Organometallics in Superacidic Media: Characterization of Remarkably Stable Platinum–Methyl Bonds in HF/SbF₅ Solution

The protolytic stability of (dfepe)­PtMe₂ (dfepe = (C₂F₂)₂PCH₂CH₂P­(C₂F₅)₂) and cis-(dfmp)₂PtMe₂ (dfmp = (C₂F₅)₂PMe) and NMR characterization of their corresponding products in SbF₅–HF superacid solvent mixtures are reported. Dissolution of (dfepe)­Pt­(Me)₂ in 10 mol % of SbF₅–HF at −60 °C resulted in the clean protonolysis of a single Pt–Me bond to form the cationic methyl complex (dfepe)­Pt­(Me)⁺; further conversion of (dfepe)­Pt­(Me)⁺ to (dfepe)­Pt²⁺ occurred upon warming to −20 °C and followed pseudo-first-order kinetics (k = [1.4(2)] × 10^–2 min^–1). In contrast, dissolution of the nonchelating analogue cis-(dfmp)₂PtMe₂ in 10 mol % of SbF₅–HF at 20 °C evolved methane and cleanly produced the stable monomethyl complex trans-(dfmp)₂Pt­(Me)⁺. trans-(dfmp)₂Pt­(Me)⁺ is the most protolytically stable organometallic known: 33% conversion to the cis dicationic product cis-(dfmp)₂Pt²⁺ requires 2 weeks in 10 mol % of SbF₅–HF at 20 °C, whereas >90% conversion was observed in 30 h in 50 mol % of SbF₅–HF. Dissolution of cis-(dfmp)₂Pt­(CD₃)₂ cleanly generated trans-(dfmp)₂Pt­(CD₃)⁺, which subsequently underwent complete proton incorporation to produce trans-(dfmp)₂Pt­(CH₃)⁺ within 1 h at 25 °C. This labeling study supports the reversible formation of the methane complex intermediate trans-(dfmp)₂Pt­(CH₄)²⁺ under these conditions. Treatment of trans-(dfmp)₂Pt­(Me)⁺ in 10 mol % of SbF₅–HF at −100 °C with 200 psi of H₂ resulted in the clean formation of the dihydrogen complex trans-(dfmp)₂Pt­(Me)­(η²-H₂)⁺, which upon warming to −20 °C underwent methane loss and generated the hydride product trans-(dfmp)₂Pt­(H)⁺. The dihydrogen complex trans-(dfmp)₂Pt­(H)­(η²-H₂)⁺ has not been directly observed but has been implicated in exchange bradening behavior observed for trans-(dfmp)₂Pt­(H)⁺ under H₂. Treatment of trans-(dfmp)₂Pt­(CD₃)⁺ in 10 mol % of SbF₅–HF at −40 °C with 200 psi of H₂ cleanly produced trans-(dfmp)₂Pt­(CD₃)­(η²-H₂)⁺ No significant H/D exchange into the Pt–CD₃ group prior to trans-(dfmp)₂Pt­(H)⁺ formation was observed.