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Synthetic Approaches to (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) Reveal Redox Non-Innocence and C–C Bond-Formation

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journal contribution
posted on 20.02.2016 by Brenda A. Frazier, Peter T. Wolczanski, Ivan Keresztes, Serena DeBeer, Emil B. Lobkovsky, Aaron W. Pierpont, Thomas R. Cundari
Attempted syntheses of (smif)2Ti (smif =1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiClnLm (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-κ33-N,N­(py)2-smif,smif) (2), (smif)­Ti­(κ3-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 d1 Ti­(III) centers AF-couple to ligand radicals: (smif)­{Li­(smif-smif)2–}­TiIII (1), [(smif2–)­TiIII]2(μ-κ33-N,N­(py)2-smif,smif) (2), [(smif2–)­TiIII]­(κ3-N,N­(py)2-smif,(smif)­H) (3), and (smif2–)­TiIII(dpma) (4). The instability of (smif)2Ti 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. Calculations support this contention.