![]() On the other hand, reaction of 4 with the strong field ligand CN tBu provides the six-coordinate, diamagnetic complex (5). ![]() Attempts to reduce or alkylate 4 provide 3 as the only isolable product, likely a consequence of the low steric hindrance of the bis(ylide)diphenylborate ligand. Further reaction of 3 with FeCl 2(THF)1.5 produces the chloride-bridged dimer (4). Depending on the reaction stoichiometry, both the “ate” complex (2) and the homoleptic complex 2Fe(3) can be prepared from FeCl 2(THF) 1.5. ![]() = ,ĭouble deprotonation of the salt (1) provides access to a bis(ylide)diphenylborate ligand that is readily transferred in situ to iron(II). Furthermore, these results demonstrate that the coordination of alkali metal ions dictate both the structure and reactivity of the imido ligand and moreover can direct the reactivity of reaction intermediates. By contrast, the same reaction with 5 does not lead to the formation of Ph 2C=NDipp. All complexes 2–4 react with benzophenone form metastable Fe(II) intermediates that subsequently eliminate the metathesis product Ph 2C=NDipp, with relative rates dependent on the alkali more » metal ion. The basicity of the imido ligands influences the relative rates of reaction with 1,4-cyclohexadiene, specifically by gating access to complex 5, which is the species that is active for HAT. Combined experimental and computational studies reveal that the alkali metal polarizes the Fe=N bond, and the basicity of imido ligand increases according to 5 < 4 ≈ 3 < 2. In contrast to 5, the imido ligands in 2–4 can be protonated and alkylated to afford Fe(II) amido complexes. Structural investigations demonstrate that the alkali metal ions modestly lengthen the Fe=N bond distance from that in the charge separated complex (5), with the longest bond observed for the smallest alkali metal ion. Here, alkali metal reduction of the Fe(III) imido complex (1) provides the series of structurally characterized Fe(II) imido complexes (2), (3), and 2 (4), in which the alkali metal cations coordinate the imido ligand. The presence of redox innocent metal ions has been proposed to modulate the reactivity of metal ligand multiple bonds however, insight from structure/function relationships is limited.
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