The Versatility of Pentalene Coordination to Transition Metals: A Density Functional Theory Investigation

Abstract

DFT calculations with full geometry optimization have been carried out on a series of real and hypothetical compounds of the type [CpM(C8H6)], [(CO)3M(C8H6)], [M(C8H6)2], [(CpM)2(C8H6)], [[(CO)3M]2(C8H6)], and [M2(C8H6)2] (M = transition metal). The bonding in all the currently known compounds is rationalized, as well as in the (so far) hypothetical stable complexes. Depending on the electron count and the nature of the metal(s), eta2 (predicted), eta3, eta5, eta8, or intermediate coordination modes can be adopted. In the case of the mononuclear species, the most favored closed-shell electron counts are 18 and 16 metal valence electrons (MVE). In the case of the dinuclear species, an electron count of 34 MVEs is most favored. However, other electron counts can be stabilized, especially in the case of dinuclear complexes. Coordinated pentalene should most often be considered as formally being a dianion, but sometimes as a neutral ligand. In the former case it can behave as an aromatic species made of two equivalent fused rings, as a C5 aromatic ring connected to an allylic anion, or even as two allylic anions bridged by a C7=C8 double bond. In the latter case, it can behave as a bond-alternating cyclic polyene or as a C5 aromatic ring connected to an allylic cation.

Bonding and electronic structure of Cp*2Ru2(B8H14), a metallaborane analogue of dinuclear pentalene complexes

“…The Cp derivative exhibits slightly shorter RueC(pentalene) and longer RueC(Cp) distances compared to its Cp* relative. Unsurprisingly, their electronic structure is very similar to that calculated previously for Cp 2 Fe 2 (C 8 H 6 ) [6,7] and other related isoelectronic species [7,9], as exemplified by the MO diagram of Cp 2 Ru 2 (C 8 H 6 ) shown in Fig. 3 (left side).…”

“…However, there are differences between the electronic structures of Cp* 2 Ru 2 B 8 H 14 and Cp* 2 Fe 2 C 8 H 6 which render Cp* 2 Ru 2 B 8 H 14 probably unique from the structural point of view [20], whereas Cp* 2 Fe 2 C 8 H 6 belongs to a series of pentalene complexes of ideal C 2h symmetry having electron counts varying between 32 and 38 and differing only by their metal hapticities [3,7]. These differences originate from the different electronegativities of B and C. Pentalenediide is a stable anion which maintains its aromaticity when coordinated.…”

“…Indeed, the pentalene derivatives Cp* 2 Co 2 (C 8 H 6 ) (36 electrons) and Cp* 2 Ni 2 (C 8 H 6 ) (38 electrons) have been shown to exist [3]. Their structures derive from that of the 34-electron Cp* 2 Fe 2 (C 8 H 6 ) by a progressive shifting of the metal hapticity from symmetrical penta-hapto (M ¼ Fe) to tri-hapto (M ¼ Ni) [3,7]. Calculations on Cp 2 Rh 2 (B 8 H 14 ), the 36-electron analogue of Cp 2 Ru 2 (B 8 H 14 ), lead to a structure which is different from that of the isoelectronic Cp 2 Co 2 (C 8 H 6 ).…”

“…2. Calculations have shown that the large HOMO-LUMO gap existing in these species makes in fact this (formally deficient) closed-shell 34-electron count the most favoured in this family of dinuclear complexes [7,8]. In this paper we investigate the electronic structure of Cp* 2 Ru 2 (B 8 H 14 ), the 34-electron metallaborane analogue of Cp* 2 M 2 (C 8 H 6 ) (M ¼ Fe, Ru) in order to compare the bonding between the two families of compounds, as well as their properties related to their actual electron count.…”

Complexes of iron(II) with silylated pentalene ligands; building blocks for homo- and heterobimetallics

“…Geometries were , reported by Saillard et al [37] The net charges on the uncomplexed part of the pentalene ring in this model complex do not show any significant carbanionic character (Fig. 10), which is consistent with it being less nucleophilic at these positions.…”