Alkenyl-vinylidene

Scheme 2.2 Competitive formation of alkenyl-vinylidene vs. allenylidene group.

Mononuclear osmium half-sandwiches, with rf-cyclopentadienyls and 7]5-indenyls alkenyls and allenyls with t/-M-C bonds, 6, 558 alkenyl vinylidenes, 6, 593 alkyl, aryl, acyl complexes, 6, 552 with alkylidyne complexes, 6, 599 alkynyl and enynyl complexes, 6, 567 allenylidene and cumulenylidene complexes,... 

The formation of allenylidene derivatives from ethynyl-hexanol and alkenyl-vinylidene mononuclear complexes (9), the formation of mononuclear ruthenium allenyl complexes from terminal alkynes (10), the intermediacy of ruthenium-allenylidene complexes in forming propargylic alcohols (II), and in the cyclization of propargyl alcohols (12), and the use of mononuclear ruthenium compounds in allylic alkylation catalysis (13) have also been reported. 

In agreement with the above mentioned proposal, it has been observed that the addition of 1 equiv of HBF4-OEt2 to diethyl ether solutions of 200 affords the alkenyl-vinylidene complex 202 as a yellow solid in 65% yield and that the treatment of 202 with NaCl gives 201 in 91% yield. 

Formation from Alkenyl, Vinylidene or Carbyne Complexes... 

Half-sandwich cr-enynyl complexes have also been synthesized by deprotonation of isolated monosubstituted alkenyl-vinylidene complexes. In this way, indenyl-Ru(ii) and indenyl-Os(ii) cr-enynyl derivatives 137 have been prepared in high yields by treatment of vinylidene precursors 136 with AI2O3 or KOBu under mild conditions (RT) (Equation (g)) 60,109,132,132a related CpRu(ii) complex [Ru(G=GC6H9)Cp(GO)(PPr 3)]... 

G6H9= 1-cyclohexenyl) has also been obtained by deprotonation of the corresponding alkenyl-vinylidene... 

Activation of propargylic alcohols containing a G-H bond in / -position with respect to the OH group by a coordinatively unsaturated complex is probably the most general route for the preparation of alkenyl-vinylidene derivatives [M]=G=GHGR =GR R (Scheme 24). This process proceeds through the initial formation of an unstable hydroxy-vinylidene intermediate, which undergoes a spontaneous dehydration. In some cases, stable... 

Following this synthetic approach, the cationic alkenyl-vinylidene derivatives 136 (see Equation (8)) have been selectively synthesized through the activation of 1-ethynyl-l-cycloalkanols by the indenyl-chloride precursors [MCl(y-C9H7)(L )(L )] (M = Ru, Os, L = L = PPh3 M = Ru, = The related species... 

Treatment of the Os(ii) precursor [OsGlGp(PPr 3)2] with 2-methyl-3-butyn-2-ol and 1-ethynylcyclohexanol in toluene at 85 °G results in the formation of the neutral alkenyl vinylidenes [OsGl =G=G(H)R Gp(PPr 3)] (R = GMe=GH2, 1-cyclohexenyl) via release of PPr 3. Intermediate species containing these propargylic alcohols 7r-coordinated to osmium could be isolated working at RT. The related allenyl vinylidene [0sGl =G=G(G02Me)G-... 

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