Synthesis of oligometallic compounds from tripodiron(II) species using cyano bridging ligands - Electronic coupling of two metal termini through metal dicyano and diisocyano entities

Organometallic monocyanometalates [M-CN](-) (1(-)) [M = Cr(CO)(5) 1a(-), Cr (eta (6)-CF3C6H5)(CO)(2) 1b(-), Mn(eta (5)-CH3C5H4)(CO)(2) 1c(-)] produce t etrametallic (2(-)) and trimetallic (3) aggregates upon reaction with tripo d and iron(II) salts [tripod = CH3C(CH2PPh2)(3)]. The tetranuclear compound [tripodFe{NC-M}(3)](-) (2(-)) [M = Cr(CO)(5)] or the trinuclear species [t ripodFe(CO)[NC-M](2)] (3) [M = Cr(CO)(5) 3a, Cr(eta (6)-CF3C6H5)(CO)(2) 3b, Mn(Tl1-CH3C5H4)(CO)2 3c] can be selectively formed by following the approp riate reaction protocols. Organometallic dicyanometalates [NC-M'-CN](-) (4- ) [M' = Mn(CO)(4) 4a(-), CpFe(CO) 4b(-), CpCo(CN) 4c(-)] react in a similar manner to give pentanuclear species [tripodFe[NC-M'-CN](3)Fetripod](+) (5( +)), - In compounds 2-and 3, two easily oxidizable organometallic groups ar e linked through a tripodFe(NC)(2) unit, while in 5(+) two tripodiron(II) e ntities are linked through a less readily oxidizable M'(CN)2 unit. For both types of compound, at least two distinct reversible oxidations are observe d by cyclic voltammetry. The potentials at which these oxidations occur are characteristic of the terminal groups in each case. The potentials of the two consecutive oxidation steps are separated by between 150 and 350 mV The oxidation products of compounds 2-, 3, and 5(+) can hence be classified as class III mixed-valence species with comproportionation constants K-C of b etween 10(2) and 10(6). The extent of electronic coupling mediated by the M '(CN)(2) or M'(NC)(2) bridging entities is thus similar to that mediated by [RC(CN)(2)](-) bridging ligands in otherwise analogous compounds, for whic h Kc values of around 10(4) are observed. All the aforementioned compounds have been characterized by analytical and spectroscopic techniques, includi ng cyclic voltammetry and UV/Vis spectroscopy. In addition, X-ray crystallo graphic data are reported for 2(-), 3a, 3b, 3c, and 5a(+).