Alkylidene chain-transfer mechanism

An alternative to the Maitlis scheme was provided by Gaube and Klein (37) (Scheme 5). In this mechanism too, CH2" is the key intermediate that is inserted into the chain. The growing chain is an alkylidene species. The sequence is terminated by desorption of an alkene this step competes with the hydrogen transfer step that generates the alkenyl intermediate necessary for chain growth. Neither this mechanism nor the Maitlis mechanism has yet been investigated computationally. 

While in alkane metathesis mechanism (Scheme 20, b), the n-decane undergoes o-bond metathesis to generate methane and the W-bis-decyl species which, upon P-H elimination, produces the W-H with a coordinated olefin. Further, the a-hydrogen transfer from the alkyl to alkylidyne forms the hydrido W-bis-carbene [55, 76]. This upon [2-1-2] cycloaddition and cycloreversion gives an internal olefin and hydrido W-bis-carbene. Successive insertion/elimination steps (by chain walking) [77] give the terminal alkene, which reacts to a new W-alkylidene. The CH activation of the pendant W-hydride with -decane followed by p-H elimination provides 1-decene. A second metathesis between 1-decene and newly formed W-alkylidene followed by hydrogenolysis produces the alkane. 

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