Synthesis and Structures of cis- and trans-[Os(Bcat)(aryl)(CO)2(PPh3)2]: Compounds of Relevance to the Metal-Catalyzed Hydroboration Reaction and the Metal-Mediated Borylation of Arenes

Support for key steps of the mechanism for the transition metal catalyzed hydroboration reaction is provided by the characterization and reactions of 1, a cis-(boryl)(aryl) complex of osmium(II). This compound readily eliminates o-tolylBcat to give the osmium(0) intermediate 2, which in the presence of HBcat reestablishes the osmium-boron bond by forming 3. R=o-tolyl, H2 cat=catechol=1,2-(HO)2 C6 H4 .