Facile Addition of B–H and B–B Bonds to an Iron(IV) Nitride Complex

The nitride ligand in the iron(IV) complex PhB(iPr2Im)3FeN reacts with boron hydrides to afford PhB(iPr2Im)3FeN(B)H (B = 9-BBN (1), Bpin (2)) and with (Bpin)2 to afford PhB(iPr2Im)3FeN(Bpin)2 (3). The iron(II) borylamido products have all been structurally and spectroscopically characterized, demonstrating facile insertion into B–H and B–B bonds by PhB(iPr2Im)3FeN. Density functional theory (DFT) calculations reveal that the quintet state (S = 2) is significantly lower in energy than the singlet (S = 0) and triplet (S = 1) states for all products. Stoichiometric reaction with (Bpin)2 does not produce the mono-borylated iron imido species PhB(iPr2Im)3FeN(Bpin). DFT calculations suggest that this is because PhB(iPr2Im)3FeN(Bpin) is unstable toward disproportionation to the starting iron(IV) nitride and PhB(iPr2Im)3FeN(Bpin)2. Attempts at B–C bond insertion using phenyl- and benzyl-pinacol borane were unsuccessful, which we attribute to unfavorable kinetics.