The reactions between tetracyanoethene (TCNE) and organometallic 16 valence electron fragments from the early, middle and late transition series such as V(C5R5)2Br (R = H, Me), M(PiPr3)2(CO)(H)Cl (M = Os, Ru) or Co(C5H5)(CO) (with Co(C5H5)(CO)2 as precursor) yield complexes which exhibit rather different electronic structures as evident from electrochem., IR and UV-visible absorption spectroscopy, and magnetic susceptibility measurements. With V(C5R5)2Br, the resulting compds. are VIV(C5R5)2Br(TCNE-I) and VIV(C5R5)2Br2(TCNE-II); for R = Me, the nonconjugated dinuclear complex exhibits magnetically weakly coupled d1 centers and nitrile stretching bands which are very similar to those of the room temp. magnet V(TCNE)x·yCH2Cl2 and of structurally characterized IrI(PPh3)2(CO)2(TCNE-II). In contrast to this spectroscopic and magnetic evidence for two consecutive metal-to-TCNE electron transfers, the reaction of TCNE with M(PiPr3)2(CO)(H)Cl (M = Ru, Os) involves an electron transfer process only for the 1st metal coordination step. Di- and tetranuclear Os(PiPr3)2(CO)(H)Cl2,4(TCNE) show a similar behavior to the recently reported organomanganese and pentaammineruthenium compds. with corresponding d electron configurations. Attempts are made to correlate spectroscopic results with the structurally detd. p conjugation and the extent of metal-to-ligand electron transfer in the ground state. Three different kinds of electron configurations in dinuclear systems of m,h1:h1-TCNEn- are thus described: nonconjugated d1-(TCNE2-)-d1 (V) and d8-(TCNE2-)-d8 (Ir) and conjugated d6-(TCNE·-)-d5 (Os, Mn). In contrast, the 16-electron species Co(C5H5)(CO) probably binds to reduced TCNE only once and in a side-on fashion. on SciFinder(R)
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