Synthesis and Characterization of Group 4 Permethylpentalene Dichloride Complexes

We
report the high-yield syntheses of the (η8-Pn*)­MCl2 complexes (η8-Pn* = C8Me6; M = Ti, Zr, Hf), utilizing the cis-(SnMe3)2Pn* or cis-Li2Pn*­(TMEDA)x synthons. Stereoselective synthesis of the
appropriate Pn* precursor [cis-Li2Pn*
and cis-(SnMe3)2Pn*] can be
achieved by the appropriate choice of solvent. Treatment of cis-(SnMe3)2Pn* with TiCl4·2THF enabled the first high-yielding synthesis of a group 4
η8-Pn* complex, [η8-Pn*TiCl­(μ-Cl)]2 (1). Analogous complexes for the remaining group
4 congeners have been synthesized via the reaction of Li2Pn*­(TMEDA)x with MCl4·2THF
(M = Zr, Hf). These have been found to incorporate LiCl, resulting
in the chemical formula [η8-Pn*M­(μ-Cl)3/2]2(μ-Cl)2Li·THFx [M = Zr (2), Hf (3)]. 1, 2, and 3 have all been fully
characterized in the solution phase and in the solid state via single-crystal
X-ray diffraction, revealing all three to be dimeric; 3 is the first structurally elucidated hafnium pentalene compound.
The solid-state structure of trans-(SnMe3)2Pn* has also been reported. All three compounds have
been produced in sufficiently high yields to act as excellent entry
points to further group 4 η8-Pn* species via salt
metathesis reactions.