Cyclometalation of Dimesitylphosphine in Cationic Palladium(II) and Platinum(II) Complexes: P−H vs C−H Activation

The cationic complexes [M(dppe)(R)(PHMes 2 )][OTf] (M = Pd, R = Me ( 1 ), Ph ( 2 ); M = Pt, R = Me ( 3 ), Et ( 4 ); dppe = Ph 2 PCH 2 CH 2 PPh 2, Mes = 2,4,6-Me 3 C 6 H 2, OTf = OSO 2 CF 3 ) 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 CH 2 Cl 2 solution, the Pd complexes underwent cyclometalation, forming [Pd(dppe)(CH 2 C 6 H 2 (Me) 2 PHMes)][OTf] ( 5 ). Thermolysis of Pt complexes 3 and 4 gave [Pt(dppe)(CH 2 C 6 H 2 (Me) 2 PHMes)][OTf] ( 6 ), along with ethylene in the latter case. Reaction of Pt(dppe)(Et)(Cl) with AgOTf generated [Pt(dppe)(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 cyclometalation 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.