Synthesis of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4-, a highly active ethylene dimerization catalyst

The synthesis of cationic adducts (dfepe)Pt(Me)(L)(+) (dfepe = (C2F5)(2)PCH2CH2P(C2F5)(2); L = MeCN, CO, C2H4, C5F5N, mu-Cl) are reported. Treatment of (cod)Pt(Me)Cl with AgSbF6 in acetonitrile followed by the addition of dfepe afforded (dfepe)Pt(Me)(CH3CN)+SbF6-. Addition of B(C-6F5)(3) to (dfepe)Pt(Me)(O2CCF3) in methylene chloride afforded the structurally characterized borane association product (dfepe)Pt(Me)[(O2CCF3)B(C6F5)(3)] in high yield. Attempts to displace the [(O2CCF3)B(C6F5)(3)](-) anion with donor ligands resulted in loss of borane and regeneration of (dfepe)Pt(Me)(O2CCF3). Addition of the mesitylenium acid (1,3,5-C6H4Me3)B+(C6F5)(4)(-) to (dfepe)PtMe2 in methylene chloride at ambient temperatures resulted in chloride abstraction and the precipitation of the chloride-bridged dimeric complex [{(dfepe)Pt(Me)}(2)(mu-Cl)]B+(C6F5)(4)(-), which has been structurally characterized. In contrast, treatment of (dfepe)PtMe2 with (1,3,5-C6H4Me3)B+(C6F5)(4)(-) in pentafluoropyridine at ambient temperature resulted in the precipitation of the structurally characterized pentafluoropyridine adduct [(dfepe)Pt(Me)(NC5F5)]B+(C6F5)(4)(-) in good yield. Exposure of [(dfepe)Pt(Me)(NC5F5)]B+(C6F5)(4)(-) to 1 atm of CO in o-difluorobenzene gave the carbonyl complex [(dfepe)Pt(Me)(CO)]B+(C6F5)(4)(-). In marked contrast to previously reported platinum systems, [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)(4)(-) is a very active ethylene dimerization catalyst at ambient temperature (600 psi ethylene, 22 degrees C in ortho-difluorobenzene, 150 turnovers h(-1)). The ethylene adduct [(dfepe)Pt(Me)(eta(2) -C2H4)]B+(C6F5)(4)(-) has been spectroscopically characterized at -20 degrees C.