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

The reactions between tetracyanoethene (TCNE) and organometallic 16 va lence electron fragments from the early, middle and late transition se ries such as V(C(5)R(5))(2)Br (R=H, Me), M((PPr3)-Pr-i)(2)(CO)(H)Cl (M =Os, Ru) or Co(C5H5)(CO) (with Co(C5H5)(CO)(2) as precursor) yield com plexes which exhibit rather different electronic structures as evident from electrochemistry, IR and W-Vis absorption spectroscopy, and magn etic 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(-I)) and [V-IV(C (5)R(5))(2)Br](2)(TCNE(-II)); 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 temperat ure magnet [V(TCNE)(x)]. yCH(2)Cl(2) and of structurally characterized [Ir-I(PPh(3))(2)(CO)](2)(TChTE(-II)). In contrast to this spectroscop ic and magnetic evidence for two consecutive metal-to-TCNE electron tr ansfer the reaction of TCNE with M((PPr3)-Pr-i)(2)(CO)(H)Cl (M = Ru, O s) involves an electron transfer process only for the first metal coor dination step. Di- and tetranuclear complexes [Os((PPr3)-Pr-i)(2)(CO)( H)Cl](2,4)(TCNE) show a similar behavior to the recently reported orga nomanganese and pentaammineruthenium compounds with corresponding d el ectron configurations. Attempts are made to correlate spectroscopic re sults with the structurally determined pi conjugation and the extent o f metal-to-ligand electron transfer in the ground state. Three differe nt kinds of electron configurations in dinuclear systems of mu,eta(1): eta(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(C5H5)(CO) probably binds to reduced TCNE only once and in a side-on fashion.