REACTIONS OF DIARYLNITRENIUM IONS WITH ELECTRON-RICH ALKENES - AN EXPERIMENTAL AND THEORETICAL-STUDY

Photolysis of (diphenylamino)-2,4,6-trimethylpyridinium tetrafluorobor ate (1a) and is(4-methylphenyl)amino]-2,4,6-trimethylpyridinium salt ( 1b) gives products attributable to diarylnitrenium ion (Ar2N+, 2). The major products of these reactions include products from nucleophilic addition of various pi-nucleophiles (e.g. electron rich alkenes) to th e ortho and para positions of one of the phenyl rings. Nanosecond and EPR spectroscopy show that radicals also form. These radicals are thou ght to give rise to the diarylamines isolated as minor products from t he photolysis of 1a and 1b. In addition to the para addition products and Ph2NH, N-phenylindoles and N-phenylindolinones are isolated when s ilyl enol ethers and silyl ketene acetals are used as trapping agents, respectively. The indoles and indolinones are generated from initial addition of the nucleophile to the ortho position on 2 followed by cyc lization of the resulting intermediate. A product resulting from N add ition of the nucleophile to 2 is isolated only when silyl ketene aceta ls are used. A number of electronic structure calculations at differen t levels of molecular orbital and density functional theory were carri ed out on Ph2N+. There do not seem to be effects associated with eithe r the charge distribution or the LUMO that would strongly influence or tho/para/N selectivity in nucleophilic trapping. Laser flash photolysi s on la provides absolute rate constants for the nucleophilic addition of various alkenes to Ph2N+. These fall in the range of 10(9)-10(10) M-1 s(-1) and correlate with the oxidation potential of the alkene. Fr om these data it is clear that the more easily oxidized the alkene the faster it will react with Ph2N+.