ca01 only detailed ToC 1..24

2.6.2 Metal–Carbyne Complexes 105
N
M
N
N
Cl TMS
TMS
N
TMS
R 1 CH2Li
Et 2O
or THF
M = Mo, W; R 1 = H, Me, Pr, Ph, TMS, t-Bu
WBr 2(PMe 3) 4
THF, 69 o TMS
C
90%
TMS
TMS N
N
CH2R
N
M
1
TMS
N
CEt
PMe3
Me3P W PMe3 Me3P Br
41
25−80 o C
− H 2
73−91%
TMS
TMS N
N
CR 1 TMS
Tris(2,2-dimethylpropyl)(2,2-dimethylpropylidyne)tungsten(VI) (39): [68]
A soln of WCl 3(OMe) 3 (19.1 g, 50 mmol) in a mixture of THF and Et 2O was added very slowly
to 1 M t-BuCH 2MgCl (0.3 mol) in Et 2Oat–78 8C with vigorous stirring. The color of the
soln gradually turned yellow-green. After the addition was complete, no significant
amount of precipitate was apparent. The mixture was allowed to warm slowly from –78
to 258C over a period of 10 h to give a red-brown soln and abundant precipitate. After filtration
from Celite followed by washing of the filter cake with Et 2O, the solvent was removed
in vacuo to give a thick red-brown oily liquid. Pentane (200 mL) was added to the
residue, followed by another filtration and evaporation to dryness. The resulting oily red
liquid was distilled at ca. 808C/0.001 Torr through a short-path distillation apparatus;
yield 55–60%. An additional 5–10% yield can usually be recovered by extracting the tarlike
residue with pentane, filtering off the insolubles, removing the pentane in vacuo, and
again distilling the residue as before. 1 H NMR (benzene-d 6, ä): 1.66 (Ct-Bu); 13 C{ 1 H} NMR
(benzene-d 6, ä): 316.2 (W”C).
Ethylidyne(N¢-(trimethylsilyl)-N,N-bis{2-[(trimethylsilyl)amino-kN]ethyl}ethane-1,2-diamido-kN,kN¢)tungsten(VI)
(40, M=W;R 1 = Me); Typical Procedure: [71]
An Et 2O (25 mL) soln of [WCl{N(CH 2CH 2NTMS) 3}] (0.20 g, 0.345 mmol) was treated with
EtLi (0.019 g, 0.52 mmol) at 258C. The mixture turned light yellow as gas evolved. The resulting
mixture was stirred for another 3 h and then evaporated to dryness in vacuo. The
yellow residue was extracted with pentane (60 mL), and the extract was filtered. The filtrate
was concentrated to ca. 5 mLin vacuo and chilled at –408C for several h to yield the
product as light yellow crystals; yield: 0.16 g (81%); 1 H NMR (benzene-d 6, ä): 3.73
(W”CCH 3, 3 J WH = 7.9 Hz); 13 C{ 1 H} NMR (benzene-d 6, ä): 274.33 (W”C).
2.6.2.2 Method 2:
By Addition of Alkynes to Compounds with Metal-Metal Triple Bonds
Symmetrical alkynes provide access to carbyne complexes 42 upon reaction with symmetrical
triply bonded tungsten alkoxy, aryloxy, and mixed alkyl–alkoxy complexes
(Scheme 15). [74,75] This reaction occurs readily when R 1 is a simple alkyl group but also
for functionalized alkynes, more easily so in the presence of nitrogen donors (in which
case the base adducts are obtained). [74] This reaction is very sensitive to steric factors.
The formation of alkyne adducts, bis-alkyne adducts, and products of C-C couplings are
possible alternatives. [75,76] Other group 6 triply bonded dimers such as hexakis(dimethylamido)-
or hexaalkylditungsten(III) and molybdenum alkoxides do not cleave internal alkynes.
M
N
40
N
for references see p 135