A Redox-Switchable Hemilabile Ligand: Electrochemical Control of the Coordination Environment of a Rh~I Complex

摘要

We report the synthesis and characterization of a redox-switchable hemilabilc ligand (RHL). FcOCH_2CH_2PPh_2 (1. Fc=(eta~5-C_5H_5)Fe(eta~5-C_5H_4), and its complexation to Rh~I to Form the square-planar, cis-phosphane, cis-ether Rh' complex 2 (Scheme1 ). This new iigand type can yield electrochemical control over ihe electronic and stenc environments of the Rh~I center. Bidentate ligand 1, which was designed for complexation to late transition metals, has two important characteristics. First, for the example reported herein (2). ligand 1 is hemilabile because the phosphane moiety binds strongly to Rh1 to form a stibstitutionally inert bond, while the ether functionality forms a weak bond to Rh~I. which is substiuitionalh labile: hemikibile ligandshave been studied extensively. Second, the ferrocenyl group in 1 is covaiently attached to the ether moiety: therefore. the binding affinity of the O atom for Rh is dependent on the oxidation state of the fetmcenyl group With this RHL design. coordination sites at the trar.Mtion-metal center which i is chelated can be labilized selectively by applying a potential that can oxidize the ferroceny 1 group. thereby yieidmu electroehemi-cal conlroi over transition-metal coordination ensironment. Electrochemical control over the coordination enMronment of the transition-metal complex controls the reactnity of the complex and in principle, its catalytic properties. To this end. we are designing a series of new electrocatulysts based on the RHL concept.