N2 Functionalization at Iron Metallaboratranes

The reactivity of the anionic dinitrogen complex [(TPB)Fe(N2)]− (TPB = tris[2-(diisopropylphosphino)phenyl]borane) toward silicon electrophiles has been examined. [(TPB)Fe(N2)]− reacts with trimethylsilyl chloride to yield the silyldiazenido complex (TPB)Fe(NNSiMe3), which is reduced by Na/Hg in THF to yield the corresponding sodium-bound anion [(TPB)Fe(NNSiMe3)]Na(THF). The use of 1,2-bis(chlorodimethylsilyl)ethane in the presence of excess Na/Hg results in the disilylation of the bound N2 molecule to yield the disilylhydrazido(2−) complex (TPB)FeNR (R = 2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopentyl). One of the phosphine arms of TPB in (TPB)FeNR can be substituted by CO or tBuNC to yield crystalline adducts (TPB)(L)FeNR (L = CO, tBuNC). The N–N bond in (TPB)(tBuNC)FeNR is cleaved upon standing at room temperature to yield a phosphoraniminato/disilylamido iron(II) complex. The flexibility of the Fe–B linkage is thought to play a key role in these transformations of Fe-bound dinitrogen.