Synthesis and Reactivity of Highly Electron-Rich Zerovalent Group 10 Diborabenzene Pogo-Stick Complexes

A cyclic alkyl(amino) carbene (CAAC)-stabilized 1,4-diborabenzene (DBB, 1) reacts with the group 10 precursor [Ni(CO)4] to yield the DBB pogo-stick complex [(.6-DBB)Ni(CO)] (2) as a dark-green crystalline solid. The IR-spectroscopic and X-ray crystallographic data of 2 highlight the strong p-donor properties of the DBB ligand. The reaction of 1 with [M(nbe)2] (M = Pd, Pt; nbe = norbornene) yields the unique zerovalent heavier group 10 arene pogo-stick complexes [(.6-DBB)M(nbe)] (3-M), isolated as dark-purple and black crystalline solids, respectively. 3-Pd and 3-Pt show strong near-IR (NIR) absorptions at 835 and 904 nm, respectively. Time- dependent density functional theory (TD-DFT) calculations show that these result from the S0.S1 excitation, which corresponds to a transfer of electron density from a metal d orbital aligned with the z direction (dxz or dyz) to a d orbital located in the xy plane (dxy or dx 2 -y2), with the redshift for 3-Pt resulting from the higher spin-orbit coupling (SOC). In complex 2, electron donation from the nickel center into the carbonyl 2p* orbital destabilizes the DBB center dot center dot center dot Ni interaction, resulting in an absorption at a higher energy. Complexes 2 and 3-M react with [Fe(CO)5] to yield the doubly CO-bridged M(0). Fe(0) (M = Ni, Pd, Pt) metal-only Lewis pairs (MOLPs) 4-M as black (M = Ni, Pt) and dark-turquoise (M = Pd) crystalline solids. Furthermore, 3-Pt undergoes oxidative Sn-H addition with Ph3SnH to yield the corresponding Pt(II) stannyl hydride, [(.6DBB)PtH(SnPh3)] (5).

Automated summary

A study found that stable pogo-stick complexes can be synthesized through a series of reactions, and their characteristics were confirmed by infrared spectroscopy and X-ray crystallography. These complexes exhibited strong absorption in the near-infrared region. Theoretical calculations further elucidated the mechanism of these absorptions. Additionally, the complexes can react with other compounds to form new substances.