Reactivity of Terminal Iron Borylenes and Bis(borylenes) with Carbodiimides: Cycloaddition, Metathesis, Insertion and C-H Activation Pathways

The reactions of carbodiimides with the iron arylborylene complex [Fe=BDur(CO)(3)(PMe3)] (Dur=2,3,5,6-Me4C6H) and the iron bis(borylene) complex [Fe{=BDur}{=BN(SiMe3)(2)}(CO)(3)] yield a wide variety of temperature-dependent products, including known FeBNC and novel FeBNB metallacycles, complexes of N-heterocyclic boracarbene and spiro-boracarbene ligands and a unique 1,3,2,4-diazadiborolyl pianostool complex, characterized by NMR spectroscopy and X-ray crystallography. The product distributions can be rationalized by considering sequences of cycloaddition, metathesis, insertion, and C-H activation pathways mainly governed by sterics.