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.