Alkylidynes coupling

Fe, (CO) (ju.-CMe) (jLi.-COEt) reacts reversibly with CO to couple the alkylidyne ligands, giving Fe (CO)(u -n -MeCHCOEt) alkylidyne coupling is also observed on reaction with RC=CR (R= Ph, SiMOg) to give ferracyclopentadiene derivaties. ... 

Facile dithiocarbamate-induced carbonyl-alkylidyne coupling is also observed upon addition of dithiocarbamate salts (R = Me, Et) to cyclic alkyUdyne complexes [W(CO)2(MeCN)(dppe) CCH=(CH2) ] ( =4, 7) (Eq. 103), a monodentate dithiocarbamate intermediate being proposed (1094). 

Reactions of alkynes with trinuclear group 6-group 9 clusters incorporating bridging alkylidyne ligands proceeded by coupling the C-donor ligands. 

The synthetic method leading to Nb-alkylidenes and Nb-alkylidynes was particularly successful, due to a quite remarkable difference in the reaction rate of 29 with ketones or aldehydes, vs the subsequent reaction of the alkylidene with ketones and aldehydes (see Scheme 37). The former reaction takes a few minutes at -40°C, while the latter one occurs in hours at room temperature.88 The reaction between 178 and benzaldehyde led to triphenylethylene and the niobyl derivative 184. Due to the difference in reaction rates between a and b in Scheme 37, it was found that the sequential addition of two different ketones or aldehydes to a THF solution of 29 produced a nonsymmetric olefin in a stepwise McMurry-type reaction.84 This is exemplified in the coupling shown in reaction c (Scheme 37). The proposed reaction pathway does not involve the intermediacy of a pinacolato ligand and therefore differs from the mechanism of the McMurry reaction and related reductive couplings at activated metal sites.89... 

The general synthetic approaches for expanded porphycenes rely upon the insertion of alkylidene or alkylidyne moieties either as the meso-bridge or between the 2 and 2 positions of the bipyrrole subunits. Thus, the vinylogous dialdehyde 72 (Scheme 35) obtained from 4,4 -dipropyl-2,2 -bipyrrole with 3-(dimethyl-l-amino)acrolein has been converted to (1993PAC143) to 73 using a standard McMurry-type coupling. Expanded porphycene 73 with TFA precipitates as dication 74. 

The bis(alkylidyne) clusters Cp3Co3(CR)2 react with elemental sulfur to give CpCoS2C2R2 (R = Bu, Ph, C02Me, C2SiMe3). Labeling studies show that the two alkylidyne units from the same cluster are coupled in this reaction, which probably begins with attack of sulfur on a Co—Co bond (294). 

The first examples were prepared in reactions of aUcynes with M3(CO)i2, M = Ru and Os. The C3 unit can also be produced by alkylidyne-aUcyne coupling. 

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