Regio- and Stereoselective C−C Bond Formation between Alkynes:  Synthesis of Linear Dienynes from Alkynes

Abstract

Reactions of the iridacyclopentadienes (2a) and (2b) with RC⋮CH (R = C6H5, p-C6H4CH3) give linear conjugated dienynes (RC⋮CCHCHCHCH2 (3) and (5)) and benzene derivatives (RC6H5 (4) and RC6H3C6H8 (6, 6-aryl-1,2,3,4-tetrahydronaphthalene)). Linear conjugated dienynes 3 and 5 are exclusively obtained from the reactions of alkynyl iridacyclopentadienes (7) and (8) (R = C6H5 (a), p-C6H4CH3 (b), cyclohex-1-enyl (c)) with HOTf, respectively. The di- and trinuclear alkynyl iridacyclopentadienes (9a), (9b), and (10) (L3 = (CO)(PPh3)2) react with HOTf to produce the extended and conjugated dienynes p-C6H4(C⋮CCHCHCHCH2)2 (11), (12), and m,m-C6H3(C⋮CCHCHCHCH2)3 (13), respectively, in high yields. Iridacyclohexadienes (17, R‘ = H (a), CH3 (b)) are obtained from the reactions of 7 with HBF4 through a C−C bond-forming reaction between the α-carbons of alkynyl and 1,3-butadiene-1,4-diyl ligands. Plausible reaction pathways are suggested for the C−C bond-forming reaction between RC⋮CH and 1,3-butadiene-1,4-diyl ligands of iridacyclopentadienes to produce linear dienynes.

Recent Advances in Metallabenzene Chemistry

“…[76] + with two equivalents of acetylene and subsequent addition of an equivalent of a terminal arylacetylene, produced alkynyl iridacyclopentadienes such as 89 (Scheme 25). [77] Upon acidification with HBF 4 , 89 rearranged cleanly into iridacyclohexadiene 90, the product of a formal [2+2+1] alkyne cyclization.…”

“…Although zwitterionic iridabenzene resonance structures such as 90' and 91' were invoked to help explain these types of rearrangements, metalla-aromatic species were not observed. [76] More recently though, Chin and Lee found that if MeCN is present during acidification of 90 with HBF 4 , cationic iridabenzene 93 is then isolated. Unique to 93 is its ability to reversibly react with weak Lewis bases such as CO and Et 3 N to form iridacyclohexadiene complexes 91 and 92, respectively.…”

“…The facile interconversion of cyclohexadienes 91 and 92 and iridabenzene 93 supports the presumed intermediacy of iridabenzenes in the original studies. [76] This reactivity could be a result of the amphiprotic benzylic carbon atom connected to the carbon atom ortho to the Ir center. Resonance structures 90' and 91' could at least partly explain this behavior.…”

“…This chemistry is related to the known reactions of alkynyl complexes with H + which lead to CÀC coupling with neighboring unsaturated ligands. [76,77] Paneque, Poveda, and co-workers have recently reported an interesting variation of the [2+2+1] protocol by the coupling of an alkene and an iridacyclopentadiene. [78] Reaction of diene 98 with propene at 60 8C furnished iridabenzene 99 (Scheme 27).…”

Multinuclear Silver Ethynide Supramolecular Synthons for the Construction of Coordination Networks

“…The reported coordination modes of the transition‐metal complexes of p ‐phenylenediethynide and its derivatives are presented in Scheme 2 (modes I, V, IX–XI). The mode that occurs most frequently is μ 1 ,μ 1 mode I, in which the terminal metal atoms can be palladium,33 iridium,34 platinum,35 gold,3a, 36 rhodium,37 or manganese38 in homometallic complexes, and also iron and rhenium in heterometallic complexes 39. The symmetrical μ 2 ,μ 2 mode V was reported recently by Lalinde and co‐workers through the reaction of [{Pt(PPh 3 ) 2 } 2 {μ‐η 2 :η 2 ‐(1,4‐HCC) 2 C 6 H 4 }] with cis ‐[PtR 2 S 2 ] complexes 40.…”