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, ) reacts with the group 10 precursor [Ni(CO)] to yield the DBB pogo-stick complex [(η-DBB)Ni(CO)] () as a dark-green crystalline solid. The IR-spectroscopic and X-ray crystallographic data of highlight the strong π-donor properties of the DBB ligand. The reaction of with [M(nbe)] (M = Pd, Pt; nbe = norbornene) yields the unique zerovalent heavier group 10 arene pogo-stick complexes [(η-DBB)M(nbe)] (), isolated as dark-purple and black crystalline solids, respectively. and 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 S→S excitation, which corresponds to a transfer of electron density from a metal d orbital aligned with the direction (d or d) to a d orbital located in the plane (d or d), with the redshift for resulting from the higher spin-orbit coupling (SOC). In complex , electron donation from the nickel center into the carbonyl 2π* orbital destabilizes the DBB···Ni interaction, resulting in an absorption at a higher energy. Complexes and react with [Fe(CO)] to yield the doubly CO-bridged M(0)→Fe(0) (M = Ni, Pd, Pt) metal-only Lewis pairs (MOLPs) as black (M = Ni, Pt) and dark-turquoise (M = Pd) crystalline solids. Furthermore, undergoes oxidative Sn-H addition with PhSnH to yield the corresponding Pt(II) stannyl hydride, [(η-DBB)PtH(SnPh)] ().