Synthesis of mono-, di- and tripalladated 1,3,5-benzenetristyryl complexes. CO insertion to give a dipalladated indenone.

Abstract

The tribrominated arenes 1,3,5-C6(E-CHCHAr)3Br3 (Ar = Ph, (I), p-To (I')), add oxidatively to [Pd(dba)2] ([Pd2(dba)3]·dba) in the presence of two equivalents of a phosphine (PPh3 or PMe2Ph) to form the monopalladated complexes trans-[Pd{C6(E-CHCHAr)3Br2}Br(L)2] (Ar = Ph, L = PPh3 (1a), Ar = p-To, L = PPh3 (1a'), Ar = Ph, L = PMe2Ph (1b)), while the reaction in a 1 : 2 : 4 arene : Pd : PMe2Ph molar ratio affords the dipalladated complex [{trans-PdBr(PMe2Ph)2}2{μ2-C6(E-CHCHPh)3Br}] (2b). Both I and I' add oxidatively to 3 equivalents of [Pd(dba)2] in the presence of the chelating N-donor ligand tmeda (N,N,N',N'-tetramethylethylenediamine) to form the tripalladated complexes [{PdBr(tmeda)}3{μ3-C6(E-CHCHAr)3}] (Ar = Ph, (3c), p-To (3c')). Complex 3c reacts with PMe3 to form [{trans-PdBr(PMe3)2}3{μ3-C6(E-CHCHPh)3}] (3d). Compound 3c also reacts with CO to give the novel dipalladated indenone [2-Ph-4,6-{PdBr(tmeda)}2-5,7-(E-CHCHPh)2-inden-1-one] (4). The crystal structures of 1a' and 1b were determined by X-ray diffraction studies.