Synergistic effects between a transition metal and an appropriate ligand are required to promote a desired catalytic reaction. Ancillary ligands, provided by the versatile functionality of certain elements, give rise to an almost infinite potential for catalytic applications. Recently, the study of the synergistic effect between transition metals and boron has become easy on account of the development of various rigid multidentate frameworks. In this Review, we mainly focus on the chemistry of σ-acceptor (Z-type) borane ligands, particularly the key achievements of their unique reactivity and catalytic applications. Conceptually, the unique character of σ-acceptor borane ligands provides a new strategy for developing remarkable reactivity and novel catalytic applications. This study discusses recent developments in the field in this context. The chemistry of boron-based multidentate ligands that involve a covalent MB bond such as the boryl ligand (BR2), in which a boron moiety serves as a strong electron-donating ligand, is also rapidly developing. The effect of the boryl ligand on a metal center is totally different from that of the borane (BR3) ligand, and different boron-based functionalities confer opposing electronic properties to the metal center. The interesting character of boryl-based chelating ligands augments their unique coordination chemistry, which is also summarized in this context.