Mononuclear Pentalene and Methylpentalene Complexes of Titanium, Zirconium, and Hafnium

Abstract

In the compounds 8a, 8b, and 8 d the vanadium atom has a distorted pseudo-trigonal geometry. The magnitudes of the angles DI-V-D2 and Dl-V-D3 differ only slightly (148-152"), as of necessity do those of D2-V-D3 (59-61"). The V-C bond lengths within the vanadium-Cp and vanadium-Cp* moieties lie between 2.20 and 2.26 A and in all cases V-D1 is 1.89 A. The most prominent structural feature of the new vanadium complexes 8 is the strong folding of the pentalene or methylpentalene ligand towards the metal atom along the bond between the bridging carbon atoms. In all three vanadium complexes the angle between the plane through the atoms C7-C9, C13, and C14 @a, 8d) and C7-C9, C8*, and C9* (Sb), respectively, and that through the plane of the atoms C9-Cl3 and C9-Cl1, C9*, and C10*, respectively, is 137". The distances between vanadium and the C atoms of the pentalene ligands can be divided into three groups: V-C9zV-C13 (2.04-2.07 A)<V-C8-(2.30-2.35 A). The methyl substituent in 8d causes the 2methylpentalene ligand to be coordinated unsymmetrically to vanadium, that is within the relevant groups of bond lengths, the distances V-C14 and V-C7 in 8 d are the shortest and V-C10 and V-C11 are the longest. The methyl carbon atom C15 liesjust 0.03 Aoutofthemeanplaneoftheatoms C9-Cl3.We are currently carrying out further NMR studies and ab initio calculations in order to understand better the bonding situation in these novel vanadium complexes 8.

Bonding in pentalene complexes and their recent applications

“…For example, the mononuclear tantalum(V) complexes (η 8 -Pn † )TaClxMe3-x for x = 0-3, which show a small but discernable increase in FA as the number of electron withdrawing chloride ligands increases. [15] Furthermore, the electronic properties of the pentalene ligand itself have an effect on FA, as first shown by comparison of the FAs for (η 8 -Pn)ZrCpCl (33.0°) [16] and (η 8 -Pn*)ZrCpCl (30.7°), [14,17] which provides evidence for the enhanced donor ability of the permethylated ligand.…”

“…Bis(pentalene) sandwich compounds where the pentalene ligand is octohaptic have been characterised for Ti, Zr, Hf, [16] Ce [22,23] Th [20] and U. [20,21] The d-block Group 4 M(η 8 -Pn)2 compounds lack X-ray structural data but low temperature NMR studies suggest a D2 structure.…”

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

“…23 Due to the incipient nature of pentalene titanium chemistry, Cp remains the only carbon based ligand to be incorporated into any ''PnTi''-fragment. 19 27,28 Herein we report the synthesis and characterisation of the first Pn*Ti dialkyl complexes and investigate their subsequent reactivity with CO 2 .…”

Synthesis of organometallic pentalenide complexes

“…Again similar to MCp chemistry, Jonas et al reported that [Li 2 (DME) x ]Pn would react cleanly with Cp 2 VCl by substitution of one Cp − ligand and chloride. 58 The resulting η 5 CpVη 8 Pn complex (Fig. 34) is air sensitive but could be sublimed under vacuum to give pure product in high yields.…”