η2-Coordination and C−H Activation of Electron-Poor Arenes

Abstract

The reductive elimination of neopentane from (dtbpm)Pt(Np)H (dtbpm = bis(di-tert-butylphosphino)methane, Np = neopentyl) results in the formation of the highly reactive intermediate [(dtbpm)Pt0]. This species reacts with a variety of electron-deficient benzenes (1,4-bis(trifluoromethyl)benzene and 1,3,5-tris(trifluoromethyl)benzene) and biphenyls (3,5,4‘-tris(trifluoromethyl)biphenyl and 3,5,3‘,5‘-tetrakis(trifluoromethyl)biphenyl) to form η2-arene complexes. X-ray crystallography confirms the η2-bonding motif. The arene complexes all display broad 1H NMR spectroscopic features at room temperature that sharpen considerably at lower temperatures. Thermolysis or photolysis of the arene complexes results in C−H activation and the formation of platinum(II) aryl hydride complexes. The products observed depend on whether the reaction is thermal or photolytic. Reaction with 4,4‘-bis(trifluoromethyl)biphenyl yields two C−H activated products directly. Oxidative addition occurs at the 2 and 3 positions of the biphenyl in a 5:1 ratio, respectively. Continued heating of the mixture results in a second C−H activation to form a platinacyclopentane.