Osvaldo L. Casagrande

Recent Advances in Olefin Polymerization Using Binary Catalyst Systems

Several homogeneous and heterogeneous binary systems have been applied to olefin polymerization in order to produce polymers with improved physical and/or chemical characteristics. This article reviews the recent developments in this area focusing mainly on polymer properties, the relationship between the types of catalyst present in the binary systems, their use in the homopolymerization of ethylene and propene, and the copolymerization of ethylene and higher α-olefins.

Copolymerization of Ethylene with 1‐Hexene Using Sterically Hindered Tris(pyrazolyl)borate Titanium (IV) Compounds

The copolymerization of ethylene/1-hexene was studied using {Tp Ms }TiCl 3 (1) (Tp Ms = hydriodotris(3-mesitylpyarzol-1-yl) and {Tp Ms* }TiCl3(2) (Tp Ms* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) compounds in the presence of methylaluminoxane at 65°C. for both catalysts it was observed that the productivities decreased with increasing the 1-hexene concentration in the milieu exhibiting a negative comonomer effect. The highest productivities and 1-hexene incorporations were achieved in the case of {Tp Ms* }TiCl3 catalyst system. The resulting copolymers were not soluble in TCB even at 165°C. 1-hexene incorporations were very low; ca. 1.2 and 3.3 mol-%, respectively (1) and (2). The r 1 and r 2 parameters for both (1) and (2)/MAO catalyst systems clearly indicated a strong tendency of these catalytic precursors to preferentially promote ethylene homopolymerization. According to X-ray photolectron spectroscopy, from the analysis of the Ti2p 3/2 peak, Tp Ms* catalyst seems to present a stronger cationic character after MAO treatment, which can explain in part its higher catalyst activity.

Scandium versus yttrium{amino-alkoxy-bis(phenolate)} complexes for the stereoselective ring-opening polymerization of racemic lactide and β-butyrolactone

Scandium and yttrium amide complexes Ln{ONXO(R1,R2)}(N(SiHMe2)2)(THF)n (Ln = Sc, n = 0 or Y, n = 1; X = NMe2 or OMe; R(1) = Cumyl or p-Cl-Cumyl; R(2) = Me or Cumyl) were prepared by aminolysis of Ln[N(SiHMe2)2]3(THF) with the corresponding tetradentate diamino- or alkoxy-amino-bis(phenol) pro-ligands {ONXO(R1,R2)}H2. In the solid state and in toluene solution, the scandium complexes are monomeric and 5-coordinated, while the analogous yttrium complexes all bear an extra THF-coordinated molecule and are 6-coordinated. Sc{ONXO(R1,R2)}(N(SiHMe2)2) complexes are single-site initiators for the ring-opening polymerization (ROP) of racemic lactide but are less active than their yttrium analogues Y{ONXO(R1,R2)}(N(SiHMe2)2)(THF); also, in contrast to the latter ones, they are inactive in the ROP of the more demanding racemic β-butyrolactone. On the other hand, the scandium amide complexes feature a significantly improved control over the ROP of lactide, yielding PLAs with much narrower molecular weight distributions (Đ(M) < 1.1 for Sc vs. 1.5-2.0 for Y). The yttrium complex with the very bulky o,p-dicumyl-substituted ligand is more heteroselective than its scandium analogue (P(r) = 0.88 vs. 0.83), while the opposite is observed with complexes based on p-methyl-substituted ligands (P(r) = 0.50 in toluene or 0.72-0.75 in THF for Y vs. P(r) = 0.75-0.83 for Sc in toluene). These reactivity and selectivity trends are rationalized by a much more sterically crowded coordination sphere in scandium than in yttrium complexes.

Synthesis and structure of a new heteronuclear (eta(6)-arene) tricarbonylchromium compound incorporating propargyl amine unit

Univ Fed Rio Grande Sul, Inst Quim, Lab Mol Catalysis, BR-91509900 Porto Alegre, RS, Brazil

Hydroruthenation of Propargyl Amines Promoted by the 16-Electron Complex RuHCl(CO)(PiPr3)2

Abstract The 16-electron complex RuHCl(CO)(PiPr3)2 (1) reacts with propargyl amines H‒C≡C(CH2) n Y (2–5) (n=1,2; Y = NMe2, N(Me)CH2Ph, or Py) by insertion to afford the five-coordinate vinyl-complexes RuCl{(E)‒CH˭CH(CH2) n Y}(CO)(PiPr3)2 (6, Y = NMe2, n = 1; 7, Y = N(Me)CH2Ph, n = 1; 8, Y = Py, n = 2; 9, Y = NMe2, n = 2) in good yield. Addition of CO to 7 produces the six-coordinate vinyl-complex RuCl{(E)‒CH˭CH(CH2) n Y}(CO)2(PiPr3)2 (10). The trans stereochemistry at the C˭C bond is observed in all compounds. All compounds were characterized by IR, 1H, 13C and 31P NMR spectroscopy.