Abstract
Both single tucked-in permethyltitanocene 1 and double tucked-in permethyltitanocene 2 react with excess CO2 by insertion into their Ti-CH2 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 Ti bonds were not sterically hindered. The latter bond dissociates when [3](n) is oxidized by chlorination with CDCl3 or CD2Cl2 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)-C5Me5) to give the half-tethered carbodiolate 10.
The non-tethered carbodiolate 12 was obtained from [Cp*(2)TiH] and CO2 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 CO2 slowly in m-xylene at 100 °C using only one of its two Ti-CH2 moieties. The structure of the obtained carbodiolate 13 indicates that the primary product analogous to 3 reacts with 2 more rapidly than with CO2.