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 degrees 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)(CNArTripp2)(2) [Ar-Tripp2, 2,6-(2,4,6-(i-Pr)(3)C6H2](2)C6H3; i-Pr, iso-propyl], featuring a terminal BF ligand. Single-crystal x-ray diffraction as well as nuclearmagnetic resonance, infrared, and Mossbauer spectroscopic studies on Fe(BF)(CO)(2)(CNArTripp2)(2) and the isoelectronic dinitrogen (N-2) and CO complexes Fe(N-2)(CO)(2)(CNArTripp2)(2) and Fe(CO)(3)(CNArTripp2)(2) demonstrate that the terminal BF ligand possesses particularly strong sigma-donor and pi-acceptor properties. Density functional theory and electron-density topology calculations support this conclusion.