Quadruple bonding between iron and boron in the BFe(CO)₃^- complex

Area of Science:

• Inorganic Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Main group elements typically exhibit limited bonding capabilities due to their valence orbitals.
• Quadruple bonding is exceptionally rare for main group elements, with few documented examples.

Purpose of the Study:

• To investigate the possibility of quadruple bonding between main group elements and transition metals.
• To characterize the structure and bonding in the BFe(CO)3- anion complex.

Main Methods:

• Quantum chemical calculations were employed to model the electronic structure and bonding.
• Mass-selected infrared photodissociation spectroscopy was used for experimental identification and characterization in the gas phase.

Main Results:

• The BFe(CO)3- anion complex was synthesized and characterized with C3v symmetry.
• Experimental and computational data revealed an unprecedented quadruple bond between boron and iron (B≣Fe).
• The B-Fe bond distance was significantly shorter than expected for a triple bond, supporting quadruple bonding.

Conclusions:

• The study demonstrates that main group element boron can participate in quadruple bonding with a transition metal (iron).
• The observed quadruple bonding involves a combination of sigma, dative pi, and dative sigma interactions.
• This discovery opens avenues for exploring a broader range of boron-metal complexes with high-multiplicity chemical bonds.