Abstract
A novel ${\it C_s}$-symmetric yttrocene complex, {\it ansa}-Me$_2$Si($\eta^3$-Flu)( $\eta^5$-Cp’)YCl$_2$Li(OEt$_2$)$_2$ ({\bf 3}) (Flu = C$_13$H$_8$, fluorenyl; Cp’ = C$_5$Me$_4$) has been prepared via salt metathesis reaction from anhydrous YCl$_3$ and dilithium salt of the ligand {\it ansa}-Me$_2$Si(FluH)(Cp`H). Treatment of {\bf 3} with NaN(SiMe$_3$)$_2$ gave the corresponding bis(trimethylsilyl)amide derivative, {\it ansa}-Me$_2$Si(Flu)($\eta^5$-Cp’)YN(SiMe$_3$)$_2$ ({\bf 4}). The X-ray structure of {\bf 3} reveals unusual $\eta^3$-fluorenyl coordination to the Y$^{3+}$ ion. In {\bf 4}, the Y-Flu bonding being partially slipped toward $\eta^3$ from $\eta^5$, $\pi$-dative bonding nature in Y-N bond and a direct interaction of the Y atom with one methyl group of N(SiMe$_3$)$_2$ fragment are present. Both compounds constitute the first examples of structurally characterized fluorenyl {\it ansa}-yttrocenes. The neutral compound {\bf 4} is active for the polymerization of methyl methacrylate (MMA) in toluene, affording iso-rich poly(MMA)s.
A series of novel ${\it C_1}$-symmetric group 4 {\it ansa}-metallocene complexes, Me$_2$Si(C$_5$Me$_4$)(R-Ind)MCl$_2$ (R = H, M = Ti ({\bf 5a}), Zr ({\bf 5b}); R = 2-Me, M = Ti ({\bf 6a}), Zr ({\bf 6b}); R = 3-Me, M = Ti ({\bf 7a}), Zr ({\bf 7b}); R = 3-{\it t}-Bu, M = Ti ({\bf 8a}), Zr ({\bf 8b})) were prepared from the reaction of dilithium salt of the corresponding ligands Me$_2$Si(C$_5$Me$_4$H)(R-IndH) (R = H ({\bf 5}), 2-Me ({\bf 6}), 3-Me ({\bf 7}), and 3-{\it t}-Bu ({\bf 8})) with appropriate group 4 metal halides. Crystal structures of {\bf 5a, 6a, 6b}, and {\bf 8b} have been determined by X-ray diffraction study, which showed chiral, ${\it C_1}$-symmetric nature of them irrespective of kinds of the metal and the ligand. The complexes {\bf 5a, 5b, 6a}, and {\bf 6b} were also tested for the polymerization of propylene in the presence of methylaluminoxane(MAO) under various reaction temperatures. All of Ti and Zr complexes proved to be highly active in propylene polymerization, and afforded moderate to high isotactic polypropylenes. In case of titanocenes ({\bf 5a} and {\bf 6a}), polymerization activity, molecular weight, and isotacticity of polypropylene sharply increase as the polymerization temperature decreases, while the increase of polymerization activity and the decrease of isotacticity and molecular weight of polypropylene were observed upon increasing the polymerization temperature in case of zirconocenes ({\bf 5b} and {\bf 6b}). The effect of 2-Me substituent at the indenyl ring on propylene polymerization was apparent in terms of polymerization activity and molecular weight of polypropylene, especially, in zirconocenes, but was minor in titanocenes.
