Two-state reactivity in C-H activation by a four-coordinate iron(0) complex.

The ground state structure of [Ph2B(tBuIm)2Fe(CO)2]- is trigonal pyramidal (S = 1), with a thermally accessible square planar (S = 0) geometry. Experimentally calibrated electronic structure calculations provide evidence for two-state reactivity, with C-H oxidative addition on the singlet surface providing an iron(ii) product (S = 0).