Terminal coordination of diatomic boron monofluoride to iron

Boron monofluoride (BF) is a diatomic molecule with 10 valence electrons, isoelectronic to carbon monoxide (CO). Unlike CO, which is a stable molecule at room temperature and readily serves as both a bridging and terminal ligand to transition metals, BF is unstable below 1800°C in the gas phase, and its coordination chemistry is substantially limited. Here, we report the isolation of the iron complex Fe(BF)(CO) 2 (CNAr Tripp2 ) 2 [Ar Tripp2 , 2,6-(2,4,6-( i- Pr) 3 C 6 H 2 ] 2 C 6 H 3 ; i -Pr, iso -propyl], featuring a terminal BF ligand. Single-crystal x-ray diffraction as well as nuclear magnetic resonance, infrared, and Mossbauer spectroscopic studies on Fe(BF)(CO) 2 (CNAr Tripp2 ) 2 and the isoelectronic dinitrogen (N 2 ) and CO complexes Fe(N 2 )(CO) 2 (CNAr Tripp2 ) 2 and Fe(CO) 3 (CNAr Tripp2 ) 2 demonstrate that the terminal BF ligand possesses particularly strong σ-donor and π-acceptor properties. Density functional theory and electron-density topology calculations support this conclusion.