Organoboron compounds have broad applications in organic synthesis, chemical sensing, and catalysis. For example the C-B bond in arylboronic acids is an extremely versatile synthon for constructing C-C bonds in catalyzed cross-coupling reactions with aromatic halides (commonly known as the Miyaura-Suzuki cross-coupling reaction). Thus, a significant portion of our research centers on B-C bond-forming reactions. Goals include inventing new catalytic transformations and investigating mechanistic features that dictate selectivity. The fruits of these efforts have included unique catalytic chemistry, such as arene borylations and diborations of olefins. Reactions between Borane Reagents and Olefin Complexes. Our work in this area reflects the diverse pathways of B-X addition to transition metal complexes. For instance, Doug Motry studied reactions where Ti complexes reacted via ring-opening processes to afford substituted ethylene complexes, whereas Dean Lantero found that Nb and Ta olefin-hydride complexes react with boranes to give borane and boryl complexes, respectively. These systems provide a unique framework for probing fundamental interactions of boryl fragments with the metal center and hydride co-ligands. Meanwhile, Carl Iverson used olefin complexes to develop a useful route to boryl complexes. In this case, the olefin ligand masks a low-valent metal center, which oxidatively adds B-X bonds with the generation of free olefin. This synthetic route allowed us to investigate important insertion chemistry of metal boryl complexes. Alkyne and Olefin Insertion Chemistry. In 1995, we synthesized a Pt diboryl complex that Miyaura and Suzuki had postulated to be the catalyst in catalytic additions of B-B bonds to alkynes. A subsequent detailed mechanistic study established phosphine dissociation as an important pre-equilibrium for generating the catalytically active Pt species. This intermediate inserts alkynes into a Pt-B bond and the diborylalkene is formed via an irreversible reductive elimination. Our study led to improved catalysts for diboration of alkynes and suggested that olefin diboration, which had not been observed for phosphine supported Pt catalysts, might be achieved with phosphine-free Pt catalysts. This proved to be the case, and we are exploring applications of these unique diborated products. Catalytic Aromatic Borylation. The selective activation of C-H bonds remains one of Chemistry's "Holy Grails". In 1997, Carl Iverson was studying stoichiometric reactions of boranes with Ir and Rh alkyl complexes in attempts to design a system for converting C-H bonds to C-B bonds with extrusion of dihydrogen. He devised an experiment to test the plausibility of a particular pathway and noticed that the NMR solvent was catalytically converted to an arylboronate ester in the presence of borane and certain Rh and Ir complexes providing one of the simplest routes to arylboronic acids. A unique feature of our catalytic chemistry is the influence of steric effects on regioselectivity. For example, 1,3-substituted benzene rings are selectively borylated at the 5-position, which is typically the least activated site towards aromatic substitution. This selectivity and the fact that the direct C-B bond formation from arenes and boranes obviates the present requirement of aryl Grignard reagents for synthesis of boronic esters and is an exciting development in organometallic chemistry. Currently, Jian-Yang Cho and Man Kin Tse are working to unravel the mechanistic details and expand the scope of this important transformation.