Reactions of permethyltitanocene tucked-in derivatives with carbon dioxide.

Both single tucked-in permethyltitanocene 1 and double tucked-in permethyltitanocene 2 react with excess CO 2 by insertion into their Ti-CH 2 bonds. The former one precipitates instantly a yellow carboxylate-tethered oligomer [3] n which is insoluble in aprotic solvents and in a vacuum it sublimes as a monomer without decomposition. Computations for n ≤ 4 optimised the structure of the monomer [3] and showed that open chain oligomers bound by dative O → Ti bonds were not sterically hindered. The latter bond dissociates when [3] n is oxidized by chlorination with CDCl 3 or CD 2 Cl 2 to give Ti(IV) chloride 4 or upon metathesis of [3] n with Me 3 SiCl yielding Ti(III) chloride 5. Oxidative addition of MeCN affords a C-C coupled dinuclear titanocene diimine 6. Compound [3] n also reacts with 1 to give the tethered carbodiolate 8 or with [Cp* 2 TiH] (where Cp* = η 5 -C 5 Me 5 ) to give the half-tethered carbodiolate 10. The non-tethered carbodiolate 12 was obtained from [Cp* 2 TiH] and CO 2 yielding titanocene formate by reaction of the latter with another equivalent of [Cp* 2 TiH]. All these carbodiolates contain Ti(III) metal atoms forming electronic triplet states of axial or orthorhombic symmetry. In contrast to the rapidly reacting 1 compound 2 reacts with excess CO 2 slowly in m -xylene at 100 °C using only one of its two Ti-CH 2 moieties. The structure of the obtained carbodiolate 13 indicates that the primary product analogous to 3 reacts with 2 more rapidly than with CO 2 .