The novel metal-catalyzed cross-coupling reaction of indium organometallics with organic electrophiles is described. Triorganoindium compounds (R(3)In) containing alkyl, vinyl, aryl, and alkynyl groups are efficiently prepared from the corresponding lithium or magnesium organometallics by reaction with indium trichloride. The cross-coupling reaction of R(3)In with aryl halides and pseudohalides (iodide 2, bromide 5, and triflate 4), vinyl triflates, benzyl bromides, and acid chlorides proceeds under palladium catalysis in excellent yields and with high chemoselectivity. Indium organometallics also react with aryl chlorides as under nickel catalysis. In the cross-coupling reaction the triorganoindium compounds transfer, in a clear example of atom economy, all three of the organic groups attached to the metal, as shown by the necessity of using only 34 mol % of indium. The feasibility of using R(3)In in reactions with different electrophiles, along with the high yields and chemoselectivities obtained, reveals indium organometallics to be useful alternatives to other organometallics in cross-coupling reactions.
The triptycene-substituted [3]- and [4]helicenes 1 and 2 were examined as possible molecular versions of mechanical ratchets, where the triptycene serves as the ratchet wheel and the helicenes as pawl and spring. The syntheses of 1 and 2b are described. 1H NMR was employed to examine rotation around the triptycene/helicene single bond; at 20 °C rotation is frozen for both 1 and 2b, but the NMR of 1 revealed a plane of symmetry, indicating that 1 cannot function as a unidirectional ratchet. In contrast, NMR revealed that, like a ratchet, triptycyl[4]helicene 2b lacks the symmetry of 1 and has a barrier to rotation of 24.5 kcal/mol, but spin polarization transfer NMR experiments indicated the triptycene in 2b nonetheless rotates equally in both directions. That outcome is rationalized from the standpoint of thermodynamics.
COMMUNICATIONS tural feature of these (TMPDO),TCNE arrays is rectangular four-site 0 -C binding at the TCNE olefinic carbon atoms, which appear to interact through their K* lobes. The topological requirement for DA complexation at the N-oxide center is more flexible, allowing the formation of both ladder and web (crosslinked ladder) DA arrays in the (TMPDO),TCNE crystals as the N-0-C angle flexes. TMPDO (2.58 g, 69%, m.p. 498 K (493 K 1221) was prepared by treatment of 2,3,5,6-tetramethylpyrazine (2.95 g, Aldrich) in CH,CI, (50 mL) with potassium peroxomonosulfate (66.6 g, 5 equiv; OXONE, Aldrich) in H,O (400 mL) with vigorous stirring at 298 K for 24 h. TCNE (Aldrich) was purified by multiple sublimation (373 K, 0.05 mmHg) through activated charcoal. Conditions for the Benesi-Hildebrand analysis: [TMPDO] = 1 . 9 0 m~; [TCNE] =18.7, 34.0, 51.1, 66.4, 75.7, and 9 0 . 6 m~. Purple crystals of (TMPDO),TCNE were prepared by cooling a mixture of TMPDO ( 4 0 m~) and TCNE ( 2 0 m~) in CH,CN to 253 K for 2-5 h. Red prismatic crystals of (TMPDO),TCNE were prepared analogously, after 2-3 d crystallization. Crystal X-ray diffraction was performed on a Siemens SMART diffractometer with CCD area detection at 293 (purple (111) and 173 K (red 1131) with monochromatic Mo,.radiation ( A = 0.71073 8,). Solution and refinement (against were performed with SHELXTL. No absorption correction was employed. Hydrogen atoms were placed in calculated positions (0.95 8, from the methyl carbon atom with tetrahedral angles). They were given torsional freedom and their thermal parameters were set to 1.2 x Oc, of the bonded carbon atom. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-100438. Copies of the data can be obtained free of charge on application to ). Powder Cu,. X-ray spectra were obtained on a Rigaku powder diffractometer. Experimental Section
The palladium-catalyzed cross-coupling reaction of organogold(I) reagents (alkyl, alkenyl, aryl, and alkynyl) with organic electrophiles, such as aryl and alkenyl halides, aryl triflates, benzyl bromide, and benzoyl chloride is reported. The reaction takes place, under palladium catalysis, at room temperature with short reaction times to give the corresponding cross-coupling products in high yields.
The first enantioselective sp-sp3 cross-coupling reaction between alkynyl organometals and racemic benzyl bromides is reported. The coupling is performed at room temperature by using NiBr2diglyme and (S)-(iPr)-Pybox as the catalytic system and trialkynylindium reagents as nucleophiles. The reaction is stereoconvergent, both enantiomers of the racemic benzyl bromide are converted into one enantiomer of the product, and stereospecific. The reaction takes place efficiently in good yields and with high atom economy, as the triorganoindium reagents transfer the three organic groups attached to indium (only 40 mol % of R3In is used).
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