Alkylidene complex

Ring-opening metathesis polymerization of cycloolefins,93-99 a reaction of significant practical importance (see Section 12.3), is catalyzed by a number of well-defined transition-metal complexes. Alkylidene and metallacyclobutane... 

Peterson olefination involving cyclopropabenzenyl and cyclopropa[Z ]naphthalenyl anion intervention, respectively. Particularly noteworthy is the fact that subjection of disilyl-containing chromium(O) complexes (104, or its anthracene analogue) to r-BuOK provides C(i) anion without the loss of chromium in the case of 104 Peterson olefination has provided the corresponding complexed alkylidene derivative in high yield (equation 25) ", but the compound is unstable and decomposes upon attempted purification. 

Thermolysis of ()) -cyclopentadienyl)bis(neopentyl)(tri-methylphosphine)vanadium(I) (82) in the presence of 1,2-bis(dimethylphosphuio)ethane leads to the formation of the Schrock-type see Schrock-type Carbene Complexes) alkylidene vanadium complex (83), which is supported by X-ray crystallographic analysis (Scheme 45). " The imido vanadium complex (84) is converted to the corresponding alkylidene complex (86) on treatment with ben-zylidene(triphenyl)phosphorane (85) via substitution of the phosphine ligand (Scheme 46). ... 

With other Ta complexes, alkylidene transfer does not occur. Instead, a-hydrogen atom abstraction gives carbyne compounds ... 

Compared with electrophilic carbene complexes, relatively few procedures exist for preparing nucleophilic carbene complexes (alkylidenes).26 Generally, these... 

A limited number of ylides are available which allow the transfer of more complex alkylidene units, such as an isopropylidene group (entries 9 and 10) or a cyclopropylidene group (entries 11 and 12). The oxaspiropentanes formed by reaction of aldehydes and ketones with diphenylsulfonium cyclopropylide are useful intermediates in a number of transformations such as acid-catalyzed isomerization to cyclobutanones. 

Alkylidene and alkylidyne complexes are also referred to as carbene and carbyne complexes. Alkylidene complexes are of two types. The ones in which the metal is in a low oxidation state, like the chromium complex 2.37, are called Fischer carbenes. In contrast, complex 2.38, wha e the metal ion is in a high oxidation state, is referred to as a Schrock carbene. 

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