Reactions of Cp*₂Yb(THF)₂ with TCNQ and TCNB. A Novel Type of Reactivity of TCNQ toward Metallocenes. The First Example of the π-Dimer [TCNB₂]²⁻

Abstract

The reaction of Cp*2Yb(THF)2 with an equimolar amount of 7,7,8,8-tetracyanoquinodimethane (TCNQ) affords the Yb(III) complex [Cp*2Yb(CH3CN){(μ-CN)2C(C6H4)C(CN)2(C5Me5)}]2, containing a monoanionic polycyano ligand arising from one-electron reduction of TCNQ and the coupling of its methylidene carbon with the allylic carbon atom of a Cp* fragment. Reaction of Cp*2Yb(THF)2 with 1,2,4,5-tetracyanobenzene (TCNB) in a 1:1 molar ratio results in oxidation of the ytterbium atom and the formation of the Yb(III) complex [Cp*2Yb{(μ-CN)2(C6H4)(CN)2}]2the first example of the dianionic π-dimer [TCNB2]2− participating in μ:η4 bonding with two metal centers.

Orientational Preference of Long, Multicenter Bonds in Radical Anion Dimers: A Case Study of π‐[TCNB]22−and π‐[TCNP]22−

“…[48] Therefore, al ong, multicenter bond occurs fort he D 2h (q = 08)a nd C 2 (q % 308)c onformations of p- [ ,w hich has a q % 608 relative orientation. [21] This differs from the q % 308 conformation observed for [TCNP] 2 2À (see above). The groundstate electronic structure for the C 2 (q % 608)o rientation of p-[TCNB] 2 2À wast hus analyzed for completeness, and the D 2h (q = 08)a nd D 2d (q = 908)orientations were also included in the analysis.…”

“…As already mentioned, to date only two structures with p- 20] and only one with p-[TCNB] 2 2À have been reported. [21] The two structures of p-[TCNP] 2 2À have different relative orientationso ft his dimer,t hat is, they are eclipsed Figure 1a) [20] [21] has the shortest interfragment C···Cd istance of 3.15 , and the benzene rings are relatively rotated by q % 608 ( Figure 3a)a nd the radical dimer has C 2 symmetry.Note that, owing to their symmetry,inanisolated p-[TCNB] 2 2À dimer a q % 608 rotationi se quivalent to a q % 1208 rotation. Amongt he three orientations investigated for p-[TCNP] 2 2À (Figure 1c), the one with the largest E int (MP) (that is, the most stable one according to the Maximin Principle) is shown in Figure 2c.I ts hould also be mentioned that [TDAE] [TCNB] 3 ·MeCN, [47] obtained by reducing TCNB with tetrakis(dimethylamino)ethylene (TDAE;F igure 3b), possesses [TCNB] 3 2À trimers with the two negative charges distributed over the three fragments.…”

“…However, it significantly failed in p-[TCNE] 2 2À ,afailure also pointed out by its originators: [18] These dimers were predicted to have an oneclipsed, displaced disposition; however,a ll experimentally reported structures of p-[TCNE] 2 2À possess an eclipsed orientation. With the goal of identifying the key factors that control the relative orientations in dimers of radical anionsw hilea lso increasingt he number of cases in which the Maximin Principle has been tested, the different orientationso bserved for p- 20] and p-[TCNB] 2 2À [21] (TCNP = 1,2,4,5-tetracyanopyrazine; TCNB = 1,2,4,5-tetracyanobenzene) drew our attention. Owing to the similars hape and electronic structure of TCNB and TCNP,a nd [TCNB]C À and [TCNP]C À ,s imilar relative orientations are expected.…”

The Tetracyanopyridinide Dimer Dianion, σ‐[TCNPy]22−

“…For π‐ or σ‐dimers of both [TCNE] 2 2−[1, 2, 10, 14, 15] and [TCNQ] 2 2− (TCNQ=7,7,8,8‐tetracyano‐ p ‐quinodimethane) composition as well as only π‐[TCNB] 2 2− (TCNB=1,2,4,5‐tetracyanobenzene) and π‐[TCNP] 2 2− (TCNP=1,2,4,5‐tetracyanopyrazine) composition have been reported. π‐[TCNB] 2 2− and π‐[TCNP] 2 2− each have a 2 e − /8c C−C bond and have the identical symmetry ( D 2 h ), size and shape; nonetheless, they have different orientational preferences .…”

“…(TCNQ = 7,7,8,8-tetracyano-p-quinodimethane) [11,16] composition as well as only p-[TCNB] 2 2À (TCNB = 1,2,4,5-tetracyanobenzene) [17,18] and p-[TCNP] 2 2À (TCNP = 1,2,4,5-tetracyanopyrazine) [18,19] composition have been reported. p-[TCNB] 2 2À and p-…”