ca01 only detailed ToC 1..24

2.6.2 Metal–Carbyne Complexes 109
ç 5 -Cyclopentadienyl(3,3-dimethylbutylidyne)bis(trimethyl phosphite-P)molybdenum(IV):
[84]
A soln of [MoCp{ó-(E)-CH=CHt-Bu}{P(OMe) 3} 3] (0.35 g, 0.5 mmol) in hexane (10 mL) contained
in an evacuated sealed tube (50 mL) fitted with a Westoff stopcock was heated at
808C for 12 h. The mixture became bright yellow. The volatile material was removed in
vacuo and the residue was dissolved in Et 2O (5 mL) and chromatographed on an aluminapacked
column. Elution with hexane gave a bright yellow band, which was collected and
the volume of the solvent was reduced (to 5 mL); cooling (–788C, 3 d) afforded the product
as bright yellow crystals; yield: 0.21 g (85%); 1 H NMR (benzene-d 6, ä): 5.2 (s, 5H, Cp), 2.2 (t,
2H, CH 2t-Bu, 3 J HP = 4.0 Hz); 13 C{ 1 H} NMR (benzene-d 6, ä): 299.8 (t, Mo”C, 2 J CP = 27.0 Hz).
2.6.2.6 Method 6:
By Other Rearrangement Processes
The stability of the metal–alkylidyne bond, especially for tungsten, induces other remarkable
rearrangements from a variey of systems. The high-yield synthesis of compound 49
upon photolysis of hexamethyltungsten(VI) in neat trimethylphosphine involves a methyl
migration onto a proposed carbyne intermediate (Scheme 19). [86]
Other rearrangement processes have been established for selected cycloalkyl complexes.
[13,72] For molybdenum complexes, the cyclobutyl complex 50 converts into the butylidyne
product 52 without observation of a metallacyclopentene intermediate 51. [72] For
tungsten complexes, on the other hand, alkylation of the chloro precursor complex with
cyclobutyllithium yields the stable complex 51 directly, which is further transformed to
the carbyne product 52 upon warming (Scheme 19). [71] Cyclopropyl derivatives undergo
elimination of ethene and formation of a methylidyne product, while the cyclopentyl derivatives
do not undergo the ring-opening step.
Scheme 19 Other Rearrangement Processes [71,72,86]
WMe 6
Me3P (neat), hν
− 2CH4 TMS
TMS
TMS N
N
M
N
N
50
[W( CH)(Me) 3(PMe 3) n]
TMS
TMS
TMS N
N
M
N
N
51
M = W quant
− CH 4
90%
[W(Me) 2( CHMe)(PMe 3) n]
W(Me)( CMe)(PMe3) 4
49
TMS
TMS
TMS N
N
M
N
N
52 M = Mo 86%
Butylidyne(N¢-(trimethylsilyl)-N,N-bis{2-[(trimethylsilyl)amino-kN]ethyl}ethane-1,2diamido-kN,kN¢)molybdenum(VI)
(52, M = Mo); Typical Procedure: [72]
Compound 50 (M = Mo; 124 mg, 0.243 mmol) was dissolved in toluene (5 mL), and the soln
was heated in a sealed tube to 608C for 2 h. The toluene was removed in vacuo, and the
residue was dissolved in a minimum amount of pentane. The pentane soln was cooled to
–40 8C to give brown crystals of the product after 24 h; yield: 107 mg (86%); 13 C{ 1 H} NMR
(benzene-d 6, ä): 298.3 (Mo”C).
for references see p 135