Julien Thuilliez

Neutral ansa-bis(fluorenyl)silane neodymium borohydrides: synthesis, structural study and behaviour as catalysts in butadiene–ethylene copolymerisation

The reaction of silylene-bridged bis(fluorenyl)dipotassium salts with neodymium tris(borohydride) afforded new neutral ansa-bis(fluorenyl)silane neodymium borohydrides: (Flu2SiR2)Nd(BH4)(THF) [R2 = Me2, Et2, (CH2)3, Me(Ph), Flu = C13H8] that were better characterised and more soluble than the previously described anionic [(Flu2SiMe2)Nd(BH4)2]−. The X-ray structures of three of these complexes were determined, and their solid-state geometrical parameters are very similar, despite the ring strain introduced by the silacyclobutane bridge in [Flu2Si(CH2)3]Nd(BH4)(THF). The main geometrical features were satisfactorily reproduced by DFT calculations. The catalytic activity of the title complexes in ethylene–butadiene copolymerisation reactions was assessed and compared to that of the reported activity of [(Flu2SiMe2)Nd(BH4)2]− under similar conditions. From these results it can be concluded that the cyclo-copolymerisation of ethylene with butadiene is characteristic of a catalyst featuring silylene-bridged bis(fluorenyl) ligands around neodymium, and appears to be independent of the substituents at the silicon atom.

New insights on Ni-based catalysts for stereospecific polymerization of butadiene

A new class of nickel catalysts for stereospecific polymerization of butadiene Ni(COD)2/[X][B(C6F5)4] (X = CPh3 or HNMe2Ph) was investigated and compared to the conventional ternary system Ni(O2CC7H15)2/BF3·OEt2/AlEt3. Both families of catalysts showed high activity and stereospecificity but catalysts based on the relatively non-coordinating anion B(C6F5)4− displayed lower molar masses. The combinations of Ni(O2CR)2 with AlEt3/[CPh3][B(C6F5)4] and of Ni(COD)2 with BF3·OEt2, [CPh3][B(C6F5)4]/BF3·OEt2 and AlEt3/BF3·OEt2 were also implemented. The polymerization tests using the resulting catalysts demonstrated that in the case of the industrial catalyst Ni(O2CR)2/BF3·OEt2/AlEt3, the formation of the active species is based on the reduction of Ni(O2CR)2 in the presence of AlEt3 followed by the re-oxidation of nickel(0) to nickel(II) by butadiene leading to the bis(allyl) complex Ni(C12H18). A cationic active species is finally obtained by the activation of Ni(C12H18) with a fluorinated compound formed by the reaction of BF3·OEt2 with AlEt3.