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.