Bending Ferrocenes with Low Coordinated Bridging Units: The Investigation of Carbenes and Their Analogues with a Ferrocenophane Backbone

Abstract

[3]­ferrocenophanes with X–E–X ansa moieties containing a low coordinated center E stabilized by adjacent donor units X were studied by density functional theory methods. The cyclopentadienyl (Cp) rings favor an eclipsed position in most cases and exhibit a shortened C(1)–C(1′) distance compared to parent ferrocene. In case of bridges with the second row elements, the tilt of the Cp rings is more significant than that in case of third row elements; however, the estimated strain does not exceed 6 kcal/mol. The ansa unit has similar structural characteristics to the X–E–X-fragment in a six-membered saturated ring, with bond angles larger than that in the well-known heterocycles featuring five-membered cyclic systems. For compounds with X = PMe and E = C, Si, Ge, the non-planar coordination of the phosphorus atoms yields two symmetric minimum structures that are distinguished by trans and cis alignment of the PMe groups and are connected by a low-energy asymmetric transition structure with one planarized and one highly pyramidal phosphorus. In case of the analogous species with E = P+, this asymmetric structure was located as the sole minimum. A detailed analysis of the Kohn–Sham orbitals and the analysis of the electron density show that the electronic system of the ferrocene fragment is not mixing considerably with that of the low coordinated center of the ansa unit.

Gradual Donor Stabilization of a Transient Ferrocene Bridged Bisphosphanyl Phosphenium Cation

“…To understand this behavior, DFT calculations (at ωB97X-D/6-311+G**) were carried out. The formation of 2 [AlCl 4 ] 2 is an exergonic process (Δ G = −42.4 kcal/mol) in agreement with our previous findings in the case of the related tetrylenes (X = Ge, Sn, Pb), where ∼−35 kcal/mol was computed at ωB97X-D/6-31+G* . Interestingly, the reaction of 2 [AlCl 4 ] 2 with IMe 4 is highly exergonic (Δ G = −73.6 kcal/mol) which is in contrast with the experimental findings and suggests that the lack of the formation of the desired product could have kinetic reason.…”

“…The formation of 2[AlCl 4 ] 2 is an exergonic process (ΔG = −42.4 kcal/mol) in agreement with our previous findings in the case of the related tetrylenes (X = Ge, Sn, Pb), where ∼−35 kcal/mol was computed at ωB97X-D/6-31+G*. 19 Interestingly, the reaction of 2[AlCl 4 ] 2 with IMe 4 is highly exergonic (ΔG = −73.6 kcal/mol) which is in contrast with the experimental findings and suggests that the lack of the formation of the desired product could have kinetic reason. Moreover, the question arises why 2 2+ behaves differently compared to the related tetrylenes and a possible answer could be the structural rigidity of 2 2+ .…”

“…18 On top of that, we have demonstrated in our recent computational study that the phosphenium center exerts a flattening effect that is able to planarize not one but two adjacent phosphanyl units. 19 It needs to be pointed out that�despite their name�the here discussed bisphosphanylphosphenium ions are only distantly related to so called triphosphenium ions, which feature an electron octet at the central phosphorus atom, 20 in contrast to phosphenium ions with an electron sextet in this position.…”