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Abstract
A comparative study of new platinum methyl complexes cis-(dfmp) 2Pt(Me)2 and trans-(dfmp)2Pt(Me)(X) (dfmp = (C2F5)2P(Me); X = O2CCF 3, OTf, OSO2F) with previously reported acceptor chelate analogues (dfepe)Pt(Me)X (dfepe = (C2F5)2PCH 2CH2P(C2F5)2; X = Me, O 2CCF3, OTf, OSO2F) is presented. In contrast to (dfepe)Pt(Me)2, which is inert to both H2 and CO addition, cis-(dfmp)2Pt(Me)2 reacts readily to form (dfmp) 4Pt and cis-(dfmp)(CO)Pt(Me)2, respectively. Similarly, whereas (dfepe)Pt(Me)2 is stable up to 180°C, thermolysis of cis-(dfmp)2Pt(Me)2 in benzene- d6 at 80°C leads to ethane reductive elimination and production of (dfmp)4Pt. Dissolving cis(dfmp) 2Pt(Me)2 in neat trifluoroacetic, triflic, or fluorosulfonic acid at ambient temperature cleanly produces the corresponding trans -(dfmp)2Pt(Me)(X) complexes. Monitoring the thermolysis of trans-(dfmp)2Pt(Me)(X) complexes by 31P NMR in their respective neat acids reveals a kinetic protolytic stability that is dependent on the nature of the trans X ligand: whereas trans-(dfmp)2Pt(Me)(O2CCF3) is less stable than the corresponding (dfepe)Pt(Me)(O2CCF3) complex, trans-(dfmp)2Pt(Me)(OTf) and trans(dfmp)2Pt(Me)(OSO2F) are significantly more resistant to protolytic cleavage than the chelating analogues. Thermolysis in CF3CO2D or DOTf resulted in deuteration of the methyl ligand prior to methane loss, indicating the reversible formation of a methane adduct intermediate.
The reactivity of trans-(dfmp)2Pt(Me)(X) with various small molecule adducts is discussed. In trifluoroacetic acid, reaction of trans-(dfmp)2Pt(Me)(O2CCF 3) with CO results in loss of dfmp to form the mixed phosphine/carbonyl complex (dfmp)(CO)Pt(Me)(O2CCF3). However, in triflic and fluorosulfonic acids the respective trans-(dfmp) 2Pt(Me)(X) precursors react with CO to form trans-(dfmp) 2PtMe(CO)+(X). All three complexes react with H 2 in neat acid to form stable trans-(dfmp)2Pt(H)(X) complexes. Attempts have been made to prepare a labile source of trans-(dfmp)2Pt(Me)+. Reaction of cis-(dfmp)2Pt(Me)2 with SbF5 on graphite, (C5F5NH)+(SbF6) -, and tris-pentafluorophenylborane is discussed.
Finally, the homoleptic (dfmp)4Pt(0) complex acts as a model system for the thermally unstable Pt(CO)4 analogue. Displacement of cod from (cod)Pt(Ph)2 by 2 equivalents of dfmp followed by reductive elimination of biphenyl gives (dfmp)4Pt in good yield. However, recrystallization from hexanes at 4°C yields (dfmp)3Pt which has been structurally characterized. (dfmp)3Pt is resistant to oxidative addition reacting slowly with MeOTf and MeI. Reaction with 1 atm ethylene in C6D6 gives (dfmp)2Pt(η 2-C2H4), but the ethylene interacts weakly with the metal center.
