Ling Huang, U. Aulwurm, F. Heinemann
Dec 1, 1998
Citations
0
Influential Citations
13
Citations
Journal
European Journal of Inorganic Chemistry
Abstract
RhCl(PPh3)3 in the presence of excess hydrochloric acid and azobenzene in refluxing 1-pentanol catalyzes the cyclodimerization of arylalkynes to 1,2,3-substituted naphthalene derivatives. This enables an easy access to 1,2,3-triphenylnaphthalene (1), 7-methoxy-1,2,3-tris(p-methoxyphenyl)naphthalene (2), 7-methyl-1,2,3-tris(p-methylphenyl)naphthalene (3), and 7-nitro-3-(p-nitrophenyl)-1,2-diphenylnaphthalene (4). A co-cyclodimerization of tolan with 4-octyne affords 3-phenyl-1,2-dipropylnaphthalene (5). The structure of 4 was resolved by single-crystal X-ray structural analysis. The rate of formation of 1 is first-order with respect to tolan and RhCl(PPh3)3 and exhibits activation parameters of ΔH‡ = 94.7 ± 10 kJ mol−1 and ΔS‡ = 36 ± 6 J K−1mol−1. Replacing HCl by HBr and HI decreases the rate by 28 and 55%, respectively. Although naphthalene formation occurs also in the absence of azobenzene, its presence stabilizes the catalyst, accelerates the reaction, and inhibits formation of 1-chlorostilbene, which is the major by-product. When RhCl(PCy3)2 is used as the catalyst, naphthalene formation even in the absence of azobenzene is highly selective, but proceeds much slower. No reaction is observed in non-protic solvents.