Iron(II) Complexes of an Anionic Bis(ylide)diphenylborate Ligand.

Double deprotonation of the salt [Ph2B(PMe3)2][OTf] (1) provides access to a bis(ylide)diphenylborate ligand that is readily transferred in situ to iron(II). Depending on the reaction stoichiometry, both the "ate" complex [Ph2B(Me2PCH2)2Fe(μ-Cl)2Li(THF)2] (2) and the homoleptic complex [Ph2B(Me2PCH2)2]2Fe(3) can be prepared from FeCl2(THF)1.5. Further reaction of 3 with FeCl2(THF)1.5 produces the chloride-bridged dimer [Ph2B(Me2PCH2)2Fe(μ-Cl)2Fe(CH2PMe2)2BPh2](4). 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. On the other hand, reaction of 4 with the strong field ligand CNtBu provides the six-coordinate, diamagnetic complex [Ph2B(Me2PCH2)2Fe(CNtBu)4][Cl](5). Electronic structure calculations for the bis(ylide)diphenylborate ligand and homoleptic complex 3 suggest that the C(ylide) atoms are strong σ-donors with little π-bonding character. These initial results suggest the potential for this bis(ylide)diphenylborate ligand in coordination chemistry.