Dimerization of 1-alkynes catalyzed by RhCl(PMe3)3. Isolation of the intermediate (alkynyl)(vinyl)rhodium(III) complexes

Transition metal-catalyzed couplings of alkynes to 1,3-enynes: modern methods and synthetic applications

“…As early as the 1970s, ruthenium-catalyzed dimerizations of alkyl alkynes to cumulenes were known. 7a,7b,16 While head-to-head and head-to-tail enyne products were also identified in those processes, they were present only as minor products. In the early 1990s, however, Bianchini and co-workers reported the selective, catalytic dimerization of both phenylacetylene ( 16 ) and trimethylsilylacetylene ( 20 ).…”

“…7 From these studies, some general mechanistic understandings have emerged (Scheme 2). In one possible mode of reactivity, a metal acetylide may form upon the interaction of a terminal alkyne with a transition metal complex (Scheme 2, Eqns A and B).…”

“…Hydrido(alkynyl)metal species have been identified spectroscopically, as have the alkynyl(vinyl)metal complexes that result upon regioselective insertion of an acceptor alkyne into the M-H bond. 7g C−C bond formation can occur upon thermally promoted reductive elimination, generating either the head-to-tail (Eqn. C) or the ( E )-head-to-head (Eqn.…”

“…7g 1-Pentyne ( 4 ) was converted to a 2.4:1 mixture of ( E )-head-to-head product 5 and head-to-tail product 6 upon exposure to the catalyst in refluxing acetone (Scheme 4). Similar results were obtained with other aliphatic substrates, but aryl alkynes, ethyl propiolate, and ethoxyacetylene failed to dimerize.…”

Unsymmetrically Substituted Butenynyl‐Iron(II) Complexes

“…Attempts to prepare complexes incorporating a trimethylsilyl group met with limited success. The first step in butenyne formation is generally taken to be protonation at one of the acetylide β-carbon atoms to yield a mixed vinylidene/ acetylide complex, [12,28] The lability of carbon-silicon bonds is well established, and, although the cleavage of trimethylsilyl groups from trimethylsilylacetylide complexes to form the parent acetylido complexes has been reported to be particularly difficult in some cases, [29] the use of ammonium hexafluorophosphate appears to allow the isolation of vinylidene complexes bearing the C=CH 2 moiety in good yields. [30] The desilylation of 2gЈ occurs early in the reaction to yield the deprotected vinylidene complex, which then undergoes ligand coupling to give the final product.…”