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

The tribrominated arenes 1,3,5-C 6 ( E -CHCHAr) 3 Br 3 (Ar = Ph, (I), p -To (I')), add oxidatively to [Pd(dba) 2 ] ([Pd 2 (dba) 3 ]·dba) in the presence of two equivalents of a phosphine (PPh 3 or PMe 2 Ph) to form the monopalladated complexes trans -[Pd{C 6 ( E -CHCHAr) 3 Br 2 }Br(L) 2 ] (Ar = Ph, L = PPh 3 (1a), Ar = p -To, L = PPh 3 (1a'), Ar = Ph, L = PMe 2 Ph (1b)), while the reaction in a 1 : 2 : 4 arene : Pd : PMe 2 Ph molar ratio affords the dipalladated complex [{ trans -PdBr(PMe 2 Ph) 2 } 2 {μ 2 -C 6 ( E -CHCHPh) 3 Br}] (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 {μ 3 -C 6 ( E -CHCHAr) 3 }] (Ar = Ph, (3c), p -To (3c')). Complex 3c reacts with PMe 3 to form [{ trans -PdBr(PMe 3 ) 2 } 3 {μ 3 -C 6 ( 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.