Palladium-catalyzed cross-coupling of phenyl, vinyl, and allyl siloxane derivatives proceeded in good to excellent yield with aryl iodides, electron-deficient aryl bromides, and allylic benzoates. Methyl and 2,2,2-trifluoroethyl siloxane derivatives can be employed in the coupling reaction. Electron-donating and -withdrawing groups are tolerated on the aryl halide without affecting the coupling. The scope and limitations of this alternative to Stille and Suzuki couplings is outlined.

[formula: see text] The scope of the palladium-catalyzed cross coupling reaction of aryl halides with phenyltrimethoxysilane has been expanded to include aryl bromides, heteroaryl bromides, and aryl chlorides. A more general Pd(0)-catalyst/ligand system has been developed to activate bromides: palladium(II) acetate (Pd(OAc)2) is activated with triphenylphosphine (PPh3) or tri-o-tolylphosphine (P(o-tol)3) (1:2 molar ratio of Pd:phosphine). Coupling of aryl chloride derivatives required addition of 2-(dicyclohexylphosphino)biphenyl (Buchwald's ligand) to Pd2dba3 (tris-(dibenzylideneacetone)dipalladium(0)) (1:1.5 molar ratio of Pd:phosphine).

Palladium-catalyzed cross coupling of arenes with tetrabutylammonium triphenyldifluorosilicate, a hypervalent silicon reagent, to give unsymmetrical biaryls is reported. The Pd(0)-catalyzed process proceeds in good yield with aryl iodides, most aryl triflates, and electron-deficient aryl bromides.

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Siloxane methodology is extended to couplings with iodo-and bromoanilines, hindered arylbromides, and substituted siloxanes as substrates. Additionally, initial studies with 5-bromoindole and other heteroaromatics suggest that the siloxane-mediated cross coupling methodology will also be applicable in these systems.