Titanium and zirconium complexes of the N,N'-bis(2,6-dilsopropylphenyl)-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)(2)DADLi(2)] afforded the monocyclopentadienyl titanium complex (eta(5)-CpTi((Dipp)(2)DAD)CI] (2) bearing a dianionic ene-diamide tigand, while the analogous reaction of zirconocene dichloride (Cp2ZrCl2) with the dilithium salt 1 gave the bis-cyclopentadienyl zirconium complex (Cp2Zr{(Dipp)(2)DAD}] (3). The metal dichloride complexes (Ti((Dipp)(2)DAD)Cl-2] (4) and R(Dipp)(2)DADZra(g-00)(2)(K-3-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 homoteptic titanium complex (TifflDipp)2DAD)}21 (6) was isolated in good yield by the treatment of 1 with Tiat in a 1: 2 molar ratio in diethyl ether. The complexes 2 and 5 were further reacted with neosityl lithium to afford mono- and bisalkyl complexes of titanium (eta(5)-CpTi{(Dipp)(2)DAD}(CH2SiMe3)(1) (7) and zirconium (Zr{(Dipp)2DAD)(CH2SiMe3)21 (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)(2)DAD](2-) moiety, satisfying the sigma(2),pi 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.