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 was found to have cis-bromide ligands and a mer-Triphos ligand by single crystal X-ray diffraction. Once characterized, the reactivity of this compound toward 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 are discussed.