Novel linked cyclopentadienyl-{\it o}-carboranyl group 4 metal complexes of the general type [Cp’YCBMX$_2$] (M = Ti, Zr; Cp’= C$_5$Me$_4$, indenyl; Y = SiMe$_2$, CMe$_2$; CB = {\it o}-C$_2$B$_{10}$H$_{10}$; X = Cl, NMe$_2$, CH$_2$Ph) have been prepared via salt metathesis and amine elimination reactions utilizing the linked {\it o}-carboranyl ligands Me$_2$Si(C$_5$Me$_4$H) (C$_2$B$_{10}$-H$_{11}$) ({\bf 1}), Me$_2$Si(IndH) (C$_2$B$_{10}$H$_ {11}$) ({\bf 2}), and Me$_2$C(IndH)(C$_2$B$_{10}$H$_{11}$) ({\bf 3}). They were characterized by $^1$H, $^{13}$C, and $^{11}$B NMR spectroscopy, and finally X-ray diffraction method. Crystal structures of the complexes [$\eta^5$:$\eta^1$-Me$_2$Si(C$_5$Me$_4$)(C$_2$B$_{10}$H$_{10}$)]TiCl$_2$ ({\bf 4}), [$\eta^5$: $\eta^1$-Me2Si(C$_5$Me$_4$)(C$_2$B$_{10}$H$_{10}$)]Zr(Nme$_2$)$_2$ ({\bf 9}), and [$\eta^5$:$\eta^1$-Me$_2$Si(Ind)(C$_2$B$_{10}$H$_{10}$)]Ti-
(NMe$_2$)$_2$ ({\bf 10}) revealed that these complexes show “constrained geometry”, and are the first examples of the electron deficient group 4 metal complexes containing linked $\eta^5$:$\eta^1$-metal-carbon bonds. Several complexes were tested for the polymerization of ethylene in the presence of appropriate cocatalysts, but showed moderate to low polymerization activity.
A novel synthesis of nonbridged zirconocene complexes containing a 1-biphenyl-3,4-dimethylcyclopentadienyl ring fragment was developed. All of three complexes (1-Biph-3,4-Me$_2$Cp)$_2$ZrCl$_2$ ({\bf 3}), Cp$^*$(1-Biph-3,4-Me$_2$Cp)ZrCl$_2$ ({\bf 4}), and Cp(1-Biph-3,4-Me$_2$Cp)ZrCl$_2$ ({\bf 5}) were characterized by X-ray diffraction method, and their crystal structures showed that the huge biphenyl groups are oriented away from the chlorines atoms. Furthermore, the sturucture of {\bf 3} revealed {\it racemic}, ${\it C_2}$-symmetric nature in the solid state. In ethylene polymerization, they all afforded high-density polyethylenes with very high activity. Especially, the catalytic properties of {\bf 3} were most marked in terms of both polymerization activity and molecular weight of polyethylene among them. They also showed good activity on the polymerization of propylene, but resulted in nearly atactic, amorphous polypropylene, indicating that they failed in the formation of isotactic-atactic stereoblock sequence in the polymer under the given reaction conditions.
The first well-defined dinuclear group 4 metallocene catalysts, [4,4’-(C$_5$Me$_4$)$_2$(C$_6$H$_4$)$_2$][CpZrCl$_2$]$_2$ ({\bf 2}), [4,4’-(C$_5$Me$_4$)$_2$(C$_6$H$_4$)$_2$][TiCl$_3$]$_2$ ({\bf 3}), and [4,4’-(C$_5$Me$_4$)$_2$(C$_6$H$_4$)$_2$][Ti(O-2,6-iPr$_2$Ph)Cl$_2$]$_2$ ({\bf 4}) containing a biphenylene bridge have been prepared, and crystal structures of {\bf 2} and {\bf 4} were determined by X-ray diffraction method. The structures revealed that both dinuclear complexes {\bf 2} and {\bf 4} constitute two equivalent and independent metal units with respect to the biphenylene bridge. The catalytic properties of {\bf 2}, {\bf 3}, and {\bf 4} were examined with a direct comparison of those of the corresponding mononuclear complexes (C$_5$Me$_4$Ph)(Cp)ZrCl$_2$ ({\bf 5}), (C$_5$Me$_4$biPh)(Cp)ZrCl$_2$ ({\bf 6}), Cp$^*$TiCl$_3$ ({\bf 7}), and Cp$^*$Ti(O-2,6-$^{\it I}$Pr$_2$Ph)Cl$_2$ ({\bf 8}) in the polymerization of {\alpha}-olefins such as ethylene, styrene, and 1-hexene. The dinuclear catalysts consistently exhibited the increased molecular weight of polyethylene and polystyrene as well as comparable or higher catalyst activity compared with those by the corresponding mononuclear catalysts, while both activity and molecular weight of poly(1-hexene) by {\bf 4} dropped sharply. This characteristic features in olefin polymerization appear to be strongly involved with the cooperative participation of both electronic effect of two cationic metal centers through the biphenylene bridge and steric effect between two centers.
