Alkylidyne groups

From the above, a parallel appears to exist between the metathesis of alkenes and alkynes. Both reactions result in a redistribution of, respectively, alkylidene and alkylidyne groups. Moreover, the results obtained so far suggest that in both cases the reaction might proceed via a metallocyclic intermediate. 

Scheme 1. Alkene-and alkyne-metal complexes may be formulated with metallacyclo-propane (A) or -propene (B) structures, respectively. Similarly, complexation of a metal atom with an alkylidene or alkylidyne group gives rise to a dimetallacyclopropane (C) or -propene (D) ring system.

REACTIONS LEADING TO TRANSFER OF ALKYLIDYNE GROUPS TO THE CARBABORANE CAGE... 

The complete transfer of an alkylidyne group to the carbaborane cage was first observed with tungsten-platinum species. In acetone, the salts 2d... 

The firm identification of the alkylidyne group was particularly unexpected. These are almost certainly adsorbed on triangular 3-fold bridging sites on (111)... 

Coordinated alkyne and alkylidyne groups can form new C-C bonds by reactions with other compounds such as isocyanates (468), isocyanides (469), or by a reduction mechanism (470) (Fig. 43). 

Trivalent fragments such as RC= (carbyne or alkylidyne group) and N= (nitride) that are triply bound to a metal are three-electron donors. 

Treatment of (22) with CbH = carbazole (38) in hydrocarbon solvents gave [Cb2M]2(/x2-CR)2 ((39) Scheme 4). The reactivity of this species towards hydrogenation (M = Ta) and to organic isocyanides was studied.69,70 Reaction of (39) with 1 eq EtC=CEt produced the di-metallacyclic compound (40) by alkyne insertion into one of the bridging alkylidyne groups.71,72... 

Studies concerning the behavior of the alkylidyne groups supported by the trinuclear [Cp Ti(0)]3 unit as a molecular model for the interactions of hydrocarbons with metal-oxide surfaces have revealed unprecedented chemical reactivity. Firstly, reactions where the Ti303 core is maintained without participation in the processes have been observed. 

Table V shows that the position of the ck-W(CO)2 infrared stretch is highly sensitive to the Jt-acidity of the alkylidyne group. Conjugation of the M C triple bond with Jt-donating alkylidyne substituents (Scheme 32) leads to a decrease in the 7t-acidity of the M=C bond in line with the heteroallenic (heterovinylidene) canonical form and a subsequent increase in available electron density for the n-acidic carbonyls, which leads to a decrease in the frequency of vco-...

Scheme 76. Synthesis of bimetallic tungsten-rhodium complexes with bridging alkylidyne groups (R = C6H4Me-4, Me L = PPh3, X = Pp6 L = 2 cod, X = Bp4).

The reaction of /-Bu-phospha-alkyne, Bu G=P, with the di(/ 3-alkylidyne) cluster compound, Fe3(GO)9(/W3-GX) (/X3-GY) 57 (X = Y = H, F, Gl, Br), results in a three-component coupling among the G=P moiety and the two /X3-alkylidyne groups to form the triiron phosphaferrole complexes 60 (Scheme 7)." Upon treatment with labile... 

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