Pentadienyl Complexes of Alkali Metals: Structure and Bonding

Abstract

A systematic density functional study of the structure and bonding in the alkali-metal pentadienyl complexes C 5 H 7 E (E ) Li-Cs) and their analogues derived from the 2,4-dimethylpentadienyl ligand is performed. The bonding in these structures has been analyzed in some detail with reference to molecular orbital analysis, and energy partition analysis, obtained by density functional calculations. An energy decomposition analysis indicates that the electrostatic interaction is the main factor to be considered in the stabilization of the gas-phase complexes we have studied. The stability of the U-shaped minimum energy structure decreases (the potential energy surface becomes more shallow) as the metal atom gets larger. We trace this behavior to a weakening of the metal-ligand binding due to the increasing diffuseness of the metal p orbitals on going down group 1. A significant pyramidalization at the terminal carbons in the coordinate U-shaped structure correlates with the strength of the metal-ligand binding. Initial results for the structural preferences of the complexes in solution for the lithium pentadienyl complex are examined in view of contrary experimental data. There still remains plenty of work to be done in modeling metal complexes in solution, and we suggest a way forward.

Bonding and Mobility of Alkali Metals in Helicenes

“…In this work, we analyzed the interaction of alkali metals( E + ) with [6]-and [14]helicene and the mobility of (E + )t herein. For the cases of complexes formed with [6]helicene, it was found that when the Li + is located above the center of each ring, the structure corresponds to an energy minimum, and an additional energy minimum structure arises when the Li + is placed at the middle of the helix.…”

“…Note that for both cations, the complexes formed with [ 14]helicene have higher interaction energy with respectt ot heir [6]helicene counterparts, (7.5-9.0 kcal mol À1 higher for Li + ,a nd 4.5-5.5 kcal mol À1 higher for Cs + ,s ee Ta ble 4). Note that for both cations, the complexes formed with [ 14]helicene have higher interaction energy with respectt ot heir [6]helicene counterparts, (7.5-9.0 kcal mol À1 higher for Li + ,a nd 4.5-5.5 kcal mol À1 higher for Cs + ,s ee Ta ble 4).…”

“…Note that for both cations, the complexes formed with [ 14]helicene have higher interaction energy with respectt ot heir [6]helicene counterparts, (7.5-9.0 kcal mol À1 higher for Li + ,a nd 4.5-5.5 kcal mol À1 higher for Cs + ,s ee Ta ble 4). Interestingly,a lthough the bindingn ature of the lithium with the [14]helicene complexes is mainly orbital-based (77.2 %), the most extensive contributions of this type occur in the [6]helicene structures (81.6 %). Interestingly,a lthough the bindingn ature of the lithium with the [14]helicene complexes is mainly orbital-based (77.2 %), the most extensive contributions of this type occur in the [6]helicene structures (81.6 %).…”

“…Cesium complexes are also mostlyo rbital-based but to al esser extent.A nother term with significant differences in the longerc omplexes is the distortion energy.F or the Li + - [14]helicene complex, the highest value is again for 5-Li + (7.5 kcal mol À1 ), because, as explained above, the first ring must not only open but also turn outwards. The numbered rings of [14]helicene and the PBE0-D3/def2-SVP structures for A-Cs + and 6-Cs + . The case of the Cs + series is different since the largest deformation of the carbon skeleton does not occur when the metal enters the helicene but inside it, where both the upper Figure 4.…”

Construction of double- and triple-decker sandwich compounds from half-sandwich compounds: a theoretical assessment

“…A series of donor-acceptor heteroleptic open sandwiches with the formula CpM-M'Pyl (M = B, Al, Ga; M' = Li, Na; Cp = cyclopentadienyl; Pyl=pentadienyl) has been designed using density functional theory by Merino et al [35] in 2006. Cerpa et al [36] studied the structure and bonding in C 5 H 7 E (E=Li-Cs) and their analogues with density functional theory (DFT) calculations. In addition, the analogous metallocenes, such as CpM n Cp (M=Be, Mg, Ca, and Zn with n=2-5) [37], Fe(η 5 -E 5 ) 2 and FeCp(η 5 -E 5 ) (E=N, P, As, Sb) [38], [Ti(η 5 -E 5 ) 2 ] 2 − (E=CH, N, P, As, Sb) [39], Zn 2 (η 5 -Cp*) 2 [40], Cp−Zn− Cd−Cp [41], (η 5 -P 5 )-MM'(η 5 -P 5 ) and (η 5 -C 5 H 5 )MM'(η 5 -P 5 ) (M, M'=Zn, Cd) [42], were investigated.…”