiently reactive metal substrates
are usually generated in situ from more stable precursors by either a thermal or a photochemical
dissociation or reductive elimination process. For example, the tungstenocene
leading to product 63 is generated by photolytic reductive elimination of dihydrogen
from bis(ç 5 -cyclopentadienyl)dihydridotungsten(IV). [112] Tungstenocene may also be generated
by thermal alkane elimination from a dicyclopentadienyl–alkyl–hydride system.
[113] The product of the oxidative addition step may further evolve to afford more stable
alkyl or aryl products, as is the case for the synthesis of compound 64.
Scheme 26 Oxidative Addition of Alkanes and Arenes [112,114]
W(Cp) 2H 2
ON
hν, benzene
− H2 W
CH2But CH2But Me4Si (neat)
70 oC, 2.5 d
W
benzene
>80%
W
ON CHBu t
Me4Si
90%
H
(Cp) 2W
Ph
63
ON
W
CH2TMS CH2But (2,2-Dimethylpropyl)nitrosyl(ç 5 -pentamethylcyclopentadienyl)[(trimethylsilyl)methyl]tungsten(II)
(64); Typical Procedure: [114]
In a glovebox an ampule (Teflon stopcock) was charged with [W(CH 2t-Bu) 2Cp*(NO)]
(0.048 g, 0.098 mmol) and Me 4Si (1 mL). The resulting wine-red mixture was stirred and
heated at 708C for 2.5 d, during which time it changed to a darker red soln. The organic
volatiles were removed under reduced pressure. The remaining dark wine-red solid was
redissolved in pentane and filtered through Celite. The resulting soln was stored for several
days to provide 64 as maroon crystals; yield: 0.045 g (90%); 1 H NMR (benzene-d 6, ä):
1.54 (s, 15H, C 5Me 5), 1.35 (s, 9H, t-Bu), 0.38 (s, 9H, TMS).
64
for references see p 135