GROUND STATE ELECTRON TRANSFER BETWEEN TCNE AND ONE OR MORE 16-ELECTRON SPECIES CONTAINING VANADIUM, OSMIUM, RUTHENIUM OR COBALT

Abstract The reactions between tetracyanoethene (TCNE) and organometallic 16 valence electron fragments from the early, middle and late transition series such as V(C 5 R 5 ) 2 Br (R = H, Me), M(P i Pr 3 ) 2 (CO)(H)Cl (M = Os, Ru) or Co(C 5 H 5 ) (CO) (with Co(C 5 H 5 )(CO) 2 as precursor) yield complexes which exhibit rather different electronic structures as evident from electrochemistry, IR and UV-Vis absorption spectroscopy, and magnetic susceptibility measurements. With V(C 5 R 5 ) 2 Br, the resulting compounds are formulated as V IV (C 5 R 5 ) 2 Br(TCNE −1 ) and [V IV (C 5 R 5 ) 2 Br] 2 (TCNE −11 ); for R = Me, the non-conjugated dinuclear complex exhibits magnetically weakly coupled d 1 centers and nitrile stretching bands which are very similar to those of the room temperature magnet [V(TCNE) x ]· y CH 2 Cl 2 and of structurally characterized [1r 1 (PPh 3 ) 2 (CO)] 2 (TCNE −11 ). In contrast to this spectroscopic and magnetic evidence for two consecutive metal-to-TCNE electron transfers, the reaction of TCNE with M(P i Pr 3 ) 2 (CO)(H)Cl (M = Ru, Os) involves an electron transfer process only for the first metal coordination step. Di- and tetranuclear complexes [Os(P i Pr 3 ) 2 (CO)(H)Cl] 2,4 (TCNE) show a similar behavior to the recently reported organomanganese and pentaammineruthenium compounds with corresponding d electron configurations. Attempts are made to correlate spectroscopic results with the structurally determined π conjugation and the extent of metal-to-ligand electron transfer in the ground state. Three different kinds of electron configurations in dinuclear systems of μ,η 1 :η 1 -TCNE n are thus described: non-conjugated d 1 -(TCNE 2− )-d 1 (V) and d 8 -(TCNE 2− )-d 8 (Ir) and conjugated d 6 -(TCNE ·− )-d 5 (Os, Mn). In contrast, the 16-electron species Co(C 5 H 5 )(CO) probably binds to reduced TCNE only once and in a side-on fashion.