A weak absorption in this region has been reported by Andrews and Ozin for matrix-isolated Cr2.& Hot bands arising from ( v ,~ = 0) -(uh = n, n = 1-3) transitions to this excited state, shown at X5 magnification in Figure 1, yield we = 470 f 25 cm-I and w,x, = 20 f IO cm-' for the Cr2-anion.The X20 inset to Figure 1 displays an expansion of the spectrum near the ground-state transition. As shown on the right side of the inset, vibrational states of neutral Cr2 from v = 2 to v = 6 are observed 875, 1275, 1650, 1995, and 2305 cm-' (f15 cm-') above the 0-0 transition. These features are far more intense than would be expected on the basis of Franck-Condon factors for a direct photodetachment process. With the u = 1 level constrained to its literature value: the observed energies can be fit to within our experimental uncertainty to a Morse potential with we = 479 f 2 cm-l and w x = 13.5 f 1 .O cm-I. This anharmonicity constant is unusually large: w,x, values for all other neutral homonuclear first-row transition-metal dimers measured to date3 fall in the range 1-4 cm-I. Interestingly, the excellent Morse potential fit to vibrational levels up to v = 6 (0.3 eV above the zero-point level) extrapolates to a dissociation asymptote of only 0.5 eV, far below the true4 Cr2 bond energy (0,) of 1.44 f 0.05 eV. Thus, it is clear that the Cr2 ground-state potential energy curve strongly diverges from a Morse potential at higher energies.A weak vibrational progression of the neutral molecule comprising more than a dozen peaks is observed from 5100 to 6700 cm-l above the 0-0 transition, as shown on the left side of the X20 inset to Figure 1. Surprisingly, the peak spacings are only 130 f IO cm-I, and they exhibit no detectable anharmonicity. This

The palladium-catalyzed coupling of 2-iodoaniline and the corresponding N-methyl, -acetyl, and -tosyl derivatives with a wide variety of internal alkynes provides 2,3-disubstituted indoles in good-to-excellent yields. The best results are obtained by employing an excess of the alkyne and a sodium or potassium acetate or carbonate base plus 1 equiv of either LiCl or n-Bu4NCl, occasionally adding 5 mol % PPh3. The yields with LiCl appear to be higher and more reproducible than those obtained with n-Bu4NCl. The process is quite general as far as the types of substituents which can be accommodated on the nitrogen of the aniline and the two ends of the alkyne triple bond. The reaction is quite regioselective, placing the aryl group of the aniline on the less sterically hindered end of the triple bond and the nitrogen moiety on the more sterically hindered end. This methodology readily affords 2-silylindoles, which can be easily protodesilylated, halogenated, or reacted with alkenes and Pd(OAc)2 to produce 3-substituted indoles, 2-haloindoles, or 2-(1-alkenyl)indoles, respectively. The presence of alcohol groups in the alkyne seems to have a particularly strong directing effect, perhaps due to coordination with palladium. This catalytic process apparently involves arylpalladium formation, regioselective addition to the C−C triple bond of the alkyne, and subsequent intramolecular palladium displacement.

No abstract

No abstract

[reaction: see text] A number of highly substituted indenes have been prepared in good yields by treating functionally substituted aryl halides with various internal alkynes in the presence of a palladium catalyst. The reaction is believed to proceed by regioselective arylpalladation of the alkyne and subsequent nucleophilic displacement of the palladium in the resulting vinylpalladium intermediate.