Abstract
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)2Br]2(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)Cl]2,4(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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