C-C bond formation and related reactions at the CNC backbone in (smif)FeX (smif = 1,3-di-(2-pyridyl)-2-azaallyl): dimerizations, 3 + 2 cyclization, and nucleophilic attack; transfer hydrogenations and alkyne trimerization (X = N(TMS)2, dpma = (di-(2-pyridyl-methyl)-amide)).

Molecular orbital analysis depicts the CNC(nb) backbone of the smif (1,3-di-(2-pyridyl)-2-azaallyl) ligand as having singlet diradical and/or ionic character where electrophilic or nucleophilic attack is plausible. Reversible dimerization of (smif)Fe{N(SiMe3)2} (1) to [{(Me3Si)2N}Fe]2(μ-κ(3),κ(3)-N,py2-smif,smif) (2) may be construed as diradical coupling. A proton transfer within the backbone-methylated, and o-pyridine-methylated smif of putative ((b)Me2(o)Me2smif)FeN(SiMe3)2 (8) provides a route to [{(Me3Si)2N}Fe]2(μ-κ(4),κ(4)-N,py2,C-((b)Me,(b)CH2,(o)Me2(smif)H))2 (9).

Synthetic approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) reveal redox non-innocence and C-C bond-formation.

Attempted syntheses of (smif)(2)Ti (smif =1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiCl(n)L(m) (n = 2-4) with M(smif) (M = Li, Na), in the presence of a reducing agent (Na/Hg) when necessary, failed, but several apparent Ti(II) species were identified by X-ray crystallography and multidimensional NMR spectroscopy: (smif){Li(smif-smif)}Ti (1, X-ray), [(smif)Ti](2)(μ-κ(3),κ(3)-N,N(py)(2)-smif,smif) (2), (smif)Ti(κ(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif)Ti(dpma) (4, dpma = di-2-pyridylmethyl-amide). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox noninnnocent, such that d(1) Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)(2-)}Ti(III) (1), [(smif(2-))Ti(III)](2)(μ-κ(3),κ(3)-N,N(py)(2)-smif,smif) (2), [(smif(2-))Ti(III)](κ(3)-N,N(py)(2)-smif,(smif)H) (3), and (smif(2-))Ti(III)(dpma) (4). The instability of (smif)(2)Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical dianion ligands, which are also common to 3 and 4.

Synthesis and characterization of (smif)2M(n) (n = 0, M = V, Cr, Mn, Fe, Co, Ni, Ru; n = +1, M = Cr, Mn, Co, Rh, Ir; smif =1,3-di-(2-pyridyl)-2-azaallyl).

A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)(2)M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe(3))(2)(THF)(n) (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated ((o)Mesmif)(2)Fe (2-Fe) and ((o)Me(2)smif)(2)Fe (3-Fe) were similarly prepared. Metatheses of MX(2) variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru).

A theoretical study of the 3d-M(smif)2 complexes: structure, magnetism, and oxidation states.

We carry out a theoretical investigation of the recently reported M(smif)(2) series1,2 and find a number of interesting phenomena. These include complex potential energy surfaces with near-degenerate stationary points, low-lying states, non-trivial electron configurations, as well as non-innocent ligand behavior. The M(smif)(2) exhibit a delicate balance between geometry and electronic structure, which has implications not only for their reactivity but also for controlling their properties through ligand design.

Aryl-containing chelates and amine debenzylation to afford 1,3-di-2-pyridyl-2-azaallyl (smif): structures of {kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}FeBr and (smif)CrN(TMS)(2).

Aryl-bromide ligand precursors have been prepared with the potential to afford tetradentate chelates (2-pyridylmethyl)(3-x)N(CH(2)-2-Aryl)(x) (x = 1, 2) containing metal-aryl linkages that promise to impart stronger fields about first row transition metals. Oxidative addition to Ni(COD)(2) afforded two diamagnetic Ni(II) complexes, {kappa-C,N,N(py)-(2-pyridylmethyl)N(CH(2)(4-(t)Bu-phenyl-2-yl))(CH(2)(4-(t)Bu-phenyl-2-Br))}NiBr (1-Ni) and {(kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}NiBr (2-Ni) in 96% and 67% yield, respectively. Extending these synthetic efforts to iron provided {kappa-C,N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-yl))}FeBr (2-Fe, X-ray) in 91% yield via reduction of an adduct, {kappa-N,N(py)(2)-(2-pyridylmethyl)(2)N(CH(2)(4-(t)Bu-phenyl-2-Br))}FeBr(2) (3-Fe).

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 approximately 18,000 cm(-1) and B approximately 470 cm(-1). (smif)(2)Co (2) has S = 1/2 according to SQUID data at 10 K.