High‐Resolution Photoelectron Imaging of IrB 3 − : Observation of a π‐Aromatic B 3 + Ring Coordinated to a Transition Metal

In a high‐resolution photoelectron imaging and theoretical study of the IrB 3 − cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B 3 ring coordinated with the Ir atom. The isomer with the higher EA consists of a B 3 ring with a bridge‐bonded Ir atom ( C s , 2 A′), and the second isomer features a tetrahedral structure ( C 3 v , 2 A 1 ). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutral C 3 v isomer involves significant covalent Ir−B bonding and weak ionic bonding with charge transfer from B 3 to Ir, and can be viewed as an Ir–(η 3 ‐B 3 + ) complex. This study provides the first example of a boron‐to‐metal charge‐transfer complex and evidence of a π‐aromatic B 3 + ring coordinated to a transition metal.