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

Abstract

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 [(η 6 -DBB)Ni-(CO)] (2) as a dark-green crystalline solid. The IR-spectroscopic and X-ray crystallographic data of 2 highlight the strong π-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 [(η 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 S 0 →S 1 excitation, which corresponds to a transfer of electron density from a metal d orbital aligned with the z direction (d xz or d yz ) to a d orbital located in the xy plane (d xy or d x 2 −y 2 ), 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 2π* orbital destabilizes the DBB•••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 Ph 3 SnH to yield the corresponding Pt(II) stannyl hydride, [(η 6 -DBB)PtH(SnPh 3 )] (5).

CAAC-stabilised 9,10-diboraanthracene: an electronically and structurally flexible platform for small-molecule activation and metal complexation

“…Given the strong electron-donating properties of the related doubly CAAC-stabilised 1,4-diborabenzene (DBB), which has been exploited by our group for the synthesis of unusual half-sandwich complexes of low-valent group 6, 8 and 10 metals, as well as actinides, 25–28 we decided to explore the use of DBA II as a ligand in transition metal chemistry. The reaction of DBA II with [(MeCN) 3 M(CO) 3 ] (M = Cr, Mo, W) cleanly afforded the three-legged half-sandwich complexes [(η 6 -DBA)M(CO) 3 ] ( 4-M ) (M = Cr, Mo, W) after 4 days at 60 °C, accompanied by a colour change to dark green.…”