Me3Si C

Ethyl diazoacetate adds endo to Me3Si(C=C)2SiMe3 to give 3-ethoxycarbonyl-4-trimethylsilylethynyl-5-trimethylsilylpyrazole (88JOM247). 

Strained cyclic alkynes are the most powerful olefinic 7r-donors for gold(i) centers. This has been demonstrated for the cycloheptynes shown in Scheme 80. The Au-C distances are in the range from 2.050 to 2.100 A.318 There is also evidence for the coordination of AuCl to Me3Si-C=C-SiMe3, but no details are available.319... 

Me2S+-7-PhCH2NH-ll-Bu(Me3Si)C=CH- 5-Me2S-6-Bu(Me3Si)C=CH-B10H11, BuNC Benzene, 61%206... 

The reaction (a Schlenk dimerization) between the phosphine-borane-substituted alkene nPr2P(BH3) (Me3Si)C=CH2 and elemental lithium in THF yields the complex [(pmdeta)Li Prn2P(BH3) (Me3Si)CCH2]2 123 which in the solid state has a lithium bound to the BH3 hydrogens of the ligand, and no Li-C(carbanion) contact (pmdeta = N,N,N, N",N"-pentamethyldiethylenetriamine).85... 

These studies have indicated that while two adjacent C=C triple bonds may be coordinated to Co2(CO)g or Co2(/r-dppm)(CO)4 groups, introduction of a third such group to the next adjacent C=C triple bond is restricted by steric constraints. Thus, the reaction of Me3Si(C=C)4SiMc3 with a large excess of Co2(CO)g gave 86... 

Me3Si(C=C)4SiMe3 failed. It was suggested that that the steric demands of the cluster carbonium ion prevented reaction with the bis(silyl)alkyne, while attempts to isolate the higher congeners Co3 /U3-C(C=C) SiMe3 (CO)9 were hampered by their instability. ... 

An example of the next higher homolog in the series of odd-numbered cumuleny-lidene complexes, heptahexaenylidene complexes, was already proposed in 1996 as an intermediate in the formation of the alkenyl(dimethylamino)pentatetraenylidene tungsten complex 27 (Scheme 3.21) in the sequential reaction of triyne Me3Si-(C = C)3-C(NMe2)3 with LiMe LiBr, (CO)5W(thf)], and BFj OEtz [37]. The putative heptahexaenylidene complex 26 could neither be isolated nor spectroscopically... 

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