Cyclometalation of dimesitylphosphine in cationic palladium(II) and platinum(II) complexes: P-H vs C-H activation

The cationic complexes IM(dppe)(R)(PHMes(2))][OTf] (M = Pd, R = Me (1), Ph (2); M = Pt, R = Me (3), Et (4); dppe = Ph2PCH2CH2PPh2, Mes = 2,4,6-Me3C6H2 , OTf = OSO2CF3) were prepared by the reaction of the corresponding M(dppe) (R)(X) (X = Cl, I) with AgOTf and PHMes(2). When they were allowed to stand in THF or CH2Cl2 solution, the Pd complexes underwent cyclometalation, for ming [Pd(dppe)(CH2C6H2(Me)(2)PHMes)][OTf] (5). Thermolysis of Pt complexes 3 and 4 gave [Pt(dppe)(CH2C6H2(Me)(2)PHMes)][OTf] (6), along with ethylene in the latter case. Reaction of Pt(dppe)(Et)(Cl) with AgOTf generated [Pt(d ppe)(H)](2)(2+), which on treatment with PHMes(2) also yielded 6. Treatment of 1, 2 and 3, 4 with triflic acid gave 5 and 6, respectively. The cyclome talation of 1 is acid-catalyzed; the intermediacy of [Pd(dppe)(PHMes(2))](2 +) in these reactions was supported by formation of 5 from sources of the [ Pd(dppe)](2+) fragment and dimesitylphosphine.