Reversible CO-Induced Chloride Shuttling in Rh^I Tweezer Complexes Containing Urea-Functionalized Hemilabile Ligands

The urea moiety, which acts as a good hydrogen-bond donor, has been incorporated into a hemilabile phosphinoalkyl thioether ligand. Upon reaction of the ligand with a RhI precursor, a tweezer complex with near-parallel planar urea moieties 2 forms. The host−guest interaction of 2 with Cl− has been characterized in solution and in the solid state. Cl− binding with the urea groups in 2 is retained under CO in nonpolar solvents to give a five-coordinate CO adduct 3. In polar solvents, CO binding to RhI results in a Cl− shift from the urea host site to the RhI metal center with a concomitant breaking of the Rh−S bonds. This is an unusual example of how two types of different interactions important in molecular recognition (ligand coordination to a metal and hydrogen bonding) can be regulated within one molecule through small-molecule coordination chemistry.