Titanium and zirconium complexes of the N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligand: syntheses, structures and uses in catalytic hydrosilylation reactions

We report here a number of dianionic 1,4-diaza-1,3-butadiene complexes of titanium and zirconium synthesised by a salt metathesis reaction. The reaction of either CpTiCl3 or Cp2TiCl2 with the dilithium salt of N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene [1; abbreviated (Dipp)2DADLi2] afforded the mono-cyclopentadienyl titanium complex [η5-CpTi((Dipp)2DAD)Cl] (2) bearing a dianionic ene-diamide ligand, while the analogous reaction of zirconocene dichloride (Cp2ZrCl2) with the dilithium salt 1 gave the bis-cyclopentadienyl zirconium complex [Cp2Zr{(Dipp)2DAD}] (3). The metal dichloride complexes [Ti((Dipp)2DAD)Cl2] (4) and [{(Dipp)2DADZrCl(μ-Cl)}2(κ3-Cl)(Li)(OEt2)2] (5) were obtained by the reaction of 1 and anhydrous metal tetrachloride in a 1 : 1 molar ratio in diethyl ether at room temperature. Meanwhile, the homoleptic titanium complex [Ti{((Dipp)2DAD)}2] (6) was isolated in good yield by the treatment of 1 with TiCl4 in a 1 : 2 molar ratio in diethyl ether. The complexes 2 and 5 were further reacted with neosilyl lithium to afford mono- and bis-alkyl complexes of titanium [η5-CpTi{(Dipp)2DAD}(CH2SiMe3)] (7) and zirconium [Zr{(Dipp)2DAD}(CH2SiMe3)2] (8) respectively. Molecular structures of the complexes 2, 3, and 5–8 in the solid states were confirmed by single crystal X-ray diffraction analysis. The solid state structures of all the complexes reveal that the metal ions are chelated through the amido-nitrogen atoms and the olefinic carbons of the [(Dipp)2DAD]2− moiety, satisfying the σ2,π coordination mode. Compound 8 was used as a catalyst for the intermolecular hydrosilylation reaction of a number of olefins, and moderate activity of catalyst 8 was observed