Reactivity of (Triphos)FeBr₂(CO) towards sodium borohydrides

The addition of CO to (Triphos)FeBr₂ (Triphos = PhP(CH₂CH₂PPh₂)₂) resulted in formation of six-coordinate (Triphos)FeBr₂(CO)_. This coordination compound has cis-bromide ligands and a mer-Triphos ligand by single crystal X-ray diffraction. Once characterized, the reactivity of this compound towards NaEt₃BH and NaBH₄ was investigated. Adding 1 eq. of NaEt₃BH to (Triphos)FeBr₂(CO) resulted in formation of (Triphos)FeH(Br)(CO), while the addition of 2.2 eq. afforded previously described (Triphos)Fe(CO)₂. In contrast, adding 2.2 eq. of NaBH₄ to (Triphos)FeBr₂(CO) resulted in carbonyl dissociation and formation of diamagnetic (Triphos)FeH(η²-BH₄), which has been structurally characterized. Notably, efforts to prepare (Triphos)FeH(η²-BH₄) following 2.2 eq. NaBH₄ addition to (Triphos)FeBr₂ were unsuccessful. The importance of these observations as they relate to previously reported (Triphos)Fe reactivity and recent developments in Fe catalysis is discussed.