Synthesis and Characterization of Group 4 Permethylpentalene Dichloride Complexes

Abstract

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·THF x [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.

Double CO2 activation by 14-electron η8-permethylpentalene titanium dialkyl complexes

“…The complexes Pn*TiR 2 [R = Me (1), CH 2 Ph (2)], were synthesised by salt metathesis reactions between [Pn*TiCl(m-Cl)] 2 22 and the appropriate Grignard reagent (Scheme 1). † Subsequent work-up yielded 1 and 2 as microcrystalline solids, both in high yield.…”

Zirconium and Hafnium Permethylpentalene Compounds

“…Overall the structural metrics are very similar for 2 M , with slightly shorter M−C bond lengths for 2 Hf , which has been previously observed in other Pn*Hf and Pn*Zr compounds. 15,17 In the solid state, the allyl units are bound in an η 3 -fashion, making 2 M 18-electron complexes. The allyl units tilt away from the metal centers presumably to optimize the overlap between the d-orbitals on the metals and the p-orbitals of the allyl carbons (demonstrated by the M1− Ct3−C16 and M1−Ct4−C19 angles, Figure 2).…”

“…This has already been seen in the dimerization of the starting material A M and its incorporation of LiCl. 15 The Li is solvated by two molecules of 1,4-dioxane, which bridge to another lithium cation in an adjacent monomer unit and thus form a one-dimensional polymer extending in the ab-plane ( Figure 5B). …”

Synthesis of organometallic pentalenide complexes

“…67 In another example of a substituted Pn 2− transmetallation reaction, Cooper et al described the reactivity of Pn* 2− with group 4 metal halides. 68 ZrCl 4 and HfCl 4 mixed with [Li 2 (TMEDA) x ]Pn* in benzene gave, after filtration and recrystallization, halide-bridged dinuclear η 8 complexes of zirconium and hafnium as LiCl adducts (Fig. 37).…”

“…33. 68 Interestingly, the use of a non-polar solvent such as benzene lead to formation of the syn product, whereas the use of THF exclusively gave the anti-isomer. Both could be isolated in very high yields after filtration and recrystallisation from toluene or pentane.…”