Boryl/Borane Interconversion and Diversity of Binding Modes of Oxygenous Ligands in PBP Pincer Complexes of Rhodium

A series of Rh complexes derived from a PBP-type pincer ligand have been synthesized and characterized. It was previously reported that reaction of [(COD)­RhCl]2 with 2,2′-bis­(diisopropylphino)­triphenylborane (1) resulted in a mixture of complexes containing a Z-type borane interaction (2-Cl), a boryl pincer (3a-Cl), and a η2 binding of the B–Ph bond to Rh (4-Cl). In this work, we demonstrate that analogous complexes are accessible by replacement of chloride with potentially bidentate acetylacetonate, carboxylate, and trifluoromethanesulfonate ligands. In addition, a new type of isomer was observed in complexes with acetate and pivalate, where the carboxylate bridges between Rh and B (3b-OAc, 3b-OPiv). All of these types of complexes are isomeric, and the preference for particular isomers for different anionic ligands varies. These isomers differ and are related by a change in the coordination mode of the oxygenous ligands and the migration of the Ph group between B and Rh.