Redox-Induced Reversible P—P Bond Formation to Generate an Organometallic σ~4λ~4-1,2-Biphosphane Dication

摘要

Many well-established methods exist for fine-tuning the properties of phosphorus compounds, and these allow the creation of tailored stereoelectronic environments that exert exact and predefined control over systems for catalysis or molecular electronics. In principle, the capacity to change the properties of a phosphorus center actively during a process creates further important potential, such as on-off switching in catalysis, or profound gating of the properties of electronic materials. Studies of how phosphorus centers can be efficiently modulated using ferrocenes, cobalto-cenes, TTF derivatives, or other redox-active groups have appeared; however, these redox-active groups are often spatially close to the phosphorus center, so the electronic outcome of the redox change can be conflated with significant steric effects. This is obviously undesirable if geometrical properties need to be maintained, so the possibility of modulating the properties of a phosphorus atom by a molecular wire is attractive. Herein we report a study that concerns metallophosphanes la,b (Scheme 1) having a [Fe-(dppe)(η~5-C5Me5)] redox center linked to a σ~3λ~3-phosphorus atom by an alkyne that functions as a short molecular wire.'10' Within such a system, oxidation of the redox-active organo-iron(II) center is expected to trigger significant changes at phosphorus because of the very efficient electronic communication that occurs across alkyne bridges.