Unusual Electronic Features and Reactivity of the Dipyridylazaallyl Ligand: Characterizations of (smif)2M [M = Fe, Co, Co+, Ni; smif = {(2-py)CH}2N] and [(TMS)2NFe]2(smif)2

Application of the dipyridylazaallyl ligand (2-py)CHNCH(2-py) (smif) to a series of first-row transition metals afforded (smif)(2)M-n [n = 0, M = Fe (1), Co (2), Ni (3); n = +1, M = CO (2+)] and {(TMS)(2)NFe}(2)(smif)(2) (4(2)) via metathetical procedures. The Mossbauer spectrum of 1 (S = 0) and TDDFT calculations, including a UV-vis spectral. simulation, reveal it to be a covalent, strong-field system with Delta(o) estimated as similar to 18000 cm(-1) and B = 470 cm(-1). (smif)(2)Co (2) has S = 1/2 according to SQUID data at 10 K. DFT calculations suggest that the odd electron is localized in a smif Pi* orbital, i.e., smif is redox-active. EPR-silent (smif)(2)Ni (3) has S = 1 (SQUID), and calculations show that the unpaired spins reside in the d(z)(2) and d(x)(-y)(2)(2) orbitals. X-ray structural parameters suggest that low-spin d(6) 1 and 2+ are relatively symmetric D-2d species, but 2 and 3 manifest a distortion in which one smif is canted in the plane perpendicular to the other. (smif)FeN(TMS)(2) (4) is principally monomeric in solution, but reversibly dimerizes (K-eq approximate to 10(-4) M-1) via C-C bond formation in the azaallyl, backbone to crystallize as {(TMS)(2)NFe}(2)(smif)(2) (4(2)). The azaallyl compounds possess extraordinary UV-vis absorptivities (epsilon = 18000-52000) at 580 +/- 15 nm and 406(25) nm that have been identified as intraligand bands with C-nb -> smif Pi* character.