Heterolytic CH Activation with a Cyclometalated Platinum(II) 6-Phenyl-4,4‘-di-tert-butyl-2,2-Bipyridine Complex

Abstract

The more electron-rich, thermally, air, and protic stable, cyclometalated Pt(II)(NNC) trifluoroacetate complex (3) (NNC = κ^3-6-phenyl-4,4‘-di-tert-butyl-2,2‘-bipyridine) was synthesized with the expectation that it would be less susceptible to H_2O inhibition than the Pt(bpym)(TFA)_2 system (bpym = κ^2-2,2‘-bipyrimidine) for the catalytic oxidation of hydrocarbons. Complex 3 was found to catalyze the H/D exchange between benzene and trifluoroacetic acid via CH activation but at a rate slower than the Pt(bpym) complex. Experimental and theoretical studies show that while the use of the more electron-rich NNC ligand motif lowered the ΔH for substrate coordination relative to the Pt(bpym) system, a larger increase in the barrier for CH cleavage led to an increase in the overall barrier for CH activation.