Normal-to-Abnormal Rearrangement and NHC Activation in Three-Coordinate Iron(II) Carbene Complexes

The ‘normal’ three-coordinate iron–NHC complex [(IPr)­Fe­(N′′)2] (N″ = N­(SiMe3)2) rearranges to its abnormal NHC analogue [(aIPr)­Fe­(N″)2] (6) on heating, providing a rare abnormal iron–aNHC complex, and the first such three-coordinate complex. The tert-butyl-substituted complex [(ItBu)­Fe­(N″)2] (4) undergoes a thermal decomposition that has not previously been observed in iron–NHC chemistry, resulting in the bis­(imidazole) complex [(tBuIm)2Fe­(N″)2] (7). A mechanism that involves consecutive C–H and C–N activation is proposed to account for the formation of 7.