Extending the Boundaries With Electron‐Rich Tris(pyridyl)borates in Classical Silver and Gold Carbonyl Complexes

Abstract

This study reports the synthesis, structures, and bonding of silver(I) and gold(I) carbonyl complexes supported by a bulky, mesityl-group-decorated, electron-rich tris(pyridyl)borate ligand. This ligand offers steric protection and strong σ-donation, allowing isolation of classical carbonyls [MeB(6-(Mes)Py)3]Ag(CO) and [MeB(6-(Mes)Py)3]Au(CO). Both show notably low CO stretching frequencies (2115 and 2063 cm−1), lowest for structurally authenticated Ag(I)–CO and Au(I) species, respectively, indicating enhanced metal→CO π-backbonding. X-ray crystallography shows tetrahedral κ3-NNN coordination and linear M–C–O fragments (M = Ag, Au), while 13C NMR spectrum of the silver complex reveals 107/109Ag-13C coupling. Computational studies indicate that electrostatic interactions dominate the interaction between M and CO, but gold(I) shows stronger orbital contributions and π-backdonation than silver(I), consistent with experimental trends. Buried-volume calculations highlight the ligand’s steric bulk. These findings expand the chemistry of isolable Ag(I) and Au(I) carbonyls, providing examples of classical CO complexes and insights into bonding and stabilization strategies. Spectroscopic data on the copper analog, [MeB(6-(Mes)Py)3]Cu(CO), have also been included for comparison.