Mono(aryloxido)Titanium(IV) Complexes and Their Application in the Selective Dimerization of Ethylene

We report on the synthesis of mono(aryloxido)titanium(IV) complexes of general formula {Ti[O(o‐R)Ar]X3}, with X = OiPr, ArO = 2‐tert‐butyl‐4‐methylphenoxy and R = CMe3 (2a), CMe2Ph (2b) and CH2NMe2 (2c). Attempts to reach pure mono(aryloxido) complexes when R = CH2NMe(CH2Ph) (2d) or CH2N(CH2Ph)2 (2e) were unsuccessful. When R = CH2OMe, the analogous mononuclear complex was not obtained, and instead, a dinuclear complex [(2‐tert‐butyl‐4‐methyl‐6‐methoxymethylphenoxy) TiCl(OiPr)(μ2‐OiPr)2TiCl(OiPr)2] (3) was formed. Complexes 2b and 3 were characterized by single‐crystal X‐ray diffraction. The former contains a tetrahedrally coordinated TiIV centre, whereas in the latter the aryloxido ligand behaves as a chelating–bridging ligand between the two, chemically very different metal centres that form two face‐sharing octahedra. Different synthetic approaches starting from [Ti(OiPr)4] or [TiCl(OiPr)3] were evaluated and are discussed. The hemilabile behaviour of the aryloxido ligand resulting from reversible coordination of its side arm was studied by variable‐temperature 1H NMR spectroscopy for 2c (R = CH2NMe2). Complexes 2a–d were contacted with ethylene and AlEt3 as cocatalyst. When activated with AlEt3 (3 equiv.) at 20 bar and 60 °C, complex 2c exhibits interesting activity (2100 g/gTi/h) for the selective dimerization of ethylene to 1‐butene (92 % C4=; 99+% C4=1). Noticeable differences in catalyst activity were observed when the R group was modified. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) Functionalized mono‐ and dinuclear mono(aryloxido)titanium(IV) complexes were prepared. Evidence for the hemilabile behaviour of the CH2NMe2‐substitutedaryloxido ligand is discussed. Interesting activities for the selective dimerization of ethylene to 1‐butene [2100 g/gTi/h, selectivity C4=(α) = 92 % (99+%)] were observed.