Observation of Four-Fold Boron–Metal Bonds in RhB(BO^–) and RhB

Abstract

The maximum bond order between two main-group atoms was known to be three. However, it has been suggested recently that there is quadruple bonding in C 2 and analogous eight-valence electron species. While the quadruple bond in C 2 has aroused some debates, an interesting question is: are main-group elements capable of forming quadruple bonds? Here we use photoelectron spectroscopy and computational chemistry to probe the electronic structure and chemical bonding in RhB 2 O − and RhB − and show that the boron atom engages in quadruple bonding with rhodium in RhB(BO) − and neutral RhB. The quadruple bonds consist of two πbonds formed between the Rh 4d xz /4d yz and B 2p x /2p y orbitals and two σ-bonds between the Rh 4d z 2 and B 2s/2p z orbitals. To confirm the quadruple bond in RhB, we also investigate the linear RhB−H + species and find a triple bond between Rh and B, which has a longer bond length, lower stretching frequency, and smaller bond dissociation energy in comparison with that of the Rh≣B quadruple bond in RhB.

Observation of Transition‐Metal–Boron Triple Bonds in IrB2O− and ReB2O−

“…Above 5.5 eV, the signal-to-noise ratios are poor, and no definite spectral transitions can be identified. It should be pointed out that the overall 193 nm spectral pattern of IrB 2 O À shows some similarities to that of the recently reported RhB 2 O À , [10] suggesting they may have similar structures.…”

“…[6] The structure and bonding of IrB 2 O À are similar to RhB 2 O À , which has a Rh B quadruple-bond character. [10] The difference of bonding in the two isoelectronic systems lies in the BÀMÀB bond angles and the 3c-2e BÀMÀB bond. The BÀRhÀB bond angle is 99.88 and therefore larger than the BÀIrÀB bond angle of 91.58.…”

“…To search for the first transition-metal-borylyne complex, we recently examined RhB 2 O À using photoelectron spectroscopy (PES) and theoretical chemistry and found that it does not have the expected linear [Rh B À B O] À structure. [10] Instead, it was found to have a bent structure with BO À coordinated to the Rh atom, which features a very short RhÀB bond exhibiting quadruple-bond character, ( À OB)Rh B. This led to the discovery of the first Rh B quadruple bond in a diatomic molecule involving boron.…”

Observation of Transition‐Metal–Boron Triple Bonds in IrB2O− and ReB2O−

“…Chemie Zuschriften global minimum of RhB 2 O À reported recently. [10] The linear isomer for IrB 2 O À ( 1 S + ) was found to be 0.58 eV higher in energy ( Figure S1 a). However, we found that the global minimum of ReB 2 O À is linear with a short ReÀB bond and a BO À unit bonded to the B atom.…”

“…This led to the discovery of the first Rh B quadruple bond in a diatomic molecule involving boron. [10,11] In the meantime, a combined infrared and theoretical study on BFe(CO) 3…”