η5-Cyclopentadienylpalladium(II) complexes: Synthesis, characterization and use for the vinyl addition polymerization of norbornene and the copolymerization with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene

Dinuclear complexes of palladium(II), containing two bridging halogen (Cl or Br) ligands, [N n Bu 4 ] 2 [(X 5 C 6 ) 2 Pd(μ-Cl) 2 Pd(C 6 X 5 ) 2 ] and [(X 5 C 6 )(L)Pd(μ-Y) 2 Pd(C 6 X 5 )(L)] (X = F, Cl; Y = Cl, Br), readily react with cyclopentadienylthallium, C 5 H 5 Tl, to give the corresponding air stable half-sandwich, pseudo-trigonal η 5 -cyclopentadienylpalladium complexes, [N n Bu 4 ][(η 5 -C 5 H 5 )Pd(C 6 X 5 ) 2 ] (X = F 1 , Cl 2 ) and (η 5 -C 5 H 5 )Pd(C 6 X 5 )(L) (X = F, L = CNBu t 3 , PPh 3 4 , PMe 2 Ph 5 , PEt 3 6 , AsPh 3 7 , SbPh 3 8 ; X = Cl, L = PMe 2 Ph 9 , PEt 3 10 ), respectively. With tetraphenylcyclopentadienylthallium, C 5 Ph 4 HTl or pentabenzylcyclopentadienylthallium, C 5 Bn 5 Tl (Bn = CH 2 Ph) the air stable half-sandwich complexes (η 5 -C 5 Ph 4 H)Pd(C 6 F 5 )(AsPh 3 ), 12 and (η 5 -C 5 Bn 5 )Pd(C 6 F 5 )(AsPh 3 ), 13 are synthesized accordingly. The molecular structures were verified by NMR-spectroscopy, X-ray crystallography ( 7 , 12 , 13 ) and electron impact-mass spectrometry (EI-MS). The precatalysts 4 and 7 can be activated with methylalumoxane (MAO) for the homopolymerization of norbornene (NB) and 5-ethylidene-2-norbornene (ENB) and for the copolymerization of NB with 5-vinyl-2-norbornene (VNB) or ENB with activities of more than 10 6 g PNB /(mol Pd ·h). The higher activity of 7 /MAO over 4 /MAO towards NB homopolymerization was reversed when the olefin-substituted VNB or ENB were added. Then, the more strongly bound PPh 3 ligand of 4 (versus AsPh 3 of 7 ) can compete with the olefin functionality of VNB or ENB and assume a directing role for the insertion of the ring double bond. As a consequence 4 /MAO shows almost the same activity in NB and ENB homopolymerization.