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⁻

The reaction of Cp* 2 Yb(THF) 2 with an equimolar amount of 7,7,8,8-tetracyanoquinodimethane (TCNQ) affords the Yb(III) complex [Cp* 2 Yb(CH 3 CN){(μ-CN) 2 C(C 6 H 4 )C(CN) 2 (C 5 Me 5 )}] 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* 2 Yb(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* 2 Yb{(μ-CN) 2 (C 6 H 4 )(CN) 2 }] 2 —the first example of the dianionic π-dimer [TCNB 2 ] 2− participating in μ:η 4 bonding with two metal centers.