Lithium, Tin(II), and Zinc Amino-Boryloxy Complexes: Synthesis and Characterization

Analogous to the ubiquitous alkoxide ligand, metal boroxide and boryloxy complexes are an underexplored class of hard anionic O- ligand. A new series of amine-stabilized Li, Sn(II), and Zn boryloxy complexes, comprising electron-rich tetrahedral boron centers have been synthesized and characterized. All complexes have been characterized by one-dimensional (1D), two-dimensional (2D), and DOSY NMR, which are consistent with the solid-state structures unambiguously determined via single-crystal X-ray diffraction. Electron-rich mu 2-(Sn and Zn) and mu 3-(Li) boryloxy binding modes are observed. Compounds 6-9 are the first complexes of this class, with the chelating bis-and tris-phenol ligands providing a scaffold that can be easily functionalized and provides access to the boronic acid pro-ligand, hence allowing facile direct synthesis of the resulting compounds. Computational quantum chemical studies suggest a significant enhancement of the x-donor ability of the amine-stabilized boryloxy ligand because of electron donation from the amine functionality into the p -orbital of the boron atom.

Automated summary

Analogous to alkoxide ligands, metal boroxide and boryloxy complexes are a lesser studied type of hard anionic O- ligands. A new series of amine-stabilized Li, Sn(II), and Zn boryloxy complexes with electron-rich tetrahedral boron centers were synthesized and characterized. The complexes were characterized using 1D, 2D, and DOSY NMR, and solid-state structures were determined via single-crystal X-ray diffraction. The amine-stabilized boryloxy ligand showed enhanced x-donor ability due to electron donation from the amine functionality into the p-orbital of the boron atom, as evidenced by computational quantum chemical studies.