Synthesis of Cross-Conjugated Olefins from Alkynes:  Regioselective C−C Bond Formation between Alkynes

Abstract

Reactions of cis-dihydrido complex [Ir(H) 2 (NCCH 3 ) 2 (PPh 3 ) 2 ] + (1) with HCtCH and RCt CH (R ) C 6 H 5 , p-C 6 H 4 CH 3 , cyclohex-1-enyl, C(CH 3 )dCH 2 , C(CH 3 ) 3 ) produce cross-conjugated hexatrienes (RCHdC(CHdCH 2 ) 2 , R-HEX) and octatetraenes (H 2 CdCH-CRdCH-C(-CHd CH 2 )dCHR, R 2 -OCT). Two molecules of HCtCH are inserted into Ir-H bonds of 1 to give cis-bis (ethenyl) from which R-HEX-d 1 are obtained in the presence of a base. Di-and trinuclear alkynyl-bis(alkenyl) complexes [L 5 Ir-CtCp-C 6 H 4 -CtC-IrL 5 ] (7, L 5 ) (-CHdCH 2 ) 2 (CO)(PPh 3 ) 2 ) and [L 5 Ir-CtC-m,m-C 6 H 3 -(CtC-IrL 5 ) 2 ] (8, L 5 ) (-CHdCH 2 ) 2 (CO)(PPh 3 ) 2 ) react with H + to produce extended cross-conjugated olefins, p-C 6 H 4 -(HEX) 2 and m,m-C 6 H 3 -(HEX) 3 , respectively, in high yields. Plausible reaction pathways involve alkenyl-vinylidene complexes that undergo the C-C bond formation reaction between the two hydrocarbyl ligands to produce the cross-conjugated olefins.

Dendralenes Branch Out: Cross‐Conjugated Oligoenes Allow the Rapid Generation of Molecular Complexity

“…In other studies, iridium-dendralene complexes of the type [Ir(h 4 -(RCH=C(CH=CH 2 ) 2 )(PPh 3 ) 2 (CO)] + have been prepared by reaction of the alkynylbis(ethenyl) complexes [Ir(CH = CH 2 ) 2 (C CR)(PPh 3 ) 2 (CO)] with HBF 4 . [238] It has also been shown that when treated with iron dodecacarbonyl, acetylene forms two metal complexes, one of which has the structure of a [3]dendralene bound to two {Fe(CO) 3 } fragments. [239] Finally, another report exists in the literature involving complexation of {Fe(CO) 3 } to a cross-conjugated triene-one referred to as "pseudoionone".…”

Synthesis and Applications of Tricarbonyliron Complexes of Dendralenes

“…The complexation of unstable dienes by the Fe(CO) 3 group to generate stable complexes is well established. [6][7][8] Nevertheless, the preparation and reactions of metal complexes of dendralenes has been poorly investigated, [9][10][11] with only one early study describing direct complexation of a dendralene. [9] We found that the tricarbonyliron complex of [3]dendralene 2 could be readily prepared in good yield on a multigram scale through an azabutadiene-catalyzed [12] reaction of Fe 2 (CO) 9 with the parent hydrocarbon 1 (Scheme 2).…”

Successive Activation of C–H and C–O Bonds of Vinyl Ethers by a Diphosphine and Hydrido-Bridged Diiridium Complex

“…The molecular geometry of 3 is shown in Figure 2. The length of the Ir(1)-C(26) bond [1.978(11) Å] is slightly longer than that of typical iridium-carbon double bond [63,64] but it is considerably shorter than that of the iridium-alkenyl carbon single bond [65,66]. The distance between Ir(2) and C (26) [2.875(12) Å] indicates that there is no bonding interaction.…”