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42806-B3
Compounds of Bidentate Phosphines with Metallocene Backbones: Electrochemistry and Catalysis

Chip Nataro, Lafayette College

            Undergraduates in my lab have continued to investigate the properties of bidentate phosphines that have metallocene backbones.  To date our work has focused on the synthesis, electrochemistry and structural analysis of compounds containing either           

1,1'-bis(diphenylphosphino)metallocene (metallocene = ferrocene (dppf), ruthenocene (dppr) or osmocene (dppo)) or 1,1'-bis(dialkylphosphino)ferrocene (alkyl = i-propyl (dippf), cyclohexyl (dcpf) or t-butyl (dtbpf)).   

In the past year, we have completed an investigation of the asymmetric compound 1-diphenylphsophino-1'-ditertbutylphosphinoferrocene (dppdtbpf).  The oxidation of dppdtbpf is chemically reversible.  Upon complexation, the oxidation of dppdtbpf is typically chemically and electrochemically reversible.    A series of phosphine sulfide, phosphine selenide and mixed phosphine sulfide/selenide compounds of dppdtbpf were prepared and characterized (Figure 1).  The electrochemistry of these complexes is complicated if there is at least one selenium present.

Figure 1.  X-ray structures of C₃₀H₃₆FeP₂SSe.

            We have also been investigating the synthesis, electrochemistry and reactivity of a series of CpRu(P-P)H complexes (P-P = dppf, dppr, dppo, dippf or dppc).  The reaction we have been examining is the transfer of the hydride ligand from the ruthenium center to an iminium cations (Figure 2).  During this time we developed a collaboration with Jack Norton at Columbia University and we are currently working on a manuscript detailing this work.

Figure 2.  Hydride transfer reaction.

-CF₃ group, the dtbpf gave the most efficient catalyst.  Additional catalytic studies are currently underway. 

Finally, we have continued or investigation of commercially available chiral, bidentate phosphines with metallocene backbones.  We have examined the electrochemistry and complexation of a series of Taniaphos and Walphos ligands (Figure 3).  The electrochemistry of the ligands displays multiple oxidation waves that are not greatly influenced by R or R'.  Upon complexation, the electrochemistry typically

Taniaphos

Walphos

Figure 3.  Taniaphos and Walphos ligands.

simplifies to a single, chemically and electrochemically reversible wave.  The structures of three new compounds were reported and the bite angles for Taniaphos and Walphos were examined (Figure 4).

Figure 4.  X-ray structures of [(P-P)PdCl₂] (P-P = Taniaphos or Walphos).

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