Allenyls and propargyls: versatile ligands in transition-metal chemistry

CC Bond Formation in Diiron Complexes

“…The reactivity of these bridging C 3 fragment consequently accounts for a rather complex amount of observations that are difficult to summarise, even though restricted to diiron complexes. Specific review articles on allenes, [92] allenyls and propargyls [93] and vinylalkylidenes [30] have been published, providing information that also include diiron complexes. This chapter will offer a few selected examples, mostly concerning bridging allenyl and vinyliminium ligands, aimed at remarking the huge potential represented by bridging C 3 ligands in bond-forming reactions, which so far has been underexploited for possible synthetic applications.…”

Ligand Bite Angle‐Dependent Palladium‐Catalyzed Cyclization of Propargylic Carbonates to 2‐Alkynyl Azacycles or Cyclic Dienamides

“…However,f or substrates 4l and 4m,t he reduced driving force for six-memberedring formation now restored high regioselectivity for the formation of azepane enamides 6l and 6m, although the latter reaction only proceeded with partial conversion, even with extended reaction times. Thec ontrasting outcomes of these reactions can be explained by am echanism that begins with anti-S N 2' oxidative addition [13] by the bidentate-phosphine-complexed palladium(0) catalyst to give an h 1 -allenylpalladium species 9 (Scheme 3). Through ligand dissociation, the metal is able to bind to the remote double bond of the allene to form an onlinear cationic h 3 -allenylpalladium species 10.…”

Dinuclear NHC Gold(I) Allenyl and Propargyl Complexes: An Experimental and Theoretical Study

“…38,39 Although there has still been no consideration of σ-coordinated gold(I) allenyl intermediates in gold catalysis studies, the synthesis of such complexes deepens our knowledge about the structure and properties of such species in general and thus is fundamental to the understanding of more complex systems. 40 The first isolated σ-coordinated gold(I) allene complex was reported by Gimeno and co-workers in 2014 (Scheme 2). 41 They applied triphenyl(propargyl)phosphonium bromide as an allene precursor; the resulting complex is not a pure gold(I) allenyl complex but due to the phosphonium substituent can be rationalized as the first isolated gold(I) vinylidenoid complex and thus was the first ever, but so far overlooked, gold carbenoid.…”

“…Two years later, Widenhoefer and co-workers synthesized the first example of a gold­(I) allene π complex which demonstrated that the gold was positioned at the less substituted CC bond of the allene. , Although there has still been no consideration of σ-coordinated gold­(I) allenyl intermediates in gold catalysis studies, the synthesis of such complexes deepens our knowledge about the structure and properties of such species in general and thus is fundamental to the understanding of more complex systems …”